Dr. Patrick: It does. Circling back to something you mentioned sort of briefly when you were talking about blood-brain barrier not functioning well, you mentioned glucose metabolism and you decrease...you know, it's important for the...the blood-brain barrier being intact is also very important for glucose transport. Reduced brain glucose metabolism can be measured, you know, up to decades, even before any Alzheimer's disease symptoms or dementia symptoms occur. Hence, you hear the term type 3 diabetes. What effect does the breakdown of the blood-brain barrier have on brain glucose metabolism?

Dr. Montagne: That's another great question and ongoing studies are tackling this because it's not that clear and quite controversial. Just to tell you a bit more, so the main transporter of glucose at the blood-brain barrier to make sure glucose comes to the brain is GLUT1. So, that's a receptor, GLUT1, that has been found to be reduced in Alzheimer's disease. So, people have looked at, again, postmortem brain tissue bank and looking at the microvasculature and bigger vessels, and they found that Alzheimer's patients, they have much less GLUT1 at the blood-brain barrier, which means that there's less potential for the flowing glucose in the blood to penetrate the brain.

So, that's one thing, and we can measure that with several techniques, but one of them is FGD/PET. So, it's Positron Emission Tomography, and we can measure what we call FDG, which is a marker of what people say neuronal activity and things like that. So, we know that when we inject that tracer, it's a fluoro-deoxy-glucose tracer, into a patient. If you have Alzheimer's and if you don't, you will have much less FDG signal if you have Alzheimer's compared to a control. But what is interesting and there's a bit of controversy, I don't want to tell too much about this, but people are explaining this data and just saying that there's less neuronal activity and that's all. But what they don't take into account is these people have less GLUT1, so there's less probability that the radioligand will go, if there's less GLUT1 receptor, into the brain.

So, I think the FDG-PET signal has to be carefully analyzed in the sense that it could be a neuronal activity, but it also could be indirectly a marker of vascular problems because of what I've just said. But again, there's experts in the PET field that will tell you the reason why it is not and vice versa. It's very technical, and I don't have that expertise. But again, we know there's less GLUT1 independently of the reduction of the vascular network in Alzheimer's disease. So, I think the root cause is playing a big role here and it's currently investigated. I don't know much more than that, sorry.

Dr. Patrick: Well, I mean, I think it's very interesting and it certainly doesn't seem like we have, you know, the consensus, you know, on the answer to that question. I'll just mention, I remember reading a couple of studies years ago, animal studies, where omega-3 deficiency caused a reduction in GLUT1 transporters in the brain. Again, of course, omega-3 deficiency also breaks down the blood-brain barrier, you know, so it's kind of what's first, you know? Like, is the reduced glucose getting into the brain affecting the blood-brain barrier? Is the blood-brain barrier affecting the glucose transporters? Or both? You know, I mean, it seems tricky to sort of figure out but...

Dr. Montagne: That's the chicken and egg question all the time. Same thing with...I mean, I'm not an expert on omega-3 but it's basically the same thing when it comes to pericyte loss, endothelial activation, like pro-inflammation, breakdown of the barrier, loss of blood flow, what is happening first? And it's always difficult to address those questions because in human, most of the clinical studies are cross-sectional, you look at one time point. Now, I think there's more and more studies that follow individuals longitudinally with scanning, with looking at biomarkers, looking at neuro-psych testings. So, we're going to get more into this very, very soon, there's big centers working to do that. But for the omega-3, yeah, I'm not surprised you said that omega-3 deficiency leads to a reduction of GLUT1. Is that what you said?

Dr. Patrick: Yes, correct.

Dr. Montagne: I haven't read that paper but it goes well with what we said earlier, right? There is a vicious circle, where I think it's likely that, of course, the endothelial-pericyte crosstalk should be very involved in that problem, in my opinion, and that's something I would love to study.

Dr. Patrick: I'll send you my paper, I wrote a sort of interactive review article back in...gosh, it must have been like 2018 or something, I think. And it was on the important role of Mfsd2a and omega-3 in APOE4 carriers. And I have references for a lot of the studies, like the deficiency in omega-3 causing GLUT1 transporters to go down. So, I'll send you my review, you might be interested in...of course, it's a little bit of a hypothesis sort of review, you know? So, I review the literature, but there's a lot of my sort of thoughts for people that are actually exploring the field because I'm not doing these studies, you know, so you might be interested in that.

Dr. Montagne: And it's just...oops, sorry.

Dr. Patrick: Go ahead.

Dr. Montagne: It just rings a bell, I just remember reading a couple of stories and it's very relevant to what we do in the lab, is that, yeah, omega-3...the fact that you give omega-3 to aged animals...and I told you, as you age, you have pro-inflammation, like a hyperactivation of the brain endothelium. And a couple of studies have given some omega-3 to the mice and I remember seeing a reduction of one particular protein that I really like to study and what we are currently studying is VCAM1, vascular cell adhesion molecule 1, and omega-3 was able to reduce these levels. And in the lab, we know that VCAM1 plays a major role upstream of pericyte detachment. So, again, there's a lot of things that can be connected. I think it's very interesting.

And just another word on VCAM1 is Tony Wyss-Coray in Stanford University, one of the big labs working on proteomics and all these fancy omics techniques, he looked at Alzheimer's and healthy controls, he looked at their plasma and he has looked at using proteomics, looking at different proteins which...Alzheimer's, sorry, and normal aging. And what he found...I think the most striking finding was normal aging, he found, I think, 30-plus proteins in the plasma that were elevated with normal aging that were related to the blood-brain barrier. And if you look down, I think the top five candidates were proteins that are part of the endothelial cells, obviously, but the number one that stood out as the number one protein that is elevated with normal aging was soluble VCAM1. So, everything...you know, if you put some studies together, it kind of makes sense, there is a bit more to dig. But I think it makes sense and it might go well with also what omega-3 is doing to the vasculature, so it'd be nice to dig further.

Dr. Patrick: It's very interesting that you mentioned Tony Wyss-Coray as well because if I recall correctly, he's also been involved in research where he's transplanted young plasma into, you know, older mice and it's sort of rejuvenated in the brain and it's like, "Well, are there proteins...?" I think the opposite was done as well, where old plasma was transplanted into younger mice and it sort of accelerated and I think if I recall correctly, blood-brain barrier breakdown was part of that. And so, it's like identifying those proteins that is causing this.

Dr. Montagne: I think he's doing fantastic work and yes, correct, he is looking at the proteins that we have in the young blood that will help not only brain functions or anything, like, to help not aging too fast, but also he found a few key proteins that are involved in maintaining blood-brain barrier as we age. So, I think it's very interesting. And he's using also the parabiosis model where he kind of linked, you know, aged and young mice, but I think it's a very important study.