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Introduction: Ventricular unloading during prolonged bed rest, mechanical circulatory support or microgravity has repeatedly been linked to potentially life-threatening arrhythmias. It is unresolved, whether this arrhythmic phenotype is caused by the reduction in cardiac workload or rather by underlying diseases or external stimuli. We hypothesized that the reduction in cardiac workload alone is sufficient to impair ventricular repolarization and to induce arrhythmias in hearts. Methods: Rat hearts were unloaded using the heterotopic heart transplantation. The ECG of unloaded and of control hearts were telemetrically recorded over 56 days resulting in >5x106 cardiac cycles in each heart. Long-term electrical remodeling was analyzed using a novel semi-automatic arrhythmia detection algorithm. Results: 56 days of unloading reduced left ventricular weight by approximately 50%. While unloading did not affect average HRs, it markedly prolonged the QT interval by approximately 66% and induced a median tenfold increase in the incidence of ventricular arrhythmias in comparison to control hearts. Conclusion: The current study provides direct evidence that the previously reported hypertrophic phenotype of repolarization during cardiac unloading translates into an impaired ventricular repolarization and ventricular arrhythmias in vivo. This supports the concept that the reduction in cardiac workload is a causal driver of the development of arrhythmias during ventricular unloading. [ABSTRACT FROM AUTHOR]

IntroductionVentricular unloading during prolonged bed rest, mechanical circulatory support or microgravity has repeatedly been linked to potentially life-threatening arrhythmias. It is unresolved, whether this arrhythmic phenotype is caused by the reduction in cardiac workload or rather by underlying diseases or external stimuli. We hypothesized that the reduction in cardiac workload alone is sufficient to impair ventricular repolarization and to induce arrhythmias in hearts.MethodsRat hearts were unloaded using the heterotopic heart transplantation. The ECG of unloaded and of control hearts were telemetrically recorded over 56 days resulting in >5 × 106 cardiac cycles in each heart. Long-term electrical remodeling was analyzed using a novel semi-automatic arrhythmia detection algorithm.Results56 days of unloading reduced left ventricular weight by approximately 50%. While unloading did not affect average HRs, it markedly prolonged the QT interval by approximately 66% and induced a median tenfold increase in the incidence of ventricular arrhythmias in comparison to control hearts.ConclusionThe current study provides direct evidence that the previously reported hypertrophic phenotype of repolarization during cardiac unloading translates into an impaired ventricular repolarization and ventricular arrhythmias in vivo. This supports the concept that the reduction in cardiac workload is a causal driver of the development of arrhythmias during ventricular unloading.

Objectives: The aim of this work was to elucidate the role of GalR2 receptor activation in protecting the rat heart in vivo from ischemia/reperfusion (I/R) damage by a pharmacological peptide agonist WTLNSAGYLLGPβAH‐OH (G1) and full‐length rat galanin GWTLNSAGYLLGPHAIDNHRSFSDKHGLT‐NH2 (G2) using M871, a selective inhibitor of GalR2. Methods: The peptides were prepared by the automatic solid‐phase synthesis using the Fmoc‐strategy and purified by high‐performance liquid chromatography (HPLC). A 40‐min left anterior descending (LAD) coronary artery occlusion followed by a 60‐min reperfusion was performed. The criteria for damage/protection of the heart were the infarct size (IS) and plasma activity of creatine kinase‐MB (CK‐MB) at the end of reperfusion. Results: Intravenous injection of G1 or G2 at an optimal dose of 1 mg/kg at the fifth minute of reperfusion significantly reduced the IS (by 35% and 32%, respectively) and activity of CK‐MB at the end of reperfusion (by 43% and 38%, respectively) compared with the control. Administration of M871 (8 mg/kg) 5 min before the onset of reperfusion abolished the effects of G1 on IS and CK‐MB activity, returning them to control values. Co‐administration of M871 (8 mg/kg) with G2 attenuated protective effect of G2 on both IS and plasma СK‐MB activity. However, differences in these parameters between the M871+G2 and G2 groups did not reach statistical significance (P = 0.139 and P = 0.121, respectively). Conclusion: Thus, GalR2 is the principal receptor subtype that transduces the protective effects of galanin and ligand G1 in myocardial I/R injury. This suggests that GalR2‐specific peptide agonists could be used as drug candidates for treating ischemic heart disease. [ABSTRACT FROM AUTHOR]

Melatonin has been reported to cause myocardial electrophysiological changes and prevent ventricular tachycardia or fibrillation (VT/VF) in ischemia and reperfusion. We sought to identify electrophysiological targets responsible for the melatonin antiarrhythmic action and to explore whether melatonin receptor-dependent pathways or its antioxidative properties are essential for these effects. Ischemia was induced in anesthetized rats given a placebo, melatonin, and/or luzindole (MT1/MT2 melatonin receptor blocker), and epicardial mapping with reperfusion VT/VFs assessment was performed. The oxidative stress assessment and Western blotting analysis were performed in the explanted hearts. Transmembrane potentials and ionic currents were recorded in cardiomyocytes with melatonin and/or luzindole application. Melatonin reduced reperfusion VT/VF incidence associated with local activation time in logistic regression analysis. Melatonin prevented ischemia-related conduction slowing and did not change the total connexin43 (Cx43) level or oxidative stress markers, but it increased the content of a phosphorylated Cx43 variant (P-Cx43368). Luzindole abolished the melatonin antiarrhythmic effect, slowed conduction, decreased total Cx43, protein kinase Cε and P-Cx43368 levels, and the IK1 current, and caused resting membrane potential (RMP) depolarization. Neither melatonin nor luzindole modified INa current. Thus, the antiarrhythmic effect of melatonin was mediated by the receptor-dependent enhancement of impulse conduction, which was associated with Cx43 phosphorylation and maintaining the RMP level. [ABSTRACT FROM AUTHOR]

