Meta-analysis of epigenome-wide association studies of carotid intima-media thickness

Common carotid intima-media thickness (cIMT) is an index of subclinical atherosclerosis that is associated with ischemic stroke and coronary artery disease (CAD). We undertook a cross-sectional epigenome-wide association study (EWAS) of measures of cIMT in 6400 individuals. Mendelian randomization analysis was applied to investigate the potential causal role of DNA methylation in the link between atherosclerotic cardiovascular risk factors and cIMT or clinical cardiovascular disease. The CpG site cg05575921 was associated with cIMT (beta?=??0.0264, p value?=?3.5?×?10^–8) in the discovery panel and was replicated in replication panel (beta?=??0.07, p value?=?0.005). This CpG is located at chr5:81649347 in the intron 3 of the aryl hydrocarbon receptor repressor gene (AHRR). Our results indicate that DNA methylation at cg05575921 might be in the pathway between smoking, cIMT and stroke. Moreover, in a region-based analysis, 34 differentially methylated regions (DMRs) were identified of which a DMR upstream of ALOX12 showed the strongest association with cIMT (p value?=?1.4?×?10^–13). In conclusion, our study suggests that DNA methylation may play a role in the link between cardiovascular risk factors, cIMT and clinical cardiovascular disease.

     

Eighth European meeting on hypertension

The Eighth European Meeting on Hypertension, held in Milan, Italy, was attended by approximately 4000 people. The programme consisted of 120 presentations, 337 poster sessions, 6 invited lectures/debates (endothelin antagonists; cardiac renin-angiotensin system; cancer and hypertension; adducin; angiotensin converting enzyme (ACE) gene polymorphism; pulse pressure) and 2 plenary sessions on 'sleep apnea and hypertension' and 'treatment of hypertension in the elderly'.     

69th scientific sessions of the American Heart Association

Out of more than 12,000 abstract submissions, 4359 were selected for presentation at the 69th Scientific Sessions of the American Heart Association, held in New Orleans, Louisiana, USA. The abstracts have been published in a supplement to Circulation (Volume 94, Number 8).     

Superoxide does not mediate the acute vasoconstrictor effects of angiotensin II: a study in human and porcine arteries

OBJECTIVE: To investigate whether superoxide mediates angiotensin (Ang) II-induced vasoconstriction. METHODS: Human coronary arteries (HCAs), porcine femoral arteries (PFA) and porcine coronary arteries (PCAs) were mounted in organ baths and concentration-response curves to Ang II, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and the NAD(P)H oxidase substrate NADH were constructed in the absence and presence of superoxide inhibiting and activating drugs. Extracellular superoxide was measured using cytochrome c reduction. RESULTS: Ang II constricted both HCAs and PFAs. In HCAs, the NAD(P)H inhibitors diphenyleneiodonium (DPI) and apocynin, and the xanthine oxidase (XO) inhibitor allopurinol, but not the superoxide dismutase (SOD) mimetic tempol or the SOD inhibitor diethyldithiocarbamate (DETCA), reduced this constriction. Catalase potentiated Ang II in HCAs, indicating a vasodilator role for H2O2. DPI, tempol and SOD did not affect Ang II in PFAs. DPI, apocynin and allopurinol relaxed preconstricted HCAs. Although the relaxant effects of the NO donor SNAP in PCAs was reduced by DETCA, indicating that superoxide-induced constrictions depend on NO inactivation, the apocynin-induced relaxations were NO independent. Moreover, NADH relaxed all vessels, and this effect was blocked by KCl but not DPI or NO removal. Xanthine plus XO also relaxed HCAs and PCAs. Incubation of human or porcine arteries with Ang II or NADH did not result in detectable increases of extracellular superoxide within 1 h. CONCLUSIONS: Acute vasoconstriction by Ang II is not mediated via superoxide generated through NAD(P)H oxidase and/or XO activation. Such activation, if occurring, rather results in the generation of the vasodilator H2O2.     

The (pro)renin receptor. A decade of research: what have we learned?

