Increased Superoxide Generation is Associated with Decreased Superoxide Dismutase Activity and MRNA Expression in Placental Trophoblast Cells in Pre-eclampsia

Pre-eclampsia is a multi-system disorder unique to human pregnancy. Although the aetiology of pre-eclampsia is still unknown, increased placental oxidative stress contributes to the pathophysiology of this pregnancy disorder. The goal of this study was to determine if placental trophoblast cells generate superoxide, and if there was a difference in superoxide generation and superoxide dismutase (SOD) activity between trophoblast cells isolated from pre-eclamptic placentae versus normal placentae. Placentae were obtained from nine normal and 10 pre-eclamptic pregnancies immediately after delivery. Trophoblast cells were isolated and purified by Percoll density gradient centrifugation. Superoxide generation and SOD activity were determined by spectrophotometric assays. Localization of CuZn-SOD protein within the placenta was examined by immunohistochemical staining. mRNA expression of CuZn-SOD was determined in trophoblast cells isolated from five normal and five pre-eclamptic pregnancies by Northern blot analysis. 18S ribosomal mRNA expression was used as an internal standard. We found: (1) trophoblast cells from pre-eclamptic placentae generated significantly more superoxide than trophoblast cells from normal placentae: 17.62+/-3.19 versus 4.70+/-0.76 nmol/5x10(6) cells (mean+/-s.e.), P< 0.01; (2) protein and mRNA expression for CuZn-SOD was mainly localized in the trophoblast cells within the placenta; and (3) SOD activity and relative mRNA expression for CuZn-SOD were significantly decreased in trophoblast cells from pre-eclamptic placentae as compared to trophoblast cells from normal placentae, SOD activity: 6.46+/-1.76 versus 13.01+/-1.67 units/mg protein, P< 0.05; relative mRNA expression for CuZn-SOD: 0.25+/-0.09 versus 0.73+/-0.07, P< 0.01. We conclude that increased superoxide generation was associated with decreased SOD activity and mRNA expression for CuZn-SOD in trophoblast cells isolated from pre-eclamptic placentae. These findings support the notion of increased oxidative stress in the pre-eclamptic placenta, which may contribute to the pathophysiology of this pregnancy disorder.