Cytochrome P450-mediated enzyme activities and polychlorinated biphenyl accumulation in harp seal (Phoca groenlandica)

The presence and activities of hepatic cytochrome P450 (CYP) isoforms in Barents Sea harp seals (n=13) were studied using catalytic activities, selective inhibitors, and western blots. In addition the polychlorinated biphenyl (PCB) burden was measured in both the blubber and the food of the seals. The CYP activities and CYP isoforms present were related to the blubber PCB load and the relative presence of each PCB congener in seals relative to their food (metabolic index). The CYP activities measured were 2–7 times higher than in ringed and harp seals from other studies, suggesting induction due to contaminant exposure. However, PCB burdens were surprisingly low and were not related to the CYP activities. Probably these high activities were due to exposure to other contaminants or due to the diet consisting mainly of crustaceans, which are rich in carotenes. Carotenes have been shown to be potent CYP inducers in several laboratory animals. The CYP studies indicated the presence of CYP1A, -2B and -3A isoforms. A decrease in the relative presence of a number of PCB congeners in seal blubber relative to their food, supposed to be due to CYP-mediated metabolism, corresponded with the metabolic capabilities of the CYP isoforms found.