SGLT2 inhibitors break the vicious circle between heart failure and insulin resistance: targeting energy metabolism

Heart failure (HF) often coexists with insulin resistance (IR), and the incidence of HF in type 2 diabetes mellitus (T2DM) patients is significantly higher. The reciprocal relationship between HF and IR has long been recognized, and the integration complicates the therapy of both. A number of mechanisms ascribe to the progression of cardiac IR, in which the main factors are the shift of myocardial substrate metabolism. Studies have found that SGLT2 inhibitors, an anti-diabetic drug, can improve the cardiac prognosis of patients with T2DM, which may be at least partially due to the relief of cardiac IR. Basic and clinical studies have revealed the important role of cardiac IR in the pathogenesis and progression of HF, and studies suggest that energy metabolism plays an important role in the pathogenesis of cardiac IR and HF. SGLT2 inhibitors mediated cardiovascular benefits through various mechanisms such as improving substrate utilization and improving myocardial energy. The regulation of SGLT2 inhibitors on cardiac energy status including carbohydrates, fatty acids (FA), amino acids and ketones, ATP transfer to the cytoplasm, and mitochondrial functional status have received extensive attention in HF, but its specific mechanism of action is still unclear. Therefore, this article reviews the relationship between IR and HF from the perspective of energy metabolism; subsequently, targeting energy metabolism discusses the pivotal role of SGLT2 inhibitors in improving cardiac IR and HF based on basic and clinical research evidences, and sought to clarify the molecular mechanism involved. (Fig. 1).

Ketone Therapy for Heart Failure: Current Evidence for Clinical Use

During conditions that result in depleted circulating glucose levels, ketone bodies synthesized in the liver are necessary fuel substrates for the brain. In other organs such as the heart, the reliance on ketones for generating energy is less life threatening as the heart can utilize alternative fuel sources such as fatty acids. However, during pathophysiological conditions such as heart failure, cardiac defects in metabolic processes that normally allow for sufficient energy production from fatty acids and carbohydrates contribute to a decline in contractile function. As such, it has been proposed that the failing heart relies more on ketone bodies as an energy source than previously appreciated. Furthermore, it has been suggested that ketone bodies may function as signaling molecules that can suppress systemic and cardiac inflammation. Thus, it is possible that intentionally elevating circulating ketones may be beneficial as an adjunct treatment for heart failure. Although many approaches can be used for 'ketone therapy', each of these has their own advantages and disadvantages in the treatment of heart failure. Thus, we summarize current preclinical and clinical studies involving various types of ketone therapy in cardiac disease and discuss the advantages and disadvantages of each modality as possible treatments for heart failure.

The role of sodium glucose co-transporter inhibitors in heart failure prevention

The worldwide prevalences of diabetes mellitus (DM) and of heart failure (HF) have collectively been on the rise. HF accounts for a large portion of the cardiovascular mortality and morbidity associated with DM. DM increases the risk of developing heart failure by promoting atherosclerosis and exerting direct deleterious effects on the myocardium. Sodium-glucose co-transporter-2 (SGLT-2) inhibitors are agents approved for the treatment of DM; they exert their anti-hyperglycemic effects by blocking renal reabsorption of glucose and inducing glycosuria. SGLT-2 inhibitors have consistently decreased the hospitalization rate of HF and cardiovascular mortality in several clinical trials. SGLT-2 inhibitors also possess anti-inflammatory, anti-fibrotic, and antihypertensive in addition to beneficial effects on the myocardial metabolism, which may account for their heart failure benefits. However, further research still needs to be done to evaluate the use of SGLT-2 inhibitors in non-diabetic patients and their efficacy in preventing or treating different heart failure phenotypes.

Protective effects of dapagliflozin against oxidative stress-induced cell injury in human proximal tubular cells

Elevated reactive oxygen species (ROS) in type 2 diabetes cause cellular damage in many organs. Recently, the new class of glucose-lowering agents, SGLT-2 inhibitors, have been shown to reduce the risk of developing diabetic complications; however, the mechanisms of such beneficial effect are largely unknown. Here we aimed to investigate the effects of dapagliflozin on cell proliferation and cell death under oxidative stress conditions and explore its underlying mechanisms. Human proximal tubular cells (HK-2) were used. Cell growth and death were monitored by cell counting, water-soluble tetrazolium-1 (WST-1) and lactate dehydrogenase (LDH) assays, and flow cytometry. The cytosolic and mitochondrial (ROS) production was measured using fluorescent probes (H2DCFDA and MitoSOX) under normal and oxidative stress conditions mimicked by addition of H₂O₂. Intracellular Ca²⁺ dynamics was monitored by FlexStation 3 using cell-permeable Ca²⁺ dye Fura-PE3/AM. Dapagliflozin (0.1–10 μM) had no effect on HK-2 cell proliferation under normal conditions, but an inhibitory effect was seen at an extreme high concentration (100 μM). However, dapagliflozin at 0.1 to 5 μM showed remarkable protective effects against H₂O₂-induced cell injury via increasing the viable cell number at phase G0/G1. The elevated cytosolic and mitochondrial ROS under oxidative stress was significantly decreased by dapagliflozin. Dapagliflozin increased the basal intracellular [Ca²⁺]_i in proximal tubular cells, but did not affect calcium release from endoplasmic reticulum and store-operated Ca²⁺ entry. The H₂O₂-sensitive TRPM2 channel seemed to be involved in the Ca²⁺ dynamics regulated by dapagliflozin. However, dapagliflozin had no direct effects on ORAI1, ORAI3, TRPC4 and TRPC5 channels. Our results suggest that dapagliflozin shows anti-oxidative properties by reducing cytosolic and mitochondrial ROS production and altering Ca²⁺ dynamics, and thus exerts its protective effects against cell damage under oxidative stress environment.

Immuno-metabolic interfaces in cardiac disease and failure

The interplay between the cardiovascular system, metabolism, and inflammation plays a central role in the pathophysiology of a wide spectrum of cardiovascular diseases, including heart failure. Here, we provide an overview of the fundamental aspects of the interrelation between inflammation and metabolism, ranging from the role of metabolism in immune cell function to the processes how inflammation modulates systemic and cardiac metabolism. Furthermore, we discuss how disruption of this immuno-metabolic interface is involved in the development and progression of cardiovascular disease, with a special focus on heart failure. Finally, we present new technologies and therapeutic approaches that have recently emerged and hold promise for the future of cardiovascular medicine.

Cardioprotective mechanism of SGLT2 inhibitor against myocardial infarction is through reduction of autosis

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular mortality in patients with diabetes mellitus but the protective mechanism remains elusive. Here we demonstrated that the SGLT2 inhibitor, Empagliflozin (EMPA), suppresses cardiomyocytes autosis (autophagic cell death) to confer cardioprotective effects. Using myocardial infarction (MI) mouse models with and without diabetes mellitus, EMPA treatment significantly reduced infarct size, and myocardial fibrosis, thereby leading to improved cardiac function and survival. In the context of ischemia and nutritional glucose deprivation where autosis is already highly stimulated, EMPA directly inhibits the activity of the Na⁺/H⁺ exchanger 1 (NHE1) in the cardiomyocytes to regulate excessive autophagy. Knockdown of NHE1 significantly rescued glucose deprivation-induced autosis. In contrast, overexpression of NHE1 aggravated the cardiomyocytes death in response to starvation, which was effectively rescued by EMPA treatment. Furthermore, in vitro and in vivo analysis of NHE1 and Beclin 1 knockout mice validated that EMPA’s cardioprotective effects are at least in part through downregulation of autophagic flux. These findings provide new insights for drug development, specifically targeting NHE1 and autosis for ventricular remodeling and heart failure after MI in both diabetic and non-diabetic patients.

