Causal association between heart failure and bone mineral density: Insights from a two-sample bidirectional Mendelian randomization study.

In recent times, the association between HF and BMD has attracted enormous interest in the scientific community. However, published epidemiological observational studies on the relationship between HF and BMD remain inconclusive. Herein, we evaluated from the analytical perspective a two-sample bidirectional MR study to analyze the causal association between HF and BMD using a summary-level GWAS Catalog. To select instrumental SNPs strongly associated with exposure, we took a series of rigorous quality control steps at the time of analysis. The causal MR assessment of HF on the risk of BMD was performed first and then in the opposite direction. To make the conclusions more reliable and robust, the fixed-effects IVW, weighted median-based method, MR-Egger, simple mode and weighted mode were utilized. A maximum likelihood model was also used if necessary. MR-Egger regression, IVW "leave-one-out" sensitivity analysis, MR-PRESSO, MR-Egger intercept test and Cochran's Q statistic methods were used to assess heterogeneity and pleiotropy. Our MR studies supported a meaningful causal association between HF and TB-BMD (IVW: OR = 0.78, 95% CI: 0.68-0.87, p = 0.00588). At the same time, we did not find a significant causal relationship between HF and FA-BMD, FN-BMD or LS-BMD. No significant causal relationships between BMD and HF were observed. This bidirectional MR analysis suggested a causal association of HF with only low TB-BMD, while the reverse causality hypothesis was not found. Studies of the prevention and treatment of total bone mineral density decline in patients with heart failure need to be performed.

Increased circulating trimethylamine N-oxide contributes to endothelial dysfunction in a rat model of chronic kidney disease.

Chronic kidney disease (CKD) is strongly associated with increased cardiovascular risk. Impaired endothelial function, a key initiating step in the pathogenesis of cardiovascular disease, has been reported in patients with CKD, but the mechanisms responsible for endothelial dysfunction in CKD remain elusive. Emerging evidence reveals that trimethylamine-N-oxide (TMAO), a gut microbiota-generated metabolite, is involved in the pathogenesis of many cardiovascular diseases. Circulating TMAO is elevated in CKD. Here we tested the hypothesis that elevated TMAO plays a contributory role in the pathogenesis of endothelial dysfunction in CKD. Rats underwent 5/6 nephrectomy to induce CKD or sham operation, and were treated with 1.0% 3,3-Dimethyl-1-butanol (DMB, an inhibitor of trimethylamine formation) or vehicle. Eight weeks after nephrectomy and DMB treatment, circulating TMAO levels were markedly elevated in CKD-vehicle rats compared with sham-vehicle rats, but were reduced in CKD-DMB rats. Acetylcholine-induced endothelium-dependent vasodilation was impaired in CKD-vehicle rats compared with sham-vehicle rats as indicated by reduced maximal relaxation (Emax) and decreased area under the curve (AUC). Emax and AUC were both normalized in CKD-DMB rats. No difference in sodium nitroprusside-induced endothelial-independent vasodilation was observed across groups. Molecular studies revealed that endothelial nitric-oxide synthase activity was decreased, while superoxide production and proinflammatory cytokine expression were increased in the aorta of CKD-vehicle rats compared with sham-vehicle rats. Of note, the abnormalities in above molecular parameters were completely restored in CKD-DMB rats. These results suggest that CKD elevates circulating TMAO levels, which may reduce eNOS-derived NO production by increasing vascular oxidative stress and inflammation, contributing to CKD-associated endothelial dysfunction and cardiovascular disease.

Elevated Oxidative Stress and Inflammation in Hypothalamic Paraventricular Nucleus Are Associated With Sympathetic Excitation and Hypertension in Rats Exposed to Chronic Intermittent Hypoxia.

