Relationship between the biological activities of methylated derivatives of (-)-epigallocatechin-3-O-gallate (EGCG) and their cell surface binding activities

It was previously reported that (-)-epigallocatechin-3-O-gallate (EGCG) suppresses the expression of the high-affinity IgE receptor FcεRI in human basophilic cells and that this suppressive effect is associated with EGCG binding to the cell surface. This study examined the effects of five methylated derivatives of EGCG, (-)-epigallocatechin-3-O-(3-O-methyl)gallate (EGCG 3″Me), (-)-epigallocatechin-3-O-(4-O-methyl)gallate (EGCG 4″Me), (-)-4′-O-methyl-epigallocatechin-3-O-gallate (EGCG 4′Me), (-)-epigallocatechin-3-O-(3,4-O-methyl)gallate (EGCG 3″4″diMe), and (-)-4′-O-methyl-epigallocatechin-3-O-(4-O-methyl)gallate (EGCG 4′4″diMe) on FcεRI expression and ERK1/2 phosphorylation, and each of their cell surface binding activities was measured. Of these five methylated derivatives, three that are methylated at the 3″- and/or 4″-position, EGCG 3″Me, EGCG 4″Me, and EGCG 3″4″diMe, suppressed FcεRI expression and ERK1/2 phosphorylation, although the suppressive effects were lower than that of EGCG. EGCG 4′Me and EGCG 4′4″diMe, both of which are methylated at the 4′-position, did not demonstrate a suppressive effect. Furthermore, it was found that EGCG 3″Me, EGCG 4″Me, EGCG 3″4″diMe, and EGCG 4′Me, which are methylated at the 3″-and/or 4″-positions or the 4′-position, could bind to the cell surface even though their binding activities were lower than that of EGCG. Only EGCG 4′4″diMe, which is methylated at both the 4′- and 4″-positions, could not bind. These results suggest that the trihydroxyl structure of the B ring is essential for EGCG to exert the suppressive effects and that the hydroxyl groups on both the 4′-position in the B ring and the 4″-position in the gallate are crucial for the cell surface binding activity of EGCG.