Branched-chain α-ketoacids are preferentially reaminated and activate protein synthesis in the heart

PFKP inhibition protects against pathological cardiac hypertrophy by regulating protein synthesis

Metabolic reprogramming precedes most alterations during pathological cardiac hypertrophy and heart failure (HF). Recent studies have revealed that Phosphofructokinase, platelet (PFKP) has a wealth of metabolic and non-metabolic functions. In this study, we explored the role of PFKP in cardiac hypertrophic growth and HF. The expression level of PFKP was elevated both in pathological cardiac remodeling mouse model challenged by transverse aortic constriction (TAC) surgery and in the neonatal rat cardiomyocytes (NRCMs) stimulated by phenylephrine (PE). In global PFKP knockout (PFKP-KO) mice, cardiac hypertrophy was ameliorated under TAC surgery, while overexpression of PFKP by intravenous injection of adeno-associated virus 9 (AAV9) under the cardiac troponin T (cTnT) promoter worsened myocardial hypertrophy and fibrosis. In NRCMs, small interfering RNA (SiRNA) knockdown or adenovirus (Adv) overexpression of PFKP was employed and the intervention of PFKP showed a similar phenotype. Mechanistically, immunoprecipitation combined with liquid chromatography-tandem mass spectrometry (IP-MS/MS) analysis was used to identify the interacting proteins of PFKP. Eukaryotic translation initiation factor 2 subunit beta (EIF2S2) was identified as the downstream target of PFKP. In the PE-stimulated NRCM hypertrophy model and mouse TAC model, knocking down EIF2S2 after PFKP overexpression reduced the synthesis of new proteins and alleviated the hypertrophy phenotype. Our findings illuminate that PFKP participates in pathological cardiac hypertrophy partly by regulating protein synthesis through EIF2S2, which provides a new clue for the involvement of metabolic intermediates in signal transduction.

Anaplerotic filling in heart failure: a review of mechanism and potential therapeutics

Heart failure (HF) is a complex syndrome and a leading cause of mortality worldwide. While current medical treatment is based on known pathophysiology and is effective for many patients, the underlying cellular mechanisms are poorly understood. Energy deficiency is a characteristic of HF, marked by complex alterations in metabolism. Within the tricarboxylic acid cycle, anaplerosis emerges as an essential metabolic process responsible for replenishing lost intermediates, thereby playing a crucial role in sustaining energy metabolism and consequently cardiac function. Alterations in cardiac anaplerosis are commonly observed in HF, demonstrating potential for therapeutic intervention. This review discusses recent advances in understanding the anaplerotic adaptations that occur in HF. We also explore therapeutics that can directly modulate anaplerosis or are likely to confer cardioprotective effects through anaplerosis, which could potentially be implemented to rescue the failing heart.

The attenuated hepatic clearance of propionate increases cardiac oxidative stress in propionic acidemia

Propionic acidemia (PA), arising from PCCA or PCCB variants, manifests as life-threatening cardiomyopathy and arrhythmias, with unclear pathophysiology. In this work, propionyl-CoA metabolism in rodent hearts and human pluripotent stem cell-derived cardiomyocytes was investigated with stable isotope tracing analysis. Surprisingly, gut microbiome-derived propionate rather than the propiogenic amino acids (valine, isoleucine, threonine, and methionine) or odd-chain fatty acids was found to be the primary cardiac propionyl-CoA source. In a Pcca-/-(A138T) mouse model and PA patients, accumulated propionyl-CoA and diminished acyl-CoA synthetase short-chain family member 3 impede hepatic propionate disposal, elevating circulating propionate. Prolonged propionate exposure induced significant oxidative stress in PCCA knockdown HL-1 cells and the hearts of Pcca-/-(A138T) mice. Additionally, Pcca-/-(A138T) mice exhibited mild diastolic dysfunction after the propionate challenge. These findings suggest that elevated circulating propionate may cause oxidative damage and functional impairment in the hearts of patients with PA.

Liraglutide Protects Against Diastolic Dysfunction and Improves Ventricular Protein Translation

PURPOSE

Diastolic dysfunction is an increasingly common cardiac pathology linked to heart failure with preserved ejection fraction. Previous studies have implicated glucagon-like peptide 1 (GLP-1) receptor agonists as potential therapies for improving diastolic dysfunction. In this study, we investigate the physiologic and metabolic changes in a mouse model of angiotensin II (AngII)-mediated diastolic dysfunction with and without the GLP-1 receptor agonist liraglutide (Lira).

METHODS

Mice were divided into sham, AngII, or AngII+Lira therapy for 4 weeks. Mice were monitored for cardiac function, weight change, and blood pressure at baseline and after 4 weeks of treatment. After 4 weeks of treatment, tissue was collected for histology, protein analysis, targeted metabolomics, and protein synthesis assays.

RESULTS

AngII treatment causes diastolic dysfunction when compared to sham mice. Lira partially prevents this dysfunction. The improvement in function in Lira mice is associated with dramatic changes in amino acid accumulation in the heart. Lira mice also have improved markers of protein translation by Western blot and increased protein synthesis by puromycin assay, suggesting that increased protein turnover protects against fibrotic remodeling and diastolic dysfunction seen in the AngII cohort. Lira mice also lost lean muscle mass compared to the AngII cohort, raising concerns about peripheral muscle scavenging as a source of the increased amino acids in the heart.

CONCLUSIONS

Lira therapy protects against AngII-mediated diastolic dysfunction, at least in part by promoting amino acid uptake and protein turnover in the heart. Liraglutide therapy is associated with loss of mean muscle mass, and long-term studies are warranted to investigate sarcopenia and frailty with liraglutide therapy in the setting of diastolic disease.

