The mechanisms mediating the hypertension of preeclampsia (PE) are unclear. Endogenous digitalis-like factors (EDLFs) are specific sodium pump (SP) inhibitors implicated in essential and experimental hypertension, but they have not been fully explored in the setting of PE. This study uses a digoxin antibody Fab fragment to address the question of whether such factors are present and increased in PE, to investigate a possible treatment of PE, and to isolate and characterize all EDLFs present in PE. Sera and placenta from women with PE did show a significant increase in SP inhibition in comparison to women with normal pregnancy and Digibind® was found to bind EDLFs and essentially block or reverse SP inhibition. Sera were collected in a Phase II, double-blind, placebo controlled clinical study in which women with severe preeclampsia were dosed with Digibind®, as a therapeutic, and the SP activity measured. Sera and placenta from women with PE was also investigated for their inhibitory effects on the SP. Known candidates for EDLFs were investigated for their SP inhibitory effects, as well as how digitalis antibody immune Fab fragments, Digibind® and DigiFab™, bound them and affected the SP activity. Digibind® is also a sufficient affinity material used to isolate and purify PE EDLFs. Additionally, the placentas of preeclamptic women have high levels of similar EDLFs. These studies provide evidence for the existence of EDLFs that circulate in women with PE, and Digibind® is an effective and novel tool to bind, isolate and purify EDLFs in PE.

The sodium pump (SP or Na+,K+-ATPase) is a membrane embedded protein complex that pumps 3 sodium ions out and 2 potassium ions into the cell per cycle and in so doing creates a cell membrane electrochemical potential. The membrane potential is critical for any functional cell. In the vasculature, reduction in the voltage potential causes vascular smooth muscle contraction and a narrowing of blood vessels (vasoconstriction) which can lead to increased blood pressure (hypertension). Substantial research over the past several decades has provided a vast amount of research on SP inhibitors, sometimes called endogenous digitalis-like factors (EDLF). Increased levels of these factors have been implicated in many hypertensive disorders including preeclampsia (PE), a life-threatening complication of pregnancy. It has been demonstrated that EDLF might be a causative factor in the pathophysiology of hypertension in PE. In order to elucidate EDLF production and regulation in PE, We developed a radioimmunoassay (RIA) measuring EDLF that could be applied to serum from pregnant women, placental homogenate and placental tissue culture. This assay employs Digibind, a commercially available Fab fragment derived from polyclonal antidigoxin antibodies that cross reacts with EDLF, as the primary antibody. Using Digibind RIA, we demonstrated that placenta is a source of EDLF production and regulation. Moreover, the identification of an inhibitor, ketoconazole and a substrate, 17-hydroxyprogesterone of the synthetic pathway of EDLF in placenta proved that this pathway shares steps with the steroid synthetic pathway. Some potential regulatory agents which have elevated levels in PE or be associated in PE and thus are thought to mediate PE, such as hydrogen peroxide, tumor necrosis factor-α (TNF-α) and hypoxia have also been demonstrated to be stimuli of EDLF production in placenta. These findings are helpful to the further study on EDLF synthesis and regulation in placenta. Once we elucidate the mechanisms, it could be easier to provide deeper insights into the pathogenesis of PE and subsequently develop earlier diagnosis and effective prevention of or therapeutic approaches to PE.