Nicotinic cholinergic modulation: galantamine as a prototype

Inhibitory Mechanism of Baicalein on Acetylcholinesterase: Inhibitory Interaction, Conformational Change, and Computational Simulation

Alzheimer’s disease (AD) is the most prevalent chronic neurodegenerative disease in elderly individuals, causing dementia. Acetylcholinesterase (AChE) is regarded as one of the most popular drug targets for AD. Herbal secondary metabolites are frequently cited as a major source of AChE inhibitors. In the current study, baicalein, a typical bioactive flavonoid, was found to inhibit AChE competitively, with an associated IC₅₀ value of 6.42 ± 0.07 µM, through a monophasic kinetic process. The AChE fluorescence quenching by baicalein was a static process. The binding constant between baicalein and AChE was an order of magnitude of 10⁴ L mol⁻¹, and hydrogen bonding and hydrophobic interaction were the major forces for forming the baicalein−AChE complex. Circular dichroism analysis revealed that baicalein caused the AChE structure to shrink and increased its surface hydrophobicity by increasing the α-helix and β-turn contents and decreasing the β-sheet and random coil structure content. Molecular docking revealed that baicalein predominated at the active site of AChE, likely tightening the gorge entrance and preventing the substrate from entering and binding with the enzyme, resulting in AChE inhibition. The preceding findings were confirmed by molecular dynamics simulation. The current study provides an insight into the molecular-level mechanism of baicalein interaction with AChE, which may offer new ideas for the research and development of anti-AD functional foods and drugs.

Acetylcholinesterase and butyrylcholinesterase inhibitory activities of khellactone coumarin derivatives isolated from Peucedanum japonicum Thurnberg

Cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors have been attracted as candidate treatments for Alzheimer's disease (AD). Fifteen khellactone-type coumarins from the roots of Peucedanum japonicum Thunberg were tested for acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and MAO inhibitory activities. Compound 3′-angeloyl-4′-(2-methylbutyryl)khellactone (PJ13) most potently inhibited AChE (IC₅₀ = 9.28 µM), followed by 3′-isovaleryl-4′-(2-methylbutyroyl)khellactone (PJ15) (IC₅₀ = 10.0 μM). Compound senecioyl-4′-angeloyl-khellactone (PJ5) most potently inhibited BChE (IC₅₀ = 7.22 μM) and had the highest selectivity index (> 5.54), followed by 3′-senecioyl-4′-(2-methylbutyryl)khellactone (PJ10) and 3′,4′-disenecioylkhellactone (PJ4) (IC₅₀ = 10.2 and 10.7 μM, respectively). Compounds PJ13, PJ15, and PJ5 showed reversible and mixed-types of inhibition with K_i values of 5.98, 10.4 (for AChE), and 4.16 µM (for BChE), respectively. However, all 15 compounds weakly inhibited MAO-A and MAO-B. Molecular docking simulation revealed that PJ13 had a higher binding affinity (− 9.3 kcal/mol) with AChE than PJ15 (− 7.8 kcal/mol) or PJ5 (− 5.4 kcal/mol), due to the formation of a hydrogen bond with Tyr121 (distance: 2.52 Å). On the other hand, the binding affinity of PJ5 (− 10.0 kcal/mol) with BChE was higher than for PJ13 (− 7.7 kcal/mol) or PJ15 (− 8.1 kcal/mol), due to the formation of a hydrogen bond with Ser198 (distance: 2.05 Å). These results suggest that PJ13 and PJ5 are potential reversible selective inhibitors of AChE and BChE, respectively, for the treatment of AD.

A modeling informed quantitative approach to salvage clinical trials interrupted due to COVID-19

Many ongoing Alzheimer's disease central nervous system clinical trials are being disrupted and halted due to the COVID-19 pandemic. They are often of a long duration' are very complex; and involve many stakeholders, not only the scientists and regulators but also the patients and their family members. It is mandatory for us as a community to explore all possibilities to avoid losing all the knowledge we have gained from these ongoing trials. Some of these trials will need to completely restart, but a substantial number can restart after a hiatus with the proper protocol amendments. To salvage the information gathered so far, we need out-of-the-box thinking for addressing these missingness problems and to combine information from the completers with those subjects undergoing complex protocols deviations and amendments after restart in a rational, scientific way. Physiology-based pharmacokinetic (PBPK) modeling has been a cornerstone of model-informed drug development with regard to drug exposure at the site of action, taking into account individual patient characteristics. Quantitative systems pharmacology (QSP), based on biology-informed and mechanistic modeling of the interaction between a drug and neuronal circuits, is an emerging technology to simulate the pharmacodynamic effects of a drug in combination with patient-specific comedications, genotypes, and disease states on functional clinical scales. We propose to combine these two approaches into the concept of computer modeling-based virtual twin patients as a possible solution to harmonize the readouts from these complex clinical datasets in a biologically and therapeutically relevant way.

