Supply Of Branched-chain Amino Acids Research Articles

Effect of additionally BCAA supply on imazamox-treated sunflower and antioxidative defense system

Sunflower is an economically important oilseed crop worldwide and weeds have a negative effect on its yields. The herbicide imazamox, combined with imazamox-resistant (IMI-R) sunflower hybrids, is a technology known as the Clearfield production system and successfully controls weeds. The mechanism of action of the herbicide imazamox is related to blocking the AHAS enzyme, which catalyzes the first step in the biosynthetic pathway of the branched-chain amino acids (BCAA). In the present study, we investigated the effect of the supplementary addition of BCAA to imazamox-treated IMI-R sunflower plants and antioxidative metabolism. Our results showed that the additional application of BCAA has a beneficial effect on both the total protein content and the activity of the antioxidant defense system of plants. This amelioration is probably a secondary effect of the enhanced protein metabolism and the supposed direct involvement of the three amino acids in the overall protein turnover.

Amino Acid Metabolism Controls Fatty Acid Structure in Staphylococcus aureus

Staphylococcus aureus produces a combination of branched and straight chain fatty acids to maintain membrane homeostasis. Recently, we showed that the branched:straight chain ratio in fatty acids is controlled by amino acid metabolism that supplies the branched‐chain acyl‐CoA primers for fatty acid biosynthesis. The fatty acid composition is determined when FabH catalyzes the initial condensation using the available short‐chain acyl‐CoA primers with malonyl‐acyl carrier protein. Branched‐chain ketoacid dehydrogenase (Bkd) is recognized as the primary enzyme responsible for the formation of branched‐chain acyl‐CoA primers. Most experiments with S. aureus are carried out in media with an abundant supply of branched‐chain amino acids where the Bkd pathway for the utilization of Ile dominates. However, branched‐chain fatty acids are still produced in bkd knockout strains and the enzyme(s) responsible for this alternate biosynthetic pathway is unknown. It is important to understand how S. aureus copes with limited availability of Ile because multiple laboratories conclude that isoleucine is a limiting nutrient at S. aureus infection sites that regulates metabolism and virulence.Mass tracing experiments with heavy amino acids show that Bkd is the key step in a pathway that selectively converts extracellular Ile into 2‐methyl‐butyryl‐CoA (anteiso‐C5‐CoA) that FabH uses to initiate anteiso fatty acid synthesis. The phosphatidylglycerol (PG) molecular species in wild‐type strains consists of a mixture of anteiso‐17:0 and ‐19:0 and 18:0 and 20:0 straight chain fatty acids in the 1‐position paired with anteiso‐15:0 in the 2‐position. If Ile is removed from the medium, Leu metabolism results in the introduction of iso‐15:0 into the 2‐position. Val is not significantly metabolized by the Bkd pathway. The analysis of the PG molecular species in strains lacking an active Bkd complex have a straight chain fatty acid in the 1‐position paired with either iso‐14:0 or anteiso‐15:0 in the 2‐position. This same switch in PG molecular species composition is observed when wild‐type strains are grown in defined medium lacking both Ile and Leu. Our metabolomics analyses show that C5‐CoA derived from the Bkd pathway is the most abundant acyl‐CoA primer available for FabH in wild‐type strains; however, when Ile and Leu are not present in the medium, iso‐C4‐CoA increases and anateiso‐C5‐CoA decreases. In the bkd knockout strains, the C4‐CoA pool is even more elevated, and the C5‐CoA pool is substantially lower. This means that in the absence of Bkd, a second pathway creates a supply of iso‐C4‐CoA for FabH to prime fatty acid synthesis and produce iso‐14:0 for the 2‐position. Thus, there are two pathways for the formation of branched‐chain acyl‐CoA substrates for FabH. The Bkd pathway is responsible for the utilization of extracellular Ile (and to a lesser extent, Leu) to initiate fatty acid synthesis, whereas the alternate, de novo biosynthetic pathway makes a significant contribution in wild‐type strain growth without exogenous Ile and is the only process operating in the bkd knockout strains. We are testing the hypothesis that the key enzyme in the de novo pathway to iso‐C4‐CoA is CidC, an enzyme related to pyruvate oxidase.

Dietary branched-chain amino acid restriction alters fuel selection and reduces triglyceride stores in hearts of Zucker fatty rats.

