Activation Of Α7 Nicotinic Acetylcholine Receptor Research Articles

ID: 212135 Noninvasive Human Immunotyping Through Machine Learning Using the Autonomic Nervous System

The extreme diversity of the human immune system, forged and maintained throughout evolutionary history, has to date provided a potent defense against pathogens [1]. Intrinsically variable autonomic neuro-immune regulation via β-adrenergic receptor and α7-nicotinic acetylcholine receptor activity is controlled by polymorphic genes and environmental sensors [2, 3]. While most healthy humans have the capacity to activate various types of immune cells, interferons, inflammasome activity, and vagal anti-inflammatory reflexes, individuals differ in the degree to which they are primed for each functional configuration. Virulent emerging pathogens inherently circumvent these functional immune configurations and can impose a dysregulated hyperinflammatory response [4]. Here we detect host-dependent baseline autonomic gradient drive (AGD) bias through high temporal resolution physiological monitoring. Similar to immune bias, AGD bias shown to predict current inflammatory status as well as severity of future inflammatory sequela and disease.

Induction of tetraspanin 13 contributes to the synergistic anti-inflammatory effects of parasympathetic and sympathetic stimulation in macrophages

The autonomic nervous system plays an important role in the regulation of peripheral inflammation. Sympathetic nervous activation stimulates inflammatory gene expression and cytokines, whereas parasympathetic nervous activation suppresses the production of inflammatory cytokines by immune cells. However, most studies on the relationship between the autonomic nervous system and immune processes have analyzed a single branch of the autonomic nerves in isolation. Therefore, this study aimed to examine the effects of sympathetic and parasympathetic stimulation on macrophages, which are controlled by autonomic regulation.Macrophages were stimulated with lipopolysaccharide (LPS) to induce TNF-α. Then, the effects of β2 adrenergic receptor and α7 nicotinic acetylcholine receptor activation on TNF-α production were assessed using concentration-dependent assays. RNA-seq data were also used to identify genes whose expression was enhanced by parasympathetic and sympathetic stimulation.The simultaneous activation of β2 adrenergic receptors and α7 nicotinic acetylcholine receptors suppressed LPS-induced TNF-α production in a concentration-dependent manner. Moreover, simultaneous activation of these receptors had synergistic anti-inflammatory effects and induced Tspan13 expression, thereby contributing to anti-inflammatory mechanisms in macrophages.Our study revealed the synergistic anti-inflammatory effects of the parasympathetic and sympathetic stimulation of macrophages. Our results suggest that targeting both sympathetic and parasympathetic signaling is a promising therapeutic approach for inflammatory diseases.

Activating α7nAChR helps post-myocardial infarction healing by regulating macrophage polarization via the STAT3 signaling pathway.

Monocytes/macrophages play critical roles in inflammation and cardiac remodeling following myocardial infarction (MI). The cholinergic anti-inflammatory pathway (CAP) modulates local and systemic inflammatory responses by activating α7 nicotinic acetylcholine receptors (α7nAChR) in monocytes/macrophages. We investigated the effect of α7nAChR on MI-induced monocyte/macrophage recruitment and polarization and its contribution to cardiac remodeling and dysfunction. Adult male Sprague Dawley rats underwent coronary ligation and were intraperitoneally injected with the α7nAChR-selective agonist PNU282987 or the antagonist methyllycaconitine (MLA). RAW264.7 cells were stimulated with lipopolysaccharide (LPS) + interferon-gamma (IFN-γ) and treated with PNU282987, MLA, and S3I-201 (a STAT3 inhibitor). Cardiac function was evaluated by echocardiography. Masson's trichrome and immunofluorescence were used to detect cardiac fibrosis, myocardial capillary density, and M1/M2 macrophages. Western blotting was used to detect protein expression, and the proportion of monocytes was measured using flow cytometry. Activating the CAP with PNU282987 significantly improved cardiac function and reduced cardiac fibrosis and 28-day mortality after MI. On days 3 and 7 post-MI, PNU282987 reduced the percentage of peripheral CD172a + CD43low monocytes and the infiltration of M1 macrophages in the infarcted hearts, whereas it increased the recruitment of peripheral CD172a + CD43high monocytes and M2 macrophages. Conversely, MLA exerted the opposite effects. In vitro, PNU282987 inhibited M1 macrophage polarization and promoted M2 macrophage polarization in LPS + IFN-γ-stimulated RAW264.7 cells. These PNU282987-induced changes in LPS + IFN-γ-stimulated RAW264.7 cells were reversed by administering S3I-201. Activating α7nAChR inhibits the early recruitment of pro-inflammatory monocytes/macrophages during MI and improves cardiac function and remodeling. Our findings suggest a promising therapeutic target for regulating monocyte/macrophage phenotypes and promoting healing after MI.

