Nitric oxide generated from isoniazid activation by KatG:: Source of nitric oxide and activity against Mycobacterium tuberculosis

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 N-15-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 anti mycobacterial 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 INK.