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Reiss R, Loccisano A, Deines A, Kim M, Nallani G, Chandrasekaran A, Whatling P. A physiologically-based pharmacokinetic/pharmacodynamic (PBPK/PD) model for the insecticide dimethoate. Xenobiotica 2023; 53:382-395. [PMID: 37706283 DOI: 10.1080/00498254.2023.2258507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 09/10/2023] [Indexed: 09/15/2023]
Abstract
1. Dimethoate is an organophosphate insecticide that is converted in vivo to omethoate, the active toxic moiety. Omethoate inhibits acetylcholinesterase (AChE) in the brain and red blood cells (RBCs). This paper describes the development of rat and human physiologically-based pharmacokinetic/pharmacodynamic (PBPK/PD) models for dimethoate.2. The model simulates the absorption and distribution of dimethoate and omethoate, the conversion of dimethoate to omethoate and to other metabolites, the metabolism and excretion of omethoate, and the inhibition of RBC and brain AChE. An extensive data collection program to estimate metabolism and inhibition parameters is described.3. The suite of models includes an adult rat, post-natal rat, and human model. The rat models were evaluated by comparing model predictions of dimethoate and omethoate to measured blood time course data, and with RBC and brain AChE inhibition estimates from an extensive database of in vivo AChE measurements.4. After the demonstration of adequately fitted rat models that were robust to sensitivity analysis, the human model was applied for estimation of points-of-departure (PODs) for risk assessment using the human-specific parameters in the human PBPK/PD model. Thus, the standard interspecies uncertainty factor can be reduced from 10X to 1X.
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van Melis LVJ, Heusinkveld HJ, Langendoen C, Peters A, Westerink RHS. Organophosphate insecticides disturb neuronal network development and function via non-AChE mediated mechanisms. Neurotoxicology 2023; 94:35-45. [PMID: 36347328 DOI: 10.1016/j.neuro.2022.11.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 11/02/2022] [Accepted: 11/03/2022] [Indexed: 11/06/2022]
Abstract
Exposure to organophosphate (OP) insecticides has been related to several adverse health effects, including neurotoxicity. The primary insecticidal mode of action of OP insecticides relies on (irreversible) binding to acetylcholine esterase (AChE), with -oxon metabolites having a much higher potency for AChE inhibition than the parent compounds. However, OP insecticides can also have non-AChE-mediated effects, including changes in gene expression, neuroendocrine effects, disruption of neurite outgrowth and disturbance of the intracellular calcium (Ca2+) homeostasis. Since Ca2+ is involved in neurotransmission and neuronal development, our research aimed to assess the effects of two widely used OP insecticides, chlorpyrifos (CPF) and diazinon (DZ) and their respective -oxon metabolites, on intracellular Ca2+ homeostasis in human SH-SY5Y cells and rat primary cortical cultures. Furthermore, we assessed the acute and chronic effects of exposure to these compounds on neuronal network maturation and function in rat primary cortical cultures using microelectrode array (MEA) recordings. While inhibition of AChE appears to be the primary mode of action of oxon-metabolites, our data indicate that both parent OP insecticides (CPF and DZ) inhibit depolarization-evoked Ca2+ influx and neuronal activity at concentrations far below their sensitivity for AChE inhibition, indicating that inhibition of voltage-gated calcium channels is a common mode of action of OP insecticides. Notably, parent compounds were more potent than their oxon metabolites, with exposure to diazinon-oxon (DZO) having no effect on both neuronal activity and Ca2+ influx. Human SH-SY5Y cells were more sensitive to OP-induced inhibition of depolarization-evoked Ca2+ influx than rat cortical cells. Acute exposure to OP insecticides had more potent effects on neuronal activity than on Ca2+ influx, suggesting that neuronal activity parameters are especially sensitive to OP exposure. Interestingly, the effects of DZ and chlorpyrifos-oxon (CPO) on neuronal activity lessened after 48 h of exposure, while the potency of CPF did not differ over time. This suggests that neurotoxicity after exposure to different OPs has different effects over time and occurs at levels that are close to human exposure levels. In line with these results, chronic exposure to CPF during 10 days impaired neuronal network development, illustrating the need to investigate possible links between early-life OP exposure and neurodevelopmental disorders in children and highlighting the importance of non-AChE mediated mechanisms of neurotoxicity after OP exposure.
