In vitro neurotoxicity hazard characterization of exhaust–derived particulate matter in rat primary cortical cultures using micro-electrode array recordings

Abstract

Exposure to air pollution and particulate matter (PM) is linked to adverse health effects, including neurodegenerative diseases. While underlying mechanisms are still unknown, epidemiological studies have shown a strong correlation of these diseases with ultrafine particles (< 100 nm; UFP), which are mainly derived from traffic-related air pollution. Due to the small size, UFP can translocate to the brain through the cardiovascular system or directly enter the brain through the olfactory route and may negatively affect the central nervous system. The size distribution and chemical composition of traffic-related UFP can vary substantially between different types of engines and fuels, which in return potentially alters the neurotoxic potency of emitted PM. Aiming to shed light on the impact that different types of engine and fuel as well as UFP fractions have on the neurotoxic potency of traffic-related UFP, we screened several diesel exhaust-derived UFP and PM for their neurotoxic hazard. UFP test samples where generated by light and heavy duty diesel engines fueled with high- or low-aromatic diesel and the non-volatile and semi-volatile UFP fractions were collected on Teflon filters. UFP samples were extracted and used for further neurotoxicity screening in rat primary cortical cell cultures grown on multi-well microelectrode arrays (MEA). To do so, spontaneous neuronal network activity was determined before and up to 120 h during UFP exposure (1-100 μg/mL and 1-20 L/mL). Additionally, cell viability was assessed after the final MEA recording to distinguish between specific neurotoxic effects and general cytotoxicity. Exposure to diesel and biodiesel exhaust-derived PM decreased neuronal activity dosedependent without affecting cell viability. However, diesel exhaust-derived PM was evidently more potent. Semi-volatile organic compounds (SVOC) UFP originating from high-aromatic (A20) and low-aromatic (A0) diesel fuel decreased the neuronal activity, although higher doses also exhibiting cytotoxicity. Interestingly, the non-volatile UFP fraction of A0 and A20 diesel fuel did not affect neuronal activity and cytotoxicity, indicating that the SVOC exhibited considerably higher neurotoxic potency than non-volatile UFP. In the presented work, we demonstrated that diesel engine exhaust-derived UFP exhibit neurotoxic hazard, but also that the potency is dependent on sample generation conditions. Concluding, our data suggest that more emphasis should be placed on the emission of the SVOC fraction, which represent a larger hazard for brain health compared to the non-volatile fraction.