Basic Study
Copyright ©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Aug 14, 2017; 23(30): 5530-5537
Published online Aug 14, 2017. doi: 10.3748/wjg.v23.i30.5530
Autophagic cell death induced by reactive oxygen species is involved in hyperthermic sensitization to ionizing radiation in human hepatocellular carcinoma cells
Guang-Jin Yuan, Jun-Jian Deng, De-Dong Cao, Lei Shi, Xin Chen, Jin-Ju Lei, Xi-Ming Xu
Guang-Jin Yuan, Department of Oncology, Nationality Hospital of Qianjiang, Chongqing 409000, China
Jun-Jian Deng, De-Dong Cao, Lei Shi, Xin Chen, Jin-Ju Lei, Xi-Ming Xu, Cancer Center, Renmin Hospital of Wuhan University, Wuhan 430060, Hubei Province, China
Author contributions: Yuan GJ designed the study and wrote the manuscript; Deng JJ performed the majority of experiments; Cao DD, Shi L, Chen X and Lei JJ performed some experiments of the study and data analysis; Xu XM provided partial financial support for this work and was involved in editing the manuscript.
Supported by Science and Technology Program of Chongqing, No. 2013-2-179.
Institutional review board statement: HepG2 cells were used in the study, and no specimens were taken clinically. Therefore, the ethic approval was not required.
Conflict-of-interest statement: No conflict of interest exists.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Xi-Ming Xu, Professor, PhD, Cancer Center, Renmin Hospital of Wuhan University, Wuhan 430060, No. 9 Ziyang road, Hubei Province, China. rm001271@whu.edu.cn
Telephone: +86-27-88041911 Fax: +86-27-88042292
Received: March 15, 2017
Peer-review started: March 17, 2017
First decision: May 16, 2017
Revised: May 26, 2017
Accepted: July 4, 2017
Article in press: July 4, 2017
Published online: August 14, 2017
Abstract
AIM

To investigate whether autophagic cell death is involved in hyperthermic sensitization to ionizing radiation in human hepatocellular carcinoma cells, and to explore the underlying mechanism.

METHODS

Human hepatocellular carcinoma cells were treated with hyperthermia and ionizing radiation. MTT and clonogenic assays were performed to determine cell survival. Cell autophagy was detected using acridine orange staining and flow cytometric analysis, and the expression of autophagy-associated proteins, LC3 and p62, was determined by Western blot analysis. Intracellular reactive oxygen species (ROS) were quantified using the fluorescent probe DCFH-DA.

RESULTS

Treatment with hyperthermia and ionizing radiation significantly decreased cell viability and surviving fraction as compared with hyperthermia or ionizing radiation alone. Cell autophagy was significantly increased after ionizing radiation combined with hyperthermia treatment, as evidenced by increased formation of acidic vesicular organelles, increased expression of LC3II and decreased expression of p62. Intracellular ROS were also increased after combined treatment with hyperthermia and ionizing radiation. Pretreatment with N-acetylcysteine, an ROS scavenger, markedly inhibited the cytotoxicity and cell autophagy induced by hyperthermia and ionizing radiation.

CONCLUSION

Autophagic cell death is involved in hyperthermic sensitization of cancer cells to ionizing radiation, and its induction may be due to the increased intracellular ROS.

Keywords: Autophagic cell death, Hyperthermia, Ionizing radiation, Hepatocellular carcinoma, Reactive oxygen species

Core tip: Increased cell autophagy and intracellular reactive oxygen species (ROS), accompanied by decreased cell viability and surviving fraction, were observed in HepG2 cells treated with hyperthermia and ionizing radiation. Pretreatment with N-acetylcysteine, an ROS scavenger, markedly inhibited the above cytotoxicity and cell autophagy. The results suggest that autophagic cell death is involved in the hyperthermic sensitization to ionizing radiation, and its induction may be due to the increased intracellular ROS.