Ketone body β-hydroxybutyrate is an autophagy-dependent vasodilator

SGLT2 inhibition leads to a restoration of hepatic and circulating metabolites involved in the folate cycle and pyrimidine biosynthesis

Inhibition of sodium-glucose cotransporter 2 (SGLT2) by empagliflozin (EMPA) and other "flozins" can improve glycemic control under conditions of diabetes and kidney disease. Though they act on the kidney, they also offer cardiovascular and liver protection. Previously, we found that EMPA decreased circulating triglycerides and hepatic lipid and cholesterol esters in male TallyHo mice fed a high-milk-fat diet (HMFD). The goal of this study was to determine whether the liver protection is associated with a change in metabolic function by characterizing the hepatic and circulating metabolic and lipidomic profiles using targeted LC-MS. In both male and female mice, HMFD feeding significantly altered the circulating and hepatic metabolome compared with low-fat diet (LFD). Addition of EMPA resulted in the restoration of circulating orotate (intermediate in pyrimidine biosynthesis) and hepatic dihydrofolate (intermediate in the folate and methionine cycles) levels in males and acylcarnitines in females. These changes were partially explained by altered expression of rate-limiting enzymes in these pathways. This metabolic signature was not detected when EMPA was incorporated into an LFD, suggesting that the restoration requires the metabolic shift that accompanies the HMFD. Notably, the HMFD increased expression of 18 of 20 circulating amino acids in males and 11 of 20 in females, and this pattern was reversed by EMPA. Finally, we confirmed that SGLT2 inhibition upregulates ketone bodies including β-hydroxybutyrate. Collectively, this study highlights the metabolic changes that occur with EMPA treatment, and sheds light on the possible mechanisms by which this drug offers liver and systemic protection.NEW & NOTEWORTHY Sodium-glucose cotransporter 2 (SGLT2) inhibitors, including empagliflozin, have emerged as a new treatment option for individuals with type 2 diabetes that have positive impacts on kidney and cardiovascular disease. However, less is known about their impact on other tissues, including the liver. Here, we report that empagliflozin reduces hepatic steatosis that is associated with restoring metabolic intermediates in the folate and pyrimidine biosynthesis pathways. These changes may lead to new approaches to treat nonalcoholic fatty liver disease.

β-hydroxybutyrate and ischemic stroke: roles and mechanisms

Stroke is a significant global burden, causing extensive morbidity and mortality. In metabolic states where glucose is limited, ketone bodies, predominantly β-hydroxybutyrate (BHB), act as alternative fuel sources. Elevated levels of BHB have been found in the ischemic hemispheres of animal models of stroke, supporting its role in the pathophysiology of cerebral ischemia. Clinically, higher serum and urinary BHB concentrations have been associated with adverse outcomes in ischemic stroke, highlighting its potential utility as a prognostic biomarker. In both animal and cellular models, exogenous BHB administration has exhibited neuroprotective effects, reduction of infarct size, and improvement of neurological outcomes. In this review, we focus on the role of BHB before and after ischemic stroke, with an emphasis on the therapeutic potential and mechanisms of ketone administration after ischemic stroke.

Crosstalk among Reactive Oxygen Species, Autophagy and Metabolism in Myocardial Ischemia and Reperfusion Stages

Myocardial ischemia is the most common cardiovascular disease. Reperfusion, an important myocardial ischemia tool, causes unexpected and irreversible damage to cardiomyocytes, resulting in myocardial ischemia/reperfusion (MI/R) injury. Upon stress, especially oxidative stress induced by reactive oxygen species (ROS), autophagy, which degrades the intracellular energy storage to produce metabolites that are recycled into metabolic pathways to buffer metabolic stress, is initiated during myocardial ischemia and MI/R injury. Excellent cardioprotective effects of autophagy regulators against MI and MI/R have been reported. Reversing disordered cardiac metabolism induced by ROS also exhibits cardioprotective action in patients with myocardial ischemia. Herein, we review current knowledge on the crosstalk between ROS, cardiac autophagy, and metabolism in myocardial ischemia and MI/R. Finally, we discuss the possible regulators of autophagy and metabolism that can be exploited to harness the therapeutic potential of cardiac metabolism and autophagy in the diagnosis and treatment of myocardial ischemia and MI/R.

Emerging Pathophysiological Roles of Ketone Bodies

The discovery of insulin approximately a century ago greatly improved the management of diabetes, including many of its life-threatening acute complications like ketoacidosis. This breakthrough saved many lives and extended the healthy lifespan of many patients with diabetes. However, there is still a negative perception of ketone bodies stemming from ketoacidosis. Originally, ketone bodies were thought of as a vital source of energy during fasting and exercise. Furthermore, in recent years, research on calorie restriction and its potential impact on extending healthy lifespans, as well as studies on ketone bodies, have gradually led to a reevaluation of the significance of ketone bodies in promoting longevity. Thus, in this review, we discuss the emerging and hidden roles of ketone bodies in various organs, including the heart, kidneys, skeletal muscles, and brain, as well as their potential impact on malignancies and lifespan.

Efficacy and safety of prolonged water fasting: a narrative review of human trials

The goal of this narrative review is to summarize the effects of prolonged fasting on various metabolic health measures, including body weight, blood pressure, plasma lipids, and glycemic control. Prolonged fasting is characterized by consciously eating little to no food or caloric beverages for several days to weeks. Results reveal that prolonged fasting for 5-20 days produces potent increases in circulating ketones, and mild to moderate weight loss of 2-10%. Approximately two-thirds of the weight lost is lean mass, and one-third is fat mass. The excessive lean mass loss suggests that prolonged fasting may increase the breakdown of muscle proteins, which is a concern. Systolic and diastolic blood pressure consistently decreased with prolonged fasting. However, the impact of these protocols on plasma lipids is less clear. While some trials demonstrate decreases in LDL cholesterol and triglycerides, others show no benefit. With regard to glycemic control, reductions in fasting glucose, fasting insulin, insulin resistance, and glycated hemoglobin (HbA1c) were noted in adults with normoglycemia. In contrast, these glucoregulatory factors remained unchanged in patients with type 1 or type 2 diabetes. The effects of refeeding were also examined in a few trials. It was shown that 3-4 months after the fast was completed, all metabolic benefits were no longer observed, even when weight loss was maintained. With regard to adverse events, metabolic acidosis, headaches, insomnia, and hunger were observed in some studies. In summary, prolonged fasting appears to be a moderately safe diet therapy that can produce clinically significant weight loss (>5%) over a few days or weeks. However, the ability of these protocols to produce sustained improvements in metabolic markers warrants further investigation.

