Dose dependent radiation-induced hypotension in the canine

Radiation-induced early transient incapacitation (ETI) is often accompanied by severe systemic hypotension. However, postradiation hypotension does not occur with equal frequency in all species and is not reported with consistency in the canine. In an attempt to clarify the differences in reported canine postradiation blood pressures, canine systemic blood pressures were determined both before and after exposure to gamma radiation of either 80 Gy or 100 Gy. Data obtained from six sham-radiated beagles and 12 radiated beagles indicated that 100 Gy, whole-body, gamma radiation produced a decrease in systemic mean blood pressure while 80 Gy, whole-body, gamma radiation did not. Analysis of this data could be consistent with a quantal response to a gamma radiation dose between 80 Gy and 100 Gy.     

Arsenic trioxide enhances radiation response of 9L glioma in the rat brain

Arsenic trioxide (ATO) at low doses induces leukemia cells to undergo apoptosis and at higher doses causes blood flow to solid tumors to shut down. To determine whether a potential synergistic interaction exists between ATO at the non-toxic dose level in the rat and radiation, the present study was carried out with orthotopic 9L malignant gliomas growing in the brains of rats. Animals died within 50 days of treatment when 12-day-old 9L gliomas growing in the brain of Fischer rats were treated with either the drug alone (8 mg/kg) or radiation alone (25 Gy). In contrast, the overall tumor cure rate exceeded 50% at a follow-up time of 120 days after the combined treatment with radiation and ATO. Long-term surviving animals showed no clinical or disproportionately enhanced histopathological changes in the brain parenchyma. Early changes in tumor physiology showed that the vascular leakage of FITC-dextran conjugates was apparent within 8 h of drug administration. Last, the use of diffusion magnetic resonance imaging as an early surrogate marker of therapeutic efficacy corroborated the effects of drug with and without radiation on brain histology and animal survival.     

Time- and dose-dependent changes in neuronal activity produced by X radiation in brain slices

A new method of exposing tissues to X rays in a lead Faraday cage has made it possible to examine directly radiation damage to isolated neuronal tissue. Thin slices of hippocampus from brains of euthanized guinea pigs were exposed to 17.4 ke V X radiation. Electrophysiological recordings were made before, during, and after exposure to doses between 5 and 65 Gy at a dose rate of 1.54 Gy/min. Following exposure to doses of 40 Gy and greater, the synaptic potential was enhanced, reaching a steady level soon after exposure. The ability of the synaptic potential to generate a spike was reduced and damage progressed after termination of the radiation exposure. Recovery was not observed following termination of exposure. These results demonstrate that an isolated neuronal network can show complex changes in electrophysiological properties following moderate doses of ionizing radiation. An investigation of radiation damage directly to neurons in vitro will contribute to the understanding of the underlying mechanisms of radiation-induced nervous system dysfunction.     

The effect of ionizing radiation at superhigh doses on the processes of dopamine release and reuptake by nerve endings in different sections of the brain]

Rats exposed to fast 24 MeV electrons (100 Gy) at the state of early transient incapacity (ETI) exhibited active release and reuptake of dopamine in nerve terminals of the striatum. No changes in the indices under study were found in rats exposed to 25 Gy radiation that did not cause the ETI development. The in vitro irradiation of the isolated synaptosomes (100 Gy) inhibited dopamine reuptake and increased the number of sites of 3H-spiperone binding to D2-receptors in a membrane fraction isolated from the striatum.     

