Metabolism and functions of L-glutamate in the epithelial cells of the small and large intestines

Short Communication: Differences in Levels of Free Amino Acids and Total Protein in Human Foremilk and Hindmilk

Free amino acids (FAAs) in human milk are indicated to have specific functional roles in infant development. Studies have shown differences between human milk that is expressed at the beginning of a feed (i.e., foremilk) and the remainder of the milk expressed (i.e., hindmilk). For example, it is well established that human hindmilk is richer in fat and energy than foremilk. Hence, exclusively feeding hindmilk is used to enhance weight gain of preterm, low birthweight infants. Whether FAAs occur differently between foremilk and hindmilk has never been reported, but given their bioactive capacities, this is relevant to consider especially in situations where hindmilk is fed exclusively. Therefore, this study analyzed and compared the FAA and total protein content in human foremilk and hindmilk samples donated by 30 healthy lactating women. The total protein content was found to be significantly higher in hindmilk (p < 0.001), whereas foremilk contained a significantly higher total content of FAAs (p = 0.015). With regards to individual FAAs, foremilk contained significantly higher levels of phenylalanine (p = 0.009), threonine (p = 0.003), valine (p = 0.018), alanine (p = 0.004), glutamine (p < 0.001), and serine (p = 0.012) than hindmilk. Although statistical significance was reached, effect size analysis of the milk fraction on FAA levels in milk revealed that the observed differences were only small. To what extent these differences are of physiological importance for infant development remains to be examined in future research.

Oral administration of antibiotics results in fecal occult bleeding due to metabolic disorders and defective proliferation of the gut epithelial cell in mice

Antibiotics sometimes exert adverse effects on the pathogenesis of colitis due to the dysbiosis resulting from the disruption of gut homeostasis. However, the precise mechanisms underlying colitogenic effects of antibiotic-induced colitis are largely unknown. Here, we show a novel murine fecal occult bleeding model induced by the combinatorial treatment of ampicillin and vancomycin, which is accompanied by an enlarged cecum, upregulation of pro-inflammatory cytokines IL-6 and IL-12, a reduction in Ki-67-positive epithelial cell number and an increase in the apoptotic cell number in the colon. Moreover, gas chromatography-tandem mass analysis showed that various kinds of metabolites, including glutamic acid and butyric acid, were significantly decreased in the cecal contents. In addition, abundance of butyric acid producer Clostridiales was dramatically reduced in the enlarged cecum. Interestingly, supplementation of monosodium glutamate or its precursor glutamine suppressed colonic IL-6 and IL-12, protected from cell apoptosis and prevented fecal occult blood indicating that the reduced level of glutamic acid is a possible mechanism of antibiotic-induced fecal occult bleeding. Our data showed a novel mechanism of antibiotic-induced fecal occult bleeding providing a new insight into the clinical application of glutamic acid for the treatment of antibiotic-induced colitis.

Plasma citrulline concentration, a marker for intestinal functionality, reflects exercise intensity in healthy young men

BACKGROUND & AIMS

Plasma citrulline concentration is considered to be a marker for enterocyte metabolic mass and to reflect its reduction as may occur during intestinal dysfunction. Strenuous exercise can act as a stressor to induce small intestinal injury. Our previous studies suggest that this comprises the intestinal ability to produce citrulline from a glutamine-rich protein bolus. In this study we investigated the effects of different exercise intensities and hydration state on citrulline and iFABP levels following a post-exercise glutamine bolus in healthy young men.

METHODS

Fifteen healthy young men (20-35 yrs, VO₂ max 56.9 ± 3.9 ml kg^-1 min^-1) performed in a randomly assigned cross-over design, a rest (protocol 1) and four cycle ergometer protocols. The volunteers cycled submaximal at different percentages of their individual pre-assessed maximum workload (Wmax): 70% Wmax in hydrated (protocol 2) and dehydrated state (protocol 3), 50% Wmax (protocol 4) and intermittent 85/55% Wmax in blocks of 2 min (protocol 5). Immediately after 1 h exercise or rest, subjects were given a glutamine bolus with added alanine as an iso-caloric internal standard (7.5 g of each amino acid). Blood samples were collected before, during and after rest or exercise, up to 24 h post onset of the experiment. Amino acids and urea were analysed as metabolic markers, creatine phosphokinase and iFABP as markers of muscle and intestinal damage, respectively. Data were analysed using a multilevel mixed linear statistical model. p values were corrected for multiple testing.

RESULTS

Citrulline levels already increased before glutamine supplementation during normal hydrated exercise, while this was not observed in the dehydrated and rest protocols. The low intensity exercise protocol (50% Wmax) showed the highest increase in citrulline levels both during exercise (43.83 μmol/L ± 2.63 (p < 0.001)) and after glutamine consumption (50.54 μmol/L ± 2.62) compared to the rest protocol (28.97 μmol/L ± 1.503 and 41.65 μmol/L ± 1.96, respectively, p < 0.05). However, following strenuous exercise at 70% Wmax in the dehydrated state, citrulline levels did not increase during exercise and less after the glutamine consumption when compared to the resting condition and hydrated protocols. In line with this, serum iFABP levels were the highest with the strenuous dehydrated protocol (1443.72 μmol/L ± 249.9, p < 0.001), followed by the high intensity exercise at 70% Wmax in the hydrated condition.

CONCLUSIONS

Exercise induces an increase in plasma citrulline, irrespective of a glutamine bolus. The extent to which this occurs is dependent on exercise intensity and the hydration state of the subjects. The same holds true for both the post-exercise increase in citrulline levels following glutamine supplementation and serum iFABP levels. These data indicate that citrulline release during exercise and after an oral glutamine bolus might be dependent on the intestinal health state and therefore on intestinal functionality. Glutamine is known to play a major role in intestinal physiology and the maintenance of gut health and barrier function. Together, this suggests that in clinical practice, a glutamine bolus to increase citrulline levels after exercise might be preferable compared to supplementing citrulline itself. To our knowledge this is the first time that exercise workload-related effects on plasma citrulline are reported in relation to intestinal damage.

Weaning disrupts intestinal antioxidant status, impairs intestinal barrier and mitochondrial function, and triggers mitophagy in piglets

In the present study, we investigated the influence of weaning on antioxidant status, intestinal integrity, mitochondrial function, and the mitophagy level in piglets (weaned at 21 d) during the 1 wk after weaning. The redox status was measured by antioxidant enzymes activities, related genes expression, and malondialdehyde (MDA) content in jejunum. The intestinal barrier function was assessed by the Ussing chamber and expression of tight junction proteins in the jejunum. The function of intestine mitochondria was measured by mitochondrial DNA (mtDNA) content and activities of mitochondria oxidative phosphorylation complexes. The levels of light chain 3-1 (LC3-I), light chain 3-II (LC3-II), PTEN-induced putative kinase 1 (PINK1), and Parkin were determined to investigate whether mitophagy is involved in the weaning process. The results showed that, as compared with the preweaning phase (d 0), weaning suppressed (P < 0.05) the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) on d 3 and d 7 postweaning, decreased (P < 0.05) the expression of copper and zinc superoxide dismutase (Cu/Zn-SOD), manganese-containing superoxide dismutase (Mn-SOD) on d 3 postweaning, declined (P < 0.05) the level of glutathione peroxidase 1 (GPX-1) and glutathione peroxidase 4 (GPX-4) on d 3 and d 7 postweaning, and increased (P < 0.05) MDA content in jejunum on d 3 and d 7 postweaning. The jejunal transepithelial electrical resistance and levels of occludin, claudin-1, and zonula occludens-1 on d 3 and d 7 postweaning were reduced (P < 0.05), and paracellular flux of fluorescein isothiocyanatedextran (4 kDa) on d 3 and d 7 postweaning was increased (P < 0.05). Weaning induced mitochondrial dysfunction, as demonstrated by decreased (P < 0.05) content of mtDNA on d 3 and d 7 postweaning and declined (P < 0.05) activities of mitochondria complexes (I, II, III, IV) in jejunum on d 1, d 3, and d 7 postweaning. Weaning led to an increased (P < 0.05) expression level of mitophagy-related proteins, PINK1 and Parkin, in the intestinal mitochondria, as well as an enhancement (P < 0.05) of the ratio of LC3-II to LC3-I content in the jejunal mucosa on d 1, d 3, and d 7 postweaning. These results suggest that weaning disrupted intestinal oxidative balance, and this imbalance may impair intestinal barrier and mitochondrial function and trigger mitophagy in piglets.

