Angiotensin I Converting Enzyme Inhibiting Activity of Tea Components

Abstract

The inhibition of angiotensin I converting enzyme (ACE) by polyphenolic components of tea and its specificity was investigated in vitro. Six kinds of green tea catechins and four kinds of their dimeric compounds (theaflavins) produced oxidatively during black tea production were isolated. They were (+)-catechin (C), (-)-epicatechin (EC), (+)-gallocatechin (GC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), (-)-epigallocatechin gallate (EGCg), free theaflavin (TF 1), theaflavin monogallates (TF 2 A, TF 2 B), and theaflavin digallate (TF 3). ACE inhibition activity of each was tested. ECg, EGCg and all theaflavins had a notable inhibitory effect, whereas the inhibitory activity (IC₅₀) of these against carboxypeptidase A (CPA) was weaker than against ACE. The effect was scarcely interfered by the addition of zinc chloride.
These results suggest that the ACE inhibiting ability of gallate catechins and theaflavins is specific and attributable to their molecular structure rather than to their chelating activity. The binding mode of these polyphenols to ACE may be similar to that of captopril, an artificially designed ACE inhibitor. They are likely to bind to zinc ion, hydrogen-bonding site and positively charged site of ACE.