Histamine release and its effects in ischaemia-reperfusion injury of the isolated rat heart

Sex Difference in Cardioprotection against Acute Myocardial Infarction in MAO-B Knockout Mice In Vivo

The cardiomyocyte-specific knockout (KO) of monoamine oxidase (MAO)-B, an enzyme involved in the formation of reactive oxygen species (ROS), reduced myocardial ischemia/reperfusion (I/R) injury in vitro. Because sex hormones have a strong impact on MAO metabolic pathways, we analyzed the myocardial infarct size (IS) following I/R in female and male MAO-B KO mice in vivo. Method and Results: To induce the deletion of MAO-B, MAO-B KO mice (Myh6 Cre+/MAO-Bfl/fl) and wild-type (WT, Cre-negative MAO-Bfl/fl littermates) were fed with tamoxifen for 2 weeks followed by 10 weeks of normal mice chow. Myocardial infarction (assessed by TTC staining and expressed as a percentage of the area at risk as determined by Evans blue staining)) was induced by 45 min coronary occlusion followed by 120 min of reperfusion. Results: The mortality following I/R was higher in male compared to female mice, with the lowest mortality found in MAO-B KO female mice. IS was significantly higher in male WT mice compared to female WT mice. MAO-B KO reduced IS in male mice but had no further impact on IS in female MAO-B KO mice. Interestingly, there was no difference in the plasma estradiol levels among the groups. Conclusion: The cardiomyocyte-specific knockout of MAO-B protects male mice against acute myocardial infarction but had no effect on the infarct size in female mice.

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.

Clemastine Fumarate Attenuates Myocardial Ischemia Reperfusion Injury Through Inhibition of Mast Cell Degranulation

Mast cell (MC) activation is associated with myocardial ischemia reperfusion injury (MIRI). Suppression of MC degranulation might be a target of anti-MIRI. This study aimed to determine whether clemastine fumarate (CLE) could attenuate MIRI by inhibiting MC degranulation. A rat ischemia and reperfusion (I/R) model was established by ligating the left anterior descending coronary artery for 30 min followed by reperfusion for 120 min. Compound 48/80 (C48/80) was used to promote MC degranulation. The protective effect of CLE by inhibiting MC degranulation on I/R injury was detected by cardiac function, 2,3,5-triphenyl tetrazolium chloride (TTC) staining, hematoxylin-eosin (HE) staining, arrhythmia, and myocardial enzyme detection. Inflammatory factor mRNA levels, such as TNF-α, interleukin (IL)-1β, and IL-6, were detected. Cultured RBL-2H3 mast cells were pretreated with CLE and subjected to C48/80 treatment to determine whether CLE suppressed MC degranulation. Degranulation of MCs was visualized using tryptase release, Cell Counting Kit-8 (CCK-8), and cell toluidine blue (TB) staining. RBL cells were conditionally cultured with H9C2 cells to explore whether CLE could reverse the apoptosis of cardiomyocytes induced by MC degranulation. Apoptosis of H9C2 cells was detected by CCK-8, the LDH Cytotoxicity Assay Kit (LDH), TUNEL staining, and protein expression of BAX and Bcl-2. We found that CLE pretreatment further inhibited cardiac injury manifested by decreased infarct size, histopathological changes, arrhythmias, MC degranulation, and myocardial enzyme levels, improving cardiac function compared with that in the I/R group. C48/80 combined with I/R exacerbated these changes. However, pretreatment with CLE for C48/80 combined with I/R significantly reversed these injuries. In addition, CLE pretreatment improved the vitality of RBL cells and reduced tryptase release in vitro. Similarly, the supernatant of RBL cells pretreated with CLE decreased the cytotoxicity, TUNEL-positive cell rate, and BAX expression of conditioned H9C2 cells and increased the cell vitality and expression of Bcl-2. These results suggested that pretreatment with CLE confers protection against I/R injury by inhibiting MC degranulation.

A cell-based phenotypic assay to identify cardioprotective agents

RATIONALE

Tissue ischemia/reperfusion (IR) injury underlies several leading causes of death such as heart-attack and stroke. The lack of clinical therapies for IR injury may be partly due to the difficulty of adapting IR injury models to high-throughput screening (HTS).

OBJECTIVE

To develop a model of IR injury that is both physiologically relevant and amenable to HTS.

METHODS AND RESULTS

A microplate-based respirometry apparatus was used. Controlling gas flow in the plate head space, coupled with the instrument's mechanical systems, yielded a 24-well model of IR injury in which H9c2 cardiomyocytes were transiently trapped in a small volume, rendering them ischemic. After initial validation with known protective molecules, the model was used to screen a 2000-molecule library, with post-IR cell death as an end point. Po2 and pH monitoring in each well also afforded metabolic data. Ten protective, detrimental, and inert molecules from the screen were subsequently tested in a Langendorff-perfused heart model of IR injury, revealing strong correlations between the screening end point and both recovery of cardiac function (negative, r2=0.66) and infarct size (positive, r2=0.62). Relationships between the effects of added molecules on cellular bioenergetics and protection against IR injury were also studied.

CONCLUSIONS

This novel cell-based assay can predict either protective or detrimental effects on IR injury in the intact heart. Its application may help identify therapeutic or harmful molecules.

