Intestinal Absorption Of Amino Acids Research Articles

Response of Turbot Scophthalmus maximus (Linnaeus, 1758) to Imbalanced Branched-Chain Amino Acids in Diets

The aim of this study was to investigate the effects of imbalanced dietary BCAAs, especially Leu, on the growth and BCAA metabolism in turbot. A control diet was formulated by keeping optimum levels of Leu, Ile and Val. Four experimental diets were prepared by removing supplemental crystalline Leu (deficiency) or supplementing double the amount of Leu, Ile or Val (excess) in the control diet. The growth was not significantly decreased by an excess of Leu, Ile or Val. Fish fed an excess of any particular BCAA significantly increased its postprandial (2 and 6 h) concentration in the plasma, muscles, and liver, but did not decrease the other two BCAA concentrations. The expression of intestinal b0at1 was down-regulated by excessive dietary Leu, Ile or Val. For BCAA catabolism, the mRNA levels of bcat2 in the muscles as well as bckdha and bckdhb in the livers of the Leu-deficient group were the lowest among all the groups, but were up-regulated by excess dietary Leu, Ile or Val. In conclusion, in terms of growth, turbot had high plasticity to an excess of any particular BCAA. Meanwhile, the antagonistic effect caused by an excess of one BCAA were reflected in intestinal amino acid absorption and BCAA catabolism.

Lysinuric protein intolerance presenting as pancytopenia and splenomegaly mimicking acute leukaemia: a case report

BackgroundLysinuric protein intolerance is a rare inherited metabolic disease due to autosomal recessive mutations of the SLC7A7 gene. The affected patients commonly present with protein-rich food intolerance, failure to thrive, hepatosplenomegaly, muscle hypotonia and lung involvement due to impaired intestinal absorption and excessive urinary excretion of dibasic amino acids. Presentation with splenomegaly and cytopenia without other features has not been reported. Here we report a Sri Lankan girl with lysinuric protein intolerance presenting with pancytopenia and splenomegaly mimicking acute leukaemia.Case presentationTwo years and six months old Sri Lankan girl presented with persistent pancytopenia following a viral illness. She was asymptomatic without vomiting, diarrhoea, abdominal pain or irritability. Physical examination revealed pallor and isolated firm splenomegaly of 2 cm. Growth parameters and other system examinations were normal. Full blood count revealed anaemia, leukopenia and thrombocytopenia. The blood picture showed a mixture of hypochromic microcytic and normochromic normocytic red cells with occasional pencil cells and macrocytes. Bone marrow examination was normal except for occasional megaloblasts; however, serum vitamin B12 and red blood cell folate were normal. The metabolic screen showed a high anion gap compensated metabolic acidosis, high lactate and ketosis. Genetic mutation analysis using whole exome sequencing revealed compound heterozygous variants of the SLC7A7 gene, confirming the diagnosis of lysinuric protein intolerance.ConclusionWe report a child with lysinuric protein intolerance presenting with pancytopenia and splenomegaly without other disease features. This case report adds to the heterogenic presentations of lysinuric protein intolerance, which is considered a multifaceted disease.

L-Theanine Regulates the Abundance of Amino Acid Transporters in Mice Duodenum and Jejunum via the mTOR Signaling Pathway

The intestine is a key organ for the absorption of amino acids. L-theanine (LTA) is a structural analog of glutamine and a characteristic non-protein amino acid found in tea (Camellia sinensis) that regulates lipid and protein metabolism. The present study explored the role of LTA in intestinal amino acid absorption, protein synthesis, and its mechanisms. Overall, our findings suggest that LTA supplementation not only affects serum alkaline phosphatase (AKP), total protein (TP), and urea nitrogen (BUN) levels, but it also upregulates the mRNA and protein expression of amino acid transporters (EAAT3, EAAT1, 4F2hc, y+LAT1, CAT1, ASCT2, and B0AT1), and activates the mTOR signaling pathway. The downstream S6 and S6K1 proteins are regulated, and the expression of amino acid transporters is regulated. These findings suggest that LTA increases intestinal AA absorption, promotes protein metabolism, and increases nitrogen utilization by upregulating AAT expression, activating the mTOR signaling pathway, and phosphorylating the mTOR downstream proteins S6 and S6K1.

