Eur J Cardiothorac Surg 2006;29:334-342
© 2006 Elsevier Science NL
Adjunct brachytherapy: a new concept to prevent intimal hyperplasia after surgical endarterectomy?
Carsten J. Beller
a
,
*
,
Jens Kosse
a
,
Tamás Radovits
a
,
Robert Krempien
b
,
Marie-Luise Gross
c
,
Irina Berger
c
,
Siegfried Hagl
a
,
Gábor Szabó
a
a Department of Cardiac Surgery, University of Heidelberg, INF 110, 69120 Heidelberg, Germany
b Department of Clinical Radiology, University of Heidelberg, Germany
c Department of Pathology, University of Heidelberg, Germany
Received 28 July 2005;
received in revised form 28 November 2005;
accepted 5 December 2005.
* Corresponding author. Tel.: +49 6221 566246; fax: +49 6221 564571. (Email: Carsten.Beller{at}urz.uni-heidelberg.de).
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Abstract
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Objective: Endarterectomy represents a therapeutical option for patients with advanced coronary artery disease. The mid-term results are compromised by restenosis due to neointima formation. The aim of this study was to evaluate a new treatment concept – endarterectomy with consecutive gamma-irradiation – in a rat model. Methods: Male Sprague–Dawley rats underwent left carotid endarterectomy with removal of intima: control (n
= 10) or were irradiated with 15 Gray (Gy) (n
= 13) or 20 Gy (n
= 10) postoperatively and compared with sham-operated rats (n
= 10). After 3 weeks, carotid arteries were perfusion-fixed and vessel compartment areas were measured. Transmission electron microscopy and immunohistochemical staining were used to confirm neointima formation. Results: Three weeks after endarterectomy, neointimal hyperplasia was found in the control group (0.07 ± 0.04 mm2). After irradiation, a dose-dependent reduction of neointima was observed (0.003 mm2 at 15 Gy and 0.0007 mm2 at 20 Gy, P
< 0.0001). However, immunohistochemical staining revealed that thin re-endothelialization after irradiation was not inhibited. Conclusions: Gamma-irradiation significantly suppressed neointimal hyperplasia in a rat model of surgical endarterectomy. Despite inhibition of intimal hyperplasia, re-endothelialization after adjuvant brachytherapy was present. Adjuvant brachytherapy may be therefore a new concept to prevent restenosis after endarterectomy in patients.
Key Words: Endarterectomy • Brachytherapy • Neointima • Restenosis
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1. Introduction
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Carotid endarterectomy (CEA) is supported by level 1 evidence as the standard treatment of severe carotid stenosis in both symptomatic and asymptomatic patients [1–3]. Operative repair is not without potential complications, one of which is postoperative restenosis. The overall restenosis rate can be as high as 31% [4]; a recent analysis of CEA anatomic durability during a median follow-up period of 5.9 years identified a 7.7% failure rate with elevated serum cholesterol as risk factor for early restenosis [5].
With the increased frequency of interventional procedures, patients referred for coronary revascularization often present a surgical challenge. Coronary endarterectomy with or without venous patch reconstruction is a treatment option for these patients to achieve complete revascularization. However, surgical risk is increased compared to conventional revascularization [6]. The patency rate of endarterectomized coronary arteries (72 ± 11% at 30.4 months) is lower compared to those after carotid endarterectomy [6]. Despite technical problems, the main causes for restenosis after surgical vessel reconstruction are neointimal hyperplasia (IH), recurrent atherosclerosis and arterial wall remodeling.
Adjunct brachytherapy, so far only shown to be effective to reduce in-stent restenosis after primary coronary interventions [7], may positively affect the unresolved problem of restenosis after surgical vessel reconstruction. Serial intravascular ultrasound studies have shown that the long-term results after brachytherapy in conjunction with interventional procedures depend on a balance between arterial remodeling and neointimal hyperplasia [8]. Late thrombosis after irradiation is a serious complication with an incidence of 3–10%; recently a persistent upregulation of platelet endothelial cell adhesion molecule (PECAM)-1 (CD31) after radiation exposure was shown to play a key role in platelet adhesion and aggregation on endothelial cells [7].
Therefore, we investigated in carotid arteries of rats the influence of adjunct gamma-irradiation on neointima proliferation and arterial wall remodeling after endarterectomy. Furthermore, potential adverse effects of this new treatment concept were assessed, paying special attention to the vascular responsiveness after irradiation.
