Update on Blood Tests for Alzheimer’s Disease

Transcript

Intro: I’m Dr. Nathaniel Chin, and you’re listening to Dementia Matters, a podcast about Alzheimer's disease. Dementia Matters is a production of the Wisconsin Alzheimer's Disease Research Center. Our goal is to educate listeners on the latest news in Alzheimer's disease research and caregiver strategies. Thanks for joining us.

Dr. Nathaniel Chin: Welcome back to Dementia Matters. My guest today is Dr. Thomas Karikari, an assistant professor at the University of Gothenburg in Sweden and also the University of Pittsburgh here in the United States. Dr. Karikari studies early Alzheimer's disease-related brain changes and is working to develop new blood tests for Alzheimer's disease. Dr. Karikari's episode on Dementia Matters is a preview of his upcoming keynote address at our center's Alzheimer's Disease and Related Dementias Research Day. If you're listening to this episode before April 5th, head over to our website and register for Alzheimer's Disease and Related Dementias Research Day. If you're listening after April 5th, a recording of Dr. Karikari's research day talk will be available after the event. Dr. Karikari, welcome to Dementia Matters.

Dr. Thomas Karikari: Thank you.

Chin: Now your work is dedicated to a hot topic in Alzheimer's disease science – blood tests that predict or identify Alzheimer's disease. You and your colleagues are the world's leading researchers on this topic. How did your research journey lead you to where you are today?

Karikari: Thank you for a very interesting question. That’s a very interesting topic that actually brings me back a few years. My fascination with these aspects and looking at molecular aspects of medicine I discovered when I was in undergraduate education in Ghana in West Africa, where I was born and raised. I was really fascinated about the molecular aspect of medicine, how the small things that go in the molecular aspect of things that are going in the body especially, for example, when you eat and then how the digestion and the food goes through all the very tiny processes to generate energy for you. I continued in the same direction and that's how I find myself now in my doctoral research, doing Alzheimer research and looking at biochemical and also cellular aspects. After that I wanted to move into more translational aspects so that's why I moved into postdoctoral studies in an area that is now a very hot topic, looking at developing blood biomarkers. At that time, it was not clear that we were going to be able to succeed.

Chin: Your keynote address at Research Day will be an overview of fluid biomarker research in Alzheimer's disease and related dementias. By fluid biomarkers, we mean information in the blood or the cerebral spinal fluid, otherwise known as just spinal fluid, that indicates a risk for Alzheimer's disease just like a test of measuring cholesterol to predict heart disease risk. How close do you think we are to having these tests done in doctor's offices?

Karikari: I think we're pretty close because, as we speak now, there's several efforts to actually bring these to the doctor's offices. Even to reiterate that, there are some tests that are already available in some hospitals. For example, there's a blood test for plasma neurofilament light. It's a good measure of brain degeneration for some of the changes that happen in the brain in Alzheimers and other forms of dementia that are already available. For example, in Europe, it’s available in some countries, like Sweden and in the Netherlands, these tests can be requested from some of the central labs. Then, as you know, there are these tests from C2N that look at amyloid, that also have received this clearance and it's also available to request. The more recent ones that we have been also involved to develop have gained a lot of momentum. A lot of the research grid assets that we developed, those are being used in the clinical studies that have been published in high impact journals and have shown pretty good diagnostic accuracies and also robustness for use across multiple sites, and also across different studies and different cohorts. These ones have now been moved into commercial forms. For example, those that were developed in research labs have now – some of them have already been commercialized and also automated. That makes them easier to access for clinical use. In addition, there are some that are also being used in clinical trials. And some for example, phospho-tau 181 and phospho-tau 217 have already been used in clinical trials as surrogate markers for amyloid pathology. It means that we are quite close in seeing this being used in a doctor's office and it signals a very exciting time in the future of Alzheimer's disease diagnosis and also management.

