Expression of xenobiotic-metabolizing enzymes in propagatable cell cultures and induction of micronuclei by 13 compounds.

Activities of various xenobiotic-metabolizing enzymes were determined in 18 cell lines. Activities of cytochrome P450 reductase, microsomal epoxide hydrolase and glutathione transferase were detectable in all lines. The highest values were similar to the activities found in freshly isolated rat hepatocytes. Catalase activity was also present in all 12 investigated cell lines. Activity of UDP-glucuronosyl transferase was high in some lines, but low or undetectable in others. Activity of cytosolic epoxide hydrolase was not measurable in most lines, and was low in the others. Metabolism of benzo[a]pyrene was observed in eight out of nine examined lines, no activity being found in V79 cells. V79 and three epithelial cell lines were then used as target cells in a genotoxicity assay in which the frequency of micronucleated cells was determined. In V79 cells, 7,12-dimethyl- benz[a]anthracene, benzo[a]pyrene, benzo[a]pyrene-trans-7,8-dihydrodiol, aflatoxin B1, N-nitrosomorpholine and 2-acetylaminofluorene showed negative responses, whereas N-methyl-N'-nitro-N-nitrosoguanidine, 9-hydroxybenzo[a]pyrene, 2-nitrofluorene, dibenz[a,h]anthracene 1,2-catechol, dibenz[a,h]anthracene, 1,2-quinone hydroquinone and p-benzoquinone proved positive in the test. All 13 compounds, however, induced micronuclei in rat intestinal cells (IEC-17 and IEC-18) and in embryonal human liver cells (HuFoe-15). Thus, these epithelial cell lines are capable of activating and detecting a broad spectrum of chemically diverse genotoxic compounds. They may also be useful for the detection of hazardous compounds whose active metabolites are not able to penetrate from the extracellular space into the indicator cell.