Treatment with 2-AAF blocks the small hepatocyte-like progenitor cell response in retrorsine-exposed rats

Liver regeneration after partial hepatectomy (PH) in retrorsine-exposed rats is accomplished through proliferation and differentiation of small hepatocyte-like progenitor cells (SHPCs). The cells of origin of SHPCs are not known. We investigated the possibility that SHPCs are directly derived from oval cells, a known liver progenitor cell, by combining the retrorsine/PH (RP) model with 2-acetamidofluorene (2-AAF), an anti-mitotic agent that elicits an oval cell reaction in response to liver deficit.

Male Fischer 344 rats were treated with retrorsine (30 mg/kg ip) at 6 and 8 weeks of age, with PH 5 weeks after the final treatment. Seven days prior to PH, a 21-day 2-AAF (50mg) time-release pellet was inserted subcutaneously. Livers were harvested at 3, 7, 10, 14, and 21-days post-PH.

Liver sections from animals treated with 2-AAF/retrorsine/PH (2-AAF/RP) contain significant numbers of proliferating oval cells, but no SHPCs at 7-days post-PH, while RP animals exhibit significant numbers of SHPCs and minimal oval cell reaction. Between 10 and 14-days post-PH, new hepatocyte clusters appear in 2-AAF/RP treated rats. Labeling of proliferating oval cells with BrdU at 6-days post-PH demonstrated that these new hepatocytes represent the progeny of differentiating oval cells.

The observed differences in progenitor cell responses between 2-AAF/RP and RP animals strongly suggest that SHPCs are not the progeny of oval cell precursors, but represent an independent liver progenitor cell population.