Cholinesterases colocalize with sites of neurofibrillary degeneration in aged and Alzheimer's brains

Conjugates of amiridine and thiouracil derivatives as effective inhibitors of butyrylcholinesterase with the potential to block β-amyloid aggregation

New amiridine-thiouracil conjugates with different substituents in the pyrimidine fragment (R = CH3 , CF2 Н, CF3 , (CF2 )2 H) and different spacer lengths (n = 1-3) were synthesized. The conjugates rather weakly inhibit acetylcholinesterase (AChE) and exhibit high inhibitory activity (IC50 up to 0.752 ± 0.021 µM) and selectivity to butyrylcholinesterase (BChE), which increases with spacer elongation; the lead compounds are 11c, 12c, and 13c. The conjugates are mixed-type reversible inhibitors of both cholinesterases and practically do not inhibit the structurally related off-target enzyme carboxylesterase. The results of molecular docking to AChE and BChE are consistent with the experiment on enzyme inhibition and explain the structure-activity relationships, including the rather low anti-AChE activity and the high anti-BChE activity of long-chain conjugates. The lead compounds displace propidium from the AChE peripheral anion site (PAS) at the level of the reference compound donepezil, which agrees with the mixed-type mechanism of AChE inhibition and the main mode of binding of conjugates in the active site of AChE due to the interaction of the pyrimidine moiety with the PAS. This indicates the ability of the studied conjugates to block AChE-induced aggregation of β-amyloid, thereby exerting a disease-modifying effect. According to computer calculations, all synthesized conjugates have an ADME profile acceptable for drugs.

Conjugates of Tacrine and Salicylic Acid Derivatives as New Promising Multitarget Agents for Alzheimer's Disease

A series of previously synthesized conjugates of tacrine and salicylamide was extended by varying the structure of the salicylamide fragment and using salicylic aldehyde to synthesize salicylimine derivatives. The hybrids exhibited broad-spectrum biological activity. All new conjugates were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. The structure of the salicylamide moiety exerted little effect on anticholinesterase activity, but AChE inhibition increased with spacer elongation. The most active conjugates were salicylimine derivatives: IC₅₀ values of the lead compound 10c were 0.0826 µM (AChE) and 0.0156 µM (BChE), with weak inhibition of the off-target carboxylesterase. The hybrids were mixed-type reversible inhibitors of both cholinesterases and displayed dual binding to the catalytic and peripheral anionic sites of AChE in molecular docking, which, along with experimental results on propidium iodide displacement, suggested their potential to block AChE-induced β-amyloid aggregation. All conjugates inhibited Aβ₄₂ self-aggregation in the thioflavin test, and inhibition increased with spacer elongation. Salicylimine 10c and salicylamide 5c with (CH₂)₈ spacers were the lead compounds for inhibiting Aβ₄₂ self-aggregation, which was corroborated by molecular docking to Aβ₄₂. ABTS^•+-scavenging activity was highest for salicylamides 5a-c, intermediate for salicylimines 10a-c, low for F-containing salicylamides 7, and non-existent for methoxybenzoylamides 6 and difluoromethoxybenzoylamides 8. In the FRAP antioxidant (AO) assay, the test compounds displayed little or no activity. Quantum chemical analysis and molecular dynamics (MD) simulations with QM/MM potentials explained the AO structure-activity relationships. All conjugates were effective chelators of Cu²⁺, Fe²⁺, and Zn²⁺, with molar compound/metal (Cu²⁺) ratios of 2:1 (5b) and ~1:1 (10b). Conjugates exerted comparable or lower cytotoxicity than tacrine on mouse hepatocytes and had favorable predicted intestinal absorption and blood-brain barrier permeability. The overall results indicate that the synthesized conjugates are promising new multifunctional agents for the potential treatment of AD.

