The role of rye bran and antibiotics on the digestion, fermentation process and short-chain fatty acid production and absorption in an intact pig model.

The effects of arabinoxylan (AX)-rich rye bran based diet (RB) and antibiotics on digestion, fermentation and short-chain fatty acids (SCFA) absorption were studied compared with an iso-dietary fibre (DF) cellulose based diet (CEL). Thirty female pigs (body weight 72.5 ± 3.9 kg) were fed a standard swine diet in week 1, CEL as wash-out for bran-associated bioactive components in week 2 and then divided into 3 groups fed either the CEL (n = 10) or RB (n = 20) for 2 weeks, where 10 pigs from RB had daily intramuscular antibiotic injections (RB+) and the other 10 pigs were untreated (RB-) in week 4. In RB, the degradation of AX mainly occurred in caecum and proximal colon (P < 0.01) and to a higher extent than cellulose, which on the other hand, irrespective of antibiotic treatment, was less degraded in the RB groups than in the CEL (P < 0.01). The apparent digestibility of fat and protein in the distal small intestine was lower for RB than CEL (P < 0.05), the protein digestibility remained lower in most of the colon, and the digestibility was not affected by treatment with antibiotics. The colonic concentrations of SCFA, acetate and propionate as well as the butyrate concentration in the distal colon were lower with the RB treatments compared with CEL (P < 0.01). Caecal butyrate concentrations were on the other hand higher, and a significant reduction was seen with antibiotic treatment (P < 0.001). The daily net absorption of SCFA and acetate was lower with RB than with CEL (P < 0.01). In conclusion, RB resulted in different DF degradation processes and SCFA production compared with CEL, whereas antibiotic treatment had marginal effects on the intestinal DF degradation but hampered butyrate production.

Synthesis, Characterization, and in†vivo Distribution of Intracellular Delivered Macrolide Short-Chain Fatty Acid Derivatives.

Short-chain fatty acids (SCFAs) have a range of effects in metabolism and immune regulation. We have observed that delivery of SCFAs to lysosomes has potent immune regulatory effects, possibly as a surrogate signal for the presence of anaerobic organisms. To better understand the pharmacology of lysosomal SCFA donors, we investigated the distribution and metabolism of propionate and butyrate donors. Each analog (1 a and 2 a) can donate three SCFA equivalents via ester hydrolysis through six intermediate metabolites. The compounds are stabilized by low pH, and stability in cells is usually higher than in medium, but is cell-type specific. Butyrate derivatives were found to be more stable than propionates. Tri-esters were more stable than di- or mono-esters. The donors were surprisingly stable in vivo, and hydrolysis of each position was organ specific. Jejunum and liver caused rapid loss of 4'' esters. The gut metabolite pattern by i. v. differed from that of p.o. application, suggesting luminal and apical enzyme effects in the gut epithelium. Central organs could de-esterify the 11-position. Levels in lung relative to other organs were higher by p.o. than via i. v., suggesting that delivery route can influence the observed pharmacology and that gut metabolites distribute differently. The donors were largely eliminated by 24 h, following near linear decline in organs. The observed levels and distribution were found to be consistent with pharmacodynamic effects, particularly in the gut.

Delivery of Acetate to the Peripheral Blood after Consumption of Foods High in Short-Chain Fatty Acids.

SCOPE: To promote local and systemic benefits of short-chain fatty acids (SCFA), methods of increasing their delivery to the gastrointestinal tract are needed. SCFA in foods and beverages represents a poorly characterized source. Main aims of this study are: 1) quantify SCFA in commonly consumed foods and beverages, and 2) explore the pharmacokinetics of consuming oral SCFA from dietary sources. METHODS AND RESULTS: Gas-chromatography coupled to flame ionization detection is used measure SCFA in 38 commonly consumed foods and beverages. Acetate is the most abundant SCFA detected, with kombucha and vinegar found to provide >1000 mg of acetate per serve. An acute pharmacokinetic study is conducted in 10 participants. Acetate is stable across the 2-h sampling period after consumption of a control drink, with consumption of a vinegar drink containing 25 mmol acetate significantly increasing plasma acetate concentration after 60 min and increasing acetate delivery to the blood upon assessment of the area under the pharmacokinetic curve. CONCLUSION: Fermented foods and beverages are a natural source of dietary SCFA that acutely deliver SCFA to the blood. If systemic delivery is needed for immunological and metabolic effects to occur, these may be achieved if delivered over a longer period of time.

