Inhibition of human neutrophil binding to hydrogen peroxide-treated endothelial cells by cAMP and hydroxyl radical scavengers

Hydrogen peroxide (H₂O₂) increases adherence of human polymorphonuclear 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 myristate acetate (PMA) and thrombin, showing that the observed effect was H₂O₂- and HO·-specific. This effect was inhibited by hydroxyl radicals (HO·) scavengers and not by iron-chelators that do not penetrate the cells, suggesting the involvement of intracellular HO· in the increased adherence mechanism. An increase in cAMP inhibited H₂O₂-induced adherence, as observed with isoproterenol, isobutylmethylxanthine, and dibutyryl-cAMP. Similarly, pentoxifylline (Ptx), an HO· scavenger that also increases cAMP, inhibited H₂O₂-mediated adherence but had no effect on that induced by PMA or thrombin. PKA inhibitors cancelled the Ptx-induced inhibition of H₂O₂- mediated adherence. However, PKA inhibitors or atrial natriuretic peptide that decreases cAMP did not increase adherence, showing that decrease in cAMP is not responsible for increased adherence. HO· scavengers did not alter the H₂O₂-induced reduction in cAMP levels, but did inhibit the effect of H₂O₂ on adherence. We conclude that HO· mediates the H₂O₂-induced increased in PMN adherence to HUVEC, and that the increase in cAMP that mediates PKA activation downregulates this effect.