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2. Materials and methods
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2.1 Rat CEA model
The protocol was approved by the Regional Ethical Committee for Laboratory Animal Use and all animals received humane care in compliance with the European Convention on Animal Care.
Thirty-three male Sprague–Dawley rats (350–400 g body weight) underwent left carotid endarterectomy with removal of intima. Animals were randomly assigned to the different treatment groups. For the sham operation, the carotid artery was exposed but not incised.
After adequate anesthesia with an intraperitoneal injection of ketamine hydrochloride (100 mg/kg) and xylazine hydrochloride (5 mg/kg) the left common carotid artery was exposed under a dissecting microscope via a midline cervical incision. After placing two Yasargil clamps at the proximal and distal ends of the carotid artery a longitudinal arteriotomy was made with a corneal blade and extended to 6 mm with micro-scissors. To denude the endothelium, a sterile cotton-tipped applicator immersed in saponin (0.1%) was rubbed on the inner vessel surface; this chemical skinning technique was used to preserve vascular smooth muscle function postoperatively [9]. Compared to mechanical removal of intima, this method was found to be easily standardized and being especially suitable for small vessels [9]. Completeness of endothelial removal after saponin treatment was assessed by histologic cross-sections and additional analysis of vasomotor function (using the protocol described below). The arteriotomy was closed with a running 10-0 monofilament nylon suture (Ethilon, Ethicon Inc., Somerville, USA). The superficial cervical muscles and skin were closed with running 4-0 adsorbable sutures.
Directly after the operation, while animals were still under anesthesia, a long-distance (1 cm x 2 cm) external gamma-radiation with 15 Gray (Gy) (N
= 13) and 20 Gy (N
= 10) from a 10 MV linear accelerator (Siemens KD2, Concorde, USA) or no radiation (N
= 10) was applied. Animals were placed postoperatively on standard rat diet and water ad libitum. After 21 days carotid arteries were perfusion-fixed with 4% neutral buffered formalin and harvested.
2.2 Histological analysis
All histologic evaluations were done independently by two pathologists blinded to the study protocol. Morphometry was performed in three hematoxylin–eosin stained cross-sections of each animal (proximal, mid and distal region of the operated vessel segment) using computer-aided planimetry (Q-Win, Leica, Germany). Luminal, intimal and medial dimensions were computed using the internal and external elastic laminae as delimeters. Histologic evaluation of the corresponding cross-sections included the degree of injury and inflammatory response. A numeric value from 0 (no injury) to 3 (most injury) was assigned: 0 = no injury, 1 = break in internal elastic membrane, 2 = perforation of the media and 3 = perforation of the external elastic membrane to the adventitia. Furthermore, the inflammatory response in these cross-sections was scored as follows: 0 = no inflammatory cells present, 1 = light lymphohistiocytic infiltrate, 2 = moderate to dense localized cellular aggregates and 3 = circumferential dense lymphohistiocytic cell infiltration. Inter-rater variability was low and consistent injury and inflammatory scores were obtained.
2.3 Immunohistochemical staining
Immunohistochemistry was performed in six representative animals of each group. Antibodies for markers with a potential role in the pathogenesis of atherosclerosis were chosen in order to characterize the cellular infiltrate and the expression of various antigens during arterial remodeling after endarterectomy. The samples were embedded in paraffin and were reacted with the following antibodies using the avidin biotin method: 
-smooth muscle actin (-sm actin, monoclonal mouse, Sigma, Steinheim, Germany), transforming growth factor ß1 (TGF-ß1, anti-TGF-ß1 rabbit polyclonal IgG, Santa Cruz Biotechnology, Santa Cruz, CA, USA), platelet-derived growth factor-AB (PDGF-AB, polyclonal goat, Upstate Biotechnology, Lake Placid, NY, USA), von Willebrand factor (vWF, polyclonal goat, Santa Cruz, CA, USA), C-reactive protein (CRP, polyclonal sheep, Biotrend, Cologne, Germany) and PECAM-1 (CD31) (polyclonal goat, Santa Cruz, CA, USA). The concentration that was optimal for staining was evaluated testing different dilution series in a pilot study. The following dilutions of antibodies were used: -sm actin 1:50, TGF-ß1 1:40, PDGF-AB 1:100, vWf 1:25, CRP 1:200 and PECAM-1 (CD31) 1:100. Immunohistochemical staining for nitrotyrosine (NT) as marker of nitrosative stress, and more specifically of the generation of peroxynitrite, was performed to assess the potential trauma of adjunct brachytherapy. Primary antibody was rabbit polyclonal antibody (dilution 1:400, Upstate Biotechnology). Negative controls were performed by omitting the primary antibody.