Bis-Amiridines as Acetylcholinesterase and Butyrylcholinesterase Inhibitors: N-Functionalization Determines the Multitarget Anti-Alzheimer’s Activity Profile

Using two ways of functionalizing amiridine—acylation with chloroacetic acid chloride and reaction with thiophosgene—we have synthesized new homobivalent bis-amiridines joined by two different spacers—bis-N-acyl-alkylene (3) and bis-N-thiourea-alkylene (5) —as potential multifunctional agents for the treatment of Alzheimer’s disease (AD). All compounds exhibited high inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity for BChE. These new agents displayed negligible carboxylesterase inhibition, suggesting a probable lack of untoward drug–drug interactions arising from hydrolytic biotransformation. Compounds 3 with bis-N-acyl-alkylene spacers were more potent inhibitors of both cholinesterases compared to compounds 5 and the parent amiridine. The lead compounds 3a–c exhibited an IC₅₀(AChE) = 2.9–1.4 µM, IC₅₀(BChE) = 0.13–0.067 µM, and 14–18% propidium displacement at 20 μM. Kinetic studies of compounds 3a and 5d indicated mixed-type reversible inhibition. Molecular docking revealed favorable poses in both catalytic and peripheral AChE sites. Propidium displacement from the peripheral site by the hybrids suggests their potential to hinder AChE-assisted Aβ₄₂ aggregation. Conjugates 3 had no effect on Aβ₄₂ self-aggregation, whereas compounds 5c–e (m = 4, 5, 6) showed mild (13–17%) inhibition. The greatest difference between conjugates 3 and 5 was their antioxidant activity. Bis-amiridines 3 with N-acylalkylene spacers were nearly inactive in ABTS and FRAP tests, whereas compounds 5 with thiourea in the spacers demonstrated high antioxidant activity, especially in the ABTS test (TEAC = 1.2–2.1), in agreement with their significantly lower HOMO-LUMO gap values. Calculated ADMET parameters for all conjugates predicted favorable blood–brain barrier permeability and intestinal absorption, as well as a low propensity for cardiac toxicity. Thus, it was possible to obtain amiridine derivatives whose potencies against AChE and BChE equaled (5) or exceeded (3) that of the parent compound, amiridine. Overall, based on their expanded and balanced pharmacological profiles, conjugates 5c–e appear promising for future optimization and development as multitarget anti-AD agents.

Conjugation of Aminoadamantane and γ-Carboline Pharmacophores Gives Rise to Unexpected Properties of Multifunctional Ligands

A new series of conjugates of aminoadamantane and γ-carboline, which are basic scaffolds of the known neuroactive agents, memantine and dimebon (Latrepirdine) was synthesized and characterized. Conjugates act simultaneously on several biological structures and processes involved in the pathogenesis of Alzheimer’s disease and some other neurodegenerative disorders. In particular, these compounds inhibit enzymes of the cholinesterase family, exhibiting higher inhibitory activity against butyrylcholinesterase (BChE), but having almost no effect on the activity of carboxylesterase (anti-target). The compounds serve as NMDA-subtype glutamate receptor ligands, show mitoprotective properties by preventing opening of the mitochondrial permeability transition (MPT) pore, and act as microtubule stabilizers, stimulating the polymerization of tubulin and microtubule-associated proteins. Structure–activity relationships were studied, with particular attention to the effect of the spacer on biological activity. The synthesized conjugates showed new properties compared to their prototypes (memantine and dimebon), including the ability to bind to the ifenprodil-binding site of the NMDA receptor and to occupy the peripheral anionic site of acetylcholinesterase (AChE), which indicates that these compounds can act as blockers of AChE-induced β-amyloid aggregation. These new attributes of the conjugates represent improvements to the pharmacological profiles of the separate components by conferring the potential to act as neuroprotectants and cognition enhancers with a multifunctional mode of action.

Expression profiling of precuneus layer III cathepsin D-immunopositive pyramidal neurons in mild cognitive impairment and Alzheimer's disease: Evidence for neuronal signaling vulnerability

