Amino Acid Flux Research Articles

Plasma Metabolic Signatures of Healthy Overweight Subjects Challenged With an Oral Glucose Tolerance Test.

Insulin secretion following ingestion of a carbohydrate load affects a multitude of metabolic pathways that simultaneously change direction and quantity of interorgan fluxes of sugars, lipids and amino acids. In the present study, we aimed at identifying markers associated with differential responses to an OGTT a population of healthy adults. By use of three metabolite profiling platforms, we assessed these postprandial responses of a total of 202 metabolites in plasma of 72 healthy volunteers undergoing comprehensive phenotyping and of which half enrolled into a weight-loss program over a three-month period. A standard oral glucose tolerance test (OGTT) served as dietary challenge test to identify changes in postprandial metabolite profiles. Despite classified as healthy according to WHO criteria, two discrete clusters (A and B) were identified based on the postprandial glucose profiles with a balanced distribution of volunteers based on gender and other measures. Cluster A individuals displayed 26% higher postprandial glucose levels, delayed glucose clearance and increased fasting plasma concentrations of more than 20 known biomarkers of insulin resistance and diabetes previously identified in large cohort studies. The volunteers identified by canonical postprandial responses that form cluster A may be called pre-pre-diabetics and defined as “at risk” for development of insulin resistance. Moreover, postprandial changes in selected fatty acids and complex lipids, bile acids, amino acids, acylcarnitines and sugars like mannose revealed marked differences in the responses seen in cluster A and cluster B individuals that sustained over the entire challenge test period of 240 min. Almost all metabolites, including glucose and insulin, returned to baseline values at the end of the test (at 240 min), except a variety of amino acids and here those that have been linked to diabetes development. Analysis of the corresponding metabolite profile in a fasting blood sample may therefore allow for early identification of these subjects at risk for insulin resistance without the need to undergo an OGTT.

Grafting improves tolerance to combined drought and heat stresses by modifying metabolism in citrus scion

Mediterranean basin and other citrus-growing areas, such as Florida or California, are among the most vulnerable regions to the impacts of global warming. Therefore, citrus will be likely subjected to increasing periods of water scarcity combined with high temperatures that will impair plant growth, development and yield. In citrus industry, grafting is used to improve varietal characteristics, such as abiotic stress tolerance. Previous research showed that under drought and heat stress conditions, Carrizo citrange ( Poncirus trifoliata × Citrus sinensis ) is a better rootstock than Cleopatra mandarin ( Citrus reshni ) because it induces a higher antioxidant activity on the scion, reducing oxidative damage and increasing plant tolerance. Here, it is shown that metabolic reconfiguration, including changes in carbohydrate and amino acid fluxes, are key responses for plant acclimation to stress conditions. Moreover, the importance of the rootstock on scion metabolic and hormonal responses to drought and heat stress combination has been addressed by using reciprocal grafting between Carrizo and Cleopatra genotypes. Thus, Carrizo as a rootstock improves the metabolic and hormonal response of Cleopatra scions to the stress combination by inducing the accumulation of protective compounds such as raffinose, galactinol and salicylic acid. In turn, Cleopatra as a rootstock reduces levels of raffinose, galactinol, proline, phenylalanine and tryptophan in Carrizo scions, which impairs plant tolerance to the stress combination. Our findings show the effect of the rootstock on scion metabolic response to stress combination and remark the importance of the rootstock in citrus plants exposed to harsh environmental conditions. • Drought and heat stress combination caused in citrus a specific metabolic response. • Rootstock influences metabolic responses of scion to abiotic stresses. • Proline is a key compound in citrus tolerance to drought and heat combination. • Carrizo rootstock improves metabolic response of scion to stress combination.

γ-Aminobutyric acid plays a key role in plant acclimation to a combination of high light and heat stress.

