Effects of local irradiation combined with sunitinib on early remodeling, mitochondria, and oxidative stress in the rat heart

Effects of confounding and effect-modifying lifestyle, environmental and medical factors on risk of radiation-associated cardiovascular disease

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of death worldwide. It has been known for some considerable time that radiation is associated with excess risk of CVD. A recent systematic review of radiation and CVD highlighted substantial inter-study heterogeneity in effect, possibly a result of confounding or modifications of radiation effect by non-radiation factors, in particular by the major lifestyle/environmental/medical risk factors and latent period.

METHODS

We assessed effects of confounding by lifestyle/environmental/medical risk factors on radiation-associated CVD and investigated evidence for modifying effects of these variables on CVD radiation dose-response, using data assembled for a recent systematic review.

RESULTS

There are 43 epidemiologic studies which are informative on effects of adjustment for confounding or risk modifying factors on radiation-associated CVD. Of these 22 were studies of groups exposed to substantial doses of medical radiation for therapy or diagnosis. The remaining 21 studies were of groups exposed at much lower levels of dose and/or dose rate. Only four studies suggest substantial effects of adjustment for lifestyle/environmental/medical risk factors on radiation risk of CVD; however, there were also substantial uncertainties in the estimates in all of these studies. There are fewer suggestions of effects that modify the radiation dose response; only two studies, both at lower levels of dose, report the most serious level of modifying effect.

CONCLUSIONS

There are still large uncertainties about confounding factors or lifestyle/environmental/medical variables that may influence radiation-associated CVD, although indications are that there are not many studies in which there are substantial confounding effects of these risk factors.

Early and Accurate Detection of Radiation-induced Heart Damage by Cardiodynamicsgram

Cardiodynamicsgram (CDG) has emerged recently as a noninvasive spatiotemporal electrocardiographic method for subtle cardiac dynamics information analysis within electrocardiogram (ECG). This study explored the feasibility of CDG for detecting radiation-induced heart damage (RIHD) in a rat model. A single radiation dose of 40 Gy was delivered to the cardiac apex of female Wistar rats. First, CDG was generated through dynamic modeling of ECG signals using the deterministic learning algorithm. Furthermore, CDG indexes were calculated using the wavelet transform and entropy. In this model, CDG entropy indexes decreased significantly after radiotherapy. The shape of CDG changed significantly after radiotherapy (irregular shape) compared with controls (regular shape). Macrophage and fibrosis in myocardium of rats increased significantly after radiotherapy. CDG changes after radiotherapy were significantly correlated with histopathological changes and occurred significantly earlier than histopathological changes. This study provides an experimental basis for the clinical application of CDG for the early detection of RIHD.

Methods to assess radiation-induced cardiotoxicity in rodent models

Cancer survivors who have received thoracic radiation as part of their primary treatment are at risk for developing radiation-induced cardiotoxicity (RICT) due to incidental radiation delivered to the heart. In recent decades, advancements in radiation delivery have dramatically improved the therapeutic ratio of radiation therapy (RT)-efficiently targeting malignancies while sparing the heart; yet, in many patients, incidental radiation to the heart cannot be fully avoided. Cardiac radiation exposure can cause long-term morbidity and contribute to poorer survival in cancer patients. Severe cardiac effects can occur within 2years of treatment. Currently, there is no way to predict who is at higher or lower risk of developing cardiotoxicity from radiation, and the critical factors that alter RICT have not yet been clearly identified. Thus, pre-clinical investigations are an important step towards better prevention, detection, and management of RICT in cancer survivors. The overarching aim of this chapter is to provide researchers with foundational and technical knowledge in the use of mice and rats for RICT investigations. After a brief overview of RICT pathophysiology and clinical manifestations, we discuss important considerations of RICT study design, including animal selection and radiation planning. We then provide example protocols for murine tissue harvesting and processing that can support use in downstream applications of the reader's choosing.

