Review article: the role of butyrate on colonic function

Effect of Bifidobacterium animalis subsp lactis supplementation in preterm infants: a systematic review of randomized controlled trials

OBJECTIVE

To systematically evaluate and update evidence on the efficacy and safety of Bifidobacterium animalis subsp lactis CNCM I-3446 supplementation in preterm infants.

MATERIALS AND METHODS

The Cochrane Library and MEDLINE databases and major pediatric conference proceedings were searched in December 2008 for randomized controlled trials (RCTs). The company that manufactures B lactis was contacted for unpublished data. The review was restricted to RCTs performed in preterm infants <37 weeks of gestation and/or with a birth weight <2500 g.

RESULTS

Four RCTs involving 324 infants met the inclusion criteria. Compared with controls, B lactis supplementation has the potential to increase fecal bifidobacteria counts and to reduce Enterobacteriaceae and Clostridium spp counts. It also can reduce stool pH and fecal calprotectin concentrations, increase fecal immunoglobulin A and short-chain fatty acid concentrations, and decrease intestinal permeability. Compared with controls, B lactis supplementation had no effect on the risk of necrotizing enterocolitis stage > or = 2 (3 RCTs, n = 293, risk ratio [RR] 0.53, 95% CI 0.16-1.83), risk of sepsis (2 RCTs, 397 cultures, RR 0.6, 95% CI 0.07-5.2), and use of antibiotics (2 RCTs, n = 255, RR 0.67, 95% CI 0.28-1.62). The power of these studies, however, does not allow for a definitive statement regarding a reduced risk of necrotizing enterocolitis. B lactis supplementation did have some effects on anthropometric parameters. No adverse events associated with B lactis supplementation were reported.

CONCLUSIONS

Evidence regarding the potential beneficial effects of B lactis supplementation in preterm infants is encouraging. Further studies to assess clinically relevant outcomes are needed.

Is the abundance of Faecalibacterium prausnitzii relevant to Crohn's disease?

Reports that bacteria within the Firmicutes phylum, especially the species Faecalibacterium prausnitzii, are less abundant in Crohn's disease (CD) patients and supernatants from cultures of this bacterium are anti-inflammatory prompted the investigation of the possible correlations between the abundance of F. prausnitzii and the response to treatment in patients with gut diseases and healthy controls. In a randomized, double-blind trial, faeces were collected from healthy volunteers, and from patients with active CD, ulcerative colitis (UC) and irritable bowel syndrome before and after treatment. The levels of F. prausnitzii DNA in faecal suspensions were determined by PCR. Treatment by an elemental diet was effective, resulting in decreases in both the Harvey and Bradshaw index (P<0.001) and the concentrations of serum C-reactive protein (P<0.05). The total levels of F. prausnitzii in faecal samples from CD patients at presentation were lower than those in the other groups both before and after the treatment. There was no correlation between F. prausnitzii abundance and the severity of CD before treatment. Clinical improvement unexpectedly correlated with a significant decrease in the abundance of F. prausnitzii, especially the A2-165 subgroup (P<0.05). Our data suggest that a paucity of F. prausnitzii in the gastrointestinal microbial communities is likely to be a minor aetiological factor in CD: recovery following elemental diet is attributed to lower levels of gut flora.

Intestinal fermentation in patients with self-reported food hypersensitivity: painful, but protective?

PURPOSE

Enterometabolic disturbances may cause meal-related symptoms. We performed a functional evaluation of the intestinal microflora in patients with unexplained, self-reported food hypersensitivity by measuring fecal short-chain fatty acids (SCFAs).

PATIENTS AND METHODS

Thirty-five consecutive patients with self-reported food hypersensitivity and 15 healthy volunteers of similar age, gender, and body mass index collected all feces for 72 hours. Fecal concentrations of acetic, propionic, n-butyric, i-butyric, n-valeric, i-valeric, n-caproic, and i-caproic acids were analyzed by gas-liquid chromatography. Concentrations and excretions (output) of SCFAs in patients and controls were compared and related to gastrointestinal symptoms.

RESULTS

Despite nonsignificant differences between patients and controls for both total and individual SCFA concentrations and excretions, n-butyric acid comprised a higher (P = 0.035) and acetic acid a lower (P = 0.012) proportion of total SCFA in patients compared to controls. There were no significant correlations between symptom scores and concentrations or excretions of individual or total SCFAs, but the proportion of n-butyric acid was significantly higher in patients with severe symptoms compared to patients with moderate symptoms (P = 0.016).

CONCLUSION

The results indicate an enterometabolic disturbance in patients with self-reported food hypersensitivity. Higher proportions of n-butyric acid may be related to abdominal symptom generation, but may also protect against organic bowel disease. Further studies are needed to clarify these aspects.

Blockade of dendritic cell development by bacterial fermentation products butyrate and propionate through a transporter (Slc5a8)-dependent inhibition of histone deacetylases

Mammalian colon harbors trillions of bacteria, yet there is no undue inflammatory response by the host against these bacteria under normal conditions. The bacterial fermentation products acetate, propionate, and butyrate are believed, at least in part, to be responsible for these immunosuppressive effects. Dendritic cells play an essential role in presentation of antigens to T lymphocytes and initiation of adaptive immune responses. Here we report that butyrate and propionate block the generation of dendritic cells from bone marrow stem cells, without affecting the generation of granulocytes. This effect is dependent on the Na(+)-coupled monocarboxylate transporter Slc5a8, which transports butyrate and propionate into cells, and on the ability of these two bacterial metabolites to inhibit histone deacetylases. Acetate, which is also a substrate for Slc5a8 but not an inhibitor of histone deacetylases, does not affect dendritic cell development, indicating the essential role of histone deacetylase inhibition in the process. The blockade of dendritic cell development by butyrate and propionate is associated with decreased expression of the transcription factors PU.1 and RelB. Butyrate also elicits its biologic effects through its ability to activate the G-protein-coupled receptor Gpr109a, but this mechanism is not involved in butyrate-induced blockade of dendritic cell development. The participation of Slc5a8 and the non-involvement of Gpr109a in butyrate effects have been substantiated using bone marrow cells obtained from Slc5a8(-/-) and Gpr109a(-/-) mice. These findings uncover an important mechanism underlying the anti-inflammatory functions of the bacterial fermentation products butyrate and propionate.

Role of gut microbiota in the control of energy and carbohydrate metabolism

PURPOSE OF REVIEW

To describe the recent developments and insights gained in the role played by the colonic microbiota in energy and carbohydrate metabolism related to obesity in humans.

RECENT FINDINGS

Previous findings that the ratio of Firmicutes and Bacteriodetes is important in energy harvesting and obesity have not been confirmed in recent studies. In fact, sometimes, the opposite results were obtained. Nevertheless, it is clear that the microbiota plays a role in energy extraction from nondigested carbohydrates in the form of production of short-chain fatty acids. Also, the microbiota plays a role in host metabolism by influencing and modulating host gene expression in various tissues.