The dawn of the four-drug era? SGLT2 inhibition in heart failure with reduced ejection fraction

Sodium-glucose cotransporter type 2 (SGLT2) inhibitors are a relatively new class of antihyperglycemic drug with salutary effects on glucose control, body weight, and blood pressure. Emerging evidence now indicates that these drugs may have a beneficial effect on outcomes in heart failure with reduced ejection fraction (HFrEF). Post-approval cardiovascular outcomes data for three of these agents (canagliflozin, empagliflozin, and dapagliflozin) showed an unexpected improvement in cardiovascular endpoints, including heart failure hospitalization and mortality, among patients with type 2 diabetes mellitus (T2DM) and established cardiovascular disease or risk factors. These studies were followed by a placebo controlled trial of dapagliflozin in patients with HFrEF both with and without T2DM, showing a reduction in all-cause mortality comparable to current guideline-directed HFrEF medical therapies such as angiotensin-converting enzyme inhibitors and beta-blockers. In this review, we discuss the current landscape of evidence, safety and adverse effects, and proposed mechanisms of action for use of these agents for patients with HFrEF. The United States (US) and European guidelines are reviewed, as are the current US federally approved indications for each SGLT2 inhibitor. Use of these agents in clinical practice may be limited by an uncertain insurance environment, especially in patients without T2DM. Finally, we discuss practical considerations for the cardiovascular clinician, including within-class differences of the SGLT2 inhibitors currently available on the US market (217/300).

Sodium glucose cotransporter 2 inhibitors: mechanisms of action in heart failure

Diabetes is a key independent risk factor in the development of heart failure (HF) and a strong, adverse prognostic factor in HF patients. HF remains the primary cause of hospitalisation for diabetics and, as previous studies have shown, when HF occurs in these patients, intensive glycaemic control does not directly improve the prognosis. Recent clinical studies assessing a new class of antidiabetic drugs, sodium-glucose cotransporter 2 inhibitors (SGLT2is) showed some unexpected beneficial results. Patients treated with SGLT2is had a significant decrease in both cardiovascular (CV) and all-cause mortality and less hospitalisations due to HF compared to those given a placebo. These significant clinical benefits occurred quickly after the drugs were administered and were not solely due to improved glycaemic control. These groundbreaking clinical trials’ results have already changed clinical practice in the management of patients with diabetes at high CV risk. These trials have triggered numerous experimental studies aimed at explaining the mechanisms of action of this unique group of drugs. This article presents the current state of knowledge about the mechanisms of action of SGLT2is developed for the treatment of diabetes and which, thanks to their cardioprotective effects, may, in the future, become a treatment for patients with HF.

Effect of Sodium-Glucose Cotransporter-2 Inhibitors on Endothelial Function: A Systematic Review of Preclinical Studies

INTRODUCTION

While the beneficial effects of sodium-glucose cotransporter-2 (SGLT-2) inhibitors on cardiovascular and renal outcomes are recognized, their direct effects on endothelial function remain unclear. We, therefore, undertook a systematic review to evaluate the current literature in this area.

METHODS

Electronic databases (PubMed, EMBASE, and Medline) were systematically searched using PRISMA guidelines for studies involving the in vitro, in vivo, or ex vivo administration of SGLT-2 inhibitors to animals, vascular tissue, or vascular endothelial cells.

RESULTS

Of 144 retrieved publications, 24 experimental studies met the inclusion criteria. Reporting of possible sources of bias were poor, making the overall risk of bias difficult to assess. Within the 24 studies, the SGLT-2 inhibitors canagliflozin, ipragliflozin, empagliflozin, dapagliflozin, tofogliflozin, and luseogliflozin were assessed as interventions. Animal model studies (n = 17) demonstrated that all SGLT-2 inhibitors prevented endothelial dysfunction and enhanced endothelium-dependent vasorelaxation in diabetic and non-diabetic models. In vitro studies (n = 9) using human endothelial cells indicated a direct anti-inflammatory effect of dapagliflozin (1-100 nM) and canagliflozin, (10 µM), while empagliflozin (1 and 10 µM) improved viability of hyperglycemic cells. Potential mechanisms of action of the SGLT-2 inhibitors include a reduction in oxidative stress, modulation of adhesion molecules and reductions in pro-inflammatory cytokines.

CONCLUSIONS

Preclinical studies indicate that SGLT-2 inhibitors attenuate vascular dysfunction in preclinical models via a combination of mechanisms that appear to act independently of glucose-lowering benefits.

Neue Antidiabetika

Diabetes steigert das Risiko für Herz-Kreislauf-Erkrankungen und hat eine zunehmende Prävalenz. Die Therapie des Diabetes stellte bisher ein Dilemma dar, da viele Therapien zwar den Blutzucker, aber nicht kardiovaskuläre Ereignisse reduzierten. Erst Glukagon-like Peptid-1-Rezeptor-Agonisten (GLP1) und Natrium/Glukose-Cotransporter-2(SGLT2)-Inhibitoren senkten deutlich kardiovaskuläre Endpunkte, und SGLT2-Inhibitoren beugten darüber hinaus der Entwicklung einer Herzinsuffizienz vor. Die Glukosesenkung an sich ist daher nicht entscheidend für den Schutz vor Herz-Kreislauf-Erkrankungen. Die neuen Leitlinien der Europäischen Gesellschaft für Kardiologie stellen daher bei Patienten mit Diabetes und hohem kardiovaskulären Risiko die Verwendung von GLP1-Rezeptor-Agonisten und SGLT2-Inhibitoren der Behandlung mit Metformin voran. Die neuen Studiendaten eröffnen zudem neue metabolische Ansatzpunkte für die Behandlung von Herz-Kreislauf-Erkrankungen auch unabhängig vom Vorliegen eines Diabetes.

Role of Deranged Energy Deprivation Signaling in the Pathogenesis of Cardiac and Renal Disease in States of Perceived Nutrient Overabundance

Sodium-glucose cotransporter 2 inhibitors reduce the risk of serious heart failure and adverse renal events, but the mechanisms that underlie this benefit are not understood. Treatment with SGLT2 inhibitors is distinguished by 2 intriguing features: ketogenesis and erythrocytosis. Both reflect the induction of a fasting-like and hypoxia-like transcriptional paradigm that is capable of restoring and maintaining cellular homeostasis and survival. In the face of perceived nutrient and oxygen deprivation, cells activate low-energy sensors, which include sirtuin-1 (SIRT1), AMP-activated protein kinase (AMPK), and hypoxia inducible factors (HIFs; especially HIF-2α); these enzymes and transcription factors are master regulators of hundreds of genes and proteins that maintain cellular homeostasis. The activation of SIRT1 (through its effects to promote gluconeogenesis and fatty acid oxidation) drives ketogenesis, and working in concert with AMPK, it can directly inhibit inflammasome activation and maintain mitochondrial capacity and stability. HIFs act to promote oxygen delivery (by stimulating erythropoietin and erythrocytosis) and decrease oxygen consumption. The activation of SIRT1, AMPK, and HIF-2α enhances autophagy, a lysosome-dependent degradative pathway that removes dangerous constituents, particularly damaged mitochondria and peroxisomes, which are major sources of oxidative stress and triggers of cellular dysfunction and death. SIRT1 and AMPK also act on sodium transport mechanisms to reduce intracellular sodium concentrations. It is interesting that type 2 diabetes mellitus, obesity, chronic heart failure, and chronic kidney failure are characterized by the accumulation of intracellular glucose and lipid intermediates that are perceived by cells as indicators of energy overabundance. The cells respond by downregulating SIRT1, AMPK, and HIF-2α, thus leading to an impairment of autophagic flux and acceleration of cardiomyopathy and nephropathy. SGLT2 inhibitors reverse this maladaptive signaling by triggering a state of fasting and hypoxia mimicry, which includes activation of SIRT1, AMPK, and HIF-2α, enhanced autophagic flux, reduced cellular stress, decreased sodium influx into cells, and restoration of mitochondrial homeostasis. This mechanistic framework clarifies the findings of large-scale randomized trials and the close association of ketogenesis and erythrocytosis with the cardioprotective and renoprotective benefits of these drugs.

Delayed ischaemic contracture onset by empagliflozin associates with NHE1 inhibition and is dependent on insulin in isolated mouse hearts

AIMS

Sodium glucose cotransporter 2 (SGLT2) inhibitors have sodium-hydrogen exchanger (NHE) inhibition properties in isolated cardiomyocytes, but it is unknown whether these properties extend to the intact heart during ischaemia-reperfusion (IR) conditions. NHE inhibitors as Cariporide delay time to onset of contracture (TOC) during ischaemia and reduce IR injury. We hypothesized that, in the ex vivo heart, Empagliflozin (Empa) mimics Cariporide during IR by delaying TOC and reducing IR injury. To facilitate translation to in vivo conditions with insulin present, effects were examined in the absence and presence of insulin.

