Reymond J.-L.,University of Bern |
Van Deursen R.,University of Bern |
Biochemical Pharmacology | Year: 2011
The activity of ligand gated channels is crucial for proper brain function and dysfunction of a single receptor subtype have led to neurological impairments ranging from benign to major diseases such as epilepsy, startle diseases, etc. Molecular biology and crystallography allowed the characterization at the atomic scale of the first four transmembrane ligand gated channels and of proteins sharing a high degree of homology with the neurotransmitter-binding domain. Gaining an adequate knowledge of the structural features of the ligand binding pocket led to the possibilities of developing virtual screening based approaches and probing in silico the docking of very large numbers of molecules. Development of new computing tools further extended such possibilities and rendered possible the screening of the chemical universe database GDB-11, which contains all possible organic molecules up to 11 atoms of C, N, O and F. In the case of the nicotinic acetylcholine receptors molecules identified using such screening methods were synthesized and characterized in binding assays and their pose determined in crystal structure with the acetylcholine binding protein. However, in spite of these thorough approaches, functional studies revealed that these molecules had a greater affinity for the pore domain of the channel and acted as open channel blocker rather than binding site antagonist. In this work, we discuss the potential and current limitations of how progresses made with the crystal structures of ligand gated channels, or ligand binding proteins, can be used in combination with virtual screening and functional assays, to identify novel compounds. © 2011 Elsevier Inc.
Rollema H.,Rollema Biomedical Consulting |
Russ C.,Pfizer |
Lee T.C.,Pfizer |
Hurst R.S.,Pfizer |
Nicotine and Tobacco Research | Year: 2014
Introduction: It has been suggested that varenicline-induced activation of nicotinic acetylcholine receptors (nAChRs) could play a role in the cardiovascular (CV) safety of varenicline. However, since preclinical studies showed that therapeutic varenicline concentrations have no effect in models of CV function, this study examined in vitro profiles of varenicline and nicotine at nAChR subtypes possibly involved in CV control. Methods: Concentration-dependent functional effects of varenicline and nicotine at human α3β4, α3α5β4, α7, and α4β2 nAChRs expressed in oocytes were determined by electrophysiology. The proportion of nAChRs predicted to be activated and inhibited by concentrations of varenicline (1mg b.i.d.) and of nicotine in smokers was derived from activation-inhibition curves for each nAChR subtype. Results: Human varenicline and nicotine concentrations can desensitize and inhibit nAChRs but cause only low-level activation of α3β4, α4β2 (<2%), α7 (<0.05%), and α3α5β4 (<0.01%) nAChRs, which is consistent with literature data. Nicotine concentrations in smokers are predicted to inhibit larger fractions of α3β4 (48%) and α3α5β4 (10%) nAChRs than therapeutic varenicline concentrations (11% and 0.6%, respectively) and to inhibit comparable fractions of α4β2 nAChRs (42%-56%) and α7 nAChRs (16%) as varenicline. Conclusions: Nicotine and varenicline concentrations in patients and smokers are predicted to cause minimal activation of ganglionic α3β4* nAChRs, while their functional profiles at α3β4, α3α5β4, α7, and α4β2 nAChRs cannot explain that substituting nicotine from tobacco with varenicline would cause CV adverse events in smokers who try to quit. Other pharmacological properties that could mediate varenicline-induced CV effects have not been identified. © The Author 2014. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved.
Wallace T.L.,SRI International |
Biochemical Pharmacology | Year: 2013
The prefrontal cortex (PFC) is responsible for integrating cortical and subcortical inputs to execute essential cognitive functions such as attention, working memory planning and decision-making. The importance of this brain region in regulating complex cognitive processes is underscored by a decline in PFC-mediated ability observed in aging and disease. The cholinergic system plays a vital role in cognitive function and treatments (e.g., cholinesterase inhibitors) to improve cholinergic neurotransmission provide the standard-of-care for diseases such as Alzheimer's. Nicotinic receptors (nAChRs) are a primary site of action for acetylcholine (ACh), and the resulting pro-cognitive effects observed by stimulating nAChRs with nicotine has long been appreciated by tobacco users, prompting investigation of therapeutic development for diseases (e.g., schizophrenia, Alzheimer or attention-deficit- hyperactivity disorder) by targeting the neuronal nAChR system. Noteworthy, improvements in attention, working memory and executive processes mediated by the PFC have been reported following nicotinic agonist exposure. Relevance of these ligand gated channels in higher brain function is further supported by the association of cognitive deficits reported in humans with mutations in CHRNB2 or CHRNA7 the genes encoding for the nicotinic receptor β2 and α7 subunits, respectively. In this work we review, in light of the latest findings, how nicotinic agonists may be acting in the PFC to influence cognitive function. © 2013 Elsevier Inc. All rights reserved.
Marger L.,HiQScreen |
Schubert C.R.,Pfizer |
Biochemical Pharmacology | Year: 2014
The divalent cation, zinc is the second most abundant metal in the human body and is indispensable for life. Zinc concentrations must however, be tightly regulated as deficiencies are associated with multiple pathological conditions while an excess can be toxic. Zinc plays an important role as a cofactor in protein folding and function, e.g. catalytic interactions, DNA recognition by zinc finger proteins and modulation ion channel activity. There are 24 mammalian proteins specific for zinc transport that are subdivided in two groups with opposing functions: ZnT proteins reduce cytosolic zinc concentration while ZIP proteins increase it. The mammalian brain contains a significant amount of zinc, with 5-15% concentrated in synaptic vesicles of glutamatergic neurons alone. Accumulated in these vesicles by the ZnT3 transporter, zinc is released into the synaptic cleft at concentrations from nanomolar at rest to high micromolar during active neurotransmission. Low concentrations of zinc modulate the activity of a multitude of voltage- or ligand-gated ion channels, indicating that this divalent cation must be taken into account in the analysis of the pathophysiology of CNS disorders including epilepsy, schizophrenia and Alzheimer's disease. In the context of the latest findings, we review the role of zinc in the central nervous system and discuss the relevance of the most recent association between the zinc transporter, ZIP8 and schizophrenia. An enhanced understanding of zinc transporters in the context of ion channel modulation may offer new avenues in identifying novel therapeutic entities that target neurological disorders. © 2014 Elsevier Inc. All rights reserved.
Wallace T.L.,SRI International |
Expert Opinion on Therapeutic Targets | Year: 2013
Introduction: Schizophrenia is a profoundly debilitating disease that represents not only an individual, but a societal problem. Once characterized solely by the hyperactivity of the dopaminergic system, therapies directed to dampen dopaminergic neurotransmission were developed. However, these drugs do not address the significant impairments in cognition and the negative symptoms of the disease, and it is now apparent that disequilibrium of many neurotransmitter systems is involved. Despite enormous efforts, minimal progress has been made toward the development of safer, more effective therapies to date. Areas covered: The high preponderance of smoking in schizophrenics suggests that nicotine may provide symptomatic improvement, which has led to investigation for selective molecules targeted to individual nicotinic receptor (nAChR) subtypes. Of special interest is activation of the homomeric α7nAChR, which is widely distributed in the brain and has been implicated in the pathophysiology of schizophrenia through numerous approaches. Expert opinion: Preclinical and clinical data suggest that neuronal α7nAChRs play an important role in cognitive functions. Moreover, some, but not all, early clinical trials conducted with α7nAChR agonists show cognitive benefits in schizophrenics. These encouraging results suggest that development of compounds targeting α7nAChRs will represent a valuable tool to mitigate symptoms associated with schizophrenia, and open new strategies for better pharmacological treatment of these patients. © 2013 Informa UK, Ltd.