A very-low carbohydrate content in a high-fat diet modifies the plasma metabolome and impacts systemic inflammation and experimental atherosclerosis

Ketogenic diets (KDs) are very high-fat low-carbohydrate diets that promote nutritional ketosis and are widely used for weight loss, although concerns about potential adverse cardiovascular effects remain. We investigated a very high-fat KD's vascular impact and plasma metabolic signature compared to a non-ketogenic high-fat diet (HFD). Apolipoprotein E deficient (ApoE -/-) mice were fed a KD (%kcal:81:1:18, fat/carbohydrate/protein), a non-ketogenic high-fat diet with half of the fat content (HFD) (%kcal:40:42:18, fat/carbohydrate/protein) for 12 weeks. Plasma samples were used to quantify the major ketone body beta-hydroxybutyrate (BHB) and several pro-inflammatory cytokines (IL-6, MCP-1, MIP-1alpha, and TNF alpha), and to targeted metabolomic profiling by mass spectrometry. In addition, aortic atherosclerotic lesions were quantified ex-vivo by magnetic resonance imaging (MRI) on a 14-tesla system. KD was atherogenic when compared to the control diet, but KD mice, when compared to the HFD group (1) had markedly higher levels of BHB and lower levels of cytokines, confirming the presence of ketosis that alleviated the well-established fat-induced systemic inflammation; (2) displayed significant changes in the plasma metabolome that included a decrease in lipophilic metabolites and an increase in hydrophilic metabolites; (3) had significantly lower levels of several atherogenic lipid metabolites, including phosphatidylcholines, cholesterol esters, sphingomyelins, and ceramides; and (4) presented significantly lower aortic plaque burden. KD was atherogenic and was associated with specific metabolic changes but alleviated the fat-induced inflammation and lessened the progression of atherosclerosis when compared to the HFD.

Genome-wide characterization of circulating metabolic biomarkers

Genome-wide association analyses using high-throughput metabolomics platforms have led to novel insights into the biology of human metabolism1-7. This detailed knowledge of the genetic determinants of systemic metabolism has been pivotal for uncovering how genetic pathways influence biological mechanisms and complex diseases8-11. Here we present a genome-wide association study for 233 circulating metabolic traits quantified by nuclear magnetic resonance spectroscopy in up to 136,016 participants from 33 cohorts. We identify more than 400 independent loci and assign probable causal genes at two-thirds of these using manual curation of plausible biological candidates. We highlight the importance of sample and participant characteristics that can have significant effects on genetic associations. We use detailed metabolic profiling of lipoprotein- and lipid-associated variants to better characterize how known lipid loci and novel loci affect lipoprotein metabolism at a granular level. We demonstrate the translational utility of comprehensively phenotyped molecular data, characterizing the metabolic associations of intrahepatic cholestasis of pregnancy. Finally, we observe substantial genetic pleiotropy for multiple metabolic pathways and illustrate the importance of careful instrument selection in Mendelian randomization analysis, revealing a putative causal relationship between acetone and hypertension. Our publicly available results provide a foundational resource for the community to examine the role of metabolism across diverse diseases.

Relationship between serum β-hydroxybutyrate and hepatic fatty acid oxidation in individuals with obesity and NAFLD

Nonalcoholic fatty liver disease (NAFLD) is characterized by excess lipid accumulation that can progress to inflammation (nonalcoholic steatohepatitis, NASH), and fibrosis. Serum β-hydroxybutyrate (β-HB), a product of the ketogenic pathway, is commonly used as a surrogate marker for hepatic fatty acid oxidation (FAO). However, it remains uncertain whether this relationship holds true in the context of NAFLD in humans. We compared fasting serum β-HB levels with direct measurement of liver mitochondrial palmitate oxidation in humans stratified based on NAFLD severity (n = 142). Patients were stratified based on NAFLD activity score (NAS): NAS = 0 (no disease), NAS = 1-2 (mild), NAS = 3-4 (moderate), and NAS ≥ 5 (advanced). Moderate and advanced NAFLD is associated with reductions in liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), serum β-HB, but not 3-hydroxy-3-methylglutaryl-CoA lyase (HMGCL) mRNA, relative to no disease. Worsening liver mitochondrial complete palmitate oxidation corresponded with lower HMGCS2 mRNA but not total (complete + incomplete) palmitate oxidation. Interestingly, we found that liver HMGCS2 mRNA and serum β-HB correlated with liver mitochondrial β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity and CPT1A mRNA. Also, lower mitochondrial mass and markers of mitochondrial turnover positively correlated with lower HMGCS2 in the liver. These data suggest that liver ketogenesis and FAO occur at comparable rates in individuals with NAFLD. Our findings support the utility of serum β-HB to serve as a marker of liver injury and hepatic FAO in the context of NAFLD.NEW & NOTEWORTHY Serum β-hydroxybutyrate (β-HB) is frequently utilized as a surrogate marker for hepatic fatty acid oxidation; however, few studies have investigated this relationship during states of liver disease. We found that the progression of nonalcoholic fatty liver disease (NAFLD) is associated with reductions in circulating β-HB and liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2). As well, decreased rates of hepatic fatty acid oxidation correlated with liver HMGCS2 mRNA and serum β-HB. Our work supports serum β-HB as a potential marker for hepatic fatty acid oxidation and liver injury during NAFLD.

