Cardiometabolic risk factor clustering in patients with deficient branched-chain amino acid catabolism: A case-control study

Classical organic acidemias (OAs) result from defective mitochondrial catabolism of branched-chain amino acids (BCAAs). Abnormal mitochondrial function relates to oxidative stress, ectopic lipids and insulin resistance (IR). We investigated whether genetically impaired function of mitochondrial BCAA catabolism associates with cardiometabolic risk factors, altered liver and muscle energy metabolism, and IR. In this case-control study, 31 children and young adults with propionic acidemia (PA), methylmalonic acidemia (MMA) or isovaleric acidemia (IVA) were compared with 30 healthy young humans using comprehensive metabolic phenotyping including in vivo ³¹ P/¹ H magnetic resonance spectroscopy of liver and skeletal muscle. Among all OAs, patients with PA exhibited abdominal adiposity, IR, fasting hyperglycaemia and hypertriglyceridemia as well as increased liver fat accumulation, despite dietary energy intake within recommendations for age and sex. In contrast, patients with MMA more frequently featured higher energy intake than recommended and had a different phenotype including hepatomegaly and mildly lower skeletal muscle ATP content. In skeletal muscle of patients with PA, slightly lower inorganic phosphate levels were found. However, hepatic ATP and inorganic phosphate concentrations were not different between all OA patients and controls. In patients with IVA, no abnormalities were detected. Impaired BCAA catabolism in PA, but not in MMA or IVA, was associated with a previously unrecognised, metabolic syndrome-like phenotype with abdominal adiposity potentially resulting from ectopic lipid storage. These findings suggest the need for early cardiometabolic risk factor screening in PA.

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.

Sodium phenylbutyrate decreases plasma branched-chain amino acids in patients with urea cycle disorders

Sodium phenylbutyrate (NaPBA) is a commonly used medication for the treatment of patients with urea cycle disorders (UCDs). Previous reports involving small numbers of patients with UCDs have shown that NaPBA treatment can result in lower plasma levels of the branched-chain amino acids (BCAA) but this has not been studied systematically. From a large cohort of patients (n=553) with UCDs enrolled in the Longitudinal Study of Urea Cycle Disorders, a collaborative multicenter study of the Urea Cycle Disorders Consortium, we evaluated whether treatment with NaPBA leads to a decrease in plasma BCAA levels. Our analysis shows that NaPBA use independently affects the plasma BCAA levels even after accounting for multiple confounding covariates. Moreover, NaPBA use increases the risk for BCAA deficiency. This effect of NaPBA seems specific to plasma BCAA levels, as levels of other essential amino acids are not altered by its use. Our study, in an unselected population of UCD subjects, is the largest to analyze the effects of NaPBA on BCAA metabolism and potentially has significant clinical implications. Our results indicate that plasma BCAA levels should to be monitored in patients treated with NaPBA since patients taking the medication are at increased risk for BCAA deficiency. On a broader scale, these findings could open avenues to explore NaPBA as a therapy in maple syrup urine disease and other common complex disorders with dysregulation of BCAA metabolism.

Branched-chain amino acids in liver diseases

Branched chain amino acids (BCAAs) have been shown to affect gene expression, protein metabolism, apoptosis and regeneration of hepatocytes, and insulin resistance. They have also been shown to inhibit the proliferation of liver cancer cells in vitro, and are essential for lymphocyte proliferation and dendritic cell maturation. In patients with advanced chronic liver disease, BCAA concentrations are low, whereas the concentrations of aromatic amino acids such as phenylalanine and tyrosine are high, conditions that may be closely associated with hepatic encephalopathy and the prognosis of these patients. Based on these basic observations, patients with advanced chronic liver disease have been treated clinically with BCAA-rich medicines, with positive effects.

A subset of Actinobacillus pleuropneumoniae in vivo induced promoters respond to branched-chain amino acid limitation

Actinobacillus pleuropneumoniae is the causative agent of a necrotizing hemorrhagic pleuropneumonia in swine. In this study, we investigate the possibility that the limitation of branched-chain amino acids is a stimulus that A. pleuropneumoniae will encounter during infection and will respond to by up-regulation of genes involved in branched-chain amino acid biosynthesis and virulence. Actinobacillus pleuropneumoniae genetic loci that are specifically induced during infection were screened in vitro for expression in response to limitation of branched-chain amino acids. Of 32 in vivo induced promoter clones screened in vitro, eight were induced on chemically defined medium without isoleucine, leucine and valine as compared to complete chemically defined medium. We identify the genomic context of each clone and discuss its relevance to branched-chain amino acid limitation and virulence. We conclude that limitation of branched-chain amino acids is a cue for expression of a subset in vivo induced genes, including not only genes involved in the biosynthesis of branched-chain amino acids, but also other genes that are induced during infection of the natural host. These results suggest that limitation of branched-chain amino acids may be one of an array of environmental cues responsible for the induction of virulence-associated genes in A. pleuropneumoniae.

