Nov 19, 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.
Is there a unique lipoprotein profile for incident peripheral artery disease as opposed to coronary or cerebral vascular disease? Well, you're just gonna have to wait for our feature discussion to find out. That's coming right up after these summaries.
Our first original paper this week tells us that gene variance known to be associated with idiopathic and peripartum cardiomyopathy are also associated with preeclampsia. First and corresponding author Dr Gammill from University of Washington and colleagues studied 181 participants with confirmed preeclampsia from the Preeclampsia Registry in BioBank. Saliva samples were collected for DNA isolation and whole exome sequencing was performed to detect rare variants in 43 genes known to be associated with cardiomyopathy.
Results were compared with data from two controlled groups, unrelated women with a gynecological disorder, sequence using the same methods and instruments, as well as published variant data from 33,000 subjects in the Exome Aggregation Consortium.
The results showed that women who developed preeclampsia are more likely to carry protein altering mutations in genes associated with cardiomyopathy, particularly, the TTN gene which encodes the sarcomeric protein titin. Thus, detecting these gene variants may allow more specific diagnosis, classification, counseling and management of women at risk.
Prior trials have shown that nonsteroidal anti-inflammatory drugs or NSAIDS confer cardiovascular risk. Now this has been postulated to be due to enhanced formation of methyl arginines in the kidney that would limit the action of nitric oxide throughout the vasculature. However, the next original paper in this week's journal suggests that this may not be correct. First author, Dr Ricciotti, corresponding author, Dr FitzGerald from University of Pennsylvania Perelman School of Medicine and colleagues, used multiple genetic and pharmacological approaches to disrupt the COX 2 pathway in mice and analyze plasma from patients taking NSAIDS.
However, they did not observe an increase in methyl arginines. In contrast, they did observe an increase in plasma asymmetric dimethylarginine or EDMA in mice-rendered hypertensive by infusion of angiotensin II at a dose that also caused renal impairment. After a four week washout period following the infusion of angiotensin II, blood pressure, creatinine, and ADMA levels all fell back to normal levels.
Celecoxib-treated mice also exhibited increased ADMA and plasma creatinine in response to infusion of angiotensin II and their levels also returned to normal thereafter. Thus, it seems likely that the previous reported elevations in ADMA reflected renal dysfunction rather than a direct consequence of COX 2 deletion or inhibition. The authors end by suggesting that the most plausible mechanism by which NSAIDS confer a cardiovascular risk, is by suppression of COX 2 derived cardioprotective prostaglandins such as Prostacyclin rather than by enhanced formation of methyl arginines.
The next original paper identifies new targets with the potential to prevent vascular malformations in patients with hereditary hemorrhagic telangiectasia. Co-corresponding authors, Dr Ola and Eichmann from Yale University School of Medicine and colleagues looked at SMAD4, which is a downstream effector of transforming growth factor-beta/bone morphogenetic protein family ligands that signal via activin-like kinase receptors.
The authors generated a tamoxifen inducible postnatal endo-fetal specific SMAD for a mutant mouse and showed that SMAD4 prevented flow-induced arterial venous malformations by inhibiting casein kinase II. The uncovered pathways provided novel targets for the treatment of vascular lesions in hereditary hemorrhagic telangiectasia related juvenile polyposis patients carrying SMAD4 mutations.
The next original paper provides important data for the accurate diagnosis of long QT syndrome. Long QT syndrome can be a challenging diagnosis partly because the optimal method for QT assessment is not unequivocally established. QT experts advocate manual measurements with a tangent or threshold method.
In today's paper, first and corresponding author, Dr Vink from Academic Medical Center University of Amsterdam and colleagues, aimed to assess similarities and differences between these two methods of QT interval analysis among 1,484 patients with a confirmed pathogenic variant in either KCNQ1, KCNH2 or SNC5A genes from 265 families. Both QT measurement methods yielded a high inter and intra reader validity and a high diagnostic accuracy.
Using the same current guideline cutoff of QTC interval 480 milliseconds, both methods had similar specificity but yielded a different sensitivity. QTC interval cutoff values for the QT measured by the tangent method was lower compared to that measured by the threshold method. Plus, values were different depending on the correction for heart rate, age, and sex.
