The Allosteric Potentiation of Nicotinic Acetylcholine Receptors by Galantamine Is Transduced into Cellular Responses in Neurons: Ca2+ Signals and Neurotransmitter Release

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope. Neuroplasticity, in broad terms the ability of the brain to modify its structure in response to external stimulation or damage, has received growing attention as a possible therapeutic target, since the disruption of plastic mechanisms in the brain appear to correlate with various forms of cognitive impairment present in AD patients. Several pre-clinical and clinical studies have attempted to enhance neuroplasticity via different mechanisms, for example, regulating glucose or lipid metabolism, targeting the activity of neurotransmitter systems, or addressing neuroinflammation. In this review, we first describe several structural and functional aspects of neuroplasticity. We then focus on the current status of pharmacological approaches to AD stemming from clinical trials targeting neuroplastic mechanisms in AD patients. This is followed by an analysis of analogous pharmacological interventions in animal models, according to their mechanisms of action.

Physiologic Functions and Therapeutic Applications of α7 Nicotinic Acetylcholine Receptor in Brain Disorders

Accumulating data suggest that α7 nicotinic acetylcholine receptors (α7nAChRs) are an important therapeutic target for the treatment of Alzheimer's disease (AD) and schizophrenia. The homopentameric ligand-gated ion channel α7nAChR consists of five identical α7 subunits that are encoded by the CHRNA7 (cholinergic receptor nicotinic alpha7 subunit) gene. Moreover, α7nAChRs are densely distributed throughout the hippocampus, cortex, and thalamus brain regions, but sparsely in the striatum, forebrain, and medulla. Compared with other nAChRs, α7nAChR binds with low affinity to the naturally occurring neurotransmitter acetylcholine and the non-specific exogenous agonist nicotine, and with high affinity to the specific antagonists α-bungarotoxin and methyllycaconitine. Reports indicate that α7nAChR plays important roles in neurotransmitter release, cognitive functioning, and the cholinergic anti-inflammatory response. Genetic variations that alter CHRNA7 mRNA and protein expression or cause α7nAChR dysfunction are associated with many brain disorders. Our previous studies revealed that α7nAChR exerts neuroprotection in AD by acting as a cargo receptor for binding the autophagosomal marker protein LC3 and engulfing extracellular neurotoxic Aβ_1-42 during autophagic degradation of the α7nAChR-Aβ_1-42 complex. However, the role of α7nAChRs in other diseases remains unknown. Here, we review and summarize the essential characteristics and current findings concerning α7nAChRs in four common brain diseases (AD, Parkinson's disease, schizophrenia, and depression), which may elucidate the role of α7nAChRs and inform innovative research and novel treatments that target α7nAChRs in brain disease.

Natural Products from Plants and Algae for Treatment of Alzheimer’s Disease: A Review

Neurodegenerative disorders including Parkinson’s disease (PD), Huntington’s disease (HD) and the most frequent, Alzheimer’s disease (AD), represent one of the most urgent medical needs worldwide. Despite a significantly developed understanding of disease development and pathology, treatments that stop AD progression are not yet available. The recent approval of sodium oligomannate (GV-971) for AD treatment in China emphasized the potential value of natural products for the treatment of neurodegenerative disorders. Many current clinical studies include the administration of a natural compound as a single and combination treatment. The most prominent mechanisms of action are anti-inflammatory and anti-oxidative activities, thus preserving cellular survival. Here, we review current natural products that are either approved or are in testing for a treatment of neurodegeneration in AD. In addition to the most important compounds of plant origin, we also put special emphasis on compounds from algae, given their neuroprotective activity and their underlying mechanisms of neuroprotection.

New Galantamine Derivatives with Inhibitory Effect on Acetylcholinesterase Activity

BACKGROUND

Inhibitors of acetylcholinesterase (AChE) are used to treat many disorders, among which are neurodegenerative upsets, like Alzheimer's disease (AD). One of the limited licensed AChE inhibitors (AChEIs) used as drugs is the natural compound galantamine (Gal).

OBJECTIVE

As Gal is a toxic compound, here we expose data about its four derivatives in hybrid peptide-norgalantamine molecules, which have shown 100 times lower toxicity.

METHODS

Four newly synthesized galantamine derivatives have been involved in docking analysis made by Molegro Virtual Docker. Biological assessments were performed on ICR male mice. The change in short and long-term memory performance was evaluated by passive avoidance test. AChE activity and levels of main oxidative stress parameters: lipid peroxidation, total glutathione (GSH), enzyme activities of catalase (CAT), superoxide dismutase, and glutathione peroxidase were measured in brain homogenates.

RESULTS

Our experimental data revealed that the new hybrid molecules did not impair memory performance in healthy mice. Two of the compounds demonstrated better than Gal AChE inhibitory activity in the brain. None of them changed the level of lipid peroxidation products, one of the compounds increased GSH levels, and all of them increased CAT enzyme activity.

CONCLUSION

The new galantamine-peptide hybrids demonstrated a potential for inhibition of AChE and antioxidant activity and deserve further attention.

Discovery of a Novel Acetylcholinesterase Inhibitor by Fragment-Based Design and Virtual Screening

Despite extensive and intensive research efforts in recent decades, there is still no effective treatment for neurodegenerative diseases. On this background, the use of drugs inhibiting the enzyme acetylcholinesterase (AChE) remains an eternal evergreen in the symptomatic treatment of mild to moderate cognitive impairments. Even more, the cholinergic hypothesis, somewhat forgotten in recent years due to the shift in focus on amyloid cascade, is back to life, and the search for new, more effective AChE inhibitors continues. We generated a fragment-based library containing aromatic moieties and linkers originating from a set of novel AChE inhibitors. We used this library to design 1220 galantamine (GAL) derivatives following the model GAL (binding core) - linker (L) - aromatic fragment (Ar). The newly designed compounds were screened virtually for blood–brain barrier (BBB) permeability and binding to AChE. Among the top 10 best-scored compounds, a representative lead molecule was selected and tested for anti-AChE activity and neurotoxicity. It was found that the selected compound was a powerful non-toxic AChE inhibitor, 68 times more active than GAL, and could serve as a lead molecule for further optimization and development.

A Novel Galantamine-Curcumin Hybrid as a Potential Multi-Target Agent against Neurodegenerative Disorders

The acetylcholinesterase (AChE) inhibitors are the main drugs for symptomatic treatment of neurodegenerative disorders like Alzheimer’s disease. A recently designed, synthesized and tested hybrid compound between the AChE inhibitor galantamine (GAL) and the antioxidant polyphenol curcumin (CU) showed high AChE inhibition in vitro. Here, we describe tests for acute and short-term toxicity in mice as well as antioxidant tests on brain homogenates measured the levels of malondialdehide (MDA) and glutathione (GSH) and in vitro DPPH, ABTS, FRAP and LPO inhibition assays. Hematological and serum biochemical analyses were also performed. In the acute toxicity tests, the novel AChE inhibitor given orally in mice showed LD₅₀ of 49 mg/kg. The short-term administration of 2.5 and 5 mg/kg did not show toxicity. In the ex vivo tests, the GAL-CU hybrid performed better than GAL and CU themselves; in a dose of 5 mg/kg, it demonstrates 25% reduction in AChE activity, as well as a 28% and 73% increase in the levels of MDA and GSH, respectively. No significant changes in blood biochemical data were observed. The antioxidant activity of 4b measured ex vivo was proven in the in vitro tests. In the ABTS assay, 4b showed radical scavenging activity 10 times higher than the positive control butylhydroxy toluol (BHT). The GAL-CU hybrid is a novel non-toxic AChE inhibitor with high antioxidant activity which makes it a prospective multitarget drug candidate for treatment of neurodegenerative disorders.

