#147 - Hussein Yassine, M.D.: Deep dive into the "Alzheimer's gene" (APOE), brain health, and omega-3s

Hey everyone.

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My guest this week is Dr. Hussain Yazin. Hussain is an Associate professor in the Department of Medicine at the Keck School of Medicine at usc. His lab has focused for almost a decade now on lipid metabolism and nutrition and the effect these have on cognition and the risk of developing Alzheimer's disease. Paying specific attention to the ApoE4 allele, many of you listening to this podcast will no doubt be familiar with Apoe 4 genotypes. We've spoken about this at great length in a number of podcasts. This is really the deep dive into APO E4, what the implications are. I actually wanted to speak with Hussein after we were part of a journal club where he presented a couple of papers that he authored that were simply beyond fascinating. And it was definitely one of the deepest dives I'd ever seen into the inner workings of EPA and DHA's role in the brain. Now we do get to that near the end of the podcast, but I realize that it's important for people to really understand a lot about the brain. And so I would consider this kind of a fundamental core coursework on brain biology. We really explain the architecture of the brain, the energy systems of the brain, and what goes wrong. What are the various things that go wrong? Because it's not just one thing as a person develops Alzheimer's disease and then we get into what APOE is and then why we might have these three different variants or isoforms of it, E2, E3 and E4 and what turns out to be different depending on which of those you have. The obvious thing of course is your risk for Alzheimer's disease, but why? We have a little side tangent that goes into sort of the role of EPA in cardiovascular disease with or without dha, and then kind of bring it back to this discussion around the role of DHA in Alzheimer's disease and also what some of the specific things that we understand to date with respect to patients that have E4 and what they can do to reduce risk. I'm going to give you a warning up front. Unfortunately, if you're anything like me, you're going to come away from this episode, I think, frustrated that our state of knowledge is still so pedestrian. But nevertheless, this is a very important discussion and I certainly learned a lot in it and it will actually have an impact on how I think about taking care of my patients. So without further delay, please enjoy my conversation with Hussein Yazin. Hussein, thanks so much for making time to sit down today. I'm really looking forward to this. Obviously, I had the pleasure of doing doing Journal Club with you a few weeks ago, which is what made me realize we needed to do this for a much broader audience. Let's kind of go back to the beginning a little bit, though. I'm kind of curious as to what got you interested in this space. I know you grew up in Lebanon. Did you do medical school there as well as college?

Yeah. Thank you, Peter, for the invitation. I'm happy to be part of your show. Yes, I grew up in Beirut, Lebanon. That's my medical school. And then shortly after moved to the US to do some residency training followed by a fellowship. And then I got to where I am right now.

Tell me a little bit about that path. Your fellowship was in what?

I trained in endocrinology. I come from a family with strong heart disease and diabetes, so I decided to sub specialize in lipid disorders and I studied lipids for a good of two to three years before I had the opportunity to study brain lipids. And I switched from blood lipids to the brain.

Well, this is a topic that I think a lot of people are interested in because I remember 10 years ago when you would check an APOE genotype on somebody, it was a very unusual thing to do. Today, it's not as unusual. It's probably still not incredibly common that people are walking around knowing their APOE genotype. But it's certainly, I mean, it seems a log order more common than it was a decade ago. And I suspect a decade from now that might be one of the genes that kind of everybody knows about themselves. So where do you think is a good place to start? I think this topic is complicated enough that it probably warrants at least some discussion of what makes up the brain. Like we talk about neuronal cells, we talk about glial cells. Can you maybe help explain the Architecture of the brain so that as we get into the different types of cells, what a blood brain barrier means, where CSF resides, these things will become important in this discussion. And I think we should assume that most people listening don't necessarily understand those things.

Sure. So you first asked about the APOE genotype. And I have seen in my practice calls, I would say even monthly, from people who did 23andMe and found out that they are E4 carriers and they wanted to know more. So I not uncommonly get calls to figure out what is it that I have APOE 4, what does that mean for my brain? You typically see in the report some discussion that they are at an increased risk of Alzheimer's disease and people are interested to figure out if there's anything they can do. So, yes, Apoe 4 will be something important to deal with. Now, regarding the brain itself. The brain is a unique compartment that is mostly a lipid organ. So by weight, the brain contains a large amount of lipids, from cholesterol, which is esterol, to different forms of fatty acids. And the brain is largely composed of three types of cells, although it's much more than that. But the main cells are the neurons, which are responsible for firing and forming synapses, which regulate how the brain functions. The neurons cannot do their own function. Had it not been for helper cells, and these include, in general, glial cells, Glial cells could be astrocytes, and these are cells which are tightly associated with neurons and they regulate the energy storage production and so forth that the neuron would need to keep firing. Astrocytes have a lot of functions, but they they're mostly viewed as taking up glucose or fat and providing substrates that the neuron could use to be able to generate ATP and keep firing. And then you've got the glial cells, the microglial cells, which have gained a lot of traction in the last decade or so because they have been linked to neurodegenerative diseases such as Alzheimer's disease. And glial cells are immune cells responsible for cleaning up. Whether it's going to be a beta or an infection, these immune cells have the responsibility of making sure that the house is in order. There's also the oligodendrocytes and other kinds of cells, but those three cells are the main type of cells that we study in the brain. The brain is surrounded by a blood brain barrier, and this is an important concept because the brain is protected from the outside of the brain and for a good reason. The brain needs to have a stable Environment to be able to function. The blood brain barrier regulates what gets in and out of the brain and stands as a barrier to prevent toxic proteins, infectious organisms, and other things from getting free access. The blood brain barrier separates the blood vessels and the blood inside the blood vessels from the brain. And it's composed of capillary cells. These are endothelial cells which have a lining of tight junctions. These are very tight in the sense that they would act as a barrier, followed by pericytes, which surround those endothelial cells. And these are supporting cells for the endothelium to maintain the integrity of the blood brain barrier. And around those, you have the mural cells, or wall cells, which make up the matrix surrounding those two cell types and maintains the integrity as well of the blood brain barrier. So you've got this elaborate system that is designed to protect the brain and to maintain a stable environment. Now, finally, cerebrospinal fluid is, in a simplistic way, the sewage system of the brain. When the brain receives its metabolites, its nutrients from the circulation, it crosses the blood brain barrier through the junction of the endothelial cells into brain cells. There is a fluid surrounding brain cells that we call the interstitial fluid. Brain cells will take up whatever they need, whether it's an astrocyte, a microglia, or a neuron, and produce some byproducts. One of the commonly studied byproducts are a beta proteins which are accumulating in diseases like Alzheimer's. Those byproducts will then get cleared into the csf. The csf, or cerebrospinal fluid, as I mentioned before, is a form of a system that allows drainage from the brain cells from the interstitial fluid. It's run by a pump. That pump is in a system known as the choroid plexus. The choroid plexus will be pumping clear water like fluid into the csf. And this motion of movement of the fluid throughout the brain washes the brain off. At some point, the choroid plexus interferes with the blood circulation to clear off these metabolites from the CSF back into the blood for excretion. So if we take a beta amyloid peptides, for example, they're produced by the neuron as the neuron is firing. These are peptides which come off the membrane of a neuron, and then they leak into the csf. And then from the csf, they get into the blood, and the blood clears those a beta peptides through the liver or other organs. And this constant CSF activity is critical for maintaining the sewage system of the brain and order. So I hope I have addressed some of the questions that you were asking.

Yeah, absolutely. And we can even sort of talk about some illnesses that occur that get in the way of this. So, for example, sometimes children are born with abnormalities that make it very difficult for them to clear csf. Or children can be born with malformations that obstruct the flow of CSF and they develop conditions where some of these compartments within the brain expand and enlarge. And it's a very intricate system. In situations like that, for example, you have to come up with other ways to drain the system. And some of these children's require shunts where you have to place an exogenous tube into their brain and drain it into their abdomen or something like that. It's all such an amazing organ. I remember I had one rotation in general surgery where we did a month of neurosurgery. And it is quite remarkable. When you're operating on the brain and you remove the dura, the brain is a bloodless organ. So, you know, it looks unlike any other organ. Like, you know, when you're operating on the kidney and you get right down to the kidney, you still see the sort of pulp like redness of the kidney or the lung or the liver, any of these other organs. But the brain is quite distinct in that it doesn't have that. And once that dura is peeled back and you see it bathing in this csf, it looks unusually sterile. Which is not to say, of course, as you cut into the parenchyma, you wouldn't get blood. But at that level it's not. You mentioned something earlier, and I want to just make sure we put it in context, which is that by weight the brain is disproportionately lipid laden relative to other organs. So let's make sure people understand what that means. Every cell in our body has a bilayer of cholesterol that makes up its cell membrane. That's what allows it to have fluidity. That's what allows it to hold transporters across its cell membrane. E, et cetera. How does, say, a cardiac myocyte, the muscle cell of a heart, differ in terms of its lipid content from either the neuron or the astrocyte or the microglia? What is it about these cells in the brain that structurally requires such an abundance of lipid and cholesterol?

That's a fundamentally important question and, and it actually begs to ask perhaps a slightly different question. How is the Brain functionally different than a myocyte. And one way to look at this question is to understand that the brain operates by firing. So you're looking at perhaps an electric system where you have wires connected to each other, and these wires have to fire constantly. And by firing, you need electricity to move from one piece of the wire to the other. This requires specific cables. In our modern day language, you need a form of fiber optics or high speed wiring that allows this firing to happen in instantaneous manners. And it's carefully regulated and separated by location, by speed, and by changes in a micro environment. To be able to achieve this delicate and elaborate map of wires attached to each other, you need lipids. Specifically, for example, for talking about a neuron, we're talking about myelin. If we're talking about synapse, we're talking about a synaptism, that's a synapse body. The synaptic zone by itself, to be able to conduct and depolarize, meaning to change the electric potential across the cell membrane, it requires a certain environment of lipids that allows it to do the signaling, allows the glutamate or glutamine to go inside the cell and then release certain mediators to open certain channels, for example, calcium channels. So this particular environment necessitates that you have an elaborate system of lipids that facilitate this process. This is a very taxing system, meaning that to be able to constantly talk to me through this podcast, you would need an immense amount of ATP and the extraction of glucose and the utilization of lipids is adapted to be able to answer this. This particular environment, in contrast, a cardiac myocyte, outside of its being regulated by the foci that regulates heartbeats in the atria and so forth, the AV node and other areas. The cardiac myocyte is simply a mechanical cell that has to pump all the time to be able to maintain a certain pressure and blood flow. So that environment by itself requires strong cytoskeletal elements such as actin or myosin, that are efficiently packaged for pumping and may require less lipids than the wiring that we discussed in the brain.

