Uptake Of Short-chain Fatty Acids Research Articles

2-[18F]Fluoropropionic Acid PET Imaging of Doxorubicin-induced Cardiotoxicity.

Purpose Treatment of pediatric cancers with doxorubicin is a common and predictable cause of cardiomyopathy. Early diagnosis of treatment-induced cardiotoxicity and intervention are major determinants for the prevention of advanced disease. The onset of cardiomyopathies is often accompanied by profound changes in lipid metabolism, including an enhanced uptake of short-chain fatty acids (SCFA). Therefore, we explored the utility of 2-[ 18 F]fluoropropionic acid ([ 18 F]FPA), an SCFA analog, as an imaging biomarker of cardiac injury in mice exposed to doxorubicin. Procedures : Cardiotoxicity and cardiac dysfunction were induced in mice by an 8-dose regimen of doxorubicin (cumulative dose 24 mg/kg) administered over 14 days. The effects of doxorubicin exposure were assessed by measurement of heart weights, left ventricular ejection fractions, and blood cardiac troponin levels. Whole body and cardiac [ 18 F]FPA uptakes were determined by PET and tissue gamma counting in the presence or absence of AZD3965, a pharmacological inhibitor of monocarboxylate transporter 1 (MCT1). Radiation absorbed doses were estimated using tissue time-activity concentrations. Results Significantly higher cardiac [ 18 F]FPA uptake was observed in doxorubicin-treated animals. This uptake remained constant from 30 min to 120 min post-injection. Pharmacological inhibition of MCT1-mediated transport by AZD3965 selectively decreased the uptake of [ 18 F]FPA in tissues other than the heart. Co-administration of [ 18 F]FPA and AZD3965 enhanced the imaging contrast of the diseased heart while reducing overall exposure to radioactivity. Conclusions [ 18 F]FPA, especially when co-administered with AZD3965, is a new tool for imaging changes in fatty acid metabolism occurring in response to doxorubicin-induced cardiomyopathy by PET.

Cutaneotrichosporon curvatum and Yarrowia lipolytica as key players for green chemistry: efficient oil producers from food waste via the carboxylate platform

ABSTRACT Cutaneotrichosporon curvatum and Yarrowia lipolytica can accumulate microbial oils using short-chain fatty acids (SCFA) as carbon sources. SCFAs-rich media often contain significant amounts of nitrogen that prevent high carbon:nitrogen (C:N) ratios necessary to boost lipid production. This work assessed the intrinsic ability of C. curvatum and Y. lipolytica to produce high amounts of microbial oils from these unusual carbon sources. Results demonstrated that minor differences in SCFA concentration (only 2 g/L) had a significant effect on yeast growth and lipid production. A C:N of 80 promoted yeast growth at all SCFA concentrations and favored SCFA consumption at 19 g/L SCFAs. The different SCFA uptake preferences in C. curvatum and Y. lipolytica highlighted the importance of considering the SCFA profile to select a suitable yeast strain for microbial oils production. At the most challenging SCFA concentration (19 g/L), 57.2% ±1.6% (w/w) and 78.4 ± 0.6% (w/w) lipid content were obtained in C. curvatum and Y. lipolytica, respectively. These values are among the highest reported for wild-type strains. To circumvent the challenges associated with media with high nitrogen content, this report also proved struvite precipitation as an effective method for increasing lipid production (from 17.9 ± 3.9% (w/w) to 41.9 ± 2.6% (w/w)) after nitrogen removal in food waste-derived media.

Effect of sodium concentration and mucosal pH on apical uptake of acetate and butyrate, and barrier function of the isolated bovine ruminal epithelium

