Acetylcholinesterase interaction with a lipoprotein matrix

The effect of temperature on the activity of acetylcholinesterase preparations from rat brain

Homogenization of rat brain with dilute buffer shows that about 15% of the acetylcholinesterase is soluble while the remaining 85% is present in a membrane-bound form which can be brought into solution by extraction with Triton X-100. The effect of temperature on the values of V(max) and K(m) of the buffer-soluble, the membrane-bound and the Triton-soluble forms of acetylcholinesterase have been compared and the results discussed in terms of possible changes in the conformation, dissociation or aggregation of the enzyme molecule. Gradient-gel electrophoresis of the soluble preparations carried out at 4 degrees C or 37 degrees C suggest that the normal tetrameric structure present at 4 degrees C dissociates into monomers and forms some higher molecular weight species at 37 degrees C. The effect of prior storage of the brains in toluene on these properties is also considered.

Behavioral and neurochemical effects of proline

Proline is an amino acid with an essential role for primary metabolism and physiologic functions. Hyperprolinemia results from the deficiency of specific enzymes for proline catabolism, leading to tissue accumulation of this amino acid. Hyperprolinemic patients can present neurological symptoms and brain abnormalities, whose aetiopathogenesis is poorly understood. This review addresses some of the findings obtained, mainly from animal studies, indicating that high proline levels may be associated to neuropathophysiology of some disorders. In this context, it has been suggested that energy metabolism deficit, Na(+),K(+)-ATPase, kinase creatine, oxidative stress, excitotoxicity, lipid content, as well as purinergic and cholinergic systems are involved in the effect of proline on brain damage and spatial memory deficit. The discussion focuses on the relatively low antioxidant defenses of the brain and the vulnerability of neural tissue to reactive species. This offers new perspectives for potential therapeutic strategies for this condition, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on special diets poor in proline.

Effect of oxidative stress induced by paradoxical sleep deprivation on the activities of Na+, K+-ATPase and acetylcholinesterase in the cortex and hippocampus of rat

Several studies revealed the importance of paradoxical sleep as a homeostatic mechanism by which the brain can control oxidative stress. The aim of the present study is to investigate the effect of 72 h of paradoxical sleep deprivation on the oxidative stress markers and its insults on the activities of Na(+), K(+)-ATPase and acetylcholinesterase in the cortex and hippocampus of albino rat. Animals were subjected to paradoxical sleep deprivation for 72 h. At the end of the experiment, the rats were sacrificed, and catalase activity, levels of reduced glutathione, lipid peroxidation, and nitric oxide were assayed together with the activities of Na(+), K(+)-ATPase and acetylcholinesterase in the cortex and hippocampus. The present study revealed a significant increase in lipid peroxidation accompanied by a significant decrease in reduced glutathione in the cortex and hippocampus. Na(+), K(+)-ATPase decreased significantly in both areas. However, acetylcholinesterase showed a significant increase in the investigated brain regions. The present data showed that 72 h of paradoxical sleep deprivation induced oxidative stress in the cortex and hippocampus. It could be suggested that the inhibition of Na(+), K(+)-ATPase and the increased acetylcholinesterase activity may underlie memory impairment, increased brain excitability, and anxiety induced by paradoxical sleep deprivation.

Effect of isoquinoline alkaloids from two Hippeastrum species on in vitro acetylcholinesterase activity

The treatment of neurological disorders and neurodegenerative diseases is related to the levels of acetylcholine (ACh) through the inhibition of acetylcholinesterase (AChE). Galanthamine, an important alkaloid isolated from the Amaryllidaceae family, is approved for the pharmacological treatment of Alzheimer's disease (AD) and acts by inhibiting the acetylcholinesterase (AChE) activity. In the present study, Ellman's method was used to verify the inhibition of AChE activity of some isoquinolines alkaloids such as galanthamine, montanine, hippeastrine and pretazettine. At the concentrations 1mM, 500 microm and 100 microm, galanthamine presented an AChE inhibition higher than 90%. Montanine inhibited, in a dose-dependent manner, more than 50% of the enzyme at 1mM concentration. With the concentrations 500 microm and 100 microm, 30-45% of AChE activity inhibition was detected. The alkaloids hippeastrine and pretazettine presented no significant inhibition of the AChE activity. The results demonstrate that montanine significantly inhibits AChE activity at the tested concentrations, suggesting the necessity of further investigations on this alkaloid use in treating neurological disorders.