Gastrointestinal digestion of Pickering emulsions stabilised by hydrophobically modified cellulose nanocrystals: Release of short-chain fatty acids.

This study aimed to deliver short-chain fatty acids (SCFAs, including propionic and butyric acids) using Pickering emulsions stabilised by hydrophobically modified cellulose nanocrystals (MCNCs). The emulsions (20 wt% oil, 1 wt% MCNCs) were subjected to two in vitro digestion pathways. In the first pathway, the emulsions were used for direct intestinal digestion by bypassing the gastric phase while in the second pathway, the emulsions were subjected to sequential gastrointestinal digestion. Flocculation of emulsion droplets occurred because of charge screening effects by the gastric electrolytes. Such gastric flocculation reduced the droplet surface area, overall lipolysis kinetics and consequently decreased the extent of SCFA release, latter was 40-45% in the gastric-bypassed emulsions and 30-35% in the sequentially-digested emulsions. High proportion of SCFAs remaining after the intestinal digestion (~65%) shows promise in the use of Pickering emulsions for the colon-targeted delivery of SCFAs.

B cell-intrinsic epigenetic modulation of antibody responses by dietary fiber-derived short-chain fatty acids.

Short-chain fatty acids (SCFAs) butyrate and propionate are metabolites from dietary fiber's fermentation by gut microbiota that can affect differentiation or functions of T cells, macrophages and dendritic cells. We show here that at low doses these SCFAs directly impact B cell intrinsic functions to moderately enhance class-switch DNA recombination (CSR), while decreasing at higher doses over a broad physiological range, AID and Blimp1 expression, CSR, somatic hypermutation and plasma cell differentiation. In human and mouse B cells, butyrate and propionate decrease B cell Aicda and Prdm1 by upregulating select miRNAs that target Aicda and Prdm1 mRNA-3'UTRs through inhibition of histone deacetylation (HDAC) of those miRNA host genes. By acting as HDAC inhibitors, not as energy substrates or through GPR-engagement signaling in these B cell-intrinsic processes, these SCFAs impair intestinal and systemic T-dependent and T-independent antibody responses. Their epigenetic impact on B cells extends to inhibition of autoantibody production and autoimmunity in mouse lupus models.

Organic overloading affects the microbial interactions during anaerobic digestion in sewage sludge reactors.

There is still a lack of information about microbial interactions of anaerobic digestion microbiome during process disturbance which limits our ability to predict the mechanisms that drive community dynamics on these events. This paper aims to determine how an organic overloading affects these interactions and to characterize in detail the microbiome structure and diversity in sewage sludge anaerobic reactors during an acidosis event. Two identical sewage sludge anaerobic reactors were subjected to an organic loading shock by adding glycerol waste. As consequence, volatile fatty acids accumulated after only 24 h (up to 2.5 g/L) while Bacteroidales and Methanomicrobiales became displaced by Firmicutes and Methanosaeta sp, showing that reactor acidosis can occur without an immediate decline of this methanogen. Network analysis revealed 9 clusters of co-occurring microorganisms with different behaviors during overloading. At first, Veillonellaceae family, the main glycerol degrading, associated with Candidatus Cloacimonetes, volatile fatty acids fermenters, increased their relative abundance in detriment of the syntrophic bacteria; although as conditions become more acidic, these groups were displaced by other fermenters like Porphyromonadaceae and Chitinophagaceae. Eventually, the methanogenesis failed 72 h after organic overloading, when pH reached values lower than 6. Overall, our results showed a succession of functionally redundant microorganisms, most likely because of niche specialization during organic overloading. The detailed temporal analysis elucidated the processes governing the dynamics anaerobic digestion microbiome, a knowledge required to develop anaerobic digestion management strategies based on its microbiome during process disturbances.

Original Research: Effect of various dietary fats on fatty acid profile in duck liver: Efficient conversion of short-chain to long-chain omega-3 fatty acids.