Simulating the Effects of Common Comedications and Genotypes on Alzheimer's Cognitive Trajectory Using a Quantitative Systems Pharmacology Approach

BACKGROUND

Many Alzheimer's disease patients in clinical practice are on polypharmacy for treatment of comorbidities.

OBJECTIVE

While pharmacokinetic interactions between drugs have been relatively well established with corresponding treatment guidelines, many medications and common genotype variants also affect central brain circuits involved in cognitive trajectory, leading to complex pharmacodynamic interactions and a large variability in clinical trials.

METHODS

We applied a mechanism-based and ADAS-Cog calibrated Quantitative Systems Pharmacology biophysical model of neuronal circuits relevant for cognition in Alzheimer's disease, to standard-of-care cholinergic therapy with COMTVal158Met, 5-HTTLPR rs25531, and APOE genotypes and with benzodiazepines, antidepressants, and antipsychotics, all together 9,585 combinations.

RESULTS

The model predicts a variability of up to 14 points on ADAS-Cog at baseline (COMTVV 5-HTTLPRss APOE 4/4 combination is worst) and a four-fold range for the rate of progression. The progression rate is inversely proportional to baseline ADAS-Cog. Antidepressants, benzodiazepines, first-generation more than second generation, and most antipsychotics with the exception of aripiprazole worsen the outcome when added to standard-of-care in mild cases. Low dose second-generation benzodiazepines revert the negative effects of risperidone and olanzapine, but only in mild stages. Non APOE4 carriers with a COMTMM and 5HTTLPRLL are predicted to have the best cognitive performance at baseline but deteriorate somewhat faster over time. However, this effect is significantly modulated by comedications.

CONCLUSION

Once these simulations are validated, the platform can in principle provide optimal treatment guidance in clinical practice at an individual patient level, identify negative pharmacodynamic interactions with novel targets and address protocol amendments in clinical trials.

Effect of photoperiod and plant growth regulators on in vitro mass bulblet proliferation of Narcissus tazzeta L. (Amaryllidaceae), a potential source of galantamine

Narcissus tazetta L., a bulbous plant belongs to the Amaryllidaceae family, contains alkaloid galantamine (GAL) with acetylcholinesterase inhibitory activity which has been recently considered to treat Alzheimer's disease (AD). In the current work, the effect of photoperiod (16/8 h light/dark and 24 h dark) and various concentrations of NAA, BAP, and GA₃ (0, 0.5, 1 and 2 mg l^‒1) on the in vitro mass bulblet regeneration of N. tazetta was studied. The GAL production ability of the regenerated bulblets was assessed by HPLC-UV-MS. Light treatments significantly affected the number of bulblet and leaf, the ratio of bulblet/leaf, and leaf length. The maximum number of bulblet (31.0 ± 1.58) and leaf (13.3 ± 1.33) was recorded from the cultures fortified with NAA and BAP (2 mg l^‒1) kept in 16/8 h light/dark, while the maximum leaf length (2.1 ± 0.92 cm) was measured on the MS medium containing 0.5 mg l^‒1 NAA and 2 mg l^‒1 BAP incubated in the same photoperiod. The average ratio of bulblet proliferation per explant was significantly different between studied photoperiod (1.1 ± 0.86) and 24 h dark (0.62 ± 0.31). The regenerated bulblets contained 40 and 20 µg g^‒1 DW GAL underexposed photoperiod and 24 h dark, respectively. This information could be useful in the commercial production of GAL as a valuable anti-AD compound through in vitro mass bulblet proliferation of N. tazetta.

Learning from amyloid trials in Alzheimer's disease. A virtual patient analysis using a quantitative systems pharmacology approach

BACKGROUND

Many trials of amyloid-modulating agents fail to improve cognitive outcome in Alzheimer's disease despite substantial reduction of amyloid β levels.

METHODS

We applied a mechanism-based Quantitative Systems Pharmacology model exploring the pharmacodynamic interactions of apolipoprotein E (APOE), Catechol -O -methyl Transferase (COMTVal158Met), and 5-HT transporter (5-HTTLPR) rs25531 genotypes and aducanumab.

RESULTS

The model predicts large clinical variability. Anticipated placebo differences on Alzheimer's Disease Assessment Scale (ADAS)-COG in the aducanumab ENGAGE and EMERGE ranged from 0.77 worsening to 1.56 points improvement, depending on the genotype-comedication combination. 5-HTTLPR L/L subjects are found to be the most resilient. Virtual patient simulations suggest improvements over placebo between 4% and 20% at the 10 mg/kg dose, depending on the imbalance of the 5-HTTLPR genotype and exposure. In the Phase II PRIME trial, maximal anticipated placebo difference at 10 mg/kg ranges from 0.3 worsening to 5.3 points improvement.

