Single-Dose and Fractionated Irradiation Promote Initiation and Progression of Atherosclerosis and Induce an Inflammatory Plaque Phenotype in ApoE−/− Mice

Radiation-Induced Endothelial Ferroptosis Accelerates Atherosclerosis via the DDHD2-Mediated Nrf2/GPX4 Pathway

This study sought to explore potential roles of endothelial ferroptosis in radiation-associated atherosclerosis (RAA) and molecular mechanisms behind this phenomenon. Here, an in vivo RAA mouse model was used and treated with ferroptosis inhibitors. We found that the RAA group had a higher plaque burden and a reduction in endothelial cells with increased lipid peroxidation compared to the control group, while ameliorated by liproxstatin-1. In vitro experiments further confirmed that radiation induced the occurrence of ferroptosis in human artery endothelial cells (HAECs). Then, proteomics analysis of HAECs identified domain-containing protein 2 (DDHD2) as a co-differentially expressed protein, which was enriched in the lipid metabolism pathway. In addition, the level of lipid peroxidation was elevated in DDHD2-knockdown HAECs. Mechanistically, a significant decrease in the protein and mRNA expression of glutathione peroxidase 4 (GPX4) was observed in HAECs following DDHD2 knockdown. Co-immunoprecipitation assays indicated a potential interaction between DDHD2 and nuclear factor erythroid 2-related factor 2 (Nrf2). The downregulation of Nrf2 protein was also detected in DDHD2-knockdown HAECs. In conclusion, our findings suggest that radiation-induced endothelial ferroptosis accelerates atherosclerosis, and DDHD2 is a potential regulatory protein in radiation-induced endothelial ferroptosis through the Nrf2/GPX4 pathway.

High-Dose Ionizing Radiation Accelerates Atherosclerotic Plaque Progression by Regulating P38/NCOA4-Mediated Ferritinophagy/Ferroptosis of Endothelial Cells

PURPOSE

Radiation therapy (RT) significantly increased the incidence of coronary artery diseases, especially atherosclerosis. Endothelial dysfunction has been the major side effect of RT among tumor patients who received RT. However, the involvement between endothelial dysfunction and radiation-induced atherosclerosis (RIA) remains unclear. Here, we constructed a murine model of RIA, aiming to uncover its underlying mechanisms and identify novel strategies for RIA prevention and treatment.

METHODS AND MATERIALS

Eight-week-old ApoE-/- mice that were fed a Western diet were subjected to partial carotid ligation (PCL). Four weeks later, ionizing radiation (IR) of 10 Gy was performed to verify the detrimental role of IR on atherogenesis. Ultrasound imaging, RT quantitative polymerase chain reaction, histopathology and immunofluorescence, and biochemical analysis were performed 4 weeks after IR. To study the involvement of endothelial ferroptosis induced by IR in RIA, mice after IR were administrated with ferroptosis agonist (cisplatin) or antagonist (ferrostatin-1) intraperitoneally. Western blotting, autophagic flux measurement, reactive oxygen species level detection, and coimmunoprecipitation assay were carried out in vitro. Furthermore, to determine the effect of ferritinophagy inhibition on RIA, in vivo knockdown of NCOA4 was carried out by pluronic gel.

RESULTS

We verified that accelerated plaque progression was concomitant with endothelial cell (EC) ferroptosis after IR induction, as suggested by a higher level of lipid peroxidation and changes in ferroptosis-associated genes in the PCL + IR group than in the PCL group within vasculature. In vitro experiments further validated the devastating effects of IR on oxidative stress and ferritinophagy in ECs. Mechanistic experiments revealed that IR induced EC ferritinophagy and subsequent ferroptosis in a P38/NCOA4-dependent manner. Both in vitro and in vivo experiments confirmed the therapeutic effect of NCOA4 knockdown in alleviating IR-induced ferritinophagy/ferroptosis of EC and RIA.

CONCLUSIONS

Our findings provide novel insights into the regulatory mechanisms of RIA and first prove that IR accelerates atherosclerotic plaque progression by regulating ferritinophagy/ferroptosis of ECs in a P38/NCOA4-dependent manner.

Endothelial activation and fibrotic changes are impeded by laminar flow-induced CHK1-SENP2 activity through mechanisms distinct from endothelial-to-mesenchymal cell transition

Background

The deSUMOylase sentrin-specific isopeptidase 2 (SENP2) plays a crucial role in atheroprotection. However, the phosphorylation of SENP2 at T368 under disturbed flow (D-flow) conditions hinders its nuclear function and promotes endothelial cell (EC) activation. SUMOylation has been implicated in D-flow-induced endothelial-to-mesenchymal transition (endoMT), but the precise role of SENP2 in counteracting this process remains unclear.

Method

We developed a phospho-specific SENP2 S344 antibody and generated knock-in (KI) mice with a phospho-site mutation of SENP2 S344A using CRISPR/Cas9 technology. We then investigated the effects of SENP2 S344 phosphorylation under two distinct flow patterns and during hypercholesteremia (HC)-mediated EC activation.

Result

Our findings demonstrate that laminar flow (L-flow) induces phosphorylation of SENP2 at S344 through the activation of checkpoint kinase 1 (CHK1), leading to the inhibition of ERK5 and p53 SUMOylation and subsequent suppression of EC activation. We observed a significant increase in lipid-laden lesions in both the aortic arch (under D-flow) and descending aorta (under L-flow) of female hypercholesterolemic SENP2 S344A KI mice. In male hypercholesterolemic SENP2 S344A KI mice, larger lipid-laden lesions were only observed in the aortic arch area, suggesting a weaker HC-mediated atherogenesis in male mice compared to females. Ionizing radiation (IR) reduced CHK1 expression and SENP2 S344 phosphorylation, attenuating the pro-atherosclerotic effects observed in female SENP2 S344A KI mice after bone marrow transplantation (BMT), particularly in L-flow areas. The phospho-site mutation SENP2 S344A upregulates processes associated with EC activation, including inflammation, migration, and proliferation. Additionally, fibrotic changes and up-regulated expression of EC marker genes were observed. Apoptosis was augmented in ECs derived from the lungs of SENP2 S344A KI mice, primarily through the inhibition of ERK5-mediated expression of DNA damage-induced apoptosis suppressor (DDIAS).

Summary

In this study, we have revealed a novel mechanism underlying the suppressive effects of L-flow on EC inflammation, migration, proliferation, apoptosis, and fibrotic changes through promoting CHK1-induced SENP2 S344 phosphorylation. The phospho-site mutation SENP2 S344A responds to L-flow through a distinct mechanism, which involves the upregulation of both mesenchymal and EC marker genes.

Effects of Simulated 5-Ion Galactic Cosmic Radiation on Function and Structure of the Mouse Heart

Missions into deep space will expose astronauts to the harsh space environment, and the degenerative tissue effects of space radiation are largely unknown. To assess the risks, in this study, male BALB/c mice were exposed to 500 mGy 5-ion simulated GCR (GCRsim) at the NASA Space Radiation Laboratory. In addition, male and female CD1 mice were exposed to GCRsim and administered a diet containing Transforming Growth Factor-beta (TGF-β)RI kinase (ALK5) inhibitor IPW-5371 as a potential countermeasure. An ultrasound was performed to investigate cardiac function. Cardiac tissue was collected to determine collagen deposition, the density of the capillary network, and the expression of the immune mediator toll-like receptor 4 (TLR4) and immune cell markers CD2, CD4, and CD45. In male BALB/c mice, the only significant effects of GCRsim were an increase in the CD2 and TLR4 markers. In male CD1 mice, GCRsim caused a significant increase in total collagens and a decrease in the expression of TLR4, both of which were mitigated by the TGF-β inhibitor diet. In female CD1 mice, GCRsim caused an increase in the number of capillaries per tissue area in the ventricles, which may be explained by the decrease in the left ventricular mass. However, this increase was not mitigated by TGF-β inhibition. In both male and female CD1 mice, the combination of GCRsim and TGF-β inhibition caused changes in left ventricular immune cell markers that were not seen with GCRsim alone. These data suggest that GCRsim results in minor changes to cardiac tissue in both an inbred and outbred mouse strain. While there were few GCRsim effects to be mitigated, results from the combination of GCRsim and the TGF-β inhibitor do point to a role for TGF-β in maintaining markers of immune cells in the heart after exposure to GCR.

