Variation In Acetylcholinesterase Activity Research Articles

A novel fluorescence based assay for the detection of organophosphorus pesticide exposed cholinesterase activity using 1-naphthyl acetate

Acetylcholinesterase (AChE) is the primary target of organophosphorus pesticides (OPs). Ellman's method using Acetylthiocholine (ATCh) is the standard approach for the detection of AChE activity. Though ATCh is a popular substrate, it has certain drawbacks as well. Because of these limitations, there is a need for the development of reliable and rapid assays for determination of AChE activity in cases of OP poisoning. In the present work, we have used 1-Naphthyl acetate (1-NA) as a fluorogenic substrate for the estimation of AChE activity of human erythrocytes. It is well known that due to inter-individual variation in AChE activity, the baseline value cannot be correctly predicted. Therefore, using 1-NA, we have developed a rapid, sensitive and baseline free assay for the estimation of AChE activity. The assay is based on reactivation and fluorescence quenching using a cocktail of oximes for the determination of cholinesterase activity in a post-exposure sample. Moreover, it is free from interference due to oximolysis which is an established limitation of ATCh. We feel that such an assay using 1-NA has the potential to be explored at the point of care for rapid detection of OP poisoning.

Variations in Acetylcholinesterase Activity within Human Cortical Pyramidal Neurons Across Age and Cognitive Trajectories.

We described an extensive network of cortical pyramidal neurons in the human brain with abundant acetylcholinesterase (AChE) activity. Emergence of these neurons during childhood/adolescence, attainment of highest density in early adulthood, and virtual absence in other species led us to hypothesize involvement of AChE within these neurons in higher cortical functions. The current study quantified the density and staining intensity of these neurons using histochemical procedures. Few faintly stained AChE-positive cortical pyramidal neurons were observed in children/adolescents. These neurons attained their highest density and staining intensity in young adulthood. Compared with the young adult group, brains of cognitively normal elderly displayed no significant change in numerical density but a significant decrease in staining intensity of AChE-positive cortical pyramidal neurons. Brains of elderly above age 80 with unusually preserved memory performance (SuperAgers) showed significantly lower staining intensity and density of these neurons when compared with same-age peers. Conceivably, low levels of AChE activity could enhance the impact of acetylcholine on pyramidal neurons to counterbalance other involutional factors that mediate the decline of memory capacity during average aging. We cannot yet tell if elderly with superior memory capacity have constitutively low neuronal AChE levels or if this feature reflects adaptive neuroplasticity.

Temporal and seasonal variation in acetylcholinesterase activity and glutathione-S-transferase in amphipods collected in mats of Lyngbya wollei in the St-Lawrence River (Canada)

Mats of filamentous algae Lyngbya wollei cover large areas on top of the sediments along the St-Lawrence River. Like most cyanobacteria, L. wollei produce toxins, named lyngbyatoxin (LYNGTX), an analog of saxitoxin. In order to verify the neurotoxic potential of these filamentous cyanobacteria, we collected amphipods within local vegetation at three sites in summer months: a site rich in L. wollei (Lake St-Louis [LSL]) and two urban sites composed of macrophytes but devoid of L. wollei mats (Richelieu River [RICH] and L'Assomption River [ASSO] outlets). The body weight of each amphipod was measured, and the neurotoxicity was estimated with the measurement of acetylcholinesterase (AChE) and glutathione-s-transferase (GST) activities. Levels of protein-bound phosphates were also evaluated, to rule out contamination by Microcystis sp. The results showed that the activity of acetylcholinesterase measured in amphipods in ASSO and RICH was lower than the activity found in amphipods collected in L. wollei mats in LSL. In addition, amphipods found in L. wollei mats at the LSL site have significantly higher GST activity than those located at the two devoid sites, RICH and ASSO. No significant change was observed for protein-bound phosphate levels. This study suggests that the presence of L. wollei triggers potential toxicity.