Chin: Yeah, exciting seems to be the right word for that because it's taken a long time for the field itself to get to this really important moment. In your answer, I think you really differentiated two important processes: one, there's research use of blood tests and looking at biomarkers, but then there's clinical use. Obviously in research use you have a lot of control over who you're studying and what you're doing, and then clinical, that's a whole different game and you mentioned then the word commercialized. What you're doing now, there is still another process after this – correct? – that then has to make it available for clinical use.

Karikari: Yes, and that's why, for example, when you have big companies they have research and development departments compared to those that do the massive production. It’s the same thing that we also have in research. You go through the different processes and you're able to discover or develop something new, then you want to be able to test it. You do these things on small scales because, for example, if you have a cohort of 1,000 individuals, then you have reagents and you prepare your reagents in a way that you can control and be able to measure. When you're looking at global use, then you're looking at hundreds of thousands of individuals, right? These tests have to be available for each of the centers that order the tests, and one of the important things is that you have to make sure that there's a very good control, like the performances between different batches of these reagents have to be very comparable. The capacity to do these is often not found within research settings. It’s at that point basically, after you've done the development and the research, then you move it to more factories or industries with a capacity to do that. It's typical to what we saw with the COVID vaccine, for example. I realized that because the need was so, so huge at that time and a lot of the industries that discovered some of the COVID vaccines did not have the capacity to meet the demands, then they started contracting other companies to really take on some of the production for them so that they could meet the demand of what we needed. It’s actually quite similar to that. Research industries, research companies, and research institutes have the capacity to develop new things, but then when it comes to needing to serve a massive population we do not have that. At that point, we have to work well with biotech companies or pharmaceutical companies that have the capacity for that.

Chin: One of the other things you said, which I think is really important, is you use the word access. I think that when you look at this disease, it affects the global community and that means people all over the world are experiencing thinking troubles and being diagnosed with Alzheimer's disease. The work that you're doing can't stay in Sweden or in the United States alone. We need to make sure that there's access to this technology throughout the world, but that also speaks to the value of what you're doing with blood because it's easier to collect blood than it is to do a lumbar puncture and collect spinal fluid or to get very advanced imaging techniques that usually only occur at an academic center. Before we get into the implications of that, which I'm very excited to ask of you, I want to go to just the basics of the test itself. How accurate are the current tests in truly reflecting what's happening in the brain? Starting with the spinal fluid that you study, and then also then the blood.

Karikari: Yeah, that's a question that we ask ourselves all the time, because one thing that I also quite love about working with a very diverse group of scientists across multiple centers is that we try to be quite critical. We try to ask questions like, what do we know and why do we think we know this? What further evidence could we generate? One of the first things I would say in sort of being able to reflect what's happening in the brain, when we started, for example, with our plasma phospho-tau, I was quite curious to see that – although from the start we're showing that they correlate quite well with clinical diagnoses and also with data from, for example, CSF and also from imaging like amyloid-PET and tau-PET imaging studies, I was quite curious to see how do these measures reflect what happens in the brain because the brain is the ultimate source of the pathological diagnosis of Alzheimer's when someone unfortunately passes from the disease. Continuously there's data that comes into parts to show that in some unique studies where individuals – early adults – gave blood samples, either at one point or over several years before they passed on, and then after death they had signed to donate their brain to research then there were pathological diagnoses that were done by board certified pathologists. What was beautiful was that we could take the blood samples that were given up to ten years before these people passed on, and then measure these new markets blindly. Then you get to reveal the pathological report, then we can try to match them and see how they agree. One important thing that these results have revealed is that when you look at those, the blood markers agree better with the pathological diagnosis. The diagnosis of the changes in the brain after death at autopsy are better than clinical diagnosis, which means that if we use biomarkers which actually reveal the biological changes in the disease it's going to provide a better way of characterizing Alzheimer's disease and also, importantly, to differentiate it from very similar forms of the disease that are seen by clinicians who look at such diseases because one thing we see is that, for example with plasma phospho-tau, levels are increased only in individuals who have Alzheimer’s at autopsy. Those who have Alzheimer’s plus other forms of dementia also have high levels of the biomarker, which means that as long as someone has Alzheimer's disease the levels of this biomarker is going to increase regardless of any other pathologies that the individual might have. The levels also are low and almost normal when you look at individuals who were diagnosed with other pathologies and not AD or not Alzheimer’s form. Basically it’s similar to if someone passes on with let's say Parkinson's disease, for example, then the biomarker levels give you basically the same readout – similar to someone who passed on and then the pathological diagnosis was done and in the brain they didn't find any abnormalities that would signal the person having died of or from any dementia form. It's a very good way. It means that if you use the blood, it can predict and it can also provide a good measure of what is happening in the brain. I think, in addition also, we've been able to look at some studies that show that what you measure in the brain, it's quite similar to what you’re measuring the CSF or what you measure in the blood as well because the absolute levels do differ. At the same time also, there's some studies that are using a method called SILK that they use some radio ligand-labeled materials and then those ones go into the persons when – some people swallow it, for example – then they can be metabolized in a way that can go into the CSF or that go into the blood and also reflects in the brain. In that way we can be sure that what we measure agrees with the metabolism of the forms of tau and amyloid that exist in the brain, and some come down to a CSF and some go down to the blood as well.

