Radiation-induced cardiovascular injury

Distinguish response of low-dose radiation with different dose-rate on gene expression of human coronary artery endothelial cells: a bioinformatic study based on transcriptomic sequencing

PURPOSE

People are exposed to low-dose radiation in medical diagnosis, occupational, or life circumstances, but the effect of low-dose radiation on human health is still controversial. The biological effects of radiation below 100 mGy are still unproven. In this study, we observed the effects of low-dose radiation (100 mGy) on gene expression in human coronary artery endothelial cells (HCAECs) and its effect on molecular signaling.

MATERIALS AND METHODS

HCAECs were exposed to 100 mGy ionizing radiation at 6 mGy/h (low-dose-rate) or 288 mGy/h (high-dose-rate). After 72 h, total RNA was extracted from sham or irradiated cells for Quant-Seq 3'mRNA-Seq, and bioinformatic analyses were performed using Metascape. Gene profiling was validated using qPCR.

RESULTS

Compared to the non-irradiated control group, 100 mGy of ionizing radiation at 6 mGy/h altered the expression of 194 genes involved in signaling pathways related to heart contraction, blood circulation, and cardiac myofibril assembly differentially. However, 100 mGy at 288 mGy/h altered expression of 450 genes involved in cell cycle-related signaling pathways, including cell division, nuclear division, and mitosis differentially. Additionally, gene signatures responding to low-dose radiation, including radiation dose-specific gene profiles (HIST1H2AI, RAVER1, and POTEI) and dose-rate-specific gene profiles (MYL2 for the low-dose-rate and DHRS9 and CA14 for the high-dose-rate) were also identified.

CONCLUSIONS

We demonstrated that 100 mGy low-dose radiation could alter gene expression and molecular signaling pathways at the low-dose-rate and the high-dose-rate differently. Our findings provide evidence for further research on the potential impact of low-dose radiation on cardiovascular function.

Ubiquinol attenuates γ-radiation induced coronary and aortic changes via PDGF/p38 MAPK/ICAM-1 related pathway

Endothelial vascular injury is one of the most pivotal disorders emerging during radiotherapy. It is crucial to rely on strong antioxidants to defend against vascular damage. The current study was carried out to investigate the ameliorative effect of ubiquinol (Ubq) against gamma (γ)-radiation induced aortic and coronary changes, with highlighting its role in suppression of p38 mitogen activated protein kinase (MAPK). Exposure to γ-radiation was adopted as a potent detrimental model that induces vascular tissue damage. Concisely, male albino rats were irradiated at a dose level of 7 Gy and treated daily with Ubq (10 mg/kg/day, p.o.) for 7 days pre-and post-irradiation. At the end of the experiment, lipid profile, 8-hydroxydeoxyguanosine (8-OHdG), gene expression of intercellular adhesion molecule (ICAM-1), platelet derived growth factor (PDGF), p38 MAPK and matrix metalloproteinase-9 (MMP-9) were estimated. Exposure to radiation significantly deteriorates aortic and coronary tissues. Conversely, administration of Ubq significantly reduced serum t-cholesterol, LDL and triglycerides (p = 0.001). In addition, Ubq prevented oxidative DNA damage (8-OHdG) (p = 0.1) and reduced serum MMP-9 (p = 0.001) which contributed to the endothelial cells damage. The positive impact of Ubq was more apparent in suppression of both PDGF (p = 0.001) and p38 MAPK (p = 0.1) protein concentrations, leading subsequently in reduction of ICAM-1 (p = 0.001) gene expression. As a conclusion, vascular endothelial damage brought on by γ-radiation is one of the leading causes of coronary and aortic deteriorations which could be successfully mitigated by Ubq.

Cardiovascular disease in space: A systematic review

BACKGROUND

With expanding commercial space programs, uncertainty remains about the cardiovascular effects of space environmental exposures including microgravity, confinement, isolation, space radiation, and altered bacterial virulence. Current limited data suggests additional health threats compared to Earth.

METHODS

We systematically reviewed PubMed, CENTRAL, Web of Science, EMBASE and Cochrane databases for prospective studies on spaceflight and cardiovascular outcomes. Search terms combined cardiovascular disease topics with spaceflight concepts. No date or language restrictions were imposed.

RESULTS

35 studies representing 2696 space travelers met inclusion criteria. Studies were grouped into spaceflight associations with: atherosclerosis, mortality, cardiac function, orthostatic intolerance, and arrhythmias. Atherosclerosis evidence was limited, with animal studies linking space radiation to endothelial damage, oxidative stress, and inflammation. However, human data showed no significantly increased atherosclerotic disease in astronauts. Mortality studies demonstrated lower cardiovascular mortality in astronauts compared to the general population however there was conflicting data. Cardiac function studies revealed physiologic ventricular atrophy, increased arterial stiffness, and altered blood flow distribution attributed to microgravity exposure. Effects appeared transient and reversible post-flight. Orthostatic intolerance studies found astronauts experienced altered heart rate variability, baroreflex response, and blood pressure changes post-flight. Arrhythmia studies showed increased ventricular ectopy during spaceflight, but limited data on long term flights.

