Determination of acetylcholinesterase activity by a new chemiluminescence assay with the natural substrate

Attenuation of PI3K/AKT signaling pathway by Ocimum gratissimum leaf flavonoid-rich extracts in streptozotocin-induced diabetic male rats

Diabetes is a group of medical conditions characterized by the body's inability to effectively control blood glucose levels, due to either insufficient insulin synthesis in type 1 diabetes or inadequate insulin sensitivity in type 2 diabetes. According to this research, the PI3K/AKT pathway of Ocimum gratissimum leaf flavonoid-rich extracts in streptozotocin-induced diabetic rats was studied. We purchased and used a total of forty (40) male Wistar rats for the study. We divided the animals into five (5) different groups: normal control (Group A), diabetic control (Group B), low dose (150 mg/kg body weight) of Ocimum gratissimum flavonoid-rich leaf extract (LDOGFL) (Group C), high dose (300 mg/kg body weight) of Ocimum gratissimum flavonoid-rich leaf extract (HDOGFL) (Group D), and 200 mg/kg of metformin (MET) (Group E). Streptozotocin induced all groups except Group A, which serves as the normal control group. The experiment lasted for 21 days, following which we sacrificed the animals and harvested their brains for biochemical analysis on the 22nd day. We carried out an analysis that included reduced glutathione (GSH), glutathione transferases (GST), catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), along with GLUT4, MDA, pro-inflammatory cytokines, NO, neurotransmitters, cholinergic enzyme activities, cardiolipin, and the gene expression of PI3K/AKT. The obtained result indicates that the flavonoid-rich extracts of O. gratissimum significantly enhanced the levels of GSH, GST, CAT, GPx, and SOD, as well as GLUT4 and cardiolipin. The levels of GSH, GST, CAT, GPx, and SOD, as well as GLUT4 and cardiolipin, were significantly increased by gratissimum. Moreover, the extracts decrease the levels of MDA, pro-inflammatory cytokines, NO, neurotransmitters, and cholinergic enzyme activities. Additionally, the flavonoid-rich extracts of O. gratissimum significantly improved the AKT and PI3K gene expressions in diabetic rats. gratissimum had their AKT and PI3K gene expressions significantly (p < 0.05) improved. The findings indicate that O. gratissimum leaf flavonoids have the potential to treat diabetes mellitus. gratissimum leaf flavonoids possess therapeutic potential in themselves and can be applied in the management of diabetes mellitus. Although further analysis can be carried out in terms of isolating, profiling, or purifying the active compounds present in the plant's extract.

High Peroxidase-Mimicking Metal-Organic Frameworks Decorated with Platinum Nanozymes for the Colorimetric Detection of Acetylcholine Chloride and Organophosphorus Pesticides via Enzyme Cascade Reaction

The sensitive detection of acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) is very important for the protection of human health. Herein, a hybrid material, Pt NPs/Fe-MOF, consisting of a metal-organic framework (MIL-88B-NH2, Fe-MOF) decorated with platinum nanoparticles (Pt NPs), was prepared first and exhibited remarkably improved and excellent peroxidase-mimicking activity compared to the Fe-MOF material resulting from the synergistic catalysis effect between Fe-MOF and Pt NPs, which can effectively catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to generate a blue product (oxidized TMB, oxTMB). Interestingly, in the presence of AChE and acetylcholinesterase, the peroxidase-mimicking activity from Pt NPs/Fe-MOF was inhibited obviously, and thus, a colorimetric sensing platform for AChE can be constructed; more importantly, after the addition of OPs, this nanozyme activity can be recovered, inducing the further successful construction of a sensitive colorimetric sensing platform for OPs. The related sensing mechanism and condition optimization were studied, and the as-prepared Pt NPs/Fe-MOF nanozyme-based colorimetric method for AChE and OP detection displayed superior analytical performances with wide linearities and low detection limits. Furthermore, the designed method offers satisfactory real application ability. We expect the as-proposed Pt NPs/Fe-MOF nanozyme-based colorimetric sensing platform for AChE and OPs via the enzyme cascade reaction to show great potential application.

