On the cellular origin and development of atheromatous plaques. A light and electron microscopic study of combined X-ray and hypercholesterolemia-induced atheromatosis in the carotid artery of the rabbit

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 Vascular Disease-A State-of-the-Art Review

Since the 1990s, there has been a steady increase in the number of cancer survivors to an estimated 17 million in 2019 in the US alone. Radiation therapy today is applied to a variety of malignancies and over 50% of cancer patients. The effects of ionizing radiation on cardiac structure and function, so-called radiation-induced heart disease (RIHD), have been extensively studied. We review the available published data on the mechanisms and manifestations of RIHD, with a focus on vascular disease, as well as proposed strategies for its prevention, screening, diagnosis, and management.

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.

Cardiovascular effects of space radiation: implications for future human deep space exploration

BACKGROUND

A manned mission to Mars has been contemplated by the world's largest space agencies for a number of years. The duration of the trip would necessitate a much longer exposure to deep space radiation than any human has ever been exposed to in the past. Concern regarding cancer risk has thus far stalled the progress of deep space exploration; however, the effect of space radiation on the cardiovascular system is significantly less well understood.

DISCUSSION

Damage by radiation in space is mediated by a number of sources, including X-rays, protons and heavier charged atomic nuclei (HZE ions, the high-energy component of galactic cosmic rays). Previously, only lunar mission astronauts have been exposed to significant deep space radiation, with all other missions being low earth orbits only. The effect of this radiation on the human body has been inconclusively studied, and the long-term damage caused to the vascular endothelium by this radiation due to the effect of high-energy particles is not well known.

CONCLUSION

Current radiation shielding technology, which would be viable for use in spacecraft, would not eliminate radiation risk. Similar to how a variety of shielding techniques are used every day by radiographers, again without full risk elimination, we need to explore and better understand the effect of deep space radiation in order to ensure the safety of those on future space missions.

Effect of age-related baseline risk on radiation dose response for coronary heart disease

We attempted to estimate the mortality risk of radiation-associated coronary heart disease (CHD) by using a model in which radiation was assumed to participate in the atherosclerotic process jointly with ageing. Model parameters were determined by fitting the Life Span Study data of atomic bomb survivors. According to the model, the excess relative risk (ERR) varies depending on the baseline risk; when applied to the death statistics of Japan and the USA, the estimated ERR was consistently higher in the Japanese population. The absolute risk showed an opposite trend, such that the estimated lifetime attributable risk was approximately two times higher in the US population. Excess cases were expected to appear in old age almost synchronously with spontaneous cases; in contrast, the risk is practically unnoticeable for those young to middle aged. Our model suggests that the radiation dose-response curve for CHD, as well as the latency in epidemiological studies, could be modified by the baseline risk.

Mechanisms of vascular dysfunction evoked by ionizing radiation and possible targets for its pharmacological correction

Ionizing radiation (IR) leads to a variety of the cardiovascular diseases, including the arterial hypertension. A number of studies have demonstrated that blood vessels represent important target for IR, and the endothelium is one of the most vulnerable components of the vascular wall. IR causes an inhibition of nitric oxide (NO)-mediated endothelium-dependent vasodilatation and generation of reactive oxygen (ROS) and nitrogen (RNS) species trigger this process. Inhibition of NO-mediated vasodilatation could be due to endothelial NO synthase (eNOS) down-regulation, inactivation of endothelium-derived NO, and abnormalities in diffusion of NO from the endothelial cells (ECs) leading to a decrease in NO bioavailability. Beside this, IR suppresses endothelial large conductance Ca²⁺-activated K⁺ channels (BK_Ca) activity, which control NO synthesis. IR also leads to inhibition of the BK_Ca current in vascular smooth muscle cells (SMCs) which is mediated by protein kinase C (PKC). On the other hand, IR-evoked enhanced vascular contractility may result from PKC-mediated increase in SMCs myofilament Ca²⁺ sensitivity. Also, IR evokes vascular wall inflammation and atherosclerosis development. Vascular function damaged by IR can be effectively restored by quercetin-filled phosphatidylcholine liposomes and mesenchymal stem cells injection. Using RNA-interference technique targeted to different PKC isoforms can also be a perspective approach for pharmacological treatment of IR-induced vascular dysfunction.

