ATP-sensitive K+ channel openers prevent Ca2+ overload in rat cardiac mitochondria

Erucin Exerts Cardioprotective Effects on Ischemia/Reperfusion Injury through the Modulation of mitoKATP Channels

Modulation of mitochondrial K channels represents a pharmacological strategy to promote cardioprotective effects. Isothiocyanates emerge as molecules capable of releasing hydrogen sulfide (H2S), an endogenous pleiotropic gasotransmitter responsible for anti-ischemic cardioprotective effects also through the involvement of mitoK channels. Erucin (ERU) is a natural isothiocyanate resulting from the enzymatic hydrolysis of glucosinolates (GSLs) present in Eruca sativa Mill. seeds, an edible plant of the Brassicaceae family. In this experimental work, the specific involvement of mitoKATP channels in the cardioprotective effect induced by ERU was evaluated in detail. An in vivo preclinical model of acute myocardial infarction was reproduced in rats to evaluate the cardioprotective effect of ERU. Diazoxide was used as a reference compound for the modulation of potassium fluxes and 5-hydroxydecanoic acid (5HD) as a selective blocker of KATP channels. Specific investigations on isolated cardiac mitochondria were carried out to evaluate the involvement of mitoKATP channels. The results obtained showed ERU cardioprotective effects against ischemia/reperfusion (I/R) damage through the involvement of mitoKATP channels and the consequent depolarizing effect, which in turn reduced calcium entry and preserved mitochondrial integrity.

Sevoflurane-mediated modulation of oxidative myocardial injury

Introduction

Volatile anesthetics offer protection when administered throughout an ischemic injury. We examined how volatile anesthetics modulate the cardiac myocytic injury associated with hydrogen peroxide.

Methods

Forty-eight Long-Evans rats were divided into four groups depending on the treatment: none (CONT), Glibenclamide (GLB); Sevoflurane (SEV); or GLB+SEV. Each group was further divided into two, one of which was exposed to hydrogen peroxide (H2O2). Oral GLB was administered 48 hours before myocardial isolation. All rats were anesthetized by intraperitoneal injection of Ketamine, and the hearts were harvested after heparinization. Cardiomyocytes were isolated using a combination of mechanical mincing and enzymatic digestion. After isolation, the aliquots of cells were exposed to H2O2 and FeSO4 for 30 minutes. The cell suspensions were then bubbled for 10 minutes with 100% oxygen and 1.5% SEV if appropriate. Apoptosis was detected by fluorescein-bound annexin-V (ANX-V), necrosis by propidium iodide, and ELISA assessed caspase-3 activity in all groups.

Results

There was an increase in apoptosis, necrosis, and caspase-3 activity in the cells following exposure to hydrogen peroxide. SEV reduced the rate of cell necrosis and apoptosis. Pretreatment with GLB did not alter the effects of SEV. Similarly, caspase-3 activity did not change with GLB, although SEV administration reduced this enzymatic activity in response to hydrogen peroxide.

Conclusion

In this oxidant injury model, we demonstrated that incubating isolated cardiomyocytes with SEV profoundly diminished H2O2-induced apoptotic and necrotic cells compared to their CONTs. These results support the hypothesis that KATP channels are not the sole mediators associated with anesthetic preconditioning.

Regulation of Mitochondrial Permeability Transition Pore Opening by Monovalent Cations in Liver Mitochondria

The opening of the permeability transition pore (PTP) in mitochondria is a key event in the initiation of cell death in various pathologic states, including ischemia/reperfusion. The activation of K⁺ transport into mitochondria protects cells from ischemia/reperfusion. However, the role of K⁺ transport in PTP regulation is unclear. Here, we studied the role of K⁺ and other monovalent cations in the regulation of the PTP opening in an in vitro model. The registration of the PTP opening, membrane potential, Ca²⁺-retention capacity, matrix pH, and K⁺ transport was performed using standard spectral and electrode techniques. We found that the presence of all cations tested in the medium (K⁺, Na⁺, choline⁺, and Li⁺) strongly stimulated the PTP opening compared with sucrose. Several possible reasons for this were examined: the effect of ionic strength, the influx of cations through selective and non-selective channels and exchangers, the suppression of Ca²⁺/H⁺ exchange, and the influx of anions. The data obtained indicate that the mechanism of PTP stimulation by cations includes the suppression of K⁺/H⁺ exchange and acidification of the matrix, which facilitates the influx of phosphate. Thus, the K⁺/H⁺ exchanger and the phosphate carrier together with selective K⁺ channels compose a PTP regulatory triad, which might operate in vivo.

Cannabis, cocaine, methamphetamine, and opiates increase the risk of incident atrial fibrillation

AIMS

Atrial fibrillation (AF) is now regarded as a preventable disease, requiring a search for modifiable risk factors. With legalization of cannabis and more lenient laws regarding the use of other illicit substances, investigation into the potential effects of methamphetamine, cocaine, opiate, and cannabis exposure on incident AF is needed.

METHODS AND RESULTS

Using Office of Statewide Health Planning and Development databases, a longitudinal analysis was performed of adult Californians ≥18 years of age who received care in an emergency department, outpatient surgery facility, or hospital from 1 January 2005 to 31 December 2015. Associations between healthcare coding for the use of each substance and a new AF diagnosis were assessed. Among 23,561,884 patients, 98 271 used methamphetamine, 48 701 used cocaine, 10 032 used opiates, and 132 834 used cannabis. Of the total population, 998 747 patients (4.2%) developed incident AF during the study period. After adjusting for potential confounders and mediators, use of methamphetamines, cocaine, opiates, and cannabis was each associated with increased incidence of AF: hazard ratios 1.86 [95% confidence interval (CI) 1.81-1.92], 1.61 (95% CI 1.55-1.68), 1.74 (95% CI 1.62-1.87), and 1.35 (95% CI 1.30-1.40), respectively. Negative control analyses in the same cohort failed to reveal similarly consistent positive relationships.

CONCLUSION

Methamphetamine, cocaine, opiate, and cannabis uses were each associated with increased risk of developing incident AF. Efforts to mitigate the use of these substances may represent a novel approach to AF prevention.

ATP-sensitive potassium channels: A double-edged sword in neurodegenerative diseases

ATP-sensitive potassium channels (K_ATP channels), a group of vital channels that link the electrical activity of the cell membrane with cell metabolism, were discovered on the ventricular myocytes of guinea pigs by Noma using the patch-clamp technique in 1983. Subsequently, K_ATP channels have been found to be expressed in pancreatic β cells, cardiomyocytes, skeletal muscle cells, and nerve cells in the substantia nigra (SN), hippocampus, cortex, and basal ganglia. K_ATP channel openers (KCOs) diazoxide, nicorandil, minoxidil, and the K_ATP channel inhibitor glibenclamide have been shown to have anti-hypertensive, anti-myocardial ischemia, and insulin-releasing regulatory effects. Increasing evidence has suggested that K_ATP channels also play roles in Alzheimer's disease (AD), Parkinson's disease (PD), vascular dementia (VD), Huntington's disease (HD) and other neurodegenerative diseases. KCOs and K_ATP channel inhibitors protect neurons from injury by regulating neuronal excitability and neurotransmitter release, inhibiting abnormal protein aggregation and Ca²⁺ overload, reducing reactive oxygen species (ROS) production and microglia activation. However, K_ATP channels have dual effects in some cases. In this review, we focus on the roles of K_ATP channels and their related openers and inhibitors in neurodegenerative diseases. This will enable us to precisely take advantage of the K_ATP channels and provide new ideas for the treatment of neurodegenerative diseases.

