Therapeutic Effect of Targeting Branched-Chain Amino Acid Catabolic Flux in Pressure-Overload Induced Heart Failure

Dietary Branched Chain Amino Acids Modify Post-Infarct Cardiac Remodeling and Function in the Murine Heart

Introduction

Branch-chain amino acids (BCAA) are markedly elevated in the heart following myocardial infarction (MI) in both humans and animal models. Nevertheless, it remains unclear whether dietary BCAA levels influence post-MI remodeling. We hypothesize that lowering dietary BCAA levels prevents adverse cardiac remodeling after MI.

Methods and Results

To assess whether altering dietary BCAA levels would impact circulating BCAA concentrations, mice were fed a low (1/3×), normal (1×), or high (2×) BCAA diet over a 7-day period. We found that mice fed the low BCAA diet had >2-fold lower circulating BCAA concentrations when compared with normal and high BCAA diet feeding strategies; notably, the high BCAA diet did not further increase BCAA levels over the normal chow diet. To investigate the impact of dietary BCAAs on cardiac remodeling and function after MI, male and female mice were fed either the low or high BCAA diet for 2 wk prior to MI and for 4 wk after MI. Although body weights or heart masses were not different in female mice fed the custom diets, male mice fed the high BCAA diet had significantly higher body and heart masses than those on the low BCAA diet. Echocardiographic assessments revealed that the low BCAA diet preserved stroke volume and cardiac output for the duration of the study, while the high BCAA diet led to progressive decreases in cardiac function. Although no discernible differences in cardiac fibrosis, scar collagen topography, or cardiomyocyte cross-sectional area were found between the dietary groups, male mice fed the high BCAA diet showed longer cardiomyocytes and higher capillary density compared with the low BCAA group.

Conclusions

Provision of a diet low in BCAAs to mice mitigates eccentric cardiomyocyte remodeling and loss of cardiac function after MI, with dietary effects more prominent in males.

The role of BCAA metabolism in metabolic health and disease

It has long been postulated that dietary restriction is beneficial for ensuring longevity and extending the health span of mammals, including humans. In particular, a reduction in protein consumption has been shown to be specifically linked to the beneficial effect of dietary restriction on metabolic disorders, presumably by reducing the activity of the mechanistic target of rapamycin complex (mTORC) 1 and the reciprocal activation of AMP-activated protein kinase (AMPK) and sirtuin pathways. Although it is widely used as a dietary supplement to delay the aging process in humans, recent evidence suggests that branched-chain amino acids (BCAAs) might be a major cause of the deteriorating effect of a protein diet on aging and related disorders. In this review, we delineate the regulation of metabolic pathways for BCAAs at the tissue-specific level and summarize recent findings regarding the role of BCAAs in the control of metabolic health and disease in mammals.

Effect of mTORC Agonism via MHY1485 with and without Rapamycin on C2C12 Myotube Metabolism

The mechanistic target of rapamycin complex (mTORC) regulates protein synthesis and can be activated by branched-chain amino acids (BCAAs). mTORC has also been implicated in the regulation of mitochondrial metabolism and BCAA catabolism. Some speculate that mTORC overactivation by BCAAs may contribute to insulin resistance. The present experiments assessed the effect of mTORC activation on myotube metabolism and insulin sensitivity using the mTORC agonist MHY1485, which does not share structural similarities with BCAAs.

METHODS

C2C12 myotubes were treated with MHY1485 or DMSO control both with and without rapamycin. Gene expression was assessed using qRT-PCR and insulin sensitivity and protein expression by western blot. Glycolytic and mitochondrial metabolism were measured by extracellular acidification rate and oxygen consumption. Mitochondrial and lipid content were analyzed by fluorescent staining. Liquid chromatography-mass spectrometry was used to assess extracellular BCAAs.

RESULTS

Rapamycin reduced p-mTORC expression, mitochondrial content, and mitochondrial function. Surprisingly, MHY1485 did not alter p-mTORC expression or cell metabolism. Neither treatment altered indicators of BCAA metabolism or extracellular BCAA content.

CONCLUSION

Collectively, inhibition of mTORC via rapamycin reduces myotube metabolism and mitochondrial content but not BCAA metabolism. The lack of p-mTORC activation by MHY1485 is a limitation of these experiments and warrants additional investigation.

Duality of Branched-Chain Amino Acids in Chronic Cardiovascular Disease: Potential Biomarkers versus Active Pathophysiological Promoters

Branched-chain amino acids (BCAAs), comprising leucine (Leu), isoleucine (Ile), and valine (Val), are essential nutrients vital for protein synthesis and metabolic regulation via specialized signaling networks. Their association with cardiovascular diseases (CVDs) has become a focal point of scientific debate, with emerging evidence suggesting both beneficial and detrimental roles. This review aims to dissect the multifaceted relationship between BCAAs and cardiovascular health, exploring the molecular mechanisms and clinical implications. Elevated BCAA levels have also been linked to insulin resistance (IR), type 2 diabetes mellitus (T2DM), inflammation, and dyslipidemia, which are well-established risk factors for CVD. Central to these processes are key pathways such as mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-light-chain-enhancer of activate B cells (NF-κB)-mediated inflammation, and oxidative stress. Additionally, the interplay between BCAA metabolism and gut microbiota, particularly the production of metabolites like trimethylamine-N-oxide (TMAO), adds another layer of complexity. Contrarily, some studies propose that BCAAs may have cardioprotective effects under certain conditions, contributing to muscle maintenance and metabolic health. This review critically evaluates the evidence, addressing the biological basis and signal transduction mechanism, and also discusses the potential for BCAAs to act as biomarkers versus active mediators of cardiovascular pathology. By presenting a balanced analysis, this review seeks to clarify the contentious roles of BCAAs in CVD, providing a foundation for future research and therapeutic strategies required because of the rising prevalence, incidence, and total burden of CVDs.

Off-target depletion of plasma tryptophan by allosteric inhibitors of BCKDK

The activation of branched chain amino acid (BCAA) catabolism has garnered interest as a potential therapeutic approach to improve insulin sensitivity, enhance recovery from heart failure, and blunt tumor growth. Evidence for this interest relies in part on BT2, a small molecule that promotes BCAA oxidation and is protective in mouse models of these pathologies. BT2 and other analogs allosterically inhibit branched chain ketoacid dehydrogenase kinase (BCKDK) to promote BCAA oxidation, which is presumed to underlie the salutary effects of BT2. Potential "off-target" effects of BT2 have not been considered, however. We therefore tested for metabolic off-target effects of BT2 in Bckdk-/- animals. As expected, BT2 failed to activate BCAA oxidation in these animals. Surprisingly, however, BT2 strongly reduced plasma tryptophan levels and promoted catabolism of tryptophan to kynurenine in both control and Bckdk-/- mice. Mechanistic studies revealed that none of the principal tryptophan catabolic or kynurenine-producing/consuming enzymes (TDO, IDO1, IDO2, or KATs) were required for BT2-mediated lowering of plasma tryptophan. Instead, using equilibrium dialysis assays and mice lacking albumin, we show that BT2 avidly binds plasma albumin and displaces tryptophan, releasing it for catabolism. These data confirm that BT2 activates BCAA oxidation via inhibition of BCKDK but also reveal a robust off-target effect on tryptophan metabolism via displacement from serum albumin. The data highlight a potential confounding effect for pharmaceutical compounds that compete for binding with albumin-bound tryptophan.

