Epigallocatechin gallate (EGCG), the major flavonoid in green tea, is consumed via tea products and dietary supplements, and has been tested in clinical trials. However, EGCG can cause hepatotoxicity in humans and animals by unknown mechanisms. Here EGCG effects on rat liver mitochondria were examined. EGCG showed negligible effects on oxidative phosphorylation at 7.5-100μM in normal mitochondria. However, respiratory chain complexes (RCCs) were profoundly inhibited by EGCG in mitochondria undergoing Ca(2+) overload-induced mitochondrial permeability transition (MPT). As RCCs are located in mitochondrial inner membranes (IM) and matrix, it was reasoned that EGCG could not readily pass through IM to affect RCCs in normal mitochondria but may do so when IM integrity is compromised. This speculation was substantiated in three ways. (1) Purified EGCG-bound proteins were barely detectable in normal mitochondria and contained no RCCs as determined by Western blotting, but swelling mitochondria contained about 1.5-fold more EGCG-bound proteins which included four RCC subunits together with cyclophilin D that locates in mitochondrial matrix. (2) Swelling mitochondria consumed more EGCG than normal ones. (3) The MPT blocker cyclosporine A diminished the above-mentioned difference. Among four subunits of RCC II, only SDHA and SDHB which locate in mitochondrial matrix, but not SDHC or SDHD which insert into the IM, were found to be EGCG targets. Interestingly, EGCG promoted Ca(2+) overload-induced MPT only when moderate MPT already commenced. This study identified hepatic RCCs as targets for EGCG in swelling but not normal mitochondria, suggesting EGCG may trigger hepatotoxicity by worsening pre-existing mitochondria abnormalities.
Keywords: ATP; CsA; DS; EGCG; Epigallocatechin gallate; FDA; GTE; Green tea; HPLC; IC(50); IM; Liver; MGST1; MPT; MT-CO1; Mitochondria; NADH dehydrogenase [ubiquinone] iron-sulfur protein 3; NADH dehydrogenase [ubiquinone] iron-sulfur protein 8; NDUFS3; NDUFS8; RCCs; Rat; Respiratory chain complexes; SDHA; SDHB; SDHC; SDHD; U.S. Food and Drug Administration; UQCRC1; UQCRC2; adenosine triphosphate; cyclosporine A; dietary supplements; epigallocatechin gallate; green tea extract; half maximal inhibitory concentration; high-performance liquid chromatography; inner membranes; microsomal glutathione S-transferase 1; mitochondrial permeability transition; mitochondrially encoded cytochrome c oxidase I; respiratory chain complexes; succinate dehydrogenase complex, subunit A; succinate dehydrogenase complex, subunit B; succinate dehydrogenase complex, subunit C; succinate dehydrogenase complex, subunit D; ubiquinol-cytochrome c reductase core protein I; ubiquinol-cytochrome c reductase core protein II.
Published by Elsevier Inc.