8, 9, 26 When Lombardi et al. combined CD with azaserine27 (not known to be a hepatocarcinogen) or with either of the liver carcinogens ethionine10 and acetylaminofluorene28 and fed to Sprague-Dawley rats at approximately 8 weeks of age, they reported rapid development of HCC, with an incidence of up to 80% after 6 months, and only selleck screening library a 38% incidence of CCAs.28 When initiation by diethylnitrosamine was followed by CDE, Takahashi et al. obtained similar results.29 Mikol et al.30 found a 90%-100% incidence of HCC in Fischer 344 rats initiated with diethylnitrosamine and fed a diet devoid of methionine and choline. We have no clear explanation

for why our present finding of a high incidence of CCA in rats fed cyclic CDE beginning at 3 weeks of age but no HCC in either the rats started on CDE at 3 weeks or 8 weeks, is different from other results previously reported. Clearly, most investigators have reported HCC in the various hepatocarcinogenic regimens that induce oval cell proliferation. However, AG-014699 order to the best of our knowledge,

no other study used cyclic CDE exposure. Perhaps the week off during each cycle allows putative liver stem cells to evade death or differentiation and thus be able to give rise to CCAs; in contrast, with continuous CDE exposure, the stem cells would be forced to differentiate, such that they give rise to relatively few CCAs and more HCCs. An alternative explanation is that the default differentiation pathway of oval cells is to form ducts. If this Niclosamide is true, then when hepatocarcinogenic regimens induce large numbers of oval cells, CCAs would be expected rather than HCCs. We chose a cyclic CDE dietary schedule for two principal reasons. The main reason was to reduce morbidity and mortality during a chronic feeding schedule, based on previous studies using a cyclic feeding of acetylaminofluorene.31, 32 Rats continuously fed CDE for more than 2 weeks in our previous studies died with massive oval cell proliferation.33 A secondary reason was as an attempt to augment oval cell proliferation and tumor development, by repetitive exposure to a CD diet.10, 28 Choline deficiency induces a state of fat deposition, apoptosis, and compensatory regeneration; in this

abnormal situation, hepatocytes are forced to divide repeatedly, such that the deficiency has been termed a nutritional partial hepatectomy.34 The aberrant hepatocyte proliferation within the liver is believed to be the fundamental alteration that is ultimately responsible for the development of HCC from a methyl-deficient diet.35 As discussed above, our results are in contrast to those found previously. In a study entailing a CD diet, only 51% of male F344 rats fed that CD diet for 13-24 months had developed HCC by the end of the 24-month period.36 Three months duration on a continuous CD diet has been considered to be the minimum period required to induce HCC.34 It is thus possible that we did not expose the rats to total CDE for a sufficiently long enough period.