Early Diabetic Cardiomyopathy Research Articles

An Update on Molecular Modes Implicated in Diastolic Impairment in Early Diabetic Cardiomyopathy; Probable Modes of Therapy &Avoidance-A Narrative Review

In case of diabetic patients cardiomyopathy is a significant etiology of heart failure (HF); howeverno clarification exists regarding its pathophysiology. Myocardial hypertrophy as well as diastolic impairment are the logo for Diabetic cardiomyopathy (DbCM), whereas systolic function gets impacted in the latter phase of this disease. Previously we had reviewed Diabetic cardiomyopathy (DbCM with emphasis on epigenetic alterations ,miR changes apart from adipocyte impairment in HF induction, role of SGLT2 hampering agents in beneficial Cardiovascular Outcome Trials (CVOT’s)and renal benefits, role of sirtuins in macrophage Polarization for Diabesity therapy .Here our aim was to posit the pathophysiological mode implicated in myocardial hypertrophy and escalated myocardial stiffness resulting in diastolic impairment .This myocardial stiffness takes place from cellular and extracellular matrix(ECM ) stiffness &cell- matrix crosstalk. Escalated inherent cardiomyocytes stiffness plausibly is the maximum significant cause responsible for myocardial stiffness. It leads to dysfunctional cardiomyocytes cytoskeleton stiffness. Various other modes are implicatedbyT2DM; particularly having significant influence on myocardial stiffening i.e dysfunctional nitric oxide (NO), coronary microvascular impairment, escalated inflammation, as well as Oxidative stress(OS), myocardial Sodium –glucose specific cotransporter 2(SGLT2) modulated actions. Greater insight aids in planning better therapy.Anti diabeticagents, SGLT2 hampering agents have revealed newer ways of benefit ,like sirtuins action , upregulation of nutrient deprivation signaling in addition to downregulation of nutrient surplus signaling, escalated expression &activity of AMP-activated protein kinase(AMPK), Sirtuins (SIRT1), SIRT3 andSIRT6, & Peroxisome Proliferator Activated Receptor γCoactivator -1α(PGC-1α) ,reduction in activation of mammalian target of rapamycin inhibitors (mTOR). Recently Ghosh et al. (2023),advocated targeting sarcoplasmic / cytosolic endoplasmic reticulum Ca2+ -ATPase(SERCA2) ,use of imeglimin which escalates insulin action& along with reverses Pancreatic βcells impairment ,use of anti oxidants, angiotensin receptor neprilysin hampering agents(ARNi),NO stimulating agents. More work is being done regarding combination of empagliflozin with linagliptin &others like semaglutide with .Gradually we will get answers by getting more insight.

The combination of exercise and metformin inhibits TGF-β1/Smad pathway to attenuate myocardial fibrosis in db/db mice by reducing NF-κB–mediated inflammatory response

Persistent hyperglycemia increases inflammation response, promoting the development of myocardial fibrosis. Based on our previous research that exercise and metformin alone or their combination intervention could attenuate myocardial fibrosis in db/db mice, this study aimed to further explore the underlying mechanisms by which these interventions attenuate myocardial fibrosis in early diabetic cardiomyopathy. Forty BKS db/db mice were randomly divided into four groups. Diabetic db/db mice without intervention were in the C group. Aerobic exercise (7–12 m/min, 30–40 min/day, 5 days/week) was performed in the E group. Metformin (300 mg·kg−1·day−1) was administered in the M group. Exercise combined with metformin was performed in the EM group. Ten wild-type mice were in the WT group. All interventions were administered for 8 weeks. Results showed that the expression levels of α-SMA, Collagen I, and Collagen III were increased in 16-week-old db/db mice, which were reversed by exercise and metformin alone or their combination intervention. All interventions attenuated the level of TGF-β1/Smad2/3 pathway–related proteins and reduced the expression of inflammatory signaling pathway–regulated proteins TNF-α, p-IκBα/IκBα, and p-NF-κB p65/NF-κB p65 in db/db mice. Furthermore, metformin intervention inhibited HNF4α expression via AMPK activation, whereas exercise intervention increased the expression of IL-6 instead of activating AMPK. In conclusion, exercise and metformin alone or their combination intervention inhibited the TGF-β1/Smad pathway to attenuate myocardial fibrosis by reducing NF-κB–mediated inflammatory response. The anti-fibrotic effects were regulated by metformin-activated AMPK or exercise-induced elevation of IL-6, whereas their combination intervention showed no synergistic effects.

