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.
TRANSCRIPT BELOW:
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.