MECHANISMS INVOLVED IN THE ANTIPLATELET ACTIVITY OF ESCHERICHIA-COLI LIPOPOLYSACCHARIDE IN HUMAN PLATELETS

In this study, Escherichia coli lipopolysaccharide (LPS) dose-dependen tly (100-300 mu g/ml) and time-dependently (10-60 min) inhibited plate let aggregation in human platelets stimulated by agonists, LPS also do se-dependently inhibited the phosphoinositide breakdown and the intrac ellular Ca+2 mobilization in human platelets stimulated by collagen, L PS (300 mu g/ml) also significantly inhibited the thromboxane A(2) for mation stimulated by collagen in human platelets. Moreover, LPS (100-3 00 mu g/ml) dose-dependently decreased the fluorescence of platelet me mbranes tagged with diphenylhexatrience. In addition, LPS (200 and 300 mu g/ml) significantly increased the formation of cyclic GMP but not cyclic AMP in platelets. LPS (200 mu g/ml) also significantly increase d the production of nitrate within a 30 min incubation period, Rapid p hosphorylation of a platelet protein of M-r 47 000, a marker of protei n kinase C activation, was triggered by phorbol-12-13-dibutyrate (PDBu , 50 nM). This phosphorylation was markedly inhibited by LPS (200 mu g /ml) within a 30 min incubation period. These results indicate that th e antiplatelet activity of LPS may be involved in two important pathwa ys. (1) LPS may induce conformational changes in the platelet membrane , leading to change in the activity of phospholipase C. (2) LPS also a ctivated the formation of nitric oxide (NO)/cyclic GMP in human platel ets, resulting in inhibition of platelet aggregation. Therefore, LPS-m ediated alteration of platelet function may contribute to bleeding dia thesis in septicaemic and endotoxaemic patients.