Role of protein kinase C, PI3 kinase, tyrosine kinases, NO-synthase, KATP channels and MPT pore in the signaling pathway of the cardioprotective effect of chronic continuous hypoxia.

It was established that adaptation to chronic continuous normobaric hypoxia (CCNH) increases cardiac tolerance to ischemia and reperfusion. It was performed coronary artery occlusion (20 min) and reperfusion (3 h) in Wistar rats. CCNH promoted a decrease in the infarct size/area at risk ratio in 2-fold. CCNH promoted an increase in the nitrite/nitrate levels in blood serum and myocardium. Pretreatment with protein kinase C (PKC) inhibitor chelerythrine, NO-synthase (NOS) inhibitor L-NAME, iNOS inhibitor S-methylisothiourea, KATP channel blocker glibenclamide, mitoKATP channel blocker 5-hydroxydecanoic acid abolished the infarct-reducing effect of CCNH. The non-selective tyrosine kinase inhibitor genistein attenuated but not eliminated infarct-sparing effect of CCNH. The nNOS inhibitor 7-nitroindazole, sarcKATP channel blocker HMR 1098, MPT pore inhibitor atractyloside, PI3 kinase inhibitor wortmannin did not reverse infarct-limiting effect of CCNH. It was concluded that infarct-reducing effect of CCNH is mediated via PKC, iNOS activation and mitoKATP channel opening. While nNOS, PI3 kinase, sarcKATP channel, MPT pore are not involved in the development of CCNH-induced cardiac tolerance to impact of ischemia-reperfusion.

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists.

It has now been demonstrated that the µ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

Preserved cardiac mitochondrial function and reduced ischaemia/reperfusion injury afforded by chronic continuous hypoxia: role of opioid receptors.

Chronic continuous normobaric hypoxia (CNH) increases cardiac tolerance to acute ischaemia/reperfusion injury. The objective of this study was to find out whether the cardioprotective effect of CNH mediated by opioid receptors is associated with preservation of mitochondrial function. Rats were adapted to CNH (12% oxygen) for 3 weeks. Isolated perfused hearts were subjected to 45 min of global ischaemia and 30 min of reperfusion; subgroups were pretreated with non-selective opioid receptor antagonist naloxone (300 nmol/L) for 10 min. Cardiac contractile function, creatine kinase activity in coronary effluent, mitochondrial respiration rate, and calcium retention capacity were assessed. Adaptation to CNH decreased myocardial creatine kinase release during reperfusion and improved the post-ischaemic recovery of contractile function, mitochondrial state 3 and uncoupled respiration rates, and calcium retention capacity compared to the normoxic group. These protective effects were completely abolished by naloxone. The contractile recovery positively correlated with state 3 respiration and calcium retention capacity. The results suggest that the preserved mitochondrial function contributes to the protected cardiac phenotype afforded by adaptation to CNH and point to an important role of opioid receptor activation.

Evaluation of Nephroprotective Efficacy of Hypoxic Preconditioning in Patients Undergoing Coronary Artery Bypass Surgery.

BACKGROUND: Nonpulsatile blood flow plays an important role in the pathogenesis of renal dysfunction in patients with extracorporeal circulation. In our opinion, hypoxic preconditioning (HP) can be used to protect kidneys from postsurgical dysfunction. The aim of this study was to evaluate nephroprotective efficacy of HP in myocardial revascularization with extracorporeal circulation. METHODS: The randomized, controlled trial was performed in 63 patients undergoing coronary artery bypass grafting (CABG). Thirty-three patients were subjected to HP during CABG; 30 patients were included in the comparison group. All patients underwent dynamic renal scintigraphy with (99m)Тc-diethylenetriaminepentaacetic acid and were subjected to measuring the concentration of lipocalin in blood serum before and after CABG. RESULTS: After CABG, the mean values of the total glomerular filtration rate (GFR) and GFR for each kidney significantly decreased only in patients of the comparison group. Significant increases in the concentration of serum neutrophil gelatinase-associated lipocalin occurred 5 h after surgery both in the group with HP (70.65 ± 46.71 to 127.58 ± 98.46 ng/ml) and in the comparison group (65.01 ± 38.64 to 171.65 ± 89.91 ng/ml). At the same time, the mean difference values between pre- and postoperative lipocalin levels were 56.94 ± 51.75 ng/ml in the study group and 106.64 ± 51.27 ng/ml in the comparison group; these differences were highly statistically significant (р = 0.004). CONCLUSION: The results of our study showed that (i) HP exerts nephroprotection in patients undergoing on-pump CABG, and (ii) determination of the lipocalin-2 level can be used for early diagnosis of acute kidney injury in cardiac surgery patients.

Activation of peripheral delta opioid receptors increases cardiac tolerance to arrhythmogenic effect of ischemia/reperfusion.