Mixed-effect circadian rhythm model for human erythrocyte acetylcholinesterase activity—application to the proof of concept of cholinesterase inhibition by acorn extract in healthy subjects with galantamine as positive control

The aim of this study was to develop a non-linear mixed effect circadian rhythm model of acetylcholinesterase (AChE) activity variation and to evaluate the inhibitory effect of acorn extract (2 g) and galantamine (16 mg), used as positive control, on human AChE in red blood cells (RBC). This was an open-label, randomized, three-way crossover study involving 12 healthy subjects who received one of the treatments in each study period: no treatment, acorn extract, and galantamine. RBC AChE activity was measured in peripheral blood samples collected at 0 (pre-dose), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16 and 24 h post-dose administration. Non-linear mixed effect modeling was performed using NONMEM (ver. 7.0). The circadian variation of AChE activity was best described using two mixed effect cosine functions, with periods of 24 and 12 h, respectively. When the inhibitory effect terms were added, the model was significantly improved for both acorn extract and galantamine. In terms of the effect, a 2-g single dose of acorn extract showed AChE inhibition (about 5%) similar to that of a 16-mg single dose of galantamine, in the first 24 h after administration. Based on the very pronounced inter- and intra-day variation in AChE activity in RBC, we conclude that the model-based approach is essential for the proof of concept and quantitation of AChE inhibition in human subjects.

A Multivariate Data Analysis of the Clam Ruditapes Decussatus as Sentinel Organism of the Bizerta Lagoon (Tunisia)

From May 1998 to May 1999, the clams Ruditapes decussatus were collected each month at three stations of the Bizerta lagoon. This paper represents a synthesis between the results already published of catalase (CAT) activity, of glutathione S-transferase (GST) activity and acetylcholinesterase (AChE) activity measured in the clams. Hydrological parameters (temperature, salinity, dissolved oxygen, pH) were determined. Microbial loads (total aerobic bacteria, faecal bacteria and Vibrionaceae) were analyzed in the clams and the sediments. A global Principal Component Analysis was performed including all parameters. On the first principal axis, the temperature, salinity and bacterial loads as well as CAT activities were important factors always opposed to dissolved oxygen, whereas, on the second axis, AChE activity was opposed to pH. Principal Component Analyses were also carried out for results at each station with all parameters. CAT activities were generally high in summer from July to October. AChE activities were low during the months of January, February and March at one station whereas these low activities were shifted to the months of May, June and July at the two other stations. Among the biochemical biomarkers studied, the variations in CAT activities appeared to be the most significant factor of the multivariate analysis. The variations in AChE activity were also significant whereas those in GST activity appeared to be less significant.

The use of acetylcholinesterase activity in Ruditapes decussatus and Mytilusgalloprovincialis in the biomonitoring of Bizerta lagoon

The variations of acetylcholinesterase activity, considered to be a biochemical biomarker of organophosphorus and carbamate compounds, was followed in Mediterranean clams ( Ruditapes decussatus) and mussels ( Mytilus galloprovincialis) as a function of season and sampling sites in the lagoon of Bizerta (Tunisia). Results show that acetylcholinesterase activity in clams collected from station A was the lowest and was so throughout the year. This low activity may be due to the input of non-treated waste waters in the lagoon. Heavy metal contamination has been reported in the sediments of this area, suggesting that acetylcholinesterase activity in clams may be inhibited by this type of pollution. Clams harvested from station F, a site adjacent to an agricultural area, were characterized by a decrease in acetylcholinesterase activity, especially after rain periods. Clams from station J presented the highest activity throughout the greater part of the year. This phenomenon may imply that this location is less affected by pollutants inhibiting AChE activity than the others. In the mussels from station C, located in the channel from the lagoon to the Mediterranean and submitted to pollutants (urban wastes from Bizerta and hydrocarbons from the maritime traffic), acetylcholinesterase activities were lower than in those from station J. In conclusion, the variations in acetylcholinesterase activity observed between stations in both species may be the result of pollution and of the environmental conditions.

