Lung Stereotactic Arc Therapy in Mice: Development of Radiation Pneumopathy and Influence of HIF-1α Endothelial Deletion.

PURPOSE: Stereotactic body radiation therapy offers good lung local tumor control by the administration of a high dose per fraction in small volumes. Stereotactic body radiation therapy preclinical modeling is now possible, and our aim was to develop a model of focal irradiation of the mouse lung and to investigate the impact of conditional hypoxia-inducible factor 1α (HIF-1α) deletion in the endothelium on radiation-induced tissue damage. METHODS AND MATERIALS: The Small Animal Radiation Research Platform was used to create a mouse model of focal irradiation of the lung using arc therapy. HIF-1α conditional deletion was obtained by crossing mice expressing Cre recombinase under the endothelial promoter VE-cadherin (VECad-Cre+/+ mice) with HIF-1α floxed mice. RESULTS: Lung stereotactic arc therapy allows thoracic wall sparing and long-term studies. However, isodose curves showed that neighboring organs received significant doses of radiation, as revealed by ipsilateral lung acute red hepatization and major gene expression level modifications. Conditional HIF-1α deletion reduced acute lung edema and tended to diminish neutrophil infiltrate, but it had no impact on long-term global tissue damage. CONCLUSIONS: Arc therapy for focal high-dose irradiation of mouse lung is an efficient model for long-term studies. However, irradiation may have a strong impact on the structure and function of neighboring organs, which must be considered. HIF-1α conditional deletion has no beneficial impact on lung damage in this irradiation schedule.

Pentoxifylline Regulates Plasminogen Activator Inhibitor-1 Expression and Protein Kinase A Phosphorylation in Radiation-Induced Lung Fibrosis.

Purpose. Radiation-induced lung fibrosis (RILF) is a serious late complication of radiotherapy. In vitro studies have demonstrated that pentoxifylline (PTX) has suppressing effects in extracellular matrix production in fibroblasts, while the antifibrotic action of PTX alone using clinical dose is yet unexplored. Materials and Methods. We used micro-computed tomography (micro-CT) and histopathological analysis to evaluate the antifibrotic effects of PTX in a rat model of RILF. Results. Micro-CT findings showed that lung density, volume loss, and mediastinal shift are significantly increased at 16 weeks after irradiation. Simultaneously, histological analysis demonstrated thickening of alveolar walls, destruction of alveolar structures, and excessive collagen deposition in the irradiated lung. PTX treatment effectively attenuated the fibrotic changes based on both micro-CT and histopathological analyses. Western analysis also revealed increased levels of plasminogen activator inhibitor- (PAI-) 1 and fibronectin (FN) and PTX treatment reduced expression of PAI-1 and FN by restoring protein kinase A (PKA) phosphorylation but not TGF-ß/Smad in both irradiated lung tissues and epithelial cells. Conclusions. Our results demonstrate the antifibrotic effect of PTX on radiation-induced lung fibrosis and its effect on modulation of PKA and PAI-1 expression as possible antifibrotic mechanisms.

Regulatory T Cells Promote ß-Catenin--Mediated Epithelium-to-Mesenchyme Transition During Radiation-Induced Pulmonary Fibrosis.

