Etsuko Uematsu

Telmisartan ameliorates insulin sensitivity by activating the AMPK/SIRT1 pathway in skeletal muscle of obese db/db mice

BackgroundTelmisartan is a well-established angiotensin II type 1 receptor blocker that improves insulin sensitivity in animal models of obesity and insulin resistance, as well as in humans. Telmisartan has been reported to function as a partial agonist of the peroxisome proliferator-activated receptor (PPAR) γ, which is also targeted by the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase (SIRT1). Here, we investigated the pathways through which telmisartan acts on skeletal muscle, in vitro as well as in vivo.MethodsNine-week-old male db/db mice were fed a 60% high-fat diet, with orally administrated either vehicle (carboxymethyl-cellulose, CMC), 5 mg/kg telmisartan, or 5 mg/kg telmisartan and 1 mg/kg GW9662, a selective irreversible antagonist of PPARγ, for 5 weeks. Effects of telmisartan on Sirt1 mRNA, AMPK phosphorylation, and NAD+/NADH ratio were determined in C2C12 cultured myocytes.Results and discussionTelmisartan treatment improved insulin sensitivity in obese db/db mice fed a high-fat diet and led to reduction in the size of hypertrophic pancreatic islets in these mice. Moreover, in vitro treatment with telmisartan led to increased expression of Sirt1 mRNA in C2C12 skeletal muscle cells; the increase in Sirt1 mRNA in telmisartan-treated C2C12 myoblasts occurred concomitantly with an increase in AMPK phosphorylation, an increase in NAD+/NADH ratio, and increases in the mRNA levels of PGC1α, FATP1, ACO, and GLUT4.ConclusionsOur results indicate that telmisartan acts through a PPARγ-independent pathway, but at least partially exerts its effects by acting directly on skeletal muscle AMPK/SIRT1 pathways.

Exendin-4, a glucagon-like peptide-1 receptor agonist, attenuates neointimal hyperplasia after vascular injury

Exendin-4 is a glucagon-like peptide-1 receptor agonist that has been used as a drug for treatment of type 2 diabetes. To investigate the effect of exendin-4 on the cardiovascular system, we investigated the impact of exendin-4 on neointimal hyperplasia of the femoral artery after vascular injury. We performed wire-mediated endovascular injury in C57BL/6 mice, followed by administration of exendin-4 24 nmol/kg/day via infusion pump. Four weeks after the injury, exendin-4 treatment significantly attenuated neointimal hyperplasia of the injured artery, although it did not affect glucose metabolism and lipid profile in wild-type mice. Immunofluorescence study revealed abundant expression of GLP-1 receptor on α-smooth muscle actin-positive cells in the injured vessel. Cell proliferation assay using rat aortic smooth muscle cells showed that exendin-4 reduced PDGF-BB induced smooth muscle cell proliferation through the cAMP/PKA pathway. Exendin-4 also inhibited TNFα production by peritoneal macrophages in response to inflammatory stimulus. Our findings indicate that a GLP-1 receptor agonist attenuated neointimal formation after vascular injury. GLP-1 receptor agonists or drugs that raise endogenous GLP-1 level might be effective in the treatment of vascular diseases.

Activation of AMPK–Sirt1 pathway by telmisartan in white adipose tissue: A possible link to anti-metabolic effects

