Comparative genetic activity of cis- and trans-1,2-dichloroethylene in yeast

The cis and trans isomers of 1,2-dichloroethylene were tested for mutagenic effects in a diploid strain (D7) of the yeast Saccharomyces cerevisiae in suspension tests with and without a mammalian microsomal activation system, an S9 mouse liver fraction, and by an in vivo intrasanguineous host mediated assay. The effects of the same agents on aminopyrine N-demethylase activity and cytochrome P-450 level in liver were studied in nonpretreated and in phenobarbital + beta-naphtoflavone-pretreated mice. In the suspension test, both isomers exhibited dose dependent toxicity, and survival was lower with metabolic activation than without. In this test also, both isomers exhibited genetic activity as measured by increases in recombinants at the ade 2 locus in experiments with metabolic activation. In the host-mediated assay, only the cis isomer showed evidence of mutagenic activity with significant increases in convertants at the trp locus and revertants at the ilv locus. Such mutagenic activity was found both after acute and chronic doses and in liver, kidney, and lung tissue. The two isomers exhibited different effects with respect to aminopyrine N-demethylase activity and cytochrome P-450 level. In general, the trans isomer appeared to emphasize induction of enzyme activity or level while the cis isomer more frequently tended to inhibit activity or destroy the enzyme.