CONCLUSIONS

Environmental space hazards impact the cardiovascular system through multiple mechanisms. Microgravity causes cardiac atrophy and orthostatic intolerance while space radiation may potentially accelerate atherosclerosis. Further research is needed, especially regarding long-term spaceflights.

Human Health during Space Travel: State-of-the-Art Review

The field of human space travel is in the midst of a dramatic revolution. Upcoming missions are looking to push the boundaries of space travel, with plans to travel for longer distances and durations than ever before. Both the National Aeronautics and Space Administration (NASA) and several commercial space companies (e.g., Blue Origin, SpaceX, Virgin Galactic) have already started the process of preparing for long-distance, long-duration space exploration and currently plan to explore inner solar planets (e.g., Mars) by the 2030s. With the emergence of space tourism, space travel has materialized as a potential new, exciting frontier of business, hospitality, medicine, and technology in the coming years. However, current evidence regarding human health in space is very limited, particularly pertaining to short-term and long-term space travel. This review synthesizes developments across the continuum of space health including prior studies and unpublished data from NASA related to each individual organ system, and medical screening prior to space travel. We categorized the extraterrestrial environment into exogenous (e.g., space radiation and microgravity) and endogenous processes (e.g., alteration of humans' natural circadian rhythm and mental health due to confinement, isolation, immobilization, and lack of social interaction) and their various effects on human health. The aim of this review is to explore the potential health challenges associated with space travel and how they may be overcome in order to enable new paradigms for space health, as well as the use of emerging Artificial Intelligence based (AI) technology to propel future space health research.

Out-of-field effects: lessons learned from partial body exposure

Partial body exposure and inhomogeneous dose delivery are features of the majority of medical and occupational exposure situations. However, mounting evidence indicates that the effects of partial body exposure are not limited to the irradiated area but also have systemic effects that are propagated outside the irradiated field. It was the aim of the "Partial body exposure" session within the MELODI workshop 2020 to discuss recent developments and insights into this field by covering clinical, epidemiological, dosimetric as well as mechanistic aspects. Especially the impact of out-of-field effects on dysfunctions of immune cells, cardiovascular diseases and effects on the brain were debated. The presentations at the workshop acknowledged the relevance of out-of-field effects as components of the cellular and organismal radiation response. Furthermore, their importance for the understanding of radiation-induced pathologies, for the discovery of early disease biomarkers and for the identification of high-risk organs after inhomogeneous exposure was emphasized. With the rapid advancement of clinical treatment modalities, including new dose rates and distributions a better understanding of individual health risk is urgently needed. To achieve this, a deeper mechanistic understanding of out-of-field effects in close connection to improved modelling was suggested as priorities for future research. This will support the amelioration of risk models and the personalization of risk assessments for cancer and non-cancer effects after partial body irradiation.

Cardiovascular risk in high-hazard occupations: the role of occupational cardiology

Work is beneficial for health, but many individuals develop cardiovascular disease (CVD) during their working lives. Occupational cardiology is an emerging field that combines traditional cardiology sub-specialisms with prevention and risk management unique to specific employment characteristics and conditions. In some occupational settings incapacitation through CVD has the potential to be catastrophic due to the nature of work and/or the working environment. These are often termed 'hazardous' or 'high-hazard' occupations. Consequently, many organizations that employ individuals in high-hazard roles undertake pre-employment medicals and periodic medical examinations to screen for CVD. The identification of CVD that exceeds predefined employer (or regulatory body) risk thresholds can result in occupational restriction, or disqualification, which may be temporary or permanent. This article will review the evidence related to occupational cardiology for several high-hazard occupations related to aviation and space, diving, high altitude, emergency workers, commercial transportation, and the military. The article will focus on environmental risk, screening, surveillance, and risk management for the prevention of events precipitated by CVD. Occupational cardiology is a challenging field that requires a broad understanding of general cardiology, environmental, and occupational medicine principles. There is a current lack of consensus and contemporary evidence which requires further research. Provision of evidence-based, but individualized, risk stratification and treatment plans is required from specialists that understand the complex interaction between work and the cardiovascular system. There is a current lack of consensus and contemporary evidence in occupational cardiology and further research is required.