Longitudinal Variation of Amino Acid Levels in Human Milk and Their Associations with Infant Gender

It is discussed that specific amino acids (AAs) have functional roles in early life. Understanding the AA composition in human milk (HM) during lactation assists in specifying these roles. To this end we assessed the levels of free AAs (FAAs), total AAs (free and bound, TAAs) and protein levels in HM in the first 6 months of lactation, and evaluated possible associations with infant gender. HM samples of 25 healthy Dutch mothers participating in the PreventCD study were collected monthly during the first 6 months of lactation. Of the participating mothers, 12 gave birth to a boy and 13 gave birth to a girl. Analyses of the HM samples revealed that levels of free glutamate, glutamine, aspartate, glycine, and serine significantly increased during months 1–3 of lactation, both in absolute sense and relative to TAA levels. Evaluation of gender differences by mixed model analyses revealed an association between female infant gender and higher protein content (p = 0.0465) and TAA content (p = 0.0362) in HM during the first 3 months of lactation. Furthermore, there was a tendency for an association of male infant gender with higher levels of free glutamine (p = 0.0948) in HM during the first 3 months of lactation. These results show that FAA, TAA and protein levels in HM display a time-specific occurrence during lactation. Moreover, although confirmation is necessary in view of the small sample size, this study indicates that the AA composition in HM shows differential effects of the infant’s sex.

L-Glutamate nutrition and metabolism in swine

L-Glutamate (Glu) has traditionally not been considered as a nutrient needed in diets for humans and other animals (including swine) due to the unsubstantiated assumption that animals can synthesize sufficient amounts of Glu to meet their needs. The lack of knowledge about Glu nutrition has contributed to suboptimal efficiency of global livestock production. Over the past 25 years, there has been growing interest in Glu metabolism in the pig, which is an agriculturally important species and also a useful model for studying human biology. Because of analytical advances in its analysis, Glu is now known to be a highly abundant free amino acid in milk and intracellular fluid, a major constituent of food and tissue proteins, and a key regulator of gene expression, cell signaling, and anti-oxidative reactions. Emerging evidence shows that dietary supplementation with 2% Glu maintains gut health and prevents intestinal dysfunction in weanling piglets, while enhancing their growth performance and survival. In addition, the inclusion of 2% Glu is required for dietary arginine to maximize the growth performance and feed efficiency in growing pigs, whereas dietary supplementation with 2% Glu reduces the loss of skeletal muscle mass in endotoxin-challenged pigs. Furthermore, supplementing 2% Glu to a corn- and soybean-meal-based diet promotes milk production by lactating sows. Thus, an adequate amount of dietary Glu as a quantitatively major nutrient is necessary to support maximum growth, development, and production performance of swine. These results also have important implications for improving the nutrition and health of humans and other animals.

Maternal L-glutamine supplementation during late gestation alleviates intrauterine growth restriction-induced intestinal dysfunction in piglets

Maternal dietary supplementation with L-glutamine (Gln) has been considered as an option to improve fetal growth and to prevent the occurrence of intrauterine growth restriction (IUGR). This study investigated whether maternal Gln supplementation could improve fetal growth as well as the intestinal development during late pregnancy. Sixty pregnant Landrace × Large White multiparous sows were assigned to two groups, either the group fed the control diet or the group with the diet supplemented with 1% Gln from d 85 of gestation until farrowing. One normal body weight piglet and one IUGR piglet were obtained from six litters in each group. Reproductive performance, plasma concentrations of free amino acids and related metabolites as well as piglet growth and tissue indexes were determined. Maternal Gln supplementation during late gestation increased the average birth weight, while decreasing the within-litter variation of newborn piglets. The concentrations of Gln in plasma were lower in IUGR piglets than in normal piglets. Glutamine supplementation enhanced Gln concentrations in maternal and piglet plasma and the piglet jejunum, compared with the Control group. Supplementing Gln suppressed intestinal miR-29a levels, and increased the abundance of extracellular matrix (ECM) and tight junction (TJ) proteins, resulting in increased intestinal weight and improved morphologies of the piglets. Collectively, Gln supplementation to the sow's diet increased fetal growth, decreased the within-litter variation of newborn piglets, and alleviated the IUGR-induced intestinal impairment. These findings suggest the possibility of maternal glutamine supplementation in the prevention and treatment of IUGR in animal production and human medicine.

Enterocyte glycosylation is responsive to changes in extracellular conditions: implications for membrane functions

Epithelial cells in the lining of the intestines play critical roles in maintaining homeostasis while challenged by dynamic and sudden changes in luminal contents. Given the high density of glycosylation that encompasses their extracellular surface, environmental changes may lead to extensive reorganization of membrane-associated glycans. However, neither the molecular details nor the consequences of conditional glycan changes are well understood. Here we assessed the sensitivity of Caco-2 and HT-29 membrane N-glycosylation to variations in (i) dietary elements, (ii) microbial fermentation products and (iii) cell culture parameters relevant to intestinal epithelial cell growth and survival. Based on global LC-MS glycomic and statistical analyses, the resulting glycan expression changes were systematic, dependent upon the conditions of each controlled environment. Exposure to short chain fatty acids produced significant increases in fucosylation while further acidification promoted hypersialylation. Notably, among all conditions, increases of high mannose type glycans were identified as a major response when extracellular fructose, galactose and glutamine were independently elevated. To examine the functional consequences of this discrete shift in the displayed glycome, we applied a chemical inhibitor of the glycan processing mannosidase, globally intensifying high mannose expression. The data reveal that upregulation of high mannose glycosylation has detrimental effects on basic intestinal epithelium functions by altering permeability, host-microbe associations and membrane protein activities.

Activation of Pyruvate Dehydrogenase by Sodium Dichloroacetate Shifts Metabolic Consumption from Amino Acids to Glucose in IPEC-J2 Cells and Intestinal Bacteria in Pigs

The extensive metabolism of amino acids (AA) as fuel is an important reason for the low use efficiency of protein in pigs. In this study, we investigated whether regulation of the pyruvate dehydrogenase kinase (PDK)/pyruvate dehydrogenase alpha 1 (PDHA1) pathway affected AA consumption by porcine intestinal epithelial (IPEC-J2) cells and intestinal bacteria in pigs. The effects of knockdown of PDHA1 and PDK1 with small interfering RNA (siRNA) on nutrient consumption by IPEC-J2 cells were evaluated. IPEC-J2 cells were then cultured with sodium dichloroacetate (DCA) to quantify AA and glucose consumption and nutrient oxidative metabolism. The results showed that knockdown of PDHA1 using siRNA decreased glucose consumption but increased total AA (TAA) and glutamate (Glu) consumption by IPEC-J2 cells ( P < 0.05). Opposite effects were observed using siRNA targeting PDK1 ( P < 0.05). Additionally, culturing IPEC-J2 cells in the presence of 5 mM DCA markedly increased the phosphorylation of PDHA1 and PDH phosphatase 1, but inhibited PDK1 phosphorylation ( P < 0.05). DCA treatment also reduced TAA and Glu consumption and increased glucose depletion ( P < 0.05). These results indicated that PDH was the regulatory target for shifting from AA metabolism to glucose metabolism and that culturing cells with DCA decreased the consumption of AAs by increasing the depletion of glucose through PDH activation.

