Effects of São Paulo air pollution on the upper airways of mice

The nose is the first region of the respiratory tract to come in contact with airborne pollutants. Previous studies have shown that the nasal mucosa can be altered in response to air pollution. In this study, we quantified neutral and acidic mucus in three different levels of the nasal cavity of mice exposed to ambient levels of air pollution in the city of São Paulo, Brazil. Two groups of 6-day-old male Swiss mice were placed in two exposure chambers. Mice were maintained in the chambers 24 h/day, 7 days/week for 5 months. The first chamber contained an air filter device (clean chamber; n=20), whereas the second one received ambient air pollution (polluted chamber; n=20). We measured the concentration of PM2.5, nitrogen dioxide (NO2), and black carbon inside both chambers. The nasal cavity was transversely sectioned at three specific anatomic locations (proximal, medial, and distal levels) and submitted to quantitative analysis of the amounts of neutral and acidic mucosubstances. We observed a 37.85% decrease in NO2, 54.77% decrease in PM2.5, and 100% decrease in black carbon concentration in the clean chamber compared to the polluted chamber. Significant differences between polluted and clean chambers were observed in the epithelium lining the septum of proximal and medial levels of the nasal mucosa, with an increase in the percentage of acidic mucus in the polluted chamber (P=0.037, proximal level; P=0.023, medial level). We conclude that prolonged exposure to low levels of ambient air pollution from an early age shows evidence of causing secretory changes in the nasal cavity of mice, with increased production of acidic mucosubstances.