The nicotinic acetylcholine receptor: structure and autoimmune pathology

Nicotinic acetylcholine receptors in cancer: Limitations and prospects

Nicotinic acetylcholine receptors (nAChRs) have long been considered to solely mediate neurotransmission. However, their widespread distribution in the human body suggests a more diverse physiological role. Additionally, the expression of nAChRs is increased in certain cancers, such as lung cancer, and has been associated with cell proliferation, epithelial-to-mesenchymal cell transition, angiogenesis and apoptosis prevention. Several compounds that interact with these receptors have been identified as potential therapeutic agents. They have been tested as drugs for treating nicotine addiction, alcoholism, depression, pain and Alzheimer's disease. This review focuses on nAChR-mediated signalling in cancer, presenting opportunities for the development of innovative nAChR-based anticancer drugs. It displays the differences in expression of each nAChR subunit between normal and cancer cells for selected cancer types, highlighting their possible involvement in specific cases. Antagonists of nAChRs that could complement existing cancer therapies are summarised and critically discussed. We hope that this review will stimulate further research on the role of nAChRs in cancer potentially leading to innovative cancer therapies.

Distinct patterns of auto-reactive antibodies associated with organ-specific immune-related adverse events

The roles of preexisting auto-reactive antibodies in immune-related adverse events (irAEs) associated with immune checkpoint inhibitor therapy are not well defined. Here, we analyzed plasma samples longitudinally collected at predefined time points and at the time of irAEs from 58 patients with immunotherapy naïve metastatic non-small cell lung cancer treated on clinical protocol with ipilimumab and nivolumab. We used a proteomic microarray system capable of assaying antibody reactivity for IgG and IgM fractions against 120 antigens for systemically evaluating the correlations between auto-reactive antibodies and certain organ-specific irAEs. We found that distinct patterns of auto-reactive antibodies at baseline were associated with the subsequent development of organ-specific irAEs. Notably, ACHRG IgM was associated with pneumonitis, anti-cytokeratin 19 IgM with dermatitis, and anti-thyroglobulin IgG with hepatitis. These antibodies merit further investigation as potential biomarkers for identifying high-risk populations for irAEs and/or monitoring irAEs during immunotherapy treatment.

Trial registration

ClinicalTrials.gov identifier: NCT03391869.

The controversial effect of smoking and nicotine in SARS-CoV-2 infection

The effects of nicotine and cigarette smoke in many diseases, notably COVID-19 infection, are being debated more frequently. The current basic data for COVID-19 is increasing and indicating the higher risk of COVID-19 infections in smokers due to the overexpression of corresponding host receptors to viral entry. However, current multi-national epidemiological reports indicate a lower incidence of COVID-19 disease in smokers. Current data indicates that smokers are more susceptible to some diseases and more protective of some other. Interestingly, nicotine is also reported to play a dual role, being both inflammatory and anti-inflammatory. In the present study, we tried to investigate the effect of pure nicotine on various cells involved in COVID-19 infection. We followed an organ-based systematic approach to decipher the effect of nicotine in damaged organs corresponding to COVID-19 pathogenesis (12 related diseases). Considering that the effects of nicotine and cigarette smoke are different from each other, it is necessary to be careful in generalizing the effects of nicotine and cigarette to each other in the conducted researches. The generalization and the undifferentiation of nicotine from smoke is a significant bias. Moreover, different doses of nicotine stimulate different effects (dose-dependent response). In addition to further assessing the role of nicotine in COVID-19 infection and any other cases, a clever assessment of underlying diseases should also be considered to achieve a guideline for health providers and a personalized approach to treatment.

Nicotine in Inflammatory Diseases: Anti-Inflammatory and Pro-Inflammatory Effects

As an anti-inflammatory alkaloid, nicotine plays dual roles in treating diseases. Here we reviewed the anti-inflammatory and pro-inflammatory effects of nicotine on inflammatory diseases, including inflammatory bowel disease, arthritis, multiple sclerosis, sepsis, endotoxemia, myocarditis, oral/skin/muscle inflammation, etc., mainly concerning the administration methods, different models, therapeutic concentration and duration, and relevant organs and tissues. According to the data analysis from recent studies in the past 20 years, nicotine exerts much more anti-inflammatory effects than pro-inflammatory ones, especially in ulcerative colitis, arthritis, sepsis, and endotoxemia. On the other hand, in oral inflammation, nicotine promotes and aggravates some diseases such as periodontitis and gingivitis, especially when there are harmful microorganisms in the oral cavity. We also carefully analyzed the nicotine dosage to determine its safe and effective range. Furthermore, we summarized the molecular mechanism of nicotine in these inflammatory diseases through regulating immune cells, immune factors, and the vagus and acetylcholinergic anti-inflammatory pathways. By balancing the “beneficial” and “harmful” effects of nicotine, it is meaningful to explore the effective medical value of nicotine and open up new horizons for remedying acute and chronic inflammation in humans.

α1-nAchR-Mediated Signaling Through Lipid Raft Is Required for Nicotine-Induced NLRP3 Inflammasome Activation and Nicotine-Accelerated Atherosclerosis

Background

Nicotine exerts direct effects on multiple cell types in the cardiovascular system by associating with its high-affinity nicotinic acetylcholine receptors (nAchRs). Lipid raft is a membrane microdomain that recruits various receptors and signaling molecules for coordinating cellular immune response and many others signaling processes. Here, we aim to identify the essential role of lipid raft in mediating nicotine-triggered inflammatory and nicotine-accelerated atherosclerosis, and to figure out the specific receptor of nicotine-induced Nod-like receptor protein 3 (NLRP3) inflammasome activation in macrophage.

Methods and Results

ApoE^–/– mice were fed with a high-fat diet to build atherosclerosis model. Methyl-β-cyclodextrin was used to interrupt intact lipid raft. We confirmed that nicotine triggered NLRP3 inflammasome activation and induced macrophage migration into atherosclerotic plaque, thus accelerated atherosclerosis in apoE^–/– mice fed with a high-fat diet. Mechanically, nicotine increased the expression of α1-nAChR and stimulated the accumulation of α1-nAChR in lipid raft, leading to NLRP3 inflammasome activation in macrophage. Conversely, silencing of α1-nAChR in macrophage sufficiently blocked the pro-inflammasome activation effect of nicotine, indicating that α1-nAChR was the specific receptor for nicotine in triggering NLRP3 inflammasome in macrophage. Furthermore, both the destruction of lipid raft by methyl-β-cyclodextrin and the interference of lipid raft clustering by silencing acid sphingomyelinase reversed nicotine-induced NLRP3 inflammasome activation by reducing the accumulation of α1-nAChR in lipid raft in macrophage, suggesting lipid raft–mediated accumulation of α1-nAChR was the key event in regulating the pro-inflammatory effects of nicotine in macrophage. Importantly, nicotine-induced NLRP3 inflammasome activation and macrophage migration into atherosclerotic plaque were reversed by methyl-β-cyclodextrin, making a significant improvement for atherosclerosis in apoE^–/– mice fed with a high-fat diet.

Conclusion

α1-nAChR-mediated signaling through lipid raft is required for NLRP3 inflammasome activation and pro-atherosclerotic property of nicotine.

