3,3 ',4,4 '-tetrachlorobiphenyl oxidation in fish, bird and reptile species: relationship to cytochrome P450 1A inactivation and reactive oxygen production

Previously we showed that the polychlorinated biphenyl 3,3',4,4'-tetrachlor obiphenyl (TCB) caused a release of reactive oxygen species (ROS) from cyto chrome P450 1A (CYP1A) of the fish scup (Stenotomus chrysops), and from rat and human CYP1A1. This was linked to a TCB- and NADPH-dependent oxidative inactivation of the enzyme, which in scup and rat was inversely related to the rates of TCB oxidation. We examined the relationship between rates of T CB oxidation, CYP1A inactivation and ROS production in liver microsomes fro m additional vertebrate species, including skate (Raja erinacea), eel (Angu illa rostrata), killifish (Fundulus heteroclitus), winter flounder (Pleuron ectes americanus), chicken (Gallus domesticus), cormorant (Phalacrocorax au ritus), gull (Larus argentatus), and turtle (Chrysemys picta picta). TCB ox idation rates were induced in all fish and birds treated with aryl hydrocar bon receptor agonists. Induced rates of TCB oxidation were < 1 pmol/min/mg microsomal protein in all fish, and 6-14 pmol/min/mg in the birds. In all s pecies but one, TCB oxidation rates correlated positively with EROD rates, indicating likely involvement of CYP1A in TCB oxidation. Incubation of live r microsomes of most species with TCB + NADPH resulted in an immediate (TCB -dependent) inhibition of EROD, and a progressive loss of EROD capacity, in dicating an oxidative inactivation of CYP1A like that in scup. NADPH stimul ated production of ROS (H2O2 and/or O-2(-.)) by liver microsomes, slightly in some species (eel) and greatly in others (chicken, turtle). Among the bi rds and the fish, NADPH-stimulated ROS production correlated positively wit h EROD activity. TCB caused a significant stimulation of ROS production by liver microsomes of flounder, killifish, cormorant and gull, as well as scu p. The stimulation of CYP1A inactivation and ROS generation indicates an un coupling of CYP1A by TCB in many species, and when compared between species , the rates of CYP1A inactivation correlated inversely with rates of TCB ox idation. Some feature(s) of binding/active site topology may hinder TCB oxi dation, enhancing the likelihood for attack of an oxidizing species in the active site. (C) 2000 Elsevier Science Inc. All rights reserved.