Free Amino Acid–Enriched Diets Containing Rapidly but Not Slowly Digested Carbohydrate Promote Amino Acid Absorption from Intestine and Net Fluxes across Skeletal Muscle of Pigs

The approach to matching appropriate carbohydrates alongside free amino acids to achieve optimal muscle growth remains unclear. We investigated whether the consumption of a diet containing rapidly digested carbohydrate and free amino acids can enhance intestinal absorption and muscular uptake of amino acids in pigs. Twelve barrows (28 kg; 11 wk old) with catheters installed in the portal vein, mesenteric vein, femoral artery, and femoral vein were randomly assigned to consume 1 of 2 free amino acid-enriched diets (3.34%) containing rapidly [waxy corn starch (WCS)] or slowly [pea starch (PS)] digested carbohydrate for 27 d. Blood was collected to determine the fluxes of plasma glucose and amino acids across the portal vein and the hindlimb muscle. Dietary in vitro carbohydrate digestive rates were also determined. Data were analyzed using repeated-measures (time × group) ANOVA. Carbohydrate in vitro cumulative digestibility at 30 and 240 min was 69.00% and 95.25% for WCS and 23.25% and 81.15% for PS, respectively. The animal experiment presented WCS increased individual amino acids (lysine, 0.67 compared with 0.53 mmol/min; threonine, 0.40 compared with 0.29 mmol/min; isoleucine, 0.33 compared with 0.22 mmol/min; glutamate, 0.51 compared with 0.35 mmol/min; and proline, 0.51 compared with 0.27 mmol/min), essential amino acid (EAA; 3.26 compared with 2.65 mmol/min), and branched-chain amino acid (BCAA; 0.86 compared with 0.65 mmol/min) fluxes across the portal vein during 8 h postprandial, as well as individual amino acids (isoleucine, 0.08 compared with 0.02 mmol/min; leucine, 0.06 compared with 0.02 mmol/min; and glutamine, 0.44 compared with 0.25 mmol/min), EAA (0.50 compared with 0.21 mmol/min), and BCAA (0.17 compared with 0.06 mmol/min) net fluxes across the hindlimb muscle during 8 h postprandial compared with PS (P < 0.05). A diet containing rapidly digested carbohydrate and free amino acids can promote intestinal absorption and net fluxes across hindlimb muscle of amino acids in pigs.

Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency.

Protein catabolism ultimately yields toxic ammonia, which must be converted to urea by the liver for renal excretion. In extrahepatic tissues, ammonia is temporarily converted primarily to glutamine for subsequent hepatic extraction. Urea cycle disorders (UCDs) are inborn errors of metabolism causing impaired ureagenesis, leading to neurotoxic accumulation of ammonia and brain glutamine. Treatment includes dietary protein restriction and oral "ammonia scavengers." These scavengers chemically combine with glutamine and glycine to yield excretable products, creating an alternate pathway of waste nitrogen disposal. The amino acid transporter SLC6A19 is responsible for >95% of absorption and reabsorption of free neutral amino acids in the small intestine and kidney, respectively. Genetic SLC6A19 deficiency causes massive neutral aminoaciduria but is typically benign. We hypothesized that inhibiting SLC6A19 would open a novel and effective alternate pathway of waste nitrogen disposal. To test this, we crossed SLC6A19 knockout (KO) mice with spfash mice, a model of ornithine transcarbamylase (OTC) deficiency. Loss of SLC6A19 in spfash mice normalized plasma ammonia and brain glutamine and increased median survival in response to a high protein diet from 7 to 97 days. While induced excretion of amino acid nitrogen is likely the primary therapeutic mechanism, reduced intestinal absorption of dietary free amino acids, and decreased muscle protein turnover due to loss of SLC6A19 may also play a role. In summary, the results suggest that SLC6A19 inhibition represents a promising approach to treating UCDs and related aminoacidopathies.

Influence of alimentary factors on the absorption of feed nutrients and poultry productivity

The article is a summary of the literature on the main aspects of the modern bird feeding system. Theoretical aspects and results of experimental research of scientists on the substantiation of parameters of protein and amino acid nutrition are given, which is an important factor that, under appropriate conditions can significantly guarantee the realization of the genetic potential of corresponding breeds and crosses of poultry. It is shown that an important aspect of protein nutrition is the ratio of feed amino acids. Their negative interaction can be caused by a deficiency of one or more amino acids, an imbalance between them, antagonism, and toxicity. This is accompanied by effects on various physiological and biochemical processes, significantly affects appetite, intestinal absorption, renal reabsorption and transport of amino acids, their catabolism, rate of protein decomposition, synthesis, and formation of toxic metabolic products. The data show that the required level of energy for the bird's body is provided by carbohydrates (mainly of plant origin) and lipids (fat supplements of various origins). It is noted that lipids promote the absorption, transport, and deposition of fat-soluble vitamins. The effectiveness of using fat supplements as energy depends on their source. At the same time, among the indispensable nutrients that have a significant impact on growth intensity, reproductive quality, poultry productivity, and biological value of products, an important role is played by macro-and micronutrients. Many researchers emphasize that along with the use of traditional feeds in poultry feeding, the possibilities of non-traditional cereals rich in protein and lipids are not fully used. A limiting factor in their use is the presence in their composition of anti-nutrients contained in many feeds. Once in the digestive tract of animals, they negatively affect the absorption of feed nutrients. In most cases, the consumption of such feed by animals is manifested in growth retardation, increased feed consumption, hormonal effects, and, less frequently, in the dysfunction of certain organs.

