Sex modifies response to ozone and nitrogen dioxide: a controlled human exposure study

Background Ozone (O3) and nitrogen dioxide (NO2) are highly reactive gases associated with all cause-mortality. Epidemiology studies suggest that the risk from O3 and NO2 exposure is modified by sex. O3 is more strongly associated with declines in pulmonary function in males, but females show stronger associations with cardiovascular disease (CVD). For NO2 exposure, females show stronger associations for increased risk of CVD, loss of lung function, and mortality. It remains unclear if these differences stem from social constructs or underlying biologic responses.Methods To investigate sex differences after pollutant exposure, we used a single blind, randomized crossover, controlled exposure study to examine the pulmonary, inflammatory, and clotting/fibrinolysis response after exposure to O3 and NO2 relative to clean air. Healthy adult participants (n = 22 male = 10, female = 12) underwent separate two-hour exposures to clean air, 300 ppb O3, and 500 ppb NO2 exposures while exercising intermittently.Results Compared to air, exposure to O3 resulted in a mean percent change in FEV1 (-5.74%, 95%CI: −7.83, −3.65, p < 0.001), FVC (-3.94%, 95%CI: −5.59, −2.30, p < 0.001), and FEV1/FVC (-1.90%, 95%CI: −3.54, −0.25, p < 0.01), and elevated IL-6 (16.3%, 95%CI: 0.51, 32.14, p < 0.01), C-Reactive Protein (CRP) (44.54%; 95%CI: 15.44, 73.65, p < 0.001), and Serum amyloid A (SAA) (33.6%; 95%CI: 7.30, 60.0, p < 0.01). NO2 exposure resulted in a mean percent change of D-dimer (10.9%, 95%CI: −0.23, 21.93, p < 0.05). When stratified by sex, after O3 exposure, males displayed greater decrements in FEV1 (males; −7.81% (95%CI: −11.45, −4.19) females: −4.00% (95%CI: −6.20, −1.80; p < 0.05)) and CRP increased in males by 78.50% (95%CI: 27.50, 129.50) compared to 16.20% (95%CI: −10.43, 42.84) in females (p < 0.01) and SAA increased in males by 60.25% (95%CI: 12.02, 108.48) compared to 15.18% (95%CI: −14.53, 44.90) in females (p = 0.051). TNFα was elevated in females by an average of 10.9% (95%CI: 0.75, 21.23) compared to males (-2.29%, 95%CI: −12.32, 7.75) (p < 0.05). After NO2, D-dimer was elevated in females by 18.98% (95%CI: 4.69, 33.26) compared to males (1.52%, 95%CI: −16.12,19.16) (p = 0.062).Conclusions Sex modified the pulmonary and inflammatory response to O3 and NO2, a finding consistent with epidemiological observations of sex differences after O3 and NO2 exposure.