Xiao Wen Mao

Acute Effects of Whole-Body Proton Irradiation on the Immune System of the Mouse

Abstract Kajioka, E. H., Andres, M. L., Li, J., Mao, X. W., Moyers, M. F., Nelson, G. A., Slater, J. M. and Gridley, D. S. Acute Effects of Whole-Body Proton Irradiation on the Immune System of the Mouse. The acute effects of proton whole-body irradiation on the distribution and function of leukocyte populations in the spleen and blood were examined and compared to the effects of photons derived from a 60Co γ-ray source. Adult female C57BL/6 mice were exposed to a single dose (3 Gy at 0.4 Gy/min) of protons at spread-out Bragg peak (SOBP), protons at the distal entry (E) region, or γ rays and killed humanely at six different times thereafter. Specific differences were noted in the results, thereby suggesting that the kinetics of the response may be variable. However, the lack of significant differences in most assays at most times suggests that the RBE for both entry and peak regions of the Bragg curve was essentially 1.0 under the conditions of this study. The greatest immunodepression was observed at 4 days postexposure. Flow cytometry and mitogenic stimulation analyses of the spleen and peripheral blood demonstrated that lymphocyte populations differ in radiosensitivity, with B (CD19+) cells being most sensitive, T (CD3+) cells being moderately sensitive, and natural killer (NK1.1+) cells being most resistant. B lymphocytes showed the most rapid recovery. Comparison of the T-lymphocyte subsets showed that CD4+ T helper/inducer cells were more radiosensitive than the CD8+ T cytotoxic/suppressor cells. These findings should have an impact on future studies designed to maximize protection of normal tissue during and after proton-radiation exposure.

Spaceflight Environment Induces Mitochondrial Oxidative Damage in Ocular Tissue

A recent report shows that more than 30% of the astronauts returning from Space Shuttle missions or the International Space Station (ISS) were diagnosed with eye problems that can cause reduced visual acuity. We investigate here whether spaceflight environment-associated retinal damage might be related to oxidative stress-induced mitochondrial apoptosis. Female C57BL/6 mice were flown in the space shuttle Atlantis (STS-135), and within 3–5 h of landing, the spaceflight and ground-control mice, similarly housed in animal enclosure modules (AEMs) were euthanized and their eyes were removed for analysis. Changes in expression of genes involved in oxidative stress, mitochondrial and endothelial cell biology were examined. Apoptosis in the retina was analyzed by caspase-3 immunocytochemical analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Levels of 4-hydroxynonenal (4-HNE) protein, an oxidative specific marker for lipid peroxidation were also measured. Evaluation of spaceflight mice and AEM ground-control mice showed that expression of several genes playing central roles in regulating the mitochondria-associated apoptotic pathway were significantly altered in mouse ocular tissue after spaceflight compared to AEM ground-control mice. In addition, the mRNA levels of several genes, which are responsible for regulating the production of reactive oxygen species were also significantly up-regulated in spaceflight samples compared to AEM ground-control mice. Further more, the level of HNE protein was significantly elevated in the retina after spaceflight compared to controls. Our results also revealed that spaceflight conditions induced significant apoptosis in the retina especially inner nuclear layer (INL) and ganglion cell layer (GCL) compared to AEM ground controls. The data provided the first evidence that spaceflight conditions induce oxidative damage that results in mitochondrial apoptosis in the retina. This data suggest that astronauts may be at increased risk for late retinal degeneration.

What is the Role of Radiation in the Treatment of Subfoveal Membranes: Review of Radiobiologic, Pathologic, and Other Considerations to Initiate a Multimodality Discussion

BACKGROUND Single-dose-fraction conformal proton beam and multiple-fraction X ray dose schedules have been used to treat subfoveal neovascular membranes. All schedules successfully controlled membrane progression, stabilized vision in most patients, and increased visual acuity in some. Conformal protons also decreased the radiation dose to healthy tissues outside the designated volume (16 mm in diameter). It appears that radiation therapy could be useful and cost-effective, but neither the optimal time-dose schedule single or multiple dose fractions nor the type of radiation proton conformal beam or x-ray therapy are defined. METHODS By means of an extensive literature survey, we reviewed the rationale for using radiation to treat subfoveal neovascularization, examined a paradigm of radiation interaction with tissue, reviewed the histopathology of neovascular membranes, and documented the role of growth factors in the pathophysiology of the disease. Accepting that the eye is an extracranial brain extension, and that its microvasculature has properties similar to brain microvessels, we reviewed the radiobiologic response of brain microvessels. We also revisited the controversy concerning the efficacy of single-dose-fraction vs. multifraction schedules. RESULTS This paper outlines parameters within which radiation therapys role might be defined, and proposes a clinical radiation-biology scoring program to evaluate radiation effects, based on the SOMA concept. CONCLUSION A prospective, controlled clinical trial is feasible and is indicated to determine radiation therapys role in managing the proliferative component of age-related macular degeneration.