Central nervous system regulation of organismal energy and glucose homeostasis

Growing evidence implicates the brain in the regulation of both immediate fuel availability (for example, circulating glucose) and long-term energy stores (that is, adipose tissue mass). Rather than viewing the adipose tissue and glucose control systems separately, we suggest that the brain systems that control them are components of a larger, highly integrated, 'fuel homeostasis' control system. This conceptual framework, along with new insights into the organization and function of distinct neuronal systems, provides a context within which to understand how metabolic homeostasis is achieved in both basal and postprandial states. We also review evidence that dysfunction of the central fuel homeostasis system contributes to the close association between obesity and type 2 diabetes, with the goal of identifying more effective treatment options for these common metabolic disorders.

Cholesterol in myasthenia gravis

The cholinergic neuromuscular junction is the paradigm peripheral synapse between a motor neuron nerve ending and a skeletal muscle fiber. In vertebrates, acetylcholine is released from the presynaptic site and binds to the nicotinic acetylcholine receptor at the postsynaptic membrane. A variety of pathologies among which myasthenia gravis stands out can impact on this rapid and efficient signaling mechanism, including autoimmune diseases affecting the nicotinic receptor or other synaptic proteins. Cholesterol is an essential component of biomembranes and is particularly rich at the postsynaptic membrane, where it interacts with and modulates many properties of the nicotinic receptor. The profound changes inflicted by myasthenia gravis on the postsynaptic membrane necessarily involve cholesterol. This review analyzes some aspects of myasthenia gravis pathophysiology and associated postsynaptic membrane dysfunction, including dysregulation of cholesterol metabolism in the myocyte brought about by antibody-receptor interactions. In addition, given the extensive therapeutic use of statins as the typical cholesterol-lowering drugs, we discuss their effects on skeletal muscle and the possible implications for MG patients under chronic treatment with this type of compound.

Nicotinic Receptor Subunits Atlas in the Adult Human Lung

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels responsible for rapid neural and neuromuscular signal transmission. Although it is well documented that 16 subunits are encoded by the human genome, their presence in airway epithelial cells (AECs) remains poorly understood, and contribution to pathology is mainly discussed in the context of cancer. We analysed nAChR subunit expression in the human lungs of smokers and non-smokers using transcriptomic data for whole-lung tissues, isolated large AECs, and isolated small AECs. We identified differential expressions of nAChRs in terms of detection and repartition in the three modalities. Smoking-associated alterations were also unveiled. Then, we identified an nAChR transcriptomic print at the single-cell level. Finally, we reported the localizations of detectable nAChRs in bronchi and large bronchioles. Thus, we compiled the first complete atlas of pulmonary nAChR subunits to open new avenues to further unravel the involvement of these receptors in lung homeostasis and respiratory diseases.

Upregulated nicotinic ACh receptor signaling contributes to intestinal stem cell function through activation of Hippo and Notch signaling pathways

BACKGROUNDS

Recent studies have shown that various mammalian non-neuronal cells synthesize acetylcholine (ACh) in situ and operate cholinergic signaling via nicotinic and muscarinic ACh receptors (nAChRs and mAChRs). Understanding the mechanisms that control intestinal stem cell (ISC) function through activation of nAChR signaling is critical for developing therapeutic interventions for diseases such as inflammatory bowel disease (IBD). Previously, by conducting RNA sequencing (RNA-Seq) analysis using crypt-villus organoid cultures, we found that the Hippo signaling pathway, a stem cell regulating network, is upregulated in ISCs after treatment with nicotine. Here, we explored the roles of nAChR signaling through activation of the Hippo signaling pathway.

METHODS

RNA-Seq data were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis. β4-knock-in mice were generated, and experiments using the knock-in mice and their intestinal organoids were carried out.

RESULTS

RNA-Seq and qRT-PCR analyses demonstrated that the expression of YAP1/TAZ and Notch1/Dll1 was upregulated after treatment with nicotine. However, a nAChR antagonist, mecamylamine, strongly inhibited the expression of these genes. Notably, we found that in β4-knock-in mouse small intestines, expression of YAP1 and Notch1 was significantly reduced, but not that of TAZ and Dll1, suggesting that Hippo and Notch signaling pathways are putative targets for nAChR signaling. Furthermore, fluorescent signals were detected in Paneth cells that interact with ISCs at the crypt bottom, indicating an interaction between Paneth cells and ISCs via nAChR signaling through the activation of Hippo and Notch signaling pathways.

CONCLUSION

Our results indicate that upregulated nAChR signaling contributes to the maintenance of ISC activity and balances differentiation through activation of Hippo and Notch signaling pathways.

Endothelial to mesenchymal transition contributes to nicotine-induced atherosclerosis

Rationale: Nicotine exposure via cigarette smoking is strongly associated with atherosclerosis. However, the underlying mechanisms remain poorly understood. The current study aimed to identify whether endothelial to mesenchymal transition (EndMT) contributes to nicotine-induced atherosclerosis. Methods: ApoE-/- mice were administered nicotine in their drinking water for 12 weeks. The effects of nicotine on EndMT were determined by immunostaining on aortic root and RNA analysis in aortic intima. In vitro nicotine-treated cell model was established on human aortic endothelial cells (HAECs). The effects of nicotine on the expression of EndMT-related markers, ERK1/2 and Snail were quantified by real-time PCR, western blot and immunofluorescent staining. Results: Nicotine treatment resulted in larger atherosclerotic plaques in ApoE-/- mice. The vascular endothelial cells from nicotine-treated mice showed mesenchymal phenotype, indicating EndMT. Moreover, nicotine-induced EndMT process was accompanied by cytoskeleton reorganization and impaired barrier function. The α7 nicotine acetylcholine receptor (α7nAChR) was highly expressed in HAECs and its antagonist could effectively relieve nicotine-induced EndMT and atherosclerotic lesions in mice. Further experiments revealed that ERK1/2 signaling was activated by nicotine, which led to the upregulation of Snail. Blocking ERK1/2 with inhibitor or silencing Snail by small interfering RNA efficiently preserved endothelial phenotype upon nicotine stimulation. Conclusion: Our study provides evidence that EndMT contributes to the pro-atherosclerotic property of nicotine. Nicotine induces EndMT through α7nAChR-ERK1/2-Snail signaling in endothelial cells. EndMT may be a therapeutic target for smoking-related endothelial dysfunction and cardiovascular disease.

RIC3, the cholinergic anti-inflammatory pathway, and neuroinflammation

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels having many functions including inflammation control, as part of the cholinergic anti-inflammatory pathway. Genome wide association studies implicated RIC3, a chaperone of nAChRs, in multiple sclerosis (MS), a neuroinflammatory disease. To understand the involvement of RIC3 in inflammatory diseases we examined its expression, regulation, and function in activated immune cells. Our results show that immune activation leads to dynamic changes in RIC3 expression, in a mouse model of MS and in human lymphocytes and macrophages. We also show similarities in the expression dynamics of RIC3 and CHRNA7, encoding for the α7 nAChR subunit. Homomeric α7 nAChRs were shown to mediate the anti-inflammatory effects of cholinergic agonists. Thus, similarity in expression dynamics between RIC3 and CHRNA7 is suggestive of functional concordance. Indeed, siRNA mediated silencing of RIC3 in a mouse macrophage cell line eliminates the anti-inflammatory effects of cholinergic agonists. Furthermore, we show increased average expression of RIC3 and CHRNA7 in lymphocytes from MS patients, and a strong correlation between expression levels of these two genes in MS patients but not in healthy donors. Together, our results are consistent with a role for RIC3 and for the mechanisms regulating its expression in inflammatory processes and in neuroinflammatory diseases.

