Histopathologic Studies on Liver Tumorigenesis Induced in Mice by Technical Polychlorinated Biphenyls and Its Promoting Effect on Liver Tumors Induced by Benzene Hexachloride 2

Abstract

The effects of technical polychlorinated biphenyls (P'<Bs) on mouse liver were examined histologically and ultrastructurally. Pathologic studies were also made on the effects of PCBs on tumorigenesis induced by benzene hexachloride (BHC) in mouse liver. Neoplastic changes were observed in livers of mice fed a basal diet containing 500 parts per million (ppm) of the PCBs, Kanechlor 500, for 32 weeks. Amyloid degeneration in the liver of mice was observed in groups fed a diet containing lower concentrations of PCBs. Histologically and ultrastructurally, the neoplastic areas of mouse liver induced by PCBs appeared to be typical nodular hyperplasias and well-differentiated hepatocellular carcinomas. The effects of PCBs on neoplastic changes induced by isomers of BHC in the livers of mice fed a diet containing BHC with or without PCBs for 24 weeks were studied. Among groups fed BHC alone, only the group receiving 250 ppm of the a-isomer developed nodular hyperplasia and hepatocellular carcinoma. However, among the groups fed BHC plus PCBs, only those receiving 100 or 50 ppm of a-BHC or 250 or 100 ppm of p-BHC developed nodular hyperplasia and hepatocellular carcinoma. Groups fed 'Y-BHC with or without PCBs did not show neoplastic changes of the liver. Thus PCBs themselves induced hepatic neoplasms in mice and also promoted the induction of tumors bya-BHC and p-BHC.

Polychlorinated Biphenyls and Polybrominated Biphenyls

“…Groups of 12 male dd strain albino mice (age, 8 weeks) were fed basal diets supplemented with one of three PCB mixtures (Kanechlor 300, 400, or 500) at a concentration of 100, 250, or 500 ppm for 32 weeks; a control group of six mice was fed basal diet alone (Ito et al, 1973;Faroon et al, 2001). The incidences of hepatocellular carcinoma (5 out of 12 [not significant]) and liver hyperplastic nodules [some of which may have been hepatocellular adenomas] (7 out of 12 [P < 0.05]) were increased in mice fed diets containing Kanechlor 500 at 500 ppm compared with controls (0 out of 6).…”

“…A study by Ito et al (1973) examined the effects of co-administration of Kanechlor 500 and one isomer of benzene hexachloride (BHC) [hexachlorocyclohexane] on the incidence of nodular hyperplasia of the liver and hepatocellular carcinoma. Groups of male dd mice (age, 8 weeks) were given diets containing α-, β-, or γ-BHC (50, 100 or 250 mg/kg) for 24 weeks, with or without Kanechlor 500 (250 mg/kg).…”

Proposed Occupational Exposure Limits for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals

“…The carcinogenic effects of PCBs have been shown to be dependent on chlorine content in mice and rats fed diets containing 30-60% chlorine PCBs (Ito et al 1974;Ito et al 1973, reported in ACGIH 2001c. In mice, no tumors occurred in groups fed less than 54% chlorine PCB.…”

Proliferative lesions of the glandular stomach and liver in F344 rats fed diets containing Aroclor 1254.

“…Polychlorinated biphenyls (PCBs) have been shown to induce liver tumors in rats (1)(2)(3)(4)(5)) and mice (6)(7)(8) and to promote development of liver preneoplastic foci and tumors initiated by other carcinogens in liver (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). In the early 1970s, little was known of the carcinogenic potential of PCBs.…”