Hepatitis B virus (HBV) transgenic mice (official designation, Tg [Alb-1 HBV] Bri 44)
invariably develop macroscopically evident tumors within the 20th month of life. Sustained
proliferative activity seems to play an important role in the development of these lesions. We
previously showed that ursodeoxycholate (UDC) stimulates hepatocyte proliferation in
various experimental settings. Herein, we tested the assumption that biological factors able
to further increase liver cell proliferation, such as UDC, could accelerate tumor development
in this animal model. For this study, 22 eight-week-old male transgenic mice were divided
into 2 groups; 11 animals received a standard diet, and 11 received a UDC-enriched diet. The
2 groups were further divided into 2 subgroups of 5 and 6 animals each and were sacrificed
at 3 and 15 months of age, respectively. These different times were chosen to exclude
diet-related toxicity (in 3-month-old mice) and evaluate tumor growth (in 15-month-old
mice). In addition, hepatocyte proliferation was assessed in all animals. In 3-month-old mice
receiving UDC, cholestatic and cytolytic indices as well as liver histology were comparable to
those in controls. At 15 months, all UDC-treated mice showed large multinodular tumors
whereas only 33% of controls developed smaller uninodular neoplasms. Hepatocyte proliferation
was increased in all animals receiving UDC compared with controls. In conclusion,
the increase in serum UDC (undetectable in mice fed a standard diet), in the absence of any
toxic effect on the liver, suggests the involvement of this bile salt in the stimulation of
hepatocyte proliferation and tumor growth