Photo-activation of mitochondrial ATP synthesis

ATP production by mitochondria isolated from Saccharomyces cerevisiae cells was accelerated upon both direct and indirect mitochondrial photo-activation (MPA). The extent of direct MPA was dependent on the wavelength of excitation light. Direct MPA was created by light in cytochrome c spectral absorption bands (440, 520 and 550 nm), this light was absorbed producing electronically excited cytochrome c, and the excitation energy of the latter was used in the ATP production chain. The activity of cytochrome c was tested with 600 nm light, where cytochrome c does not absorb, and thus ATP production rate remained the same as in darkness. Note that ATP production rates were significantly larger under light at 550, 520 and 440 nm. Therefore, photo-activation of cytochrome c was the first step of MPA synthesis of ATP. Indirect MPA of ATP production also proceeded via electronically excited cytochrome c, by energy transfer from electronically excited Co/BN film to cytochrome c located in the inner mitochondrial membrane (IMM). Co/BN excitons were generated by photons absorbed by the Co/BN film, which was not in contact with the mitochondrial sample. Next, these excitons propagated along the Co/BN film to the part of the film that was in contact with the mitochondrial sample. There the exciton energy was transferred to cytochrome c located in the IMM, producing electronically excited cytochrome c. Thus, excited cytochrome c was generated in a way different from that of direct MPA. Next, the energy of excited cytochrome c was used in activated ATP synthesis, with virtually the same effect for 519 and 427 nm excitation. Thus, the first step of ATP synthesis in indirect MPA was the exciton energy transfer from Co/BN film to cytochrome c located in the IMM, producing an electronically excited cytochrome c molecule. A phenomenological mechanism of direct and indirect MPA was proposed, and the model parameters were obtained by fitting the model to the experimental data. However, more information is needed before the detailed mechanism of ATP synthesis activation by electronically excited cytochrome c could be understood. The present results support the earlier proposed hypothesis of indirect MPA of ATP production in vertebrate retina in daylight.

ATP Synthase K+- and H+-fluxes Drive ATP Synthesis and Enable Mitochondrial K+-"Uniporter" Function: II. Ion and ATP Synthase Flux Regulation

We demonstrated that ATP synthase serves the functions of a primary mitochondrial K⁺ "uniporter," i.e., the primary way for K⁺ to enter mitochondria. This K⁺ entry is proportional to ATP synthesis, regulating matrix volume and energy supply-vs-demand matching. We show that ATP synthase can be upregulated by endogenous survival-related proteins via IF₁. We identified a conserved BH3-like domain of IF₁ which overlaps its "minimal inhibitory domain" that binds to the β-subunit of F₁. Bcl-xL and Mcl-1 possess a BH3-binding-groove that can engage IF₁ and exert effects, requiring this interaction, comparable to diazoxide to augment ATP synthase's H⁺ and K⁺ flux and ATP synthesis. Bcl-xL and Mcl-1, but not Bcl-2, serve as endogenous regulatory ligands of ATP synthase via interaction with IF₁ at this BH3-like domain, to increase its chemo-mechanical efficiency, enabling its function as the recruitable mitochondrial K_ATP-channel that can limit ischemia-reperfusion injury. Using Bayesian phylogenetic analysis to examine potential bacterial IF₁-progenitors, we found that IF₁ is likely an ancient (∼2 Gya) Bcl-family member that evolved from primordial bacteria resident in eukaryotes, corresponding to their putative emergence as symbiotic mitochondria, and functioning to prevent their parasitic ATP consumption inside the host cell.

Computational Modeling of Mitochondria to Understand the Dynamics of Oxidative Stress

Mitochondria are complex organelles that use catabolic metabolism to produce ATP which is the critical energy source for cell function. Oxidative phosphorylation by the electron transport chain, which receives reducing equivalents (NADH and FADH₂) from the tricarboxylic acid cycle, also produces reactive oxygen species (ROS) as a by-product at complex I and III. ROS play a significant role in health and disease. In order to better understand this process, a computational model of mitochondrial energy metabolism and the production of ROS has been developed. The model demonstrates the process regulating ROS production and removal and how different energy substrates can affect ROS production.

The cardioprotective actions of statins in targeting mitochondrial dysfunction associated with myocardial ischaemia-reperfusion injury

During cardiac reperfusion after myocardial infarction, the heart is subjected to cascading cycles of ischaemia reperfusion injury (IRI). Patients presenting with this injury succumb to myocardial dysfunction resulting in myocardial cell death, which contributes to morbidity and mortality. New targeted therapies are required if the myocardium is to be protected from this injury and improve patient outcomes. Extensive research into the role of mitochondria during ischaemia and reperfusion has unveiled one of the most important sites contributing towards this injury; specifically, the opening of the mitochondrial permeability transition pore. The opening of this pore occurs during reperfusion and results in mitochondria swelling and dysfunction, promoting apoptotic cell death. Activation of mitochondrial ATP-sensitive potassium channels (mitoK_ATP) channels, uncoupling proteins, and inhibition of glycogen synthase kinase-3β (GSK3β) phosphorylation have been identified to delay mitochondrial permeability transition pore opening and reduce reactive oxygen species formation, thereby decreasing infarct size. Statins have recently been identified to provide a direct cardioprotective effect on these specific mitochondrial components, all of which reduce the severity of myocardial IRI, promoting the ability of statins to be a considerate preconditioning agent. This review will outline what has currently been shown in regard to statins cardioprotective effects on mitochondria during myocardial IRI.

Uridine treatment prevents myocardial injury in rat models of acute ischemia and ischemia/reperfusion by activating the mitochondrial ATP-dependent potassium channel

The effect of uridine on the myocardial ischemic and reperfusion injury was investigated. A possible mechanism of its cardioprotective action was established. Two rat models were used: (1) acute myocardial ischemia induced by occlusion of the left coronary artery for 60 min; and (2) myocardial ischemia/reperfusion with 30-min ischemia and 120-min reperfusion. In both models, treatment with uridine (30 mg/kg) prevented a decrease in cell energy supply and in the activity of the antioxidant system, as well as an increase in the level of lipid hydroperoxides and diene conjugates. This led to a reduction of the necrosis zone in the myocardium and disturbances in the heart rhythm. The blocker of the mitochondrial ATP-dependent potassium (mitoKATP) channel 5-hydroxydecanoate limited the positive effects of uridine. The data indicate that the cardioprotective action of uridine may be related to the activation of the mitoKATP channel. Intravenously injected uridine was more rapidly eliminated from the blood in hypoxia than in normoxia, and the level of the mitoKATP channel activator UDP in the myocardium after uridine administration increased. The results suggest that the use of uridine can be a potentially effective approach to the management of cardiovascular diseases.

Effects of Aging on Cardiac Oxidative Stress and Transcriptional Changes in Pathways of Reactive Oxygen Species Generation and Clearance

Background Age-related heart diseases are significant contributors to increased morbidity and mortality. Emerging evidence indicates that mitochondria within cardiomyocytes contribute to age-related increased reactive oxygen species (ROS) generation that plays an essential role in aging-associated cardiac diseases. Methods and Results The present study investigated differences between ROS production in cardiomyocytes isolated from adult (6 months) and aged (24 months) Fischer 344 rats, and in cardiac tissue of adult (18-65 years) and elderly (>65 years) patients with preserved cardiac function. Superoxide dismutase inhibitable ferricytochrome c reduction assay (1.32±0.63 versus 0.76±0.31 nMol/mg per minute; P=0.001) superoxide and H2O2 production, measured as dichlorofluorescein diacetate fluorescence (1646±428 versus 699±329, P=0.04), were significantly higher in the aged versus adult cardiomyocytes. Similarity in age-related alteration between rats and humans was identified in mitochondrial-electron transport chain-complex-I-associated increased oxidative-stress by MitoSOX fluorescence (53.66±18.58 versus 22.81±12.60; P=0.03) and in 4-HNE adduct levels (187.54±54.8 versus 47.83±16.7 ng/mg protein, P=0.0063), indicative of increased peroxidation in the elderly. These differences correlated with changes in functional enrichment of genes regulating ROS homeostasis pathways in aged human and rat hearts. Functional merged collective network and pathway enrichment analysis revealed common genes prioritized in human and rat aging-associated networks that underlay enriched functional terms of mitochondrial complex I and common pathways in the aging human and rat heart. Conclusions Aging sensitizes mitochondrial and extramitochondrial mechanisms of ROS buildup within the heart. Network analysis of the transcriptome highlights the critical elements involved with aging-related ROS homeostasis pathways common in rat and human hearts as targets.