METHODS AND RESULTS

Isolated C57Bl/6NCrl mouse hearts were subjected to 25 min I and 120 min R without and with 50 mU/L insulin. Without insulin, Empa and Cari delayed TOC by 100 and 129 s, respectively, yet only Cariporide reduced IR injury [infarct size (mean ± SEM in %) from 51 ± 6 to 34 ± 5]. Empa did not delay TOC in the presence of the NHE1 inhibitor Eniporide. Insulin perfusion increased tissue glycogen content at baseline (from 2 ± 2 µmol to 42 ± 1 µmol glycosyl units/g heart dry weight), amplified G6P and lactate accumulation at end-ischaemia, thereby decreased mtHKII and exacerbated IR injury. Under these conditions, Empa (1 µM) and Cariporide (10 µM) were without effect on TOC and IR injury. Empa and Cariporide both inhibited NHE activity, in isolated cardiomyocytes, independent of insulin.

CONCLUSIONS

In the absence of insulin, Empa and Cariporide strongly delayed the time to onset of contracture during ischaemia. In the presence of insulin, both Empa and Cari were without effect on IR, possibly because of severe ischaemic acidification. Insulin exacerbates IR injury through increased glycogen depletion during ischaemia and consequently mtHKII dissociation. The data suggest that also in the ex vivo intact heart Empa exerts direct cardiac effects by inhibiting NHE during ischaemia, but not during reperfusion.

Autophagy-dependent and -independent modulation of oxidative and organellar stress in the diabetic heart by glucose-lowering drugs

Autophagy is a lysosome-dependent intracellular degradative pathway, which mediates the cellular adaptation to nutrient and oxygen depletion as well as to oxidative and endoplasmic reticulum stress. The molecular mechanisms that stimulate autophagy include the activation of energy deprivation sensors, sirtuin-1 (SIRT1) and adenosine monophosphate-activated protein kinase (AMPK). These enzymes not only promote organellar integrity directly, but they also enhance autophagic flux, which leads to the removal of dysfunctional mitochondria and peroxisomes. Type 2 diabetes is characterized by suppression of SIRT1 and AMPK signaling as well as an impairment of autophagy; these derangements contribute to an increase in oxidative stress and the development of cardiomyopathy. Antihyperglycemic drugs that signal through insulin may further suppress autophagy and worsen heart failure. In contrast, metformin and SGLT2 inhibitors activate SIRT1 and/or AMPK and promote autophagic flux to varying degrees in cardiomyocytes, which may explain their benefits in experimental cardiomyopathy. However, metformin and SGLT2 inhibitors differ meaningfully in the molecular mechanisms that underlie their effects on the heart. Whereas metformin primarily acts as an agonist of AMPK, SGLT2 inhibitors induce a fasting-like state that is accompanied by ketogenesis, a biomarker of enhanced SIRT1 signaling. Preferential SIRT1 activation may also explain the ability of SGLT2 inhibitors to stimulate erythropoiesis and reduce uric acid (a biomarker of oxidative stress)—effects that are not seen with metformin. Changes in both hematocrit and serum urate are the most important predictors of the ability of SGLT2 inhibitors to reduce the risk of cardiovascular death and hospitalization for heart failure in large-scale trials. Metformin and SGLT2 inhibitors may also differ in their ability to mitigate diabetes-related increases in intracellular sodium concentration and its adverse effects on mitochondrial functional integrity. Differences in the actions of SGLT2 inhibitors and metformin may reflect the distinctive molecular pathways that explain differences in the cardioprotective effects of these drugs.

Interplay of adenosine monophosphate-activated protein kinase/sirtuin-1 activation and sodium influx inhibition mediates the renal benefits of sodium-glucose co-transporter-2 inhibitors in type 2 diabetes: A novel conceptual framework

Long-term treatment with sodium-glucose co-transporter-2 (SGLT2) inhibitors slows the deterioration of renal function in patients with diabetes. This benefit cannot be ascribed to an action on blood glucose, ketone utilization, uric acid or systolic blood pressure. SGLT2 inhibitors produce a striking amelioration of glomerular hyperfiltration. Although initially ascribed to an action of these drugs to inhibit proximal tubular glucose reabsorption, SGLT2 inhibitors exert renoprotective effects, even in patients with meaningfully impaired levels of glomerular function that are sufficient to abolish their glycosuric actions. Instead, the reduction in intraglomerular pressures may be related to an action of SGLT2 inhibitors to interfere with the activity of sodium-hydrogen exchanger isoform 3, thereby inhibiting proximal tubular sodium reabsorption and promoting tubuloglomerular feedback. Yet, experimentally, such an effect may not be sufficient to prevent renal injury. It is therefore noteworthy that the diabetic kidney exhibits an important defect in adenosine monophosphate-activated protein kinase (AMPK) and sirtuin-1 (SIRT1) signalling, which may contribute to the development of nephropathy. These transcription factors exert direct effects to mute oxidative stress and inflammation, and they also stimulate autophagy, a lysosomally mediated degradative pathway that maintains cellular homeostasis in the kidney. SGLT2 inhibitors induce both AMPK and SIRT1, and they have been shown to stimulate autophagy, thereby ameliorating cellular stress and glomerular and tubular injury. Enhanced AMPK/SIRT1 signalling may also contribute to the action of SGLT2 inhibitors to interfere with sodium transport mechanisms. The dual effects of SGLT2 inhibitors on AMPK/SIRT1 activation and renal tubular sodium transport may explain the protective effects of these drugs on the kidney in type 2 diabetes.

Empagliflozin improves left ventricular diastolic function of db/db mice

OBJECTIVES

Investigation of the effect of SGLT2 inhibition by empagliflozin on left ventricular function in a model of diabetic cardiomyopathy.

BACKGROUND

SGLT2 inhibition is a new strategy to treat diabetes. In the EMPA-REG Outcome trial empagliflozin treatment reduced cardiovascular and overall mortality in patients with diabetes presumably due to beneficial cardiac effects, leading to reduced heart failure hospitalization. The relevant mechanisms remain currently elusive but might be mediated by a shift in cardiac substrate utilization leading to improved energetic supply to the heart.

METHODS

We used db/db mice on high-fat western diet with or without empagliflozin treatment as a model of severe diabetes. Left ventricular function was assessed by pressure catheter with or without dobutamine stress.

RESULTS

Treatment with empagliflozin significantly increased glycosuria, improved glucose metabolism, ameliorated left ventricular diastolic function and reduced mortality of mice. This was associated with reduced cardiac glucose concentrations and decreased calcium/calmodulin-dependent protein kinase (CaMKII) activation with subsequent less phosphorylation of the ryanodine receptor (RyR). No change of cardiac ketone bodies or branched-chain amino acid (BCAA) metabolites in serum was detected nor was cardiac expression of relevant catabolic enzymes for these substrates affected.

CONCLUSIONS

In a murine model of severe diabetes empagliflozin-dependent SGLT2 inhibition improved diastolic function and reduced mortality. Improvement of diastolic function was likely mediated by reduced spontaneous diastolic sarcoplasmic reticulum (SR) calcium release but independent of changes in cardiac ketone and BCAA metabolism.

Sodium-Glucose Cotransporter-2 inhibitors are potential therapeutic agents for treatment of non-diabetic heart failure patients

Despite recent developments in various therapies, heart failure remains a leading cause of morbidity and mortality worldwide. New pharmacological approaches are therefore needed to improve the outcomes of patients with heart failure. Diabetes mellitus is an important risk factor for heart failure, but until recently there had been no evidence that hypoglycemic agents prevent heart failure. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have now been shown to prevent cardiovascular events, especially hospitalization for heart failure, in three large randomized clinical trials: EMPA-REG OUTCOME, the CANVAS program, and the DECLARE-TIMI58 trial. It is expected, therefore, that SGLT2 inhibitors will be useful therapeutic agents for the treatment of heart failure. The DAPA-HF trial recently demonstrated that dapagliflozin significantly reduces cardiovascular death and hospitalization for heart failure in patients with heart failure with reduced ejection fraction (HFrEF). Importantly, these benefits of dapagliflozin were similarly observed in patients with or without diabetes, suggesting the drug's efficacy is independent of glycemic reduction. The results of that study highlight the significance of SGLT2 inhibition as a novel therapeutic approach to treating HFrEF, irrespective of the presence or absence of diabetes. Findings of the DAPA-HF trial may also challenge current assumptions about the mechanisms underlying the cardioprotective action of SGLT2 inhibitors. It is anticipated that ongoing clinical trials, mainly using dapagliflozin and empagliflozin, will provide further insight into the clinical importance of these drugs for the treatment of heart failure, including heart failure with preserved ejection fraction (HFpEF), and also the mechanisms underlying those clinical benefits.

