Absorption Of Lysine Research Articles

Assessing seromuscular layer and serosa removal on intestinal permeability measurements in weaned piglet everted sac segments.

The integrity of the intestinal barrier is crucial for regulating the passage of pathogens and toxins, while facilitating nutrient absorption. The everted gut sac technique, an ex-vivo technique, can be used to study interventions on barrier function. This cost-effective approach utilizes relatively large gut segments to study specific intestinal regions. Typically, intact (non-stripped) intestinal segments are used, but their use may underestimate permeability due to the medial positioning of blood vessels relative to the seromuscular layer and serosa. However, removing these layers risks physical damage, resulting in an overestimation of intestinal permeability. Therefore, we investigated the impact of stripping jejunal segments on permeability to fluorescein isothiocyanate-dextran (FITC, 4kDa) and tetramethylrhodamine isothiocyanate-dextran (TRITC, 40kDa), and on the absorption of glucose, lysine, and methionine in jejunal segments from 80 piglets at 8 d postweaning. Piglets were subjected to either high or low sanitary housing conditions and diets provoking intestinal protein fermentation or not, expected to influence intestinal permeability. Stripping of the seromuscular layer and serosa increased the passage of 4kDa FITC-dextran (stripped vs. non-stripped; 1.1 vs. 0.9 pmol/cm2/min, P < 0.001), glucose (40.0 vs. 19.1 pmol/cm2/min, P < 0.001), lysine (2.5 vs. 2.0 nmol/cm2/min, P < 0.001), and methionine (4.1 vs. 2.7 pmol/cm2/min, P < 0.001). As permeability increased, the differences in methionine passage between stripped and non-stripped intestinal segments also increased (slope = 1.30, P = 0.009). The coefficients of variation were comparable between stripped and non-stripped intestines (over all treatments, stripped vs. non-stripped 38% vs. 40%). Stripping, by isolating mucosal processes without introducing additional variation, is thus recommended for studies on intestinal permeability or absorption.

Oral Administration of Animal and Plant Protein Mixture with Lactiplantibacillus plantarum IDCC 3501 Improves Protein Digestibility

A combined usage of animal and plant proteins-mixture could aid to solve environmental and social problems arising from the use of animal protein alone, while also improving the taste and texture of plant protein. Protein mixtures could be a better protein source due to the high availability of amino acids in the body compared with single proteins. Consuming proteins with probiotics can provide more beneficial health effects by helping to hydrolyze protein and absorb amino acids in the body. In this study, coadministration of an animal and plant protein mixture with a high concentration of probiotics was investigated to increase protein digestibility and amino acids absorbability in a mice model. Lactiplantibacillus plantarum IDCC 3501, which has the maximum ability to hydrolyze a protein mixture, composed of soybean protein and milk protein, was selected, and the changes in mice (C57BL/6J, male, six weeks) were investigated after the coadministration of protein mixture and 5 × 108 or 5 × 109 CFU/mL of L. plantarum for eight weeks. Normal diet, high-protein diet (HPD), and HPD supplementing L. plantarum were separately administered to mice. Food and water consumption of the mice did not differ depending on diet type. Measurements of the serum concentrations of amino acids showed that the absorption of aspartate, glutamate, isoleucine, leucine, valine, and lysine increased when high concentrations of protein and probiotics were administered. Thus, high L. plantarum concentrations could be a protein diet supplementation to improve health by promoting the absorption of amino acids.

Abstract 4879: Inhibition of amino acid transporters as a novel mechanism of action of the repurposed anti-cancer agent tranexamic acid