Elevations in circulating levels of branched-chain amino acids (BCAAs) are associated with a variety of cardiometabolic diseases and conditions. Restriction of dietary BCAAs in rodent models of obesity lowers circulating BCAA levels and improves whole-animal and skeletal-muscle insulin sensitivity and lipid homeostasis, but the impact of BCAA supply on heart metabolism has not been studied. Here, we report that feeding a BCAA-restricted chow diet to Zucker fatty rats (ZFRs) causes a shift in cardiac fuel metabolism that favors fatty acid relative to glucose catabolism. This is illustrated by an increase in labeling of acetyl-CoA from [1-13C]palmitate and a decrease in labeling of acetyl-CoA and malonyl-CoA from [U-13C]glucose, accompanied by a decrease in cardiac hexokinase II and glucose transporter 4 protein levels. Metabolomic profiling of heart tissue supports these findings by demonstrating an increase in levels of a host of fatty-acid-derived metabolites in hearts from ZFRs and Zucker lean rats (ZLRs) fed the BCAA-restricted diet. In addition, the twofold increase in cardiac triglyceride stores in ZFRs compared with ZLRs fed on chow diet is eliminated in ZFRs fed on the BCAA-restricted diet. Finally, the enzymatic activity of branched-chain ketoacid dehydrogenase (BCKDH) is not influenced by BCAA restriction, and levels of BCAA in the heart instead reflect their levels in circulation. In summary, reducing BCAA supply in obesity improves cardiac metabolic health by a mechanism independent of alterations in BCKDH activity.

Short-term dietary reduction of branched-chain amino acids reduces meal-induced insulin secretion and modifies microbiome composition in type 2 diabetes: a randomized controlled crossover trial

ABSTRACTBackgroundEpidemiological studies have shown that increased circulating branched-chain amino acids (BCAAs) are associated with insulin resistance and type 2 diabetes (T2D). This may result from altered energy metabolism or dietary habits.ObjectiveWe hypothesized that a lower intake of BCAAs improves tissue-specific insulin sensitivity.MethodsThis randomized, placebo-controlled, double-blinded, crossover trial examined well-controlled T2D patients receiving isocaloric diets (protein: 1 g/kg body weight) for 4 wk. Protein requirements were covered by commercially available food supplemented ≤60% by an AA mixture either containing all AAs or lacking BCAAs. The dietary intervention ensured sufficient BCAA supply above the recommended minimum daily intake. The patients underwent the mixed meal tolerance test (MMT), hyperinsulinemic-euglycemic clamps (HECs), and skeletal muscle and white adipose tissue biopsies to assess insulin signaling.ResultsAfter the BCAA− diet, BCAAs were reduced by 17% during fasting (P < 0.001), by 13% during HEC (P < 0.01), and by 62% during the MMT (P < 0.001). Under clamp conditions, whole-body and hepatic insulin sensitivity did not differ between diets. After the BCAA− diet, however, the oral glucose sensitivity index was 24% (P < 0.01) and circulating fibroblast-growth factor 21 was 21% higher (P < 0.05), whereas meal-derived insulin secretion was 28% lower (P < 0.05). Adipose tissue expression of the mechanistic target of rapamycin was 13% lower, whereas the mitochondrial respiratory control ratio was 1.7-fold higher (both P < 0.05). The fecal microbiome was enriched in Bacteroidetes but depleted of Firmicutes.ConclusionsShort-term dietary reduction of BCAAs decreases postprandial insulin secretion and improves white adipose tissue metabolism and gut microbiome composition. Longer-term studies will be needed to evaluate the safety and metabolic efficacy in diabetes patients.This trial was registered at clinicaltrials.gov as NCT03261362.

Controlled branched-chain amino acids auxotrophy in Listeria monocytogenes allows isoleucine to serve as a host signal and virulence effector.