The BCKDH kinase inhibitor BT2 promotes BCAA disposal and mitochondrial proton leak in both insulin-sensitive and insulin-resistant C2C12 myotubes

Elevated circulating branched-chain amino acids (BCAAs) have been correlated with the severity of insulin resistance, leading to recent investigations that stimulate BCAA metabolism for the potential benefit of metabolic diseases. BT2 (3,6-dichlorobenzo[b]thiophene-2-carboxylic acid), an inhibitor of branched-chain ketoacid dehydrogenase kinase, promotes BCAA metabolism by enhancing BCKDH complex activity. The purpose of this report was to investigate the effects of BT2 on mitochondrial and glycolytic metabolism, insulin sensitivity, and de novo lipogenesis both with and without insulin resistance. C2C12 myotubes were treated with or without low or moderate levels of BT2 with or without insulin resistance. Western blot and quantitative real-time polymerase chain reaction were used to assess protein and gene expression, respectively. Mitochondrial, nuclei, and lipid content were measured using fluorescent staining and microscopy. Cell metabolism was assessed via oxygen consumption and extracellular acidification rate. Liquid chromatography-mass spectrometry was used to quantify BCAA media content. BT2 treatment consistently promoted mitochondrial uncoupling following 24-h treatment, which occurred largely independent of changes in expressional profiles associated with mitochondrial biogenesis, mitochondrial dynamics, BCAA catabolism, insulin sensitivity, or lipogenesis. Acute metabolic studies revealed a significant and dose-dependent effect of BT2 on mitochondrial proton leak, suggesting BT2 functions as a small-molecule uncoupler. Additionally, BT2 treatment consistently and dose-dependently reduced extracellular BCAA levels without altering expression of BCAA catabolic enzymes or pBCKDHa activation. BT2 appears to act as a small-molecule mitochondrial uncoupler that promotes BCAA utilization, though the interplay between these two observations requires further investigation.

The BCKDK inhibitor BT2 is a chemical uncoupler that lowers mitochondrial ROS production and de novo lipogenesis

Elevated levels of branched chain amino acids (BCAAs) and branched-chain α-ketoacids are associated with cardiovascular and metabolic disease, but the molecular mechanisms underlying a putative causal relationship remain unclear. The branched-chain ketoacid dehydrogenase kinase (BCKDK) inhibitor BT2 (3,6-dichlorobenzo[b]thiophene-2-carboxylic acid) is often used in preclinical models to increase BCAA oxidation and restore steady-state BCAA and branched-chain α-ketoacid levels. BT2 administration is protective in various rodent models of heart failure and metabolic disease, but confoundingly, targeted ablation of Bckdk in specific tissues does not reproduce the beneficial effects conferred by pharmacologic inhibition. Here, we demonstrate that BT2, a lipophilic weak acid, can act as a mitochondrial uncoupler. Measurements of oxygen consumption, mitochondrial membrane potential, and patch-clamp electrophysiology show that BT2 increases proton conductance across the mitochondrial inner membrane independently of its inhibitory effect on BCKDK. BT2 is roughly sixfold less potent than the prototypical uncoupler 2,4-dinitrophenol and phenocopies 2,4-dinitrophenol in lowering de novo lipogenesis and mitochondrial superoxide production. The data suggest that the therapeutic efficacy of BT2 may be attributable to the well-documented effects of mitochondrial uncoupling in alleviating cardiovascular and metabolic disease.

Advances in Metabolic Remodeling and Intervention Strategies in Heart Failure

The heart is the most energy-demanding organ throughout the whole body. Perturbations or failure in energy metabolism contributes to heart failure (HF), which represents the advanced stage of various heart diseases. The poor prognosis and huge economic burden associated with HF underscore the high unmet need to explore novel therapies targeting metabolic modulators beyond conventional approaches focused on neurohormonal and hemodynamic regulators. Emerging evidence suggests that alterations in metabolic substrate reliance, metabolic pathways, metabolic by-products, and energy production collectively regulate the occurrence and progression of HF. In this review, we provide an overview of cardiac metabolic remodeling, encompassing the utilization of free fatty acids, glucose metabolism, ketone bodies, and branched-chain amino acids both in the physiological condition and heart failure. Most importantly, the latest advances in pharmacological interventions are discussed as a promising therapeutic approach to restore cardiac function, drawing insights from recent basic research, preclinical and clinical studies.

The Role of Branched-chain Amino Acids and Their Metabolism in Cardiovascular Diseases

Branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, are essential amino acids for protein synthesis. Recent studies have yielded new insights into their diverse physiological and pathological roles in health and disease. Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality globally. An increasing number of clinical studies have demonstrated that high levels of circulating BCAAs are associated with an increased risk of CVDs. Animal studies have provided preliminary evidence linking BCAA intake and metabolism with cardiovascular diseases. Despite these insights, the causal relationship between BCAA metabolism and CVD remains poorly established, and the underlying mechanisms remain incompletely understood. Here, we aim to provide an update on the current understanding of the roles of BCAAs and their metabolism in the development and progression of various CVDs. We also discuss the potential strategies targeting BCAA nutrition and metabolism for the prevention and treatment of CVDs.

Late-life isoleucine restriction promotes physiological and molecular signatures of healthy aging

In defiance of the paradigm that calories from all sources are equivalent, we and others have shown that dietary protein is a dominant regulator of healthy aging. The restriction of protein or the branched-chain amino acid isoleucine promotes healthspan and extends lifespan when initiated in young or adult mice. However, many interventions are less efficacious or even deleterious when initiated in aged animals. Here, we investigate the physiological, metabolic, and molecular consequences of consuming a diet with a 67% reduction of all amino acids (Low AA), or of isoleucine alone (Low Ile), in male and female C57BL/6J.Nia mice starting at 20 months of age. We find that both diet regimens effectively reduce adiposity and improve glucose tolerance, which were benefits that were not mediated by reduced calorie intake. Both diets improve specific aspects of frailty, slow multiple molecular indicators of aging rate, and rejuvenate the aging heart and liver at the molecular level. These results demonstrate that Low AA and Low Ile diets can drive youthful physiological and molecular signatures, and support the possibility that these dietary interventions could help to promote healthy aging in older adults.

Cardiac Metabolism

The heart is composed of a heterogeneous mixture of cellular components perfectly intermingled and able to integrate common environmental signals to ensure proper cardiac function and performance. Metabolism defines a cell context-dependent signature that plays a critical role in survival, proliferation, or differentiation, being a recognized master piece of organ biology, modulating homeostasis, disease progression, and adaptation to tissue damage. The heart is a highly demanding organ, and adult cardiomyocytes require large amount of energy to fulfill adequate contractility. However, functioning under oxidative mitochondrial metabolism is accompanied with a concomitant elevation of harmful reactive oxygen species that indeed contributes to the progression of several cardiovascular pathologies and hampers the regenerative capacity of the mammalian heart. Cardiac metabolism is dynamic along embryonic development and substantially changes as cardiomyocytes mature and differentiate within the first days after birth. During early stages of cardiogenesis, anaerobic glycolysis is the main energetic program, while a progressive switch toward oxidative phosphorylation is a hallmark of myocardium differentiation. In response to cardiac injury, different signaling pathways participate in a metabolic rewiring to reactivate embryonic bioenergetic programs or the utilization of alternative substrates, reflecting the flexibility of heart metabolism and its central role in organ adaptation to external factors. Despite the well-established metabolic pattern of fetal, neonatal, and adult cardiomyocytes, our knowledge about the bioenergetics of other cardiac populations like endothelial cells, cardiac fibroblasts, or immune cells is limited. Considering the close intercellular communication and the influence of nonautonomous cues during heart development and after cardiac damage, it will be fundamental to better understand the metabolic programs in different cardiac cells in order to develop novel interventional opportunities based on metabolic rewiring to prevent heart failure and improve the limited regenerative capacity of the mammalian heart.

