E4: why no urgent push for structure correctors, gene editting?

[Julie G]

I appreciate your deep thinking on this, Fiver. Would you mind sharing the recent papers that you're referencing. Are they specific to cerebral APOE levels? I find the work using peripheral APOE to be pretty compelling; higher levels appear to be protective against cognitive decline, even with our genotype. Also, I was wondering if you had considered that a statin could further impair the lipidation of APOE?

There is no HDL made in the brain, as far as I know. There are HDL-like particles containing apoe, however, made primarily in astrocytes. Apoe and apoj production increase greatly following head trauma.

My understanding based on this paper, is that our peripheral HDL-C is able to traverse the blood brain barrier where it could be very helpful in counteracting E4 deficits. Please correct me if I've misunderstood.

[Fiver]

Hi again Julie. Sorry for the delay - it's a busy Monday! So many questions. Here is a disorganized (sorry) reply. Thanks for the paper - more good reading!

HDL in the brain. I totally agree that HDL-C can cross into the brain from general circulation. HDL in general circulation seems to be a good thing. I haven't followed those studies enough yet to know if HDL getting into the brain would be helpful. I would suspect that the HDL would contain more apoA than apoE (as is typical) and would be well-lipidated, so at least it shouldn't raise free or poorly-lipidated apoE there and, thus, would probably not have detrimental effects in the brain. I presume that HDL in the brain probably can't do it's normal job - reverse CHO transport back to the liver - so I don't know what to make of it myself. But HDL is not made in the brain, as far as I know. Most CHO synthesis in a healthy brain happens in astrocytes and they export it in particles that are somewhat similar to HDL but have only apoE as the lipoprotein (no apoA).

Why did I conclude that lowering apoe in the brain was the way to go? I guess it was a general reaction....kind of sloppy on my part not pointing out specific papers (ugh)....to being overwhelmed by various papers showing all of the bad ("toxic" effects of apoe4 on gene expression, AB aggregation, APP synthesis and cleavage, etc. I assume that lowering apoe4 is one way to lower free/poorly lipidate E4, which seems to be the goal.

Examples convincing me that lower E4 would be good:

Like studies showing that correcting E4 structure to be E3-like (the oft discussed "Gladstone" papers)

Using gene editing to actually change E4 to E3 in human cell lines and mice. Here is one example: Huang, Y. A., Zhou, B., Wernig, M., & Südhof, T. C. (2017). ApoE2, ApoE3, and ApoE4 differentially stimulate APP transcription and aβ secretion. Cell, 168(3), 441.e21. 10.1016/j.cell.2016.12.044 Retrieved from https://www.sciencedirect.com/science/a ... 7416317603

Bredesen's gene expression paper (and other more recent, similar ones) just seem to show free E4 as the root cause of "badness". Here is that paper: Theendakara, V., Peters-Libeu, C. A., Spilman, P., Poksay, K. S., Bredesen, D. E., & Rao, R. V. (2016). Direct transcriptional effects of apolipoprotein E. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 36(3), 685. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/26791201

Here is a not-very-organized collection of papers I was recently reading:

Boehm-Cagan et al 2016 Differential effects of apoE4 and activation of ABCA1 on brain and plasmo lipoproteins PLOS ONE November 8, 2016. A good review of apoE4 and other lipoproteins and a good summary of how levels change differently and have different effects in the CNS compared to general circulation. Also: shows importance of ABCA1 for lipidating the particles and making them safe. They have a compound that encourages this in cells.

Liao et al. May 2018. Targeting of nonlipidated, aggregated apoE with antibodies inhibit amyloid accumulation. Journal of Clinical Investigation 128:5 page 2144- The study shows that binding up free/non-lipidated apoe(4) with antibodies or gene-therapy type silencing decrease amyloid formation. This paper seemed important.

So, here is what I am thinking, currently:
Apoe4 in general circulation can be good, in part because it is an important part of HDL which is beneficial and higher levels could be better BUT free or poorly lipidated apoe4 in the brain is toxic and, in my assessment, the root cause of most pathology.