The therapeutic potential of ketones in cardiometabolic disease: impact on heart and skeletal muscle

β-Hydroxybutyrate (βOHB) is the major ketone in the body, and it is recognized as a metabolic energy source and an important signaling molecule. While ketone oxidation is essential in the brain during prolonged fasting/starvation, other organs such as skeletal muscle and the heart also use ketones as metabolic substrates. Additionally, βOHB-mediated molecular signaling events occur in heart and skeletal muscle cells, and via metabolism and/or signaling, ketones may contribute to optimal skeletal muscle health and cardiac function. Of importance, when the use of ketones for ATP production and/or as signaling molecules becomes disturbed in the presence of underlying obesity, type 2 diabetes, and/or cardiovascular diseases, these changes may contribute to cardiometabolic disease. As a result of these disturbances in cardiometabolic disease, multiple approaches have been used to elevate circulating ketones with the goal of optimizing either ketone metabolism or ketone-mediated signaling. These approaches have produced significant improvements in heart and skeletal muscle during cardiometabolic disease with a wide range of benefits that include improved metabolism, weight loss, better glycemic control, improved cardiac and vascular function, as well as reduced inflammation and oxidative stress. Herein, we present the evidence that indicates that ketone therapy could be used as an approach to help treat cardiometabolic diseases by targeting cardiac and skeletal muscles.

Acute fasting reduces tolerance to progressive central hypovolemia in humans

Potential health benefits of an acute fast include reductions in blood pressure and increases in vagal cardiac control. These purported health benefits could put fasted humans at risk for cardiovascular collapse when exposed to central hypovolemia. The purpose of this study was to test the hypothesis that an acute 24-h fast (vs. 3-h postprandial) would reduce tolerance to central hypovolemia induced via lower body negative pressure (LBNP). We measured blood ketones (β-OHB) to confirm a successful fast (n = 18). We recorded the electrocardiogram (ECG), beat-to-beat arterial pressure, muscle sympathetic nerve activity (MSNA; n = 7), middle cerebral artery blood velocity (MCAv), and forearm blood flow. Following a 5-min baseline, LBNP was increased by 15 mmHg until -60 mmHg and then increased by 10 mmHg in a stepwise manner until onset of presyncope. Each LBNP stage lasted 5-min. Data are expressed as means ± SE β-OHB increased (β-OHB; 0.12 ± 0.04 fed vs. 0.47 ± 0.11, P < 0.01 mmol/L fast). Tolerance to central hypovolemia was decreased by ∼10% in the fasted condition measured via total duration of negative pressure (1,370 [Formula: see text] 89 fed vs. 1,229 ± 94 s fast, P = 0.04), and was negatively associated with fasting blood ketones (R = -0.542, P = 0.02). During LBNP, heart rate and MSNA increased similarly, but in the fasted condition forearm vascular resistance was significantly reduced. Our results suggest that acute fasting reduces tolerance to central hypovolemia by blunting increases in peripheral resistance, indicating that prolonged fasting may hinder an individual's ability to compensate to a loss of blood volume.NEW & NOTEWORTHY An acute 24 h fasting reduces tolerance to central hypovolemia, and tolerance is negatively associated with blood ketone levels. Compared with a fed condition (3-h postprandial), fasted participants exhibited blunted peripheral vasoconstriction and greater reductions in stroke volume during stepwise lower body negative pressure. These findings suggest that a prolonged fast may lead to quicker decompensation during central hypovolemia.

Pharmacological targets at the lysosomal autophagy-NLRP3 inflammasome crossroads

Many aspects of cell homeostasis and integrity are maintained by the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome. The NLRP3 oligomeric protein complex assembles in response to exogenous and endogenous danger signals. This inflammasome has also been implicated in the pathogenesis of a range of disease conditions, particularly chronic inflammatory diseases. Given that NLRP3 modulates autophagy, which is also a key regulator of inflammasome activity, excessive inflammation may be controlled by targeting this intersecting pathway. However, specific niche areas of NLRP3-autophagy interactions and their reciprocal regulatory mechanisms remain underexplored. Consequently, we lack treatment methods specifically targeting this pivotal axis. Here, we discuss the potential of such strategies in the context of autoimmune and metabolic diseases and propose some research avenues.

Effect of Acute and Chronic Ingestion of Exogenous Ketone Supplements on Blood Pressure: A Systematic Review and Meta-Analysis

Exogenous ketone supplements have been suggested to have potential cardiovascular benefits, but their overall effect on blood pressure is unclear. Our objective was to perform a systematic review and meta-analysis on the effects of exogenous ketone supplements on blood pressure (BP) and concomitant changes in resting heart rate (HR). Five databases were searched on January 27th, 2023, for randomized and non-randomized studies. A random-effects model meta-analysis was performed including all studies jointly and separately for acute and chronic ingestion of ketone supplements. Out of 4012 studies identified in the search, 4 acute and 6 chronic studies with n = 187 participants were included. Pooled results (n = 10) showed no change in systolic (SMD [95% CI]= -0.14 [-0.40; 0.11]; I2= 30%; p = 0.17) or diastolic BP (-0.12 [-0.30; 0.05]; I2= 0%; p = 0.69), with a potential tendency observed toward increased resting heart rate (0.17 [-0.14; 0.47]; I2= 40%; p = 0.10). Similar results for systolic and diastolic BP were observed when assessing separately the effect of acute and chronic ingestion of ketone supplements (p ≥ 0.33). Supplement dosage was found to modulate the increase in resting heart rate (0.019 ± 0.006; p = 0.013; R2=100%), suggesting that higher supplement doses lead to a higher resting heart rate. Based on currently available data, acute or prolonged ingestion of ketone supplements does not seem to modulate BP. However, a tendency for HR to increase after acute ingestion was observed, particularly with higher doses. Higher quality studies with appropriate standardized measurements are needed to confirm these results.

The Ketogenic Diet in the Prevention of Migraines in the Elderly

Migraines display atypical age dependence, as the peak of their prevalence occurs between the ages of 20-40 years. With age, headache attacks occur less frequently and are characterized by a lower amplitude. However, both diagnosis and therapy of migraines in the elderly are challenging due to multiple comorbidities and polypharmacy. Dietary components and eating habits are migraine triggers; therefore, nutrition is a main target in migraine prevention. Several kinds of diets were proposed to prevent migraines, but none are commonly accepted due to inconsistent results obtained in different studies. The ketogenic diet is featured by very low-carbohydrate and high-fat contents. It may replace glucose with ketone bodies as the primary source of energy production. The ketogenic diet and the actions of ketone bodies are considered beneficial in several aspects of health, including migraine prevention, but studies on the ketogenic diet in migraines are not standardized and poorly evidenced. Apart from papers claiming beneficial effects of the ketogenic diet in migraines, several studies have reported that increased levels of ketone bodies may be associated with all-cause and incident heart failure mortality in older adults and are supported by research on mice showing that the ketogenic diets and diet supplementation with a human ketone body precursor may cause life span shortening. Therefore, despite reports showing a beneficial effect of the ketogenic diet in migraines, such a diet requires further studies, including clinical trials, to verify whether it should be recommended in older adults with migraines.

