Butyrylcholinesterase-Mediated enhancement of the enzymatic activity of trypsin

Solvents and detergents compatible with enzyme kinetic studies of cholinesterases

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are enzymes that serve a wide range of physiological functions including the hydrolysis of the neurotransmitter acetylcholine and several other xenobiotics. The development of inhibitors for these enzymes has been the focus for the treatment of several conditions, such as Alzheimer's disease. Novel chemical entities are evaluated as potential inhibitors of AChE and BChE using enzyme kinetics. A common issue encountered in these studies is low aqueous solubility of the possible inhibitor. Additives such as cosolvents or detergents can be included in these studies improve the aqueous solubility. Typical cosolvents include acetonitrile or dimethyl sulfoxide while typical detergents include Polysorbate 20 (Tween 20) or 3-((3-cholamidopropyl) dimethylammonio)-1-propanesulfonate (CHAPS). When solubility is not improved, these molecules are often not evaluated further. To address this issue eleven cosolvents and six detergents that could facilitate aqueous solubility were evaluated to understand how they would affect cholinesterase enzymes using Ellman's assay. These studies show that propylene glycol, acetonitrile, methanol, Tween 20, Polysorbate 80 (Tween 80), polyoxyethylene 23 lauryl ether (Brij 35) and polyoxyethylene 10 oleoyl ether (Brij 96v) have the least inhibitory effects towards cholinesterase activity. It is concluded that these cosolvents and detergents should be considered as solubilizing agents for evaluation of potential cholinesterase inhibitors with low aqueous solubility.

Comparison of the Binding of Reversible Inhibitors to Human Butyrylcholinesterase and Acetylcholinesterase: A Crystallographic, Kinetic and Calorimetric Study

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) hydrolyze the neurotransmitter acetylcholine and, thereby, function as coregulators of cholinergic neurotransmission. Although closely related, these enzymes display very different substrate specificities that only partially overlap. This disparity is largely due to differences in the number of aromatic residues lining the active site gorge, which leads to large differences in the shape of the gorge and potentially to distinct interactions with an individual ligand. Considerable structural information is available for the binding of a wide diversity of ligands to AChE. In contrast, structural data on the binding of reversible ligands to BChE are lacking. In a recent effort, an inhibitor competition approach was used to probe the overlap of ligand binding sites in BChE. Here, we extend this study by solving the crystal structures of human BChE in complex with five reversible ligands, namely, decamethonium, thioflavin T, propidium, huprine, and ethopropazine. We compare these structures to equivalent AChE complexes when available in the protein data bank and supplement this comparison with kinetic data and observations from isothermal titration calorimetry. This new information now allows us to define the binding mode of various ligand families and will be of importance in designing specific reversible ligands of BChE that behave as inhibitors or reactivators.

Development of acetophenone ligands as potential neuroimaging agents for cholinesterases

Association of cholinesterase with β-amyloid plaques and tau neurofibrillary tangles in Alzheimer's disease offers an opportunity to detect disease pathology during life. Achieving this requires development of radiolabelled cholinesterase ligands with high enzyme affinity. Various fluorinated acetophenone derivatives bind to acetylcholinesterase with high affinity, including 2,2,2-trifluoro-1-(3-dimethylaminophenyl)ethanone (1) and 1-(3-tert-butylphenyl)-2,2,2-trifluoroethanone (2). Such compounds also offer potential for incorporation of radioactive fluorine (¹⁸F) for Positron Emission Tomography (PET) imaging of cholinesterases in association with Alzheimer's disease pathology in the living brain. Here we describe the synthesis of two meta-substituted chlorodifluoroacetophenones using a Weinreb amide strategy and their rapid conversion to the corresponding trifluoro derivatives through nucleophilic substitution by fluoride ion, in a reaction amenable to incorporating ¹⁸F for PET imaging. In vitro kinetic analysis indicates tight binding of the trifluoro derivatives to cholinesterases. Compound 1 has a K_i value of 7nM for acetylcholinesterase and 1300nM for butyrylcholinesterase while for compound 2 these values are 0.4nM and 26nM, respectively. Tight binding of these compounds to cholinesterase encourages their development for PET imaging detection of cholinesterase associated with Alzheimer's disease pathology.