Omega-3 fatty acids, especially long-chain omega-3 fatty acids, have been associated with potential health benefits for chronic disease prevention. Our previous studies found that dietary omega-3 fatty acids could accumulate in the meat and eggs in a duck model. This study was to reveal the effects of various dietary fats on fatty acid profile and conversion of omega-3 fatty acids in duck liver. Female Shan Partridge Ducks were randomly assigned to five dietary treatments, each consisting of 6 replicates of 30 birds. The experimental diets substituted the basal diet by 2% of flaxseed oil, rapeseed oil, beef tallow, or fish oil, respectively. In addition, a dose response study was further conducted for flaxseed and fish oil diets at 0.5%, 1%, and 2%, respectively. At the end of the five-week treatment, fatty acids were extracted from the liver samples and analyzed by GC-FID. As expected, the total omega-3 fatty acids and the ratio of total omega-3/omega-6 significantly increased in both flaxseed and fish oil groups when compared with the control diet. No significant change of total saturated fatty acids or omega-3 fatty acids was found in both rapeseed and beef tallow groups. The dose response study further indicated that 59-81% of the short-chain omega-3 ALA in flaxseed oil-fed group was efficiently converted to long-chain DHA in the duck liver, whereas 1% of dietary flaxseed oil could produce an equivalent level of DHA as 0.5% of dietary fish oil. The more omega-3 fatty acids, the less omega-6 fatty acids in the duck liver. Taken together, this study showed the fatty acid profiling in the duck liver after various dietary fat consumption, provided insight into a dose response change of omega-3 fatty acids, indicated an efficient conversion of short- to long-chain omega-3 fatty acid, and suggested alternative long-chain omega-3 fatty acid-enriched duck products for human health benefits.

Systemic availability and metabolism of colonic-derived short-chain fatty acids in healthy subjects: a stable isotope study.

KEY POINTS: The short-chain fatty acids (SCFAs) are bacterial metabolites produced during the colonic fermentation of undigested carbohydrates, such as dietary fibre and prebiotics, and can mediate the interaction between the diet, the microbiota and the host. We quantified the fraction of colonic administered SCFAs that could be recovered in the systemic circulation, the fraction that was excreted via the breath and urine, and the fraction that was used as a precursor for glucose, cholesterol and fatty acids. This information is essential for understanding the molecular mechanisms by which SCFAs beneficially affect physiological functions such as glucose and lipid metabolism and immune function. ABSTRACT: The short-chain fatty acids (SCFAs), acetate, propionate and butyrate, are bacterial metabolites that mediate the interaction between the diet, the microbiota and the host. In the present study, the systemic availability of SCFAs and their incorporation into biologically relevant molecules was quantified. Known amounts of 13 C-labelled acetate, propionate and butyrate were introduced in the colon of 12 healthy subjects using colon delivery capsules and plasma levels of 13 C-SCFAs 13 C-glucose, 13 C-cholesterol and 13 C-fatty acids were measured. The butyrate-producing capacity of the intestinal microbiota was also quantified. Systemic availability of colonic-administered acetate, propionate and butyrate was 36%, 9% and 2%, respectively. Conversion of acetate into butyrate (24%) was the most prevalent interconversion by the colonic microbiota and was not related to the butyrate-producing capacity in the faecal samples. Less than 1% of administered acetate was incorporated into cholesterol and <15% in fatty acids. On average, 6% of colonic propionate was incorporated into glucose. The SCFAs were mainly excreted via the lungs after oxidation to 13 CO2 , whereas less than 0.05% of the SCFAs were excreted into urine. These results will allow future evaluation and quantification of SCFA production from 13 C-labelled fibres in the human colon by measurement of 13 C-labelled SCFA concentrations in blood.

Quantification of in Vivo Colonic Short Chain Fatty Acid Production from Inulin.

