A multicenter double-blind study of controlled-release physostigmine for the treatment of symptoms secondary to Alzheimer's disease. Physostigmine Study Group

Alkaloids as drug leads in Alzheimer's treatment: Mechanistic and therapeutic insights

Alzheimer's disease (AD) has few effective treatment options and continues to be a major global health concern. AD is a neurodegenerative disease that typically affects elderly people. Alkaloids have potential sources for novel drug discovery due to their diverse chemical structures and pharmacological activities. Alkaloids, natural products with heterocyclic nitrogen-containing structures, are considered potential treatments for AD. This review explores the neuroprotective properties of alkaloids in AD, focusing on their ability to regulate pathways such as amyloid-beta aggregation, oxidative stress, synaptic dysfunction, tau hyperphosphorylation, and neuroinflammation. The FDA has approved alkaloids such as acetylcholinesterase inhibitors like galantamine and rivastigmine. This article explores AD's origins, current market medications, and clinical applications of alkaloids in AD therapy. This review explores the development of alkaloid-based drugs for AD, focusing on pharmacokinetics, blood-brain barrier penetration, and potential adverse effects. Future research should focus on the clinical evaluation of promising alkaloids, developing recently discovered alkaloids, and the ongoing search for novel alkaloids for medical treatment. A pharmaceutical option containing an alkaloid may potentially slow down the progression of AD while enhancing its symptoms. This review highlights the potential of alkaloids as valuable drug leads in treating AD, providing a comprehensive understanding of their mechanisms of action and therapeutic implications.

Electrochemical Acetylcholinesterase Sensors for Anti-Alzheimer's Disease Drug Determination

Neurodegenerative diseases and Alzheimer's disease (AD), as one of the most common causes of dementia, result in progressive losses of cholinergic neurons and a reduction in the presynaptic markers of the cholinergic system. These consequences can be compensated by the inhibition of acetylcholinesterase (AChE) followed by a decrease in the rate of acetylcholine hydrolysis. For this reason, anticholinesterase drugs with reversible inhibition effects are applied for the administration of neurodegenerative diseases. Their overdosage, variation in efficiency and recommendation of an individual daily dose require simple and reliable measurement devices capable of the assessment of the drug concentration in biological fluids and medications. In this review, the performance of electrochemical biosensors utilizing immobilized cholinesterases is considered to show their advantages and drawbacks in the determination of anticholinesterase drugs. In addition, common drugs applied in treating neurodegenerative diseases are briefly characterized. The immobilization of enzymes, nature of the signal recorded and its dependence on the transducer modification are considered and the analytical characteristics of appropriate biosensors are summarized for donepezil, huperzine A, rivastigmine, eserine and galantamine as common anti-dementia drugs. Finally, the prospects for the application of AChE-based biosensors in clinical practice are discussed.

Anti-AChE and Anti-BuChE Screening of the Fermentation Broth Extracts from Twelve Aspergillus Isolates and GC-MS and Molecular Docking Studies of the Most Active Extracts

Nowadays, the administration of cholinesterase enzyme (acetylcholinesterase: AChE and butyrylcholinesterase: BuChE) inhibitors is very common for the symptomatic treatment of Alzheimer's disease and the other forms of dementia and CNS disorders. In this paper, the anti-AChE and anti-BuChE activities of the fermentation broth ethyl acetate extracts from twelve Aspergillus isolates were evaluated by Ellman method. The results showed that A1 (Aspergillus flavus) and A5 (Aspergillus tubingensis, isolate 1) extracts with IC50 values of 46.77 μg/mL and 75.85 μg/mL possess the greatest ability to inhibit AChE and BuChE, respectively. GC-MS analysis of the extracts (A1 and A5) demonstrated that two alkaloids named 14-methyl-16-azabicyclo[10.3.1]hexadeca-1(15),12(16),13-triene (MAHT) and 6-chloro-2-methyl-7,8,9,10-tetrahydro-phenanthridine (CMTP) account for the highest percentage of A1 (26.95%) and A5 (25.5%) extracts, respectively. A 2-pyrazoline derivative, 5-hydroxy-3-(4-pyridinyl)-5-trifluoromethyl-1-(2,4,6-trimethylphenoxyacetyl)- (PHPTT), also constituted the high percentage (9.54%) of A5 extract. The anticholinesterase and neuroprotective effects of some 2-pyrazoline derivatives have been previously reported. The interaction study of MAHT with human AChE and CMTP and PHPTT with human BuChE using molecular docking indicated that these alkaloids bind to the active site gorge of the enzymes with high affinity. The best docking scores of MAHT, CMTP, and PHPTT were -7.1, -8.2, and -9.7 kcal/mol, respectively.

Nicotinic Acetylcholine Receptor Agonists for the Treatment of Alzheimer's Dementia: An Update

A significant portion of the clinical phenotype observed in Alzheimer's disease (AD) occurs through nicotinic acetylcholine receptors (nAChRs). Degeneration of cholinergic neurons, combined with aberrant nAChR expression and activation partially through amyloid-beta peptide (Aβ)-nAChR leads to upregulation of pro-inflammatory pathways and subsequently the progressive cognitive decline of AD. Interestingly, the cholinergic anti-inflammatory pathway is also mediated through nAChR particularly α7 nAChR. Thus, agonists of these receptors will likely exert pro-cognitive benefits through multiple mechanisms including stimulating the cholinergic pathway, modulating inflammation, and buffering the effects of amyloid. Despite this promising theoretical use, trials thus far have been complicated by adverse effects or minimal improvement. This review will provide an update on several pharmacological nAChR agonists tested in clinical trials and reasons that further investigation of nAChR agonists is merited.

