Irradiation induces upregulation of CD31 in human endothelial cells

Brachytherapy via a depot of biopolymer-bound 131I synergizes with nanoparticle paclitaxel in therapy-resistant pancreatic tumours

Locally advanced pancreatic tumours are highly resistant to conventional radiochemotherapy. Here we show that such resistance can be surmounted by an injectable depot of thermally responsive elastin-like polypeptide (ELP) conjugated with iodine-131 radionuclides (131I-ELP) when combined with systemically delivered nanoparticle albumin-bound paclitaxel. This combination therapy induced complete tumour regressions in diverse subcutaneous and orthotopic mouse models of locoregional pancreatic tumours. 131I-ELP brachytherapy was effective independently of the paclitaxel formulation and dose, but external beam radiotherapy (EBRT) only achieved tumour-growth inhibition when co-administered with nanoparticle paclitaxel. Histological analyses revealed that 131I-ELP brachytherapy led to changes in the expression of intercellular collagen and junctional proteins within the tumour microenvironment. These changes, which differed from those of EBRT-treated tumours, correlated with the improved delivery and accumulation of paclitaxel nanoparticles within the tumour. Our findings support the further translational development of 131I-ELP depots for the synergistic treatment of localized pancreatic cancer.

Kidney-targeted irradiation triggers renal ischaemic preconditioning in mice

Renal ischemia/reperfusion (I/R) causes acute kidney injury (AKI). Ischemic preconditioning (IPC) attenuates I/R-associated AKI. Whole-body irradiation induces renal IPC in mice. Still, the mechanisms remain largely unknown. Furthermore, the impact of kidney-centered irradiation on renal resistance against I/R has not been studied. Renal irradiation (8.5Gy) was done in male 8-12-week-old C57bl/6 mice using Small Animal Radiation Therapy (SmART) device. Left renal I/R was performed by clamping the renal pedicles for 30 minutes, with simultaneous right nephrectomy, at 7, 14, and 28 days post-irradiation. The renal reperfusion lasted 48 hours. Following I/R, blood urea nitrogen (BUN) and creatinine (SCr) levels were lower in pre-irradiated mice compared to controls, so was the histological Jablonski score of AKI. The metabolomics signature of renal I/R was attenuated in pre-irradiated mice. The numbers of PCNA-, CD11b-, and F4-80-positive cells in the renal parenchyma post-I/R were reduced in pre-irradiated versus control groups. Such an IPC was significantly observed as early as D14 post-irradiation. RNA-Seq showed an up-regulation of angiogenesis- and stress response-related signaling pathways in irradiated non-ischemic kidneys at D28. RT-qPCR confirmed the increased expression of VEGF, ALK5, HO1, PECAM1, NOX2, HSP70, and HSP27 in irradiated kidneys compared to controls. In addition, irradiated kidneys showed an increased CD31-positive vascular area compared to controls. A 14-day gavage of irradiated mice with the anti-angiogenic drug Sunitinib before I/R abrogated the irradiation-induced IPC at both functional and structural levels. Our observations suggest that kidney-centered irradiation activates pro-angiogenic pathways and induces IPC, with preserved renal function and attenuated inflammation post-I/R.

Radiobiological Studies of Microvascular Damage through In Vitro Models: A Methodological Perspective

Ionizing radiation (IR) is used in radiotherapy as a treatment to destroy cancer. Such treatment also affects other tissues, resulting in the so-called normal tissue complications. Endothelial cells (ECs) composing the microvasculature have essential roles in the microenvironment's homeostasis (ME). Thus, detrimental effects induced by irradiation on ECs can influence both the tumor and healthy tissue. In-vitro models can be advantageous to study these phenomena. In this systematic review, we analyzed in-vitro models of ECs subjected to IR. We highlighted the critical issues involved in the production, irradiation, and analysis of such radiobiological in-vitro models to study microvascular endothelial cells damage. For each step, we analyzed common methodologies and critical points required to obtain a reliable model. We identified the generation of a 3D environment for model production and the inclusion of heterogeneous cell populations for a reliable ME recapitulation. Additionally, we highlighted how essential information on the irradiation scheme, crucial to correlate better observed in vitro effects to the clinical scenario, are often neglected in the analyzed studies, limiting the translation of achieved results.

Intermittent hypoxia exacerbates tumor progression in a mouse model of lung cancer

The purpose of this study was to evaluate whether obstructive sleep apnea (OSA)-related chronic intermittent hypoxia (CIH) influences lung cancer progression and to elucidate the associated mechanisms in a mouse model of lung cancer. C57/BL6 mice in a CIH group were exposed to intermittent hypoxia for two weeks after tumor induction and compared with control mice (room air). Hypoxia inducible factor 1α (HIF-1α), vascular endothelial growth factor (VEGF) and metastasis-related matrix metalloproteinases (MMP) were measured. The expression levels of several hypoxia-related pathway proteins including HIF-1α, Wnt/ß-catenin, the nuclear factor erythroid 2-related factor 2 (Nrf2) and mammalian target of rapamycin-ERK were measured by western blot. The number (P < 0.01) and volume (P < 0.05) of tumors were increased in the CIH group. The activity of MMP-2 was enhanced after CIH treatment. The level of VEGF was increased significantly in the CIH group (p < 0.05). ß-catenin and Nrf2 were translocated to the nucleus and the levels of downstream effectors of Wnt/ß-catenin signaling increased after IH exposure. CIH enhanced proliferative and migratory properties of tumors in a mouse model of lung cancer. ß-catenin and Nrf2 appeared to be crucial mediators of tumor growth.