The discovery of a (pro)renin receptor ((P)RR) in 2002 provided a long-sought explanation for tissue renin–angiotensin system (RAS) activity and a function for circulating prorenin, the inactive precursor of renin, in end-organ damage. Binding of renin and prorenin (referred to as (pro)renin) to the (P)RR increases angiotensin I formation and induces intracellular signalling, resulting in the production of profibrotic factors. However, the (pro)renin concentrations required for intracellular signalling in vitro are several orders of magnitude above (patho)physiological plasma levels. Moreover, the phenotype of prorenin-overexpressing animals could be completely attributed to angiotensin generation, possibly even without the need for a receptor. The efficacy of the only available putative (pro)renin receptor blocker handle region peptide remains doubtful, leading to inconclusive results. The fact that, in contrast to other RAS components, (P)RR knock-outs, even tissue-specific, are lethal, points to an important, (pro)renin-independent, function of the (P)RR. Indeed, recent research has highlighted ancillary functions of the (P)RR as an essential accessory protein of the vacuolar-type H⁺-ATPase (V-ATPase), and in this role, it acts as an intermediate in Wnt signalling independent of (pro)renin. In conclusion, (pro)renin-dependent signalling is unlikely in non-(pro)renin synthesizing organs, and the (P)RR role in V-ATPase integrity and Wnt signalling may explain some, if not all of the phenotypes previously associated with (pro)renin-(P)RR interaction.     

Methodologic Issues in the Measurement of Urinary Renin

Background and objectives

Alge et al. recently reported that urinary renin may be a prognostic biomarker for AKI after cardiac surgery. However, their urinary renin levels far exceeded published plasma renin levels, whereas normally, urinary renin is <10% of plasma renin. This result raises questions about the specificity of the new Quantikine Renin ELISA Kit used in the work by Alge et al., which is claimed to detect total renin (i.e., renin and prorenin). Therefore, this study tested this assay.

Design, setting, participants, & measurements

Plasma and urine from 30 patients with hypertension, diabetes, or preeclampsia and 10 healthy pregnant women (randomly selected from sample sets obtained earlier to investigate urinary renin-angiotensin system components) were used to compare the ELISA with a validated renin immunoradiometric assay and an in-house enzyme kinetic assay. Measurements were performed before and after in vitro prorenin activation, representing renin and total renin, respectively.

Results

Total renin measurements by ELISA, immunoradiometric assay, and enzyme kinetic assay were highly correlated. However, ELISA results were consistently ≥10-fold higher. The ELISA standard yielded low to undetectable levels in the immunoradiometric assay and enzyme kinetic assay, except after prorenin activation, when the results were ≥10-fold lower than the ELISA results. In plasma, prorenin activation increased ELISA results by 10%–15%. Urine contained no detectable prorenin.

Conclusions

The ELISA renin kit standard is prorenin, and its immunoreactivity and enzymatic activity after conversion to renin do not match the International Reference Preparation of human renin that has been used to validate previous immunoradiometric assays and enzyme kinetic assays; in fact, they are at least 10-fold lower, and thus, any measurements obtained with this ELISA kit yield levels that are at least 10-fold too high. The ELISA antibodies detect both renin and prorenin, with a preference for the former. Given these inconsistencies, urinary renin levels should be measured by established renin assays.     

Plasma levels of prorenin and Renin in blacks and whites: their relative abundance and associations with plasma aldosterone concentration

BackgroundAll renin arises from prorenin. The proportion of renin relative to prorenin could influence overall renin-angiotensin-aldosterone activity. We sought to determine whether prorenin levels were related to extracellular volume, as reflected by the levels of plasma renin activity (PRA), and to aldosterone.MethodsWe analyzed plasma levels of prorenin, renin, and aldosterone, as well as their interactions, in 129 young blacks and whites.ResultsBlacks had lower plasma renin concentration (PRC) and PRA, but had prorenin levels similar to whites (69 pg/ml in blacks vs. 62 pg/ml in whites, P = 0.41). As a result, the renin-to-total renin ratio was significantly lower in blacks (11.5% in blacks as compared to 19.8% in whites; P = 0.0001). Because prorenin also resides in tissues including the adrenal where it can bind to a specific receptor to generate angiotensin II, we examined the relationship of prorenin levels to plasma aldosterone concentrations (PAC). While a positive association between PRC and PAC was found in both blacks and whites, PAC was positively related to prorenin in whites (P = 0.04) but negatively in blacks, an observation that we hypothesize was due to reduced prorenin-to-renin conversion in blacks.ConclusionsWe observed a disproportionately high level of prorenin in blacks. These high circulating prorenin levels however do not result in greater adrenal angiotensin II and aldosterone production in healthy young blacks.American Journal of Hypertension 2012; doi:10.1038/ajh.2012.83.     

Optimal antiproteinuric dose of aliskiren in type 2 diabetes mellitus: a randomised crossover trial

Aim  

The optimal antiproteinuric dose of aliskiren is unknown. This study compared the effect of placebo and increasing doses of aliskiren on urinary albumin excretion rate (UAER).