Nutritional consequences of interspecies differences in arginine and lysine metabolism

Dietary lysine requirement for 7-16 kg pigs fed wheat-corn-soybean meal-based diets

Two experiments were conducted to determine the lysine requirement of weaned pigs [Duroc × (Yorkshire × Landrace)] with an average initial BW of 7 kg and fed wheat-corn-soybean meal-based diets. The experiments were conducted for 21 days during which piglets had free access to diets and water. Average daily gain (ADG), average daily feed intake (ADFI) and gain to feed ratio (G:F) were determined on day 7, 14 and 21. Blood samples were collected on day 0 and 14 to determine plasma urea nitrogen (PUN) concentration. In experiment 1, 96 weaned pigs were housed four per pen and allocated to four dietary treatments with six replicates per treatment. The diets contained 0.99%, 1.23%, 1.51% and 1.81% standardized ileal digestible (SID) lysine, respectively, corrected analysed values. The rest of the AA were provided to meet the ideal AA ratio for protein accretion. Increasing dietary lysine content linearly increased (p < 0.05) ADG and G:F. In experiment 2, 90 piglets were housed three per pen and allocated to five dietary treatments with six replicates per treatment. The five diets contained 1.03%, 1.25%, 1.31%, 1.36% and 1.51% SID lysine, respectively, corrected analysed values. Increasing dietary lysine content linearly increased (p < 0.05) G:F, linearly decreased (p < 0.05) day-14 PUN and quadratically (p < 0.05) increased ADG and ADFI. The ADG data from experiment 2 were subjected to linear and quadratic broken-lines regression analyses, and the SID lysine requirement was determined to be 1.29% and 1.34% respectively. On average, optimal dietary SID lysine content for optimal growth of 7-16 kg weaned piglets fed wheat-corn-SBM-based diets was estimated to be 1.32%; at this level, the ADG and ADFI were 444 and 560 g, respectively, thus representing an SID lysine requirement, expressed on daily intake basis as, 7.4 g/day or 16.76 mg/g gain.

Untargeted metabolomics approach for unraveling robust biomarkers of nutritional status in fasted gilthead sea bream (Sparus aurata)

A metabolomic study has been performed to identify sensitive and robust biomarkers of malnutrition in farmed fish, using gilthead sea bream (Sparus aurata) as a model. The metabolomic fingerprinting of serum from fasted fish was assessed by means of ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. More than 15,000 different m/z ions were detected and Partial Least Squares–Discriminant analysis allowed a clear differentiation between the two experimental groups (fed and 10-day fasted fish) with more than 90% of total variance explained by the two first components. The most significant metabolites (up to 45) were elucidated on the basis of their tandem mass spectra with a broad representation of amino acids, oligopeptides, urea cycle metabolites, L-carnitine-related metabolites, glutathione-related metabolites, fatty acids, lysophosphatidic acids, phosphatidylcholines as well as biotin- and noradrenaline-related metabolites. This untargeted approach highlighted important adaptive responses in energy and oxidative metabolism, contributing to identify robust and nutritionally-regulated biomarkers of health and metabolic condition that will serve to assess the welfare status of farmed fish.

Safety and Effectiveness of Arginine in Adults

l-Arginine (Arg) appears to have a beneficial effect on the regulation of nutrient metabolism to enhance lean tissue deposition and on insulin resistance in humans. The observed safe level for oral administration of Arg is ∼20 g/d, but higher levels have been tested in short-term studies without serious adverse effects; however, more data are needed in both animal models and humans to fully evaluate safety as well as efficacy. The primary objective of this review is to summarize the current knowledge of the safety, pharmacokinetics, and effectiveness of oral Arg in adults. Arg supplementation has been used safely in vulnerable populations, such as pregnant women, preterm infants, and individuals with cystic fibrosis. Several recent studies have shown beneficial effects of Arg in individuals with obesity, insulin resistance, and diabetes. Collectively, the data suggest that Arg supplementation is a safe and generally well-tolerated nutriceutical that may improve metabolic profiles in humans.

Di- and tripeptide transport in vertebrates: the contribution of teleost fish models

Solute Carrier 15 (SLC15) family, alias H⁺-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from 'non-conventional' animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural-functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.