Reduced fibrillar β-amyloid in subcortical structures in a butyrylcholinesterase-knockout Alzheimer disease mouse model

The serine hydrolase, butyrylcholinesterase (BChE) is known to have a variety of enzymatic and non-enzymatic functions. In the brain, BChE is expressed mainly in glia, white matter and in distinct populations of neurons in areas important in cognition. In Alzheimer's disease (AD), many β-amyloid (Aβ) plaques become associated with BChE activity, the significance of which is unclear. A mouse model of AD containing five familial AD genes (5XFAD) also exhibits Aβ plaques associated with BChE. We developed a comparable strain (5XFAD/BChE-KO) that is unable to synthesize BChE and reported diminished fibrillar Aβ deposits in the cerebral cortex of 5XFAD/BChE-KO mice, compared to 5XFAD counterparts at the same age. This effect was most significant in male mice. The present study extends comparison of the two strains with a detailed examination of fibrillar Aβ plaque burden in other regions of the brain that typically accumulate pathology and exhibit neurodegeneration. This work demonstrates that, as in the cerebral cortex, the absence of BChE leads to diminished fibrillar Aβ deposition in amygdala, hippocampal formation, thalamus and basal ganglia. This reduction is statistically significant in males, with a trend towards such reduction in female mice.

Synthesis and Preliminary Evaluation of Phenyl 4-123I-Iodophenylcarbamate for Visualization of Cholinesterases Associated with Alzheimer Disease Pathology

Acetylcholinesterase and butyrylcholinesterase accumulate with brain β-amyloid (Aβ) plaques in Alzheimer disease (AD). The overall activity of acetylcholinesterase is found to decline in AD, whereas butyrylcholinesterase has been found to either increase or remain the same. Although some cognitively normal older adults also have Aβ plaques within the brain, cholinesterase-associated plaques are generally less abundant in such individuals. Thus, brain imaging of cholinesterase activity associated with Aβ plaques has the potential to distinguish AD from cognitively normal older adults, with or without Aβ accumulation, during life. Current Aβ imaging agents are not able to provide this distinction. To address this unmet need, synthesis and evaluation of a cholinesterase-binding ligand, phenyl 4-(123)I-iodophenylcarbamate ((123)I-PIP), is described.

METHODS

Phenyl 4-iodophenylcarbamate was synthesized and evaluated for binding potency toward acetylcholinesterase and butyrylcholinesterase using enzyme kinetic analysis. This compound was subsequently rapidly radiolabeled with (123)I and purified by high-performance liquid chromatography. Autoradiographic analyses were performed with (123)I-PIP using postmortem orbitofrontal cortex from cognitively normal and AD human brains. Comparisons were made with an Aβ imaging agent, 2-(4'-dimethylaminophenyl)-6-(123)I-iodo-imidazo[1,2-a]pyridine ((123)I-IMPY), in adjacent brain sections. Tissues were also stained for Aβ and cholinesterase activity to visualize Aβ plaque load for comparison with radioligand uptake.

RESULTS

Synthesized and purified PIP exhibited binding to cholinesterases. (123)I was successfully incorporated into this ligand. (123)I-PIP autoradiography with human tissue revealed accumulation of radioactivity only in AD brain tissues in which Aβ plaques had cholinesterase activity. (123)I-IMPY accumulated in brain tissues with Aβ plaques from both AD and cognitively normal individuals.

CONCLUSION

Radiolabeled ligands specific for cholinesterases have potential for use in neuroimaging AD plaques during life. The compound herein described, (123)I-PIP, can detect cholinesterases associated with Aβ plaques and can distinguish AD brain tissues from those of cognitively normal older adults with Aβ plaques. Imaging cholinesterase activity associated with Aβ plaques in the living brain may contribute to the definitive diagnosis of AD during life.

