Development of a small animal model to simulate clinical stereotactic body radiotherapy-induced central and peripheral lung injuries

Evidence of Alveolar Macrophage Metabolic Shift Following Stereotactic Body Radiation Therapy -Induced Lung Fibrosis in Mice

PURPOSE

Radiation-induced pneumopathy is the main dose-limiting factor in cases of chest radiation therapy. Macrophage infiltration is frequently observed in irradiated lung tissues and may participate in lung damage development. Radiation-induced lung fibrosis can be reproduced in rodent models using whole thorax irradiation but suffers from limits concerning the role played by unexposed lung volumes in damage development.

METHODS AND MATERIALS

Here, we used an accurate stereotactic body radiation therapy preclinical model irradiating 4% of the mouse lung. Tissue damage development and macrophage populations were followed by histology, flow cytometry, and single-cell RNA sequencing. Wild-type and CCR2 KO mice, in which monocyte recruitment is abrogated, were exposed to single doses of radiation, inducing progressive (60 Gy) or rapid (80 Gy) lung fibrosis.

RESULTS

Numerous clusters of macrophages were observed around the injured area, during progressive as well as rapid fibrosis. The results indicate that probably CCR2-independent recruitment and/or in situ proliferation may be responsible for macrophage invasion. Alveolar macrophages experience a metabolic shift from fatty acid metabolism to cholesterol biosynthesis, directing them through a possible profibrotic phenotype. Depicted data revealed that the origin and phenotype of macrophages present in the injured area may differ from what has been previously described in preclinical models exposing large lung volumes, representing a potentially interesting trail in the deciphering of radiation-induced lung damage processes.

CONCLUSIONS

Our study brings new possible clues to the understanding of macrophage implications in radiation-induced lung damage, representing an interesting area for exploration in future studies.

GTSE1-driven ZEB1 stabilization promotes pulmonary fibrosis through the epithelial-to-mesenchymal transition

G2 and S phase-expressed protein 1 (GTSE1) has been implicated in the development of pulmonary fibrosis (PF); however, its biological function, molecular mechanism, and potential clinical implications remain unknown. Here, we explored the genomic data of patients with idiopathic PF (IPF) and found that GTSE1 expression is elevated in their lung tissues, but rarely expressed in normal lung tissues. Thus, we explored the biological role and downstream events of GTSE1 using IPF patient tissues and PF mouse models. The comprehensive bioinformatics analyses suggested that the increase of GTSE1 in IPF is linked to the enhanced gene signature for the epithelial-to-mesenchymal transition (EMT), leading us to investigate the potential interaction between GTSE1 and EMT transcription factors. GTSE1 preferentially binds to the less stable form of zinc-finger E-box-binding homeobox 1 (ZEB1), the unphosphorylated form at Ser585, inhibiting ZEB1 degradation. Consistently, the ZEB1 protein level in IPF patient and PF mouse tissues correlates with the GTSE1 protein level and the amount of collagen accumulation, representing fibrosis severity. Collectively, our findings highlight the GTSE1-ZEB1 axis as a novel driver of the pathological EMT characteristic during PF development and progression, supporting further investigation into GTSE1-targeting approaches for PF treatment.

Early, non-invasive detection of radiation-induced lung injury using PET/CT by targeting CXCR4

PURPOSE

Radiation-induced lung injury (RILI) is a severe side effect of radiotherapy (RT) for thoracic malignancies and we currently lack established methods for the early detection of RILI. In this study, we synthesized a new tracer, [18F]AlF-NOTA-QHY-04, targeting C-X-C-chemokine-receptor-type-4 (CXCR4) and investigated its feasibility to detect RILI.

METHODS

An RILI rat model was constructed and scanned with [18F]AlF-NOTA-QHY-04 PET/CT and [18F]FDG PET/CT periodically after RT. Dynamic, blocking, autoradiography, and histopathological studies were performed on the day of peak uptake. Fourteen patients with radiation pneumonia, developed during or after thoracic RT, were subjected to PET scan using [18F]AlF-NOTA-QHY-04.

RESULTS

The yield of [18F]AlF-NOTA-QHY-04 was 28.5-43.2%, and the specific activity was 27-33 GBq/μmol. [18F]AlF-NOTA-QHY-04 was mainly excreted through the kidney. Significant increased [18F]AlF-NOTA-QHY-04 uptake in the irradiated lung compared with that in the normal lung in the RILI model was observed on day 6 post-RT and peaked on day 14 post-RT, whereas no apparent uptake of [18F]FDG was shown on days 7 and 15 post-RT. MicroCT imaging did not show pneumonia until 42 days post-RT. Significant intense [18F]AlF-NOTA-QHY-04 uptake was confirmed by autoradiography. Immunofluorescence staining demonstrated expression of CXCR4 was significantly increased in the irradiated lung tissue, which correlated with results obtained from hematoxylin-eosin and Masson's trichrome staining. In 14 patients with radiation pneumonia, maximum standardized uptake values (SUVmax) were significantly higher in the irradiated lung compared with those in the normal lung. SUVmax of patients with grade 2 RILI was significantly higher than that of patients with grade 1 RILI.

CONCLUSION

This study indicated that [18F]AlF-NOTA-QHY-04 PET/CT imaging can detect RILI non-invasively and earlier than [18F]FDG PET/CT in a rat model. Clinical studies verified its feasibility, suggesting the clinical potential of [18F]AlF-NOTA-QHY-04 as a PET/CT tracer for early monitoring of RILI.

