title: Phenytoin embryotoxicity: role of enzymatic bioactivation in a murine embryo culture model.
abstract: A murine embryo culture model was developed to study the potential contribution of enzymatic bioactivation to the teratogenicity of phenytoin. To assess the relative embryonic and maternal contributions to bioactivation, embryos were cultured respectively alone or in the presence of an exogenous source of cytochromes P-450 (P-450), which are thought to bioactivate phenytoin to a teratogenic reactive intermediate. Embryological development from gestational day 9 to day 10 was assessed, and bioactivation was quantified by the irreversible binding of radiolabeled phenytoin to embryonic protein. Embryos cultured with phenytoin and an exogenous P-450 bioactivating system showed a significant decrease in the incidence of turning and closure of the anterior neuropore, yolk sac diameter, and protein content as well as growth retardation. In the absence of an exogenous P-450 system, phenytoin did not decrease the incidence of turning or anterior neuropore closure but did cause growth retardation and a lesser but significant reduction in yolk sac diameter and embryonic protein content. An exogenous P-450 system enhanced the bioactivation of phenytoin, although significant activity also was detectable in embryos cultured without an exogenous bioactivating system. These results suggest that the embryo itself can enzymatically bioactivate embryotoxically significant amounts of phenytoin, and that bioactivation and embryotoxicity can be further enhanced, qualitatively and quantitatively, by an exogenous P-450 system, implicating a possible maternal contribution to phenytoin teratogenicity.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Shanks
authors.forename: M J
authors.initials: MJ
authors.lastname: Wiley
authors.forename: S
authors.initials: S
authors.lastname: Kubow
authors.forename: P G
authors.initials: PG
authors.lastname: Wells
mesh_terms: D000818:Animals; D001711:Biotransformation; D046508:Culture Techniques; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004622:Embryo, Mammalian / Q000187:drug effects / Q000378:metabolism; D005314:Embryonic and Fetal Development / Q000187:drug effects; D008297:Male; D051379:Mice; D008954:Models, Biological; D010672:Phenytoin / Q000378:metabolism / Q000633:toxicity*; D051381:Rats; D011919:Rats, Inbred Strains; D013723:Teratogens
chemical_list: D013723:Teratogens; D010672:Phenytoin; D003577:Cytochrome P-450 Enzyme System