Cardiac ketone body metabolism. Biochim Biophys Acta Mol Basis Dis. 2020;1866:165739. [PMID: 32084511 DOI: 10.1016/j.bbadis.2020.165739]

The benefits of oral glucose-lowering agents: GLP-1 receptor agonists, DPP-4 and SGLT-2 inhibitors on myocardial ischaemia/reperfusion injury

Myocardial infarction (MI) is a life-threatening cardiovascular disease that, on average, results in 8.5 million deaths worldwide each year. Timely revascularization of occluded vessels is a critical method of myocardial salvage. However, reperfusion paradoxically leads to the worsening of myocardial damage known as myocardial ischaemia/reperfusion injury (MI/RI). Therefore, reducing the size of myocardial infarction after reperfusion is critical and remains an important therapeutic goal. The susceptibility of the myocardium to MI/RI may be increased by diabetes. Currently, some traditional antidiabetic agents such as metformin reduce MI/RI by decreasing inflammation, inhibiting oxidative stress, and improving vascular endothelial function. This appears to be a new direction for the treatment of MI/RI. Recent cardiovascular outcome trials have shown that several oral antidiabetic agents, including glucagon-like peptide-1 receptor agonists (GLP-1RAs), dipeptidyl peptidase-4 inhibitors (DPP-4is), and sodium-glucose-linked transporter-2 inhibitors (SGLT-2is), not only have good antidiabetic effects but also have a protective effect on myocardial protection. This article aims to discuss the mechanisms and effects of oral antidiabetic agents, including GLP-1RAs, DPP-4is, and SGLT-2is, on MI/RI to facilitate their clinical application.

Cardiovascular outcomes and molecular targets for the cardiac effects of Sodium-Glucose Cotransporter 2 Inhibitors: A systematic review

Sodium-glucose cotransporter 2 inhibitors (SGLT2i), a new class of glucose-lowering drugs traditionally used to control blood glucose levels in patients with type 2 diabetes mellitus, have been proven to reduce major adverse cardiovascular events, including cardiovascular death, in patients with heart failure irrespective of ejection fraction and independently of the hypoglycemic effect. Because of their favorable effects on the kidney and cardiovascular outcomes, their use has been expanded in all patients with any combination of diabetes mellitus type 2, chronic kidney disease and heart failure. Although mechanisms explaining the effects of these drugs on the cardiovascular system are not well understood, their effectiveness in all these conditions suggests that they act at the intersection of the metabolic, renal and cardiac axes, thus disrupting maladaptive vicious cycles while contrasting direct organ damage. In this systematic review we provide a state of the art of the randomized controlled trials investigating the effect of SGLT2i on cardiovascular outcomes in patients with chronic kidney disease and/or heart failure irrespective of ejection fraction and diabetes. We also discuss the molecular targets and signaling pathways potentially explaining the cardiac effects of these pharmacological agents, from a clinical and experimental perspective.

Ketone body levels and its associations with cardiac markers following an acute myocardial infarction: a post hoc analysis of the EMMY trial

BACKGROUND

Sodium-glucose co-transporter 2 inhibitors (SGLT2i) have been suggested to exert cardioprotective effects in patients with heart failure, possibly by improving the metabolism of ketone bodies in the myocardium.

METHODS

This post hoc analysis of the EMMY trial investigated the changes in serum β-hydroxybutyrate (3-βOHB) levels after acute myocardial infarction (AMI) in response to 26-week of Empagliflozin therapy compared to the usual post-MI treatment. In addition, the association of baseline and repeated measurements of 3-βOHB with cardiac parameters and the interaction effects of Empagliflozin were investigated. Cardiac parameters included N-terminal pro-B-type natriuretic peptide (NT-proBNP), left ventricular ejection fraction (LVEF), left ventricle end-systolic volume (LVESV), left ventricle end-diastolic volume (LVEDV), and left ventricular filling pressure (E/é ratio).

RESULTS

The mean 3-βOHB levels increased from baseline (46.2 ± 3.0 vs. 51.7 ± 2.7) to 6 weeks (48.8 ± 2.2 vs. 42.0 ± 2.3) and 26 weeks (49.3 ± 2.2 vs. 35.8 ± 1.9) in the Empagliflozin group compared to a consistent decline in placebo over 26 weeks (pinteraction < 0.001). Baseline and longitudinal measurements of 3-βOHB were not significantly associated with NT-proBNP and E/é ratio. Baseline 3-βOHB value was negatively associated with LVEF (coefficient: - 0.464, 95%CI - 0.863;- 0.065, p = 0.023), while an increase in its levels over time was positively associated with LVEF (0.595, 0.156;1.035, 0.008). The baseline 3-βOHB was positively associated with LVESV (1.409, 0.186;2.632, 0.024) and LVEDV (0.640, - 1.170;- 2.449, 0.488), while an increase in its levels over time was negatively associated with these cardiac parameters (LVESV: - 2.099, - 3.443;- 0.755, 0.002; LVEDV: - 2.406, - 4.341;- 0.472, 0.015). Empagliflozin therapy appears to modify the association between 3-βOHB, LVEF (pinteraction = 0.090), LVESV (pinteraction = 0.134), and LVEDV (pinteraction = 0.168), particularly at 26 weeks; however, the results were not statistically significant.

CONCLUSION

This post hoc analysis showed that SGLT2i increased 3-βOHB levels after AMI compared to placebo. Higher baseline 3-βOHB levels were inversely associated with cardiac function at follow-up, whereas a sustained increase in 3-βOHB levels over time improved these markers. This highlights the importance of investigating ketone body metabolism in different post-MI phases. Although more pronounced effect of 3-βOHB on cardiac markers was observed in the SGLT2i group, further research is required to explore this interaction effect.

Molecular mechanisms of metabolic dysregulation in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM), one of the most serious complications of diabetes mellitus, has become recognized as a cardiometabolic disease. In normoxic conditions, the majority of the ATP production (>95%) required for heart beating comes from mitochondrial oxidative phosphorylation of fatty acids (FAs) and glucose, with the remaining portion coming from a variety of sources, including fructose, lactate, ketone bodies (KB) and branched chain amino acids (BCAA). Increased FA intake and decreased utilization of glucose and lactic acid were observed in the diabetic hearts of animal models and diabetic patients. Moreover, the polyol pathway is activated, and fructose metabolism is enhanced. The use of ketones as energy sources in human diabetic hearts also increases significantly. Furthermore, elevated BCAA levels and impaired BCAA metabolism were observed in the hearts of diabetic mice and patients. The shift in energy substrate preference in diabetic hearts results in increased oxygen consumption and impaired oxidative phosphorylation, leading to diabetic cardiomyopathy. However, the precise mechanisms by which impaired myocardial metabolic alterations result in diabetes mellitus cardiac disease are not fully understood. Therefore, this review focuses on the molecular mechanisms involved in alterations of myocardial energy metabolism. It not only adds more molecular targets for the diagnosis and treatment, but also provides an experimental foundation for screening novel therapeutic agents for diabetic cardiomyopathy.

Cardiac Metabolism, Reprogramming, and Diseases

Cardiovascular diseases (CVD) account for the largest bulk of deaths worldwide, posing a massive burden on societies and the global healthcare system. Besides, the incidence and prevalence of these diseases are on the rise, demanding imminent action to revert this trend. Cardiovascular pathogenesis harbors a variety of molecular and cellular mechanisms among which dysregulated metabolism is of significant importance and may even proceed other mechanisms. The healthy heart metabolism primarily relies on fatty acids for the ultimate production of energy through oxidative phosphorylation in mitochondria. Other metabolites such as glucose, amino acids, and ketone bodies come next. Under pathological conditions, there is a shift in metabolic pathways and the preference of metabolites, termed metabolic remodeling or reprogramming. In this review, we aim to summarize cardiovascular metabolism and remodeling in different subsets of CVD to come up with a new paradigm for understanding and treatment of these diseases.

Metabolic signatures in post-myocardial infarction heart failure, including insights into prediction, intervention, and prognosis

Heart failure (HF) is a prevalent long-term complication of myocardial infarction (MI). The incidence of post-MI HF is high, and patients with the condition have a poor prognosis. Accurate identification of individuals at high risk for post-MI HF is crucial for implementation of a protective and ideally personalized strategy to prevent fatal events. Post-MI HF is characterized by adverse cardiac remodeling, which results from metabolic changes in response to long-term ischemia. Moreover, various risk factors, including genetics, diet, and obesity, can influence metabolic pathways in patients. This review focuses on the metabolic signatures of post-MI HF that could serve as non-invasive biomarkers for early identification in high-risk populations. We also explore how metabolism participates in the pathophysiology of post-MI HF. Furthermore, we discuss the potential of metabolites as novel targets for treatment of post-MI HF and as biomarkers for prognostic evaluation. It is expected to provide valuable suggestions for the clinical prevention and treatment of post-MI HF from a metabolic perspective.