Routes for Potassium Ions across Mitochondrial Membranes: A Biophysical Point of View with Special Focus on the ATP-Sensitive K+ Channel

Potassium ions can cross both the outer and inner mitochondrial membranes by means of multiple routes. A few potassium-permeable ion channels exist in the outer membrane, while in the inner membrane, a multitude of different potassium-selective and potassium-permeable channels mediate K+ uptake into energized mitochondria. In contrast, potassium is exported from the matrix thanks to an H+/K+ exchanger whose molecular identity is still debated. Among the K+ channels of the inner mitochondrial membrane, the most widely studied is the ATP-dependent potassium channel, whose pharmacological activation protects cells against ischemic damage and neuronal injury. In this review, we briefly summarize and compare the different hypotheses regarding the molecular identity of this patho-physiologically relevant channel, taking into account the electrophysiological characteristics of the proposed components. In addition, we discuss the characteristics of the other channels sharing localization to both the plasma membrane and mitochondria.

Multidimensional Regulation of Cardiac Mitochondrial Potassium Channels

Mitochondria play a fundamental role in the energetics of cardiac cells. Moreover, mitochondria are involved in cardiac ischemia/reperfusion injury by opening the mitochondrial permeability transition pore which is the major cause of cell death. The preservation of mitochondrial function is an essential component of the cardioprotective mechanism. The involvement of mitochondrial K+ transport in this complex phenomenon seems to be well established. Several mitochondrial K+ channels in the inner mitochondrial membrane, such as ATP-sensitive, voltage-regulated, calcium-activated and Na+-activated channels, have been discovered. This obliges us to ask the following question: why is the simple potassium ion influx process carried out by several different mitochondrial potassium channels? In this review, we summarize the current knowledge of both the properties of mitochondrial potassium channels in cardiac mitochondria and the current understanding of their multidimensional functional role. We also critically summarize the pharmacological modulation of these proteins within the context of cardiac ischemia/reperfusion injury and cardioprotection.

Effects of anticancer drugs on the cardiac mitochondrial toxicity and their underlying mechanisms for novel cardiac protective strategies

Mitochondria are organelles that play a pivotal role in the production of energy in cells, and vital to the maintenance of cellular homeostasis due to the regulation of many biochemical processes. The heart contains a lot of mitochondria because those muscles require a lot of energy to keep supplying blood through the circulatory system, implying that the energy generated from mitochondria is highly dependent. Thus, cardiomyocytes are sensitive to mitochondrial dysfunction and are likely to be targeted by mitochondrial toxic drugs. It has been reported that some anticancer drugs caused unwanted toxicity to mitochondria. Mitochondrial dysfunction is related to aging and the onset of many diseases, such as obesity, diabetes, cancer, cardiovascular and neurodegenerative diseases. Mitochondrial toxic mechanisms can be mainly explained concerning reactive oxygen species (ROS)/redox status, calcium homeostasis, and endoplasmic reticulum stress (ER) stress signaling. The toxic mechanisms of many anticancer drugs have been revealed, but more studying and understanding of the mechanisms of drug-induced mitochondrial toxicity is required to develop mitochondrial toxicity screening system as well as novel cardioprotective strategies for the prevention of cardiac disorders of drugs. This review focuses on the cardiac mitochondrial toxicity of commonly used anticancer drugs, i.e., doxorubicin, mitoxantrone, cisplatin, arsenic trioxide, and cyclophosphamide, and their possible chemopreventive agents that can prevent or alleviate cardiac mitochondrial toxicity.

Potential Effects of Poloxamer 188 on Rat Isolated Brain Mitochondria after Oxidative Stress In Vivo and In Vitro

Outcome after cerebral ischemia is often dismal. Reperfusion adds significantly to the ischemic injury itself. Therefore, new strategies targeting ischemia/reperfusion (I/R) injury are critically needed. Poloxamer (P)188, an amphiphilic triblock copolymer, is a highly promising pharmacological therapeutic as its capability to insert into injured cell membranes has been reported to protect against I/R injury in various models. Although mitochondrial function particularly profits from P188 treatment after I/R, it remains unclear if this beneficial effect occurs directly or indirectly. Here, rat isolated brain mitochondria underwent oxidative stress in vivo by asphyxial cardiac arrest or in vitro by the addition of hydrogen peroxide (H₂O₂) after isolation. Mitochondrial function was assessed by adenosine triphosphate synthesis, oxygen consumption, and calcium retention capacity. Both asphyxia and H₂O₂ exposure significantly impaired mitochondrial function. P188 did not preserve mitochondrial function after either injury mechanism. Further research is indicated.

Hydrogen sulfide induces Ca2+ release from the endoplasmic reticulum and suppresses ATP-induced Ca2+ signaling in rat spinal cord astrocytes

Hydrogen sulfide (H2S) has a variety of physiological functions. H2S reportedly increases intracellular Ca2+ concentration ([Ca2+]i) in astrocytes. However, the precise mechanism and functional role of this increase are not known. Here, we examined the effects of H2S on [Ca2+]i in astrocytes from the rat spinal cord and whether H2S affects ATP-induced Ca2+ signaling, which is known to be involved in synaptic function. Na2S (150 μM), an H2S donor, produced a nontoxic increase in [Ca2+]i. The [Ca2+]i increase by Na2S was inhibited by Ca2+ depletion in the endoplasmic reticulum (ER) but not by removal of extracellular Ca2+, indicating that H2S releases Ca2+ from the ER. On the other hand, Na2S inhibited ATP-induced [Ca2+]i increase when Na2S clearly increased [Ca2+]i in the astrocytes, which was not suppressed by a reducing agent. In addition, Na2S had no effect on intracellular cyclic AMP (cAMP) level. These results indicate that oxidative post-translational modification of proteins and cAMP are not involved in the inhibitory effect of H2S on ATP-induced Ca2+ signaling. We conclude that H2S indirectly inhibits ATP-induced Ca2+ signaling by decreasing Ca2+ content in the ER in astrocytes. In this way, H2S may influence intercellular communication between astrocytes and neurons, thereby contributing to neuronal signaling in the nervous system.

The role of labile Zn2+ and Zn2+-transporters in the pathophysiology of mitochondria dysfunction in cardiomyocytes

An important energy supplier of cardiomyocytes is mitochondria, similar to other mammalian cells. Studies have demonstrated that any defect in the normal processes controlled by mitochondria can lead to abnormal ROS production, thereby high oxidative stress as well as lack of ATP. Taken into consideration, the relationship between mitochondrial dysfunction and overproduction of ROS as well as the relation between increased ROS and high-level release of intracellular labile Zn²⁺, those bring into consideration the importance of the events related with those stimuli in cardiomyocytes responsible from cellular Zn²⁺-homeostasis and responsible Zn²⁺-transporters associated with the Zn²⁺-homeostasis and Zn²⁺-signaling. Zn²⁺-signaling, controlled by cellular Zn²⁺-homeostatic mechanisms, is regulated with intracellular labile Zn²⁺ levels, which are controlled, especially, with the two Zn²⁺-transporter families; ZIPs and ZnTs. Our experimental studies in mammalian cardiomyocytes and human heart tissue showed that Zn²⁺-transporters localizes to mitochondria besides sarco(endo)plasmic reticulum and Golgi under physiological condition. The protein levels as well as functions of those transporters can re-distribute under pathological conditions, therefore, they can interplay among organelles in cardiomyocytes to adjust a proper intracellular labile Zn²⁺ level. In the present review, we aimed to summarize the already known Zn²⁺-transporters localize to mitochondria and function to stabilize not only the cellular Zn²⁺ level but also cellular oxidative stress status. In conclusion, one can propose that a detailed understanding of cellular Zn²⁺-homeostasis and Zn²⁺-signaling through mitochondria may emphasize the importance of new mitochondria-targeting agents for prevention and/or therapy of cardiovascular dysfunction in humans.

