Adenosine Triphosphate-sensitive Potassium Channel Opener Research Articles

Kir1.1 and SUR1 are not implicated as subunits of an adenosine triphosphate-sensitive potassium channel involved in diazoxide cardioprotection

ObjectiveThe adenosine triphosphate-sensitive potassium channel opener diazoxide mimics ischemic preconditioning and is cardioprotective. Clarification of diazoxide's site and mechanism of action could lead to targeted pharmacologic therapies for patients undergoing cardiac surgery. Several mitochondrial candidate proteins have been investigated as potential adenosine triphosphate-sensitive potassium channel components. Renal outer medullary potassium (Kir1.1) and sulfonylurea sensitive regulatory subunit 1 have been suggested as subunits of a mitochondrial adenosine triphosphate-sensitive potassium channel. We hypothesized that pharmacologic blockade or genetic deletion (knockout) of renal outer medullary potassium and sensitive regulatory subunit 1 would result in loss of diazoxide cardioprotection in models of global ischemia with cardioplegia. MethodsMyocyte volume and contractility were compared after Tyrode's physiologic solution (20 minutes), stress (hyperkalemic cardioplegia ± diazoxide, ± VU591 (Kir1.1 inhibitor), N = 9 to 23 each, 20 min), and Tyrode's (20 minutes). Isolated mouse (wild-type, sensitive regulatory subunit 1 [−/−], and cardiac knockout renal outer medullary potassium) hearts were given cardioplegia ± diazoxide (N = 9-16 each) before global ischemia (90 minutes) and 30 minutes reperfusion. Left ventricular pressures were compared before and after ischemia. ResultsStress (cardioplegia) was associated with reduced myocyte contractility that was prevented by diazoxide. Isolated myocytes were not responsive to diazoxide in the presence of VU591. In isolated hearts, diazoxide improved left ventricular function after prolonged ischemia compared with cardioplegia alone in wild-type and knockout (sensitive regulatory subunit 1 [−/−] and cardiac knockout renal outer medullary potassium) mice. ConclusionsIsolated myocyte and heart models may measure independent and separate actions of diazoxide. By definitive genetic deletion, these data indicate that sensitive regulatory subunit 1 and renal outer medullary potassium are not implicated in cardioprotection by diazoxide.

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

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. Spinal cord injury was induced in adult male C57BL/6 mice through 7minutes 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 1.0mg/kg (direct and indirect adenosine triphosphate-sensitive potassium channel opener, n=20), Nicorandil 1mg/kg+carboxy-PTIO 1mg/kg (nitric oxide scavenger, n=21), carboxy-PTIO (n=12), diazoxide 5mg/kg (selective direct adenosine triphosphate-sensitive potassium channel opener, n=25), and DZ 5mg/kg+carboxy-PTIO 1mg/kg, carboxy-PTIO (n=23). Limb motor function was assessed using the Basso Mouse Score (0-9) at 12-hour intervals for 48hours after ischemia. 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. 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.

Abstract 15530: Renal Outer Medullary Potassium (Kir 1.1) is not the Kir Subunit of a Cardioprotective, Diazoxide - Mediated Mitochondrial Adenosine Triphosphate - Sensitive Potassium Channel

Objective: The adenosine triphosphate-sensitive potassium (K ATP ) channel opener diazoxide (DZX) mimics ischemic preconditioning and is cardioprotective. The molecular mechanism of action is unknown, although several mitochondrial candidate protein targets have been proposed. We suggested that cardioprotection occurs at a non-sarcolemmal channel, requires the inhibition of succinate dehydrogenase, and involves K ATP channel subunit SUR1. The renal outer medullary potassium channel (ROMK, or Kir1.1) subunit was proposed as the Kir subunit of a mitochondrial (m)K ATP channel. We tested the hypothesis that genetic deletion of ROMK will result in loss of DZX cardioprotection in a model of prolonged ischemia with cardioplegia. Methods: Mice lacking ROMK in cardiac myocytes (cKO) and wild-type (WT) litter mates were randomly assigned to 90 min. global ischemia in a Langendorff model following hypothermic hyperkalemic cardioplegia (CPG) or CPG + DZX (100 μM/L) (N=6-9 per group). Left ventricular developed pressure (LVDP), end diastolic pressure (EDP), and coronary flow were compared before and after global ischemia. Data acquisition and interpretation were blinded to group. Results: Similar to previous results, prolonged global ischemia was associated with a reduction in LVDP and an increase in EDP with CPG that was prevented by DZX in WT. Unexpectedly, ROMK (cKO) mice were equally responsive to DZX (Figure), indicating that DZX protection is not mediated by ROMK channels. Conclusions: Genetic deletion of ROMK in cardiac myocytes does not negate cardioprotection provided by DZX, indicating ROMK is not a subunit of a cardioprotective mK ATP channel. Alternate proposed DZX-sensitive target channels or mechanisms of action remain to be tested. Identification of the specific subunits of a mK ATP channel would allow for targeted pharmacologic therapy to reduce myocardial stunning following prolonged ischemia, similar to that seen following cardiac surgery.