Plasma Markers for Early Prediction of Radiation-Induced Myocardial Damage

There is no sensitive and effective method to predict radiation-induced myocardial damage (RIMD). The aim of this study was to explore effective plasma biomarkers for early prediction of RIMD after radiotherapy (RT) in lung cancer patients and in a rat model. Biomarker levels were measured in plasma samples collected before and after thoracic RT from 17 lung cancer patients. For the animal model, a single radiation dose of 40 Gy was delivered to the cardiac apex of female Wistar rats. Control rats received sham irradiation (0 Gy). Dynamic plasma biomarker detection and histopathological analysis to confirm RIMD were performed in rats up to 6 months after RT. In lung cancer patients, the plasma caspase-3 concentration was significantly increased after thoracic RT (P = 0.0479), with increasing but nonsignificant trends observed for caspase-1, CCL2, vascular endothelial growth factor (VEGF), interleukin-1β, and IL-6 (P > 0.05). Changes in caspase-3, VEGF, and IL-6 correlated significantly with mean heart dose (P < 0.05). In the RIMD rat model, caspase-1, caspase-3, CCl-2, VEGF, CCl-5, and TGF-β1 levels were significantly elevated in the first week post-RT (P < 0.05), which was earlier than pathological changes. Myocardial tissue of the RIMD rats also showed significant macrophage infiltration at 1 month (P < 0.01) and fibrosis at 6 months postradiation (P < 0.0001). Macrophage infiltration correlated significantly with plasma caspase-3, CCL2, CCL5, VEGF, and TGF-β1 levels from 3 weeks to 2 months post-RT. Increased plasma caspase-1, caspase-3, CCl-2, and VEGF levels were detected before RIMD-related pathological changes, indicating their clinical potential as biomarkers for early prediction of RIMD.

Murine models of radiation cardiotoxicity: A systematic review and recommendations for future studies

BACKGROUND AND PURPOSE

The effects of radiation on the heart are dependent on dose, fractionation, overall treatment time, and pre-existing cardiovascular pathology. Murine models have played a central role in improving our understanding of the radiation response of the heart yet a wide range of exposure parameters have been used. We evaluated the study design of published murine cardiac irradiation experiments to assess gaps in the literature and to suggest guidance for the harmonisation of future study reporting.

METHODS AND MATERIALS

A systematic review of mouse/rat studies published 1981-2021 that examined the effect of radiation on the heart was performed. The protocol was published on PROSPERO (CRD42021238921) and the findings were reported in accordance with the PRISMA guidance. Risk of bias was assessed using the SYRCLE checklist.

RESULTS

159 relevant full-text original articles were reviewed. The heart only was the target volume in 67% of the studies and simulation details were unavailable for 44% studies. Dosimetry methods were reported in 31% studies. The pulmonary effects of whole and partial heart irradiation were reported in 13% studies. Seventy-eight unique dose-fractionation schedules were evaluated. Large heterogeneity was observed in the endpoints measured, and the reporting standards were highly variable.

CONCLUSIONS

Current murine models of radiation cardiotoxicity cover a wide range of irradiation configurations and latency periods. There is a lack of evidence describing clinically relevant dose-fractionations, circulating biomarkers and radioprotectants. Recommendations for the consistent reporting of methods and results of in vivo cardiac irradiation studies are made to increase their suitability for informing the design of clinical studies.

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.

Radiation‑induced dysfunction of energy metabolism in the heart results in the fibrosis of cardiac tissues

Thoracic radiotherapy increases the risk of radiation‑induced heart damage (RIHD); however, the molecular mechanisms underlying these changes are not fully understood. The aim of the present study was to investigate the effects of radiation on the mouse heart using high‑throughput proteomics. Male C57BL/6J mice were used to establish a model of RIHD by exposing the entire heart to 16 Gy high‑energy X‑rays, and cardiac injuries were verified using a cardiac echocardiogram, as well as by measuring serum brain natriuretic peptide levels and conducting H&E and Masson staining 5 months after irradiation. Proteomics experiments were performed using the heart apex of 5‑month irradiated mice and control mice that underwent sham‑irradiation. The most significantly differentially expressed proteins were enriched in 'cardiac fibrosis' and 'energy metabolism'. Next, the cardiac fibrosis and changes to energy metabolism were confirmed using immunohistochemistry staining and western blotting. Extracellular matrix proteins, such as collagen type 1 α 1 chain, collagen type III α 1 chain, vimentin and CCCTC‑binding factor, along with metabolism‑related proteins, such as fatty acid synthase and solute carrier family 25 member 1, exhibited upregulated expression following exposure to ionizing radiation. Additionally, the myocardial mitochondria inner membranes were injured, along with a decrease in ATP levels and the accumulation of lactic acid in the irradiated heart tissues. These results suggest that the high doses of ionizing radiation used lead to structural remodeling, functional injury and fibrotic alterations in the mouse heart. Radiation‑induced mitochondrial damage and metabolic alterations of the cardiac tissue may thus be a pathogenic mechanism of RIHD.