Listeria monocytogenes (Lm) is a saprophyte and intracellular pathogen. Transition to the pathogenic state relies on sensing of host-derived metabolites, yet it remains unclear how these are recognized and how they mediate virulence gene regulation. We previously found that low availability of isoleucine signals Lm to activate the virulent state. This response is dependent on CodY, a global regulator and isoleucine sensor. Isoleucine-bound CodY represses metabolic pathways including branched-chain amino acids (BCAA) biosynthesis, however under BCAA depletion, as occurs during infection, BCAA biosynthesis is upregulated and isoleucine-unbound CodY activates virulence genes. While isoleucine was revealed as an important input signal, it was not identified how internal levels are controlled during infection. Here we show that Lm regulates BCAA biosynthesis via CodY and via a riboregulator located upstream to the BCAA biosynthesis genes, named Rli60. rli60 is transcribed when BCAA levels drop, forming a ribosome-mediated attenuator that cis-regulates the downstream genes according to BCAA supply. Notably, we found that Rli60 restricts BCAA production, essentially starving Lm, a mechanism that is directly linked to virulence, as it controls the internal isoleucine pool and thereby CodY activity. This controlled BCAA auxotrophy likely evolved to enable isoleucine to serve as a host signal and virulence effector.

Impact of dietary branched chain amino acids concentration on broiler chicks during aflatoxicosis

A 20-day trial was conducted to determine the effects of dietary branched-chain amino acids (BCAA) on performance, nutrient digestibility, and gene expression of the mTOR pathway in broiler chicks when exposed to aflatoxin B1 (AFB1). The 6 dietary treatments were arranged in a 2 × 3 factorial with 3 BCAA concentrations (1.16, 1.94, and 2.73%) with or without 1.5 mg/kg AFB1 (1.77 mg/kg analyzed). Each diet was fed to 8 replicate cages (6 chicks per cage) from 6 to 20 d of age. Exposure to AFB1 significantly reduced gain:feed ratio and breast muscle weight (P < 0.05), and tended to decrease cumulative BW gain (P = 0.087), while increasing dietary BCAA improved all performance measures (P ≤ 0.0002), except relative breast muscle weight. Apparent ileal digestibility of N and 9 amino acids were increased by AFB1 (P ≤ 0.05), but were reduced by higher dietary BCAA (P ≤ 0.023). Jejunum histology was not affected by AFB1, while higher dietary BCAA tended to increase villus height (P = 0.08). Additionally, the gene expression of mTOR pathway (mTOR, 4EBP1, and S6K1) from liver and jejunum were not affected by dietary treatments, while muscle expression of S6K1 tended to be increased by AFB1 (P = 0.07). No significant interaction between AFB1 and dietary BCAA were observed for any measures in the current study. Results from this study suggested that feed AFB1 contamination can significantly reduce growth performance and breast muscle growth in broiler chicks at 20 d. Higher BCAA supply may have beneficial impact on bird performance, but this effect is independent of AFB1 exposure.

Branched-chain amino acids regulate insulin-like growth factor-binding protein 1 (IGFBP1) production by decidua and influence trophoblast migration through IGFBP1.

Do branched-chain amino acids (BCAAs) influence the migration of human extravillous trophoblast (EVT) cells through changes in insulin-like growth factor-binding protein 1 (IGFBP1) production in decidual cells? Decidua-derived IGFBP1 had a stimulating effect on migration of EVT. IGFBP1 is abundantly secreted from human decidual cells and influences trophoblast migration in human placenta of early pregnancy. In hepatic cells, the expression of IGFBP1 is influenced by nutritional status and BCAAs regulate IGFBP1 production. This is a laboratory-based study using human decidual cells and trophoblast cells isolated from placental tissue of early pregnancy (n = 50) and grown as primary cultures. Production of IGFBP1 from decidual cells was examined by enzyme-linked immunosorbent assay and immunoblotting after incubation with or without BCAAs. EVT migration was evaluated using the media conditioned by decidual cells. The effect of conditioned media on phosphorylation of focal adhesion kinase (FAK) in EVT was also analyzed by immunoblotting. The same experiments were repeated in the presence of RGD peptide, which inhibits IGFBP1 binding to α5β1 integrin. An EVT migration assay and the immunoblotting of phosphorylated FAK were also conducted with exogenous IGFBP1. The effect of the conditioned media on cytotrophoblast cell number was also assessed using WST-1 in a cell proliferation assay. Deprivation of BCAAs on decidual cells significantly suppressed IGFBP1 secretion (P < 0.05, versus BCAA+). Exogenous IGFBP1-stimulated EVT migration (P < 0.05) and phosphorylation of FAK (P < 0.05), and the RGD peptide inhibited these effects. EVT migration and phosphorylation of FAK were stimulated by the conditioned media, presumably by IGFBP1 in the media. RGD treatment abrogated the stimulating effects of conditioned media. The conditioned media deprived of BCAAs had suppressive effects on EVT migration (P < 0.05, versus BCAA+) and phosphorylation of FAK (P < 0.05, versus BCAA+). The conditioned media did not affect number of cytotrophoblast cells. The conclusions are based on in vitro experiments with human decidual cells and trophoblast cells isolated from placental tissue of early pregnancy, and we were unable to ascertain whether these mechanisms actually operate in vivo. We investigated the effect of decidua-derived IGFBP1 on EVT migration, however, we cannot completely rule out the possibility that endogenous IGF could also influence cell migration. Interruption of the BCAA supply to uterine decidual cells in early pregnancy may suppress EVT migration through reduced IGFBP1 secretion, which may be one of the pathophysiological conditions responsible for pre-eclampsia. None. All funds were obtained through Kyorin University School of Medicine. The authors have no conflict of interest to declare.