Loss of Basal Forebrain Cholinergic Neurons Following Adolescent Binge Ethanol Exposure: Recovery With the Cholinesterase Inhibitor Galantamine

Binge drinking and alcohol abuse are common during adolescence and cause both cognitive deficits and lasting cholinergic pathology in the adult basal forebrain. Acetylcholine is anti-inflammatory and studies using the preclinical adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2 day on/2 day off from postnatal day [P]25 to P54) model of human adolescent binge drinking report decreased basal forebrain cholinergic neurons (BFCNs) and induction of proinflammatory genes that persist long into adulthood. Recent studies link AIE-induced neuroimmune activation to cholinergic pathology, but the underlying mechanisms contributing to the persistent loss of BFCNs are unknown. We report that treatment with the cholinesterase inhibitor galantamine (4.0 mg/kg, i.p.) administered during AIE (i.e., P25-P54) or following the conclusion of AIE (i.e., P57-P72) recovered the persistent loss of cholinergic neuron phenotype markers (i.e., ChAT, TrkA, and p75NTR) and somal shrinkage of residual ChAT + neurons known to persist in AIE-exposed adults. Galantamine treatment also recovered the AIE-increased expression of the proinflammatory receptors TLR4 and RAGE, the endogenous TLR4/RAGE agonist HMGB1, and the transcription activation marker pNF-κB p65. Interestingly, we find BFCNs express TLR4 and RAGE, and that AIE treatment increased pNF-κB p65 expression in adult ChAT + IR neurons, consistent with intracellular HMGB1-TLR4/RAGE signaling within BFCNs. AIE increased epigenetic transcription silencing markers (i.e., H3K9me2 and H3K9me3) in the adult basal forebrain and H3K9me2 occupancy at cholinergic phenotype gene promoters (i.e., ChAT and TrkA). The finding of no AIE-induced changes in total basal forebrain NeuN + neurons with galantamine reversal of AIE-induced ChAT + neuron loss, TLR4/RAGE-pNF-κB p65 signals, and epigenetic transcription silencing markers suggests that AIE does not cause cell death, but rather the loss of the cholinergic phenotype. Together, these data suggest that AIE induces HMGB1-TLR4/RAGE-pNF-κB p65 signals, causing the loss of cholinergic phenotype (i.e., ChAT, TrkA, and p75NTR) through epigenetic histone transcription silencing that result in the loss of the BFCN phenotype that can be prevented and restored by galantamine.

Evidence for positive allosteric modulation of cognitive-enhancing effects of nicotine by low-dose galantamine in rats

Cognitive-enhancing effects of nicotinic acetylcholine receptor (nAChR) agonists may be of therapeutic potential in disease states characterized by nAChR hypofunction; however, effects tend to be of small magnitude and unlikely clinical significance. The co-administration of a nAChR positive allosteric modulator (PAM) may enable larger effects by potentiating nAChR responses to an agonist. The acetylcholinesterase (AChE) inhibitor galantamine is a nAChR PAM at a low dose range. A recent clinical study testing effects of a single small dose of galantamine found evidence for synergistic effects with nicotine on one of several cognitive measures. In that study, residual AChE inhibition may have obscured interactions on other measures. The present study aimed at examining small galantamine doses devoid of AChE inhibitory activity in a rodent model of attention. The effects of galantamine (0.03-0.25 mg/kg s.c.) were tested in the presence and absence of nicotine (0.1 mg/kg s.c.) in rats performing the 5-Choice Serial Reaction Time Task, employing a within-subject factorial design. There were no effects on response accuracy of either nicotine or galantamine alone. However, the combination of nicotine and 0.06 mg/kg of galantamine significantly enhanced accuracy. AChE activity assays confirmed that, at this dose, galantamine was devoid of AChE inhibitory activity in the brain. The results suggest that cognitive-enhancing effects of nicotine may be potentiated or uncovered by an extremely small dose of galantamine, well below its typical therapeutic range in humans. Furthermore, these findings provide a general proof-of-principle for a nAChR agonist and PAM combination strategy for cognitive enhancement.

Multi-Target Drug Candidates for Multifactorial Alzheimer's Disease: AChE and NMDAR as Molecular Targets

Alzheimer's disease (AD) is one of the most common forms of dementia among elder people, which is a progressive neurodegenerative disease that results from a chronic loss of cognitive activities. It has been observed that AD is multifactorial, hence diverse pharmacological targets that could be followed for the treatment of AD. The Food and Drug Administration has approved two types of medications for AD treatment such as cholinesterase inhibitors (ChEIs) and N-methyl-D-aspartic acid receptor (NMDAR) antagonists. Rivastigmine, donepezil, and galantamine are the ChEIs that have been approved to treat AD. On the other hand, memantine is the only non-competitive NMDAR antagonist approved in AD treatment. As compared with placebo, it has been revealed through clinical studies that many single-target therapies are unsuccessful to treat multifactorial Alzheimer's symptoms or disease progression. Therefore, due to the complex nature of AD pathophysiology, diverse pharmacological targets can be hunted. In this article, based on the entwined link of acetylcholinesterase (AChE) and NMDAR, we represent several multifunctional compounds in the rational design of new potential AD medications. This review focus on the significance of privileged scaffolds in the generation of the multi-target lead compound for treating AD, investigating the idea and challenges of multi-target drug design. Furthermore, the most auspicious elementary units for designing as well as synthesizing hybrid drugs are demonstrated as pharmacological probes in the rational design of new potential AD therapeutics.

Brain-Derived Acetylcholine Maintains Peak Bone Mass in Adult Female Mice

Preclinical and clinical data support a role of the sympathetic nervous system in the regulation of bone remodeling, but the contribution of parasympathetic arm of the autonomic nervous system to bone homeostasis remains less studied. In this study, we sought to determine whether acetylcholine (ACh) contributes to the regulation of bone remodeling after peak bone mass acquisition. We show that reduced central ACh synthesis in mice heterozygous for the choline transporter (ChT) leads to a decrease in bone mass in young female mice, thus independently confirming the previously reported beneficial effect of ACh signaling on bone mass accrual. Increasing brain ACh levels through the use of the blood brain barrier (BBB)-permeable acetylcholinesterase inhibitor (AChEI) galantamine increased trabecular bone mass in adult female mice, whereas a peripheral increase in ACh levels induced by the BBB-impermeable AChEI pyridostigmine caused trabecular bone loss. AChEIs did not alter skeletal norepinephrine level, and induced an overall increase in osteoblast and osteoclast densities, two findings that do not support a reduction in sympathetic outflow as the mechanism involved in the pro-anabolic effect of galantamine on the skeleton. In addition, we did not detect changes in the commitment of skeletal progenitor cells to the osteoblast lineage in vivo in AChEI-treated mice, nor a direct impact of these drugs in vitro on the survival and differentiation of osteoblast and osteoclast progenitors. Last, ChT heterozygosity and galantamine treatment triggered bone changes in female mice only, thus revealing the existence of a gender-specific skeletal response to brain ACh level. In conclusion, this study supports the stimulatory effect of central ACh on bone mass accrual, shows that it also promotes peak bone mass maintenance in adult mice, and suggests that central ACh regulates bone mass via different mechanisms in growing versus sexually mature mice. © 2020 American Society for Bone and Mineral Research.

Galantamine-Curcumin Hybrids as Dual-Site Binding Acetylcholinesterase Inhibitors

Galantamine (GAL) and curcumin (CU) are alkaloids used to improve symptomatically neurodegenerative conditions like Alzheimer's disease (AD). GAL acts mainly as an inhibitor of the enzyme acetylcholinesterase (AChE). CU binds to amyloid-beta (Aβ) oligomers and inhibits the formation of Aβ plaques. Here, we combine GAL core with CU fragments and design a combinatorial library of GAL-CU hybrids as dual-site binding AChE inhibitors. The designed hybrids are screened for optimal ADME properties and BBB permeability and docked on AChE. The 14 best performing compounds are synthesized and tested in vitro for neurotoxicity and anti-AChE activity. Five of them are less toxic than GAL and CU and show activities between 41 and 186 times higher than GAL.

