Relationships between circulating metabolic intermediates and insulin action in overweight to obese, inactive men and women

Effect of metformin on myotube BCAA catabolism

Metformin has antihyperglycemic properties and is a commonly prescribed drug for type II diabetes mellitus. Metformin functions in part by activating 5'-AMP-activated protein kinase, reducing hepatic gluconeogenesis and blood glucose. Metformin also upregulates peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α). Several population studies have shown levels of circulating branched-chain amino acids (BCAA) positively correlate with insulin resistance. Because BCAA catabolic enzyme content is regulated by PGC-1α, we hypothesized metformin may alter BCAA catabolism. Therefore, the purpose of this work was to investigate the effect of metformin at varying concentrations on myotube metabolism and related gene and protein expression. C2C12 myotubes were treated with metformin at 30 uM (physiological) or 2 mM (supraphysiological) for up to 24 hours. Metabolic gene expression was measured via quantitative real time polymerase chain reaction, protein expression was measured using Western blot, and mitochondrial and glycolytic metabolism were measured via oxygen consumption and extracellular acidification rate, respectively. Supraphysiological metformin upregulated PGC-1α mRNA expression along with related downstream targets, yet the reduced expression of electron transport chain components as well as basal and peak cell metabolism. Supraphysiological metformin also suppressed branched-chain aminotransferase 2 (BCAT2) and branched-chain-alpha-keto acid dehydrogenase E1a (BCKDHa) mRNA expression as well as BCAT2 protein expression and BCKDHa activity, which was accompanied by decreased Kruppel-like factor 15 protein expression. Physiological levels of metformin suppressed BCKDHa and cytochrome c oxidase mRNA expression at early time points (4-12 hours) but had no effect on any other outcomes. Together these data suggest metformin may suppress BCAA catabolic enzyme expression or activity, possibly reducing levels of circulating gluconeogenic substrates.

BCAA catabolism in brown fat controls energy homeostasis through SLC25A44

Branched-chain amino acid (BCAA; valine, leucine and isoleucine) supplementation is often beneficial to energy expenditure; however, increased circulating levels of BCAA are linked to obesity and diabetes. The mechanisms of this paradox remain unclear. Here we report that, on cold exposure, brown adipose tissue (BAT) actively utilizes BCAA in the mitochondria for thermogenesis and promotes systemic BCAA clearance in mice and humans. In turn, a BAT-specific defect in BCAA catabolism attenuates systemic BCAA clearance, BAT fuel oxidation and thermogenesis, leading to diet-induced obesity and glucose intolerance. Mechanistically, active BCAA catabolism in BAT is mediated by SLC25A44, which transports BCAAs into mitochondria. Our results suggest that BAT serves as a key metabolic filter that controls BCAA clearance via SLC25A44, thereby contributing to the improvement of metabolic health.

Effect of Obesity and Exercise Training on Plasma Amino Acids and Amino Metabolites in American Indian Adolescents

CONTEXT

Amino acids (AAs) and their metabolites are altered with obesity and may be predictive of future diabetes in adults, but there are fewer studies on AAs, as well as conflicting findings on how they vary with obesity, in adolescents.

OBJECTIVE

To determine whether plasma AAs vary with body composition and insulin sensitivity and are altered in response to exercise training.

DESIGN

Cross-sectional, and an exercise intervention.

SETTING

Tribal wellness center.

PARTICIPANTS

American Indian boys and girls, 11 to 17 years of age with obesity (Ob, n = 58) or normal weight (NW, n = 36).

INTERVENTION

The Ob group completed 16 weeks of aerobic exercise training.

MAIN OUTCOME MEASURE

A panel of 42 plasma AAs.

RESULTS

Compared with the NW group, the Ob group had lower aerobic fitness and insulin sensitivity (interactive homeostasis model assessment 2), 17 AAs that were higher, and 7 AAs that were lower. Branched-chain AAs (+10% to 16%), aromatic AAs (+15% to 32%), and glutamate were among the higher AAs; all were positively correlated with body fat and negatively correlated with insulin sensitivity. The lysine metabolite 2-aminoadipic acid (2-AAA) and the valine metabolite β-aminoisobutyric acid (BAIBA) were 47% higher and 29% lower, respectively, in the Ob group, and were positively (2-AAA) and negatively (BAIBA) correlated with insulin sensitivity. Exercise training increased aerobic fitness by 10%, but body composition, insulin sensitivity, and AAs were not significantly changed.

CONCLUSIONS

Several plasma AAs are altered in American Indian adolescents with obesity and are associated with insulin sensitivity, but they were not altered with this exercise intervention.

A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome

Equine metabolic syndrome (EMS) is characterized by an abnormal insulin response to a glycemic challenge but despite the known insulinotropic effects of certain amino acids, there is a paucity of data evaluating the impact of dietary protein on insulin dynamics in these horses. The objective was therefore to assess insulin and amino acid responses following intake of a high protein meal in healthy horses and those with EMS. Six mature horses diagnosed with EMS and six age-matched control horses without EMS were used. Horses were fed 2g/kg body mass (BM) of a high protein pellet (31% crude protein) at time 0 and 30min, for a total of 4g/kg BM, following an overnight fast. Blood samples collected during a 4h period were analysed for plasma glucose, insulin, amino acids and urea concentrations. Glucose concentrations were not different between groups (P=0.2). Horses with EMS had a 9-fold greater insulinemic response to the consumption of a high protein meal compared with controls (P=0.046). Post-prandial levels of histidine, citrulline, tyrosine, valine, methionine, isoleucine, leucine and ornithine were higher in horses with EMS (P<0.05). Baseline urea nitrogen concentrations were not significantly different between groups (P=0.1). Knowing that certain amino acids are insulin secretagogues, these results illustrate that consumption of a high protein meal caused a hyperinsulinemic response and affected amino acid dynamics in horses with EMS. These findings suggest that dietary protein content should be taken into consideration in the management of horses with insulin dysregulation.

Effects of branched-chain amino acids on glucose metabolism in obese, prediabetic men and women: a randomized, crossover study

BACKGROUND

Recent studies have shown that circulating branched-chain amino acids (BCAAs) are elevated in obese, insulin-resistant individuals. However, it is not known if supplementation of additional BCAAs will further impair glucose metabolism.

OBJECTIVES

The aim of this pilot study was to determine the effects of BCAA supplementation on glucose metabolism in obese, prediabetic individuals.

METHODS

This is a randomized crossover study involving 12 obese individuals with prediabetes. Participants were randomly assigned to receive a daily supplement containing either 20 g BCAA or protein low in BCAAs for 4 wk with a 2-wk washout in between. At each visit, an oral-glucose-tolerance test (OGTT) was performed. Collected blood samples were used to measure glucose, insulin, and insulin resistance-associated biomarkers.

RESULTS

BCAA supplementation tended to decrease the plasma glucose area under the curve (AUC) measured by the OGTT (AUC percentage change from supplementation baseline, BCAA: -3.3% ± 3%; low-BCAA: 10.0% ± 6%; P = 0.08). However, BCAA supplementation did not affect plasma insulin during OGTT challenge (BCAA: -3.9% ± 8%; low-BCAA: 14.8% ± 10%; P = 0.28). The plasma concentrations of nerve growth factor (BCAA: 4.0 ± 1 pg/mL; low-BCAA: 5.7 ± 1 pg/mL; P = 0.01) and monocyte chemoattractant protein-1 (BCAA: -0.4% ± 9%; low-BCAA: 29.0% ± 18%; P = 0.02) were significantly lowered by BCAA supplementation compared to low-BCAA control. Plasma interleukin 1β was significantly elevated by BCAA supplementation (BCAA: 231.4% ± 187%; low-BCAA: 20.6% ± 33%; P = 0.05). BCAA supplementation did not affect the circulating concentrations of the BCAAs leucine (BCAA: 9.0% ± 12%; low-BCAA: 9.2% ± 11%), valine (BCAA: 9.1% ± 11%; low-BCAA: 12.0% ± 13%), or isoleucine (BCAA: 2.5% ± 11%; low-BCAA: 7.3% ± 11%).

CONCLUSIONS

Our data suggest that BCAA supplementation did not impair glucose metabolism in obese, prediabetic subjects. Further studies are needed to confirm the results seen in the present study. This study was registered at clinicaltrials.gov as NCT03715010.