Microduplication of 15q13.3 and Microdeletion of 18q21.32 in a Patient with Moyamoya Syndrome

Moyamoya angiopathy (MA) is a cerebrovascular disease determining a progressive stenosis of the terminal part of the internal carotid arteries (ICAs) and their proximal branches and the compensatory development of abnormal “moyamoya” vessels. MA occurs as an isolated cerebral angiopathy (so-called moyamoya disease) or in association with various conditions (moyamoya syndromes) including several heritable conditions such as Down syndrome, neurofibromatosis type 1 and other genomic defects. Although the mechanism that links MA to these genetic syndromes is still unclear, it is believed that the involved genes may contribute to the disease susceptibility. Herein, we describe the case of a 43 years old woman with bilateral MA and peculiar facial characteristics, having a 484-kb microduplication of the chromosomal region 15q13.3 and a previously unreported 786 kb microdeletion in 18q21.32. This patient may have a newly-recognized genetic syndrome associated with MA. Although the relationship between these genetic variants and MA is unclear, our report would contribute to widening the genetic scenario of MA, in which not only genic mutation, but also genome unbalances are possible candidate susceptibility factors.

The Coordinated Activities of nAChR and Wnt Signaling Regulate Intestinal Stem Cell Function in Mice

Cholinergic signaling, which modulates cell activities via nicotinic and muscarinic acetylcholine receptors (n- and mAChRs) in response to internal or external stimuli, has been demonstrated in mammalian non-neuronal cells that synthesize acetylcholine (ACh). One of the major pathways of excitatory transmission in the enteric nervous system (ENS) is mediated by cholinergic transmission, with the transmitter ACh producing excitatory potentials in postsynaptic effector cells. In addition to ACh-synthesizing and ACh-metabolizing elements in the ENS, the presence of non-neuronal ACh machinery has been reported in epithelial cells of the small and large intestines of rats and humans. However, little is known about how non-neuronal ACh controls physiological function in the intestine. Here, experiments using crypt-villus organoids that lack nerve and immune cells in culture suggest that endogenous ACh is synthesized in the intestinal epithelium to drive organoid growth and differentiation through activation of nAChRs. Treatment of organoids with nicotine enhanced cell growth and the expression of marker genes for stem and epithelial cells. On the other hand, the nAChR antagonist mecamylamine strongly inhibited the growth and differentiation of organoids, suggesting the involvement of nAChRs in the regulation of proliferation and differentiation of Lgr5-positive stem cells. More specifically, RNA sequencing analysis revealed that Wnt5a expression was dramatically upregulated after nicotine treatment, and Wnt5a rescued organoid growth and differentiation in response to mecamylamine. Taken together, our results indicate that coordinated activities of nAChR and Wnt signaling maintain Lgr5-positive stem cell activity and balanced differentiation. Furthermore, we could clearly separate the two groups, neuronal ACh in the ENS and non-neuronal ACh in the intestinal epithelium. Dysfunction of the non-neuronal cholinergic system is involved in the pathogenesis of disease. The data will increase our understanding of the cholinergic properties of non-neuronal cells and lead to optimization of drug therapy.

Intracerebroventricular administration of cigarette smoke condensate induced generalized seizures reduced by muscarinic receptor antagonist in rats

Tobacco smoking is considered the greatest risk factor for early death caused by noncommunicable diseases. Currently, there are more than one billion tobacco smokers in the world predisposed to many diseases including heart attack, stroke, cancer, and premature birth or birth defects related to the consumption of cigarettes. However, studies on the association between tobacco smoking and seizures or epilepsy are insufficient and not well documented. In the present study, the authors examined the convulsive effects of the intracerebroventricular administration of cigarette smoke condensate (CSC, 2μl/Rat) in rats and compared it with the intensity of seizures in the kainic acid (KA)-induced seizure model of epilepsy. The role of the cholinergic system was also investigated by testing the effect of the muscarinic acetylcholine receptors (mAChRs) antagonist atropine (2ml/kg) on CSC-induced seizures. The results indicate that a central injection of CSC produces an epileptic behavior similar to that induced by KA, the similarities include the following parameters: time latency of seizures, latency and duration of tonic-clonic seizures, duration of seizures, survival, and tonic-clonic rate. However, a pretreatment with atropine reduced seizures and all their parameters.

Stimulation of Alpha7 Nicotinic Acetylcholine Receptor Attenuates Nicotine-Induced Upregulation of MMP, MCP-1, and RANTES through Modulating ERK1/2/AP-1 Signaling Pathway in RAW264.7 and MOVAS Cells

Vagus nerve stimulation through alpha7 nicotine acetylcholine receptors (α7-nAChR) signaling had been demonstrated attenuation of inflammation. This study aimed to determine whether PNU-282987, a selective α7-nAChR agonist, affected activities of matrix metalloproteinase (MMP) and inflammatory cytokines in nicotine-treatment RAW264.7 and MOVAS cells and to assess the underlying molecular mechanisms. RAW264.7 and MOVAS cells were treated with nicotine at different concentrations (0, 1, 10, and 100 ng/ml) for 0–120 min. Nicotine markedly stimulated the phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2) and c-Jun in RAW264.7 cells. Pretreatment with U0126 significantly suppressed phosphorylation of ERK1/2 and further attenuated nicotine-induced activation of c-Jun and upregulation of MMP-2, MMP-9, monocyte chemotactic protein- (MCP-) 1, and regulated upon activation normal T cell expressed and secreted (RANTES). Similarly, nicotine treatment also increased phosphorylation of c-Jun and expressions of MMP-2, MMP-9, MCP-1, and RANTES in MOVAS cells. When cells were pretreated with PNU-282987, nicotine-induced activations of ERK1/2 and c-Jun in RAW264.7 cells and c-Jun in MOVAS cells were effectively inhibited. Furthermore, nicotine-induced secretions of MMP-2, MMP-9, MCP-1, and RANTES were remarkably downregulated. Treatment with α7-nAChR agonist inhibits nicotine-induced upregulation of MMP and inflammatory cytokines through modulating ERK1/2/AP-1 signaling in RAW264.7 cells and AP-1 in MOVAS cells, providing a new therapeutic for abdominal aortic aneurysm.

Molecular mechanisms for anthelmintic resistance in strongyle nematode parasites of veterinary importance

Veterinarians rely on a relatively limited spectrum of anthelmintic agents to control nematode parasites in domestic animals. Unfortunately, anthelmintic resistance has been an emerging problem in veterinary medicine. In particular, resistance has emerged among the strongyles, a group of gastrointestinal nematodes that infect a variety of hosts that range from large herbivores to small companion animals. Over the last several decades, a great deal of research effort has been directed toward developing an understanding of the mechanisms conferring resistance against the three major groups of anthelmintics: macrocyclic lactones, benzimidazoles, and nicotinic agonists. Our understanding of anthelmintic resistance has been largely formed by determining the mechanism of action for each drug class and then evaluating drug-resistant nematode isolates for mutations or differences in expression of target genes. More recently, drug efflux pumps have been recognized for their potential contribution to anthelmintic resistance. In this mini-review, we summarize the evidence for mechanisms of resistance in strongyle nematodes.

