Disruption of mitochondria during tocotrienol-induced apoptosis in MDA-MB-231 human breast cancer cells

Abstract

Tocotrienols, which are Vitamin E isoforms, are known to inhibit the growth of human breast cancer cells due partly to apoptosis. However, the characterization of tocotrienol-induced apoptosis is incomplete, particularly what happens during the initiation phase that precedes execution of the cells. The objective of this study was to clarify the apoptotic effects of tocotrienols, with especial emphasis in determining if the mitochondria-mediated death pathway is activated when human breast cancer cells are incubated with a specific tocotrienol isomer. During incubation with gamma-tocotrienol, MDA-MB-231 human breast cancer cells showed membrane blebbing, and apoptotic bodies were present. Upon 4',6-diamidino-2-phenylindole staining of the cells, chromatin condensation and fragmentation were observed. Additionally, the annexin V-binding assay detected the translocation of membrane phospholipid during earlier analysis of the cells. Taken together, these results further establish that gamma-tocotrienol can induce apoptosis in human breast cancer cells. To help elucidate how gamma-tocotrienol induced the apoptosis, some important parameters related to the mitochondria-mediated death pathway were examined next. In gamma-tocotrienol-treated cells, the mitochondria were disrupted. Collapse of the mitochondrial membrane potential was detected, and cytochrome c was released later from mitochondria. However, expression of Bax and Bcl-2 (mRNA and protein) did not change. Furthermore, poly-(ADP-ribose)-polymerase cleavage was not detected, suggesting that caspases were not involved in the gamma-tocotrienol-induced apoptosis. These results imply that cytochrome c is not the critical protein released from mitochondria that triggers gamma-tocotrienol-induced apoptosis in MDA-MB-231 cells.

γ-Tocotrienol Promotes TRAIL-Induced Apoptosis through Reactive Oxygen Species/Extracellular Signal-Regulated Kinase/p53–Mediated Upregulation of Death Receptors

“…T3 has been shown to mediate its activity against a variety of chronic diseases, including cardiovascular diseases, neurologic diseases, diabetes, and cancer (9)(10)(11)(12)(13)(14). T3s have shown anticancer activity against cancers such as colon, breast, liver, lung, kidney, prostate, skin, and other cancers both in vitro (15)(16)(17)(18)(19)(20) and in vivo (21)(22)(23)(24)(25). T3 has the potency to induce apoptosis in a variety of cancer cell types (types 1-5).…”

Why tocotrienols work better: insights into the in vitro anti-cancer mechanism of vitamin E

“…More recent work has demonstrated that cell cycle inhibition by T3 occurs through the control of the Rb/cdk4/ cyclin D pathway (Elangovan et al 2008) that is also affected by the HM forms of tocopherols, and particularly by c-TOH (Betti et al 2006). In the same cell models, T3 were demonstrated to induce apoptosis with d-T3 as the most potent form (Yu et al 1999) and with a mechanism that involves mitochondrial disruption and cyt c release (Takahashi and Loo 2004). As introduced above, recent studies by our group confirmed that d-T3 is the most potent T3 form with pro-apoptotic activity higher than a-TOS in breast cancer cells (Table 1) .…”

Gamma‐tocotrienol as an effective agent in targeting prostate cancer stem cell‐like population

“…35 The anticancer effect of T3 was found to be mediated through antiproliferation, 16,36,37 induction of apoptosis, 38,39 cell cycle arrest, 13,40 antiangiogenesis 41 and antiinvasion. 18 More recently, c-T3, one of the four isoforms of T3, was reported to possess chemosensitizing effects, 17,18 which led us to speculate that c-T3 may be able to target the chemoresistant cancer stem-like cells.…”