Melatonin confers cardioprotective effect against myocardial ischemia/reperfusion (MI/R) injury by reducing oxidative stress. Activation of silent information regulator 1 (SIRT1) signaling also reduces MI/R injury. We hypothesize that melatonin may protect against MI/R injury by activating SIRT1 signaling. This study investigated the protective effect of melatonin treatment on MI/R heart and elucidated its potential mechanisms. Rats were exposed to melatonin treatment in the presence or the absence of the melatonin receptor antagonist luzindole or SIRT1 inhibitor EX527 and then subjected to MI/R operation. Melatonin conferred a cardioprotective effect by improving postischemic cardiac function, decreasing infarct size, reducing apoptotic index, diminishing serum creatine kinase and lactate dehydrogenase release, upregulating SIRT1, Bcl-2 expression and downregulating Bax, caspase-3 and cleaved caspase-3 expression. Melatonin treatment also resulted in reduced myocardium superoxide generation, gp91(phox) expression, malondialdehyde level, and increased myocardium superoxide dismutase (SOD) level, which indicate that the MI/R-induced oxidative stress was significantly attenuated. However, these protective effects were blocked by EX527 or luzindole, indicating that SIRT1 signaling and melatonin receptor may be specifically involved in these effects. In summary, our results demonstrate that melatonin treatment attenuates MI/R injury by reducing oxidative stress damage via activation of SIRT1 signaling in a receptor-dependent manner.

The branched-chain amino acids (BCAA) accumulated in type 2 diabetes are independent contributors to insulin resistance. The activity of branched-chain a-keto acid dehydrogenase (BCKD) complex, rate-limiting enzyme in BCAA catabolism, is reduced in diabetic states, which contributes to elevated BCAA concentrations. However, the mechanisms underlying decreased BCKD activity remain poorly understood. Here, we demonstrate that mitochondrial phosphatase 2C (PP2Cm), a newly identified BCKD phosphatase that increases BCKD activity, was significantly downregulated in ob/ob and type 2 diabetic mice. Interestingly, in adiponectin (APN) knockout (APN 2/2 ) mice fed with a high-fat diet (HD), PP2Cm expression and BCKD activity were significantly decreased, whereas BCKD kinase (BDK), which inhibits BCKD activity, was markedly increased. Concurrently, plasma BCAA and branched-chain a-keto acids (BCKA) were significantly elevated. APN treatment markedly reverted PP2Cm, BDK, BCKD activity, and BCAA and BCKA levels in HD-fed APN 2/2 and diabetic animals.Additionally, increased BCKD activity caused by APN administration was partially but significantly inhibited in PP2Cm knockout mice. Finally, APN-mediated upregulation of PP2Cm expression and BCKD activity were abolished when AMPK was inhibited. Collectively, we have provided the first direct evidence that APN is a novel regulator of PP2Cm and systematic BCAA levels, suggesting that targeting APN may be a pharmacological approach to ameliorating BCAA catabolism in the diabetic state.The branched-chain amino acids (BCAA) are essential amino acids such as leucine, isoleucine, and valine; their homeostasis is determined largely by catabolic activities in a number of organs including liver, muscle and adipose tissue (1-3). The first step of BCAA catabolism generates a set of corresponding branched-chain a-keto acids (BCKA), which are irreversibly decarboxylated by the branched-chain a-keto acid dehydrogenase (BCKD) complex (4). As with most nutrients, maintaining of the physiological level of BCAA is critical for cell metabolism and survival. However, many researchers have described increased BCAA and BCKA levels in diabetes and obesity (3,(5)(6)(7)(8). Furthermore, BCAA and their catabolites are strongly associated with insulin resistance (9-11), and elevated BCAA contributes to the development of insulin resistance (10,12). Mechanistically, elevated BCAA levels activate mTOR/p70S6 kinase, resulting in an increased I insulin receptor substrate-1 phosphorylation, thereby inhibiting phosphatidylinositol 3-kinase. This inhibition of phosphatidylinositol 3-kinase in turn leads to impaired insulin signaling (13,14). It is also reported that BCAA are independent predictors of insulin resistance, diabetes, and cardiovascular events (15-17). Therefore, it is necessary to determine the mechanisms of abnormal BCAA catabolism in order to better understand their association with metabolic-related pathogenesis. The BCKD complex is the rate-limiting enzyme in BCAA catabolism (4,12); regulation o...