Complement component C3 and butyrylcholinesterase activity are associated with neurodegeneration and clinical disability in multiple sclerosis

Dysregulation of the complement system is evident in many CNS diseases but mechanisms regulating complement activation in the CNS remain unclear. In a recent large rat genome-wide expression profiling and linkage analysis we found co-regulation of complement C3 immediately downstream of butyrylcholinesterase (BuChE), an enzyme hydrolyzing acetylcholine (ACh), a classical neurotransmitter with immunoregulatory effects. We here determined levels of neurofilament-light (NFL), a marker for ongoing nerve injury, C3 and activity of the two main ACh hydrolyzing enzymes, acetylcholinesterase (AChE) and BuChE, in cerebrospinal fluid (CSF) from patients with MS (n = 48) and non-inflammatory controls (n = 18). C3 levels were elevated in MS patients compared to controls and correlated both to disability and NFL. C3 levels were not induced by relapses, but were increased in patients with ≥9 cerebral lesions on magnetic resonance imaging and in patients with progressive disease. BuChE activity did not differ at the group level, but was correlated to both C3 and NFL levels in individual samples. In conclusion, we show that CSF C3 correlates both to a marker for ongoing nerve injury and degree of disease disability. Moreover, our results also suggest a potential link between intrathecal cholinergic activity and complement activation. These results motivate further efforts directed at elucidating the regulation and effector functions of the complement system in MS, and its relation to cholinergic tone.

Probing the peripheral site of human butyrylcholinesterase

Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) catalyze the hydrolysis of the neurotransmitter acetylcholine and, thereby, function as coregulators of cholinergic neurotransmission. For both enzymes, hydrolysis takes place near the bottom of a 20 Å deep active site gorge. A number of amino acid residues within the gorge have been identified as important in facilitating efficient catalysis and inhibitor binding. Of particular interest is the catalytic triad, consisting of serine, histidine, and glutamate residues, that mediates hydrolysis. Another site influencing the catalytic process is located above the catalytic triad toward the periphery of the active site gorge. This peripheral site (P-site) contains a number of aromatic amino acid residues as well as an aspartate residue that is able to interact with cationic substrates and guide them down the gorge to the catalytic triad. In human AChE, certain aryl residues in the vicinity of the anionic aspartate residue (D74), such as W286, have been implicated in ligand binding and have therefore been considered part of the P-site of the enzyme. The present study was undertaken to explore the P-site of human BuChE and determine whether, like AChE, aromatic side chains near the peripheral aspartate (D70) of this enzyme contribute to ligand binding. Results obtained, utilizing inhibitor competition studies and BuChE mutant species, indicate the participation of aryl residues (F329 and Y332) in the E-helix component of the BuChE active site gorge, along with the anionic aspartate residue (D70), in binding ligands to the P-site of the enzyme.

Why has butyrylcholinesterase been retained? Structural and functional diversification in a duplicated gene

While acetylcholinesterase (EC 3.1.1.7) has a clearly defined role in neurotransmission, the functions of its sister enzyme butyrylcholinesterase (EC 3.1.1.8) are more obscure. Numerous mutations, many inactivating, are observed in the human butyrylcholinesterase gene, and the butyrylcholinesterase knockout mouse has an essentially normal phenotype, suggesting that the enzyme may be redundant. Yet the gene has survived for many millions of years since the duplication of an ancestral acetylcholinesterase early in vertebrate evolution. In this paper, we ask the questions: why has butyrylcholinesterase been retained, and why are inactivating mutations apparently tolerated? Butyrylcholinesterase has diverged both structurally and in terms of tissue and cellular expression patterns from acetylcholinesterase. Butyrylcholinesterase-like activity and enzymes have arisen a number of times in the animal kingdom, suggesting the usefulness of such enzymes. Analysis of the published literature suggests that butyrylcholinesterase has specific roles in detoxification as well as in neurotransmission, both in the brain, where it appears to control certain areas and functions, and in the neuromuscular junction, where its function appears to complement that of acetylcholinesterase. An analysis of the mutations in human butyrylcholinesterase and their relation to the enzyme's structure is shown. In conclusion, it appears that the structure of butyrylcholinesterase's catalytic apparatus is a compromise between the apparently conflicting selective demands of a more generalised detoxifier and the necessity for maintaining high catalytic efficiency. It is also possible that the tolerance of mutation in human butyrylcholinesterase is a consequence of the detoxification function. Butyrylcholinesterase appears to be a good example of a gene that has survived by subfunctionalisation.