Branched-chain amino acid catabolic defect in vascular smooth muscle cells drives thoracic aortic dissection via mTOR hyperactivation

Metabolic reprogramming of vascular smooth muscle cell (VSMC) plays a critical role in the pathogenesis of thoracic aortic dissection (TAD). Previous researches have mainly focused on dysregulation of fatty acid or glucose metabolism, while the impact of amino acids catabolic disorder in VSMCs during the development of TAD remains elusive. Here, we identified branched-chain amino acid (BCAA) catabolic defect as a metabolic hallmark of TAD. The bioinformatics analysis and data from human aorta revealed impaired BCAA catabolism in TAD individuals. This was accompanied by upregulated branched-chain α-ketoacid dehydrogenase kinase (BCKDK) expression and BCKD E1 subunit alpha (BCKDHA) phosphorylation, enhanced vascular inflammation, and hyperactivation of mTOR signaling. Further in vivo experiments demonstrated that inhibition of BCKDK with BT2 (a BCKDK allosteric inhibitor) treatment dephosphorylated BCKDHA and re-activated BCAA catabolism, attenuated VSMCs phenotypic switching, alleviated aortic remodeling, mitochondrial reactive oxygen species (ROS) damage and vascular inflammation. Additionally, the beneficial actions of BT2 were validated in a TNF-α challenged murine VSMC cell line. Meanwhile, rapamycin conferred similar beneficial effects against VSMC phenotypic switching, cellular ROS damage as well as inflammatory response. However, co-treatment with MHY1485 (a classic mTOR activator) reversed the beneficial effects of BT2 by reactivating mTOR signaling. Taken together, the in vivo and in vitro evidence showed that impairment of BCAA catabolism resulted in aortic accumulation of BCAA and further caused VSMC phenotypic switching, mitochondrial ROS damage and inflammatory response via mTOR hyperactivation. BCKDK and mTOR signaling may serve as the potential drug targets for the prevention and treatment of TAD.

Branched chain amino acids metabolism in heart failure

As a terminal stage of various cardiovascular diseases, heart failure is of great concern due to its high mortality rate and limited treatment options. Researchers are currently focusing their efforts on investigating the metabolism of carbohydrates, fatty acids, and amino acids to enhance the prognosis of cardiovascular diseases. Simultaneously, branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, play significant roles in blood glucose regulation, protein synthesis, and insulin sensitivity. However, disrupted BCAAs metabolism has been associated with conditions such as hypertension, obesity, and atherosclerosis. This article explores intricate metabolic pathways, unveiling the connection between disrupted BCAAs metabolism and the progression of heart failure. Furthermore, the article discusses therapeutic strategies, assesses the impact of BCAAs on cardiac dysfunction, and examines the potential of modulating BCAAs metabolism as a treatment for heart failure. BCAAs and their metabolites are also considered as biomarkers for evaluating cardiac metabolic risk. In conclusion, this article elucidates the multifaceted roles of BCAAs in heart failure and cardiovascular health, providing guidance for future research and intervention measures.

PPM1K mediates metabolic disorder of branched-chain amino acid and regulates cerebral ischemia-reperfusion injury by activating ferroptosis in neurons

Ischemic stroke is a neurological disorder caused by vascular stenosis or occlusion, accounting for approximately 87% of strokes. Clinically, the most effective therapy for ischemic stroke is vascular recanalization, which aims to rescue neurons undergoing ischemic insults. Although reperfusion therapy is the most effective treatment for ischemic stroke, it still has limited benefits for many patients, and ischemia-reperfusion (I/R) injury is a widely recognized cause of poor prognosis. Here, we aim to investigate the mechanism of protein phosphatase Mg2+/Mn2+ dependent 1 K (PPM1K) mediates metabolic disorder of branched-chain amino acids (BCAA) by promoting fatty acid oxidation led to ferroptosis after cerebral I/R injury. We established the I/R model in mice and used BT2, a highly specific BCAA dehydrogenase (BCKD) kinase inhibitor to promote BCAA metabolism. It was further verified by lentivirus knocking down PPM1K in neurons. We found that BCAA levels were elevated after I/R injury due to dysfunctional oxidative degradation caused by phosphorylated BCKD E1α subunit (BCKDHA). Additionally, the level of phosphorylated BCKDHA was determined by decreased PPM1K in neurons. We next demonstrated that BCAA could induce oxidative stress, lipid peroxidation, and ferroptosis in primary cultured cortical neurons in vitro. Our results further showed that BT2 could reduce neuronal ferroptosis by enhancing BCAA oxidation through inhibition of BCKDHA phosphorylation. We further found that defective BCAA catabolism could induce neuronal ferroptosis by PPM1K knockdown. Furthermore, BT2 was found to alleviate neurological behavior disorders after I/R injury in mice, and the effect was similar to ferroptosis inhibitor ferrostatin-1. Our findings reveal a novel role of BCAA in neuronal ferroptosis after cerebral ischemia and provide a new potential target for the treatment of ischemic stroke.

Energy metabolism: A critical target of cardiovascular injury

Cardiovascular diseases are the main killers threatening human health. Many studies have shown that abnormal energy metabolism plays a key role in the occurrence and development of acute and chronic cardiovascular diseases. Regulating cardiac energy metabolism is a frontier topic in the treatment of cardiovascular diseases. However, we are not very clear about the choice of different substrates, the specific mechanism of energy metabolism participating in the course of cardiovascular disease, and how to develop appropriate drugs to regulate energy metabolism to treat cardiovascular disease. Therefore, this paper reviews how energy metabolism participates in cardiovascular pathophysiological processes and potential drugs aimed at interfering energy metabolism.It is expected to provide good suggestions for promoting the clinical prevention and treatment of cardiovascular diseases from the perspective of energy metabolism.

The BCKDK inhibitor BT2 is a chemical uncoupler that lowers mitochondrial ROS production and de novo lipogenesis

Elevated levels of branched chain amino acids (BCAAs) and branched-chain α-ketoacids (BCKAs) are associated with cardiovascular and metabolic disease, but the molecular mechanisms underlying a putative causal relationship remain unclear. The branched-chain ketoacid dehydrogenase kinase (BCKDK) inhibitor BT2 is often used in preclinical models to increase BCAA oxidation and restore steady-state BCAA and BCKA levels. BT2 administration is protective in various rodent models of heart failure and metabolic disease, but confoundingly, targeted ablation of Bckdk in specific tissues does not reproduce the beneficial effects conferred by pharmacologic inhibition. Here we demonstrate that BT2, a lipophilic weak acid, can act as a mitochondrial uncoupler. Measurements of oxygen consumption, mitochondrial membrane potential, and patch-clamp electrophysiology show BT2 increases proton conductance across the mitochondrial inner membrane independently of its inhibitory effect on BCKDK. BT2 is roughly five-fold less potent than the prototypical uncoupler 2,4-dinitrophenol (DNP), and phenocopies DNP in lowering de novo lipogenesis and mitochondrial superoxide production. The data suggest the therapeutic efficacy of BT2 may be attributable to the well-documented effects of mitochondrial uncoupling in alleviating cardiovascular and metabolic disease.

Small molecule branched-chain ketoacid dehydrogenase kinase (BDK) inhibitors with opposing effects on BDK protein levels

Branched chain amino acid (BCAA) catabolic impairments have been implicated in several diseases. Branched chain ketoacid dehydrogenase (BCKDH) controls the rate limiting step in BCAA degradation, the activity of which is inhibited by BCKDH kinase (BDK)-mediated phosphorylation. Screening efforts to discover BDK inhibitors led to identification of thiophene PF-07208254, which improved cardiometabolic endpoints in mice. Structure-activity relationship studies led to identification of a thiazole series of BDK inhibitors; however, these inhibitors did not improve metabolism in mice upon chronic administration. While the thiophenes demonstrated sustained branched chain ketoacid (BCKA) lowering and reduced BDK protein levels, the thiazoles increased BCKAs and BDK protein levels. Thiazoles increased BDK proximity to BCKDH-E2, whereas thiophenes reduced BDK proximity to BCKDH-E2, which may promote BDK degradation. Thus, we describe two BDK inhibitor series that possess differing attributes regarding BDK degradation or stabilization and provide a mechanistic understanding of the desirable features of an effective BDK inhibitor.

