Elevated plasma homocysteine (Hcy) levels are associated with cardiovascular diseases such as atherosclerosis and pre-eclampsia (Rajokvic et al. 1999). Although Hcy is cytotoxic to endothelial cells, it induces vascular smooth muscle cell (SMC) prolifereration, which contributes to atherosclerotic plaque formation. Endothelial cell dysfunction induced by Hcy may be mediated by elevated oxidative stress, although its effects on SMC function remain to be elucidated. Peroxiredoxin I (PrxI) contributes to cellular anti-oxidant defences by acting as a thioredoxin-dependent peroxidase and heme binding protein (Ishii et al. 1993). PrxI also is involved in the regulation of cell proliferation (Fuji et al. 2002). In the present study, we have investigated whether induction of PrxI by Hcy is associated with proliferation in human umbilical artery vascular SMC (HUASMC) from normal and pre-eclamptic (PE) umbilical cords (collected with ethics committee approval). Cells were grown from explants in MCDB131 (Clonetics) containing 10 % fetal calf serum as described previously. Thymidine incorporation in G₀/G₁ synchronized cells was used as an index of SMC proliferation induced by Hcy (100 µM, 24 h). In parallel experiments, confocal images of PrxI immunofluorescent staining were obtained using a polyclonal antibody to PrxI. Hcy induced a significant (n = 4, P < 0.05, Student’s t test) increase in thymidine incorporation in SMC isolated from normal (mean ± S.E.M., control vs. Hcy: 32.5 ± 5.7 vs. 82.5 ± 6.3 cpm (mg protein)^-1) but not from PE (70.1 ± 11.1 vs. 64.1 ± 10.2 cpm (mg protein)^-1) umbilical arteries. Confocal image analysis revealed that Hcy markedly enhanced expression of PrxI in normal SMC but not from PE arteries. The MEK inhibitor PD98059 attenuated the expression PrxI and proliferation induced by Hcy in normal SMC. These results show that Hcy induces PrxI expression and modulates SMC proliferation in normal SMC while impaired SMC function in PE may arise from the diminished induction of this protective anti-oxidant gene.

This work was supported by The Wellcome Trust.