Neuronal nicotinic receptors: from structure to pathology

Unique effects of nicotine across the lifespan

Smoking remains the leading cause of preventable death in the United States. Although combustible cigarettes are largely being replaced by tobacco-free products, nicotine use continues to increase in vulnerable populations, including youth, adolescents, and pregnant women. Nicotine exerts unique effects on specific brain regions during distinct developmental periods due to the dynamic expression of nicotinic acetylcholine receptors (nAChRs) throughout the lifespan. Nicotine exposure is a health concern not only for adults but also has neurotoxic effects on the fetus, newborn, child, and adolescent. In this review, we aim to highlight the dynamic roles of nAChRs throughout gestation, adolescence, and adulthood. We also provide clinical and preclinical evidence of the neurodevelopmental, cognitive, and behavioral consequences of nicotine exposure at different developmental periods. This comprehensive review highlights unique effects of nicotine throughout the lifespan to help elucidate interventions and public health measures to protect sensitive populations from nicotine exposure.

Mechanism of interactions between α-conotoxin RegIIA and carbohydrates at the human α3β4 nicotinic acetylcholine receptor

Conotoxins are marine peptide toxins from marine cone snails. The α-conotoxin RegIIA can selectively act on human (h) α3β4 nicotinic acetylcholine receptor (nAChR), and is an important lead for drug development. The high-resolution cryo-electron microscopy structure of the α3β4 nAChR demonstrates several carbohydrates are located near the orthosteric binding sites, which may affect α-conotoxin binding. Oligosaccharide chains can modify the physical and chemical properties of proteins by changing the conformation, hydrophobicity, quality and size of the protein. The purpose of this study is to explore the effect of oligosaccharide chains on the binding modes and activities of RegIIA and its derivatives at hα3β4 nAChRs. Through computational simulations, we designed and synthesized RegIIA mutants at position 14 to explore the importance of residue H14 to the activity of the peptide. Molecular dynamics simulations suggest that the oligosaccharide chains affect the binding of RegIIA at the hα3β4 nAChR through direct interactions with H14 and by affecting the C-loop conformation of the binding sites. Electrophysiology studies on H14 analogues suggest that in addition to forming direct interactions with the carbohydrates, the residue might play an important role in maintaining the conformation of the peptide. Overall, this study further clarifies the structure-activity relationship of α-conotoxin RegIIA at the hα3β4 nAChR and, also provides important experimental and theoretical basis for the development of new peptide drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-021-00108-9.

Coronavirus Disease 2019 (COVID-19) and Its Neuroinvasive Capacity: Is It Time for Melatonin?

The world faces an exceptional new public health concern caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), subsequently termed the coronavirus disease 2019 (COVID-19) by the World Health Organization (WHO). Although the clinical symptoms mostly have been characterized, the scientific community still doesn´t know how SARS-CoV-2 successfully reaches and spreads throughout the central nervous system (CNS) inducing brain damage. The recent detection of SARS-CoV-2 in the cerebrospinal fluid (CSF) and in frontal lobe sections from postmortem examination has confirmed the presence of the virus in neural tissue. This finding reveals a new direction in the search for a neurotherapeutic strategy in the COVID-19 patients with underlying diseases. Here, we discuss the COVID-19 outbreak in a neuroinvasiveness context and suggest the therapeutic use of high doses of melatonin, which may favorably modulate the immune response and neuroinflammation caused by SARS-CoV-2. However, clinical trials elucidating the efficacy of melatonin in the prevention and clinical management in the COVID-19 patients should be actively encouraged.

Nicotinic acid-based cationic vectors for efficient gene delivery to glioblastoma cells

A tocopherol-conjugated nicotinic acid-based lipid (NGT) was used for liposomal formation with the co-lipid DOPE and exhibited enhanced transfection of glioblastoma cells for eGFP and β-galactosidase protein expression.

Unique Pharmacological Properties of α-Conotoxin OmIA at α7 nAChRs

OmIA, isolated from Conus omaria venom, is a potent antagonist at α7 nAChRs. We determined the co-crystal structure of OmIA with Lymnae stagnalis acetylcholine binding protein (Ls-AChBP) that identified His5, Val10 and Asn11 as key determinants for the high potency of OmIA at α7 nAChRs. Remarkably, despite a competitive binding mode observed in the co-crystal structure, OmIA and analogues displayed functional insurmountable antagonism at α7 and α3β4 nAChRs, except OmIA analogues having long side chain at position 10 ([V10Q]OmIA and [V10L]OmIA), which were partial insurmountable antagonist at α7 nAChRs in the presence of type II positive allosteric modulators (PAMs). A “two-state, two-step” model was used to explain these observations, with [V10Q]OmIA and [V10L]OmIA co-existing in a fast reversible/surmountable as well as a tight binding/insurmountable state. OmIA and analogues also showed biphasic-inhibition at α7 nAChRs in the presence of PNU120596, with a preference for the high-affinity binding site following prolonged exposure. The molecular basis of binding and complex pharmacological profile of OmIA at α7 nAChRs presented in here expands on the potential of α-conotoxins to probe the pharmacological properties of nAChRs and may help guide the development novel α7 modulators.

Social Isolation: How Can the Effects on the Cholinergic System Be Isolated?

Social species form organizations that support individuals because the consequent social behaviors help these organisms survive. The isolation of these individuals may be a stressor. We reviewed the potential mechanisms of the effects of social isolation on cholinergic signaling and vice versa how changes in cholinergic signaling affect changes due to social isolation.There are two important problems regarding this topic. First, isolation schemes differ in their duration (1–165 days) and initiation (immediately after birth to adulthood). Second, there is an important problem that is generally not considered when studying the role of the cholinergic system in neurobehavioral correlates: muscarinic and nicotinic receptor subtypes do not differ sufficiently in their affinity for orthosteric site agonists and antagonists. Some potential cholinesterase inhibitors also affect other targets, such as receptors or other neurotransmitter systems. Therefore, the role of the cholinergic system in social isolation should be carefully considered, and multiple receptor systems may be involved in the central nervous system response, although some subtypes are involved in specific functions. To determine the role of a specific receptor subtype, the presence of a specific subtype in the central nervous system should be determined using search in knockout studies with the careful application of specific agonists/antagonists.

From Crystal Structures of RgIA4 in Complex with Ac-AChBP to Molecular Determinants of Its High Potency of α9α10 nAChR

α9-containing nicotinic acetylcholine receptors (nAChRs) have been shown to play critical roles in neuropathic pain. The α-conotoxin (α-CTx) RgIA and its analog RgIA4 were identified as the most selective inhibitor of α9α10 nAChR. However, the mechanism of their selectivity toward α9α10 nAChR remains elusive. Here, we reported the co-crystal structure of RgIA and RgIA4 in complex with Aplysia californica acetylcholine binding protein (Ac-AChBP) at resolution of 2.6 Å, respectively. Based on the structure of the complexes, together with molecular dynamic simulation (MD-simulation), we suggested the key residues of α9α10 nAChR in determining its high affinity for RgIA/RgIA4. This is the first time the complex between pain-related conotoxins and Ac-AChBP was reported and the complementary side of α9 subunit in binding of the antagonists shown. These results provide realistic template for the design of new therapeutic in neuropathic pain.

Novel methyllycaconitine analogues selective for the α4β2 over α7 nicotinic acetylcholine receptors

Analogues of methyllycaconitine (MLA) based on a (3-ethyl-9-methylidene-3-azabicyclo[3.3.1]nonan-1-yl)methanol template have been designed and synthesised that incorporate the modified ester sidechains distinct from that present in the natural product. Electrophysiology experiments using Xenopus oocytes expressing nicotinic acetylcholine receptors (nAChRs) revealed selected analogues served as non-competitive inhibitors that showed selectivity for the α4β2 over α7 nAChR subtypes, and selectivity for the (α4)₃(β2)₂ over (α4)₂(β2)₃ stoichiometry. This study more clearly defines the biological effects of MLA analogues and identifies strategies for the development of MLA analogues as selective ligands for the α4β2 nAChR subtype.