The precuneus (PreC; Brodmann area 7), a key hub within the default mode network (DMN) displays amyloid and tau-containing neurofibrillary tangle (NFT) pathology during the onset of Alzheimer's disease (AD). PreC layer III projection neurons contain lysosomal hydrolase cathepsin D (CatD), a marker of neurons vulnerable to NFT pathology. Here we applied single population laser capture microdissection coupled with custom-designed microarray profiling to determine the genetic signature of PreC CatD-positive-layer III neurons accrued from postmortem tissue obtained from the Rush Religious Orders Study (RROS) cases with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI) and AD. Expression profiling revealed significant differential expression of key transcripts in MCI and AD compared to NCI that underlie signaling defects, including dysregulation of genes within the endosomal-lysosomal and autophagy pathways, cytoskeletal elements, AD-related genes, ionotropic and metabotropic glutamate receptors, cholinergic enzymes and receptors, markers of monoamine neurotransmission as well as steroid-related transcripts. Pervasive defects in both MCI and AD were found in select transcripts within these key gene ontology categories, underscoring the vulnerability of these corticocortical projection neurons during the onset and progression of dementia. Select PreC dysregulated genes detected via custom-designed microarray analysis were validated using qPCR. In summary, expression profiling of PreC CatD -positive layer III neurons revealed significant dysregulation of a mosaic of genes in MCI and AD that were not previously appreciated in terms of their indication of systems-wide signaling defects in a key hub of the DMN.

New Hybrids of 4-Amino-2,3-polymethylene-quinoline and p-Tolylsulfonamide as Dual Inhibitors of Acetyl- and Butyrylcholinesterase and Potential Multifunctional Agents for Alzheimer's Disease Treatment

New hybrid compounds of 4-amino-2,3-polymethylene-quinoline containing different sizes of the aliphatic ring and linked to p-tolylsulfonamide with alkylene spacers of increasing length were synthesized as potential drugs for treatment of Alzheimer’s disease (AD). All compounds were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. The lead compound 4-methyl-N-(5-(1,2,3,4-tetrahydro-acridin-9-ylamino)-pentyl)-benzenesulfonamide (7h) exhibited an IC₅₀ (AChE) = 0.131 ± 0.01 µM (five times more potent than tacrine), IC₅₀(BChE) = 0.0680 ± 0.0014 µM, and 17.5 ± 1.5% propidium displacement at 20 µM. The compounds possessed low activity against carboxylesterase, indicating a likely absence of unwanted drug-drug interactions in clinical use. Kinetics studies were consistent with mixed-type reversible inhibition of both cholinesterases. Molecular docking demonstrated dual binding sites of the conjugates in AChE and clarified the differences in the structure-activity relationships for AChE and BChE inhibition. The conjugates could bind to the AChE peripheral anionic site and displace propidium, indicating their potential to block AChE-induced β-amyloid aggregation, thereby exerting a disease-modifying effect. All compounds demonstrated low antioxidant activity. Computational ADMET profiles predicted that all compounds would have good intestinal absorption, medium blood-brain barrier permeability, and medium cardiac toxicity risk. Overall, the results indicate that the novel conjugates show promise for further development and optimization as multitarget anti-AD agents.

Conjugates of methylene blue with γ-carboline derivatives as new multifunctional agents for the treatment of neurodegenerative diseases

We studied the inhibitory activity of methylene blue (MB) γ-carbolines (gC) conjugates (MB-gCs) against human erythrocyte acetylcholinesterase (AChE), equine serum butyrylcholinesterase (BChE), and a structurally related enzyme, porcine liver carboxylesterase (CaE). In addition, we determined the ability of MB-gCs to bind to the peripheral anionic site (PAS) of Electrophorus electricus AChE (EeAChE) and competitively displace propidium iodide from this site. Moreover, we examined the ability of MB-gCs to scavenge free radicals as well as their influence on mitochondrial potential and iron-induced lipid peroxidation. We found that MB-gCs effectively inhibited AChE and BChE with IC₅₀ values in the range 1.73–10.5 μM and exhibited low potencies against CaE (9.8–26% inhibition at 20 μM). Kinetic studies showed that MB-gCs were mixed-type reversible inhibitors of both cholinesterases. Molecular docking results showed that the MB-gCs could bind both to the catalytic active site and to the PAS of human AChE and BChE. Accordingly, MB-gCs effectively displaced propidium from the peripheral anionic site of EeAChE. In addition, MB-gCs were extremely active in both radical scavenging tests. Quantum mechanical DFT calculations suggested that free radical scavenging was likely mediated by the sulfur atom in the MB fragment. Furthermore, the MB-gCs, in like manner to MB, can restore mitochondrial membrane potential after depolarization with rotenone. Moreover, MB-gCs possess strong antioxidant properties, preventing iron-induced lipid peroxidation in mitochondria. Overall, the results indicate that MB-gCs are promising candidates for further optimization as multitarget therapeutic agents for neurodegenerative diseases.