Mitochondrial KATP channels contribute to the protective effects of hydrogen sulfide against impairment of central chemoreception of rat offspring exposed to maternal cigarette smoke

We previously reported that maternal cigarette smoke (CS) exposure resulted in impairment of central chemoreception and induced mitochondrial dysfunction in offspring parafacial respiratory group (pFRG), the kernel for mammalian central chemoreception. We also found that hydrogen sulfide (H₂S) could attenuate maternal CS exposure-induced impairment of central chemoreception in the rat offspring in vivo. Mitochondrial ATP sensitive potassium (mitoK_ATP) channel has been reported to play a significant role in mitochondrial functions and protect against apoptosis in neurons. Thus, we hypothesize here that mitoK_ATP channel plays a role in the protective effects of H₂S on neonatal central chemoreception in maternal CS-exposed rats. Our findings revealed that pretreatment with NaHS (donor of H₂S, 22.4mM) reversed the central chemosensitivity decreased by maternal CS exposure, and also inhibited cell apoptosis in offspring pFRG, however, 5-HD (blocker of mitoK_ATP channels, 19mM) attenuated the protective effects of NaHS. In addition, NaHS declined pro-apoptotic proteins related to mitochondrial pathway apoptosis in CS rat offspring pFRG, such as Bax, Cytochrome C, caspase9 and caspase3. NaHS or 5-HD alone had no significant effect on above indexes. These results suggest that mitoK_ATP channels play an important role in the protective effect of H₂S against impairment of central chemoreception via anti-apoptosis in pFRG of rat offspring exposed to maternal CS.

Myocardial protection in cardiac surgery: how limited are the options? A comprehensive literature review

For patients undergoing cardiopulmonary bypass, myocardial protection is a key for successful recovery and improved outcomes following cardiac surgery that requires cardiac arrest. Different solutions, components and modes of delivery have evolved over the last few decades to optimise myocardial protection. These include cold and warm and blood and crystalloid solution through antegrade, retrograde or combined cardioplegia delivery approach. However, each method has its own advantages and disadvantages, posing a challenge to establish a gold-standard cardioplegic solution with an optimised mode of delivery for enhanced myocardial protection during cardiac surgery. The aim of this review is to provide a brief history of the development of cardioplegia, explain the electrophysiological concepts behind myocardial protection in cardioplegia, analyse the current literature and summarise existing evidence that warrants the use of varying cardioplegic techniques. We provide a comprehensive and comparative overview of the effectiveness of each technique in achieving optimal cardioprotection and propose novel techniques for optimising myocardial protection in the future.

Diazoxide Preconditioning of Nonhuman Primate Pancreas Improves Islet Isolation Outcomes by Mitochondrial Protection

OBJECTIVES

Previously, we showed that diazoxide (DZ), an effective ischemic preconditioning agent, protected rodent pancreas against ischemia-reperfusion injury. Here, we further investigate whether DZ supplementation to University of Wisconsin (UW) solution during pancreas procurement and islet isolation has similar cytoprotection in a preclinical nonhuman primate model.

METHODS

Cynomolgus monkey pancreata were flushed with UW or UW + 150 μM DZ during procurement and preserved for 8 hours before islet isolation.

RESULTS

First, a significantly higher islet yield was observed in UW + DZ than in UW (57,887 vs 23,574 IEq/pancreas and 5396 vs 1646 IEq/g). Second, the DZ treated islets had significantly lower apoptotic cells per islet (1.64% vs 9.85%). Third, DZ significantly inhibited ROS surge during reperfusion with a dose-response manner. Fourth, DZ improved in vitro function of isolated islets determined by mitochondrial potentials and calcium influx in responses to glucose and KCI. Fifth, the DZ treated islets had much higher cure rate and better glycemia control in diabetic mice transplant model.

CONCLUSIONS

This study showed a strong mitochondrial protection of DZ on nonhuman primate islets against ischemia-reperfusion injury that provides strong evidence for its clinical application in islet and pancreas transplantation.

Global knockout of ROMK potassium channel worsens cardiac ischemia-reperfusion injury but cardiomyocyte-specific knockout does not: Implications for the identity of mitoKATP

The renal-outer-medullary‑potassium (ROMK) channel, mutated in Bartter's syndrome, regulates ion exchange in kidney, but its extra-renal functions remain unknown. Additionally, ROMK was postulated to be the pore-forming subunit of the mitochondrial ATP-sensitive K+ channel (mitoKATP), a mediator of cardioprotection. Using global and cardiomyocyte-specific knockout mice (ROMK-GKO and ROMK-CKO respectively), we characterize the effects of ROMK knockout on mitochondrial ion handling, the response to pharmacological KATP channel modulators, and ischemia/reperfusion (I/R) injury. Mitochondria from ROMK-GKO hearts exhibited a lower threshold for Ca2+-triggered permeability transition pore (mPTP) opening but normal matrix volume changes during oxidative phosphorylation. Isolated perfused ROMK-GKO hearts exhibited impaired functional recovery and increased infarct size when I/R was preceded by an ischemic preconditioning (IPC) protocol. Because ROMK-GKO mice exhibited severe renal defects and cardiac remodeling, we further characterized ROMK-CKO hearts to avoid confounding systemic effects. Mitochondria from ROMK-CKO hearts had unchanged matrix volume responses during oxidative phosphorylation and still swelled upon addition of a mitoKATP opener, but exhibited a lower threshold for mPTP opening, similar to GKO mitochondria. Nevertheless, I/R induced damage was not exacerbated in ROMK-CKO hearts, either ex vivo or in vivo. Lastly, we examined the response of ROMK-CKO hearts to ex vivo I/R injury with or without IPC and found that IPC still protected these hearts, suggesting that cardiomyocyte ROMK does not participate significantly in the cardioprotective pathway elicited by IPC. Collectively, our findings from these novel strains of mice suggest that cardiomyocyte ROMK is not a central mediator of mitoKATP function, although it can affect mPTP activation threshold.

Pharmacological Preconditioning Using Diazoxide Regulates Store-Operated Ca2 + Channels in Adult Rat Cardiomyocytes

Voltage-dependent Ca²⁺ channels and store-operated Ca²⁺ channels (SOCs) are the major routes of Ca²⁺ entry into mammalian cells. Previously, we reported that pharmacological preconditioning (PPC) leads to a decrease in the amplitude of L-type calcium channel current in the heart. In this study, we examined PPC-associated changes in SOC function. We measured adult cardiomyocyte membrane currents using the whole-cell patch-clamp technique, and we evaluated reactive oxygen species (ROS) production and intracellular Ca²⁺ levels in cardiomyocytes using fluorescent probes. Diazoxide (Dzx) and thapsigargin (Tg) were used to induce PPC and to deplete internal stores of Ca²⁺, respectively. Ca²⁺ store depletion generated inward currents with strong rectification, which were suppressed by the SOC blocker GSK-7975-A. These currents were completely abolished by PPC, an effect that could be countered with 5-hydroxydecanoate (5-HD; a selective mitochondrial ATP-sensitive K⁺ channel blocker), an intracellular mitochondrial energizing solution, or Ni²⁺ [a blocker of sodium-calcium exchanger (NCX)]. Buffering of ROS and intracellular Ca²⁺ also prevented PPC effects on SOC currents. Refilling of intracellular stores was largely suppressed by PPC, as determined by measuring intracellular Ca²⁺ with a fluorescent Ca²⁺ indicator. These results indicate that influx of Ca²⁺ through SOCs is inhibited by their ROS and Ca²⁺-dependent inactivation during PPC and that NCX is a likely source of PPC-inactivating Ca²⁺. We further showed that NCX associates with Orai1. Down-regulation of SOCs by PPC may play a role in cardioprotection following ischemia-reperfusion.

