Elevated Plasma Branched-chain Amino Acids Research Articles

Adverse plasma branched-chain amino acid profile mirrors fatty muscle degeneration in diabetic heart failure patients.

Elevated plasma branched-chain amino acids (BCAAs) are tightly linked to incident diabetes and its complications, while lower BCAAs are associated with adverse outcomes in the elderly and heart failure (HF) patients. The interplay between body compositions and plasma BCAAs, especially under the influence of co-morbid diabetes in HF patients, is not well understood. Here, we examined the impact of diabetes on the prognostic value of plasma BCAA and its association with body compositions in HF patients. We retrospectively examined 301 HF patients (70±15years old; 59% male), among which 36% had diabetes. Blood samples for plasma BCAA measurements were collected in a fasting state after stabilization of HF and analysed using ultraperformance liquid chromatography. A dual-energy X-ray absorptiometry scan assessed regional body compositions, and muscle wasting was defined as appendicular skeletal muscle mass index (ASMI)<7.00 and <5.40kg/m2 for males and females, respectively, according to the criteria of the Asian Working Group for Sarcopenia. Although analyses of covariance revealed that plasma BCAAs were significantly higher in diabetic patients, low valine (<222.1nmol/mL) similarly predicted adverse events defined by HF hospitalization, lethal arrhythmia, or all-cause death in both diabetic and non-diabetic patients independently of age, sex, and NT-proBNP (adjusted hazard ratio [HR] 3.1, 95% confidence interval [CI] of 1.1-8.6 and adjusted HR 2.67, 95% CI 1.1-6.5, respectively; P for interaction 0.88). In multivariate linear regression analyses comprising age, sex, and regional body compositions as explanatory variables, plasma BCAAs were positively correlated with visceral adipose tissue area in non-diabetic patients (standardized β coefficients [β]=0.44, P<0.001). In contrast, in diabetic patients, plasma BCAAs were correlated positively with ASMI (β=0.49, P=0.001) and negatively with appendicular fat mass index (AFMI; β=-0.42, P=0.004). Co-morbid diabetes was independently associated with muscle wasting (adjusted odds ratio 2.1, 95% CI 1.1-4.0) and significantly higher plasma 3-methylhistidine level, a marker of myofibrillar degradation. In diabetic patients, ASMI uniquely showed a J-shaped relationship with AFMI, and in a subgroup of HF patients with muscle wasting, diabetic patients showed 12% higher AFMI than non-diabetic patients despite comparable ASMI reductions. Despite higher plasma BCAA levels in HF patients with diabetes, the prognostic value of low valine remained consistent regardless of diabetes status. However, low BCAAs were distinctly associated with fatty muscle degeneration in the extremities in diabetic patients, suggesting the importance of targeted interventions to prevent such tissue remodelling in this population.

Correlation of Salivary Occult Blood with the Plasma Concentration of Branched-Chain Amino Acids: A Cross-Sectional Study.

Background: Plasma branched-chain amino acids (BCAA) levels are predictors of glycometabolic disorders, leading to diabetes. Microbes, including periodontal pathogens, are thought to be associated with elevated plasma BCAA levels. This study aimed to evaluate the relationship between salivary occult blood (SOB) and plasma BCAA levels in middle-aged Japanese individuals. Methods: Sixty-four Japanese individuals aged ≥ 40 years were recruited for this study, which was conducted in Fukuoka Prefecture, Japan, from August to December 2021. Individuals diagnosed with and/or treated for diabetes were excluded from the study. The body mass index (BMI); plasma concentrations of total, high-density, and low-density lipoprotein cholesterol; triglyceride, glucose, and BCAA; and glycosylated hemoglobin ratio were measured. A basic periodontal examination was performed after the SOB test. Results: The median age of participants (men—20; women—44) was 55 (range, 41–78) years. The plasma BCAA concentration in the SOB-positive group (477 [400–658] μmol/L) was higher than that in the SOB-negative group (432 [307–665] μmol/L). Linear regression analysis revealed that SOB remained independently associated with the plasma BCAA level with statistical significance (β = 0.17, p = 0.02) after adjusting for sex, age, and BMI. Conclusions: SOB was positively correlated with plasma BCAA levels in middle-aged Japanese individuals. Thus, SOB may be a predictor of elevated plasma BCAA levels.

