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PubMed1981

Blood and tissue branched-chain amino and alpha-keto acid concentrations: effect of diet, starvation, and disease.

Branched-chain alpha-keto and amino acid (BCKA, BCAA) concentrations were measured in blood, plasma, and tissues of rats fed low protein (8% casein) or high protein (60% casein) diets; and in rats fed a stock diet and subjected to 3 days of starvation of chemically-induced diabetes. Concentrations of these amino and ketoacids were also measured in blood from patients with maple syrup urine disease. Valine, isoleucine, and leucine concentrations in blood from rats fed the stock diet were 124 +/- 7, 58 +/- 4 and 99 +/- 5 microM, respectively. Blood BCAA concentrations of rats fed the high protein diet and diabetic rats were elevated 2- to 3-fold; small increases were observed in blood from starved rats. Changes in blood BCAA concentrations paralleled those in tissues, except in starved rats in which the skeletal muscle free BCAA pool increased proportionately more than the circulating pool. Mean blood BCKA concentrations of rats fed the stock diet were low--7.9 +/- 0.5, 7.1 +/- 0.4 and 12.4 +/- 0.7 microM for alpha-ketoisovaleric, alpha-keto-beta-methylvaleric, and alpha ketoisocaproic acids, respectively. All treatments resulted in increases in blood BCKA concentrations of from 1.4 to 2 fold. In liver and heart, concentrations of BCKA, except for that of alpha-ketoisocaproic acid were near the limits of detection (less than 1 nmole/g). There was significant accumulation of all three BCKA in skeletal muscle which was estimated to contain about 80% of the measured body free BCKA pool. Blood BCKA are well regulated. Only in patients with maple syrup urine disease are plasma concentrations of BCKA useful indicators of altered tissue BCAA metabolism. Skeletal muscle, where oxidation of the BCKA is limited by low BCKA dehydrogenase activity, would seem to be the major source of circulating BCKA.

Amino Acids, Branched-Chain↗
PubMed1992

Nutritional support in children with end-stage liver disease: a randomized crossover trial of a branched-chain amino acid supplement.

Malnutrition is common in children with end-stage liver disease (ESLD) awaiting orthotopic liver transplantation (OLT), and nutritional support is assuming an important role in preoperative management. To evaluate preoperative nutritional therapy, 19 children (median age 1.25 y) with ESLD awaiting OLT were prospectively studied. Two high-energy, isoenergetic and isonitrogenous nutritional formulations delivered nasogastrically were compared: a branched-chain amino acid (BCAA)-enriched semielemental formulation and a matched standard semielemental formation. Twelve of 19 patients completed a randomized controlled study before OLT and 10 of 19 completed a full crossover study. Improvements in weight and height occurred during the BCAA supplements, with no statistical change on the standard formulation. Significant increases in total body potassium, midupper arm circumference, and subscapular skinfold thickness occurred during the BCAA supplements, whereas no significant changes occurred during the standard formulation period. Significantly fewer albumin infusions were required during the BCAA supplement. These findings suggest that BCAA-enriched formulas have advantages over standard semielemental formulas in improving nutritional status in children with ESLD, and are deserving of wider application and study.

Albumins↗
PubMed1991

Leucine-induced amino acid antagonism in rats: muscle valine metabolism and growth impairment.

The deleterious effects of branched-chain amino acid (BCAA) antagonism caused by excess dietary leucine include growth depression and subnormal valine and isoleucine pools. To investigate mechanisms causing these changes, rats were gavage-fed low-protein (9%) diets with or without BCAA supplements, and the metabolism of another BCAA (valine) was measured in incubated rat epitrochlearis muscles. A 10% leucine supplement (HL-10) inhibited growth; growth remained subnormal even when 2.6% isoleucine and 2.4% valine (HLIV-10) were added to the diet. Valine decarboxylation in muscle increased 170-270% in rats fed the HL-10 or HLIV-10 diets, but was still markedly lower than we previously found in muscle of rats fed a 14% protein diet. Valine incorporation into muscle protein as an estimate of protein synthesis was unaffected by any of the BCAA supplements. When a lower (4%) concentration of leucine (without or with 0.16% isoleucine and 0.16% valine) was studied, growth was also suppressed but only if rats had not been preconditioned to 9% protein. Although increased BCAA decarboxylation in muscle caused by excess dietary leucine contributes to low valine and isoleucine pools, abnormal growth appears to be independent of low valine and isoleucine levels and is not reflected in suppression of valine incorporation into muscle protein.