Branched-chain α-ketoacids aerobically activate HIF1α signalling in vascular cells

Hypoxia-inducible factor 1α (HIF1α) is a master regulator of biological processes in hypoxia. Yet, the mechanisms and biological consequences of aerobic HIF1α activation by intrinsic factors, particularly in normal (primary) cells, remain elusive. Here we show that HIF1α signalling is activated in several human primary vascular cells in normoxia and in vascular smooth muscle cells of normal human lungs. Mechanistically, aerobic HIF1α activation is mediated by paracrine secretion of three branched-chain α-ketoacids (BCKAs), which suppress PHD2 activity via direct inhibition and via LDHA-mediated generation of L-2-hydroxyglutarate. BCKA-mediated HIF1α signalling activation stimulated glycolytic activity and governed a phenotypic switch of pulmonary artery smooth muscle cells, which correlated with BCKA metabolic dysregulation and pathophenotypic changes in pulmonary arterial hypertension patients and male rat models. We thus identify BCKAs as previously unrecognized signalling metabolites that aerobically activate HIF1α and that the BCKA-HIF1α pathway modulates vascular smooth muscle cell function, an effect that may be relevant to pulmonary vascular pathobiology.

Pharmacometabolomics of sulfonylureas in patients with type 2 diabetes: a cross-sectional study

Background

Sulfonylureas have been a longstanding pharmacotherapy in the management of type 2 diabetes, with potential benefits beyond glycemic control. Although sulfonylureas are effective, interindividual variability exists in drug response. Pharmacometabolomics is a potent method for elucidating variations in individual drug response. Identifying unique metabolites associated with treatment response can improve our ability to predict outcomes and optimize treatment strategies for individual patients. Our objective is to identify metabolic signatures associated with good and poor response to sulfonylureas, which could enhance our capability to anticipate treatment outcome.

Methods

In this cross-sectional study, clinical and metabolomics data for 137 patients with type 2 diabetes who are taking sulfonylurea as a monotherapy or a combination therapy were obtained from Qatar Biobank. Patients were empirically categorized according to their glycosylated hemoglobin levels into poor and good responders to sulfonylureas. To examine variations in metabolic signatures between the two distinct groups, we have employed orthogonal partial least squares discriminant analysis and linear models while correcting for demographic confounders and metformin usage.

Results

Good responders showed increased levels of acylcholines, gamma glutamyl amino acids, sphingomyelins, methionine, and a novel metabolite 6-bromotryptophan. Conversely, poor responders showed increased levels of metabolites of glucose metabolism and branched chain amino acid metabolites.

Conclusion

The results of this study have the potential to empower our knowledge of variability in patient response to sulfonylureas, and carry significant implications for advancing precision medicine in type 2 diabetes management.

Towards Metabolomic-Based Precision Approaches for Classifying and Treating Heart Failure

Both heart failure and cardiometabolic disease are on the rise, and abnormal cardiac and peripheral metabolism are central to the syndrome of heart failure. Advances in metabolomic profiling have improved our understanding of the heart's metabolic flexibility in patients with and without heart failure. Prior studies have noted patients with heart failure display metabolomic profiles associated with marked abnormalities in the metabolism of fatty acids, branched-chain amino acids, ketones, and glucose compared with control subjects. Metabolomics can highlight specific pathways that are dysregulated; however, other metabolites beyond those related to fuel metabolism may also play a role in precision-medicine approaches. Novel approaches include metabolic flux studies, spatial and single-cell analysis, serial monitoring of treatment response, and integration with other -omics data. The goal of these innovative approaches should be to harness metabolomic technologies to affect precision care for patients with heart failure.

Branched-chain amino acids: physico-chemical properties, industrial synthesis and role in signaling, metabolism and energy production

Branched-chain amino acids (BCAAs)-leucine (Leu), isoleucine (Ile), and valine (Val)-are essential nutrients with significant roles in protein synthesis, metabolic regulation, and energy production. This review paper offers a detailed examination of the physico-chemical properties of BCAAs, their industrial synthesis, and their critical functions in various biological processes. The unique isomerism of BCAAs is presented, focusing on analytical challenges in their separation and quantification as well as their solubility characteristics, which are crucial for formulation and purification applications. The industrial synthesis of BCAAs, particularly using bacterial strains like Corynebacterium glutamicum, is explored, alongside methods such as genetic engineering aimed at enhancing production, detailing the enzymatic processes and specific precursors. The dietary uptake, distribution, and catabolism of BCAAs are reviewed as fundamental components of their physiological functions. Ultimately, their multifaceted impact on signaling pathways, immune function, and disease progression is discussed, providing insights into their profound influence on muscle protein synthesis and metabolic health. This comprehensive analysis serves as a resource for understanding both the basic and complex roles of BCAAs in biological systems and their industrial application.

BCAA mediated microbiota-liver-heart crosstalk regulates diabetic cardiomyopathy via FGF21

BACKGROUND

Diabetic cardiomyopathy (DCM) is one of leading causes of diabetes-associated mortality. The gut microbiota-derived branched-chain amino acids (BCAA) have been reported to play a central role in the onset and progression of DCM, but the potential mechanisms remain elusive.

RESULTS

We found the type 1 diabetes (T1D) mice had higher circulating BCAA levels due to a reduced BCAA degradation ability of the gut microbiota. Excess BCAA decreased hepatic FGF21 production by inhibiting PPARα signaling pathway and thereby resulted in a higher expression level of cardiac LAT1 via transcription factor Zbtb7c. High cardiac LAT1 increased the levels of BCAA in the heart and then caused mitochondrial damage and myocardial apoptosis through mTOR signaling pathway, leading to cardiac fibrosis and dysfunction in T1D mice. Additionally, transplant of faecal microbiota from healthy mice alleviated cardiac dysfunction in T1D mice, but this effect was abolished by FGF21 knockdown.

CONCLUSIONS

Our study sheds light on BCAA-mediated crosstalk among the gut microbiota, liver and heart to promote DCM and FGF21 serves as a key mediator. Video Abstract.

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

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

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.

