Myocardial Metabolomics of Human Heart Failure With Preserved Ejection Fraction

The addition of alpha-ketoglutarate to NT-proBNP improves the prediction of long-term all-cause mortality in acute heart failure patients

BACKGROUND AND OBJECTIVE

Alpha-ketoglutarate (AKG), is a major intermediate metabolite of the tricarboxylic acid cycle, and is closely associated with cardiometabolic disease prognosis. Previous studies indicated that AKG is related to myocardial energy expenditure levels and reflects adverse short-term outcomes in heart failure (HF) patients. In this prospective cohort study, we examined the long-term prognostic value of AKG levels in acute HF (AHF) patients.

METHODS

Plasma AKG levels were assessed in patients hospitalized with AHF. Hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause mortality were calculated via multiple Cox regression. All-cause mortality was compared between patients with NT-proBNP < 1000 pg/ml and those with NT-proBNP ≥ 1000 pg/ml via subgroup analysis.

RESULTS

Patients with AKG ≥ 9.83 μg/ml had higher heart rates and NT-proBNP and lower left ventricular ejection fraction (LVEF) and systolic blood pressure (SBP). After multiple adjustment, higher AKG was associated with an increased all-cause mortality risk (HR = 1.078, p < 0.001). Compared with AKG < 9.83 μg/ml, AKG ≥ 9.83 μg/ml nearly doubled (HR = 1.929, p < 0.001) and quadrupled (HR = 4.160, p < 0.001) the all-cause mortality risk in patients with NT-proBNP ≥ 1000 pg/ml and those with NT-proBNP < 1000 pg/ml, respectively.

CONCLUSIONS AND RELEVANCE

Plasma AKG was independently associated with greater all-cause mortality risk in patients with AHF. Higher AKG levels retained prognostic value for patients with relatively low NT-proBNP.

Lipidomics and cardiovascular disease

Cardiovascular diseases (CVDs) remain the leading cause of mortality worldwide, necessitating innovative approaches for early detection and personalized interventions. Lipidomics, leveraging advanced mass spectrometry techniques, has become instrumental in deciphering lipid-mediated mechanisms in CVDs. This review explores the application of lipidomics in identifying biomarkers for myocardial infarction, heart failure, stroke, and calcific aortic valve stenosis (CAVS). This review examines the technological advancements in shotgun lipidomics and LC/MS, which provide unparalleled insights into lipid composition and function. Key lipid biomarkers, including ceramides and lysophospholipids, have been linked to disease progression and therapeutic outcomes. Integrating lipidomics with genomic and proteomic data reveals the molecular underpinnings of CVDs, enhancing risk prediction and intervention strategies. This review positions lipidomics as a transformative tool in reshaping cardiovascular research and clinical practice.

Myeloid Fatty Acid Metabolism Activates Neighboring Hematopoietic Stem Cells to Promote Heart Failure With Preserved Ejection Fraction

BACKGROUND

Despite the high morbidity and mortality of heart failure with preserved ejection fraction (HFpEF), treatment options remain limited. The HFpEF syndrome is associated with a high comorbidity burden, including high prevalence of obesity and hypertension. Although inflammation is implicated to play a key role in HFpEF pathophysiology, underlying causal mechanisms remain unclear.

METHODS

Comparing patient samples and animal models, we defined the innate immune response during HFpEF in situ and through flow cytometry and single-cell RNA sequencing. After identifying transcriptional and cell signatures, we implemented a high-fat diet and hypertensive model of HFpEF and tested roles for myeloid and hematopoietic stem cells during HFpEF. Contributions of macrophage metabolism were also evaluated, including through mass spectrometry and carbon labeling. Primary macrophages were studied ex vivo to gain insight into complementary cell-intrinsic mechanisms.

RESULTS

Here we report evidence that patients with cardiometabolic HFpEF exhibit elevated peripheral blood hematopoietic stem cells. This phenotype was conserved across species in a murine mode of high-fat diet and hypertension. Hematopoietic stem cell proliferation was coupled to striking remodeling of the peripheral hematopoietic stem cell niche and expression of the macrophage adhesion molecule Vcam1. This could be partially inhibited by sodium-glucose cotransporter-2 inhibitors and explained by elevated fatty acid metabolism in macrophage mitochondria, which in turn remodeled the Vcam1 promoter to enhance its expression.

CONCLUSIONS

These findings identify a significant new stem cell signature of cardiometabolic HFpEF and support a role for myeloid maladaptive fatty acid metabolism in the promotion of systemic inflammation and cardiac diastolic dysfunction.

Association between triglyceride-glucose index and all cause mortality in critically ill patients with heart failure

The triglyceride-glucose (TyG) index is regarded as a surrogate marker of systemic insulin resistance (IR). Studies have substantiated the impact of IR on cardiovascular diseases. Nonetheless, the prognostic value of the TyG index in critical patients with heart failure (HF) with intensive care unit (ICU) admission remains unclear. This study aims to assess the association between the TyG index and all-cause mortality in critically ill patients with HF. Patients with HF requiring ICU admission were identified from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database and subsequently stratified into quartiles based on their TyG index. The primary outcome was 30-day all-cause mortality, and the secondary outcome was 1-year all-cause mortality. The relationship between the TyG index and all-cause mortality in HF patients was analyzed using multivariable Cox proportional hazards models and restricted cubic splines. A total of 1220 patients (62.4% men) were enrolled, with a mean age of 70.6 years. The 30-day and one-year all-cause mortality rate were 15.7% and 34.6%, respectively. Multivariable Cox regression revealed that TyG index was significantly associated with an elevated risk of 30-day all-cause mortality (adjusted HR, 1.360; 95% CI, 1.093-1.694; P = 0.006), but not with one-year mortality (adjusted HR 1.046; 95% CI 0.895-1.222, P = 0.574). Restricted cubic splines showed a progressively increasing risk of 30-day mortality was linearly related to an elevated TyG index. Subgroup analyses indicated a more prominent association between TyG index and 30-day mortality in patients with age ≤ 65, female or BMI > 30 kg/m2. In critically ill patients with HF, the TyG index is significantly associated with short-term all-cause mortality. Our results highlight that the TyG index can be useful in identifying HF patients at high risk of all-cause mortality and require close follow-up after discharge.

Fibroblast growth factor 23 and fibroblast growth factor receptor 4 promote cardiac metabolic remodeling in chronic kidney disease

Chronic kidney disease (CKD) is a global health epidemic that greatly increases mortality due to cardiovascular disease. Left ventricular hypertrophy (LVH) is an important mechanism of cardiac injury in CKD. High serum levels of fibroblast growth factor (FGF) 23 in patients with CKD may contribute mechanistically to the pathogenesis of LVH by activating FGF receptor (FGFR) 4 signaling in cardiac myocytes. Mitochondrial dysfunction and cardiac metabolic remodeling are early features of cardiac injury that predate development of hypertrophy, but these mechanisms have been insufficiently studied in models of CKD. We found in wild-type mice with CKD induced by adenine diet, that morphological changes occurred in mitochondrial structure and cardiac mitochondrial and that metabolic dysfunction preceded the development of LVH. In bioengineered cardio-bundles and neonatal rat ventricular myocytes grown in vitro, FGF23-mediated activation of FGFR4 caused mitochondrial pathology, characterized by increased bioenergetic stress and increased glycolysis that preceded the development of cellular hypertrophy. The cardiac metabolic changes and associated mitochondrial alterations in mice with CKD were prevented by global and cardiac-specific deletion of FGFR4. Our findings indicate that metabolic remodeling and mitochondrial dysfunction are early cardiac complications of CKD that precede structural remodeling of the heart. Mechanistically, FGF23-mediated activation of FGFR4 causes mitochondrial dysfunction, suggesting that early pharmacologic inhibition of FGFR4 might serve as novel therapeutic intervention to prevent development of LVH and heart failure in patients with CKD.

The role of sphingolipids in heart failure

Advanced heart failure (HF) is characterized by changes in the structure, function, and metabolism of cardiac muscle. As the disease progresses, cardiomyocytes shift their ATP production from fatty acid oxidation to glycolysis. This shift results in an accumulation of lipid metabolites, particularly sphingolipids, which can disrupt normal cellular function and contribute to cardiac dysfunction. In animal models of obesity, accumulation of toxic sphingolipid metabolites in the heart has been described as cardiac lipotoxicity. In humans, HF is classified into two groups based on ejection fraction (EF): HF with reduced EF of less than 40% (HFrEF) and HF with preserved EF of greater than 50% (HFpEF). Despite shared risk factors and comorbidities, the structural and cellular differences between HFrEF and HFpEF distinguish them as separate conditions. Ceramides (Cer), a type of sphingolipid, have gained significant attention for their involvement in the development and prognosis of atherosclerotic disease and myocardial infarction, while sphingosine-1-phosphate, a downstream product of Cer, has shown cardioprotective properties. The aim of this review is to describe the role of sphingolipids in HF with reduced and preserved EF. By understanding the role of sphingolipids through animal and human studies, this review aims to pave the way for developing strategies that target abnormal signalling pathways in the failing heart, ultimately bridging the gap between scientific research and clinical applications.

The plasma proteome is linked to echocardiographic parameters and stages of diastolic dysfunction, across the ejection fraction spectrum

INTRODUCTION

This study investigates the interplay between the circulating plasma proteome and echocardiographic parameters in patients across the spectrum of heart failure (HF) (ranging from patients at risk of/with preserved (HFpEF) to reduced (HFrEF) ejection fraction).

