Induced Europium Circularly Polarized Luminescence Monitors Reversible Drug Binding to Native α₁-Acid Glycoprotein

Alpha-1-acid glycoprotein (α₁-AGP) is an important blood plasma glycoprotein. Following an acute-phase reaction such as stress, inflammation, burn, or infection, the bloodstream concentration of α₁-AGP can increase up to 400 % of its normal concentration. A wide range of drugs is known to bind α₁-AGP. Increased binding of pharmacologically active compounds to α₁-AGP moderates their clinical effect by decreasing the amount of unbound drug in the bloodstream. This has important clinical ramifications for such applications as the duration of anesthesia and in determining dosage for drug therapy. In this study, the competitive binding to α₁-AGP of a dynamically racemic europium(III) complex with seven pharmacologically active drugs absorbing in the range λ 250–290 nm was monitored by following changes in europium total emission and in induced circularly polarized luminescence (CPL). Binding affinities corresponding to K_dvalues in the range 0.5–100 μm were measured, in good agreement with published data.