NO-donating aspirin and aspirin partially inhibit age-related atherosclerosis but not radiation-induced atherosclerosis in ApoE null mice

Myocardial Ischemia Related to Common Cancer Therapy-Prevention Insights

Modern antineoplastic therapy improves survival and quality of life in cancer patients, but its indisputable benefits are accompanied by multiple and major side effects, such as cardiovascular ones. Endothelial dysfunction, arterial spasm, intravascular thrombosis, and accelerated atherosclerosis affect the coronary arteries, leading to acute and chronic coronary syndromes that negatively interfere with the oncologic treatment. The cardiac toxicity of antineoplastic agents may be mitigated by using adequate prophylactic measures. In the absence of dedicated guidelines, our work provides the most comprehensive, systematized, structured, and up-to-date analyses of the available literature focusing on measures aiming to protect the coronary arteries from the toxicity of cancer therapy. Our work facilitates the implementation of these measures in daily practice. The ultimate goal is to offer clinicians the necessary data for a personalized therapeutic approach for cancer patients receiving evidence-based oncology treatments with potential cardiovascular toxicity.

Adverse Radiation Therapy Effects in the Treatment of Head and Neck Tumors

Whether used as a single modality or as part of a combined approach, radiation therapy (RT) plays an essential role in the treatment of several head and neck malignancies. Despite the improvement in radiation delivery techniques, normal structures in the vicinity of the target area remain susceptible to a wide range of adverse effects. Given their high incidence, some of these effects are referred to as expected postradiation changes (eg, mucositis, sialadenitis, and edema), while others are considered true complications, meaning they should not be expected and can even represent life-threatening conditions (eg, radionecrosis, fistulas, and radiation-induced neoplasms). Also, according to their timing of onset, these deleterious effects can be divided into four groups: acute (during RT), subacute (within weeks to months), delayed onset (within months to years), and very delayed onset (after several years).The authors provide a comprehensive review of the most important radiation-induced changes related to distinct head and neck sites, focusing on their typical cross-sectional imaging features and correlating them with the time elapsed after treatment. Radiologists should not only be familiar with these imaging findings but also actively seek essential clinical data at the time of interpretation (including knowledge of the RT dose and time, target site, and manifesting symptoms) to better recognize imaging findings, avoid pitfalls and help guide appropriate management. ^© RSNA, 2022.

Radiation-induced cardiovascular disease: an overlooked role for DNA methylation?

Radiotherapy in cancer treatment involves the use of ionizing radiation for cancer cell killing. Although radiotherapy has shown significant improvements on cancer recurrence and mortality, several radiation-induced adverse effects have been documented. Of these adverse effects, radiation-induced cardiovascular disease (CVD) is particularly prominent among patients receiving mediastinal radiotherapy, such as breast cancer and Hodgkin's lymphoma patients. A number of mechanisms of radiation-induced CVD pathogenesis have been proposed such as endothelial inflammatory activation, premature endothelial senescence, increased ROS and mitochondrial dysfunction. However, current research seems to point to a so-far unexamined and potentially novel involvement of epigenetics in radiation-induced CVD pathogenesis. Firstly, epigenetic mechanisms have been implicated in CVD pathophysiology. In addition, several studies have shown that ionizing radiation can cause epigenetic modifications, especially DNA methylation alterations. As a result, this review aims to provide a summary of the current literature linking DNA methylation to radiation-induced CVD and thereby explore DNA methylation as a possible contributor to radiation-induced CVD pathogenesis.

Total plaque score helps to determine follow-up strategy for carotid artery stenosis progression in head and neck cancer patients after radiation therapy

BACKGROUND

To identify predictors of carotid artery stenosis (CAS) progression in head and neck cancer (HNC) patients after radiation therapy (RT).

METHODS

We included 217 stroke-naïve HNC patients with mild carotid artery stenosis after RT in our hospital. These patients underwent annual carotid duplex ultrasound (CDU) studies to monitor CAS progression. CAS progression was defined as the presence of ≥50% stenosis of the internal/common carotid artery on follow-up CDU. We recorded total plaque score (TPS) and determined the cut-off TPS to predict CAS progression. We categorized patients into high (HP) and low plaque (LP) score groups based on their TPS at enrolment. We analyzed the cumulative events of CAS progression in the two groups.