Branched chain α-ketoacids aerobically activate HIF1α signaling in vascular cells

Hypoxia-inducible factor 1α (HIF1α) is a master regulator of numerous biological processes under low oxygen tensions. Yet, the mechanisms and biological consequences of aerobic HIF1α activation by intrinsic factors, particularly in primary cells remain elusive. Here, we show that HIF1α signaling is activated in several human primary vascular cells under ambient oxygen tensions, and in vascular smooth muscle cells (VSMCs) of normal human lung tissue, which contributed to a relative resistance to further enhancement of glycolytic activity in hypoxia. Mechanistically, aerobic HIFα activation is mediated by paracrine secretion of three branched chain α-ketoacids (BCKAs), which suppress prolyl hydroxylase domain-containing protein 2 (PHD2) activity via direct inhibition and via lactate dehydrogenase A (LDHA)-mediated generation of L-2-hydroxyglutarate (L2HG). Metabolic dysfunction induced by BCKAs was observed in the lungs of rats with pulmonary arterial hypertension (PAH) and in pulmonary artery smooth muscle cells (PASMCs) from idiopathic PAH patients. BCKA supplementation stimulated glycolytic activity and promoted a phenotypic switch to the synthetic phenotype in PASMCs of normal and PAH subjects. In summary, we identify BCKAs as novel signaling metabolites that activate HIF1α signaling in normoxia and that the BCKA-HIF1α pathway modulates VSMC function and may be relevant to pulmonary vascular pathobiology.

Unveiling the microbiota-metabolite-myocardium axis: a novel perspective on cardiovascular health

Introduction

Cardiovascular diseases, including myocardial infarction, remain a leading cause of death globally. Emerging evidence suggests the gut microbiota plays a crucial role in cardiovascular health. This study aims to explore the impact of gut microbiota on myocardial infarction using a mouse model.

Methods

The research utilizes a multi-omics approach, including 16S rDNA sequencing and LC-MS-based metabolomics to analyze fecal and serum samples from mice modeled to mimic myocardial infarction. This methodology allows for a comprehensive analysis of microbial populations and their metabolic output.

Results

The findings reveal a significant reduction in gut microbiota α-diversity in mice with induced myocardial infarction compared to healthy controls. Notably, there is an increase in populations of Fusobacteria and Clostridia. Metabolomic analysis indicates disruptions in amino acid and energy metabolism, suggesting a metabolic dysregulation linked to myocardial health.

Discussion

The study proposes a novel microbiota-metabolite-myocardium axis, where specific microbial metabolites may directly affect heart health. This connection points to the gut microbiota as a potential player in the pathogenesis of myocardial infarction and may open new therapeutic avenues targeting the gut microbiome to combat cardiovascular diseases.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

Proteomic and phosphoproteomic characterization of cardiovascular tissues after long term exposure to simulated space radiation

Introduction: It may take decades to develop cardiovascular dysfunction following exposure to high doses of ionizing radiation from medical therapy or from nuclear accidents. Since astronauts may be exposed continually to a complex space radiation environment unlike that experienced on Earth, it is unresolved whether there is a risk to cardiovascular health during long-term space exploration missions. Previously, we have described that mice exposed to a single dose of simplified Galactic Cosmic Ray (GCR5-ion) develop cardiovascular dysfunction by 12 months post-radiation. Methods: To investigate the biological basis of this dysfunction, here we performed a quantitative mass spectrometry-based proteomics analysis of heart tissue (proteome and phosphoproteome) and plasma (proteome only) from these mice at 8 months post-radiation. Results: Differentially expressed proteins (DEPs) for irradiated versus sham irradiated samples (fold-change ≥1.2 and an adjusted p-value of ≤0.05) were identified for each proteomics data set. For the heart proteome, there were 87 significant DEPs (11 upregulated and 76 downregulated); for the heart phosphoproteome, there were 60 significant differentially phosphorylated peptides (17 upregulated and 43 downregulated); and for the plasma proteome, there was only one upregulated protein. A Gene Set Enrichment Analysis (GSEA) technique that assesses canonical pathways from BIOCARTA, KEGG, PID, REACTOME, and WikiPathways revealed significant perturbation in pathways in each data set. For the heart proteome, 166 pathways were significantly altered (36 upregulated and 130 downregulated); for the plasma proteome, there were 73 pathways significantly altered (25 upregulated and 48 downregulated); and for the phosphoproteome, there were 223 pathways significantly affected at 0.1 adjusted p-value cutoff. Pathways related to inflammation were the most highly perturbed in the heart and plasma. In line with sustained inflammation, neutrophil extracellular traps (NETs) were demonstrated to be increased in GCR5-ion irradiated hearts at 12-month post irradiation. NETs play a fundamental role in combating bacterial pathogens, modulating inflammatory responses, inflicting damage on healthy tissues, and escalating vascular thrombosis. Discussion: These findings suggest that a single exposure to GCR5-ion results in long-lasting changes in the proteome and that these proteomic changes can potentiate acute and chronic health issues for astronauts, such as what we have previously described with late cardiac dysfunction in these mice.

Chronic exercise improves hepatic acylcarnitine handling

Exercise mediates tissue metabolic function through direct and indirect adaptations to acylcarnitine (AC) metabolism, but the exact mechanisms are unclear. We found that circulating medium-chain acylcarnitines (AC) (C12-C16) are lower in active/endurance trained human subjects compared to sedentary controls, and this is correlated with elevated cardiorespiratory fitness and reduced adiposity. In mice, exercise reduced serum AC and increased liver AC, and this was accompanied by a marked increase in expression of genes involved in hepatic AC metabolism and mitochondrial β-oxidation. Primary hepatocytes from high-fat fed, exercise trained mice had increased basal respiration compared to hepatocytes from high-fat fed sedentary mice, which may be attributed to increased Ca2+ cycling and lipid uptake into mitochondria. The addition of specific medium- and long-chain AC to sedentary hepatocytes increased mitochondrial respiration, mirroring the exercise phenotype. These data indicate that AC redistribution is an exercise-induced mechanism to improve hepatic function and metabolism.

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.

Metabolic adaptations in pressure overload hypertrophic heart

This review article offers a detailed examination of metabolic adaptations in pressure overload hypertrophic hearts, a condition that plays a pivotal role in the progression of heart failure with preserved ejection fraction (HFpEF) to heart failure with reduced ejection fraction (HFrEF). The paper delves into the complex interplay between various metabolic pathways, including glucose metabolism, fatty acid metabolism, branched-chain amino acid metabolism, and ketone body metabolism. In-depth insights into the shifts in substrate utilization, the role of different transporter proteins, and the potential impact of hypoxia-induced injuries are discussed. Furthermore, potential therapeutic targets and strategies that could minimize myocardial injury and promote cardiac recovery in the context of pressure overload hypertrophy (POH) are examined. This work aims to contribute to a better understanding of metabolic adaptations in POH, highlighting the need for further research on potential therapeutic applications.

