Radioprotection of lungs by amifostine is associated with reduction in profibrogenic cytokine activity

Adipose-derived stem cells repair radiation-induced chronic lung injury via inhibiting TGF-β1/Smad 3 signaling pathway

To investigate the effect of adipose-derived stem cells (ASCs) transplantation on radiation-induced lung injury (RILI), Sprague-Dawley rats were divided into phosphate-buffered saline (PBS) group, ASCs group, Radiation + PBS group, and Radiation + ASCs group. Radiation + PBS and Radiation + ASCs groups received single dose of 30 Gy X-ray radiation to the right chest. The Radiation + PBS group received 1 mL PBS suspension and Radiation + ASCs group received 1 mL PBS suspension containing 1 × 107 CM-Dil-labeled ASCs. The right lung tissue was collected on Days 30, 90, and 180 after radiation. Hematoxylin-eosin and Masson staining were performed to observe the pathological changes and collagen fiber content in the lung tissue. Immunohistochemistry (IHC) and western blot (WB) were used to detect levels of fibrotic markers collagen I (Collal), fibronectin (FN), as well as transforming growth factor-β1 (TGF-β1), p-Smad 3, and Smad 3. Compared with the non-radiation groups, the radiation groups showed lymphocyte infiltration on Day 30 after irradiation and thickened incomplete alveolar walls, collagen deposition, and fibroplasia on Days 90 and 180. ASCs relieved these changes on Day 180 (Masson staining, P = 0.0022). Compared with Radiation + PBS group, on Day 180 after irradiation, the Radiation + ASCs group showed that ASCs could significantly decrease the expressions of fibrosis markers Collal (IHC: P = 0.0022; WB: P = 0.0087) and FN (IHC: P = 0.0152; WB: P = 0.026) and inhibit the expressions of TGF-β1 (IHC: P = 0.026; WB: P = 0.0152) and p-Smad 3 (IHC: P = 0.0043; WB: P = 0.0087) in radiation-induced injured lung tissue. These indicated that ASCs could relieve RILI by inhibiting TGF-β1/Smad 3 signaling pathway.

Cytokines and radiation-induced pulmonary injuries

Radiation therapy is one of the most common treatment strategies for thorax malignancies. One of the considerable limitations of this therapy is its toxicity to normal tissue. The lung is the major dose-limiting organ for radiotherapy. That is because ionizing radiation produces reactive oxygen species that induce lesions, and not only is tumor tissue damaged, but overwhelming inflammatory lung damage can occur in the alveolar epithelium and capillary endothelium. This damage may result in radiation-induced pneumonitis and/or fibrosis. While describing the lung response to irradiation generally, the main focus of this review is on cytokines and their roles and functions within the individual stages. We discuss the relationship between radiation and cytokines and their direct and indirect effects on the formation and development of radiation injuries. Although this topic has been intensively studied and discussed for years, we still do not completely understand the roles of cytokines. Experimental data on cytokine involvement are fragmented across a large number of experimental studies; hence, the need for this review of the current knowledge. Cytokines are considered not only as molecular factors involved in the signaling network in pathological processes, but also for their diagnostic potential. A concentrated effort has been made to identify the significant immune system proteins showing positive correlation between serum levels and tissue damages. Elucidating the correlations between the extent and nature of radiation-induced pulmonary injuries and the levels of one or more key cytokines that initiate and control those damages may improve the efficacy of radiotherapy in cancer treatment and ultimately the well-being of patients.

Modeling radiation-induced lung injury: lessons learned from whole thorax irradiation

Models of thoracic irradiation have been developed as clinicians and scientists have attempted to decipher the events that led up to the pulmonary toxicity seen in human subjects following radiation treatment. The most common model is that of whole thorax irradiation (WTI), applied in a single dose. Mice, particularly the C57BL/6J strain, has been frequently used in these investigations, and has greatly informed our current understanding of the initiation and progression of radiation-induced lung injury (RILI). In this review, we highlight the sequential progression and dynamic nature of RILI, focusing primarily on the vast array of information that has been gleaned from the murine model. Ample evidence indicates a wide array of biological responses that can be seen following irradiation, including DNA damage, oxidative stress, cellular senescence and inflammation, all triggered by the initial exposure to ionizing radiation (IR) and heterogeneously maintained throughout the temporal progression of injury, which manifests as acute pneumonitis and later fibrosis. It appears that the early responses of specific cell types may promote further injury, disrupting the microenvironment and preventing a return to homeostasis, although the exact mechanisms driving these responses remains somewhat unclear. Attempts to either prevent or treat RILI in preclinical models have shown some success by targeting these disparate radiobiological processes. As our understanding of the dynamic cellular responses to radiation improves through the use of such models, so does the likelihood of preventing or treating RILI.

