Detection of DNA strand breaks by comet assay in sputum leucocytes of bitumen-exposed workers: a pilot study

DNA strand breaks were determined in leucocytes of induced sputum (IS) and compared with DNA strand breaks in blood lymphocytes from 42 bitumen-exposed workers pre and post shift. Comet assay results were expressed in arbitrary units based on visual scoring (sputum leucocytes) and Olive tail moment (OTM, blood lymphocytes). DNA damage in IS leucocytes was overall high but did not change during shift. Level of DNA strand breaks in IS samples correlated with total cell count and neutrophil content (Spearman rank correlation coefficient r(s) = 0.47, p = 0.001, r(s)= 0.48, p = 0.001, respectively) and with IL-8 concentration before and after shift (r(s) = 0.31, P = 0.048, and r(s) = 0.43, P = 0.005). DNA damage in IS was not associated with DNA strand breaks in blood lymphocytes (r(s) = -0.04, p = 0.802 before shift, r(s) = 0.27, p = 0.088 after shift). A higher level of DNA strand breaks was measured in blood lymphocytes before shift (median OTM 1.7 before and 1.3 after shift, p = 0.023). A strong correlation was found between the number of neutrophils and IL-8 concentration in IS before and after shift (r(s) = 0.77 and r(s)= 0.75, p < 0.001). This study showed an association between genotoxic and inflammatory effects in the lower airways and compared simultaneously DNA strand breaks in IS and blood of bitumen-exposed workers.