Characterization of cytochrome P450 isoenzymes in primary cultures of pig hepatocytes

Despite the fact that pigs are increasingly used in pharmacological and tox icological studies, knowledge on the enzymes which metabolize xenobiotics, in particular cytochrome P450 (CYP) enzymes, in pigs is still very limited. Primary cultures of pig hepatocytes were used to characterize CYP enzymes. The characterization was performed at the level of enzymatic activities, a poprotein and mRNA analyses. Enzyme inducers investigated were beta-naphtho flavone (BNF), phenobarbital (PB), dexamethasone (DEX) and rifampicin (RIF) . After 48 hr of BNF treatment, CYP1A protein and mRNA levels were increase d, and ethoxyresorufin O-deethylation and caffeine 3-demethylation were str ongly induced. PB and RIF increased the levels of CYP3A apoprotein and mRNA , whereas BNF down-regulated CYP3A and related activities. PB and RIF treat ment resulted in increased ethylmorphine N-demethylation and testosterone h ydroxylation, which appears to be the result of CYP3A induction. Hybridizat ion of pig RNA with a human CYP2C9 cDNA probe showed a PB and RIF inducible CYP, which was down-regulated by BNF. Similar inducing effects were observ ed for tolbutamide, a marker substrate for CYP2C. DEX was not a potent indu cer, although some induction of CYP3A mRNA was observed. The present result s indicate the absence of CYP2B and probably CYP2D enzymes and activities i n pig liver. Despite some dissimilarities, the results indicate that pigs, apart from their very human-like physiology, might represent a more appropr iate model species for oxidative drug metabolism in humans than rats. (C) 1 998 Elsevier Science Ltd. All rights reserved.