Assessing potentiation of the (α4)3(β2)2 nicotinic acetylcholine receptor by the allosteric agonist CMPI

The extracellular domain of the nicotinic acetylcholine receptor isoforms formed by three α4 and two β2 subunits ((α4)3(β2)2 nAChR) harbors two high-affinity “canonical” acetylcholine (ACh)-binding sites located in the two α4:β2 intersubunit interfaces and a low-affinity “noncanonical” ACh-binding site located in the α4:α4 intersubunit interface. In this study, we used ACh, cytisine, and nicotine (which bind at both the α4:α4 and α4:β2 interfaces), TC-2559 (which binds at the α4:β2 but not at the α4:α4 interface), and 3-(2-chlorophenyl)-5-(5-methyl-1-(piperidin-4-yl)-1H-pyrrazol-4-yl)isoxazole (CMPI, which binds at the α4:α4 but not at the α4:β2 interface), to investigate the binding and gating properties of CMPI at the α4:α4 interface. We recorded whole-cell currents from Xenopus laevis oocytes expressing (α4)3(β2)2 nAChR in response to applications of these ligands, alone or in combination. The electrophysiological data were analyzed in the framework of a modified Monod–Wyman–Changeux allosteric activation model. We show that CMPI is a high-affinity, high-efficacy agonist at the α4:α4 binding site and that its weak direct activating effect is accounted for by its inability to productively interact with the α4:β2 sites. The data presented here enhance our understanding of the functional contributions of ligand binding at the α4:α4 subunit interface to (α4)3(β2)2 nAChR-channel gating. These findings support the potential use of α4:α4 specific ligands to increase the efficacy of the neurotransmitter ACh in conditions associated with decline in nAChRs activity in the brain.

Monkeying around with venom: an increased resistance to α-neurotoxins supports an evolutionary arms race between Afro-Asian primates and sympatric cobras

Background

Snakes and primates have a multi-layered coevolutionary history as predators, prey, and competitors with each other. Previous work has explored the Snake Detection Theory (SDT), which focuses on the role of snakes as predators of primates and argues that snakes have exerted a selection pressure for the origin of primates’ visual systems, a trait that sets primates apart from other mammals. However, primates also attack and kill snakes and so snakes must simultaneously avoid primates. This factor has been recently highlighted in regard to the movement of hominins into new geographic ranges potentially exerting a selection pressure leading to the evolution of spitting in cobras on three independent occasions.

Results

Here, we provide further evidence of coevolution between primates and snakes, whereby through frequent encounters and reciprocal antagonism with large, diurnally active neurotoxic elapid snakes, Afro-Asian primates have evolved an increased resistance to α-neurotoxins, which are toxins that target the nicotinic acetylcholine receptors. In contrast, such resistance is not found in Lemuriformes in Madagascar, where venomous snakes are absent, or in Platyrrhini in the Americas, where encounters with neurotoxic elapids are unlikely since they are relatively small, fossorial, and nocturnal. Within the Afro-Asian primates, the increased resistance toward the neurotoxins was significantly amplified in the last common ancestor of chimpanzees, gorillas, and humans (clade Homininae). Comparative testing of venoms from Afro-Asian and American elapid snakes revealed an increase in α-neurotoxin resistance across Afro-Asian primates, which was likely selected against cobra venoms. Through structure-activity studies using native and mutant mimotopes of the α-1 nAChR receptor orthosteric site (loop C), we identified the specific amino acids responsible for conferring this increased level of resistance in hominine primates to the α-neurotoxins in cobra venom.

Conclusion

We have discovered a pattern of primate susceptibility toward α-neurotoxins that supports the theory of a reciprocal coevolutionary arms-race between venomous snakes and primates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01195-x.

Clothianidin and Thiacloprid Mixture Administration Induces Degenerative Damage in the Dentate Gyrus and Alteration in Short-Term Memory in Rats

Neonicotinoids are pesticides that act as agonists of nicotinic receptors for acetylcholine in insects' central nervous system (CNS). Chronic exposure to neonicotinoids in humans is related to autism, memory loss, and finger tremor. In this article, we evaluate the effect of subchronic oral administration of two neonicotinoids in the same mixture: clothianidin and thiacloprid. Decreasing doses of both pesticides were administered to rats starting from the lethal dose 50 (LD50) reported by the manufacturer. Our results indicate that the administration of three doses of decreasing amounts of LD50 (5/10, 4/10, and 3/10 LD50) resulted in 100% death in all cases. Ten administration times of 2/10 LD50 of the mixture caused only 20% of death cases after twenty-seven days, which was determined as a subchronic administration scheme. The animals administered 2/10 LD50 showed behavioral alterations after the first and second administration. Electrographic studies showed abnormal discharge patterns in the CNS. 72 h after the tenth dose, learning and memory tests were performed in the Morris water maze. Our results revealed significant decreases in permanence at the quadrant and the number of crosses (P=0.0447,  P=0.0193, respectively), which represent alterations in the short-term memory test, but there were no significant changes in a long-term memory test. Likewise, the brains of these animals showed tissue architecture loss, nucleosomal retraction, and a significant increase in the pycnosis of the granular neurons of the dentate gyrus analyzed at 72 h after the last dose (P=0.0125). Toxic effects and cognitive deterioration that have been found in communities living near contaminated areas are probably related to the agricultural use of neonicotinoids.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced Histone Acetylation via α7nAChR-Mediated PI3K/Akt Activation and Its Impact on γ-H2AX Generation

A typical tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known as a strong carcinogen. We previously reported that metabolized NNK induced histone H2AX phosphorylation (γ-H2AX), a DNA damage-induced histone modification. In this study, we found that NNK globally acetylated histone H3, which affected γ-H2AX generation. Human lung adenocarcinoma A549 was treated with several doses of NNK. NNK induced dose-dependent global histone H3 acetylation (Ac-H3), at 2 to 12 h after the treatment, independent of the cell cycle. The Ac-H3 pattern was not affected by CYP2A13 overexpression unlike γ-H2AX, indicating no requirement of NNK metabolism to induce Ac-H3. Immunofluorescence staining of Ac-H3 was uniform throughout the nucleus, whereas γ-H2AX was formed as foci and did not coincide with Ac-H3. Nicotinic receptor antagonist methyllycaconitine inhibited Ac-H3 and also γ-H2AX. Phosphoinositide-3-kinase (PI3K)/Akt inhibitors, LY294002, wortmannin, and GSK690693, also suppressed both Ac-H3 and γ-H2AX, whereas KU-55933, an inhibitor of ataxia telangiectasia mutated (ATM) upstream of γ-H2AX, inhibited γ-H2AX but not Ac-H3. These results suggested that binding of NNK to the nicotinic acetylcholine receptor (α7nAChR) activated the PI3K/Akt pathway, resulting in Ac-H3. The activated pathway leading to Ac-H3 enhanced γ-H2AX, suggesting that NNK-induced DNA damage is impacted by the α7nAChR-mediated signal transduction pathway.

Rigidity of loop 1 contributes to equipotency of globular and ribbon isomers of α-conotoxin AusIA

α-Conotoxins are small disulfide-rich peptides targeting nicotinic acetylcholine receptors (nAChRs) characterised by a C^IC^II-X_m-C^III-X_n-C^IV framework that invariably adopt the native globular conformations which is typically most potent. α-Conotoxins are divided into several structural subgroups based on the number of residues within the two loops braced by the disulfide bonds (m/n), with the 4/7 and 4/3 subgroups dominating. AusIA is a relatively rare α5/5-conotoxin isolated from the venom of Conus australis. Surprisingly, the ribbon isomer displayed equipotency to the wild-type globular AusIA at human α7-containing nAChR. To understand the molecular basis for equipotency, we determined the co-crystal structures of both isomers at Lymnea stagnalis acetylcholine binding protein. The additional residue in the first loop of AusIA was found to be a critical determinant of equipotency, with 11-fold and 86-fold shifts in potency in favour of globular AusIA over ribbon AusIA observed following deletion of Ala4 or Arg5, respectively. This divergence in the potency between globular AusIA and ribbon AusIA was further enhanced upon truncation of the non-conserved Val at the C-termini. Conversely, equipotency could be replicated in LsIA and TxIA [A10L] following insertion of an Ala in the first loop. These findings provide a new understanding of the role the first loop in ribbon and globular α-conotoxins can play in directing α-conotoxin nAChR pharmacology.

