Recent advances in the understanding of endothelial barrier function and fluid therapy

Targeting Rho kinase to restore endothelial barrier function following vascular scaffold implantation

Vascular scaffold implantation induces injury to the intimal layer and causes discontinuity of the regenerated endothelial monolayer, compromising barrier integrity, increasing permeability, and allowing the transmigration of leukocytes and lipoproteins into the subendothelial space. Mechanical vascular wall stretching triggers Ras homolog family member A (RhoA)/Rho kinase-mediated actomyosin contractility and destabilization of adherens junctions, leading to endothelial barrier dysfunction. Assembly of intercellular adhesion and actin cytoskeletal organization of interendothelial junctions are controlled by downregulation of RhoA guanosine triphosphatase (GTPase)-mediated barrier-disruptive activity and upregulation of repressor-activator protein 1 (Rap1) and Ras-related C3 botulinum toxin substrate 1 (Rac1) GTPase-mediated cytoskeletal reorganization, leading to endothelial barrier stabilization. This review highlights the involvement of Rho GTPases in the disruption of endothelial barrier integrity following vascular scaffold implantation and the targeting of downstream Rho-associated protein kinases, which signal the network to restore endothelial barrier integrity and stability.

Endothelial and Glycocalyx Biomarkers in Children With Sepsis After One Bolus of Unbalanced or Balanced Crystalloids

OBJECTIVES

To assess the disruption of endothelial glycocalyx integrity in children with sepsis receiving fluid resuscitation with either balanced or unbalanced crystalloids. The primary outcome was endothelial glycocalyx disruption (using perfused boundary region >2 µm on sublingual video microscopy and syndecan-1 greater than 80 mg/dL) according to the type of crystalloid. The secondary outcomes were increased vascular permeability (using angiopoietin-2 level), apoptosis (using annexin A5 level), and associated clinical changes.

DESIGN

A single-center prospective cohort study from January to December 2021.

SETTING

Twelve medical-surgical PICU beds at a university hospital.

PATIENTS

Children with sepsis/septic shock before and after receiving fluid resuscitation with crystalloids for hemodynamic instability.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We included 106 patients (3.9 yr [interquartile range, 0.60-13.10 yr]); 58 of 106 (55%) received boluses of unbalanced crystalloid. This group had greater odds of endothelial glycocalyx degradation (84.5% vs 60.4%; adjusted odds ratio, 3.78; 95% CI, 1.49-9.58; p < 0.01) 6 hours after fluid administration, which correlated with increased angiopoietin-2 (rho = 0.4; p < 0.05) and elevated annexin A5 ( p = 0.04). This group also had greater odds of metabolic acidosis associated with elevated syndecan-1 (odds ratio [OR], 4.88; 95% CI, 1.23-28.08) and acute kidney injury (OR, 1.7; 95% CI, 1.12-3.18) associated with endothelial glycocalyx damage. The perfused boundary region returned to baseline 24 hours after receiving the crystalloid boluses.

CONCLUSIONS

Children with sepsis, particularly those who receive unbalanced crystalloid solutions during resuscitation, show loss and worsening of endothelial glycocalyx. The abnormality peaks at around 6 hours after fluid administration and is associated with greater odds of metabolic acidosis and acute kidney injury.

The effect of tetrastarch on the endothelial glycocalyx layer in early hemorrhagic shock using fluorescence intravital microscopy: a mouse model

PURPOSE

To investigate vascular endothelial dysfunction based on glycocalyx impairment in massive hemorrhage and to evaluate fluid therapy.

METHODS

In this randomized controlled animal study, we withdrew 1.5 mL blood and administered 1.5 mL resuscitation fluid. Mice were divided into six groups according to the infusion type and administration timing: NS-NS (normal saline), NS-HES ([hydroxyethyl starch]130), HES-NS, NS-ALB (albumin), ALB-NS, and C (control) groups.

RESULTS

The glycocalyx index (GCXI) of a 40-μm artery was significantly larger in group C than in other groups (P < 0.01). Similarly, the GCXI for a 60-μm artery was significantly higher in group C than in NS-NS (P ≤ 0.05), NS-HES (P ≤ 0.01), and NS-ALB groups (P ≤ 0.05). The plasma syndecan-1 concentration, at 7.70 ± 5.71 ng/mL, was significantly lower in group C than in group NS-NS (P ≤ 0.01). The tetramethylrhodamine-labeled dextran (TMR-DEX40) fluorescence intensity in ALB-NS and HES-NS groups and the fluorescein isothiocyanate-labeled hydroxyethyl starch (FITC-HES130) fluorescence intensity in NS-HES and HES-NS groups were not significantly different from those of group C at any time point. FITC-HES130 was localized on the inner vessel wall in groups without HES130 infusion but uniformly distributed in HES130-treated groups in intravital microscopy. FITC-FITC-HES130 was localized remarkably in the inner vessel walls in group HES-NS in electron microscopy.

