Effect of intracellular oxygen-free radicals on the formation of lipid derived mediators in rat renomedullary interstitial cells

Abstract An intracellular generation of oxygen free radicals was induced by phenazine methosulfate (PMS) in rat renomedullary interstitial cells (RMIC) in culture. This response was associated with an increase in PGE 2 and 15 HETE production. The synthesis of cyclooxygenase and lipoxygenase derivatives in PMS-treated cells was inhibited by indomethacin and NDGA respectively. Inhibitors of PLA 2 such as mepacrine and dexamethasone were able to inhibit partially the PGE 2 synthesis induced by PMS. The formation of lyso-platelet activating factor, a product of membrane-bound phospholipid, by a PLA 2 catalyzed reaction was also stimulated in PMS-treated cells. Superoxide dismutase added to the incubation medium enhanced the PMS-dependent PGE 2 synthesis whereas catalase decreased it, suggesting the involvement of H 2 O 2 in this process. In addition, a depletion of soluble thiol groups was observed in PMS-treated cells. Treatment of RMIC by the thiol oxidative agent, diamide, mimicked the effect of PMS on PGE 2 synthesis, whereas diamide did not increase the formation of lyso-PAF indicating its inability to stimulate PLA 2 . These results suggest that cyclooxygenase may be involved in this process, indeed added arachidonate, bypassing PLA 2 , enhanced PGE 2 synthesis in PMS-treated cells further supporting the involvement of cyclooxygenase. In conclusion, generation of oxygen free radicals by PMS in RMIC enhanced the synthesis of lipid derived mediators. A decrease in the cellular thiol content is partially involved in cyclooxygenase activation but does not appear to be involved in PLA 2 activation.