Gut microbiota richness promotes its stability upon increased dietary fibre intake in healthy adults.

Gut microbiota richness and stability are important parameters in host-microbe symbiosis. Diet modification, notably using dietary fibres, might be a way to restore a high richness and stability in the gut microbiota. In this work, during a 6-week nutritional trial, 19 healthy adults consumed a basal diet supplemented with 10 or 40 g dietary fibre per day for 5 days, followed by 15-day washout periods. Fecal samples were analysed by a combination of 16S rRNA gene pyrosequencing, intestinal cell genotoxicity assay, metatranscriptomics sequencing approach and short-chain fatty analysis. This short-term change in the dietary fibre level did not have the same impact for all individuals but remained significant within each individual gut microbiota at genus level. Higher microbiota richness was associated with higher microbiota stability upon increased dietary fibre intake. Increasing fibre modulated the expression of numerous microbiota metabolic pathways such as glycan metabolism, with genes encoding carbohydrate-active enzymes active on fibre or host glycans. High microbial richness was also associated with high proportions of Prevotella and Coprococcus species and high levels of caproate and valerate. This study provides new insights on the role of gut microbial richness in healthy adults upon dietary changes and host microbes' interaction.

Ability of Lactobacillus fermentum to overcome host alpha-galactosidase deficiency, as evidenced by reduction of hydrogen excretion in rats consuming soya alpha-galacto-oligosaccharides.

BACKGROUND: Soya and its derivatives represent nutritionally high quality food products whose major drawback is their high content of alpha-galacto-oligosaccharides. These are not digested in the small intestine due to the natural absence of tissular alpha-galactosidase in mammals. The passage of these carbohydrates to the large intestine makes them available for fermentation by gas-producing bacteria leading to intestinal flatulence. The aim of the work reported here was to assess the ability of alpha-galactosidase-producing lactobacilli to improve the digestibility of alpha-galacto-oligosaccharides in situ. RESULTS: Gnotobiotic rats were orally fed with soy milk and placed in respiratory chambers designed to monitor fermentative gas excretion. The validity of the animal model was first checked using gnotobiotic rats monoassociated with a Clostridium butyricum hydrogen (H2)-producing strain. Ingestion of native soy milk by these rats caused significant H2 emission while ingestion of alpha-galacto-oligosaccharide-free soy milk did not, thus validating the experimental system. When native soy milk was fermented using the alpha-galactosidase-producing Lactobacillus fermentum CRL722 strain, the resulting product failed to induce H2 emission in rats thus validating the bacterial model. When L. fermentum CRL722 was coadministered with native soy milk, a significant reduction (50 %, P = 0.019) in H2 emission was observed, showing that alpha-galactosidase from L. fermentum CRL722 remained active in situ, in the gastrointestinal tract of rats monoassociated with C. butyricum. In human-microbiota associated rats, L. fermentum CRL722 also induced a significant reduction of H2 emission (70 %, P = 0.004). CONCLUSION: These results strongly suggest that L. fermentum alpha-galactosidase is able to partially alleviate alpha-galactosidase deficiency in rats. This offers interesting perspectives in various applications in which lactic acid bacteria could be used as a vector for delivery of digestive enzymes in man and animals.

Increased induction of apoptosis by Propionibacterium freudenreichii TL133 in colonic mucosal crypts of human microbiota-associated rats treated with 1,2-dimethylhydrazine.

Propionibacterium freudenreichii, a food-grade bacterium able to kill colon cancer cell lines in vitro by apoptosis, may exert an anticarcinogenic effect in vivo. To assess this hypothesis, we administered daily 2 x 10(10) colony-forming units (CFU) of P. freudenreichii TL133 to human microbiota-associated (HMA) rats for 18 d. Either saline or 1,2-dimethylhydrazine (DMH) was also administered on days 13 and 17 and rats were killed on day 19. The levels of apoptosis and proliferation in the mid and distal colon were assessed by terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) and proliferating cell nuclear antigen (PCNA) immunolabelling, respectively. The administration of P. freudenreichii TL133 significantly increased the number of apoptotic cells in DMH-treated rats compared to those given DMH only (P < 0.01). Furthermore, propionibacteria were able to decrease the proliferation index in the distal colon after treatment with DMH (P < 0.01). Conversely, propionibacteria alone did not exert such an effect on healthy colonic mucosa. P. freudenreichii TL133 thus facilitated the elimination of damaged cells by apoptosis in the rat colon after genotoxic insult and may play a protective role against colon cancer.