In vivo antidiabetic activity of nimesulide due to inhibition of amino acid transport

AbstractInhibiting the intestinal and renal neutral amino acid transporter B0AT1 by genetic means has improved insulin sensitivity in mice, but there are no antagonists available for preclinical or clinical use. Since the anti‐inflammatory agent nimesulide selectively inhibited B0AT1 in vitro, we hypothesized that nimesulide exhibits in vivo potential to restrict neutral amino acid absorption and, therefore, may improve insulin sensitivity. The dose‐related effect of nimesulide (10 to 100 mg/kg, PO) on intestinal absorption of neutral amino acids was estimated in C57 mice. The effect of nimesulide (50 mg/kg, PO) on renal resorption of amino acids was also assessed. The effect of chronic nimesulide (50 mg/kg, PO, BID for 14 days) was assessed in high protein diet‐fed C57 mice, diet‐induced obese mice and obese and diabetic db/db mice. Acute and chronic nimesulide treatment decreased absorption of neutral amino acids and increased their urinary excretion. Nimesulide treatment improved insulin sensitivity and glycemic control, increased GLP‐1, decreased liver lipids and improved FGF‐21 in serum. Nimesulide improved insulin sensitivity and glucose tolerance by inhibiting neutral amino acid transport in the intestine and kidneys. Thus, it can serve as a tool compound for in vivo B0AT1 inhibition.

Effects of Dietary Valine Levels on Production Performance, Egg Quality, Antioxidant Capacity, Immunity, and Intestinal Amino Acid Absorption of Laying Hens during the Peak Lay Period.

Simple SummaryIn the past, many studies have been carried out to investigate the effect of dietary valine supplementation on laying hens’ production performance and egg quality. However, knowledge concerning the optimal valine requirement during the peak lay period is limited and mainly restricted to the production performance of the hens. Within this context, the present study aimed to assess the impact of dietary valine levels on production performance, egg quality, antioxidant capacity, and immunity, as well as on intestinal amino acid absorption (i.e., serum free amino acids, digestive enzymes, and amino acid transporters). Dietary valine supplementation exerts positive effects on the production performance of the laying hens by promoting amino acid nutrient uptake and utilization. However, dietary valine supplementation might inhibit the absorption of dietary protein by downregulating peptide transporter expression of the small intestine, eventually resulting in the reduction of egg quality.The present study aimed to assess the impact of dietary valine levels on layer production performance, egg quality, immunity, and intestinal amino acid absorption of laying hens during the peak lay period. For this purpose, a total of 960 33-week-old Fengda No.1 laying hens were randomly divided into five experimental groups and fed with valine at the following different levels in a feeding trial that lasted 8 weeks: 0.59, 0.64, 0.69, 0.74, and 0.79%, respectively. Productive performances were recorded throughout the whole rearing cycle and the egg quality, serum indexes, and small intestine transporters expression were assessed at the end of the experiment after slaughter (41 weeks) on 12 hens per group. Statistical analysis was conducted by one-way ANOVA followed by LSD multiple comparison tests with SPSS 20.0 (SPSS, Chicago, IL, USA). The linear and quadratic effects were tested by SPSS 20.0. Egg mass, laying rate, broken egg rate, and feed conversion ratio were significantly improved with increasing dietary valine levels. However, the egg weight, eggshell thickness, albumen height, Haugh unit, and egg yolk color were significantly decreased with increasing dietary valine levels. Serum catalase (CAT), immunoglobulin A (IgA) and IgM levels, and malondialdehyde (MDA) levels were negative responses to valine-treated laying hens. Dietary supplemented valine enhanced the trypsin activity of duodenum chime and promoted the mRNA expression levels of ATB0,+, and LAT4 in the jejunum and corresponding serum free Ile, Lys, Phe, Val, and Tyr level. However, valine treatment significantly downregulated the mRNA expression levels of PePT1, B0AT1, LAT1, and SNAT2 in the small intestines and corresponding serum free Arg, His, Met, Thr, Ala, Asp, Glu, Gly, and Ser level. Our results suggest that 0.79% valine dietary supplementation can improve production performance by promoting amino acid nutrient uptake and utilization, and suggest a supplement of 0.79% valine to diet.

