Efficacy of tacrine and lecithin in mild to moderate Alzheimer's disease: double blind trial

Unlocking choline's potential in Alzheimer's disease: A narrative review exploring the neuroprotective and neurotrophic role of phosphatidylcholine and assessing its impact on memory and learning

BACKGROUND AND AIMS

Growing evidence suggests nutritional intervention may influence the development and progression of Alzheimer's Disease (AD). Choline, an essential dietary nutrient plays a critical role in neurological development and brain function, however, its effects on AD in humans is unclear. The research aims to investigate mechanistic links between dietary choline intake and cognitive functioning, focusing on the role of phosphatidylcholine (PC) in neuroplasticity and its interaction with amyloid beta (Aβ) peptides in neuron membranes. Additionally, human evidence on the potential benefits of PC interventions on AD, cognition, and proposed mechanisms are evaluated.

METHODS

A reproducible systematic literature search was performed using a three-tranche strategy, consisting of a review, mechanism, and intervention search. Using PubMed as the main database, 1254 titles and abstracts were screened, 149 papers were read in full and 65 peer-reviewed papers were accepted, critically appraised, and analysed in a narrative review.

RESULTS

Predominantly preclinical evidence demonstrated that PC enhances neuroplasticity, a key biological substrate for cognition, by activating intracellular neuronal signalling pathways or through neuron membrane function. Molecular dynamic simulation methods provided a mechanistic understanding of the interconnection between neuronal PC content and the potential behaviour and trajectory of Aβ peptide aggregation. The results indicate that the neuronal membrane composition of PC is critical to inhibiting Aβ aggregation and neuronal damage, protecting the neuron from Aβ toxicity. This might provide a foundation for optimising cellular PC which may prove beneficial in the treatment or prevention of neurodegenerative disease. Altered PC metabolism in AD was evidenced in observational studies; however, whether this relationship represents a cause or consequence of AD remains to be determined. Human intervention studies did not produce conclusive evidence supporting its effectiveness in enhancing cognitive function. This lack of consistency primarily stems from methodological constraints within the conducted studies. Human observational research provided the most compelling evidence linking a higher dietary PC intake to a reduced risk of dementia and significant improvements in cognitive testing.

CONCLUSION

Despite the lack of randomised control trials (RCTs) assessing the efficacy of lecithin/PC to improve cognition in AD patients, there exists promising evidence supporting its neuroprotective and neurotrophic role. This review establishes an evidence-based framework through chains of mechanistic evidence, that may provide potential strategies for enhanced neuroprotection and reduced neurodegeneration caused by AD. Considering the escalating global burden of AD and the current shortcomings in effective treatments, this review together with the limitations and gaps identified in the existing research presents valuable insights that emphasise the urgency of more comprehensive research into the relationship between PC and AD.

Advancements in the development of multi-target directed ligands for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial irreversible neurological disorder which results in cognitive impairment, loss of cholinergic neurons in synapses of the basal forebrain and neuronal death. Exact pathology of the disease is not yet known however, many hypotheses have been proposed for its treatment. The available treatments including monotherapies and combination therapies are not able to combat the disease effectively because of its complex pathological mechanism. A multipotent drug for AD has the potential to bind or inhibit multiple targets responsible for the progression of the disease like aggregated Aβ, hyperphosphorylated tau proteins, cholinergic and adrenergic receptors, MAO enzymes, overactivated N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor etc. The traditional approach of one disease-one target-one drug has been rationalized to one drug-multi targets for the chronic diseases like AD and cancer. Thus, over the last decade research focus has been shifted towards the development of multi target directed ligands (MTDLs) which can simultaneously inhibit multiple targets and stop or slow the progression of the disease. The MTDLs can be more effective against AD and eliminate any possibility of drug-drug interactions. Many important active pharmacophore units have been fused, merged or incorporated into different scaffolds to synthesize new potent drugs. In the current article, we have described various hypothesis for AD and effectiveness of the MTDLs treatment strategy is discussed in detail. Different chemical scaffolds and their synthetic strategies have been described and important functionalities are identified in the chemical scaffold that have the potential to bind to the multiple targets. The important leads identified in this study with MTDL characteristics have the potential to be developed as drug candidates for the effective treatment of AD.

Tacrine for Alzheimer's Disease: Therapeutic Considerations

Alzheimer's disease (AD) is a progressive, irreversible neurological disease that burdens both patient and family with emotional, financial, and social costs. Approximately four million people have been diagnosed as having AD. In 1991, 266,000 cases of AD were diagnosed. This number is expected to increase as our population ages. In the past numerous drugs have been studied and used clinically in an attempt to reverse or slow the memory impairment, confusion, and behavioral problems caused by AD. None have been found to be consistently effective. In November 1993 the first drug in the USA, tacrine (Cognex), was approved for the treatment of AD. This approval has not come without some controversy. A considerable debate still exists as to the efficacy of tacrine in AD. Approximately 45% of patients will have a substantial increase in their liver function tests (ALT). Patients require close monitoring, especially during the first 18 weeks of treatment. In addition to this, tacrine does appear to have a number of less serious, but bothersome side effects and possible drug-drug and drug-disease interactions. This article provides the pharmacist with practical information regarding the safe, most effective use of this interesting drug. Tacrine is the first drug approved for the treatment of AD, but almost certainly not the last.

Synthesis of Novel 3-Aryl-N-Methyl-1,2,5,6-Tetrahydropyridine Derivatives by Suzuki coupling: As Acetyl Cholinesterase Inhibitors

Alzheimer’s disease (AD) is a neurodegenerative disorder affecting the central nervous system, which is also associated with progressive loss of memory and cognition. The development of numerous structural classes of compounds with different pharmacological profile could be an evolving, promising therapeutic approach for the treatment of AD. Thus, providing a symptomatic treatment for this disease are cholinomimetics with the pharmacological profile of Acetylcholinesterase (AChE) inhibitors. In view of this, we have synthesized novel 3-aryl-N-methyl-1,2,5,6-tetrahydropyridine derivatives 5a-k by Suzuki coupling and screened the efficacy of these derivatives for their AChE inhibitor activity.