IMPLICATIONS

nAChRs have consistently presented a promising theoretical use in the treatment of AD; however, trials thus far have been complicated by adverse effects or minimal improvement. This review will provide an update on several pharmacological nAChR agonists trialed and reasons that further investigation of nAChR agonists is merited.

Clinical trials and late-stage drug development for Alzheimer's disease: an appraisal from 1984 to 2014

The modern era of drug development for Alzheimer's disease began with the proposal of the cholinergic hypothesis of memory impairment and the 1984 research criteria for Alzheimer's disease. Since then, despite the evaluation of numerous potential treatments in clinical trials, only four cholinesterase inhibitors and memantine have shown sufficient safety and efficacy to allow marketing approval at an international level. Although this is probably because the other drugs tested were ineffective, inadequate clinical development methods have also been blamed for the failures. Here, we review the development of treatments for Alzheimer's disease during the past 30 years, considering the drugs, potential targets, late-stage clinical trials, development methods, emerging use of biomarkers and evolution of regulatory considerations in order to summarize advances and anticipate future developments. We have considered late-stage Alzheimer's disease drug development from 1984 to 2013, including individual clinical trials, systematic and qualitative reviews, meta-analyses, methods, commentaries, position papers and guidelines. We then review the evolution of drugs in late clinical development, methods, biomarkers and regulatory issues. Although a range of small molecules and biological products against many targets have been investigated in clinical trials, the predominant drug targets have been the cholinergic system and the amyloid cascade. Trial methods have evolved incrementally: inclusion criteria have largely remained focused on mild-to-moderate Alzheimer's disease criteria, recently extending to early or prodromal Alzheimer disease or 'mild cognitive impairment due to Alzheimer's disease', for drugs considered to be disease modifying. The duration of trials has remained at 6-12 months for drugs intended to improve symptoms; 18- to 24-month trials have been established for drugs expected to attenuate clinical course. Cognitive performance, activities of daily living, global change and severity ratings have persisted as the primary clinically relevant outcomes. Regulatory guidance and oversight have evolved to allow for enrichment of early-stage Alzheimer's disease trial samples using biomarkers and phase-specific outcomes. In conclusion, validated drug targets for Alzheimer's disease remain to be developed. Only drugs that affect an aspect of cholinergic function have shown consistent, but modest, clinical effects in late-phase trials. There is opportunity for substantial improvements in drug discovery and clinical development methods.

Alkaloids as a source of potential anticholinesterase inhibitors for the treatment of Alzheimer's disease

Objectives

The inhibition of acetylcholinesterase (AChE), the key enzyme in the breakdown of acetylcholine, is currently the main pharmacological strategy available for Alzheimer's disease (AD). In this sense, many alkaloids isolated from natural sources, such as physostigmine, have been long recognized as acetyl- and butyrylcholinesterase (BChE) inhibitors. Since the approval of galantamine for the treatment of AD patients, the search for new anticholinesterase alkaloids has escalated, leading to promising candidates such as huperzine A. This review aims to summarize recent advances in current knowledge on alkaloids as AChE and BChE inhibitors, highlighting structure–activity relationship (SAR) and docking studies.

Key findings

Natural alkaloids belonging to the steroidal/triterpenoidal, quinolizidine, isoquinoline and indole classes, mainly distributed within Buxaceae, Amaryllidaceae and Lycopodiaceae, are considered important sources of alkaloids with anti-enzymatic properties. Investigations into the possible SARs for some active compounds are based on molecular modelling studies, predicting the mode of interaction of the molecules with amino acid residues in the active site of the enzymes. Following this view, an increasing interest in achieving more potent and effective analogues makes alkaloids good chemical templates for the development of new cholinesterase inhibitors.

Summary

The anticholinesterase activity of alkaloids, together with their structural diversity and physicochemical properties, makes them good candidate agents for the treatment of AD.

Diagnosis and management of Alzheimer's disease: past, present and future ethical issues

There is great interest in the ethical issues associated with Alzheimer's disease (AD) and related dementias given the prevalence of AD and the evolving neuroscience landscape in matters of diagnoses and therapeutics. Much of the ethics discussion arises in the tension between the principle of not doing harm (principle of non-maleficence) in this vulnerable population and the development of effective treatments (principle of beneficence). Autonomy and capacity issues are also numerous, wide-ranging, and concern (1) day to day affairs such as driving safely and spending money wisely, (2) life-time events such as designating a legal representative in case of incapacity, making a will, (3) consenting to treatment and diagnostic procedures, (4) participating in research. The latter issue is particularly thorny and illustrates well the complexity of tackling concerns related to capacity. The impetus to protect AD patients has partly led to ethics regulation and policies making research on inapt patients more difficult because of stringent requirements for signed informed consent or for showing the value of the research to this specific patient population. New issues are arising that relate to earlier diagnosis using biomarkers and (possibly soon) the use of drugs that modify disease progression. We here summarize and discuss the different ethical issues associated with AD from a historical perspective, with emphasis on diagnostic and treatments issues.

The pharmacology and therapeutic potential of (-)-huperzine A

(−)-Huperzine A (1) is an alkaloid isolated from a Chinese club moss. Due to its potent neuroprotective activities, it has been investigated as a candidate for the treatment of neurodegenerative diseases, including Alzheimer’s disease. In this review, we will discuss the pharmacology and therapeutic potential of (−)-huperzine A (1). Synthetic studies of (−)-huperzine A (1) aimed at enabling its development as a pharmaceutical will be described.

