Sep 16, 2021
This month on Episode 28 of Discover CircRes, host Cynthia St. Hilaire highlights four original research articles featured in the August 20th and September 3rd issues of Circulation Research. This episode also features an in-depth conversation with Dr Scott Cameron from the Cleveland Clinic and Dr Milka Koupenova from the University of Massachusetts Medical Center about their study, SARS-CoV-2 Initiates Programmed Cell Death in Platelets.
Article highlights:
Gupta, et al. Electronic Cigarettes and Oxidized Lipids
Bartosova, et al. Glucose Derivative Induced Vasculopathy in CKD
Atmanli, et al. DMD Correction Attenuates Cardiac Abnormalities
Ma, et al. Length Dependent Activation in Porcine Myocardium
Cindy St. Hilaire: Hi,
and welcome to Discover CircRes, the podcast for the American Heart
Association's journal, Circulation Research. I'm your host, Dr
Cindy St. Hilaire from the Vascular Medicine Institute at the
University of Pittsburgh, and today I will be highlighting articles
presented in our August 20th and September 3rd issues of
Circulation Research. I also will speak with Dr Scott Cameron from
the Cleveland Clinic and Dr Milka Koupenova from the University of
Massachusetts Medical Center about their study, SARS-CoV-2
Initiates Programmed Cell Death in Platelets.
Cindy St. Hilaire: The first article I want to share is titled Electronic and Tobacco Cigarettes Alter Polyunsaturated Fatty Acids and Oxidative Biomarkers. The first author is Rajat Gupta and the corresponding author is Jesus Araujo from UCLA. E-cigarettes have surged in popularity in the last decade and while many people switching from traditional cigarettes to smokeless ones view the latter as a safe alternative to smoking tobacco, emerging data shows that E-cigarettes cause adverse effects such as oxidative stress, inflammation and endothelial dysfunction in users. The aerosols produced during vaping contain similar levels of reactive oxygen species, also called ROS, as the vapors of tobacco smoke. However, data on the extent to which E-cigarettes, E-cigarette ROS, influences cardiovascular health is lacking.
Cindy St. Hilaire: To address this, this group recruited 32 chronic users of E-cigarettes, 29 chronic tobacco smokers, and 45 individuals that used neither and they measured their plasma levels of oxidative biomarkers. The team found both similarities and differences between the E-cigarettes and the tobacco users. For example, both smoking groups had increased plasma antioxidant capacity and decreased levels of oxidized linoleic acid compared with the levels seen in non-users, while arachidonic acid levels were raised in tobacco smokers and reduced in E-cigarette users. Overall, however, the biomarker levels were deemed to be intermediate for E-cigarette users between the non-users and the tobacco users. This study suggests that while E-cigarettes carry a lower health risk than tobacco, they are by no means safe.
Cindy St. Hilaire: The second article I want to share is titled Glucose Derivative Induced Vasculopathy in Children on Chronic Peritoneal Dialysis. The first author is Maria Bartosova and the corresponding author is Claus Schmitt and they're from the University of Heidelberg. Diabetes, high blood pressure and obesity are risk factors for both cardiovascular disease and chronic kidney disease. Worse still, loss of kidney function and even dialysis itself are thought to exacerbate cardiovascular issues. In the case of dialysis, it's thought that high levels of glucose degradation products, or GDPs, in the dialysis fluids can promote the addition of sugar moieties to vascular proteins and lipids causing vascular damage. To investigate this theory, Bartosova and colleagues studied vascular tissue from children with chronic kidney disease receiving dialysis fluids with either high levels or low levels of glucose degradation products and compared these to tissues from children not on dialysis at all.
Cindy St. Hilaire: Proteome and transcriptome analysis of the vessel tissues revealed that compared with patients or no to low GDP fluids, patients receiving high GDP fluids had higher levels of damaging glycation, increased transcription of genes involved in cell death, and decreased transcription of genes involved in cell survival and cytoskeletal reorganization. In line with these findings, vessels from high GDP patients displayed considerable evidence of damage, such as markers of apoptosis, skeletal disintegration and thickened intimas. The results confirmed GDPs can cause vasculopathy and suggest low GDP fluids should be used for dialysis patients.