Therapeutic Effects of BT2 in the Hippocampus of Alzheimer’s Disease Mouse Model

ObjectivesAlzheimer’s disease (AD) is the most common type of dementia affecting more than 6 million Americans today. Despite the increasing rates of AD there is still no effective cure for this devastating disease. Our lab has shown that elevated plasma branched-chain amino acids (BCAAs) and their metabolites are present in both AD patients and mice. Further pilot data revealed that 8 weeks of dietary BCAA restriction in AD mice alleviated AD-related brain pathology and improved cognitive function. Although we observed beneficial effects from the dietary intervention, this approach is practically challenging because BCAAs are found in a wide variety of foods. This prompted us to test the effects of lowering plasma BCAAs in AD mice pharmacologically by BT2, a small molecule that increases BCAA breakdown. MethodsWe used cognitively intact, 2-month-old 5xFAD mice or wildtype (WT) mice to test the effects of BT2 on early AD-related brain pathology. Animals were injected with BT2 or vehicle intraperitoneally (60 mg/kg) for 30 consecutive days. Brain micro punches were taken from the hippocampus for monoamine analysis, and the rest of the hippocampal tissues were used for gene analysis via RT-qPCR. Next, we treated cognitively impaired 4-month-old 5xFAD mice and WT mice with either BT2 (60 mg/kg) or vehicle for 10 consecutive days. We used Golgi-Cox staining to visualize the hippocampus. ResultsBT2 treatment in 2-month-old 5xFAD mice restored key neurotransmitters in the hippocampus, the main brain region responsible for learning and memory. BT2 also reduced mRNAs involved in ER stress, inflammation, and Aβ-42 production. Next, we sought to determine if the changes in brain pathology and neurotransmitter status induced by BT2 would result in restored neuronal morphology in the hippocampus of cognitively impaired 5xFAD mice. We observed a clear restoration in dendritic density in the hippocampus of 5xFAD mice treated with BT2 compared to WTs. We did not observe any changes in cognitive function in these mice, possibly due to the short treatment duration. ConclusionsOur findings suggest that BT2 has therapeutic effects on AD-related pathology in the hippocampus of 5xFAD mice, indicating the potential of BT2 as a novel preventive/treatment strategy for AD. Funding SourcesNIH R21 AG069140-01

Acute Exposure to Branched-Chain Amino Acids (BCAAs) Impairs Glucose Homeostasis by Promoting Insulin Resistance in Mice

ObjectivesIncreased plasma BCAAs are associated with T2D. Current evidence suggests that high BCAAs are detrimental to insulin action and glucose metabolism. Chronic supplementation of BCAAs results in development of insulin resistance whereas dietary restriction of BCAAs improves insulin sensitivity and glucose uptake. While these studies indicate a detrimental impact of long-term use of BCAAs, whether BCAAs can acutely contribute to glucose dysregulation and insulin resistance is not understood. Therefore, we tested the role of acutely elevated BCAAs in glycemic control and insulin sensitivity. Methods8-week-old C57Bl/6 mice on BCAA or vehicle-treated groups fed a normal chow diet underwent jugular catheter implantation. To determine the acute effects of BCAAs, after 2-hr fast, mice were infused with 150mM BCAAs or 0.9% saline solution through the catheter followed by a frequent glucose monitoring and blood sampling for 30 min for assessment of plasma BCAA and insulin levels. Furthermore, hyperinsulinemic-euglycemic clamps, a gold-standard method for assessing insulin sensitivity, were conducted along with raised plasma BCAAs by continuous infusion. Blood glucose was monitored at every 10 min for 120 min, and a variable rate of glucose was infused to maintain euglycemia. Blood glucose was checked by a hand-held glucometer, and plasma BCAAs and insulin were measured by enzymatic and ELISA assays, respectively. Whole-body insulin sensitivity during clamps was determined by glucose infusion rate (GIR). ResultsJugular infusion of BCAAs, but not vehicle, acutely elevated plasma BCAAs that was maintained for 30 min. Whereas vehicle-treated controls did not display any changes from baseline, BCAA-infused mice acutely raised blood glucose by 20% in spite of increasing and maintaining plasma insulin, indicative of possible insulin resistance. This was supported by a significantly lower GIR, an accurate readout of whole-body insulin sensitivity, in mice with an acute, sustained elevation of plasma BCAAs compared to vehicle-treated mice during hyperinsulinemic-euglycemic clamps. ConclusionsThese findings suggest that BCAAs can acutely disturb glucose homeostasis and insulin action. Future studies will aim to determine the underlying mechanisms for BCAA-induced metabolic dysregulation. Funding SourcesNIH R21 AG069140-01; Diabetes Action Foundation

