Reactive oxygen species signalling in the diabetic heart: emerging prospect for therapeutic targeting

Mitochondria-Mediated Cardiovascular Benefits of Sodium-Glucose Co-Transporter 2 Inhibitors

Several recent cardiovascular trials of SGLT 2 (sodium-glucose cotransporter 2) inhibitors revealed that they could reduce adverse cardiovascular events in patients with T2DM (type 2 diabetes mellitus). However, the exact molecular mechanism underlying the beneficial effects that SGLT2 inhibitors have on the cardiovascular system is still unknown. In this review, we focus on the molecular mechanisms of the mitochondria-mediated beneficial effects of SGLT2 inhibitors on the cardiovascular system. The application of SGLT2 inhibitors ameliorates mitochondrial dysfunction, dynamics, bioenergetics, and ion homeostasis and reduces the production of mitochondrial reactive oxygen species, which results in cardioprotective effects. Herein, we present a comprehensive overview of the impact of SGLT2 inhibitors on mitochondria and highlight the potential application of these medications to treat both T2DM and cardiovascular diseases.

Antioxidant Cardioprotection against Reperfusion Injury: Potential Therapeutic Roles of Resveratrol and Quercetin

Ischemia-reperfusion myocardial damage is a paradoxical tissue injury occurring during percutaneous coronary intervention (PCI) in acute myocardial infarction (AMI) patients. Although this damage could account for up to 50% of the final infarct size, there has been no available pharmacological treatment until now. Oxidative stress contributes to the underlying production mechanism, exerting the most marked injury during the early onset of reperfusion. So far, antioxidants have been shown to protect the AMI patients undergoing PCI to mitigate these detrimental effects; however, no clinical trials to date have shown any significant infarct size reduction. Therefore, it is worthwhile to consider multitarget antioxidant therapies targeting multifactorial AMI. Indeed, this clinical setting involves injurious effects derived from oxygen deprivation, intracellular pH changes and increased concentration of cytosolic Ca²⁺ and reactive oxygen species, among others. Thus, we will review a brief overview of the pathological cascades involved in ischemia-reperfusion injury and the potential therapeutic effects based on preclinical studies involving a combination of antioxidants, with particular reference to resveratrol and quercetin, which could contribute to cardioprotection against ischemia-reperfusion injury in myocardial tissue. We will also highlight the upcoming perspectives of these antioxidants for designing future studies.

Molecular Correlates of Early Onset of Diabetic Cardiomyopathy: Possible Therapeutic Targets

Diabetes mellitus (DM) is associated with mitochondrial dysfunction and oxidative stress that can lead to diabetic cardiomyopathy (DCM), which can often remain undetected until late stages of the disease. However, myocardial injury occurs before the onset of measurable cardiac dysfunction, although its molecular correlates are poorly understood. In this study, we made a DM rat induced by a high-fat diet combined with low and high doses of streptozotocin (STZ) to emulate pre and early DCM. RNA-sequencing analysis of ventricular tissue revealed a differential transcriptome profile and abnormal activation of pathways involved in fatty acid metabolism, oxidative phosphorylation, cardiac structure and function, insulin resistance, calcium signalling, apoptosis, and TNF signalling. Moreover, using high glucose-treated human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM), we recapitulated the cardiac cellular phenotype of DM and identified several molecular correlates that may promote the development of DCM. In conclusion, we have developed an experimental framework to target pathways underlying the progression of DCM.

Heart Failure and Drug Therapies: A Metabolic Review

Cardiovascular disease is the leading cause of mortality globally with at least 26 million people worldwide living with heart failure (HF). Metabolism has been an active area of investigation in the setting of HF since the heart demands a high rate of ATP turnover to maintain homeostasis. With the advent of -omic technologies, specifically metabolomics and lipidomics, HF pathologies have been better characterized with unbiased and holistic approaches. These techniques have identified novel pathways in our understanding of progression of HF and potential points of intervention. Furthermore, sodium-glucose transport protein 2 inhibitors, a drug that has changed the dogma of HF treatment, has one of the strongest types of evidence for a potential metabolic mechanism of action. This review will highlight cardiac metabolism in both the healthy and failing heart and then discuss the metabolic effects of heart failure drugs.

Supplementation with a Cocoa-Carob Blend, Alone or in Combination with Metformin, Attenuates Diabetic Cardiomyopathy, Cardiac Oxidative Stress and Inflammation in Zucker Diabetic Rats

Diabetic cardiomyopathy (DCM) is one of the main causes of mortality among diabetic patients, with oxidative stress and inflammation major contributors to its development. Dietary flavonoids show strong antioxidant and anti-inflammatory activities, although their potential additive outcomes in combination with antidiabetic drugs have been scarcely explored. The present study investigates the cardioprotective effects of a cocoa–carob blend (CCB) diet, rich in flavonoids, alone or in combination with metformin, in the development of DCM. Zucker diabetic fatty rats (ZDF) were fed with a CCB rich-diet or a control diet, with or without metformin for 12 weeks. Glucose homeostasis, cardiac structure and function, and oxidative and inflammatory biomarkers were analysed. CCB improved glucose homeostasis, and mitigated cardiac dysfunction, hypertrophy, and fibrosis in ZDF rats. Mechanistically, CCB counteracted oxidative stress in diabetic hearts by down-regulating NADPH oxidases, reducing reactive oxygen species (ROS) generation and modulating the sirtuin-1 (SIRT1)/ nuclear factor E2-related factor 2 (Nrf2) signalling pathway, overall improving antioxidant defence. Moreover, CCB suppressed inflammatory and fibrotic reactions by inhibiting nuclear factor kappa B (NFκB) and pro-inflammatory and pro-fibrotic cytokines. Noteworthy, several of these effects were further improved in combination with metformin. Our results demonstrate that CCB strongly prevents the cardiac remodelling and dysfunction observed in diabetic animals, highlighting its potential, alone or in adjuvant therapy, for treating DCM.

Glycemic Control and the Heart: The Tale of Diabetic Cardiomyopathy Continues

Cardiovascular diseases are the leading cause of death in people with diabetes. Diabetic cardiomyopathy (DC) is an important complication of diabetes and represents a distinct subtype of heart failure that occurs in absence of cardiovascular diseases. Chronic hyperglycemia and hyperinsulinemia along with insulin resistance and inflammatory milieu are the main mechanisms involved in the pathophysiology of DC. Changes in lifestyle favoring healthy dietary patterns and physical activity, combined with more innovative anti-diabetes therapies, are the current treatment strategies to safeguard the cardiovascular system. This review aims at providing an updated comprehensive overview of clinical, pathogenetic, and molecular aspects of DC, with a focus on the effects of anti-hyperglycemic drugs on the prevention of pump dysfunction and consequently on cardiovascular health in type 2 diabetes.

Ferroptosis is essential for diabetic cardiomyopathy and is prevented by sulforaphane via AMPK/NRF2 pathways

Herein, we define the role of ferroptosis in the pathogenesis of diabetic cardiomyopathy (DCM) by examining the expression of key regulators of ferroptosis in mice with DCM and a new ex vivo DCM model. Advanced glycation end-products (AGEs), an important pathogenic factor of DCM, were found to induce ferroptosis in engineered cardiac tissues (ECTs), as reflected through increased levels of Ptgs2 and lipid peroxides and decreased ferritin and SLC7A11 levels. Typical morphological changes of ferroptosis in cardiomyocytes were observed using transmission electron microscopy. Inhibition of ferroptosis with ferrostatin-1 and deferoxamine prevented AGE-induced ECT remodeling and dysfunction. Ferroptosis was also evidenced in the heart of type 2 diabetic mice with DCM. Inhibition of ferroptosis by liproxstatin-1 prevented the development of diastolic dysfunction at 3 months after the onset of diabetes. Nuclear factor erythroid 2-related factor 2 (NRF2) activated by sulforaphane inhibited cardiac cell ferroptosis in both AGE-treated ECTs and hearts of DCM mice by upregulating ferritin and SLC7A11 levels. The protective effect of sulforaphane on ferroptosis was AMP-activated protein kinase (AMPK)-dependent. These findings suggest that ferroptosis plays an essential role in the pathogenesis of DCM; sulforaphane prevents ferroptosis and associated pathogenesis via AMPK-mediated NRF2 activation. This suggests a feasible therapeutic approach with sulforaphane to clinically prevent ferroptosis and DCM.

Symbiotic Algae-Bacteria Dressing for Producing Hydrogen to Accelerate Diabetic Wound Healing

Oxidative stress induced by hyperglycemia or chronic inflammation can limit diabetic wound healing, resulting in diabetic foot ulcers. Hydrogen has the potential to act as an antioxidant and scavenge reactive oxygen species, thereby attenuating inflammation in these chronic wounds. However, most of the reported H₂ delivery systems for wound healing, including hydrogen gas, hydrogen-rich water, and hydrogen-rich saline, are very short-lived for the low solubility of hydrogen gas. Here, we introduce a hydrogen-producing hydrogel made of living Chlorella and bacteria within a cell-impermeable casing that can continuously produce hydrogen for 60 h. This microbe-hydrogel system can selectively reduce highly toxic •OH and ONOO^- species and reduce inflammation. Additional experiments indicated that the microbe-hydrogel dressing could promote cell proliferation and diabetic wound healing by almost 50% at day 3. The symbiotic algae-bacteria hydrogel has excellent biocompatibility and reactive oxygen species scavenging features, indicating it has great promise for clinical use.

