Characterization of BNF-inducible cytochrome P-450IA1 in cultures of rainbow trout liver cells

Abstract

We are investigating isolated rainbow trout hepatocytes as a model system for characterizing the carcinogenic and toxic effects of xenobiotics. For these studies, it will be important to characterize cytochrome P-450IA1, the β-naphthoflavone (BNF)-inducible isozyme, which is fundamental for the phase I metabolism of many xenobiotics. In this study, ethoxyresorufin O-deethylase (EROD) activity and immunoreactivity of P-450IA1 were measured in isolated trout liver cells maintained in culture for at least 3 days. Liver cells prepared from trout pretreated with BNF exhibited readily detectable EROD activity, which rapidly declined when cells were placed in culture, with a half-life of about 15 h. Addition of BNF, dexamethasone, glucagon, insulin or δ-aminolevulinic acid alone or in combinations neither prevented this decline nor induced EROD activity in isolated cells prepared from control animals. Acetaminophen in the culture media helped maintain EROD activity, immunoreactive P-450 and total cytochrome P-450 in hepatocytes prepared from BNF-treated trout. Light and electron microscopy revealed that concentrations of acetaminophen which were most effective in maintaining EROD produced distinctive toxic effects to the cells. The mechanism(s) by which acetaminophen influences EROD activity is not yet known; however, these findings establish one way to manipulate P-450IA1 in cultured trout hepatocytes.