Mechanisms of bacterial acetohydroxyacid synthase (AHAS) and specific inhibitors of Mycobacterium tuberculosis AHAS as potential drug candidates against tuberculosis.

On account of the ever increasing resistance of M.tuberculosis strains to orthodox therapy regimens, the task of combating tuberculosis becomes even more challenging. Therefore, there arises a need to isolate new drug targets and subsequently design specific inhibitors for the same. In bacteria, algae, plants and fungi, the synthesis of Branched Chain Amino Acids (BCAAs) is catalyzed by Acetohydroxyacid Synthases (AHAS) group of enzymes. Bacterial AHAS (EC 2.2.1.6) catalyzes the biosynthesis of isoleucine, leucine and valine by utilizing cofactors like Thiamin Diphosphate (ThDP), Flavin Adenine Dinucleotide (FAD) and a divalent metal cation (Usually Mg(2+)). The anabolic form of the enzyme which is presently under discussion consists of two subunits out of which one is catalytic while the other is regulatory in nature. The product of this enzyme catalyzed reaction is either 2-acetolactate or 2-aceto-2-hydroxybutyrate obtained from self-condensation of pyruvate or condensation of puruvate and 2-ketobutyrate, respectively. These are further converted to the BCAAs by a series of other enzymes. The step catalyzed by AHAS is the first in the entire cascade and hence can be selectively targeted for the inhibition of this pathway. M.tuberculosis AHAS, which is encoded by the ilvB and ilvN operons is structurally related to E.coli AHAS and has a similar function. Therefore, specific drugs belonging to the classes of sulfonylureas, imidazolinones and benzoyl esters can be used as inhibitors of M.tuberculosis AHAS which would consequently deplete the BCAA supply to the bacteria. Thus, efficient bacteriostasis can be achieved.

Meal patterns in relation to the supply of branched-chain amino acids in pigs1

When a diet deficient in Val with excessive Leu is offered to pigs, feed intake is reduced. The physiological mechanisms underlying the rejection of branched-chain AA (BCAA) unbalance are unknown. A meal pattern analysis was performed to determine how pigs respond to the ingestion of a diet unbalanced in BCAA to identify the mechanisms responsible for the aversive response of such a diet. Eight female pigs (initial BW of 30.7±1.7 kg at 9 wk of age) received alternatively a diet either unbalanced in BCAA supply (i.e., a diet deficient in Val with an excess supply of Leu) or a control diet (i.e., a diet with a sufficient supply of Val with an excess supply of Leu) during 4 periods of 5 consecutive days. Feed consumption was monitored continuously to determine feeding behavior. Average daily feed intake of pigs receiving the diet unbalanced in BCAA was l3% less than that in pigs offered the control diet (P<0.01). Offering the unbalanced diet had no effect on meal size but reduced the number of meals from 9.9 to 8.5 per day (P<0.01). There was no difference between diets in intermeal interval but a slight trend for an increased meal duration from 14.5 to 16.3 min in pigs receiving the unbalanced diet (P=0.13). The rejection of feed appeared within the first 2 d after offering the unbalanced diet. The results of this experiment indicate that the BCAA unbalanced diet had no effect on satiety and satiation. After initiation of a meal, pigs ate a normal-sized meal and were hungry, but the increase in meal duration and a decrease in the number of meals inferred a negative alliesthesia (less pleasant) response to the BCAA unbalanced diet. On the basis of meal patterns, the rejection of a diet unbalanced in BCAA may not involve short-term mechanisms related to oropharyngeal and gastrointestinal receptors but may be triggered by postabsorptive signals.

