Hydroxyl Radical (·OH) Played a Pivotal Role in Oridonin-Induced Apoptosis and Autophagy in Human Epidermoid Carcinoma A431 Cells

Abstract

Oridonin, a diterpenoid compound extracted and purified from Rabdosia rubescen, has been reported to induce tumor cell apoptosis through tyrosine kinase pathway. To further examine the mechanism of oridonin, we selected human epidermoid carcinoma A431 cell as a test object. Besides apoptosis, oridonin also induced A431 cell autophagy, and this autophagy antagonized apoptosis and played a protective role for A431 cells. Reactive oxygen species (ROS) played a pivotal role in induction of cytotoxicity. Therefore, a ROS scavenger, N-acetylcysteine (NAC) combined with oridonin was appiled. Results of morphologic observation, flow cytometric analysis and Western blot analysis showed that NAC could significantly reverse both ROS generation and down-regulation of mitochondrial membrane potential in oridonin treated cells. NAC inhibited oridonin induced apoptosis through both the intrinsic and extrinsic apoptotic pathways. NAC effectively inhibited both oridonin-induced apoptosis and autophagy by reducing intracellular oxidative stress. To further examine the mechanism of ROS, exogenous enzyme antioxidants (superoxide dismutase (SOD), catalase (CAT)) and non-enzyme antioxidants (glutathione (GSH)) were applied to detect the effect of oridonin on ROS generation. Only GSH exerted a similar role with NAC, suggesting that hydroxyl radical (·OH) played the major role in oridonin-induced cell death. Oridonin could decrease the GSH level in A431 cells in a dosedependent manner. In addition, after treatment with ·OH donor, Fenton reagent, the changes in A431cells were similar to the results of oridonin treatment. All the results proved that ·OH played the pivotal role in oridonin induced apoptosis and autophagy in A431 cells.Key words oridonin; apoptosis; autophagy; reactive oxygen species; hydroxyl radical Reactive oxygen species (ROS) include highly reactive hydroxyl radicals (OH·), superoxide anions (O 2− ), singlet oxygen ( 1 O 2 ), and hydrogen peroxide (H 2 O 2 ), which form as natural products of the normal cellular metabolism of oxygen. 1) They play critical roles in the determination of cell fate by eliciting a wide variety of cellular responses, such as proliferation, differentiation and apoptosis.2) Under normal conditions, having been balanced by cell's antioxidant defense systems, low levels of ROS play important roles in cell signaling. However, under environmental stress, extended high levels of ROS would cause severe damage to cellular organisms, including DNA, RNA or proteins, which eventually lead to cell death via either apoptotic or other mechanisms.3) In many reports, ROS may also act as intracellular messengers, which are induced by a range of stimuli and triggered apoptosis. In these conditions, ROS are also produced in cell organelles, especially mitochondria. During oxidative stress-induced cell death, ROS can target the mitochondrial membrane potential. 4)Apoptosis (type I cell death) is one type of programmed cell death in multicellular organisms, and apoptotic cells are characterized by a series of mo...

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The signaling involved in autophagy machinery in keratinocytes and therapeutic approaches for skin diseases

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Downregulation of Cdk1 and CyclinB1 Expression Contributes to Oridonin-induced Cell Cycle Arrest at G2/M Phase and Growth Inhibition in SGC-7901 Gastric Cancer Cells

“…Previous studies have shown that oridonin has anti-tumor activities in vivo and in vitro (Zhou et al, 2007;Lou et al, 2009;Wang et al, 2013) (Ye et al, 2012a;2012b;Yu et al, 2012;Zang et al, 2012;Liu et al, 2013), by inducing apoptosis through the mitochondrial pathway (Li et al, 2008;Zhu et al, 2013) or Fas/FasL death signal pathway (Liu et al, 2006), or by arresting the cell cycle on G 0 /G 1 phase in human breast adenocarcinoma MDA-MB-231 cell (Hsieh et al, 2005), but G 2 /M phase in human breast adenocarcinoma MCF-7 cell (Cui et al, 2007;Zhang et al, 2013), human liver hepatocellular carcinoma HepG2 cell (Wang et al, 2010), Human Pancreatic Carcinoma PANC-1 cell (Qi et al, 2012), murine fibroblast L929 cells (Cheng et al, 2009), Human Laryngeal Carcinoma Cells (Kang et al, 2010. However, little was known about the cell cycle arrest of oridonin on gastric cancer.…”