Adaptive changes in tumor cells in response to reductive stress

Reductive stress is characterized by an excess of cellular electron donors and can be linked with various human pathologies including cancer. We developed melanoma cell lines resistant to reductive stress agents: rotenone (ROTR), n-acetyl-L-cysteine, (NACR), or dithiothreitol (DTTR). Resistant cells divided more rapidly and had intracellular homeostatic redox-couple ratios that were shifted towards the reduced state. Resistance caused alterations in general cell morphology, but only ROTR cells had significant changes in mitochondrial morphology with higher numbers that were more isolated, fragmented and swollen, with greater membrane depolarization and decreased numbers of networks. These changes were accompanied by lower basal oxygen consumption and maximal respiration rates. Whole cell flux analyses and mitochondrial function assays showed that NACR and DTTR preferentially utilized tricarboxylic acid (TCA) cycle intermediates, while ROTR used ketone body substrates such as D, L-β-hydroxybutyric acid. NACR and DTTR cells had constitutively decreased levels of reactive oxygen species (ROS), although this was accompanied by activation of nuclear factor erythroid 2-related factor 2 (Nrf2), with concomitant increased expression of the downstream gene products such as glutathione S-transferase P (GSTP). Further adaptations included enhanced expression of endoplasmic reticulum proteins controlling the unfolded protein response (UPR). Although expression patterns of these UPR proteins were distinct between the resistant cells, a trend implied that resistance to reductive stress is accompanied by a constitutively increased UPR phenotype in each line. Overall, tumor cells, although tolerant of oxidative stress, can adapt their energy and survival mechanisms in lethal reductive stress conditions.

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.

Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases

Ketone bodies (KBs), such as acetoacetate and β-hydroxybutyrate, serve as crucial alternative energy sources during glucose deficiency. KBs, generated through ketogenesis in the liver, are metabolized into acetyl-CoA in extrahepatic tissues, entering the tricarboxylic acid cycle and electron transport chain for ATP production. Reduced glucose metabolism and mitochondrial dysfunction correlate with increased neuronal death and brain damage during cerebral ischemia and neurodegeneration. Both KBs and the ketogenic diet (KD) demonstrate neuroprotective effects by orchestrating various cellular processes through metabolic and signaling functions. They enhance mitochondrial function, mitigate oxidative stress and apoptosis, and regulate epigenetic and post-translational modifications of histones and non-histone proteins. Additionally, KBs and KD contribute to reducing neuroinflammation and modulating autophagy, neurotransmission systems, and gut microbiome. This review aims to explore the current understanding of the molecular mechanisms underpinning the neuroprotective effects of KBs and KD against brain damage in cerebral ischemia and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease.

The changes of cardiac energy metabolism with sodium-glucose transporter 2 inhibitor therapy

Background/aims

To investigate the specific effects of s odium-glucose transporter 2 inhibitor (SGLT2i) on cardiac energy metabolism.

Methods

A systematic literature search was conducted in eight databases. The retrieved studies were screened according to the inclusion and exclusion criteria, and relevant information was extracted according to the purpose of the study. Two researchers independently screened the studies, extracted information, and assessed article quality.

Results

The results of the 34 included studies (including 10 clinical and 24 animal studies) showed that SGLT2i inhibited cardiac glucose uptake and glycolysis, but promoted fatty acid (FA) metabolism in most disease states. SGLT2i upregulated ketone metabolism, improved the structure and functions of myocardial mitochondria, alleviated oxidative stress of cardiomyocytes in all literatures. SGLT2i increased cardiac glucose oxidation in diabetes mellitus (DM) and cardiac FA metabolism in heart failure (HF). However, the regulatory effects of SGLT2i on cardiac FA metabolism in DM and cardiac glucose oxidation in HF varied with disease types, stages, and intervention duration of SGLT2i.

Conclusion

SGLT2i improved the efficiency of cardiac energy production by regulating FA, glucose and ketone metabolism, improving mitochondria structure and functions, and decreasing oxidative stress of cardiomyocytes under pathological conditions. Thus, SGLT2i is deemed to exert a benign regulatory effect on cardiac metabolic disorders in various diseases.

Systematic review registration

https://www.crd.york.ac.uk/, PROSPERO (CRD42023484295).

Metabolic mechanisms in physiological and pathological cardiac hypertrophy: new paradigms and challenges

Cardiac metabolism is vital for heart function. Given that cardiac contraction requires a continuous supply of ATP in large quantities, the role of fuel metabolism in the heart has been mostly considered from the perspective of energy production. However, the consequence of metabolic remodelling in the failing heart is not limited to a compromised energy supply. The rewired metabolic network generates metabolites that can directly regulate signalling cascades, protein function, gene transcription and epigenetic modifications, thereby affecting the overall stress response of the heart. In addition, metabolic changes in both cardiomyocytes and non-cardiomyocytes contribute to the development of cardiac pathologies. In this Review, we first summarize how energy metabolism is altered in cardiac hypertrophy and heart failure of different aetiologies, followed by a discussion of emerging concepts in cardiac metabolic remodelling, that is, the non-energy-generating function of metabolism. We highlight challenges and open questions in these areas and finish with a brief perspective on how mechanistic research can be translated into therapies for heart failure.

LC-MS/MS method for quantitative profiling of ketone bodies, α-keto acids, lactate, pyruvate and their stable isotopically labelled tracers in human plasma: An analytical panel for clinical metabolic kinetics and interactions

An important area within clinical research is in vivo metabolism of ketone bodies (β-hydroxybutyrate and acetoacetate) and in connection metabolites that may affect their production and/or cellular transport such as the keto-acids from the branched-chain amino acids, lactate and pyruvate. To determine in vivo metabolite turnover, availability of accurate and sensitive methods for analyzing the plasma concentrations of these metabolites and their stable isotopically labeled enrichments is mandatory. Therefore, the present study describes a high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous analysis of ketone bodies, α-keto acids, lactate, pyruvate, and their tracer enrichments in humans using 2 different derivatization techniques with 4-bromo-N-methylbenzylamine and O-benzylhydroxylamine as derivatization reagents, and 1-ethyl-3-dimethylaminopropyl carbodiimide as coupling compound followed by a single LC-MS/MS run. The method was validated for matrix effects, linearity, accuracy, precision, recovery, stability, and enrichment (ratio) analysis of a stable isotopically labelled analytes (tracers) continuously infused in humans divided by the unlabeled endogenous analyte (tracee) that makes it possible to quantify the analyte in vivo synthesis and degradation rates. The applied parallel derivatization procedure yielded good sensitivity for all analytes of interest and their tracers. Despite the double derivatization method, mixing the ethyl acetate portions at the final stage made it possible to simultaneously analyze all compounds in a single LC-MS/MS run. Moreover, the liquid chromatography method was optimized to robustly quantify the keto acids derived from leucine (α-keto-isocaproic acid) and isoleucine (α-keto-β-methylvaleric acid), the compounds with similar chemical structure and identical molecular weights. The presented method is designed and validated for human plasma. However, care should be taken in blood sampling and processing procedures as well as quick freezing and storage at -80 °C due to the instability of especially acetoacetate.

The role of mitochondria in myocardial damage caused by energy metabolism disorders: From mechanisms to therapeutics

Myocardial damage is the most serious pathological consequence of cardiovascular diseases and an important reason for their high mortality. In recent years, because of the high prevalence of systemic energy metabolism disorders (e.g., obesity, diabetes mellitus, and metabolic syndrome), complications of myocardial damage caused by these disorders have attracted widespread attention. Energy metabolism disorders are independent of traditional injury-related risk factors, such as ischemia, hypoxia, trauma, and infection. An imbalance of myocardial metabolic flexibility and myocardial energy depletion are usually the initial changes of myocardial injury caused by energy metabolism disorders, and abnormal morphology and functional destruction of the mitochondria are their important features. Specifically, mitochondria are the centers of energy metabolism, and recent evidence has shown that decreased mitochondrial function, caused by an imbalance in mitochondrial quality control, may play a key role in myocardial injury caused by energy metabolism disorders. Under chronic energy stress, mitochondria undergo pathological fission, while mitophagy, mitochondrial fusion, and biogenesis are inhibited, and mitochondrial protein balance and transfer are disturbed, resulting in the accumulation of nonfunctional and damaged mitochondria. Consequently, damaged mitochondria lead to myocardial energy depletion and the accumulation of large amounts of reactive oxygen species, further aggravating the imbalance in mitochondrial quality control and forming a vicious cycle. In addition, impaired mitochondria coordinate calcium homeostasis imbalance, and epigenetic alterations participate in the pathogenesis of myocardial damage. These pathological changes induce rapid progression of myocardial damage, eventually leading to heart failure or sudden cardiac death. To intervene more specifically in the myocardial damage caused by metabolic disorders, we need to understand the specific role of mitochondria in this context in detail. Accordingly, promising therapeutic strategies have been proposed. We also summarize the existing therapeutic strategies to provide a reference for clinical treatment and developing new therapies.