Goat milk protein digestibility in relation to intestinal function

ABSTRACTBackgroundMilk is an important high-quality animal protein source in low- and middle-income countries (LMICs). Although the true ileal digestibility and absorption of milk has been shown to be high in French adults, this may be lower in individuals from LMICs who are at risk of environmental enteropathy.ObjectiveTo determine the true ileal indispensable amino acid (IAA) digestibility of intrinsically labeled goat milk protein in South Indian women of reproductive age (WRA), using the dual-isotope tracer technique, and to measure intestinal absorption of amino acid and inert sugar in the same participants using L-allo-isoleucine and a dual-sugar assay.MethodsMilk with 2H-labeled protein collected from a lactating goat fed intrinsically 2H-labeled fodder (maize and cowpea) was spray dried. Labeled milk protein was administered in a plateau feeding protocol to WRA with normal BMI, in whom urinary lactulose and mannitol recovery and the lactulose/mannitol ratio (LMR) were measured, to determine its true ileal IAA digestibility by the dual-isotope tracer technique with a reference U-13C–amino acid mixture. A phenylalanine absorption index was calculated from the plasma to meal ratio of 13C9 phenylalanine within the digestibility protocol. On a separate day, the allo-isoleucine absorption index was estimated from the ratio of plasma allo-isoleucine enrichments after oral 13C6-15N-L- and intravenous 2H10-L-allo-isoleucine administration.ResultsThe means ± SDs of true ileal IAA digestibility of goat milk protein, lactulose and mannitol recovery, LMR, allo-isoleucine and phenylalanine absorption index were 94.0 ± 2.9%, 0.09 ± 0.03%, 7.9 ± 2.3%, 0.012 ± 0.004, 88.4 ± 3.8% and 24.5 ± 1.6%, respectively. The LMR correlated with the allo-isoleucine absorption index (rs = –0.93, P = 0.008).ConclusionThe true ileal digestibility of goat milk protein in South Indian WRA with normal intestinal absorptive function and integrity was comparable to earlier estimates in healthy French adults.

Reducing protein content in the diet of growing goats: implications for nitrogen balance, intestinal nutrient digestion and absorption, and rumen microbiota

Reducing dietary CP content is an effective approach to reduce animal nitrogen excretion and save protein feed resources. However, it is not clear how reducing dietary CP content affects the nutrient digestion and absorption in the gut of ruminants, therefore it is difficult to accurately determine how much reduction in dietary CP content is appropriate. This study was conducted to investigate the effects of reduced dietary CP content on N balance, intestinal nutrient digestion and absorption, and rumen microbiota in growing goats. To determine N balance, 18 growing wether goats (25.0 ± 0.5 kg) were randomly assigned to one of three diets: 13.0% (control), 11.5% and 10.0% CP. Another 18 growing wether goats (25.0 ± 0.5 kg) were surgically fitted with ruminal, proximate duodenal, and terminal ileal fistulae and were randomly assigned to one of the three diets to investigate intestinal amino acid (AA) absorption and rumen microbiota. The results showed that fecal and urinary N excretion of goats fed diets containing 11.5% and 10.0% CP were lower than those of goats fed the control diet (P < 0.05). When compared with goats fed the control diet, N retention was decreased and apparent N digestibility in the entire gastrointestinal tract was increased in goats fed the 10% CP diet (P < 0.05). When compared with goats fed the control diet, the duodenal flow of lysine, tryptophan and phenylalanine was decreased in goats fed the 11.5% CP diet (P < 0.05) and that of lysine, methionine, tryptophan, phenylalanine, leucine, glutamic acid, tyrosine, essential AAs (EAAs) and total AAs (TAAs) was decreased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the apparent absorption of TAAs in the small intestine was increased in goats fed the 11.5% CP diet (P < 0.05) and that of isoleucine, serine, cysteine, EAAs, non-essential AAs, and TAAs in the small intestine was increased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the relative richness of Bacteroidetes and Fibrobacteres was increased and that of Proteobacteria and Synergistetes was decreased in the rumen of goats fed a diet with 10.0% CP. In conclusion, reducing dietary CP content reduced N excretion and increased nutrient utilization by improving rumen fermentation, enhancing nutrient digestion and absorption, and altering rumen microbiota in growing goats.

