Early Microvascular Dysfunction: Is the Vasa Vasorum a "Missing Link" in Insulin Resistance and Atherosclerosis.

The arterial vasa vasorum is a specialized microvasculature that provides critical perfusion required for the health of the arterial wall, and is increasingly recognized to play a central role in atherogenesis. Cardio-metabolic disease (CMD) (including hypertension, metabolic syndrome, obesity, diabetes, and pre-diabetes) is associated with insulin resistance, and characteristically injures the microvasculature in multiple tissues, (e.g., the eye, kidney, muscle, and heart). CMD also increases the risk for atherosclerotic vascular disease. Despite this, the impact of CMD on vasa vasorum structure and function has been little studied. Here we review emerging information on the early impact of CMD on the microvasculature in multiple tissues and consider the potential impact on atherosclerosis development and progression, if vasa vasorum is similarly affected.

Stenting-induced Vasa Vasorum compression and subsequent flow resistance: a finite element study.

Vascular stenting is a common intervention for the treatment for atherosclerotic plaques. However, stenting still has a significant rate of restenosis caused by intimal hyperplasia formation. In this study, we evaluate whether stent overexpansion leads to Vasa Vasorum (VV) compression, which may contribute to vascular wall hypoxia and restenosis. An idealized multilayered fibroatheroma model including Vasa Vasorum was expanded by three coronary stent designs up to a 1.3:1 stent/artery luminal diameter ratio (exp1.1, exp1.2, exp1.3) using a finite element analysis approach. Following Poiseuille's law for elliptical sections, the fold increase in flow resistance was calculated based on VV compression in the Intima (Int), Media (Med) and Adventitia (Adv). The VV beneath the plaque experiences the smallest degree of compression, while the opposite wall regions are highly affected by stent overexpansion. The highest compressions for Adv, Med and Int at exp1.1 are 60.7, 65.9, 72.3%, at exp1.2 are 62.1, 67.3, 73.5% and at expp1.3 are 63.2, 68.7, 74.8%. The consequent fold increase in resistance to flow for Adv, Med and Int at exp1.1 is 3.3, 4.4, 6.6, at exp1.2 is 3.5, 4.7, 7.2 and at exp1.3 is 3.8, 5.1, 7.9. Stent overexpansion induces significant VV compression, especially in the Intima and Media layers, in agreement with previously observed Media necrosis and loss in elasticity after stenting. The observed steep increase in flow resistance suggests the blood flow and associated oxygen delivery would drop up to five times in the Media and almost eight in the Intima, which may lead to intimal hyperplasia and restenosis.

Optical coherence tomography for observing development of pulmonary arterial vasa vasorum after bidirectional cavopulmonary connection in children.

BACKGROUND: Hypoxia and low pulmonary arterial (PA) blood flow stimulate the development of systemic-to-pulmonary collateral blood vessels, which can be an adverse factor when performing the Fontan operation. The aim of this study was to use optical coherence tomography (OCT) to elucidate the morphological changes in PA vasculature after creation of a bidirectional cavopulmonary connection (BCPC) in children. METHODS: This prospective study evaluated PA wall thickness and development of PA vasa vasorum (VV) in the distal PA of eight patients (BCPC group, 1.3 ± 0.3 years) and 20 age-matched children with normal pulmonary artery hemodynamics and morphology (Control group, 1.4 ± 0.3 years). VV development was defined by the VV area ratio, defined as the VV area divided by the adventitial area in cross-sectional images. RESULTS: There was no significant difference in PA wall thickness between the BCPC and control groups (0.12 ± 0.03 mm vs. 0.12 ± 0.02 mm, respectively). The VV area ratio was significantly greater in the BCPC group than in the Control group (14.5 ± 3.5% vs. 5.3 ± 1.6%, respectively; p<0.0001). CONCLUSION: OCT is a promising new tool for evaluating PA pathology, including the development of VV in patients after BCPC.

Spontaneous Coronary Artery Dissection: Pathophysiological Insights From Optical Coherence Tomography.

