Branched-chain Amino Acids Homeostasis Research Articles

Branched-chain amino acid metabolism: Pathophysiological mechanism and therapeutic intervention in metabolic diseases.

Branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, are essential for maintaining physiological functions and metabolic homeostasis. However, chronic elevation of BCAAs causes metabolic diseases such as obesity, type 2 diabetes (T2D), and metabolic-associated fatty liver disease (MAFLD). Adipose tissue, skeletal muscle, and the liver are the three major metabolic tissues not only responsible for controlling glucose, lipid, and energy balance but also for maintaining BCAA homeostasis. Under obese and diabetic conditions, different pathogenic factors like pro-inflammatory cytokines, lipotoxicity, and reduction of adiponectin and peroxisome proliferator-activated receptors γ (PPARγ) disrupt BCAA metabolism, leading to excessive accumulation of BCAAs and their downstream metabolites in metabolic tissues and circulation. Mechanistically, BCAAs and/or their downstream metabolites, such as branched-chain ketoacids (BCKAs) and 3-hydroxyisobutyrate (3-HIB), impair insulin signaling, inhibit adipogenesis, induce inflammatory responses, and cause lipotoxicity in the metabolic tissues, resulting in multiple metabolic disorders. In this review, we summarize the latest studies on the metabolic regulation of BCAA homeostasis by the three major metabolic tissues-adipose tissue, skeletal muscle, and liver-and how dysregulated BCAA metabolism affects glucose, lipid, and energy balance in these active metabolic tissues. We also summarize therapeutic approaches to restore normal BCAA metabolism as a treatment for metabolic diseases.

Disruption of branched-chain amino acid homeostasis promotes the progression of DKD via enhancing inflammation and fibrosis-associated epithelial-mesenchymal transition

Background and aimsThe disrupted homeostasis of branched-chain amino acids (BCAAs, including leucine, isoleucine, and valine) has been strongly correlated with diabetes with a potential causal role. However, the relationship between BCAAs and diabetic kidney disease (DKD) remains to be established. Here, we show that the elevated BCAAs from BCAAs homeostatic disruption promote DKD progression unexpectedly as an independent risk factor. Methods and resultsSimilar to other tissues, the suppressed BCAAs catabolic gene expression and elevated BCAAs abundance were detected in the kidneys of type 2 diabetic mice and individuals with DKD. Genetic and nutritional studies demonstrated that the elevated BCAAs from systemic disruption of BCAAs homeostasis promoted the progression of DKD. Of note, the elevated BCAAs promoted DKD progression without exacerbating diabetes in the animal models of type 2 DKD. Mechanistic studies demonstrated that the elevated BCAAs promoted fibrosis-associated epithelial-mesenchymal transition (EMT) by enhancing the activation of proinflammatory macrophages through mTOR signaling. Furthermore, pharmacological enhancement of systemic BCAAs catabolism using small molecule inhibitor attenuated type 2 DKD. Finally, the elevated BCAAs also promoted DKD progression in type 1 diabetic mice without exacerbating diabetes. ConclusionBCAA homeostatic disruption serves as an independent risk factor for DKD and restoring BCAA homeostasis pharmacologically or dietarily represents a promising therapeutic strategy to ameliorate the progression of DKD.

Branched-Chain Amino Acids in Liver Diseases: Complexity and Controversy.

Branched-chain amino acids (BCAAs), as essential amino acids, engage in various physiological processes, such as protein synthesis, energy supply, and cellular signaling. The liver is a crucial site for BCAA metabolism, linking the changes in BCAA homeostasis with the pathogenesis of a variety of liver diseases and their complications. Peripheral circulating BCAA levels show complex trends in different liver diseases. This review delineates the alterations of BCAAs in conditions including non-alcoholic fatty liver disease, hepatocellular carcinoma, cirrhosis, hepatic encephalopathy, hepatitis C virus infection, and acute liver failure, as well as the potential mechanisms underlying these changes. A significant amount of clinical research has utilized BCAA supplements in the treatment of patients with cirrhosis and liver cancer. However, the efficacy of BCAA supplementation in clinical practice remains uncertain and controversial due to the heterogeneity of studies. This review delves into the complicated relationship between BCAAs and liver diseases and tries to untangle what role BCAAs play in the occurrence, development, and outcomes of liver diseases.