Novel Insights Into the Pathogenesis of Diabetic Cardiomyopathy and Pharmacological Strategies

Diabetic cardiomyopathy (DCM) is a severe complication of diabetes developed mainly in poorly controlled patients. In DCM, several clinical manifestations as well as cellular and molecular mechanisms contribute to its phenotype. The production of reactive oxygen species (ROS), chronic low-grade inflammation, mitochondrial dysfunction, autophagic flux inhibition, altered metabolism, dysfunctional insulin signaling, cardiomyocyte hypertrophy, cardiac fibrosis, and increased myocardial cell death are described as the cardinal features involved in the genesis and development of DCM. However, many of these features can be associated with broader cellular processes such as inflammatory signaling, mitochondrial alterations, and autophagic flux inhibition. In this review, these mechanisms are critically discussed, highlighting the latest evidence and their contribution to the pathogenesis of DCM and their potential as pharmacological targets.

Pyrroloquinoline quinone ameliorates diabetic cardiomyopathy by inhibiting the pyroptosis signaling pathway in C57BL/6 mice and AC16 cells

Purpose

Diabetic cardiomyopathy (DCM), a common complication of diabetes mellitus and is characterized by myocardial hypertrophy and myocardial fibrosis. Pyrroloquinoline quinone (PQQ), a natural nutrient, exerts strong protection against various myocardial diseases. Pyroptosis, a type of inflammation-related programmed cell death, is vital to the development of DCM. However, the protective effects of PQQ against DCM and the associated mechanisms are not clear. This study aimed to investigate whether PQQ protected against DCM and to determine the underlying molecular mechanism.

Methods

Diabetes was induced in mice by intraperitoneal injection of streptozotocin, after which the mice were administered PQQ orally (10, 20, or 40 mg/kg body weight/day) for 12 weeks. AC16 human myocardial cells were divided into the following groups and treated accordingly: control (5.5 mmol/L glucose), high glucose (35 mmol/L glucose), and HG + PQQ groups (1 and 10 nmol/L PQQ). Cells were treated for 24 h.

Results

PQQ reduced myocardial hypertrophy and the area of myocardial fibrosis, which was accompanied by an increase in antioxidant function and a decrease in inflammatory cytokine levels. Moreover, myocardial hypertrophy—(ANP and BNP), myocardial fibrosis—(collagen I and TGF-β1), and pyroptosis-related protein levels decreased in the PQQ treatment groups. Furthermore, PQQ abolished mitochondrial dysfunction and the activation of NF-κB/IκB, and decreased NLRP3 inflammation-mediated pyroptosis in AC16 cells under high-glucose conditions.

Conclusion

PQQ improved DCM in diabetic mice by inhibiting NF-κB/NLRP3 inflammasome-mediated cell pyroptosis. Long-term dietary supplementation with PQQ may be greatly beneficial for the treatment of DCM.

Graphical abstract

Diagram of the underlying mechanism of the effects of PQQ on DCM. PQQ inhibits ROS generation and NF-κB activation, which stimulates activation of the NLRP3 inflammasome and regulates the expression of caspase-1, IL-1β, and IL-18. The up-regulated inflammatory cytokines trigger myocardial hypertrophy and cardiac fibrosis and promote the pathological process of DCM.

Empagliflozin Ameliorates Diabetic Cardiomyopathy via Attenuating Oxidative Stress and Improving Mitochondrial Function

Diabetic cardiomyopathy (DCM) is considered to be a critical contributor to the development of heart failure. Empagliflozin (EMPA), a sodium-glucose cotransporter 2 inhibitor, has been shown to prevent cardiovascular events and reduce the incidence of heart failure in randomized clinical trials. However, the mechanism of how EMPA prevents DCM is poorly understood. To study the potential mechanisms involved in the therapeutic effects of EMPA, we assessed the protective effects of EMPA on myocardial injury in type 2 diabetic db/db mice and H9C2 cardiomyocytes. 9-10-week-old male db/db mice were treated with EMPA (10 mg/kg) via oral gavage daily for 20 weeks. Afterward, cardiac function of treated mice was evaluated by echocardiography, and pathological changes in heart tissues were determined by histopathological examination and western blot assay. EMPA markedly reduced blood glucose levels, improved insulin tolerance, and enhanced insulin sensitivity of db/db mice. In addition, EMPA significantly prevented cardiac dysfunction, inhibited cardiac hypertrophy and fibrosis, and reduced glycogen deposition in heart tissues. Furthermore, EMPA improved diabetes-induced oxidative stress and mitochondrial dysfunction in both heart tissues of db/db mice and palmitate exposed H9C2 cells. EMPA significantly increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream genetic targets in cardiac tissue of type 2 diabetic db/db mice and H9C2 cells. EMPA also downregulated the expression of mitochondrial fission-related proteins and upregulated the expression of mitochondrial fusion-related proteins. Collectively, these findings indicate that EMPA may prevent DCM via attenuating oxidative stress and improving mitochondrial function in heart tissue.

Recombinant Human Growth Hormone Inhibits Lipotoxicity, Oxidative Stress, and Apoptosis in a Mouse Model of Diabetic Cardiomyopathy

Recombinant human growth hormone (rhGH), widely used in clinical studies, exerts protective effects against cardiac damage. Here, we investigated the effects and mechanisms underlying the effects of rhGH on cardiac functions in db/db mice. C57BL/6J and db/db mice were subjected to rhGH treatment. Metabolic parameters, cardiac function and morphology, oxidative stress, lipid metabolism, and apoptosis were evaluated 16 weeks after rhGH treatment. Although rhGH did not significantly affect fasting blood glucose levels in db/db mice, it protected against diabetic cardiomyopathy, by improving cardiac function and reducing oxidative stress in the heart. In addition, rhGH treatment exhibited anti-apoptotic effects in the heart of db/db mice. The rhGH treatment, besides inhibiting oxidative stress and apoptosis, ameliorated cardiac dysfunction by inhibiting lipotoxicity in mice with type 2 diabetes. These findings suggest that rhGH is a promising therapeutic agent for diabetic cardiomyopathy.

Nephroprotective effect of naringin in methotrexate induced renal toxicity in male rats

The current work aims to study the nephroprotective potential of naringin (NG), a flavanone derived from citrus fruits, in methotrexate (MTX)-induced renal toxicity. Thirty male rats were divided into five groups; control group (IP saline), MTX group (IP single dose, 20 mg/kg), and three groups co-treated with MTX and naringin (IP daily dose; 20, 40, and 80 mg/kg, respectively). Kidney tissues were used to investigate renal function, oxidative stress, lipid peroxidation, and caspase-3 activity. Biochemical cytokine analysis was performed in addition to ultrastructural examinations of kidney tissue. When compared to the MTX-treated rats, MTX+NG significantly reduced the levels of urea, creatinine, MDA, NO, TNFα, IL-6, and caspase-3 activity. A significant increase in the levels of the antioxidant enzymes and GSH were also noted. Additionally, naringin ameliorated the apparent ultrastructural changes observed in the glomeruli and renal tubules of MTX-intoxicated rats. Noticeable structural improvements of glomerular lesions, proximal, and distal convoluted tubular epithelium were observed in MTX+NG treated animals, including podocytes with regular foot processes, perfectly organized filtration barrier, no signs of GBM thickening, organized brush border, and normal architecture of microvilli. Naringin (80 mg/kg) had the maximum amelioration effect. To the best of our knowledge, this is the first study to investigate the ultrastructural manifestations of naringin and/or MTX on the kidney of rats. Taken all, naringin has a potent therapeutic effect and can be used in adjuvant therapy to prevent MTX-induced nephrotoxicity. Nevertheless, the molecular mechanism underlying the nephroprotective capacity of naringin needs further investigation.

Rutin alleviates cardiomyocyte injury induced by high glucose through inhibiting apoptosis and endoplasmic reticulum stress

Diabetic cardiomyopathy is a common complication of diabetes, in which endoplasmic reticulum stress (ERS) serves an important role. Rutin can treat the myocardial dysfunction of diabetic rats. However, to the best of our knowledge, studies on the effects of Rutin on myocardial injury caused by diabetes from the perspective of ERS have not previously been reported. In the present study, the role of rutin in the regulation of ERS in myocardial injury was assessed. Different high glucose concentrations were used to treat H9C2 myoblast cells to establish a myocardial damage model. A cell counting kit-8 assay was used to determine cell viability. A lactate dehydrogenase kit was used to detect cytotoxicity. Apoptosis levels were determined using a TUNEL assay. Western blotting was used to determine the expression levels of apoptosis-related proteins and ERS-related proteins, including heat shock protein A family member 5, inositol-requiring enzyme-1α, X-box binding protein 1, activating transcription factor 6, C/EBP-homologous protein (CHOP), cleaved caspase-12 and caspase-12. The anti-apoptotic and anti-ERS effects of Rutin on H9C2 cardiac cells induced by high glucose were examined after the administration of the ERS activator thapsigargin (TG). The results indicated that rutin could dose-dependently inhibit the level of apoptosis and ERS induced by high glucose in H9C2 cells. After administration of the ERS activator TG, it was demonstrated that TG could reverse the anti-apoptotic and anti-ERS effects of rutin on H9C2 cells stimulated with high glucose. Collectively, the present results suggested that rutin may alleviate cardiomyocyte model cell injury induced by high glucose through the inhibition of apoptosis and ERS.

