title: Identification of two biologically crucial hydroxyl groups of (-)-epigallocatechin gallate in osteoclast culture.
abstract: (-)-Epigallocatechin gallate (EGCG) induces cell death of osteoclasts in an Fe(2+)- and H(2)O(2)-dependent manner. In the present study, we further explore the cytotoxic mechanism of EGCG using four EGCG analogues. Molecules methylated at position 4' in the B ring (EGCG-4'-O-Me) or at position 4'' in the D-ring (EGCG-4''-O-Me) showed markedly decreased cytotoxicity to osteoclasts, indicating that hydroxyl groups at these two positions of EGCG are crucial for inducing cell death of osteoclasts. EGCG-4'-O-Me also showed the lowest Fe(3+)-reducing activity among five EGCGs. The Fe(3+)-reducing activity of EGCG was enhanced under conditions whereby protonated EGCG levels were increased, indicating that the protonated status of EGCG was involved in the Fe(3+)-reducing activity. The hydroxyl group at position 4'' in the D-ring was shown by quantum chemical calculation to be preferentially deprotonated among all of the hydroxyl groups in EGCGs. It was also shown that the highest occupied molecular orbital (HOMO) was localized to the B-ring of EGCGs, except for EGCG-4'-O-Me. We report here that the HOMO on the B-ring plays crucial roles in both the Fe(3+)-reducing activity of EGCG and the cytotoxicity of EGCG to osteoclasts, while deprotonation of the hydroxyl group at position 4'' in the D-ring plays a supplementary role.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Hasumi
authors.forename: Masamichi
authors.initials: M
authors.lastname: Takami
authors.forename: Sachiko
authors.initials: S
authors.lastname: Aida-Hyugaji
authors.forename: Je-Tae
authors.initials: JT
authors.lastname: Woo
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nagai
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Masaaki
authors.initials: M
authors.lastname: Wachi
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002392:Catechin / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008297:Male; D051379:Mice; D010006:Osteoblasts / Q000737:chemistry* / Q000187:drug effects; D010084:Oxidation-Reduction
chemical_list: D002392:Catechin; D006861:Hydrogen Peroxide; C045651:epigallocatechin gallate; D007501:Iron