Reaction rate of pyruvate and hydrogen peroxide: assessing antioxidant capacity of pyruvate under biological conditions

Pyruvate, a pivotal glucose metabolite, is an a-ketoacid that reacts with hydrogen peroxide (H2O2). Its pharmacological precursor, ethyl pyruvate, has shown anti-inflammatory/anti-tissue injury effects in various animal models of disease, but failed in a multicenter clinical trial. Since rodents, but not humans, can convert ethyl pyruvate to pyruvate in blood plasma, this additional source of extracellular pyruvate may have contributed to the discrepancy between the species. To examine this possibility, we investigated the kinetics of the reaction under biological conditions and determined the second order rate constant k as 2.360 +/- 0.198 M-1 s(-1). We then calculated the time required for H2O2 elimination by pyruvate. The results show that, with an average intracellular concentration of pyruvate (150 mu M), elimination of 95% H2O2 at normal to pathological concentrations (0.01-50 mu M) requires 141-185 min (2.4-3 hour). With 1,000 mu M pyruvate, a concentration that can only exist extracellularly or in cell culture media, 95% elimination of H2O2 at 5-200 mu M requires 21-25 min. We conclude that intracellular pyruvate, or other alpha-ketoacids, whose endogenous concentration is controlled by metabolism, have little role in H2O2 clearance. An increased extracellular concentration of pyruvate, however, does have remarkable peroxide scavenging effects, considering minimal peroxidase activity in this space.