Role of ATP-Sensitive K+ Channels in Myocardial Infarct Size-Limiting Effect of Chronic Continuous Normobaric Hypoxia

Pathological implications of cellular stress in cardiovascular diseases

Cellular stress has been a key factor in the development of cardiovascular diseases. Major types of cellular stress such as mitochondrial stress, endoplasmic reticulum stress, hypoxia, and replicative stress have been implicated in clinical complications of cardiac patients. The heart is the central regulator of the body by supplying oxygenated blood throughout the system. Impairment of cellular function could lead to heart failure, myocardial infarction, ischemia, and even stroke. Understanding the effect of these distinct types of cellular stress on cardiac function is crucial for the scientific community to understand and develop novel therapeutic approaches. This review will comprehensively explain the different mechanisms of cellular stress and the most recent findings related to stress-induced cardiac dysfunction.

Development of cardioprotective effect of chronic continuous hypoxia in rats with induced metabolic syndrome

   Background. It is known that adaptation to chronic continuous hypoxia leads to a pronounced cardioprotective effect. The efficiency of acute adaptation to hypoxia is reduced in metabolic syndrome. However, the effectiveness of the myocardial infarct size-limiting effect of chronic continuous hypoxia in metabolic syndrome remains an understudied fact.   The aim. To study the effectiveness of the development of the myocardial infarct size-limiting effect of chronic continuous hypoxia in rats with metabolic syndrome.   Materials and methods. The study was carried out on 43 Wistar rats. Adaptation of animals to chronic hypoxia was performed during 21 days in a hypoxic chamber (12 % O2, 0.3 % CO2). Metabolic syndrome was modeled by keeping rats on a high-carbohydrate and high-fat diet (proteins 16 %, fats 21 %, carbohydrates 46 % (including fructose 17 %), cholesterol 0.125 %, cholic acid 0.5 %) for 12 weeks with replacement of drinking water with 20% fructose solution. Coronary occlusion-reperfusion was performed in vivo. The effect of chronic hypoxia and metabolic syndrome on myocardial infarct size was assessed.   Results. It was found that myocardial infarct size in rats after chronic continuous hypoxia was 38 % less than in animals of the control group. In rats which were kept on a high-carbohydrate and high-fat diet we observed the obesity, decreased glucose tolerance, increased serum triglycerides level, and hypertension. Adaptation to chronic continuous hypoxia in animals on a high-carbohydrate and high-fat diet improved carbohydrate metabolism, but did not affect the severity of other metabolic disorders. At the same time, the myocardial infarct size-limiting effect of chronic hypoxia was not observed in rats with metabolic syndrome.   Conclusion. Metabolic syndrome eliminated myocardial infarct size-limiting effect of chronic continuous hypoxia.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Intracellular Kinase Mechanism of the Cytoprotective Action of Adaptation to Chronic Hypoxia in Anoxia/Reoxygenation of Cardiomyocytes

On the model of anoxia/reoxygenation of isolated cardiomyocytes, we studied the role of kinases in the implementation of the cytoprotective effect of chronic continuous normobaric hypoxia (21 days on continuous exposure of rats at 12% O₂). Anoxia/reoxygenation of cardiomyocytes from intact rats caused death of 16.5% cells, which was accompanied by the release of lactate dehydrogenase; in suspension of cardiomyocytes from adapted rats, only 6.8% cells died and the release of lactate dehydrogenase was lower by 60%. Incubation of cells with inhibitors of protein kinase C (chelerythrin, 10 mM), protein kinase Cδ (rottlerin, 1 μM), tyrosine kinases (genistein, 50 μM), but not with PI3K inhibitor (wortmannin, 100 nM) eliminated the cytoprotective effect of chronic continuous normobaric hypoxia. Thus, the cytoprotective effect of chronic normobaric hypoxia is realized through activation of protein kinase Cδ and tyrosine kinases, but not through PI3K.

[Protective effect of uridine on metabolic processes in rat myocardum during its ischemia/reperfusion damage]

The experimental study of the cardioprotective effect of uridine, the metabolic precursor of the endogenous activator of mitochondrial ATP-dependent K+-channels (mitoKATP-channels), was performed using the model of myocardial ischemia/reperfusion (I/RP) in rats. Ischemia for 30 min followed by reperfusion for 120 min resulted in a significant decrease in ATP and phosphocreatine (PC) content, intensification of lipid peroxidation (LPO), and inhibition of the antioxidant system (AOS) in cardiomyocytes. Uridine in a dose of 30 mg/kg, administered intravenously prior to reperfusion, had a protective effect on myocardial metabolism in the I/RP zone. It prevented the decrease of ATP and PC, limited the LPO processes, evaluated by the content of lipid hydroperoxides and conjugated dienes, and improved the AOS state by, preventing the decrease of superoxide dismutase (SOD) activity and increasing the content of reduced glutathione (GSH). The mitoKATP-channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) eliminated the ability of uridine to maintain the ATP level and to exhibit its positive effect on the intensity of the LPO and activity of AOS. The obtained data allow us to conclude that activation of mitoKATP-channels play an important role in the mechanism of the cardioprotective effect of uridine in I/RP damage of myocardium.