Myocardial fluid balance

Sodium, Interstitium, Lymphatics and Hypertension-A Tale of Hydraulics

Blood pressure is regulated by vascular resistance and intravascular volume. However, exchanges of electrolytes and water between intra and extracellular spaces and filtration of fluid and solutes in the capillary beds blur the separation between intravascular, interstitial and intracellular compartments. Contemporary paradigms of microvascular exchange posit filtration of fluids and solutes along the whole capillary bed and a prominent role of lymphatic vessels, rather than its venous end, for their reabsorption. In the last decade, these concepts have stimulated greater interest in and better understanding of the lymphatic system as one of the master regulators of interstitial volume homeostasis. Here, we describe the anatomy and function of the lymphatic system and focus on its plasticity in relation to the accumulation of interstitial sodium in hypertension. The pathophysiological relevance of the lymphatic system is exemplified in the kidneys, which are crucially involved in the control of blood pressure, but also hypertension-mediated cardiac damage. Preclinical modulation of the lymphatic reserve for tissue drainage has demonstrated promise, but has also generated conflicting results. A better understanding of the hydraulic element of hypertension and the role of lymphatics in maintaining fluid balance can open new approaches to prevent and treat hypertension and its consequences, such as heart failure.

Mechanisms of Myocardial Edema Development in CVD Pathophysiology

Myocardial edema is the excess accumulation of fluid in the myocardial interstitium or cardiac cells that develops due to changes in capillary permeability, loss of glycocalyx charge, imbalance in lymphatic drainage, or a combination of these factors. Today it is believed that this condition is not only a complication of cardiovascular diseases, but in itself causes aggravation of the disease and increases the risks of adverse outcomes. The study of molecular, genetic, and mechanical changes in the myocardium during edema may contribute to the development of new approaches to the diagnosis and treatment of this condition. This review was conducted to describe the main mechanisms of myocardial edema development at the molecular and cellular levels and to identify promising targets for the regulation of this condition based on articles cited in Pubmed up to January 2024.

Myocardial Oedema as a Consequence of Viral Infection and Persistence-A Narrative Review with Focus on COVID-19 and Post COVID Sequelae

Microvascular integrity is a critical factor in myocardial fluid homeostasis. The subtle equilibrium between capillary filtration and lymphatic fluid removal is disturbed during pathological processes leading to inflammation, but also in hypoxia or due to alterations in vascular perfusion and coagulability. The degradation of the glycocalyx as the main component of the endothelial filtration barrier as well as pericyte disintegration results in the accumulation of interstitial and intracellular water. Moreover, lymphatic dysfunction evokes an increase in metabolic waste products, cytokines and inflammatory cells in the interstitial space contributing to myocardial oedema formation. This leads to myocardial stiffness and impaired contractility, eventually resulting in cardiomyocyte apoptosis, myocardial remodelling and fibrosis. The following article reviews pathophysiological inflammatory processes leading to myocardial oedema including myocarditis, ischaemia-reperfusion injury and viral infections with a special focus on the pathomechanisms evoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In addition, clinical implications including potential long-term effects due to viral persistence (long COVID), as well as treatment options, are discussed.

Accumulation of Inflammatory Mediators in the Normal Pericardial Fluid

There is paucity of studies that focus on the composition of pericardial fluid under resting conditions. The purpose of this study is to determine the levels of inflammatory mediators in pericardial fluid and their correlation with plasma levels in patients undergoing elective cardiac surgery. We conducted a prospective cohort study on candidates for elective aortic valve replacement surgery. Pericardial fluid and peripheral venous blood samples were collected after opening the pericardium. Levels of interleukin 1α (IL-1α); interleukin 1β (IL-1β); interleukin 2 (IL-2) interleukin 4 (IL-4); interleukin 6 (IL-6); interleukin 8 (IL8); interleukin 10 (IL10); tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1) epidermal growth factor (EGF), soluble E-selectin, L-selectin, P-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) were determined in both pericardial fluid and serum samples. A total of 45 patients with a mean age of 74 years were included of which 66% were males. Serum levels of all study mediators were within normal limits. Serum and pericardial levels of IL-1 α, IL-1 β, IL-2, IL-4, and IL-10 were similar. Levels of VEGF, EGF, VCAM-2, ICAM 1, E-selectin, P-selectin, and L-selectin were significantly lower in pericardial fluid than in serum. However, levels of IL-6, IL-8, TNF-α, IFN-γ, MCP-1, and MCP-1 were significantly higher in the pericardial fluid than in serum. Under normal conditions, the pattern of distribution of different inflammatory mediators in the pericardial fluid does not reflect serum levels. This may either reflect the condition of the underlying myocardium and epicardial fat or the activity of the mesothelial and mononuclear cells present in pericardial fluid.

Cardiac and intestinal tissue conduct developmental and reparative processes in response to lymphangiocrine signaling

Lymphatic vessels conduct a diverse range of activities to sustain the integrity of surrounding tissue. Besides facilitating the movement of lymph and its associated factors, lymphatic vessels are capable of producing tissue-specific responses to changes within their microenvironment. Lymphatic endothelial cells (LECs) secrete paracrine signals that bind to neighboring cell-receptors, commencing an intracellular signaling cascade that preludes modifications to the organ tissue's structure and function. While the lymphangiocrine factors and the molecular and cellular mechanisms themselves are specific to the organ tissue, the crosstalk action between LECs and adjacent cells has been highlighted as a commonality in augmenting tissue regeneration within animal models of cardiac and intestinal disease. Lymphangiocrine secretions have been owed for subsequent improvements in organ function by optimizing the clearance of excess tissue fluid and immune cells and stimulating favorable tissue growth, whereas perturbations in lymphatic performance bring about the opposite. Newly published landmark studies have filled gaps in our understanding of cardiac and intestinal maintenance by revealing key players for lymphangiocrine processes. Here, we will expand upon those findings and review the nature of lymphangiocrine factors in the heart and intestine, emphasizing its involvement within an interconnected network that supports daily homeostasis and self-renewal following injury.

Effect of SGLT2 Inhibitor on Cardiomyopathy in a Rat Model of T2DM: Possible involvement of Cardiac Aquaporins

Diabetic cardiomyopathy (DCM) causes arrhythmia, heart failure, and sudden death. Empagliflozin, an SGLT-2 (Sodium glucose co-transporter) inhibitor, is an anti-diabetic medication that decreases blood glucose levels by stimulating urinary glucose excretion. Several aquaporins (AQPs) including AQP-1-3 and - 4 and their involvement in the pathogenesis in different cardiac diseases were detected. In the current study the effect of Empagliflozin on diabetic cardiomyopathy and the possible involvement of cardiac AQPs were investigated.

METHODS

56 adult male Sprague-Dawley rats were divided into 4 groups: Control, DCM: type 2 diabetic rats, low EMPA+DCM received empagliflozin (10 mg/kg/day) and high EMPA+DCM received empagliflozin (30 mg/kg/day) for 6 weeks.

RESULTS

Administration of both EMPA doses, especially in high dose group, led to significant improvement in ECG parameters. Also, a significant improvement in biochemical and cardiac oxidative stress markers (significant decrease in serum CK-MB, and malondialdehyde while increasing catalase) with decreased fibrosis and edema in histopathological examination and a significant attenuation in apoptosis (caspase-3) and edema (AQP-1& -4).

CONCLUSION

Both doses of Empagliflozin have a cardioprotective effect and reduced myocardial tissue edema with high dose having a greater effect. This might be due to attenuation of oxidative stress, fibrosis and edema mediated through AQP-1, - 3& - 4 expression.