Plasma metabolomics indicates metabolic perturbations in low birth weight piglets supplemented with arginine

Large profit losses in the swine industry can be attributed to morbidity and mortality of piglets before weaning, especially in the low birth weight (LBW) piglet. Recent evidence suggests sow's milk contains insufficient concentrations of Arg to support optimal growth and health of piglets. Therefore, our objective was to assess global metabolomic profiles and the potential for Arg supplementation to promote growth of LBW (≤0.9 kg BW) and average birth weight (ABW; 1.3 to 1.5 kg BW) piglets. Piglets were selected in littermate pairs at processing to receive either Arg or an isonitrogenous control (Ala) and weighed daily to assess growth rate, and blood was collected at approximately 16 d of age for metabolomics analysis. In terms of growth, LBW and ABW piglets supplemented with Arg weighed 22.3 and 12.7% less, respectively, at d 16 compared with Ala-supplemented piglets of the same birth weight group. Overall, differences ( < 0.05) were observed among treatments for metabolic pathways involving energy (i.e., tricarboxylic acid cycle intermediates), AA, nucleotides, and fatty acids. Increased nucleotide turnover, indicative of an increase in DNA damage and cell death, was particularly noted in the LBW piglet. However, Arg supplementation reduced these effects to levels comparable to those observed in ABW piglets. Moreover, changes in glucose metabolism suggested a compromised ability to extract energy from dietary sources may have occurred in the LBW piglet, but these effects were partially recovered by Arg supplementation. We conclude that a reduction in the growth potential of LBW piglets may be associated with alterations in multiple metabolic pathways, and further reduction due to Arg supplementation may have resulted from perturbations in multiple metabolic pathways.

Controlled trial of whole body protein synthesis and plasma amino acid concentrations in yearling horses fed graded amounts of lysine

Lysine has been reported as the first limiting amino acid in typical equine diets. Indicator amino acid oxidation (IAAO) has become the standard method for determining amino acid requirements in other species, but prior to this study, it has not been used to determine equine requirements. The aim of this study was to evaluate whole body protein synthesis and plasma and muscle amino acid concentrations in response to graded levels of lysine intake in yearling horses. Six Thoroughbred colts (358 ± 5 kg) were fed each of six treatment lysine intakes ranging from 76 to 136 mg/kg body weight/day. Blood samples were taken before and 90 min after the morning concentrate meal. Gluteal muscle biopsies were taken ~100 min after the morning concentrate meal. The next day, whole body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [(13)C] sodium bicarbonate followed by a 6 h primed, constant infusion of [1-(13)C] phenylalanine. Plasma lysine concentrations increased linearly (P <0.05) at both the 0 and 90 min time points with increasing lysine intakes. Free muscle asparagine, aspartate, arginine, glutamine, lysine, taurine and tryptophan concentrations responded quadratically to lysine intake (P <0.05). Phenylalanine kinetics did not differ between treatment intakes (P > 0.10). A broken line analysis of lysine intake and phenylalanine oxidation failed to yield a breakpoint from which to determine a lysine requirement. These diets may have been limiting in an amino acid other than lysine, underscoring the lack of data concerning amino acid requirements and bioavailability data in the horse.

l-Arginine Supplementation Alleviates Postprandial Endothelial Dysfunction When Baseline Fasting Plasma Arginine Concentration Is Low: A Randomized Controlled Trial in Healthy Overweight Adults with Cardiometabolic Risk Factors

BACKGROUND

Vascular endothelial dysfunction, the hallmark of early atherosclerosis, is induced transiently by a high-fat meal. High doses of free l-arginine supplements reduce fasting endothelial dysfunction.

OBJECTIVE

We sought to determine the effects of a low dose of a sustained-release (SR) l-arginine supplement on postprandial endothelial function in healthy overweight adults with cardiometabolic risk factors and to investigate whether this effect may vary by baseline arginine status.

METHODS

In a randomized, double-blind, 2-period crossover, placebo-controlled trial (4-wk treatment, 4-wk washout), we compared the effects of 1.5 g SR-l-arginine 3 times/d (4.5 g/d) with placebo in 33 healthy overweight adults [body mass index (BMI, in kg/m(2)): 25 to >30] with the hypertriglyceridemic waist (HTW) phenotype [plasma triglycerides > 150 mg/dL; waist circumference > 94 cm (men) or > 80 cm (women)]. The main outcome variable tested was postprandial endothelial function after a high-fat meal (900 kcal), as evaluated by use of flow-mediated dilation (FMD) and Framingham reactive hyperemia index (fRHI), after each treatment. By use of subgroup analysis, we determined whether the effect was related to the baseline plasma arginine concentration.

RESULTS

In the total population, the effects of SR-arginine supplementation on postprandial endothelial function were mixed and largely varied with baseline fasting arginine concentration (P-interaction < 0.05). In the lower half of the population (below the median of 78.2 μmol arginine/L plasma), but not the upper half, SR-arginine supplementation attenuated the postprandial decrease in both FMD (29% decrease with SR-arginine compared with 50% decrease with placebo) and fRHI (5% increase with SR-arginine compared with 49% decrease with placebo), resulting in significantly higher mean ± SEM values with SR-arginine (FMD: 4.0% ± 0.40%; fRHI: 0.41 ± 0.069) than placebo (FMD: 2.9% ± 0.31%; fRHI: 0.21 ± 0.060) at the end of the postprandial period (P < 0.05).

