Nephrotoxicity of the glutathione and cysteine conjugates of 2-bromo-2-chloro-1,1-difluoroethene

Abstract

The mercapturate S-(2-bromo-2-chloro-1,1-difluoroethyl)-N-acetyl-L-cysteine, which is apparently derived from the halothane degradation product 2-bromo-2-chloro-1,1-difluoroethene, is excreted in urine. S-(2-Bromo-2-chloro-1,1-difluoroethyl)glutathione (BCDFG) and S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine (BCDFC) are putative intermediates in the metabolism of 2-bromo-2-chloro- 1,1-difluoroethene and are analogs of nephrotoxic and cytotoxic S-haloalkyl glutathione and cysteine conjugates. The objective of the research was to study the nephrotoxicity and cytotoxicity of 2-bromo-2-chloro-1,1-difluoroethene-derived S-conjugates. BCDFG and BCDFC were nephrotoxic in Fischer 344 rats and caused diuresis, increases in urine glucose and protein concentrations, in blood urea nitrogen concentrations, in kidney/body weight percentages and in serum glutamate-pyruvate transaminase activities. Both S-conjugates also produced severe morphological changes in the kidneys, especially in the proximal tubules. Morphological changes indicative of hepatotoxicity were seen in some animals given BCDFG and BCDFC. Both BCDFG and BCDFC were cytotoxic to LLC-PK1 cells, as shown by lactate dehydrogenase release into the medium. The cytotoxicity of BCDFG was blocked by the gamma-glutamyltransferase inhibitor acivicin, and the cytotoxicity of both BCDFG and BCDFC was blocked by the cysteine conjugate beta-lyase inhibitor aminooxyacetic acid. Also, S-(2-bromo-2-chloro-1,1-difluoroethyl)-DL-alpha-methylcysteine, which can not be metabolized by beta-lyase, was not toxic to LLC-PK1 cells. These in vivo and in vitro data provide evidence that BCDFG and BCDFC are nephrotoxic and that their toxicity is dependent on renal bioactivation by cysteine conjugate beta-lyase.