Yeah, so I think that's a very elegant way to explain that. Basically every cell in the body, whether it be, as you said, a myocyte in the heart, or a cell in the kidney, or a cell in the liver, or a cell in the lung, or a cell of skeletal muscle, all of those things have a function that is contractile gas exchange, filtration, something like that. The brain's entire function is electron potentials and electricity. So it would make sense, as you said, that every facet of the brain has to be optimized for signal transduction. And that includes not just the myelination of the sheaths in the neurons, but even all of the other cells that would facilitate for rapid potential and recurrence of normal electron gradients. The brain. I mean, I think there's a statistic that we all learn in medical school, right? It weighs about 2% of our body weight and yet is probably responsible for something on the order of 20% of our energy consumption. Again, you've provided a very elegant explanation for why that's the case. Why is it that this tiny, tiny organ is so energy demanding? How does the brain utilize energy? So let's talk a little bit about how substrate makes its way to the brain, and let's contrast it just very quickly with, you know, pick a myocyte in your leg, right? Can take glucose out of circulation. It can, either with or without insulin, bring that glucose molecule through a GLUT4 transmitter directly into the cytoplasm. It can, depending on the speed at which it requires ATP, it can very rapidly take that to pyruvate and ultimately to lactate, or it can more slowly take the pyruvate it into the mitochondria and generate more ATP there. It can do the same thing with fatty acids. Of course, with fatty acids, it's going to go from an acetyl COA pathway into the mitochondria and take these two carbon units into ATP. So the muscles have lots of options for fuel. Even in a case of starvation, they can use ketones, but basically glucose, fatty acids, lactate, all of these things are fuels and they go directly to the cell. And then within the cell, you have aerobic and anaerobic pathways. If you're talking about glycolysis, you sort of alluded to it already. But the brain already has one thing that makes it an extra step, which is there's a blood brain barrier. So it's not even like the glucose goes directly there through the capillary. So how does the brain extract energy from circulation? And how does it differ from the rest of the body in its fuel partitioning?

I would say that I am not an expert in this field, but I'll give you my two cents. This is a complex question, and I would beg to help the listeners understand that this is a complex topic, that even as we speak, there's a huge gap in knowledge. But my understanding is that the brain prefers glucose as the predominant source of energy, and that by itself is regulated differently than the rest of the body. The rest of the body have a system by which insulin regulates specific transporters, known as GLUT4s, as you mentioned. And GLUT4 allows an insulin dependent mechanism to enter glucose into pumping muscles or adipocytes, and that responds to the outside environment. Meaning you can induce glut4 expression by exercising. You can induce glut4 expression by changes in body weight at the blood brain barrier. GLUT4 plays a minor to no role in glucose uptake. The blood brain barrier, in contrast, has a predominance of GLUT1s. GLUT1 expression is not controlled by what you eat. It's not controlled by how you exercise to a large extent. And it's not controlled by the same mechanisms that govern insulin regulated glucose signaling. Partly because your brain cannot be moody in its choices. It has to have a constant supply of glucose. Now, GLUT1 expression can be regulated, and it's largely regulated to protect the brain. Meaning if you are faced with a situation that is systemic hyperglycemia, such as type 2 diabetes, the brain protects itself by reducing GLUT1 expression at the blood brain barrier. The opposite holds true if you are, for some reason, going through a prolonged fasting period where you're dipping into glycogen stores and you're hypoglycemic. The brain upregulates GLUT1 at the blood brain barrier to extract as much as possible all the glucose in your circulation to maintain a relatively constant amount of glucose in the brain. Now, during physiological states, the glucose in the brain does not fluctuate that much, although it does fluctuate, but it doesn't fluctuate as much as that in plasma during diseased states such as Alzheimer's, for example. Leakage or destruction of the blood brain barrier associates with destruction in the GLUT1 transporters. And the brain now struggles in capturing glucose from the system, which leads to a whole new cascade that we might argue is a diseased cascade. It's compensatory, but it's responding to a glucose shortage. So in that regards, glucose regulation in the brain differs from the circulation. Now, another fundamental aspect to understand is that the brain is not efficient in utilizing fat as a source of ATP. One thing that you notice after you dissect a brain is that you don't find fat depots that you find in your adipose tissue. Yes, it's a fatty organ, but there aren't really storage sites of fat it does not store fat. To a large extent, there are lipid droplets in the brain, but they are more dynamic than the adipose tissue that we have outside. And it prefers not to use fat as a source of ATP. It prefers to use fat to integrate it into the myelin sheath or the synoptosome to regulate membrane fluidity, to help with depolarization. Nevertheless, when the brain goes through crises and they can't use glucose, they have a mechanism to extract ATP from fat. But the result is, is a price tag. The result is oxidative stress. The brain has a complicated system, as we mentioned before, that consists of astrocytes and neurons and glial cells and all sorts of stuff, and they have partitioned their roles. A neuron is like your athlete who needs to run a marathon at a certain speed. Now, for that athlete to succeed, he needs to have water bottles staged at every juncture or a mile. He used to have helpers with towels, helpers with whatever it is for the athlete to be able to do the whole 23 mile if it's a marathon. Astrocytes, the helper cells of neurons, would take up the glucose and process it to make lactate and then shuttle the lactate into the neuron. Because the neuron says, I can digest lactate more efficiently than the glucose and I can produce ATP with less damage. So the neuronal favorite food is lactate and not glucose. But glucose gets into the astrocyte, where it is shuttled and changed into lactate when glucose is no longer there, and we're talking about prolonged fasting and glycogen depletion, the brain becomes very efficient in extracting ketone bodies through the blood brain barrier to maintain its firing and to avoid someone from getting into a coma like state. So in a nutshell, to summarize what I just said, the brain does its best to regulate its glucose content that is not dependent on insulin signaling. Number two, the brain prefers glucose and not fat as a source of energy. And number three, when glucose is not available, it extracts all the ketone bodies that are produced from fatty acid oxidation outside the brain to maintain itself going.

So a couple of other things to follow up on that. So actually, I didn't realize that GLUT1 was basically regulated by gluten, peripheral glucose concentration. That's actually super interesting. And I also didn't realize that the neurons were getting their lactate from the astrocytes. So I assume the implication of that is as the astrocytes take glucose to make pyruvate, to make lactate, the Astrocytes are keeping the ATP from that process rendered to themselves while transporting or donating the lactate to the neuron. Is that what's happening?

Yeah.

And then what about the microglial cells? Are they using glucose or are they using the residual lactate?

I don't know what the source of energy for microglial cells, I am not sure how they use their energy production.

And do you have a sense, just broadly, what the distribution is of ATP consumption between the glial cells and the neurons? I mean, I know that the glial cells grossly outnumber the neurons in terms of the numbers of cells, but do you have a sense, is it like a 50, 50 division of energy consumption?

I don't know. I don't want to provide an inaccurate response, so I don't know.

Okay, so we have a pretty good handle on what's going on here. Now, you've done a great job, I think, giving us a primer on both the structure of the brain and now energy. So let's get into this idea of what is apoe, and let's talk about it not as a gene right now, but let's talk about it as an apolipoprotein, and then we can talk about the genetics of it later. But what is this thing called apoe? Your interest is also in cardiovascular disease? This is a podcast in which we talk a lot about it, so we can even contrast for the listener what APOB is. Most people listening to this are very familiar with what APOB is this apolipoprotein that wraps lipoproteins and defines a subclass of them. The morphologically distinct lineage of the VLDL to the IDL to the ldl. But what's apoe? What is that apolipoprotein?

That's a fascinating question, and that has been the focus of my own research for the past six or seven years. So APOE is. I like to give analogies, if you don't mind. Do you like music?

Sure.

Before COVID how often do you go listen to an orchestra playing the Met or any of the fancy places? And New York has beautiful music too.

Well, I'm not a fancy music guy, but I like to go to concerts prior to Covid. But I don't know if that'll fit in with the analogy.

Well, the analogy I was trying to make is that for an orchestra to play efficiently, it needs conductors. My father asked me a few months ago, and he's by no means a musician or any have never played a music instrument, but he was telling me, what is that conductor doing? I mean, can't they play without the conductor? So if I were to ask you, and if you allow me a minute to sit in your shoes, what is the conductor doing?

That's a great question. First of all, I would assume he is vital, but. And secondly, I would assume that he is somehow managing the timing of all of the different sections within the orchestra, and not just the timing, but if one is crescendoing and the other is decrescendoing. So I suspect there's just many more moving pieces than, say, a rock band where you have one guitar, one bass, one drum, maybe a keyboard and a singer.