Quantification of Myocardial Dosimetry and Glucose Metabolism Using a 17-Segment Model of the Left Ventricle in Esophageal Cancer Patients Receiving Radiotherapy

Objective

Previous studies have shown that increased cardiac uptake of ¹⁸F-fluorodeoxyglucose (FDG) on positron emission tomography (PET) may be an indicator of myocardial injury after radiotherapy (RT). The primary objective of this study was to quantify cardiac subvolume dosimetry and ¹⁸F-FDG uptake on oncologic PET using a 17-segment model of the left ventricle (LV) and to identify dose limits related to changes in cardiac ¹⁸F-FDG uptake after RT.

Methods

Twenty-four esophageal cancer (EC) patients who underwent consecutive oncologic ¹⁸F-FDG PET/CT scans at baseline and post-RT were enrolled in this study. The radiation dose and the ¹⁸F-FDG uptake were quantitatively analyzed based on a 17-segment model. The ¹⁸F-FDG uptake and doses to the basal, middle and apical regions, and the changes in the ¹⁸F-FDG uptake for different dose ranges were analyzed.

Results

A heterogeneous dose distribution was observed, and the basal region received a higher median mean dose (18.36 Gy) than the middle and apical regions (5.30 and 2.21 Gy, respectively). Segments 1, 2, 3, and 4 received the highest doses, all of which were greater than 10 Gy. Three patterns were observed for the myocardial ¹⁸F-FDG uptake in relation to the radiation dose before and after RT: an increase (5 patients), a decrease (13 patients), and no change (6 patients). In a pairing analysis, the ¹⁸F-FDG uptake after RT decreased by 28.93 and 12.12% in the low-dose segments (0–10 Gy and 10–20 Gy, respectively) and increased by 7.24% in the high-dose segments (20–30 Gy).

Conclusion

The RT dose varies substantially within LV segments in patients receiving thoracic EC RT. Increased ¹⁸F-FDG uptake in the myocardium after RT was observed for doses above 20 Gy.

Cardio-Oncology: Vascular and Metabolic Perspectives: A Scientific Statement From the American Heart Association

Cardio-oncology has organically developed as a new discipline within cardiovascular medicine as a result of the cardiac and vascular adverse sequelae of the major advances in cancer treatment. Patients with cancer and cancer survivors are at increased risk of vascular disease for a number of reasons. First, many new cancer therapies, including several targeted therapies, are associated with vascular and metabolic complications. Second, cancer itself serves as a risk factor for vascular disease, especially by increasing the risk for thromboembolic events. Finally, recent data suggest that common modifiable and genetic risk factors predispose to both malignancies and cardiovascular disease. Vascular complications in patients with cancer represent a new challenge for the clinician and a new frontier for research and investigation. Indeed, vascular sequelae of novel targeted therapies may provide insights into vascular signaling in humans. Clinically, emerging challenges are best addressed by a multidisciplinary approach in which cardiovascular medicine specialists and vascular biologists work closely with oncologists in the care of patients with cancer and cancer survivors. This novel approach realizes the goal of providing superior care through the creation of cardio-oncology consultative services and the training of a new generation of cardiovascular specialists with a broad understanding of cancer treatments.

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.

Cardiovascular complications after radiotherapy

Over the past decades, effective cancer therapies have resulted in a significant improvement in the survival rates for a number of cancers and an increase in the number of cancer survivors. Radiation therapy is widely used in the treatment of cancer, and it can induce various cardiotoxicities that differ considerably from chemotherapy-induced cardiotoxicity. They occur primarily as late radiation-induced complications, several years from the end of anticancer treatment and present as coronary artery disease, heart failure, pericardial disease, valvular heart disease and arrhythmias. Patients who recovered from cancer disease suffer from cardiac complications of anticancer treatment, it affects the quality of their lives and life expectancy, especially if the diagnosis is delayed. These patients may present distinct symptoms of cardiac injury, resulting from radiation-induced neurotoxicity and altered pain perception, which makes diagnosis difficult. This review highlights the need for a screening programme for patients who have undergone radiation therapy and which will subsequently have a potentially profound impact on morbidity and mortality.

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.

Heart in space: effect of the extraterrestrial environment on the cardiovascular system

National space agencies and private corporations aim at an extended presence of humans in space in the medium to long term. Together with currently suboptimal technology, microgravity and cosmic rays raise health concerns about deep-space exploration missions. Both of these physical factors affect the cardiovascular system, whose gravity-dependence is pronounced. Heart and vascular function are, therefore, susceptible to substantial changes in weightlessness. The altered cardiovascular function in space causes physiological problems in the postflight period. A compromised cardiovascular system can be excessively vulnerable to space radiation, synergistically resulting in increased damage. The space radiation dose is significantly lower than in patients undergoing radiotherapy, in whom cardiac damage is well-documented following cancer therapy in the thoracic region. Nevertheless, epidemiological findings suggest an increased risk of late cardiovascular disease even with low doses of radiation. Moreover, the peculiar biological effectiveness of heavy ions in cosmic rays might increase this risk substantially. However, whether radiation-induced cardiovascular effects have a threshold at low doses is still unclear. The main countermeasures to mitigate the effect of the space environment on cardiac function are physical exercise, antioxidants, nutraceuticals, and radiation shielding.