Chin: Thank you for that explanation, Dr. Karikari, because I think it's important for people to know that you've looked at how the gold standard is autopsy. You've looked at the blood in the spinal fluid and compared it to what has been seen in autopsy findings. I think that speaks to the value and the need when people donate their bodies and the gratitude that scientists have to those who have donated their brains to science, because that is the only way you can know for sure since this is a disease of the brain. I wanted to clarify, too, for our listeners when you say p-tau and and then you're saying phospho-tau and then plasma phospho-tau – plasma, for our listeners, meaning just in essence blood. Then p-tau or phospho-tau is sort of a protein, a specific protein that you're looking at. That's what you've been studying in the blood, but also you can study that same protein in the spinal fluid and you've been comparing that to what's been seen on autopsy. Is that right

Karikari: Yes, that's exactly so.

Chin: So then let me ask you this, because when we measure these types of proteins whether it's p-tau or a different type of amyloid or tau itself, are those the actual proteins from the brain when you look at it from the spinal fluid compared to the brain or the blood compared to the brain?

Karikari: Yes, I think there are some caveats there. So what we’ve seen – and then this is the hypothesis – is that when there are these changes that occur in the brain, so for example in the course of developing Alzheimer's disease, you get to have accumulation of abnormal forms of tau protein that could be phospho-related and also amyloid as well. These form the kind of clumps that are often seen at autopsy when the brain is examined by pathologists, but then we have also over the years, together of course, a lot of scientists have shown that when these clumps are building up in the brain there are some forms that do get chopped off. Basically there's some core part of these proteins. Once they're sticking together, there’s some core parts of them that like to attract to each other and keep sticking together and then they keep piling up and they form massive clumps, and there are some other parts that get chopped off. These parts that get chopped off, they are the ones that also most of the time get to reflect in the CSF and also go down to reflect in the blood that we're able to measure now. Basically what we are measuring in blood,  and also to a larger extent in CSF, are sort of indirect measures of what is happening in the brain because it means that, for example, once you have a lot more of these proteins clamping up. If you have 20 units of the protein clumping up then the amount that would also – those parts that will get chopped off now will result in the CSF and in blood will be corresponding to that 20 units of the protein that clumping up in the brain. The same way if you have, let's say, 100 units then the amounts that you see in the blood, in the CSF, will increase. That is for phospho-tau or p-tau. For amyloid it would be the reverse, and then that would reflect, so more like looking at a direct kind of association of what's happening in the brain. Although, I might say that more and more we continue to try and also target new forms or newer forms that are less studied in blood and also in spinal fluid that are core part of the tangles in the brain, because we realize that some of these core parts can still leak into a cerebrospinal fluid and also we think could go into blood and that we'll be able to measure them. But the interesting things are these core parts of the brain or of the tangles and the plaques that form, they only start to increase in the symptomatic phases, or when someone is actually far off in the disease process. That's where you’ll be able to see some of the levels showing up in blood compared to some of the other forms that we've already studied. We have shown that they tend to increase quite nicely in the disease right from the very early stages.

