Rivastigmine, a brain-region selective acetylcholinesterase inhibitor for treating Alzheimer's disease: review and current status

Alzheimer's disease is, in part, characterised by the loss of neurones in the basal forebrain cholinergic cells that project to the cerebral cortex and hippocampus. These impairments have correlated with the memory loss noted in dementia of the Alzheimer's type. This 'cholinergic hypothesis' has led to the rational design of drugs to enhance or stimulate acetylcholine-mediated neurotransmission. Early acetylcholinesterase inhibitors, such as tacrine and physostigmine, are poorly tolerated and have a short duration of action. Rivastigmine is a centrally-selective acetylcholinesterase inhibitor with a relatively long duration of action and is a 'pseudo-irreversible' cholinesterase inhibitor due to slow dissociation of a carbamoyl derivative from the esteratic site of acetylcholinesterase. Preclinical studies confirmed the central selectivity of the drug and its distribution into the cerebrospinal fluid (CSF). Early studies demonstrated that rivastigmine improved cognition and was relatively well-tolerated at moderate doses. Clinical investigations of rivastigmine administered at doses of 6 - 12 mg/day significantly improved cognition, as measured by the ADAS-Cog score, and activities of daily living, as measured by the Progressive Deterioration Scale. Significant global improvements were also noted as measured by the Clinician's Interview Based Impression of Change that required the use of caregiver information. The most frequent adverse effects noted in clinical trials were consistent with peripheral cholinergic stimulation and included nausea, vomiting, abdominal pain, dizziness and diarrhoea. These effects were dose-related and minimised by slow dose-escalation upon initiation of therapy. Rivastigmine undergoes minimal metabolism by the cytochrome P450 system. As a result, it has few drug interactions. The drug is currently marketed widely in over 60 countries worldwide. In the United States, the drug received 'approvable' status subsequent to the NDA filing, and should be available later this year.     

New tacrine-hydrazinonicotinamide hybrids as acetylcholinesterase inhibitors of potential interest for the early diagnostics of Alzheimer's disease

The syntheses and the preliminary results of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition by an affinity series of tacrine-hydrazinonicotinamide hybrids are described. These molecules were prepared by condensation of tacrine analogues with the hydrazine nicotinate moiety (HYNIC). Derivatives 6a and 6b showed lower activity than the model tacrine, while compounds 6c and 6d showed the strongest affinity to AChE. All the tested compounds exhibited lower affinity for BChE than tacrine. Alzheimer disease (AD) is characterised by a deficit of acetylcholinesterase, and these new compounds, as ligands for 99mTc complexes, are potential radiopharmaceuticals for an early diagnosis of Alzheimer's disease.     

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.     

New tacrine-huperzine A hybrids (huprines): highly potent tight-binding acetylcholinesterase inhibitors of interest for the treatment of Alzheimer's disease

Several new 12-amino-6,7,10,11-tetrahydro-7, 11-methanocycloocta[b]quinoline derivatives (tacrine-huperzine A hybrids, huprines) have been synthesized and tested as acetylcholinesterase (AChE) inhibitors. All of the new compounds contain either a methyl or ethyl group at position 9 and one or two (chloro, fluoro, or methyl) substituents at positions 1, 2, or 3. Among the monosubstituted derivatives, the more active are those substituted at position 3, their activity following the order 3-chloro > 3-fluoro > 3-methyl > 3-hydrogen. For the 1,3-difluoro and 1,3-dimethyl derivatives, the effect of the substituents is roughly additive. No significant differences were observed for the inhibitory activity of 9-methyl vs 9-ethyl derivatives mono- or disubstituted at positions 1 and/or 3. The levorotatory enantiomers of these hybrid compounds are much more active (eutomers) than the dextrorotatory forms (distomers) as AChE inhibitors. Compounds rac-20, (-)-20, rac-26, (-)-26, rac-30, (-)-30, and rac-31 showed human AChE inhibitory activities up to 28.5-fold higher than for the corresponding bovine enzyme. Also, rac-19, (-)-20, (-)-30, and rac-31 were very selective for human AChE vs butyrylcholinesterase (BChE), the AChE inhibitory activities being 438-871-fold higher than for BChE. Several hybrid compounds, specially (-)-20 and (-)-30, exhibited tight-binding character, showing higher activity after incubation of the enzyme with the inhibitor than without incubation, though the reversible nature of the enzyme-inhibitor interaction was demonstrated by dialysis. The results of the ex vivo experiments also supported the tight-binding character of compounds (-)-20 and (-)-30 and showed their ability to cross the blood-brain barrier. Molecular modeling simulations of the AChE-inhibitor complex provided a basis to explain the differences in inhibitory activity of these compounds.     

