Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Ginkgo biloba Leaf Extract Protects against Myocardial Injury via Attenuation of Endoplasmic Reticulum Stress in Streptozotocin-Induced Diabetic ApoE-/- Mice

Diabetes was induced in high-fat diet-fed ApoE^−/− mice via administration of low-dose streptozotocin (STZ) for five days. Mice were then treated with GBE (200 or 400 mg/kg) by gastric gavage daily for 12 weeks. Mice in the untreated diabetic group received saline instead, and nondiabetic C57BL/6J mice served as controls. Collagen І and ІІІ mRNA expression was measured by real-time PCR. TNF-α, IL-1β mRNA levels, and NF-κB expression were determined to analyze intramyocardial inflammation. Hallmarks of endoplasmic reticulum stress- (ERS-) related apoptosis pathways, including phosphorylated c-Jun N-terminal kinase (p-JNK), C/EBP homologous protein (CHOP), caspase-12, and cleaved caspase-3, were analyzed by Western blotting. Diabetic ApoE^−/− myocardial injury was associated with increased cardiomyocyte apoptosis (increased expression of p-JNK, CHOP, caspase-12, and cleaved caspase-3), interstitial fibrosis (increased mRNA levels of collagen І and ІІІ), and inflammation (increased mRNA levels of TNF-α and IL-1β, and NF-κB expression). GBE at 200 and 400 mg/kg/day significantly attenuated cardiomyocyte apoptosis, collagen deposition, and inflammation in diabetic mice via inhibition of the p-JNK, CHOP, and caspase-12 pathways. Serum levels of the proinflammatory cytokines (IL-6, IL-1β, and TNF-α), blood glucose, and lipid profiles were also regulated by GBE treatment. GBE might be beneficial in the treatment of diabetic myocardial injury.

Polydatin Protects Diabetic Heart against Ischemia-Reperfusion Injury via Notch1/Hes1-Mediated Activation of Pten/Akt Signaling

Diabetes exacerbates oxidative/nitrative stress during myocardial ischemia-reperfusion (MI/R) injury. Recent studies highlighted the cardioprotective actions of polydatin. However, its effect on diabetic MI/R injury and the underlying mechanisms remain unknown. This work was undertaken to evaluate the effect of polydatin on diabetic MI/R injury with a focus on Notch1/Hes1 signaling and myocardial oxidative/nitrative stress. Streptozotocin- (STZ-) induced diabetic rats were administered with polydatin (20 mg/kg/d) in the absence or presence of DAPT (a γ-secretase inhibitor) or LY294002 (a PI3K/Akt inhibitor) and then subjected to MI/R injury. Polydatin administration preserved cardiac function and reduced myocardial infarct size. Moreover, polydatin ameliorated myocardial oxidative/nitrative stress damage as evidenced by decreased myocardial superoxide generation, malondialdehyde, gp91^phox expression, iNOS expression, NO metabolite level, and nitrotyrosine content and increased eNOS phosphorylation. However, these effects were blocked by DAPT administration. DAPT also inhibited the stimulatory effect of polydatin on the Notch1/Hes1-Pten/Akt signaling pathway in a diabetic myocardium. Additionally, LY294002 not only abolished polydatin's antiapoptotic effect but also reversed its inhibitory effect on myocardial oxidative/nitrative stress. Polydatin effectively reduced MI/R injury and improved left ventricular functional recovery under diabetic condition by ameliorating oxidative/nitrative stress damage. Importantly, Notch1/Hes1-mediated activation of Pten/Akt signaling played a crucial role in this process.

Diastolic dysfunction is more apparent in STZ-induced diabetic female mice, despite less pronounced hyperglycemia

Diabetic cardiomyopathy is a distinct pathology characterized by early emergence of diastolic dysfunction. Increased cardiovascular risk associated with diabetes is more marked for women, but an understanding of the role of diastolic dysfunction in female susceptibility to diabetic cardiomyopathy is lacking. To investigate the sex-specific relationship between systemic diabetic status and in vivo occurrence of diastolic dysfunction, diabetes was induced in male and female mice by streptozotocin (5x daily i.p. 55 mg/kg). Echocardiography was performed at 7 weeks post-diabetes induction, cardiac collagen content assessed by picrosirius red staining, and gene expression measured using qPCR. The extent of diabetes-associated hyperglycemia was more marked in males than females (males: 25.8 ± 1.2 vs 9.1 ± 0.4 mM; females: 13.5 ± 1.5 vs 8.4 ± 0.4 mM, p < 0.05) yet in vivo diastolic dysfunction was evident in female (E/E' 54% increase, p < 0.05) but not male diabetic mice. Cardiac structural abnormalities (left ventricular wall thinning, collagen deposition) were similar in male and female diabetic mice. Female-specific gene expression changes in glucose metabolic and autophagy-related genes were evident. This study demonstrates that STZ-induced diabetic female mice exhibit a heightened susceptibility to diastolic dysfunction, despite exhibiting a lower extent of hyperglycemia than male mice. These findings highlight the importance of early echocardiographic screening of asymptomatic prediabetic at-risk patients.

Regulating microRNA expression: at the heart of diabetes mellitus and the mitochondrion

Type 2 diabetes mellitus is a major risk factor for cardiovascular disease and mortality. Uncontrolled type 2 diabetes mellitus results in a systemic milieu of increased circulating glucose and fatty acids. The development of insulin resistance in cardiac tissue decreases cellular glucose import and enhances mitochondrial fatty acid uptake. While triacylglycerol and cytotoxic lipid species begin to accumulate in the cardiomyocyte, the energy substrate utilization ratio of free fatty acids to glucose changes to almost entirely free fatty acids. Accumulating evidence suggests a role of miRNA in mediating this metabolic transition. Energy substrate metabolism, apoptosis, and the production and response to excess reactive oxygen species are regulated by miRNA expression. The current momentum for understanding the dynamics of miRNA expression is limited by a lack of understanding of how miRNA expression is controlled. While miRNAs are important regulators in both normal and pathological states, an additional layer of complexity is added when regulation of miRNA regulators is considered. miRNA expression is known to be regulated through a number of mechanisms, which include, but are not limited to, epigenetics, exosomal transport, processing, and posttranscriptional sequestration. The purpose of this review is to outline how mitochondrial processes are regulated by miRNAs in the diabetic heart. Furthermore, we will highlight the regulatory mechanisms, such as epigenetics, exosomal transport, miRNA processing, and posttranslational sequestration, that participate as regulators of miRNA expression. Additionally, current and future treatment strategies targeting dysfunctional mitochondrial processes in the diseased myocardium, as well as emerging miRNA-based therapies, will be summarized.

Myocardial perfusion at rest in uncomplicated type 2 diabetes patients without coronary artery disease evaluated by 320-multidetector computed tomography: A pilot study

Using computed tomography myocardial perfusion imaging (CTP) to investigate resting myocardial perfusion alterations in uncomplicated type 2 diabetes mellitus (T2DM) patients without obstructive coronary artery disease (CAD).A total of 34 participants with 544 myocardial segments were included prospectively: 17 uncomplicated T2DM patients with no significant coronary artery stenosis on coronary computed tomography angiography and 17 healthy controls. Myocardial perfusion was evaluated by transmural perfusion ratio (TPR). Parameters of cardiac structure and function were measured for cardiac comprehensive assessment. Analyses included descriptive statistics and group comparisons.TPR of segments 5, 7, 9, 10 to 14 were significantly reduced in T2DM group compared with controls (P < .05). When 16 myocardial segments were localized into different areas according to the wall orientations, axial levels of left ventricle and coronary artery territories, respectively, TPR of each area in T2DM group were significantly lower than those in the control group (P < .05). No significant differences were found in cardiac anatomy and function analyses between 2 groups.In uncomplicated T2DM patients without obstructive CAD, myocardial perfusion impairments were present and may develop prior to cardiac morphological and functional abnormalities, which can be early detected by CTP.

Comparison of speckle-tracking echocardiography with invasive hemodynamics for the detection of characteristic cardiac dysfunction in type-1 and type-2 diabetic rat models

Background

Measurement of systolic and diastolic function in animal models is challenging by conventional non-invasive methods. Therefore, we aimed at comparing speckle-tracking echocardiography (STE)-derived parameters to the indices of left ventricular (LV) pressure–volume (PV) analysis to detect cardiac dysfunction in rat models of type-1 (T1DM) and type-2 (T2DM) diabetes mellitus.

