Lack of involvement of mast cell degranulation in the antiarrhythmic effect of preconditioning in rats

Dexmedetomidine preconditioning mitigates myocardial ischemia/reperfusion injury via inhibition of mast cell degranulation

The degranulation of cardiac mast cells is associated with occurrence and development of myocardial ischemia/reperfusion (I/R) injury. Dexmedetomidine has a cardioprotective effect from I/R injury. The purpose of this study was to investigate whether dexmedetomidine preconditioning induced cardioprotection is related to suppression of degranulation of cardiac mast cell. Both in vivo and in vitro experimental results revealed that hemodynamic disorder, arrhythmia, infarct size, histopathological score, and mast cell degranulation were dramatically increased in I/R injury groups compared with non-I/R groups, and mastocyte secretagogue compound 48/80 aggravated these damages, but it can be improved by dexmedetomidine preconditioning. Similarly, compound 48/80 increased levels of cardiac troponin I (cTnI) and tryptase, cardiomyocytes apoptosis, and expression of high-mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), and nuclear factor-kappa B p65 (NF-κB p65) in cardiac tissues induced by I/R injury, but it can be partially decreased by dexmedetomidine pretreatment. Compound 48/80 inhibited proliferation of H9C2(2-1) and RBL-2H3, exacerbated apoptosis of H9C2(2-1), and elevated levels of cTnI and tryptase, while both of which were abolished by dexmedetomidine pretreatment. Our data suggest that dexmedetomidine preconditioning alleviates the degranulation of mast cells and the apoptosis of cardiomyocytes caused by I/R injury, and inhibits the activation of inflammatory related factors HMGB1, TLR4, and NF-κB p65.

Regulation of Type 2 Immunity in Myocardial Infarction

Type 2 immunity participates in the pathogeneses of helminth infection and allergic diseases. Emerging evidence indicates that the components of type 2 immunity are also involved in maintaining metabolic hemostasis and facilitating the healing process after tissue injury. Numerous preclinical studies have suggested regulation of type 2 immunity-related cytokines, such as interleukin-4, -13, and -33, and cell types, such as M2 macrophages, mast cells, and eosinophils, affects cardiac functions after myocardial infarction (MI), providing new insights into the importance of immune modulation in the infarcted heart. This review provides an overview of the functions of these cytokines and cells in the setting of MI as well as their potential to predict the severity and prognosis of MI.

Acute administration of cannabidiol in vivo suppresses ischaemia-induced cardiac arrhythmias and reduces infarct size when given at reperfusion

BACKGROUND AND PURPOSE

Cannabidiol (CBD) is a phytocannabinoid, with anti-apoptotic, anti-inflammatory and antioxidant effects and has recently been shown to exert a tissue sparing effect during chronic myocardial ischaemia and reperfusion (I/R). However, it is not known whether CBD is cardioprotective in the acute phase of I/R injury and the present studies tested this hypothesis.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats received either vehicle or CBD (10 or 50 microg kg(-1) i.v.) 10 min before 30 min coronary artery occlusion or CBD (50 microg kg(-1) i.v.) 10 min before reperfusion (2 h). The appearance of ventricular arrhythmias during the ischaemic and immediate post-reperfusion periods were recorded and the hearts excised for infarct size determination and assessment of mast cell degranulation. Arterial blood was withdrawn at the end of the reperfusion period to assess platelet aggregation in response to collagen.

KEY RESULTS

CBD reduced both the total number of ischaemia-induced arrhythmias and infarct size when administered prior to ischaemia, an effect that was dose-dependent. Infarct size was also reduced when CBD was given prior to reperfusion. CBD (50 microg kg(-1) i.v.) given prior to ischaemia, but not at reperfusion, attenuated collagen-induced platelet aggregation compared with control, but had no effect on ischaemia-induced mast cell degranulation.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that CBD is cardioprotective in the acute phase of I/R by both reducing ventricular arrhythmias and attenuating infarct size. The anti-arrhythmic effect, but not the tissue sparing effect, may be mediated through an inhibitory effect on platelet activation.

Mast cells, peptides and cardioprotection - an unlikely marriage?

1 Mast cells have classically been regarded as the 'bad guys' in the setting of acute myocardial ischaemia, where their released contents are believed to contribute both to tissue injury and electrical disturbances resulting from ischaemia. Recent evidence suggests, however, that if mast cell degranulation occurs in advance of ischaemia onset, this may be cardioprotective by virtue of the depletion of mast cell contents that can no longer act as instruments of injury when the tissue becomes ischaemic. 2 Many peptides, such as ET-1, adrenomedullin, relaxin and atrial natriuretic peptide, have been demonstrated to be cardioprotective when given prior to the onset of myocardial ischaemia, although their physiological functions are varied and the mechanisms of their cardioprotective actions appear to be diverse and often ill defined. However, one common denominator that is emerging is the ability of these peptides to modulate mast cell degranulation, raising the possibility that peptide-induced mast cell degranulation or stabilization may hold the key to a common mechanism of their cardioprotection. 3 The aim of this review was to consolidate the evidence implying that mast cell degranulation could play both a detrimental and protective role in myocardial ischaemia, depending upon when it occurs, and that this may underlie the cardioprotective effects of a range of diverse peptides that exerts physiological effects within the cardiovascular system.

