Inhibition of proliferation and induction of apoptosis by gamma-tocotrienol in human colon carcinoma HT-29 cells.
OBJECTIVE
gamma-Tocotrienol is a major component of the tocotrienol-rich fraction of palm oil, but there is limited evidence that it has antitumor activity. In particular, the effects of gamma-tocotrienol on human colon carcinoma cells have not been reported. To investigate the chemopreventive effects of gamma-tocotrienol on colon cancer, we examined its capacity to inhibit proliferation and induce apoptosis in HT-29 cells and explored the mechanism underlying these effects.


METHODS
We cultured HT-29 cells in the presence of gamma-tocotrienol. The effect of gamma-tocotrienol on cell proliferation was investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, mitotic index, and colony formation. The cell-cycle distribution was investigated by flow cytometry. We measured apoptosis by nuclear staining, transmission electron microscopy, and DNA fragmentation. Apoptosis-related proteins and the nuclear factor-kappaB p65 protein were determined by western blotting and immunofluorescence.


RESULTS
gamma-Tocotrienol inhibited cell growth and arrested HT-29 cells in G(0)/G(1) phase. The 50% inhibitory concentration was 31.7 micromol/L (48 h). gamma-Tocotrienol-induced apoptosis in HT-29 cells was accompanied by downregulation of Bcl-2, upregulation of Bax, and activation of caspase-3. Furthermore, we found that gamma-tocotrienol reduced the expression level of total nuclear factor-kappaB p65 protein and inhibited its nuclear translocation.


CONCLUSIONS
The results indicated that gamma-tocotrienol inhibits cell proliferation and induces apoptosis in HT-29 cells in a time- and dose-dependent manner, and that this process is accompanied by cell-cycle arrest at G(0)/G(1), an increased Bax/Bcl-2 ratio, and activation of caspase-3. Our data also indicated that nuclear factor-kappaB p65 protein may be involved in these effects.
Xu
Wei-Li
WL
Department of Nutrition and Food Hygiene, Public Health School, Harbin Medical University, Harbin, People's Republic of China.
Liu
Jia-Ren
JR
Liu
Hui-Kun
HK
Qi
Gui-Yun
GY
Sun
Xiang-Rong
XR
Sun
Wen-Guang
WG
Chen
Bing-Qing
BQ
D016588:Anticarcinogenic Agents / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects*; D002839:Chromans / Q000494:pharmacology / Q000627:therapeutic use*; D003110:Colonic Neoplasms / Q000517:prevention & control; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D016193:G1 Phase / Q000187:drug effects; D019073:HT29 Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D008940:Mitotic Index; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D051996:Transcription Factor RelA / Q000187:drug effects / Q000378:metabolism*; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D016588:Anticarcinogenic Agents; C494826:BAX protein, human; D002839:Chromans; D019253:Proto-Oncogene Proteins c-bcl-2; D051996:Transcription Factor RelA; D051028:bcl-2-Associated X Protein; D014810:Vitamin E; C013649:plastochromanol 8; D053148:Caspase 3