Dietary Fructo-oligosaccharide Modulates Large Intestinal Inflammatory Responses toClostridium difficilein Antibiotic-compromised Mice

Defined Nutrient Diets Alter Susceptibility to Clostridium difficile Associated Disease in a Murine Model

Background

Clostridium difficile is a major identifiable and treatable cause of antibiotic-associated diarrhea. Poor nutritional status contributes to mortality through weakened host defenses against various pathogens. The primary goal of this study was to assess the contribution of a reduced protein diet to the outcomes of C. difficile infection in a murine model.

Methods

C57BL/6 mice were fed a traditional house chow or a defined diet with either 20% protein or 2% protein and infected with C. difficile strain VPI10463. Animals were monitored for disease severity, clostridial shedding and fecal toxin levels. Select intestinal microbiota were measured in stool and C. difficile growth and toxin production were quantified ex vivo in intestinal contents from untreated or antibiotic-treated mice fed with the different diets.

Results

C. difficile infected mice fed with defined diets, particularly (and unexpectedly) with protein deficient diet, had increased survival, decreased weight loss, and decreased overall disease severity. C. difficile shedding and toxin in the stool of the traditional diet group was increased compared with either defined diet 1 day post infection. Mice fed with traditional diet had an increased intestinal Firmicutes to Bacteroidetes ratio following antibiotic exposure compared with either a 2% or 20% protein defined nutrient diet. Ex vivo inoculation of cecal contents from antibiotic-treated mice showed decreased toxin production and C. difficile growth in both defined diets compared with a traditional diet.

Conclusions

Low protein diets, and defined nutrient diets in general, were found to be protective against CDI in mice. Associated diet-induced alterations in intestinal microbiota may influence colonization resistance and clostridial toxin production in a defined nutrient diet compared to a traditional diet, leading to increased survival. However, mechanisms which led to survival differences between 2% and 20% protein defined nutrient diets need to be further elucidated.

Prebiotics and the health benefits of fiber: current regulatory status, future research, and goals

First defined in the mid-1990s, prebiotics, which alter the composition and activity of gastrointestinal (GI) microbiota to improve health and well-being, have generated scientific and consumer interest and regulatory debate. The Life Sciences Research Organization, Inc. (LSRO) held a workshop, Prebiotics and the Health Benefits of Fiber: Future Research and Goals, in February 2011 to assess the current state of the science and the international regulatory environment for prebiotics, identify research gaps, and create a strategy for future research. A developing body of evidence supports a role for prebiotics in reducing the risk and severity of GI infection and inflammation, including diarrhea, inflammatory bowel disease, and ulcerative colitis as well as bowel function disorders, including irritable bowel syndrome. Prebiotics also increase the bioavailability and uptake of minerals and data suggest that they reduce the risk of obesity by promoting satiety and weight loss. Additional research is needed to define the relationship between the consumption of different prebiotics and improvement of human health. New information derived from the characterization of the composition and function of different prebiotics as well as the interactions among and between gut microbiota and the human host would improve our understanding of the effects of prebiotics on health and disease and could assist in surmounting regulatory issues related to prebiotic use.

Nutrition modulation of gastrointestinal toxicity related to cancer chemotherapy: from preclinical findings to clinical strategy

Chemotherapy-induced gut toxicity is a major dose-limiting toxicity for many anticancer drugs. Gastrointestinal (GI) complications compromise the efficacy of chemotherapy, promote overall malnutrition, aggravate cancer cachexia, and may contribute to worsened prognosis. The GI tract is an attractive target for nutrition modulation, owing to its direct exposure to the diet, participation in uptake and metabolism of nutrients, high rate of cell turnover, and plasticity to nutrition stimuli. Glutamine, ω-3 polyunsaturated fatty acids, and probiotics/prebiotics are therapeutic factors that potentially modulate GI toxicity related to cancer treatments. Preclinical and clinical evidence are reviewed to critically define plausible benefits of these factors and their potential development into adjuncts to cancer chemotherapy. Mechanisms underlying the action of these nutrients are being unraveled in the laboratory. Optimal strategies to translate these findings into clinical care still remain to be elucidated. Key questions that remain to be answered include the following: which nutrient or combination of nutrients is selected for which patient and chemotherapy regimen? What mechanisms are responsible for modulation, and how are nutrient(s) administered in a clinically optimal manner? Research exploring interactions between different nutrients in GI protection is ongoing and demands further understanding. How nutrition preparations given to chemotherapy-treated patients are formulated in terms of component selection and dose optimization should be carefully studied and justified.