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

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

Implication of microRNAs in the development and potential treatment of radiation-induced heart disease

Radiotherapy is the most commonly used methodology to treat oncological disease, one of the most widespread causes of death worldwide. Oncological patients cured by radiotherapy applied to the mediastinal area have been shown to suffer from cardiovascular disease. The increase in the prevalence of radiation-induced heart disease has emphasized the need to seek new therapeutic targets to mitigate the negative impact of radiation on the heart. In this regard, microRNAs (miRNAs) have received considerable interest. miRNAs regulate post-transcriptional gene expression by their ability to target various mRNA sequences because of their imperfect pairing with mRNAs. It has been recognized that miRNAs modulate a diverse spectrum of cardiac functions with developmental, pathophysiological, and clinical implications. This makes them promising potential targets for diagnosis and treatment. This review summarizes the recent findings about the possible involvement of miRNAs in radiation-induced heart disease and their potential use as diagnostic or treatment targets in this respect.

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.

Pathology and biology of radiation-induced cardiac disease

Heart disease is the leading global cause of death. The risk for this disease is significantly increased in populations exposed to ionizing radiation, but the mechanisms are not fully elucidated yet. This review aims to gather and discuss the latest data about pathological and biological consequences in the radiation-exposed heart in a comprehensive manner. A better understanding of the molecular and cellular mechanisms underlying radiation-induced damage in heart tissue and cardiac vasculature will provide novel targets for therapeutic interventions. These may be valuable for individuals clinically or occupationally exposed to varying doses of ionizing radiation.

Acceleration of atherogenesis in ApoE-/- mice exposed to acute or low-dose-rate ionizing radiation

There is epidemiological evidence for increased non-cancer mortality, primarily due to circulatory diseases after radiation exposure above 0.5 Sv. We evaluated the effects of chronic low-dose rate versus acute exposures in a murine model of spontaneous atherogenesis. Female ApoE-/- mice (60 days) were chronically irradiated for 300 days with gamma rays at two different dose rates (1 mGy/day; 20 mGy/day), with total accumulated doses of 0.3 or 6 Gy. For comparison, age-matched ApoE-/- females were acutely exposed to the same doses and sacrificed 300 days post-irradiation. Mice acutely exposed to 0.3 or 6 Gy showed increased atherogenesis compared to age-matched controls, and this effect was persistent. When the same doses were delivered at low dose rate over 300 days, we again observed a significant impact on global development of atherosclerosis, although at 0.3 Gy effects were limited to the descending thoracic aorta. Our data suggest that a moderate dose of 0.3 Gy can have persistent detrimental effects on the cardiovascular system, and that a high dose of 6 Gy poses high risks at both high and low dose rates. Our results were clearly nonlinear with dose, suggesting that lower doses may be more damaging than predicted by a linear dose response.

The Influence of C-Ions and X-rays on Human Umbilical Vein Endothelial Cells

Damage to the endothelium of blood vessels, which may occur during radiotherapy, is discussed as a potential precursor to the development of cardiovascular disease. We thus chose human umbilical vein endothelial cells as a model system to examine the effect of low- and high-linear energy transfer (LET) radiation. Cells were exposed to 250 kV X-rays or carbon ions (C-ions) with the energies of either 9.8 MeV/u (LET = 170 keV/μm) or 91 MeV/u (LET = 28 keV/μm). Subculture of cells was performed regularly up to 46 days (~22 population doublings) post-irradiation. Immediately after exposure, cells were seeded for the colony forming assay. Additionally, at regular intervals, mitochondrial membrane potential (MMP) (JC-1 staining) and cellular senescence (senescence-associated β-galactosidase staining) were assessed. Cytogenetic damage was investigated by the micronucleus assay and the high-resolution multiplex fluorescence in situ hybridization (mFISH) technique. Analysis of radiation-induced damage shortly after exposure showed that C-ions are more effective than X-rays with respect to cell inactivation or the induction of cytogenetic damage (micronucleus assay) as observed in other cell systems. For 9.8 and 91 MeV/u C-ions, relative biological effectiveness values of 2.4 and 1.5 were obtained for cell inactivation. At the subsequent time points, the number of micronucleated cells decreased to the control level. Analysis of chromosomal damage by mFISH technique revealed aberrations frequently involving chromosome 13 irrespective of dose or radiation quality. Disruption of the MMP was seen only a few days after exposure to X-rays or C-ions. Cellular senescence was not altered by radiation at any time point investigated. Altogether, our data indicate that shortly after exposure C-ions were more effective in damaging endothelial cells than X-rays. However, late damage to endothelial cells was not found for the applied conditions and endpoints.