Metformin does not prevent the alteration of reticulum-mitochondria Ca2+ coupling and the progression towards early diabetic cardiomyopathy with HFpEF in a diet-induced mouse model of T2D

Diabetic cardiomyopathy, as a major complication of type 2 diabetes (T2D), shows a rising prevalence nowadays. Reticulum-mitochondria Ca2+ uncoupling was recently reported as an early but reversible trigger of cardiac dysfunction using a diet-induced murine model of DCM with heart failure and preserved ejection fraction (HFpEF). Metformin is the first-line treatment prescribed to treat T2D patients, with known protective effects against myocardial infarction. We here aimed to determine if metformin could hinder the alteration of the reticulum-mitochondria Ca2+ coupling and the cardiac dysfunction induced by a high-fat high-sucrose diet (HFHSD) in mice. Mice were either fed a HFHSD or a standard diet for 16 weeks. During the last 6 weeks of diet, HFHSD mice received a daily oral gavage with either metformin or vehicle. Reticulum-mitochondria Ca2+ coupling was assessed: 1) structrally by proximity ligation assay between IP3R and VDAC; and 2) functionally by Ca2+ imaging of the mitochondrial Ca2+ sensor, 4mtD3cpv, expressed by intramyocardial adenoviral injection. Echocardiography was perfomed on lightly anesthetized animals to assess systolic function and hypertrophy. Metformin rescued the glucose tolerance and insulinemia in HFHSD mice, but partially for the cardiac insulin resistance. However, in the HFHSD cardiomyocyte, metformin did not preclude the reduction of the proximity between IP3R and VDAC, and of the histamine-driven reticulum-mitochondria Ca2+ transfer through the IP3R-VDAC complex. Echocardiography also revealed no prevention of HFHSD-induced cardiac hypertrophy and strain rate reduction. Our data report that 6 weeks of metformin treatment did not preserve the reticulum-mitochondria Ca2+ coupling in the diabetic heart and did not prevent the progression towards early DCM with HFpEF.

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.

Effect of Metformin on T2D-Induced MAM Ca2+ Uncoupling and Contractile Dysfunction in an Early Mouse Model of Diabetic HFpEF.

Diabetic cardiomyopathy (DCM) is a leading complication in type 2 diabetes patients. Recently, we have shown that the reticulum-mitochondria Ca2+ uncoupling is an early and reversible trigger of the cardiac dysfunction in a diet-induced mouse model of DCM. Metformin is a first-line antidiabetic drug with recognized cardioprotective effect in myocardial infarction. Whether metformin could prevent the progression of DCM remains not well understood. We therefore investigated the effect of a chronic 6-week metformin treatment on the reticulum-mitochondria Ca2+ coupling and the cardiac function in our high-fat high-sucrose diet (HFHSD) mouse model of DCM. Although metformin rescued the glycemic regulation in the HFHSD mice, it did not preserve the reticulum-mitochondria Ca2+ coupling either structurally or functionally. Metformin also did not prevent the progression towards cardiac dysfunction, i.e., cardiac hypertrophy and strain dysfunction. In summary, despite its cardioprotective role, metformin is not sufficient to delay the progression to early DCM.

Potential Biomarkers as Early Detection of Diabetic Cardiomyopathy

Abstract: Diabetes mellitus (DM) is one of the most prevalent and burdensome among chronic disease worldwide. Its complications accelerate mortality rate within population. Diabetic cardiomyopathy (DCM) is one of diabetes macrovascular complications, which symptoms are frequently unforeseen. Advances in pathogenesis understanding DCM underlying mechanisms remain not fully perceived. Current diagnostic approach of DCM can hardly determine diabetic patients with asymptomatic cardiomyopathy. Previous studies suggested biomarkers might detect early stage DCM. There are numerous selective biomarkers representing several pathophysiological pathways, such as myocardial fibrosis, inflammatory response, cardiomyocyte apoptosis, and metabolic dysregulation in the development of diabetic heart anomaly It was also reported those biomarkers are useful for the prognostic assessment of the disease. However, not all biomarkers are cardiac specific and can be an auspicious diagnostic tool candidate. Recent studies show that there are certain biomarkers, such as microRNA, H-FABP, IGFBP7, and some other novel cardiac biomarkers were more specifically associated with the pathological mechanism of DCM. In this review, we aimed to discuss the role of several potential cardiac biomarkers as early detection in DCM that may predict future incident of DCM, and contribute to improving mortality prediction in patients with subclinical DCM.Keywords: Biomarker; Diabetic Cardiomyopathy