Animals↗
PubMed2006

A role for branched-chain amino acids in reducing central fatigue.

Several factors have been identified to cause peripheral fatigue during exercise, whereas the mechanisms behind central fatigue are less well known. Changes in the brain 5-hydroxytryptamine (5-HT) level is one factor that has been suggested to cause fatigue. The rate-limiting step in the synthesis of 5-HT is the transport of tryptophan across the blood-brain barrier. This transport is influenced by the fraction of tryptophan available for transport into the brain and the concentration of the other large neutral amino acids, including the BCAAs (leucine, isoleucine, and valine), which are transported via the same carrier system. Studies in human subjects have shown that the plasma ratio of free tryptophan (unbound to albumin)/BCAAs increases and that tryptophan is taken up by the brain during endurance exercise, suggesting that this may increase the synthesis of 5-HT in the brain. Ingestion of BCAAs increases their concentration in plasma. This may reduce the uptake of tryptophan by the brain and also 5-HT synthesis and thereby delay fatigue. Accordingly, when BCAAs were supplied to human subjects during a standardized cycle ergometer exercise their ratings of perceived exertion and mental fatigue were reduced, and, during a competitive 30-km cross-country race, their performance on different cognitive tests was improved after the race. In some situations the intake of BCAAs also improves physical performance. The results also suggest that ingestion of carbohydrates during exercise delays a possible effect of BCAAs on fatigue since the brain's uptake of tryptophan is reduced.

Amino Acids, Branched-Chain↗
PubMed1986

Addition of branched-chain amino acids to parenteral nutrition of stressed critically ill patients.

We compared the efficacy of a total parenteral nutrition solution supplemented with 44.6% branched-chain amino acids (BCAA) to standard total parenteral nutrition (19.0% BCAA) in the support of critically ill patients. After a 4-day administration of a randomly assigned solution, amino acids were assayed from femoral venous and arterial samples. The BCAA-supplemented solution caused increases in arterial concentrations of valine, isoleucine, and leucine compared to the control solution. The femoral arteriovenous differences for these BCAA were more positive in patients given the control solution. There were no significant differences in nitrogen balance. Since previous studies showing promotion of nitrogen balance with BCAA did not use a balanced substrate for nonprotein caloric support, the lack of a significant difference in the present study may be due to effective utilization of lipid as a fuel source by both groups.

Adult↗
PubMed1988

Changes in respiratory control induced by amino acid infusions.

We compared the metabolic and respiratory responses to a 4-h infusion of an amino acid solution consisting primarily of branched-chain amino acids (BCAA) to those after a standard amino acid solution in healthy subjects. Both the BCAA solution and the standard amino acid solution increased minute ventilation (mean increase 22%, p less than .001, and 18%, p less than .01, respectively), mean inspiratory flow (19%, p less than .01, and 19%, p less than .05) and oxygen consumption (9%, p less than .02, and 5%, NS). PaCO2 decreased (mean decrease 6%, p less than .01); there was a major increase in the ventilatory response to CO2 inhalation during administration of the BCAA solution but not the standard amino acid solution. Increased plasma norepinephrine concentration (mean increase 75%, p less than .001) during the infusion of the standard amino acid solution but not the BCAA solution suggested increased sympathetic activity. The results demonstrate augmented respiratory effects of amino acid infusions by BCAA enrichment, and a dissociation between the respiratory stimulation, metabolic rate, and sympathetic activity.

Adult↗
PubMed1997

Alanylglutamine-enriched total parenteral nutrition improves protein metabolism more than branched chain amino acid-enriched total parenteral nutrition in protracted peritonitis.

