May 20, 2019
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 of Circulation and Director of the Pauley Heart Center at VCU Health in Richmond, Virginia. Well, Carolyn, our feature article is going to focus on trastuzumab-induced cardiac dysfunction in breast cancer patients. We will discuss with Stanford investigators their use of pluripotent stem cells that are differentiated to cardiomyocytes and subsequently exposed to toxins to determine an individual's susceptibility to cardio-toxicity from cancer treatment. But before we get to that, Carolyn, do you have a paper that you'd like to discuss?
Dr Carolyn Lam: Well, the first paper deals with cardiac biomarkers and asks the questions, can these biomarkers be useful for the diagnosis and risk stratification of syncope?" Now, this paper is from Dr Mueller and colleagues from University of Hospital Basel in Switzerland. They evaluated the diagnostic and prognostic accuracy of BNP, NT-proBNP, high-sensitivity cardiac troponin T, and high-sensitivity cardiac troponin I concentrations, alone and against the ones of clinical assessments in more than 1,500 patients presented with syncope to the emergency department in a prospective, diagnostic multi-center study. Now, cardiac syncope was adjudicated in 234 or 15% of patients. What they found was that the diagnostic accuracy from cardiac syncope, as quantified by the area under curve, was 0.77 to 0.78 for all four biomarkers. That was superior to that of the syncope-specific diagnostic score, EGSYS.
Now, combining the four biomarkers further improved diagnostic accuracy to an area under curve of 0.81. Furthermore, using the four biomarkers at cutoffs achieved predefined thresholds for sensitivity and specificity and allowed rule-in or rule-out of 30% of all patients. Finally, the biomarkers predicted adverse cardiac outcomes with moderate to good prognostic accuracy and better than some of the existing syncope risk-prediction scores.
Dr Greg Hundley: Very interesting, Carolyn. Do you think we can now use this clinically? Should we be drawing these biomarkers on patients with syncope?
Dr Carolyn Lam: These results really do imply that these biomarkers look like useful tools for the early rule-out and/or rule-in of cardiac syncope in the emergency department. After all, these biomarkers are readily available, inexpensive, and results of this study suggest that they have potential to simplify diagnosis and to risk stratify in challenging presentations. However, before embracing the concept of ordering cardiac biomarkers routinely for syncope presentation, we really need to read the editorial by Dr Sandhu and Sheldon, in which important perspectives are presented, such as considerations of the certainty of the diagnosis of syncope, the usefulness of the comparative scores, the timing of testing, the potential unintended adverse consequences of testing. These editorialists concluded that, although promising, further work is needed to determine how the use of cardiac biomarkers should be incorporated into a risk-stratification algorithm.
Dr Greg Hundley: Wow, Carolyn. It sounds like we'd get a lot out of that particular editorial. I'm going to switch over and talk about NT-proBNP in patients with pulmonary hypertension. This is a paper from Dr Kelly Chin from UT Southwestern, and the study evaluated the utility of end terminal pro BNP level thresholds and assessing prognosis in pulmonary hypotension using the GRIPHON study. So GRIPHON is a global double blind, randomized placebo control event driven phase 3 study which assesses the safety and efficacy or a Prostacyclin agonist that promotes pulmonary arterial vasodilation.
They performed the study in patients that were 18 to 75 years old with a diagnosis of idiopathic pulmonary hypertension, heritable hypertension or pulmonary hypertension associated with connective tissue disease, repaired congenital systemic pulmonary shunts, HIV infection, drug use or toxin exposure; and the diagnosis of pulmonary hypertension was confirmed by right heart catheterization and by a reduced 6-minute walk distance of 50 to 450 meters.
Eligible patients were permitted to take their other therapies including Endothelin receptor agonists and phosphodiesterase type-5 inhibitors. The patients were categorized into low, medium and high in terminal BNP level subgroups according to two thresholds. First, by just the tertiles within the study overall and the secondly by the ESC guideline cutoff ranges.
Dr Carolyn Lam: Nice, so what did they find Greg?
Dr Greg Hundley: Well first of all both thresholds either the tertile one of the ESC in follow-up NT-proBNP categories were highly prognostic for future morbidity and mortality. And their time dependent analysis the risk of experience a morbidity or mortality even was 92% and 83% lower in the treated patients with a low and medium NT Pro BNP level. And 90% and 56% lower in placebo treated patients with low and medium NT-proBNP levels. So both, whether you're taking that drug of not, the NT-proBNP levels were prognostically valuable. More pronounced treatment benefit of selexipag was seen in the medium and low proBNP groups. There was a positive value for the interaction term.
Dr Carolyn Lam: Wow, sounds like two really important findings.
