Objectives: Human umbilical vascular endothelial cells (HUVECs), seeded on Matrigel (BD Biosciences, Bedford, UK), undergo an angiogenic-like process. We hypothesized that placental explants from normal pregnancies, maintained in cultures of different oxygen, would liberate factors that could be measured in this system. We further tested the angiogenic potential of placentae from intrauterine growth-restricted (IUGR) pregnancies and the effects of vascular endothelial growth factor (VEGF) blockade.
Methods: Placental villous explants were maintained in culture at 3% and 20% O2. The resultant media was added to HUVECs seeded on 80% Matrigel. Cells were incubated at 6% O2 in accordance with the natural placental environment. After 6 hours, cells were fixed and stained and the length and number of tubules measured by morphometric imaging. Finally, VEGF and soluble VEGF receptor (sVEGFR-1) were recorded in the explant conditioned media.
Results: Within the angiogenic assay, recombinant human VEGF significantly enhanced tubule outgrowth (branching and elongation) and this effect was blocked with neutralising antibody. Compared to 20% O2, media of placental explants conditioned at 3% O2 significantly encouraged tubule length and numbers. Again this affect was ablated by VEGF blockade. In cases of IUGR, conditioned media at 3% O2 showed a significant reduction in tubule growth. This was paralleled by a decline in available VEGF brought about an exaggeration in liberated sVEGFR-1. Notably, venous cord serum from IUGR pregnancies showed a similar elevation in sVEGFR-1.
Conclusion: Under restricted oxygen, placental angiogenic potential is suppressed in IUGR pregnancies through the overproduction of placental sVEGFR-1. This reduction may discourage normal placental vascularization and impact on fetal development.