CONCLUSIONS

Supplementation with low-dose SR-arginine alleviates postprandial endothelial dysfunction in healthy HTW adults when the baseline plasma arginine concentration is relatively low. The benefits of arginine supplementation may be linked to a lower ability to mobilize endogenous arginine for nitric oxide synthesis during a postprandial challenge. This trial was registered at clinicaltrials.gov as NCT02354794.

De Novo Assembly and Comparative Transcriptome Analysis Provide Insight into Lysine Biosynthesis in Toona sinensis Roem

Toona sinensis Roem is a popular leafy vegetable in Chinese cuisine and is also used as a traditional Chinese medicine. In this study, leaf samples were collected from the same plant on two development stages and then used for high-throughput Illumina RNA-sequencing (RNA-Seq). 125,884 transcripts and 54,628 unigenes were obtained through de novo assembly. A total of 25,570 could be annotated with known biological functions, which indicated that the T. sinensis leaves and shoots were undergoing multiple developmental processes especially for active metabolic processes. Analysis of differentially expressed unigenes between the two libraries showed that the lysine biosynthesis was an enriched KEGG pathway, and candidate genes involved in the lysine biosynthesis pathway in T. sinensis leaves and shoots were identified. Our results provide a primary analysis of the gene expression files of T. sinensis leaf and shoot on different development stages and afford a valuable resource for genetic and genomic research on plant lysine biosynthesis.

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.

Recapitulation of metabolic defects in a model of propionic acidemia using patient-derived primary hepatocytes

BACKGROUND

Propionic acidemia (PA) is a disorder of intermediary metabolism with defects in the alpha or beta subunits of propionyl CoA carboxylase (PCCA and PCCB respectively) enzyme. We previously described a liver culture system that uses liver-derived hemodynamic blood flow and transport parameters to restore and maintain primary human hepatocyte biology and metabolism utilizing physiologically relevant milieu concentrations.

METHODS

In this study, primary hepatocytes isolated from the explanted liver of an 8-year-old PA patient were cultured in the liver system for 10 days and evaluated for retention of differentiated polarized morphology. The expression of PCCA and PCCB was assessed at a gene and protein level relative to healthy donor controls. Ammonia and urea levels were measured in the presence and absence of amino acid supplements to assess the metabolic consequences of branched-chain amino acid metabolism in this disease.

RESULTS

Primary hepatocytes from the PA patient maintained a differentiated polarized morphology (peripheral actin staining) over 10 days of culture in the system. We noted lower levels of PCCA and PCCB relative to normal healthy controls at the mRNA and protein level. Supplementation of branched-chain amino acids, isoleucine (5mM) and valine (5mM) in the medium, resulted in increased ammonia and decreased urea in the PA patient hepatocyte system, but no such response was seen in healthy hepatocytes or patient-derived fibroblasts.

CONCLUSIONS

We demonstrate for the first time the successful culture of PA patient-derived primary hepatocytes in a differentiated state, that stably retain the PCCA and PCCB enzyme defects at a gene and protein level. Phenotypic response of the system to an increased load of branched-chain amino acids, not possible with fibroblasts, underscores the utility of this system in the better understanding of the molecular pathophysiology of PA and examining the effectiveness of potential therapeutic agents in the most relevant tissue.

Establishing an essential amino acid profile for maintenance in poultry using deletion method

This study aimed to estimate the essential amino acid profile and the ideal ratio for the maintenance of poultry by deletion method. A nitrogen balance (NB) trial was conducted using 198 adult roosters, housed individually in metabolic cages. The treatments were 33 purified diets being 11 diets with an amino acid mixture providing high protein intake of 500 mg N/BWkg (0.75) per day, 11 diets providing medium protein intake of 250 mg N/BWkg (0.75) per day (in each diet, one amino acid tested was diluted 50%) and 11 diets providing low protein intake of 125 mg N/BWkg (0.75) per day (made by omitting the amino acid tested). Each treatment had six replicates. After 48 h of fasting receiving water plus sucrose, the roosters were fed 40 g of the diets by tube once a day for 3 days. The excreta were collected within 72 h after the first feeding. The diets and excreta were analysed for nitrogen content. For each amino acid studied, a linear regression was fitted by NB and amino acid intake (AAI). The maintenance requirements were estimated as the AAI to maintain the NB equal to zero. The daily amino acid requirements for maintenance were estimated to be Lys 11, Met 29, Thr 23, Trp 5, Arg 50, Val 29, His 6, Gly 54, Phe 49, Leu 78 and Ile 21 mg/BWkg (0.75) per day. Therefore, the amino acid ratio for maintenance was concluded to be Lys 100, Met 276, Thr 220, Trp 48, Arg 467, Val 275, His 60, Gly 511, Phe 467, Leu 735 and Ile 198% independent of the scale. The essential amino acid profile and the ideal ratio for the maintenance of poultry estimated in this study contributed to improve the factorial model for estimating essential amino acid requirements for poultry.

Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review

BACKGROUND

Feline herpesvirus 1 is a highly contagious virus that affects many cats. Virus infection presents with flu-like signs and irritation of ocular and nasal regions. While cats can recover from active infections without medical treatment, examination by a veterinarian is recommended. Lysine supplementation appears to be a popular intervention (recommended by > 90 % of veterinarians in cat hospitals). We investigated the scientific merit of lysine supplementation by systematically reviewing all relevant literature.

METHODS

NCBI's PubMed database was used to search for published work on lysine and feline herpesvirus 1, as well as lysine and human herpesvirus 1. Seven studies on lysine and feline herpesvirus 1 (two in vitro studies and 5 studies with cats), and 10 publications on lysine and human herpesvirus 1 (three in vitro studies and 7 clinical trials) were included for qualitative analysis.

RESULTS

There is evidence at multiple levels that lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats. Lysine does not have any antiviral properties, but is believed to act by lowering arginine levels. However, lysine does not antagonize arginine in cats, and evidence that low intracellular arginine concentrations would inhibit viral replication is lacking. Furthermore, lowering arginine levels is highly undesirable since cats cannot synthesize this amino acid themselves. Arginine deficiency will result in hyperammonemia, which may be fatal. In vitro studies with feline herpesvirus 1 showed that lysine has no effect on the replication kinetics of the virus. Finally, and most importantly, several clinical studies with cats have shown that lysine is not effective for the prevention or the treatment of feline herpesvirus 1 infection, and some even reported increased infection frequency and disease severity in cats receiving lysine supplementation.

CONCLUSION

We recommend an immediate stop of lysine supplementation because of the complete lack of any scientific evidence for its efficacy.

Dietary arginine requirements for growth are dependent on the rate of citrulline production in mice

BACKGROUND

In many species, including humans, arginine is considered a semiessential amino acid because under certain conditions endogenous synthesis cannot meet its demand. The requirements of arginine for growth in mice are ill defined and seem to vary depending on the genetic background of the mice.

OBJECTIVE

The objective of this study was to determine the metabolic and molecular basis for the requirement of arginine in 2 mouse strains.

METHODS

Institute of Cancer Research (ICR) and C57BL/6 (BL6) male mice were fed arginine-free or arginine-sufficient diets (Expt. 1) or 1 of 7 diets with increasing arginine concentration (from 0- to 8-g/kg diet, Expt. 2) between day 24 and 42 of life to determine the arginine requirements for growth. Citrulline production and "de novo" arginine synthesis were measured with use of stable isotopes, and arginine requirements were determined by breakpoint analysis and enzyme expression by reverse transcriptase-polymerase chain reaction.

RESULTS

In Expt. 1, ICR mice grew at the same rate regardless of the arginine concentration of the diet (mean ± SE: 0.66 ± 0.04 g/d, P = 0.80), but BL6 mice had a reduced growth rate when fed the arginine-free diet (0.25 ± 0.02 g/d, P < 0.001) compared to the 8-g arginine/kg diet (0.46 ± 0.03 g/d). ICR mice showed at least a 2-fold greater expression (P < 0.001) of ornithine transcarbamylase (OTC) than BL6 mice, which translated into a greater rate of citrulline (25%) and arginine synthesis (49%, P < 0.002). In Expt. 2, breakpoint analysis showed that the requirement for growth of BL6 mice was met with 2.32 ± 0.39 g arginine/kg diet; for ICR mice, however, no breakpoint was found.

CONCLUSION

Our data indicate that a reduced expression of OTC in BL6 mice translates into a reduced production of citrulline and arginine compared with ICR mice, which results in a dietary arginine requirement for growth in BL6 mice, but not in ICR mice.

Arginine depletion by arginine deiminase does not affect whole protein metabolism or muscle fractional protein synthesis rate in mice

Due to the absolute need for arginine that certain cancer cells have, arginine depletion is a therapy in clinical trials to treat several types of cancers. Arginine is an amino acids utilized not only as a precursor for other important molecules, but also for protein synthesis. Because arginine depletion can potentially exacerbate the progressive loss of body weight, and especially lean body mass, in cancer patients we determined the effect of arginine depletion by pegylated arginine deiminase (ADI-PEG 20) on whole body protein synthesis and fractional protein synthesis rate in multiple tissues of mice. ADI-PEG 20 successfully depleted circulating arginine (<1 μmol/L), and increased citrulline concentration more than tenfold. Body weight and body composition, however, were not affected by ADI-PEG 20. Despite the depletion of arginine, whole body protein synthesis and breakdown were maintained in the ADI-PEG 20 treated mice. The fractional protein synthesis rate of muscle was also not affected by arginine depletion. Most tissues (liver, kidney, spleen, heart, lungs, stomach, small and large intestine, pancreas) were able to maintain their fractional protein synthesis rate; however, the fractional protein synthesis rate of brain, thymus and testicles was reduced due to the ADI-PEG 20 treatment. Furthermore, these results were confirmed by the incorporation of ureido [14C]citrulline, which indicate the local conversion into arginine, into protein. In conclusion, the intracellular recycling pathway of citrulline is able to provide enough arginine to maintain protein synthesis rate and prevent the loss of lean body mass and body weight.

