Interaction of chlorogenic acids and quinides from coffee with human serum albumin

Chlorogenic acids and their derivatives are abundant in coffee and their composition changes between coffee species. Human serum albumin (HSA) interacts with this family of compounds with high affinity. We have studied by fluorescence spectroscopy the specific binding of HSA with eight compounds that belong to the coffee polyphenols family, four acids (caffeic acid, ferulic acid, 5-O-caffeoyl quinic acid, and 3,4-dimethoxycinnamic acid) and four lactones (3,4-O-dicaffeoyl-1,5-c-quinide, 3-O-[3,4- (dimethoxy)cinnamoyl]-1,5-c-quinide, 3,4-O-bis[3,4-(dimethoxy)cinnamoyl]-1,5-c-quinide, and 1,3, 4-O-tris[3,4-(dimethoxy)cinnamoyl]-1,5-c-quinide), finding dissociation constants of the albumin–chlorogenic acids and albumin–quinides complexes in the micromolar range, between 2 and 30 lM. Such values are comparable with those of the most powerful binders of albumin, and more favourable than the values obtained for the majority of drugs. Interestingly in the case of 3,4-O-dicaffeoyl-1,5-c-quinide, we have observed the entrance of two ligand molecules in the same binding site, leading up to a first dissociation constant even in the hundred nanomolar range, which is to our knowledge the highest affinity ever observed for HSA and its ligands. The displacement of warfarin, a reference drug binding to HSA, by the quinide has also been demonstrated.