Preclinical Models of Cancer Therapy-Associated Cardiovascular Toxicity: A Scientific Statement From the American Heart Association

Although cardiovascular toxicity from traditional chemotherapies has been well recognized for decades, the recent explosion of effective novel targeted cancer therapies with cardiovascular sequelae has driven the emergence of cardio-oncology as a new clinical and research field. Cardiovascular toxicity associated with cancer therapy can manifest as a broad range of potentially life-threatening complications, including heart failure, arrhythmia, myocarditis, and vascular events. Beyond toxicology, the intersection of cancer and heart disease has blossomed to include discovery of genetic and environmental risk factors that predispose to both. There is a pressing need to understand the underlying molecular mechanisms of cardiovascular toxicity to improve outcomes in patients with cancer. Preclinical cardiovascular models, ranging from cellular assays to large animals, serve as the foundation for mechanistic studies, with the ultimate goal of identifying biologically sound biomarkers and cardioprotective therapies that allow the optimal use of cancer treatments while minimizing toxicities. Given that novel cancer therapies target specific pathways integral to normal cardiovascular homeostasis, a better mechanistic understanding of toxicity may provide insights into fundamental pathways that lead to cardiovascular disease when dysregulated. The goal of this scientific statement is to summarize the strengths and weaknesses of preclinical models of cancer therapy-associated cardiovascular toxicity, to highlight overlapping mechanisms driving cancer and cardiovascular disease, and to discuss opportunities to leverage cardio-oncology models to address important mechanistic questions relevant to all patients with cardiovascular disease, including those with and without cancer.

Protective Effect of RIVA Against Sunitinib-Induced Cardiotoxicity by Inhibiting Oxidative Stress-Mediated Inflammation: Probable Role of TGF-β and Smad Signaling

Sunitinib (SUN) is an oral tyrosine kinase inhibitor approved in 2006 as a first-line treatment for metastatic renal cell cancer. However, weak selectivity to kinase receptors and cardiotoxicity have limited the use of sunitinib. Rivaroxaban (RIVA) is a Factor Xa inhibitor with cardioprotective action. It inhibits atherosclerosis and numerous inflammatory cascades. The present study was designed to investigate the cardioprotective effects of RIVA in sunitinib-induced cardiotoxicity. Thirty male Wistar rats were divided into five groups. Group 1 was the normal control (control). Group 2 was administered i.p. SUN 25 mg kg^-1 thrice weekly for 3 weeks. Groups 3 and 4 received the same treatment as Group 2 followed by the administration of RIVA 5 mg kg^-1 day^-1 and 10 mg kg^-1 day^-1, respectively, for 3 weeks. Group 5 received only 10 mg kg^-1 day^-1 RIVA for 3 weeks. Serum levels of Ca²⁺, Mg²⁺, Fe³⁺/Fe²⁺, lipid profiles, and cardiac enzymes were measured. Cardiac tissues were isolated for the measurements of oxidant/antioxidant balance gene and protein expressions. Relative to the controls, the administration of SUN significantly altered serum levels of (Ca²⁺, Mg²⁺, Fe³⁺/Fe²⁺, lipid profiles, and cardiac enzymes), intracellular antioxidant enzymes, and the expression levels of the genes encoding certain proteins. RIVA treatment significantly restored these parameters to near-normal levels. RIVA treatment significantly mitigated SUN-induced cardiac injuries by restoring antioxidant enzyme levels and attenuating the proinflammatory cascades resulting from SUN-induced cardiac injuries.

