CYP1A expression in liver and gill of rainbow trout following waterborne exposure: implications for biomarker determination

Abstract

The purpose of this study was to compare the time-course for induction of cytochrome P4501A (CYP1A) mRNA levels between liver and gill tissue from rainbow trout ( Oncorhyncus mykiss) following waterborne exposure to the polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP). Liver and gill CYP1A mRNA levels and CYP1A catalytic activity were rapidly induced following exposure to BaP concentrations of less than 1 μg l −1. The rise of CYP1A mRNA levels ahead of the rise of CYP1A catalytic activity demonstrated the typical pattern of a gene that is under transcriptional control. Nuclear run-on assays with control and BaP-exposed fish demonstrated that transcriptional activation of the CYP1A gene is an important regulator of CYP1A mRNA levels during the first 24 h of exposure. Liver CYP1A mRNA levels were induced between 6 and 72 h of exposure to 1.23±0.08 μg l −1 BaP but decreased to basal levels between 72 and 120 h of exposure. In comparison, gill CYP1A mRNA levels were induced after 6 h of exposure and remained at this high level of induction through 120 h of exposure to 0.78±0.11 μg l −1 BaP. Gill BaP-hydroxylase activity was maximally induced between 24 and 120 h of exposure, and this time period corresponded with the time period when liver CYP1A mRNA levels decreased back to basal levels. Extensive first-pass metabolism of BaP by the gill after 24 h of exposure may have prevented the majority of parent BaP that was cleared by the gill from entering circulation and maintaining induction of liver CYP1A mRNA levels. The comparison between liver and gill CYP1A mRNA levels and CYP1A catalytic activity demonstrated that CYP1A expression should be measured in tissues that are proximate to the environment when assessing fish from contaminated environments.