Tacrine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in Alzheimer's disease

True or false? Alzheimer's disease is type 3 diabetes: Evidences from bench to bedside

Globally, Alzheimer's disease (AD) is the most widespread chronic neurodegenerative disorder, leading to cognitive impairment, such as aphasia and agnosia, as well as mental symptoms, like behavioral abnormalities, that place a heavy psychological and financial burden on the families of the afflicted. Unfortunately, no particular medications exist to treat AD, as the current treatments only impede its progression.The link between AD and type 2 diabetes (T2D) has been increasingly revealed by research; the danger of developing both AD and T2D rises exponentially with age, with T2D being especially prone to AD. This has propelled researchers to investigate the mechanism(s) underlying this connection. A critical review of the relationship between insulin resistance, Aβ, oxidative stress, mitochondrial hypothesis, abnormal phosphorylation of Tau protein, inflammatory response, high blood glucose levels, neurotransmitters and signaling pathways, vascular issues in AD and diabetes, and the similarities between the two diseases, is presented in this review. Grasping the essential mechanisms behind this detrimental interaction may offer chances to devise successful therapeutic strategies.

Mechanistic insights and emerging therapeutic stratagems for Alzheimer's disease

Alzheimer's disease (AD), a multi-factorial neurodegenerative disorder has affected over 30 million individuals globally and these numbers are expected to increase in the coming decades. Current therapeutic interventions are largely ineffective as they focus on a single target. Development of an effective drug therapy requires a deep understanding of the various factors influencing the onset and progression of the disease. Aging and genetic factors exert a major influence on the development of AD. Other factors like post-viral infections, iron overload, gut dysbiosis, and vascular dysfunction also exacerbate the onset and progression of AD. Further, post-translational modifications in tau, DRP1, CREB, and p65 proteins increase the disease severity through triggering mitochondrial dysfunction, synaptic loss, and differential interaction of amyloid beta with different receptors leading to impaired intracellular signalling. With advancements in neuroscience tools, new inter-relations that aggravate AD are being discovered including pre-existing diseases and exposure to other pathogens. Simultaneously, new therapeutic strategies involving modulation of gene expression through targeted delivery or modulation with light, harnessing the immune response to promote clearance of amyloid deposits, introduction of stem cells and extracellular vesicles to replace the destroyed neurons, exploring new therapeutic molecules from plant, marine and biological sources delivered in the free state or through nanoparticles and use of non-pharmacological interventions like music, transcranial stimulation and yoga. Polypharmacology approaches involving combination of therapeutic agents are also under active investigation for superior therapeutic outcomes. This review elaborates on various disease-causing factors, their underlying mechanisms, the inter-play between different disease-causing players, and emerging therapeutic options including those under clinical trials, for treatment of AD. The challenges involved in AD therapy and the way forward have also been discussed.

Pathophysiological mechanism and natural preventive and therapeutic strategies of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the presence of two types of protein deposits in the brain, amyloid plaques and neurofibrillary tangles. The first one are dense deposits of beta amyloid protein, the second one are dense deposits of the protein tau. These proteins are present in all of our brains, but in AD they act unusually, leading to neuronal degeneration. This review will provide an overview of the AD, including the role of amyloid beta and tau, and mechanisms that lead to the formation of plaques and tangles. The review will also cover the existing researches that have focused on the inhibition of amyloid beta formation, cholinesterase, tau hyperphosphorylation, the pathogenic mechanisms of apoE4, and GSK-3 as a solution that could be used to slow or prevent the disease.

Structural, harmonic force field and vibrational studies of cholinesterase inhibitor tacrine used for treatment of Alzheimer's disease

Different structures of free base (FB), two cationic forms (CA) and three hydrochloride forms (HCl) of cholinesterase inhibitor tacrine used for treatment of Alzheimer 's disease was evaluated using hybrid B3LYP calculations in order to perform their complete vibrational assignments using the scaled harmonic force fields. Structures of anhydrous form of tacrine have been optimized in gas phase and in aqueous solution. The structure of form III HCl is in agreement with the experimental determined by X-ray diffraction while the predicted IR, Raman, ¹H- ¹³C NMR and UV spectra show good correlations with the corresponding experimental ones. Energy values show that the three forms of HCl can exist in both media because these energetic values decrease from 35.15 kJ/mol in gas phase to 5.51 kJ/mol in solution. For the most stable species of tacrine, the following stability order using natural bond orbital (NBO) studies was found: form I HCl > form III HCl > form I CA > FB. CA presents the higher solvation energy value, as reported for hydrochloride species of alkaloids and antihypertensive agents. The structural parameters of form III of HCl present better concordance and corresponds to that experimental observed in the solid phase. Higher topological properties of form III together with the strong N2-H26⋯Cl31 interaction could justify the presence of this form in the solid phase and in solution and the higher stabilities in both media. The gap values support the higher reactivity of form III while FB is the less reactive species in both media. Complete vibrational assignments for FB, CA and HCl species together with the corresponding scaled force constants are reported.

Design, synthesis and biological evaluation of light-driven on-off multitarget AChE and MAO-B inhibitors

Neurodegenerative diseases are multifactorial disorders characterized by protein misfolding, oxidative stress, and neuroinflammation, finally resulting in neuronal loss and cognitive dysfunctions. Nowadays, an attractive strategy to improve the classical treatments is the development of multitarget-directed molecules able to synergistically interact with different enzymes and/or receptors. In addition, an interesting tool to refine personalized therapies may arise from the use of bioactive species able to modify their activity as a result of light irradiation. To this aim, we designed and synthesized a small library of cinnamic acid-inspired isomeric compounds with light modulated activity able to inhibit acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B), with remarkable selectivity over butyrylcholinesterase (BChE) and MAO-A, which have been investigated as the enzyme targets related to Alzheimer's disease (AD). The inhibitory activities were evaluated for the pure E-diastereomers and the E/Z-diastereomer mixtures, obtained upon UV irradiation. Molecular docking studies were carried out to rationalize the differences in the inhibition potency of the E and Z diastereomers of the best performing analogue 1c. Our preliminary findings may open-up the way for developing innovative multitarget photo-switch drugs against neurodegenerative diseases.

Therapeutic Approach to Alzheimer’s Disease: Current Treatments and New Perspectives

Alzheimer’s disease (AD) is the most common cause of dementia. The pathophysiology of this disease is characterized by the accumulation of amyloid-β, leading to the formation of senile plaques, and by the intracellular presence of neurofibrillary tangles based on hyperphosphorylated tau protein. In the therapeutic approach to AD, we can identify three important fronts: the approved drugs currently available for the treatment of the disease, which include aducanumab, donepezil, galantamine, rivastigmine, memantine, and a combination of memantine and donepezil; therapies under investigation that work mainly on Aβ pathology and tau pathology, and which include γ-secretase inhibitors, β-secretase inhibitors, α-secretase modulators, aggregation inhibitors, metal interfering drugs, drugs that enhance Aβ clearance, inhibitors of tau protein hyperphosphorylation, tau protein aggregation inhibitors, and drugs that promote the clearance of tau, and finally, other alternative therapies designed to improve lifestyle, thus contributing to the prevention of the disease. Therefore, the aim of this review was to analyze and describe current treatments and possible future alternatives in the therapeutic approach to AD.