This study was conducted to investigate the role of Na+ on ruminal short-chain fatty acid (SCFA) absorption and barrier function when isolated ruminal epithelium was exposed to high and low pH ex vivo. Nine Holstein steer calves (322 ± 50.9 kg of BW) consuming 7.05 ± 1.5 kg DM of a TMR were euthanized and ruminal tissue was collected from the caudal-dorsal blind sac. Tissues were mounted between 2 halves of Ussing chambers (3.14 cm2) and exposed to buffers that contained low (10 mM) or high (140 mM) Na+ with low (6.2) or high (7.4) mucosal pH. The same buffer solutions were used on the serosal side except that pH was maintained at 7.4. Buffers used to evaluate SCFA uptake contained bicarbonate to determine total uptake or excluded bicarbonate and included nitrate to determine non-inhibitable uptake. Bicarbonate-dependent uptake was calculated as the difference between the total and non-inhibitable uptake. Acetate (25 mM) and butyrate (25 mM) were spiked with 2-3H-acetate and 1-14C-butyrate, respectively, and were then added to the mucosal side, incubated for 1 min, and tissues were analyzed to evaluate rates of SCFA uptake. Tissue conductance (Gt) and the mucosal-to-serosal flux of 1-3H-mannitol were used to assess barrier function. There were no Na+ × pH interactions for butyrate or acetate uptake. Decreasing mucosal pH from 7.4 to 6.2 increased total acetate and butyrate uptake, and bicarbonate-dependent acetate uptake. Flux of 1-3H-mannitol was not affected by treatment. However, high Na+ concentration reduced Gt and prevented an increase in Gt from flux period 1 to flux period 2. The results of this study indicate that although providing more Na+ to the ruminal epithelium does not affect SCFA uptake or mannitol flux, it may help stabilize tissue integrity.

Screening of Lactobacillus strains that enhance SCFA uptake in intestinal epithelial cells

The objective was to screen Lactobacillus strains with strong survivability in oro-gastrointestinal tract and adhesion abilities of intestinal mucins and Caco-2 cells, and their effect on absorption of short-chain fatty acids (SCFAs) by epithelial cells was studied. The survival rate of Lactobacillus strains was studied after exposure to oral stress, gastric stress and intestinal stress successively, and then their adhesion ability was also researched. The model of intestinal epithelial cells absorbing SCFAs was established, which was used to evaluate the effect of Lactobacillus strains on Caco-2 cells absorption of SCFAs. The survival rate of Lactobacillus plantarum L58, L67, L97, L123, and L198 and Lactobacillus fermentum L146 was significantly higher than others in oro-gastrointestinal tract (P < 0.05), which also showed high adhesion to mucins and Caco-2 cells. The model was successfully established with the Caco-2 cell line, which formed a polarized cell monolayer and developed tight junctions with an appropriate permeability coefficient for phenol red lower than 1 × 10–6 cm/s after culturing for 15 days, and the viability of Caco-2 cells was significantly higher than other concentrations when the content of propionic acid or butyric acid was 1 mmol/L in the model. The propionic acid content in Caco-2 cells inoculated with L. plantarum L58, L67, L97, L123, and L198 was significantly higher than that of cells without L. plantarum inoculation (P < 0.05), and the butyric acid content in cells inoculated with L. fermentum L146 was significantly higher than that of cells without inoculation (P < 0.05). Our results highlight that L. plantarum L58, L67, L97, L123, L198 and L. fermentum L146 are more resistant to oro-gastrointestinal conditions and their high adhesion to the intestine can enhance SCFAs uptake in intestinal epithelial cells.

Inhibition of Intestinal Lipid Absorption by Cyanobacterial Strains in Zebrafish Larvae.

Obesity is a complex metabolic disease, which is increasing worldwide. The reduction of dietary lipid intake is considered an interesting pathway to reduce fat absorption and to affect the chronic energy imbalance. In this study, zebrafish larvae were used to analyze effects of cyanobacteria on intestinal lipid absorption in vivo. In total, 263 fractions of a cyanobacterial library were screened for PED6 activity, a fluorescent reporter of intestinal lipases, and 11 fractions reduced PED6 activity > 30%. Toxicity was not observed for those fractions, considering mortality, malformations or digestive physiology (protease inhibition). Intestinal long-chain fatty acid uptake (C16) was reduced, but not short-chain fatty acid uptake (C5). Alteration of lipid classes by high-performance thin-layer chromatography (HPTLC) or lipid processing by fluorescent HPTLC was analyzed, and 2 fractions significantly reduced the whole-body triglyceride level. Bioactivity-guided feature-based molecular networking of LC-MS/MS data identified 14 significant bioactive mass peaks (p < 0.01, correlation > 0.95), which consisted of 3 known putative and 11 unknown compounds. All putatively identified compounds were known to be involved in lipid metabolism and obesity. Summarizing, some cyanobacterial strains repressed intestinal lipid absorption without any signs of toxicity and could be developed in the future as nutraceuticals to combat obesity.

Ruminal epithelium: a checkpoint for cattle health.

