Submitted to: Aquatic Toxicology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/26/2005
Publication Date: 5/10/2006
Citation: Patel, M.R., Scheffler, B.E., Wang, L., Willett, K.L. 2006. Effects of benzo(a)pyrene exposure on killfish (fundulus heteroclitus) aromatase activities and mrna. Aquatic Toxicology. 77(3):267-278. Interpretive Summary: Normal reproductive function in wildlife can be altered by various endocrine disrupting chemicals which mimic sexual hormones and/or disrupt steroidogenic enzymes such as aromatase. In this study, Fundulus heteroclitus, a small estuarine fish was used to study the effects of benzo(a)pyrene on fish aromatase expression. Benzo(a)pyrene (BaP) is a environmental contaminant produced by incomplete combustion. The aim of this work was to clone and sequence the Fundulus CYP19A1 and CYP19A2 cDNAs. We analyzed the structure of CYP19 cDNAs and compared the evolutionarily conserved regions of the Fundulus aromatase with other vertebrates. Using the sequence information, we in turn measured the in vivo effects of exposure to BaP on mRNA levels and ovarian and brain aromatase activity in adult Fundulus. These findings suggest that the aromatase enzyme is a potential target for disruption of fish developmental and reproductive physiology by BaP.
Technical Abstract: Cytochrome P450 aromatase (CYP19) plays an important role in steroid homoeostasis by converting androgens to estrogens. Fundulus heteroclitus CYP19A1 cDNA (gonad form) had an ORF of 1551 bp and encoded a putative protein of 517 amino acids while CYP19A2 cDNA (brain form) contained an ORF of 1500 bp encoding 500 amino acids. To evaluate the estrogenic/anti-estrogenic potential of a model carcinogenic PAH, benzo(a)pyrene (BaP), adult Fundulus were exposed to water-borne BaP (1 and 10 ug/L) for 15 days. Effects of BaP were examined by tissue, gender, and season. Both sexes did not have significantly different CYP19A2 message levels, however females had higher brain aromatase activity. In brain tissues of both sexes there was approximately 50-fold more CYP19A2 message compared to CYP19A1. In ovary, CYP19A1 predominated by 20-60 fold over the CYP19A2, but in testis there was relatively more CYP19A2. Due to high inter-individual variability, a significant effect of BaP treatment by gender or season was not observed for either aromatase mRNA. However, ovarian aromatase activity was significantly decreased by 10 ug/L BaP, while female brain activity was increased following the winter exposure. These findings suggest that the aromatase enzyme is a potential target for disruption of fish developmental and reproductive physiology by BaP.