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

Repurposing Cholinesterase Inhibitors as Antidepressants? Dose and Stress-Sensitivity May Be Critical to Opening Possibilities

When stress becomes chronic it can trigger lasting brain and behavioral changes including Major Depressive Disorder (MDD). There is conflicting evidence regarding whether acetylcholinesterase inhibitors (AChEIs) may have antidepressant properties. In a recent publication, we demonstrated a strong dose-dependency of the effect of AChEIs on antidepressant-related behavior in the mouse forced swim test: whereas the AChEI donepezil indeed promotes depression-like behavior at a high dose, it has antidepressant-like properties at lower doses in the same experiment. Our data therefore suggest a Janus-faced dose-response curve for donepezil in depression-related behavior. In this review, we investigate the mood-related properties of AChEIs in greater detail, focusing on both human and rodent studies. In fact, while there have been many studies showing pro-depressant activity by AChEIs and this is a major concept in the field, a variety of other studies in both humans and rodents show antidepressant effects. Our study was one of the first to systematically vary dose to include very low concentrations while measuring behavioral effects, potentially explaining the apparent disparate findings in the field. The possibility of antidepressant roles for AChEIs in rodents may provide hope for new depression treatments. Importantly, MDD is a psychosocial stress-linked disorder, and in rodents, stress is a major experimental manipulation for studying depression mechanisms, so an important future direction will be to determine the extent to which these depression-related effects are stress-sensitive. In sum, gaining a greater understanding of the potentially therapeutic mood-related effects of low dose AChEIs, both in rodent models and in human subjects, should be a prioritized topic in ongoing translational research.

Characterization of phenolic profile by LC-ESI-MS/MS and enzyme inhibitory activities of two wild edible garlic: Allium nigrum L. and Allium subhirsutum L

In our study, Allium nigrum L. and Allium subhirsutum L. were investigated in terms of phenolic profile, acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and tyrosinase inhibitory potentials. The colorimetric analysis revealed that the highest levels of total phenol (45.6, 15.8 mg GAE/g extract, respectively) and total flavonoid contents (8.2, 5.7 mg QE/g extract, respectively) were found in the bulbs of both plants. About 30 compounds were determined by LC-ESI-MS/MS with validated method and 3-hydroxybenzoic acid (2,188.4 μg/g extract) and p-coumaric acid (1,700.8 μg/g extract) were major phenolic acids. (-)-Epigallocatechin gallate (998.3 µg/g extract) and genistein (159.3 μg/g extract) which are neuroprotective compounds were the predominant flavonoids for A. nigrum and A. subhirsutum, respectively. Enzyme inhibitory activities of samples were performed by spectrophotometrically with 96-well microplate reader. All samples showed anti-AChE, anti-BuChE, and anti-tyrosinase activities and the aerial part of A. nigrum was the most potent (IC₅₀ 6.1, 3.27, 22.31 µg/ml, respectively). PRACTICAL APPLICATIONS: Many Allium species, especially those cultivated, are consumed in different countries as food in different ways. In the literature, studies on these species have generally focused on organosulfur compounds of the species. In our present study, phenolic compounds having a wide range of biological activities were determined in different parts of the two Allium species consumed as food. We also investigated in vitro cholinesterases and tyrosinase inhibition activities of these species. A correlation was observed between phenolic compounds and enzyme inhibition activities. These results were further explored and confirmed by principal component analysis (PCA). PCA revealed that samples were discriminated from each other according to phenolic compounds and enzyme inhibitory potencies. Conclusively, this study determines that the chemical profiles and biological activities of A. nigrum and A. subhirsutum.

