Inhibition Of Choline Acetyltransferase Research Articles

AI-Enabled Ultra-large Virtual Screening Identifies Potential Inhibitors of Choline Acetyltransferase for Theranostic Purposes.

Alzheimer's disease (AD) and related dementias are among the primary neurological disorders and call for the urgent need for early-stage diagnosis to gain an upper edge in therapeutic intervention and increase the overall success rate. Choline acetyltransferase (ChAT) is the key acetylcholine (ACh) biosynthesizing enzyme and a legitimate target for the development of biomarkers for early-stage diagnosis and monitoring of therapeutic responses. It is also a theranostic target for tackling colon and lung cancers, where overexpression of non-neuronal ChAT leads to the production of acetylcholine, which acts as an autocrine growth factor for cancer cells. Theranostics is a hybrid of diagnostics and therapeutics that can be used to locate cancer cells using radiotracers and kill them without affecting other healthy tissues. Traditional virtual screening protocols have a lot of limitations; given the current rate of chemical database expansion exceeding billions, much faster screening protocols are required. Deep docking (DD) is one such platform that leverages the power of deep neural network (DNN)-based virtual screening, empowering researchers to dock billions of molecules in a speedy, yet explicit manner. Here, we have screened 1.3 billion compounds library from the ZINC20 database, identifying the best-performing hits. With each iteration run where the first iteration gave ∼116 million hits, the second iteration gave ∼3.7 million hits, and the final third iteration gave 168,447 hits from which further refinement gave us the top 5 compounds as potential ChAT inhibitors. The discovery of novel ChAT inhibitors will enable researchers to develop new probes that can be used as novel theranostic agents against cancer and as early-stage diagnostics for the onset of AD, for timely therapeutic intervention to halt the further progression of AD.

Mechanistic Insight into the Inhibition of Choline Acetyltransferase by Proton Pump Inhibitors.

Various pharmacoepidemiological investigational studies have indicated that Proton Pump Inhibitors (PPIs) may increase the likelihood of developing Alzheimer's disease (AD) and non-AD related dementias. Previously, we have reported the inhibition of the acetylcholine biosynthesizing enzyme choline acetyltransferase (ChAT) by PPIs, for which omeprazole, lansoprazole, and pantoprazole exhibited IC50 values of 0.1, 1.5, and 5.3 μM, respectively. In this study we utilize a battery of computational tools to perceive a mechanistic insight into the molecular interaction of PPIs with the ChAT binding pocket that may further help in designing novel ChAT ligands. Various in-silico tools make it possible for us to elucidate the binding interaction, conformational stability, and dynamics of the protein-ligand complexes within a 200 ns time frame. Further, the binding free energies for the PPI-ChAT complexes were explored. The results suggest that the PPIs exhibit equal or higher binding affinity toward the ChAT catalytic tunnel and are stable throughout the simulated time and that the pyridine ring of the PPIs interacts primarily with the catalytic residue His324. A free energy landscape analysis showed that the folding process was linear, and the residue interaction network analysis can provide insight into the roles of various amino acid residues in stabilization of the PPIs in the ChAT binding pocket. As a major factor for the onset of Alzheimer's disease is linked to cholinergic dysfunction, our previous and the present findings give clear insight into the PPI interaction with ChAT. The scaffold can be further simplified to develop novel ChAT ligands, which can also be used as ChAT tracer probes for the diagnosis of cholinergic dysfunction and to initiate timely therapeutic interventions to prevent or delay the progression of AD.

Mountain-cultivated ginseng protects against cognitive impairments in aged GPx-1 knockout mice via activation of Nrf2/ChAT/ERK signaling pathway