Chin: Well, that's very helpful. Thank you. Not everything is linear. Not everything is a static progression. There are obviously different changes as a person is changing and things are accumulating. I think it's also helpful because many people think that the blood tests means that the amyloid is starting new outside of the brain and that it's forming in the blood, but really it is leaking from the brain to the CSF to the blood, so thank you for clarifying that. Just as you've said, there are certain tests that can be useful in those who are already having symptoms but also you're showing – and your colleagues – that these proteins are actually becoming abnormal or elevated in people before they have symptoms. How far back are you identifying proteins of Alzheimer's disease – amyloid or p-tau – in people before they have symptoms?

Karikari: That's a very important question. I also like, for example, in the early stages when we looked at some of the research cohorts and then we saw the way the biomarkers were able to predict disease changes years before. In a way it was exciting that we can use this, but it was also quite frightening in that in just a little drop of blood you could provide with quite good accuracy, you could be able to tell what's happening for an individual. That raises lots of qualms and ethical issues as well. Then to answer your question, how far back, I think it also depends on several things. For example, if the person has, let's say, early-onset Alzheimer's disease, which is likely to be caused by genetic predispositions to the disease then such individuals would show signs earlier, so it could be like in their early 40s or around 40 years of age, compared to those who have late-onset and that could be after 65 years of age. It means that if someone has early-onset then you can predict that far back into maybe when about 30 years, but then if someone has late-onset then the prediction will be far back to when they're about, let's say, fifty years or so. Of course, it depends on, for example, the genetic risk when someone has ApoE 4 allele of the ApoE gene; that also has an effect. Also it’s all about the subtype and then some demographics as well. We continue to study what specific factors predispose people to build up changes in amyloid and build up changes in tau in the brain at quite quick, faster pace compared to others, and that would also allow these blood markers to be able to pick said-changes much earlier. In a nutshell, we can develop – we can predict, in some of the studies we've done, it can go quite far back about less than ten years or about a decade before, but then it depends on the person's background also in terms of the risk for the disease. For example, in terms of early-onset you have people who have down syndrome. People with down syndrome have a very, quite high risk to develop Alzheimer’s disease and it seems like in such individuals, you're almost certain that the biomarker is going to perform quite well. For such people, you can also predict – you can look at the estimate of the age of onset of the disease, so it's much cleaner for people with genetic risk. You can predict with higher accuracy how far back they will be to develop the disease, but then people with sporadic forms, which is like late-onset, because we are not exactly sure of the cause of the disease then it makes it a bit more tricky. What we know is that the biomarkers can predict changes of Alzheimer’s as far back as several years back up to like a decade and that, in some longitudinal studies that are beginning to surface, we've shown that these predictive changes are quite accurate because a lot of the individuals that, from the early stages at baseline when they were studied, showed high risk to develop the disease actually went on to develop the disease. Also in the same way, we've shown in some neuropathology studies that those who donated their blood and then you could see high predictive accuracy also went on to show Alzheimer’s disease in their brain at autopsy as well.

Chin: And when you talk about prediction, in essence you're talking about risk. You've mentioned and we've talked about accuracy of the test itself in identifying the protein, but not everyone who has elevated amyloid on these tests will actually develop symptoms. That's why I know that your group and other groups are looking at risk calculators and how do we actually share predictions for at the individual level. In these situations of risk calculation, it seems like there's multiple variables, which you mentioned: genetic risk and lifestyle risk and other factors. When you think about the future of risk calculation or prediction at the individual level, how accurate or reliable do you think these things could be?

