CHARACTERIZATION OF CYCLOOXYGENASE-1 AND CYCLOOXYGENASE-2 EXPRESSION IN MOUSE RESIDENT PERITONEAL-MACROPHAGES IN-VITRO - INTERACTIONS OF NON STEROIDAL ANTIINFLAMMATORY DRUGS WITH COX2

Resident peritoneal macrophages exposed to inflammatory stimuli (zymos an, lipopolysaccharide (LPS)) represent a widely used model for studyi ng arachidonic acid metabolism and for screening of prostaglandin (PG) synthesis inhibitors. In the present study, cyclooxygenase 1 (COX1) w as shown constitutively expressed in mouse adherent and non-adherent m acrophages whereas expression of COX2 was observed only in adherent ce lls, even when cultured in minimal conditions (Ca-, Mg- and serum-free medium). The COX2 expression was amplified by arachidonic acid cascad e stimulating agents (Ca, Mg, zymosan) and by LPS in a time-dependant manner; PGE2 by itself amplified LPS-induced COX2 expression. In well- defined experimental conditions of COX2 expression (LPS-stimulated adh erent macrophages), we studied specific interactions of some represent ative anti-inflammatory drugs with COX2 enzymatic activity and express ion, By contrast with dexamethasone, which reduced PGE2 release togeth er with a strong reduction of COX2 expression (protein and mRNA), non steroidal anti-inflammatory drugs (NSAIDs) reduced PGE2 synthesis with out any effect at the COX2 mRNA level, This reduction of PGE2 producti on by NSAIDs resulted from either an exclusive enzymatic inhibition (a spirin, NS398, 6-Methoxy naphtyl acetic acid) or an enzymatic inhibiti on associated with a slight decrease of COX2 protein level (indomethac in). For paracetamol and salicylic acid, two weak inhibitors of COX en zymatic activity, reduction of PGE2 synthesis appeared to be related t o reduced level of COX2. These findings show that the macrophage can b e used as a cellular model to study specifically COX1 and COX2. In thi s cell type, COX2 expression is dependent on adhesion, enhanced by sti mulation of arachidonic acid metabolism and auto amplified by PGE2. Fu rthermore, the results indicate that known NSAIDs differ in their inte raction with cyclooxygenase, being able to inhibit either COX2 enzymat ic activity, and/or COX2 expression, However, further studies are requ ired to determine the mechanism and the role of COX2 expression during inflammation in vivo, and to define more precisely the best target fo r new potent and safe NSAIDs.