BackgroundEscalating evidence shows that ginseng possesses an antiaging potential with cognitive enhancing activity. As mountain cultivated ginseng (MCG) is cultivated without agricultural chemicals, MCG has emerged as a popular herb medicine. However, little is known about the MCG-mediated pharmacological mechanism on brain aging. MethodsAs we demonstrated that glutathione peroxidase (GPx) is important for enhancing memory function in the animal model of aging, we investigated the role of MCG as a GPx inducer using GPx-1 (a major type of GPx) knockout (KO) mice. We assessed whether MCG modulates redox and cholinergic parameters, and memory function in aged GPx-1 knockout KOmice. ResultsRedox burden of aged GPx-1 KO mice was more evident than that of aged wild-type (WT) mice. Alteration of Nrf2 DNA binding activity appeared to be more evident than that of NFκB DNA binding activity in aged GPx-1 KO mice. Alteration in choline acetyltransferase (ChAT) activity was more evident than that in acetylcholine esterase activity. MCG significantly attenuated reductions in Nrf2 system and ChAT level. MCG significantly enhanced the co-localization of Nrf2-immunoreactivity and ChAT-immunoreactivity in the same cell population. Nrf2 inhibitor brusatol significantly counteracted MCG-mediated up-regulation in ChAT level and ChAT inhibition (by k252a) significantly reduced ERK phosphorylation by MCG, suggesting that MCG might require signal cascade of Nrf2/ChAT/ERK to enhance cognition. ConclusionGPx-1 depletion might be a prerequisite for cognitive impairment in aged animals. MCG-mediated cognition enhancement might be associated with the activations of Nrf2, ChAT, and ERK signaling cascade.

Comparative transcriptome analysis reveals the non-neuronal cholinergic system in the ovary of the oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae).

Acetylcholine (ACh), as a classical neurotransmitter, plays great roles in the nervous system. There is increasing evidence of its non-neuronal roles in regulating basic cell functions in vertebrates. However, knowledge about the non-neuronal cholinergic system in insects is scarce. A comparative transcriptome analysis was performed to investigate differences in the key molecular components of the cholinergic system between the head and ovary. The results showed that expression levels of most cholinergic system-related genes were higher in the head than in the ovary, and some cholinergic components were absent in the ovary. ACh contents ranged from 0.1 to 1.3μg mg-1 of wet weight during the development of the ovary, and weak acetylcholinesterase activity was also detected. Moreover, the ovary has a capacity for ACh synthesis. Bromoacetylcarnitine (BrACar), a specific carnitine acetyltransferase (CarAT) inhibitor, greatly inhibits ACh synthesis by 83.83% in ovary homogenates, but bromoacetylcholine (BrACh), a specific choline acetyltransferase (ChAT) inhibitor, has no effect on ACh synthesis in the ovary. These findings indicate that non-neuronal ACh in the ovary is only catalyzed by CarAT. This study reveals the existence of the non-neuronal cholinergic system in the ovary of M. separata, whose synthesis and release mechanisms are different from those of the head. These results provide novel insights into the non-neuronal cholinergic system in insects, and will be valuable in the discovery of new target genes and the future development of green pest control. © 2022 Society of Chemical Industry.

The choline acetyltransferase inhibitor BW813U inhibits angiogenesis and tumor growth in human lung adenocarcinoma

Angiogenesis refers to the development of new blood vessels from preexisting blood vessels. The angiogenic pathway is essential for the growth and progression of almost every kind of human cancer. Nicotine, the addictive component of tobacco smoke is known to accelerate the growth of human lung tumors by stimulating tumor angiogenesis. The pro‐angiogenic effects of nicotine are mediated by nicotinic acetylcholine receptors (nAChRs). The endogenous ligand for nicotine is the neurotransmitter acetylcholine (ACh). Published reports show that ACh acts as growth factor for human lung cancers. Almost all lung tissues (including fetal lung) express signaling proteins involved in the synthesis, transport of the ACh‐signaling pathway. These include choline acetyl transferase enzyme (ChAT), vesicular acetylcholine transporter (VAChT), acetylcholine esterase (AChE) and choline transporter (ChT). The primary objective of our studies was to determine if disruption of ChAT could inhibit angiogenesis and suppress the growth of human LACs. We used a small molecule inhibitor of ChAT namely BW813U for our studies. BW813U robustly suppressed angiogenesis in Matrigel assays and chicken chorioallantoic membrane (CAM) assays. The administration of BW813U potenetly decreased the growth rate of H838 tumors xenotransplanted in SCID mice. Immunohistochemical staining experiments revealed that the anti‐tumor activity of BW813U was correlated with decrease of CD31 angiogenic biomarker in H813 tumor sections. The anti‐angiogenic activity of BW813U was mediated by the alpha7‐nAChR pathway and involved the nitric oxide pathway. Taken together, our studies show that ChAT antagonists like BW813U may have applications in the treatment of LAC.

