scholarly journals In vivo Determination of Amino Acid Bioavailability in Humans and Model Animals

2005 ◽  
Vol 88 (3) ◽  
pp. 923-934 ◽  
Author(s):  
Malcolm F Fuller ◽  
Daniel Tomé
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
The Body ◽  
Whole Body ◽  
Intestinal Lumen ◽  
Stable Isotope Labelling ◽  
Ileal Digestibility ◽  
Hydrolyzed Protein ◽  
Protein Free Diet

Abstract Because the digestion of many dietary proteins is incomplete, and because there is a continuous (but variable) entry into the intestinal lumen of endogenous protein and amino acid nitrogen that is also subject to digestion, the fluxes of nitrogen, amino acids, and protein in the gut exhibit a rather complicated pattern. Methods to distinguish and quantitate the endogenous and dietary components of nitrogen and amino acids in ileal chyme or feces include the use of a protein-free diet, the enzyme-hydrolyzed protein method, different levels of protein intake, multiple regression methods, and stable-isotope labelling of endogenous or exogenous amino acids. Assessment of bioavailability can be made, with varying degrees of difficulty, in man directly but, for routine evaluation of foods, the use of model animals is attractive for several reasons, the main ones being cost and time. Various animals and birds have been proposed as models for man but, in determining their suitability as a model, their physiological, enzymological, and microbiological differences must be considered. Fecal or ileal digestibility measurements, as well as apparent and true nitrogen and amino acid digestibility measurements, have very different nutritional significance and can, thus, be used for different objectives. Measurements at the ileal level are critical for determining amino acid losses of both dietary and endogenous origin, whereas measurements at the fecal level are critical in assessing whole-body nitrogen losses. A complementary and still unresolved aspect is to take into account the recycling of intestinal nitrogen and bacterial amino acids to the body.

scholarly journals Available versus digestible amino acids – new stable isotope methods

2012 ◽  
Vol 108 (S2) ◽  
pp. S306-S314 ◽  
Author(s):  
Rajavel Elango ◽  
Crystal Levesque ◽  
Ronald O. Ball ◽  
Paul B. Pencharz
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Stable Isotope ◽  
Growing Pigs ◽  
The Body ◽  
Whole Body ◽  
Food Protein ◽  
Adult Humans

The nutritive value of food protein sources is dependent on the amino acid composition and the bioavailability of the nutritionally indispensable amino acids. Traditionally the methods developed to determine amino acid bioavailability have focused on intestinal absorption or digestibility, which is calculated as the percent of amino acid intake that does not appear in digesta or faeces. Traditional digestibility based methods do not always account for gut endogenous amino acid losses or absorbed amino acids which are unavailable due to the effect of heat processing and the presence of anti-nutritional factors, though methods have been developed to address these issues. Furthermore, digestibility based methods require the use of animal models, thus there is a need to developin vivomethods that can be applied directly in human subjects to identify the proportion of dietary amino acids which is bioavailable, or metabolically available to the body for protein synthesis following digestion and absorption. The indicator amino acid oxidation (IAAO) method developed in our laboratory for humans has been systematically applied to determine almost all indispensable amino acid requirements in adult humans. Oxidation of the indicator amino acid is inversely proportional to whole body protein synthesis and responds rapidly to changes in the bioavailability of amino acids for metabolic processes. Using the IAAO concept, we developed a newin vivomethod in growing pigs, pregnant sows and adult humans to identify the metabolic availability of amino acids in foods. The stable isotope based metabolic availability method is suitable for rapid and routine analysis in humans, and can be used to integrate amino acid requirement data with dietary amino acid availability of foods.

scholarly journals BIOSYNTHESIS IN ISOLATED ACETABULARIA CHLOROPLASTS

1972 ◽  
Vol 54 (2) ◽  
pp. 279-294 ◽  
Author(s):  
David C. Shephard ◽  
Wendy B. Levin
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Technical Problems ◽  
Hydrolyzed Protein ◽  
Protein Amino Acids ◽  
Amino Acid Labeling ◽  
Labeling Pattern

