Development of a field assay method for the determination of cholinesterase activity
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Date
2003
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Publisher
University of Colombo: UC(MED).
Abstract
Oraganophosphate insecticides are the commonest cause of poisoning in Sri Lanka. Oraganophosphates inhibit acetylcholinestertase and plasma cholinesterase (pseudocholinestertas). Available evidence suggests that there is a high probability of adverse health effects due to low level chronic exposure to Oraganophosphates. Low concentrations of cholinesterase are usually seen when liver function is diminished through liver disease or malnutrition. Genetic variants of plasma cholinesterase can also lead to low enzyme activity. Genetic variants can be identified by dibucaine inhibition. Assay methods used for plasma cholinesterase activity are the use of propionylthiocholine or butyrylthiocholine iodide as substrates and measuring the increase in absorbance using a spectrophotometer. Another method is the use of acetylcholine as the substrate and measurement of pH decrease using pH meter. These methods are expensive and require instruments which are difficult to maintain under field conditions. Therefore these methods are not suitable for large scale screening in Sri Lanka to detect chronic organophosphate poisoning. To overcome this problem we have developed a cheap reliable method to assay cholinesterase levels using the Lovibond comparator. When the cholinesterase activity was determined by measuring the decrease in pH using a pH meter and the Lovibond method the results obtained were different and the difference was significant to a 0.01 level according to the paired t-test. When the normal assay methods for plasma cholinesterase activity using propionylthiocholine (PTC) and butyrylthiocholine iodide (BTCI) was used, 367 school children and 64 pesticide sprayers were within the normal range. The normal range for propionylthiocholine is 1700-4100 U/L and for butyrylthiocholine iodide is 3500-8500 U/L. All the school children (367) and 64 pesticide sprayers had whole blood cholinesterase activity between 0.026?pH/min to 0.040?pH/min when assayed using the Lovibond method. The 40 pesticide sprayers who had low plasma cholinesterase activity as determined by propionylthiocholine(PTC) and butyrylthiocholine iodide (BTCI) methods had whole blood cholinesterase activity between 0.013?pH/min and 0.020?pH/min when assayed using the Lovibond method. This indicates that persons having low pseudo-cholinesterase activity will have 0.020?pH/min or lower values when whole blood cholinesterase activity is determined by the Lovibond method. These results indicated that the Lovibond method is suitable for identification or persons having low cholinesterase activity. There was no statistically significant correlation between plasma cholinesterase activity and Hemoglobin content and plasma cholinesterase activity and body mass index. Therefore the Lovibond method is a low cost assay, method to monitor chronic organophosphate toxicity under field conditions. In the Colombo district 20 per cent of male students and none of the female students were exposed to pesticides. The results for Anuradhapura and Matale districts were for male students 82 percent and 72 percent and for female students 75 per cent and 49 per cent. All school children tested were within the normal range for plasma cholinesterase activity. There was no statistically significant difference between plasma cholinesterase activities of school children who were exposed to pesticides and no exposed to pesticides.
Description
Dissertation: M.Sc., University of Colombo: UC(MED), 2003.
Keywords
Insecticides
Citation
MULLER, AC, Development of a field assay method for the determination of cholinesterase activity, University of Colombo UC(MED), 2003: xiv, 201p.