Neuroprotective derivatives of tacrine that target NMDA receptor and acetyl cholinesterase - Design, synthesis and biological evaluation

The complex and multifactorial nature of neuropsychiatric diseases demands multi-target drugs that can intervene with various sub-pathologies underlying disease progression. Targeting the impairments in cholinergic and glutamatergic neurotransmissions with small molecules has been suggested as one of the potential disease-modifying approaches for Alzheimer’s disease (AD). Tacrine, a potent inhibitor of acetylcholinesterase (AChE) is the first FDA approved drug for the treatment of AD. Tacrine is also a low affinity antagonist of N-methyl-D-aspartate receptor (NMDAR). However, tacrine was withdrawn from its clinical use later due to its hepatotoxicity. With an aim to develop novel high affinity multi-target directed ligands (MTDLs) against AChE and NMDAR, with reduced hepatotoxicity, we performed in silico structure-based modifications on tacrine, chemical synthesis of the derivatives and in vitro validation of their activities. Nineteen such derivatives showed inhibition with IC₅₀ values in the range of 18.53 ± 2.09 – 184.09 ± 19.23 nM against AChE and 0.27 ± 0.05 – 38.84 ± 9.64 μM against NMDAR. Some of the selected compounds also protected rat primary cortical neurons from glutamate induced excitotoxicity. Two of the tacrine derived MTDLs, 201 and 208 exhibited in vivo efficacy in rats by protecting against behavioral impairment induced by administration of the excitotoxic agent, monosodium glutamate. Additionally, several of these synthesized compounds also exhibited promising inhibitory activitiy against butyrylcholinesterase. MTDL-201 was also devoid of hepatotoxicity in vivo. Given the therapeutic potential of MTDLs in disease-modifying therapy, our studies revealed several promising MTDLs among which 201 appears to be a potential candidate for immediate preclinical evaluations.

NLX-101, a cortical 5-HT1A receptor biased agonist, reverses scopolamine-induced deficit in the delayed non-matching to position model of cognition

NLX-101 is a selective, high efficacy, biased agonist at post-synaptic cortical 5-HT_1A receptors. We have previously shown that it opposes deficits produced by blockade of NMDA receptors and has pro-cognitive activity of its own. Based on the strong interaction between 5-HT_1A receptors and the central cholinergic system, we tested NLX-101 on scopolamine-induced impairment of cognition in a delayed non-matching to position (DNMTP) model. The cholinesterase inhibitor, tacrine, was used as a comparator. In operant chambers with two retractable levers, male rats were trained to press one randomly presented lever during a "sample" phase. Following a time delay of either 1, 5 or 10 s, both levers were then presented, the rat being required to press the correct lever (i.e. the one not previously presented) to receive a food pellet reward. Scopolamine (0.16 mg/kg i.p.) significantly impaired accuracy (i.e. choice of correct lever) at 5 and 10 s delays. In contrast, NLX-101 (0.04, 0.16, 0.63 mg/kg i.p.) did not worsen accuracy, except at 0.63 mg/kg. Moreover, NLX-101 (0.04 and 0.16 mg/kg) dose-dependently and significantly opposed scopolamine-induced impairment for 5 and 10 s delays, with near-total reversal at 10 s. The acetylcholinesterase inhibitor, tacrine, also opposed scopolamine-induced impairment but was less potent and efficacious, with a single significant effect at 2.5 mg/kg and 5 s delay only. The present data suggest that biased agonism at post-synaptic, cortical 5-HT_1A receptors could prove useful in neurological or neuropsychiatric pathologies characterized by cognitive deficits consecutive to a reduced central cholinergic tone.

Synthesis, characterization, crystal structures, and the biological evaluation of 2-phenylthiazole derivatives as cholinesterase inhibitors

Four 2-phenylthiazole derivatives are synthesized, characterized, and evaluated as cholinesterase inhibitors. The structures of the 2-phenylthiazole derivatives are confirmed by 1H and 13C nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction studies, and Hirshfeld surfaces analysis. Hirshfeld surface analysis of the prepared compounds showed C–H···O intermolecular interactions. The cholinesterase inhibition activities of the synthesized compounds are tested by Ellman’s method. [2-(4-Benzyloxyphenyl)-thiazol-4-yl]-(3,5-dimethylpiperidin-1-yl)-methanone showed the best acetylcholinesterase inhibition activity with an IC50 value of 8.86 µM and the best butyrylcholinesterase inhibition activity with an IC50 value of 1.03 µM. A docking study demonstrates that the same compound interacts with the catalytic anionic site and peripheral anionic site of acetylcholinesterase and the catalytic anionic site of butyrylcholinesterase.

Efficacy of acetylcholinesterase inhibitors in Alzheimer's disease

Alzheimer's disease (AD), the most common cause of adult-onset dementia is characterized by a progressive decline of cognitive functions accompanied by behavioral manifestations. The main class of drugs currently used for the treatment of AD are acetylcholinesterase/cholinesterase inhibitors (ChE-Is). The first ChE-I licensed for symptomatic treatment of AD was tacrine. The ChE-Is currently available in the market are donepezil, rivastigmine and galantamine as tacrine is no longer in use, due to its hepatotoxicity. According to mechanism of action the ChE-Is are classified as short-acting or reversible agents such as tacrine, donepezil, and galantamine, as intermediate-acting or pseudo-irreversible agent such as rivastigmine. Overall, the efficacy of the three ChE-Is available in the market is similar and the benefit of administration of these compounds is mild and may not be clinically significant. Due to gastrointestinal side effects of these drugs, medicinal chemistry and pharmaceutical delivery studies have investigated solutions to improve the pharmacological activity of these compounds. In spite of the limited activity of ChE-Is, waiting for more effective approaches, these drugs still represent a pharmacotherapeutic resource for the treatment of AD. Other approaches in which ChE-Is were investigated is in their use in combination with other classes of drugs such as cholinergic precursors, N-methyl-d-aspartate (NMDA) receptor antagonists and antioxidant agents. After many years from the introduction in therapy of ChE-Is, the combination with other classes of drugs may represent the chance for a renewed interest of ChE-Is in the treatment of adult-onset dementia disorders.

Natural and synthetic drugs used for the treatment of the dementia

This review is devoted to comparative pharmacological analysis of synthetic drugs such as memantine and its isomers, as well as tacrine, velnacrine, rivastigmine, and donepezil, with natural alkaloids, terpenoids, and triterpenoid peroxides, which are used to treat dementia, Alzheimer's and Parkinson's diseases, myasthenia gravis and other neurodegenerative diseases. Recently discovered by French scientists from Marseille triterpenoid hydroperoxides demonstrate high activity as potential therapeutic agents for the treatment of dementia. The information presented in this review is of great interest to pharmacologists, medical chemists, physiologists, neurologists and doctors, as well as for the pharmaceutical industry.

Design and Development of Novel Transdermal Nanoemulgel for Alzheimer’s Disease: Pharmacokinetic, Pharmacodynamic and Biochemical Investigations

Background:

Alzheimer’s disease is a chronic progressive neurodegenerative disorder associated with depletion of acetylcholine. Oral treatment with tacrine hydrochloride; a reversible inhibitor of acetylcholinesterase, finds limited use in Alzheimer’s disease due to frequent dosing, hepatotoxicity and extensive pre-systemic metabolism.