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.

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.

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.

Late Effects of Treatment of Pediatric Central Nervous System Tumors

Central nervous system tumors represent the most common solid malignancy in childhood. Improvement in treatment approaches have led to a significant increase in survival rates, with over 70% of children now surviving beyond 5 years. As more and more children with CNS tumors have longer survival times, it is important to be aware of the long-term morbidities caused not only by the tumor itself but also by tumor treatment. The most common side effects including poor neurocognition, endocrine dysfunction, neurological and vascular late effects, as well as secondary malignancies, are discussed within this article.

Detection of Myocardial Metabolic Abnormalities by 18F-FDG PET/CT and Corresponding Pathological Changes in Beagles with Local Heart Irradiation

Objective

To determine the efficacy of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in the detection of radiation-induced myocardial damage in beagles by comparing two pre-scan preparation protocols as well as to determine the correlation between abnormal myocardial FDG uptake and pathological findings.

Materials and Methods

The anterior myocardium of 12 beagles received radiotherapy locally with a single X-ray dose of 20 Gy. 18F-FDG cardiac PET/CT was performed at baseline and 3 months after radiation. Twelve beagles underwent two protocols before PET/CT: 12 hours of fasting (12H-F), 12H-F followed by a high-fat diet (F-HFD). Regions of interest were drawn on the irradiation and the non-irradiation fields to obtain their maximal standardized uptake values (SUVmax). Then the ratio of the SUV of the irradiation to the non-irradiation fields (INR) was computed. Histopathological changes were identified by light and electron microscopy.

Results

Using the 12H-F protocol, the average INRs were 1.18 ± 0.10 and 1.41 ± 0.18 before and after irradiation, respectively (p = 0.021). Using the F-HFD protocol, the average INRs were 0.99 ± 0.15 and 2.54 ± 0.43, respectively (p < 0.001). High FDG uptake in irradiation field was detected in 33.3% (4/12) of 12H-F protocol and 83.3% (10/12) of F-HFD protocol in visual analysis, respectively (p = 0.031). The pathology of the irradiated myocardium showed obvious perivascular fibrosis and changes in mitochondrial vacuoles.

Conclusion

High FDG uptake in an irradiated field may be related with radiation-induced myocardial damage resulting from microvascular damage and mitochondrial injury. An F-HFD preparation protocol used before obtaining PET/CT can improve the sensitivity of the detection of cardiotoxicity associated with radiotherapy.

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.

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.

Understanding radiation-induced cardiovascular damage and strategies for intervention

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

Mechanisms and dose-response relationships for radiation-induced cardiovascular disease

Epidemiological studies have shown a clear association between therapeutic doses of thoracic irradiation and increased risk of cardiovascular disease in long-term cancer survivors. Survivors of Hodgkin's lymphoma and childhood cancers, for example, show 2- to >7-fold increases in risk of cardiac death after total tumour doses of 30-40 Gy, given in 2-Gy fractions. The risk of cardiac mortality increases linearly with dose, although there are large uncertainties for mean cardiac doses <5 Gy. Experimental studies show that doses of ≥ 2 Gy induce the expression of inflammatory and thrombotic molecules in endothelial cells. In the heart, this causes progressive loss of capillaries and eventually leads to reduced perfusion, myocardial cell death, and fibrosis. In large arteries, doses of ≥ 8 Gy, combined with elevated cholesterol, initiates atherosclerosis and predisposes to the formation of inflammatory, unstable lesions, which are prone to rupture and may cause a fatal heart attack or stroke. In contrast, doses <1 Gy inhibit inflammatory cell adhesion to endothelial cells and inhibit the development of atherosclerosis in mice. It seems likely that mechanisms other than accelerated atherosclerosis are responsible for cardiovascular effects after low total-body exposures of radiation (e.g. impaired T-cell immunity or persistent increase in systemic cytokines).