Evidence for positive allosteric modulation of cognitive-enhancing effects of nicotine in healthy human subjects

RATIONALE

Cognitive benefits of nicotinic acetylcholine receptor (nAChR) agonists are well established but have generally been of small magnitude and uncertain clinical significance. A way of raising the effect size may be to facilitate agonist-induced responses by co-administering a nAChR positive allosteric modulator (PAM).

OBJECTIVE

The aim was to test whether galantamine, a PAM at several nAChR subtypes, can potentiate the cognitive-enhancing effects of nicotine.

METHODS

Twenty-six adult never-smokers were treated, in a double-blind counterbalanced sequence, with nicotine (7 mg/24 h, transdermally) and galantamine (4 mg, p.o.) combined, nicotine alone, galantamine alone, and double placebo. A low dose of galantamine was chosen to minimize acetylcholinesterase inhibition, which was verified in blood assays. In each condition, participants were tested with three cognitive tasks.

RESULTS

Nicotine significantly improved reaction time (RT) and signal detection in a visuospatial attention task and the Rapid Visual Information Processing Task. Galantamine did not modulate these effects. A trend toward RT reduction by galantamine correlated with acetylcholinesterase inhibition. In a change detection task, there were no effects of nicotine or galantamine alone on accuracy or RT. However, both drugs combined acted synergistically to reduce RT. This effect was not associated with acetylcholinesterase inhibition.

CONCLUSIONS

A pattern consistent with allosteric potentiation of nicotine effects by galantamine was observed on one of six performance measures. This may reflect specific nAChR subtype involvement, or additional pharmacological actions of galantamine may have overshadowed similar interactions on other measures. The finding suggests that allosteric potentiation of nAChR agonist-induced cognitive benefits is possible in principle.

Differential blockade by huperzine A and donepezil of sympathetic nicotinic acetylcholine receptor-mediated nitrergic neurogenic dilations in porcine basilar arteries

Nicotinic acetylcholine receptor activation on the perivascular sympathetic nerves via axo-axonal interaction mechanism causes norepinephrine release, which triggers the neurogenic nitrergic relaxation in basilar arteries to meet the need of a brain. Donepezil and huperzine A, which are the cholinesterase inhibitors used for Alzheimer's disease therapy, exert controversial effects on nicotinic acetylcholine receptors. Therefore, we investigated how donepezil and huperzine A via the axo-axonal interaction regulate the neurogenic vasodilation of isolated porcine basilar arteries and define their action on different subtypes of the nicotinic acetylcholine receptor by using blood vessel myography, calcium imaging, and electrophysiological techniques. Both nicotine (100 μM) and transmural nerve stimulation (TNS, 8 Hz) induce NO-mediated dilation in the arteries. Nicotine-induced vasodilations were concentration-dependently inhibited by huperzine A and donepezil, with the former being 30 fold less potent than the latter. Both cholinesterase inhibitors weakly and equally decreased TNS-elicited nitrergic vasodilations. Neither huperzine A nor donepezil affected isoproterenol (a β adrenoceptor-agonist)- or sodium nitroprusside (a NO donor)-induced vasodilation. Further, huperzine A was less potent than donepezil in inhibiting nicotine-elicited calcium influxes in rodent superior cervical ganglionic neurons and inward currents in α7- and α3β2-nicotinic acetylcholine receptor-expressing Xenopus oocytes. In conclusion, huperzine A may exert less harmful effect over donepezil on maintaining brainstem circulation and on the nicotinic acetylcholine receptor-associated cognition deficits during treatment for Alzheimer's disease.

Ameliorative effect of galantamine on acetic acid-induced colitis in rats

Galantamine (GAL) is a drug for treating Alzheimer’s disease which has reasonable and no significant side effects. Studies have shown that GAL possesses antioxidant, anti-inflammatory, and cholinomimetic effects that might be beneficial for inflammatory bowel disease. Therefore, this study was aimed to investigate the anti-inflammatory effect of GAL on acetic acid-induced colitis in rats. GAL at 0.25, 1.25, 2.5 mg/kg/day was administrated orally (p.o.) to different groups of male Wistar rats 2 h before induction of ulcer with acetic acid 3% and continued for 5 consecutive days. Dicyclomine (DIC) was similarly used alone (5 mg/kg/day, p.o.) or together with GAL at doses already mentioned to delineate the impact of muscarinic pathway in probable beneficial effects of GAL on colitis. Control and reference groups received distilled water (5 mL/kg, p.o.), prednisolone (4 mg/kg/day, p.o.), or mesalazine (100 mg/kg/day, p.o.) respectively. At day 6, tissue injuries were assessed for macroscopic, histopathologic, and biochemical indices of myeloperoxidase and MPO activity. Results showed that GAL at 3 applied doses, alone or in combination with DIC diminished ulcer index, total colitis index, and MPO activity as important biomarkers of colitis. DIC alone was not effective on most parameters and its concurrent administration with GAL couldn’t reverse its antiulcerative effects. Prednisolone and mesalazine were both effective in this relation. The current research indicated that GAL had anti-inflammatory and antiulcerative activities independent of its muscarinic effects. Thus the antioxidant and anti-inflammatory effects may account for its anti-inflammatory and anti-ulcerative properties. Nevertheless, further detailed studies are warranted for exact elucidation of GAL mechanism on inflammation and colitis.

Comparison of cholinesterase inhibitor safety in real-world practice

Introduction

Cholinesterase inhibitors (ChEIs) are widely used to treat mild to moderate Alzheimer's disease and related dementia. Clinical trials have focused on placebo comparisons, inadequately addressing within-class comparative safety.

Methods

New users of ChEIs in British Columbia were categorized into five study cohorts: low-dose donepezil, high-dose donepezil, galantamine, rivastigmine patch, and oral rivastigmine. Comparative safety of ChEIs assessed hazard ratios using propensity score adjusted Cox regression.

Results

Compared with low-dose donepezil, galantamine use was associated with a lower risk of mortality (adjusted hazard ratio: 0.84, 95% confidence interval: 0.60–1.18), cardiovascular serious adverse events (adjusted hazard ratio: 0.78, 95% confidence interval: 0.62–0.98), and entry into a residential care facility (adjusted hazard ratio: 0.72, 95% confidence interval: 0.59–0.89).

Discussion

Given the absence of randomized trial data showing clinically meaningful benefit of ChEI therapy in Alzheimer's disease, our study suggests preferential use of galantamine may at least be associated with fewer adverse events than treatment with donepezil or rivastigmine.

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Galantamine was associated with fewer adverse events than donepezil or rivastigmine.

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Galantamine users experienced longer independent living.

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The 3-year risk of cardiovascular events and mortality was lowest with galantamine.

Galantamine is not a positive allosteric modulator of human α4β2 or α7 nicotinic acetylcholine receptors

BACKGROUND AND PURPOSE

The alkaloid galantamine was originally isolated from the green snowdrop Galanthus woronowii and is currently marketed as a drug for treatment of mild to moderate dementia in patients with Alzheimer's disease. In addition to a well-documented proficiency to inhibit acetylcholinesterase, galantamine has been reported to increase neuronal nicotinic ACh (nACh) receptor function by acting as a positive allosteric modulator. Yet there remains controversy regarding these findings in the literature. To resolve this conundrum, we evaluated galantamine actions at α4β2 and α7, which represent the nACh receptors most commonly associated with mammalian cognitive domains.

EXPERIMENTAL APPROACH

α4β2 [in (α4)₃ (β2)₂ and (α4)₂ (β2)₃ stoichiometries] and α7 nACh receptors were expressed in Xenopus laevis oocytes and subjected to two-electrode voltage-clamp electrophysiological experiments. Galantamine (10 nM to 100 μM) was evaluated for direct agonist effects and for positive modulation by co-application with sub-maximally efficacious concentrations of ACh. In addition, similar experiments were performed with α7 nACh receptors stably expressed in HEK293 cells using patch-clamp electrophysiology.

KEY RESULTS

In concentrations ranging from 10 nM to 1 μM, galantamine did not display direct agonism nor positive modulatory effects at any receptor combination tested. At concentrations from 10 μM and above, galantamine inhibited the activity with a mechanism of action consistent with open-channel pore blockade at all receptor types.