Mechanism of Vascular Toxicity in Rats Subjected to Treatment with a Tyrosine Kinase Inhibitor

Sunitinib (Su) is a tyrosine kinase inhibitor with antiangiogenic and antineoplastic effects that is recommended therapy for renal cell carcinoma, gastrointestinal stromal tumors, and pancreatic neuroendocrine tumors. Arterial hypertension is one of the adverse effects observed in the treatment with Su. The aim of this work was to deepen our understanding of the underlying mechanisms involved in the development of this side effect. Studies on endothelial function, vascular remodeling and nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) system were carried out in thoracic aortas from rats treated with Su for three weeks. Animals subjected to Su treatment presented with increased blood pressure and reduced endothelium-dependent vasodilation, the latter being reverted by NADPH oxidase blockade. Furthermore, vascular remodeling and stronger Masson trichrome staining, together with enhanced immunofluorescence signal for collagen 1 alpha 1 (Col1α1), were observed in aortas from treated animals. These results were accompanied by a significant elevation in superoxide anion production and the activity/protein/gene expression of NADPH oxidase isoforms (NOX1, NOX2, and NOX4), which was also prevented by NOX inhibition. Furthermore, a decrease in nitric oxide (NO) levels and endothelial nitric oxide synthase (eNOS) activation was observed in aortas from Su-treated animals. All these results indicate that endothelial dysfunction secondary to changes in vascular remodeling and oxidative stress might be responsible for the typical arterial hypertension that develops following treatment with Su.

Acquired Immunity Is Not Essential for Radiation-Induced Heart Dysfunction but Exerts a Complex Impact on Injury

While radiation therapy (RT) can improve cancer outcomes, it can lead to radiation-induced heart dysfunction (RIHD) in patients with thoracic tumors. This study examines the role of adaptive immune cells in RIHD. In Salt-Sensitive (SS) rats, image-guided whole-heart RT increased cardiac T-cell infiltration. We analyzed the functional requirement for these cells in RIHD using a genetic model of T- and B-cell deficiency (interleukin-2 receptor gamma chain knockout (IL2RG-/-)) and observed a complex role for these cells. Surprisingly, while IL2RG deficiency conferred protection from cardiac hypertrophy, it worsened heart function via echocardiogram three months after a large single RT dose, including increased end-systolic volume (ESV) and reduced ejection fraction (EF) and fractional shortening (FS) (p < 0.05). Fractionated RT, however, did not yield similarly increased injury. Our results indicate that T cells are not uniformly required for RIHD in this model, nor do they account for our previously reported differences in cardiac RT sensitivity between SS and SS.BN3 rats. The increasing use of immunotherapies in conjunction with traditional cancer treatments demands better models to study the interactions between immunity and RT for effective therapy. We present a model that reveals complex roles for adaptive immune cells in cardiac injury that vary depending on clinically relevant factors, including RT dose/fractionation, sex, and genetic background.

Differences in Expression of Mitochondrial Complexes Due to Genetic Variants May Alter Sensitivity to Radiation-Induced Cardiac Dysfunction

Radiation therapy is received by over half of all cancer patients. However, radiation doses may be constricted due to normal tissue side effects. In thoracic cancers, including breast and lung cancers, cardiac radiation is a major concern in treatment planning. There are currently no biomarkers of radiation-induced cardiotoxicity. Complex genetic modifiers can contribute to the risk of radiation-induced cardiotoxicities, yet these modifiers are largely unknown and poorly understood. We have previously reported the SS (Dahl salt-sensitive/Mcwi) rat strain is a highly sensitized model of radiation-induced cardiotoxicity compared to the more resistant Brown Norway (BN) rat strain. When rat chromosome 3 from the resistant BN rat strain is substituted into the SS background (SS.BN3 consomic), it significantly attenuates radiation-induced cardiotoxicity, demonstrating inherited genetic variants on rat chromosome 3 modify radiation sensitivity. Genes involved with mitochondrial function were differentially expressed in the hearts of SS and SS.BN3 rats 1 week after radiation. Here we further assessed differences in mitochondria-related genes between the sensitive SS and resistant SS.BN3 rats. We found mitochondrial-related gene expression differed in untreated hearts, while no differences in mitochondrial morphology were seen 1 week after localized heart radiation. At 12 weeks after localized cardiac radiation, differences in mitochondrial complex protein expression in the left ventricles were seen between the SS and SS.BN3 rats. These studies suggest that differences in mitochondrial gene expression caused by inherited genetic variants may contribute to differences in sensitivity to cardiac radiation.