The diagnostic value of 18F-FDG-PET/CT in hematopoietic radiation toxicity: a Tibet minipig model

This study was undertaken to assess the diagnostic value of 2-[(18)F]-fluoro-2-deoxy-D-glucose positron emission tomography with computed tomography ([(18)F]-FDG-PET/CT) in the detection of radiation toxicity in normal bone marrow using Tibet minipigs as a model. Eighteen Tibet minipigs were caged in aseptic rooms and randomly divided into six groups. Five groups (n = 3/group) were irradiated with single doses of 2, 5, 8, 11 and 14 Gy of total body irradiation (TBI) using an 8-MV X-ray linear accelerator. These pigs were evaluated with [(18)F]-FDG-PET/CT, and their marrow nucleated cells were counted. The data were initially collected at 6, 24 and 72 h after treatment and were then collected on Days 5-60 post-TBI at 5-day intervals. At 24 and 72 h post-TBI, marrow standardized uptake value (SUV) data showed a dose-dependent decrease in the radiation dose range from 2-8 Gy. Upon long-term observation, SUV and marrow nucleated cell number in the 11-Gy and 14-Gy groups showed a continuous and marked reduction throughout the entire time course, while Kaplan-Meier curves of survival showed low survival. In contrast, the SUVs in the 2-, 5- and 8-Gy groups showed early transient increases followed by a decline from approximately 72 h through Days 5-15 and then normalized or maintained low levels through the endpoint; marrow nucleated cell number and survival curves showed approximately the same trend and higher survival, respectively. Our findings suggest that [(18)F]-FDG-PET/CT may be helpful in quickly assessing the absorbed doses and predicting the prognosis in patients.

Radiation-induced cardiac damage in early left breast cancer patients: risk factors, biological mechanisms, radiobiology, and dosimetric constraints

Today there is general awareness of the potential damage to the heart in left-sided (more than in right-sided) breast cancer radiotherapy (RT). Historical changes in tumor and heart doses are presented here along with the impact of different RT techniques and volumes. Individual and pharmacological risk factors are also examined with respect to radiation damage. The biological mechanisms of harm are only partially understood, such as the radiobiology of heart damage due to the presence of various radiosensitive structures and their topographic heterogeneity. Furthermore, individual variability may expose patients to higher or lower risks of late cardiac damage or death. Damage mechanisms and radiobiological characteristics in heart irradiation are presented in relation to dosimetric and biological parameters.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

[Radiotherapy and atherosclerosis: current data and issues]

The continuous optimization of cancer treatment with radiotherapy raises the problem of long-term issue of patients treated and cured by ionizing radiation, with the possible occurrence of second cancers or nonmalignant complications. Among these, cardiovascular diseases are prevalent and may affect up to 40 % of patients depending on the location of the irradiation. Recent epidemiological studies show that this problem is underestimated and with no real prospective studies. The management of these patients with vascular risk, or with very high vascular risk for those with pre-existing traditional cardiovascular risk factors, remains to be determined. The pathophysiological mechanisms of radiation-induced atherosclerosis have not yet been clarified. Many efforts are still needed to identify patients at risk and to find or to propose an appropriate treatment. Prolonged vascular follow-up of patients after their radiotherapy should now be integrated into patterns of care, especially because the setting up of sophisticated technical platforms of radiotherapy do not necessarily solve the issue of cardiovascular risk after treatment. double dagger.

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.

Genes within the MHC region have a dramatic influence on radiation-enhanced atherosclerosis in mice

BACKGROUND

C3H/HeJ (C3H) mice develop much smaller atherosclerotic lesions than C57BL/6 (B6) mice when deficient in apolipoprotein E (apoE⁻(/)⁻) or fed an atherogenic diet. The 2 strains differ in H2 haplotypes, with B6 having H2(b) and C3H having H2(k). C3.SW-H2(b)/SnJ (C3.SW) is a congenic strain of C3H/HeJ in which H2(k) is replaced with H2(b).