SUMMARY

Despite numerous recent studies trying to link the composition of the microbiota to obesity, the picture is far from clear, and it remains to be seen whether changes in microbiota composition are the cause or the consequence of obesity. Molecular studies reveal the enzyme machineries used by individual members of the microbiota to break down and ferment polysaccharides. Also, the mechanisms of host-microbe mutualism are becoming unraveled. Using stable-isotope-labeled substrates, the exact microorganisms involved in fermentation of the substrates and the exact metabolites that are produced from the substrate can be deciphered.

Role of the gut microbiota in defining human health

The human superorganism is a conglomerate of mammalian and microbial cells, with the latter estimated to outnumber the former by ten to one and the microbial genetic repertoire (microbiome) to be approximately 100-times greater than that of the human host. Given the ability of the immune response to rapidly counter infectious agents, it is striking that such a large density of microbes can exist in a state of synergy within the human host. This is particularly true of the distal gastrointestinal (GI) tract, which houses up to 1000 distinct bacterial species and an estimated excess of 1 x 10(14) microorganisms. An ever-increasing body of evidence implicates the GI microbiota in defining states of health and disease. Here, we review the literature in adult and pediatric GI microbiome studies, the emerging links between microbial community structure, function, infection and disease, and the approaches to manipulate this crucial ecosystem to improve host health.

The role of intestinal microbiota in the development and severity of chemotherapy-induced mucositis

Mucositis, also referred to as mucosal barrier injury, is one of the most debilitating side effects of radiotherapy and chemotherapy treatment. Clinically, mucositis is associated with pain, bacteremia, and malnutrition. Furthermore, mucositis is a frequent reason to postpone chemotherapy treatment, ultimately leading towards a higher mortality in cancer patients. According to the model introduced by Sonis, both inflammation and apoptosis of the mucosal barrier result in its discontinuity, thereby promoting bacterial translocation. According to this five-phase model, the intestinal microbiota plays no role in the pathophysiology of mucositis. However, research has implicated a prominent role for the commensal intestinal microbiota in the development of several inflammatory diseases like inflammatory bowel disease, pouchitis, and radiotherapy-induced diarrhea. Furthermore, chemotherapeutics have a detrimental effect on the intestinal microbial composition (strongly decreasing the numbers of anaerobic bacteria), coinciding in time with the development of chemotherapy-induced mucositis. We hypothesize that the commensal intestinal microbiota might play a pivotal role in chemotherapy-induced mucositis. In this review, we propose and discuss five pathways in the development of mucositis that are potentially influenced by the commensal intestinal microbiota: 1) the inflammatory process and oxidative stress, 2) intestinal permeability, 3) the composition of the mucus layer, 4) the resistance to harmful stimuli and epithelial repair mechanisms, and 5) the activation and release of immune effector molecules. Via these pathways, the commensal intestinal microbiota might influence all phases in the Sonis model of the pathogenesis of mucositis. Further research is needed to show the clinical relevance of restoring dysbiosis, thereby possibly decreasing the degree of intestinal mucositis.

Free fatty acid receptor 2 and nutrient sensing: a proposed role for fibre, fermentable carbohydrates and short-chain fatty acids in appetite regulation

The way in which the composition of the diet may affect appetite, food intake and body weight is now receiving considerable attention in a bid to halt the global year-on-year rise in obesity prevalence. Epidemiological evidence suggests that populations who follow a fibre-rich, traditional diet are likely to have a lower body weight and improved metabolic parameters than their Western-diet counterparts. The colonic effects of fibre, and more specifically the SCFA that the fermentation process produces, may play a role in maintaining energy homeostasis via their action on the G-coupled protein receptor free fatty acid receptor 2 (FFA2; formerly GPR43). In the present review, we summarise the evidence for and against the role of FFA2 in energy homeostasis circuits and the possible ways that these could be exploited therapeutically. We also propose that the decline in fibre content of the diet since the Industrial Revolution, particularly fermentable fractions, may have resulted in the FFA2-mediated circuits being under-utilised and hence play a role in the current obesity epidemic.

Effect of butyrate enemas on inflammation and antioxidant status in the colonic mucosa of patients with ulcerative colitis in remission

BACKGROUND & AIMS

Butyrate, produced by colonic fermentation of dietary fibers is often hypothesized to beneficially affect colonic health. This study aims to assess the effects of butyrate on inflammation and oxidative stress in subjects with chronically mildly elevated parameters of inflammation and oxidative stress.

METHODS

Thirty-five patients with ulcerative colitis in clinical remission daily administered 60 ml rectal enemas containing 100mM sodium butyrate (n=17) or saline (n=18) during 20 days (NCT00696098). Before and after the intervention feces, blood and colonic mucosal biopsies were obtained. Parameters of antioxidant defense and oxidative damage, myeloperoxidase, several cytokines, fecal calprotectin and CRP were determined.

RESULTS

Butyrate enemas induced minor effects on colonic inflammation and oxidative stress. Only a significant increase of the colonic IL-10/IL-12 ratio was found within butyrate-treated patients (p=0.02), and colonic concentrations of CCL5 were increased after butyrate compared to placebo treatment (p=0.03). Although in general butyrate did not affect colonic glutathione levels, the effects of butyrate enemas on total colonic glutathione appeared to be dependent on the level of inflammation.

CONCLUSION

Although UC patients in remission were characterized by low-grade oxidative stress and inflammation, rectal butyrate enemas showed only minor effects on inflammatory and oxidative stress parameters.

Role of colonic short-chain fatty acid transport in diarrhea

Short-chain fatty acids (SCFA) are the major anion in stool and are synthesized from nonabsorbed carbohydrate by the colonic microbiota. Nonabsorbed carbohydrate are not absorbed in the colon and induce an osmotically mediated diarrhea; in contrast, SCFA are absorbed by colonic epithelial cells and stimulate Na-dependent fluid absorption via a cyclic AMP-independent process involving apical membrane Na-H, SCFA-HCO(3), and Cl-SCFA exchanges. SCFA production represents an adaptive process to conserve calories, fluid, and electrolytes. Inhibition of SCFA synthesis by antibiotics and administration of PEG, a substance that is not metabolized by colonic microbiota, both result in diarrhea. In contrast, increased production of SCFA as a result of providing starch that is relatively resistant to amylase digestion [so-called resistant starch (RS)] to oral rehydration solution (RS-ORS) improves the efficacy of ORS and represents an important approach to improve the effectiveness of ORS in the treatment of acute diarrhea in children under five years of age.

