The Novel Angiotensin II Receptor Blocker Azilsartan Medoxomil Ameliorates Insulin Resistance Induced by Chronic Angiotensin II Treatment in Rat Skeletal Muscle.

Angiotensin receptor (type 1) blockers (ARBs) can reduce both hypertension and insulin resistance induced by local and systemic activation of the renin-angiotensin-aldosterone system. The effectiveness of azilsartan medoxomil (AZIL-M), a novel imidazole-based ARB, to facilitate metabolic improvements in conditions of angiotensin II (Ang II)-associated insulin resistance is currently unknown. The aim of this study was to determine the impact of chronic AZIL-M treatment on glucose transport activity and key insulin signaling elements in red skeletal muscle of Ang II-treated rats. Male Sprague-Dawley rats were treated for 8 weeks with or without Ang II (200 ng/kg/min) combined with either vehicle or AZIL-M (1 mg/kg/day). Ang II induced significant (p < 0.05) increases in blood pressure, which were completely prevented by AZIL-M. Furthermore, Ang II reduced insulin-mediated glucose transport activity in incubated soleus muscle, and AZIL-M co-treatment increased this parameter. Moreover, AZIL-M treatment of Ang II-infused animals increased the absolute phosphorylation of insulin signaling molecules, including Akt [both Ser473 (81%) and Thr308 (23%)] and AS160 Thr642 (42%), in red gastrocnemius muscle frozen in situ. Absolute AMPKα (Thr172) phosphorylation increased (98%) by AZIL-M treatment, and relative Thr389 phosphorylation of p70 S6K1, a negative regulator of insulin signaling, decreased (51%) with AZIL-M treatment. These results indicate that ARB AZIL-M improves the in vitro insulin action on glucose transport in red soleus muscle and the functionality of the Akt/AS160 axis in red gastrocnemius muscle in situ in Ang II-induced insulin-resistant rats, with the latter modification possibly associated with enhanced AMPKα and suppressed p70 S6K1 activation.

Obesity and insulin resistance induce early development of diastolic dysfunction in young female mice fed a Western diet.

Cardiovascular disease (CVD), including heart failure, constitutes the main source of morbidity and mortality in men and women with diabetes. Although healthy young women are protected against CVD, postmenopausal and diabetic women lose this CVD protection. Obesity, insulin resistance, and diabetes promote heart failure in females, and diastolic dysfunction is the earliest manifestation of this heart failure. To examine the mechanisms promoting diastolic dysfunction in insulin-resistant females, this investigation evaluated the impact of 8 weeks of a high-fructose/high-fat Western diet (WD) on insulin sensitivity and cardiac structure and function in young C57BL6/J female versus male mice. Insulin sensitivity was determined by hyperinsulinemic-euglycemic clamps and two-dimensional echocardiograms were used to evaluate cardiac function. Both males and females developed systemic insulin resistance after 8 weeks of a WD. However, only the females developed diastolic dysfunction. The diastolic dysfunction promoted by the WD was accompanied by increases in collagen 1, a marker of stiffness, increased oxidative stress, reduced insulin metabolic signaling, and increased mitochondria and cardiac microvascular alterations as determined by electron microscopy. Aldosterone (a promoter of cardiac stiffness) levels were higher in females compared with males but were not affected by the WD in either gender. These data suggest a predisposition toward developing early diastolic heart failure in females exposed to a WD. These data are consistent with the notion that higher aldosterone levels, in concert with insulin resistance, may promote myocardial stiffness and diastolic dysfunction in response to overnutrition in females.

Dipeptidylpeptidase inhibition is associated with improvement in blood pressure and diastolic function in insulin-resistant male Zucker obese rats.

Diastolic dysfunction is a prognosticator for future cardiovascular events that demonstrates a strong correlation with obesity. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon-like peptide-1 is an emerging therapy for control of glycemia in type 2 diabetes patients. Accumulating evidence suggests that glucagon-like peptide-1 has insulin-independent actions in cardiovascular tissue. However, it is not known whether DPP-4 inhibition improves obesity-related diastolic dysfunction. Eight-week-old Zucker obese (ZO) and Zucker lean rats were fed normal chow diet or diet containing the DPP-4 inhibitor, linagliptin (LGT), for 8 weeks. Plasma DPP-4 activity was 3.3-fold higher in ZO compared with Zucker lean rats and was reduced by 95% with LGT treatment. LGT improved echocardiographic and pressure volume-derived indices of diastolic function that were impaired in ZO control rats, without altering food intake or body weight gain during the study period. LGT also blunted elevated blood pressure progression in ZO rats involving improved skeletal muscle arteriolar function, without reducing left ventricular hypertrophy, fibrosis, or oxidative stress in ZO hearts. Expression of phosphorylated- endothelial nitric oxide synthase (eNOS)(Ser1177), total eNOS, and sarcoplasmic reticulum calcium ATPase 2a protein was elevated in the LGT-treated ZO heart, suggesting improved Ca(2+) handling. The ZO myocardium had an abnormal mitochondrial sarcomeric arrangement and cristae structure that were normalized by LGT. These studies suggest that LGT reduces blood pressure and improves intracellular Cai(2+) mishandling and cardiomyocyte ultrastructure, which collectively result in improvements in diastolic function in the absence of reductions in left ventricular hypertrophy, fibrosis, or oxidative stress in insulin-resistant ZO rats.