The pathophysiology of hepatic encephalopathy

Hepatic encephalopathy (HE) is a complicated disorder, the pathophysiology of which remains to be fully understood. This article reviews the current main theories including the potential involvement of ammonia, gamma-aminobutyric acid (GABA)/benzodiazipines and false neurotransmitters. Each theory is critically examined with the evidence for each reviewed carefully, and the potential relationship of ammonia to the remaining two theories explored. Known preciptating factors of HE are also considered as evidence. The conclusions drawn from the evidence provided indicate the large role played by ammonia and suggest that this may be the key to understanding HE as science progresses.

Molecular mechanisms in the brain involved in the anorexia of branched-chain amino acid deficiency

The anterior piriform cortex (APC) of the rat is thought to be the site of indispensable amino acid (IAA) chemosensation in the brain. The branched-chain amino acids, including leucine, are among the IAA that are recognized in the APC. The behavioral outcome of IAA deficiency is an anorectic response. The specific transduction mechanisms by which IAA deficiency and repletion activate the APC are not fully understood, but clearly phosphorylation of proteins, increases in intracellular calcium, and expression of the immediate early gene c-fos, which are among the earliest events occurring after the initial drop in the concentration of the limiting IAA, cause stimulation in the APC. Subsequently, several neurotransmitter systems, including those for norepinephrine, GABA, serotonin, dopamine and nitric oxide, are activated in the APC of rats that have consumed an IAA-imbalanced diet. These systems appear to modulate the output cells from the APC, glutamatergic pyramidal cells that send neural signals to activate subsequent relays in the brain. Ultimately, the feeding circuits of the brain carry out the anorectic response. Continued consumption of a diet containing an IAA imbalance causes a conditioned taste aversion to the diet in all animals that have been studied. Such learning involves synaptic reorganization, requiring both degradation and synthesis of protein, along with alterations in genomic activity.

[Parenteral and enteral nutritional support for patients with liver cirrhosis]

In liver cirrhosis, metabolic processes deteriorate, and serum amino acid imbalances may develop. Aromatic amino acids accumulate and branched-chain amino acids (BCAA) deficiencies develop, leading to hepatic encephalopathy and malnutrition. According to Fischer's reports, parenteral nutritional support with BCAA rich solution (Aminoleban (Otsuka), Morihepamin (Morishita)) is useful in patients with hepatic encephalopathy. Enteral nutritional support with BCAA rich solution (Aminoleban EN (Otsuka), Hepan-ED (Morishita)), together with low protein diet, may correct the specific metabolic abnormalities in patients with chronic hepatic failure and contribute to regain the quality of life and survival.

Valine deficiency. 1. The effect of feeding a valine-deficient diet during the starter period on performance and feather structure of male broiler chicks

Experiments were designed to investigate the effect of feeding diets deficient in one or more of the three branched-chain amino acids (BCAA) on the performance of 3-wk-old male broilers. In the first experiment, levels of .96 and 1.46% Leu, .52 and .82% Ile, and .65 and .95% Val were used. Feeding the lowest combination of the three BCAA resulted in weight gain (WG) and feed conversion ratio (FC) of 344 g and 1.59 g:g, respectively. These parameters were not improved by adding dietary increments of the three BCAA individually. The greatest response, however, for both WG (435 g) and FC (1.41 g:g) was obtained by the addition of the three BCAA simultaneously. Chicks fed the low-Val diets in combinations with added levels of Ile and Leu exhibited feather and leg abnormalities. A second experiment was designed to investigate the effect of Val deficiency on feather protein, feather amino acids, and calcium content of the bone. Three treatments were used: a BCAA-deficient diet with .96% Leu, .52% Ile, and .63% Val; a Val-deficient diet, which contained 1.37, .82, and .63% of Leu, Ile, and Val, respectively; and a Val-supplemented diet, which was the same as the previous diets except that the Val content was .83%. Valine deficiency significantly decreased WG (243 g), FC (1.69 g:g), bone calcium (134 mg/g dry bone), and feather protein (82.7% of wet weight). Valine deficiency also decreased the level of Cys in feathers, but increased those of Asp, Glu, Met, Tyr, His, and Lys.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma amino acid and serum unesterified fatty acid deficits and the effect of nutritional support in chemotherapy treatment

