Tamara Egan Benova

Dietary omega-3 fatty acids attenuate myocardial arrhythmogenic factors and propensity of the heart to lethal arrhythmias in a rodent model of human essential hypertension.

Objective: Hypertension-induced myocardial remodeling is known to be associated with increased risk for malignant arrhythmias and alterations in electrical coupling protein, connexin-43 (Cx43), may be involved. We investigated whether omega-3 fatty acids intake affects abnormalities of Cx43 as well as protein kinase C (PKC) signaling and myosin heavy chain (MyHC) profile at the early and late stage of hypertension in the context of the hearts susceptibility to ventricular fibrillation and ability to restore sinus rhythm. Methods: Untreated young and old male spontaneously hypertensive rats (SHRs) and age-matched normotensive rats were compared with animals supplemented by omega-3 (eicosapentaneoic acid + docosahexaneoic acid, 200 mg/kg body weight/day) for 2 months. Left ventricular tissues were taken for examination of subcellular integrity of gap junctions, Cx43 mRNA and protein expression, PKC&egr; and PKC&dgr; as well as MyHC determination. Electrically inducible ventricular fibrillation and sinus rhythm restoration (SRR) were examined on Langedorff-perfused heart preparation. Results: Omega-3 intake significantly reduced cardiovascular risk factors, suppressed inducible ventricular fibrillation, and facilitated SRR in hypertensive rats. Supplementation attenuated lateralization and internalization of Cx43, suppressed elevated Cx43 mRNA, enhanced total Cx43 protein expression and/or expression of its functional phosphorylated forms as well as the expression of cardioprotective PKC-&egr; and suppressed pro-apoptotic PKC-&dgr; isoform. Moreover, the omega-3 diet normalized MyHC profiles in SHR at early stage of disease and old nonhypertensive rats, but failed to do so in old SHR at late stage of disease. Conclusion: Findings suggest that amelioration of myocardial Cx43-related abnormalities, positive modulation of PKC pathways, and normalization of MyHC can significantly contribute to the antiarrhythmic effects of omega-3 in rat model mimicking human essential hypertension. Our results support the prophylactic use of omega-3 to minimize cardiovascular risk and sudden arrhythmic death.

Melatonin attenuates hypertension-related proarrhythmic myocardial maladaptation of connexin-43 and propensity of the heart to lethal arrhythmias.

We hypothesized that the pineal hormone melatonin, which exhibits cardioprotective effects, might affect myocardial expression of cell-to-cell electrical coupling protein connexin-43 (Cx43) and protein kinase C (PKC) signaling, and hence, the propensity of the heart to lethal ventricular fibrillation (VF). Spontaneously hypertensive (SHR) and normotensive Wistar rats fed a standard rat chow received melatonin (40 μg/mL in drinking water during the night) for 5 weeks, and were compared with untreated rats. Melatonin significantly reduced blood pressure and normalized triglycerides in SHR, whereas it decreased body mass and adiposity in Wistar rats. Compared with healthy rats, the threshold to induce sustained VF was significantly lower in SHR (18.3 ± 2.6 compared with 29.2 ± 5 mA; p < 0.05) and increased in melatonin-treated SHR and Wistar rats to 33.0 ± 4 and 32.5 ± 4 mA. Melatonin attenuated abnormal myocardial Cx43 distribution in SHR, and upregulated Cx43 mRNA, total Cx43 protein, and its functional phosphorylated forms in SHR, and to a lesser extent, in Wistar rat hearts. Moreover, melatonin suppressed myocardial proapoptotic PKCδ expression and increased cardioprotective PKCε expression in both SHR and Wistar rats. Our findings indicate that melatonin protects against lethal arrhythmias at least in part via upregulation of myocardial Cx43 and modulation of PKC-related cardioprotective signaling.

Can we protect from malignant arrhythmias by modulation of cardiac cell-to-cell coupling?

Defects in intercellular coupling in the heart play a key role in the initiation and persistence of malignant arrhythmias. Such disorders result from abnormal expression and distribution of connexins, the major constituents of cardiac gap junction channels. The alterations of myocardial connexin are well established as a consistent feature of both human and animal heart disease and aging. Following these facts, the modulation of connexin mediated intercellular coupling is suggested as a new antiarrhythmic approach. This review provides recent data supporting this concept. It can be challenging for the development of new antiarrhythmic drugs. Moreover, findings point out the implication of some endogenous compounds in protection from life-threatening arrhythmias via preservation of myocardial connexin.

