Histamine H3 receptor and cholinesterases as synergistic targets for cognitive decline: Strategies to the rational design of multitarget ligands.

The role of histamine and acetylcholine in cognitive functions suggests that compounds able to increase both histaminergic and cholinergic neurotransmissions in the brain should be considered as promising therapeutic options. For this purpose, dual inhibitors of histamine H3 receptors (H3 R) and cholinesterases (ChEs) have been designed and assessed. In this context, this paper reviews the strategies used to obtain dual H3 R/ChEs ligands using multitarget design approaches. Hybrid compounds designed by linking tacrine or flavonoid motifs to H3 R antagonists were obtained with high affinity for both targets, and compounds designed by merging the H3 R antagonist pharmacophore with known anticholinesterase molecules were also reported. These reports strongly suggest that key modifications in the lipophilic region (including a second basic group) seem to be a strategy to reach novel compounds, allied with longer linker groups to a basic region. Some compounds have already demonstrated efficacy in memory models, although the pharmacokinetic and toxicity profile should be considered when designing further compounds. In conclusion, the key features to be considered when designing novel H3 R/ChEs inhibitors with improved pharmacological profile were herein summarized.

Inhibition on cholinesterase and tyrosinase by alkaloids and phenolics from Aristotelia chilensis leaves.

It is reported in this study the effect of isolates from leaves of Aristotelia chilensis as inhibitors of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase enzymes. The aim of the paper was to evaluate the activity of A. chilensis towards different enzymes. In addition to pure compounds, extracts rich in alkaloids and phenolics were tested. The most active F5 inhibited AChE (79.5% and 89.8% at 10.0 and 20.0 µg/mL) and against BChE (89.5% and 97.8% at 10.0 and 20.0 µg/mL), showing a strong mixed-type inhibition against AChE and BChE. F3 (a mixture of flavonoids and phenolics acids), showed IC50 of 90.7 and 59.6 µg/mL of inhibitory activity against AChE and BChE, inhibiting the acetylcholinesterase competitively. Additionally, F3 showed and high potency as tyrosinase inhibitor with IC50 at 8.4 µg/mL. Sample F4 (anthocyanidins and phenolic composition) presented a complex, mixed-type inhibition of tyrosinase with a IC50 of 39.8 µg/mL. The findings in this investigation show that this natural resource has a strong potential for future research in the search of new phytotherapeutic treatments for cholinergic deterioration ailments avoiding the side effects of synthetic drugs. This is the first report as cholinesterases and tyrosinase inhibitors of alkaloids and phenolics from A. chilensis leaves.

Assessment of anti-cholinesterase activity and cytotoxicity of cagaita (Eugenia dysenterica) leaves.

Eugenia dysenterica ex DC Mart. (Myrtaceae) is a Brazilian tree with pharmacological and biological properties. The aqueous leaf extract, rich in polyphenols, was tested in the human neuroblastoma cell line SH-SY5Y to evaluate its effect on cell viability. The extract and two isolated compounds were also assessed for the potential inhibitory activity on acetylcholinesterase, an enzyme related to Alzheimer's disease. A simple chromatographic method using Sephadex LH-20 was developed to separate catechin and quercetin from the aqueous leaf extract of E. dysenterica. Identification was carried out by spectroscopic techniques IR, UV, and 1H and 13C NMR. The IC50 values were obtained by constructing dose-response curves on a graph with percentage inhibition versus log of inhibitor concentration and compared with physostigmine, a well-known AChE inhibitor. The extract was toxic for SH-SY5Y cells at concentrations higher than 7.8 µg/ml given for 24 h. The decline in SH-SY5Y cell viability appears to be related to its antiproliferative activity. The extract also showed relatively moderate acetylcholinesterase inhibitory activity of 66.33% ± 0.52% at 1.0 mg/ml with an IC50 value of 155.20 ± 2.09 µg/ml. Physostigmine, quercetin, and catechin showed IC50 values of 18.69 ± 0.07, 46.59 ± 0.49, and 42.39 ± 0.67 µg/ml, respectively.

