Suppression of haptoglobin and loss of striatal neurons in mice chronically exposed to chlorpyrifos-contaminated drinking water

Exposure to agricultural chemicals is a risk factor for neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Chlorpyrifos (CPF) is an organophosphate insecticide widely used in agricultural and occupational settings. Epidemiological studies have associated CPF exposure with developmental impairments and an increased risk of AD and PD. Experimental characterization of the impact of chronic, systemic CPF exposure is essential for understanding how organophosphates actually influence disease risk. Multiple studies have assessed the effects of gestational exposure to CPF in preclinical models. To model exposure faced by adults, we administered CPF-contaminated drinking water to mice from 6 to 22 mo of age. This chronic exposure led to systemic effects, including reduced levels of the acute-phase protein haptoglobin (HTP) in both plasma and liver. Notably, the combination of aging and CPF exposure resulted in astrogliosis in the hippocampus and striatum, as well as neuronal loss in the striatum, primarily due to the loss of GAD65/67-immunoreactive interneurons. Having identified CPF-driven suppression of HPT in peripheral tissues, we examined HPT expression in brain tissues. We readily detected HPT expression in brain microglia. We then cultivated primary microglia and found that CPF exposure decreased HPT secretion in vitro. These findings indicate systemic and neurotoxic effects resulting from adult exposure to CPF-contaminated water.