Diazoxide may protect endothelial glycocalyx integrity during coronary artery bypass grafting

The role of glycosaminoglycans in blood pressure regulation

Essential hypertension (HT) is the global health problem and is a major risk factor for the development of cardiovascular and kidney disease. High salt intake has been associated with HT and impaired kidney sodium excretion is considered to be a major mechanism for the development of HT. Although kidney has a very important role in regulation of BP, this traditional view of BP regulation was challenged by recent findings suggesting that nonosmotic tissue sodium deposition is very important for BP regulation. This new paradigm indicates that sodium can be stored and deposited nonosmotically in the interstitium without water retention and without increased BP. One of the major determinants of this deposition is glycosaminoglycans (GAGs). By binding to GAGs found in the endothelial surface layer (ESL) which contains glycocalyx, sodium is osmotically inactivated and not induce concurrent water retention. Thus, GAGs has important function for homeostatic BP and sodium regulation. In the current review, we summarized the role of GAGs in ESL and BP regulation.

Endothelial glycocalyx in retina, hyperglycemia, and diabetic retinopathy

The endothelial glycocalyx (EG) is a meshlike network present on the apical surface of the endothelium. Membrane-bound proteoglycans, the major backbone molecules of the EG, consist of glycosaminoglycans attached to core proteins. In addition to maintaining the integrity of the endothelial barrier, the EG regulates inflammation and perfusion and acts as a mechanosensor. The loss of the EG can cause endothelial dysfunction and drive the progression of vascular diseases including diabetic retinopathy. Therefore, the EG presents a novel therapeutic target for treatment of vascular complications. In this review article, we provide an overview of the structure and function of the EG in the retina. Our particular focus is on hyperglycemia-induced perturbations in the glycocalyx structure in the retina, potential underlying mechanisms, and clinical trials studying protective treatments against degradation of the EG.

The microvascular endothelial glycocalyx: An additional piece of the puzzle in veterinary medicine

The endothelial glycocalyx (eGlx) is a critically important structure lining the luminal surface of endothelial cells. There is increasing evidence, in human patients and animal models, for its crucial role in the maintenance of health. Moreover, its damage is associated with the pathogenesis of multiple disease states. This review provides readers with an overview of the eGlx; summarising its structure, essential functions, and evidence for its role in disease. We highlight the lack of studies regarding the eGlx in cats and dogs, particularly in naturally occurring diseases. Importantly, we discuss techniques to aid its study, which can be applied to veterinary species. Finally, we present targeted therapies aimed at preserving, and in some cases, restoring damaged eGlx.

Protective Treatments against Endothelial Glycocalyx Degradation in Surgery: A Systematic Review and Meta-Analysis

The aim was to explore the body of literature focusing on protective treatments against endothelial glycocalyx degradation in surgery. A comprehensive systematic review of relevant articles was conducted across databases. Inclusion criteria: (1) treatments for the protection of the endothelial glycocalyx in surgery; (2) syndecan-1 used as a biomarker for endothelial glycocalyx degradation. Outcomes analysed: (1) mean difference of syndecan-1 (2) correlation between glycocalyx degradation and inflammation; (3) correlation between glycocalyx degradation and extravasation. A meta-analysis was used to present mean differences and 95% confidence intervals. Seven articles with eight randomised controlled trials were included. The greatest change from baseline values in syndecan-1 concentrations was generally from the first timepoint measured post-operatively. Interventions looked to either dampen the inflammatory response or fluid therapy. Methylprednisolone had the highest mean difference in plasma syndecan-1 concentrations. Ulinastatin showed correlations between alleviation of degradation and preserving vascular permeability. In this systematic review of 385 patients, those treated were more likely than those treated with placebo to exhibit less shedding of the endothelial glycocalyx. Methylprednisolone has been shown to specifically target the transient increase of glycocalyx degradation immediately post-operation and has displayed anti-inflammatory effects. We have proposed suggestions for improved uniformity and enhanced confidence for future randomised controlled trials.

Human glycocalyx shedding: Systematic review and critical appraisal

BACKGROUND

The number of studies measuring breakdown products of the glycocalyx in plasma has increased rapidly during the past decade. The purpose of the present systematic review was to assess the current knowledge concerning the association between plasma concentrations of glycocalyx components and structural assessment of the endothelium.

METHODS

We performed a literature review of Pubmed to determine which glycocalyx components change in a wide variety of human diseases and conditions. We also searched for evidence of a relationship between plasma concentrations and the thickness of the endothelial glycocalyx layer as obtained by imaging methods.

