Heme oxygenase expression in human placenta and placental bed: reduced expression of placenta endothelial HO-2 in preeclampsia and fetal growth restriction

In this study we tested the hypothesis that expression of heme oxygenases H O-1 and HO-2, which are responsible for the production of carbon monoxide, are reduced in the placenta and placental bed of pregnancies complicated by preeclampsia (PE) and fetal growth restriction (FGR) compared with control third-trimester pregnancies. Placental protein expression was determined b y Western blotting (n=10 in each group) and immunohistochemistry (controls n=18, PE n=19, FGR n=10), Extravillous trophoblast expression was determine d by immunohistochemistry of placental bed biopsy samples (controls n=17, P E n=19, FGR n=10), Western blot analysis of placental homogenates showed no overall differences in HO-2 among groups. However, immunohistochemical ana lysis showed a reduction in HO-2 expression in endothelial cells in both ab normal groups (PE P<0.01; FGR P<0.0005 vs. control group) but no difference s in villous trophoblast staining. HO-I was undetectable by Western blottin g in control and abnormal pregnancies and immunoreactivity was very low, su ggesting that there is little HO-I in the placenta. Within the placental be d, HO-2 but not HO-1 was detected on all populations of extravillous tropho blast, but expression of HO-2 or HO-1 did not change in PE or FGR, The redu ced expression of HO-2 on endothelial cells in PE and FGR may be responsibl e for reduced placental blood flow in these conditions. The data do not sho w changes in HO in the placental bed in PE or FGR.