A review of dietary polyphenol-plasma protein interactions: characterization, influence on the bioactivity, and structure-affinity relationship.

The interactions between polyphenols, especially flavonoids and plasma proteins, have attracted great interest among researchers. Few papers, however, have focused on the structure-affinity relationship of polyphenols on their affinities for plasma proteins. The aim of this review is to give an overview of the research reports on the characterization, influence on the bioactivity, and the structure-affinity relationship for studying the affinities between polyphenols and plasma proteins. The molecular properties that influence the affinities of polyphenols for plasma proteins are the following: 1) One or more hydroxyl groups in the B-ring (e.g., 3',4' dihydroxylated B ring catechol group) of flavonoids enhanced the binding affinities to proteins. However, the hydroxyl group in the C-ring will weaken the binding interaction. 2) The presence of an unsaturated 2,3-bond in conjugation with a 4-carbonyl group, characteristic of flavonols structure, has been associated with stronger binding affinity with plasma proteins; 3) The glycosylation of flavonoids decreases the affinities for plasma proteins by 1-3 orders of magnitude depending on the conjugation site and the class of sugar moiety; 4) The methylation of hydroxyl groups in flavonoids slightly enhanced the affinities for plasma proteins by 2-16 times; 5) The galloylated catechins have higher binding affinities for plasma proteins than do non-galloylated catechins and the pyrogallol-type catechins have higher affinities than do the catechol-type catechins. The affinity of the catechin with 2,3-trans structure was lower than those of the catechin with 2,3-cis structure; 6) The gallotannins with more gallol groups presented a much higher percentage of binding to plasma proteins. α-D-Gallotannin showed a greater affinity for plasma proteins than does the natural stereoisomer, β-D-gallotannin; 7) The binding degree of chlorogenic acid with only one caffeoyl group was lower than the binding degrees of caffeoyl quinic acids with more caffeoyl groups. The methylation of phenolic acid decreased the affinity for BSA.