Distribution and macromolecular binding of benzo[a]pyrene and two polychlorinated biphenyl congeners in female mice

PCBs are complete rodent carcinogens and their potent tumor promoting activ ity has been reported. but their tumor-initiating activity remains controve rsial. Macromolecular binding of PCB metabolites has been demonstrated in v itro, but this issue remains unclear in vivo. The purpose of this study was to determine the binding affinity of 4-chlorobiphenyl and 3,3'4,4'-tetrach lorobiphenyl to proteins and DNA in vivo. C57/BL6 female mice were treated intraperitoneally with hepatic enzyme inducers (phenobarbital and beta -nap hthoflavone) and then with C-14-labelled polychlorinated biphenyls or benzo [a]pyrene. The short-term distribution of labeled compounds into liver, lun gs and kidneys and into different sub-cellular fractions of these tissues w as assessed and the DNA and proteins from the 700 x g pellet were further p urified to assess covalent binding. All compounds were distributed in low a mounts into the liver, kidneys and lungs, with the greatest accumulation in the liver, and the lowest in lungs. In all tissues, test compounds were mo stly found in cytosols and organellar pellets (10,000 x g), and lower amoun ts were present in nuclear pellets (700 x g) and microsomes. In lungs and k idneys. only benzo[a]pyrene showed significant covalent binding to proteins . In the liver, protein binding indices were significant for all compounds (P < 0.05), but no significant binding of the test compounds to DNA could b e demonstrated with this approach. Our results suggest that at the 24 It ti me point, all Compounds were activated to electrophilic intermediates prone to macromolecular binding. Hepatic proteins apparently act as a sink for P CB-derived electrophiles, thus preventing detectable levels of covalent bin ding to hepatic DNA or to proteins in less metabolically active tissues. (C ) 2001 Elsevier Science Ireland Ltd, All rights reserved.