Telmisartan exerts anti-metabolic effects beyond its angiotensin receptor blockade activities, but the mechanisms have hitherto remained elusive. We sought to elucidate the peroxisome proliferator-activated receptor-γ (PPAR-γ)-dependent and PPAR-γ-independent mechanisms underlying the anti-metabolic effects of telmisartan in white adipose tissue. Nine-week-old male C57BL/6 mice were fed with a 60% high-fat diet for 6 weeks, with 1mg/kg telmisartan or vehicle administrated orally during the last 3 weeks. 3T3-L1 adipocytes were cultured with telmisartan either with 2-chloro-5-nitro-N-phenylbenzamide (GW9662), a selective irreversible antagonist of PPAR-γ, or compound C, an ATP-competitive inhibitor of AMPK. Western blotting and semiquantitative RT-PCR analysis were used to assess adiponectin, Sirt1, and AMPK levels. Lipid accumulation was assessed by Oil red O staining. The activation of transcription factor PPAR-γ2 was evaluated by using a luciferase reporter assay for mPPAR-γ2 expression plasmid vector. Treatment with telmisartan increased serum adiponectin levels in high-fat diet-fed mice concomitantly with an upregulation of adiponectin mRNA in visceral adipose tissue. In vitro telmisartan treatment dose-dependently increased adiponectin mRNA in 3T3-L1 cells; the increase was inhibited by compound C, but not by GW9662. Telmisartan increased expression of Sirt1 mRNA and Sirt1 protein as well as the phosphorylation of AMPK in 3T3-L1 cells. Telmisartan can increase adiponectin production in white adipose tissue partly via a PPAR-γ2-independent mechanism. Precise understanding of this molecular mechanism will require further investigation.

Expression of NLRP3 in subcutaneous adipose tissue is associated with coronary atherosclerosis

OBJECTIVES The promotion of adipose tissue inflammation by lifestyle-related diseases such as obesity and diabetes accelerates atherogenesis; however, the underlying mechanisms remain incompletely understood. Nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome contributes to chronic inflammation in adipose tissue. Here, we investigated the link between NLRP3 expression in subcutaneous adipose tissue (SAT) and the severity of coronary atherosclerosis. METHODS AND RESULTS SAT was obtained from 72 patients who underwent heart device implantation and coronary angiography. Expression of NLRP3 inflammasome-related molecules (NLRP3, IL-1β and IL-18) in SAT were evaluated by quantitative RT-PCR. Laboratory markers related to lifestyle-related diseases were measured. Patients with obesity, dyslipidemia (P < 0.05, respectively), diabetes or hyperuricemia (P < 0.01, respectively) had significantly higher expression of NLRP3. Multivariate analysis demonstrated that body mass index and serum level of uric acid were predictors of NLRP3 expression in SAT. The expression of NLRP3 in SAT correlated negatively with serum adiponectin level (r = -0.23, P < 0.05). Patients with coronary artery disease showed higher NLRP3 expression than patients without significant stenosis (P < 0.01). Furthermore, the expression of NLRP3 in SAT correlated positively with the severity of coronary atherosclerosis as determined by Gensini score (r = 0.47, P < 0.0001) or SYNTAX score (r = 0.55, P < 0.0001). Multiple regression analysis revealed that the expression of NLRP3 in SAT remains as an independent predictors for the severity of coronary atherosclerosis. CONCLUSIONS The expression of NLRP3 in SAT, which is affected by lifestyle-related diseases, is associated with the severity of coronary atherosclerosis. Our results suggest that NLRP3 inflammasome in SAT may have a role in atherogenesis.

Plasma microRNA-100 is associated with coronary plaque vulnerability.

BACKGROUND Although numerous studies have reported altered plasma levels of various microRNAs (miRNAs) in patients with cardiovascular disease, there are no data on the relationship between plasma miRNAs and vulnerable coronary plaque. In this study, we investigated whether plasma miRNAs might be a sensitive marker of coronary plaque vulnerability. METHODS AND RESULTS Integrated backscatter intravascular ultrasound (IB-IVUS) was performed in 32 consecutive patients with angina pectoris who underwent percutaneous coronary intervention. Three-dimensional analysis of IB-IVUS was performed to determine the percentage of lipid volume (%LV) and fibrous volume (%FV). Circulating miRNAs were measured in EDTA-plasma simultaneously obtained from the aorta and the coronary sinus (CS). Muscle-enriched (miR-133a, miR-208a, miR-499), vascular-enriched (miR-92a, miR-100, miR-126, miR-127, miR-145), and myeloid cell-enriched miRNAs (miR-155, miR-223) were measured. Plasma miR-100 was higher in the CS than in the aorta, but there were no significant differences in the levels of other miRNAs between the aorta and CS. Plasma miR-100 in the aorta was positively correlated with %LV (r=0.48, P<0.01) and negatively correlated with %FV (r=-0.41, P<0.05). Importantly, transcoronary concentration gradient of circulating miR-100 was more strongly correlated with %LV (r=0.53, P<0.01) and %FV (r=-0.56, P<0.01). CONCLUSIONS miR-100 might be released into the coronary circulation from vulnerable coronary plaques. This study provides insights into the role of miRNAs in coronary atherosclerotic disease.

