The role of conjugation in hepatotoxicity of troglitazone in human and porcine hepatocyte cultures

In primary human and porcine hepatocyte cultures, we investigated the relat ionship between metabolism and cytotoxicity of troglitazone. Treatment of h uman hepatocytes for 2 h with 10, 20, 25, 35, and 50 mu M troglitazone in p rotein-free medium resulted in concentration-dependent decreases in total p rotein synthesis. Decreases at 10 and 20 mu M were reversible by 24 h, howe ver protein synthesis did not recover at concentrations greater than or equ al to 25 mu M. Troglitazone at 50 mu M caused cellular death. In porcine he patocytes, 100 mu M troglitazone was lethal, whereas at 50 mu M, protein sy nthesis completely recovered by 24 h. Recovery in protein synthesis was ass ociated with metabolism of parent drug, whereas toxicity correlated (r(2) = 0.82) with accumulation of unmetabolized troglitazone. By 1 h, in human he patocytes, troglitazone was metabolized to similar amounts of sulfate and q uinone metabolites with little glucuronide detected. In contrast, porcine h epatocytes metabolized troglitazone to the similar amounts of glucuronide a nd the quinone metabolites with little sulfate detected. Exposure of human hepatocytes to a combination of 10 mu M troglitazone and 10 mu M 2,4-dichlo ro-4-nitrophenol resulted in a 70% decrease in protein synthesis, associate d with 90% inhibition in the formation of troglitazone sulfate, a 4-fold in crease in unmetabolized troglitazone, and no effect on formation of the qui none metabolite. Treatment with a combination of acetaminophen or phenobarb ital with 20 mu M troglitazone resulted in sustained decrease in protein sy nthesis associated with inhibition of sulfation and accumulation of troglit azone. These results suggest that inhibition of troglitazone sulfation may result in increased hepatotoxicity due to exposure to parent drug, or incre ased metabolism by alternate pathways.