Circulating Branched Chain Amino Acids and Cardiometabolic Disease.

Branched chain amino acids (BCAAs) are essential for protein homeostasis, energy balance, and signaling pathways. Changes in BCAA homeostasis have emerged as pivotal contributors in the pathophysiology of several cardiometabolic diseases, including type 2 diabetes, obesity, hypertension, atherosclerotic cardiovascular disease, and heart failure. In this review, we provide a detailed overview of BCAA metabolism, focus on molecular mechanisms linking disrupted BCAA homeostasis with cardiometabolic disease, summarize the evidence from observational and interventional studies investigating associations between circulating BCAAs and cardiometabolic disease, and offer valuable insights into the potential for BCAA manipulation as a novel therapeutic strategy for cardiometabolic disease.

The role of branched-chain amino acids and their downstream metabolites in mediating insulin resistance.

Elevated levels of circulating branched-chain amino acids (BCAAs) and their associated metabolites have been strongly linked to insulin resistance and type 2 diabetes. Despite extensive research, the precise mechanisms linking increased BCAA levels with these conditions remain elusive. In this review, we highlight the key organs involved in maintaining BCAA homeostasis and discuss how obesity and insulin resistance disrupt the intricate interplay among these organs, thus affecting BCAA balance. Additionally, we outline recent research shedding light on the impact of tissue-specific or systemic modulation of BCAA metabolism on circulating BCAA levels, their metabolites, and insulin sensitivity, while also identifying specific knowledge gaps and areas requiring further investigation. Finally, we summarize the effects of BCAA supplementation or restriction on obesity and insulin sensitivity.

Metabolon formation regulates branched-chain amino acid oxidation and homeostasis.

The branched-chain aminotransferase isozymes BCAT1 and BCAT2, segregated into distinct subcellular compartments and tissues, initiate the catabolism of branched-chain amino acids (BCAAs). However, whether and how BCAT isozymes cooperate with downstream enzymes to control BCAA homeostasis in an intact organism remains largely unknown. Here, we analyse system-wide metabolomic changes in BCAT1- and BCAT2-deficient mouse models. Loss of BCAT2 but not BCAT1 leads to accumulation of BCAAs and branched-chain α-keto acids (BCKAs), causing morbidity and mortality that can be ameliorated by dietary BCAA restriction. Through proximity labelling, isotope tracing and enzymatic assays, we provide evidence for the formation of a mitochondrial BCAA metabolon involving BCAT2 and branched-chain α-keto acid dehydrogenase. Disabling the metabolon contributes to BCAT2 deficiency-induced phenotypes, which can be reversed by BCAT1-mediated BCKA reamination. These findings establish a role for metabolon formation in BCAA metabolism in vivo and suggest a new strategy to modulate this pathway in diseases involving dysfunctional BCAA metabolism.

Branched-chain amino acids in cardiovascular disease.

Research conducted in the past 15 years has yielded crucial insights that are reshaping our understanding of the systems physiology of branched-chain amino acid (BCAA) metabolism and the molecular mechanisms underlying the close relationship between BCAA homeostasis and cardiovascular health. The rapidly evolving literature paints a complex picture, in which numerous tissue-specific and disease-specific modes of BCAA regulation initiate a diverse set of molecular mechanisms that connect changes in BCAA homeostasis to the pathogenesis of cardiovascular diseases, including myocardial infarction, ischaemia-reperfusion injury, atherosclerosis, hypertension and heart failure. In this Review, we outline the current understanding of the major factors regulating BCAA abundance and metabolic fate, highlight molecular mechanisms connecting impaired BCAA homeostasis to cardiovascular disease, discuss the epidemiological evidence connecting BCAAs with various cardiovascular disease states and identify current knowledge gaps requiring further investigation.

