IgE-mediated activation of human heart in vitro

Functional assessment of the right ventricle in patients with bronchial asthma of various severity

INTRODUCTION

Pulmonary artery hypertension and its consequences still constitutes an underestimated clinical problem in asthma patients and its non-invasive early detection may influence proper treatment.

AIM

To non-invasively examine the pulmonary artery flow parameters and right ventricular function in patients with asthma of various severity.

MATERIAL AND METHODS

The analysis of parameters of echocardiography and first-pass and gated radionuclide angiography, and baseline examination in 31 patients with bronchial asthma and 16 healthy controls.

RESULTS

Patients with severe asthma had higher mean pulmonary artery pressure (MPAP) compared to the healthy controls. The subgroup analysis of patients who suffered from asthma in their childhood showed that individuals with severe asthma were characterized by significantly higher MPAP than those with the mild/moderate condition (19.16 ±7.51 mm Hg vs. 5.0 ±1.15 mm Hg, p = 0.025). Gated, but not first-pass, radionuclide angiography revealed that individuals with severe asthma were characterized by a lower right ventricular ejection fraction (RVEF). Further analysis of the subgroup of patients in whom the initial manifestation of dyspnoea occurred no earlier than 6 years prior to the study showed that the RVEF of individuals with severe asthma was significantly lower compared to those with mild/moderate asthma (39.8 ±4.79% vs. 51.4 ±8.65%, p = 0.019).

CONCLUSIONS

The pulmonary artery pressure in patients with severe asthma is significantly higher than in healthy individuals; in contrast, these two groups did not differ significantly in terms of the right ventricular echocardiographic characteristics. Gated radionuclide angiography, but not the first-pass technique, allowed for the detection of subtle right ventricular ejection fraction changes in asthma patients.

Mast Cells: Key Contributors to Cardiac Fibrosis

Historically, increased numbers of mast cells have been associated with fibrosis in numerous cardiac pathologies, implicating mast cells in the development of cardiac fibrosis. Subsequently, several approaches have been utilised to demonstrate a causal role for mast cells in animal models of cardiac fibrosis including mast cell stabilising compounds, rodents deficient in mast cells, and inhibition of the actions of mast cell-specific proteases such as chymase and tryptase. Whilst most evidence supports a pro-fibrotic role for mast cells, there is evidence that in some settings these cells can oppose fibrosis. A major gap in our current understanding of cardiac mast cell function is identification of the stimuli that activate these cells causing them to promote a pro-fibrotic environment. This review will present the evidence linking mast cells to cardiac fibrosis, as well as discuss the major questions that remain in understanding how mast cells contribute to cardiac fibrosis.

Mast cells in ongoing acute rejection: increase in number and expression of a different phenotype in rat heart transplants

BACKGROUND

Mast cells (MC) are resident in healthy hearts and play important physiological and pathophysiological roles. In the transplanted heart, correlations have been found between MC number and the severity of rejection episodes, the intensity of chronic inflammation, and allograft arteriosclerotic changes. However, not much emphasis has been placed on the fact that resident donor MC, and infiltrating recipient MC do not forcedly need to share the same properties and function. To gain insight in the role of cardiac MC during acute, and ongoing acute rejection of heart transplants, we investigated MC kinetics and MC phenotype in a rat heart transplantation model.

METHODS

Donor hearts from female Brown-Norway rats were transplanted to male Lewis rats. Immunosuppression was started at day 5 using ciclosporin and prednisolone. Connective tissue type MC (CTMC) were distinguished from mucosa type MC (MMC) by immunohistochemistry for rat MC protease (RMCP) -1 and -2. Expression of RMCP-1 and -2 mRNA was quantified by real time reverse transcription-polymerase chain reaction. Infiltrating Y chromosome positive MC were detected by fluorescence in situ hybridization. mRNA expression of interleukin-3 (IL-3) and of the two differentially spliced isoforms of kit ligand (KL, stem cell factor) was quantified using reverse transcription-polymerase chain reaction.

RESULTS

Resident cardiac donor MC are almost exclusively CTMC and decrease in number during acute rejection. MC increase in number, and recipient MC invade the cardiac allograft during ongoing acute rejection. The phenotype of the invading MC is characterized by the expression of RMCP-2, or both RMCP-1 and RMCP-2, and thus resemble a MMC type. IL-3 mRNA is highly expressed, and the ratio of the differentially spliced mRNAs for KL-1 and KL-2 rises up to 2-fold during ongoing acute rejection.

