Synthesis, antinociceptive activity and pharmacokinetic profiles of nicorandil and its isomers

Nicorandil restores endothelial cell Kir6.2 expression to alleviate neuropathic pain in mice after chronic constriction injury

The clinical management of neuropathic pain (NP) remains a significant challenge, as current pharmacological treatments do not fully meet clinical needs. Nicorandil, a potassium ATP channel agonist widely used in cardiovascular medicine, has recently been shown to have significant potential for analgesia. This study aimed to investigate the effects and mechanisms of nicorandil in a chronic constriction injury (CCI) mouse model. Nicorandil significantly alleviated pain hypersensitivity and reduced neuronal injury in the sciatic nerve (SN) and dorsal root ganglion (DRG) post-CCI. Nicorandil primarily affected endothelial cells and Schwann cells in the sciatic nerve, restoring the expression of the KATP channel subunit Kir6.2. Furthermore, nicorandil attenuated the hypoxia-induced apoptosis program in sciatic nerve endothelial cells, leading to reduced expression of apoptotic proteins, which provided significant endothelial protection, improved blood-nerve barrier leakage, and decreased the release of DRG inflammatory factors and pain neurotransmitter substance P. In vitro, nicorandil attenuated the apoptosis of human umbilical vein endothelial cells (HUVECs) in a hypoxic environment while maintaining cellular functions. In addition, administering the KATP channel inhibitor glibenclamide in vitro further confirmed the crucial role of Kir6.2 in reducing endothelial hypoxic stress, as confirmed by transmission electron microscopy and behavioural experiments. Overall, these findings indicate that nicorandil significantly ameliorates CCI-induced NP in mice by targeting Kir6.2 in sciatic nerve endothelial cells, thus inhibiting pain sensitization.

Nicorandil antiallodynic activity in a model of neuropathic pain is associated with the activation of ATP-dependent potassium channels and opioidergic pathways, and reduced production of cytokines and neutrophils recruitment in paw, sciatic nerve, and dorsal root ganglia

BACKGROUND

Recently, we demonstrated that nicorandil inhibits mechanical allodynia induced by paclitaxel. In the present study, we evaluated the effect induced by nicorandil in a model of neuropathic pain induced by chronic constriction injury (CCI) in mice. We also investigated putative mechanisms underlying such an effect.

METHODS

CCI was induced by three ligatures of the left sciatic nerve. Mechanical allodynia was evaluated by measuring the paw withdrawal threshold with an electronic von Frey apparatus. Concentrations of cytokines and myeloperoxidase activity were determined in the paw tissue, sciatic nerve, and dorsal root ganglia (DRG).

RESULTS

Oral administration of two doses of nicorandil (150 mg/kg po), but not equimolar doses of nicotinamide or nicotinic acid, attenuated mechanical allodynia induced by CCI. Nicorandil activity was reduced by previous administration of glibenclamide (40 mg/kg) or naltrexone (5 mg/kg or 10 mg/kg). Two doses of nicorandil (150 mg/kg, po) reduced tumor necrosis factor-α, interleukin-1β and interleukin-6, but not CXCL-1, concentrations in the paw tissue of CCI mice. Two doses of nicorandil (150 mg/kg, po) reduced concentrations of all these mediators in the sciatic nerve and DRG. Two doses of nicorandil (150 mg/kg, po) also reduced the myeloperoxidase activity in the paw tissue, sciatic nerve, and DRG.

CONCLUSIONS

Nicorandil exhibits antiallodynic activity in a model of neuropathic pain induced by CCI. Inhibition of cytokines production and reduction of neutrophils recruitment in paw tissue, sciatic nerve, and DRG as well as activation of ATP-dependent potassium channels and opioidergic pathways, underlie nicorandil antiallodynic activity.

