Dose-dependent reversal of digoxin-inhibited activity of an in vitro Na +K +ATPase model by digoxin-specific antibody

• Published in: Toxicology letters Vol. 85; no. 2; pp. 107 - 111
• Main Authors: Cano, Nathalie J., Sabouraud, Alain E., Debray, Marcel, Scherrmann, Jean-Michel G.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.05.1996; Amsterdam Elsevier Science
• Subjects: Animals; Antigen-Antibody Reactions; Biological and medical sciences; Brain - enzymology; Cell Membrane - drug effects; Cell Membrane - metabolism; Digoxin; Digoxin - immunology; Digoxin - pharmacology; Dose-Response Relationship, Immunologic; Drug toxicity and drugs side effects treatment; Fab fragments; Immunoglobulin Fab Fragments - immunology; Immunoglobulin Fab Fragments - pharmacology; In Vitro Techniques; Isoforms; Male; Medical sciences; Microsomes - enzymology; Miscellaneous (drug allergy, mutagens, teratogens...); Na +K +ATPase activity; Pharmacology. Drug treatments; Rat brain; Rats; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; Sodium-Potassium-Exchanging ATPase - metabolism; Na +K +ATPase activity; IC 50; Digoxin; EC 50; Isoforms; Na +K +ATPase; Fab fragments; Rat brain; Rat; Enzyme; Antibody; Toxicity; Treatment efficiency; Rodentia; Prediction; Fab-Fragment; K; In vitro; Vertebrata; Mammalia; Na; Treatment; Animal; Immunotherapy; Hydrolases; exchanging ATPase; Glycoside; Brain (vertebrata)
• ISSN: 0378-4274; 1879-3169
• DOI: 10.1016/0378-4274(96)03647-8

We investigated the potency of digoxin-specific Fab fragments to reverse digoxin-induced Na +K +ATPase inhibition in rat brain microsomes according to (a) the extent of initial inhibition of Na +K +ATPase and (b) the neutralizing dose of antibody. Mathematical analysis of the digoxin concentration-Na +K +ATPase inhibition curve supports the existence of 2 digoxin sensitive Na +K +ATPase isoforms. The IC 50 was 1.3 × 10 −4 M and 2.5 × 10 −8 M for the low (α1) and high (α2) digoxin affinity isoenzyme, respectively. The reversal of digoxin-induced Na +K +ATPase inhibition was dependent on the digoxin-specific Fab concentration. The maximal effect was observed when the Fab:digoxin ratio was stoichiometrical and addition of an excess of antibodies did not result in a complete reversal of inhibition at the 4 digoxin concentrations studied. This simple and rapid in vitro model will be a useful tool to predict the efficacy of a new generation of antibodies.