The authors provided an adjusted cutoff values specified for method, correction formula, age, and sex. In addition, a freely accessible online probability calculator for long QT syndrome at www.QTcalculator.org has been made available as an aid in the interpretation of the QT interval.
The next original paper demonstrates for the first time that thrombin mediated signaling may play a role in diet-induced atherogenesis. Co-first authors, Dr Raghavan and Singh, corresponding author Dr Rao from University of Tennessee Health Science Center and colleagues, used a mouse model of diet-induced atherosclerosis and molecular biological approaches and explored the role of thrombin and its G protein coupled receptor signaling in diet-induced atherosclerosis.
They found that thrombin-induced CD36 expression and foam cell formation required protease activated receptor 1, G alpha 12, Pyk2, GAB 1, and protein kinase C theta dependent activating transcription factor 2 activation. Thus, inhibition of thrombin G protein coupled receptor signaling could be a promising target for the development of new drugs in reducing the risk of diet-induced atherogenesis.
The next study provides insights into the long- term association of LDL cholesterol with coronary heart disease mortality in individuals at low tenure risks of atherosclerotic cardiovascular disease. First and corresponding author, Dr Abdullah, from VA North Texas Medical Center and UT Southwestern Medical Center and colleagues studied more than 36,000 subjects in the Cooper Clinic Longitudinal Study cohort who are at low tenure estimated risk of atherosclerotic cardiovascular disease. In other words, a low tenure risk of less than 7.5%. They've followed these patients for more than two decades.
Results showed that LDL cholesterol and non-HDL cholesterol at or above 160 milligrams per deciliter were independently associated with a 50 to 80% increased relative risk of cardiovascular disease mortality. The associations between LDL cholesterol and cardiovascular disease mortality were more robust when follow up was extended beyond the traditional 10 year estimated risk period.
The associations remain significant in those with an estimated tenure atherosclerotic cardiovascular disease risk of less than 5%. These data suggests that LDL cholesterol levels at or above 160 milligrams per deciliter in individuals deemed to be at low tenure atherosclerotic cardiovascular risk are associated with worse long term cardiovascular disease mortality. These findings, along with other observational data and data extrapolated from clinical trials, support further consideration of appropriate LDL cholesterol thresholds for lipid lowering interventions in individuals categorized as low short-term risk.
The final paper this week uncovers a novel therapeutic target for the prevention and treatment of thoracic aortic aneurysms. First author, Dr Nogi, corresponding author Dr Shimokawa from Tohoku University Graduate School of Medicine and colleagues, used genetically modified mice to show a pathogenic role of the small GTP binding protein, GDP dissociation stimulator in the development of angiotensin 2 induced thoracic aortic aneurysms and dissection. Down regulation of this protein contributed to dysfunction of aortic smooth muscle cells and hence oxidative stress, and matrix metalloproteinase activities in the pathogenesis of thoracic aortic aneurysms and dissection.
Local over expression of this small GTB binding protein GDP dissociation stimulator around the thoracic aorta inhibited aortic dilatation and rupture in deficient mice. And that wraps it up for this week's summaries. Now for our feature discussion.
Atherosclerosis has been considered a systemic process, meaning that when we see a disease in one vascular bed, we assume that that's a risk marker for disease in other vascular territories, and that they share pathophysiology, they share risk factors. However, if we think about it, the prior studies have all been sort of focusing on coronary and cerebral vascular disease, but today's feature paper changes that a bit because it addresses a key knowledge gap in peripheral artery disease risk, and interestingly suggests that there may be a unique lipid profile that's related to peripheral artery disease.
This is gonna be an exciting discussion and I have the first author, Dr Aaron Aday from Vanderbilt University Medical Center currently. We have our editorialist, Dr Parag Joshi from UT Southwestern, and our associate editor, Dr Anand Rohatgi from UT Southwestern. Welcome gentlemen and Aaron, could we start with you sharing about your study?
