Study of interaction between drug enantiomers and serum albumin by capillary electrophoresis

Abstract

The interaction between drugs and human serum albumin (HSA) was investigated by capillary electrophoresis (CE). It involves stereoselectivity, drug displacement and synergism effects. Under protein‐drug binding equilibrium, the unbound concentrations of drug enantiomers were measured by frontal analysis (FA). The stereoselectivity of verapamil (VER) binding to HSA was proved by the different free fractions of two enantiomers. In physiological pH (7.4, ionic strength 0.17 phosphate buffer) when 300 μM (±) VER were equilibrated with 500 μM HSA, the concentration of unbound S‐VER was about 1.7 times its antipode. The binding constants of two enantiomers, KR‐VER and KS‐VER, were 2670 and 850 M—1, respectively. However, no obvious stereoselective binding of propranolol (PRO) to HSA was observed. Trimethyl‐β‐cyclodextrin (45 mM) was used as a chiral selector in pH 2.5 phosphate buffer. Several drug systems were studied by the method. When ibuprofen (IBU) was added into VER‐HSA solution. R‐VER was partially displaced while S‐VER was not displaced at all. A binding synergism effect between bupivacaine (BUP) and verapamil was observed and further study suggested that verapamil and bupivacaine occupy different binding site of HSA (site II and site III, respectively).

Capillary electrophoresis frontal analysis: Principles and applications for the study of drug‐plasma protein binding

“…Salicylic acid was added to the samples to displace bilirubin from HSA, thus, overcoming the sensitivity problems. The versatility of CE-FA for probing of binding sites on HSA by displacement studies has also been demonstrated elsewhere [34,74].…”

“…The utility and validity of binding studies performed with CE-FA have been demonstrated in several studies using HSA and various cationic ligands such as propranolol and verapamil [36,42,[71][72][73][74]. CE-FA is ideally suited for the measurement of these interactions because the electrophoretic mobilities of the cationic ligands and HSA (negatively charged at physiological pH) are very different; moreover, the interactions between HSA and cationic drugs in general are relatively weak [65,66].…”

“…Verapamil binding to HSA was found to be enantioselective, the (R)-isomer possessing the highest affinity for HSA [42]. The chiral CE-FA setup has been found applicable to other drugs and proteins as well [74,78]. See [79] for a more detailed review.…”

“…Adsorption to the capillary may be a problem especially for proteins. Different types of coated capillaries have been applied in drug-plasma protein binding studies performed [36,43,48,73,74,78]. It is not possible to obtain uniform thermostating conditions across the length of a capillary [89], therefore lack of precise temperature control in CE-FA and other CE methods may be a drawback compared to conventional methods [34].…”

Recent advances in the study of biomolecular interactions by capillary electrophoresis

“…Not only the chiral recognition of drug enantiomers by HSA but also the competitive binding of drug enantiomers to HSA can be studied. When ibuprofen was added to a verapamil-HSA sample, R-verapamil was partially displaced but S-verapamil not at all [99]. FA was applied to investigate the role of glycan structures in the enantioselective binding of basic drugs to a-acid glycoprotein (a-AGP).…”