Mechanisms of action of two different natural mixtures of persistent organic pollutants (POPs) in ovarian follicles

Abstract

The present work investigated the effects of two different natural mixtures on aryl hydrocarbon receptor (AhR) and oestrogen receptor (ER)β protein levels, as well as on the activity of cytochrome P450 (CYP) 1A1 and CYP2B. Consequently, the authors observed the effects of these mixtures on gonadotropine-stimulated steroid secretion by ovarian follicles. The natural mixtures that were studied were ‘Mjosa’ extracted from burbot liver, which contains a high level of PBDEs, and ‘Marine mix’, extracted from Atlantic cod liver, which contains a high level of polychlorinated biphenyls (PCBs).Follicular cells were exposed in vitro to ‘Marine mix’ and ‘Mjosa mix’ at doses of 3.6 and 1.4 μg ml−1, respectively. Media were collected and used for steroid analysis and cell viability assays. Cells were used to estimate aromatase activity (CYP19), AhR and ER protein levels, and CYP1A1 and CYP2B1 activity.Western blot analysis indicated down-regulation of AhR by ‘Marine mix’ and down-regulation of ERβ by Mjosa mix. Up-regulation of CYP1A1 expression and activity were seen following treatment with Marine mix, but not Mjosa mix. Increased CYP2B1 activity was noted after treatment with both ‘Marine mix’ and Mjosa mix. Both mixtures increased luteinizing hormone (LH)-stimulated progesterone and testosterone secretion, follicle-stimulating hormone (FSH)-stimulated oestradiol secretion, and CYP19 activity.These results suggest that: (1) ‘Marine mix’ is a mixed-type CYP inducer; (2) ‘Mjosa mix’ is an inducer of ERβ and CYP2B; and (3) both ‘Marine mix’ and ‘Mjosa mix’ stimulate aromatase activity as a consequence of oestradiol secretion through activation of CYP19