METHODS AND RESULTS

We performed bone marrow transplantation and found that atherosclerosis-resistant C3.SW.apoE⁻(/)⁻ mice reconstituted with bone marrow from either C3.SW.apoE⁻(/)⁻ or B6.apoE⁻(/)⁻ mice after lethal irradiation had significantly larger atherosclerotic lesions than B6.apoE⁻(/)⁻ mice receiving identical treatments and much larger lesions than C3H.apoE⁻(/)⁻ mice reconstituted with syngeneic bone marrow. For syngeneic transplantation, C3.SW.apoE⁻(/)⁻ mice exhibited a 21-fold increase in lesion size over C3H.apoE⁻(/)⁻ mice (152 800±21 937 versus 7060±2290 μm²/section) and a near 4-fold increase over B6.apoE⁻(/)⁻ mice (40 529±4675 μm²/section). C3.SW.apoE⁻(/)⁻ mice reconstituted with syngeneic marrow exhibited enhanced lesion formation relative to those reconstituted with B6 marrow (152 800±21 937 versus 107 000±9374 μm²/section; P=0.067). Sublethal irradiation led to a 6-fold increase of lesion size in C3.SW.apoE⁻(/)⁻ mice (9795±2804 versus 1550±607 μm²/section; P=0.008). Wild-type C3.SW mice reconstituted with apoE(+/+) or apoE⁻(/)⁻ bone marrow had significantly larger atherosclerotic lesions than C3H mice receiving identical treatments on an atherogenic diet.

CONCLUSIONS

These results indicate that gene(s) within the H2 region have a dramatic impact on radiation-enhanced atherosclerosis, and their effect is conveyed partially through bone marrow-derived cells.

Ionizing radiation accelerates the development of atherosclerotic lesions in ApoE-/- mice and predisposes to an inflammatory plaque phenotype prone to hemorrhage

After radiotherapy treatment, there is an increased incidence of localized atherosclerosis in patients with Hodgkin's disease, breast cancer, and head and neck cancer. Here, we established a mouse model to study the development and progression of radiation-induced atherosclerosis and to compare the phenotype of these lesions with age-related atherosclerosis. Atherosclerosis-prone ApoE-/- mice fed a regular chow diet received single radiation doses of 14 Gy or sham treatments (0 Gy) to the neck, including both carotid arteries. At 22, 28, and 34 weeks after irradiation, blood samples were taken, and the arterial tree was removed for histological examination. Cholesterol levels in irradiated mice were not significantly different from age-matched controls, and markers of systemic inflammation (soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and C-reactive protein) were not elevated. The lesions in irradiated arteries were macrophage rich, with a remarkable influx of inflammatory cells, predominantly granulocytes. Intraplaque hemorrhage and erythrocyte-containing macrophages were seen only in lesions of irradiated arteries. Based on these data, we propose that irradiation accelerates the development of macrophage-rich, inflammatory atherosclerotic lesions prone to intraplaque hemorrhage.

Neck irradiation, carotid injury and its consequences

Carotid stenosis is a major sequela of head and neck irradiation that has not received the attention it deserves. Its impact on the quality of life of patients can be substantial. This review discusses the incidence, pathogenesis and consequences of radiation-induced carotid stenosis following head and neck irradiation. This review is based on literature search (Medline and Pub Med) and cross-referencing. The incidence of significant carotid stenosis following head and neck irradiation range from 30% to 50%. Patients with carotid stenosis are at increased risk for stroke. Factors such as hypertension, diabetes, smoking and obesity increase the risk. Increased attention to the clinical signs of carotid stenosis and evaluation of these patients with appropriate imaging studies, together with strict implementation of management of hypertension and diabetes and, counseling on obesity and smoking have the potential to reduce the incidence of this sequela of head and neck irradiation. Those patients with severe carotid stenosis can be managed with endarterectomy or carotid artery stenting.

Ultrastructural changes in paravertebral muscles associated with degenerative spondylolisthesis

STUDY DESIGN

The paravertebral muscle of 30 patients with spondylolisthesis and 30 control patients were investigated histologically.

OBJECTIVE

To propose myopathologic paravertebral muscle changes in cases of degenerative lumbar spondylolisthesis.

SUMMARY OF BACKGROUND DATA

The stability of the vertebral column is based on both active and passive systems. The passive system is composed of the vertebrae, the intervertebral discs, and the ligaments. Surrounding muscles and tendons constitute the active system. The autochthonous back muscles take over support functions if the passive system is ineffective. In some cases, muscles are overstrained for a long period, ultimately leading to muscular changes. This study was performed to determine the histopathologic correlates of this permanent strain.