The Na/K-ATPase Signaling and SGLT2 Inhibitor-Mediated Cardiorenal Protection: A Crossed Road?

In different large-scale clinic outcome trials, sodium (Na⁺)/glucose co-transporter 2 (SGLT2) inhibitors showed profound cardiac- and renal-protective effects, making them revolutionary treatments for heart failure and kidney disease. Different theories are proposed according to the emerging protective effects other than the original purpose of glucose-lowering in diabetic patients. As the ATP-dependent primary ion transporter providing the Na⁺ gradient to drive other Na⁺-dependent transporters, the possible role of the sodium–potassium adenosine triphosphatase (Na/K-ATPase) as the primary ion transporter and its signaling function is not explored.

The Link Between Ferroptosis and Cardiovascular Diseases: A Novel Target for Treatment

Ferroptosis is an iron-dependent cell death, which is characterized by iron overload and lipid peroxidation. Ferroptosis is distinct from apoptosis, necroptosis, autophagy, and other types of cell death in morphology and function. Ferroptosis is regulated by a variety of factors and controlled by several mechanisms, including mitochondrial activity and metabolism of iron, lipid, and amino acids. Accumulating evidence shows that ferroptosis is closely related to a majority of cardiovascular diseases (CVDs), including cardiomyopathy, myocardial infarction, ischemia/reperfusion injury, heart failure, and atherosclerosis. This review summarizes the current status of ferroptosis and discusses ferroptosis as a potential therapeutic target for CVDs.

GDF11 Alleviates Pathological Myocardial Remodeling in Diabetic Cardiomyopathy Through SIRT1-Dependent Regulation of Oxidative Stress and Apoptosis

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor β superfamily that alleviates cardiac hypertrophy, myocardial infarction, and vascular injury by regulating oxidative stress, inflammation, and cell survival. However, the roles and underlying mechanisms of GDF11 in diabetic cardiomyopathy (DCM) remain largely unknown. In this study, we sought to determine whether GDF11 could prevent DCM. After establishing a mouse model of diabetes by administering a high-fat diet and streptozotocin, intramyocardial injection of an adeno-associated virus was used to achieve myocardium-specific GDF11 overexpression. GDF11 remarkably improved cardiac dysfunction and interstitial fibrosis by reducing the levels of reactive oxygen species and protecting against cardiomyocyte loss. Mechanistically, decreased sirtuin 1 (SIRT1) expression and activity were observed in diabetic mice, which was significantly increased after GDF11 overexpression. To further explore how SIRT1 mediates the role of GDF11, the selective inhibitor EX527 was used to block SIRT1 signaling pathway, which abolished the protective effects of GDF11 against DCM. In vitro studies confirmed that GDF11 protected against H9c2 cell injury in high glucose and palmitate by attenuating oxidative injury and apoptosis, and these effects were eliminated by SIRT1 depletion. Our results demonstrate for the first time that GDF11 protects against DCM by regulating SIRT1 signaling pathway.

Exercise and Stevia Rebaudiana (R) Extracts Attenuate Diabetic Cardiomyopathy in Type 2 Diabetic Rats: Possible Underlying Mechanisms

BACKGROUND AND AIMS

In the current work, we studied the effects of exercise and stevia rebaudiana (R) extracts on diabetic cardiomyopathy (DCM) in type 2 diabetic rats and their possible underlying mechanisms.

METHODS

Thirty-two male Sprague Dawley rats were randomly allocated into 4 equal groups; a) normal control group, b) DM group, type 2 diabetic rats received 2 ml oral saline daily for 4 weeks, c) DM+ Exercise, type 2 diabetic rats were treated with exercise for 4 weeks and d) DM+ stevia R extracts: type 2 diabetic rats received methanolic stevia R extracts. By the end of the experiment, serum blood glucose, HOMA-IR, insulin and cardiac enzymes (LDH, CK-MB), cardiac histopathology, oxidative stress markers (MDA, GSH and CAT), myocardial fibrosis by Masson trichrome, the expression of p53, caspase-3, α-SMA and tyrosine hydroxylase (TH) by immunostaining in myocardial tissues were measured.

RESULTS

T2DM caused a significant increase in blood glucose, HOMA-IR index, serum CK-MB and LDH, myocardial damage and fibrosis, myocardial MDA, myocardial α-SMA, p53, caspase-3, Nrf2 and TH density with a significant decrease in serum insulin and myocardial GSH and CAT (p< 0.05). On the other hand, treatment with either exercise or stevia R extracts significantly improved all studied parameters (p< 0.05). Moreover, the effects of stevia R was more significant than exercise (p< 0.05).

CONCLUSION

Both exercise and methanolic stevia R extracts showed cardioprotective effects against DCM and Stevia R offered more cardioprotective than exercise. This cardioprotective effect of these lines of treatment might be due to attenuation of oxidative stress, apoptosis, sympathetic nerve density and fibrosis and upregulation of the antioxidant transcription factor, Nrf2.

β-Hydroxybutyrate inhibits cardiac microvascular collagen 4 accumulation by attenuating oxidative stress in streptozotocin-induced diabetic rats and high glucose treated cells

Accumulation of collagen 4 (COL4) and thickened basement membrane are features of diabetic cardiac microvascular fibrosis that may be induced by oxidative stress. The ketone body β-hydroxybutyrate exhibits various cardiovascular protective effects, however its mechanism remains to be clarified. In the current study, the effects of β-hydroxybutyrate on cardiac microvascular fibrosis and COL4 accumulation were evaluated in streptozotocin-induced diabetic rats and in high glucose (HG) treated human cardiac microvascular endothelial cells (HCMECs). Generations of inducible nitric oxide synthase (iNOS) and copper-zinc superoxide dismutase (Cu/Zn-SOD), and the amount of nitrotyrosine (NT) were measured in vivo and in vitro. Ten weeks of β-hydroxybutyrate treatment (160, 200 and 240 mg/kg/d) attenuated cardiac microvascular fibrosis and inhibited cardiac COL4 generation and microvascular distribution in diabetic rats. Furthermore, β-hydroxybutyrate promoted cardiac Cu/Zn-SOD generation and reduced NT content, without reducing iNOS generation in diabetic rats. In HCMECs, stimulation with HG induced excess generation of COL4 via peroxynitrite. β-Hydroxybutyrate treatment (2, 4, 6 mM) attenuated HG-stimulated COL4 accumulation in a concentration-dependent manner. Similarly, 4 mM β-hydroxybutyrate promoted Cu/Zn-SOD generation and reduced NT content, without affecting excess iNOS generation in HG-stimulated HCMECs. In conclusion, this study showed that β-hydroxybutyrate promoted Cu/Zn-SOD generation, reduced peroxynitrite and inhibited cardiac microvascular COL4 accumulation in diabetes.

Concurrent diabetes and heart failure: interplay and novel therapeutic approaches

Diabetes mellitus increases the risk of developing heart failure, and the co-existence of both diseases worsens cardiovascular outcomes, hospitalization and the progression of heart failure. Despite current advancements on therapeutic strategies to manage hyperglycemia, the likelihood of developing diabetes-induced heart failure is still significant, especially with the accelerating global prevalence of diabetes and an ageing population. This raises the likelihood of other contributing mechanisms beyond hyperglycemia in predisposing diabetic patients to cardiovascular disease risk. There has been considerable interest in understanding the alterations in cardiac structure and function in the diabetic patients, collectively termed as "diabetic cardiomyopathy". However, the factors that contribute to the development of diabetic cardiomyopathies is not fully understood. This review summarizes the main characteristics of diabetic cardiomyopathies, and the basic mechanisms that contribute to its occurrence. This includes perturbations in insulin resistance, fuel preference, reactive oxygen species generation, inflammation, cell death pathways, neurohormonal mechanisms, advanced glycated end-products accumulation, lipotoxicity, glucotoxicity, and posttranslational modifications in the heart of the diabetic. This review also discusses the impact of antihyperglycemic therapies on the development of heart failure, as well as how current heart failure therapies influence glycemic control in diabetic patients. We also highlight the current knowledge gaps in understanding how diabetes induces heart failure.

Application of Animal Models in Diabetic Cardiomyopathy

Diabetic heart disease is a growing and important public health risk. Apart from the risk of coronary artery disease or hypertension, diabetes mellitus (DM) is a well-known risk factor for heart failure in the form of diabetic cardiomyopathy (DiaCM). Currently, DiaCM is defined as myocardial dysfunction in patients with DM in the absence of coronary artery disease and hypertension. The underlying pathomechanism of DiaCM is partially understood, but accumulating evidence suggests that metabolic derangements, oxidative stress, increased myocardial fibrosis and hypertrophy, inflammation, enhanced apoptosis, impaired intracellular calcium handling, activation of the renin-angiotensin-aldosterone system, mitochondrial dysfunction, and dysregulation of microRNAs, among other factors, are involved. Numerous animal models have been used to investigate the pathomechanisms of DiaCM. Despite some limitations, animal models for DiaCM have greatly advanced our understanding of pathomechanisms and have helped in the development of successful disease management strategies. In this review, we summarize the current pathomechanisms of DiaCM and provide animal models for DiaCM according to its pathomechanisms, which may contribute to broadening our understanding of the underlying mechanisms and facilitating the identification of possible new therapeutic targets.

