Uncoupling of cytochrome P450 1A and stimulation of reactive oxygen species production by co-planar polychlorinated biphenyl congeners.

The non-ortho-polychlorinated biphenyl (PCB) congener 3,3'4,4'-tetrachlorobiphenyl (PCB 77) can uncouple the catalytic cycle of fish (scup) cytochrome P4501A (CYP1A) and mammalian (rat, human) CYP1A1, stimulating release of reactive oxygen species (ROS). PCB 77 also inactivates CYP1A in an NADPH-, oxygen-, and time-dependent process, linked to uncoupling. We addressed a hypothesis that planar halogenated hydrocarbons generally will uncouple CYP1A. Thus, additional PCB congeners including non-ortho-3,3',4,4',5'-pentachlorobiphenyl (PCB 126) and 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), mono-ortho-2,3,3',4,4'-pentachlorobiphenyl (PCB 105) and di-ortho-2,2',5,5'-tetrachlorobiphenyl (PCB 52), as well as the polycyclic aromatic hydrocarbon benzo[a]pyrene (B[a]P), were examined for their ability to stimulate microsomal ROS production and to inactivate CYP1A. Incubated without NADPH, non-ortho-PCB 126 and -PCB 169 both inhibited microsomal CYP1A activity (ethoxyresorufin O-deethylase; EROD). When NADPH was included, these congeners caused a progressive inactivation of CYP1A, in addition to the inhibition. The determined K(Inact) values for inactivation were 0.14 and 0.08 microM, respectively, for PCB 126 and PCB 169, similar to the 0.05 microM for PCB 77 previously reported. The mono-ortho-PCB 105 weakly inhibited and weakly inactivated CYP1A. The di-ortho-PCB 52 neither inhibited nor inactivated CYP1A. Alone, B[a]P strongly inhibited CYP1A, but when NADPH was added that inhibition was reversed, apparently by metabolic depletion of the substrate, and there was no inactivation. PCB 126 and PCB 169 stimulated release of ROS from induced liver microsomes, while B[a]P, PCB 52 and PCB 105 did not. ROS release and CYP1A inactivation stimulated by the non-ortho-PCB 126 and PCB 169 indicate an uncoupling of CYP1A like that previously shown with PCB 77. The uncoupling and release of ROS further suggest a participation of CYP1A in the oxidative stress associated with some planar halogenated aryl hydrocarbon receptor agonists.

Persistent organochlorine pollutants in ringed seals and polar bears collected from northern Alaska.

Blubber samples from ringed seal (Phoca hispida; n = 8) and polar bear subcutaneous fat (Ursus maritimus; n = 5) were collected near Barrow, Alaska in 1996 as part of the Alaska Marine Mammal Tissue Archival Project (AMMTAP) and retained in the National Biomonitoring Specimen Bank at the National Institute of Standards and Technology in Gaithersburg, Maryland (USA). The samples were analyzed for a variety of persistent organochlorine pollutants (POPs) including polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs), chlordane and metabolites, hexachlorobenzene (HCB) and DDTs and metabolites. The geometric mean, on a wet mass basis, of sigmaPCBs (sum of 29 congeners and congener groups) were 732+/-282 ng/g (1 S.D.) in seals and 3395+/-1442 ng/g in polar bears. The geometric mean of sigmaDDTs, sigmaHCHs (alpha-, beta- and gamma- HCH) and HCB concentrations (wet mass basis) in seals and bears were 562+/-261 ng/g vs. 74.8+/-39 ng/g, 380+/-213 ng/g vs. 515 ng/g, and 17.4+/-10.1 ng/g vs. 183+/-153 ng/g, respectively. The geometric mean sum of chlordane (sigmachlordane, sum of cis- and trans-chlordane, cis- and trans-nonachlor, oxychlordane and heptachlor epoxide) and dieldrin concentrations in ringed seals and polar bears were 753+/-617 ng/g vs. 720+/-315 ng/g and 38.6+/-22.8 ng/g vs. 130+/-65 ng/g, respectively. Apparent bioaccumulation factors (polar bear/ringed seal POP concentrations) were lower in the animals sampled near Barrow, Alaska than in those from locations in the Canadian Arctic. This suggests that polar bears are also preying on marine mammals from lower trophic levels than the ringed seals with correspondingly lower organochlorine levels, such as bowhead whale carcasses. PCB congener patterns in the samples demonstrated the metabolism of certain PCB congeners in the polar bear relative to the ringed seal in agreement with previous studies. Regional comparisons of animals collected in Alaska and Arctic Canada are presented.