Abstract Background: Lactoferrin, an iron-binding glycoprotein, is known to have protective effects against intestinal and cerebral ischemia-reperfusion (IR) injuries; however, its cardioprotective effects against the stunned myocardium are unknown. This study aimed to test the hypothesis that lactoferrin has cardioprotective effects against stunned myocardium. Methods: Using isolated rat hearts (Langendorff system), we determined the effects of lactoferrin administered enterally and by direct cardiac perfusion. Rat hearts were perfused using the Langendorff system, and two experiments were performed. In experiment 1, the hearts were divided into the enteral lactoferrin (E-LF) 7.5 m, 15 m, 30 m, and 60 m groups, where lactoferrin (1000 mg/kg) was administered enterally 7.5, 15, 30, and 60 min, respectively, before perfusion; and a control group, where saline was administered 30 min before perfusion. In experiment 2, hearts were allocated to the perfusate lactoferrin (P-LF) 15 and 100 groups, where 15 mg/L and 100 mg/L lactoferrin were respectively added to the perfusate, and a control group. Each group was perfused for 20 min prior to 15 min of no-flow ischemia with pacing, followed by 20 min of reperfusion. The primary outcome was the maximum left ventricular derivative of pressure development (LV dP/dt max) 15 min after reperfusion. Myocardial phospho-protein kinase B (p-Akt) was assayed using western blotting. Results: The LV dP/dt max 15 min after reperfusion in the E-LF 15 and 30 m groups was significantly higher than that in the control group. However, the effects disappeared in the E-LF 60 m group. In the second experiment, there were no significant differences in LV dP/dt max. Myocardial p-Akt was not significantly activated in any lactoferrin group. Conclusion: Cardioprotection was observed 15–30 min after enteral lactoferrin but not by direct cardiac perfusion with lactoferrin. Myocardial p-Akt was not associated with the cardioprotective effect. The cardioprotective effect may be induced by enteral lactoferrin-induced substances.

The present study aimed to examine the biological activity and cardioprotective potential of Trametes versicolor heteropolysaccharides (TVH) in a rat model of metabolic syndrome (MetS). This study included 40 Wistar rats divided into 5 groups: CTRL—healthy non-treated rats; MetS—non-treated rats; and H-TV, M-TV and L-TV-rats with MetS treated with either 300, 200 or 100 mg/kg TVH per os for 4 weeks. After finishing the treatment, we conducted an oral glucose tolerance test (OGTT), hemodynamic measurements and the animals were sacrificed, hearts isolated and subjected to the Langendorff technique. Blood samples were used for the determination of oxidative stress parameters, lipid status and insulin levels. We showed that α-amylase inhibition was not the mode of TVH antidiabetic action, while TVH showed a moderate inhibition of pathogenic microorganisms' growth (MIC 8.00 mg·mL−1; MBC/MFC 16.00 mg·mL−1). H-TV and M-TV significantly reduced the level of prooxidants (O2−, H2O2, TBARS; p < 0.05), increased antioxidants activity (SOD, CAT, GSH; p < 0.05), reduced blood pressure (p < 0.05), improved glucose homeostasis in the OGTT test (p < 0.05), and ejection fraction (p < 0.05) and cardiac contractility (p < 0.05) compared to MetS (p < 0.05). Moreover, TVH treatment normalized the lipid status and decreased insulin levels compared to MetS rats (p < 0.05). The obtained results demonstrated that the TVH may be considered a useful agent for cardioprotection in MetS conditions. [ABSTRACT FROM AUTHOR]

Our and other studies suggest that myocardial hypertrophy in response to hypertension and hyperthyroidism increases propensity of the heart to malignant arrhythmias, while these are rare in conditions of hypothyroidism or type-1 diabetes mellitus associated with myocardial atrophy. One of the crucial factors impacting the susceptibility of the heart to life-threatening arrhythmias is gap junction channel protein connexin-43 (Cx43), which ensure cell-to-cell coupling for electrical signal propagation. Therefore, we aimed to explore Cx43 protein abundance and its topology in hypertrophic and hypotrophic cardiac phenotype. Analysis were performed in left ventricular tissue of adult male spontaneously hypertensive rat (SHR), Wistar Kyoto rats treated for 8-weeks with L-thyroxine, methimazol or strepotozotocin to induce hyperthyroid, hypothyroid and type-1 diabetic status as well as non-treated animals. Results showed that comparing to healthy rats there was a decrease of total myocardial Cx43 and its variant phosphorylated at serine368 in SHR and hyperthyroid rats. Besides, enhanced localization of Cx43 was demonstrated on lateral sides of hypertrophied cardiomyocytes. In contrast, total Cx43 protein and its serine368 variant were increased in atrophied left ventricle of hypothyroid and type-1 diabetic rats. It was associated with less pronounced alterations in Cx43 topology. In parallel, the abundance of PKC?, which phosphorylates Cx43 at serine368 that stabilize Cx43 function and distribution was reduced in hypertrophied heart while enhanced in atrophied once. Findings suggest that differences in the abundance of cardiac Cx43, its variant phosphorylated at serine368 and Cx43 topology may explain, in part, distinct propensity of hypertrophied and atrophied heart to malignant arrhythmias. [ABSTRACT FROM AUTHOR]

