Clara cell protein (CC16) in serum and bronchoalveolar lavage fluid of subjects exposed to asbestos

The Clara cell protein (CC16) is a small and readily diffusible protein of 16kDa secreted by bronchiolar Clara cells in the distal airspaces. These epithelial cells are altered in several pulmonary pathological processes induced by various lung toxicants. In the search for a new biomarker of asbestos-induced lung impairment, we used a sensitive immunoassay to determine the levels of CC16 in bronchoalveolar fluid (BALF) and serum of subjects exposed to asbestos compared with a group of healthy controls. In the BALF of asbestos-exposed subjects there was an insignificant trend towards CC16 elevation compared with controls, with a (mean ±SD of 0.81 ±0.65mg l^-1 for asbestos-exposed subjects (n = 23) versus 0.39 ±0.19mg l^-1 for controls (n = 11) (p = 0.09). In serum, CC16 concentration was significantly increased among asbestos-exposed subjects, with values of 27.2 ±24.0 µg l^-1 for asbestos-exposed subjects (n = 34) versus 16.1 ±7.6 µg l^-1 for controls (n = 34) (p = 0.01). Regarding the effects of smoking, there were significant differences between generally lower CC16 levels in serum and BALF (p = 0.05 and 0.001, respectively) of smokers compared with the higher levels in non-smokers. Serum CC16 levels positively correlated with those in BALF, which is consistent with a diffusional transfer of CC16 from the bronchoalveolar space into the serum. No association, however, emerged between the levels of CC16 in serum or BALF and either the duration of asbestos exposure or the severity of the lung impairment as assessed by chest X-ray. These findings suggest that exposure to asbestos elicits early changes in the local and, importantly, also the systemic levels of CC16. This pneumoprotein therefore appears as a promising non-invasive biomarker of asbestos-induced lung injury and occupational disease in both smoking and non-smoking exposed subjects.