Immunohistochemical stainings were evaluated by the COLIM software package (Pictron Ltd., Budapest, Hungary). A digital camera was used to input microscopic pictures from a low power (16–40x) magnification of the whole section and a high power (400x) examination of 20 adjacent fields. First, positively stained areas were separated from each other and from the background based on the intensity of different colors in the specimen. The colors were measured using densitometry and put in five color classes: one class for background staining and four classes for positively stained areas. On the basis of the measured intensity, the color classes were coupled with score values as follows: 0: no positive staining, 1–3: increasing degrees of intermediate staining and 4: extensive staining. The program automatically measured the area of the objects in each class in each field, assigned an area score (1 = up to 10% positive cells, 2 = 11–50% positive cells, 3 = 51–80% positive cells, 4 = >80% positive cells), and calculated an average score for the whole picture (intensity score multiplied by area score). Finally, each specimen was characterized with the average of the 20 adjacent fields.
2.4 Transmission electron microscopy
Part of the specimens was fixed with 1% glutaraldehyde in cacodylate buffer, postfixed in 2% OsO4 overnight, and embedded in an epoxy resin. All specimens were examined under a light microscope to determine the area of greatest intimal thickening or areas of re-endothelialization, which were then chosen for electron microscopic analysis. Thin sections were stained with uranyl acetate and lead citrate stain for transmission electron microscopy.
2.5 Analysis of vasomotor function
To evaluate vascular function after irradiation we used rat thoracic aortae, which were harvested under intraperitoneal anesthesia with ketamine hydrochloride (100 mg/kg) and xylazine hydrochloride (5 mg/kg) and quickly placed in oxygenated, cold (4 °C) Krebs–Henseleit solution (KHS). After cleaning of fat and connecting tissue under a microscope, the aortae were cut into 4 mm rings. Extreme care was taken to avoid stretching the vessels or touching the luminal surfaces to preserve the integrity of the endothelium. Then, aortic rings (n
= 27, N
= 7) were gamma-irradiated with 20 Gy from a 10 MV linear accelerator (10 Gy/min, Siemens KD2, Concorde, USA) or served as control (n
= 27, N
= 8). Aortic rings were mounted with triangle stainless steel wires and placed in organ chambers (Radnoti, Monrovia, CA, USA) filled with 30 ml KHS (pH 7.4, 37 °C) and gassed with 95% O2/5% CO2. The composition of KHS was 118 mM NaCl, 4.7 mM KCl, 0.9 mM KH2PO4, 25 mM NaHCO3, 1.2 mM MgSO4, 12.2 mM glucose and 1.7 mM CaCl2. Rings were passively stretched (2 g) and equilibrated for 60 min. Phenylephrine (PE; 5 x 10–7
mol/l) was used to achieve a submaximal contraction. An endothelium-dependent vasorelaxation was induced by the addition of cumulative acetylcholine (ACh) concentrations (10–8 to 10–3
mol/l). Sodium nitroprusside (SNP, 10–10 to 10–6
mol/l) was added to mediate a direct vascular smooth muscle cell relaxation. Finally, the contraction generated by KCl (70 mmol/l) was assessed. All chemicals were purchased from Sigma (Steinheim, Germany).
2.6 Statistical analysis
Values are expressed as mean ± SD. The results of the functional measurements are shown as mean ± SEM. Statistical comparisons were determined by Student's t-test or by ANOVA followed by an unpaired Student's t-test with Bonferroni's correction for multiple comparisons. For ordinal data Kruskal–Wallis test was carried out for comparisons between groups. A value of P
< 0.05 was considered statistically significant. N refers to the number of animals and n to the number of aortic rings for analysis of vasomotor function.
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3. Results
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3.1 Influence of external gamma-irradiation on arterial wall remodeling after surgical vessel reconstruction
Three weeks after surgical endarterectomy, an eccentric proliferating neointima was found in the control group that was significantly different from that of the irradiated groups (P
< 0.0001, Fig. 1A and C). Maximal neointima thickness was 0.23 mm in the control group. After irradiation, dose-dependent reduction of neointimal formation was observed. Neointimal growth was nearly completely suppressed in the 20 Gy group (Fig. 1A). Additionally, neointima to media thickness ratio was significantly reduced after irradiation (P
< 0.0001, Fig. 1B). However, despite inhibition of neointima hyperplasia after irradiation, homogenous areas with thin re-endothelialization were present in the 15 Gy and 20 Gy groups (Fig. 2
). Luminal area was similar in all treatment groups (Table 1
).
