Human hepatocytes were isolated from histologically normal liver and were provided by D. Geller (Department of Surgery, University of Pittsburgh, Pittsburgh, PA) according to a protocol approved by the Institutional Review Board. Human hepatocytes were prepared by a three-step collagenase perfusion technique, modified as described previously (43 (link)). Isolated human hepatocytes were cultured in William’s medium E supplemented with 5% calf serum (GE Healthcare Life Sciences), penicillin (100 U/ml), streptomycin (100 U/ml), 2 mM L-glutamine, and 15 mM Hepes.