The importance of the vascular endothelial barrier in the immune-inflammatory response induced by radiotherapy

Altered by ionising radiation, the vascular network is considered as a prime target to limit normal tissue damage and improve tumour control in radiotherapy (RT). Irradiation damages and/or activates endothelial cells, which then participate in the recruitment of circulating cells, especially by overexpressing cell adhesion molecules, but also by other as yet unknown mechanisms. Radiation-induced lesions are associated with infiltration of immune-inflammatory cells from the blood and/or the lymph circulation. Damaged cells from the tissues and immune-inflammatory resident cells release factors that attract cells from the circulation, leading to the restoration of tissue balance by fighting against infection, elimination of damaged cells and healing of the injured area. In normal tissues that surround the tumours, the development of an immune-inflammatory reaction in response to radiation-induced tissue injury can turn out to be chronic and deleterious for the organ concerned, potentially leading to fibrosis and/or necrosis of the irradiated area. Similarly, tumours can elicit an immune-inflammation reaction, which can be initialised and amplified by cancer therapy such as radiotherapy, although immune checkpoints often allow many cancers to be protected by inhibiting the T-cell signal. Herein, we have explored the involvement of vascular endothelium in the fate of healthy tissues and tumours undergoing radiotherapy. This review also covers current investigations that take advantage of the radiation-induced response of the vasculature to spare healthy tissue and/or target tumours better.

Key mechanisms involved in ionizing radiation-induced systemic effects. A current review

Organisms respond to physical, chemical and biological threats by a potent inflammatory response, aimed at preserving tissue integrity and restoring tissue homeostasis and function. Systemic effects in an organism refer to an effect or phenomenon which originates at a specific point and can spread throughout the body affecting a group of organs or tissues. Ionizing radiation (IR)-induced systemic effects arise usually from a local exposure of an organ or part of the body. This stress induces a variety of responses in the irradiated cells/tissues, initiated by the DNA damage response and DNA repair (DDR/R), apoptosis or immune response, including inflammation. Activation of this IR-response (IRR) system, especially at the organism level, consists of several subsystems and exerts a variety of targeted and non-targeted effects. Based on the above, we believe that in order to understand this complex response system better one should follow a 'holistic' approach including all possible mechanisms and at all organization levels. In this review, we describe the current status of knowledge on the topic, as well as the key molecules and main mechanisms involved in the 'spreading' of the message throughout the body or cells. Last but not least, we discuss the danger-signal mediated systemic immune effects of radiotherapy for the clinical setup.

Radiation-induced fibrosis: mechanisms and implications for therapy

PURPOSE

Radiation-induced fibrosis (RIF) is a long-term side effect of external beam radiation therapy for the treatment of cancer. It results in a multitude of symptoms that significantly impact quality of life. Understanding the mechanisms of RIF-induced changes is essential to developing effective strategies to prevent long-term disability and discomfort following radiation therapy. In this review, we describe the current understanding of the etiology, clinical presentation, pathogenesis, treatment, and directions of future therapy for this condition.

METHODS

A literature review of publications describing mechanisms or treatments of RIF was performed. Specific databases utilized included PubMed and clinicaltrials.gov, using keywords "Radiation-Induced Fibrosis," "Radiotherapy Complications," "Fibrosis Therapy," and other closely related terms.

RESULTS

RIF is the result of a misguided wound healing response. In addition to causing direct DNA damage, ionizing radiation generates reactive oxygen and nitrogen species that lead to localized inflammation. This inflammatory process ultimately evolves into a fibrotic one characterized by increased collagen deposition, poor vascularity, and scarring. Tumor growth factor beta serves as the primary mediator in this response along with a host of other cytokines and growth factors. Current therapies have largely been directed toward these molecular targets and their associated signaling pathways.

CONCLUSION

Although RIF is widely prevalent among patients undergoing radiation therapy and significantly impacts quality of life, there is still much to learn about its pathogenesis and mechanisms. Current treatments have stemmed from this understanding, and it is anticipated that further elucidation will be essential for the development of more effective therapies.

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.

Late inflammatory and thrombotic changes in irradiated hearts of C57BL/6 wild-type and atherosclerosis-prone ApoE-deficient mice

BACKGROUND AND PURPOSE

Radiation-induced heart disease represents a late complication of thoracic radiotherapy. We investigated the inflammatory and thrombotic response after local heart irradiation in wild-type and atherosclerosis-prone mice.

MATERIAL AND METHODS

Atherosclerosis-prone ApoE(-/-) and C57BL/6 wild-type mice were sacrificed 20, 40, and 60 weeks after irradiation with 0.2, 2, 8, or 16 Gy. The expression of CD31, vascular cell adhesion molecule-1 (VCAM-1), thrombomodulin (TM), and CD45 were quantified by immunofluorescence staining of heart tissue sections.