Choline deficiency decreased the growth performances and damaged the amino acid absorption capacity in juvenile grass carp (Ctenopharyngodon idella)

The present study investigated the effects of choline on growth, intestinal histology, intestinal amino acid (AA) absorption capacity and the underlying signalling in juvenile grass carp (Ctenopharyngodon idella). Fish were fed six-graded levels of choline (142.2, 407.4, 821.6, 1215.8, 1589.3, 1996.6 mg kg−1) for 70 days. The results showed that choline insufficiency deteriorated the growth performance and injured the fish intestinal health. Strikingly, choline influenced the absorptive capacity for various sorts of AAs in different intestinal segments by non-uniform mechanisms. Firstly, choline deficiency reduced the contents of free neutral AAs including Met, Trp, Thr, Ile, Leu, Val, Gly, Pro, Ser, Cys and Tau in all intestinal segments partly attributed to decrease the mRNA levels of the corresponding transporters including SLC7A7, SLC7A6, SLC1A5, SLC7A9 (except in MI), SLC7A8, SLC6A6, SLC6A19b, SLC38A2 (except in PI) and peptide transporter 1 (SLC15A1) as well as the protein level of SLC1A5 in the intestine. Secondly, choline deficiency decreased the contents of free basic AAs including Lys, Arg, and His (except in DI) in three segments partly associated with downregulating cationic AAT SLC7A1 and SLC15A1 mRNA levels as well as the protein level of SLC7A1 in gut segments. Thirdly, choline deficiency decreased the contents of free acidic AAs including Glu and Asp in three gut segments partly associated with the decreasing mRNA levels of the corresponding transporters including SLC1A2a and SLC15A1 in the intestine. Choline insufficiency depressed the TOR (target of rapamycin) signalling molecule mRNA levels and TOR protein abundance in the fish gut. In addition, choline requirement of juvenile grass carp was calculated to be 1330.7 and 1283.4 mg kg−1 diet based on the PWG (percent weight gain) and FE (feed efficiency), respectively. In general, choline deficiency attenuated the absorptive abilities of intestinal AAs in juvenile grass carp, which might be connected with the aggravation of intestinal health, the decrease of amino acid transporters might be related to restraint the TOR signalling pathway.

Soybean glycinin decreased growth performance, impaired intestinal health, and amino acid absorption capacity of juvenile grass carp (Ctenopharyngodon idella).

The present study evaluated the influence of dietary soybean glycinin on growth performance, intestinal morphology, free intestinal amino acid (AA) content, and intestinal AA transporter (AAT) mRNA levels in juvenile grass carp (Ctenopharyngodon idella). Results were displayed as follows: (1) 8% dietary glycinin decreased growth performance, inhibited intestinal growth, and caused intestinal histology damage of grass carp; (2) dietary glycinin decreased the content of free neutral AAs including Val, Ser, Tyr, Ala, Pro, and Gln in all intestinal segments, and Thr, Ile, Leu, Phe, and Gly in the MI and DI while downregulated the mRNA levels of corresponding transporters including SLC38A2, SLC6A19b, and SLC6A14 in all intestinal segments, and SLC7A5, SLC7A8, and SLC1A5 in the MI and DI. Dietary glycinin decreased the content of free basic AAs including Arg in the MI and DI and His in all intestinal segments while downregulated cationic AAT SLC7A1 mRNA levels in the MI and DI. Dietary glycinin decreased the content of free acidic AAs including Glu in all intestinal segments and Asp in the MI and DI while decreased mRNA levels of corresponding transporters including SLC1A2a in all intestinal segments and SLC1A3 in the MI and DI; (3) the digestion trial showed that basic subunits of glycinin was hard to digest in the intestine of grass carp; (4) co-administration of glutamine with glycinin partially alleviated the negative effects. Overall, glycinin decreased intestinal AA absorption capacity partly contributed by decreased AATs' mRNA levels and the indigestibility of glycinin.

N-Carbamylglutamate and l-Arginine Promote Intestinal Absorption of Amino Acids by Regulating the mTOR Signaling Pathway and Amino Acid and Peptide Transporters in Suckling Lambs with Intrauterine Growth Restriction

Previous studies have revealed that dietary N-carbamylglutamate (NCG) and l-arginine (Arg) improve intestinal integrity, oxidative state, and immune function in Hu suckling lambs with intrauterine growth restriction (IUGR). Whether these treatments alter intestinal nutrient absorption is unknown. The aim of this study was to determine the influence of dietary NCG and Arg treatment during the suckling period on intestinal amino acid (AA) absorption, alterations in the mechanistic target of rapamycin (mTOR) signaling pathway, and the abundance of AA and peptide transporters in IUGR lambs. On day 7 after birth, 48 newborn Hu lambs were selected from a cohort of 424 twin lambs. Normal-birth-weight and IUGR Hu lambs were allocated randomly (n=12/group) to a control (4.09±0.12 kg), IUGR (3.52±0.09 kg), IUGR+0.1% NCG (3.49±0.11 kg), or IUGR+1% Arg (3.53±0.10 kg). At day 28, compared with the IUGR group, the IUGR groups receiving NCG and Arg had 7.4% and 7.2% greater (P<0.05) body weight, respectively. Compared with the IUGR group, the serum concentration of insulin was greater (P<0.05) and the cortisol was lower (P<0.05) in the IUGR groups receiving NCG and Arg. Compared with the IUGR group, the IUGR groups receiving NCG and Arg had 13.2%-62.6% greater (P<0.05) serum concentrations of arginine, cysteine, isoleucine, and proline. Dietary NCG or Arg to IUGR lambs resulted in greater protein abundance (P<0.05) of peptide transporter 1 (41.9% or 38.2%) in the ileum compared with the unsupplemented IUGR lambs, respectively. Furthermore, dietary NCG or Arg treatment normalized the IUGR-induced variation (P<0.05) in the ileal ratio of phosphorylated mTOR to total mTOR protein. Both NCG and Arg can help mitigate the negative effect of IUGR on nutrient absorption in neonatal lambs.