Evaluating postoperative outcomes in patients with hostile neck anatomy undergoing transcarotid artery revascularization versus transfemoral carotid artery stenting

BACKGROUND

Carotid endarterectomy is relatively contraindicated in patients with a hostile neck anatomy who were historically revascularized with transfemoral carotid artery stenting (TFCAS). As transcarotid artery revascularization (TCAR) has progressively replaced TFCAS, evidence pertaining to hostile neck anatomy and TCAR is necessary to establish its safety and feasibility in this subgroup of patients. Therefore, we analyzed the impact of a hostile neck anatomy on outcomes in patients undergoing TCAR and further compared them with those undergoing TFCAS to establish recommendations for standard of care.

METHODS

All patients undergoing TCAR and TFCAS from November 2016 to June 2021 in the Vascular Quality Initiative database were included. Patients were characterized into two groups based on the neck anatomy. Hostile neck anatomy was defined as a history of neck radiation or prior neck surgery including prior carotid endarterectomy or radical neck dissection. Primary outcomes included technical failure, access site complications (hematoma, stenosis, infection, pseudoaneurysm and arteriovenous fistula), and stroke or death. Secondary outcomes included stroke, transient ischemic attack (TIA), myocardial infarction (MI), death, and a composite end point of stroke or TIA. Patients with nonatherosclerotic or multiple lesions were excluded from the analysis. Primary analysis was performed with all patients undergoing TCAR and outcomes between patients with hostile and nonhostile neck anatomy were compared. Further analysis included a comparison of patients with a hostile neck anatomy undergoing TCAR and TFCAS. Univariable and multivariable logistic regression was used to assess impact of hostile neck anatomy on postoperative outcomes. Results were adjusted for relevant potential confounders including age, gender, race, degree of stenosis, symptomatic status, comorbidities, preoperative medications, anesthesia type, and protamine use.

RESULTS

Among the 19,859 patients who underwent TCAR during the study period, 3636 (18.3%) had a hostile neck anatomy. On univariate analysis, both groups had comparable outcomes except for higher rates of stroke or death in patients with hostile neck anatomy. After adjusting for potential confounders, there were no differences in technical failure (adjusted odds ratio [aOR], 1.14; 95% confidence interval [CI], 0.59-2.21; P = .699), stroke (aOR, 0.86; 95% CI, 0.58-1.28; P = .464), death (aOR, 0.82; 95% CI, 0.39-1.71; P = .598), and MI (aOR, 1.18; 95% CI, 0.71-1.97; P = .518). However, patients with hostile neck were at a 30% increased risk of access site complications (aOR, 1.30; 95% CI, 1.0-1.6; P = .023). Further adjusted analysis comparing the outcomes in TFCAS and TCAR among patients with hostile neck anatomy showed an almost four-fold increase in risk of death (aOR, 3.77; 95% CI, 1.49-9.53; P = .005) and technical failure (aOR, 3.69; 95% CI, 1.82-7.47; P < .001) among patients undergoing treatment with TFCAS.

CONCLUSIONS

Patients with a hostile neck anatomy undergoing TCAR experienced an increased risk of access site complications; however, the risk for technical failure and postoperative stroke/death, stroke, TIA, MI, or death was similar among both groups. TFCAS was associated with significant increase in the risk of death and technical failure compared with TCAR in this group of patients. These results confirm that TCAR should be the preferred minimally invasive revascularization procedure for patients with hostile neck anatomy.

Summary of Radiation Research Society Online 67th Annual Meeting, Symposium on "Radiation and Circulatory Effects"

PURPOSE

This article summarizes a number of presentations from a session on "Radiation and Circulatory Effects" held during the Radiation Research Society Online 67^th Annual Meeting, October 3-6 2021.

MATERIALS AND METHODS

Different epidemiological cohorts were analyzed with various statistical means common in epidemiology. The cohorts included the one from the U.S. Million Person Study and the Canadian Fluoroscopy Cohort Study. In addition, one of the contributions in our article relies on results from analyses of the Japanese atomic bomb survivors, Russian emergency and recovery workers and cohorts of nuclear workers. The Canadian Fluoroscopy Cohort Study data were analyzed with a larger series of linear and nonlinear dose-response models in addition to the linear no-threshold (LNT) model.

RESULTS AND CONCLUSIONS

The talks in this symposium showed that low/moderate acute doses at low/moderate dose rates can be associated with an increased risk of CVD, although some of the epidemiological results for occupational cohorts are equivocal. The usually only limited availability of information on well-known risk factors for circulatory disease (e.g. smoking, obesity, hypertension, diabetes, physical activity) is an important limiting factor that may bias any observed association between radiation exposure and detrimental health outcome, especially at low doses. Additional follow-up and careful dosimetric and outcome assessment are necessary and more epidemiological and experimental research is required. Obtaining reliable information on other risk factors is especially important.

Photon- and Proton-Mediated Biological Effects: What Has Been Learned?

The current understanding of the effects of radiation is gradually becoming broader. However, it still remains unclear why some patients respond to radiation with a pronounced positive response, while in some cases the disease progresses. This is the motivation for studying the effects of radiation therapy not only on tumor cells, but also on the tumor microenvironment, as well as studying the systemic effects of radiation. In this framework, we review the biological effects of two types of radiotherapy: photon and proton irradiations. Photon therapy is a commonly used type of radiation therapy due to its wide availability and long-term history, with understandable and predictable outcomes. Proton therapy is an emerging technology, already regarded as the method of choice for many cancers in adults and children, both dosimetrically and biologically. This review, written after the analysis of more than 100 relevant literary sources, describes the local effects of photon and proton therapy and shows the mechanisms of tumor cell damage, interaction with tumor microenvironment cells and effects on angiogenesis. After systematic analysis of the literature, we can conclude that proton therapy has potentially favorable toxicological profiles compared to photon irradiation, explained mainly by physical but also biological properties of protons. Despite the fact that radiobiological effects of protons and photons are generally similar, protons inflict reduced damage to healthy tissues surrounding the tumor and hence promote fewer adverse events, not only local, but also systemic.

The Lymphatic Endothelium in the Context of Radioimmuno-Oncology

The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.

Cardiac Remodelling Following Cancer Therapy: A Review

Cardiac remodelling is characterized by abnormal changes in the function and morphological properties such as diameter, mass, normal diameter of cavities, heart shape, fibrosis, thickening of vessels and heart layers, cardiomyopathy, infiltration of inflammatory cells, and some others. These damages are associated with damage to systolic and diastolic abnormalities, damage to ventricular function, and vascular remodelling, which may lead to heart failure and death. Exposure of the heart to radiation or anti-cancer drugs including chemotherapy drugs such as doxorubicin, receptor tyrosine kinase inhibitors (RTKIs) such as imatinib, and immune checkpoint inhibitors (ICIs) can induce several abnormal changes in the heart structure and function through the induction of inflammation and fibrosis, vascular remodelling, hypertrophy, and some others. This review aims to explain the basic mechanisms behind cardiac remodelling following cancer therapy by different anti-cancer modalities.

Radiotherapy-induced isolated left main coronary artery disease presenting with cardiogenic shock: A case report

RATIONALE

Mediastinal radiotherapy is a common practice for treating breast cancer and Hodgkin's lymphoma. Radiotherapy causes cardiovascular damage and has attracted increasing attention, particularly among Hodgkin's lymphoma patients, as they receive a higher dose of radiation.

PATIENT CONCERNS

A 36-year-old woman with a past medical history of Hodgkin's lymphoma presented with persistent chest pain for 3 hours. She experienced exertional chest pain 1 month before when she was climbing stairs, which disappeared after a few minutes with rest, but recurred with a similar level of exertion. Three hours before admission to the emergency room, the chest pain persisted and was accompanied by diaphoresis and dyspnea.

DIAGNOSIS

Cardiogenic shock caused by radiotherapy-induced left main coronary artery disease.

INTERVENTIONS

Urgent angiography revealed left main coronary artery stenosis. Intravascular ultrasonography showed diffuse fibrous proliferation in the left main coronary artery. Hemodynamic instability was resolved after drug-eluting stent implantation.

