Short chain fatty acids in human large intestine, portal, hepatic and venous blood

Evidence for the occurrence of microbial breakdown of carbohydrate in the human colon has been sought by measuring short chain fatty acid (SCFA) concentrations in the contents of all regions of the large intestine and in portal, hepatic and peripheral venous blood obtained at autopsy of sudden death victims within four hours of death. Total SCFA concentration (mmol/kg) was low in the terminal ileum at 13 +/- 6 but high in all regions of the colon ranging from 131 +/- 9 in the caecum to 80 +/- 11 in the descending colon. The presence of branched chain fatty acids was also noted. A significant trend from high to low concentrations was found on passing distally from caecum to descending colon. pH also changed with region from 5.6 +/- 0.2 in the caecum to 6.6 +/- 0.1 in the descending colon. pH and SCFA concentrations were inversely related. Total SCFA (mumol/l) in blood was, portal 375 +/- 70, hepatic 148 +/- 42 and peripheral 79 +/- 22. In all samples acetate was the principal anion but molar ratios of the three principal SCFA changed on going from colonic contents to portal blood to hepatic vein indicating greater uptake of butyrate by the colonic epithelium and propionate by the liver. These data indicate that substantial carbohydrate, and possibly protein, fermentation is occurring in the human large intestine, principally in the caecum and ascending colon and that the large bowel may have a greater role to play in digestion than has previously been ascribed to it.

Fatty acids and eicosanoids regulate gene expression through direct interactions with peroxisome proliferator-activated receptors alpha and gamma

Peroxisome proliferator-activated receptors (PPARs) alpha and gamma are key regulators of lipid homeostasis and are activated by a structurally diverse group of compounds including fatty acids, eicosanoids, and hypolipidemic drugs such as fibrates and thiazolidinediones. While thiazolidinediones and 15-deoxy-Delta12, 14-prostaglandin J2 have been shown to bind to PPARgamma, it has remained unclear whether other activators mediate their effects through direct interactions with the PPARs or via indirect mechanisms. Here, we describe a novel fibrate, designated GW2331, that is a high-affinity ligand for both PPARalpha and PPARgamma. Using GW2331 as a radioligand in competition binding assays, we show that certain mono- and polyunsaturated fatty acids bind directly to PPARalpha and PPARgamma at physiological concentrations, and that the eicosanoids 8(S)-hydroxyeicosatetraenoic acid and 15-deoxy-Delta12,14-prostaglandin J2 can function as subtype-selective ligands for PPARalpha and PPARgamma, respectively. These data provide evidence that PPARs serve as physiological sensors of lipid levels and suggest a molecular mechanism whereby dietary fatty acids can modulate lipid homeostasis.

The microbiology of butyrate formation in the human colon

Butyrate arising from microbial fermentation is important for the energy metabolism and normal development of colonic epithelial cells and has a mainly protective role in relation to colonic disease. While certain dietary substrates such as resistant starch appear to be butyrogenic in the colon, it is not known to what extent these stimulate butyrate production directly, e.g. by promoting amylolytic species, or indirectly, e.g. through cross-feeding of fermentation products. Cultural and molecular studies indicate that the most numerous butyrate-producing bacteria found in human faeces are highly oxygen-sensitive anaerobes belonging to the Clostridial clusters IV and XIVa. These include many previously undescribed species related to Eubacterium, Roseburia, Faecalibacterium and Coprococcus whose distribution and metabolic characteristics are under investigation. A better understanding of the microbial ecology of colonic butyrate-producing bacteria will help to explain the influence of diet upon butyrate supply, and to suggest new approaches for optimising microbial activity in the large intestine.

