The liver fluke Opisthorchis felineus is a member of the triad of epidemiologically relevant species of the trematode family Opisthorchiidae, and the causative agent of opisthorchiasis felinea over an extensive range that spans regions of Eurasia. The International Agency for Research on Cancer classifies the infection with the liver flukes Opisthorchis viverrini and Clonorchis sinensis as group 1 agents and a major risk factor for cholangiocarcinoma. However, the carcinogenic potential of the infection with O. felineus is less clear. Here, we present findings that support the inclusion of O. felineus in the Group 1 list of biological carcinogens. Two discrete lines of evidence support the notion that infection with this liver fluke is carcinogenic. First, novel oxysterol-like metabolites detected by liquid chromatography-mass spectroscopy in the egg and adult developmental stages of O. felineus, and in bile, sera, and urine of liver fluke-infected hamsters exhibited marked similarity to oxysterol-like molecules known from O. viverrini. Numerous oxysterols and related DNA-adducts detected in the liver fluke eggs and in bile from infected hamsters suggested that infection-associated oxysterols induced chromosomal lesions in host cells. Second, histological analysis of liver sections from hamsters infected with O. felineus confirmed portal area enlargement, inflammation with severe periductal fibrosis and changes in the epithelium of the biliary tract characterized as biliary intraepithelial neoplasia, BilIN. The consonance of these biochemical and histopathological changes revealed that O. felineus infection in this rodent model induced precancerous lesions conducive to malignancy.

The food-borne liver trematode Opisthorchis felineus is an emerging source of biliary tract diseases on the territory of the former Soviet Union and Eastern Europe. This parasite along with trematodes Opisthorchis viverrini and Clonorchis sinensis belong to the triad of epidemiologically important liver flukes of the Opisthorchiidae family. It is known that O. viverrini and C. sinensis are the main risk factors of cholangiocarcinoma (CCA) in the endemic regions. The carcinogenic potential of O. felineus has not been well researched because of the absence of systematic pathomorphological, clinical, and epidemiological studies on O. felineus opisthorchiasis. In the present study, we show the results of detailed histopathological analysis and comprehensive evaluation of inflammation, bile duct dysplasia, periductal fibrosis, bile duct hyperplasia, bile duct proliferation, egg granuloma, cysts, cholangiofibrosis, and CCA from 10 to 30 weeks following infection of Syrian hamsters with O. felineus accompanied by oral administration of dimethylnitrosamine (DMN). The results revealed that O. felineus contributes to bile duct cancer development in the hamster model. During the combined action of O. felineus and DMN, morphological features of the liver underwent dramatic changes at the cellular and organ levels. Already in the early stages of the experiment, we observed extensive periductal fibrosis, active inflammation, proliferation of the bile duct, bile duct dysplasia and egg granulomas. Later, against the background of all these changes, cholangiofibrosis and CCA were found. Our work is the first step in the study of carcinogenic potential of O. felineus. Obtained data indicate the risk of CCA of patients having chronic O. felineus opisthorchiasis, and underscore the need for the development of programs for control of this helminthiasis.

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