Role of neutral amino acid transporter LAT4 in mouse epithelia

Amino acids (AAs) are not only building blocks of proteins, but also play key roles in energy metabolism and as (precursors of) neurotransmitters. To maintain amino acid homeostasis, small intestine (SI) and kidney play a major role by absorbing amino acids from food and preventing their loss in the urine, respectively. Given their zwitterionic nature, neutral AAs require transport proteins to cross cell membranes. LAT4 (Slc43a2), a facilitated diffusion uniporter specific for essential neutral amino acids (Leu, Ile, Val, Met and Phe) was first identified by Bodoy et al., 2005 and then shown by us to be highly expressed in the basolateral membranes of SI and kidney tubule epithelia. LAT4 global knockout caused a postnatal malnutrition‐like condition leading to death within 10 days, which was hypothesized to be due to a severe defect in intestinal absorption of AAs (Guetg et al. 2015). To test this hypothesis, we generated an intestine‐specific LAT4 knockout mouse model using Cre‐LoxP system. Intestine specific LAT4 knockout pups were viable and did not show any significant changes in body weight gain as compared to their control littermates even up to 2 months after birth. Quantitative PCR, western blot and immunofluorescence data showed a nearly 95% efficient knockout of LAT4 throughout the SI (n=4). However, these mice displayed no visible phenotype. Amino acid transport along the SI was then assessed by gavaging an AA mix containing radiolabelled LAT4 substrate 3H‐Leu. Blood samples were collected from the tail vein 10′ before and 2′,5′, 10′, 20′ and 60′ after gavage. Mice were then euthanized, SI divided into 4 equal parts and the intestinal tissue and its contents collected separately. Measuring the distribution of 3H‐Leu using a β‐counter revealed an accumulation of Leu in the initial segment of the SI of knockout mice (n=5, P&lt;0.001 by ANOVA), accompanied by a delayed bolus movement. Thus, we show that LAT4 knockout in SI is not the sole or major reason for the lethal phenotype of LAT4 global knockout pups, although it could have contributed to the lethality. In parallel, we have generated a doxycycline‐inducible kidney tubule‐specific LAT4 knockout mouse model to assess the effects of LAT4 deletion in kidney, both in young and adult animals. Results obtained with this new model will allow us to determine whether the urinary loss of amino acids may have strongly contributed to the lethal phenotype of LAT4 global knockout mice or whether it was caused by the defect of LAT4 in other tissues.Support or Funding InformationThis project is funded by a grant of the Swiss National Foundation (SNF) to FV.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Reproduction Rate of Peptide Transporter PEPT-1 Deficient C. elegans Is Dependent on Dietary Glutamate Supply.

Intestinal absorption of dietary amino acids is mediated via two routes. Free amino acids released by hydrolysis of dietary proteins are taken up by a multitude of amino acid transporters while di- and tripeptides released are taken up by the peptide transporter PEPT-1. Loss of PEPT-1 impairs growth, post-embryonic development and reproduction in Caenorhabditis elegans, and supplementation with a mixture of all L-amino acids only partially rescues fertility. In the present study, we demonstrate that dietary L-glutamate is the responsible amino acid that can increase fertility in hermaphrodite pept-1 worms. This effect was associated with a significantly higher uptake of glutamate/aspartate in pept-1 than in wildtype C. elegans. Furthermore, we found that the intestinal transporter proteins SNF-5 of the solute carrier SLC6 family of nutrient amino acid transporters (NAT) and AAT-6 of the SLC7 family as the light subunit of a heteromeric amino acid transporter (HAT) play a key role in glutamate homeostasis in pept-1 C. elegans. Genes encoding these transporters are highly expressed and upon silencing a 95% reduced fertility (snf-5) and sterility (aat-6) was observed. A subsequent L-glutamate supplementation failed to rescue these phenotypes. Dietary glutamate supplementation did neither influence the feeding frequency, nor did it improve mating efficiency of pept-1 males. Most strikingly, pept-1 were more prone to habituation to repeated gentle touch stimuli than wildtype C. elegans, and dietary glutamate supply was sufficient to alter this behavioral output by restoring the mechanosensory response to wildtype levels. Taken together, our data demonstrate a key role of L-glutamate in amino acid homeostasis in C. elegans lacking the peptide transporter in the intestine and demonstrate its distinct role in reproduction and for neural circuits mediating touch sensitivity.