RESULTS

The TPS of the CDU study at enrolment was a significant predictor for CAS progression (adjusted odds ratio [aOR] = 1.69, p = 0.002). The cut-off TPS was 7 (area under the curve: 0.800), and a TPS ≥ 7 strongly predicted upcoming CAS progression (aOR = 41.106, p = 0.002). The HP group had a higher risk of CAS progression during follow-up (adjusted hazard ratio = 6.15; 95% confident interval: 2.29-16.53) in multivariable Cox analysis, and also a higher trend of upcoming ischemic stroke (HP vs. LP: 8.3% vs. 2.2%, p = 0.09).

CONCLUSIONS

HNC patients with a TPS ≥ 7 in any CDU study after RT are susceptible to CAS progression and should receive close monitoring within the following 2 years.

Hypothyroidism and risks of cerebrovascular complications among patients with head and neck cancer after radiotherapy

BACKGROUND

Hypothyroidism (HT) and carotid artery stenosis (CAS) are complications of radiotherapy (RT) in patients with head and neck cancer (HNC). The impact of post-RT HT on CAS progression remains unclear.

METHODS

Between 2013 and 2014, HNC patients who had ever received RT and were under regular follow-up in our hospital were initially screened. Patients were categorized into euthyroid (EU) and HT groups. Details of RT and HNC were recorded. Total plaque scores and degrees of CAS were measured during annual extracranial duplex follow-up. Patients were monitored for CAS progression to > 50 % stenosis or ischemic stroke (IS). Cumulative time to CAS progression and IS between the 2 groups were compared. Data were further analyzed based on the use or nonuse of thyroxine of the HT group.

RESULTS

333 HNC patients with RT history were screened. Finally, 216 patients were recruited (94 and 122 patients in the EU and HT groups). Patients of the HT group received higher mean RT doses (HT vs. EU; 7021.55 ± 401.67 vs. 6869.69 ± 425.32 centi-grays, p = 0.02). Multivariate Cox models showed comparable CAS progression (p = 0.24) and IS occurrence (p = 0.51) between the 2 groups. Moreover, no significant difference was observed in time to CAS progression (p = 0.49) or IS (p = 0.31) among patients with EU and HT using and not using thyroxine supplement.

CONCLUSIONS

Our results did not demonstrate significant effects of HT and thyroxine supplementation on CAS progression and IS incidence in patients with HNC after RT.

Prevention of radiotherapy-induced arterial inflammation by interleukin-1 blockade

Aims

Radiotherapy-induced cardiovascular disease is an emerging problem in a growing population of cancer survivors where traditional treatments, such as anti-platelet and lipid-lowering drugs, have limited benefits. The aim of the study was to investigate vascular inflammatory patterns in human cancer survivors, replicate the findings in an animal model, and evaluate whether interleukin-1 (IL-1) inhibition could be a potential treatment.

Methods and results

Irradiated human arterial biopsies were collected during microvascular autologous free tissue transfer for cancer reconstruction and compared with non-irradiated arteries from the same patient. A mouse model was used to study the effects of the IL-1 receptor antagonist, anakinra, on localized radiation-induced vascular inflammation. We observed significant induction of genes associated with inflammasome biology in whole transcriptome analysis of irradiated arteries, a finding supported by elevated protein levels in irradiated arteries of both, pro-caspase and caspase-1. mRNA levels of inflammasome associated chemokines CCL2, CCL5 together with the adhesion molecule VCAM1, were elevated in human irradiated arteries as was the number of infiltrating macrophages. A similar pattern was reproduced in Apoe−/− mouse 10 weeks after localized chest irradiation with 14 Gy. Treatment with anakinra in irradiated mice significantly reduced Ccl2 and Ccl5 mRNA levels and expression of I-A^b.

Conclusion

Anakinra, administered directly after radiation exposure for 2 weeks, ameliorated radiation induced sustained expression of inflammatory mediators in mice. Further studies are needed to evaluate IL-1 blockade as a treatment of radiotherapy-induced vascular disease in a clinical setting.

