This study evaluated whether dietary resistant starch (RS) and green tea extract (GTE), which have anti-inflammatory and anti-cancer properties, protect against colitis-associated colorectal cancer (CAC) using a rat model, also investigated potential mechanisms of action of these agents including their effects on the gut microbiota. Rats were fed a control diet or diets containing 10% RS, 0.5% GTE, or a combination of the two (RS+GTE). CAC was initiated with 2 weekly azoxymethane injections (10mg/kg) followed by 2% dextran sodium sulphate in drinking water for 7 days after 2 weeks on diets. Rats were killed 20 weeks after the first azoxymethane. Colon tissues and tumours were examined for histopathology by H&E, gene/protein expression by PCR and immunohistochemistry, and digesta for analyses of fermentation products and microbiota populations. RS and RS+GTE (but not GTE) diets significantly (P<0.05) decreased tumour multiplicity and adenocarcinoma formation, relative to the control diet. Effects of RS+GTE were not different from RS alone. RS diet caused significant shifts in microbial composition/diversity, with increases in Parabacteroides, Barnesiella, Ruminococcus, Marvinbryantia and Bifidobacterium as primary contributors to the shift. RS-containing diets increased short chain fatty acids (SCFA) and expression of the SCFA receptor GPR43 mRNA, and reduced inflammation (COX-2, NF-kB, TNF-α and IL-β mRNA) and cell proliferation P<0.05. GTE had no effect. This is the first study that demonstrates chemopreventive effects of RS (but not GTE) in a rodent CAC model, suggesting RS might have benefit to patients with ulcerative colitis who are at an increased risk of developing CRC.

Epidemiological studies have identified increased colorectal cancer (CRC) risk with high red meat (HRM) intakes, whereas dietary fibre intake appears to be protective. In the present study, we examined whether a HRM diet increased rectal O⁶-methyl-2-deoxyguanosine (O⁶MeG) adduct levels in healthy human subjects, and whether butyrylated high-amylose maize starch (HAMSB) was protective. A group of twenty-three individuals consumed 300 g/d of cooked red meat without (HRM diet) or with 40 g/d of HAMSB (HRM+HAMSB diet) over 4-week periods separated by a 4-week washout in a randomised cross-over design. Stool and rectal biopsy samples were collected for biochemical, microbial and immunohistochemical analyses at baseline and at the end of each 4-week intervention period. The HRM diet increased rectal O⁶MeG adducts relative to its baseline by 21 % (P< 0·01), whereas the addition of HAMSB to the HRM diet prevented this increase. Epithelial proliferation increased with both the HRM (P< 0·001) and HRM+HAMSB (P< 0·05) diets when compared with their respective baseline levels, but was lower following the HRM+HAMSB diet compared with the HRM diet (P< 0·05). Relative to its baseline, the HRM+HAMSB diet increased the excretion of SCFA by over 20 % (P< 0·05) and increased the absolute abundances of theClostridium coccoidesgroup (P< 0·05), theClostridiumleptumgroup (P< 0·05),Lactobacillusspp. (P< 0·01),Parabacteroides distasonis(P< 0·001) andRuminococcus bromii(P< 0·05), but loweredRuminococcus torques(P< 0·05) and the proportions ofRuminococcus gnavus,Ruminococcus torquesandEscherichia coli(P< 0·01). HRM consumption could increase the risk of CRC through increased formation of colorectal epithelial O⁶MeG adducts. HAMSB consumption prevented red meat-induced adduct formation, which may be associated with increased stool SCFA levels and/or changes in the microbiota composition.

High red meat (HRM) intake is associated with increased colorectal cancer risk, while resistant starch is probably protective. Resistant starch fermentation produces butyrate, which can alter microRNA (miRNA) levels in colorectal cancer cells in vitro; effects of red meat and resistant starch on miRNA expression in vivo were unknown. This study examined whether a HRM diet altered miRNA expression in rectal mucosa tissue of healthy volunteers, and if supplementation with butyrylated resistant starch (HRM+HAMSB) modified this response. In a randomized cross-over design, 23 volunteers undertook four 4-week dietary interventions; an HRM diet (300 g/day lean red meat) and an HRM+HAMSB diet (HRM with 40 g/day butyrylated high amylose maize starch), preceded by an entry diet and separated by a washout. Fecal butyrate increased with the HRM+HAMSB diet. Levels of oncogenic mature miRNAs, including miR17–92 cluster miRNAs and miR21, increased in the rectal mucosa with the HRM diet, whereas the HRM+HAMSB diet restored miR17–92 miRNAs, but not miR21, to baseline levels. Elevated miR17–92 and miR21 in the HRM diet corresponded with increased cell proliferation, and a decrease in miR17–92 target gene transcript levels, including CDKN1A. The oncogenic miR17–92 cluster is differentially regulated by dietary factors that increase or decrease risk for colorectal cancer, and this may explain, at least in part, the respective risk profiles of HRM and resistant starch. These findings support increased resistant starch consumption as a means of reducing risk associated with an HRM diet. Cancer Prev Res; 7(8); 786–95. ©2014 AACR.

Population studies have shown that high red meat intake may increase colorectal cancer risk. Our aim was to examine the effect of different amounts and sources of dietary protein on induction of the promutagenic adduct O⁶-methyl-2-deoxyguanosine (O⁶MeG) in colonocytes, to relate these to markers of large bowel protein fermentation and ascertain whether increasing colonic carbohydrate fermentation modified these effects. Mice (n = 72) were fed 15% or 30% protein as casein or red meat or 30% protein with 10% high amylose maize starch as the source of resistant starch. Genetic damage in distal colonocytes was detected by immunohistochemical staining for O⁶MeG and apoptosis. Feces were collected for measurement of pH, ammonia, phenols, p-cresol, and short-chain fatty acids (SCFA). O⁶MeG and fecal p-cresol concentrations were significantly higher with red meat than with casein (P < 0.018), with adducts accumulating in cells at the crypt apex. DNA adducts (P < 0.01) and apoptosis (P < 0.001) were lower and protein fermentation products (fecal ammonia, P < 0.05; phenol, P < 0.0001) higher in mice fed resistant starch. Fecal SCFA levels were also higher in mice fed resistant starch (P < 0.0001). This is the first demonstration that high protein diets increase promutagenic adducts (O⁶MeG) in the colon and dietary protein type seems to be the critical factor. The delivery of fermentable carbohydrate to the colon (as resistant starch) seems to switch from fermentation of protein to that of carbohydrate and a reduction in adduct formation, supporting previous observations that dietary resistant starch opposes the mutagenic effects of dietary red meat. Cancer Prev Res; 4(11); 1920–8. ©2011 AACR.