Gold Nanoparticles Ameliorate Diabetic Cardiomyopathy in Streptozotocin-Induced Diabetic Rats

Diabetic cardiomyopathy (DCM) can lead to left ventricular hypertrophy, diastolic dysfunction, and systolic dysfunction, or all of these. Gold nanoparticles (AuNPs) have shown anti-hyperglycemic effects in animal models of streptozotocin (STZ)-induced diabetes. This study was designed to address the effects of AuNPs on the animal model of DCM. twenty-two male adult rats were randomly categorized into 3 groups (n=6-8 / group): control (non-diabetic, ND), diabetic (D), and intraperitoneally treated diabetic rats with 50 nm AuNPs (D+AuNPs; 2,5 mg/kg/day). One single dose injection of 55 mg/kg STZ was used to induce diabetes in the animals. Blood and the left ventricle were collected after seven weeks for assessment. The myocardial mRNA and protein levels of transforming growth factor β1 (TGF-β1) and tumor necrosis factor-α (TNF-α) were evaluated using real-time PCR and immunohistochemistry. The myocardial mRNA level of vascular endothelial growth factor-A (VEGF-A) was measured using real-time PCR. Besides, the myocardial collagen deposition was measured by masson trichrome stain and immunohistochemistry. Rats with DCM showed hyperglycemia, increased myocardial mRNA and protein tissue content of TGF-β1, myocardial mRNA of VEGF-A (P < 0.05), and tended to increase myocardial mRNA and protein tissue content of TNF-α (P < 0.1). An increase in myocardial collagen deposition accompanied these changes. Treatment with AuNPs reduced the above pathological conditions. These results suggest that AuNPs may have therapeutic potential in the treatment of early DCM. Further studies are needed to explore the possible mechanisms by which AuNPs may prevent the development of DCM.

Assessment of subclinical diabetic cardiomyopathy by speckle-tracking imaging.

Diastolic dysfunction is traditionally believed to be the first subclinical manifestation of diabetic cardiomyopathy (DCM), leading to systolic dysfunction and then overt heart failure. However, in the last few years, several studies suggested that systolic subclinical dysfunction measured by speckle-tracking echocardiography (STE) may appear ahead of diastolic dysfunction. In this review, the main endpoint is to show whether subclinical myocardial systolic dysfunction appears ahead of diastolic dysfunction and the implication this may have on the evolution and management of DCM. We performed a search in PubMed for all relevant publications on the assessment of DCM by STE from 1 June 2015 to 1 June 2020. The results illustrate that subclinical systolic dysfunction assessed by STE is present in early DCM stages, with or without the association of diastolic dysfunction. This could be a promising perspective for the early management of patients with DCM leading to the prevention of the overt form of disease.

Identification of potential biomarkers for predicting the early onset of diabetic cardiomyopathy in a mouse model

Type 2 diabetes (T2D) is characterized by metabolic derangements that cause a shift in substrate preference, inducing cardiac interstitial fibrosis. Interstitial fibrosis plays a key role in aggravating left ventricular diastolic dysfunction (LVDD), which has previously been associated with the asymptomatic onset of heart failure. The latter is responsible for 80% of deaths among diabetic patients and has been termed diabetic cardiomyopathy (DCM). Through in silico prediction and subsequent detection in a leptin receptor-deficient db/db mice model (db/db), we confirmed the presence of previously identified potential biomarkers to detect the early onset of DCM. Differential expression of Lysyl Oxidase Like 2 (LOXL2) and Electron Transfer Flavoprotein Beta Subunit (ETFβ), in both serum and heart tissue of 6–16-week-old db/db mice, correlated with a reduced left-ventricular diastolic dysfunction as assessed by high-resolution Doppler echocardiography. Principal component analysis of the combined biomarkers, LOXL2 and ETFβ, further displayed a significant difference between wild type and db/db mice from as early as 9 weeks of age. Knockdown in H9c2 cells, utilising siRNA of either LOXL2 or ETFβ, revealed a decrease in the expression of Collagen Type I Alpha1 (COL1A1), a marker known to contribute to enhanced myocardial fibrosis. Additionally, receiver-operating curve (ROC) analysis of the proposed diagnostic profile showed that the combination of LOXL2 and ETFβ resulted in an area under the curve (AUC) of 0.813, with a cut-off point of 0.824, thus suggesting the favorable positive predictive power of the model and further supporting the use of LOXL2 and ETFβ as possible early predictive DCM biomarkers.