RESULTS

Microvascular density decreased at 40 weeks after 16 Gy in C57BL/6 but not in ApoE(-/-) mice. CD31 expression declined in C57BL/6 mice at 40 weeks (8 Gy), but increased in ApoE(-/-) mice at 20 (2/8/16 Gy) and 60 weeks (16 Gy). Capillary area decreased in C57BL/6 at 40 weeks (8/16 Gy) but increased in ApoE(-/-) mice at 20 weeks (16 Gy). Endocardial VCAM-1 expression remained unchanged. TM-positive capillaries decreased at 40 weeks (8/16 Gy) in C57BL/6 and at 60 weeks (2/16 Gy) in ApoE(-/-) mice. Leukocyte infiltration transiently rose 40 weeks after 8 Gy (only ApoE(-/-)) and 16 Gy. After receiving a low irradiation dose of 0.2 Gy, no significant changes were observed in any of the mouse models.

CONCLUSION

This study demonstrated that local heart irradiation affects microvascular structure and induces inflammatory/thrombotic responses in mice in a dose- and time-dependent manner. Thereby, significant prothrombotic changes were found in both strains, although they were progressive in ApoE(-/-) mice only. Proinflammatory responses, like the increase of adhesion molecules and leukocyte infiltration, were more pronounced and occurred at lower doses in ApoE(-/-) vs. C57BL/6 mice. These findings indicate that metabolic risk factors, such as decreased ApoE lipoproteins, may lead to an enhanced proinflammatory and prothrombotic late response in locally irradiated hearts.

Expression of cell adhesion molecules at the collapse and recovery of haematopoiesis in bone marrow of mouse

After bone marrow transplantation (BMT) and lethal irradiation, vascular endothelial cells play an important role in the homing of haematopoietic cells and recovery of haematopoiesis. We investigated the expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1) and fibronectin in the endothelial cells of bone marrow in a collapsed state after lethal irradiation and in a recovery state after BMT in mice. After lethal irradiation, the expression of MAdCAM-1, VCAM-1 and fibronectin increased on the luminal surface of endothelial cells. In the recovery state, the expression of MAdCAM-1 and VCAM-1 was increased from 2 to 4 days after BMT, but fibronectin levels remained constant, except for a temporary increase at 4 days after BMT. The number of homing cells, however, was markedly decreased in parallel with the reduction in the haematopoietic compartment at 2 and 4 days after lethal irradiation. Next, to analyse the influence of fibronectin expression after BMT on homing activity, we performed double BMT experiment. The number of homing cells in double BMT experiment maintained high level from 2 h to 2 days after secondary BMT. Our data suggest that homing of bone marrow cells is activated until fibronectin-mediated endothelial cell repair and that transplanted haematopoietic stem/progenitor cells inhibit fibronectin expression for endothelial cell repair until the homing is completed. Therefore, the homing of haematopoietic cells in bone marrow depends on the condition of the bone marrow endothelial cells, as well as the cell adhesion molecules.

Impact of radiotherapy on microsurgical reconstruction of the head and neck

PURPOSE

To examine tissue oxygenation and perfusion of free microvascular grafts after primary reconstruction, regarding outcome for patients received adjuvant radiotherapy and different types of grafts.

PATIENTS AND METHODS

Free microvascular grafts (n = 48) after primary reconstruction of the head and neck were examined for tissue oxygenation and perfusion over a period of 6 months. 28 patients received adjuvant radiotherapy. Using a laser doppler flowmetry combined with tissue spectroscopy of the Oxygen-to-see(®)--equipment (LEA Medizintechnik, Giessen), we were able to determine oxygen saturation, hemoglobin concentration, blood flow and blood flow velocity in the graft in each of two tissue depths (2, 8 mm). Different types of graft were compared.

RESULT

Comparison of irradiated and non-irradiated grafts showed significant differences in tissue perfusion and oxygenation. Results for all radiated radial and fibula flaps showed no significant (p > 0.05) differences for all reviewed parameters. However, it showed no dose-volume effect with impaired functionality was found for irradiated grafts.

CONCLUSION

Mircovascular free tissue grafts show an increased perfusion and oxygenation after radiation compared to non-irradiated grafts.

Abscopal regression of antigen disparate tumors by antigen cascade after systemic tumor vaccination in combination with local tumor radiation

Radiation is a primary modality in cancer treatment. Radiation can also reduce tumor growth outside the treatment field, often referred to as the abscopal effect. The mechanisms and therapeutic potential of the abscopal effect have not been fully elucidated. We evaluated the role of vaccination directed against a tumor-associated antigen (TAA) in the induction and amplification of radiation induced abscopal effects. Active-specific immunotherapy with a TAA-specific vaccine regimen was used to induce and potentiate T-cell responses against carcinoembryonic antigen (CEA) in combination with local irradiation of subcutaneous tumors. We examined the potential synergy of a poxvirus-based CEA vaccine regimen in CEA-transgenic (Tg) mice in combination with either external beam radiation or brachytherapy of local tumors. The induction of CD8(+) T cells specific for multiple TAAs not encoded by the vaccine was observed after the combination therapy. In two tumor models, the antigen cascade responses induced by vaccine and local irradiation mediated the regression of antigen negative metastases at distal subcutaneous or pulmonary sites. Clinically, local control of the primary tumor is necessary and can sometimes prevent metastases; however, irradiation generally fails to control preexisting metastases. These studies suggest that by coupling tumor irradiation with immunotherapy, the abscopal effect can transcend from anecdotal observation to a defined mechanism that can be exploited for the treatment of systemic disease.

