Modulation of systemic and aortic nitric oxide by melatonin and n-3 polyunsaturated fatty acids in isoproterenol affected spontaneously hypertensive and normotensive Wistar rats.

We aimed to explore the effects of melatonin and n-3 polyunsaturated fatty acids (PUFA) supplementation on plasma and aortic nitric oxide (NO) levels in isoproterenol (Iso) affected spontaneously hypertensive (SHR) and Wistar rats. Untreated control rats were compared with Iso injected (118 mg/kg, s.c.) rats, and Iso injected plus supplemented with melatonin (10 mg/kg, p.o.) or PUFA (1.68 g/kg, p.o.) for two months. Plasma and aortic basal, L-NAME inhibited, adrenaline and acetylcholine stimulated NO were determined using Griess method. Plasma NO levels were lower in SHR versus Wistar rats. Iso decreased NO in Wistar while not in SHR. PUFA but not melatonin intake of Iso treated SHR increased plasma NO along with a decrease in systolic blood pressure. Basal aortic NO level was higher in SHR than Wistar rats and not altered by Iso. Intake of melatonin increased but PUFA decreased basal NO levels in Wistar+Iso and did not affect in SHR+Iso rats. Acetylcholine and adrenaline induced aortic NO release was significantly increased in Wistar+Iso but not SHR+Iso group. Melatonin intake increased Ach induced aortic NO in Wistar+Iso and SHR+Iso groups, whereas there was no effect of PUFA intake. Findings suggest that PUFA modulates plasma and melatonin aortic NO levels of isoproterenol affected rats in a strain-dependent manner.

Disordered myocardial Ca(2+) homeostasis results in substructural alterations that may promote occurrence of malignant arrhythmias.

We aimed to determine the impact of Ca(2+)-related disorders induced in intact animal hearts on ultrastructure of the cardiomyocytes prior to occurrence of severe arrhythmias. Three types of acute experiments were performed that are known to be accompanied by disturbances in Ca(2+) handling. Langedorff-perfused rat or guinea pig hearts subjected to K(+)-deficient perfusion to induce ventricular fibrillation (VF), burst atrial pacing to induce atrial fibrillation (AF) and open chest pig heart exposed to intramyocardial noradrenaline infusion to induce ventricular tachycardia (VT). Tissue samples for electron microscopic examination were taken during basal condition, prior and during occurrence of malignant arrhythmias. Cardiomyocyte alterations preceding occurrence of arrhythmias consisted of non-uniform sarcomere shortening, disruption of myofilaments and injury of mitochondria that most likely reflected cytosolic Ca(2+) disturbances and Ca(2+) overload. These disorders were linked with non-uniform pattern of neighboring cardiomyocytes and dissociation of adhesive junctions suggesting defects in cardiac cell-to-cell coupling. Our findings identified heterogeneously distributed high [Ca(2+)](i)-induced subcellular injury of the cardiomyocytes and their junctions as a common feature prior occurrence of VT, VF or AF. In conclusion, there is a link between Ca(2+)-related disorders in contractility and coupling of the cardiomyocytes pointing out a novel paradigm implicated in development of severe arrhythmias.

Protection of cardiac cell-to-cell coupling attenuate myocardial remodeling and proarrhythmia induced by hypertension.

Gap junction connexin channels are important determinants of myocardial conduction and synchronization that is crucial for coordinated heart function. One of the main risk factors for cardiovascular events that results in heart attack, congestive heart failure, stroke as well as sudden arrhythmic death is hypertension. Mislocalization and/or dysfunction of specific connexin-43 channels due to hypertension-induced myocardial remodeling have been implicated in the occurrence of life-threatening arrhythmias and heart failure in both, humans as well as experimental animals. Recent studies suggest that down-regulation of myocardial connexin-43, its abnormal distribution and/or phosphorylation might be implicated in this process. On the other hand, treatment of hypertensive animals with cardioprotective drugs (e.g. statins) or supplementation with non-pharmacological compounds, such as melatonin, omega-3 fatty acids and red palm oil protects from lethal arrhythmias. The antiarrhythmic effects are attributed to the attenuation of myocardial connexin-43 abnormalities associated with preservation of myocardial architecture and improvement of cardiac conduction. Findings uncover novel mechanisms of cardioprotective (antihypertensive and antiarrhythmic) effects of compounds that are used in clinical settings. Well-designed trials are needed to explore the antiarrhythmic potential of these compounds in patients suffering from hypertension.

