Vascularized organoid-on-a-chip: design, imaging, and analysis

Vascularized organoid-on-a-chip (VOoC) models achieve substance exchange in deep layers of organoids and provide a more physiologically relevant system in vitro. Common designs for VOoC primarily involve two categories: self-assembly of endothelial cells (ECs) to form microvessels and pre-patterned vessel lumens, both of which include the hydrogel region for EC growth and allow for controlled fluid perfusion on the chip. Characterizing the vasculature of VOoC often relies on high-resolution microscopic imaging. However, the high scattering of turbid tissues can limit optical imaging depth. To overcome this limitation, tissue optical clearing (TOC) techniques have emerged, allowing for 3D visualization of VOoC in conjunction with optical imaging techniques. The acquisition of large-scale imaging data, coupled with high-resolution imaging in whole-mount preparations, necessitates the development of highly efficient analysis methods. In this review, we provide an overview of the chip designs and culturing strategies employed for VOoC, as well as the applicable optical imaging and TOC methods. Furthermore, we summarize the vascular analysis techniques employed in VOoC, including deep learning. Finally, we discuss the existing challenges in VOoC and vascular analysis methods and provide an outlook for future development.

Experimental and theoretical model of microvascular network remodeling and blood flow redistribution following minimally invasive microvessel laser ablation

Overly dense microvascular networks are treated by selective reduction of vascular elements. Inappropriate manipulation of microvessels could result in loss of host tissue function or a worsening of the clinical problem. Here, experimental, and computational models were developed to induce blood flow changes via selective artery and vein laser ablation and study the compensatory collateral flow redistribution and vessel diameter remodeling. The microvasculature was imaged non-invasively by bright-field and multi-photon laser microscopy, and optical coherence tomography pre-ablation and up to 30 days post-ablation. A theoretical model of network remodeling was developed to compute blood flow and intravascular pressure and identify vessels most susceptible to changes in flow direction. The skin microvascular remodeling patterns were consistent among the five specimens studied. Significant remodeling occurred at various time points, beginning as early as days 1-3 and continuing beyond day 20. The remodeling patterns included collateral development, venous and arterial reopening, and both outward and inward remodeling, with variations in the time frames for each mouse. In a representative specimen, immediately post-ablation, the average artery and vein diameters increased by 14% and 23%, respectively. At day 20 post-ablation, the maximum increases in arterial and venous diameters were 2.5× and 3.3×, respectively. By day 30, the average artery diameter remained 11% increased whereas the vein diameters returned to near pre-ablation values. Some arteries regenerated across the ablation sites via endothelial cell migration, while veins either reconnected or rerouted flow around the ablation site, likely depending on local pressure driving forces. In the intact network, the theoretical model predicts that the vessels that act as collaterals after flow disruption are those most sensitive to distant changes in pressure. The model results correlate with the post-ablation microvascular remodeling patterns.

Reduction of Microvessel Number and Length in the Cerebellum of Purkinje Cell Degeneration Mice

Degenerative effects of nerve tissues are often accompanied by changes in vascularization. In this regard, knowledge about hereditary cerebellar degeneration is limited. In this study, we compared the vascularity of the individual cerebellar components of 3-month-old wild-type mice (n = 8) and Purkinje cell degeneration (pcd) mutant mice, which represent a model of hereditary cerebellar degeneration (n = 8). Systematic random samples of tissue sections were processed, and laminin was immunostained to visualize microvessels. A computer-assisted stereology system was used to quantify microvessel parameters including total number, total length, and associated densities in cerebellar layers. Our results in pcd mice revealed a 45% (p < 0.01) reduction in the total volume of the cerebellum, a 28% (p < 0.05) reduction in the total number of vessels and a lower total length, approaching 50% (p < 0.001), compared to the control mice. In pcd mutants, cerebellar degeneration is accompanied by significant reduction in the microvascular network that is proportional to the cerebellar volume reduction therefore does not change density of in the cerebellar gray matter of pcd mice.

Cannabidiol Attenuates In Vivo Leukocyte Recruitment to the Spinal Cord Microvasculature at Peak Disease of Experimental Autoimmune Encephalomyelitis

Introduction: Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system characterized by neuroinflammation leading to demyelination. The associated symptoms lead to a devastating decrease in quality of life. The cannabinoids and their derivatives have emerged as an encouraging alternative due to their management of symptom in MS. Objective: The aim of the study was to investigate the mechanism of action of cannabidiol (CBD), a nonpsychoactive cannabinoid, on molecular and cellular events associated with leukocyte recruitment induced by experimental autoimmune encephalomyelitis (EAE). Materials and Methods: C57BL/6 female mice were randomly assigned to the four experimental groups: C (control group), CBD (cannabidiol-treated group, 5 mg/kg i.p.; 14 days), EAE (experimental autoimmune encephalomyelitis-induced group), and EAE+CBD (experimental autoimmune encephalomyelitis-induced plus cannabidiol-treated group). Results: The results indicated that 5 mg/kg of CBD injected intraperitoneally between the 1st and 14th days of EAE could reduce the leukocyte rolling and adhesion into the spinal cord microvasculature as well cellular tissue infiltration. These results were supported by a decreased mRNA expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in the spinal cord. Conclusion: Purified CBD reduces in vivo VCAM and ICAM-mediated leukocyte recruitment to the spinal cord microvasculature at EAE peak disease.

Transmission of high arterial pressure into renal microvessels during venous-clamping augments ischaemia/reperfusion-induced acute kidney injury in anaesthetized rats

AIM

In two recent studies, we observed that a 30-min renal vein clamping caused formation of interstitial haemorrhagic congestion in ischaemic and ischaemic/reperfused kidney along with the development of severer acute kidney injury (AKI) than renal artery or pedicle clamping. It was suggested that the transmission of high arterial pressure into renal microvessels during vein occlusion probably causes the occurrence of interstitial haemorrhagic congestion that augments AKI. The present investigation aimed to evaluate this suggestion by reducing renal perfusion pressure (RPP) during renal venous occlusion.

METHODS

Anaesthetized male Sprague-Dawley rats were divided into three groups (n = 8), which underwent a 2-h reperfusion period following 30-min bilateral renal venous clamping along with reduced RPP (VIR-rRPP group) or without reduced RPP (VIR group) and an equivalent period after sham-operation (Sham group).

RESULTS

The VIR-rRPP group compared with VIR group had lower levels of kidney malondialdehyde and tissue damages as epithelial injuries of proximal tubule and thick ascending limb, vascular congestion, intratubular cast and oedema, along with the less reductions in renal blood flow, creatinine clearance, Na+ -reabsorption, K+ and urea excretion, urine osmolality and free-water reabsorption. Importantly, the formation of intensive interstitial haemorrhagic congestion in the VIR group was not observed in the VIR-rRPP group.

CONCLUSION

These results indicate that the transmission of high arterial pressure into renal microvessels during venous occlusion leads to rupturing of their walls and the formation of interstitial haemorrhagic congestion, which has an augmenting impact on ischaemia/reperfusion-induced renal structural damages and haemodynamic, excretory and urine-concentrating dysfunctions.

Towards standardising retinal OCT angiography image analysis with open-source toolbox OCTAVA

Quantitative assessment of retinal microvasculature in optical coherence tomography angiography (OCTA) images is important for studying, diagnosing, monitoring, and guiding the treatment of ocular and systemic diseases. However, the OCTA user community lacks universal and transparent image analysis tools that can be applied to images from a range of OCTA instruments and provide reliable and consistent microvascular metrics from diverse datasets. We present a retinal extension to the OCTA Vascular Analyser (OCTAVA) that addresses the challenges of providing robust, easy-to-use, and transparent analysis of retinal OCTA images. OCTAVA is a user-friendly, open-source toolbox that can analyse retinal OCTA images from various instruments. The toolbox delivers seven microvascular metrics for the whole image or subregions and six metrics characterising the foveal avascular zone. We validate OCTAVA using images collected by four commercial OCTA instruments demonstrating robust performance across datasets from different instruments acquired at different sites from different study cohorts. We show that OCTAVA delivers values for retinal microvascular metrics comparable to the literature and reduces their variation between studies compared to their commercial equivalents. By making OCTAVA publicly available, we aim to expand standardised research and thereby improve the reproducibility of quantitative analysis of retinal microvascular imaging. Such improvements will help to better identify more reliable and sensitive biomarkers of ocular and systemic diseases.

Clinical Significance of Recurrent Disc Hemorrhage and Choroidal Microvasculature Dropout on Optical Coherence Tomography Angiography in Glaucoma

Purpose

The purpose of this study was to investigate the clinical significance of recurrent disc hemorrhage (DH) and choroidal microvasculature dropout (MvD).

Methods

A retrospective cohort study was conducted of 181 eyes with open-angle glaucoma. The clinical characteristics of patients with nonrecurrent and recurrent DH with and without MvD were investigated.

