Current Alzheimer Research - Volume 2, Issue 3, 2005

Existing cholinesterase (ChE) inhibitor therapies for Alzheimer's disease (AD), while effective in improving cognitive, behavioral and functional impairments, do not alter disease progression. Novel drug design studies have focused on the classical ChE inhibitor, (-)-physostigmine, producing alterations in chemical composition and threedimensional structure, which may offer an improved therapeutic index. The phenylcarbamate derivative, (-)-phenserine, is a selective, non-competitive inhibitor of acetylcholinesterase (AChE). In vivo, (-)-phenserine produces rapid, potent, and long-lasting AChE inhibition. As a possible result of its preferential brain selectivity, (-)-phenserine is significantly less toxic than (-)-physostigmine. In studies using the Stone maze paradigm, (-)-phenserine has been shown to improve cognitive performance in both young learning-impaired and elderly rats. In addition to reducing inactivation of acetylcholine in the brain, (-)-phenserine appears to have a second mode of action. Reduced secretion of beta-amyloid (Aβ) has been observed in cell lines exposed to (-)-phenserine, occurring through translational regulation of beta-amyloid precursor protein (β-APP) mRNA via a non-cholinergic mechanism. These in vitro findings appear to translate in vivo into animal models and humans. In a small study of patients with AD, (-)-phenserine treatment tended to reduce β-APP and Aβ levels in plasma samples. Clinical studies also reveal that (-)-phenserine (5-10 mg b.i.d.) had a favorable safety and pharmacological profile, produced significant improvements in cognitive function and was well tolerated in patients with AD treated for 12 weeks. Further randomized, double-blind, placebo-controlled Phase III studies assessing the efficacy, safety/tolerability and potential disease-modifying effects of (-)-phenserine in patients with AD are currently ongoing.

Current mouse models of Alzheimer's disease show brain pathology that correlates to a degree with memory impairment, but underlying molecular mechanisms remained unknown. Here we report studies with three lines of transgenic mice: animals that doubly express mutated human amyloid precursor protein (APPswe) and human acetylcholinesterase (hAChE); and animals transgenic for only the APPswe or the hAChE. Among these genotypes, variations were observed in expression of mRNA for presenilin-1, which was highest in singly transgenic hAChE mice, and the stressinducible form of AChE, which was elevated when both transgenes were present. At the age of nine months, both double and single transgenic mice displayed working memory impairment in a radial arm water maze. However, as compared with mice expressing amyloid alone, the double transgenic animals exhibited more numerous plaques and greater amyloid burden in brain (both by histochemistry and by ELISA of amyloid protein). Moreover, the amyloid burden in double transgenics was tightly correlated with memory impairment as measured by total maze errors (r2 = 0.78, p = .002). This correlation was markedly stronger than observed in mice with amyloid alone. These new findings support the notion of cholinergic-amyloid interrelationships and highlight the double transgenic mice as a promising alternative for testing Alzheimer's therapies.

The cholinergic system impairment observed in Alzheimer's disease (AD) patients leads to the cognitive, global and behavioral dysfunction commonly associated with dementia. The only treatment for AD has been the use of inhibitors of acetylcholinesterase (AChE) (E.C. 3.1.1.7), which is one of the several proteins associated with amyloid plaque deposits. Recently, novel dual inhibitors of AChE have been developed that target both the active site of the enzyme as well as the peripheral anionic site (PAS). Such inhibitors prevent the aggregation of amyloid-β-peptide (Aβ) into Alzheimer's fibrils. The incorporation of AChE, as a "chaperone" into amyloid aggregates results in the modification of the biochemical properties of the enzyme, including: sensitivity to low pH, inhibition at high substrate concentration, and increases of the Aβ neurotoxocity. Congo Red dye stabilizes the Aβ monomer, is able to inhibit oligomerization, and inhibits the binding of AChE to Aβ. However no effect of Congo Red on the binding of AChE to the Ab preformed fibrils was observed. These studies suggest that different interactions between Aβ soluble-AChE and Aβ fibrils-AChE take place during the association between them. Docking studies were performed to evaluate the binding of Congo Red to Aβ in order to identify putative binding sites in the Ab monomer that might interact with AChE. The binding site involves a region between residues 12 and 16. Finally, recent studies are consistent with the idea that a attenuating β-catenin loss of function of Wnt signaling components may play a role in the progression of neurodegenerative disease, such as AD, providing a connection between AChE-Aβ neurotoxicity and the Wnt signal transduction pathway.