CONCLUSION AND IMPLICATIONS

Based on our data, we conclude that galantamine is not a positive allosteric modulator of α7 or α4β2 receptors, which represent the majority of nACh receptors in mammalian brain.

A Randomized Clinical Trial of Oxytocin or Galantamine for the Treatment of Negative Symptoms and Cognitive Impairments in People With Schizophrenia

PURPOSE/BACKGROUND

Negative symptoms and cognitive impairments tend to co-occur in people with schizophrenia. If their association with each other is due, in part, to shared pathophysiology, then this suggests that a single drug could potentially be effective for both domains. The current study was designed to examine this hypothesis.

METHODS/PROCEDURES

Fifty-eight participants with either Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision schizophrenia or schizoaffective disorder entered into a 6-week double-blind, placebo-controlled, double-dummy, randomized clinical trial of intranasal oxytocin and galantamine. Seventeen participants were randomized to intranasal oxytocin, 20 were randomized to galantamine, and 21 were randomized to placebo. The Scale for the Assessment of Negative Symptoms total score was used to assess change in negative symptoms (the primary outcome measure for oxytocin). The MATRICS Consensus Cognitive Battery composite score was used to assess cognition (the primary outcome measure for galantamine).

FINDINGS/RESULTS

There were no significant group differences for negative symptoms (oxytocin vs placebo: F2,47.4 = 0.19, P = 0.83; galantamine vs placebo: F2,52.5 = 0.41, P = 0.67). There were no significant group differences for cognitive impairments (galantamine vs placebo: t40 = 0.71, P = 0.48; oxytocin vs placebo: t40 = 0.50, P = 0.62). There were also no significant group differences for the functional capacity or ancillary symptom measures.

IMPLICATIONS/CONCLUSIONS

The lack of an efficacy signal for either compound precluded our ability to test whether pharmacological treatment pathways for negative symptoms and cognitive impairments overlap or are independent.

Newly Developed Drugs for Alzheimer's Disease in Relation to Energy Metabolism, Cholinergic and Monoaminergic Neurotransmission

Current options for Alzheimer's disease (AD) treatment are based on administration of cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and/or memantine, acting as an N-methyl-D-aspartate (NMDA). Therapeutic approaches vary and include novel cholinesterase inhibitors, modulators of NMDA receptors, monoamine oxidase (MAO) inhibitors, immunotherapeutics, modulators of mitochondrial permeability transition pores (mPTP), amyloid-beta binding alcohol dehydrogenase (ABAD) modulators, antioxidant agents, etc. The novel trends of AD therapy are focused on multiple targeted ligands, where mostly ChE inhibition is combined with additional biological properties, positively affecting neuronal energy metabolism as well as mitochondrial functions, and possessing antioxidant properties. The present review summarizes newly developed drugs targeting cholinesterase and MAO, as well as drugs affecting mitochondrial functions.

Docking-based design and synthesis of galantamine-camphane hybrids as inhibitors of acetylcholinesterase

Galantamine (GAL) as an acetylcholinesterase inhibitor (AChEI) is among the main drugs approved for the treatment of Alzheimer's disease. It fits perfectly into acetylcholinesterase (AChE) binding gorge, but it is too short to fill it. The amyloid beta (Aβ) peptide binds in the peripheral anionic site (PAS) at the entrance of the binding gorge of AChE and initiates the formation of amyloid plaques. The blockade of PAS prevents from AChE-induced Aβ aggregation. In this study, we describe the design of a series of galantamine-camphane hybrids as AChEIs. Camphane (CAM) is a bulky fragment that disposes well on the wide gorge entrance. The designed hybrids have linkers of different length. They were docked into AChE, and the highest scored compounds were synthesized and tested for AChE inhibitory activity. Some of the novel hybrids showed 191- and 369-fold better inhibition than GAL. The CAM fragment of the best binders fits in the same region, proximal to PAS, where the Ω-loop of Aβ binds to AChE. The hybrids cross blood-brain barrier by passive diffusion and are non-neurotoxic at the inhibitory concentrations.

Bridging Type 2 Diabetes and Alzheimer's Disease: Assembling the Puzzle Pieces in the Quest for the Molecules With Therapeutic and Preventive Potential

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two age-related amyloid diseases that affect millions of people worldwide. Broadly supported by epidemiological data, the higher incidence of AD among type 2 diabetic patients led to the recognition of T2D as a tangible risk factor for the development of AD. Indeed, there is now growing evidence on brain structural and functional abnormalities arising from brain insulin resistance and deficiency, ultimately highlighting the need for new approaches capable of preventing the development of AD in type 2 diabetic patients. This review provides an update on overlapping pathophysiological mechanisms and pathways in T2D and AD, such as amyloidogenic events, oxidative stress, endothelial dysfunction, aberrant enzymatic activity, and even shared genetic background. These events will be presented as puzzle pieces put together, thus establishing potential therapeutic targets for drug discovery and development against T2D and diabetes-induced cognitive decline-a heavyweight contributor to the increasing incidence of dementia in developed countries. Hoping to pave the way in this direction, we will present some of the most promising and well-studied drug leads with potential against both pathologies, including their respective bioactivity reports, mechanisms of action, and structure-activity relationships.

Lactucopicrin potentiates neuritogenesis and neurotrophic effects by regulating Ca2+/CaMKII/ATF1 signaling pathway

ETHNO-PHARMACOLOGICAL RELEVANCE

Lactucopicrin is one of constitutes in Cichorium intybus L, which is commonly known as chicory in worldwide. It has been used for traditional usage such as antianalgesics, antidepressants and antihyperglycemics AIM OF STUDY: We investigated the neurotrophin-mediated neuroprotective effect of lactucopicrin in in vitro and examined for the underlying mechanism.

MATERIALS AND METHOD

To verify the neuroprotective effect of lactucopicrin, we investigated the inhibitory AChE activity, neurite outgrowth-related downstream signaling in murine neuroblastoma N2a and neurotrophins secretion in rat C6 glioma cells.

RESULTS

Lactucopicrin inhibited the AChE activity and increased intracellular Ca²⁺ levels with a substantial rise in muscarinic acetylcholine receptor M1 (CHRM1) expression in N2a cells. Moreover, lactucopicrin actively promoted neurite outgrowth via Ca²⁺-mediated activation of Ca²⁺/calmodulin-dependent protein kinase-II (CaMKII). It further activates transcription factor 1 (ATF1) along with modulating the levels of tropomyosin receptor kinase A, extracellular signal-regulated kinase 1 and 2, AKT, and synaptophysin 1 in N2a cells. Additionally, the levels of neurotrophins including NGF, BDNF, and NT3 were increased by treatment of lactucopicrin in C6 cells. The effects of lactucopicrin on NGF secretion and neuritogenesis were maintained even in the presence of phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002, indicating that lactucopicrin exerts its effect on neuritogenesis in a PI3K-independent manner.

CONCLUSION

Our results suggest that the natural compound lactucopicrin may be a promising neurotrophin-mediated neuroprotective candidate for neurodegenerative diseases.

Acetylcholinesterase inhibitor treatment alleviated cognitive impairment caused by delayed encephalopathy due to carbon monoxide poisoning: Two case reports and a review of the literature

INTRODUCTION

Delayed encephalopathy due to carbon monoxide (CO) poisoning can even occur in patients with mild symptoms of acute CO poisoning. Some cases taking conventional hyperbaric oxygen (HBO) therapy or steroid-pulse therapy may be insufficient, and AchEI may be effective.

PATIENT CONCERNS AND DIAGNOSES

We report two cases of delayed encephalopathy after acute CO poisoning involving two women aged 69 (Case 1) and 60 years (Case 2) whose cognitive function improved with acetylcholinesterase inhibitor (AchEI) treatment. Delayed encephalopathy occurred 25 and 35 days after acute CO poisoning in Case 1 and Case 2, respectively. Both patients demonstrated cognitive impairment, apathy, and hypokinesia on admission.