Legumes regulate Rhizobium bacteroid development and persistence by the supply of branched-chain amino acids.

One of the largest contributions to biologically available nitrogen comes from the reduction of N(2) to ammonia by rhizobia in symbiosis with legumes. Plants supply dicarboxylic acids as a carbon source to bacteroids, and in return they receive ammonia. However, metabolic exchange must be more complex, because effective N(2) fixation by Rhizobium leguminosarum bv viciae bacteroids requires either one of two broad-specificity amino acid ABC transporters (Aap and Bra). It was proposed that amino acids cycle between plant and bacteroids, but the model was unconstrained because of the broad solute specificity of Aap and Bra. Here, we constrain the specificity of Bra and ectopically express heterologous transporters to demonstrate that branched-chain amino acid (LIV) transport is essential for effective N(2) fixation. This dependence of bacteroids on the plant for LIV is not due to their known down-regulation of glutamate synthesis, because ectopic expression of glutamate dehydrogenase did not rescue effective N(2) fixation. Instead, the effect is specific to LIV and is accompanied by a major reduction in transcription and activity of LIV biosynthetic enzymes. Bacteroids become symbiotic auxotrophs for LIV and depend on the plant for their supply. Bacteroids with aap bra null mutations are reduced in number, smaller, and have a lower DNA content than wild type. Plants control LIV supply to bacteroids, regulating their development and persistence. This makes it a critical control point for regulation of symbiosis.

Protein Characterization of Na +-Independent System L Amino Acid Transporter 3 in Mice : A Potential Role in Supply of Branched-Chain Amino Acids under Nutrient Starvation

We recently cloned the human Na(+)-independent system L neutral amino acid transporter LAT3. The aim of the present study was to characterize the molecular nature of mouse LAT3 at the protein level. Isolated mouse LAT3 showed 83% identity to human LAT3. Xenopus oocytes injected with mouse LAT3 cRNA showed the same functional property as human LAT3. Reverse transcriptase-polymerase chain reaction revealed apparent transcripts of mouse LAT3 in the liver, skeletal muscle, and pancreas, an expression pattern identical to that found in humans. Antibody generated against mouse LAT3 detected both approximately 58-kd and 48-kd bands in the sample from liver and only a 48-kd band in skeletal muscle and pancreas. Immunohistochemical study showed its clear localization in the plasma membrane of liver and skeletal muscle, whereas it was only detectable in the endoplasmic reticulum and in crystalline inclusions in pancreatic acinar cells. Starvation induced up-regulation of mouse LAT3 protein and mRNA in both liver and skeletal muscle but not in pancreas. These results suggest that LAT3 may indeed function as an amino acid transporter, transporting branched-chain amino acids from liver and skeletal muscle to the bloodstream and thereby participating in the regulatory system of interorgan amino acid nutrition.

Posttranscriptional regulation of albumin gene expression by branched-chain amino acids in rats with acute liver injury

We previously demonstrated that the integration of albumin mRNA into functional polysomes was regulated by the supply of branched-chain amino acids (BCAA) in the liver of galactosamine-treated rats. To study the mechanism of this regulation, we investigated interaction between rat liver proteins and albumin transcripts. When albumin transcript was incubated with ribosome salt wash (RSW) extracts prepared from liver, a specific RNA-protein complex (p65) formed. Competition experiments showed that a pyrimidine-rich sequence in the coding region of albumin mRNA was required for the formation of p65. The level of p65 was increased in the RSW extracts prepared from liver of galactosamine-treated rats infused with a standard amino acid formula, compared with a BCAA-enriched amino acid formula. The protein in p65 appears to be polypyrimidine tract-binding protein (PTB), because the formation of p65 was reduced in the RSW extracts pre-incubated with anti-PTB antibody. In cell-free translation analysis, immunodepletion of PTB from rabbit reticulocyte lysate caused an increase in albumin translation. These results suggest that binding of PTB to albumin mRNA suppresses its translation. A supply of BCAA may interfere with this binding and improve the translation efficiency of albumin mRNA in injured liver.