The cholinergic hypothesis of decline in dementia, whereby deficits in learning, memory and behavior are caused, at least in part, by decreased levels of acetylcholine (ACh) in the brain, first emerged more than 20 years ago. The role for acetylcholinesterase (AChE) and its inhibition in this scheme has long been accepted, but findings from preclinical experiments and clinical trials have placed butyrylcholinesterase (BuChE) alongside AChE as an important contributor to the occurrence, symptoms, progression and responses to treatment in dementia. A number of new lines of evidence suggest that both cholinesterase inhibitors (ChEs) may have broader functions in the CNS than previously thought, which relate to both 'classical' esterase activities of the enzymes as well as non-classical actions unrelated to their enzymatic function. Data suggest involvement of the ChEs in modulating glial activation, cerebral blood flow, the amyloid cascade, and tau phosphorylation. It has therefore been speculated that some actions of the ChEs could affect the underlying disease processes in Alzheimer's disease (AD), and that pharmacological manipulation with ChE inhibitors may affect longterm disease progression. Focusing on new findings relating to BuChE, we review recent evidence that has extended knowledge into the roles of ChEs in health, disease and aging.

What are the aims appropriate for a science of clinical pharmacology and clinical trials: to test drugs for efficacy and safety in the clinic, to establish the optimal effectiveness and safety of drugs in patient care or both? Current designs of clinical trials test drugs for efficacy and safety in clinical settings-they do not address the clinician's problems adequately. Clinical trials better address the effectiveness of drugs in patient care with analyses to determine drug effects for each individual in the trial. We use current standards and designs for clinical trails supplemented to control random error effects for the individuals in the trials. Test-retest standard error of measurement can control random error effects for individuals. This allows individual clinical courses to be plotted with known precision and certainty. For individuals in a clinical trial the clinical course of surrogate outcome variables can be associated with long-term health outcomes in followup to develop clinical decision rules. Clinical courses on surrogate outcome variables during patient care can be interpreted using these clinical decision rules. In this Age of the Internet, Computers and Handhelds, electronic records and interpretations of clinical examinations and tests can be a part of decision making for every patient. We conclude that practical methods are available for making clinical trials more informative for clinical practice. This modification replaces “unsystematic clinical judgments” with statistically characterized data and interpretations for individuals available as care is delivered in the doctor's office. An AD demonstration can be viewed at www.healthpragmatics.com.

Alzheimer's disease is characterized by the extracellular deposition of the amyloid β-peptide that derives from its precursor bAPP by sequential actions of β- and γ- secretases, respectively. Recent studies aimed at identifying these enzymes have been reported as it is thougth that their inhibition should hopefully lead to reduce Aβ load in the AD brains. β-secretase seems to be due to BACE1, a novel membrane-bound aspartyl protease. γ-secretase identification is still a matter of controversy. Invalidation of presenilin genes was reported to impair both γ-secretase-mediated Aβ production and Notch cleavage leading to NICD production. This observation together with another biochemical and pharmacological evidences led to suggest that presenilins could be the genuine long-searched γ-secretase that would be responsible for both APP and Notch cleavages. We have designed novel non peptidic potential inhibitors of g-secretase (referred to as JLK inhibitors) and examined their ability to prevent Aβ40 and Aβ42 secretions as well as NICD production. Three out of a series of these agents drastically lower the recoveries of both Aβ40 and Aβ42 produced by bAPP-expressing cell lines and concomitantly protect intracellular C99 and C83 recoveries. These inhibitors also prevent Aβ40/42 productions by C99-expressing cells. Interestingly, these inhibitors were totally unable to affect the DENotch cleavage leading to NICD generation. Here, we also further characterize the pharmacological properties and specificity of these JLK inhibitors.