Butyrate and propionate protect against diet-induced obesity and regulate gut hormones via free fatty acid receptor 3-independent mechanisms

Short-chain fatty acids (SCFAs), primarily acetate, propionate, and butyrate, are metabolites formed by gut microbiota from complex dietary carbohydrates. Butyrate and acetate were reported to protect against diet-induced obesity without causing hypophagia, while propionate was shown to reduce food intake. However, the underlying mechanisms for these effects are unclear. It was suggested that SCFAs may regulate gut hormones via their endogenous receptors Free fatty acid receptors 2 (FFAR2) and 3 (FFAR3), but direct evidence is lacking. We examined the effects of SCFA administration in mice, and show that butyrate, propionate, and acetate all protected against diet-induced obesity and insulin resistance. Butyrate and propionate, but not acetate, induce gut hormones and reduce food intake. As FFAR3 is the common receptor activated by butyrate and propionate, we examined these effects in FFAR3-deficient mice. The effects of butyrate and propionate on body weight and food intake are independent of FFAR3. In addition, FFAR3 plays a minor role in butyrate stimulation of Glucagon-like peptide-1, and is not required for butyrate- and propionate-dependent induction of Glucose-dependent insulinotropic peptide. Finally, FFAR3-deficient mice show normal body weight and glucose homeostasis. Stimulation of gut hormones and food intake inhibition by butyrate and propionate may represent a novel mechanism by which gut microbiota regulates host metabolism. These effects are largely intact in FFAR3-deficient mice, indicating additional mediators are required for these beneficial effects.

Role of anaerobic bacteria in the metabolic welfare of the colonic mucosa in man

Suspensions of isolated epithelial cells (colonocytes) from the human colon were used to assess utilisation of respiratory fuels which are normally available to the colonic mucosa in vivo. Cells were prepared from operative specimens of the ascending colon (seven) and descending colon (seven). The fuels that were used were the short chain fatty acid n-butyrate, produced only by anaerobic bacteria in the colonic lumen, together with glucose and glutamine, normally present in the circulation. The percentage oxygen consumption attributable to n-butyrate, when this was the only substrate, was 73% in the ascending colon and 75% in the descending colon. In the presence of 10 mM glucose these proportions changed to 59% and 72%. Aerobic glycolysis was observed in both the ascending and descending colon. Glucose oxidation accounted for 85% of the oxygen consumption in the ascending colon and 30% in the descending colon. In the presence of 10 mM n-butyrate these proportions decreased to 41% in the ascending colon and 16% in the descending colon. Based on the assumption that events in the isolated colonocytes reflect utilization of fuels in vivo, the hypothesis is put forward that fatty acids of anaerobic bacteria are a major source of energy for the colonic mucosa, particularly of the distal colon.

Molecular recognition of fatty acids by peroxisome proliferator-activated receptors

The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors for fatty acids (FAs) that regulate glucose and lipid homeostasis. We report the crystal structure of the PPAR delta ligand-binding domain (LBD) bound to either the FA eicosapentaenoic acid (EPA) or the synthetic fibrate GW2433. The carboxylic acids of EPA and GW2433 interact directly with the activation function 2 (AF-2) helix. The hydrophobic tail of EPA adopts two distinct conformations within the large hydrophobic cavity. GW2433 occupies essentially the same space as EPA bound in both conformations. These structures provide molecular insight into the propensity for PPARs to interact with a variety of synthetic and natural compounds, including FAs that vary in both chain length and degree of saturation.

Lactate-utilizing bacteria, isolated from human feces, that produce butyrate as a major fermentation product

