19F NMR spectroscopic characterization of the interaction of niflumic acid with human serum albumin

摘要

The interaction of a non-steroidal anti-inflammatory drug, niflumic acid (NFA), with human serum albumin (HSA) has been investigated by 19F nuclear magnetic resonance (NMR) spectroscopy. A 19F NMR spectrum of NFA in a buffered (pH 7.4) solution of NaCl (0.1 mol L?1) contained a single sharp signal of its CF3 group 14.33 ppm from the internal reference 2,2,2-trifluoroethanol. Addition of 0.6 mmol L?1 HSA to the NFA buffer solution caused splitting of the CF3 signal into two broadened signals, shifted to the lower fields of 14.56 and 15.06 ppm, with an approximate intensity ratio of 1:3. Denaturation of HSA by addition of 3.0 mol L?1 guanidine hydrochloride (GU) restored a single sharp signal of CF3 at 14.38 ppm, indicating complete liberation of NFA from HSA as a result of its denaturation. These results suggest that the binding is reversible and occurs in at least two HSA regions. Competitive 19F NMR experiments using warfarin, dansyl-l-asparagine, and benzocaine (site I ligands), and l-tryptophan and ibuprofen (site II ligands) revealed that NFA binds to site I at two different regions, Ia and Ib, in the ratio 1:3. By use of 19F NMR with NFA as an 19F NMR probe the nonfluorinated site I-binding drugs sulfobromophthalein and iophenoxic acid were also found to bind sites Ia and Ib, respectively. These results illustrate the usefulness and convenience of 19F NMR for investigation of the HSA binding of both fluorinated and nonfluorinated drugs.