Anti-inflammatory effect of alpha-linolenic acid and its mode of action through the inhibition of nitric oxide production and inducible nitric oxide synthase gene expression via NF-kappaB and mitogen-activated protein kinase pathways.

Alpha-linolenic acid (ALA) isolated from Actinidia polygama fruits exhibits potent anti-inflammatory activity with an unknown mechanism. To elucidate the molecular mechanisms of ALA on pharmacological and biochemical actions in inflammation, we examined the effect of ALA on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in the murine macrophages cell line, RAW 264.7. We found that ALA has a strong inhibitory effect on the production of NO. ALA also inhibited inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and tumor necrosis factor-alpha (TNF-alpha) gene expressions induced by LPS. To explore the mechanisms associated with the inhibition of iNOS gene expression by ALA, we investigated its effect on LPS-induced nuclear factor-kappaB (NF-kappaB) activation. Treatment with ALA reduced a translocation of NF-kappaB subunit and NF-kappaB-dependent transcriptional activity. The activation of NF-kappaB was inhibited by prevention of the degradation of inhibitory factor-kappaBalpha. We also found that ALA inhibited LPS-induced phosphorylation of mitogen-activated protein kinases (MAPKs). In addition, the antinociceptive effect of ALA was also assessed by means of the acetic acid-induced abdominal constriction test and Randall-Selitto assay. ALA (5 and 10 mg/kg) showed the potent antinociceptive effects in these animal models. Taken together, these results suggest that ALA downregulates inflammatory iNOS, COX-2, and TNF-alpha gene expressions through the blocking of NF-kappaB and MAPKs activations in LPS-stimulated RAW 264.7 cells, which may be the mechanistic basis for the anti-inflammatory effect of ALA.