Outer space is a complex environment with various phenomena that negatively affect bone metabolism, including microgravity and highly energized ionizing radiation. In the present study, we used four groups of male Wistar rats treated with or without four-week hindlimb suspension after 4 Gy of X-rays to test whether there is a combined effect for hindlimb suspension and X-ray radiation. We tested trabecular parameters and some cytokines of the bone as leading indicators of bone metabolism. The results showed that hindlimb suspension and X-ray radiation could cause a significant increase in bone loss. Hindlimb suspension caused a 56.6% bone loss (P = 0.036), while X-ray radiation caused a 30.7% (P = 0.041) bone loss when compared with the control group. The combined factors of hindlimb suspension and X-rays exerted a combined effect on bone mass, with a reduction of 64.8% (P = 0.003).

Potentially lethal damage (PLD) and its repair (PLDR) were studied in confluent human fibroblasts by analyzing the kinetics of chromosome break rejoining after X-ray or heavy-ion exposures. Cells were either held in the non-cycling G0 phase of the cell cycle for 12 h, or forced to proliferate immediately after irradiation. Fusion premature chromosome condensation (PCC) was combined with fluorescence in situ hybridization (FISH) to study chromosomal aberrations in interphase. The culture condition had no impact on the rejoining kinetics of PCC breaks during the 12 h after X-ray or heavy-ion irradiation. However, 12 h after X-ray and silicon irradiation, cycling cells had more chromosome exchanges than non-cycling cells. After 6 Gy X-rays, the yield of exchanges in cycling cells was 2.8 times higher than that in non-cycling cells, and after 2 Gy of 55 keV/μm silicon ions the yield of exchanges in cycling cells was twice that of non-cycling cells. In contrast, after exposure to 2 Gy 200-keV/μm or 440-keV/μm iron ions the yield of exchanges was similar in non-cycling and cycling cells. Since the majority of repair in G0/G1 occurs via the non-homologous end joining process (NHEJ), increased PLDR in X-ray and silicon-ion irradiated cells may result from improved cell cycle-specific rejoining fidelity through the NHEJ pathway, which is not the case in high-LET iron-ion irradiated cells.

High atomic number and high-energy (HZE) particles in deep space are of low abundance but substantially contribute to the biological effects of space radiation. Shielding is so far the most effective way to partially protect astronauts from these highly penetrating particles. However, simulated calculations and measurements have predicted that secondary particles resulting from the shielding of cosmic rays produce a significant fraction of the total dose and dose equivalent. In this study, we investigated the biological effects of secondary radiation with two cell types, and with cells exposed in different phases of the cell cycle, by comparing the biological effects of a 200 MeV/u iron beam with a shielded beam in which the energy of the iron ion beam was decreased from 500 MeV/u to 200 MeV/u with PMMA, polyethylene (PE), or aluminum. We found that beam shielding resulted in increased induction of 53BP1 foci and micronuclei in a cell-type-dependent manner compared with the unshielded 200 MeV/u Fe ion beam. These findings provide experimental proof that the biological effects of secondary particles resulting from the interaction between HZE particles and shielding materials should be considered in shielding design.

Lung cancer is one of the highest health risks caused by ionizing radiation, which induces both direct effects and non-targeted effects. However, whether radiation-induced non-targeted effects result in epithelial-mesenchymal transition, a critical process during tumorigenesis, in non-targeted lung tissues remains unknown. In the present study, Kunming mice were subjected to whole-body, cranial or local abdominal irradiation of single-dose or fractionated 4 Gy X-rays, and the expressions of epithelial-mesenchymal transition markers in non-targeted lung tissues were assessed by both qRT-PCR and immunofluorescent staining. It was found that the epithelial marker was downregulated while the mesenchymal markers were upregulated significantly in non-targeted lung tissues of the irradiated mice. Local abdominal irradiation was more efficient in inducing epithelial-mesenchymal transition than whole-body or cranial irradiation when the fractionated irradiation method was adopted. In addition, the intraperitoneal administration of celecoxib suppressed epithelial-mesenchymal transition in the non-targeted lung tissues. In conclusion, our findings suggest that epithelial-mesenchymal transition is induced in non-targeted lung tissues, but can be suppressed by inhibition of cyclooxygenase-2 by celecoxib.

Melanoma is a malignant tumor with high invasive and metastatic properties. Though radiation is the major therapy for melanoma, its radio-resistance has been shown to severely influence the clinical outcome. So it is imperative to enhance the sensitivity of uveal melanoma cells to radiotherapy. Previously, we found that the cell cycle of 92-1 uveal melanoma cells was suspended and remained unchanged for up to 5 days after exposure to 10 Gy of X-rays, which might be relevant to the high radio-sensitivity of 92-1 cells. To further investigate the cell cycle suspension-associated proteins, we employed two analyses with stable isotope labeling with amino acids in cell culture technology and two-dimensional liquid chromatography tandem mass spectrometry. Cells were incubated for 15 h or 48 h after irradiation with 10 Gy of X-rays. We identified a total of 737 proteins at 15 h (Group A) and 530 proteins at 48 h post-irradiation (Group B). The gene ontology biological pathway was used to obtain a systems level view of proteome changes in 92-1cells under cell cycle suspension. We further selected the significantly changed proteins for investigation of their potential contribution to cell cycle suspension, growth arrest and cell senescence. These proteins are involved in the cell cycle, stress response, glycolysis and the tricarboxylic acid cycle, etc. Our study expected to reveal potential marker proteins associated with cell suspension induced by irradiation, which might contribute to understanding the mechanism beyond the cell cycle suspension.

Radiation-induced bone loss is a potential health concern for cancer patients undergoing radiotherapy. Enhanced bone resorption by osteoclasts and decreased bone formation by osteoblasts were thought to be the main reasons. In this study, we showed that both pre-differentiating and differentiating osteoclasts were relatively sensitive to X-rays compared with osteoblasts. X-rays decreased cell viability to a greater degree in RAW264.7 cells and in differentiating cells than than in osteoblastic MC3T3-E1 cells. X-rays at up to 8 Gy had little effects on osteoblast mineralization. In contrast, X-rays at 1 Gy induced enhanced osteoclastogenesis by enhanced cell fusion, but had no effects on bone resorption. A higher dose of X-rays at 8 Gy, however, had an inhibitory effect on bone resorption. In addition, actin ring formation was disrupted by 8 Gy of X-rays and reorganized into clusters. An increased activity of Caspase 3 was found after X-ray exposure. Actin disorganization and increased apoptosis may be the potential effects of X-rays at high doses, by inhibiting osteoclast differentiation. Taken together, our data indicate high radiosensitivity of osteoclasts. X-ray irradiation at relatively low doses can activate osteoclastogenesis, but not osteogenic differentiation. The radiosensitive osteoclasts are the potentially responsive cells for X-ray-induced bone loss.