OBJECTIVES: This study used optical coherence tomography to investigate the mechanism of false lumen (FL) formation in spontaneous coronary artery dissection (SCAD) by studying: 1) differences between fenestrated and nonfenestrated SCAD; 2) vasa vasorum density; and 3) light attenuation characteristics of the FL. BACKGROUND: SCAD is an increasingly recognized cause of acute coronary syndromes, characterized by FL formation and compression of the true lumen (TL). The mechanisms underlying FL formation remain poorly understood. METHODS: A total of 65 SCAD patients (68 vessels) who underwent acute OCT imaging as part of routine clinical care were included. Images were classified by the absence or presence of a connection (fenestration) between the TL and FL. Indexed measurements of TL stenosis, external elastic lamina (EEL) area, FL area, and light attenuation of the FL were assessed. Vasa vasorum densities of SCAD cases were compared with those in control non-SCAD myocardial infarction cases. RESULTS: In nonfenestrated cases, there was significantly larger expansion of the EEL area (9.1% vs. -1.9%; p <0.05) and a larger FL area (73.6% vs. 53.2%, respectively; p <0.05) in dissected segments. No significant differences were found between vasa vasorum density in SCAD and those in control subjects. The FL contents were heterogeneous but attenuated less light than whole blood or thrombus (4.28 ± 0.55 mm-1 vs. 5.08 ± 0.56 mm-1; p < 0.05; vs. 4.96 ± 0.56 mm-1; p < 0.05). CONCLUSIONS: These observational data suggest that the absence of a fenestration leads to increased FL pressure and compression of the TL. Although vasa vasorum may still be implicated in pathogenesis, increased vasa vasorum density could be an epiphenomenon of vascular healing.

Computational imaging of aortic vasa vasorum and neovascularization in rabbits using contrast-enhanced intravascular ultrasound: Association with histological analysis.

OBJECTIVE: Neoangiogenesis is pathophysiologically related to atherosclerotic plaque growth and vulnerability. We examined the in vivo performance of a computational method using contrast-enhanced intravascular ultrasound (CE-IVUS) to detect and quantify aortic wall neovascularization in rabbits. We also compared these findings with histological data. METHODS: Nine rabbits were fed with a hyperlipidemic diet. IVUS image sequences were continuously recorded before and after the injection of a contrast agent. Mean enhancement of intensity of a region of interest (MEIR) was calculated using differential imaging algorithm. The percent difference of MEIR before and after the injection of microbubbles (d_MEIR) was used as an index of the density of plaque or/and adventitial neovascularization. Aortic segments were excised for histological analysis. RESULTS: CE-IVUS and histological analysis were performed in 11 arterial segments. MEIR was significantly increased (~20%) after microbubble injection (from 8.1±0.9 to 9.7±1.8, p=0.016). Segments with increased VV/neovessels in the tunica adventitia (histological scores 2 and 3) had significantly higher d_MEIR compared with segments with low presence of VV/neovessels (score 1); 40.5±22.9 vs. 8±14.6, p=0.024, respectively. CONCLUSION: It is possible to detect VV or neovessels in vivo using computational analysis of CE-IVUS images, which is in agreement with histological data. These findings may have critical implications on vulnerable plaque assessment and risk stratification.

Local adventitial anti-angiogenic gene therapy reduces growth of vasa-vasorum and in-stent restenosis in WHHL rabbits.