Cell cycle changes and cytotoxicity in irradiated cultures of bovine aortic endothelial cells

The purpose of this experiment was to determine the effect of ionizing radiation on cell number, lactate dehydrogenase (LDH) release, cell cycle distribution, [3H]thymidine incorporation, and autoradiographic labeling index in bovine aortic endothelial cells in vitro. Confluent endothelial monolayers were exposed to single doses of 0.5-10 Gy of 60Co gamma rays and were analyzed from 2 to 24 h postirradiation. Irradiated monolayers exhibited a time- and dose-dependent decrease in cell number, increase in LDH release, and redistribution of cells in the cell cycle. Cell cycle redistribution included an increase in the proportion of cells in S phase at 4 h after irradiation and a decrease in S phase at 24 h. The cells also exhibited a decrease in [3H]thymidine incorporation as early as 2 h after 5 Gy. This represented the most rapid radiation response observed in the present study. These data demonstrate that radiation cytotoxicity in confluent, plateau-phase endothelial monolayers is accompanied by changes in the cell cycle distribution of adherent cells, and that reduced [3H]thymidine incorporation is an early marker of radiation injury in this clinically important cell type.     

Magnetic resonance imaging and spectroscopy of the rat hippocampus 1 month after exposure to 56Fe-particle radiation

The response of the central nervous system to space radiation is largely unknown. The hippocampus, which is known for its critical role in learning and memory, was evaluated for its response to heavy-ion radiation. At 1 month, animals exposed to brain-only 56Fe-particle irradiation (0-4 Gy) were examined using contrast-enhanced T1 imaging (CET1), T2-weighted imaging (T2WI), diffusion weighted imaging (DWI), and (1)H-magnetic resonance spectroscopy (MRS). Correlative histology was performed after imaging. The T2WI, DWI and CET1 images revealed no overt anatomical changes after irradiation. Quantitative analysis demonstrated a significant increase in T2 at 2 Gy compared to 0 Gy. The apparent diffusion coefficient (ADC) revealed an inverse dose-dependent quantitative change in water mobility. Compared to 0 Gy, the ADC increased 122% at 1 Gy and declined to 44% above control levels at 4 Gy. MRS showed a significant increase in the N-acetylaspartate/choline ratio at 4 Gy and a lactate peak. Histology demonstrated no overt pathological changes in neuronal and astrocyte populations. However, a significant inverse dose-dependent morphological change in the microglial population was detected in irradiated animals. Our results suggest that early tissue matrix modifications induced by 56Fe-particle radiation can be detected by MRI in the absence of evident histopathology. These changes may indicate fundamental changes in the structure and function of the hippocampus.     

State of the reproductive system and liver in male rats after fractionated radiation exposure to low doses as well as in their progeny

Male rats were exposed to fractionated 0.1 Gy radiation in early onthogenesis (1 month). Essential changes in reproductive system and liver were found. First generation offspring of the exposed males and females showed moderate radiation changes more expressed in immature rats.     

Post-irradiation changes in the content of phospholipids and cyclic nucleotides in the mouse brain]

The effect of ionizing radiation (5, 20, 100, 200 and 400 Gy) on the content of phospholipids and cyclic nucleotides in the brain tissue has been studied in experiments on albino mice. During the development of evident behavioural disturbances in irradiated mice (2 h after irradiation with doses 100-400 Gy), significant changes were observed in the content of phosphatidylinositides and cyclic GMP. These changes may account for disturbances in the function of the central nervous system during cerebral forms of acute radiation injury.     

Changes in MicroRNA expression patterns in human fibroblasts after low-LET radiation

Exposure to radiation provokes cellular responses controlled in part by gene expression networks. MicroRNAs (miRNAs) are small non-coding RNAs which mostly regulate gene expression by degrading the messages or inhibiting translation. Here, we investigated changes in miRNA expression patterns after low (0.1 Gy) and high (2.0 Gy) doses of X-ray in human fibroblasts. At early (0.5 h) and late (6 and 24 h) time points, irradiation caused qualitative and quantitative differences in the down-regulation of miRNA levels, including miR-92b, 137, 660, and 656. A transient up-regulation of miRNAs was observed after 2 h post-irradiation following high doses of radiation, including miR-558 and 662. MicroRNA levels were inversely correlated with targets from mRNA and proteomic profiling after 2.0 Gy of radiation. MicroRNAs miR-579, 608, 548-3p, and 585 are noted for targeting genes involved in radioresponsive mechanisms, such as cell cycle checkpoint and apoptosis. We suggest here a model in which miRNAs may act as "hub" regulators of specific cellular responses, immediately down-regulated so as to stimulate DNA repair mechanisms, followed by up-regulation involved in suppressing apoptosis for cell survival. Taken together, miRNAs may mediate signaling pathways in sequential fashion in response to radiation, and may serve as biodosimetric markers of radiation exposure.     