Crystal structure and mechanism of human carboxypeptidase O: Insights into its specific activity for acidic residues

Human metallocarboxypeptidase O (hCPO) is a recently discovered digestive enzyme localized to the apical membrane of intestinal epithelial cells. Unlike pancreatic metallocarboxypeptidases, hCPO is glycosylated and produced as an active enzyme with distinctive substrate specificity toward C-terminal (C-t) acidic residues. Here we present the crystal structure of hCPO at 1.85-Å resolution, both alone and in complex with a carboxypeptidase inhibitor (NvCI) from the marine snail Nerita versicolor The structure provides detailed information regarding determinants of enzyme specificity, in particular Arg275, placed at the bottom of the substrate-binding pocket. This residue, located at "canonical" position 255, where it is Ile in human pancreatic carboxypeptidases A1 (hCPA1) and A2 (hCPA2) and Asp in B (hCPB), plays a dominant role in determining the preference of hCPO for acidic C-t residues. Site-directed mutagenesis to Asp and Ala changes the specificity to C-t basic and hydrophobic residues, respectively. The single-site mutants thus faithfully mimic the enzymatic properties of CPB and CPA, respectively. hCPO also shows a preference for Glu over Asp, probably as a consequence of a tighter fitting of the Glu side chain in its S1' substrate-binding pocket. This unique preference of hCPO, together with hCPA1, hCPA2, and hCPB, completes the array of C-t cleavages enabling the digestion of the dietary proteins within the intestine. Finally, in addition to activity toward small synthetic substrates and peptides, hCPO can also trim C-t extensions of proteins, such as epidermal growth factor, suggesting a role in the maturation and degradation of growth factors and bioactive peptides.

Expression of Glutamate Transporters in Mouse Liver, Kidney, and Intestine

Glutamate transport activities have been identified not only in the brain, but also in the liver, kidney, and intestine. Although glutamate transporter distributions in the central nervous system are fairly well known, there are still uncertainties with respect to the distribution of these transporters in peripheral organs. Quantitative information is mostly lacking, and few of the studies have included genetically modified animals as specificity controls. The present study provides validated qualitative and semi-quantitative data on the excitatory amino acid transporter (EAAT)1-3 subtypes in the mouse liver, kidney, and intestine. In agreement with the current view, we found high EAAT3 protein levels in the brush borders of both the distal small intestine and the renal proximal tubules. Neither EAAT1 nor EAAT2 was detected at significant levels in murine kidney or intestine. In contrast, the liver only expressed EAAT2 (but 2 C-terminal splice variants). EAAT2 was detected in the plasma membranes of perivenous hepatocytes. These cells also expressed glutamine synthetase. Conditional deletion of hepatic EAAT2 did neither lead to overt neurological disturbances nor development of fatty liver.

Effect of early dietary energy restriction and phosphorus level on subsequent growth performance, intestinal phosphate transport, and AMPK activity in young broilers

We aimed to determine the effect of low dietary energy on intestinal phosphate transport and the possible underlying mechanism to explain the long-term effects of early dietary energy restriction and non-phytate phosphorus (NPP). A 2 × 3 factorial experiment, consisting of 2 energy levels and 3 NPP levels, was conducted. Broiler growth performance, intestinal morphology in 0–21 days and 22–35 days, type IIb sodium-phosphate co-transporter (NaP_i-IIb) mRNA expression, adenylate purine concentrations in the duodenum, and phosphorylated adenosine monophosphate-activated protein kinase (AMPK-α) activity in 0–21 days were determined. The following results were obtained. (1) Low dietary energy (LE) induced a high feed conversion ratio (FCR) and significantly decreased body weight gain in young broilers, but LE induced significantly higher compensatory growth in low NPP (LP) groups than in the high or medium NPP groups (HP and MP). (2) LE decreased the villus height (VH) in the intestine, and LE-HP resulted in the lowest crypt depth (CD) and the highest VH:CD ratio in the initial phase. However, in the later period, the LE-LP group showed an increased VH:CD ratio and decreased CD in the intestine. (3) LE increased ATP synthesis and decreased AMP:ATP ratio in the duodenal mucosa of chickens in 0–21 days, and LP diet increased ATP synthesis and adenylate energy charges but decreased AMP production and AMP:ATP ratio. (4) LE led to weaker AMPK phosphorylation, higher mTOR phosphorylation, and higher NaP_i-IIb mRNA expression. Thus, LE and LP in the early growth phase had significant compensatory and interactive effect on later growth and intestinal development in broilers. The effect might be relevant to energy status that LE leads to weaker AMPK phosphorylation, causing a lower inhibitory action toward mTOR phosphorylation. This series of events stimulates NaP_i-IIb mRNA expression. Our findings provide a theoretical basis and a new perspective on intestinal phosphate transport regulation, with potential applications in broiler production.

Effects of medium-chain triglycerides on intestinal morphology and energy metabolism of intrauterine growth retarded weanling piglets

It has been shown that there is a relationship between intrauterine growth retardation (IUGR) and postnatal intestinal damage involved in energy deficits. Therefore, the present study was conducted to investigate the effect of medium-chain triglycerides (MCT) on the intestinal morphology, intestinal function and energy metabolism of piglets with IUGR. At weaning (21 ± 1.1 d of age), 24 IUGR piglets and 24 normal birth weight (NBW) piglets were selected according to their birth weights (BW) (IUGR: 0.95 ± 0.04 kg BW; NBW: 1.58 ± 0.04 kg BW) and their weights at the time of weaning (IUGR: 5.26 ± 0.15 kg BW; NBW: 6.98 ± 0.19 kg BW). The piglets were fed a diet of either long-chain triglycerides (LCT) (containing 5% LCT) or MCT (containing 1% LCT and 4% MCT) for 28 d. Then, the piglets' intestinal morphology, biochemical parameters and mRNA abundance related to intestinal damage and energy metabolism were determined. IUGR was found to impair intestinal morphology, with evidence of decreased villus height and increased crypt depth; however, these negative effects of IUGR were ameliorated by MCT treatment. IUGR piglets showed compromised intestinal digestion and absorption functions when compared with NBW piglets. However, feeding MCT increased the maltase activity in the jejunum and alleviated IUGR-induced reductions in plasma d-xylose concentrations and jejunal sucrase activity. IUGR decreased the efficiency of the piglets' intestinal energy metabolism; however, piglets fed an MCT diet exhibited increased adenosine triphosphate (ATP) concentrations and ATP synthase F1 complex beta polypeptide expression, as well as decreased adenosine monophosphate-activated kinase alpha 1 expression in the jejunum of piglets. In addition, up-regulation of the piglets' citrate synthase and succinate dehydrogenase levels was found to occur following MCT treatment at both the activity and the transcriptional levels of the jejunum. Therefore, it can be postulated that MCT treatment has beneficial effects in alleviating IUGR-induced intestinal morphologic damage, which is associated with improved intestinal energy metabolism.

Glutamate attenuates lipopolysaccharide-induced oxidative damage and mRNA expression changes of tight junction and defensin proteins, inflammatory and apoptosis response signaling molecules in the intestine of fish

The present study explored the possible preventive effects of dietary glutamate (Glu) on LPS-induced oxidative damage, mRNA expression changes of tight junction (TJ) and defensin proteins, inflammatory and apoptosis response signaling molecules in fish intestine. Young Jian carp were fed five diets supplemental graded levels of Glu (0, 4, 8, 16 and 32 g kg^-1 diet) for 63 days. The results indicated that Glu supplementation depressed LPS induced the production of reactive oxygen species (ROS) and severe oxidative damage (lipid peroxidation and protein oxidation) in fish intestine, which was partially due to the increased glutathione (GSH) content and antioxidant enzyme activities including superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione reductase (GR) (P < 0.05). Further investigations indicated that Glu supplementation caused elevation of those antioxidant enzyme activities are related to the up-regulation of corresponding antioxidant enzymes and the related signaling factor Nrf2 mRNA levels (P < 0.05). Meanwhile, Glu pre-treatment significantly suppressed LPS-induced COX-2 and inflammatory cytokines mRNA expression and down-regulated NF-κB p65 and MAPK p38 transcription. Furthermore, pre-treatment with Glu prevented LPS induced apoptosis-related gene expression (caspase 3 and 9, P < 0.05). Lastly, Glu supplementation also attenuated LPS induced intestinal barrier function-related gene TJ proteins (ZO-1, occludin1, claudin2, 3, and 7), β-defensin1 and 3 mRNA expressions decreasing (P < 0.05). Taken together, the present results showed Glu could attenuate LPS induced the oxidative damage by Nrf2 signal pathway and depress LPS induced inflammation response (cytokines, COX-2, NF-κB p65, and MAPK p38), apoptosis (caspase3 and 9), and barrier function (ZO-1, occludin1, claudin2, 3 and 7, and β-defensin 1 and 3)-related gene expression changes of fish intestine.