An aqueous macerate of Ziziphus jujuba reduces long-term spatial memory impairment in D-galactose treated rats: role of anti-inflammatory pathways

Pharmacological treatments against Alzheimer disease provide only symptomatic relief and are associated with numerous side effects. Previous studies showed that a concoction of Ziziphus jujuba leaves possesses anti-amnesic effects in scopolamine-treated rats. More recently, an aqueous macerate of Z. jujuba leaves has been shown to reduce short-term memory impairment in D-galactose-treated rats. However, no study on the effect of an aqueous macerate of Z. jujuba on long-term memory impairment was performed. Therefore, this study evaluates the effect of an aqueous macerate of Z. jujuba on long-term spatial memory impairment in D-galactose-treated rats. Long-term spatial memory impairment was induced in rats by administering D-galactose (350 mg/kg/day, s.c.), once dailyfor 21 days. On the 22nd day, the integrity of this memory was assessed using the Morris water maze task. Rats that developed memory impairment were treated with tacrine (10 mg/kg, p.o.), or aspirin (20 mg/kg, p.o.), or extract (41.5, 83, and 166 mg/kg, p.o.), once daily, for 14 days. At the end of the treatment, memory impairment was once more assessed using the same paradigm. Animals were then euthanized, and some pro-inflammatory cytokine markers were analyzed in the hippocampus or blood. The extract at all doses significantly reduced the latency to attain the platforming of the water maze test. The extract (83 mg/kg) also increased the time spent in the target quadrant during the retention phase. The extract markedly reduced the concentration of pro-inflammatory cytokine markers in the hippocampus and blood. Together, these results suggest that this aqueous extract Z. jujuba reduces long-term spatial memory impairment. This effect may be mediated in part by its anti-inflammatory activity.

Insights of Valacyclovir in Treatment of Alzheimer's Disease: Computational Docking Studies and Scopolamine Rat Model

BACKGROUND

Alzheimer's Disease (AD) impairs memory and cognitive functions in the geriatric population and is characterized by intracellular deposition of neurofibrillary tangles, extracellular deposition of amyloid plaques, and neuronal degeneration. Literature suggests that latent viral infections in the brain act as prions and promote neurodegeneration. Memantine possesses both anti-viral and N-methyl-D-aspartate (NMDA) receptor antagonistic activity.

OBJECTIVES

This research was designed to evaluate the efficacy of antiviral agents, especially valacyclovir, a prodrug of acyclovir in ameliorating the pathology of AD based on the presumption that anti-viral agents targeting the Herpes Simplex Virus (HSV) can have a protective effect on neurodegenerative diseases like Alzheimer's disease.

METHODS

Thus, we evaluated acyclovir's potential activity by in-silico computational docking studies against acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and beta-secretase 1 (BACE-1). These findings were further evaluated by in-vivo scopolamine-induced cognitive impairment in rats. Two doses of valacyclovir, a prodrug of acyclovir (100 mg/kg and 150 mg/kg orally) were tested.

RESULTS

Genetic Optimisation for Ligand Docking scores and fitness scores of acyclovir were comparable to donepezil. Valacyclovir improved neurobehavioral markers. It inhibited AChE and BuChE (p<0.001) enzymes. It also possessed disease-modifying efficacy as it decreased the levels of BACE-1 (p<0.001), amyloid beta 1-42 (p<0.001), amyloid beta 1-40 (p<0.001), phosphorylatedtau (p<0.001), neprilysin (p<0.01), and insulin-degrading enzyme. It ameliorated neuroinflammation through decreased levels of tumour necrosis factor α (p<0.001), nuclear factor-kappa B (p<0.001), interleukin 6 (p<0.001), interleukin 1 beta (p<0.001), and interferon-gamma (p<0.001). It also maintained synaptic plasticity and consolidated memory. Histopathology showed that valacyclovir could restore cellular density and also preserve the dentate gyrus.

CONCLUSION

Valacyclovir showed comparable activity to donepezil and thus can be further researched for the treatment of Alzheimer's disease.

A sensitive fluorescence biosensor based on metal ion-mediated DNAzyme activity for amplified detection of acetylcholinesterase

In this paper, we developed an amplified fluorescence biosensor for acetylcholinesterase (AChE) activity detection by taking advantage of the mercury ion-mediated Mgzyme (Mg2+-dependent DNAzyme) activity.