Dr Aaron Aday: So, as you mentioned, a lot of the previous epidemiologic data on atherosclerosis have been primarily in coronary artery disease and stroke, and when we looked at peripheral artery disease or PAD, there seemed to be some subtle differences. So for instance, total cholesterol on HTL cholesterol seemed to be the strongest risk factors for future peripheral artery disease and in terms of LDL cholesterol, the data are somewhat mixed. Some have found a weak association, some have actually found no association. And so building on that, we wanted to see if using nuclear magnetic resonance spectroscopy, we could elucidate more details about the litho protein pathways associated with peripheral artery disease.
And we did this in the women's health study which is a prospective cohort study of women free of cardiovascular disease, the baseline, they were aged 45 and older. And what we've found in terms of the standards with their profiles, we again found that there was no association between LDL cholesterol and future peripheral artery disease, whereas certain standard lipid measures like HDL cholesterol were strongly associated with PAD, and then using the Endemol spectroscopy tool, we found that actually, small LDL particles and total LDL particles were concentrations of both of those markers, were strong risk factors for future PAD and other measures like total HDL particle concentration were even more strongly associated with future PAD than coronary artery disease.
So essentially the signature associated with future peripheral artery disease, had some important differences than that for a composite of coronary artery disease and stroke.
Dr Carolyn Lam: Aaron thanks for that. That's beautifully described and just so intriguing. Parag, could you tell us how should we be thinking about results like this?
Dr Parag Joshi: It's a great paper and it really highlights a new and unique approach in that we ... Peripheral artery disease as an isolated incident event is fairly understudied I guess we could say and so, this is a really nice paper to start choosing out some of the risk factors for that. I think overall, when we think of peripheral arterial disease in general, I think historically, we've thought of it as similar pathophysiology, you know LDL particles and perhaps other particles depositing in the arterial space. But this does highlight some important differences that might exist and I think one of those seems to be that maybe this is more a signature of elevated remnant lipoproteins or triglyceride rich remnant lipoproteins, small dent LDL particles, low HDL, that sort of metabolic syndrome type patterns that we look at as a high risk factor that may be more contributory to peripheral artery disease than coronary disease, or at least more specific to peripheral artery disease.
I guess one of my main questions about that from your work Aaron is, how can we be sure this isn't just a pre-clinical marker of diabetic patients which we know have this type of pattern?
Dr Aaron Aday: Sure, it's certainly a possibility. I think what's notable in the cohort, at least a time enrollment. And there was a very little diabetes and actually there was a much greater prevalent of metabolic syndrome. So in my mind, it may be more of a metabolic syndrome specific marker rather than necessarily down the diabetes pathway, but it's certainly something that needs to be explored further.
Dr Parag Joshi: I wonder whether women's health studies such a healthy cohort that I wonder if this is picking up some signal before the answer to diabetes or as you said, metabolic syndrome, you know which certainly suggests an insulin resistance pattern and we know the association of diabetes with peripheral artery disease is stronger and so I wonder if this may be a sort of earlier way of picking that up.
Dr Aaron Aday: It may be. I think one thing to notice is the outcome of peripheral artery disease that we're using. So it is symptomatic disease. So, we're not picking up a lot of ulcers that are developing in the future, it's more the claudication and then people who've undergone revascularization. Certainly diabetics have both of those as well but I think that may suggest it's not fully unexplained by developing diabetes than peripheral artery disease further down the line.
Dr Parag Joshi: Yeah that's a great point.
Dr Carolyn Lam: Yeah great questions, great thoughts. Anand, what about you? Did you have questions too?
Dr Anand Rohatgi: I think from my perspective and thinking about it for circulation and its readership, we found this really interesting for several reasons. Number one, I think is, as you all have discussed, peripheral arterial disease just is not as well characterized and you can see that here in over 25,000 people, add about a 100 a bed, so I think in younger folk, it takes a lot of people to study, to be able to really understand kind of the pathophysiology of peripheral arterial disease.
The other thing that they think they really shed some light on is how this is happening in women in particular and in women, of course as we know have been understudied in all cardiovascular diseases, but in particular, diseases like this which are less common. It's really insightful to see that these lipid abnormalities in women are contributing to peripheral arterial disease more so than your typical LDL cholesterol management and interestingly enough, most of the women who had PAD events in this study, did not have other cardiovascular events.
