Xenobiotic-enhanced expression of cytochrome P450 2E1 and 2B1/2B2 in primary cultured rat hepatocytes.

Investigation of the posttranscriptional mechanisms involved in the xenobiotic-mediated enhancement of cytochrome P450 2E1 (CYP2E1) expression has been limited by a lack of a functional primary hepatocyte cell culture system. We examined the effects of ciprofibrate (CIPRO) and pyridine (PYR) treatment on the expression of CYP2E1, P450 4A (CYP4A), and P450 2B (CYP2B) in primary rat hepatocytes cultured on Vitrogen or Matrigel substratum and in the presence of Chee's medium. Cells were cultured for 72 hr or longer before initiation of treatment. Northern blot analyses indicated that 24-hr CIPRO treatment enhanced the expression of CYP4A, and CYP2B mRNA in a concentration-dependent manner, with maximal induction of CYP2E1 mRNA (2- to 3-fold) and CYP4A1 mRNA (up to approximately 15-fold) monitored at 30-300 microM CIPRO. Maximal CYP2B mRNA levels (7- to 8-fold) were monitored at 300-1000 microM CIPRO. Treatment of hepatocytes for 24, 48, and 72 hr with 30 microM CIPRO showed progressive increases in CYP2B and CYP4A mRNA levels, with approximately 13- and 60-fold elevations in the respective mRNAs occurring at 72 hr posttreatment. In contrast, CYP2E1 mRNA levels were maximally elevated between 2- and 3-fold at both 24 and 48 hr and were returning to basal levels by 72 hr. Western blot analyses revealed that 24-hr PYR (25 mM) treatment of CIPRO-treated cells, in the absence of any further increase in CYP2E1 mRNA levels, increased CYP2E1 protein levels approximately 6- to 8-fold. PYR treatment also increased CYP2B mRNA and CYP2B1/2B2 protein levels approximately 16-fold relative to cells treated only with CIPRO.(ABSTRACT TRUNCATED AT 250 WORDS)