Oct 12, 2020
This week’s episode includes author Mark Chan, editorialist Thomas Wang, and Associate Editor Wendy Post as they discuss the prioritization of candidates of post-myocardial infarction heart failure using plasma proteomics and single-cell transcriptomics.
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore.
Dr Greg Hundley: And I'm Greg Hundley, associate editor, director of the Pauley Heart Center at VCU Health in Richmond, Virginia. Well, Carolyn, this week's feature, really interesting, involving proteomics and single-cell transcriptomics, trying to identify how we could prioritize individuals after they've sustained myocardial infarction as to whether or not they'll develop heart failure. Lots to go over in that feature. But before we get to that, how about we grab a cup of coffee and start in with some of the other interesting papers in this issue?
Dr Carolyn Lam: Absolutely. I've got my coffee and I have to tell you though, I am so excited about this feature, it comes from Singapore, but my first paper too is about transcriptomic profiling. But Greg, I have to ask you first, have you heard of the cardiac cellulome?
Dr Greg Hundley: Oh my goodness, Carolyn. So you're starting the reverse-quiz strategy to help me. I have not heard of the cellulome. Help enlighten me.
Dr Carolyn Lam: I just love that word. We've heard of all kinds of other omes, but this cellulome is something I've learned through today's paper. So the authors today who are Alexander Pinto from Baker Heart and Diabetes Institute and colleagues, they developed a novel cardiac single-cell transcriptomic strategy to characterize the cardiac cellulome. And that refers to the network of cells that forms the heart.
The method was utilized to profile the cardiac cellular ecosystem in response to two weeks of angiotensin II as a pro-fibrotic stimulus. So what did they find? Well, they identified two previously undescribed cardiac fibroblasts populations that are the key drivers of fibrosis. Their names were Fibroblast-Cilp and Fibroblast-THBS4. Now, these do not correspond to smooth muscle actin-expressing myofibroblasts, which have been widely viewed as the primary drivers of fibrosis. So this is really novel. The cardiac cellular landscape was sexually dimorphic at the cell abundance and gene expression level, including cellular responses to angiotensin II induced tissue remodeling. So these data really provide insights into the cellular and molecular mechanisms that promote pathologic remodeling in the mammalian heart, and really highlight that early transcriptional changes precede chronic cardiac fibrosis.
Dr Greg Hundley: Very nice, Carolyn. Well, let me switch to the clinical realm. And my first paper comes from Professor Holger Thiele from the Heart Center Leipzig at the University of Leipzig, and it's involving general versus local anesthesia with conscious sedation for patients undergoing TAVI procedures. So the study comes from the SOLVE-TAVI study, and it's a multi-center open-label 2x2 factorial randomized trial of 447 patients with aortic stenosis undergoing transfemoral TAVR, comparing conscious sedation versus general anesthesia. And the primary efficacy endpoint was powered for equivalence, and consisted of the composite of all-cause mortality, stroke, myocardial infarction, infection requiring antibiotic treatments, and acute kidney injury at 30 days.
Dr Carolyn Lam: Wow, Greg, as I understand it, about half of patients today receive TAVI or TAVR with conscious sedation. So it's really an important question. So what did they find?
Dr Greg Hundley: You're exactly right. So the composite end point occurred in 27% of the conscious sedation patients and 26% of the general anesthesia patients. Really equivalent. And this held true for each of those composite endpoints. In addition, there was a lower need for inotropes or vasopressors with conscious sedation, versus general anesthesia. Thus, these findings suggest that conscious sedation can safely be used for patients undergoing TAVR procedures.
Dr Carolyn Lam: Very important clinical one, Greg. Well, I've got a clinical paper for you too. And this one, trying to answer the question, what's the optimal duration of dual anti-platelet therapy, or DAPT, after PCI with drug-eluting stents. A very familiar, perhaps, an important question. So these authors, led by Dr Deepak Bhatt from Brigham and Women's Hospital Heart and Vascular Center and Harvard Medical School, performed a systematic review and network meta-analysis of 24 randomized controlled trials comparing short-term DAPT, or less than six months, followed by aspirin or P2Y12 inhibitor monotherapy, versus mid-term DAPT, which was six months, versus 12 months DAPT, as well as an extended-term DAPT, which was more than a year after PCI with a drug-eluting stent.
