Potassium channel openers: clinical applications in ischemic heart disease--overview of clinical efficacy of nicorandil

Vasodilator Therapy: Nitrates and Nicorandil

Nitrates have been used to treat symptoms of chronic stable angina for over 135 years. These drugs are known to activate nitric oxide (NO)-cyclic guanosine-3',-5'-monophasphate (cGMP) signaling pathways underlying vascular smooth muscle cell relaxation, albeit many questions relating to how nitrates work at the cellular level remain unanswered. Physiologically, the anti-angina effects of nitrates are mostly due to peripheral venous dilatation leading to reduction in preload and therefore left ventricular wall stress, and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. By counteracting ischemic mechanisms, short-acting nitrates offer rapid relief following an angina attack. Long-acting nitrates, used commonly for angina prophylaxis are recommended second-line, after beta-blockers and calcium channel antagonists. Nicorandil is a balanced vasodilator that acts as both NO donor and arterial K(+) ATP channel opener. Nicorandil might also exhibit cardioprotective properties via mitochondrial ischemic preconditioning. While nitrates and nicorandil are effective pharmacological agents for prevention of angina symptoms, when prescribing these drugs it is important to consider that unwanted and poorly tolerated hemodynamic side-effects such as headache and orthostatic hypotension can often occur owing to systemic vasodilatation. It is also necessary to ensure that a dosing regime is followed that avoids nitrate tolerance, which not only results in loss of drug efficacy, but might also cause endothelial dysfunction and increase long-term cardiovascular risk. Here we provide an update on the pharmacological management of chronic stable angina using nitrates and nicorandil.

Nicorandil-induced hyperkalemia in a uremic patient

Nicorandil is an antianginal agent with nitrate-like and ATP-sensitive potassium channel activator properties. After activation of potassium channels, potassium ions are expelled out of the cells, which lead to membrane hyperpolarization, closure of voltage-gated calcium channels, and finally vasodilation. We present a uremic case suffering from repeated junctional bradycardia, especially before hemodialysis. After detailed evaluation, nicorandil was suspected to be the cause of hyperkalemia which induced bradycardia. This case reminds us that physicians should be aware of this potential complication in patients receiving ATP-sensitive potassium channel activator.

Nicorandil-associated ulcerations

This leading article refers to the paper by Abdelrazeq AS, Owen C, Smith L, McAdam JG, Pearson HJ, Leveson SH. Nicorandil-associated para-stomal ulceration: case series Eur J Gastroenterol Hepatol 2006; 18:1293-1295. We apologise to all concerned for the dissociation between the two papers, which was due to an administrative error. Nicorandil is used widely in patients with coronary artery disease. Nicorandil is well tolerated with only minor side effects. Nicorandil's association with oral, anal, gastrointestinal ulceration, and more recently para-stomal ulceration has been reported. Medical awareness of nicorandil association with ulcerations should be high to help avoid unnecessary and harmful treatment as only cessation of the drug would heal the ulceration. Nicorandil is an antianginal drug used for the treatment of symptomatic coronary artery disease. It is characterized by an arterial and venous vasodilator effect with dual mechanism of action. Nicorandil is not a first-line agent in the management of angina but it is used in combination with other antianginal medications in stable and unstable angina. It is generally well tolerated with minor side effects such as headache, nausea, flushing and dizziness. The association of nicorandil with mouth and anal ulcers as well as the association with ulceration throughout the gastrointestinal tract has been reported, and recently, an association with para-stomal ulceration has also been described. Medical awareness of the association of nicorandil with ulceration in any part of the gastrointestinal tract should be highlighted among all medical professionals to help avoid delays in withdrawing the treatment and to avoid unnecessary and sometimes invasive and costly interventions.

Gadomer-enhanced MR Imaging in the Detection of Microvascular Obstruction: Alleviation with Nicorandil Therapy

PURPOSE

To evaluate Gadomer-enhanced magnetic resonance (MR) imaging in the quantification of small microvascular obstruction regions and determine if nicroandil alleviates the formation of microvascular obstruction.