Promising therapeutics with natural bioactive compounds for improving learning and memory--a review of randomized trials

Cognitive disorders can be associated with brain trauma, neurodegenerative disease or as a part of physiological aging. Aging in humans is generally associated with deterioration of cognitive performance and, in particular, learning and memory. Different therapeutic approaches are available to treat cognitive impairment during physiological aging and neurodegenerative or psychiatric disorders. Traditional herbal medicine and numerous plants, either directly as supplements or indirectly in the form of food, improve brain functions including memory and attention. More than a hundred herbal medicinal plants have been traditionally used for learning and memory improvement, but only a few have been tested in randomized clinical trials. Here, we will enumerate those medicinal plants that show positive effects on various cognitive functions in learning and memory clinical trials. Moreover, besides natural products that show promising effects in clinical trials, we briefly discuss medicinal plants that have promising experimental data or initial clinical data and might have potential to reach a clinical trial in the near future.

The cholinesterase inhibitor physostigmine for the local treatment of dry mouth: a randomized study

Application of physostigmine to the oromucosal surface with the aim of stimulating underlying mucin-producing glands while reducing cholinergic systemic effects might be a strategy for treating dry mouth. Subjects suffering from dry mouth and with hyposalivation participated in a crossover, double-blind, randomized study. A gel containing physostigmine (0.9, 1.8, 3.6, and 7.2 mg) or placebo was applied to the inside of the lips and distributed with the tongue. The feeling of dryness was assessed using a visual analogue scale (VAS) (where a score of 100 = extremely dry) and systemic effects were registered. Based on assessments of efficacy and safety, the dose of 1.8 mg of physostigmine was selected for use in the second part of the study to make objective measurements of saliva volumes. Physostigmine (1.8 mg) produced long-lasting (120 min) relief (evident as a score reduction of 25 on the VAS) in the feeling of dryness. Judging from AUC values related to baseline over 180 min, the improvement for both mouth and lips in response to physostigmine was six times greater than that to placebo. At higher doses of physostigmine, gastrointestinal discomfort predominantly occurred. The volume of saliva collected in response to physostigmine was five times higher over 180 min than that collected in response to placebo. Physostigmine, applied locally, therefore appears to be a promising modality for dry-mouth treatment.

Size of the treatment effect on cognition of cholinesterase inhibition in Alzheimer's disease

BACKGROUND

Six cholinesterase inhibitors (ChEIs) have been tested in people with Alzheimer's disease, using methods currently required for regulatory approval. The clinical importance of their treatment effects is controversial.

OBJECTIVE

To determine whether cholinesterase inhibition produces treatment effects in Alzheimer's disease that are large enough to be clinically detectable.

METHODS

Overview analysis of published trials of ChEIs in which the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) and a global clinical measure were primary outcomes. Two quantitative summary measures of the treatment effect (Cohen's d and the standardised response mean (SRM)) were calculated and presented as funnel plots. Observed cases analyses and intention to treat (ITT) with the last observation carried forward (LOCF) analyses were compared.

RESULTS

The median Cohen's d effect sizes (ES) using ITT samples with LOCF for the ADAS-Cog were: low dose of a ChEI (n = 8 studies) median ES = 0.15, range = 0.03-0.22; medium dose (n = 13) median ES = 0.23, range = 0.12-0.29; high dose (n = 9) median ES = 0.28, range = 0.01-0.31. In general, the ES were larger when calculated as SRMs (for example, high dose ChEI studies, median SRM = 0.47; range = 0.30-0.63) and highest in the observed cases analyses (for example, high dose median SRM = 0.56, range = 0.35-0.78). Global clinical scales produced similar estimates of ES (for example, high dose ChEI, ITT/LOCF median Cohen's d = 0.29, range = 0.20-0.47).

CONCLUSIONS

ChEIs produce small-moderate effect sizes in clinical trials which are reproducible and demonstrate a dose response. Better descriptions of the patterns of treatment response are needed to guide individual patient decisions about the effectiveness of treatment, but group effects are evident and appear large enough to be clinically detectable.

The effect of cholinesterase inhibitors on the regional blood flow in patients with Alzheimer's disease and vascular dementia

The effects of therapy with cholinesterase inhibitors (ChE-I) on regional cerebral blood flow (rCBF) disturbances were investigated by means of single photon emission computed tomography (SPECT). The changes in rCBF were compared with the results of the medical examination and neuropsychological tests. The sample consisted of 41 patients with the Alzheimer's dementia (AD) and vascular dementia (VaD). The effect of ChE-I (rivastigmine) treatment was studied on 33 patients, while the nontreated control group consisted of 8 patients. In the treated patients, an increase in the rCBF was observed, while the scores of the neuropsychological tests decreased slightly. In the VaD group, the increase in rCBF was more significant in the frontal regions, whereas in the group with AD in the temporal regions, respectively. In the nontreated patients, a decrease of both rCBF and scores of neuropsychological tests were observed. The scores of the neuropsychological tests correlated with the results of rCBF. Increased levels of acetylcholine in the brain after ChE-I treatment may support the cholinergic regulation of rCBF, and in result increase it. Such effects seem to be more pronounced in the more affected brain regions.

Efficacy of cholinesterase inhibitors in the treatment of neuropsychiatric symptoms and functional impairment in Alzheimer disease: a meta-analysis

CONTEXT

Cholinesterase inhibitors are the primary treatment for the cognitive symptoms of Alzheimer disease (AD). Cholinergic dysfunction is also associated with neuropsychiatric and functional deficits, but results from randomized controlled trials of cholinesterase inhibitors are conflicting.