Protective effect of α7 nicotinic acetylcholine receptor activation on experimental colitis and its mechanism

BackgroundInflammatory bowel disease (IBD) is a common chronic remitting disease with no satisfactory treatment. The aim of this study was to investigate the protective effect of α7 nicotinic acetylcholine receptor (α7nAChR), and to determine the underlying mechanism of its activity.MethodsThe expression and distribution of α7nAChR in the intestinal tissue of patients with ulcerative colitis and Crohn’s disease were analyzed. The effects of vagal excitation on murine experimental colitis were investigated. The colitis model was induced in C57BL/6 mice by the administration of 3% dextran sulfate sodium (DSS). The therapeutic group received treatment with the α7nAChR agonist PNU-282987 by intraperitoneal injection.ResultsOur results showed that there was significantly increased expression of α7nAChR in colitis and Crohn’s disease intestinal tissue, and its expression was mainly located in macrophages and neutrophils, which were extensively infiltrated in the disease status. Treatment with an α7nAChR agonist potently ameliorated the DSS-induced illness state, including weight loss, stool consistency, bleeding, colon shortening, and colon histological injury. α7nAChR agonist exerted anti-inflammatory effects in DSS colitis mice by suppressing the secretion of multiple types of proinflammatory factors, such as IL6, TNFα, and IL1β, and it also inhibited the colonic infiltration of inflammatory cells by blocking the DSS-induced overactivation of the NF-κB and MAPK signaling pathways. Mechanistically, activation of α7nAChR decreased the number of infiltrated M1 macrophages in the colitis intestine and inhibited the phagocytosis ability of macrophages, which were activated in response to LPS stimulation.ConclusionThus, an α7nAChR agonist ameliorated colonic pathology and inflammation in DSS-induced colitis mice by blocking the activation of inflammatory M1 macrophages.

The use of choline supplementation for the prevention of chemotherapy‐related cognitive impairments

The majority of patients who report chemotherapy‐related cognitive deficits are women. Many chemotherapeutic agents suppress ovarian function, decreasing circulating estrogen. Because estrogen regulates high affinity choline uptake (HACU) and HACU is the rate‐limiting step for acetylcholine (ACh) synthesis, chemotherapeutic agents may indirectly impair cholinergic mediated cognitive processes. ACh suppresses cytokine synthesis, inhibits inflammation and prevents tissue damage and cell death by activating α7 nicotinic ACh receptors (nAChRs), thus impaired HACU and ACh synthesis following chemotherapy may exacerbate the adverse effects of neuroinflammation caused by tumors and chemotherapeutic agents. Since increasing available choline can maintain cholinergic function when demand for the precursor is high, and because choline is a full agonist at α7 nAChRs, increasing dietary choline may protect ACh systems from degeneration by attenuating pro‐inflammatory processes.We have demonstrated that one administration of cyclophosphamide (CYP) and doxorubicin (DOX) impairs HACU in the striatum (STR) and hippocampus (HCC) of non tumor‐bearing (M‐) and tumor‐bearing MMTV‐PyVT (M+) female mice. Further, we have shown that the effect of one administration of CYP+DOX on HACU is prevented by placing mice on a 2% choline diet, and a 2% choline diet slows tumor growth in female M+ mice.The present study sought to determine whether a 2% choline diet could: 1) prevent the manifestation of spatial memory deficits resulting from repeated exposure to CYP (66.7mg/kg i.v.; ≍200mg/m2/wk) and DOX (6.7mg/kg i.v.; ≍20mg/m2/wk); 2) maintain HACU in the frontal cortex (CTX), STR and HCC of mice following 4 weekly administrations of CYP+DOX; 3) prevent reductions in circulating E2 consequent to repeated CYP+DOX exposure; 4) attenuate elevations of circulating cytokines induced by repeated CYP+DOX exposure and/or the presence of tumors; and 5) suppress tumor growth and enhance the antineoplastic effects of CYP+DOX treatment in female M+ mice.Results indicate that M‐ and M+ mice exposed to CYP+DOX exhibit deficits in spatial memory 10‐12 days following 4 weekly injections of CYP+DOX and 5 weeks following the final administration. HACU was reduced in the STR and HCC following a single exposure to CYP+DOX and this effect persisted in the STR. However, reduced HACU in the HCC was transient. Supplementation with a 2% choline diet prevented the manifestation of spatial memory deficits in M‐ and M+ mice and HACU in these mice did not differ from controls, suggesting that impaired HACU mediated the deficit in spatial memory. Although we did not observe an anticipated reduction in circulating estradiol due to CYP+DOX exposure, the regular appearance of proestrous was disrupted in groups exposed to either CYP+DOX or 2% choline diet, suggestive of amenorrhea. Circulating concentrations of cytokines, including G‐CSF, IL6, IP10, MCP1 and RANTES, were altered by the presence of tumors as well as the administration of CYP+DOX. 2% choline significantly reduced circulating concentrations of IL‐5, a cytokine associated with poor prognosis and metastasis, and total tumor volume was lower in mice placed on 2% choline diet when compared to tumor bearing mice on standard diet.

