Evaluation of a Brain Acetylcholinesterase Extraction Method and Kinetic Constants after Methyl-Paraoxon Inhibition in Three Brazilian Fish Species.

Acetylcholinesterase (AChE) is an important enzyme in the control of the neuronal action potential and sensitive to organophosphate inhibition. Brain fish AChE is less sensitive to organophosphate inhibition than AChE from terrestrial animals, although this sensitivity is variable among species and has not yet been fully evaluated in fish species. In this setting, inhibition kinetic constants for progressive irreversible inhibition of brain acetylcholinesterase due to methyl-paraoxon exposure were determined in three fish species (Mugil liza, Genidens genidens and Lagocephalus laevigatus) and hen (Gallus domesticus). Enzyme extraction using a detergent was shown to be adequate, and samples presented activity inhibition in high substrate concentrations and suppression of inhibition by methyl-paraoxon in the presence of the substrate, similar to kinetic patterns from purified enzyme preparations. Catfish (G. genidens) AChE presented the highest sensitivity among the evaluated fish species (IC50 = 1031.20 nM ± 63.17) in comparison to M. liza and L. laevigatus (IC50: 2878.83 ± 421.94 and 2842.5 ± 144.63 nM respectively). The lower dissociation constant (Kd = 20.3 ± 2.95 µM) of catfish AChE showed greater enzyme affinity for methyl-paraoxon, explaining this species higher sensitivity to organophosphates. Hen AChE presented higher ki (900.57 ± 65.3 mM-1min-1) and, consequently, greater sensitivity to methyl-paraoxon, explained by a lower Kd (0.6 ± 0.13 µM). Furthermore, hen AChE did not differentiate between the propionylthiocholine and acetylthiocholine substrates, indicating easier access of methyl-paraoxon to the hen enzyme activity site. The results obtained herein indicate a suitable extraction of AChE and, despite different inhibition kinetic constants, demonstrate that fish AChE is less sensitive to methyl-paraoxon, probably due to reduced access to the catalytic center which provides greater enzyme substrate selectivity.

Cholinesterase activities determination in frozen blood samples: an improvement to the occupational monitoring in developing countries.

1. Studies were carried out on rural workers in Brazil to determine the decrease in the activity of plasma butyrylcholinesterase (BChE), erythrocyte cholinesterase (AChE) associated with exposure to organophosphorus pesticides (OP). The goal of this work is to help prevent injury to these workers. 2. In developing countries the distance between area of pesticide use and reference laboratories is a drawback for analytical techniques, since cholinesterase activity determinations require fresh blood samples. Field methodologies can be a useful alternative to laboratory tests, however they are not as sensitive as those found in laboratories. 3. The modification of Ellman's Method presented in this paper allows blood samples to be frozen and maintain enzymatic stability: 7 days for AChE and 3 days for BChE. The proposed method is also more sensitive than Ellman's Method Modified by Magnotti (EMMM). 4. The results suggest that the Ellman Method Modified by Oliveira-Silva (EMMOS) is valid for monitoring procedures. This method represents an important contribution to the process of monitoring OP exposures, since the evaluations no longer have to be conducted near the site of OP use.

[Are some Brazilian population groups subject to endocrine disrupters?]. / Estarão alguns grupos populacionais brasileiros sujeitos à ação de disruptores endócrinos?

Several chemical substances suspected of endocrine disruption are currently being used in industrial and agricultural activities in Brazil. This paper presents analytical data showing contamination of some population groups by these substances. Virtually nothing is known about the related health effects, highlighting the need to implement a national program to evaluate such impacts.

Cancer cluster among young Indian adults living near power transmission lines in Bom Jesus do Tocantins, Pará, brazil.

A case study was carried out to explore the occurrence of a cancer cluster in 1992 among young indian adults adults living in an Amazonian village near two 500 kV power transmission lines that began operating a decade ago. Current blood levels of DDT and organophosphorus pesticides and metal levels in hair samples were measured. Extremely low magnetic field exposure was determined during current daily activities carried out by the Indian villagers. Taking into account the cancer incidence rates in different Brazilian cities, the probability of the occurrence of this cluster by chance was considered remote (p< 0.003, Poisson distribution). High blood levels of p,p'-DDT (median levels ranging from 26 to 58 ppb) were observed. As a whole, this community showed a pattern of low exposure to organophosphorus pesticides, and high recent exposure was only observed in a few blood samples. Continuous exposure to extremely low electromagnetic fields originated in the power transmission lines (which reached 95.0 mG under the lines) was observed on several opportunities during daily activities carried out by Indian villagers. Further observational studies should evaluate the interaction between exposure to extremely low electromagnetic fields and prior exposure to tumor initiators in cancer development.