Ziziphus jujuba (Rhamnaceae) Alleviates Working Memory Impairment and Restores Neurochemical Alterations in the Prefrontal Cortex of D-Galactose-Treated Rats

Alzheimer's disease is a progressive cognitive dysfunction. However, pharmacological treatments are symptomatic and have many side effects, opening the opportunity to alternative medicine. This study investigated the antiamnesic effect of the aqueous extract of Ziziphus jujuba on D-galactose-induced working memory impairment in rats. Impairment of working memory was induced by subcutaneous (s.c.) injection of D-galactose (350 mg/kg/day) to rats for 21 days. These animals were then subjected to object recognition and Y-maze tests. Rats with confirmed memory impairment were treated per os (p.o.) with tacrine (10 mg/kg), aspirin (20 mg/kg, p.o.), extract (41.5, 83, and 166 mg/kg, p.o.), and distilled water (10 mL/kg, p.o.) daily for 14 days. At the end of the treatments, alteration in working memory was assessed using the above paradigms. Afterward, these animals were euthanized, and cholinergic, proinflammatory, and neuronal damage markers were analyzed in the prefrontal cortex. Rats administered D-galactose and treated with distilled water had impaired working memory (evidenced by decreased time spent on the novel object and discrimination index) and decreased spontaneous alternation in the Y-maze. D-galactose also decreased the levels of acetylcholinesterase and acetylcholine and increased the level of glial fibrillary acidic protein, ionized calcium-binding adapter molecule 1, tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), interleukin 6 (IL-6), and interferon-gamma (IFN-γ). Treatment with the extract (166 mg/kg) reversed the time spent on the novel object and the discrimination index. It equally increased the percentage of spontaneous alternation. Neurochemical analysis revealed that the extract markedly alleviated acetylcholinesterase activity and neuroinflammation. These observations were corroborated by the reduction in neuronal loss. Taken together, these results suggest that Ziziphus jujuba aqueous extract possesses an antiamnesic effect. This effect seems to involve cholinergic and anti-inflammatory modulations. This, therefore, claims using this plant in the treatment of dementia in Cameroon subject to further studies and trials.

Copper(II) complex as a turn on fluorescent sensing platform for acetylcholinesterase activity with high sensitivity

Acetylcholinesterase (AChE) is an important enzyme associated with many nervous diseases, demonstrating the great need for smarter sensing platform with improved sensitivity, selectivity and simplified operation. A "turn on" fluorometric assay is described herein for AChE activity detection, according to the specific enzyme catalyzed reaction of acetylcholine (ATCh) by AChE, which generates thiocholine (TCh) as the product. The well-designed fluorescent probe HBTP possesses ESIPT (Excited State Intramolecular Proton Transfer) nature, leading to a larger Stokes shift, which could be quenched upon coordination with Cu²⁺. The fluorescence-silent HBTP-Cu²⁺ complex could be broken by TCh generated from reaction of ATCh with AChE, giving rise to HBTP release which originates from competitive coordination of TCh with Cu²⁺. This complex probe HBTP-Cu²⁺ offers a limit detection as low as 0.02 mU mL^-1, which is lower than most reported literatures. Furthermore, both HBTP-Cu²⁺ and HBTP show little toxicity to live cells and is available in visualizing cellular AChE activity.

Assessment of Enzyme Inhibition: A Review with Examples from the Development of Monoamine Oxidase and Cholinesterase Inhibitory Drugs

The actions of many drugs involve enzyme inhibition. This is exemplified by the inhibitors of monoamine oxidases (MAO) and the cholinsterases (ChE) that have been used for several pharmacological purposes. This review describes key principles and approaches for the reliable determination of enzyme activities and inhibition as well as some of the methods that are in current use for such studies with these two enzymes. Their applicability and potential pitfalls arising from their inappropriate use are discussed. Since inhibitor potency is frequently assessed in terms of the quantity necessary to give 50% inhibition (the IC50 value), the relationships between this and the mode of inhibition is also considered, in terms of the misleading information that it may provide. Incorporation of more than one functionality into the same molecule to give a multi-target-directed ligands (MTDLs) requires careful assessment to ensure that the specific target effects are not significantly altered and that the kinetic behavior remains as favourable with the MTDL as it does with the individual components. Such factors will be considered in terms of recently developed MTDLs that combine MAO and ChE inhibitory functions.

