Nitric Oxide Generated from Isoniazid Activation by KatG: Source of Nitric Oxide and Activity against Mycobacterium tuberculosis

Abstract

ABSTRACT Isonicotinic acid hydrazide (INH) is a frontline antituberculosis agent. Once taken up by Mycobacterium tuberculosis , INH requires activation by the catalase-peroxidase KatG, converting INH from its prodrug form into a range of bactericidal reactive species. Here we used 15 N-labeled INH together with electron paramagnetic resonance spin trapping techniques to demonstrate that nitric oxide (NO˙) is generated from oxidation at the hydrazide nitrogens during the activation of INH by M. tuberculosis KatG. We also observed that a specific scavenger of NO˙ provided protection against the antimycobacterial activity of INH in bacterial culture. No significant increases in mycobacterial protein nitration were detected, suggesting that NO˙ and not peroxynitrite, a nitrating metabolite of NO · , is involved in antimycobacterial action. In conclusion, INH-derived NO · has biological activity, which directly contributes to the antimycobacterial action of INH.