In vitro and in vivo studies of cholinesterases and carboxylesterases in Planorbarius corneus exposed to a phosphorodithioate insecticide: Finding the most sensitive combination of enzymes, substrates, tissues and recovery capacity.

Organophosphate insecticides (OPs) continue to be an important class of agrochemicals used in modern agriculture worldwide. Even though these pesticides persist in the environment for a relatively short time, they show a high acute toxicity that may represent a serious hazard for wildlife. Sub-lethal effects on non-target species are a focus in pest management programs and should be used as biomarkers. Cholinesterases (ChEs) are the most used biomarker of OP exposure in vertebrate and invertebrate species. However, the combined monitoring of ChE and carboxylesterase (CE) activities may provide a more useful indication of exposure and effect of the organisms. The objective of the present work was to find the most sensitive combination of enzyme, substrate, tissue and capacity to recovery of B-esterases in the freshwater gastropod Planorbarius corneus exposed to the OP azinphos-methyl. For this purpose, ChE and CE activities in different tissues of P. corneus (head-foot, pulmonary region, digestive gland, gonads and whole organism soft tissue) were studied. Measurements of ChE activity were performed using three substrates: acetylthiocholine, propionylthiocholine and butyrylthiocholine and CE activity using four different substrates: p-nitrophenyl acetate, p-nitrophenyl butyrate, 1-naphthyl acetate, and 2-naphthyl acetate in control and exposed organisms. Finally, the recovery rates of ChE and CE activities following 48h exposure to azinphos-methyl were analyzed. Our results show a preference for acetylthiocholine as substrate, a high inhibition with eserine (a selective ChE inhibitor) and inhibition with excess of substrate in all the analyzed tissues. The highest ChE and CE activity was found in the pulmonary region and in the digestive gland, respectively. The highest CE Vmax was obtained with 1 and 2-naphthyl acetate in all the tissues. CEs were more sensitive than ChE to azinphos-methyl exposure. The highest sensitivity was found using p-nitrophenyl acetate and butyrate as substrates. On the other hand, CEs of the digestive gland and the pulmonary region were more sensitive than CEs of the whole organism soft tissue. Regarding the recovery of enzyme activities after 48h exposure, ChE and CEs with p-nitrophenyl butyrate reached control values after 14days in the digestive gland and after 21days in the pulmonary region. Our results show marked differences in P. corneus basal ChE and CE activities depending on substrates and the tissue. Also, both tissue-dependent and substrate-dependent variations in sensitivity to azinphos-methyl exposure and recovery were obtained. CEs measured with p-nitrophenyl butyrate in the pulmonary region were the best combination to be used as biomarker of exposure to azinphos-methyl due to their sensitivity and low recovery capacity. Environmental concentrations of azinphos-methyl inhibited CE activity so they could be used as effective biomarkers of aquatic contamination.

Coumarins as cholinesterase inhibitors: A review.

The first report in literature of the isolation of coumarin was in the year 1820. After this report, other papers were published demonstrating the isolation and synthesis of coumarin and analogues. These compounds have been studying along the years for several different pathologies. One of these pathologies was Alzheimer's disease (AD), being the main cause of dementia in the contemporary world. There are two hypotheses to explain the pathogenesis mechanism and disease symptoms, then having the "amyloid hypothesis" and the "cholinergic hypothesis". Some drugs for AD are based on the theory of "cholinergic hypothesis", which objective is to increase the concentration of ACh in the synaptic cleft by the inhibition of cholinesterases. Over the last twenty years, many studies with coumarins compounds were reported as cholinesterases inhibitors. The aim of the present review is to discuss the studies and development of new compounds for AD treatment.

Characterization of cholinesterases in the damselfish Sergeant major (Abudefduf saxatilis).

