Enhanced release of prostaglandin D2 during re-incubation of RAW 264.7 macrophage-like cells after treatment of both lipopolysaccharide and non-steroidal anti-inflammatory drugs.

RAW 264.7 macrophage-like cells are known to release prostaglandins (PGs), mainly PGD(2) to the culture medium after lipopolysaccharide (LPS)-treatment. This release was inhibited by non-steroidal anti-inflammatory drugs (NSAIDs), which are known to inhibit prostaglandin H(2) synthase (PGHS) activity. In this study, we examined the effect of removal of NSAID after induction of PGHS with LPS, on the release of PGs, which has not been studied well. Re-incubation of RAW 264.7 cells after treatment of both LPS and NSAIDs resulted in enhanced release of PGD(2) compared with the cells pretreated with LPS alone. Besides, PGHS activity was detectable in these cell homogenates and the amount of PGHS-2 protein showed similar changes to PGD(2) release. However, addition of NSAIDs again in the re-incubation period almost completely inhibited the PGD(2) release but increased the amount of PGHS-2 protein to the higher levels. Various types of NSAIDs used in this study showed similar effects on the changes in PGD(2) release and PGHS-2 protein amounts, except those on PGHS activity in cell homogenates; while indomethacin, aspirin, and NS-398 inhibited it, but nimesulide and acetaminophen did not. These results seem to suggest an importance for the caution that the enhanced induction of PGHS-2 protein and the concomitant release of PGs release would occur after removal of the NSAID not only from the medium in in vitro experiments but also from therapeutic prescription.