Recurrent DNA damage is associated with persistent injury in progressive radiation-induced pulmonary fibrosis

PURPOSE

Radiation-induced lung injuries (RILI), namely radiation pneumonitis and/or fibrosis, are dose-limiting outcomes following treatment for thoracic cancers. As part of a search for mitigation targets, we sought to determine if persistent DNA damage is a characteristic of this progressive injury.

METHODS

C57BL/6J female mice were sacrificed at 24 h, 1, 4, 12, 16, 24 and 32 weeks following a single dose of 12.5 Gy thorax only gamma radiation; their lungs were compared to age-matched unirradiated animals. Tissues were examined for DNA double-strand breaks (DSBs) (γ-H2A.X and p53bp1), cellular senescence (senescence-associated beta-galactosidase and p21) and oxidative stress (malondialdehyde).

RESULTS

Data revealed consistently higher numbers of DSBs compared to age-matched controls, with increases in γ-H2A.X positivity beyond 24 h post-exposure, particularly during the pathological phases, suggesting periods of recurrent DNA damage. Additional intermittent increases in both cellular senescence and oxidative stress also appeared to coincide with pneumonitis and fibrosis.

CONCLUSIONS

These novel, long-term data indicate (a) increased and persistent levels of DSBs, oxidative stress and cellular senescence may serve as bioindicators of RILI, and (b) prevention of genotoxicity, via mitigation of free radical production, continues to be a potential strategy for the prevention of pulmonary radiation injury.

Expanding the therapeutic index of radiation therapy by normal tissue protection

Normal tissue damages induced by radiation therapy remain dose-limiting factors in radiation oncology and this is still true despite recent advances in treatment planning and delivery of image-guided radiation therapy. Additionally, as the number of long-term cancer survivors increases, unacceptable complications emerge and dramatically reduce the patients' quality of life. This means that patients and clinicians expect discovery of new options for the therapeutic management of radiation-induced complications. Over the past four decades, research has enhanced our understanding of the pathophysiological, cellular and molecular processes governing normal tissue toxicity. Those processes are complex and involve the cross-talk between the various cells of a tissue, including fibroblasts, endothelial, immune and epithelial cells as well as soluble paracrine factors including growth factors and proteases. We will review the translatable pharmacological approaches that have been developed to prevent, mitigate, or reverse radiation injuries based upon the targeting of cellular and signalling pathways. We will summarize the different steps of the research strategy, from the definition of initial biological hypotheses to preclinical studies and clinical translation. We will also see how novel research and therapeutic hypotheses emerge along the way as well as briefly highlight innovative approaches based upon novel radiotherapy delivery procedures.

A Combination of Podophyllotoxin and Rutin Alleviates Radiation-Induced Pneumonitis and Fibrosis through Modulation of Lung Inflammation in Mice

Pneumonitis and pulmonary fibrosis are predominant consequences of radiation exposure, whether planned or accidental. The present study, demonstrates radioprotective potential of a formulation, prepared by combining podophyllotoxin and rutin (G-003M), in mice exposed to 11 Gy thoracic gamma radiation (TGR). Treated mice were observed for survival and other symptomatic features. Formation of reactive oxygen species (ROS)/nitric oxide (NO) was measured in bronchoalveolar lavage cells. DNA damage and cell death were assessed in alveolar cells by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Total protein (TP), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP) were measured in bronchoalveolar lavage fluid (BALF)/serum of mice to assess lung vascular permeability. Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), cluster of differentiation 45, inducible nitric oxide synthase (iNOS), and nitrotyrosine were also estimated in lungs/BALF of differentially treated mice. Our observations revealed 100% survival in G-003M-pretreated mice against 66.50% in 11 Gy TGR exposed. Other symptoms like reduction in graying of hair, weight loss, and breathing rate were also observed in pretreated groups. Significant decline in ROS/NO and cell death in formulation pretreated mice were also observed. Decreased level of TP, LDH, and ALP in BALF/serum samples revealed G-003M-induced inhibition in lung permeability. Level of IL-6, TNF-α, and TGF-β1 in the lungs of these mice was found corresponding to control group at 8 weeks posttreatment. On the contrary, these cytokines raised significantly in 11 Gy TGR-exposed mice. Lung pneumonitis and fibrosis were found significantly countered in these mice. The observations revealed that G-003M could regulate immune system by curtailing radiation-induced oxidative and inflammatory stress, which has helped in minimizing radiation-inflicted pneumonitis and fibrosis.