Pemafibrate suppresses oxidative stress and apoptosis under cardiomyocyte ischemia-reperfusion injury in type 1 diabetes mellitus

Diabetes mellitus accelerates the hyperglycemia susceptibility-induced injury to cardiac cells. The activation of peroxisome proliferator-activated receptor α (PPARα) decreases ischemia-reperfusion (IR) injury in animals without diabetes. Therefore, the present study hypothesized that pemafibrate may exert a protective effect on the myocardium in vivo and in vitro. A type 1 diabetes mellitus (T1DM) rat model and H9c2 cells exposed to high glucose under hypoxia and reoxygenation treatments were used in the present study. The rat model and the cells were subsequently treated with pemafibrate. In the T1DM rat model, pemafibrate enhanced the expression of PPARα in the diabetic-myocardial ischemia-reperfusion injury (D-IRI) group compared with the D-IRI group. The infarct size in the D-IRI group was reduced following pemafibrate treatment relative to the untreated group. The disruption of the mitochondrial structure and myofibrils in the D-IRI group was partially recovered by pemafibrate. In addition, to evaluate the mechanism of action of pemafibrate in the treatment of diabetic myocardial IR injury, an in vitro model was established. PPARα protein expression levels were reduced in the high glucose and hypoxia/reoxygenation (H/R) groups compared with that in the control or high glucose-treated groups. Pemafibrate treatment significantly enhanced the ATP and superoxide dismutase levels, and reduced the mitochondrial reactive oxygen species and malondialdehyde levels compared with the high glucose combined with H/R group. Furthermore, pemafibrate inhibited the expression of cytochrome c and cleaved-caspase-3, indicating its involvement in the regulation of mitochondrial apoptosis. Pemafibrate also reduced the expression of nuclear factor-κB (NF-κB), the activation of which reversed the protective effects of pemafibrate on diabetic myocardial IR injury in vitro. Taken together, these results suggested that pemafibrate may activate PPARα to protect the T1DM rat myocardium against IR injury through inhibition of NF-κB signaling.

KLF5 Is Induced by FOXO1 and Causes Oxidative Stress and Diabetic Cardiomyopathy

RATIONALE

Diabetic cardiomyopathy (DbCM) is a major complication in type-1 diabetes, accompanied by altered cardiac energetics, impaired mitochondrial function, and oxidative stress. Previous studies indicate that type-1 diabetes is associated with increased cardiac expression of KLF5 (Krüppel-like factor-5) and PPARα (peroxisome proliferator-activated receptor) that regulate cardiac lipid metabolism.

OBJECTIVE

In this study, we investigated the involvement of KLF5 in DbCM and its transcriptional regulation.

METHODS AND RESULTS

KLF5 mRNA levels were assessed in isolated cardiomyocytes from cardiovascular patients with diabetes and were higher compared with nondiabetic individuals. Analyses in human cells and diabetic mice with cardiomyocyte-specific FOXO1 (Forkhead box protein O1) deletion showed that FOXO1 bound directly on the KLF5 promoter and increased KLF5 expression. Diabetic mice with cardiomyocyte-specific FOXO1 deletion had lower cardiac KLF5 expression and were protected from DbCM. Genetic, pharmacological gain and loss of KLF5 function approaches and AAV (adeno-associated virus)-mediated Klf5 delivery in mice showed that KLF5 induces DbCM. Accordingly, the protective effect of cardiomyocyte FOXO1 ablation in DbCM was abolished when KLF5 expression was rescued. Similarly, constitutive cardiomyocyte-specific KLF5 overexpression caused cardiac dysfunction. KLF5 caused oxidative stress via direct binding on NADPH oxidase (NOX)4 promoter and induction of NOX4 (NADPH oxidase 4) expression. This was accompanied by accumulation of cardiac ceramides. Pharmacological or genetic KLF5 inhibition alleviated superoxide formation, prevented ceramide accumulation, and improved cardiac function in diabetic mice.

CONCLUSIONS

Diabetes-mediated activation of cardiomyocyte FOXO1 increases KLF5 expression, which stimulates NOX4 expression, ceramide accumulation, and causes DbCM.

SGLT2 inhibitors: a focus on cardiac benefits and potential mechanisms

This paper highlights the cardioprotective potential of sodium-glucose cotransporter 2 inhibitors (SLGT2i), as well as several most discussed mechanisms responsible for their cardioprotection. Cardiovascular diseases are considered a primary cause of death in nearly 80% of type 2 diabetes mellitus (T2DM) patients, with a 2-4-fold greater incidence of heart failure (HF) among diabetics. As novel hypoglycemics, SGLT2i showed exceptional cardiovascular benefits, reflected through robust reductions of cardiovascular mortality and hospitalization for HF in T2DM patients. Recently, those effects have been reported even in patients with HF and reduced ejection fraction irrespectively of diabetic status, suggesting that cardioprotective effects of SGLT2i are driven independently of their hypoglycemic actions. SGLT2i exerted hemodynamic and metabolic effects, partially driven by natriuresis and osmotic diuresis. However, those systemic effects are modest, and therefore cannot be completely related to the cardiac benefits of these agents in T2DM patients. Hence, increased circulating ketone levels during SGLT2i administration have brought out another hypothesis of a cardiac metabolic switch. Moreover, SGLT2i influence ion homeostasis and exert anti-inflammatory and antifibrotic effects. Their enviable influence on oxidative stress markers, as well as anti- and pro-apoptotic factors, have also been reported. However, since the main mechanistical contributor of their cardioprotection has not been elucidated yet, a joint action of systemic and molecular mechanisms has been suggested. In the light of ongoing trials evaluating the effects of SGLT2i in patients with HF and preserved ejection fraction, a new chapter of beneficial SGLT2i mechanisms is expected, which might resolve their main underlying action.

Dapagliflozin suppresses ER stress and protects doxorubicin-induced cardiotoxicity in breast cancer patients

Cancer patients with diabetes have an increasing risk of Dox-induced cardiotoxicity. Despite previous studies reporting benefits of dapagliflozin on the cardiovascular system, it remains unknown whether dapagliflozin has a cardioprotective effect in cancer patients with diabetes. We aimed to investigate the potential of dapagliflozin for preventing doxorubicin (Dox)-induced cardiotoxicity. Using Taiwan National Health Insurance Database, the incidence of heart failure of cancer patients with or without diabetes was investigated. Streptozotocin (STZ)-induced diabetic rats were pretreated with oral dapagliflozin for 6 weeks followed by Dox for 4 weeks via intraperitoneal injection. Sequential echocardiography was applied to assess cardiac function. For in vitro analysis, cardiomyocytes cultured in high glucose were treated with dapagliflozin at 10 μM and subsequently exposed to Dox at 1 μM. Apoptosis and endoplasmic reticulum (ER) stress-related protein expression were measured. Among the studied patients, those with diabetes had a higher risk of major adverse cardiovascular events including the development of heart failure. In diabetic rats, dapagliflozin reduced cardiac fibrosis and significantly improved cardiac function. Dapagliflozin effectively inhibited Dox-induced apoptosis and reactive oxygen species in cardiomyocytes under high glucose. Mechanistically, we showed that dapagliflozin decreased the cardiac expression of Bax and cleaved caspase 3 but increased Bcl-2. Dapagliflozin also significantly reduced ER stress-associated proteins including GRP78, PERK, eIF-2α, ATF-4, and CHOP. Our study revealed for the first time that dapagliflozin mitigated Dox-induced cardiomyocyte apoptosis in diabetes. These results indicate that dapagliflozin could be useful for preventing cardiotoxicity in diabetic cancer patients receiving Dox treatment.

Protective effects of medicinal plant against diabetes induced cardiac disorder: A review

ETHNOPHARMACOLOGY RELEVANCE

Nowadays, there is an increase in global tendency to use medicinal plants as preventive and therapeutic agents to manage diabetes and its long-term complications such as cardiovascular disorders owing to their availability and valuable traditional background.

AIM OF STUDY

This review aims to introduce common medicinal plants, which have been demonstrated to have cardioprotective effects on diabetes and their mechanisms of action.

MATERIALS AND METHODS

Online literature databases, including Web of Sciences, PubMed, Science Direct, Scopus and Google Scholar were searched without date limitation by May 2020. The following keywords (natural products or medicinal plants or herbal medicine or herb or extract) and (diabetes or antidiabetic or hyperglycemic) and (cardiomyopathy or heart or cardioprotective or cardiac or cardio) were used, and after excluding non-relevant articles, 81 original English articles were selected.