Early Prediction of Radiation-Induced Pulmonary Fibrosis Using Gastrin-Releasing Peptide Receptor-Targeted PET Imaging

Early diagnosis of radiation-induced pulmonary fibrosis (RIPF) in lung cancer patients after radiation therapy is important. A gastrin-releasing peptide receptor (GRPR) mediates the inflammation and fibrosis after irradiation in mice lungs. Previously, our group synthesized a GRPR-targeted positron emission tomography (PET) imaging probe, [⁶⁴Cu]Cu-NODAGA-galacto-bombesin (BBN), an analogue peptide of GRP. In this study, we evaluated the usefulness of [⁶⁴Cu]Cu-NODAGA-galacto-BBN for the early prediction of RIPF. We prepared RIPF mice and acquired PET/CT images of [¹⁸F]F-FDG and [⁶⁴Cu]Cu-NODAGA-galacto-BBN at 0, 2, 5, and 11 weeks after irradiation (n = 3-10). We confirmed that [⁶⁴Cu]Cu-NODAGA-galacto-BBN targets GRPR in irradiated RAW 264.7 cells. In addition, we examined whether [⁶⁴Cu]Cu-NODAGA-galacto-BBN monitors the therapeutic efficacy in RIPF mice (n = 4). As a result, the lung uptake ratio (irradiated-to-normal) of [⁶⁴Cu]Cu-NODAGA-galacto-BBN was the highest at 2 weeks, followed by its decrease at 5 and 11 weeks after irradiation, which matched with the expression of GRPR and was more accurately predicted than [¹⁸F]F-FDG. These uptake results were also confirmed by the cell uptake assay. Furthermore, [⁶⁴Cu]Cu-NODAGA-galacto-BBN could monitor the therapeutic efficacy of pirfenidone in RIPF mice. We conclude that [⁶⁴Cu]Cu-NODAGA-galacto-BBN is a novel PET imaging probe for the early prediction of RIPF-targeting GRPR expressed during the inflammatory response.

Diagnostic Value of 18F-NOTA-FAPI PET/CT in a Rat Model of Radiation-Induced Lung Damage

In this study, we explore the diagnostic value of a novel PET/CT imaging tracer that specifically targets fibroblast activation protein (FAP), ¹⁸F-NOTA-FAPI, in a radiation induced lung damage (RILD) rat model. High focal radiation (40, 60, or 90 Gy) was administered to a 5-mm diameter area of the right lung in Wistar rats for evaluation of RILD induction. Lung tissues exposed to 90 Gy radiation were scanned with ¹⁸F-NOTA-FAPI PET/CT and with ¹⁸F-FDG. Dynamic ¹⁸F-NOTA-FAPI PET/CT scanning was performed on day 42 post-irradiation. After in vivo scanning, lung cryosections were prepared for autoradiography, hematoxylin and eosin (HE) and immunohistochemical (IHC) staining. An animal model of RILD was established and validated by histopathological analysis. On ¹⁸F-NOTA-FAPI PET/CT, RILD was first observed on days 42, 35 and 7 in the 40, 60 and 90 Gy groups, respectively. After treatment with 90 Gy, ¹⁸F-NOTA-FAPI uptake in an area of RILD emerged on day 7 (0.65 ± 0.05%ID/ml) and reappeared on day 28 (0.81 ± 0.09%ID/ml), remaining stable for 4–6 weeks. Autoradiography and HE staining IHC staining revealed that ¹⁸F-NOTA-FAPI accumulated mainly in the center of the irradiated area. IHC staining confirmed the presence of FAP+ macrophages in the RILD area, while FAP+ fibroblasts were observed in the peripheral area of irradiated lung tissue. ¹⁸F-NOTA-FAPI represents a promising radiotracer for in vivo imaging of RILD in a dose- and time-dependent manner. Noninvasive imaging of FAP may potentially aiding in the clinical management of radiotherapy patients.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Is Fractionation Worthwhile?

Lung stereotactic body radiation therapy is characterized by a reduction in target volumes and the use of severely hypofractionated schedules. Preclinical modeling became possible thanks to rodent-dedicated irradiation devices allowing accurate beam collimation and focal lung exposure. Given that a great majority of publications use single dose exposures, the question we asked in this study was as follows: in incremented preclinical models, is it worth using fractionated protocols or should we continue focusing solely on volume limitation? The left lungs of C57BL/6JRj mice were exposed to ionizing radiation using arc therapy and 3 × 3 mm beam collimation. Three-fraction schedules delivered over a period of 1 week were used with 20, 28, 40, and 50 Gy doses per fraction. Lung tissue opacification, global histological damage and the numbers of type II pneumocytes and club cells were assessed 6 months post-exposure, together with the gene expression of several lung cells and inflammation markers. Only the administration of 3 × 40 Gy or 3 × 50 Gy generated focal lung fibrosis after 6 months, with tissue opacification visible by cone beam computed tomography, tissue scarring and consolidation, decreased club cell numbers and a reactive increase in the number of type II pneumocytes. A fractionation schedule using an arc-therapy-delivered three fractions/1 week regimen with 3 × 3 mm beam requires 40 Gy per fraction for lung fibrosis to develop within 6 months, a reasonable time lapse given the mouse lifespan. A comparison with previously published laboratory data suggests that, in this focal lung irradiation configuration, administering a Biological Effective Dose ≥ 1000 Gy should be recommended to obtain lung fibrosis within 6 months. The need for such a high dose per fraction challenges the appropriateness of using preclinical highly focused fractionation schedules in mice.

