The Lambeth Conventions (II): Guidelines for the study of animal and human ventricular and supraventricular arrhythmias

Protective effect of propolis on myocardial ischemia/reperfusion injury in males and ovariectomized females but not in intact females

The aim of this study is to investigate the effect of propolis, which may have estrogenic effects, on myocardial ischemia/reperfusion (mI/R) injury not only in male rats but also in intact and ovariectomized (ovx) female rats. Six groups were formed: untreated males (n = 8), treated males (n = 9), untreated intact females (n = 9), treated intact females (n = 10), untreated ovx females (n = 10), and treated ovx females (n = 8). An alcoholic extract of a single dose of propolis (200 mg/kg) was administered orally daily for 14 days. Thirty minutes of ischemia and 120 min of reperfusion were performed. Blood pressure, heart rate, arrhythmias (ventricular premature contraction [VPC], ventricular tachycardia [VT], ventricular fibrillation [VF]), and myocardial infarct size were evaluated. Total antioxidant status (TAS), total oxidant status (TOS), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and 17 beta-estradiol (E2) were measured. The untreated females showed more resistance to mI/R injury than the untreated males, as evidenced by lower duration, incidence, and score of arrhythmias, and smaller infarct size (p < .05). After ovx, this resistance disappeared. Propolis improved these values in treated males and treated ovx females (p < .05). Propolis increased TAS in treated males and decreased TOS in treated ovx females as well as elevated SOD in all treated groups (p < .05). Propolis decreased E2 level in treated intact females; however, it increased E2 level in treated ovx females (p < .05). The results revealed that propolis could protect the heart against mI/R injury in males and ovx females. PRACTICAL APPLICATIONS: It is known that the female heart has an increased sensitivity to myocardial ischemia/reperfusion (mI/R) injury due to estrogen deficiency and/or estrogen deprivation following menopause or surgical removal of the ovaries. Propolis has the potential to mimic estrogen under physiological and pathophysiological conditions, as well as its antioxidant property. The results indicated that propolis decreased myocardial infarct size, arrhythmia score, arrhythmia duration, and incidence in ovariectomized female rats and male rats. In addition, the present results demonstrated that an alcoholic extract of propolis as a natural product can effectively maintain the resistance of female heart to mI/R injury after estrogen deficiency.

Patterned Illumination Techniques in Optogenetics: An Insight Into Decelerating Murine Hearts

Much has been reported about optogenetic based cardiac arrhythmia treatment and the corresponding characterization of photostimulation parameters, but still, our capacity to interact with the underlying spatiotemporal excitation patterns relies mainly on electrical and/or pharmacological approaches. However, these well-established treatments have always been an object of somehow heated discussions. Though being acutely life-saving, they often come with potential side-effects leading to a decreased functionality of the complex cardiac system. Recent optogenetic studies showed the feasibility of the usage of photostimulation as a defibrillation method with comparatively high success rates. Although, these studies mainly concentrated on the description as well as on the comparison of single photodefibrillation approaches, such as locally focused light application and global illumination, less effort was spent on the description of excitation patterns during actual photostimulation. In this study, the authors implemented a multi-site photodefibrillation technique in combination with Multi-Lead electrocardiograms (ECGs). The technical connection of real-time heart rhythm measurements and the arrhythmia counteracting light control provides a further step toward automated arrhythmia classification, which can lead to adaptive photodefibrillation methods. In order to show the power effectiveness of the new approach, transgenic murine hearts expressing channelrhodopsin-2 ex vivo were investigated using circumferential micro-LED and ECG arrays. Thus, combining the best of two methods by giving the possibility to illuminate either locally or globally with differing pulse parameters. The optical technique presented here addresses a number of challenges of technical cardiac optogenetics and is discussed in the context of arrhythmic development during photostimulation.

Hyperleptinemia results in systemic inflammation and the exacerbation of ischemia-reperfusion myocardial injury

Aim

Hyperleptinemia potentiates the effects of many atherogenic factors, such as inflammation, platelet aggregation, migration, hypertrophy, proliferation of vascular smooth muscle cells, and endothelial cell dysfunction. The present study analysed the effects of long-term hyperleptinemia in an in vivo myocardial ischemia-reperfusion model to demonstrate whether the in vivo deleterious effect also affects cardiac structure and function.

Main methods

Rats were subcutaneously administered leptin for 8 days to estimate the involvement of the JAK/STAT pathway. Data from 58 male Wistar rats were included in the final analysis. Myocardial infarction (MI) was modelled by the 30-minute ligation of the main left coronary artery followed by 120-minute reperfusion. Hemodynamic measurements, electrocardiography monitoring, echocardiography, myocardial infarct size and area at risk, blood biochemical parameters, leptin, IL-6, TNF-alpha, FGF-21, and cardiomyocyte morphology were measured. The expression of JAK2, p-JAK2, STAT3, p-STAT3 was assessed by Western Blot analysis. Statistical analyses were performed using IBM SPSS Statistics v.26.

Key findings

Eight-day hyperleptinemia in rats leads to an increase in blood pressure and heart rate, myocardial hypertrophy, impaired LV function, the frequency of ischemic arrhythmias, dyslipidemia, systemic inflammation, and the size of induced myocardial infarction. Significance: The blockade of the JAK/STAT signalling pathway effectively reverses the negative effects of leptin, including increased blood pressure and total cholesterol.

Proarrhythmic effects induced by benzethonium chloride and domiphen bromide in vitro and in vivo

Benzethonium chloride (BZT) and domiphen bromide (DMP) are widely used as antimicrobials in drugs, vaccines and industry. However, no cardiac safety data has been developed on both compounds. Previously we reported BZT and DMP as high-affinity human ether-a-go-go related gene (HERG) channel inhibitors with unknown proarrhythmic risk. Here, we investigate the cardiotoxicity of BZT and DMP in vitro and in vivo, aiming to improve the safety-in-use of both antimicrobials. In the present study, human iPSC derived cardiomyocytes (hiPSC-CMs) were generated and rabbit models were used to examine the proarrhythmic potential of BZT and DMP. Our results found that BZT and DMP induced time- and dose-dependent decrease in the contractile parameters of hiPSC-CMs, prolonged FPDc (≥ 0.1 μM), caused tachycardia/fibrillation-like oscillation (0.3-1 μM), ultimately progressing to irreversible arrest of beating (≥ 1 μM). The IC50 values of BZT and DMP derived from normalized beat rate were 0.13 μM and 0.10 μM on hiPSC-CMs at 76 days. Moreover, in vivo rabbit ECG data demonstrated that 12.85 mg/kg BZT and 3.85 mg/kg DMP evoked QTc prolongation, noncomplex arrhythmias and ventricular tachycardias. Our findings support the cardiac safety of 0.01 μM BZT/DMP in vitro and the intravenous infusion of 3.85 mg/kg BZT and 1.28 mg/kg DMP in vivo, whereas higher concentrations of both compounds cause mild to moderate cardiotoxicity that should not be neglected during medical and industrial applications.

A comparative review on heart ion channels, action potentials and electrocardiogram in rodents and human: extrapolation of experimental insights to clinic

Electrocardiogram (ECG) is a non-invasive valuable diagnostic tool that is used in clinics for investigation and monitoring of heart electrical rhythm/conduction, ischemia/injury of heart, electrolyte disturbances and agents/drugs induced cardiac toxicity. Nowadays using animal models to study heart diseases such as electrical and mechanical disturbance is common. In addition, given to ethical consideration and availability, the use of small rodents has been a top priority for cardiovascular researchers. However, extrapolation of experimental findings from the lab to the clinic needs sufficient basic knowledge of similarities and differences between heart action potential and ECG of rodents and humans in normal and disease conditions. This review compares types of human action potentials, the dominant ion currents during action potential phases, alteration in ion channels activities in channelopathies-induced arrhythmias and the ECG appearance of mouse, rat, guinea pig, rabbit and human. Also, it briefly discusses the responsiveness and alterations in ECG following some interventions such as cardiac injury and arrhythmia induction. Overall, it provides a roadmap for researchers in selecting the best animal model/species whose studies results can be translated into clinical practice. In addition, this study will also be useful to biologists, physiologists, pharmacologists, veterinarians and physicians working in the fields of comparative physiology, pharmacology, toxicology and diseases.

Elevated miR-34a expression and altered transcriptional profile are associated with adverse electromechanical remodeling in the heart of male rats exposed to social stress

This study investigated epigenetic risk factors that may contribute to stress-related cardiac disease in a rodent model. Experiment 1 was designed to evaluate the expression of microRNA-34a (miR-34a), a known modulator of both stress responses and cardiac pathophysiology, in the heart of male adult rats exposed to a single or repeated episodes of social defeat stress. Moreover, RNA sequencing was conducted to identify transcriptomic profile changes in the heart of repeatedly stressed rats. Experiment 2 was designed to assess cardiac electromechanical changes induced by repeated social defeat stress that may predispose rats to cardiac dysfunction. Results indicated a larger cardiac miR-34a expression after repeated social defeat stress compared to a control condition. This molecular modification was associated with increased vulnerability to pharmacologically induced arrhythmias and signs of systolic left ventricular dysfunction. Gene expression analysis identified clusters of differentially expressed genes in the heart of repeatedly stressed rats that are mainly associated with morphological and functional properties of the mitochondria and may be directly regulated by miR-34a. These results suggest the presence of an association between miR-34a overexpression and signs of adverse electromechanical remodeling in the heart of rats exposed to repeated social defeat stress, and point to compromised mitochondria efficiency as a potential mediator of this link. This rat model may provide a useful tool for investigating the causal relationship between miR-34a expression, mitochondrial (dys)function, and cardiac alterations under stressful conditions, which could have important implications in the context of stress-related cardiac disease.

