Oral physostigmine treatment of patients with Alzheimer's disease

Bioactive compounds from endemic plants of Southwest Portugal: inhibition of acetylcholinesterase and radical scavenging activities

CONTEXT

Natural products are reported to have substantial neuroprotective activity due to their radical scavenging capacity, and also acetylcholinesterase (AChE) inhibitory capacity, both activities important in neurodegeneration.

OBJECTIVE

The undesirable side effects of compounds in pharmacological use make it important to identify natural neuroprotective molecules. This work assesses the potential of five endemic Portuguese plants as sources of neuroprotective compounds.

MATERIALS AND METHODS

Antioxidant capacity for peroxyl radical was determined by Oxygen Radical Absorbance Capacity method and for hydroxyl by Electron Paramagnetic Resonance, as well as AChE inhibitory capacity of the plant hydroethanolic extracts. The molecules responsible for these valuable properties were also tentatively identified by HPLC.

RESULTS AND DISCUSSION

Armeria rouyana and Thymus capitellatus presented some of the highest phenolic contents (76.60 ± 7.19 and 12.82 ± 0.24 mg GAE g−1 dw, respectively) and antioxidant capacities (592 ± 116 and 449 ± 57 μmol TE g−1 dw, respectively). The flavonoids were identified as the phytomolecules related to the antioxidant capacity of these plant extracts; in the case of A. rouyana, l-ascorbic acid also made an important contribution (3.27 ± 0.26 mg g−1 dw). Plant extracts clearly demonstrated effective AChE inhibitory activity (480 ± 98 and 490 ± 46 μg mL−1, respectively), that could be associated to polyphenols.

CONCLUSIONS

The extracts of A. rouyana and T. capitellatus and their active components, especially polyphenols, demonstrate interesting neuroprotective potential. They, therefore, deserve further study as their phytomolecules are promising sources of either natural neuroprotective products and/or novel lead compounds.

Circulating plasmalogen levels and Alzheimer Disease Assessment Scale-Cognitive scores in Alzheimer patients

BACKGROUND

Plasmalogens, which are key structural phospholipids in brain membranes, are decreased in the brain and serum of patients with Alzheimer disease (AD). We performed this pilot study to evaluate the relation between the levels of circulating plasmalogens and Alzheimer Disease Assessment Scale-Cognitive (ADAS-Cog) scores in patients with AD.

METHODS

We evaluated participants' ADAS-Cog scores and serum plasmalogen levels. For the 40 included AD patients with an ADAS-Cog score between 20 and 46, were tested their ADAS-Cog score 1 year later. The levels of docosahexaenoic acid plasmalogen were measured by use of liquid chromatography-tandem mass spectrometry.

RESULTS

We found that the ADAS-Cog score increased significantly in AD patients with circulating plasmalogen levels that were <or= 75% of that of age-matched controls at entry into the study. There was no change in score among participants with normal serum plasmalogen levels at baseline (> 75%).

LIMITATIONS

This was a pilot study with 40 patients, and the results require validation in a larger population.

CONCLUSION

Our study demonstrates that decreased levels of plasmalogen precursors in the central nervous system correlate with functional decline (as measured by ADAS-Cog scores) in AD patients. The use of both ADAS-Cog and serum plasmalogen data may be a more accurate way of predicting cognitive decline in AD patients, and may be used to decrease the risk of including patients with no cognitive decline in the placebo arm of a drug trial.

Current treatment and recent clinical research in Alzheimer's disease

The transition from either epidemiological observation or the bench to rigorously tested clinical trials in patients with Alzheimer's disease is crucial in understanding which treatments are beneficial to patients. The amyloid hypothesis has undergone scrutiny recently, as many trials aimed at reducing amyloid and plaque have been completed or are in the testing phase. Examples include modulation of the secretases involved in beta amyloid formation, anti-aggregation agents, and immunotherapeutic trials. Other therapies targeting hyperphosphorylated tau and novel targets such as enhancement of mitochondrial function, serotonin receptors, receptor for advanced glycation end products, and nerve growth factor, as well as other strategies, are discussed. A brief review of the current Food and Drug Administration-approved treatments is included.

Hormesis and medicine

Evidence is presented which supports the conclusion that the hormetic dose-response model is the most common and fundamental in the biological and biomedical sciences, being highly generalizable across biological model, endpoint measured and chemical class and physical agent. The paper provides a broad spectrum of applications of the hormesis concept for clinical medicine including anxiety, seizure, memory, stroke, cancer chemotherapy, dermatological processes such as hair growth, osteoporosis, ocular diseases, including retinal detachment, statin effects on cardiovascular function and tumour development, benign prostate enlargement, male sexual behaviours/dysfunctions, and prion diseases.

Alzheimer's disease drugs: an application of the hormetic dose-response model

This article provides an evaluation of the dose-response features of drugs that are intended to improve memory, some of which have been used in the treatment of Alzheimer's disease (AD). A common feature of these drugs is that they act via an inverted U-shaped dose response, consistent with the hormetic dose response model. This article assesses historical foundations that lead to the development of AD drugs, their dose-response features and how the quantitative features of such dose responses affected drug discovery and development, and the successes and possible failures of such agents in preclinical and clinical settings. This story begins about 150 years ago with the discovery of an active agent in the Calabar bean plant called physostigmine, its unfolding medical applications, and its implications for dose-response relationships, memory enhancement, and improved drug discovery activities. The article also demonstrates the occurrence of U-shaped dose responses for memory with numerous endogenous agonists including neurosteroids, various peptides (e.g., vasopressin, CCK-8, neuropeptide Y), and other agents (e.g., epinephrine, antagonists for platelet activity factor and nicotinic receptors), supporting the generalizability of the hormetic biphasic dose response. Finally, the significance of the U-shaped dose response is critical for successful clinical application, since it defines the therapeutic window.