Bronchopulmonary C-fibers' IL1RI contributes to the prolonged apneic response to intra-atrial injection of capsaicin by prenatal nicotinic exposure in rat pups

Prenatal nicotinic exposure (PNE) as a SIDS model reportedly sensitizes bronchopulmonary C-fibers (PCFs), contributing to the prolonged PCF-mediated apnea in rat pups, but the relevant mechanisms are not fully understood. Pulmonary IL-1β upregulated by cigarette smoke is known to stimulate or sensitize PCFs acting via IL-1 type I receptor (IL1RI) and inhibit inspiration frequency. Because of its upregulation observed in SIDS victims, we hypothesized that PNE increased pulmonary IL-1β release and IL1RI expression in pulmonary C-neurons via action on α7 nicotinic acetylcholine receptors (α7nAChR) to induce the prolonged PCF-mediated apnea. IL-1β in BALF and IL1RI in the nodose/jugular (N/J) ganglion and vagal pulmonary C-neurons retrogradely-traced were compared between Ctrl (saline) and PNE pups and among the vehicle-treated Ctrl and PNE and methyllycaconitine (a selective α7nAChR antagonist)-treated PNE pups. The effect of IL-1RI blockade (IL-1Ra) on the PCF-mediated apnea was also compared between Ctrl and PNE pups. PNE significantly elevated IL-1β in BALF and upregulated IL1RI gene and protein expression in N/J ganglia and gene in vagal pulmonary C-neurons. All of these responses were eliminated by pretreatment with blockade of α7nAChR. In addition, the prolonged PCF-mediated apnea in PNE pups was significantly shortened by right atrial bolus injection of IL-1Ra. We conclude that PNE enhances pulmonary IL-1β release and PCF IL1RI expression acting via α7nAChR in contributing to sensitization of PCFs and prolongation of the PCF-mediated apneic response.

New Insights Into Tobacco-Induced Vascular Disease: Clinical Ramifications

Tobacco smoke contains more than 4,000 compounds. These include phenols, carbonyls, and nitrosamines that may be irritants and carcinogens; particulate matter such as tars; volatiles and gases such as carbon monoxide; and nicotine. Many of these compounds may contribute to the adverse health effects of tobacco. For example, recent findings have shown that the angiogenic and proliferative effects of nicotine are mediated by activation of nicotinic receptors on the vascular cells. Nicotine-induced activation of vascular cells may contribute to pathological neovascularization in cancer, age-related macular degeneration, and atherosclerosis. This review focuses on how nicotine adversely affects cardiovascular health and highlights intriguing new data about nicotine's potent angiogenic and proliferative properties.

Mechanisms of growth-promoting and tumor-protecting effects of epithelial nicotinic acetylcholine receptors

Although the role of nicotine as a carcinogen is debatable, it is widely accepted that it contributes to cancer by promoting growth and survival of mutated cell clones and protecting them from the chemo- and radiotherapy-induced apoptosis. On the cell membrane (cm), the nicotinic acetylcholine (ACh) receptors (nAChRs) implement upregulation of proliferative and survival genes. Nicotine also can permeate cells and activate mitochondrial (mt)-nAChRs coupled to inhibition of the mitochondrial permeability transition pore (mPTP) opening, thus preventing apoptosis. In this study, we sought to pin down principal mechanisms mediating the tumor-promoting activities of nicotine resulting from activation of cm- and mt-nAChRs in oral and lung cancer cells, SCC25 and SW900, respectively. Activated cm-nAChRs were found to form complexes with receptors for EGF and VEGEF via the α7 and β2 nAChR subunits, respectively, whereas activated mt-nAChRs physically associated with the intramitochondrial protein kinases PI3K and Src via the α7 and β4 subunits. This was associated with upregulated expression of cyclin D1/activation of ERK1/2 and inhibition of mPTP opening, respectively, as well as upregulated proliferation and resistance to H(2)O(2)-induced apoptosis. The molecular synergy between cm-nAChRs and growth factor receptors helps explain how one biological mediator, such as ACh, can modulate activity of the other, such as a growth factor, and vice versa. Establishment of functional coupling of mt-nAChRs to regulation of mPTP opening provides a novel mechanism of nicotine-dependent protection from cell death. Further elucidation of this novel mechanism of tumor-promoting activities of nicotine should have a strong translational impact, because extraneuronal nAChRs may provide a novel molecular target to prevent, reverse, or retard progression of both nicotine-related and unrelated cancers.

Biomolecular recognition of antagonists by α7 nicotinic acetylcholine receptor: Antagonistic mechanism and structure-activity relationships studies

As the key constituent of ligand-gated ion channels in the central nervous system, nicotinic acetylcholine receptors (nAChRs) and neurodegenerative diseases are strongly coupled in the human species. In recently years the developments of selective agonists by using nAChRs as the drug target have made a large progress, but the studies of selective antagonists are severely lacked. Currently these antagonists rest mainly on the extraction of partly natural products from some animals and plants; however, the production of these crude substances is quite restricted, and artificial synthesis of nAChR antagonists is still one of the completely new research fields. In the context of this manuscript, our primary objective was to comprehensively analyze the recognition patterns and the critical interaction descriptors between target α7 nAChR and a series of the novel compounds with potentially antagonistic activity by means of virtual screening, molecular docking and molecular dynamics simulation, and meanwhile these recognition reactions were also compared with the biointeraction of α7 nAChR with a commercially natural antagonist - methyllycaconitine. The results suggested clearly that there are relatively obvious differences of molecular structures between synthetic antagonists and methyllycaconitine, while the two systems have similar recognition modes on the whole. The interaction energy and the crucially noncovalent forces of the α7 nAChR-antagonists are ascertained according to the method of Molecular Mechanics/Generalized Born Surface Area. Several amino acid residues, such as B/Tyr-93, B/Lys-143, B/Trp-147, B/Tyr-188, B/Tyr-195, A/Trp-55 and A/Leu-118 played a major role in the α7 nAChR-antagonist recognition processes, in particular, residues B/Tyr-93, B/Trp-147 and B/Tyr-188 are the most important. These outcomes tally satisfactorily with the discussions of amino acid mutations. Based on the explorations of three-dimensional quantitative structure-activity relationships, the structure-antagonistic activity relationships of antagonists and the characteristics of α7 nAChR-ligand recognitions were received a reasonable summary as well. These attempts emerged herein would not only provide helpful guidance for the design of α7 nAChR antagonists, but shed new light on the subsequent researches in antagonistic mechanism.

Mechanisms of tumor-promoting activities of nicotine in lung cancer: synergistic effects of cell membrane and mitochondrial nicotinic acetylcholine receptors

Background

One of the major controversies of contemporary medicine is created by an increased consumption of nicotine and growing evidence of its connection to cancer, which urges elucidation of the molecular mechanisms of oncogenic effects of inhaled nicotine. Current research indicates that nicotinergic regulation of cell survival and death is more complex than originally thought, because it involves signals emanating from both cell membrane (cm)- and mitochondrial (mt)-nicotinic acetylcholine receptors (nAChRs). In this study, we elaborated on the novel concept linking cm-nAChRs to growth promotion of lung cancer cells through cooperation with the growth factor signaling, and mt-nAChRs — to inhibition of intrinsic apoptosis through prevention of opening of mitochondrial permeability transition pore (mPTP).

Methods

Experiments were performed with normal human lobar bronchial epithelial cells, the lung squamous cell carcinoma line SW900, and intact and NNK-transformed immortalized human bronchial cell line BEP2D.

Results

We demonstrated that the growth-promoting effect of nicotine mediated by activation of α7 cm-nAChR synergizes mainly with that of epidermal growth factor (EGF), α3 — vascular endothelial growth factor (VEGF), α4 — insulin-like growth factor I (IGF-I) and VEGF, whereas α9 with EGF, IGF-I and VEGF. We also established the ligand-binding abilities of mt-nAChRs and demonstrated that quantity of the mt-nAChRs coupled to inhibition of mPTP opening increases upon malignant transformation.