Uridine treatment prevents myocardial injury in rat models of acute ischemia and ischemia/reperfusion by activating the mitochondrial ATP-dependent potassium channel

The effect of uridine on the myocardial ischemic and reperfusion injury was investigated. A possible mechanism of its cardioprotective action was established. Two rat models were used: (1) acute myocardial ischemia induced by occlusion of the left coronary artery for 60 min; and (2) myocardial ischemia/reperfusion with 30-min ischemia and 120-min reperfusion. In both models, treatment with uridine (30 mg/kg) prevented a decrease in cell energy supply and in the activity of the antioxidant system, as well as an increase in the level of lipid hydroperoxides and diene conjugates. This led to a reduction of the necrosis zone in the myocardium and disturbances in the heart rhythm. The blocker of the mitochondrial ATP-dependent potassium (mitoKATP) channel 5-hydroxydecanoate limited the positive effects of uridine. The data indicate that the cardioprotective action of uridine may be related to the activation of the mitoKATP channel. Intravenously injected uridine was more rapidly eliminated from the blood in hypoxia than in normoxia, and the level of the mitoKATP channel activator UDP in the myocardium after uridine administration increased. The results suggest that the use of uridine can be a potentially effective approach to the management of cardiovascular diseases.

Effect of age and sex on the incidence of ventricular arrhythmia in a rat model of acute ischemia

BACKGROUND

The impact of sex and age on the arrhythmic susceptibility within the setting of acute ischemia is masked by the fact that acute coronary events result from coronary artery disease appearing with age much earlier among men than among women.

METHODS AND RESULTS

LAD ligation or sham operations were performed in rats of both sexes at the age 3 and 24 months. An ECG was recorded continuously for 6 h after the operation. The number of early and late premature ventricular beats (PVBs), episodes of ventricular tachycardia (VT) and fibrillation (VF), heart rate, QRS, QT and Tpeak-Tend duration were analysed. Epicardial action potentials were recorded in vivo, Ca²⁺ signaling was evaluated in isolated cardiomyocytes, fibrosis and connexin-43 expression and localization were measured in the septum. PVBs, VT and VF episodes are much more common in older males than in young males and females independently from their age. Fibrosis with varying intensity in different muscle layers, hypertrophy of cardiomyocytes, reduced number of gap junctions and their appearance on the lateral myocyte membrane, QT prolongation, increase transmural dispersion of repolarisation and a decreased function of SERCA2a may increase the propensity to arrhythmia within the setting of acute ischemia.

CONCLUSION

We show that the male sex, especially in case of older individuals is a strong predictor of increased arrhythmic susceptibility within the acute ischemia setting regardless of its impact on the occurrence of cardiovascular diseases. A personalized sex-dependent prevention treatment is needed to reduce the mortality in acute phases of myocardial infarction.

Cardiac natriuretic peptide deficiency sensitizes the heart to stress induced ventricular arrhythmias via impaired CREB signaling

AIMS

The cardiac natriuretic peptides (atrial natriuretic peptide [ANP] and B-type natriuretic peptide [BNP]) are important regulators of cardiovascular physiology, with reduced natriuretic peptide (NP) activity linked to multiple human cardiovascular diseases. We hypothesized that deficiency of either ANP or BNP would lead to similar changes in left ventricular structure and function given their shared receptor affinities.

METHODS AND RESULTS

We directly compared murine models deficient of ANP or BNP in the same genetic backgrounds (C57BL6/J) and environments. We evaluated control, ANP deficient (Nppa-/-) or BNP deficient (Nppb-/-) mice under unstressed conditions and multiple forms of pathological myocardial stress. Survival, myocardial structure, function and electrophysiology, tissue histology, and biochemical analyses were evaluated in the groups. In vitro validation of our findings was performed using human derived induced pluripotent stem cell cardiomyocytes (iPS-CM). In the unstressed state, both ANP and BNP deficient mice displayed mild ventricular hypertrophy which did not increase up to 1 year of life. NP-deficient mice exposed to acute myocardial stress secondary to thoracic aortic constriction (TAC) had similar pathological myocardial remodeling but a significant increase in sudden death. We discovered that the NP-deficient mice are more susceptible to stress induced ventricular arrhythmias using both in vivo and ex vivo models. Mechanistically, deficiency of either ANP or BNP led to reduced myocardial cGMP levels and reduced phosphorylation of the cAMP response element-binding protein (CREBS133) transcriptional regulator. Selective CREB inhibition sensitized wild type hearts to stress induced ventricular arrhythmias. ANP and BNP regulate cardiomyocyte CREBS133 phosphorylation through a cGMP-dependent protein kinase 1 (PKG1) and p38 mitogen activated protein kinase (p38 MAPK) signaling cascade.

CONCLUSIONS

Our data show that ANP and BNP act in a non-redundant fashion to maintain myocardial cGMP levels to regulate cardiomyocyte p38 MAPK and CREB activity. Cardiac natriuretic peptide deficiency leads to a reduction in CREB signaling which sensitizes the heart to stress induced ventricular arrhythmias.

TRANSLATIONAL PERSPECTIVE

Our study found that ANP or BNP deficiency leads to increased sudden death and ventricular arrhythmias after acute myocardial stress in murine models. We discovered that ANP and BNP act in a non-redundant fashion to maintain myocardial cGMP levels and uncovered a unique role for these peptides in regulating cardiomyocyte p38 MAPK and CREB signaling through a cGMP-PKG1 pathway. Importantly, this signaling pathway was conserved in human cardiomyocytes. This study provides mechanistic insight into how modulating natriuretic peptide levels in human heart failure patients reduces sudden death and mortality.

Resveratrol Confers Protection Against Ischemia/Reperfusion Injury by Increase of Angiotensin (1-7) Expression in a Rat Model of Myocardial Hypertrophy

ABSTRACT

Left ventricular hypertrophy (LVH) makes the heart vulnerable to ischemia/reperfusion (IR) injury. Angiotensin (Ang) (1-7) is recognized as a cardioprotective peptide. We investigated the effect of polyphenol resveratrol on myocardial IR injury after hypertrophy and examined cardiac content of Ang (1-7) and transcription of its receptor (MasR). Rats were divided into sham-operated, LVH, IR, LVH + IR, and resveratrol + LVH + IR groups. Myocardial hypertrophy and IR models were created by abdominal aortic banding and left coronary artery occlusion, respectively. To evaluate the electrocardiogram parameters and incidence of arrhythmias, electrocardiogram was recorded by subcutaneous leads (lead II). Blood pressure was measured through the left carotid artery. Infarct size was determined by the triphenyl tetrazolium chloride staining. The Ang (1-7) level was evaluated by immunohistochemistry. The Mas receptor mRNA level was assessed by the real-time real time reverse transcription polymerase chain reaction technique. QT-interval duration, infarct size, and incidence of ischemia-induced arrhythmia were significantly higher in the LVH + IR group. However, in the resveratrol-treated group, these parameters were decreased significantly. The cardiac level of Ang (1-7) was decreased in untreated hypertrophied hearts (LVH and LVH + IR groups). Pretreatment with resveratrol normalized the cardiac level of Ang (1-7). The mRNA level of Mas receptor was increased in all of hypertrophied hearts in the presence or absence of resveratrol. Resveratrol can decrease IR injury in rats with LVH. The anti-ischemic effect of resveratrol may be related to the enhancement of Ang (1-7)/MasR axis.

Molecular and Electrophysiological Role of Diabetes-Associated Circulating Inflammatory Factors in Cardiac Arrhythmia Remodeling in a Metabolic-Induced Model of Type 2 Diabetic Rat

Background: Diabetic patients have prolonged cardiac repolarization and higher risk of arrhythmia. Besides, diabetes activates the innate immune system, resulting in higher levels of plasmatic cytokines, which are described to prolong ventricular repolarization. Methods: We characterize a metabolic model of type 2 diabetes (T2D) with prolonged cardiac repolarization. Sprague-Dawley rats were fed on a high-fat diet (45% Kcal from fat) for 6 weeks, and a low dose of streptozotozin intraperitoneally injected at week 2. Body weight and fasting blood glucose were measured and electrocardiograms of conscious animals were recorded weekly. Plasmatic lipid profile, insulin, cytokines, and arrhythmia susceptibility were determined at the end of the experimental period. Outward K⁺ currents and action potentials were recorded in isolated ventricular myocytes by patch-clamp. Results: T2D animals showed insulin resistance, hyperglycemia, and elevated levels of plasma cholesterol, triglycerides, TNFα, and IL-1b. They also developed bradycardia and prolonged QTc-interval duration that resulted in increased susceptibility to severe ventricular tachycardia under cardiac challenge. Action potential duration (APD) was prolonged in control cardiomyocytes incubated 24 h with plasma isolated from diabetic rats. However, adding TNFα and IL-1b receptor blockers to the serum of diabetic animals prevented the increased APD. Conclusions: The elevation of the circulating levels of TNFα and IL-1b are responsible for impaired ventricular repolarization and higher susceptibility to cardiac arrhythmia in our metabolic model of T2D.

Macrophage activation in stellate ganglia contributes to lung injury-induced arrhythmogenesis in male rats

AIM

Patients suffering from acute lung injury (ALI) are at high risk of developing cardiac arrhythmias. We hypothesized that stellate ganglia (SG) neural inflammation contributes to ALI-induced arrhythmia.

METHODS

We created an ALI rat model using a single tracheal instillation of bleomycin (2.5 mg/kg), with saline as a sham control. We recorded ECGs by implanted radiotelemetry in male bleomycin and sham rats treated with and without oral minocycline (20 mg/kg/d), an anti-inflammatory drug that inhibits microglia/macrophage activation. The SG neuronal excitability was assessed by electrophysiology experiments.