Metabolite signaling in the heart

The heart is the most metabolically active organ in the body, sustaining a continuous and high flux of nutrient catabolism via oxidative phosphorylation. The nature and relative contribution of these fuels have been studied extensively for decades. By contrast, less attention has been placed on how intermediate metabolites generated from this catabolism affect intracellular signaling. Numerous metabolites, including intermediates of glycolysis and the tricarboxylic acid (TCA) cycle, nucleotides, amino acids, fatty acids and ketones, are increasingly appreciated to affect signaling in the heart, via various mechanisms ranging from protein-metabolite interactions to modifying epigenetic marks. We review here the current state of knowledge of intermediate metabolite signaling in the heart.

Empagliflozin ameliorates diabetic cardiomyopathy via regulated branched-chain amino acid metabolism and mTOR/p-ULK1 signaling pathway-mediated autophagy

BACKGROUND

Empagliflozin, a sodium-glucose co-transporter 2 inhibitor (SGLT2i), has been reported to significantly reduce the risk of heart failure in multiple clinical studies. However, the underlying mechanisms remain elusive. This study aimed to investigate the effect of empagliflozin on branched-chain amino acid (BCAA) metabolism in diabetic cardiomyopathy.

METHODS

Thirty male 8-week KK Cg-Ay/J mice were used to study diabetic cardiomyopathy; here, 15 were used as the model group, and the remaining 15 were administered empagliflozin (3.75 mg/kg/day) by gavage daily for 16 weeks. The control group consisted of fifteen male 8-week C57BL/6J mice, whose blood glucose and body weight were measured simultaneously with the diabetic mice until 16 weeks without additional intervention. Echocardiography and histopathology were performed to evaluate cardiac structure and function. Proteomic sequencing and biogenic analysis were performed on mouse hearts. Parallel Reaction Monitoring and western blotting were performed to validate the expression levels of differentially expressed proteins.

RESULTS

The results showed that empagliflozin improved ventricular dilatation and ejection fraction reduction in diabetic hearts, as well as the elevation of myocardial injury biomarkers hs-cTnT and NT-proBNP. At the same time, empagliflozin alleviates myocardial inflammatory infiltration, calcification foci deposition, and fibrosis caused by diabetes. The results of the proteomics assay showed that empagliflozin could improve the metabolism of various substances, especially promoting the BCAA metabolism of diabetic hearts by up-regulating PP2Cm. Furthermore, empagliflozin could affect the mTOR/p-ULK1 signaling pathway by reducing the concentration of BCAA in diabetic hearts. When mTOR/p-ULK1 protein was inhibited, ULK1, the autophagy initiation molecule, increased. Moreover, autophagy substrate p62 and autophagy marker LC3B were significantly reduced, indicating that the autophagy activity of diabetes inhibition was reactivated.

CONCLUSIONS

Empagliflozin may attenuate diabetic cardiomyopathy-related myocardial injury by promoting the catabolism of BCAA and inhibiting mTOR/p-ULK1 to enhance autophagy. These findings suggest that empagliflozin could be a potential candidate drug against BCAA increase and could be used for other cardiovascular diseases with a metabolic disorder of BCAA.

Branched-Chain Amino Acid Metabolism in the Failing Heart

Branched-chain amino acids (BCAAs) are essential amino acids which have critical roles in protein synthesis and energy metabolism in the body. In the heart, there is a strong correlation between impaired BCAA oxidation and contractile dysfunction in heart failure. Plasma and myocardial levels of BCAA and their metabolites, namely branched-chain keto acids (BCKAs), are also linked to cardiac insulin resistance and worsening adverse remodelling in the failing heart. This review discusses the regulation of BCAA metabolism in the heart and the impact of depressed cardiac BCAA oxidation on cardiac energy metabolism, function, and structure in heart failure. While impaired BCAA oxidation in the failing heart causes the accumulation of BCAA and BCKA in the myocardium, recent evidence suggested that the BCAAs and BCKAs have divergent effects on the insulin signalling pathway and the mammalian target of the rapamycin (mTOR) signalling pathway. Dietary and pharmacological interventions that enhance cardiac BCAA oxidation and limit the accumulation of cardiac BCAAs and BCKAs have been shown to have cardioprotective effects in the setting of ischemic heart disease and heart failure. Thus, targeting cardiac BCAA oxidation may be a promising therapeutic approach for heart failure.

Association of branched-chain amino acids with mortality-the Ludwigshafen Risk and Cardiovascular Health (LURIC) study

Branched-chain amino acids (BCAAs) are effectors of metabolic diseases, but their impact on mortality is largely unknown. We investigated the association of BCAA with risk factors and mortality in 2,236 participants of the Ludwigshafen Risk and Cardiovascular Health (LURIC) study using linear and Cox regression. Adiponectin, hemoglobin, C-peptide, hemoglobin A_1c, and homoarginine showed the strongest association with BCAA concentration (all p < 0.001). During a median follow-up of 10.5 years, 715 participants died, including 450 cardiovascular-related deaths. BCAA concentrations were inversely associated with the risk of all-cause and cardiovascular mortality (HR [95% CI] per 1-SD increase in log-BCAA: 0.75 [0.69-0.82] and 0.72 [0.65-0.80], respectively) after adjustment for potential confounders. BCAAs are directly associated with metabolic risk but inversely with mortality in persons with intermediate-to-high cardiovascular risk. Further studies are warranted to evaluate the diagnostic and therapeutic utility of BCAA in the context of cardiovascular diseases.

Cell-autonomous effect of cardiomyocyte branched-chain amino acid catabolism in heart failure in mice

Parallel to major changes in fatty acid and glucose metabolism, defect in branched-chain amino acid (BCAA) catabolism has also been recognized as a metabolic hallmark and potential therapeutic target for heart failure. However, BCAA catabolic enzymes are ubiquitously expressed in all cell types and a systemic BCAA catabolic defect is also manifested in metabolic disorder associated with obesity and diabetes. Therefore, it remains to be determined the cell-autonomous impact of BCAA catabolic defect in cardiomyocytes in intact hearts independent from its potential global effects. In this study, we developed two mouse models. One is cardiomyocyte and temporal-specific inactivation of the E1α subunit (BCKDHA-cKO) of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which blocks BCAA catabolism. Another model is cardiomyocyte specific inactivation of the BCKDH kinase (BCKDK-cKO), which promotes BCAA catabolism by constitutively activating BCKDH activity in adult cardiomyocytes. Functional and molecular characterizations showed E1α inactivation in cardiomyocytes was sufficient to induce loss of cardiac function, systolic chamber dilation and pathological transcriptome reprogramming. On the other hand, inactivation of BCKDK in intact heart does not have an impact on baseline cardiac function or cardiac dysfunction under pressure overload. Our results for the first time established the cardiomyocyte cell autonomous role of BCAA catabolism in cardiac physiology. These mouse lines will serve as valuable model systems to investigate the underlying mechanisms of BCAA catabolic defect induced heart failure and to provide potential insights for BCAA targeted therapy.

Myocardial Metabolism in Heart Failure

PURPOSE OF REVIEW

Myocardial metabolism is intricately linked to cardiac function. Perturbations of cardiac energy metabolism result in an energy-starved heart and the development of contractile dysfunction. In this review, we discuss alterations in myocardial energy supply, transcriptional changes in response to different energy demands, and mitochondrial function in the development of heart failure.

RECENT FINDINGS

Recent studies on substrate modulation through modifying energy substrate supply have shown cardioprotective properties. In addition, large cardiovascular outcome trials of anti-diabetic agents have demonstrated prognostic benefit, suggesting the importance of myocardial metabolism in cardiac function. Understanding molecular and transcriptional controls of cardiac metabolism promises new research avenues for metabolic treatment targets. Future studies assessing the impact of substrate modulation on cardiac energetic status and function will better inform development of metabolic therapies.

