Nicorandil opens mitochondrial K(ATP) channels not only directly but also through a NO-PKG-dependent pathway

Direct and indirect activation of the adenosine triphosphate-sensitive potassium channel to induce spinal cord ischemic metabolic tolerance

OBJECTIVES

The mitochondrial adenosine triphosphate-sensitive potassium channel is central to pharmacologically induced tolerance to spinal cord injury. We hypothesized that both direct and nitric oxide-dependent indirect activation of the adenosine triphosphate-sensitive potassium channel contribute to the induction of ischemic metabolic tolerance.

METHODS

Spinal cord injury was induced in adult male C57BL/6 mice through 7 minutes of thoracic aortic crossclamping. Pretreatment consisted of intraperitoneal injection 3 consecutive days before injury. Experimental groups were sham (no pretreatment or ischemia, n = 10), spinal cord injury control (pretreatment with normal saline, n = 27), Nicorandil 1.0 mg/kg (direct and indirect adenosine triphosphate-sensitive potassium channel opener, n = 20), Nicorandil 1 mg/kg + carboxy-PTIO 1 mg/kg (nitric oxide scavenger, n = 21), carboxy-PTIO (n = 12), diazoxide 5 mg/kg (selective direct adenosine triphosphate-sensitive potassium channel opener, n = 25), and DZ 5 mg/kg+ carboxy-PTIO 1 mg/kg, carboxy-PTIO (n = 23). Limb motor function was assessed using the Basso Mouse Score (0-9) at 12-hour intervals for 48 hours after ischemia.

RESULTS

Motor function was significantly preserved at all time points after ischemia in the Nicorandil pretreatment group compared with ischemic control. The addition of carboxy-PTIO partially attenuated Nicorandil's motor-preserving effect. Motor function in the Nicorandil + carboxy-PTIO group was significantly preserved compared with the spinal cord injury control group (P < .001), but worse than in the Nicorandil group (P = .078). Motor preservation in the diazoxide group was similar to the Nicorandil + carboxy-PTIO group. There was no significant difference between the diazoxide and diazoxide + carboxy-PTIO groups.

CONCLUSIONS

Both direct and nitric oxide-dependent indirect activation of the mitochondrial adenosine triphosphate-sensitive potassium channel play an important role in pharmacologically induced motor function preservation.

Clinical outcomes of nicorandil administration in patients with acute ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Primary percutaneous coronary intervention is the treatment of choice in ST-segment elevation myocardial infarction and no-reflow phenomenon is still an unsolved problem.

METHODS

We searched PubMed, EmBase, and Cochrane Central Register of Controlled Trials for relevant randomized controlled trials. The primary endpoint was the incidence of major adverse cardiac events and the secondary endpoint was the incidences of no-reflow phenomenon and complete resolution of ST-segment elevation.

RESULTS

Eighteen randomized controlled trials were enrolled. Nicorandil significantly reduced the incidence of no-reflow phenomenon (OR, 0.46; 95% CI, 0.36-0.59; P < 0.001; I² = 0%) and major adverse cardiac events (OR, 0.42; 95% CI, 0.27-0.64; P < 0.001; I² = 52%). For every single outcome of major adverse cardiac events, only heart failure and ventricular arrhythmia were significantly improved with no heterogeneity (OR, 0.36; 95% CI, 0.23-0.57, P < 0.001; OR, 0.43; 95% CI, 0.31-0.60, P < 0.001 respectively). A combination of intracoronary and intravenous nicorandil administration significantly reduced the incidence of major adverse cardiac events with no heterogeneity (OR, 0.24; 95% CI, 0.13-0.43, P < 0.001; I² = 0%), while a single intravenous administration could not (OR, 0.66; 95% CI, 0.40-1.06, P = 0.09; I² = 52%).

CONCLUSIONS

Nicorandil can significantly improve no-reflow phenomenon and major adverse cardiac events in patients undergoing primary percutaneous coronary intervention. The beneficial effects on major adverse cardiac events might be driven by the improvements of heart failure and ventricular arrhythmia. A combination of intracoronary and intravenous administration might be an optimal usage of nicorandil.

Nicorandil decreases oxidative stress in slow- and fast-twitch muscle fibers of diabetic rats by improving the glutathione system functioning

AIMS/INTRODUCTION

Myopathy is a common complication of any diabetes type, consisting in failure to preserve mass and muscular function. Oxidative stress has been considered one of the main causes for this condition. This study aimed to search if Nicorandil, a KATP channel opener, could protect slow- and fast-twitch diabetic rat muscles from oxidative stress, and to unveil its possible mechanisms.