The reticulorumen, as the main fermentation site of ruminants, delivers energy in the form of short-chain fatty acids (SCFA) for both the animal as well as the ruminal wall. By absorbing these SCFA, the ruminal epithelium plays a major role in the maintenance of intraruminal and intraepithelial acid-base homoeostasis as well as the balance of osmolarity. It takes up SCFA via several pathways which additionally lead to either a reduction of protons in the ruminal lumen or the secretion of bicarbonate, ultimately buffering the ruminal content effectively. Nutrition of the epithelium itself is achieved by catabolism of the SCFA, especially butyrate. Catabolism of SCFA also helps to maintain a concentration gradient across the epithelium to ensure efficient SCFA uptake and stability of the epithelial osmolarity. Furthermore, the ruminal epithelium forms a tight barrier against pathogens, endotoxins or biogenic amines, which may emerge from ruminal microorganisms and feed. Under physiological conditions, it reduces toxin uptake to a minimum. Moreover, the epithelium seems to have the ability to degrade biogenic amines like histamine. Nonetheless, in high performance production animals like dairy cattle, the reticulorumen is confronted with large amounts of rapidly fermentable carbohydrates. This may push the epithelium to its limits, even though it possesses a great capacity to adapt to varying feeding conditions. If the epithelial limit is exceeded, increasing amounts of SCFA lead to an acidotic imbalance that provokes epithelial damage and thereby elevates the entrance of pathogens and other potentially harmful substances into the animal's body. Hence, the ruminal epithelium lays the foundation for the animal's health, and in order to ensure longevity and high performance of ruminant farm animals, it should never be overburdened.

Fecal Microbiota Transplant From Highly Feed Efficient Donors Affects Cecal Physiology and Microbiota in Low- and High-Feed Efficient Chickens.

Fecal microbiota transplants (FMT) may be used to improve chicken’s feed efficiency (FE) via modulation of the intestinal microbiota and microbe-host signaling. This study investigated the effect of the administration of FMT from highly feed efficient donors early in life on the jejunal and cecal microbiota, visceral organ size, intestinal morphology, permeability, and expression of genes for nutrient transporters, barrier function and innate immune response in chickens of diverging residual feed intake (RFI; a metric for FE). Chicks (n = 110) were inoculated with the FMT or control transplant (CT) on 1, 6, and 9 days posthatch (dph), from which 56 chickens were selected on 30 dph as the extremes in RFI, resulting in 15 low and 13 high RFI chickens receiving the FMT and 14 low and 14 high RFI chickens receiving the CT. RFI rank and FMT only caused tendencies for alterations in the jejunal microbiota and only one unclassified Lachnospiraceae genus in cecal digesta was indicative of high RFI. By contrast, the FMT caused clear differences in the short-chain fatty acid (SCFA) profile in the crop and cecal microbiota composition compared to the CT, which indicated alterations in amylolytic, pullulanolytic and hemicellulolytic bacteria such as Lactobacillus, Dorea, and Ruminococcus. Moreover, the FMT caused alterations in intestinal development as indicated by the longer duodenum and shallower crypts in the ceca. From the observed RFI-associated variation, energy-saving mechanisms and moderation of the mucosal immune response were indicated by higher jejunal permeability, shorter villi in the ileum, and enhanced cecal expression of the anti-inflammatory cytokine IL10 in low RFI chickens. Relationships obtained from supervised multigroup data integration support that certain bacteria, including Ruminococcocaceae-, Lactobacillus-, and unclassified Clostridiales-phylotypes, and SCFA in jejunal and cecal digesta modulated expression levels of cytokines, tight-junction protein OCLN and nutrient transporters for glucose and SCFA uptake. In conclusion, results suggest that the intestine only played a moderate role for the RFI-associated variation of the present low and high RFI phenotypes, whereas modulating the early microbial colonization resulted in long-lasting changes in bacterial taxonomic and metabolite composition as well as in host intestinal development.

Adaptive responses in short-chain fatty acid absorption, gene expression, and bacterial community of the bovine rumen epithelium recovered from a continuous or transient high-grain feeding

