AN IMMUNOHISTOCHEMICAL STUDY ON THE PROLIFERATIVE, PRENEOPLASTIC AND NEOPLASTIC HEPATOCELLULAR LESIONS BY SHORT-AND MID-TERM EXPERIMENTS IN MICE EXPOSED TO HEPATOCARCINOGENS

Abstract

Short- and mid-term model systems for analyzing the early proliferative responses of hepatocytes following administration of hepatocarcinogens were used to elucidate the biological nature and morphogenesis of preneoplastic and neoplastic lesions involving hepatocytes of B6C3F₁ mice exposed to test chemicals in a long-term carcinogenicity study. Immunohistochemical detection of bromodeoxyuridine (BrdU) incorporation and proliferating cell nuclear antigen (PCNA) expression, in addition to immunohistochemical analysis of the induction of cytochrome P-450 isozymes in the livers of these mice were compared one week after receiving a single dose of one of the following chemicals; diethylnitrosamine, safrole, phenobarbital, and non-genotoxic carcinogens (Xa and Xb). Differences in the time or the site of the appearance of PCNA-positive hepatocytes, and the regional expression of P-450 isozymes in the liver, were seen between these chemicals. Each type of preneoplastic foci of cell alteration (FCA) and neoplasia, both hepatocellular adenoma (HCA) and carcinoma (HCC), were analyzed at the 18 and 25 week stages in studies on diethylnitrosamine-initiated two-step, hepatocarcinogenesis in mice promoted by phenobarbital and/or sex hormones (testosterone in the males, and ethinylestradiol in the females). Marked heterogeneity in the staining of each phenotype of basophilic and eosinophilic FCA, or HCA with biomarkers, including PAS, P-450, G-6-Pase, γ-GT, π-GST, and PCNA, was seen. There were no apparent differences between the characteristics of each type of chemically-induced proliferative nodular lesions and the spontaneously occurring ones. Biomarker analysis of the proliferative hepatocytes from short- and mid-term model mice may help to predict the hepatocarcinogenicity and the potency of test chemicals, although further studies with a variety of known hepatocarcinogens will be needed.