Oleuropein induces apoptosis via activation of caspases and suppression of phosphatidylinositol 3-kinase/protein kinase B pathway in HepG2 human hepatoma cell line

Abstract

Abstract.Oleuropein is a polyphenol, that is found in extra-virgin olive oil. Previous studies have shown that oleuropein inhibits cell proliferation and induces apoptosis in breast cancer, colorectal cancer and thyroid cancer. The aim of the present study was to investigate the effects of oleuropein in hepatocellular carcinoma (HCC) cells. The results of Cell Counting Kit 8 and flow cytometric analysis indicated that oleuropein effectively inhibited cell viability and induced apoptosis in HepG2 human hepatoma cells in a dose-dependent manner, through activation of the caspase pathway. Proapoptotic Bcl-2 family members, BAX and Bcl-2, were involved in oleuropein-induced apoptosis. The phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway was also shown to be involved in this process. Oleuropein was demonstrated to suppress the expression of activated AKT. In addition, AKT overexpression promoted cell survival following treatment with oleuropein, while inhibition of AKT promoted cell death. Furthermore, the data demonstrated that oleuropein induces the production of reactive oxygen species (ROS) and that the function of oleuropein is, at least partially, ROS-dependent. These results suggest that oleuropein may be a promising novel chemotherapeutic agent in hepatocellular carcinoma. IntroductionHepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality (1). The predominant risk factors for HCC development are infection with hepatitis B or C virus, obesity and excess alcohol intake. The incidence and mortality of HCC is increasing as a result of the current obesity epidemic and rise in alcohol consumption (2). However, only 10-20% of patients with HCC are eligible for surgical resection, due to poorly preserved liver function, portal vein invasion or extrahepatic spread. Furthermore, the risk of recurrence following HCC resection is high (3,4). The available chemotherapeutic and radiotherapeutic treatment options for patients with advanced HCC are also extremely limited. Therefore, it is necessary to develop effective and practical chemotherapeutic agents with minimal cytotoxicity for use in this disease.A number of previous studies have shown that regular consumption of coffee, vitamin E and fish oil may be associated with a reduced risk of developing HCC (5-7). Ecological studies have investigated the association between dietary fat and certain types of cancer (8,9). Hursting et al (8) demonstrated that the intake of saturated or polyunsaturated fats was associated with incidence of breast and prostate cancer. A causal relationship was identified between cholesterol intake and colon cancer (9). Olive oil is the oil obtained from the fruit of the olive tree (Olea europaea Sativa) and its consumption is associated with lower overall mortality patterns, which are observed in Mediterranean populations (10). The primary component of olive leaf extract is oleuropein. Andreadou et al reported that oleuropein is involved in cardiomyocyte metabolism through the activati...

Extra-virgin olive oil phenols block cell cycle progression and modulate chemotherapeutic toxicity in bladder cancer cells

“…These data are of great interest since the dose of EVOOE used for this experiment was non-toxic per se to the cells themselves, and this indicates a synergic effect in combination with paclitaxel. It can be hypothesized that the cytotoxicity enhancement of paclitaxel could be attributed to the alteration in gene expression occurring at low doses of phenolic extract, as observed in our previous study (20), that chemosensitize the cells by altering pathways involved in cell growth and proliferation such as platelet-activating factor (PAF) receptor signaling or PI3K signaling (37,41,42). …”

“…This effect has been attributed to ROS production induced by polyphenols in certain experimental conditions (37,38). To clarify whether EVOOE may induce oxidative stress thus leading to apoptosis, we evaluated intracellular ROS production via a cytofluorimetric assay.…”

“…Our data indicated that EVOOE was able to decrease the basal level of oxidative stress in the T24 cells and to a lower extent also in the 5637 cells. Hence, in our model the induction of apoptosis was not due to ROS production but had to be attributed to other molecular mechanisms such as the inhibition of pro-survival cell signaling pathways (37). In the last part of this study we evaluated the ability of low concentrations of EVOOE to improve the activity of different chemotherapeutics used in common clinical practice.…”

Antitumor Perspectives of Oleuropein and Its Metabolite Hydroxytyrosol: Recent Updates

“…Olive oil phenols also have been proven effective to prevent from the liver tumorigenesis in male C3H/He mice (Thuy & Takeuchi, ). Recently, Yan, Chai, Cai, Miao, and Ma () investigated that oleuropein induced apoptosis in HepG2 human hepatoma cells and suppressed the cell viability in a dose‐fashion through activating caspase pathway, inducing apoptosis, suppressing the expression of activated AKT, respectively.…”

Phenolic Compounds Isolated from Olive Oil as Nutraceutical Tools for the Prevention and Management of Cancer and Cardiovascular Diseases

“…Concerning anti-cancer activity, previous studies have shown that OLE inhibits cell proliferation and induces apoptosis in breast, colorectal and thyroid cancer [106,107,108]. More recently, Yan et al [109] have investigated the OLE effects on hepatocellular carcinoma cells, finding a reduction of HepG2 cell viability, as well as apoptosis induction in a dose-dependent manner through activation of the caspase pathway. This effect was correlated with ROS generation that could be responsible of both effects.…”