Nicorandil reversed homocysteine-induced coronary microvascular dysfunction via regulating PI3K/Akt/eNOS pathway.

OBJECTIVE: Nicorandil exerts a protective effect against coronary microvascular dysfunction in acute myocardial infarction (AMI) patients. However, the mechanism and effect of nicorandil in hyperhomocysteinemia (HHcy) AMI patients remain unclear. METHODS: C57/BL6 mice with mild to moderate HHcy and human coronary artery endothelial cells (HCAECs) cotreated with HHcy (1 mmol/L) for 24 h and hypoxia for 6 h were selected as models. Small animal ultrasound detection was used to compare cardiac function. CD31 immunofluorescence staining and tomato lectin staining were used to assess the number of microcirculation changes in vivo. MTT, tube formation and western blotting assays were used to evaluate the effect of nicorandil on HCAECs and the PI3K/Akt/eNOS pathway. RESULTS: The results showed that nicorandil improved cell viability and p-PI3K/PI3K, p-Akt/Akt, and p-eNOS/eNOS expression in the vitro HHcy and hypoxia models. The beneficial effects of nicorandil on HCAECs could be inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the nitric oxide synthase (NOS) inhibitor L-NAME. In vivo, nicorandil improved the left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) in the post-HHcy + MI model, and the levels of CD31 and tomato lectin expression were higher in the nicorandil treatment group. The effectiveness of nicorandil was inhibited in the PI3K and L-NAME groups. CONCLUSION: The results suggest that nicorandil improves Hcy-induced coronary microvascular dysfunction through the PI3K/Akt/eNOS signalling pathway.

Neuroprotective effect of nicorandil through inhibition of apoptosis by the PI3K/Akt1 pathway in a mouse model of deep hypothermic low flow.

OBJECTIVE: Nicorandil exerts a protective effect on ischemia-reperfusion (I/R) injury in the brain and kidney through anti-apoptotic mechanisms. However, the mechanism by which nicorandil protects against I/R injury induced by deep hypothermic low flow (DHLF) remains unclear. METHODS: We used a cerebral I/R model induced by DHLF to determine the neuroprotective effects and possible mechanisms of nicorandil. RESULTS: Hematoxylin-eosin (HE) staining and in situ terminal deoxynucleotidyl transferase UTP nick end labeling (TUNEL) assay were used to detect changes in cell morphology and the number of apoptotic cells in hippocampus, respectively. The apoptotic regulators including Bcl-2, Bax, Akt, and p-Akt (the active, phosphorylated form of Akt) were examined by Western blot (WB). Histopathological findings showed that nicorandil significantly alleviated morphological damage in hippocampal and reduced the number of TUNEL-positive nuclei induced by DHLF. Nicorandil also increased the expression of Bcl-2 and decreased the expression of Bax, while increasing p-Akt level. Consistent with these results, nicorandil-mediated neuroprotection was reduced in the Akt1+/- mutant mice and inhibited by LY294002, a PI3K inhibitor. CONCLUSIONS: These findings showed that nicorandil provides a neuroprotective role in DHLF-induced I/R injury by inhibiting apoptosis via activation of the PI3K/Akt1 signaling pathway.

Nicorandil preserves myocardial function following brain death in rats by mitochondrial adenosine triphosphate-sensitive potassium channel-dependent mechanism.

OBJECTIVE: Interventions to preserve myocardial function after brain death may increase the donor pool for heart transplantation. The present study using a brain death model of rats was designed to examine the protective potential of nicorandil, an adenosine triphosphate-sensitive potassium channel opener, on myocardial function after brain death. METHODS: Rats were anesthetized with sevoflurane. A Fogarty catheter was placed intracranially for induction of brain death. The conductance catheter was inserted into the left ventricle for measurement of myocardial function. Rats were assigned randomly to two groups, one receiving nicorandil before brain death and the other receiving saline (control group). Mean blood pressure, heart rate, maximal rate of rise of left-ventricular pressure and ejection fraction were measured every 30 min for 6h after brain death. The same protocol was performed in the presence of nicorandil combined with 5-hydroxydecanoic acid, a mitochondrial adenosine triphosphate-sensitive potassium channel inhibitor. RESULTS: Nicorandil temporally, but significantly, improved ejection fraction compared with the control group. Furthermore, 5-hydroxydecanoic acid inhibited the effects of nicorandil. CONCLUSIONS: Nicorandil was effective to preserve ejection fraction after brain death, and myocardial mitochondrial adenosine triphosphate-sensitive potassium channels may be involved in this action.

