Time-dependent induction of two distinct hepatic cytochrome P4501A catalytic activities at low temperatures in Arctic charr ( Salvelinus alpinus) after oral exposure to benzo(a)pyrene

Due to increased industrial and other anthropogenic activities during the last decades, the arctic environment faces increasing levels of organic pollution. The presence of polycyclic aromatic hydrocarbons in the arctic environment is of major concern because of their carcinogenic potential and their effect on the health and reproductive performance of animals. There is an increasing demand for sensitive and relatively inexpensive diagnostic biomarkers, applicable for environmental monitoring in the Arctic seas to assess the human impact on the Arctic. As a first step to validate the use of enzymatic assays in fish as an indicator for environmental pollution, the hepatic cytochrome P450 induction in the anadromous Spitsbergen Arctic charr was studied at several time intervals during 4 days following oral exposure to benzo(a)pyrene. Three different enzyme activities were studied, i.e. testosterone-6β-hydroxylation, the ethoxyresorufin- O-deethylation and the caffeine- N3-demethylation. Both the ethoxyresorufin- O-deethylation and the caffeine- N3-demethylation activity (only the 1,7-dimethylxanthine metabolite was formed) showed a strong and time-dependent induction after exposure. Western immunoblotting revealed an increase in the amount of protein. In the exposed groups a clear time-dependent increase of protein reacting with anti-cod CYP1A was observed. Between the ethoxyresorufin- O-deethylation and the caffeine- N3-demethylation activity in the exposed animals there was a strong and linear correlation. There was no effect of benzo(a)pyrene exposure on the testosterone-6β-hydroxylation. The slow and long lasting induction, probably due to the low water temperatures 5 °C, can be regarded as advantageous for biomonitoring. Differences in inhibition (α-naphtaflavone, furafylline) characteristics between ethoxyresorufin- O-deethylation rate and caffeine- N3-demethylation rate could be interpreted in terms of possible presence of more than one P4501A isoform in this fish species.