NMR-Based Metabolomic Approach Tracks Potential Serum Biomarkers of Disease Progression in Patients with Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by chronic hyperglycemia associated with alterations in carbohydrate, lipid, and protein metabolism. The prognosis of T2DM patients is highly dependent on the development of complications, and therefore the identification of biomarkers of T2DM progression, with minimally invasive techniques, is a huge need. In the present study, we applied a ¹H-Nuclear Magnetic Resonance (¹H-NMR)-based metabolomic approach coupled with multivariate data analysis to identify serum metabolite profiles associated with T2DM development and progression. To perform this, we compared the serum metabolome of non-diabetic subjects, treatment-naïve non-complicated T2DM patients, and T2DM patients with complications in insulin monotherapy. Our analysis revealed a significant reduction of alanine, glutamine, glutamate, leucine, lysine, methionine, tyrosine, and phenylalanine in T2DM patients with respect to non-diabetic subjects. Moreover, isoleucine, leucine, lysine, tyrosine, and valine levels distinguished complicated patients from patients without complications. Overall, the metabolic pathway analysis suggested that branched-chain amino acid (BCAA) metabolism is significantly compromised in T2DM patients with complications, while perturbation in the metabolism of gluconeogenic amino acids other than BCAAs characterizes both early and advanced T2DM stages. In conclusion, we identified a metabolic serum signature associated with T2DM stages. These data could be integrated with clinical characteristics to build a composite T2DM/complications risk score to be validated in a prospective cohort.

Amino acid and fatty acid metabolomic profile during fasting and hyperinsulinemia in girls with polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is associated with insulin resistance (IR) and altered muscle mitochondrial oxidative phosphorylation. IR in adults with obesity and diabetes is associated with changes in amino acid, free fatty acid (FFA), and mitochondrial acylcarnitine (AC) metabolism. We sought to determine whether these metabolites are associated with IR and/or androgens in youth-onset PCOS. We enrolled obese girls with PCOS [ n = 15, 14.5 yr (SD 1.6), %BMI 98.5 (SD 1.0)] and without PCOS [ n = 6, 13.2 yr (SD 1.2), %BMI 98.0 (SD 1.1)]. Insulin sensitivity was assessed by hyperinsulinemic euglycemic clamp. Untargeted metabolomics of plasma was performed while fasting and during hyperinsulinemia. Fasting arginine, glutamine, histidine, lysine, phenylalanine, and tyrosine were higher ( P < 0.04 for all but P < 0.001 for valine), as were glutamine and histidine during hyperinsulinemia ( P < 0.03). Higher valine during hyperinsulinemia was associated with IR ( r = 0.59, P = 0.006). Surprisingly, end-clamp AC C4 was lower in PCOS, and lower C4 was associated with IR ( r = -0.44, P = 0.04). End-clamp FFAs of C14:0, C16:1, and C18:1 were higher in PCOS girls, and C16:1 and C18:1 strongly associated with IR ( r = 0.73 and 0.53, P < 0.01). Free androgen index related negatively to short-, medium-, and long-chain AC ( r = -0.41 to -0.71, P < 0.01) but not FFA or amino acids. Obese girls with PCOS have a distinct metabolic signature during fasting and hyperinsulinemia. As in diabetes, IR related to valine and FFAs, with an unexpected relationship with AC C4, suggesting unique metabolism in obese girls with PCOS.

Branched chain amino acids impact health and lifespan indirectly via amino acid balance and appetite control

Elevated branched chain amino acids (BCAAs) are associated with obesity and insulin resistance. How long-term dietary BCAAs impact late-life health and lifespan is unknown. Here, we show that when dietary BCAAs are varied against a fixed, isocaloric macronutrient background, long-term exposure to high BCAA diets leads to hyperphagia, obesity and reduced lifespan. These effects are not due to elevated BCAA per se or hepatic mTOR activation, but rather due to a shift in the relative quantity of dietary BCAAs and other AAs, notably tryptophan and threonine. Increasing the ratio of BCAAs to these AAs resulted in hyperphagia and is associated with central serotonin depletion. Preventing hyperphagia by calorie restriction or pair-feeding averts the health costs of a high BCAA diet. Our data highlight a role for amino acid quality in energy balance and show that health costs of chronic high BCAA intakes need not be due to intrinsic toxicity but, rather, a consequence of hyperphagia driven by AA imbalance.

Obesity and Cage Environment Modulate Metabolism in the Zucker Rat: A Multiple Biological Matrix Approach to Characterizing Metabolic Phenomena

Obesity and its comorbidities are increasing worldwide imposing a heavy socioeconomic burden. The effects of obesity on the metabolic profiles of tissues (liver, kidney, pancreas), urine, and the systemic circulation were investigated in the Zucker rat model using ¹H NMR spectroscopy coupled to multivariate statistical analysis. The metabolic profiles of the obese ( fa/ fa) animals were clearly differentiated from the two phenotypically lean phenotypes, ((+/+) and ( fa/+)) within each biological compartment studied, and across all matrices combined. No significant differences were observed between the metabolic profiles of the genotypically distinct lean strains. Obese Zucker rats were characterized by higher relative concentrations of blood lipid species, cross-compartmental amino acids (particularly BCAAs), urinary and liver metabolites relating to the TCA cycle and glucose metabolism; and lower amounts of urinary gut microbial-host cometabolites, and intermatrix metabolites associated with creatine metabolism. Further to this, the obese Zucker rat metabotype was defined by significant metabolic alterations relating to disruptions in the metabolism of choline across all compartments analyzed. The cage environment was found to have a significant effect on urinary metabolites related to gut-microbial metabolism, with additional cage-microenvironment trends also observed in liver, kidney, and pancreas. This study emphasizes the value in metabotyping multiple biological matrices simultaneously to gain a better understanding of systemic perturbations in metabolism, and also underscores the need for control or evaluation of cage environment when designing and interpreting data from metabonomic studies in animal models.

Actions of chronic physiological 3-hydroxyisobuterate treatment on mitochondrial metabolism and insulin signaling in myotubes

Branched-chain amino acids (BCAAs) are essential in the diet and may provide benefit for those who partake in regular physical activity and resistance training, yet circulating BCAAs have been repeatedly shown to correlate with severity of insulin resistance in obese/diseased populations. Recently, the valine catabolite 3-hydroxyisobuterate (3HIB) was shown to promote insulin resistance in skeletal muscle by increasing lipid content in vivo. The purpose of this study was to investigate the mechanistic effects of 3HIB on skeletal muscle insulin signaling, metabolism, and related gene expression in vitro. Given these previous observations, we hypothesized that 3HIB would depress skeletal muscle metabolism and insulin sensitivity. C2C12 myotubes were treated with 3HIB for up to 48 hours using both physiological (25-100 μmol/L) and supraphysiological (5 mmol/L) concentrations. Metabolic gene expression was measured via quantitative real-time polymerase chain reaction, mitochondrial metabolism was measured via O₂ consumption, and glycolytic metabolism was quantified using extracellular acidification rate. Western blot was used to assess insulin sensitivity following insulin stimulation (indicated by phospho-AKT expression). 3HIB did not alter expressional indicators of mitochondrial biogenesis, glycolysis, BCAA catabolism, or lipogenesis. Chronic physiological 3HIB treatment significantly increased peak oxygen consumption, whereas supraphysiological 3HIB treatment suppressed basal and peak mitochondrial and glycolytic metabolism. Both physiological and supraphysiological 3HIB reduced pAkt expression during insulin stimulation. These findings suggest that 3HIB may reduce muscle insulin sensitivity in cultured myotubes, supporting a potentially causal role of 3HIB in the development of insulin resistance in highly metabolic cell types.

A collective diabetes cross in combination with a computational framework to dissect the genetics of human obesity and Type 2 diabetes

To explore the genetic determinants of obesity and Type 2 diabetes (T2D), the German Center for Diabetes Research (DZD) conducted crossbreedings of the obese and diabetes-prone New Zealand Obese mouse strain with four different lean strains (B6, DBA, C3H, 129P2) that vary in their susceptibility to develop T2D. Genome-wide linkage analyses localized more than 290 quantitative trait loci (QTL) for obesity, 190 QTL for diabetes-related traits and 100 QTL for plasma metabolites in the outcross populations. A computational framework was developed that allowed to refine critical regions and to nominate a small number of candidate genes by integrating reciprocal haplotype mapping and transcriptome data. The efficiency of the complex procedure was demonstrated for one obesity QTL. The genomic interval of 35 Mb with 502 annotated candidate genes was narrowed down to six candidates. Accordingly, congenic mice retained the obesity phenotype owing to an interval that contains three of the six candidate genes. Among these the phospholipase PLA2G4A exhibited an elevated expression in adipose tissue of obese human subjects and is therefore a critical regulator of the obesity locus. Together, our broad and complex approach demonstrates that combined- and comparative-cross analysis exhibits improved mapping resolution and represents a valid tool for the identification of disease genes.