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.

Branched-chain amino acids promote thrombocytopoiesis by activating mTOR signaling

BACKGROUND

Megakaryocyte differentiation and platelet production disorders are the main causes of thrombocythemia and thrombocytopenia and lead to thrombosis or hemorrhage. Branched-chain amino acids (BCAAs) are essential nutrients that regulate important metabolic signals. BCAA administration could also increase platelet activation and promote the risk of thrombosis.

OBJECTIVES

To unveil the role of BCAAs in thrombocytopoiesis.

METHODS

BCAA-fed mice and megakaryocyte/platelet-specific branched-chain α-keto acid dehydrogenase E1α subunit-deficient mice were used to study the role of BCAAs in thrombocytopoiesis.

RESULTS

In this study, we found that BCAA diet could facilitate megakaryocyte differentiation and platelet production. Meanwhile, megakaryocyte/platelet-specific branched-chain α-keto acid dehydrogenase E1α subunit-deficient mice developed thrombocythemia, which was mainly caused by the excessive differentiation of megakaryocytes and proplatelet biogenesis. Moreover, the use of BT2, the agonist of BCAA catabolism, could affect proplatelet formation (PPF) and megakaryocyte polyploidization, as well as ameliorating the thrombocythemia of BCAA-fed mice.

CONCLUSION

We found that deficiency in BCAA catabolism led to the activation of p70S6K/mammalian target of rapamycin (mTOR) signaling, megakaryocyte over differentiation, and the acceleration of PPF. Activating BCAA metabolism with BT2 could inhibit mTOR signaling, reduce PPF, and ameliorate thrombocythemia in BCAA-fed mice. Therefore, this study reveals a novel role of BCAAs in megakaryocyte differentiation and platelet production, suggesting that targeting BCAA-mediated p70S6K/mTOR signaling may be a potential strategy for the treatment of thrombocytopenia or thrombocythemia.

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.

Myocardial Metabolomics of Human Heart Failure With Preserved Ejection Fraction

BACKGROUND

The human heart primarily metabolizes fatty acids, and this decreases as alternative fuel use rises in heart failure with reduced ejection fraction (HFrEF). Patients with severe obesity and diabetes are thought to have increased myocardial fatty acid metabolism, but whether this is found in those who also have heart failure with preserved ejection fraction (HFpEF) is unknown.

METHODS

Plasma and endomyocardial biopsies were obtained from HFpEF (n=38), HFrEF (n=30), and nonfailing donor controls (n=20). Quantitative targeted metabolomics measured organic acids, amino acids, and acylcarnitines in myocardium (72 metabolites) and plasma (69 metabolites). The results were integrated with reported RNA sequencing data. Metabolomics were analyzed using agnostic clustering tools, Kruskal-Wallis test with Dunn test, and machine learning.

RESULTS

Agnostic clustering of myocardial but not plasma metabolites separated disease groups. Despite more obesity and diabetes in HFpEF versus HFrEF (body mass index, 39.8 kg/m2 versus 26.1 kg/m2; diabetes, 70% versus 30%; both P<0.0001), medium- and long-chain acylcarnitines (mostly metabolites of fatty acid oxidation) were markedly lower in myocardium from both heart failure groups versus control. In contrast, plasma levels were no different or higher than control. Gene expression linked to fatty acid metabolism was generally lower in HFpEF versus control. Myocardial pyruvate was higher in HFpEF whereas the tricarboxylic acid cycle intermediates succinate and fumarate were lower, as were several genes controlling glucose metabolism. Non-branched-chain and branched-chain amino acids (BCAA) were highest in HFpEF myocardium, yet downstream BCAA metabolites and genes controlling BCAA metabolism were lower. Ketone levels were higher in myocardium and plasma of patients with HFrEF but not HFpEF. HFpEF metabolomic-derived subgroups were differentiated by only a few differences in BCAA metabolites.

CONCLUSIONS

Despite marked obesity and diabetes, HFpEF myocardium exhibited lower fatty acid metabolites compared with HFrEF. Ketones and metabolites of the tricarboxylic acid cycle and BCAA were also lower in HFpEF, suggesting insufficient use of alternative fuels. These differences were not detectable in plasma and challenge conventional views of myocardial fuel use in HFpEF with marked diabetes and obesity and suggest substantial fuel inflexibility in this syndrome.

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.

Branched chain amino acids catabolism as a source of new drug targets in pathogenic protists

Leucine, isoleucine, and valine, collectively termed Branched Chain Amino Acids (BCAA), are hydrophobic amino acids (AAs) and are essential for most eukaryotes since in these organisms they cannot be biosynthesized and must be supplied by the diet. These AAs are structurally relevant for muscle cells and, of course, important for the protein synthesis process. The metabolism of BCAA and its participation in different biological processes in mammals have been relatively well described. However, for other organisms as pathogenic parasites, the literature is really scarce. Here we review the BCAA catabolism, compile evidence on their relevance for pathogenic eukaryotes with special emphasis on kinetoplastids and highlight unique aspects of this underrated pathway.

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.

Metabolomics profile and 10-year atherosclerotic cardiovascular disease (ASCVD) risk score

Background

The intermediate metabolites associated with the development of atherosclerotic cardiovascular disease (ASCVD) remain largely unknown. Thus, we conducted a large panel of metabolomics profiling to identify the new candidate metabolites that were associated with 10-year ASCVD risk.

Methods

Thirty acylcarnitines and twenty amino acids were measured in the fasting plasma of 1,102 randomly selected individuals using a targeted FIA-MS/MS approach. The 10-year ASCVD risk score was calculated based on 2013 ACC/AHA guidelines. Accordingly, the subjects were stratified into four groups: low-risk (n = 620), borderline-risk (n = 110), intermediate-risk (n = 225), and high-risk (n = 147). 10 factors comprising collinear metabolites were extracted from principal component analysis.