Alzheimer disease (AD) and related tauopathies are all characterized histopathologically by neurofibrillary degeneration. The neurofibrillary changes, whether of paired helical filaments (PHF), twisted ribbons or straight filaments (SF) are made up of abnormally hyperphosphorylated tau. Unlike normal tau which promotes assembly and maintains structure of microtubules, the abnormal tau not only lacks these functions but also sequesters normal tau, MAP1 and MAP2, and causes disassembly of microtubules. This toxic behavior of the abnormal tau is solely due to its hyperphosphorylation because dephosphorylation restores it into a normal-like protein. The abnormal hyperphosphorylation also promotes the self-assembly of tau into PHF/SF. The state of phosphorylation of a phosphoprotein is the function of the activities of protein kinases and as well as of protein phosphatases that regulate the level of phosphorylation. A cause of the abnormal hyperphosphorylation in AD brain is a decrease in the activity of protein phosphatase (PP)-2A, a major regulator of the phosphorylation of tau. A decrease in PP-2A activity results in the abnormal hyperphosphorylation of tau not only by decreased dephosphorylation of tau but also by stimulating the activities of tau kinases like CaMKII, PKA and MAP kinases which are regulated by PP-2A. Thus, the abnormal hyperphosphorylation can be inhibited both by inhibition of the activity/s of a tau protein kinase and as well as by restoration of the activity/s of a tau protein phosphatase. The development of drugs that inhibit neurofibrillary degeneration is a very promising and feasible therapeutic approach to inhibit the progression of AD and related tauopathies.

Cholesterol-induced production of amyloid beta (Aβ) as a putative neurotoxin in Alzheimer's disease (AD), along with epidemiological evidence, suggests that statin drugs may provide benefit in treatment of the disorder. We tested the effect of once daily atorvastatin calcium (80 mg; two 40mg tablets) on cognitive and/or behavioral decline in patients with mild-to-moderate AD. The study was designed as a pilot intention-to-treat, proof-of-concept, double-blind, placebo-controlled, randomized (1:1) trial with a 1-year exposure to study medication employing last-observation-carriedforward (LOCF) ANCOVA as the primary statistical method of assessment. Alternate statistical methods were employed to further explore the effect of atorvastatin treatment on progression of deterioration. Of the 98 individuals with mild-to-moderate AD (Mini-Mental State Examination score of 12-28) providing Informed Consent, 71 were eligible for randomization, 67 were randomized and 63 completed the 3-month visit and were statistically evaluable. The primary outcome measures were change in the Alzheimer Disease Assessment Scale-Cognitive (ADAS-cog) performance and the Clinical Global Impression of Change (CGIC). Secondary outcome measures included the MMSE, Geriatric Depression Scale (GDS), the Neurospychiatric Inventory (NPI) and the ADCS Activities of Daily Living inventory (ADCS-ADL). Tertiary outcome measures included levels of total circulating cholesterol, LDL and VLDL, and circulating activity of the free radical scavenger enzymes superoxide dismutase (SOD) and gluthathione peroxidase (GpX). Atorvastatin reduced circulating cholesterol levels and produced a positive signal on each of the clinical outcome measures compared to placebo, but did not elicit a difference in circulating SOD or GpX activities. The observed beneficial clinical effect reached significance for the GDS (p = 0.040) and the ADAS-cog at 6 months (p = 0.003), was all but significant for the ADAS-cog (p = 0.055) at 12 months, and was of marginal significance for the CGIC (p = 0.073) and NPI (p = 0.071) at 12 months when employing the primary statistical approach (ANCOVA with LOCF). Application of repeated measures ANCOVA statistics revealed the difference was significant for the CGIC and marginally significant for the ADAS-cog, but not significant for the other clinical indices. This evaluation indicated significant time-by-treatment interactions (altered progression) for the ADAS-cog and MMSE, but not the CGIC. Application of random intercept regression analysis revealed a significant difference for the CGIC, ADAS-cog and MMSE. Regression analysis also indicated that atorvastatin produced change in the slope of deterioration on the MMSE. Accordingly, atorvastatin therapy may be an effective treatment and may slow the progression of AD among mild-to-moderately affected patients.