Prediction of the dose range for adverse neurological effects of amiodarone in patients from an in vitro toxicity test by in vitro\u2013in vivo extrapolation

Amiodarone is an antiarrhythmic agent inducing adverse effects on the nervous system, among others. We applied physiologically based pharmacokinetic (PBPK) modeling combined with benchmark dose modeling to predict, based on published in vitro data, the in vivo dose of amiodarone which may lead to adverse neurological effects in patients. We performed in vitro–in vivo extrapolation (IVIVE) from concentrations measured in the cell lysate of a rat brain 3D cell model using a validated human PBPK model. Among the observed in vitro effects, inhibition of choline acetyl transferase (ChAT) was selected as a marker for neurotoxicity. By reverse dosimetry, we transformed the in vitro concentration–effect relationship into in vivo effective human doses, using the calculated in vitro area under the curve (AUC) of amiodarone as the pharmacokinetic metric. The upper benchmark dose (BMDU) was calculated and compared with clinical doses eliciting neurological adverse effects in patients. The AUCs in the in vitro brain cell culture after 14-day repeated dosing of nominal concentration equal to 1.25 and 2.5 µM amiodarone were 1.00 and 1.99 µg*h/mL, respectively. The BMDU was 385.4 mg for intravenous converted to 593 mg for oral application using the bioavailability factor of 0.65 as reported in the literature. The predicted dose compares well with neurotoxic doses in patients supporting the hypothesis that impaired ChAT activity may be related to the molecular/cellular mechanisms of amiodarone neurotoxicity. Our study shows that predicting effects from in vitro data together with IVIVE can be used at the initial stage for the evaluation of potential adverse drug reactions and safety assessment in humans.

In Situ Assembly of Choline Acetyltransferase Ligands by a Hydrothiolation Reaction Reveals Key Determinants for Inhibitor Design.

The potential drug target choline acetyltransferase (ChAT) catalyses the production of the neurotransmitter acetylcholine in cholinergic neurons, T-cells, and B-cells. Herein, we show that arylvinylpyridiniums (AVPs), the most widely studied class of ChAT inhibitors, act as substrate in an unusual coenzyme A-dependent hydrothiolation reaction. This in situ synthesis yields an adduct that is the actual enzyme inhibitor. The adduct is deeply buried in the active site tunnel of ChAT and interactions with a hydrophobic pocket near the choline binding site have major implications for the molecular recognition of inhibitors. Our findings clarify the inhibition mechanism of AVPs, establish a drug modality that exploits a target-catalysed reaction between exogenous and endogenous precursors, and provide new directions for the development of ChAT inhibitors with improved potency and bioactivity.

In Situ Assembly of Choline Acetyltransferase Ligands by a Hydrothiolation Reaction Reveals Key Determinants for Inhibitor Design

AbstractThe potential drug target choline acetyltransferase (ChAT) catalyses the production of the neurotransmitter acetylcholine in cholinergic neurons, T‐cells, and B‐cells. Herein, we show that arylvinylpyridiniums (AVPs), the most widely studied class of ChAT inhibitors, act as substrate in an unusual coenzyme A‐dependent hydrothiolation reaction. This in situ synthesis yields an adduct that is the actual enzyme inhibitor. The adduct is deeply buried in the active site tunnel of ChAT and interactions with a hydrophobic pocket near the choline binding site have major implications for the molecular recognition of inhibitors. Our findings clarify the inhibition mechanism of AVPs, establish a drug modality that exploits a target‐catalysed reaction between exogenous and endogenous precursors, and provide new directions for the development of ChAT inhibitors with improved potency and bioactivity.

A novel crosslinking protocol stabilizes amyloid β oligomers capable of inducing Alzheimer's-associated pathologies.