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Fig. 1. Morphometric results and representative histologic cross-sections of the different treatment groups (hematoxylin–eosin). (A) neointima area; (B) intima/media thickness ratio; (C) wall section of the carotid artery in the sham group (magnification 100x); (D) overview of the carotid artery in the control group with eccentric neointima proliferation (magnification 50x); (E) overview of the carotid artery in the 15 Gy group (magnification 50x); (F) overview of the carotid artery in the 20 Gy group, the arrow marks an area of necrotic media and adventitia with adherent leukocytes on the luminal surface (magnification 50x).
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With increasing radiation dose an increase of media area occurred in the 15 Gy and 20 Gy groups, and there was a trend towards neoadventitia formation (Table 1).
3.2 Inflammatory response and endothelial regeneration after endarterectomy and consecutive irradiation
The overall injury score of the operated vessels was not found to be different between the treatment groups (control group vs the irradiated groups, Table 1). The overall inflammation score in the vessel wall was only significantly higher in the 20 Gy group compared to the sham and the control group (Table 1). This finding is linked to the presence of areas with focal media and adventitia necrosis with surrounding leukocyte infiltration after irradiation with 20 Gy (Fig. 1E). Correspondingly, the nitrosative stress in the adventitia was significantly higher in the irradiated groups compared to control (Table 2
) and there was a trend towards increased expression of CRP in the 20 Gy group (Table 2).
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Table 2. Immunohistochemical scores for deposition of markers for nitrosative stress (nitrotyrosine, NT) and inflammation (C-reactive protein, CRP) in the vessel wall layers of the different groups
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In the control group there was a significant immunoreactivity for nitrotyrosine and CRP only in the intima reflecting neointima formation (Table 2). However, after irradiation the NT-score of the regenerated intima was less or the same compared to native carotid arteries.
Neointima formation in the control group was confirmed by different immunohistochemical markers, namely CD31, vWf and -sm actin (Table 3
), and additionally by transmission electron microscopy. After irradiation, re-endothelialization, as layer of endothelial cells with significantly enhanced CD31 (PECAM-1) expression, was present in the 20 Gy group, although intimal hyperplasia was inhibited (Fig. 2).
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Table 3. Immunohistochemical scores for content of -smooth muscle actin (-sm actin) and von Willebrand factor (vWF) as marker for neointima proliferation, deposition of adhesion molecule CD31 and of growth factors (platelet-derived growth factor AB, PDGF-AB; transforming growth factor-ß1, TGF-ß1) in the vessel wall layers of the different groups
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3.3 Effect of irradiation on growth factor and adhesion molecule expression in the vessel wall layers after endarterectomy
The vessel wall layers of the endarterectomized vessels were analyzed regarding possible differences in expression of growth factors after consecutive irradiation to assess possible adverse effects. The results are summarized in Table 2.
In the adventitia of the 15 Gy group, there was a significantly increased score for -smooth muscle actin compared to the sham and the 20 Gy group. Expression of vWf, PDGF-AB and TGF-ß1 was also significantly higher in the adventitia of the 15 Gy group compared to sham-operated vessels. After irradiation with 20 Gy, there was only increased expression of PDGF-AB in the adventitia. This difference in deposition of growth factors and adhesion molecules may be related to areas of necrosis with less viable cells in the adventitia after irradiation with 20 Gy.
3.4 Validation of the endarterectomy model
Histologic cross-sections showed complete removal of endothelial cells after saponin treatment (Fig. 3A). In addition, lack of endothelium was confirmed by analysis of vasomotor response of rat aortic rings after saponin treatment. Endothelium-dependent relaxation in response to ACh was completely absent (Fig. 3B), whereas endothelium-independent relaxation in response to SNP was unaltered showing preserved vascular smooth muscle function (Fig. 3C).
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Fig. 3. Morphology and vasomotor response of aortic rings after saponin treatment. (A) Section of saponin-treated aortic ring (hematoxylin–eosin, magnification 400x). The complete removal of the endothelium on the luminal side (top) after saponin treatment can be appreciated with remaining intact media. (B) Absence of endothelium-dependent relaxation induced by acetylcholine (ACh) in saponin-treated rings. (C) Preserved endothelium-independent relaxation induced by sodium nitroprusside (SNP) after saponin treatment.
