Interaction of Bupropion with Muscle-Type Nicotinic Acetylcholine Receptors in Different Conformational States

To characterize the binding sites and the mechanisms of inhibition of bupropion on muscle-type nicotinic acetylcholine receptors (AChRs), structural and functional approaches were used. The results established that bupropion: (a) inhibits epibatidine-induced Ca2+ influx in embryonic muscle AChRs, (b) inhibits adult muscle AChR macroscopic currents in the resting/activatable state with ~100-fold higher potency compared to that in the open state, (c) increases desensitization rate of adult muscle AChRs from the open state and impairs channel opening from the resting state, (d) inhibits [3H]TCP and [3H]imipramine binding to the desensitized/carbamylcholine-bound Torpedo AChR with higher affinity compared to the resting/α-bungarotoxin-bound AChR, (e) binds to the Torpedo AChR in either state mainly by an entropy–driven process, and (f) interacts with a binding domain located between the serine (position 6’) and valine (position 13’) rings, by a network of van der Waals, hydrogen bond, and polar interactions. Collectively our data indicate that bupropion first binds to the resting AChR, decreasing the probability of ion channel opening. The remnant fraction of open ion channels is subsequently decreased by accelerating the desensitization process. Bupropion interacts with a luminal binding domain shared with PCP that is located between the serine and valine rings, and this interaction is mediated mainly by an entropy-driven process.Fil: Arias, Hugo Rubén. Midwestern University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gumilar, Fernanda Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; ArgentinaFil: Rosenberg, Avraham. National Institutes of Health; Estados UnidosFil: Targowska Duda, Katarzyna M.. Medical University of Lublin; PoloniaFil: Feuerbach, Dominik. Novartis Institutes for Biomedical Research; SuizaFil: Jozwiak, Krzysztof. Medical University of Lublin; PoloniaFil: Moaddel, Ruin. National Institutes of Health; Estados UnidosFil: Wainer, Irving W.. National Institutes of Health; Estados UnidosFil: Bouzat, Cecilia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentin

The roles of inflammation and immune mechanisms in Alzheimer's disease

AbstractThe Alzheimer's Association's Research roundtable met in April 2015 to explore the role of neuroinflammatory mechanisms in the progression of Alzheimer's disease (AD). The ability of innate immune cells, particularly microglia and astrocytes, to mediate neuroinflammation in AD has been implicated as a significant contributor to disease pathogenesis. Adaptive immunity, which plays an important role in responding to injury and some diseases of the central nervous system, may contribute to neuroinflammation in AD as well. Communication between the central and peripheral immune systems may also be important in AD. An increased understanding of the physiology of the innate immune system may aid the identification of new therapeutic targets or mechanisms. The development of predictive animal models and translatable neuroinflammation biomarkers for AD would also facilitate the advancement of novel treatments for innate immunity. Important challenges impeding the advancement of new therapeutic agents and strategies to overcome them were discussed

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Microglia M2A-polarization as potential link between food allergy and autism spectrum disorders

Atopic diseases are frequently co-morbid with autism spectrum disorders (ASD). Allergic responses are associated with an activation of mast cells, innate lymphoid cells, and Th2 cells. These cells produce type-2 cytokines (IL4, IL5 and IL13), which stimulate microglia and macrophages to adopt a phenotype referred to as ‘alternative activation’ or ‘M2A’. M2A-polarized macrophages and microglia play a physiological role in tissue repair by secreting growth factors such as brain-derived neurotrophic factor and insulin-like growth factor-1. In ASD there is evidence for increased type-2 cytokines, microglia activation, M2A polarization, and increased levels of growth factors. In neurons, these growth factors drive a signal transduction pathway that leads to activation of the enzyme mTOR, and thereby to the inhibition of autophagy. Notably, activation of mTOR is an effect that is common to several of the syndromic forms of autism. Inhibition of autophagy results in diminished removal of redundant synapses, which in the context of ASD is likely to be undesired. Based on this line of reasoning, atopic diseases would represent a risk factor for autism spectrum disorders

Modulatory effects of α7 nAChRs on the immune system and its relevance for CNS disorders

The clinical development of selective α7 nAChR agonists has hitherto been focused on disorders characterized by cognitive deficits (Alzheimer’s disease, schizophrenia). However, α7 nAChRs are also widely expressed on cells of the immune system and on cells with a secondary role in pathogen defense. Activation of α7 nAChRs leads to an anti-inflammatory effect. Since sterile inflammation is a frequently observed phenomenon in both psychiatric disorders (e.g. schizoaffective disorder, schizophrenia, melancholic- and bipolar depression) and neurological disorders (e.g. Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy), α7 nAChR agonists might display beneficial effects in these central nervous system disorders. In the current review, we summarize information on receptor expression, the intracellular signaling pathways, the reasons for receptor dysfunction, clinical evidence for altered α7 nAChR function (including information on tabacco smoking, vagus nerve stimulation and cholinesterase inhibitors), and finally discuss potential indications for selective α7 nAChR agonists

