Radical-induced oxidation of metformin

Metformin (1,1-dimethylbiguanide) is an antihyperglycaemic drug used to normalize glucose concentrations in type 2 diabetes. Furthermore, antioxidant benefits have been reported in diabetic patients treated with metformin. This work was aimed at studying the scavenging capacity of this drug against reactive oxygen species (ROS) like (OH)-O-. and O-2(-.) -free radicals. ROS were produced by gamma radiolysis of water. The irradiated solutions of metformin were analyzed by UV/visible absorption spectrophotometry. It has been shown that hydroxyl free radicals react with metformin in a concentration-dependent way. The maximum scavenging activity was obtained for concentrations of metformin greater than or equal to 200 mumol.L-1, under our experimental conditions. An estimated value of 10(7) L.mol(-1).s(-1) has been determined for the second order rate constant k((OH)-O-. + metformin). Superoxide free radicals and hydrogen peroxide do not initiate any oxidation on metformin in our in vitro experiments.