191-OR: Hepatic Expression of the Branched-Chain Keto Acid Dehydrogenase Kinase Is Sufficient to Cause Glucose Intolerance in Lean Mice

Perturbed branched-chain amino acid homeostasis is a feature of obesity, insulin-resistance and type 2 diabetes. Induction of the branched-chain keto acid dehydrogenase kinase (BDK) in liver is one mechanism that is thought to contribute to elevated BCAA levels in these conditions. Whether higher levels of BDK in liver are sufficient to disturb systemic BCAA homeostasis and promote glucose intolerance in the absence of obesity or insulin resistance has never been directly tested. We treated 12 week-old C57BL6/J mice with adeno-associated virus, serotype 8 (AAV8) -BDK or control AAV8-GFP to promote long term expression of BDK specifically in liver of lean mice. Mice were then maintained on a standard low-fat chow diet for 8 weeks (n= 9 AAV8-GFP and n=AAV8-BDK) . AAV8-BDK significantly raised BDK protein and mRNA expression in liver but not adipose, skeletal muscle, or cardiac tissue compared to AAV8-GFP control mice. The higher expression of BDK in liver was associated with robust inhibitory phosphorylation of the branched-chain keto acid dehydrogenase (BCKDH) on ser293. AAV8-mediated induction of BDK expression in liver in our study was sufficient to promote significant elevations in circulating levels of the direct substrate of BCKDH, the branched chain α-keto acids as well as their cognate BCAA. There was no effect of AAV8-BDK to alter food intake, weight gain or adiposity. However, glucose tolerance measured by a 1g/kg intraperitoneal glucose tolerance test at week 7 was significantly impaired in mice receiving AAV8-BDK compared to AAV8-GFP control. These data demonstrate for the first time that induction of BDK in liver, as occurs with obesity, is sufficient to disturb systemic BCAA and glucose homeostasis in lean mice. Disclosure J.Walejko: None. R.W.Mcgarrah: None. P.J.White: None. Funding American Diabetes Association (1-16-INI-17)

Branched-chain amino acid metabolism is regulated by ERR\u03b1 in primary human myotubes and is further impaired by glucose loading in type 2 diabetes

Aims/hypothesisIncreased levels of branched-chain amino acids (BCAAs) are associated with type 2 diabetes pathogenesis. However, most metabolomic studies are limited to an analysis of plasma metabolites under fasting conditions, rather than the dynamic shift in response to a metabolic challenge. Moreover, metabolomic profiles of peripheral tissues involved in glucose homeostasis are scarce and the transcriptomic regulation of genes involved in BCAA catabolism is partially unknown. This study aimed to identify differences in circulating and skeletal muscle BCAA levels in response to an OGTT in individuals with normal glucose tolerance (NGT) or type 2 diabetes. Additionally, transcription factors involved in the regulation of the BCAA gene set were identified.MethodsPlasma and vastus lateralis muscle biopsies were obtained from individuals with NGT or type 2 diabetes before and after an OGTT. Plasma and quadriceps muscles were harvested from skeletal muscle-specific Ppargc1a knockout and transgenic mice. BCAA-related metabolites and genes were assessed by LC-MS/MS and quantitative RT-PCR, respectively. Small interfering RNA and adenovirus-mediated overexpression techniques were used in primary human skeletal muscle cells to study the role of PPARGC1A and ESRRA in the expression of the BCAA gene set. Radiolabelled leucine was used to analyse the impact of oestrogen-related receptor α (ERRα) knockdown on leucine oxidation.ResultsImpairments in BCAA catabolism in people with type 2 diabetes under fasting conditions were exacerbated after a glucose load. Branched-chain keto acids were reduced 37–56% after an OGTT in the NGT group, whereas no changes were detected in individuals with type 2 diabetes. These changes were concomitant with a stronger correlation with glucose homeostasis biomarkers and downregulated expression of branched-chain amino acid transaminase 2, branched-chain keto acid dehydrogenase complex subunits and 69% of downstream BCAA-related genes in skeletal muscle. In primary human myotubes overexpressing peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α, encoded by PPARGC1A), 61% of the analysed BCAA genes were upregulated, while 67% were downregulated in the quadriceps of skeletal muscle-specific Ppargc1a knockout mice. ESRRA (encoding ERRα) silencing completely abrogated the PGC-1α-induced upregulation of BCAA-related genes in primary human myotubes.Conclusions/interpretationMetabolic inflexibility in type 2 diabetes impacts BCAA homeostasis and attenuates the decrease in circulating and skeletal muscle BCAA-related metabolites after a glucose challenge. Transcriptional regulation of BCAA genes in primary human myotubes via PGC-1α is ERRα-dependent.Graphical abstract

