Li-Man Hung

Activation of Estrogen Receptor is Crucial for Resveratrol-stimulating Muscular Glucose Uptake via Both Insulin-dependent and Independent Pathways

OBJECTIVE—Estradiol (E2) is known to modulate insulin sensitivity and, consequently, glucose homeostasis. Resveratrol (RSV), an agonist of estrogen receptor (ER), has exerted antihyperglycemic effects in streptozotocin-induced type 1 diabetic rats in our previous study and was also shown to improve insulin resistance in other reports. However, it remains unknown whether activation of ER is involved in the metabolic effects of RSV via insulin-dependent and -independent mechanisms. RESEARCH DESIGN AND METHODS—Male Sprague-Dawley rats were given a high cholesterol–fructose (HCF) diet for 15 weeks and were treated with RSV for either 15 days or 15 weeks. RESULTS—Here, we show that RSV shifts the metabolic characteristics of rats on an HCF diet toward those of rats on a standard diet. RSV treatment increased insulin-stimulated whole-body glucose uptake and steady-state glucose uptake of soleus muscle and liver in HCF-fed rats as well as enhanced membrane trafficking activity of GLUT4 and increased phosphorylation of insulin receptor in insulin-resistant soleus muscles. Interestingly, the phosphorylated ER level in insulin-resistant soleus muscle was significantly elevated in rats with RSV treatment in both basal and euglycemic-hyperinsulinemic conditions. RSV exerted an insulin-like stimulatory effect on isolated soleus muscle, epididymal fat and hepatic tissue, and C2C12 myotubes. The RSV-stimulated glucose uptake in C2C12 myotubes was dependent on extracellular signal–related kinase/p38 (early phase, 1 h) and p38/phosphoinositide 3-kinase (late phase, 14 h) activation. Inhibition of ER abrogated RSV-induced glucose uptake in both early and late phases. CONCLUSIONS—Collectively, these results indicate that ER is a key regulator in RSV-stimulating insulin-dependent and -independent glucose uptake, which might account for the protective effects of RSV on diet-induced insulin resistance syndrome.

Resveratrol retards progression of diabetic nephropathy through modulations of oxidative stress, proinflammatory cytokines, and AMP-activated protein kinase

BackgroundDiabetic nephropathy (DN) has been recognized as the leading cause of end-stage renal disease. Resveratrol (RSV), a polyphenolic compound, has been indicated to possess an insulin-like property in diabetes. In the present study, we aimed to investigate the renoprotective effects of RSV and delineate its underlying mechanism in early-stage DN.MethodsThe protective effects of RSV on DN were evaluated in streptozotocin (STZ)-induced diabetic rats.ResultsThe plasma glucose, creatinine, and blood urea nitrogen were significantly elevated in STZ-induced diabetic rats. RSV treatment markedly ameliorated hyperglycemia and renal dysfunction in STZ-induced diabetic rats. The diabetes-induced superoxide anion and protein carbonyl levels were also significantly attenuated in RSV-treated diabetic kidney. The AMPK protein phosphorylation and expression levels were remarkably reduced in diabetic renal tissues. In contrast, RSV treatment significantly rescued the AMPK protein expression and phosphorylation compared to non-treated diabetic group. Additionally, hyperglycemia markedly enhanced renal production of proinflammatory cytokine IL-1β. RSV reduced IL-1β but increased TNF-α and IL-6 levels in the diabetic kidneys.ConclusionsOur findings suggest that RSV protects against oxidative stress, exhibits concurrent proinflammation and anti-inflammation, and up-regulates AMPK expression and activation, which may contribute to its beneficial effects on the early stage of DN.

Insulin and resveratrol act synergistically, preventing cardiac dysfunction in diabetes, but the advantage of resveratrol in diabetics with acute heart attack is antagonized by insulin

Resveratrol (RSV), a natural phenolic compound, has been found to display cardiovascular protective and insulin-sensitizing properties. In this study, the effects of RSV and its combination with insulin on mortality, hemodynamics, insulin signaling, and nitrosative stress were compared in streptozotocin (STZ)-induced diabetic rats with or without acute myocardial ischemia/reperfusion (I/R) injury. Under normoxic conditions, cardiac systolic and diastolic functions and insulin-mediated Akt/GLUT4 (glucose transporter 4) activation were impaired in STZ-diabetic rats. The combination of RSV and insulin significantly prevented the above diabetes-associated abnormalities. Notwithstanding that, the diabetic state rendered the animals more susceptible to myocardial I/R injury, and the mortality rate and inducible nitric oxide synthase (iNOS)/nitrotyrosine protein expression and superoxide anion production were also further increased in I/R-injured diabetic hearts. In contrast, RSV treatment alone resulted in a lower mortality rate (from 62.5 to 18%) and better cardiac systolic function than its combination with insulin. RSV also inhibited iNOS/nitrotyrosine protein overexpression and superoxide anion overproduction in I/R-injured diabetic myocardium. Hyperglycemia, impairment of insulin signaling, overexpression of iNOS/nitrotyrosine, and superoxide anion overproduction were markedly rescued by the combination treatment, which did not show an improvement in mortality rate (30%) or cardiac performance over RSV treatment alone. These results indicate that insulin and RSV synergistically prevented cardiac dysfunction in diabetes and this may be in parallel with activation of the insulin-mediated Akt/GLUT4 signaling pathway. Although activation of the protective signal (Akt/GLUT4) and suppression of the adverse markers (iNOS, nitrotyrosine, and superoxide anion) were simultaneously observed in insulin and RSV combination treatment, insulin counteracted the advantage of RSV in diabetics with acute heart attack.