Inhibition of Bcl-2/xl With ABT-263 Selectively Kills Senescent Type II Pneumocytes and Reverses Persistent Pulmonary Fibrosis Induced by Ionizing Radiation in Mice

PURPOSE

Ionizing radiation (IR)-induced pulmonary fibrosis (PF) is an irreversible and severe late effect of thoracic radiation therapy. The goal of this study was to determine whether clearance of senescent cells with ABT-263, a senolytic drug that can selectively kill senescent cells, can reverse PF.

METHODS AND MATERIALS

C57BL/6J mice were exposed to a single dose of 17 Gy on the right side of the thorax. Sixteen weeks after IR, they were treated with 2 cycles of vehicle or ABT-263 (50 mg/kg per day for 5 days per cycle) by gavage. The effects of ABT-263 on IR-induced increases in senescent cells; elevation in the expression of selective inflammatory cytokines, matrix metalloproteinases, and tissue inhibitors of matrix metalloproteinases; and the severity of the tissue injury and fibrosis in the irradiated lungs were evaluated 3 weeks after the last treatment, in comparison with the changes observed in the irradiated lungs before treatment or after vehicle treatment.

RESULTS

At 16 weeks after exposure of C57BL/6 mice to a single dose of 17 Gy, thoracic irradiation resulted in persistent PF associated with a significant increase in senescent cells. Treatment of the irradiated mice with ABT-263 after persistent PF had developed reduced senescent cells and reversed the disease.

CONCLUSIONS

To our knowledge, this is the first study to demonstrate that PF can be reversed by a senolytic drug such as ABT-263 after it becomes a progressive disease. Therefore, ABT-263 has the potential to be developed as a new treatment for PF.

Inhibition of Radiation-Induced Oxidative Damage in the Lung Tissue: May Acetylsalicylic Acid Have a Positive Role?

The lung is relatively sensitive to irradiation. It is shown that acetylsalicylic acid (ASA) might reduce oxidative injury and that it has a place in protection from cancer. The aim of this study is to evaluate the potential radioprotective effects of ASA. Whole-body irradiation (6 Gy, single dose) was applied to the rats. Glutathione (GSH), malondialdehyde (MDA), myeloperoxidase (MPO), and nitric oxide (NO) levels in the lung tissue were measured. Control (C), Radiation (R), Radiation + ASA (R + ASA; received irradiation and 25 mg/kg of ASA intraperitoneally (i.p.)), and Radiation + Amifostine (R + WR-2721; received irradiation and 200 mg/kg of WR-2721 i.p.) groups were used. The MPO levels decreased statistically significantly in the group administered ASA. Histopathologically, a radioprotective effect of ASA was more evident in the R + ASA group. ASA is an agent which has not been used as a radioprotector in the clinic yet, and it is worth supporting with more advanced studies.

Ethyl Acetate Fraction of Amomum xanthioides Exerts Antihepatofibrotic Actions via the Regulation of Fibrogenic Cytokines in a Dimethylnitrosamine-Induced Rat Model

Amomum xanthioides has been traditionally used to treat diverse digestive system disorders in the Asian countries. We investigated antihepatofibrotic effects of ethyl acetate fraction of Amomum xanthioides (EFAX). Liver fibrosis is induced by dimethylnitrosamine (DMN) injection (intraperitoneally, 10 mg/kg of DMN for 4 weeks to Sprague-Dawley rats). EFAX (25 or 50 mg/kg), silymarin (50 mg/kg), or distilled water was orally administered every day. The DMN injection drastically altered body and organ mass, serum biochemistry, and platelet count, while EFAX treatment significantly attenuated this alteration. Severe liver fibrosis is determined by trichrome staining and measurement of hydroxyproline contents. EFAX treatment significantly attenuated these symptoms as well as the increase in oxidative by-products of lipid and protein metabolism in liver tissues. DMN induced a dramatic activation of hepatic stellate cells and increases in the levels of protein and gene expression of transforming growth factor-beta (TGF-β), platelet derived growth factor-beta (PDGF-β), and connective tissue growth factor (CTGF). Immunohistochemical analyses revealed increases in the levels of protein and gene expression of α-smooth muscle actin. These alterations were significantly normalized by EFAX treatment. Our findings demonstrate the potent antihepatofibrotic properties of EFAX via modulation of fibrogenic cytokines, especially TGF-β in the liver fibrosis rat model.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Pulmonary toxicity in a rabbit model of stereotactic lung radiation therapy: efficacy of a radioprotector