Results

C₄DC, C_8:1, C₁₆OH, citrulline, histidine, alanine, threonine, glycine, glutamine, tryptophan, phenylalanine, glutamic acid, arginine, and aspartic acid were significantly associated with the 10-year ASCVD risk score (p-values ≤ 0.044). The high-risk group had higher odds of factor 1 (12 long-chain acylcarnitines, OR = 1.103), factor 2 (5 medium-chain acylcarnitines, OR = 1.063), factor 3 (methionine, leucine, valine, tryptophan, tyrosine, phenylalanine, OR = 1.074), factor 5 (6 short-chain acylcarnitines, OR = 1.205), factor 6 (5 short-chain acylcarnitines, OR = 1.229), factor 7 (alanine, proline, OR = 1.343), factor 8 (C_18:2OH, glutamic acid, aspartic acid, OR = 1.188), and factor 10 (ornithine, citrulline, OR = 1.570) compared to the low-risk ones; the odds of factor 9 (glycine, serine, threonine, OR = 0.741), however, were lower in the high-risk group. "D-glutamine and D-glutamate metabolism", "phenylalanine, tyrosine, and tryptophan biosynthesis", and "valine, leucine, and isoleucine biosynthesis" were metabolic pathways having the highest association with borderline/intermediate/high ASCVD events, respectively.

Conclusions

Abundant metabolites were found to be associated with ASCVD events in this study. Utilization of this metabolic panel could be a promising strategy for early detection and prevention of ASCVD events.

Branched-chain α-keto acids and glutamate/glutamine: Biomarkers of insulin resistance in childhood obesity

OBJECTIVES

Insulin resistance (IR) in adolescents with obesity is associated with a sex-dependent metabolic 'signature' comprising the branched-chain amino acids (BCAAs), glutamate/glutamine, C3/C5 acylcarnitines and uric acid. Here, we compared the levels of branched-chain α-keto acids (BCKAs) and glutamate/glutamine, which are the byproducts of BCAA catabolism and uric acid among adolescents with obesity prior to and following a 6-month lifestyle-intervention program.

METHODS

Fasting plasma samples from 33 adolescents with obesity (16 males, 17 females, aged 12-18 year) were analysed by flow-injection tandem MS and LC-MS/MS. Multiple linear regression models were used to correlate changes in BCKAs, glutamate/glutamine and uric acid with changes in weight and insulin sensitivity as assessed by HOMA-IR, adiponectin and the ratio of triglyceride (TG) to HDL. In predictive models, BCKAs, glutamate/glutamine and uric acid at baseline were used as explanatory variables.

RESULTS

Baseline BCKAs, glutamate/glutamine and uric acid were higher in males than females despite comparable BMI-metrics. Following lifestyle-intervention, α-keto-β-methylvalerate (α-KMV, a metabolic by product of isoleucine) decreased in males but not in females. The ratio of BCKA/BCAA trended lower in males. In the cohort as a whole, BCKAs correlated positively with the ratio of TG to HDL at baseline and HOMA-IR at 6-month-follow-up. Glutamate/glutamine was positively associated with HOMA-IR at baseline and 6-month-follow-up. A reduction in BCKAs was associated with an increase in adiponectin, and those with higher BCKAs at baseline had higher adiponectin levels at 6-month-follow-up. Interestingly those adolescents with higher uric acid levels at baseline had greater reduction in weight.

CONCLUSIONS

BCKAs and glutamate/glutamine may serve as biomarkers of IR in adolescents with obesity, and uric acid might serve as a predictor of weight loss in response to lifestyle-intervention. Differential regulation of BCAA catabolism in adolescent males and females implicates critical roles for sex steroids in metabolic homeostasis.

An extensive bioinformatics study on the role of mitochondrial solute carrier family 25 in PC and its mechanism behind affecting immune infiltration and tumor energy metabolism

BACKGROUND

Several metabolic disorders and malignancies are directly related to abnormal mitochondrial solute carrier family 25 (SLC25A) members activity. However, its biological role in pancreatic cancer (PC) is not entirely understood.

METHODS

The lasso method was used to create a novel prognostic risk model for PC based on SLC25A members, and its roles in tumor immunology and energy metabolism were explored. Furthermore, co-expression networks were constructed for SLC25A11, SLC25A29, and SLC25A44. Single-cell RNA sequencing (ScRNA-seq) revealed the distribution of gene expression in PC. Tumor immune infiltration was examined with the TIMER database. Lastly, drug sensitivity was investigated, and co-transcriptional factors were predicted.

RESULTS

In the present study, a novel prognostic risk model was established and validated for PC based on SLC25A members. The high-risk group had a lower activation of oxidative phosphorylation and a more abundant immune infiltration phenotype than the low-risk group. According to co-expression network studies, SLC25A11, SLC25A29, and SLC25A44 were involved in the energy metabolism of PC and prevented tumor growth, invasion, and metastasis. ScRNA-seq research also pointed to their contribution to the tumor microenvironment. Moreover, the recruitment of numerous immune cells was positively correlated with SLC25A11 and SLC25A44 but negatively correlated with SLC25A29. Additionally, the sensitivity to 20 Food and Drug Administration-approved antineoplastic medicines was strongly linked to the aforementioned genes, where cisplatin sensitivity increased with the up-regulation of SLC25A29. Finally, the Scleraxis BHLH Transcription Factor (SCX) and other proteins were hypothesized to co-regulate the mRNA transcription of the genes.

CONCLUSION

SLC25A members are crucial for tumor immune and energy metabolism in PC, and SLC25A11, SLC25A29, and SLC25A44 can be used as favorable prognostic markers. The use of these markers will provide new directions to unravel their action mechanisms in PC.

Metabolon formation regulates branched-chain amino acid oxidation and homeostasis

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

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.