Nicorandil: A drug with ongoing benefits and different mechanisms in various diseased conditions

Nicorandil is a well-known antianginal agent, which has been recommended as one of the second-line treatments for chronic stable angina as justified by the European guidelines. It shows an efficacy equivalent to that of classic antianginal agents. Nicorandil has also been applied clinically in various cardiovascular diseases such as variant or unstable angina and reperfusion-induced damage following coronary angioplasty or thrombolysis. Different mechanisms have been involved in the protective effects of nicorandil in various diseases through either opening of adenosine triphosphate-sensitive potassium (KATP) channel or donation of nitric oxide (NO). The predominance or participation of any of these proposed mechanisms depends on the dose of nicorandil used, the location of diseased conditions, and if this mechanism is still functioning or not. The protection afforded by nicorandil has been shown to be mainly attributed to KATP channel opening in experimental models of myocardial and pulmonary fibrosis as well as renal injury or glomerulonephritis, whereas NO donation predominates as a mechanism of protection in hepatic fibrosis and inflammatory bowel diseases. Therefore, in different diseased conditions, it is important to know which mechanism plays the major role in nicorandil-induced curative or protective effects. This can bring new insights into the proper use of selected medication and its recommended dose for targeting certain disease.

In silico simulation of reversible and irreversible swelling of mitochondria: The role of membrane rigidity

Mitochondria have been widely accepted as the main source of ATP in the cell. The inner mitochondrial membrane (IMM) is important for the maintenance of ATP production and other functions of mitochondria. The electron transport chain (ETC) generates an electrochemical gradient of protons known as the proton-motive force across the IMM and thus produces the mitochondrial membrane potential that is critical to ATP synthesis. One of the main factors regulating the structural and functional integrity of the IMM is the changes in the matrix volume. Mild (reversible) swelling regulates mitochondrial metabolism and function; however, excessive (irreversible) swelling causes mitochondrial dysfunction and cell death. The central mechanism of mitochondrial swelling includes the opening of non-selective channels known as permeability transition pores (PTPs) in the IMM by high mitochondrial Ca²⁺ and reactive oxygen species (ROS). The mechanisms of reversible and irreversible mitochondrial swelling and transition between these two states are still unknown. The present study elucidates an upgraded biophysical model of reversible and irreversible mitochondrial swelling dynamics. The model provides a description of the PTP regulation dynamics using an additional differential equation. The rigidity tensor was used in numerical simulations of the mitochondrial parameter dynamics with different initial conditions defined by Ca²⁺ concentration in the sarco/endoplasmic reticulum. We were able to estimate the values of the IMM rigidity tensor components by fitting the model to the previously reported experimental data. Overall, the model provides a better description of the reversible and irreversible mitochondrial swelling dynamics.

Ischemia Reperfusion Injury Produces, and Ischemic Preconditioning Prevents, Rat Cardiac Fibroblast Differentiation: Role of KATP Channels

Ischemic preconditioning (IPC) and activation of ATP-sensitive potassium channels (K_ATP) protect cardiac myocytes from ischemia reperfusion (IR) injury. We investigated the influence of IR injury, IPC and K_ATP in isolated rat cardiac fibroblasts. Hearts were removed under isoflurane anesthesia. IR was simulated in vitro by application and removal of paraffin oil over pelleted cells. Ischemia (30, 60 and 120 min) followed by 60 min reperfusion resulted in significant differentiation of fibroblasts into myofibroblasts in culture (mean % fibroblasts ± SEM in IR vs. time control: 12 ± 1% vs. 63 ± 2%, 30 min ischemia; 15 ± 3% vs. 71 ± 4%, 60 min ischemia; 8 ± 1% vs. 55 ± 2%, 120 min ischemia). IPC (15 min ischemia, 30 min reperfusion) significantly attenuated IR-induced fibroblast differentiation (52 ± 3%) compared to 60 min IR. IPC was mimicked by opening K_ATP with pinacidil (50 μM; 43 ± 6%) and by selectively opening mitochondrial K_ATP (mK_ATP) with diazoxide (100 μM; 53 ± 3%). Furthermore, IPC was attenuated by inhibiting K_ATP with glibenclamide (10 μM; 23 ± 5%) and by selectively blocking mK_ATP with 5-hydroxydecanoate (100 μM; 22 ± 9%). These results suggest that (a) IR injury evoked cardiac fibroblast to myofibroblast differentiation, (b) IPC attenuated IR-induced fibroblast differentiation, (c) K_ATP were involved in IPC and (d) this protection involved selective activation of mK_ATP.

Preprodynorphin gene mutation causes progressive cardiac conduction disease: A whole-exome analysis of a pedigree

AIMS

Progressive cardiac conduction disease (PCCD) is a rare heart disease that usually shows familial inheritance. Potential genetic risk factors for PCCD have been mostly limited to genes that encode ion channels, cardiac transcription factors, T-box transcription factors, gap junction proteins, energy metabolism regulators and structural proteins.

MAIN METHODS

Subjects in the present study came from a family who exhibited the autosomal dominant inheritance of PCCD. The primary proband had syncope and an electrocardiogram typical for PCCD, which started in the left bundle branch block, and passed to the atrioventricular block. The patient received a permanent pacemaker in 2013. Pathogenic mutations in the proband's family were identified using whole-exome sequencing and Sanger sequencing.

KEY FINDINGS

The results for the family members were verified using Sanger sequencing, while the results for healthy unrelated individuals were verified using SNaPShot. All patients in the family shared two adjacent missense mutations in the preprodynorphin (PDYN) gene (c.581A > T, c.580G > C; p.D194L).

SIGNIFICANCE

The PDYN double mutation c.581A > T and c.580G > C (p.D194L) may be linked to the onset of familial PCCD. The effects of these mutations on electrophysiology require further investigation.

Burden of arrhythmia in hospitalizations with opioid overdose

BACKGROUND

Opioid overdose-related hospitalizations continue to rise in the United States. These hospitalizations are frequently associated with arrhythmia which can increase in-hospital mortality and resource utilization. We describe temporal trends in the hospitalizations for opioid overdose, associated arrhythmias, and their impact on in-hospital mortality, length of stay and cost of hospitalizations. The purpose of this study was to identify incidence of arrhythmia and their impact on in-hospital outcomes with opioid overdose hospitalizations.

METHODS

The study utilized data from the National Inpatient Sample from January 2005 to September 2015. Previously employed International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes were utilized to identify opioid overdose and associated arrhythmias. The analysis was performed using SAS (SAS Institute Inc., Cary, NC). Temporal trends were measured using Jonckheere-Terpstra Trend test.

RESULTS

A total of 430,460 adult hospitalizations with opioid overdose were included in this study. Atrial fibrillation (N = 17,695, 4.1%) was the most frequent arrhythmia associated with opioid overdose, the trend of which increased significantly during the study period. All-cause in-hospital mortality increased substantially with arrhythmias, highest with ventricular fibrillation and ventricular tachycardia. The incidence of arrhythmias was associated with longer length of stay and higher cost of hospitalizations as well.

CONCLUSIONS

Incidence of new-onset arrhythmia with opioid overdose lead to higher in-hospital mortality which can further increase the length of hospitalization and cost of care.

Mitochondrial depolarization stimulates vascular repair-relevant functions of CD34+ cells via reactive oxygen species-induced nitric oxide generation

BACKGROUND AND PURPOSE

CD34⁺ haematopoietic stem/progenitor cells have revascularization potential and are now being tested for the treatment of ischaemic vascular diseases in clinical trials. We tested the hypothesis that mitochondrial depolarization stimulates the reparative functions of CD34⁺ cells.

EXPERIMENTAL APPROACH

Peripheral blood was obtained from healthy individuals (n = 63), and mononuclear cells (MNCs) were separated. MNCs were enriched for lineage negative cells, followed by isolation of CD34⁺ cells. Vascular repair-relevant functions of CD34⁺ cells, proliferation and migration, were evaluated in the presence and absence of diazoxide. Mitochondrial membrane potential, ROS and NO levels were evaluated by flow cytometry by using JC-1, mitoSOX and DAF-FM respectively.