Branched-chain amino acids in cardiovascular disease

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

Downregulation of extramitochondrial BCKDH and its uncoupling from AMP deaminase in type 2 diabetic OLETF rat hearts

Systemic branched-chain amino acid (BCAA) metabolism is dysregulated in cardiometabolic diseases. We previously demonstrated that upregulated AMP deaminase 3 (AMPD3) impairs cardiac energetics in a rat model of obese type 2 diabetes, Otsuka Long-Evans-Tokushima fatty (OLETF). Here, we hypothesized that the cardiac BCAA levels and the activity of branched-chain α-keto acid dehydrogenase (BCKDH), a rate-limiting enzyme in BCAA metabolism, are altered by type 2 diabetes (T2DM), and that upregulated AMPD3 expression is involved in the alteration. Performing proteomic analysis combined with immunoblotting, we discovered that BCKDH localizes not only to mitochondria but also to the endoplasmic reticulum (ER), where it interacts with AMPD3. Knocking down AMPD3 in neonatal rat cardiomyocytes (NRCMs) increased BCKDH activity, suggesting that AMPD3 negatively regulates BCKDH. Compared with control rats (Long-Evans Tokushima Otsuka [LETO] rats), OLETF rats exhibited 49% higher cardiac BCAA levels and 49% lower BCKDH activity. In the cardiac ER of the OLETF rats, BCKDH-E1α subunit expression was downregulated, while AMPD3 expression was upregulated, resulting in an 80% lower AMPD3-E1α interaction compared to LETO rats. Knocking down E1α expression in NRCMs upregulated AMPD3 expression and recapitulated the imbalanced AMPD3-BCKDH expressions observed in OLETF rat hearts. E1α knockdown in NRCMs inhibited glucose oxidation in response to insulin, palmitate oxidation, and lipid droplet biogenesis under oleate loading. Collectively, these data revealed previously unrecognized extramitochondrial localization of BCKDH in the heart and its reciprocal regulation with AMPD3 and imbalanced AMPD3-BCKDH interactions in OLETF. Downregulation of BCKDH in cardiomyocytes induced profound metabolic changes that are observed in OLETF hearts, providing insight into mechanisms contributing to the development of diabetic cardiomyopathy.

Evaluation of therapeutic strategies targeting BCAA catabolism using a systems pharmacology model

Background: Abnormal branched-chained amino acids (BCAA) accumulation in cardiomyocytes is associated with cardiac remodeling in heart failure. Administration of branched-chain α-keto acid dehydrogenase (BCKD) kinase inhibitor BT2 has been shown to reduce cardiac BCAA levels and demonstrated positive effects on cardiac function in a preclinical setting. The current study is focused on evaluating the impact of BT2 on the systemic and cardiac levels of BCAA and their metabolites as well as activities of BCAA catabolic enzymes using a quantitative systems pharmacology model. Methods: The model is composed of an ordinary differential equation system characterizing BCAA consumption with food, disposal in the proteins, reversible branched-chain-amino-acid aminotransferase (BCAT)-mediated transamination to branched-chain keto-acids (BCKA), followed by BCKD-mediated oxidation. Activity of BCKD is regulated by the balance of BCKDK and protein phosphatase 2Cm (PP2Cm) activities, affected by BT2 treatment. Cardiac BCAA levels are assumed to directly affect left ventricular ejection fraction (LVEF). Biochemical characteristics of the enzymes are taken from the public domains, while plasma and cardiac BCAA and BCKA levels in BT2 treated mice are used to inform the model parameters. Results: The model provides adequate reproduction of the experimental data and predicts synchronous BCAA responses in the systemic and cardiac space, dictated by rapid BCAA equilibration between the tissues. The model-based simulations indicate maximum possible effect of BT2 treatment on BCAA reduction to be 40% corresponding to 12% increase in LVEF. Model sensitivity analysis demonstrates strong impact of BCKDK and PP2Cm activities as well as total BCKD and co-substrate levels (glutamate, ketoglutarate and ATP) on BCAA and BCKA levels. Conclusion: Model based simulations confirms using of plasma measurements as a marker of cardiac BCAA changes under BCKDK inhibition. The proposed model can be used for optimization of preclinical study design for novel compounds targeting BCAA catabolism.

Extra-cardiac BCAA catabolism lowers blood pressure and protects from heart failure

Pharmacologic activation of branched-chain amino acid (BCAA) catabolism is protective in models of heart failure (HF). How protection occurs remains unclear, although a causative block in cardiac BCAA oxidation is widely assumed. Here, we use in vivo isotope infusions to show that cardiac BCAA oxidation in fact increases, rather than decreases, in HF. Moreover, cardiac-specific activation of BCAA oxidation does not protect from HF even though systemic activation does. Lowering plasma and cardiac BCAAs also fails to confer significant protection, suggesting alternative mechanisms of protection. Surprisingly, activation of BCAA catabolism lowers blood pressure (BP), a known cardioprotective mechanism. BP lowering occurred independently of nitric oxide and reflected vascular resistance to adrenergic constriction. Mendelian randomization studies revealed that elevated plasma BCAAs portend higher BP in humans. Together, these data indicate that BCAA oxidation lowers vascular resistance, perhaps in part explaining cardioprotection in HF that is not mediated directly in cardiomyocytes.

The involvement of branched-chain amino acids (BCAAs) in aromatic trihalogenated DBP exposure-induced kidney damage in mice

Disinfection by-products (DBPs) are inevitably generated in the process of disinfection. Among them, aromatic halogenated DBPs, such as 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP), have attracted considerable interest for their high toxicity. A systematic nephrotoxicity evaluation of 2,4,6-trihalophenols is still lacking. In this study, mice were exposed to TCP, TBP and TIP ranging from environmental-related low concentration to high concentration that commonly used in animal study (0.5-200 μg/L). Kidney histopathology, urine protein detection and urine metabolomics were performed. Remarkable changes including kidney damage, proteinuria and glomerular mesangial cell proliferation were observed after three 2,4,6-trihalophenol exposure, even at low concentration of 0.5 μg/L. The nephrotoxicity rank order was TIP > TBP > TCP. Additionally, in vivo exposure to 2,4,6-trihalophenols also led to apparent changes in urinary metabolic profiles. Biosynthesis pathways of branched-chain amino acids (BCAAs, containing valine, leucine and isoleucine) were disturbed even at the early stage of exposure (4 weeks). Intriguingly, it has been reported that BCAAs could promote the proliferation of glomerular mesangial cells. Thus, in vitro cell experiments were further performed on mouse glomerular mesangial cell line MES-13. Consistently with in vivo results, cell proliferation was observed in MES-13 cells after exposure to 2,4,6-trihalophenols, especially to TBP and TIP. Meanwhile, TCP at high concentration, TBP and TIP at not only high concentration but also low concentration, induced BCAAs accumulation in glomerular mesangial cells, which was completely commensurate to that observed in cell proliferation assay. Then the proliferation of MES-13 cells induced by 2,4,6-trihalophenols was remarkably inhibited after BCAAs interference. Here we provide direct link between disturbed BCAAs and the nephrotoxicity of 2,4,6-trihalophenols. 2,4,6-trihalophenols could induce excess BCAAs, which further led to proliferation of glomerular mesangial cells and renal injury. This study revealed the nephrotoxicity of aromatic trihalogenated DBPs and provided new insights into the potential toxic mechanisms.

Cardiac Mitochondria Dysfunction in Dyslipidemic Mice

Dyslipidemia triggers many severe pathologies, including atherosclerosis and chronic inflammation. Several lines of evidence, including our studies, have suggested direct effects of dyslipidemia on cardiac energy metabolism, but details of these effects are not clear. This study aimed to investigate how mild dyslipidemia affects cardiac mitochondria function and vascular nucleotide metabolism. The analyses were performed in 3- and 6-month-old knock-out mice for low-density lipoprotein receptor (Ldlr−/−) and compared to wild-type C57Bl/6J mice (WT). Cardiac isolated mitochondria function was analyzed using Seahorse metabolic flux analyzer. The mechanical function of the heart was measured using echocardiography. The levels of fusion, fission, and mitochondrial biogenesis proteins were determined by ELISA kits, while the cardiac intracellular nucleotide concentration and vascular pattern of nucleotide metabolism ecto-enzymes were analyzed using reverse-phase high-performance liquid chromatography. We revealed the downregulation of mitochondrial complex I, together with a decreased activity of citrate synthase (CS), reduced levels of nuclear respiratory factor 1 and mitochondrial fission 1 protein, as well as lower intracellular adenosine and guanosine triphosphates’ pool in the hearts of 6-month Ldlr−/− mice vs. age-matched WT. The analysis of vascular ecto-enzyme pattern revealed decreased rate of extracellular adenosine monophosphate hydrolysis and increased ecto-adenosine deaminase activity (eADA) in 6-month Ldlr−/− vs. WT mice. No changes were observed in echocardiography parameters in both age groups of Ldlr−/− mice. Younger hyperlipidemic mice revealed no differences in cardiac mitochondria function, CS activity, intracellular nucleotides, mitochondrial biogenesis, and dynamics but exhibited minor changes in vascular eADA activity vs. WT. This study revealed that dysfunction of cardiac mitochondria develops during prolonged mild hyperlipidemia at the time point corresponding to the formation of early vascular alterations.