Synthesis and preliminary evaluation of piperidinyl and pyrrolidinyl iodobenzoates as imaging agents for butyrylcholinesterase

PURPOSE

The purpose of this study is to synthesize and evaluate specific agents for molecular imaging of butyrylcholinesterase (BuChE), known to be associated with neuritic plaques and neurofibrillary tangles in Alzheimer's disease (AD). In this study, these agents were tested in a normal rat model. The distribution of radiolabel was compared with known BuChE histochemical distribution in the rat brain.

PROCEDURES

Iodobenzoate esters were synthesized and tested, through spectrophotometric analysis, as specific substrates for BuChE. These compounds were converted to the corresponding (123)I esters from tributyltin intermediates and purified for studies in the rat model. Whole body dynamic scintigraphic images were obtained for biodistribution studies. Autoradiograms of brain sections were obtained and compared to histochemical distribution of the enzyme in this model system.

RESULTS

The three iodobenzoate esters studied were specific substrates for BuChE. Whole body biodistribution studies with (123)I-labeled compounds showed rapid disappearance from the body while radioactivity was retained in the head region. Brain section autoradiography of animals injected with these labeled compounds indicated that most areas known to contain BuChE corresponded to areas of radioactivity accumulation.

CONCLUSION

BuChE-specific radiolabeled iodobenzoates enter the brain and, in general, label areas known to exhibit BuChE activity in histochemical studies. Such molecules may represent a new direction for the development of agents for the molecular imaging of BuChE in the living brain, especially in regions where BuChE-containing neuropathological structures appear in AD.

Butyrylcholinesterase is associated with β-amyloid plaques in the transgenic APPSWE/PSEN1dE9 mouse model of Alzheimer disease

Histochemical analysis of Alzheimer disease (AD) brain tissues indicates that butyrylcholinesterase (BuChE) is present in β-amyloid (Aβ) plaques. The role of BuChE in AD pathology is unknown, but an animal model developing similar BuChE-associated Aβ plaques could provide insights. The APPSWE/PSEN1dE9 transgenic mouse (ADTg), which develops Aβ plaques, was examined to determine if BuChE associates with these plaques, as in AD. We found that in mature ADTg mice, BuChE activity associated with Aβ plaques. The Aβ-, thioflavin-S- and BuChE-positive plaques mainly accumulated in the olfactory structures, cerebral cortex, hippocampal formation, amygdala, and cerebellum. No plaques were stained for acetylcholinesterase activity. The distribution and abundance of plaque staining in ADTg closely resembled many aspects of plaque staining in AD. Butyrylcholinesterase staining consistently showed fewer plaques than were detected with Aβ immunostaining but a greater number of plaques than were visualized with thioflavin-S. Double-labeling experiments demonstrated that all BuChE-positive plaques were Aβ positive, whereas only some BuChE-positive plaques were thioflavin-S positive. These observations suggest that BuChE is associated with a subpopulation of Aβ plaques and may play a role in AD plaque maturation. A further study of this animal model could clarify the role of BuChE in AD pathology.

Cysteine thioesters as myelin proteolipid protein analogues to examine the role of butyrylcholinesterase in myelin decompaction

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disorder involving demyelination, axonal transection, and neuronal loss in the brain. Recent studies have indicated that active MS lesions express elevated levels of butyrylcholinesterase (BuChE). BuChE can hydrolyze a wide variety of esters, including fatty acid esters of protein. Proteolipid protein (PLP), an important transmembrane protein component of myelin, has six cysteine residues acylated, via thioester linkages, with fatty acids, usually palmitic, that contribute to the stability of myelin. Experimental chemical deacylation of PLP has been shown to lead to decompaction of myelin. Because of elevated levels of BuChE in active MS lesions and its propensity to catalyze the hydrolysis of acylated protein, we hypothesized that this enzyme may contribute to deacylation of PLP in MS, leading to decompaction of myelin and contributing to demyelination. To test this hypothesis, a series of increasing chain length (C2-C16) acyl thioester derivatives of N-acetyl-l-cysteine methyl ester were synthesized and examined for hydrolysis by human cholinesterases. All N-acetyl-l-cysteine fatty acyl thioester derivatives were hydrolyzed by BuChE but not by the related enzyme acetylcholinesterase. In addition, it was observed that the affinity of BuChE for the compound increased the longer the fatty acid chain, with the highest affinity for cysteine bound to palmitic acid. This suggests that the elevated levels of BuChE observed in active MS lesions could be related to the decompaction of myelin characteristic of the disorder.