INTERVENTIONS AND OUTCOMES

Although hyperbaric oxygen therapy did not yield any significant improvements, cognitive dysfunction improved substantially. This was evidenced by an improved Mini-Mental State Examination score ffom 9 to 28 points in Case 1 and an improved Hasegawa's dementia rating scale score from 4 to 25 points in Case 2 after administration of an AchEI. In Case 1, we administered galantamine hydrobromide, which was related with improved white matter lesions initially detected on brain magnetic resonance imaging. However, in Case 2 white matter lesions persisted despite AchEI treatment. AchEI treatment may result in improved cognitive and frontal lobe function by increasing low acetylcholine concentrations in the hippocampus and frontal lobe caused by decreased nicotinic acetylcholine receptor levels in delayed encephalopathy after CO poisoning.

CONCLUSION

Physicians should consider AchEIs for patients demonstrating delayed encephalopathy due to CO poisoning.

Multi-target therapeutics for neuropsychiatric and neurodegenerative disorders

Historically, neuropsychiatric and neurodegenerative disease treatments focused on the 'magic bullet' concept; however multi-targeted strategies are increasingly attractive gauging from the escalating research in this area. Because these diseases are typically co-morbid, multi-targeted drugs capable of interacting with multiple targets will expand treatment to the co-morbid disease condition. Despite their theoretical efficacy, there are significant impediments to clinical success (e.g., difficulty titrating individual aspects of the drug and inconclusive pathophysiological mechanisms). The new and revised diagnostic frameworks along with studies detailing the endophenotypic characteristics of the diseases promise to provide the foundation for the circumvention of these impediments. This review serves to evaluate the various marketed and nonmarketed multi-targeted drugs with particular emphasis on their design strategy.

ASS234, As a New Multi-Target Directed Propargylamine for Alzheimer's Disease Therapy

HIGHLIGHTS

ASS2324 is a hybrid compound resulting from the juxtaposition of donepezil and the propargylamine PF9601N ASS2324 is a multi-target directed propargylamine able to bind to all the AChE/BuChE and MAO A/B enzymesASS2324 shows antioxidant, neuroprotective and suitable permeability propertiesASS2324 restores the scopolamine-induced cognitive impairment to the same extent as donepezil, and is less toxicASS2324 prevents β-amyloid induced aggregation in the cortex of double transgenic miceASS2324 is the most advanced anti-Alzheimer agent for pre-clinical studies that we have identified in our laboratories The complex nature of Alzheimer's disease (AD) has prompted the design of Multi-Target-Directed Ligands (MTDL) able to bind to diverse biochemical targets involved in the progress and development of the disease. In this context, we have designed a number of MTD propargylamines (MTDP) showing antioxidant, anti-beta-amyloid, anti-inflammatory, as well as cholinesterase and monoamine oxidase (MAO) inhibition capacities. Here, we describe these properties in the MTDL ASS234, our lead-compound ready to enter in pre-clinical studies for AD, as a new multipotent, permeable cholinesterase/monoamine oxidase inhibitor, able to inhibit Aβ-aggregation, and possessing antioxidant and neuroprotective properties.

Docking-based Design of Galantamine Derivatives with Dual-site Binding to Acetylcholinesterase

The enzyme acetylcholinesterase is a key target in the treatment of Alzheimer's disease because of its ability to hydrolyze acetylcholine via the catalytic binding site and to accelerate the aggregation of amyloid-β peptide via the peripheral anionic site (PAS). Using docking-based predictions, in the present study we design 20 novel galantamine derivatives with alkylamide spacers of different length ending with aromatic fragments. The galantamine moiety blocks the catalytic site, while the terminal aromatic fragments bind in PAS. The best predicted compounds are synthesized and tested for acetylcholinesterase inhibitory activity. The experimental results confirm the predictions and show that the heptylamide spacer is of optimal length to bridge the galantamine moiety bound in the catalytic site and the aromatic fragments interacting with PAS. Among the tested terminal aromatic fragments, the phenethyl substituent is the most suitable for binding in PAS.

Multi-Target Directed Donepezil-Like Ligands for Alzheimer's Disease

HIGHLIGHTS ASS234 is a MTDL compound containing a moiety from Donepezil and the propargyl group from the PF 9601N, a potent and selective MAO B inhibitor. This compound is the most advanced anti-Alzheimer agent for preclinical studies identified in our laboratory.Derived from ASS234 both multipotent donepezil-indolyl (MTDL-1) and donepezil-pyridyl hybrids (MTDL-2) were designed and evaluated as inhibitors of AChE/BuChE and both MAO isoforms. MTDL-2 showed more high affinity toward the four enzymes than MTDL-1.MTDL-3 and MTDL-4, were designed containing the N-benzylpiperidinium moiety from Donepezil, a metal- chelating 8-hydroxyquinoline group and linked to a N-propargyl core and they were pharmacologically evaluated.The presence of the cyano group in MTDL-3, enhanced binding to AChE, BuChE and MAO A. It showed antioxidant behavior and it was able to strongly complex Cu(II), Zn(II) and Fe(III).MTDL-4 showed higher affinity toward AChE, BuChE.MTDL-3 exhibited good brain penetration capacity (ADMET) and less toxicity than Donepezil. Memory deficits in scopolamine-lesioned animals were restored by MTDL-3.MTDL-3 particularly emerged as a ligand showing remarkable potential benefits for its use in AD therapy. Alzheimer's disease (AD), the most common form of adult onset dementia, is an age-related neurodegenerative disorder characterized by progressive memory loss, decline in language skills, and other cognitive impairments. Although its etiology is not completely known, several factors including deficits of acetylcholine, β-amyloid deposits, τ-protein phosphorylation, oxidative stress, and neuroinflammation are considered to play significant roles in the pathophysiology of this disease. For a long time, AD patients have been treated with acetylcholinesterase inhibitors such as donepezil (Aricept®) but with limited therapeutic success. This might be due to the complex multifactorial nature of AD, a fact that has prompted the design of new Multi-Target-Directed Ligands (MTDL) based on the "one molecule, multiple targets" paradigm. Thus, in this context, different series of novel multifunctional molecules with antioxidant, anti-amyloid, anti-inflammatory, and metal-chelating properties able to interact with multiple enzymes of therapeutic interest in AD pathology including acetylcholinesterase, butyrylcholinesterase, and monoamine oxidases A and B have been designed and assessed biologically. This review describes the multiple targets, the design rationale and an in-house MTDL library, bearing the N-benzylpiperidine motif present in donepezil, linked to different heterocyclic ring systems (indole, pyridine, or 8-hydroxyquinoline) with special emphasis on compound ASS234, an N-propargylindole derivative. The description of the in vitro biological properties of the compounds and discussion of the corresponding structure-activity-relationships allows us to highlight new issues for the identification of more efficient MTDL for use in AD therapy.

Galantamine promotes adult hippocampal neurogenesis via M₁ muscarinic and α7 nicotinic receptors in mice

Galantamine, an inhibitor of acetylcholinesterase, promotes hippocampal neurogenesis, but the exact mechanism for this is not known. In the present study, we examined the mechanisms underlying the effects of acute galantamine on neurogenesis in the mouse hippocampus. Galantamine (3 mg/kg) increased the number of 5-bromo-2'-deoxyuridine (BrdU)-positive cells in the subgranular zone of the dentate gyrus. This effect was blocked by the muscarinic receptor antagonist scopolamine and the preferential M1 muscarinic receptor antagonist telenzepine, but not by the nicotinic receptor antagonists mecamylamine and methyllycaconitine. Galantamine did not alter the ratio of neuronal nuclei (NeuN)- or glial fibrillary acidic protein (GFAP)-positive cells to BrdU-labeled cells in the subgranular zone and granule cell layer. Galantamine (1, 3 mg/kg) promoted the survival of 2-wk-old newly divided cells in mice in the granule cell layer of the dentate gyrus, whereas it did not affect the survival of newly divided cells at 1 and 4 wk. Galantamine-induced increases in cell survival were blocked by the α7 nicotinic receptor antagonist methyllycaconitine, but not by scopolamine. Bilateral injection of recombinant IGF2 into the dentate gyrus of the hippocampus mimicked the effects of galantamine. The effects of galantamine were blocked by direct injection of the IGF1 receptor antagonist JB1. These findings suggest that galantamine promotes neurogenesis via activation of the M1 muscarinic and α7 nicotinic acetylcholine receptors. The present study also suggests that IGF2 is involved in the effects of galantamine on the survival of 2-wk-old immature cells in the granule cell layer.