The microbial community of the human colon contains many bacteria that produce lactic acid, but lactate is normally detected only at low concentrations (<5 mM) in feces from healthy individuals. It is not clear, however, which bacteria are mainly responsible for lactate utilization in the human colon. Here, bacteria able to utilize lactate and produce butyrate were identified among isolates obtained from 10(-8) dilutions of fecal samples from five different subjects. Out of nine such strains identified, four were found to be related to Eubacterium hallii and two to Anaerostipes caccae, while the remaining three represent a new species within clostridial cluster XIVa based on their 16S rRNA sequences. Significant ability to utilize lactate was not detected in the butyrate-producing species Roseburia intestinalis, Eubacterium rectale, or Faecalibacterium prausnitzii. Whereas E. hallii and A. caccae strains used both D- and L-lactate, the remaining strains used only the d form. Addition of glucose to batch cultures prevented lactate utilization until the glucose became exhausted. However, when two E. hallii strains and one A. caccae strain were grown in separate cocultures with a starch-utilizing Bifidobacterium adolescentis isolate, with starch as the carbohydrate energy source, the L-lactate produced by B. adolescentis became undetectable and butyrate was formed. Such cross-feeding may help to explain the reported butyrogenic effect of certain dietary substrates, including resistant starch. The abundance of E. hallii in particular in the colonic ecosystem suggests that these bacteria play important roles in preventing lactate accumulation.

Reduced dietary intake of carbohydrates by obese subjects results in decreased concentrations of butyrate and butyrate-producing bacteria in feces

Weight loss diets for humans that are based on a high intake of protein but low intake of fermentable carbohydrate may alter microbial activity and bacterial populations in the large intestine and thus impact on gut health. In this study, 19 healthy, obese (body mass index range, 30 to 42) volunteers were given in succession three different diets: maintenance (M) for 3 days (399 g carbohydrate/day) and then high protein/medium (164 g/day) carbohydrate (HPMC) and high protein/low (24 g/day) carbohydrate (HPLC) each for 4 weeks. Stool samples were collected at the end of each dietary regimen. Total fecal short-chain fatty acids were 114 mM, 74 mM, and 56 mM (P < 0.001) for M, HPMC, and HPLC diets, respectively, and there was a disproportionate reduction in fecal butyrate (18 mM, 9 mM, and 4 mM, respectively; P < 0.001) with decreasing carbohydrate. Major groups of fecal bacteria were monitored using nine 16S rRNA-targeted fluorescence in situ hybridization probes, relative to counts obtained with the broad probe Eub338. No significant change was seen in the relative counts of the bacteroides (Bac303) (mean, 29.6%) or the clostridial cluster XIVa (Erec482, 23.3%), cluster IX (Prop853, 9.3%), or cluster IV (Fprau645, 11.6%; Rbro730 plus Rfla729, 9.3%) groups. In contrast, the Roseburia spp. and Eubacterium rectale subgroup of cluster XIVa (11%, 8%, and 3% for M, HPMC, and HPLC, respectively; P < 0.001) and bifidobacteria (4%, 2.1%, and 1.9%, respectively; P = 0.026) decreased as carbohydrate intake decreased. The abundance of butyrate-producing bacteria related to Roseburia spp. and E. rectale correlated well with the decline in fecal butyrate.

Phylogenetic relationships of butyrate-producing bacteria from the human gut

Butyrate is a preferred energy source for colonic epithelial cells and is thought to play an important role in maintaining colonic health in humans. In order to investigate the diversity and stability of butyrate-producing organisms of the colonic flora, anaerobic butyrate-producing bacteria were isolated from freshly voided human fecal samples from three healthy individuals: an infant, an adult omnivore, and an adult vegetarian. A second isolation was performed on the same three individuals 1 year later. Of a total of 313 bacterial isolates, 74 produced more than 2 mM butyrate in vitro. Butyrate-producing isolates were grouped by 16S ribosomal DNA (rDNA) PCR-restriction fragment length polymorphism analysis. The results indicate very little overlap between the predominant ribotypes of the three subjects; furthermore, the flora of each individual changed significantly between the two isolations. Complete sequences of 16S rDNAs were determined for 24 representative strains and subjected to phylogenetic analysis. Eighty percent of the butyrate-producing isolates fell within the XIVa cluster of gram-positive bacteria as defined by M. D. Collins et al. (Int. J. Syst. Bacteriol. 44:812-826, 1994) and A. Willems et al. (Int. J. Syst. Bacteriol. 46:195-199, 1996), with the most abundant group (10 of 24 or 42%) clustering with Eubacterium rectale, Eubacterium ramulus, and Roseburia cecicola. Fifty percent of the butyrate-producing isolates were net acetate consumers during growth, suggesting that they employ the butyryl coenzyme A-acetyl coenzyme A transferase pathway for butyrate production. In contrast, only 1% of the 239 non-butyrate-producing isolates consumed acetate.

