Assessment of alterations in X-ray irradiation-induced DNA damage of glioma cells by using proton nuclear magnetic resonance spectroscopy

Glioma is one of the most common types of brain tumors. DNA damage is closely associated with glioma cell apoptosis induced by X-ray irradiation. Alterations of metabolites in glioma can be detected noninvasively by proton nuclear magnetic resonance (1H NMR) spectroscopy. To noninvasively explore the micro mechanism in X-ray irradiation-induced apoptosis, the relationship between metabolites and DNA damage in glioma cells was investigated. Three glioma cell lines (C6, U87 and U251) were randomly designated as control (0 Gy) and treatment groups (1, 5, 10, 15 Gy). After X-ray exposure, each group was separated into four parts: (i) to detect metabolites by 1H NMR spectroscopy; (ii) to make cell colonies; (iii) to detect cell cycle distribution and apoptosis rate by flow cytometry; and (iv) to measure DNA damage by comet assay. The metabolite ratios of lactate/creatine and succinate/creatine decreased (lactate/creatine: C6, 22.17–66.27%; U87, 15.93–44.56%; U251, 26.27–74.48%. succinate/creatine: C6, 14.41–48.35%; U87, 22.03–70.62%; U251, 17.33–60.06%) and choline/creatine increased (C6, 52.22–389.68%; U87, 56.15–82.36%; U251, 31.87–278.62%) in the treatment groups compared with the control group (each P < 0.05), which linearly depended on DNA damage. An increasing dose of X-ray irradiation increased numbers of apoptotic cells (P < 0.01), and the DNA damage parameters were dose-dependent (P < 0.05). The colony-forming rate declined (P < 0.01) and the percentage of cells at G1 stage increased when exposed to 1 Gy X-ray (three cell lines, P < 0.05). Metabolite alterations detected by 1H NMR spectroscopy can be used to determine DNA damage induced by X-ray irradiation. 1H NMR spectroscopy is a noninvasive method to predict DNA damage of glioma cell at the micro level.