Effect of arginine supplementation of broiler breeder hens on progeny performance

Fernandes, J. I. M., Murakami, A. E., Gomes de Souza, L. M., Ospina-Rojas, I. C. and Rossi, R. M. 2014. Effect of arginine supplementation of broiler breeder hens on progeny performance. Can. J. Anim. Sci. 94: 313–321. Two experiments were conducted to determine the effects of arginine (Arg) supplementation of broiler breeder hens on the performance, carcass yield, and bone measurements of their progeny. In both experiments, the maternal diet was supplemented with five levels of digestible Arg (0.94, 1.09, 1.24, 1.39 and 1.54%). In exp. 1, a total progeny of 1050 chicks were housed in pens according to maternal diet and fed a typical diet without L-Arg supplementation. In exp. 2, a total progeny of 960 chicks were kept in pens according to maternal diet and fed diets containing supplemental L-Arg from 1.30 to 1.90% in the starter phase and from 1.15 to 1.75% in the grower phase. The data obtained in both experiments were deployed in orthogonal polynomials to allow for an analysis of variance and a regression analysis. In the starter phase, there was a quadratic effect (P<0.05) of Arg level in the maternal diet on the feed:gain ratio of the non-supplemented progeny. In the Arg-supplemented progeny, there was a quadratic effect (P<0.05) of Arg level on the feed intake and feed:gain ratio and a linear increase (P<0.05) in body weight gain, and carcass and breast yields (P<0.05). Femur length, tibia diameter, and the Seedor index of both bones increased linearly (P<0.05) in broilers fed the Arg-supplemented diet. Arg supplementation in the broiler breeder hen diets had little positive effect on the non-supplemented progeny; thus, Arg supplementation in the progeny diet is necessary to optimize performance, carcass yield, and bone quality of these hens’ progeny.

Feed intake and brain neuropeptide Y (NPY) and cholecystokinin (CCK) gene expression in juvenile cobia fed plant-based protein diets with different lysine to arginine ratios

Cobia (Rachycentron canadum, Actinopterygii, Perciformes;10.5±0.1g) were fed to satiation with three plant-based protein test diets with different lysine (L) to arginine (A) ratios (LL/A, 0.8; BL/A, 1.1; and HL/A, 1.8), using a commercial diet as control for six weeks. The test diets contained 730 g kg(-1) plant ingredients with 505-529 g protein, 90.2-93.9 g lipid kg(-1) dry matter; control diet contained 550 g protein and 95 g lipid kg(-1) dry matter. Periprandial expression of brain NPY and CCK (npy and cck) was measured twice (weeks 1 and 6). At week one, npy levels were higher in pre-feeding than postfeeding cobia for all diets, except LL/A. At week six, npy levels in pre-feeding were higher than in postfeeding cobia for all diets. cck in pre-feeding cobia did not differ from that in postfeeding for all diets, at either time point. Cobia fed LL/A had lower feed intake (FI) than cobia fed BL/A and control diet, but no clear correlations between dietary L/A ratio and FI, growth and expression of npy and cck were detected. The data suggest that NPY serves as an orexigenic factor, but further studies are necessary to describe links between dietary L/A and regulation of appetite and FI in cobia.

Intestinal absorption of amino acids in the Pacific bluefin tuna (Thunnus orientalis): in vitro lysine-arginine interaction using the everted intestine system

The interaction between lysine (Lys) and arginine (Arg) in the proximal intestinal region of Pacific bluefin tuna (Thunnus orientalis) was evaluated using the everted intestine method. This in vitro intestinal system has been shown to be an effective tool for studying the nutrient absorption without the need to handle the tuna fish in marine cages as needed for digestibility and amino acid (AA) absorption. We used a factorial design with two sets of variables: low and high Lys concentration (10 and 75 mM) and four different Arg concentrations (3, 10, 20, and 30 mM). Both amino acids were dissolved in marine Ringer solution with a basal amino acidic composition consisting of a tryptone solution (9 mg mL(-1)). No interaction was observed between the absorption of Lys and Arg during the first 10 min of the experiment when low concentration of Lys and Arg was used in the hydrolyzate solution. However, there seemed to be a positive effect on Lys absorption when both amino acids were at high concentrations (30 and 75 mM, respectively). This type of studies will led us to test different formulations and/or additives to better understand the efficiency of AA supplementation as an alternative to in situ studies that are difficult to follow to design with the Pacific Bluefin Tuna.