Pharmacologic Inhibition of HIF-1α Attenuates Radiation-Induced Pulmonary Fibrosis in a Preclinical Image Guided Radiation Therapy

PURPOSE

Radiation-induced pulmonary fibrosis (RIPF) is a long-term side effect of thoracic radiation therapy. Hypoxia-induced vascular endothelial mesenchymal transition (EndMT) can occur during the development of RIPF. Here, we examined the direct contribution of endothelial HIF-1α (EC-HIF1α) on RIPF.

METHODS AND MATERIALS

An inducible Cre-lox-mediated endothelial Hif1a deletion mouse line was used to evaluate the potential of HIF-1α inhibition to suppress RIPF. To evaluate the effects of a pharmacologic HIF-1α inhibitor on RIPF after image guided radiation therapy (IGRT) for spontaneous lung adenocarcinoma, we generated conditional tdTomato; K-RasG12D; and p53 flox/flox mice to facilitate tracking of tumor cells expressing tdTomato.

RESULTS

We found that vascular endothelial-specific HIF-1α deletion shortly before radiation therapy inhibited the progression of RIPF along with reduced EndMT, whereas prolonged deletion of endothelial HIF-1α before irradiation did not. Moreover, we revealed that postirradiation treatment with the novel HIF-1α inhibitor, 2-methoxyestradiol (2-ME) could efficiently inhibit RIPF and EndMT. In addition, IGRT using primary mouse models of non-small cell lung cancer showed that combined treatment of 2-ME with ablative high-dose radiation therapy efficiently inhibited RIPF and the growth of both multifocal and single tumors, concomitantly reducing radiation-induced EndMT of normal as well as tumor regions.

CONCLUSION

These results suggest that a negative regulator of HIF-1α-mediated EndMT, such as 2-ME, may serve as a promising inhibitor of RIPF in radiation therapy.

PM014 attenuates radiation-induced pulmonary fibrosis via regulating NF-kB and TGF-b1/NOX4 pathways

Radiation therapy is the mainstay in the treatment of lung cancer, and lung fibrosis is a radiotherapy-related major side effect that can seriously reduce patient’s quality of life. Nevertheless, effective strategies for protecting against radiation therapy-induced fibrosis have not been developed. Hence, we investigated the radioprotective effects and the underlying mechanism of the standardized herbal extract PM014 on radiation-induced lung fibrosis. Ablative radiation dose of 75 Gy was focally delivered to the left lung of mice. We evaluated the effects of PM014 on radiation-induced lung fibrosis in vivo and in an in vitro model. Lung volume and functional changes were evaluated using the micro-CT and flexiVent system. Fibrosis-related molecules were evaluated by immunohistochemistry, western blot, and real-time PCR. A orthotopic lung tumour mouse model was established using LLC1 cells. Irradiated mice treated with PM014 showed a significant improvement in collagen deposition, normal lung volume, and functional lung parameters, and these therapeutic effects were better than those of amifostine. PM104 attenuated radiation-induced increases in NF-κB activity and inhibited radiation-induced p65 translocation, ROS production, DNA damage, and epithelial-mesenchymal transition. PM104 effectively alleviated fibrosis in an irradiated orthotopic mouse lung tumour model while not attenuating the efficacy of the radiation therapy by reduction of the tumour. Standardized herbal extract PM014 may be a potential therapeutic agent that is able to increase the efficacy of radiotherapy by alleviating radiation-induced lung fibrosis.

LXA4-FPR2 signaling regulates radiation-induced pulmonary fibrosis via crosstalk with TGF-β/Smad signaling

Radiation therapy is an important modality in the treatment of lung cancer, but it can lead to radiation pneumonitis, and eventually radiation fibrosis. To date, only few available drugs can effectively manage radiation-induced pulmonary fibrosis. Lipoxins are endogenous molecules exhibit anti-inflammatory and pro-resolving effects. These molecules play a vital role in reducing excessive tissue injury and chronic inflammation; however, their effects on radiation-induced lung injury (RILI) are unknown. In this study, we investigated the effects of lipoxin A4 (LXA4) on RILI using our specialized small-animal model of RILI following focal-ablative lung irradiation (IR). LXA4 significantly inhibited immune-cell recruitment and reduced IR-induced expression of pro-inflammatory cytokines and fibrotic proteins in the lung lesion sites. In addition, micro-CT revealed that LXA4 reduced IR-induced increases in lung consolidation volume. The flexiVentTM assays showed that LXA4 significantly reversed IR-induced lung function damage. Moreover, LXA4 downregulated the activities of NF-κB and the Smad-binding element promoters. The expression of FPR2, an LXA4 receptor, increased during the development of IR-induced pulmonary fibrosis, whereas silencing of endogenous LXA4 using an antagonist (WRW4) or FPR2 siRNA resulted in impaired development of pulmonary fibrosis in response to IR. Collectively, these data suggest that LXA4 could serve as a potent therapeutic agent for alleviating RILI.