Spatial recognition test: A novel cognition task for assessing topographical memory in mice

Dysfunction in topographical memory is a core feature of several neurological disorders. There is a large unmet medical need to address learning and memory deficits as a whole in central nervous system disease. There are considerable efforts to identify pro-cognitive compounds but current methods are either lengthy or labour intensive. Our test used a two chamber apparatus and is based on the preference of rodents to explore novel environments. It was used firstly to assess topographical memory in mice at different retention intervals (RI) and secondly to investigate the effect of three drugs reported to be beneficial for cognitive decline associated with Alzheimer's disease, namely: donepezil, memantine and levetiracetam. Animals show good memory performance at all RIs tested under four hours. At the four-hour RI, animals show a significantly poorer memory performance which can be rescued using donepezil, memantine and levetiracetam. Using this test we established and validated a spatial recognition paradigm to address topographical memory in mice by showing a decremental time-induced forgetting response and reversing this decrease in performance using pharmacological tools. The spatial recognition test differs from more commonly used visuospatial laboratory tests in both throughput capability and potentially neuroanatomical substrate. This test has the potential to be used to assess cognitive performance in transgenic animals, disease models and to screen putative cognitive enhancers or depressors.

Age-dependent modulation of fasting and long-term dietary restriction on acetylcholinesterase in non-neuronal tissues of mice

Dietary restriction (DR) without malnutrition is a robust intervention that extends lifespan and slows the onset of nervous system deficit and age-related diseases in diverse organisms. Acetylcholinesterase (AChE), a thoroughly studied enzyme better known for hydrolyzing acetylcholine (ACh) in neuronal tissues, has recently been linked with multiple unrelated biological functions in different non-neuronal tissues. In the present study, the activity and protein expression level of AChE in liver, heart, and kidney of young (1 month), adult (6 month), and aged (18 month) mice were investigated. We also studied age- and tissue-specific changes in AChE activity and protein expression level after the mice were subjected to 24-h fasting and long-term DR. Our results showed that AChE activity and protein expression in kidney and heart of aged mice decreased significantly in comparison with young mice. On the contrary, long-term DR decreases the AChE activity and the protein expression level in all tissues irrespective of ages studied. We summarized that changes in AChE with age in different tissues studied reflects its different roles at different phases of an organism's life. Conversely, the cumulative modulation manifested in the form of lowering AChE by long-term DR may prevent the futile synthesis and accumulation of unwanted AChE besides the added compensatory benefit of enhanced ACh availability needed during the period of starvation. This, in turn, may help in preventing the declining homeostatic roles of this important neurotransmitter in different tissues.

True alignment of preclinical and clinical research to enhance success in CNS drug development: a review of the current evidence

Central nervous system pharmacological research and development has reached a critical turning point. Patients suffering from disorders afflicting the central nervous system are numerous and command significant attention from the pharmaceutical industry. However, given the numerous failures of promising drugs, many companies are no longer investing in or, indeed, are divesting from this therapeutic area. Central nervous system drug development must change in order to develop effective therapies to treat these patients. Preclinical research is a cornerstone of drug development; however, it is frequently criticised for its lack of predictive validity. Animal models and assays can be shown to be more predictive than reported and, on many occasions, the lack of thorough preclinical testing is potentially to blame for some of the clinical failures. Important factors such as translational aspects, nature of animal models, variances in acute versus chronic dosing, development of add-on therapies and understanding of the full dose-response relationship are too often neglected. Reducing the attrition rate in central nervous system drug development could be achieved by addressing these important questions before novel compounds enter the clinical phase. This review illustrates the relevance of employing these criteria to translational central nervous system research, better to ensure success in developing new drugs in this therapeutic area.

Effects of imperatorin on scopolamine-induced cognitive impairment and oxidative stress in mice

RATIONALE

Imperatorin, a naturally occurring furanocoumarin, inactivates gamma-aminobutyric acid transaminase and inhibits acetylcholinesterase activity.

OBJECTIVES

The purpose of our experiment was to examine the influence of imperatorin on cognitive impairment and oxidative stress in the brain induced by scopolamine in male Swiss mice.

METHODS

In the present studies, we used scopolamine-invoke memory deficit measured in passive avoidance (PA) paradigm as an animal model of Alzheimer disease (AD).

RESULTS

Our finding revealed that imperatorin administered acutely at the doses of 5 and 10 mg/kg prior to the injection of scopolamine (1 mg/kg) improved memory acquisition and consolidation impaired by scopolamine. Furthermore, repeatable (7 days, twice daily) administration of the highest dose of imperatorin (10 mg/kg) significantly attenuated the effects of scopolamine on memory acquisition, whereas the doses of 5 and 10 mg/kg of this furanocoumarin were effective when memory consolidation was measured. Imperatorin, administered with scopolamine, increased antioxidant enzymes activity and decreased concentration of malondiamide, an indicator of lipid peroxidation level.

