Warfarin and Flavonoids Do Not Share the Same Binding Region in Binding to the IIA Subdomain of Human Serum Albumin

Abstract

Human serum albumin (HSA) binds a variety of xenobiotics, including flavonoids and warfarin. The binding of another ligand to the IIA binding site on HSA can cause warfarin displacement and potentially the elevation of its free concentration in blood. Studies dealing with flavonoid-induced warfarin displacement from HSA provided controversial results: estimated risk of displacement ranged from none to serious. To resolve these controversies, in vitro study of simultaneous binding of warfarin and eight different flavonoid aglycons and glycosides to HSA was carried out by fluorescence spectroscopy as well as molecular docking. Results show that warfarin and flavonoids do not share the same binding region in binding to HSA. Interactions were only observed at high warfarin concentrations not attainable under recommended dosing regimes. Docking experiments show that flavonoid aglycons and glycosides do not bind at warfarin high affinity sites, but rather to different regions within the IIA HSA subdomain. Thus, the risk of clinically significant warfarin–flavonoid interaction in binding to HSA should be regarded as negligible.

Indomethacin Increases Quercetin Affinity for Human Serum Albumin: A Combined Experimental and Computational Study and Its Broader Implications

“…The obtained results are in accordance with results obtained by Zsila et al [18] and Dufour and Dangles [7], as well as with the crystallographic structures obtained by Petitpas et al [34] and Yamasaki et al [35,36], stating that the binding site in the subdomain IIA of HSA is large enough to accommodate multiple ligands at the same time. This was also confirmed for the case of interactions between warfarin and quercetin [29]. The difference in QUE fluorescence is likely brought about either by (i) conformational changes within the ligand; (ii) potential changes in the size and shape of the IIA binding site caused by the presence of IND; or (iii) through the direct interaction of IND and QUE, which decreases QUE's rotational and translational freedom and consequently stabilizes the ternary HSA-IND-QUE complex.…”

“…Apart from the regular, competitive displacement interactions and non-interactions (e.g., warfarin-quercetin [29]), the obtained insight into the binding process suggests a third option for ligand-ligand interactions in a simultaneous binding to the same protein binding site, where one ligand increases the binding constant of the other ligand. At this moment, we are not aware of other studies that have reported similar results, which could have important consequences for the fate of xenobiotics inside the body.…”

“…An alternative way to measure the binding of QUE to HSA is based on the fact that, when it is unbound in solution, QUE fluorescence is negligible, but when it is bound to HSA, its fluorescence increases dramatically. In this way both the binding of QUE to HSA and its dissociation from HSA caused by displacement can be observed [7,28,29]. The structures of QUE and IND are shown in Figure 1.…”

“…For determination of the IND and QUE binding constants, Formulae 1-3 were used, as is explained in the Experimental section. Both IND and QUE bind in the vicinity of the Trp214 residue in the subdomain IIA [5,29], and their binding constants were determined to be (1.73 ± 0.64) × 10 5 and (1.44 ± 0.05) × 10 5 mol −1 dm 3 , respectively. To evaluate the risk of drug-drug interactions while binding to HSA, in vitro techniques have been used for a long time [22,30,31].…”

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin

“…Site II more actively binds indole and aromatic compounds, such as ibuprofen [ 36 ]. Warfarin and ibuprofen are routinely used to probe sites I and II, respectively [ 37 ]. As shown in Figure 7 and Table 6 , quenching of HSA fluorescence intensity by about 20% and a blue shift were also observed in all groups.…”