Kupffer cell-mediated differential down-regulation of cytochrome P450 metabolism in rat hepatocytes

Nonparenchymal cells, particularly Kupffer cells, might play an important r ole in the modulation of xenobiotic metabolism in liver and its pharmacolog ical and toxicological consequences. This intercellular communication via t he exchange of soluble factors was investigated in primary rat Kupffer cell s and hepatocytes. Freshly isolated rat Kupffer cells were seeded onto cell culture inserts and cocultured with 5 day old serum-free rat hepatocyte mo nolayer cultures at a ratio of 1:1 for 2 days. Hepatocyte cultures, Kupffer cell cultures or cocultures were treated with 0.1 ng/ml-10 mu g/ml lipopol ysaccharide (LPS). Within this concentration range, no significant toxicity was observed in either cell type. In LPS-exposed cocultures, tumor necrosi s factor alpha (TNF alpha) levels rose up to 5 ng/ml within 5 h; nitric oxi de (NO) levels increased up to 70 mu M within 48 h of treatment, both in a dose-dependent fashion. The release of negative (albumin) and positive (alp ha 1-acid-glycoprotein) acute phase proteins from the hepatocytes was stron gly down- and up-regulated, respectively. The simultaneous treatment of the cocultures with phenobarbital and LPS (10 ng/ml) or 3-methylcholanthrene a nd LPS (10 ng/ml) resulted in a strong down-regulation (85%) of the phenoba rbital-induced cytochrome P450 (CYP) isoform CYP2B1 in the hepatocytes wher eas the 3-methylcholanthrene-induced isoform CYP1A1 was only weakly affecte d (15%). This specific down-regulation of CYP2B1 was mediated exclusively b y TNF alpha, released from the Kupffer cells. It was not linked with NO rel ease from or inducible NO synthase activity in the hepatocytes. The TNF alp ha release was not affected by the two xenobiotics. Acetaminophen tested in these cocultures showed no direct interaction with the Kupffer cells. The use of liver cell cocultures is therefore a useful approach to investigate the influence of intercellular communication on xenobiotic metabolism in Li ver. (C) 1999 Elsevier Science B.V. All rights reserved.