OUTCOMES

The patient was discharged uneventfully 5 days after the procedure, with a prescription for dual antiplatelet and statin therapy. She was asymptomatic with good exercise tolerance at the 3-month follow-up.

CONCLUSION

Radiotherapy-induced isolated left main coronary artery disease is a rare complication of cancer radiotherapy and can occur years or decades after treatment. Fibrous proliferation is a characteristic pathologic change in the exposed coronary arteries.

Lisinopril Mitigates Radiation-Induced Mitochondrial Defects in Rat Heart and Blood Cells

The genetic bases and disparate responses to radiotherapy are poorly understood, especially for cardiotoxicity resulting from treatment of thoracic tumors. Preclinical animal models such as the Dahl salt-sensitive (SS) rat can serve as a surrogate model for salt-sensitive low renin hypertension, common to African Americans, where aldosterone contributes to hypertension-related alterations of peripheral vascular and renal vascular function. Brown Norway (BN) rats, in comparison, are a normotensive control group, while consomic SSBN6 with substitution of rat chromosome 6 (homologous to human chromosome 14) on an SS background manifests cardioprotection and mitochondrial preservation to SS rats after injury. In this study, 2 groups from each of the 3 rat strains had their hearts irradiated (8 Gy X 5 fractions). One irradiated group was treated with the ACE-inhibitor lisinopril, and a separate group in each strain served as nonirradiated controls. Radiation reduced cardiac end diastolic volume by 9-11% and increased thickness of the interventricular septum (11-16%) and left ventricular posterior wall (14-15%) in all 3 strains (5-10 rats/group) after 120 days. Lisinopril mitigated the increase in posterior wall thickness. Mitochondrial function was measured by the Seahorse Cell Mitochondrial Stress test in peripheral blood mononuclear cells (PBMC) at 90 days. Radiation did not alter mitochondrial respiration in PBMC from BN or SSBN6. However, maximal mitochondrial respiration and spare capacity were reduced by radiation in PBMC from SS rats (p=0.016 and 0.002 respectively, 9-10 rats/group) and this effect was mitigated by lisinopril (p=0.04 and 0.023 respectively, 9-10 rats/group). Taken together, these results indicate injury to the heart by radiation in all 3 strains of rats, although the SS rats had greater susceptibility for mitochondrial dysfunction. Lisinopril mitigated injury independent of genetic background.

The Impact of Radiation Dose to Heart Substructures on Major Coronary Events and Patient Survival after Chemoradiation Therapy for Esophageal Cancer

Background: There is a paucity of data regarding the association between radiation exposure of heart substructures and the incidence of major coronary events (MCEs) in patients with esophageal cancer (ESOC) undergoing chemoradiation therapy. We studied radiation dosimetric determinants of MCE risk and measured their impact on patient prognosis using a cohort of ESOC patients treated at a single institution. Methods: Between March 2005 and October 2015, 355 ESOC patients treated with concurrent chemoradiotherapy were identified from a prospectively maintained and institutional-regulatory-board-approved clinical database. Dose-distribution parameters of the whole heart, the atria, the ventricles, the left main coronary artery, and three main coronary arteries were extracted for analysis. Results: Within a median follow-up time of 67 months, 14 patients experienced MCEs at a median of 16 months. The incidence of MCEs was significantly associated with the left anterior descending coronary artery (LAD) receiving ≥30 Gy (V30Gy) (p = 0.048). Patients receiving LAD V30Gy ≥ 10% of volume experienced a higher incidence of MCEs versus the LAD V30Gy < 10% group (p = 0.044). The relative rate of death increased with the left main coronary artery (LMA) mean dose (Gy) (p = 0.002). Furthermore, a mutual promotion effect of hyperlipidemia and RT on MCEs was observed. Conclusion: Radiation dose to coronary substructures is associated with MCEs and overall survival in patients with ESOC. In this study, the doses to these substructures appeared to be better predictors of toxicity outcomes than mean heart dose (MHD) or whole-heart V30Gy. These findings have implications for reducing coronary events through radiation therapy planning.

Radiation-Induced Macrophage Senescence Impairs Resolution Programs and Drives Cardiovascular Inflammation

Radiation is associated with tissue damage and increased risk of atherosclerosis, but there are currently no treatments and a very limited mechanistic understanding of how radiation impacts tissue repair mechanisms. We uncovered that radiation significantly delayed temporal resolution programs that were associated with decreased efferocytosis in vivo. Resolvin D1 (RvD1), a known proresolving ligand, promoted swift resolution and restored efferocytosis in sublethally irradiated mice. Irradiated macrophages exhibited several features of senescence, including increased expression of p16^INK4A and p21, heightened levels of SA-β-gal, COX-2, several proinflammatory cytokines/chemokines, and oxidative stress (OS) in vitro, and when transferred to mice, they exacerbated inflammation in vivo. Mechanistically, heightened OS in senescent macrophages led to impairment in their ability to carry out efficient efferocytosis, and treatment with RvD1 reduced OS and improved efferocytosis. Sublethally irradiated Ldlr ^-/- mice exhibited increased plaque necrosis, p16^INK4A cells, and decreased lesional collagen compared with nonirradiated controls, and treatment with RvD1 significantly reduced necrosis and increased lesional collagen. Removal of p16^INK4A hematopoietic cells during advanced atherosclerosis with p16-3MR mice reduced plaque necrosis and increased production of key intraplaque-resolving mediators. Our results demonstrate that sublethal radiation drives macrophage senescence and efferocytosis defects and suggest that RvD1 may be a new therapeutic strategy to limit radiation-induced tissue damage.

Expert consultation is vital for adverse outcome pathway development: a case example of cardiovascular effects of ionizing radiation

BACKGROUND

The circulatory system distributes nutrients, signaling molecules, and immune cells to vital organs and soft tissues. Epidemiological, animal, and in vitro cellular mechanistic studies have highlighted that exposure to ionizing radiation (IR) can induce molecular changes in cellular and subcellular milieus leading to long-term health impacts, particularly on the circulatory system. Although the mechanisms for the pathologies are not fully elucidated, endothelial dysfunction is proven to be a critical event via radiation-induced oxidative stress mediators. To delineate connectivities of events specifically to cardiovascular disease (CVD) initiation and progression, the adverse outcome pathway (AOP) approach was used with consultation from field experts. AOPs are a means to organize information around a disease of interest to a regulatory question. An AOP begins with a molecular initiating event and ends in an adverse outcome via sequential linkages of key event relationships that are supported by evidence in the form of the modified Bradford-Hill criteria. Detailed guidelines on building AOPs are provided by the Organisation for Economic Cooperation and Development (OECD) AOP program. Here, we report on the questions and discussions needed to develop an AOP for CVD resulting from IR exposure. A recent workshop jointly organized by the MELODI (Multidisciplinary European Low Dose Initiative) and the ALLIANCE (European Radioecology Alliance) associations brought together experts from the OECD to present the AOP approach and tools with examples from the toxicology field. As part of this workshop, four working groups were formed to discuss the identification of adverse outcomes relevant to radiation exposures and development of potential AOPs, one of which was focused on IR-induced cardiovascular effects. Each working group comprised subject matter experts and radiation researchers interested in the specific disease area and included an AOP coach.

CONCLUSION

The CVD working group identified the critical questions of interest for AOP development, including the exposure scenario that would inform the evidence, the mechanisms of toxicity, the initiating event, intermediate key events/relationships, and the type of data currently available. This commentary describes the four-day discussion of the CVD working group, its outcomes, and demonstrates how collaboration and expert consultation is vital to informing AOP construction.

Irradiation Accelerates Plaque Formation and Cellular Senescence in Flow-Altered Carotid Arteries of Apolipoprotein E Knock-Out Mice

Background

Chronic inflammation through cellular senescence, known as the senescence‐associated secretory phenotype, is a mechanism of various organ diseases, including atherosclerosis. Particularly, ionizing radiation (IR) contributes to cellular senescence by causing DNA damage. Although previous clinical studies have demonstrated that radiotherapy causes atherosclerosis as a long‐term side effect, the detailed mechanism is unclear. This study was conducted to investigate the relationship between radiation‐induced atherosclerosis and senescence‐associated secretory phenotype in murine carotid arteries.