Immunohistochemical analysis of hippocampal butyrylcholinesterase: Implications for regional vulnerability in Alzheimer's disease

Studies of acetylcholine degrading enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in Alzheimer's disease (AD) have suggested their potential role in the development of fibrillar amyloid-β (Aβ) plaques (amyloid plaques). A recent genome-wide association study analysis identified a novel association between genetic variations in the BCHE locus and amyloid burden. We studied BChE immunoreactivity in hippocampal tissue sections from AD and control cases, and examined its relationship with amyloid plaques, neurofibrillary tangles (NFT), dystrophic neurites (DN) and neuropil threads (NT). Compared to controls, AD cases had greater BChE immunoreactivity in hippocampal neurons and neuropils in CA2/3, but not in the CA1, CA4 and dentate gyrus. The majority of amyloid plaques (> 80%, using a pan-amyloid marker X-34) contained discrete neuritic clusters which were dual-labeled with antibodies against BChE and phosphorylated tau (clone AT8). There was no association between overall regional BChE immunoreaction intensity and amyloid plaque burden. In contrast to previous reports, BChE was localized in only a fraction (~10%) of classic NFT (positive for X-34). A similar proportion of BChE-immunoreactive pyramidal cells were AT8 immunoreactive. Greater NFT and DN loads were associated with greater BChE immunoreaction intensity in CA2/3, but not in CA1, CA4 and dentate gyrus. Our results demonstrate that in AD hippocampus, BChE accumulates in neurons and plaque-associated neuritic clusters, but only in a small proportion of NFT. The association between greater neurofibrillary pathology burden and markedly increased BChE immunoreactivity, observed selectively in CA2/3 region, could reflect a novel compensatory mechanism. Since CA2/3 is generally considered more resistant to AD pathology, BChE upregulation could impact the cholinergic modulation of glutamate neurotransmission to prevent/reduce neuronal excitotoxicity in AD hippocampus.

Neuronal AChE splice variants and their non-hydrolytic functions: redefining a target of AChE inhibitors?

AChE enzymatic inhibition is a core focus of pharmacological intervention in Alzheimer's disease (AD). Yet, AChE has also been ascribed non-hydrolytic functions, which seem related to its appearance in various isoforms. Neuronal AChE presents as a tailed form (AChE-T) predominantly found on the neuronal synapse, and a facultatively expressed readthough form (AChE-R), which exerts short to medium-term protective effects. Notably, this latter form is also found in the periphery. While these non-hydrolytic functions of AChE are most controversially discussed, there is evidence for them being additional targets of AChE inhibitors. This review aims to provide clarification as to the role of these AChE splice variants and their interplay with other cholinergic parameters and their being targets of AChE inhibition: AChE-R is particularly involved in the mediation of (anti-)apoptotic events in cholinergic cells, involving adaptation of various cholinergic parameters and a time-dependent link to the expression of neuroprotective factors. The AChE-T C-terminus is central to AChE activity regulation, while isolated AChE-T C-terminal fragments mediate toxic effects via the α7 nicotinic acetylcholine receptor. There is direct evidence for roles of AChE-T and AChE-R in neurodegeneration and neuroprotection, with these roles involving AChE as a key modulator of the cholinergic system: in vivo data further encourages the use of AChE inhibitors in the treatment of neurodegenerative conditions such as AD since effects on both enzymatic activity and the enzyme's non-hydrolytic functions can be postulated. It also suggests that novel AChE inhibitors should enhance protective AChE-R, while avoiding the concomitant up-regulation of AChE-T.