Abstract Tranexamic Acid (TA) is an anti-fibrinolytic agent that inhibits Plasminogen activation and is used to control bleeding. Past studies have suggested that the ability of TA to block Plasminogen activation may be useful for ablating the growth or invasion of cancer. Based on the similarity of TA to the amino acid Lysine we hypothesize that TA might exhibit novel mechanisms of action independent of blocking Plasminogen activation. Analysis of a series of signaling pathways indicated that TA inhibits phosphorylation of S6K1 and STAT3 on sites required for their activation and reduces expression of the MYC oncogene in a concentration-dependent manner. Interestingly, MYC transformed MCF10A human mammary epithelial cells exhibited enhanced sensitivity to TA-mediated reduction of cell viability, suggesting that TA may exhibit selectivity for MYC overexpressing breast cancers. Treatment of breast tumor bearing mice with TA strongly blocked tumor growth and was associated with extensive cancer cell death compared with control tumors. Analysis of extracts from TA or vehicle treated tumors showed that TA blocked S6K1 phosphorylation in vivo in a statistically significant manner. Since S6K1 phosphorylation is regulated by amino acid levels, we hypothesized that due to the structural similarity between TA and Lysine and Arginine, TA may block Lysine or Arginine uptake by blocking cationic amino acid transporters (CATs). Molecular docking simulations utilizing the structure of the bacterial CAT predicted that TA binds to CAT with affinity similar to that of Lysine. Amino acid uptake experiments performed with radiolabeled Arginine and Lysine showed that TA blocked both Arginine and Lysine absorption by cancer cells in a concentration-dependent manner. Together, these results indicate a novel mechanism by which TA inhibits uptake of Arginine and Lysine, triggering loss of S6K1 activity in parallel with tumor growth inhibition. Initial studies suggest the feasibility of designing TA analogs with significantly improved potency for amino acid transporters, and with corresponding increases in selective toxicity to breast cancer cells. Based on these novel mechanisms of TA action, we expect TA to exhibit anti-cancer activity against a broad range of human malignancies. Citation Format: Brian K. Law, Mary E. Law, Amanda F. Ghilardi, Elham Yaaghubi, Brad J. Davis, Zaafir M. Dulloo, Mengxiong Wang, Olga A. Guryanova, Coy D. Heldermon, Stephan C. Jahn, Ronald K. Castellano. Inhibition of amino acid transporters as a novel mechanism of action of the repurposed anti-cancer agent tranexamic acid. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4879.

Chitosan Increases Lysine Content through Amino Acid Transporters in Flammulina filiformis.

HighlightsChitosan treatment increased the lysine content of F. filiformis. Results from this study provide insights for industrial-scale trials potentially resulting in higher-quality F. filiformis.Response surface methodology (RSM) was used to optimize the conditions of chitosan-induced amino acid content in F. filiformis for the first time.The amino acid transporters in F. filiformis were systematically screened for the first time. The involvement of AAT3 and AAT4 genes in chitosan-induced lysine biosynthesis in F. filiformis was investigated by gene-silenced strains.Lysine content is considered an important indicator of the quality of Flammulina filiformis. In this study, chitosan was used to improve lysine content of F. filiformis. Optimal design conditions were obtained using central combination design (CCD): treatment concentration was 14.61 μg/mL, treatment time was 52.90 h, and the theoretical value of lysine content was 30.95 mg/g. We used Basic Local Alignment Search Tool Protein (BLASTP) to search the F. filiformis genome database using known AATs in the NCBI database. There were 11 members of AAT in F. filiformis. The expression levels of AAT3 and AAT4 genes increased significantly with chitosan treatment. Subsequently, AAT3 and AAT4 silencing strains were constructed using RNAi technology. The lysine content of the wild-type (WT) strain treated with chitosan increased by 26.41%. Compared with the chitosan-induced WT strain, chitosan-induced lysine content decreased by approximately 24.87% in the AAT3 silencing strain, and chitosan-induced lysine content in the AAT4 silencing strain increased by approximately 13.55%. The results indicate that AAT3 and AAT4 are involved in the regulation of the biosynthesis of lysine induced by chitosan in F. filiformis. AAT3 may participate in the absorption of lysine, and AAT4 may be involved in the excretion of lysine with chitosan treatment.

Abstract MP39: Metabolic And Gene Expression Profiling Reveal Disparities In Absorption And Metabolism Of Butyrate And Lysine In The Colon Of Spontaneously Hypertensive Rodents