The effect of nicorandil on ischemia-reperfusion injury in a porcine total hepatic vascular exclusion model.

BACKGROUND: We evaluated the effectiveness of nicorandil, which has both K(ATP) channel opener-like and nitrate-like properties, in liver ischemia-reperfusion (IR) injury using a porcine total hepatic vascular exclusion (THVE) model. METHODS: Mexican hairless pigs weighing 25-55 kg were used in this study. The animals were divided into three groups. In the nicorandil group (n = 6), a 100 µg/kg bolus of nicorandil was injected intravenously 30 min before the ischemia, and then a continuous infusion (10 µg/kg/min) was administered intravenously for 30 min until just before the ischemia. In the control group (n = 6), a saline solution was injected in the same manner. In the glibenclamide group (n = 6), glibenclamide (0.1 mg/kg), which closes the K(ATP) channel gate, was orally administered 180 min before the hepatic ischemia, and then nicorandil was injected in the same manner as in the nicorandil group. THVE was performed for 120 min, and animals were observed until 360 min after reperfusion. Serum AST and LDH levels, hepatic tissue blood flow (HTBF), and histologic analyses were compared among the three groups. RESULTS: Serum AST and LDH levels in the nicorandil group were significantly lower than in the other two groups after reperfusion, while no significant difference was observed between the control and the glibenclamide groups. HTBF in the nicorandil group was also significantly higher than in the other two groups after reperfusion, while no significant difference was observed between the control and glibenclamide groups. Additionally, histopathologic analyses revealed that the hepatic tissue was better maintained in the nicorandil group than in the other two groups. CONCLUSION: Our results using a porcine THVE model suggest that nicorandil inhibits hepatic IR injury. The K(ATP) channel-opener aspect of nicorandil might be primarily responsible for the hepatoprotective effect.

Inhibitory effect of nicorandil on the contraction of isolated human urinary bladder detrusor muscle.

This study was performed to determine whether the antianginal drug nicorandil relaxes isolated human detrusor muscle. Ten strips of detrusor muscle obtained from 10 pediatric patients who underwent surgery on the urinary bladder were contracted with 80 mM potassium chloride (KCl) before and after incubation with four concentrations of nicorandil (100, 200, 400 and 800 microM). The percent inhibition by nicorandil of the height and area under the curve (AUC) of KCl-induced contractions of the detrusor strips was calculated. The effect of glibenclamide (10 microM) on nicorandil (800 microM)-induced inhibition of KCl-induced detrusor contractions was also studied. Nicorandil caused a concentration-dependent inhibition of KCl-induced contractions of the detrusor strips. The percent inhibition of the height of KCl-induced contractions of the detrusor by nicorandil was significant at concentrations of 200, 400 and 800 microM. The percent inhibition of the AUC for KCl-induced detrusor contractions was significant at all four concentrations of nicorandil used. Glibenclamide reversed the inhibitory effect of 800 microM nicorandil on KCl-induced detrusor contractions. These results suggest that nicorandil inhibits KCl-induced contractions of isolated human detrusor muscle and may therefore be useful in clinical conditions requiring detrusor muscle relaxation.

The nicorandil-induced vasodilation in humans is inhibited by miconazole.

Nicorandil, N-(2-hydroxyethyl)-nicotinamide nitrate, exerts its vasodilatory effects by opening ATP-sensitive potassium (K-ATP) channels and by acting as the exogenous nitric oxide (NO). It is not clear, however, whether the actions of other endothelium-dependent vasodilators, such as NO, endothelium-derived hyperpolarizing factor (EDHF), and prostaglandins, contribute to nicorandil-induced vasodilation in the vasculature in humans. We evaluated forearm blood flow (FBF) response to intraarterial infusion of nicorandil alone and in the presence of glibenclamide, a K-ATP channel inhibitor, N(G)-monomethyl-L-arginine, an NO synthase inhibitor, indomethacin, a cyclooxygenase inhibitor, or miconazol, a cytochrome P-450 inhibitor, in 24 healthy male subjects. FBF was measured using strain-gauge plethysmography. Infusion of nicorandil significantly increased the FBF response in a dose-dependent manner. Intraarterial infusion of glibenclamide attenuated nicorandil-induced vasodilation (160.9 +/- 21.2% versus 90.2 +/- 19.4%, P < 0.01), and miconazole also attenuated the FBF response to nicorandil (160.9 +/- 21.2% versus 66.1 +/- 9.2%, P < 0.001). N-monomethyl-L-arginine or indomethacin did not alter the FBF response to nicorandil. These findings suggest that nicorandil causes vasodilation in forearm circulation in humans, at least in part through a pathway that is dependent on K-ATP channels and cytochrome P-450, but not on endogenous NO and prostaglandins. EDHF may contribute to nicorandil-induced vasodilation in humans.