KEY RESULTS

Diazoxide stimulated the proliferation and migration of CD34⁺ cells that were comparable to the responses induced by stromal-derived factor-1α (SDF) or VEGF. Effects of diazoxide were blocked by either 5-hydroxydecanoate (5HD), a selective mitochondrial ATP-sensitive potassium channel (mitoK_ATP ) inhibitor, or by L-NAME. Diazoxide induced mitochondrial depolarization, and NO and cGMP generation that were 5HD-sensitive. The generation of NO and cGMP by diazoxide was blocked by an endothelial NOS (eNOS)-selective inhibitor, NIO, but not by a neuronal (n)NOS-selective inhibitor, N^ω -propyl-L-arginine (NPA). A Ca²⁺ chelator, BAPTA, Akt inhibitor, triciribine, or PI3K inhibitor, LY294002, inhibited the NO release induced by diazoxide. Phosphorylation of eNOS at Ser¹¹⁷⁷ and dephosphorylation at Thr⁴⁹⁵ were increased. Diazoxide-induced ROS generation and phosphorylation of eNOS at Ser¹¹⁷⁷ were reduced by NPA.

CONCLUSION AND IMPLICATIONS

Diazoxide stimulates vascular repair-relevant functions of CD34⁺ cells via the mitoK_ATP -dependent release of NO and ROS.

LINKED ARTICLES

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Gas Signaling Molecules and Mitochondrial Potassium Channels

Recently, gaseous signaling molecules, such as carbon monoxide (CO), nitric oxide (NO), and hydrogen sulfide (H₂S), which were previously considered to be highly toxic, have been of increasing interest due to their beneficial effects at low concentrations. These so-called gasotransmitters affect many cellular processes, such as apoptosis, proliferation, cytoprotection, oxygen sensing, ATP synthesis, and cellular respiration. It is thought that mitochondria, specifically their respiratory complexes, constitute an important target for these gases. On the other hand, increasing evidence of a cytoprotective role for mitochondrial potassium channels provides motivation for the analysis of the role of gasotransmitters in the regulation of channel function. A number of potassium channels have been shown to exhibit activity within the inner mitochondrial membrane, including ATP-sensitive potassium channels, Ca²⁺-activated potassium channels, voltage-gated Kv potassium channels, and TWIK-related acid-sensitive K⁺ channel 3 (TASK-3). The effects of these channels include the regulation of mitochondrial respiration and membrane potential. Additionally, they may modulate the synthesis of reactive oxygen species within mitochondria. The opening of mitochondrial potassium channels is believed to induce cytoprotection, while channel inhibition may facilitate cell death. The molecular mechanisms underlying the action of gasotransmitters are complex. In this review, we focus on the molecular mechanisms underlying the action of H₂S, NO, and CO on potassium channels present within mitochondria.

Myocardial ischaemia reperfusion injury: the challenge of translating ischaemic and anaesthetic protection from animal models to humans

Myocardial ischaemia reperfusion injury is the leading cause of death in patients with cardiovascular disease. Interventions such as ischaemic pre and postconditioning protect against myocardial ischaemia reperfusion injury. Certain anaesthesia drugs and opioids can produce the same effects, which led to an initial flurry of excitement given the extensive use of these drugs in surgery. The underlying mechanisms have since been extensively studied in experimental animal models but attempts to translate these findings to clinical settings have resulted in contradictory results. There are a number of reasons for this such as dose response, the intensity of the ischaemic stimulus applied, the duration of ischaemia and lost or diminished cardioprotection in common co-morbidities such as diabetes and senescence. This review focuses on current knowledge regarding myocardial ischaemia reperfusion injury and cardioprotective interventions both in experimental animal studies and in clinical trials.

Use the Protonmotive Force: Mitochondrial Uncoupling and Reactive Oxygen Species

Mitochondrial respiration results in an electrochemical proton gradient, or protonmotive force (pmf), across the mitochondrial inner membrane. The pmf is a form of potential energy consisting of charge (∆ψ_m) and chemical (∆pH) components, that together drive ATP production. In a process called uncoupling, proton leak into the mitochondrial matrix independent of ATP production dissipates the pmf and energy is lost as heat. Other events can directly dissipate the pmf independent of ATP production as well, such as chemical exposure or mechanisms involving regulated mitochondrial membrane electrolyte transport. Uncoupling has defined roles in metabolic plasticity and can be linked through signal transduction to physiologic events. In the latter case, the pmf impacts mitochondrial reactive oxygen species (ROS) production. Although capable of molecular damage, ROS also have signaling properties that depend on the timing, location, and quantity of their production. In this review, we provide a general overview of mitochondrial ROS production, mechanisms of uncoupling, and how these work in tandem to affect physiology and pathologies, including obesity, cardiovascular disease, and immunity. Overall, we highlight that isolated bioenergetic models-mitochondria and cells-only partially recapitulate the complex link between the pmf and ROS signaling that occurs in vivo.

Mitochondria from rat uterine smooth muscle possess ATP-sensitive potassium channel

The objective of this study was to detect ATP-sensitive K⁺ uptake in rat uterine smooth muscle mitochondria and to determine possible effects of its activation on mitochondrial physiology. By means of fluorescent technique with usage of K⁺-sensitive fluorescent probe PBFI (potassium-binding benzofuran isophthalate) we showed that accumulation of K ions in isolated mitochondria from rat myometrium is sensitive to effectors of K_ATP-channel (ATP-sensitive K⁺-channel) – ATP, diazoxide, glibenclamide and 5HD (5-hydroxydecanoate). Our data demonstrates that K⁺ uptake in isolated myometrium mitochondria results in a slight decrease in membrane potential, enhancement of generation of ROS (reactive oxygen species) and mitochondrial swelling. Particularly, the addition of ATP into incubation medium led to a decrease in mitochondrial swelling and ROS production, and an increase in membrane potential. These effects were eliminated by diazoxide. If blockers of K_ATP-channel were added along with diazoxide, the effects of diazoxide were removed. So, we postulate the existence of K_ATP-channels in rat uterus mitochondria and assume that their functioning may regulate physiological conditions of mitochondria, such as matrix volume, ROS generation and polarization of mitochondrial membrane.

Prevention of contrast-induced nephropathy by limb ischemic preconditioning: underlying mechanisms and clinical effects

Contrast-induced nephropathy (CIN) is an important complication following diagnostic radiographic imaging and interventional therapy. It results from administration of intravascular iodinated contrast media (CM) and is currently the third most common cause of hospital-acquired acute kidney injury. CIN is associated with increased morbidity, prolonged hospitalization, and higher mortality. Although the importance of CIN is widely appreciated, and its occurrence can be mitigated by the use of pre- and posthydration protocols and low osmolar instead of high osmolar iodine-containing CM, specific prophylactic therapy is lacking. Remote ischemic preconditioning (RIPC), induced through short cycles of ischemia-reperfusion applied to the limb, is an intriguing new strategy that has been shown to reduce myocardial infarction size in patients undergoing emergency percutaneous coronary intervention. Furthermore, multiple proof-of-principle clinical studies have suggested benefit in several other ischemia-reperfusion syndromes, including stroke. Perhaps somewhat surprisingly, RIPC also is emerging as a promising strategy for CIN prevention. In this review, we discuss current clinical and experimental developments regarding the biology of CIN, concentrating on the pathophysiology of CIN, and cellular and molecular mechanisms by which limb ischemic preconditioning may confer renal protection in clinical and experimental models of CIN.

