γ-H2AX as a Marker for Dose Deposition in the Brain of Wistar Rats after Synchrotron Microbeam Radiation

Abstract

ObjectiveSynchrotron radiation has shown high therapeutic potential in small animal models of malignant brain tumours. However, more studies are needed to understand the radiobiological effects caused by the delivery of high doses of spatially fractionated x-rays in tissue. The purpose of this study was to explore the use of the γ-H2AX antibody as a marker for dose deposition in the brain of rats after synchrotron microbeam radiation therapy (MRT).MethodsNormal and tumour-bearing Wistar rats were exposed to 35, 70 or 350 Gy of MRT to their right cerebral hemisphere. The brains were extracted either at 4 or 8 hours after irradiation and immediately placed in formalin. Sections of paraffin-embedded tissue were incubated with anti γ-H2AX primary antibody.ResultsWhile the presence of the C6 glioma does not seem to modulate the formation of γ-H2AX in normal tissue, the irradiation dose and the recovery versus time are the most important factors affecting the development of γ-H2AX foci. Our results also suggest that doses of 350 Gy can trigger the release of bystander signals that significantly amplify the DNA damage caused by radiation and that the γ-H2AX biomarker does not only represent DNA damage produced by radiation, but also damage caused by bystander effects.ConclusionIn conclusion, we suggest that the γ-H2AX foci should be used as biomarker for targeted and non-targeted DNA damage after synchrotron radiation rather than a tool to measure the actual physical doses.

Blackboard to Bedside: A Mathematical Modeling Bottom-Up Approach Toward Personalized Cancer Treatments

“…This indicates that bystander effects might play a role in low-dose radiation hypersensitivity, as observed in multiple experimental studies, such as one shown in Figure 4C (which compares curves for the LQ model and the LQ model with bystander effects). These in silico results are also confirmed with experiments by Fernandez et al 59…”

“…48,56,58 It is difficult to study these effects independently of direct effects, and, moreover, mediators and targets for bystander signals are poorly understood even after several experimental studies. 49,57,[59][60][61][62][63][64] Recently, several modeling attempts have been made to study and understand radiation bystander effects. 65,66 In one of these attempts, Powathil et al 66 used a multiscale mathematical modeling framework (Fig 2) to study the impact of radiation and radiation-induced bystander effects on both normal and tumor cells.…”

“…Here, bystander effects are considered to be produced by bystander signals that diffuse through the medium/microenvironment. 48,59 Radiated and nonirradiated cells that are exposed to these signals are assumed to respond probabilistically, in which varying outcomes, such as cell death, repair delay, and mutation, depend on localized signal intensity. Figures 4A and 4B show the survival fraction of the cells after radiation, with and without bystander-induced cell kill, for two cases of dose delivery.…”

Animal Models in Microbeam Radiation Therapy: A Scoping Review

“…C6 glioma-bearing rats were also employed by Fernandez-Palomo et al for the study of bystander and abscopal effects when comparing MRT with BB [19]; both MRT and BB promoted radiation-induced bystander effects in the non-irradiated portion of the brain and in the bladder of the tumour-bearing animals. This same model has been used to study the dose deposition of MRT (25 µm; 200 ctc; at 35, 70 or 350 Gy peak-dose) using the marker of DNA damage γ-H2AX [44]. Moreover, the damage of the optic nerve was studied after treating the same C6 glioma in Wistar rat with cross-fired MRTs (25 µm; 200 ctc, 350 Gy peak-dose) [45].…”

A correlation of long term effects and radiation quality in the progeny of bystander cells after microbeam radiations: The experimental study of radiotherapy for cancer risk mitigation

“…In recent years, heavy ions radiotherapy such as high-LET carbon ion is one of the most effective treatment for cancer patients compared to conventional radiotherapy (such as X rays and  rays). By delivering higher doses to tumour volume and sparing healthy normal tissues through manipulation of the Bragg peak area, resulting in the increased therapeutic ratio, and a higher relative biological effectiveness (RBE) in cell killing and induction of DNA damage [13][14][15][16][17]. However, the underlying bystander responses and genomic instability mechanisms after high-LET carbon ions are still poorly understood and investigated.…”