CONCLUSIONS

These results demonstrate that imperatorin may offer protection against scopolamine-induced memory impairments and possesses antioxidant properties, thus after further preclinical and clinical studies this compound may provide an interesting approach in pharmacotherapy, as well as prophylactics of AD.

Effects of imperatorin on nicotine-induced anxiety- and memory-related responses and oxidative stress in mice

The purpose of the reported experiments was to examine the effects of imperatorin [9-[(3-methylbut-2-en-1-yl)oxy]-7H-furo[3,2-g]chromen-7-one] on anxiety and memory-related responses induced by nicotine in mice and their relation to the level of nicotine-induced oxidative stress in brain as well as in the hippocampus and the prefrontal cortex. Male Swiss mice were tested for anxiety in the elevated plus maze test (EPM), and for cognition using passive avoidance (PA) procedures. Imperatorin, purified by high-speed counter-current chromatography from methanol extract of fruits of Angelica officinalis, acutely administered at the doses of 10 and 20mg/kg impaired the anxiogenic effect of nicotine (0.1mg/kg, s.c.). Furthermore, acute injections of subthreshold dose of imperatorin (1mg/kg, i.p.) improved processes of memory acquisition when co-administered with nicotine used at non-active dose of 0.05 mg/kg, s.c. Additionally, repeated administration of imperatorin (1mg/kg, i.p., twice daily, for 6 days) improved different stages of memory processes (both acquisition and consolidation) when injected in combination with non-active dose of nicotine (0.05 mg/kg, s.c.) in the PA task. Oxidative stress was assessed by determination of antioxidant enzymes (glutathione peroxidases (GPx), superoxide dismutase (SOD), glutathione reductase (GR)) activities as well as of malondialdehyde (MDA) concentration in the whole brain, the hippocampus and the prefrontal cortex after repeated administration of imperatorin (1mg/kg, 6 days) and single nicotine injection (0.05 mg/kgs.c.) on the seventh day. The results of our research suggest strong behavioural interaction between imperatorin and nicotine at the level of anxiety- and cognitive-like processes. Furthermore, imperatorin inhibited nicotine-induced changes in examined indicators of oxidative stress, especially in the hippocampus and the cortex.

Potential of pretreatment neural activity in the visual cortex during emotional processing to predict treatment response to scopolamine in major depressive disorder

CONTEXT

The need for improved treatment options for patients with major depressive disorder (MDD) is critical. Faster-acting antidepressants and biomarkers that predict clinical response will facilitate treatment. Scopolamine produces rapid antidepressant effects and thus offers the opportunity to characterize potential biomarkers of treatment response within short periods.

OBJECTIVE

To determine if baseline brain activity when processing emotional information can predict treatment response to scopolamine in MDD.

DESIGN

A double-blind, placebo-controlled, crossover study together with repeated functional magnetic resonance imaging, acquired as participants performed face-identity and face-emotion working memory tasks.

SETTING

National Institute of Mental Health Division of Intramural Research Programs.

PARTICIPANTS

Fifteen currently depressed outpatients meeting DSM-IV criteria for recurrent MDD and 21 healthy participants, between 18 and 55 years of age.

MAIN OUTCOME MEASURE

The magnitude of treatment response to scopolamine (percentage of change in the Montgomery-Asberg Depression Rating Scale score between study end and baseline) was correlated with blood oxygen level-dependent (BOLD) signal associated with each working memory component (encode, maintenance, and test) for both identity and emotion tasks. Treatment response also was correlated with change in BOLD response (scopolamine vs baseline). Baseline activity was compared between healthy and MDD groups.

RESULTS

Baseline BOLD response in the bilateral middle occipital cortex, selectively during the stimulus-processing components of the emotion working memory task (no correlation during the identity task), correlated with treatment response magnitude. Change in BOLD response following scopolamine administration in overlapping areas in the middle occipital cortex while performing the same task conditions also correlated with clinical response. Healthy controls showed higher activity in the same visual regions than patients with MDD during baseline.

