DIFFERENTIATION OF OVAL CELLS INTO DUCT-LIKE CELLS IN PRENEOPLASTIC LIVER OF RATS PLACED ON A CHOLINE-DEFICIENT DIET SUPPLEMENTED WITH ETHIONINE

Feeding male Wistar rats a choline-deficient diet containing 0.07% DL-ethionine (CDE diet) for up to 5 weeks results in the production of two distinct non-parenchymal cell populations, oval and duct-like cells, These cells can undergo replication and display different patterns of expression of glutathione S-transferases (GSTs) and pyruvate kinases (PKs). Oval cells were first detected around the periportal region after 1 week of CDE treatment and infiltrated the parenchyma after 2 weeks, Duct-like structures first appeared as isolated ducts in the parenchymal region at 2 weeks and were easily detected after 2.5 weeks, These duct-like structures differed from the bile ducts which reside in the portal region, Large concentrations of duct-like structures in cyst-like clusters were detected after 5 weeks, Enlargement of these structures from single ducts to clusters of up to 20 ducts was observed over 3-5 weeks of CDE treatment, The number of cells forming a duct increased from 5 to 30 cells, We established a double immunocytochemical staining technique to characterize the oval and duct-like cells for their expression of GSTs and PKs, pi GST and M(2)-PK, which are fetal hepatocytes isoenzymes, are present in virtually all the oval and duct-like cells. Most of the oval cells are devoid of the adult hepatocytes markers, alpha GST, mu GST and L-PK. There are two sub-populations of duct-like cells, one which expresses only fetal markers and the other which co-expresses the adult and fetal isoenzymes. Hence, oval cells display characteristics of fetal hepatocytes and some duct-like cells appear more mature than oval cells, Using a combination of double immunocytochemical and [H-3]thymidine labelling techniques we have established that oval cells differentiate into duct-like cells.