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Affiliation(s)
- Lennart V J van Melis
- Neurotoxicology Research Group, Division of Toxicology, Institute for Risk Assessment Sciences (IRAS), Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands
| | - Harm J Heusinkveld
- Neurotoxicology Research Group, Division of Toxicology, Institute for Risk Assessment Sciences (IRAS), Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands; Centre for Health Protection, National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands
| | - Celine Langendoen
- Neurotoxicology Research Group, Division of Toxicology, Institute for Risk Assessment Sciences (IRAS), Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands
| | - Anouk Peters
- Neurotoxicology Research Group, Division of Toxicology, Institute for Risk Assessment Sciences (IRAS), Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands
| | - Remco H S Westerink
- Neurotoxicology Research Group, Division of Toxicology, Institute for Risk Assessment Sciences (IRAS), Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands.
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Sette KN, Alugubelly N, Glenn LB, Guo-Ross SX, Parkes MK, Wilson JR, Seay CN, Carr RL. The mechanistic basis for the toxicity difference between juvenile rats and mice following exposure to the agricultural insecticide chlorpyrifos. Toxicology 2022; 480:153317. [PMID: 36096317 DOI: 10.1016/j.tox.2022.153317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/01/2022] [Accepted: 09/07/2022] [Indexed: 10/14/2022]
Abstract
At high exposure levels, organophosphorus insecticides (OPs) exert their toxicity in mammals through the inhibition of brain acetylcholinesterase (AChE) leading to the accumulation of acetylcholine in cholinergic synapses and hyperactivity of the nervous system. Currently, there is a concern that low-level exposure to OPs induces negative impacts in developing children and the chemical most linked to these issues is chlorpyrifos (CPF). Our laboratory has observed that a difference in the susceptibility to repeated exposure to CPF exists between juvenile mice and rats with respect to the inhibition of brain AChE. The basis for this difference is unknown but differences in the levels of the detoxification mechanisms could play a role. To investigate this, 10-day old rat and mice pups were exposed daily for 7 days to either corn oil or a range of dosages of CPF via oral gavage. Four hours following the last administration of CPF on day 16, brain, blood, and liver were collected. The inhibition of brain AChE activity was higher in juvenile rats as compared to juvenile mice. The levels of activity of the detoxification enzymes and the impact of CPF exposure on their activity were determined in the two species at this age. In blood and liver, the enzyme paraoxonase-1 (PON1) hydrolyzes the active metabolite of CPF (CPF-oxon), and the enzymes carboxylesterase (CES) and cholinesterase (ChE) act as alternative binding sites for CPF-oxon removing it from circulation and providing protection. Both species had similar levels of PON1 activity in the liver and serum. Mice had higher ChE activity in liver and serum than rats but, following CPF exposure, the percentage inhibition was similar between species at an equivalent dosage. Even though rats had slightly higher liver CES activity than mice, the level of inhibition following exposure was higher in rats. In serum, juvenile mice had an 8-fold higher CES activity than rats, and exposure to a CPF dosage that almost eliminated CES activity in rats only resulted in 22% inhibition in mice suggesting that the high serum CES activity in mice as compared to rats is a key component in this species difference. In addition, there was a species difference in the sensitivity of CES to inhibition by CPF-oxon with rats having a lower IC50 in both liver and serum as compared to mice. This greater enzyme sensitivity suggests that saturation of CES would occur more rapidly in juvenile rats than in mice, resulting in more CPF reaching the brain to inhibit AChE in rats.
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Affiliation(s)
- Katelyn N Sette
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Navatha Alugubelly
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Lauren B Glenn
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Shirley X Guo-Ross
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - M Katherine Parkes
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Juliet R Wilson
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Caitlin N Seay
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA
| | - Russell L Carr
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, MS, USA.