Blocking C-Raf alleviated high-dose small-volume radiation-induced epithelial mesenchymal transition in mice lung

The goal of this study was to develop a potential druggable target for lung injury after SABR through the small animal model. Utilising the model, a radiation dose of 70 Gy or 90 Gy was focally (small volume) delivered to the left lung of mice. The highly expressed phosphorylation form of C-Raf was discovered through a protein array experiment, with the protein being extracted from the area of radiated mouse lung tissue, and was confirmed by IHC and western blot. C-Raf activation, along with morphological change and EMT (Epithelial to Mesenchymal Transition) marker expression, was observed after radiation to the mouse type II alveolar cell line MLE-12. C-Raf inhibitor GW5074 was able to reverse the EMT in cells effectively, and was found to be dependent on Twist1 expression. In the animal experiment, pretreatment of GW5074 alleviated EMT and lung injury after 70 Gy radiation was focally delivered to the lung of mice. Conclusively, these results demonstrate that C-Raf inhibitor GW5074 inhibits high-dose small-volume radiation-induced EMT via the C-Raf/Twist1 signalling pathway in mice. Therefore, pharmacological C-Raf inhibitors may be used effectively as inhibitors of SABR-induced lung fibrosis.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Effect of Beam Size Changes and Dose Effect at Constant Collimation

PURPOSE

Stereotactic body radiation therapy is a therapeutic option offered to high surgical risk patients with lung cancer. Focal lung irradiation in mice is a new preclinical model to help understand the development of lung damage in this context. Here we developed a mouse model of lung stereotactic therapy using arc delivery and monitored the development of lung damage while varying the beam size and dose delivered.

METHODS AND MATERIALS

C57BL/6JRj mice were exposed to 90 Gy focal irradiation on the left lung using 1-mm diameter, 3 × 3 mm², 7 × 7 mm², or 10 × 10 mm² beam collimation for beam size effect and using 3 × 3 mm² beam collimation delivering 20 to 120 Gy for dose effect. Long-term lung damage was monitored with micro-computed tomography imaging with anatomopathologic and gene expression measurements in the injured patch and the ipsilateral and contralateral lungs.

RESULTS

Both 1-mm diameter and 3 × 3 mm² beam collimation allow long-term studies, but only 3-mm beam collimation generates lung fibrosis when delivering 90 Gy. Dose-effect studies with constant 3-mm beam collimation revealed a dose of 60 Gy as the minimum to obtain lung fibrosis 6 months postexposure. Lung fibrosis development was associated with club cell depletion and increased type II pneumocyte numbers. Lung injury developed with ipsilateral and contralateral consequences such as parenchymal thickening and gene expression modifications.

CONCLUSIONS

Arc therapy allows long-term studies and dose escalation without lethality. In our dose-delivery conditions, dose-effect studies revealed that 3 × 3 mm² beam collimation to a minimum single dose of 60 Gy enables preclinical models for the assessment of lung injury within a 6-month period. This model of lung tissue fibrosis in a time length compatible with mouse life span may offer good prospects for future mechanistic studies.

Stereotactic Lung Irradiation in Mice Promotes Long-Term Senescence and Lung Injury

PURPOSE

Lung cancer will be treated more frequently using stereotactic body radiation therapy, and preclinical research to model long-term toxicity of ablative doses of radiation is crucial. Stereotactic lung irradiation of a small volume can induce radiation pneumonitis and fibrosis in normal tissues.

METHODS AND MATERIALS

Senescence has been reported to contribute to lung fibrosis, and we investigated in vivo the effects of ablative doses of ionizing radiation on senescence-associated processes. The left lung of p16^INK4a-LUC knock-in mice was exposed to a single dose or fractionated radiation doses in a millimetric volume using a small animal radiation research platform.

RESULTS

Single or fractionated ablative radiation induces acute and very long-term p16^INK4a activation in the irradiated lung target volume associated with lung injury. We observed a panel of heterogeneous senescent cells including pneumocytes, macrophages, and endothelial cells that accumulated around the radiation-induced lung focal lesion, suggesting that different senescent cell types may contribute to radiation injury.

CONCLUSIONS

This work provides important information on the long-term effects of ablative radiation doses in the normal lung and strongly suggests that stress-induced senescence is involved in stereotactic body radiation therapy-induced late fibrosis.

Hyperoxia-induced lung structure-function relation, vessel rarefaction, and cardiac hypertrophy in an infant rat model

BACKGROUND

Hyperoxia-induced bronchopulmonary dysplasia (BPD) models are essential for better understanding and impacting on long-term pulmonary, cardiovascular, and neurological sequelae of this chronic disease. Only few experimental studies have systematically compared structural alterations with lung function measurements.

METHODS

In three separate and consecutive series, Sprague-Dawley infant rats were exposed from day of life (DOL) 1 to 19 to either room air (0.21; controls) or to fractions of inspired oxygen (FiO2) of 0.6, 0.8, and 1.0. Our primary outcome parameters were histopathologic analyses of heart, lungs, and respiratory system mechanics, assessed via image analysis tools and the forced oscillation technique, respectively.

RESULTS

Exposure to FiO2 of 0.8 and 1.0 resulted in significantly lower body weights and elevated coefficients of lung tissue damping (G) and elastance (H) when compared with controls. Hysteresivity (η) was lower due to a more pronounced increase of H when compared with G. A positive structure-function relation was demonstrated between H and the lung parenchymal content of α-smooth muscle actin (α-SMA) under hyperoxic conditions. Moreover, histology and morphometric analyses revealed alveolar simplification, fewer pulmonary arterioles, increased α-SMA content in pulmonary vessels, and right heart hypertrophy following hyperoxia. Also, in comparison to controls, hyperoxia resulted in significantly lower plasma levels of vascular endothelial growth factor (VEGF). Lastly, rats in hyperoxia showed hyperactive and a more explorative behaviour.

CONCLUSIONS

Our in vivo infant rat model mimics clinical key features of BPD. To the best of our knowledge, this is the first BPD rat model demonstrating an association between lung structure and function. Moreover, we provide additional evidence that infant rats subjected to hyperoxia develop rarefaction of pulmonary vessels, augmented vascular α-SMA, and adaptive cardiac hypertrophy. Thus, our model provides a clinically relevant tool to further investigate diseases related to O2 toxicity and to evaluate novel pharmacological treatment strategies.