Plants are frequently subjected to different combinations of abiotic stresses, such as high light (HL) intensity, and elevated temperatures. These environmental conditions pose a threat to agriculture production, affecting photosynthesis, and decreasing yield. Metabolic responses of plants, such as alterations in carbohydrates and amino acid fluxes, play a key role in the successful acclimation of plants to different abiotic stresses, directing resources toward stress responses, and suppressing growth. Here we show that the primary metabolic response of Arabidopsis (Arabidopsis thaliana) plants to HL or heat stress (HS) is different from that of plants subjected to a combination of HL and HS (HL+HS). We further demonstrate that the combined stress results in a unique metabolic response that includes increased accumulation of sugars and amino acids coupled with decreased levels of metabolites participating in the tricarboxylic acid cycle. Among the amino acids exclusively accumulated during HL+HS, we identified the nonproteinogenic amino acid γ-aminobutyric acid (GABA). Analysis of different mutants deficient in GABA biosynthesis (GLUTAMATE DESCARBOXYLASE 3 [gad3]) as well as mutants impaired in autophagy (autophagy-related proteins 5 and 9 [atg5 and atg9]), revealed that GABA plays a key role in the acclimation of plants to HL+HS, potentially by promoting autophagy. Taken together, our findings identify a role for GABA in regulating plant responses to combined stress.

248 Maternal Nutrient Restriction During Mid-gestation Decreases Uteroplacental Release and Fetal Uptake of Essential Amino Acids in Sheep

Abstract To examine the effects of maternal nutrient restriction on net uteroplacental flux during mid-gestation, 14 singleton ewes (48.2 ± 4.0 kg body weight) were fed 100% (control; CON; n = 7) or 60% of nutrient requirements (restricted; RES; n = 7) from day 50–90 (mid-gestation). On day 90, uteroplacental blood flow was measured via Doppler ultrasonography and blood samples were collected from the femoral artery, uterine vein, umbilical artery, and umbilical vein. Blood vessel glucose and amino acids (AA) concentrations were measured and arterial-venous (uterine, AV; fetal, va) differences and net fluxes were calculated. Data were analyzed using the GLM procedure of SAS for effects of treatment. Nutrient restriction during mid-gestation did not influence (P ≥ 0.17) uterine or umbilical blood flows. Uterine AV and fetal va differences of total, essential, and nonessential AA were not influenced (P > 0.10) by nutrient restriction. Nutrient restriction decreased (P ≤ 0.05) uterine and uteroplacental release of total AA and tended to decrease (P = 0.07) total AA uptake by the fetus. Uteroplacental release and fetal uptake of essential AA were decreased (P = 0.03) with RES by 53.4% and 45%, respectively. Uterine and uteroplacental release of nonessential AA were decreased (P = 0.03) with RES but, fetal uptake was not affected (P = 0.14). Nutrient restriction decreased (P ≤ 0.04) fetal uptake of methionine, phenylalanine, threonine, and valine and tended to decrease (P ≤ 0.10) fetal uptake of isoleucine, leucine, and tryptophan. Umbilical artery glucose concentrations were 32% lesser (P = 0.01) with RES and RES tended to increase (P = 0.08) fetal glucose uptake. Nutrient restriction during mid-gestation altered uteroplacental and fetal flux of AA in the current study. The results may indicate that fetal metabolism shifts to adapt to reduced AA supply which results in greater glucose utilization.

Epithelial argininosuccinate synthetase is dispensable for intestinal regeneration and tumorigenesis

The epithelial signaling pathways involved in damage and regeneration, and neoplastic transformation are known to be similar. We noted upregulation of argininosuccinate synthetase (ASS1) in hyperproliferative intestinal epithelium. Since ASS1 leads to de novo synthesis of arginine, an important amino acid for the growth of intestinal epithelial cells, its upregulation can contribute to epithelial proliferation necessary to be sustained during oncogenic transformation and regeneration. Here we investigated the function of ASS1 in the gut epithelium during tissue regeneration and tumorigenesis, using intestinal epithelial conditional Ass1 knockout mice and organoids, and tissue specimens from colorectal cancer patients. We demonstrate that ASS1 is strongly expressed in the regenerating and Apc-mutated intestinal epithelium. Furthermore, we observe an arrest in amino acid flux of the urea cycle, which leads to an accumulation of intracellular arginine. However, loss of epithelial Ass1 does not lead to a reduction in proliferation or increase in apoptosis in vivo, also in mice fed an arginine-free diet. Epithelial loss of Ass1 seems to be compensated by altered arginine metabolism in other cell types and the liver.