Amyloid β oligomers (AβOs) accumulate early in Alzheimer's disease (AD) and experimentally cause memory dysfunction and the major pathologies associated with AD, for example, tau abnormalities, synapse loss, oxidative damage, and cognitive dysfunction. In order to develop the most effective AβO-targeting diagnostics and therapeutics, the AβO structures contributing to AD-associated toxicity must be elucidated. Here, we investigate the structural properties and pathogenic relevance of AβOs stabilized by the bifunctional crosslinker 1,5-difluoro-2,4-dinitrobenzene (DFDNB). We find that DFDNB stabilizes synthetic Aβ in a soluble oligomeric conformation. With DFDNB, solutions of Aβ that would otherwise convert to large aggregates instead yield solutions of stable AβOs, predominantly in the 50-300 kDa range, that are maintained for at least 12 days at 37°C. Structures were determined by biochemical and native top-down mass spectrometry analyses. Assayed in neuronal cultures and i.c.v.-injected mice, the DFDNB-stabilized AβOs were found to induce tau hyperphosphorylation, inhibit choline acetyltransferase, and provoke neuroinflammation. Most interestingly, DFDNB crosslinking was found to stabilize an AβO conformation particularly potent in inducing memory dysfunction in mice. Taken together, these data support the utility of DFDNB crosslinking as a tool for stabilizing pathogenic AβOs in structure-function studies.

Murine remote preconditioning increases glucose uptake and suppresses gluconeogenesis in hepatocytes via a brain-liver neurocircuit, leading to counteracting glucose intolerance

AimsOur previous study revealed that cyclic hindlimb ischaemia–reperfusion (IR) activates cardiac acetylcholine (ACh) synthesis through the cholinergic nervous system and cell-derived ACh accelerates glucose uptake. However, the mechanisms regulating glucose metabolism in vivo remain unknown. We investigated the effects and mechanisms of IR in mice under pathophysiological conditions. MethodsUsing IR-subjected male C57BL/6J mice, the effects of IR on blood sugar (BS), glucose uptake, central parasympathetic nervous system (PNS) activity, hepatic gluconeogenic enzyme expression and those of ACh on hepatocellular glucose uptake were assessed. ResultsIR decreased BS levels by 20% and increased c-fos immunoreactivity in the center of the PNS (the solitary tract and the dorsal motor vagal nucleus). IR specifically downregulated hepatic gluconeogenic enzyme expression and activities (glucose-6-phosphatase and phosphoenolpyruvate carboxykinase) and accelerated hepatic glucose uptake. Transection of a hepatic vagus nerve branch decreased this uptake and reversed BS decrease. Suppressed gluconeogenic enzyme expression was reversed by intra-cerebroventricular administration of a choline acetyltransferase inhibitor. Moreover, IR significantly attenuated hyperglycaemia in murine model of type I and II diabetes mellitus. ConclusionsIR provides another insight into a therapeutic modality for diabetes mellitus due to regulating gluconeogenesis and glucose-uptake and advocates an adjunctive mode rectifying disturbed glucose metabolism.

Discovery of novel choline acetyltransferase inhibitors using structure-based virtual screening

Alzheimer disease and related dementias are major challenges, demanding urgent needs for earliest possible diagnosis to optimize the success rate in finding effective therapeutic interventions. Mounting solid scientific premises point at the core acetylcholine-biosynthesizing cholinergic enzyme, ChAT as a legitimate in vivo target for developing positron emission tomography biomarker for early diagnosis and/or monitoring therapeutic responses in the neurodegenerative dementias. Up-to-date, no PET tracer ligands for ChAT are available. Here we report for the first time a novel hierarchical virtual screening approach on a commercial library of ~300,000 compounds, followed by in vitro screening of the hits by a new High-Throughput ChAT assay. We report detailed pharmacodynamic data for three identified selective novel ChAT ligands with IC50 and Ki values ranging from ~7 to 26 µM. In addition, several novel selective inhibitors of the acetylcholine-degrading enzymes, AChE and BuChE were identified, with one of the compounds showing an IC50-value of ~6 µM for AChE. In conclusion, this report provides an excellent starting platform for designing and optimizing potent and selective ChAT ligands, with high potential as PET-imaging probe for early diagnosis of AD, and related dementias, such as Down’s syndrome and Lewy body disorders.

Cholinergic System and Oxidative Stress Changes in the Brain of a Zebrafish Model Chronically Exposed to Ethanol.

