Biomarkers aiming at cancer risk estimation of polycyclic aromatic hydrocarbons

Sammanfattning: Polycyclic aromatic hydrocarbons (PAH), a family of compounds that are formed in incomplete combustion of organic matter, occur as general pollutants in air and food. Exposure to PAH is, according to preliminary estimates, associated with non-acceptable cancer risks showing the need for improved data to be used in risk estimation. Risk assessment of PAH is a complex matter, i.a. because certain PAH could increase cancer risk by more than one mechanism, with different dose-response.This study deals mainly with development and evaluation of biomarkers for dose. Benzo[a]pyrene (BaP), and fluoranthene in the early experiments, were chosen as indicators of PAH exposure. Among BaP metabolites, ± (anti)r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) is regarded to be the predominant cancer initiator. In mice with deficient DNA repair, given BaP by gavage, the dGuo-N2 adduct levels in DNA, reflecting doses of BPDE, were approximately the same in different tissues. The results indicate that BPDE markers in blood could be used to measure the average target dose. The large amounts of blood proteins (serum-albumin (SA) and hemoglobin (Hb)) and the well defined in vivo turnover kinetics, without repair, make blood proteins more suitable dose monitors than DNA.A new way of isolating and measuring histidine (His) adducts of BPDE in SA and Hb has been developed. His adducts were released from the proteins by treatment with hydrazine. After derivatization and enrichment with C18 and cation solid phase extraction the His adduct was obtained in a form suitable for analysis by liquid chromatography/mass spectrometry. The hydrazinolysis of BPDE-treated human Hb and SA released both new and earlier known adducts from the proteins. The level observed of His adducts in the SA and Hb corresponded to 70 and 10 %, respectively, of the total adduct level in the in vitro-treated proteins.Following acute treatment (i.p.) of mice with radiolabelled BaP the adducts in SA, Hb and DNA were determined. In the SA samples the His adducts from BPDE were quantified, as well as two other so far unidentified products from BaP metabolites. The levels of the His adduct were roughly 10 times higher in SA than in Hb. The dGuo-N2 adduct levels in liver and lung DNA were 14 - 40 times higher than the His adduct in SA per unit of weight.The mutagenic effectiveness of BPDE and g-radiation were determined in V79 cells. An incremental formation of one dGuo-N2 adduct per 108 nucleotides was found to have a mutagenic potency corresponding to that of about 1 cGy.The usefulness of biomarkers for genotoxic and immunotoxic effects in mice exposed to low levels of diesel exhaust (10 mg PAH per kg body weight) were examined. Ethoxyresorufin O-deethylase activity was used to measure induction status of CYP1 isoenzymes and it was concluded that exposure to ambient levels of diesel exhaust would probably not lead to induction.On the basis of the results obtained some gaps in quantitative knowledge necessary in risk estimation of BaP has been filled and remaining gaps could be defined. It is indicated that the present methods together with other sensitive techniques are applicable in risk estimation of PAH at current exposure levels, that is in the low-dose range, below exposure levels leading to enzyme induction including promotion.