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3.5 Vasomotor function after irradiation
After irradiation with 20 Gy, rat aortic rings were precontracted to submaximal level with PE (5 x 10–7
mol/l). Maximal contraction induced with KCl (70 mmol/l) was similar in both groups, whereas PE-induced contraction in irradiated aortic rings was significantly less than in native rings (Fig. 4A). However, endothelium-dependent relaxation induced by ACh did not differ between irradiated and non-irradiated rings (Fig. 4B). Furthermore, direct vascular smooth muscle cell relaxation in response to SNP was not impaired after irradiation (Fig. 4C).
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Fig. 4. Vasomotor response of aortic rings after irradiation with 20 Gy. (A) Phenylephrine-induced (PE, 5 x 10–7
mol/l) and potassium chloride-induced (KCl, 70 mmol/l) contraction forces. (B) Endothelium-dependent relaxation induced by acetylcholine (ACh). (C) Endothelium-independent relaxation induced by sodium nitroprusside (SNP).
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4. Discussion
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To our knowledge, this is the first study to assess the effects of irradiation on arterial wall remodeling after surgical vessel reconstruction in a rat CEA model. This endarterectomy model produced a substantial neointima hyperplasia in the control group, which was inhibited 21 days after external irradiation with 15 Gy and 20 Gy. Despite this inhibitory effect of irradiation, re-endothelialization in the endarterectomized vessel segments was present. Furthermore, after irradiation with 20 Gy vasorelaxation was not impaired.
In rat carotid injury models this inhibitory dose-dependent effect of external gamma-irradiation on neointima proliferation has been shown only after vessel overstretch using a balloon catheter [10,11]. However, we believe our surgical model with an arteriotomy, removal of intima and suture line more closely mimics endarterectomy in patients. Furthermore, in our surgical model the vascular injury was defined and similar in all groups, and no dilatation of the arterial wall occurred.
Interestingly, the nitrosative stress in the intima after irradiation was significantly lower than in the non-irradiated groups, whereas neointima formation was associated with increased nitrosative stress probably as signaling mechanism for the vascular response after injury [12]. The eccentric proliferating neointima was positive for -sm actin and vWF, which reflects the atherogeneous property. The re-endothelialized vessel segments after irradiation expressed mostly CD31 (PECAM-1), which was significantly higher in the 20 Gy group. Recently this upregulation of endothelial PECAM-1 was shown to be persistent up to 21 days in human microvascular endothelial cells from lung after irradiation with 10 Gy [13], and our study underlines the possible thrombogenity of re-endothelialized vessel segments after irradiation. Therefore, postoperative enforced anti-platelet therapy seems mandatory for the proposed treatment concept in the clinical arena.
After irradiation with 20 Gy, areas of focal necrosis of the media and adventitia were observed in the vessel wall. This is in accordance with another animal study of brachytherapy application after arterial injury, which showed media necrosis after external radiation with 20 Gy and severe media fibrosis after 25 Gy [14]. Corresponding to necrosis development leukocytes were infiltrating the vessel wall and the resulting inflammatory response led to increased expression of CRP in the adventitia after irradiation with 20 Gy. The increased nitrosative stress in the outer vessel wall layers after irradiation may trigger this process.
The observed increase of media area after irradiation may be partly related to edema and necrosis formation in the 20 Gy group, whereas in the 15 Gy group enlarged intact media was found. Although gamma-irradiation with 20 Gy is an established dose for human application after cardiological interventions [15], referring to our study this dose seems too high for application after endarterectomy and may contribute to adverse effects of brachytherapy such as spontaneous dissection or aneurysm formation.
