Dietary Supplementation with Black Raspberries Altered the Gut Microbiome Composition in a Mouse Model of Colitis-Associated Colorectal Cancer, although with Differing Effects for a Healthy versus a Western Basal Diet

Abstract

Black raspberries (BRB) are rich in anthocyanins with purported anti-inflammatory properties. However, it is not known whether dietary supplementation would ameliorate Western-diet enhanced gut inflammation and colon tumorigenesis. We employed a mouse model of colitis-associated colorectal cancer (CAC) to determine the effects of dietary supplementation with 5 to 10% (w/w) whole, freeze-dried BRB in male C57BL/6J mice fed either a standard healthy diet (AIN93G) or the total Western diet (TWD). In a pilot study, BRB suppressed colitis and colon tumorigenesis while also shifting the composition of the fecal microbiome in favor of taxa with purported health benefits, including Bifidobacterium pseudolongum. In a follow-up experiment using a 2 ´ 2 factorial design with AIN and TWD basal diets with and without 10% (w/w) BRB, supplementation with BRB reduced tumor multiplicity and increased colon length, irrespective of the basal diet, but it did not apparently affect colitis symptoms, colon inflammation or mucosal injury based on histopathological findings. However, BRB intake increased alpha diversity, altered beta diversity and changed the relative abundance of Erysipelotrichaceae, Bifidobacteriaceae, Streptococcaceae, Rikenellaceae, Ruminococcaceae and Akkermansiaceae, among others, of the fecal microbiome. Notably, changes in microbiome profiles were inconsistent with respect to the basal diet consumed. Overall, these studies provide equivocal evidence for in vivo anti-inflammatory effects of BRB on colitis and colon tumorigenesis; yet, BRB supplementation led to dynamic changes in the fecal microbiome composition over the course of disease development.

Basal Diet Fed to Recipient Mice Was the Driving Factor for Colitis and Colon Tumorigenesis, despite Fecal Microbiota Transfer from Mice with Severe or Mild Disease

“…11562). The husbandry procedures and facilities for housing the mice were exactly the same as described in a previous study [ 22 ].…”

“…The principal research question of this study is whether the fecal microbiome associated with a Western diet enhances colitis symptoms, colon tumorigenesis, and microbiome modulation, when it is transferred into recipient mice fed either a healthy diet (AIN93G) or the total Western diet (TWD). Fecal material was collected weekly in a previous study [ 22 ] from mice that were fed either the AIN basal diet or the TWD in a longitudinal study employing the AOM + DSS model of chemical carcinogenesis ( Figure S1a ) and was used for FMT to recipients, as outlined below. The fecal samples were collected and stored in a −80 °C freezer.…”

“…TD.180497), the formulation of which was previously published [ 7 ], with an energy density of 4.4 kcal/g, and which was designed to emulate typical macro- and micronutrient intakes on an energy density basis. The diets were administered, and food intake was monitored as previously described [ 22 ].…”

“…The protocol for inducing colitis and colon tumorigenesis had been described in a previous study [ 22 ] and was followed in this experiment with only slight modifications. On day 14, the mice were dosed i.p.…”

“…While multiple studies have pointed to gut dysbiosis as a common feature of colitis and/or colon tumorigenesis in humans and animal models, it is not clear whether changes in the gut microbiome composition associated with different nutritional patterns are the drivers of this disease process, leading to the progression from initial inflammation to neoplasia and then advanced tumorigenesis. Therefore, to better understand the involvement of the microbiome in the development and/or exacerbation of colitis and colon tumorigenesis, we designed an FMT experiment using fecal material collected from a prior study, in which donor mice were fed either the AIN93G diet or the TWD and subjected to our standard protocol for mouse CAC [ 22 ]. This experimental design incorporated the standard AIN93G diet or the total Western diet for the donor animals as well as for the recipient mice in a 2 × 2 factorial design.…”