The Regulation Effect of α7nAChRs and M1AChRs on Inflammation and Immunity in Sepsis.

The inflammatory storm in the early stage and immunosuppression in the late stage are responsible for the high mortality rates and multiple organ dysfunction in sepsis. In recent years, studies have found that the body's cholinergic system can spontaneously and dynamically regulate inflammation and immunity in sepsis according to the needs of the body. Firstly, the vagus nerve senses and regulates local or systemic inflammation by means of the Cholinergic Anti-inflammatory Pathway (CAP) and activation of α7-nicotinic acetylcholine receptors (α7nAChRs); thus, α7nAChRs play important roles for the central nervous system (CNS) to modulate peripheral inflammation; secondly, the activation of muscarinic acetylcholine receptors 1 (M1AChRs) in the forebrain can affect the neurons of the Medullary Visceral Zone (MVZ), the core of CAP, to regulate systemic inflammation and immunity. Based on the critical role of these two cholinergic receptor systems in sepsis, it is necessary to collect and analyze the related findings in recent years to provide ideas for further research studies and clinical applications. By consulting the related literature, we draw some conclusions: MVZ is the primary center for the nervous system to regulate inflammation and immunity. It coordinates not only the sympathetic system and vagus system but also the autonomic nervous system and neuroendocrine system to regulate inflammation and immunity; α7nAChRs are widely expressed in immune cells, neurons, and muscle cells; the activation of α7nAChRs can suppress local and systemic inflammation; the expression of α7nAChRs represents the acute or chronic inflammatory state to a certain extent; M1AChRs are mainly expressed in the advanced centers of the brain and regulate systemic inflammation; neuroinflammation of the MVZ, hypothalamus, and forebrain induced by sepsis not only leads to their dysfunctions but also underlies the regulatory dysfunction on systemic inflammation and immunity. Correcting the neuroinflammation of these regulatory centers and adjusting the function of α7nAChRs and M1AChRs may be two key strategies for the treatment of sepsis in the future.

Cellular responses and functions of α7 nicotinic acetylcholine receptor activation in the brain: a narrative review.

The α7 nicotinic acetylcholine receptor (α7nAChR) has been studied for many years since its discovery. Although many functions and characteristics of brain α7nAChR are widely understood, much remains to be elucidated. The α7nAChR is widely expressed in the central nervous system, not only in neurons but also in astrocytes, microglia, and endothelial cells. α7nAChR can be activated by endogenous agonist like acetylcholine or exogenous agonists like nicotine and PNU282987. Its agonists can be divided into selective agonists and non-selective agonists. The activation of α7nAChR results in a series of physiological processes which have both short-term and long-term effects on cells, for example, calcium influx, neurotransmitter release, synaptic plasticity, and excitatory transmission. It also induces other downstream events, such as inflammation, autophagy, necrosis, transcription, and apoptosis. The cellular responses to α7nAChR activation vary according to cell types and conditions. For example, α7nAChR activation in pyramidal neurons leads to long-term potentiation, while α7nAChR activation in GABAergic interneurons leads to long-term depression. Studies have also shown some contradictory phenomena, which requires further study for clarification. Herein, the cellular responses of α7nAChR activation are summarized, and the functions of α7nAChR in neurons and non-neuronal cells are discussed. We also summarized contradictory conclusions to show where we stand and where to go for future studies.

Nicotine Prevents Oxidative Stress-Induced Hippocampal Neuronal Injury Through α7-nAChR/Erk1/2 Signaling Pathway.

