Vasculoprotective properties of the endothelial glycocalyx: effects of fluid shear stress

Basal endothelial glycocalyx's response to shear stress: a review of structure, function, and clinical implications

The endothelial glycocalyx encompasses the entire endothelial cell, transducing extracellular signals and regulating vascular permeability and barrier functions. The apical glycocalyx, which forms the lumen of the vessel, and the basal glycocalyx, at the smooth muscle cell interface, are often investigated separately as they are exposed to vastly different stimuli. The apical glycocalyx directly senses fluid shear forces transmitting them intracellularly through connection to the cytoskeleton of the endothelial cell. The basal glycocalyx has demonstrated sensitivity to shear due to blood flow transmitted through the cytoskeleton, promoting alternate signaling processes. In this review, we discuss current literature on the basal glycocalyx's response to shear stress in the context of mechanotransduction and remodeling. The possible implications of basal glycocalyx degradation in pathologies are also explored. Finally, this review seeks to highlight how addressing the gaps discussed would improve our wholistic understanding of the endothelial glycocalyx and its role in maintaining vascular homeostasis.

Disruption of the endothelial glycocalyx layer is associated with idiopathic complete atrioventricular block in the elderly population: An observational pilot study

Idiopathic atrioventricular block (iCAVB) is the most common reason for the need for a permanent pacemaker in the elderly population. The fibrotic process that occurs in the conduction system of the heart with aging is the main pathogenesis in the development of iCAVB. However, the processes that trigger the development of iCAVB in the elderly population have not been fully elucidated. In this study, we aimed to reveal the possible relationship between the endothelial glycocalyx (EG) layer and idiopathic complete atrioventricular block. A group of 68 consecutive patients who developed iCAVB and a group of 68 healthy subjects matched for age, sex, and cardiovascular risk factors were included in the study. The groups were compared for clinical, laboratory, and levels of Syndecan-1 (SDC1), an EG layer marker. In the study, SDC1 levels were found to be significantly higher in the iCAVB group compared to the control group (23.7 ± 7.5 vs 16.7 ± 5.2; p = 0.009). In multivariable regression analysis, SDC1 was determined as an independent potential predictor for iCAVB (OR: 1.200; 95% CI: 1.119-1.287; p < 0.001). In the receiver operating characteristic curve analysis, SDC1 predicted iCAVB with 74% sensitivity and 72% specificity at the best cut-off value of 18.5 ng/mL (area under the curve: 0.777; confidence interval: 0.698-0.856; p < 0.001). Disruption of the endothelial glycolic layer may be one of the main triggering factors for the process leading to iCAVB.

Soluble vascular endothelial glycocalyx proteoglycans as potential therapeutic targets in inflammatory diseases

Reducing the activity of cytokines and leukocyte extravasation is an emerging therapeutic strategy to limit tissue-damaging inflammatory responses and restore immune homeostasis in inflammatory diseases. Proteoglycans embedded in the vascular endothelial glycocalyx, which regulate the activity of cytokines to restrict the inflammatory response in physiological conditions, are proteolytically cleaved in inflammatory diseases. Here we critically review the potential of proteolytically shed, soluble vascular endothelial glycocalyx proteoglycans to modulate pathological inflammatory responses. Soluble forms of the proteoglycans syndecan-1, syndecan-3 and biglycan exert beneficial anti-inflammatory effects by the removal of chemokines, suppression of proinflammatory cytokine expression and leukocyte migration, and induction of autophagy of proinflammatory M1 macrophages. By contrast, soluble versikine and decorin enhance proinflammatory responses by increasing inflammatory cytokine synthesis and leukocyte migration. Endogenous syndecan-2 and mimecan exert proinflammatory effects, syndecan-4 and perlecan mediate beneficial anti-inflammatory effects and glypican regulates Hh and Wnt signaling pathways involved in systemic inflammatory responses. Taken together, targeting the vascular endothelial glycocalyx-derived, soluble syndecan-1, syndecan-2, syndecan-3, syndecan-4, biglycan, versikine, mimecan, perlecan, glypican and decorin might be a potential therapeutic strategy to suppress overstimulated cytokine and leukocyte responses in inflammatory diseases.

Shear Stress and Endothelial Mechanotransduction in Trauma Patients with Hemorrhagic Shock: Hidden Coagulopathy Pathways and Novel Therapeutic Strategies

Massive trauma remains a leading cause of death and a global public health burden. Post-traumatic coagulopathy may be present even before the onset of resuscitation, and correlates with severity of trauma. Several mechanisms have been proposed to explain the development of abnormal coagulation processes, but the heterogeneity in injuries and patient profiles makes it difficult to define a dominant mechanism. Regardless of the pattern of death, a significant role in the pathophysiology and pathogenesis of coagulopathy may be attributed to the exposure of endothelial cells to abnormal physical forces and mechanical stimuli in their local environment. In these conditions, the cellular responses are translated into biochemical signals that induce/aggravate oxidative stress, inflammation, and coagulopathy. Microvascular shear stress-induced alterations could be treated or prevented by the development and use of innovative pharmacologic strategies that effectively target shear-mediated endothelial dysfunction, including shear-responsive drug delivery systems and novel antioxidants, and by targeting the venous side of the circulation to exploit the beneficial antithrombogenic profile of venous endothelial cells.

Resuscitating the Endothelial Glycocalyx in Trauma and Hemorrhagic Shock

The endothelium is lined by a protective mesh of proteins and carbohydrates called the endothelial glycocalyx (EG). This layer creates a negatively charged gel-like barrier between the vascular environment and the surface of the endothelial cell. When intact the EG serves multiple functions, including mechanotransduction, cell signaling, regulation of permeability and fluid exchange across the microvasculature, and management of cell-cell interactions. In trauma and/or hemorrhagic shock, the glycocalyx is broken down, resulting in the shedding of its individual components. The shedding of the EG is associated with increased systemic inflammation, microvascular permeability, and flow-induced vasodilation, leading to further physiologic derangements. Animal and human studies have shown that the greater the severity of the injury, the greater the degree of shedding, which is associated with poor patient outcomes. Additional studies have shown that prioritizing certain resuscitation fluids, such as plasma, cryoprecipitate, and whole blood over crystalloid shows improved outcomes in hemorrhaging patients, potentially through a decrease in EG shedding impacting downstream signaling. The purpose of the following paragraphs is to briefly describe the EG, review the impact of EG shedding and hemorrhagic shock, and begin entertaining the notion of directed resuscitation. Directed resuscitation emphasizes transitioning from macroscopic 1:1 resuscitation to efforts that focus on minimizing EG shedding and maximizing its reconstitution.

Research Progress of Flavonoids Regulating Endothelial Function

The endothelium, as the guardian of vascular homeostasis, is closely related to the occurrence and development of cardiovascular diseases (CVDs). As an early marker of the development of a series of vascular diseases, endothelial dysfunction is often accompanied by oxidative stress and inflammatory response. Natural flavonoids in fruits, vegetables, and Chinese herbal medicines have been shown to induce and regulate endothelial cells and exert anti-inflammatory, anti-oxidative stress, and anti-aging effects in a large number of in vitro models and in vivo experiments so as to achieve the prevention and improvement of cardiovascular disease. Focusing on endothelial mediation, this paper introduces the signaling pathways involved in the improvement of endothelial dysfunction by common dietary and flavonoids in traditional Chinese medicine and describes them based on their metabolism in the human body and their relationship with the intestinal flora. The aim of this paper is to demonstrate the broad pharmacological activity and target development potential of flavonoids as food supplements and drug components in regulating endothelial function and thus in the prevention and treatment of cardiovascular diseases. This paper also introduces the application of some new nanoparticle carriers in order to improve their bioavailability in the human body and play a broader role in vascular protection.