Supplementation with vitamins E plus C or soy isoflavones in ovariectomized rats: effect on the activities of Na(+), K (+)-ATPase and cholinesterases

Since a previous study demonstrated that ovariectomized rats present an activation of Na(+), K(+)-ATPase and acetylcholinesterase (AChE) activities, in the present study we investigated the influence of vitamins E plus C or soy isoflavones on the effects elicited by ovariectomy on the activities of these enzyme in hippocampus of ovariectomized rats. We also determined the effect of the same compounds on the reduction of serum butyrylcholinesterase (BuChE) activity caused by ovariectomy. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomized. Seven days after surgery, animals were treated for 30 days with a single daily intraperitoneous injection of vitamins E (40 mg/kg) plus C (100 mg/kg) or saline (control). In another set of experiments, the rats were fed for 30 days on a special diet with soy protein or a standard diet with casein (control). Rats were sacrificed after treatments and the hippocampus was dissected and serum was separated. Data demonstrate that vitamins E plus C reversed the activation of Na(+), K(+)-ATPase and AChE in hippocampus of ovariectomized rats. Conversely, soy protein supplementation reversed the increase of AChE activity, but not of Na(+), K(+)-ATPase activity, caused by ovariectomized group. Neither treatment was able to reverse the reduction of serum BuChE activity. Furthermore, treatments with vitamins E plus C or soy were unable to reverse the decrease in estradiol levels caused by ovariectomy. Our findings show that the treatment with vitamins E plus C significantly reversed the effect of ovariectomy on hippocampal Na(+), K(+)-ATPase and AChE activities. However, a soy diet that was rich in isoflavones was able to reverse just the increase of AChE. Neither treatment altered the reduction in serum BuChE activity. Taken together, these vitamins and soy may have a protective role against the possible brain dysfunction observed in some menopause women. Vitamins E plus C and soy isoflavones may be a good alternative as a novel therapeutic strategy.

Intrastriatal hypoxanthine administration affects Na+,K+‐ATPase, acetylcholinesterase and catalase activities in striatum, hippocampus and cerebral cortex of rats

The aim of this study was to investigate the effects of a single intrastriatal injection of hypoxanthine, the major metabolite accumulating in Lesch-Nyhan disease, on Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities in striatum, cerebral cortex and hippocampus of rats at different post-infusion periods. Adult Wistar rats were divided in two groups: (1) vehicle-injected group (control) and (2) hypoxanthine-injected group. For Na(+),K(+)-ATPase activity determination, the animals were sacrificed 3h, 24h and 7 days after drug infusion. For the evaluation of acetylcholinesterase and catalase activities, the animals were sacrificed 30min, 3h, 24h and 7 days after hypoxanthine infusion. Results show regional and time dependent effects of hypoxanthine on Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities. The in vitro effect of hypoxanthine on the same enzymes in striatum was also investigated. Results showed that hypoxanthine inhibited Na(+),K(+)-ATPase, but not the activities of acetylcholinesterase and catalase in rat striatum. We suggest that these modification on cerebral biochemical parameters (Na(+),K(+)-ATPase, acetylcholinesterase and catalase activities) induced by intrastriatal administration of hypoxanthine in all cerebral structures studied, striatum, hippocampus and cerebral cortex, could be involved in the pathophysiology of Lesch-Nyhan disease.

Ovariectomy increases Na+, K+-ATPase, acetylcholinesterase and catalase in rat hippocampus

In the present work we investigated the effect of ovariectomy on Na+, K+-ATPase and acetylcholinesterase (AChE) activities in rat hippocampus. We also studied some parameters of oxidative stress, namely total radical-trapping antioxidant potential (TRAP), thiobarbituric acid-reactive substances (TBA-RS), as well as the antioxidant enzyme activities superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities. Our hypothesis is that ovariectomy might cause alterations in essential enzyme activities necessary to brain normal functioning and that these chances could be caused by oxidative stress. Female adult Wistar rats were divided into three groups: (1) naive (control); (2) sham-operated; and (3) ovariectomized. Thirty days after ovariectomy rats were sacrificed. Results showed that rats subjected to ovariectomy presented a significant increase in Na+, K+-ATPase, AChE and CAT activities, but did not change the oxidative stress parameters studied when compared to sham or naive rats. Since ovariectomy mimics postmenopausal changes, our findings showing alteration in the activities of brain Na+, K+-ATPase, AChE and CAT may be related to problems in postmenopausal women.

