Altered mitochondrial function and genome frequency post exposure to γ-radiation and bystander factors

Purpose: To further evaluate irregular mitochondrial function and mitochondrial genome damage induced by direct γ-irradiation and bystander factors in human keratinocyte (HPV-G) epithelial cells and hamster ovarian fibroblast (CHO-K1) cells. This is as a follow-up to our recent reports of γ-irradiation-induced loss of mitochondrial function and mitochondrial DNA (mtDNA) damage. Materials and methods: Mitochondrial function was evaluated post direct radiation and irradiated cell conditioned medium (ICCM) by determining: Activity of the individual complexes of oxidative phosphorylation (OxPhos); mtDNA-encoded protein synthesis; and mitochondrial genome frequency and mtDNA damage. Results: Mitochondria show a loss of OxPhos enzyme function as early as 4 h post treatment with recovery observed 12–96 h in some but not all complexes demonstrating a non-uniform sensitivity to γ-radiation. We also identified irregular mtDNA-directed protein synthesis. Long range Polymerase Chain Reaction (PCR) analysis identified mitochondrial genome damage and real-time PCR identified increases in mitochondrial genome frequency. Conclusions: The study reaffirms the sensitive nature of mitochondria to both low-level direct radiation exposure and radiation-induced bystander factor mediated damage. Furthermore, we report for the first time, the loss of function in the enzymes of OxPhos post exposure to bystander factors and identify altered mtDNA-directed protein synthesis post both direct radiation and bystander factors.