Inactivation of thrombomodulin by ionizing radiation in a cell-free system: possible implications for radiation responses in vascular endothelium

Study the relationship of endothelial damage / dysfunction due to occupational exposure to low dose ionizing radiation versus high dose exposure during radiotherapy

BACKGROUND

Vascular injuries caused by irradiation include acute vasculitis with neutrophil invasion, endothelial cell (EC) swelling, capillary loss, and activation of coagulator mechanisms, along with local ischemia and fibrosis. The circulating endothelial cells (CECs), increase dramatically in diseases with vascular damage.

AIM

The aim of this study is to provide data on the endothelial dysfunction due to occupational exposure to low dose ionizing radiation versus high dose exposure during radiotherapy (RT).

PATIENTS AND METHODS

This study included 100 subjects divided into three main groups: Group I: High dose exposure group: 50 breast cancer patients treated with post-operative radiotherapy. Group II: Low dose exposure group: 25 hospital radiation workers. Group III: 25 healthy volunteers' age and sex matched as control group who had never worked in radiation-related jobs. TM levels measured by enzyme linked immunosorbent assay (ELISA). Circulating endothelial cells (CEC) enumerated in peripheral blood by flow cytometric analysis of their signature receptor CD146.

RESULTS

% CD146+ cells and plasma TM were significantly increased in radiation workers and after exposure to radiotherapy treatment in breast cancer patients. When comparing patients group with radiation workers group, we found significant elevation in plasma TM in radiation workers while insignificant difference was found in % CD146+ cells.

CONCLUSION

CECs and plasma TM both are increased in radiation workers and patients treated with radiotherapy. They may constitute valuable markers of endothelial injury. Workers exposed to low doses of ionizing radiation may develop significant endothelial dysfunction predisposes them to cardiovascular complications namely thrombosis, mostly due to oxidative stress among other causes.

Pravastatin Alleviates Radiation Proctitis by Regulating Thrombomodulin in Irradiated Endothelial Cells

Although radiotherapy plays a crucial in the management of pelvic tumors, its toxicity on surrounding healthy tissues such as the small intestine, colon, and rectum is one of the major limitations associated with its use. In particular, proctitis is a major clinical complication of pelvic radiotherapy. Recent evidence suggests that endothelial injury significantly affects the initiation of radiation-induced inflammation. The damaged endothelial cells accelerate immune cell recruitment by activating the expression of endothelial adhesive molecules, which participate in the development of tissue damage. Pravastatin, a cholesterol lowering drug, exerts persistent anti-inflammatory and anti-thrombotic effects on irradiated endothelial cells and inhibits the interaction of leukocytes and damaged endothelial cells. Here, we aimed to investigate the effects of pravastatin on radiation-induced endothelial damage in human umbilical vein endothelial cell and a murine proctitis model. Pravastatin attenuated epithelial damage and inflammatory response in irradiated colorectal lesions. In particular, pravastatin improved radiation-induced endothelial damage by regulating thrombomodulin (TM) expression. In addition, exogenous TM inhibited leukocyte adhesion to the irradiated endothelial cells. Thus, pravastatin can inhibit endothelial damage by inducing TM, thereby alleviating radiation proctitis. Therefore, we suggest that pharmacological modulation of endothelial TM may limit intestinal inflammation after irradiation.

Radiation, inflammation and the immune response in cancer

Radiation is an important component of cancer treatment with more than half of all patients receive radiotherapy during their cancer experience. While the impact of radiation on tumour morphology is routinely examined in the pre-clinical and clinical setting, the impact of radiation on the tumour microenvironment and more specifically the inflammatory/immune response is less well characterised. Inflammation is a key contributor to short- and long-term cancer eradication, with significant tumour and normal tissue consequences. Therefore, the role of radiation in modulating the inflammatory response is highly topical given the current wave of targeted and immuno-therapeutic treatments for cancer. This review provides a general overview of how radiation modulates the inflammatory and immune response—(i) how radiation induces the inflammatory/immune system, (ii) the cellular changes that take place, (iii) how radiation dose delivery affects the immune response, and (iv) a discussion on research directions to improve patient survival, reduce side effects, improve quality of life, and reduce financial costs in the immediate future. Harnessing the benefits of radiation on the immune response will enhance its maximal therapeutic benefit and reduce radiation-induced toxicity.

Venous thromboembolism in radiation therapy cancer patients: Findings from the RIETE registry

BACKGROUND

Cancer patients are at high risk of venous thromboembolism, particularly during cancer treatment. Conversely to chemotherapy, data on the epidemiology and clinical features of venous thromboembolism during radiation therapy are scarce. There is lack of evidence on the influence of radiation therapy (RT) on outcome in cancer patients with acute venous thromboembolism (VTE).

