Effect of subchronic administration of metrifonate, rivastigmine and donepezil on brain acetylcholine in aged F344 rats

Long-Term Acetylcholinesterase Depletion Alters the Levels of Key Synaptic Proteins while Maintaining Neuronal Markers in the Aging Zebrafish (Danio rerio) Brain

INTRODUCTION

Interventions targeting cholinergic neurotransmission like acetylcholinesterase (AChE) inhibition distinguish potential mechanisms to delay age-related impairments and attenuate deficits related to neurodegenerative diseases. However, the chronic effects of these interventions are not well described.

METHODS

In the current study, global levels of cholinergic, cellular, synaptic, and inflammation-mediating proteins were assessed within the context of aging and chronic reduction of AChE activity. Long-term depletion of AChE activity was induced by using a mutant zebrafish line, and they were compared with the wildtype group at young and old ages.

RESULTS

Results demonstrated that AChE activity was lower in both young and old mutants, and this decrease coincided with a reduction in ACh content. Additionally, an overall age-related reduction in AChE activity and the AChE/ACh ratio was observed, and this decline was more prominent in wildtype groups. The levels of an immature neuronal marker were upregulated in mutants, while a glial marker showed an overall reduction. Mutants had preserved levels of inhibitory and presynaptic elements with aging, whereas glutamate receptor subunit levels declined.

CONCLUSION

Long-term AChE activity depletion induces synaptic and cellular alterations. These data provide further insights into molecular targets and adaptive responses following the long-term reduction of AChE activity that was also targeted pharmacologically to treat neurodegenerative diseases in human subjects.

Effects of 3R, 16S-2-hydroxyethyl apovincaminate (HEAPO), donepezil and galantamine on learning and memory retention in naïve Wistar rats

The effects of 3R,16S-2-hydroxyethyl apovincaminate (HEAPO, RGH-10885) compared with those of two cholinesterase inhibitors, donepezil and galantamine, were examined in naïve Wistar rats using standard active and passive avoidance tests. The active avoidance test (shuttle box) and two passive avoidance tests (step-through and step-down) were performed according to the experimental design. There were 10 groups of rats (n = 8) and the substances studied were applied orally before each testing session. In the active avoidance test, the number of conditioned stimuli (avoidances), unconditioned stimuli (escapes) and intertrial crossings were observed. In step-down and step-through passive avoidance tests, the latencies of reactions were observed. All the studied compounds showed positive effects in the learning and memory tests, compared to the controls. It was concluded that HEAPO, donepezil and galantamine had a memory-enhancing effect in active and passive avoidance tests.

Increased Hippocampal-Inferior Temporal Gyrus White Matter Connectivity following Donepezil Treatment in Patients with Early Alzheimer's Disease: A Diffusion Tensor Probabilistic Tractography Study

The incidence of Alzheimer's disease (AD) has been increasing each year, and a defective hippocampus has been primarily associated with an early stage of AD. However, the effect of donepezil treatment on hippocampus-related networks is unknown. Thus, in the current study, we evaluated the hippocampal white matter (WM) connectivity in patients with early-stage AD before and after donepezil treatment using probabilistic tractography, and we further determined the WM integrity and changes in brain volume. Ten patients with early-stage AD (mean age = 72.4 ± 7.9 years; seven females and three males) and nine healthy controls (HC; mean age = 70.7 ± 3.5 years; six females and three males) underwent a magnetic resonance (MR) examination. After performing the first MR examination, the patients received donepezil treatment for 6 months. The brain volumes and diffusion tensor imaging scalars of 11 regions of interest (the superior/middle/inferior frontal gyrus, the superior/middle/inferior temporal gyrus, the amygdala, the caudate nucleus, the hippocampus, the putamen, and the thalamus) were measured using MR imaging and DTI, respectively. Seed-based structural connectivity analyses were focused on the hippocampus. The patients with early AD had a lower hippocampal volume and WM connectivity with the superior frontal gyrus and higher mean diffusivity (MD) and radial diffusivity (RD) in the amygdala than HC (p < 0.05, Bonferroni-corrected). However, brain areas with a higher (or lower) brain volume and WM connectivity were not observed in the HC compared with the patients with early AD. After six months of donepezil treatment, the patients with early AD showed increased hippocampal-inferior temporal gyrus (ITG) WM connectivity (p < 0.05, Bonferroni-corrected).

Characterization of Orange Peel Extract and Its Potential Protective Effect against Aluminum Chloride-Induced Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Hence, developing an effective treatment or protective agent is crucial for public health. The present study aims to characterize orange peel extract (OPE) through in vitro and in silico studies. Furthermore, it examines the protective effect of OPE against experimentally-induced Alzheimer's disease in rats. The total phenolic and flavonoid content of OPE was 255.86 ± 1.77 and 52.06 ± 1.74 (mg/100 g), respectively. Gallic acid, the common polyphenol in OPE detected by HPLC was 3388.60 μg/100 g. OPE antioxidant IC₅₀ was 67.90 ± 1.05, 60.48 ± 0.91, and 63.70 ± 0.30 by DPPH, ABTS and Hydroxyl radical scavenging activity methods, respectively. In vitro anti-acetylcholinesterase (AChE) IC₅₀ was 0.87 ± 0.025 mg/mL for OPE and 2.45 ± 0.001 mg/mL for gallic acid. Molecular docking analysis for human AChE (4EY7) with donepezil, gallic acid, and acetylcholine showed binding energy ΔG values of -9.47, -3.72, and -5.69 Kcal/mol, respectively. Aluminum chloride injection (70 mg/Kg/day for 6 weeks) induced Alzheimer's-like disease in male rats. OPE (100 and 200 mg/kg/d) and gallic acid (50 mg/kg/d) were administered orally to experimental animals for 6 weeks in addition to aluminum chloride injection (as protective). OPE was found to protect against aluminum chloride-induced neuronal damage by decreasing both gene expression and activity of acetylcholinesterase (AChE) and a decrease in amyloid beta (Aβ42) protein level, thiobarbituric acid-reactive substances (TBARS), and nitric oxide (NO), and increased reduced glutathione (GSH) level and activity of the antioxidant enzymes in the brain tissues. Additionally, gene expressions for amyloid precursor protein (APP) and beta secretase enzyme (BACE1) were downregulated, whereas those for presinilin-2 (PSEN2) and beta cell lymphoma-2 (BCL2) were upregulated. Furthermore, the reverse of mitochondrial alternation and restored brain ultrastructure might underlie neuronal dysfunction in AD. In conclusion, our exploration of the neuroprotective effect of OPE in vivo reveals that OPE may be helpful in ameliorating brain oxidative stress, hence protecting from Alzheimer's disease progression.

Antimuscarinic Cascade Across Individual Cholinesterase Inhibitors in Older Adults with Dementia

BACKGROUND

Acetylcholinesterase inhibitors (AChEIs) have been associated with an increased risk of starting antimuscarinic treatment to treat overactive bladder (OAB)-an example of a prescribing cascade. Limited comparative data exist regarding the prescribing cascade of antimuscarinics across individual AChEIs in older adults with dementia.

OBJECTIVE

This study examined the association between individual AChEI use and antimuscarinic cascade in older adults with dementia.

METHODS

We conducted a new user retrospective cohort study from January 2005 to December 2018 using data from the TriNetX electronic medical record database, a federated electronic medical records network in the US. The cohort included patients 65 years or older with a diagnosis of dementia using AChEIs (donepezil, galantamine, or rivastigmine). Individual AChEIs were identified with index dates from 1 January 2006 to 31 June 2018, with a 1-year washout period. The study excluded patients with any antimuscarinic use and OAB diagnosis 1 year before the AChEI index date. The primary outcome of interest was the prescription of antimuscarinics within 6 months of the AChEI index date. A Cox proportional hazard model was used to assess the association between individual incident AChEI use and antimuscarinic prescribing cascade after controlling for several covariates.

RESULTS

The study included 47,059 older adults with dementia who were incident users of AChEIs. Most of these patients were initiated with donepezil (83.1%), followed by rivastigmine (12.3%) and galantamine (4.6%). Overall, 8.16% of the study cohort had incident OAB diagnosis or antimuscarinic prescription. Antimuscarinics were initiated by 1725 (3.7%) older adults with dementia within 6 months of AChEI prescription, and cascade varied widely across individual agents-donepezil (3.9%), rivastigmine (2.6%), and galantamine (2.9%). Cox proportional hazard analyses revealed that donepezil users had an increased risk of receiving antimuscarinics (adjusted hazard ratio 1.55, 95% confidence interval 1.31-1.83) compared with rivastigmine. The findings were consistent in sensitivity analyses.