The effect of endurance exercise on intestinal integrity in well-trained healthy men

Exercise is one of the external factors associated with impairment of intestinal integrity, possibly leading to increased permeability and altered absorption. Here, we aimed to examine to what extent endurance exercise in the glycogen‐depleted state can affect intestinal permeability toward small molecules and protein‐derived peptides in relation to markers of intestinal function. Eleven well‐trained male volunteers (27 ± 4 years) ingested 40 g of casein protein and a lactulose/rhamnose (L/R) solution after an overnight fast in resting conditions (control) and after completing a dual – glycogen depletion and endurance – exercise protocol (first protocol execution). The entire procedure was repeated 1 week later (second protocol execution). Intestinal permeability was measured as L/R ratio in 5 h urine and 1 h plasma. Five‐hour urine excretion of betacasomorphin‐7 (BCM7), postprandial plasma amino acid levels, plasma fatty acid binding protein 2 (FABP‐2), serum pre‐haptoglobin 2 (preHP2), plasma glucagon‐like peptide 2 (GLP2), serum calprotectin, and dipeptidylpeptidase‐4 (DPP4) activity were studied as markers for excretion, intestinal functioning and recovery, inflammation, and BCM7 breakdown activity, respectively. BCM7 levels in urine were increased following the dual exercise protocol, in the first as well as the second protocol execution, whereas 1 h‐plasma L/R ratio was increased only following the first exercise protocol execution. FABP2, preHP2, and GLP2 were not changed after exercise, whereas calprotectin increased. Plasma citrulline levels following casein ingestion (iAUC) did not increase after exercise, as opposed to resting conditions. Endurance exercise in the glycogen depleted state resulted in a clear increase of BCM7 accumulation in urine, independent of DPP4 activity and intestinal permeability. Therefore, strenuous exercise could have an effect on the amount of food‐derived bioactive peptides crossing the epithelial barrier. The health consequence of increased passage needs more in depth studies.

Effects of porcine epidemic diarrhea virus infection on nursery pig intestinal function and barrier integrity

The pig intestinal epithelium can be compromised by pathogens leading to reduced integrity and function. Porcine epidemic diarrhea virus (PEDV), recently detected in North America, exemplifies intestinal epithelial insult. Although several studies have investigated the molecular aspects and host immune response to PEDV, there are little data on the impact of PEDV on pig intestinal physiology. The objective of this study was to investigate the longitudinal impact of PEDV on nursery pig intestinal function and integrity. Fifty recently-weaned, 5-week-old barrows and gilts (BW=9.92±0.49kg) were sorted based on body weight (BW) and sex into two treatments: 1) Control or 2) PEDV inoculated. At 2, 5, 7, and 14days post inoculation (dpi), 4 pigs per treatment were euthanized and jejunum sections collected. PEDV antigen was detected in inoculated pigs by immunohistochemistry in 50% (2/4) at dpi 2, 100% (4/4) at dpi 5, and none at later time points. PEDV-infected pigs had reduced (P<0.05) villus height and decreased transepithelial resistance compared with controls. Total acidic mucins, particularly sialomucin, were reduced in PEDV pigs at dpi 2 and then increased compared with controls at dpi 7 and 14. In addition, PEDV pigs had increased stem cell proliferation (P<0.05) and a numerical increase in DNA fragmentation compared with controls through dpi 7 which coincided with an observed return of digestive function to that of controls. Collectively, these data reveal that PEDV infection results in time-dependent changes not only in intestinal morphology but also barrier integrity and function.

Therapeutic Potential of Amino Acids in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes both ulcerative colitis and Crohn’s disease, is a chronic relapsing inflammation of the gastrointestinal tract, and is difficult to treat. The pathophysiology of IBD is multifactorial and not completely understood, but genetic components, dysregulated immune responses, oxidative stress, and inflammatory mediators are known to be involved. Animal models of IBD can be chemically induced, and are used to study etiology and to evaluate potential treatments of IBD. Currently available IBD treatments can decrease the duration of active disease but because of their adverse effects, the search for novel therapeutic strategies that can restore intestinal homeostasis continues. This review summarizes and discusses what is currently known of the effects of amino acids on the reduction of inflammation, oxidative stress, and cell death in the gut when IBD is present. Recent studies in animal models have identified dietary amino acids that improve IBD, but amino acid supplementation may not be adequate to replace conventional therapy. The animal models used in dietary amino acid research in IBD are described.

Prevention of Histological Changes after Colonic Diversion in Rats: An Experimental Study

AIM

To determine the beneficial effects of Glutamine, Psyllium, Short Chain Fatty Acids (SCFA), and Maharishi Amrit Kalash (MAK), in preventing the histological changes after diversion colostomy.

MATERIAL AND METHODS

After ethical clearance, male wistar rats (n=40) underwent diversion colostomy. Rats were divided into five groups of 8 rats each. Each group was given, after diversion colostomy, per rectally, one of the five agents being tested as an enema (3 ml/kg/day). Group I: Normal saline. Group II: Glutamine Group III: Psyllium, Group IV: MAK. Group V: Short chain fatty acid. The rats were euthanised 45 days after performing diversion colostomy. Morphometrical analysis of defunctionalised colon was done. Statistical analysis was done using SSPS statistical analysis software.

RESULTS

On comparison with Group I epithelial cell height and mucosal thickness was significantly higher in Group II. Muscularis externae thickness was significantly higher in Group III on comparison with Group I. Group V had least inflammatory changes.

CONCLUSIONS

Atrophic and inflammatory changes in the diverted colon can be prevented by per rectal administration of Glutamine, Psyllium and Short chain fatty acids.

Inbred Mouse Populations Exhibit Intergenerational Changes in Intestinal Microbiota Composition and Function Following Introduction to a Facility

Inbred mice are used to investigate many aspects of human physiology, including susceptibility to disease and response to therapies. Despite increasing evidence that the composition and function of the murine intestinal microbiota can substantially influence a broad range of experimental outcomes, relatively little is known about microbiome dynamics within experimental mouse populations. We investigated changes in the intestinal microbiome between C57BL/6J mice spanning six generations (assessed at generations 1, 2, 3, and 6), following their introduction to a stringently controlled facility. Fecal microbiota composition and function were assessed by 16S rRNA gene amplicon sequencing and liquid chromatography mass spectrometry, respectively. Significant divergence of the intestinal microbiota between founder and second generation mice, as well as continuing inter-generational variance, was observed. Bacterial taxa whose relative abundance changed significantly through time included Akkermansia, Turicibacter, and Bifidobacterium (p < 0.05), all of which are recognized as having the potential to substantially influence host physiology. Shifts in microbiota composition were mirrored by corresponding differences in the fecal metabolome (r = 0.57, p = 0.0001), with notable differences in levels of tryptophan pathway metabolites and amino acids, including glutamine, glutamate and aspartate. We related the magnitude of changes in the intestinal microbiota and metabolome characteristics during acclimation to those observed between populations housed in separate facilities, which differed in regards to husbandry, barrier conditions and dietary intake. The microbiome variance reported here has implications for experimental reproducibility, and as a consequence, experimental design and the interpretation of research outcomes across wide range of contexts.

Dietary Protein and Amino Acid Supplementation in Inflammatory Bowel Disease Course: What Impact on the Colonic Mucosa?