Vascular toxic effects of cancer therapies

Cancer therapies can lead to a broad spectrum of cardiovascular complications. Among these, cardiotoxicities remain of prime concern, but vascular toxicities have emerged as the second most common group. The range of cancer therapies with a vascular toxicity profile and the clinical spectrum of vascular toxic effects are quite broad. Historically, venous thromboembolism has received the greatest attention but, over the past decade, the arterial toxic effects, which can present as acute vasospasm, acute thrombosis and accelerated atherosclerosis, of cancer therapies have gained greater recognition. This Review focuses on these types of cancer therapy-related arterial toxicity, including their mechanisms, and provides an update on venous thromboembolism and pulmonary hypertension associated with cancer therapies. Recommendations for the screening, treatment and prevention of vascular toxic effects of cancer therapies are outlined in the context of available evidence and society guidelines and consensus statements. The shift towards greater awareness of the vascular toxic effects of cancer therapies has further unveiled the urgent needs in this area in terms of defining best clinical practices. Well-designed and well-conducted clinical studies and registries are needed to more precisely define the incidence rates, risk factors, primary and secondary modes of prevention, and best treatment modalities for vascular toxicities related to cancer therapies. These efforts should be complemented by preclinical studies to outline the pathophysiological concepts that can be translated into the clinic and to identify drugs with vascular toxicity potential even before their widespread clinical use.

Prognosis of acute coronary syndromes after radiotherapy for breast cancer

BACKGROUND AND PURPOSE

Breast cancer patients treated with radiotherapy are at increased risk of subsequent acute coronary syndromes (ACS). We aimed to study if radiotherapy also influences the prognosis of these ACS.

MATERIALS AND METHODS

We included all 398 patients diagnosed with ACS following radiotherapy from our hospital-based cohort of early breast cancer patients aged <71 years, treated 1970-2009. Cardiovascular disease incidence and cause of death were acquired through questionnaires to general practitioners and cardiologists. Internal mammary chain (IMC) irradiation delivers the highest heart doses in breast cancer radiotherapy. Hence, we compared ACS prognosis between patients treated with/without IMC-irradiation. ACS prognosis was assessed through cardiac death, death due to ACS and cardiovascular disease incidence, using multivariable Cox proportional hazard models and by estimating cumulative incidence.

RESULTS

In total, 62% of patients with ACS had received IMC-irradiation and 38% did not (median age at ACS diagnosis, 67 years). Median time between breast cancer and ACS was 15 years. After ACS, ten-year cumulative risk of cardiac death was 35% for patients who had IMC-irradiation (95% confidence interval [95%CI] 29-41) compared to 24% (95%CI 17-31) for patients without IMC-irradiation (p = 0.04). After correction for confounders, IMC-irradiation remained associated with a less favourable prognosis of ACS compared to no IMC-irradiation (hazard ratio cardiac death = 1.7, 95%CI 1.1-2.5).

CONCLUSION

Our results suggest that radiotherapy, in case of substantial heart doses,may worsen ACS prognosis. This is an important, novel finding that may impact upon the risk-based care for breast cancer survivors with ACS.

Radiotherapy-induced heart disease: a review of the literature

Radiotherapy as one of the four pillars of cancer therapy plays a critical role in the multimodal treatment of thoracic cancers. Due to significant improvements in overall cancer survival, radiotherapy-induced heart disease (RIHD) has become an increasingly recognized adverse reaction which contributes to major radiation-associated toxicities including non-malignant death. This is especially relevant for patients suffering from diseases with excellent prognosis such as breast cancer or Hodgkin’s lymphoma, since RIHD may occur decades after radiotherapy. Preclinical studies have enriched our knowledge of many potential mechanisms by which thoracic radiotherapy induces heart injury. Epidemiological findings in humans reveal that irradiation might increase the risk of cardiac disease at even lower doses than previously assumed. Recent preclinical studies have identified non-invasive methods for evaluation of RIHD. Furthermore, potential options preventing or at least attenuating RIHD have been developed. Ongoing research may enrich our limited knowledge about biological mechanisms of RIHD, identify non-invasive early detection biomarkers and investigate potential treatment options that might attenuate or prevent these unwanted side effects. Here, we present a comprehensive review about the published literature regarding clinical manifestation and pathological alterations in RIHD. Biological mechanisms and treatment options are outlined, and challenges in RIHD treatment are summarized.