Dr Greg Hundley: Yes, exactly Carolyn. So first, NT-proBNP levels are highly prognostic for pulmonary arterial hypertension progression. And having NT-proBNP in the low range, by improving to or maintaining low NT-proBNP levels is a clinically relevant treatment goal for those with pulmonary artery hypertension. And of course as we described this was a very diverse well represented group of many different types of patients with pulmonary hypertension. Then second, while selexipag the study drug was beneficial in all NT-proBNP categories, the treatment effect was greater in those with low and medium categories versus the very high. Suggesting that earlier selexipag treatment may be of greater benefit. But very interesting biomarker study that follows up on yours Carolyn.
Dr Carolyn Lam: Indeed!
Dr Greg Hundley: Carolyn what about your next paper?
Dr Carolyn Lam: Well I want to switch tracks now and talk about iron. And the question is, how does intravenous iron repletion augment exercise capacity in chronic heart failure? Even if hemoglobin doesn't change. So, first some background right, now, besides hemoglobin it's important to recognize that iron is an obligate component of the mitochondrial enzymes that generate cellular energy in the form of adenosine triphosphate and phosphocreatine. So dynamic phosphorous magnetic resonance spectroscopy is a noninvasive tool that can really quantify the in vivo muscle energetics by measuring the kinetics of phosphocreatine recovery after exertion. These authors use this technique, and these are Dr Okonko from King's College, London British Heart Foundation sender of excellence, school of cardiovascular medicine and sciences. The James Black Center in London and colleagues. And what they did was they tested the hypothesis that intravenous iron repletion in chronic heart failure would enhance skeletal muscle energetics as reflected by a shorter phosphocreatine recovery halftime on phosphorous magnetic resonance spectroscopy imagining of the skeletal muscles. And they looked at 40 patients with chronic heart failure with reduced deduction and iron deficiency in a randomized double blind placebo controlled ferric iron and heart failure trial.
Dr Greg Hundley: So, what did they find?
Dr Carolyn Lam: They found that a single total dose infusion of intravenous iron repleted iron stores and augmented skeletal muscle energetics at 2 weeks post infusion. Enhancements in the skeletal muscle energetics which implied better mitochondrial function were accompanies by improved symptoms despite no change in hemoglobin at 2 weeks. So, this trial really provides mechanistic support for iron repletion in patients with chronic heart failure and its very importantly discussed in an editorial by Peter van der Meer, Haye van der Wal, and Vojtech Melenovsky. And I really suggest that everybody read that.
Dr Greg Hundley: Well, I'm going to talk a little bit about dietary omega-6 fatty acids and the incidence of cardiovascular disease and mortality. And this paper is from Matti Marklund from the Georgia Institute for Global Health and the University of New South Wales in Sydney, Australia. The study focuses on linoleic acid which is an omega-6 polyunsaturated fatty acid that we get from pumpkin seeds, flax seeds, walnuts, soybean oil, canola oil and grapeseed. It's been associated with a decrease in cardiovascular risk, but others have worried about an effect of consumption mainly the downstream production of arachidonic acid which can give rise to eicosanoids that are both pro inflammatory and pro thrombotic.
And it's interesting Carolyn, several organizations suggest replacing saturated fat and carbohydrates with linoleic acid. So this study was really performed to address whether consumption of linoleic acid is associated with future cardiovascular events. In the study, investigators measured linoleic acid as well as arachidonic acid levels and from a global consortium across 30 perspective observational studies from 13 countries they performed multi variable adjusted associations of circulating an adipose tissue linoleic and arachidonic acid biomarkers with incident total cardiovascular disease and subtypes of cardiovascular disease including, coronary heart disease, ischemic stroke and cardiovascular mortality and this was all done as pre-specified analytic plan.
Dr Carolyn Lam: Wow, so what did they find?
Dr Greg Hundley: Well did I put you to sleep discussing all of that?
Dr Carolyn Lam: No! You have to tell me what they found. I'm seriously so interested in this topic because being vegetarian I actually get my source of omega fatty acids exactly from these sources.
Dr Greg Hundley: Okay, so Carolyn, higher levels of linoleic acid were associated with lower risk of total cardiovascular disease, ischemic stroke, cardiovascular mortality. While arachidonic acid was not associated with cardiovascular risks. And so, the clinical implications of the results support the potential benefits of main dietary omega- 6 fatty acid. That is linoleic acid for cardiovascular disease prevention. Now, while the trial is not randomized so we don't have definitive answers, the results do not support any theorized cardiovascular harms of consuming omega-6 fatty acids. And there is an excellent review on polyunsaturated versus saturated fat intake by Thomas Sanders from King's College, London as an editorial to this piece. So Carolyn I think we're safe right now in consuming linoleic acid. So how about a transition to our featured article and learn a little bit more about trastuzumab-induced cardiac dysfunction.