MATERIALS AND METHODS

Approval of the institutional committee on animal research was obtained, and this study complied with guidelines for care and use of animals. Rats underwent coronary artery occlusion and reperfusion. After 24 hours, Gadomer-enhanced T1-weighted spin-echo MR imaging was used to define microvascular obstruction in animals in control and nicorandil groups. Sequential MR images obtained at two midventricular levels were acquired to measure microvascular obstruction and ischemically injured regions and monitor diffusive and/or convective transport of Gadomer in microvascular obstruction regions. Two investigators working in consensus and using threshold signal intensity measured differentially enhanced regions. Left-ventricular (LV) end-systolic and end-diastolic MR images obtained at the same two midventricular levels were used to measure regional wall thickening and systolic reduction in LV relative volumes. Agreement and correlation between MR imaging and postmortem data were determined with Bland-Altman and linear regression analyses. Animals were sacrificed 3 minutes after intravenous injection of blue dye.

RESULTS

On Gadomer-enhanced MR images, two differentially enhanced regions were observed in ischemically injured myocardium, namely, the hypoenhanced region and the surrounding hyperenhanced region. Hypoenhanced regions at MR imaging and unstained regions at blue dye administration were identical 3 minutes after administration (17% +/- 1 and 17% +/- 2; P = .6; r = 0.98). In the control group, Gadomer provided a prolonged imaging window (eg, 6 minutes) for accurately quantifying small microvascular obstruction regions. Microvascular obstruction was observed in all animals in the control group and 27% of animals in the nicorandil group. Microvascular obstruction regions were smaller in the nicorandil group (eg, 3% +/- 1) than in the control group (eg, 17% +/- 2) (P < .001). Hyper- and hypoenhanced regions were also smaller (eg, 20% +/- 2) in rats in the nicorandil group than in those in the control group (37% +/- 4, P < .001). Improvement in LV function in the nicorandil group is likely related to alleviation and reduction in infarct size.

CONCLUSION

Gadomer-enhanced MR imaging can be used to quantify small microvascular obstruction regions 24 hours after reperfusion. Intravenous therapy with nicorandil reduces formation of microvascular obstruction regions.

Nicorandil: a review of its use in the management of stable angina pectoris, including high-risk patients

Nicorandil (Adancor, Angicor, Dancor, Nikoril [Europe], Ikorel [Europe and Oceania], Sigmart [Japan, Korea and Taiwan]) is an adenosine triphosphate (ATP)-sensitive potassium (KATP) channel agonist with nitrate-like properties used in the management of stable angina pectoris. With well established monotherapeutic antianginal activity and a beneficial effect (when added to optimal antianginal therapy) on clinical outcomes in high-risk patients with stable angina, twice-daily oral nicorandil is a useful alternative or addition to other antianginal therapy.

Management of stable angina

Ischaemic heart disease may present as a wide variety of clinical entities including unstable or stable angina pectoris, acute myocardial infarction, and occasionally heart failure. Chronic stable angina is a common condition and results in a considerable burden for both the individual and society. The goals in management are (i) treatment of other conditions that may worsen angina; (ii) modification of risk factors and treatment with medications for coronary artery disease to improve outcome; and (iii) effective relief of anginal symptoms. There are limitations to the methods available to risk-stratify patients, and the optimal treatment strategy remains unclear. The benefits of lifestyle modification cannot be over-emphasised, and appropriate attention to modifiable risk factors is paramount. The mortality benefit of lipid lowering treatment and antiplatelet therapy is well proved. However the evidence base for anti-ischaemic therapy is less rigorous, being based mainly on extrapolations from studies of acute coronary syndromes. Angioplasty has been shown to be more effective in relief of symptoms than medical therapy alone, but provides no mortality benefit. Coronary artery bypass surgery, however, has been shown to reduce mortality in patients with severe proximal coronary disease when compared with medical management alone.

Safety of oral nicorandil before coronary artery bypass graft surgery

Nicorandil is a K(ATP) channel opener used to treat angina. It is cardioprotective and a vasodilator. We conducted a prospective, randomized, double-blind, placebo-controlled study to assess oral nicorandil in patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB). Twenty-two patients received nicorandil (10 mg twice a day) and 23 patients received placebo. Haemodynamic data were recorded before induction of anaesthesia (T0), 5 and 20 min after starting mechanical ventilation (T1, T2), before aortic cannulation (T3), after 30 min of CPB (T4), 10 min after CPB (T5) and after 3, 8 and 18 h in the intensive care unit (T6, T7, T8). Serum proteins (creatine kinase metabolite and cardiac troponin I) were measured before and 8 and 18 h after surgery. Haemodynamic values did not differ between the two groups. There was no tachycardia during the study, no significant difference in hypotensive episodes, ST segment changes and no changes in cardiac enzymes. Myocardial infarction after surgery was similar in the two groups. Vasoactive therapy was similar in the two groups. Nicorandil can be continued safely up to premedication without deleterious haemodynamic consequences, but a myocardial protective effect of nicorandil in CABG surgery was not found.