RESULTS

The surveyed medicinal plants induced cardioprotective effects mostly through increasing antioxidant effects leading to attenuating ROS production as well as by inhibiting inflammatory signaling pathways and related cytokines. Moreover, they ameliorated the Na+/K + ATPase pump, the L-type Ca₂⁺ channel current, and the intracellular ATP. They also reduced cardiac remodeling and myocardial cell apoptosis through degradation of caspase-3, Bax, P53 protein, enhancement of Bcl-2 protein expression as well as downregulation of TGFβ1 and TNFα expression. In addition, the extracts improved cardiac function through increasing EF% and FS% as well as restoring hemodynamic parameters.

CONCLUSIONS

The reviewed medicinal plants demonstrated cardioprotective manifestations in diabetes through intervention with mechanisms involved in the diabetic heart to restore cardiovascular complications.

Fenofibrate Protects Cardiomyocytes from Hypoxia/Reperfusion- and High Glucose-Induced Detrimental Effects

Lesions caused by high glucose (HG), hypoxia/reperfusion (H/R), and the coexistence of both conditions in cardiomyocytes are linked to an overproduction of reactive oxygen species (ROS), causing irreversible damage to macromolecules in the cardiomyocyte as well as its ultrastructure. Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARα) agonist, promotes beneficial activities counteracting cardiac injury. Therefore, the objective of this work was to determine the potential protective effect of fenofibrate in cardiomyocytes exposed to HG, H/R, and HG+H/R. Cardiomyocyte cultures were divided into four main groups: (1) control (CT), (2) HG (25 mM), (3) H/R, and (4) HG+H/R. Our results indicate that cell viability decreases in cardiomyocytes undergoing HG, H/R, and both conditions, while fenofibrate improves cell viability in every case. Fenofibrate also decreases ROS production as well as nicotinamide adenine dinucleotide phosphate oxidase (NADPH) subunit expression. Regarding the antioxidant defense, superoxide dismutase (SOD Cu²⁺/Zn²⁺ and SOD Mn²⁺), catalase, and the antioxidant capacity were decreased in HG, H/R, and HG+H/R-exposed cardiomyocytes, while fenofibrate increased those parameters. The expression of nuclear factor erythroid 2-related factor 2 (Nrf2) increased significantly in treated cells, while pathologies increased the expression of its inhibitor Keap1. Oxidative stress-induced mitochondrial damage was lower in fenofibrate-exposed cardiomyocytes. Endothelial nitric oxide synthase was also favored in cardiomyocytes treated with fenofibrate. Our results suggest that fenofibrate preserves the antioxidant status and the ultrastructure in cardiomyocytes undergoing HG, H/R, and HG+H/R preventing damage to essential macromolecules involved in the proper functioning of the cardiomyocyte.

Fisetin protects against streptozotocin-induced diabetic cardiomyopathy in rats by suppressing fatty acid oxidation and inhibiting protein kinase R

This study examined if the Fisetin against streptozotocin-induced diabetic cardiomyopathy (DC) in rats involves regulating cardiac metabolism and suppressing protein kinase R (PKR). Male rats were divided (12/groups) as control (non-diabetic), control + Fisetin, T1DM, and T1DM + Fisetin. Fisetin was administered orally at a final dose of 2.5 mg/kg for 12 weeks. In T1DM1-induced rats, Fisetin prevented heart and final body weights loss, lowered circulatory levels troponin I and creatinine kinase-MB (CK-MB), increased fasting insulin levels, and improved ventricular systolic and diastolic functions. It also preserved the structure of the cardiomyocytes and reduced oxidative stress, fibrosis, protein levels of transforming growth factor-β1 (TGF-β1), collagenase 1A, caspase-3, and the activation of JNK, p53, and p38 MAPK. In the control and diabetic rats, Fisetin attenuated fasting hyperglycaemia, the increases in glucose levels after the oral and insulin tolerance tests, and HOMA-IR. It also increased cardiac glucose oxidation by increasing the activity of private dehydrogenase (PDH), phosphofructokinase (PFK), protein levels of PPAR-α and suppressed cardiac inflammation by inhibiting NF-κB. These effects were associated with a reduction in the activity of PKR and subsequent increase in the activity of eeukaryotic initiation factor 2 (eIF2) with a parallel increase in protein levels of p67, a cellular inhibitor of PKR. In cultured cardiomyocytes, Fisetin, prevented high glucose (HG)-induced activation of PKR and reduction in p67, in a dose-dependent manner. However, the effect of Fisetin on PKR was diminished in LG and HG-treated cardiomyocytes with p67-siRNA. In conclusion, Fisetin protects against DC in rats by improving cardiac glucose metabolism and suppressing PKR.

Blockade of Renin Angiotensin System Ameliorates the Cardiac Arrhythmias and Sympathetic Neural Remodeling in Hearts of Type 2 DM Rat Model

OBJECTIVE

The present study was designed to investigate the effects of renin angiotensin system (RAS) blockade on cardiac arrhythmias and sympathetic nerve remodelling in heart tissues of type 2 diabetic rats.

METHODS

Thirty-two male Sprague Dawley rats were randomly allocated into 4 equal groups; a) normal control group: normal rats, b) DM group; after type 2 diabetes induction, rats received 2ml oral saline daily for 4 weeks, c) DM+ ACEi: after type 2 diabetes induction, rats were treated with enalapril (10 mg/kg, orally for 4 weeks) and d) DM+ ARBs: after type 2 diabetes induction, rats were treated with losartan (30 mg/kg, orally for 4 weeks).

RESULTS

In type 2 diabetic rats, the results demonstrated significant prolongation in Q-T interval and elevation of blood sugar, HOMA-IR index, TC, TGs, LDL, serum CK-MB, myocardial damage, myocardial MDA, myocardial norepinephrine and tyrosine hydroxylase (TH) density with significant reduction in serum HDL, serum insulin and myocardial GSH and CAT. On the other hand, blockade of RAS at the level of either ACE by enalapril or angiotensin (Ag) receptors by losartan resulted in significant improvement in ECG parameters (Q-T), cardiac enzymes (CK-MB), cardiac morphology, myocardial oxidative stress (low MDA, high CAT and GSH) and myocardial TH density.

CONCLUSION

RAS plays a role in the cardiac sympathetic nerve sprouting and cardiac arrhythmias induced by type 2 DM and its blockade might have a cardioprotective effect via attenuation of sympathetic nerve fibres remodelling, myocardial norepinephrine contents and oxidative stress.

Histone Deacetylases in the Pathogenesis of Diabetic Cardiomyopathy

The global burden of diabetes mellitus and its complications are currently increasing. Diabetic cardiomyopathy (DCM) is the main cause of diabetes mellitus associated morbidity and mortality; therefore, a comprehensive understanding of DCM development is required for more effective treatment. A disorder of epigenetic posttranscriptional modification of histones in chromatin has been reported to be associated with the pathology of DCM. Recent studies have implicated that histone deacetylases could regulate cardiovascular and metabolic diseases in cellular processes including cardiac fibrosis, hypertrophy, oxidative stress and inflammation. Therefore in this review, we summarized the roles of histone deacetylases in the pathogenesis of DCM, aiming to provide insights into exploring potential preventative and therapeutic strategies of DCM.

Cardioprotective effects of polydatin against myocardial injury in diabetic rats via inhibition of NADPH oxidase and NF-κB activities

Background

Diabetic cardiomyopathy is a main cause of the increased morbidity in diabetic patients, no effective treatment is available so far. Polydatin, a resveratrol glucoside isolated from the Polygonum cuspidatum, was found by our and others have antioxidant and cardioprotective activities. Therapeutic effects of polydatin on diabetic cardiomyopathy and the possible mechanisms remains unclear. This study aimed to investigate the cardioprotective effects and underlying mechanisms of polydatin on myocardial injury induced by hyperglycemia.

Methods

Diabetes in rats was made by high-fat diet combined with multiple low doses of streptozotocin, and then treated with polydatin (100 mg·kg-1·day-1, by gavage) for 8 weeks. Cardiac function was examined by echocardiography. Myocardial tissue and blood samples were collected for histology, protein and metabolic characteristics analysis. In cultured H9c2 cells with 30 mM of glucose, the direct effects of polydatin on myocyte injury were also observed.

Results

In diabetic rats, polydatin administration significantly improved myocardial dysfunction and attenuated histological abnormalities, as evidenced by elevating left ventricular shortening fraction and ejection fraction, as well as reducing cardiac hypertrophy and interstitial fibrosis. In cultured H9c2 cells, pretreatment of polydatin dose-dependently inhibited high glucose-induced cardiomyocyte injury. Further observation evidenced that polydatin suppressed the increase in the reactive oxygen species levels, NADPH oxidase activity and inflammatory cytokines production induced by hyperglycemia in vivo and in vitro. Polydatin also prevented the increase expression of NOX4, NOX2 and NF-κB in the high glucose -stimulated H9c2 cells and diabetic hearts.

Conclusions

Our results demonstrate that the cardioprotective effect of polydatin against hyperglycemia-induced myocardial injury is mediated by inhibition of NADPH oxidase and NF-κB activity. The findings may provide a novel understanding the mechanisms of the polydatin to be a potential treatment of diabetic cardiomyopathy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-020-03177-y.

