Office of Biological and Environmental Research
DOE Lowdose Radiation Program Workshop IV
Abstract
Title: Effects of Low Dose Ionizing Radiation on Gene Expression in Human
Subjects Undergoing Radiotherapy
Authors: Chad W. Schwietert, M.S.(1), Robin L. Stern, Ph.D. (1), Joerg Lehmann, Ph.D.(1,2), Christine Hartmann Siantar, Ph.D.(1, 2), Bruce E. Lehnert, Ph.D. (3), and Zelanna Goldberg, M.D., FRCPC (1),
Institutions: (1) University of California, Davis, Dept. of Radiation Oncology (2) Lawrence Livermore National Laboratory, (3)– Los Alamos National Laboratory (retired) zgoldberg@ucdavis.edu
Several investigations have demonstrated that significant biological effects can occur
in animals, animal cells, immortalized human cell lines, and primary human cells after exposure to doses of ionizing radiation (IR) in the low dose, <1-10 cGy region (LDIR). Yet little information is available as to how these and other observations pertain to human responses to LDIR, though such knowledge is ultimately required for reducing the uncertainty of assessing human risks due to these exposures. We therefore undertook these translational studies to begin the development of a unique dataset of human cellular responses to LDIR as measured by gene expression changes when exposure occurs to a tissue with its normal complex cellular mixture and 3-dimensional architecture.
To evaluate LDIR effects in human tissue we have obtained freshly explanted full
thickness human skin samples obtained from aesthetic surgery, and subjected them to ex vivo irradiation as a translational research model system of a complex human tissue. Ionizing radiation (IR) exposures were delivered at 1, 10, or 100 cGy. The temporal response to IR was assessed by harvesting RNA at multiple time points out to 24 hours post IR. Gene expression changes were quantitated by real time PCR. Genes of interest include those reported to have altered expression following LDIR from in vitro cell culture models, such as those associated with cell cycle regulation, DNA repair and various cytokines. Primary fibroblast cell strains have also been established from these surgical specimens to further compare tissue responses with monolayer cell culture systems.
To directly test the hypothesis that LDIR is biologically active in human tissue exposed in vivo, fully consenting volunteer patients being irradiated for the primary
treatment of their prostate cancers underwent biopsies of full thickness skin following a single fraction of therapeutic IR over the same dose range as the ex vivo irradiated
samples. RNA was extracted and subjected to quantitative real time PCR analyses.
The pattern of IR induced alterations of gene expression are quantitatively different in primary fibroblasts, ex vivo irradiated tissues samples and tissues biopsies from patients irradiated in vivo. Both in vitro models appear to have limitations, likely
related to insufficient complexity, to their being able to accurately reflect in vivo human responses, with the cell culture model showing greater variance from the patient in vivo response.