Highly sensitive assay for acetylcholinesterase activity and inhibition based on a specifically reactive photonic nanostructure

Assays for acetylcholinesterase (AChE) with high sensitivity and high selectivity as well as facile manipulation have been urgently required in various fields. In this work, a reaction-based photonic strategy was developed for the efficient assay of AChE activity and inhibition based on the synergetic combination of the specific thiol-maleimide addition reaction with photonic porous structure. It was found that various applications including detection of AChE activity, measurement of the related enzymatic kinetics, and screening of inhibitors could be efficiently implemented using such strategy. Remarkably, the unique photonic nanostructure endows the constructed sensing platform with high sensitivity with a limit of detection (LOD) of 5 mU/mL for AChE activity, high selectivity, and self-reporting signaling. Moreover, the label-free solid film-based sensing approach described here has advantages of facile manipulation and bare-eye readout, compared with conventional liquid-phase methods, exhibiting promising potential in practical application for the AChE assay.

Real-time fluorometric assay for acetylcholinesterase activity and inhibitor screening through the pyrene probe monomer-excimer transition

A choline labeled pyrene probe (Py-Ch) was designed and synthesized. Poly(vinylsulfonate) (PVS) could induce Py-Ch aggregation. The aggregation and deaggregation process could be finely controlled by the acetylcholinesterase (AChE) enzymatic hydrolysis of Py-Ch. The resulting excimer-monomer transition provided a facile way for real-time AChE activity fluorometric assay and inhibitor screening.

Cholinergic properties of soy

OBJECTIVES

Soybeans have been shown to have numerous health benefits, but the underlying mechanisms are poorly understood. The aim of this study was to characterize some pharmacologic properties of active substances in aqueous soy extract.

METHODS

The pharmacologic actions of the extract were tested by measuring mechanical activity of isolated guinea-pig ileum in an organ bath.

RESULTS

The ileum contracted in response to soy extract in a concentration-dependent manner. This response was unaffected by the nerve blocker tetrodotoxin (10(-6) M) but was completely inhibited by atropine (10(-9) M), indicating an action via muscarinic receptors on the muscle. In the presence of the M(3) muscarinic antagonist 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide and to a lesser extent in the presence of the M(2) muscarinic antagonist 11-([2-[(diethylamino)methyl]-1-piperidinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one, the response was decreased. When acetylcholine (ACh) esterase inhibitors were added to the medium before the addition of soy extract, the response to the extract was potentiated. Preincubation of the extract with exogenous ACh esterase reduced its activity. The response to choline, ACh, and phosphorylcholine was also tested, and none of these substances accurately replicated the response to soy extract. However, some qualitative similarities were observed between the effect of choline and ACh to that of the extract.

CONCLUSION

These results indicate the presence of an ACh-like substance in soy. Due to the abundance and importance of muscarinic receptors, the presence of a cholinergic substance in soy could have numerous implications. The role of this substance in the beneficial effect of soy on various body systems merits further investigation.

Behavioural correlates of the release and subsequent action of acetylcholinesterase secreted in the substantia nigra

Acetylcholinesterase is secreted in the central nervous system (independently of cholinergic transmission) in a non-classic, non-enzymatic capacity. A light-emitting reaction has recently been established that demonstrates release of this protein from the substantia nigra of a guinea pig with a temporal resolution corresponding to real time, i.e. 'on-line'. In this study the technique has been applied to investigate the significance of this novel phenomenon in the generation of specific types of movement. During locomotion a 'pulsatile' release of acetylcholinesterase occurs much more frequently than in other situations. However, these pulses of released acetylcholinesterase are of shorter duration than the respective periods of locomotion that caused them. Furthermore, as episodes of movement are repeated, the release of acetylcholinesterase becomes less likely. These observations suggest that the phenomenon does not simply reflect ongoing movement. Indeed, chewing behaviour is frequently initiated when acetylcholinesterase release occurs during locomotor activity. Hence, acetylcholinesterase released in association with locomotion may favour the onset of further types of movement.

