Thrombomodulin as a marker of radiation-induced endothelial cell injury

Von Willebrand factor promotes radiation-induced intestinal injury (RIII) development and its cleavage enzyme rhADAMTS13 protects against RIII by reducing inflammation and oxidative stress

Patients with abdominopelvic cancer undergoing radiotherapy commonly develop radiation-induced intestinal injury (RIII); however, its underlying pathogenesis remains elusive. The von Willebrand factor (vWF)/a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) axis has been implicated in thrombosis, inflammation, and oxidative stress. However, its role in RIII remains unclear. In this study, the effect of radiation on vWF and ADAMTS13 expression was firstly evaluated in patients with cervical cancer undergoing radiotherapy and C57BL/6J mice exposed to different doses of total abdominal irradiation. Then, mice with the specific deletion of vWF in the platelets and endothelium were established to demonstrate the contribution of vWF to RIII. Additionally, the radioprotective effect of recombinant human (rh) ADAMTS13 against RIII was assessed. Results showed that both the patients with cervical cancer undergoing radiotherapy and RIII mouse model exhibited increased vWF levels and decreased ADAMTS13 levels. The knockout of platelet- and endothelium-derived vWF rectified the vWF/ADAMTS13 axis imbalance; improved intestinal structural damage; increased crypt epithelial cell proliferation; and reduced radiation-induced apoptosis, inflammation, and oxidative stress, thereby alleviating RIII. Administration of rhADAMTS13 could equally alleviate RIII. Our results demonstrated that abdominal irradiation affected the balance of the vWF/ADAMTS13 axis. vWF exerted a deleterious role and ADAMTS13 exhibited a protective role in RIII progression. rhADAMTS13 has the potential to be developed into a radioprotective agent.

ADAMTS13 protease or lack of von Willebrand factor protects irradiation and melanoma-induced thrombotic microangiopathy in zebrafish

BACKGROUND

Severe deficiency of plasma ADAMTS13 activity may result in potentially fatal thrombotic thrombocytopenic purpura and relative deficiency of plasma ADAMTS13 activity may be associated with adverse outcomes of certain malignancies. Here, we report the role of ADAMTS13 or lack of von Willebrand factor (VWF) in reducing irradiation and melanoma-induced thrombotic microangiopathy (TMA) and mortality in zebrafish.

METHODS

Zebrafish melanoma cell line (ZMEL) was injected subcutaneously into wild-type (wt), adamts13-/- (a13-/- ), von Willebrand factor (vwf-/- ), and a13-/- vwf-/- zebrafish following total body irradiation; the tumor growth, its gene expression pattern, the resulting thrombocytopenia, and the mortality were determined.

RESULTS

Total body irradiation at 30 Gy alone resulted in a transient thrombocytopenia in both wt and a13-/- zebrafish. However, thrombocytopenia occurred earlier and more profound in a13-/- than in wt zebrafish, which was resolved 2 weeks following irradiation alone. An inoculation of ZMEL following the irradiation resulted in more severe and persistent thrombocytopenia, as well as earlier death in a13-/- than in wt zebrafish. The vwf-/- or a13-/- vwf-/- zebrafish were protected from developing severe thrombocytopenia following the same maneuvers. RNA-sequencing revealed significant differentially expressed genes associated with oxidation-reduction, metabolism, lipid, fatty acid and cholesterol metabolic processes, steroid synthesis, and phospholipid efflux in the melanoma explanted from a13-/- zebrafish compared with that from the wt controls.

CONCLUSIONS

Our results indicated that plasma ADAMTS13 or lack of VWF may offer a significant protection against the development of irradiation- and/or melanoma-induced TMA. Such a microenvironment may directly affect melanoma cell phenotypes via alternation in the oxidation-reduction and lipid metabolic pathways.

Understanding Molecular Mechanisms and Identifying Key Processes in Chronic Radiation Cystitis

Chronic radiation cystitis (CRC) is a consequence of pelvic radiotherapy and affects 5–10% of patients. The pathology of CRC is without curative treatment and is characterized by incontinence, pelvic pain and hematuria, which severely degrades patients’ quality of life. Current management strategies rely primarily on symptomatic measures and have certain limitations. Thanks to a better understanding of the pathophysiology of radiation cystitis, studies targeting key manifestations such as inflammation, neovascularization and cell atrophy have emerged and are promising avenues for future treatment. However, the mechanisms of CRC are still better described in animal models than in human models. Preclinical studies conducted to elucidate the pathophysiology of CRC use distinct models and are most often limited to specific processes, such as fibrosis, vascular damage and inflammation. This review presents a synthesis of experimental studies aimed at improving our understanding of the molecular mechanisms at play and identifying key processes in CRC.

The Evolution of Safe and Effective Coaguligands for Vascular Targeting and Precision Thrombosis of Solid Tumors and Vascular Malformations

In cardiovascular and cerebrovascular biology, control of thrombosis and the coagulation cascade in ischemic stroke, myocardial infarction, and other coagulopathies is the focus of significant research around the world. Ischemic stroke remains one of the largest causes of death and disability in developed countries. Preventing thrombosis and protecting vessel patency is the primary goal. However, utilization of the body’s natural coagulation cascades as an approach for targeted destruction of abnormal, disease-associated vessels and tissues has been increasing over the last 30 years. This vascular targeting approach, often termed “vascular infarction”, describes the deliberate, targeted delivery of a thrombogenic effector to diseased blood vessels with the aim to induce localized activation of the coagulation cascade and stable thrombus formation, leading to vessel occlusion and ablation. As systemic delivery of pro-thrombotic agents may cause consternation amongst traditional stroke researchers, proponents of the approach must suitably establish both efficacy and safety to take this field forward. In this review, we describe the evolution of this field and, with a focus on thrombogenic effectors, summarize the current literature with respect to emerging trends in “coaguligand” development, in targeted tumor vessel destruction, and in expansion of the approach to the treatment of brain vascular malformations.

