METABOLISM OF TRICHLOROETHYLENE AND CHLORAL HYDRATE BY THE JAPANESE MEDAKA (ORYZIAS-LATIPES) IN-VITRO

Trichloroethylene (TRI), a common groundwater contaminant, is readily metabolited by mammals to produce chloral hydrate (CH), trichloroaceti c acid (TCA), and trichloroethanol (TCOH). Cytochrome P450 (CYP) and o ther enzymes are responsible for formation of these metabolites, which are implicated in TRI's toxicity and carcinogenicity. To establish th e validity of the Japanese medaka (Oryzias latipes) as an alternate te st species for TRI, we examined the metabolism of TRI and CH, as well as CYP expression, in medaka liver preparations. Trichloroethylene was incubated with medaka microsomal protein, and metabolites were extrac ted and analyzed using gas chromatography. Microsome-mediated metaboli sm of TRI was observed, and a K-m value for TRI oxidation of 540 mu M and a V-max value of 213 pmol/min.mg(-1) protein were obtained. Conver sion of TRI to CH, TCA, and TCOH was found with medaka hepatic subcell ular fractions. In addition, a sex difference in hepatic microsomal TR I metabolism, specific CYP content, and ethoxyresorufin O-deethylase a ctivity was noted. The lower specific activity of preparations from th e livers of female medaka is compensated for by increased total protei n in the larger liver mass of the female. Immunochemical analysis show ed that CYP1A was readily detectable in medaka liver, but CYP2E1 was p resent at very low levels. These data suggest that TRI metabolism in m edaka liver preparations mimics that observed in mammalian systems and supports their use as an alternative test species in the evaluation o f the toxicity of TRI.