Rapamycin improves insulin resistance and hepatic steatosis in type 2 diabetes rats through activation of autophagy

Insulin resistance (IR) is a hallmark of type 2 diabetes mellitus (T2DM). This study aimed to explore the effects of rapamycin, a specific inhibitor of kinase mammalian target of rapamycin (mTOR), on IR in T2DM rats, and to validate whether the underlying mechanism was associated with autophagy. In this study, the model of T2DM rats was established by feeding the animals with a high-fat diet (HFD) and intraperitoneal injection of streptozotocin (STZ). Diabetic rats were randomly divided into model of T2DM control group (DM-C, n=15), metformin group (DM-M, n=15), rapamycin group (DM-Rapa, n=15), 3-methyladenine (3-MA) group (DM-3-MA, n=15), and rapamycin+3-MA group (DM-Rapa-3-MA, n=15). Rats in different treatment groups were given by corresponding therapy from gastric tube. Meanwhile, normal control group was established (n=10). As expected, HFD- and STZ- induced T2DM rats exhibited significantly impaired glucose tolerance, reduced insulin sensitivity, dysglycemia and dyslipidemia, aggravated hepatic steatosis, enhanced hepatic inflammation, elevated p-mTOR, and suppressed hepatic autophagy. Importantly, rapamycin and metformin significantly ameliorated IR, relieved disorders of glucose and lipid metabolism, reduced inflammatory level, inhibited mTOR, and promoted autophagy. Importantly, the autophagy inhibitor 3-MA significantly reversed the effects exerted by rapamycin. Collectively, our study suggests that rapamycin improved IR and hepatic steatosis in T2DM rats via activation of autophagy.