No abstract

Eighteen-mo feeding trials of rainbow trout were used to test the carcinogenicity of 5 chemicals in this species. A single exposure level was used for each substance. The doses and chemicals tested were 1,556 ppm 2,6-dimethylnltrosomorpholine (DMNM), 500 ppm N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 2,000 ppm 1,2-dibromoethane (DBE), 2,000 ppm 1,1-dichloroethylene (DCE), and 200 ppm cyclophosphamide (CP). Liver and/or glandular stomach neoplasms were produced by DMNM (liver and stomach), MNNG (stomach), and DBE (chiefly, stomach tumors). In addition, DMNM produced a low incidence of swimbladder papillomas and caused testicular atrophy in 50% of treated males. DCE and CP produced no neoplasms at the exposure levels used. No evidence of other chronic toxicity was seen for any of the 5 compounds.

No abstract

Indole-3-carbinol (I3C), a component of cruciferous vegetables, was previously shown to inhibit aflatoxin B1 (AFB1) carcinogenesis in trout. The purpose of this study was to examine the effect of I3C on AFB1 metabolism and hepatic DNA adduct formation in vivo and in vitro. When fed at 0.2%, I3C produced a 70% reduction in average in vivo hepatic DNA binding of injected AFB1 over a 21-day period when compared to controls. A 24-h distribution study of injected tritiated AFB1 in I3C fish showed less total radioactivity in the blood and liver at all times examined, compared to controls. These reductions were due primarily to reduced levels of AFB1 bound to red blood cell DNA, reduced plasma levels of the primary metabolite aflatoxicol (AFL), and decreased levels of AFB1 and polar metabolites present in the liver of I3C fish. In contrast to blood, total radioactivity was significantly elevated in the bile of I3C fish resulting from a 7-fold increase in aflatoxicol-M1 glucuronide levels over controls. No difference was observed in concentration of AFL glucuronide, the primary conjugate present in control fish. There was no difference in total radioactivity remaining in the carcass of I3C or control fish. AFB1 metabolism in freshly isolated hepatocytes from I3C fish showed 20% less DNA binding in a 1-h assay, with a 2-fold increase in aflatoxin M1 production. Addition of I3C to control hepatocytes at levels of 1, 10 or 100 microM had no effect on AFB1 DNA binding. These findings indicate that I3C inhibition of AFB1 hepatocarcinogenesis in trout involves substantial changes in the pharmacokinetics of carcinogen distribution, metabolism and elimination, leading to significantly reduced initial hepatic-nuclear DNA damage in vivo.

No abstract