Immunological modulation of human cardiac mast cells

Histamine receptors in heart failure

The biogenic amine, histamine, is found predominantly in mast cells, as well as specific histaminergic neurons. Histamine exerts its many and varied actions via four G-protein-coupled receptors numbered one through four. Histamine has multiple effects on cardiac physiology, mainly via the histamine 1 and 2 receptors, which on a simplified level have opposing effects on heart rate, force of contraction, and coronary vasculature function. In heart failure, the actions of the histamine receptors are complex, the histamine 1 receptor appears to have detrimental actions predominantly in the coronary vasculature, while the histamine 2 receptor mediates adverse effects on cardiac remodeling via actions on cardiomyocytes, fibroblasts, and even endothelial cells. Conversely, there is growing evidence that the histamine 3 receptor exerts protective actions when activated. Little is known about the histamine 4 receptor in heart failure. Targeting histamine receptors as a therapeutic approach for heart failure is an important area of investigation given the over-the-counter access to many compounds targeting these receptors, and thus the relatively straight forward possibility of drug repurposing. In this review, we briefly describe histamine receptor signaling and the actions of each histamine receptor in normal cardiac physiology, before describing in more detail the known role of each histamine receptor in adverse cardiac remodeling and heart failure. This includes information from both clinical studies and experimental animal models. It is the goal of this review article to bring more focus to the possibility of targeting histamine receptors as therapy for heart failure.

The emerging prominence of the cardiac mast cell as a potent mediator of adverse myocardial remodeling

Cardiac mast cells store and release a variety of biologically active mediators, several of which have been implicated in the activation of matrix metalloproteinases in the volume-overloaded heart, while others are involved in the fibrotic process in pressure-overloaded hearts. Increased numbers of mast cells have been reported in explanted human hearts with dilated cardiomyopathy and in animal models of experimentally induced hypertension, myocardial infarction, and chronic cardiac volume overload. Also, there is evolving evidence implicating the cardiac mast cell as having a major role in the adverse remodeling underlying these cardiovascular disorders. Thus, the cardiac mast cell is the focus of this chapter that begins with a historical background, followed by sections on methods for their isolation and characterization, endogenous secretagogues, phenotype, and ability of estrogen to alter their phenotype so as to provide cardioprotection. Finally the role of mast cells in myocardial remodeling secondary to a sustained cardiac volume overload, hypertension, and ischemic injury and future research directions are discussed.

Human heart as a shock organ in anaphylaxis

Anaphylaxis is a potentially fatal, immediate hypersensitivity reaction. Mast cells and basophils, by elaborating vasoactive mediators and cytokines, are the main primary effector cells of anaphylaxis. Mast cells have been identified in human heart between myocardial fibers, perivascularly, in the adventitia, and in the arterial intima. Mast cells isolated from human heart tissue (HHMC) of patients undergoing cardiac transplantation express high affinity immunglobulin E (IgE) receptors (FcεRI), C3a, C5a, and kit receptors (KIT). Anti-IgE, anti-FcεRI, and immunoglobulin superallergens induce in vitro secretion of preformed mediators (histamine, tryptase, chymase, and renin) and the de novo synthesis of cysteinyl leukotriene C4 (LTC4) and prostaglandin D2 (PGD2) from HHMC. Complement is activated and anaphylatoxin forms during anaphylaxis. C5a and C3a cause the in vitro release of histamine and tryptase from HHMC. Therapeutic (general anesthetics, protamine, etc.) and diagnostic agents (radio contrast media, etc.), which can cause anaphylactoid reactions, activate HHMC in vitro. Low concentrations of histamine and cysteinyl leukotrienes given to subjects undergoing diagnostic catheterisation caused significant systemic and coronary hemodynamic effects. These data indicate that human heart mast cells and their mediators play a role in severe anaphylactic reactions.

Deficiency of mast cells in coronary artery endarterectomy of male patients with type 2 diabetes

Background

Type 2 diabetes is an important risk factor for the development of coronary artery disease (CAD). Focal or diffuse inflammation is often present in the vessels of patients with CAD. Mast cells are frequently present in the plaques as well as in the inflammatory infiltrates in the atherosclerotic vessel wall. In the study we wanted to examine whether there are differences in the morphology, number and distribution of mast cells and in their ability to modify the atherosclerotic process in coronary arteries (CA) in the diabetic vs. the hypertensive population of patients with CAD.

Methods

Coronary artery endarterectomy specimens were obtained from patients with diabetes or hypertension as the only risk factor for CAD. The specimens were stained with haematoxylin-eosin and Sulphated Alcian Blue for mast cells and with immunofluorescent methods for fibrinogen-fibrin and IgG deposits in the vessel wall. Both morphological and stereological assessments were conducted for mast cells and mononuclear cell infiltrates.