Production of cooling water by Ti3C2Tx MXene interlayered forward osmosis membranes for post-combustion CO2 capture system

Forward osmosis (FO) technology has the potential to replace the trim cooler and to supply cooling water for a post-combustion CO2 capture system. Herein, a high-performance MXene (Ti3C2Tx) interlayered FO membrane was fabricated. Thanks to the ability of MXene to adjust the structures of substrate and polyamide, the MXene interlayered FO (MXene-FO) membrane showed improved permeability and selectivity in a monoethanolamine (MEA) draw solution. The performance of MXene-FO membrane was investigated at different membrane orientations and temperatures with amino acid/salt (AAS) solutions (taurine/KOH and β-alanine/KOH) as draw solutions. Because the osmotic pressures provided by AAS solutions (104.4 ± 0.3 bar for 3 mol/L taurine/KOH and 153.7 ± 0.2 bar for 5 mol/L β-alanine/KOH solutions) are higher than that of 5 mol/L MEA solution (93.0 ± 0.1 bar), the MXene-FO membrane exhibited higher water fluxes in AAS solutions. Besides, the good performance of the MXene-FO membrane was shown with the presence of small specific amino acid fluxes and specific KOH fluxes. To investigate the feasibility of using saline water as the feed solution, 3.5 wt% NaCl solution was applied and the results indicated that the MXene-FO membrane maintained stable water fluxes and small specific solute fluxes. This work demonstrates the potential of nanomaterials interlayered FO membranes for cooling water production in a post-combustion CO2 capture system.

Signatures and Clinical Significance of Amino Acid Flux in Sarcopenia: A Systematic Review and Meta-Analysis.

BackgroundDysregulation of amino acids is closely linked to the initiation and progression of sarcopenia. We summarized recent advancements in the studies of amino acid profiles in sarcopenia and systematically presented the clinical significance of amino acid flux in sarcopenia.MethodsWe systematically searched in MEDLINE, EMBASE, and Cochrane library from inception to June 1, 2021 to capture all studies examining metabolomics of sarcopenia. We used the following keywords: sarcopenia, metabonomics, metabolomics, amino acid profile, and mass spectrometry. Original articles comparing amino acid patterns between persons with and without sarcopenia were included. Two independent investigators independently completed title and abstract screening, data extraction, and quality evaluation. We used a random effects model to examine the association between amino acids levels and sarcopenia. Sensitivity analyses restricted the analyses to studies in which muscle mass was measured by bioelectrical impedance analysis. Study quality was evaluated according to the Agency for Healthcare Research and Quality (AHRQ) checklist.ResultsThe systematic research yielded six eligible articles, comprising 1,120 participants. Five studies used muscle mass in combination with physical performance and/or muscle strength as the criteria to diagnose sarcopenia, while one study used muscle mass as a diagnostic criterion alone. We found that the concentrations of branched-chain amino acids leucine (standardized mean difference [SMD] -1.249; 95% confidence interval [CI]: -2.275, -0.223, P = 0.02, I2 = 97.7%), isoleucine (SMD -1.077; 95% CI: -2.106, -0.049, P = 0.04, I2 = 97.8%), and aromatic amino acid tryptophan (SMD -0.923; 95% CI: -1.580, -0.265, P = 0.01, I2 = 89.9%) were significantly reduced in individuals with sarcopenia. Study results were robust in sensitivity analysis.ConclusionsThe homeostasis of amino acids is critical to maintaining muscle health. The profiles of amino acids might be useful biomarkers for the characterization of sarcopenia. Future studies are warranted to study the clinical significance of amino acids in the diagnosis and treatment of sarcopenia.

