The central role of thromboxane and platelet activating factor receptors in ex vivo regulation of endotoxin-induced monocyte tissue factor activity in human whole blood

Abstract

Expression of tissue factor (TF) by activated monocytes may initiate thrombotic episodes associated with diseases, such as thrombosis and atherosclerosis. In this study, steps in the regulatory pathways of lipopolysaccharide (LPS)-induced monocyte TF activity and released TNF-α in human whole blood were probed for using an array of inhibitors, comprising specific inhibitors of cytosolic phospholipase A2 (PLA2) (AACOCF3), secretory PLA (SB-203347), protein kinase (PK) (staurosporine), PKC (GF109203; BIM), and serine protease (Pefabloc SC), antagonists of thromboxane prostanoid (TP) receptor (R) (SQ-29548), platelet activating factor (PAF) R (BN-52021), leukotriene B4 R (SC-41930), serotonin R (cyproheptadine), fibronectin/fibrinogen R (RGDS), and finally, creatine phosphate/creatine phosphokinase (CP/CPK) which removes ADP. Whereas when added alone neither of these agents significantly inhibited LPS-induced TF or TNF-α, when presented as a reference cocktail comprising all the agents, TF activity and TNF-α were reduced by 77% and 49%, respectively. By subsequently testing a series of incomplete inhibitory cocktails equal to the reference except for deleted single agents or combinations of two or three active agents, the inhibitory effect of the reference cocktail could be shown to depend on the presence of the protease inhibitor and the thromboxane A2 and PAF antagonists.