The ability of chloroplasts isolated from Acetabulana mediterranea to synthesize the protein amino acids has been investigated. When this chloroplast isolate was presented with 14CO2 for periods of 6–8 hr, tracer was found in essentially all amino acid species of their hydrolyzed protein Phenylalanine labeling was not detected, probably due to technical problems, and hydroxyproline labeling was not tested for The incorporation of 14CO2 into the amino acids is driven by light and, as indicated by the amount of radioactivity lost during ninhydrin decarboxylation on the chromatograms, the amino acids appear to be uniformly labeled. The amino acid labeling pattern of the isolate is similar to that found in plastids labeled with 14CO2 in vivo. The chloroplast isolate did not utilize detectable amounts of externally supplied amino acids in light or, with added adenosine triphosphate (ATP), in darkness. It is concluded that these chloroplasts are a tight cytoplasmic compartment that is independent in supplying the amino acids used for its own protein synthesis. These results are discussed in terms of the role of contaminants in the observed synthesis, the "normalcy" of Acetabularia chloroplasts, the synthetic pathways for amino acids in plastids, and the implications of these observations for cell compartmentation and chloroplast autonomy.

Amino acid modulation of in vivo intestinal zinc absorption in freshwater rainbow trout

2002 ◽  
Vol 205 (1) ◽  
pp. 151-158 ◽  
Author(s):  
Chris N. Glover ◽  
Christer Hogstrand
Keyword(s):  
Amino Acids ◽  
Rainbow Trout ◽  
Amino Acid ◽  
Zinc Ion ◽  
Zinc Uptake ◽  
Intestinal Lumen ◽  
Zinc Absorption ◽  
Zinc Accumulation ◽  
Rainbow Trout Oncorhynchus Mykiss

SUMMARY The composition of the intestinal lumen is likely to have considerable influence upon the absorption, and consequently the nutrition and/or toxicity, of ingested zinc in aquatic environments, where zinc is both a nutrient and a toxicant of importance. The effects of amino acids upon intestinal zinc uptake in freshwater rainbow trout (Oncorhynchus mykiss) were studied using an in vivo perfusion technique. The presence of histidine, cysteine and taurine had distinct modifying actions upon quantitative and qualitative zinc absorption, compared to perfusion of zinc alone. Alterations in zinc transport were not correlated with changes in levels of free zinc ion. The chemical nature of the zinc–amino acid chelate, rather than the chelation itself, appeared to have the most important influence upon zinc absorption. l-histidine, despite a strong zinc-chelating effect, maintained quantitative zinc uptake at control (zinc alone) levels. This effect correlated with the formation of Zn(His)2 species. d-histidine at a luminal concentration of 100 mmol l–1 significantly enhanced subepithelial zinc accumulation, but reduced the fraction of zinc that was retained and absorbed by the fish. The possibility of a Zn(His)2-mediated pathway for intestinal uptake is discussed. l-cysteine specifically stimulated the accumulation of zinc post-intestinally, an effect attributed to enhanced zinc accumulation in the blood. Taurine increased subepithelial zinc accumulation, but decreased the passage of zinc to post-intestinal compartments. Amino acids are proposed to have important roles in modifying intestinal zinc uptake with potential implications for environmental toxicity as well as aquaculture.

scholarly journals Critical evaluation of a method for estimating amino acid requirements for maintenance in the rat by measurement of the rate of 14C-labelled amino acid oxidation in vivo

1974 ◽  
Vol 32 (2) ◽  
pp. 257-272 ◽  
Author(s):  
R. J Neale ◽  
J. C Waterlow
Keyword(s):  
Amino Acid ◽  
Critical Evaluation ◽  
Specific Radioactivity ◽  
The Body ◽  
Acid Oxidation ◽  
Acid Diet ◽  
Fractional Rate ◽  
Protein Free Diet ◽  
Maintenance Requirements

1. The object of the experiments was to estimate the maintenance requirements for lysine and leucine by a radioactive method. Rats were given a single dose of 14C-labelled lysine or leucine and groups of animals were killed after 15, 20 and 30 d.2. After 20 d the specific radioactivity (SR) of protein was approximately the same in liver, muscle and viscera; it was somewhat lower in skin. Once uniform SR is achieved, the rate of loss of radioactivity is a measure of the rate of endogenous loss of the amino acid.3. The rate of loss between 20 and 30 d was measured in two ways: from the daily output of expired 14CO2, and from the decrease, over the 10 d interval, of the total amount of radioactivity retained in the body.4. For the first 15 d after administration of the labelled amino acid, all rats were given a low-protein or low-amino acid diet on which body-weight was maintained constant. For the second 15 d period some rats were kept on this diet; others were transferred either to a protein-free diet or to a diet lacking the specific amino acid (lysine or leucine) which had been administered in the labelled form.5. The fractional rate of amino acid loss in the different experiments ranged from 1.5 to 3.5%/d, being greatest with the protein-free diet. The absolute rates of loss were calculated from measurements of the total lysine and leucine content of rats.6. The best estimates of the rate of endogenous amino acid loss obtained in this way, expressed as mg/kg0.75 per d were: lysine 136, leucine 80. These estimates are higher than most estimates of maintenance requirements obtained by growth or nitrogen balance methods and possible reasons for these discrepancies are discussed.