Cardioprotective mechanisms of mitochondria-targeted S-nitrosating agent and adenosine triphosphate-sensitive potassium channel opener are mutually exclusive

BackgroundMyocytes exposed to stress exhibit significant swelling and reduced contractility. These consequences are ameliorated by adenosine triphosphate–sensitive potassium (KATP) channel opener diazoxide (DZX) via an unknown mechanism. KATP channel openers also provide cardioprotection in multiple animal models. Nitric oxide donors are similarly cardioprotective, and their combination with KATP activation may provide synergistic benefit. We hypothesized that mitochondria-targeted S-nitrosating agent (MitoSNO) would provide synergistic cardioprotection with DZX. MethodsMyocyte volume and contractility were compared following Tyrode's physiologic solution (20 minutes) and stress (hyperkalemic cardioplegia [CPG] ± DZX; n = 5-20 each; 20 minutes) with or without MitoSNO (n = 5-11 each) at the end of stress, followed by Tyrode's solution (20 minutes). Isolated mouse hearts received CPG ± DZX (n = 8-10 each) before global ischemia (90 minutes) with or without MitoSNO (n = 8 each) at the end of ischemia, followed by reperfusion (30 minutes). Left ventricular (LV) pressures were compared using a linear mixed model to assess the impact of treatment on the outcome, adjusting for baseline and balloon volume. ResultsStress (CPG) was associated with reduced myocyte contractility that was prevented by DZX and MitoSNO individually; however, their combination was associated with loss of cardioprotection. Similarly, DZX and MitoSNO improved LV function after prolonged ischemia compared with CPG alone, and cardioprotection was lost with their combination. ConclusionsMitoSNO and DZX provide cardioprotection that is lost with their combination, suggesting mutually exclusive mechanisms of action. The lack of a synergistic beneficial effect informs the current knowledge of the cardioprotective mechanisms of DZX and will aid planning of future clinical trials.

Abstract 15316: Paradoxical Reduction in Myocardial Performance When Combining Two Independently Cardioprotective Agents: Mitochondrial-targeted Antioxidant MitoSNO and Adenosine Triphosphate-sensitive Potassium Channel Opener Diazoxide

Introduction: Adenosine triphosphate-sensitive potassium (K ATP ) channel opener diazoxide (DZX) and Antioxidant MitoSNO are both independently cardioprotective in animal models. The cardioprotective mechanism of diazoxide is unknown, and involves a non-sarcolemmal location, requires the inhibition of succinate dehydrogenase, and the K ATP channel subunit SUR1. Mitochondrial - targeted Antioxidant MitoSNO is a S-nitrosylating agent that stalls complex 1, reduces ROS production and succinate accumulation. In an isolated myocyte model of stress due to hyperkalemic cardioplegia (CPG), that the combination of DZX and MitoSNO negated the beneficial effects of each alone. Hypothesis: We hypothesized that the combination of DZX and MitoSNO would negate the beneficial effects of each alone in an isolated heart model of global ischemia. Methods: Isolated mouse hearts underwent assessment of end diastolic pressure (EDP) and left ventricular developed pressure (LVDP) utilizing an LV balloon in a Langendorff model before and after 90 min of global ischemia. Hearts received test solution (CPG (9°C) or CPG±DZX (100μM) at onset of ischemia +/- MitoSNO (1μM/L) at end of ischemia), followed by 30 min reperfusion. LVDP and EDP were compared between groups utilizing a linear mixed model to assess the impact of treatment on the outcome, adjusting for baseline and balloon volume. Results: Similar to previous results, DZX improved LVDP and reduced EDP after ischemia compared to CPG (Figure). Similarly, MitoSNO improved LVDP and reduced EDP compared to CPG (Figure). The addition of MitoSNO with DZX was associated with the loss of cardioprotection observed with MitoSNO or DZX alone. Conclusions: Similar to data in a myocyte model, both MitoSNO and DZX provide cardioprotection that is lost with the combination of both, suggesting mutually exclusive mechanisms of action and that DZX’s mechanism requires a functional complex 1, ROS production, or succinate accumulation.