Objectives:

The objective of the study was to evaluate pharmacokinetic, pharmacodynamic, safety and stability profile of transdermal w/o nanoemulsion gel of tacrine hydrochloride and determine its relative bioavailability from transdermal nanogel in contrast to marketed capsule and conventional hydrogel.

Methods:

The optimized nanoemulsion gel NEGT4 (droplet size 156.4 ±0.48 nm, with poly dispersity index 0.36 ±0.4, permeation flux 6.172±2.94 µg/cm2/h across rat skin) was prepared by spontaneous emulsification followed by sonication. NEGT4 contained 7 mg of drug in 10% w/w distilled water, 30% w/w surfactant (Labrafil M) and cosurfactant (Transcutol P) mixture in ratio 1:4 and 60 % Capryol 90 as oily phase thickened with 98.9 mg ethyl cellulose (20 cps). In vivo studies were carried out on male Wistar rats following standard guidelines. Scopolamine was used to induce amnesia in rats which is a characteristic of Alzheimer’s disease. Various formulations were compared by performing pharmacokinetic, histopathological, behavioural and biochemical studies on rats. Stability studies on nanoemulsion gels were carried out in accordance with The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines.

Results:

Pharmacokinetic studies exhibited significantly greater extent of absorption from NEGT4 in comparison to capsule and hydrogel with a 2.18 and 5.26-fold increase respectively. Significant improvement in neurobehavioral parameters was observed with NEGT4 in scopolamine-induced amnesic rats. Biochemical assessment showed superior anti-amnesic activity of NEGT4 through augmentation of antioxidant enzymes, decreased lipid peroxidation and acetylcholinesterase activity. Low value of serum aminotransferase in rats treated with NEGT4 indicated the absence of hepatotoxicity. NEGT4 was found to be non-irritant and possessed a shelf life of 4.11 years.

Conclusion:

Developed nanoemulsion gel of tacrine hydrochloride was found to be safe, stable, and efficacious and has immense potential to be used in the therapy of Alzheimer’s disease.

Alzheimer's Disease Pharmacotherapy in Relation to Cholinergic System Involvement

Alzheimer’s disease, a major and increasing global health challenge, is an irreversible, progressive form of dementia, associated with an ongoing decline of brain functioning. The etiology of this disease is not completely understood, and no safe and effective anti-Alzheimer’s disease drug to prevent, stop, or reverse its evolution is currently available. Current pharmacotherapy concentrated on drugs that aimed to improve the cerebral acetylcholine levels by facilitating cholinergic neurotransmission through inhibiting cholinesterase. These compounds, recognized as cholinesterase inhibitors, offer a viable target across key sign domains of Alzheimer’s disease, but have a modest influence on improving the progression of this condition. In this paper, we sought to highlight the current understanding of the cholinergic system involvement in Alzheimer’s disease progression in relation to the recent status of the available cholinesterase inhibitors as effective therapeutics.

Tacrine and its 7-methoxy derivate; time-change concentration in plasma and brain tissue and basic toxicological profile in rats

The search for tacrine derivatives, as potential Alzheimer´s disease treatment, is still being at the forefront of scientific efforts. 7-MEOTA was found to be a potent, centrally active acetylcholinesterase inhibitor free of the serious side effects observed for tacrine. Unfortunately, a relevant argumentation about pharmacokinetics and potential toxicity is incomplete; information about tacrine derivatives absorption and especially CNS penetration are still rare as well as detailed toxicological profile in vivo. Although the structural changes between these compounds are not so distinctive, differences in plasma profile and CNS targeting were found. The maximum plasma concentration were attained at 18^th min (tacrine; 38.20 ± 3.91 ng/ml and 7-MEOTA; 88.22 ± 15.19 ng/ml) after i.m. application in rats. Although the brain profiles seem to be similar; tacrine achieved 19.34 ± 0.71 ng/ml in 27 min and 7-MEOTA 15.80 ± 1.13 ng/ml in 22 min; the tacrine Kp (AUC_brain/AUC_plasma) fit 1.20 and was significantly higher than 7-MEOTA Kp 0.10. Administration of tacrine and 7-MEOTA showed only mild elevation of some biochemical markers following single p.o. application in 24 hours and 7 days. Also histopathology revealed only mild-to-moderate changes following repeated p.o. administration for 14 days. It seems that small change in tacrine molecule leads to lower ability to penetrate through the biological barriers. The explanation that lower p.o. acute toxicity of 7-MEOTA depends only on differences in metabolic pathways may be now revised to newly described differences in pharmacokinetic and toxicological profiles.

Therapeutic strategies and nano-drug delivery applications in management of ageing Alzheimer's disease

In recent years, the incidental rate of neurodegenerative disorders has increased proportionately with the aging population. Alzheimer's disease (AD) is one of the most commonly reported neurodegenerative disorders, and it is estimated to increase by roughly 30% among the aged population. In spite of screening numerous drug candidates against various molecular targets of AD, only a few candidates - such as acetylcholinesterase inhibitors are currently utilized as an effective clinical therapy. However, targeted drug delivery of these drugs to the central nervous system (CNS) exhibits several limitations including meager solubility, low bioavailability, and reduced efficiency due to the impediments of the blood-brain barrier (BBB). Current advances in nanotechnology present opportunities to overcome such limitations in delivering active drug candidates. Nanodrug delivery systems are promising in targeting several therapeutic moieties by easing the penetration of drug molecules across the CNS and improving their bioavailability. Recently, a wide range of nano-carriers, such as polymers, emulsions, lipo-carriers, solid lipid carriers, carbon nanotubes, metal based carriers etc., have been adapted to develop successful therapeutics with sustained release and improved efficacy. Here, we discuss few recently updated nano-drug delivery applications that have been adapted in the field of AD therapeutics, and future prospects on potential molecular targets for nano-drug delivery systems.

Features and outcomes of drugs for combination therapy as multi-targets strategy to combat Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD), a deleterious neurodegenerative disorder that impairs memory, cognitive functions and may lead to dementia in late stage of life. The pathogenic cause of AD remains incompletely understood and FDA approved drugs are partial inhibitors rather than curative. Most of drugs are synthetic or natural products as galanthamine is an alkaloid obtained from Galanthus spp. Huperzine A, an alkaloid found in Huperzia spp., gingkolides a diterpenoids from Gingko biloba and many ethnobotanicals like Withania somnifera (L.) Dunal., Physostigma venenosum Balf., Bacopa monnieri (L.) Wettst., Centella asiatica (L.) Urb. have been used by traditional Indian, Chinese, and European system of medicines in AD. Clinical significance opioid alkaloid in Papaver somniferum has shown another dimension to this study. Over exploitation of medicinal plants with limited bioactive principles has provided templates to design synthetic drugs in AD e.g. rivastigmine, phenserine, eptastigmine based on chemical structure of physostigmine of Physostigma venenosum Balf. Even ZT-1 a prodrug of Hup A and memogain a prodrug of galantamine has achieved new direction in drug development in AD. All these first-line cholinesterase-inhibitors are used as symptomatic treatments in AD. Single modality of "One-molecule-one-target" strategy for treating AD has failed and so future therapies on "Combination-drugs-multi-targets" strategy (CDMT) will need to address multiple aspects to block the progression of pathogenesis of AD. Besides, cholinergic and amyloid drugs, in this article we summarize proteinopathy-based drugs as AD therapeutics from a variety of biological sources. In this review, an attempt has been made to elucidate the molecular mode of action of various plant products, and synthetic drugs investigated in various preclinical and clinical tests in AD. It also discusses current attempts to formulate a comprehensive CDMT strategy to counter complex pathogenesis in AD.