The emerging importance of lymphatics in health and disease: an NIH workshop report

The lymphatic system (LS) is composed of lymphoid organs and a network of vessels that transport interstitial fluid, antigens, lipids, cholesterol, immune cells, and other materials in the body. Abnormal development or malfunction of the LS has been shown to play a key role in the pathophysiology of many disease states. Thus, improved understanding of the anatomical and molecular characteristics of the LS may provide approaches for disease prevention or treatment. Recent advances harnessing single-cell technologies, clinical imaging, discovery of biomarkers, and computational tools have led to the development of strategies to study the LS. This Review summarizes the outcomes of the NIH workshop entitled "Yet to be Charted: Lymphatic System in Health and Disease," held in September 2022, with emphasis on major areas for advancement. International experts showcased the current state of knowledge regarding the LS and highlighted remaining challenges and opportunities to advance the field.

The Lymphatic Vasculature in Cardiac Development and Ischemic Heart Disease

In recent years, the lymphatic system has received increasing attention due to the fast-growing number of findings about its diverse novel functional roles in health and disease. It is well documented that the lymphatic vasculature plays major roles in the maintenance of tissue-fluid balance, the immune response, and in lipid absorption. However, recent studies have identified an additional growing number of novel and sometimes unexpected functional roles of the lymphatic vasculature in normal and pathological conditions in different organs. Among those, cardiac lymphatics have been shown to play important roles in heart development, ischemic cardiac disease, and cardiac disorders. In this review, we will discuss some of those novel functional roles of cardiac lymphatics, as well as the therapeutic potential of targeting lymphatics for the treatment of cardiovascular diseases.

Regulating Lymphatic Vasculature in Fibrosis: Understanding the Biology to Improve the Modeling

Fibrosis occurs in many chronic diseases with lymphatic vascular insufficiency (e.g., kidney disease, tumors, and lymphedema). New lymphatic capillary growth can be triggered by fibrosis-related tissue stiffening and soluble factors, but questions remain for how related biomechanical, biophysical, and biochemical cues affect lymphatic vascular growth and function. The current preclinical standard for studying lymphatics is animal modeling, but in vitro and in vivo outcomes often do not align. In vitro models can also be limited in their ability to separate vascular growth and function as individual outcomes, and fibrosis is not traditionally included in model design. Tissue engineering provides an opportunity to address in vitro limitations and mimic microenvironmental features that impact lymphatic vasculature. This review discusses fibrosis-related lymphatic vascular growth and function in disease and the current state of in vitro lymphatic vascular models while highlighting relevant knowledge gaps. Additional insights into the future of in vitro lymphatic vascular models demonstrate how prioritizing fibrosis alongside lymphatics will help capture the complexity and dynamics of lymphatics in disease. Overall, this review aims to emphasize that an advanced understanding of lymphatics within a fibrotic disease-enabled through more accurate preclinical modeling-will significantly impact therapeutic development toward restoring lymphatic vessel growth and function in patients.

Promoting Lymphangiogenesis and Lymphatic Growth and Remodeling to Treat Cardiovascular and Metabolic Diseases

Lymphatic vessels are low-pressure, blind-ended tubular structures that play a crucial role in the maintenance of tissue fluid homeostasis, immune cell trafficking, and dietary lipid uptake and transport. Emerging research has indicated that the promotion of lymphatic vascular growth, remodeling, and function can reduce inflammation and diminish disease severity in several pathophysiologic conditions. In particular, recent groundbreaking studies have shown that lymphangiogenesis, which describes the formation of new lymphatic vessels from the existing lymphatic vasculature, can be beneficial for the alleviation and resolution of metabolic and cardiovascular diseases. Therefore, promoting lymphangiogenesis represents a promising therapeutic approach. This brief review summarizes the most recent findings related to the modulation of lymphatic function to treat metabolic and cardiovascular diseases such as obesity, myocardial infarction, atherosclerosis, and hypertension. We also discuss experimental and therapeutic approaches to enforce lymphatic growth and remodeling as well as efforts to define the molecular and cellular mechanisms underlying these processes.

The ebb and flow of cardiac lymphatics: a tidal wave of new discoveries

The heart is imbued with a vast lymphatic network that is responsible for fluid homeostasis and immune cell trafficking. Disturbances in the forces that regulate microvascular fluid movement can result in myocardial edema, which has profibrotic and proinflammatory consequences and contributes to cardiovascular dysfunction. This review explores the complex relationship between cardiac lymphatics, myocardial edema, and cardiac disease. It covers the revised paradigm of microvascular forces and fluid movement around the capillary as well as the arsenal of preclinical tools and animal models used to model myocardial edema and cardiac disease. Clinical studies of myocardial edema and their prognostic significance are examined in parallel to the recent elegant animal studies discerning the pathophysiological role and therapeutic potential of cardiac lymphatics in different cardiovascular disease models. This review highlights the outstanding questions of interest to both basic scientists and clinicians regarding the roles of cardiac lymphatics in health and disease.

Organ-on-a-chip: Its use in cardiovascular research

Organ-on-a-chip (OOAC) has attracted great attention during the last decade as a revolutionary alternative to conventional animal models. This cutting-edge technology has also brought constructive changes to the field of cardiovascular research. The cardiovascular system, especially the heart as a well-protected vital organ, is virtually impossible to replicate in vitro with conventional approaches. This made scientists assume that they needed to use animal models for cardiovascular research. However, the frequent failure of animal models to correctly reflect the native cardiovascular system necessitated a search for alternative platforms for preclinical studies. Hence, as a promising alternative to conventional animal models, OOAC technology is being actively developed and tested in a wide range of biomedical fields, including cardiovascular research. Therefore, in this review, the current literature on the use of OOACs for cardiovascular research is presented with a focus on the basis for using OOACs, and what has been specifically achieved by using OOACs is also discussed. By providing an overview of the current status of OOACs in cardiovascular research and its future perspectives, we hope that this review can help to develop better and optimized research strategies for cardiovascular diseases (CVDs) as well as identify novel applications of OOACs in the near future.

Inflamed adipose tissue: A culprit underlying obesity and heart failure with preserved ejection fraction

The incidence of heart failure with preserved ejection fraction is increasing in patients with obesity, diabetes, hypertension, and in the aging population. However, there is a lack of adequate clinical treatment. Patients with obesity-related heart failure with preserved ejection fraction display unique pathophysiological and phenotypic characteristics, suggesting that obesity could be one of its specific phenotypes. There has been an increasing recognition that overnutrition in obesity causes adipose tissue expansion and local and systemic inflammation, which consequently exacerbates cardiac remodeling and leads to the development of obese heart failure with preserved ejection fraction. Furthermore, overnutrition leads to cellular metabolic reprogramming and activates inflammatory signaling cascades in various cardiac cells, thereby promoting maladaptive cardiac remodeling. Growing evidence indicates that the innate immune response pathway from the NLRP3 inflammasome, to interleukin-1 to interleukin-6, is involved in the generation of obesity-related systemic inflammation and heart failure with preserved ejection fraction. This review established the existence of obese heart failure with preserved ejection fraction based on structural and functional changes, elaborated the inflammation mechanisms of obese heart failure with preserved ejection fraction, proposed that NLRP3 inflammasome activation may play an important role in adiposity-induced inflammation, and summarized the potential therapeutic approaches.