CONCLUSION

These results implicate cholinergic and visual processing dysfunction in the pathophysiology of MDD and suggest that neural response in the visual cortex, selectively to emotional stimuli, may provide a useful biomarker for identifying patients who will respond favorably to scopolamine.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00055575.

Dietary restriction regulates brain acetylcholinesterase in female mice as a function of age

In the present study, the normal endogenous activity level of acetylcholinesterase (AChE) was investigated in cerebral hemispheres and cerebellum of female mice as a function of age. The effects of 24-h fasting and refeeding, and dietary restriction (DR) on AChE activity and its protein expression patterns were also investigated in young (1-month) and old (18-month) mice. Our results show that the activity (U/mg protein) and level of AChE protein in the cerebral hemispheres of young mice is decreased significantly on 24-h fasting which reverses back on refeeding. On the other hand, DR produces an accumulative effect; thereby it decreases the activity of this enzyme in the cerebral hemispheres of both the young and old mice and the degree of reduction is of different magnitude, dictated in an age- and brain region-specific manner. Our findings suggest that DR regulates the activity of this enzyme which may be useful in related neurodegenerative disease conditions.

Use of acetylcholinesterase inhibitors in Alzheimer's disease

Alzheimer's disease is a growing problem in an aging Western world, estimated to have cost the US economy USD 1.75 trillion. Until recently, the management of Alzheimer's disease largely comprised support for the family, nursing care and the use of unlicensed medication to control behavioral disturbances. The three new acetylcholinesterase inhibitors licensed to treat Alzheimer's disease (donepezil, rivastigmine and galantamine) have provided clinicians with a major impetus to their desire to diagnose and treat this lethal disease. Their effects on cognition are proven. More recent work on the effects of acetylcholinesterase inhibitors on behavioral symptoms, activities of daily living and caregiver burden have also been encouraging. Emerging work indicates their likely efficacy in other dementias (e.g., vascular dementia, dementia with Lewy bodies). This review summarizes the evidence concerning the impact of acetylcholinesterase inhibitors in dementia both currently and over the next 5 years.

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.

Procholinergic and memory enhancing properties of the selective norepinephrine uptake inhibitor atomoxetine

Atomoxetine has been approved by the FDA as the first new drug in 30 years for the treatment of attention deficit/hyperactivity disorder (ADHD). As a selective norepinephrine uptake inhibitor and a nonstimulant, atomoxetine has a different mechanism of action from the stimulant drugs used up to now for the treatment of ADHD. Since brain acetylcholine (ACh) has been associated with memory, attention and motivation, processes dysregulated in ADHD, we investigated the effects of atomoxetine on cholinergic neurotransmission. We showed here that, in rats, atomoxetine (0.3-3 mg/kg, i.p.),--increases in vivo extracellular levels of ACh in cortical but not subcortical brain regions. The marked increase of cortical ACh induced by atomoxetine was dependent upon norepinephrine alpha-1 and/or dopamine D1 receptor activation. We observed similar increases in cortical and hippocampal ACh release with methylphenidate (1 and 3 mg/kg, i.p.)--currently the most commonly prescribed medication for the treatment of ADHD--and with the norepinephrine uptake inhibitor reboxetine (3-30 mg/kg, i.p.). Since drugs that increase cholinergic neurotransmission are used in the treatment of cognitive dysfunction and dementias, we also investigated the effects of atomoxetine on memory tasks. We showed that, consistent with its cortical procholinergic and catecholamine-enhancing profile, atomoxetine (1-3 mg/kg, p.o.) significantly ameliorated performance in the object recognition test and the radial arm-maze test.