CONCLUSIONS

Our data show that MC in posttransplant hearts during ongoing acute rejection differ from MC in healthy hearts and isografts by expressing a different phenotype. Changes in IL-3 and KL expression might be responsible for the predominance of MMC over CTMC. The notion is of importance that MC in cardiac allografts may have properties and functions that differ from those in nontransplanted healthy hearts.

Immunological modulation of human cardiac mast cells

Human mast cells, by elaborating various cytokines, chemokines and proinflammatory mediators play a complex role in several allergic and inflammatory disorders. Mast cells have been identified in human heart tissue in close proximity to the sarcolemma, in perivascular and adventitial locations and in the shoulder region of coronary atheroma. Human heart mast cells (HHMC) can be isolated from patients undergoing heart transplantation and can be immunologically activated in vitro to induce the release of tryptase, chymase, cysteinyl leukotriene C4 and prostaglandin D2. Several cytokines (e.g., stem cell factor and TNF-alpha) reside in secretory granules of HHMC. Mast cell density is increased in the hearts of patients with ischemic and idiopathic dilated cardiomyopathy. Cardiac mast cells might contribute to the evolution of atherosclerosis, dilated cardiomyopathy, cardiac and systemic anaphylaxis through the release of cytokines and vasoactive and proinflammatory mediators.

Stem cell factor in mast cells and increased mast cell density in idiopathic and ischemic cardiomyopathy

BACKGROUND

We compared cardiac mast cell (HHMC) density and the immunological and nonimmunological release of mediators from mast cells isolated from heart tissue of patients with idiopathic dilated (DCM) (n=24) and ischemic cardiomyopathy (ICM) (n = 10) undergoing heart transplantation and from control subjects (n = 10) without cardiovascular disease.

METHODS AND RESULTS

HHMC density in DCM (18.4+/-1.6 cells/mm2) and ICM (18.4+/-1.5 cells/mm2) was higher than that in control hearts (5.3+/-0.7 cells/mm2; P<.01). The histamine and tryptase contents of DCM and ICM hearts were higher than those of control hearts. The histamine content of the hearts was correlated with mast cell density (r(s)=.91; P<.001). Protein A/gold staining of heart tissue revealed stem cell factor (SCF), the principal growth, differentiating, and activating factor of human mast cells, in HHMC secretory granules. Histamine release from cardiac mast cells caused by immunological (anti-IgE and rhSCF) and nonimmunological stimuli (Ca2+ ionophore A23187) was higher in patients with DCM and ICM compared with control subjects. Immunological activation of HHMC induced a significantly greater release of tryptase and LTC4 in patients with DCM and ICM compared with control subjects.

CONCLUSIONS

Histamine and tryptase content and mast cell density are higher in failing hearts than in control hearts. SCF, present in secretory granules of HHMC, might represent an autocrine factor sustaining mast cell hyperplasia in heart tissue in these patients. The increased local release of fibrogenic factors (eg, histamine, tryptase, and leukotriene C4) might contribute to collagen accumulation in the hearts of patients with cardiomyopathy.

Metabolic and hemodynamic effects of peptide leukotriene C4 and D4 in man

The time course of the effects of intravenous or intracoronary administration of peptide leukotrienes on metabolic parameters and on systemic and coronary hemodynamics was evaluated in 15 patients with normal coronary arteries. Peptide leukotriene C4 (2 nmol given as a bolus intravenous injection) induced an early fall (at 2 min) in mean arterial pressure (P < 0.02) associated with a rise in heart rate (P < 0.001) and in plasma levels of epinephrine (P < 0.05) and norepinephrine (P < 0.005), but without significant changes in coronary blood flow or coronary vascular resistance. Mean arterial pressure, heart rate, norepinephrine, and epinephrine returned to baseline values 10 min after leukotriene C4 administration. In contrast, at 10 min post leukotriene C4, with coronary blood flow and myocardial oxygen consumption unchanged, an increase in coronary vascular resistance (P < 0.05) and in myocardial oxygen extraction (P < 0.01) was observed, which returned to baseline values at 20 min post leukotriene C4. Peptide leukotriene D4 (3 nmol, given in the left coronary artery) induced an early (20 s) and transient fall in mean arterial pressure (P < 0.001) paralleled by a rise in heart rate and plasma levels of epinephrine and norepinephrine, all of which returned to baseline at 10 min. Coronary vascular resistance increased at 10 and 15 min (P < 0.02 and P < 0.05, respectively) and myocardial oxygen extraction at 15 min (P < 0.02). These results suggest that small doses of peptide leukotrienes induce both an early and transient fall in mean arterial pressure associated with secondary sympathoadrenergic activation, and a late increase in small coronary arteriolar resistance.