G protein-coupled receptor kinase-2: A potential biomarker for early diabetic cardiomyopathy.

BackgroundG protein‐coupled receptor kinase‐2 (GRK2) has been shown as a key regulator of cardiac function, and the myocardial GRK2 levels are mirrored by the levels in peripheral blood mononuclear cells (PBMCs). In this study, we evaluated the myocardial and PBMCs GRK2 levels in early diabetic cardiomyopathy (DCM).MethodsC57BL/KS‐db/db male diabetic mice at 12 weeks of age, as the type 2 diabetes (T2DM) animal model of early DCM were evaluated. Forty‐four T2DM patients with left ventricular diastolic dysfunction (LVDD), without evidence of hypertension, coronary artery diseases, congestive heart failure, and diabetic complications and without evidence of ischemia in a maximal treadmill exercise test, were recruited as the DM + LVDD group; 30 age‐matched T2DM patients without LVDD were recruited as the DM control group. Left ventricular diastolic function was evaluated by cardiac tissue Doppler. The pseudonormal pattern of ventricular filling and E′/A′ < 1 were regarded as LVDD.ResultsCompared to 8‐week‐old diabetic mice and 12‐week‐old control mice, GRK2‐mRNA level and expression in myocardial tissues of 12‐week‐old diabetic mice were significantly increased, as well as the left ventricular wall thickness and systolic function. And the collagen volume fraction (CVF), collagen‐3 expression, P53 expression, and cell apoptotic rate in the myocardium of 12‐week‐old diabetic mice elevated as well. The GRK2‐mRNA level in PBMCs of DM with LVDD was significantly higher than in DM control without LVDD.ConclusionsGRK2 expression increased in the myocardial tissue and the PBMCs at the early stage of DCM. These data support further research on the role of GRK2 as the clinical biomarker for early DCM.

Genome-wide differential expression profiling of lncRNAs and mRNAs associated with early diabetic cardiomyopathy

Diabetic cardiomyopathy is one of the main causes of heart failure and death in patients with diabetes. There are no effective approaches to preventing its development in the clinic. Long noncoding RNAs (lncRNA) are increasingly recognized as important molecular players in cardiovascular disease. Herein we investigated the profiling of cardiac lncRNA and mRNA expression in type 2 diabetic db/db mice with and without early diabetic cardiomyopathy. We found that db/db mice developed cardiac hypertrophy with normal cardiac function at 6 weeks of age but with a decreased diastolic function at 20 weeks of age. LncRNA and mRNA transcripts were remarkably different in 20-week-old db/db mouse hearts compared with both nondiabetic and diabetic controls. Overall 1479 lncRNA transcripts and 1109 mRNA transcripts were aberrantly expressed in 6- and 20-week-old db/db hearts compared with nondiabetic controls. The lncRNA-mRNA co-expression network analysis revealed that 5 deregulated lncRNAs having maximum connections with differentially expressed mRNAs were BC038927, G730013B05Rik, 2700054A10Rik, AK089884, and Daw1. Bioinformatics analysis revealed that these 5 lncRNAs are closely associated with membrane depolarization, action potential conduction, contraction of cardiac myocytes, and actin filament-based movement of cardiac cells. This study profiles differently expressed lncRNAs in type 2 mice with and without early diabetic cardiomyopathy and identifies BC038927, G730013B05Rik, 2700054A10Rik, AK089884, and Daw1 as the core lncRNA with high significance in diabetic cardiomyopathy.