Absolutely. And in the lipoprotein orchestra, APOB would be one of the principal players. Let's assume it's your violinist. APO A would be your piano player. And you need both. You know, sometimes you need the violinist to run the show and you need piano for certain pieces. But what puts the orchestra together in the peripheral circulation, largely two conductors, in this case Apoe and Apo C3. What Apoe and Apo C3 do is that they regulate the speed of which things are happening. They're different than APOB because you can argue they're promiscuous. APOB is matted to LDL particles, maybe to some extent VLDL, LDL, and this whole pipeline, APOA1 to a large extent, is matter to the HDL family of particles. Now, APOE and APO C3, also known as exchangeable lipoproteins, are not. They can jump from different populations of lipoproteins, and by taking different roles, they can decide whether a lipoprotein is going to stay in the circulation. And that would be your APOC 3 or get cleared, and that would be your APOE. So this is a simplified version because I think in real life it's way more complex. But the reason why APOE has been elusive and difficult to study is because of its multiple roles. And it appears on hdl, it can appear on ldl, it can appear on idl, it can appear on vldl, it changes whether you're fasting or postprandial, and it determines to some extent the fate of your lipoprotein. So if we take a second to imagine, you know, what happens after we drink a milkshake. So when you drink a milkshake, you're absorbing all the fat from the milk and you're packaging it into chylomicrons, which are known to carry APOB48, APOB48 will then have to circulate and eventually get cleared by forming remnants. As APOB 48 chylomicron containing particle is circulating, it start changing its apolipoprotein composition. In the beginning it would have a larger amount of APO C3 which would maintain it from getting lipolyzed. And at some point when it gets to a certain size, HDL will donate the APOE and allow that remnant to get taken up by an APOE receptor into the liver. Typical APOE receptors include LRP1. That also happens with VLDL particles when they are produced, when they are large, they acquire an APOC3 that blocks lipoprotein lipase and as they shrink in size, APO3C3 will fall off. APOE would get reassembled and that will assist this VLDL particle of getting cleared. One of the fundamental aspects of metabolic syndrome is an inefficient process where these particles are the APOES and the APOC 3s are not as mobile and you end up having an Apoc3 enriched small dense LDL particle that is not cleared. So we're talking now about APOE in the blood. So that APOE in the blood has maybe a different role than the APOE in the brain.

By the way, before we go to the brain, Hussein, I'm very familiar with Apoc3 in the scenarios you've described it and frankly I'm quite hopeful that in the near Future we'll have APOC 3 assays in the periphery as an increase in in our armamentarium as we try to use biomarkers to better understand cardiovascular disease risk. And can Apoc3 levels be a part of residual risk Once you've minimized APOB? Will APOC 3 tell us something above and beyond it? And as you said, it tracks so closely with insulin resistance and metabolic syndrome. I'm less familiar with APOE in the periphery and wasn't actually aware of just how promiscuous it was. It seems to have affinity for a number of receptors at the liver. Doesn't it also have affinity for the LDL receptor itself?

It does have an affinity for the LDL receptor, but its affinity is higher for LRP1, which is one of the LDL receptor family members. Yeah, APOE is a bit more complicated than the rest of the lipoproteins because it can take many shapes and forms and the affinities can change based on lipid binding. It has two arms, an N terminus, a C terminus. Typically the N terminus binds to the receptor and the C terminus is buried Inside the lipid core of a lipoprotein particle, it can dislodge and become lipid free or it can lipidate. And these interactions are critical to our understanding of how APOE functions. And the reason why we've had an investment in science in APOE largely is due to APOE4, because that mutation that substitute the arginine, the cysteine with the arginine, changes how APOE folds and unfolds and starts to carrying lipids.

Now we can measure the concentration of APOB in the circulation. We can measure the concentration of apoa in circulation. And in fact, as you said, APOB is so predictably linked to lp, vldl, IDL and LDL that we effectively use APOB concentration as a surrogate for LDL concentration. And we effectively use APOA1 concentration as a surrogate for HDL concentration. What does APOE concentration mean? If I mean to my knowledge there is no commercial assay to measure APOE concentration in the periphery. But should you measure it in the lab, what would it tell you?

It's like asking me what instrument does the conductor play?

Does he not at the time he's conducting? He plays them all, I suppose, but indirectly.

Right. So the APOE concentration is elusive because it doesn't matter what the concentration is. That doesn't tell you the same amount of information that APOB or APOA1 does. There is a one to one correlation ratio between every APOB particle and every LDL particle. So you're really closely estimating how much LDL particles there is by measuring APOB. APOA is a little bit more complex. It's not one to one, it could be one to four. But you can estimate for every four APOA one apolipoproteins, one HDL particle. Now when we talk about APOE, what are we talking about? APOE, HDL, APOE 3, APOE VLDL, APOE IDL, APOE, LDL. So if you have at one given concentration, tons of APOE on HDL, you have a completely different phenotype than if you have it on vldl. Because as we mentioned with the conductor is trying to now make all the orchestra work, they have to stretch themselves and they have to make the violinist play harder or they have to make the piano pick up. At certain point. You can't make an assessment of the function of APOE by just measuring it its concentrations. And to some extent that holds true for Apoc3, although Apoc3 at extremes of measurements is more predictable and could be useful toward understanding Residual risk and metabolic diseases. But APOE is more elusive.

So what is APOE again, the apolipoprotein? Let's, we'll, we'll wait until we understand this a bit better before we get down to the genetic isoforms. Or is APOE doing in the brain? How does the conductor regulate things in the brain?

Oh, so that conductor analogy may not hold because we don't have our traditional LDL VLDL in the brain. We only have apolipoprotein particles that you may argue are completely different than what you're finding in plasma. Some group of scientists believe that apolipoproteins in the brain are hdl, but that by itself also is not accurate. They could have the size of hdl, but the composition might be very different. So APOE in the brain is not facilitating clearance of lipids or the rate by which lipolysis is happening. Its role in the brain is largely supporting the astrocytes. So astrocytes are supporting neurons. But for astrocytes to support neurons, they need a mechanism that can efficiently crosstalk different cell types. And APOE happens to be able to do many different things. For example, an APOE in a glial cell can regulate through the exchange of lipids, how inflammatory the glial cell is going to be. An APOE in an astrocyte can take out cholesterol from the astrocyte and give it through an LRP1 mediated uptake in the neuron to the neuron itself. Apoes are notorious for being robust. One of the earliest studies I have done, maybe seven, eight years ago, was, was cutting the nerve of a rat model. And at that point we did a mass spec experiment and found out one of the largest changes in hundreds, if not thousands of proteins after you just take a neuron and cut it, are drastic changes in apoe. APOE exponentially goes up after damage. Whether it's a stroke, whether it's an artificial severing of a nerve, APOE will be released at very high rates to make sure repair is going to happen. APOE uses its flexibility, structural flexibility, to transport lipids, uses its structural flexibility to regulate what receptors and transporters the cell can actually express. One fundamental difference between APOB and APOE is, is that apob, once it's taken up by a liver cell, typically goes and gets a lysosomal degradation pathway. And that biology by Goldstein and others have led to therapies, including statins and later PCSK9 inhibitors. Because APOB can get degraded in the lysosome. And if you can figure out how APOB is degraded, you can make a medication. Now, one fundamental difference about APOB from APOE is that APOE to a large extent escapes degradation. And once it's taken up by a liver cell or an astrocyte or a neuron, it recycles back. So it's a notorious APO lipoprotein that can get inside the cell and then outside the cell, recycling most of the time. And by recycling, maybe the conductor analogy or the thermostat analogy works. It controls or fine tunes how much lipids there is in the cell, and it fine tunes a lot of different pathways which are tied to lipid metabolism, most importantly, the inflammatory pathways.

Now, I assume the blood brain barrier prevents peripheral APOE from entering the brain and vice versa.

The dogma says yes, but our research, recent research, suggests that ApoE4, but not ApoE3, might be able to slip.

Slip through all of those tight junctions.

No, not through the tight junctions. The affinity of Apoe 4 to the LRP1 is quite higher than Apoe 3 and Apoe 2. And LRP1 is expressed at the blood brain barrier, so it could hack the system and get through endothelial LRP1 into the brain.

And do we have a sense of what the half life is of apoe? I mean, apob, as you said, is a relatively short half life. I mean, and even without medication, its life, its residence time in circulation is probably less than a week before it's going to get recycled vis a vis the liver. How long is APOE hanging around?

It's a complicated question. The answer to that is which particle are we talking about?

Well, I'm actually saying the APOE itself, in any form, whether it be free or bound to something else. The actual apoe, it sounds like what you're saying is it can be around for a very long period of time and take multiple forms.

Yeah. So if it's a lipid free form, APOE can be rapidly excreted or disappear from the circulation. If it's bound to hdl, it tends to hang longer. And if it's bound to vldl, it tends to hang out less because VLDL clearance rates are faster than that of hdl. And this is a marriage. So APOE is confetting those properties to the lipoprotein that's actually going to.

All right, let's now talk a bit about the genetics that regulate these different isoforms, because APOE is a protein that exists in different forms, and that's not true of all of our genes. Now, thousands and thousands of Years ago, say hundreds of thousands of years ago, there was really only one isoform, to the best of our knowledge. Correct. And that's the one that today we give the moniker e4to. Is that correct?

That's right.

So just for the sake of argument, a couple hundred thousand years ago, all of our ancestors had one version of this gene. So you had two copies of the E4, because you have two copies of every gene. And what do we believe was the reason for that? I mean, presumably evolution has strong copies.

Pressure.

Do we have a sense of what an Apoe 4? Well, actually, before we do that, Hussein, let's ask maybe the more relevant question, which is when did that change? And what was the next isoform to show up? And do we have a sense of why?

