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Isoniazid accumulation in Mycobacterium smegmatis is modulated by proton motive force-driven and ATP-dependent
B S Choudhuri1, S Sen, P Chakrabarti
1Department of Chemistry, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Calcutta, 700 009, India.
Abstract:
Resistance to isoniazid (INH), a frontline, antituberculosis drug, presents a major problem in the chemotherapy of tuberculosis. Although several targets of INH have been identified, the mechanism of INH resistance remains incompletely understood. This report demonstrates that INH accumulation in Mycobacterium smegmatis is enhanced both upon addition of both a proton motive force (pmf) uncoupler, carbonylcyanide m-chlorophenylhydrazone (CCCP), and upon addition of ortho-vanadate, an inhibitor of ATP-dependent efflux pumps. Both the Deltapsi and DeltapH components of the pmf are likely to be involved as judged by the effects of valinomycin and nigericin, respectively. Reserpine, an inhibitor of the human MDR1 P-glycoprotein, enhances INH accumulation in a manner similar to o-vanadate. Verapamil, a calcium channel blocker, also enhances INH uptake. Taken together, the results provide evidence of the involvement of both pmf- and ATP-dependent extrusion systems in INH efflux in M. smegmatis, making it important to evaluate the role of such systems in INH resistance in pathogenic mycobacteria.
Insights
Isoniazid (INH) resistance in tuberculosis is poorly understood. This study shows that INH accumulation in Mycobacterium smegmatis is increased by blocking efflux pumps, suggesting these systems contribute to drug resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Drug Resistance
Background:
- Isoniazid (INH) is a crucial first-line drug for tuberculosis treatment.
- Mechanisms underlying INH resistance in mycobacteria are not fully elucidated.
- Understanding INH efflux is vital for developing effective tuberculosis therapies.
Purpose of the Study:
- To investigate the role of efflux systems in isoniazid accumulation and resistance in Mycobacterium smegmatis.
- To determine the involvement of proton motive force (pmf) and ATP-dependent pumps in INH efflux.
Main Methods:
- Utilized Mycobacterium smegmatis as a model organism.
- Assessed INH accumulation in the presence of pmf uncouplers (e.g., CCCP, valinomycin, nigericin).
- Investigated the effect of inhibitors of ATP-dependent efflux pumps (e.g., ortho-vanadate, reserpine) and calcium channel blockers (verapamil) on INH accumulation.
Main Results:
- INH accumulation in M. smegmatis was enhanced by pmf uncouplers, indicating pmf-dependent efflux.
- Inhibition of ATP-dependent efflux pumps (ortho-vanadate, reserpine) also increased INH accumulation.
- Verapamil, a calcium channel blocker, further enhanced INH uptake.
- Both pmf and ATP-dependent systems appear to mediate INH efflux.
Conclusions:
- Mycobacterium smegmatis employs both proton motive force and ATP-dependent mechanisms for isoniazid efflux.
- These efflux systems are potential targets for overcoming INH resistance in mycobacteria.
- Further research is warranted to explore the role of these efflux systems in pathogenic mycobacteria.