Branched chain amino acids (BCAAs) and glutamine are both recommended in catabolic states. The object of this study was to compare the efficacies of alanylglutamine (Ala-Gln)-enriched and BCAA-enriched total parenteral nutrition (TPN) on the protein kinetics in peritonitis. Rats were divided into Ala-Gln and BCAA groups after intraperitoneal implantation of an osmotic pump, delivering a continuous infusion of Escherichia coli. Glutamine composed 30.0% (w/v) of the total amino acids in the Ala-Gln group, and BCAA composed 30.5% (w/v) of the total amino acids in the BCAA group. The two solutions were isocaloric and isonitrogenous. Whole body protein turnover and organ fractional protein synthetic rates (FSR) were measured on days 3 and 5. Serum amino acid levels and mucosal morphology were determined. Ala-Gln group had higher rates of whole body protein turnover, and hepatic FSR on both days. Serum glutamine levels correlated with hepatic and muscle FSR. Ala-Gln TPN group had greater mucosal thickness, numbers of mitoses per crypt, and FSR in distal intestine. Ala-Gln-enriched TPN may be a useful nutritional treatment modality in sepsis.

Amino Acids↗
PubMed2005

Update on nutritional supplementation with branched-chain amino acids.

PURPOSE OF REVIEW: Branched-chain amino acids (BCAAs) have a peculiar role in whole-body nitrogen metabolism. BCAAs are not only a substrate for protein synthesis, but also modulate several components of the synthetic machinery and help to conserve muscle mass; accordingly, several conditions, characterized by protein loss and catabolic status, are likely to benefit from amino acid administration. In addition, the competitive action of BCAAs on amino acid transport across the blood-brain barrier may ultimately alter the synthesis of brain neurotransmitters, involved in neurological diseases. RECENT FINDINGS: Both putative actions of BCAAs have been tested in controlled clinical studies in the last few years. The beneficial effects on nutrition were reported to improve muscle performance, reduce protein loss during bed-rest, favor weight loss in obesity, reduce catabolism in trauma patients and improve clinical outcomes in patients with advanced cirrhosis. In this last area, the effects on nutrition might be coupled with the effects on hepatic encephalopathy mediated by improved neurotransmission, successfully tested in mania, tardive dyskinesia and spinocerebellar degeneration. SUMMARY: After 30 years of investigation with BCAAs, new studies each year provide further evidence supporting their beneficial effect in a variety of diseases. There is a need for long-term, randomized clinical studies, both in the prevention and in the treatment of various pathological conditions.

Amino Acids, Branched-Chain↗
PubMed2004

Intracellular effectors regulating the activity of the Lactococcus lactis CodY pleiotropic transcription regulator.

CodY is a pleiotropic transcriptional regulator conserved in low-G+C Gram-positive bacteria. Two distinct signals have been shown independently to influence the activity of this regulator: the level of intracellular GTP in Bacillus subtilis and the level of intracellular branched-chain amino acids (BCAA) isoleucine, leucine and valine in Lactococcus lactis. Measurement of BCAA and GTP levels in several environmental conditions showed that L. lactis CodY responded to the intracellular BCAA concentrations but not to physiological fluctuations in intracellular GTP. In addition, we demonstrated that CodY from L. lactis did not respond to intracellular GTP even when complementing CodY activity in B. subtilis. However, L. lactis CodY activity could still be modulated in B. subtilis by adding a rich nitrogen source to the growth media. This finding suggests that only BCAA are sensed by L. lactis CodY, whereas both GTP and BCAA signals may be integrated by B. subtilis CodY. The difference in the function of CodY from B. subtilis and L. lactis seems to reflect the difference in the physiology of these two bacteria.

Adaptation, Physiological↗
PubMed2000

Branched-chain amino acid biosynthesis is essential for optimal growth of Streptococcus thermophilus in milk.

Lactic acid bacteria are nutritionally demanding bacteria which need, among other things, amino acids for optimal growth. We identified the branched-chain amino acid (BCAA) biosynthesis pathway as an essential pathway for optimal growth of Streptococcus thermophilus in milk. Through random insertional mutagenesis, we isolated and characterized two mutants for which growth in milk is affected as a consequence of ilvB and ilvC gene interruptions. This situation demonstrates that the BCAA biosynthesis pathway is active in S. thermophilus. BCAA biosynthesis is necessary but not sufficient for optimal growth of S. thermophilus and is subject to retro-inhibition processes. The specificity of the BCAA biosynthesis pathway in S. thermophilus lies in the independent transcription of the ilvC gene encoding a keto acid reductoisomerase acting on acetolactate at the junction of the BCAA and acetoin biosynthesis pathways. The possible advantages for S. thermophilus of keeping this biosynthesis pathway active could be linked either to adaptation of the organism to milk, which is different than that of other dairy bacteria, or to the role of the pathway in maintaining the internal pH.

