Gamma radiation effect on vascular smooth muscle cells in culture

An integrative review of nonobvious puzzles of cellular and molecular cardiooncology

Oncologic patients are subjected to four major treatment types: surgery, radiotherapy, chemotherapy, and immunotherapy. All nonsurgical forms of cancer management are known to potentially violate the structural and functional integrity of the cardiovascular system. The prevalence and severity of cardiotoxicity and vascular abnormalities led to the emergence of a clinical subdiscipline, called cardiooncology. This relatively new, but rapidly expanding area of knowledge, primarily focuses on clinical observations linking the adverse effects of cancer therapy with deteriorated quality of life of cancer survivors and their increased morbidity and mortality. Cellular and molecular determinants of these relations are far less understood, mainly because of several unsolved paths and contradicting findings in the literature. In this article, we provide a comprehensive view of the cellular and molecular etiology of cardiooncology. We pay particular attention to various intracellular processes that arise in cardiomyocytes, vascular endothelial cells, and smooth muscle cells treated in experimentally-controlled conditions in vitro and in vivo with ionizing radiation and drugs representing diverse modes of anti-cancer activity.

Intracranial aneurysms formation after radiotherapy for head and neck cancer: a 10-year nationwide follow-up study

Background

Intracranial aneurysms after radiotherapy (RT) have previously been reported. However, the majority of studies were case reports. Therefore, we performed a nationwide study to explore the risk of radiation-induced intracranial aneurysms.

Methods

This study included patients diagnosed with head and neck cancer (ICD9: 140–149, 161). Intracranial aneurysms formation was identified using the following ICD9 codes: nonruptured cerebral aneurysm (ICD9:4373), aneurysm clipping (ICD9:3951). Patients who did not receive curative treatment and those with intracranial aneurysms before the diagnosis of head and neck cancer were excluded.

Results

In total, 70,691 patients were included in the final analysis; they were categorized into the following three groups: nasopharyngeal carcinoma (NPC) with RT, non-NPC with RT, and non-NPC without RT. Patients in the NPC with RT group had the highest risk of developing intracranial aneurysms (hazard ratio (HR) 2.57; P <  0.001). In addition, hypertension was also a risk factor of developing intracranial aneurysms (HR 2.14; P <  0.01). The mean time interval from cancer diagnosis to intracranial aneurysm formation in the NPC with RT group was 4.3 ± 3.1 years.

Conclusions

Compared with the non-NPC with RT and the non-NPC without RT groups, patients with NPC who received RT had a higher risk of developing intracranial aneurysms.

Pathological effects of ionizing radiation: endothelial activation and dysfunction

The endothelium, a tissue that forms a single layer of cells lining various organs and cavities of the body, especially the heart and blood as well as lymphatic vessels, plays a complex role in vascular biology. It contributes to key aspects of vascular homeostasis and is also involved in pathophysiological processes, such as thrombosis, inflammation, and hypertension. Epidemiological data show that high doses of ionizing radiation lead to cardiovascular disease over time. The aim of this review is to summarize the current knowledge on endothelial cell activation and dysfunction after ionizing radiation exposure as a central feature preceding the development of cardiovascular diseases.

An organotypical in vitro model for vascular tissue remodelling and its application to study radiation effects

An organotypic in vitro model, to study vascular tissueremodeling, was evaluated as a function of culture period. Inorder to validate the model as a tool for studying vascularresponses to damage, a dose-response analysis to ionizingirradiation was included.Rat aortic rings were explanted in vitro after being irradiatedwith single doses of (60)Co gamma-rays, namely 0, 5, 10, 15, 20or 25 Gy. Irradiated and sham-irradiated aortic rings werecultured for 3 weeks. Explant outgrowth on an adhesivesubstrate was evaluated by macroscopical scoring, and ringsderived from each irradiation group together with theoutgrowths were fixed and embedded in paraffin after 2, 7, 14and 21 days. Bromodeoxyuridine incorporation, alpha smoothmuscle actin and collagen types I and III were scored onimmunohistochemically stained sections. For each studiedparameter, irradiated and sham-irradiated rings were compared.In cultures of sham-irradiated rings, alterations from acontractile towards a synthetic/migratory smooth muscle cellphenotype were confirmed. After 3 weeks, fullgrown cultures hadformed. Irradiation slowed down the phenotypical modifications.After 15 Gy, irradiation explant outgrowth was already retarded;after 25 Gy, the outgrowth was completely blocked. On the otherhand, a dose of 15 Gy or more induced an increased collagen Iproduction in the tunica media.In conclusion, the present organotypical in vitro model fits toanalyse dynamics in the original vascular tissues as well as inthe primary outgrowth. It enables to confirm features oftissular reorganization and effects of ionizing radiationdescribed in vivo.

Responses of arteriovenous malformations to radiosurgery: ultrastructural changes

OBJECTIVE

To examine the ultrastructural changes in arteriovenous malformations (AVMs) after radiosurgery and to explore the possible mechanisms of posttreatment obliteration and hemorrhage.

METHODS

Twenty-two specimens, among them three irradiated AVMs (size, 3-6 cm), 15 nonirradiated AVMs, and four normal controls were processed for ultrastructural study immediately after removal. Transmission electron microscopy was used to compare the vasculature of irradiated AVMs with nonirradiated AVMs and normal controls.