METHODS

We used the RIETE (Registro Informatizado de Enfermedad ThromboEmbolica) database to assess the clinical characteristics and outcome of prospectively-collected consecutive patients with cancer-associated thrombosis occurred during the course of radiation therapy for cancer. Death, venous thromboembolism recurrences and major bleeding rates during long-term follow-up according to cancer site and treatment were compared RESULTS: 9284 Patients with active cancer and VTE were enrolled in RIETE: 4605 with pulmonary embolism (PE) and 4679 with deep vein thrombosis (DVT). In all, 1202 (13%) were receiving RT. This last sub-population had a higher rate of PE recurrences and a similar rate of DVT recurrences or major bleeding than those not receiving RT. Patients on RT had a higher rate of cerebral bleeding.

CONCLUSIONS

In this cohort of cancer patients with VTE, a significant proportion of them received RT before VTE, the latter experienced a higher risk of cerebral bleeding.

Novel concepts in radiation-induced cardiovascular disease

Radiation-induced cardiovascular disease (RICVD) is the most common nonmalignant cause of morbidity and mortality among cancer survivors who have undergone mediastinal radiation therapy (RT). Cardiovascular complications include effusive or constrictive pericarditis, cardiomyopathy, valvular heart disease, and coronary/vascular disease. These are pathophysiologically distinct disease entities whose prevalence varies depending on the timing and extent of radiation exposure to the heart and great vessels. Although refinements in RT dosimetry and shielding will inevitably limit future cases of RICVD, the increasing number of long-term cancer survivors, including those treated with older higher-dose RT regimens, will ensure a steady flow of afflicted patients for the foreseeable future. Thus, there is a pressing need for enhanced understanding of the disease mechanisms, and improved detection methods and treatment strategies. Newly characterized mechanisms responsible for the establishment of chronic fibrosis, such as oxidative stress, inflammation and epigenetic modifications, are discussed and linked to potential treatments currently under study. Novel imaging modalities may serve as powerful screening tools in RICVD, and recent research and expert opinion advocating their use is introduced. Data arguing for the aggressive use of percutaneous interventions, such as transcutaneous valve replacement and drug-eluting stents, are examined and considered in the context of prior therapeutic approaches. RICVD and its treatment options are the subject of a rich and dynamic body of research, and patients who are at risk or suffering from this disease will benefit from the care of physicians with specialty expertise in the emerging field of cardio-oncology.

Thrombomodulin contributes to gamma tocotrienol-mediated lethality protection and hematopoietic cell recovery in irradiated mice

Systemic administration of recombinant thrombomodulin (TM) confers radiation protection partly by accelerating hematopoietic recovery. The uniquely potent radioprotector gamma tocotrienol (GT3), in addition to being a strong antioxidant, inhibits the enzyme hydroxy-methyl-glutaryl-coenzyme A reductase (HMGCR) and thereby likely modulates the expression of TM. We hypothesized that the mechanism underlying the exceptional radioprotective properties of GT3 partly depends on the presence of endothelial TM. In vitro studies confirmed that ionizing radiation suppresses endothelial TM (about 40% at 4 hr after 5 Gy γ-irradiation) and that GT3 induces TM expression (about 2 fold at the mRNA level after 5 μM GT3 treatment for 4 hr). In vivo survival studies showed that GT3 was significantly more effective as a radioprotector in TM wild type (TM+/+) mice than in mice with low TM function (TMPro/-). After exposure to 9 Gy TBI, GT3 pre-treatment conferred 85% survival in TM+/+ mice compared to only 50% in TMPro/-. Thus, GT3-mediated radiation lethality protection is partly dependent on endothelial TM. Significant post-TBI recovery of hematopoietic cells, particularly leukocytes, was observed in TM+/+ mice (p = 0.003), but not in TMPro/- mice, despite the fact that GT3 induced higher levels of granulocyte colony stimulating factor (G-CSF) in TMPro/- mice (p = 0.0001). These data demonstrate a critical, G-CSF-independent, role for endothelial TM in GT3-mediated lethality protection and hematopoietic recovery after exposure to TBI and may point to new strategies to enhance the efficacy of current medical countermeasures in radiological/nuclear emergencies.

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.