Peimine, an Anti-Inflammatory Compound from Chinese Herbal Extracts, Modulates Muscle-Type Nicotinic Receptors

Fritillaria bulbs are used in Traditional Chinese Medicine to treat several illnesses. Peimine (Pm), an anti-inflammatory compound from Fritillaria, is known to inhibit some voltage-dependent ion channels and muscarinic receptors, but its interaction with ligand-gated ion channels remains unexplored. We have studied if Pm affects nicotinic acetylcholine receptors (nAChRs), since they play broad functional roles, both in the nervous system and non-neuronal tissues. Muscle-type nAChRs were incorporated to Xenopus oocytes and the action of Pm on the membrane currents elicited by ACh (I_AChs) was assessed. Functional studies were combined with virtual docking and molecular dynamics assays. Co-application of ACh and Pm reversibly blocked I_ACh, with an IC₅₀ in the low micromolar range. Pm inhibited nAChR by: (i) open-channel blockade, evidenced by the voltage-dependent inhibition of I_Ach, (ii) enhancement of nAChR desensitization, revealed by both an accelerated I_ACh decay and a decelerated I_ACh deactivation, and (iii) resting-nAChR blockade, deduced from the I_ACh inhibition elicited by Pm when applied before ACh superfusion. In good concordance, virtual docking and molecular dynamics assays demonstrated that Pm binds to different sites at the nAChR, mostly at the transmembrane domain. Thus, Pm from Fritillaria bulbs, considered therapeutic herbs, targets nAChRs with high affinity, which might account for its anti-inflammatory actions.

Ultra-structural morphology analysis of human cranial bone marrow mesenchymal stromal cells during neural differentiation

Neural differentiation of mesenchymal stromal cells has been widely studied. However, a comparative characterization of ultrastructural changes during neural differentiation has not been performed. In this study, we conducted scanning electron microscopy and transmission electron microscopy analysis to show the morphological changes in mesenchymal stromal cells upon induction of neural differentiation. In addition, transmission electron microscopy results demonstrated ultrastructural differences between human cranial bone marrow mesenchymal stromal cells and iliac crest bone marrow mesenchymal stromal cells. We propose that enriched microvesicles in cranial bone marrow mesenchymal stromal cells may be responsible for the increased efficiency of neural differentiation.

Remodeling tumor immune microenvironment (TIME) for glioma therapy using multi-targeting liposomal codelivery

BACKGROUND

Glioblastoma (GBM) treatment is undermined by the suppressive tumor immune microenvironment (TIME). Seek for effective methods for brain TIME modulation is a pressing need. However, there are two major challenges against achieving the goal: first, to screen the effective drugs with TIME-remodeling functions and, second, to develop a brain targeting system for delivering the drugs.

METHODS

In this study, an α7 nicotinic acetylcholine receptors (nAChRs)-binding peptide ^DCDX was used to modify the codelivery liposomes to achieve a 'three-birds-one-stone' delivery strategy, that is, multi-targeting the glioma vessel endothelium, glioma cells, and tumor-associated macrophages that all overexpressed α7 nAChRs. A brain-targeted liposomal honokiol and disulfiram/copper codelivery system (CDX-LIPO) was developed for combination therapy via regulating mTOR (mammalian target of rapamycin) pathway for remodeling tumor metabolism and TIME. Honokiol can yield a synergistic effect with disulfiram/copper for anti-GBM.

RESULTS

It was demonstrated that CDX-LIPO remarkably triggered tumor cell autophagy and induced immunogenic cell death, and meanwhile, activated the tumor-infiltrating macrophage and dendritic cells, and primed T and NK (natural killer) cells, resulting in antitumor immunity and tumor regression. Moreover, CDX-LIPO promoted M1-macrophage polarization and facilitated mTOR-mediated reprogramming of glucose metabolism in glioma.

CONCLUSION

This study developed a potential combinatory therapeutic strategy by regulation of TIME and a 'three-birds-one-stone'-like glioma-targeting drug delivery system.

Efficient Anti-Glioma Therapy Through the Brain-Targeted RVG15-Modified Liposomes Loading Paclitaxel-Cholesterol Complex

Background

Glioma is the most common primary malignant brain tumor with a dreadful overall survival and high mortality. One of the most difficult challenges in clinical treatment is that most drugs hardly pass through the blood–brain barrier (BBB) and achieve efficient accumulation at tumor sites. Thus, to circumvent this hurdle, developing an effectively traversing BBB drug delivery nanovehicle is of significant clinical importance. Rabies virus glycoprotein (RVG) is a derivative peptide that can specifically bind to nicotinic acetylcholine receptor (nAChR) widely overexpressed on BBB and glioma cells for the invasion of rabies virus into the brain. Inspired by this, RVG has been demonstrated to potentiate drugs across the BBB, promote the permeability, and further enhance drug tumor-specific selectivity and penetration.

Methods

Here, we used the RVG15, rescreened from the well-known RVG29, to develop a brain-targeted liposome (RVG15-Lipo) for enhanced BBB permeability and tumor-specific delivery of paclitaxel (PTX). The paclitaxel-cholesterol complex (PTX-CHO) was prepared and then actively loaded into liposomes to acquire high entrapment efficiency (EE) and fine stability. Meanwhile, physicochemical properties, in vitro and in vivo delivery efficiency and therapeutic effect were investigated thoroughly.

Results

The particle size and zeta potential of PTX-CHO-RVG15-Lipo were 128.15 ± 1.63 nm and −15.55 ± 0.78 mV, respectively. Compared with free PTX, PTX-CHO-RVG15-Lipo exhibited excellent targeting efficiency and safety in HBMEC and C6 cells, and better transport efficiency across the BBB in vitro model. Furthermore, PTX-CHO-RVG15-Lipo could noticeably improve the accumulation of PTX in the brain, and then promote the chemotherapeutic drugs penetration in C6^luc orthotopic glioma based on in vivo imaging assays. The in vivo antitumor results indicated that PTX-CHO-RVG15-Lipo significantly inhibited glioma growth and metabasis, therefore improved survival rate of tumor-bearing mice with little adverse effect.

Conclusion

Our study demonstrated that the RVG15 was a promising brain-targeted specific ligands owing to the superior BBB penetration and tumor targeting ability. Based on the outstanding therapeutic effect both in vitro and in vivo, PTX-CHO-RVG15-Lipo was proved to be a potential delivery system for PTX to treat glioma in clinic.

Effects of nicotinic acetylcholine receptor-activating alkaloids on anxiety-like behavior in zebrafish

Alkaloids are a structurally complex group of natural products that have a diverse range of biological activities and significant therapeutic applications. In this study, we examined the acute, anxiolytic-like effects of nicotinic acetylcholine receptor (nAChR)-activating alkaloids with reported neuropharmacological effects but whose effects on anxiety are less well understood. Because α4β2 nAChRs can regulate anxiety, we first demonstrated the functional activities of alkaloids on these receptors in vitro. Their effects on anxiety-like behavior in zebrafish were then examined using the zebrafish novel tank test (NTT). The NTT is a relatively high-throughput behavioral paradigm that takes advantage of the natural tendency of fish to dive down when stressed or anxious. We report for the first time that cotinine, anatabine, and methylanatabine may suppress this anxiety-driven zebrafish behavior after a single 20-min treatment. Effective concentrations of these alkaloids were well above the concentrations naturally found in plants and the concentrations needed to induce anxiolytic-like effect by nicotine. These alkaloids showed good receptor interactions at the α4β2 nAChR agonist site as demonstrated by in vitro binding and in silico docking model, although somewhat weaker than that for nicotine. Minimal or no significant effect of other compounds may have been due to low bioavailability of these compounds in the brain, which is supported by the in silico prediction of blood-brain barrier permeability. Taken together, our findings indicate that nicotine, although not risk-free, is the most potent anxiolytic-like alkaloid tested in this study, and other natural alkaloids may regulate anxiety as well.