Biochemical differentiation of cholinesterases from normal and Alzheimer's disease cortex

In Alzheimer's disease, histochemically visualized cholinesterases with altered pH optimum for activity and inhibitable by indoleamines and the protease inhibitor bacitracin emerge in association with plaques and tangles. It has been suggested that these cholinesterases may participate in the pathologic process. However, it is not known whether the properties of cholinesterases observed in Alzheimer's disease are due to requirements of histochemical procedures or actual biochemical properties of these enzymes. Using biochemical assays of acetylcholinesterase and butyrylcholinesterase activities, we demonstrate here that serotonin and bacitracin result in a significantly greater and dose-dependent inhibition of cholinesterases in Alzheimer's disease cortex when compared with age-matched controls. In contrast, variations in pH did not distinguish cholinesterases in Alzheimer's disease and control cortex. We also confirmed significant reduction of acetylcholinesterase activity in Alzheimer's disease cortex and increased butyrylcholinesterase activity that only approached significance. We conclude that inhibition by indoleamines and bacitracin is a biochemical characteristic of a proportion of cholinesterases in Alzheimer's disease that most likely represents the pool associated with plaques and tangles. Most of the available cholinesterase inhibitors are relatively incapable of inhibiting cholinesterases associated with plaques and tangles. The findings of the present investigation open the way for attempts to isolate cholinesterases associated with plaques and tangles and design or discovery of inhibitors specifically targeted to cholinesterases in these lesions.

Association between acetylcholinesterase and beta-amyloid peptide in Alzheimer's cerebrospinal fluid

The altered expression of acetylcholinesterase (AChE) in the brains of patients with Alzheimer's disease (AD) has raised much interest of late. Despite an overall decrease in the AD brain, the activity of AChE increases around beta-amyloid plaques and indeed, the beta-amyloid peptide (Abeta) can influence AChE levels. Such evidence stimulated our interest in the possibility that the levels of AChE and amyloid might vary together in AD. We previously found that the different AChE forms present in both the brain and in the cerebrospinal fluid (CSF) of AD patients varied in conjunction with abnormal glycosylation. Thus, the alterations in glycosylation are correlated with the accumulation of a minor subspecies of AChE monomers. We also recently analysed whether long-term exposure to the cholinesterase inhibitor (ChE-I) donepezil influences the AChE species found in AD CSF. The marked increase in CSF-AChE activity in AD patients following long-term treatment with donepezil was not paralleled by a rise in this subset of light variants. Hence, the correlation with the levels of CSF-Abeta is unique to these AChE species in patients receiving such treatment. The aim of this report is to review the links between AChE and beta-amyloid, and to discuss the significance of the responses of the distinct AChE species to ChE-I during the treatment of AD.

Presenilin 1 interacts with acetylcholinesterase and alters its enzymatic activity and glycosylation

Presenilin 1 (PS1) plays a critical role in the gamma-secretase processing of the amyloid precursor protein to generate the beta-amyloid peptide, which accumulates in plaques in the pathogenesis of Alzheimer's disease (AD). Mutations in PS1 cause early onset AD, and proteins that interact with PS1 are of major functional importance. We report here the coimmunoprecipitation of PS1 and acetylcholinesterase (AChE), an enzyme associated with amyloid plaques. Binding occurs through PS1 N-terminal fragment independent of the peripheral binding site of AChE. Subcellular colocalization of PS1 and AChE in cultured cells and coexpression patterns of PS1 and AChE in brain sections from controls and subjects with sporadic or familial AD indicated that PS1 and AChE are located in the same intracellular compartments, including the perinuclear compartments. A PS1-A246E pathogenic mutation expressed in transgenic mice leads to decreased AChE activity and alteration of AChE glycosylation and the peripheral binding site, which may reflect a shift in protein conformation and disturbed AChE maturation. In both the transgenic mice and humans, mutant PS1 impairs coimmunoprecipitation with AChE. The results indicate that PS1 can interact with AChE and influence its expression, supporting the notion of cholinergic-amyloid interrelationships.

