Journal Article

Nonadditive Hepatic Tumor Promoting Effects by a Mixture of Two Structurally Different Polychlorinated Biphenyls in Female Rat Livers

C. E. Dean, S. A. Benjamin, L. S. Chubb, J. D. Tessari and T. J. Keefe

in Toxicological Sciences

Volume 66, issue 1, pages 54-61
Published in print March 2002 | ISSN: 1096-6080
Published online March 2002 | e-ISSN: 1096-0929 | DOI: http://dx.doi.org/10.1093/toxsci/66.1.54
Nonadditive Hepatic Tumor Promoting Effects by a Mixture of Two Structurally Different Polychlorinated Biphenyls in Female Rat Livers

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This study evaluates and quantifies the interactive hepatic tumor promoting effects of two PCBs, the Ah receptor agonist PCB 126 (3,3`,4,4`,5-pentachlorobiphenyl) and the constitutive androstane receptor (CAR) agonist PCB 153 (2,2`,4,4`,5,5`-hexachlorobiphenyl). Promotion of altered hepatic foci was evaluated utilizing a medium-term 8-week bioassay for promoters of hepatocarcinogenesis. The assay employs placental glutathione-S-transferase positive (GST-P+) liver cell foci as markers of preneoplasia in female Fischer 344 rats treated with the known initiator diethylnitrosamine followed by partial hepatectomy and by gavage exposure to test chemicals. GST-P+ foci were quantified by histomorphometry and were reported as areas and numbers of GST-P+ foci within the area of liver examined. For PCB 126, the doses were 0.1, 1.0, and 10 μg/kg body weight. For PCB 153, the doses were 10, 100, 1000, 5000, and 10,000 μg/kg body weight. Combined PCB 126 and 153 exposures were 0.1 + 10, 1 + 100, 10 + 1000, 10 + 5000, and 10 + 10,000 μg/kg, respectively. Individual PCB treatment resulted in dose dependent increases in liver and adipose concentrations. Hepatic PCB 153 levels were significantly increased (p < 0.01) after combined exposure. Treatment with PCB 126 or PCB 153 alone resulted in a significant (p < 0.01) dose dependent increase in GST-P+ foci area and number compared with controls. Treatment with the mixture of PCB 126 and 153 resulted in antagonistic GST-P+ focus formation (p < 0.001) for both foci area and number. The less than additive effect was present at all 5 PCB 126/PCB 153 dose combinations, including the low doses of PCB 126 and 153 that did not show significant promotional activity alone.

Keywords: carcinogenesis; polychlorinated biphenyls; liver; rat; promotion; altered hepatic foci; GST-P

Journal Article.  6019 words.  Illustrated.

Subjects: Medical Toxicology ; Toxicology (Non-medical)

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