Introduction: Metabolic dysregulation and gut dysbiosis are linked to hypertension. The proximal colon is the main site of metabolism and absorption of short chain fatty acid butyrate. Reduced circulating butyrate concurrently with elevated fecal levels have been reported in human and rodent hypertension. We tested the hypothesis that both the transport and metabolism of butyrate as well as the overall metabolic profile are dysregulated in the colon of the Spontaneously Hypertensive rats (SHR) compared to the Wistar Kyoto (WKY) rats. Methods: Proximal colons from adult male WKY and SHR were placed in oxygenated warmed Ussing chamber buffer containing dextrose, and physiologically relevant concentration of butyrate (40mM) was applied to the luminal side of the colon. Following 1hr incubation, butyrate levels from the luminal and basolateral sides of the Ussing chamber were measured with high performance liquid chromatography to establish butyrate colonic transport and metabolism. Global metabolomics was performed in Ussing chamber media and in the plasma of WKY and SHR to determine the overall metabolic profile. RNA-seq data in the gut epithelium of WKY and SHR was used to elucidate putative signaling pathways altered in rodent hypertension. Results: Both the colonic transport and metabolism of butyrate were significantly impaired in the SHR. In addition, global metabolomics identified reduced levels of essential amino acid L-lysine, among other metabolites, on the basolateral side of the Ussing chamber and in the plasma of the SHR compared to WKY. Enriched metabolite pathways disrupted in the SHR included lysine degradation. RNA-seq revealed differential expression of several fatty acid and amino acid transporters in the colonic epithelium of the SHR. Conclusion: Colonic transport and metabolism of butyrate are reduced in the SHR, accompanied by dysregulation in the metabolism of the essential amino acid lysine in the gut. This, coupled with reduced expression levels of several fatty acid and amino acid transporters in the gut, suggest aberrant host-microbiota communication and colonic metabolic dysfunction in the context of hypertension.

Putative imbalanced amino acid metabolism in rainbow trout long term fed a plant-based diet as revealed by 1H-NMR metabolomics.

The long-term effect of a plant (P)-based diet was assessed by proton nuclear magnetic resonance (1H-NMR) metabolomics in rainbow trout fed a marine fish meal (FM)-fish oil (FO) diet (M), a P-based diet and a control commercial-like diet (C) starting with the first feeding. Growth performances were not heavily altered by long-term feeding on the P-based diet. An 1H-NMR metabolomic analysis of the feed revealed significantly different soluble chemical compound profiles between the diets. A set of soluble chemical compounds was found to be specific either to the P-based diet or to the M diet. Pterin, a biomarker of plant feedstuffs, was identified both in the P-based diet and in the plasma of fish fed the P-based diet. 1H-NMR metabolomic analysis on fish plasma and liver and muscle tissues at 6 and 48 h post feeding revealed significantly different profiles between the P-based diet and the M diet, while the C diet showed intermediate results. A higher amino acid content was found in the plasma of fish fed the P-based diet compared with the M diet after 48 h, suggesting either a delayed delivery of the amino acids or a lower amino acid utilisation in the P-based diet. This was associated with an accumulation of essential amino acids and the depletion of glutamine in the muscle, together with an accumulation of choline in the liver. Combined with an anticipated absorption of methionine and lysine supplemented in free form, the present results suggest an imbalanced essential amino acid supply for protein metabolism in the muscle and for specific functions of the liver.

Dye/metal ion-based chemosensing ensemble towards l-histidine and l-lysine determination in water via different optical responses.

In this study, a novel simple type of label-free, ultra-sensitive, and highly selective UV-Vis absorption and naked-eye detection of histidine (His) and lysine (Lys) using a dye/metal ion ensemble is developed. The outcoming high sensitivity and selectivity for histidine and lysine were attained by changing the metal ions. The indicator is released due to its displacement from the murexide (Mure)/Cu2+ complex by histidine and the change in absorbance may be due to the further complexation of lysine with the additional coordination sites present in the zinc atom of Mure/Zn2+ complex. The label-free chemosensor provided sensitive and selective detection of l-histidine and l-lysine with detection limits of 9.1 and 9.4nmolL-1, respectively. The protocol especially offers high selectivity for the determination of His and Lys among amino acids found in human urine samples. Furthermore, INHIBIT and NAND molecular logic gates were obtained using chemical inputs and UV-Vis absorbance signal output.

Production of high-lysine-content biscuit and examination of the absorption of lysine in humans

AbstractIn the Medical and Health Centre of the University of Debrecen, we examined the changes in the free amino acid content of the blood serum of control and experimental individuals after consumption of 2,000 mg of lysine-laden biscuits. We baked the biscuits at 130 °C, during which the greater part (70–75%) of the lysine was not converted into Maillard reaction products. After 30–60 minutes of consumption of the biscuits, the free lysine content of the blood serum increased significantly in the experimental and control group with 41–46%, and even after three hours of consumption the level was 20% higher than in the initial concentration. The free arginine content of the blood serum did not change after the consumption of control and lysine biscuits neither in the control nor in the experimental group. Therefore, the free lysine/free arginine ratio of the individuals consuming lysine increased significantly compared to the initial and the control group’s value. The antioxidant level of the blood serum in the control group remained unchanged after the consumption of the control biscuit, while in the case of the experimental individuals who consumed lysine-fortified biscuits it increased by 40–45% compared to the initial level. Summing up: After consumption of the biscuits with 2,000 mg of free lysine, the concentration of free lysine in the blood serum, its free lysine/free arginine ratio and antioxidant level increased significantly. Our researches have clearly demonstrated that the active substances of the biscuit got into the blood serum, so the investigation of the active substance and the evaluation of the physiological effects are definitely recommended in the long run.

