Dose-dependent protein adduct formation in kidney, liver, and blood of rats and in human blood after perchloroethene inhalation

Perchloroethene (PER) was a widely used solvent and is an environmental contaminant. In bioassays for carcinogenicity, PER was found to increase the incidence of liver tumors in mice and of renal tumors in male rats. Toxic effects of PER after repeated administration are likely caused by bioactivation. PER bioactivation occurs by two pathways. Oxidation by cytochrome P450 results in trichloroacetyl chloride, which binds to lipids and proteins. Glutathione S-conjugate formation from PER and further processing of the formed S-(trichlorovinyl)glutathione to S-(trichlorovinyl)-L-cysteine, followed by cysteine conjugate beta-lyase catalyzed cleavage, resulted in the reactive dichlorothioketene, which binds to proteins under formation of N-epsilon-(dichloroacetyl)-L-lysine in proteins. The objective of this study was to comparatively quantify the dose-dependent formation of protein adducts from PER in rats and humans using antibodies with high specificity for either N-epsilon-(trichloroacetyl)-L-lysine or N-epsilon-(dichloroacetyl) -L-lysine in proteins. Male and female rats (n = 2, per concentration and time point) were exposed to 400, 40, and 10 ppm PER for 6 h and killed at various time points. Formation of N-epsilon-(dichloroacetyl)-L-lysine and N-epsilon-(trichloroacetyl)-L-lysine in proteins was comparatively quantified in subcellular fractions from liver and kidney and in blood. In addition, three male and three female human volunteers were exposed to 10 and 40 ppm PER, and formation of protein adducts in blood was analyzed using the antibodies and GC/MS after immunoaffinity enrichment of modified proteins. In liver and kidney subcellular fractions and blood of PER-exposed rats, dose-dependent formation of N-epsilon-(dichloroacetyl)-L-lysine and N epsilon-(trichloroacetyl)-L-lysine in proteins was observed. Highest concentrations of N-epsilon-(dichloroacetyl)-L-lysine in proteins were formed in kidney mitochondria, followed by kidney cytosol. Only low concentrations of N-epsilon-(dichloroacetyl)-L-lysine in proteins were present in liver proteins; blood concentrations of N-epsilon-(dichloroacetyl)-L-lysine in proteins were 5 to 10 fold lower than in kidney mitochondria. Highest concentrations of N-epsilon-(trichloroacetyl) -L-lysine were found in microsomal and cytosolic proteins from the liver of rats exposed to PER. A higher protein adduct formation was seen in PER-exposed-male than -female rats for N-epsilon-(dichloroacetyl)-L-lysine in renal mitochondrial proteins, after exposure to 400 ppm PER. In human blood samples taken 0 and 24 h after the 6 h exposures to PER, N-epsilon-(trichloroacetyl)-L-lysine-containing proteins were present in low concentrations. N epsilon-(Dichloroacetyl)L-lysine-containing proteins were not detected either by Western blotting or GC/MS after immunoaffinity chromatography. The obtained results indicate a dose-dependent covalent binding of PER metabolites to proteins in rat liver, kidney, and blood and suggest that the concentration of covalent protein adducts is much lower in blood of humans as compared to the blood of rats exposed under identical conditions.