IN VITRO METABOLISM OF POLYCHLORINATED BIPHENYLS BY DOG HEPATIC CYTOCHROMES P-450
AuthorDUIGNAN, DAVID BERNARD.
AdvisorSipes, I. Glenn
Halpert, James R.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe biochemical basis for the unique ability of Beagle dog liver microsomes to metabolize 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB) was investigated. The major phenobarbital (PB)-inducible cytochrome P-450 isozyme, called PBD-2, was purified to 95% homogeneity from liver microsomes of both control and PB-treated dogs, as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In a reconstituted system containing cytochrome b₅, PBD-2 metabolized 245-HCB at a rate greater than three-fold that seen in liver microsomes from PB-treated dogs. Immunoblot analysis revealed that, upon PB treatment, the increase in the level of PBD-2 in dog liver microsomes correlated well with the increase in the rate of hepatic microsomal metabolism of 245-HCB by dogs. Anti-PBD-2 IgG caused a > 90% inhibition of 245-HCB metabolism by microsomes obtained from control and PB-treated dogs. Studies were also conducted to assess the ability of PBD-2 to metabolize 2,2',3,3',6,6'-hexachlorobiphenyl (236-HCB) and 4,4'-dichlorobiphenyl (4-DCB). Dog liver microsomes readily metabolized 236-HCB, and PB treatment led to a dramatic increase in this rate of metabolism, suggesting a role for PBD-2 in the metabolism of 236-HCB. In a reconstituted system containing cytochrome b₅, PBD-2 metabolized 236-HCB at a rate greater than two-fold that observed in microsomes from PB-treated dogs. Pretreatment of microsomes obtained from PB-treated dogs with chloramphenicol (a highly selective inactivator of PBD-2) caused a nearly 70% decrease in the microsomal metabolism of 236-HCB. Anti-PBD-2 IgG inhibited by > 90% 236-HCB metabolism by microsomes from both control and PB-treated dogs. In contrast, PB treatment caused no significant alteration in the metabolism of 4-DCB by dog liver microsomes, and PBD-2 metabolized this compound poorly, even in the presence of cytochrome b₅. Taken together, these data indicate that the dog hepatic cytochrome P-450 isozyme, PBD-2, is present in microsomes obtained from both control and PB-treated animals. PBD-2 is responsible for the microsomal metabolism of 245-HCB, and this isozyme likely accounts for the unique ability of Beagle dogs to readily metabolize and eliminate this compound in vivo. The data also strongly suggest that PBD-2 is responsible for the microsomal metabolism of 236-HCB in dogs. However, PBD-2 is not likely involved in the microsomal metabolism of 4-DCB by this species.
Degree ProgramPharmacology & Toxicology