Facilitated Ca2+ homeostasis and attenuated myocardial autophagy contribute to alleviation of diabetic cardiomyopathy after bariatric surgery

Duodenal-jejunal bypass surgery activates eNOS and enhances antioxidant system by activating AMPK pathway to improve heart oxidative stress in diabetic cardiomyopathy rats

BACKGROUND

Diabetic cardiomyopathy is a serious complication of obesity with type 2 diabetes and is a major cause of mortality. Metabolic surgery, such as duodenal-jejunal bypass (DJB), can effectively improve diabetic cardiomyopathy; however, the underlying mechanisms remain elusive. Oxidative stress is one of the pivotal mechanisms of diabetic cardiomyopathy. Our objective was to investigate the effect and potential mechanisms of DJB on oxidative stress in the heart of diabetic cardiomyopathy rats.

METHODS

High-fat diet combined with intraperitoneal injection of streptozotocin was used to establish diabetic cardiomyopathy rats. DJB was performed on diabetic cardiomyopathy rats, and high glucose and palmitate were used to simulate diabetic cardiomyopathy in H9C2 cells in vitro. Sera from different groups of rats were used for experiments in vivo and in vitro.

RESULTS

DJB effectively improved oxidative stress and activated the adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway to increase endothelial nitric oxide synthase (eNOS) phosphorylation level and the expression of antioxidative system-related proteins and genes in the heart of diabetic cardiomyopathy rats. AMPK agonists and serum from DJB rats activated the AMPK pathway to increase eNOS phosphorylation level and the expression of antioxidative system-related proteins and genes and decreased the content of reactive oxygen species in H9C2 cells, but this improvement was almost eliminated by the addition of AMPK inhibitors.

CONCLUSIONS

DJB activates eNOS and enhances the antioxidant system by activating the AMPK pathway-and not solely by improving blood glucose-to improve oxidative stress in the heart of diabetic cardiomyopathy rats.

Mitochondria-associated endoplasmic reticulum membrane (MAM): a dark horse for diabetic cardiomyopathy treatment

Diabetic cardiomyopathy (DCM), an important complication of diabetes mellitus (DM), is one of the most serious chronic heart diseases and has become a major cause of heart failure worldwide. At present, the pathogenesis of DCM is unclear, and there is still a lack of effective therapeutics. Previous studies have shown that the homeostasis of mitochondria and the endoplasmic reticulum (ER) play a core role in maintaining cardiovascular function, and structural and functional abnormalities in these organelles seriously impact the occurrence and development of various cardiovascular diseases, including DCM. The interplay between mitochondria and the ER is mediated by the mitochondria-associated ER membrane (MAM), which participates in regulating energy metabolism, calcium homeostasis, mitochondrial dynamics, autophagy, ER stress, inflammation, and other cellular processes. Recent studies have proven that MAM is closely related to the initiation and progression of DCM. In this study, we aim to summarize the recent research progress on MAM, elaborate on the key role of MAM in DCM, and discuss the potential of MAM as an important therapeutic target for DCM, thereby providing a theoretical reference for basic and clinical studies of DCM treatment.

Bariatric surgery for diabetic comorbidities: A focus on hepatic, cardiac and renal fibrosis

Continuously rising trends in diabetes render this disease spectrum an epidemic proportion worldwide. As the disease progresses, the pathological effects of diabetes may impair the normal function of several vital organs, eventually leading to increase the risk of other diabetic comorbidities with advanced fibrosis such as non-alcoholic fatty liver disease, diabetic cardiomyopathy, and diabetic kidney disease. Currently, lifestyle changes and drug therapies of hypoglycemic and lipid-lowering are effective in improving multi-organ function, but therapeutic efficacy is difficult to maintain due to poor compliance and drug reactions. Bariatric surgery, including sleeve gastrectomy and Roux-en-Y gastric bypass surgery, has shown better results in terms of prognosis for diabetes through long-term follow-up. Moreover, bariatric surgery has significant long-term benefits on the function of the heart, liver, kidneys, and other organs through mechanisms associated with reversal of tissue fibrosis. The aim of this review is to describe the impact of type 2 diabetes mellitus on hepatic, cardiac and renal fibrosis and to summarize the potential mechanisms by which bariatric surgery improves multiple organ function, particularly reversal of fibrosis.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Attenuation of ROS/Chloride Efflux-Mediated NLRP3 Inflammasome Activation Contributes to Alleviation of Diabetic Cardiomyopathy in Rats after Sleeve Gastrectomy

