Cardiac Mast Cells Research Articles

Mast Cell Deficient W/Wv Mice Have Lower Serum IL-6 and Less Cardiac Tissue Necrosis Than Their Normal Littermates following Myocardial Ischemia-Reperfusion

Myocardial ischemia-reperfusion (IR) injury complicates all forms of coronary artery revascularization. Circulating interleukin-6 (IL-6) has been implicated in cell death following a variety of stimuli. Macrophages, platelets, neutrophils and the endothelium have been shown to release IL-6 after IR injury. Cardiac mast cells have been implicated in IR; however, their involvement has never been quantified. In this randomized, prospective study, we compared cardiac tissue susceptibility and serum IL-6 changes between mast cell deficient (W/Wv) mice and their normal littermates (+/+). Twenty-eight male W/Wv mice (n=14) and their +/+ littermates (n=14) were anaesthetized with 2.5% isoflurane. The left coronary artery (LCA) was ligated for 30 minutes or a sham procedure was performed. After 6 hours of reperfusion, the animals were sacrificed. The muscle viability was assessed on fresh whole-mount slices by nitroblue tetrazolium (NBT) histochemical assay and serum IL-6 concentrations measured by ELISA. Cardiac muscle viability was significantly higher in W/Wv mice than the +/+ mice. Serum IL-6 levels were higher in the +/+ sham mice (465 +/- 32 pg/ml, n=6) than the W/Wv mice (185 +/- 31 pg/ml, n=6), p < 0.001. The IL-6 levels increased significantly after reperfusion only in the +/+ mice (698 +/- 41 pg/ml, n=8, p = 0.001), while it remained similar in the W/Wv mice (202 +/- 48 pg/ml, n=8, p = 0.783). These results show that the absence of mast cells reduces the myocardial damage associated with IR injury. Furthermore, there is an attenuation in the inflammatory response, as measured by serum IL-6 levels, following this local insult. This finding entertains the prospect of developing prophylactic therapy--targeting selective inhibition of cardiac mast cell activation, in clinical situations involving medical or surgical myocardial revascularization.

Cardiac Nociception

Cardiac Nociception

Insights from knock-out models concerning postischemic release of TNFα from isolated mouse hearts

The inflammatory cytokine tumor necrosis factor alpha (TNFα) is controversially discussed in ischemia/reperfusion damage of the heart. Purpose of this study was to elucidate cellular sources of TNFα and parameters which possibly influence its release in the heart following ischemia. Isolated hearts of mice were subjected to 15 min of global ischemia and 90 min of reperfusion. We employed hearts of various mice knock-out strains (interleukin-6−/−, matrix metalloprotease-7−/−, mast-cell deficient WBB6F1-KitW/KitW-v, TNF-R1−/−) and wildtype mice, the latter perfused without and with infusion of cycloheximide or TNFα-cleaving-enzyme inhibitor (TAPI-2). Normoxic control hearts showed basal release of TNFα during the whole experiment. Immunohistology identified cardiac mast cells, macrophages and endothelial cells as main sources. TNFα release was stimulated during postischemic reperfusion, occurring in a two-peak pattern: directly after ischemia (0–10 min) and again after 60–90 min. The first peak mainly reflects tissue washout of TNFα accumulated during ischemia. The second, protracted peak arose continuously from the basal level and was abolished by protein synthesis inhibitor cycloheximide. Both properties are characteristic for de novo synthesis of TNFα, e.g., in cardiac muscle cells. However, immunohistological staining for TNFα failed in cardiomyocytes after 90 min of reperfusion. In contrast to hearts of TNF-R1−/− and KitW/W-v-mice, those of IL-6−/− and MMP-7−/− mice lacked the late TNFα peak. TAPI did not suppress release of TNFα. While autostimulation via TNF-R1 also does not seem obligatory and mast cell can be ignored as source of the second peak, IL-6 may support de novo synthesis of TNFα. Additionally, TNFα release may essentially involve cleavage of membrane bound TNFα by MMP-7.

