COX-1 and COX-2 contribute differentially to the LPS-induced release of PGE2 and TxA2 in liver macrophages.

LPS induces an immediate release of thromboxane TxA2 and a delayed release of PGE2. Dexamethasone suppresses the LPS-induced release of TxA2 and PGE2. In the first 8 h after LPS addition, the specific COX-2 inhibitor SC236 inhibits the PGE2 and TxA2 release by about 80% and 20%, whereas the release of PGE2 and TxA2 between 8 and 24 h is inhibited by about 40% and 35%, respectively. Resident liver macrophages express substantial amounts of COX-1, TxAS, cPGES and mPGES-2, small amounts of COX-2 but almost no detectable amounts of mPGES-1. LPS induces an increase of COX-2 and mPGES-1, but does not change COX-1, cPGES, mPGES-2 and TxAS at protein level. Dexamethasone suppresses almost completely the LPS-induced effects on COX-2 and mPGES-1. It is concluded that (1) COX-1 and COX-2 are involved in the LPS-induced synthesis of TxA2 and PGE2; (2) TxA2 release is catalyzed at early time-points by the combined action of COX-1 and TxAs, whereas at later time points the newly expressed COX-2 couples to TxAS and contributes to the TxA2 release; (3) PGE2 release within the first 8 h is predominantly catalyzed by COX-2, whereas at later time-points COX-1 couples to the newly expressed mPGES-1 and contributes to the PGE2 release.

PGE2 exerts its effect on the LPS-induced release of TNF-alpha, ET-1, IL-1alpha, IL-6 and IL-10 via the EP2 and EP4 receptor in rat liver macrophages.

Lipopolysaccharide (LPS) induces a release of tumor necrosis factor (TNF)-alpha, endothelin (ET)-1, interleukin (IL)-1alpha, IL-6 and IL-10 in rat liver macrophages (Kupffer cells). Prostaglandin (PG)E2 inhibits the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and enhances the release of the anti-fibrogenic mediators IL-6 and IL-10. This effect of PGE2 is mimicked by specific agonists for the PGE2 receptors EP2 and EP4; whereas, agonists for the PGE2 receptors EP1 and EP3 are inactive. Rat liver macrophages express mRNA encoding the PGE2 receptors EP2 and EP4 but not the PGE2 receptors EP1 and EP3. These data suggest that PGE2 exerts its anti-fibrogenic effect through the EP2 and EP4 receptor by inhibiting the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and by enhancing the release of the anti-fibrogenic mediators IL-6 and IL-10 in liver macrophages.

Diverse functional coupling of cyclooxygenase 1 and 2 with final prostanoid synthases in liver macrophages.

Lipopolysaccharide (LPS) treatment of resident liver macrophages resulted in a coordinated enhanced expression of cytosolic phospholipase A(2) (cPLA(2)), cyclooxygenase (COX)-2 and prostaglandin E(2)-synthase. LPS-pretreated liver macrophages showed a higher release of PGE(2) after zymosan, phorbol ester and A23187, of PGF(2alpha) after zymosan and A23187, whereas the release of thromboxane B(2) and PGD(2) was unchanged. Inhibition of COX-1 and -2 by specific inhibitors (SC560, SC236) inhibited the prostanoid release between 50-80% and 20-40%, respectively, indicating a predominant role for COX-1. In detail (1) the zymosan-induced release of all prostanoids was inhibited to a similar degree by the COX-1 inhibitor (about 70%) and the COX-2 inhibitor (20-30%), (2) PGE(2) release after all stimuli was inhibited to a greater extent by SC560 (70-90%) compared to SC236 (5-30%), (3) the phorbol ester- and A23187-induced release of PGF(2alpha) and PGD(2) was inhibited equally (40-50%) by both inhibitors, (3) TxB(2) release after phorbol ester and A23187 was inhibited by SC560 by 50 and 30%, and by SC236 by 50 and 70%, respectively. cPLA(2), COX-1 and -2, and the final prostanoid synthases were found in different subcellular fractions. These results indicate, that the functional coupling of COX-1 and -2 to final prostanoid synthases depends on the stimulation of the cells.