Safety of long-term feeding of dl-alpha-lipoic acid and its effect on reduced glutathione:oxidized glutathione ratios in beagles.

Alpha-lipoic acid is touted as a powerful antioxidant and possibly a conditionally essential nutrient in older mammals. The safety and efficacy of dl-alpha-lipoic acid was evaluated in 30 adult beagles that were evenly randomized into five groups, each of which was fed one of five different foods with varying inclusion rates of dl-alpha-lipoic acid (0, 150, 1500, 3000, and 4500 ppm). All dogs were fed their respective portion of food daily as their sole source of nutrition for 6 months. Evaluations included general health, body weight, food intake, hematologic and serum biochemical parameters, and glutathione:oxidized glutathione (GSH:GSSG) ratios in lymphocytes. No signs of toxicity were observed at any except the highest level of dl-alpha-lipoic acid inclusion, and no consistent abnormalities were noted in hematologic or biochemical measures at any level. There was a significant overall effect (P< .05) of food on the difference of GSH:GSSG ratio between Day 84 and Day 0. All inclusions of dl-alpha-lipoic acid increased the ratio of GSH:GSSG with the largest numeric improvement occurring at the lowest inclusion rate (150 ppm).