RESULTS

ECG data showed that bleomycin-exposed rats exhibited significantly more spontaneous premature ventricular contractions (PVCs) from 1- to 3-week post-induction compared with sham rats, which was mitigated by chronic oral administration of minocycline. The bleomycin-exposed rats displayed a robust increase in both the number of Iba1-positive macrophages and protein expression of interferon regulatory factor 8 in the SG starting as early at 1-week post-exposure and lasted for at least 4 weeks, which was largely attenuated by minocycline. Heart rate variability analysis indicated autonomic imbalance during the first 2-week post-bleomycin, which was significantly attenuated by minocycline. Electrical stimulation of the decentralized SG triggered more PVCs in bleomycin-exposed rats than sham and bleomycin + minocycline rats. Patch-clamp data demonstrated enhanced SG neuronal excitability in the bleomycin-exposed rats, which was attenuated by minocycline. Co-culture of lipopolysaccharide (LPS)-pretreated macrophages with normal SG neurons enhanced SG neuronal excitability.

CONCLUSION

Macrophage activation in the SG contributes to arrhythmogenesis in bleomycin-induced ALI in male rats.

Age-Related Changes in Cardiac Autonomic Modulation and Heart Rate Variability in Mice

Objective

The aim of this study was to assess age-related changes in cardiac autonomic modulation and heart rate variability (HRV) and their association with spontaneous and pharmacologically induced vulnerability to cardiac arrhythmias, to verify the translational relevance of mouse models for further in-depth evaluation of the link between autonomic changes and increased arrhythmic risk with advancing age.

Methods

Heart rate (HR) and time- and frequency-domain indexes of HRV were calculated from Electrocardiogram (ECG) recordings in two groups of conscious mice of different ages (4 and 19 months old) (i) during daily undisturbed conditions, (ii) following peripheral β-adrenergic (atenolol), muscarinic (methylscopolamine), and β-adrenergic + muscarinic blockades, and (iii) following β-adrenergic (isoprenaline) stimulation. Vulnerability to arrhythmias was evaluated during daily undisturbed conditions and following β-adrenergic stimulation.

Results

HRV analysis and HR responses to autonomic blockades revealed that 19-month-old mice had a lower vagal modulation of cardiac function compared with 4-month-old mice. This age-related autonomic effect was not reflected in changes in HR, since intrinsic HR was lower in 19-month-old compared with 4-month-old mice. Both time- and frequency-domain HRV indexes were reduced following muscarinic, but not β-adrenergic blockade in younger mice, and to a lesser extent in older mice, suggesting that HRV is largely modulated by vagal tone in mice. Finally, 19-month-old mice showed a larger vulnerability to both spontaneous and isoprenaline-induced arrhythmias.

Conclusion

The present study combines HRV analysis and selective pharmacological autonomic blockades to document an age-related impairment in cardiac vagal modulation in mice which is consistent with the human condition. Given their short life span, mice could be further exploited as an aged model for studying the trajectory of vagal decline with advancing age using HRV measures, and the mechanisms underlying its association with proarrhythmic remodeling of the senescent heart.

Hyper-O-GlcNAcylation impairs insulin response against reperfusion-induced myocardial injury and arrhythmias in obesity

Myocardial ischemia/reperfusion (I/R) injury is a major determinant of morbidity and mortality in patients undergoing treatment for cardiac disease. A variety of treatments are reported to have benefits against reperfusion injury, yet their cardioprotective effects seem to be diminished in obesity, and the underlying mechanism remains elusive. In this study, we found that db/db mice exhibit cardiac hyper-O-GlcNAcylation. In parallel, palmitate treatment (200 mM; 12 h) in H9c2 cells showed an increase in global protein O-GlcNAcylation, along with an impaired insulin response against reperfusion injury. To investigate whether O-GlcNAcylation underlies this phenomenon, glucosamine was used to increase global protein O-GlcNAc levels. Interestingly, histological staining, electrophysiological studies, serum cardiac markers and oxidative stress biomarker assays showed that preischemic treatment with glucosamine attenuated insulin cardioprotection against myocardial infarction, arrhythmia and oxidative stress. Mechanistically, glucosamine treatment decreased insulin-stimulated Akt phosphorylation, a key modulator of cell survival. Furthermore, inhibition of O-GlcNAcylation via 6-diazo-5-oxo-l-norleucine (DON) apparently increased insulin-induced Akt phosphorylation and restored its cardioprotective response against reperfusion injury in palmitate-induced insulin-resistant H9c2 cells. Our findings demonstrated that obesity-induced hyper-O-GlcNAcylation might contribute to the attenuation of insulin cardioprotection against I/R injury.

Donepezil attenuated cardiac ischemia/reperfusion injury through balancing mitochondrial dynamics, mitophagy, and autophagy

Cardiac autonomic imbalance including sympathetic overactivity and diminished parasympathetic activity is associated with left ventricular (LV) dysfunction in cases of cardiac ischemia/reperfusion (I/R) injury. Electrical stimulation to increase vagal activity has been shown to reduce infarct size and decrease fatal arrhythmias in cardiac I/R injury. However, the benefits of a parasympathomimetic drug on the heart during I/R are unclear. We hypothesized that administration of donepezil provides cardioprotection in cardiac I/R injury via reducing cellular apoptosis, oxidative stress, mitochondrial dysfunction, mitochondrial dynamic imbalance, increasing autophagy, and mitophagy. Fifty-four male Wistar rats were randomly assigned into sham and I/R groups. Acute cardiac I/R injury was induced by 30-minutes left anterior descending (LAD) coronary artery occlusion followed by 120-minutes reperfusion. These rats with induced I/R injury were randomly assigned to be treated with either: (1) Saline (vehicle group) or donepezil 3 mg/kg via intravenous injection given (2) before ischemia, (3) during ischemia, or (4) at the onset of reperfusion. Rats with cardiac I/R injury showed an increase in infarct size and arrhythmia score, LV dysfunction, impaired mitochondrial dynamic balance, autophagy and mitophagy, mitochondrial dysfunction, and increased apoptosis. All the donepezil-treated rats, regardless of the time of administration, showed a similar reduction in these impairments, and rebalancing in cardiac mitochondrial dynamics, leading to reduced myocardial infarct size and arrhythmia, and improved LV function. These findings suggested that donepezil effectively protected the heart against I/R injury through cardiac mitochondrial protection regardless of the time of administration.

Paraquat herbicide diminishes chemoreflex sensitivity, induces cardiac autonomic imbalance and impair cardiac function in rats

Paraquat (PQT) herbicide is widely used in agricultural practices despite being highly toxic to humans. It has been proposed that PQT exposure may promote cardiorespiratory impairment. However, the physiological mechanisms involved in cardiorespiratory dysfunction following PQT exposure are poorly known. We aimed to determine the effects of PQT on ventilatory chemoreflex control, cardiac autonomic control, and cardiac function in rats. Male Sprague-Dawley rats received two injections/week of PQT (5 mg·kg-1 ip) for 4 wk. Cardiac function was assessed through echocardiography and pressure-volume loops. Ventilatory function was evaluated using whole body plethysmography. Autonomic control was indirectly evaluated by heart rate variability (HRV). Cardiac electrophysiology (EKG) and exercise capacity were also measured. Four weeks of PQT administration markedly enlarged the heart as evidenced by increases in ventricular volumes and induced cardiac diastolic dysfunction. Indeed, end-diastolic pressure was significantly higher in PQT rats compared with control (2.42 ± 0.90 vs. 4.01 ± 0.92 mmHg, PQT vs. control, P < 0.05). In addition, PQT significantly reduced both the hypercapnic and hypoxic ventilatory chemoreflex response and induced irregular breathing. Also, PQT induced autonomic imbalance and reductions in the amplitude of EKG waves. Finally, PQT administration impaired exercise capacity in rats as evidenced by a ∼2-fold decrease in times-to-fatigue compared with control rats. Our results showed that 4 wk of PQT treatment induces cardiorespiratory dysfunction in rats and suggests that repetitive exposure to PQT may induce harmful mid/long-term cardiovascular, respiratory, and cardiac consequences.NEW & NOREWORTHY Paraquat herbicide is still employed in agricultural practices in several countries. Here, we showed for the first time that 1 mo paraquat administration results in cardiac adverse remodeling, blunts ventilatory chemoreflex drive, and promotes irregular breathing at rest in previously healthy rats. In addition, paraquat exposure induced cardiac autonomic imbalance and cardiac electrophysiology alterations. Lastly, cardiac diastolic dysfunction was overt in rats following 1 mo of paraquat treatment.

Hyperinsulinaemic hypoglycaemia in non-anaesthetized Göttingen minipigs induces a counter-regulatory endocrine response and electrocardiographic changes

The potentially fatal cardiovascular effects of hypoglycaemia are not well understood and large animal models of the counter-regulatory responses and cardiovascular consequences of insulin-induced hypoglycaemia are needed to understand the mechanisms in humans. The aim of this study was to develop a human-like minipig model of hypoglycaemia including healthy and diabetic pigs to investigate endocrine, electrocardiographic and platelet effects. Hypoglycaemia was induced using a hyperinsulinaemic, hypoglycaemic clamp and an insulin bolus protocol. Plasma glucose, glucagon, C-peptide, insulin, epinephrine and platelet aggregation responses were measured before, during and after hypoglycaemia. Continuous electrocardiographic recordings were obtained. Hypoglycaemia at a plasma glucose concentration of 0.8–1.0 mM in the clamp induced 25-fold increase in epinephrine and sixfold and threefold increase in glucagon for healthy and diabetic pigs, respectively. The hypoglycaemic clamp induced QTc-interval prolongation and increase in cardiac arrhythmias. In the bolus approach, the non-diabetic group reached plasma glucose target of 1.5 mM and QTc-interval was prolonged after insulin injection, but before glucose nadir. The diabetic group did not reach hypoglycaemic target, but still demonstrated QTc-interval prolongation. These results demonstrate effects of hyperinsulinaemic hypoglycaemia closely resembling human physiology, indicating the minipig as a translational animal model of counter-regulatory endocrine and myocardial effects of hypoglycaemia.