Results

Fifty-eight patients (32.0%) had a single, nonrecurrent DH, and 63 (34.8%) had more than one DH. Sixty eyes (33.1%) with no history of DH were presented as a control group. MvD was more frequent in the recurrent DH group (44.4%) than in the nonrecurrent DH group (27.6%, P = 0.041). The recurrent DH with MvD group experienced more frequent central visual field (VF) progression (71.4%) than the recurrent DH without MvD group (17.1 %, P < 0.001). The recurrent DH without MvD group had a higher frequency of DH recurrence at different locations (42.9%) and more vascular symptoms (37.1%) than the recurrent DH with MvD group (14.3% and 7.1%, P = 0.013 and P = 0.005, respectively). Presence of DH, presence of MvD, vascular symptoms, and DH recurrence at different locations were the factors associated with central VF progression in multivariate analysis.

Conclusions

DH occurrence and the presence of MvDs constitute critical parameters associated with central VF progression. In the presence of MvD, recurrent DH was more likely to recur at the same location as the MvD, whereas recurrent DH without MvD was related to vascular symptoms and recurred at other locations. When eyes present with recurrent DH and MvD, closer follow-up and more aggressive treatment are required to prevent the progression of central VF.

The proteome of the blood-brain barrier in rat and mouse: highly specific identification of proteins on the luminal surface of brain microvessels by in vivo glycocapture

BACKGROUND

The active transport of molecules into the brain from blood is regulated by receptors, transporters, and other cell surface proteins that are present on the luminal surface of endothelial cells at the blood-brain barrier (BBB). However, proteomic profiling of proteins present on the luminal endothelial cell surface of the BBB has proven challenging due to difficulty in labelling these proteins in a way that allows efficient purification of these relatively low abundance cell surface proteins.

METHODS

Here we describe a novel perfusion-based labelling workflow: in vivo glycocapture. This workflow relies on the oxidation of glycans present on the luminal vessel surface via perfusion of a mild oxidizing agent, followed by subsequent isolation of glycoproteins by covalent linkage of their oxidized glycans to hydrazide beads. Mass spectrometry-based identification of the isolated proteins enables high-confidence identification of endothelial cell surface proteins in rats and mice.

RESULTS

Using the developed workflow, 347 proteins were identified from the BBB in rat and 224 proteins in mouse, for a total of 395 proteins in both species combined. These proteins included many proteins with transporter activity (73 proteins), cell adhesion proteins (47 proteins), and transmembrane signal receptors (31 proteins). To identify proteins that are enriched in vessels relative to the entire brain, we established a vessel-enrichment score and showed that proteins with a high vessel-enrichment score are involved in vascular development functions, binding to integrins, and cell adhesion. Using publicly-available single-cell RNAseq data, we show that the proteins identified by in vivo glycocapture were more likely to be detected by scRNAseq in endothelial cells than in any other cell type. Furthermore, nearly 50% of the genes encoding cell-surface proteins that were detected by scRNAseq in endothelial cells were also identified by in vivo glycocapture.

CONCLUSIONS

The proteins identified by in vivo glycocapture in this work represent the most complete and specific profiling of proteins on the luminal BBB surface to date. The identified proteins reflect possible targets for the development of antibodies to improve the crossing of therapeutic proteins into the brain and will contribute to our further understanding of BBB transport mechanisms.

MICROVASCULATURE ALTERATIONS OF PERIPAPILLARY RETINA AND MACULA IN SYSTEMIC LUPUS ERYTHEMATOSUS PATIENTS WITHOUT OCULAR INVOLVEMENT BY OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

PURPOSE

To evaluate microvasculature alterations of the peripapillary retina and macula and to assess whether the changes can detect preclinical retinopathy in systemic lupus erythematosus patients.

METHODS

Cross-sectional study of 32 systemic lupus erythematosus patients without retinopathy and 22 normal controls. Optical coherence tomography angiography was used to measure the microvasculature of the peripapillary retina and macula. Vessel densities (VD, %) and fractal dimensions of superficial capillary plexus (SCP) and deep capillary plexus were calculated.

RESULTS

Compared with controls, macular vessel densities of the whole image SCP (macular vessel density of SCP-wi) and macular vessel density of inferior SCP (macular vessel density of SCP-i) were significantly reduced in systemic lupus erythematosus patients ( P < 0.05). The peripapillary vessel densities (peripapillary vessel density [pVD]) of a 2.5-mm circle of SCP (pVD of SCP Φ2.5 ), pVD of SCP Φ3.5 , and pVD of inferior region of the inner circle of SCP (pVD of SCP-ii) were significantly reduced in patients treated with hydroxychloroquine >5 years. Macular vessel density of SCP-wi declined with age (β = -0.12; P < 0.01) and pVD of SCP-ii declined with hydroxychloroquine cumulative dose (β = -0.01; P < 0.01). Macular vessel density of SCP-i had the best discrimination power of 0.77 ( P < 0.01).

CONCLUSION

Systemic lupus erythematosus patients without ocular involvement had microvasculature alterations that were particularly evident in the SCP. Peripapillary retina microvasculature may be reduced in patients with longer hydroxychloroquine treatment.

Revisiting hemodynamics and blood oxygenation in a microfluidic microvasculature replica

The complexity of microvascular circulation has led to the development of advanced imaging techniques and biomimetic models. This study developed a multifaceted microfluidic-based microdevice as an in vitro model of microvasculature to replicate important geometric and functional features of in vivo perfusion in mice. The microfluidic device consisted of a microchannel for blood perfusion, mirroring the natural hierarchical branching vascular structures found in mice. Additionally, the device incorporated a steady gradient of oxygen (O2) which diffused through the polydimethylsiloxane (PDMS) layer, allowing for dynamic blood oxygenation. The assembled multi-layered microdevice was accompanied by a dual-modal imaging system that combined laser speckle contrast imaging (LSCI) and intrinsic signal optical imaging (ISOI) to visualize full-field blood flow distributions and blood O2 profiles. By closely reproducing in vivo blood perfusion and oxygenation conditions, this microvasculature model, in conjunction with numerical simulation results, can provide quantitative information on physiologically relevant hemodynamics and key O2 transport parameters that are not directly measurable in traditional animal studies.

Hemodynamic regulation allows stable growth of microvascular networks

How do vessels find optimal radii? Capillaries are known to adapt their radii to maintain the shear stress of blood flow at the vessel wall at a set point, yet models of adaptation purely based on average shear stress have not been able to produce complex loopy networks that resemble real microvascular systems. For narrow vessels where red blood cells travel in a single file, the shear stress on vessel endothelium peaks sharply when a red blood cell passes through. We show that stable shear-stress-based adaptation is possible if vessel shear stress set points are cued to the stress peaks. Model networks that respond to peak stresses alone can quantitatively reproduce the observed zebrafish trunk microcirculation, including its adaptive trajectory when hematocrit changes or parts of the network are amputated. Our work reveals the potential for mechanotransduction alone to generate stable hydraulically tuned microvascular networks.

Central visual field damage in glaucoma eyes with choroidal microvasculature dropout with and without high axial myopia

PURPOSE

To characterise the relationship between a deep-layer microvasculature dropout (MvD) and central visual field (VF) damage in primary open-angle glaucoma (POAG) patients with and without high axial myopia.

DESIGN

Cross-sectional study.

METHODS

Seventy-one eyes (49 patients) with high axial myopia and POAG and 125 non-highly myopic POAG eyes (97 patients) were enrolled. Presence, area and angular circumference of juxtapapillary MvD were evaluated on optical coherence tomography angiography B-scans and en-face choroidal images.

RESULTS

Juxtapapillary MvD was detected more often in the highly myopic POAG eyes (43 eyes, 86%) than in the non-highly myopic eyes (73 eyes, 61.9%; p=0.002). In eyes with MvD, MvD area and angular circumference (95% CI) were significantly larger in the highly myopic eyes compared with the non-highly myopic eyes (area: (0.69 (0.40, 0.98) mm2 vs 0.31 (0.19, 0.42) mm2, p=0.011) and (angular circumference: 84.3 (62.9, 105.8) vs 74.5 (58.3, 90.9) degrees, p<0.001), respectively. 24-2 VF mean deviation (MD) was significantly worse in eyes with MvD compared with eyes without MvD in both groups (p<0.001). After adjusting for 24-2 MD VF, central VF defects were more frequently found in eyes with MvD compared with eyes without MvD (82.7% vs 60.9%, p<0.001). In multivariable analysis, higher intraocular pressure, worse 24-2 VF MD, longer axial length and greater MvD area and angular circumference were associated with worse 10-2 VF MD.

CONCLUSIONS

MvD was more prevalent and larger in POAG eyes with high myopia than in non-highly myopic POAG eyes. In both groups, eyes with MvD showed worse glaucoma severity and more central VF defects.

