Noriko Ejiri

Ethylnitrosourea Induces Apoptosis and Growth Arrest in the Trophoblastic Cells of Rat Placenta

Abstract Ethylnitrosourea (ENU), a well known alkylating agent, induces congenital anomalies in fetuses when it is administered to pregnant animals. In previous studies, we reported that ENU induced apoptosis and growth arrest in fetal tissues and organs immediately after its administration to pregnant rats. In the present study, we investigated the histopathological changes of the placenta after ENU administration to pregnant rats on Day 13 of gestation (GD13) to obtain a clue for clarifying the role of the placenta in the process of fetal developmental disability induced by genotoxic stress. Apoptotic cells increased and DNA-replicating cells decreased in the trophoblastic cells in the placental labyrinth zone of the ENU-treated group by 3 h after treatment. The number of apoptotic cells peaked at 6 h after treatment and returned to control levels at 48 h after treatment. The number of DNA-replicating cells reached minimum levels at 6 h after treatment and returned to control levels at 48 h after treatment. By immunohistochemistry, p53-positive signals were observed in trophoblastic cells in the labyrinth zone of the ENU-treated group from 3 to 6 h after treatment. Significant decreases in fetal and placental weights were observed in the ENU-treated group at 2 days (GD15) and 8 days (GD21) after treatment. A reduction in the thickness of the labyrinth zone was histopathologically significant in the ENU-treated group. These results indicate that ENU induces apoptosis and growth arrest not only in fetal tissues, but also in trophoblastic cells in the rat placental labyrinth zone, and these placental changes may have roles in the induction of fetotoxicity and teratogenicity of ENU. Moreover, a possible involvement of p53 in the induction of apoptosis and growth arrest is suggested.

Induction of CYP3A1 by dexamethasone and pregnenolone-16α-carbonitrile in pregnant rat and fetal livers and placenta

Cytochrome P450 (CYP) 3A1 was detected in the cytoplasm of giant cells in the trophoblastic region of rat placenta through pregnancy (Ejiri et al. 2001). In the present study, changes in the expression of CYP3A1 protein as well as in the histology of pregnant rat and fetal livers and placenta after treatment with dexamethasone (DEX) or pregnenolone-16alpha-carbonitrile (PCN), well-known CYP3A1 inducers, at 16 day of gestation (DG) (DEX1 and PCN1 groups: 100 mg/kg) or from 13 to 16 DG (DEX4 group: 25 mg/kg/day; PCN4 group: 50 mg/kg/day). All animals were killed at 17 DG, and Western blot and immunohistochemical analyses on CYP3A1 expression and histological examination were done. Western blot analysis revealed that PCN induced CYP3A1 more clearly than DEX and that the induction was most prominent in the fetal liver and lowest in the placenta. Except for the placenta, changes in the immunohistochemical stainability for CYP3A1 almost corresponded to those in the expression of CYP3A1 by Western blot analysis. In addition, swelling and and/or vacuolization of hepatocytes were generally observed in the mother and fetal livers showing increased expression of CYP3A1. These results suggest that DEX and PCN might pass through the placenta with no prominent induction of CYP3A1 at the placenta and be distributed to the fetal liver rapidly, resulting in high induction of CYP3A1 in the fetal liver.