Specific antibodies to digoxin were isolated from antisera of sheep immunized with a digoxin-human serum albumin conjugate. The antibody was purified by adsorption to an immunoadsorbent, synthesized by coupling a ouabain-ribonuclease conjugate to bromoacetyl-cellulose, followed by elution with 25 mM ouabain. Ouabain was dissociated from antibody by denaturation in 6 M guanidine. The renatured antibody bound 1.6 mol of digoxin per mol and had an association constant of 1.6 X 108 M-1. At near-stoichiometric concentrations, either purified antibody to digoxin, or its papain-digested product (Fab-Fc), reversed digoxin-induced: (a) inhibition of 86Rb transport in human erythrocytes, (b) increase in developed tension in isolated guinea-pig atrial strips, and (c) ventricular tachycardia in intact dogs, and also corrected digoxin-induced automaticity in isolated guineapig atrial strips.Digoxin-specific antisera are capable of reversing the biological effects of the cardiac glycoside digoxin in in vivo and in vitro preparations* (1, 2). rThe investigations performed to date with unfractionated antisera do not allow precise quantitation of the interaction of the antibodies with digoxin. Other serum components present in these antisera may obscure the results and their interpretation. Furthermore, the full potential for digoxiin-specific antibodies in the therapy of digoxin toxicity, a common clinical problem, will not be realized until they are available in pure form.In this investigation digoxin-specific antibodies were produced in sheep immunized with a digoxin-human serum albumin conjugate (digoxin-HSA, ref. 3) and subsequently isolated with an immunoadsorbent. Theisolated antibodies bound digoxin with an affinity and capacity comparable to that of the antiserum. Both the isolated antibodies and their papain digests (Fab-Fc) were effective in reversing digoxininduced inhibition of rubidium uptake by human erythrocytes and digoxin-induced inotropic and arrhythmic effects in isolated guinea pig atrial strips. In addition, digoxin-induced ventricular tachycardia in dogs was rapidly abolished by the intravenous administration of Fab-Fc prepared from digoxinspecific antisera.Abbreviation: Me2F, dimethylformamide; HSA, human serum albumin; PBS, phosphate-buffered saline, pH 7.4; BAC, bromoacetyl cellulose; * Schmidt, D. H., and V. P. Butler, Jr., J. Clin. Invest., 48, Abstr. 74a (1969).
MATERIALS AND METHODS
AntigenDigoxin (Burroughs Wellcome Co., Inc.) was coupled to human serum albumin (3).
ImmunizationA 50-kg sheep was injected intramuscularly each week with 3 mg of digoxin-HSA emulsified in 1 ml of Freund's adjuvant to which 10 mg of killed tubercle bacilli had been added. After 20 weeks, 250-ml aliquots of blood were collected each week. The serum was separated and stored at -20"C.
Preparation of immunoadsorbentA crossreacting immunoadsorbent was prepared by reacting conjugates consisting of ouabain covalently bound to ribonuclease (ouabain-RNase) with bromoacetyl cellulose (BAC). The ouabain-RNase conjugates ...