The effects of added sulphur amino acids, threonine and an ideal amino acid ratio on nitrogen metabolism in mature, overweight dogs

The objectives of this study were to investigate the effects of added essential amino acids in conjunction with a dietary lysine/MJ of 0.72 on nitrogen (N) metabolism in dogs. Treatments were; a control diet, a diet that provided an ideal amino acid profile (IAA), a diet with added total sulphur amino acids (TSAA), and a diet with added TSAA and threonine (TT). Diets were fed to eight overweight, mature, female hounds using a replicated 4 x 4 Latin Square design. Food intake was similar across treatments, however, food N intake was higher (p < 0.001) for TSAA than control, IAA or TT. Nitrogen absorbed was higher (p < 0.01) for TSAA than IAA and control. Urea N excretion was greater for control than TT (p < 0.05). Urine N excretion did not differ between diets. There were no differences in digestibility or N retention of diets. There were no differences in protein turnover, synthesis, or degradation. Blood metabolites were within normal ranges and did not differ due to dietary treatment. Based on the measurements made in this study, there is no benefit for added TSAA, TT or additional EAA in diets for mature dogs formulated to provide a 0.72 g lysine/MJ ME ratio.

Amino acid supplementation does not alter whole-body phenylalanine kinetics in Arabian geldings

Stable isotope infusion methods have not been extensively used in horses to study protein metabolism. The objectives were to develop infusion and sampling methodologies for [1-(13)C] phenylalanine and apply these methods to determine whether the addition of supplemental amino acids to a control diet affected whole-body phenylalanine kinetics in mature horses. Arabian geldings were studied using a 6-h primed (9 μmol/kg), constant (6 μmol · kg(-1) · h(-1)) i.v. infusion of L-[1-(13)C] phenylalanine, with blood and breath sampled every 30 min, to measure whole-body phenylalanine kinetics in response to receiving the control diet (n = 12) or the control diet supplemented with equimolar amounts of glutamate (+Glu; 55 mg · kg(-1) · d(-1); n = 5), leucine (+Leu; 49 mg · kg(-1) · d(-1); n = 5), lysine (+Lys; 55 mg · kg(-1) · d(-1); n = 5), or phenylalanine (+Phe; 62 mg · kg(-1) · d(-1); n = 6). The plasma concentrations of the supplemented amino acid in horses receiving the +Leu, +Lys, and +Phe diets were 58, 53, and 36% greater, respectively, than for the control treatment (P < 0.05). Isotopic plateau was attained in blood [1-(13)C] phenylalanine and breath (13)CO(2) enrichments by 60 and 270 min, respectively. Phenylalanine flux (+20%) and oxidation (+110%) were greater (P < 0.05) in horses receiving the +Phe treatment than in those fed the control diet. There was no effect of treatment diet on nonoxidative phenylalanine disposal or phenylalanine release from protein breakdown. The developed methods are a valuable way to study protein metabolism and assess dietary amino acid adequacy in horses and will provide a useful tool for studying amino acid requirements in the future.

Effects of starter diet supplementation with arginine on broiler production performance and on small intestine morphometry

The effects of starter diet (days 1 to 21) supplemented with arginine (Arg) on the production performance and duodenum and jejunum mucosa morphometry of broilers were studied. Male Cobb broiler chickens (990) were randomly assigned to one of five treatments in a complete random design. Measurements of 33 chicks per treatment were made in six repetitions. The treatments consisted of a basal diet with 1.390% digestible Arg (no supplementation) and four dietary levels (1.490%, 1.590%, 1.690%, and 1.790%), providing a relationship with lysine of 1.103; 1.183; 1.262; 1.341 and 1.421%, respectively. From the age of 22 days on, all birds received conventional grower diet. The data were submitted to regression analysis by polynomial decomposition of the degrees of freedom in relation to the levels of Arg. The Arg supplementation increased (P<0.05) the live weight and the feed conversion ratio without increasing the feed intake of the birds. However, no effect was observed (P>0.05) in the growth phase (days 22 to 42) in the absence of the Arg supplementation. The supplementation of Arg over of NRC recommendation during the starter phase may be necessary for the expression of the maximal weight gain potential in birds. No effect (P<0.05) of Arg dietary supplementation was observed either on small intestine weight and length at any age. However, the duodenum villus:crypt ratio increased and the crypt depth decreased in the first week in response to increasing dietary Arg. It is concluded that broiler Arg dietary supplementation in the starter diet improved production performance and small intestine morphometry, especially in the first week.