Value of peak strain dispersion in discovering left ventricular dysfunction in diabetes mellitus

Cardiovascular disease is one of the main causes of death in diabetes mellitus (DM) patients. The aim of the current study was to explore the value of peak strain dispersion (PSD) for discovering early-stage left ventricular (LV) dysfunction in type 2 diabetes mellitus (T2DM) patients. One hundred and one T2DM patients and sixty healthy subjects were selected for this study. T2DM patients were further divided into controlled blood glucose (HbA1c < 7%, n = 46) and uncontrolled blood glucose (HbA1c ≥ 7%, n = 55) subgroups. All participants underwent conventional echocardiography and two-dimensional speckle-tracking echocardiography. Our results showed that an obvious difference was not observed in global longitudinal strain (GLS) between the controlled blood glucose group and the control group (− 20.34% vs − 21.22%, P = 0.068). Compared with the healthy controls, the uncontrolled blood glucose group showed an impaired GLS (− 18.62% vs − 21.22%, P < 0.001). Nevertheless, PSD was appreciably increased in the controlled blood glucose group (36.02 ms vs 32.48 ms, P = 0.01) and uncontrolled blood glucose group (57.51 ms vs 32.48 ms, P < 0.001). Multivariate linear regression analysis showed that HbA1c was closely related to PSD lesion in the LV in the T2DM group (β = 0.520, P < 0.001). PSD plays an important role in evaluating the coordination and synchronization of myocardial movement and provides a more accurate and sensitive index assessment of early LV systolic function in T2DM patients. In addition, HbA1c levels were related to LV dysfunction.

Effect and Mechanism of Ganoderma lucidum Spores on Alleviation of Diabetic Cardiomyopathy in a Pilot in vivo Study

BACKGROUND

Ganoderma lucidum spores (GLS) exhibit disease prevention properties, but no study has been carried out on the anti-diabetic cardiomyopathy property of GLS. The aim of this study was to evaluate the hyperglycemia-mediated cardiomyopathy protection and mechanisms of GLS in streptozotocin (STZ)induced diabetic rats.

METHODS

Male SD rats were randomly divided into three groups. Two groups were given STZ (50 mg/kg, i.p.) treatment and when their fasting plasma glucose was above 16.7 mmol/L, among them, one group was given placebo, as diabetic group, and another group was given GLS (300 mg/kg) treatment. The group without STZ treatment was given placebo as a control group. The experiment lasted 70 days. The histology of myocardium and biomarkers of antioxidants, myocardial injury, pro-inflammatory cytokines, pro-apoptotic proteins and phosphorylation of key proteins in PI3K/AKT pathway were assessed.

RESULTS

Biochemical analysis showed that GLS treatment significantly reduced the blood glucose (-20.3%) and triglyceride (-20.4%) levels compared to diabetic group without treatment. GLS treatment decreased the content of MDA (-25.6%) and activity of lactate dehydrogenase (-18.9%) but increased the activity of GSH-Px (65.4%). Western blot analysis showed that GLS treatment reduced the expression of both alpha-smooth muscle actin and brain natriuretic peptide. Histological analysis on the cardiac tissue micrographs showed that GLS treatment reduced collagen fibrosis and glycogen reactivity in myocardium. Both Western blot and immunohistochemistry analyses showed that GLS treatment decreased the expression levels of pro-inflammatory factors (cytokines IL-1β, and TNF-α) as well as apoptosis regulatory proteins (Bax, caspase-3 and -9), but increased Bcl-2. Moreover, GLS treatment significantly increased the phosphorylation of key proteins involved in PI3K/AKT pathway, eg, p-AKT p-PI3K and mTOR.

CONCLUSION

The results indicated that GLS treatment alleviates diabetic cardiomyopathy by reducing hyperglycemia, oxidative stress, inflammation, apoptosis and further attenuating the fibrosis and myocardial dysfunction induced by STZ through stimulation of the PI3K/Akt/mTOR signaling pathway.

Worsening baroreflex sensitivity on progression to type 2 diabetes: localized vs. systemic inflammation and role of antidiabetic therapy

Cardiac autonomic neuropathy (CAN) is an early cardiovascular manifestation of type 2 diabetes (T2D) that constitutes an independent risk factor for cardiovascular mortality and morbidity. Nevertheless, its underlying pathophysiology remains poorly understood. We recently showed that localized perivascular adipose tissue (PVAT) inflammation underlies the incidence of parasympathetic CAN in prediabetes. Here, we extend our investigation to provide a mechanistic framework for the evolution of autonomic impairment as the metabolic insult worsens. Early metabolic dysfunction was induced in rats fed a mild hypercaloric diet. Two low-dose streptozotocin injections were used to evoke a state of late decompensated T2D. Cardiac autonomic function was assessed by invasive measurement of baroreflex sensitivity using the vasoactive method. Progression into T2D was associated with aggravation of CAN to include both sympathetic and parasympathetic arms. Unlike prediabetic rats, T2D rats showed markers of brainstem neuronal injury and inflammation as well as increased serum levels of IL-1β. Experiments on PC12 cells differentiated into sympathetic-like neurons demonstrated that brainstem injury observed in T2D rats resulted from exposure to possible proinflammatory mediators in rat serum rather than a direct effect of the altered metabolic profile. CAN and the associated cardiovascular damage in T2D only responded to combined treatment with insulin to manage hyperglycemia in addition to a nonhypoglycemic dose of metformin or pioglitazone providing an anti-inflammatory effect, coincident with the effect of these combinations on serum IL-1β. Our present results indicate that CAN worsening upon progression to T2D involves brainstem inflammatory changes likely triggered by systemic inflammation.

Bakuchiol Alleviates Hyperglycemia-Induced Diabetic Cardiomyopathy by Reducing Myocardial Oxidative Stress via Activating the SIRT1/Nrf2 Signaling Pathway

Bakuchiol (BAK), a monoterpene phenol reported to have exerted a variety of pharmacological effects, has been related to multiple diseases, including myocardial ischemia reperfusion injury, pressure overload-induced cardiac hypertrophy, diabetes, liver fibrosis, and cancer. However, the effects of BAK on hyperglycemia-caused diabetic cardiomyopathy and its underlying mechanisms remain unclear. In this study, streptozotocin-induced mouse model and high-glucose-treated cell model were conducted to investigate the protective roles of BAK on diabetic cardiomyopathy, in either the presence or absence of SIRT1-specific inhibitor EX527, SIRT1 siRNA, or Nrf2 siRNA. Our data demonstrated for the first time that BAK could significantly abate diabetic cardiomyopathy by alleviating the cardiac dysfunction, ameliorating the myocardial fibrosis, mitigating the cardiac hypertrophy, and reducing the cardiomyocyte apoptosis. Furthermore, BAK achieved its antifibrotic and antihypertrophic actions by inhibiting the TGF-β1/Smad3 pathway, as well as decreasing the expressions of fibrosis- and hypertrophy-related markers. Intriguingly, these above effects of BAK were largely attributed to the remarkable activation of SIRT1/Nrf2 signaling, which eventually strengthened cardiac antioxidative capacity by elevating the antioxidant production and reducing the reactive oxygen species generation. However, all the beneficial results were markedly abolished with the administration of EX527, SIRT1 siRNA, or Nrf2 siRNA. In summary, these novel findings indicate that BAK exhibits its therapeutic properties against hyperglycemia-caused diabetic cardiomyopathy by attenuating myocardial oxidative damage via activating the SIRT1/Nrf2 signaling.

Mechanisms of diabetic cardiomyopathy and potential therapeutic strategies: preclinical and clinical evidence

The pathogenesis and clinical features of diabetic cardiomyopathy have been well-studied in the past decade, but effective approaches to prevent and treat this disease are limited. Diabetic cardiomyopathy occurs as a result of the dysregulated glucose and lipid metabolism associated with diabetes mellitus, which leads to increased oxidative stress and the activation of multiple inflammatory pathways that mediate cellular and extracellular injury, pathological cardiac remodelling, and diastolic and systolic dysfunction. Preclinical studies in animal models of diabetes have identified multiple intracellular pathways involved in the pathogenesis of diabetic cardiomyopathy and potential cardioprotective strategies to prevent and treat the disease, including antifibrotic agents, anti-inflammatory agents and antioxidants. Some of these interventions have been tested in clinical trials and have shown favourable initial results. In this Review, we discuss the mechanisms underlying the development of diabetic cardiomyopathy and heart failure in type 1 and type 2 diabetes mellitus, and we summarize the evidence from preclinical and clinical studies that might provide guidance for the development of targeted strategies. We also highlight some of the novel pharmacological therapeutic strategies for the treatment and prevention of diabetic cardiomyopathy.

Mitochondrial Dysfunction in Diabetic Cardiomyopathy: The Possible Therapeutic Roles of Phenolic Acids

As the powerhouse of the cells, mitochondria play a very important role in ensuring that cells continue to function. Mitochondrial dysfunction is one of the main factors contributing to the development of cardiomyopathy in diabetes mellitus. In early development of diabetic cardiomyopathy (DCM), patients present with myocardial fibrosis, dysfunctional remodeling and diastolic dysfunction, which later develop into systolic dysfunction and eventually heart failure. Cardiac mitochondrial dysfunction has been implicated in the development and progression of DCM. Thus, it is important to develop novel therapeutics in order to prevent the progression of DCM, especially by targeting mitochondrial dysfunction. To date, a number of studies have reported the potential of phenolic acids in exerting the cardioprotective effect by combating mitochondrial dysfunction, implicating its potential to be adopted in DCM therapies. Therefore, the aim of this review is to provide a concise overview of mitochondrial dysfunction in the development of DCM and the potential role of phenolic acids in combating cardiac mitochondrial dysfunction. Such information can be used for future development of phenolic acids as means of treating DCM by alleviating the cardiac mitochondrial dysfunction.