BACKGROUND: Antiproliferative drugs in drug eluting stents (DES) are associated with complications due to impaired re-endothelialization. Additionally, adventitial neovascularization has been suggested to contribute to in-stent restenosis (ISR). Since Vascular Endothelial Growth Factors (VEGFs) are the key mediators of angiogenesis, we investigated feasibility and efficacy of local gene therapy for ISR utilizing soluble decoy VEGF receptors to reduce biological activity of adventitial VEGFs. METHOD: Sixty-nine adult WHHL rabbit aortas were subjected to endothelial denudation. Six weeks later catheter-mediated local intramural infusion of 1.5x10e10 pfu adenoviruses encoding soluble VEGF Receptor-1 (sVEGFR1), sVEGFR2, sVEGFR3 or control LacZ and bare metal stent implantation were performed in the same aortic segment. Marker protein expression was assessed at 6d in LacZ cohort. Immunohistochemistry, morphometrical analyses and angiography were performed at d14, d42 and d90. RESULTS: Transgene expression was localized to adventitia. All decoy receptors reduced the size of vasa-vasorum at 14d, AdsVEGFR2 animals also had reduced density of adventitial vasa-vasorum, whereas AdsVEGFR3 increased the density of vasa-vasorum. At d42, AdsVEGFR1 and AdsVEGFR2 reduced ISR (15.7 ±â€¯6.9% stenosis, P < 0.01 and 16.5 ±â€¯2.7%, P < 0.05, respectively) vs. controls (28.3 ±â€¯7.6%). Moreover, AdsVEGFR-3 treatment led to a non-significant trend in the reduction of adventitial lymphatics at all time points and these animals had significantly more advanced neointimal atherosclerosis at 14d and 42d vs. control animals. CONCLUSIONS: Targeting adventitial neovascularization using sVEGFR1 and sVEGFR2 is a novel strategy to reduce ISR. The therapeutic effects dissipate at late follow up following short expression profile of adenoviral vectors. However, inhibition of VEGFR3 signaling accelerates neoatherosclerosis.

Absence of adventitial vasa vasorum formation at the coronary segment with myocardial bridge - An optical coherence tomography study.

BACKGROUND: Myocardial bridge (MB) is a myocardial bundle through which coronary segment tunnels and could compress coronary arteries causing myocardial ischemia. However, the characteristic structural findings of MB remain to be fully elucidated. Recently, we demonstrated that optical coherence tomography (OCT) enables us to visualize adventitial vasa vasorum (VV) formation in humans. In this study, we examined adventitial VV formation at the coronary segment with MB in humans using OCT. METHODS: We examined 15 consecutive patients with suspected angina pectoris and MB in the left anterior descending (LAD) coronary arteries but no angiographic coronary stenosis. MB was detected on coronary angiography as a segment with milking effect. We performed intracoronary OCT imaging along the entire LAD. Morphometric analysis was performed at MB and proximal/distal segments at every 1mm. RESULTS: OCT examination showed the absence of adventitial VV formation at MB in the LAD, while VV was clearly noted at both the proximal and distal reference segments. Adventitial VV area was significantly less at MB compared with the proximal or distal references. CONCLUSIONS: These results with OCT imaging indicate that coronary segments with MB lack adventitial VV formation in humans, suggesting that MB could influence morphological and functional changes of the coronary artery.

Targeting vasa vasorum dysfunction to prevent atherosclerosis.

Vasa vasorum are blood microvessels which penetrate the adventitia and outer layers of the media of large blood vessels, supplying them with nutrients and oxygen. A growing body of evidence suggests that vasa vasorum play a central role in the pathogenesis of atherosclerosis. In this review, we will make a case for the role of microvascular dysfunction in the initiation of disease. When seen through this lens, new therapeutic opportunities for prevention can be envisioned. In particular, we discuss how targeting the cellular metabolism and epigenetic machinery of vasa vasorum neovessels could be harnessed to render vasa vasorum endothelial cells less sensitive to atherogenic stimuli.

Construction and histological analysis of a 3D human arterial wall model containing vasa vasorum using a layer-by-layer technique.

