Role of endogenous digitalis-like factors in the clinical manifestations of severe preeclampsia: a sytematic review

Endogenous digitalis-like factor(s), originally proposed as a vasoconstrictor natriuretic hormone, was discovered in fetal and neonatal blood accidentally because it cross-reacts with antidigoxin antibodies (ADAs). Early studies using immunoassays with ADA identified the digoxin-like immuno-reactive factor(s) (EDLF) in maternal blood as well, and suggested it originated in the feto-placental unit. Mammalian digoxin-like factors have recently been identified as at least two classes of steroid compounds, plant derived ouabain (O), and several toad derived bufodienolides, most prominent being marinobufagenin (MBG). A synthetic pathway for MBG has been identified in mammalian placental tissue. Elevated maternal and fetal EDLF, O and MBG have been demonstrated in preeclampsia (PE), and inhibition of red cell membrane sodium, potassium ATPase (Na, K ATPase (NKA)) by EDLF is reversed by ADA fragments (ADA-FAB). Accordingly, maternal administration of a commercial ADA-antibody fragment (FAB) was tested in several anecdotal cases of PE, and two, small randomized, prospective, double-blind clinical trials. In the first randomized trial, ADA-FAB was administered post-partum, in the second antepartum. In the post-partum trial, ADA-FAB reduced use of antihypertensive drugs. In the second trial, there was no effect of ADA-FAB on blood pressure, but the fall in maternal creatinine clearance (CrCl) was prevented. In a secondary analysis using the pre-treatment maternal level of circulating Na, K ATPase (NKA) inhibitory activity (NKAI), ADA-FAB reduced the incidence of pulmonary edema and, unexpectedly, that of severe neonatal intraventricular hemorrhage (IVH). The fall in CrCl in patients given placebo was proportional to the circulating level of NKAI. The implications of these findings on the pathophysiology of the clinical manifestations PE are discussed, and a new model of the respective roles of placenta derived anti-angiogenic (AAG) factors (AAGFs) and EDLF is proposed.

Endogenous cardiotonic steroids in kidney failure: a review and an hypothesis

In response to progressive nephron loss, volume and humoral signals in the circulation have increasing relevance. These signals, including plasma sodium, angiotensin II, and those related to volume status, activate a slow neuromodulatory pathway within the central nervous system (CNS). The slow CNS pathway includes specific receptors for angiotensin II, mineralocorticoids, and endogenous ouabain (EO). Stimulation of the pathway leads to elevated sympathetic nervous system activity (SNA) and increased circulating EO. The sustained elevation of circulating EO (or ouabain) stimulates central and peripheral mechanisms that amplify the impact of SNA on vascular tone. These include changes in synaptic plasticity in the brain and sympathetic ganglia that increase preganglionic tone and amplify ganglionic transmission, amplification of the impact of SNA on arterial tone in the vascular wall, and the reprogramming of calcium signaling proteins in arterial myocytes. These increase SNA, raise basal and evoked arterial tone, and elevate blood pressure (BP). In the setting of CKD, we suggest that sustained activation/elevation of the slow CNS pathway, plasma EO, and the cardiotonic steroid marinobufagenin, comprises a feed-forward system that raises BP and accelerates kidney and cardiac damage. Block of the slow CNS pathway and/or circulating EO and marinobufagenin may reduce BP and slow the progression to ESRD.

Digoxin-like immunoreactive substance: monoclonal and polyclonal RIA and FPIA compared

Digoxin-like immunoreactive substance (DLIS) was measured in 34 samples obtained from subjects not receiving digoxin: 10 uremic, 10 third trimester pregnancy, seven cord blood and seven normal. DLIS concentration was measured by four commercial polyclonal radioimmunoassay (RIA) systems: Clinical Assay (CA), Corning Immophase (CI), Diagnostic Products Double Antibody (DP), Kallestad Quantitope (KK), a monoclonal antibody (MA) assay and a Fluorescence Polarization Immunoassay (FPIA). In general, the cord blood samples were richer in DLIS. Digoxin immunoassays, MA and DP showed minimal interference by DLIS in all samples, whereas FPIA and CA exhibited the maximal cross-reactivity with DLIS. In cord blood samples, mean +/- SD DLIS concentration ranged from 0.41 +/- 0.13 (by CA) to 0.034 +/- 0.02 ng ml-1 as measured by MA assay. In uremics, the mean DLIS concentration was below the detection limit of all RIA assays. The FPIA method showed a higher degree of cross-reactivity to DLIS, especially in the cord and pregnancy samples (0.42 +/- 0.13 and 0.4 +/- 0.14 ng ml-1, respectively). DLIS in uremics was below the FPIA detection limit of 0.2 ng ml-1. Overall, the degree of interference by DLIS in decreasing order was FPIA greater than CA greater than CI greater than or equal to KQ greater than DP greater than or equal to MA. The cord blood samples were re-analysed by FPIA (Digoxin-II assay) 4 months later, resulting in 2-4-fold higher DLIS concentrations for these samples. This appears to be due to the substitution of 5-sulphosalicylic acid as a protein precipitating reagent and this effect may have been accentuated by freeze-thaw cycles.