Cholinesterase (ChE) activity has been used for many years as a biomarker of exposure to organophosphate and carbamate pesticides. Recent studies have demonstrated that there could be biological factors that determine ChE type and levels; thus, juvenile Sergeant major (Abudefduf saxatilis) ChE enzymes were biochemically characterized. ChE enzymes found in the head and trunk were evaluated for their substrate preference and sensitivity to selective inhibitors. The use of the head and trunk was chosen as a strategy to reduce dissection time and to ensure sample uniformity between stations. The results indicated that there are two types of ChE enzymes in the head: acetylcholinesterase (AChE) and atypical butyrylcholinesterase (BChE) that exhibits intermediate characteristics of human AChE and BChE activities. Atypical BChE is predominantly found in the trunk. The results also indicated that the ChE activity found in A. saxatilis may be used as a biomarker in studies monitoring the Mexican Caribbean.

Structural insights into cholinesterases inhibition by harmane ß-carbolinium derivatives: a kinetics-molecular modeling approach.

The natural indole alkaloids, the ß-carbolines, are often associated with cholinesterase inhibition, especially their quaternary salts, which frequently have higher activity than the free bases. Due to lack of information explaining this fact in the literature, the cholinesterase inhibition by the natural product harmane and its two ß-carbolinium synthetic derivative salts (N-methyl and N-ethyl) was explored, together with a combination of kinetics and a molecular modeling approach. The results, mainly for the ß-carbolinium salts, demonstrated a noncompetitive inhibition profile, ruling out previous findings which associated cholinesterase inhibition by ß-carbolinium salts to a possible mimicking of the choline moiety of the natural substrate, acetylcholine. Molecular modeling studies corroborate this kind of inhibition through analyses of inhibitor/enzyme and inhibitor/substrate/enzyme complexes of both enzymes.

Inhibition of two different cholinesterases by tacrine.

Kinetic parameters of the effect of tacrine as a cholinesterase inhibitor have been studied in two different sources: snake venom (Bungarus sindanus) acetylcholinesterase (AChE) and human serum butyrylcholinesterase (BChE). Tacrine inhibited both venom acetylcholinesterase (AChE) as well as human serum butyrylcholinesterase (BChE) in a concentration-dependent manner. Kinetic studies indicated that the nature of inhibition was mixed for both enzymes, i.e. Km values increase and Vmax decrease with the increase of the tacrine concentration. The calculated IC50 for snake venom and for human serum were 31 and 25.6 nM, respectively. Ki was observed to be 13 nM for venom acetylcholinesterase (AChE) and 12 nM for serum butyrylcholinesterase (BChE). KI (constant of AChE-ASCh-tacrine complex into AChE-ASCh complex and tacrine) was estimated to be 20 nM for venom and 10 nM for serum butyrylcholinesterase (BChE), while the gammaKm (dissociation constant of AChE-ASCh-tacrine complex into AChE-tacrine complex and ASCh) were 0.086 and 0.147 mM for snake venom AChE and serum BChE, respectively. The present results suggest that this therapeutic agent used for the treatment of Alzheimer's disease can also be considered an inhibitor of snake venom and human serum butyrylcholinesterase. Values of Ki and KI show that tacrine had more affinity with these enzymes as compared with other cholinesterases from the literature.

Modificación de un método para colinesterasa plasmática empleando la reducción del ferricianuro como indicador / Modification in the method for serum cholinesterase in ferricyanide reduction how indicatory

