Fish oil augments macrophage cyclooxygenase II (COX-2) gene expression induced by endotoxin

Background. Fish oil-supplemented diets have antiinflammatory and immunomodulating effects. Although fish oil is readily incorporated into the cell membrane and influences the production of eicosanoids, the exact mechanism is not clear. This study was designed to investigate the effects of eicosapentaenoic acid (EPA), a major component of fish oil, on macrophage (M phi) cyclooxygenase (COX) gene expression induced by LPS. Methods. RAW 264.7 cells, a mouse M phi cell line, were grown in EPA-rich media for 24 h, M phi were washed and exposed to Escherichia coli LPS (10 mu g/ml). Membrane lipid profile was determined by gas chromatographic analysis. COX-1 and COX-2 mRNA expressions were determined by Northern blot assays with mouse-specific cDNA probes. PGE(2) production of M phi was measured by ELISA. M phi production of COX-2 protein was determined by Western blot assays with an anti-COX-2 antibody. Results. Incubation in EPA-rich media increased membrane EPA and decreased arachidonic acid (AA) composition. COX-2 mRNA expression was induced by EPA and further augmented by LPS stimulation. EPA also augmented M phi production of COX-2 protein. In comparison, COX-1 mRNA expression was not affected by either LPS stimulation or EPA incubation. EPA reduced PGE(2) production by LPS-stimulated M phi. To further support that COX-2 mRNA was regulated by COX product, exogenous PGE(2) was added to M phi prior to LPS stimulation. PGE(2) reduced COX-2 mRNA of LPS-stimulated M phi. Conclusion. EPA displaces AA and reduces PGE(2) production by LPS-stimuIated M phi. Fish oil inhibition of M phi PGE(2) production induces COX-2 mRNA expression through a COX-2 product-mediated feedback mechanism. (C) 1999 Academic Press.