Cindy St. Hilaire: The next article I want to share is titled Cardiac Myoediting Attenuates Cardiac Abnormalities in Human and Mouse Models of Duchenne Muscular Dystrophy. The first author is Ayhan Atmanli and the corresponding author is Eric Olson from UT Southwestern. Duchenne Muscular Dystrophy, or DMD, affects one in 5,000 baby boys and is caused by mutations in gene for dystrophin, an architectural protein essential for muscle cell integrity. Patients display profound muscle degeneration and weakness, with respiratory and heart muscle dysfunction being a major cause for death. With the recent improvements in respiratory medicine that extend the lives of patients, this group now focused on heart dysfunction and specifically, whether gene editing could mitigate it. The team created induced pluripotent stem cells, or iPSCs, from Duchenne Muscular Dystrophy patient and his healthy brother and showed that gene editing from the DMD cells enabled their development into normal-looking cardiomyocytes with normal contractile function and calcium handling, equivalent to that seen in healthy control cells. The unedited DMD cells, by contrast, did not develop normally. For great clinical relevance, the team edited DMD cells after cardiomyocyte differentiation showing that this reduced their propensity for arrhythmia, compared with that of unedited cells.
Cindy St. Hilaire: Lastly, the team provided evidence to suggest gene editing may improve heart abnormalities in mice with the same mutation. All together the results are proof of principle and support of the development of gene editing therapy as treatment for DMD.
Cindy St. Hilaire: The last article I want to share is titled The Super-Relaxed State and Length Dependent Activation in Porcine Myocardium. The first authors are Weikang Ma and Marcus Henze and the corresponding author is Thomas Irving and they're from the Illinois Institute of Technology. Myofilament length-dependent activation or LDA is the fundamental mechanism coupling the force of the heart's contraction to it's proceeding diastolic volume. In other words, LDA ensures that the more the heart fills, the stronger it contracts. Studies of rodent hearts have given insights into LDA mechanics. However, how it operates in large mammalian hearts is unknown. Using structural and biochemical analysis of pig myocardial fibers, this group found that compared with small stretches of the fibers which were equivalent to small diastolic volumes, long stretches induced greater ATP turnover and greater numbers of cross bridges between myosin and actin filaments which are critical contractile machinery proteins.
Cindy St. Hilaire: Myosin motors can be found in three stages, engaged with actin, unengaged in a disordered, relaxed state but ready to engage, or super-relaxed state where they are essentially switched off. The team showed that as muscle stretch increased, the amount of super-relaxed myosin motors diminished with more myosin motors becoming engaged to enable a stronger contraction. When the fibers were treated with a myosin motor inhibitor, these stretch effects were impaired. In revealing the mechanisms of myofilament length-dependent activation, this study provides a platform for studying cardiomyopathies in which this system goes awry.
Cindy St. Hilaire: So today, Dr Scott Cameron from the Cleveland Clinic and corresponding author of the paper, Dr Milka Koupenova from the University of Massachusetts Medical Center, are both with me to discuss their study, SARS-CoV-2 Initiates Programmed Cell Death in Platelets. And this article is in our September 3rd issue of Circ Research and for full disclosure, the editor of Circ Res, Dr Jane Freedman is also an author on this manuscript. And for full double disclosure, I know Dr Koupenova quite well as we were both graduate students together back in the Ravid Lab at Boston University. However, the full Editorial Board selects these articles, not just me alone and this one is timely, novel, and an amazing story. So thank you both for joining me today.
Milka Koupenova: Thank you for having us.
Scott Cameron: Privileged to be here.
Cindy St. Hilaire: So before we jump into the story that is your paper, can you give us a little bit of background about platelets? I know for years, I guess certainly before Katya's lab, I just thought of platelets as little nucleus-free particles that clot. But we know they are so much more than that. So why are they so important? And how do they function to do more than just stop a bleed?
Milka Koupenova: So this is a great question, Cindy, and I am happy that you alluded exactly to the anucleated nature of platelets. So platelets are cell fragments. They're precursors in the bone marrow, the megakaryocyte. They are the second most abundant blood component after the red blood cells. And traditionally, platelets have been known, as what you pointed out, as these little units that change their conformation once there is some form of a problem with either the vascular, which we have a cut, they come together, they form this clot, and bleeding is prevented. But as we have learned perhaps in the past 20 years that platelets have a profound immune role during various immune processes and infections for different kind of microbes. And particularly relevant to this paper is that we understand that platelets have clearly a role responding to the viruses and activating the immune system.