Activation of Neuronal Nicotinic Receptors Inhibits Acetylcholine Release in the Neuromuscular Junction by Increasing Ca2+ Flux through Cav1 Channels

Cholinergic neurotransmission is a key signal pathway in the peripheral nervous system and in several branches of the central nervous system. Despite the fact that it has been studied extensively for a long period of time, some aspects of its regulation still have not yet been established. One is the relationship between the nicotine-induced autoregulation of acetylcholine (ACh) release with changes in the concentration of presynaptic calcium levels. The mouse neuromuscular junction of m. Levator Auris Longus was chosen as the model of the cholinergic synapse. ACh release was assessed by electrophysiological methods. Changes in calcium transients were recorded using a calcium-sensitive dye. Nicotine hydrogen tartrate salt application (10 μM) decreased the amount of evoked ACh release, while the calcium transient increased in the motor nerve terminal. Both of these effects of nicotine were abolished by the neuronal ACh receptor antagonist dihydro-beta-erythroidine and Cav1 blockers, verapamil, and nitrendipine. These data allow us to suggest that neuronal nicotinic ACh receptor activation decreases the number of ACh quanta released by boosting calcium influx through Cav1 channels.

RIC3 variants are not associated with Parkinson's disease in large European, Latin American, or East Asian cohorts

Parkinson’s disease (PD) is a complex neurodegenerative disorder in which both rare and common genetic variants contribute to disease risk. Multiple genes have been reported to be linked to monogenic PD but these only explain a fraction of the observed familial aggregation. Rare variants in RIC3 have been suggested to be associated with PD in the Indian population. However, replication studies yielded inconsistent results. We further investigate the role of RIC3 variants in PD in European cohorts using individual-level genotyping data from 14,671 PD patients and 17,667 controls, as well as whole-genome sequencing data from 1,615 patients and 961 controls. We also investigated RIC3 using summary statistics from a Latin American cohort of 1,481 individuals, and from a cohort of 31,575 individuals of East Asian ancestry. We did not identify any association between RIC3 and PD in any of the cohorts. However, more studies of rare variants in non-European ancestry populations, in particular South Asian populations, are necessary to further evaluate the world-wide role of RIC3 in PD etiology.

Modulation of preeclampsia by the cholinergic anti-inflammatory pathway: Therapeutic perspectives

The cholinergic anti-inflammatory pathway (CAP) is vital for the orchestration of the immune and inflammatory responses under normal and challenged conditions. Over the past two decades, peripheral and central circuits of CAP have been shown to be critically involved in dampening the inflammatory reaction in a wide array of inflammatory disorders. Additionally, emerging evidence supports a key role for CAP in the regulation of the female reproductive system during gestation as well as in the advent of serious pregnancy-related inflammatory insults such as preeclampsia (PE). Within this framework, the modulatory action of CAP encompasses the perinatal maternal and fetal adverse consequences that surface due to antenatal PE programming. Albeit, a considerable gap still exists in our knowledge of the precise cellular and molecular underpinnings of PE/CAP interaction, which hampered global efforts in safeguarding effective preventive or therapeutic measures against PE complications. Here, we summarize reports in the literature regarding the roles of peripheral and reflex cholinergic neuroinflammatory pathways of nicotinic acetylcholine receptors (nAChRs) in reprogramming PE complications in mothers and their progenies. The possible contributions of α7-nAChRs, cholinesterases, immune cells, adhesion molecules, angiogenesis, and endothelial dysfunction to the interaction have also been reviewed.

Multifactorial Etiology of Adolescent Nicotine Addiction: A Review of the Neurobiology of Nicotine Addiction and Its Implications for Smoking Cessation Pharmacotherapy

Nicotine is the primary pharmacologic component of tobacco, and its highly addictive nature is responsible for its widespread use and significant withdrawal effects that result in challenges to smoking cessation therapeutics. Nicotine addiction often begins in adolescence and this is at least partially attributed to the fact that adolescent brain is most susceptible to the neuro-inflammatory effects of nicotine. There is increasing evidence for the involvement of microglial cells, which are the brain's primary homeostatic sensor, in drug dependence and its associated behavioral manifestations particularly in the adolescent brain. A hallmark of neuro-inflammation is microglial activation and activation of microglia by nicotine during adolescent development, which may result in long-term addiction to nicotine. This non-systematic review examines multifactorial etiology of adolescent nicotine addiction, neurobiology of nicotine addiction and the potential mechanisms that underlie the effects of nicotine on inflammatory signaling in the microglia, understanding how nicotine affects the adolescent brain. We speculate, that modulating homeostatic balance in microglia, could have promising therapeutic potential in withdrawal, tolerance, and abstinence-related neural adaptations in nicotine addiction, in the adolescent brain. Further, we discuss nicotine addiction in the context of the sensitization-homeostasis model which provides a theoretical framework for addressing the potential role of microglial homeostasis in neural adaptations underlying nicotine abuse.

GABAB receptors blockage modulates somatic and aversive manifestations induced by nicotine withdrawal

There is substantial evidence that GABA_B agonist, baclofen, prevents somatic and motivational responses induced by nicotine withdrawal and may target drug cue vulnerabilities in humans. In this context, we explored different aspects associated with the possible mechanisms whereby the GABA_B receptors might influence nicotine withdrawal. Male mice received nicotine (2.5 mg/kg, s.c.) 4 times daily, for 7 consecutive days. Nicotine-treated mice received the nicotinic acetylcholine receptor antagonist, mecamylamine (MEC, 2 or 3.5 mg/kg, s.c.), to precipitate the withdrawal state. A second group of dependent mice received 2-hydroxysaclofen (GABA_B receptor antagonist, 1 mg/kg, s.c.) before MEC-precipitated abstinence. Somatic signs of nicotine withdrawal were measured for 30 min. Anxiogenic-like response associated to nicotine withdrawal was assessed by the elevated plus maze test. The dysphoric/aversive effect induced by nicotine withdrawal was evaluated using conditioned place aversion paradigm. Dopamine, serotonin and its metabolites concentrations were determined by HPLC in the striatum, cortex and hippocampus. Finally, α4β2 nicotinic acetylcholine receptor density was determined in several brain regions using autoradiography assays. The results showed that MEC-precipitated nicotine withdrawal induced somatic manifestations, anxiogenic-like response and dysphoric/aversive effect, and 2-hydroxysaclofen potentiated these behavioral responses. Additionally, 2-hydroxysaclofen was able to change striatal dopamine levels and α4β2 nicotinic acetylcholine receptor density, both altered by MEC-precipitated nicotine withdrawal. These findings provide important contributions to elucidate neurobiological mechanisms implicated in nicotine withdrawal. We suggest that GABA_B receptor activity is necessary to control alterations induced by nicotine withdrawal, which supports the idea of targeting GABA_B receptors to treat tobacco addiction in humans.

Cytisine and cytisine derivatives. More than smoking cessation aids

Cytisine, a natural bioactive compound that is mainly isolated from plants of the Leguminosae family (especially the seeds of Laburnum anagyroides), has been marketed in central and eastern Europe as an aid in the clinical management of smoking cessation for more than 50 years. Its main targets are neuronal nicotinic acetylcholine receptors (nAChRs), and pre-clinical studies have shown that its interactions with various nAChR subtypes located in different areas of the central and peripheral nervous systems are neuroprotective, have a wide range of biological effects on nicotine and alcohol addiction, regulate mood, food intake and motor activity, and influence the autonomic and cardiovascular systems. Its relatively rigid conformation makes it an attractive template for research of new derivatives. Recent studies of structurally modified cytisine have led to the development of new compounds and for some of them the biological activities are mediated by still unidentified targets other than nAChRs, whose mechanisms of action are still being investigated. The aim of this review is to describe and discuss: 1) the most recent pre-clinical results obtained with cytisine in the fields of neurological and non-neurological diseases; 2) the effects and possible mechanisms of action of the most recent cytisine derivatives; and 3) the main areas warranting further research.