Plasma tyrosine and its interaction with low high-density lipoprotein cholesterol and the risk of type 2 diabetes mellitus in Chinese

AIMS/INTRODUCTION

Metabolomic markers have the potential to improve the predicting accuracy of existing risk scores for type 2 diabetes mellitus. The present study aimed to test the associations between plasma tyrosine and type 2 diabetes mellitus with special attention to identifying possible cut-off points for type 2 diabetes mellitus, and its interactive effects with low high-density lipoprotein cholesterol (HDL-C) and/or high triglyceride for type 2 diabetes mellitus.

METHODS

From 27 May 2015 to 3 August 2016, we retrieved the medical notes of 1,898 inpatients with type 2 diabetes mellitus as the cases, and 1,522 individuals without diabetes as the controls who attended annual medical checkups from the same tertiary care center in Jinzhou, China. Logistic regression analyses were carried out to obtain odds ratios (ORs) and 95% confidence intervals (CIs). Restricted cubic spline analysis nested in the logistic regression analysis was used to identify possible cut-off points of tyrosine for type 2 diabetes mellitus. The additive interaction was used to estimate interactions between high tyrosine and low HDL-C in type 2 diabetes mellitus patients.

RESULTS

The OR of tyrosine for type 2 diabetes mellitus did not increase until 46 μmol/L and after that point, the OR rapidly rose with increasing tyrosine in a nearly linear manner. If 46 μmol/L was used to define high tyrosine, high tyrosine was associated with an increased OR of type 2 diabetes mellitus (adjusted OR 1.88, 95% CI 1.44-2.45). The presence of low HDL-C greatly enhanced the ORs of tyrosine for type 2 diabetes mellitus from 1.11 (95% CI 0.82-1.51) to 54.11 (95% CI 33.96-86.22) with significant additive interaction.

CONCLUSIONS

In Chinese adults, tyrosine >46 μmol/L was associated with increased odds of type 2 diabetes mellitus, which was contingent on low HDL-C.

Chronic maternal cortisol excess during late gestation leads to metabolic alterations in the newborn heart

Our laboratory has previously shown in an ovine model of pregnancy that abnormal elevations in maternal cortisol during late gestation lead to increased fetal cardiac arrhythmias and mortality during peripartum. Furthermore, transcriptomic analysis of the fetal heart suggested alterations in TCA cycle intermediates and lipid metabolites in animals exposed to excess cortisol in utero. Therefore, we utilized a sheep model of pregnancy to determine how chronic increases in maternal cortisol alter maternal and fetal serum before birth and neonatal cardiac metabolites and lipids at term. Ewes were either infused with 1 mg·kg^-1·day^-1 of cortisol starting at gestational day 115 ( n = 9) or untreated ( n = 6). Serum was collected from the mother and fetus (gestational day 125), and hearts were collected following birth. Proton nuclear magnetic resonance (¹H-NMR) spectroscopy was conducted to measure metabolic profiles of newborn heart specimens as well as fetal and maternal serum specimens. Mass spectrometry was conducted to measure lipid profiles of newborn heart specimens. We observed alterations in amino acid and TCA cycle metabolism as well as lipid and glycerophospholipid metabolism in newborn hearts after excess maternal cortisol in late gestation. In addition, we observed alterations in amino acid and TCA cycle metabolites in fetal but not in maternal serum during late gestation. These results suggest that fetal exposure to excess maternal cortisol alters placental and fetal metabolism before birth and limits normal cardiac metabolic maturation, which may contribute to increased risk of peripartum cardiac arrhythmias observed in these animals or later life cardiomyopathies.

Changes of urine metabolites in response to n-3 fatty acid supplements and their correlation with metabolic risk factors in patients with type 2 diabetes

The present study aimed to investigate the effects of n-3 fatty acid supplements on urine metabolite profiling and their correlation with metabolic risk factors in Chinese T2D patients.

Decreases in Circulating Concentrations of Long-Chain Acylcarnitines and Free Fatty Acids During the Glucose Tolerance Test Represent Tissue-Specific Insulin Sensitivity

Background: Insulin plays a pivotal role in the regulation of both carbohydrate and lipid intermediate turnover and metabolism. In the transition from a fasted to fed state, insulin action inhibits lipolysis in adipocytes, and acylcarnitine synthesis in the muscles and heart. The aim of this study was to measure free fatty acid (FFA) and acylcarnitine levels during the glucose tolerance test as indicators of tissue-specific insulin resistance. Results: Insulin release in response to glucose administration decreased both FFA and long-chain acylcarnitine levels in plasma in healthy control animals by 30% (120 min). The glucose tolerance test and [³H]-deoxy-D-glucose uptake in tissues revealed that high fat diet-induced lipid overload in C57bl/6N mice evoked only adipose tissue insulin resistance, and plasma levels of FFAs did not decrease after glucose administration. In comparison, db/db mice developed type 2 diabetes with severely impaired insulin sensitivity and up to 70% lower glucose uptake in both adipose tissues and muscles (skeletal muscle and heart), and both plasma concentrations of FFAs and long-chain acylcarnitines did not decrease in response to glucose administration. Conclusions: These results link impaired adipose tissue insulin sensitivity with continuous FFA release in the transition from a fasted to postprandial state, while a blunted decrease in long-chain acylcarnitine levels is associated with muscle and heart insulin resistance.

Plasma Sulphur-Containing Amino Acids, Physical Exercise and Insulin Sensitivity in Overweight Dysglycemic and Normal Weight Normoglycemic Men

Plasma sulphur-containing amino acids and related metabolites are associated with insulin sensitivity, although the mechanisms are unclear. We examined the effect of exercise on this relationship. Dysglycemic (n = 13) and normoglycemic (n = 13) men underwent 45 min cycling before and after 12 weeks exercise intervention. We performed hyperinsulinemic euglycemic clamp, mRNA-sequencing of skeletal muscle and adipose tissue biopsies, and targeted profiling of plasma metabolites by LC-MS/MS. Insulin sensitivity increased similarly in dysglycemic and normoglycemic men after 12 weeks of exercise, in parallel to similar increases in concentration of plasma glutamine, and decreased concentrations of plasma glutamate, cysteine, taurine, and glutathione. Change in plasma concentrations of cysteine and glutathione exhibited the strongest correlations to exercise-improved insulin sensitivity, and expression of a cluster of genes essential for oxidative phosphorylation and fatty acid metabolism in both skeletal muscle and adipose tissue, as well as mitochondria-related genes such as mitofilin. Forty-five min of cycling decreased plasma concentrations of glutamine and methionine, and increased plasma concentrations of glutamate, homocysteine, cystathionine, cysteine, glutathione, and taurine. Similar acute responses were seen in both groups before and after the 12 weeks training period. Both acute and long-term exercise may influence transsulphuration and glutathione biosynthesis, linking exercise-improved insulin sensitivity to oxidative stress and mitochondrial function.

Interorgan Metabolic Crosstalk in Human Insulin Resistance

Excessive energy intake and reduced energy expenditure drive the development of insulin resistance and metabolic diseases such as obesity and type 2 diabetes mellitus. Metabolic signals derived from dietary intake or secreted from adipose tissue, gut, and liver contribute to energy homeostasis. Recent metabolomic studies identified novel metabolites and enlarged our knowledge on classic metabolites. This review summarizes the evidence of their roles as mediators of interorgan crosstalk and regulators of insulin sensitivity and energy metabolism. Circulating lipids such as free fatty acids, acetate, and palmitoleate from adipose tissue and short-chain fatty acids from the gut effectively act on liver and skeletal muscle. Intracellular lipids such as diacylglycerols and sphingolipids can serve as lipotoxins by directly inhibiting insulin action in muscle and liver. In contrast, fatty acid esters of hydroxy fatty acids have been recently shown to exert a series of beneficial effects. Also, ketoacids are gaining interest as potent modulators of insulin action and mitochondrial function. Finally, branched-chain amino acids not only predict metabolic diseases, but also inhibit insulin signaling. Here, we focus on the metabolic crosstalk in humans, which regulates insulin sensitivity and energy homeostasis in the main insulin-sensitive tissues, skeletal muscle, liver, and adipose tissue.