Myocardial ischemic adenosine production decreases in subsequent events that may blunt its protective functions. To test the relation between total or mitochondrial cardiac adenine nucleotide pool (TAN) on the energy status with adenosine production, Langendorff perfused rat hearts were subjected to three protocols: 1 min ischemia at 40 min, 10 min ischemia at 50 min, and 1 min ischemia at 85 min in Group I; additional infusion of adenosine (30 µM) for 15 min after 10 min ischemia in Group I-Ado, and 1 min ischemia at 40 and 85 min in the controls (Group No I). A 31P NMR and an HPLC were used for the analysis of nucleotide and catabolite concentrations in the heart and coronary effluent. Cardiac adenosine production in Group I measured after 1 min ischemia at 85 min decreased to less than 15% of that at 40 min in Group I, accompanied by a decrease in cardiac ATP and TAN to 65% of the initial results. Adenosine production at 85 min was restored to 45% of that at 40 min in Group I-Ado, accompanied by a rebound of ATP and TAN by 10% vs. Group I. Mitochondrial TAN and free AMP concentrations paralleled that of total cardiac TAN. Changes in energy equilibrium or mitochondrial function were minor. This study highlights that only a fraction of the cardiac adenine nucleotide pool is available for adenosine production, but further studies are necessary to clarify its nature. [ABSTRACT FROM AUTHOR]

Background: Lactoferrin, an iron-binding glycoprotein, is known to have protective effects against intestinal and cerebral ischemia-reperfusion (IR) injuries; however, its cardioprotective effects against the stunned myocardium are unknown. This study aimed to test the hypothesis that lactoferrin has cardioprotective effects against stunned myocardium. Methods: Using isolated rat hearts (Langendorff system), we determined the effects of lactoferrin administered enterally and by direct cardiac perfusion. Rat hearts were perfused using the Langendorff system, and two experiments were performed. In experiment 1, the hearts were divided into the enteral lactoferrin (E-LF) 7.5 m, 15 m, 30 m, and 60 m groups, where lactoferrin (1000 mg/kg) was administered enterally 7.5, 15, 30, and 60 min, respectively, before perfusion; and a control group, where saline was administered 30 min before perfusion. In experiment 2, hearts were allocated to the perfusate lactoferrin (P-LF) 15 and 100 groups, where 15 mg/L and 100 mg/L lactoferrin were respectively added to the perfusate, and a control group. Each group was perfused for 20 min prior to 15 min of no-flow ischemia with pacing, followed by 20 min of reperfusion. The primary outcome was the maximum left ventricular derivative of pressure development (LV dP/dt max) 15 min after reperfusion. Myocardial phospho-protein kinase B (p-Akt) was assayed using western blotting. Results: The LV dP/dt max 15 min after reperfusion in the E-LF 15 and 30 m groups was significantly higher than that in the control group. However, the effects disappeared in the E-LF 60 m group. In the second experiment, there were no significant differences in LV dP/dt max. Myocardial p-Akt was not significantly activated in any lactoferrin group. Conclusion: Cardioprotection was observed 15–30 min after enteral lactoferrin but not by direct cardiac perfusion with lactoferrin. Myocardial p-Akt was not associated with the cardioprotective effect. The cardioprotective effect may be induced by enteral lactoferrin-induced substances. [ABSTRACT FROM AUTHOR]

The aim of the research is to study the structure, innervation, and state of epicardial adipose tissue of the aortic-pulmonary region of the heart in rats at the age of 3–4 and 18–23 months using neural immunohistochemical markers. Using a complex of histological and immunohistochemical methods, different nervous apparatuses (ganglia, clusters of chromaffin cells, nerve trunks, nerve-fiber bundles, nerve plexuses, synaptic endings) with different mediators are detected in lobules of white and brown adipose tissue of the base of the rat heart. It is established that parasympathetic and sympathetic postganglionic nerve fibers are involved in the innervation of white and brown adipose tissue. They penetrate into the lobules as a part of Remak's cords of varicose axons along arterial vessels, form terminal synaptic plexuses of the en-passant type, and are involved in the innervation of adipocytes of both types of epicardial adipose tissue. It is established that PGP 9.5+ cholinergic terminal nerve fibers prevail over catecholaminergic ones in mature rats. In the process of aging, common neurodegenerative, involutive (desimatization), and destructive pathological changes are noted in the epicardial adipose tissue of the studied animals. [ABSTRACT FROM AUTHOR]

We aimed to investigate the cardioprotective effects of ethanolic Melissa officinalis L. extract (ME) in the rat model of myocardial ischemia/reperfusion (I/R) injury. Thirty-two Wistar rats were randomly divided into a CTRL non-treated control group with myocardial I/R injury and three experimental groups of rats treated with 50, 100, or 200 mg/kg of ME for 7 days per os. Afterward, hearts were isolated, and cardiodynamic function was assessed via the Langendorff model of global 20 min ischemia and 30 min reperfusion. Oxidative stress parameters were determined spectrophotometrically from the samples of coronary venous effluent (O2−, H2O2, TBARS, and NO2−,) and heart tissue homogenate (TBARS, NO2−, SOD, and CAT). H/E and Picrosirius red staining were used to examine cardiac architecture and cardiac collagen content. ME improved cardiodynamic parameters and achieved to preserve cardiac architecture after I/R injury and to decrease fibrosis, especially in the ME200 group compared to CTRL. ME200 and ME100 markedly decreased prooxidants TBARS, O2−, and H2O2 while increasing NO2−. Hereby, we confirmed the ME's ability to save the heart from I/R induced damage, even after short-term preconditioning in terms of preserving cardiodynamic alterations, cardiac architecture, fibrosis, and suppressing oxidative stress, especially in dose of 200 mg/kg. [ABSTRACT FROM AUTHOR]

