Vladimir Knezl

Prolonged population aging and unhealthy lifestyles contribute to the progressive prevalence of arterial hypertension. This is accompanied by low-grade inflammation and over time results in heart dysfunction and failure. Hypertension-induced myocardial structural and ion channel remodeling facilitates the development of both atrial and ventricular fibrillation, and these increase the risk of stroke and sudden death. Herein, we elucidate hypertension-induced impairment of “connexome” cardiomyocyte junctions. This complex ensures cell-to-cell adhesion and coupling for electrical and molecular signal propagation. Connexome dysfunction can be a key factor in promoting the occurrence of both cardiac arrhythmias and heart failure. However, the available literature indicates that arterial hypertension treatment can hamper myocardial structural remodeling, hypertrophy and/or fibrosis, and preserve connexome function. This suggests the pleiotropic effects of antihypertensive agents, including anti-inflammatory. Therefore, further research is required to identify specific molecular targets and pathways that will protect connexomes, and it is also necessary to develop new approaches to maintain heart function in patients suffering from primary or pulmonary arterial hypertension.

Light pollution disturbs circadian rhythm, and this can also be deleterious to the heart by increased susceptibility to arrhythmias. Herein, we investigated if rats exposed to continuous light had altered myocardial gene transcripts and/or protein expression which affects arrhythmogenesis. We then assessed if Omacor^® supplementation benefitted affected rats. Male and female spontaneously hypertensive (SHR) and normotensive Wistar rats (WR) were housed under standard 12 h/12 h light/dark cycles or exposed to 6-weeks continuous 300 lux light for 24 h. Half the rats were then treated with 200 mg/100 g b.w. Omacor^®. Continuous light resulted in higher male rat vulnerability to malignant ventricular fibrillation (VF). This was linked with myocardial connexin-43 (Cx43) down-regulation and deteriorated intercellular electrical coupling, due in part to increased pro-inflammatory NF-κB and iNOS transcripts and decreased sarcoplasmic reticulum Ca²⁺ATPase transcripts. Omacor^® treatment increased the electrical threshold to induce the VF linked with amelioration of myocardial Cx43 mRNA and Cx43 protein levels and the suppression of NF-κB and iNOS. This indicates that rat exposure to continuous light results in deleterious cardiac alterations jeopardizing intercellular Cx43 channel-mediated electrical communication, thereby increasing the risk of malignant arrhythmias. The adverse effects were attenuated by treatment with Omacor^®, thus supporting its potential benefit and the relevance of monitoring omega-3 index in human populations at risk.

Cardiac β-adrenergic overstimulation results in oxidative stress, hypertrophy, ischemia, lesion, and fibrosis rendering the heart vulnerable to malignant arrhythmias. We aimed to explore the anti-arrhythmic efficacy of the anti-oxidative and anti-inflammatory compounds, melatonin, and omega-3, and their mechanisms of actions in normotensive and hypertensive rats exposed to isoproterenol (ISO) induced β-adrenergic overdrive. Eight-month-old, male SHR, and Wistar rats were injected during 7 days with ISO (cumulative dose, 118 mg/kg). ISO rats were either untreated or concomitantly treated with melatonin (10 mg/kg/day) or omega-3 (Omacor, 1.68 g/kg/day) until 60 days of ISO withdrawal and compared to non-ISO controls. Findings showed that both melatonin and omega-3 increased threshold current to induce ventricular fibrillation (VF) in ISO rats regardless of the strain. Prolonged treatment with these compounds resulted in significant suppression of ISO-induced extracellular matrix alterations, as indicated by reduced areas of diffuse fibrosis and decline of hydroxyproline, collagen-1, SMAD2/3, and TGF-β1 protein levels. Importantly, the highly pro-arrhythmic ISO-induced disordered cardiomyocyte distribution of electrical coupling protein, connexin-43 (Cx43), and its remodeling (lateralization) were significantly attenuated by melatonin and omega-3 in Wistar as well as SHR hearts. In parallel, both compounds prevented the post-ISO-related increase in Cx43 variant phosphorylated at serine 368 along with PKCε, which are known to modulate Cx43 remodeling. Melatonin and omega-3 increased SOD1 or SOD2 protein levels in ISO-exposed rats of both strains. Altogether, the results indicate that anti-arrhythmic effects of melatonin and omega-3 might be attributed to the protection of myocardial Cx43 topology and suppression of fibrosis in the setting of oxidative stress induced by catecholamine overdrive in normotensive and hypertensive rats.

