Role of matrix metalloproteases in the kinetics of leukocyte-endothelial adhesion in post-capillary venules

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.

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 endothelial glycocalyx: Structure and function in health and critical illness

OBJECTIVE

To conduct a narrative review of the current literature in reference to the structure and function of the endothelial glycocalyx (EG) and its contribution to the pathophysiology of conditions relevant to the veterinary emergency and critical care clinician. Novel therapies for restoring or preserving the EG will also be discussed.

DATA SOURCES

Online databases (PubMed, CAB abstracts, Scopus) were searched between January 1st 2017 and May 1st 2017 for English language articles without publication date restriction. Keywords included EG, endothelial surface layer, degradation, syndecan-1, heparan sulfate, critical illness, sepsis, trauma, and therapeutics.

DATA SYNTHESIS

The EG is a complex and important structure located on the luminal surface of all blood vessels throughout the body. It plays an important role in normal vascular homeostasis including control of fluid exchange across the vascular barrier. Loss or degradation of the EG has an impact on inflammation, coagulation, and vascular permeability and tone. These changes are essential components in the pathophysiology of many conditions including sepsis and trauma. A substantial body of experimental animal and human clinical research over the last decade has demonstrated increased circulating concentrations of EG degradation products in these conditions. However, veterinary-specific research into the EG and critical illness is currently lacking. The utility of EG degradation products as diagnostic and prognostic tools continues to be investigated and new therapies to preserve or improve EG structure and function are under development.

CONCLUSIONS

The recognition of the presence of the EG has changed our understanding of transvascular fluid flux and the pathophysiology of many conditions of critical illness. The EG is an exciting target for novel therapeutics to improve morbidity and mortality in conditions such as sepsis and trauma.

Role of the Glycocalyx as a Barrier to Leukocyte-Endothelium Adhesion

Leukocyte (WBC) to endothelial cell (EC) adhesion is a receptor-mediated process governed by the avidity and affinity of selectins, which modulate adhesive forces during WBC rolling, and integrins, which determine the strength of firm adhesion. Adhesion receptors on the EC surface lie below an endothelial surface layer (ESL) comprised of the EC glycocalyx and adsorbed proteins which, in vivo, have a thickness on the order 500 nm. The glycocalyx consists of a matrix of the glycosaminoglycans heparan sulfate and chondroitin sulfate, bound to proteoglycans and encased in hyaluronan. Together, these carbohydrates form a layer that varies in glycan content along the length of post-capillary venules where WBC-EC adhesion occurs. Thickness and porosity of the glycocalyx can vary dramatically during the inflammatory response as observed by increased infiltration and diffusion of macromolecules within the layer following activation of the EC by cytokines and chemoattractants. In models of inflammation in the living animal, the shedding of glycans and diminished thickness of the glycocalyx rapidly occur to facilitate penetration by the WBCs and adhesion to the EC. The primary effectors of glycan shedding appear to be metalloproteases and heparanase released by the EC. Retardation of glycan shedding and WBC-EC adhesion has been demonstrated in vivo using MMP inhibitors and low-molecular-weight heparin (LMWH), where the latter competitively binds to heparanase liberated by the EC. Together, these agents may serve to stabilize the ESL and provide a useful strategy for treatment of inflammatory disorders.