Combining Angiogenesis Inhibitors with Radiation: Advances and Challenges in Cancer Treatment

BACKGROUND

Radiation therapy is a widely employed modality that is used to destroy cancer cells, but it also tends to induce changes in the tumor microenvironment and promote angiogenesis. Radiation, when used as a sole means of therapeutic approach to treat cancer, tends to trigger the angiogenic pathways, leading to the upregulation of several angiogenic growth factors such as VEGF, bFGF, PDGF and angiogenin. This uncontrolled angiogenesis leads to certain angiogenic disorders like vascular outgrowth and an increase in tumor progression that can pose a serious threat to patients.

OBJECTIVE

This review emphasizes on various components of the tumor microenvironment, angiogenic growth factors and biological effects of radiation on tumors in provoking the relapse. It also describes the angiogenic mechanisms that trigger the tumor relapse after radiation therapy and how angiogenesis inhibitors can help in overcoming this phenomenon. It gives an overview of various angiogenesis inhibitors in pre-clinical as well as in clinical trials.

CONCLUSION

The review focuses on the beneficial effects of the combinatorial therapeutic approach of anti-angiogenesis therapy and radiation in tumor management.

Biomarkers of radiation-induced vascular injury

OBJECTIVE

Cancer survivorship has thrown the spotlight on the incidence of nonmalignant chronic diseases in cancer patients. Endothelial injury is increasingly recognized as a consequence of cancer treatment, particularly after radiation therapy (RT). This review is to provide a current understanding on the pathophysiological mechanisms and predictive biomarkers of radiation-induced vascular injury.

RECENT FINDINGS

Radiation directly impacts vasculature by causing endothelial apoptosis and senescence, and alterations in normal homeostasis. This altered milieu at the endothelial surface may contribute to a systemic chronic inflammatory state that is superimposed upon the cascade of normal senescence processes leading to acceleration of age-related disorders, atherosclerosis, and chronic fibrosis. Vasculature imaging, blood-based or cell-component biomarkers, and signatures of genomics, proteomics, metabolomics, and radiomics are potential tools for detection of vascular damage after irradiation.

CONCLUSIONS

Development of a valid prediction model by combining an array of imaging tools, blood-based biomarkers, coupled with novel predictors like exosomes and metabolic degradation products can serve to identify RT-induced vascular injury early for subsequent introduction of newer therapeutic approaches to counter radiation morbidity.

Pathological effects of ionizing radiation: endothelial activation and dysfunction

The endothelium, a tissue that forms a single layer of cells lining various organs and cavities of the body, especially the heart and blood as well as lymphatic vessels, plays a complex role in vascular biology. It contributes to key aspects of vascular homeostasis and is also involved in pathophysiological processes, such as thrombosis, inflammation, and hypertension. Epidemiological data show that high doses of ionizing radiation lead to cardiovascular disease over time. The aim of this review is to summarize the current knowledge on endothelial cell activation and dysfunction after ionizing radiation exposure as a central feature preceding the development of cardiovascular diseases.

Potential markers and metabolic processes involved in the mechanism of radiation-induced heart injury

Irradiation of normal tissues leads to acute increase in reactive oxygen/nitrogen species that serve as intra- and inter-cellular signaling to alter cell and tissue function. In the case of chest irradiation, it can affect the heart, blood vessels, and lungs, with consequent tissue remodelation and adverse side effects and symptoms. This complex process is orchestrated by a large number of interacting molecular signals, including cytokines, chemokines, and growth factors. Inflammation, endothelial cell dysfunction, thrombogenesis, organ dysfunction, and ultimate failing of the heart occur as a pathological entity - "radiation-induced heart disease" (RIHD) that is major source of morbidity and mortality. The purpose of this review is to bring insights into the basic mechanisms of RIHD that may lead to the identification of targets for intervention in the radiotherapy side effect. Studies of authors also provide knowledge about how to select targeted drugs or biological molecules to modify the progression of radiation damage in the heart. New prospective studies are needed to validate that assessed factors and changes are useful as early markers of cardiac damage.

Basic Fibroblast Growth Factor Ameliorates Endothelial Dysfunction in Radiation-Induced Bladder Injury

This study was designed to explore the effect of basic fibroblast growth factor (bFGF) on radiation-induced endothelial dysfunction and histological changes in the urinary bladder. bFGF was administrated to human umbilical vein cells (HUVEC) or urinary bladder immediately after radiation. Reduced expression of thrombomodulin (TM) was indicated in the HUVEC and urinary bladder after treatment with radiation. Decreased apoptosis was observed in HUVEC treated with bFGF. Administration of bFGF increased the expression of TM in HUVEC medium, as well as in the urinary bladder at the early and delayed phases of radiation-induced bladder injury (RIBI). At the early phase, injection of bFGF increased the thickness of urothelium and reduced inflammation within the urinary bladder. At the delayed phase, bFGF was effective in reducing fibrosis within the urinary bladder. Our results indicate that endothelial dysfunction is a prominent feature of RIBI. Administration of bFGF can ameliorate radiation-induced endothelial dysfunction in urinary bladder and preserve bladder histology at early and delayed phases of RIBI.

Low-dose irradiation affects expression of inflammatory markers in the heart of ApoE -/- mice