METHODS

Data from two cohort studies, HELPFul and Bio-SHiFT, were analyzed. We measured 4210 circulating plasma proteins in a total of 750 patients using SomaScan® proteomics. Echocardiographic parameters in both studies included left ventricular ejection fraction (LVEF) and the ratio of the peak early left ventricular (LV) filling velocity and early diastolic mitral annular velocity (E/e'). In further analyses, we classified patients in left ventricular diastolic dysfunction (LVDD) groups according to the prevailing guidelines.

RESULTS

Out of the 4210 plasma proteins, 21 proteins were significantly associated with E/e' in patients at risk of/with HFpEF, whereas 9 proteins were associated with LVEF. Approximately 43 % (n = 1822) of the proteins showed significant interactions between E/e' and HF subtype. All of these proteins showed weaker associations with E/e' in patients at risk of/with HFpEF compared to the ones with HFrEF. These proteins were related to the extracellular matrix, cellular processes, insulin-like growth factor (IGF) transport, metabolic and catabolic processes. Furthermore, comparisons between LVDD groups and those with normal diastolic function identified 40 proteins associated with grade 2 (top 5: Cystatin C, TMEDA, NT-proBNP, GDF-15 and PXDN) and 198 with grade 3 LVDD (top 5: NT-proBNP, Cystatin C, PXDN, RNasa1, and Factor D).

CONCLUSION

In patients at risk of/with HFpEF, biological processes and pathways showed weaker associations with E/e' compared to patients with HFrEF. Varying pathways identified through proteomics were associated with deterioration of LVDD across the ejection fraction spectrum. Our results are in line with the mechanistic frameworks currently thought to underlie the various types of HF.

Valine acts as an early biomarker and exacerbates pathological cardiac hypertrophy by impairing mitochondrial quality control

OBJECTIVE

Pathological cardiac hypertrophy is an independent risk factor for heart failure (HF). Early identification and timely treatment are crucial for significantly delaying the progression of HF.

METHODS

Targeted amino acid metabolomics and RNA sequencing (RNA-seq) were combined to explore the underlying mechanism. In vitro, H9c2 cells were stimulated with angiotensin II (Ang II) or were incubated with extra valine after Ang II stimulation. The branched chain alpha-ketoate dehydrogenase kinase (Bckdk) inhibitor 3,6-dichlorobenzo[b]thiophene-2-carboxylic acid (BT2) and rapamycin were utilized to confirm the role of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in this process.

RESULTS

A significant accumulation of valine was detected within hypertrophic hearts from spontaneously hypertensive rats (SHR). When branched chain amino acid (BCAA) degradation was increased by BT2, the most pronounced decrease was observed in the valine level (Δ = 0.185 μmol/g, p < 0.001), and cardiac hypertrophy was ameliorated. The role of imbalanced mitochondrial quality control (MQC), including the suppression of mitophagy and excessive mitochondrial fission, was revealed in myocardial hypertrophy. In vitro, high concentrations of valine exacerbated cardiomyocyte hypertrophy stimulated by Any II, resulting in the accumulation of impaired mitochondria and respiratory chain dysfunction. BT2, rapamycin, and mitochondrial division inhibitor 1 (Mdivi-1) all ameliorated MQC imbalance, mitochondrial damage and oxidative stress in hypertensive models with high valine concentration.

CONCLUSION

Valine exacerbated pathological cardiac hypertrophy by causing a MQC imbalance, probably as an early biomarker for cardiac hypertrophy under chronic hypertension.

Impaired cardiac branched-chain amino acid metabolism in a novel model of diabetic cardiomyopathy

BACKGROUND

Systemic insulin resistance plays an important role in the pathogenesis of type 2 diabetes and its complications. Although impaired branched-chain amino acid (BCAA) metabolism has been reported to be involved in the development of diabetes, the relationship between cardiac BCAA metabolism and the pathogenesis of diabetic cardiomyopathy (DbCM) remains unclear.

OBJECTIVES

The aim of this study was to investigate BCAA metabolism in insulin-resistant hearts by using a novel mouse model of DbCM.

METHODS

The cardiac phenotypes of adipocyte-specific 3'-phosphoinositide-dependent kinase 1 (PDK1)-deficient (A-PDK1KO) mice were assessed by histological analysis and echocardiography. The metabolic characteristics and cardiac gene expression were determined by mass spectrometry or RNA sequencing, respectively. Cardiac protein expression was evaluated by Western blot analysis.

RESULTS

A-PDK1KO mouse hearts exhibited hypertrophy with prominent insulin resistance, consistent with cardiac phenotypes and metabolic disturbances previously reported as DbCM characteristics. RNA sequencing revealed the activation of BCAA uptake in diabetic hearts. In addition, the key enzymes involved in cardiac BCAA catabolism were downregulated at the protein level in A-PDK1KO mice, leading to the accumulation of BCAAs in the heart. Mechanistically, the accumulation of the BCAA leucine caused cardiac hypertrophy via the activation of mammalian target of rapamycin complex 1 (mTORC1).

CONCLUSIONS

A-PDK1KO mice closely mimic the cardiac phenotypes and metabolic alterations observed in human DbCM and exhibit impaired BCAA metabolism in the heart. This model may contribute to a better understanding of DbCM pathophysiology and to the development of novel therapies for this disease.

Plasma metabolomics identifies signatures that distinguish heart failure with reduced and preserved ejection fraction

AIMS

Two general phenotypes of heart failure (HF) are recognized: HF with reduced ejection fraction (HFrEF) and with preserved EF (HFpEF). To develop phenotype-specific approaches to treatment, distinguishing biomarkers are needed. The goal of this study was to utilize quantitative metabolomics on a large, diverse population to replicate and extend existing knowledge of the plasma metabolic signatures in human HF.

METHODS

Plasma metabolomics and proteomics was conducted on 787 samples collected by the Penn Medicine BioBank from subjects with HFrEF (n = 219), HFpEF (n = 357) and matched controls (n = 211). A total of 90 metabolites were analysed, comprising 28 amino acids, 8 organic acids and 54 acylcarnitines. Seven hundred thirty-three of these samples also underwent proteomic profiling via the O-Link proteomics panel.

RESULTS

Unsaturated forms of medium-/long-chain acylcarnitines were elevated in the HFrEF group. Amino acid derivatives, including 1- and 3-methylhistidine, homocitrulline and symmetric and asymmetric (ADMA) dimethylarginine were elevated in HF, with ADMA elevated uniquely in HFpEF. While the branched-chain amino acids (BCAAs) were minimally changed, short-chain acylcarnitine species indicative of BCAA catabolism were elevated in both HF groups. 3-hydroxybutyrate (3-HBA) and its metabolite, C4-OH carnitine, were uniquely elevated in the HFrEF group. Linear regression models demonstrated a significant correlation between plasma 3-HBA and N-terminal pro-brain natriuretic peptide in both forms of HF, stronger in HFrEF.

CONCLUSIONS

These results identify plasma signatures that are shared as well as potentially distinguish HFrEF and HFpEF. Metabolite markers for ketogenic metabolic re-programming were identified as unique signatures in the HFrEF group, possibly related to increased levels of BNP. Our results set the stage for future studies aimed at assessing selected metabolites as relevant biomarkers to guide HF phenotype-specific therapeutics.

Metabolomic profiling in heart failure as a new tool for diagnosis and phenotyping

Classifying heart failure (HF) by stages and ejection fraction (EF) remains a debated topic in cardiology. Metabolomic profiling (MP) offers a means to identify unique pathophysiological changes across different phenotypes, presenting a promising approach for the diagnosis and prognosis of HF, as well as for the development of targeted therapies. In our study, MP was performed on 408 HF patients (54.9% male). The mean ages of patients were 62 [53;68], 67 [65;74], 68 [61;72], and 69 [65;73] years for stages A, B, C, and D, respectively. This study demonstrates high accuracy in HF stage classification, distinguishing Stage A from Stage B with an AUC ROC of 0.91 and Stage B from Stage C with an AUC ROC of 0.97, by integrating chromatography-mass spectrometry data through multiparametric machine learning models. The observed metabolic similarities between HF with mildly reduced EF and HF with reduced EF phenotypes (AUC ROC 0.96) once again highlight the fundamental differences at the cellular and molecular levels between HF with preserved EF and HF with EF < 50%. Hierarchical clustering based on MP identified four distinct HF phenotypes and 26 key metabolites, including metabolites of tryptophan catabolism, glutamine, riboflavin, norepinephrine, serine, and long- and medium-chain acylcarnitines. The average follow-up period was 542.37 [16;1271] days. A downward change in the trajectory of EF [HR 3,008, 95% CI 1,035 to 8,743, p = 0,043] and metabolomic cluster 3 [HR 2,880; 95% CI 1,062 to 7,810, p = 0,0376] were associated with increased risk of all-cause mortality. MP can refine HF phenotyping and deepen the understanding of its underlying mechanisms. Metabolomic analysis illuminates the biochemical landscape of HF, aiding in its classification and suggesting new therapeutic pathways.