Engineering primitive multiscale chimeric vasculature by combining human microvessels with explanted murine vessels

Strategies to separately manufacture arterial-scale tissue engineered vascular grafts and microvascular networks have been well-established, but efforts to bridge these two length scales to create hierarchical vasculature capable of supporting parenchymal cell functions or restoring perfusion to ischemic tissues have been limited. This work aimed to create multiscale vascular constructs by assessing the capability of macroscopic vessels isolated from mice to form functional connections to engineered capillary networks ex vivo. Vessels of venous and arterial origins from both thoracic and femoral locations were isolated from mice, and then evaluated for their abilities to sprout endothelial cells (EC) capable of inosculating with surrounding human cell-derived microvasculature within bulk fibrin hydrogels. Comparing aortae, vena cavae, and femoral vessel bundles, we identified the thoracic aorta as the rodent macrovessel that yielded the greatest degree of sprouting and interconnection to surrounding capillaries. The presence of cells undergoing vascular morphogenesis in the surrounding hydrogel attenuated EC sprouting from the macrovessel compared to sprouting into acellular hydrogels, but ultimately sprouted mouse EC interacted with human cell-derived capillary networks in the bulk, yielding chimeric vessels. We then integrated micromolded mesovessels into the constructs to engineer a primitive 3-scale vascular hierarchy comprising capillaries, mesovessels, and macrovessels. Overall, this study yielded a primitive hierarchical vasculature suitable as proof-of-concept for regenerative medicine applications and as an experimental model to better understand the spontaneous formation of host-graft vessel anastomoses.

Microfluidic-Based Reconstitution of Functional Lymphatic Microvasculature: Elucidating the Role of Lymphatics in Health and Disease

The knowledge of the blood microvasculature and its functional role in health and disease has grown significantly attributable to decades of research and numerous advances in cell biology and tissue engineering; however, the lymphatics (the secondary vascular system) has not garnered similar attention, in part due to a lack of relevant in vitro models that mimic its pathophysiological functions. Here, a microfluidic-based approach is adopted to achieve precise control over the biological transport of growth factors and interstitial flow that drive the in vivo growth of lymphatic capillaries (lymphangiogenesis). The engineered on-chip lymphatics with in vivo-like morphology exhibit tissue-scale functionality with drainage rates of interstitial proteins and molecules comparable to in vivo standards. Computational and scaling analyses of the underlying transport phenomena elucidate the critical role of the three-dimensional geometry and lymphatic endothelium in recapitulating physiological drainage. Finally, the engineered on-chip lymphatics enabled studies of lymphatic-immune interactions that revealed inflammation-driven responses by the lymphatics to recruit immune cells via chemotactic signals similar to in vivo, pathological events. This on-chip lymphatics platform permits the interrogation of various lymphatic biological functions, as well as screening of lymphatic-based therapies such as interstitial absorption of protein therapeutics and lymphatic immunomodulation for cancer therapy.

A novel gas embolotherapy using microbubbles electrocoalescence for cancer treatment

BACKGROUND AND OBJECTIVE

Embolotherapy has been increasingly used to disrupt tumor growth. Despite its success in the occlusion of microvessels, it has drawbacks such as limited access to the target location, limited control of the blocker size, and inattention to the tumor characteristics, especially high interstitial fluid pressure. The present work introduces a novel numerical method of gas embolotherapy for cancer treatment through tumor vessel occlusion.

METHODS

The gas microbubbles are generated from Levovist bolus injection into the tumor microvessel. The microbubble movement in the blood flow is innovatively controlled by an electric field applied to the tumor-feeding vessel. The interaction between the Levovist microbubbles and the electric field is resolved by developing a fully coupled model using the phase-field model, Carreau model for non-Newtonian blood, Navier-Stokes equations and Maxwell stress tensor. Additionally, the critical effect of high interstitial fluid pressure as a characteristic of solid tumors is included.

RESULTS

The findings of this study indicate that the rates of microbubble deformation and displacement increase with the applied potential intensity to the microvessel wall. Accordingly, the required time for a microbubble to join the upper microvessel wall reduces from 1.97ms to 22 μs with an increase of the electric potential from 3.5V to 12.5V. Additionally, an electric potential of 12.5V causes the microbubbles coalescence and formation of a gas column against the bloodstream.

CONCLUSIONS

Clinically, our novel embolization procedure can be considered a non-invasive targeted therapy, and under a controlled electric field, the blocker size can be precisely controlled. Also, the proposed method has the potential to be used as a gradual treatment in advanced cancers as tumors develop resistance and relapse.

Clinical characteristics of open-angle glaucoma progression with peripapillary microvasculature dropout in different locations

OBJECTIVE

The study attempted to identify clinical characteristics associated with structural progression in open-angle glaucoma (OAG) in the presence of MvD in different locations.

METHODS

A total of 181 consecutive OAG eyes (follow-up 7.3 ± 4.0 years), which demonstrated peripapillary choroidal MvD (defined as a focal capillary loss with no visible microvascular network in choroidal layer) on optical coherence tomography (OCT) angiography (OCTA), were divided based on the location of MvD. Structural progression was determined using trend-based analysis of the Guided Progression Analysis software of Cirrus OCT.

RESULTS

MvD was identified in the temporal quadrant in 110 eyes (temporal MvD; 60.5 ± 12.6 years), and in the inferior quadrant in 71 eyes (inferior MvD; 60.3 ± 11.1 years). After adjusting for age, average intraocular pressure (IOP) and baseline retinal nerve fibre layer (RNFL) thickness and visual field mean deviation, inferior MvD eyes showed faster rates of thinning in the inferior RNFL (mean (95% CI); -0.833 (-1.298 to -0.367)) compared to temporal MvD eyes (-0.144 (-0.496 to 0.207)) when long-term IOP fluctuation was larger than the median value (1.7 mmHg; P = 0.022). Long-term IOP fluctuations were independently associated with inferior RNFL thinning in eyes with inferior MvD (P = 0.002) but not in eyes with temporal MvD.

CONCLUSIONS

In OAG eyes, the rates of RNFL and GCIPL thinning were comparable regardless of MvD locations. However, inferior MvD is associated with faster RNFL and GCIPL thinning in the same quadrant when long-term IOP fluctuation is present. Structural progression in the presence of temporal MvD was less associated with IOP fluctuation.

Diabetes and the Microvasculature of the Bone and Marrow

PURPOSE OF REVIEW

The purpose of this review is to highlight the evidence of microvascular dysfunction in bone and marrow and its relation to poor skeletal outcomes in diabetes mellitus.

RECENT FINDINGS

Diabetes mellitus is characterized by chronic hyperglycemia, which may lead to microangiopathy and macroangiopathy. Micro- and macroangiopathy have been diagnosed in Type 1 and Type 2 diabetes, coinciding with osteopenia, osteoporosis, enhanced fracture risk and delayed fracture healing. Microangiopathy has been reported in the skeleton, correlating with reduced blood flow and perfusion, vasomotor dysfunction, microvascular rarefaction, reduced angiogenic capabilities, and augmented vascular permeability. Microangiopathy within the skeleton may be detrimental to bone and manifest as, among other clinical abnormalities, reduced mass, enhanced fracture risk, and delayed fracture healing. More investigations are required to elucidate the various mechanisms by which diabetic microvascular dysfunction impacts the skeleton.

Ultrasound microflow patterns help in distinguishing malignant from benign thyroid nodules

BACKGROUND

Vascular features are not commonly used to evaluate thyroid nodules by conventional ultrasound due to the low sensitivity. Superb Microvascular Imaging (SMI) is a new ultrasonic Doppler technology that specializes in depicting microvessels and low-speed flow. The objective of this study was to explore the value of microflow features on SMI in differentiating malignant from benign thyroid nodules.

METHODS

One hundred and seventy-seven adult patients with thyroid nodules in our center from October 2021 to June 2022 with available histopathological results were recruited, including 125 malignant nodules and 123 benign nodules. Preoperative ultrasound was performed using greyscale, Color Doppler Flow Imaging (CDFI), monochrome SMI (mSMI) and color SMI (cSMI). Vascular features such as flow richness, microflow distribution and microflow patterns of malignant thyroid nodules were compared with those of benign nodules.

RESULTS

Penetrating vessel ≥ 1 (82.4% in the malignant group vs. 30.9% in the benign group, P < 0.001), the crab claw-like pattern (64.0% vs. 10.6%, P < 0.001) and the root hair-like pattern (8.0% vs. 2.4%, P = 0.049) were common in malignant thyroid nodules, among which the crab claw-like pattern was an independent risk factor for malignant thyroid nodules. The wheel-like pattern (1.6% in the malignant group vs. 33.3% in the benign group, P < 0.001) and the arborescent pattern (0 vs. 19.5%, P < 0.001) were more likely to appear in benign nodules. The diagnostic specificities of the crab claw-like pattern and the root hair-like pattern for malignant thyroid nodules were 0.894, 0.976, and the positive predictive values were 0.860, 0.769. The diagnostic specificities of the wheel-like pattern and the arborescent pattern for benign thyroid nodules were 0.984, 1.000, and the positive predictive values were 0.953, 1.000.