Epidemiological studies indicate long-term risks of ionizing radiation on the heart, even at moderate doses. In this study, we investigated the inflammatory, thrombotic and fibrotic late responses of the heart after low-dose irradiation (IR) with specific emphasize on the dose rate. Hypercholesterolemic ApoE-deficient mice were sacrificed 3 and 6 months after total body irradiation (TBI) with 0.025, 0.05, 0.1, 0.5 or 2 Gy at low (1 mGy/min) or high dose rate (150 mGy/min). The expression of inflammatory and thrombotic markers was quantified in frozen heart sections (CD31, E-selectin, thrombomodulin, ICAM-1, VCAM-1, collagen IV, Thy-1, and CD45) and in plasma samples (IL6, KC, MCP-1, TNFα, INFγ, IL-1β, TGFβ, INFγ, IL-10, sICAM-1, sE-selectin, sVCAM-1 and fibrinogen) by fluorescence analysis and ELISA. We found that even very low irradiation doses induced adaptive late responses, such as increases of capillary density and changes in collagen IV and Thy-1 levels indicating compensatory regulation. Slight decreases of ICAM-1 levels and reduction of Thy 1 expression at 0.025–0.5 Gy indicate anti-inflammatory effects, whereas at the highest dose (2 Gy) increased VCAM-1 levels on the endocardium may represent a switch to a pro-inflammatory response. Plasma samples partially confirmed this pattern, showing a decrease of proinflammatory markers (sVCAM, sICAM) at 0.025–2.0 Gy. In contrast, an enhancement of MCP-1, TNFα and fibrinogen at 0.05–2.0 Gy indicated a proinflammatory and prothrombotic systemic response. Multivariate analysis also revealed significant age-dependent increases (KC, MCP-1, fibrinogen) and decreases (sICAM, sVCAM, sE-selectin) of plasma markers. This paper represents local and systemic effects of low-dose irradiation, including also age- and dose rate-dependent responses in the ApoE^-/- mouse model. These insights in the multiple inflammatory/thrombotic effects caused by low-dose irradiation might facilitate an individual evaluation and intervention of radiation related, long-term side effects but also give important implications for low dose anti-inflammatory radiotherapy.

Radiation-induced changes in levels of selected proteins in peripheral blood serum of breast cancer patients as a potential triage biodosimeter for large-scale radiological emergencies

The threat of a large scale radiological emergency, where thousands of people may require fast biological dosimetry for the purpose of triage, makes it necessary to search for new, high throughput biological dosimeters. The authors tested an assay based on the quantitative analysis of selected proteins in peripheral blood serum. They were particularly interested in testing proteins that are specific to irradiation of skin, as these can be used in cases of partial body exposure. Candidate proteins were identified in an earlier study with mice, where skin of the animals was exposed to different doses of radiation and global expression of serum proteins was analyzed. Eight proteins were found, the expression of which showed a consistent dose-response relationship. Human analogues of these proteins were identified, and their expression was measured in peripheral blood serum of 16 breast cancer patients undergoing external beam radiotherapy. The proteins were Apolipoprotein E; Apolipoprotein H; Complement protein 7; Prothrombinase; Pantothenate Kinase 4; Alpha-2-macroglobulin; Fetuin B and Alpha-1-Anti-Chymotrypsin. Measurements were carried out in blood samples collected prior to exposure (control), on the day after one fraction (2 Gy), on the day after five fractions (10 Gy), on the day after 10 fractions (20 Gy), and 1 mo after 23-25 fractions (total dose of 46-50 Gy). Multivariate analysis was carried out, and a multinomial logistic regression model was built. The results indicate that the combined analysis of Apolipoprotein E, Factor X, and Pantothenate Kinase 4 allows discriminating between exposure to 2 Gy and lower and between 10 Gy and higher. The discrimination is possible up to 1 mo after exposure.

Late effects of local irradiation on the expression of inflammatory markers in the Arteria saphena of C57BL/6 wild-type and ApoE-knockout mice

Combined action of irradiation (IR), shear stress, and high blood pressure is well recognized to induce damage to vasculature, while data on pathological effects of IR in large peripheral vessels with low blood pressure are scarce. The purpose of the present study was hence to investigate time- and dose-dependent effects of local IR on inflammatory and prothrombotic processes in the Arteria (A.) saphena of C57BL/6 wild-type and apolipoprotein E (ApoE)-knockout mice. Single doses of 2, 5, 8, 10, or 16 Gy were locally delivered to the A. saphena of the left leg of the animals. The expression of CD31, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin, monocyte chemoattractant protein-1 (MCP-1), and thrombomodulin (TM) was quantified by semiautomatic TissueFax fluorescence analysis in frozen arterial sections. Follow-up periods were 3, 6, 9, 12, or 18 months. Protein expression in the arterial wall displayed dose-dependent changes. Proinflammatory reactions were observed for CD31, E-selectin, ICAM, and VCAM already at doses of 2 Gy. Anti-inflammatory changes were detected for MCP-1 and TM. The effects were more pronounced in wild-type versus ApoE(-/-) mice. Changes remain mostly transient up to 16 Gy. Dose- and time-dependent changes in inflammatory and thrombotic mediators in the wall of the A. saphena were found after local IR but did not transform into histopathological consequences.

Cardiovascular complications of radiotherapy

Chest radiotherapy is routinely used to treat malignancies such as Hodgkin disease and breast cancer but is commonly associated with a variety of cardiovascular complications involving the pericardium, myocardium, valves, coronary arteries, and conduction system. Cardiovascular complications are related to the total dose of radiation and the fractionation of the dose. They are usually progressive, portend poor prognosis, and are often refractory to treatment after significant radiation exposure. The mechanism of injury is multifactorial and likely involves endothelial damage of the microvasculature and coronary arteries and liberation of multiple inflammatory and profibrotic cytokines. In conclusion, routine follow-up with a cardiologist, which might include screening for valvular disease with echocardiography and coronary artery disease with computed tomography angiography or coronary artery calcium scoring, should be considered in patients with a history of chest radiotherapy.

Mast cells and ionizing radiation induce a synergistic expression of inflammatory genes in endothelial cells by a mechanism involving p38α MAP kinase and (p65) NF-κB activation

Vascular endothelium is a key compartment involved in the development of normal tissue toxicity associated with cancer radiation therapy, i.e., acute inflammation and late fibrosis. Radiation-induced endothelial cell activation has been extensively studied, and activated endothelial cells are characterized by increased expression of inflammatory mediators and adhesion molecules, and activation of the coagulation and thrombosis pathways. However, little is known about the role of vascular endothelium interaction with resident immune cells, such as mast cells on its response to irradiation. Here, we report that endothelial exposure to mast cell conditioned medium and irradiation induces a synergistic expression of many inflammatory genes including interleukin-6 and interleukin-8, CXCL2 and E-selectin. This synergy is blocked by the histamine H1 receptor antagonist mepyramine and partially mimicked by exogenous histamine addition before irradiation. Using pharmacological and molecular inhibition approaches, we show the p38α MAP kinase and p65 (NF-κB) dependence of the synergy. Moreover, our data show a link between both pathways, with p65 (NF-κB) being downstream of p38. These data highlight the possible exacerbation of the radiation-induced endothelial inflammatory response by its interactions with immune cells. It also suggest that p38α MAP kinase and p65 (NF-κB) inhibition in vascular endothelium may limit excessive tissue inflammation induced by radiation therapy, and thereby limit the associated acute and late tissue damage.

