Ingestion of a bolus of free amino acids is followed by more rapid amino acid absorption and greater postprandial plasma amino acid availability when compared to the ingestion of an equivalent amount of intact protein

Abstract Objectives The rate of protein digestion and amino acid absorption determines the postprandial rise in circulating amino acids and, as such, modulates postprandial muscle protein synthesis rates. This study compares protein digestion and amino acid absorption kinetics and the subsequent muscle protein synthetic response following ingestion of intact protein versus an equivalent amount of free, crystalline amino acids. Methods Twenty-four healthy, young subjects (age: 22 ± 3 y, BMI: 23 ± 2 kg·m−2, sex: 12 M/12F) ingested 30 g intrinsically L-[1–13C]-phenylalanine and L-[1–13C]-leucine labeled milk protein (PROT; n = 12) or an equivalent amount of free amino acids (AA; n = 12). In addition, subjects received primed continuous L-[ring-2H5]-phenylalanine, L-[ring-3,5–2H2]-tyrosine, and L-[1–13C]-leucine infusions. Blood samples and muscle biopsies were obtained frequently to assess protein digestion and amino acid absorption kinetics and subsequent muscle protein synthesis rates over a 6 h postprandial period. An unpaired t-test was used to compare overall exogenous phenylalanine release in plasma. For other parameters repeated measures ANOVA were applied to determine differences between groups over time (time as within, and group as between-subjects factor). Data are expressed as mean ± SD. Results Postprandial plasma amino acid concentrations and exogenous phenylalanine appearance rates increased after ingestion of PROT and AA (both, P < 0.001), with a greater increase following ingestion of AA when compared to PROT (time*group interaction P < 0.001). Exogenous phenylalanine release in plasma assessed over the 6 h postprandial period, was greater in AA (76 ± 9%) compared with PROT (59 ± 10%; P < 0.001). Ingestion of AA and PROT strongly increased muscle protein synthesis rates based upon L-[ring-2H5]-phenylalanine (time effect P < 0.001), with no differences between groups (from 0.037 ± 0.015 to 0.053 ± 0.014%·h−1 and from 0.039 ± 0.016 to 0.051 ± 0.010%·h−1, respectively; time*group interaction P = 0.629). Conclusions Ingestion of free amino acids as opposed to intact milk protein is followed by more rapid amino acid absorption and greater postprandial plasma amino acid availability, but this does not further augment postprandial muscle protein synthesis rates. Funding Sources This research did not receive external funding.

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Optimising amino acid absorption: essential to improve nitrogen balance and metabolic control in phenylketonuria

Nutrition Research Reviews ◽

10.1017/s0954422418000173 ◽

2018 ◽

Vol 32 (1) ◽

pp. 70-78 ◽

Cited By ~ 5

Author(s):

Anita MacDonald ◽

Rani H. Singh ◽

Júlio César Rocha ◽

Francjan J. van Spronsen

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Free Amino ◽

N Balance ◽

Intact Protein ◽

Hydroxylase Deficiency ◽

Strict Adherence ◽

Acid Absorption ◽

Amino Acid Absorption ◽

The Impact

AbstractIt has been nearly 70 years since the discovery that strict adherence to a diet low in phenylalanine prevents severe neurological sequelae in patients with phenylalanine hydroxylase deficiency (phenylketonuria; PKU). Today, dietary treatment with restricted phenylalanine intake supplemented with non-phenylalanine amino acids to support growth and maintain a healthy body composition remains the mainstay of therapy. However, a better understanding is needed of the factors that influence N balance in the context of amino acid supplementation. The aim of the present paper is to summarise considerations for improving N balance in patients with PKU, with a focus on gaining greater understanding of amino acid absorption, disposition and utilisation. In addition, the impact of phenylalanine-free amino acids on 24 h blood phenylalanine/tyrosine circadian rhythm is evaluated. We compare the effects of administering intact protein v. free amino acid on protein metabolism and discuss the possibility of improving outcomes by administering amino acid mixtures so that their absorption profile mimics that of intact protein. Protein substitutes with the ability to delay absorption of phenylalanine and tyrosine, mimicking physiological absorption kinetics, are expected to improve the rate of assimilation into protein and minimise fluctuations in quantitative plasma amino acid levels. They may also help maintain normal glycaemia and satiety sensation. This is likely to play an important role in improving the management of patients with PKU.