METHODS

Between July 1998 and July 1999, paravertebral muscle biopsies were performed for 30 patients with monosegmental degenerative spondylolisthesis undergoing posterior lumbar interbody fusion. The tissue samples were submitted to histologic analysis including immune and enzyme histochemistry and electron microscopy. In addition, the muscle fibers were submitted to morphometry.

RESULTS

Severe pathologic alterations were found. The findings showed that 22 patients (73.3%) had ragged red fibers with evident ultrastructural mitochondrial anomalies. The cristae appeared irregular in 12 patients (40%) Type 1 paracrystalline inclusions were detected in five samples (16.6%) and dense bodies in eight (26.6%). Fibers with ubiquitin-positive inclusions were detected by immunohistochemistry in 13 patients (43.3%). As shown by the electron microscope, these corresponded to granulofilamentous inclusions and polyglucosan bodies. The samples were submitted to genetical analysis because biochemical studies showed reduced activity of the respiratory chain enzymes. Normal mitochondrial deoxyribonucleic acids of unchanged length were detected.

CONCLUSIONS

Apart from nonspecific myopathic changes such as those observed in rimmed vacuoles and rods, increased numbers of polyglucosan bodies were detected. This increase in polyglucosan bodies currently has not been described in patients with otherwise normal muscles.

Late postirradiation occlusive vasculopathy in childhood medulloblastoma. Report of two cases

The authors report two cases of ischemic stroke secondary to occlusive vasculopathy two decades after radiation therapy (RT) for medulloblastoma. Both patients underwent posterior fossa medulloblastoma partial resection, followed by craniospinal RT in which a cobalt 60 source was used; 40 Gy were given to the whole brain plus a 15-Gy boost to the posterior fossa. Both patients received multiagent chemotherapy, immediately following radiation therapy in the first case and after repeated craniotomy for recurrence 13 years after radiation in the second case. They experienced multiple sequelae from radiation and chemotherapy, including growth retardation and psychomotor delay. However, 20 years after treatment, they remained tumor free and able to work, until they presented with focal neurological deficits and seizures. Computerized tomography and magnetic resonance imaging of the brain in both cases showed no tumor recurrence, but did demonstrate ischemia in a posterior cerebral artery distribution. Cerebral angiography revealed multiple mid-sized arterial wall irregularities as well as focal stenoses consistent with a postirradiation vasculopathy. The pathophysiological mechanisms, radiological appearance, and incidence of this syndrome are reviewed from the literature.

Effect of bone marrow transplantation on lipoprotein metabolism and atherosclerosis in LDL receptor-knockout mice

The LDL receptor (LDLR) plays an important role in the removal of LDL and its precursors, the intermediate and very low density lipoproteins, from the blood circulation. The receptor is expressed on various cell types. In this study the relative importance of the LDLR on macrophages for lipoprotein metabolism and atherogenesis was assessed. For this purpose, irradiated LDLR-knockout (-/-) mice were transplanted with bone marrow of normal C57BL/6J mice. DNA analysis showed that the transplanted mice were chimeric. The transplantation resulted in a slight decrease of total serum cholesterol when compared with LDLR-/- mice that were transplanted with LDLR-/- bone marrow. This modest decrease, however, did not reach statistical significance at all time points examined. This decrease can be almost completely attributed to a decrease in LDL cholesterol. The specific lowering of LDL cholesterol could clearly be observed at 4 weeks after transplantation, but the decrease was less at 12 weeks after transplantation. Quantification of atherosclerotic lesions of mice fed a 1% cholesterol diet for 6 months revealed that there were no differences in mean lesion area between mice transplanted with wild-type bone marrow or LDLR-/- bone marrow. We anticipate that in LDLR-/- mice transplanted with wild-type bone marrow, the LDLR is downregulated by the relatively high concentrations of circulating cholesterol. In vitro incubations of peritoneal macrophages with 125I-LDL indicated that the LDLR of these cells could be downregulated by 25-hydroxycholesterol. Peritoneal macrophages isolated from LDLR-/- mice transplanted with wild-type bone marrow, in contrast to those transplanted with LDLR-/- bone marrow, were able to degrade 125I-LDL, indicating that the capacity to express functional LDLR was achieved. In conclusion, introduction of the LDLR into LDLR -/- mice via bone marrow transplantation resulted in only a relatively modest decrease of LDL cholesterol that became less pronounced at later time points, possibly due to downregulation of the LDLR. To utilize the LDLR in macrophages for effective cholesterol lowering, either the sterol-regulatory elements have to be "silenced" or a high-expression LDLR construct has to be introduced into macrophages, eg, via transplantation of in vitro transfected hematopoietic stem cells.