Rivastigmine, a new-generation cholinesterase inhibitor for the treatment of Alzheimer's disease

Rivastigmine is a cholinesterase inhibitor (ChEI) with a structural formula different from that of currently available ChEIs. Tacrine and donepezil are classified as short-acting or reversible agents since binding to acetylcholinesterase enzyme (AChE) is hydrolyzed within minutes. Rivastigmine is classified as an intermediate-acting or pseudo-irreversible agent due to its long inhibition on AChE of up to 10 hours. Preclinical biochemical studies indicated that rivastigmine has central nervous system selectivity over peripheral inhibition. It ameliorated memory impairment in rats with forebrain lesions. The drug is rapidly absorbed orally, with a bioavailability of 0.355 and low protein binding (40%). Its elimination half-life is less than 2 hours, and it is converted to an inactive metabolite at the site of action, bypassing hepatic metabolic pathways. Its disposition essentially is unaltered in patients with renal or hepatic impairment. It also has dose-dependent effects on AChE inhibition. In the two large multicenter clinical trials (total 1324 patients) that used a forced-dosage titration scheme, rivastigmine 6-12 mg/day was superior to placebo on three cognitive and functioning scales (p<0.001). Gastrointestinal symptoms are the most frequently reported adverse events. They occurred mostly during the dosage titration phase and decreased during the maintenance phase. Rivastigmine offers clinicians another therapeutic agent to treat Alzheimer's disease.     

The acetylcholinesterase inhibitor, Donepezil, regulates a Th2 bias in Alzheimer's disease patients

The increased pro-inflammatory cytokine production was previously observed in Alzheimer's disease (AD). We sought to explore whether acetylcholinesterase inhibitor (AChEI) therapy ameliorates clinical symptoms in AD through down-regulation of inflammation. Expression and release of monocyte chemotactic protein-1 (MCP-1), a positive regulator of Th2 differentiation, and interleukin (IL)-4, an anti-inflammatory cytokine from peripheral blood mononuclear cells (PBMC) in AD patients, were investigated. PBMC were purified from AD patients at time of enrollment (T0) and after 1 month of treatment with AChEI (T1) and from healthy controls (HC). Supernatants were analyzed for cytokine levels by ELISA methods. mRNA expression were determined by RT-PCR. Expression and production of MCP-1 and IL-4 were significantly increased in AD subjects under therapy with the AChEI Donepezil, compared to the same AD patients at time of enrollment (P < 0.001). Our data suggest another possible explanation for the ability of Donepezil [diethyl(3,5-di-ter-butyl-4-hydroxybenzyl)phosphonate] to delay the progression of AD; in fact, Donepezil may modulate MCP-1 and IL-4 production, which may reflect a general shift towards type Th0/Th2 cytokines which could be protective in AD disease. The different amounts of MCP-1 and IL-4 observed might reflect the different states of activation and/or responsiveness of PBMC, that in AD patients could be kept in an activated state by pro-inflammatory cytokines.     

Tacrine-huperzine A hybrids (huprines): a new class of highly potent and selective acetylcholinesterase inhibitors of interest for the treatment of Alzheimer's disease

Tacrine-huperzine A hybrids (huprines) are a new class of very potent and selective acetylcholinesterase (AChE) inhibitors. Huprines were designed from tacrine and (-)-huperzine A through a conjunctive approach. They combine the 4-aminoquinoline substructure of tacrine with the carbobicyclic substructure of (-)-huperzine A. Structural variations on several parts of a lead structure have allowed to complete a structure-activity relationship exploration of this new structural family and have led to several huprines more active than other known AChE inhibitors.     