Acute effects of β-hydroxybutyrate on left ventricular function in young, healthy adults

Interest in ketones as a cardiac "super fuel" has grown significantly following reports of a marked increase in cardiac output after exogenous ketone administration in heart failure. However, the extent to which this increase in cardiac output is related to changes in cardiac contractility, and dependent on the presence of heart failure, remains incompletely understood. Therefore, we performed a randomized, double-blind, placebo-controlled study of oral ketone ester in young healthy volunteers. Baseline cardiac magnetic resonance imaging was performed and repeated every 15 min for 60 min after ketone and placebo ingestion to assess changes in left ventricular function. As expected, circulating β-hydroxybutyrate increased rapidly after ketone ingestion, but did not change with placebo (interaction: P < 0.001). Consistent with prior investigations, ketone ingestion resulted in an average 1 L/min increase in cardiac output after 60 min that did not occur with placebo (interaction: P = 0.026). This increase in cardiac output was primarily driven by an increase in heart rate after ketone ingestion (interaction: P = 0.018), with only a modest increase in stroke volume (interaction: P = 0.037). Changes in left ventricular strain and twist mechanics were limited. Taken together, the increase in cardiac output following an acute elevation in circulating β-hydroxybutyrate is primarily driven by changes in cardiac chronotropy, with minimal inotropic contribution.NEW & NOTEWORTHY In this randomized, double-blind, placebo-controlled study of oral ketone ester in young healthy volunteers, we show a marked increase in cardiac output (∼1 L/min), driven primarily by changes in chronotropy. The cardiac magnetic resonance imaging data support the limited role for inotropy.

Metabolic Messengers: ketone bodies

Prospective molecular targets and therapeutic applications for ketone body metabolism have increased exponentially in the past decade. Initially considered to be restricted in scope as liver-derived alternative fuel sources during periods of carbohydrate restriction or as toxic mediators during diabetic ketotic states, ketogenesis and ketone bodies modulate cellular homeostasis in multiple physiological states through a diversity of mechanisms. Selective signalling functions also complement the metabolic fates of the ketone bodies acetoacetate and D-β-hydroxybutyrate. Here we discuss recent discoveries revealing the pleiotropic roles of ketone bodies, their endogenous sourcing, signalling mechanisms and impact on target organs, and considerations for when they are either stimulated for endogenous production by diets or pharmacological agents or administered as exogenous wellness-promoting agents.

Ketone body 3-hydroxybutyrate elevates cardiac output through peripheral vasorelaxation and enhanced cardiac contractility

The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output and myocardial perfusion without affecting blood pressure in humans, but the cardiovascular sites of action remain obscure. Here, we test the hypothesis in rats that 3-OHB acts directly on the heart to increase cardiac contractility and directly on blood vessels to lower systemic vascular resistance. We investigate effects of 3-OHB on (a) in vivo hemodynamics using echocardiography and invasive blood pressure measurements, (b) isolated perfused hearts in Langendorff systems, and (c) isolated arteries and veins in isometric myographs. We compare Na-3-OHB to equimolar NaCl added to physiological buffers or injection solutions. At plasma concentrations of 2-4 mM in vivo, 3-OHB increases cardiac output (by 28.3±7.8%), stroke volume (by 22.4±6.0%), left ventricular ejection fraction (by 13.3±4.6%), and arterial dP/dtmax (by 31.9±11.2%) and lowers systemic vascular resistance (by 30.6±11.2%) without substantially affecting heart rate or blood pressure. Applied to isolated perfused hearts at 3-10 mM, 3-OHB increases left ventricular developed pressure by up to 26.3±7.4 mmHg and coronary perfusion by up to 20.2±9.5%. Beginning at 1-3 mM, 3-OHB relaxes isolated coronary (EC50=12.4 mM), cerebral, femoral, mesenteric, and renal arteries as well as brachial, femoral, and mesenteric veins by up to 60% of pre-contraction within the pathophysiological concentration range. Of the two enantiomers that constitute racemic 3-OHB, D-3-OHB dominates endogenously; but tested separately, the enantiomers induce similar vasorelaxation. We conclude that increased cardiac contractility and generalized systemic vasorelaxation can explain the elevated cardiac output during 3-OHB administration. These actions strengthen the therapeutic rationale for 3-OHB in heart failure management.

Lipid and glucose metabolism in senescence

Senescence is an inevitable biological process. Disturbances in glucose and lipid metabolism are essential features of cellular senescence. Given the important roles of these types of metabolism, we review the evidence for how key metabolic enzymes influence senescence and how senescence-related secretory phenotypes, autophagy, apoptosis, insulin signaling pathways, and environmental factors modulate glucose and lipid homeostasis. We also discuss the metabolic alterations in abnormal senescence diseases and anti-cancer therapies that target senescence through metabolic interventions. Our work offers insights for developing pharmacological strategies to combat senescence and cancer.