Methods

Rat models of T1DM (induced by 60 mg/kg streptozotocin, n = 8) and T2DM (32-week-old Zucker Diabetic Fatty rats, n = 7) and corresponding control animals (n = 5 and n = 8, respectively) were compared. Echocardiography and LV PV analysis were performed. LV short-axis recordings were used for STE analysis. Global circumferential strain, peak strain rate values in systole (SrS), isovolumic relaxation (SrIVR) and early diastole (SrE) were measured. LV contractility, active relaxation and stiffness were measured by PV analysis.

Results

In T1DM, contractility and active relaxation were deteriorated to a greater extent compared to T2DM. In contrast, diastolic stiffness was impaired in T2DM. Correspondingly, STE described more severe systolic dysfunction in T1DM. Among diastolic STE parameters, SrIVR was more decreased in T1DM, however, SrE was more reduced in T2DM. In T1DM, SrS correlated with contractility, SrIVR with active relaxation, while in T2DM SrE was related to cardiac stiffness, cardiomyocyte diameter and fibrosis.

Conclusions

Strain and strain rate parameters can be valuable and feasible measures to describe the dynamic changes in contractility, active relaxation and LV stiffness in animal models of T1DM and T2DM. STE corresponds to PV analysis and also correlates with markers of histological myocardial remodeling.

Electronic supplementary material

The online version of this article (10.1186/s12933-017-0645-0) contains supplementary material, which is available to authorized users.

Combination of high-fat/high-fructose diet and low-dose streptozotocin to model long-term type-2 diabetes complications

The epidemic of type 2 diabetes mellitus (T2DM) is fueled by added fructose consumption. Here, we thus combined high-fat/high-fructose diet, with multiple low-dose injections of streptozotocin (HF/HF/Stz) to emulate the long-term complications of T2DM. HF/HF/Stz rats, monitored over 56 weeks, exhibited metabolic dysfunctions associated with the different stages of the T2DM disease progression in humans: an early prediabetic phase characterized by an hyperinsulinemic period with modest dysglycemia, followed by a late stage of T2DM with frank hyperglycemia, normalization of insulinemia, marked dyslipidemia, hepatic fibrosis and pancreatic β-cell failure. Histopathological analyses combined to [¹⁸F]-FDG PET imaging further demonstrated the presence of several end-organ long-term complications, including reduction in myocardial glucose utilization, renal dysfunction as well as microvascular neuropathy and retinopathy. We also provide for the first time a comprehensive µ-PET whole brain imaging of the changes in glucose metabolic activity within discrete cerebral regions in HF/HF/Stz diabetic rats. Altogether, we developed and characterized a unique non-genetic preclinical model of T2DM adapted to the current diet and lifestyle that recapitulates the major metabolic features of the disease progression, from insulin resistance to pancreatic β-cell dysfunction, and closely mimicking the target-organ damage occurring in type 2 diabetic patients at advanced stages.

Protective effect of angiotensin-(1-7) against hyperglycaemia-induced injury in H9c2 cardiomyoblast cells via the PI3K̸Akt signaling pathway

Angiotensin-(1-7) [Ang-(1-7)], a heptapeptide mainly generated from cleavage of AngⅠ and AngⅡ, possesses physiological and pharmacological properties, including anti‑inflammatory and antidiabetic properties. Activation of the phosphoinositide 3-kinase and protein kinase B (PI3K̸Akt) signaling pathway has been confirmed to participate in cardioprotection against hyperglycaemia-induced injury. The aim of the present study was to test the hypothesis that Ang-(1-7) protects H9c2 cardiomyoblast cells against high glucose (HG)-induced injury by activating the PI3K̸Akt pathway. To examine this hypothesis, H9c2 cells were treated with 35 mmol/l (mM) glucose (HG) for 24 h to establish a HG-induced cardiomyocyte injury model. The cells were co-treated with 1 µmol/l (µM) Ang-(1-7) and 35 mM glucose. The findings of the present study demonstrated that exposure of H9c2 cells to HG for 24 h markedly induced injury, as evidenced by an increase in the percentage of apoptotic cells, generation of reactive oxygen species and level of inflammatory cytokines, as well as a decline in cell viability and mitochondrial luminosity. These injuries were significantly attenuated by co-treatment of the cells with Ang-(1-7) and HG. In addition, PI3K̸Akt phosphorylation was suppressed by HG treatment, but this effect was abolished when the H9c2 cells were co-treated with Ang-(1-7) and HG. Furthermore, the cardioprotection of Ang-(1-7) against HG-induced injury in H9c2 cardiomyoblasts was highly attenuated in the presence of either D-Ala7-Ang-(1-7) (A-779, an antagonist of the Mas receptor) or LY294002 (an inhibitor of PI3K̸Akt). In conclusion, the present study provided new evidence that Ang-(1-7) protects H9c2 cardiomyoblasts against HG-induced injury by activating the PI3K̸Akt signaling pathway.

Hyperoxia-induced cardiotoxicity and ventricular remodeling in type-II diabetes mice

Hyperoxia, or supplemental oxygen, is regularly used in the clinical setting for critically ill patients in ICU. However, several recent studies have demonstrated the negative impact of this treatment in patients in critical care, including increased rates of lung and cardiac injury, as well as increased mortality. The purpose of this study was to determine the predisposition for arrhythmias and electrical remodeling in a type 2 diabetic mouse model (db/db), as a result of hyperoxia treatment. For this, db/db and their heterozygous controls were treated with hyperoxia (> 90% oxygen) or normoxia (normal air) for 72-h. Immediately following hyperoxia or normoxia treatments, mice underwent surface ECG. Excised left ventricles were used to assess ion channel expression, including for Kv1.4, Kv1.5, Kv4.2, and KChIP2. Serum cardiac markers were also measured, including cardiac troponin I and lactate dehydrogenase. Our results showed that db/db mice have increased sensitivity to arrhythmia. Normoxia-treated db/db mice displayed features of arrhythmia, including QTc and JT prolongation, as well as QRS prolongation. A significant increase in QRS prolongation was also observed in hyperoxia-treated db/db mice, when compared to hyperoxia-treated heterozygous control mice. Db/db mice were also shown to exhibit ion channel dysregulation, as demonstrated by down-regulation in Kv1.5, Kv4.2, and KChIP2 under hyperoxia conditions. From these results, we conclude that: (1) diabetic mice showed distinct pathophysiology, when compared to heterozygous controls, both in normoxia and hyperoxia conditions. (2) Diabetic mice were more susceptible to arrhythmia at normal air conditions; this effect was exacerbated at hyperoxia conditions. (3) Unlike in heterozygous controls, diabetic mice did not demonstrate cardiac hypertrophy as a result of hyperoxia. (4) Ion channel remodeling was also observed in db/db mice under hyperoxia condition similar to its heterozygous controls.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

Endogenous Annexin-A1 Regulates Haematopoietic Stem Cell Mobilisation and Inflammatory Response Post Myocardial Infarction in Mice In Vivo

Endogenous anti-inflammatory annexin-A1 (ANX-A1) plays an important role in preserving left ventricular (LV) viability and function after ischaemic insults in vitro, but its long-term cardioprotective actions in vivo are largely unknown. We tested the hypothesis that ANX-A1-deficiency exaggerates inflammation, haematopoietic stem progenitor cell (HSPC) activity and LV remodelling in response to myocardial ischaemia in vivo. Adult ANX-A1^−/− mice subjected to coronary artery occlusion exhibited increased infarct size and LV macrophage content after 24–48 h reperfusion compared with wildtype (WT) counterparts. In addition, ANX-A1^−/− mice exhibited greater expansion of HSPCs and altered pattern of HSPC mobilisation 8 days post-myocardial infarction, with increased circulating neutrophils and platelets, consistent with increased cardiac inflammation as a result of increased myeloid invading injured myocardium in response to MI. Furthermore, ANX-A1^−/− mice exhibited significantly increased expression of LV pro-inflammatory and pro-fibrotic genes and collagen deposition after MI compared to WT counterparts. ANX-A1-deficiency increased cardiac necrosis, inflammation, hypertrophy and fibrosis following MI, accompanied by exaggerated HSPC activity and impaired macrophage phenotype. These findings suggest that endogenous ANX-A1 regulates mobilisation and differentiation of HSPCs. Limiting excessive monocyte/neutrophil production may limit LV damage in vivo. Our findings support further development of novel ANX-A1-based therapies to improve cardiac outcomes after MI.

