title: A co-cultivation system as a model for in vitro studies of modulating effects of naturally occurring indoles on the genotoxicity of model compounds.
abstract: An in vitro model system, consisting of primary chick embryo hepatocytes as the metabolizing system co-cultured with V79 Chinese hamster cells as the target cells for the SCE assay, was used to study the modulating effects of naturally occurring indoles on the genotoxicity of benzo[a]pyrene (B[a]P) and N-nitrosodimethylamine (NDMA). At 25 mug/ml, indole-3-carbinol (I3C) induced ethoxyresorufin-O-deethylase (ERROD) activity 3.9-fold and ethoxycoumarin-O-deethylase (ETCO) activity 2-fold. Indole-3-acetonitrile (I3A; 35 mug/ml) induced ERROD activity 1.6-fold and ETCO activity 2-fold. Pretreatment with I3C resulted in a 20-40% decrease in genotoxicity for both B[a]P and NDMA. Pretreatment with I3A resulted in a similar decrease in genotoxicity for B[a]P, whereas no decrease was observed for NDMA. When a microsomal fraction prepared from I3C-pretreated hepatocytes was used, no decrease in B[a]P-induced genotoxicity was found; in contrast, use of an S-9 fraction prepared from the same cells resulted in a 45% decrease. Exposure of cells to B[a]P after pretreatment with I3C for suboptimal times also resulted in a significant decrease in genotoxic activity. The data indicate that the protective effects of pretreatment with the indoles, observed in this study, are not directly correlated with induction of cytochrome P-450-associated enzymes. Instead they seem to be more the result of a changed balance in the enzyme systems involved in the indole biotransformation process and point to an essential role of conjugating enzyme systems.
authors.affiliation: Department of Toxicology, Agricultural University, De Dreijen 12, 6073 BC Wageningen, The Netherlands.
authors.forename: W M
authors.initials: WM
authors.lastname: Jongen
authors.forename: R J
authors.initials: RJ
authors.lastname: Topp
authors.forename: H G
authors.initials: HG
authors.lastname: Tiedink
authors.forename: E J
authors.initials: EJ
authors.lastname: Brink