Associations between ambient air pollutants and serum Clara cell protein concentrations among elderly men in Oslo, Norway

OBJECTIVE: This study aims to investigate associations between serum Clara cell protein concentrations, among a population of elderly men in Oslo, Norway, and exposures to ambient air pollutants. METHODS: A variety of methods have been used to study the effects of ambient air pollution on human health. Recently, a new approach referred to as, "pneumoproteinemia" was developed to evaluate the integrity of the pulmonary epithelium by measuring the concentration of lung-specific proteins in serum. The prototypic pneumoprotein is the 16-kDa Clara cell protein (CC16), an anti-inflammatory protein secreted by Clara cells in the respiratory tract and predominantly in terminal bronchioles from where it leaks into serum. This study used an enzyme-linked immunosorbent assay (ELISA) to determine serum CC16 concentrations for 1200 blood samples that were drawn during the Oslo Study II. RESULTS: Unadjusted serum CC16 concentrations ranged from 1.2 to 115.2 ìg/L with a geometric mean of 9.4 ìg/L. Statistically significant associations were found between serum CC16 concentrations and the following: age; chronic bronchitis and/or emphysema; smoking status; number of cigarettes smoked per day; and particulate matter (PM10 and PM2.5) exposures (one-week before the basic clinical examination). No associations were found between serum CC16 concentrations and the following: education level; NO2, PM10, and PM2.5 exposures one-year before the basic clinical examination. There was a 0.2 percent change in serum CC16 concentrations for each one µg/m3 change in PM10 exposure that occurred one-week before the basic clinical examination. In addition, there was a 0.2 percent change in serum CC16 concentrations for each one µg/m3 change in PM2.5 exposure that occurred one-week before the basic clinical examination. These effects remained unchanged after adjusting for age, self-reported chronic bronchitis and/or emphysema, smoking status, and number of cigarettes smoked per day. CONCLUSIONS: The findings of this study support other studies that have found evidence of associations between serum CC16 concentrations and ambient air pollutants. In addition, results of this study are consistent with other studies that have reported small but statistically significant increases in adverse respiratory effects as a result of recent PM2.5 and PM10 exposures. Lastly, the results indicate that effects of PM2.5 and PM10 exposures that occurred one-week before the basic clinical examination on serum CC16 concentrations were less than that of other known factors such as cigarette smoking. Keywords: ambient air pollution, cross-sectional study, cigarette smoking, respiratory disease, serum Clara cell protein (CC16)