SGLT2 Inhibitors in Aging-Related Cardiovascular Disease: A Review of Potential Mechanisms

Population aging combined with higher susceptibility to cardiovascular diseases in older adults is increasing the incidence of conditions such as atherosclerosis, myocardial infarction, heart failure, myocardial hypertrophy, myocardial fibrosis, arrhythmia, and hypertension. sodium-glucose cotransporter 2 inhibitors (SGLT2i) were originally developed as a novel oral drug for patients with type 2 diabetes mellitus. Unexpectedly, recent studies have shown that, beyond their effect on hyperglycemia, SGLT2i also have a variety of beneficial effects on cardiovascular disease. Experimental models of cardiovascular disease have shown that SGLT2i ameliorate the process of aging-related cardiovascular disease by inhibiting inflammation, reducing oxidative stress, and reversing endothelial dysfunction. In this review, we discuss the role of SGLT2i in aging-related cardiovascular disease and propose the use of SGLT2i to prevent and treat these conditions in older adults.

Association between Impaired Ketogenesis and Metabolic-Associated Fatty Liver Disease

Metabolic (dysfunction) associated fatty liver disease (MAFLD) is generally developed with excessive accumulation of lipids in the liver. Ketogenesis is an efficient pathway for the disposal of fatty acids in the liver and its metabolic benefits have been reported. In this review, we examined previous studies on the association between ketogenesis and MAFLD and reviewed the candidate mechanisms that can explain this association.

D-β-Hydroxybutyrate Dehydrogenase Mitigates Diabetes-Induced Atherosclerosis through the Activation of Nrf2

BACKGROUND

 We aimed to investigate the role and mechanism of β-hydroxybutyrate dehydrogenase 1 (Bdh1) in regulating macrophage oxidative stress in diabetes-induced atherosclerosis (AS).

METHODS

 We performed immunohistochemical analysis of femoral artery sections to determine differences in Bdh1 expression between normal participants, AS patients, and patients with diabetes-induced AS. Diabetic Apoe-/- mice and high-glucose (HG)-treated Raw264.7 macrophages were used to replicate the diabetes-induced AS model. The role of Bdh1 in this disease model was determined by adeno-associated virus (AAV)-mediated overexpression of Bdh1 or overexpression or silencing of Bdh1.

RESULTS

 We observed reduced expression of Bdh1 in patients with diabetes-induced AS, HG-treated macrophages, and diabetic Apoe-/- mice. AAV-mediated Bdh1 overexpression attenuated aortic plaque formation in diabetic Apoe-/- mice. Silencing of Bdh1 resulted in increased reactive oxygen species (ROS) production and an inflammatory response in macrophages, which were reversed by the ROS scavenger N-acetylcysteine. Overexpression of Bdh1 protected Raw264.7 cells from HG-induced cytotoxicity by inhibiting ROS overproduction. In addition, Bdh1 induced oxidative stress through nuclear factor erythroid-related factor 2 (Nrf2) activation by fumarate acid.

CONCLUSION

 Bdh1 attenuates AS in Apoe-/- mice with type 2 diabetes, accelerates lipid degradation, and reduces lipid levels by promoting ketone body metabolism. Moreover, it activates the Nrf2 pathway of Raw264.7 by regulating the metabolic flux of fumarate, which inhibits oxidative stress and leads to a decrease in ROS and inflammatory factor production.

The Ketogenic Diet and Cardiovascular Diseases

The most common and increasing causes of death worldwide are cardiovascular diseases (CVD). Taking into account the fact that diet is a key factor, it is worth exploring this aspect of CVD prevention and therapy. The aim of this article is to assess the potential of the ketogenic diet in the prevention and treatment of CVD. The article is a comprehensive, meticulous analysis of the literature in this area, taking into account the most recent studies currently available. The ketogenic diet has been shown to have a multifaceted effect on the prevention and treatment of CVD. Among other aspects, it has a beneficial effect on the blood lipid profile, even compared to other diets. It shows strong anti-inflammatory and cardioprotective potential, which is due, among other factors, to the anti-inflammatory properties of the state of ketosis, the elimination of simple sugars, the restriction of total carbohydrates and the supply of omega-3 fatty acids. In addition, ketone bodies provide "rescue fuel" for the diseased heart by affecting its metabolism. They also have a beneficial effect on the function of the vascular endothelium, including improving its function and inhibiting premature ageing. The ketogenic diet has a beneficial effect on blood pressure and other CVD risk factors through, among other aspects, weight loss. The evidence cited is often superior to that for standard diets, making it likely that the ketogenic diet shows advantages over other dietary models in the prevention and treatment of cardiovascular diseases. There is a legitimate need for further research in this area.

Intravenous and oral whole body ketone dosimetry, biodistribution, metabolite correction and kinetics studied by (R)-[1-11C]β-hydroxybutyrate ([11C]OHB) PET in healthy humans

BACKGROUND

Ketones are increasingly recognized as an important and possibly oxygen sparing source of energy in vital organs such as the heart, the brain and the kidneys. Drug treatments, dietary regimens and oral ketone drinks designed to deliver ketones for organ and tissue energy production have therefore gained popularity. However, whether ingested ketones are taken up by various extra-cerebral tissues and to what extent is still largely unexplored. It was therefore the aim of this study to use positron emission tomography (PET) to explore the whole body dosimetry, biodistribution and kinetics of the ketone tracer (R)-[1-¹¹C]β-hydroxybutyrate ([¹¹C]OHB). Six healthy subjects (3 women and 3 men) underwent dynamic PET studies after both intravenous (90 min) and oral (120 min) administration of [¹¹C]OHB. Dosimetry estimates of [¹¹C]OHB was calculated using OLINDA/EXM software, biodistribution was assessed visually and [¹¹C]OHB tissue kinetics were obtained using an arterial input function and tissue time-activity curves.

RESULTS

Radiation dosimetry yielded effective doses of 3.28 [Formula: see text]Sv/MBq (intravenous administration) and 12.51 [Formula: see text]Sv/MBq (oral administration). Intravenous administration of [¹¹C]OHB resulted in avid radiotracer uptake in the heart, liver, and kidneys, whereas lesser uptake was observed in the salivary glands, pancreas, skeletal muscle and red marrow. Only minimal uptake was noted in the brain. Oral ingestion of the tracer resulted in rapid radiotracer appearance in the blood and radiotracer uptake in the heart, liver and kidneys. In general, [¹¹C]OHB tissue kinetics after intravenous administration were best described by a reversible 2-tissue compartmental model.

CONCLUSION

The PET radiotracer [¹¹C]OHB shows promising potential in providing imaging data on ketone uptake in various physiologically relevant tissues. As a result, it may serve as a safe and non-invasive imaging tool for exploring ketone metabolism in organs and tissues of both patients and healthy individuals. Trial registration Clinical trials, NCT0523812, Registered February 10th 2022, https://clinicaltrials.gov/ct2/show/NCT05232812?cond=NCT05232812&draw=2&rank=1 .

Stimulation of the Hydroxycarboxylic Acid Receptor 2 With the Ketone Body 3-Hydroxybutyrate and Niacin in Patients With Chronic Heart Failure: Hemodynamic and Metabolic Effects

Background The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output (CO) in patients with heart failure through unknown mechanisms. 3-OHB activates the hydroxycarboxylic acid receptor 2 (HCA₂), which increases prostaglandins and suppresses circulating free fatty acids. We investigated whether the cardiovascular effects of 3-OHB involved HCA₂ activation and if the potent HCA₂-stimulator niacin may increase CO. Methods and Results Twelve patients with heart failure with reduced ejection fraction were included in a randomized crossover study and examined by right heart catheterization, echocardiography, and blood sampling on 2 separate days. On study day 1, patients received aspirin to block the HCA₂ downstream cyclooxygenase enzyme, followed by 3-OHB and placebo infusions in random order. We compared the results with those of a previous study in which patients received no aspirin. On study day 2, patients received niacin and placebo. The primary end point was CO. 3-OHB increased CO (2.3 L/min, P<0.01), stroke volume (19 mL, P<0.01), heart rate (10 bpm, P<0.01), and mixed venous saturation (5%, P<0.01) with preceding aspirin. 3-OHB did not change prostaglandin levels, neither in the ketone/placebo group receiving aspirin nor the previous study cohort. Aspirin did not block 3-OHB-induced changes in CO (P=0.43). 3-OHB decreased free fatty acids by 58% (P=0.01). Niacin increased prostaglandin D₂ levels by 330% (P<0.02) and reduced free fatty acids by 75% (P<0.01) but did not affect CO. Conclusions The acute increase in CO during 3-OHB infusion was not modified by aspirin, and niacin had no hemodynamic effects. These findings show that HCA₂ receptor-mediated effects were not involved in the hemodynamic response to 3-OHB. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04703361.