This study aimed to assess the efficacy of the radioprotector amifostine in limiting radiation toxicity in a rabbit model of lung stereotactic body radiation therapy (SBRT) by correlating contrast-enhanced magnetic resonance angiography (ce-MRA), computed tomography (CT), and helium-3 (He-3) magnetic resonance imaging (MRI) with histopathology. Multiple MRI techniques were tested to obtain complementing physiologic information. Thirteen rabbits received SBRT to the right lower lobe of the lung. Specifically, 4 received 3 × 11 Gray (Gy), 6 received 3 × 11 Gy and 50 mg/kg of amifostine pre-SRBT, and 3 received 3 × 7, 3 × 9, or 3 × 13 Gy. Imaging was performed at baseline and 4, 8, 12, and 16 weeks post-SBRT. Ce-MRA perfusion difference between lungs in the irradiated group at 16 weeks post-treatment was statistically significant (P = .04) whereas the difference in the irradiated + amifostine group was not (P = .30). Histologically observed low red blood cell (RBC) count and CT hypodensity suggests changes were primarily related to perfusion; however, structural changes, such as increased alveolar size, were also present. No changes in He-3 MRI lung ventilation were observed in either group. Although radiation-induced injury detected in rabbits as CT hypodensity contrasted with increased density observed in humans/rodents, the changes in ce-MRA and CT were still significantly reduced after the addition of amifostine to SBRT. Use of CT and selected MRI techniques helped to pinpoint primary physiologic changes.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

Angiotensin converting enzyme inhibitors mitigate collagen synthesis induced by a single dose of radiation to the whole thorax

Our long-term goal is to use angiotensin converting enzyme (ACE) inhibitors to mitigate the increase in lung collagen synthesis that is induced by irradiation to the lung, which could result from accidental exposure or radiological terrorism. Rats (WAG/RijCmcr) were given a single dose of 13 Gy (dose rate of 1.43 Gy/min) of X-irradiation to the thorax. Three structurally-different ACE inhibitors, captopril, enalapril and fosinopril were provided in drinking water beginning 1 week after irradiation. Rats that survived acute pneumonitis (at 6-12 weeks) were evaluated monthly for synthesis of lung collagen. Other endpoints included breathing rate, wet to dry lung weight ratio, and analysis of lung structure. Treatment with captopril (145-207 mg/m(2)/day) or enalapril (19-28 mg/m(2)/day), but not fosinopril (19-28 mg/m(2)/day), decreased morbidity from acute pneumonitis. Lung collagen in the surviving irradiated rats was increased over that of controls by 7 months after irradiation. This increase in collagen synthesis was not observed in rats treated with any of the three ACE inhibitors. Analysis of the lung morphology at 7 months supports the efficacy of ACE inhibitors against radiation-induced fibrosis. The effectiveness of fosinopril against fibrosis, but not against acute pneumonitis, suggests that pulmonary fibrosis may not be a simple consequence of injury during acute pneumonitis. In summary, three structurally-different ACE inhibitors mitigate the increase in collagen synthesis 7 months following irradiation of the whole thorax and do so, even when therapy is started one week after irradiation.

Mitigation of lung injury after accidental exposure to radiation

There is a serious need to develop effective mitigators against accidental radiation exposures. In radiation accidents, many people may receive nonuniform whole-body or partial-body irradiation. The lung is one of the more radiosensitive organs, demonstrating pneumonitis and fibrosis that are believed to develop at least partially because of radiation-induced chronic inflammation. Here we addressed the crucial questions of how damage to the lung can be mitigated and whether the response is affected by irradiation to the rest of the body. We examined the widely used dietary supplement genistein given at two dietary levels (750 or 3750 mg/kg) to Fischer rats irradiated with 12 Gy to the lung or 8 Gy to the lung + 4 Gy to the whole body excluding the head and tail (whole torso). We found that genistein had promising mitigating effects on oxidative damage, pneumonitis and fibrosis even at late times (36 weeks) when drug treatment was initiated 1 week after irradiation and stopped at 28 weeks postirradiation. The higher dose of genistein showed no greater beneficial effect. Combined lung and whole-torso irradiation caused more lung-related severe morbidity resulting in euthanasia of the animals than lung irradiation alone.