Radiation-Induced Cardiovascular Disease: Mechanisms and Importance of Linear Energy Transfer

Radiation therapy (RT) in the form of photons and protons is a well-established treatment for cancer. More recently, heavy charged particles have been used to treat radioresistant and high-risk cancers. Radiation treatment is known to cause cardiovascular disease (CVD) which can occur acutely during treatment or years afterward in the form of accelerated atherosclerosis. Radiation-induced cardiovascular disease (RICVD) can be a limiting factor in treatment as well as a cause of morbidity and mortality in successfully treated patients. Inflammation plays a key role in both acute and chronic RICVD, but the underling pathophysiology is complex, involving DNA damage, reactive oxygen species, and chronic inflammation. While understanding of the molecular mechanisms of RICVD has increased, the growing number of patients receiving RT warrants further research to identify individuals at risk, plans for prevention, and targets for the treatment of RICVD. Research on RICVD is also relevant to the National Aeronautics and Space Administration (NASA) due to the prevalent space radiation environment encountered by astronauts. NASA's current research on RICVD can both contribute to and benefit from concurrent work with cell and animal studies informing radiotoxicities resulting from cancer therapy. This review summarizes the types of radiation currently in clinical use, models of RICVD, current knowledge of the mechanisms by which they cause CVD, and how this knowledge might apply to those exposed to various types of radiation.

Ionising radiation increases permeability of endothelium through ADAM10-mediated cleavage of VE-cadherin

The association between ionising radiation (IR) exposure and risk of cardiovascular diseases (CVD) is well documented, but the underlying mechanism is still poorly understood. As atherosclerotic plaques are the most common cause of CVD, we investigated the effects of IR on one of the critical parameters for atherosclerotic plaque formation – endothelium permeability to macromolecules.

We used endothelial cells from human coronary artery as a model of the endothelial layer. Our results show that exposure of this endothelial layer to IR increased its permeability to macromolecules of various sizes in a dose-dependent manner. Immunofluorescence analysis revealed disruption of cell junctions caused by decreased amounts of two junction proteins, one of which is vascular endothelial cadherin (VE-cadherin). The reduction in the level of this protein was not due to diminished transcription but to protein processing instead. We observed a radiation dose-dependent increase in the cleavage of VE-cadherin by ADAM10. This was not mediated through the canonical VEGF route but was instead accompanied by intra-cellular calcium release. Importantly, inhibition of ADAM10 activity rescued IR-induced permeability.

Our observations demonstrate that exposure to IR activates ADAM10 to cleave VE-cadherin leading to augmented endothelium permeability; a feature that can lead to the development of atherosclerotic plaques and increase the risk of cardiovascular disease.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

Evaluating the Primary Prevention of Ischemic Stroke of Oral Antithrombotic Therapy in Head and Neck Cancer Patients with Radiation Therapy

Although previous studies demonstrated the risk of ischemic stroke (IS) in patients with head and neck cancer (HNC), the impact of oral antithrombotic therapy (OAT) on this risk has not yet been assessed. We aimed to evaluate the effectiveness and safety of OAT in patients with HNC treated with RT. This retrospective cohort study was performed using the National Health Insurance Research Database of Taiwan. A total of 37,638 patients diagnosed with HNC included in the study were classified as users and nonusers of OAT. Primary outcome was IS or transient ischemic attack (TIA), and secondary outcomes were death and major bleeding. The Cox proportional hazards model was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). There was no significant difference in the risk of IS or TIA between patients on continuous OAT and nonusers (adjusted HR, 0.812; 95% CI, 0.199-3.309). The risk of major bleeding was not significantly different between the groups. From a national population database, we did not find an association between OAT and decreasing risk of ischemic stroke/TIA or increasing hazard of major bleeding.

Effects of ionizing radiation on the heart

This article provides an overview of studies addressing effects of ionizing radiation on the heart. Clinical studies have identified early and late manifestations of radiation-induced heart disease, a side effect of radiation therapy to tumors in the chest when all or part of the heart is situated in the radiation field. Studies in preclinical animal models have contributed to our understanding of the mechanisms by which radiation may injure the heart. More recent observations in human subjects suggest that ionizing radiation may have cardiovascular effects at lower doses than was previously thought. This has led to examinations of low-dose photons and low-dose charged particle irradiation in animal models. Lastly, studies have started to identify non-invasive methods for detection of cardiac radiation injury and interventions that may prevent or mitigate these adverse effects. Altogether, this ongoing research should increase our knowledge of biological mechanisms of cardiovascular radiation injury, identify non-invasive biomarkers for early detection, and potential interventions that may prevent or mitigate these adverse effects.