Cindy St. Hilaire: Yeah, and that was actually my next question. You and Jane are the world-leading experts on platelets and viral responses. So what was known about that interaction, I guess before we started looking at SARS-CoV-2, what was known about that platelet virus or even type of virus interaction?
Milka Koupenova: So SARS-CoV-2 is a RNA virus--respiratory virus that we actually thought similarly to influenza that it mostly stays in the lower respiratory tract where it becomes problematic. However, from our work with influenza, when we saw that in certain patients you actually can detect the virus in platelet. In the beginning of the pandemic, we hypothesized that perhaps, in some people, the virus crosses over into the circulation. And based on our previous studies with influenza, we wanted to see if that indeed is the case. Hence we initiated a study here at UMass with the department head who is also on the paper, Dr Finberg, who is a leading expert in influenza and novel virus and we collected platelets from people to see if we can detect it. And so in the beginning, we were not able to detect SARS-CoV-2 in platelets. So we collected platelets from 17 patients and by qPCR with the primers that the CDC has, for whatever reason I couldn't detect anything. And I was really frustrated because previous reports have shown that about 25%, in some people even 35% of the study population, SARS can be detected. So very interesting observations.
Milka Koupenova: I could see it by immunofluorescence but I couldn't detect the RNA. And the story goes, that I attended a seminar on SARS-CoV-2 and the person was actually referencing a company that started from University of Pitt where you are.
Cindy St. Hilaire: Oh, very nice.
Milka Koupenova: And they do specific, it's called amplicon ARTIC v3 sequencing so they enrich for the SARS-CoV-2 RNA and screen by sequencing. And when we did that, we were able to detect it in all patients. So I freaked out and I said, "Oh my gosh, something is wrong."
Milka Koupenova: And so I sent plasma, and I sent controls, and actually RNA from the virus and you can see beautifully that it's only in platelets. Four of the 17 people actually had RNA in the plasma, but what you can observe in all these people is that the virus is fragmented, meaning it's not infectious. And in a way what this tells us, it suggests that platelets are super important in the removing it from the circulation and they probably serve as a dead-end for the virus because you cannot find virus coming out of platelets and the RNA is chopped off. So what I would say, is that platelets are these amazing little units that serve as removal of the viral RNA for these particular viruses, respiratory viruses that are RNA viruses.
Cindy St. Hilaire: I think that is so interesting. So essentially, they're almost like little composters that are chewing it up and preventing it from spreading in the organism.
Milka Koupenova: Yes, and as a result there is a response.
Cindy St. Hilaire: Scott, probably the most common thing that people know with SARS is that loss of smell, or taste, and things like that, but really that doesn't send anybody to the hospital. So really what are the symptoms of COVID-19 patients that tie in with platelets specifically? I feel like that's a lot of things that we maybe in the public, or on Twitter, and things didn't hear as much about. So really what are those big symptoms linking COVID and platelets and what are the implications of platelet death in the pathogenesis of COVID?
Scott Cameron: So certainly I think several investigators are in the world of now showing that platelets are hyperactivated, Robbie Campbell and Matt Rondina put a really nice paper in Blood last year showing that platelets are hyperactive and there are other investigators who found something similar. And so the question is, what are the symptoms of hyperactive platelets in the SARS-CoV-2 patient? So what most of them would find is shortness of breath or dyspnea, and when they present to the emergency department, and certainly we saw this, the oxygen saturation which should be in the mid to high 90s on room air on an average person, was quite often low. It was in the 80s or 70s, sometimes even the 60s.
Scott Cameron: And the real surprising thing was those are patients that would normally immediately be on a ventilator, but yet they could still be talking to you. And so if you have a platelet that's activated in a hyperthrombotic condition, like SARS-CoV-2, COVID-19, and then that forms a blood clot, you have a situation where the amount of oxygen the patients taking in and the amount of oxygen you're measuring in the artery is quite discrepant and we call that the alveolar arterial or oxygen gradient. So if you've got lots of platelet plugs through the microvasculature, it's going to take up some space the oxygen should be using for diffusing in. And so that would be manifested as shortness of breath and that's certainly one of the biggest tip-offs that a patient might have a blood clot, particularly in the lung.
