Nicotinic Acetylcholine Receptor Agonist Research Articles

Absolute Configuration and Pharmacology of the Poison Frog Alkaloid Phantasmidine.

Phantasmidine, a rigid congener of the well-known nicotinic acetylcholine receptor agonist epibatidine, is found in the same species of poison frog ( Epipedobates anthonyi). Natural phantasmidine was found to be a 4:1 scalemic mixture, enriched in the (2a R,4a S,9a S) enantiomer by chiral-phase LC-MS comparison to the synthetic enantiomers whose absolute configurations were previously established by Mosher's amide analysis. The major enantiomer has the opposite S configuration at the benzylic carbon to natural epibatidine, whose benzylic carbon is R. Pharmacological characterization of the synthetic racemate and separated enantiomers established that phantasmidine is ∼10-fold less potent than epibatidine, but ∼100-fold more potent than nicotine in most receptors tested. Unlike epibatidine, phantasmidine is sharply enantioselective in its activity and the major natural enantiomer whose benzylic carbon has the 4a S configuration is more active. The stereoselective pharmacology of phantasmidine is ascribed to its rigid and asymmetric shape as compared to the nearly symmetric conformations previously suggested for epibatidine enantiomers. While phantasmidine itself is too toxic for direct therapeutic use, we believe it is a useful platform for the development of potent and selective nicotinic agonists, which may have value as pharmacological tools.

Muscarinic and nicotinic acetylcholine receptor agonists: current scenario in Alzheimer's disease therapy

Alzheimer's disease (AD) has become the primary cause of dementia. It shows a progressive cognitive dysfunction with degenerating neurons. Acetylcholine receptors (AChRs) propagate the cognitive ability and it consists of two primary members namely muscarinic (mAChRs) and nicotinic receptors (nAChRs). Where mAChRs is G-protein coupled receptor, (nAChRs) are ligand-gated ion channels. The conventional therapeutic regimen for AD consists of three acetylcholinestearse inhibitors while a single NMDA receptor antagonist. Researchers around the globe are developing new and modifying the existing AChRs agonists to develop lead candidates with lower risk to benefit ratio where benefits clearly outweigh the adverse events. We have searched PubMed, MEDLINE, Google scholar, Science Direct and, Web of Science with keywords "Muscarinic/Nicotinic acetylcholine receptor, agonists and, AD". The literature search included articles written in English. Scientific relevance for clinical studies, basic science studies is eligibility criteria for articles referred in this paper. M1 is the primary muscarinic subtype while α7 is the primary nAChR subtype that is responsible for cognition and memory and these two have been the major recent experimental targets for mAChR agonist strategy. The last cholinergic receptor agonist to enter phase 3 trial was EVP-6124 (Enceniclin) but was withdrawn due to severe gastrointestinal adverse effects. We aim to present an overview of the efforts and achievements in targeting Muscarinic and Nicotinic acetylcholine receptor in the current review for development of better AD therapeutics.

Multiple Discriminative Stimulus Effects of the α4β2*‐Selective Agonists Ispronicline and Metanicotine

Ispronicline and metanicotine are selective ligands at central nicotinic acetylcholine α4β2* receptors (Gao et al. Pain 2010: 149, 33; Grady et al. Neuropharmacol 2010: 58, 1054). In our study, a group of rats was trained to discriminate the stimulus properties of the nicotinic acetylcholine receptor (nAChR) agonist nicotine, and a separate group of rats was trained to discriminate the stimulus properties of the muscarinic acetylcholine receptor agonist arecoline. Ispronicline and metanicotine produced full dose‐related selection of the drug‐appropriate response option in both the nicotine‐trained and the arecoline‐trained rats. The nAChR antagonist mecamylamine blocked the discriminative stimulus effects of ispronicline and metanicotine in both groups of rats, as did the α4β2*‐selective antagonist, dihydro‐beta‐erythroidine. Neither antagonist blocked the discriminative stimulus effects of arecoline in these experiments. These data raise the possibility that ispronicline, metanicotine and similar drugs may have novel effects and require a more extensive characterization of receptor activities, through both agonists and antagonistsSupport or Funding InformationResearch supported by NIMH Grant 107499This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inhibition of peripheral macrophages by nicotinic acetylcholine receptor agonists suppresses spinal microglial activation and neuropathic pain in mice with peripheral nerve injury

