Broccoli Consumption Alters Microbial Diversity, Intestinal Gene Expression and Reduces Susceptibility to Bacterial Infection in Mice Fed a Total Western Diet (TWD)

Objectives: Cruciferous vegetables and their derived compounds, such as glucosinolates, have demonstrated anti-inflammatory properties in animal models. The mechanism (s) are unclear, but the gut microbiota may play a role in the metabolism of these compounds into bioactives that influence these pathways. The objectives of the current studies were 1). To examine broccoli diet-induced changes in the gut microbiome and gene expression in animals following consumption of the TWD, which is based on NHANES data and represents the composition of a typical American diet, and 2.) to examine susceptibility to bacterial-induced colitis in animals fed the same diets. Methods: C57BL/6 male mice were fed a TWD for six weeks followed by a supplementation of 0, 0.5, 1 or 2.5% broccoli powder (BP, Koyah) for three weeks. In a second study, mice were infected with Citrobacter rodentium (Cr), after consumption of the same broccoli diets. Fecal excretion of Cr was measured on days 4, 7 and 11 post-infection (PI) to monitor bacterial burden, and the mice were euthanized on day 12 PI. Cecal contents were analyzed by 16S sequencing, and cecum and distal colon tissues were collected for RNASeq analysis. Results: In uninfected mice, α-diversity significantly increased (Simpson Index, p = 0.008) in mice fed the 2.5% BP diet compared to the control group. PERMANOVA analyses showed β-diversity was significantly higher (p ≤ 0.00014 - 0.01236) for mice fed the 2.5% BP diet compared to all other groups. Differential gene expression and associated pathway analysis revealed a >4 fold enrichment of upregulation of genes associated with bile acid, fatty acid and vitamin A metabolism (FDR adjusted p = 1.3e-5, 7.8e-03 and 3.6e-5, respectively) pathways in the colon. In the cecum, activation of the aryl hydrocarbon receptor pathway in the cecum was evident. These pathways are known to influence inflammation and susceptibility to Cr infection. Infected mice fed higher levels of BP had a trend toward lower fecal Cr excretion at day 4 post-infection (p = 0.051) and a significantly lower increase in Cr infection-induced spleen and colon/body weight ratios but Cr clearance was unaffected. Conclusions: Consumption of a broccoli-supplemented TWD changes the gut microbiome and intestinal gene expression which may reduce susceptibility to intestinal infection. Funding Sources: USDA appropriated project #8040-53000-021-000-D.