Suppression of free fatty acid-induced insulin resistance by phytopolyphenols in C2C12 mouse skeletal muscle cells.

It was reported that increased plasma levels of free fatty acids (FFAs) are associated with profound insulin resistance in skeletal muscle and may also play a critical role in the insulin resistance of obesity and type 2 diabetes mellitus. Skeletal muscle is the major site for insulin-stimulated glucose uptake and is involved in energy regulation and homeostasis. In this study, we used 12-O-tetradecanoylphorbol 13-acetate (TPA), a protein kinase C (PKC) activator, and palmitate to induce insulin resistance in C2C12 mouse skeletal muscle cells. Our data show that epigallocatechin gallate (EGCG) and curcumin treatment reduce insulin receptor substrate-1 (IRS-1) Ser307 phosphorylation, and curcumin is more potent to increase Akt phosphorylation in TPA induction. Moreover, we found that after 5 h of palmitate incubation, epicatechin gallate (ECG) can suppress IRS-1 Ser307 phosphorylation and significantly promote Akt, ERK1/2, p38 MAPK, and AMP-activated protein kinase activation. With a longer incubation with palmitate, IRS-1 exhibited a dramatic depletion, and treatment with EGCG, ECG, and curcumin could reverse IRS-1 expression, Akt phosphorylation, and MAPK signaling cascade activation and improve glucose uptake in C2C12 skeletal muscle cells, especially ECG and curcumin. In addition, treatment with these polyphenols can suppress acetyl-CoA carboxylase activation, but only EGCG could inhibit lipid accumulation in the intracellular site. These findings may suggest that curcumin shows the best capacity to improve FFA-induced insulin resistance than the other two, and ECG was more effective than EGCG in attenuating insulin resistance.

EGCG inhibits the invasion of highly invasive CL1-5 lung cancer cells through suppressing MMP-2 expression via JNK signaling and induces G2/M arrest.

Tumor metastasis is the main obstacle to the treatment of lung cancer. According to previous findings, matrix metalloproteinase-2 (MMP-2) is closely correlated with metastatic potential in lung cancer. This study showed that epigallocatechin-3-gallate (EGCG), a natural polyphenol in green tea, is a potent inhibitor of MMP-2 expression. EGCG effectively suppressed the invasion and migration of highly invasive CL1-5 lung cancer cells. Gelatin zymography, Western blot analysis, and RT-PCR were used to investigate the effects of EGCG on MMP-2 expression. The effects of EGCG on cell cycle and apoptosis were determined by flow cytometry analysis. To investigate the effects of EGCG on cell migration and cell invasion, Transwell migration/invasion assays were used. EGCG downregulated MMP-2 expression at the transcriptional level in CL1-5 cells. Moreover, the treatment of CL1-5 cells with EGCG caused downregulation of c- Jun N-terminal kinase (JNK), resulting in repression of the translocation of transcriptional factors, Sp1, and NF-κB, from the cytosol into the nucleus. In addition, EGCG significantly and synergistically enhanced the antitumor effects of the clinical drug, docetaxel, in CL1-5 cells. Further, EGCG induced G2/M arrest at dosages higher than those of suppression in cell invasion in CL1-5 cells. These results reveal that EGCG might decrease MMP-2 mRNA expression through JNK signaling, further suggesting that a combination of EGCG and docetaxel may be a promising strategy to help increase the efficacy of docetaxel in suppressing metastasis in lung cancer cells. In addition, EGCG may suppress cell proliferation in CL1-5 cells through inducing G2/M arrest.

Rotenone induces apoptosis in MCF-7 human breast cancer cell-mediated ROS through JNK and p38 signaling.

Rotenone is an inhibitor of the mitochondrial electron transport chain complex I, resulting in the generation of reactive oxygen species (ROS). Rotenone has been shown to display anticancer activity through the induction of apoptosis in various cancer cells. However, the underlying mechanism is still not fully understood. Here, rotenone showed a strong growth inhibitory effect against human breast cancer MCF-7 cells. DNA flow cytometric analysis, chromatin condensation, and poly (ADP-ribose) polymerase (PARP) cleavage indicated rotenone actively induced apoptosis in MCF-7 cells. The antiapoptotic protein, Bcl-2, was decreased, whereas the apoptotic protein, Bax, was increased in a time-dependent manner in rotenone-induced apoptosis. Moreover, the treatment of rotenone in MCF-7 cells caused the activation of c-jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs), and the inactivation of extracellular signal-regulated protein kinase 1/2 (ERK1/2). The pharmacological inhibition of JNK and p38 MAPK revealed significant protection against rotenone-induced apoptosis. Taken together, these results indicate rotenone may induce apoptosis through ROS and JNK/p38 MAPKs activation in MCF-7 cells.