Effect of irradiation on gene expression of rat liver adhesion molecules: in vivo and in vitro studies

BACKGROUND AND PURPOSE

Migration of leukocytes into tissue is a key element of innate and adaptive immunity. An animal study showed that liver irradiation, in spite of induction of chemokine gene expression, does not lead to recruitment of leukocytes into the parenchyma. The aim of this study was to analyze gene expression of adhesion molecules, which mediate leukocyte recruitment into organs, in irradiated rat liver in vivo and rat hepatocytes in vitro.

MATERIAL AND METHODS

Rat livers in vivo were irradiated selectively at 25 Gy. Isolated hepatocytes in vitro were irradiated at 8 Gy. RNA extracted within 48 h after irradiation in vivo and in vitro was analyzed by real-time PCR (polymerase chain reaction) and Northern blot. Adhesion molecule concentration in serum was measured by ELISA (enzyme-linked immunosorbent assay). Cryostat sections of livers were used for immunohistology.

RESULTS

Significant radiation-induced increase of ICAM-1 (intercellular adhesion molecule-1), VCAM-1 (vascular cell adhesion molecule-1), JAM-1 (junctional adhesion molecule-1), beta1-integrin, beta2-integrin, E-cadherin, and P-selectin gene expression could be detected in vivo, while PECAM-1 (platelet-endothelial cell adhesion molecule-1) gene expression remained unchanged. In vitro, beta1-integrin, JAM-1, and ICAM-2 showed a radiation-induced increased expression, whereas the levels of P-selectin, ICAM-1, PECAM-1, VCAM-1, Madcam-1 (mucosal addressin cell adhesion molecule-1), beta2-integrin, and E-cadherin were downregulated. However, incubation of irradiated hepatocytes with either tumor necrosis factor-(TNF-)alpha, interleukin-(IL-)1beta, or IL-6 plus TNF-alpha led to an upregulation of P-selectin, ICAM-1 and VCAM-1.

CONCLUSION

The findings suggest that liver irradiation modulates gene expression of the main adhesion molecules in vivo and in cytokine-activated hepatocytes, with the exception of PECAM-1. This may be one reason for the lack of inflammation in the irradiated rat liver.

[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.

Effects of radiotherapy and chemotherapy on angiogenesis and leukocyte infiltration in rectal cancer

BACKGROUND

We and others have shown that angiogenesis and leukocyte infiltration are important prognostic factors in rectal cancer. However, little is known about its possible changes in response to radiotherapy (RTX), which is frequently given to rectal tumors as a neoadjuvant treatment to improve the prognosis. We therefore investigated the biologic effects of RTX on these parameters using fresh-frozen biopsy samples of tumor and normal mucosa tissue before and after RTX.

METHODS

Biopsy samples were taken from a total of 34 patients before and after either a short course or long course of RTX combined with chemotherapy. The following parameters were analyzed by immunohistochemistry, flow cytometry, or quantitative real-time polymerase chain reaction: Microvessel density, leukocyte infiltration, proliferating epithelial and tumor cells, proliferating endothelial cells, adhesion molecule expression on endothelial cells, and the angiogenic mRNA profile.

RESULTS

The tumor biopsy samples taken after RTX treatment demonstrated a significant decrease in microvessel density and the number of proliferating tumor cells and proliferating endothelial cells (p < 0.001). In contrast, the leukocyte infiltration, the levels of basic fibroblast growth factor in carcinoma tissue, and the adhesion molecule expression on endothelial cells in normal as well as carcinoma tissue increased significantly (p < 0.05).

CONCLUSION

Our data show that together with an overall decrease in tumor cell and endothelial cell proliferation, RTX results in an increase in the expression of adhesion molecules that stimulate leukocyte infiltration. This suggests the possibility that, in addition to its direct cytotoxic effect, radiation may also stimulate an immunologic tumor response that could contribute to the documented improvement in local tumor control and distal failure rate of rectal cancers.

Adhesion molecules in radiotherapy

Recent studies have documented changes in adhesion molecule expression and function after exposure to ionizing radiation. Adhesion molecules mediate cell-cell and cell-matrix interactions and are essential for a variety of physiological and pathological processes including maintenance of normal tissue integrity as well as tumor development and progression. Consequently, modulation of adhesion molecules by radiation may have a role in radiation-induced tumor control and normal tissue damage by interfering with cell signaling, radioresistance, metastasis, angiogenesis, carcinogenesis, immune response, inflammation and fibrosis. In addition, the interactions of radiation with adhesion molecules could have a major impact in developing new strategies to increase the efficacy of radiation therapy. Remarkable progress has been made in recent years to design targeted drug delivery to radiation-up-regulated adhesion molecules. Furthermore, the inhibition of adhesion, migration, invasion and angiogenesis by blocking adhesion receptors may represent a new therapeutic approach to improve tumor control and decrease radiation toxicity. This review is focused on current data concerning the mechanistic interactions of radiation with adhesion molecules and the possible clinical-pathological implications in radiotherapy.