RESULTS

Thirty-three months postradiosurgery, partial vaso-occlusion (36-74% lumen) occurred by coagulation of cytoplasmic debris and proteinaceous material leaking from the endothelium. Forty-eight months postradiosurgery, heterogeneous thrombus formation (86-96% lumen) with fibrinoid and proteinaceous materials was observed. Sixty-four months postradiosurgery, complete luminal closure (90-100% lumen) by a fibrin thrombus was seen in vessels with diameters up to 5.5 mm including feeding arteries and draining veins. In occluded vessels, there was extensive degeneration of endothelial cells, subendothelial fibroblasts, and myofibroblasts. Neoproliferation and endothelialization of smooth muscle cells with Weibel-Palade bodies was observed in arteries.

CONCLUSION

Radiosurgery causes irreversible cellular damage of the vascular wall. Partial vaso-occlusion that increases blood flow in remaining vessels and degenerative changes on the blood-brain barrier may contribute to hemorrhage at early stage postradiosurgery. Radiosurgery stimulates neoproliferating and endothelializing smooth muscle cells in vessel walls, which might lead to narrowing of the vessel lumina. Complete vaso-occlusion achieved 64 months postradiosurgery suggested a minimum follow-up duration of 5 years to determine final outcome of radiosurgery. Histological end point of vaso-occlusion of AVMs takes longer time than neuroimaging endpoint of complete obliteration.

Ionizing radiation to prevent arterial intimal hyperplasia at the edges of the stent: induces necrosis and fibrosis

BACKGROUND

Although ionizing radiation has been proposed for the prevention of intimal hyperplasia in coronary and peripheral arteries in multicenter clinical trials, information is lacking on how irradiation affects arterial histology after stenting and especially how it affects the edges of the stent. We investigated intimal hyperplasia recasting with histological changes in arterial wall at the edges of the stent after arterial stenting followed by adequate external radiation for the prevention of intimal hyperplasia in pigs.

MATERIALS AND METHODS

The aorta was experimentally stented in 30 pigs who were then assigned to two groups: irradiation with 20 Gy and a control group with no irradiation. The aorta was resected for morphometric and histological studies 6 weeks after procedure.

RESULTS

Intimal thickness was reduced and the intima/media ratio was significantly lower in irradiated groups than in control pigs. In the irradiated group histological examination at the edges of the stent showed thin neointimal proliferation with an intact endothelium. In all sections analyzed in the 20-Gy irradiated group the vascular media at 45 days contained necrotic areas and fibrosis with calcifications.

CONCLUSIONS

After arterial injury, adequate ionizing radiation effectively reduces neointimal thickening. Irradiation-induced histological changes include previously undetected recasting with necrosis and fibrosis at the arterial edges of the stent. The parietal recasting we observed in animal arteries irradiated at high doses is unclear and a cause of concern especially after clinical spontaneous dissection was recently reported. The use of ionizing radiation for the prevention of arterial restenosis awaits confirmation with a long-term follow-up including specific experimental histological analyses.

Different responses by cultured aortic and venous smooth muscle cells to gamma radiation

BACKGROUND

Stenosis of hemodialysis arteriovenous grafts is usually focal and caused by the proliferation of vascular smooth muscle cells (SMCs). External radiation of the graft is a potential strategy to prevent stenosis; however, the relative responsiveness of arterial and venous SMCs to radiation is unknown.

METHODS

Human aortic and saphenous vein SMCs were cultured in a medium containing growth factors and serum and treated with 0 to 50 Gy in a gamma irradiator. At 2 to 20 days post-irradiation, cell counting, methylthiazoletetrazolium dye reduction, [(3)H]-thymidine uptake, and bromodeoxyuridine (BrdU) incorporation assays were performed.

RESULTS

All assays showed that 1 to 50 Gy inhibited the proliferation of both aortic and venous SMCs in a dose-dependent manner. Importantly, venous cells were less susceptible to radiation in all assays, compared to aortic cells. At day 10, 1 to 50 Gy of radiation inhibited the increase in the number of aortic cells by 24% to 66% and venous cells by 8% to 25% (P < 0.01) (aortic vs. venous). The differences between aortic and venous cells varied among different assays and were most pronounced in the BrdU assay.

CONCLUSION

Inasmuch as myointimal hyperplasia occurs at both arterial and venous anastomoses, future strategies using radiation to prevent hemodialysis vascular access stenosis should take these differences into consideration.

Regulation of the collagen phenotype expression of gamma-irradiated vascular smooth muscle cells by heparan mimetics (RGTA)

Restenosis is characterized by vascular smooth muscle cell (VSMC) proliferation and accumulation of collagen III in a hypertrophic and disorganized extracellular matrix. Restenosis is prevented by antimitotic agents or irradiation but no significant progress has been made to control collagen expression deregulation. Previously, we have shown that a new family of biopolymers named RGTA (heparan mimetics elaborated by grafting on dextran of carboxylate, sulfate, and benzylamide units) stimulate in vivo tissue repair and reduce fibrosis in various models. Using VSMC in vitro (pig aortic VSMC irradiated with a 60Co source and labeled with [3H]Proline), we now show that gamma-irradiation reduced cell survival by 50% and collagen synthesis 6-fold with a major increase in the ratio of collagen III to collagen I biosynthesis taken as a fibrotic index. RGTA added to the cells enhanced their survival up to 80% and reduced collagen III/I ratio back to values found in normal vascular tissues. These results suggest that RGTA combined with gamma-radiation could be an efficient strategy against restenosis.

Gamma-irradiation modulates vascular smooth muscle cell and extracellular matrix function: Implications for neointimal development

OBJECTIVE

Migration of vascular smooth muscle cells (SMCs) into the subintimal space, and their proliferation and resultant deposition of extracellular matrix are key processes in the development of intimal hyperplasia, leading to vascular recurrent stenosis. The purpose of this study was to investigate the effects of clinically administered doses of gamma-radiation on SMCs and extracellular matrix proteins in vitro, to better understand how it impinges on cellular and extracellular components of recurrent stenosis.