Dr Carolyn Lam: Absolutely!
Dr Greg Hundley: Great.
Welcome everybody, we have a fantastic paper to discuss. We're going to review human induced pluripotent stem cell derived cardiomyocytes and how they can be used to identify individuals at risk of trastuzumab-induced cardiac dysfunction after treatment for breast cancer. We have today Nazish Sayed and also Dr Joseph Wu, both from Stanford University in California.
Dr Joseph Wu: Thank you for inviting us.
Dr Nazish Sayed: Thank you.
Dr Greg Hundley: Nazish tell us a little bit about what are these human induced pluripotent stem cells and then also describe your experiment and what were your results?
Dr Nazish Sayed: So, induced pluripotent stem cells is about 10 years ago I knew technology where you can actually turn back the clock by you taking human fiber blast or blood cells and then you can test full reprogramming factors and turn back differentiated cells to pluripotent stem cells will mimic like catalytic stem cells. The catalytics include self-renewal, pluripotency and the most important that they can be differentiated to any cell type in the body. For example, cardiomyocytes or endothelial cells the neuron and kind of mimic these differentiated cells from the same individual from where the IPSCs were derived from.
So, what we did in our study is we used this platform to derive these pluripotent stem cells from patients and then differentiated them into a cardiomyocyte to understand what would these human cardiomyocytes behave in a dish when treated with a Herceptin or trastuzumab and then kind of determine the underlying mechanism for this cardiac dysfunction. It seemed really difficult to model trastuzumab and use cardiac dysfunction as a heart which is the receptor for the trastuzumab is expressed only in humans.
People have usually relied on animal model and for the first time what we did is we used these ideas of cardiomyocytes to model this dysfunction in a dish. Our results were pretty straightforward. We found that the IPSCs cardiomyocytes when treated with the chemotherapy agent showed cardiac dysfunction in the case of decrease contractility. The contraction velocity of these each individual cardiomyocytes is significantly reduced. More with this was also confirmed by having impaired calcium cycling which is very important for the contractility of these cardiomyocytes.
But I think the most important thing which we determined from the study is that individuals who are treated with trastuzumab have a metabolic impairment in these cardiomyocytes which is convenient but however have a severe impact on this contractility and calcium handling in these cardiomyocytes. And that was one of the gist of these papers to figure out the metabolic impairment could be a target where we can improve this cardiac dysfunction in these patients.
Dr Greg Hundley: And so, after you discovered this, I noticed you also did some work with AMPK activators and perhaps would reverse some of the dysfunction. Could you describe a little bit what are AMPK activators and then how did they reverse the dysfunction that you observed?
Dr Nazish Sayed: In our study we characterized these IPS cardiomyocytes from these individuals and then we ran a whole sequencing of them after treatment where trastuzumab to see which of the pathways which could be down regulated or dysfunction when compared to the control patients which are not treated with trastuzumab. And one of the most significant pathways which we found was in PK pathways which was down regulated in the trastuzumab treated IPSC cardiomyocytes. So knowing that the AMPK activators are used for metabolic diseases, for example being diabetes and metabolic dysfunction, we thought that this same thing could be used in a dish where we can take these AMPK activators and simultaneously cotreat cardiomyocytes with Herceptin or trastuzumab to see if we can rescue the phenotype and indeed you can see in our paper we used 4 different AMPK activators with metformin which is a commonly used diabetic drug. Showing the best rescue for that trastuzumab induced cardiac dysfunction.
Dr Greg Hundley: Very intriguing because it looks like you've been able to harvest cells from individuals and then pre-treat them, understand the mechanism of dysfunction, understand who's at risk of dysfunction and then offer therapeutic interventions to perhaps prevent that dysfunction in this patient population. Joe, turning to you now, this is really revolutionary technology it seems to me. Can you describe how long does this process take? Is this something that we see might come into clinical medicine soon?
Dr Joseph Wu: We're really excited about this technology that Nazish has described. I think as you know we've been working on this platform for the past 10+ years. In terms of the timeline, right now it takes us about a month to generate the induced pluripotent stem cells. It takes us another month to expand, propagate the IP itself. It takes us another month to generate the IPS cardiomyocytes. And it will take us probably another month to do all the phenotypic characterization in terms of using these IPS cardiomyocytes to expose them to various chemotherapy drugs and see how the chemotherapy drugs have an effect on these cardiomyocytes.
