title: Apparent hydroxyl radical generation without transition metal catalysis and tyrosine nitration during oxidation of the anti-tubercular drug, isonicotinic acid hydrazide.
abstract: Aromatic hydroxylation and formation of thiobarbituric acid-reactive substances occurred in a mixture of isonicotinic acid hydrazide (isoniazid) and catalase. Since these reactions were stimulated by phytic acid (a potent metal chelator), rather than inhibited, transition metal-catalysed hydroxyl radical generation was not implicated. Hydroxylation also occurred with isoniazid and phytic acid in the absence of catalase, albeit to a lesser extent. The independent effects of catalase and phytic acid are related to their abilities to catalyse isoniazid oxidation. In the presence of tyrosine, both the isoniazid/phytic acid system and authentic peroxynitrite generated dityrosine. Authentic peroxynitrite, as well as a phytic acid-mediated isoniazid oxidation product, have absorbance maxima at 302 nm. The yield of this isoniazid-derived product increased with pH and in the presence of a superoxide-generating system. A good correlation existed between absorbance at 302 nm and aromatic hydroxylation. Acid-induced decomposition of the 302 nm absorbance in the presence of superoxide dismutase led to the formation of a product absorbing in the same region as peroxynitrite-modified superoxide dismutase (350 nm at acid pH). Catalase catalysed peroxynitrite-mediated, as well as isoniazid/phytic acid-mediated tyrosine nitration, which was accompanied by Compound II formation (ferryl-catalase) in both cases. We postulate that peroxynitrite or a similar species is formed during isoniazid oxidation.
authors: Department of Pharmacology, Medical School, University of Stellenbosch, Tygerberg, South Africa.
authors: J M
authors: JM
authors: Van Zyl
authors: B J
authors: BJ
authors: Van der Walt
mesh_terms: D002374:Catalase / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D007538:Isoniazid / Q000737:chemistry*; D007700:Kinetics; D008670:Metals / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D008670:Metals; D009566:Nitrates; D017392:Thiobarbituric Acid Reactive Substances; C039642:peroxynitric acid; D017665:Hydroxyl Radical; D014443:Tyrosine; D002374:Catalase; D007538:Isoniazid