Ethanol is a widely used drug, and excess or even moderate consumption of ethanol is associated with changes in several neurotransmitter systems, including the cholinergic system. The incidence of alcoholic dementia and its insults are well supported by multiple studies, although the mechanisms of neurotoxicity are still poorly understood. Considering that zebrafish have a complete central nervous system (CNS) and that several signaling systems have already been identified in zebrafish, this neurotoxicological model has become useful. In the present study, we investigated the long-term effects of ethanol consumption on the cholinergic system, on oxidative stress, and on inflammatory parameters in the zebrafish brain. Animals were exposed to 0.5% (v/v) ethanol for 7, 14, and 28days. Ethanol inhibited choline acetyltransferase activity after 7 and 14days but not after 28days. Acetylcholinesterase activity did not change after any of the exposure periods. When compared to the control group, thiobarbituric acid reactive species and dichlorodihydrofluorescein levels were increased after chronic ethanol exposure. Antioxidant activity promoted by the CAT/SOD ratio was altered after chronic ethanol exposure, suggesting that EtOH can induce oxidative damage in the zebrafish brain. In contrast, nitrate and nitrite levels and sulfhydryl content were not altered. Ethanol did not modify gene expression of the inflammatory cytokines il-1b, il-10, or tnf-α in the zebrafish brain. Therefore, the cholinergic system and the oxidative balance were targeted by chronic ethanol toxicity. This neurochemical regulatory mechanism may play an important role in understanding the effects of long-term ethanol consumption and tolerance in zebrafish model studies.

The choline acetyltransferase inhibitor BW813U suppresses the growth of lung adenocarcinoma from smokers

The clinicopathological profile of lung adenocarcinoma (LAC) in smokers is completely different from those in non‐smokers. One of the unique features of LAC in smokers is that it is relatively resistant to therapies. For example, targeted therapeutic agents like EGFR‐inhibitors (erlotinib and gefitinib) are highly effective in LACs which develop in non‐smokers. However, these EGFR‐inhibitors display much lower anti‐tumor activity in LACs in patients who are active smokers. Similarly, lung cancer patients (who are active smokers) show lower response to chemotherapy than those who are non‐smokers. However, majority of LAC patients are smokers. This underlines the need to identify novel molecular targets relevant for LAC therapy in patients who are exposed to cigarette smoke via active smoking or exposure to secondhand smoke. Several convergent studies show that nicotine (the addictive component of cigarette smoke) accelerates the growth of lung cancers, as well as confers resistance to chemotherapy. One of the mechanisms underlying these biological activity of nicotine is that it promotes the secretion of the neurotransmitter acetylcholine (ACh) from LAC cells. ACh is known to be an autocrine growth factor for LAC cells and is synthesized by the enzyme choline acetyltransferase (ChAT). The present study investigates the feasibility of ChAT as a molecular target for LAC in smokers. We find that ChAT levels are upregulated in human LAC cell lines and tissues in a manner dependent on the smoking history. Finally, the ChAT inhibitor BW813U causes robust apoptosis in human LAC cells. The magnitude of BW813U‐induced apoptosis is similar across LAC cell lines (irrespective of smoking history); however, the concentration of BW813U which causes apoptosis is lower in LAC cell lines belonging to heavy smokers. Our studies validate choline acetyltransferase (CHAT) as a viable drug target for the majority of population of lung cancer patients who are smokers.Support or Funding InformationFunding for our study was supported by the an NIH R15‐AREA Grant (2R15CA161491‐02), WVU‐MU Health Partnership Grant and by ACTSI Grant from Marshall University. Furthermore, this study was supported in part by an Institutional Development Award (IDeA) Grant number P20GM104932 from the National Institute of General Medical Sciences (NIGMS) and the Research Core B of COBRE, a component of the National Institutes of Health (NIH).

P2 The action of endothelial–derived acetylcholine is impaired in diabetes

The endothelium is highly sensitive to acetylcholine and responds to the neurotransmitter by releasing vasodilators that control smooth muscle tone. However, acetylcholine is not expected to reach the endothelium through the vessel wall or via blood. Here, by studying calcium signalling in large areas of the endothelium of intact arteries, we show: (1) the endothelium itself is a source of acetylcholine, (2) acetylcholine release from the endothelium underlies flow-mediated vascular responses; and (3) flow-mediated responses are all but abolished in a rat model of diabetes. Calcium signalling was studied in large fields of intact endothelia (~150 cells) of carotid and mesenteric arteries from healthy and diabetic rats (Sprague-Dawley, 150–250 g). In both carotid and mesenteric arteries, flow evoked repeatable endothelial calcium signalling. Importantly, flow-mediated calcium responses could be manipulated by modulating cholinergic signalling pathways: the muscarinic receptor blocker, atropine (100 nM), and the acetylcholine hydrolase, acetylcholinesterase (4 U/ml), each abolished flow-induced calcium activity, whilst the acetylcholinesterase inhibitor, neostigmine (10 µM), enhanced calcium activity, and the choline acetyltransferase inhibitor, bromoacetylcholine (50?µM), attenuated responses. Significantly, responses were reduced in diabetic, compared to control, endothelia. Indeed, the number of diabetic endothelial cells responding to flow was 45% of control, and the peak and time-averaged magnitude of calcium signals was reduced to 54% and 12% of control, respectively. These results identify the endothelium as a source of non-neuronal acetylcholine release and thus demonstrate the reason for the endothelium’s sensitivity to acetylcholine. Significantly, reduced acetylcholine release may underlie the pathophysiology and endothelial dysfunction that occurs in diabetes.

