The major risk factors for human liver cancer: hepatitis B virus (HBV) related liver injury, male gender, aflatoxin exposure, and p53 expression, are evaluated and compared in experimental transgenic mouse models. Transgenic mice that express hepatitis B surface antigen (HBsAg) in their liver and develop liver tumors at 18 months of age (HBVϩ mice) were bred to p53 null mice (p53Ϫ/Ϫ) to produce mice p53ϩ/Ϫ, HBVϩ mice. These mice and control littermates ([p53ϩ/ϩ, HBVϩ], [p53ϩ/Ϫ, HBVϪ], and [p53ϩ/ϩ, HBVϪ]) were divided into groups that did or did not receive an injection of aflatoxin at 1 week of age. At sacrifice at 13 months of age, 100% (7/7) of male mice with each of the three risk factors (p53ϩ/Ϫ, HBVϩ, AFB 1 ϩ) developed high-grade hepatocellular carcinomas (HCC). If any one of the risk factors was absent, the incidence drops: if both p53 alleles are present, 62% (10/16); if HBsAg is not expressed, 14% (1/7); if AFB 1 is not given, 25% (2/8). If only one of the risk factors is present no tumors above grade I are found. Similar results were observed in female mice except that HCC incidence in each group is less than in male mice. Some of the tumors in mice with more than one risk factor are of unusual histological types, such as hepatocholangiocarcinomas, adenocarcinomas and undifferentiated carcinomas that are not usually seen in HBV transgenic C57BL/6 mice. No loss or mutation of the p53 gene is detected in any of the tumors. Possibilities of how the four major risk factors for HCC interact to produce malignant liver tumors in these transgenic mouse models of hepatocarcinogenesis are discussed. (HEPATOLOGY 1998;27:383-391.)
MATERIALS AND METHODS
Experimental Procedures
Mice. C57BL/6 mice have been used extensively in chemical hepatocarcinogenesis studies. They do not develop HCCs spontaneously and are resistant to chemical hepatocarcinogenesis. They are well suited for hepatocarcinogenesis studies and therefore were Abbreviations: HCC, hepatocellular carcinoma; AFB 1 , aflatoxin B 1 ; HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen; PCR, polymerase chain reaction; LOH, loss of heterozygosity; SSCP, single strand conformational polymorphism.