Relaxin ameliorates high glucose-induced cardiomyocyte hypertrophy and apoptosis via the Notch1 pathway

The present study aimed to investigate the role of relaxin (RLX) on high glucose (HG)-induced cardiomyocyte hypertrophy and apoptosis, as well as the possible molecular mechanism. H9c2 cells were exposed to 33 mmol/l HG with or without RLX (100 nmol/ml). Cell viability, apoptosis, oxidative stress, cell hypertrophy and the levels of Notch1, hairy and enhancer of split 1 (hes1), atrial natriuretic polypeptide (ANP), brain natriuretic peptide (BNP), manganese superoxide dismutase (MnSOD), cytochrome C and caspase-3 were assessed in cardiomyocytes. Compared with the HG group, the viability of H9c2 cells was increased by RLX in a time- and dose-dependent manner, and was accompanied with a significant reduction in apoptosis. Furthermore, RLX significantly suppressed the formation of reactive oxygen species and malondialdehyde, and enhanced the activity of SOD. In addition, the levels of ANP, BNP, cytochrome C and caspase-3 were increased and Notch1, hes1 and MnSOD were inhibited in the HG group compared with those in the normal group. However, the Notch inhibitor DAPT almost abolished the protective effects of RLX. These results suggested that RLX protected cardiomyocytes from HG-induced hypertrophy and apoptosis partly through a Notch1-dependent pathway, which may be associated with reducing oxidative stress.

Molecular mechanisms of cardiac pathology in diabetes - Experimental insights

Diabetic cardiomyopathy is a distinct pathology independent of co-morbidities such as coronary artery disease and hypertension. Diminished glucose uptake due to impaired insulin signaling and decreased expression of glucose transporters is associated with a shift towards increased reliance on fatty acid oxidation and reduced cardiac efficiency in diabetic hearts. The cardiac metabolic profile in diabetes is influenced by disturbances in circulating glucose, insulin and fatty acids, and alterations in cardiomyocyte signaling. In this review, we focus on recent preclinical advances in understanding the molecular mechanisms of diabetic cardiomyopathy. Genetic manipulation of cardiomyocyte insulin signaling intermediates has demonstrated that partial cardiac functional rescue can be achieved by upregulation of the insulin signaling pathway in diabetic hearts. Inconsistent findings have been reported relating to the role of cardiac AMPK and β-adrenergic signaling in diabetes, and systemic administration of agents targeting these pathways appear to elicit some cardiac benefit, but whether these effects are related to direct cardiac actions is uncertain. Overload of cardiomyocyte fuel storage is evident in the diabetic heart, with accumulation of glycogen and lipid droplets. Cardiac metabolic dysregulation in diabetes has been linked with oxidative stress and autophagy disturbance, which may lead to cell death induction, fibrotic 'backfill' and cardiac dysfunction. This review examines the weight of evidence relating to the molecular mechanisms of diabetic cardiomyopathy, with a particular focus on metabolic and signaling pathways. Areas of uncertainty in the field are highlighted and important knowledge gaps for further investigation are identified. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Folic acid prevents cardiac dysfunction and reduces myocardial fibrosis in a mouse model of high-fat diet-induced obesity

Background

Folic acid (FA) is an antioxidant that can reduce reactive oxygen species generation and can blunt cardiac dysfunction during ischemia. We hypothesized that FA supplementation prevents cardiac fibrosis and cardiac dysfunction induced by obesity.

Methods

Six-week-old C57BL6/J mice were fed a high-fat diet (HFD), normal diet (ND), or an HFD supplemented with folic acid (FAD) for 14 weeks. Cardiac function was measured using a transthoracic echocardiographic exam. Phenotypic analysis included measurements of body and heart weight, blood glucose and tissue homocysteine (Hcy) content, and heart oxidative stress status.

Results

HFD consumption elevated fasting blood glucose levels and caused obesity and heart enlargement. FA supplementation in HFD-fed mice resulted in reduced fasting blood glucose, heart weight, and heart tissue Hcy content. We also observed a significant cardiac systolic dysfunction when mice were subjected to HFD feeding as indicated by a reduction in the left ventricular ejection fraction and fractional shortening. However, FAD treatment improved cardiac function. FA supplementation protected against cardiac fibrosis induced by HFD. In addition, HFD increased malondialdehyde concentration of the heart tissue and reduced the levels of antioxidant enzyme, glutathione, and catalase. HFD consumption induced myocardial oxidant stress with amelioration by FA treatment.

Conclusion

FA supplementation significantly lowers blood glucose levels and heart tissue Hcy content and reverses cardiac dysfunction induced by HFD in mice. These functional improvements of the heart may be mediated by the alleviation of oxidative stress and myocardial fibrosis.

Alterations in NO/ROS ratio and expression of Trx1 and Prdx2 in isoproterenol-induced cardiac hypertrophy

The development of cardiac hypertrophy is a complicated process, which undergoes a transition from compensatory hypertrophy to heart failure, and the identification of new biomarkers and targets for this disease is greatly needed. Here we investigated the development of isoproterenol (ISO)-induced cardiac hypertrophy in an in vitro experimental model. After the induction of hypertrophy with ISO treatment in H9c2 cells, cell surface area, cell viability, cellular reactive oxygen species (ROS), and nitric oxide (NO) levels were tested. Our data showed that the cell viability, mitochondrial membrane potential, and NO/ROS balance varied during the development of cardiac hypertrophy in H9c2 cells. It was also found that the expression of thioredoxin1 (Trx1) and peroxiredoxin2 (Prdx2) was decreased during the cardiac hypertrophy of H9c2 cells. These results suggest a critical role for Trx1 and Prdx2 in the cardiac hypertrophy of H9c2 cells and in the transition from compensated hypertrophy to de-compensated hypertrophy in H9c2 cells, and our findings may have important implications for the management of this disease.

11β-HSD1 inhibition ameliorates diabetes-induced cardiomyocyte hypertrophy and cardiac fibrosis through modulation of EGFR activity

11β-HSD1 has been recognized as a potential therapeutic target for type 2 diabetes. Recent studies have shown that hyperglycemia leads to activation of 11β-HSD1, increasing the intracellular glucocorticoid levels. Excess glucocorticoids may lead to the clinical manifestations of cardiac injury. Therefore, the aim of this study is to investigate whether 11β-HSD1 activation contributes to the development of diabetic cardiomyopathy. To investigate the role of 11β-HSD1, we administered a selective 11β-HSD1 inhibitor in type 1 and type 2 murine models of diabetes and in cultured cardiomyocytes. Our results show that diabetes increases cortisone levels in heart tissues. 11β-HSD1 inhibitor decreased cortisone levels and ameliorated all structural and functional features of diabetic cardiomyopathy including fibrosis and hypertrophy. We also show that high levels of glucose caused cardiomyocyte hypertrophy and increased matrix protein deposition in culture. Importantly, inhibition of 11β-HSD1 attenuated these changes. Moreover, we show that 11β-HSD1 activation mediates these changes through modulating EGFR phosphorylation and activity. Our findings demonstrate that 11β-HSD1 contributes to the development of diabetic cardiomyopathy through activation of glucocorticoid and EGFR signaling pathway. These results suggest that inhibition of 11β-HSD1 might be a therapeutic strategy for diabetic cardiomyopathy, which is independent of its effects on glucose homeostasis.

Liver X receptor α is targeted by microRNA-1 to inhibit cardiomyocyte apoptosis through a ROS-mediated mitochondrial pathway

Diabetic cardiomyopathy (DCM) is defined as ventricular dysfunction occurring independently of a recognized cause such as hypertension or coronary artery disease. Liver X receptor α (LXRα), a subtype of ligand-activated transcription factors LXRs, has been considered as a potential pharmacological target in the pathogenesis of cardiovascular and metabolic diseases. However, the potential mechanism of how LXRα is regulated in cardiomyocytes is still unclear. This study investigated the effect of activating LXRα with GW3965 on cardiomyocyte apoptosis and its upstream regulator in glucose-induced H9C2 cells. Our data indicated that GW3965 up-regulated the expression of LXRα, inhibited cardiomyocyte apoptosis, and altered the apoptosis-related proteins in glucose-induced H9C2 cells. In addition, GW3965 restored the mitochondrial membrane potential level and decreased the ROS production induced by glucose. Moreover, LXRα was confirmed as a direct target of microRNA-1 (miR-1) that was involved in cardiomyocyte apoptosis of DCM, and overexpression of miR-1 abrogated the inhibiting effect of GW3965 on glucose-induced apoptosis in H9C2 cells. This study highlights an important role of LXRα in the development of DCM and brings new insights into the complex mechanisms involved in the pathogenesis of DCM.

