Blood-based Biomarkers for Alzheimer’s Disease in Women

Podcast Transcript

Introduction: Neuro Pathways, a Cleveland Clinic podcast exploring the latest research discoveries and clinical advances in the fields of neurology, neurosurgery, neurorehab, and psychiatry.

Glen Stevens, DO, PhD: Nearly two thirds of individuals living with Alzheimer's disease are women, and while the mechanisms driving this discrepancy are not fully understood it underscores the need to pinpoint sex-specific biomarkers that could aid an early detection and diagnosis. In this episode of Neuro Pathways, we're discussing ongoing research that seeks to identify candidate blood-based biomarkers that could be utilized to improve clinical care for women with Alzheimer's disease.

I'm your host, Glen Stevens, neurologist/neuro-oncologist in Cleveland Clinic's Neurological Institute. And joining me for today's conversation is Dr. Lynn Bekris. Dr. Bekris is Associate Staff in the Genomic Medicine Institute within Cleveland Clinic's Lerner Research Institute, Director of the Cleveland Alzheimer's Disease Research Center Biomarker Core, and Co-director of the Cleveland Clinic Lou Ruvo Center for Brain Health, Aging and Neurodegenerative Disease Biobank. Lynn, welcome to Neuro Pathways.

Lynn Bekris, PhD: Thank you for having me.

Glen Stevens, DO, PhD: So, Lynn, I get more interested in these topics as I get older. I know we're concentrating on women today, but as I get older, I'm much more interested in what's going on in the Alzheimer area. And, as I always tell my wife, females always live longer than males, and I think age is probably the strongest risk factor for dementia. But I think you're going to tell us, and you're going to educate us, on some other specific sex differences.

So, your research, specifically, is focused on biomarkers for Alzheimer's disease. So, to start can you define for us what a biomarker is, and then give us an overview of validated biomarkers for Alzheimer's disease and how they can be utilized? So, biomarker first.

Lynn Bekris, PhD: Yeah. So, what is a biomarker? It is a characteristic that is objectively measured and evaluated as an indicator of normal biological processes or pathogenic processes or pharmacologic responses to a therapeutic intervention. So, biomarkers can serve as a warning that something is disrupted in a person's normal healthy function. Some examples are elevated blood pressure or cholesterol levels, and if there is a therapeutic intervention, for example, treatment with an antihypertensive drug, then lowering of the biomarker, such as blood pressure, indicates that the treatment is effective.

Glen Stevens, DO, PhD: And, specifically, can you give us an overview of validated biomarkers in Alzheimer's disease?

Lynn Bekris, PhD: Yeah, so in Alzheimer's the hallmarks of the disease are the pathological accumulation of amyloid and tau proteins in the brain. And amyloid and tau are validated biomarkers of the disease and can be measured in cerebrospinal fluid, which is the fluid that bathes the brain and can be sampled from the base of the spinal column. Amyloid can also be measured by brain imaging during the life of the patient as well as in the brain after death. So, for Alzheimer's disease we have good biomarkers of amyloid and tau proteins, and these include brain imaging and amyloid tau proteins found in cerebrospinal fluid.

Glen Stevens, DO, PhD: So, I know there's been a number of drugs released recently and still coming on the market to treat amyloid deposition, and I think you're going to talk to us about maybe some other potential abnormalities in Alzheimer's disease, possibly looking at inflammatory reaction, those types of things. So, you have a project going on investigating blood-based biomarkers for Alzheimer's disease, specifically in women. What was the impetus behind focusing on women? And then we'll get to your study.

Lynn Bekris, PhD: So, we're very excited about this project. This project is supported by a Women's Alzheimer's Movement Research Award, and we came upon the premise of the study because we had done a pilot study, that we focused on a question because Alzheimer's disease risk is genetically linked to multiple immune system genes. So, we did a study to address the question of whether people with Alzheimer's disease have a different immune factor signature in the circulation, so in blood plasma. And that study was funded by the Aging Mind Foundation, and it revealed that immune factor signatures are significantly different in people with or without amyloid and tau proteins. But another really interesting finding was that we observed there was a difference in the immune factor signatures in women compared to men with or without Alzheimer's disease related amyloid and tau.

So, we think that this finding is really important because a disproportionate number of women have Alzheimer's and more women than men have immune system related disease. So, our finding could be revealing why women are more susceptible to Alzheimer's disease than men. And this is why, going forward, we'll focus on women. But this was just a pilot study, so we want to investigate this further. And the Women's Alzheimer's Movement award will help us do that.

Glen Stevens, DO, PhD: Well, congratulations on the award. It sounds very exciting. Now, my understanding, if we go into the weeds a little bit with this, that you have a novel design with the project where you're looking at CSF markers to define Alzheimer's disease.

Lynn Bekris, PhD: Yeah. So, what we're going to do is we're going to measure amyloid and tau in the cerebrospinal fluid. And we now, as an Alzheimer's research community, have a well-designed guideline for how we can use amyloid and tau biomarkers for categorizing people into amyloid positive only versus amyloid and tau positive, compared to amyloid, tau and the neurodegeneration positive. So it's a kind of staging that we can do. So, we're going to take a group of Alzheimer's patients and also people of a similar age that are cognitively normal, and we're going to measure a big panel of proteins in the plasma. We're going to measure over 7,000 proteins and then try to tease apart which ones are specific to these Alzheimer's disease-related biomarkers, amyloid and tau.