Acetylcholine Released by the Endothelium Mediates Flow‐induced Endothelial Ca2+ Signalling and Vascular Relaxation

The flow of blood generates mechanical forces (e.g. shear‐stress) that are important physiological regulators of vascular tone. The vascular endothelium senses these forces and, in response, releases various vasodilators (e.g. nitric oxide) that relax smooth muscle cells in a process termed flow‐mediated vasodilation. Whilst some elements of the signalling mechanisms have been identified, precisely how flow is sensed and then transduced to cause the release of relaxing factors is poorly understood. In intact, pressurized arteries we show that flow induces relaxation of phenylephrine‐induced contractions. In large areas of the endothelium of surgically opened arteries, encompassing ~150 cells, flow (shear‐stress: 3 dyne cm−2) induced endothelial Ca2+ signalling and the release of nitric oxide. The Ca2+ signals were complex and transmitted between cells as intercellular “waves”, resulting in spatiotemporally heterogeneous activity across the endothelium. The Ca2+ signals were evoked both by IP3‐mediated Ca2+ release and Ca2+ influx from the extracellular space. Both components of the Ca2+ signals (release and influx) arose from the activation of the endothelium by acetylcholine (ACh) released in response to shear‐stress. In support, flow‐induced Ca2+ signals were abolished by atropine and by acetylcholinesterase. The flow‐induced Ca2+ signals were also attenuated by the choline acetyltransferase inhibitor, bromoacetylcholine, and potentiated by the acetylcholinesterase inhibitor, neostigmine. Flow‐induced responses were also blocked by depolarization and by inhibitors of chloride channels, but were unaffected by inhibitors of ATP‐mediated signalling pathways, organic cation transporters, or Panx hemichannels. Together, these results suggest that physiological shear‐stress induced activation of endothelial chloride channels mediates the release of ACh and hence flow‐mediated vasodilation. Significantly, these results also suggest that ACh is an autocrine signalling molecule released from endothelial cells.Support or Funding InformationSupported by the Wellcome Trust and the British Heart Foundation

New Trends and Perspectives in the Function of Non-neuronal Acetylcholine in Crypt-Villus Organoids in Mice.

Acetylcholine (ACh) is a neurotransmitter that is present in central, parasympathetic, and neuromuscular synapses of mammals. However, non-neuronal ACh is also predicted to function as a local cell signaling molecule. The physiological significance of the presence of non-neuronal ACh in the intestine remains unclear. Here, experiments using cultured crypt-villus organoids that lack nerve and immune cells led us to suggest that endogenous ACh is synthesized in the intestinal epithelium to evoke growth and differentiation of the organoids through activation of muscarinic ACh receptors (mAChRs). Extracts of cultured organoids exhibited a noticeable capacity for ACh synthesis that was sensitive to a potent inhibitor of choline acetyltransferase. Treatment of organoids with carbachol downregulated growth of organoids and expression of marker genes for each epithelial cell type. On the other hand, mAChR antagonists enhanced growth and differentiation of Lgr5-positive stem cells. Collectively, our data provide evidence that endogenous ACh released from mouse intestinal epithelium maintains the homeostasis of intestinal epithelial cell growth and differentiation via mAChRs.