The feeding of high-grain diets to dairy cows commonly results in lowered pH and ruminal dysbiosis, characterized by changes in absorption dynamics of short-chain fatty acids (SCFA) across the reticuloruminal wall, epithelial function, and the epithelial bacteria community structure. Therefore, the present study evaluated the effect of high-grain feeding persistence on the absorption kinetics of reticuloruminal SCFA, gene expression in the rumen epithelium, and the associated shifts in the epithelial bacteria in cows recovering from either a long-term continuous high-grain feeding model or a long-term transient high-grain feeding model. In a crossover study design, 8 nonlactating Holstein cows were fed 60% concentrate either continuously for 4 wk (continuous) or with a 1-wk break in the second week of the high-grain feeding (transient). After the high-grain feeding, all animals were fed a diet of 100% forage (recovery) for an additional 8 wk. Rumen papilla biopsies and SCFA absorption measurements were taken at the start of the trial (baseline), after the 4-wk high-grain feeding (49 d), after 2-wk recovery forage feeding (63 d), and after 8-wk recovery forage (105 d). Absorption of SCFA was determined in vivo using the washed and isolated reticulorumen technique. Rumen papillae biopsies were used for adherent bacterial DNA and host RNA extraction. The epithelial bacteria were determined using Illumina MiSeq (Microsynth AG, Balgach, Switzerland) sequencing of the 16S rRNA gene. No significant effects of the high-grain feeding model were seen for bacterial diversity. However, bacterial diversity increased with time spent in the recovery forage feeding period regardless of feeding model. The relative abundance of Acidobacteria phyla and Acetivibrio spp. increased when animals were fed a transient high-grain feeding model. A trend toward increased CLDN4 expression was observed in the continuous model. Furthermore, there were interactions between feeding model and sampling day for gene targets CD14, DRA, NHE2, NHE3, and MCT2. When comparing length of recovery, in the continuous model increased relative absorption of SCFA was sustained at 63 d but dropped to baseline measurements at 105 d. A similar pattern was found with the transient model but it did not reach significance. The only gene target that was found to significantly correlate to relative absorption of SCFA was DRA (correlation coefficient ≤ -0.41). Whereas, genera Alkalibaculum, Anaerorhabdus, Coprococcus, and Dethiobacter all showed positive correlations to gene targets for pH regulation (NHE2 and NHE3) and SCFA uptake (MCT1) but negative correlations to SCFA absorption. We conclude that while the rumen absorption and epithelial bacteria were able to recover to baseline levels after 8 wk of forage feeding, the time needed for re-establishment of homeostasis in host gene expression is longer, especially when high-grain feeding is interrupted.

A look at the smelly side of physiology: transport of short chain fatty acids.

Fermentative organs such as the caecum, the colon, and the rumen have evolved to produce and absorb energy rich short chain fatty acids (SCFA) from otherwise indigestible substrates. Classical models postulate diffusional uptake of the undissociated acid (HSCFA). However, in net terms, a major part of SCFA absorption occurs with uptake of Na+ and resembles classical, coupled electroneutral NaCl transport. Considerable evidence suggests that the anion transporting proteins expressed by epithelia of fermentative organs are poorly selective and that their main function may be to transport acetate-, propionate-, butyrate- and HCO3- as the physiologically relevant anions. Apical uptake of SCFA thus involves non-saturable diffusion of the undissociated acid (HSCFA), SCFA-/HCO3- exchange via DRA (SLC26A3) and/or SCFA--H+ symport (MCT1, SLC16A1). All mechanisms lead to cytosolic acidification with stimulation of Na+/H+ exchange via NHE (SLC9A2/3). Basolaterally, Na+ leaves via the Na+/K+-ATPase with recirculation of K+. Na+ efflux drives the transport of SCFA- anions through volume-regulated anion channels, such as maxi-anion channels (possibly SLCO2A1), LRRC8, anoctamins, or uncoupled exchangers. When luminal buffering is inadequate, basolateral efflux will increasingly involve SCFA-/ HCO3- exchange (AE1/2, SCL4A1/2), or efflux of SCFA- with H+ (MCT1/4, SLC16A1/3). Furthermore, protons can be basolaterally removed by NHE1 (SCL9A1) or NBCe1 (SLC4A4). The purpose of these transport proteins is to maximize the amount of SCFA transported from the tightly buffered ingesta while minimizing acid transport through the epithelium. As known from the rumen for many decades, a disturbance of these processes is likely to cause severe colonic disease.

Epithelial, metabolic and innate immunity transcriptomic signatures differentiating the rumen from other sheep and mammalian gastrointestinal tract tissues.