Critical examination of mechanisms underlying the reduction in heart failure events with SGLT2 inhibitors: identification of a molecular link between their actions to stimulate erythrocytosis and to alleviate cellular stress

Sodium-glucose co-transporter 2 (SGLT2) inhibitors reduce the risk of serious heart failure events, even though SGLT2 is not expressed in the myocardium. This cardioprotective benefit is not related to an effect of these drugs to lower blood glucose, promote ketone body utilization or enhance natriuresis, but it is linked statistically with their action to increase haematocrit. SGLT2 inhibitors increase both erythropoietin and erythropoiesis, but the increase in red blood cell mass does not directly prevent heart failure events. Instead, erythrocytosis is a biomarker of a state of hypoxia mimicry, which is induced by SGLT2 inhibitors in manner akin to cobalt chloride. The primary mediators of the cellular response to states of energy depletion are sirtuin-1 and hypoxia-inducible factors (HIF-1α/HIF-2α). These master regulators promote the cellular adaptation to states of nutrient and oxygen deprivation, promoting mitochondrial capacity and minimizing the generation of oxidative stress. Activation of sirtuin-1 and HIF-1α/HIF-2α also stimulates autophagy, a lysosome-mediated degradative pathway that maintains cellular homoeostasis by removing dangerous constituents (particularly unhealthy mitochondria and peroxisomes), which are a major source of oxidative stress and cardiomyocyte dysfunction and demise. SGLT2 inhibitors can activate SIRT-1 and stimulate autophagy in the heart, and thereby, favourably influence the course of cardiomyopathy. Therefore, the linkage between erythrocytosis and the reduction in heart failure events with SGLT2 inhibitors may be related to a shared underlying molecular mechanism that is triggered by the action of these drugs to induce a perceived state of oxygen and nutrient deprivation.

Altered mitochondrial metabolism in the insulin-resistant heart

Obesity-induced insulin resistance and type 2 diabetes mellitus can ultimately result in various complications, including diabetic cardiomyopathy. In this case, cardiac dysfunction is characterized by metabolic disturbances such as impaired glucose oxidation and an increased reliance on fatty acid (FA) oxidation. Mitochondrial dysfunction has often been associated with the altered metabolic function in the diabetic heart, and may result from FA-induced lipotoxicity and uncoupling of oxidative phosphorylation. In this review, we address the metabolic changes in the diabetic heart, focusing on the loss of metabolic flexibility and cardiac mitochondrial function. We consider the alterations observed in mitochondrial substrate utilization, bioenergetics and dynamics, and highlight new areas of research which may improve our understanding of the cause and effect of cardiac mitochondrial dysfunction in diabetes. Finally, we explore how lifestyle (nutrition and exercise) and pharmacological interventions can prevent and treat metabolic and mitochondrial dysfunction in diabetes.

SGLT-2 inhibitors and GLP-1 receptor agonists for nephroprotection and cardioprotection in patients with diabetes mellitus and chronic kidney disease. A consensus statement by the EURECA-m and the DIABESITY working groups of the ERA-EDTA

Chronic kidney disease (CKD) in patients with diabetes mellitus (DM) is a major problem of public health. Currently, many of these patients experience progression of cardiovascular and renal disease, even when receiving optimal treatment. In previous years, several new drug classes for the treatment of type 2 DM have emerged, including inhibitors of renal sodium-glucose co-transporter-2 (SGLT-2) and glucagon-like peptide-1 (GLP-1) receptor agonists. Apart from reducing glycaemia, these classes were reported to have other beneficial effects for the cardiovascular and renal systems, such as weight loss and blood pressure reduction. Most importantly, in contrast to all previous studies with anti-diabetic agents, a series of recent randomized, placebo-controlled outcome trials showed that SGLT-2 inhibitors and GLP-1 receptor agonists are able to reduce cardiovascular events and all-cause mortality, as well as progression of renal disease, in patients with type 2 DM. This document presents in detail the available evidence on the cardioprotective and nephroprotective effects of SGLT-2 inhibitors and GLP-1 analogues, analyses the potential mechanisms involved in these actions and discusses their place in the treatment of patients with CKD and DM.

Novel Basic Science Insights to Improve the Management of Heart Failure: Review of the Working Group on Cellular and Molecular Biology of the Heart of the Italian Society of Cardiology

Despite important advances in diagnosis and treatment, heart failure (HF) remains a syndrome with substantial morbidity and dismal prognosis. Although implementation and optimization of existing technologies and drugs may lead to better management of HF, new or alternative strategies are desirable. In this regard, basic science is expected to give fundamental inputs, by expanding the knowledge of the pathways underlying HF development and progression, identifying approaches that may improve HF detection and prognostic stratification, and finding novel treatments. Here, we discuss recent basic science insights that encompass major areas of translational research in HF and have high potential clinical impact.

Autophagy stimulation and intracellular sodium reduction as mediators of the cardioprotective effect of sodium-glucose cotransporter 2 inhibitors

In five large-scale trials involving >40 000 patients, sodium-glucose cotransporter 2 (SGLT2) inhibitors decreased the risk of serious heart failure events by 25-40%. This effect cannot be explained by control of hyperglycaemia, since it is not observed with antidiabetic drugs with greater glucose-lowering effects. It cannot be attributed to ketogenesis, since it is not causally linked to ketone body production, and the benefit is not enhanced in patients with diabetes. The effect cannot be ascribed to a natriuretic action, since SGLT2 inhibitors decrease natriuretic peptides only modestly, and they reduce cardiovascular death, a benefit that diuretics do not possess. Although SGLT2 inhibitors increase red blood cell mass, enhanced erythropoiesis does not favourably influence the course of heart failure. By contrast, experimental studies suggest that SGLT2 inhibitors may reduce intracellular sodium, thereby preventing oxidative stress and cardiomyocyte death. Additionally, SGLT2 inhibitors induce a transcriptional paradigm that mimics nutrient and oxygen deprivation, which includes activation of adenosine monophosphate-activated protein kinase, sirtuin-1, and/or hypoxia-inducible factors-1α/2α. The interplay of these mediators stimulates autophagy, a lysosomally-mediated degradative pathway that maintains cellular homeostasis. Autophagy-mediated clearance of damaged organelles reduces inflammasome activation, thus mitigating cardiomyocyte dysfunction and coronary microvascular injury. Interestingly, the action of hypoxia-inducible factors-1α/2α to both stimulate erythropoietin and induce autophagy may explain why erythrocytosis is strongly correlated with the reduction in heart failure events. Therefore, the benefits of SGLT2 inhibitors on heart failure may be mediated by a direct cardioprotective action related to modulation of pathways responsible for cardiomyocyte homeostasis.

Empagliflozin attenuates ischemia and reperfusion injury through LKB1/AMPK signaling pathway

The beneficial effects of empagliflozin (EMPA) on cardiac functions during ischemia and reperfusion were characterized. The contractile functions of isolated cardiomyocytes from adult C57BL/6J mice were determined with IonOptix SoftEdgeMyoCam system. The mitochondrial superoxide production was measured by MitoSOX fluorescent probe. The ex vivo isolated heart perfusion system was used to determine the pharmacological effects of EMPA on heart's contractile functions under both physiological and pathological conditions. The in vivo regional myocardial ischemia and reperfusion by ligation of left artery coronary artery descending (LAD) was used to measure the myocardial infarction caused by ischemia and reperfusion with or without EMPA treatment. The results demonstrated that EMPA treatment significantly improves cardiomyocyte contractility under hypoxia conditions and augments the post-ischemic recovery in the ex vivo heart perfusion system. Furthermore, the in vivo myocardial infarction measurement shows that EMPA treatment significantly reduce myocardial infarct size caused by ischemia and reperfusion. The biochemical analysis demonstrated that EMPA can trigger cardiac AMPK signaling pathway and attenuate mitochondrial superoxide production under hypoxia and reoxygenation conditions. In conclusion, EMPA can trigger AMPK signaling pathways and modulate myocardial contractility and reduce myocardial infarct size caused by ischemia and reperfusion independent of hypoglycemic effect. The results for the first time demonstrate that the activation of AMPK by EMPA could one reason about EMPA's beneficial effects on heart disease.

