Hanigan and Devarajan: Molecular mechanisms of cisplatin nephrotoxicity at identifying the programmed cell death pathways induced by cisplatin. These investigations have been facilitated by the establishment and elucidation of cell culture models. Cisplatin was first shown to cause apoptosis in cultured mouse proximal tubular cells (Lieberthal et al, 1996; Takeda et al, 1997; Takeda et al, 1998; Fukuoka et al, 1998). Several subsequent studies have now documented the ability of cisplatin to induce apoptosis in pig proximal tubular (Kruidering et al, 1998; Lau 1999; Okuda et al, 1999; Zhan et al, 1999; Kaushal et al, 2001; Park et al, 2002), human proximal tubular (Razzaque et al, 1999; van de Water et al, 2000; Nowak 2002; Cummings and Schnellmann 2002), and even collecting duct cells (Liu et al, 1998; Lee et al, 2001). A recurrent theme gleaned from these works is that cisplatin induces apoptosis in a dose- and duration-dependent manner, and that while this agent activates programmed cell death at lower (10-100 µM) doses, it can also result in necrotic cell death at higher (200-800 µM) concentrations.
drugs such as cisplatin induce apoptosis in tumor cells (Friesen et al, 1999). A possible role for this pathway in cisplatin nephrotoxicity was first suggested by experiments done in cultured human proximal tubular epithelial cells, in which cisplatin (20-80 µM) resulted in apoptosis which was temporally correlated with an increased expression of Fas (Razzaque et al, 1999). A subsequent detailed analysis in mouse and rat kidney as well as in cultured murine proximal tubular cells has recently provided substantial support for this mechanism (Tsuruya et al, 2003). In this study, wild-type mice subjected to cisplatin displayed renal dysfunction, tubular cell apoptosis, and an increase in mRNAs encoding Fas and Fas ligand in the kidneys, whereas Fas-mutant B6lpr/lpr mice exhibited an attenuated response. Proximal tubular cells cultured from wild-type mice responded to cisplatin by upregulation of Fas mRNA and protein, increase in caspase 8 activity, and apoptosis, all of which were blunted in cells from kidneys of Fas-mutant mice (Tsuruya et al, 2003). Furthermore, the cells derived from wild-type mice exhibited increased TNF-! secretion following cisplatin exposure, and kidneys of TNFR1deficient mice displayed an attenuated functional and apoptotic response to cisplatin (Ramesh and Reeves 2002; Tsuruya et al, 2003). Taken together, these results suggest that cisplatin induces renal epithelial cell apoptosis at least in part via activation of death receptor pathways, as illustrated in Figure 3.
VIII. Activation of death receptor pathways Renal tubular epithelial cells upregulate Fasdependent pathways and undergo apoptosis following ischemic injury both in vitro (Feldenberg et al, 1999) and in vivo (Nogae et al, 1998), and activation of the Fas pathway is a common mechanism by which cytotoxic
Figure 3. Proposed apoptotic pathways in cisplatin nephrotoxicity. See text for details. ROM = reactive oxygen metabolites; Casp = caspase. Death receptor pathways are shown in green, and mitochondrial pathways are in purple. All arrows indicate stimulatory influences, except Bcl2 which is inhibitory.
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