CONCLUSIONS

The crab claw-like pattern and the root hair-like pattern were microflow characteristics of malignant thyroid nodules. The wheel-like pattern and the arborescent pattern could help exclude the diagnosis of thyroid cancer.

Partitioning of dense RBC suspensions in single microfluidic bifurcations: role of cell deformability and bifurcation angle

Red blood cells (RBCs) are a key determinant of human physiology and their behaviour becomes extremely heterogeneous as they navigate in narrow, bifurcating vessels in the microvasculature, affecting local haemodynamics. This is due to partitioning in bifurcations which is dependent on the biomechanical properties of RBCs, especially deformability. We examine the effect of deformability on the haematocrit distributions of dense RBC suspensions flowing in a single, asymmetric Y-shaped bifurcation, experimentally. Human RBC suspensions (healthy and artificially hardened) at 20% haematocrit (Ht) were perfused through the microchannels at different flow ratios between the outlet branches, and negligible inertia, and imaged to infer cell distributions. Notable differences in the shape of the haematocrit distributions were observed between healthy and hardened RBCs near the bifurcation apex. These lead to more asymmetric distributions for healthy RBCs in the daughter and outlet branches with cells accumulating near the inner channel walls, exhibiting distinct hematocrit peaks which are sharper for healthy RBCs. Although the hematocrit distributions differed locally, similar partitioning characteristics were observed for both suspensions. Comparisons with RBC distributions measured in a T-shaped bifurcation showed that the bifurcation angle affects the haematocrit characteristics of the healthy RBCs and not the hardened ones. The extent of RBC partitioning was found similar in both geometries and suspensions. The study highlights the differences between local and global characteristics which impact RBC distribution in more complex, multi-bifurcation networks.

Ocular microvascular complications in diabetic retinopathy: insights from machine learning

INTRODUCTION

Diabetic retinopathy (DR) is a leading cause of preventable blindness among working-age adults, primarily driven by ocular microvascular complications from chronic hyperglycemia. Comprehending the complex relationship between microvascular changes in the eye and disease progression poses challenges, traditional methods assuming linear or logistical relationships may not adequately capture the intricate interactions between these changes and disease advances. Hence, the aim of this study was to evaluate the microvascular involvement of diabetes mellitus (DM) and non-proliferative DR with the implementation of non-parametric machine learning methods.

RESEARCH DESIGN AND METHODS

We conducted a retrospective cohort study that included optical coherence tomography angiography (OCTA) images collected from a healthy group (196 eyes), a DM no DR group (120 eyes), a mild DR group (71 eyes), and a moderate DR group (66 eyes). We implemented a non-parametric machine learning method for four classification tasks that used parameters extracted from the OCTA images as predictors: DM no DR versus healthy, mild DR versus DM no DR, moderate DR versus mild DR, and any DR versus no DR. SHapley Additive exPlanations values were used to determine the importance of these parameters in the classification.

RESULTS

We found large choriocapillaris flow deficits were the most important for healthy versus DM no DR, and became less important in eyes with mild or moderate DR. The superficial microvasculature was important for the healthy versus DM no DR and mild DR versus moderate DR tasks, but not for the DM no DR versus mild DR task-the stage when deep microvasculature plays an important role. Foveal avascular zone metric was in general less affected, but its involvement increased with worsening DR.

CONCLUSIONS

The findings from this study provide valuable insights into the microvascular involvement of DM and DR, facilitating the development of early detection methods and intervention strategies.

Association between functional network connectivity, retina structure and microvasculature, and visual performance in patients after thalamic stroke: An exploratory multi-modality study

BACKGROUND AND OBJECTIVE

Neuro-ophthalmologic symptoms and retinal changes have been increasingly observed following thalamic stroke, and there is mounting evidence indicating distinct alterations occurring in the vision-related functional network. However, the intrinsic correlations between these changes are not yet fully understood. Our objective was to explore the altered patterns of functional network connectivity and retina parameters, and their correlations with visual performance in patients with thalamic stroke.

METHODS

We utilized resting-state functional MRI to obtain multi-modular functional connectivity (FC), and optical coherence tomography-angiography to measure various retina parameters, such as the retinal nerve fiber layer (RNFL), ganglion cell-inner plexiform layer (GCIPL), superficial vascular complex (SVC), and deep vascular complex. Visual acuity (VA) was used as a metric for visual performance.

RESULTS

We included 46 patients with first-ever unilateral thalamic stroke (mean age 59.74 ± 10.02 years, 33 males). Significant associations were found between FC of attention-to-default mode and SVC, RNFL, and GCIPL, as well as between FC of attention-to-visual and RNFL (p < .05). Both RNFL and GCIPL exhibited significant associations with FC of visual-to-visual (p < .05). Only GCIPL showed an association with VA (p = .038). Stratified analysis based on a disease duration of 6 months revealed distinct and significant linking patterns in multi-modular FC and specific retina parameters, with varying correlations with VA in each subgroup.

CONCLUSION

These findings provide valuable insight into the neural basis of the associations between brain network dysfunction and impaired visual performance in patients with thalamic stroke. Our novel findings have the potential to inform future targeted and individualized therapies. However, further comprehensive studies are necessary to validate our results.

Thrombosis in the Coronary Microvasculature Impairs Cardiac Relaxation and Induces Diastolic Dysfunction

BACKGROUND

Heart failure with preserved ejection fraction is proposed to be caused by endothelial dysfunction in cardiac microvessels. Our goal was to identify molecular and cellular mechanisms underlying the development of cardiac microvessel disease and diastolic dysfunction in the setting of type 2 diabetes.

METHODS

We used Leprdb/db (leptin receptor-deficient) female mice as a model of type 2 diabetes and heart failure with preserved ejection fraction and identified Hhipl1 (hedgehog interacting protein-like 1), which encodes for a decoy receptor for HH (hedgehog) ligands as a gene upregulated in the cardiac vascular fraction of diseased mice.

RESULTS

We then used Dhh (desert HH)-deficient mice to investigate the functional consequences of impaired HH signaling in the adult heart. We found that Dhh-deficient mice displayed increased end-diastolic pressure while left ventricular ejection fraction was comparable to that of control mice. This phenotype was associated with a reduced exercise tolerance in the treadmill test, suggesting that Dhh-deficient mice do present heart failure. At molecular and cellular levels, impaired cardiac relaxation in DhhECKO mice was associated with a significantly decreased PLN (phospholamban) phosphorylation on Thr17 (threonine 17) and an alteration of sarcomeric shortening ex vivo. Besides, as expected, Dhh-deficient mice exhibited phenotypic changes in their cardiac microvessels including a prominent prothrombotic phenotype. Importantly, aspirin therapy prevented the occurrence of both diastolic dysfunction and exercise intolerance in these mice. To confirm the critical role of thrombosis in the pathophysiology of diastolic dysfunction, we verified Leprdb/db also displays increased cardiac microvessel thrombosis. Moreover, consistently, with Dhh-deficient mice, we found that aspirin treatment decreased end-diastolic pressure and improved exercise tolerance in Leprdb/db mice.

CONCLUSIONS

Altogether, these results demonstrate that microvessel thrombosis may participate in the pathophysiology of heart failure with preserved ejection fraction.

A Comprehensive Look at In Vitro Angiogenesis Image Analysis Software

One of the complex challenges faced presently by tissue engineering (TE) is the development of vascularized constructs that accurately mimic the extracellular matrix (ECM) of native tissue in which they are inserted to promote vessel growth and, consequently, wound healing and tissue regeneration. TE technique is characterized by several stages, starting from the choice of cell culture and the more appropriate scaffold material that can adequately support and supply them with the necessary biological cues for microvessel development. The next step is to analyze the attained microvasculature, which is reliant on the available labeling and microscopy techniques to visualize the network, as well as metrics employed to characterize it. These are usually attained with the use of software, which has been cited in several works, although no clear standard procedure has been observed to promote the reproduction of the cell response analysis. The present review analyzes not only the various steps previously described in terms of the current standards for evaluation, but also surveys some of the available metrics and software used to quantify networks, along with the detection of analysis limitations and future improvements that could lead to considerable progress for angiogenesis evaluation and application in TE research.

Noninvasive urinary protein signatures combined clinical information associated with microvascular invasion risk in HCC patients

BACKGROUND

Microvascular invasion (MVI) is the main factor affecting the prognosis of patients with hepatocellular carcinoma (HCC). The aim of this study was to identify accurate diagnostic biomarkers from urinary protein signatures for preoperative prediction.

METHODS

We conducted label-free quantitative proteomic studies on urine samples of 91 HCC patients and 22 healthy controls. We identified candidate biomarkers capable of predicting MVI status and combined them with patient clinical information to perform a preoperative nomogram for predicting MVI status in the training cohort. Then, the nomogram was validated in the testing cohort (n = 23). Expression levels of biomarkers were further confirmed by enzyme-linked immunosorbent assay (ELISA) in an independent validation HCC cohort (n = 57).