BackgroundNeuro–immune interaction underlies chronic neuroinflammation and aberrant sensory processing resulting in neuropathic pain. Despite the pathological significance of both neuroinflammation-driven peripheral sensitization and spinal sensitization, the functional relationship between these two distinct events has not been understood.MethodsIn this study, we determined whether inhibition of inflammatory macrophages by administration of α4β2 nicotinic acetylcholine receptor (nAChR) agonists improves neuropathic pain and affects microglial activation in the spinal dorsal horn (SDH) in mice following partial sciatic nerve ligation (PSL). Expression levels of neuroinflammatory molecules were evaluated by RT-qPCR and immunohistochemistry, and PSL-induced mechanical allodynia was defined by the von Frey test.ResultsFlow cytometry revealed that CD11b+ F4/80+ macrophages were accumulated in the injured sciatic nerve (SCN) after PSL. TC-2559, a full agonist for α4β2 nAChR, suppressed the upregulation of interleukin-1β (IL-1β) in the injured SCN after PSL and attenuated lipopolysaccharide-induced upregulation of IL-1β in cultured macrophages. Systemic (subcutaneous, s.c.) administration of TC-2559 during either the early (days 0–3) or middle/late (days 7–10) phase of PSL improved mechanical allodynia. Moreover, local (perineural, p.n.) administration of TC-2559 and sazetidine A, a partial agonist for α4β2 nAChR, during either the early or middle phase of PSL improved mechanical allodynia. However, p.n. administration of sazetidine A during the late (days 21–24) phase did not show the attenuating effect, whereas p.n. administration of TC-2559 during this phase relieved mechanical allodynia. Most importantly, p.n. administration of TC-2559 significantly suppressed morphological activation of Iba1+ microglia and decreased the upregulation of inflammatory microglia-dominant molecules, such as CD68, interferon regulatory factor 5, and IL-1β in the SDH after PSL.ConclusionThese findings support the notion that pharmacological inhibition of inflammatory macrophages using an α4β2 nAChR agonist exhibit a wide therapeutic window on neuropathic pain after nerve injury, and it could be nominated as a novel pharmacotherapy to relieve intractable pain.

Nicotine dependence and neuropsychotic effects of varenicline

Varenicline is a partial agonist of nicotinic acetylcholine receptors for the therapy of nicotine addiction. The efficacy and safety of the use of varenicline in the treatment of nicotine dependence have been demonstrated in clinical trial EAGLES. These studies describe adverse reactions such us mental disorders: depression, suicidal thoughts, suicidal behavior. However, data on the increase in the incidence of these adverse reactions during longer treatment with varenicline was not obtained. In 2016, the FDA has been presented with information about the risk of development the following serious neuropsychiatric adverse reactions on the using of varenicline: depression, manic syndrome, psychosis, hallucinations, delusions, homicidal ideation, aggression, agitation, anxiety, panic, suicidal ideation, attempt of suicide. These adverse reactions were observed in patients with and without psychiatric disorders.

Aminobenzisoxazole compounds as agonists of α7 nicotinic acetylcholine receptors: a patent evaluation (WO 2017027600)

ABSTRACTIntroduction: alpha 7 subtype nicotinic acetylcholine receptor (α7 nAChR) ligands, that is, ligands that interact with the orthosteric or allosteric binding sites of α7 nAChR, hold great potential for several therapeutic applications. Numerous compounds have been designed targeting α7 nAChR but most of them cannot be used therapeutically for various reasons.Areas covered: The patent application describes a series of germinal substituted aminobenzisoxazole compounds as α7 nAChR ligands. These compounds were claimed as potential therapeutics for treating and/or improving cognitive function. All of the (R)-stereoisomer presented high binding activities for α7 nAChR and several compounds displayed excellent selectivity over 5-HT3R.Expert opinion: The privileged structure-derived modification via bioisosterism and scaffold hopping is an important approach for seeking novel α7 nAChR ligands. The claimed germinal substituted aminobenzisoxazole derivatives with low tPSA values as well as low number of hydrogen bond donors and acceptors are supposed to have sufficient BBB penetration. Although there is a lack of essential biological data and the molecular mechanisms are not clear, these compounds stand for a new type of α7 nAChR ligands and deserve further studies.

Repeated Administration of Cigarette Smoke Condensate Increases Glutamate Levels and Behavioral Sensitization.