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A COMPARISON OF THE EFFECT OF DIETARY FAT AND CARBOHYDRATE ON FREE AMINO ACIDS IN THEBLOOD PLASMA OF CHICKS

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y67-025 ◽

1967 ◽

Vol 45 (2) ◽

pp. 225-234 ◽

Cited By ~ 8

Author(s):

Tsang-Cheng Shao ◽

D. C. Hill

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Dietary Fat ◽

Free Amino Acids ◽

Free Amino ◽

Plasma Amino Acid ◽

Considerable Time ◽

Lower Plasma ◽

Amino Acid Levels ◽

Plasma Free Amino Acids

As previously reported, an increased concentration of plasma free amino acids, particularly lysine and threonine, was found when chicks were fasted for 24 hours. This increase was suppressed where a nonprotein diet was fed. Dextrose as the chief energy source in the nonprotein diet was more effective than shortening or lard in this respect. However, the degree to which the two energy sources differed was less where birds were adapted to the utilization of fat by feeding a diet rich in fat for a considerable time before making the comparison. Insulin administration to fasted chicks was found to lower plasma amino acid levels. The possible influence of interrelationships among dextrose, fat, and insulin on plasma amino acid levels is discussed.

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Influence of dietary protein concentration on the oxidation of phenylalanine by the young pig

British Journal Of Nutrition ◽

10.1079/bjn19860071 ◽

1986 ◽

Vol 55 (3) ◽

pp. 651-658 ◽

Cited By ~ 43

Author(s):

Ronald O. Ball ◽

Henry S. Bayley

Keyword(s):

Amino Acids ◽

Amino Acid ◽

G Protein ◽

Dietary Protein ◽

Free Amino Acids ◽

Free Amino ◽

Crude Protein ◽

Protein Concentration ◽

Skim Milk ◽

Intact Protein

1. Piglets were weaned at 3 d of age and reared to 2.5 kg on a liquid diet in which the protein was supplied by dried skim milk and a mixture of free amino acids. The oxidation of L-[l-14C]phenyIalanine was measured as an indication of the partition of amino acids between retention and catabolism in pigs (2.5 kg) offered meals containing vaned concentrations of crude protein (nitrogen x 6.25).2. The dietary protein concentration was varied either by increasing the inclusion of a mixture of free amino acids in a series of diets containing 100 g protein/kg from skim milk, or by increasing the level of inclusion of the skim milk in a series of diets containing the equivalent of 100 g protein/kg from the free amino acid mixture.3. The oxidation of phenylalanine was minimized by dietary protein concentrations of 240 and 258 g/kg for the diets containing increasing concentrations of free amino acids or skim milk respectively.4. These results show that a mixture of free amino acids is used more effectively than intact protein for promoting retention of essential amino acids.5. The recovery of radioactivity in expired carbon dioxide was inversely related to the recovery of radioactivity in liver tissue when the concentration of dietary crude protein was increased from deficient to adequate, demonstrating that the fractional oxidation of the indicator amino acid was inversely related to protein synthesis.

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Effect of rumen-protected lysine on growth performance, carcass characteristics, and plasma amino acid profile in feedlot steers

Translational Animal Science ◽

10.1093/tas/txaa128 ◽

2020 ◽

Vol 4 (3) ◽

Author(s):

