Abstract. Curcumin has been found to exhibit anticancer activity and certain studies have shown that curcumin triggers the apoptosis of human A549 lung adenocarcinoma cells. However, the mechanism underlying curcumin-mediated apoptosis is not completely understood. The present study was designed to investigate the effect of curcumin on the induction of apoptosis and apoptosis-related factors in human A549 lung adenocarcinoma cells. Treatment of A549 cells with curcumin caused a concentration-dependent inhibition of cell growth and an increase in apoptosis, as confirmed by THE MTT assay, flow cytometry and morphology analysis. Curcumin-treatment of A549 cells induced a loss of the mitochondrial membrane potential and increased cytosolic cytochrome c. Furthermore, curcumin-induced apoptosis was accompanied by changes in intracellular oxidative stress-related enzymes, including decreased intracellular reactive oxygen species levels, increased superoxide dismutase and decreased malondialdehyde and 4-hydroxynonenal. In addition, induction of apoptosis was also accompanied by phosphorylation and activation of mitogen-activated protein kinase signaling pathway factors c-Jun N-terminal kinase, p38 and extracellular signal-regulated kinase.
IntroductionLung cancer is the main leading cause of cancer-related fatality worldwide, with a rapidly increasing rate in China and other Asian countries (1-4). Chemotherapy is currently the most frequently used treatment for lung cancer and other types of cancer. However, while this method of treatment kills cancer cells, it also destroys some normal cells. Thus, the identification of novel natural compounds with low toxicity and high selectivity for killing cancer cells is a significant area in cancer research (5), and several natural products have been used as alternative treatments for cancer (6,7).Curcumin, a natural and crystalline compound isolated from the plant Curcuma longa, has been widely studied for its anti-inflammatory, antiangiogenic, antioxidant and anticancer effects in Chinese systems of medicine (8,9). Additionally, previous studies have shown that curcumin exhibits antiproliferative and anticarcinogenic properties in a wide variety of cell lines and animals (10,11). Previous studies have demonstrated that curcumin inhibits the growth and apoptosis of human A549 lung adenocarcinoma cells (12)(13)(14). However, the mechanisms of curcumin-induced apoptosis via oxidative stress remain unclear.The physiological status of the reactive oxygen species (ROS) levels can regulate cell proliferation: When intracellular ROS levels are above a certain threshold, ROS inhibit the cell cycle, leading to increased cell apoptosis and necrosis. In the tumor cells it often maintains a higher state of oxidation, with higher levels of oxygen free radicals and lower levels of the antioxidant enzyme activity. This higher oxidation state can activate certain transcription factors and associated genes, such as NF-κB and API, thus, ensuring the survival, proliferation and migration of tumor ...