CONCLUSION

This study found that donepezil use is more likely to lead to antimuscarinic cascade than rivastigmine. Future studies are needed to determine the potential consequences of this cascade in dementia.

Exploring the Multifunctional Neuroprotective Promise of Rasagiline Derivatives for Multi-Dysfunctional Alzheimer's Disease

Alzheimer's disease (AD) is a chronic, age-related, and irreversible brain disorder that typically develops slowly and gets worse over time. The potent auspicious drug candidate for the treatment of AD is supposed to perform the simultaneous modulation of several targets linked to AD. The new therapeutic approach involves drug candidates that are designed to act on multiple targets and have various pharmacological properties. This trend has triggered the development of various multimodal drugs including TV-3326 (i.e. ladostigil) and M-30 (i.e. a new multitarget iron chelator). TV-3326 combines the neurorestorative/neuroprotective effects of the cholinesterase (ChE) inhibitory activity of rivastigmine with rasagiline (a selective monoamine oxidase-B inhibitor and novel antiparkinsonian agent) in a single molecule. M-30, the second derivative of rasagiline, was developed by combining the propargyl moiety of rasagiline into the skeleton of VK-28 (i.e. a novel brain permeable neuroprotective iron chelator). It has been revealed that both the compounds possess anti-AD effects and therefore, the clinical development is directed to the treatment of this type of neurodegenerative diseases (NDs). In this article, we have reviewed the neuroprotective molecular mechanisms and multimodal effects of TV-3326 and M-30.

White Matter Connectivity and Gray Matter Volume Changes Following Donepezil Treatment in Patients With Mild Cognitive Impairment: A Preliminary Study Using Probabilistic Tractography

The donepezil treatment is associated with improved cognitive performance in patients with mild cognitive impairment (MCI), and its clinical effectiveness is well-known. However, the impact of the donepezil treatment on the enhanced white matter connectivity in MCI is still unclear. The purpose of this study was to evaluate the thalamo-cortical white matter (WM) connectivity and cortical thickness and gray matter (GM) volume changes in the cortical regions following donepezil treatment in patients with MCI using probabilistic tractography and voxel-based morphometry. Patients with MCI underwent magnetic resonance examinations before and after 6-month donepezil treatment. Compared with healthy controls, patients with MCI showed decreased WM connectivity of the thalamo-lateral prefrontal cortex, as well as reduced thickness in the medial/lateral orbitofrontal cortices (p < 0.05). The thalamo-lateral temporal cortex connectivity in patients with MCI was negatively correlated with Alzheimer's disease assessment scale-cognitive subscale (ADAS-cog) (r = −0.76, p = 0.01). The average score of the Korean version of the mini-mental state examination (K-MMSE) in patients with MCI was improved by 7.9% after 6-months of donepezil treatment. However, the patterns of WM connectivity and brain volume change in untreated and treated patients were not significantly different from each other, resulting from multiple comparison corrections. These findings will be valuable in understanding the neurophysiopathological mechanism on MCI as a prodromal phase of Alzheimer's disease in connection with brain functional connectivity and morphometric change.

A pilot study of brain morphometry following donepezil treatment in mild cognitive impairment: volume changes of cortical/subcortical regions and hippocampal subfields

The efficacy of donepezil is well known for improving the cognitive performance in patients with mild cognitive impairment (MCI) and Alzheimer’s disease (AD). Most of the recent neuroimaging studies focusing on the brain morphometry have dealt with the targeted brain structures, and thus it remains unknown how donepezil treatment influences the volume change over the whole brain areas including the cortical and subcortical regions and hippocampal subfields in particular. This study aimed to evaluate overall gray matter (GM) volume changes after donepezil treatment in MCI, which is a prodromal phase of AD, using voxel-based morphometry. Patients with MCI underwent the magnetic resonance imaging (MRI) before and after 6-month donepezil treatment. The cognitive function for MCI was evaluated using the questionnaires of the Korean version of the mini-mental state examination (K-MMSE) and Alzheimer’s disease assessment scale-cognitive subscale (ADAS-Cog). Compared with healthy controls, patients with MCI showed significantly lower GM volumes in the hippocampus and its subfields, specifically in the right subiculum and left cornu ammonis (CA3). The average scores of K-MMSE in patients with MCI improved by 8% after donepezil treatment. Treated patients showed significantly higher GM volumes in the putamen, globus pailldus, and inferior frontal gyrus after donepezil treatment (p < 0.001). However, whole hippocampal volume in the patients decreased by 0.6% after 6-month treatment, and the rate of volume change in the left hippocampus was negatively correlated with the period of treatment. These findings will be useful for screening and tracking MCI, as well as understanding of the pathogenesis of MCI in connection with brain morphometric change.

TV 3326 for Alzheimer's dementia: a novel multimodal ChE and MAO inhibitors to mitigate Alzheimer's-like neuropathology

OBJECTIVES

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders and a well-recognized cause of dementia with ageing. In this review, we have represented the ChE and MAO inhibitory potential of TV 3326 against AD based on current scientific evidence.

KEY FINDINGS

The aetiology of AD is quite complex and not completely understood. However, it has been observed that AD involves the deposition of abnormal amyloid beta (Aβ), along with hyperphosphorylation of tau, oxidative stress, low acetylcholine (ACh) level and biometal dyshomeostasis. Due to the complex nature of AD aetiology, active research is required in the areas of development of multitarget drugs with 2 or more complementary biological functions, as they might represent significant progress in the AD treatment. Interestingly, it has been found that TV 3326 (i.e. ladostigil) is regarded as a novel therapeutic agent since it has the potential to cause inhibition of monoamine oxidase (MAO) A and B, and acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the brain. Furthermore, it has the capacity to reverse memory impairments, which further suggests the ability of this drug to elevate cholinergic activity in the brain.

SUMMARY

TV 3326 can avert oxidative-nitrative stress and gliosis. It has also been confirmed that TV 3326 contains neuroprotective and anti-apoptotic properties. Therefore, this distinctive combined inhibition of ChE and MAO along with its neuroprotective property makes TV 3326 a useful drug in the treatment of AD.

Targeted acetylcholinesterase-responsive drug carriers with long duration of drug action and reduced hepatotoxicity

PURPOSE

Acetylcholinesterase (AChE) plays a critical role in the transmission of nerve impulse at the cholinergic synapses. Design and synthesis of AChE inhibitors that increase the cholinergic transmission by blocking the degradation of acetylcholine can serve as a strategy for the treatment of AChE-associated disease. Herein, an operational targeted drug delivery platform based on AChE-responsive system has been presented by combining the unique properties of enzyme-controlled mesoporous silica nanoparticles (MSN) with clinical-used AChE inhibitor.

METHODS

Functionalized MSNs were synthesized by liquid phase method and characterized by using different analytical methods. The biocompatibility and cytotoxicity of MSNs were determined by hemolysis experiment and MTT assay, respectively. Comparison of AChE activity between drug-loading system and inhibitor was developed with kits and by ELISA method. The efficacy of drug-loaded nanocarriers was investigated in a mouse model.

RESULTS

Compared with AChE inhibitor itself, the inhibition efficiency of this drug delivery system was strongly dependent on the concentration of AChE. Only AChE with high concentration could cause the opening of pores in the MSN, leading to the controlled release of AChE inhibitor in disease condition. Critically, the drug delivery system can not only exhibit long duration of drug action on AChE inhibition but also reduce the hepatotoxicity in vivo.

CONCLUSION

In summary, AChE-responsive drug release systems have been far less explored. Our results would shed lights on the design of enzyme controlled-release multifunctional system for enzyme-associated disease treatment.

Co-treatment with rivastigmine and idalopirdine reduces the propensity for falls in a rat model of falls in Parkinson's disease

RATIONALE

Falls in patients with Parkinson's disease (PD) are associated with cognitive, specifically attentional impairments and with losses in cholinergic projection systems. We previously established an animal model of the combined basal forebrain cholinergic-striatal dopaminergic losses of PD fallers (Dual Lesioned, DL, rats) and demonstrated that treating DL rats with an acetylcholinesterase inhibitor (AChEI), donepezil, together with a 5HT₆ receptor antagonist, idalopirdine, reduced fall frequency and improved associated aspects of the performance of DL rats traversing rotating rods.