DISCUSSION

These virtual patient simulations, once validated against clinical data, could lead to better informed future clinical trial designs.

Early administration of galantamine from preplaque phase suppresses oxidative stress and improves cognitive behavior in APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease that progressively impairs memory and cognition. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark of AD. Oxidative stress induced by generation of reactive oxygen species (ROS) is a prominent phenomenon in AD and known to occur early in the course of AD. Several reports suggest a relationship between change in redox status and AD pathology including progressive Aβ deposition, glial cell activation, and inflammation. Galantamine is an acetylcholinesterase inhibitor and has been reported to have an oxidative stress inhibitory function. In the present study, galantamine was administered orally to AD model mice from before the appearance of Aβ plaques (preplaque phase), and in vivo change in redox status of the brain was measured using electron paramagnetic resonance (EPR) imaging. Administration of galantamine from the preplaque phase ameliorated memory decline in Morris water maze test and novel object recognition test. Monitoring of the redox status of the brain using EPR imaging showed that galantamine treatment improved the unbalanced redox state. Additionally, galantamine administration enhanced microglial function to promote Aβ clearance, reducing the Aβ-positive area in the cortex and amount of insoluble Aβ in the brain. In contrast, galantamine treatment from the preplaque phase suppressed the production of proinflammatory cytokines through neurotoxic microglial activity. Therefore, galantamine administration from the preplaque phase may have the potential of clinical application for the prevention of AD. In addition, our results demonstrate the usefulness of EPR imaging for speedy and quantitative evaluation of the efficacy of disease-modifying drugs for AD.

Peptides isolated from animal venom as a platform for new therapeutics for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that deeply affects patients, their family and society. Although scientists have made intense efforts in seeking the cure for AD, no drug available today is able to stop AD progression. In this context, compounds isolated from animal venom are potentially successful drugs for neuroprotection, since they selectively bind to nervous system targets. In this review, we presented different studies using peptides isolated from animal venom for the treatment of AD. This is a growing field that will be very helpful in understanding and even curing neurodegenerative diseases, especially AD.

Co-modulation of an allosteric modulator of nicotinic receptor-cholinesterase inhibitor (galantamine) and a 5-HT4 receptor agonist (RS-67333): effect on scopolamine-induced memory deficit in the mouse

AIM

It is widely assumed that the upcoming therapeutics for Alzheimer's disease will require to act on more than one target to be effective. We investigated here whether a combination of the nicotinic receptor allosteric modulator/cholinesterase inhibitor galantamine can act synergistically with the type 4 serotonin receptor (5-HT4R) partial agonist, RS-67333, to counterbalance deficits in short- and long-term memory. To select sub-efficacious doses of both drugs, dose-response studies were first performed on the scopolamine-induced deficits of spontaneous alternation in the Y-maze task and of acquisition and retrieval processes in a passive avoidance task.

RESULT

For spontaneous alternation behavior, combination of 1 mg/kg galantamine and 0.5 mg/kg RS-67333 fully reversed the deficit. In the passive avoidance task, no sub-efficacious doses could be found in the retention paradigm, but a beneficial effect of the association has been demonstrated in the acquisition paradigm.

CONCLUSION

Mnesic effects of galantamine can be thus potentiated by activation of 5-HT4R. Such a combination treatment might (1) strengthen symptomatic relief, (2) attenuate adverse effects given the lower doses of each compound required, and (3) afford a disease-modifying effect given the known action of 5-HT4R on amyloidogenesis cascade.

Acetylcholinesterase Inhibitors and Drugs Acting on Muscarinic Receptors- Potential Crosstalk of Cholinergic Mechanisms During Pharmacological Treatment

BACKGROUND

Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.

METHODS

We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.

RESULTS

Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.

CONCLUSION

Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.

