A mechanism of haloalkene-induced renal carcinogenesis

Several halogenated alkenes are nephrotoxic; some others induce renal tubular adenocarcinomas in rodents after lifelong administration. A bioactivation mechanism accounting for the organ-selective tumor induction has been elucidated: conjugation of the parent compounds with glutathione (GSH), catalyzed by hepatic GSH S-transferases, results in the formation of haloalkyl and halovinyl glutathione S-conjugates. Formation of S-conjugates (identified by NMR and mass spectrometry) could be demonstrated with trichloroethene, tetrachloroethene, hexachlorobutadiene, perfluoropropene, trichlorotrifluoropropene, and dichloroacetylene in incubations with rat liver microsomes and in the isolated perfused rat liver. The GSH conjugates formed are eliminated from the rat liver with the bile and may be translocated to the kidney, intact or after metabolism to the corresponding cysteine S-conjugates that are metabolized in the kidney by renal tubular cysteine conjugate beta-lyase (beta-lyase) to reactive intermediates, most likely thioacylchlorides and thioketenes. Interaction of these potent electrophiles with DNA [demonstrated for intermediates formed from S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine] causes mutagenicity in bacteria, genotoxicity in cultured renal cells, and cytotoxicity in kidney cells. As an alternative to beta-lyase-catalyzed cleavage, the cysteine S-conjugates may be acetylated to the corresponding mercapturic acids, which have been identified in urine. The ability of the kidney to concentrate GSH and cysteine S-conjugates and the intensive metabolism of GSH S-conjugates to cysteine S-conjugates in this organ are evidently responsible for the organotropic carcinogenicity.