OBJECTIVES

Here, we employed a longer and more taxing rotating beam apparatus to determine the potential therapeutic efficacy of idalopirdine when combined with the pseudo-irreversible, and thus relatively long-acting, AChE- and butyrylcholinesterase- (BuChE) inhibitor rivastigmine.

RESULTS

As before, vehicle-treated DL rats fell more frequently, committed more slips, and exhibited more movement stoppages than intact control rats. Repeated intermittent administration of rivastigmine and idalopirdine significantly improved the performance of DL rats. Rivastigmine alone also produced strong trends for reducing falls and slips. The combination treatment was more effective than rivastigmine alone in reducing stoppages and stoppage-associated falls. As before, idalopirdine treatment alone was ineffective.

CONCLUSIONS

These results extend the prediction that the combined treatment with idalopirdine and an AChEI improves complex movement control and reduces the propensity for falls in patients with movement disorders. Because of the importance of finding better treatments for gait and balance deficits in PD, the present results may further motivate a clinical exploration of the usefulness of this combination treatment.

Cholinergic Modification of Neurogenesis and Gliosis Improves the Memory of AβPPswe/PSEN1dE9 Alzheimer's Disease Model Mice Fed a High-Fat Diet

We previously reported that neuroinflammation contributes to the amnesia of AβPPswe/PSEN1dE9 Alzheimer's disease model mice fed a high-fat diet to induce type-2 diabetes (T2DM-AD mice), but the underlying mechanism for the memory decline remained unclear. Recent studies have suggested that cholinergic modulation is involved in neuroinflammatory cellular reactions including neurogenesis and gliosis, and in memory improvement. In this study, we administered a broad-spectrum cholinesterase inhibitor, rivastigmine (2 mg/kg/day, s.c.), into T2DM-AD mice for 6 weeks, and evaluated their memory performance, neurogenesis, and neuroinflammatory reactions. By two hippocampal-dependent memory tests, the Morris water maze and contextual fear conditioning, rivastigmine improved the memory deterioration of the T2DM-AD mice (n = 8, p < 0.01). The number of newborn neurons in the hippocampal dentate gyrus was 1138±324 (Ave±SEM) in wild-type littermates, 2573±442 in T2DM-AD-Vehicle, and 2165±300 in T2DM-AD-Rivastigmine mice, indicating that neurogenesis was accelerated in the two T2DM-AD groups (n = 5, p < 0.05). The dendritic maturation of new neurons in T2DM-AD-Vehicle mice was severely abrogated, and rivastigmine treatment reversed this retarded maturation. In addition, the hippocampus of T2DM-AD-Vehicle mice showed increased proinflammatory cytokines IL-1β and TNF-α and gliosis, and rivastigmine treatment blocked these inflammatory reactions. Rivastigmine did not change the insulin abnormality or amyloid pathology in these mice. Thus, cholinergic modulation by rivastigmine treatment led to enhanced neurogenesis and the suppression of gliosis, which together ameliorated the memory decline in T2DM-AD model mice.

Synergistic enhancing-memory effect of donepezil and S 47445, an AMPA positive allosteric modulator, in middle-aged and aged mice

Positive allosteric modulators of AMPA receptors (AMPA-PAMs) are described to facilitate cognitive processes in different memory-based models. Among them, S 47445 is a novel potent and selective AMPA-PAM. In order to assess its efficacy after repeated administration, S 47445 effect was evaluated in two aging-induced memory dysfunction tasks in old mice, one short-term working memory model evaluated in a radial maze task and one assessing contextual memory performance. S 47445 was shown to improve cognition in both models sensitive to aging. In fact, administration of S 47445 at 0.3 mg/kg (s.c.) reversed the age-induced deficits of the working memory model whatever the retention interval. Moreover, in the contextual task, S 47445 also reversed the age-induced deficit at all tested doses (from 0.03 to 0.3 mg/kg, p.o.). Since donepezil, an acetylcholinesterase inhibitor, induces only moderate symptomatic effects on memory in Alzheimer's disease patients, an alternative strategy for treatment of cognitive symptoms could be to act simultaneously on both glutamatergic AMPA receptors and cholinergic pathways by combining pharmacological treatments. The present study further examined such effects by assessing combinations of S 47445 and donepezil given orally during 9 days in aged C57/Bl6J mice using contextual memory task (CSD) and the working memory model of serial alternation task (AT). Interestingly, a significant synergistic memory-enhancing effect was observed with the combination of donepezil at 0.1 mg/kg with S 47445 at 0.1 mg/kg p.o. in the CSD or with S 47445 at 0.1 and 0.3 mg/kg in AT in comparison to compounds given alone and without any pharmacokinetic interaction.

Scopolamine disrupts place navigation in rats and humans: a translational validation of the Hidden Goal Task in the Morris water maze and a real maze for humans

RATIONALE

Development of new drugs for treatment of Alzheimer's disease (AD) requires valid paradigms for testing their efficacy and sensitive tests validated in translational research.

OBJECTIVES

We present validation of a place-navigation task, a Hidden Goal Task (HGT) based on the Morris water maze (MWM), in comparable animal and human protocols.

METHODS

We used scopolamine to model cognitive dysfunction similar to that seen in AD and donepezil, a symptomatic medication for AD, to assess its potential reversible effect on this scopolamine-induced cognitive dysfunction. We tested the effects of scopolamine and the combination of scopolamine and donepezil on place navigation and compared their effects in human and rat versions of the HGT. Place navigation testing consisted of 4 sessions of HGT performed at baseline, 2, 4, and 8 h after dosing in humans or 1, 2.5, and 5 h in rats.

RESULTS

Scopolamine worsened performance in both animals and humans. In the animal experiment, co-administration of donepezil alleviated the negative effect of scopolamine. In the human experiment, subjects co-administered with scopolamine and donepezil performed similarly to subjects on placebo and scopolamine, indicating a partial ameliorative effect of donepezil.

CONCLUSIONS

In the task based on the MWM, scopolamine impaired place navigation, while co-administration of donepezil alleviated this effect in comparable animal and human protocols. Using scopolamine and donepezil to challenge place navigation testing can be studied concurrently in animals and humans and may be a valid and reliable model for translational research, as well as for preclinical and clinical phases of drug trials.

The Synergistic Enhancing-Memory Effect of Donepezil and S 38093 (a Histamine H3 Antagonist) Is Mediated by Increased Neural Activity in the Septo-hippocampal Circuitry in Middle-Aged Mice

Donepezil, an acetylcholinesterase inhibitor, induces only moderate symptomatic effects on memory in Alzheimer’s disease patients. An alternative strategy for treatment of cognitive symptoms could be to act simultaneously on both histaminergic and cholinergic pathways, to create a synergistic effect. To that aim, 14 month old C57/Bl6 mice were administered per oesophagy during nine consecutive days with Donepezil (at 0.1 and 0.3 mg/kg) and S 38093 (at 0.1, 0.3, and 1.0 mg/kg), a H3 histaminergic antagonist developed by Servier, alone or in combination and tested for memory in a contextual memory task that modelized the age-induced memory dysfunction. The present study shows that the combination of Donepezil and S 38093 induced a dose-dependent synergistic memory-enhancing effect in middle-aged mice with a statistically higher size of effect never obtained with compounds alone and without any pharmacokinetic interaction between both compounds. We demonstrated that the memory-enhancing effect of the S 38093 and Donepezil combination is mediated by its action on the septo-hippocampal circuitry, since it canceled out the reduction of CREB phosphorylation (pCREB) observed in these brain areas in vehicle-treated middle-aged animals. Overall, the effects of drug combinations on pCREB in the hippocampus indicate that the synergistic promnesiant effects of the combination on memory performance in middle-aged mice stem primarily from an enhancement of neural activity in the septo-hippocampal system.

Differential metformin dose-dependent effects on cognition in rats: role of Akt

RATIONAL

Epidemiological evidence suggests that individuals with diabetes mellitus are at greater risk of developing Alzheimer's disease, and controversy overwhelms the usefulness of the widely prescribed insulin-sensitizing drug, metformin, on cognition.

OBJECTIVES

Through the scopolamine-induced memory deficit model, we investigated metformin influence on cognitive dysfunction and explored underlying mechanisms.