Effects of SGLT2 inhibitors on cardiovascular outcomes and mortality in type 2 diabetes: A meta-analysis

BACKGROUND

Optimal glycemic control is required to restrain the increase of cardiovascular events in patients with type 2 diabetes. The effects of sodium-glucose cotransporter-2 (SGLT-2) inhibitors on cardiovascular events and mortality in those patients are not well established. This meta-analysis was conducted to assess the effects of SGLT2 inhibitors on cardiovascular events and mortality in patients with type 2 diabetes.

METHODS

We conducted a systematic literature search of Medline, Embase and Cochrane Library and included randomized controlled trials (RCTs) of 3 different SGLT2 inhibitors (canagliflozin, dapagliflozin and empagliflozin) that evaluated the effects on cardiovascular outcomes and mortality in the final meta-analysis. The intervention arm was defined either as SGLT2 inhibitor monotherapy or as SGLT2 inhibitor add-on to other non-SGLT2 inhibitor antidiabetic agents (ADAs).

RESULTS

Forty-two trials with a total of 61,076 patients with type 2 diabetes were included in the meta-analysis. Compared with the control, SGLT2 inhibitor treatment was associated with a reduction in the incidence of major adverse cardiovascular events (MACEs) (OR = 0.86, 95% CI 0.80-0.93, P < .0001), myocardial infarction (OR = 0.86, 95% CI 0.79-0.94, P = .001), cardiovascular mortality (OR = 0.74, 95% CI 0.67-0.81, P < .0001) and all cause mortality (OR = 0.85, 95% CI 0.79-0.92, P < .0001). However, the risk of ischemic stroke was not reduced after SGLT2 inhibitor treatment in patients with type 2 diabetes (OR = 0.95, 95% CI 0.85-1.07, P = .42).

CONCLUSION

These data suggest a decreased risk of harm with SGLT2 inhibitor as a class with respect to cardiovascular events and mortality.

Calcium Signaling and Reactive Oxygen Species in Mitochondria

In heart failure, alterations of Na⁺ and Ca²⁺ handling, energetic deficit, and oxidative stress in cardiac myocytes are important pathophysiological hallmarks. Mitochondria are central to these processes because they are the main source for ATP, but also reactive oxygen species (ROS), and their function is critically controlled by Ca²⁺ During physiological variations of workload, mitochondrial Ca²⁺ uptake is required to match energy supply to demand but also to keep the antioxidative capacity in a reduced state to prevent excessive emission of ROS. Mitochondria take up Ca²⁺ via the mitochondrial Ca²⁺ uniporter, which exists in a multiprotein complex whose molecular components were identified only recently. In heart failure, deterioration of cytosolic Ca²⁺ and Na⁺ handling hampers mitochondrial Ca²⁺ uptake and the ensuing Krebs cycle-induced regeneration of the reduced forms of NADH (nicotinamide adenine dinucleotide) and NADPH (nicotinamide adenine dinucleotide phosphate), giving rise to energetic deficit and oxidative stress. ROS emission from mitochondria can trigger further ROS release from neighboring mitochondria termed ROS-induced ROS release, and cross talk between different ROS sources provides a spatially confined cellular network of redox signaling. Although low levels of ROS may serve physiological roles, higher levels interfere with excitation-contraction coupling, induce maladaptive cardiac remodeling through redox-sensitive kinases, and cell death through mitochondrial permeability transition. Targeting the dysregulated interplay between excitation-contraction coupling and mitochondrial energetics may ameliorate the progression of heart failure.

Empagliflozin normalizes the size and number of mitochondria and prevents reduction in mitochondrial size after myocardial infarction in diabetic hearts

To explore mechanisms by which SGLT2 inhibitors protect diabetic hearts from heart failure, we examined the effect of empagliflozin (Empa) on the ultrastructure of cardiomyocytes in the noninfarcted region of the diabetic heart after myocardial infarction (MI). OLETF, a rat model of type 2 diabetes, and its nondiabetic control, LETO, received a sham operation or left coronary artery ligation 12 h before tissue sampling. Tissues were sampled from the posterior ventricle (i.e., the remote noninfarcted region in rats with MI). The number of mitochondria was larger and small mitochondria were more prevalent in OLETF than in LETO. Fis1 expression level was higher in OLETF than in LETO, while phospho‐Ser637‐Drp1, total Drp1, Mfn1/2, and OPA1 levels were comparable. MI further reduced the size of mitochondria with increased Drp1‐Ser616 phosphorylation in OLETF. The number of autophagic vacuoles was unchanged after MI in LETO but was decreased in OLETF. Lipid droplets in cardiomyocytes and tissue triglycerides were increased in OLETF. Empa administration (10 mg/kg per day) reduced blood glucose and triglycerides and paradoxically increased lipid droplets in cardiomyocytes in OLETF. Empa suppressed Fis1 upregulation, increased Bnip3 expression, and prevented reduction in both mitochondrial size and autophagic vacuole number after MI in OLETF. Together with the results of our parallel study showing upregulation of SOD2 and catalase by Empa, the results indicate that Empa normalizes the size and number of mitochondria in diabetic hearts and that diabetes‐induced excessive reduction in mitochondrial size after MI was prevented by Empa via suppression of ROS and restoration of autophagy.

Chronic Kidney Disease as a Risk Factor for Heart Failure With Preserved Ejection Fraction: A Focus on Microcirculatory Factors and Therapeutic Targets

Heart failure (HF) and chronic kidney disease (CKD) co-exist, and it is estimated that about 50% of HF patients suffer from CKD. Although studies have been performed on the association between CKD and HF with reduced ejection fraction (HFrEF), less is known about the link between CKD and heart failure with preserved ejection fraction (HFpEF). Approximately, 50% of all patients with HF suffer from HFpEF, and this percentage is projected to rise in the coming years. Therapies for HFrEF are long established and considered quite successful. In contrast, clinical trials for treatment of HFpEF have all shown negative or disputable results. This is likely due to the multifactorial character and the lack of pathophysiological knowledge of HFpEF. The typical co-existence of HFpEF and CKD is partially due to common underlying comorbidities, such as hypertension, dyslipidemia and diabetes. Macrovascular changes accompanying CKD, such as hypertension and arterial stiffening, have been described to contribute to HFpEF development. Furthermore, several renal factors have a direct impact on the heart and/or coronary microvasculature and may underlie the association between CKD and HFpEF. These factors include: (1) activation of the renin-angiotensin-aldosterone system, (2) anemia, (3) hypercalcemia, hyperphosphatemia and increased levels of FGF-23, and (4) uremic toxins. This review critically discusses the above factors, focusing on their potential contribution to coronary dysfunction, left ventricular stiffening, and delayed left ventricular relaxation. We further summarize the directions of novel treatment options for HFpEF based on the contribution of these renal drivers.

Metabolic remodelling in heart failure

The heart consumes large amounts of energy in the form of ATP that is continuously replenished by oxidative phosphorylation in mitochondria and, to a lesser extent, by glycolysis. To adapt the ATP supply efficiently to the constantly varying demand of cardiac myocytes, a complex network of enzymatic and signalling pathways controls the metabolic flux of substrates towards their oxidation in mitochondria. In patients with heart failure, derangements of substrate utilization and intermediate metabolism, an energetic deficit, and oxidative stress are thought to underlie contractile dysfunction and the progression of the disease. In this Review, we give an overview of the physiological processes of cardiac energy metabolism and their pathological alterations in heart failure and diabetes mellitus. Although the energetic deficit in failing hearts - discovered >2 decades ago - might account for contractile dysfunction during maximal exertion, we suggest that the alterations of intermediate substrate metabolism and oxidative stress rather than an ATP deficit per se account for maladaptive cardiac remodelling and dysfunction under resting conditions. Treatments targeting substrate utilization and/or oxidative stress in mitochondria are currently being tested in patients with heart failure and might be promising tools to improve cardiac function beyond that achieved with neuroendocrine inhibition.