202-OR: Cell-Autonomous Impairment of BCAA Catabolism in White Adipocytes Leads to Systemic Metabolic Dysregulation

Increased levels of serum branched-chain amino acids (BCAA) is associated with obesity, insulin resistance (IR), and type 2 diabetes (T2D). However, the mechanisms that trigger perturbations in BCAA homeostasis, and whether elevated BCAA causes obesity and other metabolic impairments or is a consequence of them is not clear. Young knock-in mice bearing the human T2D-linked R1788W variant in the cytoskeletal protein ankyrin-B (AnkB) show normal body weight and composition. These mice display increased glucose uptake by white adipose tissue (WAT) due to deficient internalization of the glucose transporter GLUT4. We reported that sustained elevation in glucose disposal in WAT leads to the onset of increased adiposity, lipotoxicity, systemic inflammation, and IR in AnkB mutant mice with age or in young animals fed Western diets. Non-obese R1788W AnkB mice also exhibit transcriptional changes consistent with lower BCAA catabolism in WAT. Here, we show that AnkB deficits impair BCAA catabolism in WAT prior to the onset of obesity. Lean R1788W AnkB mice show reduction in surface levels of the BCAA transporter Asct2 and BCAA uptake together with downregulation of BCAA catabolic enzymes in WAT. These deficits are concomitant with elevations in serum levels of BCAA and related acylcarnitines. Reduced expression of BCAA catabolic enzymes was also observed in WAT of lean WAT-specific AnkB KO mice. In contrast, AnkB deficiency did not alter BCAA oxidation in skeletal muscle (SKM), brown adipose tissue, or liver. Studies in control and R1788W AnkB mice fed isocaloric low and high fat (HFD) diets enriched in BCAA suggest that BCAA elevation triggers mitochondrial dysfunction, impairments in insulin secretion by the pancreas and in insulin signaling in SKM. Our data indicates that elevated circulating BCAA impair glucose tolerance and insulin sensitivity independently of obesity, and that these deleterious effects are potentiated by HFD. Disclosure J. Tzeng: None. A. Aguillard: None. D. Lorenzo: None. Funding American Diabetes Association (1-19-JDF-081 to D.L.)

Whole-body metabolic fate of branched-chain amino acids.

Oxidation of branched-chain amino acids (BCAAs) is tightly regulated in mammals. We review here the distribution and regulation of whole-body BCAA oxidation. Phosphorylation and dephosphorylation of the rate-limiting enzyme, branched-chain α-ketoacid dehydrogenase complex directly regulates BCAA oxidation, and various other indirect mechanisms of regulation also exist. Most tissues throughout the body are capable of BCAA oxidation, and the flux of oxidative BCAA disposal in each tissue is influenced by three key factors: 1. tissue-specific preference for BCAA oxidation relative to other fuels, 2. the overall oxidative activity of mitochondria within a tissue, and 3. total tissue mass. Perturbations in BCAA oxidation have been implicated in many disease contexts, underscoring the importance of BCAA homeostasis in overall health.

Branched-Chain Amino Acids Depletion during Hemodialysis Is Associated with Fatigue

Background: Fatigue is one of the most debilitating symptoms reported by maintenance hemodialysis (MHD) patients. Hemodialysis causes marked depletion in plasma essential amino acids. We studied the cross-sectional relationship of pre- and post-hemodialysis branched-chain amino acids (BCAAs) concentrations with fatigue in MHD patients. Methods: MHD patients self-reported fatigue during a dialysis session using the Brief Fatigue Inventory. Pre- and post-dialysis plasma levels of BCAAs (valine, leucine, and isoleucine) were measured using HPLC-mass spectrometry. Results: The mean age of study participants (n = 114) was 54.8 ± 12.8 years. Plasma levels of BCAAs decreased significantly post-dialysis compared to pre-dialysis (303.8 ± 9.4 vs. 392.1 ± 9.4 μM/L, p < 0.0001). Fatigue score increased as a function of age (p = 0.015). There was no association between pre-dialysis plasma levels of BCAAs and fatigue. A significant negative correlation was found between post-dialysis plasma levels of BCAAs and fatigue (p < 0.05). Conclusions: These preliminary findings suggest that disruption in BCAAs homeostasis may play a role in precipitating fatigue.