Karikari: Yeah, when it comes to these predictive algorithms, they can be only as good as what you put in them. As you said, there are different aspects of – I mean when it comes to Alzheimer’s, it's quite easy for someone to look at a blood test and that predicts that the person can have the disease. I'm quite wary of that. We shouldn't just focus on this. We should integrate with the existing paradigm where it looks at, you know, how does a clinician look at Alzheimer’s as of now and then integrate these blood tests to be another way of providing a tool to the clinician to make a good diagnosis. You could have the clinical, the neuropsychological testing and that would also give a predictive accuracy but then you have to add in a lot more. You have to add in the ApoE genotype, other forms of genetic risk that we know or we don't know about, and then the person’s – but another thing is that a lot of studies continue to show that there might be other things, for example, some comorbidities like people with cardiovascular disease hypertension and some other forms of disease that could increase one's risk for Alzheimer's disease. One issue there is that these risk factors or these risk models have not been tested in a lot of populations. It makes me a bit wary because before we can roll out anything to be a very good predictive model of Alzheimer’s in a global population using blood, because one thing we should remember is that once you talk about blood, blood is available everywhere. Blood can be taken anywhere, so we have to validate these models in a wide group of people before we can be sure. For example, the ApoE 4 genotype that we know is very well associated with Alzheimer’s, in more recent studies that are beginning to surface what we've seen is that – and these are actually new pathological, so brain studies of people who've passed on, who've died from Alzheimer's and related dementias – what they've shown is that for people of non-European ancestry the ApoE 4 gene – the allele – may not be a very good predictor, so it’s not a well-associated biomarker or risk factor when it comes to developing Alzheimer’s in people of non-European ancestry. However, this ApoE 4 allele genotype is very well established and it's very well used in clinical scenarios. So we have to try these models, and I like that these models are beginning to show up. We have to try them in a wide variety of people to get to understand where does it work, where does it not work, and in what conditions does it work, in what conditions does it not work. Also, what are some of the risk factors or what are the special disease factors that would affect the performance of these calculators?

Chin: Well you answered one of my next questions, Dr. Karikari, which really was knowing as much as you do about the actual test itself and what it can do, what concerns you have about you using it outside of research. Do you have any other concerns that come to mind, outside of what you just said that these tests have primarily been utilized in people of European descent and the need to study it in other populations? Are there other things that you think worry you if we were to just immediately start implementing the blood test today?

Karikari: Yeah, I think there are few things. One is that even within people of European descent that have been studied quite extensively, there's one thing that also worries me. We, you know, as scientists we depend on our volunteers who are well in to donate their time and the biospecimen to be taken for research, but then more often than not these are people who you don't need to explain much to them to come to donate their time from research or they might have spare time to spend. These people tend to be those who are well educated, those who live in quite affluent suburbs, and also might have time on their hands. We don't have a lot from people from the other part of the working class, so those people who live in suburbs that are highly likely to have, let’s say, high cardiovascular burden or other kinds of diseases that we often don't see. Basically what I'm trying to say is that the research cohorts that we have studied so far tend to be quite clean, right? These are people who have the capacity to live quite healthy lifestyles and it doesn't allow you to study the disease in the very real world setting that we would – that you would like to. For example, once we go into the clinic with these blood tests this is going to be quite a big test for the test themselves. Are they going to perform as well in the cohorts that we've studied? In addition to all the other things I've said, these other cohorts are also very well phenotyped because we've studied them – most of those cohorts have been studied with, like they've gone through all the extensive biomarker testing before they were used for the blood testing as well. It means that anyone with quite questionable diagnosis oftentimes get to be excluded as a basic setup for the cohort from the start. We have to start looking at real world data. We have to start looking at populations that just include people from everyday life, people from all walks of life, people from all the different classes of suburbs that you would see or the classes of occupations, and also from the classes of ethnicity, you know, people from all the aspects of life. One aspect, for example – when we often look at these cohorts, we tend to see the people that we study. One thing we should look at, for example, is when it comes to immigrants, we don't have a lot of cohorts to look at. When these tests go into the clinic, it’s not going to discriminate against anyone. We're going to be using them the same way for every individual. There are few studies that we have been looking at that tend to suggest that, for example when it comes to the blood test, the way they perform may not be exactly the same across the board. We're still very interested to try to understand why and how that these things do happen. Our working hypothesis is that there could be some specific factors that may interact with the development of the disease and that these ones could be more predominant in specific populations of people compared to others. To be able to understand this as much, there's a lot more that we have to do. In as much as the tests going to the clinic, there's a lot more that we should do in terms of identifying what affects the performance of the test from a very physiological point of view as well.

