High and low dose responses of transcriptional biomarkers in ex vivo X-irradiated human blood

Abstract

Purpose: Modifications of gene expression following ionizing radiation (IR) exposure of cells in vitro and in vivo are well documented. However, little is known about the dose-responses of transcriptionally responsive genes, especially at low doses. In this study, we investigated these dose-responses and assessed inter-individual variability.Materials and methods: High dose (0.5–4 Gy) and low dose (5–100 mGy) gene expression responses at 2 h and 24 h using 13 biomarkers transcriptionally regulated through the DNA damage response by the tumor suppressor p53 were investigated. Inter-individual variation was also examined.Results: High dose-response curves were best constructed using a polynomial fit while the low dose-response curves used a linear fit with linear R2 values of 0.841–0.985. Individual variation was evident in the high and low dose ranges. The FDXR, DDB2 high dose gene combination produced a mean dose estimate of 0.7 Gy for 1 Gy irradiated ‘unknown’ samples (95% CIs of 0.3–1.1 Gy) and 1.4 Gy for 2 Gy exposure (95% CIs of 0.6–2.1 Gy). The FDXR, DDB2, CCNG1 low dose gene combination estimated 98 mGy (95% CIs of 27–169 mGy) for 100 mGy exposure.Conclusions: These findings identify genes that fulfill some of the requirements of a good exposure biomarker even at low doses, such as sensitivity, reproducibility and simple proportionality with dose.