MATERIALS AND METHODS

Diabetes was induced in male Wistar rats by applying intraperitoneally streptozotocin (STZ) at 100 mg/kg doses. Nicorandil (3 mg/kg/day) was administered along 4 weeks. An insulin tolerance test and assessment of fasting blood glucose (FBG), TBARS, reduced (GSH), and disulfide (GSSG) glutathione levels, GSH/GSSG ratio, and mRNA expression of glutathione metabolism-related genes were performed at end of treatment in soleus and gastrocnemius muscles.

RESULTS

Nicorandil significantly reduced FBG levels and enhanced insulin tolerance in diabetic rats. In gastrocnemius and soleus muscles, Nicorandil attenuated the oxidative stress by decreasing lipid peroxidation (TBARS), increasing total glutathione and modulating GPX1-mRNA expression in both muscle's types. Nicorandil also increased GSH and GSH/GSSG ratio and downregulated the GCLC- and GSR-mRNA in gastrocnemius, without significative effect on those enzymes' mRNA expression in diabetic soleus muscle.

CONCLUSIONS

In diabetic rats, Nicorandil attenuates oxidative stress in slow- and fast-twitch skeletal muscles by improving the glutathione system functioning. The underlying mechanisms for the modulation of glutathione redox state and the transcriptional expression of glutathione metabolism-related genes seem to be fiber type-dependent.

Optimizing Nicorandil for Spinal Cord Protection in a Murine Model of Complex Aortic Intervention

There are currently no clinically utilized pharmacological agents for the induction of metabolic tolerance to spinal cord ischemia-reperfusion injury in the setting of complex aortic intervention. Nicorandil, a nitric oxide donor and ATP-sensitive potassium (KATP) channel opener, has shown promise in neuroprotection. However, the optimized clinical application of the drug and its mechanism of neuroprotection remains unclear. We hypothesized that 3-days pretreatment would confer the most effective neuroprotection, mediated by mitochondrial KATP channel activation. Spinal cord injury was induced by 7 minutes of thoracic aortic cross-clamping in adult male C57BL/6 mice. Time course: mice received 0.1 mg/kg nicorandil for 10 min, 4 hours, and 3 consecutive days prior to ischemia compared with control. Dose challenge: mice received 3-days nicorandil pretreatment comparing 0.1 mg/kg, 1.0 mg/kg, 5.0 mg/kg, and saline administration. Mitochondrial KATP channel blocker 5-hydroxy-decanoate (5HD) was co-administered to elucidate mechanism. Limb motor function was evaluated, and viable anterior horn neurons quantified. Nicorandil pretreatment at 4 hours and 3 days before ischemia demonstrated significant motor function preservation; administration 10 minutes before ischemia showed no neuroprotection. All nicorandil doses showed significant motor function preservation. Three days administration of Nicorandil 1.0 mg/kg was most potent. Neuroprotection was completely abolished by 5HD co-administration. Histological analysis showed significant neuron preservation with nicorandil pretreatment, which was attenuated by 5HD co-administration. Three days administration of Nicorandil 1.0 mg/kg showed near-total motor function preservation in a murine spinal cord ischemia-reperfusion model, mediated by the mitochondrial KATP channel.

Reactive Oxygen Species Mediate Nicorandil-induced Metabolic Tolerance to Spinal Cord Injury

BACKGROUND

Spinal cord injury remains a devastating complication of thoracoabdominal aortic surgery. We previously demonstrated that pretreatment with nicorandil preserved motor function in a murine spinal cord injury model through mitochondrial adenosine triphosphate-sensitive potassium channel activation. We hypothesized that the neuroprotective effect of nicorandil is mediated by downstream generation of reactive oxygen species.

METHODS

Spinal cord injury was induced by 7 minutes of thoracic aortic cross-clamping in adult male C57BL/6 mice. Five groups were evaluated: ischemic control (n = 19); nicorandil 1.0 mg/kg (n = 17); nicorandil 1.0 mg/kg plus N acetyl L-cysteine (NAC [reactive oxygen species scavenger, n = 18)]) 150 mg/kg; NAC 150 mg/kg (n = 13); and sham (n = 10). Limb motor function and the number of viable neurons within the anterior horn of the spinal cord were evaluated.

