Zymosan-induced glycerylprostaglandin and prostaglandin synthesis in resident peritoneal macrophages: roles of cyclo-oxygenase-1 and -2

COX [cyclo-oxygenase; PG (prostaglandin) G/H synthase] oxygenates AA (arachidonic acid) and 2-AG (2-arachidonylglycerol) to endoperoxides that are converted into PGs and PG-Gs (glycerylprostaglandins) respectively. In vitro, 2-AG is a selective substrate for COX-2, but in zymosan-stimulated peritoneal macrophages, PG-G synthesis is not sensitive to selective COX-2 inhibition. This suggests that COX-1 oxygenates 2-AG, so studies were carried out to identify enzymes involved in zymosan-dependent PG-G and PG synthesis. When macrophages from COX-1^−/− or COX-2^−/− mice were treated with zymosan, 20–25% and 10–15% of the PG and PG-G synthesis observed in wild-type cells respectively was COX-2 dependent. When exogenous AA and 2-AG were supplied to COX-2^−/− macrophages, PG and PG-G synthesis was reduced as compared with wild-type cells. In contrast, when exogenous substrates were provided to COX-1^−/− macrophages, PG-G but not PG synthesis was reduced. Product synthesis also was evaluated in macrophages from cPLA_2α (cytosolic phospholipase A_2α)^−/− mice, in which zymosan-induced PG synthesis was markedly reduced, and PG-G synthesis was increased approx. 2-fold. These studies confirm that peritoneal macrophages synthesize PG-Gs in response to zymosan, but that this process is primarily COX-1-dependent, as is the synthesis of PGs. They also indicate that the 2-AG and AA used for PG-G and PG synthesis respectively are derived from independent pathways.