Cardiorenal protection of SGLT2 inhibitors—Perspectives from metabolic reprogramming

Sodium-glucose co-transporter 2 (SGLT2) inhibitors, initially developed as a novel class of anti-hyperglycaemic drugs, have been shown to significantly improve metabolic indicators and protect the kidneys and heart of patients with or without type 2 diabetes mellitus. The possible mechanisms mediating these unexpected cardiorenal benefits are being extensively investigated because they cannot solely be attributed to improvements in glycaemic control. Notably, emerging data indicate that metabolic reprogramming is involved in the progression of cardiorenal metabolic diseases. SGLT2 inhibitors reprogram systemic metabolism to a fasting-like metabolic paradigm, involving the metabolic switch from carbohydrates to other energetic substrates and regulation of the related nutrient-sensing pathways, which might explain some of their cardiorenal protective effects. In this review, we will focus on the current understanding of cardiorenal protection by SGLT2 inhibitors, specifically its relevance to metabolic reprogramming.

Role of branched-chain amino acid metabolism in the pathogenesis of obesity and type 2 diabetes-related metabolic disturbances BCAA metabolism in type 2 diabetes

Branched-chain amino acid (BCAA) catabolism has been considered to have an emerging role in the pathogenesis of metabolic disturbances in obesity and type 2 diabetes (T2D). Several studies showed elevated plasma BCAA levels in humans with insulin resistance and patients with T2D, although the underlying reason is unknown. Dysfunctional BCAA catabolism could theoretically be an underlying factor. In vitro and animal work collectively show that modulation of the BCAA catabolic pathway alters key metabolic processes affecting glucose homeostasis, although an integrated understanding of tissue-specific BCAA catabolism remains largely unknown, especially in humans. Proof-of-concept studies in rodents -and to a lesser extent in humans – strongly suggest that enhancing BCAA catabolism improves glucose homeostasis in metabolic disorders, such as obesity and T2D. In this review, we discuss several hypothesized mechanistic links between BCAA catabolism and insulin resistance and overview current available tools to modulate BCAA catabolism in vivo. Furthermore, this review considers whether enhancing BCAA catabolism forms a potential future treatment strategy to promote metabolic health in insulin resistance and T2D.

Aberrant branched-chain amino acid catabolism in cardiovascular diseases

Globally, cardiovascular diseases are the leading cause of death. Research has focused on the metabolism of carbohydrates, fatty acids, and amino acids to improve the prognosis of cardiovascular diseases. There are three types of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine) required for protein homeostasis, energy balance, and signaling pathways. Increasing evidence has implicated BCAAs in the pathogenesis of multiple cardiovascular diseases. This review summarizes the biological origin, signal transduction pathways and function of BCAAs as well as their significance in cardiovascular diseases, including myocardial hypertrophy, heart failure, coronary artery disease, diabetic cardiomyopathy, dilated cardiomyopathy, arrhythmia and hypertension.

A randomized placebo-controlled clinical trial for pharmacological activation of BCAA catabolism in patients with type 2 diabetes

Elevations in plasma branched-chain amino acid (BCAA) levels associate with insulin resistance and type 2 diabetes (T2D). Pre-clinical models suggest that lowering BCAA levels improve glucose tolerance, but data in humans are lacking. Here, we used sodium phenylbutyrate (NaPB), an accelerator of BCAA catabolism, as tool to lower plasma BCAA levels in patients with T2D, and evaluate its effect on metabolic health. This trial (NetherlandsTrialRegister: NTR7426) had a randomized, placebo-controlled, double-blind cross-over design and was performed in the Maastricht University Medical Center (MUMC+), the Netherlands, between February 2019 and February 2020. Patients were eligible for the trial if they were 40-75years, BMI of 25-38 kg/m², relatively well-controlled T2D (HbA1C < 8.5%) and treated with oral glucose-lowering medication. Eighteen participants were randomly assigned to receive either NaPB 4.8 g/m²/day and placebo for 2 weeks via controlled randomization and sixteen participants completed the study. The primary outcome was peripheral insulin sensitivity. Secondary outcomes were ex vivo muscle mitochondrial oxidative capacity, substrate oxidation and ectopic fat accumulation. Fasting blood samples were collected to determine levels of BCAA, their catabolic intermediates, insulin, triglycerides, free fatty acids (FFA) and glucose. NaPB led to a robust 27% improvement in peripheral insulin sensitivity compared to placebo (ΔRd:13.2 ± 1.8 vs. 9.6 ± 1.8 µmol/kg/min, p = 0.02). This was paralleled by an improvement in pyruvate-driven muscle mitochondrial oxidative capacity and whole-body insulin-stimulated carbohydrate oxidation, and a reduction in plasma BCAA and glucose levels. No effects were observed on levels of insulin, triglycerides and FFA, neither did fat accumulation in muscle and liver change. No adverse events were reported. These data establish the proof-of-concept in humans that modulating the BCAA oxidative pathway may represent a potential treatment strategy for patients with T2D.

Mitochondrial H2S Regulates BCAA Catabolism in Heart Failure

BACKGROUND

Hydrogen sulfide (H₂S) exerts mitochondria-specific actions that include the preservation of oxidative phosphorylation, biogenesis, and ATP synthesis, while inhibiting cell death. 3-MST (3-mercaptopyruvate sulfurtransferase) is a mitochondrial H₂S-producing enzyme whose functions in the cardiovascular disease are not fully understood. In the current study, we investigated the effects of global 3-MST deficiency in the setting of pressure overload-induced heart failure.

METHODS

Human myocardial samples obtained from patients with heart failure undergoing cardiac surgeries were probed for 3-MST protein expression. 3-MST knockout mice and C57BL/6J wild-type mice were subjected to transverse aortic constriction to induce pressure overload heart failure with reduced ejection fraction. Cardiac structure and function, vascular reactivity, exercise performance, mitochondrial respiration, and ATP synthesis efficiency were assessed. In addition, untargeted metabolomics were utilized to identify key pathways altered by 3-MST deficiency.

RESULTS

Myocardial 3-MST was significantly reduced in patients with heart failure compared with nonfailing controls. 3-MST KO mice exhibited increased accumulation of branched-chain amino acids in the myocardium, which was associated with reduced mitochondrial respiration and ATP synthesis, exacerbated cardiac and vascular dysfunction, and worsened exercise performance following transverse aortic constriction. Restoring myocardial branched-chain amino acid catabolism with 3,6-dichlorobenzo1[b]thiophene-2-carboxylic acid (BT2) and administration of a potent H₂S donor JK-1 ameliorates the detrimental effects of 3-MST deficiency in heart failure with reduced ejection fraction.

CONCLUSIONS

Our data suggest that 3-MST derived mitochondrial H₂S may play a regulatory role in branched-chain amino acid catabolism and mediate critical cardiovascular protection in heart failure.