Ovariectomy enhances acetylcholinesterase activity but does not alter ganglioside content in cerebral cortex of female adult rats

In the present work we investigated the effect of ovariectomy on acetylcholinesterase (AChE) activity and ganglioside content in cerebral cortex of female rats. We also studied the activity of butyrylcholinesterase (BuChE) in serum of these animals. Adult Wistar rats were divided into three groups: (1) naive females (control), (2) sham-operated females and (3) castrated females (ovariectomy). Thirty days after ovariectomy, rats were sacrificed by decapitation without anaesthesia. Blood was collected and the serum used for BuChE determination. Cerebral cortex was homogenized to determine AChE activity and extracted with chlorophorm:methanol for ganglioside evaluation. Results showed that rats subjected to ovariectomy presented a significant increase of AChE activity, but did not change the content and the profile of gangliosides in cerebral cortex when compared to sham or naive rats. BuChE activity was decreased in serum of rats ovariectomized. Our findings suggest that the alteration in the activity of brain AChE, as well as serum BuChE activity caused by ovariectomy may contribute to the impaired cognition and/or other neurological dysfunction found in post-menopausal women.

Na+,K(+)-ATPase and acetylcholinesterase activities: changes in postnatally developing rat brain induced by bilirubin

Na+,K(+)-ATPase, Mg(++)-ATPase, and acetylcholinesterase activities were determined in brain homogenates of rats in different ages, which were decapitated 30 min after administration of various bilirubin doses. Bilirubin serum and brain tissue levels should be dependent upon the dose administered. At these concentrations, a progressive enzyme inactivation was observed, which reached 25-30% for acetylcholinesterase and 70-80% for Na+,K(+)-ATPase in neonate rats and 15-20% for acetylcholinesterase and only 30-40% for Na+,K(+)-ATPase in the brain of aged rats (20 mo). However, Mg(++)-ATPase activity was not affected by bilirubin deposition in the developing brain. Moreover, brain albumin content increased 53% in suckling, 40% in adult, and 33% in aged rats at high drug administration. These results may indicate an opening of the blood-brain barrier and a bilirubin entry into the rat brain. The bilirubin immediate toxic effects on brain acetylcholinesterase and Na+,K(+)-ATPase, and probably on brain electrical activity, may be modulated by the developmental state of membrane-bound enzymes.

The effects of ethanol on the structural stability of acetylcholine receptor and the activity of various molecular forms of acetylcholinesterase

The actions of ethanol on the structural stability of acetylcholine receptor (AchR)-enriched membrane vesicles and the activity of various molecular forms of acetylcholinesterase (AchE) were investigated, using the receptor and the enzyme isolated from the electric organ of Torpedo californica. In the presence of ethanol up to 200 mM, the thermogram of AchR-enriched membranes exhibited no significant decrease in the temperature (td) of receptor transition at 57 degrees C, but a decrease in the enthalpy change (delta Hd) indicated a slight ethanol-induced structural perturbation. The presence of 12.5 nmol alpha-bungarotoxin also caused a decrease in delta Hd. A complete loss of the receptor transition was observed at a higher concentration 500 nmol of alpha-bungarotoxin and no recovery of the transition was found with the addition of 200 mM ethanol. The results suggested a noncompetitive interaction of ethanol with the receptor. In the presence of 200-1000 mM ethanol, the activity of two soluble forms of AchE, a higher (117 S) aggregate and a lower (10 S) aggregate was not significantly affected. Comparing the activity of these two aggregates over a wide concentration range of ethanol (200-2000 mM) revealed no obvious difference in the level of ethanol effect between them. However, after removal of ethanol, the higher aggregate form of AchE exhibited a greater recoverability of the activity, suggesting a possible slightly greater structure-functional stability for it. Studies of soluble AchE and membrane-bound AchE showed that the presence of 200 or 600 mM ethanol caused a greater level of inhibition in membrane-bound enzyme than in soluble enzyme, possible due to a disruption of protein-lipid interaction needed to maintain the conformation of membrane-bound AchE. Interestingly, at a much higher concentration of ethanol (2.0 M), membrane-bound AchE became more resistant to ethanol than did the soluble forms of AchE. In this case, the effective concentration of ethanol felt by the enzyme was expected to be less for membrane-bound AchE, owing to ethanol's solubility in lipids.