Nicotine, a nicotinic acetylcholine receptor agonist, produces the reinforcing effects of tobacco dependence by potentiating dopaminergic and glutamatergic neurotransmission. Non-nicotine alkaloids in tobacco also contribute to dependence by activating the cholinergic system. However, glutamatergic neurotransmission in the dorsal striatum associated with behavioral changes in response to cigarette smoking has not been investigated. In this study, the authors investigated alterations in glutamate levels in the rat dorsal striatum related to behavioral alterations after repeated administration of cigarette smoke condensate (CSC) using the real-time glutamate biosensing and an open-field behavioral assessment. Repeated administration of CSC including 0.4 mg nicotine (1.0 mL/kg/day, subcutaneous) for 14 days significantly increased extracellular glutamate concentrations more than repeated nicotine administration. In parallel with the hyperactivation of glutamate levels, repeated administration of CSC-evoked prolonged hypersensitization of psychomotor activity, including locomotor and rearing activities. These findings suggest that the CSC-induced psychomotor activities are closely associated with the elevation of glutamate concentrations in the rat dorsal striatum.

N-methyl-d-aspartate-type glutamate receptor modulators and related medications for the enhancement of auditory system plasticity in schizophrenia

Deficits in N-methyl-d-aspartate-type (NMDAR) function contribute to cognitive deficits in schizophrenia, particularly dysfunction in neuroplasticity, defined as reduced learning during training on exercises that place implicit, increasing demands on early sensory (auditory and visual) information processing. Auditory mismatch negativity (MMN) can be both a target engagement biomarker for the NMDAR and a proxy measure of neurophysiological plasticity. This review covers the evidence for using NMDAR modulator and related compounds for enhancement of cognition, with a particular focus on early auditory processing/plasticity. Compounds covered include glycine site agonists, glycine and system A-type transporter inhibitors, d-amino acid oxidase inhibitors, memantine and nicotinic alpha-7 acetylcholine receptor agonists. As opposed to daily treatment studies focusing on schizophrenia in general, intermittent, non-daily treatment combining NMDAR modulators with neuroplasticity-based paradigms, using MMN as target-engagement biomarkers show promise as treatments to both remediate plasticity deficits and overall functional deficits.

Complete inhibition of fetal movement in the day 40 pregnant goat model by the piperidine alkaloid anabasine but not related alkaloids

Four chemically similar alkaloids, anabasine, anabaseine, epibatidine and dimethylphenylpiperazinium (DMPP), are potent nicotinic acetylcholine receptor agonists of fetal muscle nicotinic acetylcholine receptors in human TE-671 cells. Based on results with these cells, we hypothesized that the alkaloids would completely inhibit ultrasound-monitored fetal movement in a goat model. Different, single doses of anabasine, anabaseine, epibatidine, DMPP, or saline control were administered I.V. to pregnant goats on day 40 of gestation and the number of fetal movements per 5 min sample was measured by ultrasound at times 0, 0.5, 1, 2, 4 and 8 h. The differences among does in fetal movements were more consistent at dosing and following recovery for doses of anabasine above 0.125 mg/kg compared to the other compounds and dosages. Anabasine actions were dose-dependent with an IC50 value of ∼0.1 mg/kg, and, at a dose of 0.8 mg/kg, completely inhibited fetal movement for 1.5 h after dosing. Anabaseine, epibatidine, and DMPP failed to completely inhibit fetal movement in day 40 pregnant goats at doses predicted to be effective. These results suggest that while experiments with TE-671 cells provide valuable information and predictions of the actions of plant alkaloids on fetal movement, in vivo experiments are still required in order to determine the ability of an alkaloid to inhibit fetal movement in livestock species. Moreover, other pharmacological properties such as receptor differences between mammalian species and differences in the pharmacokinetic properties of the alkaloids also are likely to weaken teratologic predictions based solely on the in vitro data.

Role of α7nAChR-NMDAR in sevoflurane-induced memory deficits in the developing rat hippocampus.