Effects of KRN2391 on ionic currents in rabbit femoral arterial myocytes

The effects of KRN2391, an ATP-sensitive K+ channel opener (KCO) which also acts as a nitrate, on ionic membrane currents in rabbit femoral arterial myocytes were examined. Under whole-cell clamp conditions where cells were superfused with physiological salts solution containing 5.9 mM K+, KRN2391 elicited an outward current at a holding potential of -30 mV. KRN2391-induced current had a reversal potential of -78 mV and was abolished by glibenclamide (glib). KRN2391 was approximately 25 times more potent than nicorandil to activate an ATP-sensitive K+ current (I:(KATP)). On the other hand, 10 microM KRN2391 did not affect either voltage-dependent Ca(2+) or delayed rectifier K+ channel currents. In the inside-out patch configuration, KRN2391 activated 47 pS K+ channels in the presence of nucleotide diphosphates (NDPs) under the symmetrical 140 mM K+ conditions. Glib and intracellular ATP reversibly inhibited the activity of the 47 pS K+ channels. The 47 pS K+ channels activated by KRN2391 are similar in their conductance and other properties to NDP-sensitive K+ channels (K(NDP) channels) described in other smooth muscles and the cloned channels. KRN2391 is a potent activator of the 47 pS K+ channels and the activation can contribute to the KRN2391-induced vasodilation in arterial muscles.

Additive effects of nicorandil on coronary blood flow during continuous administration of nitroglycerin

OBJECTIVES

We examined whether patients with ischemic heart disease (IHD) should be treated with nicorandil, an adenosine triphosphate-sensitive potassium channel opener, in addition to the regular use of nitrates.

BACKGROUND

It has been reported that nicorandil possibly has additive effects on nitroglycerin (NTG) treatment for angina, but the mechanism is not clear.

METHODS

We directly measured anterograde coronary blood flow (CBF) with a Doppler guide wire to examine the effects of intravenous administration of NTG (0.3 mg) and nicorandil (6 mg) during continuous administration of NTG at a sufficient dose (25 microg/min) in subjects with normal and stenotic coronary arteries.

RESULTS

Additional systemic administration of NTG decreased anterograde CBF (normal -19.7%; stenotic -21.2%). In contrast, nicorandil increased anterograde CBF in both normal (54.6%) and stenotic (89.6%) coronary arteries, without the coronary steal phenomenon. There was a tendency toward nicorandil-dilated diameters in the patients with stenotic arteries (p = 0.06). There were no effects of additional administration on pulmonary artery wedge pressure. There was no difference in changes in heart rate and mean aortic blood pressure between NTG and nicorandil therapy.

CONCLUSIONS

These results suggest that in patients treated with nitrates, additional administration of nicorandil is more useful, in terms of increasing CBF, than additional administration of nitrates. Adjunctive use of nicorandil with nitrates may provide the further benefit of myocardial protection and may improve the prognosis of patients with IHD.

Mechanisms of ischemic preconditioning in skeletal muscle

BACKGROUND

Ischemic preconditioning (IP) (one or more cycles each consisting of a short period of ischemia and a short period of reperfusion, before the sustained ischemia) reduces ischemia-related organ damage in heart and skeletal muscle but the underlying mechanisms are not clear. This study was intended to assess the possible involvement of K(ATP) channels and of adenosine receptors in IP of skeletal muscle in a rat model of skeletal muscle ischemia.

MATERIALS AND METHODS

Groups of 8-15 rats were given the following in vivo treatments: ischemia-reperfusion (I-R: 2.5 h tourniquet-induced ischemia of the right hindlimb, then 2 h reperfusion); IP (three cycles of 5 min ischemia, then 5 min reperfusion) before I-R; cromakalim and I-R; glibenclamide, cromakalim, and I-R; glibenclamide, IP, and I-R; [R]-N(6)-[1-methyl-2-phenylethyl]adenosine (R-PIA) and I-R; adenosine and I-R; and glibenclamide, IP, and I-R. Parameters of muscle function (postischemic maximal force, performance, contraction index, and force after 1 min of stimulation) were then assessed in vitro in the extensor digitorum longus muscle.