OBJECTIVE

To conduct a systematic review and meta-analysis to quantify the efficacy of cholinesterase inhibitors for neuropsychiatric and functional outcomes in patients with mild to moderate AD.

DATA SOURCES

We performed a literature search of trials using MEDLINE (January 1966-December 2001), Dissertations Abstracts On-line, PSYCHINFO, BIOSIS, PubMed, and the Cochrane Controlled Trials Register. We retrieved English- and non-English-language articles for review and collected references from bibliographies of reviews, original research articles, and other articles of interest. We searched for both published and unpublished trials, contacting researchers and pharmaceutical companies.

STUDY SELECTION

We included 29 parallel-group or crossover randomized, double-blind, placebo-controlled trials of outpatients who were diagnosed as having mild to moderate probable AD and were treated for at least 1 month with a cholinesterase inhibitor. Sixteen trials included neuropsychiatric and 18 included functional measures.

DATA EXTRACTION

Two investigators (N.H.T. and J.H.) independently extracted study methods, sources of bias, and outcomes. Neuropsychiatric outcomes were measured with the Neuropsychiatric Inventory (NPI, 0-120 points) and the Alzheimer Disease Assessment Scale, noncognitive (ADAS-noncog, 0-50 points) and were analyzed with the weighted mean difference method. Functional outcomes were measured with several activities of daily living (ADL) and instrumental activities of daily living (IADL) scales and analyzed with the standardized mean difference method.

DATA SYNTHESIS

For neuropsychiatric outcomes, 10 trials included the ADAS-noncog and 6 included the NPI. Compared with placebo, patients randomized to cholinesterase inhibitors improved 1.72 points on the NPI (95% confidence interval [CI], 0.87-2.57 points), and 0.03 points on the ADAS-noncog (95% CI, 0.00-0.05 points). For functional outcomes, 14 trials used ADL and 13 trials used IADL scales. Compared with placebo, patients randomized to cholinesterase inhibitors improved 0.1 SDs on ADL scales (95% CI, 0.00-0.19 SDs), and 0.09 SDs on IADL scales (95% CI, 0.01 to 0.17 SDs). There was no difference in efficacy among various cholinesterase inhibitors.

CONCLUSIONS

These results indicate that cholinesterase inhibitors have a modest beneficial impact on neuropsychiatric and functional outcomes for patients with AD. Future research should focus on how such improvements translate into long-term outcomes such as patient quality of life, institutionalization, and caregiver burden.

Alzheimer's disease and the basal forebrain cholinergic system: relations to beta-amyloid peptides, cognition, and treatment strategies

Alzheimer's disease (AD) is the most common form of degenerative dementia and is characterized by progressive impairment in cognitive function during mid- to late-adult life. Brains from AD patients show several distinct neuropathological features, including extracellular beta-amyloid-containing plaques, intracellular neurofibrillary tangles composed of abnormally phosphorylated tau, and degeneration of cholinergic neurons of the basal forebrain. In this review, we will present evidence implicating involvement of the basal forebrain cholinergic system in AD pathogenesis and its accompanying cognitive deficits. We will initially discuss recent results indicating a link between cholinergic mechanisms and the pathogenic events that characterize AD, notably amyloid-beta peptides. Following this, animal models of dementia will be discussed in light of the relationship between basal forebrain cholinergic hypofunction and cognitive impairments in AD. Finally, past, present, and future treatment strategies aimed at alleviating the cognitive symptomatology of AD by improving basal forebrain cholinergic function will be addressed.

Effects of a flexible galantamine dose in Alzheimer's disease: a randomised, controlled trial

OBJECTIVE

To assess the efficacy and safety of galantamine in Alzheimer's disease at 3 months using flexible dose escalation.

METHODS

A randomised, double blind, placebo controlled trial in 43 centres in the United States, Canada, Great Britain, South Africa, Australia, and New Zealand. Patients with probable Alzheimer's disease (n=386; 171 women) with a score of 11-24 on the mini mental state examination, and a score> or =12 on the cognitive subscale of the Alzheimer's disease assessment scale (ADAS-cog) were randomised to placebo, or galantamine escalated over 4 weeks to a maintenance dose of 24 or 32 mg/day. The primary outcome measures were the change in ADAS-cog score and the clinician's interview based impression of change plus caregiver input (CIBIC-plus) score. Activities of daily living (ADL) and behavioural symptoms were secondary outcomes. To compare the effects of highest levels of dosing, an observed cases (OC) analysis was undertaken, with classic intention to treat (ITT) and ITT with last observation carried forward (LOCF) as confirmatory analyses.

RESULTS

At 3 months, galantamine (24-32 mg/day) produced a significantly better outcome on cognitive function than placebo (treatment difference=1.9 points on ADAS-cog, p=0.002) and a significantly better global response than placebo, as measured by CIBIC-plus (deterioration in 21% of patients on galantamine v 37% on placebo; p<0.001). Galantamine produced significant benefits on basic and instrumental ADL. Behavioural symptoms did not change significantly from baseline levels in either group. Adverse events (primarily gastrointestinal) were of mild to moderate intensity. There were no important differences between the OC, ITT, and ITT/LOCF analyses. Most patients (82%) who were maintained on the higher dose of galantamine completed the study.

CONCLUSIONS

Patients on galantamine, compared with those on placebo, experienced benefits in cognitive function and instrumental and basic activities of daily living. Flexible dose escalation of galantamine was well tolerated.