Strategies for optimizing the serum persistence of engineered human arginase I for cancer therapy

Systemic L-arginine depletion following intravenous administration of l-arginine hydrolyzing enzymes has been shown to selectively impact tumors displaying urea cycle defects including a large fraction of hepatocellular carcinomas, metastatic melanomas and small cell lung carcinomas. However, the human arginases display poor serum stability (t(1/2)=4.8h) whereas a bacterial arginine deiminase evaluated in phase II clinical trials was reported to be immunogenic, eliciting strong neutralizing antibody responses. Recently, we showed that substitution of the Mn(2+) metal center in human Arginase I with Co(2+) (Co-hArgI) results in an enzyme that displays 10-fold higher catalytic efficiency for L-Arg hydrolysis, 12-15 fold reduction in the IC(50) towards a variety of malignant cell lines and, importantly a t(1/2)=22h in serum. To investigate the utility of Co-hArgI for L-Arg depletion therapy in cancer we systematically investigated three strategies for enhancing the persistence of the enzyme in circulation: (i) site specific conjugation of Co-hArgI engineered with an accessible N-terminal Cys residue to 20kDa PEG-maleimide (Co-hArgI-C(PEG-20K)); (ii) engineering of the homotrimeric Co-hArgI into a linked, monomeric 110kDa polypeptide (Co-hArgI x3) and (iii) lysyl conjugation of 5kDa PEG-N-hydroxysuccinimide (NHS) ester (Co-hArgI-K(PEG-5K)). Surprisingly, even though all three formulations resulted in proteins with a predicted hydrodynamic radius larger than the cut-off for renal filtration, only Co-hArgI amine conjugated to 5kDa PEG remained in circulation for sufficiently long durations. Using Co-hArgI-K(PEG-5K) labeled with an end-terminal fluorescein for easy detection, we demonstrated that following intraperitoneal administration at 6mg/kg weight, a well tolerated dose, the circulation t(1/2) of the protein in Balb/c mice is 63±10h. Very low levels of serum L-Arg (<5μM) could be sustained for over 75h after injection, representing a 9-fold increase in pharmacodynamic efficacy relative to similarly prepared Mn(2+)-containing hArgI conjugated to 5kDa PEG-NHS ester (Mn-hArgI-K(PEG-5K)). The favorable pharmacokinetic and pharmacodynamic properties of Co-hArgI-K(PEG-5K) reported here, coupled with its human origin which should reduce the likelihood of adverse immune responses, make it a promising candidate for cancer therapy.

Detection of Local Prostate Metabolites by Hrmas Nmr Spectroscopy: A Comparative Study of Human and Rat Prostate Tissues

The use of magnetic resonance spectroscopy (MRS) for the detection of in-vivo metabolic perturbations is increasing in popularity in Prostate Cancer (PCa) research on both humans and rodent models. However, there are distinct metabolic differences between species and prostate areas; a fact making general conclusions about PCa difficult. Here, we use High Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HRMAS NMR) spectroscopy to provide tissue specific identification of metabolites and their relative ratios; information useful in providing insight into the biochemical pathways of the prostate. As our NMR-based approach reveals, human and rat prostate tissues have different metabolic signatures as reflected in numerous key metabolites, including citrate and choline compounds, but also aspartate, lysine, taurine, glutamate, glutamine, creatine and inositol. In general, distribution of these metabolites is not only highly dependent on the species (human versus rat), but also on the location (lobe/zone) in the prostate tissue and the sample pathology; an observation making HRMAS NMR of intact tissue samples a promising method for extracting differences and common features in various experimental prostate cancer models.

Does the pelleting process affect the nutritive value of a pre-starter diet for suckling piglets? Ex vivo studies on mineral absorption

BACKGROUND

The effects of pelleting on the extent of the Maillard reaction (MR) and on calcium, magnesium and zinc solubility and absorption were analysed in a conventional pre-starter diet for suckling piglets. Development was tested measuring colour, absorbance (280/420 nm), fluorescence, residual free lysine, furosine, hydroxymethylfurfural (HMF) and furfural contents before and after pelleting. Fluorescence, absorbance and mineral solubility were also measured after in vitro digestion of diets. The effects on mineral absorption were tested using Caco-2 cells.

RESULTS

MR indexes confirmed the development of the reaction during the pelleting of this particular diet compared with the meal diet. The CIE-Lab colour parameters showed a decrease in luminosity (L*) and progress of the colour to the red zone (a*) in the pelleted diet. A 36% decrease in free lysine content was observed. Significant correlations were observed between fluorescence intensity and furosine levels, HMF and furfural. The pelleting process did not modify calcium and magnesium solubility after in vitro digestion, but soluble zinc increased. The efficiency of calcium and zinc transport across Caco-2 cell monolayers was greater in the pelleted diet.

CONCLUSIONS

Evidence of MR development is shown, resulting in various nutritional consequences. Optimisation of pelleting could result in a better formulation of diets for feedstuffs.

Enteral administration of alanyl-[2-(15)N]glutamine contributes more to the de novo synthesis of arginine than does intravenous infusion of the dipeptide in humans

BACKGROUND

We previously confirmed in humans the existence of a pathway of glutamine into citrulline and arginine, which is preferentially stimulated by luminally provided glutamine. However, because glutamine is unstable, we tested this pathway with a stable dipeptide of glutamine.