Chin: Well you’ve given us a lot to think about. I guess my question – my last question – to you, Dr. Karikari, is what is the next most important study in fluid biomarkers and Alzheimer's disease that you're working on or that you're going to work on or that you feel the field needs to address?

Karikari: Thank you. This is something that I discuss with my bosses sometimes. We just wonder what's next for the field because it seems we've been – we’ve seen quite good successes lately and those successes tend to show that there isn't much to do. However, I think that there's a lot more to do, to try, as we talked about. With these tests going to the clinic, there's a lot more to do to identify what affects the test performances and also how to improve the ability of the test to work the same way for everyone, but when it comes to the next stages we're quite interested in looking at the other forms of pathology in the brain. Alzheimer’s, as we know, is not a very pure form of pathology in the brain. People with Alzheimer’s are likely to have other pathologies and that would include TDP-43. It could be alpha-Synuclein. It could be other aspects. What we're trying to do is focus on developing new tests for these pathologies so that we'll be able to provide a better way of characterizing not just Alzheimer’s but all the spectrum of dementia that we get to see. At present, the best way that we can say is that – with these tests you can say, ‘Oh the person doesn't have a high level of, let's say, phospho-tau or amyloid in the blood, so then they are not likely to have Alzheimer's,’ but then there's a lot more as a huge spectrum of diseases that could they could belong to. What we want to do is to better characterize that other spectrum to try to better differentiate what forms of disease that these individuals are likely to have. We think this would be extremely important now that these steps are being used in clinical trials and also new drugs are emerging for Alzheimer’s and hopefully for the related dementias as well.

Chin: Well, thank you for your time today, Dr. Karikari. I look forward to catching your presentation at Research Day. For our listeners who are interested in hearing more from Dr. Karikari, visit adrc.wisc.edu/adrd2022 to register for our April 5th Alzheimer's Disease and Related Dementias Research Day where Dr Karikari is our keynote speaker. Thank you again, Dr. Karikari, for your time and this very thoughtful discussion. 

Karikari: Thank you.

Outro: Thanks for listening to Dementia Matters. Be sure to follow us on Apple Podcasts, Spotify, Google Podcasts, or wherever you get your podcasts to be notified about upcoming episodes. You can also listen to our show by asking your smart speaker to play the Dementia Matters podcast. And please rate us on your favorite podcast app -- it helps other people find our show and lets us know how we are doing. Dementia Matters is brought to you by the Wisconsin Alzheimer's Disease Research Center. The Wisconsin Alzheimer's Disease Research Center combines academic, clinical, and research expertise from the University of Wisconsin School of Medicine and Public Health and the Geriatric Research Education and Clinical Center of the William S. Middleton Memorial Veterans Hospital in Madison, Wisconsin. It receives funding from private university, state, and national sources, including a grant from the National Institutes of Health for Alzheimer's Disease Centers. This episode of Dementia Matters was produced by Rebecca Wasieleski and edited by Caoilfhinn Rauwerdink. Our musical jingle is "Cases to Rest" by Blue Dot Sessions. To learn more about the Wisconsin Alzheimer's Disease Research Center and Dementia Matters, check out our website at adrc.wisc.edu. You can also follow our Facebook page at Wisconsin Alzheimer’s Disease Research Center and our Twitter @wisconsinadrc. If you have any questions or comments, email us at dementiamatters@medicine.wisc.edu. Thanks for listening.