The present study aimed to examine the biological activity and cardioprotective potential of Trametes versicolor heteropolysaccharides (TVH) in a rat model of metabolic syndrome (MetS). This study included 40 Wistar rats divided into 5 groups: CTRL—healthy non-treated rats; MetS—non-treated rats; and H-TV, M-TV and L-TV-rats with MetS treated with either 300, 200 or 100 mg/kg TVH per os for 4 weeks. After finishing the treatment, we conducted an oral glucose tolerance test (OGTT), hemodynamic measurements and the animals were sacrificed, hearts isolated and subjected to the Langendorff technique. Blood samples were used for the determination of oxidative stress parameters, lipid status and insulin levels. We showed that α-amylase inhibition was not the mode of TVH antidiabetic action, while TVH showed a moderate inhibition of pathogenic microorganisms’ growth (MIC 8.00 mg·mL−1; MBC/MFC 16.00 mg·mL−1). H-TV and M-TV significantly reduced the level of prooxidants (O2−, H2O2, TBARS; p < 0.05), increased antioxidants activity (SOD, CAT, GSH; p < 0.05), reduced blood pressure (p < 0.05), improved glucose homeostasis in the OGTT test (p < 0.05), and ejection fraction (p < 0.05) and cardiac contractility (p < 0.05) compared to MetS (p < 0.05). Moreover, TVH treatment normalized the lipid status and decreased insulin levels compared to MetS rats (p < 0.05). The obtained results demonstrated that the TVH may be considered a useful agent for cardioprotection in MetS conditions.

Myocardial ischemic adenosine production decreases in subsequent events that may blunt its protective functions. To test the relation between total or mitochondrial cardiac adenine nucleotide pool (TAN) on the energy status with adenosine production, Langendorff perfused rat hearts were subjected to three protocols: 1 min ischemia at 40 min, 10 min ischemia at 50 min, and 1 min ischemia at 85 min in Group I; additional infusion of adenosine (30 µM) for 15 min after 10 min ischemia in Group I-Ado, and 1 min ischemia at 40 and 85 min in the controls (Group No I). A 31P NMR and an HPLC were used for the analysis of nucleotide and catabolite concentrations in the heart and coronary effluent. Cardiac adenosine production in Group I measured after 1 min ischemia at 85 min decreased to less than 15% of that at 40 min in Group I, accompanied by a decrease in cardiac ATP and TAN to 65% of the initial results. Adenosine production at 85 min was restored to 45% of that at 40 min in Group I-Ado, accompanied by a rebound of ATP and TAN by 10% vs. Group I. Mitochondrial TAN and free AMP concentrations paralleled that of total cardiac TAN. Changes in energy equilibrium or mitochondrial function were minor. This study highlights that only a fraction of the cardiac adenine nucleotide pool is available for adenosine production, but further studies are necessary to clarify its nature.

Cellular changes in different parts of the heart of Wistar rats at the age of 18–23 months are studied using histological methods of staining with toluidine blue, hematoxylin-eosin, and immunohistochemical reactions for PGP 9.5 protein, tyrosine hydroxylase (TH), and Iba-1 protein. Focal inflammatory infiltrates are found in the connective tissue of the heart base, near which PGP 9.5+ and TH+ plexuses consisting of parasympathetic and sympathetic nerve fibers are detected. In the area of the valvular heart apparatus and at the border between the fibrous ring and myocardium of the right atrium, the following pathological changes in nerve structures are observed: degeneration of nerve fibers and granular destruction of varicose axons of the terminal plexus. A close relationship is established between the axons of the terminal neural network and cells of inflammatory infiltrates and blood capillaries. The features of the localization of neurocellular inflammatory complexes consisting of nerve fibers, blood capillaries, and cells participating in the local inflammatory process (mast cells, macrophages, fibroblasts, and plasma cells) are described in various parts of the myocardium in old animals. The chronic nature of neurogenic inflammation is determined for the heart during aging. [ABSTRACT FROM AUTHOR]

Doxorubicin (DOX) is one of the secondary metabolites of Streptomyces peucetius var. caesius. It is a common and effective chemotherapeutic agent used for the treatment of different diseases, including lymphoma, leukemia, breast cancer, and solid tumors. However, this medicine causes cardiotoxic side effects, which limit its clinical application. The present study examined the cardiomyopathy induced by DOX via echocardiography and transmission electron microscopy (TEM). The main objective was to evaluate the capacity of echocardiography and TEM as diagnostic tools for DOX-induced cardiotoxicity. Moreover, the correlation between intracellular and functional changes due to cardiotoxicity was assessed in a rat model. Cardiomyopathy was induced in rats by two cumulative doses of DOX. Group I received DOX 12 [i.e., 12 mg/kg, intraperitoneal (IP)] and group II received DOX 15 (i.e., 15 mg/kg, IP) in six equal doses over two weeks. Group III as the control (Ctrl) group received normal saline as a vehicle. Mortality during the study was only observed in the DOX 15 group. The echocardiographic assessments revealed significant changes in ejection fraction, fractional shortening, and heart rate in the groups which received DOX. In addition, severe cardiac arrhythmia was evident in DOX-treated groups. Remarkable adverse effects, such as moderately degenerated cells and inflated mitochondria were observed in the TEM analysis of rat hearts in the DOX groups. The present study indicated that rat models are suitable for investigating DOX-induced cardiomyopathy, especially at the dose of 12 mg/kg. Furthermore, echocardiography and TEM examinations were found to be valuable methods for the determination of cardiotoxicity in rats due to DOX.