So I'm not an evolutionary biologist to give you accurate responses, but I can probably ask the first question better than the second question. And I think fundamentally I was alluding to in a few minutes ago to an important inflammatory function for ApoE. ApoE is capable of turning a cell into an acute inflammatory state, especially glial cells or immune cells such as the macrophage. When the cell expresses apoe, it changes why it substantially its lipid content, and it might be better equipped to become an inflamed cell or the opposite. When the cell exchanges apoe, it's also better equipped to be less inflamed cell. I know these are contradicting statements, but you have to realize that APOE can regulate things. You know, you can turn your thermostat on and off. It's not one thing or the other. It could be in different forms, depending on the situation, on the interaction, on the time it can flip because of its structural flexibility. Now, APOE 4, which is our ancestral variant, has a greater capacity to aggregate than APOE 3 and APOE 2. This aggregation means that they're not suspended in solution, favors a strong inflammatory response. So when Apoe4 starts aggregating inside a microglia, it makes an acute inflammatory response much more efficient and much more directed toward what the microglia is fighting. So let's step back and imagine that we are 300, 200,000 years ago, and then out of every 1020 births, few are surviving and the others are dying from purple sepsis from other forms of infection. We know now that Apoe4Women had a better chance of giving childbirth and protection from peripheral sepsis compared to non E4 women in the slums of Brazil or in certain areas in Africa. We know that based on studies that E4 confers some form of an advantage. We also know that those who have had E4 may have had better luck surviving not only parasitic infections. So in certain countries in Nigeria, people who have the E4 and eosinophilia tend to be much healthier than E4 carriers without eosinophilia and more importantly, non E4 carriers with eosinophilia. So if you are living in a place where parasites are common and they're constantly testing your immune system, you are much better off carrying the ApoE4 allele than not locally, the macrophage is much better equipped to deal with the parasite, and importantly, your brain is much better equipped to deal with whether it's tb, meningitis, and the mother would be better equipped to fight a septic event during childbirth. So from that perspective, APOE 4 is our ancestral gene. Now, what happened over the last few hundred thousand years, Perhaps maybe over the last few hundred years, and let's not go far, we turned from aseptic environment to gradually an aseptic environment. And the second change that happened is that we've prolonged our lifespan. And I know that you have a dear interest in aging, so we have. Now. It's surprising to me, reading from history books, that just a hundred years ago, we're not talking 100,000 years ago. A hundred years ago, the mean age was something of the 47. Am I making things up? Does that make sense to you?

It depends on where you look. But it was a little more than 4,700 years ago in the developed world. But you're right, I mean, I think about, you could say about 100 to 150 years ago was really when we saw a big uptick in lifespan, right?

So if that's the case, and let's assume we're not talking about the kings and queens in England, and let's talk about those people living in Nigeria or in Africa, anywhere, or in Brazil. And let's imagine that these people have several milestones that they have to go through to be able to survive to their next decade. And you would notice two things. One, that Apoe 4 carriers are surviving better. Two, that you're not seeing a disadvantage of Apoe 4 because these people are not living to 80. Some of them would probably die at 50 or 60 or 70, but certainly they may not have the resources to make it to 96. So what happens to E4 carriers when they're dying at 60 or 65? I mean, what I'm trying to say is what doesn't happen to APOE4 carriers? When they're dying at 65, they don't get Alzheimer's. In that regards, it might provide a plausible explanation of why this ancestral gene worked for us in the past, but may not work for us in this modern aging population.

It's always been confusing to me why there was any evolutionary pressure to create variants of E3 and E2. Because the best of my reading is that the E3 showed up about 50,000 years ago and E2 showed up about 10,000 years ago. And again, from a functional standpoint, 10,000, 50,000 and 100,000 are basically the same. Nobody was really living long enough to recoup the benefit of Alzheimer's disease risk reduction going from 300,000 years ago to 50 to 10,000.

No, I would look at that from a different perspective. I'm again no anthropologist, and my knowledge is really as mediocre as any of your readers or listeners. I would look at it as mass movement and change in environment. From 200,000 years to 100,000 years ago, there was mass movement from the African continents all the way to Europe, and that was associated with a drastic change in diet. And my understanding is that there was a heavily favored meat consumption, including fish, in the rift valleys in Africa and in the savannas. And when they moved to a plant based diet in northern Europe and where they started farming, I think that put pressure on APOE 4 and allowed APOE 3 and APOE 2 to be more successful. And this is a slightly different twist, because APOE 4, as much as it's very strong against inflammation, it thrives on a specific dietary lipid providing environment. And remember that Apoe 4, one of the fundamental aspects that we learned from Alzheimer's is that ApoE4 makes GLUT1 less successful at the blood brain barrier. So what ApoE4 does, it somehow tells the brain, you know, I don't want you to be eating sugar all the time. You have to be more resilient and rely on fat. And again, this is a hypothesis. This is not based on true hard science. But the idea is that our ancestral APOE4 diets matched APOE4. And then when they moved to a plant based diet, the effect of ApoE4 on GLUT1 was now counterintuitive. Now there's more carbohydrates and you want something that will help GLUT1 and not oppose it. And APOE3 and APOE2 would actually favor a more robust GLUT1 expression at the blood brain barrier, which means they favor a more glucose utilization of the brain.

So when did it first become apparent, either to epidemiologists or neurologists, or anybody else studying it for that matter, that these three isoforms predicted a very different risk of Alzheimer's disease in modern humans?

The story is we're in the late 80s and this is a time where genetics is gaining traction. You know, I recently watched a very nice series, I think on PBS Masterpieces, discussing how a revolution in genetic fingerprinting changed how we do policing to figure out who is guilty and who's not. And that happened. What's interesting is that this science was happening between 81 and 84. So around 1988, 89, a researcher at Duke by the name of Alan Roses was running an Alzheimer's group and had access to a very robust at that time, robust enough, obviously now it's not robust at all. But he had the ability to genetically profile a large number of common variants of people dying with and without Alzheimer's at that point in time. He publishes a case series, a few hundreds with and without Alzheimer's, and identifies that patients with Alzheimer's had substantially higher APOE4 compared to non Alzheimer's. And you know, remember that we have known Apoe 4 since the 60s, so this is not a new discovery, but we didn't know anything about APOE 4 and Alzheimer's disease and until that time. So he meets a lot of backlash because the prevailing hypothesis at that time is that Alzheimer's is amyloid accumulating and leading to the amyloid cascade hypothesis where you form amyloid plaques and then you get tau tangles. And the field at that point was heavily vested in this amyloid hypothesis. So Alan Roses later on, a few years later, publishes a larger study which contains now longitudinal follow up people, you know progressing to disease and confirms the observation that if you are an APOE 4 carrier, chances of getting Alzheimer's are substantially higher than if you are a non APOE 4 carrier. And we're talking about late onset Alzheimer's disease, the most common form, which happens after age of 60. So at that time, Alan Rosas cemented his name as among those who identified the association of APOE 4 with AD.

Do you have a rough sense at the time? And I think it's probably quite different today. But do you have a broad sense at the time of what the hazard ratios were of E44 versus 34 versus 3 3?

I don't think the hazard ratios would change substantially in a matter of two to three decades. So what we know now is that if you have two copies of Apoe 4, your chance of getting Alzheimer's increases twelve fold. If you have one copy of Apoe 4, your chance of having Alzheimer's increases anywhere from two to fourfold.

And what does that matter, by the way, if it's a 4:2 or a 4:3?

Yeah. So 4:3 means you have one copy of Apoe 4. And the question becomes a little difficult when you have 2 4, because 2 is supposed to be protective. Those who have APOE 2 are protected from getting Alzheimer's disease. So the 2, 4 carriers sometimes behave as 4, sometimes behave as 2. And this might have to do with how well these proteins are getting expressed.

In the inside the cells and potentially other genes as well, like Tom 40 or FGF and things like that that seem to also play a role here, or frankly things that we haven't understood. Like you see families with a very involved family history and they might only have one copy of the E4, but it behaves in a very virulent way. I mean, you see the same thing in cardiovascular disease, disease where some families have LP and the level is not particularly high, but it still behaves very aggressively. And you'll see other families where LP is, I mean, astronomically high, and yet they seem largely spared of premature atherosclerosis.

Correct. So I think one way to rephrase the question is how do we explain that not all Apoe 4 carriers have the same risk of Alzheimer's disease, and that's largely seen by ethnicity. So people who live in Nigeria, for example, the risk of having Alzheimer's disease is substantially less than people who live in the US or in Japan. The Hispanic Latino Latinx population carrying an E4 does not produce the same risk of AD compared to white people or Japanese people carrying the APOE4. So how do we explain that? And that's a fundamentally important question. And as you just alluded TO or noted, APOE 4 is part of a gene locus that in other words, it's part of a haplotype that's a section of a chromosome where a bunch of different gene variants are getting co inherited. They are within the same locus. So ApoE4 is found on chromosome 19. Around ApoE4 is approximately 20 to 30 different gene variants that happen to be co inherited with APOE 4. And the description between these gene variants are described by what we call linkage disequilibrium. If the linkage disqualified equilibrium is closer to 1. It means every time you have APOE 4. Let's assume now we're talking about the long version of tom40, you can have the long version of tom40 expressed with it. Now, that linkage disequilibrium is what differs between ethnicities and can largely also explain why certain ethnicities develop disease and certain don't. So, so as humans or generations are getting interbred and crossed, the fidelity of this linkage disequilibrium can start getting breached. Meaning now you can start introducing the short version of Tom40 next to ApoE4, or you can start introducing another version of ApoC1 or ApoC2 or ApoC3. All these are in the same location as the ApoE, together with again another 20 to 30 other genes. So that doesn't diminish the importance of ApoE4, but tells us that ApoE4 by itself may not be sufficient to provide disease. It has to be in an environment that promotes its pathogenicity.

And all things equal, from a clinical perspective, we are more worried when someone of Asian or Caucasian ethnicity has it versus someone of Latin or African descent. Is that a fair assessment? Again, it's an oversimplification, but just based on the epidemiology and also based on, frankly, potentially what you said earlier, which is the origin of the gene. Right. This is a gene that takes its roots very early in our ancestry and offered an important protection. And potentially by the time we migrated to a more northern climate, some of that protection was less necessary. Again, that's a teleologic sort of hand waving rationalization. But is that a safe assessment that everything you're saying risk is just going to be higher in Caucasians and Asians?

I wouldn't go with a blank statement. Maybe in general, yes, but maybe there are what we call either gene gene interactions or gene environment interactions that have to take into account. Let me give you a simple example. In a Colombian study, they show that APOE 4 by itself may not substantially increase the risk of Alzheimer's disease. But since diabetes is prevalent in a certain city in Colombia, diabetics who were Apoe 4 carriers had some substantial increase in AD risk compared to diabetics alone or Apoe 4 carriers alone. And this is an example of a gene by environment interaction.

