Stimulation of microsomal production of reactive oxygen intermediates by rifamycin SV: Effect of ferric complexes and comparisons between NADPH and NADH

Rifamycins are antibacterial antibiotics which are especially useful for the treatment of tuberculosis. Reactive oxygen intermediates are produced in the presence of rifamycin SV and metals such as copper or manganese. Experiments were carried out to evaluate the interaction of rifamycin SV with rat liver microsomes to catalyze the production of reactive oxygen species. At a concentration of 1 mm, rifamycin SV increased microsomal production of superoxide with NADPH as cofactor 3-fold, and with NADH as reductant by more than 5-fold. Rifamycin SV increased rates of H₂O₂ production by the microsomes twofold with NADPH, and 4- to 8-fold with NADH. In the presence of various iron complexes, microsomes generated hydroxyl radical-like (· OH) species. Rifamycin SV had no effect on NADPH-dependent microsomal · OH production, irrespective of the iron chelate. A striking stimulation of · OH production was found with NADH as the reductant, ranging from 2- to 4-fold with catalyst such as ferric-EDTA and ferric-DTPA to more than 10-fold with ferric-ATP, -citrate, or -histidine. Catalase and competitive · OH scavengers lowered rates of · OH production (chemical scavenger oxidation) and prevented the stimulation by rifamycin. Superoxide dismutase had no effect on the NADH-dependent rifamycin stimulation of · OH production with ferric-EDTA or -DTPA, but was inhibitory with the other ferric complexes. In contrast to the stimulatory effects on production of O_{{minus sign, dot below}2}, H₂O₂, and · OH, rifamycin SV was a potent inhibitor of microsomal lipid peroxidation. These results show that rifamycin SV stimulates microsomal production of reactive oxygen intermediates, and in contrast to results with other redox cycling agents, is especially effective with NADH as the microsomal reductant. These interactions may contribute to the hepatotoxicity associated with use of rifamycin, and, since alcohol metabolism increases NADH availability, play a role in the elevated toxic actions of rifamycin plus alcohol.