MATERIALS AND METHODS

Information were collected from classical books on medicinal plants, pharmacopoeias and scientific databases like PubMed, Scopus, GoogleScholar, Web of Science and electronic searches were performed using Cochrane Library, Medline and EMBASE. Also published scientific literatures from Elsevier, Taylor and Francis, Springer, ACS, Wiley publishers and reports by government bodies and documentations were assessed.

RESULTS

60 no. of natural and synthetic drugs have been studied with their significant bioactivities. A decision matrix designed for evaluation of drugs for considering to the hypothetic "CDMT" strategy in AD. We have introduced the scoring pattern of individual drugs and based on scoring pattern, drugs that fall within the scoring range of 18-25 are considered in the proposed CDMT. It also highlights the importance of available natural products and in future those drugs may be considered in CDMT along with the qualified synthetic drugs.

CONCLUSION

A successful validation of the CDMT strategy may open up a debate on health care reform to explore other possibilities of combination therapy. In doing so, it should focus on clinical and molecular relationships between AD and CDMT. A better understanding of these relationships could inform and impact future development of AD-directed treatment strategies. This strategy also involves in reducing costs in treatment phases which will be affordable to a common man suffering from AD.

The concept of hybrid molecules of tacrine and benzyl quinolone carboxylic acid (BQCA) as multifunctional agents for Alzheimer's disease

Novel tacrine-benzyl quinolone carboxylic acid (tacrine-BQCA) hybrids were designed based on multi-target directed ligands (MTLDs) paradigm, synthesized and evaluated in vitro as inhibitors of human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE). Tacrine moiety is represented herein as 7-methoxytacrine, 6-chlorotacrine or unsubstituted tacrine forming three different families of seven members, i.e. 21 compounds in overall. Introducing BQCA, a positive modulator of M1 muscarinic acetylcholine receptors (mAChRs), the action of novel compounds on M1 mAChRs was evaluated via Fluo-4 NW assay on the Chinese hamster ovarian (CHO-M1WT2) cell line. All the novel tacrine-BQCA hybrids were able to block the action of hAChE and hBChE in micromolar to nanomolar range. The hAChE kinetic profile of 5p was found to be mixed-type which is consistent with our docking experiments. Moreover, selected ligands were assessed for their potential hepatotoxicity on HepG2 cell line and presumable permeation through the blood-brain barrier by PAMPA assay. Expected agonistic profile towards M1 mAChRs delivered by BQCA moiety was not confirmed. From all the hybrids, 5o can be highlighted as non-selective cholinesterase inhibitor (hAChE IC₅₀ = 74.5 nM; hBChE IC₅₀ = 83.3 nM) with micromolar antagonistic activity towards M1 mAChR (IC₅₀ = 4.23 μM). A non-selective pattern of cholinesterase inhibition is likely to be valuable during the onset as well as later stages of AD.

The pharmacology of tacrine at N-methyl-d-aspartate receptors

The mechanism of tacrine as a precognitive drug has been considered to be complex and not fully understood. It has been reported to involve a wide spectrum of targets involving cholinergic, gabaergic, nitrinergic and glutamatergic pathways. Here, we review the effect of tacrine and its derivatives on the NMDA receptors (NMDAR) with a focus on the mechanism of action and biological consequences related to the Alzheimer's disease treatment. Our findings indicate that effect of tacrine on glutamatergic neurons is both direct and indirect. Direct NMDAR antagonistic effect is often reported by in vitro studies; however, it is achieved by high tacrine concentrations which are not likely to occur under clinical conditions. The impact on memory and behavioral testing can be ascribed to indirect effects of tacrine caused by influencing the NMDAR-mediated currents via M1 receptor activation, which leads to inhibition of Ca²⁺-activated potassium channels. Such inhibition prevents membrane repolarization leading to prolonged NMDAR activation and subsequently to long term potentiation. Considering these findings, we can conclude that tacrine-derivatives with dual cholinesterase and NMDARs modulating activity may represent a promising approach in the drug development for diseases associated with cognitive dysfunction, such as the Alzheimer disease.

Long-Term Nicergoline Treatment of Mild to Moderate Senile Dementia : Results of a Multicentre, Double-Blind, Placebo-Controlled Study

The efficacy and tolerability of nicergoline were evaluated in a long-term, double-blind, placebo-controlled trial. 108 patients, fulfilling DSM III-R criteria for mild to moderate senile dementia of degenerative, vascular or mixed origin, were selected from a pool of outpatients attending five Italian neurological centres and randomised to receive nicergoline 30mg twice daily (54 patients) or placebo (54 patients) for 12 months. Treatment efficacy on cognitive and behavioural performances was assessed by the Sandoz Clinical Assessment Geriatric scale (SCAG) and Mini Mental State Examination (MMSE), at baseline and after 3, 6, 9 and 12 months of treatment. Investigators and patients or caregivers provided a global evaluation of treatment outcome at study end. The efficacy analysis was carried out on 101 patients (51 nicergoline; 50 placebo) who completed the 12-month study. At study end, the SCAG total score and its clusters showed statistically significant improvement in the nicergoline-treated group compared with placebo-treated patients. The MMSE total score was maintained with nicergoline treatment. Global treatment evaluations, both by physician and patients, were consistently in favour of nicergoline (p < 0.001). Nicergoline was well tolerated; incidence of adverse events (7% in the nicergoline and 2% in the placebo group), withdrawals and haemodynamic changes were comparable with placebo.

Possibility of Acetylcholinesterase Overexpression in Alzheimer Disease Patients after Therapy with Acetylcholinesterase Inhibitors

Acetylcholinesterase is an enzyme responsible for termination of excitatory transmission at cholinergic synapses by the hydrolyzing of a neurotransmitter acetylcholine. Nowadays, other functions of acetylcholinesterase in the organism are considered, for example its role in regulation of apoptosis. Cholinergic nervous system as well as acetylcholinesterase activity is closely related to pathogenesis of Alzheimer disease. The mostly used therapy of Alzheimer disease is based on enhancing cholinergic function using inhibitors of acetylcholinesterase like rivastigmine, donepezil or galantamine. These drugs can influence not only the acetylcholinesterase activity but also other processes in treated organism. The paper is aimed mainly on possibility of increased expression and protein level of acetylcholinesterase caused by the therapy with acetylcholinesterase inhibitors.