Metabolic rewiring and inter-organ crosstalk in diabetic HFpEF

Heart failure with preserved ejection fraction (HFpEF) represents a significant and growing clinical challenge. Initially, for an extended period, HFpEF was simply considered as a subset of heart failure, manifesting as haemodynamic disorders such as hypertension, myocardial hypertrophy, and diastolic dysfunction. However, the rising prevalence of obesity and diabetes has reshaped the HFpEF phenotype, with nearly 45% of cases coexisting with diabetes. Currently, it is recognized as a multi-system disorder that involves the heart, liver, kidneys, skeletal muscle, adipose tissue, along with immune and inflammatory signaling pathways. In this review, we summarize the landscape of metabolic rewiring and the crosstalk between the heart and other organs/systems (e.g., adipose, gut, liver and hematopoiesis system) in diabetic HFpEF for the first instance. A diverse array of metabolites and cytokines play pivotal roles in this intricate crosstalk process, with metabolic rewiring, chronic inflammatory responses, immune dysregulation, endothelial dysfunction, and myocardial fibrosis identified as the central mechanisms at the heart of this complex interplay. The liver-heart axis links nonalcoholic steatohepatitis and HFpEF through shared lipid accumulation, inflammation, and fibrosis pathways, while the gut-heart axis involves dysbiosis-driven metabolites (e.g., trimethylamine N-oxide, indole-3-propionic acid and short-chain fatty acids) impacting cardiac function and inflammation. Adipose-heart crosstalk highlights epicardial adipose tissue as a source of local inflammation and mechanical stress, whereas the hematopoietic system contributes via immune cell activation and cytokine release. We contend that, based on the viewpoints expounded in this review, breaking this inter-organ/system vicious cycle is the linchpin of treating diabetic HFpEF.

High triglyceride-to-high-density lipoprotein cholesterol ratio predicts poor prognosis in new-onset heart failure: a retrospective study

BACKGROUND

There is limited research on the relationship between the triglyceride-to-high-density lipoprotein cholesterol (TG/HDL-C) ratio and outcomes in new-onset heart failure (HF). Therefore, this study aimed to explore the association between TG/HDL-C ratio and clinical outcomes in these patients.

METHODS

A retrospective cohort of 614 adults with new-onset HF hospitalized at The First Affiliated Hospital of Nanchang University between July 2021 and December 2022 was analyzed. The primary endpoint was major adverse cardiovascular events (MACE), defined as cardiovascular (CV) death and HF rehospitalizations within 12 months after discharge. Kaplan-Meier (K-M) curves, restricted cubic spline (RCS) analysis, and Cox regression evaluated the association between TG/HDL-C ratio and MACE risk.

RESULTS

Patients were divided into four quartiles (Quartile 1, 2,3 and 4) based on their TG/HDL-C ratios. The mean age was 68.94 ± 14.34 years, with 59.12% male. The mean left ventricular ejection fraction (LVEF) was 46.59 ± 10.89%, with 45.11% having an LVEF ≤ 40%. During the 12-month follow-up, 156 patients experienced MACE, comprising 18 CV deaths and 138 HF rehospitalizations. The Quartile 4 group had the highest MACE risk incidence compared to other groups (P < 0.001). K-M analysis confirmed that the Quartile 4 group was associated with an increased cumulative incidence of MACE, HF rehospitalization, and CV death (all P < 0.001). RCS analysis revealed a positive nonlinear relationship between the TG/HDL-C ratio and MACE risk (P for nonlinear = 0.026), with a sharp risk increase above a ratio of 1.08. After adjustment, TG/HDL-C ratio was independently associated with MACE (HR: 1.44, 95% CI: 1.29-1.60). Compared to Quartile 1, adjusted HRs were significantly higher in Quartiles 2, 3, and 4 (all P < 0.005).

CONCLUSIONS

The TG/HDL-C ratio is independently associated with 12-month MACE risk in new-onset HF patients. It may serve as a simple, cost-effective marker to improve early risk stratification and guide closer monitoring and tailored management in this high-risk population.

Physical activity of moderate-intensity optimizes myocardial citrate cycle in a murine model of heart failure

Introduction

There is growing body of evidence that an enhanced concentration of branched-chain amino acids (BCAAs), as a consequence of an impaired myocardial oxidative metabolism, is involved in the occurrence and progression of heart failure (HF). The purpose of this study was to examine the effect of 8 weeks of spontaneous wheel running (8-sWR) (reflecting low-to-moderate intensity physical activity) on the myocardial [BCAAs] and mitochondrial oxidative metabolism markers, such as tricarboxylic acid (TCA) cycle intermediates (TCAi), mitochondrial electron transport chain (ETC) proteins and mitochondrial DNA copy number (mtDNA/nDNA) in a murine model of HF.

Methods

Adult heart failure (Tgαq*44) and wild-type (WT) mice were randomly assigned to either the sedentary or exercising group. Myocardial concentrations of [TCAi] and [BCAAs] were measured by LC-MS/MS, ETC proteins were determined by Western immunoblotting and mtDNA/nDNA was assessed by qPCR.

Results

Heart failure mice exhibited decreased exercise performance capacity as reflected by a lower total distance covered and time of running in wheels. This was accompanied by impaired TCA cycle, including higher citrate concentration and greater [BCAAs] in the heart of Tgαq*44 mice compared to their control counterparts. No impact of disease at its current stage i.e., in the transition phase from the compensated to decompensated stage of HF on the myocardial mitochondrial ETC, proteins content was observed, however the altered basal level of mitochondrial biogenesis (lower mtDNA/nDNA) in the heart of Tgαq*44 mice compared to their control counterparts was detected. Interestingly, 8-sWR significantly decreased myocardial citrate content in the presence of unchanged myocardial [BCAAs], ETC proteins content and mtDNA copy number.

Conclusion

Moderate-intensity physical activity, even of short duration, could be considered an effective intervention in heart failure. Our results suggest that central metabolic pathway - TCA cycle appears to be more sensitive to moderate-intensity physical activity (as reflected by the lowering of myocardial citrate concentration) than the mechanism(s) regulating the BCAAs turnover in the heart. This observation may have a particular importance in heart failure, since an improvement of impaired myocardial oxidative metabolism may contribute to the upgrading of the clinical status of patients.

High-resolution DNA methylation changes reveal biomarkers of heart failure with preserved ejection fraction versus reduced ejection fraction

Novel biomarkers are needed to better identify-and distinguish-heart failure with preserved ejection fraction (HFpEF) from other clinical phenotypes. The goal of our study was to identify epigenetic-sensitive biomarkers useful to a more accurate diagnosis of HFpEF. We performed a network-oriented genome-wide DNA methylation study of circulating CD4+ T lymphocytes isolated from peripheral blood using reduced representation bisulfite sequencing (RRBS) in two cohorts (i.e., discovery/validation) each of both male and female patients with HFpEF (n = 12/10), HF with reduced EF (HFrEF; n = 7/5), and volunteers lacking clinical evidence of HF (CON; n = 7/5). RRBS is the gold-standard platform for measuring genome-wide DNA methylation changes at single-cytosine resolution in hypothesis-generating studies. We identified three hypomethylated HFpEF-specific differentially methylated positions (DMPs) associated with FOXB1, ELMOD1, and DGKH genes wherein ROC curve analysis revealed that increased expression levels had a reasonable diagnostic performance in predicting HFpEF (AUC ≥ 0.8, p < 0.05). Network analysis identified additional three genes including JUNB (p = 0.037), SETD7 (p = 0.003), and MEF2D (p = 0.0001) which were significantly higher in HFpEF vs. HFrEF patients. ROC curve analysis showed that integrating the functional H2FPEF classification with the expression levels of the FOXB1, ELMOD1, and DGKH as well as the JUNB, SETD7, and MEF2D genes improved diagnostic accuracy, with AUC = 0.8 (p < 0.0001) as compared to H2FPEF score alone (p > 0.05). Besides, increased expression levels of SETD7-RELA-IL6 axis significantly discriminated overweight/obese HFpEF vs. HFrEF patients (AUC = 1; p = 0.001, p = 0.006, p = 0.006, respectively). We support an emerging dogma that indirect epigenetic testing via high-resolution RRBS methylomics represents a non-invasive tool that may enable easier access to both diagnostic and mechanistic insights of HFpEF. An epigenetic-oriented dysregulation of network-derived SETD7-RELA-IL6 axis in circulating CD4+ T lymphocytes may drive pro-inflammatory responses which, in turn, may lead to cardiac remodeling in overweight/obese HFpEF.

Sodium-glucose exchanger 2 inhibitor canagliflozin promotes mitochondrial metabolism and alleviates salt-induced cardiac hypertrophy via preserving SIRT3 expression

INTRODUCTION

Excess salt intake is not only an independent risk factor for heart failure, but also one of the most important dietary factors associated with cardiovascular disease worldwide. Metabolic reprogramming in cardiomyocytes is an early event provoking cardiac hypertrophy that leads to subsequent cardiovascular events upon high salt loading. Although SGLT2 inhibitors, such as canagliflozin, displayed impressive cardiovascular health benefits, whether SGLT2 inhibitors protect against cardiac hypertrophy-related metabolic reprogramming upon salt loading remain elusive.

OBJECTIVES

To investigate whether canagliflozin can improve salt-induced cardiac hypertrophy and the underlying mechanisms.

METHODS

Dahl salt-sensitive rats developed cardiac hypertrophy by feeding them an 8% high-salt diet, and some rats were treated with canagliflozin. Cardiac function and structure as well as mitochondrial function were examined. Cardiac proteomics, targeted metabolomics and SIRT3 cardiac-specific knockout mice were used to uncover the underlying mechanisms.