Inotropic Effects of Nicorandil on Cardiac Contractility Assessed by Left Ventricular Pressure-Volume Relationship Analyses in Anesthetized Monkeys

Nicorandil is a representative antianginal drug that has dual properties of a nitrate and adenosine triphosphate-sensitive potassium (KATP) channel agonist; however, its effects on integrated cardiac function have not been fully understood. This study was conducted to clarify the functional, hemodynamic, and electrophysiological effects of nicorandil using ventricular pressure-volume loop analysis in isoflurane-anesthetized monkeys. Nicorandil was given intravenously at therapeutic doses of 0.2 and 2 mg/kg over 10 minutes to cynomolgus monkeys (n = 5) with a pause of 10 minutes between the 2 doses. Nicorandil at 0.2 mg/kg caused decreases in systemic blood pressure and left ventricular end-diastolic pressure by its vasodilating action. Nicorandil at 2 mg/kg also exhibited positive inotropic action demonstrated by increased slopes of preload recruitable stroke work relationship, which is a load-independent inotropic parameter. In load-dependent inotropic parameters, positive inotropy of nicorandil was also indicated by the shortened QA interval and increased contractility index; however, significant changes were not observed in the maximal upstroke velocity of left ventricular pressure. Moreover, reflex tachycardia accompanied by shortening of QT/QTc intervals was observed. Overall, the isoflurane-anesthetized monkey model with pressure-volume loop analysis revealed cardiac variables of nicorandil, including a positive inotropy contributable to cardiac performance in addition to its vasodilatory effect. These findings provide useful information when considering the prescription of nicorandil in patients.

Proenkephalin in Heart Failure

The opioid system is activated in heart failure, which may be cardioprotective but may also be counter-regulatory. Recently, systemic proenkephalin activation has been investigated in various conditions predicting mortality and kidney injury. In acute heart failure, proenkephalin independently predicts mortality and heart failure rehospitalization in addition to traditional risk markers. It also predicts worsening renal function, increasingly recognized as an important risk predictor for poor outcome in heart failure. This article explores the role of enkephalins and delta-opioid receptors in the heart, then reviews studies measuring proenkephalin levels in the circulation and their associations with prognosis.

Mitochondrial Transplantation in Myocardial Ischemia and Reperfusion Injury

Ischemic heart disease remains the leading cause of death worldwide. Mitochondria are the power plant of the cardiomyocyte, generating more than 95% of the cardiac ATP. Complex cellular responses to myocardial ischemia converge on mitochondrial malfunction which persists and increases after reperfusion, determining the extent of cellular viability and post-ischemic functional recovery. In a quest to ameliorate various points in pathways from mitochondrial damage to myocardial necrosis, exhaustive pharmacologic and genetic tools have targeted various mediators of ischemia and reperfusion injury and procedural techniques without applicable success. The new concept of replacing damaged mitochondria with healthy mitochondria at the onset of reperfusion by auto-transplantation is emerging not only as potential therapy of myocardial rescue, but as gateway to a deeper understanding of mitochondrial metabolism and function. In this chapter, we explore the mechanisms of mitochondrial dysfunction during ischemia and reperfusion, current developments in the methodology of mitochondrial transplantation, mechanisms of cardioprotection and their clinical implications.

Bioenergetic and volume regulatory effects of mitoKATP channel modulators protect against hypoxia-reoxygenation-induced mitochondrial dysfunction

The mitochondrial ATP-sensitive K(+) (mitoKATP) channel plays a significant role in mitochondrial physiology and protects against ischemic reperfusion injury in mammals. Although fish frequently face oxygen fluctuations in their environment, the role of the mitoKATP channel in regulating the responses to oxygen stress is rarely investigated in this class of animals. To elucidate whether and how the mitoKATP channel protects against hypoxia-reoxygenation (H-R)-induced mitochondrial dysfunction in fish, we first determined the mitochondrial bioenergetic effects of two key modulators of the channel, diazoxide and 5-hydroxydecanoate (5-HD), using a wide range of doses. Subsequently, the effects of low and high doses of the modulators on mitochondrial bioenergetics and volume under normoxia and after H-R using buffers with and without magnesium and ATP (Mg-ATP) were tested. In the absence of Mg-ATP (mitoKATP channel open), both low and high doses of diazoxide improved mitochondrial coupling, but only the high dose of 5-HD reversed the post-H-R coupling-enhancing effect of diazoxide. In the presence of Mg-ATP (mitoKATP channel closed), diazoxide at the low dose improved coupling post-H-R, and this effect was abolished by 5-HD at the low dose. Interestingly, both low and high doses of diazoxide reversed H-R-induced swelling under mitoKATP channel open conditions, but this effect was not sensitive to 5-HD. Under mitoKATP channel closed conditions, diazoxide at the low dose protected the mitochondria from H-R-induced swelling and 5-HD at the low dose reversed this effect. In contrast, diazoxide at the high dose failed to reduce the swelling caused by H-R, and the addition of the high dose of 5-HD enhanced mitochondrial swelling. Overall, our study showed that in the presence of Mg-ATP, both opening of mitoKATP channels and bioenergetic effects of diazoxide were protective against H-R in fish mitochondria, while in the absence of Mg-ATP only the bioenergetic effect of diazoxide was protective.

Effect of Potassium-Channel Opener Therapy on Reperfused Infarction in Hypertrophied Hearts: Demonstration of Preconditioning by Using Functional and Contrast-Enhanced Magnetic Resonance Imaging

Effects of therapy with the potassium-channel opener and vasodilator nicorandil were studied in reperfused infarction of hypertrophied hearts by using magnetic resonance imaging (MRI), hemodynamic measurements, and histochemical staining. Aortic banding was performed on 22 Sprague-Dawley rats to induce left ventricular (LV) hypertrophy; 11 were the controls. Eight weeks later, the left coronary artery was occluded for 25 minutes in all 33 animals, followed by 3 hours of reperfusion. During occlusion, 11 rats with LV hypertrophy received nicorandil (0.1 mg/kg bolus and 1.5 mg/kg/h for 3 hours). The new necrosis-specific contrast agent Gadophrin-3 was administered to all animals to delineate infarction on multislice T1-weighted spin-echo MRI. Nicorandil increased ischemic tolerance of LV hypertrophy as shown by the reduction of infarction size from 19.3% ± 1.3% to 10.0% ± 2.5% LV ( P= .005). Infarction size in treated animals was identical to control (9.3% ± 1.6%). Close correlation was found between MRI and postmortem findings. Functional MRI revealed an improvement in ejection fraction in nicorandil-treated hearts (48.5% ± 3.4% vs 38.1% ± 3.2%, P = .04). LV end-diastolic volume and pressure, aortic pressure, and peripheral vascular resistance were highest in untreated hypertrophied hearts. Brief ischemia caused severe injury in hypertrophied hearts. Infusing nicorandil increased the tolerance of hypertrophied hearts to ischemia. MRI is a suitable technique for the evaluation of new therapies in LV hypertrophy.

Expression and function of Kv7.4 channels in rat cardiac mitochondria: possible targets for cardioprotection

AIMS

Plasmalemmal Kv7.1 (KCNQ1) channels are critical players in cardiac excitability; however, little is known on the functional role of additional Kv7 family members (Kv7.2-5) in cardiac cells. In this work, the expression, function, cellular and subcellular localization, and potential cardioprotective role against anoxic-ischaemic cardiac injury of Kv7.4 channels have been investigated.

METHODS AND RESULTS

Expression of Kv7.1 and Kv7.4 transcripts was found in rat heart tissue by quantitative polymerase chain reaction. Western blots detected Kv7.4 subunits in mitochondria from Kv7.4-transfected cells, H9c2 cardiomyoblasts, freshly isolated adult cardiomyocytes, and whole hearts. Immunofluorescence experiments revealed that Kv7.4 subunits co-localized with mitochondrial markers in cardiac cells, with ∼ 30-40% of cardiac mitochondria being labelled by Kv7.4 antibodies, a result also confirmed by immunogold electron microscopy experiments. In isolated cardiac (but not liver) mitochondria, retigabine (1-30 µM) and flupirtine (30 µM), two selective Kv7 activators, increased Tl(+) influx, depolarized the membrane potential, and inhibited calcium uptake; all these effects were antagonized by the Kv7 blocker XE991. In intact H9c2 cells, reducing Kv7.4 expression by RNA interference blunted retigabine-induced mitochondrial membrane depolarization; in these cells, retigabine decreased mitochondrial Ca(2+) levels and increased radical oxygen species production, both effects prevented by XE991. Finally, retigabine reduced cellular damage in H9c2 cells exposed to anoxia/re-oxygenation and largely prevented the functional and morphological changes triggered by global ischaemia/reperfusion (I/R) in Langendorff-perfused rat hearts.

