Dose-dependent survival of K562 cells subjected to irradiation, time course of endogenous enzyme activity and protective effect of applied superoxide dismutase.

PURPOSE: Irradiation-generated reactive species are proven to affect the cell survival and antioxidant enzyme levels. Radioresistance is a phenomenon which includes many cell mechanisms and signaling pathways. Superoxide dismutase (SOD) acts in and outside of cells after irradiation. The aim of this study was to determine LD50 (lethal dose for 50% of K562 cells), to monitor the effect of a chosen dose and exogenously applied superoxide dismutase (ExSOD) on the cell number and the activity of SOD, glutathione peroxidase (GSH-Px) and catalase (CAT). METHODS: The survival of irradiated (20-32.5 Gy) K562 cells was determined using the trypan-blue exclusion. Besides irradiated and non-irradiated cells (controls), another two groups of cells were treated with SOD (10-6 M) which then served as SOD-treated controls or were irradiated (30 Gy) one hour later. The number of cells and the activity of SOD, GSH-Px and CAT (using kinetic methods) were monitored after 1, 24, 48, 72 and 96 hrs in unirradiated, irradiated, SOD-treated and SOD-treated/irradiated experimental groups. RESULTS: K562 cells showed dose-dependent survival in the chosen range of doses. A dose of 30 Gy induced 50% cell mortality and increased the activity of all three investigated enzymes after 24 hrs. Pretreatment with SOD preserved the survival of irradiated cells and increased SOD, GSH-Px and CAT activity. ExSOD induced an increase of the activity of all examined enzymes. CONCLUSION: A balanced enhancement in endogenous antioxidative activity may be the cause of the increased radioresistance of K562 SOD-pretreated cells.

Modification of antioxidative and antiapoptotic genes expression in irradiated K562 cells upon fullerenol C60(OH)24 nanoparticle treatment.

Recent data established the prospective applications for fullerenol (C60(OH)24) nanoparticle (FNP) in many fields, such as antioxidants, neuroprotective agents, and potential anti-radiation drugs. Leukemia cell sensitization to apoptosis induced by ionizing radiation is achieved by upregulation of ROS production and/or downregulation of antioxidative enzymes. Therefore, our aim was to analyze the potential role of fullerenol nanoparticle in modulation of the leukemic cellular response to irradiation. We used the qRT-PCR to analyze the expression level of mRNA for 11 genes in irradiated and FNP pre-treated irradiated K562 cells, and compared the gene expression level with the overall cell survival. Our results of the improved cell survival in FNP-treated irradiated cells and significant overexpression of anti-apoptotic Bcl-2 and Bcl-xL and cytoprotective genes such as GSTA4, MnSOD, NOS, CAT and HO-1 genes, may indicate that FNP exerts cytoprotective function in K562 leukemic cells, rendering K562 cells more tolerant to radiotherapy.