Comparative Metabolomics in Single Ventricle Patients after Fontan Palliation: A Strong Case for a Targeted Metabolic Therapy

Most studies on single ventricle (SV) circulation take a physiological or anatomical approach. Although there is a tight coupling between cardiac contractility and metabolism, the metabolic perspective on this patient population is very recent. Early findings point to major metabolic disturbances, with both impaired glucose and fatty acid oxidation in the cardiomyocytes. Additionally, Fontan patients have systemic metabolic derangements such as abnormal glucose metabolism and hypocholesterolemia. Our literature review compares the metabolism of patients with a SV circulation after Fontan palliation with that of patients with a healthy biventricular (BV) heart, or different subtypes of a failing BV heart, by Pubmed review of the literature on cardiac metabolism, Fontan failure, heart failure (HF), ketosis, metabolism published in English from 1939 to 2023. Early evidence demonstrates that SV circulation is not only a hemodynamic burden requiring staged palliation, but also a metabolic issue with alterations similar to what is known for HF in a BV circulation. Alterations of fatty acid and glucose oxidation were found, resulting in metabolic instability and impaired energy production. As reported for patients with BV HF, stimulating ketone oxidation may be an effective treatment strategy for HF in these patients. Few but promising clinical trials have been conducted thus far to evaluate therapeutic ketosis with HF using a variety of instruments, including ketogenic diet, ketone esters, and sodium-glucose co-transporter-2 (SGLT2) inhibitors. An initial trial on a small cohort demonstrated favorable outcomes for Fontan patients treated with SGLT2 inhibitors. Therapeutic ketosis is worth considering in the treatment of Fontan patients, as ketones positively affect not only the myocardial energy metabolism, but also the global Fontan physiopathology. Induced ketosis seems promising as a concerted therapeutic strategy.

SGLT2 inhibitors: role in protective reprogramming of cardiac nutrient transport and metabolism

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce heart failure events by direct action on the failing heart that is independent of changes in renal tubular function. In the failing heart, nutrient transport into cardiomyocytes is increased, but nutrient utilization is impaired, leading to deficient ATP production and the cytosolic accumulation of deleterious glucose and lipid by-products. These by-products trigger downregulation of cytoprotective nutrient-deprivation pathways, thereby promoting cellular stress and undermining cellular survival. SGLT2 inhibitors restore cellular homeostasis through three complementary mechanisms: they might bind directly to nutrient-deprivation and nutrient-surplus sensors to promote their cytoprotective actions; they can increase the synthesis of ATP by promoting mitochondrial health (mediated by increasing autophagic flux) and potentially by alleviating the cytosolic deficiency in ferrous iron; and they might directly inhibit glucose transporter type 1, thereby diminishing the cytosolic accumulation of toxic metabolic by-products and promoting the oxidation of long-chain fatty acids. The increase in autophagic flux mediated by SGLT2 inhibitors also promotes the clearance of harmful glucose and lipid by-products and the disposal of dysfunctional mitochondria, allowing for mitochondrial renewal through mitochondrial biogenesis. This Review describes the orchestrated interplay between nutrient transport and metabolism and nutrient-deprivation and nutrient-surplus signalling, to explain how SGLT2 inhibitors reverse the profound nutrient, metabolic and cellular abnormalities observed in heart failure, thereby restoring the myocardium to a healthy molecular and cellular phenotype.

Ketones and the cardiovascular system

Ketone bodies, the main one being β-hydroxybutyrate, have emerged as important regulators of the cardiovascular system. In healthy individuals, as well as in individuals with heart failure or post-myocardial infarction, ketones provide a supplemental energy source for both the heart and the vasculature. In the failing heart, this additional energy may contribute to improved cardiac performance, whereas increasing ketone oxidation in vascular smooth muscle and endothelial cells enhances cell proliferation and prevents blood vessel rarefication. Ketones also have important actions in signaling pathways, posttranslational modification pathways and gene transcription; many of which modify cell proliferation, inflammation, oxidative stress, endothelial function and cardiac remodeling. Attempts to therapeutically increase ketone delivery to the cardiovascular system are numerous and have shown mixed results in terms of effectiveness. Here we review the bioenergetic and signaling effects of ketones on the cardiovascular system, and we discuss how ketones can potentially be used to treat cardiovascular diseases.

D-beta-hydroxybutyrate reduced the enhanced cardiac microvascular endothelial FoxO1 to play protective roles in diabetic rats and high glucose-stimulated human cardiac microvascular endothelial cells

The O subfamily of forkhead (FoxO) 1 may participate in the pathogenesis of diabetic microvascular endothelial injury. However, it is unknown whether D-beta-hydroxybutyrate (BHB) regulates cardiac microvascular endothelial FoxO1 to play protective roles in diabetes. In the study, limb microvascular morphological changes, endothelial distribution of the tight junction protein Claudin-5 and FoxO1, and FoxO1 content in limb tissue from clinical patients were evaluated. Then the effects of BHB on cardiac microvascular morphological changes, cardiac FoxO1 generation and its microvascular distribution in diabetic rats were measured. And the effects of BHB on FoxO1 generation in high glucose (HG)-stimulated human cardiac microvascular endothelial cells (HCMECs) were further analyzed. The results firstly confirmed the enhanced limb microvascular FoxO1 distribution, with reduced Claudin-5 and endothelial injury in clinical patients. Then the elevated FoxO1 generation and its enhanced cardiac microvascular distribution were verified in diabetic rats and HG-stimulated HCMECs. However, BHB inhibited the enhanced cardiac FoxO1 generation and its microvascular distribution with attenuation of endothelial injury in diabetic rats. Furthermore, BHB reduced the HG-stimulated mRNA expression and protein content of FoxO1 in HCMECs. In conclusion, BHB reduced the enhanced cardiac microvascular endothelial FoxO1 to play protective roles in diabetic rats and HG-stimulated HCMECs.

High-salt diet augments systolic blood pressure and induces arterial dysfunction in outbred, genetically diverse mice

