Reversible binding of celecoxib and valdecoxib with human serum albumin using fluorescence spectroscopic technique

Mechanism of interaction of non-steroidal anti-inflammatory drugs, celecoxib and valdecoxib with human serum albumin has been studied using fluorescence spectroscopic technique. There was only one high affinity site on serum albumin for both the drugs with association constants of the order of 104 in the case of celecoxib and 105 in the case of valdecoxib. Thermodynamic parameters for the binding indicated that hydrogen bonding interactions are predominantly involved in the binding of these drugs to human serum albumin. Binding studies in the presence of hydrophobic probe, 1-anilinonaphthalene-8-sulfonate (ANS) suggested that the mode of interaction of drugs and ANS with HSA is different and hydrophobic interactions are not primarily involved in the binding. Studies carried out in the presence of site-specific probe showed that drugs are bound at site II and phenolic oxygen of 411Tyr is involved in binding. Stern-Volmer analysis of the quenching data indicated that predominantly static quenching mechanism is operative and the tryptophan residues of albumin are fully accessible to celecoxib and only partially accessible to valdecoxib. The presence of salt caused a decrease in the association constant and significant increase in the concentration of free drug.