Maternal Exercise and Paternal Exercise Induce Distinct Metabolite Signatures in Offspring Tissues

That maternal and paternal exercise improve the metabolic health of adult offspring is well established. Tissue and serum metabolites play a fundamental role in the health of an organism, but how parental exercise affects offspring tissue and serum metabolites has not yet been investigated. Here, male and female breeders were fed a high-fat diet and housed with or without running wheels before breeding (males) and before and during gestation (females). Offspring were sedentary and chow fed, with parents as follows: sedentary (Sed), maternal exercise (MatEx), paternal exercise (PatEx), or maternal+paternal exercise (Mat+PatEx). Adult offspring from all parental exercise groups had similar improvement in glucose tolerance and hepatic glucose production. Targeted metabolomics was performed in offspring serum, liver, and triceps muscle. Offspring from MatEx, PatEx, and Mat+PatEx each had a unique tissue metabolite signature, but Mat+PatEx offspring had an additive phenotype relative to MatEx or PatEx alone in a subset of liver and muscle metabolites. Tissue metabolites consistently indicated that the metabolites altered with parental exercise contribute to enhanced fatty acid oxidation. These data identify distinct tissue-specific adaptations and mechanisms for parental exercise-induced improvement in offspring metabolic health. Further mining of this data set could aid the development of novel therapeutic targets to combat metabolic diseases.

Myocardial disturbances of intermediary metabolism in Barth syndrome

Barth Syndrome (BTHS) is a rare X-linked mitochondrial disorder due to mutations in the gene TAFAZZIN, which leads to immature cardiolipin (CL) remodeling and is characterized by the development of cardiomyopathy. The immature CL remodeling in BTHS results in electron transport chain respiratory defects and destabilization of supercomplexes, thereby impairing ATP production. Thus, BTHS-related cardiomyopathy appears to share metabolic characteristics of the failing heart being an "engine out of fuel." As CL associates with numerous mitochondrial enzymes involved in ATP production, BTHS is also characterized by several defects in intermediary energy metabolism. Herein we will describe the primary disturbances in intermediary energy metabolism relating to the heart's major fuel sources, fatty acids, carbohydrates, ketones, and amino acids. In addition, we will interrogate whether these disturbances represent potential metabolic targets for alleviating BTHS-related cardiomyopathy.

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.

Tirzepatide induces a thermogenic-like amino acid signature in brown adipose tissue

Objectives

Tirzepatide, a dual GIP and GLP-1 receptor agonist, delivered superior glycemic control and weight loss compared to selective GLP-1 receptor (GLP-1R) agonism in patients with type 2 diabetes (T2D). These results have fueled mechanistic studies focused on understanding how tirzepatide achieves its therapeutic efficacy. Recently, we found that treatment with tirzepatide improves insulin sensitivity in humans with T2D and obese mice in concert with a reduction in circulating levels of branched-chain amino (BCAAs) and keto (BCKAs) acids, metabolites associated with development of systemic insulin resistance (IR) and T2D. Importantly, these systemic effects were found to be coupled to increased expression of BCAA catabolic genes in thermogenic brown adipose tissue (BAT) in mice. These findings led us to hypothesize that tirzepatide may lower circulating BCAAs/BCKAs by promoting their catabolism in BAT.

Methods

To address this question, we utilized a murine model of diet-induced obesity and employed stable-isotope tracer studies in combination with metabolomic analyses in BAT and other tissues.

Results

Treatment with tirzepatide stimulated catabolism of BCAAs/BCKAs in BAT, as demonstrated by increased labeling of BCKA-derived metabolites, and increases in levels of byproducts of BCAA breakdown, including glutamate, alanine, and 3-hydroxyisobutyric acid (3-HIB). Further, chronic administration of tirzepatide increased levels of multiple amino acids in BAT that have previously been shown to be elevated in response to cold exposure. Finally, chronic treatment with tirzepatide led to a substantial increase in several TCA cycle intermediates (α-ketoglutarate, fumarate, and malate) in BAT.

Conclusions

These findings suggest that tirzepatide induces a thermogenic-like amino acid profile in BAT, an effect that may account for reduced systemic levels of BCAAs in obese IR mice.

•

Tirzepatide augments the catabolism of BCAA in brown adipose tissue (BAT) of obese mice.

•

Tirzepatide promotes BCAA catabolism in BAT, despite its lower potency to activate the mouse GIPR relative to mouse GIP.

•

Tirzepatide increases amino acids and TCA cycle intermediates in BAT, as also observed in BAT thermogenesis.

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.

Proteomics and phosphoproteomics datasets of a muscle-specific STIM1 loss-of-function mouse model

STIM1 is an ER/SR transmembrane protein that interacts with ORAI1 to activate store operated Ca2+ entry (SOCE) upon ER/SR depletion of calcium. Normally highly expressed in skeletal muscle, STIM1 deficiency causes significant changes to mitochondrial ultrastructure that do not occur with loss of ORAI1 or other components of SOCE. The datasets in this article are from large-scale proteomics and phosphoproteomics experiments in an inducible mouse model of skeletal muscle-specific STIM1 knock out (KO). These data reveal statistically significant changes in the relative abundance of specific proteins and sites of protein phosphorylation in STIM1 KO gastrocnemius. Protein samples from five biological replicates of each condition (+/- STIM1) were enzymatically digested, the resulting peptides labeled with tandem mass tag (TMT) reagents, mixed, and fractionated. Phosphopeptides were enriched and a small amount of each input retained for protein abundance analysis. All phosphopeptide and input fractions were analyzed by nano LC-MS/MS on a Q Exactive Plus Orbitrap mass spectrometer, searched with Proteome Discoverer software, and processed with in-house R-scripts for data normalization and statistical analysis. Article published in Molecular Metabolism [1].

Temporal proteomics reveal specific cell cycle oncoprotein downregulation by p97/VCP inhibition

Targeting protein quality control (PQC) pathways using proteasome or p97/VCP inhibition can effectively treat blood tumors. However, in solid tumors, only p97/VCP inhibitors are effective. To probe this difference in efficacy, we tracked HCT116 colon cancer cells using temporal proteomics to define the cellular and molecular responses to proteasome and p97 inhibition. Proteins involved in general PQC pathways were similarly upregulated by both treatments, suggesting that the proteotoxic stress caused by inhibitors does not explain the differential therapeutic effectiveness. Unexpectedly, proteins specifically dysregulated by two p97 inhibitors are involved in cell cycle control. Indeed, eleven cell cycle proteins were downregulated by p97 inhibition but not by proteasome inhibition. Western blot analysis validated the degradation of cyclin D1 and Securin, which depends on proteasome but not on p97. Differing regulation of cell cycle proteins by p97 and the proteasome may, therefore, explain the therapeutic efficacy of p97 inhibitors in colon cancer.

