Intimal Regeneration Research Articles

Biomimetic modification on the microporous surface of cardiovascular materials to accelerate endothelialization and regulate intimal regeneration

Vascular stents are widely used in the clinical treatment of coronary heart disease, but the long-term safety still needs to be improved. Surface biological functional modification is an effective way to improve the biocompatibility and clinical performance of cardiovascular materials, but how to achieve long-term effective and precise regulation of in situ vascular intimal repair through the reasonable construction of the surface physical and chemical structure is still an important task in the current surface modification research. In this study, ECM-derived components, including laminin, heparin, and SDF-1, were incorporated into the titanium surface with a microporous structure. It was found that the modified surface could effectively control the continuous release of biomolecules. In vitro biocompatibility evaluation results showed that the constructed functional layer could effectively inhibit the activation of platelet adhesion and excessive proliferation of smooth muscle cells. In addition, the modified surface also showed the potential to induce rapid regeneration of vascular endothelium. In vivo animal tests further proved that the modified sample may contribute to inhibiting vascular intimal hyperplasia. This study provided a new approach for the surface biological function modification of Ti-based vascular stents.

Carotid Ulceration in a Young Woman with SAPHO Syndrome

A 25 year old woman was recently diagnosed with SAPHO (synovitis-acne-pustulosis-hyperostosis-osteitis) syndrome. On magnetic resonance imaging, performed for chronic left sternoclavicular pain, incidental left common carotid artery (CCA) occlusion was diagnosed. During further diagnostic work up, duplex ultrasound also revealed newly appeared but asymptomatic intima-media ulceration of the contralateral CCA, (A, arrow), confirmed by computed tomography (B, right CCA ulceration, arrow; left CCA occlusion, asterisk). Characteristic arterial involvement associated with recurrent oral ulceration and skin lesions indicated Behçet's disease. Treatment included steroids, methotrexate, and infliximab. Duplex ultrasound after two weeks revealed healing of the ulcerated right CCA, with intimal regeneration clearly noted.Image 1

Intimal regeneration after coronary endarterectomy and onlay grafting in coronary artery bypass grafting

Coronary onlay grafting, with or without endarterectomy, has been widely used for the treatment of diffuse lesions. Recent studies have demonstrated excellent long-term patency and favorable remodeling of onlay anastomosis; however, the underlying mechanisms remain unknown. Here, we describe the mechanism of intimal regeneration based on postmortem pathological evaluation of a patient who had undergone onlay grafting with coronary endarterectomy. The onlay anastomosis was analyzed using a combination of immunohistological stainings, namely, H&E, vimentin, α-SMA, factor VIII, and Ki-67, to identify the source and mechanism of intimal regeneration after onlay grafting with endarterectomy. Our results suggest that the regenerated endothelium derives from the smooth muscle cells of the endarterectomized media of the coronary artery and that it circumferentially covers the internal lumen of the arterial graft. Intimal regeneration, derived from the smooth muscle cells of the endarterectomized coronary artery that proliferate toward the graft lumen, may be a key mechanism that underlies the observed favorable remodeling after onlay grafting during coronary endarterectomy.

Radiosurgical Dose Selection for Secreting Pituitary Adenomas

Although the healing response after carotid balloon injury and carotid patch angioplasty injury has been well-documented in animal models, there is limited information about this process after carotid endarterectomy (CEA) in human patients.We describe the autopsy results of a 79-year-old man who died 18 days after CEA with patch angioplasty. The treated carotid artery had an adequate luminal diameter. Elastica-Masson staining revealed that the treated portion was covered with neointima but the patch graft was exposed to the arterial lumen at 18 days after CEA. Immunohistochemistry staining for alpha-smooth muscle actin (α-SMA), von-Willebrand factor, and vascular endothelial growth factor receptor-2 revealed that the neointima was mainly composed of α-SMA-positive cells. In addition, the α-SMA-rich neointima had many more Ki-67-positive cells than did the internal carotid artery intima in the area beyond the CEA-treated portion.This case report is the first to describe an entire carotid artery specimen in the acute stage after CEA with patch angioplasty. These findings suggest that an α-SMA-rich neointima with prominent proliferative activity covers the inner surface of the treated carotid artery, but patch grafts are left uncovered. The intrinsic arterial wall may have an important role in intimal regeneration after CEA, although the nature of the neointima and the mechanism by which it regulates proliferative activity remain unclarified.