Eptastigmine: ten years of pharmacology, toxicology, pharmacokinetic, and clinical studies

Eptastigmine (heptyl-physostigmine tartrate) is a carbamate derivative of physostigmine in which the carbamoylmethyl group in position 5 of the side chain has been substituted with a carbamoylheptyl group. In vitro and ex vivo results suggest that eptastigmine has a long-lasting reversible brain cholinesterase (i.e., acetylcholinesterase and butyryl-cholinesterase) inhibitory effect. When administered in vivo to rodents by various routes, eptastigmine inhibits cerebral acetylcholinesterases (AChE) and increases acetylcholine (Ach) brain levels by 2500-3000%, depending on the dose. This effect leads to an improvement in the cerebral blood flow in the ischemic brain, excitatory and inhibitory effects on the gastrointestinal tract and to a protection from acute soman and diisopropylfluorophosphate intoxication. Eptastigmine, by either acute or chronic administration, has been found to have memory enhancing effects in different species of normal, aged and lesioned animals. It also restored to normal the age-related increase of EEG power without affecting spontaneous motor activity. Clinical investigations on more than 1500 patients with Alzheimer's disease demonstrated that eptastigmine significantly improved cognitive performance (as assessed by the cognitive subscale of the Alzheimer's Disease Assessment Scale) as compared with placebo. This improvement was most evident in patients with more severe cognitive impairment at the baseline. The relationship between patient performance and average steady-state AChE inhibition was described by an inverted U-shaped dose-response curve. Pharmacokinetic studies have revealed that after oral administration eptastigmine is rapidly distributed to the tissues and readily enters the CNS, where it can be expected to inhibit AChE for a prolonged period. Eptastigmine is generally well tolerated and the majority of adverse events (cholinergic) were mild to moderate in intensity. However, the adverse hematologic (granulocytopenia) effects reported in two studies have resulted in the suspension of further clinical trials.

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.

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.

Cholinesterase inhibitors stabilize Alzheimer disease

During the last decade, a systematic effort to develop a pharmacological treatment for Alzheimer disease (AD) has resulted into three drugs being registered for the first time in USA and Europe for this specific indication. All three are cholinesterase inhibitors (ChEI). The major therapeutic effect of ChEI on AD patients is to maintain cognitive function at a constant level during a 6 months to one year period of treatment as compared to placebo. Additional drug effects might be slowing cognitive deterioration and improving behavioral and daily living conditions. Comparison of clinical effects of 6 ChEI demonstrates a rather similar magnitude of improvement in cognitive measures. For some drugs. this may represent an upper limit while for other it may still be possible to increase further the benefit. In order to maximize and prolong positive drug effects it is important to start early and adjust dosage during the treatment. Recent studies show that in many patients the stabilization effect produced by ChEI can be prolonged for as long as a 24 month period. In order to explain the stabilizing effect of ChEI, a mechanism other than AChE inhibition, based on beta-amyloid metabolism, is postulated.

Effects of cholinesterase inhibitors on a two-component chained schedule performance in rats

The acetylcholinesterase (AChE) inhibitors physostigmine (PHY), tacrine (THA), and heptylphysostigmine (HEP) have been evaluated as potential therapeutics for treatment of Alzheimer's disease (AD) and as prophylactics against organophosphate (OP) poisoning. The above medical applications are based upon the neurochemical principles of elevation of transient levels of acetylcholine (ACh) in brain and reversible inhibition of AChE in blood and brain, respectively. The present study was undertaken to evaluate the effects of these drugs on performance of a two-component chained schedule of differential-reinforcement-of-high-rate (DRH) reward/differential-reinforcement-of-low-rate (DRL) nonreward contingencies, for water reinforcement in 2-h experimental sessions in rats. Both PHY (0.031-0.25 mg/kg, SC) and HEP (0.625-10.0 mg/kg, SC) decreased overall reinforcement rate and nonreinforced response in a dose-related and parallel manner, whereas THA (0.625-5.0 mg/kg) decreased the overall reinforcement rate in a dose-related manner, but did not significantly affect nonreinforced response. The least significant doses of PHY (0.625 mg/kg), THA (1.25 mg/kg), and HEP (1. 25 mg/kg) on the behavioral performance were associated with oral movements and/or muscle fasciculation. Moderate to high doses of these drugs (i.e., PHY >/= 0.624, THA >/= 1.25, and HEP >/= 1.25 mg/kg) produced behavioral suppression, which resulted mostly from the cessation of responding in the presence of cholinergic adverse events. The ED(50) values of the behavioral disruption (as documented by overall reinforcer loss) for PHY, THA, and HEP were 0. 081, 3.87, and 2.89 mg/kg, respectively, and the behavioral-deficit-free (BDF) doses were 0.031, 0.625, and 0.625 mg/kg, respectively. Preclinical data revealed that the BDF doses of both PHY and HEP have moderate inhibition of AChE, which leads to an efficacious elevation of ACh level in the brain, whereas the BDF dose of THA shows no significant AChE inhibition or elevation of brain ACh level; however, they all have cognition enhancing effects at their respective safety doses. The above data suggest that the BDF doses of PHY and HEP may have prophylactic efficacy against OP poisoning, whereas THA may not. The BDF doses of these three drugs are comparable to the maximum tolerated doses in clinical practice, suggesting that the present rat model may have potential value in predicting the clinical safety of AChE inhibitors developed for therapy of AD and prophylaxis against OP poisoning as well.

