Radical generation by the non-enzymatic reaction of methylglyoxal and hydrogen peroxide

Background: In various disorders, the reactive α-oxoaldehyde compounds methylglyoxal (MG) and glyoxal (GO) are thought to contribute to oxidative injury. However, the exact mechanism by which these molecules induce oxidative stress is unclear. We hypothesized that intermediate compounds, such as free radicals, are generated during the chemical reaction between H₂O₂ and MG or GO. Mateiials and Methods: Chemiluminescence signals emitted from the 'test mixture' of MG/GO, luminol, and H₂O₂ were measured. To confirm radical generation, the electron spin resonance (ESR) spectrum of MG/GO and H₂O₂ was observed using the spin-trap method, in which 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) were used as spin trap reagents for free radicals. Results: Luminol chemiluminescence as a function of MG concentration was increased by MG and partly decreased by DMPO. The MG increase was about 10 times that of GO. The free radicals generated by MG and H₂O₂ included methyl and other carbon-centered radicals. Discussion: We demonstrated that free radicals are generated via a non-enzymatic reaction between MG and H₂O₂ in vitro. The finding provides a novel perspective for understanding the toxicological aspects of MG and the pathophysiology of disorders associated with increased MG levels in vivo.