Up-regulation of ABC xenobiotic transporters and complementary contaminant-metabolizing enzymes in mummichogs (Fundulus heteroclitus) from the Sydney Tar Ponds, Nova Scotia, Canada

Aquatic organisms prevent bioaccumulation of pollutants by cellular detoxification mediated by phase I and II enzymes and ABC transporters. The relationship among ABC transporters Mdr1/Abcb1, Spgp/Abcb11, Mrp2/Abcc2, Bcrp/Abcg2, phase I enzyme CYP1A1 and phase II enzyme GST was investigated by quantifying hepatic transcript abundance in mummichogs (Fundulus heteroclitus) from the Sydney Tar Ponds, NS, Canada, a site heavily polluted with polycyclic aromatic hydrocarbons. In Mammals, MDR1 transports moderately hydrophobic, neutral or slightly positively charged substrates while MRP2 and BCRP transport organic anions that may be conjugated to large polar groups such as glutathione or sulphate. Phase I and II enzyme activity biotransforms hydrophobic substances to more hydrophilic and conjugated metabolites, respectively. In Tar Pond mummichogs, hepatic mRNA levels of Mrp2, Bcrp, CYP1A1 and GST were elevated compared to reference sites, suggesting that hydrophobic contaminants undergo phase I and II metabolism and are then excreted into the bile. Hepatic Mdr1 and Spgp mRNA were not up-regulated in fish from the Tar Ponds compared to two reference sites. The results suggest that up-regulation of phase I and II enzymes and complementary ABC transporters may confer contaminant resistance to Tar Pond fish.