The relative radiation sensitivities of the various compartments of the heart are poorly characterized. Cardiac fibrosis is a common side effect of radiotherapy, suggesting that endothelial barrier function is an important factor in radiation-induced pathology. We employed Electric Cell Substrate Impedance Sensing (ECIS) to assess cytoskeletal rearrangement, permeability changes and endothelial barrier function changes in response to radiation in studies of human coronary arterial endothelial cells (HCAECs). A 5-Gy dose of γ radiation resulted in a significant sixfold transient decrease in transmonolayer resistance 3 h postirradiation (P = 0.001). This decrease in resistance coincided with changes in fluorescent tracer flux (P = 0.05) and display of an actin bundling phenotype. After irradiation, decreases in wound healing (P = 0.03) and micromotion within the monolayer (P = 0.02) were also observed. Time-lapse video studies confirmed that the monolayer is dynamic and showed that cells are extruded from the monolayer at a higher frequency after irradiation. These findings suggest that perturbed endothelial barrier function in the heart can occur at lower doses of γ radiation than previously reported.

Cells generate 2′-deoxyribonucleoside triphosphates (dNTPs) for both replication and repair of damaged DNA predominantly through de novo reduction of intracellular ribonucleotides by ribonucleotide reductase (RNR). Cells can also salvage deoxynucleosides by deoxycytidine kinase/thymidine kinase 1 in the cytosol or by deoxyguanosine kinase/thymidine kinase 2 in mitochondria. In this study we investigated whether the salvage dNTP supply pathway facilitates DNA damage repair, promoting cell survival, when pharmacological inhibition of RNR by 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP, NSC no. 663249) impairs the de novo pathway. Human cervical cancer cells were subjected to radiation with or without 3-AP under medium deoxynucleoside concentrations of 0, 0.05, 0.5 and 5.0 µM. Efficacy of DNA damage repair was assessed by γ-H2AX flow cytometry and focus counts, by single cell electrophoresis (Comet assay), and by caspase 3 cleavage assay as a marker of treatment-induced apoptosis. Cell survival was assessed by colony formation. We found that deoxyribonucleotide salvage facilitates DNA repair during RNR inhibition by 3-AP and that salvage reduces the radiochemosensitivity of human cervical cancer cells.

The sphingomyelin pathway involves the enzymatic cleavage of sphingomyelin to produce ceramide, a second messenger that serves as a key mediator in the rapid apoptotic response to various cell stressors. Low-linear energy transfer (LET) γ radiation can initiate this pathway, independent of DNA damage, via the cell membrane. Whether short-ranged, high-LET α particles, which are of interest as potent environmental carcinogens, radiotherapies and potential components of dirty bombs, can act through this mechanism to signal apoptosis is unknown. Here we show that irradiation of Jurkat cells with α particles emitted by the ²²⁵Ac-DOTA-anti-CD3 IgG antibody construct results in dose-dependent apoptosis. This apoptosis was significantly reduced by pretreating cells with cholesterol-depleting nystatin, a reagent known to inhibit ceramide signaling by interfering with membrane raft coalescence and ceramide-rich platform generation. The effects of nystatin on α-particle-induced apoptosis were related to disruption of the ceramide pathway and not to microdosimetry alterations, because similar results were obtained after external irradiation of the cells with a broad beam of collimated α particles using a planar ²⁴¹Am source. External irradiation allowed for more precise control of the dosimetry and geometry of the irradiation, independent of antibody binding or cell internalization kinetics. Mechanistically consistent with these findings, Jurkat cells rapidly increased membrane concentrations of ceramide after external irradiation with an average of five α-particle traversals per cell. These data indicate that α particles can activate the sphingomyelin pathway to induce apoptosis.

