Intestinal health functions of colonic microbial metabolites: a review

Potential applications of gut microbiota to control human physiology

The microorganisms living in our gut have been a black box to us for a long time. However, with the recent advances in high throughput DNA sequencing technologies, it is now possible to assess virtually all microorganisms in our gut including non-culturable ones. With the use of powerful bioinformatics tools to deal with multivariate analyses of huge amounts of data from metagenomics, metatranscriptomics, metabolomics, we now start to gain some important insights into these tiny gut inhabitants. Our knowledge is increasing about who they are, to some extent, what they do and how they affect our health. Gut microbiota have a broad spectrum of possible effects on health, from preventing serious diseases, improving immune system and gut health to stimulating the brain centers responsible for appetite and food intake control. Further, we may be on the verge of being capable of manipulating the gut microbiota by diet control to possibly improve our health. Diets consisting of different components that are fermentable by microbiota are substrates for different kinds of microbes in the gut. Thus, diet control can be used to favor the growth of some selected gut inhabitants. Nowadays, the gut microbiota is taken into account as a separate organ in human body and their activities and metabolites in gut have many physiological and neurological effects. In this mini-review, we discuss the diversity of gut microbiota, the technologies used to assess them, factors that affect microbial composition and metabolites that affect human physiology, and their potential applications in satiety control via the gut-brain axis.

Transporters and receptors for short-chain fatty acids as the molecular link between colonic bacteria and the host

The mutually beneficial relationship between colonic bacteria and the host has been recognized but the molecular aspects of the relationship remain poorly understood. Dietary fiber is critical to this relationship. The short-chain fatty acids acetate, propionate and butyrate, generated by bacterial fermentation of dietary fiber, serve as messengers between colonic bacteria and the host. The beneficial effects of these bacterial metabolites in colon include, but are not limited to, suppression of inflammation and prevention of cancer. Recent studies have identified the plasma membrane transporter SLC5A8 and the cell-surface receptors GPR109A and GPR43 as essential for the biologic effects of short-chain fatty acids in colon. These three proteins coded by the host genome provide the molecular link between colonic bacteria and the host.

Effect of early enteral nutrition on postoperative nutritional status and immune function in elderly patients with esophageal cancer or cardiac cancer

OBJECTIVE

To explore the effect of early enteral nutrition (EN) on postoperative nutritional status, intestinal permeability, and immune function in elderly patients with esophageal cancer or cardiac cancer.

METHODS

A total of 96 patients with esophageal cancer or cardiac cancer who underwent surgical treatment in our hospital from June 2007 to December 2010 were enrolled in this study. They were divided into EN group (n=50) and parenteral nutrition (PN) group (n=46) based on the nutrition support modes. The body weight, time to first flatus/defecation, average hospital stay, complications and mortality after the surgery as well as the liver function indicators were recorded and analyzed. Peripheral blood samples were collected on the days 1, 4 and 7 after surgery. The plasma diamine oxidase (DAO) activity and D-lactate level were determined to assess the intestinal permeability. The plasma endotoxin levels were determined using dynamic turbidimetric assay to assess the protective effect of EN on intestinal mucosal barrier. The postoperative blood levels of inflammatory cytokines and immunoglobulins were determined using enzyme-linked immunosorbent assay (ELISA).

RESULTS

After the surgery, the time to first flatus/defecation, average hospital stay, and complications were significantly less in the EN group than those in the PN group (P<0.05), whereas the EN group had significantly higher albumin levels than the PN group (P<0.05). On the 7th postoperative day, the DAO activity, D-lactate level and endotoxin contents were significantly lower in the EN group than those in the PN group (all P<0.05). In addition, the EN group had significantly higher IgA, IgG, IgM, and CD4 levels than the PN group (P<0.05) but significantly lower IL-2, IL-6, and TNF-α levels (P<0.05).

CONCLUSIONS

In elderly patients with esophageal cancer or cardiac cancer, early EN after surgery can effectively improve the nutritional status, protect intestinal mucosal barrier (by reducing plasma endoxins), and enhance the immune function.

Complex interactions among diet, gastrointestinal transit, and gut microbiota in humanized mice

BACKGROUND & AIMS

Diet has major effects on the intestinal microbiota, but the exact mechanisms that alter complex microbial communities have been difficult to elucidate. In addition to the direct influence that diet exerts on microbes, changes in microbiota composition and function can alter host functions such as gastrointestinal (GI) transit time, which in turn can further affect the microbiota.

METHODS

We investigated the relationships among diet, GI motility, and the intestinal microbiota using mice that are germ-free (GF) or humanized (ex-GF mice colonized with human fecal microbiota).

RESULTS

Analysis of gut motility revealed that humanized mice fed a standard polysaccharide-rich diet had faster GI transit and increased colonic contractility compared with GF mice. Humanized mice with faster transit due to administration of polyethylene glycol or a nonfermentable cellulose-based diet had similar changes in gut microbiota composition, indicating that diet can modify GI transit, which then affects the composition of the microbial community. However, altered transit in mice fed a diet of fermentable fructooligosaccharide indicates that diet can change gut microbial function, which can affect GI transit.

CONCLUSIONS

Based on studies in humanized mice, diet can affect GI transit through microbiota-dependent or microbiota-independent pathways, depending on the type of dietary change. The effect of the microbiota on transit largely depends on the amount and type (fermentable vs nonfermentable) of polysaccharides present in the diet. These results have implications for disorders that affect GI transit and gut microbial communities, including irritable bowel syndrome and inflammatory bowel disease.

