Adaptive regulation of intestinal lysine metabolism

Dietary xylo-oligosaccharides and arabinoxylans improved growth efficiency by reducing gut epithelial cell turnover in broiler chickens

BACKGROUND

One of the main roles of the intestinal mucosa is to protect against environmental hazards. Supplementation of xylo-oligosaccharides (XOS) is known to selectively stimulate the growth of beneficial intestinal bacteria and improve gut health and function in chickens. XOS may have an impact on the integrity of the intestinal epithelia where cell turnover is critical to maintain the compatibility between the digestive and barrier functions. The aim of the study was to evaluate the effect of XOS and an arabinoxylan-rich fraction (AXRF) supplementation on gut function and epithelial integrity in broiler chickens.

METHODS

A total of 128 broiler chickens (Ross 308) were assigned into one of two different dietary treatments for a period of 42 d: 1) control diet consisting of a corn/soybean meal-based diet; or 2) a control diet supplemented with 0.5% XOS and 1% AXRF. Each treatment was randomly distributed across 8 pens (n = 8) with 8 chickens each. Feed intake and body weight were recorded weekly. On d 42, one male chicken per pen was selected based on average weight and euthanized, jejunum samples were collected for proteomics analysis.

RESULTS

Dietary XOS/AXRF supplementation improved feed efficiency (P < 0.05) from d 1 to 42 compared to the control group. Proteomic analysis was used to understand the mechanism of improved efficiency uncovering 346 differentially abundant proteins (DAP) (Padj < 0.00001) in supplemented chickens compared to the non-supplemented group. In the jejunum, the DAP translated into decreased ATP production indicating lower energy expenditure by the tissue (e.g., inhibition of glycolysis and tricarboxylic acid cycle pathways). In addition, DAP were associated with decreased epithelial cell differentiation, and migration by reducing the actin polymerization pathway. Putting the two main pathways together, XOS/AXRF supplementation may decrease around 19% the energy required for the maintenance of the gastrointestinal tract.

CONCLUSIONS

Dietary XOS/AXRF supplementation improved growth efficiency by reducing epithelial cell migration and differentiation (hence, turnover), actin polymerization, and consequently energy requirement for maintenance of the jejunum of broiler chickens.

Messages from the Small Intestine Carried by Extracellular Vesicles in Prediabetes: A Proteomic Portrait

Extracellular vesicles (EVs) mediate communication in physiological and pathological conditions. In the pathogenesis of type 2 diabetes, inter-organ communication plays an important role in its progress and metabolic surgery leads to its remission. Moreover, gut dysbiosis is emerging as a diabetogenic factor. However, it remains unclear how the gut senses metabolic alterations and whether this is transmitted to other tissues via EVs. Using a diet-induced prediabetic mouse model, we observed that protein packaging in gut-derived EVs (GDE), specifically the small intestine, is altered in prediabetes. Proteins related to lipid metabolism and to oxidative stress management were more abundant in prediabetic GDE compared to healthy controls. On the other hand, proteins related to glycolytic activity, as well as those responsible for the degradation of polyubiquitinated composites, were depleted in prediabetic GDE. Together, our findings show that protein packaging in GDE is markedly modified during prediabetes pathogenesis, thus suggesting that prediabetic alterations in the small intestine are translated into modified GDE proteomes, which are dispersed into the circulation where they can interact with and influence the metabolic status of other tissues. This study highlights the importance of the small intestine as a tissue that propagates prediabetic metabolic dysfunction throughout the body and the importance of GDE as the messengers. Data are available via ProteomeXchange with identifier PXD028338.

Precision intestinal nutrition: knowledge and gaps regarding the role of amino acids during an enteric challenge

Poultry nutritionists continually strive for more “precision” nutritional programs that provide the exact balance of nutrients that maximize broiler growth performance without economically and environmentally costly excesses. Many factors affect the precise amount and balance of nutrients needed by the broiler, including genetics, age, sex, and environment. Furthermore, broilers in intensive rearing environments will almost always be subjected to some degree of enteric stress that can alter nutrient needs. Exposure to enteric pathogens such as Eimeria spp., the intestinal parasites that cause avian coccidiosis, induces physical damage to the intestinal epithelium and activates immune responses, ultimately resulting in the repartitioning of amino acids (AA) in response to these prioritized demands. Even without any pathogenic challenge, the intestine has an already high demand for many AA, with 30 to 100% of dietary AA extracted during first pass intestinal metabolism. In many cases, increasing dietary protein from intact proteins has been shown to be a viable option to ameliorate impaired AA digestion and absorption and heightened need for certain AA of birds under an enteric stress. However, increasing dietary protein often results in concomitant increases in indigestible protein and carbohydrates that can stimulate the overgrowth of pathogenic bacteria (i.e., Clostridium perfringens). Alternative options to increase dietary AA levels are to increase all feed-grade, free AA (e.g., Met, Lys, Thr, Val), or specific individual feed-grade AA. Therefore, the objectives of this paper are to discuss precision nutrition, the dietary AA demands of the intestine, consequences of coccidiosis on AA needs of the intestine, and formulation approaches to meet these altered needs. In summary, increased dietary protein met by intact proteins has consistently demonstrated its benefits during an Eimeria spp. infection; however, to further the goal of precision nutritional programs, feeding higher levels of a specific AA to support desired functions such as intestinal recovery or immune function for birds experiencing an enteric stress still require further evaluation.

Effects of Dietary Crude Protein Levels on Fecal Crude Protein, Amino Acids Flow Amount, Fecal and Ileal Microbial Amino Acids Composition and Amino Acid Digestibility in Growing Pigs

Simple Summary

The purpose of this experiment was to evaluate a low protein corn-soybean meal-based diet with the same Lys, Met + Cys, Thr and Trp level as a high protein diet on fecal crude protein (CP), amino acid (AA) flow amount, AA digestibility and fecal and ileal microbial AA composition in growing pigs. Eighteen pigs with an initial body weight of (30 ± 1.35) kg were randomly divided into three groups, with six replicates in each group, and fed a corn-soybean meal-based diets with 12%, 15% and 18% CP levels, respectively. Our aim was to explain whether the addition of four crystalline essential AAs (EAA) to a low diet affected the digestibility of protein-bound NEAA (non-essential amino acid) and EAA and the composition of microbial AA in ileum and feces.

Abstract

The purpose of this experiment was to evaluate the effects of low protein corn-soybean meal-based diets on fecal CP, amino acid (AA) flow amount, AA digestibility and fecal and ileal microbial AA composition in growing pigs. Eighteen pigs (initial body weight = 30 ± 1.35) were randomly divided into three groups and fed with basal diets with CP levels of 12%, 15% and 18%, respectively. The Lys, Met + Cys, Thr and Trp level in the 12% CP and 15% CP groups is the same as 18% CP group by the addition of four crystalline Lys, Met + Cys, Thr and Trp to the diet. The results showed that with the decrease of dietary CP level from 18% to 12%, the fecal total nitrogen (N), CP and total AA (TAA) flow amount decreased linearly (p < 0.05). Dry matter (DM) digestibility, CP digestibility, TAA digestibility, essential amino acid (EAA) digestibility and non-essential amino acid (NEAA) digestibility increased linearly with the decrease of dietary CP concentration from 18% to 12%. Compared with 18% CP group, the flow amount of Asp, Ser, Glu, Gly, Tyr, Val, Leu and Phe in feces of pigs in the 15% CP group and 12% CP group decreased significantly, while the flow amount of Arg in the 15% CP group was lower than that in the 18% CP group and 12% CP group. The fecal microbial N and AA of the 15% CP group were higher than those of the 18% CP and 12% CP groups. Fecal TAA flow amount decreased linearly with the decrease of the dietary CP levels from 18% to 12%. Fecal TAA and NEAA flow amount also decreased linearly with the decrease of dietary CP level from 18% to 12%. Except for Glu, Gly, Met, Tyr, Thr and Phe, there were significant differences among the three groups in the composition of 17 kinds of AAs in fecal microorganisms. Among the 17 AA compositions of ileal microorganisms, except Tyr and Lys, the other AAs were significantly different among the three groups (p < 0.05)

