P-32 POSTLABELING ANALYSIS OF DNA ADDUCT FORMATION AND PERSISTENCE INENGLISH SOLE (PLEURONECTES-VETULUS) EXPOSED TO BENZOA!PYRENE AND 7H-DIBENZOC,G!CARBAZOLE

The formation and persistence of benzoa!pyrene (BaP)- and 7H-dibenzo c,g!carbazole (DBC)-DNA adducts in liver of English sole (Pleuronectes vetulus) were investigated. BaP is a putative hepatocarcinogen in Eng lish sole based on its ability to induce formation of preneoplastic fo ci, while DBC is a hepatocarcinogen in mammals but whose carcinogenici ty in fish is not known. English sole liver was sampled from 2 h throu gh 84 days after a single intermuscular injection of a BaP and DBC mix ture (100 mumol of each/kg body wt.), and DNA adduct levels were measu red by the nuclease Pl version of the P-32-postlabeling assay. The maj or BaP adducts detected were from binding of BaP-7,8-diol-9,10-epoxide to DNA, whereas multiple uncharacterized DBC-DNA adducts were detecte d. Total adduct levels for both BaP and DBC reached a maximum at 2 day s post exposure. The levels of DBC-DNA adducts were greater than the l evels of BaP adducts at all time points and increased more rapidly tha n did the levels of BaP-DNA adducts. The DBC to BaP adduct ratio was 3 3 +/- 8.8 at 2 h and declined to 4.2 +/- 0.48 by 12 h post exposure. F rom 2 to 28 days, the levels of both BaP and DBC adducts declined with apparent half-lives of 11 and 13 days, respectively. There was no app arent decline from 28 to 84 days in the levels of the remaining BaP or DBC adducts; these persistent adducts represented 32 and 36% of maxim um levels, respectively. These results provide the first data on the k inetics of adduct formation and removal of a carcinogenic nitrogen-con taining polycyclic aromatic compound in fish. The results showing grea ter binding and similar persistence of DBC-DNA adducts compared to BaP -DNA adducts suggest that DBC may be hepatotoxic and potentially carci nogenic in English sole. In a separate experiment, the effect of multi ple doses of BaP (30 mumol/kg body wt.) on the levels of hepatic BaP-D NA adducts showed that adduct levels increased linearly (r = 0.815, P = 0.0007) with 5 successive doses administered at 2 day-intervals and sampled 2 days after the last dose. The persistence of both BaP-DNA an d DBC-DNA adducts in liver, together with the increase in BaP-DNA addu cts in English sole exposed to successive doses of BaP, suggest that h epatic xenobiotic-DNA adducts in English sole are molecular dosimeters of relatively longterm environmental exposure to genotoxic polycyclic aromatic compounds.