CYP1A-catalyzed uroporphyrinogen oxidation in hepatic microsomes from non-mammalian vertebrates (chick and duck embryos, scup and alligator).
Uroporphyrin (URO) accumulation in the liver of animals treated with polyhalogenated aromatic hydrocarbons (PHAH) is associated with increased microsomal oxidation of uroporphyrinogen catalyzed by rodent CYP1A2 and by a similar form in chicken, CYP1A5. The planar biphenyl, 3,3',4,4'-tetrachlorobiphenyl (TCB) stimulates uroporphyrinogen oxidation (UROX) in chick hepatic microsomes, but inhibits UROX activity in hepatic microsomes from mice and rats pre-induced by CYP1A2. Here we investigated whether TCB would stimulate or inhibit UROX in other non-mammalian species. UROX was stimulated 1.5-3-fold by TCB and 2-4-fold by 3,3',4,4',5,5'-hexachlorobiphenyl in hepatic microsomes from duck, alligator and scup treated with inducers of CYP1A. Hexachlorobenzene stimulated chick UROX, but was ineffective with microsomes from the other species. The stimulation of UROX by TCB was also observed in chick hepatocyte cultures. Pretreatment with up to 5 nM TCB induced CYP1A, but did not result in accumulation of URO. However, URO did accumulate if additional (post-induction) TCB was added along with 5-aminolevulinic acid. In this post-inductional TCB treatment, cycloheximide was included to prevent further induction of CYP1A. In duck hepatocytes, pretreatment with 25 nM TCB resulted in URO accumulation from 5-aminolevulinic acid. Post-induction TCB was not required and caused no further increase in URO accumulation. The differences in PHAH stimulation of UROX among the non-mammalian species have implications in the evolutionary changes in CYP1A, as well as the mechanism of development of PHAH-stimulated uroporphyria in different species.
Gorman
N
N
VA Medical Center (151), White River Junction, VT 05009, USA.
Walton
H S
HS
Sinclair
J F
JF
Sinclair
P R
PR
D000818:Animals; D002384:Catalysis; D003429:Cross Reactions; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D011078:Polychlorinated Biphenyls / Q000494:pharmacology; D013045:Species Specificity; D014577:Uroporphyrinogens / Q000378:metabolism*; D014714:Vertebrates