The protective effect of H2-receptor activation against the duration of myocardial hypoxia/reoxygenation-induced ventricular fibrillation in sensitized guinea-pig hearts

Patients with high serum immunoglobulin E levels were reported to be protected against sudden death during acute myocardial infarction. The protection mechanism might be attributed to the facilitation of histamine release from sensitized mast cells; however, this remains to be clarified. In this study, we examined the influence of sensitization on ventricular fibrillation (VF) induced by myocardial hypoxia/reoxygenation (H/R). Guinea pigs were actively sensitized by subcutaneous injection of ovalbumin in Bordetella pertussis vaccine. Hearts isolated from non-sensitized and sensitized guinea pigs were subjected to 30-min hypoxia / 30-min reoxygenation using a Langendorff apparatus. The amount of histamine released in the sensitized guinea-pig hearts was elevated, and the duration of VF was found to be reduced. The treatment with a histamine H2-receptor antagonist inhibited the reduction of VF duration. Treatment of the non-sensitized hearts with the histamine H2-receptor agonist resulted in the decrease of VF duration to the same level as that in the sensitized hearts. In conclusion, these results suggest that the risk of sudden death during myocardial H/R may be attenuated in the sensitized hearts and that histamine H2-receptor activation due to the released histamine may be involved in the protective effect.

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.

Effects of chloropyramine and famotidine on postischaemic and posthypoxic myocardial damage in isolated rat hearts

In isolated rat hearts effects of chloropyramine (CP), histamine H1 antagonist, and famotidine (FA), H2 antagonist, upon two different myocardial injuries, ischaemia-reperfusion and hypoxia-reoxygenation were studied. In both types of injury the effects of drugs were seen mainly during reperfusion and reoxygenation, respectively. During reperfusion neither CP nor FA influenced amplitude of contractions, but CP lowered heart rate, +dp/dtmax and coronary flow. During reoxygenation CP and FA lowered early posthypoxic contractions, whereas CP decreased and FA increased heart rate. CP and FA did not significantly influence the post-ischaemic and posthypoxic lactate dehydrogenase (LDH) release. Present results indicate the existence of H1 and H2 receptors in rat heart as well as their involvement in both types of studied injuries.

Activity of histamine metabolizing and catabolizing enzymes during reperfusion of isolated, globally ischemic rat hearts

Myocardial ischemia-reperfusion injury increases both tissue levels and release of histamine. To study the possible effects of ischemia-reperfusion on histamine metabolism tissue activities of histidine decarboxylase (HDC), histamine N-methyl transferase (HNMT) and diamine oxidase (DAO) were investigated in isolated rat hearts subjected to either 20 min global ischemia and 40 min reperfusion (n = 10) or control perfusion (n = 8). Histamine in the coronary effluent increased from 21 +/- 4 nmol/min (mean +/- SEM) before ischemia to 55 +/- 5 and 50 +/- 7 nmol/min after 4 and 10 min reperfusion (p < 0.004 and p < 0.004). Tissue HDC activity did not change during observation in any group. HNMT activity was unchanged in controls, but increased from 0.37 +/- 0.04 to 0.84 +/- 0.18 and 0.96 +/- 0.22 pmol methylhistamine/mg protein hour after 4 and 10 min reperfusion (p < 0.008 and p < 0.01). DAO decreased similarly in controls and ischemic-reperfused hearts during observation. In conclusion, the previously observed increase of tissue histamine during reperfusion cannot be explained by increased histamine synthesis or decreased histamine catabolism.

Cardiac release of histamine after ventricular fibrillation and defibrillation during insertion of implantable cardioverter defibrillators (ICD)

Histamine has inotropic, chronotropic, arrhythmogenic, and vasoactive effects, and is released from the heart in ischaemia-reperfusion injury. The effect of ventricular fibrillation (VF) and defibrillation (DEF) on histamine release was investigated in 9 anaesthetized patients undergoing transvenous implantation of ICD. Concomitant arterial and coronary sinus (CS) blood samples were drawn before induction of VF (duration 20 seconds), immediately after, and 2 and 5 min after DEF (18-24 Joules). Basal arterial histamine was 2.5 +/- 6 nmol/l, and did not increase after VF. The histamine level in CS was 1.1 +/- 0.2 nmol/l before VF (p < 0.008 compared to arterial), and increased to 2.5 +/- 0.6 nmol/l immediately after (p < 0.045 compared to basal), to 3 +/- 1.1 nmol/l 2 min after (p < 0.45), and to 2.4 +/- 0.8 nmol/l 5 min after VF. In the basal state there was an uptake of histamine across the coronary circulation. After VF/DEF the level of histamine increased in coronary venous blood, suggesting cardiac release of histamine.

The effects of exogenous histamine in isolated rat hearts

The role of histamine in cardiac physiology and pathophysiology is not clarified, but is dependent on species. The effects of exogenous histamine in Langendorff-perfused rat hearts were investigated. 1 mM, 100, 10, 1 and 0.1 microM of histamine (n = 7 each) as 15 min infusions were employed in a dose-response study, and compared to control perfused hearts (n = 7). In another experimental series, 100 microM histamine (n = 15) was added during reperfusion after 25 min global ischemia, and compared to control ischemia-reperfusion (n = 15). The maximal response to histamine in the dose-response study (100 microM) was an increase of left ventricular developed pressure to 126 +/- 8% of initial value (mean +/- SEM, p < 0.04), and increase of coronary flow to 152+6% (p < 0.02) after 5 min infusion. 100 microM histamine did not significantly influence heart rate or rhythm. The lowest concentration (0.1 microM) did not have effects cardiac performance. Reperfusion with histamine for 2 min after ischemia reduced left ventricular developed pressure to 68 +/- 10% of initial value versus 116+17% in ischemic controls (p < 0.05), and increased left ventricular end-diastolic pressure to 24 +/- 8 mmHg compared to 6 +/- 2 mmHg in controls (p < 0.04). Left ventricular pressures were similar in hearts reperfused with histamine and in ischemic controls for the rest of the observation. Coronary flow increased during reperfusion in hearts given histamine. Histamine had a dose-dependent positive inotropic and vasodilatory effect in isolated rat hearts. Exogenous histamine had only minor effects on post-ischemic cardiac function.