So just to be sure we got that right, E4 with diabetes was higher risk than E4 without diabetes and higher risk than diabetes without E4?

Yes.

By way of comparison, do you recall what the risk was of E4 without diabetes to diabetes without E4, which was second?

I don't recall the numbers, but I can tell you they were not striking at all. So when I actually looked at the data, the E4 risk by itself seemed barely above non, you know, non E4 carriers. So if you looked at it and you'd say this is a healthy Colombian who is, you know, farming all day long lean, and they have absolutely no metabolic diseases, the E4 is doing nothing.

Yeah. You mentioned something earlier that I thought was super fascinating. I want to come back to it, which is some of the diet interactions. So let's go back to where you left it, which was, when talking about it through the lens of the E4 carrier, the first thing you mention is, look, E4 makes GLUT1 less successful at the blood brain barrier. And you've already established for us that GLUT1 is basically regulated by peripheral glucose concentration in its purpose is to make sure that when glucose is in low abundance, the brain gets first dibs on it and that when glucose is in overly high abundance, the brain is protected from it. So now you have an E4, you have a person who's an E4 variant, they're less sensitive to that mechanism. Presumably that means in an environment richer in glucose, they're less able to appropriately partition fuel. Is that a safe assessment?

Yes. You can argue that in an environment that is rich of glucose, or maybe in a different term, an insulin resistant environment, ApoE4 carriers are less capable of regulating by many mechanisms, including GLUT1, the fluctuations in glucose and they're more susceptible to disease. But by no means this is a restricted relationship of Apoe 4 to Glut 1, because we also know from studies that we have done and others that ApoE4 also affect the transporters that transport omega 3 fatty acids into the brain.

Now, we're going to come to that in a moment because that of course is, I mean, in many ways one of the most interesting things to now talk about. But before we go there, I do want to come back to this idea of do we have an understanding of type 2 diabetes, which is simply a very extreme version of insulin resistance and metabolic dysregulation? Does it disproportionately then? I hate to use the word, but punish carriers of APOE 4 versus E3 versus E2. Is that clearly established in the epidemiology?

I don't think so. I wouldn't look at it as type 2 diabetes is a distinct disease that punishes APOE 4, because type 2 diabetes to me is a syndrome, not a disease. So what are we talking about?

And it's frankly a pretty significant spectrum for that matter.

Correct. So are we talking about an individual who is consuming a large amount of carbohydrates? Who gets type 2 diabetes? Are we talking about APOE 4 itself? Because as you probably know may know, APOE 4 by itself creates a system with aging that makes an individual insulin resistant. So in one regards, Apoe 4 could be a factor for why a certain person may get type 2 diabetes. So in that regards, APOE4 is not conspiring with type 2 diabetes, it might be behind type 2 diabetes. So you have to look at type 2 diabetes from a more individualized causal. What's causing type 2 diabetes here? Is it the diet? Is it genetics? And how is APOE4 interacting with this phenotype is probably more complicated than an A1C and a genotype in a large population. Because when you look deep enough into these studies, you find quite a bit of discordant results that makes it hard to explain, explain.

You sort of alluded to it earlier that the E4 carriers, as they migrated ancestrally, say out of Africa or even out of South America, were primarily consuming a diet lower in carbohydrates, presumably higher in protein and fat. Do we have any reason to believe today that there is a rationale for matching diet to genotype?

So right now, in major studies that looked at APOE4 dietary patterns in the western world, they don't differ by genotype. So if you're looking at the US or Europe, an Apoe 4 carrier may well likely be eating a similar diet to a non carrier. Now would that lead to the same detrimental effect?

Yeah, yeah, sorry. My question is less about the existing dietary pattern and more of the prospective ask of is there a reason to change dietary pattern to produce a better outcome?

Yes, of course. So this is part of what we're studying is how does APOE 4 interact with the diet and how that interaction can change disease processes. And what we know is that the first concept that your listeners should be aware of is that APOE4 is a disease of aging.

Do you mean Alzheimer's disease is a disease of aging or Alzheimer's disease is.

A disease of aging? But APOE4's risk of developing Alzheimer's and aging related diseases is fundamentally based on the aged model. Younger 35 year olds Apoe 4 carriers, to my knowledge, do not have frank presentations of a disease. A younger Apoe 4 carrier, who could be myself or you or anybody else could be fully functional. It's only when you hit a certain age that Apoe 4 carriers start to have problems, and not all of them. So you've the majority of Apoe 4 carriers, you may argue, are, you know, surviving. They're thriving, they're doing okay. So there's only a subset of APOE4 carriers who are aging and. And getting disease. So then the question is, who are these people? How do we explain them? Is it only genetics or is there a dietary genetic interaction? And I think the answer to this question has to do with what is happening with these people as they age. Are they developing other diseases? Are they? For example, we know that an APOE 4 carriers who happen to be the victim of a traumatic brain injury injury has much worse outcomes than that without traumatic brain injury. We know that an APOE4 carrier, possibly with type 2 diabetes, may have worse outcomes than an APOE4 carrier without. But again, as I mentioned to you, this is a little bit more complicated because not all type 2 diabetes is the same. We know that an APOE 4 carrier who may have a second hit could be a genetic second hit. They're inheriting another protein that increases the risk of Alzheimer's disease. Now their path toward disease is much more accelerated. So what we also know is that as we age, our ability, our cells lose the ability to regenerate and to sustain a certain status. And that is associated with lapses in energy production. That is associated with several complications which include at the blood brain barrier, reduced ability to express those Glut 1 transporters, Omega 3 transporters, and even ketone body transporters. So the aging Apoe 4 individual who has second and third hits is now straining the brain and leading to an environment where, in this situation, the diet may make a difference. Another angle to look at this question is there are certain diets, and, you know, coming from the cardiovascular background, we both agree that there are certain diets that can, you know, accelerate aging or create a form of stress. That can be the second hit that APOE 4 carriers are exposed to to accelerate toward an aging brain that is diseased. I know the answers may not be crystal clear, but the diet interaction with APOE4 is contingent upon aging and a second or a third hit.

But what seems interesting in what you just said to me is a big part of the manner in which APOE 4 transmits its risk to the individual is through an energy crisis. Much of what you said had to do with substrate. It had to do with reducing the utilization of and or access to substrate. Is that a fair assessment?

That is one hypothesis. It's a prevailing energy hypothesis that links APOE4.4 with disease and aging. There are other hypotheses which do not have to be exclusive of this hypothesis. Meaning that you could also have an energy inflammation differences that predispose ApoE4 to neuroinflammation and that by itself could lead to an accelerated disease pathway. You could also have an Apoe 4 backslash.

Could be a vascular component here as well.

Yeah, vascular or leakage component. And there's a group at USC where I work that has shown that, you know, there is leakage in the blood brain barrier allowing toxins to get into the brain and shrink cells. And that is by itself non exclusively related to the dietary or the inflammation. We do not want to say this is it and that's only it. It is plausible that there are multiple hits, but you could look at it from different angles.

Well, not only that, I mean, those hits are synergistic and in the wrong direction. Right. So if you have leaky blood brain barrier and you're more predisposed to inflammation, which again as you pointed out, was very helpful 300,000 years ago when we were fraught with parasites, you now have two hits within the same hit, which is you're more likely to get toxins across the blood brain barrier, which is bad in and of itself. And then secondly, you're more likely to have an overreactive immune response to it. And if you couple that with say a third hit of neuronal energy starvation, these things begin to circle. So let's pivot for a moment now to another enormous area of focus for you, which is the role of omega 3 fatty acids. This is such an interesting topic. There's nobody listening to this who hasn't heard of omega 3 fatty acids. And even if they haven't heard of them in exactly those terms, people have certainly heard the terms EPA and dha and there's no shortage of confusion about these things. So I guess for the odd person who maybe just doesn't know exactly what we're talking about, can you give just a brief overview of what EPA and DHA are and why we spend so much time and energy trying to study and understand their role in human health?

There isn't really a short answer to a complicated question like this one. But in a nutshell, when you break down the components of the brain, you find that a significant portion in some studies, 50 or 40%, of the brain, is composed of polyunsaturated fatty acids such as DHA, EPA, and arachidonic acid. The EPA, DHA, and add to that alpha linoleic acid ala, are known as omega 3s. In contrast, arachidonic acid is an omega 6. So the brain is highly enriched in both omega 3s and omega 6. And you contemplate why. Why do we have so much of these fatty acids in the brain? And the fundamental answer has to do with membrane fluidity. Having polyunsaturated fatty acids in neuronal membrane facilitates to a large extent the neuronal firing that we just talked about in the beginning. So this composition of fat allows the brain or the neurons to conduct their work very efficiently. So DHA is the predominant building block, the most commonly found Omega 3 in the brain. EPA is not that common. DHA or glucosa hexaenoic acid is given that name because of the number of fatty acids and the number of double bonds. It's six, EPA has five of, and we're talking about the location of the double bonds, the structure of DHEA or epa. EPA is not very abundant in the brain, but that doesn't mean it's not very important. EPA is less abundant, but has perhaps stronger anti inflammatory effects than dha. There is limited interconversion between DHA and epa, but DHA can become EPA and also EEPA can become DHA, but that process is also limited. The reason people talk about omega 3s and they make a big deal out of it is because the human body doesn't have an efficient system to make them from scratch. In fact, you can't make them from scratch. If you want to make them, you need a precursor known as alpha linoleic acids or ala, by a group of desaturases. ALA can get transformed into to DHA and EPA. However, it is widely believed that only 0.5% of DHA and EPA are made from conversion of ALA. That number though, you have to take it with a grain of salt. Because there might be evidence that in diets, vegetarians or vegans who do not eat fish, that conversion rate may actually be much higher. But despite that, that conversion rate has not been documented to exceed 5%. So at the most, 5% of DHA and EPA can come from ALA, although most people argue that it's only 0.5%. So what does that mean for us? If we can't make DHA and EPA and we rely on diet to get them, what does it mean that we are not getting them? So what I've just alluded to is the US diet, and you probably know as much as I do, or even more, that the US diet is not enriched in DHA or EPA. The consumption of DHA and EPA in the US I can give you an example DHA is averaging 100 milligrams per day is low. That consumption may not provide enough Omega 3s to the brain. And the question is, does that result in disease? And the answer is likely, yes. Now, what we don't know is the supplementing people with omega 3s makes a difference. And the answer to that question is at this point, we don't know that that makes a difference simply because research on supplements have not panned out. It's very conflicted. There are positive studies, there are negative studies, and the supplements themselves are quite distinct and different in production and concentrations and quantities and qualities. So I know I have alluded to a lot of different aspects of this field, but the answer to your question is that these omega 3 fatty acids are, are important for the brain. We can't make them efficiently and we're not consuming enough of them.