Cholinesterase inhibitors for behavioral disturbance in dementia

The authors review the literature from the last year examining the benefits of cholinesterase inhibitors in the treatment of behavioral disturbance in Alzheimer's disease (AD) and other dementias. Previous review has indicated that cholinesterase inhibitors have psychotropic properties. We found more evidence to support both the benefits of cholinesterase inhibitors in behavioral disturbance, and that specific behaviors may be selectively responsive to treatment.

The use of medications for cognitive enhancement

OBJECTIVE

To provide Canadian physicians and allied health care professionals with the evidence they need to help them make treatment decisions in the management of patients with Alzheimer's disease or other dementias.

OPTIONS

The full range and quality of diagnostic and therapeutic modalities available to Canadian physicians for the management of dementia.

OUTCOMES

Improvement in the treatment of dementias, leading to reduced suffering, increased functional capacity and decreased economic burden. EVIDENCE AND VALUES: The creation of these evidence-based consensus statements involved literature reviews of the subject by the authors; comparison of alternative clinical pathways and description of the methods whereby published data were analyzed; definition of the level of evidence for data in each case; evaluation and revision in a conference setting (involving primary care physicians, neurologists, psychiatrists, geriatricians, psychologists, consumers and other interested parties); insertion of tables showing key variables and data from various studies and tables of data with recommendations; and reassessment by all authors.

BENEFITS, HARMS, AND COSTS

A rational plan for the therapy of dementias is likely to lead to substantial benefits in both human and economic terms.

RECOMMENDATIONS

Treatment decisions should be made taking into account the severity or stage of the disease, the availability of caregivers, the presence of disease affecting other bodily systems and the ability of the subject to pay the cost of the medications. Donepezil is considered to have positive effects upon certain tests of neuropsychological function and may produce some improvement in Alzheimer's disease of mild to moderate severity as measured by rating scales. Its ability to improve quality of life remains uncertain. No other drug treatments (apart from symptomatic therapies) are at present approved for the treatment of Alzheimer's disease*.

VALIDATION

These recommendations were created by a writing committee, evaluated and revised at a consensus conference and further reviewed and revised by the writing committee prior to publication.

Physostigmine for Alzheimer's disease

BACKGROUND

The main pharmacological approach for the treatment of Alzheimer's disease (AD) has been based on the use of agents potentiating cholinergic transmission, particularly by inhibiting acetylcholinesterase (AChE), the enzyme that destroys acetylcholine after it has been secreted into the synaptic clefts. Physostigmine is an AChE inhibitor originally extracted from calabar beans. It is licensed in many countries as an agent for reversing the effect of drugs and poisons causing the anticholinergic syndrome. Studies conducted more than 20 years ago suggested that physostigmine could improve memory in people with or without dementia. Investigation of this property has been limited by the very short half-life of physostigmine. Various forms of administering the drug have been tried to overcome this problem, most recently a controlled-release (CR) oral formulation, and a skin patch. It has been proposed as a potential drug for the symptomatic treatment of AD.

OBJECTIVES

To determine whether there is evidence of beneficial effects for the use of physostigmine in Alzheimer's disease. To assess the incidence and severity of adverse effects.

SEARCH STRATEGY

The Cochrane Controlled Trials Register was searched using the following terms: 'physostigmine', 'physostigmine salicylate', 'Synapton' and 'Antilirium' in accordance with the Cochrane Dementia and Cognitive Improvement Group's search strategy. The pharmaceutical company was contacted.

SELECTION CRITERIA

All relevant unconfounded, double-blind, randomized, placebo-controlled trials in which physostigmine was administered for more than one day to patients with dementia of Alzheimer type. Trials in which the allocation to the treatment was not randomized, or in which the allocation to the treatment was not concealed were excluded.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two reviewers (JMC & JB), pooled where appropriate and possible, and the weighted or standardized mean differences or Peto odds ratios (95% CI) were estimated. Where possible, intention-to-treat analysis was used.

MAIN RESULTS

Fifteen studies were included using four different methods of administration of physostigmine. Four studies, involving 29 people in total, used intravenous infusion; seven, involving 131 people, used a conventional oral form; four, involving 1456 participants, used a controlled-release oral form, and one study of 181 people used a verum skin patch. There are no usable results from the intravenous infusion trials, and the few results from the conventional oral form showed no benefit of physostigmine compared with placebo. The results from two of the four studies of the controlled-release physostigmine apply only to a group of patients identified as responders in a pre-randomization titration period. The best dose physostigmine (mean 25mg/day) was associated with a 1.75 point improvement on ADAS-Cog score (mean difference -1.75, 95% confidence interval -2.90, -0.60 on an intention-to-treat basis) and a 0.26 point improvement on the CGIC score (treated as a continuous scale) (mean difference -0.26, 95% confidence interval 0.06, 0.46 on an intention-to-treat basis) compared with placebo at 6 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial (22/183 vs 2/183)(OR 5.92, 95% confidence limits 2.59, 13.54) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, flatulence or sweating compared with placebo at 6 weeks. The best dose physostigmine (mean 27mg/day) was associated with a 2.0 point improvement on ADAS-Cog score (mean difference -2.02, 95% confidence interval -3.59, -0.45 on an intention to treat basis) compared with placebo at 12 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial due to adverse events (13/83 vs 5/93)(OR 3.05, 95% confidence limits 1.15, 8.07) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, tremor, asthenia or sweating compared with placebo at 12 weeks. When no attempt was made to identify responders and all relevant patients with Alzheimer's disease were randomized, fixed dose physostigmine (mean 33 mg/day) was associated with a statistically significantly higher number withdrawing (234/358 vs 31/117)(OR 4.82, 95% confidence limits 3.17, 7.33), withdrawing due to adverse events (196/358 vs 10/117) (OR 6.54, 95%confidence limits 4.29, 9.95) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, dyspepsia, sweating, asthenia, dyspnoea or abnormal dreaming compared with placebo at 24 weeks. The results from the study of the verum patch physostigmine show that the double dose (delivering mean dose 12mg/day) was associated with statistically significantly higher numbers suffering at least one adverse event of vomiting, nausea or abdominal cramps compared with placebo at 24 weeks, but placebo was associated with statistically significantly greater numbers of gastrointestinal complaints at 24 weeks compared with single-dose physostigmine.