Amelioration of the pathological changes induced by radiotherapy in normal tissues

Damage to normal tissues remains the most important limiting factor in the treatment of cancer by radiotherapy. In order to deliver a radiation dose sufficient to eradicate a localised tumour, the normal tissues need to be protected. A number of pharmacological agents have been used experimentally, and some clinically, to alleviate radiation damage to normal tissues but at present there is no effective clinical treatment to protect normal tissues against radiation injury. This paper reviews the efficacy of pharmacological substances used after radiation exposure. The limited evidence available suggests that radiation insult, like many other tissue injuries, is amenable to pharmacological intervention. However, care must be taken in the administration of these substances for the management of different aspects of radiation damage because there appears to be a tissue-specific response to different pharmacological agents. Also, one must be aware of the limitations of results obtained from animal models, which do not necessarily correlate to benefits in the clinic; the conflicting results reported with some modifiers of radiation damage; and the toxicity of these substances and radiation doses used in published studies. Conflicting results may arise from differences in the pathophysiologic processes involved in the development of radiation lesions in different tissues, and in the markers used to assess the efficacy of treatment agents.

Partial volume rat lung irradiation: Temporal fluctuations of in-field and out-of-field DNA damage and inflammatory cytokines following irradiation

PURPOSE

The current study investigated the early activation of inflammatory cytokines and macrophages in different regions of the lung following partial volume irradiation. We examined temporal fluctuations in DNA damage, cytokine expression and macrophage activation during 16 weeks post-irradiation.

MATERIALS AND METHODS

We irradiated the lower lung of Sprague-Dawley rats with 10 Gy. A micronucleus assay was used to examine DNA damage. Real-time Reverse Transcription-Polymerase Chain Reaction (RT-PCR) was used to analyse the RNA expression of Interleukin-1 alpha (IL-1a), Interleukin-1 beta (IL-1ss), Interleukin-6 (IL-6), Tumour Necrosis Factor alpha (TNF-a) and Transforming Growth Factor beta (TGF-ss) relative to Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH). The activation of macrophages was determined using the antibody ED-1 for immunohistochemical analysis.

RESULTS

The expression of DNA damage, the activation of macrophages and the expression of inflammatory cytokines all fluctuated in a cyclic pattern. The initial induction of cytokine expression and the activation of macrophages occurred at very early times (1 h) following irradiation. Waves of cytokine expression and macrophage activation were also seen at later times (up to 16 weeks) following irradiation. DNA damage also occurred in a cyclic pattern though this was less pronounced out-of-field. The levels of cytokines and activated macrophages were elevated to a similar degree both in- and out-of-field, whereas there was a greater micronuclei yield in-field than out-of-field.

CONCLUSIONS

An inflammatory response triggered by the partial volume irradiation occurs in the whole rat lung at very early times following irradiation and is maintained in a cyclic pattern to later times when the onset of functional symptoms is expected. We hypothesize that Reactive Oxygen Species (ROS) induced by this response play an important role in the induction of both in-field and out-of-field DNA damage.

Radioprotective effects of amifostine on acute and chronic esophageal injury in rodents

PURPOSE

This study was performed to evaluate the protective benefit of amifostine against esophageal injury from fractionated radiation in a rodent model.

METHODS

Fractionated or sham esophageal irradiation was administered to Fisher-344 rats for 5 consecutive daily fractions of 9 Gy using 150 kV X-rays. Animals received an intraperitoneal injection of amifostine or placebo 30 min before each fraction. Histopathologic analyses for mucosal thickness, submucosal collagen deposition, activation of macrophages, oxidative stress and expression/activation of integrinalphavbeta6 and transforming growth factor (TGF)-beta were performed 5 days and 10 weeks after irradiation.

RESULTS

Pre-RT mean mucosal thickness was 35 microm in both the placebo and the amifostine groups. Five days post-RT, mean mucosal thicknesses were 30 microm in the placebo group versus 37 microm in the amifostine group (p = 0.024). At 10 weeks post-RT, the group receiving amifostine experienced a significant decrease in tunica muscularis damage (p = 0.002), submucosal collagen deposition (p = 0.027), and macrophage accumulation (p = 0.026) when compared with the placebo group. The levels of immunoreactivity for oxidative stress, TGF-beta, and integrinalphavbeta6 were significantly decreased 10 weeks post-RT in the group receiving amifostine treatment compared with placebo group.

CONCLUSIONS

This study demonstrates that amifostine given before each radiation fraction protects against acute and chronic esophageal injury in a rodent model. Protection of the mucosal epithelium integrity by amifostine prevents integrinalphavbeta6 expression which reduces TGF-beta activation and subsequent development of chronic esophageal injury in this model. Further investigation is necessary to determine the clinical relevance of these findings.

