22nd Annual NASA Space Radiation Investigators' Workshop (2011)
7066.pdf
Evidence for non-Targeted Biological Effects Induced by Space Radiation
Edouard I. Azzam1, Sonia M. de Toledo1, Manuela Buonanno1, Di Feng1, Min Li1, Geraldine Gonon1, Bernie M.
Rabin2 and Betsy J. Barnes1
1
New Jersey Medical School Cancer Center, Newark, NJ, 2Department of Psychology, UMBC, Baltimore, MD
We tested the hypothesis that the linear energy transfer (LET) and dose of space radiation determine the
nature and the extent of persistent biological effects induced in irradiated normal mammalian cells, their neighboring
bystanders and their progeny; further, induced non-targeted effects, including genomic instability, bystander effects
and adaptive responses, involve redox-regulated processes that greatly depend on intercellular communication.
Twenty population doublings after exposure to low or high doses of 1 GeV/u iron ions (LET~151 keV/µm),
the progeny of irradiated AG1522 normal human fibroblasts exhibited reduced proliferative capacity and harbored
higher levels of micronuclei and reactive oxygen species (ROS) than control. In contrast, the progeny of cells
exposed to low or high doses of 1 GeV protons (LET ~ 0.2 keV/µm) had similar cloning efficiency and harbored
similar levels of micronuclei and ROS as control.
Similar to progeny of high-LET-irradiated cells, the progeny of bystander cells that were co-cultured with
cells exposed to low/moderate fluences of 1 GeV/u iron or 0.6 GeV/u silicon ions (LET ~ 51 keV/μm) harbored
higher levels of micronuclei, protein oxidation, and lipid peroxidation than respective control. This correlated with
decreased activity of antioxidant enzymes, inactivation of the redox-sensitive metabolic enzyme aconitase, and
altered expression of proteins encoded by mitochondrial DNA (1). A significant increase in the spontaneous
neoplastic transformation frequency in the progeny of bystander cells was also observed when C3H 10T½ mouse
embryo fibroblasts were used (2). The increase, which greatly depended on events communicated through gap
junction channels linking irradiated cells with bystander cells, was not observed when irradiated cells were targeted
with low LET protons. These results were consistent with the observation that bystander cells co-cultured with low
dose proton-irradiated cells are protected from the clastogenic effects of a subsequent challenge dose from 1 GeV/u
iron ions delivered during 24 h after co-culture.
We also investigated redox-modulated responses in non-targeted organs of rats following cranial irradiation
by energetic heavy ions (3). At 20 months after exposure, relative to control, mitochondrial protein import was
decreased in non-targeted liver of rats exposed to 50 cGy from 500 MeV/n titanium ions (LET ~ 134 keV/ μm) or 25
cGy from 600 MeV/n oxygen ions (LET ~ 16.4 keV/ μm). The decrease in import was associated with increased
level of HSP60 and Tom20 that participate in the import process. In peripheral blood, notable decreases in CD4+ (Thelper) and CD8+ (T-cytotoxic) lymphocytes occurred following cranial mean doses of 5 cGy from 600 MeV/n
oxygen ions. Further, relative to controls, changes in the level of inflammatory cytokines, chemokines and
nitrosylated proteins were detected in the plasma of irradiated rats long (20 months) after the exposure.
Collectively, the in vitro data indicate that exposure to space radiations of different LET induces
differential delayed non-targeted effects that involve oxidative metabolism and intercellular communication through
gap junctions (4,5). By multiple endpoints, high LET radiation was more effective than low LET radiation at
inducing persistent oxidative stress in progeny cells, and the extent of the effects was dependent on the dose
delivered to the irradiated cell population. The occurrence of in vivo non-targeted effects may be relevant to the
setting of adequate radiation protection guidelines and to radiotherapy.
Supported by grant NNJ06HD91G from NASA
References
1. Buonanno et al. (2011) Long-Term Consequences of Radiation-Induced Bystander Effects Depend on Radiation
Quality and Dose and Correlate with Persistent Oxidative Stress. Radiation Research 175: 405-15.
2. Buonanno et al. (2011) Increased Frequency of Spontaneous Neoplastic Transformation in Progeny of Bystander
Cells from Cultures Exposed to Densely-Ionizing Radiation. PLoS ONE 6(6): e21540.
3. Jain et al. (2011) In Vivo Space Radiation-Induced non-Targeted Responses: Late Effects on Molecular Signaling
in Mitochondria. Current Molecular Pharmacology 4: 106-114.
4. Autsavapromporn et al. (2011) Intercellular communication amplifies stressful effects in high-charge, high-energy
(HZE) particle-irradiated human cells. J Radiat Res (Tokyo) in press.
5. de Toledo et al. (2011) The Impact of Adaptive and Non-Targeted Effects in the Biological Responses to Low
Dose/Low Fluence Ionizing Radiation: the Modulating Effect of Linear Energy Transfer. Health Physics 100:290292.