Hepatic oval cell response to the choline-deficient, ethionine supplemented model of murine liver injury is attenuated by the administration of a cyclo-oxygenase 2 inhibitor

Oval cell proliferation precedes neoplasia in many rodent models of hepatocellular carcinoma and prevention of this proliferative response can reduce the risk of subsequent carcinoma. This study aimed to determine whether a selective cyclo-oxygenase-2 (COX-2) inhibitor, SC-236, affects (i) the oval cell response to liver injury in a mouse model of hepatocarcinogenesis and (ii) an oval cell line. Four-week-old mice were fed either normal chow or a choline deficient, ethionine supplemented (CDE) diet in the presence or absence of SC-236. Liver histology and oval cell numbers were determined after 2, 4, 12 and 52 weeks of treatment. Oval cells were scored using morphological criteria and positive immuno-staining for the M-2-isozyme of pyruvate kinase (M2PK) or A6. An immortalized oval cell line (PIL-2) was used to study the in vitro effects of SC-236 on oval cell proliferation, apoptosis and Akt phosphorylation. The percentage of M2PK-positive oval cells and COX-2-positive cells was reduced by 80% and 45%, respectively, in CDE-fed mice receiving SC-236 compared with CDE-fed animals not receiving SC-236. Some M2PK-positive oval cells were also COX-2 positive. The percentage of A6-positive cells was not affected by SC-236 administration to CDE-fed mice. Administration of SC-236 increased apoptosis as evidenced by a 73% increase in the number of TUNEL-positive cells at 2 weeks in CDE-fed mice. Primary oval cells and PIL-2 cells expressed COX-2. In vitro treatment of PIL-2 cells with SC-236 resulted in a dose-dependent preferential death of A6-negative cells. Administration of 25 and 50 mu M Prostaglandin E-2 partially attenuated SC-236 induced cell death by 25%. In vitro oval cell death was associated with apoptosis and a 70% reduction in Akt phosphorylation. These results suggest that the SC-236 induced reduction of M2PK-positive oval cell numbers may be due to COX-2 dependent inhibition of Akt phosphorylation and induction of apoptosis.