Tyrosine phosphorylation differentially fine-tunes ionotropic and metabotropic responses of human α7 nicotinic acetylcholine receptor

The α7 nicotinic acetylcholine receptor is involved in neurological, neurodegenerative, and inflammatory disorders. It operates both as a ligand-gated cationic channel and as a metabotropic receptor in neuronal and non-neuronal cells. As protein phosphorylation is an important cell function regulatory mechanism, deciphering how tyrosine phosphorylation modulates α7 dual ionotropic/metabotropic molecular function is required for understanding its integral role in physiological and pathological processes. α7 single-channel activity elicited by ACh appears as brief isolated openings and less often as episodes of few openings in quick succession. The reduction of phosphorylation by tyrosine kinase inhibition increases the duration and frequency of activation episodes, whereas the inhibition of phosphatases has the opposite effect. Removal of two tyrosine residues at the α7 intracellular domain recapitulates the effects mediated by tyrosine kinase inhibition. The tyrosine-free mutant receptor shows longer duration-activation episodes, reduced desensitization rate and significantly faster recovery from desensitization, indicating that phosphorylation decreases α7 channel activity by favoring the desensitized state. However, the mutant receptor is incapable of triggering ERK1/2 phosphorylation in response to the α7-agonist. Thus, while tyrosine phosphorylation is absolutely required for α7-triggered ERK pathway, it negatively modulates α7 ionotropic activity. Overall, phosphorylation/dephosphorylation events fine-tune the integrated cell response mediated by α7 activation, thus having a broad impact on α7 cholinergic signaling.

Smoking is associated with impaired verbal learning and memory performance in women more than men

Vascular contributions to cognitive impairment and dementia (VCID) include structural and functional blood vessel injuries linked to poor neurocognitive outcomes. Smoking might indirectly increase the likelihood of cognitive impairment by exacerbating vascular disease risks. Sex disparities in VCID have been reported, however, few studies have assessed the sex-specific relationships between smoking and memory performance and with contradictory results. We investigated the associations between sex, smoking, and cardiovascular disease with verbal learning and memory function. Using MindCrowd, an observational web-based cohort of ~ 70,000 people aged 18-85, we investigated whether sex modifies the relationship between smoking and cardiovascular disease with verbal memory performance. We found significant interactions in that smoking is associated with verbal learning performance more in women and cardiovascular disease more in men across a wide age range. These results suggest that smoking and cardiovascular disease may impact verbal learning and memory throughout adulthood differently for men and women.

Differential effects of alkaloids on memory in rodents

Nicotinic acetylcholine receptors (nAChRs) play a critical role in the neuropharmacology of learning and memory. As such, naturally occurring alkaloids that regulate nAChR activity have gained interest for understanding and potentially improving memory function. In this study, we tested the acute effects of three known nicotinic alkaloids, nicotine, cotinine, and anatabine, in suppressing scopolamine-induced memory deficit in rodents by using two classic memory paradigms, Y-maze and novel object recognition (NOR) in mice and rats, respectively. We found that all compounds were able to suppress scopolamine-induced spatial memory deficit in the Y-maze spontaneous alternation paradigm. However, only nicotine was able to suppress the short-term object memory deficit in NOR, despite the higher doses of cotinine and anatabine used to account for their potential differences in nAChR activity. These results indicate that cotinine and anatabine can uniquely regulate short-term spatial memory, while nicotine seems to have more robust and general role in memory regulation in rodents. Thus, nAChR-activating alkaloids may possess distinct procognitive properties in rodents, depending on the memory types examined.

Potentiation of (α4)2(β2)3, but not (α4)3(β2)2, nicotinic acetylcholine receptors reduces nicotine self-administration and withdrawal symptoms

The low sensitivity (α4)3(β2)2 (LS) and high sensitivity (α4)2(β2)3 (HS) nAChR isoforms may contribute to a variety of brain functions, pathophysiological processes, and pharmacological effects associated with nicotine use. In this study, we examined the contributions of the LS and HS α4β2 nAChR isoforms in nicotine self-administration, withdrawal symptoms, antinociceptive and hypothermic effects. We utilized two nAChR positive allosteric modulators (PAMs): desformylflustrabromine (dFBr), a PAM of both the LS and HS α4β2 nAChRs, and CMPI, a PAM selective for the LS nAChR. We found that dFBr, but not CMPI, decreased intravenous nicotine self-administration in male mice in a dose-dependent manner. Unlike dFBr, which fully reverses somatic and affective symptoms of nicotine withdrawal, CMPI at doses up to 15 mg/kg in male mice only partially reduced nicotine withdrawal-induced somatic signs, anxiety-like behavior and sucrose preference, but had no effects on nicotine withdrawal-induced hyperalgesia. These results indicate that potentiation of HS α4β2 nAChRs is necessary to modulate nicotine's reinforcing properties that underlie nicotine intake and to reverse nicotine withdrawal symptoms that influence nicotine abstinence. In contrast, both dFBr and CMPI enhanced nicotine's hypothermic effect and reduced nicotine's antinociceptive effects in male mice. Therefore, these results indicate a more prevalent role of HS α4β2 nAChR isoforms in mediating various behavioral effects associated with nicotine, whereas the LS α4β2 nAChR isoform has a limited role in mediating body temperature and nociceptive responses. These findings will facilitate the development of more selective, efficacious, and safe nAChR-based therapeutics for nicotine addiction treatment.

Nicotine induces morphological and functional changes in astrocytes via nicotinic receptor activity

Nicotine is a highly addictive compound present in tobacco, which causes the release of dopamine in different regions of the brain. Recent studies have shown that astrocytes express nicotinic acetylcholine receptors (nAChRs) and mediate calcium signaling. In this study, we examine the morphological and functional adaptations of astrocytes due to nicotine exposure. Utilizing a combination of fluorescence and atomic force microscopy, we show that nicotine-treated astrocytes exhibit time-dependent remodeling in the number and length of both proximal and fine processes. Blocking nAChR activity with an antagonist completely abolishes nicotine's influence on astrocyte morphology indicating that nicotine's action is mediated by these receptors. Functional studies show that 24-hr nicotine treatment induces higher levels of calcium activity in both the cell soma and the processes with a more substantial change observed in the processes. Nicotine does not induce reactive astrocytosis even at high concentrations (10 μM) as determined by cytokine release and glial fibrillary acidic protein expression. We designed tissue clearing experiments to test whether morphological changes occur in vivo using astrocyte specific Aldh1l1-tdTomato knock in mice. We find that nicotine induces a change in the volume of astrocytes in the prefrontal cortex, CA1 of the hippocampus, and the substantia nigra. These results indicate that nicotine directly alters the functional and morphological properties of astrocytes potentially contributing to the underlying mechanism of nicotine abuse.

Cholinergic Modulation of the Immune System in Neuroinflammatory Diseases

Frequent diseases of the CNS, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and psychiatric disorders (e.g., schizophrenia), elicit a neuroinflammatory response that contributes to the neurodegenerative disease process itself. The immune and nervous systems use the same mediators, receptors, and cells to regulate the immune and nervous systems as well as neuro-immune interactions. In various neurodegenerative diseases, peripheral inflammatory mediators and infiltrating immune cells from the periphery cause exacerbation to current injury in the brain. Acetylcholine (ACh) plays a crucial role in the peripheral and central nervous systems, in fact, other than cells of the CNS, the peripheral immune cells also possess a cholinergic system. The findings on peripheral cholinergic signaling, and the activation of the “cholinergic anti-inflammatory pathway” mediated by ACh binding to α7 nAChR as one of the possible mechanisms for controlling inflammation, have restarted interest in cholinergic-mediated pathological processes and in the new potential therapeutic target for neuro-inflammatory-degenerative diseases. Herein, we focus on recent progress in the modulatory mechanisms of the cholinergic anti-inflammatory pathway in neuroinflammatory diseases.

Alzheimer's disease as a chronic maladaptive polyamine stress response

Polyamines are nitrogen-rich polycationic ubiquitous bioactive molecules with diverse evolutionary-conserved functions. Their activity interferes with numerous genes' expression resulting in cell proliferation and signaling modulation. The intracellular levels of polyamines are precisely controlled by an evolutionary-conserved machinery. Their transient synthesis is induced by heat stress, radiation, and other traumatic stimuli in a process termed the polyamine stress response (PSR). Notably, polyamine levels decline gradually with age; and external supplementation improves lifespan in model organisms. This corresponds to cytoprotective and reactive oxygen species scavenging properties of polyamines. Paradoxically, age-associated neurodegenerative disorders are characterized by upsurge in polyamines levels, indicating polyamine pleiotropic, adaptive, and pathogenic roles. Specifically, arginase overactivation and arginine brain deprivation have been shown to play an important role in Alzheimer's disease (AD) pathogenesis. Here, we assert that a universal short-term PSR associated with acute stimuli is beneficial for survival. However, it becomes detrimental and maladaptive following chronic noxious stimuli, especially in an aging organism. Furthermore, we regard cellular senescence as an adaptive response to stress and suggest that PSR plays a central role in age-related neurodegenerative diseases' pathogenesis. Our perspective on AD proposes an inclusive reassessment of the causal relationships between the classical hallmarks and clinical manifestation. Consequently, we offer a novel treatment strategy predicated upon this view and suggest fine-tuning of arginase activity with natural inhibitors to preclude or halt the development of AD-related dementia.