Cardiac Insulin Resistance in Heart Failure: The Role of Mitochondrial Dynamics

Heart failure (HF) frequently coexists with conditions associated with glucose insufficiency, such as insulin resistance and type 2 diabetes mellitus (T2DM), and patients with T2DM have a significantly high incidence of HF. These two closely related diseases cannot be separated on the basis of their treatment. Some antidiabetic drugs failed to improve cardiac outcomes in T2DM patients, despite lowering glucose levels sufficiently. This may be, at least in part, due to a lack of understanding of cardiac insulin resistance. Basic investigations have revealed the significant contribution of cardiac insulin resistance to the pathogenesis and progression of HF; however, there is no clinical evidence of the definition or treatment of cardiac insulin resistance. Mitochondrial dynamics play an important role in cardiac insulin resistance and HF because they maintain cellular homeostasis through energy production, cell survival, and cell proliferation. The innovation of diagnostic tools and/or treatment targeting mitochondrial dynamics is assumed to improve not only the insulin sensitivity of the myocardium and cardiac metabolism, but also the cardiac contraction function. In this review, we summarized the current knowledge on the correlation between cardiac insulin resistance and progression of HF, and discussed the role of mitochondrial dynamics on the pathogenesis of cardiac insulin resistance and HF. We further discuss the possibility of mitochondria-targeted intervention to improve cardiac metabolism and HF.

Dapagliflozin Attenuates Na+/H+ Exchanger-1 in Cardiofibroblasts via AMPK Activation

PURPOSE

We assessed whether the SGLT-2 inhibitor dapagliflozin (Dapa) attenuates the upregulation of the cardiac Na⁺/H⁺ exchanger (NHE-1) in vitro in mouse cardiofibroblasts stimulated with lipopolysaccharides (LPS) and whether this effect is dependent on adenosine monophosphate kinase (AMPK) activation.

METHODS

Mouse cardiofibroblasts were exposed for 16 h to Dapa (0.4 μM), AMPK activator (A769662 (10 μM)), AMPK inhibitor (compound C (CC) (10 μM)), an SGLT-1 and SGLT-2 inhibitor (phlorizin (PZ) (100 μM)), Dapa+CC, or Dapa+PZ, and then stimulated with LPS (10 ng/ml) for 3 h. NHE-1 mRNA levels were assessed by rt-PCR and total AMPK, phosphorylated-AMPK (P-AMPK), NHE-1, and heat shock protein-70 (Hsp70) protein levels in the whole cell lysate by immunoblotting. In addition, NHE-1 protein levels attached to Hsp70 were assessed by immunoprecipitation.

RESULTS

Exposure to LPS significantly reduced P-AMPK levels in the cardiofibroblasts. A769662 and Dapa equally increased P-AMPK. The effect was blocked by CC. Phlorizin had no effect on P-AMPK. LPS exposure significantly increased NHE-1 mRNA levels. Both Dapa and A769662 equally attenuated this increase. The effect of Dapa was blocked with CC. Interestingly, none of the compounds significantly affected NHE-1 and Hsp70 protein levels in the whole cell lysate. However, LPS significantly increased the concentration of NHE-1 attached to Hsp70. Both Dapa and A69662 attenuated this association and CC blocked the effect of Dapa. Again, phlorizin had no effect and did not alter the effect of Dapa.

CONCLUSIONS

Dapa increases P-AMPK in cardiofibroblasts exposed to LPS. Dapa attenuated the increase in NHE-1 mRNA and the association between NHE-1 and Hsp70. This effect was dependent on AMPK.

Uric acid and the cardio-renal effects of SGLT2 inhibitors

Sodium/glucose co-transporter-2 (SGLT2) inhibitors, which lower blood glucose by increasing renal glucose elimination, have been shown to reduce the risk of adverse cardiovascular (CV) and renal events in type 2 diabetes. This has been ascribed, in part, to haemodynamic changes, body weight reduction and several possible effects on myocardial, endothelial and tubulo-glomerular functions, as well as to reduced glucotoxicity. This review evaluates evidence that an effect of SGLT2 inhibitors to lower uric acid may also contribute to reduced cardio-renal risk. Chronically elevated circulating uric acid concentrations are associated with increased risk of hypertension, CV disease and chronic kidney disease (CKD). The extent to which uric acid contributes to these conditions, either as a cause or an aggravating factor, remains unclear, but interventions that reduce urate production or increase urate excretion in hyperuricaemic patients have consistently improved cardio-renal prognoses. Uric acid concentrations are often elevated in type 2 diabetes, contributing to the "metabolic syndrome" of CV risk. Treating type 2 diabetes with an SGLT2 inhibitor increases uric acid excretion, reduces circulating uric acid and improves parameters of CV and renal function. This raises the possibility that the lowering of uric acid by SGLT2 inhibition may assist in reducing adverse CV events and slowing progression of CKD in type 2 diabetes. SGLT2 inhibition might also be useful in the treatment of gout and gouty arthritis, especially when co-existent with diabetes.

Hypoxia-inducible factor 1-alpha (HIF-1α) as a factor mediating the relationship between obesity and heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF), a common condition with an increased mortality, is strongly associated with obesity and the metabolic syndrome. The latter two conditions are associated with increased epicardial fat that can extend into the heart. This review advances the proposition that hypoxia-inhibitory factor-1α (HIF-1α) maybe a key factor producing HFpEF. HIF-1α, a highly conserved transcription factor that plays a key role in tissue response to hypoxia, is increased in adipose tissue in obesity. Increased HIF-1α expression leads to expression of a potent profibrotic transcriptional programme involving collagen I, III, IV, TIMP, and lysyl oxidase. The net effect is the formation of collagen fibres leading to fibrosis. HIF-1α is also responsible for recruiting M1 macrophages that mediate obesity-associated inflammation, releasing IL-6, MCP-1, TNF-α, and IL-1β with increased expression of thrombospondin, pro α2 (I) collagen, transforming growth factor β, NADPH oxidase, and connective tissue growth factor. These factors can accelerate cardiac fibrosis and impair cardiac diastolic function. Inhibition of HIF-1α expression in adipose tissue of mice fed a high-fat diet suppressed fibrosis and reduces inflammation in adipose tissue. Delineation of the role played by HIF-1α in obesity-associated HFpEF may lead to new potential therapies.

Sodium-glucose Cotransporter 2 Inhibitors in Heart Failure: Potential Mechanisms of Action, Adverse Effects and Future Developments

Heart failure is a common complication in patients with diabetes, and people with both conditions present a worse prognosis. Sodium–glucose cotransporter 2 inhibitors (SGLT2Is) increase urinary glucose excretion, improving glycaemic control. In type 2 diabetes (T2D), some SGLT2Is reduce major cardiovascular events, heart failure hospitalisations and worsening of kidney function independent of glycaemic control. Multiple mechanisms (haemodynamic, metabolic, hormonal and direct cardiac/renal effects) have been proposed to explain these cardiorenal benefits. SGLT2Is are generally well tolerated, but can produce rare serious adverse effects, and the benefit/risk ratio differs between SGLT2Is. This article analyses the mechanisms underlying the cardiorenal benefits and adverse effects of SGLT2Is in patients with T2D and heart failure and outlines some questions to be answered in the near future.

The sodium-glucose co-transporter 2 inhibitor empagliflozin attenuates cardiac fibrosis and improves ventricular hemodynamics in hypertensive heart failure rats

BACKGROUND

Sodium glucose co-transporter 2 inhibitor (SGLT2i), a new class of anti-diabetic drugs acting on inhibiting glucose resorption by kidneys, is shown beneficial in reduction of heart failure hospitalization and cardiovascular mortality. The mechanisms remain unclear. We hypothesized that SGLT2i, empagliflozin can improve cardiac hemodynamics in non-diabetic hypertensive heart failure.