Preconditioning and anti-apoptotic effects of Metformin and Cyclosporine-A in an isolated bile duct-ligated rat heart

Despite all previous studies relating to the mechanism of cirrhotic cardiomyopathy (CCM), the role of cirrhosis on Ischemic Preconditioning (IPC) has not yet been explored. The present study strives to assess the cardioprotective role of IPC in bile duct ligated (BDL) rats as well as the cardioprotective role of Cyclosporin-A (CsA) and Metformin (Met) in CCM. Cirrhosis was induced by bile duct ligation (BDL). Rats' hearts were isolated and attached to a Langendorff Apparatus. The pharmacological preconditioning with Met and CsA was done before the main ischemia. Myocardial infarct size, hemodynamic and electrophysiological parameters, biochemical markers, and apoptotic indices were determined at the end of the experiment. Infarct size, apoptotic indices, arrhythmia score, and incidence of VF decreased significantly in the IPC group in comparison with the I/R group. These significant decreases were abolished in the IPC (BDL) group. Met significantly decreased the infarct size and apoptotic indices compared with I/R (BDL) and normal groups, while CsA led to similar decreases except in the level of caspase-3 and -8. Met and CsA decreased and increased the arrhythmia score and incidence of VF in the BDL groups, respectively. Functional recovery indices decreased in the I/R (BDL) and IPC (BDL) groups. Met improved these parameters. Therefore, the current study depicted that the cardioprotective effect of Met and CsA on BDL rats is mediated through the balance between pAMPK and apoptosis in the mitochondria.

Decreasing myocardial estrogen receptors and antioxidant activity may be responsible for increasing ischemia- and reperfusion-induced ventricular arrhythmia in older female rats

AIMS

This study aimed to investigate the relationship between ischemia- and reperfusion-induced arrhythmia and blood serum estrogen levels, myocardial estrogen receptor levels, antioxidant enzyme activities, and the effects of the estrogen receptor blocker, fulvestrant (ICI 182 780).

MAIN METHODS

A total of 102 female Sprague-Dawley rats of different ages (2-3, 6-7, 14-15, and 20-21 months) were used in this study. Myocardial ischemia was produced by ligation of the descending branch of the left anterior descending coronary artery, and reperfusion was produced by releasing this artery. An electrocardiogram (ECG) and blood pressure were recorded for 6 min of ischemia and 6 min of reperfusion. The levels of superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), estrogen receptor α (ERα), and estrogen receptor β (ERβ) in myocardial tissue and 17 beta-estradiol (E2) in blood serum were measured via enzyme-linked immunosorbent assay (ELISA). The results were compared using a Mann-Whitney U test, one-way analysis of variance (ANOVA), and a student's t-test.

KEY FINDINGS

It is not the changes in serum estrogen levels but the decreasing myocardial estrogen receptors and antioxidant activities that could be responsible for the occurrence of more severe arrhythmia in response to reperfusion in older female rats.

SIGNIFICANCE

The death rate due to a heart attack in younger men is higher than in women. However, it equalizes after the menopausal stage in women. In this study, the reason for the increasing sudden post-menopausal death rate in women was investigated experimentally.

Sexual Dimorphisms, Anti-Hormonal Therapy and Cardiac Arrhythmias

Significant variations from the normal QT interval range of 350 to 450 milliseconds (ms) in men and 360 to 460 ms in women increase the risk for ventricular arrhythmias. This difference in the QT interval between men and women has led to the understanding of the influence of sex hormones on the role of gender-specific channelopathies and development of ventricular arrhythmias. The QT interval, which represents the duration of ventricular repolarization of the heart, can be affected by androgen levels, resulting in a sex-specific predilection for acquired and inherited channelopathies such as acquired long QT syndrome in women and Brugada syndrome and early repolarization syndrome in men. Manipulation of the homeostasis of these sex hormones as either hormonal therapy for certain cancers, recreational therapy or family planning and in transgender treatment has also been shown to affect QT interval duration and increase the risk for ventricular arrhythmias. In this review, we highlight the effects of endogenous and exogenous sex hormones in the physiological and pathological states on QTc variation and predisposition to gender-specific pro-arrhythmias.

Paeonol Protects Against Myocardial Ischemia/Reperfusion-Induced Injury by Mediating Apoptosis and Autophagy Crosstalk

Many studies have shown that crosstalk exists between apoptosis and autophagy, despite differences in mechanisms between these processes. Paeonol, a major phenolic compound isolated from Moutan Cortex Radicis, the root bark of Paeonia × suffruticosa Andrews (Paeoniaceae), is widely used in traditional Chinese medicine as an antipyretic, analgesic and anti-inflammatory agent. In this study, we investigated the detailed molecular mechanisms of the crosstalk between apoptosis and autophagy underlying the cardioprotective effects of paeonol in rats subjected to myocardial ischemia/reperfusion (I/R) injury. Myocardial I/R injury was induced by occlusion of the left anterior descending coronary artery (LAD) for 1 h followed by 3 h of reperfusion. Paeonol was intravenously administered 15 min before LAD ligation. We found that paeonol significantly improved cardiac function after myocardial I/R injury and significantly decreased myocardial I/R-induced arrhythmia and mortality. Paeonol also significantly decreased myocardial infarction and plasma LDH activity and Troponin-I levels in carotid blood after I/R. Compared with vehicle treatment, paeonol significantly upregulated Bcl-2 protein expression and significantly downregulated the cleaved forms of caspase-8, caspase-9, caspase-3 and PARP protein expression in the I/R injured myocardium. Myocardial I/R-induced autophagy, including the increase of Beclin-1, p62, LC3-I, and LC3-II protein expression in the myocardium was significantly reversed by paeonol treatment. Paeonol also significantly increased the Bcl-2/Bax and Bcl-2/Beclin-1 ratios in the myocardium after I/R injury. The cardioprotective role of paeonol during I/R injury may be due to its mediation of crosstalk between apoptotic and autophagic signaling pathways, which inhibits apoptosis and autophagic cell death.

The Agonist of Inward Rectifier Potassium Channel (IK1) Attenuates Rat Reperfusion Arrhythmias Linked to CaMKII Signaling

Inward rectifier potassium channels (IK1, Kir) are known to play critical roles in arrhythmogenesis. Thus, how IK1 agonist affects reperfusion arrhythmias needs to be clarified, and its underlying mechanisms should be determined. Reperfusion arrhythmias were modeled by coronary ligation (ischemia, 15 minutes) and release (reperfusion, 15 minutes). Zacopride (1.5-50 μg/kg in vivo, or 0.1-10 μmol/Lex vivo) was applied in the settings of pretreatment (3 minutes before coronary ligation) and posttreatment (5 minutes after coronary ligation). Hypoxia (45 minutes) /reoxygenation (30 minutes) model was established in cultured H9c2 (2-1) cardiomyocytes. Zacopride or KN93 was applied before hypoxia (pretreatment). In the setting of pre- or posttreatment, zacopride at 15 μg/kg in vivo or 1 μmol/Lin vitro exhibited superlative protections on reperfusion arrhythmias or intracellular calcium overload. Western blot data from ex vivo hearts or H9c2 (2-1) cardiomyocytes showed that I/R (H/R) induced the inhibition of Kir2.1 (the dominant subunit of IK1 channel in ventricle), phosphorylation and oxidation of CaMKII, downregulation of SERCA2, phosphorylation of phospholamban (at Thr17), and activation of caspase-3. Zacopride treatment (1 μmol/L) was noted to strikingly restore the expression of Kir2.1 and SERCA2 and decrease the activity of CaMKII, phospholamban, and caspase-3. These effects were largely eliminated by co-application of IK1 blocker BaCl2. CaMKII inhibitor KN93 attenuated calcium overload and p-PLB (Thr17) in an IK1-independent manner. IK1-depedent inhibition of CaMKII activity is found to be a key cardiac salvage signaling under Ca2+ dyshomeostasis and reactive oxygen species (ROS) stress. IK1 might be a novel target for pharmacological conditioning of reperfusion arrhythmia, especially for the application after unpredictable ischemia.

Pinocembrin Decreases Ventricular Fibrillation Susceptibility in a Rat Model of Depression

Background: Depression is associated with the increased risk of mortality and morbidity and is an independent risk factor for many cardiovascular diseases. Depression may promote cardiac arrhythmias, but little is known about the mechanisms. Pinocembrin mitigated depressive-like behaviors and exhibited cardioprotective effects in several models; however, whether pinocembrin benefits ventricular arrhythmias in depression models has not been elucidated. Thus, this study was to evaluate the effects of pinocembrin on ventricular fibrillation susceptibility in rat models of depression.

Methods: Male Sprague-Dawley rats were randomly assigned into control, control + pinocembrin, MDD (major depressive disorder), and MDP (MDD + pinocembrin) groups, respectively. Depressive-like behaviors, ventricular electrophysiological parameters, electrocardiogram parameters, heart rate variability, ventricular histology, serum norepinephrine, tumor necrosis factor-α, and interleukin-1β were detected. Protein levels in left ventricle were measured by Western blot assays.

Results: Compared with the MDD group, pinocembrin significantly mitigated depressive-like behaviors, prolonged ventricular effective refractory period, action potential duration, QT, and corrected QT (QTc) interval, improved heart rate variability, decreased Tpeak–Tend interval, ventricular fibrillation inducibility rate, ventricular fibrosis, ventricular positive nerve densities, and protein expression of tyrosine hydroxylase and growth associated protein-43, reduced serum norepinephrine, tumor necrosis factor-α, interleukin-1β concentrations, and the expression levels of p-IκBα and p-p65, and increased the protein expression of Cx43, Cav1.2, and Kv.4.2 in the MDP group.

Conclusion: Pinocembrin attenuates ventricular electrical remodeling, autonomic remodeling, and ion-channel remodeling, lowers ventricular fibrosis, and suppresses depression-induced inflammatory responses, providing new insights in pinocembrin and ventricular arrhythmias in depressed patients.