Homeostasis of branched-chain amino acids is critical for the activity of TOR signaling in Arabidopsis.

The target of rapamycin (TOR) kinase is an evolutionarily conserved hub of nutrient sensing and metabolic signaling. In plants, a functional connection of TOR activation with glucose availability was demonstrated, while it is yet unclear whether branched-chain amino acids (BCAAs) are a primary input of TOR signaling as they are in yeast and mammalian cells. Here, we report on the characterization of an Arabidopsis mutant over-accumulating BCAAs. Through chemical interventions targeting TOR and by examining mutants of BCAA biosynthesis and TOR signaling, we found that BCAA over-accumulation leads to up-regulation of TOR activity, which causes reorganization of the actin cytoskeleton and actin-associated endomembranes. Finally, we show that activation of TOR is concomitant with alteration of cell expansion, proliferation and specialized metabolism, leading to pleiotropic effects on plant growth and development. These results demonstrate that BCAAs contribute to plant TOR activation and reveal previously uncharted downstream subcellular processes of TOR signaling.

Targeting BCAA Catabolism to Treat Obesity-Associated Insulin Resistance.

Recent studies implicate a strong association between elevated plasma branched-chain amino acids (BCAAs) and insulin resistance (IR). However, a causal relationship and whether interrupted BCAA homeostasis can serve as a therapeutic target for diabetes remain to be established experimentally. In this study, unbiased integrative pathway analyses identified a unique genetic link between obesity-associated IR and BCAA catabolic gene expression at the pathway level in human and mouse populations. In genetically obese (ob/ob) mice, rate-limiting branched-chain α-keto acid (BCKA) dehydrogenase deficiency (i.e., BCAA and BCKA accumulation), a metabolic feature, accompanied the systemic suppression of BCAA catabolic genes. Restoring BCAA catabolic flux with a pharmacological inhibitor of BCKA dehydrogenase kinase (BCKDK) ( a suppressor of BCKA dehydrogenase) reduced the abundance of BCAA and BCKA and markedly attenuated IR in ob/ob mice. Similar outcomes were achieved by reducing protein (and thus BCAA) intake, whereas increasing BCAA intake did the opposite; this corroborates the pathogenic roles of BCAAs and BCKAs in IR in ob/ob mice. Like BCAAs, BCKAs also suppressed insulin signaling via activation of mammalian target of rapamycin complex 1. Finally, the small-molecule BCKDK inhibitor significantly attenuated IR in high-fat diet–induced obese mice. Collectively, these data demonstrate a pivotal causal role of a BCAA catabolic defect and elevated abundance of BCAAs and BCKAs in obesity-associated IR and provide proof-of-concept evidence for the therapeutic validity of manipulating BCAA metabolism for treating diabetes.

Enhanced cerebral branched-chain amino acid metabolism in R6/2 mouse model of Huntington's disease.