The new approach in development of anti-Alzheimer's disease drugs via the cholinergic hypothesis

A wide range of evidences show that cholinesterase (ChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The earliest known ChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of AD patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase (AChE) inhibitor that would overcome the disadvantages of these two compounds. During the study, by chance we found a seed compound. We then conducted a structure-activity relationship (SAR) study of this compound. After four years of exploratory research, we found donepezil hydrochloride (donepezil). Recently, acetylcholinesterase inhibitors (AChEIs) have been studied for other mechanisms of action, such as neuroprotective action and lowering of beta-amyloid (beta-amyloid). Donepezil also reduced beta-amyloid plaque in in vitro. The amyloid hypothesis is believed to be the most promising approach in the development of anti-AD drugs. We speculate the mechanism of lowering beta-amyloid by donepezil implicate alpha-secretase (alpha-secretase) enhancer.

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.

Tritium labelling and characterization of the cognition enhancing drug tacrine using several precursors

Tacrine and its analogues have shown promise as cognition enhancers and potential chemotherapeutic agents for Alzheimer's disease. [3H]tacrine was required to explore its mechanism of action via receptor binding assay and the radioligand was prepared by means of catalytic dehalogenation of several brominated precursors.

Applications of hormesis in toxicology, risk assessment and chemotherapeutics

There is much debate over the fundamental shape of the dose-response curve in the low-dose zone, particularly in the fields of toxicology and risk assessment. The defaults, principally accepted dose-response models in the major texts in these areas and in government regulatory activities, are a threshold model for non-carcinogens and a linear model for most carcinogens. We have argued that in properly designed studies the U-shaped hormetic response predominates and is more fundamental. In this article, a broad range of basic issues associated with the acceptance of U-shaped dose responses as central to toxicology, pharmacology and their applications to risk assessment and medicine will be discussed.

The Stereotypy Rating Inventory for frontotemporal lobar degeneration

A many behavioral disturbances, Stereotypic behaviors are among the best discriminators of Frontotemporal Lobar Degeneration (FTLD). A recent preliminary report suggests many of the behavioral symptoms, including stereotypic behaviors in FTLD patients, respond to medication with selective serotonin re-uptake inhibitors. However, there is no scale that evaluates stereotypic behaviors comprehensively. To assess the wide range of stereotypic behaviors encountered in FTLD, we developed a new instrument, the Stereotypy Rating Inventory (SRI). The SRI assesses five distinctive stereotypic behavioral disturbances often seen in patients with FTLD: eating and cooking behaviors, roaming, speaking, movements, and daily rhythm. The SRI uses the same technique as the Neuropsychiatric Inventory (NPI) in that both the frequency and the severity of each behavior are determined. The studies reported here demonstrate the content and concurrent validity, as well as inter-rater and test-retest reliability, of the instrument. Scores of FTLD patients (n=26) on the SRI were much higher than those of patients with Alzheimer's disease (n=46), patients with vascular dementia (n=26), and normal control subjects (n=40). The SRI appears to be a useful instrument for detecting stereotypic behaviors and monitoring of therapies in FTLD patients.

Research and development of donepezil hydrochloride, a new type of acetylcholinesterase inhibitor

A wide range of evidence shows that cholinesterase (ChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The earliest known ChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of AD patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters, while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase (AChE) inhibitor that would overcome the disadvantages of these two compounds. During the study, by chance we found a seed compound. We then conducted a structure-activity relationship study of this compound. After four years of exploratory research, we found donepezil hydrochloride (donepezil). Donepezil showed several positive characteristics including the following: 1) It has a novel structure compared to other conventional ChE inhibitors; 2) It shows strong anti-AChE activity and has long lasting efficacy; 3) The inhibitory characteristic of donepezil shows that it is highly selective for AChE as compared to butyrylcholinesterase (BuChE) and showed reversibility; 4) The results of clinical studies on donepezil show a very high significant difference on ADAS cog and CIBIC plus scores of AD patients. Donepezil is currently marketed in 56 countries all over the world.

Cholinesterase inhibitors, beta-amyloid precursor protein and amyloid beta-peptides in Alzheimer's disease

The extracellular deposition of amyloid beta-peptide (Abeta) in the form of cerebrovascular amyloid and extracellular plaques is one of the major neuropathological manifestations of Alzheimer's disease (AD). Abeta is generated proteolytically from the large beta-amyloid precursor protein (APP). APP is cleaved by a group of proteases called "secretase" to generate soluble derivatives of APP (sAPP), which are secreted in human plasma, CSF and cultured cells. Neurochemically, there is a severe loss of cholinergic neurons and a decreased synthesis of acetylcholine in neocortex in AD. Current approved AD drugs, such as aricept and tacrine, are based on the use of cholinesterase inhibitors (ChEIs) and have been reported to improve memory deficits and cognitive decline in some patients with AD. To compare the effects of ChEIs on APP processing, we have tested a series of ChEIs such as tacrine, physostigmine, metrifonate, phenserine and cymserine in cultured human neuroblastoma cells. We analyzed levels of sAPP by immunochemical techniques with APP-specific antibodies and assayed levels of Abeta by a sensitive sandwich ELISA. Based on these results, ChEIs can be divided into three groups: the first group of ChEIs had no effect on sAPP secretion, the second decreased the sAPP secretion only, and third group affected the secretion of sAPP and Abeta. The difference in the action of metrifonate, physostigmine, phenserine and tacrine on APP processing is independent of their selectivity for the cholinesterase enzymes. This possibly is due to the different targets that are used by ChEIs. Studying the effects of ChEIs on different targets is useful to maximize the benefit of ChEIs for the treatment of AD subjects.