Background. Ruminants are successful herbivorous mammals, in part due to their specialized forestomachs, the rumen complex, which facilitates the conversion of feed to soluble nutrients by micro-organisms. Is the rumen complex a modified stomach expressing new epithelial (cornification) and metabolic programs, or a specialised stratified epithelium that has acquired new metabolic activities, potentially similar to those of the colon? How has the presence of the rumen affected other sections of the gastrointestinal tract (GIT) of ruminants compared to non-ruminants?Methods. Transcriptome data from 11 tissues covering the sheep GIT, two stratified epithelial and two control tissues, was analysed using principal components to cluster tissues based on gene expression profile similarity. Expression profiles of genes along the sheep GIT were used to generate a network to identify genes enriched for expression in different compartments of the GIT. The data from sheep was compared to similar data sets from two non-ruminants, pigs (closely related) and humans (more distantly related).Results. The rumen transcriptome clustered with the skin and tonsil, but not the GIT transcriptomes, driven by genes from the epidermal differentiation complex, and genes encoding stratified epithelium keratins and innate immunity proteins. By analysing all of the gene expression profiles across tissues together 16 major clusters were identified. The strongest of these, and consistent with the high turnover rate of the GIT, showed a marked enrichment of cell cycle process genes (P = 1.4 E−46), across the whole GIT, relative to liver and muscle, with highest expression in the caecum followed by colon and rumen. The expression patterns of several membrane transporters (chloride, zinc, nucleosides, amino acids, fatty acids, cholesterol and bile acids) along the GIT was very similar in sheep, pig and humans. In contrast, short chain fatty acid uptake and metabolism appeared to be different between the species and different between the rumen and colon in sheep. The importance of nitrogen and iodine recycling in sheep was highlighted by the highly preferential expression of SLC14A1-urea (rumen), RHBG-ammonia (intestines) and SLC5A5-iodine (abomasum). The gene encoding a poorly characterized member of the maltase-glucoamylase family (MGAM2), predicted to play a role in the degradation of starch or glycogen, was highly expressed in the small and large intestines.Discussion. The rumen appears to be a specialised stratified cornified epithelium, probably derived from the oesophagus, which has gained some liver-like and other specialized metabolic functions, but probably not by expression of pre-existing colon metabolic programs. Changes in gene transcription downstream of the rumen also appear have occurred as a consequence of the evolution of the rumen and its effect on nutrient composition flowing down the GIT.

TRANSPORTERS OF MONOCARBOXYLATES: CHARACTERIZAITON AND FUNCTIONAL ROLES

The rapid transport of monocarboxylates, such as lactate, pyruvate and β-hydroxybutyrate, across membranes is essential for maintaining cellular homeostasis. They are mainly transported by three well-characterized protein carrier families: SLC16/monocarboxylate transporters (MCTs), SLC5/sodium-coupled monocarboxylate transporters (SMCTs), and mitochondrial pyruvate carriers (MPCs). There are 14 members in the SLC16 family (MCT1-14), however, only 5 of them (MCT1-4 and MCT7) can transport monocarboxylates. This transport process is proton-linked, electroneutral and driven by a concentration gradient of their substrates. MCT1, MCT2 and MCT4 have a broad expression pattern in various tissues with affinities in the order of MCT2&gt;MCT1&gt;MCT4. They play important roles in local functions and malfunctions of MCTs have been associated with devastating disorders such as cancer, obesity and ischemia. Two members of the SLC5 family, SLC5A8 (SMCT1) and SLC5A12 (SMCT2), transport monocarboxylates in a Na+-dependent, electrogenic manner with a stoichiometry being 2:1 for Na+/substrate. They play particularly important roles in short-chain fatty acids uptake in large intestine and regulation of uric acid reabsorption in kidney. MPCs (MPC1-2) form a large heterocomplex at the inner membrane of mitochondria and are mainly responsible for pyruvate transport into mitochondrial matrix to fuel Krebs cycle. Genetic mutations within these monocarboxylates carrier genes have been identified as causal factors for many diseases. Thus, a better understanding of their functions and regulations will help advance novel therapeutic interventions under certain pathological conditions.

Expression of monocarboxylate transporters I and IV and the ancillary protein CD147 in the intestinal tract of healthy horses and ponies.

To characterize the expression of monocarboxylate transporters (MCTs) 1 and 4 and the ancillary protein CD147 in the intestinal tract of healthy equids and determine the cellular location of CD147 in the intestinal epithelium. 12 healthy horses and ponies slaughtered for meat production or euthanized for reasons unrelated to gastrointestinal tract disease. The entire gastrointestinal tract was removed from each equid within 45 minutes after slaughter or euthanasia. Tissue samples were obtained from the antimesenteric side of the duodenum, jejunum, ileum, middle part of the cecum, sternal flexure of the ventral colon, pelvic flexure, sternal flexure of the dorsal colon, and descending colon (small colon). Expressions of MCT1, MCT4, and the ancillary protein CD147 were examined in tissue samples from each of the 8 intestinal locations by means of quantitative PCR assay, immunoblotting, and immunohistochemical analyses. Expression of MCT1 was most abundant in the cecum and colonic sites, whereas expression of MCT4 was predominantly in the proximal section of the intestine (small intestinal sites and cecum). Immunohistochemical analysis revealed that MCT1 and CD147 were present in the membranes of enterocytes (in crypts and villi). The anatomic distribution of MCT1 and MCT4 in the equine intestinal tract determined in this study together with the previous knowledge of the sites of substrate absorption indicated that MCT1 might predominantly contribute to the uptake of short-chain fatty acids in the large intestine and MCT4 might predominantly contribute to the uptake of lactate in the small intestine.