Variation of dominance of newly arisen adaptive genes.

Newly arisen adaptive alleles such as insecticide resistance genes represent a good opportunity to investigate the theories put forth to explain the molecular basis of dominance and its possible evolution. Dominance levels of insecticide resistance conferred by insensitive alleles of the acetylcholinesterase gene were analyzed in five resistant strains of the mosquito Culex pipiens. Dominance levels were found to differ between strains, varying from partial recessivity to complete dominance. This variation was not explained by differences in catalytic properties of the enzyme, since four of the five resistant strains had identical inhibition properties for the insensitive acetylcholinesterase. Among these four laboratory strains and in individuals collected from natural populations, we found a correlation between increased acetylcholinesterase activities and higher dominance levels. We propose a molecular explanation for how variation in acetylcholinesterase activity may result in variation of dominance level. We also conjecture that the four resistant strains did not differ in their amino acid sequence in the catalytically active regions of acetylcholinesterase, but that the expression of the gene was regulated by either neighboring or distant sites, thereby modifying the dominance level. Under this interpretation, dominance levels may evolve in this system, since heritable variation in acetylcholinesterase activity was found.

Regional and laminar variations in acetylcholinesterase activity within the frontal cortex of the dog

Two different histochemical methods were applied to analyse acetylcholinesterase (AChE) activity within the frontal lobe cortex (FC) of the dog. Both staining methods revealed AChE reactivity in neuronal cell bodies and fibres. AChE-positive neuronal perikarya varied in size, shape, character and intensity of staining. Both pyramidal and non-pyramidal AChE-rich neurons were found. The pyramidal neurons predominated in layers III and V of the dog FC. The non-pyramidal cells were present in deep cortical layers and white matter. Labelled cells were distributed in a consistent pattern across regions of the dog frontal lobe. AChE reactivity in fibres showed, in general, a characteristic bilaminar appearance due to the more intense staining in cortical layers I and V. However, in contrast to the cellular labelling, differences in the laminar distribution of AChE-rich fibre bands distinguished three subregions of the FC: (1) rostral and middle prefrontal and anterior premotor areas, where AChE was distributed in a bilaminar pattern with two bands of similar, medium-intensive staining overlying layers I and V; (2) dorso-caudal primary and secondary motor areas distinguished by much lighter staining of the deep band of AChE activity in layer V; and (3) ventro-caudal subcallosal region in which the bilaminar pattern of extremely dark labelling in layers I and V was augmented by a third band of strong AChE activity in layer VI. These findings show that differences in the pattern of AChE activity parallel some of the cytoarchitectonic zones of the FC previously described in this laboratory (Rajkowska and Kosmal, 1988).

THE DISTRIBUTION OF CHOLINESTERASES IN THE SENSORY GANGLIA OF MAN AND OF SOME MAMMALS

The distribution of cholinesterases in the cranial and spinal sensory ganglia was investigated in the cat, guinea-pig, rat, mole and man using a modified Koelle's histochemical technique. It was found that the cytoplasm of the sensory nerve cells contained acetylcholinesterase in all species, but the concentration of the enzyme varied from cell to cell. Nerve fibers gave a negative acetylcholinesterase reaction in the cat and guinea-pig, and a weak to moderate positive reaction in the rat, mole and man. Non-specific cholinesterase was only found in the sensory ganglia of the cat and guinea-pig. In human sensory ganglia, it was found during the fetal life but not after birth. The sensory ganglia of the rat were found to be nearer to those of man than the ganglia of the cat or guinea-pig in respect of cholinesterase distribution. It is suggested that the variations in acetyl-cholinesterase activity among different nerve cells may signify the existence of several cell types in the sensory ganglia. The role of intracytoplasmic cholinesterase in the sensory nerve cells is discussed.