Threshold doses and circulatory disease risks

Tissue reactions (deterministic effects) become manifest either early or late after doses above a threshold dose, which is the basis for recommended dose limits for avoiding such effects. Threshold doses have been defined for comparative purposes at 1% incidence of an effect, although the choice of incidence level may be scenario-dependent in practice. Latency time before manifestation is related to cell turnover rates and tissue complexity. In general, threshold doses become lower for longer follow-up times because of the slow progression of injury before manifestation, particularly after lower doses. Radiosensitive individuals may contribute to low threshold doses, which would provide a safety margin for the majority of a population. A threshold dose of 0.5 Gy was proposed for radiation-induced circulatory disease, after acute or chronic exposures, in the International Commission on Radiological Protection Publication 118. However, more recent meta-analyses of low-dose population studies suggest that, if a linear dose-incidence is assumed, the risk of some types of circulatory disease after doses <0.5 Gy or <10 mGy day(-1) may be positive and similar to that for induced cancer. Animal studies show that doses >2 Gy induce the expression of inflammatory and thrombotic molecules in endothelial cells. This causes progressive loss of capillaries in the heart and leads to reduced perfusion, myocardial cell death, and fibrosis. However, doses <1 Gy inhibit both inflammatory cell adhesion to endothelial cells and the development of atherosclerosis in mice. Different mechanisms of injury at low and high doses preclude the simple extrapolation of risk on a linear-quadratic basis from acute to chronic exposures.

Mechanisms of cardiac radiation injury and potential preventive approaches

In addition to cytostatic treatment and surgery, the most common cancer treatment is gamma radiation. Despite sophisticated radiological techniques however, in addition to irradiation of the tumor, irradiation of the surrounding healthy tissue also takes place, which results in various side-effects, depending on the absorbed dose of radiation. Radiation either damages the cell DNA directly, or indirectly via the formation of oxygen radicals that in addition to the DNA damage, react with all cell organelles and interfere with their molecular mechanisms. The main features of radiation injury besides DNA damage is inflammation and increased expression of pro-inflammatory genes and cytokines. Endothelial damage and dysfunction of capillaries and small blood vessels plays a particularly important role in radiation injury. This review is focused on summarizing the currently available data concerning the mechanisms of radiation injury, as well as the effectiveness of various antioxidants, anti-inflammatory cytokines, and cytoprotective substances that may be utilized in preventing, mitigating, or treating the toxic effects of ionizing radiation on the heart.

Impact of Cancer Therapy-Related Exposures on Late Mortality in Childhood Cancer Survivors

Survival of children and adolescents diagnosed with cancer has improved dramatically in recent decades, but the substantial burden of late morbidity and mortality (i.e., more than 5 years after cancer diagnosis) associated with pediatric cancer treatments is increasingly being recognized. Progression or recurrence of the initial cancer is a primary cause of death in the initial postdiagnosis period, but as survivors age, there is a dramatic shift in the cause-specific mortality profile. By 15 years postdiagnosis, the death rate attributable to health-related causes other than recurrence or external causes (e.g., accidents, suicide, assault) exceeds that due to primary disease, and by 30 years, these causes account for the largest proportion of cumulative mortality. The two most prominent causes of treatment-related mortality in childhood cancer survivors are subsequent malignant neoplasms and cardiovascular problems, the incidence of which can be largely attributed to the long-term toxicities of radiation and chemotherapy exposures. These late effects of treatment are likely to increase in importance as survivors continue to age, inspiring continued research to better understand their etiology and to inform early detection or prevention efforts.

Adhesion molecule expression and function of primary endothelial cells in benign and malignant tissues correlates with proliferation

Background

Comparative analysis of the cellular biology of the microvasculature in different tissues requires the availability of viable primary endothelial cells (ECs). This study describes a novel method to isolate primary ECs from healthy organs, repair blastemas and tumors as examples of non-proliferating and proliferating benign and malignant tissues and their functional characterization.

Methodology/Principal Findings

Single cell suspensions from hearts, lungs, repair blastemas and tumors were incubated consecutively with an anti-CD31 antibody and magnetic micro-beads, coupled to a derivative of biotin and streptavidin, respectively. Following magnetic bead separation, CD31-positive ECs were released by biotin-streptavidin competition. In the absence of micro-beads, ECs became adherent to plastic surfaces. ECs from proliferating repair blastemas and tumors were larger and exhibited higher expression densities of CD31, CD105 and CD102 compared to those from non-proliferating normal tissues such as heart and lung. The expression density of CD34 was particularly high in tumor-derived ECs, and that of CD54 and CD144 in ECs of repair blastemas. Functionally, ECs of non-proliferating and proliferating tissues differed in their capacity to form tubes in matrigel and to align under flow conditions.

