Interplay Between Cruciferous Vegetables and the Gut Microbiome: A Multi-Omic Approach

Cruciferous vegetable consumption has been associated with a decreased risk of multiple types of cancers, thus presenting a cost-effective, non-pharmacological approach to cancer prevention through dietary intervention. Broccoli sprouts and Brussels sprouts are among the leading cruciferous vegetables under study and contain some similar and some distinct phytochemicals which can activate different, but complementary, mechanisms to promote health. While the cancer-preventative effects of cruciferous vegetables are typically attributed to glucosinolates and their metabolic products, isothiocyanates and indoles, other components of cruciferous vegetables could play a synergistic role in conferring cancer-protective and health promoting effects. Additionally, metabolism of phytochemicals from cruciferous vegetables by the gut microbiome could further lead to the production, inactivation, or clearance of bioactive dietary components. The gut microbiome is essential to the production of bioactive compounds from various food sources. For example, with soy isoflavones and pomegranate urolithins, the presence or absence of specific microbial taxa directly dictates which metabolites are produced. A similar paradigm could be extended to cruciferous vegetables in which the gut microbiome may play an important role in driving inter-individual metabolism of glucosinolates and isothiocyanates.Compounds from cruciferous vegetables are also known to alter microbiome composition and metabolism, suggesting a complex interplay between the microbiome and diet. Additionally, the microbes responsible for metabolism of glucosinolates, and other cruciferous vegetable phytochemicals, are still unclear, representing a major gap in knowledge. Many studies have been conducted in vivo, in human and rodent models, to examine the impact of cruciferous vegetable consumption on the gut microbiome, however, these analyses are typically strictly taxonomical and do not examine specific microbe-metabolite relationships. We recently reported (Bouranis et. al, Nutrients 2021) that the gut microbiome composition can influence production of glucosinolate-derived nitriles from cruciferous vegetables, showing that the presence or absence of specific microbes can influence the abundance of a single metabolite. Thus, we sought to take an untargeted approach to investigate other phytochemicals from cruciferous vegetables which the gut microbiome could play a role in generating. To investigate plant- and microbe-derived metabolites of cruciferous vegetable digestion and capture information about the microbiome, we utilized an ex vivo fecal incubation system. Our goals were to 1) understand the impact of cruciferous vegetables on the gut microbiome, 2) describe changes to the digestive metabolome following cruciferous vegetable consumption and 3) identify relationships between specific members of the gut microbiome and specific metabolites.