Level of Opisthorchis infestation and carcinogen dose-dependence of cholangiocarcinoma induction in Syrian golden hamsters.

The relationship between different levels of liver fluke, Opisthorchis viverrini infestation and dimethylnitrosamine (DMN) dosage in the induction of cholangiocarcinomas was investigated in Syrian golden hamsters. Two hundred and eighty male, weanling animals were divided into 4 groups: Group 1 served as untreated controls; group 2 received O. viverrini metacercariae only at levels of 100, 50, 25 or 12 per animal; group 3 received DMN only at doses of 12.5, 6.25 or 3.125 ppm; group 4 received various combinations of metacercariae and DMN. Only 2 of 17 animals (12%) in group 3 receiving 12.5 ppm had detectable tumours and no neoplastic lesions were seen in the 6.25 and 3.125 ppm DMN subgroups or in parasite alone or untreated control hamsters. In contrast, high carcinogen and parasite dose-dependent yields of cholangiocarcinomas (incidences up to 93%) and putative preneoplastic cholangiofibrotic lesions were observed in group 4. Thus the results indicate clear dose-dependent synergistic effects for the two agents and reveal the crucial importance of the presence of parasite, even at levels as low as 12 metacercariae, for DMN induction of bile duct carcinogenesis.