Effects of Atorvastatin on Vascular Intimal Hyperplasia: An Experimental Rodent Model

Vascular intimal hyperplasia is associated with increased mortality and morbidity. The authors investigated the effects of atorvastatin on vascular intimal hyperplasia. Rats were divided into 4 groups. Groups 1, 2, and 3 had experimental aortic injury and received intraperitoneal injection of atorvastatin, solvent, or 0.9% NaCl, respectively. Group 4 was a nonintervention (laparotomy only) control group. Animals were sacrificed after 3 weeks. Blood samples and injured aortic segment were analyzed. Atorvastatin administration significantly lowered total and low-density lipoprotein cholesterol levels (P = .012 and P = .001, respectively), intima-media ratio (P = .002), and intimal smooth muscle cell accumulation (P < .05) in group 1. Luminal narrowing in animals in group 1 was significantly lower than that in animals in groups 2 and 3, but was higher than in animals in group 4 (P = .009). Atorvastatin suppresses intimal hyerplasia and aids in intimal regeneration by lowering blood lipids and intimal smooth muscle cell accumulation.

Adrenomedullin gene transfer induces neointimal apoptosis and inhibits neointimal hyperplasia in injured rat artery

Arterial wall injury leads to inflammatory reaction and release of growth factors that may mediate intimal regrowth. It is hypothesized that the neointimal cells may originate from adventitial myofibroblasts, medial smooth muscle cells, or differentiated bone marrow derived cells. Adrenomedullin (AM), an auto/paracrine cardiovascular peptide that is secreted from fibroblasts, endothelial cells, and vascular smooth muscle cells, may have a regulatory role in the intimal regeneration. In order to investigate the role of AM in neointimal growth, stimulation of stem cell migration, and apoptosis, we overexpressed AM with recombinant adenovirus in a rat arterial injury model. The intimae were significantly thinner in the arteries treated with AM adenovirus compared to the control group. Intima/media ratios were 0.48 +/- 0.18 and 1.01 +/- 0.20 (P < 0.05) in the AM group and the control group, respectively. In addition, a significantly higher apoptotic index of neointimal cells was seen in the AM gene transfer group compared to the control (2.78 +/- 0.5 vs. 0.57 +/- 0.20, P < 0.01). The neointimal cells stained positive for alpha-smooth muscle actin and negative for desmin suggesting possible myofibroblast origin. Very few c-Kit+ or MDR1+ cells were detected 2 weeks after the injury. We conclude that AM overexpression inhibits neointimal growth. The inhibition is associated with enhanced apoptosis of the neointimal cells which may be of myofibroblast origin.

Synovial regeneration in the equine carpus after arthroscopic mechanical or carbon dioxide laser synovectomy.

To compare synovial regeneration in the equine carpus after mechanical or CO(2) laser synovectomy. Arthroscopic partial synovectomy was performed in the radiocarpal and intercarpal joints. Twelve horses, 3 to 6 years of age, were randomly divided into 3 groups. The antebrachiocarpal and intercarpal joints in each horse were randomly assigned a treatment such that each horse had one joint treated as a control (arthroscopic lavage), one in which a mechanical or CO(2) laser partial dorsal carpal synovectomy was performed, and one in which a combination of the mechanical and laser techniques was performed. The groups were euthanized for collection of specimens, respectively, at 1, 3, and 6 months postoperatively. The synovial membrane was evaluated grossly, histologically, and by transmission and scanning electron microscopes (TEM and SEM). The synovial villi failed to regenerate in all groups. At 1 month, the intimal cell layer was incomplete and the surface was still granulating. At 3 months, intimal regeneration was complete but more mature in the CO(2) laser synovectomy groups than in the mechanical synovectomy groups. Intimal regeneration was complete in all groups at 6 months. The subintima was replaced with fibrous tissue that separated the original subintimal vascular bed from the regenerated synovial surface. The CO(2) laser required preliminary training to operate effectively, and the air environment altered the intraoperative evaluation of the synovectomy site. Villous regeneration does not occur in horses after surgical synovectomy. All synovial membranes healed with a fibrous subintima and less populated intima. The CO(2) laser is capable of performing a more superficial synovectomy than that achieved with mechanical synovectomy using a motorized arthroscopic synovial resector. Mechanical or CO(2) laser synovectomy may be performed in the horse; however, additional evaluation is needed to determine the physiological significance of the lack of villus regeneration in this species. A combination of the resection techniques is not advised because of the increased risk of full-thickness capsular defects.