Effect of Resveratrol on Oxidative and Inflammatory Stress in Liver and Spleen of Streptozotocin-Induced Type 1 Diabetic Rats

It has been well known that both oxidative stress and inflammatory activity play crucial roles in the pathogenesis of type 1 diabetes mellitus (T1DM). Resveratrol (RSV), a naturally occurring polyphenol found in grapes and red wine, has recently been shown to exert potent anti-diabetic, anti-oxidative and anti-inflammatory actions. In the present study, we investigated the effect of RSV on oxidative stress and inflammatory response in the liver and spleen of streptozotocin (STZ)-induced type 1 diabetic animal models. Male Long-Evans rats were injected with 65 mg/kg STZ to induce diabetes for 2 weeks, and subsequently administrated with the dosage of 0.1 or 1 mg/kg/day RSV for 7 consecutive days. Hepatic and splenic tissues were dissected for evaluation of oxidative and inflammatory stress. Oxidative stress was assessed by quantification of oxidative indicators including superoxide anion content, lipid and protein oxidative products, as well as manganese superoxide dismutase (Mn-SOD) and nitro-tyrosine protein expression levels. Inflammatory stress was evaluated by the levels of nuclear factor κB (NF-κB) and the proinflammatory cytokine tumor necrosis factor α(TNF-α), interleukin 1β (IL-1β) and IL-6. The experimental results indicated that RSV significantly decreased oxidative stress (superoxide anion content, protein carbonyl level and Mn-SOD expression) in both tissues and hepatic inflammation (NF-κB and IL-1β), but implicated proinflammatory potential of RSV in diabetic spleen (TNF-α and IL-6). The results of this study suggest that RSV may serve as a potent antioxidant, but RSV possesses a proinflammatory potential in certain circumstances in diabetes.

Resveratrol exerts anti-obesity effects in high-fat diet obese mice and displays differential dosage effects on cytotoxicity, differentiation, and lipolysis in 3T3-L1 cells

Studies on resveratrol in a wide range of concentrations on obese mice and adipose cells are necessary to comprehend its range of diverse and contradictory effects. In this study, we examined the anti-obesity effects of resveratrol on high-fat diet (HFD)-induced obese mice at dosages ranging from 1 to 30 mg/kg treatment for 10 wk. We also evaluated the effects of resveratrol on cytotoxicity, proliferation, adipogenic differentiation, and lipolysis of 3T3-L1 cells at concentrations ranging from 0.03 to 100 μM. In HFD obese mice, resveratrol treatment for 10 wk without decreased calories intake significantly attenuated HFD-induced weight gain in a dose-dependent manner. Resveratrol treatment also protected against HFD-induced lipid deposition in adipose tissues and liver. In cultured 3T3-L1 preadipocytes, high dosage (10 to 100 μM) resveratrol treatment produced cytotoxicity in both preadipocytes and mature adipocytes. In contrast, low concentration resveratrol treatment (1 to 10 μM) significantly inhibited the capacity of 3T3-L1 cells differentiated into mature adipocytes. Low dose resveratrol treatment also downregulated peroxisome proliferator-activated receptor gamma (PPARγ) and perilipin protein expressions in differentiated adipocytes. Additionally, tumor necrosis factor alpha (TNFα)-induced lipolysis was inhibited by low concentration resveratrol treatment in mature adipocytes. At concentrations of 10-100 μM, resveratrol exerted cytotoxicity. In contrast, at concentrations of 1-10 μM resveratrol inhibited adipogenic differentiation in preadipocytes and suppressed lipolysis in mature adipocytes. Our results suggest that resveratrol possessed anti-obesity effects by induction of cytotoxicity at high dosage and that it influences preadipocyte differentiation and mature adipocyte lipolysis at low concentration.

Establishing a composite auricle allotransplantation model in rats: introduction to transplantation of facial subunits.