Development of 3D-QSAR Model for Acetylcholinesterase Inhibitors Using a Combination of Fingerprint, Molecular Docking, and Structure-Based Pharmacophore Approaches

Acetylcholinesterase (AChE), a serine hydrolase vital for regulating the neurotransmitter acetylcholine in animals, has been used as a target for drugs and pesticides. With the increasing availability of AChE crystal structures, with or without ligands bound, structure-based approaches have been successfully applied to AChE inhibitors (AChEIs). The major limitation of these approaches has been the small applicability domain due to the lack of structural diversity in the training set. In this study, we developed a 3 dimensional quantitative structure-activity relationship (3D-QSAR) for inhibitory activity of 89 reversible and irreversible AChEIs including drugs and insecticides. A 3D-fingerprint descriptor encoding protein-ligand interactions was developed using molecular docking and structure-based pharmacophore to rationalize the structural requirements responsible for the activity of these compounds. The obtained 3D-QSAR model exhibited high correlation value (R(2) = 0.93) and low mean absolute error (MAE = 0.32 log units) for the training set (n = 63). The model was predictive across a range of structures as shown by the leave-one-out cross-validated correlation coefficient (Q(2) = 0.89) and external validation results (n = 26, R(2) = 0.89, and MAE = 0.38 log units). The model revealed that the compounds with high inhibition potency had proper conformation in the active site gorge and interacted with key amino acid residues, in particular Trp84 and Phe330 at the catalytic anionic site, Trp279 at the peripheral anionic site, and Gly118, Gly119, and Ala201 at the oxyanion hole. The resulting universal 3D-QSAR model provides insight into the multiple molecular interactions determining AChEI potency that may guide future chemical design and regulation of toxic AChEIs.

Enduring effects of tacrine on cocaine-reinforced behavior: Analysis by conditioned-place preference, temporal separation from drug reward, and reinstatement

Previous work by our laboratory has shown that tacrine can produce long-lasting reductions in cocaine-reinforced behavior, when administered to rats as daily intravenous infusions over four days. Tacrine causes dose-related liver toxicity in different species, and its manufacture for human use was recently discontinued. This study was conducted to further characterize its actions on cocaine reward. Cocaine-experienced animals that had no contact with drug over one week resumed self-administration at levels similar to their initial baseline. When tacrine was administered over four days which were preceded and followed by washout periods to allow elimination of cocaine and tacrine respectively, subsequent cocaine self-administration was attenuated by more than one-half. Tacrine administered at 10 mg/kg-day as a chronic infusion by osmotic pump did not modify cocaine-induced increases in locomotor activity or conditioned-place preference. In rats that exhibited persistent attenuation of cocaine-self-administration after receiving tacrine, cocaine-induced reinstatement was also attenuated. No changes in plasma measures of renal or hepatic function were observed in rats receiving tacrine. In conclusion, pretreatment with tacrine can decrease cocaine-motivated behavior measured by self-administration or reinstatement, but not conditioned-place preference. Reductions in cocaine self-administration following pretreatment with tacrine do not require direct interaction with cocaine and are not secondary to either liver or kidney toxicity.

Managing memory impairment in patients with Alzheimer’s disease

SUMMARY Memory impairment in patients with Alzheimer’s disease (AD) may be treated with cholinesterase inhibitors. Attention, alertness, initiative and memory (indirectly) may be treated with memantine. In addition to pharmacologic treatments, nonpharmacologic treatments, including external systems and devices, participation in social activities and exercise, as well as the use of habits, pictures and strategies, improve memory. We believe that although memory loss cannot be halted, both pharmacologic and nonpharmacologic treatments may help to improve AD patients’ memory and allow them to continue independent activities. Patients with mild cognitive impairment due to AD may be treated with nonpharmacologic therapies and with off-label cholinesterase inhibitors.

Hypolipidemic and weight reducing activity of the ethanolic extract of Tamarindus indica fruit pulp in cafeteria diet- and sulpiride-induced obese rats

Objectives:

To investigate the effect of ethanolic extract of fruit pulp of Tamarindus indica Linn. (Family: Caesalpiniaceae) on obesity in rats using cafeteria diet-induced obesity and antipsychotic drug (sulpiride)-induced obesity.

Materials and Methods:

Cafeteria dietwas administered for 40 successive days to male Wistar rats and sulpiride (20 mg/kg, i.p.) was administered for 28 successive days to female Wistar rats. In separate groups of animals, the ethanolic extract (50 and 100 mg/kg p.o.) of Tamarindus indica fruit was administered along with cafeteria diet for 40 successive days to Wistar male rats and along with sulpiride for 28 successive days to Wistar female rats.

Results:

Cafeteria diet alone significantly increased body weight, serum total cholesterol, triglycerides, and glucose levels and decreased HDL cholesterol in male rats as compared to control. Sulpiride per se significantly increased the levels of glucose, triglycerides, cholesterol and there was no significant effect on HDL-cholesterol in female rats as compared to control. Ethanolic extract showed a significant decrease in body weight, serum cholesterol, and triglycerides and a significant increase in HDL-cholesterol in cafeteria diet- and sulpiride-induced obese rats as compared to their respective control groups.

Conclusions:

Thus, the ethanolic extract of Tamarindus indica fruit pulp showed a significant weight-reducing and hypolipidemic activity in cafeteria diet- and sulpiride-induced obese rats.

Albumin nanoparticles carrying cyclodextrins for nasal delivery of the anti-Alzheimer drug tacrine

Peroral administration of tacrine, the first acetylcholinestearse inhibitor licensed for the treatment of Alzheimer's disease, is associated with low bioavailability, due to an extended first-pass methabolism, short elimination half-life and hepatotoxicity. Nasal drug delivery may reduce the degree of these problems. Tacrine hydrochloride nasal delivery is here investigated by means of albumin nanoparticles carrying beta cyclodextrin and two different beta cyclodextrin derivatives (hydroxypropyl beta cyclodextrin and sulphobutylether beta cyclodextrin). Bovine serum albumin nanoparticles were obtained using a coacervation method, followed by thermal cross-linking, starting from protein solution at alkaline pH. After preparation, nanoparticles were loaded by soaking from solutions of tacrine hydrochloride and lyophilised. Thermal analysis (differential scanning calorimetry and thermogravimetric analysis) supported by Fourier Transform Infrared Spectroscopy were performed in order to confirm protein cross-linking in nanosphere structure and possible drug/carrier interaction occurred after the loading process. Moreover, size, polydispersity, zeta potential and morphology of the nanoparticles were investigated as well as drug loading, mucoadhesion properties and ex-vivo drug permeation ability. Results indicate that all the nanoparticles presented a mean size and a polydispersity lower than 300nm and 0.33nm, respectively, were spherical shaped and negatively charged even after drug loading. Moreover, the presence of the different beta cyclodextrins in the polymeric network affected drug loading and could differently modulate nanoparticle mucoadhesiveness and drug permeation behaviour.

Nantenine as an acetylcholinesterase inhibitor: SAR, enzyme kinetics and molecular modeling investigations

Nantenine, as well as a number of flexible analogs, were evaluated for acetylcholinesterase (AChE) inhibitory activity in microplate spectrophotometric assays based on Ellman's method. It was found that the rigid aporphine core of nantenine is an important structural requirement for its anticholinesterase activity. Nantenine showed mixed inhibition kinetics in enzyme assays. Molecular docking experiments suggest that nantenine binds preferentially to the catalytic site of AChE but is also capable of interacting with the peripheral anionic site (PAS) of the enzyme, thus accounting for its mixed inhibition profile. The aporphine core of nantenine may thus be a useful template for the design of novel PAS or dual-site AChE inhibitors. Inhibiting the PAS is desirable for prevention of aggregation of the amyloid peptide Aβ, a major causative factor in the progression of Alzheimer's disease (AD).