OBJECTIVES: The objective of this study was to investigate the role of peripheral µ, δ1, δ2, and nociceptin opioid receptors agonists in the regulation of cardiac tolerance to the arrhythmogenic effect of ischemia/reperfusion in rats. METHODS: Anesthetized open-chest male Wistar rats were subjected to either 45 minutes of left coronary artery occlusion (phase 1a 10 minutes and phase 2b 35 minutes) and 2 hours of reperfusion in Experiment 1 or 10 minutes of ischemia and 10 minutes of reperfusion in Experiment 2. In Experiment 1, saline or vehicle controls and the mu-specific opioids dermorphin-H (Derm-H) and ([d-Ala2, N-Me-Phe4, Gly-ol5] enkephalin (DAMAGO); the delta-1-specific opioid d-Pen2,5enkephalin (DPDPE); nociceptin; and the delta-2-specific opioids deltorphin-II (Delt-II), Delt-Dvariant (Delt-Dvar), and deltorphin-E (Delt-E) were infused 15 minutes prior to ischemia. In Experiment 2, DPDPE, Delt-D, Delt-Dvar, and Delt-E were infused at 15 minutes prior to ischemia. The universal opioid receptor antagonist naltrexone, the peripherally acting antagonist naloxone methiodide, the selective δ1 antagonist 7-benzylidene naltrexone maleate, and the specific δ2 antagonist naltriben mesylate were infused 25 minutes prior to ischemia. RESULTS: In Experiment 1, pretreatment with the µ opioids Derm-H and DAMGO, DPDPE, and nociceptin at all doses tested did not reduce the incidence of ischemia-induced arrhythmias compared to controls during 45 minutes of ischemia. The δ2 opioids Delt-II (0.12 mg/kg), Delt-Dvar (0.3 mg/kg), and Delt-E (0.18 mg/kg) all demonstrated significant antiarrhythmic effects at the 150 nmol/kg dose compared to saline or vehicle controls. Nine of 19 animals treated with Delt-II were tolerant without ventricular arrhythmias to the arrhythmogenic effect of ischemia during the first 10 minutes of ischemia (phase 1a) and 11 of 19 were without ventricular arrhythmias during the following 35 minutes of ischemia (phase 1b). Delt-II also decreased the incidence of premature ventricular contractions and ventricular tachycardia by almost half during phase 1a. Delt-II did not affect the incidence of ventricular fibrillation (VF). Pretreatment with Delt-Dvar and Delt-E completely blocked the incidence of VF in phase 1b. Delt-E also decreased premature ventricular contractions by 50%, and the incidence of ventricular tachycardia decreased over twofold in phase 1b of ischemia. There was no enhanced tolerance by any of the delta-2 opioids to the arrhythmogenic effect of reperfusion after long-term ischemia. In Experiment 2, after 10 minutes of ischemia and 10 minutes of reperfusion, Delt-II (0.12 mg/kg) reduced the incidence of premature ventricular contractions and ventricular tachycardia compared to controls, and completely blocked the incidence of VF following 10 minutes of reperfusion. Delt-Dvar and Delt-E were without effect, as was DPDPE following 10 minutes of reperfusion. The antiarrhythmic effect of Delt-II during 10 minutes of ischemia and 10 minutes of reperfusion was completely blocked by the peripherally acting opioid receptor inhibitor naloxone methiodide and the selective delta-2 opioid receptor inhibitor naltriben mesylate, but not by the selective delta-1 inhibitor 7-benzylidene naltrexone maleate. The antagonists alone had no effect on arrhythmogenesis. CONCLUSIONS: Peripheral delta-2 opioid receptor activation by Delt-II, Delt-Dvar, and Delt-E enhanced cardiac tolerance to the arrhythmogenic effects of ischemia.

Role of endogenous opioid peptides in the infarct size-limiting effect of adaptation to chronic continuous hypoxia.

AIMS: The objective of this study was to examine the involvement of endogenous opioid peptides and opioid receptor (OR) subtypes in the cardioprotective effect of adaptation to chronic hypoxia in rats. MAIN METHODS: Rats were exposed to continuous normobaric hypoxia (CNH; 12% oxygen) for 3 weeks. Myocardial ischemia was induced by 20-min coronary artery occlusion followed by 3-h reperfusion in anesthetized open-chest animals. Various OR antagonists were administered to rats prior to ischemia. The size of myocardial infarction and the incidence of ischemic ventricular arrhythmias were assessed. Myocardial and plasma concentrations of opioid peptides (met-enkephalin, ß-endorphin, and endomorphins) were determined. KEY FINDINGS: Adaptation to CNH significantly increased myocardial and plasma concentrations of opioids, potentiated their further elevation by ischemia/reperfusion, and reduced myocardial infarct size, but it did not affect the incidence of ischemic arrhythmias. The infarct size-limiting effect of CNH was abolished by OR antagonists naltrexone (non-selective), naloxone methiodide (non-selective peripherally acting), TIPP[ψ] (δ-OR), naltriben (δ2-OR), or CTAP (µ-OR), while BNTX (δ1-OR) and nor-binaltorphimine (κ-OR) had no effect. SIGNIFICANCE: The results suggest that the infarct size-limiting effect afforded by adaptation to CNH is mediated by activation of peripheral δ2- and µ-ORs by elevated levels of endogenous opioid peptides.