METHODS AND RESULTS

The hypertensive heart failure model had been created by feeding spontaneous hypertensive rats (SHR) with high fat diet for 32 weeks (total n = 13). Half SHRs were randomized to be administered with SGLT2i, empagliflozin at 20 mg/kg/day for 12 weeks. After evaluation of electrocardiography and echocardiography, invasive hemodynamic study was performed and followed by blood sample collection and tissue analyses. Empagliflozin exhibited cardiac (improved atrial and ventricular remodeling) and renal protection, while plasma glucose level was not affected. Empagliflozin normalized both end-systolic and end-diastolic volume in SHR, in parallel with parameters in echocardiographic evaluation. Empagliflozin also normalized systolic dysfunction, in terms of the reduced maximal velocity of pressure incline and the slope of end-systolic pressure volume relationship in SHR. In histological analysis, empagliflozin significantly attenuated cardiac fibrosis in both atrial and ventricular tissues. The upregulation of atrial and ventricular expression of PPARα, ACADM, natriuretic peptides (NPPA and NPPB), and TNF-α in SHR, was all restored by treatment of empagliflozin.

CONCLUSIONS

Empagliflozin improves hemodynamics in our hypertensive heart failure rat model, associated with renal protection, attenuated cardiac fibrosis, and normalization of HF genes. Our results contribute some understanding of the pleiotropic effects of empagliflozin on improving heart function.

SGLT2 inhibitors and cardioprotection: a matter of debate and multiple hypotheses

Sodium-glucose co-transporter 2 (SGLT2) inhibitors inhibit glucose re-absorption in the proximal renal tubules. Two trials have shown significant reductions of cardiovascular (CV) events with empagliflozin and canagliflozin, which could not be attributed solely to their antidiabetic effects. The aim of the review is the critical presentation of suggested mechanisms/hypotheses for the SGLT2 inhibitors' cardioprotection. The search of the literature revealed many possible cardioprotective mechanisms, because SGLT2 inhibitors (i) increase natriuresis and act as diuretics with unique properties leading to a reduction in preload and myocardial stretch (the diuretic hypothesis); (ii) decrease blood pressure and afterload (the blood pressure lowering hypothesis), (iii) favor the production of ketones, which can act as a 'superfuel' in the cardiac and renal tissue (the 'thrifty substrate' hypothesis), (iv) improve many metabolic variables (the metabolic effects hypothesis), (v) exert many anti-inflammatory effects (the anti-inflammatory effects hypothesis), (vi) can act through the angiotensin II type II receptors in the context of simultaneous renin-angiotensin-aldosterone-system (RAAS) blockade leading to vasodilation and positive inotropic effects (the RAAS hypothesis), (vii) directly decrease the activity of the upregulated in heart failure Na⁺-H⁺ exchanger in myocardial cells leading to restoration of mitochondrial calcium handling in cardiomyocytes (the sodium hypothesis). Additionally, some SGLT2 inhibitors exhibit also SGLT1 inhibitory action possibly resulting in an attenuation of oxidative stress in ischemic myocardium (the SGLT1 inhibition hypothesis). Thus, many mechanisms have been suggested (and possibly act cumulatively) for the cardioprotective effects of SGLT2 inhibitors.

AMPK is associated with the beneficial effects of antidiabetic agents on cardiovascular diseases

Diabetics have higher morbidity and mortality in cardiovascular disease (CVD). A variety of antidiabetic agents are available for clinical choice. Cardiovascular (CV) safety assessment of these agents is crucial in addition to hypoglycemic effect before clinical prescription. Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an important cell energy sensor, which plays an important role in regulating myocardial energy metabolism, reducing ischemia and ischemia/reperfusion (I/R) injury, improving heart failure (HF) and ventricular remodeling, ameliorating vascular endothelial dysfunction, antichronic inflammation, anti-apoptosis, and regulating autophagy. In this review, we summarized the effects of antidiabetic agents to CVD according to basic and clinical research evidence and put emphasis on whether these agents can play roles in CV system through AMPK-dependent signaling pathways. Metformin has displayed definite CV benefits related to AMPK. Sodium-glucose cotransporter 2 inhibitors also demonstrate sufficient clinical evidence for CV protection, but the mechanisms need further exploration. Glucagon-likepeptide1 analogs, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors and thiazolidinediones also show some AMPK-dependent CV benefits. Sulfonylureas and meglitinides may be unfavorable to CV system. AMPK is becoming a promising target for the treatment of diabetes, metabolic syndrome and CVD. But there are still some questions to be answered.

Dysregulation of Glucagon Secretion by Hyperglycemia-Induced Sodium-Dependent Reduction of ATP Production

Diabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their β cells (Fh1βKO mice) develop progressive hyperglycemia and dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na+ accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in α cells from hyperglycemic Fh1βKO and β-V59M gain-of-function KATP channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1βKO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.

Cardiovascular protection in type 2 diabetes: Insights from recent outcome trials

This review examines recent randomized controlled cardiovascular (CV) outcome trials of glucose-lowering therapies in type 2 diabetes and their impact on the treatment of patients with type 2 diabetes. The trials were designed to comply with regulatory requirements to confirm that major adverse cardiac events (MACE) are not detrimentally affected by such therapies. Trials involving dipeptidyl peptidase-4 (DPP-4) inhibitors did not alter a composite MACE outcome comprising CV deaths, non-fatal myocardial infarction and non-fatal stroke; however, the possibility that some members of this class might incur a small increased risk or worsening of heart failure cannot be excluded. Some studies on glucagon-like peptide-1 receptor agonists (liraglutide: LEADER trial; semaglutide: SUSTAIN-6 trial) found significant benefits for MACE, while treatment with sodium-glucose co-transporter-2 inhibitors (empagliflozin: EMPA-REG OUTCOME trial; canagliflozin: CANVAS trial) also significantly reduced MACE and reduced hospitalization for heart failure. Comparisons among trials are complicated by variance in the populations recruited, particularly CV status at randomization, and differences in trial design, data collection and analyses. A large proportion of patients recruited into these trials have previously experienced adverse CV events; thus, the therapies are mostly assessing secondary prevention of a further event. This contrasts with the overall type 2 diabetes population receiving glucose-lowering therapies, of whom the majority will not have had MACE and will be regarded as primary prevention. Overall, the trials provide reassuring evidence that new glucose-lowering medications do not adversely affect CV events and some of these agents may offer CV protection.

Hormonal, Metabolic and Hemodynamic Adaptations to Glycosuria in Type 2 Diabetes Patients Treated with Sodium-Glucose Co-Transporter Inhibitors

BACKGROUND & INTRODUCTION

The advent of the sodium-glucose cotransporter-2 inhibitors [SGLT-2i] provides an additional tool to combat diabetes and complications. The use of SGLT-2i leads to effective and durable glycemic control with important reductions in body weight/fat and blood pressure. These agents may delay beta-cell deterioration and improve tissue insulin sensitivity, which might slow the progression of the disease.

METHODS & RESULTS

In response to glycosuria, a compensatory rise in endogenous glucose production, sustained by a decrease in plasma insulin with an increase in glucagon has been described. Other possible mediators have been implicated and preliminary findings suggest that a sympathoadrenal discharge and/or rapid elevation in circulating substrates (i.e., fatty acids) or some yet unidentified humoral factors may have a role in a renal-hepatic inter-organ relationship. A possible contribution of enhanced renal gluconeogenesis to glucose entry into the systemic circulation has not yet been ruled out. Additionally, tissue glucose utilization decreases, whereas adipose tissue lipolysis is stimulated and, there is a switch to lipid oxidation with the formation of ketone bodies; the risk for keto-acidosis may limit the use of SGLT-2i. These metabolic adaptations are part of a counter-regulatory response to avoid hypoglycemia and, as a result, limit the SGLT-2i therapeutic efficacy. Recent trials revealed important cardiovascular [CV] beneficial effects of SGLT-2i drugs when used in T2DM patients with CV disease. Although the underlying mechanisms are not fully understood, there appears to be "class effect". Changes in hemodynamics and electrolyte/body fluid distribution are likely involved, but there is no evidence for anti-atherosclerotic effects.

CONCLUSION

It is anticipated that, by providing durable diabetes control and reducing CV morbidity and mortality, the SGLT-2i class of drugs is destined to become a priority choice in diabetes management.