Overcoming Challenges in O-Nitration: Selective Alcohol Nitration Deploying N,6-Dinitrosaccharin and Lewis Acid Catalysis

Nitrate esters hold pivotal roles in pharmaceuticals, energetic materials, and atmospheric processes, motivating the development of efficient synthesis routes. Here, we present a novel catalytic method for the synthesis of nitrates via the direct O-nitration of alcohols, addressing limitations of current traditional methods. Leveraging bench-stable and recoverable N,6-dinitrosaccharin reagent, our catalytic strategy employs magnesium triflate to achieve mild and selective O-nitration of alcohols, offering broad substrate scope and unprecedentedly large functional group tolerance (e.g. alkenes, alkynes, carbonyls). DFT mechanistic studies reveal a dual role of the magnesium catalyst in the activation of both the nitrating reagent and the alcohol substrate. They also unveil a barrierless proton transfer upon formation of a widely-accepted - yet elusive in solution - nitrooxonium ion intermediate. Overall, our work contributes to the development of mild, selective, and sustainable approaches to nitrates synthesis, with potential applications in drug discovery, materials science, and environmental chemistry.

Nicorandil/ morphine crosstalk accounts for antinociception and hepatoprotection in hepatic fibrosis in rats: Distinct roles of opioid/cGMP and NO/KATP pathways

Previous report indicated that nicorandil potentiated morphine antinociception and attenuated hepatic injury in liver fibrotic rats. Herein, the underlying mechanisms of nicorandil/morphine interaction were investigated using pharmacological, biochemical, histopathological, and molecular docking studies. Male Wistar rats were injected intraperitoneally (i.p.) with carbon tetrachloride (CCl4, 40%, 2 ml/kg) twice weekly for 5 weeks to induce hepatic fibrosis. Nicorandil (15 mg/kg/day) was administered per os (p.o.) for 14 days in presence of the blockers; glibenclamide (KATP channel blocker, 5 mg/kg, p.o.), L-NG-nitro-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor, 15 mg/kg, p.o.), methylene blue (MB, guanylyl cyclase inhibitor, 2 mg/kg, i.p.) and naltrexone (opioid antagonist, 20 mg/kg, i.p.). At the end of the 5th week, analgesia was evaluated using tail flick and formalin tests along with biochemical determinations of liver function tests, oxidative stress markers and histopathological examination of liver tissues. Naltrexone and MB inhibited the antinociceptive activity of the combination. Furthermore, combined nicorandil/morphine regimen attenuated the release of endogenous peptides. Docking studies revealed a possible interaction of nicorandil on µ, κ and δ opioid receptors. Nicorandil/morphine combination protected against liver damage as evident by decreased liver enzymes, liver index, hyaluronic acid, lipid peroxidation, fibrotic insults, and increased superoxide dismutase activity. Nicorandil/morphine hepatoprotection and antioxidant activity were inhibited by glibenclamide and L-NAME but not by naltrexone or MB. These findings implicate opioid activation/cGMP versus NO/KATP channels in the augmented antinociception, and hepatoprotection, respectively, of the combined therapy and implicate provoked cross talk by nicorandil and morphine on opioid receptors and cGMP signaling pathway. That said, nicorandil/morphine combination provides a potential multitargeted therapy to alleviate pain and preserve liver function.

Nicorandil Exerts Anticonvulsant Effects in Pentylenetetrazol-Induced Seizures and Maximal-Electroshock-Induced Seizures by Downregulating Excitability in Hippocampal Pyramidal Neurons