The Use of Hemoglobin-Based Oxygen Carriers in Ex Vivo Machine Perfusion of Donor Organs for Transplantation

There has been significant progress in the development of ex vivo machine perfusion for the nonischemic preservation of donor organs. However, several complications remain, including the logistics of using human blood for graft oxygenation and hemolysis occurring as a result of mechanical technology. Recently, hemoglobin-based oxygen carriers, originally developed for use as blood substitutes, have been studied as an alternative to red blood cell-based perfusates. Although research in this field is somewhat limited, the findings are promising. We offer a brief review of the use of hemoglobin-based oxygen carriers in ex vivo machine perfusion and discuss future directions that will likely have a major impact in progressing oxygen carrier use in clinical practice.

Myocardial oedema: pathophysiological basis and implications for the failing heart

Myocardial fluid homeostasis relies on a complex interplay between microvascular filtration, interstitial hydration, cardiomyocyte water uptake and lymphatic removal. Dysregulation of one or more of these mechanisms may result in myocardial oedema. Interstitial and intracellular fluid accumulation disrupts myocardial architecture, intercellular communication, and metabolic pathways, decreasing contractility and increasing myocardial stiffness. The widespread use of cardiac magnetic resonance enabled the identification of myocardial oedema as a clinically relevant imaging finding with prognostic implications in several types of heart failure. Furthermore, growing experimental evidence has contributed to a better understanding of the physical and molecular interactions in the microvascular barrier, myocardial interstitium and lymphatics and how they might be disrupted in heart failure. In this review, we summarize current knowledge on the factors controlling myocardial water balance in the healthy and failing heart and pinpoint the new potential therapeutic avenues.

The role of AQP3 and AQP4 channels in cisplatin-induced cardiovascular edema and the protective effect of melatonin

BACKGROUND

The present study evaluates the development of edema, the change in the AQP3, AQP4, p53 and Bax gene expressions, and the protective effects of melatonin in rat hearts administered with cisplatin.

METHODS AND RESULTS

A total of 28 Wistar albino rats were divided into four groups. The vehicle was administered intraperitoneally (i.p.) to the rats in the control group. The melatonin group (Mel) received melatonin at a dose of 10 mg/kg for 13 days. The cisplatin group (Cis) received cisplatin on days 1, 5, 9 and 13 at a dose of 4 mg/kg. The rats in the cisplatin + melatonin (Cis+Mel) group underwent the procedures both in the Mel and Cis groups. Blood and left ventricular samples were taken and analyzed on day 14 of the study. AQP3, p53 and Bax gene expressions were found to be significantly increased following cisplatin administration compared to the control, while melatonin administration significantly decreased the expression of these genes (p < 0.05). Melatonin administration also significantly decreased the level of AQP4 gene expression compared to the cis. On histological examination, congestion, hemorrhage, extracellular and intracellular edema, and degenerative changes were significantly more common in the Cis than in the control. Melatonin administration significantly decreased intracellular edema (p = 0.010) and degenerative changes (p = 0.010), and the improvement in extracellular edema was close to statistical significance (p = 0.051) in melatonin.

CONCLUSIONS

These results indicate that melatonin had an ameliorative effect on myocardial edema and AQP channels, and that it may be used as a protective molecule against myocardial edema secondary to cisplatin administration.

Myocardial Edema Revisited in a New Paradigm of Cardiac Electrical Microcurrent Application in Heart Failure

Undisturbed bioelectricity is a prerequisite for normal organ function. This is especially true for organs with high electrical activity such as the heart and the nervous system. Under clinical conditions, however, this can hardly be determined in patients with disturbed organ function and is therefore largely ignored. Here, based on clinical data, we will discuss whether the direct application of an external electric current (in the physiological μA range) together with an electrical field to hearts with impaired pump function can explain the functional improvement of the hearts by edema reduction triggered by electro-osmosis.

Assessing the influence of perfusion on cardiac microtissue maturation: A heart-on-chip platform embedding peristaltic pump capabilities

Heart‐on‐chip is an unprecedented technology for recapitulating key biochemical and biophysical cues in cardiac pathophysiology. Several designs have been proposed to improve its ability to mimic the native tissue and establish it as a reliable research platform. However, despite mimicking one of most vascularized organs, reliable strategies to deliver oxygen and substrates to densely packed constructs of metabolically demanding cells remain unsettled. Herein, we describe a new heart‐on‐chip platform with precise fluid control, integrating an on‐chip peristaltic pump, allowing automated and fine control over flow on channels flanking a 3D cardiac culture. The application of distinct flow rates impacted on temporal dynamics of microtissue structural and transcriptional maturation, improving functional performance. Moreover, a widespread transcriptional response was observed, suggesting flow‐mediated activation of critical pathways of cardiomyocyte structural and functional maturation and inhibition of cardiomyocyte hypoxic injury. In conclusion, the present design represents an important advance in bringing engineered cardiac microtissues closer to the native heart, overcoming traditional bulky off‐chip fluid handling systems, improving microtissue performance, and matching oxygen and energy substrate requirements of metabolically active constructs, avoiding cellular hypoxia. Distinct flow patterns differently impact on microtissue performance and gene expression program.

The evolving cardiac lymphatic vasculature in development, repair and regeneration

The lymphatic vasculature has an essential role in maintaining normal fluid balance in tissues and modulating the inflammatory response to injury or pathogens. Disruption of normal development or function of lymphatic vessels can have severe consequences. In the heart, reduced lymphatic function can lead to myocardial oedema and persistent inflammation. Macrophages, which are phagocytic cells of the innate immune system, contribute to cardiac development and to fibrotic repair and regeneration of cardiac tissue after myocardial infarction. In this Review, we discuss the cardiac lymphatic vasculature with a focus on developments over the past 5 years arising from the study of mammalian and zebrafish model organisms. In addition, we examine the interplay between the cardiac lymphatics and macrophages during fibrotic repair and regeneration after myocardial infarction. Finally, we discuss the therapeutic potential of targeting the cardiac lymphatic network to regulate immune cell content and alleviate inflammation in patients with ischaemic heart disease.

Role of Cardiac Lymphatics in Myocardial Edema and Fibrosis: JACC Review Topic of the Week

The cardiac lymphatic network plays a key role in regulation of myocardial extracellular volume and immune cell homeostasis. In different pathological conditions cardiac lymphatics undergo significant remodeling, with insufficient lymphatic function and/or lymphangiogenesis leading to fluid accumulation and development of edema. Additionally, by modulating the reuptake of tissue-infiltrating immune cells, lymphatics regulate immune responses. Available evidence suggests that both edema and inadequate immune response resolution may contribute to extracellular matrix remodeling and interstitial myocardial fibrosis. Interestingly, stimulation of lymphangiogenesis has been shown to improve cardiac function and reduce the progression of myocardial fibrosis during heart failure development after myocardial infarction. This review goes through the available clinical and experimental data supporting a role for cardiac lymphatics in cardiac disease, focusing on the current evidence linking poor cardiac lymphatic transport to the fibrogenic process and discussing potential avenues for novel biomarkers and therapeutic targets to limit cardiac fibrosis and dysfunction.

The role of the cardiac lymphatic system in the development and progression of heart failure and novel therapeutic approaches for its management in post-infarction cardiac remodeling

Cardiac lymphatic vessels play a vital role in maintaining homeostasis in both physiological and pathological conditions, providing outflow of metabolites. It has been shown that myocardial infarction and postinfarction cardiac remodeling is accompanied by the lymphatic remodeling, which entails functional disorders and is of great importance in heart failure pathogenesis. As a result of progressive myocardial edema, hypoxia and fibrosis of the interstitial space increase, aggravating edema. Other pathways of additional myocardial damage and contractility reduction are triggered. Lymphatic efflux is associated with arrhythmias. Experimental models showed the positive effect of exogenous activation of lymphangiogenesis in relation to the prevention and treatment of heart failure, which can be further used to improve treatment regimens. This review discusses cardiac lymphatic remodeling after myocardial infarction, as well as the pathogenesis of related complications.