Improving the ex vivo stability of drug ester compounds in rat and dog serum: inhibition of the specific esterases and implications on their identity

In drug development, it has been noticed that some drug compounds, especially esters, are unstable in serum samples ex vivo. This can lead to a substantial underestimation of the actual drug concentration. The rat and the dog, representing a rodent and non-rodent species, respectively, are widely used in preclinical studies. We studied the degradation of three structurally different drug esters in rat and dog serum. Moreover, the efficiency of selected enzyme inhibitors to prevent these degradations was investigated. Furthermore, we found indications of the identity of the drug-specific esterases by means of their inhibitor sensitivity as well as by protein purification and identification. The studied drugs were sagopilone, drospirenone, and methylprednisolone aceponate (MPA) all of which are used in (pre-)clinical drug development. The sagopilone-cleaving esterases in rat serum were inhibited by serine hydrolase inhibitors. We partly purified these esterases resulting in an activity yield of 5% and a purification factor of 472. Using matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF)-mass spectrometry (MS), the rat carboxylesterase isoenzyme ES-1 was identified in these fractions, thus pointing to its involvement in sagopilone cleavage. Drospirenone cleavage in rat serum was effected by butyrylcholinesterase (BChE) and paraoxonase 1 (PON1) as we deduced from the high efficacy of certain serine hydrolase and metallohydrolase inhibitors, respectively. Likewise, some inhibition characteristics implied that MPA was cleaved in rat serum by BChE and serine proteases. Partial purification of the MPA-specific esterases resulted in activity yields of 1-2%, exhibiting up to 10,000-fold purification. In dog serum, we found that sagopilone was not degraded which was in contrast to MPA and drospirenone. MPA degradation was mainly prevented by serine hydrolase inhibitors. We used a three-step purification to isolate the esterases cleaving MPA. This procedure resulted in an activity yield of 12% and 645-fold purification. By protein identification using liquid chromatography (LC)-electrospray ionization (ESI)-MS, we identified alpha(2)-macroglobulin (alpha(2)M) in the active fractions. We therefore assumed that serine hydrolases, probably butyrylcholinesterase, known to form esteratically active complexes with alpha(2)M, were responsible for MPA cleavage. In contrast, PON1 was assumed to be involved in drospirenone cleavage due to the high efficiency of metallohydrolase inhibitors. This indication was supported by the presence of PON1 in drospirenone-cleaving fractions as we found by affinity chromatography and Western immunoblotting for isolation and detection of PON1, respectively. The identity of the assumed cleaving enzymes remains, however, to be further studied. The inhibitors we found can serve as a tool for stabilizing drug ester compounds in biological samples ex vivo.

Differential CSF butyrylcholinesterase levels in Alzheimer's disease patients with the ApoE epsilon4 allele, in relation to cognitive function and cerebral glucose metabolism

Butyrylcholinesterase (BuChE) is increased in the cerebral cortex of Alzheimer's disease (AD) patients, particularly those carrying epsilon4 allele of the apolipoprotein E gene (ApoE) and certain BuChE variants that predict increased AD risk and poor response to anticholinesterase therapy. We measured BuChE activity and protein level in CSF of eighty mild AD patients in relation to age, gender, ApoE epsilon4 genotype, cognition and cerebral glucose metabolism (CMRglc). BuChE activity was 23% higher in men than women (p<0.03) and 40-60% higher in ApoE epsilon4 negative patients than in those carrying one or two epsilon4 alleles (p<0.0004). CSF BuChE level correlated with cortical CMRglc. Patients with high to moderate CSF BuChE showed better cognitive function scores than others. We hypothesize that CSF BuChE varies inversely with BuChE in cortical amyloid plaques. Thus, low BuChE in a patient's CSF may predict extensive incorporation in neuritic plaques, increased neurotoxicity and greater central neurodegeneration.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Rivastigmine is a potent inhibitor of acetyl- and butyrylcholinesterase in Alzheimer's plaques and tangles

