Identification of two biologically crucial hydroxyl groups of (-)-epigallocatechin gallate in osteoclast culture
Identification of two biologically crucial hydroxyl groups of (-)-epigallocatechin gallate in osteoclast culture
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DOI：
10.1016/j.bcp.2006.09.002
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发表时间：
2007-01-01
影响因子：
5.8
通讯作者：
Wachi, Masaaki
中科院分区：
文献类型：
--
作者：
Nakagawa, Hiroshi;Hasumi, Keiji;Wachi, Masaaki
（-）-表没食子儿茶素没食子酸酯（EGCG）以依赖Fe2+-和h2o2的方式诱导破骨细胞死亡。在本研究中，我们使用四种EGCG类似物进一步探索EGCG的细胞毒性机制。在B环4′位（EGCG-4′-O-Me）或d环4′位（EGCG-4′-O-Me）甲基化的分子对破骨细胞的细胞毒性显著降低，这表明EGCG这两个位置的羟基对诱导破骨细胞死亡至关重要。EGCG-4′-O-Me还原Fe3+的活性最低。在质子化EGCG水平升高的条件下，EGCG的Fe3+还原活性增强，说明质子化状态参与了EGCG的Fe3+还原活性。量子化学计算表明，在egcg的所有羟基中，d环上4”位的羟基优先去质子化。除了EGCG-4'-O-Me外，其他egcg的最高已占据分子轨道（HOMO）都位于b环上。我们在这里报道了b环上的HOMO在EGCG的Fe3+还原活性和EGCG对破骨细胞的细胞毒性中起着至关重要的作用，而d环上4 ‘ ’位羟基的去质子化起着补充作用。(c) 2006爱思唯尔公司版权所有。
(-)-Epigallocatechin gallate (EGCG) induces cell death of osteoclasts in an Fe2+- and H2O2-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 Fe3+-reducing activity among five EGCGs. The Fe3+-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 Fe3+-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 Fe3+-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. (c) 2006 Elsevier Inc. All rights reserved.