Myocardial Fluid Balance and Pathophysiology of Myocardial Edema in Coronary Artery Bypass Grafting

Myocardial edema is one of the most common complications of coronary artery bypass grafting (CABG) that is linearly related to many coronary artery diseases. Myocardial edema can cause several consequences including systolic dysfunction, diastolic dysfunction, arrhythmia, and cardiac tissue fibrosis that can increase mortality in CABG. Understanding myocardial fluid balance and tissue and systemic fluid regulation is crucial in order to ultimately link how coronary artery bypass grafting can cause myocardial edema in such a setting. The identification of susceptible patients by using imaging modalities is still challenging. Future studies about the technique of imaging modalities, examination protocols, prevention, and treatment of myocardial edema should be carried out, in order to limit myocardial edema occurrence and prevent complications.

Microvascular and lymphatic dysfunction in HFpEF and its associated comorbidities

Heart failure with preserved ejection fraction (HFpEF) is a complex heterogeneous disease for which our pathophysiological understanding is still limited and specific prevention and treatment strategies are lacking. HFpEF is characterised by diastolic dysfunction and cardiac remodelling (fibrosis, inflammation, and hypertrophy). Recently, microvascular dysfunction and chronic low-grade inflammation have been proposed to participate in HFpEF development. Furthermore, several recent studies demonstrated the occurrence of generalized lymphatic dysfunction in experimental models of risk factors for HFpEF, including obesity, hypercholesterolaemia, type 2 diabetes mellitus (T2DM), hypertension, and aging. Here, we review the evidence for a combined role of coronary (micro)vascular dysfunction and lymphatic vessel alterations in mediating key pathological steps in HFpEF, including reduced cardiac perfusion, chronic low-grade inflammation, and myocardial oedema, and their impact on cardiac metabolic alterations (oxygen and nutrient supply/demand imbalance), fibrosis, and cardiomyocyte stiffness. We focus primarily on HFpEF caused by metabolic risk factors, such as obesity, T2DM, hypertension, and aging.

A murine model of increased coronary sinus pressure induces myocardial edema with cardiac lymphatic dilation and fibrosis

Myocardial edema is a consequence of many cardiovascular stressors, including myocardial infarction, cardiac bypass surgery, and hypertension. The aim of this study was to establish a murine model of myocardial edema and elucidate the response of cardiac lymphatics and the myocardium. Myocardial edema without infarction was induced in mice by cauterizing the coronary sinus, increasing pressure in the coronary venous system, and inducing myocardial edema. In male mice, there was rapid development of edema 3 h following coronary sinus cauterization (CSC), with associated dilation of cardiac lymphatics. By 24 h, males displayed significant cardiovascular contractile dysfunction. In contrast, female mice exhibited a temporal delay in the formation of myocardial edema, with onset of cardiovascular dysfunction by 24 h. Furthermore, myocardial edema induced a ring of fibrosis around the epicardial surface of the left ventricle in both sexes that included fibroblasts, immune cells, and increased lymphatics. Interestingly, the pattern of fibrosis and the cells that make up the fibrotic epicardial ring differ between sexes. We conclude that a novel surgical model of myocardial edema without infarct was established in mice. Cardiac lymphatics compensated by exhibiting both an acute dilatory and chronic growth response. Transient myocardial edema was sufficient to induce a robust epicardial fibrotic and inflammatory response, with distinct sex differences, which underscores the sex-dependent differences that exist in cardiac vascular physiology.NEW & NOTEWORTHY Myocardial edema is a consequence of many cardiovascular stressors, including myocardial infarction, cardiac bypass surgery, and high blood pressure. Cardiac lymphatics regulate interstitial fluid balance and, in a myocardial infarction model, have been shown to be therapeutically targetable by increasing heart function. Cardiac lymphatics have only rarely been studied in a noninfarct setting in the heart, and so we characterized the first murine model of increased coronary sinus pressure to induce myocardial edema, demonstrating distinct sex differences in the response to myocardial edema. The temporal pattern of myocardial edema induction and resolution is different between males and females, underscoring sex-dependent differences in the response to myocardial edema. This model provides an important platform for future research in cardiovascular and lymphatic fields with the potential to develop therapeutic interventions for many common cardiovascular diseases.

Myocardial edema in paroxysmal permeability disorders: The paradigm of Clarkson's disease

PURPOSE

Paroxysmal Permeability Disorders (PPDs) comprise a variety of diseases characterized by recurrent and transitory increase of endothelial permeability. Idiopathic Systemic Capillary Leak Syndrome (ISCLS) is a rare PPD that leads to an abrupt massive shift of fluids and proteins from the intravascular to the interstitial compartment. In some cases, tissue edema may involve the myocardium, but its role in the development of shock has not been elucidated so far.

MATERIALS AND METHODS

Assessment of cardiac involvement during ten life-threatening ISCLS episodes admitted to ICU.

RESULTS

Transthoracic echocardiographic examination was performed in eight episodes, whereas a poor acoustic window prevented cardiac ultrasound assessment in two episodes. Myocardial edema was detected by echocardiography in eight episodes and marked pericardial effusion in one-episode. Cardiac magnetic resonance showed diffuse myocardial edema in another episode. In one case, myocardial edema caused fulminant left ventricular dysfunction, which required extracorporeal life support. The mean septum thickness was higher during the shock phase compared to the recovery phase [15.5 mm (13.1-21 mm) vs. 9.9 mm (9-11.3 mm), p = .0003]. Myocardial edema resolved within 72 h.

CONCLUSIONS

During early phases of ISCLS, myocardial edema commonly occurs and can induce transient myocardial dysfunction, potentially contributing to the pathogenesis of shock.

Cardiac lymphatics in health and disease

The lymphatic vasculature, which accompanies the blood vasculature in most organs, is indispensable in the maintenance of tissue fluid homeostasis, immune cell trafficking, and nutritional lipid uptake and transport, as well as in reverse cholesterol transport. In this Review, we discuss the physiological role of the lymphatic system in the heart in the maintenance of cardiac health and describe alterations in lymphatic structure and function that occur in cardiovascular pathology, including atherosclerosis and myocardial infarction. We also briefly discuss the role that immune cells might have in the regulation of lymphatic growth (lymphangiogenesis) and function. Finally, we provide examples of how the cardiac lymphatics can be targeted therapeutically to restore lymphatic drainage in the heart to limit myocardial oedema and chronic inflammation.

New insights about the lymphatic vasculature in cardiovascular diseases

The heart contains a complex network of blood and lymphatic vessels. The coronary blood vessels provide the cardiac tissue with oxygen and nutrients and have been the major focus of research for the past few decades. Cardiac lymphatic vessels, which consist of lymphatic capillaries and collecting lymphatic vessels covering all layers of the heart, transport excess fluid from the interstitium and play important roles in maintaining tissue fluid balance. Unlike for the coronary blood vessels, until a few years ago, not much information was available on the origin and function of the cardiac-associated lymphatic vasculature. A growing body of evidence indicates that cardiac lymphatic vessels (lymphatics) may serve as a therapeutic cardiovascular target.

