Computational studies on cholinesterases: Strengthening our understanding of the integration of structure, dynamics and function.

Computational approaches have proved valuable in elucidating structure/function relationships in the cholinesterases in the context of their unusual three-dimensional structure. In this review we survey several recent studies that have enhanced our understanding of how these enzymes function, and have utilized computational approaches both to modulate their activity and to improve the design of lead compounds for their inhibition. An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:Neuropharmacology:2.

[Study of cholinesterase activity in mixed saliva of patients with somatic pathology.]

Cholinesterase activity in mixed saliva of patients with somatic pathology was investigated. The results showed differences in enzyme activity depending on the disease. The highest salivary cholinesterase activity was detected in patients with bronchopulmonary pathology, and the lowest - in cardiovascular diseases. A reliable relationship between the changes in the activity of cholinesterase in saliva and the rate of salivation, and with patients taking atypical antipsychotics and M, H-anticholinergic drugs, was revealed.

[Interest of the cholinesterase assay during organophosphate poisonings]. / Intérêt du dosage des cholinestérases dans le cadre des intoxications aux organophosphorés.

Cholinesterases are the main targets of organophosphorus compounds. The two enzymes present in the blood (butyrylcholinesterase, BChE; acetylcholinesterase, AChE) are biomarkers of their systemic toxicity. Activity of the plasma BChE is very often determined as it allows a rapid diagnostic of poisoning and is a marker of the persistence of the toxicant in the blood. The activity of the red blood cell AChE gives a better picture of the synaptic inhibition in the nervous system but the assay is less commonly available in routine laboratories. Better biomarker of the exposure, it allows a diagnosis of the severity of the poisoning and helps to assess the efficacy of oxime therapy. Besides the practical aspects of blood collection and sample processing, and the interpretation of the assays, this review stresses the complementarity of both enzyme assays and recalls their crucial interest for the confirmation of poisoning with an organophosphorus in a situation of war or terrorist attack and for the monitoring of occupational exposures.

Alkaloids as a source of potential anticholinesterase inhibitors for the treatment of Alzheimer's disease.

OBJECTIVES: The inhibition of acetylcholinesterase (AChE), the key enzyme in the breakdown of acetylcholine, is currently the main pharmacological strategy available for Alzheimer's disease (AD). In this sense, many alkaloids isolated from natural sources, such as physostigmine, have been long recognized as acetyl- and butyrylcholinesterase (BChE) inhibitors. Since the approval of galantamine for the treatment of AD patients, the search for new anticholinesterase alkaloids has escalated, leading to promising candidates such as huperzine A. This review aims to summarize recent advances in current knowledge on alkaloids as AChE and BChE inhibitors, highlighting structure-activity relationship (SAR) and docking studies. KEY FINDINGS: Natural alkaloids belonging to the steroidal/triterpenoidal, quinolizidine, isoquinoline and indole classes, mainly distributed within Buxaceae, Amaryllidaceae and Lycopodiaceae, are considered important sources of alkaloids with anti-enzymatic properties. Investigations into the possible SARs for some active compounds are based on molecular modelling studies, predicting the mode of interaction of the molecules with amino acid residues in the active site of the enzymes. Following this view, an increasing interest in achieving more potent and effective analogues makes alkaloids good chemical templates for the development of new cholinesterase inhibitors. SUMMARY: The anticholinesterase activity of alkaloids, together with their structural diversity and physicochemical properties, makes them good candidate agents for the treatment of AD.

Nature as a source of metabolites with cholinesterase-inhibitory activity: an approach to Alzheimer's disease treatment.

OBJECTIVES: Alzheimer's disease (AD) is the most common cause of dementia, being responsible for high healthcare costs and familial hardships. Despite the efforts of researchers, no treatment able to delay or stop AD progress exists. Currently, the available treatments are only symptomatic, cholinesterase inhibitors being the most widely used drugs. Here we describe several natural compounds with anticholinesterase (acetylcholinesterase and butyrylcholinesterase) activity and also some synthetic compounds whose structures are based on those of natural compounds. KEY FINDINGS: Galantamine and rivastigmine are two cholinesterase inhibitors used in therapeutics: galantamine is a natural alkaloid that was extracted for the first time from Galanthus nivalis L., while rivastigmine is a synthetic alkaloid, the structure of which is modelled on that of natural physostigmine. Alkaloids include a high number of compounds with anticholinesterases activity at the submicromolar range. Quinones and stilbenes are less well studied regarding cholinesterase inhibition, although some of them, such as sargaquinoic acid or (+)-α-viniferin, show promising activity. Among flavonoids, flavones and isoflavones are the most potent compounds. Xanthones and monoterpenes are generally weak cholinesterase inhibitors. SUMMARY: Nature is an almost endless source of bioactive compounds. Several natural compounds have anticholinesterase activity and others can be used as leader compounds for the synthesis of new drugs.