Prebiotics, immune function, infection and inflammation: a review of the evidence

Beta2-1 fructans are carbohydrate molecules with prebiotic properties. Through resistance to digestion in the upper gastrointestinal tract, they reach the colon intact, where they selectively stimulate the growth and/or activity of beneficial members of the gut microbiota. Through this modification of the intestinal microbiota, and by additional mechanisms, beta2-1 fructans may have beneficial effects upon immune function, ability to combat infection, and inflammatory processes and conditions. In this paper, we have collated, summarised and evaluated studies investigating these areas. Twenty-one studies in laboratory animals suggest that some aspects of innate and adaptive immunity of the gut and the systemic immune systems are modified by beta2-1 fructans. In man, two studies in children and nine studies in adults indicate that the adaptive immune system may be modified by beta2-1 fructans. Thirteen studies in animal models of intestinal infections conclude a beneficial effect of beta2-1 fructans. Ten trials involving infants and children have mostly reported benefits on infectious outcomes; in fifteen adult trials, little effect was generally seen, although in specific situations, certain beta2-1 fructans may be beneficial. Ten studies in animal models show benefit of beta2-1 fructans with regard to intestinal inflammation. Human studies report some benefits regarding inflammatory bowel disease (four positive studies) and atopic dermatitis (one positive study), but findings in irritable bowel syndrome are inconsistent. Therefore, overall the results indicate that beta2-1 fructans are able to modulate some aspects of immune function, to improve the host's ability to respond successfully to certain intestinal infections, and to modify some inflammatory conditions.

Non–digestible oligosaccharides and defense functions: lessons learned from animal models

Animals are constantly exposed to a diversity of health challenges and the gastrointestinal tract (GIT) is a major, if not the principal, site of exposure. Animal models and a limited number of human clinical studies have shown that the assemblages and metabolic activities of the resident bacteria are important determinants of the effectiveness of the various host defense mechanisms and thereby influence the ability of animals to respond to health challenges. The assemblages of bacteria resident in the GIT provide a first line of defense that can exclude invading pathogens, reduce the proliferation of opportunistic pathogens already resident in the GIT, and reduce the availability, carcinogenicity, or toxicity of noxious chemicals. The mucosa of the GIT is a second, multilayered line of defense that includes the mucous and other secretions, the epithelial cells, and immune-associated cells scattered within and under the epithelium. The final line of defense contends with pathogens or noxious chemicals that transcend the mucosal barrier and enter the host and consists of the innate and acquired components of the systemic immune system and the xenobiotic metabolizing enzymes. The lactic acid producing bacteria (LAB) are considered to be immunomodulatory and directly or indirectly influence the GIT and systemic defense functions. Corresponding with this, supplementing the diet with inulin, oligofructose, or other nondigestible oligosaccharides that increase the densities and metabolic capacities of the LAB enhances defense mechanisms of the host, increases resistance to various health challenges, and accelerates recovery of the GIT after disturbances.