Bacteria, colonic fermentation, and gastrointestinal health

The colonic microbiota plays an important role in human digestive physiology and makes a significant contribution to homeostasis in the large bowel. The microbiome probably comprises thousands of different bacterial species. The principal metabolic activities of colonic microorganisms are associated with carbohydrate and protein digestion. Nutrients of dietary and host origin support the growth of intestinal organisms. Short-chain fatty acids (SCFAs), predominantly acetate, propionate, and butyrate, are the principal metabolites generated during the catabolism of carbohydrates and proteins. In contrast, protein digestion yields a greater diversity of end products, including SCFAs, amines, phenols, indoles, thiols, CO2, H2, and H2S, many of which have toxic properties. The majority of SCFAs are absorbed from the gut and metabolized in various body tissues, making a relatively small but significant contribution to the body's daily energy requirements. Carbohydrate fermentation is, for the most part, a beneficial process in the large gut, because the growth of saccharolytic bacteria stimulates their requirements for toxic products associated with putrefaction, for incorporation into cellular proteins, thereby protecting the host. However, as digestive materials move along the gut, carbohydrates become depleted, which may be linked to the increased prevalence of colonic disease in the distal bowel.

Intestinal microbiota-derived short-chain fatty acids regulation of immune cell IL-22 production and gut immunity

Innate lymphoid cells (ILCs) and CD4+ T cells produce IL-22, which is critical for intestinal immunity. The microbiota is central to IL-22 production in the intestines; however, the factors that regulate IL-22 production by CD4+ T cells and ILCs are not clear. Here, we show that microbiota-derived short-chain fatty acids (SCFAs) promote IL-22 production by CD4+ T cells and ILCs through G-protein receptor 41 (GPR41) and inhibiting histone deacetylase (HDAC). SCFAs upregulate IL-22 production by promoting aryl hydrocarbon receptor (AhR) and hypoxia-inducible factor 1α (HIF1α) expression, which are differentially regulated by mTOR and Stat3. HIF1α binds directly to the Il22 promoter, and SCFAs increase HIF1α binding to the Il22 promoter through histone modification. SCFA supplementation enhances IL-22 production, which protects intestines from inflammation. SCFAs promote human CD4+ T cell IL-22 production. These findings establish the roles of SCFAs in inducing IL-22 production in CD4+ T cells and ILCs to maintain intestinal homeostasis.

Two routes of metabolic cross-feeding between Bifidobacterium adolescentis and butyrate-producing anaerobes from the human gut

Dietary carbohydrates have the potential to influence diverse functional groups of bacteria within the human large intestine. Of 12 Bifidobacterium strains of human gut origin from seven species tested, four grew in pure culture on starch and nine on fructo-oligosaccharides. The potential for metabolic cross-feeding between Bifidobacterium adolescentis and lactate-utilizing, butyrate-producing Firmicute bacteria related to Eubacterium hallii and Anaerostipes caccae was investigated in vitro. E. hallii L2-7 and A. caccae L1-92 failed to grow on starch in pure culture, but in coculture with B. adolescentis L2-32 butyrate was formed, indicating cross-feeding of metabolites to the lactate utilizers. Studies with [(13)C]lactate confirmed carbon flow from lactate, via acetyl coenzyme A, to butyrate both in pure cultures of E. hallii and in cocultures with B. adolescentis. Similar results were obtained in cocultures involving B. adolescentis DSM 20083 with fructo-oligosaccharides as the substrate. Butyrate formation was also stimulated, however, in cocultures of B. adolescentis L2-32 grown on starch or fructo-oligosaccharides with Roseburia sp. strain A2-183, which produces butyrate but does not utilize lactate. This is probably a consequence of the release by B. adolescentis of oligosaccharides that are available to Roseburia sp. strain A2-183. We conclude that two distinct mechanisms of metabolic cross-feeding between B. adolescentis and butyrate-forming bacteria may operate in gut ecosystems, one due to consumption of fermentation end products (lactate and acetate) and the other due to cross-feeding of partial breakdown products from complex substrates.