And as you also alluded to, when we supplement them, they can come in various forms, right? We can get them from microalgae, which tend to be triglyceride based. We can refine them from fish oils directly, which are ethyl esters, or they can come from krill oils, which are phospholipid based. Does that sound about right?

Yes. Yes. You can get Omega 3s from all these sources.

It basically has to be marine. I mean, that's sort of the bottom line is it has to have some sort of tie to algae or microalgae either being consumed by other things like fish. And it's funny, I sort of remember many years ago reading something very interesting that explained why EPA and DHA had to have some sort of a marine origin predominantly. And it had to do with the formation of the third carbon double bond. And I can't remember any more than that. Does that ring a bell, anything about this?

I can tell you that the complexity of the structural distribution of these double bonds requires certain machinery to make them that is present in algae. Now why wouldn't other species make it? I don't know.

Yeah, it had to do exactly with the very, very complex carbon fixation that only algae could do. Let's start with what we know. We have a pretty good sense that people who have higher levels of EPA and DHA from consumption of fish have better outcomes than people who don't. Do we know that pretty well?

I don't know. I honestly don't know if this is very clear. What my knowledge is is that the opposite might be closer to truth, meaning that people who don't eat at all fish or seafood or omega 3 rich diets might be at a higher increased risk of disease as opposed to the other statement, which means people who eat a lot of them have less disease. So what I'm trying to point out is that there could be a deficiency state that predisposes somebody to disease, but once you meet that threshold, may or may not get much more benefit.

Yeah. So in other words, you can get scurvy from insufficient vitamin C, but there's probably little evidence to suggest that supplementing vitamin C offers health protection and benefit beyond the rda.

Yes.

By the way, for what it's worth, I believe that's true with vitamin C. I think there's no evidence to suggest it's helpful in massive doses. Nevertheless, there's been no shortage of attempts to study this question. And there have been some significant studies that have gone to great lengths to do this. Now, although we're talking about the brain, you are no stranger to the heart. So can we pivot for a moment to talk about a very interesting study published probably about 18 months ago that looked at a very high dose of EPA, 4 grams in individuals with elevated triglycerides and a number of other risks. And I have to be honest with you, to my surprise, produced kind of an amazing outcome. It was not what I expected. Of course, I'm speaking about the Reduce it study. Do you want to give people just a quick overview of that study and what it found and what your thoughts are on that study?

So the background is some Japanese studies over a decade ago has suggested that a certain EPA to arachidonic acid ratio was associated with substantially less cardiovascular disease in certain regions in Japan. And there were some trials in Japan at that point that have attempted supplementing epa. And the results were positive, but there were not, were not conclusive. So they were using something around 2 grams of EPA and they found out some trends which were very exciting, but again, they were not strong enough to make an official recommendation. So somehow this led to a concerted effort in the US to try to answer this question. Can we give high doses of EPA to mimic this ratio that they found in Japan of EPA consumption and translate into less cardiovascular events? So it became an interesting question to pursue. And the Reduce it investigators decided to go ahead and run a large multicenter trial where they gave 4 grams of pure EPA and they selected people who they thought would benefit the most from this intervention. And those included people with diabetes, high triglycerides, because EPA is known to lower triglycerides. And they monitored them for cardiovascular events over a Period of a few years. And they found out that compared to their placebo arm, those who were given 4 grams of EPA per day did substantially better. The study had one flaw, and I don't know if it's a fatal flaw or not. I think that needs to be figured out. The placebo in that arm was not your typical placebo. So typically when you do omega 3 or fatty acid intervention trials, the most common placebo is corn oil, soybean oil, and in this case, so they used mineral oil. And they were criticized at the time of publication whether EPA indeed reduced cardiovascular events or did mineral oil increase cardiovascular events.

Before we leave that, let's understand that a bit more. So corn oil, safflower, canola, Those are more E6 than E3. They have a little bit of ALA in them, and they still have some monounsaturated fats in them. But is it safe to say that they're probably more than 50% Omega 6?

Yes, but the concentrations given in them is not high. The concentration of E6 is really a low amount. These people are not consuming grams of E6.

And what's mineral oil's breakdown? What's it formed from? I mean, my only interaction with mineral oil is to polish my cutting board or to make sure my cutting board doesn't get too dry.

Yeah. I mean, to be honest with you, I don't know. But all of this came after the fact. We've never considered in our trial's mineral oil because it was. Was never an option. And it was very obscure that that mineral oil was chosen in that trial to be the placebo. And I don't think they even thought about this until the study was published. And then people started asking.

I see. Yeah. And I mean, I think mineral oil, frankly, is totally different. I mean, I don't.

I don't.

It probably more resembles like a petroleum based product or something like that. I don't think it's like a fatty acid in the sense that corn oil is or anything like that. Yeah, that is odd that they would use that. But they were given presumably 4 grams of mineral oil every day as well in a placebo.

Right. And I think the decision to make or to create mineral oil as the placebo at that point in time was not thought of from a health perspective, but mostly from maybe what's available or economic or. Or matching the taste of the intervention itself. So there wasn't deep thinking about what would happen if you added so much mineral oil in a study like this one. And I think the investigators have Regretted that decision. But, you know, Hindsight is always 2020.

Yeah. And it's certainly a plausible explanation given just how significant the effect was in reduce it. I mean, it was. Wasn't the absolute risk reduction something on the order of 4% or something like that? I mean, it was in excess. It was certainly on par with what you see in some of the most potent drug trials.

Yes, yes. And this was surprising. And what's important is in science, you always have to be skeptical and you always need to find whether any particular study can be replicated or not before you make strong recommendations and adopt any drastic change in how you are consuming certain things or whether it's a medication or a diet or a supplement. So the company was able to make very strong claims that high doses of EPA are important addition to the standard management of diabetes, cardiovascular disease, atherosclerosis at the time of its publication, and even urged the FDA to add that indication, which the FDA appeared to agree to. But at the same time, other studies were going on the pipeline to confirm, although they did not use the same identical ethyl ester epa, because that is perhaps patented by the company that made that particular drug. And I don't want to mention any particular drug in the show because I'm not trying to promote anything. So, long story short, what we have learned from the American Heart Association a few months ago is that high doses of EPA did not translate into cardiovascular benefit when compared to corn oil or, you know, the other standard form of placebo.

Now, you're referring to the strength trial, correct?

Yes.

Now, was that a high dose of EPA or was that EPA and DHA combined?

It was predominantly a high dose epa, although I think there was DHA in it. The predominant form that was given was EPA.

And what was the dose that was 4 grams, omega 3. Yeah, I think you're right. I think it was probably about 3 grams and 1 gram, is my recollection.

Yeah, I can look it up. I do not want to give your listeners any inaccurate information, so if you like, we could just look up. But it was a predominantly EPA supplement.

Yeah. And as you said, when compared to a corn oil, that study showed essentially zero difference between them. So again, what's different? Right. So it begs the question, is the mineral oil the problem in the first study? Was the dose not correct, 3 or the ratio of 3 to 1 of EPA to DHA? Is it simply irrelevant to your point earlier? Maybe these people didn't have a deficiency and supplementing to excess made no difference. The other thing is these were Relatively sick patients. Right. These were patients that I can't recall off the top of my head what the strength patients looked like. But if they were anything like the reduce it patients, which I remember more, I mean, almost 80% of these patients had type 2 diabetes. All of them had dyslipidemia. So the other argument is, is four years of treating patients that are at high, high risk of major adverse cardiac event enough time to steer the ship? Are you better off treating people in their 40s for two decades to try to mitigate that risk? And I think, frankly, that question probably becomes even more interesting from the standpoint of brain health and heart health. Right. Where we have fewer options.

Let me tell you that how I think about this, and it may or may not make sense to you or to your readers, when we're talking about reduce it or epa, are we talking about a supplement or are we talking about a drug?

In the case of reduce it, it's a drug. I mean, that's a pharmaceutical prescribed drug.

Right? So this distinction is important because if we're talking about a drug, then we are thinking about a cascade. We're thinking of, you give a statin, you inhibit HMG CoA reductase, you decrease the expression of the or, you increase the expression of the LDL receptor in the liver, and then you suck cholesterol circulating by LDL or VLDL particles and you excrete it. You lower LDL cholesterol, you decrease small dents on atherogenic LDL cholesterol particles that translate into less atherosclerosis and then this translates into less cardiovascular events. This is the prevailing hypothesis of how we view statins work. Now, if I were to ask you, how does EPA work, how does it reduce cardiovascular events? And if we can come up with a cascade similar to that of statins, I think we can argue that you could use high dose EPA as a drug. But if we're stuttering and we can't really map the actual cycle, we might be fishing for results.

Yeah, and it's also interesting when, I mean, I don't think this analysis has been done, but it would be a clever study, would be like a pairing study where you take the same patients, of course, and you pair one group to phenofibrate to another with high dose epa such that they get equal reduction of triglycerides, and you ask the question, does that make a difference? In other words, how much of this benefit, if any, comes from the triglyceride reduction, which all things equal, is going to lower apob Concentration as you reduce the lipid carrying capacity of lipoprotein. And did that, you know, is that the mechanism? Now again, that's more of a thought experiment. I can't imagine anybody would go and do the actual study of trilipics versus Vascepa. But you're right, we don't have a very clear mechanistic pathway for why this would make sense.