Natural and chemically modified N-terminal galanin fragments (WTLNSAGYLLGPHA-OH (G1) and WTLNSAGYLLGPβAH-OH (G2), respectively) reduce functional and metabolic disturbances in the heart during experimental ischemia and reperfusion. The aim of this work was to examine whether these peptides and full-length rat galanin (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2, G3) decrease the formation of reactive oxygen species (ROS) and lipid peroxidation products in the heart with ischemia/reperfusion (I/R) injury. The peptides were synthesized by the automatic solid phase method using Fmoc technology. Their structure was identified by 1H-NMR spectroscopy and MALDI-TOF mass spectrometry. Experiments were performed on anaesthetized open-chest rats subjected to myocardial regional ischemia and reperfusion. The microdialysis method and the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin trap were used to monitor ROS content in the area at risk (AAR). Intravenous administration of G1, G2 or G3 after occlusion of coronary artery significantly decreased the content of DMPO-OH spin adduct in interstitium of the AAR during reperfusion compared to the control. These effects were accompanied by limitation of infarct size, reduction of the plasma activity of creatine kinase-MB and lactate dehydrogenase, and better preservation of the energy state of the AAR. In addition, peptides G2 and G3 significantly reduced the formation of thiobarbituric acid reactive substances in the AAR. The overall protective action of the peptides decreased in the order G2 > G3 > G1. The results suggest that pharmacological agonists of galanin receptors can be considered as promising agents to reduce oxidative stress in myocardial I/R injury. [ABSTRACT FROM AUTHOR]

We aimed to investigate the cardioprotective effects of ethanolic Melissa officinalis L. extract (ME) in the rat model of myocardial ischemia/reperfusion (I/R) injury. Thirty-two Wistar rats were randomly divided into a CTRL non-treated control group with myocardial I/R injury and three experimental groups of rats treated with 50, 100, or 200 mg/kg of ME for 7 days per os. Afterward, hearts were isolated, and cardiodynamic function was assessed via the Langendorff model of global 20 min ischemia and 30 min reperfusion. Oxidative stress parameters were determined spectrophotometrically from the samples of coronary venous effluent (O2−, H2O2, TBARS, and NO2−,) and heart tissue homogenate (TBARS, NO2−, SOD, and CAT). H/E and Picrosirius red staining were used to examine cardiac architecture and cardiac collagen content. ME improved cardiodynamic parameters and achieved to preserve cardiac architecture after I/R injury and to decrease fibrosis, especially in the ME200 group compared to CTRL. ME200 and ME100 markedly decreased prooxidants TBARS, O2−, and H2O2 while increasing NO2−. Hereby, we confirmed the ME`s ability to save the heart from I/R induced damage, even after short-term preconditioning in terms of preserving cardiodynamic alterations, cardiac architecture, fibrosis, and suppressing oxidative stress, especially in dose of 200 mg/kg.

Type 1 diabetes mellitus (T1DM) is the most severe form of diabetes, which is characterized by absolute insulin deficiency induced by the destruction of pancreatic beta cells. The aim of this study was to evaluate the effect of a structural analogue of apelin-12 ((NαMe)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, metilin) on hyperglycemia, mitochondrial (MCh) respiration in permeabilized cardiac left ventricular (LV) fibers, the myocardial energy state, and cardiomyocyte membranes damage in a model of streptozotocin (STZ) diabetes in rats. Metilin was prepared by solid-phase synthesis using the Fmoc strategy and purified using HPLC. Four groups of animals were used: initial state (IS); control (C), diabetic control (D) and diabetic animals additionally treated with metilin (DM). The following parameters have been studied: blood glucose, MCh respiration in LV fibers, the content of cardiac ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr), the activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) in blood plasma. Administration of metilin to STZ-treated rats decreased blood glucose, increased state 3 oxygen consumption, the respiratory control ratio in MCh of permeabilized LV fibers, and increased the functional coupling of mitochondrial CK (mt-CK) to oxidative phosphorylation compared with these parameters in group D. In STZ-treated animals metilin administration caused an increase in the PCr content and prevention of the loss of total creatine (ΣCr=PCr+Cr) in the diabetic hearts, as well as restoration of the PCr/ATP ratio in the myocardium and a decrease in the activity of CK-MB and LDH in plasma to initial values. Thus, metilin prevented energy disorders disturbances in cardiomyocytes of animals with experimental T1DM.

The aim of our study was to determine a chemical composition of methanol extract of Galium verum as well as to assess its effects on functional recovery and redox status of isolated rat heart after ischemia. Rats were divided into control and G. verum group, which included animals treated with 500 mg/kg of methanol extract of G. verum for 28 days. Parameters of heart function and oxidative stress markers were estimated. Cell morphology was evaluated by hematoxylin and eosin (HE) staining. Our results demonstrated for the first time that G. verum extract preserved cardiac contractility, systolic, and diastolic function as wells as structural damage of the heart after ischemia. Furthermore, G. verum extract modulated the activity of antioxidant enzymes and alleviated the production of pro-oxidants. [ABSTRACT FROM AUTHOR]