Pharmacologic approaches to radiation protection

The concept of the therapeutic ratio (TR) is central to understanding the rationale for using radioprotectors. The TR relates tumor control probabilities and normal tissue complication probabilities to one another. An ideal radioprotector will reduce the latter without compromising the former. It should also be minimally toxic itself. Radioprotective strategies can be classified under the categories of protection, mitigation, and treatment. Protectors are administered before radiotherapy (RT) and are designed to prevent radiation-induced injury. Amifostine is the prototype drug. Mitigants are administered after RT but before the phenotypic expression of injury and are intended to ameliorate injury. Palifermin can be considered as the prototype mitigant. Treatment is a strategy that is predominantly palliative and supportive in nature. Pharmacologic radioprotective strategies should be integrated with physical strategies such as intensity-modulated radiotherapy to realize their maximum clinical potential.

Responses of normal cells to ionizing radiation

Radiation-induced alterations in cellular tissue homeostasis triggered by various molecular responses at the level of inter- and intracellular signaling processes cause both acute and late effects in normal tissue after radiation therapy. Some of the underlying molecular and cellular response pathways leading to radiation-induced tissue remodeling will be discussed, with special emphasis on vascular and parenchymal tissues.

Radiation pneumonitis and fibrosis: Mechanisms underlying its pathogenesis and implications for future research

Radiation pneumonitis and subsequent radiation pulmonary fibrosis are the two main dose-limiting factors when irradiating the thorax that can have severe implications for patients' quality of life. In this article, the current concepts about the pathogenetic mechanisms underlying radiation pneumonitis and fibrosis are presented. The clinical course of fibrosis, a postulated acute inflammatory stage, and a late fibrotic and irreversible stage are discussed. The interplay of cells and the wide variety of molecules orchestrating the immunologic response to radiation, their interactions with specific receptors, and the cascade of events they trigger are elucidated. Finally, the implications of this knowledge with respect to the therapeutic interventions are critically presented.

Cytokine profiling for prediction of symptomatic radiation-induced lung injury

PURPOSE

To analyze plasma cytokine profiles before the initiation of radiation therapy to define a cytokine phenotype that correlates with risk of developing symptomatic radiation-induced lung injury (SRILI).

METHODS AND MATERIALS

Symptomatic radiation-induced lung injury was evaluated in 55 patients (22 with SRILI and 33 without SRILI), according to modified National Cancer Institute common toxicity criteria. These plasma samples were analyzed by the multiplex suspension bead array system (Bio-Rad Laboratories; Hercules, CA), which included the following cytokines: interleukin (IL)-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p70, IL-13, IL-17, granulocyte/macrophage colony-stimulating factor, interferon-gamma, monocyte chemotactic protein 1, macrophage inflammatory protein 1beta, tumor necrosis factor alpha, and granulocyte colony-stimulating factor.

RESULTS

Significant differences in the median values of IL-8 were observed between patients with and without SRILI. Patients who did not develop SRILI had approximately fourfold elevated levels of IL-8 as compared with patients who did subsequently develop SRILI. Significant correlations were not found for any other cytokine in this study, including transforming growth factor beta1.

CONCLUSIONS

Patients with lower levels of plasma IL-8 before radiation therapy might be at increased risk for developing SRILI. Further studies are necessary to determine whether IL-8 levels are predictive of SRILI in a prospective trial and whether this marker might be used to determine patient eligibility for dose escalation.

The protective effect of amifostine on radiation-induced acute pulmonary toxicity: Detection by 99mTc-DTPA transalveolar clearances

PURPOSE

The purpose of this study was to determine by using (99m)Tc-diethylenetriaminepentaacetic acid (DTPA) lung scintigraphy whether amifostine given before irradiation protects alveolocapillary integrity in a rabbit model.

METHODS AND MATERIALS

Twenty white New Zealand rabbits were randomly divided into 4 groups: (1) control (CONT), (2) amifostine alone (AMF), (3) radiation (RAD), and (4) radiation plus amifostine (RAD+AMF). The AMF and RAD+AMF groups received amifostine. The RAD and RAD+AMF groups were irradiated to the right hemithorax with a single dose of 20 Gy using a (60)Co treatment unit. Amifostine (200 mg/kg) was given i.p. 30 min before irradiation. The (99m)Tc-DTPA radioaerosol study was performed 14 day after irradiation.

RESULTS

The mean clearance rate of (99m)Tc-DTPA in control subjects was 140 +/- 21 min. The highest t((1/2)) value was noted in the RAD group (603 +/- 105 min, p = 0.001). There were no significant differences between the (99m)Tc-DTPA lung clearance rates of the CONT, RAD+AMF (238 +/- 24 min), and AMF groups (227 +/- 54 min). The mean penetration index values of CONT, RAD, AMF, and RAD+AMF are 63% +/- 1.6%, 63% +/- 2.5%, 60% +/- 2.9%, and 63% +/- 2%, respectively.