Rat cardiac mast cell maturation and differentiation following acute ventricular volume overload

Cardiac mast cell numbers increase significantly within 12 h following the creation of an aortocaval (AV) fistula in rats and play a central role in mediating adverse left ventricular remodeling. We studied whether this increase was related to maturation of resident immature mast cells. We measured percentages of immature and mature cardiac mast cells at 1, 2 and 7 days following AV-fistula or sham surgery and in non-surgical control rats using the alcian-blue safranin reaction. Relative to sham-operated and control rats, there was a significant shift from immature to a greater percentage of mature cardiac mast cells at 1 day and 2 days post-fistula that returned to a normal distribution by 7 days. We conclude that the acute increase in mast cell density following volume overload is due to a paracrine response in the heart that stimulates the maturation and differentiation of resident immature cardiac mast cells.

Identification and localization of adrenomedullin-storing cardiac mast cells

Adrenomedullin (AM), a potent vasodilatory hypotensive peptide, is expressed in the heart, where it is known to play a protective action. Light-microscopy immunocytochemistry (ICC) demonstrated the presence of AM immunoreactivity not only in the coronary-vessel wall and ventricular myocytes of the human and rat heart, but also in sparse voluminous cells located in the perivascular space. These cells displayed the same location of toluidine blue-positive mast cells, and electron microscopy ICC showed AM-immunogold staining over the granules of rat cardiac mast cells. The incubation of rat left ventricle fragments with the mast-cell histamine releaser compound 48/80 evidenced groups of AM-positive cells undergoing degranulation and caused an increase of approximately 50% in the AM concentration in the incubation medium. Collectively, our findings provide evidence that at least a subset of cardiac mast cells are able to synthesize and store AM, and upon stimulation to release it near coronary arterioles and venules.

Cardiac mast cell-derived renin promotes local angiotensin formation, norepinephrine release, and arrhythmias in ischemia/reperfusion

Having identified renin in cardiac mast cells, we assessed whether its release leads to cardiac dysfunction. In Langendorff-perfused guinea pig hearts, mast cell degranulation with compound 48/80 released Ang I-forming activity. This activity was blocked by the selective renin inhibitor BILA2157, indicating that renin was responsible for Ang I formation. Local generation of cardiac Ang II from mast cell-derived renin also elicited norepinephrine release from isolated sympathetic nerve terminals. This action was mediated by Ang II-type 1 (AT1) receptors. In 2 models of ischemia/reperfusion using Langendorff-perfused guinea pig and mouse hearts, a significant coronary spillover of renin and norepinephrine was observed. In both models, this was accompanied by ventricular fibrillation. Mast cell stabilization with cromolyn or lodoxamide markedly reduced active renin overflow and attenuated both norepinephrine release and arrhythmias. Similar cardioprotection was observed in guinea pig hearts treated with BILA2157 or the AT1 receptor antagonist EXP3174. Renin overflow and arrhythmias in ischemia/reperfusion were much less prominent in hearts of mast cell-deficient mice than in control hearts. Thus, mast cell-derived renin is pivotal for activating a cardiac renin-angiotensin system leading to excessive norepinephrine release in ischemia/reperfusion. Mast cell-derived renin may be a useful therapeutic target for hyperadrenergic dysfunctions, such as arrhythmias, sudden cardiac death, myocardial ischemia, and congestive heart failure.

Interactions between mast cells and the endothelin system in radiation‐induced heart disease

Objectives Mast cells may influence the development of radiation-induced heart disease (RIHD), an important sequela after thoracic radiotherapy. Moreover, mast cells regulate levels of endothelin 1 (ET-1), which plays a role in cardiovascular remodeling via its receptors, ETA and ETB. This study used a mast cell-deficient rat model to investigate interactions between mast cells and the cardiac endothelin system in RIHD. Methods Mast cell-deficient (Ws/Ws) and mast cell-competent (+/+) rats were exposed to 18 Gy localized irradiation of the heart. Cardiac functional changes were assessed using echocardiography and Langendorff isolated heart preparation 6 months after irradiation. Localization and mRNA levels of ET-1, ETA and ETB were examined at 1 week and 3 months. Results Irradiated hearts from mast cell-competent rats exhibited more severe myocardial degeneration, but less severe diastolic dysfunction than irradiated hearts from mast cell-deficient rats. Post-radiation ET-1 mRNA levels were strikingly increased in mast cell-competent, but not in mast cell-deficient hearts. Cardiac mast cells exhibited prominent ETA and ETB immunoreactivity. Conclusions These data suggest that crosstalk between mast cells and the endothelin system may be important during the development of RIHD and point to ET-1 and/or its receptors as possible therapeutic targets to reduce RIHD. Research support National Institutes of Health and the American Heart Association.