The immune-enhancing effects of dietary fibres and prebiotics

The gastrointestinal tract is subjected to enormous and continual foreign antigenic stimuli from food and microbes. This organ must integrate complex interactions among diet, external pathogens, and local immunological and non-immunological processes. It is critical that protective immune responses are made to potential pathogens, while hypersensitivity reactions to dietary antigens are minimised. There is increasing evidence that fermentable dietary fibres and the newly described prebiotics can modulate various properties of the immune system, including those of the gut-associated lymphoid tissues (GALT). This paper reviews evidence for the immune-enhancing effects of dietary fibres. Changes in the intestinal microflora that occur with the consumption of prebiotic fibres may potentially mediate immune changes via: the direct contact of lactic acid bacteria or bacterial products (cell wall or cytoplasmic components) with immune cells in the intestine; the production of short-chain fatty acids from fibre fermentation; or by changes in mucin production. Although further work is needed to better define the changes, mechanisms for immunomodulation, and the ultimate impact on immune health, there is convincing preliminary data to suggest that the consumption of prebiotics can modulate immune parameters in GALT, secondary lymphoid tissues and peripheral circulation. Future protocols on the physiological impact of consuming prebiotics should be designed to include assessments of the gut microflora, gut physiology and the function and composition of the various regions of GALT.

Inulin, oligofructose and immunomodulation

Diet is known to modulate immune functions in multiple ways and to affect host resistance to infections. Besides the essential nutrients, non-essential food constituents such as non-digestible carbohydrates may also have an impact on the immune system, especially in the area of the gut-associated lymphoid tissue (GALT). Recent data now provide first evidence that prebiotics such as inulin/oligofructose (IN/OF) modulate functions of the immune system. In animal studies IN/OF primarily activated immune cells in Peyer's patches including IL-10 production and natural killer (NK) cell cytotoxicity. Other immune functions modulated by IN/OF included the concentration of secretory IgA in ileum and caecum, splenic NK cell cytotoxicity as well as splenocyte cytokine production. In different tumour models, a lower incidence of tumours was observed, which in the case of colonic tumours was associated with enhanced NK cell cytotoxicity in the GALT. Few human studies so far have investigated the effects of IN/OF alone or in combination with other dietary supplements on immunocompetence. Supplementation of IN/OF resulted in minor changes of systemic immune functions such as decrease in phagocytic activity. No data are available on the effects of IN/OF on the GALT in man. The mechanisms of the reported effects of IN/OF on the immune system are currently investigated and include: (i) direct effects of lactic acid-producing bacteria or bacterial constituents on immune cells; (ii) the production of SCFA and binding to SCFA receptors on leucocytes. In conclusion, the current data suggest that IN/OF primarily modulate immune parameters in the GALT, but splenocytes are also activated by IN/OF. Human studies are needed to find out whether IN/OF have the potential to modulate systemic immunity in well-nourished individuals and to lower the risk of diseases such as colon cancer.

Molecular ecological analysis of dietary and antibiotic-induced alterations of the mouse intestinal microbiota

A cultivation-independent approach, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), was used to characterize changes in fecal bacterial populations resulting from consumption of a low residue diet or oral administration of a broad-spectrum antibiotic. C57BL/6NHsd mice were weaned to either a standard nonpurified diet (LC-diet) or a low residue diet (LR-diet) and at 17 wk of age were randomly assigned to receive drinking water with or without 25 ppm cefoxitin for 14 d. On d 1, 2, 7 and 14, microbial DNA was extracted from feces, and the V3 region of the 16S rDNA gene was amplified by PCR and analyzed by DGGE. The diversity of fecal microbial populations, assessed using Shannon's index (H'), which incorporates species richness (number of species, or in this case, PCR-DGGE bands) and evenness (the relative distribution of species), was not affected by cefoxitin. However, use of Sorenson's pairwise similarity coefficient (C(s)), an index that measures the species in common between different habitats, indicated that the species composition of fecal bacterial communities was altered by cefoxitin in mice fed either diet. Dietary effects on fecal microbial communities were more pronounced, with greater H' values (P < 0.05) in mice fed the LR-diet (1.9 +/- 0.1) compared with the LC-diet (1.6 +/- 0.1). The C(s) values were also greater (P < 0.05) in fecal bacterial populations from mice fed the LR-diet (C(s) = 69.8 +/- 2.0%) compared with mice fed the LC-diet (C(s) = 50.1 +/- 3.8%), indicating greater homogeneity of fecal bacterial communities in mice fed the LR-diet. These results demonstrate the utility of cultivation-independent PCR-DGGE analysis combined with measurements of ecological diversity for monitoring diet- and antibiotic-induced alterations of the complex intestinal microbial ecosystem.