Loss of Estrogen Receptor α Signaling Leads to Insulin Resistance and Obesity in Young and Adult Female Mice.

BACKGROUND/AIMS: There are important sex-related differences in the prevalence of obesity, type 2 diabetes mellitus and cardiovascular disease. Indeed, premenopausal women have a lower prevalence of these conditions relative to age-matched men. Estrogen participates in the modulation of insulin sensitivity, energy balance, and body composition. In this paper, we investigated the impact of estrogen signaling through estrogen receptor α (ERα) on systemic insulin sensitivity and insulin signaling in skeletal muscle. METHODS: In 14- and 30-week-old female ERα knockout (ERαKO) mice and age-matched controls, we assessed insulin sensitivity by a euglycemic-hyperinsulinemic clamp and intraperitoneal glucose tolerance testing. Blood pressure was evaluated by tail cuff and telemetry. We studied ex vivo insulin-stimulated glucose uptake in skeletal muscle tissue, as well as insulin metabolic signaling molecule phosphorylation by immunoblotting and oxidative stress by immunostaining for 3-nitrotyrosine. RESULTS: Body weight was higher in ERαKO mice at 14 and 30 weeks of age. At 30 weeks, intraperitoneal glucose tolerance testing and clamp results demonstrated impaired systemic insulin sensitivity in ERαKO mice. Insulin-stimulated glucose uptake in soleus was lower in ERαKO mice at both ages. The insulin receptor substrate 1/phosphatidylinositol 3-kinase association and the activation of protein kinase B were decreased in ERαKO mice, whereas immunostaining for 3-nitrotyrosine was increased. CONCLUSIONS: Our data demonstrate a critical age-dependent role for estrogen signaling through ERα on whole-body insulin sensitivity and insulin metabolic signaling in skeletal muscle tissue. These findings have potential translational implications for the prevention and management of type 2 diabetes mellitus and cardiovascular disease in women, who are at increased risk for these conditions.

Overweight female rats selectively breed for low aerobic capacity exhibit increased myocardial fibrosis and diastolic dysfunction.

The statistical association between endurance exercise capacity and cardiovascular disease suggests that impaired aerobic metabolism underlies the cardiovascular disease risk in men and women. To explore this connection, we applied divergent artificial selection in rats to develop low-capacity runner (LCR) and high-capacity runner (HCR) rats and found that disease risks segregated strongly with low running capacity. Here, we tested if inborn low aerobic capacity promotes differential sex-related cardiovascular effects. Compared with HCR males (HCR-M), LCR males (LCR-M) were overweight by 34% and had heavier retroperitoneal, epididymal, and omental fat pads; LCR females (LCR-F) were 20% heavier than HCR females (HCR-F), and their retroperitoneal, but not perireproductive or omental, fat pads were heavier as well. Unlike HCR-M, blood pressure was elevated in LCR-M, and this was accompanied by left ventricular (LV) hypertrophy. Like HCR-F, LCR-F exhibited normal blood pressure and LV weight as well as increased spontaneous cage activity compared with males. Despite normal blood pressures, LCR-F exhibited increased myocardial interstitial fibrosis and diastolic dysfunction, as indicated by increased LV stiffness, a decrease in the initial filling rate, and an increase in diastolic relaxation time. Although females exhibited increased arterial stiffness, ejection fraction was normal. Increased interstitial fibrosis and diastolic dysfunction in LCR-F was accompanied by the lowest protein levels of phosphorylated AMP-actived protein kinase [phospho-AMPK (Thr(172))] and silent information regulator 1. Thus, the combination of risk factors, including female sex, intrinsic low aerobic capacity, and overweightness, promote myocardial stiffness/fibrosis sufficient to induce diastolic dysfunction in the absence of hypertension and LV hypertrophy.

A putative azoreductase gene is involved in the Shewanella oneidensis response to heavy metal stress.

The Shewanella oneidensis MR-1 gene SO3585, which is annotated as a putative flavin mononucleotide-dependent azoreductase, shares 28% sequence identity with Bacillus subtilis azoreductase and Pseudomonas putida ChrR, a soluble flavoprotein exhibiting chromate reductase activity. Reverse transcription polymerase chain reaction demonstrated that the SO3585 gene is co-transcribed with two downstream open reading frames: SO3586 (a glyoxalase family protein) and SO3587 (a predicted membrane-associated hypothetical protein). The transcriptional start site of the so3585 transcript was localized using 5' rapid amplification of complementary DNA ends analysis. To investigate the cellular function of SO3585, an in-frame deletion of the so3585 locus was generated in MR-1, and the phenotype of the resulting mutant was characterized. The so3585 deletion mutant was comparable to the parental strain in its ability to decolorize two sulfonated azo dyes (Orange II, Direct Blue 15) under aerobic conditions. By contrast, growth of the so3585 deletion mutant was sensitive to different exogenous transition heavy metals [Cr(VI), Cd(II), Cu(II), and Zn(II)], while the most severe growth deficiencies were observed in the presence of Cd(II) and Cu(II). In addition, the rate of extracellular chromate disappearance by the deletion strain was initially impaired, although both the so3585 mutant and MR-1 wild type reduced Cr(VI) within the same time period.