Dr Greg Hundley: So Dr Carolyn, three groups, what did they find?
Dr Carolyn Lam: Compared to 12 months DAPT, short-term DAPT followed by P2Y12 inhibitor monotherapy reduced major bleeding after PCI with a drug-eluting stent, whereas extended-term DAPT reduce myocardial infarction at the expense of more bleeding events. Overall, the extended-term DAPT was associated with a higher risk of major bleeding compared with all other DAPT groups, except in patients with acute coronary syndrome.
Dr Greg Hundley: So extended, more bleeding complications. So take me home on this, Carolyn, what is the final message here?
Dr Carolyn Lam: Here's the message. Compared with 12-month DAPT, the net clinical benefit appears to favor short-term DAPT followed by P2Y12 inhibitor monotherapy instead of aspirin in select patients. Although, extended term DAPT has a role for patients who have a low bleeding risk, but a higher ischemic risk, such as those with acute coronary syndrome, thus a personalized approach appears to be warranted.
Dr Greg Hundley: Very good. Well, I'm going to turn back to the world of basic science and discuss a paper related to pulmonary hypertension. And it comes from Dr Sébastien Bonnet from the University Laval. So Carolyn, the subcellular mechanisms that govern the transition from a compensated to a de-compensated right ventricle in patients with pulmonary hypertension remain poorly understood, and as a consequence, there are no clinically established treatments for RV failure and a paucity of clinically useful biomarkers. So this study investigated the long non-encoding RNAs, powerful regulators of cardiac development disease, in relation to adverse RV remodeling in pulmonary artery hypertension.
Dr Carolyn Lam: So these LNK RNAs, I think that's what they're called, right? Long non-coding RNAs, what did they find?
Dr Greg Hundley: This was another one of our really nice translational articles, because they combined results from both animals and human subjects. The authors demonstrated that the long non-coding RNA H19 is upregulated in decompensated right ventricles due to pulmonary hypertension, and the finding correlated with RV hypertrophy and fibrosis. Now, similar findings were observed in monocrotaline and pulmonary artery banded rats. The authors found that silencing H19 limits pathological RV hypertrophy, fibrosis, and capillary rarefaction, thus preserving RV function in those two models of pulmonary hypertension, both the monocrotaline and the pulmonary artery banded rats, without effecting pulmonary vascular remodeling.
And finally, Carolyn, the authors found that circulating H19 levels in plasma of patients, discriminate pulmonary arterial hypertension patients from controls correlated with RV function and predicted long-term survival in two independent idiopathic pulmonary artery hypertension cohorts. Moreover, H19 levels delineated subgroups of patients with differential prognosis, when combined with NT-proBNP levels or the risk score proposed by both the Reveal and the 2015 European Pulmonary Hypertension Guidelines.
So, in summary, these authors findings identify H19 as a potentially new therapeutic target to impede the development of maladaptive RV remodeling, and thus a promising biomarker as well of pulmonary arterial hypertension severity and prognosis.
Dr Carolyn Lam: Oh, Greg, I love that. Not just the paper, but the way you explained it. Thanks so much. Well, let's dip into what else there is in today's issue, shall we? First, there's Global Rounds by Dr Yacoub entitled, Towards Meeting the Challenges of Improving Cardiovascular Health in Egypt. There's a research letter by Dr Cheng on imaging the sarcoplasmic reticulum calcium signaling in intact cardiac myocytes. There's another Research Letter by Dr Angiolillo on the pharmacodynamic and pharmacokinetic effects of a low maintenance dose ticagrelor regimen, versus standard dose clopidogrel, in patients with diabetes without prior major cardiovascular events, undergoing elective PCI. And this is the OPTIMUS-6 study. There's an On my Mind paper by Dr Santos on coronary artery calcification and familial hypercholesterolemia, and an ECG Challenge by Dr Liu, which is not your uncommon electrocardiographic findings, and really looking at Q waves with post-QRS deflections. I'll let you take a look.