Conclusions

These results indicated that the biological sum of simultaneous activation of cm- and mt-nAChRs produces a combination of growth-promoting and anti-apoptotic signals that implement the tumor-promoting action of nicotine on lung cells. Therefore, nAChRs may be a promising molecular target to arrest lung cancer progression and re-open mitochondrial apoptotic pathways.

Inhibition of allergen-induced basophil activation by ASM-024, a nicotinic receptor ligand

BACKGROUND

Nicotinic acetylcholine receptors (nAChRs) were identified on eosinophils and shown to regulate inflammatory responses, but nAChR expression on basophils has not been explored yet.

OBJECTIVE

We investigated surface receptor expression of nAChR α4, α7 and α1/α3/α5 subunits on basophils. Furthermore, we examined the effects of ASM-024, a synthetic nicotinic ligand, on in vitro anti-IgE and in vivo allergen-induced basophil activation.

METHODS

Basophils were enriched from the peripheral blood of allergic donors and the expression of nAChR subunits and muscarinic receptors was determined. Purified basophils were stimulated with anti-IgE in the presence of ASM-024 with or without muscarinic or nicotinic antagonists for the measurement of CD203c expression and histamine release. The effect of 9 days of treatment with 50 and 200 mg ASM-024 on basophil CD203c expression was examined in the blood of mild allergic asthmatics before and after allergen inhalation challenge.

RESULTS

nAChR α4, α7 and α1/α3/α5 receptor subunit expression was detected on basophils. Stimulation of basophils with anti-IgE increased CD203c expression and histamine release, which was inhibited by ASM-024 (10(-5) to 10(-)(3) M, p < 0.05). The effect of ASM-024 was reversed in the presence of muscarinic and nicotinic antagonists. In subjects with mild asthma, ASM-024 inhalation significantly inhibited basophil CD203c expression measured 24 h after allergen challenge (p = 0.03).

CONCLUSION

This study shows that ASM-024 inhibits IgE- and allergen-induced basophil activation through both nicotinic and muscarinic receptors, and suggests that ASM-024 may be an efficacious agent for modulating allergic asthma responses.

Connections of nicotine to cancer

This Opinion article discusses emerging evidence of direct contributions of nicotine to cancer onset and growth. The list of cancers reportedly connected to nicotine is expanding and presently includes small-cell and non-small-cell lung carcinomas, as well as head and neck, gastric, pancreatic, gallbladder, liver, colon, breast, cervical, urinary bladder and kidney cancers. The mutagenic and tumour-promoting activities of nicotine may result from its ability to damage the genome, disrupt cellular metabolic processes, and facilitate growth and spreading of transformed cells. The nicotinic acetylcholine receptors (nAChRs), which are activated by nicotine, can activate several signalling pathways that can have tumorigenic effects, and these receptors might be able to be targeted for cancer therapy or prevention. There is also growing evidence that the unique genetic makeup of an individual, such as polymorphisms in genes encoding nAChR subunits, might influence the susceptibility of that individual to the pathobiological effects of nicotine. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the evaluation of regulations on nicotine product manufacturing, distribution and marketing.

The pro-proliferative effects of nicotine and its underlying mechanism on rat airway smooth muscle cells

Recent studies have shown that nicotine, a major component of cigarette smoke, can stimulate the proliferation of non-neuronal cells. Cigarette smoking can promote a variety of pulmonary and cardiovascular diseases, such as chronic obstructive pulmonary disease (COPD), atherosclerosis, and cancer. A predominant feature of COPD is airway remodeling, which includes increased airway smooth muscle (ASM) mass. The mechanisms underlying ASM remodeling in COPD have not yet been fully elucidated. Here, we show that nicotine induces a profound and time-dependent increase in DNA synthesis in rat airway smooth muscle cells (RASMCs) in vitro. Nicotine also significantly increased the number of RASMCs, which was associated with the increased expression of Cyclin D1, phosphorylation of the retinoblastoma protein (RB) and was dependent on the activation of Akt. The activation of Akt by nicotine occurred within minutes and depended upon the nicotinic acetylcholine receptors (nAchRs). Activated Akt increased the phosphorylation of downstream substrates such as GSK3β. Our data suggest that the binding of nicotine to the nAchRs on RASMCs can regulate cellular proliferation by activating the Akt pathway.

Acetylcholine receptor subunit and P-glycoprotein transcription patterns in levamisole-susceptible and -resistant Haemonchus contortus

The mechanism of resistance to the anthelmintic levamisole in parasitic nematodes is poorly understood, although there is some evidence implicating changes in expression of nicotinic acetylcholine receptor (nAChR) subunit genes. Hence, in order to define levamisole resistance mechanisms in some Australian field-derived isolates of Haemonchus contortus we examined gene expression patterns and SNPs in nAChR subunit genes, as well as expression levels for P-glycoprotein (P-gp) and receptor ancillary protein genes, in various life stages of one levamisole-sensitive and three levamisole-resistant isolates of this species. Larvae of two isolates showed high-level resistance to levamisole (resistance ratios at the IC50 > 600) while the third isolate showed a degree of heterogeneity, with a resistance factor of only 1.1-fold at the IC50 alongside the presence of a resistant subpopulation. Transcription patterns for nAChR subunit genes showed a great degree of variability across the different life stages and isolates. The most consistent observation was the down-regulation of Hco-unc-63a in adults of all resistant isolates. Transcription of this gene was also reduced in the L3 stage of the two most resistant isolates, highlighting its potential as a resistance marker in the readily accessible free-living stages. There was down regulation of all four Hco-unc-29 paralogs in adults of one resistant isolate. There were no consistent changes in expression of P-gps or ancillary protein genes across the resistant isolates. The present study has demonstrated a complex pattern of nAChR subunit gene expression in H. contortus, and has highlighted several instances where reduced expression of subunit genes (Hco-unc-63a, Hco-unc-29) may be associated with the observed levamisole resistance. The data also suggests that it will be difficult to detect resistance using gene transcription-based methods on pooled larval samples from isolates containing only a resistant subpopulation due to the averaging of gene expression data across the whole population.

Neural pathways in allergic inflammation

Allergy is on the rise worldwide. Asthma, food allergy, dermatitis, and systemic anaphylaxis are amongst the most common allergic diseases. The association between allergy and altered behavior patterns has long been recognized. The molecular and cellular pathways in the bidirectional interactions of nervous and immune systems are now starting to be elucidated. In this paper, we outline the consequences of allergic diseases, especially food allergy and asthma, on behavior and neural activity and on the neural modulation of allergic responses.

Novel role of Egr-1 in nicotine-related neointimal formation

AIMS

The aim of this study was to investigate the mechanisms by which nicotine increases vascular smooth muscle cell (VSMC) proliferation and post-injury neointimal formation.

METHODS AND RESULTS

Vascular injury was inflicted in the right iliac artery of nicotine-treated and control rats. Nicotine increased post-injury VSMC proliferation (Ki67(+) cells) and neointimal formation (neointima/media ratio, 0.42 ± 0.23 vs. 0.14 ± 0.07, P= 0.02). To determine the mechanisms by which nicotine exacerbates VSMC proliferation, cultured cells were exposed to nicotine, and signalling pathways leading to cell proliferation were studied. Nicotine activated extracellular signal-regulated kinase (ERK) 1/2 in a dose- and time-dependent manner. The blockade of this signalling axis abolished nicotine-mediated proliferation. Functional nicotinic acetylcholine receptors and Ca(2+) influx were necessary for ERK1/2 activation and nicotine-induced mitogenesis in VSMCs. Downstream to ERK1/2, nicotine induced the phosphorylation of Ets-like gene 1 in a timely co-ordinated manner with the up-regulation of the atherogenic transcription factor, early growth response 1 (Egr-1). The treatment of balloon-injured arteries with a lentivirus vector carrying a short hairpin RNA against Egr-1 abolished the deleterious effect of nicotine on vascular remodelling.