Amino Acids, Branched-Chain↗
PubMed2000

Transcriptional and translational regulation of alpha-acetolactate decarboxylase of Lactococcus lactis subsp. lactis.

The alpha-acetolactate decarboxylase (ALDC) gene, aldB, is the penultimate gene of the leu-ilv-ald operon, which encodes the three branched-chain amino acid (BCAA) biosynthesis genes in Lactococcus lactis. Its product plays a dual role in the cell: (i) it catalyzes the second step of the acetoin pathway, and (ii) it controls the pool of alpha-acetolactate during leucine and valine synthesis. It can be transcribed from the two promoters present upstream of the leu and ilv genes (P1 and P2) or independently under the control of its own promoter (P3). In this paper we show that the production of ALDC is limited by two mechanisms. First, the strength of P3 decreases greatly during starvation for BCAAs and under other conditions that generally provoke the stringent response. Second, although aldB is actively transcribed from P1 and P2 during BCAA starvation, ALDC is not significantly produced from these transcripts. The aldB ribosome binding site (RBS) appears to be entrapped in a stem-loop, which is itself part of a more complex RNA folding structure. The function of the structure was studied by mutagenesis, using translational fusions with luciferase genes to assess its activity. The presence of the single stem-loop entrapping the aldB RBS was responsible for a 100-fold decrease in the level of aldB translation. The presence of a supplementary secondary structure upstream of the stem-loop led to an additional fivefold decrease of aldB translation. Finally, the translation of the ilvA gene terminating in the latter structure decreased the level of translation of aldB fivefold more, leading to the complete extinction of the reporter gene activity. Since three leucines and one valine are present among the last six amino acids of the ilvA product, we propose that pausing of the ribosomes during translation could modulate the folding of the messenger, as a function of BCAA availability. The purpose of the structure-dependent regulation could be to ensure the minimal production of ALDC required for the control of the acetolactate pool during BCAA synthesis but to avoid its overproduction, which would dissipate acetolactate. Large amounts of ALDC, necessary for operation of the acetoin pathway, could be produced under favorable conditions from the P3 transcripts, which do not contain the secondary structures.

Base Sequence↗
PubMed2006

Identification and functional characterization of the Lactococcus lactis CodY-regulated branched-chain amino acid permease BcaP (CtrA).

Transcriptome analyses have previously revealed that a gene encoding the putative amino acid transporter CtrA (YhdG) is one of the major targets of the pleiotropic regulator CodY in Lactococcus lactis and Bacillus subtilis. The role of ctrA in L. lactis was further investigated with respect to both transport activity as well as CodY-mediated regulation. CtrA is required for optimal growth in media containing free amino acids as the only amino acid source. Amino acid transport studies showed that ctrA encodes a secondary amino acid transport system that is specific for branched-chain amino acids (BCAAs) (isoleucine, leucine, and valine) and methionine, which is in disagreement with its previously proposed function (a cationic amino acid transporter), which was assigned based on homology. We propose to rename CtrA BcaP, for branched-chain amino acid permease. BcaP is a member of a group of conserved transport systems, as homologs are widely distributed among gram-positive bacteria. Deletion of bcaP resulted in the loss of most of the BCAA uptake activity of L. lactis, indicating that BcaP is the major BCAA carrier of this organism. Deletion of bcaP together with a second (putative) BCAA permease, encoded by brnQ, further reduced the viability of the strain. DNA microarray analysis showed that deletion of bcaP predominantly affects genes belonging to the regulons of the transcriptional regulator CodY, which is involved in global nitrogen metabolism and needs BCAAs for its activation, and of CmbR, which is involved in sulfur amino acid metabolism.

Amino Acid Transport Systems↗
PubMed2004

Branched-chain amino acid supplementation and human performance when hypohydrated in the heat.