[The high-pressure chemistry, barophysiological chemistry, comparative enzymology of cholinesterase the 100th anniversary from the birth of A. P. Brestkin].

There are exposed the main landmarks of the scientific biography of Professor Aleksandr Pavlovich Brestkin, connected with his investigations in the field of chemistry of high pressures, physiological chemistry of caisson disease, kinetics of esterase catalysis, and in comparative enzymology of cholinesterases.

Co-opting functions of cholinesterases in neural, limb and stem cell development.

Acetylcholinesterase (AChE) is a most remarkable protein, not only because it is one of the fastest enzymes in nature, but also since it appears in many molecular forms and is regulated by elaborate genetic networks. As revealed by sensitive histochemical procedures, AChE is expressed specifically in many tissues during development and in many mature organisms, as well as in healthy and diseased states. Therefore it is not surprising that there has been a long-standing search for additional, "non-classical" functions of cholinesterases (ChEs). In principle, AChE could either act nonenzymatically, e.g. exerting cell adhesive roles, or, alternatively, it could work within the frame of classic cholinergic systems, but in non-neural tissues. AChE might be considered a highly co-opting protein, since possibly it combines such various functions within one molecule. By presenting four different developmental cases, we here review i) the expression of ChEs in the neural tube and their close relation to cell proliferation and differentiation, ii) that AChE expression reflects a polycentric brain development, iii) the retina as a model for AChE functioning in neural network formation, and iv) nonneural ChEs in limb development and mature bones. Also, possible roles of AChE in neuritic growth and of cholinergic regulations in stem cells are briefly outlined.

[To the 80-anniversary of cholinesterase. The cholinesterase club in Sechenov Institute of Evolutionary Physiology and Biochemistry].

For the second half of the XX century, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences was the center of the Russian cholinesterase investigations ("the Russian cholinesterase club"). The close cooperation with chemists-syntheticians of different scientific schools provided success and fruitfulness of this scientific search. All these years, there was preserved dualism of this investigation: a study of the mechanism of functioning and kinetics of cholinesterase catalysis as well as the comparative-enzymological character of studies of cholinesterases of the animals being at different levels of evolutionary development.

[Update on the current role of plasma cholinesterase]. / Papel de las colinesterasas plasmáticas. Actualización.

The antagonism of steroidal nondepolarizing neuromuscular blockers (NDMBs) moved forward recently with the introduction of sugammadex, the only drug able to immediately reverse the effects of curarization produced by NDMBs. This advance has necessitated reflection on the future role of pseudocholinesterase. In spite of the side effects of succinylcholine and published opinions on its use, this NDMB continues to be used in clinical anesthesia. Pseudocholinesterase is mainly found in the liver, plasma, and nervous system. The enzyme is synthesized in the liver in greater amounts than required although certain conditions lead to deficiency, which is usually asymptomatic. The only clinical expression is the apnea which develops after administration of succinycholine because this NDMB cannot be metabolized. In some patients, slight reductions in the antagonism of succinylcholine lead to rising neuromuscular concentrations of the drug in accordance with the degree and duration of the blockade. We review the various forms of pseudocholinesterase deficiency, including a discussion of genetic variants, clinical manifestations, and management. In addition to discussing the diagnosis of this condition and the clinical implications, we highlight the importance of practice protocols and access to a referral laboratory if one is not available within the immediate hospital.

Scutellarin protects against Aß-induced learning and memory deficits in rats: involvement of nicotinic acetylcholine receptors and cholinesterase.