Short chain fatty acids (SCFA), including acetate, propionate, and butyrate, are produced during bacterial fermentation of undigested carbohydrates in the human colon. In this study, we applied a stable-isotope dilution method to quantify the in vivo colonic production of SCFA in healthy humans after consumption of inulin. Twelve healthy subjects performed a test day during which a primed continuous intravenous infusion with [1-(13)C]acetate, [1-(13)C]propionate and [1-(13)C]butyrate (12, 1.2 and 0.6 µmol·kg(-1)·min(-1), respectively) was applied. They consumed 15 g of inulin with a standard breakfast. Breath and blood samples were collected at regular times during the day over a 12 h period. The endogenous rate of appearance of acetate, propionate, and butyrate was 13.3 ± 4.8, 0.27 ± 0.09, and 0.28 ± 0.12 µmol·kg(-1)·min(-1), respectively. Colonic inulin fermentation was estimated to be 137 ± 75 mmol acetate, 11 ± 9 mmol propionate, and 20 ± 17 mmol butyrate over 12 h, assuming that 40%, 10%, and 5% of colonic derived acetate, propionate, and butyrate enter the systemic circulation. In conclusion, inulin is mainly fermented into acetate and, to lesser extents, into butyrate and propionate. Stable isotope technology allows quantifying the production of the three main SCFA in vivo and proved to be a practical tool to investigate the extent and pattern of SCFA production.

La dieta con bajo contenido en hidratos de carbono de cadena corta y polioles fermentables mejora los síntomas en pacientes con trastornos funcionales gastrointestinales en España / The diet low in fermentable carbohydrates short chain and polyols improves symptoms in patients with functional gastrointestinal disorders in Spain

FUNDAMENTOS Y OBJETIVOS: El tratamiento satisfactorio de los pacientes con síndrome de intestino irritable (SII) sigue siendo a menudo difícil. Estudios recientes en Australia, Reino Unido y Nueva Zelanda han sugerido la eficacia de la dieta baja en hidratos de carbono de cadena corta y polioles fermentables (FODMAPs) en el manejo de estos pacientes. Los objetivos del presente estudio son determinar si la dieta con bajo contenido en FODMAPs mejora los síntomas de pacientes con trastornos funcionales gastrointestinales (TFGI) en España y analizar factores predictivos de buena respuesta. PACIENTES Y MÉTODOS: Estudio prospectivo de pacientes consecutivos con TFGI tipo SII y distensión abdominal funcional. A su inclusión a todos los pacientes se les realizó una valoración basal mediante cuestionarios demográfico, de síntomas, de ansiedad y depresión y de calidad de vida. Se realizó test de aliento de hidrógeno con lactosa y fructosa y se indicó una dieta con bajo contenido en FODMAPs por 2 meses por dietistas expertas, tomando como referencia estos test. Se definió como respuesta positiva la mejora de al menos 5 puntos sobre 10 posibles en el cuestionario de síntomas. RESULTADOS: Se incluyeron 30 pacientes (24 mujeres con una edad media de 39 [12] años). La respuesta a la dieta con bajo contenido en FODMAPs fue positiva en el control de los síntomas de forma global y de síntomas específicos como distensión abdominal, dolor abdominal, diarrea, flatos, náuseas y fatiga en más del 70% de los pacientes (p < 0,05), mientras que el estreñimiento mejoró en un 48% de los pacientes (p > 0,05). La adherencia a la dieta fue buena en un 87% de los pacientes y esta se asoció como factor predictivo de respuesta positiva en el análisis univariante. CONCLUSIONES: La dieta con bajo contenido en FODMAPs se asocia a una mejora de los síntomas en pacientes con SII y distensión abdominal funcional, siendo la adherencia a la dieta un factor determinante

BACKGROUND AND AIMS: Successful treatment of patients with irritable bowel syndrome (IBS) often remains elusive. Recent studies in Australia, the United Kingdom and New Zealand have suggested the efficacy of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) in the management of these patients. The aims of this study were to determine whether a diet low in FODMAPs improves symptoms in patients with functional gastrointestinal disorders (FGID) in Spain and to analyse the predictors of a good response. PATIENTS AND METHODS: A prospective study was carried out in consecutive patients with FGID type IBS and functional abdominal bloating. At inclusion all patients underwent an assessment through a baseline demographic questionnaire of symptoms of anxiety and depression and quality of life. A hydrogen breath test with lactose and fructose was performed and a low FODMAPs diet was indicated for 2 months by expert dietitians. These tests were taken as a reference. A positive response was defined as an improvement of at least 5 points out of a possible 10 in the symptom questionnaire. RESULTS: We included 30 patients (24 women, 39 [12] years). The response to the low FODMAPs diet was positive in controlling overall symptoms and specific symptoms such as functional abdominal bloating, abdominal pain, diarrheal, flatulence, nausea and fatigue in more than 70% of patients (P < .05). By contrast, constipation was controlled in only 48% of patients (P > .05). Adherence to the diet was good in 87% of patients and was a predictor of positive response in the univariate analysis. CONCLUSIONS: A diet low in FODMAPs is associated with symptom improvement in patients with IBS and functional abdominal bloating. Adherence to the diet was a determining factor