Disruption of STIM1-mediated Ca2+ sensing and energy metabolism in adult skeletal muscle compromises exercise tolerance, proteostasis, and lean mass

OBJECTIVE

Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane endoplasmic/sarcoplasmic reticulum (E/SR) protein recognized for its role in a store operated Ca2+ entry (SOCE), an ancient and ubiquitous signaling pathway. Whereas STIM1 is known to be indispensable during development, its biological and metabolic functions in mature muscles remain unclear.

METHODS

Conditional and tamoxifen inducible muscle STIM1 knock-out mouse models were coupled with multi-omics tools and comprehensive physiology to understand the role of STIM1 in regulating SOCE, mitochondrial quality and bioenergetics, and whole-body energy homeostasis.

RESULTS

This study shows that STIM1 is abundant in adult skeletal muscle, upregulated by exercise, and is present at SR-mitochondria interfaces. Inducible tissue-specific deletion of STIM1 (iSTIM1 KO) in adult muscle led to diminished lean mass, reduced exercise capacity, and perturbed fuel selection in the settings of energetic stress, without affecting whole-body glucose tolerance. Proteomics and phospho-proteomics analyses of iSTIM1 KO muscles revealed molecular signatures of low-grade E/SR stress and broad activation of processes and signaling networks involved in proteostasis.

CONCLUSION

These results show that STIM1 regulates cellular and mitochondrial Ca2+ dynamics, energy metabolism and proteostasis in adult skeletal muscles. Furthermore, these findings provide insight into the pathophysiology of muscle diseases linked to disturbances in STIM1-dependent Ca2+ handling.

New Insights Into Energy Substrate Utilization and Metabolic Remodeling in Cardiac Physiological Adaption

Cardiac function highly relies on sufficient energy supply. Perturbations in myocardial energy metabolism play a causative role in cardiac pathogenesis. Accumulating evidence has suggested that modifications of cardiac metabolism are also an essential part of the adaptive responses to various physiological conditions in the heart to meet specific energy needs. The review highlighted some new studies on basic myocardial energy substrate metabolism and updated recent findings regarding cardiac metabolic remodeling and their associated mechanisms under physiological conditions, including exercise and cardiac development. Studying basic metabolic profiles in the heart in these conditions can contribute to understanding the significance of metabolic regulation in the heart during physiological adaption and gaining further insights into the maladaptive metabolic changes associated with cardiac pathogenesis, thus opening up new avenues to exploring novel therapeutic strategies in cardiac diseases.

A Novel Compound, Tanshinol Borneol Ester, Ameliorates Pressure Overload-Induced Cardiac Hypertrophy by Inhibiting Oxidative Stress via the mTOR/β-TrCP/NRF2 Pathway

Tanshinol borneol ester (DBZ) exerts anti-atherosclerotic and anti-inflammatory effects. However, its effects on cardiac hypertrophy are not well understood. In this work, we investigated the treatment effects and potential mechanisms of DBZ on the hypertrophic heart under oxidative stress and endoplasmic reticulum (ER) stress. A hypertrophic model was established in rats using transverse-aortic constriction (TAC) surgery and in neonatal rat cardiomyocytes (NRCMs) using angiotensin II (Ang II). Our results revealed that DBZ remarkably inhibited oxidative stress and ER stress, blocked autophagy flow, and decreased apoptosis in vivo and in vitro through nuclear NRF2 accumulation, and enhanced NRF2 stability via regulating the mTOR/β-TrcP/NRF2 signal pathway. Thus, DBZ may serve as a promising therapeutic for stress-induced cardiac hypertrophy.

Mitochondria in Pathological Cardiac Remodeling

Adverse cardiac remodeling is often precipitated by chronic stress or injury inflicted upon the heart during the progression of cardiovascular diseases. Mitochondria play an important role in the cardiomyocyte response to stress by serving as a signaling hub for changes in cellular energetics, redox balance, contractile function, and cell death. Cardiac remodeling involves alterations to mitochondrial form and function that are either compensatory to maintain contractility or maladaptive, which promotes heart failure progression. In this mini-review, we focus on three mitochondrial processes that contribution to cardiac remodeling: Ca²⁺ signaling, mitochondrial dynamics, and mitochondrial metabolism.

The early reduction of left ventricular mass after sleeve gastrectomy depends on the fall of branched-chain amino acid circulating levels

Introduction

Body-mass index is a major determinant of left-ventricular-mass (LVM). Bariatric-metabolic surgery (BMS) reduces cardiovascular mortality. Its mechanism of action, however, often encompasses a weight-dependent effect. In this translational study, we aimed at investigating the mechanisms by which BMS leads to LVM reduction and functional improvement.

Methods

Twenty patients (45.2 ± 8.5years) were studied with echocardiography at baseline and at 1,6,12 and 48 months after sleeve-gastrectomy (SG). Ten Wistar rats aged 10-weeks received high-fat diet ad libitum for 10 weeks before and 4 weeks after SG or sham-operation. An oral-glucose-tolerance-test was performed to measure whole-body insulin-sensitivity. Plasma metabolomics was analysed in both human and rodent samples. RNA quantitative Real-Time PCR and western blots were performed in rodent heart biopsies. The best-fitted partial-least-square discriminant-analysis model was used to explore the variable importance in the projection score of all metabolites.

Findings

Echocardiographic LVM (-12%,-23%,-28% and -43% at 1,6,12 and 48 months, respectively) and epicardial fat decreased overtime after SG in humans while insulin-sensitivity improved. In rats, SG significantly reduced LVM and epicardial fat, enhanced ejection-fraction and improved insulin-sensitivity compared to sham-operation. Metabolomics showed a progressive decline of plasma branched-chain amino-acids (BCAA), alanine, lactate, 3-OH-butyrate, acetoacetate, creatine and creatinine levels in both humans and rodents.

Hearts of SG rats had a more efficient BCAA, glucose and fatty-acid metabolism and insulin signaling than sham-operation. BCAAs in cardiomyocyte culture-medium stimulated lipogenic gene transcription and reduced mRNA levels of key mitochondrial β-oxidation enzymes promoting lipid droplet accumulation and glycolysis.

