Isolation and identification of aliphatic short-chain acylcarnitines from beef heart: possible role for carnitine in branched-chain amino acid metabolism.

Aliphatic acylearnitines isolated from a water-soluble fraction of beef heart have been characterized by gas chromatography and mass spectrometry. The following acyl residues derived from the acylcarnitine fraction were unequivocally identified: acetyl, propionyl, isobutyryl, butyryl, alpha-methylbutyryl, valeryl, isovaleryl, tiglyl, and caproyl. beta-methylcrotonyl and methacrylyl were tentatively identified. This occurrence of considerable quantities of branched-chain acylcarnitines indicates a role for carnitine in branched-chain amino acid metabolism.     

Insulin-dependent metabolism of branched-chain amino acids in obesity

The effect of euglycemic hyperinsulinism on branched-chain amino acids (BCAA; valine, isoleucine and leucine) was evaluated in five obese subjects and five controls. A continuous intravenous insulin infusion raised plasma insulin to a steady-state level. An artificial endocrine pancrease that infused glucose was used to sustain euglycemia. Basal and steady-state insulin levels were significantly higher in the obese subjects than in the controls. The amount of glucose infused to maintain euglycemia and its ratio to steady-state insulin levels was significantly lower in the obese subjects, suggesting an impaired insulin action on glucose metabolism. Basal BCAA levels were similar in the two groups of subjects. During insulin infusion the decremental areas of BCAA below basal levels were significantly lower in the obese patients (63 +/- 5 nmol/mL X min v 143 +/- 8 nmol/mL X min, P less than 0.001), as was the ratio of the decremental areas of BCAA to the incremental areas of insulin (1.11 +/- 0.05 nmol/microU v 3.30 +/- 0.24 nmol/microU, P less than 0.001). Our data suggest that insulin resistance in obesity reduces hormonal effects on glucose as well as on BCAA metabolism.     

Effects of branched-chain amino acids on nitrogen metabolism in patients with cirrhosis

This study was conducted to determine whether an amino acid solution enriched with branched-chain amino acids altered protein catabolic rates and plasma ammonia in patients with cirrhosis. Nine stable subjects were given two peripheral intravenous infusions: a standard amino acid solution (solution A) and a branched-chain-enriched solution containing 97% more leucine (solution B). Each solution was given for separate 9-day (group 1, n = 6) or 3-day (group 2, n = 3) periods. Amino acid solutions delivered 0.7 gm protein.kg-1.day-1. Diets provided an additional 0.3 gm protein plus maintenance calories. Protein turnover was assessed by a primed continuous infusion of [1-14C] leucine in six patients (three patients in group 1 and three patients in group 2). Nitrogen balance and urinary 3-methyl histidine excretion were determined in group 1 patients. Compared with solution A, solution B increased leucine flux and leucine oxidation but had no significant effect on protein synthesis or catabolism based on the plasma specific activity of either leucine or alpha-ketoisocaproic acid. The additional leucine infused with solution B was quantitatively oxidized. Nitrogen balance did not differ with the two solutions and there was also no difference in the urinary excretion of 3-methyl histidine, suggesting that muscle protein catabolism was unchanged. Plasma ammonia concentration decreased significantly during the infusion of solution B and was associated with a slight fall in plasma glucagon concentration. The results indicated that a branched-chain-enriched amino acid solution did not alter protein synthesis or catabolism although it did lower the plasma ammonia when compared with a standard amino acid formula in stable cirrhotic patients.     

Impaired oxidation of branched-chain amino acids in the medial thalamus of thiamine-deficient rats

Thiamine, in its diphosphate form, is a required cofactor for enzymes of glucose metabolism and branched-chain α-ketoacid dehydrogenase (BCKDH). Although metabolic impairments in glucose metabolism have been found to occur in selectively vulnerable brain regions of the thiamine-deficient (TD) brain, the effects of thiamine deficiency on BCKDH have not been studied. BCKDH activity was assayed radiochemically in brain extracts of vulnerable (medial thalamus; MT) versus non-vulnerable (frontal cortex; FC) brain regions of rats made TD by administration of the central thiamine antagonist, pyrithiamine. A significant regional variation in BCKDH within the TD rat brain was noted, with a higher capacity for branched-chain amino acid oxidation in FC compared to MT: BCKDH activity was significantly reduced in MT of TD rats, resulting in selective accumulation of BCAAs in this brain region. Leucine concentrations were elevated over fivefold in the MT of symptomatic TD rats, compared with pair-fed control (PFC) rats. Impaired branched-chain ketoacid metabolism in rats may contribute to the neuronal dysfunction and ultimate thalamic neuronal cell death observed in thiamine deficiency.     