One possibility, although I'm not trying to be against or for epa, I'm just trying to think out loud, one possibility is that EPA has potent anti inflammatory effects. And it is plausible that EPA, not by any triglyceride lowering potential but by a local anti inflammatory effect on the plaques has resulted in less plaque rupture and less events. But again, these are all ideas because we don't fully understand what happened and why they did get substantial reduction in events. Now this is irrelevant because you know, to me I don't study right now cardiovascular disease disease and I'm not trying to understand exactly an application for EPA on patients at risk of heart disease. But my, my lab is more interested in figuring out a link between omega 3s and the brain. And the reason why I brought reduce it or we brought this example of high dose EPA and cardiovascular disease is to contrast completely different systems. Unlike cardiovascular disease where you have a very well described process where you have a plaque that ruptures and you get an event, your typical Alzheimer dementia is often a chronic low grade slow process that happens over years and that eventually manifests in loss of function of the daily activities, cognitive deficits and so forth. The role of DHA in this disease is more closer to the analogy that you used with scurvy. In landmark studies done decades ago at nih, they showed when you took a mouse model and you deprived the pregnant mice from DHA completely and then you looked at her offsprings, they found that the these baby litters, the offsprings of the mouse, had a condition that we call microcephaly where the brain failed to form and develop and was very small. When you looked under the microscope, you found out that these neurons formed from a DHA deficient diet were not making enough synapses under the microscope compared to neurons who were exposed to a deficient or a non deficient or a regular child diet when the mother was nursing or having the children in utero. So that by itself told us that DHA deficiency is detrimental to the function of the brain. Now we also know that from many studies that in humans during development not having enough polyunsaturated fatty acids Whether it's lactating breast milk or in the diet itself was associated with poorer outcomes in school. And these are large studies published in the 90s which have led the FDA in 2001 or two, I believe, to agree to the recommendation of, of supplementing infant formula with both DHA and arachidonic acid aa. So, you know, any listeners who has bought infant formula or any have used infant formula, and if they look at the actual formula, they see the tag DHA and AA fortified. So the concept that there is something called DHA or EPA or Omega 3 deficiency exists is probably solid. Now, what's less known or more confusing or more difficult to ascertain is that what age range does this deficiency make the largest impact and how does aging affect that deficiency? Question. So to put this question in a different perspective, the brain develops rapidly from conception to possibly three to five years. And by, by the age of six, the human brain is almost fully developed. And then you start slowly accreting. Accretion refers to retention of lipids and material such as protein and the structure of the brain, where it's not exchanging with plasma anymore or blood, so it's kind of stuck in the brain. So the accretion of lipids or omega 3s in the brain slows considerably between the ages of 6 all the way to 12 and 13. And then beyond that, the pools are relatively stable and expansion of brain size is very slow. And then after certain age cutoffs like 60s and above, you start seeing the opposite, where atrophy starts to happen with aging. So we can clearly visualize that figure and grasp the concept that during rapid accretion of lipids, it's really important for, you know, babies and kids to get exposed to enough Omega 3s to allow their brain to fully develop. And that doesn't have to be supplementation. That could well be the. A good diet. Now, what happens between the ages of 6 and 60 is quite elusive. Meaning that what happens to a population that is 35 that is completely not consuming any omega 3s? Are they in any diseased states? And I can't point out a single large study that can say yes. All what I can point out to is a myriad of small studies which show discrepant results. Some studies suggest there are subtle cognitive impairments. Other studies suggest anxiety disorders, mood disorders, depression. But other studies don't find these associations. So that tells us that the role of omega 3 in the diet between the ages of 6 and 60 is more difficult to understand. Now, that doesn't mean it's not important.

Is there any scenario in which having lower consumption of EPA and DHA is beneficial in those smaller small studies, or is this basically a difference of neutral to negative?

I think it's the latter, neutral to negative. But I think the concept that I haven't discussed yet, but might be important to understand is that the half life of lipids in the brain is quite different than the half life of lipids in different compartments in the body. So for example, if you take DHA or EPA and you study after somebody is injected or consumed labeled DHA or epa, how long does it take for the DHA or EPA to disappear from blood? You understand that it takes a matter of weeks. Within three to six weeks that dose will disappear. And the opposite is true. It takes three to six weeks for the dose to reach plateauing or saturation kinetics after being fed a maximal dose of DHA or epa. But that has to do with the half life of these lipids on the transporting proteins such as hdl. So HDL may define the half life because it's going to be the major carrier of phospholipids. Now, when we talk about other compartments such as the brain, that may not be the case. The amount of time the DHA hangs out in neuronal membranes is substantially longer than the amount of time that DHEA hangs out on the surface of a phospholipid on HDL or with an albumin carrier and blood. And if we think about this more deeply, that makes sense. We do not want brains that are fluctuating with DHA and aa. We want a stable depot of lipids that does not dramatically fluctuate. So what does that mean? That means if you took somebody in a trial where they're not consuming DHA or EPA and then you gave them high doses of DHA and epa, and you know, if you look at these trials, they range anywhere from 12 weeks to a year and the majority are three months or six months. It's not surprising that these trials are finding not much. And in fact, when they find something, most of the time it's either a gut effect or an inflammatory effect because some of these omega 3s have anti inflammatory effects. So that presents a distinct challenge to the Omega 3 field, is that we may not have the resources to do a five or a ten year study, but we are privy to epidemiology studies which can give us a longer vision of what happens to those who consume enough omega 3s versus those who don't consume omega 3s at all.

And then I'll just layer in the question to bring it back to our discussion of apoe. Do we have a flavor to add to this, which is how does everything you say change in the context of APOE type, if at all it does.

So this is what my lab is particularly interested in solving, which is what is the best diet that we can give an Apoe 4 carrier to actually prevent cognitive decline? So we've been doing studies to examine this from multiple angles. And one of the studies that we found is that we took younger 35 year old Apoe 4 carriers and injected them with labeled DHA into their blood. And we estimated how much DHA is getting into the brain using a PET scan. And what we found is that younger APOE4 carriers had greater uptake of DHA in their brain compared to non carriers. Meaning that a younger, cognitively normal Apoe 4 carrier is sucking all the DHA it can take from blood to maintain a certain form of cognitive profile, to maintain your normal cognitive behavior. And ApoE4 carriers love the DHA. It's seen in blood and the brain of an E4 carrier is on fire, it's firing more, and it is using the DHA that is sucked from the blood. And that could probably provide us some deep insights about our ancestors and their diets. I mean, we know that APOE 4 carrier rate is highest in Africa, and We know that E4 carriers in Africa were consuming possibly more fish and meat than E4 carriers in Asia or E4 carriers in Europe. So in that regard, we looked at epidemiology studies and found a relatively large epidemiology study from Finland suggesting that E4 carriers who consumed a good amount of fatty fish combined with red leafy vegetables, antioxidants. When you looked at these individuals two decades or more into the future, when they were 60, those who were consuming the highest amounts of omega 3s from fish and other sources in the diet had substantially and significantly less disease than those who were not. So to us, that gave us insights that Perhaps the younger Apoe 4 brain loves to consume Omega 3s. Now, I hope the story ends here, and you know that that gives us a nice recommendation, but it doesn't, because we were continuously studying APOE 4 carriers across the age spectrum. And what we found is that after a certain age, and I would say this goes anywhere from 55 to 60, 70, the ability of the APOE4 brain to capture APOE4 from blood gets compromised. And this happens around the same time that the GLUT1 receptors are compromised. This happens around the same time that the blood brain barrier itself starts to get compromised, because you have to imagine that the blood brain barrier is tightly coupled. So when it starts disintegrating, your glut ones are not working, your omega 3 transporters are not working. So what does that mean? So we were part of a large randomized clinical trial where patients with mild Alzheimer's disease were fed high doses of DHA versus placebo over a period of a year and a half. And what that trial found is that in this trial, 2 grams of omega 3s had no effect on everyone, zero effect. The trial was negative, was published in 2010 in JAMA and the lead author was Joe Quinn. When we looked at that trial, we tried to understand how did APOE4 affect the response. And in that trial, APOE4 carriers had zero response and non carriers appeared to improve on the primary outcome, the ADAS CoG, and on a secondary outcome, which is the MLS. So in that trial, APOE4 carriers were less likely to respond than non carriers.

And again, the age of those participants.

Was what these people were between 65 and 80.

Got it. And was that DHA only or EPA and DHA in that?

That was DHA only.

And what you said earlier about the young people massively assimilating dha, was that also shown with EPA or only dha?

We were only studying DHA for the main reason is that the DHA is the main Omega 3 that makes the building blocks of synapses in the brain. And EPA more behaves as a signaling molecule that's anti inflammatory. So an application for EPA in the brain may be quite different than dha. So if you're more focused on vascular disease and perhaps the small embolic or thrombotic atherosclerotic strokes, then an EPA application may make more sense. But if you're looking at the synapse and what it requires to form neurotransmission, we think from a DHA perspective.

So what you just described fits with the previous observation, which is there may be a critical window in which DHA is essential. And once you're outside of that window, you lose the ability to integrate or assimilate dha. At about the same time, your blood brain barrier is failing and your ability to regulate even glucose is beginning to diminish.

Absolutely. So you hit it right on. We are actively doing a large trial that we have called Prevent E4 to partially address this question. If we took younger Apoe 4 carriers before they have dementia or before they have clinical symptoms, can we show Any effect on the brain. And we had this immensely challenging question of should we look at 30 to 40 year olds or should we look at 55 to 70 year olds? And in 2017 we made the decision to look at the 55 to 70 year olds because those people do cognitively decline with time. So we have the opportunity within two to three years to figure out if they're dropping. If we did this trial in a 35 year old, we may end up with a futile study because neither arm would change. So we are running a big risk though it is plausible that between the ages of 55 and 70, you're still too late. So where do you hold this? Where do you go? Is unknown. But Prevent E4 is ongoing. It started in 2019 and unfortunately now because of COVID we had to halt and Los Angeles had a substantial share of COVID cases. So we have, we had to hold recruitment in the last six months, but hopefully, you know, we hope to open recruitment again in the next few months. The study will possibly wrap up in 2023 and get published between 2024, 2025. So that's an ongoing effort where we're giving 2 grams high dose DHA based on pilot study that we have done before, showing that you need higher doses of DHA to get into the brain in APOE 4 carriers who do not have cognitive disease yet. They may have mild disease, but definitely not dementia, and to see whether apo, you know, high dose DHA supplementation can slow down the progression of disease in this population.

