Comparative metabolism of benzo(a)pyrene and covalent binding to hepatic DNA in English sole, starry flounder, and rat.

Metabolism of benzo(a)pyrene (BaP) in vivo and in vitro was studied using two benthic fish species, English sole (Parophrys vetulus) and starry flounder (Platichthys stellatus), and Sprague-Dawley rats. At 24 h after administration of BaP (7.9 mumol/kg of body weight) to fish either p.o. (Experiment 1) or i.p. (Experiment 2), the specific activity of binding of BaP metabolites to hepatic DNA (pmol of BaP equivalent per mg of DNA) was higher in sole [2.1 in Experiment 1; 28 +/- 5 (SE) in Experiment 2] than in flounder (0.5 in Experiment 1; 14 +/- 4 in Experiment 2). Treatment of bile with beta-glucuronidase and arylsulfatase released a significantly higher proportion of 7,8-dihydroxy-7,8-dihydro-BaP (BaP 7,8-diol) from sole bile than from flounder bile in both experiments. However, the rate of BaP metabolism and rate of formation of BaP 7,8-diol by hepatic microsomes were comparable for both fish species. Thus, the differences in both the level of DNA binding and the concentration of BaP 7,8-diol in bile of BaP-exposed sole and flounder were apparently due to differences in detoxication, rather than formation, of BaP 7,8-oxide and BaP 7,8-diol-9,10-epoxide. The rate of formation of BaP 7,8-diol by rat liver microsomes (28 +/- 1 pmol of BaP 7,8-diol formed per min per mg of protein) was comparable to that by hepatic microsomes from both fish species (50 +/- 10 for sole and 33 +/- 6 for flounder), although the rate of BaP metabolism (600 +/- 200) was approximately 3 times greater than that by the fish species (190 +/- 60 for sole and 180 +/- 40 for flounder). Thus, greater proportion of BaP was converted to BaP 7,8-diol by liver microsomes of fish species than rat. These differences in BaP metabolism in vitro help explain, in part, the substantially lower binding (0.3 +/- 0.1; Experiment 2) for hepatic DNA in BaP-exposed rat than that in either sole or flounder.

Formation and persistence of benzo[a]pyrene-diolepoxide-DNA adducts in liver of English sole (Parophrys vetulus).

The formation of DNA adducts from the carcinogenic environmental pollutant benzo[a]pyrene (BaP) was investigated in liver of English sole (Parophrys vetulus), a fish species that exhibits a high prevalence of liver neoplasms in several polycyclic aromatic hydrocarbon (PAH)-contaminated areas of Puget Sound, WA. Analysis by the 32P-postlabeling assay of hepatic DNA digests from English sole exposed parenterally to BaP showed the presence of BaP-diol epoxide (BaPDE)-DNA adducts. When English sole were injected with 2-15 mg BaP/kg body wt., one major adduct was detected and was identified as the anti-BaPDE-DNA adduct. Moreover, in English sole sampled at 1, 28 and 60 days post-exposure to 15 mg BaP/kg body wt., there was no significant change in the level of the anti-BaPDE-DNA adduct. The autoradiographs of 32P-labeled hepatic DNA digests from fish exposed to 100 mg BaP/kg body wt. showed an elongated spot suggesting the presence of more than one adduct. Chromatography on large polyethyleneimine sheets (20 x 20 cm) showed 2 spots with the same chromatographic characteristics as those of syn- and anti-BaPDE-deoxyguanosine adduct standards. Mild acid hydrolysis of hepatic DNA of English sole, exposed to 100 mg BaP/kg body wt., also revealed the presence of tetrols derived from both anti- and syn-BaPDE, thus confirming the presence of syn- and anti-BaPDE. In fish exposed to 2-100 mg BaP/kg body wt., a linear (0.996) dose response for anti-BaPDE-DNA adduct formation was observed. The results from this study offer the first direct evidence for the formation of the suspected ultimate carcinogen, BaPDE, in liver of English sole exposed to BaP in vivo and thus further support the hypothesis that exposure to PAHs is an important factor in the etiology of hepatic neoplasms in English sole from contaminated sites.