A longitudinal study of maternal digoxin-like immunoreactive substances in normotensive pregnancy and pregnancy-induced hypertension

Endogenous Digitalis-like Factors as a Key Molecule in the Pathophysiology of Pregnancy-Induced Hypertension and a Potential Therapeutic Target in Preeclampsia

Preeclampsia (PE), the most severe presentation of hypertensive disorders of pregnancy, is the major cause of morbidity and mortality linked to pregnancy, affecting both mother and fetus. Despite advances in prophylaxis and managing PE, delivery of the fetus remains the only causative treatment available. Focus on complex pathophysiology brought the potential for new treatment options, and more conservative options allowing reduction of feto-maternal complications and sequelae are being investigated. Endogenous digitalis-like factors, which have been linked to the pathogenesis of preeclampsia since the mid-1980s, have been shown to play a role in the pathogenesis of various cardiovascular diseases, including congestive heart failure and chronic renal disease. Elevated levels of EDLF have been described in pregnancy complicated by hypertensive disorders and are currently being investigated as a therapeutic target in the context of a possible breakthrough in managing preeclampsia. This review summarizes mechanisms implicating EDLFs in the pathogenesis of preeclampsia and evidence for their potential role in treating this doubly life-threatening disease.

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.

Review Paper. Transplacental Digoxin Treatment In Prenatal Cardiac Problems In Singleton Pregnancies - Meta Analysis (Based On Literature: 1992–2015)

Based on fourteen case reports from various centres from 1992-2015 and three original studies in 2006-2011, 122 fetuses were subjected to analysis. In these reports, transplacental digoxin treatment was administered to different cardiac anomalies such as SVT , Ebstein’s anomaly, critical AS , absent pulmonary valve syndrome, complete heart block, in foetuses with aneurysm/diverticulum of LV, in tricuspid atresia or dysplasia, rhabdomyoma, pulmonary atresia, HLHS with fibroelastosis, in TTTS and in extracardiac anomalies such as atriovenous malformation or sacrococcygeal teratoma. There was no statistical difference to suggest (Chi-square test) that digoxin was more efficient to control fetal arrhythmias than fetal congestive heart failure in nonarrhythmic patients.

Conclusions: Foetal cardiac insufficiency may appear due to different reasons (in normal heart anatomy or in heart defects, in normal sinus rhythm or due to foetal arrhythmias: tachycardias or severe bradycardia) and may be a cause of intrauterine demise. So far, we do not have strong evidence that digoxin treatment may prevent foetal death or prematurity. More research is needed to ascertain if the prolonging of pregnancy resulted from digoxin treatment or if improvement in foetal circulatory insufficiency was influenced by spontaneous regression of foetal cardiac symptoms.

The hemodynamic effects of intravenous digoxin-binding fab immunoglobulin in severe preeclampsia: a double-blind, randomized, clinical trial

OBJECTIVE

An endogenous digitalis-like factor (EDLF) has been implicated in the pathophysiology of preeclampsia (PE). This hypothesis is supported by two cases of preeclampsia in which administration of digoxin immune Fab (DIF) reduced mean arterial pressure (MAP).

STUDY DESIGN

To study this observation further, we performed a double-blind, placebo-controlled, randomized clinical trial to examine the effects on MAP of intravenous DIF given after delivery in 26 subjects with severe preeclampsia. Treating obstetricians were blinded to subject assignment and were allowed to use standard antihypertensive drugs during the trial.

RESULTS

The primary outcome, a significant difference in blood pressure between the two groups over the 24-h period of observation after the intervention, was not supported. However, mean MAP was significantly lower in the DIF-treated subjects for the first 4 h after therapy as compared with controls (P=0.05). Six subjects (46.2%) in the placebo arm were given conventional antihypertensive medications by their obstetrician for blood pressure >160 mm Hg systolic or >110 mm Hg diastolic, compared with zero subjects in the treatment arm (P=0.01). A trend towards increased creatinine clearance was observed in DIF-treated subjects (137.6+/-42.6 versus 104.1+/-43.4, P=0.07).

CONCLUSION

These results support the hypothesis that EDLF contributes to the elevated blood pressure in preeclampsia and suggests a possible role for DIF as a treatment for this condition.

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

Postmortem digoxin-like immunoreactive substances (DLIS) in patients not treated with digoxin

Endogenous digoxin-like immunoreactive substances (DLIS) cross-react in immunoassays of digoxin. The postmortem rise in digoxin levels in patients treated with the drug may be due to its redistribution. It is unclear what is the contribution of DLIS to this increase and whether DLIS are present postmortem in patients not treated with digoxin. The objectives of this study were to determine whether DLIS are present after death in patients not treated with digoxin, whether a postmortem increase in DLIS is detectable and whether sampling site can affect DLIS concentrations. DLIS (measured as digoxin, TDx Abott) were determined in blood samples drawn antemortem from ICU patients; postmortem samples from femoral artery and cardiac chambers were taken at least 12 h after the death of these same patients. DLIS concentrations > or = 0.2 ng/ml were measured in 44 and 40% of patients antemortem and postmortem (femoral), respectively. No difference was found in DLIS levels between antemortem and postmortem femoral and cardiac samples. Age, ICU stay and postmortem sampling time did not affect the postmortem increase in DLIS. None of the levels was in the toxic range. DLIS may be present after death and their concentration does not increase postmortem. The interpretation of postmortem digoxin concentrations that fall in the therapeutic range should be done cautiously; such measurable levels do not necessarily indicate misuse or malicious intent even in patients who had not been treated with the drug.

