INHIBITION OF HUMAN NEUTROPHIL BINDING TO HYDROGEN PEROXIDE-TREATED ENDOTHELIAL-CELLS BY CAMP AND HYDROXYL RADICAL SCAVENGERS

Hydrogen peroxide (H2O2) increases adherence of human polymorphonuclea r neutrophils (PMN) to cultured human umbilical vein endothelial cells (HUVEC). Catalase and HO. scavengers did not affect the increased PMN adherence to HUVEC stimulated by other compounds such as phorbol myri state acetate (PMA) and thrombin, showing that the observed effect was H2O2- and HO.-specific. This effect was inhibited by hydroxyl radical s (HO.) scavengers and not by iron-chelators that do not penetrate the cells, suggesting the involvement of intracellular HO. in the increas ed adherence mechanism. An increase in cAMP inhibited H2O2-induced adh erence, as observed with isoproterenol, isobutylmethylxanthine, and di butyryl-cAMP. Similarly, pentoxifylline (Ptx), an HO. scavenger that a lso increases cAMP, inhibited H2O2-mediated adherence but had no effec t on that induced by PMA or thrombin. PKA inhibitors cancelled the Ptx -induced inhibition-of H2O2-mediated adherence. However, PKA inhibitor s or atrial natriuretic peptide that decreases cAMP did not increase a dherence, showing that decrease in cAMP is not responsible for increas ed adherence. HO. scavengers did not alter the H2O2-induced reduction in cAMP levels, but did inhibit the effect of H2O2 on adherence. are c onclude that HO. mediates the H2O2-induced increased in PMN adherence to HUVEC, and that the increase in cAMP that mediates PKA activation d ownregulates this effect.