REVIEWERS' CONCLUSIONS

The evidence of effectiveness of physostigmine for the symptomatic treatment of Alzheimer's disease is limited. Even in a controlled release formulation designed to overcome the short half-life, physostigmine showed no convincing benefit and adverse effects remained common leading to a high rate of withdrawal.

RBC cholinesterase inhibition: a useful surrogate marker for cholinesterase inhibitor activity in Alzheimer disease therapy?

Red blood cell (RBC) acetylcholinesterase (AChE) inhibition has been used as a peripheral surrogate marker for the activity of centrally acting AChE inhibitors (AChEIs) in the treatment of Alzheimer disease. As a valid peripheral surrogate marker, RBC AChE inhibition should reflect the central pharmacodynamic activity of the compound and should demonstrate a relation with cognitive or global improvement in patients with Alzheimer disease. As a useful clinical tool, RBC AChE inhibition should also provide an advantage in dose optimization. However, the application of surrogate markers in research and clinical use is controversial (Prentice, 1989; Gotzsche, 1996; Colburn, 1997; De Gruttola et al., 1997). For instance, surrogate markers that have been identified or applied inappropriately can lead to erroneous conclusions, slowing the drug development process (Colburn, 1997). Also, the validation of surrogate markers for the pharmacodynamic activity of central nervous system drugs is not always possible because samples of brain tissue cannot be analyzed in humans. Finally, although validation of peripheral markers for central nervous system drugs has been approached via analysis of cerebrospinal fluid (Cutler et al., 1998a), few markers have been subjected to such rigorous evaluation in clinical studies. The extent to which measures of peripheral AChE inhibition accurately model central drug activity and therapeutic effectiveness of AChEIs, both as individual agents and as a drug class, is the focus of this review. AChEIs comprise a group of structurally diverse compounds with a wide range of relative specificities for the various molecular species of cholinesterase found in plasma, RBCs, and the brain. Studies of RBC AChE inhibition after administration of AChEIs in animals are of limited utility because of the differential sensitivity of AChEIs for human versus animal forms of AChE, the poor correlation between effective doses in animals and humans, and the lack of standardized measurements of effectiveness. Although clinical studies of donepezil, metrifonate, and eptastigmine have suggested the potential use of RBC AChE inhibition as a predictor of clinical response, the degree of inhibition yielding maximum cognitive improvements was highly variable from compound to compound (30-80%). Further, investigators did not prove a relation between central and peripheral pharmacodynamics or demonstrate an advantage over dose in the ability of RBC AChE inhibition to predict clinical response. A study of rivastigmine in patients with Alzheimer disease revealed that cerebrospinal fluid AChE inhibition correlated well with cognitive performance, whereas peripheral inhibition did not. Therefore, RBC cholinesterase inhibition is not a reliable surrogate marker for the activity of AChEIs as a class of drugs, and its usefulness as a dose optimization tool for individual agents has yet to be demonstrated clearly.

Anaerobic stability of aqueous physostigmine solution

The anaerobic stability of physostigmine was studied in this report. Physostigmine and two important degradants, eseroline and rubreserine, were identified by a high-performance liquid chromatography (HPLC) system using a photodiode array detector and a UV detector at the retention times of 12.4, 9.2, and 7.9 min. Under anaerobic treatment, the minimum degradation rate constant was found at pH 3.4, evaluating from pH-rate profiles at 45 degrees C, 55 degrees C, and 70 degrees C with the pH range 2.4-6.8. The degradation of physostigmine was suggested as specific acid-base catalysis. Anaerobic activation energies of KH, K(OH), and Kobs were 9.4, 8.3, and 17.9 kcal/mol, respectively. The ratios of observed aerobic and anaerobic rate constants were 2-33 at 88 degrees C, which had a trend to increase ratios as pH increased in the range 2.4-5.2. The shelf life of physostigmine solution was estimated to be 4 years at room temperature under anaerobic conditions at pH 3.4.

Long-term efficacy and safety of donepezil in the treatment of Alzheimer's disease: final analysis of a US multicentre open-label study

This multicentre, open-label study evaluated the long-term efficacy and safety of donepezil in the treatment of patients with mild to moderately severe Alzheimer's disease (AD). The 133 patients who entered the study had previously completed a 14-week randomized, double-blind, placebo-controlled study with donepezil. In this open-label study, patients were treated initially with 3 mg per day donepezil, which could be increased to 5, 7 and 10 mg per day in a step-wise fashion. Patients attended the clinic for assessments at 3-week intervals for the first 12 weeks, then subsequently at 12-week intervals for up to 240 weeks (254 cumulative weeks). Efficacy was assessed using the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and the Clinical Dementia Rating-Sum of the Boxes scale (CDR-SB), and data were compared with those predicted for historical untreated AD patients. During the first 6-9 months of the study, mean ADAS-cog and CDR-SB scores showed evidence of clinical improvement from baseline. After this time scores gradually deteriorated. Overall the decline was less than that estimated if this cohort of patients had not been treated. The most common adverse events were related to the nervous and digestive systems, and were generally mild and transient, resolving without the need for dose modifications. There was no evidence of hepatotoxicity. In conclusion, these data demonstrate that donepezil is a well-tolerated, realistic symptomatic treatment for AD over a period of up to 4.9 years. An interim report of the first 98 weeks of the study has been published previously.