Katie J Heiderscheit ◽

Stephanie L Hansen

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Growth Performance ◽

Free Amino Acids ◽

Free Amino ◽

Carcass Characteristics ◽

Fixed Effect ◽

Plasma Amino Acid ◽

Deficient Diet ◽

Feedlot Steers

Abstract The objective of this study was to evaluate growth performance, carcass characteristics, and plasma amino acid profiles of feedlot steers fed rumen-protected Lys. Forty-two Angus-cross steers (304 ± 25 kg) were blocked by weight and fed treatment diets for 180 d (growing days 0 to 55; finishing days 56 to 180): 1) Lys-deficient diet (CON; n = 12 steers), 2) Lys-adequate diet containing soybean meal (POS; n = 12 steers), or 3) Lys-deficient diet plus supplemental rumen-protected Lys (RPL; AjiPro-L; Ajinomoto Animal Nutrition North America, Eddyville, IA; n = 18 steers). Consecutive day bodyweights (BWs) were recorded to begin and end growing and finishing. Individual steer dry matter intake (DMI) was recorded. Blood was collected on days 0, 56, and 179 for analysis of physiological free amino acids. Steers were harvested on day 180 and carcass characteristics were recorded. Data were analyzed using Proc Mixed of SAS 9.4. Steer was the experimental unit and treatment was the fixed effect for all parameters. Block was a fixed effect for growth performance, feed intake, and carcass data. The day 0 value for each parameter of physiological free amino acids was used as a covariate during analysis. The CON steers had greater BW, average daily gain (ADG), and gain to feed (G:F) at the end of growing (day 56; P ≤ 0.05) vs. POS and RPL. The CON steers also had greater final BW (P = 0.04) and overall ADG (P = 0.04) than RPL, while POS was intermediate. Carcass characteristics were not different across treatments [hot carcass weight, dressing percent, ribeye area, back fat, kidney/pelvic/heart (KPH) percent, marbling, or calculated yield grade; P ≥ 0.13]. Plasma urea N was greater in POS steers on days 56 and 179 (P ≤ 0.04). Plasma Lys and Arg concentrations were greater in POS at day 56 (P ≤ 0.02); however, there was no difference among treatments for these two variables at day 179 (P ≥ 0.44). Steers in all treatments had greater DMI than predicted, causing a negative metabolizable Lys balance for all treatments during growing. Though the metabolizable Lys balance was positive for POS and RPL-fed steers during finishing, the increased metabolizable Lys in these treatments may have decreased performance if other amino acids were imbalanced due to increased intakes.

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Nitrogen from ammonia is as efficient as that from free amino acids or protein for improving growth performance of pigs fed diets deficient in nonessential amino acid nitrogen

Journal of Animal Science ◽

10.2527/jas2016.0959 ◽

2017 ◽

Vol 95 (7) ◽

pp. 3093

Author(s):

W. D. Mansilla ◽

J. K. Htoo ◽

C. F. M. de Lange

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Growth Performance ◽

Free Amino Acids ◽

Free Amino ◽

Amino Acid Nitrogen ◽

Nonessential Amino Acid

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Biochemische Aspekte des Aminosäuren-Stoffwechsels bei Psoriasis vulgaris / Biochemical Aspects of Amino Acid Metabolism in Psoriasis vulgaris

Zeitschrift für Naturforschung C ◽

10.1515/znc-1973-7-816 ◽

1973 ◽

Vol 28 (7-8) ◽

pp. 449-451 ◽

Cited By ~ 2

Author(s):

G. Peter ◽

H. Angst ◽

U. Koch

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Free Amino Acids ◽

Free Amino ◽

Amino Acid Metabolism ◽

Acid Metabolism ◽

Psoriasis Vulgaris ◽

Normal Subjects ◽

Pathological Process

Free and protein-bound amino acids in serum and scales were investigated. In serum the bound amino acids of psoriatics are significantly higher with exception of Pro, Met, Tyr and Phe in contrast to normal subjects. For free amino acids the differences between normal subjects and psoriatics found in serum and scales are not significant. Results are discussed in relation to the single amino acids and the biochemical correlations are outlined which takes the pathological process as a basis.

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Liver extract and its free amino acids equally stimulate gastric acid secretion

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1980.239.6.g493 ◽

1980 ◽

Vol 239 (6) ◽

pp. G493-G496 ◽

Cited By ~ 5

Author(s):

E. J. Feldman ◽

M. I. Grossman

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Acid Secretion ◽

Gastric Acid Secretion ◽

Free Amino Acid ◽

Free Amino Acids ◽

Free Amino ◽

Liver Extract ◽

Amino Acid Mixture ◽

Acid Mixture

Using intragastric titration in dogs with gastric fistulas, dose-response studies were carried out with liver extract and with a mixture of amino acids that matched the free amino acids found in liver extract. All solutions were adjusted to pH 7.0 and osmolality to 290 mosmol x kg-1. Doses are expressed as the sum of the concentrations of all free amino acids. At each dose studied (free amino acid concentration: 2.8, 5.6, 11, 23, and 45 mM), acid secretion in response to the free amino acid mixture was not significantly different from that of liver extract. The peak response to both liver extract and the free amino acid mixture occurred with the 23-mM dose and represented about 60% of the maximal response to histamine. The serum concentrations of gastrin after liver extract and the amino acid mixture were not significantly different. It is concluded that in dogs with gastric fistula, gastric acid secretion and release of gastrin were not significantly different in response to liver extract and to a mixture of amino acids that simulated the free amino acid content of liver extract.

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