Increased myocardial extracellular volume assessed by cardiovascular magnetic resonance T1 mapping and its determinants in type 2 diabetes mellitus patients with normal myocardial systolic strain

BackgroundCardiac magnetic resonance (CMR) T1 mapping and tissue-tracking strain analysis are useful quantitative techniques that can characterize myocardial tissue and mechanical alterations, respectively, in patients with early diabetic cardiomyopathy. The purpose of this study was to assess the left ventricular myocardial T1 value, extracellular volume fraction (ECV), and systolic strain in asymptomatic patients with type 2 diabetes mellitus (T2DM) and their underlying relationships with clinical parameters.MethodsWe recruited 50 T2DM patients (mean age: 55 ± 7 years; 28 males) and 32 sex-, age-and BMI-matched healthy volunteers to undergo contrast-enhanced CMR examinations. The myocardial native T1, post-contrast T1 and ECV values of the left ventricle were measured from T1 and ECV maps acquired using the modified Look-Locker inversion recovery technique. The left ventricular global systolic strain and the strain rates were evaluated using routine cine images and tissue-tracking analysis software. The baseline clinical and biochemical indices were collected before the CMR examination.ResultsThe myocardial ECV and native T1 values were significantly higher in the diabetic patients than in the controls. (ECV: 27.4 ± 2.5% vs. 24.6 ± 2.2%, p < 0.001; native T1: 1026.9 ± 30.0 ms vs. 1011.8 ± 26.0 ms, p = 0.022). However, the left ventricular global systolic strain, strain rate, volume, myocardial mass, ejection fraction, and left atrial volume were similar between the diabetic patients and the healthy controls. In the diabetic patients, the native T1 values were independently correlated with the hemoglobin A1c levels (standardized β = 0.368, p = 0.008). The ECVs were independently associated with the hemoglobin A1c levels (standardized β = 0.389, p = 0.002), angiotensin-converting enzyme inhibitor (ACEI) treatment (standardized β = − 0.271, p = 0.025) and HCT values (standardized β = − 0.397, p = 0.001).ConclusionsType 2 diabetes mellitus patients with normal myocardial systolic strain exhibit increased native T1 values and ECVs indicative of myocardial extracellular interstitial expansion, which might be related to poor glycemic control. The amelioration of myocardial interstitial matrix expansion might be associated with ACEI treatment. A valid assessment of the association of glucose control and ACEI treatment with myocardial fibrosis requires notably larger trials.

Alterations of mTOR pathway and autophagy in early type 2 diabetic cardiomyopathy in rats

Objective: To investigate the alterations of mTOR signaling pathway and autophagy in the development of type 2 diabetes and early diabetic cardiomyopathy and to study their roles in pathogenesis of diabetic myocardium. Methods: A type 2 diabetes rat model was established by injection of streptozocin after five-week of high fat diet. The rats were randomly divided into control group, experiment group of 2 weeks and experiment group of 4 weeks. Alterations of mTOR, p-mTOR, S6K1, Beclin-1 and LC3-Ⅱ expression in myocardium were determined by Western blot and immunohistochemistry. Results: Compared with the control group, the expression of mTOR, p-mTOR, S6K1, Beclin-1 and LC3-Ⅱ level increased significantly in the experiment group of 2 weeks. The expression of p-mTOR and S6K1 increased significantly in the experiment group of 4 weeks compared with those of the experiment group of 2 weeks. Conclusions: mTOR signaling pathway is activated in early diabetic myocardial injury via autophagy. The findings may provide a new therapeutic target for diabetic cardiomyopathy.

Role of Serum Biomarkers in Early Detection of Diabetic Cardiomyopathy in the West Virginian Population

Objectives: Diabetic cardiomyopathy (DCM) is an established complication of diabetes mellitus. In West Virginia, the especially high incidence of diabetes and heart failure validate the necessity of developing new strategies for earlier detection of DCM. Since most DCM patients remain asymptomatic until the later stages of the disease when the fibrotic complications become irreversible, we aimed to explore biomarkers that can identify early-stage DCM. Methods: The patients were grouped into 4 categories based on clinical diabetic and cardiac parameters: Control, Diabetes (DM), Diastolic dysfunction (DD), and Diabetes with diastolic dysfunction (DM+DD), the last group being the preclinical DCM group. Results: Echocardiography images indicated severe diastolic dysfunction in patients with DD+DM and DD compared to DM or control patients. In the DM and DM+DD groups, TNFα, isoprostane, and leptin were elevated compared to control (p<0.05), as were clinical markers HDL, glucose and hemoglobin A1C. Fibrotic markers IGFBP7 and TGF-β followed the same trend. The Control group showed higher beneficial levels of adiponectin and bilirubin, which were reduced in the DM and DM+DD groups (p<0.05). Conclusion: The results from our study support the clinical application of biomarkers in diagnosing early stage DCM, which will enable attenuation of disease progression prior to the onset of irreversible complications.