Circulating ketone bodies and cardiovascular outcomes: the MESA study

AIMS

Ketone bodies (KB) are an important alternative metabolic fuel source for the myocardium. Experimental and human investigations suggest that KB may have protective effects in patients with heart failure. This study aimed to examine the association between KB and cardiovascular outcomes and mortality in an ethnically diverse population free from cardiovascular disease (CVD).

METHODS AND RESULTS

This analysis included 6796 participants (mean age 62 ± 10 years, 53% women) from the Multi-Ethnic Study of Atherosclerosis. Total KB was measured by nuclear magnetic resonance spectroscopy. Multivariable-adjusted Cox proportional hazard models were used to examine the association of total KB with cardiovascular outcomes. At a mean follow-up of 13.6 years, after adjusting for traditional CVD risk factors, increasing total KB was associated with a higher rate of hard CVD, defined as a composite of myocardial infarction, resuscitated cardiac arrest, stroke, and cardiovascular death, and all CVD (additionally included adjudicated angina) [hazard ratio, HR (95% confidence interval, CI): 1.54 (1.12-2.12) and 1.37 (1.04-1.80) per 10-fold increase in total KB, respectively]. Participants also experienced an 87% (95% CI: 1.17-2.97) increased rate of CVD mortality and an 81% (1.45-2.23) increased rate of all-cause mortality per 10-fold increase in total KB. Moreover, a higher rate of incident heart failure was observed with increasing total KB [1.68 (1.07-2.65), per 10-fold increase in total KB].

CONCLUSION

The study found that elevated endogenous KB in a healthy community-based population is associated with a higher rate of CVD and mortality. Ketone bodies could serve as a potential biomarker for cardiovascular risk assessment.

The role of histone deacetylases in cardiac energy metabolism in heart diseases

Heart diseases are associated with substantial morbidity and mortality worldwide. The underlying mechanisms and pathological changes associated with cardiac diseases are exceptionally complex. Highly active cardiomyocytes require sufficient energy metabolism to maintain their function. Under physiological conditions, the choice of fuel is a delicate process that depends on the whole body and organs to support the normal function of heart tissues. However, disordered cardiac metabolism has been discovered to play a key role in many forms of heart diseases, including ischemic heart disease, cardiac hypertrophy, heart failure, and cardiac injury induced by diabetes or sepsis. Regulation of cardiac metabolism has recently emerged as a novel approach to treat heart diseases. However, little is known about cardiac energy metabolic regulators. Histone deacetylases (HDACs), a class of epigenetic regulatory enzymes, are involved in the pathogenesis of heart diseases, as reported in previous studies. Notably, the effects of HDACs on cardiac energy metabolism are gradually being explored. Our knowledge in this respect would facilitate the development of novel therapeutic strategies for heart diseases. The present review is based on the synthesis of our current knowledge concerning the role of HDAC regulation in cardiac energy metabolism in heart diseases. In addition, the role of HDACs in different models is discussed through the examples of myocardial ischemia, ischemia/reperfusion, cardiac hypertrophy, heart failure, diabetic cardiomyopathy, and diabetes- or sepsis-induced cardiac injury. Finally, we discuss the application of HDAC inhibitors in heart diseases and further prospects, thus providing insights into new treatment possibilities for different heart diseases.

Targeting immunometabolism during cardiorenal injury: roles of conventional and alternative macrophage metabolic fuels

Macrophages play critical roles in mediating and resolving tissue injury as well as tissue remodeling during cardiorenal disease. Altered immunometabolism, particularly macrophage metabolism, is a critical underlying mechanism of immune dysfunction and inflammation, particularly in individuals with underlying metabolic abnormalities. In this review, we discuss the critical roles of macrophages in cardiac and renal injury and disease. We also highlight the roles of macrophage metabolism and discuss metabolic abnormalities, such as obesity and diabetes, which may impair normal macrophage metabolism and thus predispose individuals to cardiorenal inflammation and injury. As the roles of macrophage glucose and fatty acid metabolism have been extensively discussed elsewhere, we focus on the roles of alternative fuels, such as lactate and ketones, which play underappreciated roles during cardiac and renal injury and heavily influence macrophage phenotypes.

Oral ketone esters acutely improve myocardial contractility in post-hospitalized COVID-19 patients: A randomized placebo-controlled double-blind crossover study

Background

COVID-19 is associated with subclinical myocardial injury. Exogenous ketone esters acutely improve left myocardial function in healthy participants and patients with heart failure, but the effects have not been investigated in participants previously hospitalized for COVID-19.

Methods

This is a randomized placebo-controlled double-blind crossover study comparing a single oral ketone ester dose of 395 mg/kg with placebo. Fasting participants were randomized to either placebo in the morning and oral ketone ester in the afternoon or vice versa. Echocardiography was performed immediately after intake of the corresponding treatment. Primary outcome was left ventricular ejection fraction (LVEF). Secondary outcomes were absolute global longitudinal strain (GLS), cardiac output and blood oxygen saturation. Linear mixed effects models were used to assess differences.

Results

We included 12 participants previously hospitalized for COVID-19 with a mean (±SD) age of 60 ± 10 years. The mean time from hospitalization was 18 ± 5 months. Oral ketone esters did not increase LVEF between placebo and oral ketone ester [mean difference: -0.7% (95% CI -4.0 to 2.6%), p = 0.66], but increased GLS [1.9% (95% CI: 0.1 to 3.6%), p = 0.04] and cardiac output [1.2 L/min (95% CI: -0.1 to 2.4 L/min), p = 0.07], although non-significant. The differences in GLS remained significant after adjustment for change in heart rate (p = 0.01). There was no difference in blood oxygen saturation. Oral ketone esters increased blood ketones over time (peak level 3.1 ± 4.9 mmol/L, p < 0.01). Ketone esters increased blood insulin, c-peptide, and creatinine, and decreased glucose and FFA (all p ≤ 0.01) but did not affect glucagon, pro-BNP, or troponin I levels (all p > 0.05).

Conclusion

In patients previously hospitalized with COVID-19, a single oral dose of ketone ester had no effect on LVEF, cardiac output or blood oxygen saturation, but increased GLS acutely.

Clinical trial registration

https://clinicaltrials.gov/, identifier NCT04377035.

Quantification and Proteomic Characterization of β-Hydroxybutyrylation Modification in the Hearts of AMPKα2 Knockout Mice

AMP-activated protein kinase alpha 2 (AMPKα2) regulates energy metabolism, protein synthesis, and glucolipid metabolism myocardial cells. Ketone bodies produced by fatty acid β-oxidation, especially β-hydroxybutyrate, are fatty energy-supplying substances for the heart, brain, and other organs during fasting and long-term exercise. They also regulate metabolic signaling for multiple cellular functions. Lysine β-hydroxybutyrylation (Kbhb) is a β-hydroxybutyrate-mediated protein posttranslational modification. Histone Kbhb has been identified in yeast, mouse, and human cells. However, whether AMPK regulates protein Kbhb is yet unclear. Hence, the present study explored the changes in proteomics and Kbhb modification omics in the hearts of AMPKα2 knockout mice using a comprehensive quantitative proteomic analysis. Based on mass spectrometry (LC-MS/MS) analysis, the number of 1181 Kbhb modified sites in 455 proteins were quantified between AMPKα2 knockout mice and wildtype mice; 244 Kbhb sites in 142 proteins decreased or increased after AMPKα2 knockout (fold change >1.5 or <1/1.5, p < 0.05). The regulation of Kbhb sites in 26 key enzymes of fatty acid degradation and tricarboxylic acid cycle was noted in AMPKα2 knockout mouse cardiomyocytes. These findings, for the first time, identified proteomic features and Kbhb modification of cardiomyocytes after AMPKα2 knockout, suggesting that AMPKα2 regulates energy metabolism by modifying protein Kbhb.

