Nontargeted Stressful Effects in Normal Human Fibroblast Cultures Exposed to Low Fluences of High Charge, High Energy (HZE) Particles: Kinetics of Biologic Responses and Significance of Secondary Radiations

Abstract

The induction of nontargeted stressful effects in cell populations exposed to low fluences of high charge (Z) and high energy (E) particles is relevant to estimates of the health risks of space radiation. We investigated the up-regulation of stress markers in confluent normal human fibroblast cultures exposed to 1,000 MeV/u iron ions [linear energy transfer (LET) ~151 keV/μm] or 600 MeV/u silicon ions (LET ~50 keV/μm) at mean absorbed doses as low as 0.2 cGy, wherein 1–3% of the cells were targeted through the nucleus by a primary particle. Within 24 h postirradiation, significant increases in the levels of phospho-TP53 (serine 15), p21Waf1 (CDKN1A), HDM2, phospho-ERK1/2, protein carbonylation and lipid peroxidation were detected, which suggested participation in the stress response of cells not targeted by primary particles. This was supported by in situ studies that indicated greater increases in 53BP1 foci formation, a marker of DNA damage. than expected from the number of primary particle traversals. The effect was expressed as early as 15 min after exposure, peaked at 1 h and decreased by 24 h. A similar tendency occurred after exposure of the cell cultures to 0.2 cGy of 3.7 MeV α particles (LET ~109 keV/μm) that targets ~1.6% of nuclei, but not after 0.2 cGy from 290 MeV/u carbon ions (LET ~13 keV/μm) by which, on average, ~13% of the nuclei were hit, which highlights the importance of radiation quality in the induced effect. Simulations with the FLUKA multi-particle transport code revealed that fragmentation products, other than electrons, in cell cultures exposed to HZE particles comprise <1% of the absorbed dose. Further, the radial spread of dose due to secondary heavy ion fragments is confined to approximately 10–20 μm. Thus, the latter are unlikely to significantly contribute to stressful effects in cells not targeted by primary HZE particles.

Gap Junction Communication and the Propagation of Bystander Effects Induced by Microbeam Irradiation in Human Fibroblast Cultures: The Impact of Radiation Quality

“…The ranges of δ rays produced after high-LET radiation such as high energy and high atomic number (HZE) particles can extend up to several cell diameters (40, 41). The cells traversed by δ rays may therefore also experience biological change.…”

Health Risks of Space Exploration: Targeted and Nontargeted Oxidative Injury by High-Charge and High-Energy Particles

“…The accumulation of 4-hydroxynonenal (4-HNE) adducts in proteins from the same cultures indicates that increased lipid peroxidation was involved (Fig. 8B) (101). Together, these data strongly suggest the propagation of oxidative stress to cells not targeted by primary iron ions.…”

“…In this respect, the evaluation of the cellular absorbed dose due to d rays is essential when apparent nontargeted effects are assessed following the exposure of confluent cell cultures to very low fluences of HZE particles. This dose can be as high as 30-40% of the total dose deposited by an HZE particle (62,101,209). However, a particles emitted from common radioactive sources (e.g., 238 Pu or 241 Am) used for cellular experiments do not pose such problems.…”

“…These studies allow the estimation of the fraction of cells that are not targeted by fragmentation products and also the fraction of cells that are hit by these products together with the doses received. Importantly, they permit the quantification of the radial distribution of the secondary particles as was recently shown (101).…”

“…3). Monte-Carlo simulations using programs such as FLUKA and MCNPX multiparticle transport codes are greatly enhancing our understanding of the contribution of secondary radiations in HZE particle-induced bystander effects (101,162). These studies allow the estimation of the fraction of cells that are not targeted by fragmentation products and also the fraction of cells that are hit by these products together with the doses received.…”