Epithelial capacity for apical uptake of short chain fatty acids is a key determinant for intraruminal pH and the susceptibility to subacute ruminal acidosis in sheep.

Subacute ruminal acidosis (SARA) is a common digestive disorder occurring in ruminants, with considerable variation in the severity of SARA observed among animals fed the same diet. Our aim in this study was to determine whether differences in the capacity of the ruminal epithelium for the apical uptake of acetate and butyrate (determined in Ussing chambers after slaughter) explains differences observed for the severity of a preceding episode of SARA in vivo. Adult sheep with an indwelling small ruminant ruminal pH measurement system (SRS) were randomly assigned to either a SARA induction treatment (oral drench containing 5 g glucose/kg body weight; n = 17) or a sham treatment (SHAM; n = 7; 12 mL water/kg body weight). Sheep receiving the glucose drench were further classified as nonresponders (NR; n = 7) or responders (RES; n = 7) according to their ruminal pH profile for the 3 h following the oral drench. Mean ruminal pH for the 3 h following the drench differed among groups (P < 0.001), with it being highest for SHAM (6.67 +/- 0.08), intermediate for NR (5.97 +/- 0.05), and lowest for RES (5.57 +/- 0.08) sheep. The apical uptake of acetate and butyrate did not differ between SHAM and RES sheep. However, NR sheep had greater in vitro apical uptake of acetate and butyrate and a higher plasma beta-hydroxybutyrate concentration than RES sheep, suggesting greater absorptive capacity for NR. Differences between NR and RES were attributed to greater bicarbonate-independent, nitrate-sensitive uptake of acetate (P = 0.007), a tendency for greater bicarbonate-dependent uptake of acetate (P = 0.071), and greater bicarbonate-independent uptake of butyrate (P = 0.022). These data indicate that differences in the rates and pathways for the uptake of acetate and butyrate explain a large proportion of the individual variation observed for the severity of SARA.

Mixtures of SCFA, composed according to physiologically available concentrations in the gut lumen, modulate histone acetylation in human HT29 colon cancer cells.

Intake of fibre has beneficial properties on gut health. Butyrate, a product of bacterial gut fermentation, is thought to contribute to positive effects by retarding growth and enhancing apoptosis of tumour cells. One mechanism is seen in its capacity to modulate histone acetylation and thereby transcriptional activity of genes. Next to butyrate, propionate and acetate are also major products of gut fermentation and together they may exert different potencies of cellular effects than butyrate alone. Since virtually nothing is known on combination effects by SCFA mixtures, here we had the aim to assess how physiological relevant concentrations and mixtures of SCFA modulate histone acetylation in human colon cells. HT29 colon cancer cells were incubated with mixtures of butyrate, acetate and propionate and with the individual compounds as controls. Histone acetylation was determined with acid-urea gel electrophoresis and immunoblotting. Acetylated histones slowly increased over 24 h and persisted up to 72 h in butyrate-treated HT29 cells. Butyrate (5-40 mM) and propionate (20-40 mM) enhanced histone acetylation significantly after 24 h incubation, whereas acetate (2.5-80 mM) was ineffective. Mixtures of these SCFA also modulated histone acetylation, mainly due to additive effects of butyrate and propionate, but not due to acetate. In conclusion, physiological concentrations of propionate together with butyrate could have more profound biological activities than generally assumed. Together, these SCFA could possibly mediate important processes related to an altered transcriptional gene activation and thus contribute to biological effects possibly related to cancer progression or prevention.

Comparison of techniques to determine the clearance of ruminal volatile fatty acids.