Radiation-induced heart disease: a clinical update

Cardiovascular diseases and cancer are the two leading causes of morbidity and mortality worldwide. Improvement in cancer therapy has led to increasing number of cancer survivors, some of whom may suffer from adverse cardiovascular effects of radiation therapy. Longterm followup is essential, as the cardiac complication may manifest years after completion of radiation therapy. In this paper, we have discussed the cardiovascular effects of radiation therapy.

Indigowood root extract protects hematopoietic cells, reduces tissue damage and modulates inflammatory cytokines after total-body irradiation: does Indirubin play a role in radioprotection?

Radix of Isatis indigotica (indigowood root, IR) has been used in traditional medicine for its potential anti-inflammatory effect. The purpose of this study is to investigate the radioprotective effects of radiation caused damages in hematopoietic system and normal tissues in mice. A total of 57 BALB/c mice were randomized into six treatment groups: control, IR treatment (0.195, 0.585 and 1.170 g/kg, p.o. daily), L-glutamine (0.520 g/kg) and sham group. All mice except the sham group were irradiated and then administered for one week. The radioprotective effect on hematopoietic system, serum cytokines, and intestinal toxicity was studied. Protective effects on spleen and thymus are found in IR-treated groups. IR assisted in restoration of leukocytopenia after whole mice irradiation with significant reduction of serum TNF-alpha, IL-1beta, and IL-6. These enhancements of hematopoietic effects are due to an increase in the serum G-CSF concentration in IR treated groups. In histopathological assessment, significant improvement of intestine toxicity is observed in high-dose IR and L-glutamine group. Evidences show that IR has potentials to be a radioprotector, especially in recovery of hematopoietic system, reduction of inflammatory cytokines and intestinal toxicity. Indirubin may play a crucial role, but the underlying mechanism is not very clear and warrants further studies.

Intracoronary β‐irradiation enhances balloon‐injury‐induced tissue factor expression in the porcine injury model

Intracoronary brachytherapy (ICBT) effectively reduces restenosis but is associated with late thrombosis. Since tissue factor (TF) is an important mediator of arterial thrombosis, we tested the hypothesis that ICBT results in persistently augmented TF expression. Coronary arteries from 12 pigs were randomized to: control (C; no injury), oversized balloon injury (BI), or BI followed by ICBT. Animals were sacrificed at 1, 7, 14, or 60 days postprocedure, and coronary arteries collected for expression analyses and immunostaining. ICBT-treated arteries had higher TF antigen and activity at all time-points compared to BI arteries (Western blot: 16 571 +/- 2090 vs 10 135 +/- 2939 densitometric units, p = 0.001; ELISA: 0.42 +/- 0.13 nM vs 0.25 +/- 0.14 nM, p = 0.001; TF activity assay: 0.303 +/- 0.11 nM vs 0.18 +/- 0.07 nM, p = 0.01; immunohistochemical staining: 30.6 +/- 6.6% vs 11.5% +/- 3.2%, p = 0.01). TF expression increased following BI, increased further following ICBT, and persisted for the duration of the study. We conclude that TF expression increases after BI, but is further increased and persists for a longer duration following ICBT, suggesting that a TF-mediated mechanism may play a role in late thrombosis following ICBT.

Endothelial molecular changes in a rodent model of arteriovenous malformation

Object

The cellular and molecular processes underlying arteriovenous malformation (AVM) development and response to radiosurgery are largely unknown. An animal model mimicking the molecular properties of AVMs is required to examine these processses. This study was performed to determine whether the endothelial molecular changes in an animal model of arteriovenous fistula (AVF) are similar to those in human AVMs.

Methods

Arteriovenous fistulas were created in 18 Sprague–Dawley rats by end-to-side anastomosis of the left jugular vein to the common carotid artery creating a model “nidus” of arterialized branching veins that coalesce into a “draining vein” (sigmoid sinus). Six control animals underwent sham operations.

Results

After 1 or 3 days, or 1, 3, 6, or 12 weeks, fresh-frozen sections of the fistula, nidus vessels, and contralateral vessels were studied immunohistochemically for thrombomodulin, von Willebrand factor, E-selectin, P-selectin, and vascular endothelial growth factor.

Conclusions

The AVF model has a “nidus” with endothelial molecular changes similar to those observed in human AVMs, supporting its use as a model for studying the effects of radiosurgery on AVMs.

[Role of endothelium in radiation-induced normal tissue damages]

More than half of cancers are treated with radiation therapy alone or in combination with surgery and/or chemotherapy. The goal of radiation therapy is to deliver enough ionising radiation to destroy cancer cells, without exceeding the level that the surrounding healthy cells can tolerate. Unfortunately, radiation-induced normal tissue injury is still a dose limiting factor in the treatment of cancer with radiotherapy. Early and late side-effects not only limit radiation dose escalation, but might also affect the patient's quality of life. Vascular injury is one of the most common effects of radiotherapy on normal tissues. Radiation-induced fibrogenesis is characterized by an orchestrated pathological wound-healing response in which the radiation-induced endothelium dysfunction plays a critical role. Irradiated endothelial cells acquire a proinflammatory, procoagulant and prothrombotic phenotype. The knowledge of molecular mechanisms involved in endothelium dysfunction following radiation is needed to identify therapeutic targets and develop strategies to prevent and /or reduce side-effects of radiation therapy.