Conclusions/Significance

This method provides a powerful tool to generate high yields of viable, primary ECs of different origins. The results suggest that an altered expression of adhesion molecules on ECs in proliferating tissues contribute to loss of EC function that might cause a chaotic tumor vasculature.

Cardiovascular effects after low-dose exposure and radiotherapy: what research is needed?

The authors of this report met at the Head Quarter of the International Atomic Energy Agency (IAEA) in Vienna, Austria, on 2-4 July 2012, for intensive discussions of an abundance of original publications on new epidemiological studies on cardiovascular effects after low-dose exposure and radiotherapy and radiobiological experiments as well as several comprehensive reviews that were published since the previous meeting by experts sponsored by the IAEA in June 2006. The data necessitated a re-evaluation of the situation with special emphasis on the consequences current experimental and clinical data may have for clinical oncology/radiotherapy and radiobiological research. The authors jointly arrived at the conclusions and recommendations presented here.

Radiation-induced noncancer risks in interventional cardiology: optimisation of procedures and staff and patient dose reduction

Concerns about ionizing radiation during interventional cardiology have been increased in recent years as a result of rapid growth in interventional procedure volumes and the high radiation doses associated with some procedures. Noncancer radiation risks to cardiologists and medical staff in terms of radiation-induced cataracts and skin injuries for patients appear clear potential consequences of interventional cardiology procedures, while radiation-induced potential risk of developing cardiovascular effects remains less clear. This paper provides an overview of the evidence-based reviews of concerns about noncancer risks of radiation exposure in interventional cardiology. Strategies commonly undertaken to reduce radiation doses to both medical staff and patients during interventional cardiology procedures are discussed; optimisation of interventional cardiology procedures is highlighted.

Persistence of apoptosis and inflammatory responses in the heart and bone marrow of mice following whole-body exposure to ²⁸Silicon (²⁸Si) ions

It has been well established that the bone marrow (BM) is a radiosensitive tissue, but the radiosensitivity of the heart is poorly understood. In this study, we investigated the comparative effects of ²⁸Silicon (²⁸Si) ions (one type of heavy ion found in space) on tissue from the heart and the BM of exposed mice. We gave adult male CBA/CaJ mice a whole-body exposure to a total dose of 0, 0.1, 0.25, or 0.5 Gy of 300 MeV/nucleon (n) ²⁸Si ions, using a fractionated schedule (two exposures, 15 days apart that totaled each selected dose). The heart and BM were collected from 5 mice per treatment group at various times up to 6 months post-irradiation. In each mouse, we obtained tissue lysates from the heart and from the total population of BM cells for measuring the levels of cleaved poly (ADP-ribose) polymerase (cleaved PARP, a marker of apoptotic cell death) and the levels of activated nuclear factor-kappa B (NF-κB) and selected NF-κB-regulated cytokines known to be involved in inflammatory responses. Our data showed that, up to 6 months post-irradiation, the levels of apoptotic cell death and inflammatory responses in tissues from the heart and BM collected from exposed mice were statistically higher than those in sham controls. Hence, these findings are suggestive of chronic apoptotic cell death and inflammation in both tissues after exposure to ²⁸Si ions. In summary, our data are indicative of a possible association between exposure to ²⁸Si ions during space flight and long-term health risk.

Late effects in the era of modern therapy for Hodgkin lymphoma

Extended-field and subtotal nodal radiation therapy (RT), developed in the 1960s, was the first reliably curative treatment for early-stage Hodgkin lymphoma (HL). However, the large volume of normal tissue irradiated resulted in significant delayed toxicity, including cardiac disease and second cancers (SCs). The 30-year cumulative incidence of heart disease among adult survivors receiving 40-45 Gy of extended-field or mantle RT is approximately 30%; the incidence of SCs is similar. Improving disease control while reducing the toxicity of treatment has been a major objective of HL trials for more than 2 decades. Contemporary involved-field RT (IFRT) reduces irradiated volumes and produces significant reductions in normal tissue dose compared with historic treatments. Recent data indicate that, compared with mantle RT, IFRT reduces the relative risk of breast cancer among young females receiving mediastinal RT by approximately 60% and also reduces cardiac dose. The recent transition to involved-node RT allows further reductions in normal tissue dose. Response-adapted therapy is being evaluated in clinical trials as a means of identifying those patients most likely to benefit from treatment reduction or intensification, enhanced screening will facilitate early intervention to reduce the clinical burden of late effects, and there is increasing interest in elucidating the genetic correlates of treatment toxicity.