Antiarrhythmic and cardiac electrophysiological effects of SZV-270, a novel compound with combined Class I/B and Class III effects, in rabbits and dogs

Cardiovascular diseases are the leading causes of mortality. Sudden cardiac death is most commonly caused by ventricular fibrillation (VF). Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and a major cause of stroke and heart failure. Pharmacological management of VF and AF remains suboptimal due to limited efficacy of antiarrhythmic drugs and their ventricular proarrhythmic adverse effects. In this study, the antiarrhythmic and cardiac cellular electrophysiological effects of SZV-270, a novel compound, were investigated in rabbit and canine models. SZV-270 significantly reduced the incidence of VF in rabbits subjected to coronary artery occlusion/reperfusion and reduced the incidence of burst-induced AF in a tachypaced conscious canine model of AF. SZV-270 prolonged the frequency-corrected QT interval, lengthened action potential duration and effective refractory period in ventricular and atrial preparations, blocked I _Kr in isolated cardiomyocytes (Class III effects), and reduced the maximum rate of depolarization (V _max) at cycle lengths smaller than 1000 ms in ventricular preparations (Class I/B effect). Importantly, SZV-270 did not provoke Torsades de Pointes arrhythmia in an anesthetized rabbit proarrhythmia model characterized by impaired repolarization reserve. In conclusion, SZV-270 with its combined Class I/B and III effects can prevent reentry arrhythmias with reduced risk of provoking drug-induced Torsades de Pointes.

Ivabradine is as effective as metoprolol in the prevention of ventricular arrhythmias in acute non-reperfused myocardial infarction in the rat

Ventricular arrhythmias are a major source of early mortality in acute myocardial infarction (MI) and remain a major therapeutic challenge. Thus we investigated effects of ivabradine, a presumably specific bradycardic agent versus metoprolol, a β-blocker, at doses offering the same heart rate (HR) reduction, on ventricular arrhythmias in the acute non-reperfused MI in the rat. Immediately after MI induction a single dose of ivabradine/ metoprolol was given. ECG was continuously recorded and ventricular arrhythmias were analyzed. After 6 h epicardial monophasic action potentials (MAPs) were recorded and cardiomyocyte Ca²⁺ handling was assessed. Both ivabradine and metoprolol reduced HR by 17% and arrhythmic mortality (14% and 19%, respectively, versus 33% in MI, p < 0.05) and ventricular arrhythmias in post-MI rats. Both drugs reduced QTc prolongation and decreased sensitivity of ryanodine receptors in isolated cardiomyocytes, but otherwise had no effect on Ca²⁺ handling, velocity of conduction or repolarization. We did not find any effects of potential I_Kr inhibition by ivabradine in this setting. Thus Ivabradine is an equally effective antiarrhythmic agent as metoprolol in early MI in the rat. It could be potentially tested as an alternative antiarrhythmic agent in acute MI when β-blockers are contraindicated.

Canonical and Non-Canonical Roles of Connexin43 in Cardioprotection

Since the mid-20th century, ischemic heart disease has been the world’s leading cause of death. Developing effective clinical cardioprotection strategies would make a significant impact in improving both quality of life and longevity in the worldwide population. Both ex vivo and in vivo animal models of cardiac ischemia/reperfusion (I/R) injury are robustly used in research. Connexin43 (Cx43), the predominant gap junction channel-forming protein in cardiomyocytes, has emerged as a cardioprotective target. Cx43 posttranslational modifications as well as cellular distribution are altered during cardiac reperfusion injury, inducing phosphorylation states and localization detrimental to maintaining intercellular communication and cardiac conduction. Pre- (before ischemia) and post- (after ischemia but before reperfusion) conditioning can abrogate this injury process, preserving Cx43 and reducing cell death. Pre-/post-conditioning has been shown to largely rely on the presence of Cx43, including mitochondrial Cx43, which is implicated to play a major role in pre-conditioning. Posttranslational modifications of Cx43 after injury alter the protein interactome, inducing negative protein cascades and altering protein trafficking, which then causes further damage post-I/R injury. Recently, several peptides based on the Cx43 sequence have been found to successfully diminish cardiac injury in pre-clinical studies.

Acute metformin treatment provides cardioprotection via improved mitochondrial function in cardiac ischemia / reperfusion injury

Cardiac ischemia/reperfusion (I/R) injury following reperfusion therapy in acute myocardial infarction results in mitochondrial dynamic imbalance and cardiomyocyte apoptosis. Although diabetic patients taking metformin have been shown to have a lower risk of myocardial infarction, the efficacy of the cardioprotection conferred by metformin regarding the mitochondrial function and dynamic in cardiac I/R injury are still inconclusive. In addition, the comparative effects between different doses of metformin given acutely prior to cardiac I/R injury have never been investigated. Fifty 8-week-old male Wistar rats weighing 300-350 g were divided into sham-operated (n = 10) and cardiac I/R-operated (n = 40) groups. In the cardiac I/R group, rats underwent 30-min ischemia followed by 120-min reperfusion and were randomly divided into four subgroups (n = 10/group): control (received normal saline), metformin (100, 200, and 400 mg/kg). The arrhythmia score, cardiac function, infarct size, mortality rate, mitochondrial function and apoptosis, were determined. Metformin (200 mg/kg) exerted the highest level of cardioprotection through reduction in arrhythmia, infarct size, mitochondrial fission, and apoptosis, in addition to preservation of mitochondrial function, leading to the attenuation of cardiac dysfunction. Doses of metformin (100 and 400 mg/kg) also improved mitochondrial and cardiac function, but to a lesser extent than metformin (200 mg/kg). In conclusion, metformin exerts cardioprotection by attenuating mitochondrial dysfunction, mitochondrial dynamic imbalance, and apoptosis. These led to decreased infarct size and eventual improvement in cardiac function in rats with acute cardiac I/R injury. These findings indicate the potential clinical benefits of acute metformin treatment in acute myocardial infarction.

Social defeat: Vagal reduction and vulnerability to ventricular arrhythmias

Previously, a sub-population of defeated anesthetized rats (Dlow) was characterized by persistent low blood levels of brain-derived neurotrophic factor (BDNF) at day 29 and autonomic alteration at day 30 after social challenge, while the other population (Dhigh) was similar to non-defeated (ND) animals. The aims of this study were to determine the time-course of autonomic dysfunction in awake animals, and whether Dhigh and/or Dlow were vulnerable to cardiac events. Defeated animals were exposed to four daily episodes of social defeats from day 1 to day 4. At day 30, anesthetized Dlow displayed decreased experimental and spontaneous reflex responses reflecting lower parasympathetic efficiency. In addition, Dlow but not Dhigh were characterized by left ventricular hypertrophy at day 30. Telemetric recordings revealed that Dlow had increased low frequency-to-high frequency ratio (LF/HF) and diastolic (DBP) and systolic (SBP) blood pressure, associated with decreased HF and spontaneous baroreflex responses (BRS) from day 3 to day 29. LF/HF, DBP and SBP recovered at day 5, and HF and BRS recovered at day 15 in Dhigh. Ventricular premature beats (VPBs) occurred in Dlow and Dhigh animals from day 5. Time course of VBP fluctuations in Dhigh mirrored that of HF and BRS, but not that of LF/HF, DBP and SBP. These results suggest that a psychosocial stress associated to low serum BDNF levels can lead to vulnerability to persistent autonomic dysfunction, cardiac hypertrophy and ventricular ectopic beats. The parasympathetic recovery seen in Dhigh may provide protection against cardiac events in this population.

The conductive function of biopolymer corrects myocardial scar conduction blockage and resynchronizes contraction to prevent heart failure

Myocardial fibrosis, resulting from ischemic injury, increases tissue resistivity in the infarct area, which impedes heart synchronous electrical propagation. The uneven conduction between myocardium and fibrotic tissue leads to dys-synchronous contraction, which progresses towards ventricular dysfunction. We synthesized a conductive poly-pyrrole-chitosan hydrogel (PPY-CHI), and investigated its capabilities in improving electrical propagation in fibrotic tissue, as well as resynchronizing cardiac contraction to preserve cardiac function. In an in vitro fibrotic scar model, conductivity increased in proportion to the amount of PPY-CHI hydrogel added. To elucidate the mechanism of interaction between myocardial ionic changes and electrical current, an equivalent circuit model was used, which showed that PPY-CHI resistance was 10 times lower, and latency time 5 times shorter, compared to controls. Using a rat myocardial infarction (MI) model, PPY-CHI was injected into fibrotic tissue 7 days post MI. There, PPY-CHI reduced tissue resistance by 30%, improved electrical conduction across the fibrotic scar by 33%, enhanced field potential amplitudes by 2 times, and resynchronized cardiac contraction. PPY-CHI hydrogel also preserved cardiac function at 3 months, and reduced susceptibility to arrhythmia by 30% post-MI. These data demonstrated that the conductive PPY-CHI hydrogel reduced fibrotic scar resistivity, and enhanced electrical conduction, to synchronize cardiac contraction.

Botulinum Toxin-Chitosan Nanoparticles Prevent Arrhythmia in Experimental Rat Models

Several experimental studies have recently demonstrated that temporary autonomic block using botulinum toxin (BoNT/A1) might be a novel option for the treatment of atrial fibrillation. However, the assessment of antiarrhythmic properties of BoNT has so far been limited, relying exclusively on vagal stimulation and rapid atrial pacing models. The present study examined the antiarrhythmic effect of specially formulated BoNT/A1-chitosan nanoparticles (BTN) in calcium chloride-, barium chloride- and electrically induced arrhythmia rat models. BTN enhanced the effect of BoNT/A1. Subepicardial injection of BTN resulted in a significant antiarrhythmic effect in investigated rat models. BTN formulation antagonizes arrhythmia induced by the activation of Ca, K and Na channels.