Modeling the Interaction betweenβ-Amyloid Aggregates and Choline Acetyltransferase Activity and Its Relation with Cholinergic Dysfunction through Two-Enzyme/Two-Compartment Model

The effect of β-amyloid aggregates on activity of choline acetyltransferase (ChAT) which is responsible for synthesizing acetylcholine (ACh) in human brain is investigated through the two-enzyme/two-compartment (2E2C) model where the presynaptic neuron is considered as compartment 1 while both the synaptic cleft and the postsynaptic neuron are considered as compartment 2 through suggesting three different kinetic mechanisms for the inhibition effect. It is found that the incorporation of ChAT inhibition by β-amyloid aggregates into the 2E2C model is able to yield dynamic solutions for concentrations of generated β-amyloid, ACh, choline, acetate, and pH in addition to the rates of ACh synthesis and ACh hydrolysis in compartments 1 and 2. It is observed that ChAT activity needs a high concentration of β-amyloid aggregates production rate. It is found that ChAT activity is reduced significantly when neurons are exposed to high levels of β-amyloid aggregates leading to reduction in levels of ACh which is one of the most significant physiological symptoms of AD. Furthermore, the system of ACh neurocycle is dominated by the oscillatory behavior when ChAT enzyme is completely inhibited by β-amyloid. It is observed that the direct inactivation of ChAT by β-amyloid aggregates may be a probable mechanism contributing to the development of AD.

No evidence for role of extracellular choline-acetyltransferase in generation of gamma oscillations in rat hippocampal slices in vitro

Acetylcholine (ACh) is well known to induce persistent γ-oscillations in the hippocampus when applied together with physostigmine, an inhibitor of the ACh degrading enzyme acetylcholinesterase (AChE). Here we report that physostigmine alone can also dose-dependently induce γ-oscillations in rat hippocampal slices. We hypothesized that this effect was due to the presence of choline in the extracellular space and that this choline is taken up into cholinergic fibers where it is converted to ACh by the enzyme choline-acetyltransferase (ChAT). Release of ACh from cholinergic fibers in turn may then induce γ-oscillations. We therefore tested the effects of the choline uptake inhibitor hemicholinium-3 (HC-3) on persistent γ-oscillations either induced by physostigmine alone or by co-application of ACh and physostigmine. We found that HC-3 itself did not induce γ-oscillations and also did not prevent physostigmine-induced γ-oscillation while washout of physostigmine and ACh-induced γ-oscillations was accelerated. It was recently reported that ChAT might also be present in the extracellular space (Vijayaraghavan et al., 2013). Here we show that the effect of physostigmine was prevented by the ChAT inhibitor (2-benzoylethyl)-trimethylammonium iodide (BETA) which could indicate extracellular synthesis of ACh. However, when we tested for effects of extracellularly applied acetyl-CoA, a substrate of ChAT for synthesis of ACh, physostigmine-induced γ-oscillations were attenuated. Together, these findings do not support the idea that ACh can be synthesized by an extracellularly located ChAT.

Non-neuronal acetylcholine as an endogenous regulator of proliferation and differentiation of Lgr5-positive stem cells in mice.

Non-neuronal acetylcholine (ACh) is predicted to function as a local cell signaling molecule. However, the physiological significance of the synthesis of non-neuronal ACh in the intestine remains unclear. Here, experiments using crypt-villus organoids that lack nerve and immune cells in culture led us to suggest that endogenous ACh is synthesized in the intestinal epithelium to evoke growth and differentiation of the organoids through activation of muscarinic ACh receptors (mAChRs). The extracts of the cultured organoids showed a noticeable capacity for ACh synthesis that was sensitive to a potent inhibitor of choline acetyltransferase. Imaging MS revealed endogenous ACh localized in the epithelial layer in mouse small intestinal epithelium in vivo, suggesting that there are non-neuronal resources of ACh. Treatment of organoids with carbachol downregulated the growth of organoids and the expression of marker genes for epithelial cells. On the other hand, antagonists for mAChRs enhanced the growth and differentiation of organoids, indicating the involvement of mAChRs in regulating the proliferation and differentiation of Lgr5-positive stem cells. Collectively, our data provide evidence that endogenous ACh released from intestinal epithelium maintains homeostasis of intestinal epithelial cell growth and differentiation via mAChRs in mice.

A commentary on: Overexpression of Dyrk1A inhibits choline acetyltransferase induction by oleic acid in cellular models of Down syndrome

A commentary on: Overexpression of Dyrk1A inhibits choline acetyltransferase induction by oleic acid in cellular models of Down syndrome