Enzymatic and nonenzymatic superoxide-generating reactions of isoniazid

During the course of horseradish peroxidase-mediated oxidation of either o-dianisidine or 2-2'-azino-di(3-ethyl-benzthiazoline-6-sulfonic acid) (ABTS), no O2 consumption took place. When isonicotinic acid hydrazide (isoniazid) (INH) was included in the reaction mixture, O2 was consumed in amounts linearly related to the INH concentration. Nicotinic acid hydrazide at equimolar concentrations induced lower rates of O2 consumption. Superoxide dismutase activated O2 consumption. At equimolar concentrations, INH, nicotinic acid hydrazide, and phenylhydrazine induced bleaching of p-nitrosodimethylaniline in the horseradish peroxidase mediation of ABTS oxidation. Bleaching was not inhibited by hydroxyl radical (. OH) scavengers. After a short lag period, INH reacted with NADH at alkaline pH to produce superoxide radical (O2-), as detected by superoxide dismutase-inhibitable Nitro Blue Tetrazolium reduction. Nicotinic acid hydrazide with NADH caused a lower rate of O2- production after a longer lag period than INH.