Molecular basis of indomethacin-human serum albumin interaction

Studies on the strength and extent of binding of the non-steroidal anti-inf lammatory drug indomethacin to human serum albumin (HSA) have provided conf licting results. In the present work, the serum-binding of indomethacin was studied in 55 mM sodium phosphate buffer (pH 7.0) at 28 degrees C, by usin g a fluorescence quench titration technique. The interaction of indomethacin with human serum albumin has been studied a s a function of temperature, ionic strength and pH. The results suggest tha t electrostatic interaction plays a major role in the binding. The possible role of lysine residues in this interaction was studied by modifying expos ed and buried lysine residues of HSA with potassium cyanate and studying in domethacin binding with the modified HSA. The data suggest that the interac tion takes place via a salt bridge formation between the carboxylate group of indomethacin and a buried lysine residue of HSA. A technique involving fluorescence enhancement of bilirubin upon its intera ction with HSA was used to study its displacement by indomethacin. The disp lacement, although apparently competitive in nature, was not strong suggest ing that the primary sites of interaction of bilirubin and indomethacin are different.