A mechanism for primaquine mediated oxidation of NADPH in red blood cells

The incubation of NADPH with primaquine results in the formation of free radicals which were demonstrated by the electron spin resonance (ESR) technique of spin trapping using 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the spin trap. The free radicals formed were identified as the superoxide (DMPO-OOH) and hydroxyl (DMPO-OH) spin adducts of DMPO. Copper/zinc superoxide dismutase inhibited the formation of DMPO-OOH while it only partly inhibited the formation of DMPO-OH which could be totally inhibited by catalase. This indicates that the formation of hydroxyl radicals is not totally arising from the Haber-Weiss reaction. However since the formation of hydroxyl radicals is dependent on hydrogen peroxide, a non-metal catalysed reduction of hydrogen peroxide is postulated for their formation. Oxygen consumption during the reaction between primaquine and NADPH was found to be consistent with the spin trapping experiments and the rate of production of DMPO-OH indicates the formation of 1:1 catalytic complex between the two reactants. Quenching of the fluorescence of NADPH at 460 nm in the presence of primaquine indicates the formation of a charge transfer complex. When red blood cells are incubated with primaquine a hydroxyl spin adduct (DMPO-OH) is observed. The formation of this radical is probably the main cause of primaquine mediated toxicity.