Cardiac mast cell regulation of matrix metalloproteinase-related ventricular remodeling in chronic pressure or volume overload

The chronic elevation in ventricular wall stress secondary to ventricular volume or pressure overload leads to structural remodeling of the muscular, vascular and extracellular matrix components of the myocardium. While initially a compensatory response, the progressive hypertrophy and ventricular dilatation induced by this condition ultimately have a detrimental effect on ventricular function, resulting in heart failure. Fibrillar collagen provides the skeletal framework which interconnects the cardiomyocytes, thereby maintaining ventricular shape and size and contributing to tissue stiffness. Accordingly, these myocardial collagen fibers must be disrupted for ventricular dilatation, sphericalization and wall thinning to occur. The presence of an abundant, latent matrix metalloproteinase (MMP) population which coexists with myocardial fibrillar collagen has been documented. Thus, the potential for collagen degradation to exceed synthesis exists should there be significant activation of this latent MMP system. Mast cells are known to store and release a variety of biologically active mediators including TNF-alpha and proteases such as tryptase and chymase, which can induce MMP activation. Increased cardiac mast cell density has been implicated in the pathophysiology of human end-stage cardiomyopathy and experimental myocardial infarction, hypertension and chronic volume overload secondary to mitral regurgitation and aorto-caval fistula. The potential role of cardiac mast cells in activating MMPs, which then results in fibrillar collagen degradation and adverse myocardial remodeling secondary to chronic volume and pressure overload will be the subject of this review.

Quantitative Changes in Mast Cell Populations After Left Ventricular Assist Device Implantation

Mast cells have been implicated as important in tissue remodeling and fibrosis. We investigated the effect of mechanical ventricular unloading upon myocardial fibrosis and cardiac mast cell density in patients undergoing left ventricular assist device (LVAD) implantation. Paired myocardial tissue samples were obtained from 30 patients with end-stage cardiomyopathy at the time of LVAD implantation and at the time of removal and were compared with samples taken from donor hearts. Tissue sections were stained and quantitated for mast cells and myocardial fibrosis. Mast cell density (tryptase positive cells) in cardiomyopathy was higher than that in donor hearts (33.5 +/- 3.6 SEM cells/10 fields vs.15.2 +/- 2.0 SEM cells/10 fields respectively, p = 0.04) and was lower than LVAD supported hearts (33.5 +/- 3.6 SEM cells/10 fields vs. 49.8 +/- 5.7 SEM cells/10 fields respectively, p = 0.01). Mast cells are primarily localized in areas of increased interstitial fibrosis adjacent to myocardial cells and not vessels. There was statistically significant correlation between mast cells and interstitial collagen (p = 0.03) in patients before LVAD implantation that did not persist after mechanical support (p = 0.18). These results suggest that mechanical support with left ventricular assist devices induces an increase in mast cell number in the myocardium and an associated decrease in myocardial fibrosis. We believe these data demonstrate a dual role for cardiac mast cells in the increase in fibrosis in heart failure and the decrease after LVAD and its associated cardiac improvement.

The Mast Cell: A Potential Therapeutic Target in Myocardial Infarction

Mast cells are multifunctional effector cells of the immune system, capable of producing a variety of vasoactive mediators, cytokines and growth factors. The presence of resident mast cells in the myocardium has been established; however, their exact role in cardiac pathology remains unclear. The current review presents evidence suggesting the importance of mast cells in the infarcted myocardium. Myocardial ischemia and reperfusion results in degranulation of cardiac mast cells, and release of preformed inflammatory mediators, such as TNF-α and histamine in the ischemic area. Mast cell derived products may modulate endothelial gene expression and mononuclear cell cytokine synthesis. During the proliferative phase of healing, significant mast cell accumulation is noted in areas of fibrosis and myofibroblast proliferation. Stem Cell Factor (SCF), the obligate growth factor for mast cells, is induced in the healing myocardium. Mast cells may have an important role in scar formation through the secretion of growth factors and fibrogenic substances (such as TGF-β, basic FGF, tryptase and VEGF), that may promote collagen deposition and angiogenesis. Understanding the role of the mast cell in myocardial infarction is important in order to design site-specific pharmacological interventions that could mitigate inflammatory injury, without interfering with myocardial healing.