Galantamine and Environmental Enrichment Enhance Cognitive Recovery after Experimental Traumatic Brain Injury But Do Not Confer Additional Benefits When Combined

Environmental enrichment (EE) enhances cognition after traumatic brain injury (TBI). Galantamine (GAL) is an acetylcholinesterase inhibitor that also may promote benefits. Hence, the aims of this study were to assess the efficacy of GAL alone (standard [STD] housing) and in combination with EE in adult male rats after TBI. The hypothesis was that both therapies would confer motor, cognitive, and histological benefits when provided singly, but that their combination would be more efficacious. Anesthetized rats received a controlled cortical impact or sham injury, then were randomly assigned to receive GAL (1, 2, or 3 mg/kg; intraperitoneally [i.p.]) or saline vehicle (VEH; 1 mL/kg; i.p.) beginning 24 h after surgery and once daily for 21 days (experiment 1). Motor (beam-balance/walk) and cognitive (Morris water maze [MWM]) assessments were conducted on post-operative Days 1-5 and 14-19, respectively. Cortical lesion volumes were quantified on Day 21. Sham controls were better versus all TBI groups. No differences in motor function or lesion volumes were observed among the TBI groups (p > 0.05). In contrast, GAL (2 mg/kg) enhanced MWM performance versus VEH and GAL (1 and 3 mg/kg; p < 0.05). In experiment 2, GAL (2 mg/kg) or VEH was combined with EE and the data were compared with the STD-housed groups from experiment 1. EE alone enhanced motor performance over the VEH-treated and GAL-treated (2 mg/kg) STD-housed groups (p < 0.05). Moreover, both EE groups (VEH or GAL) facilitated spatial learning and reduced lesion size versus STD + VEH controls (p < 0.05). No additional benefits were observed with the combination paradigm, which does not support the hypothesis. Overall, the data demonstrate that EE and once daily GAL (2 mg/kg) promote cognitive recovery after TBI. Importantly, the combined therapies did not negatively affect outcome and thus this therapeutic protocol may have clinical utility.

Brain Food at High Altitude

Scenic view at high altitude is a pleasure to the eyes, but it has some shortcoming effects as well. High altitude can be divided into different categories, i.e., high altitude (3000-5000 ft), very high altitude (5000-8000 ft), and extreme altitude (above 8000 ft). Much of the population resides at high altitude, and others go there for tourism. Military personnel are also posted there to defend boundaries. As we ascent to high altitude, partial pressure of oxygen reduces, whereas concentration remains the same; this reduces the availability of oxygen to different body parts. This pathophysiological condition is known as hypobaric hypoxia (HH) which leads to oxidative stress and further causes cognitive dysfunction in some cases. Hypoxia causes neurodegeneration in different brain regions; however, the hippocampus is found to be more prone in comparison to other brain regions. As the hippocampus is affected most, therefore, spatial memory is impaired most during such condition. This chapter will give a brief review of the damaging effect of high altitude on cognition and also throw light on possible herbal interventions at high altitude, which can improve cognitive performance as well as provide protection against the deteriorating effect of hypobaric hypoxia at high altitude.

Assessing the synergy between cholinomimetics and memantine as augmentation therapy in cognitive impairment in schizophrenia. A virtual human patient trial using quantitative systems pharmacology

While many drug discovery research programs aim to develop highly selective clinical candidates, their clinical success is limited because of the complex non-linear interactions of human brain neuronal circuits. Therefore, a rational approach for identifying appropriate synergistic multipharmacology and validating optimal target combinations is desperately needed. A mechanism-based Quantitative Systems Pharmacology (QSP) computer-based modeling platform that combines biophysically realistic preclinical neurophysiology and neuropharmacology with clinical information is a possible solution. This paper reports the application of such a model for Cognitive Impairment In Schizophrenia (CIAS), where the cholinomimetics galantamine and donepezil are combined with memantine and with different antipsychotics and smoking in a virtual human patient experiment. The results suggest that cholinomimetics added to antipsychotics have a modest effect on cognition in CIAS in non-smoking patients with haloperidol and risperidone and to a lesser extent with olanzapine and aripiprazole. Smoking reduces the effect of cholinomimetics with aripiprazole and olanzapine, but enhances the effect in haloperidol and risperidone. Adding memantine to antipsychotics improves cognition except with quetiapine, an effect enhanced with smoking. Combining cholinomimetics, antipsychotics and memantine in general shows an additive effect, except for a negative interaction with aripiprazole and quetiapine and a synergistic effect with olanzapine and haloperidol in non-smokers and haloperidol in smokers. The complex interaction of cholinomimetics with memantine, antipsychotics and smoking can be quantitatively studied using mechanism-based advanced computer modeling. QSP modeling of virtual human patients can possibly generate useful insights on the non-linear interactions of multipharmacology drugs and support complex CNS R&D projects in cognition in search of synergistic polypharmacy.