Comparative study on the utilization of different lysine sources by channel catfish (Ictalurus punctatus)

In this study, five diets were formulated, namely positive control, negative control (lysine deficient) without or with the addition of crystalline l-Lys·HCl, l-Lys·H2SO4 and microcapsulated l-lysine·HCl (M-Lys), and then fed to channel catfish with an initial body weight of 76.0 ± 0.3 g to investigate the effects of various lysine sources on the growth. After 8-week feeding, the fish fed M-Lys diet, but not Lys·HCl or Lys·H2SO4 diet, had a higher weight gain, a higher protein retention ratio and a lower feed conversion ratio than that fed negative control (P < 0.05), and showed a similar growth as positive control. The serum free amino acid level of Lys·HCl and Lys·H2SO4 group reached the plateau at the 2nd h after feeding, while the other three groups peaked at the 4th h. In Lys·HCl and Lys·H2SO4 groups, the activities of liver aspartate aminotransferase and alanine aminotransferase peaked at the 2nd h, but M-Lys group peaked at the 6th and 4th h after feeding, respectively. The above results indicated that the supplementation of M-Lys rather than Lys·HCl or Lys·H2SO4 in lysine-deficient diet could improve the growth performance of channel catfish, due to the delayed absorption of supplemental lysine.

Intestinal absorption of nutrients using rats fed different diets

Absorption of glucose, sucrose, glutamic acid, methionine, lysine and cysteine was studied using the intestinal everted sac technique. Rats were fed rice diets Basmati 370, Pusa Basmati 1 and Haryana Basmati 1 using as a casein control. Absorption of nutrients was monitored spectrophotometrically and of glucose, sucrose and glutamic acid by 14c radio assay using scintillation counting. Positive correlation coefficients between the two assay methods for glucose (r = 0.84), sucrose (r = 0.38) and glutamic acid (r = 0.80) were observed. Glucose showed higher absorption than sucrose and glutamic acid than lysine, cysteine and methionine. Absorption of glucose, sucrose and glutamic acid were higher in rats fed on Haryana Basmati 1 diet as demonstrated by both the methods. Rats on Basmati 370 diet exhibited higher methionine, lysine and cysteine absorption. Absorption of nutrients differed significantly between casein and rice.

Effects of dietary l-lysine intake on the intestinal mucosa and expression of CAT genes in weaned piglets

The objective of this study was to evaluate effects of dietary L-lysine on the intestinal mucosa and expression of cationic amino acid transporters (CAT) in weaned piglets. Twenty-eight piglets weaned at 21 days of age (Duroc × Landrace × Yorkshire; 6.51 ± 0.65 kg body weight) were assigned randomly into one of the four groups: Zein + LYS (zein-based diet + 1.35 % supplemental lysine), Zein - LYS (zein-based diet), NF (nitrogen-free diet), and CON (basal diet). The experiment lasted for 3 weeks, during which food intake and body weight were recorded. At the end of the trial, blood was collected from the jugular vein of all pigs, followed by their euthanasia. Dietary supplementation with lysine enhanced villus height and crypt depth in the jejunum (P < 0.05). Jejunal mRNA levels for the b(0,+)-AT, y(+)LAT1 and CAT1 genes were greater (P < 0.05) in the Zein + LYS group than in the control, and the opposite was observed for CAT1. Dietary content of lysine differentially affected intestinal CAT expression to modulate absorption of lysine and other basic amino acids. Thus, transport of these nutrients is a key regulatory step in utilization of dietary protein by growing pigs and lysine in the diet influences the expression of amino acid transporters in the small intestine.