Simvastatin ameliorates radiation enteropathy development after localized, fractionated irradiation by a protein C-independent mechanism

PURPOSE

Microvascular injury plays a key role in normal tissue radiation responses. Statins, in addition to their lipid-lowering effects, have vasculoprotective properties that may counteract some effects of radiation on normal tissues. We examined whether administration of simvastatin ameliorates intestinal radiation injury, and whether the effect depends on protein C activation.

METHODS AND MATERIALS

Rats received localized, fractionated small bowel irradiation. The animals were fed either regular chow or chow containing simvastatin from 2 weeks before irradiation until termination of the experiment. Groups of rats were euthanized at 2 weeks and 26 weeks for assessment of early and delayed radiation injury by quantitative histology, morphometry, and quantitative immunohistochemistry. Dependency on protein C activation was examined in thrombomodulin (TM) mutant mice with deficient ability to activate protein C.

RESULTS

Simvastatin administration was associated with lower radiation injury scores (p < 0.0001), improved mucosal preservation (p = 0.0009), and reduced thickening of the intestinal wall and subserosa (p = 0.008 and p = 0.004), neutrophil infiltration (p = 0.04), and accumulation of collagen I (p = 0.0003). The effect of simvastatin was consistently more pronounced for delayed than for early injury. Surprisingly, simvastatin reduced intestinal radiation injury in TM mutant mice, indicating that the enteroprotective effect of simvastatin after localized irradiation is unrelated to protein C activation.

CONCLUSIONS

Simvastatin ameliorates the intestinal radiation response. The radioprotective effect of simvastatin after localized small bowel irradiation does not appear to be related to protein C activation. Statins should undergo clinical testing as a strategy to minimize side effects of radiation on the intestine and other normal tissues.

Significance of endothelial dysfunction in the pathogenesis of early and delayed radiation enteropathy

This review summarizes the current state of knowledge regarding the role of endothelial dysfunction in the pathogenesis of early and delayed intestinal radiation toxicity and discusses various endothelial-oriented interventions aimed at reducing the risk of radiation enteropathy. Studies published in the biomedical literature during the past four decades and cited in PubMed, as well as clinical and laboratory data from our own research program are reviewed. The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. During treatment of abdominal and pelvic tumors, the intestine is frequently a major dose-limiting factor. Microvascular injury is a prominent feature of both early (inflammatory), as well as delayed (fibroproliferative) radiation injuries in the intestine and in many other normal tissues. Evidence from our and other laboratories suggests that endothelial dysfunction, notably a deficiency of endothelial thrombomodulin, plays a key role in the pathogenesis of these radiation responses. Deficient levels of thrombomodulin cause loss of vascular thromboresistance, excessive activation of cellular thrombin receptors by thrombin, and insufficient activation of protein C, a plasma protein with anticoagulant, anti-inflammatory, and cytoprotective properties. These changes are presumed to be critically involved in many aspects of early intestinal radiation toxicity and may sustain the fibroproliferative processes that lead to delayed intestinal dysfunction, fibrosis, and clinical complications. In conclusion, injury of vascular endothelium is important in the pathogenesis of the intestinal radiation response. Endothelial-oriented interventions are appealing strategies to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

Effect of sesamol on radiation-induced cytotoxicity in Swiss albino mice

The radio-protective ability of sesamol (SM) at various doses viz., 0, 10, 25, 40, 50, 70 and 100mg/kg bw, administered intraperitoneally 30min prior to 9.5Gy whole-body gamma-irradiation was studied in Swiss albino mice. Radiation toxicity and mortality were observed during a period of 30 days and the percentage mortality was calculated. SM pretreatment with 50mg/kg bw was found to be the most effective dose in maintaining body weight and in reducing the percentage mortality, while 100mg/kg bw was found to be more effective in maintaining the spleen index and in stimulation of endogenous spleen colony-forming units. Pretreatment with SM (50mg/kg bw) in mice irradiated with 15Gy significantly reduced dead, inflammatory, mitotic and goblet cells in irradiated jejunum. SM at 50mg/kg bw also increased crypt cells, maintained villus height, and prevented mucosal erosion. Nuclear enlargement in epithelial cells was found less in SM-treated mice compared with the irradiated control. The radiation-induced decrease in endogenous antioxidant enzymes (GSH, GST, catalase) and the increase in lipid peroxidation were also reduced by pretreatment with SM [50 and 100mg/kg bw] at all monitored post-irradiation intervals. There was no protection at a dose less than 25mg/kg bw.

Effect of ticlopidine in the prevention of radiation enteropathy

Impairment of vascular function is considered to play an important role in chronic radiation enteropathy. In this experimental study, the role of ticlopidine, an inhibitor of ADP-induced platelet aggregation, was investigated in radiation enteropathy. 80 male Wistar albino rats, each weighing 170-200 g, were divided into four groups: (a) radiation alone (n = 20); (b) radiotherapy plus ticlopidine (n = 20); (c) ticlopidine control (n = 20) and (d) control (n = 20). Both radiation groups received 19 Gy radiation to the exteriorized intestinal segments in a single fraction. Ticlopidine or vehicle was administered 12 h after radiotherapy and continued for 1 month. Rats from every group were euthanized randomly at intervals of 6 weeks from 2 weeks to 26 weeks. Histopathological radiation injury was assessed using radiation injury scoring (RIS). Radiation with ticlopidine or radiation alone groups showed significant RIS deterioration compared with controls in all time points studied. Comparison of median RIS of radiotherapy and radiotherapy+ticlopidine groups at the 2nd, 14th and 26th weeks yielded statistically significant RIS in favour of radiotherapy+ticlopidine group (p = 0.05). However, these differences were less pronounced at the 8th and 20th week (p = 0.07). Both radiation groups had poor weight gain when compared with control and ticlopidine groups. The weight gain in radiotherapy+ticlopidine group was significantly superior to only radiation group between 10th and 20th weeks (p = 0.05). This study showed that inhibition of platelet aggregation with ticlopidine might be useful in radiation enteropathy. However, the precise role of antiaggregant therapies on radiation enteropathy should be comprehensively studied before clinical consideration.