Oxidative stress-induced neuronal damage has been implicated to play a dominant role in neurodegenerative disorders, such as Alzheimer’s disease (AD). Nicotine, a principal additive compound for tobacco users, is thought as a candidate to attenuate amyloid-β-mediated neurotoxicity and NMDA-induced excitotoxicity. Previous studies demonstrated that nicotine exerted this neuroprotective action on oxidative stress. However, the mechanisms underlying how nicotine contributes on oxidative injury in immortalized hippocampal HT-22 cells remain largely unknown. Therefore, in this study we investigated that the potential effects of nicotine on hydrogen peroxide (H2O2)-induced oxidative injury and underlying mechanisms in HT-22 cells. We found that pretreatment with nicotine at low concentrations markedly recovered the cell cycle that was arrested at the G2/M phase in the presence of H2O2 through reduced intracellular ROS generation. Moreover, nicotine attenuated H2O2-induced mitochondrial dysfunctions. Mechanistically, the application of nicotine significantly upregulated the levels of phosphorylated Erk1/2. The neuroprotective effects of nicotine, in turn, were abolished by PD0325901, a selective Erk1/2 inhibitor. Further obtained investigation showed that nicotine exerted its neuroprotective effects via specifically activating α7 nicotinic acetylcholine receptors (α7-nAChRs). A selective inhibitor of α7-nAChRs, methyllycaconitine citrate (MLA), not only completely prevented nicotine-mediated antioxidation but also abolished expression of p-Erk1/2. Taken together, our findings suggest that nicotine suppresses H2O2-induced HT-22 cell injury through activating the α7-nAChR/Erk1/2 signaling pathway, which indicates that nicotine may be a novel strategy for the treatment of neurodegenerative disorders.

Increasing dietary choline to prevent chemotherapy related cognitive deficits and attenuate tumor growth in MMTV‐PyVT mice.

Women constitute the majority of patients who report deficits of learning, memory, attention and processing speed during and following chemotherapy. These chemotherapy‐related cognitive deficits (CRCDs) are persistent and can impair day‐to‐day functioning for decades, adversely impacting quality of life. Many chemotherapeutic agents suppress ovarian function, decreasing circulating estrogen levels, a fact that may underlie the manifestation and/or persistence of CRCDs in females. Because estrogen regulates high affinity choline uptake (HACU) and HACU is the rate‐limiting step for acetylcholine synthesis, chemotherapeutic agents may indirectly impair processes mediated by cholinergic systems. Both tumors and chemotherapeutic agents can elevate pro‐inflammatory cytokines/chemokines, a consequence that may mediate the manifestation of CRCDs. Because acetylcholine (ACh) suppresses cytokine synthesis, inhibits inflammation and prevents tissue damage and cell death by activating α7 nicotinic acetylcholine receptors (nAChRs) located on cytokine producing cells, impaired HACU and ACh synthesis following chemotherapy may exacerbate the adverse effects of neuroinflammation caused by tumors and chemotherapeutic agents. Since increasing available choline can maintain cholinergic function when demand for the precursor is high, and because choline is a full agonist at α7 nAChRs, increasing dietary choline may maintain cholinergic function and protect cholinergic systems from degeneration by attenuating pro‐inflammatory processes.We have previously demonstrated that a single administration of the chemotherapeutic agents cyclophosphamide (CYP) and doxorubicin (DOX) resulted in a small, non‐significant, reduction in circulating estradiol (E2), and impaired HACU in the striatum (STR) and hippocampus (HCC) of nontumor‐bearing (C57Bl/6J) and tumor‐bearing (MMTV‐PyVT) female mice. We further demonstrated that the effect of a single administration of CYP+DOX on HACU could be prevented by placing mice on a 2% choline diet 2 weeks prior to exposure to CYP+DOX, and that a 2% choline diet could slow the growth of tumors in female tumor‐bearing MMTV‐PyVT mice. The present study sought to determine whether a 2% choline diet could: 1) maintain HACU in the frontal cortex, STR and HCC of nontumor‐bearing and tumor‐bearing mice following 4 weekly administrations of CYP+DOX, a regimen similar to that used for the treatment of some breast cancer patients; 2) prevent reductions in circulating E2 consequent to repeated CYP+DOX exposure; 3) attenuate elevations of central and circulating cytokines induced by repeated CYP+DOX exposure and/or the presence of tumors; 4) prevent spatial memory deficits in the Morris water maze following repeated exposure to CYP+DOX; and 5) suppress tumor growth and enhance the antineoplastic effects of CYP+DOX treatment in female tumor‐bearing MMTV‐PyVT mice. The results of these studies are discussed.Support or Funding InformationSupported by: NCCIH 1R21AT009734

The α7-nAChR/heme oxygenase-1/carbon monoxide pathway mediates the nicotine counteraction of renal inflammation and vasoconstrictor hyporeactivity in endotoxic male rats.