Effect of rivastigmine on scopolamine-induced memory impairment in rats

The effect of rivastigmine on memory impairments induced in rats by scopolamine (0.5 mg/kg) was assessed in the Morris water maze and passive avoidance tests and compared with that of tacrine (2.5-17.7 mg/kg). Rivastigmine, (0.5-2.5 mg/kg) inhibited cholinesterase in the cortex and hippocampus by 21-60% and antagonised the deficits in working and reference memory. Tacrine (12.5 and 17.7 mg/kg) produced significantly less inhibition of cholinesterase in the hippocampus but more in the striatum than rivastigmine (0.75 and 1.5 mg/kg) and only antagonised the deficit in reference memory. Rivastigmine (1.5 and 2.5 mg/kg) or tacrine (12.5 mg/kg), injected immediately after completion of the acquisition trial in the passive avoidance test, antagonised the deficit induced by scopolamine (1 mg/kg) in memory retention. The inability of higher doses of the cholinesterase inhibitors to antagonise memory deficits induced by scopolamine may be related to excessive cholinergic stimulation in the central nervous system.

NXX-066 in patients with Alzheimer's disease: a bridging study

Reduced cholinergic transmission is a key neurotransmitter dysfunction in Alzheimer's Disease (AD). NXX-066, a physostigmine analog and acetylcholinesterase (AChE) inhibitor, has demonstrated activity in animal models of memory function, and was well tolerated in healthy subjects up to a single dose of 64 mg and multiple doses of 60 mg QD for seven days. Since AChE inhibitors are often tolerated differently in AD patients than in healthy volunteers, a randomized, placebo-controlled, double-blind, single-center, inpatient bridging study was conducted to determine the maximum tolerated dose (MTD) of NXX-066 in the target patient population. Seven consecutive panels of eight AD patients each (6 active, 2 placebo) received fixed oral doses of NXX-066 (20, 30, 40, 50, 60, 70, or 80 mg BID) for seven days. Initiation of each subsequent panel (dose group) was contingent upon the tolerability of lower dose levels. The MTD was determined to be 70 mg BID when four of six patients receiving 80 mg BID were prematurely discontinued from the study due to nausea and/or vomiting, accompanied in some patients by mild to moderate dizziness, headache, asthenia, and gastric symptoms. Wide variability in plasma levels of NXX-066 was observed in all dose panels. AChE inhibition in whole blood correlated with both maximum plasma concentration and dose; however, AChE inhibition was not predictive of adverse events. In this study, AD patients tolerated larger daily doses of NXX-066 on a BID regimen than healthy normal subjects had tolerated with QD dosing. Further studies are warranted to examine whether differing tolerability between patients and healthy subjects or the reduced dosing interval explains these findings.

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.

Efficacy and safety of eptastigmine for the treatment of patients with Alzheimer's disease

OBJECTIVE

To evaluate the efficacy and safety of eptastigmine in patients with moderate to moderately severe AD.

BACKGROUND

Eptastigmine is a centrally acting cholinesterase inhibitor.