Effects of lysine and methionine in a low crude protein diet on the growth performance and gene expression of immunity genes in broilers

Globally, the poultry industry is 1 of the most advanced livestock industries. Feed contributes to the biggest proportion (65-70%) of the production cost. Most feed ingredients in Malaysia are imported, which contributes to the high food bill annually, and alternative feed formulation may help decrease the cost of poultry feed. Feed formulation are improved to efficiently meet the dietary requirements of the broilers and 1 of the ways is by reducing the level of crude protein in the diet while supplementing essential amino acids. In this study, the effects of methionine and lysine, which are the 2 most limiting amino acids in the chicken diet, were supplemented in a low crude protein diet, and its effects on the growth and expression of immunity genes such as MUC2, SLC, GAL6, and LEAP-2 were studied. A total of 300 Cobb500 broilers were tested with 10 different dietary treatments. Experimental treatment diets consist of high, standard, and low levels of methionine and lysine in the diet with reduced crude protein. The control group consists of diet with standard levels of lysine, methionine, and crude protein as recommended for Cobb500 broilers. Ribonucleic acid was extracted from the jejunum, spleen, and liver for gene expression analysis which was performed with real-time polymerase chain reaction using SYBR Green chemistry. Results of the growth performance at 6 wk showed improved feed conversion ratio when lysine was increased by 0.2% in a low crude protein diet at 1.96 ± 0.11. Gene expression of MUC2 gene in the jejunum showed a significant increase across all experimental diets with the treatment with higher lysine in low crude protein diet with the highest increase of 3.8 times as compared with the control diet. The other genes expressed in the spleen and liver were mostly downregulated. It was concluded that supplementation of high lysine with standard methionine in a low crude protein diet performed better in terms of lowest feed conversion ratio and high upregulation of MUC2 gene.

Effects of vitamin B6 on the growth performance, intestinal morphology, and gene expression in weaned piglets that are fed a low-protein diet1

Vitamin B6 (VB6), which is an essential functional substance for biosome, plays an irreplaceable role in animal health. However, there are few studies that focus on the correlation between VB6 and intestinal health in weaned piglets. This study was conducted to investigate the effects of VB6 on the growth performance, intestinal morphology, and inflammatory cytokines and amino acid (AA) transporters mRNA expression in weaned piglets that are fed a low crude-protein (CP, 18%) diet. Eighteen crossbred piglets with initial body weights of 7.03 ± 0.17 kg (means ± SEM), weaned at 21-d age, were randomly assigned three diets with 0, 4, and 7 mg/kg VB6 supplementation, respectively. The experimental period lasted 14 days. Our results showed that there were no significant differences in growth performance, diarrhea rate, and biochemical parameters among the three treatments. In the jejunum, dietary VB6 supplementation did not affect the morphology and positive Ki67 counts. Dietary supplementation with 4 mg/kg VB6 decreased the mRNA expression of COX-2, IL-10, and TGF-β (P < 0.05). Dietary supplementation with 7 mg/kg VB6 increased the mRNA expression of SLC7A1, SLC7A6, SLC16A14, and SLC38A5 (P < 0.05) and 4 or 7 mg/kg VB6 decreased SLC36A1 mRNA expression (P < 0.05). In the ileum, VB6 supplementation did not affect positive Ki67 counts but significantly decreased villus area (P < 0.05) and tended to decrease villus height (P = 0.093). Dietary supplementation with 4 mg/kg VB6 had significantly increased the mRNA expression of IL-1β, TNF-α, COX-2, IL-10, and TGF-β (P < 0.05). Dietary supplementation with 4 or 7 mg/kg VB6 had significantly decreased SLC6A20, SLC7A1, SLC7A6, SLC16A14, and SLC38A5 mRNA expression (P < 0.05). These findings suggest that dietary supplementation of VB6 mainly down-regulated inflammatory cytokines and up-regulated AA transporters mRNA expression in jejunum, while up-regulated (4 mg/kg) inflammatory cytokines and down-regulated AA transporters mRNA expression in ileum, which may provide a reference for the intestinal development of weaned piglets that are fed a low-CP diet.

Microbial Metabolites and Intestinal Stem Cells Tune Intestinal Homeostasis

Microorganisms that colonize the gastrointestinal tract, collectively known as the gut microbiota, are known to produce small molecules and metabolites that significantly contribute to host intestinal development, functions, and homeostasis. Emerging insights from microbiome research reveal that gut microbiota-derived signals and molecules influence another key player maintaining intestinal homeostasis-the intestinal stem cell niche, which regulates epithelial self-renewal. In this review, the literature on gut microbiota-host crosstalk is surveyed, highlighting the effects of gut microbial metabolites on intestinal stem cells. The production of various classes of metabolites, their actions on intestinal stem cells are discussed and, finally, how the production and function of metabolites are modulated by aging and dietary intake is commented upon.

Impact of viral disease hypophagia on pig jejunal function and integrity

Pathogen challenges are often accompanied by reductions in feed intake, making it difficult to differentiate impacts of reduced feed intake from impacts of pathogen on various response parameters. Therefore, the objective of this study was to determine the impact of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) and feed intake on parameters of jejunal function and integrity in growing pigs. Twenty-four pigs (11.34 ± 1.54 kg BW) were randomly selected and allotted to 1 of 3 treatments (n = 8 pigs/treatment): 1) PRRSV naïve, ad libitum fed (Ad), 2) PRRSV-inoculated, ad libitum fed (PRRS+), and 3) PRRSV naïve, pair-fed to the PRRS+ pigs' daily feed intake (PF). At 17 days post inoculation, all pigs were euthanized and the jejunum was collected for analysis. At days post inoculation 17, PRRS+ and PF pigs had decreased (P < 0.05) transepithelial resistance compared with Ad pigs; whereas fluorescein isothiocyanate-dextran 4 kDa permeability was not different among treatments. Active glucose transport was increased (P < 0.05) in PRRS+ and PF pigs compared with Ad pigs. Brush border carbohydrase activity was reduced in PRRS+ pigs compared with PF pigs for lactase (55%; P = 0.015), sucrase (37%; P = 0.002), and maltase (30%; P = 0.015). For all three carbohydrases, Ad pigs had activities intermediate that of PRRS+ and PF pigs. The mRNA abundance of the tight junction proteins claudin 2, claudin 3, claudin 4, occludin, and zonula occludens-1 were reduced in PRRS+ pigs compared with Ad pigs; however, neither the total protein abundance nor the cellular compartmentalization of these tight junction proteins differed among treatments. Taken together, this study demonstrates that the changes that occur to intestinal epithelium structure, function, and integrity during a systemic PRRSV challenge can be partially explained by reductions in feed intake. Further, long term adaptation to PRRSV challenge and caloric restriction does reduce intestinal transepithelial resistance but does not appear to reduce the integrity of tight junction protein complexes.

