title: Altered NADH/NAD+ ratio mediates coresistance to isoniazid and ethionamide in mycobacteria.
abstract: The front-line antituberculosis drug isoniazid (INH) and the related drug ethionamide (ETH) are prodrugs that upon activation inhibit the synthesis of mycolic acids, leading to bactericidal activity. Coresistance to INH and ETH can be mediated by dominant mutations in the target gene inhA, encoding an enoyl-ACP reductase, or by recessive mutations in ndh, encoding a type II NADH dehydrogenase (NdhII). To address the mechanism of resistance mediated by the latter, we have isolated novel ndh mutants of Mycobacterium smegmatis and Mycobacterium bovis BCG. The M. smegmatis ndh mutants were highly resistant to INH and ETH, while the M. bovis BCG mutants had low-level resistance to INH and ETH. All mutants had defects in NdhII activity resulting in an increase in intracellular NADH/NAD(+) ratios. Increasing NADH levels were shown to protect InhA against inhibition by the INH-NAD adduct formed upon INH activation. We conclude that ndh mutations mediate a novel mechanism of resistance by increasing the NADH cellular concentration, which competitively inhibits the binding of INH-NAD or ETH-NAD adduct to InhA.
authors.affiliation: Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Vilchèze
authors.forename: Torin R
authors.initials: TR
authors.lastname: Weisbrod
authors.forename: Bing
authors.initials: B
authors.lastname: Chen
authors.forename: Laurent
authors.initials: L
authors.lastname: Kremer
authors.forename: Manzour H
authors.initials: MH
authors.lastname: Hazbón
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Alland
authors.forename: James C
authors.initials: JC
authors.lastname: Sacchettini
authors.forename: William R
authors.initials: WR
authors.lastname: Jacobs
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D015153:Blotting, Western; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D005000:Ethionamide / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial; D007538:Isoniazid / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D009161:Mycobacterium / Q000187:drug effects* / Q000235:genetics; D009163:Mycobacterium bovis / Q000187:drug effects / Q000235:genetics; D020102:Mycobacterium smegmatis / Q000187:drug effects / Q000235:genetics; D009243:NAD / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000235:genetics; D010641:Phenotype; D010957:Plasmids; D011808:Quinone Reductases / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014170:Transformation, Genetic
chemical_list: D000995:Antitubercular Agents; D003470:Culture Media; D009243:NAD; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases; D009245:NADH Dehydrogenase; D005000:Ethionamide; D007538:Isoniazid