Excess salt consumption contributes to hypertension and arterial dysfunction in humans living in industrialized societies. However, this arterial phenotype is not typically observed in inbred, genetically identical mouse strains that consume a high-salt (HS) diet. Therefore, we sought to determine the effects of HS diet consumption on systolic blood pressure (BP) and arterial function in UM-HET3 mice, an outbred, genetically diverse strain of mice. Male and female UM-HET3 mice underwent a low-salt [LS (1% NaCl)] or HS (4% NaCl) diet for 12 wk. Systolic BP and aortic stiffness, determined by pulse wave velocity (PWV), were increased in HS after 2 and 4 wk, respectively, compared with baseline and continued to increase through week 12 (P < 0.05). Systolic BP was higher from weeks 2-12 and PWV was higher from weeks 4-12 in HS compared with LS mice (P < 0.05). Aortic collagen content was ∼81% higher in HS compared with LS (P < 0.05), whereas aortic elastin content was similar between groups (P > 0.05). Carotid artery endothelium-dependent dilation (EDD) was ∼10% lower in HS compared with LS (P < 0.05), endothelium-independent dilation was similar between groups (P > 0.05). Finally, there was a strong relationship between systolic BP and PWV (r2 = 0.40, P < 0.05), as well as inverse relationship between EDD and systolic BP (r2 = 0.21, P < 0.05) or PWV (r2 = 0.20, P < 0.05). In summary, HS diet consumption in UM-HET3 mice increases systolic BP, which is accompanied by aortic stiffening and impaired EDD. These data suggest that outbred, genetically diverse mice may provide unique translational insight into arterial adaptations of humans that consume an HS diet.NEW & NOTEWORTHY Excess salt consumption is a contributor to hypertension and arterial dysfunction in humans living in industrialized societies, but this phenotype is not observed in inbred, genetically identical mice that consume a high-salt (HS) diet. This study reveals that a HS diet in outbred, genetically diverse mice progressively increases systolic blood pressure and induce arterial dysfunction. These data suggest that genetically diverse mice may provide translational insight into arterial adaptations in humans that consume an HS diet.

Ketones and the Heart: Metabolic Principles and Therapeutic Implications

The ketone bodies beta-hydroxybutyrate and acetoacetate are hepatically produced metabolites catabolized in extrahepatic organs. Ketone bodies are a critical cardiac fuel and have diverse roles in the regulation of cellular processes such as metabolism, inflammation, and cellular crosstalk in multiple organs that mediate disease. This review focuses on the role of cardiac ketone metabolism in health and disease with an emphasis on the therapeutic potential of ketosis as a treatment for heart failure (HF). Cardiac metabolic reprogramming, characterized by diminished mitochondrial oxidative metabolism, contributes to cardiac dysfunction and pathologic remodeling during the development of HF. Growing evidence supports an adaptive role for ketone metabolism in HF to promote normal cardiac function and attenuate disease progression. Enhanced cardiac ketone utilization during HF is mediated by increased availability due to systemic ketosis and a cardiac autonomous upregulation of ketolytic enzymes. Therapeutic strategies designed to restore high-capacity fuel metabolism in the heart show promise to address fuel metabolic deficits that underpin the progression of HF. However, the mechanisms involved in the beneficial effects of ketone bodies in HF have yet to be defined and represent important future lines of inquiry. In addition to use as an energy substrate for cardiac mitochondrial oxidation, ketone bodies modulate myocardial utilization of glucose and fatty acids, two vital energy substrates that regulate cardiac function and hypertrophy. The salutary effects of ketone bodies during HF may also include extra-cardiac roles in modulating immune responses, reducing fibrosis, and promoting angiogenesis and vasodilation. Additional pleotropic signaling properties of beta-hydroxybutyrate and AcAc are discussed including epigenetic regulation and protection against oxidative stress. Evidence for the benefit and feasibility of therapeutic ketosis is examined in preclinical and clinical studies. Finally, ongoing clinical trials are reviewed for perspective on translation of ketone therapeutics for the treatment of HF.

Hallmarks of aging: An expanding universe

Aging is driven by hallmarks fulfilling the following three premises: (1) their age-associated manifestation, (2) the acceleration of aging by experimentally accentuating them, and (3) the opportunity to decelerate, stop, or reverse aging by therapeutic interventions on them. We propose the following twelve hallmarks of aging: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, disabled macroautophagy, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis. These hallmarks are interconnected among each other, as well as to the recently proposed hallmarks of health, which include organizational features of spatial compartmentalization, maintenance of homeostasis, and adequate responses to stress.

Pathogenic Mechanisms of the Severe Acute Respiratory Syndrome Coronavirus 2 and Potential Direct and Indirect Counteractions by Intermittent Fasting

The coronavirus disease 2019 (COVID-19) pandemic created an unprecedented burden on human health and on the function and interaction of societies across the globe. Public health preventive measures, vaccines, and antivirals were key components of the world-wide response to the health emergency. Due to the uncoordinated and variably successful response to COVID-19 and the ability of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to rapidly mutate, SARS-CoV-2 continues to create considerable difficulty for humanity today. Additional preventive or therapeutic modalities are needed to help people to achieve the best possible health outcomes in the context of the evolving COVID-19 threat. Intermittent fasting is a potential complementary therapy that not only impacts chronic disease risk but also has good evidence of an impact on infectious diseases. While the data regarding fasting and COVID-19 outcomes are very limited, the conceptual connection of fasting to better outcomes includes a variety of mechanisms in human biology. This paper reviews the known mechanisms of disease impacted by SARS-CoV-2 infection and the potential or likely direct or indirect counteractions that fasting may provide that may reduce the severity of COVID-19 and help to realize the best possible health outcomes. Furthermore, fasting adds no financial cost to a care plan and, when practiced safely, is available to most adults without limitation. Further research is needed on the impact of intermittent fasting on human health in the fight against infectious diseases including COVID-19.

New developments in translational microcirculatory research

Microvascular disease plays a critical role in systemic end-organ dysfunction, and treatment of microvascular pathologies may greatly reduce cardiovascular morbidity and mortality. The Call for Papers collection: New Developments in Translational Microcirculatory Research highlights key advances in our understanding of the role of microvessels in the development of chronic diseases as well as therapeutic strategies to enhance microvascular function. This Mini Review provides a concise summary of these advances and draws from other relevant research to provide the most up-to-date information on the influence of cutaneous, cerebrovascular, coronary, and peripheral microcirculation on the pathophysiology of obesity, hypertension, cardiovascular aging, peripheral artery disease, and cognitive impairment. In addition to these disease- and location-dependent research articles, this Call for Papers includes state-of-the-art reviews on coronary endothelial function and assessment of microvascular health in different organ systems, with an additional focus on establishing rigor and new advances in clinical trial design. These articles, combined with original research evaluating cellular, exosomal, pharmaceutical, exercise, heat, and dietary interventional therapies, establish the groundwork for translating microcirculatory research from bench to bedside. Although numerous studies in this collection are focused on human microcirculation, most used robust preclinical models to probe mechanisms of pathophysiology and interventional benefits. Future work focused on translating these findings to humans are necessary for finding clinical strategies to prevent and treat microvascular dysfunction.