Identification and Structure-Activity Relationship of Intestinal Epithelial Barrier Function Protective Collagen Peptides from Alaska Pollock Skin

The effect of collagen peptides (CPs) in intestinal mucosal protection has been approved in both cell and animal models. However, its structure–activity relationship and efficient peptide sequences are unclear, which hinders the in-depth study of its action mechanism and relative nutraceuticals and pharmaceuticals development. In this work, size exclusion chromatography, cation-exchange chromatography, and RP-HPLC were used to separate Alaska pollock skin-derived collagen hydrolysates based on their molecular weight, charge property, and hydrophobicity. The intestinal epithelial barrier function (IEBF) protective effect of separated peptide fractions were evaluated by tumor necrosis factor (TNF)-α-induced Caco-2 cell model. Results indicated that lower molecular weight (500–1000 Da) and higher hydrophilicity of CPs were related to better IEBF protective effect. Two high-efficiency IEBF protective peptide sequences, GPSGPQGSR and GPSGLLGPK with the corresponding molecular weights of 841.41 Da and 824.38 Da, were subsequently identified by UPLC-QToF-MS/MS. Their IEBF protective ability are comparable or even better than the currently used intestinal health supplements glutamine and arginine. The present findings suggested that the hydrophilic CPs, with molecular weight between 500 Da to 1000 Da, should be preferred in IEBF protective peptides preparation. GPSGPQGSR and GPSGLLGPK might have the potential of being IEBF protective ingredients used in intestinal health supplements and drugs.

Metabolomic analysis reveals metabolic characteristics of children with short stature caused by growth hormone deficiency

The diagnosis of short stature (SS) is of widespread importance for later treatment. In the present paper, a metabolomic method was used to analyze the metabolic characteristics of SS children caused by endocrine metabolic diseases in order to understand the underlying biochemical mechanism and provide a potential intervention strategy for SS. According to the clinical diagnosis and family investigation, all patients with SS were confirmed to be due to the endocrine disorders, especially GH deficiency (GHD). A nuclear magnetic resonance (NMR)-based metabolomic analysis of serum was used to identify the metabolic changes in 45 SS children from the 35 healthy controls (HCs). The disturbed metabolic network related to SS was correspondingly derived from the differential metabolites. The SS children demonstrated higher serum levels of citrate, phenylalanine, creatinine, and tyrosine and lower serum levels of glucose, serine, betaine, inositol, lysine, glycerol, and glutamine compared with the HCs. The results demonstrated that the disturbed glucose metabolism and metabolism and biosynthesis of amino acids are typical metabolic features of SS, and the lower levels of lysine and glutamine are the metabolic characterization of the affected growth axes and stress state of SS, respectively. The significant changes of those serum metabolites are able to be regarded as potential biomarkers for the diagnosis of SS. Accordingly, supplemental betaine in dietary pattern, the improvement of glycometabolism, and endogenous replenishment of lysine and glutamine allow the possible treatment strategy for SS.

Energy metabolism in the intestinal crypt epithelial cells of piglets during the suckling period

We tested the hypothesis that energy metabolism in the intestinal crypt epithelial cells of piglets changes during the suckling period. The experiment began with 24 piglets from 8 litters (3 piglets per litter). One piglet from each litter was randomly selected and euthanized at 7, 14, or 21 d of age, respectively. Crypt cells were isolated from the mid-jejunum and protein synthesis was analyzed using isobaric tags for relative and absolute quantification. The production of proteins related to glycolysis was mainly decreased from Days 7 to 14 before increasing up to Day 21. Synthesis of proteins involved in fatty acids, amino acids (glutamate and glutamine), and citrate cycle metabolism was generally down-regulated for samples collected on Days 14 and 21 when compared with levels on Day 7. These results indicate that energy metabolism in the intestinal crypt epithelial cells changes during the suckling period. Furthermore, this pattern of metabolism varies among glucose, fatty acids, and amino acids. Therefore, these findings may be useful in efforts to regulate the intestinal development of piglets.

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.

Investigation and application of photochemically induced direct UV detection of low or non-UV absorbing compounds by capillary electrophoresis

Some low or non-UV absorbing compounds like amino acids might be accessible to direct UV detection by capillary electrophoresis (CE), due to the photochemical reaction in the detection window of the separation capillary under extremely strong alkaline conditions. However, with regards to the photochemical reaction procedure and the influencing factors in CE, no comprehensive studies have been done. Herein, two strategies were applied to investigate the photochemical reaction mechanism including the introduction of an additional UV lamp and the utilization of driving pressure. The former confirmed the occurrence of photolysis, while the latter solved the interference of electroosmotic flow (EOF). Furthermore, the online photochemical reaction and online preconcentration technique were combined to develop a rapid, simple and sensitive method for determination of seven essential amino acids (valine, leucine, phenylalanine, methionine, tryptophan, threonine and lysine). Eventually, the developed method was successfully applied to the analysis of real samples with good reproducibility and reliability. This novel and simple method, based on the photochemical reactions occurring in the detection window and coupling with online preconcentration techniques, shows a great potential for the rapid and sensitive detection of low or non-UV absorbing compounds.

Energy metabolism in intestinal epithelial cells during maturation along the crypt-villus axis

Intestinal epithelial cells continuously migrate and mature along crypt-villus axis (CVA), while the changes in energy metabolism during maturation are unclear in neonates. The present study was conducted to test the hypothesis that the energy metabolism in intestinal epithelial cells would be changed during maturation along CVA in neonates. Eight 21-day-old suckling piglets were used. Intestinal epithelial cells were isolated sequentially along CVA, and proteomics was used to analyze the changes in proteins expression in epithelial cells along CVA. The identified differentially expressed proteins were mainly involved in cellular process, metabolic process, biological regulation, pigmentation, multicellular organizational process and so on. The energy metabolism in intestinal epithelial cells of piglets was increased from the bottom of crypt to the top of villi. Moreover, the expression of proteins related to the metabolism of glucose, most of amino acids, and fatty acids was increased in intestinal epithelial cells during maturation along CVA, while the expression of proteins related to glutamine metabolism was decreased from crypt to villus tip. The expression of proteins involved in citrate cycle was also increased intestinal epithelial cells during maturation along CVA. Moreover, dietary supplementation with different energy sources had different effects on intestinal structure of weaned piglets.

Effect of ruminal ammonia supply on lysine utilization by growing steers

Six ruminally cannulated Holstein steers (202 ± 15 kg) were used to study the effects of ruminal ammonia loading on whole-body lysine (Lys) utilization. Steers were housed in metabolism crates and used in a 6 × 6 Latin square design. All steers received 2.52 kg DM/d of a diet (10.1% CP) containing 82% soybean hulls, 8% wheat straw, 5% cane molasses, and 5% vitamins and minerals, and 10 g/d of urea (considered to be part of the basal diet) was ruminally infused continuously to ensure adequate ruminal ammonia concentrations. All steers were ruminally infused continuously with 200 g/d of acetic acid, 200 g/d of propionic acid, and 50 g/d of butyric acid and abomasally infused with 300 g/d of glucose continuously to increase energy supply without increasing microbial protein supply. Steers were also abomasally infused continuously with an excess of all essential AA except Lys to ensure that Lys was the only limiting AA. Treatments were arranged as a 3 × 2 factorial with 3 levels of urea (0, 40, or 80 g/d) continuously infused ruminally to induce ammonia loading and 2 levels of Lys (0 or 6 g/d) continuously infused abomasally. Treatments did not affect fecal N output ( = 0.37). Lysine supplementation decreased ( < 0.01) urinary N excretion from 51.9 g/d to 44.3 g/d, increased ( < 0.01) retained N from 24.8 to 33.8 g/d, increased ( < 0.01) plasma Lys, and decreased ( ≤ 0.05) plasma serine, tyrosine, valine, leucine, and phenylalanine. Lysine supplementation also tended ( = 0.09) to reduce plasma urea-N. Urea infusions linearly increased ( = 0.05) retained N (27.1, 29.3, and 31.5 g/d) and also linearly increased ( < 0.01) urinary N excretion (31.8, 48.1, and 64.4 g/d), urinary urea (21.9, 37.7, and 54.3 g/d), urinary ammonia (1.1, 1.4, and 1.9 g/d), and plasma urea (2.7, 4.0, and 5.1 mM), and linearly decreased plasma alanine ( = 0.04) and plasma glycine ( < 0.01). Assuming that retained protein is 6.25 × retained N and contains 6.4% Lys, the incremental efficiencies of infused Lys utilization were 51%, 59%, and 69% for steers receiving 0, 40, and 80 g/d of urea, respectively, indicating that ruminal ammonia loads may improve the efficiency of Lys utilization. This is supported by observed increases in whole body-protein deposition in response to ammonia loading of our steers that were, by design, Lys deficient.

