The cytochrome P-450-mediated metabolism of biphenyl and the 4-halobiphenyls

In vitro estrogenicity of the catechol metabolites of selected polychlorinated biphenyls

A considerable body of work has demonstrated that phenolic polychlorinated biphenyl (PCB) metabolites, structural analogues to estradiol, bind to the soluble estrogen receptor (ER) and that hydroxy PCB-ER complexes will translocate into the nucleus and bind to ER response elements in cultured cells. Although catechol estrogens exhibit weak estrogenic activity, the catechol PCB metabolites which are structurally similar to these ER agonists have gone untested for potential estrogenicity. In the present work we have assessed the estrogenicity of this second group of PCB metabolites, the catechols. The test compounds used in the present study were chosen to elucidate the effects of chlorine and catechol position on in vitro estrogenicity. Cultured HeLa cells, transfected with the estrogen reporter gene ERET81CAT and mouse ER cDNA, were incubated with PCB catechols. The cells were harvested at 28 h posttransfection and assayed for chloramphenicol acetyl transferase (CAT) activity. The responses elicited by the PCB catechols tested fell within the range of effect measured for the catechol estrogens and phenolic PCBs, and were within the range previously reported for other "environmental estrogens" such as nonylphenol and o,p'-DDT. Maximal measured responses were achieved at concentrations approximately two to three orders of magnitude higher than that of 17-beta-estradiol, indicating that PCB catechols have estrogenic activity in vitro. The extent of chlorination and the position of the catechol (3,4 vs 2,3 substitution) were important in determining estrogenicity in the compounds tested. The 2,3-catechol showed no detectable activity in this system, while activity of the 3, 4-catechols increased with the degree of chlorination. The observed estrogenicity of PCB catechols suggests that further oxidative metabolism of estrogenic PCB phenolic metabolites would not necessarily result in lowering the total estrogenic burden of a PCB-exposed organism. The present results imply that if estrogenic activity is assigned to an individual phenol, the potential contribution of its catechol metabolites to the total estrogenic burden should also be taken into consideration.

The effect of chlorine substitution on the dermal absorption of polychlorinated biphenyls

The fate of selected mono-, di-, tetra-, and hexachlorobiphenyls was investigated following single dermal administration (0.4 mg/kg) to determine the effects of chlorine substitution on the dermal absorption and disposition of polychlorinated biphenyls (PCBs). Single dermal doses of 14C-labeled mono-, di-, tetra-, and hexachlorobiphenyls were administered to 1-cm2 areas on the backs of F-344 male rats. Unabsorbed radioactivity was removed from the dose site either at euthanasia or 48 h postdose. Distribution of radioactivity in the dose site and selected tissues was determined by serial sacrifice at time points up to 2 weeks. Dermal penetration varied inversely with degree of chlorination and at 48 h ranged from ca. 100% for monochlorobiphenyl to ca. 30% for the hexachlorobiphenyl. Penetration rate constants correlated well with log kow. PCBs were retained in the epidermis for up to 2 weeks postdose. The data from these studies suggest that systemic absorption of PCBs involves a combination of sequential processes including penetration across the stratum corneum, possibly metabolism in the epidermis and/or dermis, adsorption to proteins, and finally absorption into the systemic circulation. The skin favors the rapid absorption of less chlorinated PCBs, but the relatively rapid metabolism and elimination of these compounds would result in lower body burdens. More highly chlorinated PCBs penetrate less rapidly but remain in the site of exposure and slowly enter the systemic circulation. The dermal absorption of a commercial PCB mixture was modeled, and the results suggest that the net result of the differences in absorbance rates would be a greater body burden of higher chlorinated PCBs relative to those that have a lower chlorine content.