Inflammatory bowel diseases (IBD), after disease onset, typically progress in two cyclically repeated phases, namely inflammatory flare and remission, with possible nutritional status impairment. Some evidence, either from epidemiological, clinical, and experimental studies indicate that the quantity and the quality of dietary protein consumption and amino acid supplementation may differently influence the IBD course according to the disease phases. For instance, although the dietary protein needs for mucosal healing after an inflammatory episode remain undetermined, there is evidence that amino acids derived from dietary proteins display beneficial effects on this process, serving as building blocks for macromolecule synthesis in the wounded mucosal area, energy substrates, and/or precursors of bioactive metabolites. However, an excessive amount of dietary proteins may result in an increased intestinal production of potentially deleterious bacterial metabolites. This could possibly affect epithelial repair as several of these bacterial metabolites are known to inhibit colonic epithelial cell respiration, cell proliferation, and/or to affect barrier function. In this review, we present the available evidence about the impact of the amount of dietary proteins and supplementary amino acids on IBD onset and progression, with a focus on the effects reported in the colon.

Changes in the Luminal Environment of the Colonic Epithelial Cells and Physiopathological Consequences

Evidence, mostly from experimental models, has accumulated, indicating that modifications of bacterial metabolite concentrations in the large intestine luminal content, notably after changes in the dietary composition, may have important beneficial or deleterious consequences for the colonic epithelial cell metabolism and physiology in terms of mitochondrial energy metabolism, reactive oxygen species production, gene expression, DNA integrity, proliferation, and viability. Recent data suggest that for some bacterial metabolites, like hydrogen sulfide and butyrate, the extent of their oxidation in colonocytes affects their capacity to modulate gene expression in these cells. Modifications of the luminal bacterial metabolite concentrations may, in addition, affect the colonic pH and osmolarity, which are known to affect colonocyte biology per se. Although the colonic epithelium appears able to face, up to some extent, changes in its luminal environment, notably by developing a metabolic adaptive response, some of these modifications may likely affect the homeostatic process of colonic epithelium renewal and the epithelial barrier function. The contribution of major changes in the colonocyte luminal environment in pathological processes, like mucosal inflammation, preneoplasia, and neoplasia, although suggested by several studies, remains to be precisely evaluated, particularly in a long-term perspective.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs II: Intestinal integrity and function

The objective of this study was to determine if intestinal function and integrity is altered due to porcine reproductive and respiratory syndrome (PRRS) virus and porcine epidemic diarrhea (PED) virus infection in growing pigs. Forty-two gilts (16.8 ± 0.6 kg BW), naïve for PRRS and PED, were selected and randomly assigned to 1 of 4 treatments: 1) a control (CON; = 6), 2) PRRS virus challenge only (PRRS; = 12), 3) PED virus challenge only (; = 12), or 4) coinfection of PRRS + PED viruses (PRP; = 12). Treatments 2 and 4 were inoculated with a live field strain of PRRS virus on d 0 after inoculation. Treatments 3 and 4 were inoculated with PED virus on 14 d after inoculation (dpi) and all pigs were euthanized 7 d later (21 dpi). Infection with PRRS virus was determined by viremia and seroconversion. Fecal quantitative PCR was used to confirm PED virus infection. Control pigs remained PRRS and PED virus negative throughout the study. Compared with the CON, intestinal morphology was unaffected by PRRS. As expected, PED and PRP treatments resulted in duodenum, jejunum, and ileum villus atrophy compared with the CON treatment ( < 0.01). Ex vivo transepithelial electrical resistance (TER) did not differ between CON and PRRS pigs (P < 0.05) but was reduced by 40% in PED alone ( < 0.01). Interestingly, TER was increased ( < 0.01) in the PRP pigs. Active transport of glucose was increased in PRRS pigs over CON pigs ( < 0.01), whereas PED had pigs increased ( < 0.01) active glutamine transport over the CON pigs. Jejunum GLUT2 mRNA abundance and sucrase, maltase, and Na+/K+ adenosine triphosphatase activities tended to be increased in PRRS pigs compared with CON pigs ( < 0.06). The jejunum AA transporter, SLC6A14, and mucin 2 mRNA abundance tended to be increased in PED-only pigs ( < 0.10). These data suggest that PRRS infection supports a higher affinity for glucose uptake, whereas PED favors glutamine uptake. Interestingly, digestive machinery during PED challenge remained intact. Altogether, PED but not PRRS challenges alter intestinal morphology and integrity in growing pigs.

Hepatic encephalopathy: Ever closer to its big bang

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that commonly complicates the course of patients with liver disease. Despite the fact that the syndrome was probably first recognized hundreds of years ago, the exact pathogenesis still remains unclear. Minimal hepatic encephalopathy (MHE) is the earliest form of HE and is estimated to affect more that 75% of patients with liver cirrhosis. It is characterized by cognitive impairment predominantly attention, reactiveness and integrative function with very subtle clinical manifestations. The development of MHE is associated with worsen in driving skills, daily activities and the increase of overall mortality. Skeletal muscle has the ability to shift from ammonia producer to ammonia detoxifying organ. Due to its large size, becomes the main ammonia detoxifying organ in case of chronic liver failure and muscular glutamine-synthase becomes important due to the failing liver and brain metabolic activity. Gut is the major glutamine consumer and ammonia producer organ in the body. Hepatocellular dysfunction due to liver disease, results in an impaired clearance of ammonium and in its inter-organ trafficking. Intestinal bacteria, can also represent an extra source of ammonia production and in cirrhosis, small intestinal bacterial overgrowth and symbiosis can be observed. In the study of HE, to get close to MHE is to get closer to its big bang; and from here, to travel less transited roads such as skeletal muscle and intestine, is to go even closer. The aim of this editorial is to expose this road for further and deeper work.

Role of glutamatergic neurotransmission in the enteric nervous system and brain-gut axis in health and disease

Several studies have been carried out in the last 30 years in the attempt to clarify the possible role of glutamate as a neurotransmitter/neuromodulator in the gastrointestinal tract. Such effort has provided immunohistochemical, biomolecular and functional data suggesting that the entire glutamatergic neurotransmitter machinery is present in the complex circuitries of the enteric nervous system (ENS), which participates to the local coordination of gastrointestinal functions. Glutamate is also involved in the regulation of the brain-gut axis, a bi-directional connection pathway between the central nervous system (CNS) and the gut. The neurotransmitter contributes to convey information, via afferent fibers, from the gut to the brain, and to send appropriate signals, via efferent fibers, from the brain to control gut secretion and motility. In analogy with the CNS, an increasing number of studies suggest that dysregulation of the enteric glutamatergic neurotransmitter machinery may lead to gastrointestinal dysfunctions. On the whole, this research field has opened the possibility to find new potential targets for development of drugs for the treatment of gastrointestinal diseases. The present review analyzes the more recent literature on enteric glutamatergic neurotransmission both in physiological and pathological conditions, such as gastroesophageal reflux, gastric acid hypersecretory diseases, inflammatory bowel disease, irritable bowel syndrome and intestinal ischemia/reperfusion injury.

Dietary Supplementation with α-Ketoglutarate Activates mTOR Signaling and Enhances Energy Status in Skeletal Muscle of Lipopolysaccharide-Challenged Piglets

BACKGROUND

Skeletal muscle undergoes rapid loss in response to inflammation. α-Ketoglutarate (AKG) has been reported to enhance muscle growth in piglets, but the underlying mechanisms are largely unknown.

OBJECTIVES

This study tested the hypothesis that dietary AKG supplementation activates mechanistic target of rapamycin (mTOR) signaling and improves skeletal muscle energy metabolism in lipopolysaccharide (LPS)-challenged piglets.

METHODS

Forty-eight male piglets (Duroc × Landrace × Yorkshire) were weaned at 21 d of age to a corn- and soybean meal-based diet. After a 3-d period of adaptation, piglets with a mean weight of 7.21 kg were randomly assigned to control, LPS (intraperitoneal administration of 80 μg LPS/kg body weight on days 10, 12, 14, and 16), or LPS plus 1% dietary AKG (LPS+AKG) groups. On day 16, blood samples were collected from 8 piglets/group 3 h after LPS administration. On day 17, piglets were killed to obtain gastrocnemius muscle from 8 piglets/group for biochemical analysis.