Animal Models of Dysregulated Cardiac Metabolism

As a muscular pump that contracts incessantly throughout life, the heart must constantly generate cellular energy to support contractile function and fuel ionic pumps to maintain electrical homeostasis. Thus, mitochondrial metabolism of multiple metabolic substrates such as fatty acids, glucose, ketones, and lactate is essential to ensuring an uninterrupted supply of ATP. Multiple metabolic pathways converge to maintain myocardial energy homeostasis. The regulation of these cardiac metabolic pathways has been intensely studied for many decades. Rapid adaptation of these pathways is essential for mediating the myocardial adaptation to stress, and dysregulation of these pathways contributes to myocardial pathophysiology as occurs in heart failure and in metabolic disorders such as diabetes. The regulation of these pathways reflects the complex interactions of cell-specific regulatory pathways, neurohumoral signals, and changes in substrate availability in the circulation. Significant advances have been made in the ability to study metabolic regulation in the heart, and animal models have played a central role in contributing to this knowledge. This review will summarize metabolic pathways in the heart and describe their contribution to maintaining myocardial contractile function in health and disease. The review will summarize lessons learned from animal models with altered systemic metabolism and those in which specific metabolic regulatory pathways have been genetically altered within the heart. The relationship between intrinsic and extrinsic regulators of cardiac metabolism and the pathophysiology of heart failure and how these have been informed by animal models will be discussed.

Protein restriction and branched-chain amino acid restriction promote geroprotective shifts in metabolism

The proportion of humans suffering from age‐related diseases is increasing around the world, and creative solutions are needed to promote healthy longevity. Recent work has clearly shown that a calorie is not just a calorie—and that low protein diets are associated with reduced mortality in humans and promote metabolic health and extended lifespan in rodents. Many of the benefits of protein restriction on metabolism and aging are the result of decreased consumption of the three branched‐chain amino acids (BCAAs), leucine, isoleucine, and valine. Here, we discuss the emerging evidence that BCAAs are critical modulators of healthy metabolism and longevity in rodents and humans, as well as the physiological and molecular mechanisms that may drive the benefits of BCAA restriction. Our results illustrate that protein quality—the specific composition of dietary protein—may be a previously unappreciated driver of metabolic dysfunction and that reducing dietary BCAAs may be a promising new approach to delay and prevent diseases of aging.

Deletion of BCATm increases insulin-stimulated glucose oxidation in the heart

BACKGROUNDS

Branched chain amino acid (BCAA) oxidation is impaired in cardiac insulin resistance, leading to the accumulation of BCAAs and the first products of BCAA oxidation, the branched chain ketoacids. However, it is not clear whether it is the BCAAs, BCKAs or both that are mediating cardiac insulin resistance. To determine this, we produced mice with a cardiac-specific deletion of BCAA aminotransferase (BCATm^-/-), the first enzyme in the BCAA oxidation pathway that is responsible for converting BCAAs to BCKAs.

METHODS

Eight-week-old BCATm cardiac specific knockout (BCATm^-/-) male mice and their α-MHC (myosin heavy chain) - Cre expressing wild type littermates (WT-Cre^+/+) received tamoxifen (50 mg/kg i.p. 6 times over 8 days). At 16-weeks of age, cardiac energy metabolism was assessed in isolated working hearts.

RESULTS

BCATm^-/- mice have decreased cardiac BCAA oxidation rates, increased cardiac BCAAs and a reduction in cardiac BCKAs. Hearts from BCATm^-/- mice showed an increase in insulin stimulation of glucose oxidation and an increase in p-AKT. To determine the impact of reversing these events, we perfused isolated working mice hearts with high levels of BCKAs, which completely abolished insulin-stimulated glucose oxidation rates, an effect associated with decreased p-AKT and inactivation of pyruvate dehydrogenase (PDH), the rate-limiting enzyme in glucose oxidation.

CONCLUSION

This implicates the BCKAs, and not BCAAs, as the actual mediators of cardiac insulin resistance and suggests that lowering cardiac BCKAs can be used as a therapeutic strategy to improve insulin sensitivity in the heart.

Inhibition of the canonical Wnt signaling pathway by a β-catenin/CBP inhibitor prevents heart failure by ameliorating cardiac hypertrophy and fibrosis

In heart failure (HF) caused by hypertension, the myocyte size increases, and the cardiac wall thickens. A low-molecular-weight compound called ICG001 impedes β-catenin-mediated gene transcription, thereby protecting both the heart and kidney. However, the HF-preventive mechanisms of ICG001 remain unclear. Hence, we investigated how ICG001 can prevent cardiac hypertrophy and fibrosis induced by transverse aortic constriction (TAC). Four weeks after TAC, ICG001 attenuated cardiac hypertrophy and fibrosis in the left ventricular wall. The TAC mice treated with ICG001 showed a decrease in the following: mRNA expression of brain natriuretic peptide (Bnp), Klf5, fibronectin, β-MHC, and β-catenin, number of cells expressing the macrophage marker CD68 shown in immunohistochemistry, and macrophage accumulation shown in flow cytometry. Moreover, ICG001 may mediate the substrates in the glycolysis pathway and the distinct alteration of oxidative stress during cardiac hypertrophy and HF. In conclusion, ICG001 is a potential drug that may prevent cardiac hypertrophy and fibrosis by regulating KLF5, immune activation, and the Wnt/β-catenin signaling pathway and inhibiting the inflammatory response involving macrophages.

Insulin signaling in the heart

Insulin receptors are highly expressed in the heart and vasculature. Insulin signaling regulates cardiac growth, survival, substrate uptake, utilization, and mitochondrial metabolism. Insulin signaling modulates the cardiac responses to physiological and pathological stressors. Altered insulin signaling in the heart may contribute to the pathophysiology of ventricular remodeling and heart failure progression. Myocardial insulin signaling adapts rapidly to changes in the systemic metabolic milieu. What may initially represent an adaptation to protect the heart from carbotoxicity may contribute to amplifying the risk of heart failure in obesity and diabetes. This review article presents the multiple roles of insulin signaling in cardiac physiology and pathology and discusses the potential therapeutic consequences of modulating myocardial insulin signaling.

Is branched-chain amino acid nutritional supplementation beneficial or detrimental in heart failure?

Sarcopenia or cachexia is often complicated in heart failure. Nutritional support, particularly branched-chain amino acid (BCAA) supplementation, is a candidate treatment for improving sarcopenia or cachexia in elderly patients. However, the efficacy of BCAA supplementation in patients with heart failure has not been established, and the issue is comparatively more complex. Indeed, there are conflicting reports on the efficacy of BCAA supplementation. The evidence for including BCAA supplementation in treating patients with heart failure was reviewed, and the complexity of the issue was discussed.

Metal dependent protein phosphatase PPM family in cardiac health and diseases

Protein phosphorylation and dephosphorylation is central to signal transduction in nearly every aspect of cellular function, including cardiovascular regulation and diseases. While protein kinases are often regarded as the molecular drivers in cellular signaling with high specificity and tight regulation, dephosphorylation mediated by protein phosphatases is also gaining increasing appreciation as an important part of the signal transduction network essential for the robustness, specificity and homeostasis of cell signaling. Metal dependent protein phosphatases (PPM, also known as protein phosphatases type 2C, PP2C) belong to a highly conserved family of protein phosphatases with unique biochemical and molecular features. Accumulating evidence also indicates important and specific functions of individual PPM isoform in signaling and cellular processes, including proliferation, senescence, apoptosis and metabolism. At the physiological level, abnormal PPM expression and activity have been implicated in major human diseases, including cancer, neurological and cardiovascular disorders. Finally, inhibitors for some of the PPM members have been developed as a potential therapeutic strategy for human diseases. In this review, we will focus on the background information about the biochemical and molecular features of major PPM family members, with emphasis on their demonstrated or potential roles in cardiac pathophysiology. The current challenge and potential directions for future investigations will also be highlighted.