A 12-month study of the efficacy of rivastigmine in patients with advanced moderate Alzheimer's disease

The efficacy of a centrally active cholinesterase inhibitor, rivastigmine tartrate (ENA 713), in patients with advanced moderate Alzheimer's disease (AD) was evaluated in a 12-month placebo-controlled study. We aimed to investigate whether there was any evidence for the benefits of rivastigmine in patients with severe disease. These patients were compared with matched controls. In this study, 24 patients with advanced moderate AD received rivastigmine for 12 months. Another 20 patients received placebo. Mean daily doses of rivastigmine in the higher-dose group at 3, 6, 9, and 12 months were 6.1 +/- 1.0, 8.3 +/- 1.2, 8.9 +/- 1.3, and 10.7 +/- 1.6 mg/day, respectively. Cognitive abilities were assessed using the 11-item cognitive subscale of the Alzheimer Disease Assessment Scale (ADAS-cog). Forty-five percent of placebo-treated patients declined by at least 4 points on the ADAS-cog. Conversely, only 18.3% of patients treated with rivastigmine declined by 4 or more points. Functional disabilities, as assessed using the Disability Assessment for Dementia Scale, remained significantly superior in rivastigmine-treated patients compared with placebo-treated patients. Patients benefited from high-dose rivastigmine treatment on all outcome measures, including the Mini-Mental State Examination, Progressive Deterioration Scale, as well as the Global Deterioration Scale. Patients receiving rivastigmine for 12 months significantly improved compared with placebo-treated patients (p < 0.001). By 52 weeks, patients originally treated with 6-12 mg/day rivastigmine had a significantly better cognitive function than patients originally treated with placebo. Long-term rivastigmine treatment appeared to be well tolerated in patients with advanced moderate AD and significantly benefits the cognitive and functional symptoms of AD.

Serotonin, locomotion, exploration, and place recall in the rat

Intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) led to a 90% reduction of the 5-hydroxytryptamine (5-HT) reuptake site. Behavioural symptoms were studied early (45 to 93 h) as well as late (11 to 14 days) in the postoperative period. Forty-five hours postoperatively, recall of a place navigation task in a water maze was clearly impaired in 5,7-DHT-treated animals. This impairment had disappeared by the fifth postoperative session. During the early test period, injection of scopolamine (0.5 mg/kg) or d-amphetamine (3.0 mg/kg) did not affect place recall of the vehicle-treated control group. In contrast, 5,7-DHT-treated animals were impaired by administration of scopolamine, but not d-amphetamine. During the late test period, the place recall of both groups was affected by scopolamine, but only the performance of the 5,7-DHT lesioned animals was sensitive to d-amphetamine. Locomotion was not severely affected at any time after 5,7-DHT treatment. The vertical hole-board test indicated that the exploratory activities of the animals were relatively unaffected by 5,7-DHT when measured 48 h postoperatively. At 14 days postsurgery, the 5,7-DHT-treated animals demonstrated an impaired habituation of the exploratory behaviour.

Complementary and Alternative Medicines in the Treatment of Dementia

Alternative medicines may have potential beneficial results in treating certain forms of dementia and related symptoms, as well as slowing disease progression. Alternative medicines may ameliorate disturbances in cognition, mood, sleep and activities of daily living. Primary mechanisms of action include modifications in neurotransmitter synthesis, inhibition of neurotransmitter reuptake and enzyme-induced neurotransmitter breakdown, antioxidant and anti-platelet activity, enhanced blood flow and glucose metabolism. Adverse events can include cardiovascular, gastrointestinal, mood, autonomic and dermatologic effects. However, adverse events, when reported represent, a small percentage of treated groups and direct links between adverse events and alternative therapies are tenuous. Many studies of alternative medicines in dementia are inconclusive and characterised by methodological deficiencies such as small sample sizes and inadequate controls. If alternative medicines can be shown to be efficacious using more rigorous experimental designs, both consumers and clinicians could avail themselves of a wider range of pharmacological substances that may offer the advantage of being better tolerated and exhibiting safer therapeutic margins than some allopathic medicines. While a number of complementary interventions have shown both strengths and weaknesses, huperzine A, levacecarnine and EGB 761, based on the overall quality of the studies, identified mechanisms of activity and safety profiles merit further examination in controlled clinical outcome studies.

Enhancement of neuronal nicotinic receptor activity of rat chromaffin cells by a novel class of peptides

The N-terminal 1-7 fragment of the neuropeptide CGRP inhibits neuronal nicotinic acetylcholine receptors (nAChRs) of rat chromaffin cells. To identify the structural motif responsible for this action, we investigated the effects of shorter CGRP fragments on patch-clamped rat chromaffin cells in culture. CGRP(1-6) evoked no direct change in baseline current or input conductance, but it strongly potentiated inward currents induced by very fast, nondesensitizing applications of nicotine. Potentiation was use independent and present even when coapplied with nicotine. The action of CGRP(1-6) was voltage independent and agonist independent. Because equimolar concentrations of CGRP(1-6) and CGRP(1-7) left nicotine-induced submaximal currents unchanged, these peptides presumably acted via a similar site through which they generated opposite effects. This observation also suggests that a single amino acid deletion could transform a peptide antagonist into a potentiating one. Deleting one amino acid from the COO(-) end of the CGRP(1-6) sequence yielded CGRP(1-5), which retained smaller potentiating activity. Even the CGRP(1-4) fragment possessed slight potentiation, which was lost with CGRP(1-3). CGRP(1-6) preferentially potentiated small over large responses to nicotine. One possibility is that CGRP(1-6) interacted with nAChRs like an allosteric modulator (e.g., physostigmine). Coapplication of enhancing concentrations of physostigmine and CGRP(1-6) led to linear summation of the individual effects, while CGRP(1-6) could partly reverse the depression by a large concentration of physostigmine. These data indicate functionally distinct sites of action for CGRP(1-6) and physostigmine. Potentiation of nicotinic receptors by CGRP(1-6) and its derivatives suggests them to be a new class of molecules enhancing activity mediated by nAChRs.