Endothelial Cells Exhibit Differential Chemokinetic and Mitogenic Responsiveness to α-Thrombin

Rapid regeneration of the endothelium is a critical component of vascular wall repair because limitations of this process enhance early thrombotic and vasospastic complications, as well as late sequelae of recurrent lesion formation. We have postulated that direct activation of the thrombin receptor initiates both mitogenic and chemokinetic endothelial behavior which facilitates intimal repair. To characterize the role of the thrombin receptor in human endothelial cell (EC) proliferation and migration, we investigated the effects of both α-thrombin (0.5–10 U/ml) and its receptor-activating peptide (TRAP; 1–100 μM). Responses of human aortic (HAEC) and umbilical vein (HUVEC) were characterized using [3H]thymidine and51Cr microcarrier bead assays of proliferation and migration, respectively. Expression of motility-related genes was evaluated using a ribonuclease protection assay. Thrombin exerts both of its chemokinetic and mitogenic effects differentially in human endothelial cells. Following 2 or 4 days in culture, HUVEC proliferation increased two- to threefold after exposure to thrombin, primarily in the low concentration range (P< 0.05). However, HAEC proliferation was inhibited up to 50% after a 4-day incubation period (P< 0.005). These mitogenic effects, including the inhibition of aortic endothelial cell proliferation, were reproduced, in part, by thrombin receptor activation with TRAP. In contrast, thrombin stimulates migratory responses in HAEC, but not HUVEC. However, this behavior was not reproduced by TRAP. It is noteworthy that urokinase-plasminogen activator (u-PA) expression was much more strongly expressed in migrating HAEC than in the HUVEC population. Moreover, when stimulated with thrombin, u-PA gene expression was significantly augmented in HAEC. It has been speculated that an effective human thrombin receptor (HTR) antagonist may reduce the proliferation of vascular smooth muscle cells and the development of a restenotic lesion following arterial wall injury. Our data suggest that such an inhibitor will likely also accelerate intimal regeneration through a dominant effect on limiting the HTR inhibitory effect on endothelial proliferation.

Fibronectin Biosynthesis in Endothelial Regeneration after Intimal Injury

In this experiment, we sought to identify the major fibronectin (FN) synthesizing cells, the source of FN production, and the role of FN in intimal regeneration. In rats in which vascular endothelial denudation had been induced, serial morphologic changes after intimal injury were studied by light and electron microscopic examination using immunohistochemical techniques and in situ hybridization. At 2 weeks after intimal injury, regenerated endothelial cells had pleomorphic cytoplasm and loose cellular junctions. Immunohistochemically, factor VIII-related antigen was localized in the regenerated endothelial cells, and immunoreaction products of FN were increased in the thickened neointima. Ultrastructurally, FN was localized in the proliferated endoplasmic reticulum of regenerated endothelial cells in the intima, while the α5 subunit of α5β1 integrin, one of the fibronectin receptors, was localized in the plasma membrane and increased endoplasmic reticulum of regenerated endothelial cells. FN mRNA was localized in a large number of regenerated endothelial cells (87.2 and 89.8%) by in situ hybridization at 2 and 4 weeks after intimal injury. These findings indicate that FN may mainly contribute to endothelial cell functions such as spreading and adhesion in the regenerative stage.