PURPOSE: Radiation-induced pulmonary fibrosis results from thoracic radiation therapy and severely limits radiation therapy approaches. CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) as well as epithelium-to-mesenchyme transition (EMT) cells are involved in pulmonary fibrosis induced by multiple factors. However, the mechanisms of Tregs and EMT cells in irradiation-induced pulmonary fibrosis remain unclear. In the present study, we investigated the influence of Tregs on EMT in radiation-induced pulmonary fibrosis. METHODS AND MATERIALS: Mice thoraxes were irradiated (20 Gy), and Tregs were depleted by intraperitoneal injection of a monoclonal anti-CD25 antibody 2 hours after irradiation and every 7 days thereafter. Mice were treated on days 3, 7, and 14 and 1, 3, and 6 months post irradiation. The effectiveness of Treg depletion was assayed via flow cytometry. EMT and ß-catenin in lung tissues were detected by immunohistochemistry. Tregs isolated from murine spleens were cultured with mouse lung epithelial (MLE) 12 cells, and short interfering RNA (siRNA) knockdown of ß-catenin in MLE 12 cells was used to explore the effects of Tregs on EMT and ß-catenin via flow cytometry and Western blotting. RESULTS: Anti-CD25 antibody treatment depleted Tregs efficiently, attenuated the process of radiation-induced pulmonary fibrosis, hindered EMT, and reduced ß-catenin accumulation in lung epithelial cells in vivo. The coculture of Tregs with irradiated MLE 12 cells showed that Tregs could promote EMT in MLE 12 cells and that the effect of Tregs on EMT was partially abrogated by ß-catenin knockdown in vitro. CONCLUSIONS: Tregs can promote EMT in accelerating radiation-induced pulmonary fibrosis. This process is partially mediated through ß-catenin. Our study suggests a new mechanism for EMT, promoted by Tregs, that accelerates radiation-induced pulmonary fibrosis.

Recruitment of Gr1(+)CD11b (+)F4/80 (+) population in the bone marrow and spleen by irradiation-induced pulmonary damage.

Radiation-induced lung injury is a kind of sterile inflammation, which may lead to morbidity and mortality. The mechanism by which ionizing radiation activate the immune system is not well understood. In the present study, we have investigated the immunological responses induced by local irradiation-induced damage in mouse lung. The left lungs of C57BL/6 mice were irradiated at a high dose of 100 Gy. The histology of the lungs and spleen showed evidences of alveolar inflammation and congestion at 2 weeks after X-ray treatment. Also, prominent increase in cells expressing the cell surface markers, Gr(+)CD11b(+)F4/80(+) and Ly6C(+) Ly6G(+) were observed 2 weeks after X-ray treatment (100 Gy). Gr1(+)CD11b(+)F4/80(+) cell depletion by clodronate treatment reversed the histological effects and also failed to recruit Gr(+)CD11b(+) cells or F4/80(+) cells caused by irradiation. The origin of recruited Gr1(+)CD11b(+) cells was found to be a mixed resident and recruited phenotype.

Lupus erythematosus cell phenomenon in pediatric bronchoalveolar lavages: possible manifestation of early radioadaptive response in radiation induced alveolitis.

A ten-year (December 1992 - December 2002) evaluation of 225 pediatric bronchoalveolar lavage (BAL) differential cell counts showed appearance of the cells corresponding to the cytological entity - lupus erythematosus cell (LEC) in 47 specimens of which not a single case was associated with the coexistent autoimmune disease. There was a significant increase in the percentage of LEC in BAL samples of the examinees during the first 6 months after the bombing of targets in Serbia (July-December 1999) in comparison to the period 1992 to March 24, 1999, and after the bombing of targets in Serbia (2000-2002). Maintaining the character of occurrence of LEC in BAL as nonspecific (Zunic et al. 1996), the devastating power of alpha particles (originated from uranium decay) gives an opportunity to discuss this phenomenon more comprehensibly and perceive a new vista related to the pathogenesis of LEC phenomenon in BAL. Since the period after 1991 corresponds to the time after the first Gulf War, and later the bombing of targets in Bosnia, the possibility of occurrence of LEC in BAL as a manifestation of radiation alveolitis due to contamination by air transferred depleted uranium (DU) particles could not be excluded.

Effects of thoracic irradiation on pulmonary endothelial compared to alveolar type-II cells in fibrosis-prone C57BL/6NTac mice.