Taurine with combined aerobic and resistance exercise training alleviates myocardium apoptosis in STZ-induced diabetes rats via Akt signaling pathway

AIM

The aim of this study was considering the effects of taurine supplementation with combined aerobic and resistance training (CARE) on myocardial apoptosis and Protein Kinase B (akt) level changes in diabetic rat.

MAIN METHODS

Forty male Wistar rats were randomly divided in to 5 groups of 8 animals in each: 1) control, 2) Diabetes Mellitus (DM), 3) DM with taurine supplementation (DM/T), 4) DM with CARE (DM/CARE), and 5) DM with combination of taurine and CARE (DM/T/CARE). DM was induced by injection of streptozotocin (STZ) and nicotine amid (NA) for 2, 3, 4 and 5 groups. Supplement groups received taurine in gavage, 100 mg/kg of body weight, 6 day per weeks, 8 weeks. CARE was performed at maximal speed and 1RM (40-60% of maximum for both).

KEY FINDINGS

The results of this study showed that DM significantly increased blood glucose and caspase 3, caspase 9 expressions and apoptosis cells in heart tissue and reduced Akt expression (p < 0.001). However, taurine and CARE interventions significantly decreased apoptosis markers (caspase 3 and caspase 9) and significantly increased Akt in heart of diabetic rats compare to DM groups (p < 0.05). The highest improvement observed in DM/T/CARE group (p < 0.05).

SIGNIFICANCE

Based on these results, it seems that the use of taurine with combined aerobic and exercise training minimize the cardiac damage caused by diabetes (especially apoptosis) trough increasing protein kinase Akt expression. This could improve cardiac remodeling after diabetes. However, more research is needed, especially on the human samples.

Protective Mechanisms of Quercetin Against Myocardial Ischemia Reperfusion Injury

Quercetin has attracted more attention in recent years due to its protective role against ischemia/reperfusion injury. Quercetin can alleviate oxidative stress injury through the inhibition of NADPH oxidase and xanthine oxidase, blockage of the Fenton reaction, and scavenging of reactive oxygen species. Quercetin can also exert anti-inflammatory and anti-apoptotic effects by reducing the response to inflammatory factors and inhibiting cell apoptosis. Moreover, it can induce vasodilation effects through the inhibition of endothelin-1 receptors, the enhancement of NO stimulation and the activation of the large-conductance calcium-activated potassium channels. Finally, Quercetin can also antagonize the calcium overload. These multifaceted activities of Quercetin make it a potential therapeutic alternative for the treatment of ischemia/reperfusion injury.

Diabetes aggravates myocardial ischaemia reperfusion injury via activating Nox2-related programmed cell death in an AMPK-dependent manner

Cardiovascular diseases such as myocardial ischaemia have a high fatality rate in patients with diabetes. This study was designed to expose the crosstalk between oxidative stress and AMPK, a vital molecule that controls biological energy metabolism, in myocardial ischaemia reperfusion injury (I/RI) in diabetic rats. Diabetes was stimulated in rats using streptozotocin injection. Rats were separated on random into control, control + I/R, Diabetes, Diabetes + I/R, Diabetes + I/R + N-acetylcysteine and Diabetes + I/R + Vas2870 groups. Myocardial infarct size was determined, and the predominant Nox family isoforms were analysed. In vitro, the H9C2 cells were administered excess glucose and exposed to hypoxia/reoxygenation to mimic diabetes and I/R. The AMPK siRNA or AICAR was used to inhibit or activate AMPK expression in H9C2 cells, respectively. Then, myocardial oxidative stress and programmed cell death were measured. Diabetes or high glucose levels were found to aggravate myocardial I/RI or hypoxia/reoxygenation in H9C2 cells, as demonstrated by an increase in myocardial infarct size or lactate dehydrogenase levels, oxidative stress generation and induction of programmed cell death. In diabetic rat hearts, cardiac Nox1, Nox2 and Nox4 were all heightened. The suppression of Nox2 expression using Vas2870 or Nox2-siRNA treatment in vivo or in vitro, respectively, protected diabetic rats from myocardial I/RI. AMPK gene knockout increased Nox2 protein expression while AMPK agonist decreased Nox2 expression. Therefore, diabetes aggravates myocardial I/RI by generating of Nox2-associated oxidative stress in an AMPK-dependent manner, which led to the induction of programmed cell death such as apoptosis, pyroptosis and ferroptosis.

Basic Mechanisms of Diabetic Heart Disease

Diabetes mellitus predisposes affected individuals to a significant spectrum of cardiovascular complications, one of the most debilitating in terms of prognosis is heart failure. Indeed, the increasing global prevalence of diabetes mellitus and an aging population has given rise to an epidemic of diabetes mellitus-induced heart failure. Despite the significant research attention this phenomenon, termed diabetic cardiomyopathy, has received over several decades, understanding of the full spectrum of potential contributing mechanisms, and their relative contribution to this heart failure phenotype in the specific context of diabetes mellitus, has not yet been fully resolved. Key recent preclinical discoveries that comprise the current state-of-the-art understanding of the basic mechanisms of the complex phenotype, that is, the diabetic heart, form the basis of this review. Abnormalities in each of cardiac metabolism, physiological and pathophysiological signaling, and the mitochondrial compartment, in addition to oxidative stress, inflammation, myocardial cell death pathways, and neurohumoral mechanisms, are addressed. Further, the interactions between each of these contributing mechanisms and how they align to the functional, morphological, and structural impairments that characterize the diabetic heart are considered in light of the clinical context: from the disease burden, its current management in the clinic, and where the knowledge gaps remain. The need for continued interrogation of these mechanisms (both known and those yet to be identified) is essential to not only decipher the how and why of diabetes mellitus-induced heart failure but also to facilitate improved inroads into the clinical management of this pervasive clinical challenge.

Mitochondrial fusion promoter restores mitochondrial dynamics balance and ameliorates diabetic cardiomyopathy in an optic atrophy 1-dependent way

AIM

Imbalanced mitochondrial dynamics including suppressed mitochondrial fusion has been observed in diabetic hearts. However, it is still unknown whether mitochondrial fusion promoter is an effective protection to diabetic hearts. This study was designed to explore the efficacy of mitochondrial fusion promoter on diabetic cardiomyopathy (DCM).

METHODS

Male Sprague-Dawley rats were injected with streptozotocin (STZ, 65 mg/kg/d) intraperitoneally to induce diabetes. Seven weeks after vehicle or STZ injection, control or diabetic rats were treated with the vehicle or a mitochondrial fusion promoter-M1 (2 mg/kg/d) intraperitoneally for 6 weeks. Moreover, M1 was administrated to the primary cardiomyocytes cultured in normal glucose medium (NG, 5.5 mmol/L) or high glucose (HG, 33 mnol/L).

RESULTS

Administration of M1 significantly promoted mitochondrial fusion and attenuated the reduction in optic atrophy 1 (Opa1) expression in diabetic hearts. Importantly, M1 treatment attenuated oxidative stress, improved mitochondrial function and alleviated DCM in diabetic rats. In HG-treated cardiomyocytes, M1 treatment consistently increased the expression of Opa1, promoted mitochondrial fusion, enhanced mitochondrial respiratory capacity and reduced mitochondria-derived superoxide production, all of which were blunted by Opa1 siRNA knockdown. In addition, selective upregulation of Opa1 alone can also promote mitochondrial fusion, improve mitochondrial function and inhibit mitochondria-derived superoxide production in HG-cultured cardiomyocytes.

CONCLUSION

Our findings show for the first time that mitochondrial fusion promoter M1 effectively balances mitochondrial dynamics and protects against diabetic cardiomyopathy (DCM) via an Opa1-dependent way, suggesting that promoting mitochondrial fusion might be a potential therapeutic strategy for DCM.

Cyclovirobuxine D protects against diabetic cardiomyopathy by activating Nrf2-mediated antioxidant responses

Diabetic cardiomyopathy (DCM) is the principal cause of death in people with diabetes. However, there is currently no effective strategy to prevent the development of DCM. Although cyclovirobuxine D (CVB-D) has been widely used to treat multiple cardiovascular diseases, the possible beneficial effects of CVB-D on DCM remained unknown. The present aim was to explore the potential effects and underlying mechanisms of CVB-D on DCM. We explored the effects of CVB-D in DCM by using high fat high sucrose diet and streptozotocin-induced rat DCM model. Cardiac function and survival in rats with DCM were improved via the amelioration of oxidative damage after CVB-D treatment. Our data also demonstrated that pre-treatment with CVB-D exerted a remarkable cytoprotective effect against high glucose -or H₂O₂ -induced neonatal rat cardiomyocyte damage via the suppression of reactive oxygen species accumulation and restoration of mitochondrial membrane potential; this effect was associated with promotion of Nrf2 nuclear translocation and its downstream antioxidative stress signals (NQO-1, Prdx1). Overall, the present data has provided the first evidence that CVB-D has potential therapeutic in DCM, mainly by activation of the Nrf2 signalling pathway to suppress oxidative stress. Our findings also have positive implications on the novel promising clinical applications of CVB-D.

