MECHANISMS INVOLVED IN THE INDUCTION OF HUMAN ENDOTHELIAL-CELL NECROSIS

The effects of the inflammatory mediators lipopolysaccharide (LPS) and tumor necrosis factor-alpha (TNF) and unstimulated and activated neut rophils (PMNs) on endothelial cell (EC) necrosis were studied using th e cultured human EC line (ECV-304) and human PMNs in vitro. LPS and TN F alone or their combination failed to induce EC necrosis. Activated P MNs, as evidenced by augmentations in CD11b expression and respiratory burst, induced significant EC necrosis commencing at 12 hr of cocultu re, which was strongly dependent on the ratio of PMN:ECs and the durat ion of PMN:EC coculture. In contrast, unstimulated PMNs induced no sig nificant increases in EC necrosis. To examine the mechanisms of activa ted PMN-mediated EC necrosis, the oxygen radical scavengers superoxide dismutase (SOD) and catalase, as well as the protease inhibitors phen ylmethysulfonyl fluoride (PMSF), alpha(1)-antitrypsin (alpha(1)-AT), s oybean trypsin-chymotrypsin inhibitor (TCI), and aprotinin, were studi ed in coculture experiments. EC necrosis induced by activated PMNs cou ld be markedly attenuated by SOD, PMSF, alpha(1)-AT, TCI, aprotinin, o r their combinations. Although aprotinin enhanced respiratory burst, t his agent inhibited necrosis by downregulating PMN CD11b and PMN-EC ad hesion. These results demonstrate that the inflammatory mediators LPS and TNF and quiescent PMNs fail to induce EC necrosis. However, PMNs a ctivated by inflammatory mediators can induce EC necrosis through oxid ative and nonoxidative mechanisms and this process is dependent on PMN -EC adhesion. (C) 1996 Academic Press, Inc.