Effects of Weaning on Intestinal Upper Villus Epithelial Cells of Piglets

The intestinal upper villus epithelial cells represent the differentiated epithelial cells and play key role in digesting and absorbing lumenal nutrients. Weaning stress commonly results in a decrease in villus height and intestinal dysfunction in piglets. However, no study have been conducted to test the effects of weaning on the physiology and functions of upper villus epithelial cells. A total of 40 piglets from 8 litters were weaned at 14 days of age and one piglet from each litter was killed at 0 d (w0d), 1 d (w1d), 3 d (w3d), 5 d (w5d), and 7 d (w7d) after weaning, respectively. The upper villus epithelial cells in mid-jejunum were isolated using the distended intestinal sac method. The expression of proteins in upper villus epithelial cells was analyzed using the isobaric tags for relative and absolute quantification or Western blotting. The expression of proteins involved in energy metabolism, Golgi vesicle transport, protein amino acid glycosylation, secretion by cell, transmembrane transport, ion transport, nucleotide catabolic process, translational initiation, and epithelial cell differentiation and apoptosis, was mainly reduced during the post-weaning period, and these processes may be regulated by mTOR signaling pathway. These results indicated that weaning inhibited various cellular processes in jejunal upper villus epithelial cells, and provided potential new directions for exploring the effects of weaning on the functions of intestine and improving intestinal functions in weaning piglets.

Lysine requirements of moderately undernourished school-aged Indian children are reduced by treatment for intestinal parasites as measured by the indicator amino acid oxidation technique

BACKGROUND

Lysine requirements of well-nourished children from developing regions have been found to be similar to those of children from developed regions (33.5 mg · kg⁻¹ · d⁻¹). However, intestinal parasites have been shown to increase lysine requirements in undernourished adults, and it is not known if a similar phenomenon occurs in undernourished children from poor and unsanitary environments.

OBJECTIVE

Our objective was to measure the lysine requirement of moderately undernourished school-aged Indian children by the indicator amino acid oxidation technique before and after successful treatment for intestinal parasites.

METHODS

Twenty-one undernourished school-aged children (∼8 y of age) with z scores between -2 SD and -3 SD for height-for-age or weight-for-age, who tested positive for intestinal parasites, were studied before and after successful antiparasite treatment. Children were fed any 2 of 7 levels of lysine intakes (5, 15, 25, 35, 50, 65, and 80 mg · kg⁻¹ · d⁻¹) in random order. The lysine requirement was determined by applying a 2-phase linear regression crossover analysis on the fractional oxidation rate of the tracer L-[1-¹³C] phenylalanine in response to the graded lysine intakes.

RESULTS

The lysine requirement of undernourished children with intestinal parasite infestations was determined to be 42.8 mg · kg⁻¹ · d⁻¹ (95% CI: 32.6, 53.1 mg · kg⁻¹ · d⁻¹), and after successful antiparasitic treatment it was determined to be 35.5 mg · kg⁻¹ · d⁻¹ (95% CI: 25.5, 45.5 mg · kg⁻¹ · d⁻¹). The results were significantly different (P < 0.05), although the 95% CIs overlapped.

CONCLUSIONS

The lysine requirement in undernourished children is similar to that of well-nourished children, and intestinal parasitic infestation increased the lysine requirement by ∼20%.

Lysine nutrition in swine and the related monogastric animals: muscle protein biosynthesis and beyond

Improving feed efficiency of pigs with dietary application of amino acids (AAs) is becoming increasingly important because this practice can not only secure the plasma AA supply for muscle growth but also protect the environment from nitrogen discharge with feces and urine. Lysine, the first limiting AA in typical swine diets, is a substrate for generating body proteins, peptides, and non-peptide molecules, while excess lysine is catabolized as an energy source. From a regulatory standpoint, lysine is at the top level in controlling AA metabolism, and lysine can also affect the metabolism of other nutrients. The effect of lysine on hormone production and activities is reflected by the change of plasma concentrations of insulin and insulin-like growth factor 1. Lysine residues in peptides are important sites for protein post-translational modification involved in epigenetic regulation of gene expression. An inborn error of a cationic AA transporter in humans can lead to a lysinuric protein intolerance condition. Dietary deficiency of lysine will impair animal immunity and elevate animal susceptibility to infectious diseases. Because lysine deficiency has negative impact on animal health and growth performance and it appears that dietary lysine is non-toxic even at a high dose of supplementation, nutritional emphasis should be put on lysine supplementation to avoid its deficiency rather than toxicity. Improvement of muscle growth of monogastric animals such as pigs via dietary lysine supply may be due to a greater increase in protein synthesis rather than a decrease in protein degradation. Nevertheless, the underlying metabolic and molecular mechanisms regarding lysine effect on muscle protein accretion merits further clarification. Future research undertaken to fully elucidate the metabolic and regulatory mechanisms of lysine nutrition could provide a sound scientific foundation necessary for developing novel nutritional strategies to enhance the muscle growth and development of meat animals.

Supplementing monosodium glutamate to partial enteral nutrition slows gastric emptying in preterm pigs(1-3)

Emerging evidence suggests that free glutamate may play a functional role in modulating gastroduodenal motor function. We hypothesized that supplementing monosodium glutamate (MSG) to partial enteral nutrition stimulates gastric emptying in preterm pigs. Ten-day-old preterm, parenterally fed pigs received partial enteral nutrition (25%) as milk-based formula supplemented with MSG at 0, 1.7, 3.0, and 4.3 times the basal protein-bound glutamate intake (468 mg·kg(-1)·d(-1)) from d 4 to 8 of life (n = 5-8). Whole-body respiratory calorimetry and (13)C-octanoic acid breath tests were performed on d 4, 6, and 8. Body weight gain, stomach and intestinal weights, and arterial plasma glutamate and glutamine concentrations were not different among the MSG groups. Arterial plasma glutamate concentrations were significantly higher at birth than after 8 d of partial enteral nutrition. Also at d 8, the significant portal-arterial concentration difference in plasma glutamate was substantial (∼500 μmol/L) among all treatment groups, suggesting that there was substantial net intestinal glutamate absorption in preterm pigs. MSG supplementation dose-dependently increased gastric emptying time and decreased breath (13)CO2 enrichments, (13)CO2 production, percentage of (13)CO2 recovery/h, and cumulative percentage recovery of (13)C-octanoic acid. Circulating glucagon-like peptide-2 (GLP-2) concentration was significantly increased by MSG but was not associated with an increase in intestinal mucosal growth. In contrast to our hypothesis, our results suggest that adding MSG to partial enteral nutrition slows the gastric emptying rate, which may be associated with an inhibitory effect of increased circulating GLP-2.