Melatonin Improves Laying Performance by Enhancing Intestinal Amino Acids Transport in Hens.

The high concentration of melatonin (MEL) in the intestinal mucosa suggests that it has a special physiological function in intestine. In hens, previous studies have shown that MEL treatment promoted egg-laying performance. Considering the importance of amino acids (AA) for egg formation, we hypothesized that MEL may enhance the intestinal absorption of AA from the feed, thus promoting egg laying performance. In this study, we supplemented the hens with MEL for two consecutive weeks. The results showed that, compared with control group, feeding with 0.625 mg MEL/kg diets gave rise to higher egg laying rate (by 4.3%, P = 0.016), increased eggshell thickness (by 16.9%, P < 0.01) and albumen height (by 4.5%, P = 0.042). Meanwhile, feeding with 0.625 and 2.5 mg MEL/kg diets could significantly increase serum levels of aspartic acid, threonine, serine, glutamic acid, glycine, alanine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline. Furthermore, a 0.625 mg MEL/kg diets could significantly increase the expression of PepT1 (by 3949.9%), B0AT (by 6045.9%), b0, +AT (by 603.5%), and EAAT3 (by 412.7%) in the jejunum. Additionally, in the cultured intestinal crypt “organoids,” treatment with 0.5 μM MEL could significantly enhance the expression of PepT1, b0, +AT and EAAT3 mRNAs by 35.4%, 110.0%, and 160.1%, respectively. Detection of MEL concentration in serum and intestinal fluid suggested that lower dosage of MEL feeding was mainly acted on intestine locally, and further increased intestinal antioxidases (GPx-3, SOD-1 or PRDX-3) mRNA expression. Taken together, we demonstrated that MEL feeding in laying hens could locally promote the expression and function of AA transporter in small intestine by up-regulating antioxidases expression, and finally elevate laying performance.

Gossypol reduced the intestinal amino acid absorption capacity of young grass carp (Ctenopharyngodon idella)

This study was conducted to evaluate the effects of gossypol on the growth, intestinal histology, intestinal amino acid (AA) absorption capacity and the safe upper limit of gossypol in the diets for young grass carp (Ctenopharyngodon idella) growth. The fish were fed six diets containing different levels of free gossypol (0, 125 (121.38), 250 (243.94), 375 (363.89), 775 (759.93) and 1175 (1162.06) mg kg−1 diet) from gossypol-acetic acid for 60 days. Results indicated that gossypol could reduce the growth performance and damage the intestines of young grass carp. Interestingly, gossypol modulated the absorptive abilities of various AAs, and mechanisms are not unified in fish. Firstly, gossypol decreased the contents of tryptophan (Trp), threonine (Thr), valine (Val), phenylalanine (Phe), glycine (Gly), serine (Ser) and tyrosine (Tyr) in the three intestinal segments of fish associated with down-regulating the mRNA levels of solute carrier (SLC) 6A19b, SLC7A5, SLC7A8, SLC1A5, SLC38A2 and peptide transporter 1 (PepT1) in the intestine. Secondly, gossypol reduced the contents of methionine (Met), isoleucine (Ile), proline (Pro), cysteine (Cys) and arginine (Arg) in the proximal intestine (PI) and mid intestine (MI) of fish by down-regulating the mRNA levels of SLC7A7, SLC7A6, SLC7A1, SLC6A19b, SLC7A5, SLC7A8, SLC1A5, SLC38A2 and PepT1 in the PI and MI. Thirdly, gossypol inhibited the aspartic acid (Asp) and taurine (Tau) contents in the PI and MI of fish by down-regulating the mRNA levels of SLC1A2a, SLC1A3, PepT1 and SLC6A6 in the PI and MI. Fourthly, gossypol suppressed the lysine(Lys) and histidine (His) contents in the MI and distal intestine (DI) of fish due to down-regulating the mRNA levels of SLC7A7, SLC7A5 and SLC38A2 in the MI, and SLC7A6, SLC7A1, SLC7A8 and PepT1 in the MI and DI. Gossypol down-regulated the above AA and peptide transporters in the intestine of fish partly related to suppressing the target of rapamycin (TOR) signalling pathway. Based on percent weight gain (PWG) and feed efficiency (FE), the safe upper limit of gossypol in the diets for young grass carp growth were estimated to be 182 and 179 mg kg−1 diet, respectively. In summary, gossypol reduced the intestinal AA absorption capacity of young grass carp partly relate to damaging the intestinal structure, down-regulating the mRNA levels of AA and peptide transporters, and inhibiting the TOR signalling pathway.

