THE ROLE OF NITRIC-OXIDE IN LIPOXIN A(4)-INDUCED POLYMORPHONUCLEAR NEUTROPHIL-DEPENDENT CYTOTOXICITY TO HUMAN VASCULAR ENDOTHELIUM IN-VITRO

Objective. To assess the mechanism for the cytotoxicity of human polymorphonuclear neutrophils (PMN) to human umbilical vein endothelial cells (HUVEC) induced by the 5- and 15-lipoxygenase product of arachidonate, lipoxin A(4) (LXA(4)), and the phorbol ester, phorbol myristate acetate (PMA). Methods. HUVEC were grown to confluence and labeled with Cr-51. PMN and stimuli were added, and the release of Cr-51 info supernatants was assessed after 4 hours. Results. Both LXA(4) and PMA conferred highly significant PMN-dependent cytolysis. The cytotoxicity activated by LXA(4) was inhibited by N-G-monomethyl-L-arginine (L-NMA) and by nitro-L-arginine methyl ester, specific inhibitors of the nitric oxide (NO)-producing enzyme NO synthase. Also, the scavenger of extracellular NO, oxyhemoglobin (HbO(2)), prevented LXA(4)-induced cytolysis in a dose-dependent manner. In sharp contrast, L-NMA did not significantly affect the cytolysis induced by PMA, whereas HbO(2) showed a modest inhibitory action. In experiments without PMN, addition of the NO donor S-nitroso-N-acetyl-penicillamine to HUVEC induced marked cytolysis, which was inhibited by HbO,, but not by L-NMA. Addition of L-arginine or arginine analogs did not affect superoxide anion production in a cell-free hypoxanthine/xanthine oxidase system. Both LXA(4) and PMA induced the production of superoxide anion from PMN and of NO from HUVEC. Conclusion. NO produced by HUVEC, interacting with PMN which produce superoxide anions, is of marked significance for the endothelial cell damage in this in vitro model of vasculitis, This is probably due to the subsequent formation, via a radical-radical interaction between NO and O-2(-), of cytotoxic products, such as peroxynitrite and its metabolites, Furthermore, although LXA(4) and PMA induced comparable cytolysis at optimal concentrations, the relative importance of NO compared with other mechanisms mediating cytotoxicity was stimulus dependent, and NO was relatively more important for LXA(4)-induced PMN-dependent endothelial injury.