Calorie restriction and its impact on gut microbial composition and global metabolism

Calorie restriction (CR) is a dietary regimen that reduces calorie intake without incurring malnutrition or a reduction in essential nutrients. It has long been recognized as a natural strategy for promoting health, extending longevity, and prevents the development of metabolic and age-related diseases. In the present review, we focus on the general effect of CR on gut microbiota composition and global metabolism. We also propose mechanisms for its beneficial effect. Results showed that probiotic and butyrate-producing microbes increased their relative abundance, whereas proinflammatory strains exhibited suppressed relative abundance following CR. Analyses of the gut microbial and host metabolisms revealed that most host microbial co-metabolites were changed due to CR. Examples of dramatic CR-induced changes in host metabolism included a decrease in the rate of lipid biosynthesis and an increase in the rates of fatty acid catabolism, β-oxidation, glycogenolysis, and gluconeogenesis. The observed phenotypes and the further verification of the direct link between gut microbiota and metabolome may benefit patients that are at risk for developing metabolic disease. Thus, improved gut microbiota composition and metabolome are potential biomarkers for determining the effectiveness of dietary interventions for age-related and metabolic diseases.

Effects of weight loss using supplementation with Lactobacillus strains on body fat and medium-chain acylcarnitines in overweight individuals

Our previous study showed that supplementation with a combination of Lactobacillus curvatus (L. curvatus) HY7601 and Lactobacillus plantarum (L. plantarum) KY1032 reduced the body weight, body fat percentage, body fat mass and L1 subcutaneous fat area in overweight subjects. We aimed to evaluate whether the changes in adiposity after supplementation with Lactobacillus strains were associated with metabolic intermediates. A randomized, double-blind, placebo-controlled study was conducted on 66 non-diabetic and overweight individuals. Over a 12-week period, the probiotic group consumed 2 g of probiotic powder, whereas the placebo group consumed the same product without the probiotics. To investigate metabolic alterations, we performed plasma metabolomics using ultra-performance liquid chromatography and mass spectrometry (UPLC-LTQ/Orbitrap MS). Probiotic supplementation significantly increased the levels of octenoylcarnitine (C8:1), tetradecenoylcarnitine (C14:1), decanoylcarnitine (C10) and dodecenoylcarnitine (C12:1) compared with the levels from placebo supplementation. In the probiotic group, the changes in the body weight, body fat percentage, body fat mass and L1 subcutaneous fat area were negatively associated with changes in the levels of C8:1, C14:1, C10 and C12:1 acylcarnitines. In overweight individuals, probiotic-induced weight loss and adiposity reduction from the probiotic supplementation were associated with an increase in medium-chain acylcarnitines.

Branched Chain Amino Acids in Metabolic Disease

PURPOSE OF REVIEW

Elevations in circulating branched chain amino acids (BCAAs) have gained attention as potential contributors to the development of insulin resistance and diabetes.

RECENT FINDINGS

Epidemiological evidence strongly supports this conclusion. Suppression of BCAA catabolism in adipose and hepatic tissues appears to be the primary drivers of plasma BCAA elevations. BCAA catabolism may be shunted to skeletal muscle, where it indirectly leads to FA accumulation and insulin resistance, via a number of proposed mechanisms. BCAAs have an important role in the development of IR, but our understanding of how plasma BCAA elevations occur, and how these elevations lead to insulin resistance, is still limited.

l-Alanine activates hepatic AMP-activated protein kinase and modulates systemic glucose metabolism

Objective

AMP activated protein kinase (AMPK) is recognized as an important nutrient sensor contributing to regulation of cellular, tissue, and systemic metabolism. We aimed to identify specific amino acids which could modulate AMPK and determine effects on cellular and systemic metabolism.

Methods

We performed an unbiased amino acid screen to identify activators of AMPK. Detailed analysis of cellular signaling and metabolism was performed in cultured hepatoma cells, and in vivo glucose metabolism and metabolomic patterns were assessed in both chow-fed mice and mice made obese by high-fat diet feeding.

Results

Alanine acutely activates AMP kinase in both cultured hepatic cells and in liver from mice treated in vivo with Ala. Oral alanine administration improves systemic glucose tolerance in both chow and high fat diet fed mice, with reduced efficacy of Ala in mice with reduced AMPK activity. Our data indicate that Ala activation of AMPK is mediated by intracellular Ala metabolism, which reduces TCA cycle metabolites, increases AMP/ATP ratio, and activates NH₃ generation.

Conclusions

Ala may serve as a distinct amino acid energy sensor, providing a positive signal to activate the beneficial AMPK signaling pathway.

•

Unbiased amino acid screen identified alanine as a unique activator of AMP kinase.

•

Alanine acutely activates AMP kinase in both cultured cells and in vivo.

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Alanine and NH₃ metabolism contribute to regulation of AMP kinase activation.

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Effects of Ala are reduced in absence of AMP kinase.

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Oral alanine improves glucose tolerance in vivo in both chow and HFD-fed mice.

Branched-chain amino acids promote endothelial dysfunction through increased reactive oxygen species generation and inflammation

Branched‐chain amino acids (BCAA: leucine, isoleucine and valine) are essential amino acids implicated in glucose metabolism and maintenance of correct brain function. Elevated BCAA levels can promote an inflammatory response in peripheral blood mononuclear cells. However, there are no studies analysing the direct effects of BCAA on endothelial cells (ECs) and its possible modulation of vascular function. In vitro and ex vivo studies were performed in human ECs and aorta from male C57BL/6J mice, respectively. In ECs, BCAA (6 mmol/L) increased eNOS expression, reactive oxygen species production by mitochondria and NADPH oxidases, peroxynitrite formation and nitrotyrosine expression. Moreover, BCAA induced pro‐inflammatory responses through the transcription factor NF‐κB that resulted in the release of intracellular adhesion molecule‐1 and E‐selectin conferring endothelial activation and adhesion capacity to inflammatory cells. Pharmacological inhibition of mTORC1 intracellular signalling pathway decreased BCAA‐induced pro‐oxidant and pro‐inflammatory effects in ECs. In isolated murine aorta, BCAA elicited vasoconstrictor responses, particularly in pre‐contracted vessels and after NO synthase blockade, and triggered endothelial dysfunction, effects that were inhibited by different antioxidants, further demonstrating the potential of BCAA to induce oxidative stress with functional impact. In summary, we demonstrate that elevated BCAA levels generate inflammation and oxidative stress in ECs, thereby facilitating inflammatory cells adhesion and endothelial dysfunction. This might contribute to the increased cardiovascular risk observed in patients with elevated BCAA blood levels.

Progress in Metabonomics of Type 2 Diabetes Mellitus

With the improvement of living standards and a change in lifestyle, the incidence of type 2 diabetes mellitus (T2DM) is increasing. Its etiology is too complex to be completely understand yet. Metabonomics techniques are used to study the changes of metabolites and metabolic pathways before and after the onset of diabetes and make it more possible to further understand the pathogenesis of T2DM and improve its prediction, early diagnosis, and treatment. In this review, we summarized the metabonomics study of T2DM in recent years and provided a theoretical basis for the study of pathogenesis and the effective prevention and treatment of T2DM.

Dietary Patterns among Asian Indians Living in the United States Have Distinct Metabolomic Profiles That Are Associated with Cardiometabolic Risk

Background

Recent studies, primarily in non-Hispanic whites, suggest that dietary patterns have distinct metabolomic signatures that may influence disease risk. However, evidence in South Asians, a group with unique dietary patterns and a high prevalence of cardiometabolic risk, is lacking.

Objective

We investigated the metabolomic profiles associated with 2 distinct dietary patterns among a sample of Asian Indians living in the United States. We also examined the cross-sectional associations between metabolomic profiles and cardiometabolic risk markers.

Methods

We used cross-sectional data from 145 Asian Indians, aged 45-79 y, in the Metabolic Syndrome and Atherosclerosis in South Asians Living in America (MASALA) pilot study. Metabolomic profiles were measured from fasting serum samples. Usual diet was assessed by using a validated food-frequency questionnaire. We used principal components analysis to derive dietary and metabolomic patterns. We used adjusted general linear regression models to examine associations between dietary patterns, individual food groups, metabolite patterns, and cardiometabolic risk markers.