N-(2-hydroxyethyl) nicotinamide nitrate (nicorandil), a nitrate that activates adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels, is generally used in the treatment of angina and offers long-term cardioprotective effects. It has been reported that several K_ATP channel openers can effectively alleviate the symptoms of seizure. The purpose of this study was to investigate the improvement in seizures induced by nicorandil. In this study, seizure tests were used to evaluate the effect of different doses of nicorandil by analysing seizure incidence, including minimal clonic seizure and generalised tonic-clonic seizure. We used a maximal electroshock seizure (MES) model, a metrazol maximal seizure (MMS) model and a chronic pentylenetetrazol (PTZ)-induced seizure model to evaluate the effect of nicorandil in improving seizures. Each mouse in the MES model was given an electric shock, while those in the nicorandil group received 0.5, 1, 2, 3 and 6 mg/kg of nicorandil by intraperitoneal injection, respectively. In the MMS model, the mice in the PTZ group and the nicorandil group were injected subcutaneously with PTZ (90 mg/kg), and the mice in the nicorandil group were injected intraperitoneally with 1, 3 and 5 mg/kg nicorandil, respectively. In the chronic PTZ-induced seizure model, the mice in the PTZ group and the nicorandil group were injected intraperitoneally with PTZ (40 mg/kg), and the mice in the nicorandil group were each given 1 and 3 mg/kg of PTZ at a volume of 200 nL. Brain slices containing the hippocampus were prepared, and cell-attached recording was used to record the spontaneous firing of pyramidal neurons in the hippocampal CA1 region. Nicorandil (i.p.) significantly increased both the maximum electroconvulsive protection rate in the MES model and the seizure latency in the MMS model. Nicorandil infused directly onto the hippocampal CA1 region via an implanted cannula relieved symptoms in chronic PTZ-induced seizures. The excitability of pyramidal neurons in the hippocampal CA1 region of the mice was significantly increased after both the acute and chronic administration of PTZ. To a certain extent, nicorandil reversed the increase in both firing frequency and proportion of burst spikes caused by PTZ (P < 0.05). Our results suggest that nicorandil functions by downregulating the excitability of pyramidal neurons in the hippocampal CA1 region of mice and is a potential candidate for the treatment of seizures.

Nicorandil reduces morphine withdrawal symptoms, potentiates morphine antinociception, and ameliorates liver fibrosis in rats

AIMS

Chronic liver disease (CLD) is a serious medical condition affecting patients globally and pain management poses a unique challenge. ATP-sensitive potassium channels (K_ATP) are expressed in nociceptive neurons and hepatic cells. We tested the hypothesis whether morphine and nicorandil, K_ATP channel opener, alone and in combination possess hepatoprotective, antinociceptive effect and alter morphine physical dependence.

MAIN METHODS

Intraperitoneal injection (i.p.) of carbon tetrachloride (CCl₄) induced liver fibrosis in male Wistar rats. Nicorandil (15 mg/kg/day) was administered per os for two weeks. Morphine (3.8, 5, 10 mg/kg, i.p.) was administered prior to antinociception testing in tail flick and formalin tests. Morphine physical dependence following naloxone injection, fibrotic, oxidative stress markers, and liver histopathology were assessed.

KEY FINDINGS

Morphine alone, produced insignificant changes of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), hyaluronic acid (HA), hepatic hydroxyproline (Hyp), malondialdehyde (MDA), and superoxide dismutase (SOD) levels and exerted significant antinociception in the pain models. Nicorandil alone protected against liver damage (decreased serum ALT, AST, HA, hepatic Hyp, MDA, increased SOD levels, improved fibrosis scores). Nicorandil/morphine combination produced remarkable hepatoprotection and persistent analgesia compared to morphine alone as evidenced by reduced (EC50) of morphine. Nicorandil augmented morphine analgesia and markedly decreased withdrawal signs in morphine-dependent rats.

SIGNIFICANCE

The data showed for the first time, the hepatoprotection and augmented antinociception mediated by nicorandil/morphine combination in liver fibrosis via antioxidant and antifibrotic mechanisms. Nicorandil ameliorated withdrawal signs in morphine dependence in CLD. Thus, combining nicorandil/morphine provides a novel treatment strategy to ameliorate hepatic injury, potentiate antinociception and overcome morphine-induced physical dependence in liver fibrosis.

Role of nitric oxide donor in methotrexate-induced testicular injury via modulation of pro-inflammatory mediators, eNOS and P-glycoprotein