The objective of the study was to test the hypothesis that nicotine guards against endotoxemia-associated renal inflammation and vasoconstrictor dysfunction via the activation of α7-nicotinic acetylcholine receptors (α7-nAChRs)/heme oxygenase-1 (HO-1) cascade. 91 male and female rats were included in the study. Lipopolysaccharide (LPS, 5mgkg-1), nicotine (0.5-2mgkg-1), pentoxifylline (PTX, TNFα inhibitor, 3mgkg-1), methyllycaconitine (MLA, α7-nAChR blocker), zinc protoporphyrin (ZnPP, HO-1 inhibitor), hemin (HO-1 inducer), tricarbonyldichlororuthenium (carbon monoxide-releasing molecule, CORM-2) or bilirubin was administered before LPS. Isolated perfused kidney was used to evaluate renal vasoconstriction and immunohistochemistry to assess inflammatory cytokines. LPS reduced renal vasoconstrictions induced by phenylephrine or vasopressin in perfused kidneys of male, but not female, rats. Higher elevations in serum interleukin-1β and renal expressions of inducible nitric oxide synthase (iNOS) and nuclear factor-κB (NF-κB) were observed in LPS-treated male rats, whereas greater HO-1 expression was evident in endotoxic female rats. LPS effects were reversed by nicotine or PTX. Further, the favorable nicotine actions were (i) diminished by MLA or ZnPP and (ii) replicated by hemin or CORM-2, but not bilirubin, and (iii) associated with exaggerated and MLA-sensitive increases in HO-1 expression. α7-nAChR/HO-1/CO signaling mediates nicotine protection against renal inflammation and vasoconstrictor hyporeactivity in endotoxic male rats.

Neuroprotective mechanism involved in spinal cord stimulation postconditioning

ObjectivesDelayed paraplegia developed postoperatively after thoracoabdominal aneurysm surgery is primarily associated with spinal cord ischemia/reperfusion injury. Our previous study suggested that spinal cord stimulation postconditioning protected the spinal cord from ischemia/reperfusion injury through microglia inhibition. In this study, we further investigated whether α7 nicotinic acetylcholine receptors were involved in the neuroprotective mechanism of spinal cord stimulation. MethodsRabbits were randomly assigned to sham, control, 2 Hz, α-bungarotoxin, and 2 Hz-α-bungarotoxin groups (n = 24/group). Transient spinal cord ischemia was performed on all rabbits except rabbits in the sham group. Rabbits in the control group received no further intervention, rabbits in the 2 Hz group were given 2 Hz spinal cord stimulation, rabbits in the α-bungarotoxin group received prescribed intrathecal α-bungarotoxin (α-bungarotoxin, a specific α7 nicotinic acetylcholine receptor antagonist) injections, and rabbits in the 2 Hz-α-bungarotoxin group received both α-bungarotoxin injections and 2 Hz spinal cord stimulation. Hind-limb neurologic function was assessed, and spinal cord histologic examination, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining, and microglia staining were performed at 8 hours, 1 day, 3 days, and 7 days of reperfusion. ResultsRabbits in the 2 Hz group had significantly better neurologic functions, more α-motor neurons, and lower terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling–positive neuron rates and microglia area/anterior horn area ratios (microglia area ratios) than the control group. The neurologic functions of the α-bungarotoxin group were significantly worse than those of the control group, whereas other results were not significantly different from the control group. The results of the 2 Hz-α-bungarotoxin group were insignificant to the control group except for the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling–positive neuron rates, which were significantly lower than in the control group. ConclusionsThe neuroprotective effects of spinal cord stimulation postconditioning against spinal cord ischemia/reperfusion injury were partially mediated by activating α7 nicotinic acetylcholine receptors.

Anti-tumoral activity of the human-specific duplicated form of α7-nicotinic receptor subunit in tobacco-induced lung cancer progression

Objectives: Tobacco smoking is strongly correlated with the onset and progression of non-small cell lung cancer (NSCLC). By activating α7 nicotinic acetylcholine receptors (α7-nAChRs) in these tumors nicotine and its tobacco-derived nitrosamine, NNK, contribute to these oncogenic processes. Here, we investigated whether the human-specific duplicated form of the α7-nAChR subunit (dupα7) behaves as an endogenous negative regulator of α7-nAChR-mediated tumorigenic activity induced by tobacco in NSCLC cells, similarly to its influence on other α7-nAChR-controlled functions in non-tumor cells.Methods: Two human NSCLC cell lines, lung adenocarcinoma (A549) and squamous cell carcinoma of the lung (SK-MES-1), both wild-type or with stable overexpression of dupα7 (A549dupα7 or SK-MES-1dupα7), were used to investigate in vitro anti-tumor activity of dupα7 on nicotine- or NNK-induced tumor progression. For this purpose, migration, proliferation or epithelial-mesenchymal transition (EMT) were examined. The anti-tumor effect of dupα7 on nicotine-promoted tumor growth, proliferation or angiogenesis was also assessed in vivo in an athymic mouse model implanted with A549dupα7 or A549 xenografts.Results: Overexpression of dupα7 in both cell lines almost completely suppresses the in vitro tumor-promoting effects induced by nicotine (1 μM) or NNK (100 nM) in wild-type cells. Furthermore, in mice receiving nicotine, A549dupα7 xenografts show: (i) a significant reduction of tumor growth, and (ii) decreased expression of cell markers for proliferation (Ki67) or angiogenesis (VEGF) compared to A549 xenografts.Conclusion: Our study demonstrates, for the first time, the in vitro and in vivo anti-tumor capacity of dupα7 to block the α7-nAChR-mediated tumorigenic effects of tobacco in NSCLC, suggesting that up-regulation of dupα7 expression in these tumors could offer a potential new therapeutic target in smoking-related cancers.

