32P-postlabeling analysis of DNA adduct formation and persistence in English sole (Pleuronectes vetulus) exposed to benzo[a]pyrene and 7H-dibenzo[c,g]carbazole.
The formation and persistence of benzo[a]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 English sole based on its ability to induce formation of preneoplastic foci, while DBC is a hepatocarcinogen in mammals but whose carcinogenicity in fish is not known. English sole liver was sampled from 2 h through 84 days after a single intermuscular injection of a BaP and DBC mixture (100 mumol of each/kg body wt.), and DNA adduct levels were measured by the nuclease P1 version of the 32P-postlabeling assay. The major BaP adducts detected were from binding of BaP-7,8-diol-9,10-epoxide to DNA, whereas multiple uncharacterized DBC-DNA adducts were detected. Total adduct levels for both BaP and DBC reached a maximum at 2 days post exposure. The levels of DBC-DNA adducts were greater than the levels of BaP adducts at all time points and increased more rapidly than did the levels of BaP-DNA adducts. The DBC to BaP adduct ratio was 33 +/- 8.8 at 2 h and declined to 4.2 +/- 0.48 by 12 h post exposure. From 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 apparent decline from 28 to 84 days in the levels of the remaining BaP or DBC adducts; these persistent adducts represented 32 and 36% of maximum levels, respectively. These results provide the first data on the kinetics of adduct formation and removal of a carcinogenic nitrogen-containing polycyclic aromatic compound in fish. The results showing greater binding and similar persistence of DBC-DNA adducts compared to BaP-DNA adducts suggest that DBC may be hepatotoxic and potentially carcinogenic in English sole. In a separate experiment, the effect of multiple doses of BaP (30 mumol/kg body wt.) on the levels of hepatic BaP-DNA 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 and DBC-DNA adducts in liver, together with the increase in BaP-DNA adducts in English sole exposed to successive doses of BaP, suggest that hepatic xenobiotic-DNA adducts in English sole are molecular dosimeters of relatively longterm environmental exposure to genotoxic polycyclic aromatic compounds.
Stein
J E
JE
Environmental Conservation Division, National Oceanic and Atmospheric Administration, Seattle, WA 98112-2097.
Reichert
W L
WL
French
B
B
Varanasi
U
U
D000818:Animals; D001564:Benzo(a)pyrene / Q000633:toxicity*; D002227:Carbazoles / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D004247:DNA / Q000032:analysis / Q000187:drug effects*; D004357:Drug Synergism; D005399:Fishes; D007553:Isotope Labeling; D008099:Liver / Q000187:drug effects; D010761:Phosphorus Radioisotopes
D002227:Carbazoles; D002273:Carcinogens; D010761:Phosphorus Radioisotopes; D001564:Benzo(a)pyrene; D004247:DNA; C013478:7H-dibenzo(c,g)carbazole