The serotonin system may contribute to reduced human performance when hypohydrated in the heat. This study determined whether branched-chain amino acid (BCAA) supplementation could sustain exercise and cognitive performance in the heat (40 degrees C dry bulb, 20% relative humidity) when hypohydrated by 4% of body mass. Seven heat-acclimated men completed two experimental trials, each consisting of one preparation and one test day. On day 1, a low-carbohydrate diet was eaten and subjects performed exhaustive cycling (morning) and treadmill exercise in the heat (afternoon) to lower muscle glycogen and achieve the desired hypohydration level. On day 2, subjects consumed an isocaloric BCAA and carbohydrate (BC) or carbohydrate-only drink during exercise. Experimental trials included 60 min of cycle ergometry (50% peak oxygen uptake) followed by a 30-min time trial in the heat. A cognitive test battery was completed before and after exercise, and blood samples were taken. BC produced a 2.5-fold increase (P < 0.05) in plasma BCAA and lowered (P < 0.05) the ratios of total tryptophan to BCAA and large neutral amino acid. Blood prolactin, glucose, lactate, and osmolality were not different between trials but increased over time. Cardiovascular and thermoregulatory data were also similar between trials. BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated.

Adult↗
PubMed2003

Nutritional and clinical evaluation of a modified soy protein with covalently bound branched-chain amino acids in cirrhotic sprague-dawley rats.

Several studies suggested that branched-chain amino acids (BCAA) improve plasma amino acid imbalance as well as protein metabolism in patients with cirrhosis. However, commercial formulas supplemented with free BCAA have their limitations. We evaluated a modified soy protein diet with covalently bound BCAA (diet M) by comparing it with diets based on casein (diet C) or Hepatic Aid II (diet H; commercial formula) as protein sources. After 3 weeks of bile duct obstruction, 24 Sprague-Dawley rats divided into three groups received diets with 9% (w/w) protein/amino acids for 7 days. Nutritional and clinical parameters were determined. Nitrogen balance and weight gain (g)/protein intake (g) with diet M (0.19 +/- 0.31 and 1.33 +/- 1.43 g, respectively) were significantly higher (p < 0.05) than with diet H (-0.34 +/- 0.20 and -0.34 +/- 1.11 g), but comparable to those with diet C (0.04 +/- 0.38 and 0.20 +/- 0.93 g). Animals on diet M had a significantly (p < 0.05) increased plasma BCAA:aromatic amino acid ratio (1.8 +/- 0.3) as compared with those on diets H (1.3 +/- 0.1) and C (0.8 +/- 0.0). There were no significant differences in organ weight or liver function among the groups. We conclude that the BCAA-modified protein is an attractive option in the nutritional support of patients having cirrhosis.

Amino Acids↗
PubMedDate not supplied

Enriched branched-chain amino acid formula versus a casein-based supplement in the treatment of cirrhosis.

An orally administered branched-chain amino acid (BCAA) rich supplement (T), Travasorb-Hepatic was compared to a casein based supplement (E), Ensure, in a randomized double-blind cross-over study in eight malnourished, stable cirrhotics unable to achieve a daily dietary protein intake of 1.0 g/kg. Doses of antiportal systemic encephalopathy drugs remained constant and a baseline 1000 kcal, 40 g dietary protein intake was encouraged. To this diet, supplemental protein was added in daily 20-g increments to a maximum of 60 g supplemental protein. Mental status, asterixis, and number connection tests were assessed daily and an antiportal systemic encephalopathy index calculated. There was no significant difference in the mean intake of dietary protein (T, 33.7 +/- 4.0 g; E, 26.7 +/- 10.8 g), supplemental protein (T, 43.1 +/- 8.3 g; E, 47.9 +/- 7.1 g), or N2 balance (T, 4.2 +/- 3.7 g; E, 3.4 +/- 4.4) between treatment trials. The antiportal systemic encephalopathy index improved on E, with no significant change in the BCAA:aromatic acid molar ratio. This ratio improved on T (1.02 +/- 2.0 to 2.7 +/- 1.1), but was not accompanied by improvement in the antiportal systemic encephalopathy index. The improved protein tolerance in both groups was not further increased by a highly enriched BCAA formula compared to one with a moderate BCAA content from a natural dietary protein source. Thus, both conventional casein-based supplements and enriched BCAA formulas are well tolerated and can be safely and effectively used as an integral part of diet therapy.

Amino Acids↗
PubMedDate not supplied

Intravenous branched chain amino acid trial in marrow transplant recipients.

