Role of phospholipase A(2) in the cytotoxic effects of oxalate in culturedrenal epithelial cells

Background. Oxalate, a common constituent of kidney stones, is cytotoxic fo r renal epithelial cells. Although the exact mechanism of oxalate-induced c ell death remains unclear, studies in various cell types, including renal e pithelial cells, have implicated phospholipase A(2) (PLA(2)) as a prominent mediator of cellular injury. Thus, these studies examined the role of PLA( 2) in the cytotoxic effects of oxalate. Methods. The release of [H-3]-arachidonic acid (AA) or [H-3]oleic acid (OA) from prelabeled Madin-Darby canine kidney (MDCK) cells was measured as an index for PLA(2) activity. The cell viability was assessed by the exclusion of ethidium homodimer-l. Results. Oxalate exposure (175 to 550 mu M free) increased the release of [ H-3]-AA in MDCK cells but had no effect on the release of [H-3]-OA. Oxalate -induced [H-3]-AA release was abolished by arachidonyl trifluoromethyl keto ne (AACOCF(3)), a selective inhibitor of cytosolic PLA(2) (cPLA(2)), but wa s not affected by selective inhibitors of secretory PLA(2) and calcium-inde pendent PLA(2). The [H-3]-AA release could be demonstrated within 15 minute s after exposure to oxalate, which is considerably earlier than the observe d changes in cell viability. Furthermore, AACOCF(3) significantly reduced o xalate toxicity in MDCK cells. Conclusions. Oxalate increases AA release from MDCK cells by a process invo lving cPLA(2). In addition, based on the evidence obtained using a selectiv e inhibitor of this isoform, it would appear that the activity of this enzy me is responsible, at least in part, for the cytotoxic effects of oxalate. The finding that oxalate can trigger a known lipid-signaling pathway may pr ovide new insight into the initial events in the pathogenesis of nephrolith iasis.