The molecular mechanisms by which dimethyl sulfoxide (DMSO) enhances CYP3A protein in phenobarbital-treated primary cultured rat hepatocytes were examined. DMSO treatment rapidly increased CYP3A protein levels in the absence of an increase in CYP3A mRNA levels or an increase in CYP2B protein or mRNA levels. CYP3A levels were increased approximately 3.7- and 9-fold following 0.1% DMSO treatment for 6 and 48 h, respectively. Analyses of the polysomal distribution of CYP3A mRNA suggested that DMSO treatment did not significantly alter the translational efficiency of the CYP3A mRNA. Comparative analyses of immunodetectable protein levels following treatment with cycloheximide showed that DMSO clearly decreased the rate of CYP3A protein turnover but not that of CYP2B. Examination of testosterone metabolism in hepatocyte cultures revealed that DMSO pretreatment increased CYP3A-catalyzed 2 beta- and 6 beta-testosterone hydroxylation. When DMSO was in the culture medium, no inhibitory affect on CYP3A-catalyzed testosterone metabolism was observed, although a slight (15-21%) inhibitory effect was noted for CYP2B-catalyzed 16 alpha- and 16 beta-testosterone hydroxylation. These data provide evidence that DMSO increased CYP3A protein levels as a result of decreased protein degradation. DMSO increased both immunodetectable CYP3A protein levels and catalytic activity, in contrast to compounds that have been reported to stabilize CYP3A protein and inhibit activity.
Copyright 1998 Academic Press.