Diazoxide Protects against Myocardial Ischemia/Reperfusion Injury by Moderating ERS via Regulation of the miR-10a/IRE1 Pathway.

Nowadays, reperfusion is still the most effective treatment for ischemic heart disease. However, cardiac reperfusion therapy would lead to reperfusion injury, which may have resulted from endoplasmic reticulum stress (ERS) during reperfusion. Diazoxide (DZ) is a highly selective mitochondrial adenosine triphosphate-sensitive potassium channel opener. Its protective effect on I/R injury has been confirmed in many organs such as the heart and brain. However, the mechanism of its protective effect has not been fully elucidated. MicroRNAs (miRNAs) are widely involved in pathologies of heart disease. In this study, we found that miR-10a expression was highly upregulated in the myocardial I/R groups, and DZ treatment significantly reduced the expression of miR-10a. More importantly, we found that DZ treatment can moderate ERS via regulation of the miR-10a/IRE1 pathway in the I/R and H/R models, thereby protecting myocardial H/R injury.

ATP sensitive potassium (KATP) channel inhibition: A promising new drug target for migraine.

Recently, the adenosine triphosphate (ATP) sensitive potassium channel opener levcromakalim was shown to induce migraine attacks with a far higher incidence than any previous provoking agent such as calcitonin gene-related peptide. Here, we show efficacy of ATP sensitive potassium channel inhibitors in two validated rodent models of migraine. In female spontaneous trigeminal allodynic rats, the sensitivity of the frontal region of the head was tested by an electronic von Frey filament device. In mice, cutaneous hypersensitivity was induced by repeated glyceryl trinitrate or levcromakalim injections over nine days, as measured with von Frey filaments in the hindpaw. Release of calcitonin gene-related peptide from dura mater and trigeminal ganglion was studied ex vivo. The ATP sensitive potassium channel inhibitor glibenclamide attenuated the spontaneous cephalic hypersensitivity in spontaneous trigeminal allodynic rats and glyceryl trinitrate-induced hypersensitivity of the hindpaw in mice. It also inhibited CGRP release from dura mater and the trigeminal ganglion isolated from spontaneous trigeminal allodynic rats. The hypersensitivity was also diminished by the structurally different ATP sensitive potassium channel inhibitor gliquidone. Mice injected with the ATP sensitive potassium channel opener levcromakalim developed a progressive hypersensitivity that was completely blocked by glibenclamide, confirming target engagement. The results suggest that ATP sensitive potassium channel inhibitors could be novel and highly effective drugs in the treatment of migraine.

Nicorandil prevents doxorubicin-induced human umbilical vein endothelial cell apoptosis

