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

Pyruvate, a pivotal glucose metabolite, is an α-ketoacid that reacts with hydrogen peroxide (HO). 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 s. We then calculated the time required for HO elimination by pyruvate. The results show that, with an average intracellular concentration of pyruvate (150 µM), elimination of 95% HO at normal to pathological concentrations (0.01-50 µM) requires 141-185 min (2.4-3 hour). With 1,000 µM pyruvate, a concentration that can only exist extracellularly or in cell culture media, 95% elimination of HO at 5-200 µM requires 21-25 min. We conclude that intracellular pyruvate, or other α-ketoacids, whose endogenous concentration is controlled by metabolism, have little role in HO clearance. An increased extracellular concentration of pyruvate, however, does have remarkable peroxide scavenging effects, considering minimal peroxidase activity in this space.