Donepezil for Alzheimer's disease: pharmacodynamic, pharmacokinetic, and clinical profiles

Donepezil was developed in order to overcome the disadvantages of physostigmine and tacrine. Its use is based on the cholinergic hypothesis. Donepezil is a piperidine-based, reversible acetylcholinesterase inhibitor, that is chemically unrelated to other cholinesterase inhibitors. It was developed for the symptomatic treatment of Alzheimer's disease (AD). Donepezil is highly selective for acetylcholinesterase with a significantly lower affinity for butyrylcholinesterase, which is present predominantly in the periphery. Phase I and II clinical trials demonstrated donepezil's favorable pharmacokinetic, pharmacodynamic and safety profile. There is no need to modify the dose of donepezil in the elderly or in patients with renal and hepatic failure. Pivotal phase-III trials in the US, European countries, and Japan showed that donepezil significantly improved cognition and global function in patients with mild to moderate AD. In long-term trials, donepezil maintained cognitive and global function for up to 1 year prior to the resumption of gradual deterioration. Donepezil is generally well tolerated; most of its adverse events are mild, transient and cholinergic in nature. Donepezil produces no clinically significant changes in laboratory parameters, including liver function. The drug is approved for the treatment of mild to moderate Alzheimer's disease, but donepezil therapy does not have to be discontinued if a patient continues to deteriorate. Possible new indications for donepezil in psychiatric and neurologic diseases, other than AD, include dementia with Lewy bodies, brain injury, attention deficit hyperactivity, multiple sclerosis, Down's syndrome, delirium, mood disorders, Huntington's disease and sleep disorders.

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.

A double-blind, placebo-controlled, multicenter study of Cerebrolysin for Alzheimer's disease

OBJECTIVE

To assess the efficacy and safety of Cerebrolysin over 4 weeks in patients with probable Alzheimer's disease (AD).

DESIGN

A 4-week randomized, double-blind, placebo-controlled, multicenter clinical trial. An unequal (Cerebrolysin:placebo = 2:1) randomization was used to assign more patients to the treatment group.

SETTINGS

University medical centers and community geriatric hospitals in Korea.

PARTICIPANTS

Fifty-three men and women at least 50 years of age admitted to hospitals with mild to moderate AD and otherwise in good health.

INTERVENTION

The treatment group (n = 34) received Cerebrolysin (30 mL Cerebrolysin in 100 mL physiologic saline IV) once a day from Monday to Friday for 4 weeks. The control group (n = 19) received placebo.

MEASUREMENTS

Primary outcome measures were the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog) and the Clinical Global Impression of Severity/ Change (CGIS/C). Secondary outcome measures included Mini-Mental State Examination (MMSE), Geriatric Depression Scale (GDS), Katz Index of Activities of Daily Living (ADL), and Lawton Instrumental Activities of Daily Living (IADL) Scale.

RESULTS

After 4 weeks of treatment, Cerebrolysin-treated patients demonstrated significant improvements in the ADAS-Cog (P = .02), CGIS/C (P = .01), and MMSE (P = .04) compared with placebo-treated patients. Among Cerebrolysin-treated patients, 82%, 62%, and 44% were rated improved on ADAS-Cog, CGIS/C, and MMSE, respectively, compared with 31.6%, 22%, and 17% of placebo-treated patients, respectively. However, there were no significant improvements in the Cerebrolysin group compared with the placebo group on the GDS, ADL, and IADL. There were no dropouts in either groups, with 100% compliance to Cerebrolysin and placebo. Only one patient reported a febrile sensation, which was transient and mild in severity.

CONCLUSIONS

This study indicates that Cerebrolysin is a safe drug that improves the cognitive deficits and global function in patients with mild to moderate AD. Long-term efficacy and safety of Cerebrolysin in Alzheimer's patients should be evaluated in the future.

On neurodegenerative diseases, models, and treatment strategies: lessons learned and lessons forgotten a generation following the cholinergic hypothesis

Life's Journey If life is indeed a journey, then poetry must be the map that reveals all its topographic possibilitiesellipsis while science is the compass that keeps us from getting lost. -R. T. Bartus, Simple Words for Complex Lives, (c) 1998 In the nearly 20 years since the cholinergic hypothesis was initially formulated, significant progress has been achieved. Initial palliative treatments for Alzheimer's disease (AD) have proven beneficial and have gained FDA approval, the use of animal models for studying AD and other neurodegenerative diseases has achieved wider acceptance, and important insight into the potential causes and pathogenic variables associated with various neurodegenerative diseases continues to increase. This paper reviews the current status of the cholinergic hypothesis in the context of continuing efforts to improve upon existing treatments for AD and explores the role that animal models might continue to play. Using the benefit of hindsight, particular emphasis is placed on an analysis of the approaches, strategies, and assumptions regarding animal models that proved useful in developing the initial treatments and those that did not. Additionally, contemporary issues of AD are discussed within the context of the cholinergic hypothesis, with particular attention given to how they may impact the further refinement of animal models, and the development of even more effective treatments. Finally, arguments are presented that, despite the deserved enthusiasm and optimism for identifying means of halting the pathogenesis of AD, a clear need for more effective palliative treatments will continue, long after successful pathogenic treatments are available. This review, therefore, focuses on issues and experiences intended to: (a) facilitate further development and use of animal models for AD and other neurodegenerative diseases, and (b) accelerate the identification of newer, even more effective treatments.

Quality of life in dementia patients in long-term care

OBJECTIVE

To evaluate variables associated with quality of life (QOL) in dementia residents in a long-term care facility using a recently standardized and validated dementia-specific QOL scale (ADRQL).

METHOD

A cross-sectional, case-control design was employed using validated scales to assess dementia-related symptomatology. Thirty-two facility staff members were interviewed to assess the QOL of 120 patients meeting DSM-IV for dementia criteria residing in long-term care.

RESULTS

ADRQL scores were higher in assisted living residents than in skilled nursing facility residents. In univariate analyses, worse orientation, greater physical dependency, depression, and treatment with anxiolytics were associated with lower ADRQL scores. In multivariate analyses, lower scores were associated with worse orientation, greater physical dependency, depression, and anxiolytic treatment.

