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Circulation on the Run

Jan 15, 2018

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. This week's feature paper takes a deep dive into nitric oxide signaling, that extremely important pathway in cardiovascular health and disease. This time, taking a novel look at genetic predisposition, phenotypic consequences, and therapeutic implications. All that coming right up after these summaries.

                                                The first original paper describes the derivation and validation of a novel model to stratify the risk of death due to circulatory etiology in patients resuscitated from cardiac arrest without an ST elevation MI.

                                                First author, Dr. Bascom, corresponding author Dr. Setter from Maine Medical Center in Portland and their colleagues use the International Cardiac Arrest Registry to derive a novel model termed the CREST Model, which describes an incrementally high risk of circulatory etiology death with an increasing score.

                                                Now, CREST is a simple score with components of C for prior coronary artery disease. R for non-shockable rhythm. E for ejection fraction less than 30% on admission. S for shock at the time of admission. T for ischemic time more than 25 minutes. The authors showed that this CREST tool may allow for estimation of circulatory risk and improve triage of cardiac arrest survivors without STEMI at the point of care.

                                                The next study reports associations between usual sodium, potassium and blood pressure using gold standard 24-hour urinary data collected for the first time among a nationally representative sample of adults in the United States.

                                                First and corresponding author Dr. Jackson from Centers for Disease Control and Prevention used cross-sectional data from 766 participants aged 20 to 69 years with complete blood pressure and 24-hour urine collections in the 2014 national health and nutrition examination survey.

                                                They found that there was a strong direct relationship between higher sodium excretion and higher blood pressure and hypertension. In addition, there was an inverse relationship between potassium excretion and blood pressure and hypertension. When added to the evidence based from longitudinal and interventional studies, these results support clinicians dietary advise to lower sodium intake and increase consumption of potassium containing foods.

                                                The next two studies in this week's journal examine the utility of circulating biomarkers to aid in the diagnosis of acute aortic dissection. As a reminder, the AHA/ACC guidelines published in 2010, proposed using the aortic dissection detection risk score or ADD risk score as a primary screening tool based on scoring the presence of three categorical risks.

                                                Number one, high risk conditions such as Marfan Syndrome, a family history of aortic disease, known aortic valve disease, known thoracic aortic aneurysm or previous aortic manipulation. Number two, The pain features such as chest, back or abdominal pain described as being of abrupt onset severe intensity or ripping, tearing. Number three, the examination features such as evidence of profusion deficit, systolic blood pressure difference, spoken neurological deficit or aortic diastolic murmur and hypertension or shock.

                                                The presence of one or more markers within each of these categorical features is given an ADD score of one with a maximum cumulative score of three if all three categorical features are present. In the first of these two papers in this week's journal, first author Dr. Nazareen, corresponding author Dr. Morello and colleagues from Molinette Hospital in Italy performed the advised International Multi Centers Study, which prospectively assessed the diagnostic performance of standardized strategies integrating pre-test probability assessment and D-dimer in 1,850 patients from the emergency department.

                                                They found that in patients with an ADD risk score above one and D-dimer less than 500 nanograms per milliliter, the rate of acute aortic syndromes was significant at one in 22 cases. Rule out strategies for acute aortic syndromes integrating an ADD risk score of zero or one with D-dimer less than 500 were found to miss only around 1 in 300 cases of acute aortic syndrome.

                                                Integrating the ADD risk score with D-dimer could help to standardize diagnostic decisions on advanced imaging for suspected acute aortic syndrome balancing the risks of misdiagnosis and over testing. The authors concluded that patients at high probability of acute aortic syndrome such as with an ADD risk score above one should proceed to computer tomography and geography or other conclusive imaging irrespective of D-dimer levels.  However, in those with an ADD risk score of zero or one, with a D-dimer of less than 500 were possible rule out diagnostic strategies for acute aortic syndrome.

                                                The second manuscript in the present issue suggests that soluble ST2 might be an even better biomarker than D-dimer to rule out aortic dissection. In this paper by first author, Dr. Wang, co-corresponding authors, Dr. Du and Guo from Beijing Anzhen Hospital and Peking University respectively, the authors measured plasma concentrations of soluble ST2 using the R&D Systems assay in 1,360 patients including 1,027 participants in the retrospective discovery set and 330 patients with an initial suspicion of acute aortic dissection and ruled in a prospective validation cohort.