Anabolic effects of oral leucine-rich protein with and without β-hydroxybutyrate on muscle protein metabolism in a novel clinical model of systemic inflammation—a randomized crossover trial

β-lactoglobulin (BLG) stimulates muscle protein synthesis and β-hydroxybutyrate (BHB) inhibits muscle breakdown. Whether combining the 2 can additively attenuate disease-induced muscle loss is unknown. Based on previous observations of anticatabolic effects of protein and ketone bodies during inflammation, and using a novel model combining ongoing systemic inflammation, fasting, and immobilization, we tested whether the anticatabolic muscle response to oral amino acids is altered compared with control conditions, as well as whether coadministration of oral BHB and BLG further improves the muscle anabolic response. Muscle net balance (NBphe) was the primary outcome and intramyocellular signals were assessed. In a randomized crossover design, 8 young men underwent either preconditioning with LPS (prestudy day: 1 ng/kg, study day: 0.5 ng/kg) combined with a 36-h fast and bed rest to mimic catabolic inflammatory disease (CAT) or an overnight fast (control [CTR]) prior to isocaloric nutritional interventions on 3 occasions separated by ∼6 wk (range 42 to 83 d). NBphe increased similarly upon all conditions (interaction P=0.65). From comparable baseline rates, both Rdphe [muscle synthesis, median ratio (95% CI): 0.44 (0.23, 0.86) P=0.017] and Raphe [muscle breakdown, median ratio (95% CI): 0.46 (0.27, 0.78) P=0.005] decreased following BHB+BLG compared with BLG. BLG increased Rdphe more under CAT conditions compared with CTR (interaction P=0.02). CAT increased inflammation, energy expenditure, and lipid oxidation and decreased Rdphe and anabolic signaling [mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4EPB1) phosphorylation]. In contrast to our initial hypothesis, NBphe increased similarly following BLG during CAT and CTR conditions; CAT however, specifically stimulated the BLG-mediated increase in protein synthesis, whereas BHB coadministration did not affect NBphe, but distinctly dampened the BLG-induced increase in muscle amino acid fluxes thereby liberating circulating amino acids for anabolic actions elsewhere.

No effect of long-term soil warming on diffusive soil inorganic and organic nitrogen fluxes in a temperate forest soil

Climate warming affects nitrogen (N) cycling in forest soils, but implications for plant available N have remained unclear. We estimated in situ diffusive fluxes of amino acids and inorganic N in a temperate forest soil after 14 years of soil warming. Results from four sampling campaigns (n = 1152 microdialysis samples) during the growing season showed no effect of warming on diffusive N fluxes. Diffusive NH4+ fluxes increased from spring towards autumn while NO3− fluxes followed an opposite trend. Overall, the proportion of amino acids in the total diffusive N flux was low (13–30%) in this carbonate soil compared to other temperate and boreal forest soils.