RESULTS

Urinary proteomic features of healthy controls are mainly characterized by active metabolic processes. Cell adhesion and cell proliferation-related pathways were highly defined in the HCC group, such as extracellular matrix organization, cell-cell adhesion, and cell-cell junction organization, which confirms the malignant phenotype of HCC patients. Based on the expression levels of four proteins: CETP, HGFL, L1CAM, and LAIR2, combined with tumor diameter, serum AFP, and GGT concentrations to establish a preoperative MVI status prediction model for HCC patients. The nomogram achieved good concordance indexes of 0.809 and 0.783 in predicting MVI in the training and testing cohorts.

CONCLUSIONS

The four-protein-related nomogram in urine samples is a promising preoperative prediction model for the MVI status of HCC patients. Using the model, the risk for an individual patient to harbor MVI can be determined.

The testicular microvasculature in Klinefelter syndrome is immature with compromised integrity and characterized by excessive inflammatory cross-talk

STUDY QUESTION

Does Klinefelter syndrome (KS) lead to a distinct gene expression pattern at single-cell level in the testes that could provide insight into the reported microvascular dysfunction in the testes?

SUMMARY ANSWER

A distinct gene expression pattern within microvascular-associated cells of males with KS suggests excessive endothelial cell (EC) activation, disorganized vessel formation, and the presence of immature vessels with compromised integrity.

WHAT IS KNOWN ALREADY

Recent studies show that males with KS exhibit microvascular dysfunction in their testes, which affects blood flow and is associated with lower circulating levels of testosterone.

STUDY DESIGN, SIZE, DURATION

A comparative cross-sectional study of males with KS (n = 6), non-obstructive azoospermia (NOA) (n = 5), cryptozoospermia (n = 3), and controls (n = 15) was carried out.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We analyzed publicly available single-cell RNA sequencing data of testicular cells from males with KS, males with NOA, males with cryptozoospermia, and controls. The integration of these datasets allowed us to analyze gene expression profiles and communication patterns among the cell types within the testis and to identify capillary ECs to investigate changes at the microvascular level.

MAIN RESULTS AND THE ROLE OF CHANCE

Rooted in changes at the single-cell level, our study demonstrates a shift in gene expression forming the foundation for altered cellular communication, microvascular remodeling, and pro-inflammatory responses within the testes of males with KS. We identified genes that were dysregulated in capillary ECs from males with KS (Padj < 0.05). Specifically, the unique microvascular gene expression in males with KS indicated enhanced capillary EC activation and increased inflammatory cross-talk, leading to impaired vessel maturation and increased EC barrier permeability.

LIMITATIONS, REASONS FOR CAUTION

Our study is constrained by an unbalanced design, with varying sample sizes and number of cells within each group. We acknowledge the restricted access to clinical information. In addition, our findings were deduced from changes in gene expression, which limits us to infer potential biological consequences arising from these alterations. Furthermore, the absence of a pre-pubertal age group limits the generalizability of our findings and warrants further investigation.

WIDER IMPLICATIONS OF THE FINDINGS

This study offers novel insights into the testicular pathophysiology in KS and underscores the potential contribution of microvascular dysfunction to the hypogonadism and infertility observed in males with KS. While this study aims to better understand the microvascular dysfunction in KS, the precise connections to testosterone deficiency and testicular atrophy remain to be fully elucidated.

STUDY FUNDING/COMPETING INTEREST(S)

A.S. was supported by the Independent Research Fund Denmark (0134-00130B). C.H.G. was supported by Novo Nordisk Foundation (NNF15OC0016474, NNF20OC0060610), 'Fonden til lægevidenskabens fremme', the Familien Hede Nielsen foundation and the Independent Research Fund Denmark (0134-00406A). E.B.J. was supported by Aarhus University and E.B.J. and C.H.G by the Independent Research Fund Denmark (2096-00165A). J.M.K. was supported by Lundbeckfonden (R307-2018-3667), Carlsberg Fonden (CF19-0687), Novo Nordisk Fonden (0073440) and Steno Diabetes Center Aarhus (SDCA). The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Angiotensin II type 2 receptor-mediated dilation is greater in the cutaneous microvasculature of premenopausal women compared with men

Differential activation of the renin-angiotensin system (RAS) likely contributes to sex differences in cardiovascular outcomes in premenopausal women compared with age-matched men. Women demonstrate reduced activation of the vasoconstrictor angiotensin II type 1 receptors (AT1R) compared with men, and evidence suggests that women also likely have increased sensitivity of the vasodilatory angiotensin II type 2 receptors (AT2R). However, few in vivo studies have directly examined sex differences in AT2R-mediated dilation, or the balance between AT1R- and AT2R-mediated vascular responses in humans. Using the cutaneous microcirculation as a model, we hypothesized that AT2R-mediated dilation would be greater in premenopausal women compared with men, and that AT1R-blockade would augment AT2R-mediated dilation to a greater extent in men than in women. Twelve healthy women (22 ± 3 yr) and 12 men (23 ± 5 yr) had two intradermal microdialysis fibers placed in the ventral forearm for graded infusions of compound 21 (AT2R agonist; 10-12 to 10-8 M) in a control fiber site and a site treated with 43 µM losartan (AT1R antagonist). Red blood cell flux was measured continuously by laser-Doppler flowmetry, and cutaneous vascular conductance [CVC = flux/mean arterial pressure (MAP)] was normalized to maximum [%max; 28 mM sodium nitroprusside (SNP) + 43 °C]. Women had greater AT2R-mediated dilation compared with men (women: 25 ± 4 vs. men: 15 ± 2%max, P = 0.03). Local AT1R inhibition increased AT2R-mediated dilation in men (losartan: 26 ± 4 vs. control: 15 ± 2%max, P < 0.001) but had no effect in women (losartan: 27 ± 6 vs. control: 25 ± 4%max, P > 0.05). These data suggest that premenopausal women have a greater AT2R-mediated vasodilation response than men, and that AT1R activation inhibits AT2R-mediated dilation in men, but not in women.NEW & NOTEWORTHY Premenopausal women have greater protection against cardiovascular disease than age-matched men. However, the role of vasoconstrictor angiotensin II type 1 receptors (AT1R) and vasodilatory angiotensin II type 2 receptors (AT2R) in mediating these sex differences is unclear. Here, we demonstrate that women have greater AT2R-mediated vasodilation than men and that AT1R negates AT2R-mediated dilation in men, but not in women.

Effect of perfluoropropane (C3F8) versus sulfurhexafluoride (SF6) tamponades on the retinal microvasculature after macular hole surgery

PURPOSE

To determine the effects of C3F8 and SF6 gasses by using optical coherence tomography angiography (OCTA) in patients with surgically closed idiopathic full-thickness macular holes (FTMH).

METHODS

A prospective, comparative study, in which 38 eyes of 38 patients with an idiopathic FTMH were studied. Twenty patients were randomized to the C3F8 group and 18 patients to the SF6 group. All patients underwent pars plana vitrectomy, internal limiting membrane peeling with 14 % C3F8 or 20 % SF6 gasses. The superficial capillary plexus (SCP) and deep capillary plexus (DCP) vessel densities (VD), foveal avascular zone (FAZ) area in SCP, the choriocapillaris flow area; and subfoveal choroidal thickness (SFCT) were examined at preoperative and postoperative first- and third-month controls using OCTA.

RESULTS

When the changes in the FAZ, SFCT, SCP and DCP VDs were compared, no significant differences were found between the groups (p>0.05 for all). It was determined that the 1-mm radius flow area increases in the C3F8 group at the first and third months after the surgery were significantly higher than in the SF6 group (p<0.05). A significant gain was observed in the BCVA values compared to their preoperative values for both groups; however any differences between the C3F8 and SF6 groups in terms of BCVA were not detected in this study.

CONCLUSION

This is the first report to compare the effects of C3F8 and SF6 gasses on idiopathic FTMH surgery by using OCTA. C3F8 and SF6 gasses may have similar effect on the remodeling process of vascular tissues.

Comparison of the retinal microvasculature between compressive and glaucomatous optic neuropathy

PURPOSE

To compare the patterns of retinal microvasculature change in the peripapillary and macular region between compressive optic neuropathy (CON) and glaucomatous optic neuropathy (GON), and to assess the ability of optical coherence tomography angiography (OCTA) in differentiating the two conditions.

METHODS

This cross-sectional study included 108 participants (108 eyes), 36 with CON, 36 with GON, and 36 healthy controls. The CON and GON eyes were matched by the average peripapillary retinal nerve fiber layer (pRNFL) thickness (1:1). Optical coherence tomography (OCT) and OCTA were performed to compare the structural and vascular change of the peripapillary and macular region between groups.