scholarly journals The amino acid composition of human milk corrected for amino acid digestibility

1998 ◽  
Vol 80 (1) ◽  
pp. 25-34 ◽  
Author(s):  
Alison J. Darragh ◽  
Paul J. Moughan
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Human Milk ◽  
Amino Acid Composition ◽  
Acid Composition ◽  
Experimental Period ◽  
Human Infant ◽  
Ileal Digestibility ◽  
Model Animal ◽  
Protein Free Diet

Human milk was collected from women in their 10th–14th weeks of lactation, and was analysed for amino acids. Corrections were made for losses of amino acids which were presumed to occur during acid hydrolysis, using a non-linear mathematical model that describes the simultaneous processes of amino acid yield and decay. The mean amino acid composition of the human milk was found to be similar to previously reported estimates, although the cysteine content of the human milk in the present study was 20% higher than the average literature estimate. True (corrected for endogenous amino acid excretions) ileal amino acid digestibility of human milk was determined using the 3-week-old piglet as a model animal for the human infant. The piglets were given either human milk (n 6) or a protein-free diet (n 6) for a 6 d experimental period. Cr2O3 was added as an indigestible marker, to both the human milk and protein-free diet. At the end of the experimental period the piglets were anaesthetized and samples of digesta removed from the terminal ileum of each piglet. After sampling the piglets were killed. Endogenous ileal excretions of amino acids were determined in piglets fed on the protein-free diet. The true digestibilities of total N and amino acid N were 88% and 95% respectively. The true ileal digestibility of the non-amino acid N fraction in human milk, when calculated by difference was only 50%. The true digestibility of the amino acids in human milk ranged from 81–101% with threonine (86%) being the least digestible essential amino acid. When the true ileal digestibility values were used to correct the amino acid composition of human milk, the pattern of digestible amino acids in human milk was different compared with the currently recommended pattern of amino acid requirements for the infant.

Effects of i.v. amino acids on human splanchnic and whole body oxygen consumption, blood flow, and blood temperatures

1994 ◽  
Vol 266 (3) ◽  
pp. E396-E402 ◽  
Author(s):  
T. Brundin ◽  
J. Wahren
Keyword(s):  
Amino Acids ◽  
Blood Flow ◽  
Cardiac Output ◽  
Oxygen Consumption ◽  
Amino Acid ◽  
The Body ◽  
Whole Body ◽  
Acid Infusion ◽  
Amino Acid Infusion ◽  
Splanchnic Oxygen

The thermic effect of amino acid administration was examined in healthy subjects. Pulmonary and splanchnic oxygen uptake, cardiac output, splanchnic blood flow, and blood temperatures were measured in eight healthy men before and during 2.5 h of intravenous infusion of 600 kJ of a mixture of 19 amino acids. Indirect calorimetry and catheter techniques were used, including thermometry in arterial and a hepatic venous blood. During the infusion, pulmonary oxygen uptake rose progressively from a basal value of 269 +/- 6 to 321 +/- 8 ml/min after 2.5 h. The splanchnic oxygen consumption increased from a basal level of 64 +/- 4 to a peak value of 91 +/- 7 ml/min after 2 h of infusion. The 2.5 h average splanchnic proportion of the amino acid-induced whole body thermogenesis was 51 +/- 11%. Cardiac output increased from 6.2 +/- 0.3 in the basal state to 7.3 +/- 0.4 l/min, whereas the splanchnic blood flow remained unchanged during the infusion period. The arteriohepatic venous oxygen difference increased from 51 +/- 4 in the basal state to 65 +/- 5 ml/l after 2 h of amino acid infusion. The blood temperature rose by approximately 0.25 degrees C during the amino acid infusion, reflecting an increased heat accumulation in the body. It is concluded that the splanchnic tissues account for approximately one-half of the amino acid-induced whole body thermogenesis, that amino acid infusion augments blood flow in the extrasplanchnic but not in the splanchnic tissues, and stimulates the accumulation of heat in the body most likely via a resetting of the central thermosensors.