Effects of dietary protein and amino acid levels on the expression of selected cationic amino acid transporters and serum amino acid concentration in growing pigs

The absorption of lysine is facilitated by leucine, but there is no information regarding the effect of crude protein, lysine and leucine levels on the expression of cationic amino acid transporters in pigs. Therefore, an experiment was conducted with 20 pigs (14.9 ± 0.62 kg initial body weight) to evaluate the effect of two protein levels, and the content of lysine, threonine, methionine and leucine in low crude protein diets on the expression of b0,+ and CAT-1 mRNA in jejunum, Longissimus dorsi and Semitendinosus muscles and serum concentration of amino acids. Treatments were as follows: (i) wheat–soybean meal diet, 20% crude protein (Control); (ii) wheat diet deficient in lysine, threonine and methionine (Basal diet); (iii) Basal diet plus 0.70% l-lysine, 0.27% l-threonine, 0.10% dl-methionine (Diet LTM); (iv) Diet LTM plus 0.80% l-leucine (Diet LTM + Leu). Despite the Basal diet, all diets were formulated to meet the requirements of lysine, threonine and methionine; Diet LTM + Leu supplied 60% excess of leucine. The addition of lysine, threonine and methionine in Diet LTM increased the expression of b0,+ in jejunum and CAT-1 in the Semitendinosus and Longissiums muscles and decreased CAT-1 in jejunum; the serum concentration of lysine was also increased (p < 0.01). Further addition of l-leucine (Diet LTM + Leu) decreased the b0,+ expression in jejunum and CAT-1 in the Longissimus dorsi muscle (p < 0.05), increased the serum concentration of leucine and arginine and decreased the concentration of isoleucine (p < 0.05). Pigs fed the Control diet expressed less b0,+ in jejunum, and CAT-1 in the Semitendinosus and Longissiums muscles expressed more CAT-1 in jejunum (p < 0.05) and had lower serum concentration of isoleucine, leucine and valine (p < 0.05), but higher lysine concentrations (p < 0.01) than those fed Diet LTM. These results indicated that both, the level and the source of dietary amino acids, affect the expression of cationic amino acid transporters in pigs fed wheat-based diets.

Differences in portal flow rates of amino acids and liver composition between rats fed casein or lactalbumin

The portal appearance rates and net rates of amino acids’ absorption were studied in rats fed semi-synthetic diets containing either casein or lactalbumin (CAS and LA, respectively) as the only protein sources. Rats were pre-adapted to the experimental diets for 5 days prior to the absorption studies. Rats fed the LA diet had higher (p < 0.05) portal vein concentrations of free essential amino acids than those fed the CAS diet at 0, 60, 105 and 150 min after feeding. Portal and arterial concentrations of arginine, leucine, tryptophan, lysine and methionine were higher (p < 0.05) in rats fed LA at most time points tested, while concentrations of tyrosine were higher (p < 0.05) in CAS fed rats. When portal flow rates were compared, values for arginine, threonine, alanine, leucine, tryptophan and lysine were higher (p < 0.05) in LA at most time points tested, while proline, tyrosine and valine were higher (p < 0.05) for CAS fed rats after 60 and 105 min feeding. Portal blood flow varied (p < 0.05) with time in rats fed protein-free or LA diets, and was higher (p < 0.05) than that of CAS at 105 min. Intestinal net rates of absorption of tyrosine, valine, leucine and lysine were higher (p < 0.05) for LA fed rats as compared to those fed CAS at most time points tested, while alanine and proline net rates were higher (p < 0.05) for CAS fed rats at 60, 105 and 150 min. Amounts of protein in stomach contents of rats fed the CAS diet were significantly higher (p < 0.05) than those in LA fed rats at 60, 105 and 150 min after feeding. The relative liver weight of the rats fed the CAS diet was lower (p < 0.05) than that of animals fed the LA diet. Lower (p < 0.05) liver glycogen and lipid contents were determined in rats fed CAS diet respect to LA or protein-free fed rats. Results indicate that dietary and plasma amino acids profile are only partially related, and that under normal feeding conditions amino acids from CAS and LA are absorbed at different rates, which is likely to affect liver composition and metabolism.