RESULTS

Both CON and GON eyes showed more severe structural and vascular damage than the control eyes. The CON eyes had lower pRNFL thickness than the GON eyes in the temporal and nasal quadrants, and thicker pRNFL thickness in the inferior quadrant. The average GCC thickness did not differ between the two groups. The peripapillary vessel density of the CON group was significantly higher in the inferior sectors than that of the GON group. In the macular region, the CON group had significantly higher vessel density in the whole image, the temporal sector in parafovea region, and the temporal, superior, and inferior sectors in perifovea region.

CONCLUSION

To a similar degree of structural damage, CON had less retinal vascular impairment than GON, especially in the macular region, and the significance of the finding needs further evaluation.

A cell-and-plasma numerical model reveals hemodynamic stress and flow adaptation in zebrafish microvessels after morphological alteration

The development of a functional cardiovascular system ensures a sustainable oxygen, nutrient and hormone delivery system for successful embryonic development and homeostasis in adulthood. While early vessels are formed by biochemical signaling and genetic programming, the onset of blood flow provides mechanical cues that participate in vascular remodeling of the embryonic vascular system. The zebrafish is a prolific animal model for studying the quantitative relationship between blood flow and vascular morphogenesis due to a combination of favorable factors including blood flow visualization in optically transparent larvae. In this study, we have developed a cell-and-plasma blood transport model using computational fluid dynamics (CFD) to understand how red blood cell (RBC) partitioning affect lumen wall shear stress (WSS) and blood pressure in zebrafish trunk blood vascular networks with altered rheology and morphology. By performing live imaging of embryos with reduced hematocrit, we discovered that cardiac output and caudal artery flow rates were maintained. These adaptation trends were recapitulated in our CFD models, which showed reduction in network WSS via viscosity reduction in the caudal artery/vein and via pressure gradient weakening in the intersegmental vessels (ISVs). Embryos with experimentally reduced lumen diameter showed reduced cardiac output and caudal artery flow rate. Factoring in this trend into our CFD models, simulations highlighted that lumen diameter reduction increased vessel WSS but this increase was mitigated by flow reduction due to the adaptive network pressure gradient weakening. Additionally, hypothetical network CFD models with different vessel lumen diameter distribution characteristics indicated the significance of axial variation in lumen diameter and cross-sectional shape for establishing physiological WSS gradients along ISVs. In summary, our work demonstrates how both experiment-driven and hypothetical CFD modeling can be employed for the study of blood flow physiology during vascular remodeling.

Dual-color miniscope imaging of microvessels and neuronal activity in the hippocampus CA1 region of freely moving mice following alcohol administration

Moderate-to-heavy episodic ("binge") drinking is the most common form of alcohol consumption in the United States. Alcohol at binge drinking concentrations reduces brain artery diameter in vivo and in vitro in many species including rats, mice, and humans. Despite the critical role played by brain vessels in maintaining neuronal function, there is a shortage of methodologies to simultaneously assess neuron and blood vessel function in deep brain regions. Here, we investigate cerebrovascular responses to ethanol by choosing a deep brain region that is implicated in alcohol disruption of brain function, the hippocampal CA1, and describe the process for obtaining simultaneous imaging of pyramidal neuron activity and diameter of nearby microvessels in freely moving mice via a dual-color miniscope. Recordings of neurovascular events were performed upon intraperitoneal injection of saline versus 3 g/kg ethanol in the same mouse. In male mice, ethanol mildly increased the amplitude of calcium signals while robustly decreasing their frequency. Simultaneously, ethanol decreased microvessel diameter. In females, ethanol did not change the amplitude or frequency of calcium signals from CA1 neurons but decreased microvessel diameter. A linear regression of ethanol-induced reduction in number of active neurons and microvessel constriction revealed a positive correlation (R = 0.981) in females. Together, these data demonstrate the feasibility of simultaneously evaluating neuronal and vascular components of alcohol actions in a deep brain area in freely moving mice, as well as the sexual dimorphism of hippocampal neurovascular responses to alcohol.

Macro, Micro, and Everything in Between. Bridging the Gap: A Vision Toward the Creation of Multiscale Vascular Networks

Vascularization is a key issue for the clinical translation of tissue engineering strategies. This has been recognized in the field for almost two decades. Several strategies to solve this issue are proposed but none has decisively tackled the problem. This is in part due to an excessive focus on microvascularization that ignores the need of having macrovessels capable of being surgically connected to the patient's circulation upon implantation. Indeed, a strategy for macrovessel engineering must co-exist with a strategy for microvessels. And if this is true, all the intermediate scales have to be addressed as well. Therefore, multiscale vascular networks must be the focus of tissue engineering vascularization efforts. In this work, a reflection is made on a possible path forward for researchers and engineers in the field to achieve the ultimate goal of efficient vascularization of engineered tissues and organs.

The Association of Retinal Microvasculature With Gray Matter Changes and Structural Covariance Network: A Voxel-Based Morphometry Study

Purpose

Increasing evidence suggests that retinal microvasculature may reflect global cerebral atrophy. However, little is known about the relation of retinal microvasculature with specific brain regions and brain networks. Therefore, we aimed to unravel the association of retinal microvasculature with gray matter changes and structural covariance network using a voxel-based morphometry (VBM) analysis.

Methods

One hundred and forty-four volunteers without previously known neurological diseases were recruited from West China Hospital, Sichuan University between April 1, 2021, and December 31, 2021. Retinal microvasculature of superficial vascular plexus (SVP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP) were measured by optical coherence tomography angiography using an automatic segmentation. The VBM and structural covariance network analyses were applied to process brain magnetic resonance imaging (MRI) images. The associations of retinal microvasculature with voxel-wise gray matter volumes and structural covariance network were assessed by linear regression models.

Results

In the study, 137 participants (mean age = 59.72 years, 37.2% men) were included for the final analysis. Reduced perfusion in SVP was significantly associated with reduced voxel-wise gray matter volumes of the brain regions including the insula, putamen, occipital, frontal, and temporal lobes, all of which were located in the anterior part of the brain supplied by internal carotid artery, except the occipital lobe. In addition, these regions were also involved in visual processing and cognitive impairment (such as left inferior occipital gyrus, left lingual gyrus, and right parahippocampal gyrus). In regard to the structural covariance, the perfusions in SVP were positively related to the structural covariance of the left lingual gyrus seed with the left middle occipital gyrus, the right middle occipital gyrus, and the left middle frontal gyrus.

Conclusions

Poor perfusion in SVP was correlated with reduced voxel-wise gray matter volumes and structural covariance networks in regions related to visual processing and cognitive impairment. It suggests that retinal microvasculature may offer a window to identify aging related cerebral alterations.

Diabetic microvascular disease in non-classical beds: the hidden impact beyond the retina, the kidney, and the peripheral nerves

Diabetes microangiopathy, a hallmark complication of diabetes, is characterised by structural and functional abnormalities within the intricate network of microvessels beyond well-known and documented target organs, i.e., the retina, kidney, and peripheral nerves. Indeed, an intact microvascular bed is crucial for preserving each organ's specific functions and achieving physiological balance to meet their respective metabolic demands. Therefore, diabetes-related microvascular dysfunction leads to widespread multiorgan consequences in still-overlooked non-traditional target organs such as the brain, the lung, the bone tissue, the skin, the arterial wall, the heart, or the musculoskeletal system. All these organs are vulnerable to the physiopathological mechanisms that cause microvascular damage in diabetes (i.e., hyperglycaemia-induced oxidative stress, inflammation, and endothelial dysfunction) and collectively contribute to abnormalities in the microvessels' structure and function, compromising blood flow and tissue perfusion. However, the microcirculatory networks differ between organs due to variations in haemodynamic, vascular architecture, and affected cells, resulting in a spectrum of clinical presentations. The aim of this review is to focus on the multifaceted nature of microvascular impairment in diabetes through available evidence of specific consequences in often overlooked organs. A better understanding of diabetes microangiopathy in non-target organs provides a broader perspective on the systemic nature of the disease, underscoring the importance of recognising the comprehensive range of complications beyond the classic target sites.

Changes in peripapillary microvasculature in patients with type 2 diabetes patients: effect of systemic hypertension

To determine the effect of hypertension (HTN) on the peripapillary microvasculature in type 2 diabetes mellitus (T2DM) patients without diabetic retinopathy (DR). The patients were classified into three groups: the control group (group 1), T2DM group (group 2), and both T2DM and HTN group (group 3). Peripapillary vessel density (VD) was compared using analysis of covariance and linear regression analysis was performed to identify the factors affecting the peripapillary VD. A total of 286 eyes were enrolled: 124 in group 1, 111 in group 2, and 51 in group 3. The peripapillary VDs for the full area were 18.3 ± 0.6, 17.8 ± 1.0, and 17.3 ± 1.2 mm-1 in group 1, group 2, and group 3, respectively, which were significantly different after adjustment for age and best-corrected visual acuity (P < 0.001). In post hoc analyses, group 1 versus group 2 (P < 0.001), group 1 versus group 3 (P < 0.001), and group 2 versus group 3 (P = 0.001) showed significant differences. In linear regression analysis, HTN (B =  - 0.352, P = 0.043) and peripapillary retinal nerve fiber layer (pRNFL) thickness (B = 0.045, P < 0.001) were significantly associated with peripapillary VD in T2DM patients. Peripapillary VD in T2DM patients without clinical DR were lower compared to normal controls, and they were more decreased when HTN was comorbid. The combination of ischemic damage by high blood pressure and impairment of the neurovascular unit by hyperglycemia would result in more severe deterioration of peripapillary microvasculature, and this impairment could be also reflected by pRNFL thinning.