Detrimental effects of volatile anaesthetics, including sevoflurane, on the structure and function of the developing brain have been reported. The internalization of N-methyl-D-aspartate receptors (NMDARs) contributes to anaesthetic neurotoxicity. Both nicotinic acetylcholine receptors (nAChRs) and NMDAR play a critical role in the development of the nervous system. Moreover, nAChR can interact with NMDAR, and previous studies have demonstrated modulation of NMDAR by nAChR. In our study, we used an α7 nicotinic acetylcholine receptor (α7nAChR) agonist and α7nAChR antagonist to explore the role of α7nAChR and NMDAR in sevoflurane-induced long-term effects on memory and dendritic spine both in vivo and in vitro. The results revealed that the activation of α7nAChR attenuated the development of sevoflurane-induced memory deficit and dendritic spine changes, which might be by regulating NR2B-containing NMDAR trafficking from the intracellular pool to the cell surface pool in the hippocampus. Moreover, we demonstrated that α7nAChR could regulate NR2B-containing NMDAR via Src-family tyrosine kinase (SFK). Thus, our current study indicates that the trafficking of NR2B-containing NMDAR is regulated by α7nAChR via SFK in neonatal rat hippocampus, which may be secondary to sevoflurane-induced cognitive deficits in the developing hippocampus.

Mechanism underlying inhibition of inflammatory responses induced by α7nAChR agonist postconditioning alone or in combination with remote limb ischemic postconditioning during myocardial I/R in rats: the relationship with GSK-3β

Objective To evaluate the relationship between the mechanism underlying inhibition of inflammatory responses induced by α7 nicotinic acetylcholine receptor(α7nAChR)agonist postconditioning alone or in combination with remote limb ischemic postconditioning during myocardial ischemia-reperfusion(I/R)and glycogen synthase kinase-3β(GSK-3β)in rats. Methods Eighty adult male Sprague-Dawley rats, aged 8 weeks, weighing 290-320 g, were divided into 4 groups(n=20 each)using a random number table: I/R group, α7nAChR agonist postconditioning group(group P), remote limb ischemic postconditioning group(group L)and α7nAChR agonist postconditioning plus remote limb ischemic postconditioning group(group P+ L). Myocardial I/R was induced by 30 min occlusion of the left anterior descending branch of coronary artery followed by 120 min reperfusion.Specific α7nAChR agonist PNU282987 2 mg/kg was intravenously injected immediately before reperfusion in group P. In group L, limb ischemia was induced by tourniquet occlusion of bilateral hind paws for 10 min starting from 20 min of myocardial ischemia, and the tourniquet was released at the beginning of reperfusion.Combination of intervention measures previously described in P and L groups was performed in group P+ L.Venous blood samples were taken at 120 min of reperfusion for determination of serum troponin I(TnI)and creatine kinase-MB(CK-MB)concentrations, myocardial infarct size(IS)and expression of phosphorylated GSK-3β [p-GSK-3β(Ser536)], NF-κBp65 and phosphorylated nuclear factor-κBp65(p-NF-κBp65)in myocardial tissues(by Western blot). Results Compared with group I/R, myocardial IS and serum cTnI and CK-MB concentrations were significantly decreased, the expression of p-GSK-3β(Ser9)in ischemic area was up-regulated, and the expression of p-NF-κBp65 in ischemic area was down-regulated in P, L and P+ L groups(P<0.05). Compared with group L, myocardial IS and serum cTnI and CK-MB concentrations were significantly decreased, the expression of p-GSK-3β(Ser9)in ischemic area was up-regulated, and the expression of p-NF-κBp65 in ischemic area was down-regulated in group P+ L(P<0.05). Conclusion The mechanism by which α7nAChR agonist postconditioning alone or in combination with remote limb ischemic postconditioning inhibits inflammatory responses during myocardial I/R may be related to inhibiting GSK-3β activity in rats. Key words: Myocardial reperfusion injury; Inflammation; Glycogen synthase kinase 3; Cholinergic agonists; Extremities; Ischemic postconditioning

Neonicotinoids and Other Insect Nicotinic Receptor Competitive Modulators: Progress and Prospects.

