Preeclampsia is a hypertensive disease that affects 3-5% of pregnancies. The pathogenesis of preeclampsia is unclear but it is known that an early step involves the secretion of a placental factor which triggers maternal endothelial cell dysfunction. Microparticles that are shed from the placenta into the maternal circulation may be one such trigger by expressing proteins that affect endothelial cell function, such as Flt-1. Currently, a range of centrifugation speeds (13,000g-150,000g) have been employed to isolate microparticles, meaning that microparticles from different studies may have different properties. Furthermore, many studies have focused on microparticles from term placentae, whereas the pathogenesis of preeclampsia begins early in gestation. In this study, we investigated the effect of centrifugation speed on the nature of microparticles harvested from first trimester placental explants.

Low-speed and high-speed microparticles were harvested by sequential centrifugation at 15,000g and 75,000g, respectively. The size and morphology of microparticles was investigated by dynamic light scattering and transmission electron microscopy. Microparticle expression of Flt-1 was investigated by Western blotting.

Microparticles isolated by centrifugation at 15,000g had a mean diameter of 567.0±87.1nm (n=7 placentae) and a mean weight of 26.7±13.7mg/gram of placenta (n=14). Centrifugation of the 15,000g supernatant at 75,000g harvested microparticles with a mean diameter of 174.5±11.5nm (n=7) and a mean weight of 61.7±21.6mg/gram of placenta (n=14). Electron microscopy showed that the microparticles harvested at both centrifugation speeds were approximately spherical and enclosed by a lipid bilayer (n=3). Microparticles harvested at both centrifugation speeds expressed full-length Flt-1 (n=7).

Altering the centrifugation speed for harvesting microparticles from cultured placental explants affected the size of the microparticles obtained, but not their morphology nor expression of Flt-1. This is the first study to show that Flt-1 is present in microparticles shed from first trimester placentae, suggesting a possible mechanism by which placental microparticles can contribute to the pathogenesis of preeclampsia in early pregnancy.