The objective of this experiment was to compare measurements of fractional clearance rates obtained by using an unlabeled valerate-CoEDTA technique with measurements obtained by using a (13)C-labeled volatile fatty acids (VFA) technique. The exponential decay rate of the (13)C/(12)C ratio after pulse-dosing (13)C-acetate, (13)C-propionate, or (13)C-butyrate into the rumen was compared with the decay rate of rumen valerate concentration following a simultaneous pulse dose. The unlabeled valerate, CoEDTA, and each labeled VFA, one at a time, were concurrently mixed with the evacuated ruminal content of 6 lactating cows in two 3 x 3 Latin squares. The clearance of VFA by passage to the omasum was assumed to be equivalent to the decay in ruminal Co concentration and was around 50% of the total clearance. Acetate, propionate, and butyrate had similar fractional clearance rates (31.2, 33.4, 30.4%/h, respectively), but propionate had a higher absorption rate (19.2%/h) than butyrate (14.2%/h). Linear regression determination coefficients using the valerate clearance rate as an estimator for acetate, propionate, and butyrate rumen clearance were 0.51, 0.56, and 0.99, respectively. In a second experiment, the (13)C-valerate fractional clearance rate estimate (33.7%/h) was similar to the estimate obtained with unlabeled valerate (35.0%/h) by the valerate-Co technique. No (13)C enrichment of rumen microbes was noted 4 h after the intraruminal infusion of (13)C-valerate. Fractional VFA absorption rate estimates obtained in both techniques were similar, although both were lower than estimates reported in the literature by other methods.

Transport of acetate and sodium in sheep omasum: mutual, but asymmetric interactions.

We have studied the transport of acetate across the isolated epithelium of sheep omasum; no net transport was observed (J(ms) approximately = J(sm)) under Ussing chamber conditions. Low mucosal pH (pH 6.4) significantly enhanced J(ms) acetate and the transport rates of acetate increased linearly and significantly (r2=0.99) with the luminal acetate concentration. The presence of another short chain fatty acid (propionate) did not affect J(ms) acetate significantly. Neither addition of 1 mmol l(-1) DIDS to the mucosal side nor HCO3 replacement caused changes of J(ms) acetate; this does not support the assumption of acetate transport via anion exchange. Addition of 1 mmol l(-1) amiloride to the mucosal side significantly decreased acetate fluxes at high mucosal acetate concentration (100 mmol l(-1)) and low pH (6.4) indicating interaction between acetate uptake in the undissociated form, intracellular release of protons and activation of Na+/H+ exchange (NHE). However, the mutual interaction between Na transport via NHE and acetate transport is asymmetric. Stimulation or inhibition of Na transport via NHE is much more pronounced than the corresponding changes of acetate fluxes. Thus, the obtained results support the conclusion that acetate is transported via simple diffusion and probably predominantly in the protonated form, thereby explaining the positive and mutual interaction between Na transport and short chain fatty acids.

Induction of fetal globin in beta-thalassemia: Cellular obstacles and molecular progress.

Accelerated apoptosis of erythroid progenitors in beta-thalassemia is a significant barrier to definitive therapy because the beneficial effects of fetal globin-inducing agents on globin chain balance may not be inducible in cells in which programmed cell death is established early. Accordingly, our objectives have been to identify methods to decrease cellular apoptosis and to identify orally tolerable fetal globin gene inducers. A pilot clinical trial was conducted to determine whether combined use of a fetal globin gene inducer (butyrate) and rhu-erythropoietin (EPO), the hematopoietic growth factor that prolongs erythroid cell survival and stimulates erythroid proliferation, would produce additive hematologic responses in any thalassemia subjects. Butyrate and EPO were administered in 10 patients. Novel fetal globin gene inducers that also stimulate erythroid proliferation were evaluated for pharmacokinetic profiles. Patients with beta+-thalassemia had relatively low levels of endogenous EPO (<145 mU/mL) and had additive responses to administered EPO and butyrate. Patients with at least one beta 0-globin mutation had higher baseline HbF levels (>60%) and EPO levels (>160 mU/mL), and three-fourths of these subjects responded to the fetal globin gene inducer alone. A few select fetal globin-inducing short-chain fatty acid derivatives that stimulated cell proliferation also had favorable pharmacokinetics. These studies identify a significant subset of thalassemia patients who appear to require exogenous EPO to respond optimally to any HbF inducer, as well as new therapeutic candidates that act on both cellular and molecular pathologies of beta-thalassemia. Both approaches now offer excellent potential for tolerable, definitive treatment of beta-thalassemia.

