In vitro and in vivo study of phloretin-induced apoptosis in human liver cancer cells involving inhibition of type II glucose transporter

Authors

  • Chih-Hsiung Wu,

    1. Graduate Institute of Clinical Medicine, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan
    2. Department of Surgery, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan
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    • The first two authors contributed equally to this work.

  • Yuan-Soon Ho,

    1. Graduate Institute of Biomedical Technology, Taipei Medical University, Taipei, Taiwan
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    • The first two authors contributed equally to this work.

  • Chia-Yi Tsai,

    1. Division of Transfusion Medicine, Department of Pathology and Laboratory Medicine, Shin Kong Wu Ho-Su Memorial Hospital Taipei, Taiwan
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  • Ying-Jan Wang,

    1. Department of Environmental and Occupational Health, National Cheng Kung University Medical College, Tainan, Taiwan
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  • How Tseng,

    1. Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, Taiwan
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  • Po-Li Wei,

    1. Graduate Institute of Clinical Medicine, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan
    2. Department of Surgery, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan
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  • Chia-Hwa Lee,

    1. Graduate Institute of Biomedical Technology, Taipei Medical University, Taipei, Taiwan
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  • Ren-Shyan Liu,

    1. Department of Nuclear Medicine, Veterans General Hospital, Taipei, Taiwan
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  • Shyr-Yi Lin

    Corresponding author
    1. Department of Internal Medicine and Primary Care Medicine, School of Medicine, Taipei Medical University and Hospital, Taipei, Taiwan
    2. Cancer Research Center, Taipei Medical University Hospital, Taipei, Taiwan
    • Department of Internal Medicine, School of Medicine, Taipei Medical University Hospital, 252 Wu-Hsing Street, Taipei 110, Taiwan
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    • Fax: 886-2-27393422.


Abstract

Phloretin (Ph), a natural product found in apples and pears with glucose transporter (GLUT) inhibitory activity, exerts antitumor effects. However, little is known about its effects on human liver cancer. The purpose of this study is to test the cytotoxic effects of Ph on HepG2 cells and to identify the underlying molecular pathways. Human hepatocellular carcinoma specimens and HepG2 show a high level of GLUT2 transporter activity in the cell membrane. Real-time PCR and MTT assays demonstrate that Ph-induced cytotoxicity correlates with the expression of GLUT2. Flow cytometry and DNA fragmentation studies show that 200 μM Ph induces apoptosis in HepG2, which was reversed by glucose pretreatment. GLUT2 siRNA knockdown induced HepG2 apoptosis, which was not reversed by glucose. Western blot analysis demonstrates that both intrinsic and extrinsic apoptotic pathways in addition to Akt and Bcl-2 family signaling pathways are involved in Ph-induced cell death in HepG2 cells. Furthermore, using flow cytometry analysis, a mitochondrial membrane potential assay and Western blot analysis, we show that cytochalasin B, a glucose transport inhibitor, enhances the Ph-induced apoptotic effect on HepG2 cells, which was reversed by pretreatment with glucose. Furthermore, we found significant antitumor effects in vivo by administering Ph at 10 mg/kg intraperitoneally to severe combined immune deficiency mice carrying a HepG2 xenograft. A microPET study in the HepG2 tumor-bearing mice showed a 10-fold decrease in 18F-FDG uptake in Ph-treated tumors compared to controls. Taken together, these results suggest that Ph-induced apoptosis in HepG2 cells involves inhibition of GLUT2 glucose transport mechanisms. © 2008 Wiley-Liss, Inc.

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