Acetylcholinesterase inhibition in electric eel and human donor blood: an in vitro approach to investigate interspecies differences and human variability in toxicodynamics

Abstract

In chemical risk assessment, default uncertainty factors are used to account for interspecies and interindividual differences, and differences in toxicokinetics and toxicodynamics herein. However, these default factors come with little scientific support. Therefore, our aim was to develop an in vitro method, using acetylcholinesterase (AChE) inhibition as a proof of principle, to assess both interspecies and interindividual differences in toxicodynamics. Electric eel enzyme and human blood of 20 different donors (12 men/8 women) were exposed to eight different compounds (chlorpyrifos, chlorpyrifos-oxon, phosmet, phosmet-oxon, diazinon, diazinon-oxon, pirimicarb, rivastigmine) and inhibition of AChE was measured using the Ellman method. The organophosphate parent compounds, chlorpyrifos, phosmet and diazinon, did not show inhibition of AChE. All other compounds showed concentration-dependent inhibition of AChE, with IC50s in human blood ranging from 0.2–29 µM and IC20s ranging from 0.1–18 µM, indicating that AChE is inhibited at concentrations relevant to the in vivo human situation. The oxon analogues were more potent inhibitors of electric eel AChE compared to human AChE. The opposite was true for carbamates, pointing towards interspecies differences for AChE inhibition. Human interindividual variability was low and ranged from 5–25%, depending on the concentration. This study provides a reliable in vitro method for assessing human variability in AChE toxicodynamics. The data suggest that the default uncertainty factor of ~ 3.16 may overestimate human variability for this toxicity endpoint, implying that specific toxicodynamic-related adjustment factors can support quantitative in vitro to in vivo extrapolations that link kinetic and dynamic data to improve chemical risk assessment.

Antioxidant and Protective Effects of Artemisia campestris Essential Oil Against Chlorpyrifos-Induced Kidney and Liver Injuries in Rats

“…Serum creatinine, uric acid, and urea indicators of kidney function increased significantly in rats after CPF treatment which may indicate degradation of both purines and pyrimidines and impaired kidney function. Many reports investigated an increase of creatinine, urea and uric acid in serum of rats exposed to toxic compounds including pesticides ( Badraoui et al, 2007 , 2012 ; Hakim et al, 2008 ; Amri et al, 2017 ; Meligi and Hassan, 2017 ; Kasteel et al, 2020 ). Levels of serum cholesterol, triglycerides, LDL, and glucose were statistically enhanced in rats exposed to CPF.…”

“…The present results are in accordance with those of Mosbah et al (2016) who demonstrated a significant increase in LPO level and decreases of SOD, CAT, and GPx activities in plasma and testis after treatment of male rats with CPF. In fact, CPF can be responsible for increasing the production of reactive oxygen species (ROS) in cells, which lead to increased lipid peroxidation levels and oxidative damage ( Kasteel et al, 2020 ). The decrease in antioxidant enzyme activities in liver and kidney tissues was due to cellular injury and death of healthy cells that are able to respond to the oxidative insult.…”

Prediction of dose-dependent in vivo acetylcholinesterase inhibition by profenofos in rats and humans using physiologically based kinetic (PBK) modeling-facilitated reverse dosimetry

“…One would expect that effect concentrations would decrease with longer incubation times until 100% of the binding sites is inhibited, as shown before by Aurbek et al ( 2006 ) and Krstić et al ( 2008 ). With a relatively long pre-incubation time of 15 min as we have used in the present study, similar to incubation times previously applied by other research groups (e.g., Aurbek et al 2006 ; Kasteel et al 2020 ), we aimed to obtain a relevant and conservative estimation of the effect concentrations, as also indicated by the small difference between the BMDL 10 value obtained with our predicted rat dose–response data and the BMDL 10 value from a reported in vivo study in rats.…”

Modelling human variability in toxicokinetic and toxicodynamic processes using Bayesian meta‐analysis, physiologically‐based modelling and in vitro systems

“…Electric eel enzyme and human blood of 20 different donors (12 men/8 women) were exposed to eight different compounds (chlorpyrifos, chlorpyrifos-oxon, phosmet, phosmet-oxon, diazinon, diazinon-oxon, pirimicarb, rivastigmine) and inhibition of AChE was measured using the Ellman method. The methods are described in detail in the accompanying publication (Kasteel et al, 2020b). The present document has been produced and adopted by the bodies identified above as authors.…”

“…In all, this study provides a reliable in vitro method for assessing human variability in AChE toxicodynamics. The data suggest that the default uncertainty factor of ~3.16 may overestimate human variability for this toxicity endpoint, implying that specific toxicodynamicrelated adjustment factors can support quantitative in vitro to in vivo extrapolations that link kinetic and dynamic data in order to improve chemical risk assessment (Kasteel et al, 2020b). Measured IC50s and IC20s are reported in Table 27 for both electric eel and human AChE.…”