Bidirectional airflow in lung airway-on-a-chip with matrix-derived membrane elicits epithelial glycocalyx formation

Organ-on-a-chip systems are rapidly advancing as a viable alternative to existing experimental models in respiratory research. To date, however, epithelial cell cultures within lung airway-on-a-chip devices have yet to demonstrate the presence of an epithelial glycocalyx, a thin layer of proteoglycans, glycoproteins, and glycolipids known to play an important role in regulating epithelial function. Here, we demonstrate that an airway-on-a-chip device that incorporates bidirectional flow mimicking breathing cycles in combination with an ultra-thin matrix-derived membrane (UMM) layer can generate a glycocalyx layer comprised of heparan sulfate. Results with this device and airflow system showed dramatic differences of airway epithelial cell viability and expression of tight junctions, cilia, and mucus over a wide range of flow rates when cultured under oscillatory flow. More importantly, for the first time in a microfluidic organ-on-a-chip setting, we achieved the visualization of an airflow-induced epithelial glycocalyx layer. Our experiments highlight the importance of physiological mimicry in developing in vitro models, as bidirectional airflow showed more representative mucociliary differentiation compared to continuous unidirectional airflow. Thus, the lung airway-on-a-chip platform demonstrated in this study holds great potential as a lung epithelial barrier model for studying the mechanisms of various respiratory diseases and for testing the efficacy of therapeutic candidates in the presence of bidirectional airflow and the glycocalyx.

Endothelial Glycocalyx Integrity in Treatment-Naïve People Living with HIV before and One Year after Antiretroviral Treatment Initiation

Endothelial glycocalyx (EG) derangement has been associated with cardiovascular disease (CVD). Studies on EG integrity among people living with HIV (PLWH), are lacking. We conducted a prospective cohort study among treatment-naïve PLWH who received emtricitabine/tenofovir alafenamide, combined with either an integrase strand transfer inhibitor (INSTI, dolutegravir, raltegravir or elvitegravir/cobicistat), or a protease inhibitor (PI, darunavir/cobicistat). We assessed EG at baseline, 24 (±4) and 48 (±4) weeks, by measuring the perfused boundary region (PBR, inversely proportional to EG thickness), in sublingual microvessels. In total, 66 consecutive PLWH (60 (90.9%) males) with a median age (interquartile range, IQR) of 37 (12) years, were enrolled. In total, 40(60.6%) received INSTI-based regimens. The mean (standard deviation) PBR decreased significantly from 2.17 (0.29) μm at baseline to 2.04 (0.26) μm (p = 0.019), and then to 1.93 (0.3) μm (p < 0.0001) at 24 (±4) and 48 (±4) weeks, respectively. PBR did not differ among treatment groups. PLWH on INSTIs had a significant PBR reduction at 48 (±4) weeks. Smokers and PLWH with low levels of viremia experienced the greatest PBR reduction. This study is the first to report the benefit of antiretroviral treatment on EG improvement in treatment-naïve PLWH and depicts a potential bedside biomarker and therapeutic target for CVD in PLWH.

Inflammatory stimuli induce shedding of heparan sulfate from arterial but not venous porcine endothelial cells leading to differential proinflammatory and procoagulant responses

Endothelial dysfunction is an early event of vascular injury defined by a proinflammatory and procoagulant endothelial cell (EC) phenotype. Although endothelial glycocalyx disruption is associated with vascular damage, how various inflammatory stimuli affect the glycocalyx and whether arterial and venous cells respond differently is unknown. Using a 3D round-channel microfluidic system we investigated the endothelial glycocalyx, particularly heparan sulfate (HS), on porcine arterial and venous ECs. Heparan sulfate (HS)/glycocalyx expression was observed already under static conditions on venous ECs while it was flow-dependent on arterial cells. Furthermore, analysis of HS/glycocalyx response after stimulation with inflammatory cues revealed that venous, but not arterial ECs, are resistant to HS shedding. This finding was observed also on isolated porcine vessels. Persistence of HS on venous ECs prevented complement deposition and clot formation after stimulation with tumor necrosis factor α or lipopolysaccharide, whereas after xenogeneic activation no glycocalyx-mediated protection was observed. Contrarily, HS shedding on arterial cells, even without an inflammatory insult, was sufficient to induce a proinflammatory and procoagulant phenotype. Our data indicate that the dimorphic response of arterial and venous ECs is partially due to distinct HS/glycocalyx dynamics suggesting that arterial and venous thrombo-inflammatory disorders require targeted therapies.

Malondialdehyde as an Important Key Factor of Molecular Mechanisms of Vascular Wall Damage under Heart Diseases Development

This mini review is devoted to a specific issue: the role of malondialdehyde (MDA)-a secondary product of free radical lipid peroxidation-in the molecular mechanisms of the formation of primary atherosclerotic vascular wall lesions. The principal difference between this review and the available literature is that it discusses in detail the important role in atherogenesis not of "oxidized" LDL (i.e., LDL particles containing lipohydroperoxides), but of LDL particles chemically modified by the natural low-molecular weight dicarbonyl MDA. To confirm this, we consider the data obtained by us earlier, indicating that "atherogenic" are not LDL oxidized as a result of free radical lipoperoxidation and containing lipohydroperoxy derivatives of phospholipids in the outer layer of particles, but LDL whose apoprotein B-100 has been modified due to the chemical reaction of terminal lysine residue amino groups of the apoB-100 with the aldehyde groups of the MDA (Maillard reaction). In addition, we present our original data proving that MDA injures endothelial glycocalyx that suppress the ability of the endothelium to control arterial tone according to changes in wall shear stress. In summary, this mini review for the first time exhaustively discloses the key role of MDA in atherogenesis.

Modeling the Endothelial Glycocalyx Layer in the Human Conventional Aqueous Outflow Pathway

A layer of proteoglycans and glycoproteins known as glycocalyx covers the surface of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm's canal (SC) inner wall of the conventional aqueous outflow pathway in the eye. This has been shown to play a role in the mechanotransduction of fluid shear stress and in the regulation of the outflow resistance. The outflow resistance in the conventional outflow pathway is the main determinant of the intraocular pressure (IOP) through an active, two-way, fluid-structure interaction coupling between the outflow tissues and aqueous humor. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex with interspersed aqueous humor was constructed. A very thin charged double layer that represents the endothelial glycocalyx layer covered the surface of the elastic outflow tissues. The aqueous humor was modeled as electroosmotic flow that is charged when it is in contact with the outflow tissues. The electrical-fluid-structure interaction (EFSI) method was used to couple the charged double layer (glycocalyx), fluid (aqueous humor), and solid (outflow tissues). When the IOP was elevated to 15 mmHg, the maximum aqueous humor velocity in the EFSI model was decreased by 2.35 mm/s (9%) compared to the fluid-structure interaction (FSI) model. The charge or electricity in the living human conventional outflow pathway generated by the charged endothelial glycocalyx layer plays a minor biomechanical role in the resultant stresses and strains as well as the hydrodynamics of the aqueous humor.

Arterial hypertension as a consequence of endothelial glycocalyx dysfunction: a modern view of the problem of cardiovascular diseases

Arterial hypertension (AH) is a leading risk factor for the development of cardiovascular, cerebrovascular, and renal diseases, which are among the top 10 most common causes of death in the world. The etiology of hypertension has not been fully elucidated, but it has been established that endothelial dysfunction is the most significant pathogenetic link in the formation and progression of the disease. The data obtained in the last 10-15 years on endothelial glycocalyx (eGC) studies indicate that endothelial dysfunction is preceded 

by destabilization and shedding of eGC with the appearance of its soluble components in the blood, which is equivalent to a process that can be designated as eGC dysfunction. Signs of eGC dysfunction are expressed in the development of hypertension, diseases of the cardiovascular system, and their complications. The purpose of this review is to analyze and substantiate the pathophysiological role of eGC dysfunction in hypertension and cardiovascular diseases and to describe approaches for its assessment and pharmacological correction. Abstracts and full-size articles of 425 publications in Pubmed/MEDLINE databases over 20 years were studied. The review discusses the role of eGC in the regulation of vascular tone, endothelial barrier function, and anti-adhesive properties of eGC. Modifications of eGC under the influence of pro-inflammatory stimuli, changes in eGC with age, and with increased salt load are considered. The aspect associated with eGC dysfunction in atherosclerosis, hyperglycemia and hypertension is covered. Assessment of eGC dysfunction is difficult but can be performed by indirect methods, in particular by detecting eGC components in blood. A brief description of the main approaches to pharmacoprevention and pharmacocorrection of hypertension is given from the position of exposure effects on eGC, which currently has more a fundamental than practical orientation. This opens up great opportunities for clinical studies of eGC dysfunction for the prevention and treatment of hypertension and justifies a new direction in the clinical pharmacology of antihypertensive drugs.