So again, of course the experiment that can't be done is taking the 35 year old E4 carriers, putting them on DHA for the rest of their lives. Because you're basically giving them DHEA at the time when, you know, they can assimilate it and following them for long enough to see a hard outcome, which is is there a meaningful reduction in the actual disease we care about studying. Since that experiment can't be done and will never be done, we then have to basically think about this through the lens of. This is a question that medicine does not have a tool to solve through the neat package called the clinical trial.

Yeah, the way to approach this problem would actually be finding surrogate biomarkers that you believe and trust that will hold long and behold, for example, we now maybe in the last five years have finally agreed that LDL cholesterol is a good target to lower for cardiovascular disease prevention. Although every now and then you'd get somebody who shows you lower LDL cholesterol may not translate into cardiovascular events. But for the most of people in the field agree that lowering LDL cholesterol by a statin or by ezetimibe or by any other measurement can associate with less atherosclerosis. Can we find a biomarker in 35, 45 year old individuals, a brain biomarker where if you change it, you would convince most people that this may protect you against dementia or cognitive decline a couple of decades? That's a fundamentally important question that needs to be tackled because without brain biomarkers we may not be able to answer these complicated questions.

I mean, I'm a bit skeptical that we're going to find anything anytime soon that fits exactly that description. And I think it's worth noting that one of the first drugs ever approved to lower LDL did so, but did not reduce events. I'm blanking on the name of the drug, but it actually was a drug that inhibited the enzyme that converted desmosterol to cholesterol. I think it's something called Delta 60 Saturase or something. And in doing so it did lower cholesterol and by extension LDL cholesterol. Although frankly at the time they probably only looked at total cholesterol. But events actually went up, presumably because desmosterol went up so much and acted as a sterol that had the same oxidizing properties. So in the end, events matter. But you're right, look, most drugs today that lower APOB also reduce events, but in the absence of such a biomarker or functional study, it doesn't have to be a biomarker. I guess if you had, you know, an imaging study or a functional study, that could matter. You know, hippocampal volume, if that be, if we believe that that was sensitive enough. But absent that, it still comes down to a question of what's the asymmetry of risk on each side. Right. So option one is do nothing. Option two is either through diet or supplement, take a given amount of dha. What is the downside of the latter? What is the downside of the former? I think those are questions that we have to spend more time thinking about because I don't think that clinical trials can give us answers to some of the most important questions facing disease prevention.

Yeah, so this is exactly where diseases like Alzheimer's disease or vascular dementia or any form of dementia represents a deep, painstaking challenge compared to atherosclerosis, where you can have an event within a couple of years and still see an effect on plaque reduction. Lower event rates, whether It's MI or amputations or strokes. Dementia, on the other hand, is much more subtle, much more complicated, and requires completely new set of tools. And as we speak, there's a massive amount of brain imaging studies, from functional MRIs to PET scans that are looking at different tracers, including amyloid and tau, which to date have not really panned out in the AD field, but with the premise that we can find a biomarker that, if you can modulate, can predict something a decade later. So one more thing that I just want to share with you before we wrap up is that, you know, my lab has also done very exciting studies that will be published in the next two to three months, showing that the older APOE 4 brain, once it gets into the dementia stage, starts up regulating enzymes that facilitates its own autodigestion. Because of the failure in utilizing glucose as a source of energy, we find that enzymes like phospholipase A2 are upregulated and activated in the APOE4 brain to perhaps extract fatty acids from its own myelin sheath to produce ATP. And that tells us about that. Recommendations that we should Give the younger APOE 4 carrier may be completely different than a recommendation that we give an older APOE 4 carrier who is in a state of energy deprivation and energy failure.

Say a little bit more about that. I mean, you're talking about someone who now actually is in the, the stages of early cognitive decline, who, presumably. I mean, when you say autodigesting, I mean you're referring to an enzymatic degradation of the cell.

Yes. So what we did is in the last three years, we've looked at enzymes that control omega 3s and omega 6s in the brain, and we found out that a specific enzyme known as phospholipase A2, which is the calcium dependent version of phospholipase A2, is strongly upregulated in Alzheimer's disease brains who carry the APOE 4 genotype compared to non Alzheimer's disease brains who carry the APOE 4 genotype. So we had access to a large database of brain tissues from Rush. Rush has one of the largest Alzheimer's disease research centers in the country. And we looked at many enzymes and stumbled across CPLA2 and showed that CPLA2 is hyperactivated or phosphorylated in E4AD brains. So you've got the Apoe4 carriers who developed AD as opposed to the Apoe4 carrier who died without AD. And we found that the Apoe4 AD brain activates these enzymes which, which take away fatty acids from the phospholipid membrane and then perhaps degrades the fatty acid to be used for many reasons. To us, the most obvious reason why you are extracting fatty acids from phospholipid is possibly to generate ATP. Now, there is a side effect to doing that, and that would be neuroinflammation and oxidative stress.

And I assume that this is something you're not seeing in the non E4 carrier who is in the comparable stage of dementia.

We are not seeing the same pattern of activation in a non E4 carrier who has a comparable state of dementia. That's correct.

Now, there's a lot of people out there who are talking about things like ketone supplementation. So not necessarily using ketosis in its nutritional or starvation form, but even using exogenous ketones as a supplemental fuel. Is there any reason to believe that that or a nutritional approach to ketosis would be a benefit to somebody with E4, especially when they're in that second wave? Or is the answer, well, anything that's going to prevent glucose from getting into the brain sufficiently is probably going to prevent ketones from getting there too.

You have fantastic insights and questions. So I think people have thought about ketone meals, ketone body meals, for treatment of dementia. And the largest studies to date have shown that Apoe 4 carriers, once they have the disease, are reluctant or less likely to benefit from the supplementation compared to non carriers. And exactly to your point, it is possible that the degenerating blood brain barrier is compromising the transport of ketone bodies the same way it has compromised the glucose and the same way it has compromised omega 3 fatty acids. So that makes us think that the aging Alzheimer's disease brain is a late stage that is refractory to the. Unless you are trying to fix the fundamental issue that is related to nutrient transport by a medication or an intervention. Dietary interventions at this stage may not be very effective and highlights the importance of getting the right intervention before you get to that stage to prevent it from happening.

I hate being asked questions like I'm about to ask you, so forgive me, but you know that everybody listening to this, and by definition about 25% of these people listening to this are going to be a carrier of at least one variant of E4. So this is a very relevant question question, what do you recommend to people? Let's just limit this to people who are, you know, have no stage of disease. I mean, you've certainly made the case for DHA.

Yeah, so I don't recommend Omega 3 supplementation for a simple reason. We don't have the evidence to actually support once we publish or others publish high quality evidence supporting going to a pharmacy and picking up a supplement. Until that happens, I don't think we have the evidence to support omega 3 supplements. But what I do recommend, though, is for people to take at least one serving of fatty fish per week. We know from epidemiology, APOE 4 carriers who consume 1 serving of fatty fish per week may be providing enough Omega 3s to their brains and helping themselves long term.

Is there anything else that you have learned in your travels vis a vis exercise, other things within nutrition? I know that's not the focus of your research, but do we know anything about the E4 carriers being more benefited if such a term exists through exercise? I mean, we know the importance of exercise in Alzheimer's prevention is enormous. But do we know if E4s bend one way or the other in that wind?

We don't have high quality randomized clinical trials, but we may have some epidemiology studies. Morris and his team at WASHU have shown in a PET study, this is an imaging study where you scan amyloid load in the brain, that APOE 4 carriers who exercise have less amyloid plaque buildup compared to APOE 4 carriers who do not exercise. Now, again, we would need an intervention to demonstrate that, but as we discussed in a minute, it's very difficult to find younger APOE 4 carriers, put them in a lifestyle intervention and then look at the outcome three to four to a decade later. Logistically, it's complicated and expensive. We also know from a Swedish group that looked at multiple factors of what determines pathology in APOE4 carriers, and they concluded that a high level of education, hypertension control protected ApoE4 carriers from dementia compared to ApoE4 carriers who had less education and worse blood pressure control. So to answer your question, I think if you knew at birth that you had Apoe 4, if your parents new and you have the ethnicity, the risk, the family history, the best advice that we have is to maintain an adequate omega 3 consumption from fatty fish, not supplements, to make sure that the blood pressure is controlled and to make sure that there is some at least minimal amount of exercise carried out throughout the lifespan to provide a modifiable element to the APOE 4. And when we talk about modifying APOE 4 risk, we often are referring to modifying the vascular effects of APOE4. So not only will you get cardiovascular benefit, but you will also get brain benefit because the blood vessels in Alzheimer's disease have as much of a role as the actual neurons and astrocytes and so forth.

Hussein this has been very interesting. Again, I think a lot of people are going to find this to be relevant to themselves or to people that they care about. I won't lie. It's a little frustrating that we're still so early in the study of this something that is so relevant and I believe probably quite preventable if we had a better sense of what the interventions were. And I think you're absolutely right. Biomarkers and or other functional imaging studies would really speed things up. If we we could do clinical trials in two years and get answers, we'd be a lot better off than if we had to study people over the course of their lifetime or rely on epidemiology, which is fraught with so many challenges that make it very difficult to disentangle causal relationships. But nevertheless, this has been illuminating and I thank you greatly for your generosity of time and effort.

Absolutely. Thank you for inviting me. It was a pleasure talking to you too.

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