Modification of radiation damage in the canine kidney by hyperthermia: a histologic and functional study

The purpose of this study was to evaluate the effect of hyperthermia on the histologic and functional response of the canine kidney, a late-responding normal tissue, to irradiation. Both kidneys were irradiated. Radiation was delivered in single doses of 0, 10, or 15 Gy. Whole-body hyperthermia was used to produce renal kidney temperatures approximating 42.0 degrees C for 60 min. Thirty-six beagles were placed randomly in the following six treatment groups: control, whole-body hyperthermia alone, 10 Gy alone, 10 Gy + whole-body hyperthermia, 15 Gy alone, and 15 Gy + whole-body hyperthermia. Renal histologic and functional changes were assessed at 1 to 9 months after therapy. No changes were seen in glomerular filtration rate or renal tissue volumes in control or hyperthermia alone groups. Renal vascular and glomerular volumes were not affected significantly by any combination of hyperthermia and/or radiation. In all groups receiving radiation, glomerular filtration rate decreased, percentage renal tubular volume decreased, and interstitial volume increased significantly after therapy. The magnitude of these changes in the functional and histologic response of the kidney and the latent period before expression of this damage were dependent on radiation dose. However, hyperthermia did not modify expression of radiation damage in the kidney based on glomerular filtration rate and histologic quantification of renal tissue components.     

The effect of ionizing radiation at superhigh dosages on the ATP content in the rat brain

The ATP content of rat brain was shown to decrease considerably (20-60%) during the first minutes following high-energy electron irradiation with doses of 300 and 500 Gy. A transient nature of changes and a more pronounced decrease in ATP with increasing radiation dose and manifest neurologic disturbances indicate that the energy metabolism is involved in the pathogenesis of early neurologic disturbances in animals.     

Karyometric characteristics of the rat sensorimotor cortex in non-uniform gamma irradiation

Neurocyte nuclei increase in volume without structural changes in karyoplasm at early times after gamma-irradiation of rat head with doses of 50 to 100 Gy. Irradiation of 200 Gy causes a diminution of the nuclei volume while at a dose of 400 Gy the nuclei do not change their volume. A dose as high as 1000 Gy causes severe changes in the karyoplasm leading to nucleus swelling. At later times (24-72 h), the increase in the nuclei volume is associated with the changes in the karyoplasm structure. At one and the same dose, radiation causes either a decrease (irradiation of the head) or increase (exposure of the body) in the neurocyte nuclei volume. At early times after wholebody uniform irradiation no karyometric changes are detected. The nucleus swelling is more pronounced at lower dose-rates.     

Response of avian embryonic brain to spatially segmented x-ray microbeams.