Glycocalyx Sensing with a Mathematical Model of Acoustic Shear Wave Biosensor

The article deals with an idea of exploiting an acoustic shear wave biosensor for investigating the glycocalyx, a polysaccharide polymer molecule layer on the endothelium of blood vessels that, according to recent studies, plays an important role in protecting against diseases. To test this idea, a mathematical model of an acoustic shear wave sensor and corresponding software developed earlier for proteomic applications are used. In this case, the glycocalyx is treated as a layer homogenized over the thin polymer “villi”. Its material characteristics depend on the density, thickness, and length of the villi and on the viscous properties of the surrounding liquid (blood plasma). It is proved that the model used has a good sensitivity to the above parameters of the villi and blood plasma. Numerical experiments performed using real data collected retrospectively from premature infants show that the use of acoustic shear wave sensors may be a promising approach to investigate properties of glycocalyx-like structures and their role in prematurity.

Flow-induced glycocalyx formation and cell alignment of HUVECs compared to iPSC-derived ECs for tissue engineering applications

The relevance of cellular in vitro models highly depends on their ability to mimic the physiological environment of the respective tissue or cell niche. Static culture conditions are often unsuitable, especially for endothelial models, since they completely neglect the physiological surface shear stress and corresponding reactions of endothelial cells (ECs) such as alignment in the direction of flow. Furthermore, formation and maturation of the glycocalyx, the essential polysaccharide layer covering all endothelial surfaces and regulating diverse processes, is highly dependent on applied fluid flow. This fragile but utterly important macromolecular layer is hard to analyze, its importance is often underestimated and accordingly neglected in many endothelial models. Therefore, we exposed human umbilical vein ECs (HUVECs) and human induced pluripotent stem cell-derived ECs (iPSC-ECs) as two relevant EC models in a side-by-side comparison to static and physiological dynamic (6.6 dyn cm⁻²) culture conditions. Both cell types demonstrated an elongation and alignment along the flow direction, some distinct changes in glycocalyx composition on the surface regarding the main glycosaminoglycan components heparan sulfate, chondroitin sulfate or hyaluronic acid as well as an increased and thereby improved glycocalyx thickness and functionality when cultured under homogeneous fluid flow. Thus, we were able to demonstrate the maturity of the employed iPSC-EC model regarding its ability to sense fluid flow along with the general importance of physiological shear stress for glycocalyx formation. Additionally, we investigated EC monolayer integrity with and without application of surface shear stress, revealing a comparable existence of tight junctions for all conditions and a reorganization of the cytoskeleton upon dynamic culture leading to an increased formation of focal adhesions. We then fabricated cell sheets of EC monolayers after static and dynamic culture via non-enzymatic detachment using thermoresponsive polymer coatings as culture substrates. In a first proof-of-concept we were able to transfer an aligned iPSC-EC sheet to a 3D-printed scaffold thereby making a step in the direction of vascular modelling. We envision these results to be a valuable contribution to improvements of in vitro endothelial models and vascular engineering in the future.

Endothelial Glycocalyx

The glycocalyx is a polysaccharide structure that protrudes from the body of a cell. It is primarily conformed of glycoproteins and proteoglycans, which provide communication, electrostatic charge, ionic buffering, permeability, and mechanosensation-mechanotransduction capabilities to cells. In blood vessels, the endothelial glycocalyx that projects into the vascular lumen separates the vascular wall from the circulating blood. Such a physical location allows a number of its components, including sialic acid, glypican-1, heparan sulfate, and hyaluronan, to participate in the mechanosensation-mechanotransduction of blood flow-dependent shear stress, which results in the synthesis of nitric oxide and flow-mediated vasodilation. The endothelial glycocalyx also participates in the regulation of vascular permeability and the modulation of inflammatory responses, including the processes of leukocyte rolling and extravasation. Its structural architecture and negative charge work to prevent macromolecules greater than approximately 70 kDa and cationic molecules from binding and flowing out of the vasculature. This also prevents the extravasation of pathogens such as bacteria and virus, as well as that of tumor cells. Due to its constant exposure to shear and circulating enzymes such as neuraminidase, heparanase, hyaluronidase, and matrix metalloproteinases, the endothelial glycocalyx is in a continuous process of degradation and renovation. A balance favoring degradation is associated with a variety of pathologies including atherosclerosis, hypertension, vascular aging, metastatic cancer, and diabetic vasculopathies. Consequently, ongoing research efforts are focused on deciphering the mechanisms that promote glycocalyx degradation or limit its syntheses, as well as on therapeutic approaches to improve glycocalyx integrity with the goal of reducing vascular disease. © 2022 American Physiological Society. Compr Physiol 12: 1-31, 2022.

Dicarbonyl-Dependent Modification of LDL as a Key Factor of Endothelial Dysfunction and Atherosclerotic Vascular Wall Damage

The review presents evidence that the main damage to the vascular wall occurs not from the action of “oxidized” LDL, which contain hydroperoxy acyls in the phospholipids located in their outer layer, but from the action of LDL particles whose apoprotein B-100 is chemically modified with low molecular weight dicarbonyls, such as malondialdehyde, glyoxal, and methylglyoxal. It has been argued that dicarbonyl-modified LDL, which have the highest cholesterol content, are particularly “atherogenic”. High levels of dicarbonyl-modified LDL have been found to be characteristic of some mutations of apoprotein B-100. Based on the reviewed data, we hypothesized a common molecular mechanism underlying vascular wall damage in atherosclerosis and diabetes mellitus. The important role of oxidatively modified LDL in endothelial dysfunction is discussed in detail. In particular, the role of the interaction of the endothelial receptor LOX-1 with oxidatively modified LDL, which leads to the expression of NADPH oxidase, which in turn generates superoxide anion radical, is discussed. Such hyperproduction of ROS can cause destruction of the glycocalyx, a protective layer of endotheliocytes, and stimulation of apoptosis in these cells. On the whole, the accumulated evidence suggests that carbonyl modification of apoprotein B-100 of LDL is a key factor responsible for vascular wall damage leading to atherogenesis and endothelial dysfunction. Possible ways of pharmacological correction of free radical processes in atherogenesis and diabetogenesis are also discussed.

Endothelial Glycocalyx Morphology in Different Flow Regions of the Aqueous Outflow Pathway of Normal and Laser-Induced Glaucoma Monkey Eyes

Glycocalyx morphology was examined in the trabecular outflow pathway of monkey eyes with and without experimental glaucoma. Laser burns were administered along ~270 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey until intraocular pressure remained elevated. Portions of the TM were not laser-treated. Unlasered eyes (n = 6) served as controls. Enucleated eyes were perfused at 15 mmHg to measure the outflow facility, perfused with fluorescein to evaluate the outflow pattern, perfusion-fixed for glycocalyx labeling, and processed for electron microscopy. Coverage and thickness of the glycocalyx were measured in the TM, Schlemm’s canal (SC), collector channels (CCs), intrascleral veins (ISVs), and episcleral veins (ESVs) in non-lasered regions and high- and low-flow regions of controls. Compared to controls, laser-treated eyes had decreased outflow facility (p = 0.02). Glycocalyx thickness increased from the TM to ESVs in non-lasered regions and controls (p < 0.05). Glycocalyx coverage was generally greater distally in non-lasered regions (p < 0.05). In lasered regions, TM, SC, and CCs were partly to completely obliterated, and ISVs and ESVs displayed minimal glycocalyx. Whether the glycocalyx is decreased in the trabecular outflow pathway of human glaucomatous eyes warrants investigation.