Differential effect of anionic and cationic drugs on the synaptosome-associated acetylcholinesterase activity of dog brain

The evoked effects of the negatively charged drugs phenobarbital and barbituric acid, the positively charged imipramine, perphenazine and trifluoperazine, and the neutral primidone, on the synaptosome-associated acetylcholinesterase activity were studied. A marked increase in the enzyme activity was exhibited in the presence of low concentrations (up to 3 mM) of phenobarbital, barbituric acid and primidone. Higher concentrations (up to 10 mM), however, led to a progressive inhibition of the enzyme activity. However, the activity of the enzyme was not affected by imipramine, but it was decreased by perphenazine and trifluoperazine. Arrhenius plots of acetylcholinesterase activity exhibited a break point at 23.4 degrees C for the untreated (control) synaptosomes, which was shifted to around 16 degrees C in the synaptosomes treated with the charged drugs. The allosteric inhibition by F- of acetylcholinesterase was studied in control synaptosomes and in those treated with the charged drugs. Changes in the Hill coefficients in combination with changes in Arrhenius activation energy produced by the charged drugs would be expected if it is assumed that charged drugs 'fluidize' the synaptosomal plasma membranes.

Aggregation properties of the acetylcholinesterase from the central nervous system of Manduca sexta

The CNS of the tobacco hornworm, Manduca sexta, provides a rich source of true acetylcholinesterase (AChE, acetylcholine, hydrolase, EC 3.1.1.7). Optimal extraction of the enzyme was obtained with a nonionic detergent at high ionic strength (1% Triton X-100, 0.5 M NaCl). Velocity sedimentation of the Triton + salt-extracted enzyme demonstrated a single peak whose sedimentation coefficient was dependent upon the enzyme concentration layered on top of the gradient. When more than 20 units were applied to the gradient, a sedimentation coefficient of 8.6 S (205,000) was obtained, and extrapolation to zero units yielded a 5.7 S (110,500) species. Sedimentation in the absence of detergents (1.0 M NaCl or 10 mM phosphate buffer, pH 7.4) yielded pelleted enzyme and species with mean values of 18.6 S (650,000) and 17.5 S (600,000), respectively. The detergent-extracted enzyme also demonstrated a concentration-dependent size in gel filtration experiments. When less than 300 units were applied to the column, a single species was recovered, with a molecular radius of 40.15 +/- 2.08 A (108,000) or 43.4 +/- 2.38 A (117,000) calculated by different methods. If the sample contained 300 to 1,300 units, two species were observed, with molecular radii of 40.15 +/- 2.08 A or 43.4 +/- 2.38 A and 78.4 +/- 3.94 A (319,000) or 80.25 +/- 3.01 A (326,000). Velocity sedimentation and gel filtration of AChE have demonstrated that the enzyme has a minimum molecular weight of approximately 110,000 and also exists as higher-molecular-weight aggregates of this value.

Action of barbiturates on activity of acetylcholinesterase from synaptosomal membranes

The acetylcholinesterase from synaptosomal membranes is inhibited by anesthetics: Nembutal, brietal, and thiopental. Nembutal and brietal decrease the Km for acetylthiocholine, without changes in Vmas. A noncompetitive type of inhibition is produced by thiopental. This anesthetic decreases Arrhenius plot discontinuity by about 4 degrees C and increases activation energies. Nembutal and brietal do not change Arrhenius plot discontinuities, but they increase activation energies. These results suggest that barbiturates change lipid-protein interactions in synaptosomal membranes.

