The risk of persistent asthma increases with plasma fluorescent oxidation product (FlOPs) levels, and new evidence has been uncovered on the role of oxidative stress in association with asthma and outdoor air pollution, according to study results published in Environmental Health.
Evidence continues to grow on the association between outdoor air pollution and persistent asthma; however, this association has not been studied extensively in adults. Researchers hypothesized that oxidative stress may be an underlying biological mechanism involved in the association between persistent asthma and outdoor air pollution. In the Epidemiological study of the Genetic and Environmental factors of Asthma, researchers reported that higher plasma FlOPs were significantly associated with asthma attacks, poor lung function, and poor asthma control. The objective of this study was to evaluate the role of FlOPs — oxidative stress-related biomarkers — as potential mediators in the association between persistent asthma and outdoor air pollution.
In this study, researchers conducted analyses on 204 adults with asthma from the Epidemiological study of the Genetic and Environmental factors of Asthma who were followed up at 12 years after baseline. Among this group, researchers studied the associations between persistent asthma and nitrogen dioxide, nitrogen oxides, road traffic, and particulate matter (PM) using the European Study of Cohorts for Air Pollution Effects models. Mediation analysis was used to evaluate the mediated effect by FlOPs levels and the interaction between outdoor air pollution and FlOPs levels.
Results revealed that plasma FlOPs levels increased with exposures to PM₁₀ and ozone (adjusted , 0.04, 95% CI, 0.001-0.08, P =.03 and adjusted β, 0.04, 95% CI, 0.009-0.07 per 10 μg/m³, P =.02, respectively), and that the risk for persistent asthma increased with plasma FlOPs levels (adjusted odds ratio [aOR], 1.81, 95% CI, 1.08-3.02, P =.02). The risk for persistent asthma decreased, though not significantly, with exposures to nitrogen dioxide, nitrogen oxides, and PM₂.₅ (aOR ranging from 0.62-0.94), and increased, though not significantly, with exposures to PM₁₀, ozone, ozone-summer, and road traffic, with the greater effect being observed for ozone (aOR, 1.78, 95% CI, 0.73-4.37).
Results from meditation analysis between ozone, persistent asthma, and plasma FlOPs levels revealed a positive total effect (OR total effect=2.16, 95% CI, 0.70-11.9, P >.05), a positive natural direct effect of ozone on persistent asthma (OR natural direct effect=1.68, 95% CI, 0.57-7.25, P >.05), and a positive natural indirect effect mediated by plasma FlOPs levels (OR natural indirect effect, 1.28, 95% CI, 1.01-2.29, P =.04). The percentage of total effect mediated by plasma FlOPs levels was 41.1%.
Estimates from mediation analysis may be imprecise due to this study’s small sample size; therefore, researchers warn that results should be interpreted with caution. Additionally, results may be biased, since researchers lacked the data needed to properly assess the extent of acute exposure to ozone.
The study researchers concluded that the risk for persistent asthma increased in tandem with plasma FlOPs levels. They also concluded that findings from this study add insight into the potential role of plasma FlOPs levels in the association between persistent asthma and ozone and into the role of oxidative stress in the association between asthma and outdoor air pollution.
Havet A, Li Z, Zerimech F, et al. Does the oxidative stress play a role in the associations between outdoor air pollution and persistent asthma in adults? Findings from the EGEA study [published online October 29, 2019. Environ Health. doi: 10.1186/s12940-019-0532-0