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Live Tumor-Promoting Effect of β-Naphthoflavone, a Strong CYP 1A1/2 Inducer, and the Relationship between CYP 1A1/2 Induction and Cx32 Decrease in Its Hepatocarcinogenesis in the RatDivision of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan Interrelationships among induction of cytochrome P-450 (CYP) 1A1/2, decrease in connexin 32 (Cx32), and liver tumor-promoting activity by β-naphthoflavone (BNF) in the promotion stage were examined in a 2-stage liver carcinogenesis model. A total of 20 male Fischer 344 rats were initiated with a single intraperitoneal injection of 150 mg/kg of diethylnitrosamine (DEN) or were given the saline vehicle alone. Starting 2 weeks later, they were fed a diet containing 2%, 1%, or 0% BNF for 6 weeks. All animals were subjected to a two-thirds partial hepatectomy at week 3 and were sacrificed at week 8. Absolute and relative liver weights were significantly increased in the DEN+BNF groups as compared to the DEN-alone group. Diffuse hepatocellular hypertrophy with cytoplasmic eosinophilia, sometimes accompanied by development of adenoma-like hepatic foci, was observed in the BNF-treated rats. Remarkable induction of cytochrome CYP 1A1/2 and significant increase in CYP 2E1 were noted in the DEN+BNF groups, and positive immunohistochemical staining for both was observed diffusely. The areas of Cx32-positive spots per hepatocyte in the centrilobular areas of livers of the BNF-treated rats were significantly decreased, but no changes were observed in periportal areas. The numbers and areas of foci positive for glutathione S-transferase placental form were increased in the BNF-treated groups. These results suggest that BNF is a liver tumor promoter that, unlike phenobarbital, does not induce CYP 2B1/2 isozymes, and there seems to be no direct relationship between CYP 1A1/2 induction and Cx32 reduction in BNF hepatocarcinogenesis.
Key Words: Connexin • gap junction • neoplasm • P-450 • phenobarbital • promotion
Toxicologic Pathology, Vol. 28, No. 4,
540-547 (2000) This article has been cited by other articles:
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