Investigations of the cytotoxicity of epigallocatechin-3-gallate against PC-3 cells in the presence of Cd2+ in vitro

Epigallocatechin gallate and mitochondria-A story of life and death

Epigallocatechin gallate (EGCG) is a flavonoid belonging to the chemical class of falvan-3-ols (catechins) esterified with gallic acid. It is the main catechin found in green tea (Camellia sinensis L.) accounting for about 50% of its total polyphenols. Extensive research performed in recent years has revealed that green tea demonstrates a wide range of positive biological activities against serious chronic diseases such as cardiovascular and neurodegenerative pathologies, cancer, metabolic syndrome and type 2 diabetes. These protective properties can be traced back to the potent antioxidant and anti-inflammatory activities of EGCG. Recent studies have suggested that it may exert its beneficial effects by modulating mitochondrial functions impacting mitochondrial biogenesis, bioenergetic control (ATP production and anabolism), alteration of the cell cycle, and mitochondria-related apoptosis. This review evaluates recent evidence on the ability of EGCG to exert critical influence on the above mentioned pathways.

Active extracts of black tea (Camellia Sinensis) induce apoptosis of PC-3 prostate cancer cells via mitochondrial dysfunction

Cancer of the prostate gland is the most common invasive malignancy and the second leading cause of cancer-related death in human males. Many studies have shown that black tea reduces the risk of several types of cancer. We studied the effects of active extracts of black tea and the black tea polyphenols theaflavins (TFs), on the cellular proliferation and mitochondria of the human prostate cancer cell line PC-3. Our studies revealed that Yinghong black tea extracts (YBT), Assam black tea extracts (ABT) and TFs inhibited cell proliferation in a dose-dependent manner. We also showed that TFs, YBT and ABT affected the morphology of PC-3 cells and induced apoptosis or even necrosis in PC-3 cells. In addition, it was observed that the samples significantly caused loss of the mitochondrial membrane potential, release of cytochrome c from the intermembrane space into the cytosol, decrease of the ATP content and activation of caspase-3 compared with the control. Taken together, these findings suggest that black tea could act as an effective anti-proliferative agent in PC-3 cells, and TFs, YBT and ABT induced apoptosis of PC-3 cells through mitochondrial dysfunction.

(-)-Epigallocatechin-3-gallate, a green tea-derived catechin, synergizes with celecoxib to inhibit IL-1-induced tumorigenic mediators by human pancreatic adenocarcinoma cells Colo357

Despite their toxic side effects prostaglandin H(2) synthase-2 (PGHS-2) inhibitors hold promise for cancer chemoprevention. In order to overcome adverse effects lower doses of PGHS-2 inhibitors could be applied in combination with other agents exhibiting complementary effects. Herein, the effects of the PGHS-2-specific inhibitor celecoxib either alone or in combination with the green tea-derived catechin (-)-epigallocatechin-3-gallate (EGCG) were studied on the expression of interleukin (IL)-1-induced tumorigenic factors in Colo357 human pancreatic adenocarcinoma cells. This approach mimics tumor-associated pancreatic inflammation which is considered as a key player in pancreatic malignancy. We found that co-incubation of Colo357 with celecoxib and EGCG synergistically diminished metabolic activity via apoptosis induction and down-regulated release of pro-angiogenic vascular endothelial growth factor (VEGF) and invasiveness-promoting matrix metalloproteinase (MMP)-2 to a maximum of 30%. Celecoxib and EGCG synergistically reduced IL-1-induced production of pro-inflammatory IL-6 and pro-angiogenic IL-8 to 23-50%. Celecoxib dose-dependently increased PGHS-2 levels. Whereas EGCG was able to compensate for celecoxib-mediated increase of PGHS-2, it failed to potentiate celecoxib-mediated suppression of prostaglandin E(2) (PGE(2)) release. Thus, in Colo357, EGCG synergistically boosts celecoxib-mediated effects and reduces the levels of celecoxib required to elicit beneficial effects on tumorigenic mediators by a factor of ten.

Mechanism of free Zn(2+) enhancing inhibitory effects of EGCG on the growth of PC-3 cells: interactions with mitochondria

Green tea and its major constituent epigallocatechin gallate (EGCG) are known for their chemopreventive effects including those against prostate cancer, which could be mediated by metal ions. Zn(2+) is an essential trace element that is required for human health and plays an important role in the normal function of the prostate gland. In the present study, the effect of EGCG on cell membrane and mitochondria of PC-3 (prostate carcinoma) cells in the presence and absence of Zn(2+) was studied. These studies revealed that EGCG, Zn(2+), or EGCG + Zn(2+) affected the morphology of PC-3 cells and induced apoptosis in PC-3 cells. It was observed that effects of treatment with EGCG, Zn(2+), or EGCG + Zn(2+)on mitochondria showed EGCG + Zn(2+) > Zn(2+) > EGCG, including cytochrome C release from the intermembrane space into the cytosol, inhibited the synthesis of ATP, loss of mitochondrial membrane potential, and activation of caspase-9. However, the order of effect on depressing membrane fluidity of PC-3 cells was EGCG > EGCG + Zn(2+) > Zn(2+). In summary, these findings suggest that EGCG, Zn(2+), and EGCG + Zn(2+) induce necrosis or apoptosis of PC-3 cells through mitochondria-mediated apoptotic pathway and free Zn(2+)-enhanced effects of EGCG on PC-3 cells due to its interactions with mitochondria.

Effect of laminin tyrosine-isoleucine-glycine-serine-arginine peptide on the growth of human prostate cancer (PC-3) cells in vitro

The laminin tyrosine-isoleucine-glycine-serine-arginine (YIGSR) peptide, corresponding to the 929-933 sequence of beta1 chain, is known to inhibit tumor growth and metastasis. In the present study, we observed that YIGSR not only inhibited the growth and migration of prostate cancer cells in a dose-dependent manner but also decreased mitochondrial membrane potential, inhibited ATP synthesis and increased caspase-9 activity. Investigation into the interaction of YIGSR with 67LR, the receptor for laminin and polyphenol (-) epigallocatechin-3-gallate (EGCG) employing MVD (Molegro Virtual Docker, an integrated platform for predicting protein ligand interactions), revealed that the binding site of YIGSR was the same as that of EGCG that explains as to why YIGSR is able to inhibit the cytotoxicity of EGCG against PC-3 cells.

Stress-induced down-regulation of tumor-associated NADH oxidase during apoptosis in transformed cells

Tumor-associated NADH oxidase (tNOX) is a growth-related protein expressed in transformed cells. tNOX knockdown using RNA interference leads to a significant reduction in HeLa cell proliferation and migration, indicating an important role for tNOX in growth regulation and the cancer phenotype. Here, we show that tNOX is down-regulated during apoptosis in HCT116 cells. Treatment with diverse stresses induced a dose- and time-dependent decrease in tNOX expression that was concurrent with apoptosis. Moreover, shRNA-mediated tNOX knockdown rendered cells susceptible to apoptosis, whereas re-expression of tNOX partially recovered cell proliferation. Our results indicate that tNOX is suppressed during apoptosis and demonstrate that tNOX down-regulation sensitizes cells to stress-induced growth reduction, suggesting that tNOX is required for transformed cell growth.