Proteome-wide analysis of lysine β-hydroxybutyrylation in the myocardium of diabetic rat model with cardiomyopathy

Lysine ß-hydroxybutyrylation (kbhb), a novel modification of lysine residues with the ß-hydroxybuty group, is associated with ketone metabolism in numerous species. However, its potential role in diabetes, especially in diabetic cardiomyopathy (DCM), remains largely unexplored. In this study, using affinity enrichment and liquid chromatography-mass spectrometry (LC-MS/MS) method, we quantitatively analyze the kbhb residues on heart tissues of a DCM model rat. A total of 3,520 kbhb sites in 1,089 proteins were identified in this study. Further analysis showed that 336 kbhb sites in 143 proteins were differentially expressed between the heart tissues of DCM and wild-type rats. Among them, 284 kbhb sites in 96 proteins were upregulated, while 52 kbhb sites in 47 proteins were downregulated. Bioinformatic analysis of the proteomic results revealed that these kbhb-modified proteins were widely distributed in various components and involved in a wide range of cellular functions and biological processes (BPs). Functional analysis showed that the kbhb-modified proteins were involved in the tricarboxylic acid cycle, oxidative phosphorylation, and propanoate metabolism. Our findings demonstrated how kbhb is related to many metabolic pathways and is mainly involved in energy metabolism. These results provide the first global investigation of the kbhb profile in DCM progression and can be an essential resource to explore DCM's pathogenesis further.

Longitudinal Changes in Circulating Ketone Body Levels in Patients With Acute Heart Failure: A Post Hoc Analysis of the EMPA-Response-AHF Trial

BACKGROUND

Ketone bodies are endogenous fuels produced by the liver under conditions of metabolic or neurohormonal stress. Circulating ketone bodies are increased in patients with chronic heart failure (HF), yet little is known about the effect of acute HF on ketosis. We tested the hypothesis that ketogenesis is increased in patients with acute decompensated HF.

METHODS AND RESULTS

This was a post hoc analysis of 79 patients with acute HF included in the EMPA-RESPONSE-AHF trial, which compared sodium-dependent glucose-cotransporter protein 2 inhibitor treatment with empagliflozin for 30 days with placebo in patients with acute HF [NCT03200860]. Plasma concentrations of ketone bodies acetone, β-hydroxybutyrate, and acetoacetate were measured at baseline and 5 different timepoints. Changes in ketone bodies over time were monitored using repeated measures analysis of variance. In the total cohort, median total ketone body concentration was 251 µmol/L (interquartile range, 178-377 µmol/L) at baseline, which gradually decreased to 202 µmol/L (interquartile range, 156-240 µmol/L) at day 30 (P = .041). Acetone decreased from 60 µmol/L (interquartile range, 34-94 µmol/L) at baseline to 30 µmol/L (interquartile range, 21-42 µmol/L) ( P < .001), whereas β-hydroxybutyrate and acetoacetate remained stable over time. Higher acetone concentrations were correlated with higher N-terminal pro brain natriuretic peptide levels (r = 0.234; P = .039). Circulating ketone bodies did not differ between patients treated with empagliflozin or placebo throughout the study period. A higher acetone concentration at baseline was univariately associated with a greater risk of the composite end point, including in-hospital worsening HF, HF rehospitalizations, and all-cause mortality after 30 days. However, after adjustment for age and sex, acetone did not remain an independent predictor for the combined end point.

CONCLUSIONS

Circulating ketone body concentrations, and acetone in particular, were significantly higher during an episode of acute decompensated HF compared with after stabilization. Treatment with empagliflozin did not affect ketone body concentrations in patients with acute HF.

Cardiac Metabolism and MiRNA Interference

The aberrant increase in cardio-metabolic diseases over the past couple of decades has drawn researchers' attention to explore and unveil the novel mechanisms implicated in cardiometabolic diseases. Recent evidence disclosed that the derangement of cardiac energy substrate metabolism plays a predominant role in the development and progression of chronic cardiometabolic diseases. Hence, in-depth comprehension of the novel molecular mechanisms behind impaired cardiac metabolism-mediated diseases is crucial to expand treatment strategies. The complex and dynamic pathways of cardiac metabolism are systematically controlled by the novel executor, microRNAs (miRNAs). miRNAs regulate target gene expression by either mRNA degradation or translational repression through base pairing between miRNA and the target transcript, precisely at the 3' seed sequence and conserved heptametrical sequence in the 5' end, respectively. Multiple miRNAs are involved throughout every cardiac energy substrate metabolism and play a differential role based on the variety of target transcripts. Novel theoretical strategies have even entered the clinical phase for treating cardiometabolic diseases, but experimental evidence remains inadequate. In this review, we identify the potent miRNAs, their direct target transcripts, and discuss the remodeling of cardiac metabolism to cast light on further clinical studies and further the expansion of novel therapeutic strategies. This review is categorized into four sections which encompass (i) a review of the fundamental mechanism of cardiac metabolism, (ii) a divulgence of the regulatory role of specific miRNAs on cardiac metabolic pathways, (iii) an understanding of the association between miRNA and impaired cardiac metabolism, and (iv) summary of available miRNA targeting therapeutic approaches.

Maternal use of methamphetamine induces sex-dependent changes in myocardial gene expression in adult offspring

Methamphetamine is a commonly abused illicit stimulant that has prevalent use among women of child-bearing age. While there are extensive studies on the neurological effects of prenatal methamphetamine exposure, relatively little is known about the effect of prenatal methamphetamine on the adult cardiovascular system. Earlier work demonstrated that prenatal methamphetamine exposure sex dependently (females only) sensitizes the adult heart to ischemic injury. These data suggest that prenatal exposure to methamphetamine may induce sex-dependent changes in cardiac gene expression that persist in adult offspring. The goal of this study was to test the hypothesis that prenatal methamphetamine exposure induces changes in cardiac gene expression that persist in the adult heart. Hearts of prenatally exposed female offspring exhibited a greater number of changes in gene expression compared to male offspring (184 changes compared with 74 in male offspring and 89 changes common between both sexes). Dimethylarginine dimethylaminohydrolase 2 and 3-hydroxybutyrate dehydrogenase 1 (genes implicated in heart failure) were shown by Western Blot to be under expressed in adult females that were prenatally exposed to methamphetamine, while males were deficient in 3-Hydroxybutyrate Dehydrogenase 1 only. These data indicate that prenatal methamphetamine exposure induces changes in gene expression that persist into adulthood. This is consistent with previous findings that prenatal methamphetamine sex dependently sensitizes the adult heart to ischemic injury and may increase the risk of developing cardiac disorders during adulthood.

Molecular Mechanisms for Ketone Body Metabolism, Signaling Functions, and Therapeutic Potential in Cancer

The ketone bodies (KBs) β-hydroxybutyrate and acetoacetate are important alternative energy sources for glucose during nutrient deprivation. KBs synthesized by hepatic ketogenesis are catabolized to acetyl-CoA through ketolysis in extrahepatic tissues, followed by the tricarboxylic acid cycle and electron transport chain for ATP production. Ketogenesis and ketolysis are regulated by the key rate-limiting enzymes, 3-hydroxy-3-methylglutaryl-CoA synthase 2 and succinyl-CoA:3-oxoacid-CoA transferase, respectively. KBs participate in various cellular processes as signaling molecules. KBs bind to G protein-coupled receptors. The most abundant KB, β-hydroxybutyrate, regulates gene expression and other cellular functions by inducing post-translational modifications. KBs protect tissues by regulating inflammation and oxidative stress. Recently, interest in KBs has been increasing due to their potential for treatment of various diseases such as neurological and cardiovascular diseases and cancer. Cancer cells reprogram their metabolism to maintain rapid cell growth and proliferation. Dysregulation of KB metabolism also plays a role in tumorigenesis in various types of cancer. Targeting metabolic changes through dietary interventions, including fasting and ketogenic diets, has shown beneficial effects in cancer therapy. Here, we review current knowledge of the molecular mechanisms involved in the regulation of KB metabolism and cellular signaling functions, and the therapeutic potential of KBs and ketogenic diets in cancer.