About the statins potentially limiting the ability of ABCA1 to "fill up" apoE4 particles, making things worse. Yeah, I had the same concern you did. My readings convinced me that the availability of CHO in the brain and at the site of APOE "filling" specifically are in excess and are not limiting. I am still looking for any evidence that brain lipoparticle size is altered by statin use - but that's a rather specific question I can't find an answer to so far. You know I tend to be on the "pro-statin side" of things. I'll admit it's a tough question. In my case I had to make a call. I was greatly encouraged by several lines of evidence supporting statin use:

Love this paper! Geifman, N., Brinton, R. D., Kennedy, R. E., Schneider, L. S., & Butte, A. J. (2017). Evidence for benefit of statins to modify cognitive decline and risk in alzheimer’s disease. Alzheimer's Research & Therapy, 9(1)10.1186/s13195-017-0237-y

This one too. Wanamaker, B. L., Swiger, K. J., Blumenthal, R. S., & Martin, S. S. (2015). Cholesterol, statins, and dementia: What the cardiologist should know. Clinical Cardiology, 38(4), 243-250. 10.1002/clc.22361 Retrieved from https://onlinelibrary.wiley.com/doi/abs ... /clc.22361

Conclusions less clear in this one. Wood, W. G., Eckert, G. P., Igbavboa, U., & Muller, W. E. (2010). Statins and neuroprotection: A prescription to move the field forward. Annals of the New York Academy of Sciences, 1199(1), 69-76. 10.1111/j.1749-6632.2009.05359.x Retrieved from http://www.ingentaconnect.com/content/b ... 1/art00007

I've also read that the secretase enzymes that cleave APP into good or bad parts act differently when floating in lipid rafts rich in CHO. As best I can tell, the less CHO there the better.

I also want to not have a heart attack.

I'll share a bit of recent good news: my labs came back after 6 months of really serious diet, exercise, and lifestyle ReCODE-like stuff. And they were GREAT! It is absolutely amazing! Started out with all sorts of problems - and now the numbers are about as good as I could ever hope for. In this case, my own version of the program included a statin. I think the statin counteracted any tendency of the ketoflex diet to send lipids in the wrong direction (as they had been over the winter). And the diet counteracted any tendency of the statin to raise blood sugar. They worked well together. Dr. Bredesen would probably not agree, I know. But my version of the program raised my HDL more than anything my cardiologist did in the past ten years. And that was actually the least impressive of the numbers. All of the markers are unbelievable good. Even some other chronic metabolic issues - ones I couldn't ever seem to improve - were dramatically improved. Of course, I have no indication of what is really happening inside of my thick skull. But the numbers were so good, so much improved, that I'm going to stick with it as long as I can.

But again, I could be wrong. Please point out any holes in my logic.

I still hope for a nice E4 structure corrector.....

[Fiver]

Julie, here is one that seems to support your line of thinking...

Reduced levels of human apoE4 protein in an animal model of cognitive impairment
https://www.sciencedirect.com/science/a ... 8009001730
The APOE4 allele is the most common genetic determinant for Alzheimer's disease (AD) in the developed world. APOE genotype specific differences in brain apolipoprotein E protein levels have been observed in numerous studies since the discovery of APOE4's link to AD. Since the human apoE4 targeted replacement mice display characteristics of cognitive impairment we sought to determine if reduced levels of apoE might provide one explanation for this impairment. We developed a novel mass spectrometry method to measure apoE protein levels in plasma. Additionally, we developed an ELISA that replicates the mass spectrometry data and enables the rapid quantitation of apoE in plasma, brain and cerebrospinal fluid. We detected a significant decrease in plasma, brain and cerebrospinal fluid apoE levels in the apoE4 mice compared to apoE2 and E3 mice. We also measured a small (∼19%) decrease in brain apoE levels from aged, non-demented APOE4 carriers. Our findings suggest that a fraction of APOE4-linked AD may be due to insufficient levels of functional apoE required to maintain neuronal health.

[Fiver]

Hi again. Sorry for the long posts. This one is a toughie.

The above paper support the idea that RAISING apoe would be good, including in E4s.

But here is a recent one showing that LOWERING apoe would be good, including in e4s.

Halving the levels of apoE significantly attenuates accumulation in aged mice Interestingly, this
effect is independent of isoform, as the genetic reduction of either apoE3 or apoE4
attenuates accumulation.

Clear as mud.

2012
Neurobiology of Disease
Reducing Human Apolipoprotein E Levels Attenuates
Age-Dependent A Accumulation in Mutant Human
Amyloid Precursor Protein Transgenic Mice
Nga Bien-Ly,1,3 Anna K. Gillespie,1,3 David Walker,1,2 Seo Yeon Yoon,1 and Yadong Huang1,2,3,4,5

[Fiver]

...and this one is back to RAISING apoE.
I'm getting a headache trying to pin this one down...it seems like a really simple and important question.

