Acute exposure to chlorpyrifos caused NADPH oxidase mediated oxidative stress and neurotoxicity in a striatal cell model of Huntington's disease

- A disease-toxicant interaction between mutant Huntingtin and chlorpyrifos (CPF).
- Mutant huntingtin enhances CPF-induced neurotoxicity in a striatal cell model.
- NADPH-oxidase (NOX) mediated ROS production is involved in the neurotoxicity.
- Exogenous antioxidants and NOX inhibitors ameliorate CPF-induced neurotoxicity.

We hypothesized that expression of mutant Huntingtin (HTT) would modulate the neurotoxicity of the commonly used organophosphate insecticide, chlorpyrifos (CPF), revealing cellular mechanisms underlying neurodegeneration. Using a mouse striatal cell model of HD, we report that mutant HD cells are more susceptible to CPF-induced cytotoxicity as compared to wild-type. This CPF-induced cytotoxicity caused increased production of reactive oxygen species, reduced glutathione levels, decreased superoxide dismutase activity, and increased malondialdehyde levels in mutant HD cells relative to wild-type. Furthermore, we show that co-treatment with antioxidant agents attenuated the CPF-induced ROS levels and cytotoxicity. Co-treatment with a NADPH oxidase (NOX) inhibitor, apocynin, also attenuated the CPF-induced ROS production and neurotoxicity. CPF caused increased NOX activity in mutant HD lines that was ameliorated following co-treatment with apocynin. Finally, CPF-induced neurotoxicity significantly increased the protein expression of nuclear factor erythroid 2-related factor (Nrf2) in mutant HD cells as compared to wild-type. This study is the first report of CPF-induced toxicity in HD pathophysiology and suggests that mutant HTT and CPF exhibit a disease-toxicant interaction wherein expression of mutant HTT enhances CPF-induced neurotoxicity via a NOX-mediated oxidative stress mechanism to cause neuronal loss in the full length HTT expressing striatal cells.

Model for mutant Huntingtin (HTT) and chlorpyrifos (CPF)-induced oxidative stress in HD striatal cells. Expression of mutant HTT exacerbates CPF-induced neurotoxicity in HD striatal cells via NADPH-oxidase (NOX)-mediated oxidative stress mechanism that results in increased production of ROS, decreased antioxidant buffering capacity, increased lipid peroxidation, and upregulated Nrf2 protein expression. The mutant HTT and CPF-induced neurotoxicity and ROS production can be attenuated by treatment with exogenous antioxidants (N-acetyl cysteine, curcumin, and ascorbic acid) and apocynin, a NOX inhibitor.87