Ultrasound standing wave spatial patterning of human umbilical vein endothelial cells for 3D micro-vascular networks formation

Generating functional and perfusable micro-vascular networks is an important goal for the fabrication of large and three-dimensional tissues. Up to now, the fabrication of micro-vascular networks is a complicated multitask involving several different factors such as time consuming, cells survival, micro-diameter vasculature and strict alignment. Here, we propose a technique combining multi-material extrusion and ultrasound standing wave forces to create a network structure of human umbilical vein endothelial cells within a mixture of calcium alginate and decellularized extracellular matrix. The functionality of the matured microvasculature networks was demonstrated through the enhancement of cell-cell adhesion, angiogenesis process, and perfusion tests with microparticles, FITC-dextran, and whole mouse blood. Moreover, animal experiments exhibited the implantability including that the pre-existing blood vessels of the host sprout towards the preformed vessels of the scaffold over time and the microvessels inside the implanted scaffold matured from empty tubular structures to functional blood-carrying microvessels in two weeks.

Correlation Between Corneal Whorl-Like Nerve and Retinal Neurodegenerative Changes and Their Association With Microvessel Perfusion in Diabetes

Purpose

The purpose of this study was to compare the evolution of changes in the corneal nerves, retinal nerves, and cells and blood vessels at a single time point in early diabetic retinopathy (DR).

Methods

Eighty participants (60 with diabetes and 20 nondiabetic controls) were examined. DR was graded according to the International Classification of Diabetic Retinopathy. Inferior whorl length (IWL), spiral orientation, central nerve fiber length (CNFL), retinal nerve fiber layer (RNFL) thickness, ganglion cell complex (GCC) layer thickness, global loss volume (GLV), focal loss volume (FLV) indices, superficial (sVD), and deep vessel densities (dVD) were examined.

Results

Compared with those of healthy controls, the IWL, CNFL, and FLV were decreased in the diabetic groups (P < 0.001). The IWL was significantly positively correlated with the RNFL and GCC thicknesses in the diabetic group (r = 0.248, P = 0.006 and r = 0.207, P = 0.023, respectively) and significantly negatively correlated with the FLV (r = -0.535, P < 0.001). The sVD was significantly positively correlated with the RNFL thickness (r = 0.314, P < 0.001) and negatively correlated with the GLV (r = -0.229, P = 0.012).

Conclusions

Our findings suggest a correlation between corneal whorl-like nerve plexus and retinal nerve changes in the early stages of DR and that the IWL of the cornea may be able to indicate the extent of DR. Retinal nerve changes are associated with retinal microvessel perfusion, and nerve changes may precede vessel lesions.

Quantitative Assessment of Retinal and Choroidal Microvasculature in Asymptomatic Patients with Carotid Artery Stenosis

SIGNIFICANCE

Carotid disease contributes to 15 to 20% of all ischemic strokes, one of the leading causes of permanent disabilities and mortality globally. With its growing prevalence and the inflicted disability rates, screening for anomalies that precede the onset of its serious complications is of crucial global significance.

PURPOSE

This study aimed to assess the relationship between retinal and choroidal perfusion changes with the degree of stenosis using quantitative swept-source optical coherence tomography angiography in patients with internal carotid artery stenosis.

METHODS

A retrospective cohort study was conducted in 72 eyes with carotid stenosis. According to the degree of stenosis, the participants were divided into a healthy group (group 1: 34 eyes), a mild-moderate stenosis group (group 2: 22 eyes), and a severe stenosis group (group 3: 16 eyes). Swept-source optical coherence tomography angiography was performed to scan macular fovea. Capillary density values in the different retinal and choroidal layers were the major measurements for our study.

RESULTS

Mean vessel density in the midchoroid layer was significantly higher in groups 2 and 3 compared with group 1. Deep choroid disclosed significantly superior vascular density values in group 3 compared with groups 2 and 1. Superficial and deep capillary plexus showed decreased vascular density values when comparing group 3 with groups 1 and 2, although they were not significant.

CONCLUSIONS

Our report provides the first evidence that choroidal microvascular changes were correlated with severity of carotid artery stenosis. Optical coherence tomography angiography can sensitively detect subtle, early changes in the ocular blood in carotid disease representing a useful, noninvasive, and objective approach to the retinal microvasculature.

Automated evaluation of parapapillary choroidal microvasculature in thyroid eye disease

PURPOSE

The purpose of the study was to investigate the parapapillary choroidal microvasculature in thyroid eye disease (TED) using optical coherence tomography angiography (OCTA).

METHODS

Only one eye of each subject was included in the study. Patients with TED and controls were included in the study. Participants were divided into three groups: control, inactive TED (ITED) and active TED (ATED). OCTA scans of the optic discs were obtained in a 4.5 × 4.5-mm rectangular area. Radial peripapillary capillary (RPC) density and peripapillary retinal nerve fibre layer (pRNFL) thickness were automatically calculated by the device software. Parapapillary choroidal microvasculature (PPCMv) density was automatically calculated using MATLAB software.

RESULTS

Forty-one patients with TED and 40 controls were included in the study. RPC density was significantly decreased in the ATED and dysthyroid optic neuropathy (DON) group compared to the controls and ITED group. There was significant increase in pRNFL in the ATED group. PPCMv density increased in the ATED group compared to the controls in whole ring area. The RPC density was significantly correlated with the TSHr Ab level (r < - 0.396, p < 0.001). Clinical activity score correlated positively with PPCMv density (r = 0.349, p = 0.001) but negatively with RPC density (r = - 0.321, p = 0.004).

CONCLUSION

Changes in peripapillary microvascular perfusion may play a role in the development of DON. As the severity of TED increases with clinical activity, so do the changes observed in peripapillary parameters. The decrease in RPC density may be due to compression caused by optic disc oedema, which may result in reduced blood flow. The increase in PPCMv density may be related to factors such as orbital congestion.

Rate of Retinal Nerve Fiber Layer Thinning in Glaucomatous Eyes With Optic Disc and Parapapillary Deep-Layer Microvasculature Loss

PRCIS

Microvasculature dropout in the parapapillary choroidal layer was a more important biomarker of glaucomatous nerve fiber layer thinning when it presented with deep-layer microvasculature of the optic disc rather than when it presents by itself.

PURPOSE

To characterize open angle glaucoma eyes with optic nerve head deep-layer microvasculature dropout (MvD-D) and parapapillary choroidal layer microvasculature dropout (MvD-P) and compare their retinal nerve fiber layer (RNFL) thinning rate.

MATERIAL AND METHODS

This study included 122 open angle glaucoma eyes that underwent ≥5 serial spectral-domain optical coherence tomography scans during a mean follow-up of 5.4 years. Swept-source optical coherence tomography angiography was used to evaluate MvD-P and MvD-D. Subjects were classified into 3 groups according to the presence of MvD-P and MvD-D: (1) no dropout (n=37); (2) solely MvD-P (n=40), and (3) both MvD-P and MvD-D (n=45). The RNFL thinning rate was compared among the 3 groups, and the associated factors were assessed by Cox proportional hazard analysis.

RESULTS

RNFL thinning rates were highest in the group with both MvD-P and MvD-D, followed by the group with solely MvD-P and finally by the no dropout group (-0.24 vs. -0.65 vs. -1.20 μm/y, P <0.001). Thinner central corneal thickness [hazard ratio (HR)0.990, P =0.003], presence of disc hemorrhage (HR=1.802, P =0.035), and coexistence of MvD-P and MvD-D (HR=2.941, P <0.001) were the factors associated with RNFL thinning.

CONCLUSIONS

The coexistence of MvD-P and MvD-D was associated with faster RNFL thinning than MvD-P alone or no dropout, which suggested that observing the optic disc deep microvasculature along with parapapillary choroidal layer using Swept-source optical coherence tomography angiography may be clinically relevant in monitoring glaucoma progression.