Methods and Results

Partial ligation of the left carotid artery branches in 9‐week‐old male apolipoprotein E‐deficient mice was performed to induce atherosclerosis. The mice received total body irradiation at a dose of 6 Gy using gamma rays at 2 weeks post operation. We compared the samples collected 4 weeks after IR with unirradiated control samples. The IR and control groups presented pathologically progressive lesions in 90.9% and 72.3% of mice, respectively. Plaque volume, macrophage accumulation, and phenotype switching of vascular smooth muscle cells were advanced in the IR group. Irradiated samples showed increased persistent DNA damage response (53BP1 [p53 binding protein 1]), upregulated cyclin‐dependent kinase inhibitors (p16INK4a and p21), and elevated inflammatory chemokines expression (monocyte chemotactic protein‐1, keratinocyte‐derived chemokine, and macrophage inflammatory protein 2).

Conclusions

IR promoted plaque growth in murine carotid arteries. Our findings support the possibility that senescence‐associated secretory phenotype aggravates atherogenesis in irradiated artery. This mice model might contribute to mechanism elucidation of radiation‐induced atherosclerosis.

Exposure to Low to Moderate Doses of Ionizing Radiation Induces A Reduction of Pro-Inflammatory Ly6chigh Monocytes and a U-Curved Response of T Cells in APOE -/- Mice

Low dose ionizing radiation (LDIR) is known to have a protective effect on atherosclerosis in rodent studies, but how it impacts different cells types involved in lesion formation remains incompletely understood. We investigated the immunomodulatory response of different doses and dose-rates of irradiation in ApoE^-/- mice. Mice were exposed to external γ rays at very low (1.4 mGy.h^-1) or low (50 mGy.h^-1) dose-rates, with cumulative doses spanning 50 to 1000 mGy. Flow cytometry of circulating cells revealed a significant decrease in pro-inflammatory Ly6C^Hi monocytes at all cumulative doses at low dose-rate, but more disparate effects at very low dose-rate with reductions in Ly6C^Hi cells at doses of 50, 100 and 750 mGy only. In contrast, Ly6C^Lo monocytes were not affected by LDIR. Similarly, proportions of CD4⁺ T cell subsets in the spleen did not differ between irradiated mice and non-irradiated controls, whether assessing CD25⁺FoxP3⁺ regulatory or CD69⁺ activated lymphocytes. In the aorta, gene expression of cytokines such as IL-1 and TGF-ß and adhesion molecules such as E-Selectin, ICAM-1, and VCAM-1 were reduced at the intermediate dose of 200 mGy. These results suggest that LDIR may reduce atherosclerotic plaque formation by selectively reducing blood pro-inflammatory monocytes and by impairing adhesion molecule expression and inflammatory processes in the vessel wall. In contrast, splenic T lymphocytes were not affected by LDIR. Furthermore, some responses to irradiation were nonlinear; reductions in aortic gene expression were significant at intermediate doses, but not at either highest or lowest doses. This work furthers our understanding of the impact of LDIR with different dose-rates on immune system response in the context of atherosclerosis.

A Preconditioning Strategy to Augment Retention and Engraftment Rate of Donor Cells During Hepatocyte Transplantation

BACKGROUND

Hepatocyte transplantation has been extensively investigated as an alternative to orthotopic liver transplantation. However, its application in routine clinical practice has been restricted because of low initial engraftment and subsequent repopulation.

METHODS

Using mice as a model, we have developed a minimally invasive and nontoxic preconditioning strategy based on preadministration of antibodies against hepsin to increase donor hepatocyte retention and engraftment rate.

RESULTS

Liver sinusoid diameters decreased significantly with antihepsin pretreatment, and graft cell numbers increased nearly 2-fold in the recipients' liver parenchyma for 20 days after hepatocyte transplantation. Postoperative complications such as hepatic ischemia injury or apparent immune cell accumulation were not observed in recipients. In a hemophilia B mouse model, antihepsin preconditioning enhanced the expression and clotting activity of coagulation factor IX (FIX) to nearly 2-fold that of immunoglobulin G-treated controls and maintained higher plasma FIX clotting activity relative to the prophylactic range for 50 days after hepatocyte transplantation. Antihepsin pretreatment combined with adeno-associated virus-transduced donor hepatocytes expressing human FIX-Triple, a hyperfunctional FIX variant, resulted in plasma FIX levels similar to those associated with mild hemophilia, which protected hemophilia B mice from major bleeding episodes for 50 days after transplantation. Furthermore, antihepsin pretreatment and repeated transplantation resulted in extending the therapeutic period by 30 days relative to the immunoglobulin G control.

CONCLUSIONS

Thus, this antihepsin strategy improved the therapeutic effect of hepatocyte transplantation in mice with tremendous safety and minimal invasion. Taken together, we suggest that preconditioning with antihepsin may have clinical applications for liver cell therapy.

X‑irradiation induces acute and early term inflammatory responses in atherosclerosis‑prone ApoE‑/‑ mice and in endothelial cells

Thoracic radiotherapy is an effective treatment for many types of cancer; however it is also associated with an increased risk of developing cardiovascular disease (CVD), appearing mainly ≥10 years after radiation exposure. The present study investigated acute and early term physiological and molecular changes in the cardiovascular system after ionizing radiation exposure. Female and male ApoE^‑/‑ mice received a single exposure of low or high dose X‑ray thoracic irradiation (0.1 and 10 Gy). The level of cholesterol and triglycerides, as well as a large panel of inflammatory markers, were analyzed in serum samples obtained at 24 h and 1 month after irradiation. The secretion of inflammatory markers was further verified in vitro in coronary artery and microvascular endothelial cell lines after exposure to low and high dose of ionizing radiation (0.1 and 5 Gy). Local thoracic irradiation of ApoE^‑/‑ mice increased serum growth differentiation factor‑15 (GDF‑15) and C‑X‑C motif chemokine ligand 10 (CXCL10) levels in both female and male mice 24 h after high dose irradiation, which were also secreted from coronary artery and microvascular endothelial cells in vitro. Sex‑specific responses were observed for triglyceride and cholesterol levels, and some of the assessed inflammatory markers as detailed below. Male ApoE^‑/‑ mice demonstrated elevated intercellular adhesion molecule‑1 and P‑selectin at 24 h, and adiponectin and plasminogen activator inhibitor‑1 at 1 month after irradiation, while female ApoE^‑/‑ mice exhibited decreased monocyte chemoattractant protein‑1 and urokinase‑type plasminogen activator receptor at 24 h, and basic fibroblast growth factor 1 month after irradiation. The inflammatory responses were mainly significant following high dose irradiation, but certain markers showed significant changes after low dose exposure. The present study revealed that acute/early inflammatory responses occurred after low and high dose thoracic irradiation. However, further research is required to elucidate early asymptomatic changes in the cardiovascular system post thoracic X‑irradiation and to investigate whether GDF‑15 and CXCL10 could be considered as potential biomarkers for the early detection of CVD risk in thoracic radiotherapy‑treated patients.

Radiotherapy, immunotherapy, and the tumour microenvironment: Turning an immunosuppressive milieu into a therapeutic opportunity

Immune checkpoint blockade (ICB) has revolutionised the treatment of solid tumours, yet most patients do not derive a clinical benefit. Resistance to ICB is often contingent on the tumour microenvironment (TME) and modulating aspects of this immunosuppressive milieu is a goal of combination treatment approaches. Radiation has been used for over a century in the management of cancer with more than half of all cancer patients receiving radiotherapy. Here, we outline the rationale behind combining radiotherapy with ICB, a potential synergy through mutually beneficial remodelling of the TME. We discuss the pleiotropic effects radiation has on the TME including immunogenic cell death, activation of cytosolic DNA sensors, remodelling the stroma and vasculature, and paradoxical infiltration of both anti-tumour and suppressive immune cell populations. These events depend on the radiation dose and fractionation and optimising these parameters will be key to develop safe and effective combination regimens. Finally, we highlight ongoing efforts that combine radiation, immunotherapy and inhibitors of DNA damage response, which can help achieve a favourable equilibrium between the immunogenic and tolerogenic effects of radiation on the immune microenvironment.