Butyrate-stimulated H2S production in colon cancer cells

Butyrate is a short-chain fatty acid that arrests growth of various types of cells. H(2)S can be endogenously produced by cystathionine gamma-lyase (CSE) or cystathionine beta-synthase (CBS) or both in colonic tissues. In this study, we observed endogenous H(2)S production in a colon cancer cell line (WiDr) and colonic tissues through the activity of both CSE and CBS. After 24 h of incubation of WiDr cells, butyrate increased cell production of H(2)S and upregulated CBS and CSE expressions. Both butyrate and NaHS (a H(2)S donor) decreased cell viability in a dose-dependent manner. Blockade of CBS, but not CSE, decreased butyrate-stimulated H(2)S production and reversed butyrate-inhibited cell viability. In addition, NaHS treatment stimulated the phosphorylation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), but not c-Jun N-terminal kinase (JNK). Inhibition of the phosphorylation of either p38 MAPK or ERK did not abolish NaHS-induced cell death. Butyrate treatment increased the phosphorylation of ERK, not p38 MAPK and JNK, but inhibition of ERK and p38 MAPK phosphorylation did not inhibit butyrate-reduced cell viability. In conclusion, butyrate regulates endogenous H(2)S production by stimulating CBS expression in colon cancer cells, but butyrate and H(2)S inhibit cancer cell growth through different mechanisms.

Short-chain fatty acids regulate the enteric neurons and control gastrointestinal motility in rats

BACKGROUND & AIMS

Little is known about the environmental and nutritional regulation of the enteric nervous system (ENS), which controls gastrointestinal motility. Short-chain fatty acids (SCFAs) such as butyrate regulate colonic mucosa homeostasis and can modulate neuronal excitability. We investigated their effects on the ENS and colonic motility.

METHODS

Effects of butyrate on the ENS were studied in colons of rats given a resistant starch diet (RSD) or intracecal perfusion of SCFAs. Effects of butyrate were also studied in primary cultures of ENS. The neurochemical phenotype of the ENS was analyzed with antibodies against Hu, choline acetyltransferase (ChAT), and neuronal nitric oxide synthase (nNOS) and by quantitative polymerase chain reaction. Signaling pathways involved were analyzed by pharmacologic and molecular biology methods. Colonic motility was assessed in vivo and ex vivo.

RESULTS

In vivo and in vitro, RSD and butyrate significantly increased the proportion of ChAT- but not nNOS-immunoreactive myenteric neurons. Acetate and propionate did not reproduce the effects of butyrate. Enteric neurons expressed monocarboxylate transporter 2 (MCT2). Small interfering RNAs silenced MCT2 and prevented the increase in the proportion of ChAT- immunoreactive neurons induced by butyrate. Butyrate and trichostatin A increased histone H3 acetylation in enteric neurons. Effects of butyrate were prevented by inhibitors of the Src signaling pathway. RSD increased colonic transit, and butyrate increased the cholinergic-mediated colonic circular muscle contractile response ex vivo.

CONCLUSION

Butyrate or histone deacetylase inhibitors might be used, along with nutritional approaches, to treat various gastrointestinal motility disorders associated with inhibition of colonic transit.

A human gut microbial gene catalogue established by metagenomic sequencing

To understand the impact of gut microbes on human health and well-being it is crucial to assess their genetic potential. Here we describe the Illumina-based metagenomic sequencing, assembly and characterization of 3.3 million non-redundant microbial genes, derived from 576.7 gigabases of sequence, from faecal samples of 124 European individuals. The gene set, approximately 150 times larger than the human gene complement, contains an overwhelming majority of the prevalent (more frequent) microbial genes of the cohort and probably includes a large proportion of the prevalent human intestinal microbial genes. The genes are largely shared among individuals of the cohort. Over 99% of the genes are bacterial, indicating that the entire cohort harbours between 1,000 and 1,150 prevalent bacterial species and each individual at least 160 such species, which are also largely shared. We define and describe the minimal gut metagenome and the minimal gut bacterial genome in terms of functions present in all individuals and most bacteria, respectively.

A human gut microbial gene catalogue established by metagenomic sequencing

To understand the impact of gut microbes on human health and well-being it is crucial to assess their genetic potential. Here we describe the Illumina-based metagenomic sequencing, assembly and characterization of 3.3 million non-redundant microbial genes, derived from 576.7 gigabases of sequence, from faecal samples of 124 European individuals. The gene set, approximately 150 times larger than the human gene complement, contains an overwhelming majority of the prevalent (more frequent) microbial genes of the cohort and probably includes a large proportion of the prevalent human intestinal microbial genes. The genes are largely shared among individuals of the cohort. Over 99% of the genes are bacterial, indicating that the entire cohort harbours between 1,000 and 1,150 prevalent bacterial species and each individual at least 160 such species, which are also largely shared. We define and describe the minimal gut metagenome and the minimal gut bacterial genome in terms of functions present in all individuals and most bacteria, respectively.

Butyrate utilization by the colonic mucosa in inflammatory bowel diseases: a transport deficiency

The short-chain fatty acid butyrate, which is mainly produced in the lumen of the large intestine by the fermentation of dietary fibers, plays a major role in the physiology of the colonic mucosa. It is also the major energy source for the colonocyte. Numerous studies have reported that butyrate metabolism is impaired in intestinal inflamed mucosa of patients with inflammatory bowel disease (IBD). The data of butyrate oxidation in normal and inflamed colonic tissues depend on several factors, such as the methodology or the models used or the intensity of inflammation. The putative mechanisms involved in butyrate oxidation impairment may include a defect in beta oxidation, luminal compounds interfering with butyrate metabolism, changes in luminal butyrate concentrations or pH, and a defect in butyrate transport. Recent data show that butyrate deficiency results from the reduction of butyrate uptake by the inflamed mucosa through downregulation of the monocarboxylate transporter MCT1. The concomitant induction of the glucose transporter GLUT1 suggests that inflammation could induce a metabolic switch from butyrate to glucose oxidation. Butyrate transport deficiency is expected to have clinical consequences. Particularly, the reduction of the intracellular availability of butyrate in colonocytes may decrease its protective effects toward cancer in IBD patients.

Fermentation supernatants of wheat ( Triticum aestivum L.) aleurone beneficially modulate cancer progression in human colon cells

Wheat aleurone contains high amounts of dietary fibers that are fermented by the microflora, resulting in the formation of short-chain fatty acids (SCFA), which are recognized for their chemopreventive potential. This study investigated the effects of fermented aleurone on growth, apoptosis, differentiation, and expression of several genes using two different human colon cell lines (LT97 and HT29). In LT97 cells, the fermentation supernatant (fs) aleurone reduced significantly the cell growth (EC(50) after 48 h = 7.6-8.3%), whereas the level of apoptotic cells was significantly increased (2.1-2.3-fold). Differentiation was enhanced in HT29 cells (1.8-fold) more than in LT97 cells (1.6-fold). Cell growth and apoptosis-related genes, namely WNT2B and p21, were induced by the fs (LT97, 1.7-3.3-fold; HT29, 7.9-22.2-fold). In conclusion, fermented wheat aleurone is able to act as a secondary chemopreventive agent by modulating parameters of cell growth and survival, whereas cells of an early transformation stage are more sensitive.

