Studies on the Mechanism of Nitrofurantoin-Mediated Red Cell

The mechanism of nitrofurantoin-mediated depletion of red cell reduced glutathione (GSH) was investigated. Nitrofurantoin caused cellular depletion of GSH in vitro under aerobic and oxygen-depleted conditions, an eftect which could be partially inhibited by coincubation with the hemeprotein ligand ethyl isocyanide, or completely prevented by coincubation with 2’-AMP, an inhibitor of NADPH-dependent reductase enzymes. Covalent binding of nitrofurantoin to red cell macromolecules appeared to be a minor process and was not substantially inhibited by either ethyl isocyanide or 2’-AMP. Covalent binding was only slightly greater under oxygen-depleted conditions. Nitrofurantoin increased the rate of superoxide formation in red cell lysate, an effect inhibited by ethyl isocyanide but not by 2’-AMP. These data suggest different mechanisms for nitrofu-rantoin-mediated depletion of GSH under aerobic and oxygen-depleted conditions. In the presence of oxygen, nitrofurantoin causes the release of superoxide from oxyhemoglobin. The superoxide thus formed may deplete GSH via several mecha-nisms. In the absence of oxygen, nitrofurantoin is reduced to reactive metabolites via reactions which appear to require the participation of both an NADPH-dependent flavoprotein and hemoglobin. Persons genetically deficient in the enzyme glucose 6-phos-phate dehydrogenase are susceptible to episodes of red cell hemolysin when administered various drugs, among them the antimicrobial NF. The metabolic effects of NF on normal human red cells incubated in vitro have been described (Dersh-witz and Novak, 1979, 1980) (manuscript in preparation). NF was found to deplete red cells ofATP and GSH, while producing a concomitant elevation in the cellular levels of methemoglobin and hydrogen peroxide. The ED, values for these effects, approximately 10 M, are similar to concentrations attained in ViL’() after conventional doses of the drug