CONCLUSIONS

Residents exhibited better QOL than expected. Future longitudinal studies should address if reorientation, activity therapy, treatment of depression, and avoidance of benzodiazepines might improve QOL in this population. Interventions that might improve orientation and physical abilities, such as cholinomimetic therapies, psychosocial interventions, or behavioral strategies, should also be studied in future research on QOL.

The role of norepinephrine in the pathophysiology of cognitive disorders: potential applications to the treatment of cognitive dysfunction in schizophrenia and Alzheimer's disease

The role of noradrenergic neurotransmission in normal cognitive functions has been extensively investigated, however, the involvement of noradrenergic functions in the cognitive impairment associated with schizophrenia and Alzheimer's disease has not been as intensively considered. The limited ability of atypical antipsychotics to treat the cognitive impairment of schizophrenia, and cholinomimetics to treat the cognitive impairment of Alzheimer's disease, may be related to the influence of a multiplicity of neurotransmitter abnormalities including noradrenergic dysfunction, which these treatments do not address. The evidence of noradrenergic dysfunction occurring concomitantly with dopamine dysfunction in schizophrenia and acetylcholine dysfunction in Alzheimer's disease supports therapeutic approaches using noradrenergic drugs in combination with neuroleptics and cholinesterase inhibitors, respectively, to enhance the treatment of cognitive impairment. Given the results of animal and human studies, it appears that alpha-2A agonists may be the optimal choice for this purpose.

Physostigmine challenge before and after chronic cholinergic blockade in elderly volunteers

BACKGROUND

As a test of possible muscarinic up-regulation, the cortisol response to intravenous (i.v.) physostigmine (an anticholinesterase) was measured in 9 elderly volunteers before and after chronic cholinergic blockade with the muscarinic cholinergic antagonist scopolamine.

METHODS

Each of the 9 elderly control subjects was given two physostigmine (0.5 mg i.v.) infusions separated by 21 doses of nightly scopolamine (1.2 mg p.o.). No scopolamine was administered the night before infusions, and glycopyrrolate (0.2 mg i.v.) was administered prior to physostigmine, to block its peripheral effects. Vital signs were monitored and blood samples were collected at six time points surrounding the physostigmine infusion (-10, +10, +20, +30, +50, and +70 min). Behavioral measures and cognitive tests were administered prior to and 30 min after the physostigmine.

RESULTS

The cortisol response to physostigmine was greater after the second (post-chronic scopolamine) infusion study compared to the first (p < .05) as measured by an area under the curve analysis of all time points. When individual time points were compared, the mean cortisol response was significantly increased after the second physostigmine infusion at the +50- and +70-min time points (p < .05). There were no significant changes in behavioral rating scales, cognitive tests, or vital signs between the two physostigmine infusion study days.

CONCLUSIONS

This study demonstrates increased hypothalamic-pituitary-adrenocortical axis responsivity to a central nervous system cholinergic stimulus after chronic muscarinic blockade in 9 elderly control subjects. It also gives further evidence to support previous suggestions of muscarinic plasticity, specifically postsynaptic up-regulation, in the aging brain following exposure to chronic anticholinergic treatment.

Clinical benefits of a new piperidine-class AChE inhibitor

Alzheimer's disease (AD) is associated with a deficiency of acetylcholine (ACh) in the forebrain that correlates with brain pathology and cognitive dysfunction. The most promising approach to enhancing central ACh neurotransmission has been the utilization of agents that inhibit cholinesterases which block its catabolism. Initially, the success of this strategy was limited by subtherapeutic levels of acetylcholinesterase (AChE) inhibition, tolerability problems and toxicity of the first agents. Donepezil HCI represents a new chemical class of AChE inhibitors, the piperidines. In clinical trials, donepezil has been shown to improve significantly cognition and global function in patients with mild to moderately severe AD, and has demonstrated an excellent tolerability and safety profile. These benefits, as well as a simple, once-daily dosing regimen, make donepezil a viable therapeutic option for AD patients.

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.

Effects of Jen-San-Yaung-Jung-Tang on scopolamine-induced amnesia in rats

The effect of Jen-San-Yaung-Jung-Tang (YJT) on scopolamine (SCOP)-induced amnesia was investigated in a step-through passive avoidance task in rats. It was observed that YJT (0.5 and 1.0 g/kg) significantly improved SCOP-induced amnesia and did not change the horizontal activity and pain threshold. YJT at 0.5 and 1.0 g/kg also did not change SCOP-treated horizontal activity and pain threshold. Furthermore, the antiamnesic effect of YJT at 1.0 g/kg on the SCOP-induced amnesia was augmented by physostigmine, but was not altered by neostigmine or scopolamine N-methylbromide. These results suggest that the antiamnesic effect of YJT could only be related to the memory-related process, and to an increase in central cholinergic neuronal activity.

Tacrine efficacy in Lewy body dementia

BACKGROUND

Response to tacrine varies among patients with Alzheimer's disease (AD). Lewy body dementia (LBD) could be a high responder subtype of AD. The aim of the study was to compare the effects of tacrine in LBD and AD.

METHODS

Seventy-five consecutive outpatients with mild or moderate AD were screened. Tacrine was given at a dose of 40 mg/day during 6 weeks. During the next 6 weeks, the patients were treated with 80 mg/day and afterwards with 120 mg/day. Patients were assessed at baseline and treated with a dose of 120 mg/day tacrine for 2 weeks.

RESULTS

Analysis was performed on 39 patients (AD, N = 20; LBD, N = 19). Eight patients were lost to follow-up, eight patients manifested with side-effects, six suffered from an intercurrent somatic disease during the study and 14 patients had poor compliance or were treated with incompatible drugs. Twenty-two patients (11 AD/11 LBD) increased their cognitive performances with tacrine. Among the 22 patients, the improvement differed between the AD and the LBD groups. In AD, conceptualization improved; in LBD, the improvements occurred in verbal initiation and digit span.

