Reactive oxygen species (ROS) are implicated in the pathogenesis of pre-eclampsia (PE), and we have previously reported abnormalities in Ca²⁺ regulation in fetal endothelial cells from PE pregnancies (Steinert et al. 2002). Homocysteine (HCy), a sulphydryl-containing amino acid, generates ROS when oxidised and plasma levels are elevated in PE (Cotter et al. 2001). 4-hydroxynonenal (4-HNE), a lipid oxidation product, has also been localised in placental tissue from normal and PE pregnancies (Santoso et al. 2002). In the present study we have investigated the effects of HCy and 4-HNE on expression of the antioxidant defence genes heme oxygenase-1 (HO-1) and peroxiredoxin 1 (Prx-1) in human umbilical vein endothelial cells (HUVEC) cultured from normal or pre-eclamptic pregnancies. HO-1 metabolises heme to the chain-breaking antioxidants bilirubin and biliverdin whilst Prx-1 catalyses the breakdown of H₂O₂ (Siow et al. 1999). HUVEC from normal and PE pregnancies were treated for 24h with HCy (1-200μM, normal cells only), 4-HNE (10-40μM) or the electrophilic agent diethylmaleate (DEM, 100μM). Cell lysates were assayed for intracellular glutathione (GSH) and ATP levels or analysed by western blotting for expression of HO-1 and Prx 1. Under normal culture conditions, basal levels of GSH in normal HUVEC were 32±3.6 nmol/mg protein (n=5) and unaffected by HCy (1-200μM). Basal expression of HO-1 was low whereas expression of Prx-1 initially was high. HCy (200 μM)significantly induced HO-1 expression (P<0.05, n=5, unpaired, two-tailed Student's t test) in a dose-dependent manner but did not alter Prx-1 expression or GSH and ATP levels. In normal HUVEC, HNE caused a dose- and time-dependent increase in HO-1 expression, with maximal levels detected after 24h treatment. Induction of HO-1 in PE HUVEC in response to either 4-HNE (10-40μM) or DEM (100μM) was markedly attenuated compared to HO-1 expression in normal HUVEC. The basal levels of GSH in PE cells were approximately half that of normal HUVEC. Treatment of PE HUVEC with 4-HNE (10-40μM) resulted in a diminished induction of HO-1 expression compared to normal cells. Results from this study suggest that HUVEC from PE pregancies have impaired antioxidant defences compared to normal cells.