Synthesis and in vitro muscarinic activities of a series of 1,3-diazacycloalkyl carboxaldehyde oxime derivatives

A series of 1,3-diazacycloalkyl carboxaldehyde oxime derivatives was synthesized and tested for muscarinic activity in receptor binding assays using [3H]-oxotremorine-M (OXO-M) and [3H]-pirenzepine (PZ) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies measuring their potencies to inhibit the binding of OXO-M and PZ. Preferential inhibition of OXO-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs.

A novel class of peptides with facilitating action on neuronal nicotinic receptors of rat chromaffin cells in vitro: functional and molecular dynamics studies

Peptides related to the N-terminal region of calcitonin gene-related peptide (CGRP) were tested for their ability to modulate neuronal nicotinic acetylcholine receptors (nAChRs) of rat cultured chromaffin cells under whole cell patch-clamp conditions. Although CGRP(1-7) and CGRP(2-7) depressed responses mediated by nAChRs, CGRP(1-6), CGRP(1-5), or CGRP(1-4) rapidly and reversibly potentiated submaximal nicotine currents while sparing maximal currents. CGRP(1-3) was inactive. The threshold concentration for the enhancing effect of CGRP(1-6) was 0.1 microM. CGRP(1-5) or CGRP(1-4) were less effective than CGRP(1-6). Coapplication of CGRP(1-6) and of the allosteric potentiator physostigmine (0.5 microM) gave additive effects on nicotine currents. CGRP(1-6) did not enhance responses generated by muscle-type nicotinic receptors of cultured myoblasts or by gamma-aminobutyric acid(A) receptors expressed by human embryonic kidney cells. Molecular dynamics (MD) simulations suggested that CGRP(1-7) exhibited a relatively rigid ring structure imparted by the disulfide bridge between Cys(2) and Cys(7). The circular dichroism (CD) spectrum recorded from the same peptide was in agreement with this result. Shorter peptides, missing such a bridge, exhibited propensity for alpha-helix configuration. Replacing Cys(7) with Ala yielded CGRP(1-7A), a fragment with partial alpha-helix structure and ability to enhance nicotine currents. CD measurements on CGRP(1-6) were compatible with these MD structural findings. Short terminal fragments of CGRP represent a novel class of substances with selective, rapid, and reversible potentiation of nAChRs.

Acetyl-L-carnitine physical-chemical, metabolic, and therapeutic properties: relevance for its mode of action in Alzheimer's disease and geriatric depression

Acetyl-L-carnitine (ALCAR) contains carnitine and acetyl moieties, both of which have neurobiological properties. Carnitine is important in the beta-oxidation of fatty acids and the acetyl moiety can be used to maintain acetyl-CoA levels. Other reported neurobiological effects of ALCAR include modulation of: (1) brain energy and phospholipid metabolism; (2) cellular macromolecules, including neurotrophic factors and neurohormones; (3) synaptic morphology; and (4) synaptic transmission of multiple neurotransmitters. Potential molecular mechanisms of ALCAR activity include: (1) acetylation of -NH2 and -OH functional groups in amino acids and N terminal amino acids in peptides and proteins resulting in modification of their structure, dynamics, function and turnover; and (2) acting as a molecular chaperone to larger molecules resulting in a change in the structure, molecular dynamics, and function of the larger molecule. ALCAR is reported in double-blind controlled studies to have beneficial effects in major depressive disorders and Alzheimer's disease (AD), both of which are highly prevalent in the geriatric population.

Tacrine interacts with different sites on nicotinic receptor subtypes in SH-SY5Y neuroblastoma and M10 cells

The effect of chronic treatment with the cholinesterase inhibitor tacrine on nicotinic receptor subtypes was investigated in human SH-SY5Y neuroblastoma cells and in a fibroblast cell line (M10 cells) stably transfected with alpha4beta2 nicotinic receptors. Tacrine significantly increased the number of nicotinic receptors in SH-SY5Y cells, in a concentration dependent manner (10(-9) to 10(-4) M), when using [3H]epibatidine as labelled ligand. Chronic tacrine treatment of M10 cells significantly increased and decreased the number of alpha4beta2 nicotinic receptors in a concentration dependent manner (10(-9) to 5 x 10(-6) M and 2 x 10(-5) to 10(-4) M, respectively). The tacrine induced increase of nicotinic receptors in SH-SY5Y cells, was not blocked in the presence of the nicotinic antagonists tubocurarine or mecamylamine. A further increase in the number of nicotinic receptors was, however, observed in the presence of mecamylamine. This study demonstrates that the effect of tacrine on the number of nicotinic receptor subtypes is different in human SH-SY5Y neuroblastoma and M10 cells. The up-regulation of different nicotinic receptor subtypes obtained with tacrine might be achieved through interaction via different binding sites on the receptor, i.e. the acetylcholine binding site as well as an allosteric site.