Galantamine efficacy and tolerability as an augmentative therapy in autistic children: A randomized, double-blind, placebo-controlled trial

The role of cholinergic abnormalities in autism was recently evidenced and there is a growing interest in cholinergic modulation, emerging for targeting autistic symptoms. Galantamine is an acetylcholinesterase inhibitor and an allosteric potentiator of nicotinic receptors. This study aimed to evaluate the possible effects of galantamine as an augmentative therapy to risperidone, in autistic children. In this randomized, double-blind, placebo-controlled, parallel-group study, 40 outpatients aged 4-12 years whom had a diagnosis of autism (DSM IV-TR) and a score of 12 or higher on the Aberrant Behavior Checklist-Community (ABC-C) Irritability subscale were equally randomized to receive either galantamine (up to 24 mg/day) or placebo, in addition to risperidone (up to 2 mg/day), for 10 weeks. We rated participants by ABC-C and a side effects checklist, at baseline and at weeks 5 and 10. By the study endpoint, the galantamine-treated patients showed significantly greater improvement in the Irritability (P = 0.017) and Lethargy/Social Withdrawal (P = 0.005) subscales than the placebo group. The difference between the two groups in the frequency of side effects was not significant. In conclusion, galantamine augmentation was shown to be a relatively effective and safe augmentative strategy for alleviating some of the autism-related symptoms.

Synthesis, pharmacological assessment, and molecular modeling of acetylcholinesterase/butyrylcholinesterase inhibitors: effect against amyloid-β-induced neurotoxicity

The synthesis, molecular modeling, and pharmacological analysis of phenoxyalkylamino-4-phenylnicotinates (2-7), phenoxyalkoxybenzylidenemalononitriles (12, 13), pyridonepezils (14-18), and quinolinodonepezils (19-21) are described. Pyridonepezils 15-18 were found to be selective and moderately potent regarding the inhibition of hAChE, whereas quinolinodonepezils 19-21 were found to be poor inhibitors of hAChE. The most potent and selective hAChE inhibitor was ethyl 6-(4-(1-benzylpiperidin-4-yl)butylamino)-5-cyano-2-methyl-4-phenylnicotinate (18) [IC(50) (hAChE) = 0.25 ± 0.02 μM]. Pyridonepezils 15-18 and quinolinodonepezils 20-21 are more potent selective inhibitors of EeAChE than hAChE. The most potent and selective EeAChE inhibitor was ethyl 6-(2-(1-benzylpiperidin-4-yl)ethylamino)-5-cyano-2-methyl-4-phenylnicotinate (16) [IC(50) (EeAChE) = 0.0167 ± 0.0002 μM], which exhibits the same inhibitory potency as donepezil against hAChE. Compounds 2, 7, 13, 17, 18, 35, and 36 significantly prevented the decrease in cell viability caused by Aβ(1-42). All compounds were effective in preventing the enhancement of AChE activity induced by Aβ(1-42). Compounds 2-7 caused a significant reduction whereas pyridonepezils 17 and 18, and compound 16 also showed some activity. The pyrazolo[3,4-b]quinolines 36 and 38 also prevented the upregulation of AChE induced by Aβ(1-42). Compounds 2, 7, 12, 13, 17, 18, and 36 may act as antagonists of voltage sensitive calcium channels, since they significantly prevented the Ca(2+) influx evoked by KCl depolarization. Docking studies show that compounds 16 and 18 adopted different orientations and conformations inside the active-site gorges of hAChE and hBuChE. The structural and energetic features of the 16-AChE and 18-AChE complexes compared to the 16-BuChE and 18-BuChE complexes account for a higher affinity of the ligand toward AChE. The present data indicate that compounds 2, 7, 17, 18, and 36 may represent attractive multipotent molecules for the potential treatment of Alzheimer's disease.

Galantamine increases hippocampal insulin-like growth factor 2 expression via α7 nicotinic acetylcholine receptors in mice

RATIONALE AND OBJECTIVE

Galantamine, a drug for the treatment of Alzheimer's disease, has neuroprotection in several experimental models and stimulates adult neurogenesis in the rodent brain, but the exact mechanism remains unclear. This study examined whether galantamine affects the expression of neurotrophic/growth factors in the mouse hippocampus and prefrontal cortex.

METHODS

Nine-week-old male ddY mice were used. The mRNA levels of neurotrophic/growth factors were analyzed by a real-time quantitative PCR. The protein levels of insulin-like growth factor 2 (IGF2) were analyzed by Western blotting.

RESULTS

Acute administration of galantamine (0.3-3 mg/kg, i.p.) increased IGF2 mRNA levels in the hippocampus, but not in the prefrontal cortex, in time- and dose-dependent manner. Galantamine (3 mg/kg, i.p.) caused a transient increase in fibroblast growth factor 2 mRNA levels and a decrease in brain-derived neurotrophic factor mRNA levels in the hippocampus, while it did not affect the mRNA levels of other neurotrophic/growth factors. The galantamine-induced increase in the hippocampal IGF2 mRNA levels was blocked by mecamylamine, a nonselective nicotinic acetylcholine (ACh) receptor (nAChR) antagonist, and methyllycaconitine, a selective α7 nAChR antagonist, but not by telenzepine, a preferential M(1) muscarinic ACh receptor antagonist. Moreover, the selective α7 nAChR agonist PHA-543613 increased the IGF2 mRNA levels, while donepezil, an acetylcholinesterase inhibitor, did not. Galantamine also increased hippocampal IGF2 protein, which was blocked by methyllycaconitine.

CONCLUSIONS

These findings suggest that galantamine increases hippocampal IGF2 levels via α7 nAChR activation in mice and imply that the effect may contribute to its neuroprotection or neurogenesis.

Modulation of innate immune-related pathways in nicotine-treated SH-SY5Y cells

Although nicotine has a broad impact on both the central and peripheral nervous systems, the molecular mechanisms remain largely unknown, especially at the signaling pathway level. To investigate that aspect, we employed both conventional molecular techniques, such as quantitative real-time PCR and Western blotting analysis, and high-throughput microarray approach to identify the genes and signaling pathways that are modulated by nicotine. We found 14 pathways significantly altered in SH-SY5Y neuroblastoma cells. Of these, the Toll-like receptor pathway (TLR; p = 2.57 × 10(-4)) is one of the most important innate immune pathways. The death receptor pathway (DR; p = 8.71 × 10(-4)), whose transducers coordinate TLR signals and help conduct the host immune response to infection, was also significantly changed by nicotine. Furthermore, we found that several downstream pathways of TLR and DR signaling, such as PI3K/AKT signaling (p = 9.55 × 10(-6)), p38 signaling (p = 2.40 × 10(-6)), and ERK signaling (p = 1.70 × 10(-4)), were also significantly modulated by nicotine. Interestingly, most of the differentially expressed genes in these pathways leading to nuclear factor κB (NF-κB) activation and those important inhibitors of pathways leading to apoptosis, including FLIP and Bcl-2, were up-regulated by nicotine. Taken together, our findings demonstrate that nicotine can regulate multiple innate immune-related pathways, and our data thus provide new clues to the molecular mechanisms underlying nicotine's regulatory effects on neurons.