Peroxisome Proliferator-Activated Receptor γ Ligand Pioglitazone Alters Neointimal Composition in a Balloon-Denuded and Radiated Hypercholesterolemic Rabbit

Peroxisome proliferator-activated receptor (PPAR)-gamma activation suppresses inflammatory response, monocyte recruitment, and vascular cell proliferation. Because inflammation, deregulated growth, and migration of monocytes and vascular smooth muscle cells (VSMC) play important roles in the development of neointima, we tested the effect of pioglitazone, a high-affinity ligand, for PPAR-gamma on neointima formation in the iliac arteries of a balloon-denuded and radiated hypercholesterolemic rabbit. Rabbits were fed a 1.0% cholesterol diet for 7 days followed by denudation of endothelial layer and continued on a 0.15% cholesterol diet. On day 32, animals were divided into 2 groups. One group received a 0.15% cholesterol diet (n = 7) and the other group received a 0.15% cholesterol diet supplemented with 400 mg of pioglitazone per kilogram. On day 35, the balloon-denuded area was radiated. Four weeks after radiation, animals were sacrificed and arterial segments were processed for morphometry and immunohistochemistry. Data analysis showed that the pioglitazone group had smaller neointima (0.85 +/- 0.36 vs. 1.41 +/- 0.56, P < 0.05), with more cells positive for VSMC (23.07 +/- 6.16 vs. 18.33 +/- 5.19, P = 0.04), less for monocytes (16.01 +/- 5.33 vs. 21.29 +/- 4.33, P < 0.05), and fewer cells expressing metalloproteinase (MMP)-1 and MMP-9 (3.69 +/- 0.47 vs. 4.82 +/- 0.93, P < 0.05 and 3.24 +/- 0.71 vs. 4.29 +/- 0.74, P < 0.05, respectively). Pioglitazone reduced neointimal area and modified its composition in a balloon-denuded and radiated hypercholesterolemic rabbit model.

Influence of endothelial cells on vascular smooth muscle cells phenotype after irradiation: implication in radiation-induced vascular damages

Damage to vessels is one of the most common effects of therapeutic irradiation on normal tissues. We undertook a study in patients treated with preoperative radiotherapy and demonstrated in vivo the importance of proliferation, migration, and fibrogenic phenotype of vascular smooth muscle cells (VSMCs) in radiation-induced vascular damage. These lesions may result from imbalance in the cross talk between endothelial cells (ECs) and VSMCs. Using co-culture models, we examined whether ECs influence proliferation, migration, and fibrogenic phenotype of VSMCs. In the presence of irradiated ECs, proliferation and migration of VSMCs were increased. Moreover, expressions of alpha-smooth muscle actin, connective tissue growth factor, plasminogen activator inhibitor type 1, heat shock protein 27, and collagen type III, alpha 1 were up-regulated in VSMCs exposed to irradiated ECs. Secretion of transforming growth factor (TGF)-beta1 was increased after irradiation of ECs, and irradiated ECs activated the Smad pathway in VSMCs by inducing Smad3/4 nuclear translocation and Smad-dependent promoter activation. Using small interferring RNA targeting Smad3 and a TGFbeta-RII neutralizing antibody, we demonstrate that a TGF-beta1/TGF-beta-RII/Smad3 pathway is involved in the fibrogenic phenotype of VSMCs induced by irradiated ECs. In conclusion, we show the importance of proliferation, migration, and fibrogenic phenotype of VSMCs in patients. Moreover, we demonstrate in vitro that ECs influence these fundamental mechanisms involved in radiation-induced vascular damages.

Radiation-induced cell death and dendritic cells: potential for cancer immunotherapy?

Dendritic cells are key orchestrators of the immune system. There is considerable interest in their use for treating cancer. Whether they initiate an effective cytotoxic response against antigen-bearing cells, or produce tolerance, depends on the context in which those antigens are presented. Ionising radiation, and the cell death it causes, has several properties that may facilitate such an effective response. A range of in-vitro and in-vivo data supports this, although potential problems exist that may require concurrent strategies.

PECAM-1 (CD31) is required for interactions of platelets with endothelial cells after irradiation

Sustained adhesion of platelets to endothelial cells (EC) is believed to contribute to thrombosis and vascular occlusions following radiation exposure leading to organ functional impairment and even death. Our objective was to evaluate the role of platelet endothelial cell adhesion molecule (PECAM)-1 in the prothrombotic response of EC after irradiation. Endothelial PECAM-1 expression was determined by cell-enzyme linked immunosorbent assay (ELISA) on human microvascular EC from lung (HMVEC-L) up to 21 days after a 10 Gy irradiation. Platelet- and leukocyte-endothelial cell interactions were assessed using a flow adhesion assay with fluorescently labeled whole blood, and the function of PECAM-1 in these processes was measured by using blocking antibody. PECAM-1 expression was significantly increased on irradiated HMVEC-L and remained elevated at 21 days. Anti-PECAM-1 antibody significantly inhibited adhesion of single platelets and thrombi on irradiated HMVEC-L. This inhibitory effect persisted at day 21. Anti-PECAM-1 also reduced leukocyte adhesion to irradiated HMVEC-L. The up-regulation of endothelial PECAM-1 following radiation exposure is persistent. PECAM-1 plays a key role platelet adhesion/aggregation on irradiated EC. Therefore, strategies targeting this adhesion molecule may prevent the development of radiation pathologies.