Neuronal nicotinic receptors in the human brain

Neuronal nicotinic acetylcholine receptors (nAChRs) are a family of ligand gated ion channels which are widely distributed in the human brain. Multiple subtypes of these receptors exist, each with individual pharmacological and functional profiles. They mediate the effects of nicotine, a widely used drug of abuse, are involved in a number of physiological and behavioural processes and are additionally implicated in a number of pathological conditions such as Alzheimer's disease, Parkinson's disease and schizophrenia. The nAChRs have a pentameric structure composed of five membrane spanning subunits, of which nine different types have thus far been identified and cloned. The multiple subunits identified provide the basis for the heterogeneity of structure and function observed in the nAChR subtypes and are responsible for the individual characteristics of each. A substantial amount of information on human nAChR structure and function has come from studies on neuroblastoma cell lines which naturally express nAChRs and from recombinant nAChRs expressed in Xenopus oocytes. In vitro brain nAChR distribution can be mapped with a number of appropriate agonist and antagonist radioligands and subunit distribution may be mapped by in situ hybridization using subunit specific mRNA probes. Receptor distribution in the living human brain can be studied with noninvasive imaging techniques such as PET and SPECT, with a significant reduction in nAChRs in the brains of Alzheimer's patients having been identified with [11C] nicotine in PET studies. Despite the significant body of knowledge now accumulated about nAChRs, much remains to be elucidated. This review will attempt to describe the current knowledge on the nAChR subtypes in the human brain, their functional roles and neuropathological involvement.

Synthesis and in vitro muscarinic activities of a series of 3-(pyrazol-3-yl)-1-azabicyclo[2.2.2]octanes

A series of 3-(pyrazol-3-yl)-1-azabicyclo[2.2.2]octane derivatives C (Fig. 1) was synthesized and tested for muscarinic activity in receptor binding assays using [3H]-oxotremorine-M (OXO-M) and [3H]-pirenzepine (PZ) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies measuring their potencies to inhibit the binding of OXO-M and PZ. Preferential inhibition of OXO-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs.

Tacrine for Alzheimer's disease

BACKGROUND

Tacrine is one of the first drugs to be widely marketed for the loss of memory and intellectual decline in Alzheimer's disease. The alleged success of tacrine in the treatment of these symptoms has been heralded as confirmation of the cholinergic theory of Alzheimer's disease. However, the efficacy of tacrine for symptoms of dementia remains controversial. This is reflected by the low rate of prescription of tacrine in countries where it is approved and the lack of approval by several regulatory authorities in Europe and elsewhere. The uncertainty about the efficacy of tacrine is due to the difficulties in interpretation of the results from the clinical trials. The reasons for this are the small effects of tacrine compared to placebo for all outcomes; the high incidence of adverse events; the lack of benefit observed in several trials; the use of cross-over designs and their associated methodological problems in a disease like dementia; the use of different measurement scales to assess outcome in different trials; and the problem of high dropout rates.

OBJECTIVES

To determine the clinical efficacy of tacrine for the symptoms of Alzheimer's disease.

SEARCH STRATEGY

The Cochrane Dementia Group Register of Clinical Trials was searched using the terms 'tacrine', 'tetrahydroaminoacridine' and 'THA' (see the Group's search strategy for full details).

SELECTION CRITERIA

All unconfounded, double-blind, randomized trials in which treatment with tacrine was administered for more than a day and compared to placebo in patients with dementia of the Alzheimer's type.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two reviewers, pooled if appropriate and possible, and the pooled odds ratios (95%CI) or the average differences (95%CI) were estimated. Where possible, intention-to-treat data were used.

MAIN RESULTS

This review produced no clear results. The results were compatible with tacrine producing improvement, no change or even harm for those with Alzheimer's disease. It was not possible to use many of the published results in a combined analysis. For measures of overall clinical improvement, the intention-to-treat analyses failed to detect any difference between tacrine and placebo (OR 0.87; 95%CI 0.61 - 1.23). Behavioural disturbance, as measured by the Alzheimer's Disease Assessment Scale-noncognitive, failed to detect any difference between tacrine and placebo (SMD -0.04; 95%CI -0.52 - 0.43). For cognition function, the effect of tacrine was not statistically significantly different from placebo for the MiniMental State Examination score (0-30; high =good) (SMD 0.14; 95%CI -0.02 - 0.30) and was barely statistically significantly in favour of treatment for the Alzheimer's Disease Assessment Scale-cognitive scale (SMD -0.22; 95%CI -0.32 - -0.13). Adverse events were not reported in a systematic way in the different trials, making formal comparison difficult. Raised serum liver enzymes was the major reason for withdrawal. The odds ratio for withdrawal due to an adverse event was significantly different from one, the control group experienced fewer events (OR 5.7; 95%CI 4.1-7.9). Gastrointestinal side effects (diarrhoea, anorexia, dyspepsia and abdominal pain) were the other major cause of adverse events and for withdrawal, and the odds ratio for withdrawal was also significantly different from one in favour of the control group (OR 3.8; 95%CI 2.8-5.1). No deaths were reported in any of the studies during the trial period, up to six months.

REVIEWER'S CONCLUSIONS

This review provides no convincing evidence that tacrine is a useful treatment for the symptoms of Alzheimer's disease. However, as so few trials presented data in a format suitable for pooling, the results of this review may be modified when further data from all relevant trials are included. There is an urgent need for the independent evaluation of the data already existing in the trials but not accessible through published or grouped data. A

Memory assessment in studies of cognition-enhancing drugs for Alzheimer's disease

There is an increasing number of cognition-enhancing drugs for Alzheimer's Disease (AD) and, consequently, drug trials represent a growing field of interest in research. As memory dysfunction is generally the first and most severe cognitive impairment in AD, the choice of memory testing to be used in these studies is of great importance. It should reflect an understanding of memory systems being assessed with neuropsychological tests and the fact that some tests can be more appropriate than others to show benefit with certain classes of cognition-enhancing drugs. Severe deterioration of episodic and semantic memory occurs very early in the AD process while working memory shows a gradual deterioration over time. Some aspects of working and implicit memory can be spared in the mild to moderate stages of AD. Tests of working, episodic, semantic and implicit memory are used as outcomes in trials with acetylcholinesterase inhibitors, drugs with other neurotransmitter strategies, metabolic enhancers and drugs which may impact upon a variety of CNS processes. The clinical scales and observational measures are largely used in trials of cognition-enhancing drugs for AD (46.66% of all the studies reviewed). The Digit Span test, the Rey Auditory Verbal Learning Test, the Buschke Selective Reminding Test and the verbal fluency tasks are the most sensitive memory tests, whereas the most sensitive scales are the Sandoz Clinical Assessment-Geriatric, the Gottfried-Bräne-Steel scale and the Blessed Dementia Scale. Finally, we suggest that future investigations should use sensitive memory tests, together with behavioural and psychiatric scales, rather than general observational evaluations.