Understanding the effects of diet on bacterial metabolism in the large intestine

Recent analyses of ribosomal RNA sequence diversity have demonstrated the extent of bacterial diversity in the human colon, and have provided new tools for monitoring changes in the composition of the gut microbial community. There is now an excellent opportunity to correlate ecological niches and metabolic activities with particular phylogenetic groups among the microbiota of the human gut. Bacteria that associate closely with particulate material and surfaces in the gut include specialized primary degraders of insoluble substrates, including resistant starch, plant structural polysaccharides and mucin. Butyrate-producing bacteria found in human faeces belong mainly to the clostridial clusters IV and XIVa. In vitro and in vivo evidence indicates that a group related to Roseburia and Eubacterium rectale plays a major role in mediating the butyrogenic effect of fermentable dietary carbohydrates. Additional cluster XIVa species can convert lactate to butyrate, while some members of the clostridial cluster IX convert lactate to propionate. The metabolic outputs of the gut microbial community depend not only on available substrate, but also on the gut environment, with pH playing a major role. Better understanding of the colonic microbial ecosystem will help to explain and predict the effects of dietary additives, including nondigestible carbohydrates, probiotics and prebiotics.

Acetate utilization and butyryl coenzyme A (CoA):acetate-CoA transferase in butyrate-producing bacteria from the human large intestine

Seven strains of Roseburia sp., Faecalibacterium prausnitzii, and Coprococcus sp. from the human gut that produce high levels of butyric acid in vitro were studied with respect to key butyrate pathway enzymes and fermentation patterns. Strains of Roseburia sp. and F. prausnitzii possessed butyryl coenzyme A (CoA):acetate-CoA transferase and acetate kinase activities, but butyrate kinase activity was not detectable either in growing or in stationary-phase cultures. Although unable to use acetate as a sole source of energy, these strains showed net utilization of acetate during growth on glucose. In contrast, Coprococcus sp. strain L2-50 is a net producer of acetate and possessed detectable butyrate kinase, acetate kinase, and butyryl-CoA:acetate-CoA transferase activities. These results demonstrate that different functionally distinct groups of butyrate-producing bacteria are present in the human large intestine.

Gut microbiome-derived metabolites modulate intestinal epithelial cell damage and mitigate graft-versus-host disease

The effect of alterations in intestinal microbiota on microbial metabolites and on disease processes such as graft-versus-host disease (GVHD) is not known. Here we carried out an unbiased analysis to identify previously unidentified alterations in gastrointestinal microbiota-derived short-chain fatty acids (SCFAs) after allogeneic bone marrow transplant (allo-BMT). Alterations in the amount of only one SCFA, butyrate, were observed only in the intestinal tissue. The reduced butyrate in CD326(+) intestinal epithelial cells (IECs) after allo-BMT resulted in decreased histone acetylation, which was restored after local administration of exogenous butyrate. Butyrate restoration improved IEC junctional integrity, decreased apoptosis and mitigated GVHD. Furthermore, alteration of the indigenous microbiota with 17 rationally selected strains of high butyrate-producing Clostridia also decreased GVHD. These data demonstrate a heretofore unrecognized role of microbial metabolites and suggest that local and specific alteration of microbial metabolites has direct salutary effects on GVHD target tissues and can mitigate disease severity.

The colonic epithelium in ulcerative colitis: an energy-deficiency disease?