METHODS

The effects of gamma-irradiation (10, 20 Gy) on SMC migration into three-dimensional collagen matrix gels was quantitated by calibrated light microscopy, and the release of metalloproteinases into conditioned media was investigated with an enzyme-linked immunosorbent assay and zymography. Collagen production was assayed with [(3)H]-proline incorporation, and SMC phenotype changes with confocal microscopy with a fluorescent alpha-actin antibody. The effect of gamma-irradiation on extracellular matrix was investigated by quantitating untreated SMC proliferation ((3)H-thymidine incorporation) on irradiated endothelial cell-derived matrix and by assessing structural collagen matrix changes with sodium dodecylsulfate polyacrylamide gel electrophoresis. All groups were compared with nonirradiated control groups.

RESULTS

SMC vertical migration was significantly decreased by gamma-irradiation (48% and 55%, respectively; P <.0001). Irradiation did not generate measurable matrix protein crosslinks, nor did it alter the production of metalloproteinases or collagen synthesis. However, gamma-irradiation decreased the ability of extracellular matrix to induce nonirradiated SMC proliferation (15% reduction; P =.0028). Moreover, gamma-irradiation reversed the secretory phenotype of cultured SMCs to a contractile type.

CONCLUSIONS

The gamma-irradiation-induced reduction of cellular migration, changes in SMC phenotype, and functional activity of matrix-bound factors, and no measurable effects on the production of extracellular matrix proteins, may in part explain the diverse effects of gamma-irradiation on the restenotic response.

Cobalt-60 gamma radiation increased the nitric oxide generation in cultured rat vascular smooth muscle cells

Radiation is a promising and new treatment for restenosis following angioplasty. Nitric oxide has been proposed as a potential "anti-restenotic" molecule. We radiated the cultured rat vascular smooth muscle cells with Cobalt-60 gamma radiation at doses of 14 and 25Gy and observed nitrite production, cGMP content, L-arginine uptake, inducible nitric oxide synthase (iNOS) activity, and the gene expression of iNOS. Results showed that radiation at doses of 14 and 25Gy increased cGMP content by 92.4% and 86.4%, respectively. Radiation at the dose of 25Gy increased the iNOS activity and nitrite content, but radiation at the dose of 14Gy had no significant effect on iNOS activity and NO production. Both doses of radiation significantly decreased the L-arginine transport. Radiation at the doses of 14 and 25Gy increased iNOS gene expression significantly, which was consistent with the effect of radiation on iNOS activity. In conclusion, radiation induces the NO generation by up-regulating the iNOS activity.

Morphometric and histological changes in the vascular wall after external radiation for the prevention of intimal hyperplasia

BACKGROUND

Recent reports describe spontaneous dissections and aneurysms after coronary and peripheral artery irradiation for the prevention of intimal hyperplasia. We investigated histological changes and the vasomotor reaction in the vascular wall after external radiation for the prevention of intimal hyperplasia in rabbits.

MATERIALS AND METHODS

The aorta was experimentally injured in 34 rabbits who were then assigned to one of three groups: irradiation with 20 Gy; with 25 Gy; and a control group with no irradiation. Before the arterial injury and 45 days later, vasomotor function was assessed with an intravascular ultrasound catheter. The aorta was resected for morphometric and histological studies.

RESULTS

After injury and irradiation, vasomotor responses were significantly lower in the two irradiated groups (P < 0.05). Intimal thickness and the intima/media ratio were significantly lower in irradiated groups. In the irradiated group histological examination showed reduced intimal proliferation with an intact endothelium. In the 20-Gy irradiated group the vascular media contained necrotic areas, and in the 25-Gy irradiated group, severe fibrosis.

CONCLUSION

After arterial injury, external irradiation at 20 and 25 Gy effectively reduces aortic intimal and medial thickening. Histological changes include recasting with necrosis and fibrosis causing a decreased vasomotor response. Further investigations are needed to confirm medial necrosis and replacement with fibrosis. Because the irradiation doses in this study match those currently used and also recommended for experimental and clinical use, if confirmed in humans parietal recasting might possibly explain the reported spontaneous dissections and aneurysm formation after irradiation.

Protective effects of melatonin and vitamin E in brain damage due to gamma radiation: an experimental study

Gamma radiation is known to cause serious damage in the brain, and many agents have been used for neuroprotection. In this study, lipid peroxidation levels and histopathological changes in brain tissues of whole-body irradiated rats with likely radiation injury were compared to those with melatonin and vitamin E protection. Forty rats in four equal groups were used. The control group received neither radiation nor medication. The remaining groups received doses of 720 cGy in two equal fractions 12 h apart. The second group received radiation but no medication, the third received radiation plus 100 mg/kg per day of vitamin E i.p., and the fourth received radiation plus 100 mg/kg per day of melatonin i.p. over 5 days. On the 10th postoperative day, all the rats were decapitated and specimens from parietal cortices were analyzed for tissue malondialdehyde (MDA) levels and histopathological changes. Increases in MDA were relatively well prevented by melatonin treatment but less so with vitamin E therapy. On histopathological examination, melatonin significantly reduced the rates of edema, necrosis, and neuronal degeneration, whereas vitamin E reduced only necrosis. Neither substance was capable of preventing vasodilatation. In conclusion, melatonin may be useful in preventing the pathological changes of secondary brain damage as a result of free oxygen radicals generated by irradiation.