scholarly journals Effects of L-amino Acids on Human Peripheral Neutrophil Granulocyte Activation

2014 ◽  
Vol 8 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Sándor Sipka ◽  
Tamás Keresztes ◽  
Ildikó Kovács ◽  
Sándor Sipka Jr ◽  
Sándor Baráth ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Ex Vivo ◽  
The Body ◽  
Human Neutrophils ◽  
Neutrophil Granulocyte ◽  
Amino Acid Supplementation ◽  
Glucose Levels ◽  
Serum Glutamate

Objective: The objective was to investigate the early (20 minutes) effects of 21 L-amino acids on the activation of human neutrophils and to determine in healthy individuals the effects of a meal on the 1) number and relative luminescence unit (RLU) of peripheral neutrophils, 2) serum glutamate and glucose levels and 3) mTOR signaling network. Methods: The RLU of neutrophils stimulated by Ca2+ ionophor (CaI) and phorbol myristate acetate (PMA) following amino acid supplementation (3 x 10-4 M) or after consuming a meal was determined. L-glutamate was measured by HPLC. Results: All amino acids resulted in significant inhibitions of neutrophil RLU, except for arginine, which stimulated neutrophils. The ratios of amino acid induced inhibition were significantly higher in the cells stimulated by PMA than by CaI. The consumption of a meal resulted in a significant serum glutamate elevation compared to baseline (2.3 versus 0.9 x10-4 M) 90 minutes after ingestion of the meal. It was independent of the body mass index and returned near fasting levels after 150 minutes. The number of neutrophils was significantly elevated 90 minutes after the meal but the PMA induced RLU was significantly decreased. Conclusion: Our ex vivoand in vivoresults suggest that the L-amino acids, independent of their metabolic significance, may continuosly and quickly modify the activity of human peripheral neutrophils, and also the outcome of various immunologic reactions. The activation of the mTORC1 complex likely involves a transient impairment in the function of mTORC2 complex in these processes.

Characterization of whole body compositional growth of male ducks during the twenty-nine day post-hatch period

2013 ◽  
Vol 93 (1) ◽  
pp. 113-122 ◽  
Author(s):  
A. P. Schinckel ◽  
M. E. Einstein ◽  
K. M. Ajuwon ◽  
O. Adeola
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Dry Matter ◽  
The Body ◽  
Whole Body ◽  
Nutrient Requirements ◽  
Accretion Rates ◽  
Indispensable Amino Acids ◽  
Hatch Period

Schinckel, A. P., Einstein, M. E., Ajuwon, K. M. and Adeola, O. 2013. Characterization of whole body compositional growth of male ducks during the twenty-nine day post-hatch period. Can. J. Anim. Sci. 93: 113–122. Changes in whole body dry matter, lipid, ash, energy, crude protein, and amino acids were evaluated during a 29 d post-hatch period in White Pekin ducks. Drakes were assigned to slaughter 1, 8, 15, 22, or 29 d post-hatch with four replicates of four ducks per slaughter period. The body weight (BW) data were fitted to the Weibull function with the form:[Formula: see text]where BWit is the BW of the ith duck at t days of age and A, B, C, and IP are parameters. The value of IP, the inflection point, which minimized the residual SD, was 40 d. Values of A (8591 g, SE=190), B (42.87, SE=11.5), and C (1.7399, SE=0.050) resulted in an R 2 of 0.9836 and residual SD of 83.7 g. Allometric (Y=A BWB), linear-quadratic and exponential (Y=exp (b0+b1BW+b2 (BW)2) functions of BW were fitted to the chemical component and amino acid mass data. Dry matter percentage of the ducks increased (P<0.01) with age. The protein content of the dry matter decreased (P<0.01) from day 1 to day 8 (69 to 58.2%) and then increased to 60% by d 29. Concentrations of several amino acids were affected (P<0.05) by age. The predicted accretion rates of Lys, Trp, and Met relative to protein accretion increased as age increased. The predicted daily accretion rates for major indispensable amino acids increased rapidly the first 5 d post-hatch and subsequently increased but at a decreasing rate to day 29 post-hatch. The relative growth rates of chemical components and indispensable amino acids were affected by age indicating that the nutrient requirements of ducks differ from day 1 to day 29 post-hatch. Compositional growth and amino acid accretion data can be used to model the nutrient requirements of ducks.