Results

We observed 2 major principal components or metabolite clusters, the first comprised primarily of medium- to long-chain acylcarnitines (metabolite pattern 1) and the second characterized by branched-chain amino acids, aromatic amino acids, and short-chain acylcarnitines (metabolite pattern 2). A "Western/nonvegetarian" pattern was significantly and positively associated with metabolite pattern 2 (all participants: β ± SE = 0.180 ± 0.090, P = 0.05; participants without type 2 diabetes: β ± SE = 0.323 ± 0.090, P = 0.0005). In all participants, higher scores on metabolite pattern 2 were adversely associated with measures of glycemia (fasting insulin: β ± SE = 2.91 ± 1.29, P = 0.03; 2-h insulin: β ± SE = 22.1 ± 10.3, P = 0.03; homeostasis model assessment of insulin resistance: β ± SE = 0.94 ± 0.42, P = 0.03), total adiponectin (β ± SE = -1.46 ± 0.47, P = 0.002), lipids (total cholesterol: β ± SE = 7.51 ± 3.45, P = 0.03; triglycerides: β ± SE = 14.4 ± 6.67, P = 0.03), and a radiographic measure of hepatic fat (liver-to-spleen attenuation ratio: β ± SE = -0.83 ± 0.42, P = 0.05).

Conclusions

Our findings suggest that a "Western/nonvegetarian" dietary pattern is associated with a metabolomic profile that is related to an adverse cardiometabolic profile in Asian Indians. Public health efforts to reduce cardiometabolic disease burden in this high-risk group should focus on consuming a healthy plant-based diet.

Evolution of ARDS biomarkers: Will metabolomics be the answer?

To date, there is no clinically agreed-upon diagnostic test for acute respiratory distress syndrome (ARDS): the condition is still diagnosed on the basis of a constellation of clinical findings, laboratory tests, and radiological images. Development of ARDS biomarkers has been in a state of continuous flux during the past four decades. To address ARDS heterogeneity, several studies have recently focused on subphenotyping the disease on the basis of observable clinical characteristics and associated blood biomarkers. However, the strong correlation between identified biomarkers and ARDS subphenotypes has yet to establish etiology; hence, there is a need for the adoption of other methodologies for studying ARDS. In this review, we will shed light on ARDS metabolomics research in the literature and discuss advances and major obstacles encountered in ARDS metabolomics research. Generally, the ARDS metabolomics studies focused on identification of differentiating metabolites for diagnosing ARDS, but they were performed to different standards in terms of sample size, selection of control cohort, type of specimens collected, and measuring technique utilized. Virtually none of these studies have been properly validated to identify true metabolomics biomarkers of ARDS. Though in their infancy, metabolomics studies exhibit promise to unfold the biological processes underlying ARDS and, in our opinion, have great potential for pushing forward our present understanding of ARDS.

Lower Concentrations of Circulating Medium and Long-Chain Acylcarnitines Characterize Insulin Resistance in Persons with HIV

In human immunodeficiency virus (HIV)-negative individuals, a plasma metabolite profile, characterized by higher levels of branched-chain amino acids (BCAA), aromatic amino acids, and C3/C5 acylcarnitines, is associated with insulin resistance and increased risk of diabetes. We sought to characterize the metabolite profile accompanying insulin resistance in HIV-positive persons to assess whether the same or different bioenergetics pathways might be implicated. We performed an observational cohort study of 70 nondiabetic, HIV-positive individuals (50% with body mass index ≥30 kg/m²) on efavirenz, tenofovir, and emtricitabine with suppressed HIV-1 RNA levels (<50 copies/mL) for at least 2 years and a CD4⁺ count over 350 cells/μL. We measured fasting insulin resistance using the homeostatic model assessment 2, plasma free fatty acids (FFA) using gas chromatography, and amino acids, acylcarnitines, and organic acids using liquid chromatography/mass spectrometry. We assessed the relationship of plasma metabolites with insulin resistance using multivariable linear regression. The median age was 45 years, median CD4⁺ count was 701 cells/μL, and median hemoglobin A1c was 5.2%. Insulin resistance was associated with higher plasma C3 acylcarnitines (p = .01), but not BCAA or C5 acylcarnitines. However, insulin resistance was associated with lower plasma levels of C18, C16, C12, and C2 acylcarnitines (p ≤ .03 for all), and lower C18 and C16 acylcarnitine:FFA ratios (p = .002, and p = .03, respectively). In HIV-positive persons, lower levels of plasma acylcarnitines, including the C2 product of complete fatty acid oxidation, are a more prominent feature of insulin resistance than changes in BCAA, suggesting impaired fatty acid uptake and/or mitochondrial oxidation is a central aspect of glucose intolerance in this population.

Combined Inflammation and Metabolism Biomarker Indices of Robust and Impaired Physical Function in Older Adults

OBJECTIVES

To determine whether combinations of inflammatory markers are related to physical function.

DESIGN AND SUBJECTS

secondary analysis of baseline of three observational studies of community-dwelling older adults MEASUREMENTS: The baseline data from 3 cohorts of older adults with different health and disease status were employed. Twenty markers of inflammation and metabolism were individually assessed for correlation with usual gait speed and were separated into robust and impairment quartiles. For the robustness and impairment indices, individual markers were selected using step-wise regression over bootstrapping iterations, and regression coefficients were estimated for the markers individually and collectively as an additive score.

RESULTS

We developed a robustness index involving 6 markers and an impairment index involving 8 markers corresponding positively and negatively with gait speed. Two markers, glycine and tumor necrosis factor receptor 1 (TNFR1), appeared only in the robustness index, and TNFR2; regulated on activation, normal T-cell expressed and secreted; the amino acid factor; and matrix metallopeptidase 3; appeared only in the impairment index.

CONCLUSION

Indices of biomarkers were associated with robust and impaired physical performance but differ, in composition suggesting potential biological differences that may contribute to robustness and impairment.

Effect of Eicosapentaenoic acid (EPA) supplementation on cardiovascular markers in patients with type 2 diabetes mellitus: A randomized, double-blind, placebo-controlled trial

AIMS

Cardiovascular complications are one of main cause of increased mortality and morbidity among Diabetes Mellitus (DM) patients. Altered metabolism of sulphur amino acids in diabetes reflected as increases in concentration of methionine and cysteine/cystine in the blood which known as a markers of Cardiovascular Diseases (CVD). The aim of present study was to determine the effect of Eicosapentaenoic acid (EPA) supplementation on sulfhydryl amino acids and Atherogenic Index of Plasma (AIP) in patients with type 2 DM (T2DM).

METHOD

A randomized, double-blind, placebo-controlled clinical trial was performed in 36 control and patients with DM. The subjects were randomly assigned to obtain 2 g/d EPA (n = 18) or placebo (n = 18) for 8 weeks. Fasting serum level of Cystein and Methionine were measured using HPLC method and atherogenic index of plasma (AIP) as a proxy measure of atherosclerosis was computed.

RESULTS

Eight weeks supplementation with EPA led to significant reductions in Met (p < 0.002) and Cys (p < 0.001) compared with the placebo (p < 0.06). In addition, compared to placebo a significant reduction in AIP were seen after taking EPA (p < 0.04).

CONCLUSION

EPA supplementation in patients with T2DM for eight weeks had beneficial effects on Met, Cys and AIP, which may attribute to the prevention of vascular complications in the T2DM patients.

Cardiovascular Metabolomics

Disturbances in cardiac metabolism underlie most cardiovascular diseases. Metabolomics, one of the newer omics technologies, has emerged as a powerful tool for defining changes in both global and cardiac-specific metabolism that occur across a spectrum of cardiovascular disease states. Findings from metabolomics studies have contributed to better understanding of the metabolic changes that occur in heart failure and ischemic heart disease and have identified new cardiovascular disease biomarkers. As technologies advance, the metabolomics field continues to evolve rapidly. In this review, we will discuss the current state of metabolomics technologies, including consideration of various metabolomics platforms and elements of study design; the emerging utility of stable isotopes for metabolic flux studies; and the use of metabolomics to better understand specific cardiovascular diseases, with an emphasis on recent advances in the field.

Metabolic changes in urine and serum during progression of diabetic kidney disease in a mouse model

Diabetic kidney disease (DKD) involves various pathogenic processes during progression to end stage renal disease, and activated metabolic pathways might be changing based on major pathophysiologic mechanisms as DKD progresses. In this study, nuclear magnetic resonance spectroscopy (NMR)-based metabolic profiling was performed in db/db mice to suggest potential biomarkers for early detection and its progression. We compared concentrations of serum and urinary metabolites between db/m and db/db mice at 8 or 20 weeks of age and investigated whether changes between 8 and 20 weeks in each group were significant. The metabolic profiles demonstrated significantly increased urine levels of glucose and tricarboxylic acid cycle intermediates at both 8 and 20 weeks of age in db/db mice. These intermediates also exhibited strong positive associations with urinary albumin excretion, suggesting that they may be potential biomarkers for early diagnosis. On the contrary, branched chain amino acid and homocysteine-methionine metabolism were activated early in the disease, whereas ketone and fatty acid metabolism were significantly changed in the late phase of the disease. We demonstrated phase-specific alterations in metabolites during progression of DKD. This study provides insights into perturbed mechanisms during evolution of the disease and identifies potential novel biomarkers for DKD.

