Treatment of Alzheimer's disease: future directions

Pharmacologic management of Alzheimer disease part III: nonsteroidal antiinflammatory drugs--emerging protective evidence?

OBJECTIVE

To provide information about research evaluating the role of nonsteroidal antiinflammatory drugs (NSAIDs) in the prevention, or delay in the onset of, Alzheimer disease (AD).

DATA SOURCES

Studies, review articles, and editorials identified from MEDLINE searches (January 1990-December 1996) and bibliographies of identified articles. The addendum lists articles from 1996 to June 1999.

STUDY SELECTION

Studies, review articles, and editorials addressing NSAIDs and AD pharmacotherapy research.

DATA EXTRACTION

Pertinent information was selected and the data synthesized into a review format.

DATA SYNTHESIS

AD is a complex disorder and there are numerous factors involved in the process. The pathology of AD is characterized by the development of amyloid plaques and neurofibrillary tangles. In addition, more than 40 immunoprotective proteins that are not unique to AD are found at autopsy that are normally absent, or present in very low concentrations, in normal brain. These findings suggest that AD may involve an inflammatory process. Preliminary results from studies investigating the incidence and onset of AD in patients with arthritis who have taken NSAIDs suggest that NSAIDs may have a protective effect. Studies evaluating the possible association between arthritis, NSAIDs, and AD are reviewed.

CONCLUSIONS

Preliminary evidence suggests that NSAIDs may have a protective effect against the development of AD. Further prospective, double-blind, placebo-controlled studies are needed to determine the role of NSAIDs in AD. These dose-finding studies should focus on specific agents and identify the dosage and duration of therapy necessary for a protective or therapeutic effect. Additionally, not all elderly patients are candidates for NSAIDs. Determining the definitive mechanism of action of NSAIDs in AD may suggest alternative agents that have similar pharmacologic activity, but are associated with fewer adverse effects.

Reappraising neurotransmitter-based strategies

A number of observations support the hypothesis that a central deficit in acetylcholine (ACh) may be responsible for the initiation of Alzheimer's disease (AD). For example, cholinergic innervation in AD is reduced in areas of the brain important for processing information. Further, reduced concentrations of choline acetyltransferase (ChAT), the enzyme responsible for the synthesis of ACh, correlate with the number of beta-amyloid senile plaques and cognitive dysfunction in AD patients. Consequently, several strategies to increase cholinergic neurotransmission have been developed, including ACh precursors, ACh release enhancers, cholinesterase (ChE) inhibitors and receptor agonists. Although ChE inhibitors appear to be the most promising, tacrine, the first ChE inhibitor to be registered and approved for the treatment of AD, has significant tolerability problems. Thus, ChE inhibitors with improved side-effect profiles have been developed and subsequently awarded marketing approval. However, in addition to the cholinergic system that is the most severely affected neurotransmitter system in AD, other neurotransmitter systems may be involved (e.g. serotonergic, noradrenergic and glutamatergic). Therefore, bifunctional compounds or combinations of drugs may provide additional therapeutic value.

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.

Behavioral effects of neurotrophic factor supplementation in aging

Neurotrophic factors are now recognized to play important roles in the normal function of the mature central nervous system. This knowledge has motivated experiments to evaluate the potential benefits of administering neurotrophic factors to the aged brain. This article provides a review of studies to date that have determined the behavioral effects of such treatments. Nerve growth factor (NGF) administration appears to reliably enhance learning and memory in aged rats, while glial-derived neurotrophic factor (GDNF) causes some improvement in motor function. Problems associated with neurotrophic factor administration to humans are discussed.

Influence of BDNF and FCS on viability and programmed cell death (PCD) of developing cortical chicken neurons in vitro

Programmed cell death (PCD) has been proposed to occur in vitro after withdrawal of growth factors and serum deprivation. In the present study the influence of brain derived neurotrophic factor (BDNF) and different serum (FCS) concentrations on viability, survival and apoptotic cell death of cortical cells from 8 days old chicken embryos after 3, 5 or 7 DIV was investigated. Results show that BDNF as well as fetal calf serum (FCS) influence the metabolism of neurons. Furthermore, serum, but not BDNF, is able to protect neurons from cell death. For the detection of apoptosis TUNEL-staining and DNA gel electrophoresis was performed. These methods supplied contrary information about the type of cell death in neurons raised without serum. The first technique indicates the occurrence of apoptosis whereas the second suggests necrosis. In addition, by the means of DNA gel electrophoresis it was exhibited that cortical cells from 8 days old chicken embryos are committed to undergo PCD already in vivo at time of preparation.

Experimental and clinical methods in the development of anti-Alzheimer drugs

Methodology used for the development of anti-Alzheimer's disease (AD) drugs raises specific problems which are rarely examined in the literature. While the general development scheme is similar to that required for most drugs, some specific aspects must be analyzed, highly dominated by the dual goal of pharmacology, i.e., to obtain both symptomatic and etiopathogenic drugs. During preclinical studies, aged or lesioned animals are mainly useful for symptomatic drugs, whereas transgenic models or neurodegeneration-induced techniques would probably lead to etiopathogenic drugs potentially slowing down the process of AD. The first administrations of a new compound to human beings raise the question of the activity measurement techniques. Psychometry remains the most informative procedure to detect and analyze the activity of the drugs on the different components of cognition. Electrophysiology and neuroimaging need some complementary studies before they can be proposed as surrogate criteria in phase III trials. At this stage of development, American and the recently published European guidelines are of great help while insisting on long-term (6 months) placebo controlled trials with the use of the triple efficacy criterion: an objective cognition scale, a global assessment, and the opinion of the caregiver. In the long term, pharmacoepidemiology and pharmacoeconomy will have to confirm the rationale of this recent progress in the methodology of anti-AD drug development.

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.