There is considerable global demand for three-dimensional (3D) functional tissues which mimic our native organs and tissues for use as in vitro drug screening systems and in regenerative medicine. In particular, there has been an increasing number of patients who suffer from arterial diseases such as arteriosclerosis. As such, in vitro 3D arterial wall models that can evaluate the effects of novel medicines and a novel artificial graft for the treatment are required. In our previous study, we reported the rapid construction of 3D tissues by employing a layer-by-layer (LbL) technique and revealed their potential applications in the pharmaceutical fields and tissue engineering. In this study, we successfully constructed a 3D arterial wall model containing vasa vasorum by employing a LbL technique for the first time. The cells were coated with extracellular matrix nanofilms and seeded into a culture insert using a cell accumulation method. This model had a three-layered hierarchical structure: a fibroblast layer, a smooth muscle layer, and an endothelial layer, which resembled the native arterial wall. Our method could introduce vasa vasorum into a fibroblast layer in vitro and the 3D arterial wall model showed barrier function which was evaluated by immunostaining and transendothelial electrical resistance measurement. Furthermore, electron microscopy observations revealed that the vasa vasorum was composed of single-layered endothelial cells, and the endothelial tubes were surrounded by the basal lamina, which are known to promote maturation and stabilization in native blood capillaries. These models should be useful for tissue engineering, regenerative medicine, and pharmaceutical applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 814-823, 2017.

Plaque Composition and No-Reflow Phenomenon During Percutaneous Coronary Intervention of Low-Echoic Structures in Grayscale Intravascular Ultrasound.

It has been reported that coronary vasa vasorum is associated with plaque vulnerability, and low-echoic structures in grayscale intravascular ultrasound (IVUS) are consistent pathologically with vasa vasorum. However, the association of low-echoic structures with plaque composition and no-reflow phenomenon during percutaneous coronary intervention (PCI) is unclear. We investigated plaque composition in virtual histology IVUS (VH-IVUS) and no-reflow phenomenon during PCI of low-echoic structures.A total of 106 lesions being treated by VH-IVUS before PCI were included in this study. Low-echoic structure was defined as a small tubular structure exterior to media without a connection to the vessel lumen in ≥ 3 consecutive crosssectional IVUS images. Lesions with low-echoic structures were found in 42% (45/106).Lesions with low-echoic structures were more prevalent in acute coronary syndrome (ACS) patients (53% [24/45] versus 20% [12/61], P < 0.001), had more positive remodeling (49% [22/45] versus 21% [13/61], P = 0.003), a larger number of VH-IVUS derived thin-cap fibroatheromas (VH-TCFAs) (0.64 ± 0.53 versus 0.05 ± 0.22, P < 0.001), more VH-TCFAs with a baseline plaque burden of 70% or more and minimal luminal area of 4.0 mm(2) or less (29% [13/45] versus 2% [1/61], P < 0.001), and more frequent no-reflow phenomenon after stent implantation and more final TIMI flow grade 0/1/2 (38% [17/45] versus 5% [3/61], P < 0.001; 9% [4/45] versus 0% [0/61], P = 0.03) than lesions without low-echo structures.Lesions with low-echoic structures in grayscale IVUS had high plaque vulnerability and were more prevalent in ACS patients, positive remolding, and VH-TCFAs, and they had more frequent no-reflow phenomenon during PCI than lesions without low-echoic structures.

Corkscrew Collateral Vessels in Buerger Disease: Vasa Vasorum or Vasa Nervorum.

PURPOSE: To investigate the origin of "corkscrew" collateral vessels around the occluded popliteal artery in patients with Buerger disease by Doppler ultrasound (US) and magnetic resonance (MR) imaging in tandem with digital subtraction angiography (DSA). MATERIALS AND METHODS: Between January 2013 and June 2015, 42 patients diagnosed with Buerger disease were identified retrospectively. Patients in whom occlusion of the popliteal artery was found on DSA of the lower extremity were subjected to Doppler US and MR imaging prospectively. Fifteen of 42 patients were identified as having the required characteristics, of whom 10 participated in the present study. RESULTS: Ten patients with occlusion of the popliteal artery were selected for inclusion, and 12 lower limbs of these patients were investigated. The study cohort comprised one woman and nine men with a mean age of 41 years ± 10 (standard deviation; range, 39-58 y). Corkscrew collateral vessels identified on DSA examinations were also identified on secondary imaging (Doppler US and MR imaging) in all patients except one in whom the popliteal artery was reconstituted after short-segment occlusion. The origin of the corkscrew collateral vessels was identified as the vasa nervorum of the tibial nerve in nine patients. CONCLUSIONS: Data from the present study suggest that corkscrew collateral vessels at the knee level in patients with Buerger disease originate from the vasa nervorum of the tibial nerve rather than the vasa vasorum of the popliteal artery if the latter is occluded.

