Mitochondrial oxidative damage and its mechanism in tumor cells induced by 100 MeV proton irradiation

Objective: To study the mechanism of oxidative damage induced by 100 MeV proton irradiation in human cervical cancer HeLa cells. Methods: A 100 MeV high-current proton cyclotron was used at the dose rate of 0.8 Gy/min in China Institute of Atomic Energy. Cells were divided into three groups: the non-irradiated group (0 Gy), low-dose proton irradiation group (0.5 Gy) and high-dose proton irradiation group (8 Gy). Cell proliferation activity was evaluated by CCK-8 assay and apoptosis rate was analyzed by flow cytometry in 24, 48 and 72 h after irradiation. Reactive oxygen species (ROS) contents were detected by DCFH-DA labeling within 12-72 h after irradiation and mitochondrial respiratory chain complex I activity was detected using complex I enzyme activity assay kit within 24-48 h after irradiation. Gene expression was analyzed at 12 and 24 h after 8 Gy proton irradiation by mRNA chip hybridization. Results: Compared with the non-irradiated group, changes in cell proliferation, apoptosis, reactive oxygen species (ROS) content, and mitochondrial respiratory chain complex I activity in the low-dose 0.5 Gy proton-irradiated group were not significant. In the high-dose 8 Gy proton irradiation group, cell proliferation was inhibited at 72 h after irradiation. Apoptosis in the high dose 8 Gy proton irradiation group increased at 24, 48 and 72 h after irradiation in a time-dependent manner. It was found that cellular ROS increased at 16 h after 8 Gy proton irradiation, increased significantly at 24 h, and gradually decreased after 36 h. Mitochondrial respiratory chain complex I activity was significantly decreased at 24 and 48 h after 8 Gy proton irradiation. KEGG analysis showed that differentially expressed genes were mainly involved in the mitogen-activated protein kinase (MAPK) signal pathway, PI3K/Akt signal pathway, and peroxisome proliferator activated receptor (PPAR) signaling path-way after high dose 8 Gy proton irradiation. Conclusion: High dose proton irradiation can inhibit HeLa cell proliferation and promote apoptosis, which may be due to the increase in oxidative stress and the inhibition of mitochondrial respiratory chain complex I activity. (authors)