Nicorandil is an adenosine triphosphate-sensitive potassium channel opener with additional antioxidant properties. Doxorubicin (DOX) is an anticancer drug that exerts oxidation-mediated adverse cardiovascular effects. This study examined the effects of nicorandil on DOX-induced cytotoxicity in human umbilical vein endothelial cells (HUVECs) and underlying intracellular signaling mechanisms. Cultured HUVECs were pretreated with nicorandil (0.1, 0.3, 1, 3, and 10 μM) for 12 h and then treated with DOX (1 μM) for 24 h. Cell viability and cytotoxicity were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase assays, respectively. Cell apoptosis was examined using a caspase-3 activity assay, and DNA fragmentation was detected through TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) staining. Western blot analysis was conducted to determine the related protein expression. DOX markedly increased reactive oxygen species production, p53 expression, caspase-3 activity, cleaved caspase-3 levels, and TUNEL-positive cell numbers but reduced Bcl-2 expression and intracellular antioxidant enzyme levels; these effects were effectively antagonized through nicorandil (3 μM, 12 h) pretreatment, which resulted in HUVECs being protected from DOX-induced apoptosis. Activating transcription factor 3 (ATF3), a stress-induced transcription factor, was induced by nicorandil (3 μM). Furthermore, nicorandil (3 μM) enhanced nuclear factor erythroid 2–related factor 2 (Nrf2) translocation and heme oxygenase-1 (HO-1) expression. ATF3 short interfering RNA significantly attenuated nicorandil-mediated Nrf2 translocation, HO-1 expression, and inhibitory effects on DOX-stimulated reactive oxygen species production and cell apoptosis. In summary, nicorandil may protect HUVECs from DOX-induced apoptosis, in part through ATF3-mediated Nrf2/HO-1 signaling pathways, which potentially protect the vessels from severe DOX toxicity.

Decreased cardiac mortality with nicorandil in patients with ischemic heart failure

BackgroundEffective treatments in heart failure (HF) patients with ischemic etiology have not been fully established. Nicorandil, combination of nitrate component and sarcolemmal adenosine triphosphate-sensitive potassium channel opener, is a potent vasodilator of coronary and peripheral vessels and has been used as an antianginal agent. Therefore, we examined impacts of nicorandil on cardiac mortality in ischemic HF patients.MethodsConsecutive 334 HF patients with ischemic etiology were retrospectively registered and divided into 2 groups based on oral administration of nicorandil: nicorandil group (n = 116) and non-nicorandil group (n = 218). We retrospectively examined cardiac mortality.ResultsIn the Kaplan-Meier analysis (mean follow-up period 963 days), cardiac mortality was significantly lower in the nicorandil group than in the non-nicorandil group (11.2% vs. 19.7%, P = 0.032). In the Cox proportional hazard analysis, usage of nicorandil was a suppressor of cardiac mortality (hazard ratio 0.512, 95% confidence interval 0.275–0.953, P = 0.035), and this result was consistent in several subgroup analyses, such as left ventricular ejection fraction, percutaneous coronary intervention, coronary artery bypass graft, diabetes, β-blockers, and statins.ConclusionNicorandil is potentially effective for reducing mortality in patients with ischemic heart failure.Trial registrationThis was a retrospective study.

Potassium Channelopathies and Gastrointestinal Ulceration.

Potassium channels and transporters maintain potassium homeostasis and play significant roles in several different biological actions via potassium ion regulation. In previous decades, the key revelations that potassium channels and transporters are involved in the production of gastric acid and the regulation of secretion in the stomach have been recognized. Drugs used to treat peptic ulceration are often potassium transporter inhibitors. It has also been reported that potassium channels are involved in ulcerative colitis. Direct toxicity to the intestines from nonsteroidal anti-inflammatory drugs has been associated with altered potassium channel activities. Several reports have indicated that the long-term use of the antianginal drug Nicorandil, an adenosine triphosphate-sensitive potassium channel opener, increases the chances of ulceration and perforation from the oral to anal regions throughout the gastrointestinal (GI) tract. Several of these drug features provide further insights into the role of potassium channels in the occurrence of ulceration in the GI tract. The purpose of this review is to investigate whether potassium channelopathies are involved in the mechanisms responsible for ulceration that occurs throughout the GI tract.

Nicorandil Inhibits Cyclic Strain-Induced Interleukin-8 Expression in Human Umbilical Vein Endothelial Cells