AIM: To examine the protective effects of scutellarin (Scu) on rats with learning and memory deficit induced by ß-amyloid peptide (Aß). METHODS: Fifty male Wistar rats were randomly divided into 5 groups: control, sham operation, Aß, Aß+Scu, and Aß+piracetam groups. Aß(25-35) was injected into the lateral ventricle (10 µg each side). Scu (10 mg/2 mL) or piracetam (10 mg/2 mL was intragastrically administered per day for 20 consecutive days following Aß treatment. Learning and memory was assessed with Morris water maze test. The protein and mRNA levels of nicotinic acetylcholine receptor (nAChR) α4, α7, and ß2 subunits in the brain were examined using Western blotting and real-time PCR, respectively. The activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the brain and plasma were measured using Ellman's colorimetric method. RESULTS: In Aß group, the escape latency period and first platform cross was significantly increased, and the total number of platform crossings was significantly decreased, as compared with the control and the sham operation groups. Both Scu and piracetam treatment significantly reduced the escape latency period and time to cross platform, and increased the number of platform crosses, but there were no significant differences between Aß+Scu and Aß+piracetam groups. In Aß group, the protein levels of nAChR α4 and α7 subunits in the cerebral cortex were significantly decreased by 42%-47% and 58%-61%, respectively, as compared to the control and the sham operation groups. Scu treatment caused upregulation of α4 and α7 subunit proteins by around 24% and 30%, respectively, as compared to Aß group, but there were no significant differences between Aß+Scu and Aß+piracetam groups. The protein level of nAChR ß2 subunit had no significant difference among different groups. The mRNA levels of nAChR α4, α7, and ß2 subunits were not significantly changed. In Aß group, the activities of AChE and BuChE in the brain were significantly increased, but were significantly decreased in the plasma, as compared to the control and the sham operation groups. Scu or piracetam treatment restored the activities in brain and plasma nearly to the levels in the control group. CONCLUSION: The results suggest that Scu may rescue some of the deleterious effects of Aß, possibly by stimulating nAChR protein translation and regulating cholinesterase activity.

Cholinesterases, a target of pharmacology and toxicology.

BACKGROUND: Cholinesterases are a group of serine hydrolases that split the neurotransmitter acetylcholine (ACh) and terminate its action. Of the two types, butyrylcholinesterase and acetylcholinesterase (AChE), AChE plays the key role in ending cholinergic neurotransmission. Cholinesterase inhibitors are substances, either natural or man-made that interfere with the break-down of ACh and prolong its action. Hence their relevance to toxicology and pharmacology. METHODS AND RESULTS: The present review summarizes current knowledge of the cholinesterases and their inhibition. Particular attention is paid to the toxicology and pharmacology of cholinesterase-related inhibitors such as nerve agents (e.g. sarin, soman, tabun, VX), pesticides (e.g. paraoxon, parathion, malathion, malaoxon, carbofuran), selected plants and fungal secondary metabolites (e.g. aflatoxins), drugs for Alzheimer's disease (e.g. huperzine, metrifonate, tacrine, donepezil) and Myasthenia gravis (e.g. pyridostigmine) treatment and other compounds (propidium, ethidium, decamethonium). CONCLUSIONS: The crucial role of the cholinesterases in neural transmission makes them a primary target of a large number of cholinesterase-inhibiting drugs and toxins. In pharmacology, this has relevance to the treatment of neurodegenerative disorders.

Role of cholinesterase activity on pharmacodynamics of mivacurium preceded by pancuronium in elderly and young adults.