Blood supply to the oral and maxillofacial tissues following radiation therapy: a prospective ultrasonographic study

In this prospective clinical study of the early radiation effects on blood supply to the mouth and face, 44 patients (31 men-13 women, mean age 63.4 yrs) with oral tumors underwent surgery and adjuvant postoperative radiotherapy with conventional fractionation (mean dose at the neck approximately equal to 50 Gy). Blood flow parameters 1 cm below the bifurcation of the common carotid artery (mean velocity time averaged, lumen diameter, resistivity index-RI) as well as perivascular reaction, were recorded on Color Doppler Imaging video tapes in a series of five consecutive examinations up to six months postirradiation. There were no statistically significant changes shown between the initial and follow-up examinations for any of the parameters investigated. There was no difference in blood flow between the ipsilateral (operated-irradiated) and contralateral side of the neck. Results did not seem to correlate with known vascular disease risk factors such as sex, arterial pressure, cholesterol levels, smoking and diabetes. After the effect of age was controlled, flow measurements remained statistically stable. Radiation dosage did not appear to influence carotid flow parameters. Perivascular reaction had the highest peak immediately postirradiation but regressed with time. This study suggests that therapeutic radiation of the neck at this dose level may not have important effects on the maxillofacial region blood supply for approximately eight months postoperatively; however, these patients should be closely evaluated for symptoms or signs of carotid artery lesions on a long-term basis.

Experimental cerebral atherosclerosis in the rabbit. Scanning electron microscopic study of the initial lesion site

The development and initial lesion sites of cerebral atherosclerosis were studied in hypertensive rabbits fed 0.5 g/day cholesterol in their diet. The earliest lesions developed at remarkably localized areas of the basilar artery-posterior cerebral artery Y-bifurcation (area A) and vertebral arteries-basilar artery confluence (area B). These findings were obtained from a thorough scanning electron microscopic survey of the dorsal surface of the cerebral artery segment covering from the vertebral arteries to the posterior cerebral arteries. By light microscopy intimal lesions were mainly composed of accumulations of foam cells and smooth muscle cells. Electron microscopically foam cells accumulated in the intima resembled those of a monocyte-macrophage lineage. Early lesions involving only a few endothelial cells with adherent leukocytes occurred at the dividing and confluent portions of the endothelial arrays formed in areas A and B, respectively. The results indicate that hypertension coupled with hypercholesterolemia induces atherosclerosis in particular vulnerable regions of the cerebral arteries.

Vastatins inhibit cholesterol ester accumulation in human monocyte-derived macrophages

Human monocyte-derived macrophages were incubated for 48 hours in Medium 199 with 1% human serum albumin, and with 100 micrograms acetyl low density lipoprotein (LDL) or beta-very low density lipoprotein (beta-VLDL), with or without various concentrations of compactin, lovastatin, simvastatin, or pravastatin. The mass of free (FC) and esterified (CE) cholesterol was determined, as well as the incorporation of [1-14C]acetate in sterols, that of [1-14C]oleate in CE, and that of [methyl-14C]choline in phospholipids. Moreover, we assessed the high-affinity association and degradation of 125I-labeled acetyl LDL. Compactin markedly decreased the cellular accumulation of CE induced by acetyl LDL or beta-VLDL and increased the content of FC. Compactin also decreased the incorporation of [1-14C]oleate in CE (by 70-90%) in incubations with or without added lipoproteins. The half-maximal inhibitory concentration for this effect of compactin was 30 nM. Lovastatin and simvastatin were more potent, but pravastatin was about 100-fold less potent. Although compactin also caused a clear inhibition of cholesterol synthesis in the presence of acetyl LDL, the effect on CE formation did not seem to be related to decreased cholesterol synthesis, since this was already very low in the presence of acetyl LDL. Compactin did not affect the association and degradation of labeled acetyl LDL and also had no effect on the rate of cholesterol loss after preloading the cells with CE by incubation with acetyl LDL. However, compactin had a slight stimulatory effect on the synthesis of phosphatidylcholine and sphingomyelin when compactin was added to incubations in the presence of acetyl LDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherosclerosis and macrophages