Advances and challenges in the treatment of branched-chain amino/keto acid metabolic defects

Disorders of branched-chain amino/keto acid metabolism encompass diverse entities, including maple syrup urine disease (MSUD), the ‘classical’ organic acidurias isovaleric acidemia (IVA), propionic acidemia (PA), methylmalonic acidemia (MMA) and, among others, rarely described disorders such as 2-methylbutyryl-CoA dehydrogenase deficiency (MBDD) or isobutyryl-CoA dehydrogenase deficiency (IBDD). Our focus in this review is to highlight the biochemical basis underlying recent advances and ongoing challenges of long-term conservative therapy including precursor/protein restriction, replenishment of deficient substrates, and the use of antioxidants and anaplerotic agents which refill the Krebs cycle. Ongoing clinical assessments of affected individuals in conjunction with monitoring of disease-specific biochemical parameters remain essential. It is likely that mass spectrometry-based ‘metabolomics’ may be a helpful tool in the future for studying complete biochemical profiles and diverse metabolic phenotypes. Prospective studies are needed to test the effectiveness of adjunct therapies such as antioxidants, ornithine-alpha-ketoglutarate (OKG) or creatine in addition to specialized diets and to optimize current therapeutic strategies in affected individuals. With the individual life-time risk and degree of severity being unknown in asymptomatic individuals with MBDD or IBDD, instructions regarding risks for metabolic stress and fasting avoidance along with clinical monitoring are reasonable interventions at the current time. Overall, it is apparent that carefully designed prospective clinical investigations and multicenter cohort-controlled trials are needed in order to leverage that knowledge into significant breakthroughs in treatment strategies and appropriate approaches.     

支链氨基酸代谢异常在心力衰竭发生发展中作用的研究进展

心肌能量代谢改变在心力衰竭的发生发展中起着重要作用。近年来研究发现,血浆中支链氨基酸(BCAAs)及其代谢产物水平的增高是心力衰竭的重要特征,并形成恶性反馈环,最终导致心力衰竭进展。因此,促进BCAAs分解代谢、减少代谢产物蓄积及恢复BCAAs代谢平衡,有望成为心力衰竭的新治疗靶点。本文对BCAAs代谢异常与心力衰竭的关系进行综述。     

Neuroinflammatory responses following zinc or branched-chain amino acids supplementation in obese rats

Metabolic Brain Disease - The excessive production of pro-inflammatory mediators, characteristic of obesity, leads to neuroinflammation. Zinc (Zn) and the branched-chain amino acids (BCAA) are...     

Influence of branched-chain amino acids and branched-chain keto acids on protein synthesis in isolated hepatocytes

We investigated the effects of the branched-chain amino acids--valine, leucine and isoleucine--or their keto analogs, the branched-chain keto acids--alpha-ketoisovaleric acid, alpha-ketoisocaproic acid and alpha-keto-beta-methylvaleric acid--on protein synthesis and secretion by monolayers of rabbit hepatocytes incubated with [35S] methionine in pulse-chase and steady-state experiments. The branched-chain amino acids (2.0 mM or 1.0 mM), in the presence or absence of insulin (2 X 10(-4) IU per dish) and in both types of experiments, reduced the trichloroacetic acid-precipitable 35S-protein secreted into the medium. The branched-chain keto acids (2.0 mM or 1.0 mM) had a stimulatory effect on secreted trichloroacetic acid-precipitable 35S-protein which was observed only by the pulse-chase technique in the presence of insulin. Immunoaffinity chromatography of medium demonstrated a slight inhibition by branched-chain amino acids and a slight stimulation by branched-chain keto acids on secretion of 35S-albumin and no effect of either treatment on secretion of 35S-fibrinogen. ELISA analysis of total (i.e., 35S-labeled and unlabeled) secreted albumin revealed an inhibitory effect of the branched-chain amino acids in both pulse-chase and steady-state experiments, and a small stimulatory effect, in steady-state experiments, of the branched-chain keto acids; both effects were insulin-dependent. Total secreted fibrinogen, under steady-state conditions, was increased by the branched-chain keto acids in the presence of insulin, while transferrin production was unaffected by any treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of individual branched-chain amino acids deprivation on insulin sensitivity and glucose metabolism in mice

Objective

We recently discovered that leucine deprivation increases hepatic insulin sensitivity via general control nondepressible (GCN) 2/mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) pathways. The goal of the present study was to investigate whether the above effects were leucine specific or were also induced by deficiency of other branched chain amino acids including valine and isoleucine.

