Airway microbiota dysbiosis and metabolic disorder in ozone and PM2.5 co-exposure induced lung inflammatory injury in mice

Co-exposure to ground-level ozone (O3) and fine particles (PM2.5, <= 2.5 mu m in diameter) has become a primary scenario for air pollution exposure of urbanites in China. Recent studies have suggested a synergistic effect of PM2.5 and O3 on induction of lung inflammatory injury. However, the underlying mechanisms for respiratory toxicity induced by this co-exposure have not been adequately elucidated. In this study, a realistic exposure was based to set up the co-exposure condition of an animal model. Specifically, eighty male C57BL/6 mice (10 months old) were randomly divided into four groups: control, O3, PM2.5 and co-exposure (O3 + PM2.5). Mice in the co-exposure group breathed O3 and orally inhaled PM2.5 suspension. The scenario for O3 exposure was 0.6 ppm, 4 h/d, for 30 consecutive days while that for PM2.5 exposure was oral inhalation of PM2.5 suspension (5.6 mg/kg bw) once every other day and 4 h prior to O3 exposure. After last exposure, bronchoalveolar lavage fluids (BALF) were collected for inflammatory biomarker measurement, 16S rRNA sequencing and metabolite profiling. Lung tissues were processed for histological examination. The results demonstrated that co-exposure to O3 and PM2.5 exacerbated the pathological changes and inflammatory response induced by O3 or PM2.5. Further studies revealed that co-exposure to O3 and PM2.5 increased the abundance of Prevotella in the airways and caused more severe metabolic disorders compared to O3 or PM2.5 exposure. Spearman correlation analysis demonstrated correlations among airway microbiota dysbiosis, metabolic disorder, inflammation, and pathological alterations induced by co-exposure to O3 and PM2.5. In summary, co-exposure to O3 and PM2.5 worsens airway inflammatory injury, possibly through interrelated airway microbiota dysbiosis and metabolic disorder.