Jul 3, 2017
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. What is the association between fetal congenital heart defects and maternal risk of hypertensive disorders of pregnancy? We will be discussing new data in this area in just a moment, following these summaries.
The first paper describes the effect of long-term metformin and lifestyle measures on coronary artery calcium. This is a paper from Dr. Goldberg of George Washington University Biostatistics Center and colleagues of the Diabetes Prevention Program Research Group. The Diabetes Prevention Program and its outcome study is a long-term intervention study in subjects with prediabetes, which showed reduced diabetes risk with lifestyle and metformin compared to placebo.
In the current study, the authors looked at subclinical atherosclerosis, which was assessed in 2,029 participants using coronary artery calcium measurements after 14 years of average follow-up. They found that men but not women with prediabetes treated with metformin for an average duration of 14 years had lower coronary calcium scores than their placebo counterparts. No difference in coronary calcium scores was observed in the group receiving a lifestyle intervention as compared to the placebo group.
These findings provide the first evidence that metformin may protect against coronary atherosclerosis in men with prediabetes, although demonstration that metformin reduces cardiovascular disease events in these subjects is still needed before firm therapeutic implications of these findings can be made. The reason for an absence of an effect in women is unclear and deserves further study.
The next study provides insights on the physiology of angina from invasive catheter laboratory measurements during exercise. Dr. Asrress of Royal North Shore Hospital in Sydney, Australia, and colleagues, studied 40 patients with exertional angina and coronary artery disease who underwent cardiac catheterization via radial axis and performed incremental exercise using a supine cycle ergometer. As they developed limiting angina, sublingual GTN was administered to half the patients and all patients continued to exercise for two minutes at the same workload. Throughout exercise, distal coronary pressure and flow velocity, and central aortic pressure were recorded using sensor wires.
Using this novel invasive approach, the authors showed that administration of GTN ameliorated angina by reducing myocardial oxygen demand as well as increasing supply with a key component being the reversal of exercise-induced coronary lesion vasoconstriction. This was evidenced by the fact that there was a relationship between the diastolic velocity pressure gradient with significant increase in relative stenosis severity. In keeping with exercise-induced vasoconstriction of stenosed epicardial segments and dilation of normal segments, with trends towards reversal with GTN.
Thus, this study describes the development of a paradigm where patients with coronary artery disease can exercise while simultaneously having coronary and central aortic hemodynamics measured invasively, and has shown that this provides a unique opportunity to study mechanisms underlying the physiology of angina. In treating patients with exercise-induced angina, the results highlight the importance of after-load reduction and the use of agents that reduce arterial wave reflection and promote coronary artery vasodilation.
The next study provides mechanistic insights into reverse cholesterol transport, where excess cholesterol is removed from macrophage-derived foam cells in atherosclerotic plaques. It suggests that melanocortin receptor-1, or MC1-R, may play a role. As background, the melanocortin system, consisting of melanocyte-stimulating hormones and their receptors, regulate a variety of physiological functions, ranging from skin pigmentation to centrally-mediated energy balance control. At the cellular level, the biological actions are mediated by G protein-coupled melanocortin receptors, such as MC1-R. MC1-R not only affects melanogenesis in the skin but also has immunomodulatory effects through its wide expression in the cells of the immune system.
In the current study from Dr. Rinne of University of Turku in Finland, and colleagues, human and mouse atherosclerotic samples and primary mouse macrophages were used to study the regulatory functions of MC1-R. The impact of pharmacological MC1-R activation on atherosclerosis was further assessed in apolipoprotein E deficient mice. Their findings identified a novel role for MC1-R in macrophage cholesterol transport. Activation of MC1-R conferred protection against macrophage foam cell formation through a dual mechanism. It prevented cholesterol uptake while it concomitantly promoted reverse cholesterol transport by increasing the expression of ATP-binding cassette transporters, ABCA1 and ABCG1.
Thus, the identification of MC1-R in lesional macrophages, demonstration of its role in regulating reverse cholesterol transport, combined with its established anti-inflammatory effects, suggests that MC1-R could be a novel new therapeutic target for preventing atherosclerosis.
The next study suggests that obesity-related heart failure with preserved ejection fraction, or HFpEF, is a genuine form of cardiac failure and a clinically relevant phenotype that may require specific treatments. First author, Dr. Obokata, corresponding author, Dr. Borlaug, and colleagues from Mayo Clinic Rochester and Minnesota studied 99 patients with obese HFpEF with a BMI above 35, with 96 non-obese HFpEF with a BMI less than 30, and 71 non-obese controls without heart failure. All subjects underwent detailed clinical assessment, echocardiography, and invasive hemodynamic exercise testing.