Preclinical analysis of nonsteroidal anti-inflammatory drug usefulness for the simultaneous prevention of steatohepatitis, atherosclerosis and hyperlipidemia

Nonalcoholic steatohepatitis (NASH) is currently one of the primary liver diseases. Recent studies have shown a clinical relation between NASH and atherosclerosis. There is much interest in these two diseases because they are both associated with great morbidity and mortality. Inflammation and the overexpression of COX-2 participate in the pathophysiology of the two diseases, and therefore simultaneous treatment is feasible. The role of the four NSAIDs, meclofenamate, mefenamate, flufenamate, and aspirin, was analyzed in a mouse model of NASH, as well as preclinical atherosclerosis induced by a high-fat diet (HFD). Six mouse groups were formed. Five of the groups were fed a high-fat diet for 6 months and one group was fed a standard diet, acting as the normality reference. Of the five groups fed a high-fat diet, four received a NSAID, each of them identified by the specific drug administered. One group received no treatment. Serum markers (cholesterol, triglycerides, ALT, and AST) and histologic changes in the aorta and liver were analyzed for the study. Aspirin significantly reduced the hepaticsteatosis. All the drugs significantly reduced the hepatic inflammatory infiltrate. In relation to atherosclerosis, there were significant reductions in all the study variables with the use of aspirin and flufenamate. The four medications were able to stop steatosis from progressing into steatohepatitis by reducing inflammation. However, aspirin was the most beneficial, simultaneously reducing steatosis, atherosclerosis, and serum cholesterol levels.

Irradiated U937 cells trigger inflammatory bystander responses in human umbilical vein endothelial cells through the p38 pathway

Radiation-induced bystander effects are a well-known phenomenon that are observed when treating cancer and other diseases after radiotherapy, and even after occupational exposure to radiation. However, little is known about the crosstalk between irradiated macrophages and endothelial cells that line the circulatory system, which may play a role in the development of atherosclerosis. In the current study, we found that the expression of inducible nitric oxide synthase (iNOS) and the intracellular level of nitric oxide (NO) in gamma-irradiated U937 macrophage cells were significantly increased. When human umbilical vein endothelial cells (HUVECs) were co-cultured with gamma-irradiated U937 cells, additional micronuclei (MN) and apoptosis were induced so that the plating efficiency of the bystander HUVECs decreased and P38 was overexpressed in the bystander HUVECs cells. In addition, the contents of vascular cell adhesion molecule 1 (VCAM-1) and the activities of matrix metalloproteinase-9 (MMP-9) in the culture medium of bystander HUVECs were increased. Furthermore, during cell co-culture the adhesive ability of irradiated U937 cells to the bystander HUVECs increased. When U937 cells were treated with 500 μM S-methylisothiourea sulfate (SMT) (iNOS inhibitor) before irradiation, and HUVECs were treated with 10 μM SB203580 (p38 inhibitor) before cell co-culture or treated with 20 μM c-PTIO (NO scavenger) in the co-culture medium, the bystander micronuclei and the amounts of VCAM-1 and MMP-9 in the medium of bystander HUVECs were diminished, and the ability of irradiated U937 cells adhering to HUVECs was also reduced, while the plating efficiency of bystander HUVECs partially recovered. These results demonstrated that irradiated U937 cells appear to release nitric oxide and thereby further trigger apoptosis and inflammatory responses in the bystander HUVECs through a p38-dependent pathway.

Increased long-term expression of pentraxin 3 in irradiated human arteries and veins compared to internal controls from free tissue transfers

BACKGROUND

Clinical studies have shown that radiotherapy increases the risk of cardiovascular disease at irradiated sites years after exposure. However, there is a lack of biological explanations in humans. We therefore examined human blood vessels exposed to radiotherapy and studied C-reactive protein (CRP) and pentraxin 3 (PTX3), a new marker for adverse cardiovascular outcome dependent on TNF- alpha (TNFα) or interleukin-1beta (IL-1β) expression.