Importance of timing of antiaggregant treatment in the prevention of radiation induced enteropathy

Chronic radiation enteropathy (CRE) is an undesirable radiation-induced toxicity and a common health problem in patients with pelvic or abdominal malignancies. Damage to microvascular endothelial cells and connective tissue is blamed to cause this adverse effect. It is shown that platelets are the first cellular elements that initiate the homeostatic and inflammatory responses and release of several proinflammatory and fibrinogenic mediators. Antiplatelet agents such as ticlopidine and clopidogrel were shown to prevent CRE and this effect is believed to be directed by their activities against thrombocytes. However, recent studies have shown that these drugs also induce apoptosis in endothelial cells and may lead to decreased expression of endothelial prostacyclin and thrombomodulin (TM) and increased release of von Willebrand factor which are shown to be major contributors of coagulation process. Assuming that radiation induced apoptosis occur 6-10h after irradiation, we think that timing of these antiaggregant drugs with irradiation is important and a 6-10h interval between these may be beneficial to avoid this adverse interaction.

Hirudin ameliorates intestinal radiation toxicity in the rat: support for thrombin inhibition as strategy to minimize side-effects after radiation therapy and as countermeasure against radiation exposure

BACKGROUND

The small bowel is a dose-limiting normal tissue in radiation therapy of malignancies in the abdomen and pelvis, as well as an important determinant of survival after non-therapeutic radiation exposure. Irradiation of normal tissues, including intestine, causes loss of vascular thromboresistance and upregulation of thrombin receptors. Radiation-induced endothelial dysfunction is thought to be involved in both early and delayed radiation responses. Hence, thrombin may be a potential target for ameliorating normal tissue radiation toxicity.

OBJECTIVE

To assess direct thrombin inhibition as a protective strategy against small bowel radiation toxicity.

METHODS

Rat small intestine was exposed to localized orthovoltage X-radiation. Recombinant hirudin, a direct thrombin inhibitor, or vehicle was infused from 2 days before irradiation to 14 days after irradiation. Structural, cellular, and molecular aspects of intestinal radiation injury were assessed at 2 weeks (early toxicity) and 26 weeks (chronic toxicity) after irradiation.

RESULTS

Compared with unirradiated intestine, irradiated intestine showed increased expression of tissue factor, increased immunoreactivity for enzymatically active thrombin, and increased extravascular fibrin(ogen) deposition. Hirudin treatment significantly attenuated radiation-induced mucosal damage (P = 0.04), reactive intestinal wall thickening (P = 0.02), transforming growth factor-beta immunoreactivity levels (P = 0.0002), and collagen III deposition (P = 0.003). The differences between hirudin-treated and control rats were more pronounced at 2 weeks than at 26 weeks after irradiation. Hirudin treatment did not affect postradiation granulocyte infiltration.

CONCLUSIONS

Short-term thrombin inhibition attenuates important aspects of intestinal radiation toxicity. Thrombin is a promising target for minimizing normal tissue injury after radiation therapy of cancer, as well as for protecting normal tissues from the adverse effects of non-therapeutic radiation exposure.

Radiation injury and the protein C pathway

OBJECTIVE

To summarize current knowledge regarding the role of the thrombomodulin (TM)-protein C system in acute and chronic radiation responses in normal tissues.

DATA SOURCE

Studies published in the biomedical literature during the past three decades and cited in PubMed and unpublished clinical and laboratory data from our own research program. STUDY SUMMARY: The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. Microvascular injury is a prominent feature of normal tissue radiation injury and plays a critical role in both acute (inflammatory) and chronic (fibrotic) radiation responses. Evidence from our own and other laboratories strongly suggests that dysfunction of the TM-protein C system plays a key role in the pathogenesis of radiation-induced injury to normal tissue. Exposure of normal tissues to ionizing radiation causes a pronounced, sustained deficiency of endothelial TM. This is likely to be due to a combination of initial inactivation of TM by reactive oxygen species, reduced transcription of TM, and release of TM into the circulation. Deficient levels of endothelial TM cause loss of local vascular thrombo-resistance, excessive activation of protease-activated receptor-1 by thrombin, and insufficient activation of protein C. These changes are presumed to be critically involved in many aspects of acute radiation toxicity and in sustaining the fibroproliferative processes that lead to chronic radiation-induced organ dysfunction and clinical complications.

CONCLUSION

Injury of vascular endothelium may be key to the acute responses of normal tissues to ionizing radiation and to the progressive nature of chronic radiation fibrosis. Restitution of the TM-protein C pathway is an appealing strategy by which to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

Combinations of Cytokines Promote Survival of Mice and Limit Acute Radiation Damage in Concert with Amelioration of Vascular Damage

Recovery from hematopoietic aplasia is a predominant factor in the survival of total-body-irradiated mice within 30 days after exposure. However, other radiation-induced pathophysiological events have been shown to play a role, among which an inflammatory reaction must be considered. In the present study, we evaluated the therapeutic potential of a hematopoietic growth factor (thrombopoietin, Tpo) and pleiotropic cytokines (Il4 or Il11), used alone or in combination, on the survival of mice, hematopoietic reconstitution, inflammatory reaction and vascular changes. All treatments including Tpo induced a higher level of survival than did treatment with a placebo, with combinations being the most efficient. The increased survival could not be explained solely by an improved hematopoietic recovery. Treatments with Tpo also reduced the level of the chemokine KC in plasma and the level of expression of mRNA for inflammatory and coagulation proteins in the lungs of irradiated mice. In addition, radiation- induced vascular hyperpermeability was reduced with the use of Tpo. In summary, our results show that Tpo may improve survival by limiting vascular leakage, which in turn could limit inflammatory reactions and the ensuing tissue damage.