The role of connexin proteins and their channels in radiation-induced atherosclerosis

Radiotherapy is an effective treatment for breast cancer and other thoracic tumors. However, while high-energy radiotherapy treatment successfully kills cancer cells, radiation exposure of the heart and large arteries cannot always be avoided, resulting in secondary cardiovascular disease in cancer survivors. Radiation-induced changes in the cardiac vasculature may thereby lead to coronary artery atherosclerosis, which is a major cardiovascular complication nowadays in thoracic radiotherapy-treated patients. The underlying biological and molecular mechanisms of radiation-induced atherosclerosis are complex and still not fully understood, resulting in potentially improper radiation protection. Ionizing radiation (IR) exposure may damage the vascular endothelium by inducing DNA damage, oxidative stress, premature cellular senescence, cell death and inflammation, which act to promote the atherosclerotic process. Intercellular communication mediated by connexin (Cx)-based gap junctions and hemichannels may modulate IR-induced responses and thereby the atherosclerotic process. However, the role of endothelial Cxs and their channels in atherosclerotic development after IR exposure is still poorly defined. A better understanding of the underlying biological pathways involved in secondary cardiovascular toxicity after radiotherapy would facilitate the development of effective strategies that prevent or mitigate these adverse effects. Here, we review the possible roles of intercellular Cx driven signaling and communication in radiation-induced atherosclerosis.

Ionizing radiation-induced circulatory and metabolic diseases

Risks to health are the prime consideration in all human situations of ionizing radiation exposure and therefore of relevance to radiation protection in all occupational, medical, and public exposure situations. Over the past few decades, advances in therapeutic strategies have led to significant improvements in cancer survival rates. However, a wide range of long-term complications have been reported in cancer survivors, in particular circulatory diseases and their major risk factors, metabolic diseases. However, at lower levels of exposure, the evidence is less clear. Under real-life exposure scenarios, including radiotherapy, radiation effects in the whole organism will be determined mainly by the response of normal tissues receiving relatively low doses, and will be mediated and moderated by systemic effects. Therefore, there is an urgent need for further research on the impact of low-dose radiation. In this article, we review radiation-associated risks of circulatory and metabolic diseases in clinical, occupational or environmental exposure situations, addressing epidemiological, biological, risk modelling, and systems biology aspects, highlight the gaps in knowledge and discuss future directions to address these gaps.

Prevalence of carotid plaque stenosis after head and neck radiotherapy – an observational study of 156 survivors

Summary: Background: Radiotherapy for head and neck cancer (HNC) represents a well-known predisposing factor for asymptomatic carotid artery lesions and acute cerebrovascular accidents. Our aim is to provide contemporary estimates on the prevalence, severity, and characteristics of carotid artery lesions in HNC survivors. Patients and methods: We prospectively included HNC patients who underwent radiotherapy and were free from the disease at the time of duplex ultrasound evaluation. Patients were re-contacted telephonically and those who agreed to participate were invited for an ambulatory visit when the investigators collected clinical information and performed duplex ultrasound examination based on a predefined protocol. Results: A total of 156 patients were included and underwent duplex ultrasound examination after a mean of 65.2 months from the last session of radiotherapy. A total of 36 patients (23.1%) had normal carotid arteries; mild, non-stenotic lesions were observed in 49.4% (n = 77) of patients; severe stenotic plaques were found in 27.5% (n = 43) of patients. One patient found with an asymptomatic occlusion of the left ICA. The prevalence of major cardiovascular risk factors and high radiation dose increased proportionally with plaque severity. Low echogenicity plaque was found in 59 (37.8%) patients on the right side and 57 (36.5%) on the left side; long segment plaque in 49 (31.4%) patients on the right side and in 47 (30.1%) on the left side; an atypical location of the lesions in 42 (26.9%) patients on the right side and in 48 (30.8%) on the left side. Conclusions: The prevalence of occlusion and severe stenosis after radiotherapy for HNC was very low in our study population. Low echogenicity plaque, long segment plaque, and an atypical location were common findings. Classic cardiovascular risk factors appear to have had a causative role: a routine screening of radiotherapy-treated patients might be necessary only in patients with concomitant cardiovascular risk factors or exposed to high-dose neck radiation.

A Novel Anticancer Therapeutic Strategy to Target Autophagy Accelerates Radiation-Associated Atherosclerosis

PURPOSE

Autophagy inhibition is a novel therapeutic strategy suggested for patients with advanced cancer, especially those who have undergone radiation therapy. In the present study, we investigated whether autophagy inhibitors accelerate the progression of radiation-associated atherosclerosis (RAA).

METHODS AND MATERIALS

Eight-week-old apolipoprotein (ApoE^-/-) mice were fed a Western diet, and their left common carotid arteries were partially ligated to induce atherogenesis. Four weeks later, local ionizing radiation (IR) at a dose of 5 or 10 Gy was used to induce RAA in the left common carotid artery. After another 4 weeks, severe plaque burden associated with increased macrophage infiltration and lipid deposition, reduced smooth muscle cells, and decreased collagen expression was observed. In addition, these changes occurred in a dose-dependent manner. Improved autophagic flux caused by IR was observed in both macrophages of the atherosclerotic plaque and peritoneal macrophages in vitro. The inhibition of autophagic flux by chloroquine (50 mg/kg/d) further accelerated the progression of RAA in the left common carotid arteries of ApoE^-/- mice. Furthermore, chloroquine treatment exacerbated IR-induced p65 nuclear translocation, IκBα degradation, and transcription of nuclear factor-κB (NF-κB) target genes in peritoneal macrophages.

CONCLUSIONS

IR promotes atherogenesis and increases autophagic flux. In addition, autophagy inhibition by chloroquine accelerates the progression of RAA lesions by stimulating NF-κB-mediated inflammatory responses in macrophages.

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.

The Role of NLRP3 Inflammasome in Radiation-Induced Cardiovascular Injury

The increasing risk of long-term adverse effects from radiotherapy on the cardiovascular structure is receiving increasing attention. However, the mechanisms underlying this increased risk remain poorly understood. Recently, the nucleotide-binding domain and leucine-rich-repeat-containing family pyrin 3 (NLRP3) inflammasome was suggested to play a critical role in radiation-induced cardiovascular injury. However, the relationship between ionizing radiation and the NLRP3 inflammasome in acute and chronic inflammation is complex. We reviewed literature detailing pathological changes and molecular mechanisms associated with radiation-induced damage to the cardiovascular structure, with a specific focus on NLRP3 inflammasome-related cardiovascular diseases. We also summarized possible therapeutic strategies for the prevention of radiation-induced heart disease (RIHD).

Connexin43 Hemichannel Targeting With TAT-Gap19 Alleviates Radiation-Induced Endothelial Cell Damage

BACKGROUND

Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before.

MATERIALS AND METHODS

Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19).

RESULTS

We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1β, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19.

CONCLUSION

Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects.

Radio-biologically motivated modeling of radiation risks of mortality from ischemic heart diseases in the Canadian fluoroscopy cohort study

Recent analyses of the Canadian fluoroscopy cohort study reported significantly increased radiation risks of mortality from ischemic heart diseases (IHD) with a linear dose-response adjusted for dose fractionation. This cohort includes 63,707 tuberculosis patients from Canada who were exposed to low-to-moderate dose fractionated X-rays in 1930s-1950s and were followed-up for death from non-cancer causes during 1950-1987. In the current analysis, we scrutinized the assumption of linearity by analyzing a series of radio-biologically motivated nonlinear dose-response models to get a better understanding of the impact of radiation damage on IHD. The models were weighted according to their quality of fit and were then mathematically superposed applying the multi-model inference (MMI) technique. Our results indicated an essentially linear dose-response relationship for IHD mortality at low and medium doses and a supra-linear relationship at higher doses (> 1.5 Gy). At 5 Gy, the estimated radiation risks were fivefold higher compared to the linear no-threshold (LNT) model. This is the largest study of patients exposed to fractionated low-to-moderate doses of radiation. Our analyses confirm previously reported significantly increased radiation risks of IHD from doses similar to those from diagnostic radiation procedures.

