Abstract

Troglitazone (TRO) is an insulin sensitizer used in the treatment of type II diabetes. TRO is known to increase the activity of cytochrome P-450 (CYP) 3A in vivo. We have investigated the effect of TRO on CYP3A protein content and the activity of CYP3A (as measured by the formation of 6β-hydroxytestosterone formation) in primary cultures of human hepatocytes in comparison with rifampicin (RIF). Hepatocytes were isolated from four human livers by perfusion with collagenase, plated on collagen-coated plates, and maintained in William’s E medium. After 48 h in culture, cells were exposed to RIF (10 μM) or TRO (0–50 μM) twice, each over a period of 24 h, and the activity of CYP3A was measured. TRO increased the activity of CYP3A in a concentration-dependent manner, reaching a maximal response at 5 μM. Pretreatment of the hepatocytes with 10 μM TRO or 10 μM RIF resulted in a 4- to 15-fold increase in the activity of CYP3A. Maximum increase in CYP3A protein was observed at 5 μM TRO. There was a significant correlation (R² = 0.89) between the content of immunoreactive CYP3A protein in the hepatocytes and the rate of formation of 6β-hydroxytestosterone. These results indicate that TRO is a potent inducer of CYP3A and is similar to RIF in inducing CYP3A in human hepatocytes. At concentrations of 25 μM and above, TRO was toxic to the cells, as determined by a decrease in the activity of CYP3A, a reduction in the amount of immunoreactive protein, and changes in the morphology of the cells.