Understanding the Mechanism Underlie the Antidiabetic Activity of Oleuropein Using Ex-Vivo Approach.

Background: Oleuropein, the main constituent of olive fruit and leaves, has been reported to protect against insulin resistance and diabetes. While many experimental investigations have examined the mechanisms by which oleuropein improves insulin resistance and diabetes, much of these investigations have been carried out in either muscle cell lines or in vivo models two scenarios with many drawbacks. Accordingly, to simplify identification of mechanisms by which oleuropein regulates specific cellular processes, we resort, in the present study, to isolated muscle preparation which enables better metabolic milieu control and permit more detailed analyses. Methods: For this purpose, soleus muscles were incubated for 12 h without or with palmitate (1.5 mM) in the presence or absence of oleuropein (1.5 mM), and compound C. Insulin-stimulated glucose transport, glucose transporter type 4 (GLUT4) translocation, Akt substrate of 160 kDa (AS160) phosphorylation and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation were examined. Results: Palmitate treatment reduced insulin-stimulated glucose transport, GLUT4 translocation and AS160 phosphorylation, but AMPK phosphorylation was not changed. Oleuropein administration (12 h) fully rescued insulin-stimulated glucose transport, but partially restored GLUT4 translocation. However, it fully restored AS160 phosphorylation, raising the possibility that oleuropein may also have contributed to the restoration of glucose transport by increased GLUT4 intrinsic activity. Inhibition of AMPK phosphorylation with compound C (50 µM) prevented oleuropein -induced improvements in insulin-stimulated glucose transport, GLUT4 translocation, and AS160 phosphorylation. Conclusion: Our results clearly indicate that oleuropein alleviates palmitate-induced insulin resistance appears to occur via an AMPK-dependent mechanism involving improvements in the functionality of the AS160-GLUT4 signaling system.

Antitumor Action of Amygdalin on Human Breast Cancer Cells by Selective Sensitization to Oxidative Stress.

The treatment of MCF-7 and T47D human breast cancer cell lines with amygdalin was able to reduce the growth of both cells, in concentration and time-dependent manners. The potency of this inhibition against MCF-7 and T47D cells produced IC50 values of 39 and 45 mM, respectively. To investigate the correlation of this inhibition with oxidative stress, an amygdalin treatment of both cell lines was capable of inducing the generation of malondialdehyde (MDA) and oxidized glutathione levels. Also, this treatment caused the decrease of total glutathione and glutathione reductase activity. The proportional survival of tumor cells from this inhibition was positively correlated with the total glutathione, but it was inversely correlated with amygdalin or MDA levels (P < 0.001). In MCF-7 cells, the production of total glutathione was six times higher in the untreated than in amygdalin-treated cells, whereas this difference was reduced to 2.1 times in the T47D cells. Similarly, the production of MDA in MCF-7 cells was 2.4 times higher in the amygdalin-treated than in the untreated cultures, which were lowered to 1.3 times in the T47D cells. These data support a mechanism of amygdalin antitumor action against breast cancer cells based on the induction of oxidative stress.