Biomarkers of Glycocalyx Injury and Endothelial Activation are Associated with Clinical Outcomes in Patients with Sepsis: A Systematic Review and Meta-Analysis

OBJECTIVE

Sepsis is one of the main causes of morbidity and mortality worldwide. Microcirculatory impairment, especially damage to the endothelium and glycocalyx, is often not assessed. The objective of this systematic review and meta-analysis was to summarize the available evidence of the risk of unsatisfactory outcomes in patients with sepsis and elevated glycocalyx injury and endothelial activation biomarkers.

DESIGN

A systematic search was carried out on PubMed/MEDLINE, Embase, Cochrane and Google Scholar up to December 31, 2021, including studies in adults and children with sepsis which measured glycocalyx injury and endothelial activation biomarkers within 48 hours of hospital admission. The primary outcome was the risk of mortality from all causes and the secondary outcomes were the risk of developing respiratory failure (RF) and multiple organ dysfunction syndrome (MODS) in patients with elevations of these biomarkers.

MEASUREMENTS AND MAIN RESULTS

A total of 17 studies (3,529 patients) were included: 11 evaluated syndecan-1 (n=2,397) and 6 endocan (n=1,132). Syndecan-1 was higher in the group of patients who died than in those who survived [255 ng/mL (IQR: 139-305) vs. 83 ng/mL (IQR:40-111); p=0.014]. Patients with elevated syndecan-1 had a greater risk of death (OR 2.32; 95% CI 1.89, 3.10: p<0.001), MODS (OR 3.3; 95% CI 1.51, 7.25: p=0.003;), or RF (OR 7.53; 95% CI 1.86-30.45: p=0.005). Endocan was higher in patients who died [3.1 ng/mL (IQR 2.3, 3.7) vs. 1.62 ng/mL (IQR 1.2, 5.7); OR 9.53; 95% CI 3.34, 27.3; p<0.001], who had MODS (OR 8.33; 95% CI 2.07, 33.58; p=0.003) and who had RF (OR 9.66; 95% CI 2.26, 43.95; p=0.002).

CONCLUSION

Patients with sepsis and abnormal glycocalyx injury and endothelial activation biomarkers have a greater risk of developing respiratory failure, multiple organ failure, and death. Microcirculatory impairment should be routinely evaluated in patients with sepsis, using biomarkers to stratify risk groups.

Variability in Retinal Neuron Populations and Associated Variations in Mass Transport Systems of the Retina in Health and Aging

Aging is associated with a broad range of visual impairments that can have dramatic consequences on the quality of life of those impacted. These changes are driven by a complex series of alterations affecting interactions between multiple cellular and extracellular elements. The resilience of many of these interactions may be key to minimal loss of visual function in aging; yet many of them remain poorly understood. In this review, we focus on the relation between retinal neurons and their respective mass transport systems. These metabolite delivery systems include the retinal vasculature, which lies within the inner portion of the retina, and the choroidal vasculature located externally to the retinal tissue. A framework for investigation is proposed and applied to identify the structures and processes determining retinal mass transport at the cellular and tissue levels. Spatial variability in the structure of the retina and changes observed in aging are then harnessed to explore the relation between variations in neuron populations and those seen among retinal metabolite delivery systems. Existing data demonstrate that the relation between inner retinal neurons and their mass transport systems is different in nature from that observed between the outer retina and choroid. The most prominent structural changes observed across the eye and in aging are seen in Bruch’s membrane, which forms a selective barrier to mass transfers at the interface between the choroidal vasculature and the outer retina.

Influence of microflow on hepatic sinusoid blood flow and red blood cell deformation

Hepatic sinusoids present complex anatomical structures such as the endothelial sieve pores and the Disse space, which govern the microscopic blood flow in the sinusoids and are associated with structural variations in liver fibrosis and cirrhosis. However, the contributions of the permeability of endothelial and collagen layers and the roughness of hepatocyte microvilli to the features of this microflow remain largely unknown. Here, an immersed boundary method coupled with a lattice Boltzmann method was adopted in an in vitro hepatic sinusoidal model, and flow field and erythrocyte deformation analyses were conducted by introducing three new source terms including permeability of the endothelial layer, resistance of hepatocyte microvilli and collagen layers, and deformation of red blood cells (RBCs). Numerical calculations indicated that alterations in endothelial permeability could significantly affect the flow velocity and flow rate distributions in hepatic sinusoids. Interestingly, a biphasic regulating pattern of shear stress occurred simultaneously on the surface of hepatocytes and the lower side of endothelium, i.e., the shear stress increased with increased thickness of hepatocyte microvilli and collagen layer when the endothelial permeability was high but decreased with the increase of the thickness at low endothelial permeability. Additionally, this specified microflow manipulates typical RBC deformation inside the sinusoid, yielding one-third of the variation of deformable index with varied endothelial permeability. These simulations not only are consistent with experimental measurements using in vitro liver sinusoidal chip but also elaborate the contributions of endothelial and collagen layer permeability and wall roughness. Thus, our results provide a basis for further characterizing this microflow and understanding its effects on cellular migration and deformation in the hepatic sinusoids.

Capillary-size flow of human blood plasma: Revealing hidden elasticity and scale dependence

The dynamical mechanical analysis of blood generally uses models inspired by conventional flows, assuming scale-independent homogeneous flows and without considering fluid-surface boundary interactions. The present experimental study highlights the relevance of using an approach in line with physiological reality providing a strong interaction between the fluid and the boundary interface. New dynamic properties of human blood plasma are found: a finite shear elastic response (solid-like property) is identified in nearly static conditions, which also depends on the scale (being reinforced at small scales). The elastic behavior is confirmed by the induction, without heat transfer, of local hot and cold thermodynamic states evidencing a thermo-mechanical coupling in blood plasma so far known only in elastic materials. This finding opens new routes for medical diagnosis and device fabrication.

Cross talk between endothelial and red blood cell glycocalyces via near-field flow

Vascular endothelial cells and circulating red blood cell (RBC) surfaces are both covered by a layer of bushy glycocalyx. The interplay between these glycocalyx layers is hardly measurable and insufficiently understood. This study aims to investigate and qualify the possible interactions between the glycocalyces of RBCs and endothelial cells using mathematical modeling and numerical simulation. Dissipative particle dynamics (DPD) simulations are conducted to investigate the response of the endothelial glycocalyx (EG) to varying ambient conditions. A two-compartment model including EG and flow and a three-compartment model comprising EG, RBC glycocalyx, and flow are established. The two-compartment analysis shows that a relatively fast flow is associated with a predominantly bending motion of the EG, whereas oscillatory motions are predominant in a relatively slow flow. Results show that circulating RBCs cause the contactless deformation of EG. Its deformation is dependent on the chain layout, chain length, bending stiffness, RBC-to-EG distance, and RBC velocities. Specifically, shorter EG chains or RBC-to-EG distance leads to greater relative deflections of EG. Deformation of EG is enhanced when the EG chains are rarefied or RBCs move faster. The bending stiffness maintains stretching conformation of EG. Moreover, a compact EG chain layout and shedding EG chains disturb the neighboring flow field, causing disordered flow velocity distributions. In contrast, the movement of EG chains on RBC surfaces exerts a marginal driving force on RBCs. The DPD method is used for the first time, to our knowledge, in the three-compartment system to explore the cross talk between EG and RBC glycocalyx. This study suggests that RBCs drive the EG deformation via the near-field flow, whereas marginal propulsion of RBCs by the EG is observed. These new, to our knowledge, findings provide a new angle to understand the roles of glycocalyx in mechanotransduction and microvascular permeability and their perturbations under idealized pathophysiologic conditions associated with EG degradation.

