(A) HPHs from four donors were treated with vehicle control (0.1 % DMSO), PB (1 mM) or CITCO (2 µM) in the presence and absence of proteasome inhibitor [MG-132 (MG); 1 or 10 µM]. Total RNA, extracted after 24 h treatment, was subjected to real-time PCR analysis. The results were normalized against GAPDH and are represented as the means ± S.D. Significantly different from DMSO (*), PB (#) or CITCO (+ +), P < 0.05. (B) In a separate experiment, homogenates were harvested from liver donor HPH1900 treated for 48 h with DMSO, PB (1 mM), CITCO (2 µM) in the presence and absence of MG-132 (0.1, 1 and 10 µM). CYP2B6/CYP3A4 protein levels were assessed with Western immunoblotting.