Modulation of cardiac mast cell-mediated extracellular matrix degradation by estrogen

There are fundamental differences between males and females with regard to susceptibility to heart disease. Although numerous animal models of heart failure have demonstrated that premenopausal females are afforded cardioprotection and, therefore, fare better in the face of cardiac disease than their male counterparts, many questions as to how this occurs still exist. Recently, we showed that 1) increased mast cell density is associated with adverse ventricular remodeling and 2) chemically induced mast cell degranulation using compound 48/80 resulted in remarkable changes in matrix metalloproteinase (MMP) activity, cardiac collagen structure, and cardiac diastolic function in normal male rats. With the known gender differences in cardiac disease in mind, we sought to examine the effects of chemically induced cardiac mast cell degranulation in isolated, blood-perfused hearts of intact female rats, ovariectomized female rats, and ovariectomized female rats treated with 17beta-estradiol. In response to mast cell degranulation, no significant differences in cardiac function, MMP-2 activity, or collagen volume fraction were observed between intact female rats and ovariectomized female rats treated with estrogen. In the ovariectomized female group, a significant rightward shift in the left ventricular pressure-volume relation, accompanied by a marked 133% increase in active MMP-2 values over that in the intact female group, was noted after treatment with compound 48/80 (P < or = 0.05), along with a significant reduction in collagen volume fraction below control (0.46 +/- 0.23 vs. 0.73 +/- 0.13%, P < or = 0.05). These findings indicate that estrogen's cardioprotective role can be partially mediated by its effects on cardiac mast cells, MMPs, and the extracellular matrix.

Cardiac chymase: pathophysiological role and therapeutic potential of chymase inhibitors

On release from cardiac mast cells, alpha-chymase converts angiotensin I (Ang I) to Ang II. In addition to Ang II formation, alpha-chymase is capable of activating TGF-beta1 and IL-1beta, forming endothelins consisting of 31 amino acids, degrading endothelin-1, altering lipid metabolism, and degrading the extracellular matrix. Under physiological conditions the role of chymase in the mast cells of the heart is uncertain. In pathological situations, chymase may be secreted and have important effects on the heart. Thus, in animal models of cardiomyopathy, pressure overload, and myocardial infarction, there are increases in both chymase mRNA levels and chymase activity in the heart. In human diseased heart homogenates, alterations in chymase activity have also been reported. These findings have raised the possibility that inhibition of chymase may have a role in the therapy of cardiac disease. The selective chymase inhibitors developed to date include TY-51076, SUN-C8257, BCEAB, NK320, and TEI-E548. These have yet to be tested in humans, but promising results have been obtained in animal models of myocardial infarction, cardiomyopathy, and tachycardia-induced heart failure. It seems likely that orally active inhibitors of chymase could have a place in the treatment of cardiac diseases where injury-induced mast cell degranulation contributes to the pathology.

Mast cell tryptase may modulate endothelial cell phenotype in healing myocardial infarcts