Inflammatory reaction and changes in expression of coagulation proteins on lung endothelial cells after total-body irradiation in mice

Inflammatory reaction is a classical feature of radiation exposure, and pneumonitis is a dose-limiting complication in the handling of hematological disorders treated with total-body irradiation. In the present study, we first evaluated the inflammatory response in C57BL6/J mice exposed to lethal doses of gamma rays treated with antibiotics or not. Both interleukin 6 and KC (also known as Gro1) were increased in the plasma 10 to 18 days after radiation exposure, independent of bacterial infection, whereas fibrinogen release was linked to a bacterial infection. Furthermore, both Il6 and KC were increased in the lungs of irradiated mice. Our second objective was to characterize the endothelial cell changes in the lungs of total-body-irradiated mice. For this purpose, a quantitative RT-PCR was used to determine the expression of genes involved in inflammatory and coagulation processes. We found that the adhesion molecules P-selectin and platelet endothelial cell adhesion molecule 1 were up-regulated, whereas E-selectin remained unchanged. Tissue factor expression was up-regulated as well, and thrombomodulin gene expression was down-regulated. The investigation by immunohistochemistry of adhesion molecules confirmed the increase in the basal expression of both P-selectin and platelet endothelial cell adhesion molecule 1 on pulmonary endothelial cells. All together, our results suggest the involvement of endothelial cells in the development of radiation-induced inflammatory and thrombotic processes.

Deficiency of microvascular thrombomodulin and up-regulation of protease-activated receptor-1 in irradiated rat intestine: possible link between endothelial dysfunction and chronic radiation fibrosis

Microvascular injury is believed to be mechanistically involved in radiation fibrosis, but direct molecular links between endothelial dysfunction and radiation fibrosis have not been established in vivo. We examined radiation-induced changes in endothelial thrombomodulin (TM) and protease-activated receptor-1 (PAR-1) in irradiated intestine, and their relationship to structural, cellular, and molecular aspects of radiation injury. Rat small intestine was locally exposed to fractionated X-radiation. Structural injury was assessed 24 hours and 2, 6, and 26 weeks after the last radiation fraction using quantitative histology and morphometry. TM, neutrophils, transforming growth factor-beta, and collagens I and III were assessed by quantitative immunohistochemistry. PAR-1 protein was localized immunohistochemically, and cells expressing TM or PAR-1 transcript were identified by in situ hybridization. Steady-state PAR-1 mRNA levels in intestinal smooth muscle were determined using laser capture microdissection and competitive reverse transcriptase-polymerase chain reaction. Radiation caused a sustained, dose-dependent decrease in microvascular TM. The number of TM-positive vessels correlated with all parameters of radiation enteropathy and, after adjusting for radiation dose and observation time in a statistical model, remained independently associated with neutrophil infiltration, intestinal wall thickening, and collagen I accumulation. PAR-1 immunoreactivity and transcript increased in vascular and intestinal smooth muscle cells in irradiated intestine. PAR-1 mRNA increased twofold in irradiated intestinal smooth muscle. Intestinal irradiation up-regulates PAR-1 and causes a dose-dependent, sustained deficiency of microvascular TM that is independently associated with the severity of radiation toxicity. Interventions aimed at preserving or restoring endothelial TM or blocking PAR-1 should be explored as strategies to increase the therapeutic ratio in clinical radiation therapy.

The radiotherapeutic injury--a complex 'wound'

Radiotherapeutic normal tissue injury can be viewed as two simultaneously ongoing and interacting processes. The first has many features in common with the healing of traumatic wounds. The second is a set of transient or permanent alterations of cellular and extracellular components within the irradiated volume. In contrast to physical trauma, fractionated radiation therapy produces a series of repeated insults to tissues that undergo significant changes during the course of radiotherapy. Normal tissue responses are also influenced by rate of dose accumulation and other factors that relate to the radiation therapy schedule. This article reviews the principles of organised normal tissue responses during and after radiation therapy, the effect of radiation therapy on these responses, as well as some of the mechanisms underlying the development of recognisable injury. Important clinical implications relevant to these processes are also discussed.

Pathology of radiation myelopathy

Radiation myelopathy is principally a white matter injury of the spinal cord induced by ionizing radiation after a certain latent period. It involves myelinated fibers and blood vessels, and the lateral funiculi is most preferentially affected. Several factors, such as radiation dose, fractionation or linear energy transfer, modify its occurrence and severity. Although glial cells and vascular endothelium are proposed to be the main targets, and to play a role in the pathogenesis of radiation myelopathy, experimental researches support that radiation-induced vascular damage resulting in vascular hyperpermeability and venous exudation is a basic process. Effect of ionizing radiation on each cellular component of the central nervous system, their contribution to radiation myelopathy, mechanisms of selective permeability and remaining problems are discussed.

Effects of radiation on cerebral vasculature: a review

Radiation therapy plays a critical role in the treatment of central nervous system neoplasms and cerebral arteriovenous malformations. The deleterious effects of radiation on cerebral arteries may be the primary limitation to these treatment methods, as radiation may cause a variety of cerebrovascular injuries and hemodynamic changes. Radiation-induced changes in the cerebral arterial wall are determined by a number of cellular processes in endothelium and smooth muscle cells that modulate differences in radiosensitivity and phenotypic expression. The histopathological findings in arterial radiation injury include vessel wall thickening, thrombosis, luminal occlusion, and occasional telangiectases. Mechanisms for radiation injury to blood vessels include phenotypic changes in normal vessel wall cells (especially endothelium) manifested by the expression or suppression of specific gene and protein products that affect cell cycle progression or cellular proliferation or demise via cytotoxic injury or apoptosis. This review describes the molecular and cellular events involved in the systemic and cerebral vascular response to radiation and the potential means by which these responses may be influenced to augment the therapeutic effects of radiation while minimizing the untoward consequences.

Circulating thrombomodulin during radiation therapy of lung cancer

The endothelial cell glycoprotein, thrombomodulin (TM), is an important physiological anticoagulant. TM is downregulated and released from the cell membrane into the circulation by ionizing radiation and during inflammation. The present study measured plasma TM in 17 patients before, during, and after radiation therapy of lung cancer: nine patients developed radiation pneumonitis, whereas eight matched patients did not. Plasma TM did not change significantly in patients who developed radiation pneumonitis. In contrast, patients who did not develop pneumonitis exhibited a moderate, but statistically significant, decrease in plasma TM antigen during the initial 1-2 weeks, with complete normalization towards the end of treatment. Our study suggests that decreased release of TM during the early phase of radiation therapy may be associated with reduced pulmonary toxicity. The use of plasma TM as a marker of pulmonary toxicity needs further study.