Hematopoietic Progenitor Stem Cell Homing in Mice Lethally Irradiated with Ionizing Radiation at Differing Dose Rates

It has recently been shown that specific lineage-depleted murine hematopoietic stem cells that home to the bone marrow 2 days after transplantation of ablated primary recipients are capable of long-term engraftment and repopulation of secondary recipients. We were interested in determining whether the rate at which the ablating radiation dose was delivered to the mice affected the homing of lineage-depleted stem cells to the bone marrow and/or sites of tissue damage. Fractionated, lineage-depleted donor marrow cells were isolated and labeled with the membrane dye PKH26. Recipient mice were lethally irradiated with 11 Gy ionizing radiation using varying dose rates and were immediately injected with PKH26-labeled progenitor stem cells. With the exception of the lowest dose-rate group, all irradiated mice had an approximately fivefold (P = 0.014 to 0.025) reduction in stem cell homing to the bone marrow compared to unirradiated control animals. A fivefold reduction of stem cell homing to the spleen compared to unirradiated animals was also observed, though this was not statistically significant for any dose-rate group (P = 0.072 to 0.233). This difference in homing could not be explained by increased stem cell apoptosis/necrosis or non-marrow tissue homing to the intestine, lung or liver. We show that the dose rate at which a lethal dose of total-body radiation is delivered does not augment hematopoietic progenitor stem cell homing to the bone marrow, spleen or sites of early radiation-mediated tissue damage at either 2 or 5 days postirradiation/transplantation. The observation that greater homing was seen in unirradiated control mice calls into question the concept that adequate bone marrow stem cell homing requires radiation-induced "space" to be made in the marrow, certainly for the enriched early progenitor hematopoietic stem cells used for this set of experiments. Further experiments will be needed to determine whether these homed cells are as capable of giving rise to long-term engraftment/repopulation of the marrow of secondary recipients as they are in irradiated recipients.

Irradiation increases the interactions of platelets with the endothelium in vivo: analysis by intravital microscopy

Adhesion of platelets to the endothelium is believed to be a major factor contributing to thrombosis and vascular occlusion after radiotherapy or endovascular irradiation. In the present study, platelet-endothelium interactions were analyzed in vivo by intravital microscopy in mesenteric venules of mice according to three parameters: (1) platelet rolling, (2) platelet adhesion, and (3) the presence of platelet clusters. A 10-Gy total-body irradiation of mice resulted in an increase in the frequency of appearance of these three types of platelet-endothelium interactions in postcapillary venules 6 and 24 h after exposure, whereas only minor alterations were seen in large venules. In addition, the duration of platelet adhesion was increased 24 h after irradiation in both postcapillary and large venules. However, P-selectin was not up-regulated on the platelet membrane and platelet-leukocytes were not seen rolling together, suggesting that changes in platelet-endothelial cell interaction result from endothelial cell activation rather than platelet activation. Our data suggest that irradiation transforms resting endothelial cells to a pro-adhesive surface for platelets, which could ultimately lead to thrombosis.

Radiation-Induced Atherosclerotic Plaque Progression in a Hypercholesterolemic Rabbit

PURPOSE

Human observations provide rich soil for making hypotheses, but good animal models are essential for understanding the disease and to test treatment modalities. Currently, there is no standard animal model of vulnerable plaque; therefore, the purpose of this study is to develop a pathophysiologically relevant vulnerable plaque model.

METHODS

New Zealand White rabbits were fed with 1% hypercholesterolemic (HC) diet for 7 days, followed by balloon denudation of both the iliac arteries, and continued on 1% HC diet. Four weeks later, in 12 rabbits one of the iliac arteries was radiated (192-Ir, 15 Gy), and in five rabbits both the iliac arteries were sham treated. Following that, rabbits were fed with 0.15% HC diet. Four weeks later, arteries were processed for histomorphometry or immunohistochemistry.

RESULTS

Serum cholesterol levels were similar in all the groups. In radiated arteries, plaque area was significantly larger (32% larger then in sham). Macrophage-positive area in radiated arteries was 2.4 times greater than the macrophage-positive area in the nonradiated arteries. The area positive for macrophages is also positive for metalloproteinases (MMP)-1. The extent of alpha-actin positive area was significantly less (2.3-fold) in radiated arteries.

CONCLUSION

The atherosclerotic plaque developed in the current model is predominantly composed of macrophages expressing metalloproteinases with few smooth muscle cells (SMC)--a characteristic of vulnerable plaque. The animal model presented in this study can elucidate at least part of the mechanism of plaque vulnerability and could be used to test treatment modalities to test plaque stability.

Antioxidants attenuate atherosclerotic plaque development in a balloon-denuded and -radiated hypercholesterolemic rabbit

BACKGROUND

Oxidation of lipoproteins is considered to be a key contributor to atherogenesis. Antioxidants are potential antiatherogenic agents because they can inhibit lipoprotein oxidation. Radiation has been shown to increase oxidative stress leading to increased atherogenesis. This study is designed to test the potential of antioxidants to inhibit atherosclerotic plaque progression in balloon-denuded and -radiated rabbits.