Pentraxin 3 is a local inflammatory marker in atrial fibrillation

Increasing evidence indicates that inflammation contributes to the pathogenesis of atrial fibrillation (AF). Pentraxin 3 (PTX3) is produced abundantly in local inflammatory lesions while C-reactive protein (CRP) is produced mainly in the liver. In this study, we investigated whether a local level of PTX3 might be a sensitive marker for the local inflammation of AF. Blood from the periphery and left atrial appendage (LAA) was sampled from 23 patients with AF undergoing pulmonary vein isolation, and from 10 control subjects with Wolff–Parkinson–White syndrome. We measured peripheral and LAA plasma concentrations of CRP, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and PTX3. Plasma PTX3 concentrations in both locations were higher in patients with AF than in control subjects. PTX3 concentrations were significantly higher in the LAA than the periphery in patients with AF (3.7 ± 1.4 vs 3.3 ± 1.2 ng/ml, P < 0.01), but not in control subjects (2.4 ± 0.5 vs 2.4 ± 0.5 ng/ml, not significant). Patients and controls showed no significant differences in CRP, IL-6, or TNF-α concentrations between the periphery and LAA. Interestingly, there was a significant positive correlation between LAA plasma concentrations of PTX3 and left atrial volume (r = 0.55, P < 0.01). These data demonstrate that Local PTX3 production in the left atrium might reflect the local inflammation of AF.

A synthetic prostacyclin agonist with thromboxane synthase inhibitory activity, ONO-1301, protects myocardium from ischemia/reperfusion injury☆

ONO-1301, a synthetic prostacyclin agonist with thromboxane synthase inhibitory activity, promotes the production of hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) by various cell types. Here, we evaluated the therapeutic efficacy of ONO-1301 in rats with ischemia/reperfusion injury. Ligation of the left anterior descending arteries was performed in 10-week-old Wistar rats, and released 30 min later. A slow-release form of ONO-1301 was administered subcutaneously at 3h and 3 weeks after reperfusion injury. Hemodynamic parameters were significantly improved in the ONO-1301 group. Histological analysis revealed that ONO-1301 suppressed ischemic and fibrotic changes in the myocardium (ischemic area, control group: 58.6 ± 8.7% vs. ONO-1301 group: 44.4 ± 5.8%, fibrotic area, 33.5 ± 5.9% vs. 22.3 ± 6.2%, P<0.05, respectively), and enhanced neovascularization in the border zone. HGF expression was up-regulated by ONO-1301. Double-immunostaining revealed that myofibroblasts in the border zone of ischemic myocardium mainly expressed HGF. Our findings suggest that ONO-1301 might have therapeutic potential in treating ischemic heart disease.