No abstract

AimsIschemic preconditioning (IPC) is a potent form of endogenous protection. However, IPC-induced cardioprotective effect is significantly blunted in insulin resistance-related diseases and the underlying mechanism is unclear. This study aimed to determine the role of glucose metabolism in IPC-reduced reperfusion injury.MethodsNormal or streptozotocin (STZ)-treated diabetic rats subjected to 2 cycles of 5 min ischemia/5 min reperfusion prior to myocardial ischemia (30 min)/reperfusion (3 h). Myocardial glucose uptake was determined by 18F-fluorodeoxyglucose-positron emission tomography (PET) scan and gamma-counter biodistribution assay.ResultsIPC exerted significant cardioprotection and markedly improved myocardial glucose uptake 1 h after reperfusion (P<0.01) as evidenced by PET images and gamma-counter biodistribution assay in ischemia/reperfused rats. Meanwhile, myocardial translocation of glucose transporter 4 (GLUT4) to plasma membrane together with myocardial Akt and AMPK phosphorylation were significantly enhanced in preconditioned hearts. Intramyocardial injection of GLUT4 siRNA markedly decreased GLUT4 expression and blocked the cardioprotection of IPC as evidence by increased myocardial infarct size. Moreover, the PI3K inhibitor wortmannin significantly inhibited activation of Akt and AMPK, reduced GLUT4 translocation, glucose uptake and ultimately, depressed IPC-induced cardioprotection. Furthermore, IPC-afforded antiapoptotic effect was markedly blunted in STZ-treated diabetic rats. Exogenous insulin supplementation significantly improved glucose uptake via co-activation of myocardial AMPK and Akt and alleviated ischemia/reperfusion injury as evidenced by reduced myocardial apoptosis and infarction size in STZ-treated rats (P<0.05).ConclusionsThe present study firstly examined the role of myocardial glucose metabolism during reperfusion in IPC using direct genetic modulation in vivo. Augmented glucose uptake via co-activation of myocardial AMPK and Akt in reperfused myocardium is essential to IPC-alleviated reperfusion injury. This intrinsic metabolic modulation and cardioprotective capacity are present in STZ-treated hearts and can be triggered by insulin.

Diabetic cardiac fibrosis increases ventricular stiffness and facilitates the occurrence of diastolic dysfunction. Our previous studies have shown that berberine, a natural alkaloid, attenuates cardiac ischemia-reperfusion injury in diabetic rats. The aim of present study was to investigate the effects of long-term berberine treatment on cardiac remodeling in diabetic rats and the underlying mechanisms. Diabetic rats induced by low-dose streptozotocin injection combined with 8 wk of high-fat diet displayed significant cardiac matrix collagen deposition and dysfunction, whereas berberine administration (200 mg·kg·day, gavage 4 wk) significantly ameliorated cardiac fibrosis and dysfunction and reduced cardiac IGF-1 receptor (IGF-1R) expression in diabetic rats. Interestingly, IGF-1R expression was upregulated in cardiac fibroblasts isolated from diabetic hearts or cultured in high-glucose conditions (30 mM). High glucose treatment or IGF-1R overexpression increased matrix metalloproteinase (MMP)-2/MMP-9 expression, α-smooth muscle actin (α-SMA), and collagen type I expression in cardiac fibroblasts. In contrast, berberine treatment significantly inhibited IGF-1R expression and exerted an antifibrotic effect in high glucose-cultured cardiac fibroblasts, as manifested by decreased MMP-2/MMP-9, α-SMA, and collagen type I expression, whereas IGF-1R siRNA plus berberine treatment did not further enhance this antifibrotic effect compared with berberine treatment alone. Taken together, long-term berberine treatment ameliorates cardiac fibrosis and dysfunction by downregulating IGF-1R expression in cardiac fibroblasts and subsequently reducing MMP-2/MMP-9, α-SMA, and collagen type I expression in diabetic hearts. The findings suggest the therapeutic potential of berberine for diabetic cardiomyopathy associated with cardiac fibrosis. NEW & NOTEWORTHY Berberine downregulated IGF-1 receptor expression and matrix metalloproteinase-2/matrix metalloproteinase-9 levels in cardiac fibroblasts and thus inhibited fibroblast differentiation and collagen overproduction in diabetic hearts, suggesting a novel mechanism for antifibrotic cardioprotection of berberine in type 2 diabetes.