Aquaporin Channels in the Heart-Physiology and Pathophysiology

Mammalian aquaporins (AQPs) are transmembrane channels expressed in a large variety of cells and tissues throughout the body. They are known as water channels, but they also facilitate the transport of small solutes, gasses, and monovalent cations. To date, 13 different AQPs, encoded by the genes AQP0–AQP12, have been identified in mammals, which regulate various important biological functions in kidney, brain, lung, digestive system, eye, and skin. Consequently, dysfunction of AQPs is involved in a wide variety of disorders. AQPs are also present in the heart, even with a specific distribution pattern in cardiomyocytes, but whether their presence is essential for proper (electro)physiological cardiac function has not intensively been studied. This review summarizes recent findings and highlights the involvement of AQPs in normal and pathological cardiac function. We conclude that AQPs are at least implicated in proper cardiac water homeostasis and energy balance as well as heart failure and arsenic cardiotoxicity. However, this review also demonstrates that many effects of cardiac AQPs, especially on excitation-contraction coupling processes, are virtually unexplored.

Acute intramyocardial lipid accumulation in rats does not slow cardiac conduction per se

Diabetic patients suffer from both cardiac lipid accumulation and an increased risk of arrhythmias and sudden cardiac death. This correlation suggests a link between diabetes induced cardiac steatosis and electrical abnormalities, however, the underlying mechanism remains unknown. We previously showed that cardiac conduction velocity slows in Zucker diabetic fatty rats and in fructose-fat fed rats, models that both exhibit prominent cardiac steatosis. The aim of this study was to investigate whether acute cardiac lipid accumulation reduces conduction velocity per se. Cardiac lipid accumulation was induced acutely by perfusing isolated rat hearts with palmitate-glucose buffer, or subacutely by fasting rats overnight. Subsequently, longitudinal cardiac conduction velocity was measured in right ventricular tissue strips, and intramyocardial triglyceride and lipid droplet content was determined by thin layer chromatography and BODIPY staining, respectively. Perfusion with palmitate-glucose buffer significantly increased intramyocardial triglyceride levels compared to perfusion with glucose (2.16 ± 0.17 (n = 10) vs. 0.92 ± 0.33 nmol/mg WW (n = 9), P < 0.01), but the number of lipid droplets was very low in both groups. Fasting of rats, however, resulted in both significantly elevated intramyocardial triglyceride levels compared to fed rats (3.27 ± 0.43 (n = 10) vs. 1.45 ± 0.24 nmol/mg WW (n = 10)), as well as a larger volume of lipid droplets (0.60 ± 0.13 (n = 10) vs. 0.21 ± 0.06% (n = 10), P < 0.05). There was no significant difference in longitudinal conduction velocity between palmitate-glucose perfused and control hearts (0.77 ± 0.025 (n = 10) vs. 0.75 m/sec ± 0.029 (n = 9)), or between fed and fasted rats (0.75 ± 0.042 m/sec (n = 10) vs. 0.79 ± 0.047 (n = 10)). In conclusion, intramyocardial lipid accumulation does not slow cardiac longitudinal conduction velocity per se. This is true for both increased intramyocardial triglyceride content, induced by palmitate-glucose perfusion, and increased intramyocardial triglyceride and lipid droplet content, generated by fasting.

Cardiac Arrhythmias as Manifestations of Nanopathies: An Emerging View

A nanodomain is a collection of proteins localized within a specialized, nanoscale structural environment, which can serve as the functional unit of macroscopic physiologic processes. We are beginning to recognize the key roles of cardiomyocyte nanodomains in essential processes of cardiac physiology such as electrical impulse propagation and excitation–contraction coupling (ECC). There is growing appreciation of nanodomain dysfunction, i.e., nanopathy, as a mechanistic driver of life-threatening arrhythmias in a variety of pathologies. Here, we offer an overview of current research on the role of nanodomains in cardiac physiology with particular emphasis on: (1) sodium channel-rich nanodomains within the intercalated disk that participate in cell-to-cell electrical coupling and (2) dyadic nanodomains located along transverse tubules that participate in ECC. The beat to beat function of cardiomyocytes involves three phases: the action potential, the calcium transient, and mechanical contraction/relaxation. In all these phases, cell-wide function results from the aggregation of the stochastic function of individual proteins. While it has long been known that proteins that exist in close proximity influence each other’s function, it is increasingly appreciated that there exist nanoscale structures that act as functional units of cardiac biophysical phenomena. Termed nanodomains, these structures are collections of proteins, localized within specialized nanoscale structural environments. The nano-environments enable the generation of localized electrical and/or chemical gradients, thereby conferring unique functional properties to these units. Thus, the function of a nanodomain is determined by its protein constituents as well as their local structural environment, adding an additional layer of complexity to cardiac biology and biophysics. However, with the emergence of experimental techniques that allow direct investigation of structure and function at the nanoscale, our understanding of cardiac physiology and pathophysiology at these scales is rapidly advancing. Here, we will discuss the structure and functions of multiple cardiomyocyte nanodomains, and novel strategies that target them for the treatment of cardiac arrhythmias.

Sublingual functional capillary rarefaction in chronic heart failure

BACKGROUND AND OBJECTIVE

Microcirculatory changes contribute to clinical symptoms and disease progression in chronic heart failure (CHF). A depression of coronary flow reserve is associated with a lower myocardial capillary density in biopsies. We hypothesized that changes in cardiac microcirculation might also be reflected by a systemic reduction in capillaries and visualized by sublingual videomicroscopy. The aim was to study in vivo capillary density and glycocalyx dimensions in patients with CHF vs healthy controls.

METHODS

Fifty patients with ischaemic and nonischaemic CHF and standard treatment were compared to 35 healthy age-matched subjects in a prospective cross-sectional study. Sublingual microcirculation was visualized using a sidestream darkfield videomicroscope. Functional and perfused total capillary densities were compared between patients and controls. A reduced glycocalyx thickness was measured by an increased perfused boundary region (PBR).

RESULTS

Median functional and total perfused capillary densities were 30% and 45% lower in patients with CHF (both P < .001). Intake of oral vitamin K antagonists was associated with significantly lower capillary densities (P < .05), but not independent of NT-proBNP. Dimensions of the glycocalyx were marginally lower in CHF patients than in healthy controls (<7% difference). However, PBR correlated significantly with inflammation markers (fibrinogen: r = .58; C-reactive protein: r = .42), platelet counts (r = .36) and inversely with measures of liver/renal function such as bilirubin (r = -.38) or estimated glomerular filtration rate (r = -.34) in CHF patients.

CONCLUSION

CHF patients have got a markedly lower functional and total perfused capillary density in sublingual microvasculature when compared to controls, indicating a systemic decrease in microcirculation.

Cardiac Lymphatic Vessels, Transport, and Healing of the Infarcted Heart

The lymphatic vasculature plays a key role in regulating tissue fluid homeostasis, lipid transport, and immune surveillance throughout the body. Although it has been appreciated that the heart relies on lymphatic vessels to maintain fluid balance and that such balance must be tightly maintained to allow for normal cardiac output, it has only recently come to light that the lymphatic vasculature may serve as a therapeutic target with which to promote optimal healing following myocardial ischemia and infarction. This article reviews the subject of cardiac lymphatic vessels and highlights studies that imply targeting of lymphatic vessel development or transport using vascular endothelial growth factor-C therapy may serve as a promising avenue for future clinical application in the context of ischemic injury.