Myocardial connexin-43 is upregulated in response to acute cardiac injury in rats1

We aimed to explore whether myocardial intercellular channel protein connexin-43 (Cx43) along with PKCε and MMP-2 might be implicated in responses to acute cardiac injury induced by 2 distinct sublethal interventions in Wistar rats. Animals underwent either single chest irradiation at dose of 25 Gy or subcutaneous injection of isoproterenol (ISO, 120 mg/kg) and were compared with untreated controls. Forty-two days post-interventions, the hearts were excised and left ventricles were used for analysis. The findings showed an increase of total as well as phosphorylated forms of myocardial Cx43 regardless of the type of interventions. Enhanced phosphorylation of Cx43 coincided with increased PKCε expression in both models. Elevation of Cx43 was associated with its enhanced distribution on lateral surfaces of the cardiomyocytes in response to both interventions, while focal areas of fibrosis without Cx43 were found in post-ISO but not post-irradiated rat hearts. In parallel, MMP-2 activity was decreased in the former while increased in the latter. Cardiac function was maintained and the susceptibility of the hearts to ischemia or malignant arrhythmias was not deteriorated 42 days after interventions when compared with controls. Altogether, the findings indicate that myocardial Cx43 is most likely implicated in potentially salutary responses to acute heart injury.

Myocardial Connexin-43 is Implicated in the Prevention of Malignant Arrhythmia in Rats Suffering from Essential Hypertension

Gap-junction connexin (Cx) channels are important determinants of myocardial conduction and synchronization that is crucial for heart function. Hypertensioninduced structural remodeling is associated with an increased risk of life-threatening arrhythmias and heart failure in both humans and experimental animals. Recent studies suggest that abnormal distribution and/or downregulation of Cx43 accompanied with altered protein kinase C (PKC)ε signaling in spontaneously hypertensive rats were linked with increased propensity to ventricular fibrillation compared to normotensive rats. By contrast, the long-term treatment of hypertensive rats with cardioprotective compounds such as melatonin, omega-3 fatty acids, or red palm oil resulted in protection from lethal arrhythmia. Their antiarrhythmic effect was attributed to the attenuation of abnormal Cx43 topology and modulation of Cx43 mRNA as well as protein expression and its functional phosphorylated forms. The latter might be attributed to upregulation of PKCε. It appears that maladaptive consequences of hypertension resulting in abnormal myocardial distribution of Cx43 and its downre‐ gulation can contribute to arrhythmogenesis and occurrence of malignant arrhyth‐ mias. On the other hand, the attenuation of myocardial Cx43 abnormalities by treatment with melatonin, omega-3 fatty acids, or red palm oil confers arrhythmia protection in rodent model of essential hypertension. Findings uncover novel mechanisms of cardioprotective effects of melatonin, omega-3 fatty acids, and red palm oil. Welldesigned clinical trials are needed to explore antiarrhythmic potential of these compounds in human essential hypertension.

Irradiation-Induced Cardiac Connexin-43 and miR-21 Responses Are Hampered by Treatment with Atorvastatin and Aspirin

Radiation of the chest during cancer therapy is deleterious to the heart, mostly due to oxidative stress and inflammation related injury. A single sub-lethal dose of irradiation has been shown to result in compensatory up-regulation of the myocardial connexin-43 (Cx43), activation of the protein kinase C (PKC) signaling along with the decline of microRNA (miR)-1 and an increase of miR-21 levels in the left ventricle (LV). We investigated whether drugs with antioxidant, anti-inflammatory or vasodilating properties, such as aspirin, atorvastatin, and sildenafil, may affect myocardial response in the LV and right ventricle (RV) following chest irradiation. Adult, male Wistar rats were subjected to a single sub-lethal dose of chest radiation at 25 Gy and treated with aspirin (3 mg/day), atorvastatin (0.25 mg/day), and sildenafil (0.3 mg/day) for six weeks. Cx43, PKCε and PKCδ proteins expression and levels of miR-1 as well as miR-21 were determined in the LV and RV. Results showed that the suppression of miR-1 was associated with an increase of total and phosphorylated forms of Cx43 as well as PKCε expression in the LV while having no effect in the RV post-irradiation as compared to the non-irradiated rats. Treatment with aspirin and atorvastatin prevented an increase in the expression of Cx43 and PKCε without change in the miR-1 levels. Furthermore, treatment with aspirin, atorvastatin, and sildenafil completely prevented an increase of miR-21 in the LV while having partial effect in the RV post irradiation. The increase in pro-apoptotic PKCδ was not affected by any of the used treatment. In conclusion, irradiation and drug-induced changes were less pronounced in the RV as compared to the LV. Treatment with aspirin and atorvastatin interfered with irradiation-induced compensatory changes in myocardial Cx43 protein and miR-21 by preventing their elevation, possibly via amelioration of oxidative stress and inflammation.

