Background and Purpose: Interaction of a drug with the carrier protein in the circulation determines its distribution, free or bound concentration and metabolism. Structural alteration in the major transport protein, human serum albumin (HSA) under several pathological conditions may affect its drug binding ability. The objective of the present investigation was to explore the binding of warfarin to structurally-altered HSA. Methods: Effect of urea, a denaturant on the interaction of warfarin with HSA was investigated using fluorescence spectroscopy. Results and Discussion: Fluorescence spectra of native HSA were characterized by the presence of an emission maximum around 339 and 343 nm, when excited at 280 and 295 nm, respectively. Warfarin binding to HSA was marked by a significant decrease in the fluorescence intensity and red shift in the emission maximum, being more pronounced at lower (1-5 µM) and smaller at higher (10-40 µM) drug concentrations. Presence of urea affected these signals to a significant extent even at lower concentrations. A significant decrease in both quenching and binding constants with increasing urea concentrations, suggested separation of excited fluorophore (Trp) of HSA and warfarin leading to the loss in its drug binding ability.

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