Association between heart rate variability indices and features of spontaneous ventricular tachyarrhythmias in mice

Direct evidence is limited for the association between heart rate variability (HRV) indices and ventricular tachyarrhythmias (VTAs). While galectin-3 (Gal-3) is regarded as a causal factor for cardiac remodelling and a biomarker for arrhythmias, its regulation on VTAs and HVR is unknown. Using aged transgenic (TG) mice with cardiac overexpression of β2 -adrenoceptors and spontaneous VTAs, we studied whether changes in HRV indices correlated with the severity of VTAs, and whether Gal-3 gene knockout (KO) in TG mice might limit VTA. Body-surface ECG was recorded (10-minute period) in 9- to 10-month-old mice of non-transgenic (nTG), TG and TG × Gal-3 knockout (TG/KO). Time-domain, frequency-domain and nonlinear-domain HRV indices were calculated using the R-R intervals extracted from ECG signals and compared with frequency of VTAs. TG and TG/KO mice developed frequent VTAs and showed significant changes in certain time-domain and nonlinear-domain HRV indices relative to nTG mice. The severity of VTAs in TG and TG/KO mice in combination, estimated by VTA counts and arrhythmia score, was significantly correlated with certain time-domain and nonlinear-domain HRV indices. In conclusion, significant changes in HRV indices were evident and correlated with the severity of spontaneous VTAs in TG mice. The frequency of VTA and HRV indices were largely comparable between TG and TG/KO mice. Deletion of Gal-3 in TG mice altered certain HRV indices implying influence by neuronally localized Gal-3 on autonomic nervous activity.

Transgenic LQT2, LQT5, and LQT2-5 rabbit models with decreased repolarisation reserve for prediction of drug-induced ventricular arrhythmias

Background and Purpose

Reliable prediction of pro‐arrhythmic side effects of novel drug candidates is still a major challenge. Although drug‐induced pro‐arrhythmia occurs primarily in patients with pre‐existing repolarisation disturbances, healthy animals are employed for pro‐arrhythmia testing. To improve current safety screening, transgenic long QT (LQTS) rabbit models with impaired repolarisation reserve were generated by overexpressing loss‐of‐function mutations of human HERG (HERG‐G628S, loss of I_Kr; LQT2), KCNE1 (KCNE1‐G52R, decreased I_Ks; LQT5), or both transgenes (LQT2‐5) in the heart.

Experimental Approach

Effects of K⁺ channel blockers on cardiac repolarisation and arrhythmia susceptibility were assessed in healthy wild‐type (WT) and LQTS rabbits using in vivo ECG and ex vivo monophasic action potential and ECG recordings in Langendorff‐perfused hearts.

Key Results

LQTS models reflect patients with clinically “silent” (LQT5) or “manifest” (LQT2 and LQT2‐5) impairment in cardiac repolarisation reserve: they were more sensitive in detecting I_Kr‐blocking (LQT5) or I_K1/I_Ks‐blocking (LQT2 and LQT2‐5) properties of drugs compared to healthy WT animals. Impaired QT‐shortening capacity at fast heart rates was observed due to disturbed I_Ks function in LQT5 and LQT2‐5. Importantly, LQTS models exhibited higher incidence, longer duration, and more malignant types of ex vivo arrhythmias than WT.

Conclusion and Implications

LQTS models represent patients with reduced repolarisation reserve due to different pathomechanisms. As they demonstrate increased sensitivity to different specific ion channel blockers (I_Kr blockade in LQT5 and I_K1 and I_Ks blockade in LQT2 and LQT2‐5), their combined use could provide more reliable and more thorough prediction of (multichannel‐based) pro‐arrhythmic potential of novel drug candidates.

Pralidoxime-Induced Potentiation of the Pressor Effect of Adrenaline and Hastened Successful Resuscitation by Pralidoxime in a Porcine Cardiac Arrest Model

PURPOSE

Pralidoxime potentiated the pressor effect of adrenaline and facilitated restoration of spontaneous circulation (ROSC) after prolonged cardiac arrest. In this study, we hypothesised that pralidoxime would hasten ROSC in a model with a short duration of untreated ventricular fibrillation (VF). We also hypothesised that potentiation of the pressor effect of adrenaline by pralidoxime would not be accompanied by worsening of the adverse effects of adrenaline.

METHODS

After 5 min of VF, 20 pigs randomly received either pralidoxime (40 mg/kg) or saline, in combination with adrenaline, during cardiopulmonary resuscitation (CPR). Coronary perfusion pressure (CPP) during CPR, and ease of resuscitation were compared between the groups. Additionally, haemodynamic data, severity of ventricular arrhythmias, and cerebral microcirculation were measured during the 1-h post-resuscitation period. Cerebral microcirculatory blood flow and brain tissue oxygen tension (PbtO₂) were measured on parietal cortices exposed through burr holes.

RESULTS

All animals achieved ROSC. The pralidoxime group had higher CPP during CPR (P = 0.014) and required a shorter duration of CPR (P = 0.024) and smaller number of adrenaline doses (P = 0.024). During the post-resuscitation period, heart rate increased over time in the control group, and decreased steadily in the pralidoxime group. No inter-group differences were observed in the incidences of ventricular arrhythmias, cerebral microcirculatory blood flow, and PbtO₂.

CONCLUSION

Pralidoxime improved CPP and hastened ROSC in a model with a short duration of untreated VF. The potentiation of the pressor effect of adrenaline was not accompanied by the worsening of the adverse effects of adrenaline.

Acute dapagliflozin administration exerts cardioprotective effects in rats with cardiac ischemia/reperfusion injury

BACKGROUND

A sodium-glucose co-transporter 2 (SGLT-2) inhibitor had favorable impact on the attenuation of hyperglycemia together with the severity of heart failure. However, the effects of acute dapagliflozin administration at the time of cardiac ischemia/reperfusion (I/R) injury are not established.

METHODS

The effects of dapagliflozin on cardiac function were investigated by treating cardiac I/R injury at different time points. Cardiac I/R was instigated in forty-eight Wistar rats. These rats were then split into 4 interventional groups: control, dapagliflozin (SGLT2 inhibitor, 1 mg/kg) given pre-ischemia, at the time of ischemia and at the beginning of reperfusion. Left ventricular (LV) function and arrhythmia score were evaluated. The hearts were used to evaluate size of myocardial infarction, cardiomyocyte apoptosis, cardiac mitochondrial dynamics and function.

RESULTS

Dapagliflozin given pre-ischemia conferred the maximum level of cardioprotection quantified through the decrease in arrhythmia, attenuated infarct size, decreased cardiac apoptosis and improved cardiac mitochondrial function, biogenesis and dynamics, leading to LV function improvement during cardiac I/R injury. Dapagliflozin given during ischemia also showed cardioprotection, but at a lower level of efficacy.

CONCLUSIONS

Acute dapagliflozin administration during cardiac I/R injury exerted cardioprotective effects by attenuating cardiac infarct size, increasing LV function and reducing arrhythmias. These benefits indicate its potential clinical usefulness.

Characterisation of mexiletine's translational therapeutic index for suppression of ischaemia-induced ventricular fibrillation in the rat isolated heart

The 'translational therapeutic index' (TTI) is a drug's ratio of nonclinical threshold dose (or concentration) for significant benefit versus threshold for adversity. In early nonclinical research, discovery and safety studies are normally undertaken separately. Our aim was to evaluate a novel integrated approach for generating a TTI for drugs intended for prevention of ischaemia-induced ventricular fibrillation (VF). We templated the current best available class 1b antiarrhythmic, mexiletine, using the rat Langendorff preparation. Mexiletine's beneficial effects on the incidence of VF caused by 120 min regional ischaemia were contrasted with its concurrent adverse effects (on several variables) in the same hearts, to generate a TTI. Mexiletine 0.1 and 0.5 µM had no adverse effects, but did not reduce VF incidence. Mexiletine 1 µM reduced VF incidence to 0% but had adverse effects on atrioventricular conduction and ventricular repolarization. Separate studies undertaken using an intraventricular balloon revealed no detrimental effects of mexiletine (1 and 5 µM) on mechanical function, or any benefit against reperfusion-related dysfunction. Mexiletine's TTI was found to be less than two, which accords with its clinical therapeutic index. Although non-cardiac adversity, identifiable from additional in vivo studies, may reduce the TTI further, it cannot increase it. Our experimental approach represents a useful early-stage integrated risk/benefit method that, when TTI is found to be low, would eliminate unsuitable class 1b drugs prior to next stage in vivo work, with mexiletine's TTI defining the gold standard that would need to be bettered.

Cardiac remodeling and arrhythmogenesis are ameliorated by administration of Cx43 mimetic peptide Gap27 in heart failure rats

Alterations in connexins and specifically in 43 isoform (Cx43) in the heart have been associated with a high incidence of arrhythmogenesis and sudden death in several cardiac diseases. We propose to determine salutary effect of Cx43 mimetic peptide Gap27 in the progression of heart failure. High-output heart failure was induced by volume overload using the arterio-venous fistula model (AV-Shunt) in adult male rats. Four weeks after AV-Shunt surgery, the Cx43 mimetic peptide Gap27 or scrambled peptide, were administered via osmotic minipumps (AV-Shunt_Gap27 or AV-Shunt_Scr) for 4 weeks. Cardiac volumes, arrhythmias, function and remodeling were determined at 8 weeks after AV-Shunt surgeries. At 8^th week, AV-Shunt_Gap27 showed a marked decrease in the progression of cardiac deterioration and showed a significant improvement in cardiac functions measured by intraventricular pressure-volume loops. Furthermore, AV-Shunt_Gap27 showed less cardiac arrhythmogenesis and cardiac hypertrophy index compared to AV-Shunt_Scr. Gap27 treatment results in no change Cx43 expression in the heart of AV-Shunt rats. Our results strongly suggest that Cx43 play a pivotal role in the progression of cardiac dysfunction and arrhythmogenesis in high-output heart failure; furthermore, support the use of Cx43 mimetic peptide Gap27 as an effective therapeutic tool to reduce the progression of cardiac dysfunction in high-output heart failure.

