Mixture of dominant PBDE congeners (BDE-47, -99, -100 and -209) at levels noted in human blood dramatically enhances progesterone secretion by ovarian follicles

Abstract

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide variety of products. They show an accumulation pattern similar to that of well-known persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), DDT and others. So far, most of information showing adverse effects of various POPs was based on the exposure to single chemicals. However, in this study we intended to evaluate in vitro effect of the mixture of four most abundant PBDE congeners (PBDE-47, -99, -100 and -209) as usually found in wildlife and humans on the secretion of gonad hormones by ovarian follicles. Cocultures of theca and granulosa cells collected from medium size follicles of cycling pigs were exposed for 24 or 48 h to three different levels of respective PBDE congeners mixture: 1. low level (0.5; 0.25; 0.1; 0.05 ng/ml); 2. medium level (25; 10; 4.0; 0.25 ng/ml) and high level (50; 17.5; 12.5; 0.5 ng/ml). Additionally, to show if the effect on steroid secretion by ovarian follicles is reversible, the cells were cultured for 24 h with the reagents and, after the medium was exchanged, the cells were cultured without reagents for additional 48 h. At the end of each culture procedure, progesterone (P4), testosterone (T) and estradiol (E2) secretion in the culture medium were determined by ELISA. After short term exposure increased secretion of all investigated steroids was noted only under the influence of small dose of mixture. However, after longer time of exposure the stimulation of estradiol and testosterone secretion was observed under the influence of both the low and medium dose of mixture, while 3.0-, 6.8- and 7.2-fold increase in progesterone secretion was noted under the influence of low, medium and high doses of mixture, respectively. Taken together, our findings from this and previous studies allow several interrelated conclusions to be drawn. First, the increase of P4/T ratio with a parallel decrease of T/E2 ratio was found suggesting preterm luteinization in antral follicles followed by the disruption of ovulation and, second, it was not possible to reverse the steroidogenic effects of PBDEs mixture by removing reagents from the cell cultures.