METHODS AND RESULTS

Two groups of New Zealand white rabbits (n=36) were fed with 1% cholesterol diet (control diet) or with 1% cholesterol diet containing a mixture of various antioxidants for 1 week. Iliac arteries in all the animals were balloon denuded and continued to fed with 0.15% cholesterol diet or 0.15% cholesterol diet containing antioxidants (antioxidant diet). Four weeks after balloon denudation one iliac artery in 12 animals from each group was radiated and all the animals were continued to be fed with the same diet. Four weeks after radiation animals were sacrificed and morphometric analysis of iliac arteries (n=12) in nonradiated and radiated animals were performed. Plaque area (PA) in the rabbits that were fed with cholesterol diet is 0.2+/-0.12 mm2, and it is increased by 2.75-fold (P<.05) in the radiated arteries of animals fed with cholesterol diet. Plaque area in the animals fed with antioxidant diet is 50% less then the one in the animals fed with cholesterol diet. Similarly, plaque area in radiated arteries of the animals fed with antioxidant diet is 50% less then the animals fed with cholesterol diet.

CONCLUSION

Antioxidants significantly attenuate atherosclerotic plaque progression in balloon-injured and -radiated hypercholesterolemic rabbits.

Combination of stereotactic radiosurgery and cytokine gene-transduced tumor cell vaccination: a new strategy against metastatic brain tumors

OBJECT

To determine if the combination of radiosurgery and tumor cell vaccine would enhance the therapy of metastatic lesions of the central nervous system (CNS), the authors examined the antitumoral effects of radiosurgery and cytokine-transduced tumor cell vaccine.

METHODS

Fifty-five rats underwent intracranial implantation of 5 x 10(3) MADB 106 cells. On Day 3 after tumor implantation, 34 rats were inoculated in the flank with nonirradiated MADB 106 cells that had been retrovirally transduced to express granulocyte-macrophage colony-stimulating factor or interleukin-4. Twenty-seven rats (17 animals that had received the vaccine and 10 that had not) underwent radiosurgery performed using a gamma knife at maximum doses of 32 Gy on Day 5. No animals in the untreated group or in the vaccine-alone groups survived longer than 21 days. Animals treated by ra diosurgery alone displayed prolonged survival in comparison with untreated animals (p < 0.0001), but only one of 10 animals survived longer than 55 days. In contrast, 14 of 17 animals that received the combination therapy of radiosurgery and vaccination survived longer than 55 days (p = 0.0003 compared with animals that underwent radiosurgery alone). On Day 55, the long-term survivors were challenged by parental MADB 106 cells, which were implanted in the contralateral hemisphere. All animals from the combination therapy groups survived longer than 50 days after this challenge, but the single survivor from the radiosurgery-alone group died of tumor growth in 27 days.

CONCLUSIONS

The combination of radiosurgery and cytokine gene-transduced tumor cell vaccine markedly prolonged animal survival and protected animals from a subsequent challenge by parental tumor cells placed in the CNS. The data provided by this study indicate that this combination therapy represents a strategy that may have clinical applicability for single and/or multiple metastatic brain tumors.

Irradiated versus nonirradiated endothelial cells: effect on proliferation of vascular smooth muscle cells

PURPOSE

Endovascular radiation therapy is a promising strategy for the prevention of restenosis. Radiation prevents proliferation of vascular smooth muscle cells, thereby reducing the incidence of restenosis, but may also affect the remaining endothelial cells. For this reason, a comparison was made between irradiated and nonirradiated endothelial cells and their effects on the proliferation of vascular smooth muscle cells in a coculture system was evaluated.

MATERIALS AND METHODS

A coculture system was used, in which both endothelial cells and vascular smooth muscle cells were grown on opposite sides of a semipermeable membrane. After a period of growth arrest, the proliferation of vascular smooth muscle cells was measured during four subsequent days.

RESULTS

The presence of endothelial cells stimulated the proliferation of vascular smooth muscle cells during the first days of analysis but had an inhibitory effect during the subsequent days (P <.5). gamma-irradiation of endothelial cells resulted in a complete blockage of the proliferation of these cells. However, irradiated endothelial cells affected the proliferation of vascular smooth muscle cells in coculture in a fashion comparable to nonirradiated endothelial cells (P >.5).

CONCLUSION

The results suggest that, in endovascular radiation therapy, irradiation of endothelial cells does not change their effects on the proliferative behavior of vascular smooth muscle cells.

Irradiation enhances the support of haemopoietic cell transmigration, proliferation and differentiation by endothelial cells