Differential vasodilator effect of Dioclea rostrata lectin in conductance and resistance arteries: Mechanisms and glycoconjugate binding relationships

Lectins are proteins that recognize specific carbohydrates, and the vasorelaxant effect of legume lectins has been previously reported, for example the Dioclea rostrata lectin (DRL). This study evaluated major pathways of DRL-induced relaxation in different artery segments and the possible molecular interactions involved. Rat thoracic aorta, coronary and mesenteric resistance arteries were tested "in vitro" with concentration-response curves to DRL (0.01-100 µg/mL). L-NAME, indomethacin and high KCl were used to evaluate nitric oxide, cyclooxygenase and hyperpolarization-dependent effects. DRL promoted relaxation of all vessels throughout different mechanisms. L-NAME blunted DRL-induced effects only in the aorta and mesenteric resistance artery. By the use of depolarizing KCl solution, vasodilation was reduced in all arteries, while incubation with indomethacin indicated a role of cyclooxygenase-derived factors for DRL effects in mesenteric and coronary arteries, but not in the aorta. Molecular docking results suggested interactions between DRL and heparan sulphate, CD31 and other glycans present on the membrane surface. These data indicate that the mechanisms involved in DRL-mediated vasodilation vary between conductance and resistance arteries of different origins, and these effects may be related to the capacity of DRL to bind a diversity of glycans, especially heparan sulphate, a proposed mechanoreceptor for nitric oxide synthase and cyclooxygenase activation.

The Role of Heparan Sulfate and Neuropilin 2 in VEGFA Signaling in Human Endothelial Tip Cells and Non-Tip Cells during Angiogenesis In Vitro

During angiogenesis, vascular endothelial growth factor A (VEGFA) regulates endothelial cell (EC) survival, tip cell formation, and stalk cell proliferation via VEGF receptor 2 (VEGFR2). VEGFR2 can interact with VEGFR2 co-receptors such as heparan sulfate proteoglycans (HSPGs) and neuropilin 2 (NRP2), but the exact roles of these co-receptors, or of sulfatase 2 (SULF2), an enzyme that removes sulfate groups from HSPGs and inhibits HSPG-mediated uptake of very low density lipoprotein (VLDL), in angiogenesis and tip cell biology are unknown. In the present study, we investigated whether the modulation of binding of VEGFA to VEGFR2 by knockdown of SULF2 or NRP2 affects sprouting angiogenesis, tip cell formation, proliferation of non-tip cells, and EC survival, or uptake of VLDL. To this end, we employed VEGFA splice variant 121, which lacks an HSPG binding domain, and VEGFA splice variant 165, which does have this domain, in in vitro models of angiogenic tip cells and vascular sprouting. We conclude that VEGFA₁₆₅ and VEGFA₁₂₁ have similar inducing effects on tip cells and sprouting in vitro, and that the binding of VEGFA₁₆₅ to HSPGs in the extracellular matrix does not seem to play a role, as knockdown of SULF2 did not alter these effects. Co-binding of NRP2 appears to regulate VEGFA–VEGFR2-induced sprout initiation, but not tip cell formation. Finally, as the addition of VLDL increased sprout formation but not tip cell formation, and as VLDL uptake was limited to non-tip cells, our findings suggest that VLDL plays a role in sprout formation by providing biomass for stalk cell proliferation.

Hyaluronan and Its Receptors as Regulatory Molecules of the Endothelial Interface

On the surface of endothelial cells (ECs) lies the glycocalyx, a barrier of polysaccharides that isolates the ECs from the blood. The role of the glycocalyx is dynamic and complex, thanks to not only its structure, but its vast number of components, one being hyaluronan (HA). HA is a critical component of the glycocalyx, having been found to have a wide variety of functions depending on its molecular weight, its modification, and receptor-ligand interactions. As HA and viscous blood are in constant contact, HA can transmit mechanosensory information directly to the cytoskeleton of the ECs. The degradation and synthesis of HA directly alters the permeability of the EC barrier; HA modulation not only alters the physical barrier but also can signal the initiation of other pathways. EC proliferation and angiogenesis are in part regulated by HA fragmentation, HA-dependent receptor binding, and downstream signals. The interaction between the CD44 receptor and HA is a driving force behind leukocyte recruitment, but each class of leukocyte still interacts with HA in unique ways during inflammation. HA regulates a diverse repertoire of EC functions.

Glycocalyx sialic acids regulate Nrf2-mediated signaling by fluid shear stress in human endothelial cells

Activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway is critical for vascular endothelial redox homeostasis in regions of high, unidirectional shear stress (USS), however the underlying mechanosensitive mediators are not fully understood. The endothelial glycocalyx is disrupted in arterial areas exposed to disturbed blood flow that also exhibit enhanced oxidative stress leading to atherogenesis. We investigated the contribution of glycocalyx sialic acids (SIA) to Nrf2 signaling in human endothelial cells (EC) exposed to atheroprotective USS or atherogenic low oscillatory shear stress (OSS). Cells exposed to USS exhibited a thicker glycocalyx and enhanced turnover of SIA which was reduced in cells cultured under OSS. Physiological USS, but not disturbed OSS, enhanced Nrf2-mediated expression of antioxidant enzymes, which was attenuated following SIA cleavage with exogenous neuraminidase. SIA removal disrupted kinase signaling involved in the nuclear accumulation of Nrf2 elicited by USS and promoted mitochondrial reactive oxygen species accumulation. Notably, knockdown of the endogenous sialidase NEU1 potentiated Nrf2 target gene expression, directly implicating SIA in regulation of Nrf2 signaling by USS. In the absence of SIA, deficits in Nrf2 responses to physiological flow were also associated with a pro-inflammatory EC phenotype. This study demonstrates that the glycocalyx modulates endothelial redox state in response to shear stress and provides the first evidence of an atheroprotective synergism between SIA and Nrf2 antioxidant signaling. The endothelial glycocalyx therefore represents a potential therapeutic target against EC dysfunction in cardiovascular disease and redox dyshomeostasis in ageing.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

3D confocal microscope imaging of macromolecule uptake in the intact brachiocephalic artery

BACKGROUND AND AIMS

Elevated uptake of plasma macromolecules by the arterial wall is an early event in atherogenesis. Existing optical techniques for detecting macromolecular tracers in the wall have poor depth penetration and hence require en face imaging of flattened arterial segments. Imaging uptake in undistorted curved and branched vessels would be useful in understanding disease development.

METHODS

Depth penetration was increased by applying optical clearing techniques. The rat aorto-brachiocephalic junction was imaged intact by confocal microscopy after it had been exposed to circulating rhodamine-labelled albumin in vivo, fixed in situ, excised and then cleared with benzyl alcohol/benzyl benzoate. Tracer uptake was mapped onto a 3D surface mesh of the arterial geometry.

RESULTS

Tracer fluorescence was detectable throughout the wall closest to the objective lens and, despite a vessel diameter of c. 1 mm, in the wall on the other side of the artery, across the lumen. By tile scanning, tracer concentrations were mapped in the aorta, the brachiocephalic artery and their junction without opening or flattening either vessel. Optical clearing was also shown to be compatible with immunofluorescent staining and imaging of experimental atherosclerosis.

CONCLUSIONS

The technique obviates the need for labour-intensive sample preparation associated with standard en face imaging. More importantly, it preserves arterial geometry, facilitating co-localisation of uptake maps with maps of biomechanical factors, which typically exist on 3D surface meshes. It will permit the correlation of haemodynamic wall shear stress with macromolecule permeability more accurately in regions of high curvature or branching, such as in the coronary arteries.

It Takes Two to Tango: Endothelial TGFβ/BMP Signaling Crosstalk with Mechanobiology

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGFβ) superfamily of cytokines. While some ligand members are potent inducers of angiogenesis, others promote vascular homeostasis. However, the precise understanding of the molecular mechanisms underlying these functions is still a growing research field. In bone, the tissue in which BMPs were first discovered, crosstalk of TGFβ/BMP signaling with mechanobiology is well understood. Likewise, the endothelium represents a tissue that is constantly exposed to multiple mechanical triggers, such as wall shear stress, elicited by blood flow or strain, and tension from the surrounding cells and to the extracellular matrix. To integrate mechanical stimuli, the cytoskeleton plays a pivotal role in the transduction of these forces in endothelial cells. Importantly, mechanical forces integrate on several levels of the TGFβ/BMP pathway, such as receptors and SMADs, but also global cell-architecture and nuclear chromatin re-organization. Here, we summarize the current literature on crosstalk mechanisms between biochemical cues elicited by TGFβ/BMP growth factors and mechanical cues, as shear stress or matrix stiffness that collectively orchestrate endothelial function. We focus on the different subcellular compartments in which the forces are sensed and integrated into the TGFβ/BMP growth factor signaling.