Regulation of intestinal health by branched-chain amino acids.

Besides its primary role in the digestion and absorption of nutrients, the intestine also interacts with a complex external milieu, and is the first defense line against noxious pathogens and antigens. Dysfunction of the intestinal barrier is associated with enhanced intestinal permeability and development of various gastrointestinal diseases. The branched-chain amino acids (BCAAs) are important nutrients, which are the essential substrates for protein biosynthesis. Recently, emerging evidence showed that BCAAs are involved in maintaining intestinal barrier function. It has been reported that dietary supplementation with BCAAs promotes intestinal development, enhances enterocyte proliferation, increases intestinal absorption of amino acids (AA) and glucose, and improves the immune defenses of piglets. The underlying mechanism of these effects is mediated by regulating expression of genes and proteins associate with various signaling pathways. In addition, BCAAs promote the production of beneficial bacteria in the intestine of mice. Compelling evidence supports the notion that BCAAs play important roles in both nutrition and intestinal health. Therefore, as functional amino acids with various physiological effects, BCAAs hold key roles in promoting intestinal development and health in animals and humans.

Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport

ObjectiveGlucagon-like peptide-2 (GLP-2) is co-secreted with GLP-1 from gut endocrine cells, and both peptides act as growth factors to expand the surface area of the mucosal epithelium. Notably, GLP-2 also enhances glucose and lipid transport in enterocytes; however, its actions on control of amino acid (AA) transport remain unclear. Here we examined the mechanisms linking gain and loss of GLP-2 receptor (GLP-2R) signaling to control of intestinal amino acid absorption in mice. MethodsAbsorption, transport, and clearance of essential AAs, specifically lysine, were measured in vivo by Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) and ex vivo with Ussing chambers using intestinal preparations from Glp2r+/+ and Glp2r−/− mice. Immunoblotting determined jejunal levels of protein components of signaling pathways (PI3K-AKT, and mTORC1-pS6-p4E-BP1) following administration of GLP-2, protein gavage, and rapamycin to fasted Glp2r+/+ and Glp2r−/− mice. Expression of AA transporters from full thickness jejunum and 4F2hc from brush border membrane vesicles (BBMVs) was measured by real-time PCR and immunoblotting, respectively. ResultsAcute administration of GLP-2 increased basal AA absorption in vivo and augmented basal lysine transport ex vivo. GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxin ex vivo. Phosphorylation of mTORC1 effector proteins S6 and 4E-BP1 was significantly increased in wild-type mice in response to GLP-2 alone, or when co-administered with protein gavage, and abolished following oral gavage of rapamycin. In contrast, activation of GLP-1R signaling did not enhance S6 phosphorylation. Disruption of GLP-2 action in Glp2r−/− mice reduced lysine transport ex vivo and attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporter slc7a9 in response to refeeding, and the abundance of 4F2hc in BBMVs following protein gavage, was significantly attenuated in Glp2r−/− mice. ConclusionsThese findings reveal an important role for GLP-2R signaling in the physiological and pharmacological control of enteral amino acid sensing and assimilation, defining an enteroendocrine cell-enterocyte axis for optimal energy absorption.

Influence of Trypsin-Digested Wheat Gluten Peptides with Different Molecular Size on Intestinal Absorption of Amino Acids in Chickens.

Although a lot of food-derived peptides have been applied for medical use and therapeutic nutrition, the function of feed-derived peptides on nutritional physiology in chickens has not been clarified so far. Our previous study revealed that wheat gluten digested by trypsin could enhance the absorption of amino acids from small intestine. In the present study, we studied the influence of trypsin-digested wheat gluten peptides with different molecular weight (MW) on the intestinal absorption of amino acids in chickens. Wheat gluten was digested by trypsin and fractionated by using the ultrafiltration membrane. Wheat gluten peptides were divided into 3 fractions with different MW; MW more than 10,000, MW 3,000–10,000 and MW less than 3,000. Phosphate buffered saline and whole wheat gluten digesta were used as negative and positive controls, respectively. All of wheat gluten peptides were mixed with 2.5 M glucose-10 mM amino acid solution and administrated into the crop with a stomach tube. At 20 min after oral administration, blood samples were taken from mesenteric vein. Plasma amino acid concentration was determined using an automatic amino acid analyzer. The peptide fraction with MW more than 10,000 increased the intestinal absorption of phenylalanine and proline. The peptide fraction with MW 3,000–10,000 increased the intestinal absorption of proline. These results suggest that wheat gluten peptide with high MW might have the potency to enhance the absorption of aromatic amino acids from small intestine of young chickens.