Comprehensive metabolic amino acid flux analysis in critically ill patients

Amino acid (AA) metabolism is severely disturbed in critically ill ICU patients. To be able to make a more scientifically based decision on the type of protein or AA nutrition to deliver in ICU patients, comprehensive AA phenotyping with measurements of plasma concentrations and whole body production (WBP) is needed. Therefore, we studied ICU patients and matched control subjects using a novel pulse isotope method to obtain in-depth metabolic analysis. In 51 critically ill ICU patients (SOFA~6.6) and 49 healthy controls, we measured REE and body composition/phase-angle using BIA. In the postabsorptive state, we collected arterial (ized) blood for CRP and AA. Then, we administered an 8mL solution containing 18 stable AA tracers as a pulse and calculated WBP. Enrichments: LC-MS/MS and statistics: t-test, ANCOVA. Compared to healthy, critically ill ICU patients had lower phase-angle (p<0.00001), and higher CRP (p<0.0001). Most AA concentrations were lower in ICU patients (p<0.0001), except tau-methylhistidine and phenylalanine. WBP of most AA were significantly (p<0.0001) higher with increases in glutamate (160%), glutamine (46%), and essential AA. Remarkably, net protein breakdown was lower. There were only weak relationships between AA concentrations and WBP. Critically ill ICU patients (SOFA 8-16) had lower values for phase angle (p=0.0005) and small reductions of most plasma AA concentrations, but higher tau-methylhistidine (p=0.0223) and hydroxyproline (p=0.0028). Remarkably, the WBP of glutamate and glutamine were lower (p<0.05), as was their clearance, but WBP of tau-methylhistidine (p=0.0215) and hydroxyproline (p=0.0028) were higher. Our study in critically ill ICU patients shows that comprehensive metabolic phenotyping was able to reveal severe disturbances in specific AA pathways, in a disease severity dependent way. This information may guide improving nutritional compositions to improve the health of the critically ill patient. CLINICAL TRIAL REGISTRY: Data are from the baseline measurements of study NCT02770092 (URL: https://clinicaltrials.gov/ct2/show/NCT02770092) and NCT03628365 (URL: https://clinicaltrials.gov/ct2/show/NCT03628365).

Concurrent overexpression of amino acid permease

Using pea as our model crop, we sought to understand the regulatory control over the import of sugars and amino acids into the developing seeds and its importance for seed yield and quality. Transgenic peas simultaneously overexpressing a sucrose transporter and an amino acid transporter were developed. Pod walls, seed coats, and cotyledons were analysed separately, as well as leaves subtending developing pods. Sucrose, starch, protein, free amino acids, and endogenous cytokinins were measured during development. Temporal gene expression analyses (RT-qPCR) of amino acid (AAP), sucrose (SUT), and SWEET transporter family members, and those from cell wall invertase, cytokinin biosynthetic (IPT) and degradation (CKX) gene families indicated a strong effect of the transgenes on gene expression. In seed coats of the double transgenics, increased content and prolonged presence of cytokinin was particularly noticeable. The transgenes effectively promoted transition of young sink leaves into source leaves. We suggest the increased flux of sucrose and amino acids from source to sink, along with increased interaction between cytokinin and cell wall invertase in developing seed coats led to enhanced sink activity, resulting in higher cotyledon sucrose at process pea harvest, and increased seed number and protein content at maturity.

Comprehensive amino acid flux analysis in the post-acute phase of critically ill post-surgery patients, compared to healthy matched subjects

Rationale: ESPEN guidelines recommend administering 1.3 g/kg /d protein to stabilized critically ill patients, although insight in the specific perturbations in protein and amino acid metabolism of this population remain underexplored. Comprehensive metabolic flux analysis is a novel approach to perform metabolic phenotyping of ICU patients.

Multi-modular engineering of Saccharomyces cerevisiae for high-titre production of tyrosol and salidroside.

Tyrosol and its glycosylated product salidroside are important ingredients in pharmaceuticals, nutraceuticals and cosmetics. Despite the ability of Saccharomyces cerevisiae to naturally synthesize tyrosol, high yield from de novo synthesis remains a challenge. Here, we used metabolic engineering strategies to construct S. cerevisiae strains for high-level production of tyrosol and salidroside from glucose. First, tyrosol production was unlocked from feedback inhibition. Then, transketolase and ribose-5-phosphate ketol-isomerase were overexpressed to balance the supply of precursors. Next, chorismate synthase and chorismate mutase were overexpressed to maximize the aromatic amino acid flux towards tyrosol synthesis. Finally, the competing pathway was knocked out to further direct the carbon flux into tyrosol synthesis. Through a combination of these interventions, tyrosol titres reached 702.30 ± 0.41 mg l-1 in shake flasks, which were approximately 26-fold greater than that of the WT strain. RrU8GT33 from Rhodiola rosea was also applied to cells and maximized salidroside production from tyrosol in S. cerevisiae. Salidroside titres of 1575.45 ± 19.35 mg l-1 were accomplished in shake flasks. Furthermore, titres of 9.90 ± 0.06 g l-1 of tyrosol and 26.55 ± 0.43 g l-1 of salidroside were achieved in 5 l bioreactors, both are the highest titres reported to date. The synergistic engineering strategies presented in this study could be further applied to increase the production of high value-added aromatic compounds derived from the aromatic amino acid biosynthesis pathway in S. cerevisiae.

