Abstract
BackgroundIt is well known that a severe cell injury after exposure to ionizing radiation is the induction of DNA double-strand breaks (DSBs). After exposure, an early response to DSBs is the phosphorylation of the histone H2AX molecule regions adjacent to the DSBs, referred to as γ-H2AX foci. The γ-H2AX assay after external exposure is a good tool for investigating the link between the absorbed dose and biological effect. However, less is known about DNA DSBs and γ-H2AX foci within the tissue microarchitecture after internal irradiation from radiopharmaceuticals. Therefore, in this study, we aimed to develop and validate a quantitative ex vivo model using γ-H2AX immunofluorescence staining and confocal laser scanning microscopy (CLSM) to investigate its applicability in nuclear medicine dosimetry research. Liver and testis were selected as the organs to study after intravenous administration of 111InCl3.ResultsIn this study, we developed and validated a method that combines ex vivo γ-H2AX foci labeling of tissue sections with in vivo systemically irradiated mouse testis and liver tissues. The method includes CLSM imaging for intracellular cell-specific γ-H2AX foci detection and quantification and absorbed dose calculations. After exposure to ionizing radiation from 111InCl3, both hepatocytes and non-hepatocytes within the liver showed an absorbed dose-dependent elevation of γ-H2AX foci, whereas no such correlation was seen for the testis tissue.ConclusionIt is possible to detect and quantify the radiation-induced γ-H2AX foci within the tissues of organs at risk after internal irradiation. We conclude that our method developed is an appropriate tool to study dose–response relationships in animal organs and human tissue biopsies after internal exposure to radiation.
Highlights
It is well established that when mammalian cells are exposed to ionizing radiation, the most severe cell injury is the induction of DNA double-strand breaks (DSBs), which often results in cell death but can initiate genomic instability [1]
Assuming homogenous activity distribution in the source organ, the average self-absorbed doses for animals exposed for 4 h and 25 h were 20 mGy and 0.1 Gy, respectively, to the testis and 0.5 Gy and 3.20 Gy, respectively, to the liver
The method was exemplified by the testis and liver after systemic administration of 111InCl3
Summary
It is well established that when mammalian cells are exposed to ionizing radiation, the most severe cell injury is the induction of DNA double-strand breaks (DSBs), which often results in cell death but can initiate genomic instability [1]. Studies on the presence of γ-H2AX foci after continuous internal irradiation after systemic administration of radiopharmaceuticals used for therapy have been confined to leukocytes in the peripheral blood cells [12, 13] and mice kidneys [14]. It is currently unclear how DNA DSBs are distributed within differentiated mammalian tissue after internal irradiation originating from radionuclides or radiopharmaceuticals and how different tissues within normal organs respond. Liver and testis were selected as the organs to study after intravenous administration of 111InCl3
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