Multiple molecular forms of acetylcholinesterase from human erythrocyte membranes. Interconversion and subunit composition of forms separated by density gradient centrifugation in a zonal rotor

Quantitative separation of eight multiple molecular forms of acetylcholinesterase isolated from human erythrocyte membranes was accomplished by sucrose density gradient centrifugation in a zonal rotor. Hydrodynamic properties of the four most abundant oligomers were investigated by analytical ultracentrifugation. The S20, w values obtained for these components ranged from 12.5 S to 19.0 S with corresponding molecular weights between 500 000 and 1 131 000. These oligomers are built up of 6-14 subunits. Analysis of each isolated homogenous form after storage for 6 months at 4 degrees C revealed interconversion into the original eight components. Upon addition of Triton X-100 the oligomers disaggregate to yield a single 7-S form, which reaggregates upon removal of the detergent. Such reaggregation can be prevented by chaotropic ions indicating that hydrophobic interactions are important in the formation of these oligomeric forms.

Isoenzyme status and genetic variability of serum esterases in the lesser snow goose, Anser caerulescens caerulescens

A maximum of 22 bands comprising four esterase subgroups--acetylesterase, carboxylesterase, cholinesterase, and acetylcholinesterase--were detected following electrophoresis of lesser snow goose sera on polyacrylamide gels. A minimum of seven structural genes was surmised to be involved in the biosynthesis of these enzymes following physiochemical characterizations. The genetic variability of these loci was calculated to be 1.25% average heterozygosity, while 14.3% of the loci were polymorphic. These estimates of genetic variability were substantially lower than those reported for other vertebrate species. The low degree of genetic variability found in snow goose serum esterases coupled with the extensive protein multiplicity observed may possibly reflect an adaptive strategy based on "biochemical plasticity" rather than genic heterozygosity for this species. The nature of evolutionary forces acting upon multiple enzyme systems such as esterases is discussed. The concept of "conditional neutrality" is introduced and defined within this context.

Acetylcholinesterase and its association with lipid

Human erythrocyte acetylcholinesterase preparations which vary in lipid content, from lipid-rich to lipid-poor, have been successfully prepared using deoxycholate. It was found that the lipid content of the enzyme decreased gradually as the deoxycholate concentration used in its preparation was increased. The binding of lipid to lipid-poor preparations of the enzyme has been investigated. It was found that the activity of such preparations was highly dependent on their phospholipid contents. Maximum specific activity was associated with a fixed phospholipid content. The lipid-poor enzyme was highly activated by addition of either endogenous(membrane) or exogenous lipid. Based on the data presented, it was concluded that acetylcholinesterase is a phospholipoprotein, and its activity is highly dependent on its phospholipid component.

Multiple forms of acetylcholinesterase from rat erythrocytes. Effect of fat-free diet

Electrophoretic patterns of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) from rat erythrocyte were studied. The enzyme was solubilized by the following treatments: a) Triton X-100, b) sodium deoxycholate, or c) ultrasonic irradiation. When the erythrocyte membrane was solubilized by Triton X-100 at concentrations higher than 0.3%, by 10 mM sodium deoxycholate, or by ultrasonic irradiation for more than 5 min, a single band of acetylcholinesterase activity appeared in the gel. Two bands of activity were stained in the gel when the membrane was solubilized by Triton X-100 at concentrations between 0.1--0.2%, or by ultrasound for 5 min. Electrophoretic patterns of acetylcholinesterase from rats fed a fat-sufficient diet were similar to those for the enzyme from animals fed a fat-free diet. The recombination of lipids with the enzyme eluted from the gels confirmed the "phenotypic allosteric desensitization phenomenon".

Studies of the acetylcholinesterase from houseflies (Musca domestica L.) resistant and susceptible to organophosphorus insecticides

Acetylcholinesterase from the heads of insecticide-resistant and -susceptible houseflies (Musca domestica L.) was studied in vitro. The enzymes could not be distinguished electrophoretically, and their behaviour on polyacrylamide-disc-gel electrophoresis was influenced by the presence of Triton X-100 in both the homogenate and the gels. In the absence of detergent, the acetylcholinesterase was heterogeneous, but behaved as a single enzyme when it was present. By analogy with studies of acetylcholinesterase from other sources, these observations were attributed to aggregation of the enzyme when not bound by membranes. The enzyme from resistant flies was more slowly inhibited than the susceptible enzyme, bimolecular rate constants (ki) differing by approx. 4-20-fold for a range of organophosphorus compounds. The kinetics of inhibition of acetylcholinesterase were consistent with the results of electrophoresis, i.e. they corresponded to those of a single enzyme in the presence of Triton X-100, but a mixture of enzymes in its absence. The susceptibility of the more sensitive components in these mixtures was determined.