Abstract 10391: Elevated Plasma Branched-Chain Amino Acids Level Promotes Atherosclerosis Progression by Facilitating Macrophage Polarization Toward M1 Phenotype That Results in the Increase of Inflammation

Introduction: Few studies have reported that whether elevated plasma branched-chain amino acids (BCAA) level is causally related to atherosclerosis (AS) and the mechanism involved. Methods: First, the plasma BCAA level of 258 atherosclerotic cardiovascular disease (ASCVD) patients and 188 normal people was measured. Second, plaque volume, stability and inflammation of AS mice were evaluated. Third, we assayed BCAA level, catabolism-promoting genes and inflammation in the circulating monocytes of ASCVD patients and abdominal macrophages of AS mice. Fourth, inflammation and macrophage polarization were evaluated in BCAA catabolic deficient RAW 264.7 cells. Finally, mitochondrial hydrogen peroxide (mtH 2 O 2 ), nuclear H 2 O 2 and High mobility group box 1 (HMGB1) levels in RAW 264.7 cells were measured and RAW 264.7 cells-overexpressing catalase targeted to mitochondria (MCAT), nucleus (NCAT) and HMGB1KD RAW 264.7 cells were built to detect their effect on macrophage polarization. Results: First, we found that plasma BCAA level was an independent risk factor of ASCVD. Second, we also found plasma BCAA level was elevated in AS mice, which led to the increase of plaque volume and instability, as well as inflammation. The growth of plaque instability was characterized by increased macrophage amounts and decreased smooth muscle cells (SMCs) and collagen contents. Conversely, when plasma BCAA level was lowered, the above phenomena could be reversed. Third, elevated plasma BCAA level resulting from BCAA catabolic defect occurred in the monocytes of ASCVD patients and the abdominal macrophages of AS mice, which increased inflammatory response by promoting the polarization of macrophages toward M1 phenotype. Fourth, elevated BCAA level-mediated macrophage polarization toward M1 phenotype was regulated by increasing mtH 2 O 2 level to induce secretion of HMGB1 by increasing nuclear H 2 O 2 level. Finally, the improvement of BCAA catabolism of macrophages alleviated AS progression in mice. Conclusions: Our data demonstrates that elevated plasma BCAA level is an independent risk factor of ASCVD and promotes AS progression, indicating that plasma BCAA level might be a therapeutic target for ASCVD.

Branched-Chain Amino Acids Associate Negatively With Postprandial Insulin Secretion in Recent-Onset Diabetes.

ContextIn addition to unfavorable effects on insulin sensitivity, elevated plasma branched-chain amino acids (BCAA) stimulate insulin secretion, which, over the long-term, could impair pancreatic β-cell function.ObjectiveTo investigate cross-sectional and prospective associations between circulating BCAA and postprandial β-cell function in recently diagnosed type 1 and type 2 diabetes.MethodsThe study included individuals with well-controlled type 1 and type 2 diabetes (known diabetes duration <12 months) and glucose-tolerant participants (controls) of similar age, sex, and body mass index (n = 10/group) who underwent mixed meal tolerance tests. Plasma BCAA levels were quantified by gas chromatography–mass spectrometry, postprandial β-cell function was assessed from serum C-peptide levels, and insulin sensitivity was determined from PREDIM index (PREDIcted M-value).ResultsIn type 1 diabetes, postprandial total BCAA, valine, and leucine levels were 25%, 18%, and 19% higher vs control, and total as well as individual postprandial BCAA were related inversely to C-peptide levels. In type 2 diabetes, postprandial isoleucine was 16% higher vs the respective controls, while neither total nor individual BCAA correlated with C-peptide levels. Whole-body insulin sensitivity was lower in both diabetes groups than in corresponding controls. ConclusionInsulin deficiency associates with sustained high BCAA concentrations, which could contribute to exhausting the insulin secretory reserve in early type 1 diabetes.