Gene expression profiles in human peripheral blood mononuclear cells as biomarkers for nutritional in vitro and in vivo investigations

Identification of chemopreventive substances may be achieved by measuring biological endpoints in human cells in vitro. Since generally only tumour cells are available for such investigations, our aim was to test the applicability of peripheral blood mononuclear cells (PBMC) as an in vitro primary cell model since they mimic the human in vivo situation and are relatively easily available. Cell culture conditions were refined, and the basal variation of gene expression related to drug metabolism and stress response was determined. Results were compared with profiles of an established human colon cell line (HT29) as standard. For biomarker development of nutritional effects, PBMC and HT29 cells were treated with potentially chemopreventive substances (chrysin and butyrate), and gene expression was determined. Key results were that relevant stress response genes, such as glutathione S-transferase T2 (GSTT2) and GSTM2, were modulated by butyrate in PBMC as in HT29 cells, but the blood cells were less sensitive and responded with high individual differences. We conclude that these cells may serve as a surrogate tissue in dietary investigations and the identified differentially expressed genes have the potential to become marker genes for population studies on biological effects.

Butyrate mediates nucleotide-binding and oligomerisation domain (NOD) 2-dependent mucosal immune responses against peptidoglycan

The interaction between digestive tract microbiological flora and food has an important influence on human health. Butyrate is produced during the fermentation of dietary fibres by intestinal bacteria and plays an important role in the regulation of mucosal immunity. In this report, we studied the impact of butyrate on the defence mechanism against the bacterial membrane component peptidoglycan (PGN). Butyrate was found to enhance PGN-mediated IL-8 and GRO-alpha production. The expression of these chemokines required the activation of NF-kappaB and was dependent on the concentrations of butyrate and PGN. Butyrate was found to up-regulate nucleotide-binding and oligomerisation domain (NOD) 2, but not NOD1 or TLR2. NOD2 up-regulation was mediated by an increase in histone acetylation in the Nod2 promoter region, leading to enhanced PGN-induced IL-8 and GRO-alpha secretion. Knockdown of NOD2 and TLR2 by siRNA significantly reduced PGN-mediated chemokine production, suggesting that both NOD2 and TLR2 are required for maximal response. Our findings provide a better understanding of the mechanism by which butyrate regulates mucosal immunity for normal intestinal function. Based on the results of this study, we infer that dietary fibres can impact inflammatory bowel diseases.

Diversity of human colonic butyrate-producing bacteria revealed by analysis of the butyryl-CoA:acetate CoA-transferase gene

Butyrate-producing bacteria play an important role in the human colon, supplying energy to the gut epithelium and regulating host cell responses. In order to explore the diversity and culturability of this functional group, we designed degenerate primers to amplify butyryl-CoA:acetate CoA-transferase sequences from faecal samples provided by 10 healthy volunteers. Eighty-eight per cent of amplified sequences showed >98% DNA sequence identity to CoA-transferases from cultured butyrate-producing bacteria, and these fell into 12 operational taxonomic units (OTUs). The four most prevalent OTUs corresponded to Eubacterium rectale, Roseburia faecis, Eubacterium hallii and an unnamed cultured species SS2/1. The remaining 12% of sequences, however, belonged to 20 OTUs that are assumed to come from uncultured butyrate-producing strains. Samples taken after ingestion of inulin showed significant (P=0.019) increases in Faecalibacterium prausnitzii. Because several of the dominant butyrate producers differ in their DNA % G+C content, analysis of thermal melt curves obtained for PCR amplicons of the butyryl-CoA:acetate CoA-transferase gene provides a convenient and rapid qualitative assessment of the major butyrate producing groups present in a given sample. This type of analysis therefore provides an excellent source of information on functionally important groups within the colonic microbial community.

Probiotics and prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating disease affecting primarily premature infants. Despite advances in neonatal care, the mortality rate following NEC has not changed significantly in the past 30 years. New preventative measures are needed. In this review, we will provide information to assess the possible role of probiotics, prebiotics and related agents in the prevention of this devastating disease. We will also discuss short and long term safety issues as well as potential alternatives. Although it is tempting to rebuild the intestinal microbiota using the agents such as pro and prebiotics during infancy, routine use is not yet warranted a cautious approach on the basis of sounds scientific data is needed.

The role of innate signaling in the homeostasis of tolerance and immunity in the intestine

In the intestine innate recognition of microbes is achieved through pattern recognition receptor (PRR) families expressed in immune cells and different cell lineages of the intestinal epithelium. Toll-like receptor (TLR) and nucleotide-binding and oligomerization domain-like receptor (NLR) families are emerging as key mediators of immunity through their role as maturation factors of immune cells and triggers for the production of cytokines and chemokines and antimicrobial factors. At the mucosal surface chronic activation of the immune system is avoided through the epithelial production of a glycocalyx, steady-state production of antimicrobial factors as well as the selective expression and localization of PRRs. Additionally, the polarization of epithelial TLR signaling and suppression of NF-kappaB activation by luminal commensals appears to contribute to the homeostasis of tolerance and immunity. Several studies have demonstrated that TLR signaling in epithelial cells contributes to a range of homeostatic mechanisms including proliferation, wound healing, epithelial integrity, and regulation of mucosal immune functions. The intestinal epithelium appears to have uniquely evolved to maintain mucosal tolerance and immunity, and future efforts to further understand the molecular mechanisms of intestinal homeostasis may have a major impact on human health.

Probiotic microbes: do they need to be alive to be beneficial?

An essential symbiotic relationship exists between intestinal cells and commensal bacteria within the human gastrointestinal tract. Alteration or absence of this interaction may play a role in the development of human disease. Use of probiotic organisms has yielded improvement of certain medical conditions, such as inflammatory and infectious gastrointestinal disease, although the mechanisms of benefit remain poorly defined. The administration of live organisms is not without risk, both potential and realized, particularly in certain populations. Therefore, it is of considerable interest to determine if the health benefits of probiotics can be attained without the risks associated with administration of a live organism. Reviewed here is the evidence that heat-killed, ultraviolet-inactivated, and even components of these agents may be just as effective and considerably safer for the host.