Homozygosity for the K variant of BCHE gene increases the risk for development of neurofibrillary pathology but not amyloid deposits at young ages

The presence of the K variant of the butyrylcholinesterase gene (BCHE-K) has been associated with the severity of Alzheimer's disease (AD)-related neurofibrillary tangles (NFT) and amyloid beta-protein (Abeta). To examine the impact of BCHE-K on the development of initial NFT- and Abeta pathologies in young individuals below the age of 45 years a total of 124 cases (110 cases with NFT-only pathology, 14 cases with Abeta-only pathology) and 104 matched controls were genotyped for BCHE-K. Homozygosity for BCHE-K was highly overrepresented among NFT-only group (8.2%) compared with controls (1%, P = 0.02) or the Abeta-only group (0%). The prevalence of the K allele, however, was comparable among groups. These findings suggest that homozygosity, but not heterozygosity, for BCHE-K is a potential risk factor for the development of NFT pathology in young individuals implicating BCHE-K in the pathogenesis of early AD.

Butyrylcholinesterase, ApoE and Alzheimer's disease in a population from the Canary Islands (Spain)

AIM

Cholinergic dysfunction is a major neurochemical feature in Alzheimer's disease (AD), accountable for many cognitive dysfunctions and some psychiatric symptoms. Butyrylcholinesterase (BChE) is one of the cholinesterases with increased activity in the brain of Alzheimer's patients. Several mutations code for different BChE, such as the K variant, which is the most common and is capable of reducing BChE activity by 30%. We studied the relationship between this K variant and Alzheimer's disease in our population from the Canary Islands (Spain).

PATIENTS AND METHODS

We used DNA PCR-RFLP techniques to compare 282 patients who had been diagnosed with probable Alzheimer's disease--according to NINCS-ADRDA criteria--with 312 control subjects confirmed to be free of cognitive impairment as assessed by using the CAMDEX cognitive subscale CAMCOG.

RESULTS

In our population the K variant of BChE is linked to the age of diagnosis of Alzheimer's disease, since AD individuals with this allele presented the disease at a later stage. No other susceptibility relations are exposed in this study. In addition, the BChE allelic frequencies in our population are higher than those previously reported.

Kinetic analysis of the inhibition of human butyrylcholinesterase with cymserine

Accompanying the gradual rise in the average age of the population of most industrialized countries is a regrettable progressive rise in the number of individuals afflicted with age-related neurodegenerative disorders, epitomized by Alzheimer's disease (AD) but, additionally, including Parkinson's disease (PD) and stroke. The primary therapeutic strategy, to date, involves the use of cholinesterases inhibitors (ChEIs) to amplify residual cholinergic activity. The enzyme, acetylcholinesterase (AChE), along with other elements of the cholinergic system is depleted in the AD brain. In contrast, however, its sister enzyme, butyrylcholinesterase (BuChE), that likewise cleaves acetylcholine (ACh), is elevated and both AChE and BuChE co-localize in high amounts with the classical pathological hallmarks of AD. The mismatch between increased brain BuChE and depleted levels of both ACh and AChE, particularly late in the disease, has supported the design and development of new ChEIs with a preference for BuChE; exemplified by the novel agent, cymserine, whose binding kinetics are characterized for the first time. Specifically, as assessed by the Ellman method, cymserine demonstrated potent concentration-dependent binding with human BuChE. The IC50 was determined as 63 to 100 nM at the substrate concentration range of 25 to 800 microM BuSCh. In addition, the following new binding constants were investigated for human BuChE inhibition by cymserine: T(FPnubeta), K(nubeta), K(Bs), K(MIBA), M(IC50), D(Sc), R(f), (O)K(m), OIC100, K(sl), theta(max) and R(i). These new kinetic constants may open new avenues for the kinetic study of the inhibition of a broad array of other enzymes by a wide variety of inhibitors. In synopsis, cymserine proved to be a potent inhibitor of human BuChE in comparison to its structural analogue, phenserine.