CONCLUSION

This study emphasizes the importance of using appropriate tests to determine the positive effects of pharmacological treatments.

The cholinergic hypothesis of neuropsychiatric symptoms in Alzheimer's disease

A variety of neuropsychiatric symptoms occur in Alzheimer's disease (AD) including agitation, psychosis, depression, apathy, disinhibition, anxiety, purposeless behavior, and disorders of sleep and appetite. Neuropsychiatric symptoms have been related to cholinergic deficiency and improve after treatment with cholinomimetic agents. Cholinergic drugs are unique among psychotropic agents in exerting disease-specific and broad-spectrum effects. These observations provide the basis for the cholinergic hypothesis of the neuropsychiatric symptoms of AD, suggesting that the cholinergic deficit of AD contributes to the neuropsychiatric symptoms of AD and that cholinomimetic therapy ameliorates the behavioral disturbances accompanying 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.

The effect of tacrine and leupeptin on the secretion of the beta-amyloid precursor protein in HeLa cells

The senile plaque in Alzheimer's disease (AD) consists mainly of the amyloid beta-peptide (A beta) derived from a larger beta-amyloid precursor protein (betaAPP). The majority of betaAPP is processed by either a secretory or lysosomal/endosomal pathway. Soluble derivatives of betaAPP (sAPP) and A beta generated by the proteolytic processing of full-length betaAPP are normally secreted into the conditioned medium of cultured cells. Tacrine, a centrally active potent cholinesterase inhibitor that has been shown to improve cognitive functions in some patients with AD, inhibits the secretion of sAPP. Here we have investigated whether leupeptin, a lysosomal protease inhibitor, could influence this effect of tacrine. We analyzed levels of betaAPP derivatives in cultured HeLa cells by immunoblotting cell lysates and conditioned media using the monoclonal antibody 22C11. Levels of sAPP normally present in conditioned media were severely reduced by treating cells with tacrine. The treatment of cells with tacrine resulted in a small decrease in the intracellular levels of betaAPP. The effect of treating the cells with tacrine did not depend upon the growing state of the cells as a similar effect was observed when the drug was added either during initial plating of the cells or after the attachment of the cells. The effect of tacrine was not affected by preincubating the cells with low serum in the culture medium. The treatment of cells with tacrine plus leupeptin reduced the secretion of sAPP in the medium to the same degree as did the treatment with tacrine alone, suggesting that the tacrine-mediated inhibition of sAPP release may not involve leupeptin-sensitive proteolytic pathways. The results suggest that the inhibitory effect of tacrine on sAPP secretion is not due to the proteolytic cleavage of the holoprotein in the medium.

Vesamicol and some of its derivatives: questionable ligands for selectively labelling acetylcholine transporters in rat brain

Presynaptic cholinergic markers could be used for estimating the integrity of the cholinergic systems in the human brain with brain imaging techniques such as Single-photon emission computed tomography (SPECT). Vesamicol, an inhibitor of the vesicular acetylcholine transporter, and some of its derivatives have been suggested as potential ligands for this purpose. However, vesamicol binds not only to acetylcholine transporters but also to sigma binding sites. In the present study, we estimated the contribution of sigma site labelling to [3H](-)-vesamicol binding in different rat brain regions by selectively labelling the acetylcholine transporter, using [3H](-)-vesamicol in the presence of the sigma-ligand 1,3-di(2-tolyl)guanidine to occlude the sigma binding sites. The contribution of sigma site labelling was substantial in all brain regions and ranged from 25% in the striatum to 60% in the medulla. In addition, we investigated, in various experimental set ups, the affinities of several vesamicol derivatives for acetylcholine transporters and sigma binding sites. All vesamicol derivatives used displayed a higher affinity for the sigma1 site than for the acetylcholine transporter and also displayed a high sigma2 site affinity. This poor selectivity limits the usefulness of these compounds as selective cholinergic markers for brain imaging studies.

Pharmacological modulation of Alzheimer's beta-amyloid precursor protein levels in the CSF of rats with forebrain cholinergic system lesions

Abnormal deposition and accumulation of Alzheimer's amyloid beta-protein (A beta) and degeneration of forebrain cholinergic neurons are among the principal features of Alzheimer's disease. Studies in rat model systems have shown that forebrain cholinergic deficits are accompanied by induction of cortical beta-amyloid precursor protein (beta-APP) mRNAs and increased levels of secreted beta-APP in the CSF. The studies reported here determined whether the CSF levels of secreted beta-APP could be altered pharmacologically. In different experiments, rats with lesions of the forebrain cholinergic system received injections of vehicle, a muscarinic receptor antagonist scopolamine, or one of two cholinesterase inhibitors - diisopropyl phosphorofluoridate (DFP) or phenserine. Scopolamine was administered to determine whether the levels of beta-APP in the CSF could be increased by anticholinergic agents. The cholinesterase inhibitors were administered to determine whether the forebrain cholinergic system lesion-induced increases in CSF beta-APP could be reduced by cholinergic augmentation. Scopolamine administration led to a significant increase in the CSF levels of secreted beta-APP in sham-lesioned rats. Phenserine, a novel, reversible acetyl-selective cholinesterase inhibitor, significantly decreased the levels of secreted beta-APP in the CSF of forebrain cholinergic system-lesioned rats whereas DFP, a relatively non-specific cholinesterase inhibitor, failed to affect CSF levels of secreted beta-APP. These results suggest that the levels of secreted beta-APP in the CSF can be pharmacologically modulated but that this modulation is dependent upon the status of the forebrain cholinergic system and the pharmacological properties of the drugs used to influence it.