GW26-e1583 N-epsilon-(carboxymethyl)lysine is associated with cardiac diastolic dysfunction in alloxan-induced type 1 diabetic rabbits with early diabetic cardiomyopathy

GW26-e1583 N-epsilon-(carboxymethyl)lysine is associated with cardiac diastolic dysfunction in alloxan-induced type 1 diabetic rabbits with early diabetic cardiomyopathy

Abstract P218: Role of Metabolic Biomarkers in Early Detection of Diabetic Cardiomyopathy in West Virginian Population

Background: Diabetes Mellitus is a significant risk factor for heart failure. With the increasing global prevalence of diabetes, diabetic cardiomyopathy (DCM) represents a significant public health issue. Elevated levels of Insulin-like growth factor-binding protein 7 (IGFBP7) is an early-stage biomarker in DCM but studies are lacking on the association between IGFBP7 and DCM. Most patients with DCM remain asymptomatic until late-stage disease, therefore it becomes of utmost importance to identify biomarkers to detect early stage of DCM. The aim of this study is to determine if IGFBP7 and other biomarkers can detect the onset of preclinical DCM relative to echocardiographic irregularities exhibiting diastolic dysfunction. Methods: Eighty patients were grouped equally into four categories based on predetermined clinical diabetic and cardiac parameters: Normal, Diabetes (DM), Diastolic Heart Failure (DHF) , and DM+DHF, the last group being the preclinical DCM group. Results: Echocardiography images indicated severe diastolic dysfunction in patients with DHF + DM as compared to DHF patients alone. In the DM and DM+DHF groups, IL-6, TNF-alpha, isoprostane, and leptin were elevated compared to the control, as were clinical markers HDL, glucose and hemoglobin A1C. More importantly fibrotic markers IGFBP7 and TGF-β followed the same trend . The Normal group showed higher levels of beneficial biomarkers adiponectin and bilirubin, which were reduced in the DM and DM+DHF groups. Conclusion: This novel study demonstrates that West Virginia patients with early onset DCM were more likely to have elevated levels of detrimental biomarkers, including IGFBP7 and TGF- β, indicating potential diastolic dysfunction. The present study provides new and exciting evidence supporting the potential clinical applications of using IGFBP7 and other biomarkers in diagnosing early stage DCM in the West Virginia population.

Chronic Rho-kinase inhibition improves left ventricular contractile dysfunction in early type-1 diabetes by increasing myosin cross-bridge extension.

BackgroundImpaired actin–myosin cross-bridge (CB) dynamics correlate with impaired left ventricular (LV) function in early diabetic cardiomyopathy (DCM). Elevated expression and activity of Rho kinase (ROCK) contributes to the development of DCM. ROCK targets several sarcomeric proteins including myosin light chain 2, myosin binding protein-C (MyBP-C), troponin I (TnI) and troponin T that all have important roles in regulating CB dynamics and contractility of the myocardium. Our aim was to examine if chronic ROCK inhibition prevents impaired CB dynamics and LV dysfunction in a rat model of early diabetes, and whether these changes are associated with changes in myofilament phosphorylation state.MethodsSeven days post-diabetes induction (65 mg/kg ip, streptozotocin), diabetic rats received the ROCK inhibitor, fasudil (10 mg/kg/day ip) or vehicle for 14 days. Rats underwent cardiac catheterization to assess LV function simultaneous with X-ray diffraction using synchrotron radiation to assess in situ CB dynamics.ResultsCompared to controls, diabetic rats developed mild systolic and diastolic dysfunction, which was attenuated by fasudil. End-diastolic and systolic myosin proximity to actin filaments were significantly reduced in diabetic rats (P < 0.05). In all rats there was an inverse correlation between ROCK1 expression and the extension of myosin CB in diastole, with the lowest ROCK expression in control and fasudil-treated diabetic rats. In diabetic and fasudil-treated diabetic rats changes in relative phosphorylation of TnI and MyBP-C were not significant from controls.ConclusionsOur results demonstrate a clear role for ROCK in the development of LV dysfunction and impaired CB dynamics in early DCM.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-015-0256-6) contains supplementary material, which is available to authorized users.