Interpretation

After SG a prompt and sustained decrease of the LVM, epicardial fat and insulin resistance was found. Animal and in vitro studies showed that SG improves cardiac BCAA metabolism with consequent amelioration of fat oxidation and insulin signaling translating into decreased intra-myocytic fat accumulation and reduced lipotoxicity.

Effects of Tirzepatide, a Dual GIP and GLP-1 RA, on Lipid and Metabolite Profiles in Subjects With Type 2 Diabetes

CONTEXT

Tirzepatide substantially reduced hemoglobin A1c (HbA1c) and body weight in subjects with type 2 diabetes (T2D) compared with the glucagon-like peptide 1 receptor agonist dulaglutide. Improved glycemic control was associated with lower circulating triglycerides and lipoprotein markers and improved markers of beta-cell function and insulin resistance (IR), effects only partially attributable to weight loss.

OBJECTIVE

Assess plasma metabolome changes mediated by tirzepatide.

DESIGN

Phase 2b trial participants were randomly assigned to receive weekly subcutaneous tirzepatide, dulaglutide, or placebo for 26 weeks. Post hoc exploratory metabolomics and lipidomics analyses were performed.

SETTING

Post hoc analysis.

PARTICIPANTS

259 subjects with T2D.

INTERVENTION(S)

Tirzepatide (1, 5, 10, 15 mg), dulaglutide (1.5 mg), or placebo.

MAIN OUTCOME MEASURE(S)

Changes in metabolite levels in response to tirzepatide were assessed against baseline levels, dulaglutide, and placebo using multiplicity correction.

RESULTS

At 26 weeks, a higher dose tirzepatide modulated a cluster of metabolites and lipids associated with IR, obesity, and future T2D risk. Branched-chain amino acids, direct catabolic products glutamate, 3-hydroxyisobutyrate, branched-chain ketoacids, and indirect byproducts such as 2-hydroxybutyrate decreased compared to baseline and placebo. Changes were significantly larger with tirzepatide compared with dulaglutide and directly proportional to reductions of HbA1c, homeostatic model assessment 2-IR indices, and proinsulin levels. Proportional to metabolite changes, triglycerides and diglycerides were lowered significantly compared to baseline, dulaglutide, and placebo, with a bias toward shorter and highly saturated species.

CONCLUSIONS

Tirzepatide reduces body weight and improves glycemic control and uniquely modulates metabolites associated with T2D risk and metabolic dysregulation in a direction consistent with improved metabolic health.

In-vivo production of branched-chain amino acids, branched-chain keto acids, and β-hydroxy β-methylbutyric acid

PURPOSE OF REVIEW

The branched-chain amino acids (BCAA), branched-chain keto acids (BCKA), and β-hydroxy β-methylbutyric acid (HMB) have regained interest as food ingredients in health and disease. To support nutritional strategies, it is critical to gain insight into the whole body and transorgan kinetics of these components. We, therefore, reviewed the most recent literature in this field on in vivo analysis of BCAA, BCKA, and HMB kinetics in health and disease.

RECENT FINDINGS

With a new comprehensive metabolic flux analysis BCAA, BCKA, and HMB whole body production, interconversion and disposal rates can be measured simultaneously. Recent studies have provided us with a better understanding of whole-body and transorgan kinetics under postabsorptive, postprandial, hibernating, and lactating conditions. In human pathophysiological conditions like COPD, obesity, and diabetes, the added value of BCAA kinetic measurements over the commonly used concentration measurements only, is discussed.

SUMMARY

This article highlights the importance of implementing BCAA, BCKA, and HMB kinetic studies to further advance the field by gaining more mechanistic insights and providing direction to the development of new targeted (nutritional) strategies.

Pancreatic cancer: branched-chain amino acids as putative key metabolic regulators?

Branched-chain amino acids (BCAA) are essential amino acids utilized in anabolic and catabolic metabolism. While extensively studied in obesity and diabetes, recent evidence suggests an important role for BCAA metabolism in cancer. Elevated plasma levels of BCAA are associated with an increased risk of developing pancreatic cancer, namely pancreatic ductal adenocarcinoma (PDAC), a tumor with one of the highest 1-year mortality rates. The dreadful prognosis for PDAC patients could be attributable also to the early and frequent development of cancer cachexia, a fatal host metabolic reprogramming leading to muscle and adipose wasting. We propose that BCAA dysmetabolism is a unifying component of several pathological conditions, i.e., obesity, insulin resistance, and PDAC. These conditions are mutually dependent since PDAC ranks among cancers tightly associated with obesity and insulin resistance. It is also well-established that PDAC itself can trigger insulin resistance and new-onset diabetes. However, the exact link between BCAA metabolism, development of PDAC, and tissue wasting is still unclear. Although tissue-specific intracellular and systemic metabolism of BCAA is being intensively studied, unresolved questions related to PDAC and cancer cachexia remain, namely, whether elevated circulating BCAA contribute to PDAC etiology, what is the biological background of BCAA elevation, and what is the role of adipose tissue relative to BCAA metabolism during cancer cachexia. To cover those issues, we provide our view on BCAA metabolism at the intracellular, tissue, and whole-body level, with special emphasis on different metabolic links to BCAA intermediates and the role of insulin in substrate handling.

Relationship of Nonalcoholic Fatty Liver Disease and Heart Failure With Preserved Ejection Fraction

Although there is an established bidirectional relationship between heart failure with reduced ejection fraction and liver disease, the association between heart failure with preserved ejection fraction (HFpEF) and liver diseases, such as nonalcoholic fatty liver disease (NAFLD), has not been well explored. In this paper, the authors provide an in-depth review of the relationship between HFpEF and NAFLD and propose 3 NAFLD-related HFpEF phenotypes (obstructive HFpEF, metabolic HFpEF, and advanced liver fibrosis HFpEF). The authors also discuss diagnostic challenges related to the concurrent presence of NAFLD and HFpEF and offer several treatment options for NAFLD-related HFpEF phenotypes. The authors propose that NAFLD-related HFpEF should be recognized as a distinct HFpEF phenotype.