Mast cells and macrophages infiltrate healing myocardial infarcts and may play an important role in regulating fibrous tissue deposition and extracellular matrix remodelling. This study examined the time-course of macrophage and mast cell accumulation in healing infarcts and studied the histological characteristics and protease expression profile of mast cells in a canine model of experimental infarction. Although macrophages were more numerous than mast cells in infarct granulation tissue, macrophage density decreased during maturation of the scar, whereas mast cell numbers remained persistently elevated. During the inflammatory phase of infarction, newly recruited leucocytes infiltrated the injured myocardium and appeared to be clustered in close proximity to degranulating cardiac mast cells. During the proliferative phase of healing, mast cells had decreased granular content and were localized close to infarct neovessels. In contrast, macrophages showed no selective localization. Mast cells in healing canine infarcts were alcian blue/safranin-positive cells that expressed both tryptase and chymase. In order to explain the pro-inflammatory and angiogenic actions of tryptase--the major secretory protein of mast cells--its effects on endothelial chemokine expression were examined. Chemokines are chemotactic cytokines that play an important role in leucocyte trafficking and angiogenesis and are highly induced in infarcts. Tryptase, a proteinase-activated receptor (PAR)-2 agonist, induced endothelial expression of the angiogenic chemokines CCL2/MCP-1 and CXCL8/IL-8, but not the angiostatic chemokine CXCL10/IP-10. Endothelial PAR-2 stimulation with the agonist peptide SLIGKV induced a similar chemokine expression profile. Mast cell tryptase may exert its angiogenic effects in part through selective stimulation of angiogenic chemokines.

Mast cells: a unique source of renin.

In addition to the traditional renin-angiotensin system, a great deal of evidence favors the existence of numerous independent tissue-specific renin-angiotensin systems. We report that mast cells are an additional source of renin and constitute a unique extrarenal renin-angiotensin system. We use renin-specific antibodies to demonstrate that cardiac mast cells contain renin. Extending this observation to the human mast cell line HMC-1, we show that these mast cells also express renin. The HMC-1 renin RT-PCR product is 100% homologous to Homo sapiens renin. HMC-1 cells also contain renin protein, as demonstrated both by immunoblot and immunocytochemical analyses. Renin released from HMC-1 cells is active; furthermore, HMC-1 cells are able to synthesize renin. It is known that, in the heart, mast cells are found in the interstitium in close proximity to nerves and myocytes, which both express angiotensin II receptors. Inasmuch as myocardial interstitium contains angiotensinogen and angiotensin-converting enzyme, and because we were able to detect renin only in mast cells, we postulate that the release of renin from cardiac mast cells is the pivotal event triggering local formation of angiotensin II. Because of the ubiquity of mast cells, our results represent a unique paradigm for understanding local renin-angiotensin systems, not just in the heart, but in all tissues. Our findings provide a rationale for targeting mast cells in conjunction with renin-angiotensin system inhibitors in the management of angiotensin II-related dysfunctions.

Spontaneous histamine secretion during isolation of rat cardiac mast cells

To test the hypothesis that spontaneous release of histamine occurring during an isolation protocol may modify responses of rat cardiac mast cells (connective tissue-type mast cells) to secretagogues. We assessed two protocols for enzymatic dispersion utilizing collagenase, hyaluronidase, and deoxyribonuclease; with protease (Protocol 1, n = 8) or without protease (Protocol 2, n = 3). Spontaneous release of histamine was quantified following mechanical and enzymatic dispersion of the whole heart. Total histamine loss (Mean +/- SEM) was 963+/-92 and 833+/-60 ng/g of tissue weight following Protocols 1 and 2. Percentages of histamine release from cell isolates following Protocol 1 were 40+/-5%, 41+/-6%, and 51+/-7% at 0, 30, and 300 microg/mL of compound 48/80. Enzymatic dispersion of cardiac mast cells affects their response to secretagogues.

A role for cardiac mast cells in the pathogenesis of hypertensive heart disease.

Cardiac mast cells participate in myocardial dysfunction, but the mechanisms are presently unknown. By examining spontaneously hypertensive rats (SHRs) during their entire lifespan, we attempted to define the role of mast cells in the induction of cardiac hypertrophy and transition to heart failure. By contrast to normotensive littermates, hearts of newborn SHRs already contained mast cells. In the prehypertensive (2-week-old) SHRs, the increased expression of c-kit and soluble stem cell factor correlated with an increased number of cardiac mast cells. The mast cells contained tumour necrosis factor-alpha which, together with nuclear factor kappa-B (NF-kappaB) and interleukin (IL)-6, was significantly induced in the prehypertensive SHRs. Stimulation of cardiac mast cells with compound 48/80 in an ex-vivo Langendorff heart perfusion system resulted in increased expression of nuclear factor Kappa-B (NF-kappaB) (four-fold) and IL-6 (nine-fold) mRNA in the left ventricles of adult rat hearts. In the presence of an inhibitor of mast cell degranulation, disodium cromoglycate, the induced expression of NF-kappaB and IL-6 was inhibited. In the late hypertensive stage, the hearts of SHRs with advanced cardiac hypertrophy (12-month-old) and heart failure (20-month-old) had significantly increased levels of transforming growth factor (TGF)-beta1 and basic fibroblast growth factor (bFGF), and displayed increased myocardial fibrosis. Activated mast cells were a major source of TGF-beta1 and bFGF, and localized to areas of myocardial fibrosis. By synthesizing and secreting prohypertrophic cytokines and profibrotic growth factors, cardiac mast cells participate in the induction of cardiac hypertrophy and cardiac fibrosis, which are the key steps in the transition to heart failure.