Huntington's disease (HD) is a hereditary and fatal disease causing profound neurodegeneration. Deficits in cerebral energy and neurotransmitter metabolism have been suggested to play a central role in the neuronal dysfunction and death associated with HD. The branched-chain amino acids (BCAAs), leucine, isoleucine and valine, are important for cerebral nitrogen homeostasis, neurotransmitter recycling and can be utilized as energy substrates in the tricarboxylic acid (TCA) cycle. Reduced levels of BCAAs in HD have been validated by several reports. However, it is still unknown how cerebral BCAA metabolism is regulated in HD. Here we investigate the metabolism of leucine and isoleucine in the R6/2 mouse model of HD. Acutely isolated cerebral cortical and striatal slices of control and R6/2 mice were incubated in media containing 15N- or 13C-labeled leucine or isoleucine and slice extracts were analyzed by gas chromatography-mass spectrometry (GC-MS) to determine isotopic enrichment of derived metabolites. Elevated BCAA transamination was found from incubations with [15N]leucine and [15N]isoleucine, in both cerebral cortical and striatal slices of R6/2 mice compared to controls. Metabolism of [U-13C]leucine and [U-13C]isoleucine, entering oxidative metabolism as acetyl CoA, was maintained in R6/2 mice. However, metabolism of [U-13C]isoleucine, entering the TCA cycle as succinyl CoA, was elevated in both cerebral cortical and striatal slices of R6/2 mice, suggesting enhanced metabolic flux via this anaplerotic pathway. To support the metabolic studies, expression of enzymes in the BCAA metabolic pathway was assessed from a proteomic resource. Several enzymes related to BCAA metabolism were found to exhibit augmented expression in the R6/2 brain, particularly related to isoleucine metabolism, suggesting an increase in the BCAA metabolic machinery. Our results show that the capacity for cerebral BCAA metabolism, predominantly of isoleucine, is amplified in the R6/2 brain and indicates that perturbations in cerebral BCAA homeostasis could have functional consequences for HD pathology.

A Regulatory Hierarchy of the Arabidopsis Branched-Chain Amino Acid Metabolic Network.

The branched-chain amino acids (BCAAs) Ile, Val, and Leu are essential nutrients that humans and other animals obtain from plants. However, total and relative amounts of plant BCAAs rarely match animal nutritional needs, and improvement requires a better understanding of the mechanistic basis for BCAA homeostasis. We present an in vivo regulatory model of BCAA homeostasis derived from analysis of feedback-resistant Arabidopsis thaliana mutants for the three allosteric committed enzymes in the biosynthetic network: threonine deaminase (also named l-O-methylthreonine resistant 1 [OMR1]), acetohydroxyacid synthase small subunit 2 (AHASS2), and isopropylmalate synthase 1 (IPMS1). In this model, OMR1 exerts primary control on Ile accumulation and functions independently of AHAS and IPMS AHAS and IPMS regulate Val and Leu homeostasis, where AHAS affects total Val+Leu and IPMS controls partitioning between these amino acids. In addition, analysis of feedback-resistant and loss-of-function single and double mutants revealed that each AHAS and IPMS isoenzyme contributes to homeostasis rather than being functionally redundant. The characterized feedback resistance mutations caused increased free BCAA levels in both seedlings and seeds. These results add to our understanding of the basis of in vivo BCAA homeostasis and inform approaches to improve the amount and balance of these essential nutrients in crops.

Changes in human hepatic metabolism in steatosis and cirrhosis.

AIMTo understand the underlying metabolic changes in human liver disease we have applied nuclear magnetic resonance (NMR) metabolomics analysis to human liver tissue.METHODSWe have carried out pilot study using 1H-NMR to derive metabolomic signatures from human liver from patients with steatosis, nonalcoholic steatohepatitis (NASH) or alcohol-related liver damage (ARLD) to identify species that can predict outcome and discriminate between alcohol and metabolic-induced liver injuries.RESULTSChanges in branched chain amino acid homeostasis, tricarboxylic acid cycle and purine biosynthesis intermediates along with betaine were associated with the development of cirrhosis in both ARLD and nonalcoholic fatty liver disease. Species such as propylene glycol and as yet unidentified moieties that allowed discrimination between NASH and ARLD samples were also detected using our approach.CONCLUSIONOur high throughput, non-destructive technique for multiple analyte quantification in human liver specimens has potential for identification of biomarkers with prognostic and diagnostic significance.