Effect of physostigmine and verapamil on active avoidance in an experimental model of Alzheimer's disease

The present study was performed to investigate and compare the effect of acetylcholinesterase inhibitor, physostigmine (0.045, 0.060 and 0.075 mg/kg sc, 30 min before the tests) and Ca-antagonist, verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg sc, 30 min before the tests), on two-way active avoidance (AA) learning (acquisition and performance) in nucleus basalis magnocellularis (NBM)-lesioned rats. Bilateral electrolytic lesions of NBM induced significant decrease of acquisition and performance of AA responses in rats. Physostigmine (0.060 mg/kg) significantly improved only acquisition of AA, while verapamil (2.5 and 5.0 mg/kg) significantly improved both type of AA behavior in NBM-lesioned rats. These results suggest that altered calcium homeostasis might play significant role in pathogenesis of experimental induced Alzheimer's disease (AD) and that administration of calcium antagonist such as verapamil might successfully ameliorate disturbances of learning and memory appeared after lesions of NBM.

Pharmacological treatment of cognitive dysfunction in dementia disorders

Dementia represents a complex heterogeneity of disorders. For Alzheimer's disease great progress in the understanding of underlying genetical, neuropathological and neurochemical mechanisms of the disease has been made during recent years. A variety of therapeutic approaches with cognitive enhancing drugs have been tested in Alzheimer patients. Presently, four main treatment strategies prevail, namely transmitter replacement therapy, growth factors, anti-inflammatory drugs and drugs affecting amyloid processing in the brain. The transmitter therapy is so far the most explored and fruitful strategy. The cholinesterase inhibitor tacrine is in clinical use in many countries. Other cholinergic treatment strategies than cholinesterase inhibitors in development are selective muscarinic receptor agonists and nicotine receptor agonists. The selective 5HT re-uptake blockers might be complementary to drugs with more specific effect on cognition. Although treatment with growth factor therapy e.g. nerve growth factor in Alzheimer patients has given some promising results, further research is needed. Development of drugs affecting amyloid processing is still mainly on a preclinical level.

Effect of TAK-147, a novel AChE inhibitor, on cerebral energy metabolism

Effect of TAK-147, a novel acetylcholinesterase (AChE) inhibitor, on cerebral energy metabolism was investigated using an in vivo 31P-magnetic resonance spectroscopy (31P-MRS) technique and the autoradiographic 2-deoxy-[14C]-D-glucose method in aged Fischer 344 rats. We revealed that high-energy phosphate metabolites, phosphocreatine (PCr) and ATP, in the brain decreased gradually with aging and that significant decrement of cerebral PCr and ATP was observed from 13- and 8.5-month-old in comparison with those of 2.5-month-old rats, respectively. Daily oral administration of TAK-147 (1 mg/kg) for 40 days increased PCr and ATP levels in aged rats (29-month-old). To determine the site at which TAK-147 acts to increase high-energy phosphate metabolism, we investigated the rate of local cerebral glucose utilization (LCGU) in various brain regions. The rate of LCGU decreased in almost all brain regions in aged rats (28 months of age), and the decrease was significant in 29 out of the 35 regions. When TAK-147 was administered orally to the aged rats, the levels were dose dependently increased, especially in the auditory cortex. These results indicate that TAK-147 increases cerebral energy metabolism in aged rats.

Relationship between pharmacodynamic activity and cognitive effects of eptastigmine in patients with Alzheimer's disease. Eptastigmine Study Group

OBJECTIVE

To assess the safety, tolerability, pharmacodynamics, and preliminary efficacy of eptastigmine, a new long-acting cholinesterase inhibitor, in patients with probable Alzheimer's disease.

METHODS

This was a double-blind, randomized, placebo-controlled, unbalanced parallel-group study. One-hundred and three patients (83 in the eptastigmine group and 20 in the placebo group) were recruited by 10 centers. Patients received 20 mg eptastigmine or placebo for 4 weeks with twice-a-day or three-times-a-day regimens, depending on body weight (< or = 65 kg or > 65 kg, respectively). Patient performance on the Logical Memory Test, Semantic Word Fluency Test, Trail Making Test, Index of Independence in Activities of Daily Living, Instrumental Activities of Daily Living Scales (IADL), and the Physician and Caregiver Clinical Global Impression of Change (CGIC) was assessed at baseline and at the end of treatment.

RESULTS

Nine patients, all from the eptastigmine group, did not complete treatment because of uncooperativeness (n = 3), adverse events (n = 3), protocol violations (n = 2), and clinical decline (n = 1). Twenty-five patients receiving eptastigmine (34%) reported adverse events mainly of the cholinergic type. Cholinergic side effects were generally associated with peak red blood cell cholinesterase inhibition exceeding 50% after the first dose, or 70% at steady state. At steady state, average daily acetylcholinesterase inhibition ranged from 13% to 54%. Overall, 34% of patients receiving eptastigmine versus 0% receiving placebo (p = 0.006) improved on the Physician CGIC. This percentage increased to 46% in the subgroup of patients with average daily acetylcholinesterase inhibition ranging from 30% to 35%. Patient performance on the IADL also improved significantly compared with the placebo group (p = 0.019). In the eptastigmine group, performances on all tests and scales improved with an inverted U-shaped relation to average daily acetylcholinesterase inhibition.

CONCLUSIONS

This study shows that doses of 40 to 60 mg per day of eptastigmine are relatively safe and well tolerated and that moderate acetylcholinesterase inhibition is associated with maximal cognitive efficacy.