CONCLUSIONS

In an acute massive hemorrhage mouse model, initial fluid resuscitation therapy with saline administration impaired glycocalyx and increased vascular permeability. Prior colloid-fluid administration prevented the progression of glycocalyx damage and improve prognosis. Prior HES130 administration may protect endothelial cell function.

Vasculature-on-chip for Assessment of Bioresorbable Scaffolds and Endothelial Barrier Integrity

ABSTRACT

Endothelial cells adhere to one another through junctional structures formed by intercellular adhesion molecules. These intercellular proteins regulate barrier function in response to the hemodynamic shear rate and enable the selective passage of solutes and fluids across the endothelium. After endovascular device implantation, the endothelial barrier is compromised and becomes discontinuous, which increases permeability, allowing transmigration of leukocytes and lipoproteins and leading to the accumulation of lipid-laden foamy macrophages in the subendothelial space. Drug-coated bioresorbable vascular scaffold implants have been associated with unexpected thrombotic complications, which were not predicted in animals because of dissimilarities in endothelial regeneration and realignment between animals and humans. The development of a microengineered, microfluidics-based system of patterned channels lined with human endothelial and smooth muscle cells perfused with blood allows for the evaluation of endothelial function and barrier integrity. This review highlights the translational potential of vasculature-on-chip, which recreates the microphysiological milieu to evaluate the impact of drug-eluting bioresorbable vascular scaffolds on endothelial barrier integrity and to characterize polymer biodegradation behavior and drug release kinetic profiles over time.

A Simple Cardiovascular Model for the Study of Hemorrhagic Shock

Hemorrhagic shock is the number one cause of death on the battlefield and in civilian trauma as well. Mathematical modeling has been applied in this context for decades; however, the formulation of a satisfactory model that is both practical and effective has yet to be achieved. This paper introduces an upgraded version of the 2007 Zenker model for hemorrhagic shock termed the ZenCur model that allows for a better description of the time course of relevant observations. Our study provides a simple but realistic mathematical description of cardiovascular dynamics that may be useful in the assessment and prognosis of hemorrhagic shock. This model is capable of replicating the changes in mean arterial pressure, heart rate, and cardiac output after the onset of bleeding (as observed in four experimental laboratory animals) and achieves a reasonable compromise between an overly detailed depiction of relevant mechanisms, on the one hand, and model simplicity, on the other. The former would require considerable simulations and entail burdensome interpretations. From a clinical standpoint, the goals of the new model are to predict survival and optimize the timing of therapy, in both civilian and military scenarios.

Effect of peri-operative crystalloid fluid rate on circulating hyaluronan in healthy dogs: A pilot study

Hypervolemia can damage the endothelial glycocalyx, a key regulator of vascular permeability, coagulation and inflammation. A starting peri-operative crystalloid fluid rate of 5mL/kg/h is recommended for healthy dogs undergoing elective procedures but higher rates continue to be commonly used. This study aimed to determine if a higher starting perioperative fluid rate was associated with a greater increase in plasma concentrations of hyaluronan, a marker correlated with glycocalyx damage, in systemically healthy dogs undergoing elective surgical procedures. Based on a sample size calculation, 38 dogs undergoing ovariohysterectomy or castration were randomly assigned to receive lactated Ringer's at a starting perioperative fluid rate of 10mL/kg/h (n=19) or 5mL/kg/h (n=19). Plasma hyaluronan concentrations were measured by ELISA in pre- and post-fluid therapy samples. There were no significant differences between groups in hyaluronan values before (baseline, P=0.52) or after perioperative fluid administration (P=0.62). Compared to respective baseline values, hyaluronan values significantly increased following 5 and 10ml/kg/h fluid administration (P=0.02 for both comparisons). This preliminary study identified an increase in hyaluronan over the course of fluid therapy with both the low and high fluid rate. One possible explanation is that both fluid rates contribute to glycocalyx disruption, but it should be emphasized that hyaluronan is not specific to the glycocalyx. Further studies are needed to determine the origin of the increased circulating hyaluronan and its clinical significance in dogs undergoing elective surgical procedures.

