Furan-induced dose–response relationships for liver cytotoxicity, cell proliferation, and tumorigenicity (furan-induced liver tumorigenicity)

Rodent studies of furan are associated with liver cell necrosis, release of liver-associated enzymes, increased hepatocyte proliferation, and hepatocarcinogenesis. For carcinogens whose proposed mode of action is cytolethality, it is hypothesized that the dose–response curve for tumor development would parallel the dose–response curve for cell death with compensatory proliferation in the target organ. To prospectively test this hypothesis, female B6C3F1 mice were exposed to furan at carcinogenic doses and lower for 3 weeks or 2 years. At 3 weeks and in the 2-year study, there were dose-dependent and significant increases in hepatic cytotoxicity at 1.0, 2.0, 4.0, and 8.0 mg furan/kg. For cell proliferation as measured by 5-bromo-2′-deoxyuridine (BrdU) labeling index (LI), there was a statistically significant trend with increasing dose levels of furan and increased LI at 8.0 mg/kg. There was an increased incidence of foci of altered hepatocytes, hepatocellular adenomas, and adenomas or carcinomas at 4.0 and 8.0 mg/kg and carcinomas at 8.0 mg/kg. The multiplicity of microscopic tumors was increased and latency was decreased in mice exposed to 8.0 mg/kg. Prevalence of hepatic nodules at necropsy was increased in mice exposed to 4.0 and 8.0 mg/kg. Data demonstrate an association among furan-induced hepatic cytotoxicity, compensatory cell replication, and liver tumor formation in mice; at high doses ⩾4.0 mg/kg, furan induced hepatotoxicity, compensatory cell replication and tumorigenesis in a dose-related manner, while furan did not produce tumors at cytotoxic doses of 1.0 and 2.0 mg/kg.