Endothelial cells (ECs) are a critical component of the bone marrow stroma in the regulation of haemopoiesis. Recovery of bone marrow aplasia after radiation exposure depends, in part, on the repair of radiation-induced endothelial damage. Therefore, we assessed the ability of an irradiated human bone marrow EC line (TrHBMEC) to support transmigration, proliferation and differentiation of CD34+ bone marrow cells either irradiated or not in transendothelial migration or co-culture models. Radiation-induced EC damage was reflected by an increased release of soluble intercellular adhesion molecule (sICAM)-1 and platelet endothelial cell adhesion molecule (PECAM)-1. Irradiation of TrHBMECs with a 10 Gy dose strongly enhanced the transmigration of CD34+ cells, granulo-monocytic progenitors (CFU-GM) and erythroid progenitors (BFU-E). While ICAM-1 and PECAM-1 expression on irradiated TrHBMECs was increased, only antibodies against PECAM-1 inhibited the radiation-induced enhanced transmigration of haemopoietic cells. Irradiation of TrHBMECs (5-15 Gy) also increased proliferation and differentiation towards the granulo-monocytic lineage of co-cultured CD34+ cells, as well as colony formation by those cells and the production of interleukin 6 (IL-6), IL-8, granulocyte colony-stimulating factor (CSF) and granulocyte-macrophage CSF. Irradiated TrHBMECs were more capable of stimulating irradiated (1,2 Gy) CD34+ cells and haemopoietic progenitors than non-irradiated TrHBMECs. Together, these results suggest that, despite the radiation-induced damage, irradiated ECs may favour haemopoietic reconstitution after radiation exposure.

Increased glomerular deposits of von Willebrand factor in chronic, but not acute, rejection of primate renal allografts

BACKGROUND

In our previously described primate renal allograft model, T cell ablation leads to long-term graft survival. The role of endothelial cell alteration in chronic rejection was examined in our model.

METHODS

Renal transplants were performed in rhesus monkeys using a T cell- depleting immunotoxin, FN18-CRM9. Sections from 10 rejected kidneys (5 acute and 7 chronic rejection) were examined after immunohistochemical staining for expression of endothelium-related proteins [von Willebrand factor (vWF), CD62P, and CD31], fibrinogen, and a macrophage marker (CD68). Glomerular staining for each antigen was graded on a semiquantitative scale.

RESULTS

Intense staining for vWF was consistently observed in glomerular endothelium, subendothelium, and mesangium in all kidneys removed due to chronic rejection. vWF staining was weak in kidneys showing acute rejection. The difference in glomerular staining was statistically significant. Staining for vWF in extraglomerular vessels was nearly identical in kidneys showing acute and chronic rejection. Expression of CD62P was increased in extraglomerular vessels in allografts with chronic rejection, but the glomeruli showed little or no staining. There was no significant difference in the glomerular staining for CD62P or CD31 in organs showing acute and chronic rejection. Fibrinogen staining of glomerular mesangium was seen in kidneys with chronic rejection. Macrophages (CD68+) infiltrating glomeruli were more numerous in kidneys showing chronic rejection.

CONCLUSION

Increased glomerular deposition of vWF in renal allografts showing chronic rejection, without increased staining for CD62P or CD31, suggests increased constitutive secretion of vWF from endothelial cells as a component of the mechanism of chronic rejection in our model.

PECAM-1 (CD31) expression modulates bleeding time in vivo

PECAM-1 is a 130-kd member of the Ig superfamily present on endothelial cells, platelets, polymorphonuclear leukocytes, monocytes, and lymphocytes. Its expression begins early in development and persists through adulthood. PECAM-1 functions as an adhesion and signaling molecule between adjacent endothelial cells and between endothelial cells and circulating blood elements. Antibodies directed against PECAM-1 have been shown to affect angiogenesis, endothelial cell migration, and polymorphonuclear leukocyte transmigration. Furthermore, its dimerization is associated with the modulation of integrin affinity. Antibody inhibition studies suggest that PECAM-1 plays a role in modulating thrombosis; however, recent in vitro aggregation studies performed on platelets harvested from PECAM-1-deficient mice revealed no abnormalities. In this report we demonstrate prolonged in vivo bleeding times in PECAM-1-deficient mice. This abnormality was not corrected when wild-type hematopoietic precursors were engrafted into marrow-ablated PECAM-1-deficient mice. Furthermore, normal bleeding times were observed when marrow-ablated wild-type mice were engrafted with hematopoietic precursors harvested from PECAM-1-deficient mice. These studies are consistent with a role for PECAM-1 in modulating thrombosis in the vasculature, which is potentially mediated by endothelial cell PECAM-1 expression.

Radiation-induced normal tissue injury: role of adhesion molecules in leukocyte-endothelial cell interactions

The late onset of necrosis and fibrosis in normal tissues can be a serious consequence of radiotherapy in cancer patients. Because radiation-induced vascular injury precedes the tissue damage, vascular injury is regarded as crucial in the pathogenesis of tissue damage. An understanding of the processes responsible is essential to develop strategies for the amelioration of radiation-induced normal tissue damage. Leukocyte infiltration is commonly observed at sites of irradiation and is likely to lead to the acceleration and/or induction of parenchymal atrophy, fibrosis and necrosis in normal tissues following radiotherapy. The molecular mechanisms mediating leukocyte infiltration of tissues during inflammation have been studied extensively. It is now well established that cell adhesion molecules (CAMs) expressed on leukocytes and endothelial cells control the trafficking of leukocytes from the blood vessel lumen in these conditions. CAMs including E (endothelial), P (platelet) and L (leukocyte)-selectins, intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), beta1 and beta2 integrins and CD31 are involved in the cascade of events resulting in rolling, arrest and transmigration of leukocytes through the inflamed endothelium. Whether a similar sequence of molecular events induces leukocyte sequestration in irradiated normal tissues is not known. This review is focussed on the role of CAMs in radiation-induced leukocyte infiltration of normal tissues and the therapeutic implications of these findings.