Advances in Preclinical Research Models of Radiation-Induced Cardiac Toxicity

Radiation therapy (RT) is an important component of cancer therapy, with >50% of cancer patients receiving RT. As the number of cancer survivors increases, the short- and long-term side effects of cancer therapy are of growing concern. Side effects of RT for thoracic tumors, notably cardiac and pulmonary toxicities, can cause morbidity and mortality in long-term cancer survivors. An understanding of the biological pathways and mechanisms involved in normal tissue toxicity from RT will improve future cancer treatments by reducing the risk of long-term side effects. Many of these mechanistic studies are performed in animal models of radiation exposure. In this area of research, the use of small animal image-guided RT with treatment planning systems that allow more accurate dose determination has the potential to revolutionize knowledge of clinically relevant tumor and normal tissue radiobiology. However, there are still a number of challenges to overcome to optimize such radiation delivery, including dose verification and calibration, determination of doses received by adjacent normal tissues that can affect outcomes, and motion management and identifying variation in doses due to animal heterogeneity. In addition, recent studies have begun to determine how animal strain and sex affect normal tissue radiation injuries. This review article discusses the known and potential benefits and caveats of newer technologies and methods used for small animal radiation delivery, as well as how the choice of animal models, including variables such as species, strain, and age, can alter the severity of cardiac radiation toxicities and impact their clinical relevance.

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.

Mapping genetic modifiers of radiation-induced cardiotoxicity to rat chromosome 3

Radiation therapy is used in ~50% of cancer patients to reduce the risk of recurrence and in some cases improve survival. Despite these benefits, doses can be limited by toxicity in multiple organs, including the heart. The underlying causes and biomarkers of radiation-induced cardiotoxicity are currently unknown, prompting the need for experimental models with inherent differences in sensitivity and resistance to the development of radiation-induced cardiotoxicity. We have identified the parental SS (Dahl salt-sensitive/Mcwi) rat strain to be a highly-sensitized model of radiation-induced cardiotoxicity. In comparison, substitution of rat chromosome 3 from the resistant BN (Brown Norway) rat strain onto the SS background (SS-3BN consomic) significantly attenuated radiation-induced cardiotoxicity. SS-3BN rats had less radiation-induced cardiotoxicity than SS rats, as measured by survival, pleural and pericardial effusions, echocardiogram parameters, and histological damage. Mast cells, previously shown to have predominantly protective roles in radiation-induced cardiotoxicity, were increased in the more resistant SS-3BN hearts postradiation. RNA sequencing from SS and SS-3BN hearts at 1 wk postradiation revealed 5,098 differentially expressed candidate genes across the transcriptome and 350 differentially expressed genes on rat chromosome 3, which coincided with enrichment of multiple pathways, including mitochondrial dysfunction, sirtuin signaling, and ubiquitination. Upstream regulators of enriched pathways included the oxidative stress modulating transcription factor, Nrf2, which is located on rat chromosome 3. Nrf2 target genes were also differentially expressed in the SS vs. SS-3BN consomic hearts postradiation. Collectively, these data confirm the existence of heritable modifiers in radiation-induced cardiotoxicity and provide multiple biomarkers, pathways, and candidate genes for future analyses. NEW & NOTEWORTHY This novel study reveals that heritable genetic factors have the potential to modify normal tissue sensitivity to radiation. Gene variant(s) on rat chromosome 3 can contribute to enhanced cardiotoxicity displayed in the SS rats vs. the BN and SS-3BN consomic rats. Identifying genes that lead to understanding the mechanisms of radiation-induced cardiotoxicity represents a novel method to personalize radiation treatment, as well as predict the development of radiation-induced cardiotoxicity.