Activation of nuclear β-catenin/c-Myc axis promotes oxidative stress injury in streptozotocin-induced diabetic cardiomyopathy

Myocardial oxidative stress injury plays a crucial role in the pathogenesis of diabetic cardiomyopathy (DCM). Wnt/β-catenin signaling has been reported to involve in various heart diseases. However, the underlying mechanism associated with β-catenin in DCM remains elusive. This study intended to explore the effect of β-catenin on oxidative damage of DCM by establishing streptozotocin (STZ)-induced diabetic mouse model and hydrogen peroxide (H₂O₂)-treated myocardial cell model. Cardiac oxidative stress in DCM was detected by measurements of lipid peroxidation and anti-oxidative enzyme activities as well as DHE staining. Nuclear β-catenin activity and oxidative damage degree were measured by western blotting, qPCR, MTT assay and TUNEL staining. Cardiac function and morphology were evaluated by echocardiography and histopathology. Under diabetic oxidative stress or H₂O₂ stimulation, nuclear β-catenin accumulation upregulated downstream c-Myc and further facilitated DNA damage and p53-mediated apoptosis as well as cell viability reduction, followed by phenotypic changes of cardiac dysfunction, interstitial fibrosis deposition and myocardial atrophy. Conversely, through directly inhibiting nuclear β-catenin/c-Myc axis, not only did siRNA knockdown of β-catenin or c-Myc attenuate cell injury in H₂O₂-stimulated cardiomyocytes, but also diabetic cardiac-specific β-catenin-knockout mice displayed the same prevention of heart injury as insulin-treated diabetic mice. The present study demonstrated that activated nuclear β-catenin/c-Myc axis was responsible for oxidative cardiac impairment of DCM. Therefore, repressing functional nuclear β-catenin may provide a hopeful therapeutic strategy for DCM.

Hawthorn Leaf Flavonoids Protect against Diabetes-Induced Cardiomyopathy in Rats via PKC-α Signaling Pathway

Objectives

DCM has become one of the main reasons of death in diabetic patients. In this study, we aimed to explore the hawthorn leaf flavonoids (HLF) protective effect against diabetes-induced cardiac injury and the underlying mechanisms in experimental rats.

Methods

Experimental diabetic model was induced by intraperitoneal injection of streptozotocin (STZ, 40 mg/kg) in rats after feeding with high-fat diet for 8 weeks. The diabetic rats received a 16-week treatment of different doses of HLF (50, 100, and 200). The morphological changes of myocardial cells were observed by light microscope; the concentration of antioxidant indicator and TNF-α and the expression of PKC-α mRNA, PKC-α, and NF-κB proteins were assessed as well.

Results

STZ-induced diabetes mellitus prompted blood glucose, cardiac injury, oxidative stress, and inflammation, accompanied with suppressed body weight. On the contrary, HLF administration improved body weight and blood glucose and attenuated myocardial structural abnormalities in diabetic rats. In addition, HLF decreased MDA level and enhanced SOD activities, inhibited TNF-α expression, and downregulated PKC-α mRNA, PKC-α, and NF-κB which were induced by diabetes.

Conclusions

HLF has a protective effect against diabetic cardiomyopathy in rats. The mechanism may be involved in reducing oxidative stress and inflammation via inactivation of the PKC-α signaling pathway.

Klotho protects the heart from hyperglycemia-induced injury by inactivating ROS and NF-κB-mediated inflammation both in vitro and in vivo

Cardiac inflammation and oxidative stress play a key role in the pathogenesis of diabetic cardiomyopathy (DCM). The anti-aging protein Klotho has been found to protect cells from inflammation and oxidative stress. The current study aimed to explore the cardioprotective effects of Klotho on DCM and the underlying mechanisms. H9c2 cells and neonatal cardiomyocytes were incubated with 33mM glucose in the presence or absence of Klotho. Klotho pretreatment effectively inhibited high glucose-induced inflammation, ROS generation, apoptosis, mitochondrial dysfunction, fibrosis and hypertrophy in both H9c2 cells and neonatal cardiomyocytes. In STZ-induced type 1 diabetic mice, intraperitoneal injection of Klotho at 0.01mg/kg per 48h for 3months completely suppressed cardiac inflammatory cytokines and oxidative stress and prevented cardiac cell death and remodeling, which subsequently improved cardiac dysfunction without affecting hyperglycemia. This study revealed that Klotho may exert its protective effects by augmenting nuclear factor erythroid 2-related factor 2 (Nrf2) expression and inactivating nuclear factor κB (NF-κB) activation both in vitro and in vivo. Thus, this work demonstrated for the first time that the anti-aging protein Klotho may be a potential therapeutic agent to treat DCM by inhibiting oxidative stress and inflammation. We also demonstrated the critical roles of the Nrf2 and NF-κB pathways in diabetes-stimulated cardiac injuries and indicated that they may be key therapeutic targets for diabetic complications.

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

Despite being first described 45 years ago, the existence of a distinct diabetic cardiomyopathy remains controversial. Nonetheless, it is widely accepted that the diabetic heart undergoes characteristic structural and functional changes in the absence of ischaemia and hypertension, which are independently linked to heart failure progression and are likely to underlie enhanced susceptibility to stress. A prominent feature is marked collagen accumulation linked with inflammation and extensive extracellular matrix changes, which appears to be the main factor underlying cardiac stiffness and subclinical diastolic dysfunction, estimated to occur in as many as 75% of optimally controlled diabetics. Whether this characteristic remodelling phenotype is primarily driven by microvascular dysfunction or alterations in cardiomyocyte metabolism remains unclear. Although hyperglycaemia regulates multiple pathways in the diabetic heart, increased reactive oxygen species (ROS) generation is thought to represent a central mechanism underlying associated adverse remodelling. Indeed, experimental and clinical diabetes are linked with oxidative stress which plays a key role in cardiomyopathy, while key processes underlying diabetic cardiac remodelling, such as inflammation, angiogenesis, cardiomyocyte hypertrophy and apoptosis, fibrosis and contractile dysfunction, are redox sensitive. This review will explore the relative contributions of the major ROS sources (dysfunctional nitric oxide synthase, mitochondria, xanthine oxidase, nicotinamide adenine dinucleotide phosphate oxidases) in the diabetic heart and the potential for therapeutic targeting of ROS signalling using novel pharmacological and non-pharmacological approaches to modify specific aspects of the remodelling phenotype in order to prevent and/or delay heart failure development and progression.

The Role of Nrf2 in Cardiovascular Function and Disease

Free radicals, reactive oxygen/nitrogen species (ROS/RNS), hydrogen sulphide, and hydrogen peroxide play an important role in both intracellular and intercellular signaling; however, their production and quenching need to be closely regulated to prevent cellular damage. An imbalance, due to exogenous sources of free radicals and chronic upregulation of endogenous production, contributes to many pathological conditions including cardiovascular disease and also more general processes involved in aging. Nuclear factor erythroid 2-like 2 (NFE2L2; commonly known as Nrf2) is a transcription factor that plays a major role in the dynamic regulation of a network of antioxidant and cytoprotective genes, through binding to and activating expression of promoters containing the antioxidant response element (ARE). Nrf2 activity is regulated by many mechanisms, suggesting that tight control is necessary for normal cell function and both hypoactivation and hyperactivation of Nrf2 are indicated in playing a role in different aspects of cardiovascular disease. Targeted activation of Nrf2 or downstream genes may prove to be a useful avenue in developing therapeutics to reduce the impact of cardiovascular disease. We will review the current status of Nrf2 and related signaling in cardiovascular disease and its relevance to current and potential treatment strategies.

Simvastatin Ameliorates Diabetic Cardiomyopathy by Attenuating Oxidative Stress and Inflammation in Rats

Simvastatin is a lipid-lowering agent used to treat hypercholesterolemia and to reduce the risk of heart disease. This study scrutinized the beneficial effects of simvastatin on experimental diabetic cardiomyopathy (DCM), pointing to the role of hyperglycemia-induced oxidative stress and inflammation. Diabetes was induced by intraperitoneal injection of streptozotocin and both control and diabetic rats received simvastatin for 90 days. Diabetic rats showed significant cardiac hypertrophy, body weight loss, hyperglycemia, and hyperlipidemia. Serum creatine kinase MB (CK-MB) and troponin I showed a significant increase in diabetic rats. Simvastatin significantly improved body weight, attenuated hyperglycemia and hyperlipidemia, and ameliorated CK-MB and troponin I. Simvastatin prevented histological alterations and deposition of collagen in the heart of diabetic animals. Lipid peroxidation and nitric oxide were increased in the heart of diabetic rats whereas antioxidant defenses were decreased. These alterations were significantly reversed by simvastatin. In addition, simvastatin decreased serum inflammatory mediators and expression of NF-κB in the diabetic heart. Cardiac caspase-3 was increased in the diabetic heart and decreased following treatment with simvastatin. In conclusion, our results suggest that simvastatin alleviates DCM by attenuating hyperglycemia/hyperlipidemia-induced oxidative stress, inflammation, and apoptosis.