CONCLUSION

Nicotine acts through its receptors in VSMC to activate the ERK-Egr-1 signaling cascade that induces cell proliferation and exacerbates post-injury neointimal development.

The nicotinic acetylcholine receptor CHRNA5/A3/B4 gene cluster: dual role in nicotine addiction and lung cancer

More than 1 billion people around the world smoke, with 10 million cigarettes sold every minute. Cigarettes contain thousands of harmful chemicals including the psychoactive compound, nicotine. Nicotine addiction is initiated by the binding of nicotine to nicotinic acetylcholine receptors, ligand-gated cation channels activated by the endogenous neurotransmitter, acetylcholine. These receptors serve as prototypes for all ligand-gated ion channels and have been extensively studied in an attempt to elucidate their role in nicotine addiction. Many of these studies have focused on heteromeric nicotinic acetylcholine receptors containing α4 and β2 subunits and homomeric nicotinic acetylcholine receptors containing the α7 subunit, two of the most abundant subtypes expressed in the brain. Recently however, a series of linkage analyses, candidate-gene analyses and genome-wide association studies have brought attention to three other members of the nicotinic acetylcholine receptor family: the α5, α3 and β4 subunits. The genes encoding these subunits lie in a genomic cluster that contains variants associated with increased risk for several diseases including nicotine dependence and lung cancer. The underlying mechanisms for these associations have not yet been elucidated but decades of research on the nicotinic receptor gene family as well as emerging data provide insight on how these receptors may function in pathological states. Here, we review this body of work, focusing on the clustered nicotinic acetylcholine receptor genes and evaluating their role in nicotine addiction and lung cancer.

Auto/paracrine control of inflammatory cytokines by acetylcholine in macrophage-like U937 cells through nicotinic receptors

Although acetylcholine (ACh) is well known for its neurotransmitter function, recent studies have indicated that it also functions as an immune cytokine that prevents macrophage activation through a 'cholinergic (nicotinic) anti-inflammatory pathway'. In this study, we used the macrophage-like U937 cells to elucidate the mechanisms of the physiologic control of cytokine production by auto/paracrine ACh through the nicotinic class of ACh receptors (nAChRs) expressed in these cells. Stimulation of cells with lipopolysaccharide up-regulated expression of alpha1, alpha4, alpha5, alpha7, alpha10, beta1 and beta3 subunits, down-regulated alpha6 and beta2 subunits, and did not alter the relative quantity of alpha9 and beta4 mRNAs. Distinct nAChR subtypes showed differential regulation of the production of pro- and anti-inflammatory cytokines. While inhibition of the expression of the TNF-alpha gene was mediated predominantly by the alpha-bungarotoxin sensitive nAChRs, that of the IL-6 and IL-18 genes-by the mecamylamine-sensitive nAChRs. Both the Mec- and alphaBtx-sensitive nAChRs regulated expression of the IL-1beta gene equally efficiently. Upregulation of IL-10 production by auto/paracrine ACh was mediated predominantly through alpha7 nAChR. These findings offer a new insight on how nicotinic agonists control inflammation, thus laying a groundwork for the development of novel immunomodulatory therapies based on the nAChR subtype selectivity of nicotinic agonists.

Cholinergic stimulation attenuates the IL-4 induced expression of E-selectin and vascular endothelial growth factor by equine pulmonary artery endothelial cells

The endothelium plays a critical role in regulating leukocyte recruitment and migration during inflammation. Recent studies provide evidence that acetylcholine (ACh) and other cholinergic mediators block endothelial cells activation and leukocyte recruitment during inflammation. We thus postulated that the non-neuronal cholinergic system might modulate the recruitment of neutrophils during allergic pulmonary inflammation. In the present study, we examined the effects of cholinergic stimulation on the expression of neutrophil chemokines and adhesion molecules by endothelial cells stimulated by recombinant equine (re) IL-4. Using primary equine pulmonary artery endothelial cells culture and real-time RT-PCR method, we observed that ACh, nicotine, and muscarine inhibit the expression of E-selectin and vascular endothelial growth factor by endothelial cells stimulated by reIL-4. The expression of CXCL-8, a potent neutrophil chemotactic cytokine, remained unaffected however. These findings suggest that the cholinergic anti-inflammatory pathway may modulate pulmonary allergic inflammation and remodeling by the inhibition of selected adhesion molecules and growth factors.

Endothelial nicotinic acetylcholine receptors and angiogenesis

Nicotinic acetylcholine receptors (nAChRs) were first described in non-excitable cells just more than a decade ago. The nAChRs on endothelial cells modulate key angiogenic processes, including endothelial cell survival, proliferation, and migration. The receptors may be stimulated by endogenous agonists such as acetylcholine, or exogenous chemicals such as nicotine, to activate physiologic angiogenesis (such as in wound healing) or pathologic angiogenesis (such as retinal neovascularization or tumor angiogenesis). The endothelial nAChRs may represent a target for therapeutic modulation of disorders characterized by insufficient or pathologic angiogenesis.

Mammalian nicotinic acetylcholine receptors: from structure to function

The classical studies of nicotine by Langley at the turn of the 20th century introduced the concept of a "receptive substance," from which the idea of a "receptor" came to light. Subsequent studies aided by the Torpedo electric organ, a rich source of muscle-type nicotinic receptors (nAChRs), and the discovery of alpha-bungarotoxin, a snake toxin that binds pseudo-irreversibly to the muscle nAChR, resulted in the muscle nAChR being the best characterized ligand-gated ion channel hitherto. With the advancement of functional and genetic studies in the late 1980s, the existence of nAChRs in the mammalian brain was confirmed and the realization that the numerous nAChR subtypes contribute to the psychoactive properties of nicotine and other drugs of abuse and to the neuropathology of various diseases, including Alzheimer's, Parkinson's, and schizophrenia, has since emerged. This review provides a comprehensive overview of these findings and the more recent revelations of the impact that the rich diversity in function and expression of this receptor family has on neuronal and nonneuronal cells throughout the body. Despite these numerous developments, our understanding of the contributions of specific neuronal nAChR subtypes to the many facets of physiology throughout the body remains in its infancy.

Receptor-mediated tobacco toxicity: acceleration of sequential expression of alpha5 and alpha7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke

Tobacco products and nicotine alter the cell cycle and lead to squamatization of oral keratinocytes (KCs) and squamous cell carcinoma. Activation of nicotinic acetylcholine receptors (nAChRs) elicits Ca(2+) influx that varies in magnitude between different nAChR subtypes. Normal differentiation of KCs is associated with sequential expression of the nAChR subtypes with increasing Ca(2+) permeability, such as alpha5-containing alpha3 nAChR and alpha7 nAChR. Exposure to environmental tobacco smoke (ETS) or an equivalent concentration of nicotine accelerated by severalfold the alpha5 and alpha7 expression in KCs, which could be abolished by mecamylamine and alpha-bungarotoxin with different efficacies, suggesting the following sequence of autoregulation of the expression of nAChR subtypes: alpha3(beta2/beta4) > alpha3(beta2/beta4)alpha5 > alpha7 > alpha7. This conjecture was corroborated by results of quantitative assays of subunit mRNA and protein levels, using nAChR-specific pharmacologic antagonists and small interfering RNAs. The genomic effects of ETS and nicotine involved the transcription factor GATA-2 that showed a multifold increase in quantity and activity in exposed KCs. Using protein kinase inhibitors and dominant negative and constitutively active constructs, we characterized the principal signaling cascades mediating a switch in the nAChR subtype. Cumulative results indicated that the alpha3(beta2/beta4) to alpha3(beta2/beta4)alpha5 nAChR transition predominantly involved protein kinase C, alpha3(beta2/beta4)alpha5 to alpha7 nAChR transition-Ca(2+)/calmodulin-dependent protein kinase II and p38 MAPK, and alpha7 self-up-regulation-the p38 MAPK/Akt pathway, and JAK-2. These results provide a mechanistic insight into the genomic effects of ETS and nicotine on KCs and characterize signaling pathways mediating autoregulation of stepwise overexpression of nAChR subtypes with increasing Ca(2+) permeability in exposed cells. These observations have salient clinical implications, because a switch in the nAChR subunit composition can bring about a corresponding switch in receptor function, leading to profound pathobiologic effects observed in KCs exposed to tobacco products.