Neonicotinoids (neonics) are remarkably effective as plant systemics to control sucking insects and for flea control on dogs and cats. The nitroimines imidacloprid, clothianidin, thiamethoxam, and dinotefuran are the leaders among the seven commercial neonics that also include the nitromethylene nitenpyram, the nitromethylene-derived cycloxaprid, and the cyanoimines acetamiprid and thiacloprid. Honey bees are highly sensitive to the nitroimines and nitromethylenes, but the cyanoimines are less toxic. All neonics are nicotinic acetylcholine receptor (nAChR) agonists with a common mode of action, target-site cross-resistance, and much higher potency on insect than mammalian nAChRs at defined binding sites. The structurally related sulfoximine sulfoxaflor and butenolide flupyradifurone are also nAChR agonists, and the mesoionic triflumezopyrim is a nAChR competitive modulator with little or no target-site cross-resistance. Some neonics induce stress tolerance in plants via salicylate-associated systems. The neonics in general are readily metabolized and, except for pollinators, have favorable toxicological profiles.

Effects of Sho-ju-sen, a Japanese herbal medicine, on catechoamine secretion induced by acetylcholine in cultured bovine adrenal medullary cells

Sho-ju-sen is a Japanese herbal medicine which has been used as a nourishing tonic. It is composed of a water extract of Kumazasa leaves (Sasa kurinensis Makino et Sibata) and ethanol extracts of Japanese red pine needles (Pinus densiflora Sieb. Et Zucc) and ginseng roots (Panax ginseng C. A. Meyer). Previous studies showed that Sho-ju-sen has antidepressant and anxiolytic effects in mice (Phytother Res., 15: 142-147, 2001 and 18: 173-176, 2004). Here we report that the effects of Sho-ju-sen on catecholamine secretion in cultured bovine adrenal medullary cells. Adrenal medullary cells have provided a good material for the detailed analysis of a drug's actions on catecholamine secretion and have been used as a model of the sympathetic neurons. We found that Sho-ju-sen (0.5 - 1 %) and extract of Kumazasa leaves (0.5-1 %), but not ethanol extract of Japanese red pine needles or ginseng roots, concentration-dependently inhibited the secretion of catecholamines induced by acetylcholine, a physiological secretagogue and agonist of nicotinic acetylcholine receptors. In Xenopus oocytes expressing α3β4 nicotinic acetylcholine receptors, Sho-ju-sen (0.5 - 1 %) directly inhibited Na+ current evoked by acetylcholine. Sho-ju-sen (0.3 - 1 %) also inhibited catecholamine secretion induced by veratridine, an activator of voltage-dependent Na+ channels, but not by 56 mM K+ which depolarizes cell membranes. The present findings demonstrate that Sho-ju-sen inhibits acetylcholine- and veratridine-induced catecholamine secretion by suppression of nicotinic acetylcholine receptor-ion channels and voltage-dependent Na+ channels in adrenal medulla cells and probably sympathetic neurons, and also suggest that Sho-ju-sen has an anti-stress effect.

Choline Supplementation During Pregnancy Protects Against Gestational Lipopolysaccharide-Induced Inflammatory Responses.

To estimate the effects and mechanisms of choline, an essential nutrient and a selective α7 nicotinic acetylcholine receptor (α7nAChR) agonist, on the prevention of symptoms and the effects on the cholinergic anti-inflammatory pathways (CAP) in a lipopolysaccharide (LPS)-induced inflammatory response in a rat model. Inflammation was induced by LPS treatment (1.0 μg LPS/kg body weight) on gestational day (GD) 14. Nonpregnant and pregnant Sprague Dawley rats were placed on a normal choline diet (1.1 g/kg) or supplemented choline diet (5.0 g/kg) from GDs 1 to 20. Systolic blood pressure (SBP), urinary albumin, and pregnancy outcomes were recorded. On GD 20, serum and placentas were assayed for cytokines. Western blots were used to determine the expression of placenta α7nAChR and components of the α7nAChR-CAP, including nuclear factor-κB (NF-κB) and protein kinase B (AKT). Immunohistochemistry was used to localize placental sites for the p65 subunit of NF-κB. Lipopolysaccharide significantly increased SBP and urinary albumin and decreased pregnancy outcomes, and these effects were partially reversed by higher choline treatment. Choline supplementation also significantly attenuated the LPS-induced increase in serum and placental inflammatory cytokines, decreased the expression of placental α7nAChR, lowered the activation of NF-κB signaling in placenta mononuclear cells, and inhibited placental AKT phosphorylation. This study confirms that LPS induces inflammatory conditions in pregnant rats and shows that choline supplementation protects against the inflammatory symptoms through its action on α7nAChR and CAP. These observations have important implications for the prevention and treatment of inflammatory responses associated with pregnancy.