Duck embryo was studied as a model for assessing the effects of microbeam radiation therapy (MRT) on the human infant brain. Because of the high risk of radiation-induced disruption of the developmental process in the immature brain, conventional wide-beam radiotherapy of brain tumors is seldom carried out in infants under the age of three. Other types of treatment for pediatric brain tumors are frequently ineffective. Recent findings from studies in Grenoble on the brain of suckling rats indicate that MRT could be of benefit for the treatment of early childhood tumors. In our studies, duck embryos were irradiated at 3-4 days prior to hatching. Irradiation was carried out using a single exposure of synchrotron-generated X-rays, either in the form of parallel microplanar beams (microbeams), or as non-segmented broad beam. The individual microplanar beams had a width of 27 microm and height of 11 mm, and a center-to-center spacing of 100 microm. Doses to the exposed areas of embryo brain were 40, 80, 160 and 450 Gy (in-slice dose) for the microbeam, and 6, 12 and 18 Gy for the broad beam. The biological end point employed in the study was ataxia. This neurological symptom of radiation damage to the brain developed within 75 days of hatching. Histopathological analysis of brain tissue did not reveal any radiation induced lesions for microbeam doses of 40-160 Gy (in-slice), although some incidences of ataxia were observed in that dose group. However, severe brain lesions did occur in animals in the 450 Gy microbeam dose groups, and mild lesions in the 18 Gy broad beam dose group. These results indicate that embryonic duck brain has an appreciably higher tolerance to the microbeam modality, as compared to the broad beam modality. When the microbeam dose was normalized to the full volume of the irradiated tissue. i.e., the dose averaged over microbeams and the space between the microbeams, brain tolerance was estimated to be about three times higher to microbeam irradiation as compared with broad beam irradiation.     

Changes in vascular permeability following thorax irradiation in the rat

A double isotope technique was used to measure changes in the vascular permeability surface area product (PS) for albumin after irradiation. PS was measured in several tissues of the rat during the first 38 days following 11, 13.5, 18, or 25 Gy whole thorax irradiation. After 18 and 25 Gy most irradiated and nonirradiated (shielded) tissues showed elevated permeability at 1 day after radiation, which declined to control levels by Day 4. All irradiated tissues showed a second wave of increased permeability between 14 and 38 days after radiation that varied in onset and extent depending upon tissue and dose. Lung and heart showed a direct response to dose between 11 and 18 Gy during this period. Peak lung values averaged three times control values at 19 days after 18 Gy. Peak heart values averaged twice control values at the same time and dose. The double isotope technique has proven to be a reliable means of quantitatively determining vascular permeability response to radiation over time.     

Gene expression profiles of normal human fibroblasts after exposure to ionizing radiation: a comparative study of low and high doses

Several types of cellular responses to ionizing radiation, such as the adaptive response or the bystander effect, suggest that low-dose radiation may possess characteristics that distinguish it from its high-dose counterpart. Accumulated evidence also implies that the biological effects of low-dose and high-dose ionizing radiation are not linearly distributed. We have investigated, for the first time, global gene expression changes induced by ionizing radiation at doses as low as 2 cGy and have compared this to expression changes at 4 Gy. We applied cDNA microarray analyses to G1-arrested normal human skin fibroblasts subjected to X irradiation. Our data suggest that both qualitative and quantitative differences exist between gene expression profiles induced by 2 cGy and 4 Gy. The predominant functional groups responding to low-dose radiation are those involved in cell-cell signaling, signal transduction, development and DNA damage responses. At high dose, the responding genes are involved in apoptosis and cell proliferation. Interestingly, several genes, such as cytoskeleton components ANLN and KRT15 and cell-cell signaling genes GRAP2 and GPR51, were found to respond to low-dose radiation but not to high-dose radiation. Pathways that are specifically activated by low-dose radiation were also evident. These quantitative and qualitative differences in gene expression changes may help explain the non-linear correlation of biological effects of ionizing radiation from low dose to high dose.     

Radiation-induced vascular damage in tumors: implications of vascular damage in ablative hypofractionated radiotherapy (SBRT and SRS)

We have reviewed the studies on radiation-induced vascular changes in human and experimental tumors reported in the last several decades. Although the reported results are inconsistent, they can be generalized as follows. In the human tumors treated with conventional fractionated radiotherapy, the morphological and functional status of the vasculature is preserved, if not improved, during the early part of a treatment course and then decreases toward the end of treatment. Irradiation of human tumor xenografts or rodent tumors with 5-10 Gy in a single dose causes relatively mild vascular damages, but increasing the radiation dose to higher than 10 Gy/fraction induces severe vascular damage resulting in reduced blood perfusion. Little is known about the vascular changes in human tumors treated with high-dose hypofractionated radiation such as stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS). However, the results for experimental tumors strongly indicate that SBRT or SRS of human tumors with doses higher than about 10 Gy/fraction is likely to induce considerable vascular damages and thereby damages the intratumor microenvironment, leading to indirect tumor cell death. Vascular damage may play an important role in the response of human tumors to high-dose hypofractionated SBRT or SRS.     