Human Saphenous Vein Response to Trans-wall Oxygen Gradients in a Novel Ex Vivo Conditioning Platform.

Autologous saphenous veins are commonly used for the coronary artery bypass grafting even if they are liable to progressive patency reduction, known as 'vein graft disease'. Although several cellular and molecular causes for vein graft disease have been identified using in vivo models, the metabolic cues induced by sudden interruption of vasa vasorum blood supply have remained unexplored. In the present manuscript, we describe the design of an ex vivo culture system allowing the generation of an oxygen gradient between the luminal and the adventitial sides of the vein. This system featured a separation between the inner and the outer vessel culture circuits, and integrated a purpose-developed de-oxygenator module enabling the trans-wall oxygen distribution (high oxygen level at luminal side and low oxygen level at the adventitial side) existing in arterialized veins. Compared with standard cultures the bypass-specific conditions determined a significant increase in the proliferation of cells around adventitial vasa vasorum and an elevation in the length density of small and large caliber vasa vasorum. These results suggest, for the first time, a cause-effect relationship between the vein adventitial hypoxia and a neo-vascularization process, a factor known to predispose the arterialized vein conduits to restenosis.

Hypoperfusion of the Adventitial Vasa Vasorum Develops an Abdominal Aortic Aneurysm.

The aortic wall is perfused by the adventitial vasa vasorum (VV). Tissue hypoxia has previously been observed as a manifestation of enlarged abdominal aortic aneurysms (AAAs). We sought to determine whether hypoperfusion of the adventitial VV could develop AAAs. We created a novel animal model of adventitial VV hypoperfusion with a combination of a polyurethane catheter insertion and a suture ligation of the infrarenal abdominal aorta in rats. VV hypoperfusion caused tissue hypoxia and developed infrarenal AAA, which had similar morphological and pathological characteristics to human AAA. In human AAA tissue, the adventitial VV were stenotic in both small AAAs (30-49 mm in diameter) and in large AAAs (> 50 mm in diameter), with the sac tissue in these AAAs being ischemic and hypoxic. These results indicate that hypoperfusion of adventitial VV has critical effects on the development of infrarenal AAA.

Vasa Vasorum Restructuring in Human Atherosclerotic Plaque Vulnerability: A Clinical Optical Coherence Tomography Study.

BACKGROUND: Previous studies have suggested that vasa vasorum (VV) is associated with plaque progression and vulnerability. OBJECTIVES: The aim of this study was to investigate the relationship between coronary neovascularization structures and plaque characteristics. METHODS: We included 53 patients who underwent optical coherence tomography to observe the proximal left anterior descending coronary artery. Patients were classified into 5 groups according to lesion characteristics: normal; fibrous plaque (FP); fibroatheroma (FA); plaque rupture (PR); and fibrocalcific plaque (FC). We defined signal-poor tubuloluminal structures recognized in cross-sectional and longitudinal profiles located in adventitial layer as VV, and within plaque as intraplaque neovessels. Two types of longitudinal microvascular structure (external running and internal running) and a particular type of intraplaque neovessels (a coral tree pattern) were noted. All VV and intraplaque neovessels were manually segmented followed by quantification with Simpson method. RESULTS: Among the groups, there was significant difference (expressed as median [interquartile range (IQR)]) in VV volume (normal: 0.329 [IQR: 0.209 to 0.361] mm(3), FP: 0.433 [IQR: 0.297 to 0.706] mm(3), FA: 0.288 [IQR: 0.113 to 0.364] mm(3), PR: 0.160 [IQR: 0.141 to 0.193] mm(3), and FC: 0.106 [IQR: 0.053 to 0.165] mm(3); p = 0.003) and intraplaque neovessels volume (normal: 0.00 [IQR: 0.00 to 0.00] mm(3), FP: 0.00 [IQR: 0.00 to 0.00] mm(3), FA: 0.028 [IQR: 0.019 to 0.041] mm(3), PR: 0.035 [IQR: 0.026 to 0.042] mm(3), and FC: 0.010 [IQR: 0.005 to 0.014] mm(3); p < 0.001). Significant differences were observed in the prevalence of the internal running (normal: 0.0%, FP: 28.6%, FA: 40.0%, PR: 70.0%, and FC: 40.0%; p = 0.032) and the coral tree pattern (normal: 0.0%, FP: 7.1%, FA: 40.0%, PR: 80.0%, and FC: 10.0%; p < 0.01). The VV volume correlated with fibrous plaque volume (r = 0.71; p < 0.01). CONCLUSIONS: VV increase with fibrous plaque volume and intraplaque neovessels with particular structures are associated with plaque vulnerability. Imaging for microvasculature could become a new window for plaque vulnerability.