The value of indocyanine green-FLOW800 in microvasculature for predicting cerebral hyperperfusion syndrome in moyamoya disease patients

Among the notable complications of direct hemodynamic reconstruction for moyamoya disease (MMD) is cerebral hyperperfusion syndrome (CHS). In this study, we evaluated hemodynamic changes in small regional microvasculature (SRMV) around the anastomosis site by using indocyanine green (ICG)-FLOW800 video angiography and verified that it better predicted the onset of CHS. Intraoperative ICG-FLOW800 analysis was performed on 31 patients (36 cerebral hemispheres) with MMD who underwent superficial temporal artery-middle cerebral artery (MCA) bypass grafting at our institution. The regions of interest were established in the SRMV and thicker MCA around the anastomosis. Calculations were made for half-peak to time (TTP1/2), cerebral blood volume (CBV), and cerebral blood flow (CBF). According to the presence or absence of CHS after surgery, CHS and non-CHS groups of patients were separated. The results showed that ΔCBV and ΔCBF were substantially greater in SRMV than in MCA (p < 0.001). Compared with the non-CHS group, ΔCBF and ΔCBV of SRMV and MCA were considerably greater in the CHS group (p < 0.001). ΔCBF and ΔCBV on the ROC curve for both SRMV and MCA had high sensitivity and specificity (SRMV: ΔCBF, AUC = 0.8586; ΔCBV, AUC = 0.8158. MCA: ΔCBF, AUC = 0.7993; ΔCBV, AUC = 0.8684). ICG-FLOW800 video angiography verified the differential hemodynamic changes in the peri-anastomotic MCA and SRMV before and after bypass surgery in patients with MMD.

Improving vasculoprotective effects of MSCs in coronary microvessels - benefits of 3D culture, sub-populations and heparin

Introduction

Opening occluded coronary arteries in patients with myocardial infarction (MI) damages the delicate coronary microvessels through a process called myocardial ischaemia-reperfusion injury. Although mesenchymal stromal cells (MSCs) have the potential to limit this injury, clinical success remains limited. This may be due to (i) poor MSC homing to the heart (ii) infused MSCs, even if derived from the same site, being a heterogeneous population with varying therapeutic efficacy and (iii) conventional 2D culture of MSCs decreasing their homing and beneficial properties. This study investigated whether 3D culture of two distinctly different bone marrow (BM)-derived MSC sub-populations could improve their homing and coronary vasculoprotective efficacy.

Methods

Intravital imaging of the anaesthetised mouse beating heart was used to investigate the trafficking and microvascular protective effects of two clonally-derived BM-derived MSC lines, namely CD317neg MSCs-Y201 and CD317pos MSCs-Y202, cultured using conventional monolayer and 3D hanging drop methods.

Results

3D culture consistently improved the adhesive behaviour of MSCs-Y201 to various substrates in vitro. However, it was their differential ability to reduce neutrophil events within the coronary capillaries and improve ventricular perfusion in vivo that was most remarkable. Moreover, dual therapy combined with heparin further improved the vasculoprotection afforded by 3D cultured MSCs-Y201 by also modifying platelet as well as neutrophil recruitment, which subsequently led to the greatest salvage of viable myocardium. Therapeutic benefit could mechanistically be explained by reductions in coronary endothelial oxidative stress and intercellular adhesion molecule-1 (ICAM-1)/vascular cell adhesion molecule-1 (VCAM-1) expression. However, since this was noted by both 2D and 3D cultured MSCs-Y201, therapeutic benefit is likely explained by the fact that 3D cultured MSCs-Y201 were the most potent sub-population at reducing serum levels of several pro-inflammatory cytokines.

Conclusion

This novel study highlights the importance of not only 3D culture, but also of a specific CD317neg MSC sub-population, as being critical to realising their full coronary vasculoprotective potential in the injured heart. Since the smallest coronary blood vessels are increasingly recognised as a primary target of reperfusion injury, therapeutic interventions must be able to protect these delicate structures from inflammatory cells and maintain perfusion in the heart. We propose that relatively feasible technical modifications in a specific BM-derived MSC sub-population could achieve this.

Cortical spheroid on perfusable microvascular network in a microfluidic device

Human induced pluripotent stem cell (hiPSC)-derived brain spheroids can recapitulate the complex cytoarchitecture of the brain, as well as the genetic/epigenetic footprint of human brain development. However, hiPSC-derived 3D models such as spheroid and organoids does not have a perfusable microvascular network, which plays a vital role in maintaining homeostasis in vivo. With the critical balance of positive and negative angiogenic modulators, 3D microvascular network can be achieved by angiogenesis. This paper reports on a microfluidic-based three-dimensional, cortical spheroid grafted on the vascular-network. Vascular network was formed by inducing angiogenic sprouting using concentration gradient-driven angiogenic factors in the microfluidic device. We investigate critical factors for angiogenic vascular network formation with spheroid placement, including 1) a PKCα activator, phorbol-12-myristate-13-acetate (PMA); 2) orientation of endothelial cells under perfusion and permeability of vascular network; 3) effect of extracellular matrix (ECM) types and their densities on angiogenesis; and 4) integration with cortical spheroid on vascular network. This paper demonstrates proof of concept for the potential utility of a membrane-free in vitro cortical spheroid tissue construct with perfusable microvascular network that can be scaled up to a high throughput platform. It can provide a cost-effective alternative platform to animal testing by modeling brain diseases and disorders, and screening drugs.

Analyses of the ratio of ganglion cell-inner plexiform layer thickness to vessel density according to age in healthy eyes

PURPOSE

To identify how the inner retinal layer and microvasculature change with age by analyzing the relationships of ganglion cell-inner plexiform layer (GC-IPL) thickness, vessel density (VD), and the ratio of these measurements with age in healthy eyes.

METHODS

Participants were divided into five groups according to age. The GC-IPL thickness, VD, and GC-IPL/VD ratio were compared among the groups. Linear regression analyses were performed to identify relationships of GC-IPL/VD ratio with age.

RESULTS

The average GC-IPL thicknesses were 84.84 ± 5.28, 84.22 ± 5.30, 85.20 ± 6.29, 83.29 ± 7.06, and 82.26 ± 5.62 μm in the 20s, 30s, 40s, 50s, and 60s age groups, respectively. The VDs were 20.94 ± 1.50, 21.06 ± 1.50, 20.99 ± 1.03, 20.71 ± 0.93, and 19.74 ± 1.73 mm-1 in the 20s, 30s, 40s, 50s, and 60s age groups, respectively. The GC-IPL/VD ratio was 4.05, 4.00, 4.06, 4.02, and 4.17 in each group, respectively, and the ratio of the 60s age group was significantly higher than that of other groups. In linear regression analyses, the GC-IPL/VD ratio was significantly associated with age in the participants aged ≥ 50 years (B = 0.014, P = 0.013), whereas it was not in the participants aged < 50 years (B = 0.003, P = 0.434).

CONCLUSIONS

GC-IPL thickness and macular VD showed a tendency to decrease beginning in the 50s age group and the GC-IPL/VD ratio was significantly increased in the 60s age group. Additionally, the GC-IPL/VD ratio was positively associated with age in subjects aged ≥ 50 years, which implies a more pronounced decline over time in VD rather than GC-IPL thickness.

Development of a perfusable, hierarchical microvasculature-on-a-chip model

Several methods have been developed for generating 3D, in vitro, organ-on-chip models of human vasculature to study vascular function, transport, and tissue engineering. However, many of these existing models lack the hierarchical nature of the arterial-to-capillary-to-venous architecture that is key to capturing a more comprehensive view of the human microvasculature. Here, we present a perfusable, multi-compartmental model that recapitulates the three microvascular compartments to assess various physiological properties such as vessel permeability, vasoconstriction dynamics, and circulating cell arrest and extravasation. Viscous finger patterning and passive pumping create the larger arterial and venular lumens, while the smaller diameter capillary bed vessels are generated through self-assembly. These compartments anastomose and form a perfusable, hierarchical system that portrays the directionality of blood flow through the microvasculature. The addition of collagen channels reduces the apparent permeability of the central capillary region, likely by reducing leakage from the side channels, enabling more accurate measurements of vascular permeability-an important motivation for this study. Furthermore, the model permits modulation of fluid flow and shear stress conditions throughout the system by using hydrostatic pressure heads to apply pressure differentials across either the arteriole or the capillary. This is a pertinent system for modeling circulating tumor or T cell dissemination and extravasation. Circulating cells were found to arrest in areas conducive to physical trapping or areas with the least amount of shear stress, consistent with hemodynamic or mechanical theories of metastasis. Overall, this model captures more features of human microvascular beds and is capable of testing a broad variety of hypotheses.

Autoregulatory mission impossible: when afferent arterioles lose contractility

The myogenic response of afferent arterioles is a key autoregulatory mechanism that protects the glomeruli from barotrauma. Afferent arteriolar smooth muscle cells contract to increased intraluminal pressure through mechanosensitive cation channels and interactions between integrin and extracellular matrix that trigger calcium-dependent actomyosin contraction. The study by Feng et al. provides evidence supporting the concept that increased matrix metalloproteinase 9 in kidney microvessels of Dahl salt-sensitive rats interferes with integrin-matrix binding and promotes phenotypic transformation of afferent arterioles, causing loss of myogenic constriction and hypertensive nephropathy.

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.