Atherosclerosis is undoubtedly a disease of many facets and in this review we have merely touched one angle of this issue. The best-established cause of the disease is hypercholesterolemia. Since the important role of macrophages in lipoprotein metabolism has been confirmed, current interest is focused on the role of macrophages in atherosclerosis. The origin and tissue distribution of foam cells have been discussed in detail, because they are the principal cells in the earliest lesions, the so-called fatty streaks. Once thought to be derived exclusively from smooth muscle cells, foam cells are now known to originate largely from monocytes that enter the intima and become transformed into macrophages. Exactly how monocytes are recruited and retained in the artery wall is not fully understood, but it is certain that the initial event involves adhesion to the endothelial surface followed by penetration under the influence of a chemotactic factor(s). Hypercholesterolemia contributes much to this phenomenon by affecting both monocyte-macrophages and endothelial cells. Intensive current research is increasing our understanding of the dynamic interaction between macrophages and both lipoproteins and vascular cells, and its immediate relevance to lesion formation. Closer scrutiny of the biology and molecular mechanism of the process of atherosclerosis may ultimately permit intervention in and slowing of the progress of this catastrophic human disease using new modalities.

Surgery for radiation-induced symptomatic carotid atherosclerosis

Carotid atherosclerosis occurring secondary to cervical irradiation is known to produce stroke. Transient neurologic symptoms have necessitated surgical intervention to prevent stroke despite concern over technical problems, wound healing, operative risks, and uncertain therapeutic outcome. With this report, 26 surgical procedures in 20 patients are now documented in the literature (12 men--60%; eight women--40%). Mean age of these patients (56 years) was 10 years younger than carotid surgery patients with no prior radiation history. No relationship was noted between elevated serum cholesterol and the subsequent development of radiation-induced carotid atherosclerosis. Surgical procedures performed included carotid endarterectomy in 17 cases (65%) and arterial bypass in nine (35%). The combination of radiation therapy and previous neck surgery, including prior radical neck dissection, did not adversely influence operability. Surgical outcome was uniformly good with only one stroke (4%) documented in the perioperative period. Longer follow-up on our six cases (mean two years) disclosed neither new clinical symptoms nor the development of hemodynamically significant restenosis.

Effect of monocytopenia on trauma-induced atherosclerotic lesions in the rabbit ear artery

In a trauma model of atherosclerosis (repeated mechanical injury of the rabbit ear artery), rabbits were pretreated either with etoposid (inducing a monocytopenia) or with prednisolone (inhibiting monocyte function) to investigate the role of monocytes in traumatically induced plaque formation. Three weeks after the last injury the arteries were carefully examined. While a profound monocytopenia during the period of injuries did not at all influence the size of the plaque formation, this was almost completely inhibited in the prednisolone-treated rabbits. Obviously, the effect of prednisolone must be attributed to other pharmacological properties. Monocytes appear to be of less importance in purely trauma atherosclerosis models.

Lack of differential sparing of late ischaemic atrophy and early epidermal healing, after dose fractionation of mouse tails down to 2.6 Gy per fraction

Long-term atrophy of irradiated mouse tails began after about 5 months, and the incidence rose steadily to the end of the lifespan. The major associated histological change was atherosclerosis in the single tail artery. The incidence of the ischaemic atrophy was dependent on the size of the irradiated volume. The probability of ischaemic atrophy assessed at 3 years after irradiation was little dependent on the dose. The fractionation effect was described by alpha/beta congruent to 30 Gy, which was not lower than the range of values applicable for healing of the early epidermal reactions on the tail. Hence the general finding of a sparing of late effects in tissues using low doses per fraction was not observed in these experiments using dose fractions down to 2.6 Gy and the present endpoints.