BACKGROUND/AIM: Thoracic irradiation results in an acute inflammatory response, latent period, and late fibrosis. Little is known about the mechanisms involved in triggering late radiation fibrosis. MATERIALS AND METHODS: Thoracic irradiated fibrosis prone C57BL/6NTac mice were followed for detectable mRNA transcripts in isolated lung cells and micro-RNA in whole-tissues, and the effect of administration of water-soluble oxetanyl sulfoxide MMS350 was studied. Marrow stromal cell motility in medium from fibrotic-phase explanted pulmonary endothelial and alveolar type-II cells was measured. RESULTS: RNA and micro-RNA expression in lung correlated with fibrosis. MMS350 reduced pro-fibrotic gene expression in both endothelial and alveolar type-II cells in irradiated mice. Conditioned medium from irradiated cells did not alter cell motility in vitro. CONCLUSION: These studies should facilitate identification of potential new drug targets for ameliorating irradiation-induced pulmonary fibrosis.

The role of alveolar epithelium in radiation-induced lung injury.

Pneumonitis and fibrosis are major lung complications of irradiating thoracic malignancies. In the current study, we determined the effect of thoracic irradiation on the lungs of FVB/N mice. Survival data showed a dose-dependent increase in morbidity following thoracic irradiation with single (11-13 Gy) and fractionated doses (24-36 Gy) of (137)Cs γ-rays. Histological examination showed a thickening of vessel walls, accumulation of inflammatory cells, collagen deposition, and regional fibrosis in the lungs 14 weeks after a single 12 Gy dose and a fractionated 30 Gy dose; this damage was also seen 5 months after a fractionated 24 Gy dose. After both single and fractionated doses, i] aquaporin-5 was markedly decreased, ii] E-cadherin was reduced and iii] prosurfactant Protein C (pro-SP-c), the number of pro-SP-c(+) cells and vimentin expression were increased in the lungs. Immunofluorescence analysis revealed co-localization of pro-SP-c and α-smooth muscle actin in the alveoli after a single dose of 12 Gy. These data suggest that, i] the FVB/N mouse strain is sensitive to thoracic radiation ii] aquaporin-5, E-cadherin, and pro-SP-c may serve as sensitive indicators of radiation-induced lung injury; and iii] the epithelial-to-mesenchymal transition may play an important role in the development of radiation-induced lung fibrosis.

Cytological characteristics of lung washings from children in depleted uranium stroked region.

The study was based on theoretical interpretation of authentic findings of Lupus Erythematosus Cells (LEC) in bronchoalveolar lavage (BAL) samples of children who underwent flexible bronchoscopy for clinical symptoms and radiological changes consistent with persistent pulmonary infiltrates during the first year after the bombing of Serbia in 1999. Differential cell counts were compared and statistical significance of differences for estimated cell population percentages calculated in groups of LEC positive (LEC+) and LEC negative (LEC-) BAL specimens. Significant increase of percentages of neutrophils and eosinophils and decreased percentages of macrophages were found in the group of LEC+ in comparison with LEC- BAL specimens (p less than 0.05, p less than 0.001, p less than 0.001, respectively). Presence of decreased percentages of cells of monocyte-macrophage lineage with consequent expansion of white blood cells in BAL, argue for understanding the nature of LEC+ alveolitis as a possible nonspecific finding of radiation-induced biological response of pulmonary tissue. LEC phenomenon may be understood as an early radio adaptive tissue response. Depleted uranium (DU) radiotoxic effect with concomitant alpha particles radiation, has been associated with unpredictable and everlasting biological effects. The emission of radiation in the course of several decades due to corrosion of scattered remnants of DU armaments, which has been potentiated by the repeated bombing of the regions within range of the transfer of radioactive particles by air, strikes a broad territory and numerous populations, and unavoidably leads to in vivoPetkau effect. Except the war, peacetime nuclear disasters in various parts of the world, such as Fukushima, Chernobyl and others, contribute to this effect too. In this way, the Petkau effect is a challenge for science to declare the future health strategy with the main goal focused on minimizing the early, as well as delayed in vivo effects of depleted uranium.

Plutonium behavior after pulmonary administration according to solubility properties, and consequences on alveolar macrophage activation.