Irradiation time and dose rate are important factors in the evaluation of radiation risk for human health. We previously proposed a novel dose-rate effect model, the modified exponential (MOE) model, which predicts that radiation risks decline exponentially as the dose rate decreases. Here we show that, during the early phase of exposure, up to 1000 h, the proliferation of cells continuously exposed to γ rays at a constant dose rate is gradually suppressed, even as the total dose increases. This trend holds for a number of cell lines including tumor cells, nontransformed fibroblasts and leukocytes. The accumulation of total dose by longer exposure times does not increase this suppressive effect even in cells with a defective DNA repair system, suggesting that risk is determined solely by dose rate in the later phase. The dose-rate effect in the early phase follows the MOE model in DNA repair-proficient cell lines, while cells with impaired DNA-PK or ATM show no dose-rate effect. In the later phase, however, a certain dose-rate effect is observed even in mutant cell lines, and suppression of cell proliferation no longer follows the MOE model. Our results suggest that a distinct mechanism that can operate in the absence of intact DNA-PK or ATM influences the dose-rate effect in the later phase of continuous radiation exposure.

Radiotherapy is commonly employed to treat cancers of the head and neck and is increasingly used to treat other central nervous system (CNS) disorders. Exceeding the radiation tolerance of normal CNS tissues can result in sequelae contributing to patient morbidity and mortality. Animal studies and clinical experience suggest that neuroinflammation plays a role in the etiology of these effects; however, detailed characterization of this response has been lacking. Therefore, a dose–time investigation of the neuroinflammatory response after single-dose cranial irradiation was performed using C57BL/6 mice. Consistent with previous reports, cranial irradiation resulted in multiphasic inflammatory changes exemplified by increased transcript levels of inflammatory cytokines, along with glial and endothelial cell activation. Cranial irradiation also resulted in acute infiltration of neutrophils and a delayed increase in T cells, MHC II-positive cells, and CD11c-positive cells seen first at 1 month with doses ≥15 Gy. CD11c-positive cells were found almost exclusively in white matter and expressed MHC II, suggesting a “mature” dendritic cell phenotype that remained elevated out to 1 year postirradiation. Our results indicate that cranial irradiation leads to persistent neuroinflammatory changes in the C57BL/6 mouse brain that includes unique immunomodulatory cell populations.

Ionizing radiation has been implicated in the development of significant cardiovascular complications. Since radiation exposure is associated with space exploration, astronauts are potentially at increased risk of accelerated cardiovascular disease. This study investigated the effect of high atomic number, high-energy (HZE) iron-ion radiation on vascular and endothelial function as a model of space radiation. Rats were exposed to a single whole-body dose of iron-ion radiation at doses of 0, 0.5 or 1 Gy. In vivo aortic stiffness and ex vivo aortic tension responses were measured 6 and 8 months after exposure as indicators of chronic vascular injury. Rats exposed to 1 Gy iron ions demonstrated significantly increased aortic stiffness, as measured by pulse wave velocity. Aortic rings from irradiated rats exhibited impaired endothelial-dependent relaxation consistent with endothelial dysfunction. Acute xanthine oxidase (XO) inhibition or reactive oxygen species (ROS) scavenging restored endothelial-dependent responses to normal. In addition, XO activity was significantly elevated in rat aorta 4 months after whole-body irradiation. Furthermore, XO inhibition, initiated immediately after radiation exposure and continued until euthanasia, completely inhibited radiation-dependent XO activation. ROS production was elevated after 1 Gy irradiation while production of nitric oxide (NO) was significantly impaired. XO inhibition restored NO and ROS production. Finally, dietary XO inhibition preserved normal endothelial function and vascular stiffness after radiation exposure. These results demonstrate that radiation induced XO-dependent ROS production and nitroso-redox imbalance, leading to chronic vascular dysfunction. As a result, XO is a potential target for radioprotection. Enhancing the understanding of vascular radiation injury could lead to the development of effective methods to ameliorate radiation-induced vascular damage.

Lung cancer is the leading cause of cancer-related death in the United States despite recent advances in our understanding of this challenging disease. An animal model for high-throughput screening of therapeutic agents for advanced lung cancer could help promote the development of more successful treatment interventions. To develop our orthotopic lung cancer model, luciferase-expressing A549 cancer cells were injected into the mediastinum of athymic nude mice. To determine whether the model would allow easy monitoring of response to therapeutic interventions, tumors were treated with 30 mg/kg Paclitaxel or were irradiated with 5 fractions of 2 Gy, and tumor burden was monitored using bioluminescence imaging. Evidence of radiation-induced lung injury was assessed using immunohistochemical staining for phospho-Smad2/3 and cleaved caspase-3. We found that tumor implantation recapitulated advanced human lung cancer as evidenced by tumor establishment and proliferation within the mediastinum. The tumor responded to Paclitaxel or radiation as shown by decreased tumor bioluminescence and improved overall survival. Immunohistochemistry revealed increased phospho-Smad2/3 and cleaved caspase-3 in irradiated lungs, consistent with radiation-induced lung injury. This orthotopic lung cancer model may help provide a method to assess therapeutic interventions in a preclinical setting that recapitulates locally advanced lung cancer.