Glen Stevens, DO, PhD: So, the amyloid tau neurodegeneration marker that you're doing, or the ATN, versus a clinical diagnosis, what's the plus and minus of doing that?

Lynn Bekris, PhD: It adds another biological layer to the clinical diagnosis. We will use clinical diagnosis as well, but it gives us confirmation that we actually have people that have amyloid and tau, which defines Alzheimer's disease. We do have heterogeneity in our cohorts, so we can have a lot of different underlying biological mechanisms involved in the disease. For example, we can have other proteins like alpha-synuclein, and they can present sometimes similarly to Alzheimer's disease. So, in this design we're just being sure that we have people that are amyloid and tau positive and not people that are amyloid negative, for example, because that could be a different type of dementia than what we're interested in for this study.

Glen Stevens, DO, PhD: And it seems somewhat obvious, but what are the advantages of blood-based biomarkers?

Lynn Bekris, PhD: Yeah, so the obvious thing is really that they're a little bit less invasive, so less invasive than a spinal test, spinal tap test, or even a brain scan. They're also cheaper. But here, really, our focus is that they're in the circulation. So, the immune system can easily be measured in the circulation. And there are studies that are showing that the circulation can be giving us some evidence of what's happening in the brain. So, we're going to use a combination of biomarkers that are present in the brain, but also those that are present in the blood, and hopefully we can find differential immune response in Alzheimer's disease.

Glen Stevens, DO, PhD: And can you enlighten us on any of these biomarkers, specifically, that you're looking at or is that top secret?

Lynn Bekris, PhD: No, we're very focused on TREM2 which is a protein that is present in the circulation. It's in plasma and cerebrospinal fluid, and it has a soluble form. It also has a protein that is present on the membrane of cells that are of myeloid origin, so macrophages and microglia. And we've been studying that. We've published on that. And that has an influence on other inflammatory factors. So, there's evidence now that if TREM2 is upregulated there's influence on the broader immune response. So, we're looking for a signature that is probably going to include TREM2 because TREM2 has been linked to Alzheimer's disease genetically. And we also are seeing this relationship between TREM2 and the broader immune response.

So, we have a couple of other immune factors that look like good candidates. So, we're looking for a composite biomarker with TREM2 and these other inflammatory factors as well. But we have to validate the study before we can really be sure if those composite biomarkers are robust and feasible biomarkers. And so that's what this study is about. We're looking at a different method and more proteins, so that we can validate we found in our pilot study.

Glen Stevens, DO, PhD: And maybe it doesn't make a difference, but does timing of when the biomarkers, the blood, is drawn - morning, night - make a difference?

Lynn Bekris, PhD: Yeah, it does actually. And we have in our protocols to do our blood draws and the cerebrospinal taps early in the morning on people that have fasted overnight because, yes, it does have an effect on the measure.

Glen Stevens, DO, PhD: And, in this project, you're not comparing directly to men, is that correct? You're just comparing different degrees of normal and mild cognitive impairment in Alzheimer's females. Is that correct, or are you comparing to a male cohort?

Lynn Bekris, PhD: We are comparing to a male cohort. Our pilot study, we stratified the cohort by men and women, and then we saw that there was this big difference between the men and women within these specific ATN categories. So, we're looking at it from multiple directions. We're looking at, within the ATN groups, are there differences between men and women? And then within women, are there differences between the ATN groups, or, within men, are there differences between the ATN groups. And we are seeing that in our pilot study. We saw that there were some significant differences. So, our hypothesis is that men will have a signature that's specific to these ATN groups, and then women will have a different signature that's specific to the ATN groups. And so therefore, potentially, we would need to treat men and women differently so the therapeutics, the immunotherapies, have to be different for women and men in order to be effective.

Glen Stevens, DO, PhD: And is there any reason to believe that ethnicity would affect the biomarkers?

Lynn Bekris, PhD: Yeah, that's a really good question. Just now in the Alzheimer's field we're starting to dig into that a little bit, and people are seeing that there are differences in biomarkers. There's some differences in the levels, for example, in African Americans compared to whites. So that does complicate our studies a little bit. Unfortunately, our cohorts are primarily white, but we are now collecting more samples from other groups. So, we're hoping that a future study would include those other races so that we really can determine if this type of test is accurate in other races.

Glen Stevens, DO, PhD: And, of course, I'm way ahead on where this can go, but I assume that you would hope that the biomarker could be used as a measure of treatment effect, that you would give some anti-inflammatory type treatment and then you could measure the change in the biomarker. Is that correct? Is that your hope?

Lynn Bekris, PhD: Yes. Yes, definitely. That would be the hope that the biomarker would track with treatment, so that if we treat an individual, then the biomarker would change according to the treatment. And we do have some specific treatments now in Alzheimer's that are in clinical trials. For example, there's a TREM2 antibody in clinical trials. And so the question would be that if you treated somebody with an antibody to TREM2 and impact the cleavage process of the protein, so the function of the protein, if that has a broader impact on the inflammatory response, and could we see a difference in this biomarker, this immune response biomarker, that we're trying to develop?