METHODS

Pairs of irradiated and non-irradiated human conduit arteries and veins were harvested from the same patient during autologous free tissue transfer for cancer-reconstruction at a median time of 48 weeks after radiotherapy. Differential gene expression was studied using qRT-PCR, confirmed by immunohistochemistry and cellular origins determined by immunofluorescence.

RESULTS

Gene expression in irradiated arteries compared to non-irradiated showed a consistent up-regulation of PTX3 in all patients and in a majority of veins (p < 0.001). Both TNFα and IL-1β were increased in irradiated compared to non-irradiated arteries (p < 0.01) and IL-1β correlated to the PTX3 expression (p = 0.017). Immunohistochemical and immunofluorescence staining confirmed an increased expression of PTX3 in endothelial cells, macrophages and smooth muscle cells.

CONCLUSIONS

The sustained expression of PTX3 in arteries and veins tie biological evidence in humans to clinical studies and encourage further exploration of innate immunity in the pathogenesis of a radiation-induced vasculopathy.

Understanding radiation-induced cardiovascular damage and strategies for intervention

There is a clear association between therapeutic doses of thoracic irradiation and an increased risk of cardiovascular disease (CVD) in cancer survivors, although these effects may take decades to become symptomatic. Long-term survivors of Hodgkin's lymphoma and childhood cancers have two-fold to more than seven-fold increased risks for late cardiac deaths after total tumour doses of 30-40 Gy, given in 2 Gy fractions, where large volumes of heart were included in the field. Increased cardiac mortality is also seen in women irradiated for breast cancer. Breast doses are generally 40-50 Gy in 2 Gy fractions, but only a small part of the heart is included in the treatment fields and mean heart doses rarely exceeded 10-15 Gy, even with older techniques. The relative risks of cardiac mortality (1.1-1.4) are consequently lower than for Hodgkin's lymphoma survivors. Some epidemiological studies show increased risks of cardiac death after accidental or environmental total body exposures to much lower radiation doses. The mechanisms whereby these cardiac effects occur are not fully understood and different mechanisms are probably involved after high therapeutic doses to the heart, or part of the heart, than after low total body exposures. These various mechanisms probably result in different cardiac pathologies, e.g. coronary artery atherosclerosis leading to myocardial infarct, versus microvascular damage and fibrosis leading to congestive heart failure. Experimental studies can help to unravel some of these mechanisms and may identify suitable strategies for managing or inhibiting CVD. In this overview, the main epidemiological and clinical evidence for radiation-induced CVD is summarised. Experimental data shedding light on some of the underlying pathologies and possible targets for intervention are also discussed.

Irradiation induces different inflammatory and thrombotic responses in carotid arteries of wildtype C57BL/6J and atherosclerosis-prone ApoE(-/-) mice

BACKGROUND AND PURPOSE

We have previously shown that irradiation to the carotid arteries of hypercholesterolemic ApoE(-/-) mice accelerated the development of macrophage-rich, inflammatory atherosclerotic lesions. We now investigated the mechanism underlying the development of radiation-induced atherosclerosis.

MATERIALS AND METHODS

ApoE(-/-) and wildtype C57BL/6J mice received 0, 8 or 14 Gy to the neck and the carotid arteries were harvested 1 day, 1 or 4 weeks later. Immunohistochemical stainings were performed to evaluate well-known inflammatory and thrombotic molecules. A hypothesis-generating approach was used to compare gene expression profiles of irradiated and unirradiated carotid arteries.

RESULTS

Basal levels of endothelial VCAM-1 and thrombomodulin immunoexpression were higher in ApoE(-/-) mice than in C57BL/6J mice. At 1 week after 14 Gy VCAM-1 immunoexpression was decreased in ApoE(-/-) mice, whereas ICAM-1 immunoexpression was decreased at 1 and 4 weeks after 14 Gy in C57BL/6J mice. Thrombomodulin and tissue factor immunoexpression were elevated at 4 weeks after 14 Gy in ApoE(-/-) mice and reduced in C57BL/6J mice. There were no changes in immunoexpression of eNOS, MCP-1 or endoglin. Several canonical pathways were differentially expressed after irradiation, including tight junction pathways, leukocyte extravasation signaling and PI3K/AKT signaling.