Dr Greg Hundley: Oh, wow, Carolyn. This issue is just jammed with really nice articles. I've got a research letter entitled, Long-Term Outcomes After Infective Endocarditis, Following Transcatheter Aortic Valve Replacement, and it's from Dr Josep Rodés-Cabau from Quebec Heart and Lung Institute. And then finally, a nice exchange of letters by Drs Rozenbaum, Kemner, and Parasuraman regarding the article Cost-Effectiveness of Tafamidis Therapy for Transthyretin Amyloid Cardiomyopathy, and there's a very nice response by Dr Kazi. Now we get to proceed on to that feature article.
Dr Carolyn Lam: Yay! Let's go, Greg.
Dr Greg Hundley: Well listeners, we are to our feature discussion. And today we have Dr Mark Chan from the National University of Singapore, our own associate editor, Dr Wendy Post from Johns Hopkins, and Dr Thomas Wang from the University of Texas Southwestern Medical Center. Well, Mark, we'll start with you. Could you explain to us some of your thinking behind how you formulated this study and what was the hypothesis that you wanted to address?
Dr Mark Chan: The background, really, was to try to prioritize protein candidates in post myocardial infarction heart failure. We do know that there are several hundred candidates out there in the literature, but really, what we wanted to do was to try to enrich and select out what we thought would be the most biologically relevant proteins. And really, the hypothesis was that, by combining two very powerful unbiased discovery tools that have been developed in the last few years, we would be able to achieve this goal.
The two tools, I think, Tommy would be very familiar with, because he's used plasma proteomics as well in a lot of his work. That's one of the unbiased discovery tools that we used. Measuring 1300 proteins in blast mine. Second two was a single-cell transcriptomics where we're able to look at RNA sequences, genome RNA sequences, at the individual cell level.
So we first started off with cohorts of patients with acute myocardial infarction that were followed up for about five years for heart failure events, and we obtained plasma from these patients at about 30 days after myocardial infarction. So with the initial plasma proteomics, and found more than 200 candidates, actually very similar to what we actually see in the literature in terms of protein candidates predicting heart failure, in particular, post-MI heart failure.
We then thought that what we really want to do is prioritize the most important proteins, and that's when we went onto single-cell transcriptomics. And we found a total of 83 protein candidates, which were directionally similar across the human plasma proteomics and the single-cell transcriptomic data across different models of ischemic heart failure. And six candidates are the ones that we are hoping to discuss a bit more about, the top six candidates, today, which I'm sure you'll ask me about very soon.
Dr Greg Hundley: You've really led us into the next question. Tell us a little bit about the six candidates.
Dr Mark Chan: The top six candidates to all of us are really familiar with NT-proB natriuretic peptide that's been around for decades, cardiac troponin, that's the second well-known, well-established candidate, and four other candidates that seem to be really emerging as potential targets in heart failure and ischemic cardiomyopathy. Angiopoietin-2, thrombospondin-2, latent-transforming growth factor binding protein 4, and a less commonly investigated protein, FSLT3, or follistatin-like related protein 2.
The two candidates that are particularly interesting to me are angiopoietin-2 and thrombospondin-2 , and looking at a lot of Tommy Wang's work as well, we can see that these two candidates looking to be important future targets for biomarker discovery, validation, and maybe, potentially, druggable candidates to manage patients with post-MI heart failure and ischemic cardiomyopathy.
Dr Greg Hundley: Wendy, coming to you as an associate editor and really an expert in genetic epidemiology, what intrigued you about this article? Especially I heard Mark discuss differentially expressed genetics and transcriptomics. What brought you to this article and what increased its relevance to you?
Dr Wendy Post: We were very intrigued by both the importance of the problem that was being addressed, in that ischemic cardiomyopathy is a very common and major challenge that we all encounter as cardiologists, but also the unique approach that was used to handle a large amount of data. So with the plasma proteomic approach, which Mark described as the first step, you take thousands of data points and try to narrow it down, which he did, but still needed to narrow it down even more. And then use a complimentary, but different, approach to try to understand which of these hits, so to speak, maybe the ones that are important. And so using the single-cell transcriptomic approach, was able to narrow down to these six candidates.
And then it was very reassuring that two of the six were what we would have hypothesized. So if you didn't find those, we'd worry that maybe something was wrong with your approach. So on the one hand, you'd say, "Well, we already knew that. So what are you telling us?" But it actually was proof, so to speak, that your approach was working, and that these other four novel candidates might turn out to be the next BNP. So that was really a few of the things that intrigued us about this paper.