Background: Nicorandil, a mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel opener, exerts protective effects on the cardiovascular system. This study examined the effect of nicorandil on cyclic strain-induced interleukin-8 (IL-8) expression in human umbilical vein endothelial cells (HUVECs). Methods: Cultured HUVECs were exposed to cyclic strain in the presence or absence of nicorandil (1-10 μmol/l); we then analyzed IL-8 expression. We also assessed the effects of nicorandil on heme oxygenase-1 (HO-1) expression and cyclic strain-modulated IL-8 expression after HO-1 silencing in HUVECs. Summary: HUVECs exposed to cyclic strain showed increased IL-8 messenger RNA expression and protein secretion. Nicorandil (1-10 μmol/l) inhibited cyclic strain-induced IL-8 expression, whereas 5-hydroxydecanoate (100 μmol/l), a selective inhibitor of the mitoKATP channel, completely reversed the inhibitory effects of nicorandil on cyclic strain-induced IL-8 expression. We demonstrated that nicorandil increased HO-1 expression in HUVECs. In addition, cobalt protoporphyrin (10 μmol/l), an inducer of HO-1 expression, mimicked the effects of nicorandil and inhibited IL-8 expression under cyclic strain, whereas zinc protoporphyrin IX (10 μmol/l), an inhibitor of HO-1 expression, antagonized the effect of nicorandil. HO-1 silencing significantly abrogated the inhibitory effects of nicorandil on cyclic strain-induced IL-8 expression, suggesting that HO-1 plays a role in the mechanism of action of nicorandil. Key Messages: This study is the first to report that nicorandil inhibits cyclic strain-induced IL-8 expression through the induction of HO-1 expression in HUVECs. This finding provides valuable new insight into the molecular pathways contributing to the vasoprotective effects of nicorandil.

Effects of adding intravenous nicorandil to standard therapy on cardiac sympathetic nerve activity and myocyte dysfunction in patients with acute decompensated heart failure.

Nicorandil, an adenosine triphosphate-sensitive potassium channel opener, improves cardiac sympathetic nerve activity (CSNA) in ischemic heart disease or chronic heart failure. However, its effects on CSNA and myocyte dysfunction in acute heart failure (AHF) remain unclear. We investigated the effects of adding intravenous nicorandil to standard therapy on CSNA and myocyte dysfunction in AHF. We selected 70 patients with mild to moderate nonischemic AHF who were treated with standard conventional therapy soon after admission. Thirty-five patients were assigned to additionally receive intravenous nicorandil (4-12mg/h; group A), whereas the remaining patients continued their current drug regimen (group B). Delayed total defect score (TDS), delayed heart to mediastinum count (H/M) ratio, and washout rate (WR) were determined by (123)I-metaiodobenzylguanidine (MIBG) scintigraphy within 3days of admission and 4weeks later. High sensitivity troponin T (hs-TnT) level was also measured at the same time points. After treatment, MIBG scintigraphic parameters significantly improved in both groups. However, the extent of the changes in these parameters in group A significantly exceeded the extent of the changes in group B [TDS -11.3 ± 4.3 in group A vs -4.0 ± 6.0 in group B (p < 0.01); H/M ratio 0.31 ± 0.16 vs 0.14 ± 0.16 (p < 0.01); WR -13.8 ± 7.8% vs -6.1 ± 8.9% (p < 0.01)]. The hs-TnT level decreased significantly from 0.052 ± 0.043 to 0.041 ± 0.033ng/ml (p < 0.05) in group A, but showed no significant change in group B. Moreover, in both groups, no relationships between the extent of changes in MIBG parameters and hs-TnT level were observed. Adding intravenous nicorandil to standard therapy provides additional benefits for CSNA and myocyte dysfunction over conventional therapy alone in AHF patients. Furthermore, the mechanisms of improvement in CSNA and myocyte dysfunction after nicorandil treatment in AHF patients were distinct.

Cardioprotective benefits of adenosine triphosphate-sensitive potassium channel opener diazoxide are lost with administration after the onset of stress in mouse and human myocytes.