β-Cell mass restoration by α7 nicotinic acetylcholine receptor activation

Although it is well-established how nutrients, growth factors, and hormones impact functional β-cell mass (BCM), the influence of the central nervous system in this regard, and especially in the context of islet immune modulation, has been understudied. Here we investigated the expression and activity of pancreatic islet α7 nicotinic acetylcholine receptor (α7nAChR) in islet anti-inflammatory and prosurvival signaling. Systemic administration of α7nAChR agonists in mice improved glucose tolerance and curtailed streptozotocin-induced hyperglycemia by retaining BCM, in part through maintaining Pdx1 and MafA expression and reducing apoptosis. α7nAChR activation of mouse islets ex vivo led to reduced inflammatory drive through a JAK2-STAT3 pathway that couples with CREB/Irs2/Akt survival signaling. Because the vagus nerve conveys anti-inflammatory signals to immune cells of the spleen and other nonneural tissues in the viscera by activating α7nAChR agonists, our study suggests a novel role for β-cell α7nAChR that functions to maintain β-cell survival and mass homeostasis through modulating islet cytokine and phosphatidylinositol 3-kinase-dependent signaling pathways. Exploiting these pathways may have therapeutic potential for the treatment of autoimmune diabetes.

Toxic Effect of Cigarette Smoke on Brainstem Nicotinic Receptor Expression: Primary Cause of Sudden Unexplained Perinatal Death.

Among the neurotoxicants contained in tobacco smoke, if absorbed during pregnancy, nicotine significantly affects α7-nicotinic acetylcholine receptors, which play essential roles in the development of the brainstem regions receiving cholinergic projections in perinatal life. Immunohistochemical procedures for analysing formalin-fixed and paraffin-embedded brainstem samples from 68 fetuses and early newborns, with smoking and non-smoking mothers, who died of known and unknown causes, were carried out in order to determine if nicotine had activated the α7-nicotinic acetylcholine receptors. High α7-nicotinic acetylcholine receptor expression levels were only observed in the victims with smoking mothers. Frequently, these findings were associated with the hypoplasia of the brainstem structures controlling vital functions. The results of this study indicate that the exposition to nicotine in pregnancy exerts a strong direct effect on α7-nicotinic acetylcholine receptor activity especially in perinatal life and may be one of the primary risk factors leading to the sudden unexplained death of fetuses and newborns.

Abstract WMP82: The Role of Nicotine in the Development of Intracranial Aneurysmal Rupture

Introduction: Tobacco smoking is an independent risk factor for intracranial aneurysmal rupture. Nicotine is one of main chemicals of tobacco smoke that promotes atherosclerosis and stroke. Nicotine induces vascular remodeling through activation of α7nicotinic acetylcholine receptor (α7nAChR) that is expressed in the vascular wall. Using a mouse model of intracranial aneurysm, we examined whether the activation of α7nAChR by nicotine promotes intracranial aneurysmal rupture. Methods and Materials: To induce aneurysm, we combined induced systemic hypertension (deoxycorticosterone acetate-salt hypertension) and a single injection of elastase (17.5mU) into the cerebrospinal fluid at the right basal cistern. We used α7nAChR knockout (α7KO) mice and the wild-type (WT) mice. Mice were treated with (1) nicotine (5 mg/kg/day); (2) vehicle (saline) subcutaneously from one week before aneurysm induction, and the treatments were continued until 21 days after aneurysm induction. Results: Nicotine treatment significantly increased aneurysmal rupture compared to the vehicle treatment in the WT mice (WT + vehicle vs. WT + nicotine: 46% vs. 84%, P < 0.01). Furthermore, the harmful effect of nicotine was abolished in the α7KO mice compared (WT + nicotine vs. α7KO + nicotine: 84% vs. 27%; P < 0.05). There was no difference in the incidence aneurysmal rupture between the α7KO mice treated with nicotine and the α7KO mice treated with the vehicle (α7KO + nicotine vs. α7KO + vehicle: 27% vs. 44%; P = 1.00). Conclusion: Our data indicate that α7nAChR mediates nicotine’s promotion of intracranial aneurysmal rupture.