To detect the effects of shortwave radiation on dose-dependent cardiac structure and function in rats after radiation and to elucidate the mechanism of shortwave radiation induced cardiac injury to identify sensitive indicators and prophylactic treatment. One hundred Wistar rats were either exposed to 27 MHz continuous shortwave at a power density of 5, 10, and 30 mW/cm2 for 6 min or undergone sham exposure for the control (the rats had to be placed in the exposure system with the same schedules as the exposed animals, but with an inactive antenna). The Ca2+, glutamic oxaloacetic transaminase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH) content in the peripheral serum of the rats were detected by an automatic blood biochemical analyser. The electrocardiogram (ECG) of standard lead II was recorded by a multi-channel physiological recording and analysis system. The cardiac structure of rats was observed by light and electron microscopy. The results showed that the 5, 10, and 30 mW/cm2 shortwave radiation caused a significant increased in the levels of Ca2+, AST, CK, and LDH in the peripheral serum of rats. The cardiac structure was damaged by radiation and showed a disordered arrangement of myocardial fibres, the cavitation and swelling of myocardial mitochondria. These injuries were most significant 7 d after radiation and were not restored until 28 d after radiation. Shortwave radiation of 5, 10, and 30 mW/cm2 can damage rat cardiac function, including damage to the tissue structure and ultrastructure, especially at the level of the myocardial fibres and mitochondria. Shortwave radiation at 5, 10, and 30 mW/cm2 induced damage to rat heart function and structure with a dose-effect relationship, i.e., the greater the radiation dose was, the more significant the damage was. [ABSTRACT FROM AUTHOR]

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Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight. They are involved in tissue homeostasis, and they function by acting at several communication levels. Cardiac Cxs are responsible for regular heart function and, among them, Cx26 and Cx43 are widely expressed throughout the heart. Cx26 is present in vessels, as well as in cardiomyocytes, and its localization is scattered all over the cell aside from at the intercalated discs as is the case for the other cardiac Cxs. However, having been found in cardiomyocytes only recently, both its subcellular localization and its functional characterization in cardiomyocytes remain poorly understood. Therefore, in this study we aimed to obtain further data on the localization of Cx26 at the subcellular level. Our TEM immunogold analyses were performed on rat heart ventricles and differentiated H9c2 cardiac cell sections as well as on differentiated H9c2 derived extracellular vesicles. The results confirmed the absence of Cx26 at intercalated discs and showed the presence of Cx26 at the level of different subcellular compartments. The peculiar localization at the level of extracellular vesicles suggested a specific role for cardiac Cx26 in inter-cellular communication in an independent gap junction manner.

Species-specific computer models of the heart are a novel powerful tool in studies of life-threatening cardiac arrhythmias. Here, we develop such a model aimed at studying infarction injury in a rat heart, the most common experimental system to investigate the effects of myocardial damage. We updated the Gattoni2016 cellular ionic model by fitting its parameters to experimental data using a population modeling approach. Using four selected cellular models, we studied 2D spiral wave dynamics and found that they include meandering and break-up. Then, using an anatomically realistic ventricular geometry and fiber orientation in the rat heart, we built a model with a post-infarction scar to study the electrophysiological effects of myocardial damage. A post-infarction scar was simulated as an inexcitable obstacle surrounded by a border zone with modified cardiomyocyte properties. For cellular models, we studied the rotation of scroll waves and found that, depending on the model, we can observe different types of dynamics: anchoring, self-termination or stable rotation of the scroll wave. The observed arrhythmia characteristics coincide with those measured in the experiment. The developed model can be used to study arrhythmia in rat hearts with myocardial damage from ischemia reperfusion and to examine the possible arrhythmogenic effects of various experimental interventions.

The investigation was aimed to evaluate the effects of 3-weeks swimming exercise on blood pressure and redox status in high-salt-induced hypertensive rats. Male Wistar albino rats (n=40, 6 weeks old) were divided into 4 groups: 1. hypertensive rats that swam for 3 weeks; 2. sedentary hypertensive control rats; 3. normotensive rats that swam for 3 weeks; 4. sedentary normotensive control rats. Hypertensive animals were on high concentrated sodium (8% NaCl) solution for 4 weeks (period of induction of hypertension). After sacrificing, hearts were isolated and perfused according to Langendorff technique at gradually increased coronary per-fusion pressure from 40–120 cmH2O. The oxidative stress markers were determined in coronary venous effluent: the index of lipid peroxidation (measured as TBARS), nitrites (NO2−), superoxide anion radical (O2−) and hydrogen peroxide (H2O2). Swimming did not lead to significant changes in levels of TBARS, NO2−, O2− in any of compared groups while levels of H2O2 were significantly higher in swimming hyper-tensive group comparing to swimming normotensive group at coronary perfusion pressure of 80–120 cmH2O. Our results indicate that the short-term swimming start to reduce blood pressure. In addition it seems that this type of swimming duration does not promote cardiac oxidative stress damages. [ABSTRACT FROM AUTHOR]

Exposure to fine particulate matter (PM2.5) increased the risks of cardiovascular diseases. PM2.5-bound 1-nitropyrene (1-NP) and 9-nitroanthracene (9-NA) are released from the incomplete combustion of fossil fuels and derived from polycyclic aromatic hydrocarbons (PAHs). The toxicities of 1-NP and 9-NA are mainly reflected in their carcinogenicity and mutagenicity. However, studies of PM2.5-bound 1-NP and 9-NA on the cardiac genotoxicity are limited so far. In this study, histopathology, DNA damage, DNA repair-related gene expression, and oxidative stress were investigated in the hearts of male Wistar rats exposed to PM2.5 [1.5 mg/kg body weight (b.w.)] or three different dosages of 1-NP (1.0 × 10− 5, 4.0 × 10− 5, and 1.6 × 10− 4 mg/kg b.w.) or 9-NA (1.3 × 10− 5, 4.0 × 10− 5, and 1.2 × 10− 4 mg/kg b.w.). The results revealed that (1) PM2.5, higher dosages of 1-NP (4.0 × 10− 5 and 1.6 × 10− 4 mg/kg b.w.) and 9-NA (4.0 × 10− 5 and 1.2 × 10− 4 mg/kg b.w.) caused obvious pathological responses and DNA damage (DNA strand breaks, 8-OHdG formation and DNA–protein cross-link), accompanied by increasing OGG1 and GADD153 expression while inhibiting MTH1 and XRCC1 expression in rat hearts. Also, they elevated the hemeoxygenase-1 (HO-1), glutathione S-transferase (GST), and malondialdehyde (MDA) levels and decreased superoxide dismutase (SOD) activity compared with the control. (2) The lowest dosages 1-NP or 9-NA could not cause DNA damage and oxidative stress. (3) At the approximately equivalent dose level, PM2.5-induced DNA damage effects were more obvious than 1-NP or 9-NA along with positive correlation. Taken together, heart DNA damage caused by PM2.5, 1-NP and 9-NA may be mediated partially through influencing the DNA repair capacity and causing oxidative stress, and such negative effects might be related to the genotoxicity PM2.5, 1-NP, and 9-NA. [ABSTRACT FROM AUTHOR]