Background: Allografts from cadaveric sources may be an alternative for replacing the missing auricle. In this report, the technical aspects of orthotopic composite auricle allotransplantation and an effective short-term immunosuppression protocol in a rat model are described. Methods: A total of seven transplantations were performed in the experimental group. The donors were Brown Norway (RT1n) rats and the recipients were Lewis (RT11) rats. In the pilot study, 11 isotransplantations (Lewis to Lewis) were performed in either heterotopic (n = 4) or orthotopic (n = 7) locations to establish the surgical technique. Composite auricle allografts were harvested and transplanted based on the posterior facial vein, the external carotid artery, and the great auricular nerve. A plastic square mold sutured over the transplants was used to prevent mechanical trauma to the transplants. Cyclosporine A initiated as 16 mg/kg/day for 2 weeks and tapered to a dosage of 8 mg/kg/day for another 2 weeks was the only immunosuppression regimen. Results: All allografts survived with perfect viability for the follow-up period of 30 days. There were no signs of rejection, infection, or graft-versus-host disease, although significant weight loss was observed resulting from the immunosuppressive treatment. However, signs of rejection started 4 to 6 days after cessation of the cyclosporine A treatment, including edema, localized epidermal desquamation, and erythema formation that eventually progressed to necrosis within 11 to 14 days. The histologic outcomes were well correlated with the macroscopic appearance. Conclusions: It is feasible to elevate and transplant the composite auricle in rats as a single neurosensorial facial subunit. A tapered dose of cyclosporine A from 16 mg/kg to 8 mg/kg allows maintaining allograft survival for 30 days across a strong major histocompatibility complex barrier. This model is reliable and reproducible and has the potential to be used for future immunologic studies to prevent or to induce transplantation tolerance.

Apocynin alleviated hepatic oxidative burden and reduced liver injury in hypercholesterolaemia.

Background: This study addressed the effects of apocynin, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, on hepatic oxidative burden and liver injury during diet‐induced hypercholesterolaemia.

Impairment of insulin-stimulated Akt/GLUT4 signaling is associated with cardiac contractile dysfunction and aggravates I/R injury in STZ-diabetic Rats

In this study, we established systemic in-vivo evidence from molecular to organism level to explain how diabetes can aggravate myocardial ischemia-reperfusion (I/R) injury and revealed the role of insulin signaling (with specific focus on Akt/GLUT4 signaling molecules). The myocardial I/R injury was induced by the left main coronary artery occlusion for 1 hr and then 3 hr reperfusion in control, streptozotocin (STZ)-induced insulinopenic diabetes, and insulin-treated diabetic rats. The diabetic rats showed a significant decrease in heart rate, and a prolonged isovolumic relaxation (tau) which lead to decrease in cardiac output (CO) without changing total peripheral resistance (TPR). The phosphorylated Akt and glucose transporter 4 (GLUT 4) protein levels were dramatically reduced in both I/R and non-I/R diabetic rat hearts. Insulin treatment in diabetes showed improvement of contractile function as well as partially increased Akt phosphorylation and GLUT 4 protein levels. In the animals subjected to I/R, the mortality rates were 25%, 65%, and 33% in the control, diabetic, and insulin-treated diabetic group respectively. The I/R-induced arrhythmias and myocardial infarction did not differ significantly between the control and the diabetic groups. Consistent with its anti-hyperglycemic effects, insulin significantly reduced I/R-induced arrhythmias but had no effect on I/R-induced infarctions. Diabetic rat with I/R exhibited the worse hemodynamic outcome, which included systolic and diastolic dysfunctions. Insulin treatment only partially improved diastolic functions and elevated P-Akt and GLUT 4 protein levels. Our results indicate that cardiac contractile dysfunction caused by a defect in insulin-stimulated Akt/GLUT4 may be a major reason for the high mortality rate in I/R injured diabetic rats.

Piceatannol, a derivative of resveratrol, moderately slows INa inactivation and exerts antiarrhythmic action in ischaemia-reperfused rat hearts

Background and purpose:  Piceatannol is more potent than resveratrol in free radical scavenging in association with antiarrhythmic and cardioprotective activities in ischaemic‐reperfused rat hearts. The present study aimed to investigate the antiarrhythmic efficacy and the underlying ionic mechanisms of piceatannol in rat hearts.

Insulin renders diabetic rats resistant to acute ischemic stroke by arresting nitric oxide reaction with superoxide to form peroxynitrite

BackgroundThe functions of free radicals on the effects of insulin that result in protection against cerebral ischemic insult in diabetes remain undefined. This present study aims to explain the contradiction among nitric oxide (NO)/superoxide/peroxynitrite of insulin in amelioration of focal cerebral ischemia-reperfusion (FC I/R) injury in streptozotocin (STZ)-diabetic rats and to delineate the underlying mechanisms. Long-Evans male rats were divided into three groups (age-matched controls, diabetic, and diabetic treated with insulin) with or without being subjected to FC I/R injury.ResultsHyperglycemia exacerbated microvascular functions, increased cerebral NO production, and aggravated FC I/R-induced cerebral infarction and neurological deficits. Parallel with hypoglycemic effects, insulin improved microvascular functions and attenuated FC I/R injury in STZ-diabetic rats. Diabetes decreased the efficacy of NO and superoxide production, but NO and superoxide easily formed peroxynitrite in diabetic rats after FC I/R injury. Insulin treatment significantly rescued the phenomenon.ConclusionsThese results suggest that insulin renders diabetic rats resistant to acute ischemic stroke by arresting NO reaction with superoxide to form peroxynitrite.