Factors in Standardizing Automated Cholinesterase Assays

Abstract

A scientific panel assembled by the U.S. Environmental Protection Agency (EPA) determined that variability in cholinesterase (ChE) activities in the agency's pesticide/animal study database likely was due to a lack of accepted guidelines for ChE methodology. A series of trials was held in which participating laboratories measured ChE activity in blood and brain samples from untreated and pesticide-treated rats using a colorimetric assay method. The degree of inhibition of ChE activity in plasma and brain samples compared to controls was consistent among most of the laboratories. The ChE activity in erythrocyte samples differed more between laboratories due to a high blank, low erythrocyte AChE activity and hemoglobin absorption at the wavelength of the assay. Strategies are suggested for minimizing the variability of ChE activity in hemoglobin-rich samples.

Biochemical Markers of Neurotoxicity in Wildlife and Human Populations: Considerations for Method Development

“…Therefore, studies performed on isolated or dispersed populations require longer sample storage times under limited storage conditions prior to delivery to the laboratory for analysis. Methods have been developed for ChE measurement in the field but are not as sensitive and accurate as laboratory-based methods (Wilson et al, 1996;Oliveira et al, 2002). The measurement of stored biomarkers can be affected by several conditions including protein denaturation, oxidation, proteolysis, and microbial contamination, which may be dependent on storage conditions such as temperature, freeze/thaw cycles, and storage time.…”

“…However, surrogate neurochemical biomarkers in blood have been shown to reflect changes in the brain in response to neurotoxicants and offer an ethical way to evaluate neurotoxicity in human populations (Manzo et al, 1996). For example, cholinesterase (ChE) activity in blood is currently used as a surrogate biomarker to monitor the toxic effects and degree of organophosphate and carbamate exposure in agricultural workers who frequently use pesticides (Wilson et al, 1996(Wilson et al, ,1997. Other studies have linked manganese and styrene exposure in industrial workers with decreased monoamine oxidase (MAO) activity in peripheral blood platelets (Checkoway et al, 1992;Smargiassi et al, 1995;Bergamaschi et al, 1997;Cohen et al, 2002).…”

Intraindividual Stability of Human Erythrocyte Cholinesterase Activity

“…These measures have greatly improved the quality of RBC-ChE results, and other laboratories may benefit from adopting similar quality assurance measures. Recent reports indicate that interlaboratory reproducibility for ChE testing is still problematic within the civilian community (27,28 ), although the situation appears to be improving (3 ).…”

Regulatory Aspects of Acute Neurotoxicity Assessment

“…Specific methodology for the cholinesterase assay is as described previously, although modifications to the method have been recommended by the U.S. EPA taking account of concerns about AChE assays raised by Wilson et al (1996). In well-conducted studies, it is possible to detect statistically significant differences on the order of 5-10% in brain, 10% in red blood cells, and 20% in plasma.…”