Effects of the novel acetylcholinesterase inhibitor N-octyl-1,2,3, 4-tetrahydro-9-aminoacridine on locomotor activity and avoidance learning in mice

The acetylcholinesterase reversible inhibitor N-octyl-1,2,3, 4-tetrahydro-9-aminoacridine (THA-C8) is a new synthesized derivative of tacrine (THA) characterized by an alkyl chain in the molecular structure which ameliorates the penetrability of the compound into the central nervous system. THA-C8 (0.1-5 mg/kg) significantly reduced spontaneous locomotor activity in CD1 mice at a dose of 3 mg/kg. Moreover, THA-C8 (0.2-2 mg/kg) significantly improved shuttle-box avoidance acquisition at doses (0.25, 0.3, 1 mg/kg) not affecting locomotion and that are much lower than the doses reported to be effective for THA in animal models. From the data reported it seems that the new compound could be interesting for therapeutic purposes.

Cholinesterase inhibitors in the treatment of Alzheimer's disease: a comparison of tolerability and pharmacology

Cholinesterase inhibitors are currently the most established treatment strategy in Alzheimer's disease. The treatment effect appears mainly to be symptomatic. Effects on progression of the disease following long term treatment, and possible neuroprotective effects, have been investigated. Delay until nursing home placement has been reported. Three cholinesterase inhibitors, tacrine, donepezil and rivastigmine, are in clinical use. Other cholinesterase inhibitors, such as galantamine (galanthamine), metrifonate, physostigmine, eptastigmine, are currently under clinical evaluation. So far the efficacy appears to be comparable between the various cholinesterase inhibitors; treatment for up to 6 months has produced an improvement in Alzheimer's Disease Assessment Scale -- Cognitive Subscale score (ADAS-cog) of between 1.8 and 4.9 in patients with Alzheimer's disease. Tacrine, donepezil, galantamine and physostigmine are reversible inhibitors of acetylcholinesterase and butyrylcholinesterase, while metrifonate is considered to be an irreversible inhibitor and rivastigmine a pseudoirreversible inhibitor. Tacrine and physostigmine have lower bioavailability, 17 to 37% and 3 to 8%, respectively, than the other cholinesterase inhibitors such as rivastigmine, galantamine and donepezil (40 to 100%). The elimination half-life is considerably longer for donepezil (70 to 80h) in comparison to most of the other cholinesterase inhibitors (0.3 to 12h). Donepezil is therefore administered once daily in comparison to rivastigmine which is administered twice daily and tacrine which is administered 4 times daily. Simultaneous food intake lowers the plasma concentration of tacrine and reduces the adverse effects of rivastigmine. Drugs like theophylline and cimetidine have been reported to change the pharmacokinetics of tacrine and donepezil. In contrast, concomitant medication with various drugs with rivastigmine does not seem to cause any drug interactions in patients with Alzheimer's disease. Tacrine, donepezil and galantamine are metabolised via the cytochrome P450 (CYP) liver enzymes. Active metabolites are known for tacrine and galantamine. Rivastigmine is not metabolised via CYP enzymes, but via esterases and is excreted in the urine. Tacrine is associated with hepatotoxicity while other cholinesterase inhibitors seem devoid this adverse effect. Increased liver enzyme values have been observed in 49% of patients with Alzheimer's disease treated with tacrine. Rechallenge with tacrine reduces the incidence of elevated liver enzyme levels. Peripheral cholinergic adverse effects are common for the cholinesterase inhibitors, with an incidence ranging between 7 to 30%. For some cholinesterase inhibitors, such as rivastigmine, the cholinergic adverse effects such as nausea, vomiting, dizziness, diarrhoea and abdominal pain can be reduced by slowing the rate of dose titration.

Synthesis, and in vitro and in vivo muscarinic pharmacological properties of a series of 1,6-dihydro-5-(4H)-pyrimidinone oximes

A series of 1,6-dihydro-5-(4H)-pyrimidinone oxime derivatives I was synthesized (Scheme 1, Tables 1 and 2) and tested for muscarinic activity (Table 3) in receptor binding assays using [3H]-oxotremorine-M (Oxo-M) and [3H]-pirenzepine (Pz) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies that measured their potencies to inhibit the binding of Oxo-M and Pz. Preferential inhibition of Oxo-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs. The series produced a wide range of active compounds with differing degrees of selectivity in M1, M2, and M3 functional models. Several compounds that have mixed agonist/antagonist profiles were able to reduce cholinergic-related cognitive impairments in models of mnemonic function. Substitutions (I, e.g. R2 or R3 = Me) at the 1,6-dihydro-5-(4H)pyrimidine ring disrupted binding and efficacy, whereas systematic variation of the oximes substituent R1 resulted in various degrees of potency and selectivity dependent on the nature of the substitution.

Is there a rationale for the use of acetylcholinesterase inhibitors in the therapy of Alzheimer's disease?

Since the 1980s, the cholinergic hypothesis of the pathogenesis of Alzheimer's disease has proven to be a strong stimulus to pharmacological strategies aimed at correcting the cognitive deficit by manipulating cholinergic neurotransmission. Among these strategies, the one based on acetylcholinesterase inhibition is currently the most extensively developed for the therapy of Alzheimer's disease. The inhibitors' mechanisms of action are complex, including changes in the release of acetylcholine, and modulation of acetylcholine receptors. Various clinical trials of various inhibitors have shown that, on the whole, their effects were modest and, in the case of some drugs, were associated with frequent adverse reactions. Among the conceivable reasons for the limited efficacy of these drugs, those related to the pharmacological target deserve particular attention. This review, therefore, focuses on the complex nature of the acetylcholine system, the alterations of acetylcholinesterase and muscarinic receptor signal transduction in Alzheimer's disease, and the involvement of other neurotransmitters.

