Objective: To investigate the effect of changed ratio of polyunsaturated fatty acids (PUFA) on dextran sulfate sodium (DSS)-induced colitis in mice.
Methods: Thirty-two male BALB/c mice were randomly divided into two groups: control group and PUFA group, PUFA group was continuously divided into 3 sub-groups: PUFA ω-3/ω-6 1:3 group, PUFA ω-3/ω-6 1:15 group and PUFA ω-3/ω-6 1:30 group. According to the difference in the sub-groups, PUFA group mice were fed with the corresponding modified diet. The control group was fed with the common diet, whose ratio of PUFA ω-3/ω-6 was 1:15. After eight weeks of different diets, experimental colitis in the three sub-groups of PUFA group was induced by DSS exposure. The mice were placed on three five-day cycles of 30 g/L DSS with ten days of recovery after each cycle, then were sacrificed after the final ten-day period. Overall symptomatic score and histopathological score were evaluated. And levels of mucosal prostaglandin E2 (PGE2) in the proximal and distal colon were measured respectively by enzyme immunoassay.
Results: The changed ratio of PUFA ω-3/ω-6 had no effect on the weight gain of the growing mice. Although there were no significant differences among the PUFA groups from the three separate aspects: weight gain, stool character and blood in the stool, there were significant differences among the three groups in overall symptomatic scores. A further comparison showed the overall symptomatic score of 1:3 group was significantly lower than that of the 1:30 group (P<0.05). There were significant differences among the PUFA groups in the histopathological score. The following comparison between the sub-groups showed the histopathological score of the 1:3 group was significantly lower than that of the 1:30 group (P<0.05). One mouse in the 1:30 group died of severe hemorrhage and one mouse also in this group had a huge dysplastic adenomatous polyp. The mucosal PGE2 which could reflect the level of intestinal inflammation showed that in the distal colon, the inflammations were obvious, and the levels of mucosal PGE2 of the distal colon in the 1:15 group [(153.0 ± 49.4) ng/g tissue] and the 1:30 group [(192.4 ± 94.0) ng/g tissue] were significantly higher than that of the control group [(43.2 ± 13.4) ng/g tissue, P<0.05], but there was no significant difference between the 1:3 group [(43.4 ± 8.2) ng/g tissue] and the control group. Although the mucosa damages were sparing in proximal colon, the level of mucosal PGE2 of the proximal colon in 1:30 group [(97.4 ± 64.8) ng/g tissue] markedly increased as compared with the control group [(21.6 ± 16.0) ng/g tissue, P<0.01], there were no differences among the 1:3 group [(36.6 ± 4.6) ng/g tissue], the 1:15 group [(18.8 ± 6.4) ng/g tissue] and the control group.
Conclusion: The colonic inflammatory severity and the level of mucosal PGE2 in the experimental colitis mice were affected by the changed ratio of PUFA ω-3/ω-6 in the feed. Increased ratio of PUFA ω-3/ω-6 in the feed had a protective effect on the intestinal mucosa in the experimental colitis mice, otherwise had hazards. Before the inflammation happened, changed ratio of PUFA ω-3/ω-6 firstly altered the local inflammatory factors, such as PGE2, and then affected the inflammatory severity.