Nitrogen shuttling between neurons and glial cells during glutamate synthesis.

The relationship between neuronal glutamate turnover, the glutamate/glutamine cycle and de novo glutamate synthesis was examined using two different model systems, freshly dissected rat retinas ex vivo and in vivo perfused rat brains. In the ex vivo rat retina, dual kinetic control of de novo glutamate synthesis by pyruvate carboxylation and transamination of alpha-ketoglutarate to glutamate was demonstrated. Rate limitation at the transaminase step is likely imposed by the limited supply of amino acids which provide the alpha-amino group to glutamate. Measurements of synthesis of (14)C-glutamate and of (14)C-glutamine from H(14)CO(3) have shown that (14)C-amino acid synthesis increased 70% by raising medium pyruvate from 0.2 to 5 mM. The specific radioactivity of (14)C-glutamine indicated that approximately 30% of glutamine was derived from (14)CO(2) fixation. Using gabapentin, an inhibitor of the cytosolic branched-chain aminotransferase, synthesis of (14)C-glutamate and (14)C-glutamine from H(14)CO(3)(-) was inhibited by 31%. These results suggest that transamination of alpha-ketoglutarate to glutamate in Müller cells is slow, the supply of branched-chain amino acids may limit flux, and that branched-chain amino acids are an obligatory source of the nitrogen required for optimal rates of de novo glutamate synthesis. Kinetic analysis suggests that the glutamate/glutamine cycle accounts for 15% of total neuronal glutamate turnover in the ex vivo retina. To examine the contribution of the glutamate/glutamine cycle to glutamate turnover in the whole brain in vivo, rats were infused intravenously with H(14)CO(3)(-). (14)C-metabolites in brain extracts were measured to determine net incorporation of (14)CO(2) and specific radioactivity of glutamate and glutamine. The results indicate that 23% of glutamine in the brain in vivo is derived from (14)CO(2) fixation. Using published values for whole brain neuronal glutamate turnover, we calculated that the glutamate/glutamine cycle accounts for approximately 60% of total neuronal turnover. Finally, differences between glutamine/glutamate cycle rates in these two model systems suggest that the cycle is closely linked to neuronal activity.

Effect of Branched-Chain Amino Acids on Albumin Gene Expression in the Liver of Galactosamine-Treated Rats

Acute liver injury was induced in rats by the administration of galactosamine, which brought about inhibition of RNA synthesis and protein synthesis in the liver. The galactosamine-treated rats were infused with total parenteral nutrition solutions containing various proportions of branched-chain amino acids and the recovery from the galactosamine intoxication was followed by measuring albumin mRNA levels and polysome profiles. The levels of total cytoplasmic albumin mRNA were markedly decreased on day 2 after the galactosamine treatment, but the levels were restored to almost the control value by day 4 in all the groups irrespective of the content of branched-chain amino acids in the infusion solutions. On the contrary, the levels of β-actin mRNA changed in the opposite direction to those of albumin mRNA. It was also found that polysomes in the liver were extensively disaggregated on day 2 after the galactosamine treatment, but the polysome profiles returned to normal on day 4 in all the groups. However, when the levels of polysome-associated albumin mRNA were quantitated, we found that the extent of the recovery was dependent on the content of branched-chain amino acids in the infusion solutions; as the content of branched-chain amino acids increased, the level of polysome-associated albumin mRNA increased. These results suggest that the integration of albumin mRNA into functional polysomes in the liver is regulated by the supply of branched-chain amino acids.

Influence of ingesting a solution of branched-chain amino acids on plasma and muscle concentrations of amino acids during prolonged submaximal exercise

On two occasions, seven male endurance-trained cyclists performed sustained exhaustive exercise with reduced muscle glycogen stores. During exercise, the subjects were supplied in random order with an aqueous solution of branched-chain amino acids (BCAA) or flavored water (placebo). Ingestion of BCAA caused the concentration of these amino acids to increase by 135% in the plasma and by 57% in muscle tissue during exercise, whereas in the placebo trial there was no change or a slight decrease in the concentration in plasma and a decrease of 18% in the muscle. The plasma concentration of alanine increased by 48% during exercise when BCAA were ingested, and the increase in the muscle concentration of alanine during exercise was larger (70% versus 31% in the placebo trial), suggesting an increased rate of alanine production. Also, the plasma concentration of arginine increased by 14% during exercise when BCAA were ingested, whereas there was no change during exercise in the placebo trial. There was a smaller decrease in the muscle glutamate concentration during exercise in the BCAA trial (32% versus 47% in the placebo trial; p < 0.05), but, for the remaining amino acids, there was no difference between the BCAA and placebo trials. There was a significant decrease in the muscle glycogen concentration during exercise in the placebo trial, whereas only a small decrease was found in the BCAA trial (28 and 9 mmol/kg wet wt [ p < 0.05] in the placebo and BCAA trial, respectively). This might indicate that an increased supply of BCAA has a sparing effect on muscle glycogen degradation during exercise.

