Magnesium Sulfate Potentiates Effect of Digifab on Marinobufagenin-Induced Na/K-ATPase Inhibition

Abstract

Immunoneutralization of elevated circulating levels of endogenous digitalis-like Na/K-ATPase inhibitors (i.e. cardiotonic steroids (CTS)) represents a novel approach in the treatment of preeclampsia (PE). Recently we demonstrated that DigiFab (Fab fragments of affinity-purified ovine digoxin antibody) restores PE-induced inhibition of Na/K-ATPase in erythrocytes ex vivo. Previously magnesium ions were shown to antagonize digitalis-induced toxicity, which is mediated by Na/K-ATPase inhibition. We hypothesized that magnesium sulfate would potentiate the effect of DigiFab in the reversal of CTS-induced Na/K-ATPase inhibition. To test this hypothesis, we studied the ex vivo effect of DigiFab on Na/K-ATPase activity in erythrocytes from patients with PE in the absence and in the presence of 3 mmol/L magnesium sulfate. Compared with 11 normotensive pregnant subjects (29 ± 1 years; gestational age = 39.0 ± 0.2 weeks; blood pressure = 111 ± 2/73 ± 2 mm Hg), the 12 patients with PE (30 ± 1 years; gestational age = 37.9 ± 0.3 weeks; blood pressure = 159 ± 5/99 ± 3 mm Hg) had plasma levels of marino-bufagenin increased 3-fold (1.38 ± 0.40 vs. 0.38 ± 0.10 nmol/L; P < 0.01) and activity of Na/K-ATPase in erythrocytes was inhibited (1.16 ± 0.11 vs. 2.80 ± 0.20 μmol Pi/ml/h; P < 0.01). Ex vivo, DigiFab (1 µg/ml) restored erythrocyte Na/K-ATPase activity (1.72 ± 0.13 µmol Pi/ml/h; P < 0.01), and 3 mmol magnesium sulfate potentiated the effect of DigiFab (2.30 ± 0.20 µmol Pi/ml/h; P < 0.01). Magnesium is capable of increasing the efficacy of immunoneutralization of marinobufagenin-induced Na/K-ATPase inhibition.