Incorporation of lysine from microbial origin into tissue protein of Iberian and Landrace × Large White piglets

The distinct incorporation of lysine from microbial origin in tissues has been investigated in Iberian and Landrace × Large White piglets of 47 ± 3 d of age ( n = 8/genotype) given 15N-labelled ammonium sulphate added to the diet. Four piglets of each breed were allocated in metabolic cages to prevent coprophagy. All piglets consumed the labelled diet for 10 days and then were slaughtered. Viscera and carcass weights were recorded and gastrointestinal tissues carefully handled. Samples of carcass, liver, and bacterial pellets isolated from the last third of the small intestine, were hydrolyzed, desalted by ion-exchange, and the amino acids eluted analyzed for 15N-lysine enrichment in a GC-combustion/isotope ratio mass-spectrometer. Background 15N-lysine in tissues was also determined in 3 piglets per breed. Liver enrichment was considerably higher in Landrace × Large White than in Iberian piglets (0.0273 ± 0.0013 vs. 0.0167 ± 0.0013 APE, P < 0.05) that, opposite to our expectations, suggests higher incorporation of microbial lysine in tissues of Landrace × Large White piglets. Protein shortage in the experimental diet relative to requirements could have enhanced microbial lysine absorption in the conventional piglets.

The growth performance, carcass traits, meat pH and color, and CO2 production in pigs supplementated arginine with conjugated linoleic acid

This experiment tested the hypothesis that the combination of dietary conjugated linoleic acid (CLA) plus arginine will increase the growth performance, carcass traits, meat quality, and CO2 production. Eight pigs (80kg) were assigned to treatments in a 2 x 2 factorial design with two pigs per treatment (control: 2.05% alanine + 1% canola oil; CLA: 2.05% alanine + 1% CLA (mixed isomers); arginine: 1% arginine + 1% canola oil; arginine + CLA: 1% arginine + 1% CLA). Preliminary tests showed up to 2% arginine plus 1% CLA supplementation can be acceptable without interfering lysine absorption. There was no significant difference in growth performance including average daily feed, average daily gain over the five week treatment period. Dietary arginine and CLA did not affect either carcass or meat quality traits including loin area, back fat thickness, pH45min, pH24hr, meat color (L*, a*, and b*), and drip loss. Rates of glucose and palmitate conversion to CO2 in vitro in liver, longissimus dorsi muscle, abdominal and subcutaneous fat, and enterocytes were not affected by CLA. However, arginine increased CO2 production in all tissue except muscle. Also, CO2 production in both adipose tissue deposits were increased by CLA and arginine (P &lt; 0.05), (This project was supported by National Research Initiative Competitive Grant no. 2008‐35206‐18762 from the USDA Cooperative State Research, Education, and Extension Service).

Phytates reduce uptake of leucine and glutamate but not lysine and glucose from the intestinal lumen of chickens: Short communication

An investigation into the influence of phytates on the in situ absorption of amino acids (lysine, glutamate and leucine) and glucose from the intestinal lumen of 3-week-old chickens was carried out. Birds were anaesthetised and the intestines exteriorised. Uptake of 5 mM of each nutrient over a 4-min period was measured in the presence of four phytate concentrations (0, 50, 250 and 500 mM). Five birds were used for each nutrient at each concentration of phytate tested. Leucine uptake decreased linearly (P < 0.001) and that of glutamate showed a tendency to decrease (P = 0.055) as the phytate concentration increased. Absorption of lysine and glucose were unaffected by the presence of phytate. In conclusion, phytate in the small intestinal lumen exerted a depressive effect on the absorption of specific free amino acids from the lumen. Its depressive effect was greatest for leucine followed by glutamate, and phytate had little effect on the absorption of lysine.

Development of a novel bioassay for determining the available lysine contents of foods and feedstuffs

Lysine is an important indispensable amino acid, and describing the lysine content of a food or feedstuff provides useful information about nutritional value. However, when a food or feedstuff is subjected to heating the lysine present can be altered to nutritionally unavailable derivatives. These derivatives can revert back to lysine during the acid hydrolysis step used in amino acid analysis causing an overestimate of the lysine content. There have been many chemical methods developed to determine the reactive (unmodified) lysine content of foods and feedstuffs, but these do not take into account the incomplete absorption of lysine from the small intestine. There are also a number of animal-based assays for determining available lysine (the lysine that can be absorbed in a form that can be used for protein synthesis). The true ileal amino acid digestibility assay is commonly used to determine amino acid availability and is accurate for application to unprocessed foods and feedstuffs but is not accurate for lysine and possibly other amino acids when applied to heat-processed foods or feedstuffs. For such protein sources, assays such as the slope-ratio assay, indicator amino acid oxidation assay and the BIOLYSINEtrade mark assay (true ileal digestible reactive lysine assay) have been developed to determine available lysine. The present paper discusses the efficacy of the BIOLYSINEtrade mark assay as well as other assays for determining available lysine in processed foods and feedstuffs.

