Evaluation of non-covalent interactions between serum albumin and green tea catechins by affinity capillary electrophoresis

The natural antioxidant-associated biological responses appear contradictory since biologically active
dosages registered in vitro experiments are considerably higher if compared to concentrations found in
vivo. The recent research indicates that natural antioxidants, including the major catechins of green tea
epicatechin (EC), epigallocatechin (EGC), epicatechingallate (ECG) and epigallocatechingallate (EGCG)
form non-covalent complexes with albumin, a crucial aspect that may modulate their plasma concentration,
tissue delivery and biological activity. Affinity capillary electrophoresis (ACE) was used to
characterize the binding of the four catechins to human serum albumin (HSA) and bovine serum albumin
(BSA) at near-physiological conditions: 10 mmol/L phosphate buffer, HEPES 50 mmol/L (pH 7.5), temperature
37 ◦C. The studied flavonoids displayed affinities toward the albumin with binding constants
in the range 103−105 M−1, with a greater affinity of catechins toward HSA than BSA (between 3 and 3.5
fold higher). We also confirmed that catechins having a galloyl moiety (ECG and EGCG) have a higher
binding affinity toward albumin than the catechins lacking the galloyl moiety (EC and EGC), and that for
both albumins the order of affinity is EC < EGC < ECG < EGCG. We believe that our work can provide useful
information for better understanding the intercurrent relationships between cathechins bioavailability
and their elicited biological effects.