Blockade of Aquaporin 4 Inhibits Irradiation-Induced Pulmonary Inflammation and Modulates Macrophage Polarization in Mice

To investigate the effects of aquaporin 4 (AQP4) inhibitor in irradiation-induced pulmonary inflammation in mice. A single dose of 75 Gy was delivered to the left lung of mice to induce radiation pneumonitis. For inhibition of AQP4, 200 mg/kg of TGN-020 was administered i.p. one time per 2 days post-irradiation. Blockade of AQP4 with TGN-020 resulted in the inhibition of inflammatory cell infiltration and the downregulation of inflammatory cytokines (IL-6, IL-17, and TGF-β), chemokines (MIP1a and MCP1), fibrosis-related (Col3al and Fn1), and M2 macrophage marker (Arg1) post-irradiation. Immunofluorescence staining indicated that there was significant fewer M2 macrophage infiltration in the irradiated lung tissues from mice treated with TGN-020. Additionally, depletion of macrophages with liposome clodronate resulted in alleviated lung injury induced by irradiation. Furthermore, adoptive transfer of M1 or M2 macrophages into clodronate-treated mice was performed. The results showed that the administration of M2 macrophages fully reversed the clodronate-induced beneficial effect on inflammation score, thickness, and fibrosis. However, transfer of M1 macrophages only impacted the inflammation score and thickness and did not affect lung fibrosis. AQP4 blockade alleviated the development and severity of irradiated lung damage. This was associated with attenuated infiltration of inflammatory cell, decreased production of pro-inflammatory cytokines, and inhibited activation of M2 macrophages.

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.

Identification of molecular signatures involved in radiation-induced lung fibrosis

In radiotherapy, radiation (IR)-induced lung fibrosis has severe and dose-limiting side effects. To elucidate the molecular effects of IR fibrosis, we examined the fibrosis process in irradiated mouse lung tissues. High focal IR (90 Gy) was exposed to a 3-mm volume of the left lung in C57BL6 mice. In the diffused irradiation, 20 Gy dose delivered with a 7-mm collimator almost covered the entire left lung. Histological examination for lung tissues of both irradiated and neighboring regions was done for 4 weeks after irradiation. Long-term effects (12 months) of 20Gy IR were compared on a diffuse region of the left lung and non-irradiated right lung. Fibrosis was initiated as early as 2 weeks after IR in the irradiated lung region and neighboring region. Upregulation of gtse1 in both 90Gy-irradiated and neighboring regions was observed. Upregulation of fgl1 in both 20Gy diffused irradiated and non-irradiated lungs was identified. When gtse1 or flg1 was knock-downed, TGFβ or IR-induced epithelial-mesenchymal transition was inhibited, accompanied with the inhibition of cellular migration, suggesting fibrosis responsible genes. Immunofluorescence analysis using mouse fibrotic lung tissues suggested that fibrotic regions showed increased expressions of Gtse1 and Fgl1, indicating novel molecular signatures of gtse1and fgl1 for IR-induced lung fibrosis. Even though their molecular mechanisms and IR doses or irradiated volumes for lung fibrosis may be different, these genes may be novel targets for understanding IR-induced lung fibrosis and in treatment strategies. KEY MESSAGES: Upregulation of gtse1 by 90Gy focal irradiation and upregulation of fgl1 by 20Gy diffused irradiation are identified in mouse lung fibrosis model. Gtse1 and Fgl1 are involved in radiation or TGFβ-induced epithelial-mesenchymal transition. Radiation-induced fibrotic regions of mouse lungs showed increased expressions of Gtse1 and Fgl1. Gtse1 and Fgl1 are suggested to be novel targets for radiation-induced lung fibrosis.

Dosimetry in Micro-computed Tomography: a Review of the Measurement Methods, Impacts, and Characterization of the Quantum GX Imaging System

Purpose

X-ray micro-computed tomography (μCT) is a widely used imaging modality in preclinical research with applications in many areas including orthopedics, pulmonology, oncology, cardiology, and infectious disease. X-rays are a form of ionizing radiation and, therefore, can potentially induce damage and cause detrimental effects. Previous reviews have touched on these effects but have not comprehensively covered the possible implications on study results. Furthermore, interpreting data across these studies is difficult because there is no widely accepted dose characterization methodology for preclinical μCT. The purpose of this paper is to ensure in vivo μCT studies can be properly designed and the data can be appropriately interpreted.

Procedures

Studies from the scientific literature that investigate the biological effects of radiation doses relevant to μCT were reviewed. The different dose measurement methodologies used in the peer-reviewed literature were also reviewed. The CT dose index 100 (CTDI₁₀₀) was then measured on the Quantum GX μCT instrument. A low contrast phantom, a hydroxyapatite phantom, and a mouse were also imaged to provide examples of how the dose can affect image quality.

Results

Data in the scientific literature indicate that scenarios exist where radiation doses used in μCT imaging are high enough to potentially bias experimental results. The significance of this effect may relate to the study outcome and tissue being imaged. CTDI₁₀₀ is a reasonable metric to use for dose characterization in μCT. Dose rates in the Quantum GX vary based on the amount of material in the beam path and are a function of X-ray tube voltage. The CTDI₁₀₀ in air for a Quantum GX can be as low as 5.1 mGy for a 50 kVp scan and 9.9 mGy for a 90 kVp scan. This dose is low enough to visualize bone both in a mouse image and in a hydroxyapatite phantom, but applications requiring higher resolution in a mouse or less noise in a low-contrast phantom benefit from longer scan times with increased dose.

