Indoor particulate matter exposure is associated with increased black carbon content in airway macrophages of former smokers with COPD

Exposure to fine particulate matter (PM2.5) is associated with worse morbidity in individuals with COPD. Inhaled PM is phagocytosed by airway macrophages (AM), and black carbon measured in AM may serve as a biomarker of air pollution exposure. As there is little data on how indoor PM exposure may influence AM black carbon content in those with respiratory disease, we investigated the association of indoor PM2.5 concentration to AM black carbon content in adults with COPD.Former smokers (>10 pack-years smoking history, quit date >1 year prior to enrollment) older than 40 years of age with moderate-severe COPD were eligible. Indoor air PM2.5 concentrations were measured over 5–7 days at baseline, 3 month, and 6 month intervals. Sputum induction was performed during clinic visits concordant with home monitoring. A total of 50 macrophages per sputum specimen were photographed and quantified using appropriate software by trained staff blinded to PM concentrations. Longitudinal analyses using generalized estimating equations were used to assess the relationship between indoor PM exposure and AM black carbon content.Participants (n=20) were older (mean (SD) age 67 (4) years), predominantly Caucasian (85%) and male (70%), with an average smoking history of 52 pack-years and mean (SD) quit date of 13 (9) years prior to enrollment. The majority of daily time was reported to be spent indoors (>23h). Mean indoor PM2.5 concentration was 12.8 (13.5)µg/m3. The mean area of black carbon quantified in airway macrophages was 1.2 (0.7)µm2. In multivariate cross-sectional and longitudinal analyses, each 10µg/m3 increase in indoor PM2.5 was significantly associated with a 0.26µm2 and 0.19µm2 increase in airway macrophage black carbon total area, respectively (p<0.05).Higher indoor PM2.5 concentration is associated with an increase in black carbon content of AM in individuals with COPD. These data support the potential for AM black carbon content to be a useful non-invasive biomarker of exposure to indoor PM.