Fermented wheat aleurone inhibits growth and induces apoptosis in human HT29 colon adenocarcinoma cells

Fermentation of dietary fibre by the gut microflora may enhance levels of SCFA, which are potentially chemoprotective against colon cancer. Functional food containing wheat aleurone may prevent cancer by influencing cell cycle and cell death. We investigated effects of fermented wheat aleurone on growth and apoptosis of HT29 cells. Wheat aleurone, flour and bran were digested and fermentedin vitro. The resulting fermentation supernatants (fs) were analysed for their major metabolites (SCFA, bile acids and ammonia). HT29 cells were treated for 24–72 h with the fs or synthetic mixtures mimicking the fs in SCFA, butyrate or deoxycholic acid (DCA) contents, and the influence on cell growth was determined. Fs aleurone was used to investigate the modulation of apoptosis and cell cycle. The fermented wheat samples contained two- to threefold higher amounts of SCFA than the faeces control (blank), but reduced levels of bile acids and increased concentrations of ammonia. Fs aleurone and flour equally reduced cell growth of HT29 more effectively than the corresponding blank and the SCFA mixtures. The EC50(48 h) ranged from 10 % (flour) to 19 % (blank). Markedly after 48 h, fs aleurone (10 %) significantly induced apoptosis and inhibited cell proliferation by arresting the cell cycle in the G0/G1 phase. In conclusion, fermentation of wheat aleurone results in a reduced level of tumour-promoting DCA, but higher levels of potentially chemopreventive SCFA. Fermented wheat aleurone is able to induce apoptosis and to block cell cycle – two essential markers of secondary chemoprevention.

The effects of butyrate enemas on visceral perception in healthy volunteers

Fermentation of dietary fibres by colonic microbes leads to the production of short chain fatty acids (mainly propionate, butyrate and acetate), which are utilized by the colonic mucosa. Previous studies showed positive effects of butyrate on parameters of oxidative stress, inflammation and apoptosis. Recent studies in rats, however, showed that butyrate increased visceral sensitivity. The aim of this study was to determine the effects of physiologically relevant concentrations of butyrate on visceral perception in healthy human subjects. Eleven healthy volunteers participated in this randomized double-blind, placebo controlled cross-over study. The study consisted of three periods of 1 week each, in which the volunteers daily self-administered rectal enemas containing 100, 50 mmol L(-1) butyrate, or placebo (saline) prior to sleeping. A rectal barostat measurement was performed at the start and the end of each test period for the measurement of pain, urge and discomfort. Butyrate treatment resulted in a dose-dependent reduction of pain, urge and discomfort throughout the entire pressure range of the protocol. At a pressure of 4 mmHg, 50 and 100 mmol L(-1) butyrate concentrations resulted in a 23.9% and 42.1% reduction of pain scores, respectively, and the discomfort scores decreased by 44.2% and 69.0% respectively. At a pressure of 67 mmHg, 50 and 100 mmol L(-1) of butyrate decreased the pain scores by 23.8% and 42%, respectively, and discomfort scores 1.9% and 5.2% respectively. Colonic administration of butyrate, at physiologically relevant concentrations, dose-dependently decreases visceral sensitivity in healthy volunteers.

Current progress on butyric acid production by fermentation

Several issues of butyric acid production with bacteria through fermentation are presented in this review. The current progress including the utilization of butyric acid, the production strains, the metabolic pathway, and regulation are presented in the paper. Process operation modes such as batch, fed-batch, and continuous fermentation are being discussed. Genetic engineering technologies for microbial strain improvement are also being discussed and fermentation systems have been recommended.

Butyrate-induced transcriptional changes in human colonic mucosa

Background

Fermentation of dietary fiber in the colon results in the production of short chain fatty acids (mainly propionate, butyrate and acetate). Butyrate modulates a wide range of processes, but its mechanism of action is mostly unknown. This study aimed to determine the effects of butyrate on the transcriptional regulation of human colonic mucosa in vivo.

Methodology/Principal Findings

Five hundred genes were found to be differentially expressed after a two week daily butyrate administration with enemas. Pathway analysis showed that the butyrate intervention mainly resulted in an increased transcriptional regulation of the pathways representing fatty acid oxidation, electron transport chain and oxidative stress. In addition, several genes associated with epithelial integrity and apoptosis, were found to be differentially expressed after the butyrate intervention.

Conclusions/Significance

Colonic administration of butyrate in concentrations that can be achieved by consumption of a high-fiber diet enhances the maintenance of colonic homeostasis in healthy subjects, by regulating fatty acid metabolism, electron transport and oxidative stress pathways on the transcriptional level and provide for the first time, detailed molecular insight in the transcriptional response of gut mucosa to butyrate.

Lactate has the potential to promote hydrogen sulphide formation in the human colon

High concentrations of sulphide are toxic for the gut epithelium and may contribute to bowel disease. Lactate is a favoured cosubstrate for the sulphate-reducing colonic bacterium Desulfovibrio piger, as shown here by the stimulation of sulphide formation by D. piger DSM749 by lactate in the presence of sulphate. Sulphide formation by D. piger was also stimulated in cocultures with the lactate-producing bacterium Bifidobacterium adolescentis L2-32. Other lactate-utilizing bacteria such as the butyrate-producing species Eubacterium hallii and Anaerostipes caccae are, however, expected to be in competition with the sulphate-reducing bacteria (SRB) for the lactate formed in the human colon. Strains of E. hallii and A. caccae produced 65% and 96% less butyrate from lactate, respectively, in a coculture with D. piger DSM749 than in a pure culture. In triculture experiments involving B. adolescentis L2-32, up to 50% inhibition of butyrate formation by E. hallii and A. caccae was observed in the presence of D. piger DSM749. On the other hand, sulphide formation by D. piger was unaffected by E. hallii or A. caccae in these cocultures and tricultures. These experiments strongly suggest that lactate can stimulate sulphide formation by SRB present in the colon, with possible consequences for conditions such as colitis.

Peptide-YY is released by the intestinal cell line STC-1

Dietary modulation of the response of gut satiety hormones, which partly regulate food intake, provides a promising treatment for overweight and obesity. Gut-derived cell lines such as STC-1 are widely used to investigate these hormonal responses to nutrients. To date, no peptide-YY (PYY) secreting cell line has been identified. The aim of this study was to investigate whether STC-1 cells are able to secrete PYY and if so, whether dietary compounds can modulate PYY secretion. The effects of fatty acid types C4:0, C12:0, C14:0, C16:0, and C18:0 on PYY release were investigated by measuring PYY in the supernatant after 30, 60, 90, and 120 min of incubation, respectively, using RIA assays. The STC-1 cells were able to secrete PYY in a time-dependent manner. It was shown that after 30 min, C4:0, C12:0, C16:0, and C18:0 caused increased PYY levels compared to the control. At time points 60 and 90 min, C4:0 and C18:0 induced elevated PYY levels compared to the control. After 120 min, C4:0, C14:0, and C18:0 caused elevated levels compared to the control. We are the first to show that the STC-1 cells are also able to secrete PYY next to cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1). Addition of fatty acids resulted in increased levels of PYY, which is consistent with the literature describing human studies. We conclude that the STC-1 cell line provides an appropriate cell line for screening the effects of ingredients on the release of the satiety-related gut hormones CCK, GLP-1, and PYY.