Neuronal nicotinic alpha7 receptors modulate inflammatory cytokine production in the skin following ultraviolet radiation

The anti-inflammatory effects of the neuronal nicotinic receptor alpha7 (nAChRalpha7) are proposed to require acetylcholine release from vagal efferents. The necessity for vagal innervation in this anti-inflammatory pathway was tested in the skin, which lacks parasympathetic innervation, using ultraviolet radiation (UVB) to induce a local pro-inflammatory response. Cytokine responses to UV in mice administered chronic oral nicotine, a nAChR agonist, were reduced. Conversely, nAChRalpha7 knock-out mice exposed to UVB elicit an enhanced pro-inflammatory cytokine response in the skin. Altered pro-inflammatory responses correlated with changes in SOCS3 protein. These results demonstrate that nAChRalpha7 can participate in modulating a local pro-inflammatory response in the absence of parasympathetic innervation.

Basic and clinical aspects of non-neuronal acetylcholine: biological and clinical significance of non-canonical ligands of epithelial nicotinic acetylcholine receptors

Mucocutaneous keratinocytes and bronchial epithelial cells express nicotinic acetylcholine receptors (nAChRs). Emerging evidence indicates that nAChRs can be stimulated also by the tobacco-derived nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) that can induce tumors in laboratory animals. Nitrosamines may disturb the delicate balance between cell proliferation, growth arrest, and apoptosis. A novel paradigm of cell regulation via nAChR has been discovered in studies of SLURP (secreted mammalian Ly-6/urokinase plasminogen activator receptor-related protein)-1 and -2. Experimental results suggest that SLURP-1 and -2 regulate keratinocyte proliferation, apoptosis, and differentiation. Most importantly, SLURPs and professional nicotinic antagonists can abolish, in part, the abilities of NNK and NNN to cause tumorigenic transformation of immortalized keratinocytes. Learning the pharmacology of the nitrosamine vs. SLURP action on epithelial cells may help develop an effective anti-cancer treatment and prevention programs wherein hazardous effects of tobacco products are anticipated, or even abolished, by a pharmacologic ligand of the specific nicotinic receptor acting as an antidote.

HLA class II transgenic mice mimic human inflammatory diseases

Population studies have shown that among all the genetic factors linked with autoimmune disease development, MHC class II genes on chromosome 6 accounts for majority of familial clustering in the common autoimmune diseases. Despite the highly polymorphic nature of HLA class II genes, majority of autoimmune diseases are linked to a limited set of class II-DR or -DQ alleles. Thus a more detailed study of these HLA-DR and -DQ alleles were needed to understand their role in genetic predisposition and pathogenesis of autoimmune diseases. Although in vitro studies using class-II restricted CD4 T cells and purified class II molecules have helped us in understanding some aspects of HLA class-II association with disease, it is difficult to study the role of class II genes in vivo because of heterogeneity of human population, complexity of MHC, and strong linkage disequilibrium among different class II genes. To overcome this problem, we pioneered the generation of HLA-class II transgenic mice to study role of these molecule in inflammatory disease. These HLA class II transgenic mice were used to develop novel in vivo disease model for common autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, insulin-dependent diabetes mellitus, myasthenia gravis, celiac disease, autoimmune relapsing polychondritis, autoimmune myocarditis, thyroiditis, uveitis, as well as other inflammatory disease such as allergy, tuberculosis and toxic shock syndrome. As the T-cell repertoire in these humanized HLA transgenic mice are shaped by human class II molecules, they show the same HLA restriction as humans, implicate potential triggering mechanism and autoantigens, and identify similar antigenic epitopes seen in human. This review describes the value of these humanized transgenic mice in deciphering role of HLA class II molecules in immunopathogenesis of inflammatory diseases.

The nicotinic receptor antagonists abolish pathobiologic effects of tobacco-derived nitrosamines on BEP2D cells

Identification of the mechanisms leading to malignant transformation of respiratory cells may prove useful in the prevention and treatment of tobacco-related lung cancer. Nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) can induce tumors both locally and systemically. In addition to the genotoxic effect, they have been shown to affect lung cells due to ligating the nicotinic acetylcholine receptors (nAChRs) expressed on the plasma membrane. In this study, we sought to establish the role for nAChRs in malignant transformation caused by NNK and NNN. We used the BEP2D cells that represent a suitable model for studying the various stages of human bronchial carcinogenesis. We found that these cells express alpha1, alpha3, alpha5, alpha7, alpha9, alpha10, beta1, beta2, and beta4 nAChR subunits that can form high-affinity binding sites for NNK and NNN. Exposure of BEP2D cells to either NNK or NNN in both cases increased their proliferative potential which could be abolished in the presence of nAChR antagonists alpha-bungarotoxin, which worked most effectively against NNK, or mecamylamine, which was most efficient against NNN. The BEP2D cells stimulated with the nitrosamines showed multifold increases of the transcription of the PCNA and Bcl-2 genes by both real-time polymerase chain reaction and in-cell western assays. To gain a mechanistic insight into NNK- and NNN-initiated signaling, we investigated the expression of genes encoding the signal transduction effectors GATA-3, nuclear factor-kappaB, and STAT-1. Experimental results indicated that stimulation of nAChRs with NNK led to activation of all three signal transduction effectors under consideration, whereas NNN predominantly activated GATA-3 and STAT-1. The GATA-3 protein-binding activity induced by NNK and NNN correlated with elevated gene expression. The obtained results support the novel concept of receptor-mediated action of NNK and NNN placing cellular nAChRs in the center of the pathophysiologic loop, and suggest that an nAChR antagonist may serve as a chemopreventive agent.

Shedding light into the role of BDNF in the pharmacotherapy of Parkinson's disease

Parkinson's disease (PD) is a chronic, neurodegenerative disease with a 1% incidence in the population over 55 years of age. Movement impairments represent undoubtedly the hallmark of the disorder; however, extensive evidence implicates cognitive deficits as concomitant peculiar features. Brain-derived neurotrophic factor (BDNF) colocalizes with dopamine neurons in the substantia nigra, where dopaminergic cell bodies are located, and it has recently garnered attention as a molecule crucial for cognition, a function that is also compromised in PD patients. Thus, due to its colocalization with dopaminergic neurons and its role in cognition, BDNF might possess a dual role in PD, both as a neuroprotective molecule, since its inhibition leads to loss of nigral dopaminergic neurons, and as a neuromodulator, as its enhanced expression ameliorates cognitive processes. In this review, we discuss the mechanism of action of established as well as novel drugs for PD with a particular emphasis to those interfering with BDNF biosynthesis.