METHODS

Sixty adult male Wistar rats were randomly assigned into 5 groups (12 rats each) to receive either normal saline, scopolamine 1 mg/kg intraperitoneally once daily, scopolamine + oral metformin (100 mg/kg/day), scopolamine + oral metformin (300 mg/kg/day) or scopolamine + oral rivastigmine (0.75 mg/kg/day) for 14 days. Cognitive behaviours were tested using Morris water maze and passive avoidance tasks. Biochemically, brain oxidative (malondialdehyde) and inflammatory (TNF-α) markers, nitric oxide, Akt, phospho-Akt, phospho-tau and acetyl cholinesterase activity in hippocampal and cortical tissues were assessed.

RESULTS

The lower dose of metformin (100 mg/kg) ameliorated scopolamine-induced impaired performance in both Morris water maze and passive avoidance tasks, and was associated with significant reduction of inflammation and to a lesser extent oxidative stress versus rivastigmine. Given the role of total Akt in regulation of abnormal tau accumulation and degradation, our finding that metformin 100 decreased the elevated total Akt while increasing its phosphorylated form explains its beneficial modulatory effect on phosphorylated tau in both tissues, and could further clarify its protection against memory impairment.

CONCLUSION

Metformin, only in the average human antidiabetic dose, offers a protective effect against scopolamine-induced cognitive impairment, while no deleterious effect was observed with the higher dose, which may support a bonus effect of metformin in type 2 diabetic patients.

Effect of Donepezil, Tacrine, Galantamine and Rivastigmine on Acetylcholinesterase Inhibition in Dugesia tigrina

Dugesia tigrina is a non-parasitic platyhelminth, which has been recently utilized in pharmacological models, regarding the nervous system, as it presents a wide sensitivity to drugs. Our trials aimed to propose a model for an in vivo screening of substances with inhibitory activity of the enzyme acetylcholinesterase. Trials were performed with four drugs commercialized in Brazil: donepezil, tacrine, galantamine and rivastigmine, utilized in the control of Alzheimer's disease, to inhibit the activity of acetylcholinesterase. We tested five concentrations of the drugs, with an exposure of 24 h, and the mortality and the inhibition of acetylcholinesterase planarian seizure-like activity (pSLA) and planarian locomotor velocity (pLMV) were measured. Galantamine showed high anticholinesterasic activity when compared to the other drugs, with a reduction of 0.05 μmol·min(-1) and 63% of convulsant activity, presenting screw-like movement and hypokinesia, with pLMV of 65 crossed lines during 5 min. Our results showed for the first time the anticholinesterasic and convulsant effect, in addition to the decrease in locomotion induced by those drugs in a model of invertebrates. The experimental model proposed is simple and low cost and could be utilized in the screening of substances with anticholinesterasic action.

Neuronal AChE splice variants and their non-hydrolytic functions: redefining a target of AChE inhibitors?

AChE enzymatic inhibition is a core focus of pharmacological intervention in Alzheimer's disease (AD). Yet, AChE has also been ascribed non-hydrolytic functions, which seem related to its appearance in various isoforms. Neuronal AChE presents as a tailed form (AChE-T) predominantly found on the neuronal synapse, and a facultatively expressed readthough form (AChE-R), which exerts short to medium-term protective effects. Notably, this latter form is also found in the periphery. While these non-hydrolytic functions of AChE are most controversially discussed, there is evidence for them being additional targets of AChE inhibitors. This review aims to provide clarification as to the role of these AChE splice variants and their interplay with other cholinergic parameters and their being targets of AChE inhibition: AChE-R is particularly involved in the mediation of (anti-)apoptotic events in cholinergic cells, involving adaptation of various cholinergic parameters and a time-dependent link to the expression of neuroprotective factors. The AChE-T C-terminus is central to AChE activity regulation, while isolated AChE-T C-terminal fragments mediate toxic effects via the α7 nicotinic acetylcholine receptor. There is direct evidence for roles of AChE-T and AChE-R in neurodegeneration and neuroprotection, with these roles involving AChE as a key modulator of the cholinergic system: in vivo data further encourages the use of AChE inhibitors in the treatment of neurodegenerative conditions such as AD since effects on both enzymatic activity and the enzyme's non-hydrolytic functions can be postulated. It also suggests that novel AChE inhibitors should enhance protective AChE-R, while avoiding the concomitant up-regulation of AChE-T.

Cholinesterase inhibitors for the treatment of Alzheimer's disease:: getting on and staying on

BACKGROUND

Cholinesterase (ChE) inhibitors currently used in the treatment of Alzheimer's disease (AD) are the acetylcholinesterase (AChE)-selective inhibitors, donepezil and galantamine, and the dual AChE and butyrylcholinesterase (BuChE) inhibitor, rivastigmine. In addition to differences in selectivity for AChE and BuChE, ChE inhibitors also differ in pharmacokinetic and pharmacodynamic properties, and these differences could significantly impact on safety, tolerability, and efficacy.

OBJECTIVE

The aim of this article was to provide an overview of the ChE inhibitors widely used in AD, focusing on key pharmacologic differences among agents and how these may translate into important differences in safety, tolerability, and efficacy in clinical practice.

METHODS

Using published literature collected over time by the author, a review was conducted, focusing on the pharmacology and clinical data of donepezil, galantamine, and rivastigmine.

RESULTS

All ChE inhibitors have the potential to induce centrally mediated cholinergic adverse events (AEs), such as nausea and vomiting, if the dose is increased too rapidly or in increments that are too large. These AEs, which are most likely to occur during the "getting on," or dose-escalation, phase of treatment, may result in patients discontinuing treatment early without achieving optimum therapeutic benefit. To reduce the incidence of these AEs, a slow dose-escalation schedule has been established in clinical practice, consisting of a "start low, go slow" procedure with a minimum of 4 weeks between dose increases. After "getting on" treatment, maintaining treatment in the long term, or "staying on," may be achieved with good safety, tolerability, and sustained symptomatic efficacy across the key symptom domains (activities of daily living, behavior, and cognition).

CONCLUSIONS

ChE inhibitors provide symptomatic benefit in AD across key symptom domains. Factors influencing the safety, tolerability, and efficacy of these agents in clinical practice include ChE enzymes inhibited, brain and brain-region ChE selectivity, and metabolism route. Class-specific cholinergic AEs can be minimized using slow, flexible dose escalation.

Enhanced brain distribution and pharmacodynamics of rivastigmine by liposomes following intranasal administration

Alzheimer's disease (AD) is a common progressive neurodegenerative disorder associated with cholinergic neurons degeneration. The blood-brain barrier (BBB) not only provides protection for the brain but also hinders the treatment and diagnosis of this neurological disease, because the drugs must cross BBB to reach the lesions. The present work was aimed at formulating rivastigmine liposomes (Lp) and cell-penetrating peptide (CPP) modified liposomes (CPP-Lp) to improve rivastigmine distribution in brain and proceed to enhance pharmacodynamics by intranasal (IN) administration and minimize side effects. The results revealed that Lp especially the CPP-Lp can enhance the permeability across the BBB by murine brain microvascular endothelial cells model in vitro. IN administration of rivastigmine solution and rivastigmine liposomes demonstrated the capacity to improve rivastigmine distribution and adequate retention in CNS regions especially in hippocampus and cortex, which were the regions most affected by AD, than that of IV administration. Importantly, the lagging but intense inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities were relative to the extended release, absorption and retention. In addition, there was very mild nasal toxicity of liposomal formulations. The data suggest that rivastigmine liposomes especially CPP-Lp improve the brain delivery and enhance pharmacodynamics which respect to BBB penetration and nasal olfactory pathway into brain after IN administration, and simultaneously decrease the hepatic first pass metabolism and gastrointestinal adverse effects.