Methods

Following depletion of BCAAs, changes in metabolic parameters and the expression of genes and proteins involved in regulation of insulin sensitivity and glucose metabolism were analyzed in mice and cell lines including human HepG2 cells, primary mouse hepatocytes and a mouse myoblast cell line C2C12.

Results

Valine or isoleucine deprivation for 7 days has similar effect on improving insulin sensitivity as leucine, in wild type and insulin-resistant mice models. These effects are possibly mediated by decreased mTOR/S6K1 and increased AMPK signaling pathways, in a GCN2-dependent manner. Similar observations were obtained in in vitro studies. In contrast to leucine withdrawal, valine or isoleucine deprivation for 7 days significantly decreased fed blood glucose levels, possibly due to reduced expression of a key gluconeogenesis gene, glucose-6-phosphatase. Finally, insulin sensitivity was rapidly improved in mice 1 day following maintenance on a diet deficient for any individual BCAAs.

Conclusions

Our results show that while improvement on insulin sensitivity is a general feature of BCAAs depletion, individual BCAAs have specific effects on metabolic pathways, including those that regulate glucose level. These observations provide a conceptual framework for delineating the molecular mechanisms that underlie amino acid regulation of insulin sensitivity.     

Catabolism of branched-chain amino acids by diaphragm muscles of fasted and diabetic rats

In vitro catabolism of branched-chain amino acids, leucine and valine, was investigated using diaphragm muscles from normal, streptozotocin-diabetic and overnight fasted rats. Oxidation and transamination of [1-14C] branched-chain amino acids were both stimulated to a similar extent by diabetes or fasting, when diaphragms were incubated with glucose. Transamination of leucine and valine was increased when diaphragms were incubated with pyruvate; stimulation of transamination was greatest in diaphragms from diabetic rats. Leucine and valine oxidation by control diaphragms was inhibited by pyruvate while it was unchanged or slightly stimulated in diaphragms from fasted or diabetic rats. Thus diaphragms from diabetic rats oxidized two to threefold more branched-chain amino acids than controls when they were incubated with pyruvate. The specific radioactivity of extracellular alpha-ketoisocaproate (KIC; the product of leucine transamination) produced by diaphragms incubated with [14C]leucine was similar for all groups (fed, fasted, or diabetic) in the presence or absence of pyruvate. Oxidation of [1-14C]KIC by diaphragms from fasted or diabetic rats, incubated with glucose, was the same or less than KIC oxidation by control diaphragms. Incubation with pyruvate inhibited KIC oxidation by control diaphragms to a significantly greater degree than that by diaphragms from diabetic or fasted rats. These data suggest the following Flux through branched-chain amino acid transaminase is limited by the availability of amino group acceptors in diaphragms from normal and overnight fasted rats, and to a greater extent in diaphragms from diabetic rats. Flux through the transaminase may be a major determinant of accelerated branched-chain amino acid oxidation by diaphragms in fasting and diabetes. In diaphragms of fasted and diabetic rats, flux through the branched-chain alpha-ketoacid dehydrogenase complex is resistant to inhibition by pyruvate, which is normally observed in controls.     