Beta-glucuronidase in human intestinal microbiota is necessary for the colonic genotoxicity of the food-borne carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline in rats.

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a genotoxic/carcinogenic compound formed in meat and fish during cooking. Following absorption in the upper part of the gastrointestinal tract, IQ is mainly metabolized in the liver by xenobiotic-metabolizing enzymes. Among them, UDP-glucuronosyl transferases lead to harmless glucuronidated derivatives that are partly excreted via the bile into the digestive lumen, where they come into contact with the resident microbiota. The purpose of this study is to investigate if microbial beta-glucuronidase could contribute to IQ genotoxicity by releasing reactive intermediates from IQ glucuronides. We constructed a beta-glucuronidase-deficient isogenic mutant from a wild-type Escherichia coli strain carrying the gene uidA encoding this enzyme and compared the genotoxicity of IQ in gnotobiotic rats monoassociated with the wild-type or the mutant strain. The Comet assay performed on colonocytes and hepatocytes showed that the presence of beta-glucuronidase in the digestive lumen dramatically increased (3-fold) the genotoxicity of IQ in the colon. This deleterious effect was paralleled by slight modifications of the pharmacokinetics of IQ. The urinary and faecal excretion of the parent compound and its conjugated derivatives reached a maximum 24-48 h after gavage in rats harbouring the beta-glucuronidase-deficient strain. In rats associated with the wild-type strain, the kinetics of urinary excretion showed a biphasic curve with a second, smaller peak after 144 h. This is the first in vivo demonstration that bacterial beta-glucuronidase plays a pivotal role in the genotoxicity of a common food-borne carcinogen.

Protective effects of Brussels sprouts, oligosaccharides and fermented milk towards 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced genotoxicity in the human flora associated F344 rat: role of xenobiotic metabolising enzymes and intestinal microflora.

We investigated the chemoprotective effects of four common constituents of the human diet, i.e. a fermented milk, inulin, oligofructose and Brussels sprouts, towards 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced genotoxicity in male Fischer 344 rats harbouring a human intestinal microflora. We found that the four dietary components significantly reduced IQ-induced DNA damage in hepatocytes (reduction ranged from 74% with inulin to 39% with Brussels sprouts) and colonocytes (reduction ranged from 68% with inulin to 56% with Brussels sprouts). This chemoprotective effect correlated with the induction of hepatic UDP-glucuronosyl transferase following Brussels sprouts consumption, and with alterations of bacterial metabolism in the distal gut (acidification, increase of butyrate proportion, decrease of beta-glucuronidase activity) following inulin consumption.

Apple proanthocyanidins do not reduce the induction of preneoplastic lesions in the colon of rats associated with human microbiota.

Since the gut microbiota metabolizes various dietary constituents unabsorbed by the small intestine and modulates colon function, it plays an essential role in colon carcinogenesis. First, we have developed a model of human microbiota-associated rats (HMA), fed a human-type diet and injected with 1-2,dimethylhydrazine (DMH). We observed that the number and size of DMH-induced aberrant crypt foci (ACF) were significantly higher in HMA rats than in germ-free or conventional rats. Second, we used this model to assess the protective effect of an apple proanthocyanidin-rich extract (APE) on colon carcinogenesis. In this model, ACF number and multiplicity were not reduced by APE at 0.001% and 0.01% in drinking water. They were higher with APE 0.1% than with APE 0.01%. Therefore, the cross-talk between human microbiota and the colon epithelium should be taken into account in carcinogenesis models. Moreover, attention should be paid prior to using proanthocyanidin extracts as dietary supplements for humans.