Mechanisms underlying the effects of inulin-type fructans on calcium absorption in the large intestine of rats.

Inulin-type fructans (inulin, oligofructose, fructooligosaccharides) in the diet do increase intestinal calcium absorption in animals and humans, but the underlying mechanism has not been identified. We therefore assessed the effects of fermentation of inulin-type fructans on transepithelial calcium transport in rat large intestine. Transepithelial calcium fluxes in vitro (Ussing chamber), effects on gene expression, mucosal morphology, and composition of luminal contents were determined in rats fed a standard diet and/or a diet containing 10% (w/w) 1/1 inulin-oligofructose mixture (INOF). Net transepithelial calcium transport in large intestine of rats fed a standard diet was increased by high mucosal calcium concentrations, the presence of 100 mmol/L mucosal short-chain fatty acids (SCFAs), the presence of 10 g/L INOF at the mucosal side, but not by reducing mucosal pH. Tissues from rats fed INOF did not show altered calcium transport when compared to controls. However, when flux data were based on the total caecal surface area, INOF-fed rats nearly doubled absorption rate in caecum. INOF feeding altered transcript levels of several mucosal genes that can be linked to transcellular and paracellular calcium transport processes. In addition, a decreased luminal pH in caecum with markedly increased caecal pools of total, soluble, and ionized calcium resulted from INOF ingestion. Thus, inulin-type fructans increase the large intestinal calcium absorption by different mechanisms including enhanced pools of soluble and ionized calcium, an increase in the absorptive surface predominantly in caecum, the increased concentrations of SCFAs, and by direct interaction with the intestinal tissue.

Role of short-chain fatty acids in colonic HCO(3) secretion.

Luminal isobutyrate, a relatively poor metabolized short-chain fatty acid (SCFA), induces HCO(3) secretion via a Cl-independent, DIDS-insensitive, carrier-mediated process as well as inhibiting both Cl-dependent and cAMP-induced HCO(3) secretion. The mechanism(s) responsible for these processes have not been well characterized. HCO(3) secretion was measured in isolated colonic mucosa mounted in Lucite chambers using pH stat technique and during microperfusion of isolated colonic crypts. (14)C-labeled butyrate, (14)C-labeled isobutyrate, and (36)Cl uptake were also determined by apical membrane vesicles (AMV) isolated from surface and/or crypt cells. Butyrate stimulation of Cl-independent, DIDS-insensitive 5-nitro-3-(3-phenylpropyl-amino)benzoic acid-insensitive HCO(3) secretion is greater than that by isobutyrate, suggesting that both SCFA transport and metabolism are critical for HCO(3) secretion. Both lumen and serosal 25 mM butyrate inhibit cAMP-induced HCO(3) secretion to a comparable degree (98 vs. 90%). In contrast, Cl-dependent HCO(3) secretion is downregulated by lumen 25 mM butyrate considerably more than by serosal butyrate (98 vs. 37%). Butyrate did not induce HCO(3) secretion in isolated microperfused crypts, whereas an outward-directed HCO(3) gradient-driven induced (14)C-butyrate uptake by surface but not crypt cell AMV. Both (36)Cl/HCO(3) exchange and potential-dependent (36)Cl movement in AMV were inhibited by 96-98% by 20 mM butyrate. We conclude that 1) SCFA-dependent HCO(3) secretion is the result of SCFA transport across the apical membrane via a SCFA/HCO(3) exchange more than intracellular SCFA metabolism; 2) SCFA-dependent HCO(3) secretion is most likely a result of an apical membrane SCFA/HCO(3) exchange in surface epithelial cells; 3) SCFA downregulates Cl-dependent and cAMP-induced HCO(3) secretion secondary to SCFA inhibition of apical membrane Cl/HCO(3) exchange and anion channel activity, respectively.

New lipids in enteral feeding.

