The combined effect of metformin and l-cysteine on inflammation, oxidative stress and insulin resistance in streptozotocin-induced type 2 diabetes in rats

Increasing evidence has established causative links between obesity, chronic inflammation and insulin resistance; the core pathophysiological feature in type 2 diabetes mellitus. This study was designed to examine whether the combination of l-cysteine and metformin would provide additional benefits in reducing oxidative stress, inflammation and insulin resistance in streptozotocin-induced type 2 diabetes in rats. Male Wistar rats were fed a high-fat diet (HFD) for 8 weeks to induce insulin resistance after which they were rendered diabetic with low-dose streptozotocin. Diabetic rats were treated with metformin (300mg/kg/day), l-cysteine (300mg/kg/day) and their combination along with HFD for another 2 weeks. Control rats were fed normal rat chow throughout the experiment. At the end of treatment, fasting blood glucose, fasting serum insulin, homeostasis model assessment-insulin resistance index (HOMA-IR) and serum free fatty acids (FFAs) were measured. Serum levels of the inflammatory markers; monocyte chemoattractant protein-1 (MCP-1), C-reactive protein (CRP) and nitrite/nitrate were also determined. The liver was isolated and used for determination of malondialdehyde (MDA), reduced glutathione (GSH), caspase-3 and cytochrome c levels. The hypoglycemic effect of the combination therapy exceeded that of metformin and l-cysteine monotherapies with more improvement in insulin resistance. All treated groups exhibited significant reductions in serum FFAs, oxidative stress and inflammatory parameters, caspase-3 and cytochrome c levels compared to untreated diabetic rats with the highest improvement observed in the combination group. In conclusion, the present results clearly suggest that l-cysteine can be strongly considered as an adjunct to metformin in management of type 2 diabetes.