Mivacurium- pancuronium combination proved to be more potent than either drug given alone. The goal of this study was to evaluate the safety and efficacy of this combination in elderly group and its correlation to plasma butyryl cholinesterase (Bche) activity. Forty patients, ASA I or II scheduled for elective open cholecystectomy were allocated into two groups of twenty patients each: young group (18- 55 years) and elderly group (60-75 years). Anesthesia was induced with midazolam, fentanyl, and propofol then maintained with isoflurane and opioid supplementation. Neuromuscular blockade (NMB) was monitored by train-of-four (TOF) stimulation of the ulnar nerve. After calibration, NMB was achieved by 16 microg kg(-1) pancuronium followed by 32 microg kg(-1) mivacurium. The following parameters were recorded: The onset time, clinical duration, recovery index and the total dose of mivacurium and pancuronium together with hemodynamic data. Three blood samples for Bche activity were collected: before pancuronium injection, 3 min. and 30 min. afterwards in both groups. The onset time and the recovery index of NMB were comparable in both groups. The duration of action was significantly prolonged in elderly group (49.8 +/- 10.48 min.) compared to young one (37.13 +/- 7.81 min.). The total dose of mivacurium was significantly less in the elderly group (22.56 +/- 2.39 microg kg(-1) hr(-1)) when compared to the young group (25.78 +/- 3.05 microg kg(-1) hr(-1)). For all patients, the preoperative Bche activity was within the normal range. After pancuronium injecttion, it showed a significant reduction in both groups at three and thirty minutes except a non significant value in young at thirty minutes. This reduction showed a significantly higher percent change in the elderly group (30.37 +/- 22.01) than the young group (8.60 +/- 19.19) at thirty minutes. There were significant intra operative variations in the percent changes of hemodynamic data compared to the preoperative values, yet, still within the clinically acceptable range. So, the use of a small dose of pancuronium followed by a small dose of mivacurium with a ratio of 1:2 can produce synergism without affecting either the recovery profile of mivacurium or the clinical hemodynamic stability even in the elderly group.

Potential role of cholinesterases in the invasive capacity of the freshwater bivalve, Anodonta woodiana (Bivalvia: Unionacea): a comparative study with the indigenous species of the genus, Anodonta sp.

To address the potential role of cholinesterase enzymes in the invasive capacity of species, the present study investigated ChE activity in the invasive freshwater bivalve Anodonta woodiana (Lea, 1834) comparing it with that of the indigenous species, Anodonta sp. (Linnaeus, 1758). The invasive capacity of pests has often been linked to their ecological plasticity and high intrinsic genetic variability; however the role played by molecular and cellular mechanisms, generally known as an organism's response to pollution, is unclear. Different substrates and selective ChE enzyme inhibitors were investigated in digestive gland, foot, gonad, adductor muscle and gill tissues while sensitivity to four organophosphate (OP) insecticides was investigated in vitro only in adductor muscle. The invasive species (A. woodiana) showed significantly greater (at least one order of magnitude) ChE activity than the endemic species (Anodonta sp.) (p<0.05) using acetylthiocholine (ASCh) as substrate and the activity was more widely distributed in tissues involved in movement (adductor muscle and foot), respiration, feeding (gills) and reproduction (gonads). Moreover, only the invasive species, A. woodiana, showed detectable ChE (vs. ASCh) activity in gill tissue. No substrate specificity was observed in any tissue of either species as already described for other bivalve species. ChE activity was not inhibited by Iso-OMPA but showed high sensitivity to BW248c51 and eserine. Both species showed moderate to low sensitivities in vitro to OP insecticides in the range 10(-7)-10(-2) M. Calculated IC(50) for fenitrothion and chlorpyrifos was in the range 10(-6)-10(-3) M in muscle of A. woodiana while a higher inhibition was observed for fenitrothion (10(-7) M) and lower for chlorpyrifos (10(-2) M) in the indigenous species Anodonta sp. Similar IC(50) of 10(-5)-10(-6) M were observed for DFP and azamethiphos in both species. The hypotheses of other authors that acetylcholinesterase (AChE) is involved in the control of many essential functions, such as frontal ciliary activity of gill epithelium, temperature resistance, ciliary activity for transport of suspended particulate, valve opening and embryo development, suggest that the high catalytic efficiency of the invasive species may endow it with a competitive advantage over the endemic species. In view of the peculiar reproductive strategy of these mussels, higher ChE vs. ASCh activity in gonads of the invasive species could also favour glochidium production and embryo development under a wider range of environmental conditions.

Amyloid, cholinesterase, melatonin, and metals and their roles in aging and neurodegenerative diseases.