Long-term oral lysine supplementation in lysinuric protein intolerance

In lysinuric protein intolerance (LPI), defective transport of cationic amino acids at the basolateral membrane of the polar epithelial cells in the intestine and renal tubules leads to decreased intestinal absorption and excessive renal loss of lysine, arginine, and ornithine. Citrulline supplementation partially restores the function of the urea cycle that is impaired by deficiency of arginine and ornithine, but does not correct the chronic lysine deficiency. Previous attempts to supplement lysine orally have been hindered by profuse diarrhea, probably caused by excess lysine remaining unabsorbed in the gut. However, individually adjusted minute doses of l-lysine hydrochloride at mealtimes are tolerated well, but the long-term benefits of this therapy remain unknown. The aim of the study was to investigate the long-term benefits and possible adverse effects of oral lysine supplementation in patients with LPI. Supplementation of meals with low doses of oral lysine improved fasting plasma lysine concentrations in 27 Finnish patients with LPI without causing hyperammonemia or other recognizable side effects during 12 months of follow-up. In conclusion, low-dose oral lysine supplementation is potentially beneficial to patients with LPI and can be started safely at an early age.

Glucagon‐like Peptide 2 Stimulates Intestinal Nutrient Absorption in Parenterally Fed Newborn Pigs

Parenteral nutrition is a critically important intervention for children with intestinal dysfunctions. However, total parenteral nutrition (TPN) with no enteral feeding is associated with small intestine atrophy and malabsorption, which complicate the transition to enteral nutrition. The objective of the present study was to evaluate the therapeutic potential of the intestinotrophic peptide glucagon-like peptide 2 (GLP-2), which reduces TPN-associated atrophy and maintains nutrient absorption in adult rats, for preventing nutrient malabsorption in neonates receiving TPN. Term pigs obtained by cesarean delivery received from birth TPN alone (TPN; n = 7) or TPN with GLP-2 (25 nmol . kg(-1) . d(-1); GLP-2; n = 8) or were fed sow milk enterally (n = 7). The small intestine was removed on postnatal day 6 to measure morphological responses and absorption of glucose, leucine, lysine and proline by intact tissues and brush border membrane vesicles and to quantify the abundances of mRNA and protein for enterocyte glucose transporters (SGLT-1 and GLUT2). Relative to TPN alone, administration of GLP-2 resulted in small intestines that were larger (P < 0.01), had greater abundances of mRNA and protein for SGLT-1, but not for GLUT2, and had higher capacities to absorb nutrients (P < 0.01). Moreover, the intestines of GLP-2 pigs were comparable in size and absorptive capacities with those of pigs fed sow milk enterally. Providing GLP-2 to neonates receiving TPN prevents small intestine atrophy, results in small intestine absorptive capacities that are comparable to when nutrients are provided enterally and may accelerate the transition from TPN to enteral nutrition.

Development of the Indicator Amino Acid Oxidation Technique to Determine the Availability of Amino Acids from Dietary Protein in Pigs

Standardized ileal ("true") digestibility is currently the best estimate of amino acid digestibility, but it does not measure bioavailability. Growth assays to determine amino acid bioavailability are expensive and laborious; thus, a rapid method is needed. Applying the principle of slope-ratio assay to the indicator amino acid oxidation (IAAO) method, we hypothesized that the reduction in indicator oxidation per gram of lysine in feedstuffs relative to that per gram of free lysine represented the bioavailability of lysine, here termed "metabolic availability." Indicator oxidation in pigs was linear over increasing lysine intakes (r = 0.90, P = 0.001) when the dietary lysine contents were 2 SD below the mean lysine requirement of the pigs. Peas were treated (raw, heated to reduce lysine availability, or heated with added lysine) to test the responsiveness of the IAAO to differing lysine availability. Free lysine reduced indicator oxidation by 3.16% of dose oxidized per gram added lysine, whereas the addition of protein lysine as raw (-2.81%) and heated peas (-1.73%) reduced oxidation to a lesser degree. Adding free lysine to heated peas decreased indicator oxidation, evidence that heating had worsened the utilization of pea protein for protein synthesis by reducing the bioavailability of lysine alone. Pea diets differed only in the availability of lysine; therefore IAAO detected differences in lysine bioavailability. Because the IAAO technique responds to lysine available at the sites of protein synthesis, the metabolic availability covers all losses during digestion, absorption, and utilization of lysine. This method can determine the metabolic availability of amino acids of a feedstuff within 2 wk.