Axo-axonal interaction in autonomic regulation of the cerebral circulation

Noradrenaline (NE) and acetylcholine (ACh) released from the sympathetic and parasympathetic neurones in cerebral blood vessels were suggested initially to be the respective vasoconstricting and dilating transmitters. Both substances, however, are extremely weak post-synaptic transmitters. Compelling evidence indicates that nitric oxide (NO) which is co-released with ACh from same parasympathetic nerves is the major transmitter for cerebral vasodilation, and its release is inhibited by ACh. NE released from the sympathetic nerve, acting on presynaptic β2-adrenoceptors located on the neighbouring parasympathetic nitrergic nerves, however, facilitates NO release with enhanced vasodilation. This axo-axonal interaction mediating NE transmission is supported by close apposition between sympathetic and parasympathetic nerve terminals, and has been shown in vivo at the base of the brain and the cortical cerebral circulation. This result reveals the physiological need for increased regional cerebral blood flow in 'fight-or-flight response' during acute stress. Furthermore, α7- and α3β2-nicotinic ACh receptors (nAChRs) on sympathetic nerve terminals mediate release of NE, leading to cerebral nitrergic vasodilation. α7-nAChR-mediated but not α3β2-nAChR-mediated cerebral nitrergic vasodilation is blocked by β-amyloid peptides (Aβs). This may provide an explanation for cerebral hypoperfusion seen in patients with Alzheimer's disease. α7- and α3β2-nAChR-mediated nitrergic vasodilation is blocked by cholinesterase inhibitors (ChEIs) which are widely used for treating Alzheimer's disease, leading to possible cerebral hypoperfusion. This may contribute to the limitation of clinical use of ChEIs. ChEI blockade of nAChR-mediated dilation like that by Aβs is prevented by statins pretreatment, suggesting that efficacy of ChEIs may be improved by concurrent use of statins.

Involvement of decreased muscarinic receptor function in prepulse inhibition deficits in mice reared in social isolation

BACKGROUND AND PURPOSE

We have previously reported that galantamine, a weak acetylcholinesterase inhibitor, improves prepulse inhibition (PPI) deficits in mice reared in social isolation. ACh receptors are involved in the underlying mechanism of PPI, but whether rearing in social isolation causes dysfunction of the cholinergic system is unknown. In this study, we examined the involvement of muscarinic receptors in the improvement of PPI deficits induced by galantamine, and whether the cholinergic system is altered in mice reared in isolation.

EXPERIMENTAL APPROACH

Three-week-old male ddY mice were housed in isolated cages for 6 weeks before the initiation of experiments to create PPI deficits. Cholinergic functions were determined by measuring the behavioural and neurochemical responses to nicotinic and muscarinic receptor agonists.

KEY RESULTS

The improvement by galantamine of social isolation-induced PPI deficits was blocked by scopolamine, a non-selective muscarinic antagonist, and telenzepine, a preferential M₁ receptor antagonist. Activation of M₁ receptors improved social isolation-induced PPI deficits. Social isolation did not affect choline acetyltransferase and acetylcholinesterase activities in the prefrontal cortex and hippocampus, but it reduced the locomotor-suppressive response to muscarinic agonist oxotremorine, but not to nicotine. The isolation also attenuated the M₁ receptor agonist N-desmethylclozapine-induced increase in prefrontal dopamine release.

CONCLUSIONS AND IMPLICATIONS

Galantamine improves PPI deficits of mice reared in social isolation via activation of M₁ receptors. Social isolation reduces the muscarinic, especially M₁, receptor function and this is involved in PPI deficits.

Pharmacological aspects of the acetylcholinesterase inhibitor galantamine

Several lines of evidence suggest that cholinergic deficits may contribute to the pathophysiology of psychiatric disorders as well as Alzheimer's disease. There is growing clinical evidence that galantamine, currently used for the treatment of Alzheimer's disease, may improve cognitive dysfunction and psychiatric illness in schizophrenia, major depression, bipolar disorder, and alcohol abuse. Since galantamine is a rather weak acetylcholinesterase inhibitor, but has additional allosteric potentiating effects at nicotinic receptors, it affects not only cholinergic transmission but also other neurotransmitter systems such as monoamines, glutamate, and γ-aminobutyric acid (GABA) through its allosteric mechanism. It is likely that these effects may result in more beneficial effects. To understand the underlying mechanism for the clinical effectiveness of galantamine, neuropharmacological studies have been performed in animal models of several psychiatric disorders. These studies suggest that not only the nicotinic receptor-modulating properties but also the muscarinic receptor activation contribute to the antipsychotic effect and improvement of cognitive dysfunction by galantamine. This review summaries the current status on the pharmacology of galantamine, focusing on its effect on neurotransmitter release and pharmacological studies in animal models of psychiatric disorders.

The subtype-selective nicotinic acetylcholine receptor positive allosteric potentiator 2087101 differentially facilitates neurotransmission in the brain

Positive allosteric modulators of centrally expressed nicotinic acetylcholine receptors have therapeutic potentials in areas of cognition, motor function and reward. Several chemical classes of allosteric modulators that are selective for alpha7 nicotinic receptors have been characterised, but potentiators for the most widely expressed alpha4beta2 nicotinic receptor subtype are few and less defined, owing probably to the difficulty to achieve selectivity over other heteromeric receptor subtypes. 2087101 (2-amino-5-keto)thiazole) is a potent potentiator of both alpha7 and alpha4beta2 receptors and it has selectivity against the alpha3beta4 subtype, which may be responsible for the undesirable peripheral side effects. To further characterise its ability to differentiate between native nicotinic receptors, we examined the effects of 2087101 on alpha7, alpha4beta2* and alpha3beta4* receptor-mediated responses in the rat brain in electrophysiological and neurochemical experiments. 2087101 significantly potentiated agonist-induced, alpha7 and non-alpha7 receptor-mediated, GABAergic postsynaptic currents in cultured hippocampal neurones, but not the nicotine-stimulated [(3)H]noradrenaline release from hippocampal slices, which was primarily mediated by alpha3beta4* receptors, confirming its selectivity for alpha7 and alpha4beta2* receptors in native systems. 2087101 also significantly enhanced nicotine-stimulated firing increase in dopamine neurones of the ventral tegmental area, an effect that was dihydro-beta-erythroidine-sensitive and thereby mediated by alpha4beta2* nicotinic receptors. 2087101 can therefore enhance native nicotinic activities mediated by alpha7 and alpha4beta2*, but not alpha3beta4* receptors, showing its unique ability to discriminate between native heteromeric nicotinic receptor subtypes and its therapeutic potential for treating brain disorders by concurrent modulation of both alpha7 and alpha4beta2* nicotinic receptors.

Pharmacological strategies for enhancing cognition in schizophrenia

Researchers have long recognized that individuals with schizophrenia experience challenges in a wide range of cognitive domains, and research on cognitive impairment in schizophrenia is not a recent phenomena. However, the past 10-20 years have seen an increasing recognition of the central importance of cognition to understanding function and outcome in this illness (Green et al. in Schizophr Bull 26:119-136, 2000), an awareness that has shifted the emphasis of at least some work on schizophrenia. More specifically, there has been a rapidly growing body of work on methods of enhancing cognition in schizophrenia, as a means to potentially facilitate improved outcome and quality of life for individuals with this debilitating illness. The current chapter reviews the results of a range of studies examining adjunctive pharmacological treatments to enhance cognition in schizophrenia using a range of designs, including single-dose studies, open-label repeated dosing studies, and double-blind parallel group and crossover designs with repeated dosing. Although many of the single-dose and open-label studies have suggested positive cognitive effects from a range of agents, few of the larger-scale double-blind studies have generated positive results. The current state of results may reflect the need to identify alternative molecular mechanisms for enhancing cognition in schizophrenia or the need to reconceptualize the ways in which pharmacological agents may improve cognition in this illness, with a concomitant change in the traditional clinical trial study design used in prior studies of cognitive enhancement in schizophrenia.

The effects of galantamine on psychopathology in chronic stable schizophrenia

OBJECTIVES

Galantamine is an acetylcholinesterase inhibitor and an allosteric modulator of the alpha4beta2 and alpha7 nicotinic receptors. There are several case reports describing the potential benefits of galantamine for negative symptoms associated with schizophrenia. This secondary analysis describes the effects of galantamine on psychopathology in people with schizophrenia.