Late radiation-induced heart disease after radiotherapy. Clinical importance, radiobiological mechanisms and strategies of prevention

The clinical importance of radiation-induced heart disease, in particular in post-operative radiotherapy of breast cancer patients, has been recognised only recently. There is general agreement, that a co-ordinated research effort would be needed to explore all the potential strategies of how to reduce the late risk of radiation-induced heart disease in radiotherapy. This approach would be based, on one hand, on a comprehensive understanding of the radiobiological mechanisms of radiation-induced heart disease after radiotherapy which would require large-scale long-term animal experiments with high precision local heart irradiation. On the other hand - in close co-operation with mechanistic in vivo research studies - clinical studies in patients need to determine the influence of dose distribution in the heart on the risk of radiation-induced heart disease. The aim of these clinical studies would be to identify the critical structures within the organ which need to be spared and their radiation sensitivity as well as a potential volume and dose effect. The results of the mechanistic studies might also provide concepts of how to modify the gradual progression of radiation damage in the heart by drugs or biological molecules. The results of the studies in patients would need to also incorporate detailed dosimetric and imaging studies in order to develop early indicators of impending radiation-induced heart disease which would be a pre-condition to develop sound criteria for treatment plan optimisation.

Vascular damage as an underlying mechanism of cardiac and cerebral toxicity in irradiated cancer patients

Radiation is an independent risk factor for cardiovascular and cerebrovascular disease in cancer patients. Modern radiotherapy techniques reduce the volume of the heart and major coronary vessels exposed to high doses, but some exposure is often unavoidable. Radiation damage to the myocardium is caused primarily by inflammatory changes in the microvasculature, leading to microthrombi and occlusion of vessels, reduced vascular density, perfusion defects and focal ischemia. This is followed by progressive myocardial cell death and fibrosis. Clinical studies also demonstrate regional perfusion defects in non-symptomatic breast cancer patients after radiotherapy. The incidence and extent of perfusion defects are related to the volume of left ventricle included in the radiation field. Irradiation of endothelial cells lining large vessels also increases expression of inflammatory molecules, leading to adhesion and transmigration of circulating monocytes. In the presence of elevated cholesterol, invading monocytes transform into activated macrophages and form fatty streaks in the intima, thereby initiating the process of atherosclerosis. Experimental studies have shown that radiation predisposes to the formation of inflammatory plaque, which is more likely to rupture and cause a fatal heart attack or stroke. This paper presents a brief overview of the current knowledge on mechanisms for development of radiation-induced cardiovascular and cerebrovascular damage. It does not represent a comprehensive review of the literature, but reference is made to several excellent recent reviews on the topic.

A population-based study of cardiac morbidity among Hodgkin lymphoma patients with preexisting heart disease

The risk of cardiac hospitalization (CH) in Hodgkin lymphoma (HL) patients with preexisting heart disease was evaluated. Patients with HL were identified from a population-based registry (N = 3964). Data were abstracted from records of a randomly selected subcohort (N = 1096). A population-based registry was used to identify CH. Factors associated with CH and the incidence of CH after HL were estimated with competing risk models. Preexisting heart disease was the strongest predictor of posttreatment CH (hazard ratio = 3.98, P < .001) and significantly modified (P = .01) the effect of treatment on the risk of CH. Among patients with preexisting heart disease, treatment with mediastinal radiation therapy plus doxorubicin-based chemotherapy was associated with a 10-year incidence of CH more than 20% higher than treatment with chemotherapy alone. There is a high risk of CH after mediastinal radiation therapy plus doxorubicin-based chemotherapy among patients with preexisting heart disease; this is an important consideration when weighing treatment options, and in the follow-up of these patients.

Coronary artery disease associated with radiation therapy

Recent advancements in curative-intent therapies have led to dramatic improvements in breast cancer-specific mortality but at the direct expense of increased risk of cardiovascular-related mortality. The use of radiation therapy has led to significant improvements in survival for patients treated for breast cancer. However, as patients live longer, the potentially serious adverse effects of radiation on the heart have raised concerns. Coronary artery disease following irradiation is encountered rarely but is one of the most devastating treatable complications.In this article we review the cardiac complications associated with radiation therapy.