Conclusions

Dose management should be considered when designing μCT studies. Dose rates in the Quantum GX are compatible with longitudinal μCT imaging.

HSP27 inhibitor attenuates radiation-induced pulmonary inflammation

Radiation therapy has been used to treat over 70% of thoracic cancer; however, the method usually causes radiation pneumonitis. In the current study, we investigated the radioprotective effects of HSP27 inhibitor (J2) on radiation-induced lung inflammation in comparison to amifostine. In gross and histological findings, J2 treatment significantly inhibited immune cell infiltration in lung tissue, revealing anti-inflammatory potential of J2. Normal lung volume, evaluated by micro-CT analysis, in J2-treated mice was higher compared to that in irradiated mice. J2-treated mice reversed radiation-induced respiratory distress. However, amifostine did not show significant radioprotective effects in comparison to that of J2. In HSP27 transgenic mice, we observed increased immune cells recruitment and decreased volume of normal lung compared to wild type mice. Increased ROS production and oxidative stress after IR were down-regulated by J2 treatment, demonstrating antioxidant property of J2. The entire data of this study collectively showed that J2 may be an effective therapeutic agent for radiation-induced lung injury.

Tomographic in vivo microscopy for the study of lung physiology at the alveolar level

Lungs represent the essential part of the mammalian respiratory system, which is reflected in the fact that lung failure still is one of the leading causes of morbidity and mortality worldwide. Establishing the connection between macroscopic observations of inspiration and expiration and the processes taking place at the microscopic scale remains crucial to understand fundamental physiological and pathological processes. Here we demonstrate for the first time in vivo synchrotron-based tomographic imaging of lungs with pixel sizes down to a micrometer, enabling first insights into high-resolution lung structure. We report the methodological ability to study lung inflation patterns at the alveolar scale and its potential in resolving still open questions in lung physiology. As a first application, we identified heterogeneous distension patterns at the alveolar level and assessed first comparisons of lungs between the in vivo and immediate post mortem states.

Pro-apoptotic Noxa is involved in ablative focal irradiation-induced lung injury

Although lung injury including fibrosis is a well-documented side effect of lung irradiation, the mechanisms underlying its pathology are poorly understood. X-rays are known to cause apoptosis in the alveolar epithelial cells of irradiated lungs, which results in fibrosis due to the proliferation and differentiation of fibroblasts and the deposition of collagen. Apoptosis and BH3-only pro-apoptotic proteins have been implicated in the pathogenesis of pulmonary fibrosis. Recently, we have established a clinically analogous experimental model that reflects focal high-dose irradiation of the ipsilateral lung. The goal of this study was to elucidate the mechanism underlying radiation-induced lung injury based on this model. A radiation dose of 90 Gy was focally delivered to the left lung of C57BL/6 mice for 14 days. About 9 days after irradiation, the mice began to show increased levels of the pro-apoptotic protein Noxa in the irradiated lung alongside increased apoptosis and fibrosis. Suppression of Noxa expression by small interfering RNA protected cells from radiation-induced cell death and decreased expression of fibrogenic markers. Furthermore, we showed that reactive oxygen species participate in Noxa-mediated, radiation-induced cell death. Taken together, our results show that Noxa is involved in X-ray-induced lung injury.

Standardized Herbal Formula PM014 Inhibits Radiation-Induced Pulmonary Inflammation in Mice

Radiation therapy is widely used for thoracic cancers. However, it occasionally causes radiation-induced lung injuries, including pneumonitis and fibrosis. Chung-Sang-Bo-Ha-Tang (CSBHT) has been traditionally used to treat chronic pulmonary disease in Korea. PM014, a modified herbal formula derived from CSBHT, contains medicinal herbs of seven species. In our previous studies, PM014 exhibited anti-inflammatory effects in a chronic obstructive pulmonary disease model. In this study, we have evaluated the effects of PM014 on radiation-induced lung inflammation. Mice in the treatment group were orally administered PM014 six times for 2 weeks. Effects of PM014 on radiation pneumonitis were evaluated based on histological findings and differential cell count in bronchoalveolar lavage fluid. PM014 treatment significantly inhibited immune cell recruitment and collagen deposition in lung tissue. Normal lung volume, evaluated by radiological analysis, in PM014-treated mice was higher compared to that in irradiated control mice. PM014-treated mice exhibited significant changes in inspiratory capacity, compliance and tissue damping and elastance. Additionally, PM014 treatment resulted in the downregulation of inflammatory cytokines, chemokines, and fibrosis-related genes and a reduction in the transforming growth factor-β1-positive cell population in lung tissue. Thus, PM014 is a potent therapeutic agent for radiation-induced lung fibrosis and inflammation.

Adenovirus-mediated Foxp3 expression in lung epithelial cells ameliorates acute radiation-induced pneumonitis in mice

Forkhead transcription factor 3 (Foxp3) has a critical role in regulatory T cells (Treg). There are an increasing number of researches concerning the functions of Foxp3 in other cells, including lung epithelial cells besides Treg. However, the roles of Foxp3 in lung epithelial cells remain poorly understood. To examine the potential therapeutic benefits of Foxp3 for lung inflammation, this study investigates the effect of adenovirus-mediated Foxp3 overexpression in a radiation-induced lung damage model. Foxp3-EGFP expressing adenovirus was administered by intratracheal injection three times over 14 days after focal X-ray irradiation. To evaluate effects of Foxp3 overexpression in radiation-induced lung inflammation, immune cell profiles of bronchoalveolar lavage (BAL) fluid were analyzed. Foxp3 gene-delivered mice showed significant inhibition of immune cell infiltration, such as eosinophils, lymphocytes, macrophages and neutrophils in BAL fluid. Histopathological analysis also showed that Foxp3 overexpression inhibits inflammatory cell recruitment and collagen deposition in lung tissues. In addition, expression of inflammatory and fibrosis-related genes was decreased in the Foxp3 expression adenovirus-infected group. These results suggest that Foxp3 expression in lungs holds considerable therapeutic potential for attenuating inflammation and fibrosis in radiation-induced lung injury.

