Submitted to: Aquatic Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2008
Publication Date: 7/30/2008
Citation: Dong, W., Wang, L., Thornton, C., Scheffler, B.E., Willett, K.L. 2008. Benzo(A)pyrene Decreases Brain and Ovarian Aromatase mRNA Expression. Aquatic Toxicology. Interpretive Summary: Fundulus, an important model species in marine environmental toxicology experiments and CYP is a family of genes that encode for P450 enzymes of the aromatase class. This family of enzymes plays an important role in the modification of chemical compounds. In this manuscript we have characterized the expression of the CYP19A1 due to exposure of the hydrocarbon benzo(a)pyrene (BaP) and found that BaP reduces its expression in brain and ovarian tissue. This study provides a better understanding of the mode of action of BaP and its potential impact on reproduction or development.
Technical Abstract: The higher molecular weight polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BaP) are typically associated with genotoxicity, however newer evidence suggests that these compounds may also act as endocrine system disruptors. We hypothesized that a target for reproductive or developmental dysfunction caused by BaP exposure could be the P450 enzyme aromatase. In fish, there are two isoforms of aromatase, a predominantly ovarian form, CYP19A1, and a brain form, CYP19A2. Aromatase is at least partially responsible for estrogen homeostasis by converting androgens into estrogens. CYP19 expression was measured following BaP exposure (0, 10, 100 g/L waterborne for 10 or 15 days) in Fundulus adults, juveniles and embryos by in situ hybridization. The CYP19A1 expression was significantly decreased after BaP exposure in the 3 month old Fundulus immature oocytes, but BaP did not affect CYP19A1 expression at any stage in adult oocytes. In embryo brains, BaP significantly decreased CYP19A2 compared to controls by 3.6-fold at 14 dpf. In adults, CYP19A2 expression was decreased significantly in the pituitary and hypothalamus (81% and 85% of controls, respectively). In addition, the promoter regions of Fundulus CYP19s were cloned. Putative response elements in the CYP19A1 and CYP19A2 promoters such as CRE, AhR and ERE may be involved in BaP-mediated changes in CYP19s expression. In order to compare the BaP-mediated inhibition with that of a known aromatase inhibitor, fish were also exposed to fadrozole (20 µg/L and 100 µg/L). Fadrozole did not significantly decrease the mRNA expression in embryos or adult Fundulus. However, aromatase enzyme activity was significantly decreased in adult ovary and brain tissues. These studies provide a greater molecular understanding of the mechanisms of action of BaP and its potential to impact reproduction or development.