Medial prefrontal cortical control of reward- and aversion-based behavioral output: Bottom-up modulation

How does the brain guide our actions? This is a complex issue, where the medial prefrontal cortex (mPFC) plays a crucial role. The mPFC is essential for cognitive flexibility and decision making. These functions are related to reward- and aversion-based learning, which ultimately drive behavior. Though, cortical projections and modulatory systems that may regulate those processes in the mPFC are less understood. How does the mPFC regulate approach-avoidance behavior in the case of conflicting aversive and appetitive stimuli? This is likely dependent on the bottom-up neuromodulation of the mPFC projection neurons. In this review, we integrate behavioral-, pharmacological-, and viral-based circuit manipulation data showing the involvement of mPFC dopaminergic, noradrenergic, cholinergic, and serotoninergic inputs in reward and aversion processing. Given that an incorrect balance of reward and aversion value could be a key problem in mental diseases such as substance use disorders, we discuss outstanding questions for future research on the role of mPFC modulation in reward and aversion.

Nicotinic Receptors in the Brainstem Ascending Arousal System in SIDS With Analysis of Pre-natal Exposures to Maternal Smoking and Alcohol in High-Risk Populations of the Safe Passage Study

Pre-natal exposures to nicotine and alcohol are known risk factors for sudden infant death syndrome (SIDS), the leading cause of post-neonatal infant mortality. Here, we present data on nicotinic receptor binding, as determined by 125I-epibatidine receptor autoradiography, in the brainstems of infants dying of SIDS and of other known causes of death collected from the Safe Passage Study, a prospective, multicenter study with clinical sites in Cape Town, South Africa and 5 United States sites, including 2 American Indian Reservations. We examined 15 pons and medulla regions related to cardiovascular control and arousal in infants dying of SIDS (n = 12) and infants dying from known causes (n = 20, 10 pre-discharge from time of birth, 10 post-discharge). Overall, there was a developmental decrease in 125I-epibatidine binding with increasing postconceptional age in 5 medullary sites [raphe obscurus, gigantocellularis, paragigantocellularis, centralis, and dorsal accessory olive (p = 0.0002-0.03)], three of which are nuclei containing serotonin cells. Comparing SIDS with post-discharge known cause of death (post-KCOD) controls, we found significant decreased binding in SIDS in the nucleus pontis oralis (p = 0.02), a critical component of the cholinergic ascending arousal system of the rostral pons (post-KCOD, 12.1 ± 0.9 fmol/mg and SIDS, 9.1 ± 0.78 fmol/mg). In addition, we found an effect of maternal smoking in SIDS (n = 11) combined with post-KCOD controls (n = 8) on the raphe obscurus (p = 0.01), gigantocellularis (p = 0.02), and the paragigantocellularis (p = 0.002), three medullary sites found in this study to have decreased binding with age and found in previous studies to have abnormal indices of serotonin neurotransmission in SIDS infants. At these sites, 125I-epibatidine binding increased with increasing cigarettes per week. We found no effect of maternal drinking on 125I-epibatidine binding at any site measured. Taken together, these data support changes in nicotinic receptor binding related to development, cause of death, and exposure to maternal cigarette smoking. These data present new evidence in a prospective study supporting the roles of developmental factors, as well as adverse exposure on nicotinic receptors, in serotonergic nuclei of the rostral medulla-a finding that highlights the interwoven and complex relationship between acetylcholine (via nicotinic receptors) and serotonergic neurotransmission in the medulla.

(+)-[18F]Flubatine as a novel α4β2 nicotinic acetylcholine receptor PET ligand-results of the first-in-human brain imaging application in patients with β-amyloid PET-confirmed Alzheimer's disease and healthy controls

PURPOSES

We present the first in-human brain PET imaging data of the new α4β2 nicotinic acetylcholine receptor (nAChR)-targeting radioligand (+)-[18F]Flubatine. Aims were to develop a kinetic modeling-based approach to quantify (+)-[18F]Flubatine and compare the data of healthy controls (HCs) and patients with Alzheimer's disease (AD); to investigate the partial volume effect (PVE) on regional (+)-[18F]Flubatine binding; and whether (+)-[18F]Flubatine binding and cognitive test data respective β-amyloid radiotracer accumulation were correlated.

METHODS

We examined 11 HCs and 9 mild AD patients. All subjects underwent neuropsychological testing and [11C]PiB PET/MRI examination. (+)-[18F]Flubatine PET data were evaluated using full kinetic modeling and regional as well as voxel-based analyses.

RESULTS

With 270-min p.i., the unchanged parent compound amounted to 97 ± 2%. Adequate fits of the time-activity curves were obtained with the 1 tissue compartment model (1TCM). (+)-[18F]Flubatine distribution volume (binding) was significantly reduced in bilateral mesial temporal cortex in AD patients compared with HCs (right 10.6 ± 1.1 vs 11.6 ± 1.4, p = 0.049; left 11.0 ± 1.1 vs 12.2 ± 1.8, p = 0.046; one-sided t tests each). PVE correction increased not only (+)-[18F]Flubatine binding of approximately 15% but also standard deviation of 0.4-70%. Cognitive test data and (+)-[18F]Flubatine binding were significantly correlated in the left anterior cingulate, right posterior cingulate, and right parietal cortex (r > 0.5, p < 0.05 each). In AD patients, (+)-[18F]Flubatine binding and [11C]PiB standardized uptake value ratios were negatively correlated in several regions; whereas in HCs, a positive correlation between cortical (+)-[18F]Flubatine binding and [11C]PiB accumulation in the white matter was found. No adverse event related to (+)-[18F]Flubatine occurred.

CONCLUSION

(+)-[18F]Flubatine is a safe and stable PET ligand. Full kinetic modeling can be realized by 1TCM without metabolite correction. (+)-[18F]Flubatine binding affinity was high enough to detect group differences. Of interest, correlation between white matter β-amyloid PET uptake and (+)-[18F]Flubatine binding indicated an association between white matter integrity and availability of α4β2 nAChRs. Overall, (+)-[18F]Flubatine showed favorable characteristics and has therefore the potential to serve as α4β2 nAChR-targeting PET ligand in further clinical trials.

[Relation between tobacco smoking and pain: A narrative review of the scientific literature]

INTRODUCTION

Tobacco smoking and pain have an intimate, complex, two-way interaction. The purpose of this narrative review of the literature is to present what is currently understood about the relationship.

STATE OF KNOWLEDGE

Tobacco smoking (and the associated chronic exposure to nicotine) has been defined as a risk factor for chronic pain, involving nociceptive sensitisation. For people who smoke, pain will be both a motivational factor for tobacco consumption and a barrier to tobacco use cessation. Conversely, nicotine (acute exposure) has clearly demonstrated analgesic properties, mediated in particular by activation of nicotinic acetylcholine receptors.

PERSPECTIVES

The management of pain in people who smoke is still largely unaddressed, and further studies will be needed to develop effective strategies for tobacco use cessation in this context. Nicotine and modulators of nicotinic acetylcholine receptors represent innovative strategies for the discovery of new analgesics.

CONCLUSIONS

The effects of smoking on pain, chronic nociceptive sensitisation and acute analgesia, serve to maintain tobacco consumption via negative reinforcement. A holistic therapeutic strategy is necessary to maximise the likelihood of successful smoking cessation.

Functional α6β4 acetylcholine receptor expression enables pharmacological testing of nicotinic agonists with analgesic properties

The α6β4 nicotinic acetylcholine receptor (nAChR) is enriched in dorsal root ganglia neurons and is an attractive non-opioid therapeutic target for pain. However, difficulty expressing human α6β4 receptors in recombinant systems has precluded drug discovery. Here, genome-wide screening identified accessory proteins that enable reconstitution of human α6β4 nAChRs. BARP, an auxiliary subunit of voltage-dependent calcium channels, promoted α6β4 surface expression while IRE1α, an unfolded protein response sensor, enhanced α6β4 receptor assembly. Effects on α6β4 involve BARP's N-terminal region and IRE1α's splicing of XBP1 mRNA. Furthermore, clinical efficacy of nicotinic agents in relieving neuropathic pain best correlated with their activity on α6β4. Finally, BARP-knockout, but not NACHO-knockout mice lacked nicotine-induced antiallodynia, highlighting the functional importance of α6β4 in pain. These results identify roles for IRE1α and BARP in neurotransmitter receptor assembly and unlock drug discovery for the previously elusive α6β4 receptor.