Alpha-7 nicotinic acetylcholine receptor agonist treatment in a rat model of Huntington's disease and involvement of heme oxygenase-1.

Neuroinflammation is a common element involved in the pathophysiology of neurodegenerative diseases. We recently reported that repeated alpha-7 nicotinic acetylcholine receptor (α7nAChR) activations by a potent agonist such as PHA 543613 in quinolinic acid-injured rats exhibited protective effects on neurons. To further investigate the underlying mechanism, we established rat models of early-stage Huntington's disease by injection of quinolinic acid into the right striatum and then intraperitoneally injected 12 mg/kg PHA 543613 or sterile water, twice a day during 4 days. Western blot assay results showed that the expression of heme oxygenase-1 (HO-1), the key component of the cholinergic anti-inflammatory pathway, in the right striatum of rat models of Huntington's disease subjected to intraperitoneal injection of PHA 543613 for 4 days was significantly increased compared to the control rats receiving intraperitoneal injection of sterile water, and that the increase in HO-1 expression was independent of change in α7nAChR expression. These findings suggest that HO-1 expression is unrelated to α7nAChR density and the increase in HO-1 expression likely contributes to α7nAChR activation-related neuroprotective effect in early-stage Huntington's disease.

In vivo and in vitro ADMET profiling and in vivo pharmacodynamic investigations of a selective α7 nicotinic acetylcholine receptor agonist with a spirocyclic Δ2-isoxazoline molecular skeleton

(±)-3-Methoxy-1-oxa-2,7-diaza-7,10-ethanospiro[4.5]dec-2-ene sesquifumarate (±)-1 was previously characterized as the most selective agonist at α7 neuronal nicotinic acetylcholine receptors in a series of spirocyclic quinuclidinyl-Δ2-isoxazoline derivatives. In this study, we performed different in vitro biological assays aimed at characterizing the ADMET properties of (±)-1. Then, we tested the compound in vivo in behavioral studies including classical novel object recognition and inhibitory avoidance tests in the rat, and a spatial memory assay in zebrafish involving a rapid T-maze task. The results indicated an overall favorable profile for (±)-1 in view of potential therapeutic applications targeting the central nervous system.

Differential Modulation of GABAA and NMDA Receptors by an α7-nicotinic Acetylcholine Receptor Agonist in Chronic Glaucoma.

Presynaptic modulation of γ-aminobutyric acid (GABA) release by an alpha7 nicotinic acetylcholine receptor (α7-nAChR) agonist promotes retinal ganglion cell (RGC) survival and function, as suggested by a previous study on a chronic glaucomatous model from our laboratory. However, the role of excitatory and inhibitory amino acid receptors and their interaction with α7-nAChR in physiological and glaucomatous events remains unknown. In this study, we investigated GABAA and N-methyl-D-aspartate (NMDA) receptor activity in control and glaucomatous retinal slices and the regulation of amino acid receptor expression and function by α7-nAChR. Whole-cell patch-clamp recordings from RGCs revealed that the α7-nAChR specific agonist PNU-282987 enhanced the amplitude of currents elicited by GABA and reduced the amplitude of currents elicited by NMDA. The positive modulation of GABAA receptor and the negative modulation of NMDA receptor (NMDAR) by PNU-282987-evoked were prevented by pre-administration of the α7-nAChR antagonist methyllycaconitine (MLA). The frequency and the amplitude of glutamate receptor-mediated miniature glutamatergic excitatory postsynaptic currents (mEPSCs) were not significantly different between the control and glaucomatous RGCs. Additionally, PNU-282987-treated slices showed no alteration in the frequency or amplitude of mEPSCs relative to control RGCs. Moreover, we showed that expression of the α1 subunit of the GABAA receptor was downregulated and the expression of the NMDAR NR2B subunit was upregulated by intraocular pressure (IOP) elevation, and the changes of high IOP were blocked by PNU-282987. In conclusion, retina GABAA and NMDARs are modulated positively and negatively, respectively, by activation of α7-nAChR in in vivo chronic glaucomatous models.

