Trichloroethylene (TRI) is a major environmental contaminant, is an established animal carcinogen, and is considered a """"""""probably human carcinogen"""""""" by the National Toxicology Program and the International Agency for Research on Cancer. The kidneys are one target organ for TRI and its nephrotoxic and nephrocarcinogenic effects are mediated by metabolites derived from conjugation with glutathione (GSH). Subsequent metabolism to the cysteine conjugate S- (1,2- dichlorovinyl)-L-cysteine (DCVC) generates the penultimate toxic metabolite. It is metabolism of DCVC by either the cysteine conjugate ?-Iyase or the flavin-containing monooxygenase that generates the ultimate reactive and toxic species. Most of the previous research that has delineated the metabolism and potential modes of action for TRI and DCVC has been performed in rodents or with tissue from rodents. While these studies, some of which have been done by the PI, have provided much useful insight, there are problems in using data obtained from rodents for human health risk assessment. This is particularly true for halogenated solvents such as TRI, because of marked species differences in metabolism, transport, and overall sensitivity to toxicity. Previous studies of ours showed that DCVC can cause both apoptosis or necrosis in primary cultures of human proximal tubular (hPT) cells, depending on concentration and time of exposure. Findings also suggested effects of DCVC on expression of proteins related to stress response and regulation of cell growth. This application uses primary cultures of hPT cells as the experimental model and will investigate the ability of hPT cells exposed to moderately toxic concentrations of DCVC to undergo repair and regeneration, the potential for DCVC to induce cell proliferation by non-genotoxic mechanisms, and the requirement for mitochondrial toxicity in the course of events leading from exposure to toxicity. The application comprises three Specific Aims.
Specific Aim 1 addresses the question of whether hPT cells exposed to moderately toxic concentrations of DCVC undergo repair and regeneration. Several markers of repair will be assessed and precise conditions and potential mechanisms by which the repair and regeneration response are induced will be investigated.
Specific Aim 2 will address the question of whether DCVC can stimulate uncontrolled proliferation of hPT cells. Effects on cell cycle and cell cycle signaling molecules under various conditions of DCVC exposure will be studied. Finally, Specific Aim 3 will address the question of whether mitochondrial toxicity is sufficient and necessary for DCVC-induced toxicity in hPT cells. Although previous work has shown that mitochondria are early and potently affected intracellular targets of DCVC, it is not known whether mitochondrial toxicity is an obligatory step in the progression of events that occur after DCVC exposure or whether other pathways that are independent of mitochondria can mediate renal cell injury. Achievement of these aims should build on our previous work in human kidney cells and extend it to provide a much more complete understanding of the various and complex ways in which DCVC affects the human kidney ? ?
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