What Role do Mitochondria have in Diastolic Dysfunction? Implications for Diabetic Cardiomyopathy and Heart Failure with Preserved Ejection Function (HFpEF)

L-Arginine supplementation as mitochondrial therapy in diabetic cardiomyopathy

In patients with type II diabetes, the development of diabetic cardiomyopathy (DC) is associated with a high risk of mortality. Left ventricular hypertrophy, diastolic dysfunction, and exercise intolerance are the first signs of DC. The underlying mechanisms are not fully elucidated, and there is an urgent need for specific biomarkers and molecular targets for early diagnosis and treatment. Mitochondrial alterations play a key role in the development of DC, and microRNAs regulating mitochondrial function are emerging as potential biomarkers of metabolic stress in DC. L-Arginine (Arg) supplementation has been shown to be an effective strategy for improving mitochondrial function and energetics, with a significant impact on physical performance. The aim of the current study was to evaluate the effects of Arg supplementation on cardiac mitochondrial function, DC development, and relative phenotypes including exercise intolerance. We used db/db mice as a model of type II diabetes, chronically treated with Arg (1 mg/kg/day) for 12 weeks. Arg-treated db/db mice showed preserved diastolic function and left ventricular morphology compared with untreated diabetic mice. Arg supplementation also improved exercise tolerance and the propensity to physical activity. Mitochondrial respiration was significantly increased in cardiomyocytes isolated from treated db/db mice, as well as in diabetic cardiomyocytes treated with Arg in vitro. The improvement of cardiac mitochondrial function in db/db + Arg mice was associated with an increase in PGC-1-alpha levels, mitochondrial biogenesis, recycling, and antioxidant capacity. Arg treatment prevented the accumulation of circulating and cardiac miR-143 in db/db mice, which is an index of metabolic stress and activation of mitochondrial damage mechanisms. In conclusion, Arg supplementation is effective in preventing the development of DC, preserving diastolic function and exercise tolerance by improving mitochondrial fitness and homeostasis. Additionally, miR-143 could potentially be employed to monitor cardiac metabolic stress and the effects of Arg treatment in diabetes.

Cardiac diastolic dysfunction by cigarette smoking is associated with mitochondrial integrity in the heart

Cigarette smoking behaviors are harmful and cause one out of ten deaths due to cardiovascular disease. As population sizes grow and number of cigarette smokers increases, it is vital that we understand the mechanisms leading to heart failure in cigarette smokers. We have reported that metabolic regulation of a histone deacetylase, SIRT1, modulates cardiovascular and mitochondrial function under stress. Given this conclusion, we hypothesized that chronic cigarette smoking led to cardiovascular dysfunction via a reduction SIRT1. Mice were randomly organized into smoking or nonsmoking groups, and the smoking group received cigarette smoke exposure for 16 weeks. Following 16-week exposure, diastolic function of the heart was impaired in the smoking group as compared to sham, indicated by a significant increase in E/e'. The electrical function of the heart was also impaired in the smoking group compared to the sham group, indicated by increased PR interval and decreased QTc interval. This diastolic dysfunction was not accompanied by increased fibrosis in mouse hearts, although samples from human chronic smokers indicated increased fibrosis compared to their nonsmoker counterparts. As well as diastolic dysfunction, mitochondria from the 16-week smoking group showed significantly impaired function, evidenced by significant decreases in all parameters measured by the mitochondrial stress test. We further found biochemical evidence of a significantly decreased level of SIRT1 in left ventricles of both mouse and human smoking groups compared to nonsmoking counterparts. Data from this study indicate that decreased SIRT1 levels by cigarette smoking are associated with diastolic dysfunction caused by compromised mitochondrial integrity.

Emerging Therapy for Diabetic Cardiomyopathy: From Molecular Mechanism to Clinical Practice

Diabetic cardiomyopathy is characterized by abnormal myocardial structure or performance in the absence of coronary artery disease or significant valvular heart disease in patients with diabetes mellitus. The spectrum of diabetic cardiomyopathy ranges from subtle myocardial changes to myocardial fibrosis and diastolic function and finally to symptomatic heart failure. Except for sodium–glucose transport protein 2 inhibitors and possibly bariatric and metabolic surgery, there is currently no specific treatment for this distinct disease entity in patients with diabetes. The molecular mechanism of diabetic cardiomyopathy includes impaired nutrient-sensing signaling, dysregulated autophagy, impaired mitochondrial energetics, altered fuel utilization, oxidative stress and lipid peroxidation, advanced glycation end-products, inflammation, impaired calcium homeostasis, abnormal endothelial function and nitric oxide production, aberrant epidermal growth factor receptor signaling, the activation of the renin–angiotensin–aldosterone system and sympathetic hyperactivity, and extracellular matrix accumulation and fibrosis. Here, we summarize several important emerging treatments for diabetic cardiomyopathy targeting specific molecular mechanisms, with evidence from preclinical studies and clinical trials.

Genomic, Proteomic, and Metabolic Comparisons of Small Animal Models of Heart Failure With Preserved Ejection Fraction: A Tale of Mice, Rats, and Cats

Heart failure with preserved ejection fraction (HFpEF) remains a medical anomaly that baffles researchers and physicians alike. The overall phenotypical changes of diastolic function and left ventricular hypertrophy observed in HFpEF are definable; however, the metabolic and molecular alterations that ultimately produce these changes are not well established. Comorbidities such as obesity, hypertension, and diabetes, as well as general aging, play crucial roles in its development and progression. Various animal models have recently been developed to better understand the pathophysiological and metabolic developments in HFpEF and to illuminate novel avenues for pharmacotherapy. These models include multi‐hit rodents and feline aortic constriction animals. Recently, genomic, proteomic, and metabolomic approaches have been used to define altered signaling pathways in the heart associated with HFpEF, including those involved in inflammation, cGMP‐related, Ca²⁺ handling, mitochondrial respiration, and the unfolded protein response in endoplasmic reticulum stress. This article aims to present an overview of what has been learnt by these studies, focusing mainly on the findings in common while highlighting unresolved issues. The knowledge gained from these research models will not simply be of benefit for treating HFpEF but will undoubtedly provide new insights into the mechanisms by which the heart deals with external stresses and how the processes involved can fail.

Mimicking Metabolic Disturbance in Establishing Animal Models of Heart Failure With Preserved Ejection Fraction

Heart failure (HF), the terminal state of different heart diseases, imposed a significant health care burden worldwide. It is the last battlefield in dealing with cardiovascular diseases. HF with preserved ejection fraction (HFpEF) is a type of HF in which the symptoms and signs of HF are mainly ascribed to diastolic dysfunction of left ventricle, whereas systolic function is normal or near-normal. Compared to HF with reduced ejection fraction (HFrEF), the diagnosis and treatment of HFpEF have made limited progress, partly due to the lack of suitable animal models for translational studies in the past. Given metabolic disturbance and inflammatory burden contribute to HFpEF pathogenesis, recent years have witnessed emerging studies focusing on construction of animal models with HFpEF phenotype by mimicking metabolic disorders. These models prefer to recapitulate the metabolic disorders and endothelial dysfunction, leading to the more detailed understanding of the entity. In this review, we summarize the currently available animal models of HFpEF with metabolic disorders, as well as their advantages and disadvantages as tools for translational studies.