RESULTS

Mice in the sham group showed no functional deficits after surgery. Compared with ischemic control, motor function was significantly preserved in the nicorandil pretreatment group at every timepoint after ischemia. In the nicorandil plus NAC group, the motor-preserving effect of nicorandil was completely abolished (P < .001). Viable neuron quantification showed significant neuron preservation in the nicorandil group (29.± 2.6) compared with the ischemic control group (18.5 ± 2.1, P = .024) and nicorandil plus NAC group (14 ± 8.3, P = .001); no significant difference was observed between the ischemic control group and nicorandil plus NAC group (P = 0.768).

CONCLUSIONS

Reactive oxygen species generation plays a key role in the nicorandil-induced metabolic tolerance to spinal cord injury. Manipulation of mitochondrial adenosine triphosphate-sensitive potassium channels may lead to improvement in preventing spinal cord injury after thoracoabdominal aortic interventions.

Nicorandil Affects Mitochondrial Respiratory Chain Function by Increasing Complex III Activity and ROS Production in Skeletal Muscle Mitochondria

Adenosine triphosphate (ATP)-dependent potassium channels openers (K_ATP) protect skeletal muscle against function impairment through the activation of the mitochondrial K_ATP channels (mitoK_ATP). Previous reports suggest that modulators of the mitochondrial K_ATP channels have additional effects on isolated mitochondria. To determine whether the K_ATP channel opener nicorandil has non-specific effects that explain its protective effect through the mitochondrial function, chicken muscle mitochondria were isolated, and respiration rate was determined pollarographically. The activity of the electron transport chain (ETC) complexes (I-IV) was measured using a spectrophotometric method. Reactive oxygen species (ROS) levels and lipid peroxidation were assessed using flow cytometry and thiobarbituric acid assay, respectively. Both K_ATP channel opener nicorandil and K_ATP channel blocker 5-hydroxydecanoate (5-HD) decreased mitochondrial respiration; nicorandil increased complex III activity and decreased complex IV activity. The effects of nicorandil on complex III were antagonized by 5-HD. Nicorandil increased ROS levels, effect reverted by either 5-HD or the antioxidant N-2-mercaptopropionyl glycine (MPG). None of these drugs affected lipid peroxidation levels. These findings suggest that K_ATP channel opener nicorandil increases mitochondrial ROS production from complex III. This results by partially blocking electron flow in the complex IV, setting electron carriers in a more reduced state, which is favored by the increase in complex III activity by nicorandil. Overall, our study showed that nicorandil like other mitochondrial K_ATP channel openers might not act through mitoK_ATP channel activation.

Pharmacological preconditioning and postconditioning with nicorandil attenuates ischemia/reperfusion-induced myocardial necrosis and apoptosis in hypercholesterolemic rats

Pharmacological preconditioning and postconditioning may reduce myocardial necrosis and apoptosis during ischemia/reperfusion (I/R), however, hypercholesterolemia interferes with the associated cardioprotective mechanisms. The present study investigated whether pharmacological preconditioning and postconditioning with nicorandil could attenuate myocardial necrosis and apoptosis induced by I/R in hypercholesterolemic rats, and explored the possible mechanisms involved. Male Wistar rats (n=160) were fed normal (normocholesterolemic group, n=10) or high-cholesterol (hypercholesterolemic group, n=150) diets for 8 weeks. Hearts harvested from the normal and hypercholesterolemic rats were subsequently placed on modified Langendorff perfusion apparatus and 30-min global ischemia was performed, followed by 120-min reperfusion. Nicorandil (1, 3, 10, 30, 100 µmol/l), and mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel blocker 5-hydroxydecanoic acid sodium salt (5-HD) (100 µmol/l) or soluble guanylyl cyclase (sGC) blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µmol/l) were perfused for 10 min, prior to ischemia or at the onset of reperfusion. The myocardial infarct size was determined by triphenyltetrazolium chloride staining, and cardiomyocyte apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. In order to investigate the potential mechanisms, the expression levels of caspase-3, B-cell lymphoma-2 (Bcl-2) proteins and Bcl-2-associated X protein (Bax) were measured using western blot analysis. The present study demonstrated that, in hypercholesterolemic rats, pharmacological preconditioning and postconditioning with nicorandil decreased I/R-induced myocardial necrosis and apoptosis in a concentration-dependent manner. The optimal preconditioning and postconditioning concentration of nicorandil determined to have anti-infarct and anti-apoptosis effects was 30 µmol/l, which significantly (P<0.05) reduced the infarct size to 14.88±3.25% and 15.96±3.29%, and attenuated the percentage of cardiomyocyte apoptosis to 25.20±3.93% and 26.18±4.82%, respectively, compared with the I/R group. However, the cardioprotective effects of nicorandil were partially suppressed by cotreatment with 5-HD or ODQ. Western blot analysis demonstrated that pharmacological preconditioning and postconditioning with nicorandil significantly downregulated caspase-3 and Bax expression, and upregulated Bcl-2 expression compared with the I/R group (P<0.05). The results of the present study suggest that pharmacological preconditioning and postconditioning with nicorandil may protect hypercholesterolemic hearts against I/R-induced necrosis and apoptosis; and the cardioprotective effects of nicorandil may be due to the dual pharmacological mechanisms of opening the mitoKATP channels and a nitric oxide/sGC-dependent mechanism, and regulation of the expression of caspase-3, Bax and Bcl-2.