Adenosine triphosphate-sensitive (KATP) potassium channel opener diazoxide (DZX) maintains myocyte volume and contractility during stress via an unknown mechanism when administered at the onset of stress. This study was performed to investigate the cardioprotective potential of DZX when added after the onset of the stresses of hyperkalemic cardioplegia, metabolic inhibition, and hypo-osmotic stress. Isolated mouse ventricular and human atrial myocytes were exposed to control Tyrode's solution (TYR) for 10 to 20 minutes, test solution for 30 minutes (hypothermic hyperkalemic cardioplegia [CPG], CPG + 100uM diazoxide [CPG+DZX], metabolic inhibition [MI], MI+DZX, mild hypo-osmotic stress [0.9T], or 0.9T + DZX), with DZX added after 10 or 20 minutes of stress, followed by 20 minutes of re-exposure to TYR (±DZX). Myocyte volume (human + mouse) and contractility (mouse) were compared. Mouse and human myocytes demonstrated significant swelling during exposure to CPG, MI, and hypo-osmotic stress that was not prevented by DZX when administered either at 10 or 20 minutes after the onset of stress. Contractility after the stress of CPG in mouse myocytes significantly declined when DZX was administered 20 minutes after the onset of stress (p < 0.05 vs TYR). Contractility after hypo-osmotic stress in mouse myocytes was not altered by the addition of DZX. To maintain myocyte volume homeostasis and contractility during stress (hyperkalemic cardioplegia, metabolic inhibition, and hypo-osmotic stress), KATP channel opener diazoxide requires administration at the onset of stress in this isolated myocyte model. These data have potential implications for any future clinical application of diazoxide.

Bkca opener, NS1619 pretreatment protects against shock-induced vascular hyporeactivity through PDZ-Rho GEF–RhoA–Rho kinase pathway in rats

Our previous study showed that the ischemic preconditioning and pretreatment of adenosine triphosphate-sensitive potassium channel (KATP) opener, pinacidil, may induce a good protective effect on shock-induced vascular hyporeactivity. Whether the pretreatment of opener/activator of the large-conductance calcium-activated potassium channel (Bkca), NS1619, can also induce a protective effect on vascular reactivity and play a beneficial effect on subsequent hemorrhagic shock is not clear. With Sprague-Dawley rats subjected to hemorrhagic shock and their isolated superior mesenteric artery, the protective effect of NS1619 (0.5, 1, 2, and 4 mg/kg) pretreatment (30 minutes before hemorrhage shock) on vascular reactivity and the underlying mechanisms were observed. NS1619 pretreatment significantly improved the 72-hour survival of hemorrhagic shock rats, alleviated shock-induced decrease of vascular reactivity and calcium sensitivity, and increased the cardiac output and oxygen delivery. NS1619 2 mg/kg had the best effect. These protective effects of NS1619 pretreatment on vascular reactivity and calcium sensitivity were antagonized by RhoA inhibitor, C3 transferase, and Rho kinase antagonist, Y-27632. NS1619 pretreatment up-regulated the activities of RhoA, Rho-kinase, and PDZ-Rho GEF (guanine nucleotide exchange factor). These effects of NS1619 pretreatment were eliminated by RhoA inhibitor, C3 transferase. Bkca opener, NS1619 pretreatment has good protective effect on vascular reactivity and calcium sensitivity, which plays a good beneficial effect on hemorrhagic shock. The mechanism may be mainly through PDZ-Rho GEF-RhoA-Rho kinase pathway. Bkca channel may be a potential target for the treatment of shock-induced vascular hyporeactivity.

Nicorandil Inhibits Inflammasome Activation and Toll‐Like Receptor‐4 Signal Transduction to Protect against Oxygen–Glucose Deprivation‐Induced Inflammation in BV‐2 Cells

Our previous studies have demonstrated adenosine triphosphate-sensitive potassium channel (KATP channel) openers could protect against inflammatory response in brain disease, but little is known about the mechanisms involved in KATP channel openers inhibiting neuroinflammation. In the present study, we found that oxygen-glucose deprivation (OGD) resulted in BV-2 cells activation, significantly increased tumor necrosis factor-alpha and interleukin-1beta (IL-1β) levels, accompanied by downregulating Kir6.1 subunit. Pretreatment with nicorandil, a KATP channel opener, could attenuate OGD-induced BV-2 cells activation and inhibit pro-inflammatory factors release. Further study demonstrated that OGD activated Toll-like receptor-4 (TLR4) signaling pathway and NOD-like receptor pyrin domain containing three inflammasome, thereby increased IL-1β production. Pretreatment with nicorandil could reverse the two pathways involved in IL-1β production. Our findings reveal that KATP channel openers could protect against OGD-induced neuroinflammation via inhibiting inflammasome activation and TLR4 signal transduction.