A meta-analysis on the levels of VILIP-1 in the CSF of Alzheimer's disease compared to normal controls and other neurodegenerative conditions

Alzheimer's disease (AD) is a progressing neurodegenerative disorder and the main cause of serious irreversible cognitive decline in elderly people. Visinin-like protein 1 (VILIP-1) is a member of the family of calcium-binding proteins and plays a crucial role in AD pathophysiology. Multiple studies have shown that CSF levels of VILIP-1 are increased in AD patients compared to normal controls, or other neurodegenerative conditions. We searched online databases for studies on the levels of VILIP-1 in the CSF of AD patients in comparison to normal controls, mild cognitive impairment (MCI) patients and Dementia with Lewy bodies (DLB) patients. A total of ten studies were used for the comparison between AD and controls, three studies for the comparison between AD and MCI, two studies for AD and DLB and two studies for the comparison between stable MCI and MCI progressed to AD. We found that VILIP-1 levels are significantly higher in AD compared to normal controls, but not to the other groups, and furthermore, they are significantly higher in patient with MCI progressed to AD, than in stable MCI patients.

In silico studies of ASEM analogues targeting α7-nAChR and experimental verification

The α7 nicotinic acetylcholine receptor (α7-nAChR) is implicated in a variety of neurodegenerative and neuropsychiatric disorders, such as Alzheimer's disease (AD) and schizophrenia. The progress of these disorders can be studied using positron emission tomography (PET) with radiotracers for α7-nAChR. [18F]ASEM and [18F] para-ASEM (also referred to as [18F]DBT-10) are novel and potent α7-nAChR PET radiotracers which have successfully been used in human subjects and nonhuman primates, though further improvement of them is still a pressing task in the community of neurodegeneration research. In this work, we demonstrate the use of modern in silico techniques to predict the binding modes, binding strengths, and residence times for molecular PET tracers binding to proteins, using ASEM and DBT-10 as a showcase of the predictive and interpretational power of such techniques, in particular free energy perturbation theory. The corresponding compounds were synthesized and further tested by in vitro binding experiment for validation. Encouragingly, our in silico modeling can correctly predict the binding affinities of the ASEM analogues. The structure-activity relationships for the ortho- and para-substitutions are well explained at the atomistic level and provide structure-based guiding for the future development of PET tracers for α7-nAChR. A discussion is presented on the complementary use of in silico rational methods based on atomic and electronic principles for in vitro characterization of PET tracers.

The Role of α7nAChR-Mediated Cholinergic Anti-inflammatory Pathway in Immune Cells

Alpha 7 nicotinic acetylcholine receptor (α7nAChR) is widely distributed in the nervous and non-cholinergic immune systems. It is necessary for the cholinergic transmitter to participate in the regulation of inflammatory response and is the key element of cholinergic anti-inflammatory pathway (CAP). Because of the profound impact of CAP on the immune system, α7nAChR is considered as a potential therapeutic target for the treatment of inflammatory diseases. Available evidences confirmed that manipulation of CAP by activating α7nAChR with either endogenous acetylcholine (ACh) or cholinergic agonists can substantially alleviate inflammatory responses both in vivo and in vitro. However, the mechanism through which CAP curbs the excessive pro-inflammatory responses and maintains immune homeostasis is not fully understood. Obtained clues suggest that the crosstalk between CAP and classical inflammatory pathways is the key to elucidate the anti-inflammatory mechanism, and the impacts of CAP activation in α7nAChR-expressing immune cells are the foundation of the immunoregulatory property. In this article, we review and update the knowledge concerning the progresses of α7nAChR-based CAP, including α7nAChR properties, signal transductions, interactions with classic immune pathways, and immunoregulatory functions in different immune cells. Certain critical issues to be addressed are also highlighted. By providing a panoramic view of α7nAChR, the summarized evidences will pave the way for the development of novel anti-inflammatory reagents and strategy and inspire further researches.

The Role of β-Arrestins in Regulating Stem Cell Phenotypes in Normal and Tumorigenic Cells

β-Arrestins (ARRBs) are ubiquitously expressed scaffold proteins that mediate inactivation of G-protein-coupled receptor signaling, and in certain circumstances, G-protein independent pathways. Intriguingly, the two known ARRBs, β-arrestin1 (ARRB1) and β-Arrestin2 (ARRB2), seem to have opposing functions in regulating signaling cascades in several models in health and disease. Recent evidence suggests that ARRBs are implicated in regulating stem cell maintenance; however, their role, although crucial, is complex, and there is no universal model for ARRB-mediated regulation of stem cell characteristics. For the first time, this review compiles information on the function of ARRBs in stem cell biology and will discuss the role of ARRBs in regulating cell signaling pathways implicated in stem cell maintenance in normal and malignant stem cell populations. Although promising targets for cancer therapy, the ubiquitous nature of ARRBs and the plethora of functions in normal cell biology brings challenges for treatment selectivity. However, recent studies show promising evidence for specifically targeting ARRBs in myeloproliferative neoplasms.

The retrotrapezoid nucleus and the neuromodulation of breathing

Breathing is regulated by a host of arousal and sleep-wake state-dependent neuromodulators to maintain respiratory homeostasis. Modulators such as acetylcholine, norepinephrine, histamine, serotonin (5-HT), adenosine triphosphate (ATP), substance P, somatostatin, bombesin, orexin, and leptin can serve complementary or off-setting functions depending on the target cell type and signaling mechanisms engaged. Abnormalities in any of these modulatory mechanisms can destabilize breathing, suggesting that modulatory mechanisms are not overly redundant but rather work in concert to maintain stable respiratory output. The present review focuses on the modulation of a specific cluster of neurons located in the ventral medullary surface, named retrotrapezoid nucleus, that are activated by changes in tissue CO₂/H⁺ and regulate several aspects of breathing, including inspiration and active expiration.

Choline and nicotine increase glioblastoma cell proliferation by binding and activating α7- and α9- containing nicotinic receptors

Glioblastomas (GBMs), the most frequent and aggressive human primary brain tumours, have altered cell metabolism, and one of the strongest indicators of malignancy is an increase in choline compounds. Choline is also a selective agonist of some neuronal nicotinic acetylcholine receptor (nAChR) subtypes. As little is known concerning the expression of nAChR in glioblastoma cells, we analysed in U87MG human grade-IV astrocytoma cell line and GBM5 temozolomide-resistant glioblastoma cells selected from a cancer stem cell-enriched culture, molecularly, pharmacologically and functionally which nAChR subtypes are expressed and,whether choline and nicotine can affect GBM cell proliferation. We found that U87MG and GBM5 cells express similar nAChR subtypes, and choline and nicotine increase their proliferation rate and activate the anti-apoptotic AKT and pro-proliferative ERK pathways. These effects are blocked by the presence of non-cell-permeable peptide antagonists selective for α7- and α9-containing nicotinic receptors. siRNA-mediated silencing of α7 or α9 subunit expression also selectively prevents the effects of nicotine and choline on GBM cell proliferation. Our findings indicate that nicotine and choline activate the signalling pathways involved in the proliferation of GBM cells, and that these effects are mediated by α7 and α9-containing nAChRs. This suggests that these nicotinic receptors may contribute to the aggressive behaviour of this tumor and may indicate new therapeutic strategies against high-grade human brain tumours.