Ultrastructural localization of fibronectin in process of serial intimal regeneration

Intimal injury is considered as one of the initiation factors of atherosclerosis and intimal thickening. However the morphological elucidation after intimal injury is not so clear. On the other hand, fibronectin is a glycoprotein that play an important role in cell adhesion, migration, spreading, and differentiation. This study was designed to examine the mechanism of serial intimal regeneration after intimal injury and the localization of fibronectin using scanning and transmission electron microscope.Male Wistar rats, weighing 400g were used and endothelial denudation was produced by the modified methods of Baumgartner. A deflated vascular balloon catheter( 1.5F, DOW CORNING , Corp.) was introduced into the thoracic aorta, then inflated up to 2.5mm in diameter, and passed through the aorta three times to a length of 2.5cm. The animals were sacrificed at 15min, 3,7,14 and 28 days after denudation. For electron microscopic examination, the tissues were fixed in 2.5% glutaraldehyde in 0.1M phosphate buffer, treated with 1% osmium tetroxide in phosphate buffer, and dehydrated in a graded ethanol series.

Time course and extent of recovery of endothelium-dependent contractions and relaxations after direct arterial injury

To determine the time course of the return of endothelium-dependent relaxations and contractions during intimal regeneration, we performed balloon endothelial denudation of the thoracic and abdominal aorta of male Lewis rats and examined smooth muscle function and endothelium-dependent responses in vitro at 1, 2, 4, and 8 weeks after aortic injury. At each study interval during endothelial cell regeneration, vascular smooth muscle contracted and relaxed normally to direct stimulation with norepinephrine and sodium nitroprusside. Endothelium-dependent contractions to serotonin returned to normal at 1 week and developed into a hypercontractile response at 8 weeks. Endothelium-dependent relaxations to acetylcholine returned to normal at 8 weeks, but endothelium-dependent relaxations to adenosine diphosphate remained impaired. These experiments demonstrate that regenerating endothelium regains the ability to produce contracting factor before relaxing factor, and it even exhibits potentiated contractile activity 8 weeks after injury. Thus, after direct arterial injury, regenerating endothelium has abnormal endothelium-dependent function that predisposes the vessel to vasospasm and thrombosis.

Microvascular Anastomosis Using Horizontal Mattress Suture Technique

Horizontal mattress suture technique on microvascular anastomosis of rat(body weight : 200-250gm) femoral artery was evaluated. The present study was conducted to compare the horizontal mattress suture with simple interrupted suture on the suture time, patency rate of the sutured vessels, and the histological changes of surgical site of the vessel wall during wound healing period. The mean suture time of the vessel wall with horizontal mattress suture technique was 15min. 49sec. 2.14, which is significantly shorter than that of simple interrupted suture technique. The patency rate of the sutured vessel in both groups was statistically not different each other till post-operative 3rd day but patency rate of horizontal mattress suture was higher than that of simple interrupted suture at post-operative 3rd week. The histological findings such as intimal noss, medial degenention and intimal regeneration were similar in both groups.

Persistence of axial orientation cues in regenerating intima of cultured aortic explants.

The endothelial cells of arteries have a preferential orientation parallel to the axis of blood flow1. This axial orientation is maintained even at the interface between two branching or anastomosing vessels1, and is re-established by newly regenerated endothelial cells in regions of intimal wounds2. The cause of the orientation, however, remains unclear. Two possibilities have been proposed, shear stress from blood flow3 and ‘contact guidance’ by extracellular matrix4, but experiments to distinguish between them have been limited by the inaccessibility of the intima to systematic manipulation in vivo, and by the failure of organ-cultured vessels to demonstrate intimal regeneration comparable with that observed in vivo5,6. We have recently developed a technique for the culture of whole rat aorta explants which provides easy access to the intimal surface in vitro7. Additionally, our technique provides the first organ culture system in which the regeneration of endothelium in response to wounds performed in vitro has many of the characteristics of such regeneration in vivo. By studying the migration of regenerating endothelial cells into intimal wounds produced in vitro, we have obtained new evidence in favour of the extracellular matrix as the short-term determinant of endothelial cell orientation. Moreover, although this apparent effect of the matrix can be modified temporarily by suitable wounding procedures, axial orientation cues persist even in the absence of blood flow.