Role of O-linked N-acetylglucosamine in the homeostasis of metabolic organs, and its potential links with diabetes and its complications.

Recent studies using genetically manipulated mouse models have shown the pivotal role of O‐linked N‐acetylglucosamine modification (O‐GlcNAcylation) in the metabolism of multiple organs. The molecular mechanism involves the sensing of glucose flux by the hexosamine biosynthesis pathway, which leads to the adjustment of cellular metabolism to protect against changes in the environment of each organ through O‐GlcNAcylation. More recently, not only glucose, but also fluxes of amino acids and fatty acids have been reported to induce O‐GlcNAcylation, affecting multiple cellular processes. In this review, we discuss how O‐GlcNAcylation maintains homeostasis in organs that are affected by diabetes mellitus: skeletal muscle, adipose tissue, liver and pancreatic β‐cells. Furthermore, we discuss the importance of O‐GlcNAcylation in the pathogenesis of diabetic complications. By elucidating the molecular mechanisms whereby cellular homeostasis is maintained, despite changes in metabolic flux, these studies might provide new targets for the treatment and prevention of diabetes and its complications.

ITRAQ-based quantitative phosphoproteomics provides insights into the metabolic and physiological responses of a carnivorous marine fish (Nibea albiflora) fed a linseed oil-rich diet

The limited production of fish oil (FO) cannot meet the increasing demand of the aqua-feed industry. Accordingly, the replacement of FO with sustainable alternatives such as vegetable oils has become imperative. Linseed oil (LO), which has an abundance of α-linolenic acid (ALA), is a promising FO alternative. Nevertheless, high dietary LO inclusion generally causes abnormal hepatic lipid accumulation and growth retardation across carnivorous marine fish species. Previous studies have attempted to elucidate the mechanisms with regard to gene and protein levels; however, little is known about posttranslational modifications. In the present study, iTRAQ phosphoproteomics was conducted to investigate the metabolic and physiological responses of the yellow drum (Nibea albiflora) fed an LO-rich or FO-rich diet. Identification and analyses of differentially abundant phosphorylated proteins in hepatic tissue were conducted with parallel reaction monitoring (PRM) verification in reference to the genome sequences of the yellow drum. Among the specific peptides that passed the threshold, 203 hyperphosphorylated and 182 hypophosphorylated peptides were identified. Several functional categories and pathways were associated with these proteins that were mostly related to lipid, amino acid, and carbohydrate metabolism. In particular, the AMP-activated protein kinase (AMPK) pathway, mechanistic target of rapamycin (mTOR) pathway, and citrate (TCA) cycle are discussed. Statement of significanceDietary LO caused abnormal hepatic lipid accumulation and retarded growth performance. The abnormal hepatic lipid accumulation in the fish fed the LO-rich diet might have arisen from AMPK signaling pathway-mediated de novo synthesis of fatty acids and the synthesis of phospholipids. An mTOR signaling pathway-mediated reduction in ribosome protein synthesis could have been a factor in the growth retardation. Changes in UPS and autophagy proteins phosphorylation and aminotransferase activity levels were related to the flux of amino acids into the TCA cycle for ATP production. The results of PRM were highly correlated with the phosphoproteomics results. These findings will contribute to a better understanding of the mechanisms of abnormal hepatic lipid accumulation and retarded growth performance in carnivorous marine fish fed linseed oil-rich diets.

Muscle protein turnover and low-protein diets in patients with chronic kidney disease.