The clock gene, brain and muscle Arnt-like 1, regulates autophagy in high glucose-induced cardiomyocyte injury

High-glucose-induced cardiomyocyte injury is the major cause of diabetic cardiomyopathy, but its regulatory mechanisms are not fully understood. Here, we report that a circadian clock gene, brain and muscle Arnt-like 1 (Bmal1), increases autophagy in high-glucose-induced cardiomyocyte injury. We constructed a hyperglycemia model with cultured cardiomyocytes from neonatal rats. High-glucose-induced inhibition of autophagy and cardiomyocyte injury were attenuated by Bmal1 overexpression and aggravated by its knockdown. Furthermore, autophagy stabilization by 3-methyladenine or rapamycin partially suppressed the effects of altered Bmal1 expression on cardiomyocyte survival. Mechanistically, Bmal1 mediated resistance to high-glucose-induced inhibition of autophagy at least partly by inhibiting mTOR signaling activity. Collectively, our findings suggest that the clock gene Bmal1 is a positive regulator of autophagy through the mTOR signaling pathway and protects cardiomyocytes against high-glucose toxicity.

Insulin replacement limits progression of diabetic cardiomyopathy in the low-dose streptozotocin-induced diabetic rat

Diabetic cardiomyopathy is a major contributor to the increasing burden of heart failure globally. Effective therapies remain elusive, in part due to the incomplete understanding of the mechanisms underlying diabetes-induced myocardial injury. The objective of this study was to assess the direct impact of insulin replacement on left ventricle structure and function in a rat model of diabetes. Male Sprague-Dawley rats were administered streptozotocin (55 mg/kg i.v.) or citrate vehicle and were followed for 8 weeks. A subset of diabetic rats were allocated to insulin replacement (6 IU/day insulin s.c.) for the final 4 weeks of the 8-week time period. Diabetes induced the characteristic systemic complications of diabetes (hyperglycaemia, polyuria, kidney hypertrophy) and was accompanied by marked left ventricle remodelling (cardiomyocyte hypertrophy, left ventricle collagen content) and diastolic dysfunction (transmitral E/A, left ventricle-dP/dt). Importantly, these systemic and cardiac impairments were ameliorated markedly following insulin replacement, and moreover, markers of the diabetic cardiomyopathy phenotype were significantly correlated with the extent of hyperglycaemia. In summary, these data suggest that poor glucose control directly contributes towards the underlying features of experimental diabetic cardiomyopathy, at least in the early stages, and that adequate replacement ameliorates this.

SIRT1 Activation by Resveratrol Alleviates Cardiac Dysfunction via Mitochondrial Regulation in Diabetic Cardiomyopathy Mice

BACKGROUND

Diabetic cardiomyopathy (DCM) is a major threat for diabetic patients. Silent information regulator 1 (SIRT1) has a regulatory effect on mitochondrial dynamics, which is associated with DCM pathological changes. Our study aims to investigate whether resveratrol, a SRIT1 activator, could exert a protective effect against DCM.

METHODS AND RESULTS

Cardiac-specific SIRT1 knockout (SIRT1KO) mice were generated using Cre-loxP system. SIRT1KO mice displayed symptoms of DCM, including cardiac hypertrophy and dysfunction, insulin resistance, and abnormal glucose metabolism. DCM and SIRT1KO hearts showed impaired mitochondrial biogenesis and function, while SIRT1 activation by resveratrol reversed this in DCM mice. High glucose caused increased apoptosis, impaired mitochondrial biogenesis, and function in cardiomyocytes, which was alleviated by resveratrol. SIRT1 deletion by both SIRT1KO and shRNA abolished the beneficial effects of resveratrol. Furthermore, the function of SIRT1 is mediated via the deacetylation effect on peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), thus inducing increased expression of nuclear respiratory factor 1 (NRF-1), NRF-2, estrogen-related receptor-α (ERR-α), and mitochondrial transcription factor A (TFAM).

CONCLUSIONS

Cardiac deletion of SIRT1 caused phenotypes resembling DCM. Activation of SIRT1 by resveratrol ameliorated cardiac injuries in DCM through PGC-1α-mediated mitochondrial regulation. Collectively, SIRT1 may serve as a potential therapeutic target for DCM.

Activation of the Nkx2.5-Calr-p53 signaling pathway by hyperglycemia induces cardiac remodeling and dysfunction in adult zebrafish

Hyperglycemia is an independent risk factor for diabetic cardiomyopathy in humans; however, the underlying mechanisms have not been thoroughly elucidated. Zebrafish (Danio rerio) was used in this study as a novel vertebrate model to explore the signaling pathways of human adult cardiomyopathy. Hyperglycemia was induced by alternately immersing adult zebrafish in a glucose solution or water. The hyperglycemic fish gradually exhibited some hallmarks of cardiomyopathy such as myocardial hypertrophy and apoptosis, myofibril loss, fetal gene reactivation, and severe arrhythmia. Echocardiography of the glucose-treated fish demonstrated diastolic dysfunction at an early stage and systolic dysfunction at a later stage, consistent with what is observed in diabetic patients. Enlarged hearts with decreased myocardial density, accompanied by decompensated cardiac function, indicated that apoptosis was critical in the pathological process. Significant upregulation of the expression of Nkx2.5 and its downstream targets calreticulin (Calr) and p53 was noted in the glucose-treated fish. High-glucose stimulation in vitro evoked marked apoptosis of primary cardiomyocytes, which was rescued by the p53 inhibitor pifithrin-μ. In vitro experiments were performed using compound treatment and genetically via cell infection. Genetically, knockout of Nkx2.5 induced decreased expression of Nkx2.5, Calr and p53 Upregulation of Calr resulted in increased p53 expression, whereas the level of Nkx2.5 remained unchanged. An adult zebrafish model of hyperglycemia-induced cardiomyopathy was successfully established. Hyperglycemia-induced myocardial apoptosis was mediated, at least in part, by activation of the Nkx2.5-Calr-p53 pathway in vivo, resulting in cardiac dysfunction and hyperglycemia-induced cardiomyopathy.

Are targeted therapies for diabetic cardiomyopathy on the horizon?

Diabetes increases the risk of heart failure approximately 2.5-fold, independent of coronary artery disease and other comorbidities. This process, termed diabetic cardiomyopathy, is characterized by initial impairment of left ventricular (LV) relaxation followed by LV contractile dysfunction. Post-mortem examination reveals that human diastolic dysfunction is closely associated with LV damage, including cardiomyocyte hypertrophy, apoptosis and fibrosis, with impaired coronary microvascular perfusion. The pathophysiological mechanisms underpinning the characteristic features of diabetic cardiomyopathy remain poorly understood, although multiple factors including altered lipid metabolism, mitochondrial dysfunction, oxidative stress, endoplasmic reticulum (ER) stress, inflammation, as well as epigenetic changes, are implicated. Despite a recent rise in research interrogating these mechanisms and an increased understanding of the clinical importance of diabetic cardiomyopathy, there remains a lack of specific treatment strategies. How the chronic metabolic disturbances observed in diabetes lead to structural and functional changes remains a pertinent question, and it is hoped that recent advances, particularly in the area of epigenetics, among others, may provide some answers. This review hence explores the temporal onset of the pathological features of diabetic cardiomyopathy, and their relative contribution to the resultant disease phenotype, as well as both current and potential therapeutic options. The emergence of glucose-optimizing agents, namely glucagon-like peptide-1 (GLP-1) agonists and sodium/glucose co-transporter (SGLT)2 inhibitors that confer benefits on cardiovascular outcomes, together with novel experimental approaches, highlight a new and exciting era in diabetes research, which is likely to result in major clinical impact.