Suppression of cholesteryl ester accumulation in cultured human monocyte-derived macrophages by lipoxygenase inhibitors

Atherosclerotic lesions and xanthomas are characterized by the occurrence of cholesteryl ester (CE)-laden foam cells, which partly originate from macrophages. Little is known about the role of cyclo-oxygenase or lipoxygenase metabolites of arachidonic acid in the development of foam cells. In this study we investigated the influence of prostaglandins and inhibitors of the cyclo-oxygenase or the lipoxygenase pathway on CE accumulation in cultured human monocyte-derived macrophages. Accumulation of CE was achieved by incubation of the cells with acetylated low density lipoprotein (AcLDL). The stable prostacyclin analogue ZK 36 374 and prostaglandin E2 showed no effect on cellular CE storage. Similarly, the cyclo-oxygenase inhibitor indomethacin failed to influence AcLDL-induced CE accumulation. By contrast, however, the inhibitors of lipoxygenase activity nordihydroguaiaretic acid (NDGA) and BW 755 C markedly suppressed the accumulation of CE in monocyte-derived macrophages. The inhibitory effect of NDGA was dose-dependent. Incubation of the cells with the anti-oxidant vitamin E gave no significant reduction of CE accumulation. Our results indicate that inhibition of the lipoxygenase pathway of arachidonic acid metabolism in cultured monocyte-derived macrophages effectively decreases the rate of experimentally-induced CE accumulation.

Organisation of experimental thrombosis by blood cells. Evidence of the transformation of mononuclear cells into myofibroblasts and endothelial cells

To clarify whether thrombus organisation was carried out by local cell activity or by elements of the circulating blood we developed an artificial prosthesis, made of an impermeable polyurethane material with an athrombogenic surface but with a central part consisting of a DACRON velour ring which was thrombogenic. We implanted these devices into the aorta of 10 sheep. In these animals, organisation of the central thrombus by local aortic cells could be excluded. After varying periods of time (2-84 days), the device was removed and the organized thrombus investigated by light and electron microscopy. From our investigations the organisation process with the development of mesenchymal cellular elements proceeded in 3 steps: The activation of the mononuclear macrophage system, the appearance of myofibroblastic cells and endothelial formation. The activation of the mononuclear macrophage system is probably induced by chemospecific products of metabolism arising from aging thrombotic material. Apart from mononuclear elements such as monocytes, macrophages, and giant cells we observed fibroblast-like and myofibroblast-like cells. The matrix contained collagen. Endothelium developed on the surface of the organizing thrombus. The final stage was characterized by the formation of a pseudovessel wall, which followed the pattern of the vascular model. Our findings support the hypothesis that a thrombus may be organized by cells derived from the circulating blood.

Monocytes and radiation-induced atheromatosis in rabbits

Previous experiments have shown that local irradiation of the carotid arteries of hypercholesterolemic rabbits results in the development of atheromatosis in the irradiated areas of the arteries. The process starts with the adherence of monocytes to the endothelial layer, their entrance into the subendothelial space, and their subsequent transformation into lipophages (foam cells). Prevention of this type of plaque formation can be achieved by prednisolone (in a lower concentration than previously used) (Vos et al. 1981) and by VP16-213 (Vepesid). Differential blood cell counts demonstrated that the animals subjected to treatment with prednisolone developed a moderate relative lymphocytopenia, whereas treatment with Vepesid resulted in a severe monocytopenia. Since prednisolone treatment only partially prevented plaque formation, whereas Vepesid seemed to fully inhibit the development of plaques, we conclude that although a role of the lymphocyte in the process of plaque formation cannot be excluded, the monocyte seems to play a crucial role in the pathogenesis of radiation-induced atheromatosis.

Monocytic origin of foam cells in human atherosclerotic plaques

Foam cells in 4 human atherosclerotic plaques reacted with 3 rat monoclonal antibodies directed against T.200 ('anti-leucocyte common' antibody), HLA-Class II molecules and macrophage cytoplasm, respectively. Smooth muscle cells did not react. The results support the view that foam cells are monocyte-derived macrophages.