An ex vivo model of systemically-mediated effects of ozone inhalation on the brain.

Air pollution is associated with increased risk of neurodegenerative and neuropsychiatric conditions. While animal models have increased our understanding of how air pollution contributes to brain pathologies - including through oxidative stress, inflammatory, and stress hormone pathways - investigation of underlying mechanisms remains limited due to a lack of human-relevant models that incorporate systemic processes. Our objective was to establish an ex vivo approach that enables assessment of the roles of plasma mediators in pollutant-induced effects in the brain. As a proof-of-concept for application in the human context, we assessed whether such effects reproduced in vivo responses to pollutant exposure. Primary rat hippocampal neurons and microglia were each treated with plasma collected from rats immediately or 24 h after ozone inhalation (0 or 0.8 ppm) ± pre-treatment with the glucocorticoid synthesis inhibitor metyrapone. Microglia were further challenged with lipopolysaccharide to evaluate modification of inflammatory responses. Plasma from the ozone-exposed group produced transcriptional changes (inflammatory, antioxidant, glucocorticoid-responsive) in neurons, some of which were glucocorticoid-dependent. Ex vivo and hippocampal responses were strongly correlated, establishing the in vivo relevance of the model. Plasma from the ozone-exposed group modified inflammatory responses to lipopolysaccharide challenge in microglia, demonstrating the model's utility to assess functional changes resulting from pollutant exposure. This study establishes that an ex vivo approach can reproduce ozone-induced effects in the brain. The model was sensitive to specific plasma mediators and temporal effects, and enabled assessment of functional responses. This approach may serve to investigate mechanisms underlying effects of pollutants on the human brain.