Cardiac connexin-43 and PKC signaling in rats with altered thyroid status without and with omega-3 fatty acids intake.

Thyroid hormones are powerful modulators of heart function and susceptibility to arrhythmias via both genomic and non-genomic actions. We aimed to explore expression of electrical coupling protein connexin-43 (Cx43) in the heart of rats with altered thyroid status and impact of omega-3 polyunsaturated fatty acids (omega-3) supplementation. Adult male Lewis rats were divided into following six groups: euthyroid controls, hyperthyroid (treated with T(3)) and hypothyroid (treated with methimazol) with or without six-weeks lasting supplementation with omega-3 (20 mg/100 g/day). Left and right ventricles, septum and atria were used for immunoblotting of Cx43 and protein kinase C (PKC). Total expression of Cx43 and its phosphorylated forms were significantly increased in all heart regions of hypothyroid rats compared to euthyroid controls. In contrast, the total levels of Cx43 and its functional phosphorylated forms were decreased in atria and left ventricle of hyperthyroid rats. In parallel, the expression of PKC epsilon that phosphorylates Cx43, at serine 368, was increased in hypothyroid but decreased in hyperthyroid rat hearts. Omega-3 intake did not significantly affect either Cx43 or PKC epsilon alterations. In conclusion, there is an inverse relationship between expression of cardiac Cx43 and the levels of circulating thyroid hormones. It appears that increased propensity of hyperthyroid while decreased of hypothyroid individuals to malignant arrhythmias may be in part attributed to the changes in myocardial Cx43.

Ageing related down-regulation of myocardial connexin-43 and up-regulation of MMP-2 may predict propensity to atrial fibrillation in experimental animals.

Mechanisms underlying atrial fibrillation (AF), the most common cardiac arrhythmia, particularly in aged population, are not fully elucidated. We have previously shown an increased propensity of old guinea pigs (GPs) heart to inducible AF when comparing to young animals. This study aimed to verify our hypothesis that susceptibility of aged heart to AF may be attributed to abnormalities in myocardial connexin-43 (Cx43) and extracellular matrix that affect cardiac electrical properties. Experiments were conducted on male and female 4-week-old and 24-week-old GPs. Atrial tissue was processed for analysis of Cx43 topology using immunohistochemistry, expression of Cx43 protein using immunobloting, and expression of mRNA of Cx43 and extracellular matrix metalloproteinase-2 (MMP-2) using real time PCR. Immunohistochemistry revealed uniform Cx43 distribution predominantly on lateral sides of the cardiomyocytes of young male and female GP atria. In contrast, non-uniform distribution, mislocalization and reduced immunolabeling of Cx43 were detected in atria of old GPs. In parallel, the atrial tissue levels of Cx43 mRNA were significantly decreased, while mRNA expression of MMP-2 was significantly increased in old versus young GPs. The changes were more pronounced in old GPs males comparing to females. Findings indicate that age-related down-regulation of atrial Cx43 and up-regulation of MMP-2 as well as disordered Cx43 distribution can facilitate development of AF in old guinea pig hearts.

New aspects of pathogenesis of atrial fibrillation: remodelling of intercalated discs.

This review deals with the understanding of the role of key factors of ageing, oxidative stress and inflammation, in relation to development of age-related cardiovascular disease, atrial fibrillation. Increased production of reactive oxygen species and systemic inflammation promote cardiac structural and electrophysiologic remodeling that is crucial with respect to development and sustaining of atrial fibrillation. Data suggest that alterations in atrial connexin-43 and/or connexin-40 expression, phosphorylation and distribution affect cell-to-cell electrical coupling and molecular signalling that is proarrhythmogenic. However, studies showing causal relationship in the context of pathogenesis of atrial fibrillation are still scarce. Nevertheless, gap junctional connexin channels are considered as targets for arrhythmia prevention and therapeutic interventions aimed at mitochondria-related reactive oxygen species appear to be challenging. In addition, ageing is accompanied by abnormalities in adhesive junctions that most likely promote asynchronous contraction and arrhythmias. It is consistent with recent data that highlight a new perspective in regulation of intercalated disc function via adhesive junctions, fascia adherens and desmosomes. The crosstalk between adhesive and gap junctions is suggested to be implicated in pathogenesis of arrhythmias. On the other hand, modulation of adhesive proteins, N-cadherin and catenin may be promising tool aimed to synchronize heart function. Despite the progress in this field many questions remain to be answered by further research.

