Inhibitory effect of green tea extract and (−)-epigallocatechin-3-gallate on mammalian thioredoxin reductase and HeLa cell viability

  • Authors:
    • Yan Wang
    • Huihui Zhang
    • Arne Holmgren
    • Weixi Tian
    • Liangwei Zhong
  • View Affiliations

  • Published online on: December 1, 2008     https://doi.org/10.3892/or_00000169
  • Pages: 1479-1487
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Abstract

Mammalian cytosolic thioredoxin reductase (TrxR1) is an attractive target for developing cancer chemopreventive agents since its inhibition is associated with a reduced growth of cancer cells. However, the known inhibitors of this enzyme mostly have a toxic effect on human health. We report on a non-toxic inhibitor, green tea. TrxR1 was found to be inhibited by green tea extracts (Gte) with an IC50 value of 256 µg/ml. Catechins, the major components of Gte, showed various inhibitory effects, in which (−)-epigallocatechin-3-gallate (EGCG) exhibited a stronger inhibition than any other catechins tested. The inhibition of TrxR1 by EGCG was close to competitive (Ki = 64 µM) with substrate DTNB and was non-competitive (Ki = 92 µM) with co-enzyme NADPH. The preincubation of TrxR1 with EGCG led to irreversible enzyme inactivation in a time-dependent manner, which was highly effective in the presence of NADPH. The inactivation included an equilibrium step used to form a reversible TrxR1-EGCG complex (EI) (dissociation constant Ki* = 43 µM), and an isomerization step used to form an irreversible complex (E*I) (rate constant k3 = 4.8x10−3 s−1). We have identified thiol/selenol groups in the active site as reactive sites that mediated TrxR1 inhibition by EGCG. When cultured HeLa cells were treated with Gte or EGCG for 22-24 h, TrxR1 activity in cell extracts was significantly inhibited, accompanied by a reduction of cell viability in a concentration-dependent manner (IC50 = 40 µg/ml for Gte and 107 µM for EGCG). The inactivation of TrxR1 by Gte/EGCG is most likely linked to a reduction of HeLa cell viability.

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December 2008
Volume 20 Issue 6

Print ISSN: 1021-335X
Online ISSN:1791-2431

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Spandidos Publications style
Wang Y, Zhang H, Holmgren A, Tian W and Zhong L: Inhibitory effect of green tea extract and (−)-epigallocatechin-3-gallate on mammalian thioredoxin reductase and HeLa cell viability. Oncol Rep 20: 1479-1487, 2008.
APA
Wang, Y., Zhang, H., Holmgren, A., Tian, W., & Zhong, L. (2008). Inhibitory effect of green tea extract and (−)-epigallocatechin-3-gallate on mammalian thioredoxin reductase and HeLa cell viability. Oncology Reports, 20, 1479-1487. https://doi.org/10.3892/or_00000169
MLA
Wang, Y., Zhang, H., Holmgren, A., Tian, W., Zhong, L."Inhibitory effect of green tea extract and (−)-epigallocatechin-3-gallate on mammalian thioredoxin reductase and HeLa cell viability". Oncology Reports 20.6 (2008): 1479-1487.
Chicago
Wang, Y., Zhang, H., Holmgren, A., Tian, W., Zhong, L."Inhibitory effect of green tea extract and (−)-epigallocatechin-3-gallate on mammalian thioredoxin reductase and HeLa cell viability". Oncology Reports 20, no. 6 (2008): 1479-1487. https://doi.org/10.3892/or_00000169