RESULTS

Compared with the control group, LPS administration increased (P < 0.05) plasma concentrations of globulin (by 14%) and tumor necrosis factor α (by 59%) and the intramuscular ratio of AMP to ATP (by 93%) and abundance of phosphorylated acetyl-coenzyme A carboxylase (ACC) β protein (by 64%). Compared with the control group, LPS administration reduced (P < 0.05) weight gain (by 15%); plasma concentrations of glutamine (by 20%), glucose (by 23%), insulin, insulin-like growth factor I, and epidermal growth factor; intramuscular concentrations of glutamine (by 27%), ATP (by 12%), ADP (by 22%), and total adenine nucleotides; and intramuscular ratios of phosphorylated mTOR to total mTOR (by 38%) and of phosphorylated 70-kDa ribosomal protein S6 kinase (p70S6K) to total p70S6K (by 39%). These adverse effects of LPS were ameliorated (P < 0.05) by AKG supplementation.

CONCLUSIONS

Dietary AKG supplementation activated mTOR signaling, inhibited ACC-β, and improved energy status in skeletal muscle of LPS-challenged piglets. These results provide a biochemical basis for the use of AKG to enhance piglet growth under inflammatory or practical postweaning conditions.

Glutamate promotes nucleotide synthesis in the gut and improves availability of soybean meal feed in rainbow trout

Glutamate (Glu) plays various roles directly or through conversions to other amino acids in intracellular metabolisms such as energy source for enterocytes and precursor for nucleic acids. In this study, we examined the effect of single and chronic oral administration of Glu on cell proliferation in intestine and growth in rainbow trout fed soybean meal (SBM) based diet. In the single dose study, 30, 120 and 360 min after oral administration of 50 and 500 mg/kg Glu, the blood and intestine tissues were collected for amino acid concentration and gene expression analysis. Cell-proliferation was detected 24 h after administration using bromo-deoxy uridine (BrdU) in intestine. In the chronic experiment, fish were fed SBM-based diet added 1 and 2 % of Glu for 8 weeks. Final body weight, plasma amino acid concentrations, gene expression and cell-proliferation in the intestine were analyzed. The expressions of some nucleic acid-synthesis related genes were significantly increased 30 min after administration of 50 mg/kg of Glu. After 8 weeks of feeding, the fish fed SBM-based diet showed significantly lower body weight and microvillus thickness in proximal intestine. Supplementation of 2 % of Glu in the SBM-based feed improved both of them. Though it was not significant difference, Glu tended to increase cell-proliferation in the proximal intestine dose-dependently in both single and chronic administration. Our experiment indicates that Glu has positive effect on rainbow trout fed SBM-based feed by reforming proximal intestine through altering cell-proliferation.

Metabolic alterations in children with environmental enteric dysfunction

Environmental enteric dysfunction, an asymptomatic condition characterized by inflammation of the small bowel mucosa, villous atrophy, malabsorption, and increased intestinal permeability, is a major contributor to childhood stunting in low-income countries. Here we report the relationship of increased intestinal permeability with serum metabolites in 315 children without acute malnutrition, aged 12-59 months, in rural Malawi. Increased gut permeability was associated with significant differences in circulating metabolites that included lower serum phosphatidylcholines, sphingomyelins, tryptophan, ornithine, and citrulline, and elevated serum glutamate, taurine, and serotonin. Our findings suggest that environmental enteric dysfunction is characterized by alterations in important metabolites involved in growth and differentiation and gut function and integrity.

Glutamate ameliorates copper-induced oxidative injury by regulating antioxidant defences in fish intestine

The objective of this study was to determine the protective effect of glutamate (Glu) in Cu-induced oxidative injury in fish intestine in vivo and enterocytes in vitro. The results indicated that exposure to 6 mg/l Cu for 72 h induced the production of reactive oxygen species, thereby increasing protein oxidation and lipid peroxidation in enterocytes of grass carp in vitro. Cells exposed to Cu alone resulted in a significant increase in lactate dehydrogenase release, which is accompanied by depletions of antioxidants, including total superoxide dismutase (T-SOD), glutathione S-transferase (GST), glutathione reductase (GR), anti-superoxide anion (ASA), anti-hydroxy radical (AHR) activities and GSH content. Pre-treatment with Glu remarkably prevented the toxic effects of Cu on the T-SOD, GST, GR, AHR, and ASA activities and GSH content in enterocytes. However, Cu induced an adaptive increase in the activities of catalase and glutathione peroxidase (GPx). Glu supplementation further increased GPx activity in enterocytes. Interestingly, the experiment in vivo showed that Glu pre-supplementation significantly elevated SOD, GPx, GST, GR, ASA and AHR activities, as well as GSH content. Further results showed that pre-treatment with Glu could alleviate Cu-induced oxidative injury by elevating antioxidant enzyme activities through regulating the expression of NF-E2-related nuclear factor 2 (Nrf2) mRNA. Together, these results indicated that Glu could attenuate Cu-induced cellular oxidative damage in fish intestine, likely mediated through Nrf2 signalling pathways regulating mRNA expressions of antioxidant enzyme genes and synthesis of GSH.

Morphological and metabolic adjustments in the small intestine to energy demands of growth, storage, and fasting in the first annual cycle of a hibernating lizard (Tupinambis merianae)

Seasonal plasticity in the small intestine of neonatal tegu lizards was investigated using morphometry and analysis of enzymes involved in supplying energy to the intestinal tissue. In the autumn, the intestinal mass (Mi) was 1.0% of body mass and the scaling exponent b=0.92 indicated that Mi was larger in smaller neonates. During arousal from dormancy Mi was 23% smaller; later in spring, Mi increased 60% in relation to the autumn and the exponent b=0.14 indicated that the recovery was disproportionate in smaller tegus. During the autumn, the intestinal villi were greatly elongated; by midwinter, the Hv, SvEp, and VvEp were smaller than during the autumn (59%, 54%, 29%) and were restored to autumn levels during spring. In the active tegus, the maximum activity (Vmax) of enzymes indicated that the enterocytes can obtain energy from different sources, and possess gluconeogenic capacity. During winter, the Vmax of CS, HOAD, GDH, PEPCK was 40-50% lower in relation to the autumn and spring, while the Vmax of HK, PK, LDH, AST was unchanged. The hypoglycemia and the mucosal atrophy/ischemia during winter would prevent the enterocytes from using glucose, whereas they could slowly oxidize fatty acids released from body stores and amino acids from the tissue proteolysis to satisfy their needs of energy. Contrastingly, starvation during spring caused severe mass loss (50%); the tissue protein and the VvEp and VvLP did not change while the thickness of the muscular layer increased 51%, which suggested different effects along the length of the organ. In addition, the Vmax of the glycolytic enzymes was lower, indicating that a regulatory mechanism would spare blood glucose for vital organs during unanticipated food restriction.

Asparagine attenuates intestinal injury, improves energy status and inhibits AMP-activated protein kinase signalling pathways in weaned piglets challenged with Escherichia coli lipopolysaccharide

The intestine requires a high amount of energy to maintain its health and function; thus, energy deficits in intestinal mucosa may lead to intestinal damage. Asparagine (Asn) is a precursor for many other amino acids such as aspartate, glutamine and glutamate, which can be used to supply energy to enterocytes. In the present study, we hypothesise that dietary supplementation of Asn could alleviate bacterial lipopolysaccharide (LPS)-induced intestinal injury via improvement of intestinal energy status. A total of twenty-four weaned piglets were assigned to one of four treatments: (1) non-challenged control; (2) LPS+0 % Asn; (3) LPS+0·5 % Asn; (4) LPS+1·0 % Asn. On day 19, piglets were injected with LPS or saline. At 24 h post-injection, piglets were slaughtered and intestinal samples were collected. Asn supplementation improved intestinal morphology, indicated by higher villus height and villus height:crypt depth ratio, and lower crypt depth. Asn supplementation also increased the ratios of RNA:DNA and protein:DNA as well as disaccharidase activities in intestinal mucosa. In addition, Asn supplementation attenuated bacterial LPS-induced intestinal energy deficits, indicated by increased ATP and adenylate energy charge levels, and decreased AMP:ATP ratio. Moreover, Asn administration increased the activities of key enzymes involved in the tricarboxylic acid cycle, including citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase complex. Finally, Asn administration decreased the mRNA abundance of intestinal AMP-activated protein kinase-α1 (AMPKα1), AMPKα2, silent information regulator 1 (SIRT1) and PPARγ coactivator-1α (PGC1α), and reduced intestinal AMPKα phosphorylation. Collectively, these results indicate that Asn supplementation alleviates bacterial LPS-induced intestinal injury by modulating the AMPK signalling pathway and improving energy status.