Hypochlorous acid is a potent inhibitor of acetylcholinesterase

The role of hydrogen peroxide and peroxynitrite in the induction of airway hyperreactivity has been well described. Another reactive species which is formed during airway inflammation is hypochlorous acid (HOCl). In the present investigation the effect of HOCl on cholinergic innervation of the airway was investigated. It was observed that HOCl was capable of increasing the basal tension of electrically stimulated tracheal smooth muscle. It was found that HOCl inhibits purified acetylcholinesterase with an IC50 value of 0.66 microM. Decreased acetylcholinesterase activity could allow accumulation of acetylcholine and increased airway muscle tension. The effects of HOCl on the isolated organ and the enzyme preparation could be precluded with thiol group-containing compounds such as reduced glutathione and N-acetylcysteine. The present findings indicate that HOCl can act as inhibitor of acetylcholinesterase. The implications of this finding for the induction of airway hyperreactivity are discussed.     

Tau-aggregation inhibitor therapy for Alzheimer's disease

Many trials of drugs aimed at preventing or clearing β-amyloid pathology have failed to demonstrate efficacy in recent years and further trials continue with drugs aimed at the same targets and mechanisms.The Alzheimer neurofibrillary tangle is composed of tau and the core of its constituent filaments are made of a truncated fragment from the repeat domain of tau. This truncated tau can catalyse the conversion of normal soluble tau into aggregated oligomeric and fibrillar tau which, in turn, can spread to neighbouring neurons. Tau aggregation is not a late-life process and onset of Braak stage 1 peaks in people in their late 40s or early 50s. Tau aggregation pathology at Braak stage 1 or beyond affects 50% of the population over the age of 45.The initiation of tau aggregation requires its binding to a non-specific substrate to expose a high affinity tau–tau binding domain and it is self-propagating thereafter. The initiating substrate complex is most likely formed as a consequence of a progressive loss of endosomal–lysosomal processing of neuronal proteins, particularly of membrane proteins from mitochondria. Mutations in the APP/presenilin membrane complex may simply add to the age-related endosomal–lysosomal processing failure, bringing forward, but not directly causing, the tau aggregation cascade in carriers.Methylthioninium chloride (MTC), the first identified tau aggregation inhibitor (TAI), offers an alternative to the amyloid approach. Phase 3 trials are underway with a novel stabilized reduced form of methylthioninium (LMTX) that has improved tolerability and absorption.     

治疗阿尔茨海默病的乙酰胆碱酯酶抑制剂的分子设计: 从多位点抑制剂到一药多靶

阿尔茨海默病 (Alzheimer’s disease, AD) 是一种病因尚不明确且致病机制极为复杂的神经退行性疾病, 严重威胁老年人的健康并对整个社会发展带来沉重的负担。设计开发治疗阿尔茨海默病的药物一直是药物研发领域的热点和难点, 其中尤以乙酰胆碱酯酶 (acetylcholinesterase, AChE) 抑制剂的研究最为活跃并已在临床中成功应用。然而, 现有商品化AChE抑制剂的临床治疗效果有限, 并且都伴随不同程度的毒副作用。因此,  寻找高效、低毒的多重结合位点的AChE抑制剂和针对多重作用靶标的多功能抑制剂 (即一药多靶) 成为AChE抑制剂分子设计的主要发展方向。本文结合近年来的研究进展, 从代表性AChE抑制剂的化学结构和结合模式出发, 对AChE抑制剂分子设计的发展历程及最新成果进行了综述。     

