Ozone Generation Method Impacts Lung Toxicity and Oxidant Signaling

Ozone (O3) is a criteria pollutant that is anticipated to increase over the next decade because of climate-related activity. Varying amounts of nitrogen oxides (NOx) are produced as byproducts during O3 generation from oxygen depending on the method of production, including the source and oxygen purity. A review of the current literature confirms a lack of consistent monitoring and reporting of potential nitrogen species produced with different methods of experimental O3 generation. The lack of consistent monitoring and reporting is potentially a factor that can explain divergence of reported experimental O3 exposure outcomes from different research groups. In the present report, we compare the effects of O3 generation from either a filtered air (FA-ozone) or a pure oxygen (Oxy-ozone) source on NOx generation and measures of O3-induced lung injury. We also consider if this impacts mixed exposures with O3 and ultrafine carbon black (CB) based on if the O3 was generated from a filtered air (FA-ozone-CB) versus a pure oxygen (Oxy-ozone-CB) source. Comparing FA-ozone versus Oxy-ozone, we observed increased lung inflammation and injury in the FA-ozone group. In the FA-ozone-CB group, compared with the Oxy-ozone-CB group, the FA-ozone-CB inhalation exposure resulted in the formation of a greater amount of NOx and induced protein nitrotyrosine in the lungs. Moreover, the FA-ozone-CB group had evidence of eosinophil recruitment not observed in the Oxy-ozone-CB group. Overall, this suggests that the source of oxygen for O3 generation impacts experimental outcomes. Furthermore, measurement and reporting of nitrogen species in O3 exposure should be considered.