Docosahexaenoic acid potentiates interleukin-1β induction of nitric oxide synthase through mechanism involving p44/42 MAPK activation in rat vascular smooth muscle cells

1 The effect of docosahexaenoic acid (DHA) on nitric oxide (NO) production and inducible NO synthase (iNOS) expression induced by interleukin (IL)-1beta, and whether the effect of DHA is related to its effect on mitogen-activated protein kinase (MAPK) activation were investigated in cultured rat vascular smooth muscle cells (VSMCs). 2 DHA and eicosapentaenoic acid (EPA), although less potent, increased the NO production induced by IL-1beta (3 ng ml(-1)) in a concentration-dependent manner (3 - 30 muM) Arachidonic acid had no significant effect. The stimulatory effect of DHA (30 muM) on the NO production was more obvious at lower concentrations of IL-1beta. 3 IL-1beta induced iNOS protein and mRNA expressions, which were significantly potentiated by DHA. EPA (30 muM) had a tendency to increase the iNOS protein and mRNA expressions, but arachidonic acid had no effect. 4 IL-1beta-induced iNOS protein expression was significantly inhibited by PD 98059 (10 muM), a selective inhibitor of p44/42 MAPK kinase, both in the absence and the presence of DHA. SB 203580 (10 muM), a selective inhibitor of p38 MAPK activity, had no significant effect, although had a tendency to inhibit slightly. 5 IL-1beta increased the phosphorylation of p44/42 MAPK, while it did not apparently increase the phosphorylation of p38 MAPK. DHA significantly potentiated the IL-1beta-induced phosphorylation of p44/42 MAPK, while it had no significant effect on the phosphorylation of p38 MAPK. 6 These results suggest that DHA increases NO production by potentiating iNOS expression induced by IL-1beta through mechanism involving p44/42 MAPK signalling cascade in rat VSMCs. The present study may contribute to the understanding of basic mechanisms underlying the beneficial effects of DHA on various cardiovascular disorders.