The authors found that, compared to non-obese HFpEF, obese HFpEF patients displayed greater volume overload, more biventricular remodeling, greater right ventricular dysfunction, worse exercise capacity, more impaired pulmonary vasodilation, and more profound hemodynamic arrangements, despite a lower NT-proBNP level. Obese HFpEF patients displayed other important contributors to high left ventricular filling pressures, including greater dependence on plasma volume expansion, increased pericardial restraint, and enhanced ventricular interaction, which was exaggerated as pulmonary pressure load increased.
These data provide compelling evidence that patients with the obese HFpEF phenotype have real heart failure and display several pathophysiological mechanisms that differ from non-obese patients with HFpEF. These and other issues are discussed in an accompanying editorial by Dr. Dalane Kitzman and myself. We hope you enjoy it.
The final study identifies a novel long noncoding RNA that regulates angiogenesis. As background, although we know that the mammalian genome is pervasively transcribed, a large proportion of the transcripts do not encode a protein, and are thus regarded as noncoding RNAs. Based on their length, they can be divided into small or long noncoding RNAs, long being described as more than 200 nucleotides. Although their function is not fully understood, long noncoding RNAs have been increasingly reported to mediate the expression of other genes, affect the organization of the nucleus, and modify other RNAs.
In the current study by first author, Dr. Leisegang, corresponding author, Dr. Brandes, and colleagues of Goethe University in Frankfurt, Germany, epigenetically controlled long noncoding RNAs in human umbilical vein endothelial cells were searched by axon array analysis following knockdown of the histone demethylase JARID1B. The authors discovered a novel noncoding RNA named MANTIS to be strongly upregulated. MANTIS is located in the antisense strand of an intronic region of the gene for annexin A4, calcium- and phospholipid-binding protein. MANTIS is a nuclear long noncoding RNA that is enriched in endothelial cells but also expressed in other cell types. Reducing MANTIS levels led to impaired endothelial sprouting, tube formation, attenuated endothelial migration, and inhibition of the alignment of endothelial cells in response to shear stress.
Brahma-like gene 1, or BRG-1, was identified as a direct interaction partner of MANTIS, implying a role of MANTIS in the formation of the switch/sucrose non-fermentable chromatin remodeling complex. MANTIS binding to BRG-1 was shown to stabilize the BRG-1 interaction, hence by inducing an open chromatin conformation, MANTIS was proposed to maintain the endothelial angiogenic potential. The implications of these findings are discussed in an accompanying editorial by Dr. Zampetaki and Mayr from Kings College London.
That brings us to the end of our summaries. Now for our feature discussion.
Today, we are going to be discussing the association between fetal congenital heart defects and maternal risk of hypertensive disorders of pregnancy. To discuss this, I have the first and corresponding author of our feature paper, Dr. Heather Boyd, from Statens Serum Institut in Copenhagen, and our familiar Dr. Sharon Reimold, content editor for special populations from UT Southwestern. Welcome, Heather and Sharon.
Dr. Heather Boyd: Thank you.
Dr. Sharon Reimold: Thank you.
Dr. Carolyn Lam: Heather, it's a topic that I can't say I'm very familiar with, association between fetal congenital heart defects and maternal risk of hypertensive disorders of pregnancy. Could you start by sharing why would we think there would be a link? What was the hypothesis you were testing?
Dr. Heather Boyd: A couple years ago, there was a paper published in the European Heart Journal that reported evidence of angiogenic imbalance in women with fetuses with major congenital heart defects, so women who were pregnant with babies that had heart defects, and then in fetuses that were terminated because of this kind of defect. My research group focuses a lot of attention on preeclampsia. In the last decade or so, angiogenic imbalance in preeclampsia has been a really hot topic. Women with preeclampsia, particularly women with early-onset preeclampsia, have big angiogenic imbalances. When we saw the European Heart Journal paper, we immediately thought, "What's the connection between preeclampsia and heart defects in the offspring?"
Dr. Carolyn Lam: Oh!
Dr. Heather Boyd: Exactly. That was our entry point to it, was the term "angiogenic imbalance" in that paper sort of was a flag for us. It wasn't a completely new idea, but we in Denmark have one big advantage when considering research questions that involve either rare exposures and/or rare outcomes, and that's our National Health Registry. We have the ability to assemble these huge cohorts and study conditions like heart defects with good power, so we decided just to go for it.
Dr. Carolyn Lam: That makes a lot of sense now. Please, tell us what you did and what you found.
Dr. Heather Boyd: The first thing we did was look at the association between carrying a baby with a heart defect and then whether the mom had preeclampsia later in the same pregnancy. We had information on almost 2 million pregnancies for this part of the study. We found that women carrying a baby with a heart defect were seven times as likely as women with structurally normal babies to develop early preterm preeclampsia. We defined that as preeclampsia where the baby has to be delivered before 34 weeks, so the really severe form of preeclampsia. Then, women carrying a baby with a heart defect were almost three times as likely to develop late preterm preeclampsia as well. That's where they managed to carry it until 34 weeks but it has to be delivered some time before 37 weeks.