Long-lasting decreases in cocaine-reinforced behavior following treatment with the cholinesterase inhibitor tacrine in rats selectively bred for drug self-administration

Tacrine is a centrally acting, reversible cholinesterase inhibitor that increases synaptic levels of acetylcholine (ACh) and can potentiate the actions of dopamine (DA). The present study was conducted to evaluate effects of tacrine on cocaine-reinforced responding in a rat line selectively bred for high levels of drug self-administration (the HS line). HS rats self-administered different doses of cocaine under a fixed-ratio-5 (FR-5) schedule. Over a four-day period, vehicle or tacrine (1.0, 3.2, or 10 mg/kg-day) was infused when animals were maintained in home cages (21 h per day). Tacrine dose-dependently decreased cocaine self-administration. Actions of tacrine differed for self-administration that was initiated within 20 min of pretreatment (described as early sessions), and for self-administration that occurred between one and three days after administration of tacrine was discontinued (late sessions). Tacrine's potency for attenuating self-administration during late sessions was greater for cocaine- relative to food-reinforcement in HS rats, and for HS relative to outbred rats. In a subset of tacrine-treated HS rats, cocaine self-administration was persistently attenuated by more than 80% from pretreatment baseline levels over a one-week period during which no further tacrine was administered. In summary, pretreatment with tacrine can produce a long-lasting attenuation of cocaine-reinforced responding.

Dose-related effects of the acetylcholinesterase inhibitor tacrine on cocaine and food self-administration in rats

RATIONALE

Acetylcholine (ACh) is involved in brain reward and learning functions and contributes to opiate- and psychostimulant-motivated behaviors. Tacrine is a centrally acting, reversible cholinesterase inhibitor that also inhibits monoamine oxidase (MAO) and blocks reuptake of dopamine (DA) and serotonin.

OBJECTIVES

To determine the effects of pretreatment with tacrine on self-administration of cocaine and nondrug reinforcers.

MATERIALS AND METHODS

Male Wistar rats were trained to self-administer cocaine under a fixed-ratio-5 (FR-5) schedule during 2-h multiple-component sessions in which 0.1, 0.2, and 0.4 mg/kg per injection of cocaine were each available for 40 min. Other animals self-administered 45 mg food pellets under FR-30 or 20% Ensure (liquid food) under FR-5 in amounts of 30, 60, or 120 microl. Vehicle or tacrine was administered as single intravenous doses 20 min before self-administration of cocaine, food pellets, or liquid food.

RESULTS

Although pretreatment with 0.032 mg/kg of tacrine increased self-administration of food pellets, pretreatment with higher doses of tacrine attenuated self-administration of cocaine, food pellets, or liquid food. Tacrine's ED50 value for attenuating self-administration of 0.1 mg/kg per injection of cocaine was more than sixfold lower than values for attenuating liquid food- or food pellet-reinforced behavior. However, ED50 values for attenuating self-administration of higher doses of cocaine were similar to those observed for 30 or 60 microl of liquid food.

CONCLUSIONS

Tacrine can selectively attenuate self-administration of low-dose cocaine, but its effects on higher doses of cocaine are similar to its ability to decrease self-administration of nondrug reinforcers.

Evaluation of acute bis(7)-tacrine treatment on behavioral functions in 17-day-old and 30-day-old mice, with attention to drug toxicity

Bis(7)-tacrine was evaluated for efficacy on memory retention in mice 17 days of age and 30 days of age. The tests used were a passive-avoidance response test and a measure of spontaneous motor activity. Also, possible drug-induced hepatotoxicity and acute drug toxicity were evaluated. Behavioral studies were performed using a step-through task and an open-field test with a 24-h interval between training and evaluation tests. Bis(7)-tacrine (0.06-20 micromol/kg) was subcutaneously injected 30 min prior to the first session of both test types. During the training session of the step-through task, bis(7)-tacrine treatment reduced (by 46%, P<0.01) the number of avoidable electric shocks (footshocks) only at a high dose of 20 micromol/kg in mice 17 days of age, but dose-dependently decreased the number of footshocks (10-56%, P<0.001) in mice 30 days of age. Bis(7)-tacrine treatment at all doses tested did not produce any detectable changes in retention latency in mice 17 days of age, but the drug significantly prolonged retention latency at low doses (1.25 and 2.50 micromol/kg), and not high doses (5-20 micromol/kg), in mice 30 days of age. In the open-field test, bis(7)-tacrine decreased spontaneous motor activity in the acquisition session only at a high dose of 20 micromol/kg in mice 17 days of age and 30 days of age (by 28 and 45%, respectively), but did not affect spontaneous motor activity in the recall session. Bis(7)-tacrine treatment at a dose of 20 micromol/kg produced a more potent hepatotoxic effect in mice 30 days of age than in mice 17 days of age, (P<0.05), and the drug caused acute toxicity with comparable potencies in mice of both age groups. In conclusion, mice 30 days of age seemed to be more sensitive than mice 17 days of age to bis(7)-tacrine-induced cognitive function enhancement and hepatotoxicity. Bis(7)-tacrine appears to be more potent and more selective as a cognitive function-enhancing agent than tacrine.

Transdermal treatment options for neurological disorders: impact on the elderly

As people grow old, their need for medications increases dramatically because of the higher incidence of chronic pain, diabetes mellitus, cardiovascular and neurological diseases in the elderly population. Furthermore, the elderly require special consideration with respect to drug delivery, drug interactions and adherence. In particular, patients with chronic neurological diseases often require multiple administration of drugs during the day to maintain constant plasma medication levels, which in turn increases the likelihood of poor adherence. Consequently, several attempts have been made to develop pharmacological preparations that can achieve a constant rate of drug delivery. For example, transdermal lisuride and apomorphine have been shown to reduce motor fluctuations and duration of 'off' periods in advanced Parkinson's disease, while rotigotine allows significant down-titration of levodopa without severe adverse effects. Thus, parkinsonian patients with long-term levodopa syndrome or motor disorders during sleep could benefit from use of transdermal lisuride and apomorphine. Moreover, transdermal dopaminergic drugs, particularly rotigotine, seem the ideal treatment for patients experiencing restless legs syndrome or periodic limb movement disorder during sleep, disorders that are quite common in elderly people or in association with neurodegenerative diseases. Unlike dopaminergic drugs, transdermal treatments for the management of cognitive and behavioural dysfunction in patients with Parkinson's disease and Alzheimer's disease have inconsistent effects and no clearly established role. Nevertheless, because of their favourable pharmacological profile and bioavailability, the cholinesterase inhibitors tacrine and rivastigmine are expected to show at least the same benefits as oral formulations of these drugs, but with fewer severe adverse effects. Transdermal delivery systems play an important role in the management of neuropathic pain. The transdermal lidocaine (lignocaine) patch is recommended as first-line therapy for the treatment of postherpetic neuralgia. Furthermore, in patients with severe persistent pain, transdermal delivery systems using the opioids fentanyl and buprenorphine are able to achieve satisfactory analgesia with good tolerability, comparable to the benefits seen with oral formulations. Transdermal administration is the ideal therapeutic approach for chronic neurological disorders in elderly people because it provides sustained therapeutic plasma levels of drugs, is simple to use, and may reduce systemic adverse effects. Several transdermal delivery systems are currently under investigation for the treatment of Parkinson's disease, Alzheimer's disease and neuropathic pain. Although most transdermal delivery systems treatments cannot be considered as first-line therapy at present, some of them provide clear advantages compared with other routes of administration and may become the preferred treatment in selected patients. In general, however, most transdermal treatments still require long-term evaluation in large patient groups in order to optimise dosages and evaluate the actual incidence of local and systemic adverse effects.