Progression of atheroma: a struggle between death and procreation

Traditional thinking accorded a major role to deranged cell proliferation as a determinant of the abnormal cellularity of atheroma. However, studies conducted in several laboratories have documented the occurrence of disordered apoptosis during atherogenesis, leading to the death of lipid-rich foam cells (promoting lipid-core formation) and depletion of vascular smooth muscle cells (fostering fragility of the fibrous cap). A complex interplay of environmental factors and endogenous proteins regulates apoptosis and contributes to the struggle between cell death and procreation in atherosclerosis. In addition to a variety of growth factors, chemically modified lipids, reactive oxygen species, proinflammatory cytokines, and Fas ligand produced by activated immune cells may influence cell viability through a diversity of pathways, including the caspase cascade, the Bcl-2 protein family, and the oncogene/antioncogene system. A clarification of the molecular mechanisms responsible for vascular cell death may aid in the development of novel therapeutic strategies to treat atherosclerosis and its complications, including the acute coronary syndromes.

Rationale for coronary artery radiation therapy

Within the past decade, focus on radiation to prevent restenosis has moved from a concept developed in the animal laboratory to a clinical treatment. The initial evaluation of coronary artery radiation therapy focused on changes in the function of the artery or lesion formation following overstretch balloon injury in pigs. A number of concepts emerged from this work: (1) radiation inhibits neointima formation in a dose-dependent fashion, (2) radiation prevents negative remodeling, (3) radiation does not reverse established injury, (4) low dose irradiation in an injured area may be injurious, (5) radiation is a useful adjunct to stenting, (6) benefits of radiation in animal models at 6 months are less pronounced than at 1 month, (7) radiation delays healing, (8) permanent stents and radiation delivered from external sources may have very different effects on restenosis, and (9) radiation interferes with vessel wall function. More recent studies of irradiation have looked at the molecular biological effects of radiation in hopes of understanding how this therapy works, and how it may be improved. This article attempts to summarize the known animal and cellular work on radiation in preventing restenosis.

Early molecular changes in irradiated aortic endothelium

Irradiated aortic endothelial cells (EC) exhibit distinct morphological, functional, and physiological responses to ionizing radiation (IR). However, the molecular basis for these responses has not been fully characterized. Cultured bovine and rat aortic endothelial cells were exposed to single fraction doses (0-30 Gy) of gamma radiation. IR caused dose-dependent DNA strand breaks which were repaired to near baseline levels within 30 min. A dose-dependent inhibition of cell growth was noted for IR greater than 1 Gy. At doses greater than 2.5 Gy, morphologic changes consistent with apoptosis and loss of cell viability were present beginning 12-16 h after radiation, with subsequent detachment of EC from the cell monolayer. By Western blot analysis, expression of p53, gadd45, p21, and bax protein increased in a time-and dose-dependent manner; p53 expression was maximal at 3 h after IR, and gadd45, bax and p21 levels peaked at 6 h. By Reverse Transcriptase Polymerase Chain Reaction (RT-PCR), levels of p53 mRNA were not significantly increased after IR, whereas gadd45 exhibited time- and dose-dependent increase in mRNA synthesis after IR. Activation of intracellular caspases, manifest by proteolytic poly (ADP-ribose) polymerase (PARP) and lamin B cleavage, was maximal at 15 h after IR, concident with other indices of EC apoptosis, including oligonucleosomal DNA degradation, TUNEL immunostaining, and morphologic changes. The tripeptide protease inhibitor z-Val-Ala-Asp (zVAD) prevented PARP and lamin cleavage, DNA fragmentation, morphological changes, and cell detachment in irradiated EC. The combined data suggested that gamma radiation induces a dose- and time-dependent sequence of early events in cultured EC with modulate growth arrest, apoptosis, and possibly premature senescence in surviving cells.

External-beam radiation therapy for improved dialysis access patency: feasibility and early safety

Rectenwald, J. E., Pretus, H. A., Seeger, J. M., Huber, T. S., Mendenhall, N. P., Zlotecki, R. A., Palta, J. R., Li, Z. F., Hook, S. Y., Sarac, T. P., Welborn, M. B., Klingman, N. V., Abouhamze, Z. S. and Ozaki, C. K. External-Beam Radiation Therapy for Improved Dialysis Access Patency: Feasibility and Early Safety. Radiat. Res. 156, 53-60 (2001).Prosthetic dialysis access grafts fail secondary to neointimal hyperplasia at the venous anastomosis. We hypothesized that postoperative single-fraction external-beam radiation therapy to the venous anastomosis of hemodialysis grafts can be used safely in an effort to improve access patency. Dogs (n = 8) underwent placement of expanded polytetrafluoroethylene grafts from the right carotid artery to the left jugular vein. Five dogs received single-fraction external-beam photon irradiation (8 Gy) to the venous anastomosis after surgery. Controls were not irradiated. Shunt angiograms were completed 3 and 6 months postoperatively. Anastomoses, mid-graft, and the surrounding tissues were analyzed. Immunohistochemistry for smooth muscle cell alpha-actin, proliferating cellular nuclear antigen (PCNA), and apoptosis was performed. Incisions healed well, though all animals developed wound seromas. One control suffered graft thrombosis 4 months postoperatively. Angiography/histology confirmed severe neointimal hyperplasia at the venous anastomosis. The remaining seven dogs developed similar amounts of neointimal hyperplasia. PCNA studies showed no accelerated fibroproliferative response at irradiated anastomoses compared to controls. Skin incisions and soft tissues over irradiated anastomoses revealed no radiation-induced changes or increase in apoptosis. Thus we conclude that postoperative single-fraction external-beam irradiation of the venous anastomosis of a prosthetic arteriovenous graft that mimics the situation in humans is feasible and safe with regard to early wound healing.