Histone Deacetylase 1 Inhibition Protects Against Hypoxia-Induced Swelling in H9c2 Cardiomyocytes Through Regulating Cell Stiffness

BACKGROUND

The process of cardiomyocyte swelling involves changes of biomechanical properties and profiles of cellular genes. Although many genes have been proved to regulate cell edema of cardiomyocyte, the mechanisms involved in this event, as well as the biomechanical properties of swelling cell, remain unknown.Methods and Results:Whether histone deacetylase 1 (HDAC1) inhibition protects against hypoxia-induced H9c2 cardiomyocyte swelling is examined in this study. Hypoxia-induced changes in the biomechanical properties and cytoskeletal structure that are relevant to cell swelling were also determined. H9c2 cells were treated under a chemical hypoxia situation (cobalt chloride) with HDAC1 inhibition (chemical inhibitor or siRNA) for 5 h, followed by in vitro biological and mechanical characterization. The results showed that expression of HDAC1 instead of HDAC4 was upregulated by chemical hypoxia. HDAC1 inhibition protects H9c2 cells against chemical hypoxia-induced hypoxic injury and cell swelling. HDAC1 inhibition improved cell viability, decreased lactate dehydrogenase leakage, cell apoptosis, malondialdehyde concentration, cell volume, and particles on the cell surface, and increased superoxide dismutase activity. Moreover, chemical hypoxia induced a decrease of Young's modulus, accompanied by alterations in the integrity of acetylated histone and organization of the cytoskeletal network. HDAC1 inhibition significantly reversed these processes.

CONCLUSIONS

Based on the ideal physical model, HDAC1 inhibition protects against hypoxia-induced swelling in H9c2 cardiomyocytes through enhancing cell stiffness. Overall, HDAC1 is a potential therapeutic target for myocardial edema.

Targeting of Extracellular RNA Reduces Edema Formation and Infarct Size and Improves Survival After Myocardial Infarction in Mice

BACKGROUND

Following myocardial infarction (MI), peri-infarct myocardial edema formation further impairs cardiac function. Extracellular RNA (eRNA) released from injured cells strongly increases vascular permeability. This study aimed to assess the role of eRNA in MI-induced cardiac edema formation, infarct size, cardiac function, and survival after acute MI and to evaluate the therapeutic potential of ribonuclease 1 (RNase-1) treatment as an eRNA-degrading intervention.

METHODS AND RESULTS

C57BL/6J mice were subjected to MI by permanent ligation of the left anterior descending coronary artery. Plasma eRNA levels were significantly increased compared with those in controls starting from 30 minutes after ligation. Systemic application of RNase-1, but not DNase, significantly reduced myocardial edema formation 24 hours after ligation compared with controls. Consequently, eRNA degradation by RNase-1 significantly improved the perfusion of collateral arteries in the border zone of the infarcted myocardium 24 hours after ligation of the left anterior descending coronary artery, as detected by micro-computed tomography imaging. Although there was no significant difference in the area at risk, the area of vital myocardium was markedly larger in mice treated with RNase-1 compared with controls, as detected by Evans blue and 2,3,5-triphenyltetrazolium chloride staining. The increase in viable myocardium was associated with significantly preserved left ventricular function, as assessed by echocardiography. Moreover, RNase-1 significantly improved 8-week survival following MI.

CONCLUSIONS

eRNA is an unrecognized permeability factor in vivo, associated with myocardial edema formation after acute MI. RNase-1 counteracts eRNA-induced edema formation and preserves perfusion of the infarction border zone, reducing infarct size and protecting cardiac function after MI.

Revealing the Concealed Nature of Long-QT Type 3 Syndrome

BACKGROUND

Gain-of-function mutations in the voltage-gated sodium channel (Nav1.5) are associated with the long-QT-3 (LQT3) syndrome. Nav1.5 is densely expressed at the intercalated disk, and narrow intercellular separation can modulate cell-to-cell coupling via extracellular electric fields and depletion of local sodium ion nanodomains. Models predict that significantly decreasing intercellular cleft widths slows conduction because of reduced sodium current driving force, termed "self-attenuation." We tested the novel hypothesis that self-attenuation can "mask" the LQT3 phenotype by reducing the driving force and late sodium current that produces early afterdepolarizations (EADs).

METHODS AND RESULTS

Acute interstitial edema was used to increase intercellular cleft width in isolated guinea pig heart experiments. In a drug-induced LQT3 model, acute interstitial edema exacerbated action potential duration prolongation and produced EADs, in particular, at slow pacing rates. In a computational cardiac tissue model incorporating extracellular electric field coupling, intercellular cleft sodium nanodomains, and LQT3-associated mutant channels, myocytes produced EADs for wide intercellular clefts, whereas for narrow clefts, EADs were suppressed. For both wide and narrow clefts, mutant channels were incompletely inactivated. However, for narrow clefts, late sodium current was reduced via self-attenuation, a protective negative feedback mechanism, masking EADs.

CONCLUSIONS

We demonstrated a novel mechanism leading to the concealing and revealing of EADs in LQT3 models. Simulations predict that this mechanism may operate independent of the specific mutation, suggesting that future therapies could target intercellular cleft separation as a compliment or alternative to sodium channels.

Human Pericardial Fluid Contains Exosomes Enriched with Cardiovascular-Expressed MicroRNAs and Promotes Therapeutic Angiogenesis

The pericardial fluid (PF) is contained in the pericardial sac surrounding the heart. MicroRNA (miRNA) exchange via exosomes (endogenous nanoparticles) contributes to cell-to-cell communication. We investigated the hypotheses that the PF is enriched with miRNAs secreted by the heart and that it mediates vascular responses through exosome exchange of miRNAs. The study was developed using leftover material from aortic valve surgery. We found that in comparison with peripheral plasma, the PF contains exosomes enriched with miRNAs co-expressed in patients' myocardium and vasculature. At a functional level, PF exosomes improved survival, proliferation, and networking of cultured endothelial cells (ECs) and restored the angiogenic capacity of ECs depleted (via Dicer silencing) of their endogenous miRNA content. Moreover, PF exosomes improved post-ischemic blood flow recovery and angiogenesis in mice. Mechanistically, (1) let-7b-5p is proangiogenic and inhibits its target gene, TGFBR1, in ECs; (2) PF exosomes transfer a functional let-7b-5p to ECs, thus reducing their TGFBR1 expression; and (3) let-7b-5p depletion in PF exosomes impairs the angiogenic response to these nanoparticles. Collectively, our data support the concept that PF exosomes orchestrate vascular repair via miRNA transfer.

Intraoperative fluid balance during cardiopulmonary bypass: effects of different mean arterial pressures

Financial support . This study was financially supported by The Western Norway Regional Health Authority, The Norwegian Council on Cardiovascular Diseases, Faculty of Medicine, University of Bergen and The Frank Mohn Foundation, Norway. Introduction. This study investigated whether two levels of mean arterial pressure (MAP) during cardiopulmonary bypass did influence per-operative fluid shifts. Methods. Sixteen pigs underwent 60 minutes of normothermic cardiopulmonary bypass (CPB) followed by 90 minutes of hypothermic CPB. Eight animals had a MAP of 60—80 mmHg by norepinephrine (HP group). Another 8 animals had a MAP of 40—45 mmHg by phentolamine (LP group). Blood chemistry, plasma/interstitial colloid osmotic pressures, plasma volume, fluid balance, fluid extravasation rate and tissue water content were measured or calculated. Results. The plasma volume was significantly lower in the HP group compared with the LP group after 60 minutes of CPB. Net fluid balance was 0.18 (0.05) ml·kg-1·min -1 in the HP group and 0.21 ml·kg- 1·min-1 in the LP group (P > 0.05) while fluid extravasation rate was 1.18 (0.5) and 1.13 (0.4) ml·kg -1·min-1 in the HP group and the LP group during CPB (P > 0.05). Conclusion. Net fluid balance and fluid extravasation rate were similar in the animals with elevated and with lowered MAP during CPB. Perfusion (2007) 22, 273—278.

