I. Suppression by compound 48/80 of bacterial endotoxin-inducible monocytic tissue factor activity: direct blockade of factor VII binding to THP-1 monocytes

Hypercoagulation with upregulated monocytic tissue factor (TF) activity oft en occurs under a variety of inflammatory conditions including endotoxemia. The antagonism to bacterial endotoxin (LPS) signaling often results in the depression in TF upregulation. We herein report that compound 48/80 (48/80 ) significantly depressed LPS-induced TF activity in human and cebus monkey peripheral blood monocytes. Employing a model monocyte-like cell line (THP -1), we explored the regulatory mechanism to identify the inhibitory site(s ) of 48/80. We determine whether the inhibition results from the blockade o f LPS signaling. 48/80 dose-dependently inhibited LPS-induced TF activity. Chase of LPS-challenged cells with 48/80 also significantly offset TF upreg ulation. In immunofluorescent approaches, FACScan analysis revealed that 48 /80 had no effect on either LPS recognition or the expression of its recept ors (CD14 and CD11b). Moreover, LPS-induced TF expression as well as synthe sis remained unaffected in the presence of 48/80. Consistent with the indep endence of LPS action, 48/80 was also able to inhibit TF activity induced b y A23187, ionomycin, or Quin-2 AM. Interestingly, 48/80 significantly decre ased the FVII binding to either resting or LPS-challenged cells. In conclus ion, our results elucidate that the inhibitory action of 48/80 was independ ent of LPS signaling including recognition, receptor expression, and the in duced TF expression/ synthesis. However, 48/80 was able to directly block F VII binding to monocytic TF, thereby resulting in such antagonism to LPS-in duced TF-initiated extrinsic coagulation. (C) 1999 Published by Elsevier Sc ience B.V. All rights reserved.