Clinical potential relevance of metabolic properties of SGLT2 inhibitors in patients with heart failure

Introduction: Heart failure (HF) affects approximately 2% of the population worldwide, remaining a major cause of hospitalization and mortality despite innovative therapeutic approaches introduced in the past few decades. Type 2 diabetes mellitus (T2DM) contributes significantly to end-organ damage and HF-related complications and is associated with worse clinical status and increased all-cause and cardiovascular mortality in patients with HF with reduced (HFrEF) or with preserved ejection fraction (HFpEF), compared to HF patients without T2DM. Recently, a novel class of antidiabetic drugs has been introduced: sodium glucose co-trasport-2 inhibitors (SGLT2i). Initially designed for patients with T2DM to reduce kidney blood glucose resorption, SGLT2i rapidly gained attention among HF specialists since they were able to show a beneficial prognostic impact in patients affected by HF and T2DM, even independently from the glycemic control as suggested by the EMPA-REG OUTCOME and CANVAS trials. Areas covered: The present review focuses on the mechanisms and the current clinical evidence supporting the use of SGLT2i in HF patients with T2DM. Moreover, the SGLT2i pharmacokinetic and pharmacodynamic properties will be presented in order to better understand the rationale and the design of the ongoing clinical trials investigating directly the effect of this new class of drugs in patients with HF, even independently from T2DM. Expert opinion: SGLT2i are emerging as an effective and safe therapy for the treatment of T2DM and current evidence has unexpectedly demonstrated a robust cardiovascular protection in HF patients with T2DM. Therefore, ongoing clinical trials are investigating directly the effect of this new class of drugs in patients with HF, even independently from T2DM. However, it is methodologically disappointing that the mechanisms underlying the encouraging results in cardiovascular protection of this drug class are still not fully understood. A better understanding of the pharmacokinetic and pharmacodynamic properties of SGLT2i is necessary in order to better determine the effect of this new class of drugs in patients with HF.

The Role of Sodium in Diabetic Cardiomyopathy

Cardiovascular complications are the major cause of mortality and morbidity in diabetic patients. The changes in myocardial structure and function associated with diabetes are collectively called diabetic cardiomyopathy. Numerous molecular mechanisms have been proposed that could contribute to the development of diabetic cardiomyopathy and have been studied in various animal models of type 1 or type 2 diabetes. The current review focuses on the role of sodium (Na⁺) in diabetic cardiomyopathy and provides unique data on the linkage between Na⁺ flux and energy metabolism, studied with non-invasive ²³Na, and ³¹P-NMR spectroscopy, polarography, and mass spectroscopy. ²³Na NMR studies allow determination of the intracellular and extracellular Na⁺ pools by splitting the total Na⁺ peak into two resonances after the addition of a shift reagent to the perfusate. Using this technology, we found that intracellular Na⁺ is approximately two times higher in diabetic cardiomyocytes than in control possibly due to combined changes in the activity of Na⁺–K⁺ pump, Na⁺/H⁺ exchanger 1 (NHE1) and Na⁺-glucose cotransporter. We hypothesized that the increase in Na⁺ activates the mitochondrial membrane Na⁺/Ca²⁺ exchanger, which leads to a loss of intramitochondrial Ca²⁺, with a subsequent alteration in mitochondrial bioenergetics and function. Using isolated mitochondria, we showed that the addition of Na⁺ (1–10 mM) led to a dose-dependent decrease in oxidative phosphorylation and that this effect was reversed by providing extramitochondrial Ca²⁺ or by inhibiting the mitochondrial Na⁺/Ca²⁺ exchanger with diltiazem. Similar experiments with ³¹P-NMR in isolated superfused mitochondria embedded in agarose beads showed that Na⁺ (3–30 mM) led to significantly decreased ATP levels and that this effect was stronger in diabetic rats. These data suggest that in diabetic cardiomyocytes, increased Na⁺ leads to abnormalities in oxidative phosphorylation and a subsequent decrease in ATP levels. In support of these data, using ³¹P-NMR, we showed that the baseline β-ATP and phosphocreatine (PCr) were lower in diabetic cardiomyocytes than in control, suggesting that diabetic cardiomyocytes have depressed bioenergetic function. Thus, both altered intracellular Na⁺ levels and bioenergetics and their interactions may significantly contribute to the pathology of diabetic cardiomyopathy.

Empagliflozin rescues diabetic myocardial microvascular injury via AMPK-mediated inhibition of mitochondrial fission

Impaired cardiac microvascular function contributes to diabetic cardiovascular complications although effective therapy remains elusive. Empagliflozin, a sodium-glucose cotransporter 2 (SGLT2) inhibitor recently approved for treatment of type 2 diabetes, promotes glycosuria excretion and offers cardioprotective actions beyond its glucose-lowering effects. This study was designed to evaluate the effect of empagliflozin on cardiac microvascular injury in diabetes and the underlying mechanism involved with a focus on mitochondria. Our data revealed that empagliflozin improved diabetic myocardial structure and function, preserved cardiac microvascular barrier function and integrity, sustained eNOS phosphorylation and endothelium-dependent relaxation, as well as improved microvessel density and perfusion. Further study suggested that empagliflozin exerted its effects through inhibition of mitochondrial fission in an adenosine monophosphate (AMP)-activated protein kinase (AMPK)-dependent manner. Empagliflozin restored AMP-to-ATP ratio to trigger AMPK activation, suppressed Drp1S616 phosphorylation, and increased Drp1S637 phosphorylation, ultimately leading to inhibition of mitochondrial fission. The empagliflozin-induced inhibition of mitochondrial fission preserved cardiac microvascular endothelial cell (CMEC) barrier function through suppressed mitochondrial reactive oxygen species (mtROS) production and subsequently oxidative stress to impede CMEC senescence. Empagliflozin-induced fission loss also favored angiogenesis by promoting CMEC migration through amelioration of F-actin depolymerization. Taken together, these results indicated the therapeutic promises of empagliflozin in the treatment of pathological microvascular changes in diabetes.

Cardiovascular Safety, Long-Term Noncardiovascular Safety, and Efficacy of Sodium-Glucose Cotransporter 2 Inhibitors in Patients With Type 2 Diabetes Mellitus: A Systemic Review and Meta-Analysis With Trial Sequential Analysis

BACKGROUND

The cardiovascular and long-term noncardiovascular safety and efficacy of SGLT2 (sodium-glucose cotransporter 2) inhibitors have not been well documented.

METHODS AND RESULTS

For cardiovascular outcomes, we performed a meta-analysis with trial sequential analysis of randomized controlled trials and adjusted observational studies, each with a minimum of 26 weeks and 2000 patient-years of follow-up. For long-term noncardiovascular safety and efficacy outcome analyses, we included only randomized controlled trials with at least 2 years and 1000 patient-years of follow-up. Five studies with 351 476 patients were included in cardiovascular outcomes analysis. Meta-analyses showed that SGLT2 inhibitors significantly reduced the risks of major adverse cardiac events (hazard ratio [HR]: 0.80; 95% confidence interval [CI], 0.69-0.92; P=0.002), all-cause mortality (HR: 0.67; 95% CI, 0.54-0.84; P<0.001), cardiovascular mortality (HR: 0.77; 95% CI, 0.60-0.98; P=0.03), nonfatal myocardial infarction (HR: 0.86; 95% CI, 0.76-0.98; P=0.02), hospitalization for heart failure (HR: 0.62; 95% CI, 0.55-0.69; P<0.001), and progression of albuminuria (HR: 0.68; 95% CI, 0.58-0.81; P<0.001). No significant difference in nonfatal stroke was found. Analyses limited to randomized controlled trials showed similar findings. Trial sequential analysis provided firm evidence of a 20% reduction in major adverse cardiac events, all-cause mortality, and hospitalization for heart failure with SGLT2 inhibitors, but evidence remains inconclusive for cardiovascular mortality. Nine randomized controlled trials contributed to long-term noncardiovascular and efficacy analyses. SGLT2 inhibitors reduced incidence of hypoglycemia and acute kidney injury but increased the risks of urinary tract and genital infections.

CONCLUSIONS

SGLT2 inhibitors showed remarkable cardiovascular- and renal-protective effects and good long-term noncardiovascular safety with sustained efficacy.