Protein S-nitrosylation in preconditioning and postconditioning

The coronary artery disease is a leading cause of death and morbidity worldwide. This disease has a complex pathophysiology that includes multiple mechanisms. Among these is the oxidative/nitrosative stress. Paradoxically, oxidative/nitrosative signaling plays a major role in cardioprotection against ischemia/reperfusion injury. In this context, the gas transmitter nitric oxide may act through several mechanisms, such as guanylyl cyclase activation and via S-nitrosylation of proteins. The latter is a covalent modification of a protein cysteine thiol by a nitric oxide-group that generates an S-nitrosothiol. Here, we report data showing that nitric oxide and S-nitrosylation of proteins play a pivotal role not only in preconditioning but also in postconditioning cardioprotection.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Potassium channel openers prevent palmitate-induced insulin resistance in C2C12 myotubes

Insulin resistance (IR) of muscle cells is an early symptom of type 2 diabetes. It often results from excessive lipid accumulation in muscle fibers which under in vitro experimental conditions may be induced by incubation of muscle cells with palmitate. IR is manifested as a reduced response of cells to insulin expressed by lowered Akt kinase phosphorylation and decreased insulin-dependent glucose uptake. Stimulation of mitochondrial oxidative metabolism by mild dissipation of the mitochondrial potential is thought to increase fatty acid utilization and thereby prevent insulin resistance. Here it is shown that nicorandil and NS1619, which are openers of two different mitochondrial potassium channels, protect C2C12 myotubes from palmitate-induced insulin resistance. Preincubation of myotubes with 5-hydroxydecanoate abolishes the protective effect of nicorandil. The efficient concentrations of both openers are far below those commonly applied for cytoprotection. This is probably why their effects on the mitochondrial energy metabolism are small. These data suggest that opening of mitochondrial potassium channels could be a promising approach in prevention and therapy of insulin resistance related to dyslipidemia and obesity.

Relative similarity within purine nucleotide and ligand structures operating on nitric oxide synthetase, guanylyl cyclase and potassium (K ATP, BK Ca) channels

OBJECTIVES

Purine nucleotides play a central role in signal transduction events initiated at the cell membrane. The NO-cGMP-cGK pathway, in particular, mediates events involving NOS and some classes of K(+) ion channel. The aim of this study is to investigate relative molecular similarity within the ligands binding to NOS, K(ATP), BK(Ca) channels and regulatory nucleotides.

METHODS

Minimum energy conformers of the ligand structures were superimposed and fitted to L-arginine and the nucleotides of adenine and guanine using a computational program.

KEY FINDINGS

Distinctive patterns were evident in the fitting of NOS isoform antagonists to L-arginine. K(ATP) channel openers and antagonists superimposed on the glycosidic linkage and imidazole ring of the purine nucleotides, and guanidinium and ribose groups of GTP in the case of glibenclamide. The fits of BK(Ca) channel openers and antagonists to cGMP were characterized by the linear dimensions of their structures; distances between terminal oxy groups in respect of dexamethasone and aldosterone.

CONCLUSIONS

The findings provide structural evidence for the functional interaction between K(+) channel openers/antagonists and the regulatory nucleotides. Use of the purine nucleotide template systematizes the considerable heterogeneity evident within the structures of ligands operating on K(+) ion channels.