Lower plasma choline levels are associated with sleepiness symptoms

Sleepiness and cardiovascular disease share common molecular pathways; thus, metabolic risk factors for sleepiness may also predict cardiovascular disease risk. Daytime sleepiness predicts mortality and cardiovascular disease, although the mechanism is unidentified. This study explored the associations between subjective sleepiness and metabolite concentrations in human blood plasma within the oxidative and inflammatory pathways, in order to identify mechanisms that may contribute to sleepiness and cardiovascular disease risk.

METHODS

An exploratory case-control sample of 36 subjects, categorized based on the Epworth Sleepiness Scale (ESS) questionnaire as sleepy (ESS ≥ 10) or non-sleepy (ESS < 10), was recruited among subjects undergoing an overnight sleep study for suspected sleep apnea at the University of Pennsylvania Sleep Center. The average age was 42.4 ± 10.5 years, the mean body mass index (BMI) was 40.0 ± 9.36 kg/m², median Apnea Hypopnea Index (AHI) was 8.2 (IQR: 2.5-26.5), and 52% were male. Fasting morning blood plasma samples were collected after an overnight sleep study. Biomarkers were explored in subjects with sleepiness versus those without using the multiple linear regression adjusting for age, BMI, smoking, Apnea Hypopnea Index (sleep apnea severity), study cohort, and hypertension.

RESULTS

The level of choline is significantly lower (P = 0.003) in sleepy subjects (N = 18; mean plasma choline concentration of 8.19 ± 2.62 μmol/L) compared with non-sleepy subjects (N = 18; mean plasma choline concentration of 9.14 ± 2.25 μmol/L). Other markers with suggestive differences (P < 0.1) include isovalerylcarnitine, Alpha-Amino apidipic acid, Spingosine 1 Phosphate, Aspartic Acid, Propionylcarnitine, and Ceramides (fatty acids; C14-C16 and C-18).

CONCLUSION

This pilot study is the first to show that lower levels of plasma choline metabolites are associated with sleepiness. Further exploration of choline and other noted metabolites and their associations with sleepiness will guide targeted symptom management.

BCAA Metabolism and Insulin Sensitivity - Dysregulated by Metabolic Status?

Branched-chain amino acids (BCAAs) appear to influence several synthetic and catabolic cellular signaling cascades leading to altered phenotypes in mammals. BCAAs are most notably known to increase protein synthesis through modulating protein translation, explaining their appeal to resistance and endurance athletes for muscle hypertrophy, expedited recovery, and preservation of lean body mass. In addition to anabolic effects, BCAAs may increase mitochondrial content in skeletal muscle and adipocytes, possibly enhancing oxidative capacity. However, elevated circulating BCAA levels have been correlated with severity of insulin resistance. It is hypothesized that elevated circulating BCAAs observed in insulin resistance may result from dysregulated BCAA degradation. This review summarizes original reports that investigated the ability of BCAAs to alter glucose uptake in consequential cell types and experimental models. The review also discusses the interplay of BCAAs with other metabolic factors, and the role of excess lipid (and possibly energy excess) in the dysregulation of BCAA catabolism. Lastly, this article provides a working hypothesis of the mechanism(s) by which lipids may contribute to altered BCAA catabolism, which often accompanies metabolic disease.

Serum Metabolomics of Activity Energy Expenditure and its Relation to Metabolic Syndrome and Obesity

Modifiable lifestyle factors, including exercise and activity energy expenditure (AEE), may attenuate the unfavorable health effects of obesity, such as risk factors of metabolic syndrome (MetS). However, the underlying mechanisms are not clear. In this study we sought to investigate whether the metabolite profiles of MetS and adiposity assessed by body mass index (BMI) and central obesity are inversely correlated with AEE and physical activity. We studied 35 men and 47 women, aged 30-60 years, using doubly labeled water to derive AEE and the Sedentary Time and Activity Reporting Questionnaire (STAR-Q) to determine the time spent in moderate and vigorous physical activity. Proton nuclear magnetic resonance spectroscopy was used for serum metabolomics analysis. Serine and glycine were found in lower concentrations in participants with more MetS risk factors and greater adiposity. However, serine and glycine concentrations were higher with increasing activity measures. Metabolic pathway analysis and recent literature suggests that the lower serine and glycine concentrations in the overweight/obese state could be a consequence of serine entering de novo sphingolipid synthesis. Taken together, higher levels of AEE and physical activity may play a crucial part in improving metabolic health in men and women with and without MetS risk factors.

Profiling of plasma metabolites in postmenopausal women with metabolic syndrome

Objective:

The aim of the study was to investigate the associations of amino acids and other polar metabolites with metabolic syndrome (MetS) in postmenopausal women in a lean Asian population.

Methods:

The participants were 1,422 female residents enrolled in a cohort study from April to August 2012. MetS was defined according to the National Cholesterol Education Program Adult Treatment Panel III modified for Japanese women. Associations were examined between MetS and 78 metabolites assayed in fasting plasma samples using capillary electrophoresis-mass spectrometry. Replication analysis was performed to confirm the robustness of the results in a separate population created by random allocation.

Results:

Analysis was performed for 877 naturally postmenopausal women, including 594 in the original population and 283 in the replication population. The average age, body mass index, and levels of high- and low-density lipoprotein cholesterol of the entire population were 64.6 years, 23.0 kg/m², 72.1 mg/dL, and 126.1 mg/dL, respectively. There was no significant difference in low-density lipoprotein cholesterol levels between women with and without MetS. Thirteen metabolites were significantly related to MetS: multiple plasma amino acids were elevated in women with MetS, including branched-chain amino acids, alanine, glutamate, and proline; and alpha-aminoadipate, which is generated by lysine degradation, was also significantly increased.

Conclusions:

Our large-scale metabolomic profiling indicates that Japanese postmenopausal women with MetS have abnormal polar metabolites, suggesting altered catabolic pathways. These results may help to understand metabolic disturbance, including in persons with normal body mass index and relatively high levels of high-density lipoprotein cholesterol, and may have clinical utility based on further studies.

Changes in glucose metabolism after distal pancreatectomy: a nationwide database study

Background

This population-based study evaluated changes in glucose metabolism after distal pancreatectomy (DP).

Methods

Data from the Taiwan National Health Insurance Research Database was collected from 2001 to 2010. Of 1,980 patients who underwent DP, 507 had diabetes and 1,410 did not.

Results

Of the 1,410 non-diabetic pre-DP patients, 312 (22.1%) developed newly-diagnosed diabetes after DP. Multiple logistic regression analysis revealed that dyslipidemia [hazard ratio = 1.940; 95% confidence interval = 1.362–2.763; P < 0.001] and chronic pancreatitis (hazard ratio = 2.428; 95% confidence interval = 1.889–3.121; P < 0.001) were significantly associated with the development of diabetes after DP. On the other hand, analysis of changes in glucose metabolism among 289 pre-DP diabetes without the use of insulin revealed that 173 (59.9%) had deteriorated glucose metabolism after DP.

Conclusion

Dyslipidemia and chronic pancreatitis are risk factors for the development of diabetes. Further, more than half of the pre-DP diabetes patients without the use of insulin had deterioration of glucose metabolism after DP. Therefore, clinicians should monitor glucose metabolism and clinical symptoms of hyperglycemia among DP patients.

Metabolic Dysfunction in Heart Failure: Diagnostic, Prognostic, and Pathophysiologic Insights From Metabolomic Profiling

Metabolic impairment is an intrinsic component of heart failure (HF) pathophysiology. Although initially conceived as a myocardial defect, metabolic dysfunction is now recognized as a systemic process with complex interplay between the myocardium and peripheral tissues and organs. Specifically, HF-associated metabolic dysfunction includes alterations in substrate utilization, insulin resistance, defects in energy production, and imbalanced anabolic-catabolic signaling leading to cachexia. Each of these metabolic abnormalities is associated with significant morbidity and mortality in patients with HF; however, their detection and therapeutic management remains challenging. Given the difficulty in obtaining human cardiac tissue for research purposes, peripheral blood metabolomic profiling, a well-established approach for characterizing small-molecule metabolite intermediates from canonical biochemical pathways, may be a useful technology for dissecting biomarkers and mechanisms of metabolic impairment in HF. In this review, metabolic abnormalities in HF will be discussed with particular emphasis on the application of metabolomic profiling to detecting, risk stratifying, and identifying novel targets for metabolic therapy in this heterogeneous population.