Stereotactic Body Radiation Therapy Delivery in a Genetically Engineered Mouse Model of Lung Cancer

PURPOSE

To implement clinical stereotactic body radiation therapy (SBRT) using a small animal radiation research platform (SARRP) in a genetically engineered mouse model of lung cancer.

METHODS AND MATERIALS

A murine model of multinodular Kras-driven spontaneous lung tumors was used for this study. High-resolution cone beam computed tomography (CBCT) imaging was used to identify and target peripheral tumor nodules, whereas off-target lung nodules in the contralateral lung were used as a nonirradiated control. CBCT imaging helps localize tumors, facilitate high-precision irradiation, and monitor tumor growth. SBRT planning, prescription dose, and dose limits to normal tissue followed the guidelines set by RTOG protocols. Pathologic changes in the irradiated tumors were investigated using immunohistochemistry.

RESULTS

The image guided radiation delivery using the SARRP system effectively localized and treated lung cancer with precision in a genetically engineered mouse model of lung cancer. Immunohistochemical data confirmed the precise delivery of SBRT to the targeted lung nodules. The 60 Gy delivered in 3 weekly fractions markedly reduced the proliferation index, Ki-67, and increased apoptosis per staining for cleaved caspase-3 in irradiated lung nodules.

CONCLUSIONS

It is feasible to use the SARRP platform to perform dosimetric planning and delivery of SBRT in mice with lung cancer. This allows for preclinical studies that provide a rationale for clinical trials involving SBRT, especially when combined with immunotherapeutics.

Induction of MiR-21 by Stereotactic Body Radiotherapy Contributes to the Pulmonary Fibrotic Response

Radiation-induced lung fibrosis, the most serious effect of lung cancer radiotherapy on normal tissue, remains a major technical obstacle to the broader application of radiotherapy to patients with lung cancer. This study describes the use of an image-guided irradiation system in mice mimicking stereotactic body radiotherapy (SBRT) to examine the molecular features of chronic fibrotic response after radiation injury. MicroRNA (miR) array analysis of injured pulmonary tissue identified a set of miRs whose expression was significantly increased in damaged lung tissue. In particular, miR-21 expression was increased at the radiation injury site, concurrent with collagen deposition. Although the inhibition of miR-21 by its specific inhibitor anti-miR-21 only marginally affected endothelial-mesenchymal transition (EndMT) in lung endothelial cells, this inhibition significantly reduced collagen synthesis in lung fibroblasts. Furthermore, ectopic expression of miR-21 was sufficient to promote a fibrotic response in lung fibroblasts, enhancing Smad2 phosphorylation concurrent with Smad7 downregulation. These findings indicate that the induction of miR-21 expression is responsible for fibrotic responses observed in mesenchymal cells at the injury site through the potentiation of TGF-β signaling. Local targeting of miR-21 at the injured area could have potential therapeutic utility in mitigating radiation-induced lung fibrosis.

Regulatory T Cells Contribute to the Inhibition of Radiation-Induced Acute Lung Inflammation via Bee Venom Phospholipase A₂ in Mice

Bee venom has long been used to treat various inflammatory diseases, such as rheumatoid arthritis and multiple sclerosis. Previously, we reported that bee venom phospholipase A₂ (bvPLA₂) has an anti-inflammatory effect through the induction of regulatory T cells. Radiotherapy is a common anti-cancer method, but often causes adverse effects, such as inflammation. This study was conducted to evaluate the protective effects of bvPLA₂ in radiation-induced acute lung inflammation. Mice were focally irradiated with 75 Gy of X-rays in the lung and administered bvPLA₂ six times after radiation. To evaluate the level of inflammation, the number of immune cells, mRNA level of inflammatory cytokine, and histological changes in the lung were measured. BvPLA₂ treatment reduced the accumulation of immune cells, such as macrophages, neutrophils, lymphocytes, and eosinophils. In addition, bvPLA₂ treatment decreased inflammasome-, chemokine-, cytokine- and fibrosis-related genes' mRNA expression. The histological results also demonstrated the attenuating effect of bvPLA₂ on radiation-induced lung inflammation. Furthermore, regulatory T cell depletion abolished the therapeutic effects of bvPLA₂ in radiation-induced pneumonitis, implicating the anti-inflammatory effects of bvPLA₂ are dependent upon regulatory T cells. These results support the therapeutic potential of bvPLA₂ in radiation pneumonitis and fibrosis treatments.

HSPB1 Inhibits the Endothelial-to-Mesenchymal Transition to Suppress Pulmonary Fibrosis and Lung Tumorigenesis

The endothelial-to-mesenchymal transition (EndMT) contributes to cancer, fibrosis, and other pathologic processes. However, the underlying mechanisms are poorly understood. Endothelial HSP1 (HSPB1) protects against cellular stress and has been implicated in cancer progression and pulmonary fibrosis. In this study, we investigated the role of HSPB1 in mediating the EndMT during the development of pulmonary fibrosis and lung cancer. HSPB1 silencing in human pulmonary endothelial cells accelerated emergence of the fibrotic phenotype after treatment with TGFβ or other cytokines linked to pulmonary fibrosis, suggesting that HSPB1 maintains endothelial cell identity. In mice, endothelial-specific overexpression of HSPB1 was sufficient to inhibit pulmonary fibrosis by blocking the EndMT. Conversely, HSPB1 depletion in a mouse model of lung tumorigenesis induced the EndMT. In clinical specimens of non-small cell lung cancer, HSPB1 expression was absent from tumor endothelial cells undergoing the EndMT. Our results showed that HSPB1 regulated the EndMT in lung fibrosis and cancer, suggesting that HSPB1-targeted therapeutic strategies may be applicable for treating an array of fibrotic diseases.