Inflammation is characteristic of a broad spectrum of neurodegenerative diseases. These include Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases, amyotrophic lateral sclerosis, all of the tauopathies, multiple sclerosis and many other less common conditions. Morphologically, the level of inflammation is determined by the concentration and degree of activation of microglial cells. Biochemically, it is judged by the presence of a spectrum of inflammatory mediators. Epidemiological evidence indicates that anti-inflammatory agents such as non-steroidal anti-inflammatory drugs (NSAIDs) have a sparing effect on AD and PD indicating that inflammation exacerbates the pathology in these diseases. NSAIDs are protective in transgenic animal models of AD, providing further evidence of the negative consequences of inflammation. Here we describe an in vitro model, which was used to study the protective effects of NSAIDs in AD. This model is based on neuronal cell killing by stimulated microglia or microglia-like cells. In this model NSAIDs show protective effects at a therapeutically relevant level, which is in the low micromolar range. There are reports suggesting that NSAIDs act independently of cyclooxygenase (COX) inhibition, but only at higher doses. Classical NSAIDs are still the most logical choice for agents that will slow the progression or delay the onset of AD and other neurodegenerative diseases despite failures of naproxen, celecoxib and rofecoxib in AD clinical trials. Several other classes of anti-inflammatory drugs have been identified as potentially beneficial in this and similar assay systems. Therefore combination therapy with other anti-inflammatory agents that work through different mechanisms of action might prove to be a superior therapeutic strategy.

The statement, “neurodegenerative diseases are incurable because neurons do not regenerate during adulthood,” has been challenged, and we have now found much evidence that the matured brain is capable of regenerating neurons. In our previous study, human neural stem cells (HNSCs) transplanted into aged rat brains differentiated into neural cells and significantly improved the cognitive functions of the animals, indicating that HNSCs may be a promising candidate for neuro-replacement therapy. However, because of ethical and practical issues associated with HNSCs, development of autologous stem cell strategies may be desired. We established new technologies to differentiate adult human mesenchymal stem cells into neural cells by modifying cell fate decisions. We also found a pyrimidine derivative that increases endogenous stem cell proliferation and neurogenesis after peripheral administrations of this compound. Although these results may promise a bright future for clinical applications of stem cell strategies in Alzheimer's disease (AD) therapy, we must acknowledge the complexity of AD. For example, abnormal metabolism of the amyloid-β precursor protein (APP) may affect stem cell biology, while the prevalence of amyloid-β peptide (Aβ) toxicity theory in AD pathology tends to limit our focus on the physiological functions of APP. We found that excess APP in the environment causes glial differentiation of stem cells. Even though the glial activation may be useful to eliminate Aβ deposits, neuronal differentiation of stem cells is needed for replacement of degenerating neurons in the AD brain. Thus, further investigation of the influence of AD pathology on stem cell biology is required.

Glucagon - like peptide - 1 (7-36) - amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet β-cell proliferation, glucose-dependent insulin secretion, and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, are coupled to the cyclic AMP second messenger pathway, and are expressed throughout the brain of rodents and humans. We previously reported that GLP-1 and exendin-4, a naturally occurring, long-acting analogue of GLP-1 that binds the GLP-1 receptor (GLP-1R), possess neurotrophic properties. GLP-1R agonists protect neurons against amyloid-β peptide (Aβ) and glutamate-induced apoptosis in cell culture studies and attenuate cholinergic neuron atrophy in the basal forebrain of the rat following an excitotoxic lesion. The biochemical cascades activated by neural GLP-1R stimulation are discussed in comparison to those activated by pancreatic receptors, and, additionally, are compared to signaling pathways associated with the classical neurotrophins. GLP-1R stimulation promotes pathways that favour cell survival over apoptosis. GLP-1 readily enters brain, and its diverse physiological actions, which include insulinotropic, cardiovascular as well as neurotrophic ones, may prove beneficial in a variety of diseases prevalent in aging, including Alzheimer's disease (AD). Its ability to lower brain levels of Aβ in mice would appear to be particularly pertinent in this regard. Furthermore, the ready availability of clinical material and the clinical history of its long term use in subjects with type 2 diabetes would support testing the value of GLP-1R agonists in AD trials.