So, I would say the total timeline is 12 months at this moment. Is it possible that the timeline could be crunched, could be shrunk over time? Yes that's possible, I think the technology is improving month by month, week by week because there are many different labs trying to work on this platform trying to improve the whole process. But right now one of the limitations that as you pointed out is this 4 month time period. And also the cost that's associated with this. But we're hopeful that over time that both the time, the costs can go down so that we can offer this type of platform to help patients diagnosed with cancer, find out what kind of chemotherapy is safe to use, what kind of chemotherapy is not safe to use.
Dr Greg Hundley: So, we're working towards clinical applications but at this point in time it looks like a fantastic platform for understanding, diagnoses and understanding pathways that for patients particularly as they are treated for cancer will experience cardiovascular dysfunction. So, switching a little bit and asking a related question. Patients that receive trastuzumab often also receive doxorubicin. Especially the breast cancer patients. If you looked at this technology trying to understand, and certainly those more at risk for trastuzumab associated left ventricular dysfunction, are the patients that previously received doxorubicin. Have you and your group looked at patients that have also received doxorubicin and then went on to receive trastuzumab relative to those that received trastuzumab alone?
Dr Joseph Wu: I think for these two populations for this particular study, we tried to keep them clean. Meaning that we're looking mostly for trastuzumab treated patients, otherwise it's hard for us to piece out whether the toxicity was due to one medication or the other medication. But what you are asking is very important because as you pointed out many of these patients received both and I think for future studies we should be able to model both medications, meaning that take some IPS cardiomyocytes treated with doxorubicin, treated with Herceptin by itself and treated with both the medications.
In previous studies we have studied using IPS cardiomyocytes the effects of doxorubicin induced cardiac toxicity. In just the assessment, doxorubicin is a very common effective chemotherapy for breast cancer medications and just like Herceptin, the clinicians struggled with the issue, as we cannot predict which patient will develop toxicity. And then granted the doxorubicin induced toxicity has a slight different mechanism compared to perception induced mild cardiac dysfunction that this Nazish had mentioned about. But these are kind of the studies that we're very excited because now for the first time we have a way to model this. Otherwise they alternative would be not possible, for example it would not be possible for us to biopsy breast cancer patients woman's heart to study the cells.
Especially in the case of perception. The receptor that's being studied is not present in animal model cells. For example not present in mouse cardiomyocytes and therefore it would be very difficult to understand the mechanism and this is the reason why the patient specific and disease specific IPS cardiomyocytes become so useful.
Dr Greg Hundley: Do you find another emerging therapy in this entire realm is the immunotherapies? Do you think this technology will be applied to determine susceptibility to immune mediated toxicity?
Dr Joseph Wu: This is a very good question as well Greg. We've been thinking about studying that and as you know, it's a more complicated system because it involves patients’ immune response, the myocardial, to inflammatory infiltrates that happens. So we have a couple projects going on. One is to study direct effect of the immunotherapy on the cardiomyocytes and then the second angle is to take patients who are in full myocarditis and collect their patients urine samples, blood samples and to see if we could expose these IPS cardiomyocytes to the patients urine samples to see what is the effect. For these IPS cardiomyocytes for future studies we're also trying to make it more complicated by generating not just the cardiomyocytes by itself, but generating what we call engineered heart tissues. In which it's a chunk of human heart muscles that would have the patients cardiomyocytes, patients fibroblast, patients endothelial cells and expose them to the patients serum.
But that kind of study would take much longer period of time because the number of people who have these types of immunotherapy induced myocarditis it's relatively low compared to patients who have Herceptin or doxorubicin induced cardio toxicity. This is also part of the reason why we're very much interested in collaborating with big centers throughout the country like York Center to see if we could understand this process better as a team.
Dr Greg Hundley: Excellent. I want to thank both of you for this really elegant discussion and perfect work moving forward. In summary, you've illustrated an ability to withdraw human pluripotent stem cells, differentiate them to cardiomyocytes and then perform tests on them to forecast susceptibility to various treatments used commonly for women with breast cancer. And in this study identifying mechanisms for trastuzumab toxicity. And then perhaps therapeutic interventions using again human cells which has a marked leap as you've identified over doing mouse studies, particularly for studying trastuzumab when the receptors the HER2 receptors in mirroring models differ substantially to those in human subjects.
Dr Joseph Wu: Thank you Greg. And we want to also express our thanks to our collaborators, our colleagues who contributed to the study and most importantly to the patients who helped us with these studies.
Dr Greg Hundley: I want to thank both Nazish and Dr Wu from Stanford and Carolyn and I wish you the best for the coming week and we look forward to speaking with you again next week.
Dr Carolyn Lam: This program is copyright American Heart Association 2019.