Amino acids in the rat intestinal lumen regulate their own absorption from a distant intestinal site

2009 ◽  
Vol 297 (2) ◽  
pp. G292-G298 ◽  
Author(s):  
Fadi H. Mourad ◽  
Kassem A. Barada ◽  
Carmen Khoury ◽  
Tamim Hamdi ◽  
Nayef E. Saadé ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Inhibitory Effect ◽  
Intestinal Lumen ◽  
Jejunal Segment ◽  
Subdiaphragmatic Vagotomy ◽  
Regulatory Loop ◽  
Dependent Transport

Intestinal nutrient transport is altered in response to changes in dietary conditions and luminal substrate level. It is not clear, however, whether an amino acid in the intestinal lumen can acutely affect its own absorption from a distant site. Our aim is to study the effect of an amino acid present in rat small intestinal segment on its own absorption from a proximal or distal site and elucidate the underlying mechanisms. The effect of instillation of alanine (Ala) in either jejunum or ileum on its own absorption at ileal or jejunal level was examined in vivo. The modulation of this intestinal regulatory loop by the following interventions was studied: tetrodotoxin (TTX) added to Ala, subdiaphragmatic vagotomy, chemical ablation of capsaicin-sensitive primary afferent (CSPA) fibers, and IV administration of calcitonin gene-related peptide (CGRP) antagonist. In addition, the kinetics of jejunal Ala absorption and the importance of Na+-dependent transport were studied in vitro after instilling Ala in the ileum. Basal jejunal Ala absorption [0.198 ± 0.018 μmol·cm−1·20 min−1 (means ± SD)] was significantly decreased with the instillation of 20 mM Ala in the ileum or in an adjacent distal jejunal segment (0.12 ± 0.015; P < 0.0001 and 0.138 ± 0.014; P < 0.002, respectively). Comparable inhibition was observed in the presence of proline in the ileum. Moreover, basal Ala absorption from the ileum (0.169 ± 0.025) was significantly decreased by the presence of 20 mM Ala in the jejunum (0.103 ± 0.027; P < 0.01). The inhibitory effect on jejunal Ala absorption was abolished by TTX, subdiaphragmatic vagotomy, neonatal capsaicin treatment, and CGRP antagonism. In vitro studies showed that Ala in the ileum affects Na+-mediated transport and increases Km without affecting Vmax. Intraluminal amino acids control their own absorption from a distant part of the intestine, by affecting the affinity of the Na+-mediated Ala transporter, through a neuronal mechanism that involves CSPA and CGRP.

Plasma amino acid turnover rates and pools in rabbits: in vivo studies using stable isotopes.

1979 ◽  
Vol 237 (5) ◽  
pp. E418 ◽  
Author(s):  
I Nissim ◽  
A Lapidot
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
In Vivo Studies ◽  
Whole Body ◽  
Gas Chromatography Mass Spectrometry ◽  
Plasma Amino Acids ◽  
Isotope Enrichment ◽  
Time Decay ◽  
Turnover Rates

Gas chromatography--mass spectrometry of plasma amino acids has been used to determine the 15N enrichments of plasma glycine and alanine in rabbits in different metabolic states. Isotope-enrichment time-decay curves of plasma amino acids were linear over the course of the measurements after intravenous administration of a single dose of 15N-amino acid. Glycine and alanine pools and turnover rate constants were estimated from decay data. The effects of diurnal variation and fasting on glycine and alanine pool sizes, turnover rates, and flux in rabbits were studied to provide information on the effect of metabolic stress on amino acid kinetics in the whole body. The observations suggests that the transport of systemic glycine or alanine into the hepatocyte is under the control of a regulatory mechanism that compensates for decrease in the extracellular levels of the amino acids by enhancing the activity of the transport system. The volumes of the glycine and alanine pools were found to correspond to the extracellular space of rabbits, and the glycine and alanine pools can be identified as extracellular. We conclude that the plasma glycine and alanine 15N isotope-enrichment time-decay curves over the 1st h after a single intravenous dose of the amino acid represent mainly the hepatic uptake of glycine and alanine from the extracellular pool.

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