RESULTS

In Dahl salt-sensitive rats, canagliflozin showed a potent therapeutic effect on salt-induced cardiac hypertrophy, accompanied by lowered glucose uptake, reduced accumulation of glycolytic end-products and improved cardiac mitochondrial function, which was associated with the recovery of cardiac expression of SIRT3, a key mitochondrial metabolic regulator. Cardiac-specific knockout of SIRT3 not only exacerbated salt-induced cardiac hypertrophy but also abolished the therapeutic effect of canagliflozin. Mechanistically, high salt intake repressed cardiac SIRT3 expression through a calcium-dependent epigenetic modifications, which could be blocked by canagliflozin by inhibiting SGLT1-mediated calcium uptake. SIRT3 improved myocardial metabolic reprogramming by deacetylating MPC1 in cardiomyocytes exposed to pro-hypertrophic stimuli. Similar to canagliflozin, the SIRT3 activator honokiol also exerted therapeutic effects on cardiac hypertrophy.

CONCLUSION

Cardiac mitochondrial dysfunction caused by SIRT3 repression is a critical promotional determinant of metabolic pattern switching underlying salt-induced cardiac hypertrophy. Improving SIRT3-mediated mitochondrial function by SGLT2 inhibitors-mediated calcium handling would represent a therapeutic strategy against salt-related cardiovascular events.

Visceral obesity and HFpEF: targets and therapeutic opportunities

The effectiveness of weight-loss drugs in heart failure (HF) with preserved ejection fraction (HFpEF) highlights the link between obesity (adipose tissue) and HF (the heart). Recent guidelines incorporating the waist:height ratio for diagnosing and treating obesity reflect the growing recognition of the significance of visceral adiposity. However, its unique impact on HFpEF and their complex relationship remain underexplored. With limited treatment options for obesity-related HFpEF, novel disease-modifying treatments are urgently needed. Here, we clarify the relationship between visceral obesity and HFpEF, introducing the concept of the visceral adipose tissue-heart axis to explore its mechanisms and therapeutic potential. We also discuss promising strategies targeting visceral obesity in HFpEF and propose directions for future research.

Deciphering the causality of gut microbiota, circulating metabolites and heart failure: a mediation mendelian

Background

Growing evidence suggesting a connection between the gut microbiome, plasma metabolites, and the development of heart failure (HF). However, the causality of this relationship remains to be fully elucidated.

Methods

Utilizing summary statistics from extensive genome-wide association studies (GWAS), we investigated the interplay among the gut microbiome, 1,400 plasma metabolites and heart failure. We conducted bidirectional Mendelian randomization (MR) analyses and MR mediation analysis to discern the causality within these relationships. The inverse variance-weighted (IVW) method served as our primary analytical approach, supported by various MR methods and sensitivity analyses.

Results

We revealed casual relationships between nine microbial groups/pathways and heart failure. Additionally, 15 metabolites exhibited casual links with HF, with eight exerting protective effects. Through two-step MR analysis we also identified the metabolite, Campesterol, mediated the increasing risk from gut microbiota to HF and a metabolite ratio played the converse role.

Conclusion

This investigation has provided robust evidence supporting the causal links between the gut microbiome, plasma metabolites, and heart failure. The findings enhance our comprehension of the role of circulating metabolites and offer significant insights for future etiological research and therapeutic development in heart failure.

Cardiac Fibrosis in the Multi-Omics Era: Implications for Heart Failure

Cardiac fibrosis, a hallmark of heart failure and various cardiomyopathies, represents a complex pathological process that has long challenged therapeutic intervention. High-throughput omics technologies have begun revolutionizing our understanding of the molecular mechanisms driving cardiac fibrosis and are providing unprecedented insights into its heterogeneity and progression. This review provides a comprehensive analysis of how techniques-encompassing genomics, epigenomics, transcriptomics, proteomics, and metabolomics-are providing insight into our understanding of cardiac fibrosis. Genomic studies have identified novel genetic variants and regulatory networks associated with fibrosis susceptibility and progression, and single-cell transcriptomics has unveiled distinct cardiac fibroblast subpopulations with unique molecular signatures. Epigenomic profiling has revealed dynamic chromatin modifications controlling fibroblast activation states, and proteomic analyses have identified novel biomarkers and potential therapeutic targets. Metabolomic studies have uncovered important alterations in cardiac energetics and substrate utilization during fibrotic remodeling. The integration of these multi-omic data sets has led to the identification of previously unrecognized pathogenic mechanisms and potential therapeutic targets, including cell-type-specific interventions and metabolic modulators. We discuss how these advances are driving the development of precision medicine approaches for cardiac fibrosis while highlighting current challenges and future directions in translating multi-omic insights into effective therapeutic strategies. This review provides a systems-level perspective on cardiac fibrosis that may inform the development of more effective, personalized therapeutic approaches for heart failure and related cardiovascular diseases.

Myocardial Proteome in Human Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) constitutes more than half of all HF but has few effective therapies. Recent human myocardial transcriptomics and metabolomics have identified major differences between HFpEF and controls. How this translates at the protein level is unknown.

METHODS AND RESULTS

Myocardial tissue from patients with HFpEF and nonfailing donor controls was analyzed by data-dependent acquisition (n=10 HFpEF, n=10 controls) and data-independent acquisition (n=44 HFpEF, n=5 controls) mass spectrometry-based proteomics. Differential protein expression analysis, pathway overrepresentation, weighted coexpression network analysis, and machine learning were integrated with clinical characteristics and previously reported transcriptomics. Principal component analysis (data-dependent acquisition-mass spectrometry) found HFpEF separated into 2 subgroups: one similar to controls and the other disparate. Downregulated proteins in HFpEF versus controls were enriched in mitochondrial transport/organization, translation, and metabolism including oxidative phosphorylation. Proteins upregulated in HFpEF were related to immune activation, reactive oxygen species, and inflammatory response. Ingenuity pathway analysis predicted downregulation of protein translation, mitochondrial function, and glucose and fat metabolism in HFpEF. Expression of oxidative phosphorylation and metabolism genes (higher) versus proteins (lower) was discordant in HFpEF versus controls. Data-independent acquisition-mass spectrometry proteomics also yielded 2 HFpEF subgroups; the one most different from controls had a higher proportion of patients with severe obesity and exhibited lower proteins related to fuel metabolism, oxidative phosphorylation, and protein translation. Three modules of correlated proteins in HFpEF that correlated with left ventricular hypertrophy and right ventricular load related to (1) proteasome; (2) fuel metabolism; and (3) protein translation, oxidative phosphorylation, and sarcomere organization.

CONCLUSIONS

Integrative proteomics, transcriptomics, and pathway analysis supports a defect in both metabolism and translation in HFpEF. Patients with HFpEF with more distinct proteomic signatures from control more often had severe obesity, supporting therapeutic efforts targeting metabolism and translation, particularly in this subgroup.

Therapeutic Ketosis for Heart Failure: A State-of-the-Art Review

Heart failure is characterized by an energy-deprived heart, and in recent years it has been found that the failing heart increases ketone body oxidation to meet its energy demands. Accumulating evidence suggests that this metabolic adaptation is cardioprotective, suggesting that interventions that boost blood ketone levels could aid the failing heart. Indeed, multiple small clinical trials with short-term follow up have demonstrated that supplying the failing heart with exogenous ketone bodies may improve myocardial function across various manifestations of heart failure. As such, therapeutic ketosis, which is a metabolic state in which blood ketone levels are mildly elevated, could have great potential to ameliorate heart failure. Therapeutic ketosis can be achieved endogenously via exercise or dietary practices, exogenously via supplementation with ketone bodies, or pharmacologically via treatment with a sodium-glucose cotransporter-2 inhibitor. Although ketosis-inducing practices cannot be routinely recommended to patients with heart failure at this time due to a lack of robust data regarding the long-term benefits and risks, anecdotal evidence suggests that some patients have begun to adopt ketosis-inducing practices, so it is important for clinicians to be aware of how to manage patients optimally when they are in therapeutic ketosis. In this review, we discuss myocardial ketone metabolism in heart failure, the current evidence for therapeutic ketosis in patients with heart failure, a framework to distinguish between therapeutic ketosis and the pathologic state of ketoacidosis, and practical considerations for managing patients adhering to ketosis-inducing practices.

Contribution of Brain Intrinsic Branched-Chain Amino Acid Metabolism in a Novel Mouse Model of Maple Syrup Urine Disease

Maple syrup urine disease (MSUD) results from loss of branched-chain ketoacid dehydrogenase (BCKDH) activity, the committed, rate-limiting step of branched-chain amino acid (BCAA) oxidation. Current treatments, including a low protein diet and liver transplantation, improve peripheral biochemistry and limit episodes of metabolic decompensation but do not fully prevent chronic neuropsychiatric symptoms. The mechanisms underlying chronic neurologic phenotypes remain poorly understood. Currently available MSUD mouse models do not survive long enough to evaluate chronic central nervous system (CNS) pathology. To investigate if loss of brain-intrinsic BCAA metabolism contributes to chronic neurologic disease, we developed a new brain-specific knockout mouse model of MSUD. First, we generated a mouse harboring a floxed Dbt allele (Dbtflox/flox). Then we crossed this line with Cre recombinase driver lines to induce loss of Dbt expression in (1) all developing CNS cell populations (2) neurons alone or (3) astrocytes alone. We found that brain-specific KO mice have elevations in BCAA levels in cortex that are exacerbated by a high protein diet. They also have secondary changes in amino acids in brain that are important for neuronal function, including glutamine and glycine. These metabolic differences result in subtle functional deficits as measured by electroencephalogram and behavioral testing. Astrocyte and neuron-specific KO mice each also demonstrate mild biochemical features of MSUD in the cortex, suggesting that both cell populations may contribute to disease pathology. Collectively, these data suggest that therapies targeting the CNS directly, in addition to the periphery, may improve outcomes in MSUD.