Results

The histological analysis of the vessel wall of diabetic patients in comparison with hypertensive patients showed a damaged endothelial cells layer and deposits of fibrin-fibrinogen and IgG in the tunica intima and media. The stereological count revealed a diminished numerical density of mast cells and a significantly higher volume density of the mononuclear cells. Mast cells displayed cytoplasmic vacuolization, extracellular extrusion of granule and pyknotic nuclei.

Conclusion

This preliminary study suggests that the impaired mast cells might be the reason for more extensive inflammatory and immunologic atherosclerotic changes in the CA vessel wall of CAD patients with type 2 diabetes.

Trial registration

134/88;C3-0564-381-92

Ventricular fibrillation after a hymenoptera sting

A 54-year-old male, who had presented 2 ventricular fibrillation (VF) episodes with post-anoxic coma and later a return to consciousness and to a sinusal rhythm after defibrillation, have been placed a ventricular intracavitary stimulator (AICD). Since all the tests including the coronarygraphy have been found normal, we have paid attention to the anamnesis revealing an Apis mellifera sting before both VF episodes, previously considered irrelevant for the absence of relevant local symptoms. Intracutaneous tests were negative to Vespula sp. and positive to A. mellifera extract at a concentration of 0.01 mug/ml. Specific IgE for A. mellifera venom presented values of 2,36 U/ml for A. mellifera and <0.35 U/ml per Vespula sp. and Polistes dominulus. The patient was then submitted to ITS with A. mellifera aqueous extract. During the RASH treatment no adverse reactions have been observed, whereas we witnessed a major adverse reaction, 3 min after the first 100 mcg maintenance dose, controlled with anti-H1 and cortisone reaction, nevertheless no reactions were observed during the 3 years the same dosage has been repeated monthly. Our case supports the hypothesis of an anaphylactic reaction as trigger of vasoconstriction in individuals affected by ventricular arrhythmia not explained with other causes such as a coronary disease, a myocardiopathy or a pharmacological toxicity. Arrhythmia can be a serious outbreak of a mediated IgE allergic reaction even without any relevant local symptoms. The diagnostics with lyophilized A. mellifera venom has been proven safe in a patient who suffered a cardiac anaphylaxis.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Inflammation in variant angina: Is there any evidence?

Variant angina, defined as spontaneous angina pectoris associated with transient ST-segment elevation, has proved to be caused usually by episodic coronary spasm since Prinzmetal and his associates described a form of angina quite different from classic Heberden angina pectoris in 1959. Currently, coronary artery spasm is defined as reversible coronary stenosis, which limits coronary blood flow under resting conditions, and it plays an important role in ischemic heart disease, particularly in variant angina. Data available in respect of coronary vasospasm showed that it is closely related to atherosclerotic coronary artery disease, since intravascular ultrasound studies reveal atherosclerotic plaques in almost any spastic segment. Risk factors for coronary artery disease and coronary vasospasm, however, differ profoundly. Cigarette smoking is the only established risk factor. Although several candidates and predisposing factors, such as serotonin, histamine, thromboxane, and endothelin, have been described, the mediators and the pathogenesis of the disease remain unknown. There are abundant studies that inflammation plays an important role in the initiation, development as well as evolution of atherosclerosis, suggesting that atherosclerosis is an inflammation disease. The evidence regarding the role of inflammatory pathways in different clinical entities of coronary artery disease has significantly been accumulated. And also, primary studies have showed that inflammation may be a contributor for variant angina or vasospastic coronary disease is at least partially driven by inflammation. Although much more research is obviously needed, primary evidence provide us with some direction for that research.

Preformed angiotensin II is present in human mast cells

PURPOSE

The density of mast cells increases in the myocardium of patients suffering from heart failure. However, their function remains unclear. In this study, preformed angiotensin II (ANG II), a potent growth factor, was found to be contained in, and released by, human mast cells.

METHODS

The human mast cell line (HMC-1) was incubated with 0 to 10(-6) M calcitonin gene-related peptide (CGRP) or culture medium. The expression of renin-angiotensin system mRNA was examined using RT-PCR analysis. ELISA and immunohistochemistry with monoclonal antibody against human ANG II were performed to detect the presence of ANG II in HMC-1. The effect of CGRP on the expression of angiotensinogen mRNA was examined by quantitative RT-PCR analysis.

RESULTS

Preformed ANG II was detected in a human mast cell line (HMC-1) which is a neoplastic cell line of mast cells by ELISA and immunohistochemistry. Presence of mRNA of angiotensinogen and renin was confirmed by polymerase chain reaction in HMC-1, while mRNA of angiotensin converting enzyme (ACE) was undetectable. Since myocardial mast cells are interfaced with nerve fibers and functionally associated with CGRP, the effect of CGRP on ANG II release from HMC-1 was examined. CGRP induced the release of ANG II and increased angiotensinogen mRNA in HMC-1.