CHF2819: pharmacological profile of a novel acetylcholinesterase inhibitor

CHF2819 is a novel orally active acetylcholinesterase inhibitor (AChEI) developed for the treatment of Alzheimer's disease (AD). CHF2819 is a selective inhibitor of AChE, it is 115 times more potent against this enzyme than against butyrylcholinesterase (BuChE). Moreover, CHF2819 is more selective for inhibition of central (brain) AChE than peripheral (heart) AChE. In vivo CHF2819, 0.5, 1.5, and 4.5 mg/kg p.o., significantly and in dose-dependent manner increased acetylcholine (ACh) levels in hippocampus of young adult rats. Moreover, aging animals, with lower basal ACh levels than young adult rats, also exhibit a marked increase in hippocampal levels of this neurotransmitter after administration of CHF2819. At 1.5 mg/kg p.o. CHF2819 attenuated scopolamine-induced amnesia in a passive avoidance task. Furthermore, it decreased dopamine (DA) levels and increased extracellular levels of 5-hydroxytryptamine (5-HT) in the hippocampus, without modifying norepinephrine (NE) levels. By oral administration to young adult rats CHF2819 did not affect extracellular hippocampal levels of glutamate (Glu), aspartate (Asp), gamma-aminobutyric acid (GABA), taurine (Tau), arginine (Arg) or citrulline (Cit). Functional observational battery (FOB) screening demonstrated that CHF2819 (1.5 and 4.5 mg/kg p.o.) does not affect activity, excitability, autonomic, neuromuscular, and sensorimotor domains, as well as physiological endpoints (body weight and temperature). CHF2819 induced, however, involuntary motor movements (ranging from mild tremors to myoclonic jerks) in a dose-dependent manner. The neurochemical and behavioral profiles of CHF2819 suggest that this orally active novel AChEI could be of clinical interest for the treatment of Alzheimer-type dementia associated with multiple neurotransmitter abnormalities in the brain. In particular, CHF2819 might be a useful therapeutic drug for AD patients with cognitive impairment accompanied by depression.     

Biochemical characterization of a novel high-affinity and specific plasma kallikrein inhibitor

BACKGROUND AND PURPOSE

Kallikrein acts on high molecular weight kininogen (HK) to generate HKa (cleaved HK) and bradykinin (BK). BK exerts its effects by binding to B₂ receptors. The activation of B₂ receptors leads to the formation of tissue plasminogen activator, nitric oxide (NO) and prostacyclin (PGI₂). An elevated kallikrein-dependent pathway has been linked to cardiovascular disease risk. The aim of this study was to investigate whether our novel plasma kallikrein inhibitor abolishes kallikrein-mediated generation of BK from HK and subsequent BK-induced NO and PGI₂ formation, thereby influencing endothelial pathophysiology during chronic inflammatory diseases.

EXPERIMENTAL APPROACH

Kinetic analysis was initially used to determine the potency of PF-04886847. Biochemical ligand binding assays, immunological methods and calcium flux studies were used to determine the selectivity of the kallikrein inhibitor. In addition, the effect of PF-04886847 on BK-induced relaxation of the rat aortic ring was determined in a model of lipopolysaccharide-induced tissue inflammation.

KEY RESULTS

Evidence was obtained in vitro and in situ, indicating that PF-04886847 is a potent and specific inhibitor of plasma kallikrein. PF-04886847 efficiently blocked calcium influx as well as NO and PGI₂ formation mediated through the BK-stimulated B₂ receptor signalling pathway. PF-04886847 blocked kallikrein-induced endothelial-dependent relaxation of isolated rat aortic rings pre-contracted with phenylephrine.

CONCLUSIONS AND IMPLICATIONS

PF-04886847 was shown to be the most potent small molecule inhibitor of plasma kallikrein yet described; it inhibited kallikrein in isolated aortic rings and cultured endothelial cells. Overall, our results indicate that PF-04886847 would be useful for the treatment of kallikrein-mediated inflammatory disorders.     

Multi-target-directed drug design strategy: from a dual binding site acetylcholinesterase inhibitor to a trifunctional compound against Alzheimer's disease

A design strategy to convert a dual-binding site AChE inhibitor into triple functional compounds with promising in vitro profile against multifactorial syndromes, such as Alzheimer's disease, is proposed. The lead compound bis(7)-tacrine (2) was properly modified to confer to the new molecules the ability of chelating metals, involved in the neurodegenerative process. The multifunctional compounds show activity against human AChE, are able to inhibit the AChE-induced amyloid-beta aggregation, and chelate metals, such as iron and copper.     

SKF83959 is a novel triple reuptake inhibitor that elicits anti-depressant activity

Aim:

{"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 (3-methyl-6-chloro-7,8-hydroxy-1-(3-methylphenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine) is an atypical dopamine receptor-1 (D₁ receptor) agonist, which exhibits many D₁ receptor-independent effects. In the present work, we examined the effects of {"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 on monoaminergic transporters in vitro and its anti-depressant activity in vivo.

