PM2.5-bound metals and blood metals are associated with pulmonary function and Th17/Treg imbalance: A panel study of asthmatic adults

Growing research has demonstrated that exposure to fine particulate matter (PM2.5) was associated with decreased pulmonary function and obvious inflammatory response. However, few pieces of research focus on the effects of PM2.5-bound metals on people with asthma. Here, we assessed whether PM2.5 and PM2.5-bound metals exposure could worsen pulmonary function in asthmatic patients and further elucidate the possible mechanisms. Thirty-four asthmatic patients were recruited to follow up for one year with eight visits in 2019-2020 in Taiyuan City, China. The index of pulmonary function was detected and blood and nasal epithelial lining fluid (ELF) samples were acquired for biomarkers measurement at each follow-up. Linear mixed-effect (LME) models were used to evaluate the relations between PM2.5, PM2.5-bound metals, and blood metals with lung function and biomarkers of Th17/Treg balance. The individual PM2.5 exposure concentration varied from 37 μg/m3 to 194 μg/m3 (mean: 59.63 μg/m3) in the present study. An interquartile range (IQR) increment of PM2.5 total mass was associated with a faster decline in maximal mid-expiratory flow (MMEF) and higher interleukin-23 (IL-23). PM2.5-bound metals [e.g. copper (Cu), nickel (Ni), manganese (Mn), titanium (Ti), and zinc (Zn)] were significantly associated with IL-23 (Cu: 5.1126%, 95% CI: 9.3708, 0.8544; Mn: 14.7212%, 95% CI: 27.926, 1.5164; Ni: 1.0269%, 95% CI: 2.0273, 0.0264; Ti: 16.7536%, 95% CI: 31.6203, 1.8869; Zn: 24.5806%, 95% CI: 46.609, 2.5522). Meanwhile, blood lead (Pb) and Cu were associated with significant declines of 0.382-3.895% in MMEF and maximum ventilatory volume (MVV). Blood Pb was associated with descending transforming growth factor β (TGF-β). In conclusion, exposure to PM2.5-bound metals and blood metals is a risk factor for decreased pulmonary function, especially in small airways. These alterations might be partially attributed to the imbalance of Th17/Treg.