Cindy St. Hilaire: Some of these symptoms of COVID-19 are really worse in patients with comorbidities, diabetes, obesity and heart failure. Are platelets central to kind of the pathogenesis of those disease or the symptoms of those diseases? I guess the root of my question is, why do the comorbidities of diabetes, obesity, and heart failure make COVID worse? Is it something about those disease states themselves or is there a role for platelet?
Scott Cameron: That's a brilliant question, no one's ever asked that before. And as Dr Koupenova said, I'm a little bit biased too because I firmly believe that in different disease states, the disease educates the platelets so you've got a different platelets phenotype. So focusing on diabetes, we know the platelet phenotype is different in diabetic patients. We know that platelet reactivity seems to be higher through the P2Y12 receptor. In terms of obesity, it is true, we know that, and this has been published also, and we know that the platelet phenotype is hyperactive in a patient with obesity and so that tells me that, that's a comorbidity that might affect platelet function and also vice versa for that case. And then in terms of why is it affecting males more prominently and more severely than females, well one of the beefs, I guess, that I had is that we treat diseases in women the same as we do in men assuming that the platelet phenotype in disease must be the same, but that's absolutely not true. And that's actually a theme that we have in our lab right now, we know that the behavior of platelets, and how platelets are educated in diseases is not all the same in women as in men and I think it's a huge disservice that we really had to have a pandemic that would make that quite clear to us.
Cindy St. Hilaire: You kind of hit onto something that's really, I think it's now becoming more recognized certainly in the cardiovascular field and that is so many studies are really only on male mice, or only younger or older men, and we are missing not only a huge patient population, but probably some really interesting biology that is distinct.
Milka Koupenova: So expanding on that, we know that in platelets, the toll-like receptors, and we've looked at the expression of all 10 in a study that we published in ATVB in 2015, actually, significantly if you look at Farmingham Heart Study data and the expression of these toll-like receptors they are increased in women versus men. And also, an interesting observation that never got published, once upon a time when I was doing studies with TLR7 mice is that if you inject TLR7 agonists, male mice would have a higher level of reduced platelet count than female mice at the same time points, right? And at that time it wasn't published. Definitely there are differences, but I also want to extrapolate a little bit on what was said at the beginning. We have to understand that when it comes to these comorbidities, everything affects a unit that doesn't have a nucleus, right? And diabetes and obesity have the so called profound, chronic inflammation of cytokines, such as IL6, that keep circulating. These things have effect on platelets. So we have two responses, we have the environment that affects platelets and we have the direct response of the virus that affects platelets. And that cumulative response truly can exhaust them and once they become exhausted, once they release their contents, as we show in this paper, then you're compromising their function and you will be compromising taking out the virus from one side and from the other side you're going to be compromising the environment because all of the content that comes out from a unit that already has free form proteins, it exhibits a true insult on what's being surrounded. So these clots that form in the lung or the platelets that circulate they no longer can be resolved properly.
Cindy St. Hilaire: Yeah.
Milka Koupenova: It's a balance.
Cindy St. Hilaire: Yeah, so really it's like destroying the platelet not only are you destroying the vacuum that has to suck up those particles, you're then just dumping a whole bunch of pro-inflammatory things on all of the endothelial cell vasculature that those platelets are nearby.
Cindy St. Hilaire: Actually that was one thing that I thought you spent a decent portion of the discussion on, and that is the method by which the blood is collected really impacts the outputs you observe in quote unquote platelets. Can you talk about the importance of that because I think that's one thing, certainly as a PhD who's just like, "Oh, yeah. I'm just going to collect blood from my mice and do this thing," how critical is that point in the experiment, in the blood collection?
Milka Koupenova: So I am very adamant when it comes to platelets for the blood to be drawn in citrate. And I have to say that a lot of the studies that you would see in the literature are done using EDTA blood or serum. They all have their importance. I'm not going to dismiss it, but if you want to truly measure what's inside in plasma, versus what's inside in platelets, or what's inside in any cell for that matter, you got to go for citrate. You have to be very careful not to shake the blood. You have to be very careful not to cool down the blood. So the nurses probably hated me because often I would be like, "You can't do this. You can't put it on ice. You can't warm it up to above certain degrees. Everything has to be controlled and done correctly."