Inhibition of vascular cell growth by X-ray irradiation: comparison with gamma radiation and mechanism of action

PURPOSE

Catheter-based delivery of gamma and beta radiation effectively inhibits restenosis. Major disadvantages of these radioisotopes include continuous emission; excessive depth of penetration, creating safety hazards (gamma); and inadequate penetration, limiting effectiveness (beta). Low-voltage X-rays have a distinct potential advantage, because the source is active only when current is applied, and depth of penetration is voltage dependent. This study was performed to determine if low-voltage X-rays inhibit smooth muscle and adventitial cell growth in vitro and to determine the molecular mechanisms involved in this cellular response.

METHODS AND RESULTS

Vascular cells in culture were exposed to low-voltage X-ray radiation and analyzed for their subsequent ability to proliferate. X-ray irradiation caused a dose-dependent inhibition in proliferation, similar to the effect seen with equivalent doses of gamma radiation. The radiation-induced inhibition of proliferation did not appear to be related to apoptosis, but rather to delayed progression through the cell cycle, because a 65% increase in the proportion of cells in S phase was seen 24-96 h after X-ray exposure compared to control. Expression of p53, a cell cycle transcriptional activator, and p21, a cell cycle inhibitor, were significantly elevated after exposure to low-voltage X-rays, providing a potential mechanism for this delay.

CONCLUSIONS

Low-voltage X-rays can effectively inhibit proliferation of vascular smooth muscle and adventitial cells. This inhibition is apparently due to a delay in progression through the cell cycle, which is mediated by increases in the levels of cell cycle inhibitors.

Delayed re-endothelialization and T-cell infiltration following intracoronary radiation therapy in the porcine model

PURPOSE

To evaluate the late induction of apoptosis following intracoronary radiation (IR) and the effects of IR on inflammatory cells.

METHODS AND MATERIALS

Porcine coronaries were injured by balloon overstretch followed by either 0 or 15 Gy of 192Ir prescribed to 2 mm from the center of the source. Swine were euthanized at 3, 7, and 14 days posttreatment, and arteries were stained for markers of smooth muscle cells (SMCs alpha-actin), T cells (CD3), macrophages, endothelial cells, and apoptotic nuclei (terminal uridine nick end labeling, TUNEL). Intimal area (IA) and IA corrected for medial fracture length (IA/FL) were quantified by digital image analysis, which was also used to quantify the distribution of immunostain-positive cells in the adventitia, media, and neointima, respectively.

RESULTS

IA/FL was significantly reduced following treatment with 15 Gy, in association with decreased SMC density. Following injury and IR, TUNEL- and CD3-positive cell density increased significantly, and density of macrophages was increased in the adventitia and neointima. Staining for endothelial cells revealed a delay of re-endothelialization after radiation treatment.

CONCLUSION

Increased T-cell infiltration at the medial tear following IR, perhaps due to incomplete re-endothelialization, may indicate incomplete healing. The elevated apoptosis of these infiltrating T cells may indicate a mechanism for the resolution of inflammation.

Oxyhemoglobin produces apoptosis and necrosis in cultured smooth muscle cells

Confluent rat aortic smooth muscle cells were treated with OxyHb in a concentration- and time-dependent manner. A high concentration of OxyHb (100 microM) within 24 h decreased cell density. DNA analysis showed a smear pattern characteristic of cell necrosis. Transmission electron microscopy demonstrated disintegration of the cell membrane and destruction of cell organelles. Western blotting using PARP antibody revealed that 116 kDa PARP was not cleaved to 85 kDa, an apoptosis-related fragment. On the contrary, a low concentration of OxyHb (10 microM) produced apoptotic cell death at 72 h that was supported by DNA analysis and TUNEL staining. These results demonstrated that a high level of OxyHb induced necrosis within 24 h and a low concentration of OxyHb produced apoptosis after 72 h in cultured smooth muscle cells. Morphological alterations induced by OxyHb might contribute to the vascular wall changes in the cerebral arteries following subarachnoid hemorrhage (SAH).

Different radiosensitivity of smooth muscle cells and endothelial cells in vitro as demonstrated by irradiation from a Re-188 filled balloon catheter

There is an increasing interest in irradiation to control restenosis after balloon angioplasty by an internal radioactive source. Differences in radiosensitivity of the predominant cells of the human coronary artery (i.e. endothelial cells (HCAEC), smooth muscle cells from the media (HCMSMC) and from plaque material (HCPSMC), are issues of controversal discussion. Therefore, we investigated the graded inhibition of cells by irradiation from a balloon catheter filled with a high-energy beta-emitter (Rhenium-188) in vitro. HCPSMC, HCMSMC and HCAEC were cultured and irradiated with increasing dose from 7.5 to 37.5 Gy at a dose rate of 1.5+/-0.3 Gy/min. After irradiation, bromodeoxyuridine (BrdU) was added and cells were fixed 18 h later. In a limited field opposite to the balloon, the number of BrdU-positive cells were analysed in comparison to non-irradiated controls. Significant inhibition was demonstrated in HCPSMC and HCMSMC at 7.5 Gy while HCAEC needed 22.5 Gy for similar effects. The antiproliferative effect was dose dependent in all cell strains. The effect of irradiation with 22.5 Gy on smooth muscle alpha-actin, vimentin, and alpha-tubulin of HCPSMC and HCMSMC and on von Willebrand factor (vWF), vimentin, and alpha-tubulin of HCAEC was investigated by means of indirect immunofluorescence. Within 18 h after irradiation no effect on cytoskeletal components and vWF was documented. This in vitro study demonstrates that irradiation inhibits HCMSMC and HCPSMC at lower dose rates compared to HCAEC.