Tacrine-induced tachyphylaxis in gastric smooth muscles

Tacrine is a medication applied in cases of mild to moderate dementia in Alzheimer’s disease. By blocking acetylcholinesterase activity the drug increases the concentration of acetylcholine, whose effects influence the functions of different organs and systems of the body. The effect of tacrine on smooth muscle preparations isolated from rat stomach was studied by isometric registration of muscle contractility. Our investigations found a specific significant systematic decrease in the strength of consecutive tacrine-induced contractions of smooth muscle preparations, a phenomenon known as tachyphylaxis. The tacrineinduced tachyphylaxis was significantly inhibited by SQ22536 (inhibitor of adenylate cyclase activity), by blockers of nitric oxide synthase and KT5823 (inhibitor of protein kinase G). The process was not influenced by cyclopiazonic acid (specific blocker of sarco/endoplasmic reticulum Ca2+-ATPase,) and atropine (blocker of M-cholinergic receptors). We hypothesize that the overlapping and different time-development of the two opposing processes: smooth muscle contraction caused by acetylcholinesterase inhibition and tacrine-induced relaxation influenced by synthesis of nitric oxide, results in tachyphylaxis.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Acute but not chronic donepezil increases muscarinic receptor-mediated signaling via arachidonic acid in unanesthetized rats

Donepezil, an acetylcholinesterase (AChE) inhibitor used for treating Alzheimer's disease patients, is thought to act by increasing brain extracellular acetylcholine (ACh), and ACh binding to cholinergic receptors. Muscarinic receptors are coupled to cytosolic phospholipase A2 (cPLA2) activation and arachidonic acid (AA) release from synaptic membrane phospholipid. This activation can be imaged in rodents as an AA incorporation coefficient k*, using quantitative autoradiography. Acute and chronic effects of donepezil on the AA signal, k* for AA, were measured in 81 brain regions of unanesthetized rats. Twenty min after a single oral dose (3.0 mg/kg) of donepezil, k* was increased significantly in 37 brain regions, whereas k* did not differ from control 7 h afterwards or following chronic (21 days) of donepezil. Pretreatment with atropine prevented the 20-min increments in k* following donepezil. Donepezil also increased the brain ACh concentration and reduced brain AChE activity, but did not change cPLA2 activity, regardless of administration regimen. These results show that donepezil acutely increases the brain AA signal that is mediated by ACh acting at muscarinic receptors, but that this signal is rapidly desensitized despite continued elevated brain ACh concentration. In contrast, the AA signal in response to arecoline was not altered following donepezil.

Effects of cholinesterase inhibitors on rat nicotinic receptor levels in vivo and in vitro

Cholinesterase inhibitors (ChEIs) are the mainstay of treatment for AD but differ by secondary mechanisms of action. We determine the effects of sub-chronic dosing of ChEIs on alpha7 and non-alpha7 nAChRs and determine if differences can be observed between them. Sprague-Dawley rats were administered donepezil, galantamine; rivastigmine at two doses each, in saline SQ twice daily or with nicotine (0.4 mg/kg) as a positive control. After 14 days the animals were sacrificed, and the levels of nAChRs were measured using [3H]-EPI to measure non-alpha7 nAChRs and [3H]-MLA to measure alpha7 nAChRs. In the cortex, all compounds tested at the higher doses significantly increased the levels of both [3H]-EPI and [3H]-MLA. In the hippocampus all compounds significantly increased [3H]-EPI but had no effect on [3H]-MLA binding. No effects were observed in the striatum with treatment. There were no differences observed among the ChEIs. In cell cultures, none of the ChEIs increased non-alpha7 or alpha7 receptor binding. Treatment with ChEIs result in similar increases in receptor levels which suggest that the increases in nAChRs may be due simply to the increases in synaptic levels of acetylcholine.

The effects of rivastigmine plus selegiline on brain acetylcholinesterase, (Na, K)-, Mg-ATPase activities, antioxidant status, and learning performance of aged rats

We investigated the effects of rivastigmine (a cholinesterase inhibitor) and selegiline ((-)deprenyl, an irreversible inhibitor of monoamineoxidase-B), alone and in combination, on brain acetylcholinesterase (AChE), (Na(+), K(+))-, Mg(2+)-ATPase activities, total antioxidant status (TAS), and learning performance, after long-term drug administration in aged male rats. The possible relationship between the biochemical and behavioral parameters was evaluated.

METHODS

Aged rats were treated (for 36 days) with rivastigmine (0.3 mg/kg rat/day ip), selegiline (0.25 mg/kg rat/day im), rivastigmine plus selegiline in the same doses and way of administration as separately. Aged and adult control groups received NaCl 0.9% 0.5 ml ip.

RESULTS

TAS was lower in aged than in adult rats, rivastigmine alone does not affect TAS, decreases AChE activity, increases (Na(+), K(+))-ATPase and Mg(2+)-ATPase activity of aged rat brain and improves cognitive performance. Selegiline alone decreases free radical production and increases AChE activity and (Na(+), K(+))-ATPase activity, improving cognitive performance as well. In the combination: rivastigmine seems to cancel selegiline action on TAS and AChE activity, while it has additive effect on (Na(+), K(+))-ATPase activity. In the case of Mg(2+)-ATPase selegiline appears to attenuate rivastigmine activity. No statistically significant difference was observed in the cognitive performance.

CONCLUSION

Reduced TAS, AChE activity and learning performance was observed in old rats. Both rivastigmine and selesiline alone improved performance, although they influenced the biochemical parameters in a different way. The combination of the two drugs did not affect learning performance.

Comparative effects of the alpha7 nicotinic partial agonist, S 24795, and the cholinesterase inhibitor, donepezil, against aging-related deficits in declarative and working memory in mice

INTRODUCTION

The comparative effects of a newly described specific alpha7 nAChR partial agonist, S 24795, and a cholinesterase inhibitor, donepezil, currently used as a symptomatic Alzheimer's disease treatment were studied in two mouse models of aging-related memory deficits.

MATERIALS AND METHODS

We employed radial arm-maze paradigms assessing short-term working memory (STWM, experiment A) and mnemonic flexibility, a cardinal property of long-term declarative (LTDM, experiment B). Both compounds were administered daily at 0.3 and 1 mg/kg subcutaneously (~3 weeks).

RESULTS

In the STWM experiment, vehicle-treated aged mice displayed a severe and persistent deficit in the retention of successive arm visits in comparison to younger controls. S 24795 at 1 mg/kg (trends at 0.3 mg/kg) and donepezil at 0.3 mg/kg (but not 1 mg/kg) exerted beneficial effects on this deficit: The performance of aged mice treated with these drugs remarkably increased across the testing days and almost reached young adult performance level. In the critical test trials of memory flexibility (i.e., LTDM), in experiment B, S 24795 at 1 mg/kg (trends at 0.3 mg/kg) and donepezil at the dose of 1 mg/kg (but not 0.3 mg/kg) improved aged mice performance.

CONCLUSION

This preclinical demonstration that S 24795 restored specific age-related memory deficits with as much efficacy as donepezil adds to recent literature in highlighting the potential interest of an alpha7 nAChR drug as a symptomatic AD therapeutic.

Effects of cholinesterase inhibitor metrifonate on naive rats and rats with a model of hypoxia-induced impaired memory

Cholinesterase inhibitors are currently used in the therapy of different kind of dementia to improve brain memory functions. The acetylcholinesterase inhibitor metrifonate was studied in naive rats and in rats with a model of sodium nitrite-induced hypoxia. One active avoidance test and in two passive avoidance tests were used. In the active avoidance test metrifonate increased the number of avoidances during the learning session only. In both passive avoidance tests, metrifonate prolonged latency differently during the learning session and in short-term or in long-term memory retention. Hypoxic rats showed lower numbers of avoidances in learning and memory retention sessions. Metrifonate increased the number of avoidances during the learning session for hypoxic rats. In the step-through passive avoidance test, metrifonate increased the latency of reactions in the learning session and in long-term memory retention tests. In the step-down passive avoidance test, the groups with hypoxia and metrifonate did not change the latency of reaction in the learning and long-term memory retention sessions, but increased the latency of reactions in the short-term memory retention test. Morphological data showed a significant impaired neuronal structure in a CA1 zone of the hippocampus in hypoxic rats and a tendency to preserving in rats treated with metrifonate. Our results suggest that metrifonate improves cognitive functions in naive and in hypoxic rats.

No significant effects of single intravenous, single oral and subchronic oral administration of acetylcholinesterase inhibitors on striatal [123I]FP-CIT binding in rats

PURPOSE

[(123)I]FP-CIT SPECT is a valuable diagnostic tool to discriminate Lewy body dementia from Alzheimer's dementia. To date, however, it is uncertain whether the frequently used acetylcholinesterase inhibitors (AChEIs) by demented patients, have an effect on [(123)I]FP-CIT binding to dopamine transporters (DATs). Earlier animal studies showed a decline of DAT availability after acute intravenous injection of AChEIs. The aim of this study was to investigate effects of single intravenous, single oral and subchronic oral administration of AChEIs on DAT availability in the rat brain as measured by [(123)I]FP-CIT.