The deficits in plasma amino acids and serum unesterified fatty acids of cancer patients undergoing chemotherapy and/or radiation therapy were studied to delineate the special requirements of the patients and efficacy of our nutritional therapy. Seven general surgery patients and 13 patients treated by the Head-Neck Service had baseline levels measured as part of their nutritional evaluation prior to surgical treatment of their cancers. Fifteen chemotherapy outpatients maintained on their regular diets had fasting levels analyzed. Twenty-six patients who were admitted for their therapy had their intake of the regular hospital diet supplemented with a low-residue enteral diet formula (Vivonex High Nitrogen Diet); parenteral nutrition was used only if their oral intake was totally inadequate. Baseline and sequential measurements were made of plasma amino acid and serum unesterified fatty acid levels by gas liquid chromatographic techniques. Before operation the patients had normal levels of amino acids except for a significant deficiency of threonine and glycine observed in patients with head-neck tumors. Outpatients with and without hepatic metastases had significantly depressed levels of the essential amino acids valine, leucine, threonine, and methionine and the nonessential amino acids serine, glycine, and proline. The baseline levels of the patients admitted for treatment had similar deficiencies except for more evidence of lysine deficiency. Patients supported with total parenteral nutrition had rapid elevation of the amino acid levels. The patients whose intake was supplemented with the oral diets had improvement in their amino acid levels, but the deficiency in the leucine and threonine fractions persisted up to 4 weeks of therapy. Although the lysine levels were normal when first analyzed, significant differences developed in the patients without hepatic metastases after the start of chemotherapy with return to normal only after chemotherapy was discontinued. Fatty acid levels were not significantly different between the cancer groups except for preoperative elevated oleic acid levels noted in the general surgery tumor group; there were no deficiencies in the essential fatty acids. These studies indicate a need for enteral formulas with adequate branched-chain amino acids and enrichment with threonine and lysine for supplementing the nutrition of the cancer patient who is undergoing chemotherapy.

Increased plasma ammonia may inhibit cellular release of branched-chain amino acids in systemic portal encephalopathy

Plasma amino acid patterns were determined before and after hemofiltration (HF) and hemodialysis (HD) in 6 patients with portal systemic encephalopathy (PSE) and compared with the plasma AA patterns of 16 patients with chronic renal failure (CRF) treated either by HF or HD. The branched-chain amino acids (BCAA) increased paradoxically in PSE patients during HF but not with HD. There were no differences in BCAA's with HF as compared to HD in the CRF patients. The amount of amino acids lost was the same with both treatment modalities and in both patient groups. Much of the amino acids lost were released from the intracellular space. The BCAA release was significantly higher in PSE patients during HF. No correlation was found between plasma insulin, glucagon, and cortisol levels and BCAA release. An inverse correlation was found between the amount of BCAA's released from the intracellular space and the plasma ammonia levels. It is suggested that a selective cellular transport mechanism for BCAA exists which is inhibited by high plasma ammonia levels in PSE.

Plasma amino acids in the alcoholic: nutritional aspects

Plasma amino acid abnormalities are frequently reported in alcoholics, with the most common abnormalities being those of depressed branched chain amino acids (BCAA) and increased aromatic amino acids. The depression in branched chain amino acids is due to multiple factors including portal-systemic shunting, hyperinsulinemia, hyperglucagonemia (all due to advanced liver disease) as well as dietary deficiency. alpha-Amino-n-butyric acid is a nonessential amino acid derived primarily from the catabolism of methionine, threonine, and serine. Increased levels due to chronic alcohol consumption may reflect altered glutathione metabolism and lipid peroxidation due to alcohol and may be used empirically as a biochemical marker of heavy drinking. The high levels of aromatic amino acids such as tyrosine and tryptophan as well as their breakdown products may be due to impaired hepatic metabolism and appear to play a role in the pathogenesis of hepatic encephalopathy. The effects of high levels of aromatic amino acids may be potentiated by depressed BCAA; these normally compete with each other for CNS transport. Alterations in these amino acids may have implications for nutritional requirements for amino acids in these patients as well as therapeutic approaches.