ported by the finding that the early population of oval cells, The existence of a facultative hepatic stem cell comwhich represent the progeny of the hepatic stem cell compartpartment in bile ductules that participates in the rement, are both phenotypically similar to bile ductular cells newal process of epithelial cell populations in the liver and indeed may at least at an early stage be anatomically is well documented. The present study was undertaken connected to the bile tree. 3 The differentiation of oval cells to determine whether the immature bile epithelium reinto hepatocytes has now been shown in several experimental sponds differently to growth stimulus induced by bile models in which normal liver regeneration was impaired bestasis to that seen in the adult animal. In addition, the cause of the inability of hepatocytes to enter the cell cycle. 9-11 possible involvement of the growth factor/receptor sys-The most common experimental model used to induce extems associated with early activation of hepatic stem tensive and prolonged proliferation of bile epithelial cells in cells in bile duct proliferation was also examined. Bile duct ligation was used to induce the proliferation of bile the adult rat is the ligation of the common bile duct. 12 The epithelial cells. The expression of full-length alpha-feto-results from these experiments have shown that proliferation protein (AFP) was used as an indicator for activation of of bile-like cells are derived from existing biliary epithelium the stem cell compartment. AFP was highly and selec-and retain its characteristics; that bile duct cells divide irretively expressed in small bile ducts 7 days after bile duct spective of size of the ducts in which they are located, and ligation in immature rats up to 5 weeks of age. Although retain a lumen that is continuous with the preexisting biliary no significant increase in the expression of stem cell fac-tree. 13 Furthermore, no indications of a functioning stem cell tor (SCF) c-kit, hepatocyte growth factor (HGF), and compartment for the proliferation of either biliary epithelium transforming growth factor-a (TGF-a) was observed 7 or other cell lineages have been observed in any particular days after bile duct ligation in adult rats, the expression duct size or within the periportal connective tissue. 13 These of all these growth factors was increased in bile duct data suggest that the bile epithelium, and in particular the ligated rats up to 5 weeks of age. These results suggest bile ductular epithelium responds in a dramatically different that the bile ductular epithelium in the young rats re-way to growth stimulation induced by the ligation of the comsponds to bile stasis in a fashion that is phenotypically mon bile duct to that observed in the experimental models in similar to that seen during early activation of hepatic which oval cell proliferation occurs. Because the development stem cells in adult liver. (HEPATOLOGY 1997;25:1115-1122.) and maturation of the biliary system extends well into the perinatal period...

The expansion and differentiation of oval cells in the acetylaminofluorene (AAF)/partial hepatectomy (PH) model was studied utilizing pulse-chase labeling with both tritiated thymidine ([3H]TdR) and bromodeoxyuridine (BUdR). Animals in which a significant decrease in serum albumin and increase in alanine aminotransferase and bilirubin were observed demonstrated the most prominent differentiation of oval cells into hepatocytes. Administration of [3H]TdR or BUdR, either individually or together, to the animals on day 6 after partial hepatectomy resulted in labeling of the majority of the oval cells by days 7 and 9 after PH. A striking difference in the distribution of [3H]TdR- and BUdR-labeled cells in the double labeling experiments was observed on day 11, at which time the number of [3H]TdR-labeled cells increased 6-fold and that of double labeled cells decreased 2-fold. Furthermore, on day 11 the basophilic foci were weakly positive for BUdR and negative at later time points in animals receiving BUdR alone or together with [3H]TdR. In contrast, the cells in basophilic foci as well as transitional cells were positive for [3H]TdR. Cells heavily labeled with both [3H]TdR and BUdR were present at all time points, indicating an inhibition of the proliferative activity. Pulse labeling of rat liver epithelial cells with BUdR in vitro demonstrated that immunodetection of BUdR was lost after three or more cell divisions. We conclude that the BUdR tagging method is particularly sensitive to label dilution during cell cycling and may not be suitable for establishment of a precursor-product relationship between cell lineages when the progenitor population proliferates more than three times.

The stage of neurogenesis can be divided into three steps: proliferation, migration, and differentiation. To elucidate detailed relations between these three steps after ischemia, the authors evaluated the three steps in the adult gerbil dentate gyrus (DG) after 5 minutes of transient global ischemia using bromodeoxyuridine (BrdU), highly polysialylated neural cell adhesion molecule (PSA-NCAM), and neuronal nuclear antigen (NeuN) and glial fibrillary acidic protein (GFAP) as markers for proliferation, migration, and differentiation, respectively. Bromodeoxyuridine-labeled cells increased approximately sevenfold, and PSA-NCAM-positive cells increased approximately threefold in the subgranular zone (SGZ) with a peak 10 days after ischemia. Bromodeoxyuridine-labeled cells with PSA-NCAM expression were first detected both in the SGZ and the granule cell layer (GCL) 20 days after ischemia and gradually decreased after that, whereas BrdU-labeled cells with NeuN gradually increased in the GCL until 60 days after ischemia. A few BrdU-labeled cells with GFAP expression were detected in DG after ischemia; no PSA-NCAM-positive cells with GFAP expression were detected, but the radial processes of glial cells were partly in contact with PSA-NCAM-positive cell bodies and dendrites. These results suggest that neural stem cell proliferation begins at the SGZ, and that the cells then migrate into the GCL and differentiate mainly into neuronal cells. The majority of these three steps finished in 2 months after transient global ischemia.

3-methyl-1-phenyl-2-pyrazolin-5-one (Edaravone) is a free radical scavenger. We tested the hypothesis that combination treatment of Edaravone and recombinant tissue plasminogen activator (tPA) extends the therapeutic time window. Male Wistar rats were subjected to 1.5-, 3.0- or 4.5-hour middle cerebral artery (MCA) occlusion (MCAO) by a nylon thread. Animals were randomly divided into four groups. The Sham group rats were operated without MCAO and drug injection. In the Vehicle-treated group the same volume of saline was given every 1.5 hours from just after MCAO to just before reperfusion. In the Vehicle + tPA-treated group saline injection was given as above and tPA (5 mg/kg, i.v.) was given once just after reperfusion. Edaravone+tPA-treated group: Edaravone (3 mg/kg, i.v.) was given every 1.5 hours instead of saline and tPA injection as above. Survival rate, infarct size and evidence of apoptosis and hemorrhage were examined in the animals. Combining administration of Edaravone+tPA significantly increased survival rate after 3 hours of transient MCAO, and reduced infarct volume after 1.5 hours of transient MCAO compared with the vehicle or vehicle+tPA groups. In Edaravone+tPA-treated group, the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling (TUNEL) and 4-hydroxynonenal (4-HNE) positive cells were reduced at 16 hours after 3 hours of transient MCAO, but not in advanced glycation end products (AGEs) and 8-hydroxy-2'-deoxyguanosine (8-OHdG). Hemorrhage rate and the area decreased in the Edaravone+tPA-treated group. The combination therapy of Edaravone+tPA increased survival rate, and reduced the infarct volume and hemorrhage with reduction of lipid peroxidation. Therefore, Edaravone combination is expected to extend the therapeutic time window of tPA in the clinical situation.