Immunological characterization and functional importance of human heart mast cells

Mast cells are present in normal and even more abundant in diseased human heart tissue and their localization is of particular relevance to their function. Within heart tissue mast cells lie between myocytes and in close contact with blood vessels. They are also found in the coronary adventitia and in the shoulder regions of a coronary atheroma. The density of cardiac mast cells is markedly higher in some patients with myocarditis and dilated cardiomyopathy than in accident victims without cardiovascular diseases. More importantly, in some of these conditions there is in situ evidence of mast cell activation. We have described an original technique to isolate and purify HHMC for in vitro study. This procedure gives viable cells and after stimulation with immunological or non-immunological stimuli they release performed (histamine and tryptase) and newly generated mediators (PGD2 and LTC4). We have demonstrated that HHMC differ from those in other anatomical districts in that they are activated by specific immunological and non-immunological stimuli, and in their relation to the arachidonic acid metabolism, suggesting that the local microenvironment can influence their phenotypic and biochemical characteristics. Our own and other findings suggest that HHMC have complex and significant roles in different pathophysiological conditions involving the cardiovascular system. Direct activation of HHMC by therapeutic and diagnostic substances injected intravenously explains some of the anaphylactoid reactions caused by these agents. HHMC possess Fc epsilon RI and IgE bound to the surface and C5a receptors, which could explain how cardiac mast cells are involved in systemic and cardiac anaphylaxis. Cardiac mast cells and those in human coronary arteries also play a role in the early and late stages of atherogenesis and during ischemic myocardial injury. In conclusion, although studies of HHMC are in their infancy, their in vitro isolation may be useful in identifying additional mediators synthesized and released, stimuli relevant to human pathophysiology, and pharmacological agents selectively modulating the activation of these cells and their mediators. Drugs specifically acting on HHMC or on their mediators may eventually be useful in treating different cardiovascular diseases.

Mechanisms of activation of human mast cells and basophils by general anesthetic drugs

A study was performed about the effects of increasing concentrations of muscle relaxants (suxamethonium, d-tubocurarine, vecuronium, and atracurium), hypnotics (propofol, ketamine, and thiopental), opioids (morphine, buprenorphine, and fentanyl), and benzodiazepines (diazepam, flunitrazepam, and midazolam) on the release of preformed (histamine and tryptase) and de novo synthesized (prostaglandin D2: PGD2 and peptide-leukotriene C4: LTC4) chemical mediators from human basophils and mast cells isolated from skin (HSMC), lung parenchyma (HLMC) and heart tissue (HHMC). None of the drugs tested induced the release of histamine or LTC4 from basophils of normal donors. Suxamethonium did not induce mediator release from any type of human mast cell tested. Only the highest concentration of d-tubocurarine used caused histamine release from HSMC and HLMC. Atracurium, more than vecuronium, induced concentration-dependent histamine release from HSMC and HLMC. Propofol induced a concentration-dependent histamine release from HLMC, but not from HHMC. Only the highest concentrations of ketamine and thiopental used caused a significant release of histamine from HLMC. The muscle relaxants and hypnotics examined did not induce any de novo synthesis of PGD2 or LTC4 in mast cells. Morphine only induced histamine and tryptase release from HSMC, but not the de novo synthesis of PGD2. In contrast, buprenorphine caused histamine and tryptase release from HLMC, and not from HSMC, whilst it also induced de novo synthesis of PGD2 and LTC4 in HLMC. Fentanyl did not give any histamine and tryptase release from mast cells. Diazepam and flunitrazepam only induced a small release of histamine from mast cells, whereas midazolam caused the release of histamine from HLMC. The biochemical pathways underlying the release of mediators from human mast cells induced by drugs used during general anaesthesia are different from those underlying the immune release of histamine. From the results obtained with the in vitro model described here, it is clear that new drugs promising for the anesthesiologic arena should be tested in vitro before their potential histamine-releasing activity is experienced in vivo.