Changes in macroautophagy, chaperone-mediated autophagy, and mitochondrial metabolism in murine skeletal and cardiac muscle during aging

Aging causes a general decline in cellular metabolic activity, and function in different tissues and whole body homeostasis. However, the understanding about the metabolomic and autophagy changes in skeletal muscle and heart during aging is still limited. We thus examined markers for macroautophagy, chaperone-mediated autophagy (CMA), mitochondrial quality control, as well as cellular metabolites in skeletal and cardiac muscle from young (5 months old) and aged (27 months old) mice. We found decreased autophagic degradation of p62 and increased ubiquitinated proteins in both tissues from aged mice, suggesting a decline in macroautophagy during aging. In skeletal muscle from aged mice, there also was a decline in LC3B-I conjugation to phosphatidylethanolamine (PE) possibly due to decreased protein levels of ATG3 and ATG12-ATG5. The CMA markers, LAMP-2A and Hsc70, and mitochondrial turnover markers, Drp1, PINK1 and PGC1α also were decreased. Metabolomics analysis showed impaired β-oxidation in heart of aged mice, whereas increased branched-chain amino acids (BCAAs) and ceramide levels were found in skeletal muscle of aged mice that in turn, may contribute to insulin resistance in muscle. Taken together, our studies showed similar declines in macroautophagy but distinct effects on CMA, mitochondrial turnover, and metabolic dysfunction in muscle vs. heart during aging.

Plasma Palmitoyl-Carnitine (AC16:0) Is a Marker of Increased Postprandial Nonesterified Incomplete Fatty Acid Oxidation Rate in Adults With Type 2 Diabetes

OBJECTIVES

Enhanced mitochondrial fatty acid utilization is known to increase radical oxidative stress and induce insulin resistance. An increased level of plasma acylcarnitine (AC) has been proposed to indicate mitochondrial energy substrate overload, a possible mechanism leading to insulin resistance. The aim of our study was to determine fasting and postprandial plasma acetyl-carnitine (AC2:0), palmitoyl-carnitine (AC16:0), oleoyl-carnitine (AC18:1) and linoleoyl-carnitine (AC18:2) levels and their relationships with plasma nonesterified fatty acid appearance and oxidation rates and insulin sensitivity in participants with type 2 diabetes and normoglycemic offspring of 2 parents with type 2 diabetes (FH+) compared to healthy participants without family histories of type 2 diabetes (FH-).

METHODS

All participants underwent 3 metabolic protocols: 1) a euglycemic hyperinsulinemic clamp at fasting; 2) a 6-hour steady-state oral standard liquid meal and 3) an identical 6-hour steady-state meal intake study with a euglycemic hyperinsulinemic clamp. AC levels were measured by liquid chromatography with tandem mass spectrometry, and fatty acid oxidation (FAO) rates were measured by stable isotopic tracer techniques with indirect respiratory calorimetry.

RESULTS

During the insulin clamp at fasting, AC16:0 was significantly higher in the group with type 2 diabetes vs. FH- (p<0.05). In the postprandial state, AC2:0, AC16:0 and AC18:1 decreased significantly, but this reduction was blunted in type 2 diabetes, even during normalization of postprandial glucose levels during the insulin clamp. Fasting AC16:0 correlated with FAO (ρ=+0.604; p=0.0002); triacylglycerol (ρ=+0.427; p<0.02) and waist circumference (ρ=+0.416; p=0.02).

CONCLUSIONS

Spillover of AC occurs in type 2 diabetes but is not fully established in FH+. AC16:0 can be a useful biomarker of excessive FAO.

Amino acid profile and metabolic syndrome in a male Mediterranean population: A cross-sectional study

BACKGROUND AND AIMS

The metabolic syndrome (MetS) refers to a cluster of clinically relevant factors that increases the risk of cardiovascular diseases and all-cause mortality. Circulating levels of several amino acids and metabolites related to one-carbon metabolism have been associated with cardiometabolic risk factors and MetS. We aimed to identify the amino acid profile that is significantly associated with MetS among an all male Mediterranean population.

METHODS AND RESULTS

One hundred middle-aged men (54.6 ± 8.9 years) participated in a cross-sectional study carried out during 2011-2012. The International Diabetes Federation (IDF) criteria were used to define MetS. Fasting plasma levels of 20 common amino acids and 15 metabolites related to amino acid and one-carbon metabolism were measured using gas chromatography (GC-MS/MS) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Principal components analysis was applied. Fifty-six participants fulfilled the IDF criteria for defining MetS. Five factors were extracted from the 35 measured metabolites. The branched-chain amino acids/aromatic amino acids (BCAA/AAA) related pattern and the glutamine/glycine/serine/asparagine (Gln/Gly/Ser/Asn) related pattern were significantly associated with MetS (odds ratio, 95% confidence interval; 6.41, 2.43-16.91, and 0.47, 0.23-0.96, respectively) after adjustment for age, current smoking status, physical activity level and medical treatment for hypertension, dyslipidaemia, type 2 diabetes mellitus. Further adjustment for liver function markers (i.e. glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and γ-glutamyltransferase), and plasma adiponectin levels did not significantly affect the associations.

CONCLUSION

The BCAA/AAA pattern was positively associated, while the Gln/Gly/Ser/Asn pattern was inversely associated with established cardiometabolic risk factors and MetS. Plasma adiponectin levels or markers of liver function did not significantly affect these associations.

Early-onset and classical forms of type 2 diabetes show impaired expression of genes involved in muscle branched-chain amino acids metabolism

The molecular mechanisms responsible for the pathophysiological traits of type 2 diabetes are incompletely understood. Here we have performed transcriptomic analysis in skeletal muscle, and plasma metabolomics from subjects with classical and early-onset forms of type 2 diabetes (T2D). Focused studies were also performed in tissues from ob/ob and db/db mice. We document that T2D, both early and late onset, are characterized by reduced muscle expression of genes involved in branched-chain amino acids (BCAA) metabolism. Weighted Co-expression Networks Analysis provided support to idea that the BCAA genes are relevant in the pathophysiology of type 2 diabetes, and that mitochondrial BCAA management is impaired in skeletal muscle from T2D patients. In diabetic mice model we detected alterations in skeletal muscle proteins involved in BCAA metabolism but not in obese mice. Metabolomic analysis revealed increased levels of branched-chain keto acids (BCKA), and BCAA in plasma of T2D patients, which may result from the disruption of muscle BCAA management. Our data support the view that inhibition of genes involved in BCAA handling in skeletal muscle takes place as part of the pathophysiology of type 2 diabetes, and this occurs both in early-onset and in classical type 2 diabetes.

Acute interaction between hydrocortisone and insulin alters the plasma metabolome in humans

With the aim of identifying biomarkers of glucocorticoid action and their relationship with biomarkers of insulin action, metabolomic profiling was carried out in plasma samples from twenty healthy men who were administered either a low or medium dose insulin infusion (n = 10 each group). In addition, all subjects were given metyrapone (to inhibit adrenal cortisol secretion) + /− hydrocortisone (HC) in a randomised crossover design to produce low, medium and high glucocorticoid levels. The clearest effects of insulin were to reduce plasma levels of the branched chain amino acids (BCAs) leucine/isoleucine and their deaminated metabolites, and lowered free fatty acids and acylcarnitines. The highest dose of hydrocortisone increased plasma BCAs in both insulin groups but increased free fatty acids only in the high insulin group, however hydrocortisone did not affect the levels of acyl carnitines in either group. The clearest interaction between HC and insulin was that hydrocortisone produced an elevation in levels of BCAs and their metabolites which were lowered by insulin. The direct modulation of BCAs by glucocorticoids and insulin may provide the basis for improved in vivo monitoring of glucocorticoid and insulin action.

Branched-chain and aromatic amino acids in relation to behavioral problems among young Inuit from Nunavik, Canada: a cohort study

BackgroundObesity and insulin resistance are linked with mood disorders, and elevated concentrations of branched-chain (BCAAs) and aromatic amino acids (AAAs). Our study aimed to prospectively assess the relationship between childhood plasma BCAAs and AAAs, and behavioral problems in young Inuit from Nunavik.MethodsWe analyzed data on 181 children (with a mean age of 11.4 years at baseline) involved in the Nunavik Child Development Study. Plasma BCAA and AAA concentrations were measured in childhood (2005-2010). BCAA/AAA tertiles-the ratio of total BCAAs to AAAs-were considered as surrogate categorical independent variables. Behavioral problems were assessed with the Youth Self-Report (YSR) from the Child Behavior Checklist about 7 years later during adolescence (2013-2016). ANOVA ascertained relationships between BCAA/AAA tertiles and YSR outcomes.ResultsAscending BCAA/AAA tertiles were positively associated (P_trend<0.05) with somatic complaint scores. Scores of somatic complaints syndrome were significantly higher (P_trend <0.05) with increasing BCAA/AAA tertiles among both normal and overweight/obese participants.ConclusionOur results suggest that higher BCAA/AAA ratios in childhood are significantly associated with somatic complaints in adolescence.

