Arachidonic acid protects against hypoxic injury in rat proximal tubules

Free fatty acids (FFA) and lysophospholipids accumulate during hypoxia (H) in rat proximal tubular epithelial cells partly as a result of increased phospholipase A(2) (PLA(2)) activity. The role of FFA in mediating hypoxic injury and modulating PLA(2) activity is not dear. In the present study, the effect of several FFA including arachidonic acid (AA, 20:4) on hypoxia-induced injury and PLA(2) activity was assessed in freshly isolated rat proximal tubules. Hypoxia (H) was induced in the presence of either an unsaturated free fatty acid (uFFA) [AA or linoleic acid (LA, 18:2)] or a saturated FFA (sFFA) [palmitic (PA, 16:0) or myristic acid (MA, 14:0)]. Cell membrane injury was assessed by measuring lactate dehydrogenase release (LDH). AA markedly reduced LDH release during hypoxia in a dose dependent manner, while sFFA had no protective effect. LA showed similar protection to that observed with AA. AA did not affect buffer calcium concentration, buffer pH, intracellular pH or intracellular calcium concentration. Neither inhibiting the cyclooxygenase pathway with indomethacin, nor the lipoxygenase pathway with nordihydroguaiaretic acid (NDGA) had any effect on the AA observed cytoprotection. In vitro PLA(2) activity in the control tubular extracts was compared to that following addition of AA or PA. PLA, activity decreased significantly with AA but not with PA in a dose dependent manner. These data suggest that: (1) AA protects against hypoxic injury in rat proximal tubules. (2) This cytoprotection is not specific for AA and other uFFA have a similar effect. (3) AA significantly inhibits PLA(2) activity. (4) AA induced cytoprotection may be related to a negative feedback inhibition of PLA(2) activity.