Se describe la modificación de un método para la cuantificación de colinesterasa plasmática mediante monitoreo continuo empleando ferricianuro como indicador. La tiocolina liberada de la propioniltiocolina reduce el ferricianuro a ferrocianuro y la disminición de absorbancia a 405 nm es proporcional a la actividad de la enzima. Las precisiones día a día para muestras con valores de colinesterasa bajos y altos mostraron coeficientes de variación de 3,2 y 1,2 por ciento y en un mismo día de 1,1 y 0,52 por ciento respectivamente. La bilirrubina no presenta una interferencia importante y cada 50mg/dL de hemoglobina producen una interferencia de -4 por ciento. El reactivo de ferricianuro almacenado en botella ámbar es estable por al menos 3 meses a temperatura ambiente y 6 meses a 4-8 §C. Al comparar los resultados con un método que emplea la reacción de Ellman se obtuvo una ecuación de regresión lineal de Y = 1,22 (X) - 732, con un coeficiente de correlación (r) de 0,988 y una desviación estándar sobre la línea de regresión (Sy/x) de 378 U/L. (Rev Cost Cienc Med 1999; 20(1,2): 17-27) PALABRAS CLAVE: Colinesterasa sérica, organofosfatos, carbamatos, pesticidas, métodos colorimétrico, toxicología

Some kinetic and toxicological characteristics of thoracic ganglia cholinesterase of Chasmagnathus granulata (Decapoda, Grapsidae).

In this study, some kinetic and toxicological parameters of the thoracic ganglia cholinesterase from the estuarine crab Chasmagnathus granulata were determined. Effects of the type and concentration of substrate, pH (6.80-8.50), incubation temperature (5-35 degrees C) and eserine on the enzyme activity were studied. Enzymatic activity was higher at pH 7.40 and 8.00 and significantly reduced at lower temperatures (5-10 degrees C). Employing acetylthiocholine iodide (ATCh) as substrate, the K(m) and Vmax were estimated as 0.28 mM and 1.75 mumol.mg protein-1.min-1, respectively. A 14.11 and 24.51% decrease in enzyme activity were registered at 4.62 and 9.24 mM of ATCh, respectively. Using propionylthiocholine iodide as substrate, the K(m) and Vmax were estimated as 0.16 mM and 0.91 mumol.mg protein-1.min-1, respectively. The IC50 for eserine was estimated as 5.3 x 10(-4) mM. The Ki estimated for eserine (8.10 mM-1.min-1) indicates that the thoracic ganglia cholinesterase from C. granulata showed a low ability to generate an irreversible enzyme-inhibitor complex. The higher enzymatic activity registered with ATCh and the enzyme inhibition observed at high concentration of this substrate, suggest that thoracic ganglia cholinesterase from C. granulata is an acetylcholinesterase.

Niveles de actividad de colinesterasa en trabajadores del Ica tibaitatá programa de vigilancia epidemiológica / Colinesterasic activity in workers at ICA

Se realizó un estudio para conocer los niveles de actividad de colinesterasa en los trabajadores del ICA Tibaitatá, y su correlación con la exposición ocupacional a plaguicidas inhibidores de colinesterasa (Organofosforados y Carbamatos). Se tuvieron en cuenta también las siguientes variables: sexo, edad, uso de elementos de protección personal, antiguedad (Tiempo de exposición), ocupación, exposición extraocupacional, embarazo, lactancia, menstruación y presencia de náuseas y síntomas como vómito. El centro de investigación de Tibaitatá, el mas grande del ICA, está ubicado en la sabana de Bogotá y allí se desarrollan trabajos de investigación agrícola y pecuaria que implican exposición a plaguicidas en diversas labores. Las determinaciones de colinesterasa se hicieron por el método colorimétrico de campo, con muestra de sangre capilar y utilizando el equipo de levibond. se consideran anormales o bajos los niveles inferiores al 75 por ciento. Se tomo una muestra de 323 trabajadores, de los cuales 95 (29,4 por ciento) estaban directamente expuestos en su trabajo a plaguicidas inhibidores de colinesterasa. A estos se les aplicaron dos encuestas para conocer las variables y luego se les tomo muestra de sangre capilar, la cual fue procesada en el mismo lugar. Para comprobar la exposicion ocupacional a plaguicidas, se hizo una visita de inspeccion a las distintas dependencias. Para controlar la calidad de los resultados por el metodo de lovibons, se confrontaron los "blancos" de cada sesion con la prueba de colinesterasa por el método electrometrico de Michel, encontrandose correlacionados entre si