METHODS

Biodistribution studies were performed in Wistar rats (n = 5-16 per group). Before [(123)I]FP-CIT injection, rats were injected intravenously with a single dose of the AChEI rivastigmine (2.5 mg/kg body weight) or donepezil (0.5 mg/kg), the DAT-blocker methylphenidate (10 mg/kg) or saline. A second group was orally treated with a single dose of rivastigmine or donepezil (2.5 mg/kg), methylphenidate (10 mg/kg) or saline before injection of [(123)I]FP-CIT. Studies were also performed in rats that were orally treated during 14 consecutive days with either rivastigmine (1 mg/kg daily), donepezil (1.5 mg/kg daily), methylphenidate (2.5 mg/kg) or saline. Brain parts were assayed in a gamma counter, and specific striatum/cerebellum ratios were calculated for the [(123)I]FP-CIT binding to DATs.

RESULTS

No significant effects of either single intravenous, single oral or subchronic oral administration of AChEIs on striatal FP-CIT binding could be detected. Single pretreatment with methylphenidate resulted in an expected significantly lower striatal FP-CIT binding.

CONCLUSION

We conclude that in rats, single intravenous and single or subchronic oral administration of the tested AChEIs does not lead to an important alteration of [(123)I]FP-CIT binding to striatal DATs. Therefore, it is unlikely that these drugs will induce large effects on the interpretation of [(123)I]FP-CIT SPECT scans in routine clinical studies.

N1phenethyl-norcymserine, a selective butyrylcholinesterase inhibitor, increases acetylcholine release in rat cerebral cortex: a comparison with donepezil and rivastigmine

The effects of (-)-N(1)phenethyl-norcymserine (PEC, 5 mk/kg, i.p.) on acetylcholine release and cholinesterase activity in the rat cerebral cortex were compared with those of donepezil (1 mg/kg, i.p.), a selective acetylcholinesterase inhibitor, and rivastigmine (0.6 mg/kg, i.p.), an inhibitor of acetylcholinesterase and butyrylcholinesterase. Acetylcholine extracellular levels were measured by microdialysis coupled with HPLC; acetylcholinesterase and butyrylcholinesterase activity were measured with colorimetric and radiometric methods. It was found that comparable 2-3 fold increases in cortical extracellular acetylcholine level, calculated as areas under the curve, followed the administration of the three drugs at the doses used. At the peak of acetylcholine increase, a 27% acetylcholinesterase inhibition and no butyrylcholinesterase inhibition was found after donepezil (1 mg/kg, i.p) administration. At the same time point, rivastigmine (0.6 mg/kg, i.p.) inhibited acetylcholinesterase by 40% and butyrylcholinesterase by 25%. After PEC (5 mg/kg, i.p.) administration, there was a 39% butyrylcholinesterase inhibition and no effect on acetylcholinesterase. Since in the present study it was also confirmed that in the brain butyrylcholinesterase activity is only about 10% of acetylcholinesterase activity, it is surprising that its partial inhibition is sufficient to increase extracellular acetylcholine levels. The importance of butyrylcholinesterase as a "co-regulator" of synaptic acetylcholine levels should thus be reconsidered.

Acetylcholine release from fetal tissue homotopically grafted to the motoneuron-depleted lumbar spinal cord. An in vivo microdialysis study in the awake rat

Grafts of spinal cord (SC) tissue can survive and develop into the severed SC, but no conclusive data are available concerning the functional activity of transplanted neurons. In the present study, suspensions of prelabeled embryonic ventral SC tissue were grafted to the lumbar SC of rats with motoneuron loss induced by perinatal injection of volkensin. Eight to ten months post-grafting, acetylcholine (ACh) release was measured by microdialysis in awake rats, under either basal or stimulated conditions. In normal animals, baseline ACh output averaged 1.6 pmol/30 microl, it exhibited a 4-fold increase after KCl-induced depolarization or handling, and it was completely inhibited by tetrodotoxin administration. Moreover, ACh levels did not change following acute SC transection performed under anesthesia during ongoing dialysis, suggesting an intrinsic source for spinal ACh. Treatment with volkensin produced a severe (>85%) motoneuronal loss accompanied by a similar reduction in baseline ACh release and almost completely abolished effects of depolarization or handling. In transplanted animals, many motoneuron-like labeled cells were found within and just outside the graft area, but apparently in no case were they able to extend fibers towards the denervated muscle. However, the grafts restored baseline ACh output up to near-normal levels and responded with significantly increased release to depolarization, but not to handling. The present findings indicate that spinal neuroblasts can survive and develop within the motoneuron-depleted SC and release ACh in a near-normal, but apparently non-regulated, manner. This may be of importance for future studies involving intraspinal stem cell grafts.

Donepezil induces a cholinergic sprouting in basocortical degeneration

One of the few currently approved therapies for Alzheimer's disease (AD) consists in the administration of acetylcholinesterase inhibitors, which enhances the lifetime of the neurotransmitter acetylcholine. Despite numerous studies on the symptomatic effect of acetylcholinesterase inhibitors, there is as yet no direct morphological evidence to indicate that they have a neurorestorative action. We investigated the effect of the acetylcholinesterase inhibitor donepezil administered subcutaneously in a rat model of partial unilateral cortical devascularization that induces a loss of the cortical cholinergic terminal network and a retrograde degeneration of the cholinergic projections that originate in the nucleus basalis. For 6 weeks, lesioned and sham-operated rats received a subcutaneous infusion of donepezil (2 mg/kg/day) or vehicle, delivered by osmotic minipumps implanted 2 weeks before the cortical devascularization. In lesioned rats, donepezil treatment increased the number and the size of vesicular acetylcholine transporter immunoreactive boutons in comparison to vehicle treatment. Donepezil had no observable effect on any of these parameters in sham-operated animals. These results show that donepezil mitigates cholinergic neuronal degeneration in vivo. This suggests a neuroplastic activity of this drug and provides evidence for a potential use of donepezil as a disease modifier in neurodegenerative diseases such as AD.

Calcium-independent tacrine-induced relaxation of rat gastric corpus smooth muscles

Tacrine, a non-competitive reversible acetylcholinesterase and butyrylcholineserase inhibitor, caused a concentration-dependent tonic contraction of gastric smooth muscle preparations in the concentration range 1 × 10−7 mol/L – 1 × 10−5 mol/L, whereas concentrations higher than 2 × 10−5 mol/L induced a biphasic effect; a short-time contraction was followed by a prolonged relaxation. To shed some light on the mechanism underlying this untypical relaxation, the amplitude of mechanical reactions caused by tacrine were compared with those of tacrine in the presence of atropine, ipratropium, metrifonate, TTX, nifedipine, D-600, caffeine, apamin, and charybdotoxin. The results obtained revealed that the relaxation was neither cholinergic in nature, nor mediated by the influence of the drug on intramural neuronal structures. It was not influenced by processes inducing changes in cytosolic Ca2+ levels. This assumption was confirmed by experiments with permeabilized muscle preparations that were pre-contracted in a solution with pCa 5.5. Tacrine relaxed the smooth muscles in spite of the constant intracellular Ca2+ concentration resulting from the permeabilization. These findings argue that tacrine at concentrations higher than 2 × 10−5 mol/L has a desensitizing effect on the contractile apparatus of gastric corpus smooth muscle preparations towards Ca2+.