The arrhythmogenic potential of β1-adrenoceptor autoantibodies (β1-AA), as well as antiarrhythmic properties of omega-3 in heart diseases, have been reported while underlying mechanisms are poorly understood. We aimed to test our hypothesis that omega-3 (eicosapentaenoic acid-EPA, docosahexaenoic acid-DHA) may inhibit matrix metalloproteinase (MMP-2) activity to prevent cleavage of β1-AR and formation of β1-AA resulting in attenuation of pro-arrhythmic connexin-43 (Cx43) and protein kinase C (PKC) signaling in the diseased heart. We have demonstrated that the appearance and increase of β1-AA in blood serum of male and female 12-month-old spontaneously hypertensive rats (SHR) was associated with an increase of inducible ventricular fibrillation (VF) comparing to normotensive controls. In contrast, supplementation of hypertensive rats with omega-3 for two months suppressed β1-AA levels and reduced incidence of VF. Suppression of β1-AA was accompanied by a decrease of elevated myocardial MMP-2 activity, preservation of cardiac cell membrane integrity and Cx43 topology. Moreover, omega-3 abrogated decline in expression of total Cx43 as well as its phosphorylated forms at serine 368 along with PKC-ε, while decreased pro-fibrotic PKC-δ levels in hypertensive rat heart regardless the sex. The implication of MMP-2 in the action of omega-3 was also demonstrated in cultured cardiomyocytes in which desensitization of β1-AR due to permanent activation of β1-AR with isoproterenol was prevented by MMP-2 inhibitor or EPA. Collectively, these data support the notion that omega-3 via suppression of β1-AA mechanistically controlled by MMP-2 may attenuate abnormal of Cx43 and PKC-ε signaling; thus, abolish arrhythmia substrate and protect rats with an advanced stage of hypertension from malignant arrhythmias.

The purpose of this study was to investigate the effect of antioxidants rich red palm oil (RPO) supplementation on cardiac oxidative stress known as crucial factor deteriorating heart function in hypertension. 3-month-old, male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) were fed standard rat chow without or with RPO (0.2 mL/day/5 weeks). General characteristic of rats were registered. Left ventricular tissue (LV) was used to determine expression of superoxide dismutases (SOD1, SOD2) and glutathione peroxidases (Gpx) as well as activity of nitric oxide synthase (NOS). Functional parameters of the heart were examined during basal conditions and at the early-phase of post-ischemic reperfusion using Langendorff-perfused system. RPO intake significantly reduced elevated blood pressure and total NOS activity as well as increased lowered expression of mitochondrial SOD2 in SHR hearts during basal condition. Moreover, RPO supplementation resulted in suppression of elevated heart rate, increase of reduced coronary flow and enhancement of systolic and diastolic heart function at the early-phase of post-ischemic reperfusion. It is concluded that SHR benefit from RPO intake due to decrease of blood pressure, amelioration of oxidative stress and protection of heart function that was deteriorated by post-ischemic reperfusion.

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.

Autoantibody production to the adrenergic beta-1 receptors (b1-AAB) is known to contribute to development of dilated cardiomyopathy and arrhythmogenic substrate. Hypertension if not properly controlled is deleterious to health due to inflammation, myocardial remodelling and enhancement of b1-AAB. Cardioprotective effects of omega-3 FA supplementation are well known. We aimed to explore whether omega-3 FA intake may affect production of b1-AAB, myocardial remodelling and connexin-43 (Cx43) that ensure electric cell-to-cell coupling using aged spontaneously hypertensive rats (SHR). Male and female 12-month-old SHR as well as their age-and-sex-matched healthy Wistar rats were used. Rats fed by standard laboratory chow were compared with those supplemented with pure omega-3 ethyl ester (200 mg/kg b.w. /day) for two months. Blood serum was used for the detection of b1-AAB. Expression of Cx43, activity of matrix metalloproteinase 2 (MMP2) and ultrastructure were examined in left ventricular tissue. Susceptibility to electrically-induced ventricular fibrillation (VF) was tested using Langendorff-perfused heart. Comparing to healthy rats, male and female SHR exhibited significant increase of serum levels of b1-AAB, activity of MMP2, down-regulation and miss-localization of Cx43 and subcellular injury of the cardiomyocytes and their junctions. It was associated with higher incidence of VF. Omega-3 intake resulted in significant decrease of elevated blood pressure, b1-AAB levels and MMP2 activity in both male and female SHR. In addition, there was a clear-cut increase of Cx43 mRNA and protein expression, attenuation of Cx43 miss-localization as well as preservation of subcellular integrity of cardiomyocytes and their junctions. Incidence of VF was significantly reduced. Suppression of beta1-adrenoceptors autoantibody production is a novel mechanism implicated in cardioprotective effects of omega-3 fatty acids. It was linked with decrease of MMP-2 activity, up-regulation of myocardial Cx43, improvement of cardiomyocytes integrity and protection from VF. This work was supported by VEGA 1/0032/14, 2/0167/15, 2/0076/16 and APVV2/0348/12 grants.

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. 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 μmol. 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 μmol, while EPA and DHA were efficient at higher, 7 and 15 μmol. Moreover, bolus (150 μmol) 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. 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.