Diabetic cardiomyopathy (DCM) can develop in diabetes mellitus and is a major cause of morbidity and mortality. Surgical bariatric surgery procedures, such as sleeve gastrectomy (SG), result in remission of type 2 diabetes and have benefits regarding systolic and diastolic myocardial function. The NLR family pyrin domain containing 3 (NLRP3) inflammasome appears to participate in the development of DCM. However, whether SG surgery affects myocardial NLRP3 inflammasome-related pyroptosis to improve cardiac function remains unclear. This study was aimed at investigating the effect of SG surgery on NLRP3-associated pyroptosis in rats with DCM. We also examined cellular phenotypes and molecular mechanisms in high glucose-stimulated myocytes. The rat model of DCM was established by high-fat diet feeding and low-dose streptozotocin injection. We observed a metabolic benefit of SG, including a reduced body weight, food intake, and blood glucose levels and restored glucose tolerance and insulin sensitivity postoperatively. We observed a marked decline in glucose uptake in rats with DCM, and this was restored after SG. Also, SG alleviated the dysfunction of myocardial contraction and diastole, delayed the progression of DCM, and reduced the NLRP3 inflammasome-mediated myocardial pyroptosis in vivo. H9c2 cardiomyocytes showed membrane disruption and DNA damage under a high glucose stimulus, which suggested myocardial pyroptosis. Using a ROS scavenger or chloride channel blocker in vitro restored myocardial NLRP3-mediated pyroptosis. Furthermore, we found that chloride efflux acted downstream of ROS generation. In conclusion, SG may ameliorate or even reverse the progression of DCM. Our study provides evidence that the SG operation alleviates NLRP3 inflammasome dysregulation in DCM. Clearance of ROS overburden and suppression of chloride efflux due to SG might act as the proximal event before inhibition of NLRP3 inflammasome in the myocardium, thus contributing to morphological and functional alleviation of DCM.

Sleeve Gastrectomy-Induced AMPK Activation Attenuates Diabetic Cardiomyopathy by Maintaining Mitochondrial Homeostasis via NR4A1 Suppression in Rats

Diabetic cardiomyopathy (DCM) is characterized by impaired diastolic and systolic myocardial performance and is a major cause of morbidity and mortality in patients with diabetes. Surgical bariatric procedures, such as sleeve gastrectomy (SG), result in remission of type 2 diabetes (T2DM) and have benefits with myocardial function. Maintaining cardiac mitochondrial homeostasis is a promising therapeutic strategy for DCM. However, whether SG surgery affects mitochondrial function and its underlying mechanism remains unclear. This study aimed to investigate the effect of SG surgery on mitochondrial homeostasis and intracellular oxidative stress in rats with DCM. We also examined cellular phenotypes and molecular mechanisms in high glucose and high fat-stimulated myocytes. The rat model of DCM was established by high-fat diet feeding and low-dose streptozotocin injection. We observed a remarkably metabolic benefit of SG, including a reduced body weight, food intake, blood glucose levels, and restored glucose tolerance and insulin sensitivity post-operatively. Also, SG ameliorated the pathological cardiac hypertrophy, myocardial fibrosis and the dysfunction of myocardial contraction and diastole, consequently delayed the progression of DCM. Also, SG restored the mitochondrial dysfunction and fragmentation through the AMPK signaling activation mediated nuclear receptor subfamily 4 group A member 1 (NR4A1)/DRP1 suppression in vivo. H9c2 cardiomyocytes showed that activation of AMPK could reverse the mitochondrial dysfunction somehow. Collectively, our study provided evidence that SG surgery could alleviate mitochondrial dysfunction in DCM. Moreover, AMPK-activated NR4A1/DRP1 repression might act as a significant reason for maintaining mitochondrial homeostasis in the myocardium, thus contributing to morphological and functional alleviation of DCM.