The trend towards neoadventitia formation concomitant to neointima inhibition after irradiation in our study is in accordance to a study of Wexberg et al. [16]. However, in the 20 Gy group there were significantly fewer adventitial -sm actin-positive myofibroblasts compared to the 15 Gy group, this may explain the observed differences in deposition of various growth factors in the adventitia of both groups. Increased deposition of vWf, as seen in the 15 Gy group, has been reported as dose-dependent deposition in the capillaries of rat myocardium after irradiation with both 15 Gy and 20 Gy, preceding development of fibrosis in the subendocardial layers [17]. Additionally, there was an increased deposition of TGF-ß1 in the adventitia of the 15 Gy group. Although it is known that TGF-ß1 is a key molecule and master switch for the general fibrotic programme [18], and contributes to migration of adventitial fibroblasts in the process of neointima formation after balloon injury [19], it has to be kept in mind that activities of growth factors are highly context-dependent in nature [20], and particularly after irradiation [21]. TGF-ß1 is a multi-functional cytokine exerting in vivo three main biological activities. Firstly, it is a key cytokine in the regulation and generally inhibition of cell growth. Secondly, it exerts immunosuppressive activities. Thirdly, it regulates the deposition of extracellular matrix components. TGF-ß1 thereby regulates among other cytokines PDGF by stimulating or inhibiting their production in various cell types, including fibroblasts, endothelial cells and smooth muscle cells [22]. The observed higher content of PDGF-AB in the adventitia after irradiation may be related to TGF-ß1 activity. However, the complex interplay and pattern of irradiation-induced changes in growth factor activity is currently not fully understood and the interpretation of the observed differences regarding their biological importance seems difficult. In the clinical setting of endarterectomy, the arteriosclerotic vessels show already fibrotic changes and the beneficial effect of adjunct brachytherapy to prevent intimal hyperplasia and consecutive restenosis may outweigh the possible long-term risk of constrictive remodeling.
From animal studies it is well known that the therapeutic window for irradiation after vascular injury is limited to latest about 5 days after the injury [15]. At a later stage, the application of irradiation leads even to adverse effects such as stimulation of intimal hyperplasia [15]. For the interventional procedures in cardiology it is the preferred concept to apply irradiation directly after recanalization of a vessel. In our proposed setting it would be the best approach to irradiate the endarterectomized vessel segment by intraoperative radiation devices using electrons or by inserting a wire to apply brachytherapy, when the chest is still open. The cardioplegic arrest would facilitate this approach and reduce substantially undesired cardiac irradiation of the beating heart. Furthermore, a few days after the procedure a catheter-based approach for irradiation would be risky regarding injury of the long-distance anastomosis or it may be technically impossible to reach the vessel segment from the origin of the stenotic vessel. The use of electrons or brachytherapy with a steep dose gradient exposes only a few millimeters of the adjacent myocardium to radiation. Our proposed dose of 15 Gy is an established dose for patients in the setting of interventional procedures [15].
To assess possible adverse effects of irradiation of the new treatment concept on adjacent intact vessel segments, the vascular response of rat aortic rings to contracting and relaxing agents was examined. Both, the endothelium-dependent and –independent vasorelaxation did not differ after irradiation with 20 Gy compared to control. This finding is similar to a study of Levesque et al. [23], in which endothelium-dependent and -independent relaxation was not impaired after external beta high-dose rate irradiation. Endothelium-dependent relaxation in that study was only impaired due to vessel overstretch and endothelial disruption using a balloon catheter for gamma-irradiation, but not through gamma-irradiation itself. Although there are also studies showing endothelial dysfunction after irradiation [24], recently a study found even gamma-irradiation induced ACh-evoked endothelium-independent relaxation of endothelium-denuded pulmonary artery rings [25].
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5. Limitations of the study
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The carotid endarterectomy model used in this study does not resemble the complex situation of a severely diseased atherosclerotic artery in a patient, however, the native rat carotid artery is an established model of intimal hyperplasia [10,11]. We used this model to study our proposed treatment concept first as proof of the principle. Additionally, it has to be noted that animal models of atherosclerosis also lack direct comparability to the human situation. Even knock-out models have pathophysiological and phenotypic differences regarding plaque etiology and morphology. However, further studies with animal models of atherosclerosis are warranted in the future to address this issue.
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6. Conclusions
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Gamma-irradiation with 15 Gy and 20 Gy significantly suppressed neointimal hyperplasia after surgical endarterectomy in a rat model. Despite inhibition of intimal hyperplasia re-endothelialization after adjuvant brachytherapy was present. Vasorelaxation was preserved after irradiation. However, with the 20 Gy dose, adverse effects such as media and adventitia necrosis were observed, therefore 15 Gy seems to be a favorable dose without undesired side effects on vessel architecture. Adjunct brachytherapy may be therefore a new concept to prevent restenosis after endarterectomy in patients.
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Acknowledgments
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This work was supported by a Grant from the German Research Foundation (SFB 414) to C.J.B., S.H. and G.S.
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Abstract
1. Introduction