Cholinesterase inhibitors for the treatment of Alzheimer's disease in the elderly

The treatment of Alzheimer's disease is of increasing importance as the population ages and the number of people with the disease increases. The aetiology of Alzheimer's disease is complex and therefore treatment strategies rely on generalised pathological findings. Cholinesterase inhibitors enhance a generalised deficit of central nervous system acetylcholine and are the first class of agents specifically approved for the treatment of Alzheimer's disease. The clinical efficacy of the different cholinesterase inhibitors is similar; however, differences in pharmacodynamic and pharmacokinetic parameters can influence tolerability and safety in the elderly population. Concomitant disease states, significant drug interactions and the altered kinetics and dynamics seen in elderly patients can also affect treatment outcome. Although cholinesterase inhibitors are not 'curative' for Alzheimer's disease, clinical evidence indicates that these drugs can significantly delay the progress of cognitive impairment. Consequently, they represent a useful treatment for the symptoms of Alzheimer's disease in the elderly.

The pharmacology of donepezil: a new treatment of Alzheimer's disease

Donepezil (donepezil hydrochloride, E-2020, Aricept, Eisai), launched in March 1997, was the first drug to be marketed for the symptomatic treatment of Alzheimer's disease (AD) in the UK. It had been launched a year earlier in the US where clinicians had already had experience of tacrine (THA). Donepezil is a piperidine based, potent, specific, non-competitive and reversible inhibitor of acetylcholinesterase (AChE). It is structurally dissimilar from other established cholinesterase inhibitors, namely THA (an acridine compound) and the carbamates, physostigmine and rivastigmine and has a pharmacokinetic and tolerability profile distinct from these agents. Experimentally, donepezil inhibits AChE activity in human erythrocytes and increases extracellular acetylcholine levels in the cerebral cortex and the hippocampus of the rat. Pharmacologically, donepezil has a half-life of approximately 70 h lending itself to once daily administration. The most common adverse events reported in clinical trials have been gastrointestinal, typically nausea, vomiting, diarrhoea and constipation. Headache, dizziness and sleep disturbance have also been reported; there has been no evidence of hepatotoxicity. Clinically a number of placebo-controlled trials have shown that donepezil 5 or 10 mg daily was associated with significant improvements in cognitive function, as assessed by the Alzheimer's disease Assessment Scale-cognitive subscale (ADAS cog) after 12 or 24 weeks treatment. Significant improvements in global function and activities of daily living have also been demonstrated after 24 weeks treatment compared with placebo in patients with mild to moderate AD. Donepezil was the first rational treatment available in the UK for this disabling condition and as such received considerable attention. Much of the original attention was negative, ostensibly based on the scientific view that there was not enough published evidence to justify widespread use, but this was driven by concerns about the potentially high drug costs if all patients with AD were eligible to receive it. Considerable data have now been produced from Phase II, III and post-marketing surveillance. This drug evaluation will review the basic pharmacology of donepezil and place it in context with the trial data and the author's clinical experience with the drug.

Structural roles of acetylcholinesterase variants in biology and pathology

Apart from its catalytic function in hydrolyzing acetylcholine, acetylcholinesterase (AChE) affects cell proliferation, differentiation and responses to various insults, including stress. These responses are at least in part specific to the three C-terminal variants of AChE which are produced by alternative splicing of the single ACHE gene. 'Synaptic' AChE-S constitutes the principal multimeric enzyme in brain and muscle; soluble, monomeric 'readthrough' AChE-R appears in embryonic and tumor cells and is induced under psychological, chemical and physical stress; and glypiated dimers of erythrocytic AChE-E associate with red blood cell membranes. We postulate that the homology of AChE to the cell adhesion proteins, gliotactin, glutactin and the neurexins, which have more established functions in nervous system development, is the basis of its morphogenic functions. Competition between AChE variants and their homologs on interactions with the corresponding protein partners would inevitably modify cellular signaling. This can explain why AChE-S exerts process extension from cultured amphibian, avian and mammalian glia and neurons in a manner that is C-terminus-dependent, refractory to several active site inhibitors and, in certain cases, redundant to the function of AChE-like proteins. Structural functions of AChE variants can explain their proliferative and developmental roles in blood, bone, retinal and neuronal cells. Moreover, the association of AChE excess with amyloid plaques in the degenerating human brain and with progressive cognitive and neuromotor deficiencies observed in AChE-transgenic animal models most likely reflects the combined contributions of catalytic and structural roles.

Defining meaningful change in Alzheimer's disease trials: the donepezil experience

Regulatory guidelines in the US and Europe generally require that a drug specifically indicated for treating Alzheimer's disease (AD) must demonstrate an effect upon the core manifestations of dementia. Progressive cognitive and functional losses are the cardinal features of AD. In the US, current guidelines require that new AD treatments show effectiveness on performance-based measures of cognition and on clinician-rated global assessments. Improvement in function is also emphasized in the European guidelines. The primary instruments that have been used to evaluate changes in cognition and global function in most recent AD trials are the cognitive subscale of the Alzheimer's Disease Assessment Scale and a version of the Clinician's Interview Based Impression of Change, respectively. The results from three pivotal trials investigating the acetylcholinesterase inhibitor, donepezil, are used to demonstrate the way in which these tools are used, how to interpret the data they provide, and to determine their overall value in ascertaining efficacy in clinical practice.