Effect of galantamine on adjuvant-induced arthritis in rats

Stimulation of the vagus nerve suppresses cytokine production and macrophage activation, via the interaction of its neurotransmitter acetylcholine (ACh) with the α7 subunit of the nicotinic acetylcholine receptor (α7nAChR), present on neurons and inflammatory cells. The present study aimed to verify the potential anti-inflammatory effect of galantamine against experimental arthritis induced in rats. Fourteen days post adjuvant injection, Sprague-Dawley rats were treated orally with three doses of galantamine (1.25, 2.5 and 5 mg/kg) or leflunomide (10 mg/kg) for 2 weeks and arthritis progression was assessed by hind paw swelling. Additionally, serum biomarkers, viz., anti-cyclic citrullinated peptide antibodies (Anti-CCP), tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) were measured. Radiological examination of the hind paws was also carried out to evaluate the degree of joint damage. Adjuvant arthritis led to a significant weight loss, marked swelling of the hind paw and alteration in the serum levels of anti-CCP, TNF-α, IL-10 and MCP-1. These alterations were associated with significant radiological changes of the joints. Galantamine, in a dose-dependent manner, reduced significantly all biomarkers of inflammation, with the highest dose showing the best beneficial anti-inflammatory effect that was superior in magnitude to the reference drug leflunomide in most of the studied parameters. In conclusion, these results suggest that galantamine may represent a novel, inexpensive and effective therapeutic strategy in the treatment of rheumatoid arthritis.

Targeting brain α7 nicotinic acetylcholine receptors in Alzheimer's disease: rationale and current status

Alzheimer's disease (AD) is the most common form of dementia among older persons. Pathognomonic hallmarks of the disease include the development of amyloid senile plaques and deposits of neurofibrillary tangles. These changes occur in the brain long before the clinical manifestations of AD (cognitive impairment in particular) become apparent. Nicotinic acetylcholine receptors (AChRs), particularly the α7 subtype, are highly expressed in brain regions relevant to cognitive and memory functions and involved in the processing of sensory information. There is strong evidence that implicates the participation of AChRs in AD. This review briefly introduces current strategies addressing the pathophysiologic findings (amyloid-β-peptide plaques, neurofibrillary tangles) and then focuses on more recent efforts of pharmacologic intervention in AD, specifically targeted to the α7 AChR. Whereas cholinesterase inhibitors such as donepezil, galantamine, or rivastigmine, together with the non-competitive N-methyl-D-aspartate receptor antagonist memantine are at the forefront of present-day clinical intervention for AD, new insights into AChR molecular pharmacology are bringing other drugs, directed at AChRs, to center stage. Among these are the positive allosteric modulators that selectively target α7 AChRs and are aimed at unleashing the factors that hinder agonist-mediated, α7 AChR channel activation. This calls for more detailed knowledge of the distribution, functional properties, and involvement of AChRs in various signaling cascades-together with the corresponding abnormalities in all these properties-to be able to engineer strategies in drug design and evaluate the therapeutic possibilities of new compounds targeting this class of neurotransmitter receptors.

Galantamine, an acetylcholinesterase inhibitor and positive allosteric modulator of nicotinic acetylcholine receptors, attenuates nicotine taking and seeking in rats

Current smoking cessation pharmacotherapies have limited efficacy in preventing relapse and maintaining abstinence during withdrawal. Galantamine is an acetylcholinesterase inhibitor that also acts as a positive allosteric modulator of nicotinic acetylcholine receptors. Galantamine has recently been shown to reverse nicotine withdrawal-induced cognitive impairments in mice, which suggests that galantamine may function to prevent relapse in human smokers. However, there are no studies examining whether galantamine administration modulates nicotine self-administration and/or reinstatement of nicotine seeking in rodents. The present experiments were designed to determine the effects of galantamine administration on nicotine taking and reinstatement of nicotine-seeking behavior, an animal model of relapse. Moreover, the effects of galantamine on sucrose-maintained responding and sucrose seeking were also examined to determine whether galantamine's effects generalized to other reinforced behaviors. An inverted U-shaped dose-response curve was obtained when animals self-administered different unit doses of nicotine with the highest responding for 0.03 mg/kg per infusion of nicotine. Acute galantamine administration (5.0 mg/kg, i.p.) attenuated nicotine self-administration when animals were maintained on either a fixed-ratio 5 (FR5) or progressive ratio (PR) schedule of reinforcement. Galantamine administration also attenuated the reinstatement of nicotine-seeking behavior. No significant effects of galantamine on sucrose self-administration or sucrose reinstatement were noted. Acetylcholinesterase inhibitors have also been shown to produce nausea and vomiting in humans. However, at doses required to attenuate nicotine self-administration, no effects of galantamine on nausea/malaise as measured by pica were noted. These results indicate that increased extracellular acetylcholine levels and/or nicotinic acetylcholine receptor stimulation is sufficient to attenuate nicotine taking and seeking in rats and that these effects are reinforcer selective and not due to adverse malaise symptoms such as nausea.

