Differential modulation in binding of ketoprofen to bovine serum albumin in the presence and absence of surfactants: spectroscopic and calorimetric insights.

Surfactants have long been implicated in the unique static and dynamic effect on the structure and function of serum albumins. However, there is very little information on the mode of interactions of drugs to serum albumins in presence of surfactants. The importance of such studies lay in the fact that apart from binding to serum albumins, surfactants are known to radically influence the solvents' micro environment and protein structure. Thus, we have studied the binding of the racemic form of ketoprofen with bovine serum albumin at pH 7.4 in the presence and absence of hexadecyl trimethyl ammonium bromide, sodium dodecyl sulfate, Triton X-100, and NaCl. The structural studies of ketoprofen with bovine serum albumin as investigated by circular dichroism spectroscopy revealed a significant stabilization of bovine serum albumin. However, the combined presence of the surfactants, NaCl and ketoprofen, demonstrated an extremely erratic behavior in terms of stabilization. Further the values of Stern-Volmer and dynamic quenching constant suggested the binding site of ketoprofen to be scattered in the region of domain I B and II A, close to Trp 134. The results of differential scanning calorimetry revealed that the binding of ketoprofen to bovine serum albumin leads to its temperature-dependent separation into two units. The binding parameters of bovine serum albumin obtained from isothermal titration calorimetry in the combined presence of ketoprofen and surfactants/NaCl correlate well with the differential scanning calorimetry studies further confirming the localization of ketoprofen in domain I B and II A. In the combined presence of surfactants, NaCl and ketoprofen, the binding of ketoprofen to bovine serum albumin exhibited altered binding parameters far different from the binding of ketoprofen alone. Overall, the experimental findings strongly indicated positive as well as negative modulation in the binding of ketoprofen to bovine serum albumin in the presence of ligands.