Importance of glycans to the host-bacteroides mutualism in the mammalian intestine

Much of the mutualistic relationship between humans and their resident intestinal Bacteroides species is founded on glycans. The host provides plant polysaccharides and host-derived glycans and, in return, receives beneficial end products of bacterial fermentation. Glycans from the bacteria themselves are required for the establishment and survival of these organisms in the colonic ecosystem and provide immunomodulatory properties to the host. Coordinated synthesis and catabolism of bacterial glycans is likely to contribute to the host-bacterial mutualism.

The role of whole-wheat grain and wheat and rye ingredients on the digestion and fermentation processes in the gut--a model experiment with pigs

The effect of wheat and rye breads made from white wheat flour with added refined fibre (WFL), whole-wheat grain, wheat aleurone flour (WAF) or rye aleurone flour (RAF) on digestion and fermentation processes in the gut was studied in a model experiment with pigs. The diets were similar in dietary fibre (DF) but differed in arabinoxylan (AX) content and composition. Twenty pigs were fed the breads three times daily (08.00, 13.00 and 18.00 hours) and the digesta collected through a T-cannula for two successive periods (breakfast: 8.00-13.00; lunch: 13.00-18.00 hours). Faeces were collected for 24 h and caecal and colonic contents at slaughter. The rigid nature of the aleurone cell walls encapsulated nutrients, which resulted in reduced (P < 0.01) digestibility of protein (WAF and RAF breads) and fat (RAF bread). For the RAF bread, the digestibility of starch was also lower (P < 0.001) than of the wheat-based diets primarily due to the higher intestinal viscosity. The DF composition had an impact on (P < 0.001) the site for fibre degradation in the large intestine. Thus, AX of the WAF bread, with the lowest degree of substitution, were fermented as much in the caecum as in the colon, whereas AX of the RAF bread, with an intermediary degree of substitution, were mainly fermented in the caecum. The WFL bread, rich in cellulose, was fermented more distally. Fermentation of experimental breads in the large intestine had no effect (P>0.05) on the production of metabolites, except for butyrate which was higher (P < 0.01) after the WAF bread consumption.

In vitro kinetics of prebiotic inulin-type fructan fermentation by butyrate-producing colon bacteria: implementation of online gas chromatography for quantitative analysis of carbon dioxide and hydrogen gas production

Kinetic analyses of bacterial growth, carbohydrate consumption, and metabolite production of five butyrate-producing clostridial cluster XIVa colon bacteria grown on acetate plus fructose, oligofructose, inulin, or lactate were performed. A gas chromatography method was set up to assess H2 and CO2 production online and to ensure complete coverage of all metabolites produced. Method accuracy was confirmed through the calculation of electron and carbon recoveries. Fermentations with Anaerostipes caccae DSM 14662(T), Roseburia faecis DSM 16840(T), Roseburia hominis DSM 16839(T), and Roseburia intestinalis DSM 14610(T) revealed similar patterns of metabolite production with butyrate, CO2, and H2 as the main metabolites. R. faecis DSM 16840(T) and R. intestinalis DSM 14610(T) were able to degrade oligofructose, displaying a nonpreferential breakdown mechanism. Lactate consumption was only observed with A. caccae DSM 14662(T). Roseburia inulinivorans DSM 16841(T) was the only strain included in the present study that was able to grow on fructose, oligofructose, and inulin. The metabolites produced were lactate, butyrate, and CO2, without H2 production, indicating an energy metabolism distinct from that of other Roseburia species. Oligofructose degradation was nonpreferential. In a coculture of R. inulinivorans DSM 16841(T) with the highly competitive strain Bifidobacterium longum subsp. longum LMG 11047 on inulin, hardly any production of butyrate and CO2 was detected, indicating a lack of competitiveness of the butyrate producer. Complete recovery of metabolites during fermentations of clostridial cluster XIVa butyrate-producing colon bacteria allowed stoichiometric balancing of the metabolic pathway for butyrate production, including H2 formation.

In vitro studies on the inhibition of colon cancer by butyrate and carnitine

OBJECTIVE

Epidemiologic studies support an association between diet and the incidence of colorectal cancer. Butyrate, a short-chain fatty acid present in dietary fiber and dairy products, is a potential anticarcinogenic compound. We previously showed that carnitine can enhance the bioavailability of butyrate in vivo. In the present study, we evaluated the effects of butyrate alone and in combination with carnitine on colon cancer cells in vitro, examining proliferation and apoptosis and the molecular mechanisms by which these nutrients may inhibit colon cancer.

METHODS

Caco-2 cells, a well-established cell model, were incubated with butyrate (2.5-20mM) with or without carnitine (10mM) for various incubation periods. Proliferation was measured by incorporation of (3)H-thymidine, and apoptosis was detected using flow cytometry, and then confirmed by analyzing the presence of single-strand DNA breaks typical of apoptotic cells. Prostaglandin E(2) production was assayed and Bcl-2 and cyclo-oxygenase-2 expressions were examined by western blotting.

RESULTS

Butyrate and carnitine inhibited Caco-2 cell proliferation (P<0.05) and induced apoptosis (P<0.05). Prostaglandin E(2) production was decreased in treated Caco-2 cells. At the molecular level, the expression of proapoptotic Bax and Bak proteins were increased in cells incubated with butyrate and carnitine, whereas expression of antiapoptotic Bcl-x(L) was decreased. Cyclo-oxygenase-2 expression was decreased in cells incubated with butyrate and carnitine.

CONCLUSIONS

Butyrate and carnitine inhibit human colon carcinoma cell proliferation and induce apoptosis in human colon carcinoma cells. This is accompanied by an appreciable alteration of the Bax-to-Bcl-x(L) and Bak-to-Bcl-x(L) ratios in favor of apoptosis. This study provides a scientific rationale to study the effects of carnitine and butyrate in colon cancer in vivo.

Short chain fatty acids exchange across the gut and liver in humans measured at surgery

BACKGROUND & AIMS

Short chain fatty acids (SCFAs; acetate, propionate and butyrate) are important energy sources for colonocytes and are assumed to play a key role in gut health. Local effects of SCFAs have been investigated, but less is known about whole body metabolism of these SCFAs. The aim of the present study was to quantify the role of the gut and liver in interorgan exchange of SCFAs in humans in vivo.

METHODS

Twenty-two patients undergoing major upper abdominal surgery were studied. Blood was sampled from a radial artery, the portal and a hepatic vein. Portal, splanchnic and arterial blood flow was measured using intra-operative Duplex ultrasonography. SCFAs were measured on a liquid chromatography system combined with mass spectrometry.