Central Regulation of Branched-Chain Amino Acids Is Mediated by AgRP Neurons.

Circulating branched-chain amino acids (BCAAs) are elevated in obesity and diabetes, and recent studies support a causal role for BCAAs in insulin resistance and defective glycemic control. The physiological mechanisms underlying BCAA regulation are poorly understood. Here we show that insulin signaling in the mediobasal hypothalamus (MBH) of rats is mandatory for lowering plasma BCAAs, most probably by inducing hepatic BCAA catabolism. Insulin receptor deletion only in agouti-related protein (AgRP)-expressing neurons (AgRP neurons) in the MBH impaired hepatic BCAA breakdown and suppression of plasma BCAAs during hyperinsulinemic clamps in mice. In support of this, chemogenetic stimulation of AgRP neurons in the absence of food significantly raised plasma BCAAs and impaired hepatic BCAA degradation. A prolonged fasting or ghrelin treatment recapitulated designer receptors exclusively activated by designer drugs-induced activation of AgRP neurons and increased plasma BCAAs. Acute stimulation of vagal motor neurons in the dorsal motor nucleus was sufficient to decrease plasma BCAAs. Notably, elevated plasma BCAAs were associated with impaired glucose homeostasis. These findings suggest a critical role of insulin signaling in AgRP neurons for BCAA regulation and raise the possibility that this control may be mediated primarily via vagal outflow. Furthermore, our results provide an opportunity to closely examine the potential mechanistic link between central nervous system-driven BCAA control and glucose homeostasis.

Exploring mechanistic links between extracellular branched-chain amino acids and muscle insulin resistance: an in vitro approach.

Branched-chain amino acids (BCAAs) are essential for critical metabolic processes; however, recent studies have associated elevated plasma BCAA levels with increased risk of insulin resistance. Using skeletal muscle cells, we aimed to determine whether continued exposure of high extracellular BCAA would result in impaired insulin signaling and whether the compound sodium phenylbutyrate (PB), which induces BCAA metabolism, would lower extracellular BCAA, thereby alleviating their potentially inhibitory effects on insulin-mediated signaling. Prolonged exposure of elevated BCAA to cells resulted in impaired insulin receptor substrate 1/AKT signaling and insulin-stimulated glycogen synthesis. PB significantly reduced media BCAA and branched-chain keto acid concentrations and increased phosphorylation of AKT [+2.0 ± 0.1-fold; P < 0.001 versus without (-)PB] and AS160 (+3.2 ± 0.2-fold; P < 0.001 versus -PB); however, insulin-stimulated glycogen synthesis was further reduced upon PB treatment. Continued exposure of high BCAA resulted in impaired intracellular insulin signaling and glycogen synthesis, and while forcing BCAA catabolism using PB resulted in increases in proteins important for regulating glucose uptake, PB did not prevent the impairments in glycogen synthesis with BCAA exposure.

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.

Pre-meal protein intake alters postprandial plasma metabolome in subjects with metabolic syndrome

We examined the effect on the postprandial plasma metabolome of protein pre-meals before a fat-rich main meal. Two randomized, cross-over meal studies were conducted to test the dose-response effect (0g, 10g, 20g) of a pre-meal with whey protein (WP) (PREMEAL I), and the effect of protein quality (10g WP, casein, or gluten) and timing (- 15min vs - 30min) of the pre-meal (PREMEAL II). Participants with metabolic syndrome received one of the test meals on each test day, - 15min (or - 30min) prior to a standardized fat-rich breakfast. Plasma samples were collected at - 15min (or - 30min), 0, 120, 240 a nd 360min and analyzed using liquid chromatography-mass spectrometry with an untargeted method. Pre-meal WP intake elevated plasma branched-chain amino acids (BCAA), aromatic amino acids and methionine and decreased plasma LPC (16:0) and PC (32:1) levels before the main meal. Early (- 15 to 0min) aromatic amino acids and BCAA in response to pre-meal WP partially predict the glucose and insulin response after the main meal. A pre-meal with WP altered the postprandial plasma metabolic pattern of acyl-carnitines, specific PCs, LPCs and LPEs, betaine, citric acid, linoleic acid, and β-hydroxypalmitic acid compared to no pre-meal. The casein and WP pre-meals exhibited similar postprandial amino acid responses whereas a pre-meal with gluten resulted in lower levels of plasma amino acids and its metabolites. A pre-meal with protein affects the postprandial metabolic pattern indicating facilitated glucose and lipid disposal from plasma in participants with metabolic syndrome.