Moderate- and High-Speed Treadmill Running Exercise Have Minimal Impact on Rat Achilles Tendon

Exercise influences clinical Achilles tendon health in humans, but animal models of exercise-related Achilles tendon changes are lacking. Moreover, previous investigations of the effects of treadmill running exercise on rat Achilles tendon demonstrate variable outcomes. Our objective was to assess the functional, structural, cellular, and biomechanical impacts of treadmill running exercise on rat Achilles tendon with sensitive in and ex vivo approaches. Three running levels were assessed over the course of 8 weeks: control (cage activity), moderate-speed (treadmill running at 10 m/min, no incline), and high-speed (treadmill running at 20 m/min, 10° incline). We hypothesized that moderate-speed treadmill running would beneficially impact tendon biomechanics through increased tenocyte cellularity, metabolism, and anabolism whereas high-speed treadmill running would cause a tendinopathic phenotype with compromised tendon biomechanics due to pathologic tenocyte differentiation, metabolism, and catabolism. Contrary to our hypothesis, treadmill running exercise at these speeds had a nominal effect on the rat Achilles tendon. Treadmill running modestly influenced tenocyte metabolism and nuclear aspect ratio as well as viscoelastic tendon properties but did not cause a tendinopathic phenotype. These findings highlight the need for improved models of exercise- and loading-related tendon changes that can be leveraged to develop strategies for tendinopathy prevention and treatment.

Discovery of First Branched-Chain Ketoacid Dehydrogenase Kinase (BDK) Inhibitor Clinical Candidate PF-07328948

Inhibition of branched-chain ketoacid dehydrogenase kinase (BDK or BCKDK), a negative regulator of branched-chain amino acid (BCAA) metabolism, is hypothesized to treat cardio-metabolic diseases. From a starting point with potential idiosyncratic toxicity risk, modification to a benzothiophene core and discovery of a cryptic pocket allowed for improved potency with 3-aryl substitution to arrive at PF-07328948, which was largely devoid of protein covalent binding liability. This BDK inhibitor was shown also to be a BDK degrader in cells and in vivo rodent studies. Plasma biomarkers, including BCAAs and branched-chain ketoacids (BCKAs), were lowered in vivo with enhanced pharmacodynamic effect upon chronic dosing due to BDK degradation. This molecule improves metabolic and heart failure end points in rodent models. PF-07328948 is the first known selective BDK inhibitor candidate to be examined in clinical studies, with Phase 1 single ascending dose data showing good tolerability and a pharmacokinetic profile commensurate with once-daily dosing.

Pathophysiological insights into HFpEF from studies of human cardiac tissue

Heart failure with preserved ejection fraction (HFpEF) is a major, worldwide health-care problem. Few therapies for HFpEF exist because the pathophysiology of this condition is poorly defined and, increasingly, postulated to be diverse. Although perturbations in other organs contribute to the clinical profile in HFpEF, altered cardiac structure, function or both are the primary causes of this heart failure syndrome. Therefore, studying myocardial tissue is fundamental to improve pathophysiological insights and therapeutic discovery in HFpEF. Most studies of myocardial changes in HFpEF have relied on cardiac tissue from animal models without (or with limited) confirmatory studies in human cardiac tissue. Animal models of HFpEF have evolved based on theoretical HFpEF aetiologies, but these models might not reflect the complex pathophysiology of human HFpEF. The focus of this Review is the pathophysiological insights gained from studies of human HFpEF myocardium. We outline the rationale for these studies, the challenges and opportunities in obtaining myocardial tissue from patients with HFpEF and relevant comparator groups, the analytical approaches, the pathophysiological insights gained to date and the remaining knowledge gaps. Our objective is to provide a roadmap for future studies of cardiac tissue from diverse cohorts of patients with HFpEF, coupling discovery biology with measures to account for pathophysiological diversity.

AdipoRon ameliorates the progression of heart failure with preserved ejection fraction via mitigating lipid accumulation and fibrosis

INTRODUCTION

Obesity and imbalance in lipid homeostasis contribute greatly to heart failure with preserved ejection fraction (HFpEF), the dominant form of heart failure. Few effective therapies exist to control metabolic alterations and lipid homeostasis.

OBJECTIVES

We aimed to investigate the cardioprotective roles of AdipoRon, the adiponectin receptor agonist, in regulating lipid accumulation in the two-hit HFpEF model.

METHODS

HFpEF mouse model was induced using 60 % high-fat diet plus L-NAME drinking water. Then, AdipoRon (50 mg/kg) or vehicle were administered by gavage to the two-hit HFpEF mouse model once daily for 4 weeks. Cardiac function was evaluated using echocardiography, and Postmortem analysis included RNA-sequencing, untargeted metabolomics, transmission electron microscopy and molecular biology methods.

RESULTS

Our study presents the pioneering evidence that AdipoR was downregulated and impaired fatty acid oxidation in the myocardia of HFpEF mice, which was associated with lipid metabolism as indicated by untargeted metabolomics. AdipoRon, orally active synthetic adiponectin receptor agonist, could upregulate AdipoR1/2 (independently of adiponectin) and reduce lipid droplet accumulation, and alleviate fibrosis to restore HFpEF phenotypes. Finally, AdipoRon primarily exerted its effects through restoring the balance of myocardial fatty acid intake, transport, and oxidation via the downstream AMPKα or PPARα signaling pathways. The protective effects of AdipoRon in HFpEF mice were reversed by compound C and GW6471, inhibitors of AMPKα and PPARα, respectively.

CONCLUSIONS

AdipoRon ameliorated the HFpEF phenotype by promoting myocardial fatty acid oxidation, decreasing fatty acid transport, and inhibiting fibrosis via the upregulation of AdipoR and the activation of AdipoR1/AMPKα and AdipoR2/PPARα-related downstream pathways. These findings underscore the therapeutic potential of AdipoRon in HFpEF. Importantly, all these parameters get restored in the context of continued mechanical and metabolic stressors associated with HFpEF.

MTCH2 controls energy demand and expenditure to fuel anabolism during adipogenesis

Mitochondrial carrier homolog 2 (MTCH2) is a regulator of apoptosis, mitochondrial dynamics, and metabolism. Loss of MTCH2 results in mitochondrial fragmentation, an increase in whole-body energy utilization, and protection against diet-induced obesity. In this study, we used temporal metabolomics on HeLa cells to show that MTCH2 deletion results in a high ATP demand, an oxidized cellular environment, and elevated utilization of lipids, amino acids, and carbohydrates, accompanied by a decrease in several metabolites. Lipidomics analysis revealed a strategic adaptive reduction in membrane lipids and an increase in storage lipids in MTCH2 knockout cells. Importantly, MTCH2 knockout cells showed an increase in mitochondrial oxidative function, which may explain the higher energy demand. Interestingly, this imbalance in energy metabolism and reductive potential triggered by MTCH2-deletion prevents NIH3T3L1 preadipocytes from differentiating into mature adipocytes, an energy consuming reductive biosynthetic process. In summary, the loss of MTCH2 leads to increased mitochondrial oxidative activity and energy demand, creating a catabolic and oxidative environment that fails to fuel the anabolic processes required for lipid accumulation and adipocyte differentiation.

The Impact of Obesity on Cardiac Energy Metabolism and Efficiency in Heart Failure With Preserved Ejection Fraction

The incidence and prevalence of heart failure with preserved ejection fraction (HFpEF) continues to rise, and now comprises more than half of all heart failure cases. There are many risk factors for HFpEF, including older age, hypertension, diabetes, dyslipidemia, sedentary behaviour, and obesity. The rising prevalence of obesity in society is a particularly important contributor to HFpEF development and severity. Obesity can adversely affect the heart, including inducing marked alterations in cardiac energy metabolism. This includes obesity-induced impairments in mitochondrial function, and an increase in fatty acid uptake and mitochondrial fatty acid β-oxidation. This increase in myocardial fatty acid metabolism is accompanied by an impaired myocardial insulin signaling and a marked decrease in glucose oxidation. This switch from glucose to fatty acid metabolism decreases cardiac efficiency and can contribute to severity of HFpEF. Increased myocardial fatty acid uptake in obesity is also associated with the accumulation of fatty acids, resulting in cardiac lipotoxicity. Obesity also results in dramatic changes in the release of adipokines, which can negatively impact cardiac function and energy metabolism. Obesity-induced increases in epicardial fat can also increase cardiac insulin resistance and negatively affect cardiac energy metabolism and HFpEF. However, optimizing cardiac energy metabolism in obese subjects may be one approach to preventing and treating HFpEF. This review discusses what is presently known about the effects of obesity on cardiac energy metabolism and insulin signaling in HFpEF. The clinical implications of obesity and energy metabolism on HFpEF are also discussed.

