Photocrosslinking of Adventitial Collagen in the Porcine Abdominal Aorta: A Preliminary Approach to a Strategy for Prevention of Aneurysmal Rupture

This study was aimed at generating data for designing a potential method to prevent the rupture of the abdominal aortic aneurysm (AAA). We found that the mechanical strength and stiffness of blood vessel walls was enhanced by the crosslinking of adventitial collagen through a photochemical process promoted by ultraviolet-A (UV-A) radiation. The experiments were carried out on samples isolated from 25 normal porcine aortas. The adventitial layer was separated from the other layers and exposed to UV radiation of 365-nm wavelength, in the presence of a riboflavin compound as the photosensitizer. Mechanical testing of 30 specimens, prior to and after exposure, indicated an increase in both strength (ultimate stress) and stiffness (Young’s modulus) of the adventitial specimens following irradiation. The crosslinking process also led to an enhanced resistance to experimental collagenolysis, as determined on six specimens. At this phase of conceptual design, we suggest that by applying this method to an aneurysmal dilated wall region, the stabilization of tunica adventitia may delay or prevent the rupture of the aneurysm and, with further investigation and refinement, can become a therapeutic strategy for arresting the progression of AAA.

The Role of Fibroblasts in Atherosclerosis Progression

The following chapter addresses vascular fibroblasts in a healthy, quiescent state, as well during vascular inflammation, focusing on atherosclerosis. The development of atherosclerosis, an inflammatory disease of medium- and large-sized arteries, has traditionally been viewed as an “inside-out” mechanism, with prominent roles of the innermost layer of the artery, consisting of endothelial cells. However, emerging evidence suggests a new paradigm of “outside-in” mechanism, including an earlier role for fibroblasts, constituents of the outermost adventitial layer of the artery. Phenotypic and functional changes of fibroblasts in adventitia may even occur prior to, or alongside endothelial activation. Activated adventitial fibroblasts, implicated in atherosclerosis progression, begin to transform into myofibroblasts, upregulate production of different proinflammatory cytokines, chemokines, growth factors, proteolytic enzymes, extracellular matrix proteins and reactive oxygen species, leading to extensive matrix remodeling, chemotaxis and recruitment of immune cells. Due to their suitable location for drug delivery systems, preventing fibroblast activation, modulating their activity or inducing myofibroblast dedifferentiation could represent a promising therapeutic approach for atherosclerosis regression.

Recurrent stroke in varicella zoster associated vasculopathy

Varicella zoster virus (VZV) is well known for its neurotropism, primary infection and reactivation after variable latency periods. After reactivation from spinal or cranial nerve ganglia, viruses can affect the central nervous system and cranial vasculature via transaxonal migration followed by transmural spread from the adventitial layer to the intima. Stroke can occur following primary infection by VZV (varicella) or after reactivation (zoster). These infectious vasculitides by VZV can lead to unifocal or multifocal ischemic and hemorrhagic stroke either after cranial nerve or spinal dermatomal zoster. Usual difference between immunocompetent versus immunocompromised individuals is involvement of unifocal large vessel vasculopathy in the former while multifocal small vessel in later. This vasculopathy in some cases may be progressive leading to recurrent stroke even after antiviral treatment. Diagnosis becomes challenging and needs a high degree of suspicion in immunocompetent, younger individuals, in absence of rash and when there are comorbidities. We report a case of elderly immunocompetent women, who developed multifocal infarcts followed by ventricular and subarachnoid haemorrhage after thoracic varicella zoster. Diagnosis was confirmed by the presence of anti-VZV IgG antibodies in the cerebrospinal fluid. In view of the diverse clinic-radiological spectrum of VZV vasculopathy, early recognition of this clinical entity is warranted for improved outcome.

Treatment Failure After Rotational Atherectomy and Balloon Angioplasty in Recurrent Cystic Adventitial Disease of the Popliteal Artery: a Case Report

Background: Cystic adventitial disease (CAD) is a rare non-atherosclerotic condition in which fluid accumulates in the sub-adventitial layer, compressing the lumen of the arteries and veins. Historically, surgical treatment of CAD is preferred over endovascular or minimally invasive techniques owing to the considerably lower recurrence rates after surgery. Case presentation: We here report the first case in which rotational atherectomy was performed using Jetstream XC (Boston Scientific, Natick, MA) for recurrent CAD. Post-procedure angiography showed that satisfactory increase in the luminal diameter. However, the patient’s symptoms recurred 1 day after procedure, and repeat Computed tomography angiography (CTA) showed recurrent of the disease.Conclusions: Our experience showed that endovascular treatment is not satisfactory for CAD recurrence even with atherectomy.