Systematic review of guidelines for internal validity in the design, conduct and analysis of preclinical biomedical experiments involving laboratory animals

Over the last two decades, awareness of the negative repercussions of flaws in the planning, conduct and reporting of preclinical research involving experimental animals has been growing. Several initiatives have set out to increase transparency and internal validity of preclinical studies, mostly publishing expert consensus and experience. While many of the points raised in these various guidelines are identical or similar, they differ in detail and rigour. Most of them focus on reporting, only few of them cover the planning and conduct of studies. The aim of this systematic review is to identify existing experimental design, conduct, analysis and reporting guidelines relating to preclinical animal research. A systematic search in PubMed, Embase and Web of Science retrieved 13 863 unique results. After screening these on title and abstract, 613 papers entered the full-text assessment stage, from which 60 papers were retained. From these, we extracted unique 58 recommendations on the planning, conduct and reporting of preclinical animal studies. Sample size calculations, adequate statistical methods, concealed and randomised allocation of animals to treatment, blinded outcome assessment and recording of animal flow through the experiment were recommended in more than half of the publications. While we consider these recommendations to be valuable, there is a striking lack of experimental evidence on their importance and relative effect on experiments and effect sizes.

General Principles of Preclinical Study Design

Preclinical studies using animals to study the potential of a therapeutic drug or strategy are important steps before translation to clinical trials. However, evidence has shown that poor quality in the design and conduct of these studies has not only impeded clinical translation but also led to significant waste of valuable research resources. It is clear that experimental biases are related to the poor quality seen with preclinical studies. In this chapter, we will focus on hypothesis testing type of preclinical studies and explain general concepts and principles in relation to the design of in vivo experiments, provide definitions of experimental biases and how to avoid them, and discuss major sources contributing to experimental biases and how to mitigate these sources. We will also explore the differences between confirmatory and exploratory studies, and discuss available guidelines on preclinical studies and how to use them. This chapter, together with relevant information in other chapters in the handbook, provides a powerful tool to enhance scientific rigour for preclinical studies without restricting creativity.

Reperfusion Arrhythmias Increase after Superior Cervical Ganglionectomy Due to Conduction Disorders and Changes in Repolarization

Pharmacological concentrations of melatonin reduce reperfusion arrhythmias, but less is known about the antiarrhythmic protection of the physiological circadian rhythm of melatonin. Bilateral surgical removal of the superior cervical ganglia irreversibly suppresses melatonin rhythmicity. This study aimed to analyze the cardiac electrophysiological effects of the loss of melatonin circadian oscillation and the role played by myocardial melatonin membrane receptors, SERCA_2A, TNFα, nitrotyrosine, TGFβ, K_ATP channels, and connexin 43. Three weeks after bilateral removal of the superior cervical ganglia or sham surgery, the hearts were isolated and submitted to ten minutes of regional ischemia followed by ten minutes of reperfusion. Arrhythmias, mainly ventricular tachycardia, increased during reperfusion in the ganglionectomy group. These hearts also suffered an epicardial electrical activation delay that increased during ischemia, action potential alternants, triggered activity, and dispersion of action potential duration. Hearts from ganglionectomized rats showed a reduction of the cardioprotective MT₂ receptors, the MT₁ receptors, and SERCA_2A. Markers of nitroxidative stress (nitrotyrosine), inflammation (TNFα), and fibrosis (TGFβ and vimentin) did not change between groups. Connexin 43 lateralization and the pore-forming subunit (Kir6.1) of K_ATP channels increased in the experimental group. We conclude that the loss of the circadian rhythm of melatonin predisposes the heart to suffer cardiac arrhythmias, mainly ventricular tachycardia, due to conduction disorders and changes in repolarization.

Elevated β1-Adrenergic Receptor Autoantibody Levels Increase Atrial Fibrillation Susceptibility by Promoting Atrial Fibrosis

Objective

Beta 1-adrenergic receptor autoantibodies (β1ARAbs) have been identified as a pathogenic factor in atrial fibrillation (AF), but the underlying pathogenetic mechanism is not well understood. We assessed the hypothesis that elevated β1ARAb levels increase AF susceptibility by promoting atrial fibrosis.

Methods

A total of 70 patients with paroxysmal AF were continuously recruited. The serum levels of β1ARAb and circulating fibrosis biomarkers were analyzed by ELISA. Linear regression was used to examine the correlations of β1ARAb levels with left atrial diameter (LAD) and circulating fibrosis biomarker levels. Furthermore, we established a rabbit β1ARAb overexpression model. We conducted electrophysiological studies and multielectrode array recordings to evaluate the atrial effective refractory period (AERP), AF inducibility and electrical conduction. AF was defined as irregular, rapid atrial beats > 500 bpm for > 1000 ms. Echocardiography, hematoxylin and eosin staining, Masson's trichrome staining, and picrosirius red staining were performed to evaluate changes in atrial structure and detect fibrosis. Western blotting and PCR were used to detect alterations in the protein and mRNA expression of TGF-β1, collagen I and collagen III.

Results

Patients with a LAD ≥ 40 mm had higher β1ARAb levels than patients with a smaller LAD (8.87 ± 3.16 vs. 6.75 ± 1.34 ng/mL, P = 0.005). β1ARAb levels were positively correlated with LAD and circulating biomarker levels (all P < 0.05). Compared with the control group, the rabbits in the immune group showed the following: (1) enhanced heart rate, shortened AERP (70.00 ± 5.49 vs. 96.46 ± 3.27 ms, P < 0.001), increased AF inducibility (55% vs. 0%, P < 0.001), decreased conduction velocity and increased conduction heterogeneity; (2) enlarged LAD and elevated systolic dysfunction; (3) significant fibrosis in the left atrium identified by Masson's trichrome staining (15.17 ± 3.46 vs. 4.92 ± 1.72%, P < 0.001) and picrosirius red staining (16.76 ± 6.40 vs. 4.85 ± 0.40%, P < 0.001); and (4) increased expression levels of TGF-β1, collagen I and collagen III.

Conclusion

Our clinical and experiential studies showed that β1ARAbs participate in the development of AF and that the potential mechanism is related to the promotion of atrial fibrosis.

Hidden Cardiotoxicity of Rofecoxib Can be Revealed in Experimental Models of Ischemia/Reperfusion

Cardiac adverse effects are among the leading causes of the discontinuation of clinical trials and the withdrawal of drugs from the market. The novel concept of ‘hidden cardiotoxicity’ is defined as cardiotoxicity of a drug that manifests in the diseased (e.g., ischemic/reperfused), but not in the healthy heart or as a drug-induced deterioration of cardiac stress adaptation (e.g., ischemic conditioning). Here, we aimed to test if the cardiotoxicity of a selective COX-2 inhibitor rofecoxib that was revealed during its clinical use, i.e., increased occurrence of proarrhythmic and thrombotic events, could have been revealed in early phases of drug development by using preclinical models of ischemia/reperfusion (I/R) injury. Rats that were treated with rofecoxib or vehicle for four weeks were subjected to 30 min. coronary artery occlusion and 120 min. reperfusion with or without cardioprotection that is induced by ischemic preconditioning (IPC). Rofecoxib increased overall the arrhythmias including ventricular fibrillation (VF) during I/R. The proarrhythmic effect of rofecoxib during I/R was not observed in the IPC group. Rofecoxib prolonged the action potential duration (APD) in isolated papillary muscles, which was not seen in the simulated IPC group. Interestingly, while showing hidden cardiotoxicity manifested as a proarrhythmic effect during I/R, rofecoxib decreased the infarct size and increased the survival of adult rat cardiac myocytes that were subjected to simulated I/R injury. This is the first demonstration that rofecoxib increased acute mortality due to its proarrhythmic effect via increased APD during I/R. Rofecoxib did not interfere with the cardiprotective effect of IPC; moreover, IPC was able to protect against rofecoxib-induced hidden cardiotoxicity. These results show that cardiac safety testing with simple preclinical models of I/R injury uncovers hidden cardiotoxicity of rofecoxib and might reveal the hidden cardiotoxicity of other drugs.

Cardiac-Specific Caveolin-3 Overexpression Prevents Post-Myocardial Infarction Ventricular Arrhythmias by Inhibiting Ryanodine Receptor-2 Hyperphosphorylation

INTRODUCTION

Ventricular arrhythmia is the most important risk factor for sudden cardiac death (SCD) after acute myocardial infarction (MI) worldwide. However, the molecular mechanisms underlying these arrhythmias are complex and not completely understood.

OBJECTIVE

Here, we evaluated whether caveolin-3 (Cav3), the structural protein of caveolae, plays an important role in the therapeutic strategy for ventricular arrhythmias.

METHODS

A model of cardiac-specific overexpression of Cav3 was established to evaluate the incidence of ventricular arrhythmias after MI in mice. Ca2+ imaging was employed to detect the propensity of adult murine cardiomyocytes to generate arrhythmias, and immunoprecipitation and immunofluorescence were used to determine the relationship of proteins. Additionally, qRT-PCR and western blotting were used to detect the mRNA and protein expression.

RESULTS

We found that cardiac-specific overexpression of Cav3 delivered by a recombinant adeno-associated viral vector reduced the incidence of ventricular arrhythmias and SCD after MI in mice. Ca2+ imaging and western blotting revealed that overexpression of Cav3 reduced diastolic spontaneous Ca2+ waves by inhibiting the hyperphosphorylation of ryanodine receptor-2 (RyR2) at Ser2814, rather than at Ser2808, compared to in rAAV-red fluorescent protein control mice. Furthermore, we demonstrated that Cav3-regulated RYR2 hyperphosphorylation relied on plakophilin-2 in hypoxia-stimulated cultured cardiomyocytes by western blotting, immunoprecipitation, and immunofluorescence in vitro.