Synthesis and screening for antiacetylcholinesterase activity of (1-benzyl-4-oxopiperidin-3-ylidene)methylindoles and -pyrroles related to donepezil

The design, synthesis, and rapid evaluation of a new class of acetylcholinesterase (AChE) inhibitors related to donepezil are reported. A molecular dynamics simulation of the complex between AChE and one representative compound of the series showed a possible inhibitor binding mode in which favorable interactions are formed between the benzylpiperidinone moiety and some active-site residues. The biochemical evaluation of this newly synthesized series was performed using a chemiluminescent method suitable for high-throughput screening.

Differential release of acetylcholinesterase in vivo, from the guinea pig substantia nigra compared to the caudate putamen following dopamine depletion

In the substantia nigra acetylcholinesterase may have a novel role unrelated to acetylcholine but linked instead to dopamine. Using a sensitive chemiluminescent system, we have investigated the effects of dopamine depletion on the vivo release of acetylcholinesterase in both the substantia nigra and the caudate putamen. Dopamine levels in the caudate putamen were significantly depleted compared to the non-lesioned side, using either of two different toxins for dopaminergic nigrostriatal cells: 6-hydroxydopamine ( 1 or 3 weeks prior to study) or N-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (1 week prior to study). Spontaneous release of acetylcholinesterase from the substantia nigra was significantly reduced following all three pretreatments; however, in the caudate putamen a significant reduction in the spontaneous release of acetylcholinesterase, compared to controls, was only seen in animals studied 1 week after the administration of 6-hydroxydopamine. In all control groups, application of potassium ions (60 mM) evoked a significant release of acetylcholinesterase in the substantia nigra (p < 0.05) and this effect persisted in the surviving neurones following a partial lesion by neurotoxin pre-treatment. The results from this study are discussed in the light of a regulatory mechanism for acetylcholinesterase release from the striatum, which may come into operation depending on the extent of destruction of dopaminergic nigrostriatal neurones.

Assay of cholinesterase using a pro-enhancer of the luminol-H2O2-horseradish peroxidase reaction

2-Naphthyl acetate acts as a pro-enhancer of the luminol-H2O2-horseradish peroxidase reaction. Cholinesterase hydrolyses the bound acetyl group and produces 2-naphthol, and this compound is an enhancer of the chemiluminescent reaction. We studied the kinetics of chemiluminescent emission and the influence of 2-naphthyl acetate and cholinesterase enzyme concentrations. The cholinesterase concentration versus chemiluminescence intensity maximum was linear for cholinesterase between 0 and 181 microU/mL, with a detection limit of 8 microU/mL and a relative standard deviation of 9.5% (n = 3), for a sample containing 90.67 microU/mL of cholinesterase.

Antinociceptive activity of calcitonin and central cholinergic system: behavioural and neurochemical analyses

Behavioural and neurochemical analyses were carried out to investigate the relationship between the antinociceptive activity of porcine calcitonin (pCT) and central cholinergic system in mice and rats. Behavioural studies revealed that the antinociceptive activity of pCT encapsulated in sulphatide-containing liposomes injected intravenously into mice was significantly inhibited by atropine sulphate, but not by atropine methylnitrate, and potentiated by physostigmine, but not by neostigmine. Neurochemical studies using rat brain synaptosomes showed that pCT stimulated synaptosomal sodium-dependent high-affinity choline uptake, which was found to be closely associated with acetylcholine (ACh) synthesis (50-60%). This effect was concentration-dependent. In addition, pCT elicited a biphasic effect on ACh release from synaptosomes with an initial brief period of stimulation and subsequent prolonged inhibition. This stimulation was not affected by atropine sulphate, but markedly reduced by incubation in the presence of diltiazem or in a calcium-free medium, indicating that the modulation of ACh release by the peptide may be mediated by calcium fluxes across the synaptosomal membrane independent of cholinergic receptor activation. However, pCT does not affect the activity of synaptosomal acetylcholinesterase. Therefore, the behavioural study in vivo with the neurochemical analysis in vitro suggests that the central cholinergic system may be involved in the antinociceptive activity of calcitonin.