Effects of oral nicorandil therapy on sympathetic nerve activity and cardiac events in patients with chronic heart failure: subanalysis of our previous report using propensity score matching

Nicorandil, an adenosine triphosphate-sensitive potassium channel opener, improves cardiac sympathetic nerve activity (CSNA) in patients with ischaemic heart disease. However, the long-term effects on both CSNA, as evaluated by (123)I-metaiodobenzylguanidine (MIBG) scintigraphy, and prognosis have not been determined in patients with chronic heart failure (CHF). This study was a subanalysis of our previous results that serial (123)I-MIBG scintigraphic studies are the most useful prognostic indicator in CHF patients. The study group comprised 208 patients with CHF (left ventricular ejection fraction <45 %) but no cardiac events for at least 5 months identified on the basis of a history of decompensated acute heart failure requiring hospitalization. These patients underwent (123)I-MIBG scintigraphy and echocardiography just before leaving the hospital and again 6 months later. We selected 170 patients and used propensity propensity score matching to compare patients who received oral nicorandil (85 patients) and those who did not (85 patients). The patients were followed up for a median of 5.03 years, with the primary and secondary study end-points defined as the occurrence of a fatal cardiac event and a major adverse cardiac event (MACE), respectively. After treatment, the extent of changes in (123)I-MIBG scintigraphic and echocardiographic parameters in the nicorandil group were more favourable than in those not receiving nicorandil. Of the 170 patients, a fatal cardiac event occurred in 42, and a MACE in 68 during the study. Multivariate Cox regression analyses revealed that no nicorandil treatment was a significant predictor of both cardiac death and MACE in our patients with CHF. On Kaplan-Meier analysis, the rates of freedom from cardiac death or from MACE in the nicorandil group were significantly higher than in those not receiving nicorandil (all p<0.05). Long-term nicorandil treatment improves CSNA and left ventricular parameters in patients with CHF. Furthermore, this agent is potentially effective for reducing the incidence of cardiac events in patients with CHF.

Cardioprotective Mechanism of Diazoxide Involves the Inhibition of Succinate Dehydrogenase

The adenosine triphosphate-sensitive potassium (KATP) channel opener, diazoxide, preserves myocyte volume homeostasis and contractility during stress via an unknown mechanism. Pharmacologic overlap has been suggested between succinate dehydrogenase (SDH) activity and KATP channel modulators. Diazoxide may be cardioprotective due to the inhibition of SDH which may form a portion of the mitochondrial KATP channel. To determine the role of inhibition of SDH in diazoxide's cardioprotection, this study utilized glutathione to prevent the inhibition of SDH. SDH activity was measured in isolated mitochondria exposed to succinate (control), malonate (inhibitor of succinate dehydrogenase), diazoxide, and varying concentrations of glutathione alone or in combination with diazoxide. Enzyme activity was measured by spectrophotometric analysis. To evaluate myocyte volume and contractility, cardiac myocytes were superfused with Tyrode's physiologic solution (Tyrode's) (20 minutes), followed by test solution (20 minutes), including Tyrode's, hyperkalemic cardioplegia (stress), cardioplegia + diazoxide, cardioplegia + diazoxide + glutathione, or glutathione alone; followed by Tyrode's (20 minutes). Myocyte volume and contractility were recorded using image grabbing software. Both malonate and diazoxide inhibited succinate dehydrogenase. Glutathione prevented the inhibition of succinate dehydrogenase by diazoxide in a dose-dependent manner. The addition of diazoxide prevented the detrimental myocyte swelling due to cardioplegia alone and this benefit was lost with the addition of glutathione. However, glutathione elicited an independent cardioprotective effect on myocyte contractility. The ability of diazoxide to provide beneficial myocyte homeostasis during stress involves the inhibition of succinate dehydrogenase, which may also involve the opening of a purported mitochondrial adenosine triphosphate sensitive potassium channel.

Pinacidil stimulates osteoblast function in osteoblastic MC3T3-E1 cells

This study examined the effect of pinacidil, a nonselective adenosine triphosphate–sensitive potassium channel opener, on the function of osteoblastic MC3T3-E1 cells. Pinacidil caused a significant elevation of collagen synthesis, alkaline phosphatase activity, osteocalcin synthesis and mineralization in the cells (p < 0.05). Pinacidil significantly decreased the production of osteoclast differentiation inducing factors such as TNF-α, IL-6 and receptor activator of nuclear factor-κB ligand in the presence of antimycin A, which inhibits mitochondrial electron transport. Moreover, pinacidil prevented antimycin A-induced reactive oxygen species and nitrotyrosine production. These results demonstrate that pinacidil may have positive effects on skeletal structure.