Acetylcholine in mind: a neurotransmitter correlate of consciousness?

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a 'cholinergic component' of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer's disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson's disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.

Recent developments in the drug treatment of Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with an impact on public health which continues to increase with the increasing longevity of the population. The disease is characterised clinically by a progressive loss of cognitive and behavioural function. These deficits are thought to result from decreased cholinergic transmission; therefore, restoring cholinergic function has been the main focus in the development of drugs for AD. Several pharmacological approaches to enhancing cholinergic function have been developed for symptomatic or palliative therapy of AD. Although these strategies have resulted in modest cognitive and behavioural improvements in patients with AD, they do not address the underlying progression of the disease. New strategies will be required to slow, stop or reverse the effects of neurodegeneration in AD. A number of potential therapies are currently under investigation, including estrogen replacement, anti-inflammatory agents, free radical scavengers and antioxidants, and monoamine oxidase-B (MAO-B) inhibitors. The evidence for a protective effect of estrogens or nonsteroidal anti-inflammatory drugs (NSAIDs) is controversial, and largely based on retrospective studies. More controlled prospective studies are needed to definitively demonstrate the benefits of long term estrogen or NSAID use in the prevention of AD. Free radical scavengers/antioxidants such as idebenone, and selective prevention MAO-B inhibitors such as lazabemide are well tolerated, but require additional studies in order to demonstrate preventative effects. In addition, other approaches, such as anti-amyloid treatments that affect beta-amylase secretion, aggregation and toxicity, appear promising; treatments that hinder neurofibrillary tangle construction and nerve growth factor (NGF) induction are in the very early stages of development.

Cholinesterase inhibitors: a therapeutic strategy for Alzheimer disease

OBJECTIVE

To provide a review of acetylcholinesterase inhibitors (AChEIs) tested as therapeutic agents for Alzheimer disease (AD).

DATA SOURCES

MEDLINE searches (January 1986-July 1998) identified pertinent literature. Selected references from these articles, as well as abstracts from recent meetings and package insert literature from approved compounds, were also used as source material.

DATA EXTRACTION

AChEIs were reviewed with regard to chemical structure, mechanism of inhibition, substrate specificity, pharmacokinetics/pharmacodynamics, safety/tolerability, and efficacy.

DATA SYNTHESIS

Cholinergic deficits, leading to cognitive impairment, are a significant aspect of neurodegeneration in AD. AChEIs reduce the degradation of acetylcholine, thus enhancing cholinergic transmission. In addition to the two agents approved by the Food and Drug Administration, tacrine and donepezil, six other compounds of diverse chemical structure and mechanism of inhibition including physostigmine, metrifonate, rivastigmine, and galantamine are under investigation as potential therapy for AD. These compounds are structurally diverse, possess unique patterns of specificities for the various forms of cholinesterase enzymes, use distinct mechanisms of enzyme inhibition, present unique adverse event profiles, and offer relatively similar mean gains in cognitive abilities to patients with AD in controlled clinical trials.

CONCLUSIONS

Relative to placebo, new AChEIs in development provide modest improvements in cognition for patients with mild to moderate AD, with improved tolerability profiles and more convenient dosing relative to tacrine. The availability of a wide array of AChEIs soon to be accessible to patients with AD will provide additional options to those who cannot tolerate or do not respond to drugs currently used for AD.

Traditional pharmacology and medicine in Africa. Ethnopharmacological themes in sub-Saharan art objects and utensils

Drawing from the general description that ethnopharmacology studies the human use of crude drugs and poisons in a traditional context, ethnopharmacological themes in native art can be defined as themes visualizing different features of traditional medicines and poisons, such as natural sources, methods of preparation, containers, usage and implements, target diseases and effects. This review documents that native African art objects and utensils are a goldmine of such ethnopharmacological themes by focusing on the following subjects: (a) objects related to the use of medicines (sources as well as tools for their collection, preparation and keeping); (b) objects related to the use of poisons (e.g. for ordeals, hunting and fishing); (c) objects related to the use of psychotropic agents (e.g. alcoholic beverages, kola nuts, smoking and snuffing materials); (d) pathological representations (e.g. treponematoses, leprosy, smallpox, swollen abdomen, scrotal enlargement, goiter and distorted faces); and (e) portrayals of certain types of treatment (e.g. topical instillations, perinatal care, and surgery). To avoid the impression that ethnopharmacology has little else to offer than armchair amusement, an epilogue outlines the medical relevance of this interdisciplinary science for Western and African societies.

Combination therapy for early Alzheimer's disease: what are we waiting for?

The practical pharmacological approaches currently available to palliate the cognitive and functional losses in early Alzheimer's disease (AD) include cholinesterase inhibitors (ChEI), antioxidants (e.g., vitamin E), anti-inflammatory agents, estrogen, seligiline, vasoactive agents, and ginkgo biloba. Reviewing available data on these therapies and using models from medical illnesses such as cancer and hypertension, we highlight the urgent need for evaluating combination therapies in early AD.

Twenty years of cholinergic intervention in Alzheimer's disease: A tale of disappointment and ultimate confidence

The authors present an overview of drugs that operate on the basis of the cholinergic hypothesis, either currently available for the palliative treatment of Alzheimer's disease or in the later stages of clinical development. Of the many conceivable strategies that are being exploited, only inhibitors of acetylcholinesterase have been shown to have sufficient therapeutic potential and manageable side-effect profiles to be turned into broadly acknowledged drugs. These compounds, and others based on the modulation of cholinergic neurotransmission, are discussed and a differentiation of their clinical potential is attempted.