The aging brain shows selective neurochemical changes involving several neural cell populations. Increased brain metal levels have been associated with normal aging and a variety of diseases, including Alzheimer's disease (AD). Melatonin levels are decreased in aging, particularly in AD subjects. The loss of melatonin, which is synthesized by the pineal gland, together with the degeneration of cholinergic neurons of the basal forebrain and the deposition of aggregated proteins, such as the amyloid beta peptides (Abeta), are believed to contribute to the development of cognitive symptoms of dementia. Aging and its variants, such as AD, should be viewed as the result of multiple "hits," including alterations in the levels of Abeta, metals, cholinesterase enzymes, and neuronal gene expression. Herein, we present evidence in support of this theory, based on several studies. We discuss melatonin's neuroprotective function, which plays an important role in aging, prolongation of life span, and health in the aged individual. It interacts with metals and, in some cases, neutralizes their toxic effects. Dietary supplementation of melatonin restores its age-related loss. In mice, an elevated brain melatonin significantly reduced levels of potentially toxic Abeta peptides. Thus, compensation of melatonin loss in aging by dietary supplementation could well be beneficial in terms of reducing metal-induced toxicity, lipid peroxidation, and losses in cholinergic signaling. We propose that certain cholinesterase inhibitors and the NMDA partial antagonist memantine, which are FDA-approved drugs for AD and useful to boost central nervous system functioning, can be made more effective by their combination with melatonin or other neuroprotectants. Herein, we highlight studies elucidating the role of the amyloid pathway, metals, melatonin, and the cholinergic system in the context of aging and AD. Finally, melatonin is present in edible plants and walnuts, and consuming foodstuffs containing melatonin would be beneficial by enhancing the antioxidative capacity of the organisms.

The origin of the molecular diversity and functional anchoring of cholinesterases.

Vertebrates possess two cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) which both hydrolyze acetylcholine, but differ in their specificity towards other substrates, and in their sensitivity to inhibitors. In mammals, the AChE gene produces three types of coding regions through the choice of 3' splice acceptor sites, generating proteins which possess the same catalytic domain, associated with distinct C-terminal peptides. AChE subunits of type R ('readthrough') produce soluble monomers; they are expressed during development and induced by stress in the mouse brain. AChE subunits of type H ('hydrophobic') produce GPI-anchored dimers, but also secreted molecules; they are mostly expressed in blood cells. Subunits of type T ('tailed') exist for both AChE and BChE. They represent the enzyme forms expressed in brain and muscle. These subunits generate a variety of quaternary structures, including homomeric oligomers (monomers, dimers, tetramers), as well as hetero-oligomeric assemblies with anchoring proteins, ColQ and PRiMA. Mutations in the four-helix bundle (FHB) zone of the catalytic domain indicate that subunits of type H and T use the same interaction for dimerization. On the other hand, the C-terminal T peptide is necessary for tetramerization. Four T peptides, organized as amphiphilic alpha helices, can assemble around proline-rich motifs of ColQ or PRiMA. The association of AChE(T) or BChE subunits with ColQ produces collagen-tailed molecules, which are inserted in the extracellular matrix, e.g. in the basal lamina of neuromuscular junctions. Their association with PRiMA produces membrane-bound tetramers which constitute the predominant form of cholinesterases in the mammalian brain; in muscles, the level of PRiMA-anchored tetramers is regulated by exercise, but their functional significance remains unknown. In brain and muscles, the hydrolysis of acetylcholine by cholinesterases, in different contexts, and their possible noncatalytic functions clearly depend on their localization by ColQ or PRiMA.

Effects of single or repeated dermal exposure to methyl parathion on behavior and blood cholinesterase activity in rats.

The effects of a single or repeated dermal administration of methyl parathion on motor function, learning and memory were investigated in adult female rats and correlated with blood cholinesterase activity. Exposure to a single dose of 50 mg/kg methyl parathion (75% of the dermal LD(50)) resulted in an 88% inhibition of blood cholinesterase activity and was associated with severe acute toxicity. Spontaneous locomotor activity and neuromuscular coordination were also depressed. Rats treated with a lower dose of methyl parathion, i.e. 6.25 or 12.5 mg/kg, displayed minimal signs of acute toxicity. Blood cholinesterase activity and motor function, however, were depressed initially but recovered fully within 1-3 weeks. There were no delayed effects of a single dose of methyl parathion on learning acquisition or memory as assessed by a step-down inhibitory avoidance learning task. Repeated treatment with 1 mg/kg/day methyl parathion resulted in a 50% inhibition of blood cholinesterase activity. A decrease in locomotor activity and impairment of memory were also observed after 28 days of repeated treatment. Thus, a single dermal exposure of rats to doses of methyl parathion which are lower than those that elicit acute toxicity can cause decrements in both cholinesterase activity and motor function which are reversible. In contrast, repeated low-dose dermal treatment results in a sustained inhibition of cholinesterase activity and impairment of both motor function and memory.