Dietary Walnut Supplementation Alters Mucosal Metabolite Profiles During DSS-Induced Colonic Ulceration

Abstract

Walnuts contain a complex array of natural compounds and phytochemicals that exhibit a wide range of health benefits, including protection against inflammation and colon cancer. In this study, we assess the effects of dietary supplementation with walnuts on colonic mucosal injury induced in mice by the ulcerogenic agent, dextran sodium sulfate (DSS). C57Bl/6J mice were started on the Total Western Diet supplemented with freshly-ground whole walnuts (0, 3.5, 7 and 14% g/kg) 2 weeks prior to a 5-day DSS treatment and walnut diets were continued throughout the entire experimental period. Mice were examined at 2 days or 10 days after withdrawal of DSS. In a separate study, a discovery-based metabolite profiling analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) was performed on fecal samples and colonic mucosa following two weeks of walnut supplementation. Dietary walnut supplementation showed significant effects in the 10-day post-DSS recovery-phase study, in which the extent of ulceration was significantly reduced (7.5% vs. 0.3%, p < 0.05) with 14% walnuts. In the metabolite-profiling analysis, walnuts caused a significant increase in several polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid (DHA) and 9-oxo-10(E),12(E)-octadecadienoic acid (9-oxoODA), as well as kynurenic acid. In colon tissue samples, walnuts caused a significant increase in the levels of S-adenosylhomocysteine (SAH) and betaine, important components of fatty acid β-oxidation. These metabolite changes may contribute in part to the observed protection against DSS-induced inflammatory tissue injury.

Keywords: Inflammatory Bowel Disease; inflammation; lipid metabolites; omega-3 fatty acids; ulcerative colitis; walnuts.

Figure 1

Effects of walnut supplementation on DSS-induced acute colitis. (a) Experimental design for the acute phase study. TWD diet supplemented with 0, 3.5, 7 or 14% walnuts was started two weeks prior to the administration of 2% DSS. Mice were sacrificed 2 days after the withdrawal of DSS. The effects of walnut supplementation were examined on the following clinical endpoints: body weight change (b), linear-regression analyses of spleen weight (c) and colon length (d). DSS-induced colonic ulceration (e), with signs of restitution (f) and crypt formation (g). There was significantly less ulceration with 14% walnuts (h). Extent of colonic ulceration and restitution were scored as a percent of the entire length of the colon for each group (i). Bars represent the means ± SEM n = 9 for 0%, n = 9 for 3.5% and n = 10 for 7% and 14%. * One-way ANOVA with Bonferroni’s multiple comparison tests, p < 0.05.

Figure 2

Effects of walnut supplementation on the recovery from dextran sodium sulfate (DSS)-induced colitis. (a) Experimental design for the recovery phase study. Total Western Diet (TWD) supplemented with 0, 3.5, 7 or 14% walnuts was started two weeks prior to the administration of 1% DSS. Mice were sacrificed 10 days after the withdrawal of DSS. The effects of walnut supplementation were examined on the following clinical endpoints: body weight change (b), linear-regression analyses of spleen weight (c) and colon length (d). The effects of walnut concentration on recovery from DSS induced colitis is shown for 0% (e) 3.5% (f) 7% (g) and 14% walnuts (h). The extent of ulceration and restitution were scored as the percent of the entire length of colon for each group (i). Bars represent the means ± SEM. n = 6 for 0%, n = 9 for 3.5% and n = 10 for 7% and 14%. * One-way ANOVA with Bonferroni’s multiple comparison tests, p < 0.05.