The Role of Mitochondrial Dysfunction in Radiation-Induced Heart Disease: From Bench to Bedside

Radiation is a key modality in the treatment of many cancers; however, it can also affect normal tissues adjacent to the tumor, leading to toxic effects. Radiation to the thoracic region, such as that received as part of treatment for breast and lung cancer, can result in incidental dose to the heart, leading to cardiac dysfunction, such as pericarditis, coronary artery disease, ischemic heart disease, conduction defects, and valvular dysfunction. The underlying mechanisms for these morbidities are currently being studied but are not entirely understood. There has been increasing focus on the role of radiation-induced mitochondrial dysfunction and the ensuing impact on various cardiac functions in both preclinical models and in humans. Cardiomyocyte mitochondria are critical to cardiac function, and mitochondria make up a substantial part of a cardiomyocyte's volume. Mitochondrial dysfunction can also alter other cell types in the heart. This review summarizes several factors related to radiation-induced mitochondrial dysfunction in cardiomyocytes and endothelial cells. These factors include mitochondrial DNA mutations, oxidative stress, alterations in various mitochondrial function-related transcription factors, and apoptosis. Through improved understanding of mitochondria-dependent mechanisms of radiation-induced heart dysfunction, potential therapeutic targets can be developed to assist in prevention and treatment of radiation-induced heart damage.

Prevalence of carotid stenosis following radiotherapy for head and neck cancer: A systematic review and meta-analysis

BACKGROUND

Radiation to the head and neck is a well-established risk factor for the development of carotid artery stenosis. Our objective was to identify the prevalence, incidence, and degree of carotid stenosis in patients with a history of head and neck irradiation.

METHODS

This study was performed according to the PRISMA guidelines. A random effects model meta-analysis was conducted.

RESULTS

Nineteen studies comprising 1479 patients were included. The prevalence of carotid stenosis >50%, >70%, and carotid occlusion was 25% (95% CI: 19%-32%), 12% (95% CI: 7%-17%), and 4% (95% CI: 2%-8%), respectively. The cumulative 12-month incidence of carotid stenosis >50% was 4% (95% CI: 2%-5%), the 24-month was 12% (95% CI: 9%-15%), and the 36-month was 21% (95% CI: 9%-36%).

CONCLUSIONS

The yearly incidence of carotid stenosis >50% increased every year during the first 3 years following radiotherapy. We propose routine yearly Doppler ultrasound screening beginning 1 year after head and neck radiotherapy.

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 heart disease: a review of classification, mechanism and prevention

With the increasing incidence of thoracic tumors, radiation therapy (RT) has become an important component of comprehensive treatment. RT improves survival in many cancers, but it involves some inevitable complications. Radiation-induced heart disease (RIHD) is one of the most serious complications. RIHD comprises a spectrum of heart disease including cardiomyopathy, pericarditis, coronary artery disease, valvular heart disease and conduction system abnormalities. There are numerous clinical manifestations of RIHD, such as chest pain, palpitation, and dyspnea, even without obvious symptoms. Based on previous studies, the pathogenesis of RIHD is related to the production and effects of various cytokines caused by endothelial injury, inflammatory response, and oxidative stress (OS). Therefore, it is of great importance for clinicians to identify the mechanism and propose interventions for the prevention of RIHD.

Single and fractionated ionizing radiation induce alterations in endothelial connexin expression and channel function

Radiotherapy is an effective treatment for most tumor types. However, emerging evidence indicates an increased risk for atherosclerosis after ionizing radiation exposure, initiated by endothelial cell dysfunction. Interestingly, endothelial cells express connexin (Cx) proteins that are reported to exert proatherogenic as well as atheroprotective effects. Furthermore, Cxs form channels, gap junctions and hemichannels, that are involved in bystander signaling that leads to indirect radiation effects in non-exposed cells. We here aimed to investigate the consequences of endothelial cell irradiation on Cx expression and channel function. Telomerase immortalized human Coronary Artery/Microvascular Endothelial cells were exposed to single and fractionated X-rays. Several biological endpoints were investigated at different time points after exposure: Cx gene and protein expression, gap junctional dye coupling and hemichannel function. We demonstrate that single and fractionated irradiation induce upregulation of proatherogenic Cx43 and downregulation of atheroprotective Cx40 gene and protein levels in a dose-dependent manner. Single and fractionated irradiation furthermore increased gap junctional communication and induced hemichannel opening. Our findings indicate alterations in Cx expression that are typically observed in endothelial cells covering atherosclerotic plaques. The observed radiation-induced increase in Cx channel function may promote bystander signaling thereby exacerbating endothelial cell damage and atherogenesis.

Radiation-primed hepatocyte transplantation in murine monogeneic dyslipidemia normalizes cholesterol and prevents atherosclerosis

BACKGROUND & AIMS

Inherited abnormalities in apolipoprotein E (ApoE) or low-density lipoprotein receptor (LDLR) function result in early onset cardiovascular disease and death. Currently, the only curative therapy available is liver transplantation. Hepatocyte transplantation is a potential alternative; however, physiological levels of hepatocyte engraftment and repopulation require transplanted cells to have a competitive proliferative advantage of over host hepatocytes. Herein, we aimed to test the efficacy and safety of a novel preparative regimen for hepatocyte transplantation.

METHODS

Herein, we used an ApoE-deficient mouse model to test the efficacy of a new regimen for hepatocyte transplantation. We used image-guided external-beam hepatic irradiation targeting the median and right lobes of the liver to enhance cell transplant engraftment. This was combined with administration of the hepatic mitogen GC-1, a thyroid hormone receptor-β agonist mimetic, which was used to promote repopulation.

RESULTS

The non-invasive preparative regimen of hepatic irradiation and GC-1 was well-tolerated in ApoE^-/- mice. This regimen led to robust liver repopulation by transplanted hepatocytes, which was associated with significant reductions in serum cholesterol levels after transplantation. Additionally, in mice receiving this regimen, ApoE was detected in the circulation 4 weeks after treatment and did not induce an immunological response. Importantly, the normalization of serum cholesterol prevented the formation of atherosclerotic plaques in this model.

CONCLUSIONS

Significant hepatic repopulation and the cure of dyslipidemia in this model, using a novel and well-tolerated preparative regimen, demonstrate the clinical potential of applying this method to the treatment of inherited metabolic diseases of the liver.

LAY SUMMARY

Hepatocyte transplantation is a promising alternative to liver transplantation for the treatment of liver diseases. However, it is inefficient, as restricted growth of transplanted cells in the liver limits its therapeutic benefits. Preparative treatments improve the efficiency of this procedure, but no clinically-feasible options are currently available. In this study we develop a novel well-tolerated preparative treatment to improve growth of cells in the liver and then demonstrate that this treatment completely cures an inherited lipid disorder in a mouse model.

Analysis of interleukin-17 and interleukin-18 levels in animal models of atherosclerosis

This study investigated the correlation between the levels of interleukin (IL)-17 and IL-18 and atherosclerotic plaques. A total of 60 Apo E gene (Apo E-/-) mice were fed with high-fat diet in the model group and 20 wild male C57BL/6 mice were fed with the basic diet in the control group. The serum levels of IL-17 and IL-18 were determined by enzyme-linked immunosorbent assay. Carotid artery ultrasonography was performed and divided into stable plaque, unstable plaque and non-plaque groups. The severity of plaque was estimated by semi-quantitative method and divided into grades I, II and III. The expression levels of low-density lipoprotein cholesterol, plasma total cholesterol and blood glucose level in the model group induced by high-fat diet were significantly higher than those in the control group (P<0.05). The level in the model group was significantly higher than in the control group at the 16th week (P<0.05). The expression of IL-17 and IL-18 in the model group was significantly higher than that in the control group (t=6.903, 11.02, P<0.05). The concentration of IL-17 and IL-18 in the non-plaque group was significantly lower than that in the stable plaque and unstable plaque groups (P<0.05). The concentration of IL-17 and IL-18 in the stable plaque group was significantly lower than that in the unstable plaque group (P<0.05). Based on the correlation of IL-17 and IL-18 expressions in the model group, the expression of IL-18 increased with the expression of IL-17, indicating that the expression of IL-17 was positively correlated with that of IL-18 (r=0.7195, P<0.001). In conclusion, serum IL-17 and IL-18 played an important role in the formation and development of atherosclerotic plaque, and were related to the stability and severity of plaque. The expression of IL-17 and IL-18 was positively correlated.