Liver BCATm transgenic mouse model reveals the important role of the liver in maintaining BCAA homeostasis

Unlike other amino acids, the branched-chain amino acids (BCAAs) largely bypass first-pass liver degradation due to a lack of hepatocyte expression of the mitochondrial branched-chain aminotransferase (BCATm). This sets up interorgan shuttling of BCAAs and liver–skeletal muscle cooperation in BCAA catabolism. To explore whether complete liver catabolism of BCAAs may impact BCAA shuttling in peripheral tissues, the BCATm gene was stably introduced into mouse liver. Two transgenic mouse lines with low and high hepatocyte expression of the BCATm transgene (LivTg-LE and LivTg-HE) were created and used to measure liver and plasma amino acid concentrations and determine whether the first two BCAA enzymatic steps in liver, skeletal muscle, heart and kidney were impacted. Expression of the hepatic BCATm transgene lowered the concentrations of hepatic BCAAs while enhancing the concentrations of some nonessential amino acids. Extrahepatic BCAA metabolic enzymes and plasma amino acids were largely unaffected, and no growth rate or body composition differences were observed in the transgenic animals as compared to wild-type mice. Feeding the transgenic animals a high-fat diet did not reverse the effect of the BCATm transgene on the hepatic BCAA catabolism, nor did the high-fat diet cause elevation in plasma BCAAs. However, the high-fat-diet-fed BCATm transgenic animals experienced attenuation in the mammalian target of rapamycin (mTOR) pathway in the liver and had impaired blood glucose tolerance. These results suggest that complete liver BCAA metabolism influences the regulation of glucose utilization during diet-induced obesity.

Increased susceptibility to metabolic dysregulation in a mouse model of Alzheimer's disease is associated with impaired hypothalamic insulin signaling and elevated BCAA levels

IntroductionEpidemiologic studies have demonstrated an association between diabetes and dementia. Insulin signaling within the brain, in particular within the hypothalamus regulates carbohydrate, lipid, and branched chain amino acid (BCAA) metabolism in peripheral organs such as the liver and adipose tissue. We hypothesized that cerebral amyloidosis impairs central nervous system control of metabolism through disruption of insulin signaling in the hypothalamus, which dysregulates glucose and BCAA homeostasis resulting in increased susceptibility to diabetes. MethodsWe examined whether APP/PS1 mice exhibit increased susceptibility to aging or high-fat diet (HFD)-induced metabolic impairment using metabolic phenotyping and insulin-signaling studies. ResultsAPP/PS1 mice were more susceptible to high-fat feeding and aging-induced metabolic dysregulation including disrupted BCAA homeostasis and exhibited impaired hypothalamic insulin signaling. DiscussionOur data suggest that AD pathology increases susceptibility to diabetes due to impaired hypothalamic insulin signaling, and that plasma BCAA levels could serve as a biomarker of hypothalamic insulin action in patients with AD.

Associations between plasma branched-chain amino acids, β-aminoisobutyric acid and body composition.

Plasma branched-chain amino acids (BCAA) are elevated in obesity and associated with increased cardiometabolic risk. β-Aminoisobutyric acid (B-AIBA), a recently identified small molecule metabolite, is associated with decreased cardiometabolic risk. Therefore, we investigated the association of BCAA and B-AIBA with each other and with detailed body composition parameters, including abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). A cross-sectional study was carried out with lean (n 15) and obese (n 33) men and women. Detailed metabolic evaluations, including measures of body composition, insulin sensitivity and plasma metabolomics were completed. Plasma BCAA were higher (1·6 (se 0·08) (×10(7)) v. 1·3 (se 0·06) (×10(7)) arbitrary units; P=0·005) in obese v. lean subjects. BCAA were positively associated with VAT (R 0·49; P=0·0006) and trended to an association with SAT (R 0·29; P=0·052). The association between BCAA and VAT, but not SAT, remained significant after controlling for age, sex and race on multivariate modelling (P<0·05). BCAA were also associated with parameters of insulin sensitivity (Matsuda index: R -0·50, P=0·0004; glucose AUC: R 0·53, P<0·001). BCAA were not associated with B-AIBA (R -0·04; P=0·79). B-AIBA was negatively associated with SAT (R -0·37; P=0·01) but only trended to an association with VAT (R 0·27; P=0·07). However, neither relationship remained significant after multivariate modelling (P>0·05). Plasma B-AIBA was associated with parameters of insulin sensitivity (Matsuda index R 0·36, P=0·01; glucose AUC: R -0·30, P=0·04). Plasma BCAA levels were positively correlated with VAT and markers of insulin resistance. The results suggest a possible complex role of adipose tissue in BCAA homeostasis and insulin resistance.