Intermittent Fasting—A Healthy Dietary Pattern for Diabetic Nephropathy

Diabetic nephropathy (DN), a metabolic disease, is characterized by severe systemic metabolic disorders. A unique dietary pattern, such as intermittent fasting (IF) has shown promising protective effects on various metabolic diseases, such as diabetes and cardiovascular and nervous system diseases. However, its role in regulating kidney disease, especially in DN, is still being investigated. Here, we summarize the current research progress, highlighting the relationship between IF and the risk factors for the progression of DN, and discuss the potential mechanisms by which IF improves renal injury in DN. Finally, we propose IF as a potential strategy to prevent and delay DN progression. Abbreviation: DN: Diabetic nephropathy; IF: Intermittent fasting; CPT1A: Carnitine palmitoyltransferase 1A; L-FABP: Liver-type fatty acid-binding protein; STZ: Streptozotocin; LDL: Low-density lipoproteins; HIIT: High-intensity interval training; CKD: Chronic kidney disease; ACEI: Angiotensin-converting enzyme inhibitors; ARB: Angiotensin receptor blockers; MDA: Malondialdehyde; mtDNA: Mitochondrial DNA; UCP3: Uncoupling protein-3; MAM: Mitochondria-associated endoplasmic reticulum membrane; PBMCs: Peripheral blood mononuclear cells; ERK1/2: Extracellular signal-regulated kinase 1/2; DRP1: Dynamin-related protein 1; β-HB: β-Hydroxybutyrate; AcAc: Acetoacetate; GEO: Gene Expression Omnibus; NCBI: National Center for Biotechnology Information; mTORC1: Mechanistic target of rapamycin complex 1; HMGCS2: 3-Hydroxy-3-methylglutaryl-CoA synthase 2; GSK3β: Glycogen synthase kinase 3β; AKI: Acute kidney injury; CMA: Chaperone-mediated autophagy; FGF21: Fibroblast growth factor 21.

Could SGLT2 Inhibitors Improve Exercise Intolerance in Chronic Heart Failure?

Despite the constant improvement of therapeutical options, heart failure (HF) remains associated with high mortality and morbidity. While new developments in guideline-recommended therapies can prolong survival and postpone HF hospitalizations, impaired exercise capacity remains one of the most debilitating symptoms of HF. Exercise intolerance in HF is multifactorial in origin, as the underlying cardiovascular pathology and reactive changes in skeletal muscle composition and metabolism both contribute. Recently, sodium-related glucose transporter 2 (SGLT2) inhibitors were found to improve cardiovascular outcomes significantly. Whilst much effort has been devoted to untangling the mechanisms responsible for these cardiovascular benefits of SGLT2 inhibitors, little is known about the effect of SGLT2 inhibitors on exercise performance in HF. This review provides an overview of the pathophysiological mechanisms that are responsible for exercise intolerance in HF, elaborates on the potential SGLT2-inhibitor-mediated effects on these phenomena, and provides an up-to-date overview of existing studies on the effect of SGLT2 inhibitors on clinical outcome parameters that are relevant to the assessment of exercise capacity. Finally, current gaps in the evidence and potential future perspectives on the effects of SGLT2 inhibitors on exercise intolerance in chronic HF are discussed.

Puerarin ameliorates nonalcoholic fatty liver in rats by regulating hepatic lipid accumulation, oxidative stress, and inflammation

Nonalcoholic fatty liver disease (NAFLD) has become one of the public health problems globally. The occurrence of NAFLD is usually accompanied by a series of chronic metabolic diseases, with a prevalence rate is 25.24% among adults worldwide. Therefore, NAFLD seriously affects the quality of life in patients and causes a large economic burden. It has been reported that puerarin has the function of lowering the serum lipids, but due to the complexity of NAFLD, the specific mechanism of action has not been clarified. The aim of this study was to evaluate the preventive or ameliorating effects of two doses of puerarin (0.11% and 0.22% in diet) on high-fat and high-fructose diet (HFFD)-induced NAFLD in rats. The rats were fed with HFFD-mixed puerarin for 20 weeks. The results showed that puerarin ameliorated the levels of lipids in the serum and liver. Further exploration of the mechanism found that puerarin ameliorated hepatic lipid accumulation in NAFLD rats by reducing the expression of Srebf1, Chrebp, Acaca, Scd1, Fasn, Acacb, Cd36, Fatp5, Degs1, Plin2, and Apob100 and upregulating the expression of Mttp, Cpt1a, and Pnpla2. At the same time, after administration of puerarin, the levels of antioxidant markers (superoxide dismutase, glutathione peroxidase, and catalase) were significantly increased in the serum and liver, and the contents of serum and hepatic inflammatory factors (interleukin-18, interleukins-1β, and tumor necrosis factor α) were clearly decreased. In addition, puerarin could ameliorate the liver function. Overall, puerarin ameliorated HFFD-induced NAFLD by modulating liver lipid accumulation, liver function, oxidative stress, and inflammation.

Emerging Role of Hepatic Ketogenesis in Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver diseases, arise from non-alcoholic fatty liver (NAFL) characterized by excessive fat accumulation as triglycerides. Although NAFL is benign, it could progress to non-alcoholic steatohepatitis (NASH) manifested with inflammation, hepatocyte damage and fibrosis. A subset of NASH patients develops end-stage liver diseases such as cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD is highly complex and strongly associated with perturbations in lipid and glucose metabolism. Lipid disposal pathways, in particular, impairment in condensation of acetyl-CoA derived from β-oxidation into ketogenic pathway strongly influence the hepatic lipid loads and glucose metabolism. Current evidence suggests that ketogenesis dispose up to two-thirds of the lipids entering the liver, and its dysregulation significantly contribute to the NAFLD pathogenesis. Moreover, ketone body administration in mice and humans shows a significant improvement in NAFLD. This review focuses on hepatic ketogenesis and its role in NAFLD pathogenesis. We review the possible mechanisms through which impaired hepatic ketogenesis may promote NAFLD progression. Finally, the review sheds light on the therapeutic implications of a ketogenic diet in NAFLD.

β-Hydroxybutyrate in Cardiovascular Diseases : A Minor Metabolite of Great Expectations

Despite recent advances in therapies, cardiovascular diseases ( CVDs ) are still the leading cause of mortality worldwide. Previous studies have shown that metabolic perturbations in cardiac energy metabolism are closely associated with the progression of CVDs. As expected, metabolic interventions can be applied to alleviate metabolic impairments and, therefore, can be used to develop therapeutic strategies for CVDs. β-hydroxybutyrate (β-HB) was once known to be a harmful and toxic metabolite leading to ketoacidosis in diabetes. However, the minor metabolite is increasingly recognized as a multifunctional molecular marker in CVDs. Although the protective role of β-HB in cardiovascular disease is controversial, increasing evidence from experimental and clinical research has shown that β-HB can be a “super fuel” and a signaling metabolite with beneficial effects on vascular and cardiac dysfunction. The tremendous potential of β-HB in the treatment of CVDs has attracted many interests of researchers. This study reviews the research progress of β-HB in CVDs and aims to provide a theoretical basis for exploiting the potential of β-HB in cardiovascular therapies.

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.

Ketogenic Diet and Cardiac Substrate Metabolism

The ketogenic diet (KD) entails a high intake of fat, moderate intake of protein, and a very limited intake of carbohydrates. Ketogenic dieting has been proposed as an effective intervention for type 2 diabetes and obesity since glycemic control is improved and sustained weight loss can be achieved. Interestingly, hyperketonemia is also associated with beneficial cardiovascular effects, possibly caused by improved cardiac energetics and reduced oxygen use. Therefore, the KD has the potential to both treat and prevent cardiovascular disease. However, the KD has some adverse effects that could counteract the beneficial cardiovascular properties. Of these, hyperlipidemia with elevation of triglycerides and LDL cholesterol levels are the most important. In addition, poor diet adherence and lack of knowledge regarding long-term effects may also reduce the broader applicability of the KD. The objective of this narrative review is to provide insights into the KD and its effects on myocardial ketone body utilization and, consequently, cardiovascular health.

Cardiac mechanisms of the beneficial effects of SGLT2 inhibitors in heart failure: Evidence for potential off-target effects

Sodium glucose cotransporter 2 inhibitors (SGLT2i) constitute a promising drug treatment for heart failure patients with either preserved or reduced ejection fraction. Whereas SGLT2i were originally developed to target SGLT2 in the kidney to facilitate glucosuria in diabetic patients, it is becoming increasingly clear that these drugs also have important effects outside of the kidney. In this review we summarize the literature on cardiac effects of SGLT2i, focussing on pro-inflammatory and oxidative stress processes, ion transport mechanisms controlling sodium and calcium homeostasis and metabolic/mitochondrial pathways. These mechanisms are particularly important as disturbances in these pathways result in endothelial dysfunction, diastolic dysfunction, cardiac stiffness, and cardiac arrhythmias that together contribute to heart failure. We review the findings that support the concept that SGLT2i directly and beneficially interfere with inflammation, oxidative stress, ionic homeostasis, and metabolism within the cardiac cell. However, given the very low levels of SGLT2 in cardiac cells, the evidence suggests that SGLT2-independent effects of this class of drugs likely occurs via off-target effects in the myocardium. Thus, while there is still much to be understood about the various factors which determine how SGLT2i affect cardiac cells, much of the research clearly demonstrates that direct cardiac effects of these SGLT2i exist, albeit mediated via SGLT2-independent pathways, and these pathways may play a role in explaining the beneficial effects of SGLT2 inhibitors in heart failure.