Comparison of four digoxin immunoassays with respect to interference from digoxin-like immunoreactive factors

OBJECTIVES

Comparison of a new monoclonal digoxin assay with three polyclonal digoxin assays for their cross-reactivity to digoxin-like immunoreactive factors (DLIF) and digoxin metabolites.

DESIGN AND METHODS

Sixty-six nondigitalized patient samples from 5 different groups: neonates, women in 3rd trimester pregnancy, and patients with liver or renal diseases, or undergoing organ transplants, and 139 samples from digoxin-treated patients of 4 categories (hospital sick, liver, renal, and outpatients) were compared in 4 different digoxin assays: (a) ACS Digoxin (ACS) developed for the automated chemiluminescent Ciba Corning ACS 180 system, (b) Baxter Stratus (Stratus, a fluoroimmunoassay), (c) Ciba-Corning Magic (Magic, a radioimmunoassay), and (d) an in-house radioimmunoassay (RIA). The ACS and RIA were also compared for their cross-reactivity to four principal digoxin metabolites.

RESULTS AND CONCLUSION

Among the nondigitalized specimens, no significant DLIF interference was found for all 4 assays among the pregnant women or liver and transplant patients. However, the neonates registered high DLIF interference with Magic and RIA, but none for ACS or Stratus. DLIF interference in renal samples was highest in the Magic assay and lowest in RIA. Among the specimens with digoxin, a higher number of discrepant samples were found from the sick patients than from outpatients. In 75% of such discrepant samples, the ACS result was less than other assay results, suggesting DLIF as the probable cause. The two assays differed most in their cross-reactivity to the deglycated metabolites, digoxigenin and its mono-digitoxoside.

Treatment of toad venom poisoning with digoxin-specific Fab fragments

Toxicity from toad venom poisoning is similar to digoxin toxicity and carries a high mortality rate. We report on six previously healthy men who developed vomiting and bradycardia after ingesting a purported topical aphrodisiac. Each patient had positive apparent digoxin levels and the first four patients died of cardiac dysrhythmias. The last two patients recovered following treatment with digoxin Fab fragments. We analyzed samples of the purported aphrodisiac and found that it was identical to Chan Su, a Chinese medication made from toad venom. To our knowledge, this is the first reported use of digoxin Fab fragments to treat toad venom poisoning.

Falsely elevated serum digoxin levels secondary to endogenous digoxin-like immunoreactive substances

Endogenous digoxin-like immunoreactive substances (DLIS) are produced by the human body and can be significantly elevated in specific clinical conditions. Commercially available digoxin assays do not have the specificity to fully distinguish DLIS from exogenous digoxin, though DLIS do not possess the same therapeutic properties as do the drug. The resultant artificial elevation of a reported digoxin level or a completely factitious level in a patient not taking the drug can have clinically significant consequences.

Endogenous digoxin-immunoreactive substance in normal and preeclamptic pregnancies

AIMS

To determine the potential use of a digoxin-immunoreactive substance in the prediction of preeclampsia, to study the relationship between serum levels of this substance and gestational age, and to evaluate the correlation between this substance and blood pressure findings in preeclamptic pregnancies.

METHODS

Serum digoxin-immunoreactive substance concentrations were measured by RIA (double antibody radioimmunoassay) in normotensive (n = 14) and preeclamptic (n = 17) pregnant women in their third trimesters. Statistical evaluation was performed with the Mann-Whitney U-test and correlation-regression analysis.

RESULTS

The mean (+/- S.E.) digoxin-immunoreactive substance levels in the normal and preeclamptic patients were 0.29 +/- 0.06 and 0.31 +/- 0.05 ng/ml, respectively, the slightly higher level in the hypertensive group being statistically non-significant. Serum digoxin-immunoreactive substance levels did not demonstrate good correlation with gestational age and systolic blood pressure in preeclamptic pregnancies.

CONCLUSIONS

An endogenous digoxin-immunoreactive substance is present in the sera of third trimester pregnant women, but it does not contribute to the pathogenesis or prediction of preeclampsia.

Pregnancy induced hypertension and sodium pump function in erythrocytes

OBJECTIVE

To determine if erythrocyte sodium pump function is altered with the onset of pregnancy induced hypertension.

DESIGN

A prospective descriptive study.

SUBJECTS

Thirty-two primigravid women with pregnancy-induced hypertension (17 had proteinuria) and 32 gestation-matched normotensive primigravid pregnant women were studied and measurements repeated 20 weeks after delivery.

INTERVENTION

Erythrocyte sodium, ouabain-sensitive sodium flux and the sodium pump rate constant were measured in whole blood and the maximum velocity and sodium affinity of the sodium pump were measured in vitro.

RESULTS

Blood pressure remained higher after delivery in the women who had been hypertensive during pregnancy. In normal pregnancy erythrocyte sodium was decreased, and ouabain-sensitive sodium flux, the sodium pump rate constant and maximum velocity (Vmax) were increased compared with 20 weeks after delivery. In pregnancy-induced hypertension erythrocyte sodium and sodium pump changes were the same as in normal pregnancy. The possibility of a positive association between changes in erythrocyte sodium and in blood pressure was excluded. The rate constant of the sodium pump in blood was related to its Vmax measured in vitro but the relation had greater variance in the hypertensives with 7 of the 32 women having rate constants greater than expected from their Vmax.

CONCLUSION

There was no evidence of sodium pump inhibition or a rise in intracellular sodium associated with increased blood pressure in pregnancy. There may have been stimulation of the sodium pump by a plasma factor in some hypertensive women.