Modulation of the gut microbiota with antibiotic treatment suppresses whole body urea production in neonatal pigs

We examined whether changes in the gut microbiota induced by clinically relevant interventions would impact the bioavailability of dietary amino acids in neonates. We tested the hypothesis that modulation of the gut microbiota in neonatal pigs receiving no treatment (control), intravenously administered antibiotics, or probiotics affects whole body nitrogen and amino acid turnover. We quantified whole body urea kinetics, threonine fluxes, and threonine disposal into protein, oxidation, and tissue protein synthesis with stable isotope techniques. Compared with controls, antibiotics reduced the number and diversity of bacterial species in the distal small intestine (SI) and colon. Antibiotics decreased plasma urea concentrations via decreased urea synthesis. Antibiotics elevated threonine plasma concentrations and turnover, as well as whole body protein synthesis and proteolysis. Antibiotics decreased protein synthesis rate in the proximal SI and liver but did not affect the distal SI, colon, or muscle. Probiotics induced a bifidogenic microbiota and decreased plasma urea concentrations but did not affect whole body threonine or protein metabolism. Probiotics decreased protein synthesis in the proximal SI but not in other tissues. In conclusion, modulation of the gut microbiota by antibiotics and probiotics reduced hepatic ureagenesis and intestinal protein synthesis, but neither altered whole body net threonine balance. These findings suggest that changes in amino acid and nitrogen metabolism resulting from antibiotic- or probiotic-induced shifts in the microbiota are localized to the gut and liver and have limited impact on whole body growth and anabolism in neonatal piglets.

Continuous enteral administration can enable normal amino acid absorption in rats with methotrexate-induced gastrointestinal mucositis

It is unknown what feeding strategy to use during chemotherapy-induced gastrointestinal mucositis, which causes weight loss and possibly malabsorption. To study the absorptive capacity of amino acids during mucositis, we determined the plasma availability of enterally administered amino acids (AA), their utilization for protein synthesis, and the preferential side of the intestine for AA uptake in rats with and without methotrexate (MTX)-induced mucositis. Four days after injection with MTX (60 mg/kg) or saline (controls), rats received a primed, continuous dual-isotope infusion (intraduodenal and intravenous) of labeled L-leucine, L-lysine, L-phenylalanine, L-threonine, and L-methionine. We collected blood samples, assessed jejunal histology, and determined labeled AA incorporation in proximal and distal small intestinal mucosa, plasma albumin, liver, and thigh muscle. MTX-induced mucositis was confirmed by histology. The median systemic availability of all AA except for leucine was similar in MTX-treated rats and in controls. However, the individual availability of all AA differed substantially within the group of MTX-treated rats, ranging from severely reduced (<10% of intake) to not different from controls (>40% of intake in 5 of 9 rats). More AA originating from basolateral uptake than those originating from apical uptake were used for intestinal protein synthesis in MTX-treated rats (≥420% more, P < 0.05). We conclude that continuous enteral administration can enable normal AA absorption in rats with MTX-induced mucositis. The intestine prefers basolateral AA uptake to meet its need for AA for protein synthesis during mucositis.

Tissue distribution of indices of lysine catabolism in growing swine

The primary pathway of lysine degradation in pigs presumably depends on the bifunctional protein α-aminoadipate δ-semialdehyde synthase (AASS), which contains lysine α-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH) activities. In liver, AASS is restricted to the mitochondrial matrix and lysine is presumptively transported through the plasma membrane by a cationic AA transporter (CAT1/2) and through the inner mitochondrial membrane by 1 or both mitochondrial ornithine transporters (ORC-1/ORC-2). Lysyl oxidase (LO) may represent an alternative pathway of lysine oxidation. The objective of this experiment was to analyze the distribution of indices of lysine catabolism in various pig tissues. We assessed LKR, SDH, and LO activities, lysine oxidation, mRNA abundance of LKR, CAT1/2, and ORC1/2, and AASS protein abundance (via SDH antibody) in liver, heart, kidney medulla and cortex, triceps, longissimus, whole intestine, enterocytes, and intestine stripped of enterocytes in 10 growing pigs, weighing ∼25 kg. The LKR activity differed across tissues (P<0.001) and was greatest in liver, intestine, and kidney samples, and LKR mRNA abundance (P<0.001) was greatest in liver; although, LKR activity and mRNA abundance were detected in all other tissues. Activity of SDH (P<0.001) and SDH mRNA abundance (P<0.001) were affected by tissue and were greatest in liver compared with all other tissues analyzed. The AASS protein abundance (P<0.001) was greatest in whole intestine and liver. Activity of LO (P<0.0001) was greatest in muscle samples. The abundance of ORC-1 (P<0.001) and ORC-2 mRNA (P<0.001) differed among tissues, and ORC-1 was greatest in liver, kidney, and intestinal preparations, and ORC-2 mRNA abundance was greatest in liver and intestine. Interestingly, LKR activity was correlated with ORC-1 (r=0.32, P<0.05) and ORC-2 (r=0.41, P<0.05) expression. The expression of CAT-1 was uniform in all tissues, whereas CAT-2 (P<0.01) was greatest in liver. In conclusion, these data indicate that extra-hepatic tissues contribute to lysine catabolism as do enzymes other than LKR.

Reduced absorption of long-chain fatty acids during methotrexate-induced gastrointestinal mucositis in the rat

BACKGROUND & AIMS

Patients with chemotherapy-induced gastrointestinal mucositis suffer from weight loss and possibly malabsorption. Since long-chain fatty acids serve important functions in the body, we aimed to determine the intestinal capacity of fat absorption in rats with and without methotrexate-induced mucositis.

METHODS

Four days after intravenous injection with methotrexate (60 mg/kg) or saline, rats received saturated ([U-(13)C]palmitic acid) and unsaturated ([U-(13)C]linoleic acid) fatty acids dissolved in oil, either as a single bolus by oral gavage or by continuous intraduodenal infusion. We determined plasma and liver label concentrations at specific time points.

RESULTS

We confirmed methotrexate-induced mucositis by villus atrophy using microscopy. Methotrexate treatment severely reduced the appearance of [U-(13)C]palmitic- and [U-(13)C]linoleic acid in plasma and liver, compared to controls, either when administered as a bolus or continuously (all at least -63%, P < 0.05). Liver [U-(13)C]palmitic acid appearance was higher than [U-(13)C]linoleic acid appearance, either when administered as a bolus (2.8-fold, P < 0.01) or continuously (5.7-fold, P < 0.01).

CONCLUSIONS

The intestinal capacity to absorb long-chain fatty acids is severely reduced in rats with methotrexate-induced mucositis. Continuous administration does not overcome this impairment. The liver takes up and/or retains mainly saturated fatty acids during mucositis.

Lysine requirement of the enterally fed term infant in the first month of life

BACKGROUND

Infant nutrition has a major impact on child growth and functional development. Low and high intakes of protein or amino acids could have a detrimental effect.

OBJECTIVE

The objective of the study was to determine the lysine requirement of enterally fed term neonates by using the indicator amino acid oxidation (IAAO) method. L-[1-(13)C]phenylalanine was used as an indicator amino acid.

DESIGN

Twenty-one neonates were randomly assigned to lysine intakes that ranged from 15 to 240 mg · kg(-1) · d(-1). Breath, urine, and blood samples were collected at baseline and during the plateau. The mean lysine requirement was determined by using biphasic linear regression crossover analysis on the fraction of (13)CO(2) recovery from L-[1-(13)C]phenylalanine oxidation (F(13)CO(2)) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma.