CONCLUSION

ApoE(-/-) and C57BL/6J mice respond differently to irradiation. The thrombotic pathways were activated after irradiation in ApoE(-/-) mice only. Genes involved in tight junction regulation were up-regulated in ApoE(-/-) mice and decreased in C57BL/6J mice. These factors may have contributed to fatty-streak formation in ApoE(-/-) mice.

The effect of oxidized low-density lipoprotein (ox-LDL) on radiation-induced endothelial-to-mesenchymal transition

PURPOSE

Radiation-induced cardiovascular disease is a potentially severe side-effect of thoracic radiotherapy treatment. Clinically, this delayed side-effect presents as a form of accelerated atherosclerosis several years after irradiation. As general endothelial dysfunction is known to be an initiating event in radiation-induced vascular damage, we examined the effects of radiation on endothelial cells in radiation-induced atherosclerosis.

MATERIALS AND METHODS

The effects of radiation on human aortic endothelial cells (HAoEC) were assessed by immunoblotting and immunofluorescence assays. Radiation-induced phenotypic changes of endothelial cells (ECs) were examined using atherosclerotic tissues of irradiated apoprotein E null (ApoE(-/-)) mice.

RESULTS

Radiation induced the HAoEC to undergo phenotypic conversion to form fibroblast-like cells, called the endothelial-to-mesenchymal transition (EndMT), which leads to the upregulation of mesenchymal cell markers such as alpha-smooth muscle actin (α-SMA), fibroblast specific protein-1 (FSP-1), and vimentin, and downregulation of endothelial cell-specific markers such as CD31 and vascular endothelial (VE)-cadherin. Furthermore, compared with low-density lipoprotein (LDL), oxidized low-density lipoprotein (ox-LDL) significantly augmented radiation-induced EndMT in HAoEC. These fibrotic phenotypes of ECs were found in atherosclerotic tissues of irradiated ApoE(-/-) mice with increased levels of ox-LDL.

CONCLUSIONS

Taken together, these observations suggest that ox-LDL accelerates radiation-induced EndMT and subsequently contributes to radiation-induced atherosclerosis, providing a novel target for the prevention of radiation-induced atherosclerosis.

Anti-inflammatory and anti-thrombotic intervention strategies using atorvastatin, clopidogrel and knock-down of CD40L do not modify radiation-induced atherosclerosis in ApoE null mice

BACKGROUND AND PURPOSE

We previously showed that irradiating the carotid arteries of ApoE(-/-) mice accelerated the development of macrophage-rich, inflammatory and thrombotic atherosclerotic lesions. In this study we investigated the potential of anti-inflammatory (atorvastatin, CD40L knockout) and anti-thrombotic (clopidogrel) intervention strategies to inhibit radiation-induced atherosclerosis.

MATERIAL AND METHODS

ApoE(-/-) mice were given 0 or 14 Gy to the neck and the carotid arteries were harvested at 4 or 28 weeks after irradiation. Atorvastatin (15 mg/kg/day) or clopidogrel (20 mg/kg/day) was given in the chow; control groups received regular chow. Clopidogrel inhibited platelet aggregation by 50%. CD40L(-/-)/ApoE(-/-) and ApoE(-/-) littermates were also given 0 or 14 Gy to the neck and the carotid arteries were harvested after 30 weeks.

RESULTS

Clopidogrel decreased MCP-1 expression in the carotid artery at 4 weeks after irradiation. Expression of VCAM-1, ICAM-1, thrombomodulin, tissue factor and eNOS was unchanged in atorvastatin and clopidogrel-treated mice. Neither drug inhibited either age-related or radiation-induced atherosclerosis. Furthermore, loss of the inflammatory mediator CD40L did not influence the development of age-related and radiation-induced atherosclerosis.

CONCLUSIONS

The effects of radiation-induced atherosclerosis could not be circumvented by these specific anti-inflammatory and anti-coagulant therapies. This suggests that more effective drug combinations may be required to overcome the radiation stimulus, or that other underlying mechanistic pathways are involved compared to age-related atherosclerosis.