Branched chain amino acids (BCAA) improve nitrogen balance and end-organ function in surgical patients, but are untested in marrow transplant recipients. We compared nitrogen balance, urinary 3-methylhistidine-to-creatinine ratio, upper arm anthropometry, serum prealbumin, and day to peripheral engraftment in a randomized, double-blinded trial between 45% (high-leucine) and 23% BCAA intravenous solutions in 40 adult leukemia patients for 1 month following allogeneic marrow transplantation. Nutritional support, provided at approximately 30 nonprotein calories/kg and 0.21 g nitrogen/kg ideal weight, did not differ between groups. Despite greater nitrogen loss and muscle breakdown evidenced by increased 3-methylhistidine-to-creatinine ratio and loss of arm muscle area by study end in the 45% BCAA, no statistical differences were observed when nitrogen balance was compared by week and within stress level as defined by organ and infectious complications. It is likely the patients in the 45% BCAA experienced greater metabolic stress by study end. Serum prealbumin and day posttransplant to peripheral engraftment also did not differ between groups. The chances (power) of this study exceeded 85% in detecting a difference in nitrogen balance of 2.5 g during study week 1 and 4.0 g during week 2. The power during week 3 was 77% for detecting a difference of 4.0 g, and it is unlikely that the true difference exceeds this magnitude. Thus, we did not find any evidence that intravenous BCAA-enriched solutions improved nitrogen balance during the first month after marrow transplantation.

Adolescent↗
PubMedDate not supplied

Enteral and parenteral branched chain amino acid-supplemented nutritional support in patients with encephalopathy due to alcoholic liver disease.

The effects of branched chain amino acid (BCAA)-enriched diets (fed for 7 days) on encephalopathy, plasma amino acid concentrations, aromatic amino acid turnover, and protein synthesis rates were determined in eight patients with alcoholic liver failure. Four patients were given the diet intravenously (iv group) (total amino acids, 60-80 g/day, BCAA content 51%, energy 2000 kcal/day) and four patients (NG group) were given a semi-elemental formulation via constant nasogastric (NG) infusion (amino acids 58 g, BCAA 43%, oligopeptides 19.5 g, energy 2000 kcal/day). The enteral diet was given at one-half strength for the first 3 days. A 10-hr constant infusion of [U-14C]phenylalanine tracer was used in four patients to measure aromatic amino acid (AA) turnover and rates of incorporation into various body proteins. Seven of the eight patients made a good clinical recovery, with reversal of encephalopathy within 3 days of dietary intervention. One became septicemic and deteriorated. While plasma bilirubin concentrations dropped, liver enzymes remained elevated. Mean nitrogen balance was negative at the beginning and positive at the end of the study, in both groups. Initial amino acid profiles demonstrated low plasma BCAA content and BCAA:AA ratios. Significant improvements occurred in the iv group by day 2 and in both groups by day 7. Isotope studies showed that, whereas aromatic amino acid oxidation remained unchanged, greater quantities were incorporated in whole body protein, albumin, transferrin, fibrinogen, and immunoglobulins.

Adult↗
PubMedDate not supplied

Immediate stimulation of protein metabolism in burned rats by total parenteral nutrition enriched in branched-chain amino acids.

The effects of two kinds of total parenteral nutrition (TPN) on energy and protein metabolism were examined in rats subjected to 15% full-thickness scald burns in the absence of septic complications. One type of TPN was enriched in branched-chain amino acids (BCAAs), especially leucine (45% BCAA content), and the other was conventional TPN (21% BCAA content). Burned rats received isocaloric and isonitrogeneous TPN solutions for 48 hr after resuscitation by saline infusion for 24 hr. Liver and rectus abdominis muscle were removed from the rats at 7, 24, 48, and 72 hr. The concentrations of adenine nucleotides, RNA, protein, glucose-6-phosphate, hepatic glycogen, muscle phosphocreatine, and 3-methylhistidine were determined. Metabolic alterations occurred during the period of saline resuscitation (0-24 hr). At 48 hr the RNA and protein levels were significantly more improved in the BCAA-TPN group than in the conventional TPN group. At 72 hr, however, the results for the two groups were similar in most metabolite levels. Thus, BCAA-TPN enriched in leucine rapidly stimulated protein synthesis in the liver and muscle. This rapid effect may make it useful during the initial nutritional management of severe trauma patients.

Amino Acids, Branched-Chain↗