The Endothelial Glycocalyx: A Fundamental Determinant of Vascular Permeability in Sepsis

OBJECTIVES

Sepsis is a significant cause of morbidity and mortality. Children with sepsis often have alterations in microcirculation and vascular permeability. Our objective is current evidence regarding the role of the endothelial glycocalyx as a determinant of capillary leakage in these patients.

DATA SOURCES

We reviewed PubMed, EMBASE, and Google scholar using MeSH terms "glycocalyx", "fluids", "syndecan", "endothelium", "vascular permeability", "edema", "sepsis", "septic shock", "children".

STUDY SELECTION

Articles in all languages were included. We include all studies in animals and humans related to glycocalyx and vascular permeability.

DATA EXTRACTION

Studies in children and adults, as well as animal studies, were included.

DATA SYNTHESIS

One of the fundamental components of the endothelial barrier structure is the glycocalyx. It is a variable thickness layer distributed throughout the whole body, which fulfills a very important function for life: the regulation of blood vessel permeability to water and solutes, favoring vascular protection, modulation, and hemostasis. In the last few years, there has been a special interest in glycocalyx disorders and their relationship to increased vascular permeability, especially in patients with sepsis in whom the alterations that occur in the glycocalyx are unknown when they are subjected to different water resuscitation strategies, vasopressors, etc. This review describes the structural and functional characteristics of the glycocalyx, alterations in patients with sepsis, with regard to its importance in vascular permeability conservation and the possible impact of strategies to prevent and/or treat the injury of this fundamental structure.

CONCLUSIONS

The endothelial glycocalyx is a fundamental component of the endothelium and an important determinant of the mechanotransduction and vascular permeability in patients with sepsis. Studies are needed to evaluate the role of the different types of solutions used in fluid bolus, vasoactive support, and other interventions described in pediatric sepsis on microcirculation, particularly on endothelial integrity and the glycocalyx.

Prolonged Cardiopulmonary Bypass is Associated With Endothelial Glycocalyx Degradation

BACKGROUND

The endothelial glycocalyx (EG) is involved in critical regulatory mechanisms that maintain endothelial vascular integrity. We hypothesized that prolonged cardiopulmonary bypass (CPB) may be associated with EG degradation. We performed an analysis of soluble syndecan-1 levels in relation to duration of CPB, as well as factors associated with cell stress and damage, such as mitochondrial DNA (mtDNA) and inflammation.

METHODS

Blood samples from subjects undergoing cardiac surgery with CPB (n = 54) were obtained before and during surgery, 4-8 h and 24 h after completion of CPB, and on postoperative day 4. Flow cytometry was used to determine subpopulations of white blood cells. Plasma levels of mtDNA were determined using quantitative polymerase chain reaction and plasma content of shed syndecan-1 was measured. To determine whether syndecan-1 was signaling white blood cells, the effect of recombinant syndecan-1 on mobilization of neutrophils from bone marrow was tested in mice.

RESULTS

CPB is associated with increased mtDNA during surgery, increased syndecan-1 blood levels at 4-8 h, and increased white blood cell count at 4-8 h and 24 h. Correlation analysis revealed significant positive associations between time on CPB and syndecan-1 (r_s = 0.488, P < 0.001) and level of syndecan-1 and neutrophil count (r_s = 0.351, P = 0.038) at 4-8 h. Intravenous administration of recombinant syndecan-1 in mice resulted in a 2.5-fold increase in the number of circulating neutrophils, concurrent with decreased bone marrow neutrophil number.

CONCLUSIONS

Longer duration of CPB is associated with increased plasma levels of soluble syndecan-1, a signal for EG degradation, which can induce neutrophil egress from the bone marrow. Development of therapy targeting EG shedding may be beneficial in patients with prolonged CPB.

Mechanobiology of the abluminal glycocalyx

BACKGROUND

Endothelial cells (ECs) sense the forces from blood flow through the glycocalyx, a carbohydrate rich luminal surface layer decorating most cells, and through forces transmitted through focal adhesions (FAs) on the abluminal side of the cell.

OBJECTIVES

This perspective paper explores a complementary hypothesis, that glycocalyx molecules on the abluminal side of the EC between the basement membrane and the EC membrane, occupying the space outside of FAs, work in concert with FAs to sense blood flow-induced shear stress applied to the luminal surface.

RESULTS

First, we summarize recent studies suggesting that the glycocalyx repels the plasma membrane away from the basement membrane, while integrin molecules attach to extracellular matrix (ECM) ligands. This coordinated attraction and repulsion results in the focal nature of integrin-mediated adhesion making the abluminal glycocalyx a participant in mechanotransduction. Further, the glycocalyx mechanically links the plasma membrane to the basement membrane providing a mechanism of force transduction when the cell deforms in the peri-FA space. To determine if the membrane might deform against a restoring force of an elastic abluminal glycocalyx in the peri-FA space we present some analysis from a multicomponent elastic finite element model of a sheared and focally adhered endothelial cell whose abluminal topography was assessed using quantitative total internal reflection fluorescence microscopy with an assumption that glycocalyx fills the space between the membrane and extracellular matrix.

CONCLUSIONS

While requiring experimental verification, this analysis supports the hypothesis that shear on the luminal surface can be transmitted to the abluminal surface and deform the cell in the vicinity of the focal adhesions, with the magnitude of deformation depending on the abluminal glycocalyx modulus.

It takes more than two to tango: mechanosignaling of the endothelial surface

The endothelial surface is a highly flexible signaling hub which is able to sense the hemodynamic forces of the streaming blood. The subsequent mechanosignaling is basically mediated by specific structures, like the endothelial glycocalyx building the top surface layer of endothelial cells as well as mechanosensitive ion channels within the endothelial plasma membrane. The mechanical properties of the endothelial cell surface are characterized by the dynamics of cytoskeletal proteins and play a key role in the process of signal transmission from the outside (lumen of the blood vessel) to the interior of the cell. Thus, the cell mechanics directly interact with the function of mechanosensitive structures and ion channels. To precisely maintain the vascular tone, a coordinated functional interdependency between endothelial cells and vascular smooth muscle cells is necessary. This is given by the fact that mechanosensitive ion channels are expressed in both cell types and that signals are transmitted via autocrine/paracrine mechanisms from layer to layer. Thus, the outer layer of the endothelial cells can be seen as important functional mechanosensitive and reactive cellular compartment. This review aims to describe the known mechanosensitive structures of the vessel building a bridge between the important role of physiological mechanosignaling and the proper vascular function. Since mutations and dysfunction of mechanosensitive proteins are linked to vascular pathologies such as hypertension, they play a potent role in the field of channelopathies and mechanomedicine.

Flow-regulated endothelial glycocalyx determines metastatic cancer cell activity

Cancer metastasis and secondary tumor initiation largely depend on circulating tumor cell (CTC) and vascular endothelial cell (EC) interactions by incompletely understood mechanisms. Endothelial glycocalyx (GCX) dysfunction may play a significant role in this process. GCX structure depends on vascular flow patterns, which are irregular in tumor environments. This work presents evidence that disturbed flow (DF) induces GCX degradation, leading to CTC homing to the endothelium, a first step in secondary tumor formation. A 2-fold greater attachment of CTCs to human ECs was found to occur under DF conditions, compared to uniform flow (UF) conditions. These results corresponded to an approximately 50% decrease in wheat germ agglutinin (WGA)-labeled components of the GCX under DF conditions, vs UF conditions, with undifferentiated levels of CTC-recruiting E-selectin under DF vs UF conditions. Confirming the role of the GCX, neuraminidase induced the degradation of WGA-labeled GCX under UF cell culture conditions or in Balb/C mice and led to an over 2-fold increase in CTC attachment to ECs or Balb/C mouse lungs, respectively, compared to untreated conditions. These experiments confirm that flow-induced GCX degradation can enable metastatic CTC arrest. This work, therefore, provides new insight into pathways of secondary tumor formation.