Dr Greg Hundley: So Tommy, as a practicing clinical cardiologist, and then also, really, as a clinician researcher, what do you see as relevant with Mark's work and also Wendy's description here for all of us that are seeing patients that has sustained myocardial infarction?
Dr Thomas Wang: I think as Mark and Wendy have both nicely summarized, but I'll revisit, they're really two areas in which knowledge of these biomarkers could impact patient care down the road. One is an informative set of biomarkers to tell us which among the large number of patients with myocardial infarction might be destined to develop heart failure so that we can, as clinicians, ramp up our therapies, increase our vigilance, increase our monitoring, so that we might be able to intervene on that at a very early stage, or even before the heart failures develop.
The second, which is potentially even more exciting, is the possibility that some of these biomarkers might be so informative of pathways leading to heart failure, that we could actually directly intervene on the pathways that are reflected by these biomarkers. So in other words, biomarkers would tell us not just biology, but about therapeutically effective strategies. And I think, as Mark has nicely emphasized, there are scores, if not hundreds, of biomarkers that have been looked at in this context, and there's no amount of resource in the world that allows investigators to pursue, in prospective clinical studies or experimental studies, all of these biomarkers. And so the real value of their study is to illustrate an approach for winnowing down this large number of biomarkers down to a smaller set, a much smaller set, that seem really worth pursuing in further study.
Dr Greg Hundley: Well, with that lead in, Tommy and Mark and Wendy, maybe start with you, Mark, what do you see as the next step and this area of research moving forward?
Dr Mark Chan: I think I need to sound a word of caution first with respect to the study itself. It is, at the end of the day, still a very descriptive study. Heavy in bioinformatic elucidation of targets. So careful mechanistic validation and further understanding of these highly prioritized targets will still be important.
In terms of how we can potentially get these results closer to the post-MI heart failure patients, closer to the bedside, one concept that I think it's becoming increasingly apparent is that a lot of these bioactive proteins in circulating plasma are likely a part of the secretome. Part of what we call exosomes or micro-bubbles that are secreted by cells. And we do see the origin big cells in the single-cell studies as part of this paper. We do get an idea. A lot of these cells really are within the extracellular matrix, which is the substrate in which your cardiomyocytes are embedded. We think that enriching the plasma for the exosome fraction, which one of my colleagues is now working on, could be the best way to derive a more powerful tool for prognostication. To really determine with a high level of specificity, not just sensitivity, but highly specific
to determine which patients end up with post-myocardial infarction heart failure.
So enriching plasma for exosomes and potentially looking at the proteins within these exosomes, we've already started work on that. And so far, the results, compared to the proteins just measured in free plasma, seem to predict heart failure events a lot better when we come down to the exosome fraction.
The other project, this is using exosomes to treat post-MI large animal models. So we have injected mesenchymal cell stem cell derived exosomes, and we've shown that they can reduce infarct size in large animal models, and also prevent some of the hemodynamic complications that result in heart failure. But really, trying to find which are the proteins actually are meaningfully preventing heart failure and reducing infarct size, I think that is also going to be part of the next steps.
Dr Greg Hundley: Mark, thank you for that summary. Tommy, do you have anything to add to that?
Dr Thomas Wang: I certainly agree with all that's been said. I would also emphasize that understanding the biology of some of these newer biomarkers and how they might link heart failure or active MI is going to be really important when we consider potential clinical applications. And so, further along the experimental line, I think animal models, mouse models, and other types of models, being which the biology and pathways we would manipulate it so that we can see whether these biomarkers truly do reflect etiologic pathways in heart failure would be valuable.
Dr Greg Hundley: Thank you, Tommy. Well, listeners, we've had a great presentation from Dr Mark Chan, an excellent review by both Wendy Post and Tommy Wang, emphasizing how we are discovering new protein biomarkers using plasma proteomics for identification of those that may develop heart failure after myocardial infarction. And more to come in this area. We feel very privileged to have the opportunity to work with bright young investigators like this and present this work in Circulation
For both Carolyn and myself, we wish you a great week and look forward to catching you next week on the Run. This program is copyright American Heart Association, 2020.