Biological Effects of SLURP-1 on Human Keratinocytes

A novel paradigm of keratinocyte (KC) regulation via nicotinic acetylcholine receptors (nAChR) has been discovered in studies of SLURP (secreted mammalian Ly-6/urokinase-type plasminogen activator receptor-related protein)-1 in Mal de Meleda. We cloned human SLURP-1 and produced recombinant protein and the monoclonal antibody 336H12-1A3 that visualized native SLURP-1. SLURP-1 ligated the conventional ligand-binding site of KC nAChR, showing a higher affinity to the [(3)H]nicotine-, compared with the [(3)H]epibatidine-sensitive nAChR. SLURP-1 significantly (p<0.05) increased the activities of caspases 3 and 8, and the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling-positive cells. The pro-apoptotic activity of SLURP-1 exceeded that of tumor necrosis factor-alpha, suggesting the involvement of separate pathways. In a series of real-time PCR and in-cell western experiments, SLURP-1 significantly (p<0.05) upregulated expression of transglutaminase type I cytokeratin 10, p21, and caspase-3. In the presence of the agonist carbachol, the effects of SLURP-1 on gene expression were augmented, which is in keeping with the notion that SLURP-1 acts as an allosteric agonist at the KC nAChR. Thus, the changes in the cell state induced by SLURP-1 could result from nAChR-mediated effects on the KC gene expression. These results suggest that the biological role of SLURP-1 in the epidermis is to provide fine tuning of the physiologic regulation of KC functions through the cholinergic pathways.

Inhibition of α7-nicotinic acetylcholine receptor expression by arsenite in the vascular endothelial cells

The alpha7-nicotinic acetylcholine receptor (alpha7-nAChR), expressed in the neuronal and non-neuronal cells, has been shown to regulate cell proliferation. However, the expression and function of the alpha7-nAChR in the proliferation of the vascular endothelial cells remain unclear. In this study, we investigated the expression of the alpha7-nAChR in the arsenite-exposed vascular endothelial cells. The vascular endothelial cells SVEC4-10 and porcine aorta endothelial cells (PAEC) expressed the alpha7-nAChR proteins. Moreover, the location of the alpha7-nAChR proteins on cell membrane of the vascular endothelial cells was identified by the alpha7-nAChR binding to a tetramethylrhodamine-labeled alpha-bungarotoxin (alpha-BTX). Arsenite (20 microM, 24 h) significantly induced the cytotoxicity, cell growth inhibition, and apoptosis in the vascular endothelial cells. The level of alpha7-nAChR proteins was concentration dependently decreased in the arsenite-treated endothelial cells. Furthermore, a specific alpha7-nAChR antagonist, alpha-BTX, inhibited the cell viability in the vascular endothelial cells. Nevertheless, alpha-BTX, and a alpha7-nAChR agonist, nicotine, did not significantly alter the cytotoxicity in the arsenite-treated endothelial cells. In addition, arsenite decreased the level of endothelial nitric oxide synthase proteins but did not alter choline acetyltransferase proteins in the SVEC4-10 endothelial cells. Together, our results indicate that arsenite can inhibit the alpha7-nAChR protein expression and cause the cell injury in the vascular endothelial cells.

The smoking gun: many conditions associated with tobacco exposure may be attributable to paradoxical compensatory autonomic responses to nicotine

Tobacco exposure is implicated in many illnesses such as cardiovascular disease and cancer, but the mechanisms underlying these associations are poorly understood. The mechanisms by which tobacco induces pro-sympathetic and pro-inflammatory changes also remain elusive. Some studies have attributed these changes to the direct effects of nicotine, but such findings run counter to the pro-vagal, anti-inflammatory nature of the nicotinic pathway. We hypothesize that the illnesses associated with smoking may be partly attributable to autonomic dysfunction, sympathetic bias, and T helper (Th)2 inflammation induced by a paradoxical compensatory response to intermittent nicotinic exposure. The confusion of interpreting the adrenergia and inflammation associated with nicotine as a primary response instead of a secondary compensation may be explained by the unusually rapid absorption, action, and serum elimination of nicotine. Given the fast action and clearance of nicotine, even heavy smokers spend large portions of the day and the entire night in nicotine withdrawal, at which time rebound sympathetic bias may manifest as a result of desensitization of nicotinic receptors. This may help reconcile why the features observed in smokers such as tachycardia, hypertension, inflammation, insomnia, and anxiety, which are perhaps mistakenly attributed to the direct action of nicotine, are identical to those seen during acute nicotine withdrawal after smoking cessation. On the other hand, delayed responses to cessation of smoking such as weight gain and increased heart rate variability are compatible with reduced sympathovagal ratio and resensitization of nicotinic receptors. Sympathetic bias and the associated Th2 inflammation underlie many systemic diseases. Tobacco-related cancers may be partly attributable to immunomodulatory properties of chronic nicotine exposure by dampening Th1 immunity and enabling tumoral evasion of immune surveillance. Other conditions associated with tobacco exposure may also operate through similar autonomic and immune dysfunctions. Therapeutic implications are discussed.

Nicotine signals through muscle-type and neuronal nicotinic acetylcholine receptors in both human bronchial epithelial cells and airway fibroblasts

BACKGROUND

Non-neuronal cells, including those derived from lung, are reported to express nicotinic acetylcholine receptors (nAChR). We examined nAChR subunit expression in short-term cultures of human airway cells derived from a series of never smokers, ex-smokers, and active smokers.

METHODS AND RESULTS

At the mRNA level, human bronchial epithelial (HBE) cells and airway fibroblasts expressed a range of nAChR subunits. In multiple cultures of both cell types, mRNA was detected for subunits that constitute functional muscle-type and neuronal-type pentomeric receptors. Two immortalized cell lines derived from HBE cells also expressed muscle-type and neuronal-type nAChR subunits. Airway fibroblasts expressed mRNA for three muscle-type subunits (alpha1, delta, and epsilon) significantly more often than HBE cells. Immunoblotting of HBE cell and airway fibroblast extracts confirmed that mRNA for many nAChR subunits is translated into detectable levels of protein, and evidence of glycosylation of nAChRs was observed. Some minor differences in nAChR expression were found based on smoking status in fibroblasts or HBE cells. Nicotine triggered calcium influx in the immortalized HBE cell line BEAS2B, which was blocked by alpha-bungarotoxin and to a lesser extent by hexamethonium. Activation of PKC and MAPK p38, but not MAPK p42/44, was observed in BEAS2B cells exposed to nicotine. In contrast, nicotine could activate p42/44 in airway fibroblasts within five minutes of exposure.

CONCLUSIONS

These results suggest that muscle-type and neuronal-type nAChRs are functional in airway fibroblasts and HBE cells, that prior tobacco exposure does not appear to be an important variable in nAChR expression, and that distinct signaling pathways are observed in response to nicotine.

The airway cholinergic system: physiology and pharmacology

The present review summarizes the current knowledge of the cholinergic systems in the airways with special emphasis on the role of acetylcholine both as neurotransmitter in ganglia and postganglionic parasympathetic nerves and as non-neuronal paracrine mediator. The different cholinoceptors, various nicotinic and muscarinic receptors, as well as their signalling mechanisms are presented. The complex ganglionic and prejunctional mechanisms controlling the release of acetylcholine are explained, and it is discussed whether changes in transmitter release could be involved in airway dysfunctions. The effects of acetylcholine on different target cells, smooth muscles, nerves, surface epithelial and secretory cells as well as mast cells are described in detail, including the receptor subtypes involved in signal transmission.