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Differential cytotoxic sensitivity in mouse and human cell lines exposed to organophosphate insecticides
1U.S. Environmental Protection Agency, Neurotoxicology Division, Research Triangle Park, North Carolina 27711.
Abstract:
Neuroblastoma cell lines were used to examine the differential interspecies response (i.e., species selectivity) to organophosphates (OPs). Baseline activities of the major target esterases, i.e., cholinesterase, carboxylesterase, and neurotoxic esterase, were assayed in mouse and several human neural candidate cell lines. These activities were found to be variable within individual cell lines and among the various tested cell lines. Cytotoxicity data using the neutral red fluorometric assay were collected on both human (SH-SY5Y) and mouse (NB41A3) neuroblastoma clones exposed to a variety of OP insecticides. IC50 data indicated that the tested mouse cell line was consistently more sensitive than the human cell line to equimolar doses of various OP compounds (e.g., mipafox, parathion, paraoxon, DFP, leptophos oxon, fenthion, and fenitrothion). This difference in cytotoxic sensitivity was most pronounced in response to compounds requiring metabolic bioactivation (i.e., protoxicants). Cytotoxicity data also demonstrated that the NB41A3 mouse neuroblastoma cell line was more metabolically competent than the SH-SY5Y human cell line in converting the protoxicant parathion to its neurotoxic metabolite, paraoxon. B-lymphoblastoids, genetically engineered with human P450 cDNAs, demonstrated higher cytotoxic sensitivity to parathion than unengineered cells, indicating that cytochrome P450-associated monooxidase activity could also influence cytotoxic sensitivity to parathion in culture. These data suggest that interspecies-selectivity in response to OP-related cytotoxicity is influenced by intercellular differences in metabolism and baseline esterase activities.
Insights
Mouse neuroblastoma cells show greater sensitivity to organophosphate (OP) insecticides than human cells, highlighting species-specific differences in OP metabolism and esterase activity.
Area of Science:
- Toxicology
- Neuroscience
- In Vitro Toxicology
Background:
- Organophosphates (OPs) are widely used insecticides with varying toxicity across species.
- Understanding interspecies differences in OP response is crucial for risk assessment.
- Neuroblastoma cell lines offer a model to study OP cytotoxicity and species selectivity.
Purpose of the Study:
- To investigate the differential response of human and mouse neuroblastoma cell lines to organophosphate (OP) insecticides.
- To explore the role of esterase activity and metabolic bioactivation in OP-induced cytotoxicity.
- To determine species selectivity in OP toxicity using in vitro models.
Main Methods:
- Assay of baseline cholinesterase, carboxylesterase, and neurotoxic esterase activities in human and mouse neuroblastoma cell lines.
- Cytotoxicity assessment using the neutral red fluorometric assay upon exposure to various OP compounds.
- Evaluation of metabolic conversion of protoxicants to active metabolites in cell lines.
- Use of engineered B-lymphoblastoid cells expressing human P450 cDNAs to assess the role of monooxidase activity.
Main Results:
- Mouse neuroblastoma cells (NB41A3) exhibited significantly higher sensitivity to OPs than human neuroblastoma cells (SH-SY5Y).
- Species-selective cytotoxicity was more pronounced for OP protoxicants requiring metabolic bioactivation.
- The mouse cell line demonstrated greater metabolic competence in converting parathion to its toxic metabolite, paraoxon.
- Cytochrome P450 activity in engineered B-lymphoblastoid cells enhanced sensitivity to parathion.
Conclusions:
- Interspecies differences in organophosphate cytotoxicity are influenced by variations in cellular metabolism and baseline esterase activities.
- Metabolic bioactivation pathways, particularly those involving cytochrome P450s, play a significant role in determining OP toxicity and species selectivity.
- Neuroblastoma cell lines provide a valuable in vitro model for studying the mechanisms underlying interspecies differences in pesticide toxicity.