In a recent epidemiological study, Bayesian uncertainties on lung doses have been calculated to determine lung cancer risk from occupational exposures to plutonium. These calculations used a revised version of the Human Respiratory Tract Model (HRTM) published by the ICRP. In addition to the Bayesian analyses, which give probability distributions of doses, point estimates of doses (single estimates without uncertainty) were also provided for that study using the existing HRTM as it is described in ICRP Publication 66; these are to be used in a preliminary analysis of risk. To infer the differences between the point estimates and Bayesian uncertainty analyses, this paper applies the methodology to former workers of the United Kingdom Atomic Energy Authority (UKAEA), who constituted a subset of the study cohort. The resulting probability distributions of lung doses are compared with the point estimates obtained for each worker. It is shown that mean posterior lung doses are around two- to fourfold higher than point estimates and that uncertainties on doses vary over a wide range, greater than two orders of magnitude for some lung tissues. In addition, we demonstrate that uncertainties on the parameter values, rather than the model structure, are largely responsible for these effects. Of these it appears to be the parameters describing absorption from the lungs to blood that have the greatest impact on estimates of lung doses from urine bioassay. Therefore, accurate determination of the chemical form of inhaled plutonium and the absorption parameter values for these materials is important for obtaining reliable estimates of lung doses and hence risk from occupational exposures to plutonium.

Determination and understanding of out-of-field neutron and photon doses in accelerator-based radiotherapy is an important issue since linear accelerators operating at high energies (>10 MV) produce secondary radiations that irradiate parts of the patient's anatomy distal to the target region, potentially resulting in detrimental health effects. This paper provides a compilation of data (technical and clinical) reported in the literature on the measurement and Monte Carlo simulations of peripheral neutron and photon doses produced from high-energy medical linear accelerators and the reported risk and/or incidence of second primary cancer of tissues distal to the target volume. Information in the tables facilitates easier identification of (1) the various methods and measurement techniques used to determine the out-of-field neutron and photon radiations, (2) reported linac-dependent out-of-field doses, and (3) the risk/incidence of second cancers after radiotherapy due to classic and modern treatment methods. Regardless of the measurement technique and type of accelerator, the neutron dose equivalent per unit photon dose ranges from as low as 0.1 mSv/Gy to as high as 20.4 mSv/Gy. This radiation dose potentially contributes to the induction of second primary cancer in normal tissues outside the treated area.

Ionizing radiation reduces the numbers of neurons expressing activity-regulated cytoskeleton-associated protein (Arc) in the hippocampal dentate gyrus (DG). It is currently unclear if that change relates to cognitive function. We assessed the effects of 1 Gy of head-only ⁵⁶Fe-particle irradiation on hippocampus-dependent and hippocampus-independent fear conditioning and determined how those changes related to Arc expression within the DG. Irradiated mice that did not receive tone-shock pairings on day 1 showed less freezing in the same context on a second day and a lower fraction of Arc-expressing neurons in the free (lower) blade of the DG than sham-irradiated mice. Those data suggested reduced hippocampus-dependent spatial habituation learning. Changes in Arc expression in the free blade correlated positively with freezing in mice that did not receive tone-shock pairings. However, irradiated mice that did receive tone-shock pairings showed enhanced contextual freezing but a reduced percentage of Arc-expressing neurons in the enclosed (upper) blade. Changes in Arc expression correlated negatively with freezing in mice that received tone-shock pairings. In animals receiving cued fear conditioning, radiation did not affect cognitive performance or the fractions of Arc-expressing neurons. While the relationship between Arc expression and cognitive performance is complex, our data suggest that radiation effects on hippocampus-dependent cognition might depend on the prominence (salience) of environmental stimuli and blade-specific Arc expression.