Assessment of antidiabetogenic potential of fermented soybean extracts in streptozotocin-induced diabetic rat

Most of the available drugs for the treatment of diabetes mellitus (DM) produce detrimental side effects, which has prompted an ongoing search for plant with the antidiabetic potential. The present study investigated the effect of soybean extracts fermented with Bacillus subtilis MORI, fermented soybean extracts (BTD-1) was investigated in streptozotocin (STZ)-induced diabetic rats. The possible effects of BTD-1 against hyperglycemia and free radical-mediated oxidative stress was investigated by assaying the plasma glucose level and the activity of enzymatic antioxidants, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and malondialdehyde (MDA). A significant increase in the levels of both plasma glucose and reactive oxygen species (ROS) was observed in the diabetic rats when compared to normal control group. After administration of BTD-1 (500 and 1000mg/kg/day), the elevated plasma glucose level was significantly reduced while the plasma insulin level and the activities of SOD, GSH-Px, CAT and MDA were significantly increased. The results suggest that administration of BTD-1 can inhibit hyperglycemia and free radical-mediated oxidative stress. The administration of BTD-1 also inhibited the contractile response by norepinephrine (10^-10-10^-5M) in the presence of endothelium, and caused significant relaxation by carbachol (10^-8-10^-5M) in rat aorta. These findings indicate that BTD-1 improves vascular functions on STZ-induced diabetic rats. Therefore, subchronic administration of BTD-1 could prevent the functional changes in vascular reactivity in STZ-induced diabetic rats. The collective findings support that administration of BTD-1 may prevent some diabetes-related changes in vascular reactivity directly and/or indirectly due to its hypoglycaemic effect and inhibition of production of ROS.