V. Knezl

Thyroid hormones and cardiac arrhythmias.

Thyroid hormone plays an important role in cardiac electrophysiology and Ca2+ handling through both genomic and nongenomic mechanisms of action, while both actions can interfere. Chronic changes in the amount of circulating thyroid hormone due to thyroid dysfunction or systemic disease result in structural, electrophysiological and Ca2+ handling remodeling, while acute changes may affect basal activity of cardiac cells membrane systems. Consequently, long-term or rapid modulation of sarcolemmal ion channels, Ca2+ cycling proteins and intercellular communicating channels by thyroid hormone may affect heart function as well as susceptibility of the heart to arrhythmias. This aspect including pro- and anti-arrhythmic potential of thyroid hormone is highlighted in this review.

Protection of the vascular endothelium in experimental situations.

Protection of the vascular endothelium in experimental situations One of the factors proposed as mediators of vascular dysfunction observed in diabetes is the increased generation of reactive oxygen species (ROS). This provides support for the use of antioxidants as early and appropriate pharmacological intervention in the development of late diabetic complications. In streptozotocin (STZ)-induced diabetes in rats we observed endothelial dysfuction manifested by reduced endothelium-dependent response to acetylcholine of the superior mesenteric artery (SMA) and aorta, as well as by increased endothelaemia. Changes in endothelium-dependent relaxation of SMA were induced by injury of the nitric oxide radical (·NO)-signalling pathway since the endothelium-derived hyperpolarising factor (EDHF)-component of relaxation was not impaired by diabetes. The endothelial dysfunction was accompanied by decreased ·NO bioavailabity as a consequence of reduced activity of eNOS rather than its reduced expression. The results obtained using the chemiluminiscence method (CL) argue for increased oxidative stress and increased ROS production. The enzyme NAD(P)H-oxidase problably participates in ROS production in the later phases of diabetes. Oxidative stress was also connected with decreased levels of reduced glutathione (GSH) in the early phase of diabetes. After 10 weeks of diabetes, adaptational mechanisms probably took place because GSH levels were not changed compared to controls. Antioxidant properties of SMe1EC2 found in vitro were partly confirmed in vivo. Administration of SMe1EC2 protected endothelial function. It significantly decreased endothelaemia of diabetic rats and improved endothelium-dependent relaxation of arteries, slightly decreased ROS-production and increased bioavailability of ·NO in the aorta. Further studies with higher doses of SMe1EC2 may clarify the mechanism of its endothelium-protective effect in vivo.

Effect of Plant Polyphenols on Ischemia-Reperfusion Injury of the Isolated rat Heart and Vessels

In the present study, we investigated the potential protective effect of selected natural substances in a rat model of heart and mesenteric ischemia‐reperfusion (I/R). Experiments were performed on isolated Langendorff‐perfused rat hearts, subjected to 30‐min global ischemia, followed by 30‐min reperfusion. Arbutin, curcumin, rosmarinic acid and extract of Mentha x villosa were applied in the concentration of 1 × 10−5 mol/l 10 min before the onset of ischemia and during reperfusion, through the perfusion medium. Mesenteric ischemia was induced by clamping the superior mesenteric artery (SMA) for 60 min, subsequent reperfusion lasted 30 min. Production of reactive oxygen species (ROS) by SMA ex vivo was determined by luminol‐enhanced chemiluminiscence (CL). The effect of the substances was tested after their incubation with tissue. Curcumin and extract of Mentha x villosa were found to be the most effective in reducing reperfusion‐induced dysrhythmias ‐ ventricular tachycardia and fibrillation. This effect was accompanied by bradycardic effect. The mesenteric I/R induced an increase in CL in vascular tissue which was dampened by substances tested. All substances tested were found to have antioxidant properties, as demonstrated by a reduction in ROS production in mesenteric vessels. This effect was confirmed in curcumin and extract of Mentha x villosa which reduced reperfusion dyshythmias. Copyright