Non-Alcoholic Fatty Liver Disease and Risk of Incident Type 2 Diabetes: Role of Circulating Branched-Chain Amino Acids.

Non-alcoholic fatty liver disease (NAFLD) is likely to be associated with elevated plasma branched-chain amino acids (BCAAs) and may precede the development of type 2 diabetes (T2D). We hypothesized that BCAAs may be involved in the pathogenesis of T2D attributable to NAFLD and determined the extent to which plasma BCAAs influence T2D development in NAFLD. We evaluated cross-sectional associations of NAFLD with fasting plasma BCAAs (nuclear magnetic resonance spectroscopy), and prospectively determined the extent to which the influence of NAFLD on incident T2D is attributable to BCAA elevations. In the current study, 5791 Prevention of REnal and Vascular ENd-stage Disease (PREVEND) cohort participants without T2D at baseline were included. Elevated fatty liver index (FLI) ≥60, an algorithm based on triglycerides, gamma-glutamyltransferase, body mass index (BMI) and waist circumference, was used as proxy of NAFLD. Elevated FLI ≥ 60 was present in 1671 (28.9%) participants. Cross-sectionally, BCAAs were positively associated with FLI ≥ 60 (β = 0.208, p < 0.001). During a median follow-up of 7.3 years, 276 participants developed T2D, of which 194 (70.2%) had an FLI ≥ 60 (log-rank test, p < 0.001). Cox regression analyses revealed that both FLI ≥60 (hazard ratio (HR) 3.46, 95% CI 2.45–4.87, p < 0.001) and higher BCAA levels (HR 1.19, 95% CI 1.03–1.37, p = 0.01) were positively associated with incident T2D. Mediation analysis showed that the association of FLI with incident T2D was in part attributable to elevated BCAAs (proportion mediated 19.6%). In conclusion, both elevated FLI and elevated plasma BCAA levels are associated with risk of incident T2D. The association of NAFLD with T2D development seems partly mediated by elevated BCAAs.

Impaired Skeletal Muscle Branched-Chain Amino Acids Catabolism Contributes to Their Increased Circulating Levels in a Non-Obese Insulin-Resistant Fructose-Fed Rat Model.

Elevated plasma branched-chain amino acids (BCAA) levels are often observed in obese insulin-resistant (IR) subjects and laboratory animals. A reduced capacity of the adipose tissues (AT) to catabolize BCAA has been proposed as an explanation, but it seems restricted to obesity models of genetically modified or high fat–fed rodents. We aimed to determine if plasma BCAA levels were increased in a model of IR without obesity and to explore the underlying mechanisms. Rats were fed with a standard diet, containing either starch or fructose. BCAA levels, body weight and composition were recorded before and after 5, 12, 30, or 45 days of feeding. Elevated blood BCAA levels were observed in our IR model with unaltered body weight and composition. No changes were observed in the liver or the AT, but instead an impaired capacity of the skeletal muscle to catabolize BCAA was observed, including reduced capacity for transamination and oxidative deamination. Although the elevated blood BCAA levels in the fructose-fed rat seem to be a common feature of the IR phenotype observed in obese subjects and high fat–fed animals, the mechanisms involved in such a metabolic phenomenon are different, likely involving the skeletal muscle BCAA metabolism.

Associations Between Dietary Protein Sources, Plasma BCAA and Short-Chain Acylcarnitine Levels in Adults.

