Glutathione conjugation of trichloroethylene in human liver and kidney: Kinetics and individual variation

Isolated human hepatocytes exhibited time-, trichloroethylene (Tri) concent ration-, and cell concentration-dependent formation of S-(1,2-dichlorovinyl )glutathione (DCVG) in incubations in sealed flasks with 25 to 10,000 ppm T ri in the headspace, corresponding to 0.011 to 4.4 mM in hepatocytes, Maxim al formation of DCVG (22.5 +/- 8.3 nmol/120 min per 10(6) cells) occurred w ith 500 ppm Tri, Time-, protein concentration-, and both Tri and GSH concen tration-dependent formation of DCVG were observed in liver and kidney subce llular fractions. Two kinetically distinct systems were observed in both cy tosol and microsomes from pooled liver samples, whereas only one system was observed in subcellular fractions from pooled kidney samples. Liver cytoso l exhibited apparent K-m values (mu M Tri) of 333 and 22.7 and V-max values (nmol DCVG formed/min per mg protein) of 8.77 and 4.27; liver microsomes e xhibited apparent K-m values of 250 and 29.4 and V-max values of 3.10 and 1 .42; kidney cytosol and microsomes exhibited apparent K-m values of 26.3 an d 167, respectively, and V-max values of 0.81 and 6.29, respectively. DCVG formation in samples of liver cytosol and microsomes from 20 individual don ors exhibited a 6.5-fold variation in microsomes but only a 2.4-fold variat ion in cytosol. In coincubations of pooled liver cytosol and microsomes, ad dition of an NADPH-regenerating system produced marked inhibition of DCVG f ormation, but addition of GSH had no effect on cytochrome P-450-catalyzed f ormation of chloral hydrate. These results indicate that both human kidney and liver have significant capacity to catalyze DCVG formation, indicating that the initial step of the GSH-dependent pathway is not limiting in the f ormation of nephrotoxic and nephrocarcinogenic metabolites.