Hydrogen Sulfide Deficiency and Therapeutic Targeting in Cardiometabolic HFpEF: Evidence for Synergistic Benefit with GLP-1/Glucagon Agonism

Background

Heart failure with preserved ejection fraction (HFpEF) is a significant public health concern with limited treatment options. Dysregulated nitric oxide-mediated signaling has been implicated in HFpEF pathophysiology, however, little is known about the role of endogenous hydrogen sulfide (H 2 S) in HFpEF.

Objectives

This study evaluated H 2 S bioavailability in patients and two animal models of cardiometabolic HFpEF and assessed the impact of H 2 S on HFpEF severity through alterations in endogenous H 2 S production and pharmacological supplementation. We also evaluated the effects of the H 2 S donor, diallyl trisulfide (DATS) in combination with the GLP-1/glucagon receptor agonist, survodutide, in HFpEF.

Methods

HFpEF patients and two rodent models of HFpEF ("two-hit" L-NAME + HFD mouse and ZSF1 obese rat) were evaluated for H 2 S bioavailability. Two cohorts of two-hit mice were investigated for changes in HFpEF pathophysiology: (1) endothelial cell cystathionine-γ-lyase (EC-CSE) knockout; (2) H 2 S donor, JK-1, supplementation. DATS and survodutide combination therapy was tested in ZSF1 obese rats.

Results

H 2 S levels were significantly reduced (i.e., 81%) in human HFpEF patients and in both preclinical HFpEF models. This depletion was associated with reduced CSE expression and activity, and increased SQR expression. Genetic knockout of H 2 S -generating enzyme, CSE, worsened HFpEF characteristics, including elevated E/e' ratio and LVEDP, impaired aortic vasorelaxation and increased mortality. Pharmacologic H 2 S supplementation restored H 2 S bioavailability, improved diastolic function and attenuated cardiac fibrosis corroborating an improved HFpEF phenotype. DATS synergized with survodutide to attenuate obesity, improve diastolic function, exercise capacity, and reduce oxidative stress and cardiac fibrosis.

Conclusions

H 2 S deficiency is evident in HFpEF patients and conserved across multiple preclinical HFpEF models. Increasing H 2 S bioavailability improved cardiovascular function, while knockout of endogenous H 2 S production exacerbated HFpEF pathology and mortality. These results suggest H 2 S dysregulation contributes to HFpEF and increasing H 2 S bioavailability may represent a novel therapeutic strategy for HFpEF. Furthermore, our data demonstrate that combining H 2 S supplementation with GLP-1/glucagon receptor agonist may provide synergistic benefits in improving HFpEF outcomes.

Highlights

H 2 S deficiency is evident in both human HFpEF patients and two clinically relevant models. Reduced H 2 S production by CSE and increased metabolism by SQR impair H 2 S bioavailability in HFpEF. Pharmacological H 2 S supplementation improves diastolic function and reduces cardiac fibrosis in HFpEF models. Targeting H 2 S dysregulation presents a novel therapeutic strategy for managing HFpEF. H 2 S synergizes with GLP-1/glucagon agonist and ameliorates HFpEF.

Association between insulin resistance indices and outcomes in patients with heart failure with preserved ejection fraction

BACKGROUND

Insulin resistance (IR) plays a pivotal role in the interplay between metabolic disorders and heart failure with preserved ejection fraction (HFpEF). Various non-insulin-based indices emerge as reliable surrogate markers for assessing IR, including the triglyceride-glucose (TyG) index, the TyG index with body mass index (TyG-BMI), atherogenic index of plasma (AIP), and the metabolic score for insulin resistance (METS-IR). However, the ability of different IR indices to predict outcome in HFpEF patients has not been extensively explored.

METHODS

Patients having HFpEF were recruited from January 2012 and December 2023. The outcome was defined as major adverse cardiovascular event (MACE), encompassing all-cause mortality and rehospitalization for heart failure. The potential linear relationship was visualized by the restricted cubic spline (RCS) curve. Both univariable and multivariable Cox proportional hazards models were employed to examine the association between the IR indexes and MACE. Furthermore, to assess the incremental prognostic value of the TyG index, we conducted comprehensive analyses using area under the curve (AUC), the continuous net reclassification index (cNRI), and the integrated discrimination index (IDI).

RESULTS

A total of 8693 patients met the inclusion criteria and were included in the final analysis. The mean age of the patients was 70.59 ± 10.6 years, with 5045 (58.04%) being male. The Kaplan-Meier survival analysis revealed that higher degree of the four IR indexes was associated with higher risk of MACE (all log-rank P < 0.05). When treated as a continuous variable, the TyG index showed a significant association with MACE (HR 2.1, 95% CI 1.98-2.23, P < 0.001 in model 1; HR 1.81, 95% CI 1.73-1.9, P < 0.001 in model 2; HR 1.68, 95% CI 1.6-1.76, P < 0.001 in model 3). When categorized into quartiles, the highest quartile of the TyG index (Q4) was significantly associated with MACE (HR 2.48, 95% CI 2.24-2.76, P < 0.001 in model 3). Similar significant associations were found between TyG-BMI, AIP, METS-IR, and MACE. The TyG index was found to enhance the risk stratification capability of the MAGGIC score (AUC from 0.601 to 0.666). When compared to other IR indicators, the TyG index exhibited superior discrimination and reclassification abilities in predicting MACE. Additionally, the TyG-BMI index revealed a U-shaped correlation with MACE, indicating that both an elevated and a lower TyG-BMI index were associated with an increased risk.

CONCLUSION

All four IR indices are independently associated with MACE in patients with HFpEF. Notably, these IR indices significantly enhance the predictive accuracy of the MAGGIC score, a widely used risk assessment tool in HFpEF. Among these indices, the TyG index demonstrated the highest discriminatory and reclassification abilities, providing the greatest incremental value in predicting MACE and exhibiting significant superiority compared to the other indices. These findings highlight the importance of assessing IR indices, particularly the TyG index, in the risk assessment and management strategies for HFpEF patients. However, it should be noted that our findings need to be validated in diverse populations to ensure their applicability and generalizability.

Baicalin Mitigates Cardiac Hypertrophy and Fibrosis by Inhibiting the p85a Subunit of PI3K

Background: Heart failure (HF) is a serious public health concern. Baicalin is one of the major active ingredients of a traditional Chinese herbal medicine, Huang Qin, which is used to treat patients with chest pain or cardiac discomfort. However, the underlying mechanism(s) of the cardioprotective effect of baicalin are still not fully understood. Methods: Isoprenaline injection or transverse aortic constriction-induced animal models and isoprenaline or angiotensin 2 administration-induced cell models of heart failure were established. Baicalin (15 mg/kg/day or 25 mg/kg/day) was administered in vivo, and 10 μM baicalin was administered in vitro. Potential pharmacological targets of baicalin and genes related to heart failure were identified via different databases, which suggested that PI3K-Akt may be involved in the effects of baicalin. Molecular docking was carried out to reveal the effect of baicalin on p85a. Results: We observed significant antihypertrophic and antifibrotic effects of baicalin both in vivo and in vitro. The mean cross-sectional area of cardiomyocytes recovered from 390 μm2 in the HF group to 195 μm2 in the baicalin-treated group. The area of fibrosis was reduced from 2.8-fold in the HF group to 1.62-fold in the baicalin-treated group. Baicalin displayed a significant cardioprotective effect via the inhibition of the PI3K signaling pathway by binding with five amino acid residues of the p85a regulatory subunit of PI3K. The combination treatment of baicalin and an inhibitor of PI3K p110 demonstrated a stronger cardioprotective effect. The mean ejection fraction increased from 54% in the baicalin-treated group to 67% in the combination treatment group. Conclusions: Our work identified baicalin as a new active herbal ingredient that is able to treat isoprenaline-induced heart dysfunction and suggests that p85a is a pharmacological target. These findings reveal the significant potential of baicalin combined with an inhibitor of PI3K p110 for the treatment of heart failure and support more clinical trials in the future.

Caloric restriction and its mimetics in heart failure with preserved ejection fraction: mechanisms and therapeutic potential

The global increase in human life expectancy, coupled with an unprecedented rise in the prevalence of obesity, has led to a growing clinical and socioeconomic burden of heart failure with preserved ejection fraction (HFpEF). Mechanistically, the molecular and cellular hallmarks of aging are omnipresent in HFpEF and are further exacerbated by obesity and associated metabolic diseases. Conversely, weight loss strategies, particularly caloric restriction, have shown promise in improving health status in patients with HFpEF and are considered the gold standard for promoting longevity and healthspan (disease-free lifetime) in model organisms. In this review, we implicate fundamental mechanisms of aging in driving HFpEF and elucidate how caloric restriction mitigates the disease progression. Furthermore, we discuss the potential for pharmacologically mimicking the beneficial effects of caloric restriction in HFpEF using clinically approved and emerging caloric restriction mimetics. We surmise that these compounds could offer novel therapeutic avenues for HFpEF and alleviate the challenges associated with the implementation of caloric restriction and other lifestyle modifications to reduce the burden of HFpEF at a population level.