Methods:

Human serotonin transporter (SERT), norepinephrine transporters (NET) or dopamine transporters (DAT) were stably expressed in CHO cells. The uptake kinetics of SERT, NET, and DAT were examined using [³H]-serotonin, [³H]-norepinephrine or [³H]-dopamine, respectively. A triple reuptake inhibitor DOV21947 was used as the positive control. Tail suspension test and forced swimming test were conducted in mice. {"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 or DOV21947 (2–8 mg/kg) were intraperitoneally injected 30 min before the tests.

Results:

{"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 was a competitive inhibitor of SERT (K_i=1.43±0.45 μmol/L), but a noncompetitive inhibitor of NET (K_i=0.60±0.07 μmol/L) and DAT (K_i=9.01±0.80 μmol/L). In contrast, DOV21947 was a competitive inhibitor of SERT (K_i=0.89±0.24 μmol/L) and DAT (K_i=1.47±0.31 μmol/L) and a noncompetitive inhibitor of NET (K_i=0.18±0.04 μmol/L). In mice, both {"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 and DOV21947 elicited anti-depressant activity in a dose-dependent manner.

Conclusion:

{"type":"entrez-protein","attrs":{"text":"SKF83959","term_id":"1155968032","term_text":"SKF83959"}}SKF83959 functions as a novel triple reuptake inhibitor in vitro and exerts anti-depressant effects in vivo.     

Progress in acetylcholinesterase inhibitors for Alzheimer's disease: an update

Background: To date, the pharmacotherapy of Alzheimer's disease (AD) has been based on acetylcholinesterase inhibitors (AChEIs), and more recently on an N-methyl-d-aspartate receptor antagonist. By increasing acetylcholine concentration in the brain, AChEIs slow behavioral and functional impairments, improving cognitive function. Objective: The review provides an update on novel analogs of approved AChEIs, their combination with other anti-AD agents, natural AChEIs, and modern multitarget-directed ligands (MTDLs) able to hit different biological targets. Methods: We reviewed patents filed during 2005 – 2007 dealing with new AChEIs and their potential application for AD treatment. We point out new chemical structures and scaffolds for designing new AD therapeutic agents as well as new combinations or MTDLs. Results and conclusions: Compared to the limited number of novel commercially available AChEI analogs, many new natural compounds were patented for AD treatment. These might represent a starting point for the rational design of new MTDLs.     

Metrifonate (Trichlorfon): a review of the pharmacology, pharmacokinetics and clinical experience with a new acetylcholinesterase inhibitor for Alzheimer's disease

Metrifonate is a cholinesterase inhibitor, effective in the treatment of both the cognitive and behavioural symptoms of Alzheimer's disease (AD). Previously used as an antihelminthic and insecticide, clinical experience with metrifonate in AD patients is large and growing. The parent compound is relatively inactive; it is metabolised non-enzymatically to 2,2-dimethyl dichlorovinyl phosphate (DDVP), which irreversibly inhibits the acetylcholinesterase enzyme. The elimination half-life of DDVP is 2.1 h; cholinesterase inhibition by DDVP is stable and may persist for up to 55 days. Metrifonate can be administered once daily. In vitro and animal data regarding possible carcinogenesis of metrifonate and DDVP are conflicting; experience in the treatment of humans with schistosomiasis or AD support its safety. Animal studies demonstrate its efficacy in enhancing memory in animals with cholinergic deficits. Double-blind, placebo-controlled studies have shown the benefit of metrifonate compared to placebo in improving scores on the Clinical Global Impression of Change, Alzheimer's Disease Assessment Scale-Cognitive Subscale and the Neuropsychiatric Inventory.     