Cardioprotective and anti-inflammatory effects of combined α7 nicotinic acetylcholine receptor agonist and limb remote ischemic postconditioning in rats with myocardial ischemia/reperfusion injury

Objective To assess the cardioprotective and anti-inflammatory effects of combined α7 nicotinic acetylcholine receptor(α7nAChR) agonist and limb remote ischemic postconditioning in rats with myocardial ischemia/reperfusion injury(I/RI). Methods Sixty male SD rats were randomly divided equally into six groups(n=10): sham group(S group), control group(C group), ischemia preconditioning group(IPC group), special α7nAChR agonist PNU282987 postconditioning group(P group), lime remote ischemic postconditioning group(L group), combined PNU282987 and lime remote ischemic postconditioning group(P+L group). Throughout the experiment, HR, MAP, and a lead Ⅱ electrocardiogram were continuously monitored. Blood samples were taken at 120 min of reperfusion for measuring serum concentrations of troponin I(TnI), myocardial-bound creatine kinase(CK-MB), TNF-α, high mobility group box 1 protein(HMGB-1), IL-6 and IL-10 by the kits specifically for rats. At the end of experiment, the infarct size(IS) was assessed using excised hearts by Evans blue and triphenyltetrazolium chloride staining. Results Compared with C group, the IS,serum cTnI and CK-MB concentrations were significantly decreased in IPC, P, L and P+L groups. Compared to IPC group, the IS and serum cTnI concentration were significantly higher in P, L and P+L groups. Compared to P and L groups, the IS, serum cTnI and CK-MB concentrations were significantly decreased in P+L group. At 120 min of reperfusion, serum TNF-α concentration was significantly increased in C, IPC and L groups. Also, serum IL-6 and HMGB1 concentrations were significantly increased in C, IPC, P and L groups compared with S group. Compared to C group, serum TNF-α, IL-6 and HMGB1 concentrations were significantly decreased in IPC, P, L and P+L group. Compared to IPC and L groups, serum TNF-α, IL-6 and HMGB1 concentrations were significantly decreased in P and P+L groups. Conclusions Combined α7nAChR agonist and limb remote ischemic postconditioning can provide an improved cardioprotection, but not an enhanced anti-inflammatory effect. Key words: Myocardial; Ischemia/reperfusion injury; Inflammation; Cholinergic anti-inflammatory pathway; Limb remote ischemic postconditioning

Imidacloprid, a neonicotinoid insecticide, facilitates tyrosine hydroxylase transcription and phenylethanolamine N-methyltransferase mRNA expression to enhance catecholamine synthesis and its nicotine-evoked elevation in PC12D cells

Imidacloprid is a neonicotinoid insecticide acting as an agonist of nicotinic acetylcholine receptors (nAChRs) in the target insects. However, questions about the safety to mammals, including human have emerged. Overactivation of mammalian peripheral catecholaminergic systems leads to onset of tachycardia, hypertension, vomiting, etc., which have been observed in acutely imidacloprid-poisoned patients as well. Physiological activation of the nAChRs is known to drive catecholamine biosynthesis and secretion in mammalian adrenal chromaffin cells. Yet, the impacts of imidacloprid on the catecholaminergic function of the chromaffin cells remain to be evaluated. In this study using PC12D cells, a catecholaminergic cell line derived from the medulla chromaffin-cell tumors of rat adrenal gland, we examined whether imidacloprid itself could impact the catecholamine-synthesizing ability. Imidacloprid alone did facilitate tyrosine hydroxylase (TH) transcription via activation of α3β4 nAChR and the α7 subunit-comprising receptor. The insecticide showed the TH transcription-facilitating ability at the concentrations of 3 and 30 μM, at which acetylcholine is known to produce physiological responses, including catecholamine secretion through the nAChRs in adrenal chromaffin cells. The insecticide-facilitated TH transcription was also dependent on PKA- and RhoA-mediated signaling pathways. The insecticide coincidentally raised levels of TH and phenylethanolamine N-methyltransferase (PNMT) mRNA, and as a consequence, increased catecholamine production, although the efficacy of the neonicotinoid was lesser than that of nicotine, indicating its partial agonist-like action. Intriguingly, in cultured rat adrenal chromaffin cells, imidacloprid did increase levels of TH and PNMT protein. When the chromaffin cells were treated with nicotine in the presence of the insecticide, nicotine-elevated adrenaline production was enhanced due to facilitation of nicotine-increased TH and PNMT protein expression, and simultaneous enhancement of nicotine-elevated adrenaline secretion also took place. These findings thus suggest that imidacloprid may facilitate the physiological functions of adrenal glands in mammals.

Editorial

Editorial