Non-cancer diseases and non-targeted effects

It is well established that moderate to high doses of radiation can increase the occurrence also of a variety of non-cancer effects in exposed individuals, but for radiation protection purposes it has generally been assumed that there is a threshold of dose below which no significant non-cancer effects (apart from hereditary disease) arise. In recent years, there is growing epidemiological evidence of excess risk of late occurring cardiovascular disease at much lower radiation doses and occurring over much longer intervals after radiation exposure without a clear cut threshold. However, the epidemiological evidence available so far for non-cancer health effects after exposure to moderate or low radiation doses is suggestive rather than persuasive. The mechanisms of radiation-induced vascular disease induction are far away from being understood. However, it seems to be very likely that inflammatory responses are involved. Recent experimental studies by Stewart et al. [25] could demonstrate that high dose exposure to the cardiovascular system is associated with an earlier onset and accelerated development of macrophage-rich, inflammatory atherosclerotic lesions prone to intra-plaque hemorrhage and may also cause a decrease in myocardial perfusion. Both, macro-vascular and micro-vascular radiation effects involve the endothelium and pro-inflammatory signalling cascades. If modulation of inflammatory response is arguably also the most likely cause of radiation-induced cardiovascular disease after low dose exposure, this also implies a role for non-targeted radiation effects. In the absence of a convincing mechanistic explanation of the currently available epidemiological evidence for radiation-induced cardiovascular risk at low radiation doses, caution is required in the interpretation of the statistical associations. On the other hand, the possibility of such a causal explanation cannot be reliably excluded. Further epidemiological and biological evidence from currently ongoing research projects will allow a firmer conclusion to be drawn.

Radiation exposure and circulatory disease risk: Hiroshima and Nagasaki atomic bomb survivor data, 1950-2003

OBJECTIVE

To investigate the degree to which ionising radiation confers risk of mortality from heart disease and stroke.

DESIGN

Prospective cohort study with more than 50 years of follow-up.

SETTING

Atomic bomb survivors in Hiroshima and Nagasaki, Japan.

PARTICIPANTS

86 611 Life Span Study cohort members with individually estimated radiation doses from 0 to >3 Gy (86% received <0.2 Gy).

MAIN OUTCOME MEASURES

Mortality from stroke or heart disease as the underlying cause of death and dose-response relations with atomic bomb radiation.

RESULTS

About 9600 participants died of stroke and 8400 died of heart disease between 1950 and 2003. For stroke, the estimated excess relative risk per gray was 9% (95% confidence interval 1% to 17%, P=0.02) on the basis of a linear dose-response model, but an indication of possible upward curvature suggested relatively little risk at low doses. For heart disease, the estimated excess relative risk per gray was 14% (6% to 23%, P<0.001); a linear model provided the best fit, suggesting excess risk even at lower doses. However, the dose-response effect over the restricted dose range of 0 to 0.5 Gy was not significant. Prospective data on smoking, alcohol intake, education, occupation, obesity, and diabetes had almost no impact on the radiation risk estimates for either stroke or heart disease, and misdiagnosis of cancers as circulatory diseases could not account for the associations seen.

CONCLUSION

Doses above 0.5 Gy are associated with an elevated risk of both stroke and heart disease, but the degree of risk at lower doses is unclear. Stroke and heart disease together account for about one third as many radiation associated excess deaths as do cancers among atomic bomb survivors.

Clinical research directions in pediatric cardiology

PURPOSE OF REVIEW

Clinical research in pediatric cardiology is under-appreciated and under-funded, yet it has enormous implications for cardiovascular health and healthcare over the entire life-course. Renewed interest in federally funded clinical research makes it timely to propose a comprehensive research agenda that, with its associated rationale, will attract public funds for research into child cardiovascular health and disease.

RECENT FINDINGS

We propose here a comprehensive pediatric cardiology research agenda consisting of 22 topics and associated research questions. We describe the following five topics in more detail: the need for life-course studies of pediatric cardiac disease and epigenetic factors for later onset of cardiovascular effects; the need to study cardiometabolic disease risk in children; recent pediatric cardiology clinical trials and observational studies; the need to explore the role of physical activity in preventing and treating pediatric cardiology patients; and the need to develop and implement evidence-based interventions to manage pediatric cardiovascular problems.

SUMMARY

If the field of pediatric cardiology can adopt a comprehensive research agenda that identifies the most-needed studies, then research could be better coordinated, long-term and collaborative studies would be more readily organized and funded, and the overall financial and scientific efficiency of research in pediatric cardiology would be improved. Targeted research efforts are more likely to realize potential breakthroughs in areas such as genetic and epigenetic screening, biomarkers, cardioprotective strategies, life-course studies, long-term monitoring technologies, environmental influences on disease, evidence-based practice guidelines, and more rapid and safer development of drugs.

Stem cell therapy to reduce radiation-induced normal tissue damage

Normal tissue damage after radiotherapy is still a major problem in cancer treatment. Stem cell therapy may provide a means to reduce radiation-induced side effects and improve the quality of life of patients. This review discusses the current status in stem cell research with respect to their potential to reduce radiation toxicity. A number of different types of stem cells are being investigated for their potential to treat a variety of disorders. Their current status, localization, characterization, isolation, and potential in stem cell-based therapies are addressed. Although clinical adult stem cell research is still at an early stage, preclinical experiments show the potential these therapies may have. Based on the major advances made in this field, stem cell-based therapy has great potential to allow prevention or treatment of normal tissue damage after radiotherapy.