A soybean and fish oil mixture with different n-6/n-3 PUFA ratios modulates the inflammatory reaction in mice with dextran sulfate sodium-induced acute colitis

Inflammatory bowel disease is a recurrent disease of the gastrointestinal tract. n-3 polyunsaturated fatty acids (PUFAs) are proved to have anti-inflammatory and immunomodulatory properties. This study evaluated the effects of different dietary n-6/n-3 PUFA ratios on the mechanism of alleviating the inflammatory response in mice with dextran sulfate sodium (DSS)-induced colitis. Methods: Mice were randomly assigned to 6 groups including 3 non-colitis groups (C, LF, and HF) and 3 colitis groups (DC, DLF, and DHF). Mice in the C and DC groups were fed a common semipurified diet with soybean oil as the fat source. The other groups received an identical component except that part of the soybean oil was replaced by different amounts of fish oil. The n-6/n-3 PUFA ratio of the LF and DLF groups was 4:1, the ratio of the HF and DHF groups was 2:1. After feeding the respective diets for 2 weeks, the colitis groups were given distilled water containing 2% DSS, while the non-colitis groups were given distilled water for 5 days. After that, all mice were sacrificed at the recovery phase after drinking distilled water for another 5 days. Results: Colitis resulted in higher expressions of colonic inflammatory mediators in colon tissues and colon lavage fluid. Also, colonic peroxisome proliferator-activated receptor (PPAR)-γ and the IκBα/nuclear factor (NF)-κB p65 ratio were lower than those of the non-colitis groups. Compared to the DC group, fish oil-enriched colitis groups had lower inflammatory mediator expressions and higher PPAR-γ protein levels and IκBα/NF-κB p65 ratios in colon tissues. The DHF group had even lower colonic inflammatory gene and higher PPAR-γ protein expressions than did the DLF group. Conclusions: These findings suggest that diets enriched with fish oil upregulated PPAR-γ and decreased NF-κB activation that may consequently have reduced luminal inflammatory mediator production. Compared to a n-6/n-3 PUFA ratio 4:1, a ratio of 2:1 was more effective in reducing inflammatory reactions in DSS-induced colitis.