Glen Stevens, DO, PhD: Very exciting. Day-to-day variability of these biomarkers, have you looked at that? If you did blood work on me seven days in a row, how's the correlation?

Lynn Bekris, PhD: Yeah, so for ATNs that's been done. It depends on what stage a person's at. It looks like earlier in the development of amyloid and tau there's more variability over time, whereas later there isn't. But for the immune response signatures, or immune factors, we have not done that and we're hoping to do something like that.

Glen Stevens, DO, PhD: Okay. And is there a thought that at some point in the disease that the inflammatory reaction may burn out, or we don't know that?

Lynn Bekris, PhD: Yeah, there is. It's a really good question. We're observing differences in... For example, in TREM2, it looks like early in the disease the levels of TREM2 are different than later. And in some of the preclinical models it looks like if you have elevated soluble TREM2 there might be a beneficial impact of that, whereas later it would be detrimental in the disease. So, it's complicated. We have different results according to the different stages. So that's partly why we really want to look at the different ATN stages so we can tease apart some of that.

Glen Stevens, DO, PhD: And are there medications that patients can't take for this study?

Lynn Bekris, PhD: We are going to be looking at the comorbidities and what therapeutics the patients are on, but at this point we don't know. We would assume that if they're on anti-inflammatories that there might be an impact on that. So, it's a good question, but we don't know at this point.

Glen Stevens, DO, PhD: So, you've alluded to some of this a little bit, but anything you've found so far that's surprising or notable? And if it's something you've already discussed, feel free to raise that point again.

Lynn Bekris, PhD: Yeah, well, I think the differences that we saw between men and women, we were surprised that it was so, so different. We are seeing that in women that are amyloid positive but tau negative, there is an uncoupling with soluble TREM2. So, the broader immune response is not associated with the soluble TREM2 response in women at that stage. Whereas, in men, it's associated with an uncoupling of soluble TREM2, so a lack of relationship with the broader immune response in that early A+ stage, and also in the A+T+ stage, so the tau and amyloid stage. So, it looks like in men there's definitely a very distinct signature that might be more pronounced for a longer period of time, whereas in women it is very distinct in that amyloid-only group. So, we were surprised to see such a distinct signature.

Glen Stevens, DO, PhD: And my understanding is that females, on average, have a little more rapid decline than men. Is that correct?

Lynn Bekris, PhD: Yes. And there's some complexity there in how long women have the disease. And women, as you said earlier, there's a very strong association with age and Alzheimer's, and women can live longer than men. So, I think that is still complicated. But yes, once women are diagnosed there can be a much more rapid decline.

Glen Stevens, DO, PhD: So, what do you foresee as potential clinical applications for your findings? And I know we're way ahead here.

Lynn Bekris, PhD: Yeah, so really, for us, what we're thinking is that there might be a way to prevent the accumulation of amyloid and tau by focusing on the immune response. And this might be particularly important in women that are showing a different or maybe potentially more robust immune response early on. So, the hope is that we can develop a signature and know a precision medicine manner so that we can identify people that are having a certain type of immune response that would be detrimental and more rapid decline or accumulation of amyloid and tau. So, then those people could be targeted with a more precise type of immune therapeutic.

Glen Stevens, DO, PhD: So where are you going to go next with your research? I mean, you got this to do, then what?

Lynn Bekris, PhD: Well, our hope is to get further funding so that we can do a longitudinal study. We really like to follow people over a couple of years to see if our hypothesis is true over time. So, for example, if people have a certain immune signature and they're ATN positive, but they have a certain immune signature at one of the ATN stages, we're wondering if they convert to another signature when they're in another ATN stage. So, the only way to determine that is if we have longitudinal studies and whether we follow people over time. So that's what we're hoping to do next after this initial study.

Glen Stevens, DO, PhD: Well, it's fascinating. It makes me wonder. I did a previous podcast on the Cleveland Clinic Brain Study, and depending on if and when you develop a signature if that could even be incorporated into the longitudinal brain study. But, I guess, food for thought.

Lynn Bekris, PhD: Yes. Yeah, that's a great study. That's a definitely longitudinal study, and that's what we need in neurodegenerative disease is these longitudinal studies to really understand the biological mechanisms.

Glen Stevens, DO, PhD: Thanks for joining me today, Lynn. It sounds like an exciting time for Alzheimer's disease research and I'm looking forward to what happens next.

Lynn Bekris, PhD: Thank you.

Conclusion: This concludes this episode of Neuro Pathways. You can find additional podcast episodes on our website, clevelandclinic.org/neuropodcast, or subscribe to the podcast on iTunes, Google Play, Spotify, or wherever you get your podcasts. And don't forget, you can access real-time updates from experts in Cleveland Clinic's Neurological Institute on our Consult QD website. That's consultqd.clevelandclinic.org/neuro, or follow us on Twitter @CleClinicMD, all one word. And thank you for listening.