title: Inhibition of Na,K-ATPase by oleandrin and oleandrigenin, and their detection by digoxin immunoassays.
abstract: Ingestion of oleander plant, containing the cardiac glycoside oleandrin, has been reported to induce fatal poisonings. Derivatives of oleandrin are structurally similar to digoxin. We investigated the cross-reactivities of oleandrin and its aglycone metabolite, oleandrigenin, in several commercially available digoxin immunoassays; assessed their ability to inhibit Na,K-ATPase catalytic activity; and measured their binding to proteins in serum. As assayed with ACS:180, Stratus, RIA, On-Line, and TDx digoxin assays, oleandrin at 100 micromol/L in digoxin-free serum gave apparent digoxin values of 0, 0.83, 2.24, 2.37, and 5.34 nmol/L, respectively, whereas oleandrigenin at that concentration gave results of 0, 0.52, 0.77, 4.94, and 1.40 nmol/L. Study of Na,K-ATPase inhibition showed IC50 values (micromol/L) of 0.22 for ouabain, 0.62 for oleandrin, 1.23 for oleandrigenin, and 2.69 for digoxin. At 25 degrees C, 96% of oleandrin and 48% of oleandrigenin were bound to serum proteins. Because detection of oleandrin and oleandrigenin by digoxin immunoassays is variable between assays as well as between congeners, assessment of cross-reactivity is warranted for each assay. The inhibition of Na,K-ATPase by oleandrin and oleandrigenin confirms that they likely exert their toxic effects through inhibition of sodium pump activity. In cases of digitalis-like poisoning with suspicion of oleander ingestion, a combination of digoxin immunoassays may be useful to effectively rule out the presence of oleander.
authors.affiliation: Department of Pathology, University of Louisville School of Medicine, KY 40292, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Jortani
authors.forename: R A
authors.initials: RA
authors.lastname: Helm
authors.forename: R
authors.initials: R
authors.lastname: Valdes
mesh_terms: D001798:Blood Proteins / Q000378:metabolism; D002298:Cardenolides / Q000097:blood* / Q000494:pharmacology; D002301:Cardiac Glycosides / Q000097:blood; D004077:Digoxin / Q000097:blood*; D004791:Enzyme Inhibitors / Q000097:blood*; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000706:statistics & numerical data; D012680:Sensitivity and Specificity; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
chemical_list: D001798:Blood Proteins; D002298:Cardenolides; D002301:Cardiac Glycosides; D004791:Enzyme Inhibitors; C008701:oleandrigenin; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase; C021065:oleandrin