Sleeve Gastrectomy Ameliorates Diabetes-Induced Cardiac Hypertrophy Correlates With the MAPK Signaling Pathway

Background: Cardiac hypertrophy as a main pathological manifestation of diabetic cardiomyopathy (DCM), is a significant complication of diabetes. Bariatric surgery has been proven to relieve DCM; however, whether it can alleviate diabetes-induced cardiac hypertrophy is undefined.

Methods: Diabetic and obese rats were performed sleeve gastrectomy (SG) after having diabetes for 16weeks. The rats were euthanized 8weeks after SG. Metabolic parameters, heart function parameters, myocardial glucose uptake, morphometric and histological changes, and the expression level of mitogen-activated protein kinases (MAPKs) were determined and compared among the control group (CON group), diabetes mellitus group (DM group), sham operation group (SHAM group), and SG group.

Results: Compared with the SHAM group, the blood glucose, body weight, insulin resistance, and other metabolic parameters were significantly improved in the SG group. There was also a marked improvement in myocardial morphometric and histological parameters after SG. Furthermore, the myocardial glucose uptake and heart function were reversed after SG. Additionally, the phosphorylation of MAPKs was inhibited after SG, including p38 MAPKs, c-Jun N-terminal kinases (JNKs), and extracellular signal-regulated kinases 1/2 (ERK1/2). The expression of DUSP6, which dephosphorylates ERK1/2, was upregulated after SG. These findings suggest that SG ameliorated diabetes-induced cardiac hypertrophy correlates with the MAPK signaling pathway.

Conclusion: These results showed that diabetes-induced cardiac hypertrophy was ameliorated after SG was closely related to the inhibition of the MAPK signaling pathway and upregulation of DUSP6. Therefore, this study provides a novel strategy for treating diabetes-induced cardiac hypertrophy.

Obesity and Cardiomyopathy

While much has been written about the syndrome of diabetic cardiomyopathy, clinicians and research scientists are now beginning to realize that an entirely unique syndrome exists, albeit with several commonalities to the diabetic syndrome, that being obesity cardiomyopathy. This syndrome develops independent of such comorbidities as hypertension, myocardial infarction and coronary artery disease; and it is characterized by specific alterations in adipose tissue function, inflammation and metabolism. Recent insights into the etiology of the syndrome and its consequences have focused on the roles played by altered intracellular calcium homeostasis, reactive oxygen species, and mitochondrial dysfunction. A timely and comprehensive review by Ren, Wu, Wang, Sowers and Zhang (1) identifies unique mechanisms underlying this syndrome, its relationship to heart failure and the recently identified incidence of COVID-19-related cardiovascular mortality. Importantly, the review concludes by advancing recommendations for novel approaches to the clinical management of this dangerous form of cardiomyopathy.

Weight Loss After Laparoscopic Sleeve Gastrectomy Ameliorates the Cardiac Remodeling in Obese Chinese

