Fish oil modulates macrophage P44/P42 mitogen-activated protein kinase activity induced by lipopolysaccharide

Background: Mitogen-activated protein kinase (MAPK) cascades represent a ma jor signal system to transduce extracellular signals into cellular response s. Overactivity of MAPK has been implicated in the development of many dise ases, including cancer and sepsis. This study investigated the hypothesis t hat fish oil altered the membrane phospholipid composition and modulated MA PK activity. Methods: RAW 264.7 cells, a mouse macrophage (M phi) cell line , were grown in eicosapentaenoic acid (EPA)-rich media (114 mu mol/L) for 4 8 hours. M phi were washed and exposed to Escherichia coli lipopolysacchari de (LPS; 1 mu g/mL) for 10 minutes. Both total and activated (phosphorylate d) portions of MAPK (P44 and P42) were determined by Western blot assays. A P-1 transcription factor activity was determined by electrophoretic mobilit y gel shift assays (EMSA). M phi tumor necrosis factor (TNF) mRNA expressio n was measured by Northern blot assays. Results: LPS stimulation induced RA W cell phosphorylation of P44/P42. In contrast, RAW cells grown in EPA-rich media had less P44/P42 activation in the presence of LPS. Total P44/P42 we re not affected by EPA or LPS. Similarly, EPA also inhibited AP-1 activity. Inhibition of P44/P42 activity with PD98059 reduced both AP-1 activity and TNF mRNA expression of LPS-stimulated M phi. Conclusions: Our data suggest that fish oil regulates macrophage proinflammatory gene activation, at lea st in part, by modulating the MAPK activity.