Effects of Metformin in Combination with a Herbal Capsule (Glucoblock) on Insulin Resistance and Oxidative Stress Index in Type 2 Diabetic Rats

Aim: This study evaluated the effects of metformin in combination with a herbal capsule (glucoblock) on insulin resistance and oxidative stress index in type 2 diabetic rats.

Methodology: A total of 35 male Wistar albino rats weighing between 120-220 g were used for this study. The rats were placed on high fat diet, and diabetes was induced by a single intraperitoneal injection of freshly prepared streptozotocin (STZ) (45 mg/kg body wt). Fasting plasma glucose (FPG) was determined using the glucose oxidase method. Fasting plasma insulin (FPI), total oxidant status (TOS), total antioxidant status (TAS) and superoxide dismutase (SOD) levels were quantitatively determined by a rat-specific sandwich-enzyme linked immunosorbent assay (ELISA) method. Insulin resistance (IR) was determined using the homeostatic model assessment for insulin resistance (HOMA-IR) method. Oxidative stress index (OSI) was determined by the ratio of TOS to TAS. Phytochemical analysis on the herbal capsule was done using classical methods.

Results: The results revealed the presence of alkaloids (100.31μg/mg), flavonoids (131.45μg/mg), cardiac glycosides (55.93μg/mg) and saponins (61.47μg/mg) in the herbal drug glucoblock. The results showed significantly lower FPG levels in the treatment groups when compared to the diabetic control. Group 3 administered metformin had significantly higher FPG levels compared to the negative control. Group 4 administered the herbal drug glucoblock and group 5 administered a combination of metformin and glucoblock, showed no significant differences in FPG levels when compared to the negative control. The diabetic control had significantly higher FPI levels compared to the negative control and treatment groups. The treatment groups showed no significant differences in FPI levels when compared to the negative control. HOMA-IR was significantly higher in the diabetic control compared to the negative control and treatment groups. Also, HOMA-IR values in the treatment groups showed no significant difference compared to the negative control except for group 3 (metformin), that was significantly higher than the negative control. SOD was significantly lower in the diabetic control, compared to the negative control and treatment groups. There were no significant differences in SOD levels in the treatment groups compared to the negative control. TOS levels in the negative control group and treatment groups were significantly lower, compared to the diabetic control. TAS was significantly lower in the diabetic control and treatment groups compared to the negative control. OSI in the diabetic control was significantly higher, compared to the negative control and treatment groups. Also, the treatment groups had significantly higher OSI compared to the negative control.

Conclusion: High fat diet and streptozotocin induction produced significant insulin resistance and oxidative stress in the diabetic rats. Glucoblock was more effective in reducing insulin resistance compared to metformin. The combination showed synergistic drug-herb reaction as glucoblock potentiated the actions of metformin. Both showed antioxidant potential but were not effective in lowering oxidative stress to normal levels. There is need to incorporate antioxidant therapy in the treatment protocol for diabetes mellitus.