Complexity of NAC Action as an Antidiabetic Agent: Opposing Effects of Oxidative and Reductive Stress on Insulin Secretion and Insulin Signaling

Dysregulated redox balance is involved in the pathogenesis of type 2 diabetes. While the benefit of antioxidants in neutralizing oxidative stress is well characterized, the potential harm of antioxidant-induced reductive stress is unclear. The aim of this study was to investigate the dose-dependent effects of the antioxidant N-acetylcysteine (NAC) on various tissues involved in the regulation of blood glucose and the mechanisms underlying its functions. H2O2 was used as an oxidizing agent in order to compare the outcomes of oxidative and reductive stress on cellular function. Cellular death in pancreatic islets and diminished insulin secretion were facilitated by H2O2-induced oxidative stress but not by NAC. On the other hand, myotubes and adipocytes were negatively affected by NAC-induced reductive stress, as demonstrated by the impaired transmission of insulin signaling and glucose transport, as opposed to H2O2-stimulatory action. This was accompanied by redox balance alteration and thiol modifications of proteins. The NAC-induced deterioration of insulin signaling was also observed in healthy mice, while both insulin secretion and insulin signaling were improved in diabetic mice. This study establishes the tissue-specific effects of NAC and the importance of the delicate maintenance of redox balance, emphasizing the challenge of implementing antioxidant therapy in the clinic

<i>Sarcopoterium spinosum</i> extract improved insulin sensitivity in mice models of glucose intolerance and diabetes

<div><p>Background</p><p>The glucose lowering properties of <i>Sarcopoterium spinosum</i>, a traditional medicinal plant, were previously validated by us using KK-Ay mice as a genetic model for type 2 diabetes (T2D).</p><p>Objective</p><p>To clarify the effects of <i>Sarcopoterium spinosum</i> extract (SSE) on diet-induced glucose intolerance and to investigate SSE effects on carbohydrate and lipid metabolism in target tissues of both high-fat-diet (HFD)-fed and KK-Ay mice.</p><p>Results</p><p>Mice were given SSE (70 mg/day) for 6 weeks. SSE improved glucose tolerance and insulin sensitivity in HFD-fed mice as was demonstrated previously in KK-Ay mice. Higher insulin sensitivity was validated by lower serum insulin and activation of the insulin signaling cascade in skeletal muscle and liver of SSE-treated mice in both models. H&E staining of the livers demonstrated lower severity of steatosis in SSE-treated mice. Several model-specific effects of SSE were observed–mRNA expression of proinflammatory genes and CD36 was reduced in SSE-treated KK-Ay mice. Hepatic mRNA expression of PEPCK was also reduced in SSE-treated KK-Ay mice, while other genes involved in carbohydrates and lipid metabolism were not affected. HFD-fed mice treated by SSE had elevated hepatic glycogen stores. Gluconeogenic gene expression was not affected, while GCK expression was increased. HFD-induced hepatic steatosis was not affected by SSE. However, while genes involved in lipid metabolism were downregulated by HFD, this was not found in HFD-fed mice given SSE, demonstrating an expression profile which is similar to that of standard diet-fed mice.</p><p>Conclusion</p><p>Our study supports the insulin sensitizing activity of SSE and suggests that this extract might improve other manifestations of the metabolic syndrome.</p></div

<i>S</i>. <i>spinosum</i> improved glucose tolerance in HFD-fed mice.

<p>C57BL/J mice were fed STD or HFD with or without SSE given in their drinking water as described in <i>Methods</i>. (A) Body weight was measured every week. (B) GTT was performed at age 15 weeks as described in <i>Materials and Methods</i>. (C) Fasting serum insulin levels were measured at age 17 weeks. The result are presented as mean±SE, *p<0.05, **p< 0.005, ***p< 0.0005 by Student's <i>t</i>-test, compared to HFD-fed mice.</p

Primers list.

<p>Primers list.</p

Sarcopoterium spinosum Inhibited the Development of Non-Alcoholic Steatosis and Steatohepatitis in Mice

Non-alcoholic fatty liver disease (NAFLD) is a comorbidity of obesity, which gradually develops from hepatic steatosis into steatohepatitis (NASH) and eventually even into fibrosis or hepatic carcinoma. To date, there has been no specific and effective treatment for NAFLD. Sarcopoterium spinosum extract (SSE) was found to improve insulin sensitivity. Recognizing the intimate link between insulin resistance and NAFLD, the aim of this study was to investigate the effectivity of SSE in the prevention and management of NAFLD at various severities. SSE was given to high-fat diet (HFD)-fed mice (steatosis model) or to mice given a Western diet (WD) in the short or long term (NASH prevention or treatment, respectively). SSE reduced body weight accumulation, improved glucose tolerance and insulin sensitivity and prevented the development of hepatic steatosis. SSE also blocked the progression of liver disease toward NASH in a dose-dependent manner. The expression of genes involved in lipid metabolism, inflammation, and antioxidant machinery was regulated by SSE in both models of steatosis and NASH development. However, SSE failed to reverse the hepatic damage in the advanced model of NASH. In summary, SSE might be considered as a botanical supplement for the prevention and treatment of hepatic steatosis, and for slowing the deterioration toward NASH

<i>S</i>. <i>spinosum</i> enhances insulin signaling in liver of HFD-fed mice.

<p>C57BL/J mice model were fed STD, HFD or HFD+ <i>S</i>. <i>spinosum</i>. Liver was removed at the age of 17 weeks as described in <i>Methods</i>. (A) Western blot analysis was performed on protein lysates of liver using specific antibodies. (B) The bar graphs are the results of optical density measurements of western blots. Each bar represents the mean±SE of data obtained from 4 mice. *p<0.05, **p< 0.005 and ***p< 0.0005 compared to basal state in STD-fed mice or as indicated in graph, in One-way Anova followed by Bonferroni's post-test.</p

SSE reduced mRNA expression of atherogenic and pro-inflammatory genes.

<p>KK-Ay mice were given <i>S</i>. <i>spinosum</i> extract for 6 weeks as described in methods. Liver was removed at the age of 12 weeks as described in methods. mRNA expression of the indicated genes was measured by real-time PCR. Results were normalized to the expression of housekeeping gene, HPRT. ***P<0.0005 by Student's <i>t</i>-test.</p