Interplay between energy metabolism and NADPH oxidase-mediated pathophysiology in cardiovascular diseases

Sustained production of reactive oxygen species (ROS) and an imbalance in the antioxidant system have been implicated in the development of cardiovascular diseases (CVD), especially when combined with diabetes, hypercholesterolemia, and other metabolic disorders. Among them, NADPH oxidases (NOX), including NOX1-5, are major sources of ROS that mediate redox signaling in both physiological and pathological processes, including fibrosis, hypertrophy, and remodeling. Recent studies have demonstrated that mitochondria produce more proteins and energy in response to adverse stress, corresponding with an increase in superoxide radical anions. Novel NOX4-mediated modulatory mechanisms are considered crucial for maintaining energy metabolism homeostasis during pathological states. In this review, we integrate the latest data to elaborate on the interactions between oxidative stress and energy metabolism in various CVD, aiming to elucidate the higher incidence of CVD in individuals with metabolic disorders. Furthermore, the correlations between NOX and ferroptosis, based on energy metabolism, are preliminarily discussed. Further discoveries of these mechanisms might promote the development of novel therapeutic drugs targeting NOX and their crosstalk with energy metabolism, potentially offering efficient management strategies for CVD.

Two-hit mouse model of heart failure with preserved ejection fraction combining diet-induced obesity and renin-mediated hypertension

Heart failure with preserved ejection fraction (HFpEF) is increasingly common but its pathogenesis is poorly understood. The ability to assess genetic and pharmacologic interventions is hampered by the lack of robust preclinical mouse models of HFpEF. We developed a novel "two-hit" model, which combines obesity and insulin resistance with chronic pressure overload to recapitulate clinical features of HFpEF. C57Bl6/NJ mice fed a high-fat diet (HFD) for > 10 weeks were administered an AAV8-driven vector resulting in constitutive overexpression of mouse Renin1d. HFD-Renin (aka "HFpEF") mice demonstrated obesity and insulin resistance, moderate left ventricular hypertrophy, preserved systolic function, and diastolic dysfunction indicated by echocardiographic measurements; increased left atrial mass; elevated natriuretic peptides; and exercise intolerance. Transcriptomic and metabolomic profiling of HFD-Renin myocardium demonstrated upregulation of pro-fibrotic pathways and downregulation of metabolic pathways, in particular branched chain amino acid catabolism, similar to human HFpEF. Treatment with empagliflozin, an effective but incompletely understood HFpEF therapy, improved multiple endpoints. The HFD-Renin mouse model recapitulates key features of human HFpEF and will enable studies dissecting the contribution of individual pathogenic drivers to this complex syndrome. Additional preclinical HFpEF models allow for orthogonal studies to increase validity in assessment of interventions.

Contributions of Inflammation to Cardiometabolic Heart Failure with Preserved Ejection Fraction

The most common form of heart failure is heart failure with preserved ejection fraction (HFpEF). While heterogeneous in origin, the most common form of HFpEF is the cardiometabolic manifestation. Obesity and aging promote systemic inflammation that appears integral to cardiometabolic HFpEF pathophysiology. Accumulation of immune cells within the heart, fueled by an altered metabolome, contribute to cardiac inflammation and fibrosis. In spite of this, broad anti-inflammatory therapy has not shown significant benefit in patient outcomes. Thus, understanding of the nuances to metabolic and age-related inflammation during HFpEF is paramount for more targeted interventions. Here, we review clinical evidence of inflammation in the context of HFpEF and summarize our mechanistic understanding of immunometabolic inflammation, highlighting pathways of therapeutic potential along the way.

Intercellular Mitochondrial transfer: Therapeutic implications for energy metabolism in heart failure

Heart failure (HF) remains one of the leading causes of high morbidity and mortality globally. Impaired cardiac energy metabolism plays a critical role in the pathological progression of HF. Various forms of HF exhibit marked differences in energy metabolism, particularly in mitochondrial function and substrate utilization. Recent studies have increasingly highlighted that improving energy metabolism in HF patients as a crucial treatment strategy. Mitochondrial transfer is emerging as a promising and precisely regulated therapeutic strategy for treating metabolic disorders. This paper specifically reviews the characteristics of mitochondrial energy metabolism across different types of HF and explores the modes and mechanisms of mitochondrial transfer between different cell types in the heart, such as cardiomyocytes, fibroblasts, and immune cells. We focused on the therapeutic potential of intercellular mitochondrial transfer in improving energy metabolism disorders in HF. We also discuss the role of signal transduction in mitochondrial transfer, highlighting that mitochondria not only function as energy factories but also play crucial roles in intercellular communication, metabolic regulation, and tissue repair. This study provides new insights into improving energy metabolism in heart failure patients and proposes promising new therapeutic strategies.

Beyond weight loss: the potential of glucagon-like peptide-1 receptor agonists for treating heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous syndrome with various phenotypes, and obesity is one of the most common and clinically relevant phenotypes of HFpEF. Obesity contributes to HFpEF through multiple mechanisms, including sodium retention, neurohormonal dysregulation, altered energy substrate metabolism, expansion of visceral adipose tissue, and low-grade systemic inflammation. Glucagon-like peptide-1 (GLP-1) is a hormone in the incretin family. It is produced by specialized cells called neuroendocrine L cells located in the distal ileum and colon. GLP-1 reduces blood glucose levels by promoting glucose-dependent insulin secretion from pancreatic β cells, suppressing glucagon release from pancreatic α cells, and blocking hepatic gluconeogenesis. Recent evidence suggests that GLP-1 receptor agonists (GLP-1 RAs) can significantly improve physical activity limitations and exercise capacity in obese patients with HFpEF. The possible cardioprotective mechanisms of GLP-1 RAs include reducing epicardial fat tissue thickness, preventing activation of the renin-angiotensin-aldosterone system, improving myocardial energy metabolism, reducing systemic inflammation and cardiac oxidative stress, and delaying the progression of atherosclerosis. This review examines the impact of obesity on the underlying mechanisms of HFpEF, summarizes the trial data on cardiovascular outcomes of GLP-1 RAs in patients with type 2 diabetes mellitus, and highlights the potential cardioprotective mechanisms of GLP-1 RAs to give a pathophysiological and clinical rationale for using GLP-1 RAs in obese HFpEF patients.

Multi-omics insights into the pathogenesis of diabetic cardiomyopathy: epigenetic and metabolic profiles

AIM

Diabetic cardiomyopathy (DbCM), a complex metabolic disease, greatly threatens human health due to therapeutic limitations. Multi-omics approaches facilitate the elucidation of its intrinsic pathological changes.

METHODS

Metabolomics, RNA-seq, proteomics, and assay of transposase-accessible chromatin (ATAC-seq) were utilized to elucidate multidimensional molecular alterations in DbCM.

RESULTS

In the heart and plasma of mice with DbCM, metabolomic analysis demonstrated significant differences in branched-chain amino acids (BCAAs) and lipids. Subsequent RNA-seq and proteomics showed that the key genes, including BCKDHB, PPM1K, Cpt1b, Fabp4, Acadm, Acadl, Acadvl, HADH, HADHA, HADHB, Eci1, Eci2, PDK4, and HMGCS2, were aberrantly regulated, contributing to the disorder of BCAAs and fatty acids. ATAC-seq analysis underscored the pivotal role of epigenetic regulation by revealing dynamic shifts in chromatin accessibility and a robust positive correlation with gene expression patterns in diabetic cardiomyopathy mice. Furthermore, motif analysis identified that KLF15 as a critical transcription factor in DbCM, regulating the core genes implicated with BCAAs metabolism.

CONCLUSION

Our research delved into the metabolic alterations and epigenetic landscape and revealed that KLF15 may be a promising candidate for therapeutic intervention in DbCM.

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.

Advances in myocardial energy metabolism: metabolic remodelling in heart failure and beyond

The very high energy demand of the heart is primarily met by adenosine triphosphate (ATP) production from mitochondrial oxidative phosphorylation, with glycolysis providing a smaller amount of ATP production. This ATP production is markedly altered in heart failure, primarily due to a decrease in mitochondrial oxidative metabolism. Although an increase in glycolytic ATP production partly compensates for the decrease in mitochondrial ATP production, the failing heart faces an energy deficit that contributes to the severity of contractile dysfunction. The relative contribution of the different fuels for mitochondrial ATP production dramatically changes in the failing heart, which depends to a large extent on the type of heart failure. A common metabolic defect in all forms of heart failure [including heart failure with reduced ejection fraction (HFrEF), heart failure with preserved EF (HFpEF), and diabetic cardiomyopathies] is a decrease in mitochondrial oxidation of pyruvate originating from glucose (i.e. glucose oxidation). This decrease in glucose oxidation occurs regardless of whether glycolysis is increased, resulting in an uncoupling of glycolysis from glucose oxidation that can decrease cardiac efficiency. The mitochondrial oxidation of fatty acids by the heart increases or decreases, depending on the type of heart failure. For instance, in HFpEF and diabetic cardiomyopathies myocardial fatty acid oxidation increases, while in HFrEF myocardial fatty acid oxidation either decreases or remains unchanged. The oxidation of ketones (which provides the failing heart with an important energy source) also differs depending on the type of heart failure, being increased in HFrEF, and decreased in HFpEF and diabetic cardiomyopathies. The alterations in mitochondrial oxidative metabolism and glycolysis in the failing heart are due to transcriptional changes in key enzymes involved in the metabolic pathways, as well as alterations in redox state, metabolic signalling and post-translational epigenetic changes in energy metabolic enzymes. Of importance, targeting the mitochondrial energy metabolic pathways has emerged as a novel therapeutic approach to improving cardiac function and cardiac efficiency in the failing heart.

