Separate and Joint Effects of Polycyclic Aromatic Hydrocarbons (PAH)and Polychlorinated Biphenyls (PCB) on Aromatase CYP19A TranscriptionLevel in Atlantic Tomcod (Microgradus tomcod)

Abstract

Ovarian cytochrome 19A (CYP19A) expression is recognized as a useful biomarker for exposure of fish to environmental contaminants such as PAHs and PCBs. In this study, a laboratory approach using Atlantic tomcod (Microgradus tomcod) from the Hudson River was used to evaluate the additive and interactive effects of a PAH (benzo[a]pyrine) and a PCB mixture (Aroclor 1242) with respect to their effects on various metrics of reproduction. The experimental design was a two-way factorial with each treatment at 0, 0.1 and 1 ppm and replicated three times. Fish embryos were subjected to a short term aqueous exposure (DMSO as vehicle) whereas larvae were exposed via repeated feedings of contaminated prey (Artemia). Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) was used to evaluate the mRNA expression level of the ovarian aromatase CYP19A as a biomarker to assess reproductive stress in Microgadus tomcod. When tested alone, expression of aromatase CYP19A was significantly up regulated at the higher level of PCBs but no effect was observed from benzo-a-pyrene (B[a]P). In the PCB/PAH combined treatment, both low-PCB with both low/high levels of PAH and high-PCB with both low/high levels of PAH treatment groups had no significant effect on aromatase CYP19A transcript levels compared with the control group. Gonadosomatic Index (GSI) of reproductively mature females showed that only the high-PCB treatment group exhibited significant gonadal loss. The results confirm the expectation that transcription of both PCB and PAH responsive genes are upregulated since they both exert their toxic effects through the aryl hydrocarbons receptor (AHR) pathway