Cardiac mast cells in the transition to heart failure

Cardiac mast cells in the transition to heart failure

Reversal of cardiac fibrosis following LVAD implantation: the cardiac mast cell

Hypertrophy and fibrosis represent structural changes in the myocardium which occur in heart failure and decrease the ability of the heart to contract. We have previously demonstrated that reduction of load by LVAD support induces a decrease in cardiac interstitial fibrosis as well as myocyte size. We also have reported that cardiac mast cells increase in heart failure and that a secondary increase occurs post LVAD. The secondary increase, however, is composed of primarily chymase negative mast cells and these mast cells show an altered (reduced) bFGF content.

Modulation of guinea pig intrinsic cardiac neurons by prostaglandins.

Activation of cardiac mast cells has been shown to alter parasympathetic neuronal function via the activation of histamine receptors. The present study examined the ability of prostaglandins to alter the activity of guinea pig intracardiac neurons. Intracellular voltage recordings from whole mounts of the cardiac plexus showed that antigen-mediated mast cell degranulation produces an attenuation of the afterhyperpolarization (AHP), which was prevented by the phospholipase A2 inhibitor 5,8,11,14-eicosatetraynoic acid. Exogenous application of either PGD2 or PGE2 produced a biphasic change in the membrane potential and an inhibition of both AHP amplitude and duration. Examination of prostanoid receptors using bath perfusions (1 microM PGE2 and PGD2), specific agonists (BW245C, sulprostone, and butaprost), and antagonists (AH6809 and SC19220) found evidence for both the PGE2-specific EP2 and EP3 receptors, but not for EP1 or the PGD2-specific prostanoid (DP) receptors. Sulprostone was able to mimic the PGE2 responses in some cells, but not in all PGE2-sensitive cells. Butaprost was able to mimic the PG-induced hyperpolarization in some cells, but did not alter the AHP. Inhibition of specific potassium channels with either TEA, charybdotoxin, or apamin showed that neither TEA nor charybdotoxin could prevent the PGE2-induced AHP attenuation. Apamin alone inhibited AHP duration, with PGs having no further effect in these cells. These results demonstrate that guinea pig intracardiac neurons can be modulated by PG, most likely through either EP2, EP3, or potentially EP4 receptors, and this response is due, at least in part, to a reduction in small-conductance KCa currents.

Resident cardiac mast cells and ischemia-reperfusion injury.

The intense inflammatory reaction following reperfusion of ischemic myocardium has been implicated as a factor in the extension of myocardial injury. One of the therapeutic goals of modern cardiology is to design strategies to limit the infarct size following myocardial infarction. A sound understanding of the inflammatory cascade that involves the release of various proinflammatory mediators from cardiac cells is necessary before a specific intervention is pursued. Summarized is the role of resident cardiac mast cells, which are noted to release inflammatory mediators, in ischemia-reperfusion-induced myocardial injury. Various pharmacologic interventions, such as disodium cromoglycate and ketotifen, that stabilize cardiac mast cells, or agents such as chlorpheniramine and cetirizine that prevent their degranulation during ischemia and reperfusion, may prove to be potential therapeutic agents to limit or salvage ischemia-reperfusion-induced injury. On the basis of the effects of histamine H1 antagonists, adrenoceptor blockers, cellular calcium and nitric oxide modulators, as well as inhibitors of phosphodiesterase and mitogen-activated protein kinase on mast cells, cardiac resident mast cells may represent a novel target for the development of cardioprotective agents.