The physico-chemical form in which plutonium enters the body influences the lung distribution and the transfer rate from lungs to blood. In the present study, we evaluated the early lung damage and macrophage activation after pulmonary contamination of plutonium of various preparation modes which produce different solubility and distribution patterns. Whatever the solubility properties of the contaminant, macrophages represent a major retention compartment in lungs, with 42 to 67% of the activity from broncho-alveolar lavages being associated with macrophages 14 days post-contamination. Lung changes were observed 2 and 6 weeks post-contamination, showing inflammatory lesions and accumulation of activated macrophages (CD68 positive) in plutonium-contaminated rats, although no increased proliferation of pneumocytes II (TTF-1 positive cells) was found. In addition, acid phosphatase activity in macrophages from contaminated rats was enhanced 2 weeks post-contamination as compared to sham groups, as well as inflammatory mediator levels (TNF-α, MCP-1, MIP-2 and CINC-1) in macrophage culture supernatants. Correlating with the decrease in activity remaining in macrophages after plutonium contamination, inflammatory mediator production returned to basal levels 6 weeks post-exposure. The production of chemokines by macrophages was evaluated after contamination with Pu of increasing solubility. No correlation was found between the solubility properties of Pu and the activation level of macrophages. In summary, our data indicate that, despite the higher solubility of plutonium citrate or nitrate as compared to preformed colloids or oxides, macrophages remain the main lung target after plutonium contamination and may participate in the early pulmonary damage.

Combined CXCR1/CXCR2 antagonism decreases radiation-induced alveolitis in the mouse.

The mechanisms leading to the radiation-induced lung responses of alveolitis and fibrosis are largely unknown. Herein we investigated whether CXC receptor 1 and 2 antagonism with CXCL8((3-72))K11R/G31P (G31P), a protein that reduces neutrophil chemotaxis in acute inflammatory response models, decreases the lung response to radiation. Mice of the AKR/J (alveolitis/pneumonitis responding) and KK/HIJ (fibrosis) strains received 18 Gy whole-thorax irradiation and a subset of these mice were treated with G31P (500 µg/kg) three times per week from the day of irradiation until euthanasia due to respiratory distress symptoms or 20 weeks after radiation treatment. Irradiated mice of both strains receiving G31P survived longer than mice receiving radiation alone. Radiation- and G31P-treated AKR/J mice surviving to the end of the experiment developed significantly less alveolitis, as measured histologically, than mice receiving radiation alone, but this difference was not evident in KK/HIJ mice. Using immunohistochemistry, G31P treatment was shown to increase the numbers of Gr-1-positive cells (neutrophils) in the lungs of unirradiated mice relative to control mice injected with saline, but the antagonist did not alter the numbers of Gr-1-positive cells in the lungs of radiation-treated mice. We conclude that G31P treatment reduces radiation-induced alveolitis but not fibrosis in mice.

High dose-per-fraction irradiation of limited lung volumes using an image-guided, highly focused irradiator: simulating stereotactic body radiotherapy regimens in a small-animal model.

PURPOSE: To investigate the underlying biology associated with stereotactic body radiotherapy (SBRT), both in vivo models and image-guided, highly focal irradiation systems are necessary. Here, we describe such an irradiation system and use it to examine normal tissue toxicity in a small-animal model at lung volumes similar to those associated with human therapy. METHODS AND MATERIALS: High-dose radiation was delivered to a small volume of the left lung of C3H/HeJCr mice using a small-animal stereotactic irradiator. The irradiator has a collimation mechanism to produce focal radiation beams, an imaging subsystem consisting of a fluorescent screen coupled to a charge-coupled device camera, and a manual positioning stage. Histopathologic examination and micro-CT were used to evaluate the radiation response. RESULTS: Focal obliteration of the alveoli by fibrous connective tissue, hyperplasia of the bronchiolar epithelium, and presence of a small number of inflammatory cells are the main reactions to low-volume/high-dose irradiation of the mouse lung. The tissue response suggested a radiation dose threshold for early phase fibrosis lying between 40 and 100 Gy. The irradiation system satisfied our requirements of high-dose-rate, small beam diameter, and precise localization and verification. CONCLUSIONS: We have established an experimental model and image-guided animal irradiation system for the study of high dose per fraction irradiations such as those used with SBRT at volumes analogous to those used in human beings. It will also allow the targeting of specific anatomical structures of the thorax or ultimately, orthotopic tumors of the lung.