18F-Fluoride Positron Emission Tomographic Imaging of Penile Arteries and Erectile Dysfunction

BACKGROUND

Fluorine-18 sodium fluoride (NaF), a bone-seeking radiopharmaceutical used to detect osseous metastases, localizes in regions of microcalcification in atherosclerosis.

OBJECTIVES

To determine if atherosclerosis of penile arteries plays a role in erectile dysfunction (ED), this study analyzed NaF images in prostate cancer patients.

METHODS

NaF positron emission tomography-computed tomography bone scans were evaluated in 437 prostate cancer patients (age 66.6 ± 8.7 years). Their urologic histories were reviewed for prevalent ED (diagnosed before the scan date) or incident ED (no ED at first scan, but developed during 1-year follow-up); patients with no ED (neither before the scan nor during follow-up) were included as a control group. A semicircular region of interest was set on the dorsal one-half of the penis (to avoid residual excreted activity in the urethra) on 5 contiguous slices at the base of the penis on positron emission tomography-computed tomography coronal reconstructions, and the average standardized uptake value (SUVmax) was described as NaF uptake.

RESULTS

Of 437 patients, 336 (76.9%) had prevalent ED, 60 incident ED (13.7%), and 41 had no ED (9.4%). SUVmax in patients with prevalent (median 1.88; interquartile range [IQR]: 1.67 to 2.16) or incident (median 1.86; IQR: 1.72 to 2.08) ED was significantly higher than no ED (median 1.42; IQR: 1.25 to 1.54) patients (p < 0.001). After adjustment for other risk factors, the odds ratio of prevalent or incident ED was 25.2 (95% confidence interval: 9.5 to 67.0) for every 0.5-U increment in SUVmax with receptor operating characteristic area of 0.91 (95% confidence interval: 0.88 to 0.94).

CONCLUSIONS

NaF uptake in penile vessels suggests that atherosclerosis is associated with ED in prostate cancer patients. The importance of NaF uptake needs to be tested in noncancer subjects and cause-effect relationship needs to be established.

Adaptive responses to low doses of radiation or chemicals: their cellular and molecular mechanisms

This article reviews the current knowledge on the mechanisms of adaptive response to low doses of ionizing radiation or chemical exposure. A better knowledge of these mechanisms is needed to improve our understanding of health risks at low levels of environmental or occupational exposure and their involvement in cancer or non-cancer diseases. This response is orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways. These evolutionary highly conserved defense mechanisms determine the cellular response to chemical and physical aggression. They include DNA damage repair (p53, ATM, PARP pathways), antioxidant response (Nrf2 pathway), immune/inflammatory response (NF-κB pathway), cell survival/death pathway (apoptosis), endoplasmic response to stress (UPR response), and other cytoprotective processes including autophagy, cell cycle regulation, and the unfolded protein response. The coordinated action of these processes induced by low-dose radiation or chemicals produces biological effects that are currently estimated with the linear non-threshold model. These effects are controversial. They are difficult to detect because of their low magnitude, the scarcity of events in humans, and the difficulty of corroborating associations over the long term. Improving our understanding of these biological consequences should help humans and their environment by enabling better risk estimates, the revision of radiation protection standards, and possible therapeutic advances.

Distinct vascular genomic response of proton and gamma radiation-A pilot investigation

The cardiovascular biology of proton radiotherapy is not well understood. We aimed to compare the genomic dose-response to proton and gamma radiation of the mouse aorta to assess whether their vascular effects may diverge. We performed comparative RNA sequencing of the aorta following (4 hrs) total-body proton and gamma irradiation (0.5–200 cGy whole body dose, 10 dose levels) of conscious mice. A trend analysis identified genes that showed a dose response. While fewer genes were dose-responsive to proton than gamma radiation (29 vs. 194 genes; q-value ≤ 0.1), the magnitude of the effect was greater. Highly responsive genes were enriched for radiation response pathways (DNA damage, apoptosis, cellular stress and inflammation; p-value ≤ 0.01). Gamma, but not proton radiation induced additionally genes in vasculature specific pathways. Genes responsive to both radiation types showed almost perfectly superimposable dose-response relationships. Despite the activation of canonical radiation response pathways by both radiation types, we detected marked differences in the genomic response of the murine aorta. Models of cardiovascular risk based on photon radiation may not accurately predict the risk associated with proton radiation.

Effect of irradiation and bone marrow transplantation on angiotensin II-induced aortic inflammation in ApoE knockout mice

BACKGROUND AND AIMS

Angiotensin II (Ang II) infusion promotes the development of aortic aneurysms and accelerates atherosclerosis in ApoE^-/- mice. In order to elucidate the role of hematopoietic cells in these pathologies, irradiation and bone marrow transplantation (BMT) are commonly utilized. The aim of this study was to investigate the effects of irradiation and BMT on abdominal and thoracic aortic aneurysm formation and acute leukocyte recruitment in the aortic root and descending aorta, in an experimental mouse model of aortic aneurysm formation.

METHODS

ApoE^-/- mice were either lethally irradiated and reconstituted with ApoE^-/- bone marrow or non-irradiated. Following engraftment, mice were treated with Ang II to induce aortic inflammation and accelerate atherosclerosis.

RESULTS

Ang II infusion (0.8 mg/kg/day) in BMT mice resulted in reduced aortic aneurysms and atherosclerosis with decreased leukocyte infiltration in the aorta compared to non-BMT mice, when receiving the same dose of Ang II. Furthermore, the reduced aortic infiltration in BMT mice was accompanied by increased levels of monocytes in the spleen and bone marrow. A dose of 3 mg/kg/day Ang II was required to achieve a similar incidence of aneurysm formation as achieved with 0.8 mg/kg/day in non-BMT mice.

CONCLUSIONS

This study provides evidence that BMT can alter inflammatory cell recruitment in experimental mouse models of aortic aneurysm formation and atherosclerosis and suggests that irradiation and BMT have a considerably more complex effect on vascular inflammation, which should be evaluated.

How to prevent and manage radiation-induced coronary artery disease

Radiation-induced coronary heart disease (RICHD) is the second most common cause of morbidity and mortality in patients treated with radiotherapy for breast cancer, Hodgkin's lymphoma and other prevalent mediastinal malignancies. The risk of RICHD increases with radiation dose. Exposed patients may present decades after treatment with manifestations ranging from asymptomatic myocardial perfusion defects to ostial, triple-vessel disease and sudden cardiac death. RICHD is insidious, with a long latency and a tendency to remain silent late into the disease course. Vessel involvement is often diffuse and is preferentially proximal. The pathophysiology is similar to that of accelerated atherosclerosis, characterised by the formation of inflammatory plaque with high collagen and fibrin content. The presence of conventional risk factors potentiates RICHD, and aggressive risk factor management should ideally be initiated prior to radiation therapy. Stress echocardiography is more sensitive and specific than myocardial perfusion imaging in the detection of RICHD, and CT coronary angiography shows promise in risk stratification. Coronary artery bypass grafting is associated with higher risks of graft failure, perioperative complications and all-cause mortality in patients with RICHD. In most cases, the use of drug-eluting stents is preferable to surgical intervention, bare metal stenting or balloon-angioplasty alone.