L-Glutamate Enhances Barrier and Antioxidative Functions in Intestinal Porcine Epithelial Cells

BACKGROUND

L-Glutamate (Glu) is a major amino acid in milk and postweaning diets for mammals (including pigs and human infants). However, effects of Glu on intestinal mucosal barrier and antioxidative functions are unknown.

OBJECTIVE

This study tested the hypothesis that Glu may enhance the barrier function of intestinal porcine epithelial cell line 1 (IPEC-1) cells by upregulating the expression of tight junction proteins.

METHODS

IPEC-1 cells were cultured with or without Glu in the presence or absence of 1 mmol/L diquat (an oxidant) for indicated time points. Cell numbers, transepithelial electrical resistance (TEER), mRNA, and protein abundance of glutamate transporter, the release of lactate dehydrogenase (LDH), and the abundance of tight junction proteins were determined.

RESULTS

Compared with 0 mmol/L Glu, 0.5-, 1-, and 2 mmol/L Glu stimulated (P < 0.05) cell growth by 13-37% at 24 h and 12-34% at 48 h, respectively. In addition, 0.5 mmol/L Glu increased (P < 0.05) TEER (by 58% at 24 h and by 98% at 48 h, respectively). These effects of Glu were associated with increased mRNA abundance of Glu transporter solute carrier family 1 member 1 (SLC1A1) by 30-130% and protein abundance of excitatory amino acid transporter 3 (encoded by SLC1A1) by 19-34%, respectively. In a cell model of oxidative stress induced by 1 mmol/L diquat, 0.5 mmol/L Glu enhanced cell viability, TEER, and membrane integrity (as indicated by the reduced release of LDH) in IPEC-1 cells by increasing the abundance of the tight junction proteins occludin, claudin-3, zonula occludens (ZO)-2, and ZO-3.

CONCLUSION

These findings indicate that Glu plays an important role in mucosal barrier function by enhancing cell growth and maintaining membrane integrity in response to oxidative stress.

Differential expression of proteins involved in energy production along the crypt-villus axis in early-weaning pig small intestine

Weaning of piglets reflects intestinal dysfunction and atrophy and affected the physiological state of enterocytes. However, few studies have defined physiological state of enterocytes along the crypt-villus axis in early-weaning piglets. A total of 16 piglets from 8 litters were used in the experiment. One group of piglets was nursed by sows until age 21 days, and another group was weaned at age 14 days and then fed creep feed instead of breast milk for 7 days. Piglets were killed at 21 days, and the jejunum segments were dissected. After sequential isolation of jejunum epithelial cells along the crypt-villus axis, their proteins were analyzed through the isobaric tags for relative and absolute quantification, and proteins involved in the mammalian target of rapamycin signaling pathway and proliferating cell nuclear antigen abundances in jejunal epithelial cells of weaning or suckling group were determined by Western blotting. The differential proteins in three cell fractions were identified and analyzed. The results showed that proteins involved in the tricarboxylic acid cycle, β-oxidation, and the glycolysis pathway were significantly downregulated in the upper and middle villus of the early-weaned group. However, proteins involved in glycolysis were significantly upregulated in crypt cells. In addition, Western blot analysis showed that the expression of mammalian target of rapamycin pathway-related proteins was decreased (P < 0.05) in the early-weaned group. The present results showed that early-weaning differentially affect the expression of proteins involved in energy production of enterocytes along the jejunal crypt-villus axis.

Co-dependence of genotype and dietary protein intake to affect expression on amino acid/peptide transporters in porcine skeletal muscle

A total of 96 barrows (48 pure-bred Bama mini-pigs representing fatty genotype, and 48 Landrace pigs representing lean genotype) were randomly assigned to either a low- or adequate-protein treatment diet. The experimental period commenced at 5 weeks of age and extended to the finishing period. After euthanasia, blood and skeletal muscle samples were collected from pigs at the nursery, growing, and finishing phases. Our results indicate that the concentrations of free AAs in the plasma and muscle decreased as the age of the pigs increased. In addition, a strain × growth phase interaction (P < 0.05) was observed for the free AA pool in the plasma and muscle. The low-protein diet upregulated (P < 0.05) the mRNA levels for T1R1/T1R3 involved in glutamate binding, but downregulated (P < 0.05) the mRNA levels for PAT1, PAT2, and ASCT2, which transport neutral AAs into muscles. Bama mini-pigs had higher (P < 0.05) mRNA levels for LAT1, SNAT2, and EAAC1, but a lower (P < 0.05) mRNA level for PepT1, compared with Landrace pigs. Collectively, our findings indicate that adequate provision of dietary protein plays an important role in regulating profiles of free AA pools and expression of key AA/peptide transporters/transceptors in a genotype- and tissue-specific manner.

Dietary supplementation with L-glutamate and L-aspartate alleviates oxidative stress in weaned piglets challenged with hydrogen peroxide

This study was to evaluate the protective roles of L-glutamate (Glu) and L-aspartate (Asp) in weaned piglets challenged with H2O2. Forty weaned piglets were assigned randomly into one of five groups (8 piglets/group): (1) control group (NC) in which pigs were fed a corn- and soybean meal-based diet and received intraperitoneal administration of saline; (2) H2O2 group (PC) in which pigs were fed the basal diet and received intraperitoneal administration of 10 % H2O2 (1 ml/kg body weight once on days 8 and repeated on day 11); (3) PC + Glu group (PG) in which pigs were fed the basal diet supplemented with 2.0 % Glu before intraperitoneal administration of 10 % H2O2; (4) PC + Asp group (PA) in which pigs were fed the basal diet supplemented with 1.0 % Asp before intraperitoneal administration of 10 % H2O2; (5) PC + Glu + Asp group (PGA) in which pigs were fed the basal diet supplemented with 2.0 % Glu plus 1.0 % Asp before intraperitoneal administration of 10 % H2O2. Measured parameters included daily feed intake (DFI), average daily gain (ADG), feed conversion rate (FCR), and serum anti-oxidative enzyme activities (catalase, superoxide dismutase, glutathione peroxidase-1), serum malondialdehyde and H2O2 concentrations, serum amino acid (AA) profiles, and intestinal expression of AA transporters. Dietary supplementation with Glu, Asp or their combination attenuated the decreases in DFI, ADG and feed efficiency, the increase in oxidative stress, the alterations of serum AA concentrations, and the changed expression of intestinal AA transporters in H2O2-challenged piglets. Thus, dietary supplementation with Glu or Asp alleviates growth suppression and oxidative stress, while restoring serum the amino acid pool in H2O2-challenged piglets.

Dietary supplementation with glutamate precursor α-ketoglutarate attenuates lipopolysaccharide-induced liver injury in young pigs

There is growing interest in glutamate as a functional amino acid in nutrition and health. This study was conducted to determine whether glutamate precursor α-ketoglutarate (AKG) could alleviate lipopolysaccharide (LPS)-induced liver injury in young pigs. Twenty-four piglets were randomly assigned to the control, LPS, or LPS + AKG group. Piglets in the control and LPS groups were fed a basal diet, whereas piglets in the NAC group were fed the basal diet supplemented with 1 % AKG. On days 10, 12, 14, and 16 of the trial, piglets in the LPS and LPS + AKG groups received intraperitoneal administration of LPS (80 μg/kg BW), whereas piglets in the control group received the same volume of saline. On day 16 of the trial, blood samples were collected 3 h after LPS or saline injection. Twenty-four hours post-administration of LPS or saline (on day 17 of the trial), piglets were killed to obtain liver for analysis. Dietary AKG supplementation alleviated LPS-induced histomorphological abnormalities and mitigated LPS-induced increases in aspartate aminotransferase (AST) activity and AST/ALT ratio (P < 0.05). Compared with the LPS group, dietary supplementation with AKG decreased plasma glutamate concentration, while increasing hepatic concentrations of glutamate, glutamine, leucine, asparagine, lysine, alanine, serine, threonine, valine, and phenylalanine (P < 0.05). LPS challenge dramatically increased concentrations of malondialdehyde and decreased glutathione peroxidase activity in the liver. Additionally, LPS challenge enhanced concentrations of AMP and total protein, as well as RNA/DNA and total protein/DNA ratios, while decreasing hepatic ADP concentrations. These adverse effects of LPS challenge were ameliorated by AKG supplementation. Collectively, dietary AKG supplementation provides a new means to ameliorate LPS-induced liver injury by increasing anti-oxidative capacity and improving energy metabolism in young pigs.

