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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.

Despite prophylaxis and attempts to select a therapy, the frequency of preeclampsia does not decrease, and it still takes the leading position in the structure of maternal mortality and morbidity worldwide. In this review, we present a new theory of the etiology and pathogenesis of preeclampsia which is based on the interaction of Na/K-ATPase and its endogenous ligands including marinobufagenin. The signaling pathway of marinobufagenin involves an inhibition of transcriptional factor Fli1, a negative regulator of collagen synthesis, followed by deposition of collagen in the vascular tissues and altered vascular functions. Moreover, in vitro and in vivo neutralization of marinobufagenin is associated with restoration of Fli1. The inverse relationship between marinobufagenin and Fli1 opens new possibilities in the treatment of cancer: since Fli1 is a proto-oncogene, a hypothesis on suppression of Fli1 by cardiotonic steroids as potential anti-tumor therapeutic strategy is discussed as well. We propose a novel therapy of preeclampsia which is based on immunoneutralization of the marinobufagenin by monoclonal antibodies, which is capable to impair marinobufagenin-Na/K-ATPase interactions.