[Pathogenesis, diagnostics and treatment of radiation pneumonitis induced by radiotherapy of lung cancer].

The external beam therapy has a high significances in the treatment of lung cancer. The lung irradiation is used for radical and adjuvant treatment of lung cancer. Treatment with Ionising Radiation damages tumor as well as normal tissue round. Radiation pneumonitis and pneumofibrosis can occur as a side effect of radiation therapy for lung cancer.The treatment of radiation pneumonitis depends on the degree of pathological process. To achieve full recovery after development of radiation pneumonitis is a bootless effort; efforts should be taken to prevent the damage.

Changes in pulmonary function tests after neoadjuvant therapy predict postoperative complications.

BACKGROUND: Neoadjuvant chemotherapy or chemoradiotherapy increases the risk of pulmonary resection. Changes in specific pulmonary function tests may be predictive. METHODS: A retrospective review of a prospective database of patients with non-small cell lung cancer who underwent neoadjuvant therapy, had pulmonary function tests performed both before and after therapy, and then underwent elective pulmonary resection was performed. Final values and change in the pulmonary function tests before and after treatment were entered as independent variables into a multivariate model in which the dependent variable was major or respiratory morbidity. RESULTS: There were 132 patients. The mean duration between pretherapy and posttherapy pulmonary function tests was 4.1 months. The mean change in the percent forced expiratory volume in 1 second, in the percent diffusion capacity of the lung for carbon monoxide, and in the percent diffusion capacity of the lung for carbon monoxide corrected for the alveolar volume was +1.0, -6.4%, and -6.6%, respectively. Fifty-five patients (42%) experienced a postoperative complication, and 39 of those patients experienced a major or respiratory complication. There were 7 (5.3%) operative mortalities (5 were respiratory related). On multivariate analysis the change in the percent diffusion capacity of the lung for carbon monoxide corrected for the alveolar volume was the only factor associated with major or respiratory morbidity (p = 0.028). When the posttherapy percent diffusion capacity of the lung for carbon monoxide corrected for the alveolar volume fell by 8% or more, there was an increased likelihood of major morbidity (p = 0.01). CONCLUSIONS: A decrease in the percent diffusion capacity of the lung for carbon monoxide corrected for the alveolar volume after neoadjuvant chemotherapy or chemoradiotherapy may predict increased risk for pulmonary resection, especially if the decrease is 8% or greater. These results should be considered in the preoperative risk assessment of patients who are to undergo pulmonary resection after induction therapy.

[Biological effect of (60)Cogamma ray on alveolar type II cells and interstitial cells of alveoliar septum in radiation pulmonary injury].

AIM: To explore the biological effect of (60)Cogamma ray on alveolar type II cells and interstitial cells of alveoliar septum. METHODS: Alveolar type II cells(AT-II) and interstitial cells including interstitial macrophages and fibroblasts were irradiated by 0, 3, 5, 7 Gy of gamma ray respectively. The effect of irradiation on AT-II proliferation was observed by argentation against nucleus. The activity of MMP-2, -9 in supernatants from AT-II and interstitial cells after irradiation was determined by zymography. The levels of TGF-beta1 and collagen type IV in supernatant from interstitial cells after irradiation were measured by ELISA. RESULTS: The nucleolus number of AT-II was increased with the increase of irradiation dose and group 7 Gy reached the highest level. The activity of MMP-2, -9 in supernatant from AT-II after irradiation increased at first and then decreased gradually. The activity of MMP-2, -9 and the content of TGF-beta1 in interstitial cells increased step by step, but collagen type IV decreased at first and then increased. CONCLUSION: AT-II, macrophages and fibroblasts are all involved in pulmonary invalid remodeling course in early radiation pulmonary injury, which is related to the initiation of pulmonary fibrosis in late period.

