In this report, we compare cellular responses in the livers of rats exposed to hepatocarcinogenesis beginning at 3 weeks of age, beginning at 8 weeks of age, and in retired breeders (10-12 months of age), using a previously well-studied chemical regimen, choline-deficient, ethionine-supplemented (CDE) diet.8-10 Following the hierarchical model of Pierce et al.,11 combined with analysis of the cellular events selleck compound during chemical hepatocarcinogenesis, we

previously concluded that, in adults, liver cancers can arise from liver stem cells (oval cells), transit-amplifying cells (ducts or immature hepatocytes), or mature hepatocytes, depending on the stage of maturation arrest.12-15 Although that model fit the experimental

observations on the cellular origin of hepatocellular carcinomas (HCCs) and cholangiocarcinomas (CCAs), it did not include the step between pluripotent stem cells (teratocarcinoma) and the liver lineage cells. The missing link is a cancer known as hepatoblastoma (HB).16, 17 HB completes the cellular lineage of liver cancer that extends from pluripotent stem cells to liver-determined stem cells to ductular stem cells to mature liver cells (Fig. 1A). We reasoned that if more liver stem cells are present, or if liver stem cells have greater potential in young rats as compared to old rats, then treatment of very young rats with a potent hepatocarcinogenic regimen should induce a more intense oval cell response and result in production of less well-differentiated HCCs, possibly such as HBs, than does treatment SPTLC1 of older rats.18 We report here that cyclic CDE treatment

EPZ-6438 in vivo of rats beginning at 3 weeks of age indeed caused a much higher level proliferation of oval cells than did treatment of rats beginning at 8 weeks of age and older. However, unexpectedly, exposure of the younger rats resulted in a high incidence of cholangiofibrosis and bile duct cancers, rather than HBs, suggesting that by 3 weeks of age the reactive liver-specific stem cells of the rat that give rise to cancer are already determined beyond the hepatoblast stage to ductal cell precursors. CCA, cholangiocarcinoma; CD, choline-deficient; CDE, choline-deficient, ethionine-supplemented; HCC, hepatocellular carcinoma Male Fischer 344 rats were obtained from Taconic Farms, Germantown, NY. Rats were housed in the Wadsworth Center’s animal facility and had free access to standard laboratory chow and water when not in the cyclic CDE regimen. All animal experiments were approved by and performed under the guidelines of the Wadsworth Center’s Institutional Animal Care and Use Committee (IACUC). A choline-deficient diet was obtained from Dyets, Inc., Bethlehem, PA (catalogue #518753). D,L-Ethionine was purchased from Sigma Chemical Co., St. Louis, MO (catalogue #E5139). A cyclic feeding regimen of the CDE diet was followed. One cycle consisted of 2 weeks on the choline-deficient (CD) diet, followed by 1 week off.