Changes in cerebral neurotransmitters and metabolites induced by acute donepezil and memantine administrations: A microdialysis study

Cholinesterase inhibitors including donepezil, rivastigmine, and galantamine and the N-methyl-D-aspartate (NMDA) antagonist, memantine are the medications currently approved for the treatment of Alzheimer's disease (AD). In addition to their beneficial effects on cognitive and functional domains typically disrupted in AD, these agents have also been shown to slow down the emergence of behavioral and psychotic symptoms associated with this disease. However, the underlying mechanisms for these therapeutic effects remain poorly understood and could involve effects of these medications on non-cholinergic or non-glutamatergic neurotransmitter systems respectively. These considerations prompted us to initiate a series of investigations to examine the acute and chronic effects of donepezil (Aricept (+/-)-2,3-dihydro-5,6-dimethoxy-2-[[1-(phenylmethyl)-4-piperidinyl]methyl]-1H-inden-1-1 hydrochloride and memantine (1-amino-3,5-dimethyladamantane hydrochloride C12H21N.HCl)). The present study focuses on the acute effects of donepezil and memantine on brain extracellular levels of acetylcholine, dopamine, serotonin, norepinephrine and their metabolites. We assayed changes in the ventral and dorsal hippocampus and the prefrontal and medial temporal cortex by microdialysis. Memantine resulted in significant increases in extracellular dopamine (DA), norepinephrine (NE), and their metabolites, in the cortical regions, and in a reduction of DA in the hippocampus. Donepezil produced an increase in extracellular DA in the cortex and in the dorsal hippocampus. Norepinephrine increased in the cortex; with donepezil it increased in the dorsal hippocampus and the medial temporal cortex, and decreased in the ventral hippocampus. Interestingly both compounds decreased extracellular serotonin (5HT) levels. The metabolites of the neurotransmitters were increased in most areas. We also found an increase in extracellular acetylcholine (ACh) by memantine in the nucleus accumbens and the ventral tegmental area. Our results suggest both region and drug specific neurotransmitter effects of these agents as well as some similarities. We conclude that drugs influencing cognitive mechanisms induce changes in a number of neurotransmitters with the changes being both region and drug specific. Release and metabolism are altered and extracellular neurotransmitter levels can be increased or decreased by the drugs. Other studies are in progress to determine the pharmacological effects associated with chronic treatment with these compounds, which may be more pertinent to the clinical situation in which patients take these medications for months or years.

Effects on Cholinergic Markers in Rat Brain and Blood after Short and Prolonged Administration of Donepezil

Donepezil is a selective inhibitor of acetylcholinesterase (AChE) clinically used for treating Alzheimer's disease. Cholinergic effects after short-term exposure of donepezil (up to 12 h) have been extensively studied in rats, but few have addressed the potential long-term effects. After 14 days administration (1x3 mg/kg, decapitation 4 h after the last injection) the cerebral acetylcholine level was increased by 35% and the AChE activity was decreased by 66% and 32% in brain and blood, respectively. No change was detected in choline acetyltransferase activity, or the levels of vesicular acetylcholine transporter, choline transporter, or muscarinic receptors. Expression of various cholinergic genes was unaffected. Preliminary results of AChE activity in human blood showed 60-97% and 43-89% of pre-exposed level after one and three days of donepezil administration (5 mg daily), respectively. In conclusion, donepezil exposure in rats at doses that do not inhibit brain AChE continuously during the day, will not lead to tolerance development.

The neurochemical and behavioral effects of the novel cholinesterase-monoamine oxidase inhibitor, ladostigil, in response to L-dopa and L-tryptophan, in rats

The novel drugs, ladostigil (TV3326) and TV3279, are R and S isomers, respectively, derived from a combination of the carbamate cholinesterase (ChE) inhibitor, rivastigmine, and the pharmacophore of the monoamine oxidase (MAO) B inhibitor, rasagiline. They were developed for the treatment of comorbidity of dementia with Parkinsonism. In the present study, we determined the effects of these drugs on both aminergic neurotransmitter levels and motor behavioral activity in naïve and in L-dopa- or L-tryptophan-induced rats. Chronic treatment of rats with ladostigil (52 mg kg(-1) for 21 days) inhibited hippocampal and striatal MAO A and B activities by >90%, increased striatal levels of dopamine and serotonin, and inhibited striatal ChE activity by approximately 50%. Chronic TV3279 (26 mg kg(-1) for 21 days) similarly inhibited approximately 50% of striatal ChE activity, but did not affect MAO activity or amine levels. In sharp contrast to the inductive effect of the MAO A/B inhibitor, tranylcypromine (TCP), on stereotyped hyperactivity in response to L-dopa (50 mg kg(-1)) or L-tryptophan (100 mg kg(-1)), ladostigil completely inhibited these behavioral hyperactivity syndromes. Accordingly, acute rivastigmine (2 mg kg(-1)) and chronic TV3279 abolished the ability of TCP to initiate L-dopa-induced hyperactivity, while scopolamine (0.5 mg kg(-1)) reversed the inhibitory effect of chronic ladostigil on L-dopa-induced hyperactivity, suggesting that ladostigil may attenuate successive locomotion by activating central cholinergic muscarinic receptors.Finally, while chronic ladostigil administration to naïve rats resulted in preserved spontaneous motor behavior, acute treatment with ladostigil decreased motor performance, compared to control animals. In contrast, chronic as well as acute treatments with TV3279 reduced spontaneous motor activity. Thus, the aminergic potentiation by ladostigil may counteract its cholinergic inhibitory effect on spontaneous motor behavior. Our results suggest that potentiation of both aminergic and cholinergic transmission systems by ladostigil contributes equally to motor behavior performance, which is substantially impaired in comorbidity of dementia with Parkinsonism including dementia with Lewy bodies (DLB).

Effect of oral administration of zanapezil (TAK-147) for 21 days on acetylcholine and monoamines levels in the ventral hippocampus of freely moving rats

Zanapezil (TAK-147 (3-[1benzylpiperdin-4-yl]-1-(2,3,4,5-tetrahydro-1 H-1-benzazepin-8-yl) propan-1-one fumarate)) is a selective acetylcholine (ACh) esterase inhibitor under investigation as a drug for Alzheimer's disease (AD) treatment. In this study, the effects of TAK-147 at 2 mg kg(-1) p.o. for 21 days, compared to donepezil (E2020), on the levels of ACh, catecolamines and indoleamines were investigated in the ventral hippocampus (VH) of freely moving rats by microdialysis-high-performance liquid chromatography. The results revealed that the VH contains 92.05+/-21.97 fmol 20 microl(-1) ACh and the following monoamines levels (pg 30 microl(-1)), norepinephrine (NE) 1.92+/-0.39, epinephrine (Epi) 1.91+/-0.183, 3-methoxy-4-hydroxyphenylglycol (MHPG) 11.53+/-3.22, normetanephrine 3.26+/-0.61, dopamine (DA) 0.77+/-0.23, 3,4-dihydroxyphenylacetic acid (DOPAC) 3.37+/-1.01, homovanillic acid (4-hydroxy-3-methoxyphenylacetic acid; HVA) 4.04+/-0.93, 3-methoxytyramine 0.64+/-0.13, serotonin (5-HT) 0.73+/-0.16 and 5-hydroxyindoleacetic acid (5-HIAA) 313.15+/-18.42. On the 21st day and prior to the last dose, TAK-147 increased ACh, Epi, DA and 5-HT, whereas E2020 increased MHPG, Epi and DA. Following the last dose, TAK-147 increased NE, whereas E2020 increased NE, ACh and 5-HT in addition to their effects prior to the last dose. TAK-147 decreased HVA : DA ratio, but only marginally decreased DOPAC : DA and 5-HIAA : 5-HT ratios. On the other hand, E2020 decreased ratios of HVA : DA, DOPAC : DA (prior to the last dose), and 5-HIAA : 5-HT (90-180 min after the last dose). Both drugs decreased MHPG : NE only at 180 min after the last dose. The results also showed that TAK-147 increased Epi : NE ratio prior to and for 120 min following the last dose, whereas E2020 increased the ratio only before the last dose. The present results show that TAK-147 at a subthreshold dose could differentially increase ACh and 5-HT, compared to MHPG increased by E2020. The last dose of each drug could extend their effects to other monoamines. The increase of the monoamines levels, in addition to that on the ACh, and decrease of their oxidation could be of value in the treatment of the AD, other dementic diseases and the cohort neurological disorders depending on the type of the monoamine underlying the disorder.

Cognitive deficit associated with cholinergic and nerve growth factor down-regulation in experimental allergic encephalomyelitis in rats

Clinical symptoms in multiple sclerosis include cognitive dysfunction. Difficulties in learning and remembering new information represent the most common cognitive deficit and are associated with a general and progressive brain pathology. Possible pathogenetic mechanisms for neuronal damage such as neuroprotective strategies are under active investigation also in experimental allergic encephalomyelitis, the most widely used experimental model for multiple sclerosis. In this paper we demonstrate that a selective deficit in learning and memory performance, as investigated by the Morris water maze test, is a consistent feature in rat encephalomyelitis, which correlates with a decline in choline acetyltransferase activity and nerve growth factor mRNA level in cerebral cortex, hippocampus, and basal forebrain. Treatment aimed to restore acetylcholine content through chronic administration of selective acetylcholinesterase inhibitors (rivastigmine and donepezil) restores cognitive performance, choline acetyltransferase activity, and nerve growth factor mRNA expression.