                                                The proportion of acute aortic dissection, this acute chest pain cohort was high at more than 40%. The authors found that soluble ST2 measured using this research grade assay showed higher levels in acute aortic dissection than in acute myocardial infarction or in acute pulmonary embolism. The result suggested that soluble ST2 levels could be useful as a rule out marker possibly even to an extent moderately superior to D-dimer.

                                                A cut-off level of around 35 nanograms per milliliters using the research grade soluble ST2 assay appeared to reliably rule out acute aortic dissection if used within 24 hours after symptom onset with a negative likelihood ratio of 0.01 and a negative predictive value of more than 99%. These intriguing findings are discussed in an accompanying editorial by Dr. Toru Suzuki from University of Leicester and Dr. Kim Eagle from University of Michigan. Well, that wraps it up for our summaries. Now, for our future discussion.

                                                Nitric oxide signaling plays a key role in the regulation of vascular tone and platelet activation. In fact, the pharmacologic stimulation of nitric oxide pathway is emerging as a therapeutic strategy in cardiovascular medicine in many areas including in heart failure preserved dejection fraction.

                                                Today's paper is therefore all the more intriguing because it seeks to understand the impact of a genetic predisposition to enhanced nitric oxide signaling on the risk for cardiovascular disease as a way of informing of the potential utility of pharmacologic stimulation of the nitric oxide pathway.

                                                Intrigued? Well, I certainly and I'm so glad to have with us the corresponding author, Dr. Sekar Kathiresan from Massachusetts General Hospital as well as a familiar voice, Dr. Peipei Ping, associate editor from UCLA here to discuss this paper.

                                                Sekar, could I ask you as an introduction to tell us a little bit more of the general approach of looking at genetic predisposition as a way of perhaps forecasting potential utility of pharmacologic stimulation? Could you tell us a little bit more about that?

Dr. Sekar Kathiresan:      Yes. I'm delighted to speak a little bit more about this idea of using naturally occurring genetic variation to understand if a medicine developed against a target is going to work in terms of efficacy and also potentially lead to on target side effect.

                                                As you know, there are lots of variants for mutations in genes that eventually become targets for medicines. Over the last 10, 15 years, there's been an explosion in our understanding of human genetic variation, specifically in genes targeted by medicines.

                                                The idea here is that if there's a naturally occurring mutation in that target gene, you can simply ask what are the phenotypic consequences of carrying that mutation. Also use that information to predict, as I said, the efficacy of pharmacologic manipulation and potentially on-target side effects. This approach has become a very powerful approach.

                                                A famous recent example of gene, PCSK9, where mutation in this gene occur naturally. A lower function of PCSK9 and individuals who carry this mutations have lower LDL levels and lower risk of heart attack. This information has led to the development of medicine that mimic those mutations and those medicines have been proven now to lower LDL as well as lower risk of heart attack, a phenomenon anticipated by the genetics.

Dr. Carolyn Lam:               If I understand it right then, with regards to today's paper, the idea is that if a genetic predisposition to enhanced nitric oxide signaling associates with reduced risk of cardiovascular disease, then that would support the hypothesis that pharmacologic stimulation of the nitric oxide pathway would prevent or treat the cardiovascular disease, right? Could you further expand? Because you also did a meditation analysis. How would we understand that?

Dr. Sekar Kathiresan:      Let me walk you through the basics of this paper. Our hypothesis initially was a genetic predisposition to enhance nitric oxide signaling would actually affect a range of cardiovascular diseases. Nitric oxide is a well-known molecule, a regulator of a number of important processes; vascular tone, blood pressure, platelet aggregation.

                                                A couple of important genes in the nitric oxide pathway are, one, nitric oxide synthase, the key enzyme that generates NO. Second is a soluble guanylyl cyclase that is a regulatory molecule involved in NO biology. One of the genes that is part of that pathway is called GUCY183, which is basically a subunit of the soluble guanylyl cyclase.

                                                What we did was we looked at those two genes and asked, "Are there naturally occurring variations in those two genes that actually give us a sense that they gain function that they actually activate nitric oxide signaling. It turned out there are two polymorphisms. One in nitric oxide synthase and the other is in the soluble guanylyl cyclase subunit that are essentially gain of function. They're common polymorphisms.

                                                We know their gain of function because the carriers of these DNA variants have lower blood pressure. An indicator that there's enhanced NO signaling. We use these two polymorphisms as an instrument to understand the phenotypic consequences of having lifelong enhanced nitric oxide signaling.

                                                What we looked at was the relationship of individuals who carried both of the gene variants or gained a function and asked whether these individuals what the relationship of carrying the variant was to a range of cardiovascular diseases as well as a range of quantitative traits like blood pressure or kidney function.