Myocardial protection from either ischaemic preconditioning or nicorandil is not blocked by gliclazide.

OBJECTIVE: We compared the effects of two sulphonylureas, glibenclamide and gliclazide, on ischaemic preconditioning (IPC) and nicorandil-induced protection in the in-vivo rat. We also studied the effects of these agents on the membrane potential of isolated rat mitochondria. METHODS: Anaesthetised male Sprague-Dawley rats were used in an open chest model of myocardial infarction. Animals were randomly assigned to receive one of the following drugs: (1) saline control, (2) glibenclamide, 0.3 mg/kg, or (3) gliclazide, 1 mg/kg i.v. bolus. Each was then further randomised to one of the following treatments: (a) control, (b) IPC (consisting of 2 x 5 mins of regional ischaemia and 5 minutes reperfusion) or (c) nicorandil (50 ug/kg/min i.v). infusion. Each group then underwent 25 mins regional ischaemia and 2 hrs reperfusion. Infarct to risk zone ratio (%) was calculated by computerised planimetry of tetrazolium stained heart slices. The membrane potential of mitochondria isolated from rat ventricles was measured using flow cytometry. Comparisons were made between groups in control medium, nicorandil alone, and nicorandil with either glibenclamide or gliclazide. RESULTS: Infarct size was significantly reduced with IPC (15.0 +/- 1.1%,) and nicorandil (25.5 +/- 4.2%), versus control (44.1 +/- 3.2%), p < 0.005. Glibenclamide abolished IPC (40.8 +/- 4.6%) and nicorandil-induced protection completely (39.5 +/- 5.1%). Gliclazide had no adverse effect on IPC (20.4 +/- 1.9%) or nicorandil-induced protection (23.6 +/- 2.2%), p < 0.005. Nicorandil caused a partial depolarisation of the mitochondrial membrane potential (-14.92 +/- 2.34%), which was abolished by glibenclamide (+2.03 +/- 0.53%), but not gliclazide (-16.47 +/- 3.36%), p < 0.01. CONCLUSION: Both IPC and nicorandil-induced protection are abolished by glibenclamide but not gliclazide in-vivo. These results may have important clinical implications in type II diabetic patients at risk of acute coronary syndromes.

Potassium channel openers inhibit ATP-induced cytosolic free calcium increase in cultured rabbit aortic smooth muscle cells.

AIM: To study the effects of potassium channel openers (PCO) on cytosolic free calcium ([Ca2+]i) changes and their possible mechanisms in vascular smooth muscle cells (VSMC). METHODS: Cultured rabbit aortic VSMC were treated with Fura-2 AM 2.5 mumol.L-1 at 37 degrees C for 50 min. The PCO were pinacidil (Pin), nicorandil (Nic), lemakalim (Lem), and RP 49356 (RP). [Ca2+]i level was measured by fluorospectrometer. RESULTS: [Ca2+]i increase induced by K+ 30 mmol.L-1 was weakly inhibited by Pin, Nic, Lem, and RP (441 +/- 23, 455 +/- 48, 451 +/- 22, 370 +/- 31 vs 544 +/- 40 nmol.L-1, P < 0.01). ATP (0.1 mmol.L-1)-induced peak and sustained [Ca2+]i increase were inhibited by these agents in a concentration-dependent manner. The effects of Pin, Lem, and RP were completely canceled (peak phase: 549 +/- 39, 540 +/- 30, 564 +/- 13 vs 541 +/- 39 nmol.L-1; sustained phase: 413 +/- 25, 364 +/- 16, 377 +/- 11 vs 380 +/- 8 nmol.L-1), but that of Nic was only partially blocked (peak phase: 453 +/- 31 vs 541 nmol.L-1; sustained phase: 348 +/- 19 vs 380 +/- 8 nmol.L-1, P < 0.01) by glibenclamide (Gli, 10 mumol.L-1). Pretreated with the Pin, Nic, Lem, and RP (10 mumol.L-1), the peak [Ca2+]i elevation induced by ATP was reduced in the Ca(2+)-free solution (129 +/- 17, 142 +/- 21, 136 +/- 14, 114 +/- 9 vs 258 +/- 32 nmol.L-1, P < 0.01). CONCLUSION: Pin, Nic, Lem, and RP inhibited ATP-induced [Ca2+]i increase, associated with decreases of both Ca2+ release from intracellular store and Ca2+ influx from extracellular store.