Factorial design approach to evaluate interactions between electrically assisted enhancement and skin stripping for delivery of tacrine

The objective of this work was to study the mechanisms of action of iontophoresis and electroporation and their interaction effects on delivery of tacrine hydrochloride in vitro across intact and stripped rat skin. Experiments were done according to a full factorial design, to quantify the effects of iontophoresis (X1), electroporation (X2) and stripped skin (X3) alone and in combination on cumulative drug delivery at 6 h. Mathematical model eliciting the main effects of the factors and their interaction on cumulative tacrine delivery in 6 h shows that all three techniques examined alone have a positive impact on the permeation of tacrine, the greatest enhancement in delivery achieved by iontophoresis. However, iontophoresis in combination with electroporation or skin stripping yielded no improvement in delivery compared to iontophoresis alone. The most significant enhancement is seen when all three methods of assisted delivery are done in combination. Iontophoresis appears to control drug delivery to the exclusion of other enhancement methods. Electroporation appears to cause formation of a large depot of tacrine in the skin.

Long-term cholinesterase inhibitor treatment of Alzheimer's disease

The most prevalent cause of dementia--Alzheimer's disease--is characterised by an early cholinergic deficit that is in part responsible for the cognitive deficits, especially memory and attention defects, seen with this condition. Three cholinesterase inhibitors (ChEIs), namely donepezil, rivastigmine and galantamine, are widely used for the symptomatic treatment of patients with Alzheimer's disease. Placebo-controlled, randomised clinical trials have shown significant effects of these drugs on global function, cognition, activities of daily living (ADL) and behavioural symptoms in patients with this disorder. These trials have been conducted for up to 12 months and were followed by open-label extension studies. One placebo-controlled, randomised clinical trial followed patients for up to 4 years. Both retrospective and prospective follow-up studies suggest a treatment effect for ChEIs that lasts for up to 5 years. Studies have shown comparable effects for ChEIs in patients with moderate-to-severe Alzheimer's disease or mild Alzheimer's disease. Clinically relevant responses consist not only of improvement over 3-6 months but also stabilisation and possibly slower than expected decline. Lack of overt clinical improvement in one domain (e.g. global function, cognition, ADL or behaviour) does not preclude clinically relevant benefit(s) in other domains. If it is judged that the patient has experienced a treatment effect from ChEI therapy during the first 6 months, it is recommended that treatment be continued for at least 1 year before discontinuation is considered again. On average, patients will return to their pre-treatment status between 9 and 12 months of initiation of treatment. However, this return to pre-treatment level does not mean that the treatment effect has disappeared. At this point in time, the patient may still function better than he or she would have without treatment. Setting a fixed measurement, e.g. a Mini-Mental State Examination score, as a 'when to stop treatment limit' is not clinically rational. The length of treatment should depend on several individual patient factors. The earlier the diagnosis is made and the slower the rate of disease progression, the longer the treatment period will tend to be. Treatment duration must therefore be evaluated on an individual basis, and the patient's status compared with what would have been expected without treatment. If a clinical evaluation is conducted with a view to stopping or switching treatment, it is crucial that all domains are evaluated and that the patient is evaluated at more than one point in time before the decision is made.

Response Surface Methodology to Investigate the Iontophoretic Delivery of Tacrine Hydrochloride

PURPOSE

The objective of this work was to apply response surface approach to investigate the main and interaction effects of delivery parameters for iontophoretic delivery of tacrine HCl in vitro.

METHODS

Iontophoresis was used to deliver tacrine HCl across rat skin. Experiments were performed according to Box-Behnken design to evaluate effects of drug concentration (X1), current density (X2), and donor buffer molarity (X3) on cumulative drug delivered in 24 h (Y1), 6 h (Y2), iontophoretic flux (Y3), and post-iontophoretic flux (Y4).

RESULTS

Mathematical model for Y1 was Y1 = 0.653 + 0.163 * X1 + 0.456 * X2 - 0.156 * X3 + 0.190 * X1X2 + 0.139* X3X3. Response surface plot indicated that at low level of X2 (0.1mA/cm2), X1 had little effect on Y1. However, at high level of X2 (0.5 mA/cm2), Y1 significantly increased from 0.75 mg/cm2 to 1.46 mg/cm2 when X1 increased from 1% to 9%. Regression equations predicted responses for Y1 to Y4, for optimal formulation, which were in reasonably good agreement with experimental values.

CONCLUSIONS

Experimental design methodology revealed an interaction between drug concentration and current density, which would have been difficult to predict from one factor at a time classic experimental approach.

Long-lasting acetylcholinesterase splice variations in anticholinesterase-treated Alzheimer's disease patients

Protein levels of different acetylcholinesterase (AChE) splice variants were explored by a combination of immunoblot techniques, using two different antibodies, directed against the C-terminus of the AChE-R splice variant or the core domain common to all variants. Both AChE-R and AChE-S splice variants as well as several heavier AChE complexes were detected in brain homogenates from the parietal cortex of patients with or without Alzheimer's disease (AD) as well as the cerebrospinal fluid (CSF) of AD patients, compatible with the assumption that CSF AChEs might originate from CNS neurons. Long-term changes in the composition of CSF AChE variants were further pursued in AD patients treated with rivastigmine (n = 11) or tacrine (n = 17) in comparison to untreated AD patients (n = 5). In untreated patients, AChE-R was markedly reduced as compared with the baseline level (37%), whereas the medium size AChE-S complex was increased by 32%. Intriguingly, tacrine produced a general and profound up-regulation of all detected AChE variants (up to 117%), whereas rivastigmine treatment caused a mild and selective up-regulation of AChE-R ( approximately 10%, p < 0.05). Moreover, the change in the ratio of AChE-R to AChE-S (R/S-ratio) strongly and positively correlated with sustained cognition at 12 months (p < 0.0001). Thus, evaluation of changes in the composition of CSF AChE variants may yield important information referring to the therapeutic efficacy and/or development of drug tolerance in AD patients treated with anti-cholinesterases.

A nitric oxide-donating flurbiprofen derivative reduces neuroinflammation without interacting with galantamine in the rat

Alzheimer's disease is associated with glial activation and increased levels of the cytokines as well as impaired forebrain cholinergic function. Current therapies focus on enhancing cholinergic function by administrating acetylcholinesterase inhibitors, such as galantamine. Epidemiological results also suggest that anti-inflammatory therapies might be effective in slowing the onset of the symptoms of Alzheimer's disease. The current study investigated the ability of a nitric oxide (NO)-donating derivative of the nonsteroidal anti-inflammatory drug (NSAID) flurbiprofen, HCT1026, to reduce brain inflammation in young rats. Inflammation was produced by chronic infusion of lipopolysaccharide (LPS) into the 4th ventricle. The release of NO from HCT1026 requires the action of esterase enzymes. The current study determined whether the effectiveness of HCT1026 was attenuated by simultaneous treatment with the acetylcholinesterase inhibitor galantamine. Daily administration of the HCT1026 significantly reduced microglial activation and these effects were not attenuated by galantamine therapy.