Focal exposure of limited lung volumes to high-dose irradiation down-regulated organ development-related functions and up-regulated the immune response in mouse pulmonary tissues

Background

Despite the emergence of stereotactic body radiotherapy (SBRT) for treatment of medically inoperable early-stage non-small-cell lung cancer patients, the molecular effects of focal exposure of limited lung volumes to high-dose radiation have not been fully characterized. This study was designed to identify molecular changes induced by focal high-dose irradiation using a mouse model of SBRT.

Results

Central areas of the mouse left lung were focally-irradiated (3 mm in diameter) with a single high-dose of radiation (90 Gy). Temporal changes in gene expression in the irradiated and non-irradiated neighboring lung regions were analyzed by microarray. For comparison, the long-term effect (12 months) of 20 Gy radiation on a diffuse region of lung was also measured. The majority of genes were down-regulated in the focally-irradiated lung areas at 2 to 3 weeks after irradiation. This pattern of gene expression was clearly different than gene expression in the diffuse region of lungs exposed to low-dose radiation. Ontological and pathway analyses indicated these down-regulated genes were mainly associated with organ development. Although the number was small, genes that were up-regulated after focal irradiation were associated with immune-related functions. The temporal patterns of gene expression and the associated biological functions were also similar in non-irradiated neighboring lung regions, although statistical significance was greatly reduced when compared with those from focally-irradiated areas of the lung. From network analysis of temporally regulated genes, we identified inter-related modules associated with diverse functions, including organ development and the immune response, in both the focally-irradiated regions and non-irradiated neighboring lung regions.

Conclusions

Focal exposure of lung tissue to high-dose radiation induced expression of genes associated with organ development and the immune response. This pattern of gene expression was also observed in non-irradiated neighboring areas of lung tissue, indicating a global lung response to focal high-dose irradiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0338-9) contains supplementary material, which is available to authorized users.

An experimental model-based exploration of cytokines in ablative radiation-induced lung injury in vivo and in vitro

INTRODUCTION

Stereotactic ablative radiotherapy is a newly emerging radiotherapy treatment method that, compared with conventionally fractionated radiation therapy (CFRT), allows an ablative dose of radiation to be delivered to a confined area around a tumor. The aim of the present study was to investigate the changes of various cytokines that may be involved in ablative radiation-induced lung injury in vitro and in vivo.

METHODS

In the in vivo study, ablative-dose radiation was delivered to a small volume of the left lung of C3H/HeJCr mice using a small-animal irradiator. The levels of 24 cytokines in the peripheral blood were tested at several time points after irradiation. For the in vitro study, three mouse cell types (type II pneumocytes, alveolar macrophages, and fibroblasts) known to play important roles in radiation-induced pneumonitis and lung fibrosis were analyzed using a co-culture system.

RESULTS

In the in vivo study, we found obvious patterns of serum cytokine changes depending on the volume of tissue irradiated (2-mm vs. 3.5-mm collimator). Only the levels of 3 cytokines increased with the 2-mm collimator at the acute phase (1-2 weeks after irradiation), while the majority of cytokines were elevated with the 3.5-mm collimator. In the in vitro co-culture system, after the cells were given an ablative dose of irradiation, the levels of five cytokines (GM-CSF, G-CSF, IL-6, MCP-1, and KC) increased significantly in a dose-dependent manner.

CONCLUSIONS

The cytokine levels in our radiation-induced lung injury model showed specific changes, both in vivo and in vitro. These results imply that biological studies related to ablative-dose small-volume irradiation should be investigated using the corresponding experimental models rather than on those simulating large-volume CFRT.

The inflammasome accelerates radiation-induced lung inflammation and fibrosis in mice

Although lung inflammation and fibrosis are well-documented dose-limiting side effects of lung irradiation, the mechanisms underlying these pathologies are unknown. An improved mechanistic understanding of radiation-induced pneumonitis is a prerequisite for the development of more effective radiotherapy; this was the rationale for the current study. Mouse lungs were focally irradiated with 75 Gy. The numbers of neutrophils, lymphocytes, macrophages, and total cells in the bronchoalveolar lavage fluid were counted, and pro-inflammatory cytokine levels were measured. Histological analysis and immunohistochemical staining for Tgf-β1 and Cd68 (a macrophage-specific protein) was also performed. After irradiation, mice developed pneumonitis, and exhibited higher numbers of neutrophils, lymphocytes, eosinophils, macrophages, and total cells compared to controls. In addition, inflammasome (Nlrp3, and caspase 1, Il1a, and Il1β), adhesion molecule (Vcam1), and cytokine (Il6) genes were significantly upregulated in the IR group. Cd68 and Tgfb1 proteins were significantly increased after irradiation. Upregulation of Cd68 and Tgfb1 correlates with the onset of radiation-induced pneumonitis and fibrosis. In addition, radiation-induced pneumonitis and fibrosis are accompanied by upregulation of phenotypic markers of inflammasome activity. Our findings have implications for the onset and exacerbation of damage in normal lung tissue.