Leveraging metabolism for better outcomes in heart failure

Whilst metabolic inflexibility and substrate constraint have been observed in heart failure for many years, their exact causal role remains controversial. In parallel, many of our fundamental assumptions about cardiac fuel use are now being challenged like never before. For example, the emergence of sodium-glucose cotransporter 2 inhibitor therapy as one of the four 'pillars' of heart failure therapy is causing a revisit of metabolism as a key mechanism and therapeutic target in heart failure. Improvements in the field of cardiac metabolomics will lead to a far more granular understanding of the mechanisms underpinning normal and abnormal human cardiac fuel use, an appreciation of drug action, and novel therapeutic strategies. Technological advances and expanding biorepositories offer exciting opportunities to elucidate the novel aspects of these metabolic mechanisms. Methodologic advances include comprehensive and accurate substrate quantitation such as metabolomics and stable-isotope fluxomics, improved access to arterio-venous blood samples across the heart to determine fuel consumption and energy conversion, high quality cardiac tissue biopsies, biochemical analytics, and informatics. Pairing these technologies with recent discoveries in epigenetic regulation, mitochondrial dynamics, and organ-microbiome metabolic crosstalk will garner critical mechanistic insights in heart failure. In this state-of-the-art review, we focus on new metabolic insights, with an eye on emerging metabolic strategies for heart failure. Our synthesis of the field will be valuable for a diverse audience with an interest in cardiac metabolism.

Predicting Mortality and Hospitalization in Heart Failure With Preserved Ejection Fraction by Using Machine Learning

Background

Few studies have incorporated echocardiography and laboratory data to predict clinical outcomes in heart failure with preserved ejection fraction (HFpEF).

Objectives

This study aimed to use machine learning to find predictors of heart failure (HF) hospitalization and cardiovascular (CV) death in HFpEF.

Methods

From the Chang Gung Research Database in Taiwan, 6,092 HFpEF patients (2,898 derivation, 3,194 validation) identified between 2008 and 2017 were followed until 2019. A random survival forest model, using 58 variables, was developed to predict the composite outcome of HF hospitalization and CV death.

Results

During 2.9-year follow-up, 37.7% of derivation and 36.0% of validation cohort patients experienced HF hospitalization or CV death. The study identified 15 predictive indicators, including age ≥65 years, B-type natriuretic peptide level ≥600 pg/mL, left atrium size ≥46 mm, atrial fibrillation, frequency of HF hospitalization within 3 years, body mass index <30 kg/m2, moderate or severe mitral regurgitation, left ventricular (LV) posterior wall thickness of <10 or ≥13 mm, dysnatremia, LV end-diastolic dimension of <40 or ≥56 mm, uric acid level ≥7 mg/dL, triglyceride level of <70 or ≥200 mg/dL, blood urea nitrogen level ≥20 mg/dL, interventricular septum thickness of <11 or ≥20 mm, and glycated hemoglobin (HbA1c) level of <6% or ≥8%. The random survival forest model demonstrated robust external generalizability with an 86.9% area under curve in validation.

Conclusions

Machine learning identified 15 predictors of HF hospitalization and CV death in HFpEF patients, helping doctors identify high-risk individuals for tailored treatment.

Recent advances associated with cardiometabolic remodeling in diabetes-induced heart failure

Diabetes mellitus (DM) is characterized by chronic hyperglycemia, and despite intensive glycemic control, the risk of heart failure in patients with diabetes remains high. Diabetes-induced heart failure (DHF) presents a unique metabolic challenge, driven by significant alterations in cardiac substrate metabolism, including increased reliance on fatty acid oxidation, reduced glucose utilization, and impaired mitochondrial function. These metabolic alterations lead to oxidative stress, lipotoxicity, and energy deficits, contributing to the progression of heart failure. Emerging research has identified novel mechanisms involved in the metabolic remodeling of diabetic hearts, such as autophagy dysregulation, epigenetic modifications, polyamine regulation, and branched-chain amino acid (BCAA) metabolism. These processes exacerbate mitochondrial dysfunction and metabolic inflexibility, further impairing cardiac function. Therapeutic interventions targeting these pathways-such as enhancing glucose oxidation, modulating fatty acid metabolism, and optimizing ketone body utilization-show promise in restoring metabolic homeostasis and improving cardiac outcomes. This review explores the key molecular mechanisms driving metabolic remodeling in diabetic hearts, highlights advanced methodologies, and presents the latest therapeutic strategies for mitigating the progression of DHF. Understanding these emerging pathways offers new opportunities to develop targeted therapies that address the root metabolic causes of heart failure in diabetes.

Characterization of a novel ovine model of hypertensive heart failure with preserved ejection fraction

The lack of animal models that accurately represent heart failure with preserved ejection fraction (HFpEF) has been a major barrier to the mechanistic understanding and development of effective therapies for this prevalent and debilitating syndrome characterized by multisystem impairments. Herein, we describe the development and characterization of a novel large animal model of HFpEF in older, female sheep with chronic 2-kidney, 1-clip hypertension. At 6-wk post unilateral renal artery clipping, hypertensive HFpEF sheep had higher mean arterial pressure compared with similarly aged ewes without unilateral renal artery clipping (mean arterial pressure = 112.7 ± 15.9 vs. 76.0 ± 10.1 mmHg, P < 0.0001). The hypertensive HFpEF sheep were characterized by 1) echocardiographic evidence of diastolic dysfunction (lateral e' = 0.11 ± 0.02 vs. 0.14 ± 0.04 m/s, P = 0.011; lateral E/e' = 4.25 ± 0.77 vs. 3.63 ± 0.54, P = 0.028) and concentric left ventricular hypertrophy without overt systolic impairment, 2) elevated directly measured left ventricular end-diastolic pressure (13 ± 5 vs. 0.5 ± 1 mmHg, P = 2.1 × 10-6), and 3) normal directly measured cardiac output. Crucially, these hypertensive HFpEF sheep had impaired exercise capacity as demonstrated by their 1) attenuated cardiac output (P = 0.001), 2) augmented pulmonary capillary wedge pressure (P = 0.026), and 3) attenuated hindlimb blood flow (P = 3.4 × 10-4) responses, during graded treadmill exercise testing. In addition, exercise renal blood flow responses were also altered. Collectively, our data indicates that this novel ovine model of HFpEF may be a useful translational research tool because it exhibits similar and clinically relevant impairments as that of patients with HFpEF.NEW & NOTEWORTHY We show that older, female sheep with chronic 2-kidney, 1-clip hypertension have similar cardiac and noncardiac exercise hemodynamic abnormalities as patients with HFpEF. This clinically relevant, translatable, and novel large animal model of HFpEF may be useful for elucidating mechanisms and developing treatments for this increasingly common syndrome with few clinically impactful therapies.

Cardiometabolic effects of sacubitril/valsartan in a rat model of heart failure with preserved ejection fraction

The promising results obtained in the PARADIGM-HF trial prompted the approval of sacubitril/valsartan (SAC/VAL) as a first-in-class treatment for heart failure with reduced ejection fraction (HFrEF) patients. The effect of SAC/VAL treatment was also studied in patients with heart failure with preserved ejection fraction (HFpEF) and, although improvements in New York Heart Association (NYHA) class, HF hospitalizations, and cardiovascular deaths were observed, these results were not so promising. However, the demand for HFpEF therapies led to the approval of SAC/VAL as an alternative treatment, although further studies are needed. We aimed to elucidate the effects of a 9-week SAC/VAL treatment in cardiac function and metabolism using a preclinical model of HFpEF, the Zucker Fatty and Spontaneously Hypertensive (ZSF1) rats. We found that SAC/VAL significantly improved diastolic function parameters and modulated respiratory quotient during exercise. Ex-vivo studies showed that SAC/VAL treatment significantly decreased heart, liver, spleen, and visceral fat weights; cardiac hypertrophy and percentage of fibrosis; lipid infiltration in liver and circulating levels of cholesterol and sodium. Moreover, SAC/VAL reduced glycerophospholipids, cholesterol, and cholesteryl esters while increasing triglyceride levels in cardiac tissue. In conclusion, SAC/VAL treatment improved diastolic and hepatic function, respiratory metabolism, reduced hypercholesterolemia and cardiac fibrosis and hypertrophy, and was able to modulate cardiac metabolic profile. Our findings might provide further insight into the therapeutic benefits of SAC/VAL treatment in obese patients with HFpEF.

Exercise Therapy Rescues Skeletal Muscle Dysfunction and Exercise Intolerance in Cardiometabolic HFpEF

Exercise intolerance, a hallmark of heart failure with preserved ejection fraction (HFpEF) exacerbated by obesity, involves unclear mechanisms related to skeletal muscle metabolism. In a "2-hit" model of HFpEF, we investigated the ability of exercise therapy (voluntary wheel running) to reverse skeletal muscle dysfunction and exercise intolerance. Using state-of-the-art metabolic cages and a multiomic approach, we demonstrate exercise can rescue dysfunctional skeletal muscle lipid and branched-chain amino acid oxidation and restore exercise capacity in mice with cardiometabolic HFpEF. These results underscore the importance of skeletal muscle metabolism to improve exercise intolerance in HFpEF.