Effect of branched-chain amino acids on the composition and cytolytic activity of liver-associated lymphocytes in rats

BACKGROUND: Although branched-chain aminoacids (BCAA) are reported to be effective in prolongation of the mean survival time of patients with liver cirrhosis, it is not clear whether BCAA could influence the immune function in those patients. METHODS: Branched-chain amino acids were given as a supplement to carbon tetrachloride-induced cirrhotic rats, and an aminogram of the liver and kinetics of liver-associated lymphocytes (LAL) were then analysed. RESULTS: Liver cirrhosis was established at the 12th week, and glutathione S-transferase placental form (GST-P)-positive lesions, which are known to be pre-neoplastic lesions, occupied 1.72+/-0.84% of the liver at the 16th week in the controls. At this time the LAL showed an increase in the number of CD5-, CD8- and CD18-positive cells and augmentation of lectin-dependent cellular cytotoxicity (LDCC) activity. Furthermore, supplementation of BCAA increased the number of LAL, especially CD8-positive cells and natural killer cells, and augmented LDCC activity of LAL at the 16th week. The number of LAL was positively correlated with the valine concentration in the plasma and liver, and the area of GST-P-positive lesions tended to be decreased in the BCAA group. CONCLUSION: These findings suggest that BCAA administration has stimulatory effects on the local immune systems of the liver, which may have a potential to inhibit hepatocarcinogenesis. Moreover, among all amino acids valine might be an important amino acid for enhancing the immune function of LAL.     

Metabolism of branched-chain amino acids in leg muscles from tail-cast suspended intact and adrenalectomized rats

Degradation of branched-chain amino acids was studied in muscles of unloaded hind limbs from rats subjected to six days of tail-cast suspension. The total production of 14CO2 from uniformly labeled 14C-leucine, isoleucine, or valine, and the fluxes through leucine aminotransferase and alpha-ketoisocaproate dehydrogenase, which were measured using L-1-14C-leucine, were generally greater in the soleus and extensor digitorum longus muscles of unloaded than of weight-bearing hind limbs. Adrenalectomy abolished any difference in flux through the aminotransferase, whereas the administration of cortisol to adrenalectomized animals restored the greater flux in the unloaded soleus muscle. Adrenalectomy partially diminished the greater flux through alpha-ketoisocaproate dehydrogenase in the unloaded soleus, whereas cortisol (2 mg/100 g body weight) treatment increased this difference. In the extensor digitorum longus, adrenalectomy abolished the differences in both enzyme fluxes due to hind limb suspension. In this muscle, cortisol treatment increased these fluxes to a similar extent in both weight-bearing and suspended, adrenalectomized animals so that the normal difference was not restored. These results suggest that leucine catabolism in hind limb muscles of suspended rats was influenced primarily by increased circulating glucocorticoid hormones, which are elevated twofold to fourfold in these animals.     

Effects of fatty acids on hepatic amino acid metabolism in isolated perfused liver in rats]

Large disparity in experimental conditions concerning the use of isolated perfused liver led us to investigate the effects of two free-fatty acids on amino acid metabolism in this model. Oleate uptake was 210 +/- 46 nmol/min.g and octanoate uptake 550 +/- 60 nmol/min.g. Fatty acid utilization led to an increase in ketogenesis, enhanced by octanoate in accordance with its known availability for beta-oxidation. In our experiments neither oleate nor octanoate modified hepatic amino acid exchange and metabolism as assessed by the measurements of amino acids fluxes and glucose and urea production.     

Effect of total parenteral nutrition enriched in branched-chain amino acids on metabolite levels in septic rats

This study examined the effects of total parenteral nutrition (TPN) enriched with branched-chain amino acids (BCAAs) on metabolite levels of carbohydrate and protein metabolism in septic rats. Results also were obtained for standard amino acid hyperalimentation (conventional TPN). Septic peritonitis was induced in rats by cecal ligation and puncture. Two different experimental models were tested. In one, the two kinds of TPN were administered to the operated rats during the progress of sepsis (the septic phase). In the other, TPN was started immediately after surgical removal of the focal cecum (the recovery phase). The conventional and BCAA-enriched TPN solutions were isocaloric and isonitrogenous except that the percentage of BCAAs in the total amino acids by weight was 35.8% in BCAA-enriched TPN and 20.9% in conventional TPN. On the fifth postoperative day, TPN was discontinued, the animals were killed, and samples of arterial blood, liver, and rectus abdominis muscle were taken. BCAA-enriched TPN had a significant effect on nitrogen balance and survival rate in the septic phase model, and on muscle adenine nucleotide content in both models. Other metabolites showed similar changes in the two TPN groups. These results indicate that BCAA supplement in TPN improves nitrogen balance and peripheral cellular energy status and is thus clinically beneficial in preventive therapy for increased catabolism.