Milka Koupenova: And so I had done in the past studies in which I would take plasma from the same patient in EDTA, in citrate and then isolate the RNA, have my tech isolate the RNA, and we send it to a fragment analyzer, and you can see how much more RNA you will get in the EDTA plasma. I'm not even talking about serum.
Milka Koupenova: Serum is a very different thing, then you're definitely going to get platelet content in it, in the serum, right? So it's important to distinguish that perhaps when you're getting EDTA plasma you are looking at a content that could have been inside in platelet and I can't stress enough that when it comes to these particular studies, citrate, dextrose, phosphate is your place to go and be.
Cindy St. Hilaire: So in terms of translational potential, what do your findings suggest about future therapies or targets to investigate as therapy? And is modulating platelets a potential for combating viral infections or mitigating their severity?
Milka Koupenova: Well, Scott and I actually talk a lot about that.
Scott Cameron: That's right.
Milka Koupenova: I personally would say, control the inflammation, never let it go to platelet. Let me back up a little bit, if you have to, you have to, right? But your go to method should be inflammation, if you don't get to the point that you need to control platelets then you're in a better place because it becomes very fickle. From everything that you hear me say, you push it to one side and the balance is destroyed. You deactivate platelets or inhibit platelets well, are they now not able to pick up the virus and then you're now having the virus circulating somewhere. Now, if you don't treat platelets that's also not good. So you're in the very fickle situation if you get to the point that you need to control the activation of platelets and there are trials currently that are trying to look at those things. Scott, I'm going to refer this a little bit more to you because you have done some interesting things with that particular point.
Scott Cameron: No, it's a great question, Milka, and I think that as platelet biologists, nobody more than I wanted it to be true that platelets would be the ultimate target. I mean, clearly patients with SARS-CoV-2 have thrombosis, clearly platelets are activated, so should we inactivate them? That was the whole point of the RECOVERY trial and one of the benefits I'll tell you before I sort of go into that is, working in a large organization like the Cleveland Clinic and we have access to data and lots of it extremely quickly, and so because of that I of course could see how many patients were coming into our hospital with thrombotic events. And I could see what the independent predictors of thrombotic events was and it wasn't the platelet count, sometimes platelet count was low, sometimes it's high in the SARS-CoV-2 patient. And if you took those individuals that were on aspirin, comparing them to those that are not in a propensity match study, one of the things that we find is that aspirin doesn't seem to affect or improve mortality or the number of blood clots in the patient with SARS-CoV-2.
Scott Cameron: We compared that to all non-steroidal anti-inflammatory medications that patients may have been taking also in a propensity match study just in case it was the mechanism action of the drug, rather than the drug itself, and we found that NSAIDs not only did not protect patients, but they were not necessarily harmful either, which was one of the things that came out at the start of the pandemic. Among, I'll add, the absence of evidence based medicine and a lot of cases where naturally people, including clinicians, were scared and so they were going off label and they were trying a lot of different medications with really not a shred of randomized controlled data.
Scott Cameron: But now that we're 18 months into it, the first and biggest study that came back was the RECOVERY trial, which we were all waiting on, where patients were given aspirin and short term mortality was examined over an observational period of one month. And just like we found in a propensity match study, which is as close as you'll get to a clinical trial in a retrospective manner, the prospect of RECOVERY trial actually showed the curves were almost super imposeable, those that got aspirin versus those that didn't. So I think low dose aspirin clearly is not going to be enough for those patients, but I'll also add that over the observational period of one month they also didn't see a higher incidence of death in those patients. And I think Milka's point is really well taken that you have to remember that as well being an entity of thrombosis, platelets are immunological entities and so you've got to really consider should we be inhibiting them and if you are inhibiting them, I think the time point at which you should inhibit them is what we should examine, not just an all or nothing, inhibited or not.
Milka Koupenova: It's just in our linear brains we prefer to think of it as one straight, linear pathway, but it isn't, and I think platelets are actually a great example of how many pathways are feeding into one tiny fragment and that particular blood cell is inducing this profound response during these infections.