Radiation induced vascular injury after stereotactic radiosurgery for trigeminal neuralgia: case report

BACKGROUND

Stereotactic radiosurgery is increasingly used for the treatment of medically unresponsive trigeminal neuralgia.

CASE DESCRIPTION

We present the case of a 69-year-old man with trigeminal neuralgia who underwent stereotactic radiosurgery after a failed balloon compression procedure. The radiosurgery also failed to provide the patient with any significant pain relief, and microvascular decompression of the trigeminal nerve was performed 10 months later. At operation, two adjacent veins and the superior cerebellar artery were noted to have focal changes consistent with atheromatous disease.

CONCLUSION

We postulate that the recent radiation exposure resulted in the observed vascular injury. As a result, patients having trigeminal neuralgia radiosurgery need to be followed carefully for possible delayed ischemic events secondary to radiation-induced vascular injury.

Prevention of intimal hyperplasia by single-dose pre-insertion external radiation in canine-vein interposition grafts

OBJECTIVES

to evaluate the efficacy of single-dose pre-insertion gamma radiation of vein grafts in the prevention of intimal hyperplasia.

METHODS

femoral artery interposition grafts with internal jugular vein were inserted in 12 mongrel dogs. The animals were randomly divided into two groups. Immediately before graft replacement, jugular veins were treated with a single dose of cobalt-60 radiation at 14 Gy or received no radiation (control group). Six weeks after graft insertion, the vein grafts were pressure-perfusion fixed and harvested for the histomorphometric analysis. Quantitative data on anastomotic stenosis were calculated from Gilman parameters after cross-sectional image analysis.

RESULTS

vein grafts treated with radiation demonstrated significantly decreased neointima formation compared with grafts in the control group. The mean Gilman parameter for the control group was 1.09 S.E.M. 0.34 mm and for the radiotherapy group was 0.65 S.E. M. 0.23 mm (p<0.05). All vein grafts in the radiotherapy group had a decreased amount of intimal and cellular infiltration.

CONCLUSION

single-dose external pre-insertion gamma radiation of vein grafts reduced the amount of intimal hyperplasia in this animal model.

Irradiation for intimal hyperplasia: implications for peripheral arterial bypass

Irradiation has been shown to inhibit postangioplasty intimal hyperplasia ("restenosis") in unbranched tubes. It seems likely that irradiation will similarly be able to inhibit intimal hyperplasia after a surgical anastomosis at a biochemical and cellular level, but whether it will produce a clinically relevant or even clinically detectable difference is unproved. One possibility is that no clinical effect may occur; the search for a "cure" for intimal hyperplasia has been long and, as yet, unsuccessful. On the other hand, if a strong effect without insurmountable logistical problems could be produced, one major cause of bypass graft failure would be preventable. Not only would the incidence of late graft occlusion, need for reoperation, and limb loss be reduced, but, if patency of prosthetics could be sufficiently improved, the initial operation could be made much easier, faster, and perhaps safer.

Inhibition of rat smooth muscle proliferation by radiation after arterial injury: temporal characteristics in vivo and in vitro

Although several studies have suggested that inhibition of arterial narrowing by radiation after angioplasty is dependent on both time and dose, little is known regarding the temporal aspects of this effect and the mechanisms by which radiation affects the response of smooth muscle cells to injury. To determine the time course of inhibition of intimal hyperplasia by radiation, 135 rats were given single-fraction external gamma irradiation (1-10 Gy) to one carotid artery at intervals from 5 days before to 5 days after bilateral carotid artery balloon catheter injury, and intimal cross-sectional area was determined from histological sections at 20 days after injury. There was a prominent time- and dose-dependent inhibition of intimal hyperplasia by radiation when it was administered before or after balloon injury, with the greatest effect noted within 24 h before or after injury. To investigate the effect of radiation on smooth muscle cell growth (by cell counting) and proliferation, cell cycle kinetics (by BrdU incorporation), and cell killing (by clonogenic assay), smooth muscle cell cultures derived from rat aortic explants were seeded in equine plasma to induce quiescence, and radiation (2.5-10 Gy) was administered at various intervals before or after synchronous growth stimulation by 10% whole blood serum. A similar time and dose dependence was noted in growth kinetics, BrdU incorporation and cell killing for smooth muscle cells irradiated in vitro; in each case, the effect was most prominent for radiation administered in temporal proximity to stimulation with whole blood serum. By Western blot analysis, cultured smooth muscle cells showed a rapid time-dependent increase in Cdkn1a (formerly known as p21) protein expression, followed by a delayed increase in Tp53 (formerly known as p53) expression after irradiation. Activation of intracellular caspases, manifest by proteolytic poly(ADP-ribose) polymerase (PARP) cleavage, was not detected in smooth muscle cell cultures after irradiation. These observations suggest that radiation limits intimal hyperplasia in vivo by a transient, reversible process. Although apparent cytotoxic injury occurs in vitro, apoptosis of smooth muscle cells is not apparent. Both inhibition of proliferation of smooth muscle cells and cell cycle delay may contribute to inhibition of intimal hyperplasia in vivo by radiation.

Effects of radiation on cerebral vasculature: a review

Radiation therapy plays a critical role in the treatment of central nervous system neoplasms and cerebral arteriovenous malformations. The deleterious effects of radiation on cerebral arteries may be the primary limitation to these treatment methods, as radiation may cause a variety of cerebrovascular injuries and hemodynamic changes. Radiation-induced changes in the cerebral arterial wall are determined by a number of cellular processes in endothelium and smooth muscle cells that modulate differences in radiosensitivity and phenotypic expression. The histopathological findings in arterial radiation injury include vessel wall thickening, thrombosis, luminal occlusion, and occasional telangiectases. Mechanisms for radiation injury to blood vessels include phenotypic changes in normal vessel wall cells (especially endothelium) manifested by the expression or suppression of specific gene and protein products that affect cell cycle progression or cellular proliferation or demise via cytotoxic injury or apoptosis. This review describes the molecular and cellular events involved in the systemic and cerebral vascular response to radiation and the potential means by which these responses may be influenced to augment the therapeutic effects of radiation while minimizing the untoward consequences.