RESULTS

The mean (±SD) phenylalanine flux calculated from urine and plasma L-[1-(13)C]phenylalanine enrichment data were 88.3 ± 6.9 and 84.5 ± 7.4 μmol · kg(-1) · h(-1), respectively. Graded intakes of lysine had no effect on phenylalanine fluxes. The mean lysine requirement determined by F(13)CO(2) was 130 mg · kg(-1) · d(-1) (upper and lower CIs: 183.7 and 76.3 mg · kg(-1) · d(-1), respectively). The mean requirement was identical to the requirement determined by using phenylalanine oxidation rates in urine and plasma.

CONCLUSIONS

The mean lysine requirement of enterally fed term neonates was determined by using F(13)CO(2) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma. These methods yielded a similar result of 130 mg lysine · kg(-1) · d(-1). This study demonstrates that sampling of (13)CO(2) in expired air is sufficient to estimate the lysine requirement by using the IAAO method in infants. This trial was registered at www.trialregister.nl as NTR1610.

B-vitamin deficiency is protective against DSS-induced colitis in mice

Vitamin deficiencies are common in patients with inflammatory bowel disease (IBD). Homocysteine (Hcys) is a thrombogenic amino acid produced from methionine (Met), and its increase in patients with IBD indicates a disruption of Met metabolism; however, the role of Hcys and Met metabolism in IBD is not well understood. We hypothesized that disrupted Met metabolism from a B-vitamin-deficient diet would exacerbate experimental colitis. Mice were fed a B(6)-B(12)-deficient or control diet for 2 wk and then treated with dextran sodium sulfate (DSS) to induce colitis. We monitored disease activity during DSS treatment and collected plasma and tissue for analysis of inflammatory tissue injury and Met metabolites. We also quantified Met cycle activity by measurements of in vivo Met kinetics using [1-(13)C-methyl-(2)H(3)]methionine infusion in similarly treated mice. Unexpectedly, we found that mice given the B-vitamin-deficient diet had improved clinical outcomes, including increased survival, weight maintenance, and reduced disease scores. We also found lower histological disease activity and proinflammatory gene expression (TNF-α and inducible nitric oxide synthase) in the colon in deficient-diet mice. Metabolomic analysis showed evidence that these effects were associated with deficient B(6), as markers of B(12) function were only mildly altered. In vivo methionine kinetics corroborated these results, showing that the deficient diet suppressed transsulfuration but increased remethylation. Our findings suggest that disrupted Met metabolism attributable to B(6) deficiency reduces the inflammatory response and disease activity in DSS-challenged mice. These results warrant further human clinical studies to determine whether B(6) deficiency and elevated Hcys in patients with IBD contribute to disease pathobiology.

Postprandial oxidative losses of free and protein-bound amino acids in the diet: interactions and adaptation

Postprandial oxidation of dietary free amino acids or egg white protein was studied using the [13CO2] breath test in rats, as well as in humans. Thirty-eight male rats were assigned to four dietary test groups. Two diets only differed in their protein fraction. Diet I contained 21% egg white protein. For the breath test egg white protein, intrinsically labelled with [1-13C]-leucine, was used as a substrate. Diet II contained the same amino acids as diet I, though not as egg white protein but in free form. Free [1-13C]-leucine was used to label this diet. In addition, two 1:1 mixtures of both diets were used. During the breath test either the free amino acid or the protein fraction was labelled as in diets I or II. The animals were breath-tested following short-term (day 5) and long-term adaptation (day 20) to their experimental diet. For all diets, including the mixed diets, postprandial oxidative losses on day 5 were significantly higher for the free leucine compared with the protein-derived leucine. Differences between free and protein-derived leucine oxidation had, however, largely disappeared on day 20. The human subjects were breath-tested without any adaptation period to the diets. The oxidative losses of free leucine were also higher than those of protein-derived leucine. None of the studies showed any indication for an interaction between the oxidation of protein-derived amino acids and free amino acids. It is concluded that free and protein-derived amino acids in the diet are mainly metabolized independently.

Metabolism of select amino acids in bacteria from the pig small intestine

This study investigated the metabolism of select amino acids (AA) in bacterial strains (Streptococcus sp., Escherichia coli and Klebsiella sp.) and mixed bacterial cultures derived from the jejunum and ileum of pigs. Cells were incubated at 37°C for 3 h in anaerobic media containing 0.5-5 mM select AA plus [U-14C]-labeled tracers to determine their decarboxylation and incorporation into bacterial protein. Results showed that all types of bacteria rapidly utilized glutamine, lysine, arginine and threonine. However, rates of the utilization of AA by pure cultures of E. coli and Klebsiella sp. were greater than those for mixed bacterial cultures or Streptococcus sp. The oxidation of lysine, threonine and arginine accounted for 10% of their utilization in these pure bacterial cultures, but values were either higher or lower in mixed bacterial cultures depending on AA, bacterial species and the gut segment (e.g., 15% for lysine in jejunal and ileal mixed bacteria; 5.5 and 0.3% for threonine in jejunal mixed bacteria and ileal mixed bacteria, respectively; and 20% for arginine in ileal mixed bacteria). Percentages of AA used for bacterial protein synthesis were 50-70% for leucine, 25% for threonine, proline and methionine, 15% for lysine and arginine and 10% for glutamine. These results indicate diverse metabolism of AA in small-intestinal bacteria in a species- and gut compartment-dependent manner. This diversity may contribute to AA homeostasis in the gut. The findings have important implications for both animal and human nutrition, as well as their health and well-beings.

Lysine requirement in parenterally fed postsurgical human neonates

BACKGROUND

The lysine requirement of human neonates receiving parenteral nutrition (PN) has not been determined experimentally.

OBJECTIVE

The objective was to determine the parenteral lysine requirement for human neonates by using the minimally invasive indicator amino acid oxidation technique with l-[1-(13)C] phenylalanine as the indicator amino acid.

DESIGN

Eleven postsurgical neonates were randomly assigned to 15 lysine intakes ranging from 50 to 260 mg . kg(-1) . d(-1). Breath and urine samples were collected at baseline and at plateau for (13)CO(2) (F(13)CO(2)) and amino acid enrichment, respectively. The mean lysine requirement was determined by applying a 2-phase linear regression crossover analysis to the measured rates of F(13)CO(2) release and l-[1-(13)C]phenylalanine oxidation.

RESULTS

The mean parenteral lysine requirement determined by F(13)CO(2) release oxidation was 104.9 mg . kg(-1) . d(-1) (upper and lower CIs: 120.6 and 89.1 mg . kg(-1) . d(-1), respectively). The mean lysine parenteral requirement determined by phenylalanine oxidation was 117.6 mg . kg(-1) . d(-1) (upper and lower CIs: 157.5 and 77.6 mg . kg(-1) . d(-1), respectively). Graded intakes of lysine had no effect on phenylalanine flux.

CONCLUSION

We recommend a mean lysine requirement for the postsurgical PN-fed neonate of 104.9 mg . kg(-1) . d(-1), which is 32-43% of the lysine concentration presently found in commercial PN solutions (246-330 mg . kg(-1) . d(-1)). This trial was registered at clinicaltrials.gov as NCT00779753.