Arisugacins, selective acetylcholinesterase inhibitors of microbial origin

Synthetic inhibitors of acetylcholinesterase (AChE) recently have attracted particular attention for treatment of Alzheimer's disease. By systematic screening of microbial metabolites, we were able to discover the new AChE inhibitors, named arisugacins A and B, from the culture broth of Penicillium sp. FO-4259. The structures of arisugacins are members of the meroterpenoid compounds. Arisugacin A is a potent and highly selective inhibitor of AChE but does not inhibit butyrylcholinesterase in vitro. Arisugacin A is a good candidate as an excellent potential drug for treatment of Alzheimer's disease. Also reviewed is the current status of development of antidementia drugs.

In vivo magnetic resonance spectroscopy of human brain: the biophysical basis of dementia

Nuclear magnetic resonance spectroscopy (MRS) in low and medium magnetic fields yields well-resolved natural abundance proton and decoupled phosphorus spectra from small (1-10 cc) volumes of brain in vivo in minutes. With this tool, neurochemical research has advanced through identification and non-invasive assay of specific neuronal--(N-acetylaspartate), glial (myo-inositol)--markers, energetics and osmolytes, and neurotransmitters (glutamate, GABA). From these simple measurements, several dozen disease states are recognized, including birth injury, and white matter and Alzheimer disease. Addition of stable isotopes of carbon (in man) or nitrogen (in experimental animals) has provided in vivo assays of enzyme flux through glucose transport, glycolysis, TCA-cycle, and the glutamine-glutamate-GABA system. Finally, a number of xenobiotics are recognized with heteronuclear NMR techniques. Together, these tools are having a major impact on neuroscience and clinical medicine. Through diagnosis and therapeutic monitoring, a new generation of in vivo metabolite imaging is expected with the advent of conforming RF coils and higher field NMR systems.

A risk-benefit assessment of tacrine in the treatment of Alzheimer's disease

Tacrine, the first drug specifically approved for Alzheimer's disease, produces symptomatic improvement. The theoretical rationale behind treating Alzheimer's disease with tacrine is based on central cholinergic depletion. Tacrine is centrally acting, uncompetitive reversible inhibitor of acetylcholinesterase and butyrylcholinesterase. Multiple clinical trials support the effectiveness of tacrine in Alzheimer's disease. High dosages of tacrine are required for efficacy, with the potential for hepatic and mild gastrointestinal adverse effects. However, the benefits of tacrine currently outweigh its risks, and a trial of the drug should be offered to patients. As clinical experience with tacrine increases, the long term risk-benefit equation may be refined.

The biology of Alzheimer's disease

The pathological hallmarks of Alzheimer's disease (AD) are amyloid angiopathy (AA), neutritic plaques (NP), and neurofibrillary tangles (NFT). This article will provide an update on Alzheimer's disease as well as discuss the key elements of a proposed multi-step pathogenic pathway. In an attempt to simplify this complex process, the focus will be on the production of NP/AA and NFT and the mechanisms of disease underlying their formation. In particular, this review will explore the possibility that AD is in part an inflammatory or immunological process, the potential role of oxidative DNA damage from oxygen free radical metabolites, and/or the putative role of excitotoxicity or ischemic neurological injury. Several genes have been identified as causative of AD and the evidence supports multiple mechanisms of disease. Alzheimer's disease may represent a final common pathway of different disease processes.

Synthesis and muscarinic activities of 3-(pyrazolyl)-1,2,5,6-tetrahydropyridine derivatives

A series of 3-(pyrazolyl)-1,2,5,6-tetrahydropyridine derivatives (B) was synthesized and tested for muscarinic activity in receptor binding assays using [3H]-oxotremorine-M (3H-OXO-M) and [3H]-pirenzepine (3H-PZ) as ligands. Potential muscarinic agonistic or antagonistic properties of the compounds were determined using binding studies measuring their potencies to inhibit the binding of 3H-OXO-M and 3H-PZ. Preferential inhibition of 3H-OXO-M binding was used as an indicator for potential muscarinic agonistic properties; this potential was confirmed in functional studies on isolated organs. All compounds with agonistic properties showed 3H-PZ/3H-OXO-M potency ratios in excess of 20. In contrast, for antagonists this ratio was found to be close to unity. Mono-halogenation resulted in compounds (4b and 4d) with M3 agonistic properties as shown by their atropine sensitive stimulant properties in the guinea pig ileum, but with very little or no M1 activity. Some minor in vivo effects were observed for both these compounds, with the iodinated compound 4d inducing salivation. Compound 4d also showed some positive mnemonic properties in rats where spatial short-term memory had been compromised by temporary cholinergic depletion. These data indicate that some M3 agonism may be desired in therapeutic agents aimed at the treatment of the cognitive deficits of Alzheimer's disease patients.

Synthesis and muscarinic M3 pharmacological activities of 1-azabicyclo[2.2.2]octan-3-one oxime derivatives

A series of 1-azabicyclo[2.2.2]octan-3-one oximes and related 1-azabicyclo-[2.2.2]-octan-3-one hydroxylamines were synthesized and tested for muscarinic M3 activity. All compounds showed at least some muscarinic binding properties, however, only one member of the series demonstrated mucarinic M3 agonistic properties in vitro (contraction of guinea pig ileum) and in vivo (mydriasis, salivation). In addition, this compound partially reversed the cognitive deficit induced by central cholinergic depletion in two procedures testing memory in the rat, namely the delayed matching to position and swim maze tasks of spatial memory in the rat.