Mast cell degranulation--a mechanism for the anti-arrhythmic effect of endothelin-1?

BACKGROUND AND PURPOSE

The aim of this study was to investigate whether the previously reported anti-arrhythmic effect of endothelin-1 (ET-1) is mediated by degranulation of cardiac mast cells prior to myocardial ischaemia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats received either ET-1 (1.6 nmolxkg(-1)) in the presence or absence of disodium cromoglycate (DSCG; 20 mgxkg(-1)xh(-1)) prior to coronary artery occlusion (CAO). In separate experiments rats were given compound 48/80 (50 microgxkg(-1)) to compare the effects of ET-1 with those of a known mast cell degranulator. Ischaemia-induced ventricular arrhythmias were detected through continuous monitoring of a lead I electrocardiogram. After 30 min of CAO, the hearts were removed and mast cell degranulation determined by histological analysis. A parallel series of sham groups were performed to determine the direct effects of ET-1 and compound 48/80 on mast cell degranulation in the absence of ischaemia.

KEY RESULTS

ET-1 and compound 48/80 both exerted profound anti-arrhythmic effects, significantly reducing the total number of ventricular ectopic beats (P < 0.001) and the incidence of ventricular fibrillation (P < 0.05). These anti-arrhythmic effects were abolished by concomitant DSCG infusion prior to CAO. In sham animals ET-1 and compound 48/80 both induced mast cell degranulation (P < 0.001), an effect which was abolished by DSCG, confirming their ability to induce degranulation of mast cells.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate for the first time that when given prior to ischaemia ET-1 mediates its anti-arrhythmic effects, at least in part, via cardiac mast cell degranulation.

Resident cardiac mast cells and ischemia-reperfusion injury

BACKGROUND

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.

OBSERVATION

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.

CONCLUSION

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.

Ischaemic preconditioning and mast cell histamine release: microdialysis of isolated rat hearts

The aim of this study was to investigate the feasibility of intramyocardium kinetics of histamine release by microdialysis in the isolated rat heart and ascertain if the inhibition of histamine release is implicated in the antiarrhythmic effect of preconditioning. A 30 min normothermic global ischaemia model followed by 30 min reperfusion was carried out in the control group (n= 9). In the preconditioning group (n= 8) there was a 5 min global ischaemia followed by 10 min of reperfusion. A mast cell stabilizing group received the disodium cromoglycate ( 10 micro M, n= 10). The last group received a mast cell degranulator, compound 48/80 (1micro g ml (-1), n= 10). In the control group, the histamine release during reperfusion was significantly different from the basal concentration ( 18.4 +/- 6.5 vs 1.9 +/- 0.5 nM, P< 0.05) and was associated with a maximal period of severe arrhythmias. The ischaemic preconditioning modified the histamine release kinetics with an early mast cell degranulation ( 9.7 +/- 1.5 nM) and a significant decrease in the total period of severe arrhythmias in comparison with the control group ( P< 0.05). In the disodium cromoglycate group, the histamine release during reperfusion decreased ( 3.1 +/- 0.7 nM) and was associated with a maximal period of severe arrhythmias. In the C48/80 group, the increase in the histamine released during reperfusion ( 21.2 +/- 5.0 nM) was associated with a maximal period of severe arrhythmias. These results showed firstly the feasibility of kinetic histamine release in myocardium interstitial fluid on the isolated rat heart and secondly that the inhibition of histamine release did not play a direct role in the antiarrhythmic effect of preconditioning.

Sarpogrelate diminishes changes in energy stores and ultrastructure of the ischemic-reperfused rat heart

Although the involvement of serotonin in exacerbating vascular abnormalities in ischemic heart disease has been established, its role in mediating changes in cardiac function due to ischemia reperfusion (IR) is poorly understood. The aim of this study was to investigate the effect of a serotonin blocker, sarpogrelate (5-HT2A antagonist), in preventing cardiac injury due to IR. Isolated rat hearts were subjected to 30 min of global ischemia followed by 1 h of reperfusion. Sarpogrelate (50 nM-0.9 µM) was infused 10 min before ischemia as well as during the reperfusion period. The IR-induced changes in left ventricular developed pressure, left ventricular end diastolic pressure, rate of pressure development, and rate of pressure decay were attenuated (P < 0.05) with sarpogrelate treatment. Sarpogrelate also decreased the ultrastructural damage and improved the high energy phosphate level in the IR hearts (P < 0.05). This study provides evidence for the attenuation of IR-induced cardiac injury by 5-HT2A receptor blockade and supports the view that serotonin may contribute to the deleterious effects of IR in the heart.Key words: ischemia reperfusion, sarpogrelate, serotonin receptor blockade.