Abstract 4243: Dietary flavonoids prevent colon tumor formation in ApcMin/+ mice in a microbiome- and sex-dependent manner

Background: A diet rich in colorful fruits and vegetables is effective for the prevention of various inflammation-induced cancer types. Mechanistically, this effect has been attributed to the potent antioxidant properties of flavonoid molecules. However, contrary to observations in mice, the success of flavonoids in human dietary cancer prevention trials is often dampened due to large interpersonal variation. Antioxidant activity alone does not explain this variability, suggesting there is an additional important variable that has not been accounted for. Since flavonoids have a poor bioavailability and predominantly passage into the large intestine, we hypothesize that gut microbial metabolism is essential for flavonoid bioactivity in colon cancer prevention.

Goals and Objectives: The goal of this study was to evaluate the impact of microbiota composition on the efficacy of dietary flavonoids in preventing intestinal tumorigenesis.

Methods: We used the adenomatous polyposis coli - multiple intestinal neoplasia (ApcMin/+) mouse model, which is genetically predisposed to develop adenomas along its gastrointestinal tract. Development of these adenomas and eventual adenocarcinoma formation is further influenced by factors such as inflammation, dietary input and the gut microbiota. Animals were fed a control high fat diet (HFD) or prevention diets consisting of 1% berry extract, 1% purified flavonoid or 1% microbial catabolite, all on the HFD background. The contribution of the microbiota was modelled by including experimental groups that received an antibiotic cocktail in their drinking water throughout the course of the experiment. For these animals, microbiota community composition was determined by 16S rRNA sequencing, plasma was collected for histological profiling and metabolomics analysis and end-point measurements of intestinal tumor numbers and size were performed.

Results: Supplementation with berry extract significantly reduced colon tumor numbers and incidence in male, but not in female mice. This effect was negated in mice on antibiotic drinking water, implicating the involvement of the gut microbiota. Community analysis revealed a relative increase in Erysipelotrichaceae, Clostridia and Akkermansia in the berry supplemented versus HFD control mice. In addition, their systemic monocyte counts were reduced. Dietary supplementation with a major gut microbial flavonoid catabolite, did not reduce colon tumor formation, suggesting the functional involvement of different microbial metabolites.

Conclusions: Our study demonstrates the involvement of the mouse gut microbiota in dietary prevention of colon tumor formation. These effects impact circulating monocytes and are linked to changes in the plasma metabolome. We are currently elucidating the microbial actors and associated molecular pathways involved.

Citation Format: Beckey DeLucia, Jan Claesen. Dietary flavonoids prevent colon tumor formation in ApcMin/+ mice in a microbiome- and sex-dependent manner. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4243.

A gut microbial metabolite of dietary polyphenols reverses obesity-driven hepatic steatosis

The molecular mechanisms by which dietary fruits and vegetables confer cardiometabolic benefits remain poorly understood. Historically, these beneficial properties have been attributed to the antioxidant activity of flavonoids. Here, we reveal that the host metabolic benefits associated with flavonoid consumption hinge, in part, on gut microbial metabolism. Specifically, we show that a single gut microbial flavonoid catabolite, 4-hydroxyphenylacetic acid (4-HPAA), is sufficient to reduce diet-induced cardiometabolic disease (CMD) burden in mice. The addition of flavonoids to a high fat diet heightened the levels of 4-HPAA within the portal plasma and attenuated obesity, and continuous delivery of 4-HPAA was sufficient to reverse hepatic steatosis. The antisteatotic effect was shown to be associated with the activation of AMP-activated protein kinase α (AMPKα). In a large survey of healthy human gut metagenomes, just over one percent contained homologs of all four characterized bacterial genes required to catabolize flavonols into 4-HPAA. Our results demonstrate the gut microbial contribution to the metabolic benefits associated with flavonoid consumption and underscore the rarity of this process in human gut microbial communities.

A 3D-printable device allowing fast and reproducible longitudinal preparation of mouse intestines

Accurate and reproducible analysis of murine small and large intestinal tissue is key for preclinical models involving intestinal pathology. Currently, there is no easily accessible, standardized method that allows researchers of different skill levels to consistently dissect intestines in a time-efficient manner. Here, we describe the design and use of the 3D-printed "Mouse Intestinal Slicing Tool" (MIST), which can be used to longitudinally dissect murine intestines for further analysis. We benchmarked the MIST against a commonly used procedure involving scissors to make a longitudinal cut along the intestines. Use of the MIST halved the time per mouse to prepare the intestines and outperformed alternative methods in smoothness of the cutting edge and overall reproducibility. By sharing the plans for printing the MIST, we hope to contribute a uniformly applicable method for saving time and increasing consistency in studies of the mouse gastrointestinal tract.

A surgical method for continuous intraportal infusion of gut microbial metabolites in mice

Gut microbe–derived metabolites influence human physiology and disease. However, establishing mechanistic links between gut microbial metabolites and disease pathogenesis in animal models remains challenging. The major route of absorption for microbe-derived small molecules is venous drainage via the portal vein to the liver. In the event of presystemic hepatic metabolism, the route of metabolite administration becomes critical. To our knowledge, we describe here a novel portal vein cannulation technique using a s.c. implanted osmotic pump to achieve continuous portal vein infusion in mice. We first administered the microbial metabolite trimethylamine (TMA) over 4 weeks, during which increased peripheral plasma levels of TMA and its host liver-derived cometabolite, trimethylamine-N-oxide, were observed when compared with a vehicle control. Next, 4-hydroxyphenylacetic acid (4-HPAA), a microbial metabolite that undergoes extensive presystemic hepatic metabolism, was administered intraportally to examine effects on hepatic gene expression. As expected, hepatic levels of 4-HPAA were elevated when compared with the control group while peripheral plasma 4-HPAA levels remained the same. Moreover, significant changes in the hepatic transcriptome were revealed by an unbiased RNA-Seq approach. Collectively, to our knowledge this work describes a novel method for administering gut microbe–derived metabolites via the portal vein, mimicking their physiologic delivery in vivo.