Elevated plasma branched-chain amino acids (BCAA) and C3 and C5 acylcarnitines (AC) levels observed in individuals with insulin resistance (IR) might be influenced by dietary protein intakes. This study explores the associations between dietary protein sources, plasma BCAA levels and C3 and C5 ACs in normal weight (NW) or overweight (OW) individuals with or without metabolic syndrome (MS). Data from 199 men and women aged 18–55 years with complete metabolite profile were analyzed. Associations between metabolic parameters, protein sources, plasma BCAA and AC levels were tested. OW/MS+ consumed significantly more animal protein (p = 0.0388) and had higher plasma BCAA levels (p < 0.0001) than OW/MS− or NW/MS− individuals. Plasma BCAA levels were not associated with BCAA intakes in the whole cohort, while there was a trend for an association between plasma BCAA levels and red meat or with animal protein in OW/MS+. These associations were of weak magnitude. In NW/MS− individuals, the protein sources associated with BCAA levels varied greatly with adjustment for confounders. Plasma C3 and C5 ACs were associated with plasma BCAA levels in the whole cohort (p < 0.0001) and in subgroups based on OW and MS status. These results suggest a modest association of meat or animal protein intakes and an association of C3 and C5 ACs with plasma BCAA levels, obesity and MS.

Plasma amino acid and metabolite signatures tracking diabetes progression in the UCD-T2DM rat model.

Elevations of plasma concentrations of branched-chain amino acids (BCAAs) are observed in human insulin resistance and type 2 diabetes mellitus (T2DM); however, there has been some controversy with respect to the passive or causative nature of the BCAA phenotype. Using untargeted metabolomics, plasma BCAA and other metabolites were assessed in lean control Sprague-Dawley rats (LC) and temporally during diabetes development in the UCD-T2DM rat model, i.e., prediabetic (PD) and 2 wk (D2W), 3 mo (D3M), and 6 mo (D6M) post-onset of diabetes. Plasma leucine, isoleucine, and valine concentrations were elevated only in D6M rats compared with D2W rats (by 28, 29, and 30%, respectively). This was in contrast to decreased plasma concentrations of several other amino acids in D3M and/or D6M relative to LC rats (Ala, Arg, Glu, Gln, Met, Ser, Thr, and Trp). BCAAs were positively correlated with fasting glucose and negatively correlated with plasma insulin, total body weight, total adipose tissue weight, and gastrocnemius muscle weight in the D3M and D6M groups. Multivariate analysis revealed that D3M and D6M UCD-T2DM rats had lower concentrations of amino acids, amino acid derivatives, 1,5-anhydroglucitol, and conduritol-β-opoxide and higher concentrations of uronic acids, pantothenic acids, aconitate, benzoic acid, lactate, and monopalmitin-2-glyceride relative to PD and D2W UCD-T2DM rats. The UCD-T2DM rat does not display elevated plasma BCAA concentrations until 6 mo post-onset of diabetes. With the acknowledgement that this is a rodent model of T2DM, the results indicate that elevated plasma BCAA concentrations are not necessary or sufficient to elicit an insulin resistance or T2DM onset.

Branched-Chain Amino Acids and Insulin Metabolism: The Insulin Resistance Atherosclerosis Study (IRAS).

Recent studies using untargeted metabolomics approaches have suggested that plasma branched-chain amino acids (BCAAs) are associated with incident diabetes. However, little is known about the role of plasma BCAAs in metabolic abnormalities underlying diabetes and whether these relationships are consistent across ethnic populations at high risk for diabetes. We investigated the associations of BCAAs with insulin sensitivity (SI), acute insulin response (AIR), and metabolic clearance of insulin (MCRI) in a multiethnic cohort. In 685 participants without diabetes of the Insulin Resistance Atherosclerosis Study (IRAS) (290 Caucasians, 165 African Americans, and 230 Hispanics), we measured plasma BCAAs (sum of valine, leucine, and isoleucine) by mass spectrometry and SI, AIR, and MCRI by frequently sampled intravenous glucose tolerance tests. Elevated plasma BCAAs were inversely associated with SI and MCRI and positively associated with fasting insulin in regression models adjusted for potential confounders (β = -0.0012 [95% CI -0.0018, -0.00059], P < 0.001 for SI; β = -0.0013 [95% CI -0.0018, -0.00082], P < 0.001 for MCRI; and β = 0.0015 [95% CI 0.0008, 0.0023], P < 0.001 for fasting insulin). The association of BCAA with SI was significantly modified by ethnicity, with the association only being significant in Caucasians and Hispanics. Elevated plasma BCAAs were associated with incident diabetes in Caucasians and Hispanics (multivariable-adjusted odds ratio per 1-SD increase in plasma BCAAs: 1.67 [95% CI 1.21, 2.29], P = 0.002) but not in African Americans. Plasma BCAAs were not associated with SI-adjusted AIR. Plasma BCAAs are associated with incident diabetes and underlying metabolic abnormalities, although the associations were generally stronger in Caucasians and Hispanics.