Utilization of amino acids by bacteria from the pig small intestine

This study determined the utilization of amino acids (AA) by bacteria from the lumen of the pig small intestine. Digesta samples from different segments of the small intestine were inoculated into media containing 10 mmol/L each of select AA (L-lysine, L-threonine, L-arginine, L-glutamate, L-histidine, L-leucine, L-isoleucine, L-valine, L-proline, L-methionine, L-phenylalanine or L-tryptophan) and incubated for 24 h. The previous 24-h culture served as an inoculum for a subsequent 24-h subculture during each of 30 subcultures. Results of the in vitro cultivation experiment indicated that the 24-h disappearance rates for lysine, arginine, threonine, glutamate, leucine, isoleucine, valine or histidine were 50-90% in the duodenum, jejunum or ileum groups. After 30 subcultures, the 24-h disappearance rates for lysine, threonine, arginine or glutamate remained greater than 50%. The denaturing gradient gel electrophoresis analysis showed that Streptococcus sp., Mitsuokella sp., and Megasphaera elsdenii-like bacteria were predominant in subcultures for utilizing lysine, threonine, arginine and glutamate. In contrast, Klebsiella sp. was not a major user of arginine or glutamate. Furthermore, analysis of AA composition and the incorporation of AA into polypeptides indicated that protein synthesis was a major pathway for AA metabolism in all the bacteria studied. The current work identified the possible predominant bacterial species responsible for AA metabolism in the pig small intestine. The findings provide a new framework for future studies to characterize the metabolic fate of AA in intestinal microbes and define their nutritional significance for both animals and humans.

Nutrition and health relevant regulation of intestinal sulfur amino acid metabolism

Sulfur amino acids (SAA), particularly methionine and cysteine, are critical for the gut to maintain its functions including the digestion, absorption and metabolism of nutrients, the immune surveillance of the intestinal epithelial layer and regulation of the mucosal response to foreign antigens. However, the metabolism of SAA in the gut, specifically the transmethylation of methionine, will result in a net release of homocysteine, which is shown to be associated with cardiovascular disease and stroke. Furthermore, the extensive catabolism of dietary methionine by the intestine or by luminal microbes may result in a decrease in nutritional efficiency. Therefore, the regulation of SAA metabolism in the gut is not only nutritionally relevant, but also relevant to the overall health and well-being. The superiority of DL-2-hydroxy-4-methylthiobutyrate to DL-methionine in decreasing homocysteine production, alleviating stress responses, and reducing the first-pass intestinal metabolism of dietary methionine may provide a promising implication for nutritional strategies to manipulate SAA metabolism and thus to improve the nutrition and health status of animals and perhaps humans.

Majority of dietary glutamine is utilized in first pass in preterm infants

Glutamine is a conditionally essential amino acid for very low-birth weight infants by virtue of its ability to play an important role in several key metabolic processes of immune cells and enterocytes. Although glutamine is known to be used to a great extent, the exact splanchnic metabolism in enterally fed preterm infants is unknown. We hypothesized that preterm infants show a high splanchnic first-pass glutamine metabolism and the primary metabolic fate of glutamine is oxidation. Five preterm infants (mean + or - SD birth weight 1.07 + or - 0.22 kg and GA 29 + or - 2 wk) were studied by dual tracer ([U-(13)C]glutamine and [(15)N(2)]glutamine) cross-over techniques on two study days (at postnatal week 3 + or - 1 wk). Splanchnic and whole-body glutamine kinetics were assessed by plasma isotopic enrichment of [U-(13)C]glutamine and [(15)N(2)]glutamine and breath (13)CO(2) enrichments. Mean fractional first-pass glutamine uptake was 73 + or - 6% and 57 + or - 17% on the study days. The splanchnic tissues contributed for a large part (57 + or - 6%) to the total amount of labeled carbon from glutamine retrieved in expiratory air. Dietary glutamine is used to a great extent by the splanchnic tissues in preterm infants and its carbon skeleton has an important role as fuel source.

Effects ofdl-2-hydroxy-4-methylthiobutyrate on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability

The present study was conducted in a one-factorial arrangement to determine the effects ofdl-2-hydroxy-4-methylthiobutyrate (dl-HMTB) on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability. Barrows (n6; aged 35 d; weight 8·6 kg), implanted with arterial, portal, mesenteric and gastric catheters, were fed a diet containingdl-methionine (dl-MET) ordl-HMTB once hourly and infused intramesenterically with 1 %p-aminohippurate and intragastrically with [1-13C]methionine at 7·0 μmol/kg body weight per h. Arterial and portal blood samples were taken at hourly intervals until 6 h of tracer infusion and pigs was then killed for collection of muscle, intestine, liver and kidney samples. The net portal appearance of methionine, expressed as the fraction of ingested directly availablel-methionine, was higher (P < 0·05) in thedl-HMTB than in thedl-MET diet, and there was no difference (P = 0·26) in the fractional portal balance of [1-13C]methionine between the diets. [1-13C]methionine enrichment (tracer:tracee ratio; mol/100 mol amino acid) in the jejunum, arterial and portal plasma, liver, kidney and muscle was also not different (P>0·05) between the groups. Over the 6 h period after the start of feeding, the average concentration of citrulline both in the arterial and portal plasma was higher (P < 0·05) in thedl-HMTB than in thedl-MET group, and arterial plasma ornithine and taurine concentration was also higher (P < 0·05) in thedl-HMTB than in thedl-MET group. However, plasma urea concentration both in the arterial and portal vein was lower (P < 0·05) in thedl-HMTB than in thedl-MET group. These results suggested that the potential difference in the first-pass use of methionine by the intestine between thedl-HMTB anddl-MET diets might affect intestinal and systemic metabolism of other amino acids, which may provide new important insights into nutritional efficiency of different methionine sources.

Almost all enteral aspartate is taken up in first-pass metabolism in enterally fed preterm infants

BACKGROUND & AIMS

The intestine is a major site of amino acid metabolism, especially in neonates. Neonatal animals derive energy needed for metabolic processes from dietary glucose and amino acids. Rats were found to oxidize non-essential amino acids such as aspartate, glutamate and glutamine in the intestine at a high rate. We have previously found that glutamate and glucose are important sources of energy for the splanchnic tissues in fully fed preterm infants. However, no data are available on splanchnic aspartate metabolism in human preterm infants. In the present study we studied whole-body and splanchnic aspartate metabolism and determined the metabolic fate of aspartate.

METHODS

In eight, enterally fed, preterm infants (gestational age 31 weeks (wk)+/-3 SD, range: 26-34wk) splanchnic and whole-body aspartate kinetics were assessed by dual tracer ([U-(13)C]aspartate and [D(3)]aspartate) techniques.

RESULTS

Splanchnic first-pass aspartate uptake was almost complete (77+/-15%). Almost all (80+/-9%) of the (13)C administered as [U-(13)C]aspartate used in first-pass was recovered as CO(2) in expired breath.

CONCLUSION

The splanchnic tissues extract almost all of the dietary aspartate in preterm infants. The majority of the labeled carbon is recovered in expired breath, making it most likely that the sequestered carbon skeleton of aspartate is utilized for energy generation.

Threonine metabolism in the intestine of mice: loss of mucin 2 induces the threonine catabolic pathway

OBJECTIVES

Previous studies have shown that the intestine uses a major part of the dietary threonine intake for the synthesis of the structural component of the protective intestinal mucus layer, the secretory mucin Muc2. In this context, the high intestinal demand for dietary threonine probably results from its incorporation into secretory mucins rich in threonine residues. Therefore, we compared threonine utilization in the colon of Muc2 knockout (Muc2-/-) and wild-type (Muc2+/+) mice to investigate the intestinal dietary threonine metabolism in the absence of Muc2, which results in inflammation of the colon.

MATERIALS AND METHODS

Concentrations and isotopic enrichment of threonine were measured by gas chromatography-isotope ratio mass spectrometry in the serum, colon, and colonic content of mice given a bolus [U-(13)C]threonine enterally.

