Teratogenicity of the 13‐cis and all‐trans‐isomers of the aromatic retinoid etretin: Correlation to transplacental pharmacokinetics in mice during organogenesis after a single oral dose

Abstract

NMRI mice were treated on day 11 (day 0 = plug day) of gestation with a single oral dose of 100 mg/kg of either all‐trans‐etretin (acitretin) or 13‐cis‐etretin. For teratology studies mice were sacrificed on day 18 of gestation, and the fetuses were examined for malformations. For pharmacokinetic studies, groups of 5 mice were sacrificed after 5, 10, and 30 min and 1, 2, 4, and 8 h. The concentrations of retinoids in maternal plasma and in embryos were determined by a newly developed HPLC gradient method. All‐transetretin induced malformations in 94% of the fetuses, mainly in fore and hind limbs and cleft palate. 13‐cis‐etretin did not show any teratogenic or embryolethal effects at the dose level used. These findings could be explained by a transplacental pharmacokinetic study. The maximum peak level and also the AUC (area under the concentration‐time curve) values of all‐trans‐etretin in the embryos was 7–8 times higher than corresponding values for 13‐cis‐etretin, probably due to extensive transport of the trans‐isomer and limited transport of the cis‐isomer from maternal plasma to the embryos. The concentration quotient between embryo and the maternal plasma was between 0.43 and 1.10 for all‐trans‐etretin, and only 0.16–0.31 for 13‐cis‐etretin over the time period studied. An in vivo isomerization of the compounds was also observed which was more extensive for 13‐cis‐etretin than for all‐trans‐etretin. Our results indicate that the low teratogenic potency of 13‐cis‐etretin is due to a limited placental transfer of this compound; on the other hand, the potent teratogen all‐transetretin is rapidly and extensively transferred to the embryo.