Response patterns in adventitial layer of Echinococcus granulosus sensu stricto cysts from naturally infected cattle and sheep

Cystic echinococcosis is a zoonotic disease caused by the metacestode of Echinococcus granulosus sensu lato. The disease is characterized by the development of cystic structures inside viscera of the intermediate host, mainly liver and lungs. These cysts are formed by three layers: germinal, laminated, and adventitial layer, the latter being the local host immune response. Metacestodes that develop protoscoleces, the infective stage to the definitive host, are termed fertile, whereas cysts that do not produce protoscoleces are termed non-fertile. Sheep usually harbor fertile cysts while cattle usually harbor non-fertile cysts. Adventitial layers with fibrotic resolution are associated to fertile cysts, whereas a granulomatous reaction is associated with non-fertile cysts. The aim of this study was to analyze cellular distribution in the adventitial layer of fertile and non-fertile E. granulosus sensu stricto cysts found in liver and lungs of cattle and sheep. A total of 418 cysts were analyzed, 203 from cattle (8 fertile and 195 non-fertile) and 215 from sheep (64 fertile and 151 non-fertile). Fertile cysts from cattle showed mixed patterns of response, with fibrotic resolution and presence of granulomatous response in direct contact with the laminated layer, while sheep fertile cysts always displayed fibrotic resolution next to the laminated layer. Cattle non-fertile cysts display a granulomatous reaction in direct contact with the laminated layer, whereas sheep non-fertile cysts display a granulomatous reaction, but in direct contact with the fibrotic resolution. This shows that cattle and sheep cystic echinococcosis cysts have distinct local immune response patterns, which are associated to metacestode fertility.

A Novel Silicone Simulation Model for Microvascular Anastomosis

Purpose: Surgical simulation of microvascular anastomosis has become increasingly popular. There are several living and silicone models available. Current silicone models fail to accurately reproduce a vessel’s loose adventitial layer, which may lead to the development of improper microsurgical technique. Our purpose is to create a realistic 3-dimensional microsurgical simulator that incorporates an adventitial vessel layer for higher fidelity manipulation of vessels. Methods: A microvascular anastomosis simulator was manufactured using metal moulds and inorganic materials. Synthetic tubing was created with a metal cylinder, 1.65 mm in diameter, painted with 2 sequential layers of silicon with a shore hardness of 2A. Silicone was allowed to fully cure in-between layers. Vessel adventitia was created with a 100-micron polyester mesh adhered to the silicone vessel exterior. Once dry, the synthetic tube is removed from the metal cylinder is then clipped to reveal the inner lumen. Both Resident and attending physicians evaluated the model with and without the adventitial layer and completed a questionnaire. Results: Grasping and manipulation of the vessel were scored on Average score 4.5 and 3 out of 5, with adventitia and without, respectively ( P = .00906). Usefulness as a teaching tool was scored on average 4.9 and 4.2, with adventitia and without, respectively ( P = .0232). The analysis included: simulation realism, educational utility, and overall satisfaction. Responses in all domains were favourable, suggesting the utility of this model. Conclusion: We created a realistic, high fidelity microvascular anastomosis simulator that is low cost and easily reproducible. Initial feedback is encouraging regarding realism, educational utility, and overall usefulness. Further validation is required to assess its effectiveness in resident education and skill transfer to the operating room.

Hemodynamic Changes in an Actively Rupturing Abdominal Aortic Aneurysm

Computational fluid dynamics were used to assess hemodynamic changes in an actively rupturing abdominal aortic aneurysm (AAA) over a 9-day period. Active migration of contrast from the lumen into the thickest region of intraluminal thrombus (ILT) was demonstrated until it ultimately breached the adventitial layer. Four days after symptom onset, there was a discrete disruption of adventitial calcium with bleb formation at the site of future rupture. Rupture occurred in a region of low wall shear stress and was associated with a marked increase in AAA diameter from 6.6 to 8.4 cm. The cross-sectional area of the flow lumen increased across all time points from 6.28 to 12.08 cm². The increase in luminal area preceded the increase in AAA diameter and was characterized by an overall deceleration in recirculation flow velocity with a coinciding increase in flow velocity penetrating the ILT. We show that there are significant hemodynamic and structural changes in the AAA flow lumen in advance of any appreciable increase in aortic diameter or rupture. The significant increase in AAA diameter with rupture suggests that AAA may actually rupture at smaller sizes than those measured on day of rupture. These findings have implications for algorithms the predict AAA rupture risk.

Oxidatively Modified LDL Suppresses Lymphangiogenesis via CD36 Signaling

Arterial accumulation of plasma-derived LDL and its subsequent oxidation contributes to atherosclerosis. Lymphatic vessel (LV)-mediated removal of arterial cholesterol has been shown to reduce atherosclerotic lesion formation. However, the precise mechanisms that regulate LV density and function in atherosclerotic vessels remain to be identified. The aim of this study was to investigate the role of native LDL (nLDL) and oxidized LDL (oxLDL) in modulating lymphangiogenesis and underlying molecular mechanisms. Western blotting and immunostaining experiments demonstrated increased oxLDL expression in human atherosclerotic arteries. Furthermore, elevated oxLDL levels were detected in the adventitial layer, where LV are primarily present. Treatment of human lymphatic endothelial cells (LEC) with oxLDL inhibited in vitro tube formation, while nLDL stimulated it. Similar results were observed with Matrigel plug assay in vivo. CD36 deletion in mice and its siRNA-mediated knockdown in LEC prevented oxLDL-induced inhibition of lymphangiogenesis. In addition, oxLDL via CD36 receptor suppressed cell cycle, downregulated AKT and eNOS expression, and increased levels of p27 in LEC. Collectively, these results indicate that oxLDL inhibits lymphangiogenesis via CD36-mediated regulation of AKT/eNOS pathway and cell cycle. These findings suggest that therapeutic blockade of LEC CD36 may promote arterial lymphangiogenesis, leading to increased cholesterol removal from the arterial wall and reduced atherosclerosis.