Iridoid glucoside attenuates hyperglycemia-mediated oxidative stress and thyroid hormone function in streptozotocin–induced diabetic rats

The present study was to evaluate the effect of iridoid glucoside on the levels of blood glucose, plasma insulin, serum total protein, albumin, thyroid hormone (T3, T4), TSH, LPO and activities of both enzymic and non-enzymic antioxidants in streptozocin-induced diabetic rats. The levels of blood glucose, TBARS and hydroperoxide were significantly increased whereas the levels of plasma insulin and activities of enzymic antioxidants (SOD, CAT, GPx and GST) and the levels of non-enzymic antioxidants (vitamin C, vitamin E) and reduced glutathione were decreased in the liver and kidney tissues of diabetic rats. In addition, serum levels of total protein, albumin, T3, T4 and TSH were also decreased in diabetic rats when compared to control rats. Oral administration of iridoid glucoside to diabetic rats showed significant ameliorative effects on all the biochemical parameters studied. Moreover, the iridoid glucoside showed free radical scavenging activity assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) in vitro which may have responsible for these hypoglycemic and improved antioxidant statuses in vivo. The effect produced by iridoid glucoside on various parameters was comparable to that of glibenclamide. These results indicated that iridoid glucoside possesses antidiabetic and antioxidant potential in addition to synthesis and/or secretion of circulating thyroid hormone.