Immunoneutralization of endogenousNa/K-ATPase inhibitors in preeclampsia

Although preeclampsia (PE) is a major cause of maternal and fetal mortality, its pathogenesis is not fully understood. Endogenous digitalis-like cardiotonic steroids (CTS) are implicated in the pathophysiology of PE, as illustrated by clinical observations that Digibind, a digoxin antibody which binds CTS, lowers blood pressure in patients with PE. Recently we reported that plasma levels of marinobufagenin (MBG), a bufadienolide vasoconstrictor CTS, are increased four-fold in patients with severe PE. In the present study, we compared levels of MBG in normal and preeclamptic placentae, and tested whether antibodies against MBG, and against ouabain for their interaction with the material purified from preeclamptic placentae via high-performance liquid chromatography (HPLC). Levels of MBG, but not that of endogenous ouabain, exhibited a four-fold elevation in preeclamptic placentae. The elution time of endogenous placental MBG-like immunoreactive material from reverse-phase HPLC column was identical to that of authentic MBG. Immunoassay based on Digibind did not detect cross-reactivity with HPLC containing ouabain-like immunoreactive material, but cross-reacted with HPLC fractions having retention time similar to that of MBG and other bufadienolides. Our results demonstrate that levels of MBG are significantly elevated in preeclamptic placentae, and suggest that MBG is a potential target for immunoneutralization in patients with preeclampsia.