Radon progeny microdosimetry in human and rat bronchial airways: the effect of crossfire from the alveolar region.

The objectives of the present study were (1) to present a comprehensive analysis of the microdosimetric quantities in both human and rat bronchial airways and (2) to assess the contribution of the crossfire alpha particles emitted from the alveolar region to bronchial absorbed doses. Hit frequencies, absorbed doses and critical microdosimetric quantities were calculated for basal and secretory cell nuclei located at different depths in epithelial tissue for each bronchial airway generation for defined exposure conditions. Total absorbed doses and hit frequencies were slightly higher in rat airways than in corresponding human airways. This confirms the a priori assumption in rat inhalation experiments that the rat lung is a suitable surrogate for the human lung. While the contribution of crossfire alpha particles is insignificant in the human lung, it can reach 33% in peripheral bronchiolar airways of the rat lung. The latter contribution may even further increase with increasing alveolar 214Po activities. Hence, the observed prevalence of tumors in the bronchiolar region of the rat lung may partly be attributed to the high-linear energy transfer crossfire alpha particles.

[Effects of bone marrow mesenchymal stem cells transplantation on the apoptosis of alveolar wall cells in papain and Co60-induced pulmonary emphysema rats].

AIM: To study the effects of bone marrow MSCs transplantation on the apoptosis of alveolar wall cells and the expression of Bcl-2 and Bax of lung tissue in papain and Co60-induced pulmonary emphysema rats. METHODS: Female Lewis rats were randomly divided into three groups: control group, emphysema group, emphysema + MSCs transplantation group. Rats were sacrificed at days 14 and 28 after treatment. Morphologic analysis of the lung tissue was performed. The apoptosis of the lung cells was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The expression of Bcl-2 and Bax were determined by immunohistochemical staining. RESULTS: Emphysematous changes of the lung tissue were observed in emphysema group and emphysema + MSCs transplantation group. However, the emphysematous change in emphysema + MSCs transplantation group was improved compared with the emphysema group. There was significant difference in the number of alveolar counted per unit area (MAN), mean alveoli area (MAA) and mean linear interval(MLI) between emphysema group and emphysema + MSCs transplantation group. The apoptotic index of the alveolar wall cells in emphysema + MSCs transplantation group was less than that in the emphysema group. The percentage of Bcl-2 positive cells in emphysema + MSCs transplantation group was significantly higher than that in the emphysema group. The percentage of Bax positive cells in emphysema + MSCs transplantation group was significantly lower than that in the emphysema group. The ratio of Bcl-2/Bax of emphysema + MSCs transplantation group was significantly higher than that in the emphysema group. CONCLUSION: Bone marrow MSCs transplantation inhibits the apoptosis of alveolar wall cells, upregulates the expression of Bcl-2 and downregulates the expression of Bax. This may be part of the reason that bone marrow MSCs transplantation improves the papain and Co60-induced pulmonary emphysema.

Assessment and prevention of radioactive risk due to 222Radon on University Premises in Genoa, Italy.

From October 2004 to September 2005, Radon222 activity in high-risk indoor spaces used by employees and students at the University of Genoa was measured with CR-39 nuclear track detectors. The mean concentration in winter (78.9 Bq/m3 +/- 74.92 S.D.) was low in relation to the microenvironment considered. When data were broken down by type and location of the spaces, no significant differences were found, despite the fact that the Genoa conurbation lies on soil of variable geological composition. The dose absorbed by employees was 0.42 mSv/year, with a relative risk of 4.2/1000 cases of Radon-related lung cancer. The dose absorbed by students was 0.28 mSv/year, with a relative risk of 2.5/1000 cases of Radon-related lung cancer. The level of radon activity detected never exceeded the limit of 500 Bq/m3 established by Italian law. Nevertheless, the value of the compound uncertainty index suggested that the real level of Radon contamination could have exceeded 400 Bq/m3 in selected spaces, a value requiring annual concentration tests.