Brain levels and acetylcholinesterase inhibition with galantamine and donepezil in rats, mice, and rabbits

Galantamine is a rather weak acetylcholinesterase (AChE) inhibitor, currently approved for the symptomatic treatment of Alzheimer's disease, with possible additional allosteric potentiating effects at the nicotinic ACh receptor (nAChR). Earlier data from in vitro biochemical tests suggest that donepezil is 40- to 500-fold more potent than galantamine in inhibiting AChE. In this study, both brain levels and Ki values for AChE inhibition for donepezil and galantamine in rat, mouse, and rabbit after subcutaneous application were determined. Clearance of galantamine from the brain is in general faster that donepezil and is faster in rabbits compared to rats and mice. The brain-to-plasma ratio for galantamine and donepezil, respectively, ranges from 1.2 to 1.5 in the rabbit, 3.3 to 5.2 in the mouse, and 6.6 to 13 in the rat. Galantamine doses between 1.5 and 5 mg/kg are appropriate to reach brain levels within the documented optimal allosteric potentiating ligand dose-response. Ki values of brain AChE inhibition for galantamine and donepezil, respectively, are 7.1 and 2.3 microg/g in rats, 8.3 and 0.65 microg/g for mice, and 19.1 and 1.3 microg/g in rabbits. The data also suggest that for a similar degree of brain AChE inhibition, 3-15 times higher galantamine than donepezil doses are needed.

Cholinesterase inhibitors used in the treatment of Alzheimer's disease: the relationship between pharmacological effects and clinical efficacy

The deficiency in cholinergic neurotransmission in Alzheimer's disease has led to the development of cholinesterase inhibitors as the first-line treatment for symptoms of this disease. The clinical benefits of these agents include improvements, stabilisation or less than expected decline in cognition, function and behaviour. The common mechanism of action underlying this class of agents is an increase in available acetylcholine through inhibition of the catabolic enzyme, acetylcholinesterase. There is substantial evidence that the cholinesterase inhibitors, including donepezil, galantamine and rivastigmine, decrease acetylcholinesterase activity in a number of brain regions in patients with Alzheimer's disease. There is also a significant correlation between acetylcholinesterase inhibition and observed cognitive improvement. However, the cholinesterase inhibitors are reported to have additional pharmacological actions. Rivastigmine inhibits butyrylcholinesterase with a similar affinity to acetylcholinesterase, although it is not clear whether the inhibition of butyrylcholinesterase contributes to the therapeutic effect of rivastigmine. Based on data from preclinical studies, it has been proposed that galantamine also potentiates the action of acetylcholine on nicotinic receptors via allosteric modulation; however, the effects appear to be highly dependent on the concentrations of agonist and galantamine. It is not yet clear whether these concentrations are related to those achieved in the brain of patients with Alzheimer's disease within therapeutic dose ranges. Preclinical studies have shown that donepezil and galantamine also significantly increase nicotinic receptor density, and increased receptor density may be associated with enhanced synaptic strengthening through long-term potentiation, which is related to cognitive function. Despite these differences in pharmacology, a review of clinical data, including head-to-head studies, has not demonstrated differences in efficacy, although they may have an impact on tolerability. It seems clear that whatever the subsidiary modes of action, clinical evidence supporting acetylcholinesterase inhibition as the mechanism by which cholinesterase inhibitors treat the symptoms of Alzheimer's disease is accumulating. Certainly, as a class, the currently approved cholinesterase inhibitors (donepezil, galantamine, rivastigmine and tacrine) provide important benefits in patients with Alzheimer's disease and these drugs offer a significant advance in the management of dementia.

Comparison of the effect of TAK-147 (zanapezil) and E-2020 (donepezil) on extracellular acetylcholine level and blood flow in the ventral hippocampus of freely moving rats

The effects of zanapezil (TAK-147) and donepezil (E2020) on extracellular acetylcholine (ACh) levels were investigated by HPLC-microdialysis of ventral hippocampus (VH) in freely moving intact rats. The results showed that the basal ACh release rate in the VH is 116.7 +/- 12.4 to 158.4 +/- 22.86 fmol/20 microl. At 2, 5 and 10 mg/kg, single p.o., each drug increased ACh level by 9.4%, 106.5%, 50.8% (TAK-147) and 14.8%, 76.1%, 120.94% (E2020), respectively. The ED50 values were 4.52 mg/kg (1.43 - 14.29; R=0.52) and 4.07 mg/kg (1.77 - 9.37; R=0.985) for TAK-147 and E2020, respectively. Analysis of data revealed that the relative TAK-147/E2020 potency ratio is 0.773, but the effect of E2020 was accompanied by more prominent skeletal muscle fasciculation, gnawing, increased defecation and to lesser extent salivation. Moreover, the significant effect of TAK-147 was observed earlier (20 min) than E2020 (60 min). In this study, we also investigated the effect of both drugs at dose of 5 mg/kg p.o. on blood flow in the VH using Laser Doppler Flowmetry. The results showed that the average blood flow rate in the VH is 6.5 +/- 0.9 ml/min/100 g. TAK-147 did not change blood flow, but E2020 increased blood flow in a biphasic manner. The first increment was obtained between 5 and 40 min (11.5 +/- 2.2 to 12.7 +/- 2.2 ml/min/100 g), and the second one 80-105 min (10.7 +/- 1.6 to 13.4 +/- 3.6 ml/min/100 g). In conclusion, the present results indicate that both TAK-147 and E2020 increase ACh level in the VH. E2020 showed greater potency than TAK-147, but it induced more fasciculation and other side effects than TAK-147. Moreover, the blood flow increasing properties of E2020 could be beneficial in some patients with Alzheimer' disease especially those with chronic vascular dementia, but at the same time, it could also indicate less specific ACh increasing activity than TAK-147 and higher risk of cerebral hemorrhage. On the other hand, the fast and specific effect of TAK-147 may be useful for cure of early stages of Alzheimer's disease (AD).

Comparative effects of huperzine A, donepezil and rivastigmine on cortical acetylcholine level and acetylcholinesterase activity in rats

The cholinesterase inhibitors huperzine A, donepezil and rivastigmine were compared for their effects on extracellular acetylcholine concentration and acetylcholinesterase activity in the rat cortex. After i.p. injection, huperzine A (0.25-0.75 micromol/kg), donepezil (2-6 micromol/kg) and rivastigmine (0.75-1.5 micromol/kg) dose-dependently elevated the concentration of acetylcholine. The duration of huperzine A was longest. The time courses of cortical acetylcholinesterase inhibition with middle doses of these agents mirrored the increases of acetylcholine at the same doses. However, acetylcholinesterase inhibition was disproportionately greater after middle dose of rivastigmine than doses of huperzine A and donepezil that increased acetylcholine to a similar extent. Muscle fasciculation appeared only after donepezil with a dose-dependent incidence and intensity. In molar terms, huperzine A was 8- and 2-fold more potent than donepezil and rivastigmine, respectively, in increasing cortical acetylcholine levels, with a longer-lasting effect.

Strategies for continued successful treatment of Alzheimer's disease: switching cholinesterase inhibitors

Cholinesterase (ChE) inhibitors represent the standard therapeutic approach to the treatment of Alzheimer's disease (AD). However, a proportion of patients experience lack or loss of therapeutic benefit with an initial agent, or discontinue due to safety/tolerability issues. In many instances, no alternative treatment is offered once the initial agent has been stopped. Thus, for many patients, the total duration of treatment is relatively short in comparison with the chronic nature of AD. Switching medications is a common therapeutic strategy within many drug classes across many clinical areas following a lack/loss of efficacy or safety/tolerability problems, and is also an increasingly important concept in the management of AD with ChE inhibitors. A number of open-label studies, where patients were switched from donepezil to rivastigmine, have indicated that approximately 50% of patients experiencing a lack/loss of efficacy with donepezil (a selective acetylcholinesterase [AChE] inhibitor) respond to subsequent treatment with rivastigmine (a dual AChE and butyrylcholinesterase inhibitor). In these studies, rivastigmine was well tolerated, and the occurrence of safety/tolerability problems with donepezil was not predictive of similar problems with rivastigmine. In the summer of 2002, leading neurologists and psychiatrists attended a medical experts meeting to discuss the clinical importance of switching ChE inhibitors in AD. The expert panel examined available clinical data, shared clinical experiences, and discussed current clinical guidelines for switching. The panel also aimed to reach consensus on 'whom to switch', 'when to switch' and 'how to switch'. The key findings from that meeting are reported in this review.