Acetylcholinesterase and butyrylcholinesterase activities emerge in association with plaques and tangles in Alzheimer's disease. These pathological cholinesterases, with altered properties, are suggested to participate in formation of plaques. The present experiment assessed the ability of rivastigmine, a clinically utilized agent that inhibits acetylcholinesterase and butyrylcholinesterase activities, to inhibit cholinesterases in plaques and tangles. Cortical sections from cases of Alzheimer's disease were processed using cholinesterase histochemistry in the presence or absence of rivastigmine. Optical densities of stained sections were utilized as a measure of inhibition. The potency of rivastigmine was compared with those of other specific inhibitors. Optimum staining for cholinesterases in neurons and axons was obtained at pH 8.0. Cholinesterases in plaques, tangles and glia were stained best at pH 6.8. Butyrylcholinesterase-positive plaques were more numerous than acetylcholinesterase-positive plaques. Rivastigmine inhibited acetylcholinesterase in all positive structures in a dose-dependent manner (10(-6)-10(-4) M). However, even at the highest concentration, faint activity remained. In contrast, rivastigmine resulted in complete inhibition of butyrylcholinesterase in all structures at 10(-5) M. Rivastigmine was equipotent to the specific acetylcholinesterase inhibitor BW284C51 and more potent than the butyrylcholinesterase inhibitors iso-OMPA and ethopropazine. In conclusion, rivastigmine is a potent inhibitor of acetylcholinesterase and a more potent inhibitor of butyrylcholinesterase in plaques and tangles. Unlike other cholinesterase inhibitors tested, rivastigmine inhibited cholinesterases in normal and pathological structures with the same potency. Thus, at the therapeutic concentrations used, rivastigmine is likely to result in inhibition of pathological cholinesterases, with the potential of interfering with the disease process.

Structure-activity relationships for inhibition of human cholinesterases by alkyl amide phenothiazine derivatives

Several lines of evidence indicate that inhibition of butyrylcholinesterase (BuChE) is important in the treatment of certain dementias. Further testing of this concept requires inhibitors that are both BuChE-selective and robust. N-alkyl derivatives (2, 3, 4) of phenothiazine (1) have previously been found to inhibit only BuChE in a mechanism involving pi-pi interaction between the phenothiazine tricyclic ring system and aromatic residues in the active site gorge. To explore features of phenothiazines that affect the selectivity and potency of BuChE inhibition, a series of N-carbonyl derivatives (5-25) was synthesized and examined for the ability to inhibit cholinesterases. Some of the synthesized derivatives also inhibited AChE through a different mechanism involving carbonyl interaction within the active site gorge. Binding of these derivatives takes place within the gorge, since this inhibition disappears when the molecular volume of the derivative exceeds the estimated active site gorge volume of this enzyme. In contrast, BuChE, with a much larger active site gorge, exhibited inhibition that increased directly with the molecular volumes of the derivatives. This study describes two distinct mechanisms for binding phenothiazine amide derivatives to BuChE and AChE. Molecular volume was found to be an important parameter for BuChE-specific inhibition.

Differential effects of lipid-lowering agents on human cholinesterases

OBJECTIVES

Epidemiologic reports indicate that lipid-lowering agents (LLAs) protect against dementia. We hypothesized that LLAs might affect cholinergic systems. The effects of LLAs on the activity of cholinesterases were examined.

DESIGN AND METHODS

Odds ratios and relative risks were calculated from clinical studies of LLAs and dementia and compared with their impacts on human cholinesterases. Representative LLAs were examined for their effects on the activity of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) using Ellman's assay.

RESULTS

Epidemiological studies, but not clinical trials, showed lower odds of dementia in patients taking "statins". Comparison of LLAs indicated that "statins" most consistently produced apparent protection. Individual "statins" showed differential cholinesterase inhibition. Lovastatin and simvastatin significantly inhibited butyrylcholinesterase, while mevastatin, pravastatin and the "non-statins" did not. None of the LLAs inhibited acetylcholinesterase.

CONCLUSIONS

Some "statins" inhibit butyrylcholinesterase. This inhibition suggests a possible means whereby "statins" could protect against dementia.