Synthesis of carbon‐14 and stable isotope labeled Avagacestat: a novel gamma secretase inhibitor for the treatment of Alzheimer's disease

Bristol‐Myers Squibb and others are developing drugs that target novel mechanisms to combat Alzheimer's disease. γ‐Secretase inhibitors are one class of potential therapies that have received considerable attention. (R)‐2‐(4‐Chloro‐N‐(2‐fluoro‐4‐(1,2,4‐oxadiazol‐3‐yl)benzyl)phenylsulfonamido)‐5,5,5‐trifluoropentanamide (Avagacestat) is a γ‐secretase‐inhibiting drug that has been investigated by Bristol‐Myers Squibb in preclinical and clinical studies. An important step in the development process was the synthesis of a carbon‐14‐labeled analog for use in a human absorption, distribution, metabolism, and excretion study and a stable isotope labeled analog for use as a standard in bioanalytical assays to accurately quantify the concentration of the drug in biological samples. Carbon‐14 labeled Avagacestat was synthesized in seven steps in a 33% overall yield from carbon‐14 labeled potassium cyanide. A total of 5.95 mCi was prepared with a specific activity of 0.81 μCi/mg and a radiochemical purity of 99.9%. ¹³C₆‐Labeled Avagacestat was synthesized in three steps in a 15% overall yield from 4‐chloro[¹³C₆]aniline. A total of 585 mg was prepared with a ultraviolet purity of 99.9%.     

The renin inhibitor aliskiren as novel treatment for cardiovascular disease

The renin-angiotensin aldosterone system (RAAS) plays a key role in the regulation of blood pressure, acting via the effects of the hormone angiotensin (Ang) II. Ang II increases blood pressure and can exert growth-promoting effects leading to end-organ damage. Excess RAAS activity has been shown to be a major underlying cause of hypertension, heart failure, and related cardiovascular disorders. Inhibitors of renin block the RAAS at its first and rate-limiting step and thus appear to offer an excellent opportunity for blood pressure control. In the past two decades various potential renin inhibitors have been developed but have not been clinically useful. This review discusses a recent patent in the development of a novel class of non-peptide renin inhibitors: an alkanecarboxamide, aliskiren (SPP-100; Novartis). Aliskiren is effective in animal models, while recent results from studies in humans indicate that aliskiren is the first in a new class of orally effective renin inhibitors for the treatment of hypertension.     

Mechanisms of neuroprotective effects of therapeutic acetylcholinesterase inhibitors used in treatment of Alzheimer's disease

Donepezil, galanthamine, and tacrine are therapeutic acetylcholinesterase (AChE) inhibitors used for the treatment of Alzheimer's disease. The aim of this paper is to review recent findings on their neuroprotective properties and the mechanisms of neuroprotection against glutamate neurotoxicity in rat cortical neurons. First, the hallmark of neurotoxicity induced by two different glutamate treatment conditions was examined, revealing that acute glutamate treatment (1 mM, 10 min) induces necrotic neuronal death and that moderate glutamate treatment (100 microM, 24 hr) induces apoptotic neuronal death. Next, we showed that therapeutic AChE inhibitors protect cortical neurons from glutamate neurotoxicity in a time- and concentration-dependent manner. We examined the mechanism of this neuroprotective effect and found that the neuroprotective effects against both acute and moderate glutamate treatments are mediated through nicotinic acetylcholine receptors (nAChRs), or more specifically, the effects of donepezil and galanthamine are mediated through alpha4- and alpha7-nAChR. We also showed that donepezil and galanthamine protect cortical neurons against acute glutamate treatment-induced neurotoxicity at steps before, and that tacrine protects at steps after, nitric oxide radical formation. On the other hand, the neuroprotective effects of donepezil and galanthamine, but not of tacrine, against neurotoxicity induced by moderate glutamate treatment were mediated through the phosphatidylinositol 3-kinase-Akt pathway. These findings unveiled the hitherto unknown neuroprotective effects of therapeutic AChE inhibitors and provided valuable insights into its neuroprotective mechanisms. They may very likely form the basis for a novel treatment strategy against Alzheimer's disease.     

Peripheral and dual binding site acetylcholinesterase inhibitors: implications in treatment of Alzheimer's disease

Recently advances in understanding the molecular basis of Alzheimer's disease have led to the consideration of the relationship between cholinergic inhibitors and amyloid deposition as a new hypothesis for the future rational design of effective anti-Alzheimer drugs. In the present review, the non-cholinergic functions of acetylcholinesterase (AChE) and the therapeutic potential of peripheral and dual binding site AChE inhibitors in delaying the neurodegenerative process will be discussed.