Obstructive sleep apnea (OSA), characterized by recurrent collapse of the upper airway during sleep leading to chronic intermittent hypoxia (CIH), is an independent risk factor for hypertension. Sympathetic excitation has been shown to play a major role in the pathogenesis of OSA-associated hypertension. Accumulating evidence indicates that oxidative stress and inflammation in the hypothalamic paraventricular nucleus (PVN), a critical cardiovascular and autonomic center, mediate sympathetic excitation in many cardiovascular diseases. Here we tested the hypothesis that CIH elevates oxidative stress and inflammation in the PVN, which might be associated with sympathetic excitation and increased blood pressure in a rat model of CIH that mimics the oxygen profile in patients with OSA. Sprague-Dawley rats were pretreated with intracerebroventricular (ICV) infusion of vehicle or superoxide scavenger tempol, and then exposed to control or CIH for 7 days. Compared with control+vehicle rats, CIH+vehicle rats exhibited increased blood pressure, and increased sympathetic drive as indicated by the blood pressure response to ganglionic blockade and plasma norepinephrine levels. Pretreatment with ICV tempol prevented CIH-induced increases in blood pressure and sympathetic drive. Molecular studies revealed that expression of NAD(P)H oxidase subunits, production of reactive oxygen species, expression of proinflammatory cytokines and neuronal excitation in the PVN were elevated in CIH+vehicle rats, compared with control+vehicle rats, but were normalized or reduced in CIH rat pretreated with ICV tempol. Notably, CIH+vehicle rats also had increased systemic oxidative stress and inflammation, which were not altered by ICV tempol. The results suggest that CIH induces elevated oxidative stress and inflammation in the PVN, which lead to PVN neuronal excitation and are associated with sympathetic excitation and increased blood pressure. Central oxidative stress and inflammation may be novel targets for the prevention and treatment of hypertension in patients with OSA.

Elevated Circulating Trimethylamine N-Oxide Levels Contribute to Endothelial Dysfunction in Aged Rats through Vascular Inflammation and Oxidative Stress.

Vascular endothelial dysfunction, a characteristic of the aging process, is an important risk factor for cardiovascular disease in aging. Although, vascular inflammation and oxidative stress are major contributors to endothelial dysfunction in aging, the underlying mechanisms during the aging process are not fully understood. Accumulating evidence reveals that gut microbiota-dependent metabolite trimethylamine-N-oxide (TMAO) is implicated in the pathogenesis of many cardiovascular diseases. We tested the hypothesis that aging increases circulating TMAO levels, which induce vascular inflammation and oxidative stress, resulting in age-associated endothelial dysfunction. Old (22-mo-old) and young (4-mo-old) Fischer-344 rats were treated without (control) or with 1.0% 3,3-Dimethyl-1-butanol (DMB, an inhibitor of trimethylamine formation) in drinking water for 8 weeks. Compared with young control group, old control group had markedly higher plasma TMAO levels, which were reduced by DMB treatment. Endothelium-dependent relaxation of aorta in response to acetylcholine was impaired in old control group compared with young control group as indicated by decreased maximal relaxation (Emax) and reduced area under the curve (AUC). Emax and AUC were both normalized in old rats treated with DMB. No difference in endothelial-independent relaxation in response to sodium nitroprusside was observed among groups. Molecular studies revealed that old control group exhibits increased expression of proinflammatory cytokines and superoxide production, and decreased expression of endothelial nitric-oxide synthase (eNOS) in the aorta, all of which were restored by DMB treatment. These results suggest that aging increases circulating TMAO levels, which may impair eNOS-derived NO bioavailability by increasing vascular inflammation and oxidative stress, contributing to aging-associated endothelial dysfunction.

MicroRNA 181b promotes vascular smooth muscle cells proliferation through activation of PI3K and MAPK pathways.

Vascular smooth muscle cells (VSMCs) hyperplasia is a common feature of pathologic cardiovascular event such as restenosis and atherosclerosis. The role and mechanisms of microRNAs (miRs) in VSMCs proliferation are poorly understood. Here, we report that miR-181b promotes VSMCs proliferation and migration. In an animal model, miR-181b was significantly increased in the rat carotid artery after balloon catheter injury. Delivery of miR-181b inhibitor to injured artery exhibited a marked inhibition of neointimal hyperplasia. Transfection of miR-181b with "mimics" to A10 cells accelerated cell proliferation, which was accompanied by an increase of cell migration. The induction of A10 cells proliferation by miR-181b appeared to be involved in activation of S and G2/M checkpoint, concomitant with decreases in cell-cycle inhibitors p21 and p27, and increases in cell-cycle activators CDK4 and cyclinD1. In contract, miR-181b inhibition attenuated A10 cells proliferation, inhibited cell migration and arrested cell cycle transition. Moreover, forced miR-181b expression elevated the phosphorylation levels of Akt and Erk1/2, whereas inhibition of miR-181b produced the opposite effects. Additionally, inhibition of PI3K and MAPK signaling pathways with specific inhibitors, but not inhibition of JNK pathway, significantly abolished the effects of miR-181b in promoting cell proliferation. These findings demonstrate that miR-181b enhances the proliferation and migration of VSMCs through activation of PI3K and MAPK pathways.