Linear growth faltering in infants is associated with Acidaminococcus sp. and community-level changes in the gut microbiota

BACKGROUND

Chronic malnutrition, termed stunting, is defined as suboptimal linear growth, affects one third of children in developing countries, and leads to increased mortality and poor developmental outcomes. The causes of childhood stunting are unknown, and strategies to improve growth and related outcomes in children have only had modest impacts. Recent studies have shown that the ecosystem of microbes in the human gut, termed the microbiota, can induce changes in weight. However, the specific changes in the gut microbiota that contribute to growth remain unknown, and no studies have investigated the gut microbiota as a determinant of chronic malnutrition.

RESULTS

We performed secondary analyses of data from two well-characterized twin cohorts of children from Malawi and Bangladesh to identify bacterial genera associated with linear growth. In a case-control analysis, we used the graphical lasso to estimate covariance network models of gut microbial interactions from relative genus abundances and used network analysis methods to select genera associated with stunting severity. In longitudinal analyses, we determined associations between these selected microbes and linear growth using between-within twin regression models to adjust for confounding and introduce temporality. Reduced microbiota diversity and increased covariance network density were associated with stunting severity, while increased relative abundance of Acidaminococcus sp. was associated with future linear growth deficits.

CONCLUSIONS

We show that length growth in children is associated with community-wide changes in the gut microbiota and with the abundance of the bacterial genus, Acidaminococcus. Larger cohorts are needed to confirm these findings and to clarify the mechanisms involved.

An NMR-based metabolomic approach to investigate the effects of supplementation with glutamic acid in piglets challenged with deoxynivalenol

Deoxynivalenol (DON) has various toxicological effects in humans and pigs that result from the ingestion of contaminated cereal products. This study was conducted to investigate the protective effects of dietary supplementation with glutamic acid on piglets challenged with DON. A total of 20 piglets weaned at 28 d of age were randomly assigned to receive 1 of 4 treatments (5 piglets/treatment): 1) basal diet, negative control (NC); 2) basal diet +4 mg/kg DON (DON); 3) basal diet +2% (g/g) glutamic acid (GLU); 4) basal diet +4 mg/kg DON +2% glutamic acid (DG). A 7-d adaptation period was followed by 30 days of treatment. A metabolite analysis using nuclear magnetic resonance spectroscopy (1H-NMR)-based metabolomic technology and the determination of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities for plasma, as well as the activity of Caspase-3 and the proliferation of epithelial cells were conducted. The results showed that contents of low-density lipoprotein, alanine, arginine, acetate, glycoprotein, trimethylamine-N-oxide (TMAO), glycine, lactate, and urea, as well as the glutamate/creatinine ratio were higher but high-density lipoprotein, proline, citrate, choline, unsaturated lipids and fumarate were lower in piglets of DON treatment than that of NC treatment (P<0.05). Compared with DON treatment, dietary supplementation with glutamic acid increased the plasma concentrations of proline, citrate, creatinine, unsaturated lipids, and fumarate, and decreased the concentrations of alanine, glycoprotein, TMAO, glycine, and lactate, as well as the glutamate/creatinine ratio (P<0.05). Addition glutamic acid to DON treatment increased the plasma activities of SOD and GSH-Px and the proliferating cell nuclear antigen (PCNA) labeling indexes for the jejunum and ileum (P<0.05). These novel findings indicate that glutamic acid has the potential to repair the injuries associated with oxidative stress as well as the disturbances of energy and amino acid metabolism induced by DON.

Monosodium L-glutamate and dietary fat exert opposite effects on the proximal and distal intestinal health in growing pigs

The Chinese population has undergone rapid transition to a high-fat diet. Furthermore, monosodium L-glutamate (MSG) is widely used as a flavour enhancer in China. Previous studies have reported that high-fat diet modifies intestinal metabolism and physiology. However, little information is available on the effects of oral MSG on intestine, and no study focus on the interaction of dietary fat and MSG for intestinal health. The aim of the present study was to evaluate the effects of MSG and dietary fat on intestinal health in growing pigs, and to try to identify possible interactions between these 2 nutrients for such effects. A total of 32 growing pigs were used and fed with 4 isonitrogenous and isocaloric diets (basal diet, high-fat diet, basal diet with 3% MSG and high fat diet with 3% MSG). Parameters related to reactive oxygen species metabolism, epithelial morphology, pro-inflammation factors and tight junction protein expression and several species of intestinal microbe were measured. Overall, dietary fat and MSG had detrimental effects on several of the physiological and inflammatory parameters measured in the proximal intestine, while exerting beneficial effects on the distal intestine in growing pigs, with generally antagonistic effects. These results may be of particular relevance for nutritional concerns in patients with intestinal diseases.

Dietary glutamate supplementation ameliorates mycotoxin-induced abnormalities in the intestinal structure and expression of amino acid transporters in young pigs

The purpose of this study was to investigate the hypothesis that dietary supplementation with glutamic acid has beneficial effects on growth performance, antioxidant system, intestinal morphology, serum amino acid profile and the gene expression of intestinal amino acid transporters in growing swine fed mold-contaminated feed. Fifteen pigs (Landrace×Large White) with a mean body weight (BW) of 55 kg were randomly divided into control group (basal feed), mycotoxin group (contaminated feed) and glutamate group (2% glutamate+contaminated feed). Compared with control group, mold-contaminated feed decreased average daily gain (ADG) and increased feed conversion rate (FCR). Meanwhile, fed mold-contaminated feed impaired anti-oxidative system and intestinal morphology, as well as modified the serum amino acid profile in growing pigs. However, supplementation with glutamate exhibited potential positive effects on growth performance of pigs fed mold-contaminated feed, ameliorated the imbalance antioxidant system and abnormalities of intestinal structure caused by mycotoxins. In addition, dietary glutamate supplementation to some extent restored changed serum amino acid profile caused by mold-contaminated feed. In conclusion, glutamic acid may be act as a nutritional regulating factor to ameliorate the adverse effects induced by mycotoxins.

Glutamate-glutamine cycle and exchange in the placenta-fetus unit during late pregnancy

The present review focuses on the physiological functions of glutamate-glutamine exchange involving placental amino acid transport and umbilical amino acid uptake in mammals (particularly in sows), with special emphasis on the associated regulating mechanisms. Glutamate plus glutamine are among the most abundant and the most utilized amino acids in fetus during late gestation. During pregnancy, amino acids, notably as precursors of macromolecules including proteins and nucleotides are involved in fetal development and growth. Amino acid concentrations in fetus are generally higher than in the mother. Among amino acids, the transport and metabolism of glutamate and glutamine during fetal development exhibit characteristics that clearly emphasize the importance of the interaction between the placenta and the fetal liver. Glutamate is quite remarkable among amino acids, which originate from the placenta, and is cleared from fetal plasma. In addition, the flux of glutamate through the placenta from the fetal plasma is highly correlated with the umbilical glutamate delivery rate. Glutamine plays a central role in fetal carbon and nitrogen metabolism and exhibits one of the highest fetal/maternal plasma ratio among all amino acids in human and other mammals. Glutamate is taken up by placenta from the fetal circulation and then converted to glutamine before being released back into the fetal circulation. Works are required on the glutamate-glutamine metabolism during late pregnancy in physiological and pathophysiological situations since such works may help to improve fetal growth and development both in humans and other mammals. Indeed, glutamine supplementation appears to ameliorate fetal growth retardation in sows and reduces preweaning mortality of piglets.