The effect of sphingosine-1-phosphate on the endothelial glycocalyx during ischemia-reperfusion injury in the isolated rat heart

OBJECTIVE

Sphingosine-1-phosphate is a natural metabolite that is cardioprotective, but its effects on endothelial glycocalyx damage during ischemia-reperfusion are unknown. Therefore, we investigated the effect of sphingosine-1-phosphate on the endothelial glycocalyx during ischemia-reperfusion.

METHODS

Isolated hearts from Wistar rats were perfused on a Langendorff system with Krebs-Henseleit buffer and pretreated with sphingosine-1-phosphate (10 nmol/L) before ischemia-reperfusion. Infarct size was measured by triphenyl tetrazolium chloride staining (n ≥ 6 per group). Cardiac edema was assessed by calculating total water content (n = 7 per group) and histologically quantifying the interstitial compartment (n ≥ 3 per group). The post-ischemic coronary release of syndecan-1 was quantified using ELISA. Syndecan-1 immunostaining intensity was assessed in perfusion-fixed hearts (n ≥ 3 per group).

RESULTS

Pretreatment with sphingosine-1-phosphate decreased infarct size in isolated hearts subjected to ischemia-reperfusion (P = .01 vs ischemia-reperfusion). However, sphingosine-1-phosphate had no effect on syndecan-1 levels in the coronary effluent or on the intensity of the syndecan-1 immunostaining signal in cardiac tissue. Heart total water content was not significantly different between control and ischemic groups but was significantly decreased in hearts treated with sphingosine-1-phosphate alone.

CONCLUSION

These results suggest that sphingosine-1-phosphate-induced cardioprotection against ischemia-reperfusion injury is not mediated by the maintenance of syndecan-1 in the endothelial glycocalyx.

Endothelial Glycocalyx and the Peritoneal Barrier

Recent advances in the study of the microcirculation have demonstrated the critical role of the endothelial glycocalyx in transcapillary transport from the plasma to the tissue interstitium. Since the capillary wall represents the initial resistance to solute transfer from the plasma through the tissue to the dialysate, the glycocalyx is potentially of major importance to peritoneal dialysis. Inadvertently removed in early histological studies, this thin, delicate layer of glycosaminoglycans and proteoglycans is now recognized as a primary barrier in transendothelial solute and water transport. Subperitoneal endothelia are exposed to inflammation, angiogenesis, and hyperglycemia, which have been shown to affect the layer by increasing permeability. This entity permits new hypotheses concerning the factors that influence the transport characteristics of peritoneal dialysis patients and provides new avenues of basic research into the fundamental mechanisms of alteration of the peritoneal barrier.

Endothelial glycocalyx in acute care surgery - what anaesthesiologists need to know for clinical practice

The endothelial glycocalyx (EG) is the thin sugar-based lining on the apical surface of endothelial cells. It has been linked to the physiological functioning of the microcirculation and has been found to be damaged in critical illness and after acute care surgery. This review aims to describe the role of EG in severely injured patients undergoing surgery, discuss specific situations (e.G. major trauma, hemorrhagic shock, trauma induced coagulopathy) as well as specific interventions commonly applied in these patients (e.g. fluid therapy, transfusion) and specific drugs related to perioperative medicine with regard to their impact on EG.EG in acute care surgery is exposed to damage due to tissue trauma, inflammation, oxidative stress and inadequate fluid therapy. Even though some interventions (transfusion of plasma, human serum albumin, hydrocortisone, sevoflurane) are described as potentially EG protective there is still no specific treatment for EG protection and recovery in clinical medicine.The most important principle to be adopted in routine clinical practice at present is to acknowledge the fragile structure of the EG and avoid further damage which is potentially related to worsened clinical outcome.

Acute hyperglycemia exacerbates trauma-induced endothelial and glycocalyx injury: An in vitro model

BACKGROUND

Early hyperglycemia is associated with higher mortality in trauma and predicts multiple organ failure. Endothelial cell (EC) injury and glycocalyx (GC) degradation occur following traumatic shock and are key factors in the development of trauma-induced coagulopathy and result in impaired microvascular perfusion and accompanying organ failure. Acute hyperglycemia has been shown to result in the loss of the GC layer, EC inflammation, and activation of coagulation in vivo. We postulated that acute hyperglycemia would exacerbate trauma-induced EC injury and GC shedding and integrity. This was studied using a microfluidic device in a biomimetic in vitro model.

METHODS

Human umbilical vein endothelial cell monolayers established in the microfluidic channels of a microfluidic device well plate were perfused at constant shear overnight. Human umbilical vein endothelial cell monolayers were then exposed to hypoxia/reoxygenation and epinephrine followed by the addition of varying concentrations of glucose.

RESULTS

Glycocalyx shedding and loss of dimension, as well as EC injury/activation, were noted after exposure to the biomimetic conditions of trauma/shock in our study. Similar but less dramatic findings were noted after acute hyperglycemia. Exposure to hyperglycemia exacerbated the adverse effects on the GC and EC following hypoxia/reoxygenation plus epinephrine exposure and may be related to enhanced production of reactive oxygen species.

CONCLUSIONS

Microfluidic device study may allow the preclinical assessment and development of therapeutic strategies of the vascular barrier under stress conditions.

Endothelial Glycocalyx Shedding Occurs during Ex Vivo Lung Perfusion: A Pilot Study

Background

Damage to the endothelium has been established as a key pathological process in lung transplantation and ex vivo lung perfusion (EVLP), a new technology that provides a platform for the assessment of injured donor lungs. Damage to the lung endothelial glycocalyx, a structure that lines the endothelium and is integral to vascular barrier function, has been associated with lung dysfunction. We hypothesised that endothelial glycocalyx shedding occurs during EVLP and aimed to establish a porcine model to investigate the mechanism underlying glycocalyx breakdown during EVLP.

Methods

Concentrations of endothelial glycocalyx breakdown products, syndecan-1, hyaluronan, heparan sulphate, and CD44, were measured using the ELISA and matrix metalloproteinase (MMP) activity by zymography in the perfusate of both human (n = 9) and porcine (n = 4) lungs undergoing EVLP. Porcine lungs underwent prolonged EVLP (up to 12 hours) with perfusion and ventilation parameters recorded hourly.

Results

During human EVLP, endothelial glycocalyx breakdown products in the perfusate increased over time. Increasing MMP-2 activity over time was positively correlated with levels of syndecan-1 (r = 0.886; p=0.03) and hyaluronan (r = 0.943; p=0.02). In the porcine EVLP model, hyaluronan was the only glycocalyx product detectable during EVLP (1 hr: 19 (13–84) vs 12 hr: 143 (109–264) ng/ml; p=0.13). Porcine hyaluronan was associated with MMP-9 activity (r = 0.83; p=0.02) and also with dynamic compliance (r = 0.57; p=0.03).

Conclusion

Endothelial glycocalyx products accumulate during both porcine and human EVLP, and this accumulation parallels an accumulation of matrix-degrading enzyme activity. Preliminary evidence in our porcine EVLP model suggests that shedding may be related to organ function, thus warranting additional study.