CONCLUSIONS

We concluded that amifostine treatment before the lung irradiation protects the lung alveolocapillary integrity. This study confirms the protective effect of amifostine in an acute phase of radiation lung injury.

The potential influence of cell protectors for dose escalation in cancer therapy: an analysis of amifostine

The attempt to increase the therapeutic ratio in an effort to improve survival or quality of life is the goal of modern cancer therapy. It is commonly accepted that local and systemic tumor control would increase if the dose intensity of antineoplastic drugs, radiation therapy, or the combination were increased. Radiation dose escalation using intensity-modulated radiation therapy (IMRT), accelerated or hypofractionated radiation schemes, and multidrug chemotherapy regimens are being used to try to increase tumor kill while inflicting minimal injury to normal tissue. Modern chemoradiation techniques have led to improved local regional control and increased cure rates, but the potentially severe and debilitating adverse effects of the therapies prevent them from reaching the ultimate goal of curing the disease while leaving the patient with a good quality of life. Cell protectants such as amifostine function by reducing the effects of therapy on normal cells while maintaining tumor sensitivity to the therapy. In various studies, amifostine has been analyzed and appears to be a potentially powerful adjuvant to current cancer therapy. Administering amifostine may allow dose escalation with less or equal risk to surrounding normal tissues. This could improve therapeutic efficacy, survival, and quality of life for cancer patients.

Histopathologic amelioration of fibroproliferative change in rat irradiated lung using soluble transforming growth factor-beta (TGF-β) receptor mediated by adenoviral vector

PURPOSE

To investigate whether an adenoviral-mediated soluble transforming growth factor-beta (TGF-beta) type II receptor could ameliorate fibroproliferative change in rat irradiated lung.

METHODS AND MATERIALS

We used an adenoviral vector expressing a soluble TGF-beta receptor (AdT beta-ExR), which adsorbs TGF-beta and inhibits the function of the wild-type receptor as a dominant-negative mutant. Rats were i.v. injected with either 0.5 mL of AdT beta-ExR (1.0 x 10(9) plaque-forming units/mL) or AdLacZ (1.0 x 10(9) plaque-forming units/mL), a control adenovirus expressing bacterial beta-galactosidase, or saline, then 3 days later they received 4-MV X-ray irradiation of 30 Gy in a single fraction to the right lung. Eight weeks after irradiation, the rats were killed, and their right lungs were examined histopathologically. The respiratory rates of all rats were observed with a charge-coupled device video system before the rats were irradiated and killed.

RESULTS

A significant increase in breathing rates was observed in the saline- or AdLacZ-infected rats. The respiratory rate of the AdT beta-ExR-treated rats was significantly lower than that in the saline- or AdLacZ-infected rats. Fibroproliferative change in the irradiated lung was markedly reduced in the AdT beta-ExR-treated rats in comparison with the saline- or AdLacZ-infected rats. With respect to active TGF-beta 1 expression, myofibroblast proliferation, and macrophage/monocyte infiltration, the findings were identical to those for fibroproliferative change.

CONCLUSIONS

Our results indicate that TGF-beta plays a critical role in radiation-induced fibroproliferation of the lung and suggest that the adenoviral-mediated soluble TGF-beta receptor may have potential for use in the amelioration of this intractable pulmonary damage.

Effects of dose and schedule on the efficacy of Ethyol: preclinical studies1 1The authors are employees and shareholders of MedImmune Inc

The chemo- and radioprotectant drug amifostine (Ethyol; MedImmune, Inc, Gaithersburg, MD) is approved for intravenous (IV) administration; however, the subcutaneous (SC) route is being explored as a practical alternative. We have previously reported equivalence between IV and SC administration using a rat model of radioprotection and active metabolite (WR-1065) tissue pharmacokinetics. To examine the more clinically relevant fractionated and hyperfractionated radiation schedules and the effects of variations in the time of amifostine administration, we expanded these studies to include radioprotection and pharmacokinetic studies of WR-1065 using multiple dosing. To measure radioprotection using a fractionated radioprotection model, rats were given amifostine over a 1-week period at various doses (25 mg/kg, 50 mg/kg, 100 mg/kg; or 162.5 mg/m(2), 325 mg/m(2), 650 mg/m(2), respectively) IV or SC daily 30 minutes before exposure to 7.5 Gy/dose. Rats were fully protected from mucositis at the highest amifostine dose, with protection diminishing as the amifostine was decreased. Equivalent protection was observed whether the drug was given IV or SC. When the number of days of amifostine administration was reduced, protection was diminished. Amifostine also protected against radiation delivered using a 1-week hyperfractionated schedule (4.5 Gy/exposure twice daily), with optimal protection occurring when the drug was administered bid 30 minutes before each exposure (50 mg/kg) or every day before the morning exposure (100 mg/kg). The need for daily dosing to achieve optimal radioprotection was consistent with the tissue pharmacokinetics of the active metabolite. We found that WR-1065 did not accumulate in tissues or in SC-implanted tumors when amifostine was administered daily for 3 weeks. In addition, tissue and tumor levels of WR-1065 declined to baseline 24 hours after each amifostine dose. In a monkey pharmacokinetic model, plasma levels of WR-1065 (characterized by a pronounced spike of WR-1065 immediately after IV administration that was absent when the drug was given SC) were similar to those of humans; however, levels of WR-1065 in the tissues were higher 30 minutes following SC administration and were equivalent 60 minutes following IV or SC administration. These results suggest that maximum tissue levels and protection occur when amifostine is given 30 to 60 minutes before radiation exposure, that treatment breaks reduce the radioprotection by amifostine, and that protection from hyperfractionated radiation is dependent on amifostine dose and schedule.

