Changes in Microparticle Numbers and Cellular Origin During Pregnancy and Preeclampsia

Background: Microparticles (MP) are pro-coagulant vesicles derived from various cells. Evidence is accumulating that MP are of pathophysiological relevance in autoimmune, cardiovascular, and thromboembolic diseases and inflammatory disorders. Therefore, their role in the development of preeclampsia was investigated and MP from preeclamptic patients influenced endothelial-dependent vasodilatation. Knowledge about changes in circulating MP numbers during pregnancy and preeclampsia is lacking. We determined this longitudinally and investigated whether these numbers related to the severity of preeclampsia. Methods: Samples were obtained from pregnant women and preeclamptic patients during pregnancy and postpartum. MP were isolated and studied by flow cytometry. Results: During pregnancy, MP were decreased at 12 weeks gestation and then returned to postpartum values. In patients with preeclampsia, MP numbers were reduced at 28 and 36 weeks (both p = 0.04). Monocyte-derived MP were elevated in preeclampsia at 28 (p = 0.007), 32 (p = 0.02), and 36 weeks (p = 0.01), as were erythrocyte-derived MP at 28 weeks (p = 0.04). Placenta-derived MP increased in pregnancy and preeclampsia. During pregnancy, a correlation was present between placenta-derived MP and systolic blood pressure (r = 0.33, p = 0.015). No other correlations were found. Conclusions: During pregnancy, numbers of MP initially decrease and subsequently normalize. Placenta-derived MP increase, possibly because of placental growth. In preeclampsia, reduced numbers of PMP are due to decreased platelet counts. Increased numbers of monocyte-derived MP reflect monocyte activation, which may be an expression of the systemic inflammation in preeclampsia. Lack of correlation between numbers of MP and severity of preeclampsia suggests that MP numbers alone do not explain the reported vascular effects of MP.