Methotrexate (MTX) is a widely used chemotherapeutic agent but its clinical use is challenged with different forms of toxicities including testicular injury. The aim of the current study was to evaluate the potential protective effect of potassium channel opener, nicorandil (NIC) (3 and 10 mg/kg/day) on MTX-induced testicular injury in a rat model. Rats were randomly divided into four groups (nine rats each) and treated for 2 weeks as follows: (I) normal control (CON group) received vehicle, (II) model group (MTX group) given MTX (20 mg/kg) single intraperitoneal (i.p.) injection dose on 11th day, (III) MTX + NLD group treated with NIC (3 mg/kg/day) orally for 2 weeks and MTX (20 mg/kg) single i.p. dose on 11th day, and (IV) MTX + NHD group treated with NIC (10 mg/kg/day) orally for 2 weeks and MTX (20 mg/kg) single i.p. injection on the 11th day. The testicular injury was assessed biochemically via serum testosterone, total antioxidant capacity, testicular oxidative stress parameters, P-glycoprotein, tumor necrosis factor-alpha, and interleukin-1β. Furthermore, histopathological evaluation, endothelial nitric oxide synthase (eNOS) immunoexpression, and detection of p53 expression level using Western blotting were performed. Results showed that MTX induced testicular injury which was proved by both biochemical and histopathological evaluations. Our results concluded that NIC pretreatment attenuated MTX-induced testicular injury via significantly increased eNOS immunoexpression, antiapoptotic, anti-inflammatory, and antioxidant properties. Interestingly, NIC high dose is more protective than low dose.

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.

Vascular calcification abrogates the nicorandil mediated cardio-protection in ischemia reperfusion injury of rat heart

The present study was aimed to determine the efficacy of nicorandil in treating cardiac reperfusion injury with an underlying co-morbidity of vascular calcification (VC). Adenine diet was used to induce VC in Wistar rat and the heart was isolated to induce global ischemia reperfusion (IR) by Langendorff method, with and without the nicorandil (7.5mg/kg) pre-treatment and compared with those fed on normal diet. The adenine-treated rats displayed abnormal ECG changes and altered mitochondrial integrity compared to a normal rat heart. These hearts, when subjected to IR increased the infarct size, cardiac injury (measured by lactate dehydrogenase and creatine kinase activity in the coronary perfusate) and significantly altered the hemodynamics compared to the normal perfused heart. Nicorandil pretreatment in rat fed on normal diet enhanced the hemodynamics significantly (P<0.05) along with a substantial reduction in the mitochondrial dysfunction (measured by high ADP to oxygen consumption ratio, respiratory control ratio, enzyme activities and less swelling behavior) when subjected to IR. However, this cardio-protective effect of nicorandil was absent in rat heart with underlying calcification. Our results suggest that, the protective effect of nicorandil, a known mitochondrial ATP linked K⁺ channel opener, against myocardial reperfusion injury was confined to normal rat heart.

Neuroprotective Effects of Nicorandil in Chronic Cerebral Hypoperfusion-Induced Vascular Dementia

BACKGROUND

Ischemia-induced chronic cerebral hypoperfusion (CCH) is associated with reduced cerebral blood flow and vascular dementia (VaD). Brain mitochondrial potassium (adenosine triphosphate-sensitive potassium [K_ATP]) channels have a beneficial role in various brain conditions. The utility of K_ATP channels in CCH-induced VaD is still unknown. The aim of this study is to investigate the role of nicorandil, a selective K_ATP channel opener, in CCH-induced VaD.

METHODS

The method of 2-vessel occlusion (2VO) was used to induce CCH in mice. Cognitive impairment was assessed using Morris water maze. Serum nitrosative stress (nitrite/nitrate), brain cholinergic dysfunction (acetylcholinesterase [AChE] activity), brain oxidative stress (thiobarbituric acid reactive substances, glutathione [GSH], catalase [CAT], and superoxide dismutase [SOD]), inflammation (myeloperoxidase [MPO]), and infarct size (2,3,5-triphenyltetrazolium chloride staining) were assessed.

RESULTS

2-vessels-occluded animals have shown significant cognitive impairment, serum nitrosative stress (reduced nitrite/nitrate), cholinergic dysfunction (increased brain AChE activity), and increased brain oxidative stress (reduction in GSH content and SOD and CAT activities with a significant increase in lipid peroxidation), along with a significant increase in MPO activity and infarct size. However, nicorandil treatment has significantly attenuated various CCH-induced behavioral and biochemical impairments.

CONCLUSIONS

It may be said that 2VO provoked CCH leading to VaD, which was attenuated by the treatment of nicorandil. So, modulation of K_ATP channels may provide benefits in CCH-induced VaD.