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Renal cysteine conjugate β-lyase-mediated toxicity studied with primary cultures of human proximal tubular cells

https://doi.org/10.1016/0041-008X(90)90319-PGet rights and content

Abstract

The β-lyase pathway has been shown to mediate the nephrotoxicity of S-cysteine conjugates of a variety of haloalkenes in a number of animal models in vitro and in vivo. However, there is no information available concerning this mechanism of bioactivation in human tissues. In this investigation a well-characterized model of human proximal tubule epithelial cells, the presumed target cell, was used to investigate the toxicity of a series of glutathione and cysteine conjugates of nephrotoxic haloalkenes. Both S-(1,2-dichlorovinyl)-glutathione (DCVG) and S-(1,2-dichlorovinyl)-l-cysteine (DCVC) caused dose-dependent toxicity over a range of 25 to 500 μm. DCVC was consistently found to be more toxic than DCVG, but the inclusion of γ-glutamyltransferase (0.5 U/ml) increased the toxicity of DCVG to that observed with an equimolar concentration of DCVC, indicating that metabolism to the cysteine conjugate is an important rate-limiting step in this in vitro model. S-(1,2,3,4,4-Pentachlorobutadienyl)-l-cysteine, S-(2-chloro-1,1,2-trifluoroethyl)-l-cysteine, and S-(1,1,2,2-tetrafluoroethyl)-l-cysteine were also found to be toxic to human proximal tubular cells. Incubation with [35S]DCVC resulted in covalent binding of 35S-label, which increased linearly to a final level of 1.05 nmol/mg protein at 6 hr. Aminooxyacetic acid (250 μm), an inhibitor of pyridoxal phosphate-dependent enzymes such as β-lyase, protected the cells from the toxicity of all of the cysteine conjugates and inhibited the covalent binding of 35S-label from [35S]DCVC to cellular macromolecules. The results of the present study provide the first evidence that human proximal tubular cells are sensitive to the toxicity of glutathione and/or cysteine conjugates of a variety of chloro- and fluoroalkenes which are activated via the β-lyase pathway. The implications for human health are discussed.

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    This work was supported by grants from the American Cancer Society, BC570 (T.W.J.), as well as the National Institutes of Health, AI24179 (A.L.T.), DK38925, and CA48197 (J.L.S.).

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