Long-term intake of raw potato starch decreases back fat thickness and dressing percentage but has no effect on the longissimus muscle quality of growing–finishing pigs

This study was conducted to investigate the effects of long-term intake of raw potato starch (RPS) on carcass quality, luminal short chain fatty acid (SCFA) concentrations, the expression of host genes involved in fat metabolism in the liver, SCFA uptake, SCFA signaling and satiety regulation in the colonic mucosa of growing–finishing pigs. Thirty-six Duroc×Landrace×Large White growing barrows (70 days of age, 23.78±1.87kg) were randomly allocated to corn starch (CS) and raw potato starch (RPS) groups, each group consisting of six replicates (pen) with three pigs per pen. Pigs in the CS group were offered a corn–soybean based diet, while pigs in the RPS group were put on a diet in which 230g/kg (growing) or 280g/kg (finishing) purified corn starch was replaced with purified RPS during a 100-day trial. Results showed that long-term intake of RPS significantly increased the feed intake of the pigs, but had no effect on body weight, average daily gain or feed:gain ratio. Consumption of RPS significantly increased the weight of the stomach and large intestine and their percentage of body weight, the mucosa thickness of the cecum and colon, and SCFA concentrations in the colon of pigs. Long-term intake of RPS decreased back fat thickness and dressing percentage but had no effect on the longissimus muscle quality of growing–finishing pigs. The expression of genes MCT1, FFAR2 and FFAR3 in the colonic mucosa was significantly up-regulated in pigs fed with the RPS diet as compared to pigs fed with the CS diet. Consuming RPS significantly down-regulated the expression of genes CPT1a and PPARα, and up-regulated the expression of the SREBP1c gene in the livers of pigs. The results suggest that RPS modulates gut SCFA concentrations and the expression of host genes, which can change the adipose tissue patterning in pigs.

The short-chain fatty acid uptake fluxes by mice on a guar gum supplemented diet associate with amelioration of major biomarkers of the metabolic syndrome.

Studies with dietary supplementation of various types of fibers have shown beneficial effects on symptoms of the metabolic syndrome. Short-chain fatty acids (SCFAs), the main products of intestinal bacterial fermentation of dietary fiber, have been suggested to play a key role. Whether the concentration of SCFAs or their metabolism drives these beneficial effects is not yet clear. In this study we investigated the SCFA concentrations and in vivo host uptake fluxes in the absence or presence of the dietary fiber guar gum. C57Bl/6J mice were fed a high-fat diet supplemented with 0%, 5%, 7.5% or 10% of the fiber guar gum. To determine the effect on SCFA metabolism, 13C-labeled acetate, propionate or butyrate were infused into the cecum of mice for 6 h and the isotopic enrichment of cecal SCFAs was measured. The in vivo production, uptake and bacterial interconversion of acetate, propionate and butyrate were calculated by combining the data from the three infusion experiments in a single steady-state isotope model. Guar gum treatment decreased markers of the metabolic syndrome (body weight, adipose weight, triglycerides, glucose and insulin levels and HOMA-IR) in a dose-dependent manner. In addition, hepatic mRNA expression of genes involved in gluconeogenesis and fatty acid synthesis decreased dose-dependently by guar gum treatment. Cecal SCFA concentrations were increased compared to the control group, but no differences were observed between the different guar gum doses. Thus, no significant correlation was found between cecal SCFA concentrations and metabolic markers. In contrast, in vivo SCFA uptake fluxes by the host correlated linearly with metabolic markers. We argue that in vivo SCFA fluxes, and not concentrations, govern the protection from the metabolic syndrome by dietary fibers.

