The Effect of Taurine and Its Immediate Homologs on Diabetes-Induced Oxidative Stress in the Brain and Spinal Cord of Rats

Abstract

This study has examined the acute effects of taurine (TAU) and of its two immediate homologs aminomethanesulfonic acid (AMSA) and homotaurine (HTAU) on the oxidative stress that develops in the brain of rats as a result of type 2 diabetes mellitus. Male Sprague-Dawley rats, 220–225 g in weight, were divided into groups of 6 each, and treated with a single intraperitoneal (i.p.) dose of streptozotocin (STZ) in 10 mM citrate buffer pH 4.5 (60 mg/kg). The treatment compound (AMSA, HTAU or TAU) was administered by the i.p. route in two equal doses (1.2 mM/kg each) at 75 and 45 min before STZ. Control rats received only 10 mM citrate buffer pH 4.5 or only STZ by the i.p. route. The rats were sacrificed at 24 h after a dosing with STZ under general anesthesia, and their brains and spinal cords collected by the freeze clamp technique. A portion of brain, of a brain area (cerebellum, cortex, brain stem) or of spinal cord from each animal was extracted into 0.1 M PBS pH 7.4, and the extract was used for the assay of malondialdehyde (MDA), nitric oxide (NO), catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD). An extract for the assay of the reduced (GSH) and disulfide (GGSG) forms of glutathione was prepared in similar manner but using 2% metaphosphoric acid plus 0.1 M PBS pH 8.0 as the extracting medium. Diabetes was found to markedly increase the formation of MDA (by 160–202%), NO (by 138–313%) and GSSG (by 103–241%), and to lower the values of GSH (by 57–65%), GSH/GSSG ratio (79–89%) and activities of CAT (by 61–69%), GPx (by 52–66%) and SOD (by 55–68%) in the brain, brain areas and spinal cord relative to corresponding control values (all at p < 0.001). These effects were reduced to values that were generally at least one-half of those seen in untreated diabetic rats, with TAU providing a greater attenuation of the formation of MDA and NO, an about similar action on the depletion of GSH, and a lower action on the decrease in the GSH/GSSG ratio caused by diabetes than either AMSA or HMTAU. In contrast AMSA and HMTAU were about equipotent with each other and more potent than TAU in preventing the loss of antioxidant enzyme activities associated with diabetes. In short, pretreating diabetic rats with AMSA, HMTAU or TAU is found to protect the brain against changes in biochemical parameters indicative of oxidative stress, with potency differences among the test compounds varying within a narrow range.