Acute lung injury with endotoxin or NO2 does not enhance development of airway epithelium from bone marrow.

Adult marrow-derived stem cells can localize to lung and acquire immunophenotypic characteristics of lung epithelial cells. Lung injury increases recruitment of the marrow-derived cells. We speculated that comparing patterns of lung engraftment following different lung injuries would provide insight into potential mechanisms by which marrow-derived cells were recruited to lung. To evaluate this, adult female C57Bl/6 mice irradiated and engrafted with marrow from adult male transgenic GFP mice were exposed to either intranasal inhalation of endotoxin (25 microg/mouse) or 3 days of 25 ppm NO(2) and then compared 1 or 3 months later to transplanted but otherwise uninjured mice. In all cases, the majority of marrow-derived cells recruited to lung were CD45(+) leukocytes. In lungs of transplanted but otherwise uninjured mice, small numbers of CD45(-) donor-derived cells in alveolar septae stained positively for pro-surfactant protein C. Rare donor-derived cells located in the airway epithelium stained positively with cytokeratin. Subsequent exposure of engrafted mice to NO(2) or endotoxin did not significantly increase the number or pattern of donor-derived CD45(-) cells found in recipient lungs. These results suggest that NO(2) or endotoxin lung injury does not result in significant engraftment of marrow-derived cells in lung.

Pulmonary radiation injury: identification of risk factors associated with regional hypersensitivity.

Effective radiation treatment of thoracic tumors is often limited by radiosensitivity of surrounding tissues. Several experimental studies have suggested variations in radiosensitivity of different pulmonary regions. Mice and rat studies in part contradict each other and urge for a more detailed analysis. This study was designed to obtain a more comprehensive insight in radiation injury development, expression, and its regional heterogeneity in lung. The latter is obviously highly critical for optimization of radiotherapy treatment plans and may shed light on the mechanisms of lung dysfunction after irradiation. Six different but volume-equal regions in rat lung were irradiated. Whereas the severity of damage, as seen in histologic analysis, was comparable in all regions, the degree of lung dysfunction, measured as breathing rates, largely varied. During the pneumonitic phase (early: 6-12 weeks), the most sensitive regions contained a substantial part of alveolar lung parenchyma. Also, a trend for hypersensitivity was observed when the heart lay in the irradiation field. In the fibrotic phase (late: 34-38 weeks), lung parenchyma and heart-encompassing regions were the most sensitive. No impact of the heart was observed during the intermediate phase (16-28 weeks). The severity of respiratory dysfunction after partial thoracic irradiation is likely governed by an interaction between pulmonary and cardiac functional deficits. As a repercussion, more severe acute and delayed toxicity should be expected after combined lung and heart irradiation. This should be considered in the process of radiotherapy treatment planning of thoracic malignancies.

Radiation-induced strain differences in mouse alveolar inflammatory cell apoptosis.

Whole-thorax irradiation results in the development of the diffuse inflammatory response alveolitis in C3H/HeJ (C3H) mice and a milder alveolitis with fibrosis in C57BL/6J (B6) mice. In this study, we investigate if this mouse strain difference in response to radiation is due to differences in lung inflammatory cell apoptosis. Mice of the C3H and B6 strains were given a radiation dose of 18 Gy to the thorax and the animals were sacrificed at 11 or 18 weeks following exposure or when they were moribund. Active caspase-3 staining was used to identify apoptotic cells in the alveolar space of histological lung sections from the mice. The apoptotic index of B6 mice was greater than that of C3H mice at 11 weeks postirradiation (17.8% of airspace cells vs. 7.8%, p = 0.028) and in mice sacrificed because of illness (27.3% vs. 14.4%, p = 0.036). No C3H mice survived to the later time point. The inflammatory cells undergoing apoptosis in the mouse lungs were morphologically consistent with alveolar macrophages. We conclude that a difference in inflammatory cell apoptosis may contribute to the disparate pulmonary radiation response of these mouse strains.