                                                We looked at this in extremely large human population samples where genotype and phenotype had been collated. Most important of these samples is a recent study of a population-based cohort study called the UK Biobank, which has involved about a half million people where genotype and have phenotype have been assembled.

                                                What we found was that genetic predisposition to enhance nitric oxide signaling was associated with reduced risk of several important cardiovascular diseases. First, coronary heart disease. Second, peripheral arterial disease, and third, ischemic stroke.

                                                That provide a very compelling evidence that atherosclerotic cardiovascular disease would be lower based on enhanced nitric oxide signaling. What was surprising to us is we also found a couple of other diseases where it seemed to benefit from enhanced nitric oxide signaling namely kidney function and pulmonary function. These were a little surprising to us, but I think it really suggest that NO plays an important role in a range of diseases.

                                                In terms of your question about what aspect of NO biology is leading to be relationship to these diseases, is it simply the blood pressure effect for example or could you actually infer a mechanisms beyond the blood pressure? We looked at that specifically in the context of cardiovascular disease and we're able to show that the protection afforded by the enhanced nitric oxide signaling gene variants, that protection exceeded the amount predicted by the blood pressure change. In fact, by quite a bit suggesting that there are probably non-blood pressure mechanisms that are at play in terms of the protection afforded by enhanced nitric oxide signaling gene variants.

Dr. Carolyn Lam:               Peipei, I have to invite your thoughts now. This is such an amazing paper. We had great discussions as an editor team. Tell us your thoughts.

Dr. Peipei Ping:                 The editorial team as well as the reviewers have been very impressed with the quality of the datasets and the value and detail, the metadata analysis together with the appropriate analytical approach. The study is done in our view in a very careful manner and the analysis was performed through the highest standards.

                                                What we also recognized is the potential impact that this particular study may have on multiple areas of studies, in particularly with their findings, the spectrum of individuals, how they carry nitric oxide signaling trends. You could appreciate that the individual score or genetic score paired with the analysis of the genetic variance that they have done, they see from the mental idea that examine both genetic as well as phenotype of each individual is critically important for medicine to be prescribed in the next step of therapies.

Dr. Carolyn Lam:               Building on that thought, Sekar, could I ask you? You found some rare inactivating variance. Are these the patients then you think should be targeted for NO enhancing therapies? What's the clinical implications of your findings?

Dr. Sekar Kathiresan:      I think there are two ways to think about the implications of these findings. One is there's just a simple biologic insight, the pharmacologic activation of NO signaling maybe protective beyond pulmonary hypertension. As you know, there are actually compounds in the clinic right now that are pharmacologic activators of soluble guanylate cyclase. Those medicines work in the rare condition of pulmonary hypertension.

                                                our work suggest that those medicines are likely to work in a broader range of indications including atherosclerotic cardiovascular disease, kidney disease and pulmonary function. At a simple level, those experiments, I think, should be looked at. Those indications should be looked at.

                                                Whether we've identified a subset of a population that particularly will respond versus it will be a general phenomenon across a range of different individuals that have impaired nitric oxide signaling, I think time will tell. Certainly, one group to think about would be those who are indigenously deficient in nitric oxide signaling and we did find that there are small subset of patients who have inactivating mutations in these two genes and they have higher blood pressure and increased risk for cardiovascular disease.

                                                It was a pretty rare phenomenon, so very small number of individuals would be relevant there. I'm not sure actually that you necessarily want to limit the potential benefit of NO signaling, enhanced NO signaling to just that subgroup. In fact, my prediction would be that the medicine would be relevant for a very large percentage of the population. That you do not need to limit the potential application of this therapy to just those who carry the inactivating mutations.

Dr. Peipei Ping:                 I agree largely of what Sekar has discussed. I would add that in situations where genetic information are available with the patients, what the study has offered is fairly clear in the patients where rare variance that inactivate the NOS3 or the guanylyl cyclase off the genes. Maybe a failure it is with a higher systolic blood pressure risk. I'm entirely supportive with the general conclusion that we have come to a time point where NOS outside signaling activation is a critical new element of therapy in cardiovascular health and disease.

Dr. Sekar Kathiresan:      Thank you Peipei. Thank you Sekar for taking the time to share your thoughts with us. We are so proud to be publishing paper in circulation. So proud and happy to be chatting about this on this podcast. You've been listening to Circulation on the Run. Thank you for joining us and please tune in again next week.