Adaptation to a low-protein diet (LPD) involves a reduction in the rate of amino acid (AA) flux and oxidation, leading to more efficient use of dietary AA and reduced ureagenesis. Of note, the concept of 'adaptation' to low-protein intakes has been separated from the concept of 'accommodation', the latter term implying a decrease in protein synthesis, with development of wasting, when dietary protein intake becomes inadequate, i.e. beyond the limits of the adaptive mechanisms. Acidosis, insulin resistance and inflammation are recognized mechanisms that can increase protein degradation and can impair the ability to activate an adaptive response when an LPD is prescribed in a chronic kidney disease (CKD) patient. Current evidence shows that, in the short term, clinically stable patients with CKD Stages 3-5 can efficiently adapt their muscle protein turnover to an LPD containing 0.55-0.6 g protein/kg or a supplemented very-low-protein diet (VLPD) by decreasing muscle protein degradation and increasing the efficiency of muscle protein turnover. Recent long-term randomized clinical trials on supplemented VLPDs in patients with CKD have shown a very good safety profile, suggesting that observations shown by short-term studies on muscle protein turnover can be extrapolated to the long-term period.

AMPK-mTOR pathway is involved in glucose-modulated amino acid sensing and utilization in the mammary glands of lactating goats

BackgroundThe local supply of energy-yielding nutrients such as glucose seems to affect the synthesis of milk components in the mammary gland (MG). Thus, our study was conducted to investigate the effects of locally available MG glucose supply (LMGS) on amino acid (AA) sensing and utilization in the MG of lactating dairy goats. Six dosages of glucose (0, 20, 40, 60, 80, and 100 g/d) were infused into the MG through the external pudendal artery to investigate the dose-dependent changes in mammary AA uptake and utilization (Exp.1) and the changes in mRNA and protein expression of the AMPK-mTOR pathway (Expt.2).ResultsIn Exp.1, total milk AA concentration was highest when goats were infused with 60 g/d glucose, but lower when goats were infused with 0 and 100 g/d glucose. Increasing LMGS quadratically changed the percentages of αS2-casein and α-lactalbumin in milk protein, which increased with infusions from 0 to 60 g/d glucose and then decreased with infusions between 60 and 100 g/d glucose. The LMGS changed the AA availability and intramammary gland AA utilization, as reflected by the mammary AA flux indexes. In Exp.2, the mRNA expression of LALBA in the MG increased quadratically with increasing LMGS, with the highest expression at dose of 60 g/d glucose. A high glucose dosage (100 g/d) activated the general control nonderepressible 2 kinase, an intracellular sensor of AA status, resulting in a reduced total milk AA concentration.ConclusionsOur new findings suggest that the lactating MG in dairy goats may be affected by LMGS through regulation of the AA sensory pathway, AA utilization and protein synthesis, all being driven by the AMPK-mTOR pathway.

Net absorption and liver metabolism of amino acids and heat production of portal-drained viscera and liver in multiparous sows during transition and lactation

BackgroundDetermination of nutrient requirements in the late gestating and lactating sows is essential to optimize sow productivity. The objectives of the present study were to quantify amino acid (AA) fluxes and heat production across portal-drained viscera (PDV) and liver in multiparous sows during transition and lactation.MethodsEight second parity sows were fitted with indwelling catheters in the femoral artery and in the mesenteric, portal and hepatic veins. Eight hourly sets of blood samples were taken starting 0.5 h before feeding at − 10, − 3, + 3, and + 17 d in milk (DIM). Blood gases, plasma metabolites and apparent total tract digestibility (ATTD) of nutrients were measured.ResultsFeed intake, the ATTD of DM, energy, nitrogen, fat and crude fiber changed with DIM (P < 0.001). Except for Glu, O2, and urea, all net portal fluxes were positive, and all were affected by DIM (P < 0.05) and by sampling time (P < 0.01). Compared with pre partum levels, net portal uptake of AA was 3-63% lower at + 3 DIM but 40-100% higher at + 17 DIM. Net portal fluxes of AA peaked at 1.5 to 2.5 h after feeding except for Glu, and they were positively correlated with changes in sow feed intake across DIM. The net portal recovery was low for Met (49%), Thr (54%), and His (54%) and high for the remaining essential AA (63-69%) and none of them differed across DIM. Net hepatic uptake (i.e. hepatic oxidation) of Lys, Thr, Ile, Leu and Phe peaked at 0.5 to 2.5 h after feeding, whereas uptake of Trp, Val, and His was constant, while that of Met was close to zero.ConclusionThe net portal recovery was substantially lower for Met, Thr, and His than the remaining essential AA. Hepatic AA oxidation peaks 0.5 to 2.5 h after feeding. The heat production in PDV and liver was approximately two-fold higher at peak lactation compared to other stages. The study suggests that lysine was the limiting AA in peak lactation but not in early lactation.