High-LET Radiation-Induced Response of Microvessels in the Hippocampus

Abstract The hippocampus is critical for learning and memory, and injury to this structure is associated with cognitive deficits. The response of the hippocampal microvessels after a relatively low dose of high-LET radiation remains unclear. In this study, endothelial population changes in hippocampal microvessels exposed to 56Fe ions at doses of 0, 0.5, 2 and 4 Gy were quantified using unbiased stereological techniques. Twelve months after exposure, mice that received 0.5 Gy or 2 Gy of iron ions showed a 34% or 29% loss of endothelial cells, respectively, in the hippocampal cornu ammonis region 1 (CA1) compared to age-matched controls or mice that received 4 Gy (P < 0.05). We suggest that this “U-shaped” dose response indicates a repopulation from a sensitive subset of endothelial cells that occurred after 4 Gy that was stimulated by an initial rapid loss of endothelial cells. In contrast to the CA1, in the dentate gyrus (DG), there was no significant difference in microvessel cell and length density between irradiated groups and age-matched controls. Vascular topology differences between CA1 and DG may account for the variation in dose response. The correlation between radiation-induced alterations in the hippocampal microvessels and their functional consequences must be investigated in further studies.

Radioprotective Effect of a Metalloporphyrin Compound in Rat Eye Model

Purpose: The purpose of this study was to evaluate the efficacy of the antioxidant Mn (III) tetrakis (N-ethylpyridinium-2-yl) porphyrin (MnTE-2-PyP) in protecting ocular tissue and retinal microvasculature from radiation damage. Materials and Methods: 75 rats were treated with Mn TE-2-PyP at 2.5 μ g/injection into one eye an hour before proton irradiation. The radiation was delivered in a single fraction to total doses of 8 Gray (Gy) or 28 Gy; Rats were sacrificed 3 days and 3, 6, 9, and 12 months thereafter for histology and quantification of photoreceptor cell populations and retinal capillary changes. Results: By 6 months following radiation, there was significant loss of retinal outer and inner nuclear layers in eyes receiving radiation only (8 and 28 Gy) (p < 0.05) compared to their controls and to the eyes of rats treated with radiation plus metalloporphyrin. Retinal microvessel length density decreased significantly 6 months following 28 Gy (p < 0.05) compared to their controls and to MnTE-2-PyP treated rats. By 12 months following irradiation, irradiated eyes showed extensive damage to the photoreceptor layer, whereas the eyes of animals receiving radiation plus MnTE-2-PyP showed almost no morphological damage. MnTE-2-PyP treatment also suppressed radiation-induced apoptosis in our study. Conclusions: These results demonstrated that MnTE-2-PyP protected both photoreceptors and retinal capillaries from radiation damage, suggesting that this metalloporphyrin antioxidant is effective in regulating the damage induced by proton radiation.

Low-dose Photon and Simulated Solar Particle Event Proton Effects on Foxp3+ T Regulatory Cells and other Leukocytes

Radiation is a major factor in the spaceflight environment that has carcinogenic potential. Astronauts on missions are continuously exposed to low-dose/low-dose-rate (LDR) radiation and may receive relatively high doses during a solar particle event (SPE) that consists primarily of protons. However, there are very few reports in which LDR photons were combined with protons. In this study, C57BL/6 mice were exposed to 1.7 Gy simulated SPE (sSPE) protons over 36 h, both with and without pre-exposure to 0.01 Gray (Gy) LDR γ-rays at 0.018 cGy/h. Apoptosis in skin samples was determined by immunohistochemistry immediately post-irradiation (day 0). Spleen mass relative to body mass, white blood cells (WBC), major leukocyte populations, lymphocyte subsets (T, Th, Tc, B, NK), and CD4+ CD25+ Foxp3+ T regulatory (Treg) cells were analyzed on days 4 and 21. Apoptosis in skin samples was evident in all irradiated groups; the LDR+sSPE mice had the greatest expression of activated caspase-3. On day 4 post-irradiation, the sSPE and LDR+sSPE groups had significantly lower WBC counts in blood and spleen compared to non-irradiated controls (p < 0.05 vs. 0 Gy). CD4+ CD25+ Foxp3+ Treg cell numbers in spleen were decreased at day 4, but proportions were increased in the sSPE and LDR+sSPE groups (p < 0.05 vs. 0 Gy). By day 21, lymphocyte counts were still low in blood from the LDR+sSPE mice, especially due to reductions in B, NK, and CD8+ T cytotoxic cells. The data demonstrate, for the first time, that pre-exposure to LDR photons did not protect against the adverse effects of radiation mimicking a large solar storm. The increased proportion of immunosuppressive CD4+ CD25+ Foxp3+ Treg and persistent reduction in circulating lymphocytes may adversely impact immune defenses that include removal of sub-lethally damaged cells with carcinogenic potential, at least for a period of time post-irradiation.