Effects of entorhinal cortex lesion on learning behavior and on hippocampus in the rat

The initial stage of Alzheimer's disease is characterized by a neuropathological change in the entorhinal cortex. In a previous study it was shown that rats with excitotoxic lesion of entorhinal cortex showed an impaired acquisition of passive and active avoidance responses. In this study a rat with excitotoxic lesion of the entorhinal cortex was tested for 'more operant' behavioral learning (i.e., positive reinforcement operant learning). The hippocampus was also examined histologically as acetylcholinesterase-stained sections, and as synaptophysin immunostained sections and examined biochemically by liquid chromatography. Eight weeks after operation, the bilateral entorhinal cortex lesioned rats showed an impaired acquisition of positive reinforcement operant learning. The lesioned side of unilateral entorhinal cortex lesioned rats showed a decrease of acetylcholinesterase-positive fibers in the CA3, the dentate gyrus, and of synaptophysin-positive substances in the CA3. Biochemical study showed a decreased level of acetylcholine in the CA3, and in the dentate gyrus. The histological and biochemical findings are interpreted as indicating that the entorhinal cortex of the rat provides the major extrinsic synaptic input to the hippocampal formation via the circuit which serves as a relay passage through the dentate gyrus and via direct projections into the hippocampus. Behavioral findings confirmed the importance of the entorhinal cortex in memory acquisition and indicated that rats with a partial neuronal loss in the entorhinal cortex may be a useful model for the memory disturbance of Alzheimer's disease.

An inverted U-shaped curve for heptylphysostigmine on radial maze performance in rats: comparison with other cholinesterase inhibitors

The potential of heptylphysostigmine tartrate (pyrrolo [2,3b] indol-5-ol, 3,3a,8,8a-hexahydro-1,3a,8-trimethylheptylcarbamate [ester, (3aS-cis)]) (MF201), a new second-generation cholinesterase inhibitor, to antagonize scopolamine-induced amnesia in rats was assessed in an 8-arm radial maze. Upon completing the training session, the rats were orally administered increasing doses of MF201 (2, 3, 4, 6 and 8 mg/kg) 60 min prior to a s.c. injection of scopolamine (0.25 mg/kg). 9-Amino-1,2,3,4-tetrahydroamino-acridine hydrochloride hydrate (tacrine) (0.25, 0.37, 0.5, 1 and 2 mg/kg), 1-benzil-4-[(5,6-dimethoxy-1-indanon)-2-yl]-methyl piperidine (E2020) (0.125, 0.18, 0.25 and 0.5 mg/kg) and physostigmine (0.15, 0.25, 0.5 and 1 mg/kg) were orally administered and rats were tested in the same task. As previously described, scopolamine induced an impairment in radial maze performance, measured in terms of total number of errors, total time taken to complete the task and the percentage of amnesic animals. The reversal of scopolamine-induced impairment was characterized by the presence of an inverted U-shaped dose-response curve. A significant antagonistic effect was achieved with a dose (mg/kg) of 0.25 for E2020, 0.5 for tacrine and physostigmine and 3, 4 and 6 for MF201, the latter manifesting a broader spectrum of activity (3-6 mg/kg). While the maximal active doses restored the scopolamine-induced modified pattern of arm entry, they were ineffective in reducing hypermotility, suggesting the drugs have a specific effect on cognitive function.

Functional studies of new drugs for the treatment of Alzheimer's disease

Few treatments for Alzheimer's disease (AD) have been evaluated to date by studying their effects on functional brain activity. Neuroimaging techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) are important tools that can provide an increased understanding of functional correlates to biological and structural changes in brains of patients with AD. These techniques provide valuable information about effects of drug treatments on functional parameters including blood flow, glucose metabolism, and neurotransmitter activity. Functional study outcomes are especially valuable when they are combined with studies of the effect of treatment on EEG and cognitive tests. This paper discusses functional changes observed in the brains of patients with AD following treatment with tacrine or nerve growth factor. Although these agents represent different approaches to cognitive drug treatment for AD, functional study outcomes indicate that both drugs improve cholinergic activity in the brain during long-term treatment.

Mixed-model analysis of incomplete longitudinal data from a high-dose trial of tacrine (Cognex) in Alzheimer's patients

Mixed-model techniques are applied to incomplete longitudinal data from a double-blind, placebo-controlled, parallel-group, high-dose study of tacrine in patients with Alzheimer's disease. The study consisted of a 30-week double-blind treatment period. Patients were randomized to one of four treatment groups. Dosing was initiated at 40 mg/day and increased in increments of 40 mg/day every 6 weeks until the target dose was achieved. If the study medication was not well tolerated or there were significant elevations in alanine aminotransferase, patients were withdrawn from the study. The use of SAS procedure PROC MIXED for the analysis of incomplete longitudinal data is discussed. This approach is used to evaluate disease progression over time and the effect of incremental dose increases of tacrine on changes on the Alzheimer's Disease Assessment Scale-Cognitive subscale.

Differential effect of tacrine and physostigmine on the secretion of the beta-amyloid precursor protein in cell lines

The senile plaque in Alzheimer's disease (AD) consists mainly of the amyloid beta-peptide (A beta) derived from a family of large integral membrane glycoproteins, beta-amyloid precursor proteins (beta APP). Soluble derivatives of beta APP generated by the proteolytic processing of full-length beta APP are normally secreted into the conditioned medium of cultured cells. Here we have investigated the possibility that the processing of beta APP can be regulated by the cholinesterase inhibitors physostigmine and tacrine. Both drugs mildly improve cognitive functions in some patients with AD. We analyzed the level of beta APP in glial, neuroblastoma, and pheochromocytoma cells by immunoblotting cell lysates and conditioned media using a monoclonal antibody, MAb22C11. The levels of soluble beta APP derivatives normally present in conditioned media were severely inhibited by treating cells with tacrine but not with physostigmine. Whereas the treatment of cells with tacrine resulted in a small decrease in the intracellular levels of beta APP, treating cells with physostigmine resulted in a slight increase in the intracellular levels of beta APP compared to untreated cells. The effect of tacrine on the secretion of beta APP was not affected by cotreating cells with muscarinic agents, staurosporine, or the calcium ionophore. Our results suggest that a decrease in the secretion of beta APP by tacrine did not depend on its anticholinesterase activity and that tacrine operates via a noncholinergic mechanism.