Targeted metabolome profiling by dual-probe microdialysis sampling and treatment using Gardenia jasminoides for rats with type 2 diabetes

Diabetes causes a variety of end-stage organ complications, including diabetic nephropathy. Metabolomics offers an approach for characterizing biofluid metabolic changes, but studies focusing on diabetic nephropathy are limited due to the loss of tissue-specific metabolic information. A microdialysis application for the sampling of intact endogenous metabolites has been developed, utilizing two probes simultaneously inserted into the kidney tissues and jugular vein of rats with type 2 diabetes. The comprehensive and quantitative analysis of 20 diagnostic biomarkers closely realated to type 2 diabetes and its complications were performed. Results indicated that amino acid and nucleotide levels were lower in diabetic rats, revealing that the metabolic pathways of amino acid, as well as purine and pyrimidine, were disturbed. Targeted metabolomics using mass spectrometry was performed to find potential therapeutic biomarkers and related metabolic pathways of Gardenia jasminoides (G. jasminoides) for treating diabetes. Results suggested that seven biomarkers in the kidney and five biomarkers in the blood were related to G. jasminoides. In addition, the marked perturbations of pathways were regulated after treatment with G. jasminoides, including amino acid metabolism and purine metabolism. These biomarkers and metabolic pathways provided new understanding for molecular mechanisms of G. jasminoides for treating diabetes and its complications.

Untargeted metabolomics identifies a plasma sphingolipid-related signature associated with lifestyle intervention in prepubertal children with obesity

OBJECTIVE

Childhood obesity is a strong risk factor for adult obesity and metabolic diseases, including type 2 diabetes and cardiovascular disease. Early lifestyle intervention in children with obesity reduces future disease risk. The objective of this study is to identify metabolic signatures associated with lifestyle intervention in prepubertal children with obesity.

METHODS

Thirty-five prepubertal children (7-10 years) with obesity (body mass index (BMI)>2 standard deviations) were enrolled in the study and participated in a 6-month-long lifestyle intervention program. Physiological and biochemical data and blood samples were collected both at baseline and after the intervention. A liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach was applied to obtain a comprehensive profiling of plasma samples, identifying 2581 distinct metabolite. Principal component analysis (PCA) was performed to consolidate all features into 8 principal components. Associations between metabolites and physiological and biochemical variables were investigated.

RESULTS

The intervention program significantly decreased mean (95% CI) BMI standard deviation score from 3.56 (3.29-3.84) to 3.11 (2.88-3.34) (P<0.001). PCA identified one component (PC1) significantly altered by the intervention (Bonferroni adjusted P=0.008). A sphingolipid metabolism-related signature was identified as the major contributor to PC1. Sphingolipid metabolites were decreased by the intervention, and included multiple sphingomyelin, ceramide, glycosylsphingosine and sulfatide species. Changes in several sphingolipid metabolites were associated with intervention-induced improvements in HbA1c levels.

CONCLUSIONS

Decreased circulating sphingolipid-related metabolites were associated with lifestyle intervention in prepubertal children with obesity, and correlated to improvements in HbA1c.

Decreased long-chain acylcarnitines from insufficient β-oxidation as potential early diagnostic markers for Parkinson's disease

Increasing evidence shows that metabolic abnormalities in body fluids are distinguishing features of the pathophysiology of Parkinson’s disease. However, a non-invasive approach has not been established in the earliest or pre-symptomatic phases. Here, we report comprehensive double-cohort analyses of the metabolome using capillary electrophoresis/liquid chromatography mass-spectrometry. The plasma analyses identified 18 Parkinson’s disease-specific metabolites and revealed decreased levels of seven long-chain acylcarnitines in two Parkinson’s disease cohorts (n = 109, 145) compared with controls (n = 32, 45), respectively. Furthermore, statistically significant decreases in five long-chain acylcarnitines were detected in Hoehn and Yahr stage I. Likewise, decreased levels of acylcarnitine(16:0), a decreased ratio of acylcarnitine(16:0) to fatty acid(16:0), and an increased index of carnitine palmitoyltransferase 1 were identified in Hoehn and Yahr stage I of both cohorts, suggesting of initial β-oxidation suppression. Receiver operating characteristic curves produced using 12–14 long-chain acylcarnitines provided a large area of under the curve, high specificity and moderate sensitivity for diagnosing Parkinson’s disease. Our data demonstrate that a primary decrement of mitochondrial β-oxidation and that 12–14 long-chain acylcarnitines decreases would be promising diagnostic biomarkers for Parkinson’s disease.

Branched-chain amino acid, meat intake and risk of type 2 diabetes in the Women's Health Initiative

Knowledge regarding association of dietary branched-chain amino acid (BCAA) and type 2 diabetes (T2D), and the contribution of BCAA from meat to the risk of T2D are scarce. We evaluated associations between dietary BCAA intake, meat intake, interaction between BCAA and meat intake and risk of T2D. Data analyses were performed for 74 155 participants aged 50-79 years at baseline from the Women's Health Initiative for up to 15 years of follow-up. We excluded from analysis participants with treated T2D, and factors potentially associated with T2D or missing covariate data. The BCAA and total meat intake was estimated from FFQ. Using Cox proportional hazards models, we assessed the relationship between BCAA intake, meat intake, and T2D, adjusting for confounders. A 20 % increment in total BCAA intake (g/d and %energy) was associated with a 7 % higher risk for T2D (hazard ratio (HR) 1·07; 95 % CI 1·05, 1·09). For total meat intake, a 20 % increment was associated with a 4 % higher risk of T2D (HR 1·04; 95 % CI 1·03, 1·05). The associations between BCAA intake and T2D were attenuated but remained significant after adjustment for total meat intake. These relations did not materially differ with or without adjustment for BMI. Our results suggest that dietary BCAA and meat intake are positively associated with T2D among postmenopausal women. The association of BCAA and diabetes risk was attenuated but remained positive after adjustment for meat intake suggesting that BCAA intake in part but not in full is contributing to the association of meat with T2D risk.

Metabolism and acetylation contribute to leucine-mediated inhibition of cardiac glucose uptake

High plasma leucine levels strongly correlate with type 2 diabetes. Studies of muscle cells have suggested that leucine alters the insulin response for glucose transport by activating an insulin-negative feedback loop driven by the mammalian target of rapamycin/p70 ribosomal S6 kinase (mTOR/p70S6K) pathway. Here, we examined the molecular mechanism involved in leucine's action on cardiac glucose uptake. Leucine was indeed able to curb glucose uptake after insulin stimulation in both cultured cardiomyocytes and perfused hearts. Although leucine activated mTOR/p70S6K, the mTOR inhibitor rapamycin did not prevent leucine's inhibitory action on glucose uptake, ruling out the contribution of the insulin-negative feedback loop. α-Ketoisocaproate, the first metabolite of leucine catabolism, mimicked leucine's effect on glucose uptake. Incubation of cardiomyocytes with [¹³C]leucine ascertained its metabolism to ketone bodies (KBs), which had a similar negative impact on insulin-stimulated glucose transport. Both leucine and KBs reduced glucose uptake by affecting translocation of glucose transporter 4 (GLUT4) to the plasma membrane. Finally, we found that leucine elevated the global protein acetylation level. Pharmacological inhibition of lysine acetyltransferases counteracted this increase in protein acetylation and prevented leucine's inhibitory action on both glucose uptake and GLUT4 translocation. Taken together, these results indicate that leucine metabolism into KBs contributes to inhibition of cardiac glucose uptake by hampering the translocation of GLUT4-containing vesicles via acetylation. They offer new insights into the establishment of insulin resistance in the heart.NEW & NOTEWORTHY Catabolism of the branched-chain amino acid leucine into ketone bodies efficiently inhibits cardiac glucose uptake through decreased translocation of glucose transporter 4 to the plasma membrane. Leucine increases protein acetylation. Pharmacological inhibition of acetylation reverses leucine's action, suggesting acetylation involvement in this phenomenon.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/leucine-metabolism-inhibits-cardiac-glucose-uptake/.