Significance of Short Chain Fatty Acid Transport by Members of the Monocarboxylate Transporter Family (MCT)

Metabolism of short-chain fatty acids (SCFA) in the brain, particularly that of acetate, appears to occur mainly in astrocytes. The differential use has been attributed to transport, but the extent to which transmembrane movement of SCFA is mediated by transporters has not been investigated systematically. Here we tested the possible contribution of monocarboxylate transporters to SCFA uptake by measuring fluxes with labelled compounds and by following changes of the intracellular pH in Xenopus laevis oocytes expressing the isoforms MCT1, MCT2 or MCT4. All isoforms mediated significant transport of acetate. Formate, however, was transported only by MCT1. The contribution of MCT1 to SCFA transport was determined by using phloretin as a high-affinity inhibitor, which allowed a paired comparison of oocytes with and without active MCT1.

Monocarboxylate transporter‐1 genotype and breastfeeding status protect against elevated BMI in preschool aged Caucasian children

The gut microbiota has been implicated in the development of obesity in part through fermenting dietary fibers to short chain fatty acids (SCFAs). The monocarboxylate transporter‐1 (MCT‐1), coded for by the SLC16A1 gene, facilitates the uptake of SCFAs in the colon. The association between genetic variants of the SLC16A1 gene at rs4839273 and obesity phenotypes in Caucasian 2–5 year‐old children (n=128) in the STRONG Kids Program was studied. The marker was in Hardy‐Weinberg Equilibrium (χ2=0.38, p=0.54) and polymorphic information content was 0.34. Genomic DNA was obtained from saliva samples and was genotyped by fluorescence polarization. After adjusting for age, sex, and breastfeeding (BF) status, children with the CC genotype had lower BMI than children with CA or AA alleles (15.3 ± 0.6 vs. 16.6 ± 0.1, p=0.02). Breastfeeding status moderated this effect; individuals with CC genotype that were BF had lower BMI than those with CA or AA alleles who were not BF (15.9 ± 0.4 vs. 16.7 ± 0.2, p=0.05). Thus, genetic variation within the SLC16A1 gene was associated with BMI of the children in our study and this relationship was mediated by BF status.Grant Funding Source : UI Research Board

Multi‐factorial engineering of heterologous polyketide production in Escherichia coli reveals complex pathway interactions

Polyketides represent a significant fraction of all natural products. Many possess pharmacological activity which makes them attractive drug candidates. The production of the parent macrocyclic aglycones is catalyzed by multi-modular polyketide synthases utilizing short-chain acyl-CoA monomers. When producing polyketides through heterologous hosts, one must not only functionally express the synthase itself, but activate the machinery used to generate the required substrate acyl-CoA's. As a result, metabolic engineering of these pathways is necessary for high-level production of heterologous polyketides. In this study, we over-express three different pathways for provision of the two substrates (propionyl-CoA and (2S)-methylmalonyl-CoA) utilized for the biosynthesis of 6-deoxyerythronolide B (6-dEB; the macrolactone precursor of erythromycin): (1) a propionate → propionyl-CoA → (2S)-methylmalonyl-CoA pathway, (2) a methylmalonate → methylmalonyl-CoA → propionyl-CoA pathway, and (3) a succinate → succinyl-CoA → (2R)-methylmalonyl-CoA → (2S)-methylmalonyl-CoA → propionyl-CoA pathway. The current study revealed that propionate is a necessary component for greater than 5 mg L(-1) titers. Deletion of the propionyl-CoA:succinate CoA transferase (ygfH) or over-expression of the transcriptional activator of short chain fatty acid uptake improved titer to over 100 mg L(-1), while the combination of the two improved titer to over 130 mg L(-1). The addition of exogenous methylmalonate could also improve titer to over 100 mg L(-1). Expression of a Streptomyces coelicolor A3(2) methylmalonyl-CoA epimerase, in conjunction with over-expression of Escherichia coli's native methylmalonyl-CoA mutase, allowed for the incorporation of exogenously fed succinate into the 6-dEB core.

M2053 Spectral Analysis of the Dominant Frequency of Upper GI Motility-Assessment of Invasive Versus Non-Invasive Techniques