Cindy St. Hilaire: I think most people have heard that angiotensin-converting enzyme 2, also called ACE2 is the receptor of SARS-CoV-2. The virus itself uses it to bind and become internalized into the cell, but there's been some discussion or even some discrepancy of data as to whether platelets truly express ACE2 and if that is the means for the virus to enter the platelets. So can you share with us what is the current state of knowledge about that?
Scott Cameron: Yeah, just as a segue of some of the things that Milka said, I think the preparation of your sample is part of the answer. If you draw in the incorrect tube, if you the tube is not completely filled, and the ratio of citrates to whole blood isn't correct you're going to have discrepant results. If you biomechanically activate the platelets by drawing through a short needle, in a small-bore needle for example, that's going to activate the platelets. If you cool them, it's going to activate them. But then also, depending on how you decide to separate them, we always washed platelets in my lab, we wash them two or sometimes three times, and I can tell you if you use flow cytometer we get one white blood cell for every 12,000 platelets.
Scott Cameron: And some investigators might go one step further and they'll a CD45 depletion set, which is certainly important if you're studying RNA. But one of the issues, as you well know, a CD45 is also on the surface of platelets, so if you start with a low expressing protein and you CD45 deplete them, you are actually going to get a decrease in your platelet yields. I've seen it, I think Milka's seen it, various other investigators have, and you might find yourself at the threshold of what your antibody can detect. It's also variably expressed. If you look at even healthy individuals, some of them have almost none. So if you look at 10 individuals, you might actually find none, but then if you look at another 10, the amount of expression that we see is kind of all over the place. It's not like other receptors where one tends to express a certain amount and that's the way it is in health. ACE2 doesn't seem to be that way for whatever reason.
Milka Koupenova: We were able to detect in some of the people by qPCR, but what was interesting is that from the three primers that I used there was never the same person who we were able to detect all three primers with for that receptor. That tells you that maybe they are changes of one base that is not enough for the primer to detect it, right? That becomes another possibility of not being able to detect.
Milka Koupenova: And so I go to confocal microscopy where I use 100 lens and tons of hours in the microscope room, and Scott is completely right, it's really hard to see it particularly in healthy people. And it starts to pick a little bit more in people with cardiovascular disease or people with COVID that are old. So it's a bit complicated, but the important thing here is, besides the fact that we are detecting ACE2 and we're detecting proteins and I use controls, biological controls to prove that this is the case and it's not just an antibody problem, is that the virus will get picked up by platelets even if you don't have ACE2. That is the take home message from this paper is that the platelet has evolved various mechanisms by which is utilizes getting it inside. It is that important for this virus. This type of virus is not recirculating. In this case, what we observed is that the virus is attached to microparticles that are of platelet origin for that matter.
Cindy St. Hilaire: So really what you're saying, what I'm hearing is the platelet is the superhero of the body.
Milka Koupenova: Definitely. Absolutely. No bias, absolutely.
Cindy St. Hilaire: Unbiasedly, it is a superhero. Well, Dr Cameron and Dr Koupenova, thank you so much not only for this amazing discussion, but for really an elegant, elegant paper that is really bringing to light the complex interaction between SARS-CoV-2 and platelets. So thank you so much for joining me and keep publishing amazing stories like this.
Milka Koupenova: Thank you for having us.
Scott Cameron: Thank you, an honor to be here. Thanks again.
Cindy St. Hilaire: That's it for the highlights from August 20th and September 3rd issues of Circulation Research. Thank you for listening. Please check out the CircRes Facebook page and follow us on Twitter and Instagram with the handle @CircRes and #DiscoverCircRes. Thank you to our guests, Dr Scott Cameron and Dr Milka Koupenova. This podcast is produced by Ashara Ratnayaka, edited by Melissa Stoner, and supported by the editorial team of Circulation Research. Some of the copy text for the highlighted articles is provided by Ruth Williams. I'm your host, Dr Cynthia St. Hilaire, and this is Discover CircRes, your on-the-go source for the most exciting discoveries in basic cardiovascular research. This program is copyright of the American Heart Association, 2021. The opinions expressed by speakers in this podcast are their own and not necessarily those of the editors or of the American Heart Association. For more information, please visit ahajournals.org.