The janus face of ketone bodies in hypertension

Hypertension is the most important risk factor for the development of terminal cardiovascular diseases, such as heart failure, chronic kidney disease, and atherosclerosis. Lifestyle interventions to lower blood pressure are generally desirable prior to initiating pharmaceutical drug treatments, which may have undesirable side effects. Ketogenic interventions are popular but the scientific literature supporting their efficacy is specific to certain interventions and outcomes in animal models and patient populations. For example, although caloric restriction has its own inherent difficulties (e.g. it requires high levels of motivation and adherence is difficult), it has unequivocally been associated with lowering blood pressure in hypertensive patients. On the other hand, the antihypertensive efficacy of ketogenic diets is inconclusive, and this is surprising, given that these diets have been largely helpful in mitigating metabolic syndrome and promoting longevity. It is possible that side effects associated with ketogenic diets (e.g. dyslipidemia) aggravate the hypertensive phenotype. However, given the recent data from our group, and others, reporting that the most abundant ketone body, β-hydroxybutyrate, can have positive effects on endothelial and vascular health, there is hope that ketone bodies can be harnessed as a therapeutic strategy to combat hypertension. Therefore, we conclude this review with a summary of the type and efficacy of ketone supplements. We propose that ketone supplements warrant investigation as low-dose antihypertensive therapy that decreases total peripheral resistance with minimal adverse side effects.

Targeting SIRT1 Rescues Age- and Obesity-Induced Microvascular Dysfunction in Ex Vivo Human Vessels

BACKGROUND

Experimental evidence suggests a key role of SIRT1 (silent information regulator 1) in age- and metabolic-related vascular dysfunction. Whether these effects hold true in the human microvasculature is unknown. We aimed to investigate the SIRT1 role in very early stages of age- and obesity-related microvascular dysfunction in humans.

METHODS

Ninety-five subjects undergoing elective laparoscopic surgery were recruited and stratified based on their body mass index status (above or below 30 kg/m²) and age (above or below 40 years) in 4 groups: Young Nonobese, Young Obese, Old Nonobese, and Old Obese. We measured small resistance arteries' endothelial function by pressurized micromyography before and after incubation with a SIRT1 agonist (SRT1720) and a mitochondria reactive oxygen species (mtROS) scavenger (MitoTEMPO). We assessed vascular levels of mtROS and nitric oxide availability by confocal microscopy and vascular gene expression of SIRT1 and mitochondrial proteins by qPCR. Chromatin immunoprecipitation assay was employed to investigate SIRT1-dependent epigenetic regulation of mitochondrial proteins.

RESULTS

Compared with Young Nonobese, obese and older patients showed lower vascular expression of SIRT1 and antioxidant proteins (FOXO3 [forkhead box protein O3] and SOD2) and higher expression of pro-oxidant and aging mitochondria proteins p66^Shc and Arginase II. Old Obese, Young Obese and Old Nonobese groups endothelial dysfunction was rescued by SRT1720. The restoration was comparable to the one obtained with mitoTEMPO. These effects were explained by SIRT1-dependent chromatin changes leading to reduced p66^Shc expression and upregulation of proteins involved in mitochondria respiratory chain.

CONCLUSIONS

SIRT1 is a novel central modulator of the earliest microvascular damage induced by age and obesity. Through a complex epigenetic control mainly involving p66^Shc and Arginase II, it influences mtROS levels, NO availability, and the expression of proteins of the mitochondria respiratory chain. Therapeutic modulation of SIRT1 restores obesity- and age-related endothelial dysfunction. Early targeting of SIRT1 might represent a crucial strategy to prevent age- and obesity-related microvascular dysfunction.

Effect of 5:2 Fasting Diet on Liver Fat Content in Patients with Type 2 Diabetic with Nonalcoholic Fatty Liver Disease

Background: The prevalence of nonalcoholic fatty liver disease (NAFLD) is rapidly growing in China, especially in patients with type 2 diabetes mellitus (T2DM). Weight loss strategies have been shown to treat NAFLD effectively. We conducted a 24-week, prospective, randomized study in T2DM patients with NAFLD to evaluate the effects of a 5:2 fasting diet on liver fat content. Methods: Sixty-one T2DM patients with NAFLD were enrolled and randomly divided into a 5:2 fasting diet intervention group (5:2 diet group, n = 31) and 1.8 mg/day liraglutide intervention group (Lira group, n = 30). The study was performed for 24 weeks. Data of the body weight, waist circumference, plasma lipids and glucose profile, fasting plasma insulin, and liver function parameters were collected. Controlled attenuation parameter (CAP) was measured to assess the liver fat content. Superoxide dismutase (SOD) and malondialdehyde (MDA) were measured to evaluate oxidative stress status. Results: At 24 weeks after intervention, compared with those at baseline, CAP was significantly decreased in both the 5:2 diet group and Lira group, which was 7.4% and 5.5%, respectively. Body weight, plasma lipids and glucose profile, and liver function parameters improved significantly, while homeostasis model assessment-β (HOMA-β) was significantly increased in both groups (all P < 0.05). Stepwise linear regression showed that increased HOMA-β and SOD, as well as reduced body mass index (BMI), were the independent predictors of CAP decrease in the Lira group (P = 0.000, 0.000, 0.015). In contrast, reduced BMI and MDA were the independent influencing factors of CAP decrease in the 5:2 diet group (P = 0.011, 0.043). The common side effects in the 5:2 diet group were hunger (60%), weakness (10%), and constipation (0.3%). Conclusions: A 5:2 fasting diet achieved comparable effects with liraglutide on liver fat content in patients with T2DM with NAFLD by reducing BMI and oxidative stress. Both treatment strategies were safe and effective for glucose control.

