Measurement of in vivo
DNA damage responses to various treatments is providing useful information to clinicians for improving human health. Hundreds of H2AX molecules are rapidly phosphorylated on serine 139 (γ-H2AX) in response to the formation of each DNA double-strand break (DSB) (Rogakou et al., 1999
; Rogakou et al., 1998
). The most sensitive assays of γ-H2AX utilize immunocyto- and immunohisto-chemistry techniques to stain for γ-H2AX foci, intranuclear structures composed of the hundreds of γ-H2AX molecules, which form at each DSB site in cells and tissues (Bonner et al., 2008
). Exposure of humans to ionizing radiation during various radiological diagnostic or therapeutic treatments (Kuefner et al., 2009
; Lobrich et al., 2005
; Porcedda et al., 2006
; Sak et al., 2007
) and space travel (Ohnishi et al., 2009
) lead to DSB formation that can be measured by counting the γ-H2AX foci in many tissues including lymphocytes, buccal cells, and skin biopsies; see reviews by (Redon et al., 2010b
; Rothkamm and Horn, 2009
Thus, counting γ-H2AX foci in cells of persons exposed to irradiation may be useful in determining the extent of exposure and in providing optimum medical care. In addition to radiation exposure from medical procedures and/or diagnostics, the risk of accidental irradiation to the general public and emergency responders has also increased in recent years. We recently utilized a non-human primate (NHP) model to further validate the γ-H2AX assay following TBI with both non-lethal and lethal radiation doses (Redon et al., 2010a
). Measuring γ-H2AX foci in NHP lymphocytes and plucked hairs enabled us to assess the subject’s exposure several days after irradiation at doses in the medical triage range, making γ-H2AX biodosimetry a robust tool for measuring TBI in macaques for several days after irradiation.
However, a serious consideration is that many radiation accidents are likely to involve inhomogeneous exposures or partial-body irradiation (PBI) (Prasanna et al.), the extent of which may be unknown both in terms of the fraction of the body irradiated and dose delivered to the irradiated fraction. In cases of acute exposure, the determination that a fraction of the blood volume had escaped irradiation would indicate that a portion of the body, and hence the bone marrow, may have also escaped lethal irradiation. Such knowledge may be critical for guiding decisions on optimal medical treatment for the victim, for example, whether a bone-marrow transplant is necessary for survival.
A method (Qdr
) to evaluate PBI in individuals was originally demonstrated by Sasaki and Miyata (Sasaki and Miyata, 1968
) utilizing the frequency of chromosomal aberrations (dicentric and ring chromosomes) in lymphocyte metaphase spreads taken from exposed subjects. It was later adapted to utilize the frequency of chromosome fragments present in lymphocytes subjected to premature chromosome condensation (Blakely et al., 1995
; Prasanna, et al.). Here, we extend this method to utilize the levels of γ-H2AX foci in the lymphocyte population of the exposed subject to assess dose and fraction of body exposed to PBI.
We also briefly introduce the use of plucked hairs as a mean to assess PBI. It may take a few minutes for blood to make a complete bodily circuit, hence, the fraction of the blood volume exposed and the dose received by that fraction may differ considerably from that received by other portions of the body, depending in large part on the dose rate and length of exposure. Exposure of sufficient duration to any part of a body could lead to irradiation of the complete blood volume. However, in these cases, measurements of γ-H2AX foci levels in plucked hair bulbs could help determine the extent of partial-body exposure.