RESULTS

We retrieved 37.8% and 40.9% of dietary threonine in Muc2 +/+ and Muc2 -/- mice, respectively, either as free or incorporated threonine. There were no major differences in the availability and concentration of free or incorporated threonine recovered in both serum and colon in both types of mice. However, the Muc2 -/- mice did show overall significantly higher threonine oxidation rates compared with Muc2 +/+ mice.

CONCLUSIONS

In the absence of Muc2, dietary threonine is mainly used for constitutive protein synthesis or becomes a substrate for metabolic oxidation. This indicates that inflammation also requires high threonine amounts.

Sulfur amino acid deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs

We recently showed that the developing gut is a significant site of methionine transmethylation to homocysteine and transsulfuration to cysteine. We hypothesized that sulfur amino acid (SAA) deficiency would preferentially reduce mucosal growth and antioxidant function in neonatal pigs. Neonatal pigs were enterally fed a control or an SAA-free diet for 7 days, and then whole body methionine and cysteine kinetics were measured using an intravenous infusion of [1-(13)C;methyl-(2)H(3)]methionine and [(15)N]cysteine. Body weight gain and plasma methionine, cysteine, homocysteine, and taurine and total erythrocyte glutathione concentrations were markedly decreased (-46% to -85%) in SAA-free compared with control pigs. Whole body methionine and cysteine fluxes were reduced, yet methionine utilization for protein synthesis and methionine remethylation were relatively preserved at the expense of methionine transsulfuration, in response to SAA deficiency. Intestinal tissue concentrations of methionine and cysteine were markedly reduced and hepatic levels were maintained in SAA-free compared with control pigs. SAA deficiency increased the activity of methionine metabolic enzymes, i.e., methionine adenosyltransferase, methionine synthase, and cystathionine beta-synthase, and S-adenosylmethionine concentration in the jejunum, whereas methionine synthase activity increased and S-adenosylmethionine level decreased in the liver. Small intestine weight and protein and DNA mass were lower, whereas liver weight and DNA mass were unchanged, in SAA-free compared with control pigs. Dietary SAA deficiency induced small intestinal villus atrophy, lower goblet cell numbers, and Ki-67-positive proliferative crypt cells in association with lower tissue glutathione, especially in the jejunum. We conclude that SAA deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs.

Small intestinal MUC2 synthesis in human preterm infants

Mucin 2 (MUC2) is the structural component of the intestinal protective mucus layer, which contains high amounts of threonine in its peptide backbone. MUC2 synthesis rate might be a potential parameter for intestinal barrier function. In this study, we aimed to determine whether systemic threonine was used for small intestinal MUC2 synthesis and to calculate the MUC2 fractional synthetic rate (FSR) in human preterm infants. Seven preterm infants with an enterostomy following bowel resection for necrotizing enterocolitis received intravenous infusion of [U-(13)C]threonine to determine incorporation of systemic threonine into secreted MUC2 in intestinal outflow fluid. Small intestinal MUC2 was isolated using cesium chloride gradient ultracentrifugation and gravity gel filtration chromatography. MUC2-containing fractions were identified by SDS-PAGE/periodic acid-Schiff staining and Western blot analysis and were subsequently pooled. Isotopic enrichment of threonine, measured in MUC2 using gas chromatography isotopic ratio mass spectrometry, was used to calculate the FSR of MUC2. Systemically derived threonine was indeed incorporated into small intestinal MUC2. Median FSR of small intestinal MUC2 was 67.2 (44.3-103.9)% per day. Systemic threonine is rapidly incorporated into MUC2 in the small intestine of preterm infants, and thereby MUC2 has a very high synthesis rate.

Intestinal nitrogen recycling and utilization in health and disease

The role of intestinal microflora in digestive and metabolic processes has received increasing attention from researchers and clinicians. Both enterocytes and small intestine luminal microorganisms can degrade peptides and amino acids (AA). Further, enterocytes can utilize ammonia via glutamate, glutamine, citrulline, and urea synthesis, whereas luminal microbes will deaminate AA, hydrolyze luminal urea, and recycle this ammonia by synthesis of new microbial cells. Although, undoubtedly, some indispensable AA may arise from N cycling and microbial synthesis in the intestinal lumen, the actual net impact on protein nutrition status appears to be limited in humans and animals. Moreover, potential contributions of the recycled N as colonic luminal microbial proteins to AA in blood depend on colonic protein digestion and AA absorption. Finally, new evidence indicates that gut microbial metabolism may be enhanced by prebiotics and probiotics, with the prospects of new treatment paradigms for eliminating undesirable secondary N metabolites and ameliorating complications in whole-body N metabolism under the conditions of intestinal stress, liver disease, and kidney failure.

Glutamate is the major anaplerotic substrate in the tricarboxylic acid cycle of isolated rumen epithelial and duodenal mucosal cells from beef cattle

In this study, we aimed to determine the contribution of substrates to tricarboxylic acid (TCA) cycle fluxes in rumen epithelial cells (REC) and duodenal mucosal cells (DMC) isolated from Angus bulls (n = 6) fed either a 75% forage (HF) or 75% concentrate (HC) diet. In separate incubations, [(13)C(6)]glucose, [(13)C(5)]glutamate, [(13)C(5)]glutamine, [(13)C(6)]leucine, or [(13)C(5)]valine were added in increasing concentrations to basal media containing SCFA and a complete mixture of amino acids. Lactate, pyruvate, and TCA cycle intermediates were analyzed by GC-MS followed by (13)C-mass isotopomer distribution analysis. Glucose metabolism accounted for 10-19% of lactate flux in REC from HF-fed bulls compared with 27-39% in REC from HC and in DMC from bulls fed both diets (P < 0.05). For both cell types, as concentration increased, an increasing proportion (3-63%) of alpha-ketoglutarate flux derived from glutamate, whereas glutamine contributed <3% (P < 0.05). Although leucine and valine were catabolized to their respective keto-acids, these were not further metabolized to TCA cycle intermediates. Glucose, glutamine, leucine, and valine catabolism by ruminant gastrointestinal tract cells has been previously demonstrated, but in this study, their catabolism via the TCA cycle was limited. Further, although glutamate's contribution to TCA cycle fluxes was considerable, it was apparent that other substrates available in the media also contributed to the maintenance of TCA fluxes. Lastly, the results suggest that diet composition alters glucose, glutamate, and leucine catabolism by the TCA cycle of REC and DMC.

Amino acids: metabolism, functions, and nutrition

Recent years have witnessed the discovery that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of AA and their metabolites (e.g., nitric oxide, polyamines, glutathione, taurine, thyroid hormones, and serotonin) are required for the functions. However, elevated levels of AA and their products (e.g., ammonia, homocysteine, and asymmetric dimethylarginine) are pathogenic factors for neurological disorders, oxidative stress, and cardiovascular disease. Thus, an optimal balance among AA in the diet and circulation is crucial for whole body homeostasis. There is growing recognition that besides their role as building blocks of proteins and polypeptides, some AA regulate key metabolic pathways that are necessary for maintenance, growth, reproduction, and immunity. They are called functional AA, which include arginine, cysteine, glutamine, leucine, proline, and tryptophan. Dietary supplementation with one or a mixture of these AA may be beneficial for (1) ameliorating health problems at various stages of the life cycle (e.g., fetal growth restriction, neonatal morbidity and mortality, weaning-associated intestinal dysfunction and wasting syndrome, obesity, diabetes, cardiovascular disease, the metabolic syndrome, and infertility); (2) optimizing efficiency of metabolic transformations to enhance muscle growth, milk production, egg and meat quality and athletic performance, while preventing excess fat deposition and reducing adiposity. Thus, AA have important functions in both nutrition and health.