Effect of galactooligosaccharides and Bifidobacterium animalis Bb-12 on growth of Lactobacillus amylovorus DSM 16698, microbial community structure, and metabolite production in an in vitro colonic model set up with human or pig microbiota

A validated in vitro model of the large intestine (TIM-2), set up with human or pig faeces, was used to evaluate the impact of potentially probiotic Lactobacillus amylovorus DSM 16698, administered alone (i), in the presence of prebiotic galactooligosaccharides (GOS) (ii), and co-administered with probiotic Bifidobacterium animalis ssp. lactis Bb-12 (Bb-12) (iii) on GOS degradation, microbial growth (L. amylovorus, lactobacilli, bifidobacteria and total bacteria) and metabolite production. High performance anion exchange chromatography revealed that GOS degradation was more pronounced in TIM-2 inoculated with pig faeces than with human faeces. Denaturing gradient gel electrophoresis profiling of PCR-amplified 16S rRNA genes detected a more complex Lactobacillus spp. community in pig faecal material than in human faecal inoculum. According to 16S rRNA gene-targeted qPCR, GOS stimulated the growth of lactobacilli and bifidobacteria in faecal material from both materials. The cumulative production of short chain fatty acids and ammonia was higher (P < 0.05) for pig than for human faeces. However, lactate accumulation was higher (P < 0.05) in the human model and increased after co-administration with GOS and Bb-12. This study reinforced the notion that differences in microbiota composition between target host organisms need to be considered when animal data are extrapolated to human, as is often done with pre- and probiotic intervention studies.

Alternative method for gas chromatography-mass spectrometry analysis of short-chain fatty acids in faecal samples

Short-chain fatty acids are the major end products of bacterial metabolism in the large bowel. They derive mostly from the bacterial breakdown of carbohydrates and are known to have positive health benefits. Due to the biological relevance of these compounds it is important to develop efficient, cheap, fast, and sensitive analytical methods that enable the identification and quantification of the short-chain fatty acids in a large number of biological samples. In this study, a gas chromatography-mass spectrometry method was developed and validated for the analysis of short-chain fatty acids in faecal samples. These volatile compounds were extracted with ethyl acetate and 4-methyl valeric acid was used as an internal standard. No further cleanup, concentration, and derivatization steps were needed and the extract was directly injected onto the column. Recoveries ranged between 65 and 105%, and no matrix effects were observed. The proposed method has wide linear ranges, good inter- and intraday variability values (below 2.6 and 5.6%, respectively) and limits of detection between 0.49 μM (0.29 μg/g) and 4.31 μM (3.8 μg/g). The applicability of this analytical method was successfully tested in faecal samples from rats and humans.

Effect of highly lipolyzed goat cheese on HL-60 human leukemia cells: antiproliferative activity and induction of apoptotic DNA damage

To establish cheese as a dairy product with health benefits, we embarked on examining the multifunctional role of cheeses, especially in the field of cancer prevention. The current study was designed to investigate whether different types of commercial goat cheeses may possess antiproliferative activity, using an HL-60 human promyelocytic leukemia cell line as a cancer cell model. Among 11 cheese extracts tested at 500μg/mL, 6 (Crottin de Chavignol, Pouligny Saint-Pierre, Chabichou du Poitou, Valencay, Kavli, and Sainte-Maure de Touraine) resulted in a significant decrease of cell viability, which is consistent with a decrease in viable cell number. Compared with the half-maximal inhibitory concentration (IC(50)) value of individual cheeses in cellular proliferation assays, the Pouligny Saint-Pierre extract showed strong inhibition. Incubation of cells in the presence of Pouligny Saint-Pierre extract resulted in induction of cellular morphological changes and apoptotic DNA fragmentation as well as expression of the active form of caspase-3 protein. Based on the quantification of the ratio of free fatty acids to triglycerides in different cheese samples, a significant correlation was detected between lipolytic ripeness and IC(50) values for antiproliferative capacity tested in HL-60 cells. Collectively, these results support a potential role of highly lipolyzed goat cheeses in the prevention of leukemic cell proliferation.

Influence of dietary phytochemicals and microbiota on colon cancer risk

Colon cancer is the third most commonly diagnosed type of cancer in the United States. Lifestyle and dietary patterns influence colon cancer risk both positively and negatively. Among the dietary factors, several plant-derived compounds have been found to afford colon cancer protection. These compounds potentially influence all aspects of colonic cellular regulation and develop complex interrelationships with the colonic microbiome. Increasing understanding of the role of microorganisms in determining the colonic environment has led to awareness of this important interrelationship among dietary factors and the microbial population. Plant-derived polyphenols are active mediators of cellular events, target key carcinogenic pathways, and modulate colonic microbial populations. In turn, the colonic microorganisms metabolize dietary compounds and mediate cellular events. In addition, the role of estrogen receptors in colon cancer and the importance of dietary components that mediate estrogen receptor-β are increasingly being discovered. Hence, dietary bioactive compounds and the intestinal microbiota create a complex milieu that directly affects the carcinogenic events of the colon. These relationships must be carefully characterized in future research to provide dietary recommendations that will reduce colon cancer risk.