Molecular Dosimetry of DNA Damage Induced by Polycyclic Aromatic Hydrocarbons; Relevance for Exposure Monitoring and Risk Assessment

Abstract

Polycyclic aromatic hydrocarbons (PAH) form a large group of organic chemicals that are widely distributed in our environment as pollutants of air, water and soil. Several PAH are carcinogenic in rodents, while exposure to these compounds has been associated with various types of human cancer. Upon entering the body, PAH may be converted into reactive electrophilic species, which can give rise to the formation of DNA adducts. DNA adduct formation is considered to be the initial event in chemical carcinogenesis. In this paper, two methods are illustrated that are widely used to determine PAH-DNA adduct formation, namely 32P-postlabelling, and immunochemical analysis with specific antibodies. The applications of the 32P-postlabelling assay comprise the following: - A study of interspecies differences in PAH bioactivation in vitro, with microsomal preparations isolated from liver tissue of various rodent species and of human origin; the results indicate that there are considerable qualitative differences between the adduct patterns obtained, which is relevant with respect to extrapolation from animal to man. - The analysis of DNA adduct formation in fish retrieved from marine environments polluted to various extents with PAH; results of these studies show a correlation between liver-DNA adduct levels in these fish and the degree of PAH contamination in the aquatic environment. - Biomonitoring of PAH exposure through analysis of adducts in blood cells obtained from heavy and light smokers; the data show a fair correlation between PAH-DNA adduct levels in white blood cells and cotinine content in blood plasma, the latter being used as a marker for exposure to cigarette smoke. The activity of the detoxifying enzyme glutathione S-transferase M (GSTM1) was also determined in these individuals. Immunochemical analysis with a benzo(a)pyrene(BP)-DNA-specific antiserum was used to investigate BP-adduct induction in situ, in different epithelial cell types—basal/non—basal cells—of hamster trachea exposed to BP in vitro, Histochemical staining of cell-specific cytokeratins was combined with adduct-specific immunostaining. The latter was quantified by immunofluorescence microscopy. The results show that removal of DNA adducts from the basal cells is more rapid during the first 24 h following exposure than from the non-basal cells. The sensitive methods for molecular dosimetry of DNA damage, as illustrated in this paper, appear suitable for determining exposure of animals and humans to PAH. Further animal experiments and in vitro model studies will provide useful additional information that will help evaluate the relevance of biomonitoring data with respect to the health risk that may be associated with the exposure.