Segments of the rat GI tract were everted and subjected to a short pronase digestion and elutriation to obtain purified mucosal epithelial cells. RNA was isolated, labelled for microarray hybridization, and comparative whole rat genome expression analysis performed.Results: 12% of all annotated genes show segment specific enrichment. The gastric (>3000 genes) and ileal (519 genes) mucosa show the most diverse expression profile. (a) Stomach: The gastric mucosa expresses the machinery for acid secretion, digestive enzyme release and hormone release by endocrine cells. Associated with acid secretion is a specific set of K+, Cl-, and bicarbonate channels. Novel is a pathway for glucose and fatty acid sensing, iodide and glutamate uptake, and taurine synthesis. Specific sets of transcription factors control epithelial (Barx1, Runx) and enteroendocrine (FoxA2/N4) cell differentiation. (b) Small Bowel: This epithelium expresses genes encoding a unique fructose/glucose uptake and utilization mechanism. Several endocrine signals for gastric function are present. The upper portion expresses genes for iron uptake, bicarbonate secretion, pH homeostasis and detoxification of food contents. Epithelial differentiation is transcriptionally controlled by Meis2/ Pdx1 and Onecut 2. Expression of digestive enzymes, lipid/bile acid uptake and utilization increases in the distal small bowel. The ileum is also involved in innate and acquired immune defence, regulation of motility and electrolyte and water re-absorption. Transcriptional regulation of enterocyte and goblet cell differentiation is mainly controlled by increasing expression of Cdx1 and 2. (c) Colon: This epithelium is mainly involved in Ca++-, K+, and water re-absorption, short-chain fatty acid uptake and sensing, and innate and acquired immune defence. Epithelial differentiation is controlled by Hox transcription factors in addition to Cdx1/2. Conclusion: This survey of gene expression by the GI tract epithelium reveals unique epithelial properties, providing novel areas of exploration to define the roles of many of the encoded proteins in gut physiology.

The cellular expression of SMCT2 and its comparison with other transporters for monocarboxylates in the mouse digestive tract

SMCT1 (slc5a8) is a sodium-coupled monocarboxylate transporter expressed in the brush border of enterocytes. It regulates the uptake of short-chain fatty acids (SCFAs) produced by bacterial fermentation in the large intestine. Another subtype, SMCT2 (slc5a12), is expressed abundantly in the small intestine, but its precise expression profile remains unknown. The present study using in situ hybridization method, immunohistochemistry, and quantitative PCR analysis examined the distribution and cellular localization of SMCT2 in the digestive tract of mice and compared the expression pattern with those of other transporters for monocarboxylates. While an abundant expression of SMCT2 was found in the jejunum, this was negligible in the duodenum, terminal ileum, and large intestine. In contrast, SMCT1 had predominant expression sites in the large bowel and terminal ileum. Subcellularly, SMCT2 was localized in the brush border of enterocytes in the intestinal villi-as is the case for SMCT1, suggesting its involvement in the uptake of food-derived monocarboxylates such as lactate and acetate. MCT (slc16) is a basolateral type transporter of the gut epithelium and conveys monocarboxylates in an H+-dependent manner. Since among the main subtypes of MCT family only MCT1 was expressed significantly in the small intestine, it is able to function as a counterpart to SMCT2 in this location.

Absorption of carbohydrate-derived nutrients in sows as influenced by types and contents of dietary fiber1

The current investigation was undertaken to study the absorption and plasma concentration of carbohydrate-derived nutrients [glucose, short-chain fatty acids (SCFA), and lactate] and the apparent insulin production in sows fed diets containing contrasting types and contents of dietary fiber. Six sows were fed 3 experimental diets, low fiber (LF; 177 g of dietary fiber and 44 g of soluble fiber/kg of DM), high soluble fiber (HF-S; 429 g of dietary fiber and 111 g of soluble fiber/kg of DM), and high insoluble fiber (HF-I; 455 g of dietary fiber and 74 g of soluble fiber/kg of DM), in a repeated crossover design. Variations in dietary concentration and solubility of dietary fiber were obtained by substituting starch-rich wheat and barley in the LF diet with dietary fiber-rich co-products (sugar beet pulp, potato pulp, pectin residue, brewers spent grain, pea hulls, and seed residue, which have distinct physicochemical properties). The main carbohydrate component of the LF diet was starch and nonstarch polysaccharides (cellulose and noncellulosic polysaccharides) for the 2 high dietary fiber diets. Consumption of the LF diet resulted in increased and rapid glucose absorption at 0 to 4 h postfeeding. With the HF-I diet, the glucose absorption pattern was similar but at a decreased rate, whereas it was decreased and delayed with the HF-S diet (diet, P < 0.001; time, P < 0.001). These differences were also reflected in the insulin response. The quantitative absorption of SCFA at 0 to 10 h postfeeding was greater when feeding the HF-S diet compared with the LF diet (P < 0.001) and intermediate when feeding the HF-I diet (P < 0.001). The study showed that feeding the high dietary fiber diets resulted in a increased and more uniform uptake of SCFA than when feeding the LF control. Moreover, the HF-S diet reduced diurnal variation in glucose and insulin concentrations.