Effect of a topical treatment in organotypic culture of human breast skin after exposure to gamma-rays

The early radiation of epidermal reactions can lead to healing of the lesion or radiation necrosis. There is no general agreement for either the prevention and/or treatment of radiation skin response, also as little is known about the immediate phases of this phenomenon. We investigated the early effects exerted by Healing and Wound Emulsion (HWE) on human skin response after ionizing radiation. Epidermal morphology, Heat Shock Protein (HSP) 70, and Transforming Growth Factor-beta1 (TGF-beta1) gene expression were investigated in organotypic human skin cultures undergoing a double dose of gamma-rays (2 Gy). HSP70 gene expression tended to be induced in the HWE group 6 hours after cream administration and was significantly up-regulated after 48 hours, when epidermal morphological alterations were evident. TGF-beta1 seems not affected in cream treated samples. HWE may stimulate skin to mount an early defensive response against damage induced by gamma rays.     

Marked depression of radiation-induced emesis in frogs following prior exposure to a brief dose of X-rays

Acute emesis response to harmful doses of X-rays on frogs (Rana porosa porosa) was examined. Results showed that the number of radioemesis events following exposure to 0.85 Gy was slightly higher than in the sham control animals. The increase in emesis action became more pronounced when the total dose of radiation was raised to 2.5 Gy. Only 1 frog out of a total of 12 did not show vomiting following radiation, while no response was observed in sham control animals. Note that animals in which the low dose rate of radiation was applied to whole body did not display any changes in the emesis response relative to control animals. The present studies, and those by others, showed that a brief dose of X-rays prior to a second exposure to a sub-lethal dose might induce a tolerance to radiation. An additional experiment was conducted to examine whether a small conditioning dose could induce a depression of radioemesis (tolerance) following an exposure to high dose X-ray. With prior exposure to 0.3 Gy, only 1 frog out of a total of 5 frogs vomited as a result of radiation exposure. Suppression of the emetic response became significant when the pre-radiation dose was decreased to 0.1 Gy. On the contrary, increasing the small conditioning dose to 0.5 Gy resulted in a remarkable rise of radiation-induced emesis. This results indicate that exposure to the smaller dose of X-rays elicits a tolerance effect to toxic dose level of radiation.     

Pathology of delayed radiation brain damage: an experimental canine model

Delayed radiation damage of normal brain can be a devastating complication of radiation therapy and generally occurs months to years after the initiation of therapy. Primarily restricted to the white matter, radiation damage is characterized by a number of histopathologic changes including coagulation necrosis, vascular alterations with fibrinoid necrosis, edema, and demyelination. Normal dogs were exposed to either 10, 15, or 30 Gy of X rays to a single hemisphere and the gross and histopathologic changes were evaluated qualitatively. A spectrum of changes was observed ranging from white matter edema to extensive white matter necrosis, and the extent, location, and type of damage were dependent upon radiation dose. Histopathologic changes were separated into three major categories based on the character and size of the lesions, with the most severe changes being similar to the types of changes described in human patients who have developed delayed radiation necrosis. Less severe forms of damage such as multifocal, sometimes confluent areas of microscopic necrosis with spongiotic borders and edema with severe axonal swelling were also observed. These latter changes are not well recognized as being due to radiation. The findings of this study also indicate that many of the changes ascribed to combined treatment with methotrexate and radiation in humans are induced in the normal dog brain by radiation alone. The results of his study show that the dog is a suitable model of the human brain for studying radiation brain injury and may be useful for investigation of drug-radiation interactions.