In vitro sensitivity of cholinesterases and [3H]oxotremorine-M binding in heart and brain of adult and aging rats to organophosphorus anticholinesterases

Abstract

Organophosphorus (OP) insecticides elicit toxicity via acetylcholinesterase inhibition, allowing acetylcholine accumulation and excessive stimulation of cholinergic receptors. Some OP insecticides bind to additional macromolecules including butyrylcholinesterase and cholinergic receptors. While neurotoxicity from OP anticholinesterases has been extensively studied, effects on cardiac function have received less attention. We compared the in vitro sensitivity of acetylcholinesterase, butyrylcholinesterase and [ 3 H]oxotremorine-M binding to muscarinic receptors in the cortex and heart of adult (3 months) and aging (18 months) rats to chlorpyrifos, methyl parathion and their active metabolites chlorpyrifos oxon and methyl paraoxon. Using selective inhibitors, the great majority of cholinesterase in brain was defined as acetylcholinesterase, while butyrylcholinesterase was the major cholinesterase in heart, regardless of age. In the heart, butyrylcholinesterase was markedly more sensitive than acetylcholinesterase to inhibition by chlorpyrifos oxon, and butyrylcholinesterase in tissues from aging rats was more sensitive than enzyme from adults, possibly due to differences in A-esterase mediated detoxification. Relatively similar differences were noted in brain. In contrast, acetylcholinesterase was more sensitive than butyrylcholinesterase to methyl paraoxon in both heart and brain, but no age-related differences were noted. Both oxons displaced [ 3 H]oxotremorine-M binding in heart and brain of both age groups in a concentration-dependent manner. Chlorpyrifos had no effect but methyl parathion was a potent displacer of binding in heart and brain of both age groups. Such OP and age-related differences in interactions with cholinergic macromolecules may be important because of potential for environmental exposures to insecticides as well as the use of anticholinesterases in age-related neurological disorders.

In vitroinhibition of plasma and brain cholinesterases of growing chicks by chlorpyrifos and dichlorvos

“…In contrast to the findings of the present study, several reports indicated that there were no age-related variations for in vitro inhibition of rodent ChEs (Atterberry et al 1997;Mortensen et al 1998a;Padilla 2007;Mirajkar & Pope 2008). Other than species variations, one reason for this discrepancy could be related to external factors (e.g.…”

Longitudinal Assessment of Blood Cholinesterase Activities Over 2 Consecutive Years Among Latino Nonfarmworkers and Pesticide-Exposed Farmworkers in North Carolina

“…Immediately after thawing, 20 μl aliquots of whole blood were added to four separate 7-ml glass scintillation vials. In two of the vials, 60 μl of 50 mM potassium phosphate buffer, pH 7 (phosphate buffer) was added while in the other two, 60 μl of the specific acetylcholinesterase inhibitor BW 284C51 19 in phosphate buffer was added (final concentration 0.5 μM; this concentration completely inhibited acetylcholinesterase activity under the assay conditions). Samples were vortexed, and then placed into a water bath at 26°C for 60 seconds before adding 20 μl of substrate ([ 3 H]acetylcholine iodide, 1 mM final concentration) in phosphate buffer.…”

Comparing Longitudinal Measures of Cholinesterase as Biomarkers for Insecticide Exposure Among Latinx Children in Rural Farmworker and Urban Nonfarmworker Communities in North Carolina

“…Blood samples on dry ice were sent to the laboratory of Dr Carey Pope at Oklahoma State University. Total ChE, AChE, and BChE activities were assayed with a modification of the radiometric method of Johnson and Russell, using differential inhibition conditions 18,19 . Immediately after thawing, whole blood was diluted (1:150 in the final reaction) using 50 mM potassium phosphate buffer (PB), pH 7.0.…”

“…Total ChE, AChE, and BChE activities were assayed with a modification of the radiometric method of Johnson and Russell, using differential inhibition conditions. 18,19 Immediately after thawing, whole blood was diluted (1:150 in the final reaction) using 50 mM potassium phosphate buffer (PB), pH 7.0. Twenty microliters of diluted whole blood was added to 4 separate scintillation vials.…”