The Role of Oxidative Stress in the Aging Heart

Medical advances and the availability of diagnostic tools have considerably increased life expectancy and, consequently, the elderly segment of the world population. As age is a major risk factor in cardiovascular disease (CVD), it is critical to understand the changes in cardiac structure and function during the aging process. The phenotypes and molecular mechanisms of cardiac aging include several factors. An increase in oxidative stress is a major player in cardiac aging. Reactive oxygen species (ROS) production is an important mechanism for maintaining physiological processes; its generation is regulated by a system of antioxidant enzymes. Oxidative stress occurs from an imbalance between ROS production and antioxidant defenses resulting in the accumulation of free radicals. In the heart, ROS activate signaling pathways involved in myocyte hypertrophy, interstitial fibrosis, contractile dysfunction, and inflammation thereby affecting cell structure and function, and contributing to cardiac damage and remodeling. In this manuscript, we review recent published research on cardiac aging. We summarize the aging heart biology, highlighting key molecular pathways and cellular processes that underlie the redox signaling changes during aging. Main ROS sources, antioxidant defenses, and the role of dysfunctional mitochondria in the aging heart are addressed. As metabolism changes contribute to cardiac aging, we also comment on the most prevalent metabolic alterations. This review will help us to understand the mechanisms involved in the heart aging process and will provide a background for attractive molecular targets to prevent age-driven pathology of the heart. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

Serum Anion Gap is Associated with Risk of All-Cause Mortality in Critically Ill Patients with Acute Myocardial Infarction

Purpose

Anion gap (AG) is a valuable and easily obtained clinical tool for differentially diagnosis of acid-base disorders. Current understanding of the prognostic impact of AG on mortality after acute myocardial infarction (AMI) is limited. We aimed to investigate whether AG is a predictor of short-term and long-term all-cause mortality after AMI.

Patients and Methods

We examined 1806 patients diagnosed with AMI in intensive care unit from the Medical Information Mart for Intensive Care III (MIMIC-III) database. We analyzed the association of AG with 30-day, 180-day and 1-year all-cause mortality on a continuous scale and in categories, using multivariable Cox regression. We utilized restricted cubic splines to evaluate the linearity between hazard ratio (HR) and AG concentrations.

Results

AG was associated with a higher risk of 30-day, 180-day and 1-year all-cause mortality, with adjusted HRs of 1.083 (95% CI 1.051 to 1.117), 1.077 (95% CI 1.049 to 1.105), and 1.074 (95% CI 1.047 to 1.101), respectively. The results were consistent in subgroup analyses. The association between AG and all-cause mortality was linear for 180-day and 1-year mortality, and near linear for 30-day mortality, as higher concentrations were associated with high all-cause mortality. When stratified according to quartiles, AG was associated with 30-day mortality (HR[95% CI]: second quartile, 2.243[1.273, 3.955]; third quartile, 3.026[1.763, 5.194]; top quartile, 4.402[2.573, 7.531]), 180-day mortality (HR[95% CI]: second quartile, 1.719[1.118, 2.645]; third quartile, 2.362[1.575, 3.542]; top quartile, 3.116[2.077, 4.676]), and 1-year mortality (HR[95% CI]: second quartile, 1.700[1.143, 2.528]; third quartile, 2.239[1.536, 3.264]; top quartile, 2.876[1.969, 4.201]) using bottom quartile as reference.

Conclusion

We firstly demonstrated that higher AG was significantly associated with increased 30-day, 180-day and 1-year all-cause mortality in AMI patients. AG as an easily obtained marker is of strong and reliable predictive value for AMI mortality during follow-up.

Veni, Vidi, Vici: Immobilized Peptide-Based Conjugates as Tools for Capture, Analysis, and Transformation

Analysis of peptide biomarkers of pathological states of the organism is often a serious challenge, due to a very complex composition of the cell and insufficient sensitivity of the current analytical methods (including mass spectrometry). One of the possible ways to overcome this problem is sample enrichment by capturing the selected components using a specific solid support. Another option is increasing the detectability of the desired compound by its selective tagging. Appropriately modified and immobilized peptides can be used for these purposes. In addition, they find application in studying the specificity and activity of proteolytic enzymes. Immobilized heterocyclic peptide conjugates may serve as metal ligands, to form complexes used as catalysts or analytical markers. In this review, we describe various applications of immobilized peptides, including selective capturing of cysteine-containing peptides, tagging of the carbonyl compounds to increase the sensitivity of their detection, enrichment of biological samples in deoxyfructosylated peptides, and fishing out of tyrosine–containing peptides by the formation of azo bond. Moreover, the use of the one-bead-one-compound peptide library for the analysis of substrate specificity and activity of caspases is described. Furthermore, the evolution of immobilization from the solid support used in peptide synthesis to nanocarriers is presented. Taken together, the examples presented here demonstrate immobilized peptides as a multifunctional tool, which can be successfully used to solve multiple analytical problems.

SGLT2 Inhibitors and Ketone Metabolism in Heart Failure

Sodium-glucose cotransporter-2 (SGLT2) inhibitors have emerged as powerful drugs that can be used to treat heart failure (HF) patients, both with preserved and reduced ejection fraction and in the presence or absence of type 2 diabetes. While the mechanisms underlying the salutary effects of SGLT2 inhibitors have not been fully elucidated, there is clear evidence for a beneficial metabolic effect of these drugs. In this review, we discuss the effects of SGLT2 inhibitors on cardiac energy provision secondary to ketone bodies, pathological ventricular remodeling, and inflammation in patients with HF. While the specific contribution of ketone bodies to the pleiotropic cardiovascular benefits of SGLT2 inhibitors requires further clarification, ketone bodies themselves may also be used as a therapy for HF.

Exogenous Ketone Supplements in Athletic Contexts: Past, Present, and Future

The ketone bodies acetoacetate (AcAc) and β-hydroxybutyrate (βHB) have pleiotropic effects in multiple organs including brain, heart, and skeletal muscle by serving as an alternative substrate for energy provision, and by modulating inflammation, oxidative stress, catabolic processes, and gene expression. Of particular relevance to athletes are the metabolic actions of ketone bodies to alter substrate utilisation through attenuating glucose utilisation in peripheral tissues, anti-lipolytic effects on adipose tissue, and attenuation of proteolysis in skeletal muscle. There has been long-standing interest in the development of ingestible forms of ketone bodies that has recently resulted in the commercial availability of exogenous ketone supplements (EKS). These supplements in the form of ketone salts and ketone esters, in addition to ketogenic compounds such as 1,3-butanediol and medium chain triglycerides, facilitate an acute transient increase in circulating AcAc and βHB concentrations, which has been termed 'acute nutritional ketosis' or 'intermittent exogenous ketosis'. Some studies have suggested beneficial effects of EKS to endurance performance, recovery, and overreaching, although many studies have failed to observe benefits of acute nutritional ketosis on performance or recovery. The present review explores the rationale and historical development of EKS, the mechanistic basis for their proposed effects, both positive and negative, and evidence to date for their effects on exercise performance and recovery outcomes before concluding with a discussion of methodological considerations and future directions in this field.

Metabolic Therapy of Heart Failure: Is There a Future for B Vitamins?

Heart failure (HF) is a plague of the aging population in industrialized countries that continues to cause many deaths despite intensive research into more effective treatments. Although the therapeutic arsenal to face heart failure has been expanding, the relatively short life expectancy of HF patients is pushing towards novel therapeutic strategies. Heart failure is associated with drastic metabolic disorders, including severe myocardial mitochondrial dysfunction and systemic nutrient deprivation secondary to severe cardiac dysfunction. To date, no effective therapy has been developed to restore the cardiac energy metabolism of the failing myocardium, mainly due to the metabolic complexity and intertwining of the involved processes. Recent years have witnessed a growing scientific interest in natural molecules that play a pivotal role in energy metabolism with promising therapeutic effects against heart failure. Among these molecules, B vitamins are a class of water soluble vitamins that are directly involved in energy metabolism and are of particular interest since they are intimately linked to energy metabolism and HF patients are often B vitamin deficient. This review aims at assessing the value of B vitamin supplementation in the treatment of heart failure.