PPARα Is Necessary for Radiation-Induced Activation of Noncanonical TGFβ Signaling in the Heart

High-dose ionizing radiation is known to induce adverse effects such as inflammation and fibrosis in the heart. Transcriptional regulators PPARα and TGFβ are known to be involved in this radiation response. PPARα, an anti-inflammatory transcription factor controlling cardiac energy metabolism, is inactivated by irradiation. The pro-inflammatory and pro-fibrotic TGFβ is activated by irradiation via SMAD-dependent and SMAD-independent pathways. The goal of this study was to investigate how altering the level of PPARα influences the radiation response of these signaling pathways. For this purpose, we used genetically modified C57Bl/6 mice with wild type (+/+), heterozygous (+/-) or homozygous (-/-) PPARα genotype. Mice were locally irradiated to the heart using doses of 8 or 16 Gy; the controls were sham-irradiated. The heart tissue was investigated using label-free proteomics 20 weeks after the irradiation and the predicted pathways were validated using immunoblotting, ELISA, and immunohistochemistry. The heterozygous PPARα mice showed most radiation-induced changes in the cardiac proteome, whereas the homozygous PPARα mice showed the least changes. Irradiation induced SMAD-dependent TGFβ signaling independently of the PPARα status, but the presence of PPARα was necessary for the activation of the SMAD-independent pathway. These data indicate a central role of PPARα in cardiac response to ionizing radiation.

Proteomics landscape of radiation-induced cardiovascular disease: somewhere over the paradigm

INTRODUCTION

Epidemiological studies clearly show that thoracic or whole body exposure to ionizing radiation increases the risk of cardiac morbidity and mortality. Radiation-induced cardiovascular disease (CVD) has been intensively studied during the last ten years but the underlying molecular mechanisms are still poorly understood. Areas covered: Heart proteomics is a powerful tool holding promise for the future research. The central focus of this review is to compare proteomics data on radiation-induced CVD with data arising from proteomics of healthy and diseased cardiac tissue in general. In this context we highlight common and unique features of radiation-related and other heart pathologies. Future prospects and challenges of the field are discussed. Expert commentary: Data from comprehensive cardiac proteomics have deepened the knowledge of molecular mechanisms involved in radiation-induced cardiac dysfunction. State-of-the-art proteomics has the potential to identify novel diagnostic and therapeutic markers of this disease.

New insight into mitochondrial changes in vascular endothelial cells irradiated by gamma ray

PURPOSE

To investigate alterations of mitochondria in irradiated endothelial cells to further elucidate the mechanism underlying radiation-induced heart disease.

MATERIALS AND METHODS

Experiments were performed using human umbilical vein endothelial cells (HUVECs). HUVECs were irradiated with single gamma ray dose of 0, 5, 10 and 20 Gy, respectively. Apoptosis was assessed by flow cytometry at 24, 48 and 72 h post-irradiation, respectively. The intracellular reactive oxygen species (ROS) was measured with 2',7'-dichlorofluorescein-diacetate (DCFH-DA) at 24 h post-irradiation. Mitochondrial membrane potential (ΔΨm) by JC-1 and the opening of mitochondrial permeability transition pore (mPTP) by a calcein-cobalt quenching method were detected at 24 h post-irradiation in order to measure changes of mitochondria induced by gamma ray irradiation.

RESULTS

Gamma ray irradiation increased HUVECs apoptosis in a dose-dependent and time-dependent manner. Irradiation also promoted ROS production in HUVECs in a dose-dependent manner. At 24 h post-irradiation, the results showed that irradiation decreases ΔΨm, however, paradoxically, flow cytometry showed green fluorescence instensity higher in irradiated HUVECs than in control HUVECs in an irradiation dose-dependent manner which indicated gamma ray irradiation inhibited mPTP opening in HUVECs.

CONCLUSIONS

Gamma ray irradiation induces apoptosis and ROS production of endothelial cells, and decreases ΔΨm meanwhile contradictorily inhibiting the opening of mPTP.

Effects of ionizing radiation on the heart

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