This study aimed to investigate the impact of weight loss after laparoscopic sleeve gastrectomy (LSG) on cardiac structural and functional remodeling in obese Chinese. A total of 44 obese participants were enrolled consecutively. The physical, laboratory, electrocardiographic, and echocardiographic parameters of pre-and postoperative were recorded. The average follow-up time was 12.28 ± 5.80 months. The body mass index (BMI) of the patients with obesity was decreased from 41.6 ± 7.44 to 30.3 ± 5.73kg/m² (P<0.001) after LSG. The systolic and diastolic blood pressure of the subjects was significantly reduced from 137.9 ± 15.7mmHg to 123.0 ± 16.0 and 83.4 ± 10.8 to 71.3 ± 11.7mmHg (P<0.001), respectively. The levels of fasting insulin and fasting blood glucose were significantly decreased (38.8 ± 32.1 to 8.43 ± 4.16 mU/L, P<0.001; 6.95 ± 2.59 to 4.64 ± 0.50mmol/L, P<0.001). Total cholesterol (TC, 4.66 ± 0.84 to 4.23 ± 0.75mmol/L, P<0.001) and triglyceride (TG, 1.92 ± 1.21 to 0.85 ± 0.30mmol/L, P<0.001) decreased significantly. Cardiovascular geometric parameters including aortic sinus diameter (ASD, 32.9 ± 2.83mm to 32.0 ± 3.10mm, P<0.05), left atrial diameter (LAD, 38.8 ± 4.03 to 36.2 ± 4.12mm, P<0.001), and interventricular septum thickness(IVS, 10.2 ± 0.93 to 9.64 ± 0.89mm, P<0.001) were significantly reduced. The ratio of weight loss (RWL) was positively correlated with the changes of LAD. The change of IVS was negatively correlated with the change of fasting blood glucose (GLU). Weight loss after LSG could effectively improve cardiac structural, but not functional, abnormality in obese Chinese.

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

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

Hemodynamic assessment of diastolic function for experimental models

Traditionally, the evaluation of cardiac function has focused on systolic function; however, there is a growing appreciation for the contribution of diastolic function to overall cardiac health. Given the emerging interest in evaluating diastolic function in all models of heart failure, there is a need for sensitivity, accuracy, and precision in the hemodynamic assessment of diastolic function. Hemodynamics measure cardiac pressures in vivo, offering a direct assessment of diastolic function. In this review, we summarize the underlying principles of diastolic function, dividing diastole into two phases: 1) relaxation and 2) filling. We identify parameters used to comprehensively evaluate diastolic function by hemodynamics, clarify how each parameter is obtained, and consider the advantages and limitations associated with each measure. We provide a summary of the sensitivity of each diastolic parameter to loading conditions. Furthermore, we discuss differences that can occur in the accuracy of diastolic and systolic indices when generated by automated software compared with custom software analysis and the magnitude each parameter is influenced during inspiration with healthy breathing and a mild breathing load, commonly expected in heart failure. Finally, we identify key variables to control (e.g., body temperature, anesthetic, sampling rate) when collecting hemodynamic data. This review provides fundamental knowledge for users to succeed in troubleshooting and guidelines for evaluating diastolic function by hemodynamics in experimental models of heart failure.

CORP: Practical tools for improving experimental design and reporting of laboratory studies of cardiovascular physiology and metabolism

The exercise consisted of: 1) a short survey to acquire baseline data on current practices regarding the conduct of animal studies, 2) a series of presentations for promoting awareness and providing advice and practical tools for improving experimental design, and 3) a follow-up survey 12 mo later to assess whether practices had changed. The surveys were compulsory for responsible investigators (n = 16; paired data presented). Other investigators named on animal ethics applications were encouraged to participate (2017, total of 36 investigators; 2018, 37 investigators). The major findings to come from the exercise included 1) a willingness of investigators to make changes when provided with knowledge/tools and solutions that were relatively simple to implement (e.g., proportion of responsible investigators showing improved practices using a structured method for randomization was 0.44, 95% CI (0.19; 0.70), P = 0.003, and deidentifying drugs/interventions was 0.40, 95% CI (0.12; 0.68), P = 0.010); 2) resistance to change if this involved more personnel and time (e.g., as required for allocation concealment); and 3) evidence that changes to long-term practices ("habits") require time and follow-up. Improved practices could be verified based on changes in reporting within publications or documented evidence provided during laboratory visits. In summary, this exercise resulted in changed attitudes, practices, and reporting, but continued follow-up, monitoring, and incentives are required. Efforts to improve experimental rigor will reduce bias and will lead to findings with the greatest translational potential.NEW & NOTEWORTHY The goal of this exercise was to encourage preclinical researchers to improve the quality of their cardiac and metabolic animal studies by 1) increasing awareness of concerns, which can arise from suboptimal experimental designs; 2) providing knowledge, tools, and templates to overcome bias; and 3) conducting two short surveys over 12 mo to monitor change. Improved practices were identified for the uptake of structured methods for randomization, and de-identifying interventions/drugs.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/experimental-design-survey-training-practical-tools/.

