Combined Electron Microscopy Approaches for Arterial Glycocalyx Visualization

Imaging the microstructure of the arterial wall - ex vivo to in vivo potential

Microstructural imaging enables researchers to visualise changes in the arterial wall, allowing for (i) a deeper understanding of the role of specific components in arterial mechanics, (ii) the observation of cellular responses, (iii) insights into pathological alterations in tissue microstructure, and/or (iv) advancements in tissue engineering aimed at replicating healthy native tissue. In this prospective review, we present various imaging modalities spanning from ex vivo to in vivo applications within arterial tissue. The pros, cons, and sensitivities of these modalities are highlighted. By consolidating the latest advancements in microstructural imaging of arterial tissue, the authors aim for this paper to serve as a guide for researchers designing experiments at various stages. Furthermore, the integration of non-invasive, non-destructive imaging techniques into studies provides an additional layer of microstructural information, enhancing scientific findings, improving our understanding of disease, and potentially enabling earlier or more effective diagnostic capabilities. STATEMENT OF SIGNIFICANCE: Imaging the specific microstructural components of the arterial wall provides critical insights into vascular biology, mechanics, and pathology. It enables the visualisation of key structural components and their roles in arterial function, supports the analysis of cell-matrix interactions, and reveals microarchitectural changes associated with disease progression. This level of specificity also informs the design of biomimetic materials and scaffolds in tissue engineering, facilitating the replication of native arterial properties. By synthesising recent developments in microstructural imaging techniques, this paper serves as a reference for investigators designing experiments across a range of vascular research applications. Moreover, the incorporation of non-invasive, non-destructive imaging methods offers a means to acquire detailed microstructural data without compromising tissue integrity. This enhances the interpretability and translational potential of findings, deepens our understanding of vascular disease mechanisms, and may ultimately contribute to the development of earlier and more precise diagnostic approaches.

Endothelial glycocalyx in different flow regions of the trabecular outflow pathway in bovine eyes

Background

Glycocalyx is a hair-like structure covering the endothelium of the aqueous outflow pathway. While trabecular outflow is segmental circumferentially around the eye, regional differences in glycocalyx morphology remain largely unexplored. This study investigated glycocalyx variations in the different structures along the trabecular outflow pathway in high-flow (HF) and low-flow (LF) regions of bovine eyes.

Methods

Enucleated bovine eyes (n = 8) were perfused with fluorescein to identify HF and LF regions. The glycocalyx was labeled with Alcian Blue 8GX, and radial wedges from the anterior chamber angles of both HF and LF regions were processed for transmission electron microscopy. Glycocalyx thickness and coverage were quantified using ImageJ and compared between different outflow pathway locations in HF and LF regions. Glycocalyx measurements at intracellular (I-pores) and border pores (B-pores), the percentage of glycocalyx-unfilled pores, as well as the percentage of giant vacuoles (GVs) with and without I-pores with glycocalyx lining the inner membrane were evaluated.

Results

Glycocalyx thickness and coverage did not differ significantly between HF and LF regions. However, thickness progressively increased from the proximal (trabecular meshwork) to the distal (episcleral veins) outflow pathway. In both I-pores and B-pores, the glycocalyx was present near the basal opening, edge, and center of the pores, with thickness increasing toward the center. No significant differences in the percentage of glycocalyx-filled pores were observed between HF and LF regions. However, the percentage of GVs with I-pores exhibiting glycocalyx lining the inner cellular membrane was significantly higher (100%) than that of those without I-pores (16%).

Conclusion

No regional differences were found between HF and LF regions, but glycocalyx thickness progressively increased from the proximal to the distal outflow pathway, potentially reflecting varying shear stress conditions. The significantly higher percentage of GVs with I-pores containing glycocalyx lining the inner cellular membrane compared to those without I-pores suggests a relationship between aqueous outflow dynamics and glycocalyx synthesis. These findings provide a morphological basis for future research on glycocalyx alterations in glaucoma and their impact on outflow resistance.

Destruction of vascular endothelial glycocalyx during formation of pre-metastatic niches

A special microenvironment called the "pre-metastatic niche" is thought to help primary tumor cells migrate to new tissues and invade them, in part because the normal barrier function of the vascular endothelium is compromised. While the primary tumor itself can promote the creation of such niches by secreting pro-metastatic factors, the underlying molecular mechanisms are still poorly understood. Here, we show that the injection of primary tumor-secreted pro-metastatic factors from B16F10 melanoma or 4T1 breast cancer cells into healthy mice can induce the destruction of the vascular endothelial glycocalyx, which is a polysaccharide coating on the vascular endothelial lumen that normally inhibits tumor cell passage into and out of the circulation. However, when human umbilical vein endothelial cultures were treated in vitro with these secreted pro-metastatic factors, no significant destruction of the glycocalyx was observed, implying that this destruction requires a complex in vivo microenvironment. The tissue section analysis revealed that secreted pro-metastatic factors could clearly upregulate macrophage-related molecules such as CD11b and tumor necrosis factor-α (TNF-α) in the heart, liver, spleen, lung, and kidney, which is associated with the upregulation and activation of heparanase. In addition, macrophage depletion significantly attenuated the degradation of the vascular endothelial glycocalyx induced by secreted pro-metastatic factors. This indicates that the secreted pro-metastatic factors that destroy the vascular endothelial glycocalyx rely primarily on macrophages. Our findings suggest that the formation of pre-metastatic niches involves degradation of the vascular endothelial glycocalyx, which may hence be a useful target for developing therapies to inhibit cancer metastasis.

Acute and repeated exposures of normal human bronchial epithelial (NHBE) cells culture to particles from a coloured pyrotechnic smoke

Coloured pyrotechnic smokes are frequently used in the military field and occasionally by civilians, but their health hazards have been little studied. The main concern could rise from inhalation of smoke particles. Our previous study showed that acute exposure to particles from a red signalling smoke (RSS) induced an antioxidant and inflammatory responses in small airway epithelial cells. The aim of this study was to further explore the toxicity of RSS particles at a more proximal level of the respiratory tract, using normal human bronchial epithelial cells grown at the Air-Liquid Interface. Acute exposure (24 h) induced an oxidative stress that persisted 24 h post-exposure, associated with particle internalization and epithelium morphological changes (cuboidal appearance and loss of cilia). Repeated exposures (4×16h) to RSS particles did not trigger oxidative stress but cell morphological changes occurred. Overall, this study provides a better overview of the toxic effects of coloured smoke particles.

Endothelial Function Assessment by Flow-Mediated Dilation Method: A Valuable Tool in the Evaluation of the Cardiovascular System

Cardiovascular diseases (CVDs) in the course of atherosclerosis are one of the most critical public health problems in the world. Endothelial cells synthesize numerous biologically active substances involved in regulating the functions of the cardiovascular system. Endothelial dysfunction is an essential element in the pathogenesis of atherosclerosis. Thus, the assessment of endothelial function in people without overt CVD allows for a more accurate estimate of the risk of developing CVD and cardiovascular events. The assessment of endothelial function is primarily used in scientific research, and to a lesser extent in clinical practice. Among the tools for assessing endothelial function, we can distinguish biochemical and physical methods, while physical methods can be divided into invasive and non-invasive methods. Flow-mediated dilation (FMD) is based on the ultrasound assessment of changes in the diameter of the brachial artery as a result of increased blood flow. FMD is a non-invasive, safe, and repeatable test, but it must be performed by qualified and experienced medical staff. The purpose of this paper is to present the literature review results on the assessment of endothelial function using the FMD method, including its methodology, applications in clinical practice and research, limitations, and future perspectives.