A Novel Metabolite of Antituberculosis Therapy Demonstrates Host Activation of Isoniazid and Formation of the Isoniazid-NAD+Adduct

Abstract

ABSTRACTOne of the most effective and widely used antituberculosis (anti-TB) drugs is isoniazid (INH), a prodrug activated via oxidation that forms an adduct with NAD+to inhibit NADH-dependent targets ofMycobacterium tuberculosis, such as enoyl-acyl carrier protein reductase (InhA). The metabolic by-products and potentially toxic intermediates resulting from INH therapy have been identified through a large body of work. However, an INH-NAD adduct or structures related to this adduct have not been identified in specimens from human TB patients or animal models of TB. Analyses by mass spectrometry of urine collected from TB patients in a study conducted by the NIAID-funded Tuberculosis Research Unit identified 4-isonicotinoylnicotinamide (C12H9N3O2) as a novel metabolite of INH therapy. This compound was formed byM. tuberculosisstrains in a KatG-dependent manner but could also be produced by mice treated with INH independent of anM. tuberculosisinfection. Thus, the 4-isonicotinoylnicotinamide observed in human urine samples is likely derived from the degradation of oxidized INH-NAD adducts and provides direct evidence of host INH activation.