1-beta-D-Arabinofuranosyicytosine (Ara-C), a DNA-damaging agent, severely inhibits fetal growth and has teratogenicity. Recently, we reported that Ara-C also causes placental growth retardation and increases placental apoptosis. The aim of the present study is to elucidate the mechanisms of placental injury induced by genotoxic stress and involvement of p53, which mediates apoptosis and cell-cycle arrest after DNA damage. We injected Ara-C into pregnant rats on Day 13 of gestation and examined the placentas from 1 to 48 h after the administration. Terminal deoxynucleotidyltransferase-mediated dUTP end-labeling (TUNEL) revealed that the apoptosis of trophoblastic cells in the placental labyrinth zone increased from 3 h after the treatment and peaked at 6 h before returning to control levels at 48 h. An increase in cleaved caspase-3 immunoreactivity was also detected at 6 h. Proliferative activity as measured by immunohistochemistry for topoisomerase IIalpha and by mitotic index significantly decreased after the treatment in the labyrinth zone. Immunoreactivity for p53 protein in the placental labyrinth zone was remarkably enhanced and peaked at 3 h after treatment, although no increase in p53 mRNA expression was detected with a reverse transcription-polymerase chain reaction. Regarding p53 target genes, p21, cyclinG1, and fas mRNA levels increased significantly and peaked at around 9 h after the treatment. These results indicate that Ara-C would induce apoptosis and impair cell proliferation in the placental labyrinth zone, and p53 and its transcriptional target genes may play an important role in the pathogenesis of the Ara-C-induced placental toxicity.