AMP-activated protein kinase regulates glycocalyx impairment and macrophage recruitment in response to low shear stress

Low shear stress (LSS) increases degradation of the endothelial glycocalyx, leading to production of endothelial inflammation and atherosclerosis. However, the underlying mechanisms of how LSS diminishes the endothelial glycocalyx remain unclear. We showed that LSS inactivated AMPK, enhanced Na⁺-H⁺ exchanger (NHE)1 activity, and induced glycocalyx degradation. Activation of AMPK prevented LSS-induced NHE1 activity and endothelial glycocalyx impairment. We further identified hyaluronidase 2 (HYAL2) as a mediator of endothelial glycocalyx impairment in HUVECs exposed to LSS. Inactivation of AMPK by LSS up-regulates the activity of HYAL2, which acts downstream of NHE1. We characterized a left common carotid artery partial ligation (PL) model of LSS in C57BL/6 mice. The results showed decreased expression of hyaluronan (HA) in the endothelial glycocalyx and decreased thickness of the endothelial glycocalyx in PL mice. Pharmacological activation of AMPK by ampkinone not only attenuated glycocalyx impairment due to HA degradation but also blocked vascular cell adhesion molecule 1 and intercellular adhesion molecule 1 expression increase and macrophage recruitment in the endothelia of PL mice. Our results revealed that AMPK dephosphorylation induced by LSS activates NHE1 and HYAL2 to promote HA degradation and glycocalyx injury, which may contribute to endothelial inflammatory reaction and macrophage recruitment.-Zhang, J., Kong, X., Wang, Z., Gao, X., Ge, Z., Gu, Y., Ye, P., Chao, Y., Zhu, L., Li, X., Chen, S. AMP-activated protein kinase regulates glycocalyx impairment and macrophage recruitment in response to low shear stress.

Postoperative microcirculatory perfusion and endothelial glycocalyx shedding following cardiac surgery with cardiopulmonary bypass

We investigated microcirculatory perfusion disturbances following cardiopulmonary bypass in the early postoperative period and whether the course of these disturbances mirrored restoration of endothelial glycocalyx integrity. We performed sublingual sidestream dark field imaging of the microcirculation during the first three postoperative days in patients who had undergone on‐pump coronary artery bypass graft surgery. We calculated the perfused vessel density, proportion of perfused vessels and perfused boundary region. Plasma was obtained to measure heparan sulphate and syndecan‐1 levels as glycocalyx shedding markers. We recruited 17 patients; the mean (SD) duration of non‐pulsatile cardiopulmonary bypass was 103 (18) min, following which 491 (29) ml autologous blood was transfused through cell salvage. Cardiopulmonary bypass immediately decreased both microcirculatory perfused vessel density; 11 (3) vs. 16 (4) mm.mm⁻², p = 0.052 and the proportion of perfused vessels; 92 (5) vs. 69 (9) %, p < 0.0001. The proportion of perfused vessels did not increase after transfusion of autologous salvaged blood following cardiopulmonary bypass; 72 (7) %, p = 0.19 or during the first three postoperative days; 71 (5) %, p < 0.0001. The perfused boundary region increased after cardiopulmonary bypass; 2.2 (0.3) vs. 1.9 (0.3) μm, p = 0.037 and during the first three postoperative days; 2.4 (0.3) vs. 1.9 (0.3) μm, p = 0.003. Increased plasma heparan sulphate levels were inversely associated with the proportion of perfused vessels during cardiopulmonary bypass; R = −0.49, p = 0.02. Plasma syndecan‐1 levels were inversely associated with the proportion of perfused vessels during the entire study period; R = −0.51, p < 0.0001. Our study shows that cardiopulmonary bypass‐induced acute microcirculatory perfusion disturbances persist in the first three postoperative days, and are associated with prolonged endothelial glycocalyx shedding. This suggests prolonged impairment and delayed recovery of both microcirculatory perfusion and function after on‐pump cardiac surgery.

Increased MMP activity in curved geometries disrupts the endothelial cell glycocalyx creating a proinflammatory environment

Wall shear stress gradients (WSSGs) induce an inflammatory phenotype in endothelial cells (ECs) which is hypothesized to be mediated by mechanotransduction through the EC glycocalyx (GCX). We used a three-dimensional in vitro cell culture model with a 180^o curved geometry to investigate if WSSGs created by curvature can cause EC inflammation and disruption of the GCX. The hydrodynamics of the model elicited a morphological response in ECs as well as a pattern of leukocyte adhesion towards the inner wall of curvature that was attenuated with enzymatic removal of GCX components. GCX degradation was also observed in regions of curvature which corresponded to increased activity of MMPs. Together, these results support the hypothesis that the EC GCX is involved in mechanotransduction of WSSGs and that components of the GCX are regulated by MMP activity in regions of curvature.

Endothelial Glycocalyx as a Shield Against Diabetic Vascular Complications: Involvement of Hyaluronan and Hyaluronidases

The endothelial glycocalyx (EG), which covers the apical surface of the endothelial cells and floats into the lumen of the vessels, is a key player in vascular integrity and cardiovascular homeostasis. The EG is composed of PGs (proteoglycans), glycoproteins, glycolipids, and glycosaminoglycans, in particular hyaluronan (HA). HA seems to be implicated in most of the functions described for EG such as creating a space between blood and the endothelium, controlling vessel permeability, restricting leukocyte and platelet adhesion, and allowing an appropriate endothelial response to flow variation through mechanosensing. The amount of HA in the EG may be regulated by HYAL (hyaluronidase) 1, the most active somatic hyaluronidase. HYAL1 seems enriched in endothelial cells through endocytosis from the bloodstream. The role of the other main somatic hyaluronidase, HYAL2, in the EG is uncertain. Damage to the EG, accompanied by shedding of one or more of its components, is an early sign of various pathologies including diabetes mellitus. Shedding increases the blood or plasma concentration of several EG components, such as HA, heparan sulfate, and syndecan. The plasma levels of these molecules can then be used as sensitive markers of EG degradation. This has been shown in type 1 and type 2 diabetic patients. Recent experimental studies suggest that preserving the size and amount of EG HA in the face of diabetic insults could be a useful novel therapeutic strategy to slow diabetic complications. One way to achieve this goal, as suggested by a murine model of HYAL1 deficiency, may be to inhibit the function of HYAL1. The same approach may succeed in other pathological situations involving endothelial dysfunction and EG damage.

Mechanical signaling through the discoidin domain receptor 1 plays a central role in tissue fibrosis

The preservation of tissue and organ architecture and function depends on tightly regulated interactions of cells with the extracellular matrix (ECM). These interactions are maintained in a dynamic equilibrium that balances intracellular, myosin-generated tension with extracellular resistance conferred by the mechanical properties of the extracellular matrix. Disturbances of this equilibrium can lead to the development of fibrotic lesions that are associated with a wide repertoire of high prevalence diseases including obstructive cardiovascular diseases, muscular dystrophy and cancer. Mechanotransduction is the process by which mechanical cues are converted into biochemical signals. At the core of mechanotransduction are sensory systems, which are frequently located at sites of cell-ECM and cell-cell contacts. As integrins (cell-ECM junctions) and cadherins (cell-cell contacts) have been extensively studied, we focus here on the properties of the discoidin domain receptor 1 (DDR1), a tyrosine kinase that mediates cell adhesion to collagen. DDR1 expression is positively associated with fibrotic lesions of heart, kidney, liver, lung and perivascular tissues. As the most common end-point of all fibrotic disorders is dysregulated collagen remodeling, we consider here the mechanical signaling functions of DDR1 in processing of fibrillar collagen that lead to tissue fibrosis.

Oligosaccharide model of the vascular endothelial glycocalyx in physiological flow

Experiments have consistently revealed the pivotal role of the endothelial glycocalyx layer in vasoregulation and the layer's contribution to mechanotransduction pathways. However, the exact mechanism by which the glycocalyx mediates fluid shear stress remains elusive. This study employs atomic-scale molecular simulations with the aim of investigating the conformational and orientation properties of highly flexible oligosaccharide components of the glycocalyx and their suitability as transduction molecules under hydrodynamic loading. Fluid flow was shown to have nearly no effect on the conformation populations explored by the oligosaccharide, in comparison with static (diffusion) conditions. However, the glycan exhibited a significant orientation change, when compared to simple diffusion, aligning itself with the flow direction. It is the tethered end of the glycan, an asparagine amino acid, which experienced conformational changes as a result of this flow-induced bias. Our results suggest that shear flow through the layer can have an impact on the conformational properties of saccharide-decorated transmembrane proteins, thus acting as a mechanosensor.