Suspensions of colonocytes (isolated colonic epithelial cells) were prepared from mucosa of the descending colon from 6 patients with quiescent ulcerative colitis (UC), 4 with acute UC, and 7 control subjects. In each group metabolic performance was investigated by assessing utilisation of n-butyrate, the main respiratory fuel of the colonic mucosa, as well as utilisation of glucose and glutamine. In both acute and quiescent UC oxidation of butyrate to CO2 and ketones was significantly lower than in the control tissues, and the decrease correlated with the state of the disease. Enhanced glucose and glutamine oxidation compensated for decreased butyrate oxidation in UC, indicating that colonocytes in colitis were not metabolically degenerate cells. Failure of butyrate oxidation reflects a variable yet definite metabolic defect in the mucosa in UC. Diminished oxidation of butyrate can explain the characteristic distribution of colitis along the colon, especially the frequency of UC in the distal colon. It is suggested that failure of fatty-acid (n-butyrate) oxidation in UC is an expression of an energy-deficiency disease of the colonic mucosa.

Modulation of polyketide synthase activity by accessory proteins during lovastatin biosynthesis

Polyketides, the ubiquitous products of secondary metabolism in microorganisms, are made by a process resembling fatty acid biosynthesis that allows the suppression of reduction or dehydration reactions at specific biosynthetic steps, giving rise to a wide range of often medically useful products. The lovastatin biosynthesis cluster contains two type I polyketide synthase genes. Synthesis of the main nonaketide-derived skeleton was found to require the previously known iterative lovastatin nonaketide synthase (LNKS), plus at least one additional protein (LovC) that interacts with LNKS and is necessary for the correct processing of the growing polyketide chain and production of dihydromonacolin L. The noniterative lovastatin diketide synthase (LDKS) enzyme specifies formation of 2-methylbutyrate and interacts closely with an additional transesterase (LovD) responsible for assembling lovastatin from this polyketide and monacolin J.

The Colonic Crypt Protects Stem Cells from Microbiota-Derived Metabolites

In the mammalian intestine, crypts of Leiberkühn house intestinal epithelial stem/progenitor cells at their base. The mammalian intestine also harbors a diverse array of microbial metabolite compounds that potentially modulate stem/progenitor cell activity. Unbiased screening identified butyrate, a prominent bacterial metabolite, as a potent inhibitor of intestinal stem/progenitor proliferation at physiologic concentrations. During homeostasis, differentiated colonocytes metabolized butyrate likely preventing it from reaching proliferating epithelial stem/progenitor cells within the crypt. Exposure of stem/progenitor cells in vivo to butyrate through either mucosal injury or application to a naturally crypt-less host organism led to inhibition of proliferation and delayed wound repair. The mechanism of butyrate action depended on the transcription factor Foxo3. Our findings indicate that mammalian crypt architecture protects stem/progenitor cell proliferation in part through a metabolic barrier formed by differentiated colonocytes that consume butyrate and stimulate future studies on the interplay of host anatomy and microbiome metabolism.

Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell

Hydrogen can be recovered by fermentation of organic material rich in carbohydrates, but much of the organic matter remains in the form of acetate and butyrate. An alternative to methane production from this organic matter is the direct generation of electricity in a microbial fuel cell (MFC). Electricity generation using a single-chambered MFC was examined using acetate or butyrate. Power generated with acetate (800 mg/L) (506 mW/m2 or 12.7 mW/ L) was up to 66% higher than that fed with butyrate (1000 mg/L) (305 mW/m2 or 7.6 mW/L), demonstrating that acetate is a preferred aqueous substrate for electricity generation in MFCs. Power output as a function of substrate concentration was well described by saturation kinetics, although maximum power densities varied with the circuit load. Maximum power densities and half-saturation constants were Pmax = 661 mW/m2 and Ks = 141 mg/L for acetate (218 ohms) and Pmax = 349 mW/m2 and Ks = 93 mg/L for butyrate (1000 ohms). Similar open circuit potentials were obtained in using acetate (798 mV) or butyrate (795 mV). Current densities measured for stable power outputwere higher for acetate (2.2 A/m2) than those measured in MFCs using butyrate (0.77 A/m2). Cyclic voltammograms suggested that the main mechanism of power production in these batch tests was by direct transfer of electrons to the electrode by bacteria growing on the electrode and not by bacteria-produced mediators. Coulombic efficiencies and overall energy recovery were 10-31 and 3-7% for acetate and 8-15 and 2-5% for butyrate, indicating substantial electron and energy losses to processes other than electricity generation. These results demonstrate that electricity generation is possible from soluble fermentation end products such as acetate and butyrate, but energy recoveries should be increased to improve the overall process performance.