Cardiac Energy Metabolism in Heart Failure

Alterations in cardiac energy metabolism contribute to the severity of heart failure. However, the energy metabolic changes that occur in heart failure are complex and are dependent not only on the severity and type of heart failure present but also on the co-existence of common comorbidities such as obesity and type 2 diabetes. The failing heart faces an energy deficit, primarily because of a decrease in mitochondrial oxidative capacity. This is partly compensated for by an increase in ATP production from glycolysis. The relative contribution of the different fuels for mitochondrial ATP production also changes, including a decrease in glucose and amino acid oxidation, and an increase in ketone oxidation. The oxidation of fatty acids by the heart increases or decreases, depending on the type of heart failure. For instance, in heart failure associated with diabetes and obesity, myocardial fatty acid oxidation increases, while in heart failure associated with hypertension or ischemia, myocardial fatty acid oxidation decreases. Combined, these energy metabolic changes result in the failing heart becoming less efficient (ie, a decrease in cardiac work/O₂ consumed). The alterations in both glycolysis and mitochondrial oxidative metabolism in the failing heart are due to both transcriptional changes in key enzymes involved in these metabolic pathways, as well as alterations in NAD redox state (NAD⁺ and nicotinamide adenine dinucleotide levels) and metabolite signaling that contribute to posttranslational epigenetic changes in the control of expression of genes encoding energy metabolic enzymes. Alterations in the fate of glucose, beyond flux through glycolysis or glucose oxidation, also contribute to the pathology of heart failure. Of importance, pharmacological targeting of the energy metabolic pathways has emerged as a novel therapeutic approach to improving cardiac efficiency, decreasing the energy deficit and improving cardiac function in the failing heart.

Metabolism and Chronic Inflammation: The Links Between Chronic Heart Failure and Comorbidities

Heart failure (HF) patients often suffer from multiple comorbidities, such as diabetes, atrial fibrillation, depression, chronic obstructive pulmonary disease, and chronic kidney disease. The coexistance of comorbidities usually leads to multi morbidity and poor prognosis. Treatments for HF patients with multi morbidity are still an unmet clinical need, and finding an effective therapy strategy is of great value. HF can lead to comorbidity, and in return, comorbidity may promote the progression of HF, creating a vicious cycle. This reciprocal correlation indicates there may be some common causes and biological mechanisms. Metabolism remodeling and chronic inflammation play a vital role in the pathophysiological processes of HF and comorbidities, indicating metabolism and inflammation may be the links between HF and comorbidities. In this review, we comprehensively discuss the major underlying mechanisms and therapeutic implications for comorbidities of HF. We first summarize the potential role of metabolism and inflammation in HF. Then, we give an overview of the linkage between common comorbidities and HF, from the perspective of epidemiological evidence to the underlying metabolism and inflammation mechanisms. Moreover, with the help of bioinformatics, we summarize the shared risk factors, signal pathways, and therapeutic targets between HF and comorbidities. Metabolic syndrome, aging, deleterious lifestyles (sedentary behavior, poor dietary patterns, smoking, etc.), and other risk factors common to HF and comorbidities are all associated with common mechanisms. Impaired mitochondrial biogenesis, autophagy, insulin resistance, and oxidative stress, are among the major mechanisms of both HF and comorbidities. Gene enrichment analysis showed the PI3K/AKT pathway may probably play a central role in multi morbidity. Additionally, drug targets common to HF and several common comorbidities were found by network analysis. Such analysis has already been instrumental in drug repurposing to treat HF and comorbidity. And the result suggests sodium-glucose transporter-2 (SGLT-2) inhibitors, IL-1β inhibitors, and metformin may be promising drugs for repurposing to treat multi morbidity. We propose that targeting the metabolic and inflammatory pathways that are common to HF and comorbidities may provide a promising therapeutic strategy.

Whole-body metabolic fate of branched-chain amino acids

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

Antihypertensive drug valsartan as a novel BDK inhibitor

Catabolism of branched-chain amino acids (BCAAs) is affected by various physiological conditions and its abnormality is associated with glucose metabolism, heart disease, and neurological dysfunction. The first two steps of the BCAA metabolic pathway are common to the three BCAAs (leucine, isoleucine, and valine). The second step is an irreversible rate-limited reaction catalyzed by branched-chain α-keto acid dehydrogenase (BCKDH), which is bound to a specific kinase, BCKDH kinase (BDK), and inactivated by phosphorylation. Here, we investigated potential new BDK inhibitors and discovered valsartan, an angiotensin II type 1 receptor (AT1R) blocker, as a new BDK inhibitor. BCKDH phosphorylation and the BCKDH-BDK interaction were inhibited by valsartan in vitro. Valsartan administration in rats resulted in increased BCKDH activity by decreasing the dephosphorylated level of BCKDH complex, bound forms of BDK from BCKDH complex as well as decreased plasma BCAA concentrations. Valsartan is a novel BDK inhibitor that competes with ATP, via a different mechanism from allosteric inhibitors. The BDK inhibitor has been shown to preserve cardiac function in pressure overload-induced heart failure mice and to attenuate insulin resistance in obese mice. Our findings suggest that valsartan is a potent seed compound for developing a powerful BDK inhibitor and useful medication for treating heart failure and metabolic diseases with suppressed BCAA catabolism.

Essential amino acid formulations to prevent mitochondrial dysfunction and oxidative stress

PURPOSE OF REVIEW

Both restriction and supplementation of specific amino acids or branched-chain amino acids (BCAAs) are described to improve metabolic homeostasis, energy balance, and health span. This review will discuss the recent findings of the role of amino acid supplements in the regulation of mitochondrial health.

RECENT FINDINGS

A mixture of essential amino acids (EAAs), BCAA enriched mixture, was found to extend healthy life span in elderly mice and prevent multiple diseases associated with an energy deficit, similarly to caloric restriction or fasting-mimicking diets. A growing body of evidence highlights mitochondria as the central target of this supplement: it promotes mitochondrial biogenesis and the activation of antioxidant defence systems in different physiological (e.g., exercise or ageing) or pathological conditions (e.g., sarcopenia, muscular dystrophy, liver steatosis, or impaired cognition). Based on these results, new formulas have been created enriched with Krebs cycle substrates, behaving more efficiently than BCAA enriched mixture.

SUMMARY

EAA-BCAA balanced supplements might be valuable not only for healthy individuals undergoing to energy deficit (e.g., athletes) during strenuous exercise or training but also against diseases characterized by a dysregulated catabolic state or mitochondrial dysfunction, such as age-related disorders. The associated mechanistic processes should be identified as potential pharmacological targets.

Changes in Myocardial Metabolism Preceding Sudden Cardiac Death

Heart disease is widely recognized as a major cause of death worldwide and is the leading cause of mortality in the United States. Centuries of research have focused on defining mechanistic alterations that drive cardiac pathogenesis, yet sudden cardiac death (SCD) remains a common unpredictable event that claims lives in every age group. The heart supplies blood to all tissues while maintaining a constant electrical and hormonal feedback communication with other parts of the body. As such, recent research has focused on understanding how myocardial electrical and structural properties are altered by cardiac metabolism and the various signaling pathways associated with it. The importance of cardiac metabolism in maintaining myocardial function, or lack thereof, is exemplified by shifts in cardiac substrate preference during normal development and various pathological conditions. For instance, a shift from fatty acid (FA) oxidation to oxygen-sparing glycolytic energy production has been reported in many types of cardiac pathologies. Compounded by an uncoupling of glycolysis and glucose oxidation this leads to accumulation of undesirable levels of intermediate metabolites. The resulting accumulation of intermediary metabolites impacts cardiac mitochondrial function and dysregulates metabolic pathways through several mechanisms, which will be reviewed here. Importantly, reversal of metabolic maladaptation has been shown to elicit positive therapeutic effects, limiting cardiac remodeling and at least partially restoring contractile efficiency. Therein, the underlying metabolic adaptations in an array of pathological conditions as well as recently discovered downstream effects of various substrate utilization provide guidance for future therapeutic targeting. Here, we will review recent data on alterations in substrate utilization in the healthy and diseased heart, metabolic pathways governing cardiac pathogenesis, mitochondrial function in the diseased myocardium, and potential metabolism-based therapeutic interventions in disease.