Open AccessEffects of mifepristone (RU‐486) on heme metabolism and cytochromes P ‐450 in cultured chick embryo liver cells
Author(s) -
Cable Edward E.,
Pepe Joyce A.,
Donohue Susan E.,
Lambrecht Richard W.,
Bonkovsky Herbert L.
Publication year - 1994
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1994.00651.x
Subject(s) - ferrochelatase , porphyria , heme , medicine , endocrinology , mifepristone , deferoxamine , cytochrome p450 , enzyme inducer , protoporphyrin , chemistry , protoporphyrin ix , porphyrin , enzyme , metabolism , biology , pharmacology , biochemistry , pregnancy , genetics , photodynamic therapy , organic chemistry
Mifepristone (RU‐486), a potent progesterone receptor antagonist and inducer of cytochromes P ‐450, is currently in use in Europe, particularly as a post‐coital oral contraceptive. Soon it will be available in the United States, as well. Since progesterone has been implicated in the pathogenesis of acute attacks of porphyria, the use of RU‐486 or related compounds might be considered in porphyric patients. However, as with other cytochrome P ‐450 inducers, RU‐486 may have the ability to precipitate or exacerbate attacks of acute porphyria. The acute porphyrias in relapse are associated with an increase in activity of δ‐aminolevulinic acid synthase, the first and normally rate‐controlling enzyme in heme biosynthesis. We have used primary cultures of chick embryo liver cells to test the ability of RU‐486 to induce δ‐aminolevulinic acid synthase activity and mRNA, cytochromes P ‐450, porphyrin accumulation, and heme oxygenase. We found that RU‐486, at concentrations observed in human plasma after a single oral dose, induced the mRNA and activity of δ‐aminolevulinic acid synthase, both by itself and in the presence of deferoxamine, a potent iron chelator that inhibits ferrochelatase. RU‐486 and deferoxamine together also produced significant accumulations of protoporphyrin. These results indicate that RU‐486 may pose a risk in patients with known acute porphyria and should be used with caution. RU‐486 increased the concentration of total cytochrome P ‐450, and the activity of erythromycin demethylase, an activity specifically catalyzed by cytochrome P ‐450 3 A. Unlike several other porphyrogens (e.g. hydantoins, barbiturates), RU‐486 does not produce accumulation of uroporphyrin or induction of heme oxygenase in chick embryo liver cells.