Donepezil: a clinical review of current and emerging indications

This article reviews the piperidine derivative, donepezil hydrochloride (E2020, Aricept), a reversible central acetylcholinesterase inhibitor currently approved for treatment of mild-to-moderate Alzheimer's disease. Donepezil is well absorbed orally, unaffected by food or by time of administration; it reaches therapeutic levels in doses of 5-10 mg/day and peak plasma concentrations are obtained 3-4 h after oral administration. A single bedtime dose is recommended due to the long elimination half-life of the drug (70 h). Donepezil does not cause liver toxicity or significant drug interactions and is relatively well-tolerated. Initial side effects include nausea, vomiting, diarrhoea, insomnia, muscle cramps, fatigue, anorexia and syncope. Caution is advised in patients with bradycardia. Long-term use of donepezil in AD has been found to delay nursing-home placement and to result in caregiver respite. Donepezil also slows deterioration of cognition and global function in patients with moderate-to-severe AD, with improvement of abnormal behaviours. In addition to AD, donepezil demonstrates significant improvement in cognition, global function and activities of daily living in comparison with placebo-treated patients with vascular dementia and has potential therapeutic benefit for other neurological conditions.

Differential distribution of butyrylcholinesterase and acetylcholinesterase in the human thalamus

It has been hypothesized that acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are coregulators of the duration of action of acetylcholine in cholinergic neurotransmission, suggesting that BuChE may also have an important role in the brain. To compare the expression of cholinesterases in the human thalamus, the distributions of BuChE and AChE activity were studied by using a modified Karnovsky-Roots method. BuChE activity was present mainly in neurons, whereas AChE activity was present in both neurons and axons. There was intense staining for BuChE or AChE throughout the thalamus, with some nuclei primarily expressing one or the other cholinesterase. BuChE staining was most intense and widespread in neurons in the anteroventral, mediodorsal, ventral, lateral, and pulvinar thalamic nuclei. AChE was predominantly expressed in neurons of the anterodorsal, midline, ventral, intralaminar, and reticular nuclei. Many nuclei contained both cholinesterases. Considering the overall patterns of labeling in the thalamus for the two cholinesterases, there were both complementary and overlapping relationships of BuChE and AChE activity. Neuronal staining in the subthalamic nucleus and hypothalamus was predominantly positive for AChE activity. The distinct distribution of BuChE activity in neurons in the human thalamus is consistent with an important role for this enzyme in neurotransmission in the human nervous system. Furthermore, BuChE activity, like AChE activity, is found in certain thalamic nuclei related to cognitive and behavioral functions. Involvement of thalamic nuclei in diseases of the nervous system such as Alzheimer's disease and schizophrenia suggests that BuChE could be a potential target for therapeutic intervention in these disorders.

CSF cholinesterase activity in demented and non-demented subjects

Samples of cerebrospinal fluid (CSF) were examined, looking mainly at total cholinesterase (ChE) and acetyl-cholinesterase (AChE) levels from 139 living subjects. At the completion of the study, 35 of the 139 patients had died and pathological confirmation of the presence of dementia had been obtained. These results, together with results from other laboratories, provide evidence that a low CSF ChE level presenting in demented patients may indicate a depletion of the brain AChE system, and this may confirm a clinical diagnosis of AD as well as other types of dementia which are associated with an alteration of the brain AChE system. The overlap in the levels of CSF biochemical markers between demented and non-demented subjects which has led to many conflicting reports has always disappointed investigators. It is suggested that some 'control' subjects with CSF ChE activity indistinguishable from that in AD patients may have an abnormal ageing process in their brains (brain at risk), although the symptoms of dementia have not yet been detected. Recognition of a pre-clinical or incubation period is very beneficial for explaining discrepancies in biochemistry and pathology in the literature, and must be considered for both the treatment and the prevention of dementia. The long used treatment, which was designed to inhibit AChE, should no longer be used: treatment must be designed to enhance the activity of the neuronal AChE system, or slow its degeneration.

Association of cholinesterases with amyloid in extracellular neurofibrillary tangles

Double-labeling techniques conclusively demonstrated that extracellular neurofibrillary tangles immunoreactive for beta protein were also positive for cholinesterases. Ultrastructurally, cholinesterases decorated bundles of amyloid-like filaments, which appeared intermingled with straight filaments and cellular processes. A lighter labeling of esterases was also seen over most straight filaments. These observations extend the consistent association of cholinesterases with fibrillary beta-amyloid protein to a new location in neurofibrillary tangles.