The effects of galantamine on nicotine withdrawal-induced deficits in contextual fear conditioning in C57BL/6 mice

Current smoking cessation aids are relatively ineffective at maintaining abstinence during withdrawal. Nicotine withdrawal is associated with a variety of symptoms including cognitive deficits and targeting these deficits may be a useful strategy for maintaining abstinence. Galantamine is an acetylcholinesterase inhibitor and allosteric modulator of nicotinic acetylcholine receptors (nAChRs) with cognitive enhancing effects that may alleviate cognitive deficits associated with nicotine withdrawal. The effects of galantamine on nicotine withdrawal-induced deficits in contextual fear conditioning in C57BL/6 mice were examined. An initial acute dose-response experiment revealed that 0.5 and 1mg/kg galantamine had no effect on fear conditioning. To determine if galantamine would reverse nicotine withdrawal-related deficits in contextual fear conditioning, mice were implanted with osmotic mini-pumps that delivered chronic saline or 6.3mg/kg/d nicotine for 12 days and then pumps were removed. Training and testing of fear conditioning occurred 24 and 48 h later, respectively. Nicotine withdrawal disrupted contextual fear conditioning, which was reversed with 1 but not 0.5mg/kg galantamine. Across all conditions in both studies 2mg/kg galantamine led to high levels of freezing that were likely due to nonspecific effects. The ability of galantamine to reverse nicotine withdrawal-deficits in contextual conditioning is likely mediated through enhanced levels of acetylcholine via inhibition of acetylcholinesterase, potentiation of hippocampal α4β2* nAChRs, or both. The present study suggests that acetylcholinesterase inhibitors and/or drugs that act as allosteric modulators of nAChRs might be targets for smoking cessation aids because they may alleviate withdrawal symptoms such as cognitive deficits that can lead to relapse.

Galantamine potentiates the protective effect of rofecoxib and caffeic acid against intrahippocampal Kainic acid-induced cognitive dysfunction in rat

Role of neuroinflammatory mediators particularly cyclooxygenase (COX), lipoxygenase (LOX), have been well suggested in the pathophysiology of neurodegenerative disorders. Rofecoxib is a selective cyclooxygenase 2 enzymes belongs to non-steroidal anti-inflammatory drug, commonly called as coxibs. Whereas, caffeic acid (3,4-dihydroxycinnamic acid) is one of the natural phenolic compounds and reported to inhibit 5-lipoxygenase (5-LOX) activity as one of mechanisms. Present study has been designed to investigate the effects of rofecoxib, caffeic acid and its potentiation by galantamine against intrahippocampal kainic acid-induced cognitive impairment, oxidative damage and mitochondrial respiratory enzyme alterations in rats. Kainic acid (KA) was administrated in the hippocampus region of rat brain. Various behavioral (locomotor activity and memory performances were assessed by using actophotometer and Morris water maze respectively) followed by oxidative stress, mitochondrial enzyme complex were assessed. Intrahippocampal administration of KA significantly impaired locomotor activity, memory performance, mitochondrial enzyme complexes and caused oxidative stress as compared to sham treatment. Rofecoxib (5 and 10mg/kg), caffeic acid (5 and 10mg/kg), Gal (2.5 and 5mg/kg) treatment for 14 days significantly improved locomotor activity, memory retention and oxidative defense (as evidenced by decrease lipid peroxidation, nitrite, increased superoxide dismutase activity and redox ratio) in hippocampus. Besides, alterations in the levels of mitochondrial enzymes and acetylcholine esterase enzyme were significantly restored by rofecoxib and caffeic acid as compared to control. Further, combination of rofecoxib (5mg/kg) with caffeic acid (5mg/kg) and lower dose of gal (2.5mg/kg) with rofecoxib (5mg/kg) treatments significantly potentiated their protective effect which was significant as compared to their effect per se. The results of the present study suggest that galantamine potentiates the protective effect of rofecoxib and caffeic acid against kainic acid induced cognitive impairment and associated oxidative damage.

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.

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.

Galantamine inhibits beta-amyloid aggregation and cytotoxicity

The ability of galantamine (Reminyl) to inhibit the aggregation and toxicity of the beta-amyloid peptide (Abeta) was investigated. Galantamine showed concentration-dependent inhibition of aggregation of both Abeta 1-40 and Abeta 1-42, as determined by an ELISA method. Electron microscope studies of Abeta 1-40 incubated in the presence of galantamine revealed fibrils that were disordered and clumped in appearance. MTT and lactate dehydrogenase assays, employing SH-SY5Y human neuroblastoma cells, showed that galantamine reduced the cytotoxicity induced by Abeta 1-40. Galantamine also dramatically reduced Abeta 1-40-induced cellular apoptosis in these cells. There is some evidence that galantamine may not be acting purely as a symptomatic treatment. Disease-modifying effects of the drug could be due to an additional effect on Abeta aggregation and/or toxicity.