Investigation of the effects of aging on the expression of aquaporin 1 and aquaporin 4 protein in heart tissue

Objective:

Aquaporin (AQP) 1 and AQP 4 are expressed in human heart and several studies have been focused on these two aquaporins. For this purpose, the present study is aimed to research the effects of aging on AQP 1 and AQP 4 in heart tissue.

Methods:

In this study, 14 Balb/C type white mice were used. Animals were divided into two equal groups. Group I consisted of 2-month-old young animals (n=7), and group II consisted of 18-month-old animals (n=7). To determine the AQP1 and AQP4 expression in the myocardium, the heart tissue was removed to perform western blotting and immunohistochemical and histopathological evaluations.

Results:

Muscle fibers of the heart in aged animals were more irregular and loosely organized in hematoxylin–eosin (H&E) stained sections. H-score analysis revealed that AQP1 and AQP4 immunoreactivity significantly increased in heart tissues of old mice compared with those of young mice (p<0.001). In addition, AQP1 and AQP4 protein expressions in the tissues of old animals were increased significantly according to western blot analysis (p=0.018 and p<0.001 for AQP1 and AQP4, respectively).

Conclusion:

Increased AQP1 and AQP4 levels in the heart tissue may be correlated with the maintenance of water and electrolytes balance, which decreases with aging. In this context, it might be the result of a compensatory response to decreased AQP4 functions. In addition, this increase with aging as demonstrated in our study might be one of the factors that increases the tendency of ischemia in elder people.

Does Roller Pump-Induced Pulsatile CPB Perfusion Affect Microvascular Fluid Shifts and Tissue Perfusion?

BACKGROUND

Pulsatile versus nonpulsatile cardiopulmonary bypass (CPB) perfusion remains debated. Beneficial effects on tissue perfusion, inflammation, and microvascular fluid exchange have been linked to pulsatile perfusion by some investigators and denied by others. This study evaluated fluid extravasation and tissue perfusion during nonpulsatile or pulsatile roller pump-induced CPB perfusion.

METHODS

Fourteen pigs underwent roller pump-induced pulsatile (n = 7) or nonpulsatile CPB perfusion (n = 7) for 90 minutes. Fluid input/losses, colloid osmotic pressures (plasma/interstitium), hematocrit, serum electrolytes, serum proteins, tissue perfusion, and total tissue water content were measured, and plasma volume and fluid extravasation were calculated.

RESULTS

Fluid additions/losses, plasma volume, and fluid extravasation changed similarly in both groups during CPB with no between-group differences. Neither was between-group differences observed for tissue perfusion and total tissue water content, with one exception. Total tissue water content of the right (3.92 ± 0.26 versus 4.32 ± 0.28 g/g dry weight) and left ventricle (4.02 ± 0.25 versus 4.33 ± 0.24 g/g dry weight) was lowered in the pulsatile group.

CONCLUSIONS

No important differences were found between pulsatile and nonpulsatile CPB perfusion for microvascular fluid balance and tissue perfusion.

Selective Stimulation of Cardiac Lymphangiogenesis Reduces Myocardial Edema and Fibrosis Leading to Improved Cardiac Function Following Myocardial Infarction

BACKGROUND

The lymphatic system regulates interstitial tissue fluid balance, and lymphatic malfunction causes edema. The heart has an extensive lymphatic network displaying a dynamic range of lymph flow in physiology. Myocardial edema occurs in many cardiovascular diseases, eg, myocardial infarction (MI) and chronic heart failure, suggesting that cardiac lymphatic transport may be insufficient in pathology. Here, we investigate in rats the impact of MI and subsequent chronic heart failure on the cardiac lymphatic network. Further, we evaluate for the first time the functional effects of selective therapeutic stimulation of cardiac lymphangiogenesis post-MI.

METHODS AND RESULTS

We investigated cardiac lymphatic structure and function in rats with MI induced by either temporary occlusion (n=160) or permanent ligation (n=100) of the left coronary artery. Although MI induced robust, intramyocardial capillary lymphangiogenesis, adverse remodeling of epicardial precollector and collector lymphatics occurred, leading to reduced cardiac lymphatic transport capacity. Consequently, myocardial edema persisted for several months post-MI, extending from the infarct to noninfarcted myocardium. Intramyocardial-targeted delivery of the vascular endothelial growth factor receptor 3-selective designer protein VEGF-CC152S, using albumin-alginate microparticles, accelerated cardiac lymphangiogenesis in a dose-dependent manner and limited precollector remodeling post-MI. As a result, myocardial fluid balance was improved, and cardiac inflammation, fibrosis, and dysfunction were attenuated.

CONCLUSIONS

We show that, despite the endogenous cardiac lymphangiogenic response post-MI, the remodeling and dysfunction of collecting ducts contribute to the development of chronic myocardial edema and inflammation-aggravating cardiac fibrosis and dysfunction. Moreover, our data reveal that therapeutic lymphangiogenesis may be a promising new approach for the treatment of cardiovascular diseases.

Aquaporin-1 Deficiency Protects Against Myocardial Infarction by Reducing Both Edema and Apoptosis in Mice

Many studies have determined that AQP1 plays an important role in edema formation and resolution in various tissues via water transport across the cell membrane. The aim of this research was to determine both if and how AQP1 is associated with cardiac ischemic injury, particularly the development of edema following myocardial infarction (MI). AQP1^+/+ and AQP1^−/− mice were used to create the MI model. Under physiological conditions, AQP1^−/− mice develop normally; however, in the setting of MI, they exhibit cardioprotective properties, as shown by reduced cardiac infarct size determined via NBT staining, improved cardiac function determined via left ventricular catheter measurements, decreased AQP1-dependent myocardial edema determined via water content assays, and decreased apoptosis determined via TUNEL analysis. Cardiac ischemia caused by hypoxia secondary to AQP1 deficiency stabilized the expression of HIF-1α in endothelial cells and subsequently decreased microvascular permeability, resulting in the development of edema. The AQP1-dependent myocardial edema and apoptosis contributed to the development of MI. AQP1 deficiency protected cardiac function from ischemic injury following MI. Furthermore, AQP1 deficiency reduced microvascular permeability via the stabilization of HIF-1α levels in endothelial cells and decreased cellular apoptosis following MI.

Esmolol added in repeated, cold, oxygenated blood cardioplegia improves myocardial function after cardiopulmonary bypass

OBJECTIVE

This study investigated if the β-receptor blocking agent esmolol, added to standard oxygenated blood cardioplegia, improved myocardial function after weaning from bypass.

DESIGN

A block-randomized, blinded study.

SETTING

A university laboratory.

PARTICIPANTS

Twenty anesthetized pigs, Norwegian Landrace.

INTERVENTIONS

After cardiopulmonary bypass, cardiac arrest was induced with cold (12°C), oxygenated blood cardioplegia, enriched with either esmolol or vehicle, repeated every 20 minutes. After 100 minutes the heart was reperfused and weaned.

