Hepatocarcinogenicity of PCB congeners

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Abstract
We have investigated the hepatocarcinogenic mechanisms of 2,2’,4,5'‐tetrachlorobiphenyl (PCB No. 49) and 2,2’,4,4’,5,5'‐hexachlorobiphenyl (PCB No. 153). PCB No. 49 was incubated with isolated hepatocytes from rats and chickens that had been stimulated with phenobarbital. We could show that this low‐chlorinated biphenyl is metabolically activated in the liver cells and covalently binds to nucleic acids and proteins in vitro. Enzyme activities (for pyruvate kinase, fructose‐1,6‐biphosphatase and malic enzyme), which show specific changes in tumor cells, were determined in liver homogenates of rats and chickens treated with diethylnitrosamine (DENA) and PCB. Our results support the concept that tumor promotors that affect the liver, alter hepatocellular activities of key enzymes.