Role of Oxidative Stress in Metabolic and Subcellular Abnormalities in Diabetic Cardiomyopathy

Although the presence of cardiac dysfunction and cardiomyopathy in chronic diabetes has been recognized, the pathophysiology of diabetes-induced metabolic and subcellular changes as well as the therapeutic approaches for the prevention of diabetic cardiomyopathy are not fully understood. Cardiac dysfunction in chronic diabetes has been shown to be associated with Ca²⁺-handling abnormalities, increase in the availability of intracellular free Ca²⁺ and impaired sensitivity of myofibrils to Ca²⁺. Metabolic derangements, including depressed high-energy phosphate stores due to insulin deficiency or insulin resistance, as well as hormone imbalance and ultrastructural alterations, are also known to occur in the diabetic heart. It is pointed out that the activation of the sympathetic nervous system and renin-angiotensin system generates oxidative stress, which produces defects in subcellular organelles including sarcolemma, sarcoplasmic reticulum and myofibrils. Such subcellular remodeling plays a critical role in the pathogenesis of diabetic cardiomyopathy. In fact, blockade of the effects of neurohormonal systems has been observed to attenuate oxidative stress and occurrence of subcellular remodeling as well as metabolic abnormalities in the diabetic heart. This review is intended to describe some of the subcellular and metabolic changes that result in cardiac dysfunction in chronic diabetes. In addition, the therapeutic values of some pharmacological, metabolic and antioxidant interventions will be discussed. It is proposed that a combination therapy employing some metabolic agents or antioxidants with insulin may constitute an efficacious approach for the prevention of diabetic cardiomyopathy.

Corosolic acid attenuates cardiac fibrosis following myocardial infarction in mice

Corosolic acid (CRA) is a pentacyclic triterpenoid isolated from Lagerstroemia speciosa. The aim of the present study was to determine whether CRA reduces cardiac remodelling following myocardial infarction (MI) and to elucidate the underlying mechanisms. C57BL/6J mice were randomly divided into control (PBS-treated) or CRA-treated groups. After 14 days of pre-treatment, the mice were subjected to either sham surgery or permanent ligation of the left anterior descending artery. Following surgery, all animals were treated with PBS or CRA (10 or 20 mg/kg/day) for 4 weeks. After 4 weeks, echocardiographic, haemodynamic, gravimetric, histological and biochemical analyses were conducted. The results revealed that, upon MI, mice with CRA treatment exhibited decreased mortality rates, improved ventricular function and attenuated cardiac fibrosis compared with those in control mice. Furthermore, CRA treatment resulted in reduced oxidative stress, inflammation and apoptosis, as well as inhibited the transforming growth factor β1/Smad signalling pathway activation in cardiac tissue. In vitro studies further indicated that inhibition of AMP-activated protein kinase α (AMPKα) reversed the protective effect of CRA. In conclusion, the study revealed that CRA attenuated MI-induced cardiac fibrosis and dysfunction through modulation of inflammation and oxidative stress associated with AMPKα.

Inhibition of PHLPP1 ameliorates cardiac dysfunction via activation of the PI3K/Akt/mTOR signalling pathway in diabetic cardiomyopathy

Background

Pleckstrin homology (PH) domain leucine‐rich repeat protein phosphatase 1 (PHLPP1) is a kind of serine/threonine phosphatase, whose dysregulation is accompanied with numerous human diseases. However, its role in diabetic cardiomyopathy remains unclear. We explored the underlying function and mechanism of PHLPP1 in diabetic cardiomyopathy (DCM).

Method

In vivo, Type 1 diabetic rats were induced by intraperitoneal injection of 60 mg/kg streptozotocin (STZ). Lentivirus‐mediated short hairpin RNA (shRNA) was used to knock down the expression of PHLPP1. In vitro, primary neonatal rat cardiomyocytes and H9C2 cells were incubated in 5.5 mmol/L glucose (normal glucose, NG) or 33.3 mmol/L glucose (high glucose, HG). PHLPP1 expression was inhibited by PHLPP1‐siRNA to probe into the function of PHLPP1 in high glucose‐induced apoptosis in H9c2 cells.

Results

Diabetic rats showed up‐regulated PHLPP1 expression, left ventricular dysfunction, increased myocardial apoptosis and fibrosis. PHLPP1 inhibition alleviated cardiac dysfunction. Additionally, PHLPP1 inhibition significantly reduced HG‐induced apoptosis and restored PI3K/AKT/mTOR pathway activity in H9c2 cells. Furthermore, pretreatment with LY294002, an inhibitor of PI3K/Akt/mTOR pathway, abolished the anti‐apoptotic effect of PHLPP1 inhibition.

Conclusion

Our study indicated that PHLPP1 inhibition alleviated cardiac dysfunction via activating the PI3K/Akt/mTOR signalling pathway in DCM. Therefore, PHLPP1 may be a novel therapeutic target for human DCM.

Comparative Study of the Effects of GLP1 Analog and SGLT2 Inhibitor against Diabetic Cardiomyopathy in Type 2 Diabetic Rats: Possible Underlying Mechanisms

The present study investigated the possible cardioprotective effects of GLP1 and SGLT2i against diabetic cardiomyopathy (DCM) in type 2 diabetic rats and the possible underlying mechanisms.

METHODS

Thirty-two male Sprague Dawley rats were randomly subdivided into 4 equal groups: a) control group, b) DM group, type 2 diabetic rats with saline daily for 4 weeks, c) DM+ GLP1, as DM group with GLP1 analogue (liraglutide) at a dose of 75 µg/kg for 4 weeks, and d) DM+ SGLT2i as DM group with SGLT2 inhibitor (dapagliflozin) at a dose of 1mg/kg for 4 weeks. By the end of treatment (4 weeks), serum blood glucose, homeostasis model assessment insulin resistance (HOMA-IR), insulin, and cardiac enzymes (LDH, CK-MB) were measured. Also, the cardiac histopathology, myocardial oxidative stress markers (malondialdehyde (MDA), glutathione (GSH) and CAT) and norepinephrine (NE), myocardial fibrosis, the expression of caspase-3, TGF-β, TNF-α, and tyrosine hydroxylase (TH) in myocardial tissues were measured.

RESULTS

T2DM caused significant increase in serum glucose, HOMA-IR, serum CK-MB, and LDH (p < 0.05). Also, DM caused significant myocardial damage and fibrosis; elevation of myocardial MDA; NE with upregulation of myocardial caspase-3, TNF-α, TGF-β, and TH; and significant decrease in serum insulin and myocardial GSH and CAT (p < 0.05). Administration of either GLP1 analog or SGLT2i caused a significant improvement in all studied parameters (p < 0.05).

CONCLUSION

We concluded that both GLP1 and SGLT2i exhibited cardioprotective effects against DCM in T2DM, with the upper hand for SGLT2i. This might be due to attenuation of fibrosis, oxidative stress, apoptosis (caspase-3), sympathetic nerve activity, and inflammatory cytokines (TNF-α and TGF-β).

Mitochondrial ROS Formation in the Pathogenesis of Diabetic Cardiomyopathy

Diabetic cardiomyopathy is a result of diabetes-induced changes in the structure and function of the heart. Hyperglycemia affects multiple pathways in the diabetic heart, but excessive reactive oxygen species (ROS) generation and oxidative stress represent common denominators associated with adverse tissue remodeling. Indeed, key processes underlying cardiac remodeling in diabetes are redox sensitive, including inflammation, organelle dysfunction, alteration in ion homeostasis, cardiomyocyte hypertrophy, apoptosis, fibrosis, and contractile dysfunction. Extensive experimental evidence supports the involvement of mitochondrial ROS formation in the alterations characterizing the diabetic heart. In this review we will outline the central role of mitochondrial ROS and alterations in the redox status contributing to the development of diabetic cardiomyopathy. We will discuss the role of different sources of ROS involved in this process, with a specific emphasis on mitochondrial ROS producing enzymes within cardiomyocytes. Finally, the therapeutic potential of pharmacological inhibitors of ROS sources within the mitochondria will be discussed.

High-density lipoprotein-mediated cardioprotection in heart failure

The prevalence of heart failure (HF), including reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF), has increased significantly worldwide. However, the prognosis and treatment of HF are still not good. Recent studies have demonstrated that high-density lipoprotein (HDL) plays an important role in cardiac repair during HF. The exact role and mechanism of HDL in the regulation of HF remain unexplained. Here, we discuss recent findings regarding HDL in the progression of HF, such as the regulation of excitation-contraction coupling, energy homeostasis, inflammation, neurohormone activation, and microvascular dysfunction. The effects of HDL on the regulation of cardiac-related cells, such as endothelial cells (ECs), cardiomyocytes (CMs), and on cardiac resident immune cell dysfunction in HF are also explained. An in-depth understanding of HDL function in the heart may provide new strategies for the prevention and treatment of HF.