PURPOSE OF REVIEW: Lipid sources for enteral nutrition continue to be an exciting area of investigation. It is timely to review recent developments which have largely contributed to thrust enteral feeding into a new era. RECENT FINDINGS: Although much more research needs to be done, there is a better understanding of the competitive relationships between n-6/n-3 fatty acids in conditions of metabolic and immune stress as well as in autoimmune and degenerative diseases. Although structured lipids are more completely absorbed and cleared, other more important clinical benefits need to be documented before they can be considered cost-effective. Immune enhancing formulas are the subject of controversy and some have been shown to be more effective than others. Enteral formulations with short-chain fatty acids are promising but more experimental work on the normal, and the sick colon is needed. Finally, there are a few isolated studies suggesting that enteral feeding with liposomes and with lipolytic products may have advantages when the digestive phase needs to be circumvented. The era of nutrigenomics, in which the effect of specific lipids on genes and proteins is being explored, is with us. We can look forward to nutrigenetics when the effect of genetic variation on the interaction between diet and disease will guide our practice. SUMMARY: Clinicians already have access to lipid sources and formulations which allow them to individualize enteral feeding programs. More clinical and technological research needs to be carried out, however, before products can be tailored to produce optimal effects in specific conditions.

Effects of volatile fatty acid supply on their absorption and on water kinetics in the rumen of sheep sustained by intragastric infusions.

Three sheep fitted with a ruminal cannula and an abomasal catheter were used to study water kinetics and absorption of VFA infused continuously into the rumen. The effects of changing VFA concentrations in the rumen by shifting VFA infusion rates were investigated in an experiment with a 3 x 3 Latin square design. On experimental days, the animals received the basal infusion rate of VFA (271 mmol/h) during the first 2 h. Each animal then received VFA at a different rate (135, 394, or 511 mmol/h) for the next 7.5 h. Using soluble markers (polyethylene glycol and Cr-EDTA), ruminal volume, liquid outflow, apparent water absorption, and VFA absorption rates were estimated. There were no significant effects of VFA infusion rate on ruminal volume and water kinetics. As the VFA infusion rate was increased, VFA concentration and osmolality in the rumen were increased and pH was decreased. There was a biphasic response of liquid outflow to changes in the total VFA concentration in the rumen, as both variables increased together up to a total VFA concentration of 80.1 mM, whereas, beyond that concentration, liquid outflow remained stable at an average rate of 407 mL/h. There were significant linear (P = 0.003) and quadratic (P = 0.001) effects of VFA infusion rate on the VFA absorption rate, confirming that VFA absorption in the rumen is mainly a concentration-dependent process. The proportion of total VFA supplied that was absorbed in the rumen was 0.845 (0.822, 0.877, and 0.910 for acetate, propionate, and butyrate, respectively). The molar proportions of acetate, propionate, and butyrate absorbed were affected by the level of VFA infusion in the rumen, indicating that this level affected to a different extent the absorption of the different acids.

Production rates and metabolism of short-chain fatty acids in the colon and whole body using stable isotopes.

Short-chain fatty acids (SCFA; mainly acetate, propionate and butyrate) are largely produced in non-ruminants during the colonic bacterial fermentation of non-digestible carbohydrates. These intestinal exogenous SCFA pass in part through the splanchnic bed and reach the peripheral bloodstream, mixing with the endogenous circulating SCFA. The whole-body turnover of SCFA is thus composed of an endogenous peripheral turnover and an exogenous production that depends on dietary intake of non-digestible carbohydrates. In the present work methods were developed for determining the SCFA turnover in animals and in human subjects using stable isotopes. The original studies performed to determine endogenous and exogenous metabolism of SCFA in animals and in human subjects are summarised. Using intravenous infusion of 13C-labelled SCFA the whole-body turnover of acetate, propionate and butyrate was assessed in rats in a fasted state. The endogenous turnover of acetate and its oxidation were determined in healthy human subjects in the post-absorptive state, using intravenous infusion of [1-13C]acetate. Intragastric tracer infusions were performed to evaluate the splanchnic first-pass retention of acetate in adults. Finally, an original model was developed in healthy human subjects using intravenous infusion of [1-13C]acetate to determine in vivo the true colonic acetate production after ingestion of a non-digestible disaccharide. These present studies using stable isotopes provide the basis for a novel strategy to evaluate in vivo, in human subjects, the production of SCFA in the large intestine.