DNA Repair and Cell Cycle Biomarkers of Radiation Exposure and Inflammation Stress in Human Blood

Abstract

DNA damage and repair are hallmarks of cellular responses to ionizing radiation. We hypothesized that monitoring the expression of DNA repair-associated genes would enhance the detection of individuals exposed to radiation versus other forms of physiological stress. We employed the human blood ex vivo radiation model to investigate the expression responses of DNA repair genes in repeated blood samples from healthy, non-smoking men and women exposed to 2 Gy of X-rays in the context of inflammation stress mimicked by the bacterial endotoxin lipopolysaccharide (LPS). Radiation exposure significantly modulated the transcript expression of 12 genes of 40 tested (2.2E-06<p<0.03), of which 8 showed no overlap between unirradiated and irradiated samples (CDKN1A, FDXR, BBC3, PCNA, GADD45a, XPC, POLH and DDB2). This panel demonstrated excellent dose response discrimination (0.5 to 8 Gy) in an independent human blood ex vivo dataset, and 100% accuracy for discriminating patients who received total body radiation. Three genes of this panel (CDKN1A, FDXR and BBC3) were also highly sensitive to LPS treatment in the absence of radiation exposure, and LPS co-treatment significantly affected their radiation responses. At the protein level, BAX and pCHK2-thr68 were elevated after radiation exposure, but the pCHK2-thr68 response was significantly decreased in the presence of LPS. Our combined panel yields an estimated 4-group accuracy of ∼90% to discriminate between radiation alone, inflammation alone, or combined exposures. Our findings suggest that DNA repair gene expression may be helpful to identify biodosimeters of exposure to radiation, especially within high-complexity exposure scenarios.

Comet Assay Assessment of DNA Damage in Buccal Mucosa Cells Exposed to X-Rays via Panoramic Radiography

“…For example, a previous study of human blood samples observed greater than twofold changes in the expression of genes involved in specific DNA repair functions (XPC, DDB2, LIGI, POLH, and RAD51) at 24 h after exposure to 2 Gy of X-rays. 18 Furthermore, two DNA damage response molecules, γ-H2AX and pChk2, were found to be expressed at approximately 0.1-48 and 0.25-32 h, respectively, after exposure to ionizing radiation from intraoral dental radiographs. 19 Therefore, it would be reasonable not to detect DSBs at 24 h after exposure.…”

Delayed activation of human microglial cells by high dose ionizing radiation

“…Damage to DNA integrity is critical and elicits a global stress response that is characterized by activation of an array of signaling pathways. Genes and proteins implicated in DNA repair, cell cycle checkpoints, apoptosis and changes in gene expression are modulated in a dose-dependent manner by ionizing radiation (Amundson and Fornace, 2001;Budworth et al, 2012;Chaudhry et al, 2012;de Toledo et al, 1998). Several reports have demonstrated that activated microglia play a critical role in IR induced impairment of hippocampal neurogenesis (Monje et al, 2002;Monje et al, 2003).…”

Radiation-induced apoptosis varies among individuals and is modified by sex and age

“…They have also been used to identify genetic determinants of pathways involved in the cytotoxic response to IR (Shukla and Dolan 2005, Hartford and Dolan 2007, Niu et al 2010). Recently, peripheral blood mononuclear cells (PBMC) isolated from a small panel of healthy volunteers were also used to identify genes associated with radiation response (Budworth et al 2012). It remains unclear, however, whether immortalized cell lines are appropriate surrogates for primary cells isolated from individuals and accurately reflect the response and the pathways involved in normal cells.…”