Effect of Arsenite on Induction of CYP1A, CYP2B, and CYP3A in Primary Cultures of Rat Hepatocytes

• Published in: Toxicology and applied pharmacology 1999-05, Vol.157 (1), p.51-59
• Main Authors: Jacobs, Judith M., Nichols, Calen E., Andrew, Angeline S., Marek, Doreen E., Wood, Sheryl G., Sinclair, Peter R., Wrighton, Steven A., Kostrubsky, Vsevolod E., Sinclair, Jacqueline F.
• Format: Article
• Language: English
• Subjects: Animals; Arsenites - toxicity; Aryl Hydrocarbon Hydroxylases; Biological and medical sciences; Cells, Cultured; Chemical and industrial products toxicology. Toxic occupational diseases; Cytochrome P-450 CYP1A1 - biosynthesis; Cytochrome P-450 CYP1A1 - genetics; Cytochrome P-450 CYP2B1 - biosynthesis; Cytochrome P-450 CYP2B1 - genetics; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System - biosynthesis; Cytochrome P-450 Enzyme System - genetics; Enzyme Induction - drug effects; Heme Oxygenase (Decyclizing) - metabolism; Liver - cytology; Liver - drug effects; Liver - enzymology; Male; Medical sciences; Metals and various inorganic compounds; Rats; Rats, Inbred F344; RNA, Messenger - analysis; Toxicology
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1006/taap.1999.8659

In earlier studies, sodium arsenite treatment was shown to decrease induction of enzymatic activities associated with hepatic CYPs in rats. Here we investigated the effect of sodium arsenite on induction of CYP2B, CYP1A, and CYP3A in primary cultures of rat hepatocytes. Arsenite decreased the induction of all three families of CYP, as measured enzymatically and immunochemically. These decreases in CYPs occurred at concentrations of arsenite (2.5–10 μM) at which no toxicity was observed; however, toxicity was observed at 25 μM arsenite. With 3-methylcholanthrene as inducer, 5 μM arsenite caused a 55% decrease in CYP1A1 immunoreactive protein and enzyme activity, but only a 25% decrease in CYP1A1 mRNA. With phenobarbital (PB) as the inducer, 2.5 μM arsenite decreased CYP2B enzyme activity and immunoreactive protein 50%, with only a 25% decrease in CYP2B1 mRNA. 5 μM Arsenite decreased CYP2B enzyme activity and immunoreactive protein 80%, but decreased CYP2B1 mRNA only 50%, while CYP3A protein was decreased greater than 75% with no decrease in CYP3A23 mRNA. With dexamethasone (DEX) as inducer, 5 μM sodium arsenite caused a 50% decrease in immunoreactive CYP3A and a 30% decrease in CYP3A23 mRNA. Although arsenite-mediated increases in heme oxygenase (HO) inversely correlated with decreases in CYP2B or CYP1A activity, inclusion of heme in cultures treated with inducers of CYP1A or CYP2B did not prevent the arsenite-mediated decreases in these CYPs. Even though added heme induced HO to similar levels with and without arsenite, decreases in CYPs were only observed in the presence of arsenite. These results suggest that, in rat hepatocytes, elevated levels of HO alone are not responsible for arsenite-mediated decreases in CYP.