Ethionamide activation and sensitivity in multidrug-resistant Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Drug Metabolism
• Tuberculosis Research

Background:

• Ethionamide (ETA) is crucial for treating multidrug-resistant tuberculosis (MDR-TB).
• Understanding ETA's activation and resistance mechanisms is vital for effective treatment strategies.

Purpose of the Study:

• To elucidate the metabolic activation pathway of Ethionamide in Mycobacterium tuberculosis.
• To identify the specific enzymes involved in ETA activation and resistance.
• To investigate the genetic basis of ETA resistance in clinical isolates.

Main Methods:

• Synthesis of radiolabeled Ethionamide for metabolic studies.
• Whole-cell metabolism assays using Mycobacterium tuberculosis.
• Genetic manipulation (overproduction) of putative regulatory (EtaR) and activating (EtaA) proteins.
• Analysis of EtaA gene sequences in clinical MDR-TB isolates.

Main Results:

• Ethionamide is activated by S-oxidation, producing a 4-pyridylmethanol metabolite.
• The monooxygenase EtaA is identified as the enzyme responsible for ETA activation and toxicity.
• Overexpression of EtaR confers ETA resistance, while EtaA overexpression leads to hypersensitivity.
• Mutations in EtaA were found in all tested multidrug-resistant tuberculosis patient isolates, conferring cross-resistance to other thiocarbonyl drugs.

Conclusions:

• Ethionamide activation is mediated by the EtaA enzyme through S-oxidation.
• Mutations in EtaA are a significant mechanism of Ethionamide resistance in clinical multidrug-resistant tuberculosis.
• EtaA-mediated resistance confers cross-resistance to other thiocarbonyl-containing drugs, impacting treatment options.