Chronic Exposure to External Low-Dose Gamma Radiation Induces an Increase in Anti-inflammatory and Anti-oxidative Parameters Resulting in Atherosclerotic Plaque Size Reduction in ApoE-/- Mice

Populations living in radiation-contaminated territories, such as Chernobyl and Fukushima, are chronically exposed to external gamma radiation and internal radionuclide contamination due to the large amount of ¹³⁷Cs released in the environment. The effect of chronic low-dose exposure on the development of cardiovascular diseases remains unclear. Previously reported studies have shown that low-dose radiation exposure could lead to discrepancies according to dose rate. In this study, we examined the effect of very low-dose and dose-rate chronic external exposure on atherosclerosis development. ApoE^-/- mice were chronically irradiated with a gamma source for 8 months at two different dose rates, 12 and 28 μGy/h, equivalent to dose rates measured in contaminated territories, with a cumulative dose of 67 and 157 mGy, respectively. We evaluated plaque size and phenotype, inflammatory profile and oxidative stress status. The results of this study showed a decrease in plaque sizes and an increase in collagen content in ApoE^-/- mice exposed to 28 μGy/h for 8 months compared to nonexposed animals. The plaque phenotype was associated with an increase in anti-inflammatory and anti-oxidative gene expression. These results suggest that chronic low-dose gamma irradiation induces an upregulation of organism defenses leading to a decrease in inflammation and plaque size. To our knowledge, this is the first study to describe the possible effect of chronic external very low-dose ionizing radiation exposure for 8 months. This work could help to identify the potential existence of a dose threshold, below that which harmful effects are not exhibited and beneficial effects are potentially observed. Furthermore, these findings permit consideration of the importance of dose rate in radiation protection.

How radiation influences atherosclerotic plaque development: a biophysical approach in ApoE⁻/⁻ mice

Atherosclerosis is the development of lipid-laden plaques in arteries and is nowadays considered as an inflammatory disease. It has been shown that high doses of ionizing radiation, as used in radiotherapy, can increase the risk of development or progression of atherosclerosis. To elucidate the effects of radiation on atherosclerosis, we propose a mathematical model to describe radiation-promoted plaque development. This model distinguishes itself from other models by combining plaque initiation and plaque growth, and by incorporating information from biological experiments. It is based on two consecutive processes: a probabilistic dose-dependent plaque initiation process, followed by deterministic plaque growth. As a proof of principle, experimental plaque size data from carotid arteries from irradiated ApoE[Formula: see text] mice was used to illustrate how this model can provide insight into the underlying biological processes. This analysis supports the promoting role for radiation in plaque initiation, but the model can easily be extended to include dose-related effects on plaque growth if available experimental data would point in that direction. Moreover, the model could assist in designing future biological experiments on this research topic. Additional biological data such as plaque size data from chronically-irradiated mice or experimental data sets with a larger variety in biological parameters can help to further unravel the influence of radiation on plaque development. To the authors' knowledge, this is the first biophysical model that combines probabilistic and mechanistic modeling which uses experimental data to investigate the influence of radiation on plaque development.

Transcervical Carotid Stent Placement in the Setting of a Hostile Neck and a Type III Aortic Arch

Previous radical neck dissection and neck irradiation pose considerable operative risks in patients requiring carotid endarterectomy for symptomatic carotid disease. Carotid stenting is an acceptable alternative for these patients but carries a higher risk of cerebrovascular accidents especially in patients with type III aortic arch anatomy. Herein, we present a technically challenging case of a patient with an irradiated neck and a history of radical neck dissection who presented with a symptomatic high-grade left internal carotid artery stenosis in the setting of a type III aortic arch. He was treated via a hybrid approach for carotid artery stenting.

Calcified carotid artery atheromas on panoramic radiographs of head and neck cancer patients before and after radiotherapy

Background

The aims of this study were to verify if head and neck radiotherapy (RT) is able to induce calcified carotid artery atheroma (CCAA) in a large head and neck cancer (HNC) population and also to compare the socio-demographic and clinical findings of patients with and without CCAA detected on panoramic radiographs.

Material and Methods

Panoramic radiographs taken before and after head and neck radiotherapy (RT) of 180 HNC patients were selected and analyzed in order to identify the presence of CCAA. In addition, CCAA presence or absence on panoramic radiographs were compared and correlated with clinicopathological findings.

Results

A high overall prevalence of CCAA was found on panoramic radiographs (63 out of 180 = 35%) of HNC patients. No significant difference of CCAA before and after RT was observed. There were also no differences between groups (with and without CCAA) regarding age, gender, tobacco and alcohol use, arterial hypertension, diabetes mellitus, acute myocardial infarction, hypercholesterolemia, tumor location, clinical stage of disease and RT dose. However, there was a greater prevalence of strokes in patients with CCAA (p<0.05).

Conclusions

Although CCAA were frequently found in panoramic radiographs of patients with HNC, RT seems not to alter the prevalence of these calcifications.

Key words:Head and neck cancer, radiotherapy, carotid artery diseases, panoramic radiography.

Pathogenesis and Prevention of Radiation-induced Myocardial Fibrosis

Radiation therapy is one of the most important methods for the treatment of malignant tumors. However, in radiotherapy for thoracic tumors such as breast cancer, lung cancer, esophageal cancer, and mediastinal lymphoma, the heart, located in the mediastinum, is inevitably affected by the irradiation, leading to pericardial disease, myocardial fibrosis, coronary artery disease, valvular lesions, and cardiac conduction system injury, which are considered radiation-induced heart diseases. Delayed cardiac injury especially myocardial fibrosis is more prominent, and its incidence is as high as 20–80%. Myocardial fibrosis is the final stage of radiation-induced heart diseases, and it increases the stiffness of the myocardium and decreases myocardial systolic and diastolic function, resulting in myocardial electrical physiological disorder, arrhythmia, incomplete heart function, or even sudden death. This article reviews the pathogenesis and prevention of radiation-induced myocardial fibrosis for providing references for the prevention and treatment of radiation-induced myocardial fibrosis.

Dosimetric Analysis of Neural and Vascular Structures in Skull Base Tumors Treated with Stereotactic Radiosurgery

Objective To examine the relationship between the prescribed target dose and the dose to healthy neurovascular structures in patients with vestibular schwannomas treated with stereotactic radiosurgery (SRS). Study Design Case series with chart review. Setting SRS center from 2011 to 2013. Subjects Twenty patients with vestibular schwannomas treated at the center from 2011 to 2013. Methods Twenty patients with vestibular schwannomas were included. The average radiation dose delivered to healthy neurovascular structures (eg, carotid artery, basilar artery, facial nerve, trigeminal nerve, and cochlea) was analyzed. Results Twenty patients with vestibular schwannomas who were treated with fused computed tomography/magnetic resonance imaging-guided SRS were included in the study. The prescribed dose ranged from 10.58 to 17.40 Gy over 1 to 3 hypofractions to cover 95% of the target tumor volume. The mean dose to the carotid artery was 5.66 Gy (95% confidence interval [CI], 4.53-6.80 Gy), anterior inferior cerebellar artery was 8.70 Gy (95% CI, 4.54-12.86 Gy), intratemporal facial nerve was 3.76 Gy (95% CI, 3.04-4.08 Gy), trigeminal nerve was 5.21 Gy (95% CI, 3.31-7.11 Gy), and the cochlea was 8.70 Gy (95% CI, 7.81-9.59 Gy). Conclusions SRS for certain vestibular schwannomas can expose the anterior inferior cerebellar artery (AICA) and carotid artery to radiation doses that can potentially initiate atherosclerotic processes. The higher doses to the AICA and carotid artery correlated with increasing tumor volume. The dose delivered to other structures such as the cochlea and intratemporal facial nerve appears to be lower and much less likely to cause immediate complications when shielded.

Cardiovascular diseases related to ionizing radiation: The risk of low-dose exposure (Review)

Traditionally, non-cancer diseases are not considered as health risks following exposure to low doses of ionizing radiation. Indeed, non-cancer diseases are classified as deterministic tissue reactions, which are characterized by a threshold dose. It is judged that below an absorbed dose of 100 mGy, no clinically relevant tissue damage occurs, forming the basis for the current radiation protection system concerning non-cancer effects. Recent epidemiological findings point, however, to an excess risk of non-cancer diseases following exposure to lower doses of ionizing radiation than was previously thought. The evidence is the most sound for cardiovascular disease (CVD) and cataract. Due to limited statistical power, the dose-risk relationship is undetermined below 0.5 Gy; however, if this relationship proves to be without a threshold, it may have considerable impact on current low-dose health risk estimates. In this review, we describe the CVD risk related to low doses of ionizing radiation, the clinical manifestation and the pathology of radiation-induced CVD, as well as the importance of the endothelium models in CVD research as a way forward to complement the epidemiological data with the underlying biological and molecular mechanisms.