Monoclonal IgE-mediated cardiac hypersensitivity reactions in the guinea-pig

Isolated heart preparations were prepared from guinea-pigs passively sensitized with mouse anti-DNP monoclonal IgE to study hemodynamic parameters and histamine release upon antigen challenge (DNP-BSA). In the best experimental conditions a triphasic response (increase, decrease, increase) in heart rate and in coronary flow occurred during 10 minutes after challenge. Coronary flow dramatically decreased (50%) at 2.5 min flanked by two periods of increase in flow and tachycardia (+ 55% of the basal heart rate). Contractile force decreased and remained at 80% of its initial value. Histamine is released within 2 minutes after antigen injection. After this period, the observed hemodynamic modifications seem to be due to other anaphylactic mediators such as prostaglandins, leukotrienes and most probably paf-acether.

Pathophysiology of human basophils and mast cells in allergic disorders

Basophil leukocytes and tissue mast cells are inflammatory cells that are found in virtually all human tissues. They appear to be involved in the pathogenesis of such allergic diseases as allergic rhinitis, bronchial asthma, anaphylaxis, atopic and contact dermatitis, chronic urticaria, and hypersensitivity pneumonitis. By releasing a variety of chemical mediators, they could also play a role in the pathophysiology of a wide range of inflammatory disorders of the joints, and of intestine, lung, coronary, and myocardial diseases. Although these two cell types are similar in several aspects, striking differences have also been observed. Moreover, human mast cells from different anatomical sites and within an individual tissue synthesize different mediators and have different release mechanisms. The recent advent of techniques that yield highly purified basophils and mast cells from diverse tissues will probably lead to major advancements in understanding the biochemical and pharmacological mechanisms that control the release process of these cells. The release of mediators from these cells is also controlled by a series of largely undefined biochemical steps that represent the basis of the concept of basophil and mast cell releasability. Alterations of basophil or mast cell releasability have already been detected in patients with allergic rhinitis, bronchial asthma, atopic dermatitis, and chronic urticaria. Taken together, these findings demonstrate that basophils, mast cells, and their chemical mediators play a pivotal role in several inflammatory disorders.

Serum immunoglobulin E response to myocardial infarction

Mast cells have been implicated in the pathogenesis of coronary heart disease. They can be activated by immunoglobulin (Ig) E-mediated mechanisms to release powerful mediators affecting local blood flow. We have determined systematically serum IgE concentrations in 100 patients with acute myocardial infarction. There was a consistent pattern of change in serum IgE, characterized by a significant increase on the third and fifth day, peak values on the seventh day, and a gradual decline to initial levels by the end of the third week after infarction. The increase in serum IgE shortly after myocardial infarction was similar to the increase in blood eosinophil count, but was in contrast to serum IgG levels. After infarction, patients with high initial IgE levels (greater than 200 IU/ml) had a greater increase in IgE and less frequent severe complications than those whose initial IgE levels were below 200 IU/ml. In 16 subjects with acute coronary insufficiency without infarction serum IgE levels remained unchanged. It is suggested that in myocardial infarction circulating IgE sensitizes both mast cells of coronary arteries and eosinophils, invading ischemic myocardium; this facilitates release of chemical mediators. Patients with high IgE levels might be protected against complications of infarction because of a favorable ratio of locally released mediators and because of decreased platelet function.

Effects of histamine on coronary hemodynamics in humans: role of H1 and H2 receptors

To evaluate whether histamine exerts a direct effect on coronary hemodynamics in humans, and to investigate the role played by H1 and H2 receptors in this response, intracoronary saline solution or histamine (4 micrograms) was administered in 10 patients with normal coronary arteries during diagnostic cardiac catheterization. Histamine injection was repeated after intravenous cimetidine (400 mg) and diphenhydramine (10 mg). The electrocardiogram, arterial pressure and thermodilution coronary blood flow were continuously monitored during and for 40 seconds after each injection. Immediately after histamine injection there was a significant increase in coronary blood flow (65 +/- 6%) and a decrease in coronary vascular resistance (-40 +/- 3%) (both p less than 0.001), with minor changes in the RR interval and the mean arterial pressure. H2 receptor blockade with cimetidine did not affect these changes, while H1 receptor blockade with diphenhydramine significantly reduced the histamine-induced increase in coronary blood flow and the decrease in coronary vascular resistance (26 +/- 6%, p less than 0.005 and -18 +/- 5%, p less than 0.001, respectively). Twenty to 30 seconds after histamine injection, a significant decrease in mean arterial pressure (-17 +/- 2%, p less than 0.001) and in the RR interval (-4 +/- 1%, p less than 0.01) was observed. These changes persisted after H2 receptor blockade with cimetidine, but were completely abolished after H1 receptor blockade with diphenhydramine. In each case coronary and systemic hemodynamics returned to normal within 40 seconds of the injection.(ABSTRACT TRUNCATED AT 250 WORDS)