Quercetin stabilizes apolipoprotein E and reduces brain A beta levels in amyloid model mice

By:Zhang, X (Zhang, Xilin)[ 1 ] ; Hu, J (Hu, Jin)[ 1 ] ; Zhong, L (Zhong, Li)[ 1 ] ; Wang, N (Wang, Na)[ 1 ] ; Yang, LY (Yang, Longyu)[ 1 ] ; Liu, CC (Liu, Chia-Chen)[ 1 ] ; Li, HF (Li, Huifang)[ 1 ] ; Wang, X (Wang, Xin)[ 1 ] ; Zhou, Y (Zhou, Ying)[ 1 ] ; Zhang, YW (Zhang, Yunwu)[ 1 ] ...More
View ResearcherID and ORCID

NEUROPHARMACOLOGY

Volume: 108

Pages: 179-192

DOI: 10.1016/j.neuropharm.2016.04.032

Published: SEP 2016

Document Type:Article

View Journal Impact
Abstract

Apolipoprotein E (apoE) is a major cholesterol carrier that regulates lipid homeostasis by mediating lipid transport from one tissue or cell type to another. In the central neural system (CNS), apoE is mainly produced by astrocytes, and transports cholesterol to neurons via apoE receptors, which are members of the low-density lipoprotein receptor family. The APOE epsilon 4 gene is a strong genetic risk factor for late-onset sporadic Alzheimer's disease (AD), likely through its strong effect on the accumulation of amyloid-beta (A(3) peptide. ApoE protein levels in cerebrospinal fluid (CSF) and plasma are reduced in APOEe4 carriers and in patients with AD. Furthermore, altered cholesterol levels are also associated with the risk of AD. A beta accumulation, oligomerization and deposition in the brain are central to the pathogenesis of AD. Mounting evidence demonstrates that apoE and apoE receptors play important roles in these processes. Astrocyte-derived apoE is pivotal for cerebral cholesterol metabolism and clearance of A beta. Thus, we hypothesized that increased apoE in the brain may be an effective therapeutic strategy for AD. We report here that quercetin can significantly increase apoE levels by inhibiting apoE degradation in immortalized astrocytes. Importantly, we show that oral administration of quercetin significantly increased brain apoE and reduced insoluble All levels in the cortex of 5xFAD amyloid model mice. Our results demonstrate that quercetin increases apoE levels through a novel mechanism and can be explored as a novel class of drug for AD therapy. (C) 2016 Elsevier Ltd. All rights reserved.

[ApropoE4]

Really good question, Fiver. A few years ago a bunch of us met with Drs. Mahley and Huang at Gladstone. They’ve made the most progress with an E4 structure corrector. They gave us an amazing presentation and felt certain the structure corrector Pharma would be available soon. For some unknown reason, it’s lagging. Many of us have donated our blood for in vitro proof of concept, but we’ve heard nothing since... I wonder if the science isn’t translating from the mouse model. Who knows? If anyone has an update, please share.

Science is translating, and the structure corrector is having the expected impact in human tissue, but so far in vitro:

https://www.nature.com/articles/s41591-018-0004-z

I am guessing that the company working on this is developing a strong enough case to allow them clinical trials on healthy adults much earlier than would be possible with mouse-only results.

[Fiver]

Probably right apropoe4.

That study is encouraging, isn't it?

[Harrison]

Hi Fiver,

I independently came to a lot of the same conclusions that you have. Specifically, apoE4 is less lipidated by ABCA1 (Boehm-Cagan et al 2016) and that non-lipidated apoE is the problem (Liao et al, 2018). One would want to increase lipidation of ApoE4, decrease apoE4 levels (preferentially non-lipidated apoE4), or alter apoE4 so that it could be more lipidated, or less toxic (Wang et al, 2018). I don't think these approaches need to be mutually exclusive either. Maybe the winning combination will be taking a drug cocktail that does all three: an ABCA1 enhancer or something that makes more CNS lipid available to apoE, something that reduces non-lipidated apoE4, and something that corrects apoE4 to reduce toxicity.

Regarding the structure corrector, E-scape Bio has been working on this for a while now. I would expect they would have published something just to keep the investments coming, but so far nothing. The drug used in the Nature paper is from 2011 and must not have moved beyond early pre-clinical testing for some reason.

[Brian4]

How disheartening. I just wrote a long post, clicked on "Submit", and now it seems to have disappeared. Too dispirited to recreate it.

Summary: Fiver, thanks for raising this critical question. Phase I trials should be starting soon. This is the most hopeful thing out there, in my view.

Brian

[Orangeblossom]

Regarding ABCA1, it is possible to look at the variants on Promethease, for this. It says things like associated with higher HDL...so there must be an association there with that as well. I wonder if you have good variants for ABCA1 that might help the lipidation of the APOE4? (hopeful )

For example https://www.snpedia.com/index.php/rs2230806

More in these here. I have the common ones for these two which apparently increases risk. Great.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2758418/