OBJECTIVES

The objectives were to explore whether alanyl-glutamine contributes to the synthesis of arginine in humans and whether this depends on the route of administration.

DESIGN

The study was conducted under postabsorptive conditions during surgery. Sixteen patients received alanyl-[2-(15)N]glutamine enterally or intravenously together with intravenously administered stable-isotope tracers of citrulline and arginine. Blood was collected from an artery, the portal vein, a hepatic vein, and the right renal vein. Arterial and venous enrichments and (tracer) net balances of alanyl-glutamine and glutamine, citrulline, and arginine across the portal-drained viscera, liver, and kidneys were determined. Parametric tests were used to test results (mean +/- SEM). P < 0.05 was considered significant.

RESULTS

Twice as much exogenous glutamine was used for the synthesis of citrulline when alanyl-glutamine was provided enterally (5.9 +/- 0.6%) than when provided intravenously (2.8 +/- 0.3%) (P < 0.01). Consequently, twice as much exogenous glutamine was used for the synthesis of arginine when alanyl-glutamine was provided enterally (5 +/- 0.7%) than when provided intravenously (2.4 +/- 0.2%) (P < 0.01). However, results at the organ level did not explain the differences due to route of administration.

CONCLUSIONS

Alanyl-glutamine contributes to the de novo synthesis of arginine, especially when provided enterally. A stable-isotope study using a therapeutic dose of alanyl-glutamine is needed to investigate the clinical implications of this finding.

The 7th workshop on the assessment of adequate intake of dietary amino acids: summary of general discussion

Extensive discussion sessions were held at the end of each of the 2 d of the workshop. Through the course of the workshop, it became clear that there were different opinions on how to use uncertainty factors to obtain upper levels of intake from no observed adverse effect levels of a particular nutrient and that the selection of an appropriate uncertainty factor would be rather arbitrary. Much of the discussion centered around the potential for using metabolic limits, expressed as the level of intake at which the major pathway of metabolism may approach saturation and at which the amino acid is metabolized by alternative pathways, as a measurable early or surrogate marker for amino acid excess and possible toxicity. After extensive discussion on various conditions that would need to be satisfied for metabolic limits to be used as markers of excessive intake of amino acids, there was a general consensus that methods such as measuring oxidation limits are an attractive approach that merit future investigation. It was noted that there are many data on the clinical use of glutamine, whereas data for proline are very scarce. There was recognition that regardless of the available data, there is regulatory pressure for setting upper levels of intake for amino acids and that much more data are required.

An approach to defining the upper safe limits of amino acid intake

The existing data on the safe upper limits of amino acid intake in humans is essentially observational; how much do individuals ingest and what side effects do they have? There are numerous studies in humans comparing the effects of high doses of amino acids given as protein bound vs. as free amino acids. These studies have shown that protein-bound amino acids have much less effect on plasma levels of the test amino acid, because protein intake stimulates protein synthesis as another sink for the increased amino acid intake. In practice, the highest amino acid intakes occur with free amino acid supplements that may be ingested by athletes who believe that the amino acids will benefit them in training and/or performance. Previously, in a piglet study, we were able to define the point at which maximal phenylalanine oxidation occurred, above which plasma phenylalanine concentration and body balance rose exponentially. We regard this value of maximal disposal (oxidation) of an amino acid as one metabolic marker of the upper limit of intake. Recently, others have demonstrated a similar maximal oxidation rate for leucine in rats. Based on these experimental data and the paucity of published human data in controlled experiments, we think that a systematic approach needs to be undertaken to define the maximal oxidation rate for all dietary indispensable amino acids and other amino acids that may be ingested in excess by humans. We believe that this will provide a rational basis to begin to define the upper limits of tolerance for dietary amino acids. However, some amino acids, such as threonine and methionine, will be more difficult to study, because they have more than 1 route of disposal or very complex metabolic regulation, in which case defining their upper limits will be more multifaceted.

Animal models in nutrition research

Current knowledge in nutrition is based largely on the use of appropriate animal models together with defined diets. Numerous examples are cited where animal models have been used to solve nutrient x nutrient interactions, to evaluate bioavailability of nutrients and nutrient precursors, and to test for nutrient tolerances and toxicities. Advantages, disadvantages, and idiosyncrasies of various animal species are discussed.

Lysine, arginine, and related amino acids: an introduction to the 6th amino acid assessment workshop

The focus of the 6th workshop is on lysine, arginine, and related amino acids. Functions, metabolic pathways, clinical uses, and upper tolerance intakes are emphasized in the articles that follow. Lysine is arguably the most deficient amino acid in the food supply of countries where poverty exists, and since the discovery of the nitric oxide synthase pathway, arginine has come into prominence clinically because of the role of nitric oxide in cardiovascular physiology and pathophysiology.