CONCLUSIONS

Our results suggested a novel role for Cav3 in the prevention of ventricular arrhythmias, thereby identifying a new target for preventing SCD after MI.

GDF11 ameliorated myocardial ischemia reperfusion injury by antioxidant stress and up-regulating autophagy in STZ-induced type 1 diabetic rats

Purpose:

To investigate whether GDF11 ameliorates myocardial ischemia reperfusion (MIR) injury in diabetic rats and explore the underlying mechanisms.

Methods:

Diabetic and non-diabetic rats subjected to MIR (30 min of coronary artery occlusion followed by 120 min of reperfusion) with/without GDF11 pretreatment. Cardiac function, myocardial infarct size, creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), superoxide dismutase (SOD) 15-F2tisoprostane, autophagosome, LC3II/I ratio and Belcin-1 level were determined to reflect myocardial injury, oxidative stress and autophagy, respectively. In in vitro study, H9c2 cells cultured in high glucose (HG, 30mM) suffered hypoxia reoxygenation (HR) with/without GDF11, hydrogen peroxide (H₂O₂) and autophagy inhibitor 3-methyladenine (3-MA) treatment, cell injury; oxidative stress and autophagy were assessed.

Results:

Pretreatment with GDF11 significantly improved cardiac morphology and function in diabetes, concomitant with decreased arrhythmia severity, infarct size, CK-MB, LDH and 15-F2tisoprostane release, increased SOD activity and autophagy level. In addition, GDF11 notably reduced HR injury in H9c2 cells with HG exposure, accompanied by oxidative stress reduction and autophagy up-regulation. However, those effects were completely reversed by H₂O₂ and 3-MA.

Conclusion:

GDF11 can provide protection against MIR injury in diabetic rats, and is implicated in antioxidant stress and autophagy up-regulation.

Cardioprotective properties of the platelet P2Y12 receptor inhibitor prasugrel on cardiac ischemia/reperfusion injury

OBJECTIVE

The effects of prasugrel, a third-generation thienopyridine, on myocardial infarction, and ischemia-induced ventricular arrhythmias was evaluated in open-chest anesthetized rats. The role of protein kinase C and phosphoinositide 3-kinase pathways in these effects was also examined.

METHODS

The effect of P2Y₁₂ receptor inhibition by prasugrel (3-10 mg/kg, po) on infarct size after 30-min coronary artery occlusion and 120-min reperfusion or on arrhythmias after 7-min coronary occlusion and 7-min reperfusion was evaluated.

RESULTS

In the control group, 31.25 ± 3.01% of the risk zone infarcted. At both prasugrel doses, infarct size was significantly smaller than that in the control group: 5.03 ± 0.81% for 3 mg/kg (p < 0.0001), and 8.78 ± 2.04% for 10 mg/kg (p < 0.0001). The protein kinase C antagonist chelerythrine abolished the anti-infarct effect of prasugrel at 24.77 ± 1.73% as did the phosphoinositide 3-kinase antagonist wortmannin abolished the anti-infarct effect of prasugrel at 27.45 ± 2.74%. Ten mg/kg prasugrel reduced the duration of VT (p = 0.0152 vs control), and wortmannin, but not chelerythrine, reversed the effect of prasugrel on arrhythmias (p = 0.0295).

CONCLUSION

The selective P2Y₁₂ inhibitor prasugrel provides effective protection against myocardial infarction and ischemia-induced ventricular arrhythmias in rats. As in ischemic postconditioning, protein kinase C and phosphoinositide 3-kinase signaling pathways play a role in this protection.

Endothelin receptors in the brain modulate autonomic responses and arrhythmogenesis during acute myocardial infarction in rats

AIMS

Endothelin has been implicated in various processes in the brain, including the modulation of sympathetic responses. The present study examined the pathophysiologic role of brain endothelin-receptors in the setting of acute myocardial infarction, characterized by high incidence of ventricular tachyarrhythmias.

MAIN METHODS

We investigated the effects of intracerebroventricular administration of antagonists of endothelin-receptors ET_A, ET_B, or both, during a 24 h-observation period post-coronary ligation in (n = 70) rats. Continuous recording was performed via implanted telemetry transmitters, followed by arrhythmia-analysis and calculation of autonomic indices derived from heart rate variability. The regional myocardial electrophysiologic properties were assessed by monophasic action potentials and multi-electrode recordings.

KEY FINDINGS

Sympathetic-activity was decreased and vagal-activity was enhanced after intracerebroventricular ET_A-receptor blockade, thus attenuating regional myocardial repolarization inhomogeneity. As a result, the incidence of ventricular tachyarrhythmias was markedly lower in this group. Such effects were also observed after intracerebroventricular blockade of ET_B-, or both, ET_A- and ET_B-receptors, although to a lesser extent.

SIGNIFICANCE

ET_A-receptors in the brain modulate sympathetic and vagal responses and alter arrhythmogenesis during evolving myocardial necrosis in rats. These findings provide insights into arrhythmogenic mechanisms during acute myocardial infarction and call for further investigation on the role of endothelin in the central autonomic network.

The role of desmin alterations in mechanical electrical feedback in heart failure

AIM

Mechanoelectric feedback (MEF) was related to malignant arrhythmias in heart failure (HF). Desmin is a cytoskeleton protein and could be involved in MEF as a mechanoelectrical transducer. In this study, we will discuss the role of desmin alterations in mechanical electrical feedback in heart failure and its mechanisms.

METHODS

We used both an in vivo rat model and an in vitro cardiomyocyte model to address this issue. For the in vivo experiments, we establish a sham group, an HF group, streptomycin (SM) group, and an MDL-28170 group. The occurrence of ventricular arrhythmias (VA) was recorded in each group. For the in vitro cardiomyocyte model, we established an NC group, a si-desmin group, and a si-desmin + NBD IKK group. The expression of desmin, IKKβ, p-IKKβ, IKBα, p-NF-κB, and SERCA2 were detected in both in vivo and in vitro experiments. The content of Ca²⁺ in cytoplasm and sarcoplasmic were detected by confocal imaging in vitro experiments.

RESULTS

An increased number of VAs were found in the HF group. SM and MDL-28170 can reduce desmin breakdown and the number of VAs in heart failure. The knockdown of desmin in the cardiomyocyte can activate the NF-κB pathway, decrease the level of SERCA2, and result in abnormal distribution of Ca²⁺. While treatment with NF-κB inhibitor can elevate the level of SERCA2 and alleviate the abnormal distribution of Ca²⁺.

SIGNIFICANCE

Overall, desmin may participate in MEF through the NF-κB pathway. This study provides a potential therapeutic target for VA in HF.

Ischemic Postconditioning Reduces Reperfusion Arrhythmias by Adenosine Receptors and Protein Kinase C Activation but Is Independent of KATP Channels or Connexin 43

Ischemic postconditioning (IPoC) reduces reperfusion arrhythmias but the antiarrhythmic mechanisms remain unknown. The aim of this study was to analyze IPoC electrophysiological effects and the role played by adenosine A1, A2A and A3 receptors, protein kinase C, ATP-dependent potassium (KATP) channels, and connexin 43. IPoC reduced reperfusion arrhythmias (mainly sustained ventricular fibrillation) in isolated rat hearts, an effect associated with a transient delay in epicardial electrical activation, and with action potential shortening. Electrical impedance measurements and Lucifer-Yellow diffusion assays agreed with such activation delay. However, this delay persisted during IPoC in isolated mouse hearts in which connexin 43 was replaced by connexin 32 and in mice with conditional deletion of connexin 43. Adenosine A1, A2A and A3 receptor blockade antagonized the antiarrhythmic effect of IPoC and the associated action potential shortening, whereas exogenous adenosine reduced reperfusion arrhythmias and shortened action potential duration. Protein kinase C inhibition by chelerythrine abolished the protective effect of IPoC but did not modify the effects on action potential duration. On the other hand, glibenclamide, a KATP inhibitor, antagonized the action potential shortening but did not interfere with the antiarrhythmic effect. The antiarrhythmic mechanisms of IPoC involve adenosine receptor activation and are associated with action potential shortening. However, this action potential shortening is not essential for protection, as it persisted during protein kinase C inhibition, a maneuver that abolished IPoC protection. Furthermore, glibenclamide induced the opposite effects. In addition, IPoC delays electrical activation and electrical impedance recovery during reperfusion, but these effects are independent of connexin 43.

CD271+ Human Mesenchymal Stem Cells Show Antiarrhythmic Effects in a Novel Murine Infarction Model

Background: Ventricular arrhythmias (VA) are a common cause of sudden death after myocardial infarction (MI). Therefore, developing new therapeutic methods for the prevention and treatment of VA is of prime importance. Methods: Human bone marrow derived CD271⁺ mesenchymal stem cells (MSC) were tested for their antiarrhythmic effect. This was done through the development of a novel mouse model using an immunocompromised Rag2^−/− γc^−/− mouse strain subjected to myocardial “infarction-reinfarction”. The mice underwent a first ischemia-reperfusion through the left anterior descending (LAD) artery closure for 45 min with a subsequent second permanent LAD ligation after seven days from the first infarct. Results: This mouse model induced various types of VA detected with continuous electrocardiogram (ECG) monitoring via implanted telemetry device. The immediate intramyocardial delivery of CD271⁺ MSC after the first MI significantly reduced VA induced after the second MI. Conclusions: In addition to the clinical relevance, more closely reflecting patients who suffer from severe ischemic heart disease and related arrhythmias, our new mouse model bearing reinfarction warrants the time required for stem cell engraftment and for the first time enables us to analyze and verify significant antiarrhythmic effects of human CD271⁺ stem cells in vivo.