Ghrelin protects the heart against ischemia-induced arrhythmias by preserving connexin-43 protein

Vagal nerve stimulation has been postulated to confer an antifibrillatory effect. We studied whether ghrelin administration would exert an antiarrhythmic effect via modulation of autonomic nerve activity in rats after acute myocardial ischemia (MI). Male Sprague-Dawley rats were exposed to 30 min of ischemia following ligation of the left coronary artery. Animals were then randomized to receive either ghrelin (n = 26) or saline (n = 26) during the period of coronary ligation. Power spectral analysis of heart-rate variability revealed that the administration of ghrelin increased the high-frequency (HF) power and decreased the low-frequency (LF)/HF ratio. Ventricular tachyarrhythmias were less frequent in rats after MI who received ghrelin in comparison with rats that received saline. Immunoblotting and immunohistochemistry revealed that rats given saline alone during MI exhibited a marked reduction in phosphorylated connexin-43 within the left ventricle, whereas those that received ghrelin displayed only minor reductions in comparison with sham-operated rats. These effects of ghrelin were diminished by the coadministration of atropine or the blockade of vagal afferents. These data demonstrate that the beneficial effect of ghrelin might be mediated by modulation of cardiac autonomic nerve activity.

Beneficial effect of a synthetic prostacyclin agonist, ONO-1301, in rat autoimmune myocarditis model.

Injury to the heart can result in cardiomyocyte hypertrophy, fibrosis, and cell death. Myocarditis sometimes progresses to dilated cardiomyopathy. We previously reported that ONO-1301, a synthetic prostacyclin agonist with thromboxane-synthase inhibitory activity, promotes production of hepatocyte growth factor (HGF) from various cell types and ameliorates ischemia-induced left ventricle dysfunction in the mouse, rat and pig. Here, we investigated the therapeutic efficacy of ONO-1301 in a rat model of myosin-induced experimental autoimmune myocarditis, in which the heart transits from an acute inflammatory phase to a chronic dilated cardiomyopathy phase. Four weeks after myosin injection to Lewis rats, ONO-1301 (6 mg/kg/day) was orally administered for 4 weeks (ONO-1301 group). Hemodynamic parameters and plasma brain natriuretic peptide (BNP) level were significantly improved by ONO-1301. Histological analysis revealed that capillary density in the myocardium was significantly increased by ONO-1301. ONO-1301 increased circulating endothelial progenitor cells (EPC) as determined by FACS analysis. These beneficial effects of ONO-1301 were partially abrogated by a neutralizing anti-HGF antibody (8 mg/kg/dose). These findings indicate beneficial effects of ONO-1301 in a rat experimental autoimmune myocarditis model.

The pathophysiological role of oxidized cholesterols in epicardial fat accumulation and cardiac dysfunction: a study in swine fed a high caloric diet with an inhibitor of intestinal cholesterol absorption, ezetimibe

Oxidized cholesterols (oxycholesterols) in food have been recognized as strong atherogenic components, but their tissue distributions and roles in cardiovascular diseases remain unclear. To investigate whether accumulation of oxycholesterols is linked to cardiac morphology and function, and whether reduction of oxycholesterols can improve cardiac performance, domestic male swine were randomized to a control diet (C), high caloric diet (HCD) or HCD+Ezetimibe, an inhibitor of intestinal cholesterol absorption, group (HCD+E) and evaluated for: (1) distribution of oxycholesterol components in serum and tissues, (2) levels of oxycholesterol-related enzymes, (3) paracardial and epicardial coronary fat thickness, and (4) cardiac performance. Ezetimibe treatment for 8weeks attenuated increases in oxycholesterols in the HCD group almost completely in liver, but reduced only levels of 4β-hydroxycholesterol in left ventricular (LV) myocardium. Ezetimibe treatment altered the expression of genes for cholesterol and fatty acid metabolism and decreased the expression of CYP3A46, which catabolizes cholesterol to 4β-hydroxycholesterol, strongly in liver. An increase in epicardial fat thickness and impaired cardiac performance in the HCD group were improved by ezetimibe treatment, and the improvement was closely related to the reduction in levels of 4β-hydroxycholesterol in LV myocardium. In conclusion, an increase in oxycholesterols in the HCD group was closely related to cardiac hypertrophy and dysfunction, as well as an increase in epicardial fat thickness. Ezetimibe may directly reduce oxycholesterol in liver and LV myocardium, and improve cardiac morphology and function.