Xenobiotic Metabolizing Enzymes Are Not Restricted to Parenchymal Cells in Rat Liver

To characterize the distribution and inducibility of drug metabolizing enzymes within different hepatic cell populations, the activities of aminopyrine N-demethylase, ethoxyresorufin O-deethylase, microsomal epoxide hydrolase and cytosolic glutathione transferase were measured in liver parenchymal, Kupffer, and endothelial cells isolated from untreated rats or rats pretreated with phenobarbital, 3-methylcholanthrene, or Aroclor 1254. Enzyme activities, measurable in all cases, were 2.3- to 5.7-fold higher in parenchymal cells than in Kupffer and endothelial cells. Phenobarbital increased aminopyrine N-demethylase, microsomal epoxide hydrolase, and cytosolic glutathione transferase activities, whereas 3-methylcholanthrene enhanced ethoxyresorufin O-deethylase, epoxide hydrolase, and glutathione transferase activities in the three cell populations. Aroclor 1254 consistently induced each of the enzyme activities in parenchymal, Kupffer, and endothelial cells. Western blot analyses revealed clear differences in the expression of proteins immunologically related to cytochrome P-450 PB-1, and glutathione transferases B and X in parenchymal cells compared with the corresponding Kupffer and endothelial cells. In contrast, only minor differences between the cell types were apparent in the expression of cytochromes P-450 PB-4, P-450 MC1a, P-450 MC1b and microsomal epoxide hydrolase. These studies establish that oxidative and postoxidative drug metabolizing enzymes are not restricted to parenchymal cells: similar but distinguishable complements of these enzymes are also found in Kupffer and endothelial cells.