Adeno-associated viruses (AAVs) provide advantages in long-term, cardiac-specific gene expression. However, AAV serotype specificity data is lacking in experimental models relevant to cardiac electrophysiology and cardiac optogenetics. We aimed to identify the optimal AAV serotype (1, 6, or 9) in pursuit of scalable rodent and human models using genetic modifications in cardiac electrophysiology and optogenetics, in particular, as well as to elucidate the mechanism of virus uptake. In vitro syncytia of primary neonatal rat ventricular cardiomyocytes (NRVMs) and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were infected with AAVs 1, 6, and 9 containing the transgene for eGFP or channelrhodopsin-2 (ChR2) fused to mCherry. In vivo adult rats were intravenously injected with AAV1 and 9 containing ChR2-mCherry. Transgene expression profiles of rat and human cells in vitro revealed that AAV1 and 6 significantly outperformed AAV9. In contrast, systemic delivery of AAV9 in adult rat hearts yielded significantly higher levels of ChR2-mCherry expression and optogenetic responsiveness. We tracked the mechanism of virus uptake to purported receptor-mediators for AAV1/6 (cell surface sialic acid) and AAV9 (37/67 kDa laminin receptor, LamR). In vitro desialylation of NRVMs and hiPSC-CMs with neuraminidase (NM) significantly decreased AAV1,6-mediated gene expression, but interestingly, desialylation of hiPSC-CMs increased AAV9-mediated expression. In fact, only very high viral doses of AAV9-ChR2-mCherry, combined with NM treatment, yielded consistent optogenetic responsiveness in hiPSC-CMs. Differences between the in vitro and in vivo performance of AAV9 could be correlated to robust LamR expression in the intact heart (neonatal rat hearts as well as adult human and rat hearts), but no expression in vitro in cultured cells (primary rat cells and hiPS-CMs). The dynamic nature of LamR expression and its dependence on environmental factors was further corroborated in intact adult human ventricular tissue. The combined transgene expression and cell surface receptor data may explain the preferential efficiency of AAV1/6 in vitro and AAV9 in vivo for cardiac delivery and mechanistic knowledge of their action can help guide cardiac optogenetic efforts. More broadly, these findings are relevant to future efforts in gene therapy for cardiac electrophysiology abnormalities in vivo as well as for genetic modifications of cardiomyocytes by viral means in vitro applications such as disease modeling or high-throughput drug testing. [ABSTRACT FROM AUTHOR]

Highlights • Oxytocin triggers anti-infarct, anti-arrhythmia and anti-apoptotic effects through SAFE pathway activation against I/R injury in the early reperfusion phase. • STAT3 and NOS inhibitors and a mitoKATP blocker abrogated the cardioprotective effects of oxytocin. • Oxytocin evokes NO release, mitoKATP opening and JAK/STAT3 activation to provide cardioprotective effects against IR injury. • Oxytocin through SAFE pathway activation protects cardiomyocites against I/R injury and it considered as a clinically useful drug in patients with coronary artery diseases. Abstract Oxytocin (OT) has a postconditioning effect against the ischemia-reperfusion (I/R) injury. However, its precise cardioprotection mechanism at the early reperfusion phase remains under debate. Our previous study revealed that OT postconditioning (OTpost) is cardioprotective by activating the Reperfusion Injury Salvage Kinase (RISK) pathway. Therefore, the present study is aimed to determine the biological effects of OTpost via the OT receptor and the activation of the JAK/STAT3 signaling pathway, mitochondrial adenosine triphosphate-dependent potassium channel (mitoKATP), nitric oxide (NO) release, and its anti-apoptotic effects against I/R injury in an isolated rat heart model. Sixty-three rats were randomly allocated to one of nine groups. OT was perfused 40 min prior to the regional ischemia or 15 min at the early reperfusion phase. AG490 (a JAK/STAT3 inhibitor), 5HD (a mitoKATP blocker), atosiban (an OT receptor antagonist), L-NAME (a nonspecific nitric oxide synthase inhibitor) were applied either alone or in combination with OT during the pre-ischemia phase and/or in the early reperfusion phase. Myocardial infarct size, hemodynamic factor, ventricular arrhythmia, coronary flow, cardiac biochemical marker, and the apoptosis index were determined at the end of reperfusion. Oxytocin postconditioning reduced infarct size, lactate dehydrogenase activity, arrhythmia score, ventricular fibrillation, and apoptosis. Moreover, AG490, 5HD, atosiban, and L-NAME abrogated the cardioprotective effects of OT. Our results demonstrated that the cardioprotective effects of OT are mediated by NO release, and the activation of mitoKATP and the SAFE pathway through the JAK/STAT3 signaling cascade that finally lead to decrease in the apoptosis index during the early reperfusion phase. [ABSTRACT FROM AUTHOR]