Butyrate production from dietary fibre and protection against large bowel cancer in a rat model

Butyrate slows the growth of cancer cells cultured in vitro. To determine the relevance of the fermentative production of butyrate in vivo, colonic butyrate concentrations were manipulated by feeding different dietary fibres and were related to tumour development in the rat dimethylhydrazine model of large bowel cancer. It has previously been shown that guar gum and oat bran, while highly fermentable, are associated with low butyrate levels in the distal colon, while wheat bran causes significantly higher concentrations. Diets containing these fibres (nominally 10% w:w) were administered for 3 weeks before, for 10 weeks during, and for 20 weeks after dimethylhydrazine administration, after which animals were killed and examined for tumours. Significantly fewer tumours were seen in the rats fed wheat bran compared with those fed guar or oat bran, and the total tumour mass was lowest in rats fed wheat bran. Rats on a 'no added fibre diet' had an intermediate tumour mass. Regression analysis, performed regardless of dietary group, showed that the concentration in stools of butyrate but not of acetate or stool volume, correlated significantly (and negatively) with tumour mass. These findings indicate that fibre which is associated with high butyrate concentrations in the distal large bowel is protective against large bowel cancer, while soluble fibres that do not raise distal butyrate concentrations, are not protective. Thus, butyrate production in vivo does bear a significant relationship to suppression of tumour formation.

The effects of short-chain fatty acids on human colon cancer cell phenotype are associated with histone hyperacetylation

The short-chain fatty acid (SCFA) butyrate is produced via anaerobic bacterial fermentation within the colon and is thought to be protective in regard to colon carcinogenesis. Although butyrate (C4) is considered the most potent of the SCFA, a variety of other SCFA also exist in the colonic lumen. Butyrate is thought to exert its cellular effects through the induction of histone hyperacetylation. We sought to determine the effects of a variety of the SCFA on colon carcinoma cell growth, differentiation and apoptosis. HT-29 or HCT-116 (wild-type and p21-deleted) cells were treated with physiologically relevant concentrations of various SCFA, and histone acetylation state was assayed by acid-urea-triton-X gel electrophoresis and immunoblotting. Growth and apoptotic effects were studied by flow cytometry, and differentiation effects were assessed using transient transfections and Northern blotting. Propionate (C3) and valerate (C5) caused growth arrest and differentiation in human colon carcinoma cells. The magnitude of their effects was associated with a lesser degree of histone hyperacetylation compared with butyrate. Acetate (C2) and caproate (C6), in contrast, did not cause histone hyperacetylation and also had no appreciable effects on cell growth or differentiation. SCFA-induced transactivation of the differentiation marker gene, intestinal alkaline phosphatase (IAP), was blocked by histone deacetylase (HDAC), further supporting the critical link between SCFA and histones. Butyrate also significantly increased apoptosis, whereas the other SCFA studied did not. The growth arrest induced by the SCFA was characterized by an increase in the expression of the p21 cell-cycle inhibitor and down-regulation of cyclin B1 (CB1). In p21-deleted HCT-116 colon cancer cells, the SCFA did not alter the rate of proliferation. These data suggest that the antiproliferative, apoptotic and differentiating properties of the various SCFA are linked to the degree of induced histone hyperacetylation. Furthermore, SCFA-mediated growth arrest in colon carcinoma cells requires the p21 gene.

