Nitric oxide mediates the insulin sensitizing effects of β-sitosterol in high fat diet-fed rats

Abstract

β-Sitosterol has been shown to have antidiabetic and antioxidant effects in animal models. The objective of the study is to investigate the effects of β-sitosterol on insulin sensitivity, oxidative and nitrosative stress and lipid abnormalities in liver of high fat-fed rat model of insulin resistance (IR) and to assess whether nitric oxide (NO) is involved in its action. Adult male albino Wistar rats of body weight 150–180g were fed either control diet (CON) or high fat diet (HFD). Each dietary group was divided into two and treated or untreated with β-sitosterol (10mg/kgb.w.−1day−1) for 4weeks. Inhibition of total nitric oxide synthase (NOS) by administration of nitro-l-arginine methyl ester (L-NAME) and inducible NOS (iNOS) by aminoguanidine (AG) in HFD and HFD+ β-sitosterol groups were accomplished to identify the role of NO. After 28days, assays were performed in plasma and liver. HFD-fed rats showed hyperglycemia, hyperinsulinemia, IR, oxidative damage, nitrosative stress, lipid accumulation and elevated serum aminotransferases. Increased expression of iNOS and decreased expression of endothelial NOS (eNOS) were observed in them. Hepatic fat accumulation was further confirmed by histology. The biochemical and histological abnormalities associated with HFD feeding were significantly reduced by β-sitosterol administration. Administration of L-NAME to HFD-fed rats caused decrease in insulin sensitivity and increase in oxidative stress. Co-administration of L-NAME for the last seven days to β-sitosterol-treated HFD rats abolished the glucose lowering effect of β-sitosterol, but the ability to decrease oxidative stress remained unaltered. On the other hand, administration of AG resulted in improved glucose homeostasis and antioxidant levels but decreased oxidative stress and enhanced antioxidant potential in both HFD and HFD+ β-sitosterol treated groups. Thus, β-sitosterol promotes insulin sensitivity in rats fed HFD possibly by improving NO levels. With additional studies, β-sitosterol might be used as a functional drug or as an adjuvant in the management of IR and associated fatty liver disease.