The relationship between visual stimulation, behaviour and continuous release of protein in the substantia nigra

In the substantia nigra, a protein (acetylcholinesterase) is secreted from the dendrites of dopaminergic pars compacta neurons, in a noncholinergic capacity. This non-classical phenomenon could be influenced by sensory stimulation: the effect of light flashing was investigated on the 'on-line' release of acetylcholinesterase and concomitant behaviour in the guinea-pig. The stimulus induced an increase in release of the protein and the appearance of chewing movements. Similarly, chewing could also be elicited by direct local application of exogenous acetylcholinesterase. The results suggest that visual stimulation causes release of AChE, which in turn facilitates movement. Therefore secretion of this protein within the substantia nigra might form an important intermediary step in visuo-motor interactions.

A noncholinergic action of acetylcholinesterase (AChE) in the brain: from neuronal secretion to the generation of movement

1. In various brain regions, there is a puzzling disparity between large amounts of acetylcholinesterase and low levels of acetylcholine. One such area is the substantia nigra. Furthermore, within the substantia nigra, a soluble form of acetylcholinesterase is released from the dendrites of dopamine-containing nigrostriatal neurons, independent of cholinergic transmission. These two issues have prompted the hypothesis that acetylcholinesterase released in the substantia nigra has an unexpected noncholinergic function. 2. Electrophysiological studies demonstrate that this dendritic release is a function, not of the excitability of the cell from which the acetylcholinesterase is released, but of the inputs to it. In order to explore this phenomenon at the behavioral level, a novel system has been developed for detecting release of acetylcholinesterase "on-line." It can be seen that release of this protein within the substantia nigra can reflect, but is not causal to, movement. 3. Once released, the possible actions of acetylcholinesterase can be studied at both the cellular and the behavioral level. Independent of its catalytic site, acetylcholinesterase has a "modulatory" action on nigrostriatal neurons. The functional consequences of this modulation would be to enhance the sensitivity of the cells to synaptic inputs. 4. Many basic questions remain regarding the release and action of acetylcholinesterase within the substantia nigra and, indeed, within other areas of the brain. Nonetheless, tentative conclusions can be formulated that begin, in a new way, to provide a link between cellular mechanisms and the control of movement.

Endo-exocytotic images and changes in synaptic transmission induced by diamide at a cholinergic junction

Small tissue fragments excised from the electric organ of Torpedo marmorata were treated with diamide, a penetrating thiol oxidizing agent, until synaptic transmission was blocked. At this stage, we found an unexpected number of exo-endocytotic images in the presynaptic plasmalemma. Omega-shaped profiles, some of them coated, were seen in thin sections of fixed tissue and pits opened in the P-face of the presynaptic membrane in freeze-fracture replicas from rapidly-frozen preparations. Diamide-treated specimens were frozen at 1 ms time intervals before, during and after a single electrical stimulus. This stimulation did not result in a further increase in the density of presynaptic pits, not in any change affecting the density or size distribution of intramembrane particles. This result is in contrast with what is observed in untreated specimens where transmission of a nerve impulse is accompanied by a momentary rise in the number of large particles. The density of synaptic vesicles--especially that of a subpopulation of small size vesicles--transiently increased within the first 2 h of diamide treatment. During the first stages of intoxication, diamide prolonged the time course of postsynaptic potentials--both spontaneous and evoked--probably by altering the gating properties of receptors (acetyl-cholinesterase activity was not impaired). Later on, all evoked responses were blocked. The spontaneous transmitter release greatly increased, first in the form of quantal miniature potentials. These then subsided whereas a class of very small potentials was generated at a high frequency. Also under the action of diamide, calcium progressively accumulated in the tissue but the number of synaptic vesicles containing calcium deposits was reduced. It is concluded that diamide causes a marked increase in the number of exo-endocytotic images in the presynaptic membrane, suppresses quantal but not subquantal release, and interferes with calcium sequestration in and extrusion from terminals.

