Placenta-derived extracellular vesicles in maternal plasma of Hb Bart's fetuses

Hemoglobin (Hb) Bart's disease is the most common cause of hydrops fetalis among Southeast Asians. Given its high fatality rate, prenatal diagnosis and treatment are the key. This condition is associated with placental hypoxia, which can trigger the release of placenta-derived extracellular vesicles (EVs) into the maternal circulation. We aimed to determine the levels of placenta-derived EVs and the proteomic profiles of plasma EVs in women with fetuses with Hb Bart. This prospective cohort study included women with: (1) normal term pregnancies (Group 1; n = 19); (2) Hb Bart's fetuses with hydropic features (Group 2; n = 4); (3) Hb Bart's fetuses without hydrops (Group 3; n = 7); (4) placental associated complications (a disease control group or Group 4; n = 4); and (5) hydrops fetalis from non-Bart's causes (Group 5; n = 5). Maternal plasma EVs were isolated as well as characterized, and their placental alkaline phosphatase (PLAP) content was quantified via ELISA. Proteomic profiles were determined via mass spectrometry. The EVs from the women with fetuses with Hb Bart's with hydrops were smaller than those from the women in the normal and disease control groups. Bart fetuses with hydropic features had higher PLAP levels per EV particle than normal pregnancies. However, PLAP levels per EV seemed to be highest in the patients with placenta-associated complications. Among the 16 differentially expressed EV proteins, hnRNPA2B1 showed the greatest difference between women who had fetuses with Hb Bart's hydrops and those with normal pregnancies or placenta-associated complications. The 16 proteins are involved in aberrant immune responses, pro-inflammatory cytokine regulation, and vascular injuries. These changes may be the result of placental hypoxia associated with Hb Bart's hydrops.