Ketone Body Metabolism in the Ischemic Heart

Ketone bodies have been identified as an important, alternative fuel source in heart failure. In addition, the use of ketone bodies as a fuel source has been suggested to be a potential ergogenic aid for endurance exercise performance. These findings have certainly renewed interest in the use of ketogenic diets and exogenous supplementation in an effort to improve overall health and disease. However, given the prevalence of ischemic heart disease and myocardial infarctions, these strategies may not be ideal for individuals with coronary artery disease. Although research studies have clearly defined changes in fatty acid and glucose metabolism during ischemia and reperfusion, the role of ketone body metabolism in the ischemic and reperfused myocardium is less clear. This review will provide an overview of ketone body metabolism, including the induction of ketosis via physiological or nutritional strategies. In addition, the contribution of ketone body metabolism in healthy and diseased states, with a particular emphasis on ischemia-reperfusion (I-R) injury will be discussed.

Breath acetone concentration: too heterogeneous to constitute a diagnosis or prognosis biomarker in heart failure? A systematic review and meta-analysis

Introduction. Exhaled breath acetone (ExA) has been investigated as a biomarker for heart failure (HF). Yet, barriers to its use in the clinical field have not been identified. The aim of this systematic review and meta-analysis was to assess the ExA heterogeneity and factors of variability in healthy controls (HC), to identify its relations with HF diagnosis and prognostic factors and to assess its diagnosis and prognosis accuracy in HF patients.Methods. A systematic search was conducted in PUBMED and Web of Science database. All studies with HC and HF patients with a measured ExA were included and studies providing ExA's diagnosis and prognosis accuracy were identified.Results. Out of 971 identified studies, 18 studies involving 833 HC and 1009 HF patients were included in the meta-analysis. In HC, ExA showed an important heterogeneity (I²= 99%). Variability factors were fasting state, sampling type and analytical method. The mean ExA was 1.89 times higher in HF patients vs. HC (782 [531-1032] vs. 413 [347-478] ppbv;p< 0.001). One study showed excellent diagnosis accuracy, and one showed a good prognosis value. ExA correlated with New York Heart Association (NYHA) dyspnea (p< 0.001) and plasma brain natriuretic peptide (p< 0.001). Studies showed a poor definition and reporting of included subjects.Discussion. Despite the between-study heterogeneity in HC, the evidence of an excellent diagnosis and prognosis value of ExA in HF from single studies can be extended to clinical populations worldwide. Factors of variability (ExA procedure and breath sampling) could further improve the diagnosis and prognosis values of this biomarker in HF patients.

Association of Circulating Ketone Bodies With Functional Outcomes After ST-Segment Elevation Myocardial Infarction

BACKGROUND

Circulating ketone bodies (KBs) are increased in patients with heart failure (HF), corresponding with increased cardiac KB metabolism and HF severity. However, the role of circulating KBs in ischemia/reperfusion remains unknown.

OBJECTIVES

This study sought to investigate longitudinal changes of KBs and their associations with functional outcomes in patients presenting with ST-segment elevation myocardial infarction (STEMI).

METHODS

KBs were measured in 369 participants from a randomized trial on early metformin therapy after STEMI. Nonfasting plasma concentrations of KBs (β-hydroxybutyrate, acetoacetate, and acetone) were measured by nuclear magnetic resonance spectroscopy at presentation, at 24 hours, and after 4 months. Myocardial infarct size and left ventricular ejection fraction (LVEF) were determined by cardiac magnetic resonance imaging at 4 months. Associations of circulating KBs with infarct size and LVEF were determined using multivariable linear regression analyses.

RESULTS

Circulating KBs were high at presentation with STEMI (median total KBs: 520 μmol/L; interquartile range [IQR]: 315-997 μmol/L). At 24 hours after reperfusion, KBs were still high compared with levels at 4-month follow-up (206 μmol/L [IQR: 174-246] vs 166 μmol/L [IQR: 143-201], respectively; P < 0.001). Increased KB concentrations at 24 hours were independently associated with larger myocardial infarct size (total KBs, per 100 μmol/L: β = 1.56; 95% confidence interval: 0.29-2.83; P = 0.016) and lower LVEF (β = -1.78; 95% CI: (-3.17 to -0.39; P = 0.012).

CONCLUSIONS

Circulating KBs are increased in patients presenting with STEMI. Higher KBs at 24 hours are associated with functional outcomes after STEMI, which suggests a potential role for ketone metabolism in response to myocardial ischemia. (Metabolic Modulation With Metformin to Reduce Heart Failure After Acute Myocardial Infarction: Glycometabolic Intervention as Adjunct to Primary Coronary Intervention in ST Elevation Myocardial Infarction (GIPS-III): a Randomized Controlled Trial; NCT01217307).

Digestive promoting effect and mechanism of Jiao Sanxian in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Jiao Sanxian, a customary term for the three Traditional Chinese Medicines of charred hawthorn (Crataegi Fructus), charred malt (Hordei Fructus Germinatus) and Liu Shenqu (Massa Medicata Fermentata), is a classic prescription for the treatment of functional dyspepsia (FD). This prescription is called "Jiao Sanxian" in China because people believe that it is a miracle medicine for enhancing digestion and improving stagnation of digestive system. Even though Jiao Sanxian is widely used in clinical treatment, the underlying mechanism has not been clarified to date.

AIM OF THE STUDY

The present study is aimed to explore the efficacy and mechanism of Jiao Sanxian in improving the symptoms of FD in rats by using multiple pharmacological methods.

MATERIALS AND METHODS

The Sprague Dawley (SD) rats were divided into control, model, Jiao Sanxian decoction low-dosage (JSXD LD), Jiao Sanxian decoction medium-dosage (JSXD MD), and Jiao Sanxian decoction high-dosage (JSXD HD) group at random. A FD model was established with reserpine, and animals were given intragastric administration. During this period, weight and food intake of animals were recorded. Samples of rat gastric antrum, spleen, and duodenum were collected for pathological staining and immunohistochemical determination of Ghrelin protein expression after 19 days of treatment. Enzyme-linked immunosorbent assay (ELISA) was used to determine the concentration of related brain gut peptides in serum. Moreover, 16S rRNA sequencing was used to valuate the influence of intestinal flora structure of the cecal contents of experimental rats. And plasma metabolomics by Ultra Performance Liquid Chromatography coupled with Quadrupole-Time-of-Flight mass spectrometry (UPLC-Q/TOF-MS) were performed to further reveal the mechanism of action.

RESULTS

Jiao Sanxian decoction (JSXD) group with different dosage could increase body weight and food intake, improve histopathological changes, and alter disordered brain gut peptides in FD rats. 16S rRNA sequencing results described that JSXD improved the disorder of structural composition, biodiversity and function of gut microbiota in FD rats. Metabolomics illustrated 26 metabolites with JSXD treatment underwent continuous changes, which revealed JSXD might exert digestive effect by ameliorating abnormal metabolic pathways. The most relevant metabolic pathways were arachidonic acid metabolism, pyruvate metabolism, glycerophospholipid metabolism, alanine, aspartate and glutamate metabolism.

CONCLUSIONS

JSXD can improve functional dyspepsia in rats and the mechanism is related to regulate secretion of brain gut peptides, significantly improve the disorder of intestinal flora and ameliorated multi-metabolic pathways.

β-hydroxybutyrate as an Anti-Aging Metabolite

The ketone bodies, especially β-hydroxybutyrate (β-HB), derive from fatty acid oxidation and alternatively serve as a fuel source for peripheral tissues including the brain, heart, and skeletal muscle. β-HB is currently considered not solely an energy substrate for maintaining metabolic homeostasis but also acts as a signaling molecule of modulating lipolysis, oxidative stress, and neuroprotection. Besides, it serves as an epigenetic regulator in terms of histone methylation, acetylation, β-hydroxybutyrylation to delay various age-related diseases. In addition, studies support endogenous β-HB administration or exogenous supplementation as effective strategies to induce a metabolic state of nutritional ketosis. The purpose of this review article is to provide an overview of β-HB metabolism and its relationship and application in age-related diseases. Future studies are needed to reveal whether β-HB has the potential to serve as adjunctive nutritional therapy for aging.

β-hydroxybutyrate as an Anti-Aging Metabolite

The ketone bodies, especially β-hydroxybutyrate (β-HB), derive from fatty acid oxidation and alternatively serve as a fuel source for peripheral tissues including the brain, heart, and skeletal muscle. β-HB is currently considered not solely an energy substrate for maintaining metabolic homeostasis but also acts as a signaling molecule of modulating lipolysis, oxidative stress, and neuroprotection. Besides, it serves as an epigenetic regulator in terms of histone methylation, acetylation, β-hydroxybutyrylation to delay various age-related diseases. In addition, studies support endogenous β-HB administration or exogenous supplementation as effective strategies to induce a metabolic state of nutritional ketosis. The purpose of this review article is to provide an overview of β-HB metabolism and its relationship and application in age-related diseases. Future studies are needed to reveal whether β-HB has the potential to serve as adjunctive nutritional therapy for aging.