Amnesia induced in mice by centrally administered beta-amyloid peptides involves cholinergic dysfunction

Substantial evidences suggest that the increased cerebral deposition, and neurotoxic action of the beta-amyloid peptide, the major constituent of senile plaques, may represent the underlying cause of the cognitive deficits observed in Alzheimer's disease. Herein, we attempted to verify this hypothesis by inducing a potential Alzheimer's-type amnesia after direct intracerebroventricular administration of aggregated beta 25-35-amyloid peptide in mice. In this aim, mnesic capacities were evaluated after 6-13 days, using spontaneous alternation in the Y-maze, step-down type passive avoidance and place learning in a water-maze. Pretraining administration of aggregated beta 25-35 peptide induced dose-dependent decreases in both alternation behaviour and passive avoidance, at doses of 3 and 9 nmol/mouse. A reduced but still significant impairment was observed when the peptide was not aggregated, or 'aged', by preincubation for 4 days at 37 degrees C. The beta 1-28 peptide, at 3 nmol/mouse, also induced a marked decrease in step-down latency. Posttraining, but not preretention, administration of beta 25-35 peptide also significantly impaired learning. The beneficial effects of cholinergic agents on beta 25-35-induced amnesia was examined using the cholinesterase inhibitor tacrine (THA, 1.3 and 4.3 mumol/kg i.p.) and the nicotinic receptor agonist (-)-nicotine (NIC, 0.06 and 0.2 mumol/kg i.p.). Both drugs induced a dose-dependent abrogation of the beta 25-35-induced decreases in alternation behaviour and passive avoidance. Furthermore, THA, at 1.3 mumol/kg, and NIC, at 0.2 mumol/kg, also reversed the beta 25-35-induced impairment of place learning and retention in the water-maze. Histological examination of Cresyl violet-stained brain sections indicated a moderate but significant cell loss within the frontoparietal cortex and the hippocampal formation of mice treated with aged beta 25-35 peptide (9 nmol). Examination of Congo red-stained sections in the same animals demonstrated the presence of numerous amyloid deposits throughout these brain areas. These results confirm that the deposition of beta-amyloid peptide in the brain is in some way related to impairment of learning and cholinergic degeneration and suggest that the [25-35] fragment of the beta-amyloid protein, sufficient to induce neuronal death in cultures, also induces an Alzheimer's-type amnesia in mice.

A double-blind, placebo-controlled study of tacrine in patients with Alzheimer's disease using SPET

BACKGROUND

the effect of single-dose and long-term cholinergic enhancement with tacrine on regional cerebral perfusion was examined in patients with Alzheimer's disease using single-photon emission tomography (SPET).

METHOD

23 patients with probable Alzheimer's disease (DSM-III-R and NINCDS-ADRDA criteria) were scanned before and after a single oral dose of tacrine at the start of the study and again after 12 weeks of randomized, double-blind treatment with tacrine or placebo, using high resolution (99m)Tc-Exametazime SPET. Patients also underwent neuropsychological testing with the CAMCOG, the Mini-Mental State Examination and the Rivermead Behavioural Memory Test before and after 12 weeks of treatment.

RESULTS

occipital count ratios in all regions of interest declined by 3% over 12 weeks, indicating a progression of the disease. Acute tacrine challenge resulted in a 16% increase in the superior frontal and a 11% decrease in the anterior temporal cortex. The acute effects of tacrine were modified by 12 weeks of treatment, particularly in the medial frontal (cingulate) cortex where active treatment was associated with a reduced acute tacrine response. There were no changes in cognitive function associated with active treatment.

CONCLUSION

the study demonstrates the sensitivity of cerebral perfusion measures to changes during acute and medium-term tacrine treatment.

Effects of tacrine (THA) on spatial reference memory and cholinergic enzymes in specific rat brain regions

Cognitive function of rats treated with saline (control), THA (8 mg/kg, i.p.), scopolamine (5 mg/kg, i.p.), or a combination of THA (8 mg/kg) and scopolamine (5 mg/kg) was tested in the Morris water maze. The latency to find the platform in the water maze was used to evaluate performance. THA did not significantly alter the latency period as compared to control rats. Scopolamine resulted in a highly significant (p<0.01) increase in latency period (183% increase) as compared to saline treated controls. However, when THA was concurrently administered with scopolamine, it was able to completely reverse the performance decrement induced by scopolamine. Immediately following spatial reference memory testing, animals were sacrificed by decapitation one hour post injection. Brains were immediately removed and the cortex, hippocampus, hypothalamus, and pituitary were dissected and their choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity were determined spectrophotometrically. THA administration resulted in a significant increase in ChAT activity in the cortex (23% increase). However, when THA was concurrently administered with scopolamine, a significant increase in ChAT activity was observed in cortex (77% increase), hippocampus (32% increase), hypothalamus (97% increase), and pituitary (92.5% increase). THA administration resulted in a significant decrease in AChE activity (p<0.001) in cortex (62% decrease), hippocampus (78% decrease), and hypothalamus (90% decrease). When tacrine was administered with scopolamine, a significant increase was found in the cortex (197% increase) and the hippocampus (207% increase). In conclusion, the increase in ChAT activity produced by tacrine may in part explain its ability to reverse the scopolamine induced decrease in spatial reference memory and may play a role in its beneficial effect in improving cognitive ability.

[New therapeutic prospects in Alzheimer disease]

The approval for marketing of tacrine (Cognex), an acetylcholinesterase inhibitor, allowed physicians and the general people to attract attention to a degenerative disease, which prevalence dramatically increases every year. This drug is hopeful. Meanwhile, we must keep in mind that it has only a symptomatic effect. Its hepatotoxicity requires regular biological tests. Many medications are actually in earlier stages of development along with various etiological approaches.

