5,5-dimethyl-1-pyrroline- N-oxide alone enhances the spontaneous superoxide generation by primaquine

Abstract

Primaquine (PQ), a well-known antimalarial drug, has been reported to generate superoxide (O 2 −) in the presence of reducing agents such as NADPH. In the present study, chemiluminescence was detected by adding only PQ to aqueous 2-methyl-6-[ p-methoxyphenyl]-3,7-dihydroimidazo-[1,2-α]pyrazin-3-one (MCLA), which is a specific chemiluminescent probe for O 2 −, and was quenched by superoxide dismutase (SOD), indicating that PQ alone can generate O 2 − in aerobic conditions. Furthermore, 5,5-dimethyl-1-pyrroline- N-oxide (DMPO) enhanced the O 2 − generation by PQ. Superoxide spin adduct, DMPO-OOH, was also detected by ESR both in aqueous solutions and in dimethyl sulfoxide with DMPO. The level of O 2 − generation showed a linear correlation with the DMPO concentration, and SOD competitively inhibited the DMPO-OOH formation. The results suggested that in aerobic conditions PQ is autoxidized to 5-hydroxy-PQ, which generates O 2 −, and DMPO accelerates the autoxidation process by trapping O 2 −. DMPO or M 4PO alone enhances the spontaneous O 2 − generation by PQ, therefore cautious evaluation is necessary in all studies using the ESR/spin trapping technique to elucidate the mechanism of PQ-related radical generation.