RESULTS

Out of 3,454 publications, we identified 228 that met our inclusion criteria. The vast majority demonstrate an increase in plasma glycocalyx products. Sepsis and trauma are most frequently studied, and comprise approximately 40 publications. They usually report 3-4-foldt increased levels of glycocalyx degradation products, most commonly of syndecan-1. Surgery shows a variable picture. Cardiac surgery and transplantations are most likely to involve elevations of glycocalyx degradation products. Structural assessment using imaging methods show thinning of the endothelial glycocalyx layer in cardiovascular conditions and during major surgery, but thinning does not always correlate with the plasma concentrations of glycocalyx products. The few structural assessments performed do not currently support that capillary permeability is increased when the plasma levels of glycocalyx fragments in plasma are increased.

CONCLUSIONS

Shedding of glycocalyx components is a ubiquitous process that occurs during both acute and chronic inflammation with no sensitivity or specificity for a specific disease or condition.

The role of endothelial glycocalyx in health and disease

The endothelium is the largest organ in the body and recent studies have shown that the endothelial glycocalyx (eGCX) plays a major role in health and disease states. The integrity of eGCX is vital for homoeostasis and disruption of its structure and function plays a major role in several pathologic conditions. An increased understanding of the numerous pathophysiological roles of eGCX may lead to the development of potential surrogate markers for endothelial injury or novel therapeutic targets. This review provides a state-of-the-art update on the structure and function of the eGCX, emphasizing the current understanding of interorgan crosstalk between the eGCX and other organs that might also contribute to the pathogenesis of kidney diseases.

Endothelial glycocalyx: basic science and clinical implications

The classic Starling principle proposed that microvascular fluid exchange was determined by a balance of hydrostatic and oncotic pressures relative to the vascular wall and this movement of water was regulated by gaps in the intercellular spaces. However, current literature on the endothelial glycocalyx (a jelly-like protective layer covering the luminal surface of the endothelium) has revised Starling's traditional concepts. This article aims to summarise the literature on the glycocalyx related to its basic science, clinical settings inciting injury, protective strategies and clinical perspectives. Perioperative damage to the glycocalyx structure can increase vascular permeability leading to interstitial fluid shifts, oedema, and increased surgical morbidity. Pathological shedding of the glycocalyx occurs in response to mechanical cellular stress, endotoxins, inflammatory mediators, atrial natriuretic peptide, ischaemia-reperfusion injury, free oxygen radicals and hyperglycaemia. Increased understanding of the endothelial glycocalyx may change perioperative fluid management, and therapeutic strategies aimed at its preservation may improve patient outcomes.

Endothelial dysfunction mediated by interleukin-18 in patients with ischemic heart disease undergoing coronary artery bypass grafting surgery

When medication management or percutaneous coronary intervention is not successful in patients with advanced ischemic heart disease, surgical revascularisation-predominantly coronary artery bypass grafting (CABG)-is considered the gold standard. However, CABG surgery can lead to ischemia/reperfusion injury, which is characterized by a strong inflammatory response. Interleukin (IL)-18, is a strong inflammatory mediator, that is released from cardiomyocytes and can be found in the systemic circulation of patients during and immediately after CABG surgery. The existing damage of endothelial glycocalyx in patients with ischemic heart disease is further impaired concurrently during the surgery due to the anaesthesia-surgical technique used and intravascular fluid loading. This results in the increased incidence of adverse events, including myocardial infarction. IL-18 leads to the activation of lymphocyte cytotoxicity via cytotoxic mediators (Fas ligand, Tumour necrosis factor (TNF)-related apoptosis-inducing ligand, perforin, and granulysin). We hypothesize that IL-18 is released locally in the heart and the systemic circulation in patients undergoing CABG surgery and may be correlated with the level of activity of circulating lymphocytes. In turn, this may lead to lymphocyte-mediated cytotoxicity directed toward damaged and activated endothelial cells. Shear stress glycocalyx, as well as damaged and activated endothelial cells then become the main the source of pro-inflammatory cytokines, chemokines, and adhesion molecules. These attract activated lymphocytes to adhere to the endothelium or enter the subintimal layer, increasing existing or initiating the formation of new plaques, which leads to the development of myocardial infarction during or shortly after surgery. To evaluate our hypothesis, we will measure the local concentration of IL-18 in the sinus coronarius and systemic circulation. These values will then be correlated with immunological and biochemical parameters, predominantly with the concentration of degradation products of glycocalyx and cytotoxic mediators in activated lymphocytes. If our hypothesis is correct, measuring the IL-18 concentration that is responsible for glycocalyx deterioration, may become a useful tool for predicting myocardial infarction occurrence in patients undergoing CABG surgery.