Inhibition of human cholinesterases by drugs used to treat Alzheimer disease

Current approaches to the treatment of cognitive and behavioral symptoms of Alzheimer disease emphasize the use of cholinesterase inhibitors. The kinetic effects of the cholinesterase inhibitors donepezil, galantamine, metrifonate, physostigmine, rivastigmine, and tetrahydroaminoacridine were examined with respect to their action on the esterase and aryl acylamidase activities of human acetylcholinesterase (AChE) and human butyrylcholinesterase (BuChE). Each of these drugs inhibited both AChE and BuChE, but to different degrees. Inhibition of BuChE by these compounds was approximately the same, or better, when acetylthiocholine, the analog of the neurotransmitter acetylcholine, was used as the substrate, instead of butyrylthiocholine. In addition, for these drugs, the inhibition of aryl acylamidase activity paralleled that observed for inhibition of esterase activity of AChE and BuChE. Given that drugs that are currently in use for the treatment of Alzheimer disease inhibit both AChE and BuChE, the development of drugs targeted toward the exclusive inhibition of one or the other cholinesterase may be important for understanding the relative importance of inhibition of BuChE and AChE in the treatment of this disease.

Enantiomer effects of huperzine A on the aryl acylamidase activity of human cholinesterases

1. Acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BuChE, EC 3.1.1.8) are serine hydrolase enzymes that catalyze the hydrolysis of acetylcholine. 2. (-) Huperzine A is an inhibitor of AChE and is being considered for the treatment of Alzheimer's disease. 3. In addition to esterase activity, AChE and BuChE have intrinsic aryl acylamidase activity. 4. The function of aryl acylamidase is unknown but has been speculated to be important in Alzheimer pathology. 5. Kinetic effects of (-) huperzine A and (+/-) huperzine A on the aryl acylamidase activity of human cholinesterases were examined. 6. (-) Huperzine A inhibited the aryl acylamidase activities of both AChE and BuChE. 7. (+/-) Huperzine A inhibited this function in AChE but stimulated BuChE aryl acylamidase suggesting that the (+) enantiomer is a powerful activator of this enzyme activity. 8. The two huperzine enantiomers may prove to be useful tools to examine the function of aryl acylamidase activity, including its role in Alzheimer pathology.

Relation between butyrylcholinesterase K variant, paraoxonase 1 (PON1) Q and R and apolipoprotein E epsilon 4 genes in early-onset coronary artery disease

OBJECTIVES

The common K variant of butyrylcholinesterase (BChE-K), an enzyme which metabolizes acetylcholine and organophosphates, has been associated with Alzheimer's disease, especially in the presence of the apolipoprotein E epsilon 4 allele (APOE-epsilon 4). Although APOE-epsilon 4 has been associated with the development of coronary artery disease (CAD), an association between the BChE-K variant and CAD has not been explored. Paraoxonase 1 (PON1), located within HDL, is an enzyme which also metabolizes organophosphates and may be antiatherogenic. The R192 variant of PON1 (PON1-R) has been associated with CAD.

DESIGN AND METHODS

To determine whether BChE-K is also associated with premature CAD, we examined the frequency of BChE-K among patients with early-onset CAD (n = 150; < 50 yr) vs. late-onset CAD (n = 150; > 65 yr) by molecular analysis. We also examined the frequency of the PON1-R allele in both groups, and explored whether there was synergism between BChE-K and APOE-epsilon 4, BChE-K and PON1-R or PON1-R and APOE-epsilon 4.

RESULTS

The frequency of the BChE-K allele tended to be greater among early-onset CAD patients compared to late-onset CAD patients (41.3% vs. 31.3%; p = 0.07), but without any significant difference between males and females. There was no difference in the prevalence of the PON1-R allele between those with early- or late-onset CAD (46.0% vs. 52.7%; p = 0.25). Twenty-two patients with early-onset CAD had both the BChE-K plus APOE-epsilon 4 alleles (14.7%) compared to 11 late-onset CAD patients (7.3%) (p = 0.04). There was no such association between BChE-K and PON1-R, nor PON1-R and APOE-epsilon 4.

CONCLUSIONS

Our study suggests that there is a minor association between BChE-K and early-onset CAD, especially in the presence of the APOE-epsilon 4 allele.