CONCLUSION

Kv7.4 channels are present and functional in cardiac mitochondria; their activation exerts a significant cardioprotective role, making them potential therapeutic targets against I/R-induced cardiac injury.

New perspectives of nitric oxide donors in cardiac arrest and cardiopulmonary resuscitation treatment

Nitric oxide (NO) is often used to treat heart failure accompanied with pulmonary edema. According to present knowledge, however, NO donors are contraindicated when systolic blood pressure is less than 90 mmHg. Based on recent findings and our own clinical experience, we formulated a hypothesis about the new breakthrough complex lifesaving effects of NO donors in patients with cardiac arrest and cardiopulmonary resuscitation therapy. It includes a direct hemodynamic effect of NO donors mediated through vasodilation of coronary arteries in cooperation with improvement of cardiac function and cardiac output through reversible inhibition of mitochondrial complex I and mitochondrial NO synthase, followed by reduction in reactive oxygen species and correction of myocardial stunning. Simultaneously, an increase in vascular sensitivity to sympathetic stimulation could lead to an increase in diastolic blood pressure. Confirmation of this hypothesis in clinical practice would mean a milestone in the treatment for cardiac arrest and cardiopulmonary resuscitation.

Liver ischemia preconditions the heart against ischemia-reperfusion arrhythmias

OBJECTIVES

This study aimed to examine the hypothesis that an antiarrhythmic effect might be obtained by ischemic preconditioning of the liver, and also to characterize the potential underlying mechanisms.

MATERIALS AND METHODS

Male Wistar rats were anesthetized by thiopental sodium (50 mg/kg, IP) followed by IV injection of heparin (250 IU). Remote ischemic preconditioning (RIPC) was induced by 3 cycles of 5 min liver ischemia followed by 5 min of reperfusion. The hearts were excised within 5 min after the final cycle of preconditioning and perfused using Langendorff's system. The isolated perfused hearts were subjected to 30 min global ischemia followed by 90 min reperfusion. The myocardial arrhythmias induced by ischemia- reperfusion (I/R) were determined in accordance with the guidelines of Lambeth Conventions. The potential role of KATP channels on RIPC was assessed by injection of glibenclamide (nonselective KATP blocker) or 5-hydroxydecanoate (mitochondrial KATP blocker) on rats 30 and 15 min before induction of RIPC in the liver, respectively.

RESULTS

Hepatic remote preconditioning of the heart significantly (P<0.0001) prevented the incidence of myocardial arrhythmias induced by I/R in the perfused hearts (5.33±1.54 vs. 32.33±6.44,). However, the protective effects of remote preconditioning was significantly (P<0.01) abolished by the KATP blocker, glibenclamide (25.5±4.9 vs. 5.33±1.54,).

CONCLUSION

Hepatic RIPC may prevent the arrhythmias induced by I/R in the isolated perfused hearts via KATP channels.

Diosgenin-induced protection against myocardial ischaemia-reperfusion injury is mediated by mitochondrial KATP channels in a rat model

Objective:

This study was aimed to evaluate the effects of diosgenin on myocardial ischaemia-reperfusion injury and the potential involvement of mitochondrial KATP (mitoKATP) channel and nitric oxide (NO) system blockades in this field.

Materials and methods:

After isolation of hearts of male Wister rats, the study was conducted on control and diosgenin- receiving hearts in the presence or absence of 5-HD and L-NAME (as antagonists of mitoKATP channel and NO system, respectively) in an isolated buffer-perfused heart model. Global ischaemia was induced by 30-min occlusion of aortic flow followed by 90-min reperfusion. Cardiac haemodynamics were recorded throughout the experiment using a PowerLab data acquisition system.

Results:

The levels of creatine kinase (CK-MB) and lactate dehydrogenase (LDH) in the coronary effluents were estimated colourimetrically. Diosgenin pre-administration significantly decreased the release of LDH and CK-MD into the coronary effluent as compared the with the control group (P<0.05). The left ventricular developed pressure (LVDP) and contractility (±dP/dt) were significantly improved and restored to pre-ischaemic values in the diosgenin-receiving group (P<0.05 ). There were no significant differences in left ventricular end-diastolic pressure, coronary flow and heart rate between the control and diosgenin-treated groups during the pre-ischaemic and reperfusion periods. Blocking the mitoKATP channels by 5-HD completely eliminated the positive effect of the diosgenin on the LVDP and ±dP/dt (P<0.05 ). However, blocking the NO system by L-NAME slightly reduced the diosgenin effects and the inhibitory effect of L-NAME was less than 5-HD.

Conclusion:

The results showed that diosgenin may have cardioprotective effects against myocardial reperfusion injury through activating the mitoKATP channels.

Uncoupling protein 3 mediates H₂O₂ preconditioning-afforded cardioprotection through the inhibition of MPTP opening

AIMS

Uncoupling protein 3 (UCP3), located in the mitochondrial inner membrane, is cardioprotective, but its mechanisms of preserving mitochondrial function during ischaemia/reperfusion (I/R) are not fully understood. This study investigated whether UCP3 mediates/mimics the cardioprotection of H₂O₂ preconditioning (H₂O₂PC) against I/R injury and the downstream pathway that mediates H₂O₂PC- and UCP3-afforded cardioprotection.

METHODS AND RESULTS

H₂O₂PC at 20 µM for 5 min significantly improved post-ischaemic functional recovery and reduced lactate dehydrogenase (LDH) release and infarct size with concurrently up-regulated UCP3 expressions in perfused rat hearts subjected to global no-flow I/R. These protections were blocked by UCP3 knockdown with short hairpin RNA but mimicked by UCP3 overexpression. Consistently, H₂O₂PC-attenuated I/R-induced cytosolic and mitochondrial Ca(2+) overload, Ca(2+) transient suppression, mitochondrial reactive oxygen species burst, and loss of mitochondrial inner membrane potential were reversed by UCP3 knockdown but mimicked by UCP3 overexpression. Moreover, co-immunoprecipitation assay revealed an interaction of UCP3 with the mitochondrial permeability transition pore (mPTP) component, adenine nucleotide translocator (ANT), while the cardioprotection induced by H₂O₂PC- and UCP3 overexpression in mitochondria, cardiac function, and cell survival was abolished by atractyloside, a mPTP opener binding to ANT, and partially inhibited by a PI3K/Akt inhibitor wortmannin. Furthermore, H₂O₂PC up-regulated the phosphorylation of Akt, and glycogen synthase kinase 3β was blocked by UCP3 knockdown but mimicked by UCP3 overexpression.

CONCLUSION

UCP3 mediates the cardioprotection of H₂O₂PC against I/R injury by preserving the mitochondrial function through inhibiting mPTP opening via the interaction with ANT and the PI3K/Akt pathway. Our findings reveal novel mechanisms of UCP3 in the cardioprotection.

Cardioprotection acquired through exercise: the role of ischemic preconditioning

A great bulk of evidence supports the concept that regular exercise training can reduce the incidence of coronary events and increase survival chances after myocardial infarction. These exercise-induced beneficial effects on the myocardium are reached by means of the reduction of several risk factors relating to cardiovascular disease, such as high cholesterol, hypertension, obesity etc. Furthermore, it has been demonstrated that exercise can reproduce the "ischemic preconditioning" (IP), which refers to the capacity of short periods of ischemia to render the myocardium more resistant to subsequent ischemic insult and to limit infarct size during prolonged ischemia. However, IP is a complex phenomenon which, along with infarct size reduction, can also provide protection against arrhythmia and myocardial stunning due to ischemia-reperfusion. Several clues demonstrate that preconditioning may be directly induced by exercise, thus inducing a protective phenotype at the heart level without the necessity of causing ischemia. Exercise appears to act as a physiological stress that induces beneficial myocardial adaptive responses at cellular level. The purpose of the present paper is to review the latest data on the role played by exercise in triggering myocardial preconditioning.