Maria Hansson

The toxicity induced by several environmental pollutants is mediated by the aryl hydrocarbon receptor (AHR), which controls the expression of many biotransformation genes, such as cytochrome P4501A1 (CYP1A1). Previous studies have indicated that fish populations can evolve tolerance to persistent chlorinated pollutants by down-regulating the AHR pathway. Here, we measure to what extent tissue loads of polychlorinated biphenyl (PCB) congeners and AHR genotypes contribute to biotransformation capacity in wild, foraging Atlantic salmon (Salmo salar L.) from the Baltic Sea. In muscle, the sum of the 21 most common PCB congeners (ΣPCB) was correlated with three extracted AHR agonists (PCBs 77/110, 118/123/149, and 105/132/153). Both the AHR agonists as well as ΣPCB were correlated with lipid content. The ΣPCB, controlled for the effects of sex and lipid content in muscle tissue, did not predict mRNA transcript levels of the measured AHRs (AHR2α, AHR2γ, and AHR2δ) or CYP1A1 in liver. However, all AHR2 mRNA transcript levels were positively correlated with CYP1A1 level. In turn, the CYP1A1 level was negatively correlated with concentration of the muscle-tissue antioxidant astaxanthin, suggesting that astaxanthin is depleted when biotransformation processes (CYP1A1) are activated. No correlation was found between ethoxyresorufin-O-deethylase activity and ΣPCB, CYP1A1, or antioxidant levels. In 5′-flanking regions of the AHR2 genes, we identified multiple allelic variants that were used for genotyping. The mRNA transcript level of AHR2α was significantly associated with the AHR2α 5′-flanking region genotype and with the interaction of the genotype and individual PCB level. These results suggest that in wild Atlantic salmon from the Baltic Sea, active production of AHR2 mRNA by means of PCB exposure may be affected by genetic polymorphisms at the AHR2 loci.