Pharmacologic Prophylactic Treatment for Perioperative Protection of Skeletal Muscle from Ischemia-Reperfusion Injury in Reconstructive Surgery

In autogenous muscle transplantation, unpredictable complications can cause prolonged ischemia, resulting in ischemia-reperfusion injury. The authors investigated the efficacy and mechanism of nicorandil, a nitrovasodilator and adenosine triphosphate-sensitive potassium channel opener, in inducing perioperative protection of muscle flaps from ischemia-reperfusion injury. Pigs (18.2 ± 2.4 kg) were assigned to one control and eight treatment groups. Bilateral latissimus dorsi muscle flaps were raised after saline administration (control) and 0, 4, 8, 12, 24, 48, 72, and 96 hours after nicorandil administration. Subsequently, flaps were subjected to 4 hours of ischemia and 48 hours of reperfusion. Viability was assessed, and biochemical probes were used to study nicorandil-induced infarct protection. Protection by nicorandil was biphasic. Infarction reduced from 40.2 ± 1.9 percent (control) to 27.3 ± 1.7 percent and 24.0 ± 2.3 percent (p < 0.05) 0 and 4 hours after nicorandil administration, respectively (early phase protection). No difference was seen between control and treatment groups between 8 and 12 hours after nicorandil administration compared with the control. Infarct protection increased again (p < 0.05) at 24 (22.4 ± 2.0 percent), 48 (25.1 ± 2.1 percent), and 72 hours (28.5 ± 2.1 percent) but not at 96 hours (43.9 ± 4.6 percent) compared with control (late phase protection). The sarcolemmal and mitochondrial channels played a central role in the trigger and mediator mechanisms, respectively. Late protection was associated with lower myeloperoxidase activity and mitochondrial calcium overload and higher adenosine triphosphate content (p < 0.05). Nicorandil induced 48-hour uninterrupted muscle infarct protection, starting 24 hours after intravenous administration. This category of clinical drug is a potential prophylactic treatment against skeletal muscle ischemia-reperfusion injury in reconstructive surgery.

Pretreatment With Xenon Protected Immature Rabbit Heart From Ischaemia/Reperfusion Injury by Opening of the mitoKATP Channel

The noble gas anaesthetic, xenon has previously been shown to protect the adult myocardium from ischaemia/reperfusion (I/R) injury, however its effect on immature myocardium is unclear. The aim of this study was to investigate the effect of xenon on the isolated immature heart. Isolated, immature (2-3weeks old) New Zealand rabbit hearts were perfused with Krebs-Henseleit buffer via Langendorff-mode. After 20min of baseline equilibration, hearts were pretreated with 75% xenon, 75% xenon+100μM diazoxide, or 75% xenon+100μM 5-hydroxydecanoate, and then subjected to 1h of global ischaemia and 3h of reperfusion. Pretreatment with 75% xenon significantly improved cardiac function (P<0.01 vs. the I/R group, respectively), limited myocardial infarct size (20.83±2.16%, P<0.01 vs. 35.82±2.14% of the I/R group), reduced cardiac enzyme release (CK-MB, 1.00±0.19IU/L, P<0.01 vs. 0.44±0.14IU/L of the I/R group; LDH, 6.15±1.06IU/L P<0.01 vs. 3.49±0.37IU/L of the I/R group) and decreased apoptosis (6.17±0.56%, P<0.01 vs. 11.31±0.93% of the I/R group). In addition, the mitochondrial structure changes caused by I/R injury were largely prevented by 75% xenon pretreatment (1.37±0.16, P<0.01 vs. 2.32±0.13 of the I/R group). The mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel opener diazoxide did not influence the effect of xenon, but the specific mitoKATP channel blocker 5-hydroxydecanoate completely abolished this effect. Our study demonstrated that pretreatment with 75% xenon protected immature heart from I/R injury, and this protection was probably mediated by preservation of myocardial mitochondria and opening of mitoKATP channel.