Is the loss of endothelial thrombomodulin involved in the mechanism of chronicity in late radiation enteropathy?

BACKGROUND AND PURPOSE

Radiation enteropathy is characterized by locally elevated levels of inflammatory and fibrogenic cytokines. Microvascular injury may sustain these alterations through persistent local hypercoagulopathy, platelet aggregation, leukocyte adhesion and release of biologically active mediators. This study assessed the relationship of endothelial thrombomodulin (TM), a key regulator of the protein C anticoagulant pathway and marker of endothelial function, with transforming growth factor beta (TGF-beta) immunoreactivity and morphologic alterations in radiation enteropathy.

MATERIALS AND METHODS

Small bowel resection specimens from 9 patients with radiation enteropathy were analyzed by computerized quantitative immunohistochemistry using antibodies against TM, von Willebrand factor (vWF) and TGF-beta. Identical measurements were performed on intestinal resection specimens from otherwise healthy penetrating trauma victims and on archived small intestines. A previously validated image analysis technique was used to assess submucosal vessels for TM and vWF immunoreactivity, and the intestinal wall for total extracellular matrix-associated TGF-beta immunoreactivity.

RESULTS

Specimens from irradiated patients showed prominent submucosal and subserosal thickening and fibrosis, and obliterative vasculopathy. Control specimens were histopathologically normal. Vascular density and vWF immunoreactivity were similar in radiation enteropathy patients and controls. The image-analysis techniques were highly reproducible, with correlation coefficients for repeated measurements ranging from 0.86 to 0.93. Radiation enteropathy specimens exhibited a highly significant reduction in the number and proportion of TM-positive submucosal vessels per unit area (P < 0.0001) and increased intestinal wall TGF-beta immunoreactivity (P = 0.002).

CONCLUSIONS

These data support the theory that sustained endothelial dysfunction is involved in the molecular pathogenesis of radiation enteropathy, and point to TM as important in the chronic nature of radiation enteropathy and a potential target for prophylactic and therapeutic interventions.

Nitric oxide release from resting human platelets

In this study, we have investigated the release of nitric oxide from resting human platelets. Nitric oxide was detected and quantitated by either measuring the conversion of oxy-hemoglobin to met-hemoglobin or generation of nitrite and nitrate by the cells. Nitric oxide was released from both intact resting platelets and platelets activated by collagen. Nitric oxide release was proportional to platelet concentration, and was equivalent to approximately 4.5 +/- 0.6 pmol (or 2.8 +/- 0.3 pmol in the presence of prostaglandin I2) and 11.2 +/- 1.3 pmol nitric oxide released per minute per 10(8) cells at 37 degrees C for resting platelets and platelets activated by collagen, respectively. The generation of nitric oxide by resting platelets was linear with respect to time over a two hour period, while the release of nitric oxide from platelets following activation was transient and was linear for only the first 10 min, after which it slowed to completion at approximately 30 min. The release of nitric oxide was it slowed to completion at approximately 30 min. The release of nitric oxide was stimulated by L-arginine, but was inhibited by L-nitro-arginine methyl ester (L-NAME). The inhibitory effect of L-NAME could be reversed by addition of L-arginine. The release of nitric oxide from platelets was also partially inhibited by prostaglandin I2, prostaglandin E1, aspirin and EDTA. The amount of nitric oxide released from resting platelets compared with that released from endothelial cells suggests that platelet-derived nitric oxide may play a significant role in the maintenance of vascular tone and blood flow.

Effects of gamma-irradiation on the M-CSF-promoter linked to a chloramphenicol aminoacyl transferase reporter gene expressed in a clonal murine bone marrow stromal cell line

The effects of cytokines produced by bone marrow stromal cells on closely associated hematopoietic cells constitute a major component of the physiology of the hematopoietic microenvironment. A major cytokine produced by marrow stromal cells is macrophage colony-stimulating factor (M-CSF). To determine the effect of gamma-irradiation on the M-CSF promoter in bone marrow stromal cells, we selected a clonal cell line from the C3H/HeJ mouse marrow stromal cell line D2XRII and stably transfected a reporter construct containing the murine M-CSF-promoter linked to a chloramphenicol aminoacyl transferase (CAT) gene. CAT activity was measured at serial time points after gamma-irradiation in vitro to doses between 500 and 10,000 cGy at a dose rate of 116 cGy/min. D2XRII marrow stromal cells treated with phorbol myristate acetate (40 micrograms/ml, four h), demonstrated a significant two-fold increase in CAT activity. In contrast, CAT activity measured immediately, 24 h, 72 h or 1 week after gamma-irradiation, showed no significant increase or decrease in CAT activity. An increase in CAT activity was detected 48 h after irradiation with cells that received 5,000 cGy. Thus, single fraction gamma-irradiation of plateau phase bone marrow stromal cells did not decrease M-CSF-promoter activity. These results are consistent with prior experimental data demonstrating stable levels of release of M-CSF protein following gamma-irradiation of bone marrow stromal cells and imply that the stability of transcription of the gene for this important cytokine is protected from irradiation.

Increase in plasma thrombomodulin and decrease in plasma von Willebrand factor after regular radiotherapy of patients with cancer

In this study, we investigated plasma levels of thrombomodulin (TM) and von Willebrand factor (vWF) in 51 patients suffering from cancer or tumor undergoing 60 cobalt radiotherapy. Plasma TM and vWF antigen were measured by immunoradiometric assay and ELISA, respectively. During radiotherapy, an increase in plasma TM in patients was observed, which was radiation-dose dependent and there was a positive correlation between plasma TM level and radiation doses. However, the level of plasma vWF in the patients was decreased during radiotherapy and there was an inverse correlation between the amount of plasma vWF and radiation doses. Our data indicate that plasma TM is an useful molecular marker for early detection of radiation injury to endothelial cells in patients undergoing radiotherapy.