Low-dose 1,3-butanediol reverses age-associated vascular dysfunction independent of ketone body β-hydroxybutyrate

With an aging global population, identifying novel therapeutics are necessary to increase longevity and decrease the deterioration of essential end organs such as the vasculature. Secondary alcohol, 1,3-butanediol (1,3-BD), is commonly administered to stimulate the biosynthesis of the most abundant ketone body β-hydroxybutyrate (βHB), in lieu of nutrient deprivation. However, suprapharmacological concentrations of 1,3-BD are necessary to significantly increase systemic βHB, and 1,3-BD per se can cause vasodilation at nanomolar concentrations. Therefore, we hypothesized that 1,3-BD could be a novel antiaging therapeutic, independent of βHB biosynthesis. To test this hypothesis, we administered a low-dose (5%) 1,3-BD to young and old Wistar-Kyoto (WKY) rats via drinking water for 4 wk and measured indices of vascular function and metabolism posttreatment. We observed that low-dose 1,3-BD was sufficient to reverse age-associated endothelial-dependent and -independent dysfunction, and this was not associated with increased βHB bioavailability. Further analysis of the direct vasodilator mechanisms of 1,3-BD revealed that it is predominantly an endothelium-dependent vasodilator through activation of potassium channels and nitric oxide synthase. In summary, we report that 1,3-BD, at a concentration that does not stimulate βHB biosynthesis, could be a nutraceutical that can reverse the age-associated decline in vascular function. These results emphasize that 1,3-BD has multiple, concentration-dependent mechanisms of action. Therefore, we suggest alternative approaches to study the physiological and cardiovascular effects of βHB.NEW & NOTEWORTHY 1,3-Butanediol (1,3-BD) is often administered to stimulate the biosynthesis of the most abundant ketone body, β-hydroxybutyrate (βHB), and its purported salubrious effects. Here, we report that a low dose of 1,3-BD (5%) is sufficient to reverse age-associated vascular dysfunction, independent of βHB. Therefore, low-dose 1,3-BD could be a novel therapeutic to increase blood flow and improve the quality of life in the elderly.

Short-Chain Carbon Sources

Heart failure (HF) remains the leading cause of morbidity and mortality in the developed world, highlighting the urgent need for novel, effective therapeutics. Recent studies support the proposition that improved myocardial energetics as a result of ketone body (KB) oxidation may account for the intriguing beneficial effects of sodium-glucose cotransporter-2 inhibitors in patients with HF. Similar small molecules, short-chain fatty acids (SCFAs) are now realized to be preferentially oxidized over KBs in failing hearts, contradicting the notion of KBs as a rescue "superfuel." In addition to KBs and SCFAs being alternative fuels, both exert a wide array of nonmetabolic functions, including molecular signaling and epigenetics and as effectors of inflammation and immunity, blood pressure regulation, and oxidative stress. In this review, the authors present a perspective supported by new evidence that the metabolic and unique nonmetabolic activities of KBs and SCFAs hold promise for treatment of patients with HF with reduced ejection fraction and those with HF with preserved ejection fraction.

Six Decades of History of Hypertension Research at the University of Toledo: Highlighting Pioneering Contributions in Biochemistry, Genetics, and Host-Microbiota Interactions

PURPOSE OF REVIEW

The study aims to capture the history and lineage of hypertension researchers from the University of Toledo in Ohio and showcase their collective scientific contributions dating from their initial discoveries of the physiology of adrenal and renal systems and genetics regulating blood pressure (BP) to its more contemporary contributions including microbiota and metabolomic links to BP regulation.

RECENT FINDINGS

The University of Toledo College of Medicine and Life Sciences (UTCOMLS), previously known as the Medical College of Ohio, has contributed significantly to our understanding of the etiology of hypertension. Two of the scientists, Patrick Mulrow and John Rapp from UTCOMLS, have been recognized with the highest honor, the Excellence in Hypertension award from the American Heart Association for their pioneering work on the physiology and genetics of hypertension, respectively. More recently, Bina Joe has continued their legacy in the basic sciences by uncovering previously unknown novel links between microbiota and metabolites to the etiology of hypertension, work that has been recognized by the American Heart Association with multiple awards. On the clinical research front, Christopher Cooper and colleagues lead the CORAL trials and contributed importantly to the investigations on renal artery stenosis treatment paradigms. Hypertension research at this institution has not only provided these pioneering insights, but also grown careers of scientists as leaders in academia as University Presidents and Deans of Medical Schools. Through the last decade, the university has expanded its commitment to Hypertension research as evident through the development of the Center for Hypertension and Precision Medicine led by Bina Joe as its founding Director. Hypertension being the top risk factor for cardiovascular diseases, which is the leading cause of human mortality, is an important area of research in multiple international universities. The UTCOMLS is one such university which, for the last 6 decades, has made significant contributions to our current understanding of hypertension. This review is a synthesis of this rich history. Additionally, it also serves as a collection of audio archives by more recent faculty who are also prominent leaders in the field of hypertension research, including John Rapp, Bina Joe, and Christopher Cooper, which are cataloged at Interviews .

Endothelial Heme Dynamics Drive Cancer Cell Metabolism by Shaping the Tumor Microenvironment

The crosstalk among cancer cells (CCs) and stromal cells within the tumor microenvironment (TME) has a prominent role in cancer progression. The significance of endothelial cells (ECs) in this scenario relies on multiple vascular functions. By forming new blood vessels, ECs support tumor growth. In addition to their angiogenic properties, tumor-associated ECs (TECs) establish a unique vascular niche that actively modulates cancer development by shuttling a selected pattern of factors and metabolites to the CC. The profile of secreted metabolites is strictly dependent on the metabolic status of the cell, which is markedly perturbed in TECs. Recent evidence highlights the involvement of heme metabolism in the regulation of energy metabolism in TECs. The present study shows that interfering with endothelial heme metabolism by targeting the cell membrane heme exporter Feline Leukemia Virus subgroup C Receptor 1a (FLVCR1a) in TECs, resulted in enhanced fatty acid oxidation (FAO). Moreover, FAO-derived acetyl-CoA was partly consumed through ketogenesis, resulting in ketone bodies (KBs) accumulation in FLVCR1a-deficient TECs. Finally, the results from this study also demonstrate that TECs-derived KBs can be secreted in the extracellular environment, inducing a metabolic rewiring in the CC. Taken together, these data may contribute to finding new metabolic vulnerabilities for cancer therapy.