Promotion of microglial M2-polarization by antidepressants

Macrophages and microglia are cells of the innate immune system. These phagocytic cells alter and adapt their phenotype depending on their prime activity, i.e. whether they participate in acute defence against pathogenic organisms (‘M1’-phenotype) or in clearing damaged tissues and performing repair activities (‘M2’-phenotype). Several risk factors for melancholic depression (agonists for Toll-like receptors, inflammatory cytokines, stress, alcohol abuse, obesity and neurological disorders) seem to promote M1-polarization. In the M1-polarized form, microglia and macrophages generate reactive oxygen- and nitrogen radicals to eradicate microbial pathogens. Inadvertently, also tetrahydrobiopterin (BH4) may become oxidized. This is an irreversible reaction that generates neopterin, a biomarker for depression. BH4 is a critical cofactor in the synthesis of dopamine, noradrenaline and serotonin and its loss could explain some of the symptoms of depression. Shifting the M1- to an M2- phenotype would limit the loss of BH4. In the current review we evaluate the evidence that antidepressant treatments (monoamine reuptake inhibitors, PDE4 inhibitors, lithium, valproate, agomelatine, tianeptine, electroconvulsive shock and vagus nerve stimulation) promote microglia/macrophage M2-polarization. We speculate that supplementation with BH4 might be an effective straightforward treatment for major depression

Bupropion and its photoreactive analog (±)-SADU-3-72 interact with luminal and non-luminal sites at human α4β2 nicotinic acetylcholine receptors

ABSTRACT The interaction of (±)-bupropion [(±)-BP] with the human (h) α4β2 nicotinic acetylcholine receptor (AChR) was compared to that for its photoreactive analog (±)-2-(N-tert-butylamino)-3’-iodo-4’-azidopropiophenone [(±)-SADU-3-72]. Ca2+ influx results indicated that (±)-SADU-3-72 and (±)-BP inhibit hα4β2 AChRs with practically the same potency. However, (±)-SADU-3-72 binds to the [3H]imipramine sites at resting and desensitized hα4β2 AChRs with 3-fold higher affinity compared to that for (±)-BP, which is supported by molecular docking results. The docking results also indicate that each isomer of BP and SADU-3-72, in the protonated state, interacts with luminal and non-luminal sites. In the channel lumen, both ligands bind to two overlapping subsites, one that overlaps the imipramine site, and another much closer to the cytoplasmic side. Regarding the non-luminal sites, there are three differentiated domains, including the transmembrane (TMD), extracellular (ECD), and ECD-TMD junctional domains. In the ECD-TMD junction, BP and SADU-3-72 bind to overlapping sites. Interestingly, only SADU-3-72 binds to intrasubunit and intersubunit sites in the TMD, and to additional sites in the ECD. Our results are consistent with a model where BP and SADU-3-72 bind to overlapping sites in the luminal and ECD-TMD junctional domains of the hα4β2, whereas only SADU-3-72 binds to additional non-luminal sites. Based on these results, (±)-SADU-3-72 is a promising photoreactive probe for mapping the BP binding sites in the hα4β2 AChR ion channel in particular, as well as to study non-luminal sites for noncompetitive antagonists in general

Interaction of (-)-reboxetine with nicotinic acetylcholine receptors in different conformational states

The interaction of (-)-reboxetine, a non-tricyclic norepinephrine selective reuptake inhibitor, with muscle-type nicotinic acetylcholine receptors (AChRs) in different conformational states was studied by functional and structural approaches. The results established that (-)-reboxetine: (a) inhibits (±)-epibatidine-induced Ca2+ influx in human (h) muscle embryonic (hα1β1γδ) and adult (hα1β1εδ) AChRs in a non-competitive manner and with potencies IC50 = 3.86 0.49 and 1.92 0.48 M, respectively, (b) binds with ~13-fold higher affinity to the luminal [3H]TCP site when the Torpedo AChR is in the desensitized state compared to the resting state, (c) enhances [3H]cytisine binding to the resting but activatable Torpedo AChR but not to the desensitized AChR, suggesting desensitizing properties. This desensitizing activity is produced in the same concentration range as that for tricyclic antidepressants (TCAs), and (d) interacts with the AChR, where it overlaps the PCP/TCA luminal sites in the resting and desensitized states, but also to non-luminal sites. The non-luminal sites are located at the top of the four transmembrane segments from the Torpedo AChR γ subunit, and whithin the / transmembrane interface on the adult muscle AChR. In conclusion, (-)-reboxetine non-competitively inhibits AChRs by binding to the PCP/TCA luminal site and by inducing receptor desensitization (maybe by interacting with non-luminal sites), a mechanism that is shared by TCAs