They really just had PAD events exclusively and I thought that was really intriguing, and the use of this advanced lipoprotein testing, this NMR modality has been very useful in terms of biology and research, and I think that's the case here where we really go under the hood Carolyn, as you said, and get kind of deep dive, the lipid metalobles on abnormalities. And I think Parag and Aaron hit the nail in the head that this is really capturing an insulin resistance of phenotype and what I really liked about this is, instead of studying people who are 70, 80 years old and a lot of things are sort of clustering, a lot of diseases are clustering and they're manifesting all at the same time, it's very hard to tease apart the effective age.
Here, we captured women in their 50s and middle aged, just as they have kind of gone through menopause and this adverse metabolite's phenotype starts to rise in women. And then we could follow them over time and see what the natural history of that is, and the women who have this phenotype go on to have this devastating consequence, this peripheral arterial disease. One of the questions I had then, Aaron for you is, what do you think the implications are from these findings? Does it mean that in terms of diagnostics, we should be doing more advanced testings looking at LDL and HDL type particles with NMR or some other mortality? Does it change therapies with new therapies beings studies right now? What do you think the implications are from your work?
Dr Aaron Aday: That's important right. I think you mentioned this and I see the inter marked tool in this study, is really a way to try to dig further into the biology of peripheral artery disease as a form of atherosclerosis. I think that we already know patients who are extremely high risk or PAD, those are patients with diabetes, smoking history, metabolic syndrome et cetera., and as you can see in a patient population in 28,000 middle aged women who are pretty healthy, we only had just over a 100 PAD events.
So, I think even if you were to scale this up in terms of cost, I'm not sure that that would necessarily be a viable option for patients, but I think it does suggest that truly focusing on LDL in a very high-risk patient population, meaning patients with PAD, or we may not be fully addressing their risk. And so I think this is a need to highlight that important gap, think about other therapeutic options and we'll soon have ongoing trials, triglyceride low in therapy that may be particularly beneficial in this patient population and so that's how I see this being used.
Dr Anand Rohatgi: That makes a lot of sense and particular because in middle aged women like this, your standard risk score algorithms will not really capture that they're at increased risk, even if they smoke, just because they're women and they're younger and so, I think this really is a call to arms to more refined risk assessment in these women.
Dr Parag Joshi: Aaron, do you think there's actually a difference in the biology in the peripheral arteries compared to the coronary and cerebral vascular beds, or is there data to kind of look at that or maybe histopathological data to look at that?
Dr Aaron Aday: We know there's a lot of overlaps, so I don't wanna suggest that PAD is not a former atherosclerosis. I think one limitation is that the primary animal model for PAD is the hyperCKemia model. That doesn't fully recapitulate what's happening in a limb with PAD and so I think that has been one limitation in understanding the biology. But I think what we're starting to see in some clinical trials that have come out in the last couple of years or starting to see a somewhat different signal for therapies in patients with PAD so for instance, in 48, we actually saw that there was a greater benefit to LDL lower [inaudible 00:21:00] inhibitors than for coronary disease. We now have the compass trial results, again, more events, higher risk among these patients but for their benefit, add on River Oxodine therapy, we've seen lymph events or lymph signals in the SGLP2 inhibitor trials. So, I think we're starting to get a sense that there may be something else on top of the traditional ascariasis biology that may be a potential target on down the road.
Dr Parag Joshi: I think it's really a fascinating biological question of how these different territories might actually differ in their pathophysiology. I think it's a really a nice time to look at this. Also I think, Anand and Aaron both mentioned ongoing trials. The omega 3 fatty acid trials I think reduce it, will be soon to be presented and hopefully published in the next month or so. It would be nice to see if they evaluate peripheral events in that group, I'm sure they will.
Dr Carolyn Lam: Indeed, these have been just such great thoughts and discussion. Nothing really much to add there. I suppose I could say something cheeky like for the first time, and I never thought I'd say it on the podcast, I feel kind of bad that there are no men included in this trial but anyway, I just learnt so much from this. I just wanna thank you gentlemen for a great discussion.
Thank you, listeners, for joining us today and don't forget to tune in again next week to Circulation on the Run.