METHODS

The study was carried out according a multicenter, randomized, double-blinded, placebo-controlled, parallel-group design. Patients received a 24-week treatment with placebo or eptastigmine 15 mg or 20 mg three times daily after a 4-week, stepwise dose escalation. The effects of treatment on cognition, global function, and activities of daily living were evaluated with the Alzheimer's Disease Assessment Cognitive Subscale (ADAS-Cog), the Clinician's Interview-Based Impression of Change Plus (CIBIC-Plus), and the Instrumental Activities of Daily Living scale (IADL), respectively.

RESULTS

Thirty-six centers recruited 491 patients: 164 on placebo, 166 on eptastigmine 15 mg three times daily, and 161 on eptastigmine 20 mg three times daily. Percentages of patients completing double-blinded treatment were 87% in the placebo group and 86% in both the eptastigmine-treated groups. At the end of treatment, the intent-to-treat analysis on 463 patients showed a dose-dependent effect of eptastigmine on all efficacy variables, with a statistically significant effect of the 20 mg three times daily dose compared with placebo on the ADAS-Cog, CIBIC-Plus, and IADL. Patients on eptastigmine 15 mg three times daily performed significantly better than placebo-treated patients only on the ADAS-Cog. Eleven patients on placebo (7%), 13 patients on eptastigmine 15 mg three times daily (8%), and 12 patients on eptastigmine 20 mg three times daily (8%) discontinued study treatment because of adverse events. Adverse events were recorded in 49% of patients on placebo compared with 54% on eptastigmine 15 mg three times daily and 48% on eptastigmine 20 mg three times daily. Cholinergic side effects (nausea, vomiting, diarrhea, and abdominal pain) were reported with similar frequency in the eptastigmine- and placebo-treated patients. There was a dose-dependent transient and mild neutropenic effect associated with eptastigmine treatment, and one patient on 20 mg three times daily had an asymptomatic pancytopenia.

CONCLUSIONS

Eptastigmine produces significant cognitive, clinical, and functional benefits in patients with probable AD. Although the cholinergic tolerability of eptastigmine was found to be favorable, its potential adverse hematologic effects limit its clinical utility.

Effect of tamoxifen on bone fractures in older nursing home residents

OBJECTIVES

To evaluate the association between tamoxifen (TAM) treatment and rate of bone fractures in older, nursing home residents.

PARTICIPANTS

A total of 93,031 women, aged 65 years and older, whose data were part of the 1993 New York State MDS and for whom there was documentation of treatment with at least one medication.

SETTING

New York State long-term care facilities.

DESIGN

Cross-sectional study via secondary analysis of 1385 matched sets of residents. Each set included one resident who was receiving TAM treatment and up to four residents who were not.

MEASUREMENTS

Measurements included age, ethnicity, TAM treatment, hormone replacement therapy, vision impairment, any bone fractures, and, specifically, hip fractures.

RESULTS

During the 1.5-year period for which bone fractures are documented in the 1993 MDS, the fracture rates were: 7.62% in women not treated with TAM, 3.20% in women receiving 10 mg TAM daily, and 6.73% in women receiving 20 mg TAM daily. The odds ratio (OR) for bone fractures among women receiving 20 mg TAM daily compared with nontreated women was 0.916 (95% confidence interval (CI): 0.720-1.164; P = .472), and was 0.312 (95% CI: 0.112-0.865; P = .025) for those receiving 10 mg daily. The rates of hip fracture were 4.98%, 2.40%, and 4.57% for controls and women receiving 10 mg and 20 mg TAM daily, respectively. Whereas the hip fracture rate for women receiving 20 mg daily was statistically similar to that of the controls (OR = .963; 95% CI: 0.718-1.291; P = .800), the difference between the controls and those receiving 10 mg daily approached significance (OR: 0.313; 95% CI: 0.096-1.018; P = .054).

CONCLUSION

Although standard treatment of 20 mg TAM daily offers no apparent protection against bone fracture in older nursing home residents, a daily 10 mg dose seems to be protective.