Role of albumin in the preservation of endothelial glycocalyx integrity and the microcirculation: a review

The endothelial glycocalyx comprises a complex layer of membrane-bound proteoglycans, secreted glycosaminoglycans, glycoproteins, glycolipids and bound plasma proteins such as albumin and antithrombin associated with the endothelial surface. The glycocalyx plays an important role in vascular homeostasis, regulating vascular permeability and cell adhesion, and acts as a mechanosensor for hemodynamic shear stresses; it also has antithrombotic and anti-inflammatory functions. Plasma proteins such as albumin are physiologically bound within the glycocalyx, thus contributing to stability of the layer. Albumin is the major determinant of plasma colloid osmotic pressure. In addition, albumin transports sphingosine-1-phosphate which has protective endothelial effects, acts as a free radical scavenger, and has immunomodulatory and anti-inflammatory effects. This review examines the physiological function of the endothelial glycocalyx and the role of human albumin in preserving glycocalyx integrity and the microcirculation.

Effect of sevoflurane and propofol on tourniquet-induced endothelial damage: a pilot randomized controlled trial for knee-ligament surgery

BACKGROUND

The glycocalyx layer is a key structure in the endothelium. Tourniquet-induced ischemic periods are used during orthopedic surgery, and the reactive oxygen species generated after ischemia-reperfusion may mediate the shedding of the glycocalyx. Here, we describe the effects of tourniquet-induced ischemia-reperfusion and compare the effects of sevoflurane and propofol on the release of endothelial biomarkers after ischemia-reperfusion in knee-ligament surgery.

METHODS

This pilot, single-center, blinded, randomized, controlled trial included 16 healthy patients. After spinal anesthesia, hypnosis was achieved with sevoflurane or propofol according to randomization. During the perioperative period, five venous blood samples were collected for quantification of syndecan-1, heparan sulfate, and thrombomodulin from blood serum by using ELISA assays kits. Sample size calculation was performed to detect a 25% change in the mean concentration of syndecan-1 with an alpha of 0.05 and power of 80%.

RESULTS

For our primary outcome, a two-way ANOVA with post-hoc Bonferroni correction analysis showed no differences in syndecan-1 concentrations between the sevoflurane and propofol groups at any time point. In the sevoflurane group, we noted an increase in syndecan-1 concentrations 90 min after tourniquet release in the sevoflurane group from 34.6 ± 24.4 ng/mL to 47.9 ± 29.8 ng/mL (Wilcoxon test, p < 0.01) that was not observed in patients randomized to the propofol group. The two-way ANOVA showed no intergroup differences in heparan sulfate and thrombomodulin levels.

CONCLUSIONS

Superficial endothelial damage without alterations in the cell layer integrity was observed after tourniquet knee-ligament surgery. There was no elevation in serum endothelial biomarkers in the propofol group patients. Sevoflurane did not show the protective effect observed in in vitro and in vivo studies.

TRIAL REGISTRATION

The trial was registered in www.clinicaltrials.gov (ref: NCT03772054, Registered 11 December 2018).

The protective effect of hydroxyethyl starch solution on the glycocalyx layer in an acute hemorrhage mouse model

PURPOSE

Fluid therapy focused on glycocalyx (GCX) protection in hemorrhagic shock is a current focus of research. Hydroxyethyl starch (HES) solution is commonly used for fluid resuscitation; however, its effects on the GCX remain unclear. The primary aim of this study was to explore the protective effect of HES130 in maintaining GCX thickness and reducing plasma syndecan-1 expression.

METHODS

An acute hemorrhage murine model with the dorsal skin chambers was used to measure GCX thickness and to evaluate vascular permeability. Groups of mice were treated with normal saline (NS), albumin (NS-A), HES130 (NS-V), or no exsanguination or infusion (C). We measured syndecan-1 plasma concentrations, performed blood gas analysis, and analyzed the 7-day cumulative mortality.

RESULTS

GCX thickness in NS mice was significantly reduced compared to that in group C, but no other groups showed a difference compared to group C. The plasma concentration of syndecan-1 was significantly higher in NS mice than in group C. There were no significant differences in the fluorescence intensity of dextran in the interstitial space. HES70 leakage was suppressed in NS-V mice compared to those in other groups. HES70 was localized to the inner vessel wall in C, NS, and NS-A mice, but not in group NS-V. Blood gas analysis indicated that pH and lactate showed the greatest improvements in NS-V mice. The 7-day cumulative mortality rate was the highest in group NS.

CONCLUSION

Resuscitation with HES130 protected the GCX and suppressed vascular permeability of HES70 during early stages of acute massive hemorrhage.