title: Low teratogenicity of 13-cis-retinoic acid (isotretinoin) in the mouse corresponds to low embryo concentrations during organogenesis: comparison to the all-trans isomer.
abstract: 13-cis-Retinoic acid (isotretinoin) is teratogenic in man at therapeutic doses (0.5-1.5 mg/kg body wt), but only marginally teratogenic in the mouse at exceedingly high doses (greater than 100 mg/kg). On the other hand, the isomer all-trans-retinoic acid (tretinoin) is teratogenic in the mouse at dose levels which are 10 times lower than those for the 13-cis isomer. We have therefore studied whether the greatly different teratogenic potencies of these two compounds in the mouse are the result of differences in their transplacental kinetics. Following a single oral dose of 100 mg all-trans- or 13-cis-retinoic acid per kg body wt, concentrations of the parent drugs, of the C-13 isomerization products, as well as of their 4-oxo metabolites were determined in maternal plasma and embryo at two sensitive stages of organogenesis, i.e., Days 9 or 11 of gestation. All-trans-retinoic acid and its 4-oxo metabolite were transferred to the embryo to a much greater extent (embryo/maternal plasma concentration ratios, approximately 0.4) than the 13-cis-retinoic acid and its 4-oxo metabolite (embryo/maternal plasma concentration ratios, approximately 0.02). Embryo concentrations of all-trans-retinoic acid on Day 9 of gestation exceeded those on Day 11, whereas the embryo levels of 13-cis-retinoic acid were minimal at both gestational stages. The concentration of the 4-oxo metabolite of all-trans-retinoic acid was generally lower than that of the parent drug, whereas the level of the 4-oxo metabolite of the 13-cis-retinoic acid was comparable with or even higher than that of the parent compound. Concentrations of the C-13 isomerization products in maternal plasma were less than 20% of corresponding parent drug levels. However, due to the different extent of transfer of the two isomers, the concentration of all-trans-retinoic acid in the embryo exceeded that of the cis isomer even after administration of 13-cis-retinoic acid. Our results indicate that the low teratogenicity of 13-cis-retinoic acid in the mouse is the result of minimal placental transfer of this compound and of its 4-oxo metabolite, which contrast sharply with extensive placental transfer and high teratogenicity of the corresponding isomers with the all-trans configuration.
authors.forename: J C
authors.initials: JC
authors.lastname: Kraft
authors.forename: D M
authors.initials: DM
authors.lastname: Kochhar
authors.forename: W J
authors.initials: WJ
authors.lastname: Scott
authors.forename: H
authors.initials: H
authors.lastname: Nau
mesh_terms: D000014:Abnormalities, Drug-Induced / Q000209:etiology*; D000818:Animals; D005260:Female; D015474:Isotretinoin; D008431:Maternal-Fetal Exchange; D051379:Mice; D008815:Mice, Inbred Strains; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D013329:Structure-Activity Relationship; D013723:Teratogens / Q000378:metabolism; D014212:Tretinoin / Q000378:metabolism / Q000633:toxicity*
chemical_list: D013723:Teratogens; D014212:Tretinoin; D015474:Isotretinoin