These findings were similar to those of other studies, but we were able to go a step further and look at individual heart defect subtypes. What we found there waws that these strong associations were similar across defect categories. Then we decided to see if we could shed any light on the origin of the problem, whether it was coming from the mom's side or the baby's side. To do this, we looked at women with at least two pregnancies in our study period to see whether preeclampsia in one pregnancy had any bearing on the chance of having a baby with a heart defect in another pregnancy or vice versa.
This part of the study included 700,000 women. We found very similar findings. We found that women with early preterm preeclampsia in one pregnancy had eight times the risk of having a baby with a heart defect in a subsequent pregnancy. Late-term preeclampsia in one pregnancy was associated with almost three times the risk of offspring heart defects in later pregnancies. Then, we found that it worked the other way around too. Women who had a baby with a heart defect were twice as likely to have preterm preeclampsia in subsequent pregnancies.
Those results were really, really exciting, because whatever mechanisms underlie the associations between preterm preeclampsia in moms and heart defects in the babies, they operate across pregnancies. Therefore, that pointed towards something maternal in origin.
Dr. Carolyn Lam: That is so fascinating. Sharon, please, share some of the thoughts, your own as well as those of the editors when we saw this paper.
Dr. Sharon Reimold: I think that there's a growing data about the links between hypertensive disorders of pregnancy and preeclampsia with subsequent abnormal maternal outcome. But this paper, I think, has implications for how we look at moms who are going to have offspring with congenital heart defects as well as those with preeclampsia. For instance, I would look at a patient now that has preeclampsia, especially in more than one pregnancy, to identify that they may be at risk to have offspring with congenital defects in the future if they have additional children. But the mom is also at risk based on other data for developing other cardiovascular risk factors and disease as she gets older. It was really the link going back and forth with the hypertensive disorders and the congenital defects that we found the most interesting.
Dr. Carolyn Lam: That struck me too, especially when you can look at multiple pregnancies and outcomes. That's amazing. You know what, Heather, could you share a little bit about what it's like working with these huge Danish databases? I think there must be a lot more than meets the eye.
Dr. Heather Boyd: It's an interesting question, because I'm a Canadian and I was trained in the US. I did my PhD in epidemiology at Emery, and then I moved to Copenhagen. When I first got here, I was absolutely floored at the possibility of doing studies with millions of women in them. It opens some amazing possibilities, like I said earlier, for certain outcomes and certain exposures. You just need to have a question where the information you want is registered.
Dr. Carolyn Lam: Yeah. But I think what I also want to put across is, having worked with big databases, and certainly not as big as that one, it's actually a lot of work. People might think, "Oh, it's just all sitting there." But, for example, how long did it take you to come to these observations and conclusions?
Dr. Heather Boyd: I have a fabulous statistician. I think she's the second author there, Saima Basit. She spends a lot of her time pulling together data from different registers. But yes, you're right. The data don't always just mesh nicely. The statisticians we have working with us are real pros at this sort of data slinging.
Dr. Carolyn Lam: Could I just pose one last question to both of you. What do you think are the remaining gaps?
Dr. Sharon Reimold: I think that this is a clinical link. Then, going back to figure more about what's going on biologically to set up this difference? Because right now there's really no intervention that's going to make a difference, it's just a risk going forward. This is sort of like medicine done backwards, that there's this association and now we need to figure out exactly why.
Dr. Heather Boyd: I can piggyback on what Sharon said a little bit, because I think one of the things we need to remember is that not all women with preeclampsia have babies with heart defects. Not by a long shot. What we need to do now is to figure out what distinguishes the women who do get this double whammy from the vast majority who don't.
One of the things that Denmark does really nicely is that there are large bio banks. One of the things we want to do is go back to bank first trimester maternal blood samples and see if we can identify biomarkers that are unique to the women with both preterm preeclampsia and babies with heart defects. That's one of the things we're thinking about to address this gap. Because, as Sharon says, we've got to figure out what the mechanism is.
The other thing we want to do is to see whether the association between preeclampsia and heart defects extends, for example, to other things, to cardiac functional deficits, for example, because it's probably not just severe structural defects. If there's an association, it's probably on a continuum. Are babies born to preeclamptic moms, do their cardiac outputs differ? Do their electrical parameters differ? Do they just have different hearts?
We're really lucky because right now the Copenhagen Baby Heart Study is offering to scan the hearts of all infants born at one of the three major university hospitals in the Copenhagen area. We're about to have echocardiography data on 30,000 newborn hearts to help us look at this. I'm really excited about that possibility.
Dr. Carolyn Lam: I've learnt so much from this conversation. I'm sure the listeners will agree with me. Thank you both very, very much.