RESULTS

SCFAs were released by the gut, 34.9 (9.1) micromol kg bodyweight(-1)h(-1). SCFAs uptake by the liver was significant for propionate and butyrate; -5.6 (1.3) and -3.8 (1.6) micromol kg bodyweight(-1)h(-1) (p=0.0002 and p=0.03) respectively and counterbalanced gut release. Liver uptake of acetate was not significant, -5.2 (6.6) micromol kg bodyweight(-1)h(-1) (p=0.434). Splanchnic (i.e., gut+liver) SCFAs release was significant for acetate and propionate, 17.3 (7.3) and 1.2 (0.4) micromol kg bodyweight(-1)h(-1) (p=0.027 and p=0.0038), respectively. Splanchnic release of butyrate was not significantly different from zero (1.9 (1.2) micromol kg bodyweight(-1)h(-1), p=0.129). BMI and previous colonic resection did not affect gut release of SCFAs.

CONCLUSION

This is the first in vivo study on the role of the gut and liver in SCFAs exchange in humans in vivo. It is shown that intestinal SCFAs release by the gut is equalled by hepatic uptake.

The role of pH in determining the species composition of the human colonic microbiota

The pH of the colonic lumen varies with anatomical site and microbial fermentation of dietary residue. We have investigated the impact of mildly acidic pH, which occurs in the proximal colon, on the growth of different species of human colonic bacteria in pure culture and in the complete microbial community. Growth was determined for 33 representative human colonic bacteria at three initial pH values (approximately 5.5, 6.2 and 6.7) in anaerobic YCFA medium, which includes a mixture of short-chain fatty acids (SCFA) with 0.2% glucose as energy source. Representatives of all eight Bacteroides species tested grew poorly at pH 5.5, as did Escherichia coli, whereas 19 of the 23 gram-positive anaerobes tested gave growth rates at pH 5.5 that were at least 50% of those at pH 6.7. Growth inhibition of B. thetaiotaomicron at pH 5.5 was increased by the presence of the SCFA mix (33 mM acetate, 9 mM propionate and 1 mM each of iso-valerate, valerate and iso-butyrate). Analysis of amplified 16S rRNA sequences demonstrated a major pH-driven shift within a human faecal bacterial community in a continuous flow fermentor. Bacteroides spp. accounted for 27% of 16S rRNA sequences detected at pH 5.5, but 86% of sequences at pH 6.7. Conversely, butyrate-producing gram-positive bacteria related to Eubacterium rectale represented 50% of all 16S rRNA sequences at pH 5.5, but were not detected at pH 6.7. Inhibition of the growth of a major group of gram-negative bacteria at mildly acidic pH apparently creates niches that can be exploited by more low pH-tolerant microorganisms.

Advances in understanding colonic function

The colon is an organ of conservation that salvages water, electrolytes, and energy. The organization of colonic function is determined by the roles played by the luminal flora, the function of the different mucosal epithelial cell types, immunocompetent cells, and the neuromusculature. These different components of the colon interact with one another and with the colonic flora, and different areas of the colon serve different functions. In the normal adult during the course of a day the colon absorbs approximately 1.5 L of fluid, but under the influence of aldosterone increases up to 5 to 6 L. Diarrhoea occurs when secretion exceeds absorptive processes by either small intestinal secretion overwhelming colonic salvage or salvage being impaired by reduced colonic absorption or increased colonic secretion.

Regulation of virulence by butyrate sensing in enterohaemorrhagic Escherichia coli

Enterohaemorrhagic Escherichia coli (EHEC) colonizes and proliferates at the mucosal surface, inducing severe diarrhoea. Short-chain fatty acids (SCFAs) are abundant in the intestine owing to the metabolic activity of microflora, and are important for colonic health. We found that, although a high concentration of SCFAs inhibited the growth of EHEC, at low concentrations, the SCFAs markedly enhanced the expression of the virulence genes required for cell adherence and the induction of attaching and effacing (A/E) lesions. Of the SCFAs tested, butyrate markedly enhanced the expression of these virulence-associated genes, even at the low concentration of 1.25 mM, but acetate and propionate showed only a small effect at concentrations higher than 40 mM. Butyrate enhanced the promoter activity of the LEE1 operon, which encodes a global regulator of the LEE genes, Ler. This enhancement was dependent on a regulator, PchA. Butyrate sensing was completely abrogated by the deletion of lrp, the gene for the leucine-responsive regulatory protein, Lrp. Expression of a constitutively active mutant of Lrp enhanced the expression of the LEE genes in the absence of butyrate, and a response-defective Lrp derivative reduced the response to butyrate. Thus, upon entering the distal ileum, EHEC may respond to the higher butyrate level via Lrp by increasing its virulence expression, leading to efficient colonization of the target niche.

GPR109A is a G-protein-coupled receptor for the bacterial fermentation product butyrate and functions as a tumor suppressor in colon

Short-chain fatty acids, generated in colon by bacterial fermentation of dietary fiber, protect against colorectal cancer and inflammatory bowel disease. Among these bacterial metabolites, butyrate is biologically most relevant. GPR109A is a G-protein-coupled receptor for nicotinate but recognizes butyrate with low affinity. Millimolar concentrations of butyrate are needed to activate the receptor. Although concentrations of butyrate in colonic lumen are sufficient to activate the receptor maximally, there have been no reports on the expression/function of GPR109A in this tissue. Here we show that GPR109A is expressed in the lumen-facing apical membrane of colonic and intestinal epithelial cells and that the receptor recognizes butyrate as a ligand. The expression of GPR109A is silenced in colon cancer in humans, in a mouse model of intestinal/colon cancer, and in colon cancer cell lines. The tumor-associated silencing of GPR109A involves DNA methylation directly or indirectly. Reexpression of GPR109A in colon cancer cells induces apoptosis, but only in the presence of its ligands butyrate and nicotinate. Butyrate is an inhibitor of histone deacetylases, but apoptosis induced by activation of GPR109A with its ligands in colon cancer cells does not involve inhibition of histone deacetylation. The primary changes in this apoptotic process include down-regulation of Bcl-2, Bcl-xL, and cyclin D1 and up-regulation of death receptor pathway. In addition, GPR109A/butyrate suppresses nuclear factor-kappaB activation in normal and cancer colon cell lines as well as in normal mouse colon. These studies show that GPR109A mediates the tumor-suppressive effects of the bacterial fermentation product butyrate in colon.

Effect of high amylose maize starches on colonic fermentation and apoptotic response to DNA-damage in the colon of rats

Background

We investigated in rats the effects of feeding different forms of high amylose maize starches (HAMS) rich in resistant starch (RS) to understand what the implications of RS heterogeneity might be for colonic biology, including innate cellular responses to DNA-damage.