PET imaging of the in vivo brain acetylcholinesterase activity and nicotine binding in galantamine-treated patients with AD

The effect of galantamine treatment on cortical acetylcholinesterase (AChE) activity and nicotinic receptor binding was investigated by positron emission tomography (PET) in 18 patients with mild Alzheimer's disease (AD) in relation to galantamine concentration and the patients' cognitive performances. The first 3 months of the study was of a randomized double-blind placebo-controlled design, during which 12 patients received galantamine (16-24mg/day) and 6 patients the placebo, and this was followed by 9 months' galantamine treatment in all patients. The patients underwent PET examinations to measure cortical AChE activity ((11)C-PMP) and (11)C-nicotine binding. Neuropsychological tests were performed throughout the study. Inhibition (30-40%) of cortical AChE activity was observed after 3 weeks to 12 months of galantamine treatment. No significant change in mean cortical (11)C-nicotine binding was observed during the study. (11)C-Nicotine binding, however, positively correlated with plasma galantamine concentration. Both the changes of AChE activity and (11)C-nicotine binding correlated positively with the results of a cognitive test of attention. In conclusion, galantamine caused sustained AChE inhibition for up to 12 months. At the individual level, the in vivo cortical AChE inhibition and (11)C-nicotine binding were associated with changes in the attention domain of cognition rather than episodic memory.

Impairments in trace EB conditioning by knife-cut lesions to the fornix in rabbits: Reversal by galantamine

Previous work in our laboratory demonstrated that galantamine, a cholinesterase inhibitor and weak cholinergic agonist, facilitated classical trace eyeblink conditioning in healthy, young rabbits [Simon, B. B., Knuckley, B., & Powell, D. A. (2004). Galantamine facilitates acquisition of a trace-conditioned eyeblink response in healthy, young rabbits. Learning & Memory, 11(1), 116-122.]. The current study investigated the effects of galantamine (0.0 or 3.0mg/kg) in rabbits sustaining knife-cut lesions to the fimbria-fornix, a major projection pathway connecting the hippocampus to cortical and subcortical brain structures involved in the formation of long-term memories. Two experiments were conducted. Experiment one assessed the effects of knife-cut lesions to the fornix or sham surgeries on trace eyeblink (EB) conditioning. Results indicate that fornix lesions significantly retarded EB conditioning when trace parameters were employed. Experiment 2 assessed whether treatment with galantamine would reverse the deficits caused by fornix damage. Results indicate that 3.0mg/kg GAL reversed trace EB conditioning deficits in animals with fornix knife-cut lesions. These findings suggest that galantamine may provide benefit in the reversal of cognitive dysfunction following certain types of brain damage, especially damage involving hippocampal structures.

Inhibition of acetylcholinesterase in CSF versus brain assessed by 11C-PMP PET in AD patients treated with galantamine

The relationship between acetylcholinesterase (AChE) activity in the CSF and brain of patients with Alzheimer's disease (AD) was investigated in 18 mild AD patients following galantamine treatment. The first 3 months of the study had a randomized double-blind placebo-controlled design, during which 12 patients received galantamine (16-24 mg/day) and six patients placebo. This was followed by 9 months galantamine treatment in all patients. Activities and protein levels of both the "read-through" AChE (AChE-R) and the synaptic (AChE-S) variants in CSF were assessed in parallel together with the regional brain AChE activity by (11)C-PMP and PET. The AChE-S inhibition was 30-36% in CSF, which correlated well with the in vivo AChE inhibition in the brain. No significant AChE inhibition was observed in the placebo group. The increased level of the AChE-R protein was 16% higher than that of AChE-S. Both the AChE inhibition and the increased level of AChE-R protein positively correlated with the patient's performance in cognitive tests associated with visuospatial ability and attention. In conclusion, AChE levels in CSF closely mirror in vivo brain AChE levels prior to and after treatment with the cholinesterase inhibitors. A positive cognitive response seems to dependent on the AChE inhibition level, which is balanced by an increased protein level of the AChE-R variant in the patients.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Acetylcholine nicotinic receptors: finding the putative binding site of allosteric modulators using the "blind docking" approach

Allosteric potentiation of acetylcholine nicotinic receptors is considered to be one of the most promising approaches for the treatment of Alzheimer's disease. However, the exact localization of the allosteric binding site and the potentiation mechanism at the molecular level are presently unknown. We have performed the "blind docking" of three known allosteric modulators (galanthamine, codeine and eserine) with the Acetylcholine Binding Protein and models of human alpha7, alpha3beta4 and alpha4beta2 nicotinic receptors, created by homology modeling. Three putative binding sites were identified in the channel pore, each one showing different affinities for the ligands. One of these sites is localized opposite to the agonist binding site and is probably implicated in the potentiation process. On the basis of these results, a possible mechanism for nicotinic acetylcholine receptor (nAChRs) activation is proposed. The present findings may represent an important advance for understanding the allosteric modulation mechanism of nAChRs. [Figure: see text].