Comparative analysis of the cardioprotective properties of opioid receptor agonists in a rat model of myocardial infarction.

OBJECTIVES: This study was conducted to test the hypothesis that opioid receptor (OR)-mediated cardioprotection is agonist specific when administered prior to coronary artery occlusion and reperfusion in a rat model. METHODS: Anesthetized open-chest male Wistar rats were subjected to 45 minutes of left coronary artery occlusion and 2 hours of reperfusion. Opioid agonists were infused 15 minutes prior to coronary artery occlusion. Two control groups and 15 opioid-treated groups were studied. Controls were infused with either saline alone (n = 16) or dimethyl sulfoxide plus hydroxypropyl-ß-cyclodextrin in saline (n = 19). The µ-selective agonist DAMGO was infused at either 150 nmol/kg (n = 15) or 1500 nmol/kg (n = 14), and dermorphin-H was infused at 150 nmol/kg (n = 14). The δ1 -selective agonist d-Pen²(,)5 enkephalin (DPDPE) was infused at 150 nmol/kg (n = 16) or 1500 nmol/kg (n = 14). The δ2 -selective agonists deltorphin II (n = 16), deltorphin-D(variant) (n = 15), and deltorphin-E (n = 14) were infused at 150 nmol/kg. The selective κ1 opioid agonist U-50488 was infused at 240 nmol/kg (n = 14), 1500 nmol/kg (n = 14), and 2,400 nmol/kg (n = 14). The selective κ2 opioid agonist GR-89696 was infused at 150 nmol/kg (n = 14) and 1500 nmol/kg (n = 15). Orphinan FQ (nociceptin), also referred to as OR-like 1 (ORL1), was infused at 220 nmol/kg (n = 15) and 1500 nmol/kg (n = 15). The infarct size/area at risk (IS/AAR) ratio was determined after reperfusion by negative staining with patent blue violet dye. Hemodynamic parameters including heart rate, mean arterial blood pressure (MAP), and rate pressure product (RPP) were determined. RESULTS: Pretreatment with the δ2 OR agonist deltorphin II (150 nmol/kg) significantly reduced the IS/AAR ratio, while deltorphin-D(variant) and deltorphin-E did not exhibit an infarct-sparing effect at that treatment dose. Activation of δ1 OR by DPDPE, κ1 OR by U-50488, κ2 OR by GR-89696, µ OR by DAMGO, dermorphin-H, and nociceptin had no effect on the IS/AAR ratio. U-50488 at 2,400 nmol/L induced a bradycardic effect. All other opioids had no effect on hemodynamic parameters at the doses tested. CONCLUSIONS: Peripheral δ2 OR activation by deltorphin II induces infarct size reduction in this animal model. Agonists of µ, δ1, κ1, κ2, and nociceptin receptors at the doses tested did not induce cardiac tolerance to ischemia/reperfusion injury in vivo.

Activation of peripheral delta2 opioid receptors increases cardiac tolerance to ischemia/reperfusion injury Involvement of protein kinase C, NO-synthase, KATP channels and the autonomic nervous system.

AIMS: This study aims to investigate the role of peripheral delta(2) opioid receptors in cardiac tolerance to ischemia/reperfusion injury and to examine the contribution of PKC, TK, K(ATP) channels and the autonomic nervous system in delta(2) cardioprotection. MAIN METHODS: Deltorphin II and various inhibitors were administered in vivo prior to coronary artery occlusion and reperfusion in a rat model. The animals were monitored for the development of arrhythmias, infarct development and the effects of selected inhibitors. KEY FINDINGS: Pretreatment with peripheral and delta(2) specific opioid receptor (OR) antagonists completely abolished the cardioprotective effects of deltorphin II. In contrast, the selective delta(1) OR antagonist 7-benzylidenenaltrexone (BNTX) had no effect. The protein kinase C (PKC) inhibitor chelerythrine and the NO-synthase inhibitor L-NAME (N-nitro-L-arginine methyl ester) also reversed both deltorphin II effects. The nonselective ATP-sensitive K+ (K(ATP)) channel inhibitor glibenclamide and the selective mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoic acid only abolished the infarct-sparing effect of deltorphin II. Inhibition of tyrosine kinase (TK) with genistein, the ganglion blocker hexamethonium and the depletion of endogenous catecholamine storage with guanethidine reversed the antiarrhythmic action of deltorphin II but did not change its infarct-sparing action. SIGNIFICANCE: The cardioprotective mechanism of deltorphin II is mediated via stimulation of peripheral delta(2) opioid receptors. PKC and NOS are involved in both its infarct-sparing and antiarrhythmic effects. Infarct-sparing is dependent upon mitochondrial K(ATP) channel activation while the antiarrhythmic effect is dependent upon TK activation. Endogenous catecholamine depletion reduced antiarrhythmic effects but did not alter the infarct-sparing effect of deltorphin II.