Long-term coronary vascular response to (32)P beta-particle-emitting stents in a canine model

BACKGROUND

The arterial placement of (32)P beta-particle-emitting stents in various experimental animal models results in discordant effects on neointimal formation. We studied the vascular effects of beta-particle-emitting stents in normal canine coronary arteries because compared with pigs and rabbits, the canine model may more closely mimic the vascular response of humans.

METHODS AND RESULTS

Thirty stents (control nonradioactive, n=10; low-activity (32)P, 3.5 to 6.0 microCi, n=11; high-activity (32)P, 6.5 to 14.4 microCi, n=8) were implanted in normal canine coronary arteries through the use of a single balloon inflation at nominal pressure. Histological analysis after 15 weeks included the measurement of neointimal and adventitial area and thickness. Neointimal fibrin area was measured with the use of computer-assisted color segmentation on Movat pentachrome sections. Luminal stenosis was significantly increased in (32)P stents compared with control stents (44.6+/-16.8% versus 32.7+/-10.8%; P=0.05) and was highest in the high-activity group (45.5+/-24.3%). No evidence of an "edge effect" was seen in adjacent, nonstented coronary segments. All (32)P stents showed incomplete vascular healing as indicated by a dose-dependent increase in fibrin area with increasing stent activity. Arterial radiation resulted in a decrease in adventitial size, which was maximal for high-activity (32)P stents, indicating an inhibitory effect on the adventitial response to injury.

CONCLUSIONS

(32)P beta-particle-emitting stents have adverse vascular effects at 15 weeks in the canine normal coronary artery model. Vascular brachytherapy with this device causes increased neointimal formation and prominent, dose-dependent lack of healing.

Modulation of protein expression and activity by radiation: relevance to intracoronary radiation for the prevention of restenosis

Restenosis is a common complication of percutaneous transluminal coronary angioplasty. Recent studies have demonstrated a striking reduction in the neointimal hyperplasia characteristic of restenosis following intracoronary radiation (IR), but the mechanisms by which radiation reduces neointima formation following balloon overstretch injury are not elucidated fully. In addition to direct antimitotic effects mediated via oxygen free radicals, ionizing radiation can induce the expression of numerous genes and thereby mediate indirect effects. Additionally, IR prevents restenosis at the cost of decreased healing and increased thrombosis, and we suggest that these adverse reactions can be modulated by adjunct pharmacology or gene-based strategies. This review discusses several genes and proteins modulated by radiation in the context of arterial injury, and their possible therapeutic relevance.

Dose and dose rate effects of beta-particle emitting radioactive stents in a porcine model of restenosis

BACKGROUND

Radioactive stents have been proposed as a means to prevent in-stent restenosis by inhibiting intimal proliferation with continuous low-dose irradiation.

OBJECTIVES

The purpose of this study is to determine the effects of cumulative dose and dose-rate delivery on neointimal formation using 32P and 90Y beta-particle emitting radioactive stents in a porcine coronary model of restenosis.

METHODS AND MATERIALS

We compared the late histologic results of 0.25 to 32.0 microCi 90Y (half-life 64 hours) (n = 64 stents) and 0.1 to 57.6 microCi 32P (half-life 14.3 days) (n = 55 stents) Beta-particle emitting radioactive stents with non-radioactive (n = 40) stents in a porcine coronary model of restenosis. A computer-based dosimetry modeling program was used to determine the 28 day cumulative dose and dose-rate delivery for the beta-particle emitting radioactive stents at a distance of 0.1 mm from the stent surface.

RESULTS

Continuous low dose-rate (1 to 5 cGy/hr) radiation delivery for > 2 weeks via a 0.1 to 0.5 microCi 32P radioactive stent effectively reduced in-stent neointimal hyperplasia at 90 days. Cumulative doses of > 55 Gy induced severe adventitial fibrosis, microvascular damage and promoted the formation of a matrix-rich neointima. Delayed vascular repair was evident at focal regions within the body of radioactive stents that delivered cumulative doses of > or = 140 Gy at 28 days and cumulative doses of 1,100 Gy at 90 days.

CONCLUSIONS

These data may be useful in predicting safe and effective dose and dose rate delivery for beta-particle emitting radioactive stents.

Cellular effects of beta-particle delivery on vascular smooth muscle cells and endothelial cells: a dose-response study

BACKGROUND

Although endovascular radiotherapy inhibits neointimal hyperplasia, the exact cellular alterations induced by beta irradiation remain to be elucidated.

METHODS AND RESULTS

We investigated in vitro the ability of 32P-labeled oligonucleotides to alter (1) proliferation of human and porcine vascular smooth muscle cells (VSMCs) and human coronary artery endothelial cells (ECs), (2) cell cycle progression, (3) cell viability and apoptosis, (4) cell migration, and (5) cell phenotype and morphological features. beta radiation significantly reduced proliferation of VSMCs (ED50 1.10 Gy) and ECs (ED50 2.15 Gy) in a dose-dependent manner. Exposure to beta emission interfered with cell cycle progression, with induction of G0/G1 arrest in VSMCs, without evidence of cell viability alteration, apoptosis, or ultrastructural changes. This strategy also proved to efficiently inhibit VSMC migration by 80% and induce contractile phenotype appearance, as shown by the predominance of alpha-actin immunostaining in beta-irradiated cells compared with control cells.

