Antitubercular drugs (ATT) are known to be majorly metabolized and detoxified in liver by both Phase I and Phase II group of drug metabolizing enzymes. These drugs as well as their metabolites are toxic and during this process cause injury to liver. In this study, we have investigated the in vitro hepatotoxic potential of both individual as well as combination ATT drugs using an in vitro model of human hepatocellular carcinoma cell line (HepG2). The cells were treated with varied concentrations of ATT drugs namely isoniazid (INH), rifampicin (RIF), and pyrazinamide (PYZ) for different durations. Cytotoxicity assay using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide) as well as morphological analysis using phase contrast microscopy have shown that concentrations used were not cytotoxic. However, pretreatment with sub-cytotoxic concentrations of INH and PYZ increased the toxicity with the same drugs. This report corroborates the clinical finding that long-term treatment as well combination drug therapy with ATT induces hepatotoxicity rather than individual drugs.

Tuberculosis (TB) is highly endemic in India. The first-line anti-TB therapy (ATT) involving isoniazid (INH), rifampicin and pyrazinamide causes hepatotoxicity in approximately 11.5% of Indian patients. Studies have shown that ATT-induced hepatotoxicity is primarily due to oxidative stress caused by the drugs and metabolites. Herbal drugs with antioxidative properties have been tested in animal studies and clinical trials for the management of hepatotoxicity. The objective of this study was to investigate the role of curcumin (CUR), silymarin (SILY) and N-acetylcysteine (N-ACET) on hepatotoxicity by ATT drugs using an in vitro model of human hepatocellular carcinoma cell line (HepG2). HepG2 cells were treated with ATT drugs alone or along with CUR, SILY or N-ACET for a 48-h duration. The cells were monitored for viability, morphology, respiring mitochondria and cell cycle. Our results suggest that the presence of hepatoprotective drugs during treatment of HepG2 cells with ATT drugs lowers the hepatotoxic effect of the latter. This is observed in terms of (a) increased cell viability, (b) healthy-looking cell morphology as revealed by phase contrast microscopy, (c) active respiring cells as observed with confocal microscopy upon staining with a mitochondrial membrane-specific dye, MitoTracker(®) Red, and reduction in the sub-G(1) peak in cell cycle analysis by flow cytometry. Our results suggest that these hepatoprotective drugs need to be further explored as potential adjuvant therapy along with ATT drugs.

Increased susceptibility to isoniazid (INH)-induced hepatotoxicity due to presence of NAT2 SA polymorphism was demonstrated in Western Indian population. NAT2 genotyping can therefore serve as an important tool for identifying patients predisposed to anti-TB DIH.

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