Ulinastatin attenuates diabetes-induced cardiac dysfunction by the inhibition of inflammation and apoptosis

Ulinastatin exhibits anti-inflammatory activity and protects the heart from ischemia/reperfusion injury. However, whether ulinastatin has a protective effect in diabetic cardiomyopathy is yet to be elucidated. The aim of the present study was to investigate the protective effects of ulinastatin against diabetic cardiomyopathy and its underlying mechanisms. A C57/BL6J mice model of diabetic cardiomyopathy was used and mice were randomly assigned to three groups: Control group, diabetes mellitus (DM) group and DM + ulinastatin treatment group. Cardiac function was assessed using echocardiography and the level of inflammatory cytokine high mobility group box 1 (HMGB1) expression was measured using histopathological examination and reverse transcription-quantitative polymerase chain reaction. The levels of tumor necrosis factor (TNF)-α and interleukin (IL)-6 were measured using western blotting and ELISA. The apoptosis rate in the myocardium was assessed by TUNEL assay. Caspase-3 activation, expression of B-cell lymphoma 2 (Bcl-2) and Bcl-2 associated × (Bax) were measured using western blotting, as was the activity of the mitogen activated protein kinase (MAPK) signaling pathway. The results indicated that ulinastatin significantly improved cardiac function in mice with DM. Ulinastatin treatment significantly downregulated HMGB1, TNF-α and IL-6 expression (P<0.05) and significantly reduced the percentage of apoptotic cardiomyocytes (P<0.05) via reduction of caspase-3 activation and the ratio of Bax/Bcl-2 in diabetic hearts (P<0.05). In addition, ulinastatin attenuated the activation of the MAPK signaling pathway. In conclusion, ulinastatin had a protective effect against DM-induced cardiac dysfunction in a mouse model. This protective effect may be associated with the anti-inflammatory and anti-apoptotic abilities of ulinastatin via the MAPK signaling pathway.

Hyperglycemia-induced oxidative stress and heart disease-cardioprotective effects of rooibos flavonoids and phenylpyruvic acid-2-O-β-D-glucoside

Diabetic patients are at an increased risk of developing heart failure when compared to their non-diabetic counter parts. Accumulative evidence suggests chronic hyperglycemia to be central in the development of myocardial infarction in these patients. At present, there are limited therapies aimed at specifically protecting the diabetic heart at risk from hyperglycemia-induced injury. Oxidative stress, through over production of free radical species, has been hypothesized to alter mitochondrial function and abnormally augment the activity of the NADPH oxidase enzyme system resulting in accelerated myocardial injury within a diabetic state. This has led to a dramatic increase in the exploration of plant-derived materials known to possess antioxidative properties. Several edible plants contain various natural constituents, including polyphenols that may counteract oxidative-induced tissue damage through their modulatory effects of intracellular signaling pathways. Rooibos, an indigenous South African plant, well-known for its use as herbal tea, is increasingly studied for its metabolic benefits. Prospective studies linking diet rich in polyphenols from rooibos to reduced diabetes associated cardiovascular complications have not been extensively assessed. Aspalathin, a flavonoid, and phenylpyruvic acid-2-O-β-D-glucoside, a phenolic precursor, are some of the major compounds found in rooibos that can ameliorate hyperglycemia-induced cardiomyocyte damage in vitro. While the latter has demonstrated potential to protect against cell apoptosis, the proposed mechanism of action of aspalathin is linked to its capacity to enhance the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression, an intracellular antioxidant response element. Thus, here we review literature on the potential cardioprotective properties of flavonoids and a phenylpropenoic acid found in rooibos against diabetes-induced oxidative injury.

In vivo administration of urolithin A and B prevents the occurrence of cardiac dysfunction in streptozotocin-induced diabetic rats

Background

Emerging evidence suggests that specific (poly)phenols may constitute new preventative strategies to counteract cell oxidative stress and myocardial tissue inflammation, which have a key role in the patho-physiology of diabetic cardiomyopathy. In a rat model of early diabetes, we evaluated whether in vivo administration of urolithin A (UA) or urolithin B (UB), the main gut microbiota phenolic metabolites of ellagitannin-rich foods, can reduce diabetes-induced microenvironmental changes in myocardial tissue, preventing cardiac functional impairment.

Methods

Adult Wistar rats with streptozotocin-induced type-1 diabetes (n = 29) were studied in comparison with 10 control animals. Diabetic rats were either untreated (n  =  9) or subjected to daily i.p. injection of UA (n = 10) or UB (n = 10). After 3 weeks of hyperglycaemia, hemodynamics, cardiomyocyte contractile properties and calcium transients were measured to assess cardiac performance. The myocardial expression of the pro-inflammatory cytokine fractalkine and proteins involved in calcium dynamics (sarcoplasmic reticulum calcium ATPase, phospholamban and phosphorylated phospholamban) were evaluated by immunoblotting. Plasma, urine and tissue distribution of UA, UB and their phase II metabolites were determined.

Results

In vivo urolithin treatment reduced by approximately 30% the myocardial expression of the pro-inflammatory cytokine fractalkine, preventing the early inflammatory response of cardiac cells to hyperglycaemia. The improvement in myocardial microenvironment had a functional counterpart, as documented by the increase in the maximal rate of ventricular pressure rise compared to diabetic group (+18% and +31% in UA and UB treated rats, respectively), and the parallel reduction in the isovolumic contraction time (−12%). In line with hemodynamic data, both urolithins induced a recovery of cardiomyocyte contractility and calcium dynamics, leading to a higher re-lengthening rate (+21%, on average), lower re-lengthening times (−56%), and a more efficient cytosolic calcium clearing (−32% in tau values). UB treatment also increased the velocity of shortening (+27%). Urolithin metabolites accumulated in the myocardium, with a higher concentration of UB and UB-sulphate, potentially explaining the slightly higher efficacy of UB administration.

Conclusions

In vivo urolithin administration may be able to prevent the initial inflammatory response of myocardial tissue to hyperglycaemia and the negative impact of the altered diabetic milieu on cardiac performance.

HMGCS2 is a key ketogenic enzyme potentially involved in type 1 diabetes with high cardiovascular risk

Diabetes increases the risk of Cardio-vascular disease (CVD). CVD is more prevalent in type 2 diabetes (T2D) than type 1 diabetes (T1D), but the mortality risk is higher in T1D than in T2D. The pathophysiology of CVD in T1D is poorly defined. To learn more about biological pathways that are potentially involved in T1D with cardiac dysfunction, we sought to identify differentially expressed genes in the T1D heart. Our study used T1D mice with severe hyperglycemia along with significant deficits in echocardiographic measurements. Microarray analysis of heart tissue RNA revealed that the T1D mice differentially expressed 10 genes compared to control. Using Ingenuity Pathway Analysis (IPA), we showed that these genes were significantly involved in ketogenesis, cardiovascular disease, apoptosis and other toxicology functions. Of these 10 genes, the 3-Hydroxy-3-Methylglutaryl-CoA Synthase 2 (HMGCS2) was the highest upregulated gene in T1D heart. IPA analysis showed that HMGCS2 was center to many biological networks and pathways. Our data also suggested that apart from heart, the expression of HMGCS2 was also different in kidney and spleen between control and STZ treated mice. In conclusion, The HMGCS2 molecule may potentially be involved in T1D induced cardiac dysfunction.

Glucose variability aggravates cardiac fibrosis by altering AKT signalling path

OBJECTIVE

To study the effect of blood glucose variability on cardiac fibrosis and its mechanism in a model of diabetic cardiomyopathy.

METHODS

A total of 45 Sprague Dawley rats were randomly divided into three groups: control, control diabetes mellitus and fluctuated blood glucose groups. Fluctuated blood glucose was induced by daily subcutaneous insulin and intraperitoneal glucose injections at different time points. Blood lipids and glycosylated haemoglobin A1c were assessed. Super oxide dismutase activity and malondialdehyde level in rat heart homogenates were determined by assay kit. Structural cardiac tissue changes were observed by haematoxylin and eosin staining and Masson's trichrome staining. Collagen type 3, fibronectin, phosphorylated Ser/Thr protein kinase, phosphorylated glycogen synthase kinase-3 beta, glycogen synthase kinase-3 beta, nuclear factor kappa-light-chain-enhancer of activated B cells, cleaved-cysteinyl aspartate-specific proteinase-3 (caspase-3) and tumour necrosis factor-α levels were determined by western blot.

