Action of defined mixtures of PCBs, p,p′-DDT and its metabolite p,p′-DDE, on co-culture of porcine theca and granulosa cells: Steroid secretion, cell proliferation and apoptosis

We recently reported on a stimulatory effect of a mixture of persistent organic pollutants (POPs) extracted from the liver oil of Atlantic cod (Gadus morhua) on estradiol (E2) secretion by porcine ovarian follicular cells [Gregoraszczuk EL, Milczarek K, Wójtowicz A, Berg V, Skaare JU, Ropstad E. Steroid secretion following exposure of ovarian follicular cells to three different natural mixtures of persistent organic pollutants (POPs). Reproductive Toxicol 2007;25:58–66]. The objective of the present study was to identify what compound or compounds within this natural mixture could be responsible for the stimulatory action on E2 secretion. Co-cultures of porcine ovarian theca and granulosa cells were exposed for 48 h to individual congeners of polychlorinated biphenyls (PCBs) alone or in combination, at environmentally relevant concentrations (PCB153 at 8 μg/ml; PCB118 at 3 μg/ml; PCB138 at 8 μg/ml; PCB180 at 3 μg/ml; PCB126 at 8 ng/ml; DDT at 5 μg/ml; p,p′-DDE at 10 μg/ml). At the end of culture media samples were collected and used for cell viability and steroid determination, and cells were used for the measurement of caspase-3 activity. A threefold decrease in E2 secretion was noted when PCB126 was added in combination with PCB153. Only DDT and DDE could reverse the action of PCB126. Stimulatory secretion of E2 occurred in parallel with a decrease in testosterone (T) secretion. Among the single congeners used in the present study, DDE had the strongest stimulatory action on E2 secretion. In conclusion, the present findings indicate that the overall effect on steroid secretion by ovarian follicular cells could be dependent on the concentration of DDE in environmental POPs and that the predicted effect of a mixture based on a sum of independent effects of individual congeners is higher than that noted under the influence of defined mixture.