"On-line" measurement of acetylcholinesterase release from the substantia nigra of the freely-moving guinea-pig

Acetylcholinesterase is released from dopaminergic cells within the substantia nigra. The functional significance of this phenomenon has been studied in the freely-moving animal by a novel system for measuring acetylcholinesterase release from the substantia nigra "on-line" and in vivo. In the unanaesthetized guinea-pig the amount of acetylcholinesterase released was significantly greater than during anaesthesia, and release occurred in a more pulsatile manner. In addition, release of acetylcholinesterase could be evoked by either pharmacological or physiological manipulations, i.e. (1) a depolarizing concentration of potassium ions administered locally; (2) metamphetamine, administered systematically, which also resulted in increased locomotor activity; (3) drinking behaviour, elicited by presentation of a water bottle. Although all three treatments were accompanied by an increase in acetylcholinesterase release within the substantia nigra, potassium-evoked release did not cause any detectable change in behaviour. It is therefore suggested that release of the protein acetylcholinesterase within the substantia nigra is not necessarily a direct cause of locomotor activity: rather, it reflects diverse sensorimotor events.

Reactions of 1-bromo-2-[14C]pinacolone with acetylcholinesterase from Torpedo nobiliana. Effects of 5-trimethylammonio-2-pentanone and diisopropyl fluorophosphate

1-Bromo-2-[14C]pinacolone, (CH3)3C14COCH2Br [( 14C]BrPin), was prepared from [1-14C]acetyl chloride and tert-butylmagnesium chloride with cuprous chloride catalyst, followed by bromination. It was examined as an active-site directed label for acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) (AcChE). AcChE, isolated from Torpedo nobiliana, has k(cat) = (4.00 +/- 0.04).10(3) s-1, Km = 0.055 +/- 0.008 mM in hydrolysis of acetylthiocholine, and k(cat) = (5.6 +/- 0.2).10(3) s-1, Km = 0.051 +/- 0.003 mM in hydrolysis of acetylcholine. BrPin, binding in the trimethyl cavity, acts initially as a reversible competitive inhibitor, Ki = 0.20 +/- 0.09 mM, and, with time, as an irreversible covalently bound inactivator. Introduction of 14C from [14C]BrPin into Torpedo AcChE at pH 7.0 was followed by SDS-PAGE, autoradiography and scintillation counting, in the absence and presence of 5-trimethylammonio-2-pentanone (TAP), a competitive inhibitor (Ki = 0.075 +/- 0.001 mM) isosteric with acetylcholine; 1.8-1.9 14C was incorporated per inactivated enzyme unit at 50% inactivation. TAP retarded inactivation by [14C]BrPin, and prevented introduction of 0.9-1.1 14C per unit of enzyme protected. Prior inactivation of AcChE by BrPin prevents reaction with [3H]diisopropyl fluorophosphate [( 3H]DFP). Prior inactivation by DFP or [3H]DFP does not prevent reaction with [14C]BrPin, and this subsequent reaction with BrPin does not displace the [3H] moiety. [14C]BrPin alkylates a nucleophile in the active site, and this reaction does not alkylate or utilize the serine-hydroxyl.

Microtiter assay for acetylcholinesterase

A microtiter plate adaptation of the classical Ellman colorimetric procedure for measurement of acetylcholinesterase activity is described. This method permits use of an enzyme-linked immunosorbent assay plate reader for rapid analysis of multiple samples and is particularly suitable for analysis of acetylcholinesterase activity on sucrose gradients. The novel procedure is rapid and sensitive and does not require use of radioactive material.

A semi-automated fluorimetric method for measuring acetylcholinesterase activity in small volumes of cerebrospinal fluid and tissue extracts using acetylcholine as substrate

A fluorimetric method for the assay of acetylcholinesterase (AChE; EC 3.1.1.7) in tissue extracts and cerebrospinal fluid, using acetylcholine as the substrate, is described. The method is based on the measurement of hydrogen peroxide, formed by the oxidation of choline resulting from the action of AChE on acetylcholine, by means of horseradish peroxidase and 4-hydroxy-3-methoxyphenylacetic acid (HVA) to yield a fluorescent derivative. Choline, if present in any sample to be analysed, is first removed by a modification of the peroxidase reaction during preincubation.