METHODS

Subjects with clinically stable chronic schizophrenia were randomized to adjunctive galantamine (24 mg/d) or placebo in a 12-week double-blind trial. Symptomatology was assessed with the Brief Psychiatric Rating Scale (BPRS) and the Clinical Global Impression Scale. The Scale for the Assessment of Negative Symptoms (SANS) was used to measure negative symptoms.

RESULTS

Eighty-six patients with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnosis of schizophrenia or schizoaffective disorder taking a stable dose of antipsychotic medications were randomized to adjunctive treatment with study drug (galantamine, n = 42; placebo, n = 44); 73 subjects completed the study (galantamine, n = 35; placebo, n = 38). No significant differences were found on BPRS total score (P = 0.585) or BPRS subfactor scores. Scale for the Assessment of Negative Symptoms total scores also did not decrease significantly (P = 0.106) in either group; however, galantamine treatment was associated with a greater benefit in the SANS subfactor, alogia (P = 0.007).

CONCLUSIONS

The lack of robust significant effects of galantamine on negative, and other symptom domains, may be due to the relatively low baseline level of these symptoms in the tested population. Galantamine may have some benefit on certain negative symptoms, particularly alogia. Studies specifically designed to address the issue of the efficacy of galantamine for negative symptoms are needed to confirm this observation.

Cholinergic deficiency involved in vascular dementia: possible mechanism and strategy of treatment

Vascular dementia (VaD) is a progressive neurodegenerative disease with a high prevalence. Several studies have recently reported that VaD patients present cholinergic deficits in the brain and cerebrospinal fluid (CSF) that may be closely related to the pathophysiology of cognitive impairment. Moreover, cholinergic therapies have shown promising effects on cognitive improvement in VaD patients. The precise mechanisms of these cholinergic agents are currently not fully understood; however, accumulating evidence indicates that these drugs may act through the cholinergic anti-inflammatory pathway, in which the efferent vagus nerve signals suppress pro-inflammatory cytokine release and inhibit inflammation, although regulation of oxidative stress and energy metabolism, alleviation of apoptosis may also be involved. In this paper, we provide a brief overview of the cholinergic treatment strategy for VaD and its relevant mechanisms of anti-inflammation.Acta Pharmacologica Sinica (2009) 30: 879-888; doi: 10.1038/aps.2009.82.

Nicotinic mechanisms influencing synaptic plasticity in the hippocampus

Nicotinic acetylcholine receptors (nAChRs) are expressed throughout the hippocampus, and nicotinic signaling plays an important role in neuronal function. In the context of learning and memory related behaviors associated with hippocampal function, a potentially significant feature of nAChR activity is the impact it has on synaptic plasticity. Synaptic plasticity in hippocampal neurons has long been considered a contributing cellular mechanism of learning and memory. These same kinds of cellular mechanisms are a factor in the development of nicotine addiction. Nicotinic signaling has been demonstrated by in vitro studies to affect synaptic plasticity in hippocampal neurons via multiple steps, and the signaling has also been shown to evoke synaptic plasticity in vivo. This review focuses on the nAChRs subtypes that contribute to hippocampal synaptic plasticity at the cellular and circuit level. It also considers nicotinic influences over long-term changes in the hippocampus that may contribute to addiction.

Galantamine improves apomorphine-induced deficits in prepulse inhibition via muscarinic ACh receptors in mice

BACKGROUND AND PURPOSE

Galantamine, a weak acetylcholine esterase (AChE) inhibitor and allosteric potentiator of nicotinic ACh receptors (nAChRs), improves apomorphine-induced deficits in prepulse inhibition (PPI), sensory information-processing deficits, via a nAChR-independent mechanism. The present study examined the role of muscarinic ACh receptors (mAChRs) in the effect of galantamine, and studied the mechanism of galantamine-induced increases in prefrontal ACh levels in mice.

EXPERIMENTAL APPROACH

Apomorphine (1 mg kg(-1)) was administered to male ddY mice (9-10 weeks old) to create a PPI deficit model. Extracellular ACh concentrations in the prefrontal cortex were measured by in vivo microdialysis.

KEY RESULTS

Galantamine- and donepezil-mediated improvements in apomorphine-induced PPI deficits were blocked by the preferential M(1) mAChR antagonist telenzepine. The mAChR agonist oxotremorine also improved apomorphine-induced PPI deficits. Galantamine, like donepezil, increased extracellular ACh concentrations in the prefrontal cortex. Galantamine-induced increases in prefrontal ACh levels were partially blocked by the dopamine D(1) receptor antagonist SCH23390, but not by antagonists of mAChRs (telenzepine) and nAChRs (mecamylamine). Galantamine increased dopamine, but not 5-HT, release in the prefrontal cortex.

CONCLUSIONS AND IMPLICATIONS

Galantamine improves apomorphine-induced PPI deficits by stimulating mAChRs through increasing brain ACh levels via a dopamine D(1) receptor-dependent mechanism and AChE inhibition.

Mammalian nicotinic acetylcholine receptors: from structure to function

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

Young and older good learners have higher levels of brain nicotinic receptor binding

Neuronal alphabeta heteromeric and alpha7 homomeric nicotinic acetylcholine receptors (nAChRs) were compared in 4- and 27-month rabbits selected for learning proficiency. Sixty 4- and 60 27-month rabbits received the alpha7 nAChR agonist (MEM-3389), galantamine, or vehicle during training in trace eyeblink classical conditioning. Brain tissue from the best and worst young and older learners was analyzed with radioligand binding. Vehicle-treated 4- and 27-month good learners had higher alphabeta heteromeric nAChR binding in hippocampus and temporal-parietal cortex than poor learners, and this result was replicated in both age groups of rabbits treated with galantamine. Results indicate that anatomically more numerous nAChRs or functional activation of a greater number of nAChRs may characterize animals demonstrating optimal learning. During normal aging the expression of high-affinity binding sites declines. Age-related changes in the expression of hippocampal alphabeta heteromeric nAChRs may account for some of the documented age-related impairment in learning. However, individual differences in alphabeta heteromeric nAChRs also exist early in life, as better learning in 4-month rabbits was associated with significantly higher binding.

Donepezil attenuates excitotoxic damage induced by membrane depolarization of cortical neurons exposed to veratridine

Long-lasting membrane depolarization in cerebral ischemia causes neurotoxicity via increases of intracellular sodium concentration ([Na+]i) and calcium concentration ([Ca2+]i). Donepezil has been shown to exert neuroprotective effects in an oxygen-glucose deprivation model. In the present study, we examined the effect of donepezil on depolarization-induced neuronal cell injury resulting from prolonged opening of Na+ channels with veratridine in rat primary-cultured cortical neurons. Veratridine (10 microM)-induced neuronal cell damage was completely prevented by 0.1 microM tetrodotoxin. Pretreatment with donepezil (0.1-10 microM) for 1 day significantly decreased cell death in a concentration-dependent manner, and a potent NMDA receptor antagonist, dizocilpine (MK801), showed a neuroprotective effect at the concentration of 10 microM. The neuroprotective effect of donepezil was not affected by nicotinic or muscarinic acetylcholine receptor antagonists. We further characterized the neuroprotective properties of donepezil by measuring the effect on [Na+]i and [Ca2+]i in cells stimulated with veratridine. At 0.1-10 microM, donepezil significantly and concentration-dependently reduced the veratridine-induced increase of [Ca2+]i, whereas MK801 had no effect. At 10 microM, donepezil significantly decreased the veratridine-induced increase of [Na+]i. We also measured the effect on veratridine-induced release of the excitatory amino acids, glutamate and glycine. While donepezil decreased the release of glutamate and glycine, MK801 did not. In conclusion, our results indicate that donepezil has neuroprotective activity against depolarization-induced toxicity in rat cortical neurons via inhibition of the rapid influx of sodium and calcium ions, and via decrease of glutamate and glycine release, and also that this depolarization-induced toxicity is mediated by glutamate receptor activation.