RESULTS

Compared with the control group, cardiac fibrosis and oxidative stress in heart tissue were aggravated in diabetic rats, which were more pronounced in glucose variability rats. However, the expression levels of AKT and glycogen synthase kinase-3 beta were not significantly different in three groups, but the expression levels of phosphorylated Ser/Thr protein kinase and phosphorylated glycogen synthase kinase-3 beta were significantly decreased in the control diabetes mellitus and fluctuated blood glucose groups compared to control group, and levels in the fluctuated blood glucose group were significantly less than in the control diabetes mellitus group. In addition, the expression levels of nuclear factor kappa B and caspase-3 in both the control diabetes mellitus and fluctuated blood glucose groups were higher than in the control group, with the highest levels measured in the fluctuated blood glucose group.

CONCLUSION

Blood glucose variability can aggravate heart tissue fibrosis, possibly involving oxidative stress by inhibiting AKT signalling path.

Ginsenoside Rh2 Improves Cardiac Fibrosis via PPARδ-STAT3 Signaling in Type 1-Like Diabetic Rats

Ginsenoside Rh2 (Rh2) is an active principal ingredient contained in ginseng (Panax ginseng Meyer), a medicinal herb used to enhance health worldwide. The present study is designed to investigate the effect of Rh2 on myocardial fibrosis in diabetic rats. In a streptozotocin-induced model of type-1 diabetic rats (STZ-diabetic rats), the increased fasting blood glucose levels and heart weight/body weight (HW/BW) ratio were substantially alleviated by Rh2. Moreover, Rh2 improved cardiac performance in STZ-diabetic rats. Histological results from Masson staining showed that Rh2 attenuated cardiac fibrosis in STZ-diabetic rats. The effects of Rh2 were reversed by GSK0660 at a dose sufficient to inhibit peroxisome proliferator-activated receptor δ (PPARδ) in STZ-diabetic rats. The role of PPARδ was subsequently investigated in vitro. Rh2 restored the decreased PPARδ expression level in high glucose-cultured cardiomyocytes. Moreover, increased protein levels of fibrotic signals, including signal transducer and activator of transcription 3 (STAT3), connective tissue growth factor (CCN2) and fibronectin, were reduced by Rh2 in high glucose-cultured cardiomyocytes. These effects of Rh2 were reversed by GSK0660 or siRNA specific for PPARδ Taken together, PPARδ activation may inhibit STAT3 activation to reduce CCN2 and fibronectin expression in diabetic rats with cardiac fibrosis. Moreover, Rh2 improves cardiac function and fibrosis by increasing PPARδ signaling. Therefore, Rh2 is suitable to develop as an alternative remedy for cardiac fibrosis.

High-Intensity Exercise Reduces Cardiac Fibrosis and Hypertrophy but Does Not Restore the Nitroso-Redox Imbalance in Diabetic Cardiomyopathy

Diabetic cardiomyopathy refers to the manifestations in the heart as a result of altered glucose homeostasis, reflected as fibrosis, cellular hypertrophy, increased oxidative stress, and apoptosis, leading to ventricular dysfunction. Since physical exercise has been indicated as cardioprotective, we tested the hypothesis that high-intensity exercise training could reverse the cardiac maladaptations produced by diabetes. For this, diabetes was induced in rats by a single dose of alloxan. Diabetic rats were randomly assigned to a sedentary group or submitted to a program of exercise on a treadmill for 4 weeks at 80% of maximal performance. Another group of normoglycemic rats was used as control. Diabetic rat hearts presented cardiomyocyte hypertrophy and interstitial fibrosis. Chronic exercise reduced both parameters but increased apoptosis. Diabetes increased the myocardial levels of the mRNA and proteins of NADPH oxidases NOX2 and NOX4. These altered levels were not reduced by exercise. Diabetes also increased the level of uncoupled endothelial nitric oxide synthase (eNOS) that was not reversed by exercise. Finally, diabetic rats showed a lower degree of phosphorylated phospholamban and reduced levels of SERCA2 that were not restored by high-intensity exercise. These results suggest that high-intensity chronic exercise was able to reverse remodeling in the diabetic heart but was unable to restore the nitroso-redox imbalance imposed by diabetes.

Phosphoinositide 3-kinase (p110α) gene delivery limits diabetes-induced cardiac NADPH oxidase and cardiomyopathy in a mouse model with established diastolic dysfunction

Phosphoinositide 3-kinase [PI3K (p110α)] is able to negatively regulate the diabetes-induced increase in NADPH oxidase in the heart. Patients affected by diabetes exhibit significant cardiovascular morbidity and mortality, at least in part due to a cardiomyopathy characterized by oxidative stress and left ventricular (LV) dysfunction. Thus, PI3K (p110α) may represent a novel approach to protect the heart from diabetes-induced cardiac oxidative stress and dysfunction. In the present study, we investigated the therapeutic potential of a delayed intervention with cardiac-targeted PI3K gene therapy, administered to mice with established diabetes-induced LV diastolic dysfunction. Diabetes was induced in 6-week-old male mice by streptozotocin (STZ). After 8 weeks of untreated diabetes, LV diastolic dysfunction was confirmed by a reduction in echocardiography-derived transmitral E/A ratio. Diabetic and non-diabetic mice were randomly allocated to receive either recombinant adeno-associated viral vector-6 carrying a constitutively-active PI3K construct (recombinant adeno-associated-virus 6-constitutively active PI3K (p110α) (caPI3K) (rAAV6-caPI3K), single i.v. injection, 2 × 1011 vector genomes) or null vector, and were followed for a further 6 or 8 weeks. At study endpoint, diabetes-induced LV dysfunction was significantly attenuated by a single administration of rAAV6-caPI3K, administered 8 weeks after the induction of diabetes. Diabetes-induced impairments in each of LV NADPH oxidase, endoplasmic reticulum (ER) stress, apoptosis, cardiac fibrosis and cardiomyocyte hypertrophy, in addition to LV systolic dysfunction, were attenuated by delayed intervention with rAAV6-caPI3K. Hence, our demonstration that cardiac-targeted PI3K (p110α) gene therapy limits diabetes-induced up-regulation of NADPH oxidase and cardiac remodelling suggests new insights into promising approaches for the treatment of diabetic cardiomyopathy, at a clinically relevant time point (after diastolic dysfunction is manifested).

Diabetic cardiomyopathy: where we are and where we are going

The global burden of diabetes mellitus and its related complications are currently increasing. Diabetes mellitus affects the heart through various mechanisms including microvascular impairment, metabolic disturbance, subcellular component abnormalities, cardiac autonomic dysfunction, and a maladaptive immune response. Eventually, diabetes mellitus can cause functional and structural changes in the myocardium without coronary artery disease, a disorder known as diabetic cardiomyopathy (DCM). There are many diagnostic tools and management options for DCM, although it is difficult to detect its development and effectively prevent its progression. In this review, we summarize the current research regarding the pathophysiology and pathogenesis of DCM. Moreover, we discuss emerging diagnostic evaluation methods and treatment strategies for DCM, which may help our understanding of its underlying mechanisms and facilitate the identification of possible new therapeutic targets.

Lipid metabolism and its implications for type 1 diabetes-associated cardiomyopathy

Diabetic cardiomyopathy was first defined over four decades ago. It was observed in small post-mortem studies of diabetic patients who suffered from concomitant heart failure despite the absence of hypertension, coronary disease or other likely causal factors, as well as in large population studies such as the Framingham Heart Study. Subsequent studies continue to demonstrate an increased incidence of heart failure in the setting of diabetes independent of established risk factors, suggesting direct effects of diabetes on the myocardium. Impairments in glucose metabolism and handling receive the majority of the blame. The role of concomitant impairments in lipid handling, particularly at the level of the myocardium, has however received much less attention. Cardiac lipid accumulation commonly occurs in the setting of type 2 diabetes and has been suggested to play a direct causal role in the development of cardiomyopathy and heart failure in a process termed as cardiac lipotoxicity. Excess lipids promote numerous pathological processes linked to the development of cardiomyopathy, including mitochondrial dysfunction and inflammation. Although somewhat underappreciated, cardiac lipotoxicity also occurs in the setting of type 1 diabetes. This phenomenon is, however, largely understudied in comparison to hyperglycaemia, which has been widely studied in this context. The current review addresses the changes in lipid metabolism occurring in the type 1 diabetic heart and how they are implicated in disease progression. Furthermore, the pathological pathways linked to cardiac lipotoxicity are discussed. Finally, we consider novel approaches for modulating lipid metabolism as a cardioprotective mechanism against cardiomyopathy and heart failure.