RESULTS

Pretreatment with either IP or the K(ATP) channel opener cromakalim significantly improved postischemic muscle function. The protective effect of cromakalim was not seen when the K(ATP) channel blocker glibenclamide was added. Glibenclamide, however, did not block IP-induced protection. Pretreatment with the adenosine A(1) receptor agonist 8-(p-sulfophenyl)-theophyllin (8-SPT) or with adenosine did not improve postischemic muscle function. The adenosine receptor agonist did not block IP-induced protection against ischemic damage.

CONCLUSIONS

The results show significant improvements in postischemic skeletal muscle function after IP or cromakalim pretreatment but they do not support a role for K(ATP) channels or for adenosine receptors in IP of skeletal muscle.

Potassium channel openers antagonize the effects of class III antiarrhythmic agents in canine Purkinje fiber action potentials. Implications for prevention of proarrhythmia induced by class III agents

We studied the effects of potassium channel openers (PCOs) on frequency dependent prolongations of action potential duration (APD), triggered activities and oscillatory action potentials (OSC) induced by E-4031 and dofetilide. The action potentials of canine Purkinje fibers were recorded by a glass microelectrode technique. The effects of E-4031 (10(-6)M) as well as that of additional nicorandil (2 x 10(-5) M) on the APD were examined. When abnormal automaticity was observed under perfusion of E-4031 (10(-5) M) or dofetilide (10(-5) M), action potentials were recorded continuously to estimate the sequential effects of additional perfusion of nicorandil (6 x 10(-5) M) or Y-26763 (10(-5) M) on triggered activities and OSC. APD prolongation by E-4031 at slower stimulation rates (cycle lengths > or = 1,000 msec) was suppressed by nicorandil in a dose dependent manner. Both nicorandil and Y-26763 abolished the train of early afterdepolarization (EAD) due to E-4031 or dofetilide with a shifting of the resting membrane potential to a more negative level. PCOs also normalized dofetilide induced abnormal automaticities (EAD, OSC). The antagonistic actions of PCOs on changes in action potential induced by class III antiarrhythmic agents may prevent the development of proarrhythmias produced by these agents.

[Nicorandil: acute hemodynamic effects of 2 different oral doses of a potassium channel opener in patients with coronary heart disease]

BACKGROUND

In medical treatment of angina pectoris the 3 major groups of antianginal agents are nitrates, beta blockers and calcium antagonists. Now a new class of drugs is introduced in the therapy: the potassium channel openers. One of the first potassium channel openers is nicorandil. We examined the acute hemodynamic effects of 2 different oral nicorandil doses in patients with coronary heart disease.

PATIENTS AND METHODS

Twenty patients with angiographic proven coronary heart disease and stable angina pectoris were treated with a dose of 2 x 10 mg Nicorandil on day 1 and 2 x 20 mg Nicorandil on day 2, while being hemodynamically monitored on an intensive care unit with a pulmonary artery catheter.

RESULTS

Through the hemodynamic monitoring a dose dependent, significant reduction of systolic blood pressure was found (6%/9%), while the heart rate increased dose dependently (6%/11%). The rate pressure product as a marker of myocardial oxygen demand did not increase significantly.

CONCLUSION

The oral application of nicorandil causes an acute, dose dependent, significant decrease in systolic blood pressure and induces a reflextachycardia.

KATP channel modulators increase survival rate during coronary occlusion-reperfusion in anaesthetized rats

We investigated the effect of ATP-sensitive K+ channel (KATP) openers (pinacidil and cromakalim), and a KATP blocker (glibenclamide) on reperfusion-induced arrhythmias in pentobarbitone-anaesthetized rats. Arrhythmias were induced by reperfusion following a 6 min ligation of the left main coronary artery. Rats were pretreated with pinacidil (0.1 or 0.3 mg/kg), or cromakalim (28 or 56 micrograms/kg), or glibenclamide (5 mg/kg), or vehicle. Pinacidil and cromakalim produced dose-related reductions in blood pressure. Pinacidil (0.1 mg/kg) and cromakalim (56 micrograms/kg) significantly decreased the incidence of reperfusion-induced ventricular fibrillation and increased survival. Glibenclamide did not decrease ventricular fibrillation incidence, yet improved survival by increasing the possibility of recovery from ventricular fibrillation. The present study suggests that both opening and blocking KATP channels may increase survival during coronary occlusion and reperfusion in anaesthetized rats.