L-deprenyl and physostigmine for the treatment of Alzheimer's disease

The present study evaluated the safety of and obtained preliminary data on the cognitive effects of L-deprenyl and physostigmine in patients with Alzheimer's Disease. Seventeen outpatients with Alzheimer's Disease participated in a double-blind crossover study in which they received 4 weeks of L-deprenyl at a dose of 10 mg p.o., q.d., and 4 weeks of placebo in random order. During both the L-deprenyl and placebo periods, patients received cognitive assessments during physostigmine (0.5 mg) and placebo infusions separated by 2 days. The cognitive effects of these agents alone and in combination were measured with digit span, verbal fluency, list learning, praxis, delayed recall, and delayed recognition tasks. Fifteen patients completed the study. The two drugs, used alone or in combination, were safe and well tolerated. Analyses of variance demonstrated that neither physostigmine nor L-deprenyl, whether given alone or in combination, significantly improved cognition, when compared with the double placebo condition.

Acetylcholinesterase inhibition by zifrosilone: pharmacokinetics and pharmacodynamics

OBJECTIVE

To determine the pharmacokinetics, pharmacodynamics and safety of the acetylcholinesterase inhibitor zifrosilone in healthy male volunteers.

METHODS

Pharmacokinetics, pharmacodynamics, and tolerance of zifrosilone were studied in a double-blind, sequential, single-escalating-dose, randomized panel design. Each panel consisted of six subjects, with four subjects receiving zifrosilone (10, 30, 60, 90, 120, 150, 200, 250, and 300 mg orally) and two subjects receiving matching placebo. Serial blood samples were obtained for zifrosilone plasma concentrations and red blood cell acetylcholinesterase and butyrylcholinesterase activities. Participating subjects (n = 54) were men between the ages of 18 and 45 years. Each subject had a normal physical examination, electrocardiogram, serum chemistries, hematology, urinalysis, and test for human immunodeficiency virus at screening.

RESULTS

A greater than proportionate increase in mean plasma concentration values for area under the curve from time zero to infinity was observed over the 200 to 300 mg dose range groups. Red blood cell acetylcholinesterase showed a dose-inhibition relationship, with a mean maximum inhibition of 20.9% at 10 mg that increased to 62.1% at 300 mg. Butyrylcholinesterase activity was relatively unaffected by zifrosilone (< 20% inhibition at 300 mg). For doses > or = 200 mg, an Emax pharmacodynamic model was used to describe the relationship between zifrosilone plasma concentration and red blood cell acetylcholinesterase inhibition (Emax = 83.8%; EC50 = 0.65 ng/ml).

CONCLUSIONS

Zifrosilone showed dose-dependent pharmacokinetics after oral administration and was effective in causing selective inhibition of red blood cell acetylcholinesterase.

Velnacrine maleate improves delayed matching performance by aged monkeys

Velnacrine maleate is a novel, orally active acetylcholinesterase inhibitor of the acridine class with a longer duration of action than physostigmine. Velnacrine has shown efficacy in the treatment of Alzheimer's disease and in improving both normal and experimentally impaired mnemonic function in animals and humans. To characterize this action further, the present study evaluated velnacrine for its ability to ameliorate the decline in short-term memory associated with aging in non-human primates at two time points after velnacrine administration: (1) 30 min and (2) 24 h. Initially, doses of 1, 2, 4, and 6 mg/kg, PO (free base corrected) were administered once to each of six aged (25-40 years), memory-impaired macaques that had been trained to perform a delayed matching-to-sample (DMTS) paradigm. The dose associated with the greatest improvement in session performance was administered three more times to the same individual. Four of the six monkeys showed improved DMTS performance during the repeated best dose phase (phase 2). Almost all of the improvement occurred during long-delay trials. Compared to placebo trials, velnacrine induced a significant improvement of long delay DMTS (58.0-66.7%, 13.4% of the placebo value). Long delay DMTS remained significantly improved during the test session conducted 24 h following velnacrine administration. Pharmacokinetic analysis following administration of 4 or 6 mg/kg velnacrine to three aged monkeys revealed peak plasma concentrations ranging from 27 to 166 ng/ml, 30-60 min after dosing. Six hours after dosing velnacrine plasma levels decreased to 5.1-11.8 ng/ml; and 24 h after dosing velnacrine plasma levels were less than the limit of quantitation (5 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of glutathione depletion and oxidative stress on the in vitro cytotoxicity of velnacrine maleate

Velnacrine maleate (Mentane) is an aminoacridine drug developed for the treatment of Alzheimer's disease. Although velnacrine maleate has not been observed to cause prominent cytotoxicity in in vitro hepatocyte cultures, this drug was associated with elevated serum levels of hepatic enzymes in clinical trials. The purpose of the present study was to manipulate cultures of rat hepatocytes in an attempt to elicit a cytotoxic response from this drug and to better understand the in vitro mechanisms of action. Cytotoxicity was evaluated by measuring lactate dehydrogenase (LDH) leakage, neutral red (NR) uptake, and 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction. Preliminary studies with fluorescent probes did not indicate a role for calcium influx or the formation of reactive oxygen species in the cytotoxicity of velnacrine maleate. However, depletion of cellular glutathione (GSH) by diamide (DA) pretreatment resulted in a cytotoxic response at concentrations of velnacrine maleate (1 and 10 micrograms/ml) which were approximately 25-fold lower than those in the absence of DA. Similarly, pretreatment with velnacrine maleate enhanced the cytotoxicity of DA. Pre-exposure of cells to a mixture of DA and t-butyl hydroperoxide (t-BHP) at non-toxic concentrations resulted in significant cytotoxicity of the hepatocyte cultures by velnacrine maleate. Results from these studies indicate that oxidative stress and GSH depletion may enhance Alzheimer patients' susceptibility to the hepatotoxic potential of aminoacridine drugs.