Colorectal cancer has the second highest mortality rate of all cancers and recent studies indicate that increasing the amount of plant-based foods in the diet could prevent 70% of colorectal cancers. Rice bran can prevent colonic tumor development in carcinogen-induced colon cancer models and promote cell death of human colon cancer cells, however little is known regarding the interactions between rice bran phytochemicals and intestinal microbes as a mechanism to elicit these preventive effects. Bioactive rice bran components may reduce inflammation as they are novel substrates for colonic microorganisms that produce short chain fatty acids (SCFA) and other anti-inflammatory metabolites. Chemopreventive rice bran chemicals include, but are not limited to phytate, gamma-oryzanol, ferulate and phytosterols and phenolics. The mechanisms of gut fermentation and microbial metabolic by-products resulting from dietary rice bran intake have not been previously examined for colonic chemoprevention. A significant gap in our knowledge exists regarding the microbial metabolites produced following dietary rice bran intake. We hypothesize that rice bran phytochemicals will stimulate populations of beneficial microbes in the colon that produce anti-inflammatory SCFA and/or metabolize rice bran components, such as gamma-oryzanol to its bioactive metabolite ferulic acid via the activity of microbial ferulate esterases. The proposed research project will identify the change in microbes and metabolites found in stool using 454 pyrosequencing, qPCR, and metabolomics techniques. Examination of changes in bacterial flora that alter metabolism of rice bran components will advance our understanding of the dietary potential for rice bran consumption to reduce colon cancer risk. Advances in high-throughput DNA sequencing and microbe-specific data analysis tools allows for culture-independent comparisons between diverse human fecal samples and for defining changes in microbes from numerous genera. Integrating this information with changes in the fecal metabolome represents an innovative approach for determining how rice bran chemicals mitigate and/or prevent colonic inflammation. The collection of stool samples following increased rice bran intake (30 g/day for 28 days) or placebo control intake in colon cancer survivors is proposed in Aim 1, and we will determine how daily rice bran intake modulates fecal microbial community structure in Aim 2.
Aim 3 will examine fecal metabolites from rice bran intake compared to control levels and will assess the effects of fecal metabolite extracts on colon cancer viability. Major outcomes from this study will be the identification of specific gut microbes and metabolites modulated by dietary rice bran intake. These findings will serve as critical, pilot data on rice bran-mediated changes in microbial metabolism for a definitive, mechanism based chemopreventive rice bran-microbe- metabolite investigation using a R01 mechanism.

Public Health Relevance

Colorectal cancer has the second highest mortality rate of all cancers and dietary intervention with rice bran components represents a promising opportunity for chemoprevention in humans. Dietary rice bran inhibits colon tumorigenesis in animal studies, but little is known regarding the effects of dietary rice bran intake in humans for reducing coloni inflammation directly or through metabolic by-products resulting from gut fermentation. Rice bran is a readily available agricultural by-product that is not yet widely consumed by humans. Clinical investigations into anti-inflammatory activity of rice bran phytochemicals, their biotransformation products, and microbial metabolites whose production is stimulated by rice bran consumption can help to advance the inclusion of rice bran as an agent to inhibit colonic inflammation and for widespread colorectal cancer prevention.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Exploratory/Developmental Grants (R21)
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Chemo/Dietary Prevention Study Section (CDP)
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Riscuta, Gabriela
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Colorado State University-Fort Collins
Other Domestic Higher Education
Fort Collins
United States
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Sheflin, Amy M; Whitney, Alyssa K; Weir, Tiffany L (2014) Cancer-promoting effects of microbial dysbiosis. Curr Oncol Rep 16:406