Casein hydrolysate supplementation in low-crude protein diets increases feed intake and nitrogen retention without affecting nitrogen utilization of growing pigs.

An extreme reduction of the crude protein (CP) level in diets, even balanced with amino acids (AAs), is detrimental for intestinal nitrogen (N) metabolism and the growth of pigs. This study investigated the effects of casein hydrolysate supplementation in low-CP diets on growth performance, N balance, and intestinal N supply for pigs. A total of 24 barrows were randomly assigned to one of three dietary treatments of 160 g kg-1 CP (control), 130 g kg-1 CP (LAA), and 130 g kg-1 CP plus casein hydrolysate (LCH) for 28 days. The LCH group had a higher average daily feed intake (ADFI) and average daily gain (ADG) than the LAA group, and a higher ADG than the control (P < 0.05). Compared with the control, both the LAA and LCH decreased N intake, serum urea N, fecal N, and N excretion, and increased apparent N availability, with LCH having higher N intake and N retention than LAA group (P < 0.05). Compared with LAA, LCH increased ileal fluxes of CP and AA (P < 0.05), and with values similar to those of the control. However, ileal flows of CP and AA were similar between LCH and LAA, both of which were lower than those in the control (P < 0.05). Using protein hydrolysate to replace some crystalline AAs in low-CP diets increased feed intake, N retention and ADG without affecting N utilization. These findings point to the important impact of protein hydrolysate supplementation on improving growth for pigs fed low-CP diets. © 2019 Society of Chemical Industry.

Absorptive transport of amino acids by the rat colon.

The capacity of the colon to absorb microbially produced amino acids (AAs) and the underlying mechanisms of AA transport are incompletely defined. We measured the profile of 16 fecal AAs along the rat ceco-colonic axis and compared unidirectional absorptive AA fluxes across mucosal tissues isolated from the rat jejunum, cecum, and proximal colon using an Ussing chamber approach, in conjunction with 1H-NMR and ultra-performance liquid chromatography-mass spectrometry chemical analyses. Passage of stool from cecum to midcolon was associated with segment-specific changes in fecal AA composition and a decrease in total AA content. Simultaneous measurement of up to 16 AA fluxes under native luminal conditions, with correction for endogenous AA release, demonstrated absorptive transfer of AAs across the cecum and proximal colon at rates comparable (30-80%) to those across the jejunum, with significant Na+-dependent and H+-stimulated components. Expression profiling of 30 major AA transporter genes by quantitative PCR revealed comparatively high levels of transcripts for 20 AA transporters in the cecum and/or colon, with the levels of 12 exceeding those in the small intestine. Our results suggest a more detailed model of major apical and basolateral AA transporters in rat colonocytes and provide evidence for a previously unappreciated transfer of AAs across the colonic epithelium that could link the prodigious metabolic capacities of the luminal microbiota, the colonocytes, and the body tissues.NEW & NOTEWORTHY This study provides evidence for a previously unappreciated transfer of microbially generated amino acids across the colonic epithelium under physiological conditions that could link the prodigious metabolic capacities of the luminal microbiota, the colonocytes, and the body tissues. The segment-specific expression of at least 20 amino acid transporter genes along the colon provides a detailed mechanistic basis for uniport, heteroexchange, Na+-cotransport, and H+-cotransport components of colonic amino acid absorption.