In ovo carcinogenicity assay (IOCA): evaluation of mannitol, caprolactam and nitrosoproline

The in ovo carcinogenicity assay (IOCA) was used to examine whether the noncarcinogens epsilon-caprolactam (CAP), D-mannitol (MAN) and nitrosoproline (NPRO) induce toxicity and subsequently morphological changes in embryonic turkey livers compared with the carcinogen diethylnitrosamine (DEN). Various doses of the test compounds were injected into fertilized turkey or quail eggs prior to incubation. Embryonic livers were collected 3-4 days before hatching and processed for histology. The positive control DEN induced hepatocyte altered foci (HAF) and karyomegalic hepatocytes, whereas histological analysis of livers from embryos exposed to CAP, MAN and NPRO did not show such histological changes. The effects of the tested compounds on liver were further examined in hepatocytes cultured from exposed turkey and quail embryos. As observed in ovo, megalocytes as well as karyomegalic hepatocytes were present in hepatocyte cultures established from DEN-exposed turkey embryos, but not from embryos exposed to CAP, MAN or NPRO. It is concluded that CAP, MAN and NPRO do not induce histological changes in embryonic liver of the type produced by the carcinogen DEN, correlating with findings for these compounds in rodent studies.