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.

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.