Mechanisms of neuroprotection against ischemic insult by stress-inducible phosphoprotein-1/prion protein complex.

Stress-inducible phosphoprotein 1 (STI1) acts as a neuroprotective factor in the ischemic brain and its levels are increased following ischemia. Previous work has suggested that some of these STI1 actions in a stroke model depend on the recruitment of bone marrow-derived stem cells to improve outcomes after ischemic insult. However, STI1 can directly increase neuroprotective signaling in neurons by engaging with the cellular prion protein (PrPC ) and activating α7 nicotinic acetylcholine receptors (α7nAChR). Given that α7nAChR activation has also been involved in neuroprotection in stroke, it is possible that STI1 can have direct actions on neurons to prevent deleterious consequences of ischemic insults. Here, we tested this hypothesis by exposing primary neuronal cultures to 1-h oxygen-glucose deprivation (OGD) and reperfusion and assessing signaling pathways activated by STI1/PrPC . Our results demonstrated that STI1 treatment significantly decreased apoptosis and cell death in mouse neurons submitted to OGD in a manner that was dependent on PrPC and α7nAChR, but also on the activin A receptor 1 (ALK2), which has emerged as a signaling partner of STI1. Interestingly, pharmacological inhibition of the ALK2 receptor prevented neuroprotection by STI1, while activation of ALK2 receptors by bone morphogenetic protein 4 (BMP4) either before or after OGD was effective in decreasing neuronal death induced by ischemia. We conclude that PrPC /STI1 engagement and its subsequent downstream signaling cascades involving α7nAChR as well as the ALK2 receptor may be activated in neurons by increased levels of STI1. This signaling pathway protects neurons from ischemic insults.

Electrophysiological investigation of the effect of structurally different bispyridinium non-oxime compounds on human α7-nicotinic acetylcholine receptor activity—An in vitro structure-activity analysis

Organophosphorus compounds, including nerve agents and pesticides, exert their toxicity through irreversible inhibition of acetylcholinesterase (AChE) resulting in an accumulation of acetylcholine and functional impairment of muscarinic and nicotinic acetylcholine receptors. Current therapy comprises oximes to reactivate AChE and atropine to antagonize effects induced by muscarinic acetylcholine receptors. Nicotinic malfunction leading to depression of the central and peripheral respiratory system is not directly treated calling for alternative therapeutic interventions. In the present study, we investigated the electrophysiological properties of the human nAChR subtype α7 (hα7-nAChR) and the functional effect of the 4-tert-butyl bispyridinium (BP) compound MB327 and of a series of novel substituted bispyridinium compounds on the receptors by an automated patch clamp technique. Activation of hα7-nAChRs was induced by nicotine and acetylcholine demonstrating rapid cationic influx up to 100μM. Agonist-induced currents decayed within a few milliseconds revealing fast desensitization of the receptors. Application of higher agonist concentrations led to a decline of current amplitudes which seemed to be due to increasing receptor desensitization. When 100μM of agonist was coapplied with low concentrations of the well characterized α7-specific positive allosteric modulator PNU-120596 (1μM–10μM), the maximum response and duration of nAChR activation were markedly augmented indicating an elongated mean open-time of receptors and prevention of receptor desensitization. However, co-application of increasing PNU-120596 concentrations (>10μM) with agonist induced a decline of potentiated current responses. Although less pronounced than PNU-120596, six of the twenty tested substituted BP compounds, in particular those with a substituent at 3-position and 4-position at the pyridinium moieties, were found to potentiate current responses of hα7-nAChRs, most pronounced MB327.This effect was clearly depended on the presence of the agonist indicating a positive allosteric mechanism of these compounds. Besides potentiation at low concentrations, these compounds seem to interact at different binding sites on hα7-nAChRs since enhancement decreased at high concentrations.The residual fourteen BP compounds, possessing either an isopropyl-group or more than one group at the pyridinium moiety, antagonized nicotinic currents exhibiting IC50 of low up to high micromolar concentrations (∼1μM–300μM).