Maximum tolerated dose and pharmacodynamics of eptastigmine in elderly healthy volunteers

Eptastigmine is a new acetylcholinesterase (AChE) inhibitor currently under development for the symptomatic treatment of Alzheimer disease. This study was conducted to establish the maximum tolerated dose and the pharmacodynamics of eptastigmine in nine healthy elderly volunteers. Subjects received single oral doses of 8 mg, 20 mg, 32 mg, and 40 mg eptastigmine and placebo according to a double-blind, randomized, rising-dose, five-way crossover design. Adverse events, blood pressure, heart rate, body temperature, forced expiratory volume, salivary flow, and pupilar activity were closely monitored during treatment. Pharmacodynamic activity of eptastigmine was evaluated with an assay of AChE activity in red blood cells. Eptastigmine doses of 8 mg, 20 mg, and 32 mg were well tolerated. Two of four subjects receiving the 40-mg dose developed profound AChE inhibition (58-59%) and reported severe adverse events (nausea, vomiting, syncope, and bradycardia), precluding further administration in the remaining subjects. Eptastigmine administration produced a weak effect on supine heart rate, body temperature, and pupil diameter. There were no effects on blood pressure, forced expiratory volume, salivary flow, and near point of focus. Acetylcholinesterase activity was inhibited in a dose-related fashion according to a sigmoidal (logistic) function. The mean (+/- SEM) maximum inhibition of AChE activity (Imax) was 14.5+/-3.3%, 20.4+/-2.3%, 28.7+/-2.9%, 45.2+/-1.3% and 53.6+/-2.9% after placebo, 8 mg, 20 mg, 32 mg, and 40 mg of eptastigmine, respectively. The theoretical maximum response (Emax) was 72.9%, and the dose that produced half of the maximum response (ED50) was 29.5 mg. At 24 hours, residual AChE inhibition ranged from 9% to 15%, with a half-life of recovery of the enzyme of approximately 10 hours. The maximum tolerated dose of eptastigmine after single-dose oral administration in healthy elderly subjects is 32 mg. Single oral doses of eptastigmine produce sustained, dose-related inhibition of AChE activity. Adverse events are related to the degree of AChE inhibition.

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.

Cognitive enhancement therapy for Alzheimer's disease. The way forward

Although at present there is no definitive treatment or cure for Alzheimer's disease, different pharmacological strategies are being actively investigated. At present, cholinergic therapy and nootropics and some neuronotrophic agents represent the available approaches to symptomatic treatment of Alzheimer's disease. The use of cholinesterase inhibitors (ChEI) constitutes the best cholinergic approach to increase acetylcholine levels. Available data suggest that about 15 to 40% of Alzheimer's disease patients show a varying degree of cognitive improvement while taking these medications; however, haematological complications (neutropenia or agranulocytosis), together with hepatotoxicity, need to be considered carefully. Recent data suggest that long term administration of nootropics may lead to a significant improvement of cognitive functions in Alzheimer's disease patients compared with untreated individuals, having excellent tolerability. Protocols for the intracerebroventricular administration of neuronotrophic substances are also ongoing. The most promising approaches for the future currently undergoing investigation involve attempts to slow the production of beta-amyloid and/or to inhibit beta-amyloid aggregation. Another rational therapeutic approach would be to inhibit the formation of paired helical filaments (PHF) by increasing and/or modulating the activities of protein phosphatases and kinases. Antioxidant therapy should disrupt or prevent the free radical/beta-amyloid recirculating cascade and the progressive neurodegeneration. Idebenone, a synthetic compound acting as an 'electron trapper' and free radical scavenger, has shown some efficacy in degenerative and vascular dementia; at present, other different molecules having antioxidative properties [lazaroids (21-aminosteroids), pyrrolopyrimidines, nitric oxide blockers, selegiline, some vitamins] are under investigation. Lowering absorption or brain tissue concentrations of aluminium also offers possible therapeutic opportunities for slowing the rate of clinical progression of the disease; in this sense, some evidence exists using the aluminium chelating agent deferoxamine (desferrioxamine). Inflammation also may play a significant pathogenetic role in Alzheimer's disease. As shown by several retrospective analyses, there is an inverse association of anti-inflammatory drug use with the frequency of Alzheimer's disease diagnosis. Consequently, clinical trials using both nonsteroidal and steroidal molecules have been proposed. These lines of pharmacological intervention represent an important premise for future therapeutic strategies capable of counteracting the pathogenesis of Alzheimer's disease.