Use of 1-anilino-8-naphthalene sulfonate as a fluorescent probe in the investigation of drug interactions with human alpha-1-acid glycoprotein and serum albumin

We report a rapid method for the characterization of the human serum albumin (HSA) and alpha-1-acid glycoprotein (AAG) interactions with drugs. The binding of 1-anilino-8-naphthalene sulfonate (ANS) to AAG and HSA was measured by fluorescence spectroscopy. Fluorescence data indicated that ANS was bound tightly to at least one site on AAG, with an affinity constant of 1.35 x 10(6) M-1. The fluorescence of an ANS:AAG complex was quenched by the binding of various drugs. Fluorescence quenching of the HSA:ANS complex showed a single site with an affinity constant of 0.72 x 10(6) M-1. The interaction of AAG and HSA with ANS or other drugs was also studied by comparative equilibrium dialysis. 14C]Pipequaline was used as an AAG and HSA site marker. 14C]Pipequaline seems to share sites I (azapropazone) and II (diazepam and ibuprofen) of HSA. However, high concentrations of warfarin were unable to displace 14C]pipequaline. On the other hand, it was shown that palmitic acid decreased, whereas bilirubin increased the pipequaline binding.