Impact of combined resistance and aerobic exercise training on branched-chain amino acid turnover, glycine metabolism and insulin sensitivity in overweight humans.

Obesity is associated with decreased insulin sensitivity (IS) and elevated plasma branched-chain amino acids (BCAAs). The purpose of this study was to investigate the relationship between BCAA metabolism and IS in overweight (OW) individuals during exercise intervention. Whole-body leucine turnover, IS by hyperinsulinaemic-euglycaemic clamp, and circulating and skeletal muscle amino acids, branched-chain α-keto acids and acylcarnitines were measured in ten healthy controls (Control) and nine OW, untrained, insulin-resistant individuals (OW-Untrained). OW-Untrained then underwent a 6 month aerobic and resistance exercise programme and repeated testing (OW-Trained). IS was higher in Control vs OW-Untrained and increased significantly following exercise. IS was lower in OW-Trained vs Control expressed relative to body mass, but was not different from Control when normalised to fat-free mass (FFM). Plasma BCAAs and leucine turnover (relative to FFM) were higher in OW-Untrained vs Control, but did not change on average with exercise. Despite this, within individuals, the decrease in molar sum of circulating BCAAs was the best metabolic predictor of improvement in IS. Circulating glycine levels were higher in Control and OW-Trained vs OW-Untrained, and urinary metabolic profiling suggests that exercise induces more efficient elimination of excess acyl groups derived from BCAA and aromatic amino acid (AA) metabolism via formation of urinary glycine adducts. A mechanism involving more efficient elimination of excess acyl groups derived from BCAA and aromatic AA metabolism via glycine conjugation in the liver, rather than increased BCAA disposal through oxidation and turnover, may mediate interactions between exercise, BCAA metabolism and IS. Clinicaltrials.gov NCT01786941.

Cross-talk between branched-chain amino acids and hepatic mitochondria is compromised in nonalcoholic fatty liver disease

Elevated plasma branched-chain amino acids (BCAA) in the setting of insulin resistance have been relevant in predicting type 2 diabetes mellitus (T2DM) onset, but their role in the etiology of hepatic insulin resistance remains uncertain. We determined the link between BCAA and dysfunctional hepatic tricarboxylic acid (TCA) cycle, which is a central feature of hepatic insulin resistance and nonalcoholic fatty liver disease (NAFLD). Plasma metabolites under basal fasting and euglycemic hyperinsulinemic clamps (insulin stimulation) were measured in 94 human subjects with varying degrees of insulin sensitivity to identify their relationships with insulin resistance. Furthermore, the impact of elevated BCAA on hepatic TCA cycle was determined in a diet-induced mouse model of NAFLD, utilizing targeted metabolomics and nuclear magnetic resonance (NMR)-based metabolic flux analysis. Insulin stimulation revealed robust relationships between human plasma BCAA and indices of insulin resistance, indicating chronic metabolic overload from BCAA. Human plasma BCAA and long-chain acylcarnitines also showed a positive correlation, suggesting modulation of mitochondrial metabolism by BCAA. Concurrently, mice with NAFLD failed to optimally induce hepatic mTORC1, plasma ketones, and hepatic long-chain acylcarnitines, following acute elevation of plasma BCAA. Furthermore, elevated BCAA failed to induce multiple fluxes through hepatic TCA cycle in mice with NAFLD. Our data suggest that BCAA are essential to mediate efficient channeling of carbon substrates for oxidation through mitochondrial TCA cycle. Impairment of BCAA-mediated upregulation of the TCA cycle could be a significant contributor to mitochondrial dysfunction in NAFLD.