TY - JOUR T1 - Characterization of the Neutralizing Activity of Digoxin-Specific Fab toward Ouabain-Like Steroids JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 319 LP - 325 DO - 10.1124/jpet.104.065250 VL - 310 IS - 1 AU - Mark A. Pullen AU - David P Brooks AU - Richard M. Edwards Y1 - 2004/07/01 UR - http://jpet.aspetjournals.org/content/310/1/319.abstract N2 - Digoxin-specific Fab (Digibind) is a mixture of antidigoxin Fab fragments prepared from sheep sera and is used as a treatment for digoxin poisoning. Digoxin-specific Fab has been shown to neutralize an endogenous Na+/K+ ATPase inhibitor (endogenous digoxin-like Na+/K+ ATPase regulatory factor; EDLF) in rats and humans and to lower blood pressure. Although the exact structure of EDLF is unknown, compounds identical to or structurally related to ouabain, bufalin, and marinobufagenin have been detected in mammalian plasma. In this study, some structural characteristics of EDLF were inferred from the ability of digoxin-specific Fab to neutralize the Na+/K+ ATPase inhibitory activity of several known cardenolides and bufodienolides. Additional structural information was obtained from [3H]ouabain binding and enzyme-linked immunosorbent assay experiments. Digoxin-specific Fab had the ability to interact to some extent with all of the cardenolides and bufodienolides tested. However, digoxin-specific Fab was more than 20-fold more potent in neutralizing ouabain and bufalin than marinobufagenin. The antihypertensive effect of digoxin-specific Fab seen in preeclampsia and animal models of hypertension may therefore be due to a molecule identical to or structurally similar to ouabain or bufalin. The American Society for Pharmacology and Experimental Therapeutics ER -