A Quantitative Study of the Effects of Ionizing Radiation on Endothelial Cells and Capillary-like Network Formation

The initial events of angiogenesis comprise endothelial cell activation, migration, and proliferation. The characteristics of retinal endothelial cells and capillaries are significantly altered in a number of diseases including cancer. Since radiation has been shown as a useful tool in radiotherapy by altering the proliferative changes, it is important to evaluate the responses of the endothelial cells and the capillary network to radiation. We quantified functional and kinetic responses of endothelial cells and capillaries to radiation in an in vitro model. An in vitro angiogenesis model was introduced in our study with endothelial cells cultured on an extracellular matrix gel in which hollow tube-like structures could be rapidly formed. Vessel formation was quantified using stereological techniques. The cell cycle kinetics of endothelial cells and accumulation of DNA damage after radiation were measured using laser scanning cytometry. To study the response of proliferative capillary-like structures to radiation, the vessel network was irradiated with 2 gray (Gy). To evaluate functional and kinetic responses and differentiation of endothelial cells to radiation, cells were irradiated with 2 and 6 Gy. Progressive time- and dose-dependent loss of endothelial cells occurred starting 24 hours after radiation. Vessel growth was significantly retarded at the higher dose. A significant percentage of DNA breaks were detected dose-dependently. A large percentage of G1 cells were measured in the irradiated endothelial cell population when compared to the respective sham-treated control population. These results indicate that radiation-induced endothelial cell injuries destroy the integrity of vascular structure. We postulated that apoptosis may represent a biologically relevant mechanism of radiation-induced endothelial cell damage.

Dose response of rat retinal microvessels to proton dose schedules used clinically: a pilot study

PURPOSE This preclinical rat pilot study quantifies retinal microvessel, endothelial, and pericyte population changes produced by proton irradiation METHODS AND MATERIALS The left eyes of rats were irradiated with single doses of 8, 14, 20, and 28 Gy protons; right eyes, with two fractions. Animals were euthanized, and eyes were removed; elastase digests were prepared, and cell populations were counted in sample fields. Results were compared with unirradiated controls. RESULTS Progressive time- and dose-dependent endothelial cell loss occurred following all schedules. Cell loss was significantly different from control values (p < 0.001) following 28 Gy and following 20 Gy (p < 0.05) in a single dose. Endothelial cell loss was the same for single- and split-dose schedules. Progressive endothelial cell loss produced vessel collapse and acellular vessel strands. Endothelial cells were in the G(0) phase of the mitotic cycle. 28 Gy produced photoreceptor cell loss. CONCLUSION The retinal digest is an elegant bioassay to quantify the microvessel population response. Single- and split-dose schedules appear to yield similar outcomes, in terms of endothelial cell density.

Effects of ionizing radiation on the heart

This article provides an overview of studies addressing effects of ionizing radiation on the heart. Clinical studies have identified early and late manifestations of radiation-induced heart disease, a side effect of radiation therapy to tumors in the chest when all or part of the heart is situated in the radiation field. Studies in preclinical animal models have contributed to our understanding of the mechanisms by which radiation may injure the heart. More recent observations in human subjects suggest that ionizing radiation may have cardiovascular effects at lower doses than was previously thought. This has led to examinations of low-dose photons and low-dose charged particle irradiation in animal models. Lastly, studies have started to identify non-invasive methods for detection of cardiac radiation injury and interventions that may prevent or mitigate these adverse effects. Altogether, this ongoing research should increase our knowledge of biological mechanisms of cardiovascular radiation injury, identify non-invasive biomarkers for early detection, and potential interventions that may prevent or mitigate these adverse effects.

Biological and metabolic response in STS-135 space-flown mouse skin

Abstract There is evidence that space flight condition-induced biological damage is associated with increased oxidative stress and extracellular matrix (ECM) remodeling. To explore possible mechanisms, changes in gene expression profiles implicated in oxidative stress and in ECM remodeling in mouse skin were examined after space flight. The metabolic effects of space flight in skin tissues were also characterized. Space Shuttle Atlantis (STS-135) was launched at the Kennedy Space Center on a 13-day mission. Female C57BL/6 mice were flown in the STS-135 using animal enclosure modules (AEMs). Within 3–5 h after landing, the mice were euthanized and skin samples were harvested for gene array analysis and metabolic biochemical assays. Many genes responsible for regulating production and metabolism of reactive oxygen species (ROS) were significantly (p < 0.05) altered in the flight group, with fold changes >1.5 compared to AEM control. For ECM profile, several genes encoding matrix and metalloproteinases involved in ECM remodeling were significantly up-/down-regulated following space flight. To characterize the metabolic effects of space flight, global biochemical profiles were evaluated. Of 332 named biochemicals, 19 differed significantly (p < 0.05) between space flight skin samples and AEM ground controls, with 12 up-regulated and 7 down-regulated including altered amino acid, carbohydrate metabolism, cell signaling, and transmethylation pathways. Collectively, the data demonstrated that space flight condition leads to a shift in biological and metabolic homeostasis as the consequence of increased regulation in cellular antioxidants, ROS production, and tissue remodeling. This indicates that astronauts may be at increased risk for pathophysiologic damage or carcinogenesis in cutaneous tissue.