Association of Adventitial Vasa Vasorum and Inflammation With Coronary Hyperconstriction After Drug-Eluting Stent Implantation in Pigs In Vivo.

BACKGROUND: The importance of adventitial inflammation has been implicated for the pathogenesis of coronary artery disease. However, the roles of adventitial changes in drug-eluting stent (DES)-induced coronary hyperconstriction remain largely unknown. In the present study, this issue in pigs in vivo with a special reference to adventitial vasa vasorum (VV) formation and Rho-kinase activation, a central mechanism of coronary vasospasm, was examined. METHODS AND RESULTS: Each animal received a sirolimus-eluting stent (SES) and a biolimus A9-eluting stent (BES), one in the left anterior descending and another in the left circumflex coronary arteries in a randomized manner (n=18). After 1, 3 and 6 months, coronary vasomotion was examined. At 1 month, coronary vasoconstriction to serotonin was significantly enhanced at the SES edges as compared with the BES edges (SES, 52±7% vs. BES, 22±3%, P<0.01), which was equally prevented by a selective Rho-kinase inhibitor, hydroxyfasudil. A significant difference in vasoconstriction between SES and BES was sustained for 6 months. A micro-CT showed VV augmentation at the SES site, extending to the proximal and distal edges. Immunostainings demonstrated that VV formation, macrophage infiltration in the adventitia and Rho-kinase expressions/activation were significantly enhanced at the SES edges as compared with the BES edges. CONCLUSIONS: The DES with durable polymers enhances VV formation and inflammation in the adventitia, associating with the pathogenesis of DES-induced coronary hyperconstriction through Rho-kinase activation in pigs in vivo.

Accuracy of optical frequency domain imaging for evaluation of coronary adventitial vasa vasorum formation after stent implantation in pigs and humans - a validation study - .

BACKGROUND: Coronary adventitia harbors a wide variety of components, such as inflammatory cells and vasa vasorum (VV). Adventitial VV initiates the development of coronary artery diseases as an outside-in supply route of inflammation. We have recently demonstrated that drug-eluting stent implantation causes the enhancement of VV formation, with extending to the stent edges in the porcine coronary arteries, and also that optical frequency domain imaging (OFDI) is capable of visualizing VV in humans in vivo. However, it remains to be fully validated whether OFDI enables the precise measurement of VV formation in pigs and humans. METHODS AND RESULTS: In the pig protocol, a total of 6 bare-metal stents and 12 drug-eluting stents were implanted into the coronary arteries, and at 1 month, the stented coronary arteries were imaged by OFDI ex vivo. OFDI data including the measurement of VV area at the stent edge portions were compared with histological data. There was a significant positive correlation between VV area on OFDI and that on histology (R=0.91, P<0.01). In the human protocol, OFDI enabled the measurement of the VV area at the stent edges after coronary stent implantation in vivo. CONCLUSIONS: These results provide the first direct evidence that OFDI enables the precise measurement of the VV area in coronary arteries after stent implantation in pigs and humans.