MEASUREMENTS AND MAIN RESULTS

Left ventricular function was evaluated with pressure-volume loops, local myocardial function with multilayer strain and strain rate by epicardial short-axis tissue Doppler imaging. One hour after declamping, preload recruitable stroke work did not differ between groups, but increased to 72±3 mmHg in esmolol-treated animals v 57±4 mmHg (p<0.001) in controls after 3 hours. Radial peak ejection strain rate also was increased by esmolol; 6.0±1.0 s(-1)v 2.9±0.3 s(-1) (p<0.001) in subendocardium and 3.9±0.5 s(-1)v 2.3±0.2 s(-1) (p<0.005) in the midmyocardium. Cardiac index was increased, 4.0±0.2 L/min/m(2) by esmolol v 3.3±0.1 L/min/m(2) for controls (p<0.05). Isovolumetric relaxation time constant was reduced by esmolol, 23±1 ms v 26±1 ms (p<0.025). Troponin-T did not differ and was 339±48 ng/L for the esmolol group and 357±55 ng/L for the control group (p = 0.81).

CONCLUSIONS

Esmolol added to blood cardioplegia preserved systolic cardiac function during the first 3 hours after reperfusion in a porcine model with 100 minutes of cardioplegic arrest.

Cardioplegia at subnormothermia facilitates rapid functional resuscitation of hearts preserved in SOMAH for transplants

Objectives

Hearts preserved ex vivo at 4°C undergo time-dependent irreversible injury due to extreme hypothermia. Studies using novel organ preservative solution SOMAH, suggest that hearts are optimally `preserved' at subnormothermic temperature of 21°C. Present study evaluates relative efficacy of SOMAH `cardioplegia' at 4 and 21°C in preservation of optimum heart function after in vitro storage at subnormothermia.

Methods

Porcine hearts arrested with SOMAH cardioplegia at 4 or 21°C were stored in SOMAH for 5-hour at 21°C (n = 5). At the end of storage, the weight of hearts was recorded and biopsies taken for cardiac tissue high energy phosphate level measurements. The hearts were then attached to a reperfusion apparatus and biochemical parameters including cardiac enzyme release and myocardial oxygen consumption and lactate production were determined in perfusate samples at regular intervals during ex vivo perfusion experiment. Functional evaluation of the hearts intraoperatively and ex vivo was performed by 2D echocardiography using trans-esophageal echocardiography probe.

Results

Post-storage heart weights were unaltered in both groups, while available high-energy phosphates (HEP) were greater in the 21°C group. Upon ex vivo reperfusion, coronary flow was significantly greater (p < 0.05) in 21°C group. 2D echo revealed a greater cardiac output, fractional area change and ejection fraction in 21°C group that was not significantly different than the 4°C group. However, unlike 4°C hearts, 21°C hearts did not require inotropic intervention. Upon reperfusion, rate of cardiac enzyme release temporally resolved in 21°C group, but not in the 4°C group. 21°C working hearts maintained their energy state during the experimental duration but not the 4°C group; albeit, both groups demonstrated robust metabolism and function during this period.

Conclusions

Rapid metabolic switch, increased synthesis of HEP, decreased injury and optimal function provides evidence that hearts arrested at 21°C remain viably and functionally superior to those arrested at 4°C when stored in SOMAH at ambient temperature pre-transplant.

Ultramini-abstract

Cardioplegic arrest and preservation of hearts in SOMAH at ambient temperature efficiently conserves metabolism and function in in vitro porcine model of heart transplant.

Electronic supplementary material

The online version of this article (doi:10.1186/s13019-014-0155-z) contains supplementary material, which is available to authorized users.

Ephaptic coupling in cardiac myocytes

While it is widely believed that conduction in cardiac tissue is regulated by gap junctions, recent experimental evidence suggests that the extracellular space may play a significant role in action potential propagation. Cardiac tissue with low gap junctional coupling still exhibits conduction, with conflicting degrees of slowing that may be due to variations in the extracellular space. Inhomogeneities in the extracellular space caused by the complex cellular structure in cardiac tissue can lead to ephaptic, or field effect, coupling. Here, we present data from simulations of a cylindrical strand of cells in which we see the dramatic effect highly resistant extracellular spaces have on propagation velocity. We find that ephaptic effects occur in all areas of small extracellular spaces and are not restricted to the junctional cleft between cells. This previously unrecognized type of field coupling, which we call lateral coupling, can allow conduction in the absence of gap junctions. We compare our results with the classically used cable theory, demonstrating the quantitative difference in propagation velocity arising from the cellular geometry. Ephaptic effects are shown to be highly dependent upon parameter values, frequently enhancing, but sometimes decreasing propagation speed. Our mathematical analysis incorporates the inhomogeneities in the extracellular microdomains that cannot be directly measured by experimental techniques and will aid in optimizing cardiac treatments that require manipulation of the cellular geometry and understanding heart functionality.

Cardiac aquaporins

Aquaporins are a group of proteins with high-selective permeability for water. A subgroup called aquaglyceroporins is also permeable to glycerol, urea and a few other solutes. Aquaporin function has mainly been studied in the brain, kidney, glands and skeletal muscle, while the information about aquaporins in the heart is still scarce. The current review explores the recent advances in this field, bringing aquaporins into focus in the context of myocardial ischemia, reperfusion, and blood osmolarity disturbances. Since the amount of data on aquaporins in the heart is still limited, examples and comparisons from better-studied areas of aquaporin biology have been used. The human heart expresses aquaporin-1, -3, -4 and -7 at the protein level. The potential roles of aquaporins in the heart are discussed, and some general phenomena that the myocardial aquaporins share with aquaporins in other organs are elaborated. Cardiac aquaporin-1 is mostly distributed in the microvasculature. Its main role is transcellular water flux across the endothelial membranes. Aquaporin-4 is expressed in myocytes, both in cardiac and in skeletal muscle. In addition to water flux, its function is connected to the calcium signaling machinery. It may play a role in ischemia-reperfusion injury. Aquaglyceroporins, especially aquaporin-7, may serve as a novel pathway for nutrient delivery into the heart. They also mediate toxicity of various poisons. Aquaporins cannot influence permeability by gating, therefore, their function is regulated by changes of expression-on the levels of transcription, translation (by microRNAs), post-translational modification, membrane trafficking, ubiquitination and subsequent degradation. Studies using mice genetically deficient for aquaporins have shown rather modest changes in the heart. However, they might still prove to be attractive targets for therapy directed to reduce myocardial edema and injury caused by ischemia and reperfusion.

Human aquaporins: regulators of transcellular water flow

BACKGROUND

Emerging evidence supports the view that (AQP) aquaporin water channels are regulators of transcellular water flow. Consistent with their expression in most tissues, AQPs are associated with diverse physiological and pathophysiological processes.

SCOPE OF REVIEW

AQP knockout studies suggest that the regulatory role of AQPs, rather than their action as passive channels, is their critical function. Transport through all AQPs occurs by a common passive mechanism, but their regulation and cellular distribution varies significantly depending on cell and tissue type; the role of AQPs in cell volume regulation (CVR) is particularly notable. This review examines the regulatory role of AQPs in transcellular water flow, especially in CVR. We focus on key systems of the human body, encompassing processes as diverse as urine concentration in the kidney to clearance of brain oedema.

MAJOR CONCLUSIONS

AQPs are crucial for the regulation of water homeostasis, providing selective pores for the rapid movement of water across diverse cell membranes and playing regulatory roles in CVR. Gating mechanisms have been proposed for human AQPs, but have only been reported for plant and microbial AQPs. Consequently, it is likely that the distribution and abundance of AQPs in a particular membrane is the determinant of membrane water permeability and a regulator of transcellular water flow.

GENERAL SIGNIFICANCE

Elucidating the mechanisms that regulate transcellular water flow will improve our understanding of the human body in health and disease. The central role of specific AQPs in regulating water homeostasis will provide routes to a range of novel therapies. This article is part of a Special Issue entitled Aquaporins.