Soluble TGFbeta type II receptor gene therapy ameliorates acute radiation-induced pulmonary injury in rats

PURPOSE

To assess whether administration of recombinant human adenoviral vector, which carries soluble TGFbeta1 Type II receptor (TbetaRII) gene, might reduce the availability of active TGFbeta1 and thereby protect the lung from radiation-induced injury.

METHODS AND MATERIALS

Female Fisher 344 rats were given a single 30 Gy dose of right hemithoracic irradiation 24 h after the injections of control (AdGFP) or treatment (AdexTbetaRII-Fc) vectors. Different end points were assessed to look for lung tissue damage.

RESULTS

There was a significant increase in the plasma level of soluble TbetaRII 24 h and 48 h after injection of treatment vector. In the radiation (RT) + AdexTbetaRII-Fc group, there was a significant reduction in respiratory rate at 4 weeks after treatment as compared to the RT-alone group. Histologic results revealed a significant reduction in lung damage and decrease in the number and activity of macrophages in the RT + AdexTbetaRII-Fc group as compared to the RT-alone group. The tissue level of active TGFbeta1 was significantly reduced in rats receiving RT + AdexTbetaRII-Fc treatment. There was also an upregulation of transmembrane TbetaRII in lung tissue in the RT-alone group as compared to the RT + gene therapy rats.

CONCLUSIONS

This study shows the ability of AdexTbetaRII-Fc gene therapy to induce an increase in circulating levels of soluble receptors, to reduce the tissue level of active TGFbeta1, and consequently to ameliorate acute radiation-induced lung injury.

The polysaccharide fraction AIP1 from Artemisia iwayomogi suppresses apoptotic death of the mouse spleen cells in culture

A polysaccharide fraction, AIP1, purified from Artemisia iwayomogi was shown to have immunomodulating and anti-tumor activities in mice. In order to determine how the AIP1 fraction exhibits the immunomodulating activity, the effect of the fraction on the apoptosis of mouse spleen cells was investigated. Treatment of the mouse spleen cells with the AIP1 fraction resulted in the suppression of apoptotic death and an extension of cell survival in culture, indicating that the fraction might modulate the death of spleen cells. Treatment of the mice with the AIP1 fraction in vivo also resulted in less apoptosis of the spleen cells, which indicates the physiological relevance of the anti-apoptosis effect of the fraction in vitro. A mouse gene array was used to determine the profile of the gene expression change showing a pattern of up- and down-regulated genes by the AIP1 treatment. This study provides preliminary information regarding the immunomodulatory mechanism of the AIP1 fraction.

Inhibitors of inducible nitric oxide synthase expression from Artemisia iwayomogi

Nitric oxide (NO) is an important bioactive agent that mediates a wide variety of physiological and pathophysiological events. NO overproduction by inducible nitric oxide synthase (iNOS) results in severe hypotension and inflammation. This investigation is part of a study to discover new iNOS inhibitors from medicinal plants using a macrophage cell culture system. Two sesquiterpenes (1 and 2) were isolated from Artemisia iwayomogi (Compositae) and were found to inhibit NO synthesis (IC50 3.64 microg/mL and 2.81 microg/mL, respectively) in lipopolysaccharide (LPS)-activated RAW 264.7 cells. Their structures were identified as 3-O-methyl-isosecotanapartholide (1) and iso-secotanapartholide (2). Compounds 1 and 2 inhibited the LPS-induced expression of the iNOS enzyme in the RAW 264.7 cells. The inhibition of NO production via the down regulation of iNOS expression may substantially modulate the inflammatory responses.