Alzheimer's disease-type neurofibrillary degeneration in verrucose dysplasias of the cerebral cortex

Verrucose dysplasias, found at autopsy in the cerebral cortex of three elderly individuals (two without neurological disorders and one with motor neuron disease), are shown to present neurofibrillary degeneration of Alzheimer's disease type. This neurofibrillary degeneration immunoreacted with antibodies against abnormally phosphorylated tau (5E2 and AT8), disclosed acetyl- and butyrylcholinesterase activity, and was consistently stained with thioflavin-S. Cortical dysplasias, found either as isolated verrucose nodules or comprising multiple nodules, contained cell-sparse areas around which a peak of neurofibrillary changes was seen. Cell-sparse areas were sometimes bridged by stripes of neurons and fibers arranged in a radial fashion, and many of these neurons showed neurofibrillary degeneration. Cytoskeletal abnormalities were conspicuous in layers II and III at the external borders of the dysplasias, as well as in neurons located in layers V and VI, and in the white matter beneath layer VI in central zones of each lesion. The morphology of cells undergoing neurofibrillary changes (from early non-fibrillar stages to late extracellular ones) suggests that neurons disturbed in their migration toward the site to which they had been committed may become vulnerable to cytoskeletal changes. Micro-environmental disturbances related to hypoxia-ischemia in the affected cortex are proposed as likely contributing factors for the long-term production of this neurofibrillary degeneration.

Inhibition of acetylcholinesterase modulates the autoregulation of cerebral blood flow and attenuates ischemic brain metabolism in hypertensive rats

We designed the present study to examine whether or not the inhibition of acetylcholinesterase modulates cerebral microcirculation in hypotension and improves brain metabolism in ischemia induced by bilateral carotid artery occlusion in hypertensive rats. Blood flow to the parietal cortex was determined by the H2 clearance method. Lactate, pyruvate, and ATP were estimated by enzymatic methods. Acetylcholinesterase inhibitor (AChEI, ENA-713), at 0.05, 0.1, or 0.5 mg/kg, was intravenously injected 10 min before either hemorrhagic hypotension or cerebral ischemia. The levels of acetylcholine in the control were 29.3 +/- 8.1 (mean +/- SD) and 39.5 +/- 8.1 pmol/mg in the cortex and hippocampus, respectively, and they were significantly decreased by 15-19% after 60 min of ischemia in the vehicle-treated rats. AChEI preserved the levels to 93-98% of the control (p < 0.05 versus vehicle). The lower limit of autoregulation was 74 +/- 9% of the resting values. The administration of AChEI helped preserve blood flow and lowered the limit to 64 +/- 6% (p < 0.05 versus control). After 60 min of ischemia, lactate increased 6.5-fold and ATP decreased to 64% of the control value. The administration of AChEI dose-dependently reduced the lactate level 1.9- to 3.9-fold and well preserved the ATP level to 94-97% of the control. The inhibition of acetylcholinesterase activity may preserve cerebral autoregulation during hypotension and protect cerebral metabolism against ischemic insult.

The inflammatory response system of brain: implications for therapy of Alzheimer and other neurodegenerative diseases

Cultured brain cells are capable of generating many molecules associated with inflammatory and immune functions. They constitute the endogenous immune response system of brain. They include complement proteins and their regulators, inflammatory cytokines, acute phase reactants and many proteases and protease inhibitors. Most of the proteins are made by microglia and astrocytes, but even neurons are producers. Many appear in association with Alzheimer disease lesions, indicating a state of chronic inflammation in Alzheimer disease brain. Such a state can apparently exist without stimulation by peripheral inflammatory mediators or the peripheral immune system. A strong inflammatory response may be autotoxic to neurons, exacerbating the fundamental pathology in Alzheimer disease and perhaps other neurological disorders. Autotoxic processes may contribute to cellular death in chronic inflammatory diseases affecting other parts of the body, suggesting the general therapeutic value of anti-inflammatory agents. With respect to Alzheimer disease, multiple epidemiological studies indicate that patients taking anti-inflammatory drugs or suffering from conditions in which such drugs are routinely used, have a decreased risk of developing Alzheimer disease. In one very preliminary clinical trial, the anti-inflammatory drug indomethacin arrested progress of the disease. New agents directed against the inflammatory processes revealed in studies of Alzheimer disease lesions may have broad therapeutic applications.