Master, Sharon

ABSTRACTIsoniazid (INH), a front-line antituberculosis agent, is activated by mycobacterial catalase-peroxidase KatG, converting INH into bactericidal reactive species. Here we investigated the requirements and the pathway of nitric oxide (NO˙) generation during oxidative activation of INH byMycobacterium tuberculosisKatG in vitro. We also provide in vivo evidence that INH-derived NO˙ can inhibit key mycobacterial respiratory enzymes, which may contribute to the overall antimycobacterial action of INH.

ABSTRACTIsonicotinic acid hydrazide (INH) is a frontline antituberculosis agent. Once taken up byMycobacterium tuberculosis, INH requires activation by the catalase-peroxidase KatG, converting INH from its prodrug form into a range of bactericidal reactive species. Here we used15N-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 byM. tuberculosisKatG. 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.