Modulation of cardiac connexin-43 by omega-3 fatty acid ethyl-ester supplementation demonstrated in spontaneously diabetic rats.

Previous data suggest that type 1 diabetes mellitus leads to the deterioration of myocardial intercellular communication mediated by connexin-43 (Cx43) channels. We therefore aimed to explore Cx43, PKC signaling and ultrastructure in non-treated and omega-3 fatty acid (omega-3) treated spontaneously diabetic Goto-Kakizaki (GK) rats considered as type 2 diabetes model. Four-week-old GK and non-diabetic Wistar-Clea rats were fed omega-3 (200 mg/kg/day) for 2 months and compared with untreated rats. Real-time PCR and immunoblotting were performed to determine Cx43, PKC-epsilon and PKC-delta expression. In situ Cx43 was examined by immunohistochemistry and subcellular alterations by electron microscopy. Omega-3 intake reduced blood glucose, triglycerides, and cholesterol in diabetic rats and this was associated with improved integrity of cardiomyocytes and capillaries in the heart. Myocardial Cx43 mRNA and protein levels were higher in diabetic versus non-diabetic rats and were further enhanced by omega-3. The ratio of phosphorylated (functional) to non-phosphorylated Cx43 was lower in diabetic compared to non-diabetic rats but was increased by omega-3, in part due to up-regulation of PKC-epsilon. In addition, pro-apoptotic PKC-delta expression was decreased. In conclusion, spontaneously diabetic rats at an early stage of disease benefit from omega-3 intake due to its hypoglycemic effect, upregulation of myocardial Cx43, and preservation of cardiovascular ultrastructure. These findings indicates that supplementation of omega-3 may be beneficial also in the management of diabetes in humans.

Acute anti-fibrillating and defibrillating potential of atorvastatin, melatonin, eicosapentaenoic acid and docosahexaenoic acid demonstrated in isolated heart model.

Cardioprotective compounds such as atorvastatin, melatonin, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) exhibit antiarrhythmic potential in clinical and/or experimental conditions but underlying mechanisms are poorly understood. We have previously shown that protection from ventricular fibrillation (VF) due to prolonged treatment with these compounds was linked with modulation of myocardial connexin-43, which is responsible for myocardial electrical coupling and synchronisation. To elucidate further the antiarrhythmic potential of atorvastatin, melatonin, EPA and DHA we aimed to explore their acute anti-fibrillating effects and defibrillating efficacy. Experiments were conducted on isolated perfused heart preparation of adult male and female hypertriglyceridemic (HTG) rats when using atorvastatin, EPA and DHA, while melatonin was examined in hearts of old male and female guinea pigs. VF inducibility was tested in hearts pre-treated for 10 min with atorvastatin, EPA or DHA (15 µmol) or melatonin (50 µmol) and compared with non-pre-treated hearts. Sustained VF was induced in all untreated HTG rat hearts. In contrast, its incidence was reduced to 30% and 60% by atorvastatin, 70% and 75% by EPA, 60% and 60% by DHA in male or female rat hearts respectively. Moreover, bolus (150 µmol) of EPA and DHA administered directly to the fibrillating heart restored sinus rhythm in 6 of 6 hearts and atorvastatin in 4 of 6 hearts. Threshold to induce sustained VF was 21.7 ± 3.8 mA in male and 38.3 ± 2.9 mA in female guinea pig hearts. However, sustained VF was not possible to induce even by the strongest (50 mA) stimulus in the heart pre-treated with melatonin regardless the sex. In conclusion, atorvastatin, melatonin, EPA and DHA exhibit clear cut acute anti-fibrillating efficacy. Findings challenge to investigate expression of connexin-43, especially its phosphorylated status associated with connexin channel function, in acute conditions.