Interaction of Digibind with endogenous cardiotonic steroids from preeclamptic placentae

Abstract

Preeclampsia is a major cause of maternal and fetal mortality, and its pathogenesis is not fully understood. Endogenous digitalis-like cardiotonic steroids (CTS) have been implicated in the pathophysiology of preeclampsia; this is illustrated by clinical observations that Digibind, a therapeutic digoxin antibody fragment which binds CTS, lowers blood pressure and reverses Na/K-ATPase inhibition in patients with preeclampsia. Recently we reported that plasma levels of marinobufagenin (MBG), a bufadienolide vasoconstrictor CTS, are increased four-fold in patients with severe preeclampsia. In the present study, we compared levels of MBG in normal and preeclamptic placentae, as well as the interactions of Digibind and antibodies against MBG and ouabain with material purified from preeclamptic placentae using high-performance liquid chromatography (HPLC). Levels of endogenous MBG, but not that of endogenous ouabain, exhibited a four-fold elevation in preeclamptic placentae vs. normal placentae (13.6 +/- 2.5 and 48.6 +/- 7.0 nmoles/g tissue; P < 0.01). The elution time of endogenous placental MBG-like immunoreactive material from reverse-phase HPLC column was identical to that of authentic MBG. A competitive immunoassay based on Digibind exhibited reactivity to HPLC fractions having retention times similar to that seen with MBG and other bufadienolides, but not to ouabain-like immunoreactive material. Our results suggest that elevated levels of endogenous bufadienolide CTS represent a potential target for immunoneutralization in patients with preeclampsia.