Structure-Function of Neuronal Nicotinic Acetylcholine Receptor Inhibitors Derived From Natural Toxins

Neuronal nicotinic acetylcholine receptors (nAChRs) are prototypical cation-selective, ligand-gated ion channels that mediate fast neurotransmission in the central and peripheral nervous systems. nAChRs are involved in a range of physiological and pathological functions and hence are important therapeutic targets. Their subunit homology and diverse pentameric assembly contribute to their challenging pharmacology and limit their drug development potential. Toxins produced by an extensive range of algae, plants and animals target nAChRs, with many proving pivotal in elucidating receptor pharmacology and biochemistry, as well as providing templates for structure-based drug design. The crystal structures of these toxins with diverse chemical profiles in complex with acetylcholine binding protein (AChBP), a soluble homolog of the extracellular ligand-binding domain of the nAChRs and more recently the extracellular domain of human α9 nAChRs, have been reported. These studies have shed light on the diverse molecular mechanisms of ligand-binding at neuronal nAChR subtypes and uncovered critical insights useful for rational drug design. This review provides a comprehensive overview and perspectives obtained from structure and function studies of diverse plant and animal toxins and their associated inhibitory mechanisms at neuronal nAChRs.

Beyond the Obvious: Smoking and Respiratory Infection Implications on Alzheimer's Disease

Tobacco smoke is not only a leading cause for chronic obstructive pulmonary disease, cardiovascular disorders, and lung and oral cancers, but also causes neurological disorders such as Alzheimer 's disease. Tobacco smoke consists of more than 4500 toxic chemicals, which form free radicals and can cross blood-brain barrier resulting in oxidative stress, an extracellular amyloid plaque from the aggregation of amyloid β (Aβ) peptide deposition in the brain. Further, respiratory infections such as Chlamydia pneumoniae, respiratory syncytial virus have also been involved in the induction and development of the disease. The necessary information collated on this review has been gathered from various literature published from 1995 to 2019. The review article sheds light on the role of smoking and respiratory infections in causing oxidative stress and neuroinflammation, resulting in Alzheimer's disease (AD). This review will be of interest to scientists and researchers from biological and medical science disciplines, including microbiology, pharmaceutical sciences and the translational researchers, etc. The increasing understanding of the relationship between chronic lung disease and neurological disease is two-fold. First, this would help to identify the risk factors and possible therapeutic interventions to reduce the development and progression of both diseases. Second, this would help to reduce the probable risk of development of AD in the population prone to chronic lung diseases.

Cisatracurium stimulates testosterone synthesis in rat and mouse Leydig cells via nicotinic acetylcholine receptor

As a cis-acting non-depolarizing neuromuscular blocker through a nicotinic acetylcholine receptor (nAChR), cisatracurium (CAC) is widely used in anaesthesia and intensive care units. nAChR may be present on Leydig cells to mediate the action of CAC. Here, by Western blotting, immunohistochemistry and immunofluorescence, we identified that CHRNA4 (a subunit of nAChR) exists only on rat adult Leydig cells. We studied the effect of CAC on the synthesis of testosterone in rat adult Leydig cells and mouse MLTC-1 tumour cells. Rat Leydig cells and MLTC-1 cells were treated with CAC (5, 10 and 50 μmol/L) or nAChR agonists (50 μmol/L nicotine or 50 μmol/L lobeline) for 12 hours, respectively. We found that CAC significantly increased testosterone output in rat Leydig cells and mouse MLTC-1 cells at 5 μmol/L and higher concentrations. However, nicotine and lobeline inhibited testosterone synthesis. CAC increased intracellular cAMP levels, and nicotine and lobeline reversed this change in rat Leydig cells. CAC may increase testosterone synthesis in rat Leydig cells and mouse MLTC-1 cells by up-regulating the expression of Lhcgr and Star. Up-regulation of Scarb1 and Hsd3b1 expression by CAC was also observed in rat Leydig cells. In addition to cAMP signal transduction, CAC can induce ERK1/2 phosphorylation in rat Leydig cells. In conclusion, CAC binds to nAChR on Leydig cells, and activates cAMP and ERK1/2 phosphorylation, thereby up-regulating the expression of key genes and proteins in the steroidogenic cascade, resulting in increased testosterone synthesis in Leydig cells.

Assessing the Binding of Venoms from Aquatic Elapids to the Nicotinic Acetylcholine Receptor Orthosteric Site of Different Prey Models

The evolution of an aquatic lifestyle from land dwelling venomous elapids is a radical ecological modification, bringing about many evolutionary changes from morphology to diet. Diet is an important ecological facet which can play a key role in regulating functional traits such as venom composition and prey-specific targeting of venom. In addition to predating upon novel prey (e.g., fish, fish eggs and invertebrates), the venoms of aquatic elapids also face the challenge of increased prey-escape potential in the aquatic environment. Thus, despite the independent radiation into an aquatic niche on four separate occasions, the venoms of aquatic elapids are evolving under convergent selection pressures. Utilising a biolayer interferometry binding assay, this study set out to elucidate whether crude venoms from representative aquatic elapids were target-specific to the orthosteric site of postsynaptic nicotinic acetylcholine receptor mimotopes of fish compared to other terrestrial prey types. Representatives of the four aquatic lineages were: aquatic coral snakes representative was Micrurus surinamensis;, sea kraits representative was Laticauda colubrina; sea snakes representatives were two Aipysurus spp. and eight Hydrophis spp; and water cobras representative was Naja annulata. No prey-specific differences in crude venom binding were observed from any species tested, except for Aipysurus laevis, which showed slight evidence of prey-potency differences. For Hydrophis caerulescens, H. peronii, H. schistosus and M. surinamensis, there was a lack of binding to the orthosteric site of any target lineage. Subsequent testing on the in vitro chick-biventer cervicis muscle preparation suggested that, while the venoms of these species bound postsynaptically, they bound to allosteric sites rather than orthosteric. Allosteric binding is potentially a weaker but faster-acting form of neurotoxicity and we hypothesise that the switch to allosteric binding is likely due to selection pressures related to prey-escape potential. This research has potentially opened up the possibility of a new functional class of toxins which have never been assessed previously while shedding light on the selection pressures shaping venom evolution.

Emerging drugs for the treatment of attention-deficit hyperactivity disorder (ADHD)

INTRODUCTION

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder affecting up to 5.3% of children and 2.5% of adults depending on the country considered. Current pharmacological treatments for ADHD are based on stimulant or non-stimulant medications, targeting dopaminergic and noradrenergic systems in the frontal cortex and dopaminergic system in the basal ganglia. These drugs are effective and safe for the majority of patients, whereas about 20% of treated patients do not tolerate current therapies or experience insufficient efficacy. The adequate treatment of ADHD is necessary to allow a proper social placement and prevent the acquisition of additional, more severe, comorbidities.

AREAS COVERED

We conducted a review of the scientific literature and of unpublished/ongoing clinical trials to summarize the advances made in the last 10 years (2010-2020) for the pharmacological treatment of ADHD. We found many pharmacological mechanisms beyond dopaminergic and noradrenergic ones have been investigated in patients.

EXPERT OPINION

Some emerging drugs for ADHD may be promising as add-on treatment especially in children, amantadine to enhance cognitive functions and tipepidine for hyperactivity/impulsivity. Stand-alone emerging treatments for ADHD include viloxazine and dasotraline, which will soon have more clinical data available to support market access requests.

Rational Design of α-Conotoxin RegIIA Analogues Selectively Inhibiting the Human α3β2 Nicotinic Acetylcholine Receptor through Computational Scanning

Engineering the selectivity of α-conotoxins for nicotinic acetylcholine receptors (nAChRs) presents considerable complexity and challenges, as it involves the optimization of their binding affinities to multiple highly conserved nAChR subtypes. Here, we applied a computational-based scanning approach for the rational design of α-conotoxin RegIIA analogues selectively targeting the human (h) α3β2 versus hα3β4 nAChRs. Binding mode analyses suggested that several residues in loop II of RegIIA (position 9, 10, and 11) formed nonconserved interactions with residues of the β2 and β4 subunits. The molecular mechanics generalized Born surface area method was applied for in silico sequence scanning of RegIIA position 9, 10, and 11 on frames extracted from single molecular dynamics simulation trajectory. RegIIA analogues with favorable predicted binding affinities solely to the hα3β2 nAChR were synthesized and tested electrophysiologically. We report three RegIIA analogues, with position 9 aromatic residue substitutions, exhibiting a 10- to 37-fold subtype selectivity improvement for hα3β2 compared to hα3β4 nAChR. The in silico scanning method proposed from this study has considerable potential for the efficient design of nAChR subtype selective antagonists in the future.