Protective effect of novel pyridoindole derivatives on ischemia/reperfusion injury of the isolated rat heart

Generation of reactive oxygen species is a major, well-known cause of heart injury induced by ischemia-reperfusion. This injury is manifested through myocardial stunning, reperfusion and lethal reperfusion injury of cardiocytes. The pyridoindole stobadine has been shown to exhibit significant antioxidant, free-radical scavenging and hypoxic-tissue-protecting properties. The present study examined the effects of stobadine and two novel derivatives, SMe1 and SMe1EC2, which exhibit improved pharmacodynamic and toxicity profiles, on the functional properties and reperfusion dysrhythmias of the isolated rat heart in ischemia-reperfusion conditions. All experiments were performed on isolated Langendorff-perfused hearts isolated from 3-month-old male Wistar rats. After 15 min of stabilization, the hearts were subjected to a 30-minute period of global no-flow ischemia, followed by a 30-minute reperfusion period. Stobadine, SMe1 and SMe1EC2 were applied at a concentration of 1 x 10(-5) 10 min before the onset of ischemia, and during reperfusion through the perfusion medium. As compared to the untreated group, addition of SMe1EC2 during reperfusion significantly increased left ventricular developed pressure, decreased pathologically elevated left ventricular end-diastolic pressure and enhanced recovery of the stunned myocardium after ischemia. Both SMe1 and stobadine failed to influence these parameters; however, all derivatives tested inhibited serious life-threatening reperfusion dysrhythmias such as ventricular tachycardia and ventricular fibrillation. Our findings suggest that SMe1EC2 promotes an improved recovery of the left ventricular function following ischemia compared to either stobadine or SMe1. However, both SMe1EC2 and SMe1 manifested a significant anti-dysrhythmic effect comparable with that of stobadine and partially reduced myocardial ischemia-reperfusion-induced injury.

Effect of stobadine on cardiac injury induced by ischemia and reperfusion.

The aim of this work was to evaluate the effect of the antioxidant stobadine on ischemia/reperfusion-induced injury of the isolated rat heart. Experiments were performed according to Langendorff. Ischemia was induced by stop-flow lasting 30 minutes and the duration of repefusion was 30 minutes. Reperfusion of the ischemic heart induced dysrhythmias, with the most severe ones occurring in the first minutes of reperfusion. A significant increase in coronary perfusion pressure was observed starting after 15 min of reperfusion. Stobadine (10(-6) M applied 3 minutes before onset of ischemia and during reperfusion) prevented the deleterious effects to develop fully. The protective effect of stobadine observed in our experiments seems to be a consequence of its antioxidant properties.

L‐thyroxine increases susceptibility of adult rats to low K+‐induced ventricular fibrillation, and sinus rhythm restoration in old rats

Hypokalaemia increases the risk for life‐threatening arrhythmias; however, data about interaction with thyroid status are lacking. The aim of this study was to investigate vulnerability of l‐thyroxine (T4)‐treated adult and old rats to low K+‐induced ventricular fibrillation (VF) as well as the ability of the heart to recover sinus rhythm. The experiments were performed on isolated heart preparations using the heart of 4‐ and 20‐month‐old female Wistar rats without and with feeding with T4 50 μg (100 g day)−1 over a period of 2 weeks. Perfusion of the isolated heart with oxygenated Krebs–Henseleit solution at constant pressure was followed by perfusion with K+‐deficient solution until occurrence of VF (< 10 min). After 2 min of sustained VF, the heart was perfused with normal solution for 10 min, during which sinus rhythm was restored. ECG, left ventricular pressure (LVP) and coronary flow were continuously monitored. The results showed that compared with untreated rats, the onset of low K+‐induced ventricular premature beats was delayed and their number was significantly decreased in both T4‐treated groups. Nevertheless, VF occurred earlier in T4‐treated than in non‐treated adult rats (6.78 ± 0.28 vs. 9.59 ± 0.55 min, P < 0.05), whereas the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T4‐treated rats compared with non‐treated rats (7.18 ± 0.57 vs. 8.94 ± 0.64 min, P < 0.05), whereas in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of a pharmacological dose of T4 can increase the risk of low K+‐induced VF in adult but not in old animals; in the latter it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T4‐treated hearts.