Lactobacillus rhamnosus GG-supplemented formula expands butyrate-producing bacterial strains in food allergic infants

Dietary intervention with extensively hydrolyzed casein formula supplemented with Lactobacillus rhamnosus GG (EHCF+LGG) accelerates tolerance acquisition in infants with cow's milk allergy (CMA). We examined whether this effect is attributable, at least in part, to an influence on the gut microbiota. Fecal samples from healthy controls (n=20) and from CMA infants (n=19) before and after treatment with EHCF with (n=12) and without (n=7) supplementation with LGG were compared by 16S rRNA-based operational taxonomic unit clustering and oligotyping. Differential feature selection and generalized linear model fitting revealed that the CMA infants have a diverse gut microbial community structure dominated by Lachnospiraceae (20.5±9.7%) and Ruminococcaceae (16.2±9.1%). Blautia, Roseburia and Coprococcus were significantly enriched following treatment with EHCF and LGG, but only one genus, Oscillospira, was significantly different between infants that became tolerant and those that remained allergic. However, most tolerant infants showed a significant increase in fecal butyrate levels, and those taxa that were significantly enriched in these samples, Blautia and Roseburia, exhibited specific strain-level demarcations between tolerant and allergic infants. Our data suggest that EHCF+LGG promotes tolerance in infants with CMA, in part, by influencing the strain-level bacterial community structure of the infant gut.

Magnetite particles triggering a faster and more robust syntrophic pathway of methanogenic propionate degradation

Interspecies electron transfer mechanisms between Bacteria and Archaea play a pivotal role during methanogenic degradation of organic matter in natural and engineered anaerobic ecosystems. Growing evidence suggests that in syntrophic communities electron transfer does not rely exclusively on the exchange of diffusible molecules and energy carriers such as hydrogen or formate, rather microorganisms have the capability to exchange metabolic electrons in a more direct manner. Here, we show that supplementation of micrometer-size magnetite (Fe3O4) particles to a methanogenic sludge enhanced (up to 33%) the methane production rate from propionate, a key intermediate in the anaerobic digestion of organic matter and a model substrate to study energy-limited syntrophic communities. The stimulatory effect most probably resulted from the establishment of a direct interspecies electron transfer (DIET), based on magnetite particles serving as electron conduits between propionate-oxidizing acetogens and carbon dioxide-reducing methanogens. Theoretical calculations revealed that DIET allows electrons to be transferred among syntrophic partners at rates which are substantially higher than those attainable via interspecies H2 transfer. Besides the remarkable potential for improving anaerobic digestion, which is a proven biological strategy for renewable energy production, the herein described conduction-based DIET could also have a role in natural methane emissions from magnetite-rich soils and sediments.

Microbial-Derived Butyrate Promotes Epithelial Barrier Function through IL-10 Receptor-Dependent Repression of Claudin-2

Commensal interactions between the enteric microbiota and distal intestine play important roles in regulating human health. Short-chain fatty acids (SCFAs), such as butyrate, produced through anaerobic microbial metabolism represent a major energy source for the host colonic epithelium and enhance epithelial barrier function through unclear mechanisms. Separate studies revealed that the epithelial anti-inflammatory IL-10 receptor α subunit (IL-10RA) is also important for barrier formation. Based on these findings, we examined if SCFAs promote epithelial barrier through IL-10RA-dependent mechanisms. Using human intestinal epithelial cells (IECs), we discovered that SCFAs, particularly butyrate, enhanced IEC barrier formation, induced IL-10RA mRNA, IL-10RA protein, and transactivation through activated Stat3 and HDAC inhibition. Loss and gain of IL-10RA expression directly correlates with IEC barrier formation and butyrate represses permeability-promoting claudin-2 tight-junction protein expression through an IL-10RA-dependent mechanism. Our findings provide a novel mechanism by which microbial-derived butyrate promotes barrier through IL-10RA-dependent repression of claudin-2.