Glutamine and ornithine-α-ketoglutarate but not branched-chain amino acids reduce the loss of muscle glutamine after surgical trauma

The concentration of free glutamine in skeletal muscle decreases characteristically after surgical trauma. In animal studies a correlation between muscle protein synthesis and the glutamine concentration is reported. For pharmaceutical reasons, commercially available amino acid solutions do not contain glutamine. Therefore, at present, postoperative total parenteral nutrition does not provide glutamine. Several modifications of the composition of the amino acid solutions given in total parenteral nutrition have been evaluated recently. Ornithine-α-ketoglutarate preserves muscle protein synthesis and spares nitrogen after elective surgery, and an extra supply of branched-chain amino acids improves muscle protein synthesis in animals. Patients undergoing elective abdominal surgery (n = 33) received isocaloric (135 kJ/kg body weight/24 h) and isonitrogenous (0.2 g N/kg body weight/24 h) total parenteral nutrition for three days immediately following surgery. Administration of glutamine and ornithine-α-ketoglutarate as part of the amino acid supply reduced the loss of muscle glutamine from 40% to 25% ( P < .05). Additional supplementation of branched-chain amino acids produced no such effect, however, as compared with the control group. Further clinical trials including glutamine and ornithine-α-ketoglutarate are advocated.

Dietetic supplementation with branched chain amino acids attenuates the severity of streptozotocin-induced diabetes in rats.

Previous studies showed that the diabetogenic action of streptozotocin is reduced in rats adapted to a high-protein, carbohydrate-free diet, that have markedly elevated plasma concentrations of valine, leucine and isoleucine. In order to test the role of these branched chain amino acids (BCAA) in the beneficial effects of the high-protein diets, rats adapted (15 days) either to a balanced synthetic diet, or to the same diet supplemented with BCAA were injected with streptozotocin (STZ) (40 mg/kg body weight) and maintained on the same diets after drug injection. Rats previously fed the BCAA enriched diet showed a partial but significant reduction in the severity of diabetes, as indicated by higher rates of body weight gain, lower food and water intake, lower excretion of glucose and higher serum insulin levels. Rats previously fed the control diet for 14 days, but transferred to the BCAA diet 3 days after STZ injection, also showed reduced severity of diabetes, as indicated by rates of body weight gain, water and food ingestion, glucose and insulin levels. The data suggest that the increased supply of BCAA is responsible, at least in part, for the previously reported beneficial effects of high-protein diets in rats with STZ-induced diabetes.

Postoperative parenteral nutrition with high supply of branched-chain amino acids: effects on nitrogen balance and liver protein synthesis.

Branched-chain amino acids (BCAA) stimulate muscle and liver protein synthesis in vitro. The significance of this action in catabolic conditions in vivo remains controversial. The effects of a high supply of BCAA in total parenteral nutrition (TPN) on nitrogen balance and liver protein synthesis were studied in a postoperative rat model. After standard operative trauma TPN was commenced with one of two isocaloric programs (I: 20.1% BCAA and II: 50% BCAA) and continued for 48 hr. The relative rate of liver protein synthesis, measured after TPN in vitro by perfusion with 14C-leucine, was similar in both groups (I: 53.4 +/- 17.3 and II: 49.0 +/- 27.3 arbitrary units of synthesis rate, mean +/- SD). The cumulative nitrogen balance was positive with both regimens and was not improved by the high supply of BCAA (I: 2.02 +/- 0.81 and II: 1.87 +/- 0.63 gN/kg/48 hr mean +/- SD). We conclude that after moderate surgical trauma TPN with a high supply of BCAA offers no advantage over conventional TPN.