Role of β-adrenergic signaling in masseter muscle

In skeletal muscle, the major isoform of β-adrenergic receptor (β-AR) is β2-AR and the minor isoform is β1-AR, which is opposite to the situation in cardiac muscle. Despite extensive studies in cardiac muscle, the physiological roles of the β-AR subtypes in skeletal muscle are not fully understood. Therefore, in this work, we compared the effects of chronic β1- or β2-AR activation with a specific β1-AR agonist, dobutamine (DOB), or a specific β2-AR agonist, clenbuterol (CB), on masseter and cardiac muscles in mice. In cardiac muscle, chronic β1-AR stimulation induced cardiac hypertrophy, fibrosis and myocyte apoptosis, whereas chronic β2-AR stimulation induced cardiac hypertrophy without histological abnormalities. In masseter muscle, however, chronic β1-AR stimulation did not induce muscle hypertrophy, but did induce fibrosis and apoptosis concomitantly with increased levels of p44/42 MAPK (ERK1/2) (Thr-202/Tyr-204), calmodulin kinase II (Thr-286) and mammalian target of rapamycin (mTOR) (Ser-2481) phosphorylation. On the other hand, chronic β2-AR stimulation in masseter muscle induced muscle hypertrophy without histological abnormalities, as in the case of cardiac muscle, concomitantly with phosphorylation of Akt (Ser-473) and mTOR (Ser-2448) and increased expression of microtubule-associated protein light chain 3-II, an autophagosome marker. These results suggest that the β1-AR pathway is deleterious and the β2-AR is protective in masseter muscle. These data should be helpful in developing pharmacological approaches for the treatment of skeletal muscle wasting and weakness.

High glucose induced calcium overload via impairment of SERCA/PLN pathway and mitochondrial dysfunction leads to oxidative stress in H9c2 cells and amelioration with ferulic acid

Oxidative stress and associated complications are the major pathological concerns of diabetic cardiomyopathy (DC). We aim to elucidate the mechanisms by which high glucose (HG) induced alteration in calcium homeostasis and evaluation of the beneficial effect of two concentrations (10 and 25 μm) of ferulic acid (FA). HG was induced in H9c2 cardiomyoblast by treating with glucose (33 mm) for 48 h, and FA was co-treated. Intracellular calcium ([Ca²⁺ ]i) overload was found increased significantly with HG. For elucidation of mechanism, the SERCA pathway and mitochondrial integrity (transmembrane potential and permeability transition pore) were explored. Then, we assessed oxidative stress, and cell injury with brain natriuretic peptide (BNP), atrial natriuretic peptide (ANP), and lactate dehydrogenase (LDH) release. HG caused significant [Ca²⁺ ]i overload through downregulation of SERCA2/1, pPLN, and pPKA C-α; and upregulation of PLN and PKA C-α and alteration in the integrity of mitochondria with HG. The [Ca²⁺ ]i overload in turn caused oxidative stress via generation of reactive oxygen species, lipid peroxidation, and protein carbonylation. This resulted in cell injury which was evident with significant release of BNP, ANP, and LDH. FA co-treatment was effective to mitigate all pathological changes caused by HG. From the overall results, we conclude that [Ca²⁺ ]i overload via SERCA pathway and altered mitochondrial integrity is the main cause for oxidative stress during HG. Based on our result, we report that FA could be an attractive nutraceutical for DC.