Delayed Varenicline Administration Reduces Inflammation and Improves Forelimb Use Following Experimental Stroke

Pharmacological activation of the cholinergic anti-inflammatory pathway (CAP), specifically by activating α7 nicotinic acetylcholine receptors, has been shown to confer short-term improvements in outcome. Most studies have investigated administration within 24 hours of stroke, and few have investigated drugs approved for use in human patients. We investigated whether delayed administration of varenicline, a high-affinity agonist at α7 nicotinic receptors and an established therapy for nicotine addiction, decreased brain inflammation and improved functional performance in a mouse model of experimental stroke. CSF-1R-EGFP (MacGreen) mice were subjected to transient middle cerebral artery occlusion and administered varenicline (2.5 mg/kg/d for 7 days) or saline (n = 10 per group) 3 days after stroke. Forelimb asymmetry was assessed in the Cylinder test every 2 days after surgery, and structural lesions were quantified at day 10. Enhanced green fluorescent protein (EGFP) and growth associated protein 43 (GAP43) immunohistochemistry were used to evaluate the effect of varenicline on inflammation and axonal regeneration, respectively. Varenicline-treated animals showed a significant increase in impaired forelimb use compared with saline-treated animals 10 days after stroke. Varenicline treatment was associated with reduced EGFP expression and increased GAP43 expression in the striatum of MacGreen mice. Our results show that delayed administration of varenicline promotes recovery of function following experimental stroke. Motor function improvements were accompanied by decreased brain inflammation and increased axonal regeneration in nonpenumbral areas. These results suggest that the administration of an exogenous nicotinic agonist in the subacute phase following stroke may be a viable therapeutic strategy for stroke patients.

Zingiberis Siccatum Rhizoma, the active component of the Kampo formula Daikenchuto, induces anti-inflammatory actions through α7 nicotinic acetylcholine receptor activation.

We previously reported that Daikenchuto (DKT), a gastrointestinal prokinetic Japanese herbal (Kampo) medicine used for the treatment of postoperative ileus (POI), has characteristic potent anti-inflammatory activity. This effect may be partly mediated by the activation of α7 nicotinic acetylcholine receptor (nAChR). In this study, we identified the specific herbs in DKT that induce anti-inflammatory action. The herbal components of DKT were individually administered orally to each mouse four times before and after intestinal manipulation (IM) was carried out on the distal ileum. The anti-inflammatory activity of each crude drug was subsequently evaluated using immunohistochemical analyses of relevant molecules. Treatment with Zingiberis Siccatum Rhizoma (ZSR) but not the other components inhibited the infiltration of cluster of differentiation 68 (CD68)-positive macrophages as effectively as DKT treatment. Selective α7nAChR antagonists, such as methyllycaconitine citrate, or transient receptor potential ankyrin 1 (TRPA1) antagonists, such as HC-030031, significantly inhibited the amelioration of macrophage infiltration by ZSR. The inhibition of macrophage infiltration by ZSR was abolished in both α7nAChR and 5-hydroxytryptamine 4 receptor (5-HT4 R) knockout mice. Daikenchuto-induced anti-inflammatory activity, which was mediated by inhibiting macrophage infiltration in POI, is dependent on the effects of ZSR. Zingiberis Siccatum Rhizoma activates TRPA1 channels possibly in enterochromaffin (EC) cells to release 5-HT, which stimulates 5-HT4 R in the myenteric plexus neurons to release ACh, which in turn activates α7nAChR on macrophages to inhibit inflammation in POI.

α7-Nicotinic acetylcholine receptor inhibition by indinavir: implications for cognitive dysfunction in treated HIV disease.

The study set out to determine if the HIV protease inhibitor, indinavir, alters responsiveness of α7-nicotinic acetylcholine receptors to acetylcholine. Treatment with HAART has dramatically reduced development of HIV-associated dementia and more severe forms of cognitive impairment. However, many individuals continue to experience cognitive decline of uncertain cause. Previous studies have failed to demonstrate significant alterations of functional brain connectivity, structural brain changes, or changes in cerebral blood flow sufficient to explain cognitive decline in virally suppressed individuals. This suggests that the mechanisms underlying development and progression of cognitive problems likely occurs at a micro rather than macro level, such as disruptions in neurotransmitter system signaling. Indinavir's effects on α7-nicotinic acetylcholine receptor activity was tested using a ScreenPatch IonWorks Barracuda-based assay in a mammalian cell model. At low concentrations (0.0003-10 μmol/l) indinavir acts as a positive allosteric modulator (EC50 = 0.021 μmol/l), whereas at concentrations greater than 10 μmol/l (30-100 μmol/l) indinavir acts as an inhibitor of the α7-nicotinic acetylcholine receptor. At concentrations greater than 10 μmol/l indinavir reduces synaptic transmission in the acetylcholine neurotransmitter system, which could possibly contribute to cognitive dysfunction. These results suggest that further experiments should be considered to assess whether patients might benefit from treatment with cholinesterase inhibitors that counteract the effects of indinavir.