High-dose methylprednisolone and endothelial glycocalyx in paediatric heart surgery

BACKGROUND

Corticosteroids are used in paediatric heart surgery to attenuate systemic inflammatory response. Glycocalyx regulates vascular permeability, shear stress and cell adhesion on the endothelium. Syndecan-1 serves as a biomarker of glycocalyx degradation. Hydrocortisone decreased endothelial glycocalyx degradation in an experimental model. Our hypothesis was that high-dose methylprednisolone decreases glycocalyx degradation as measured by plasma sydecan-1 concentration in children undergoing cardiac surgery.

METHODS

Two double-blinded, randomized, placebo-controlled trials were conducted. In the first trial ('neonatal trial'), 40 neonates undergoing open heart surgery received either 30 mg/kg intravenous methylprednisolone (n = 20) or placebo (n = 20). In the second trial ('VSD trial'), 45 infants and very young children, undergoing ventricular or atrioventricular septal defect correction received one of the following: 30 mg/kg of methylprednisolone intravenously after anaesthesia induction (n = 15), 30 mg/kg methylprednisolone in the cardiopulmonary bypass prime solution (n = 15) or placebo (n = 15). Plasma syndecan-1 concentrations were measured. Results were expressed both as absolute concentrations and in relative concentrations as multiples of the baseline values of syndecan-1.

RESULTS

There were no statistically significant differences between the neonate trial groups for absolute syndecan-1 concentrations. However, operative administration of methylprednisolone to neonates significantly reduced the relative increases of syndecan-1 at weaning from cardiopulmonary bypass (P = 0.008) and at 6 h post-operatively (P = 0.018). There were no statistically significant differences in absolute or relative increases of syndecan-1 between the VSD trial study groups.

CONCLUSION

High-dose methylprednisolone reduces shedding of glycocalyx in neonates after complex cardiac surgery but not in older infants after repair of VSD/AVSD with shorter ischaemia times.

Plasma syndecan-1 and heparan sulfate correlate with microvascular glycocalyx degradation in hemorrhaged rats after different resuscitation fluids

The endothelial glycocalyx plays an essential role in many physiological functions and is damaged after hemorrhage. Fluid resuscitation may further change the glycocalyx after an initial hemorrhage-induced degradation. Plasma levels of syndecan-1 and heparan sulfate have been used as indirect markers for glycocalyx degradation, but the extent to which these measures are representative of the events in the microcirculation is unknown. Using hemorrhage and a wide range of resuscitation fluids, we studied quantitatively the relationship between plasma biomarkers and changes in microvascular parameters, including glycocalyx thickness. Rats were bled 40% of total blood volume and resuscitated with seven different fluids (fresh whole blood, blood products, and crystalloids). Intravital microscopy was used to estimate glycocalyx thickness in >270 postcapillary venules from 58 cremaster preparations in 9 animal groups; other microvascular parameters were measured using noninvasive techniques. Systemic physiological parameters and blood chemistry were simultaneously collected. Changes in glycocalyx thickness were negatively correlated with changes in plasma levels of syndecan-1 ( r = −0.937) and heparan sulfate ( r = −0.864). Changes in microvascular permeability were positively correlated with changes in both plasma biomarkers ( r = 0.8, P < 0.05). Syndecan-1 and heparan sulfate were also positively correlated ( r = 0.7, P < 0.05). Except for diameter and permeability, changes in local microcirculatory parameters (red blood cell velocity, blood flow, and wall shear rate) did not correlate with plasma biomarkers or glycocalyx thickness changes. This work provides a quantitative framework supporting plasma syndecan-1 and heparan sulfate as valuable clinical biomarkers of glycocalyx shedding that may be useful in guiding resuscitation strategies following hemorrhage.

Vascular endothelium - Gatekeeper of vessel health

The vascular endothelium is an interface between the blood stream and the vessel wall. Changes in this single cell layer of the artery wall are believed of primary importance in the pathogenesis of vascular disease/atherosclerosis. The endothelium responds to humoral, neural and especially hemodynamic stimuli and regulates platelet function, inflammatory responses, vascular smooth muscle cell growth and migration, in addition to modulating vascular tone by synthesizing and releasing vasoactive substances. Compromised endothelial function contributes to the pathogenesis of cardiovascular disease; endothelial 'dysfunction' is associated with risk factors, correlates with disease progression, and predicts cardiovascular events. Therapies for atherosclerosis have been developed, therefore, that are directed towards improving endothelial function.