Developmentally regulated alternative splicing is perturbed in type 1 diabetic skeletal muscle

INTRODUCTION

Type 1 diabetic patients can develop skeletal muscle weakness and atrophy by molecular mechanisms that are not well understood. Alternative splicing (AS) is critical for gene expression in the skeletal muscle, and its dysregulation is implicated in muscle weakness and atrophy. Therefore, we investigated whether AS patterns are affected in type 1 diabetic skeletal muscle contributing to skeletal muscle defects.

METHODS

AS patterns were determined by reverse transcription-polymerase chain reaction and levels of RNA binding proteins were assessed by Western blot in type 1 diabetic mouse skeletal muscle and during normal mouse skeletal muscle development.

RESULTS

Five genes with critical functions in the skeletal muscle are misspliced in type 1 diabetic skeletal muscle, resembling their AS patterns at embryonic stages. AS of these genes undergoes dramatic transitions during skeletal muscle development, correlating with changes in specific RNA binding proteins.

CONCLUSION

Embryonic spliced variants are inappropriately expressed in type 1 diabetic skeletal muscle. Muscle Nerve 56: 744-749, 2017.

1,25-Dihydroxyvitamin-D3 prevents the development of diabetic cardiomyopathy in type 1 diabetic rats by enhancing autophagy via inhibiting the β-catenin/TCF4/GSK-3β/mTOR pathway

Diabetic cardiomyopathy (DCM) can increase the risk of heart failure and death in diabetic patients. However, no effective approaches are available to prevent its progression and development. Studies have shown that vitamin D is greatly implicated in cardiac hypertrophy and fibrosis, and there is a high prevalence of vitamin D deficiency in diabetic patients. In this study, we investigated whether 1,25-Dihydroxyvitamin-D3 (1,25D3) can improve DCM through a vitamin D receptor (VDR)-dependent mechanism associated with autophagy and the β-catenin/T-cell factor/lymphoid enhancer factor (TCF4)/glycogen synthase kinase-3β (GSK-3β)/mammalian target of rapamycin (mTOR) pathway. In this study, streptozotocin (STZ)-induced type 1 diabetic rats were established and were treated with 1,25D3 and/or chloroquine and/or VDR gene silencing for 8 weeks before being sacrificed. Compared with untreated diabetic rats, 1,25D3 partly attenuated the myocardial hypertrophy and interstitial fibrosis, improved cardiac function and restored the impaired cardiac autophagy in diabetic rats, all of which were reversed by silencing the VDR gene in diabetic rats. In high-glucose cultured H9C2 cells, 1,25D3 increased autophagy in a dose-dependent manner. Besides, the β-catenin/TCF4/GSK-3β and mTOR signaling were activated both in diabetic rats and in high-glucose cultured H9C2 cells. Treatment with 1,25D3 inhibited the β-catenin/TCF4/GSK-3β and mTOR signaling in H9C2 cells, whereas co-treatment with lithium chloride (LiCl) reversed this situation and abolished the beneficial effect of 1,25D3 on autophagy. These data suggest that 1,25D3 may improve DCM in type 1 diabetic rats by modulating autophagy through the β-catenin/TCF4/GSK-3β and mTOR pathway. Vitamin D may exist as a new therapeutic target for the treatment of DCM.

Novel protective role of the circadian nuclear receptor retinoic acid-related orphan receptor-α in diabetic cardiomyopathy

Diabetic cardiomyopathy is a major complication that significantly contributes to morbidity and mortality in diabetics with few therapies. Moreover, antidiabetic drugs reported inconsistent or even adverse cardiovascular effects, suggesting that it is important to exploit novel therapeutic targets against diabetic cardiomyopathy. Here, we observed that the nuclear melatonin receptor, the retinoic acid-related orphan receptor-α (RORα), was downregulated in diabetic hearts. By utilizing a mouse line with RORα disruption, we demonstrated that RORα deficiency led to significantly augmented diastolic dysfunction and cardiac remodeling induced by diabetes. Microscopic and molecular analyses further indicated that the detrimental effects of RORα deficiency were associated with aggravated myocardial apoptosis, autophagy dysfunction, and oxidative stress by disrupting antioxidant gene expression. By contrast, restoration of cardiac RORα levels in transgenic mice significantly improved cardiac functional and structural parameters at 8 weeks after diabetes induction. Consistent with genetic manipulation, pharmacological activation of RORα by melatonin and SR1078 (a synthetic agonist) showed beneficial effects against diabetic cardiomyopathy, while the RORα inhibitor SR3335 significantly exacerbated cardiac impairments in diabetic mice. Collectively, these findings suggest that cardiac-targeted manipulation of nuclear melatonin receptor RORα may hold promise for delaying diabetic cardiomyopathy development.

Cardiovascular Protective Effects and Clinical Applications of Resveratrol

Resveratrol is a naturally occurring phenol that is generated by plant species following injury or attack by bacterial and fungal pathogens. This compound was first described as the French Paradox in 1992. Later in 2003, resveratrol was reported to activate sirtuins in yeast cells. Recent experimental studies have found that resveratrol offers a variety of benefits that include both anticarcinogenic and anti-inflammatory effects in addition to the ability to reverse obesity, attenuate hyperglycemia and hyperinsulinemia, protect heart and endothelial function, and increase the life span. Multiple molecular targets are associated with the cardioprotective capabilities of resveratrol, and therefore, resveratrol has potential for a wide range of new therapeutic strategies for atherosclerosis, ischemia/reperfusion, metabolic syndrome, cardiac failure, and inflammatory alterations during aging. Expectations for application in human patients, however, suffer from a lack of sufficient clinical evidence in support of these beneficial effects. This article reviews recently reported basic research results that describe the beneficial effects of resveratrol in an attempt to condense the evidence observed in clinical trials and provide support for the future development of novel clinical therapeutics in patients with cardiovascular diseases.

Pathophysiological Fundamentals of Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) was first recognized more than four decades ago and occurred independent of cardiovascular diseases or hypertension in both type 1 and type 2 diabetic patients. The exact mechanisms underlying this disease remain incompletely understood. Several pathophysiological bases responsible for DCM have been proposed, including the presence of hyperglycemia, nonenzymatic glycosylation of large molecules (e.g., proteins), energy metabolic disturbance, mitochondrial damage and dysfunction, impaired calcium handling, reactive oxygen species formation, inflammation, cardiac cell death, and cardiac hypertrophy and fibrosis, leading to impairment of cardiac contractile functions. Increasing evidence also indicates the phenomenon called "metabolic memory" for diabetes-induced cardiovascular complications, for which epigenetic modulation seemed to play an important role, suggesting that the aforementioned pathogenic bases may be regulated by epigenetic modification. Therefore, this review aims at briefly summarizing the current understanding of the pathophysiological bases for DCM. Although how epigenetic mechanisms play a role remains incompletely understood now, extensive clinical and experimental studies have implicated its importance in regulating the cardiac responses to diabetes, which are believed to shed insight into understanding of the pathophysiological and epigenetic mechanisms for the development of DCM and its possible prevention and/or therapy. © 2017 American Physiological Society. Compr Physiol 7:693-711, 2017.

Metabolic Remodeling in Diabetic Cardiomyopathy

Diabetes is a risk factor for heart failure and cardiovascular mortality with specific changes to myocardial metabolism, energetics, structure, and function. The gradual impairment of insulin production and signalling in diabetes is associated with elevated plasma fatty acids and increased myocardial free fatty acid uptake and activation of the transcription factor PPARα. The increased free fatty acid uptake results in accumulation of toxic metabolites, such as ceramide and diacylglycerol, activation of protein kinase C, and elevation of uncoupling protein-3. Insulin signalling and glucose uptake/oxidation become further impaired, and mitochondrial function and ATP production become compromised. Increased oxidative stress also impairs mitochondrial function and disrupts metabolic pathways. The diabetic heart relies on free fatty acids (FFA) as the major substrate for oxidative phosphorylation and is unable to increase glucose oxidation during ischaemia or hypoxia, thereby increasing myocardial injury, especially in ageing female diabetic animals. Pharmacological activation of PPARγ in adipose tissue may lower plasma FFA and improve recovery from myocardial ischaemic injury in diabetes. Not only is the diabetic heart energetically-impaired, it also has early diastolic dysfunction and concentric remodelling. The contractile function of the diabetic myocardium negatively correlates with epicardial adipose tissue, which secretes proinflammatory cytokines, resulting in interstitial fibrosis. Novel pharmacological strategies targeting oxidative stress seem promising in preventing progression of diabetic cardiomyopathy, although clinical evidence is lacking. Metabolic agents that lower plasma FFA or glucose, including PPARγ agonism and SGLT2 inhibition, may therefore be promising options.