CONCLUSIONS

The presence of preformed ANG II and gene expression of the renin-angiotensin system were detected in human mast cells. The release and synthesis of ANG II in mast cells was regulated by CGRP.

Shortness of Breath, Syncope, and Cardiac Arrest Caused by Systemic Mastocytosis

During a 3-month period, a 33-year-old man presented to the emergency department on 4 occasions with dyspnea, palpitations, and syncope. His initial presentation was accompanied by acute myocardial injury and ventricular fibrillation. An extensive evaluation spanned the 3 months and included echocardiography, cardiac catheterization, electrophysiology study, tilt-table evaluation, pulmonary angiography, electroencephalography, and serum and urine analysis. Diagnosis eluded clinicians until a rash was recognized to be urticaria pigmentosa, and biopsy of the rash then implicated mastocytosis. Since the initiation of pharmacotherapy nearly 5 years ago, the patient has remained asymptomatic. This case demonstrates that systemic mastocytosis can present as recurrent syncope and even as cardiac arrest. Diagnosis of this rare but potentially fatal disease is made particularly challenging by its protean manifestations.

Utilization of serum tryptase and immunoglobulin e assay in the postmortem diagnosis of anaphylaxis

The postmortem diagnosis of anaphylaxis is difficult. Serum concentrations of tryptase (a mast cell product released during anaphylaxis) have been used after death as an indicator of possible antemortem anaphylaxis. However, studies have indicated that tryptase may be elevated with increasing postmortem interval (PMI), or in nonanaphylactic deaths with significant atherosclerosis or chest trauma. Serum total IgE has been used by some to confirm anaphylaxis when tryptase is elevated. Serum levels of tryptase from 57 decedents with varying PMI, all dying of presumed nonanaphylactic causes, were determined. In cases with elevated levels (>11.4 ng/mL), an assay of total serum IgE was also performed. Both tryptase and IgE demonstrated significant elevations with increasing PMI. Decedents were categorized according to presence of cardiovascular disease, chest trauma, or both; many demonstrated elevation of 1 or both markers, without statistically significant differences between categories. Postulated mechanisms for nonanaphylactic elevations of these markers are reviewed. The possible utility of allergen-specific IgE or allergen panels is discussed.

The histamine-cytokine network in allergic inflammation

Histamine is synthesized and released by human basophils, mast cells, and neurons. Its pleiotropic effects are mediated by the activation of 4 receptors: H(1), H(2), H(3), and H(4). With the advent of selective antagonists (the antihistamines widely used to treat allergic disorders), the H(1)-receptor was the first member of the receptor family to be pharmacologically defined. Increasing evidence indicates that, in addition to exerting immediate vascular and bronchial responses, histamine might modulate the immune reaction by interacting with T cells, macrophages, basophils, eosinophils, and monocytes. We have shown that, in vitro, histamine induces a concentration-dependent release of IL-6 and beta-glucuronidase from macrophages isolated from the human lung parenchyma. These effects are inhibited by fexofenadine, an H(1)-receptor antagonist, but not by ranitidine, an H(2)-receptor antagonist. This observation raises the possibility that long-term treatment with fexofenadine might have beneficial effects on immune dysregulation and tissue damage/remodeling associated with histamine-mediated macrophage activation.

Increased Chymase in Livers with Autoimmune Disease: Colocalization with Fibrosis

Chymase, one of the proteases contained in human mast cells, promotes myocardial and renal interstitial fibrosis by converting angiotensin I to II (AII). We previously established a method for measuring chymase in liver tissue and examined the relationship between chymase and fibrosis in chronic hepatitis. In the present study, chymase was determined in liver specimens affected by autoimmune hepatitis (AIH, n=10) or primary biliary cirrhosis (PBC, n=12). To investigate spatial relationships between hepatic fibrosis and human chymase, mast cell distribution in the specimens was determined immunohistochemically using anti-chymase antibody. The mean amounts of chymase in livers with AIH and PBC were 11.56+/-10.64 and 11.67+/-9.96 ng/mg respectively. Hepatic chymase in AIH and PBC was significantly more abundant than in acute hepatitis (AH, 2.72+/-2.23 ng/mg, n=10; p<0.05). When sections from patients with AIH and PBC were immunostained for chymase, immunoreactive mast cells were detected in portal areas and sinusoidal walls, coinciding with zones of fibrosis. Thus chymase appears to be involved in hepatic fibrosis in AIH and PBC.