The effect of metformin and taurine, alone and in combination, on the oxidative stress caused by diabetes in the rat brain

Abstract

This study has compared the effects of metformin (MET) and taurine (TAU), singly and in combination, on the oxidative stress caused by diabetes in the rat brain. For this purpose, male Sprague-Dawley rats, 200–225 g in weight, assigned to groups of 6, were intraperitoneally (i.p.) treated with the diabetogen streptozotocin (STZ, 60 mg/kg, in citrate buffer pH 4.5) on day 1 and, after 14 days, orally (p.o.) with either MET, TAU or MET-TAU (each at 2.4 mM/kg, in water). Control rats received only citrate buffer pH 4.5 (2 mL) or only STZ on day 1 by the i.p. route. All the animals were sacrificed by decapitation on day 57 and their brains collected by the freeze clamp technique. Blood samples were placed in heparinized tubes and used for the assay of the plasma glucose (GLC) and blood insulin (INS) levels. Immediately thereafter, the brains were surgically removed and a portion was used to prepare a homogenate in 0.1 M PBS pH 7.4, which was used for the assay of indices of oxidative stress. Diabetes raised the plasma GLC level (+313%) but lowered that of the blood INS (−76%) compared to corresponding values from nondiabetic rats. In addition it raised the brain malondialdehyde level (+59%) but lowered the reduced/disulfide glutathione ratio (−46%), and activities of catalase (−43%), glutathione peroxidase (−48%), superoxide dismutase (−65%), glutathione reductase (−50%) and glutathione S-transferase (−51%) significantly (all at p < 0.001). Except for the greater decrease in GLC (+90% vs. +22%) and increase in INS (−26% vs. −52%) levels seen in rats receiving MET than in rats receiving TAU, these compounds protected the brain against oxidative stress to significant (p ≤ 0.05%) and rather similar extents. Furthermore, the concurrent administration of MET and TAU to the diabetic rats led to brain values of indices of oxidative stress that were lower than those attained with MET alone, although generally not to a statistically significant degree.