Recent advances in geriatric psychopharmacology

Psychopharmacotherapy of the elderly must take into account the effects of age-related changes in the structure and function of the brain and various organs. In general, older people are more sensitive than young people to both the therapeutic and toxic effects of psychotropic medications, necessitating lower doses and longer dosage intervals. This holds true for the treatment of 5 major types of psychiatric illness (depression, bipolar disorder, anxiety, psychotic disorders and dementia). The tricyclic antidepressants, although efficacious, inexpensive, and backed by 30 years of experience, are less well tolerated by the elderly than are newer antidepressants such as the selective serotonin uptake inhibitors. Problems with monoamine oxidase (MAO) inhibitors, including orthostatic hypotension and restrictions in diet and other medication use, have been overcome by the advent of reversible selective inhibitors of MAO-A, but the efficacy of these in the elderly has yet to be proven in clinical trials. Lithium remains the mainstay for the treatment of bipolar disorder. However, careful dosing and monitoring of plasma lithium concentrations are required in the elderly due to changes in pharmacokinetics and pharmacodynamics which make older patients very sensitive to the toxic effects of this medication. Similarly, age-related changes in the pharmacokinetics and pharmacodynamics of the benzodiazepines, the most frequently prescribed medications for anxiety in the elderly, result in recommendations for lower doses and preferential use of those agents metabolised by conjugation (e.g. oxazepam). Buspirone, a partial serotonin 5-HT1A-agonist which is better tolerated than benzodiazepines in the elderly, may be used as an alternative. The elderly are extremely sensitive to extrapyramidal adverse effects which the typical antipsychotics (neuroleptics) exhibit to varying extents. The selection of a suitable agent for the treatment of a psychotic disorder should be based upon the adverse effect profile of the drug and the specific symptoms and situation of the patient. The newer atypical antipsychotics, clozapine and risperidone, have yet to be well-studied in the elderly. Dementia, exemplified by Alzheimer's disease, is almost exclusively an illness of the elderly. Only one medication, tacrine, has been approved for its treatment, based on extensive basic research and positive results of several clinical trials. Its long-term benefits have yet to be determined and it has several adverse effects, including a tendency to increase liver enzymes to the extent that the medication has to be discontinued.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical pharmacokinetics of drugs for Alzheimer's disease

Pharmacological treatment of patients with Alzheimer's disease is becoming more important, as evidenced by the number of drugs being developed in different countries. It has been shown in the majority of clinical trials that cholinesterase inhibitors, such as tacrine (tetrahydroaminoacridine), are able to induce beneficial effects in cognition and memory. Tacrine, like most of the other oral antidementia agents, is rapidly absorbed from the gastrointestinal tract. It is excreted mainly through the kidney, with a terminal elimination half-life of about 3 hours. Tacrine has nonlinear pharmacokinetics and there are large interindividual differences in pharmacokinetic parameters after oral, intravenous and rectal administration. A positive relationship between cognitive changes and plasma tacrine concentrations has been recently described. Similarly, velnacrine exhibits evidence of nonlinearity in some pharmacokinetic parameters, but renal excretion is a minor route of elimination for this drug. Pharmacokinetic data pertaining to eptastigmine, a third cholinesterase inhibitor, is more limited. However, the drug is rapidly distributed to the tissues after oral administration and readily enters the central nervous system, where it can be expected to effectively inhibit acetylcholinesterase in the brain for a prolonged period. Pharmacokinetic data for the nootropic agents are more limited. However, of the 3 agents reviewed only pramiracetam penetrates the central nervous system (CNS) poorly. Indeed, oxiracetam crosses the blood-brain barrier and persists for longer in the CNS than in the serum. Selegiline (deprenyl), a neuroprotective agent, is readily absorbed from gastrointestinal tract. It is metabolised mainly in the liver, and to a minimal extent in the lung or kidneys. The steady-state concentrations of metabolites in the cerebrospinal fluid (CSF) and serum are very similar, reflecting their easy penetration into the CNS. Idebenone, another neuroprotective agent, likewise is rapidly absorbed and achieves peak concentrations in the brain comparable to those in plasma. Similarly, CSF concentrations of metabolites of ST 200 (acetyl-L-carnitine) parallel those in plasma, suggesting that they easily cross the blood-brain-barrier. Gangliosides (GM1) can be given intramuscularly or subcutaneously, but the latter route of administration provides a concentration 50% higher both in the serum and the ganglioside fraction. However, because of its longer elimination, the intramuscular route is the best form of administration when the brain is the target organ for the treatment. Absorption of nimodipine is quite rapid. The pharmacokinetics of nimodipine during multiple-dose treatment have not been studied extensively; however, the drug does not appear to accumulate during repeated administration of standard doses.(ABSTRACT TRUNCATED AT 400 WORDS)

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

Tacrine is a centrally acting cholinesterase inhibitor with additional pharmacological activity on monoamine levels and ion channels. It has been postulated that some or all of these additional properties may also be relevant to the mode of action of the drug. There are wide interindividual variations in pharmacological and clinical response to tacrine, possibly related to interindividual variation in bioavailability. Tacrine appears to improve cognitive function and behavioural deficits in a proportion of patients with Alzheimer's disease, at dosages of 80 to 160 mg/day. In the best designed trials, 30 to 51% of evaluable patients showed an improvement of at least 4 points on the cognitive subscale of the Alzheimer's Disease Assessment Scale, versus 16 to 25% of placebo recipients. A similar proportion of tacrine recipients were judged to have improved when global assessment scales were used. There was a significant dose-response relationship up to 160 mg/day. However, large numbers of patients were withdrawn during the trials, many because of tacrine-associated increases in transaminase levels. Elevated liver enzyme levels occurred in about 50% of tacrine recipients (reaching clinical significance in about 25%). Cholinergic symptoms also occurred more often in tacrine recipients than in those receiving placebo. A gradual increase in tacrine dosage, at 6-week intervals, is recommended when initiating therapy, and weekly serum transaminase monitoring is required for 6 weeks after each dosage increase. Despite the limitations implied by the low proportion of responders and high incidence of hepatic adverse effects associated with therapy, tacrine appears to make a measurable difference in both cognitive and behavioural function in a proportion of patients with Alzheimer's disease--a welcome advance in an area previously devoid of acceptable treatment options.