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Elmorsy E, Al-Ghafari A, Al Doghaither H, Salama M, Carter WG. An Investigation of the Neurotoxic Effects of Malathion, Chlorpyrifos, and Paraquat to Different Brain Regions. Brain Sci 2022; 12:brainsci12080975. [PMID: 35892416 PMCID: PMC9394375 DOI: 10.3390/brainsci12080975] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 07/16/2022] [Accepted: 07/21/2022] [Indexed: 02/04/2023] Open
Abstract
Acute or chronic exposures to pesticides have been linked to neurotoxicity and the potential development of neurodegenerative diseases (NDDs). This study aimed to consider the neurotoxicity of three widely utilized pesticides: malathion, chlorpyrifos, and paraquat within the hippocampus (HC), corpus striatum (CS), cerebellum (CER), and cerebral cortex (CC). Neurotoxicity was evaluated at relatively low, medium, and high pesticide dosages. All pesticides inhibited acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in each of the brain regions, but esterase inhibition was greatest in the HC and CS. Each of the pesticides also induced greater disruption to cellular bioenergetics within the HC and CS, and this was monitored via inhibition of mitochondrial complex enzymes I and II, reduced ATP levels, and increased lactate production. Similarly, the HC and CS were more vulnerable to redox stress, with greater inhibition of the antioxidant enzymes catalase and superoxide dismutase and increased lipid peroxidation. All pesticides induced the production of nuclear Nrf2 in a dose-dependent manner. Collectively, these results show that pesticides disrupt cellular bioenergetics and that the HC and CS are more susceptible to pesticide effects than the CER and CC.
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Affiliation(s)
- Ekramy Elmorsy
- Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt; (E.E.); (M.S.)
- Pathology Department, Faculty of Medicine, Northern Border University, Arar 91431, Saudi Arabia
- School of Medicine, University of Nottingham, Royal Derby Hospital Centre, Derby DE22 3DT, UK
| | - Ayat Al-Ghafari
- Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia; (A.A.-G.); (H.A.D.)
- Scientific Research Center, Dar Al-Hekma University, Jeddah 22246, Saudi Arabia
| | - Huda Al Doghaither
- Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia; (A.A.-G.); (H.A.D.)
- Cancer and Mutagenesis Unit, King Fahd Medical Research Centre, King Abdulaziz University, Jeddah 22252, Saudi Arabia
| | - Mohamed Salama
- Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt; (E.E.); (M.S.)
- Institute of Global Health and Human Ecology, The American University in Cairo (AUC), Cairo 11385, Egypt
| | - Wayne G. Carter
- School of Medicine, University of Nottingham, Royal Derby Hospital Centre, Derby DE22 3DT, UK
- Correspondence: ; Tel.: +44-132-724-738
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Meek EC, Reiss R, Crow JA, Chambers JE. Inhibition Kinetics of 16 Organophosphorus Pesticides or Their Active Metabolites on Erythrocyte Acetylcholinesterase from Humans and Rats. Toxicol Sci 2021; 183:404-414. [PMID: 33720374 DOI: 10.1093/toxsci/kfab031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Inhibition kinetics assays were conducted with 16 commercial organophosphate (OP) pesticides or their metabolites on acetylcholinesterase (AChE) in erythrocyte "ghost" preparations from 18 individual humans (both sexes; adults, juveniles and cord blood samples; mixed races/ethnicities) and pooled samples from adult rats (both sexes). A well established spectrophotometric assay using acetylthiocholine as substrate and a chromogen was employed. The kinetic parameters bimolecular rate constant (ki), dissociation constant (KI) and phosphorylation constant (kp) were calculated for each compound. As expected, a wide range of potencies were displayed among the tested compounds. Statistical analysis of the resultant data indicated no differences in sex, age or race/ethnicity among the human samples that are unexpected based on chance (4.2% statistically significant out of 48 parameters calculated) and no differences between the sexes in rats. The bimolecular rate constants for 10 of the compounds were not statistically different between rats and humans. The data indicate that, consistent with the high level of conservation of AChE among species and the fact that AChE at different locations within a species arises from the same gene, the inhibition kinetic parameters calculated from rat erythrocyte ghost preparations should be useful in estimating potencies of OP compounds on target AChE in humans. Additionally the data indicate that differences in sensitivities among individual humans were not apparent. Impact Statement: These data are expected to be useful in consideration of the intraspecies and interspecies uncertainty factors in OP pesticide risk assessment.
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Affiliation(s)
- Edward C Meek
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
| | - Richard Reiss
- Exponent, 1800 Diagonal Road, Suite 500, Virginia, USA Alexandria
| | - J Allen Crow
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
| | - Janice E Chambers
- Center for Environmental Health Sciences, Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
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