CONCLUSIONS

32P-labeled oligonucleotide was highly effective in inhibiting proliferation of both VSMCs and ECs in a dose-dependent fashion, with ECs showing a higher resistance to these effects. beta irradiation-induced G1 arrest was not associated with cytotoxicity and apoptosis, thus demonstrating a potent cytostatic effect of beta-based therapy. This effect, coupled to that on VSMC migration inhibition and the appearance of a contractile phenotype, reinforced the potential of ionizing radiation to prevent neointima formation after angioplasty.

Irradiation for the treatment of intimal hyperplasia

Intimal hyperplasia represents a serious complication limiting the long-term benefits of vascular interventions such as balloon angioplasty and stent placement. Although pharmacological interventions have attempted to curtail restenosis, they have not been shown to be effective to date. Radiotherapy is one alternative that has shown promise as an inhibitor of intimal hyperplasia in several animal models. Irradiation causes cell death by producing irreparable damage to DNA. This is believed to be the mechanism of inhibition of VSMC proliferation. Delivery of irradiation can be either intraluminal via an angiographically directed catheter or extraluminal using an external radiation source such as an x-ray device. Intraluminal irradiation has generally utilized either gamma or beta-emitting sources. Both have been effective in producing a dose response, although some studies advocate the use of beta-type irradiation as a safer, more efficient means of delivery. Extraluminal irradiation also has been an effective inhibitor of intimal hyperplasia. Studies suggest that this form of irradiation provides a more even-dose distribution to vessel walls than an intravascular delivery system. The use of radiotherapy has more recently been extended to clinical trials, and initial studies have shown promising results. The success of irradiation must be balanced with its potential complications including radiation-induced arteritis, coronary artery stenosis, and secondary development of malignancy. Although these have been associated with irradiation, the dose used in these cases was often considerably higher than those used in the treatment of intimal hyperplasia. Finally, with the advent of gene therapy, irradiation may provide an additional means of supplementing this new type of therapy through radiation-inducible gene therapy.

Carotid artery stenosis in patients who have undergone radiation therapy for head and neck malignancy

Although it is established that small and medium sized arteries undergo extensive radiation damage, the effect on large vessels such as the carotid arteries is less well understood. We sought to determine if an increased severity of carotid artery stenosis is present in patients who have undergone radiotherapy for head and neck tumours. 45 patients aged 43-90 years (average 67) with head and neck malignancies treated with radiotherapy underwent colour Doppler ultrasonographic scanning of the carotid arteries. These patients were compared with a population of asymptomatic historical controls. 60% of patients demonstrated stenosis ranging from 21 to 86%. 38% of patients demonstrated a stenosis greater than or equal to 50%. Carotid artery stenosis appears to be increased in patients who have previously undergone treatment with radiotherapy to the head and neck regions compared with controls (p < 0.001). These findings suggest that radiation has an adverse effect on large vessels. Colour Doppler follow-up may be indicated for patients receiving head and neck radiation therapy.

Cellular and molecular mechanisms of radiation inhibition of restenosis. Part I: role of the macrophage and platelet-derived growth factor

PURPOSE

The major radiobiological issue in determining the rationale for the use of radiation to inhibit vascular restenosis is the identification of the target cell(s) and/or cytokine(s) responsible for neointimal hyperplasia and vascular remodeling. The central hypothesis of this report is that the macrophage/monocyte and PDGF are key elements in the process of neointimal hyperplasia seen following angioplasty, similar to their role in lesion formation and progression found in atherosclerotic thickening. Specific immunohistochemical and cytochemical stains were applied to a rat carotid model in a temporal series after balloon angioplasty to determine macrophage activity vs. smooth muscle cell proliferation, the latter being classically thought to be the cell responsible for restenosis.

METHODS AND MATERIALS

Neointimal hyperplasia was created in an established rat carotid artery model by a balloon catheter technique. Immediately following injury, treatment groups received irradiation via high dose rate (HDR) brachytherapy, the 192Ir source being placed externally to the vessel. Radiation was delivered to a length of 2 cm of the injured vessel at doses of 5, 10, and 15 Gy, and the animals were sacrificed at various time points following treatment (24 h to 6 months). Serial sections of tissue were stained immunohistochemically with the primary antibodies CD11b, mac-1, anti-PDGF, and alpha-smooth muscle actin.

RESULTS

Immediately (24 h) postinjury, there is an apparent migration of macrophages seen in the adventitia; after 1 week, proliferation and migration of macrophages could be seen clearly within all the vessel layers, especially in the intima; by 3 weeks, when there was evidence of neointimal hyperplasia, macrophages could still be seen, mainly in the intima scattered among the smooth muscle cells and myofibroblasts, and to a lesser degree at 6 months. There was corresponding expression of PDGF, whenever and wherever there were zones of activation/neointimal hyperplasia. Alpha-smooth muscle actin staining identified the smooth muscle cells distinct from the macrophages, and these SMCs exhibited activation in the neointimal hyperplasia zones at all later time points. Furthermore, we showed that radiation significantly reduced the macrophage population, while the onset of neointimal hyperplasia was accompanied by a return of the macrophage population.

CONCLUSION

Our results suggest that the activated adventitial macrophage/monocyte are the key cells responsible for initiating the arterial neointimal hyperplasia and vascular remodeling developing postangioplasty as they are in the initiation and perpetuation of atheromatous thickening. Irradiation delivered immediately postinjury is, therefore, highly effective, because the macrophage population is exquisitely radiosensitive.