The Effect of Galantamine Added to Clozapine on Cognition of Five Patients With Schizophrenia

Although clozapine may be beneficial for the treatment of cognitive dysfunction in schizophrenia, it may also impair some cognitive skills as a result of its anticholinergic activity. In this case series, the impact of galantamine administration on 5 patients with schizophrenia who had been treated with clozapine are reported. Neuropsychological assessment was administered before and after 8 weeks of 16 mg/d galantamine treatment. In this case series, galantamine was well tolerated by all of the patients. Three of the patients were much improved in sustained attention tasks. Most of the patients were also improved in psychomotor speed and selective attention tasks. Two patients with low pretreatment memory scores seemed to also be improved. Our results suggest that the possible role of galantamine as a cognitive enhancer in schizophrenia should be investigated in controlled trials.

Pharmacotherapeutic approaches to the treatment of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD), a progressive degenerative disorder of the brain, is the most common cause of cognitive impairment in the elderly. The pharmacotherapy of AD is evolving rapidly. Cholinergic stabilization with cholinesterase-inhibitor (ChEI) therapy implies neuroprotection and a resultant slowing of disability and disease progression. The moderate-affinity N-methyl-d-aspartate (NMDA)-receptor antagonist memantine may block neural excitotoxicity.

OBJECTIVE

The purpose of this review was to examine the evidence for the responsiveness to pharmacotherapy of established AD; specifically, the extent to which the benefits of therapy have been proved, the extent to which currently available ChEIs support cholinergic neurotransmission, and the extent to which currently available ChEIs and memantine provide neuroprotection.

METHODS

Relevant studies were identified through a comprehensive search of MEDLINE for articles published between January 1999 and February 2004 using the terms Alzheimer's pharmacotherapy, cholinesterase inhibitor therapy, Alzheimer's disease, donepezil, rivastigmine, galantamine, glutamatergic system modifiers, and memantine; a search of the reference lists of identified articles; and a manual search of pertinent journals. Articles were selected that contained higher-level evidence, based on explicit validated criteria.

RESULTS

ChEI therapy was associated with quality-of-life improvements that included enhanced performance of activities of daily living, reduced behavioral disturbances, stabilized cognitive impairment, decreased caregiver stress, and delay in the first dementia-related nursing home placement. In large clinical trials in moderate to severe AD (a stage that is associated with distress for patients and caregiver burden, and for which other treatments are not available), memantine showed an ability to delay cognitive and functional deterioration. The combination of memantine and ChEI therapy was significantly more efficacious than ChEI therapy alone (P < 0.001) and was well tolerated.

CONCLUSIONS

The idea that AD is pharmacologically unresponsive appears to be changing. With the use of ChEI and NMDA-receptor antagonist therapy, the symptoms and outcomes of this devastating neurodegenerative disease can be improved and its course altered.

Galantamine facilitates acquisition of a trace-conditioned eyeblink response in healthy, young rabbits

Previous work has demonstrated that drugs increasing brain concentrations of acetylcholine can enhance cognition in aging and brain-damaged organisms. The present study assessed whether galantamine (GAL), an allosteric modulator of nicotinic cholinergic receptors and weak acetylcholinesterase inhibitor, could improve acquisition and retention of an eyeblink (EB) classical conditioning task in healthy, young animals. We trained 24 rabbits (n = 8/group) in a 1000-msec trace Pavlovian EB conditioning paradigm in which a tone conditioned stimulus (CS) was presented for 500 msec, followed by a 500-msec trace period in which no stimuli were presented. A 100-msec corneal airpuff was the unconditioned stimulus (US). Acquisition sessions, consisting of 100 trials each, occurred daily for 10 consecutive days, followed by 3 d of extinction training. Animals were treated with one of three doses of GAL (0.0-3.0 mg/kg) prior to each session. Animals that received 3.0 mg/kg GAL showed significantly more EB conditioned responses (CRs) in fewer training trials than animals receiving either 1.5 mg/kg GAL or vehicle injections. GAL had no effect on CR performance during extinction. Pseudoconditioning control experiments, consisting of 200 explicitly unpaired tone-puff presentations indicated that GAL did not increase reactivity to the CS or US. These findings indicate that GAL may improve acquisition of moderately difficult associative learning tasks in healthy young organisms.