Properties of Novel Anti-digoxin Antisera in Radioimmunoassay Using Homologous and Site Heterologous Tritium-Labeled Antigens Involving a [3H]-Leucine Moiety

• Published in: Biological & Pharmaceutical Bulletin Vol. 28; no. 2; pp. 340 - 343
• Main Authors: Ikeda, Yukari, Fujii, Youichi
• Format: Journal Article
• Language: English
• Published: Japan The Pharmaceutical Society of Japan 01-02-2005; Pharmaceutical Society of Japan; Japan Science and Technology Agency
• Subjects: Animals; anti-digoxin antiserum; Antigens, Heterophile - analysis; Antigens, Heterophile - metabolism; Cattle; digoxin; Digoxin - analogs & derivatives; Digoxin - analysis; Digoxin - metabolism; digoxin 3′-hemisuccinate–bovine serum albumin conjugate; digoxin 3″-hemisuccinyl-[3H]-leucine; Dose-Response Relationship, Drug; Immune Sera - analysis; Immune Sera - metabolism; Leucine - analysis; Leucine - metabolism; Protein Binding - physiology; radioimmunoassay (RIA); Radioimmunoassay - methods; Serum Albumin, Bovine - analysis; Serum Albumin, Bovine - metabolism; Tritium - analysis; Tritium - metabolism
• ISSN: 0918-6158; 1347-5215
• DOI: 10.1248/bpb.28.340

The specificities of antisera against digoxin C-3′ or C-3″ hemisuccinate–bovine serum albumin (BSA) conjugate were assessed by cross-reactivity studies with digoxin metabolites by radioimmunoassay (RIA) using the homologous and the site heterologous tritium-labeled antigens. One of the tracers used was digoxin 3′-hemisuccinyl-[3H]-leucine; the other was digoxin 3″-hemisuccinyl-[3H]-leucine, which had been prepared from digoxin 3″-hemisuccinate. When the tracer with [3H]-leucine at the C-3′ position was used, antisera (I-1, I-3) elicited by digoxin 3′-hemisuccinate–BSA conjugate showed the following cross-reactivity: digoxigenin bisdigitoxoside (0.34%, 76%), digoxigenin monodigitoxoside (0.11%, 65%), digoxigenin (0.02%, 26%) and dihydrodigoxin (9.4%, 1.2%). However, when using the homologous antigen, antiserum (I-1) was highly specific against the digitoxose chain. When the site heterologous antigen, digoxin 3″-hemisuccinyl-[3H]-leucine was combined, this antiserum showed high cross-reactivity to digoxin degradation products. This digoxin RIA using antiserum (I-1) with the homologous antigen measures unmetabolized digoxin. On the other hand, the RIA system using antiserum (I-3) with the homologous antigen had cross-reactivity with the metabolites in accordance with their relative cardio-activities, so this system would be useful in therapeutic drug monitoring of digoxin.