Methods

A range of maize starches were compared: digestible cornstarch (Control), HYLON^® VII, Hi-maize^® 1043, Hi-maize^® 240, Hi-maize^® 260 and NOVELOSE^® 330. Included in the comparison was Cellulose. End-points after 4 weeks included: pH, short chain fatty acids (SCFA) levels, colonic epithelial cell kinetics and apoptotic response to carcinogen 'azoxymethane' in the colonic epithelium.

Results

The RS diets significantly increased SCFA and reduced pH in caecal content and faeces. Hi-maize 260 resulted in the highest butyrate concentrations. All RS diets prevented the mucosal atrophy as seen in the rats fed the Control diet. Epithelial cell turnover was increased in the Control and Cellulose groups compared to the Hi-maize 260, HYLON VII and NOVELOSE 330 groups (P < 0.01). The apoptotic response to azoxymethane was higher only in the Hi-maize 260 group compared to the Control group (P < 0.01). Butyrate correlated positively with the apoptotic response (P < 0.01).

Conclusion

The consumption of RS elicits a range of beneficial physiological and protective effects associated with the fermentation of RS. Increased production of butyrate seems a likely explanation by which RS enhances the apoptotic response to carcinogen-induced DNA damage which is consistent with the proposed role of this SCFA in promoting a normal cell phenotype and preventing the development of abnormal cell populations.

Fermentation products of inulin-type fructans reduce proliferation and induce apoptosis in human colon tumour cells of different stages of carcinogenesis

Epidemiological evidence suggests that the intake of prebiotic dietary fibres, for example, inulin, protects against colorectal cancer. However, little is known about cellular responses to complex fermentation samples. Therefore, we prepared a fermentation supernatant fraction of inulin and studied biological properties in human colon cell lines, LT97 and HT29 (representing early and late stages of colon cancer). Inulin enriched with oligofructose (Synergy 1) was incubated under anaerobic conditions with faecal inocula and the supernatant fraction was characterised for content of SCFA and secondary bile acid deoxycholic acid (DCA). A Synergy fermentation supernatant fraction (SFS) and a synthetic fermentation mixture (SFM) mimicking the SFS in SCFA and DCA content were used in the concentration range of 1.25-20 % (v/v) for 24-72 h. The effects on cell growth were determined by quantifying DNA. Effects on apoptosis were analysed by measuring poly(ADP-ribose) polymerase (PARP) cleavage using Western blotting. Compared with the faecal blank, produced without the addition of inulin, the SFS resulted in an almost 2.5-fold increase of SCFA and 3.4-fold decrease of DCA. In comparison with HT29 cells, LT97 cells responded more sensitively to the growth-inhibitory activities. Additionally, a significant increase in PARP cleavage was observed in LT97 cells after incubation with the SFS, demonstrating induction of apoptosis. The present results indicate growth-inhibiting and apoptosis-inducing effects of fermentation supernatant fractions of inulin. Moreover, since early adenoma cells were found to be more sensitive, this may have important implications for chemoprevention when translated to the in vivo situation, because survival of early transformed cells could be reduced.

The bacterial fermentation product butyrate influences epithelial signaling via reactive oxygen species-mediated changes in cullin-1 neddylation

The human enteric flora plays a significant role in intestinal health and disease. Populations of enteric bacteria can inhibit the NF-kappaB pathway by blockade of IkappaB-alpha ubiquitination, a process catalyzed by the E3-SCF(beta-TrCP) ubiquitin ligase. The activity of this ubiquitin ligase is regulated via covalent modification of the Cullin-1 subunit by the ubiquitin-like protein NEDD8. We previously reported that interaction of viable commensal bacteria with mammalian intestinal epithelial cells resulted in a rapid and reversible generation of reactive oxygen species (ROS) that modulated neddylation of Cullin-1 and resulted in suppressive effects on the NF-kappaB pathway. Herein, we demonstrate that butyrate and other short chain fatty acids supplemented to model human intestinal epithelia in vitro and human tissue ex vivo results in loss of neddylated Cul-1 and show that physiological concentrations of butyrate modulate the ubiquitination and degradation of a target of the E3- SCF(beta-TrCP) ubiquitin ligase, the NF-kappaB inhibitor IkappaB-alpha. Mechanistically, we show that physiological concentrations of butyrate induces reactive oxygen species that transiently alters the intracellular redox balance and results in inactivation of the NEDD8-conjugating enzyme Ubc12 in a manner similar to effects mediated by viable bacteria. Because the normal flora produces significant amounts of butyrate and other short chain fatty acids, these data provide a functional link between a natural product of the intestinal normal flora and important epithelial inflammatory and proliferative signaling pathways.

Diversity, metabolism and microbial ecology of butyrate-producing bacteria from the human large intestine

Butyrate-producing bacteria play a key role in colonic health in humans. This review provides an overview of the current knowledge of the diversity, metabolism and microbial ecology of this functionally important group of bacteria. Human colonic butyrate producers are Gram-positive firmicutes, but are phylogenetically diverse, with the two most abundant groups related to Eubacterium rectale/Roseburia spp. and to Faecalibacterium prausnitzii. Five different arrangements have been identified for the genes of the central pathway involved in butyrate synthesis, while in most cases butyryl-CoA : acetate CoA-transferase, rather than butyrate kinase, appears to perform the final step in butyrate synthesis. Mechanisms have been proposed recently in non-gut Clostridium spp. whereby butyrate synthesis can result in energy generation via both substrate-level phosphorylation and proton gradients. Here we suggest that these mechanisms also apply to the majority of butyrate producers from the human colon. The roles of these bacteria in the gut community and their influence on health are now being uncovered, taking advantage of the availability of cultured isolates and molecular methodologies. Populations of F. prausnitzii are reported to be decreased in Crohn's disease, for example, while populations of Roseburia relatives appear to be particularly sensitive to the diet composition in human volunteer studies.

Genes and molecules of lactobacilli supporting probiotic action

Lactobacilli have been crucial for the production of fermented products for centuries. They are also members of the mutualistic microbiota present in the human gastrointestinal and urogenital tract. Recently, increasing attention has been given to their probiotic, health-promoting capacities. Many human intervention studies demonstrating health effects have been published. However, as not all studies resulted in positive outcomes, scientific interest arose regarding the precise mechanisms of action of probiotics. Many reported mechanistic studies have addressed mainly the host responses, with less attention being focused on the specificities of the bacterial partners, notwithstanding the completion of Lactobacillus genome sequencing projects, and increasing possibilities of genomics-based and dedicated mutant analyses. In this emerging and highly interdisciplinary field, microbiologists are facing the challenge of molecular characterization of probiotic traits. This review addresses the advances in the understanding of the probiotic-host interaction with a focus on the molecular microbiology of lactobacilli. Insight into the molecules and genes involved should contribute to a more judicious application of probiotic lactobacilli and to improved screening of novel potential probiotics.