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.

Effect of novel quercetin pivaloyl ester on functions of adult rat microglia

Abstract The pathogenic mechanisms involved in the development of ageing-related neurodegenerative diseases can involve alterations of microglia, the brain counterpart of macrophages. These include microglial over-activation, replicative senescence, accumulation of autofluorescent lipofuscin and mitochondrial dysfunction. Substantial evidence suggests that dietary flavonoids are capable to modulate and probably revert the hyperactive and senescence phenotype of these cells. The present study assessed the effect of a novel semisynthetic flavonoid 3’-O-(3-chloropivaloyl)quercetin (CPQ) on the functions of adult rat microglia, isolated secondarily to the establishment of mixed glial cultures and compared it with the effect of the unmodified molecule, quercetin. CPQ suppressed NO release by lipopolysaccharide-stimulated cells more effectively than did quercetin. Unlike quercetin, CPQ inhibited the injury of cell viability due to oxidative challenge and suppressed senescence-associated β-galactosidase staining of microglia isolated from long-term mixed glial cultures. Both flavonoids tested protected the functions of microglia in response to inflammatory stimuli. Furthermore, both compounds protected the isolated microglia from adverse effects of HEPES-buffered media. This was followed by an increase of cell yields, improvement of lysosomal function, suppression of nuclear protein oxidation and inhibition of lipofuscin accumulation (at a slightly more profound effect of CPQ). In conclusion, our data support the experimental evidence suggesting beneficial effects of flavonoids in modulation of neuropathology- and ageing-related alterations of microglia. In this regard, the novel pivaloyl ester of quercetin might represent a new drug with improved potential against neurodegenerative diseases.

CARDIOPROTECTIVE EFFECT OF THE RED PALM OIL SUPPLEMENTATION ON THE CARDIAC OXIDATIVE STRESS, NITRIC OXIDE SYNTHASE AND HEART FUNCTION IN THE RATS SUFFERING FROM HYPERTENSION

Objective: We know from our previous study that myocardial protein connexin 43 (Cx43), responsible for intercellular communication, and protein kinase C epsilon which directly phosphorylates Cx43 on the serine 368, were significantly decreased in spontaneously hypertensive rats (SHR) what was also associated with increased incidence to malignant arrhythmias. Antioxidant rich red palm oil (RPO) significantly normalized all of these parameters. Therefore, we further aimed to investigate whether intake of RPO may affect endothelial dysfunction, antioxidant enzymes and heart function in SHR. Design and method: In accordance with the rules issued by the State Veterinary Administration of the Slovak Republic and European Union Council Directive 86/609/EEC we used in our experiment 3-months-old, male SHR and normotensive Wistar-Kyoto control rats fed standard rat chow without or with RPO (0.2 ml/day/5 weeks). Left ventricular tissue was used to examine expression of antioxidant enzymes such as superoxide dismutases (SOD1, SOD2) and glutathione peroxidases (GPx) as well as activity of nitric oxide synthase (NOS). Functional parameters of the heart were measured during basal conditions and at the early-phase of post-ischemic reperfusion by Langendorff-perfused system. Results: RPO supplementation significantly normalized higher blood pressure and total NOS activity as well as increased lowered expression of mitochondrial SOD2 in SHR hearts during basal condition. RPO intake resulted in the 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. Conclusions: We can conclude that SHR benefit from RPO intake due to its apparent anti-arrhythmic effects by Cx43 modulation, reduction of blood pressure, enhancement of oxidative stress and protection of heart function that was deteriorated by post-ischemic reperfusion.

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.