Synergistic radioprotection by gamma-tocotrienol and pentoxifylline: role of cAMP signaling

Purpose. This study was designed to determine the efficacy and mechanisms of radioprotection by the combination of gamma-tocotrienol (GT3) and pentoxifylline (PTX) against acute radiation injury. Materials and Methods. Post-irradiation survival was monitored to determine the most efficacious dose and time of administration of PTX. Dose reduction factor (DRF) was calculated to compare the radioprotective efficacy of the combination. To determine the mechanism of synergistic radioprotection by the combination, mevalonate or calmodulin were coadministered with the GT3-PTX combination. Mevalonate was used to reverse the inhibitory effect of GT3 on 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR), and calmodulin was used to reverse the inhibition of phosphodiesterase (PDE) by PTX. Results. The combination was most effective when 200 mg/kg of PTX was administered 15 min before irradiation along with 200 mg/kg of GT3 (-24 h) and resulted in a DRF of 1.5. White blood cells and neutrophil counts showed accelerated recovery in GT3-PTX-treated groups compared to GT3. Mevalonate had no effect on the radioprotection of GT3-PTX; calmodulin abrogated the synergistic radioprotection by GT3-PTX. Conclusion. The mechanism of radioprotection by GT3-PTX may involve PDE inhibition.

Pharmacological targeting of the thrombomodulin-activated protein C pathway mitigates radiation toxicity

Tissue damage induced by ionizing radiation in the hematopoietic and gastrointestinal systems is the major cause of lethality in radiological emergency scenarios and underlies some deleterious side effects in patients undergoing radiation therapy. The identification of target-specific interventions that confer radiomitigating activity is an unmet challenge. Here we identify the thrombomodulin (Thbd)-activated protein C (aPC) pathway as a new mechanism for the mitigation of total body irradiation (TBI)-induced mortality. Although the effects of the endogenous Thbd-aPC pathway were largely confined to the local microenvironment of Thbd-expressing cells, systemic administration of soluble Thbd or aPC could reproduce and augment the radioprotective effect of the endogenous Thbd-aPC pathway. Therapeutic administration of recombinant, soluble Thbd or aPC to lethally irradiated wild-type mice resulted in an accelerated recovery of hematopoietic progenitor activity in bone marrow and a mitigation of lethal TBI. Starting infusion of aPC as late as 24 h after exposure to radiation was sufficient to mitigate radiation-induced mortality in these mice. These findings suggest that pharmacologic augmentation of the activity of the Thbd-aPC pathway by recombinant Thbd or aPC might offer a rational approach to the mitigation of tissue injury and lethality caused by ionizing radiation.

Thrombomodulin protects endothelial cells from a calcineurin inhibitor-induced cytotoxicity by upregulation of extracellular signal-regulated kinase/myeloid leukemia cell-1 signaling

OBJECTIVE

We have recently reported that recombinant human soluble thrombomodulin (rTM) counteracted capillary leakage associated with engraftment, as well as sinusoidal obstructive syndrome after hematopoietic stem cell transplantation. These observations prompted us to explore whether rTM possessed cytoprotective effects on endothelial cells.

METHODS AND RESULTS

Exposure of human umbilical vein endothelial cells to rTM induced expression of antiapoptotic protein myeloid leukemia cell-1 through the activation of extracellular signal-regulated kinase in these cells. Additional studies found that exposure of human umbilical vein endothelial cells to cyclosporine A and FK506, an immunosuppressant used for the individuals receiving hematopoietic stem cell transplantation, induced apoptosis, which was attenuated when human umbilical vein endothelial cells were exposed to these agents in the presence of rTM. Further studies using deletion mutants of thrombomodulin (TM) identified that the epidermal growth factor domain of TM possessed cytoprotective effects. A single nucleotide substitution at codon 376 or 424 of TM, which impairs the ability of TM to produce activated protein C or bind to thrombin, respectively, did not hamper the cytoprotective effects of TM, which suggested that cytoprotective effects of rTM were distinctive from those of activated protein C.

CONCLUSIONS

TM may be useful for prevention, as well as treatment of endothelial cell damage after hematopoietic stem cell transplantation.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

PPARs in Irradiation-Induced Gastrointestinal Toxicity

The use of radiation therapy to treat cancer inevitably involves exposure of normal tissues. Although the benefits of this treatment are well established, many patients experience distressing complications due to injury to normal tissue. These side effects are related to inflammatory processes, and they decrease therapeutic benefit by increasing the overall treatment time. Emerging evidence indicates that PPARs and their ligands are important in the modulation of immune and inflammatory reactions. This paper discusses the effects of abdominal irradiation on PPARs, their role and functions in irradiation toxicity, and the possibility of using their ligands for radioprotection.