Dietary supplementation of arachidonic acid increases arachidonic acid and lipoxin A(4) contents in colon, but does not affect severity or prostaglandin E(2) content in murine colitis model

BACKGROUND: Arachidonic acid (ARA) is an essential fatty acid and a major constituent of biomembranes. It is converted into various lipid mediators, such as prostaglandin E(2) (PGE(2)) and lipoxin A(4) (LXA(4)). The effects of dietary ARA on colon maintenance are unclear because PGE(2) has both mucosal protective and proinflammatory effects, and LXA(4) has an anti-inflammatory role. Our objective is to clarify the effects of dietary ARA on an experimental murine colitis model. METHODS: C57BL/6 mice were fed three types of ARA diet (0.075%, 0.15% or 0.305% ARA in diet), DHA diet (0.315% DHA) or control diet for 6 weeks, and were then administered dextran sodium sulphate (DSS) for 7 days to induce colitis. We evaluated colitis severity, fatty acid and lipid mediator contents in colonic tissue, and the expression of genes related to lipid mediator formation. RESULTS: ARA composition of colon phospholipids was significantly elevated in an ARA dose-dependent manner. ARA, as well as DHA, did not affect colitis severity (body weight loss, colon shortening, diarrhea and hemoccult phenomena) and histological features. PGE(2) contents in the colon were unchanged by dietary ARA, while LXA(4) contents increased in an ARA dose-dependent manner. Gene expression of cyclooxygenase (COX)-1 and COX-2 was unchanged, while that of 12/15-lipoxgenase (LOX) was significantly increased by dietary ARA. ARA composition did not correlate with neither colon length nor PGE(2) contents, but significantly correlated with LXA(4) content. CONCLUSION: These results suggest that dietary ARA increases ARA and LXA(4) contents in colon, but that it has no effect on severity and PGE(2) content in a DSS-induced murine colitis model.