Expression of immunoreactive glutathione S-transferases in hepatic neoplasms induced by aflatoxin B1 or 1,2-dimethylbenzanthracene in rainbow trout (Oncorhynchus mykiss).

The expression of immunoreactive glutathione S-transferase (GST) was examined in hepatic neoplasms induced in rainbow trout by aflatoxin B1 (AFB) or 1,2-dimethylbenzanthracene (DMBA). Tumors were induced in adult trout by continuous dietary exposure to 8 p.p.b. AFB1 for 12 months or embryo bath exposure to DMBA (5 p.p.m. for 24 h, 3 times with 12 h intervals between exposures). Polyclonal antiserum specific for the two major trout hepatic GST subunits in trout liver was produced by immunizing rabbits with affinity-purified trout GST. Hepatocellular, cholangiolar and mixed neoplasms as well as foci of hepatocellular alteration were examined for GST immunoreactivity by the PAP technique. The majority of lesions were GST-deficient (AFB treated, 67%; DMBA treated, 54%), whereas GST expression was induced in 21% (AFB treated) and 31% (DMBA treated) of altered hepatic foci. The GST-induced foci were consistently small (AFB treated, 0.07 +/- 0.05 mm2; DMBA treated, 0.02 +/- 0.01 mm2) and none had progressed beyond the altered focus stage. The majority of larger advanced lesions (adenomas and carcinomas) were GST deficient (AFB treated, 2.33 +/- 0.35 mm2; DMBA treated, 2.95 +/- 0.59 mm2). These studies demonstrate that induced GST expression occurs in some small populations of hepatocytes, but not in larger advanced stages of malignant progression of aflatoxin- or PAH-induced hepatic neoplasms in rainbow trout.