Binding of (+)- and (-)-isomers and racemate of etomoxir to human serum albumin and effect of stearic acid and stanozolol

Electrospray ionization mass spectrometry as a tool for determination of drug binding sites to human serum albumin by noncovalent interaction

Most proteins in blood plasma bind ligands. Human serum albumin (HSA) is the main transport protein with a very high capacity for binding of endogenous and exogenous compounds in plasma. Many pharmacokinetic properties of a drug depend on the level of binding to plasma proteins. This work reports studies of noncovalent interactions by means of nanoelectrospray ionization mass spectrometry (nanoESI-MS) for determination of the specific binding of selected drug candidates to HSA. Warfarin, iopanoic acid and digitoxin were chosen as site-specific probes that bind to the main sites of HSA. Two drug candidates and two known binders to HSA were analyzed using a competitive approach. The drugs were incubated with the target protein followed by addition of site-specific probes, one at a time. The drug candidates showed predominant affinity to site I (warfarin site). Naproxen and glyburide showed affinity to both sites I and II. The advantages of nanoESI-MS for these studies are the sensitivity, the absence of labeled molecules and the short method development time.

Human serum albumin binding of novel antiretroviral nucleoside derivatives of AZT

The binding of novel nucleoside derivatives (2-7) to the Human Serum Albumin (HSA) was studied using zidovudine (AZT), as standard compound. The applicability of two different techniques to separate unbound drug from drug-protein complex was analyzed: the gel filtration and ultrafiltration methods. Ultrafiltration was found to be an adequate procedure for the separation of unbounded drug from the drug-protein complex. Incubation temperature ranging from 0 to 37 degrees C did not modify considerably the bound fractions. The same effects were observed as HSA concentration was modified. Binding assays of studied compounds to purified 1% (w/v) HSA at 0 degrees C, indicate that bound fraction of 2-7 ranges from 13 to 47%, exhibiting a higher affinity to HSA than AZT (12%), which would introduce some interesting improvements in their pharmacokinetic properties. In addition, by means of displacement studies using HSA site specific drugs such as diazepam and salicylate, it was determined that AZT binds to site I of the HSA molecule, by a mainly entropy driven process (DeltaS = 10.834 cal/mol degrees K), being these observations extensive to 2-7. Some structural basis to explain enhanced affinity of these novel derivatives was also established.

Study of the binding of antibiotics to human serum albumin by charge-transfer chromatography

The interaction of 13 antibiotics with human serum albumin was studied by charge-transfer reversed-phase thin-layer chromatography in neutral, acidic, basic and ionic environments (NaCl and MgCl2) and the relative strength of interaction was calculated. The pH and the presence of mono- and divalent cations markedly influenced the strength of interaction. The capacity of antibiotics to interact with HSA also considerably depended on their chemical structure.