Background: Silver fir trunk extract (SFTE) is a complex mixture of antioxidative polyphenols (lignans and phenolic acids) from the trunks of silver fir trees (Abies alba, lignum). In our previous study, we have shown that SFTE exerts strong antioxidative and protective effects against atherogenic, diet-induced arterial wall damage. Objective: The aim of the present study was to test the potential protective effects of SFTE and its compounds, two phenolic acids (p-coumaric and protocatechuic acids) in ischemia–reperfusion injury of isolated rat hearts. Design: Isolated hearts of Wistar rats aged 4–8 weeks were exposed to perfusion, ischemia, and reperfusion periods. The experiments were performed using the following five groups: control, SFTE (10 µg/L), SFTE (100 µg/L), protocatechuic acid, and p-coumaric. Aortas were isolated to measure vascular responses in the presence of Nω-Nitro-L-arginine. Results: SFTE dose-dependently reduced ischemic-reperfusion heart damage, which was indicated as the decrease in the lactate dehydrogenase (LDH) release rate and arrhythmias duration by 80% and an increase in coronary flow rate during the reperfusion period. Two tested compounds (p-coumaric and protocatechuic acids) acted less cardioprotective, since they decreased the duration of arrhythmias only by 40 and 45%, respectively, and did not decrease LDH release rates during the reperfusion period. Only p-coumaric acid increased coronary flow rates, whereas protocatechuic acid did not. Conclusions: We conclude that the SFTE exerted the strongest cardioprotective effect, whereas its constituents (the p-coumaric and protocatechuic acids) were less effective in inducing cardioprotection.

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.

Objectives: To investigate the expression dynamic of nanog gene in the development of rat myocardial tissues. Methods: SD rats were studied at 5 time points before and after birth. The techniques of immunohistochemistry, immunofluorescence, western blotting and RT-PCR were used to investigate the expression of nanog gene in the rat myocardial tissues at different embryonic (E) and postnatal (P) stages, and image analysis system was used for the quantitative analysis. Results: The immunohistochemistry, immunofluorescence and western blotting analyses have shown that expression of nanog protein was highest in the rat myocardial tissues at E18, then it gradually declined at postnatal stages (PConclusion: The mRNA transcription and protein translation of nanog gene in the rat heart gradually decreased with every consecutive growth stage. This indicates that nanog gene has potential regulatory functions in the differentiation of myocardial cells during rat development.

Diabetes mellitus is a major global health disorder and, currently, over 450 million people have diabetes with 90% suffering from type 2 diabetes. Left untreated, diabetes may lead to cardiovascular diseases which are a leading cause of death in diabetic patients. Calcium is the trigger and regulator of cardiac muscle contraction and derangement in cellular Ca2+ homeostasis, which can result in heart failure and sudden cardiac death. It is of paramount importance to investigate the regional involvement of Ca2+ in diabetes-induced cardiomyopathy. Therefore, the aim of this study was to investigate the voltage dependence of the Ca2+ transients in endocardial (ENDO) and epicardial (EPI) myocytes from the left ventricle of the Goto-Kakizaki (GK) rats, an experimental model of type 2 diabetes mellitus. Simultaneous measurement of L-type Ca2+ currents and Ca2+ transients was performed by whole-cell patch clamp techniques. GK rats displayed significantly increased heart weight, heart weight/body weight ratio, and non-fasting and fasting blood glucose compared to controls (CON). Although the voltage dependence of L-type Ca2+ current was unaltered, the voltage dependence of the Ca2+ transients was reduced to similar extents in EPI-GK and ENDO-GK compared to EPI-CON and ENDO-CON myocytes. TPK L-type Ca2+ current and Ca2+ transient were unaltered. THALF decay of L-type Ca2+ current was unaltered; however, THALF decay of the Ca2+ transient was shortened in ENDO and EPI myocytes from GK compared to CON rat hearts. In conclusion, the amplitude of L-type Ca2+ current was unaltered; however, the voltage dependence of the Ca2+ transient was reduced to similar extents in EPI and ENDO myocytes from GK rats compared to their respective controls, suggesting the possibility of dysfunctional sarcoplasmic reticulum Ca2+ transport in the GK diabetic rat hearts. [ABSTRACT FROM AUTHOR]

The well-known age-related mitochondrial dysfunction deeply affects heart because of the tissue's large dependence on mitochondrial ATP provision. Our study revealed in aged rat heart a significant 25% decrease in mtDNA relative content, a significant 29% increase in the 4.8 Kb mtDNA deletion relative content, and a significant inverse correlation between such contents as well as a significant 38% decrease in TFAM protein amount. The TFAM-binding activity to specific mtDNA regions increased at those encompassing the mtDNA replication origins, D-loop and Ori-L. The same mtDNA regions were screened for different kinds of oxidative damage, namely Single Strand Breaks (SSBs), Double Strand Breaks (DSBs), abasic sites (AP sites) and oxidized bases as 7,8-dihydro-8-oxoguanine (8oxoG). A marked increase in the relative content of mtDNA strand damage (SSBs, DSBs and AP sites) was found in the D-loop and Ori-L regions in the aged animals, unveiling for the first time in vivo an age-related, non-stochastic accumulation of oxidative lesions in these two regions that appear as hot spots of mtDNA damage. The use of Formamidopyrimidine glycosylase (Fpg) demonstrated also a significant age-related accumulation of oxidized purines particularly in the D-loop and Ori-L regions. The detected increased binding of TFAM to the mtDNA damage hot spots in aged heart suggests a link between TFAM binding to mtDNA and loss of mitochondrial genome likely through hindrance of repair processes. [ABSTRACT FROM AUTHOR]