Rho Kinase Inhibition Improves Cardiac Cross‐Bridge Dynamics in Early Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is associated with left ventricle fibrosis, hypertrophy and diastolic dysfunction. Cardiomyocyte subcellular alterations are thought to drive contractile dysfunction in early DCM. Rho kinase (ROCK) has been implicated in the pathogenesis of DCM and is known to interact with proteins in the actin-myosin cross-bridge (CB) that control myosin head extension. With the use of synchrotron radiation, we are able to examine CB dynamics in real time in the in situ beating heart. Thus, we aimed to determine if ROCK was involved in the pathogenesis of DCM. Cardiac CB dynamics and function were examined in control and diabetic rats treated a ROCK inhibitor (fasudil, 10mg/kg/day) or saline vehicle for two weeks, one week after the induction of diabetes. In the deeper subendocardial layer of the myocardium, diabetic rats had significantly reduced diastolic myosin head extension (p<0.05) compared to control rats. Fasudil treatment improved diastolic myosin head extension in the subendocardium of diabetic rats. Impaired CB function was associated with a trend for a 20% reduction in myosin binding protein C expression in diabetic rats compared to control rats, and fasudil treatment partially prevented this reduction in diabetic rats. Our results suggest ROCK may impair CB dynamics in early DCM by altering the phosphorylation of thick filament proteins.

The PKD inhibitor CID755673 enhances cardiac function in diabetic db/db mice.

The development of diabetic cardiomyopathy is a key contributor to heart failure and mortality in obesity and type 2 diabetes (T2D). Current therapeutic interventions for T2D have limited impact on the development of diabetic cardiomyopathy. Clearly, new therapies are urgently needed. A potential therapeutic target is protein kinase D (PKD), which is activated by metabolic insults and implicated in the regulation of cardiac metabolism, contractility and hypertrophy. We therefore hypothesised that PKD inhibition would enhance cardiac function in T2D mice. We first validated the obese and T2D db/db mouse as a model of early stage diabetic cardiomyopathy, which was characterised by both diastolic and systolic dysfunction, without overt alterations in left ventricular morphology. These functional characteristics were also associated with increased PKD2 phosphorylation in the fed state and a gene expression signature characteristic of PKD activation. Acute administration of the PKD inhibitor CID755673 to normal mice reduced both PKD1 and 2 phosphorylation in a time and dose-dependent manner. Chronic CID755673 administration to T2D db/db mice for two weeks reduced expression of the gene expression signature of PKD activation, enhanced indices of both diastolic and systolic left ventricular function and was associated with reduced heart weight. These alterations in cardiac function were independent of changes in glucose homeostasis, insulin action and body composition. These findings suggest that PKD inhibition could be an effective strategy to enhance heart function in obese and diabetic patients and provide an impetus for further mechanistic investigations into the role of PKD in diabetic cardiomyopathy.

Increasing Pyruvate Dehydrogenase Flux as a Treatment for Diabetic Cardiomyopathy: A Combined 13C Hyperpolarized Magnetic Resonance and Echocardiography Study

Although diabetic cardiomyopathy is widely recognized, there are no specific treatments available. Altered myocardial substrate selection has emerged as a candidate mechanism behind the development of cardiac dysfunction in diabetes. As pyruvate dehydrogenase (PDH) activity appears central to the balance of substrate use, we aimed to investigate the relationship between PDH flux and myocardial function in a rodent model of type 2 diabetes and to explore whether or not increasing PDH flux, with dichloroacetate, would restore the balance of substrate use and improve cardiac function. All animals underwent in vivo hyperpolarized [1-(13)C]pyruvate magnetic resonance spectroscopy and echocardiography to assess cardiac PDH flux and function, respectively. Diabetic animals showed significantly higher blood glucose levels (10.8 ± 0.7 vs. 8.4 ± 0.5 mmol/L), lower PDH flux (0.005 ± 0.001 vs. 0.017 ± 0.002 s(-1)), and significantly impaired diastolic function (transmitral early diastolic peak velocity/early diastolic myocardial velocity ratio [E/E'] 12.2 ± 0.8 vs. 20 ± 2), which are in keeping with early diabetic cardiomyopathy. Twenty-eight days of treatment with dichloroacetate restored PDH flux to normal levels (0.018 ± 0.002 s(-1)), reversed diastolic dysfunction (E/E' 14 ± 1), and normalized blood glucose levels (7.5 ± 0.7 mmol/L). The treatment of diabetes with dichloroacetate therefore restored the balance of myocardial substrate selection, reversed diastolic dysfunction, and normalized blood glucose levels. This suggests that PDH modulation could be a novel therapy for the treatment and/or prevention of diabetic cardiomyopathy.