Omega-3 Index and Anti-Arrhythmic Potential of Omega-3 PUFAs

Omega-3 polyunsaturated fatty acids (PUFAs), namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are permanent subjects of interest in relation to the protection of cardiovascular health and the prevention of the incidence of both ventricular and atrial arrhythmias. The purpose of this updated review is to focus on the novel cellular and molecular effects of omega-3 PUFAs, in the context of the mechanisms and factors involved in the development of cardiac arrhythmias; to provide results of the most recent studies on the omega-3 PUFA anti-arrhythmic efficacy and to discuss the lack of the benefit in relation to omega-3 PUFA status. The evidence is in the favor of omega-3 PUFA acute and long-term treatment, perhaps with mitochondria-targeted antioxidants. However, for a more objective evaluation of the anti-arrhythmic potential of omega-3 PUFAs in clinical trials, it is necessary to monitor the basal pre-interventional omega-3 status of individuals, i.e., red blood cell content, omega-3 index and free plasma levels. In the view of evidence-based medicine, it seems to be crucial to aim to establish new approaches in the prevention of cardiac arrhythmias and associated morbidity and mortality that comes with these conditions.

[PS 01-10] ANTIARRHYTHMIC EFFECT OF ACUTE ADMINISTRATION OF ATORVASTATIN AND OMEGA-3 FATTY ACIDS DEMONSTRATED IN PERFUSED HEART OF MALE AND FEMALE HEREDITARY HYPERTRIGLYCERIDEMIC RATS SUFFERING FROM HYPERTENSION

Objective: It is known that chronic treatment with statins and omega-3 FA (omega-3) exhibit cardioprotective and antiarrhythmic effects in clinical practice. We have previously shown that prolonged treatment of hereditary hypertriglyceridemic (HTG) rats suffering from hypertension with these compounds reduced the incidence of ventricular fibrillation (VF) partially due to modulation of cardiac electrical coupling protein connexin-43. To elucidate further underlying antiarrhythmic mechanisms, this study was aimed to explore whether these compounds exert acute antiarrhythmic effects. Design and Method: Experiments were conducted on adult, male and female HTG rats known to be much prone to VF than healthy rats. The hearts were excised from anesthetized rats and perfused with oxygenated Krebs-Henseleit solution at constant flow. VF inducibility was tested in control hearts and compared with the hearts, which were pre-treated during 10 min prior electrical stimulation with either atorvastatin, eicosapentanoic acid (EPA) or docosahexanoic acid (DHA) in concentration 1.5, 7, 15 &mgr;mol. Results: Sustained VF was induced in all HTG rat hearts without treatment. In contrast, the hearts subjected to atorvastatin, EPA and DHA were less susceptible to inducible VF and incidence of sustained VF was reduced to 30%, 70% and 80% in male, and to 60%, 75% and 60% in female rats. Atorvastatin suppressed VF inducibility in male rats already in concentration 1.5 &mgr;mol, while EPA and DHA were efficient at higher, 7 and 15 &mgr;mol. Moreover, bolus (150 &mgr;mol) of EPA and DHA administered directly to fibrillating hearts terminated VF in 6 out of 6 hearts and atorvastatin in 3 out of 6 hearts. Conclusions: Atorvastatin likewise EPA and DHA exhibit clear antifibrillating and defibrillating efficacy when acutely applied. Findings point out the importance of pleiotropic effects of statins and diet-related approaches in prevention of malignant arrhythmias.

Disorders of Ca2+ handling and cell-to-cell coupling are implicated in the development of acute heart failure in intact animal hearts: An ultrastructural study

BAckground: It has been previously reported that various acute interventions causing myocardial abnormalities in Ca2+ handling and defects in intercellular coupling facilitate the occurrence of malignant arrhythmias. Objectives: To comprehensively determine the impact of such Ca2+- related disorders induced in intact animal hearts on the ultrastructure of the cardiomyocytes before occurrence and during sustaining of severe arrhythmias. Methods: Three types of acute experiments known to be accompanied by disturbances in Ca2+ handling were performed. Langendorff-perfused rat and guinea pig hearts were subjected to K+-deficient perfusion to induce ventricular fibrillation; Langendorff-perfused guinea pig heart underwent burst atrial pacing to induce atrial fibrillation; and open chest pig heart was used for intramyocardial noradrenaline infusion to induce ventricular tachycardia. Tissue samples for electron microscopy examination were obtained during basal conditions, previous occurrence and during sustaining of malignant arrhythmias. Results: The comparative findings suggest that myocardial heterogeneity of high [Ca2+]i-induced subcellular injury of the cardiomyocytes and their junctions is a common feature that precede occurrence ventricular tachycardia, ventricular fibrillation or atrial fibrillation regardless of the species and atria/ventricular-related differences in Ca2+ handling and intercellular coupling. The primary changes consisted of nonuniform sarcomere shortening, which most likely reflects cytosolic Ca2+ oscillations; disturbances in Ca2+ wave propagation; and Ca2+ overload. These disturbances were linked with defects in cardiac cell-to-cell coupling that increased the propensity of the heart to malignant arrhythmias. Moreover, Ca2+overload led to disruption of myofilaments, jeopardizing contractile function. Conclusions: The results provide a novel paradigm linking Ca2+- related arrhythmogenesis and contractility disorders that may contribute to acute heart failure.