Arachidonic acid enhances the tissue factor expression of mononuclear cells by the cyclo-oxygenase-1 pathway: beneficial effect of n-3 fatty acids.

Monocytes express tissue factor (TF) upon stimulation by inflammatory agents. Dietary administration of fish oil rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) results in an impairment of TF expression by monocytes. EPA and DHA are metabolized differently from arachidonic acid (AA), the major fatty acid present in cell membranes. We examined the effects of AA on the TF expression of isolated human PBMC, and we determined whether EPA and DHA modulated this phenomenon differently. Nonstimulated PBMC had a low TF-dependent procoagulant activity. When PBMC were incubated with increasing concentrations of AA, the TF-dependent procoagulant activity increased in a dose-dependent manner to 190% at 7.5 microM. Indomethacin, a cyclo-oxygenase inhibitor, totally abolished the stimulating effect of AA, whereas specific pharmacologic inhibitors of cyclo-oxygenase-2 or of 5-lipoxygenase had no inhibitory effect. A thromboxane (TX)A2/endoperoxides receptor antagonist and a TX synthase inhibitor blocked the potentiating effect of AA. Purified PGG2 and carbocyclic TXA2, a TXA2 agonist, enhanced the procoagulant activity of PBMC in a dose-dependent manner whereas, in contrast, PGE2 inhibited it. Finally, contrary to AA, EPA or DHA did not increase TXB2 production or TF expression by PBMC. The TF-dependent procoagulant activity of isolated PBMC was increased by AA through the production of cyclo-oxygenase-1 metabolites; the combined action of PGG2 and TXA2, which potentiated it, was greater than that of PGE2, which inhibited it. Dietary n-3 fatty acids exert part of their beneficial effect by modulating this procoagulant activity differently from AA.