Identification of selective inhibitors of acetylcholinesterase from a combinatorial library of 2,5-piperazinediones

The potentiation of central cholinergic activity has been proposed as a therapeutic approach for improving cognitive function in patients with Alzheimer's disease. Increasing the acetylcholine concentration in brain by modulating acetylcholinesterase (AChE) activity is among the most promising strategies. We have used a combinatorial approach to identify different 2,5-piperazinediones (DKP) with AChE inhibitory activity. Our goal was to find inhibitors exhibiting high AChE/BuChE (butyrylcholinesterase) selectivity, in order to reduce the undesirable side effects elicited by most of the inhibitors that have been developed to date. Screening of a DKP library constructed on solid-phase using the multiple parallel synthesis format, resulted in the identification of several compounds with moderate efficacy on AChE. In particular, DKP-80 had an IC50 = 2.2 microM with no significant inhibitory activity on BuChE. Moreover, estimated values of Clog P and log BB for the most active compounds fulfilled the bioavailability requirements for enzyme inhibitors acting on the central nervous system. In order to understand the inhibitory properties of the ligand at the molecular level, molecular dynamics simulations were computed on DKP-80 complexed to AChE, and the most relevant binding interactions of this inhibitor to the active center of the enzyme were characterized. Overall the present results indicate that the DKP-based compounds identified are novel AChE inhibitors which may be considered likely lead compounds for further development of drug candidates against Alzheimer's disease.

Clinical pharmacokinetics and pharmacodynamics of cholinesterase inhibitors

Cholinesterase inhibitors are the 'first-line' agents in the treatment of Alzheimer's disease. This article presents the latest information on their pharmacokinetic properties and pharmacodynamic activity. Tacrine was the first cholinesterase inhibitor approved by regulatory agencies, followed by donepezil, rivastigmine and recently galantamine. With the exception of low doses of tacrine, the cholinesterase inhibitors exhibit a linear relationship between dose and area under the plasma concentration-time curve. Cholinesterase inhibitors are rapidly absorbed through the gastrointestinal tract, with time to peak concentration usually less than 2 hours; donepezil has the longest absorption time of 3 to 5 hours. Donepezil and tacrine are highly protein bound, whereas protein binding of rivastigmine and galantamine is less than 40%. Tacrine is metabolised by hepatic cytochrome P450 (CYP) 1A2, and donepezil and galantamine are metabolised by CYP3A4 and CYP2D6. Rivastigmine is metabolised by sulfate conjugation. Two cholinesterase enzymes are present in the body, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Tacrine and rivastigmine inhibit both enzymes, whereas donepezil and galantamine specifically inhibit AChE. Galantamine also modulates nicotine receptors, thereby enhancing acetylcholinergic activity at the synapse. These different pharmacological profiles provide distinctions between these agents. Cholinesterase inhibitors show a nonlinear relationship between dose and cholinesterase inhibition, where a plateau effect occurs. Cholinesterase inhibitors display a different profile as each agent achieves its plateau at different doses. In clinical trials, cholinesterase inhibitors demonstrate a dose-dependent effect on cognition and functional activities. Improvement in behavioural symptoms also occurs, but without a dose-response relationship. Gastrointestinal adverse events are dose-related. Clinical improvement occurs with between 40 and 70% inhibition of cholinesterase. A conceptual model for cholinesterase inhibitors has been proposed, linking enzyme inhibition, clinical efficacy and adverse effects. Currently, measurement of enzyme inhibition is used as the biomarker for cholinesterase inhibitors. New approaches to determining the efficacy of cholinesterase inhibitors in the brain could involve the use of various imaging techniques. The knowledge base for the pharmacokinetics and pharmacodynamics of cholinesterase inhibitors continues to expand. The increased information available to clinicians can optimise the use of these agents in the management of patients with Alzheimer's disease.

Cholinergic nicotinic systems in Alzheimer's disease: prospects for pharmacological intervention

Within the last few years, research into the cause and progression of Alzheimer's disease has made significant advances. Although there is still no preventative treatment or cure for this neurodegenerative illness, the development of drugs that may alleviate some of the cognitive symptoms associated with it is advancing. Cholinesterase inhibitors are at present the most effective form of treatment and have shown significant overall response rates in clinical trials. However, although some patients show substantial improvement when treated with this class of drugs, there is considerable variability in the amount of benefit gained in different individuals in terms of their cognitive and behavioural functioning. Furthermore, unfortunately some patients gain little or no benefit from these drugs. It would therefore be of great advantage to explore alternative therapeutic possibilities. This article reviews the potential involvement of the nicotinic cholinergic system in Alzheimer's disease and discusses the possibility of nicotinic pharmacotherapy. Substantial evidence indicates the involvement of the nicotinic cholinergic system in the pathology of Alzheimer's disease. Drugs targeting these sites may not only have a positive effect on cognitive function, but also have additional therapeutic benefits in terms of restoring the hypoactivity in the excitatory amino acid pyramidal system and even slowing the emergence of Alzheimer's disease pathology. The conclusion of this review is that nicotinic treatments are an important potential source of new therapeutic interventions in Alzheimer's disease.

Accurate prediction of the bound conformation of galanthamine in the active site of Torpedo californica acetylcholinesterase using molecular docking

The alkaloid (-)-galanthamine is known to produce significant improvement of cognitive performances in patients with the Alzheimer's disease. Its mechanism of action involves competitive and reversible inhibition of acetylcholinesterase (AChE). Herein, we correctly predict the orientation and conformation of the galanthamine molecule in the active site of AChE from Torpedo californica (TcAChE) using a combination of rigid docking and flexible geometry optimization with a molecular mechanics force field. The quality of the predicted model is remarkable, as indicated by the value of the RMS deviation of approximately 0.5A when compared with the crystal structure of the TcAChE-galanthamine complex. A molecular model of the complex between TcAChE and a galanthamine derivative, SPH1107, with a long chain substituent on the nitrogen has been generated as well. The side chain of this ligand is predicted to extend along the enzyme active site gorge from the anionic subsite, at the bottom, to the peripheral anionic site, at the top. The docking procedure described in this paper can be applied to produce models of ligand-receptor complexes for AChE and other macromolecular targets of drug design.

Design, synthesis, and structure-activity relationships of a series of 3-[2-(1-benzylpiperidin-4-yl)ethylamino]pyridazine derivatives as acetylcholinesterase inhibitors

Starting from the 3-[2-(1-benzylpiperidin-4-yl)ethylamino]-6-phenylpyridazine 1, we performed the design, the synthesis, and the structure-activity relationships of a series of pyridazine analogues acting as AChE inhibitors. Structural modifications were achieved on four different parts of compound 1 and led to the following observations: (i) introduction of a lipophilic environment in the C-5 position of the pyridazine ring is favorable for the AChE-inhibitory activity and the AChE/BuChE selectivity; (ii) substitution and various replacements of the C-6 phenyl group are possible and led to equivalent or slightly more active derivatives; (iii) isosteric replacements or modifications of the benzylpiperidine moiety are detrimental to the activity. Among all derivatives prepared, the indenopyridazine derivative 4g was found to be the more potent inhibitor with an IC(50) of 10 nM on electric eel AChE. Compared to compound 1, this represents a 12-fold increase in potency. Moreover, 3-[2-(1-benzylpiperidin-4-yl)ethylamino]-5-methyl-6-phenylpyridazine 4c, which showed an IC(50) of 21 nM, is 100-times more selective for human AChE (human BuChE/AChE ratio of 24) than the reference compound tacrine.