Implications of recent accumulating knowledge about endothelial glycocalyx on anesthetic management

Immediate Postoperative High Syndecan-1 is Associated with Short-Term Morbidity and Mortality After Robot-Assisted Esophagectomy: A Prospective Observational Study

BACKGROUND

Disruption of the endothelial glycocalyx (EG) is associated with a poor prognosis in various clinical settings. This study aimed to determine the association between immediate postoperative serum syndecan-1 levels, a representative marker for EG degradation, and major postoperative morbidity and mortality in patients undergoing robot-assisted esophagectomy.

METHODS

Patients who underwent robot-assisted esophagectomy between 2018 and 2022 were prospectively enrolled. The primary outcome was the association between immediate postoperative syndecan-1 levels and the occurrence of major postoperative morbidity and mortality within 30 days of surgery. Patients were classified into low and high syndecan-1 groups based on the optimal cut-off value of syndecan-1 for predicting major morbidity and mortality. A multivariable logistic regression analysis was performed to investigate the risk factors for major morbidity and mortality.

RESULTS

A total of 207 patients were analyzed. Patients with high syndecan-1 levels (≥48 ng/mL) showed a significantly greater incidence of unexpected returns to the operating room and anastomotic leaks and longer durations of hospital and intensive care unit stays than patients with low syndecan-1 levels (<48 ng/mL). Immediate postoperative syndecan-1 levels ≥48 ng/mL (odds ratio [OR] 2.32, 95% confidence interval [CI] 1.23-4.76), American Society of Anesthesiologists physical status ≥III (OR 3.36, 95% CI 1.56-7.22), and current smoker (OR 4.02, 95% CI 1.52-10.61) were independently associated with major morbidity and mortality within 30 days of esophagectomy.

CONCLUSIONS

Immediate postoperative syndecan-1 levels ≥48 ng/mL could be used for the early detection of patients at high risk of complications after robot-assisted esophagectomy.

Plasma disappearance rate of albumin when infused as a 20% solution

BACKGROUND

The transcapillary leakage of albumin is increased by inflammation and major surgery, but whether exogenous albumin also disappears faster is unclear.

METHODS

An intravenous infusion of 3 mL/kg of 20% albumin was given over 30 min to 70 subjects consisting of 15 healthy volunteers, 15 post-burn patients, 15 patients who underwent surgery with minor bleeding, 10 who underwent surgery with major bleeding (mean, 1.1 L) and 15 postoperative patients. Blood Hb and plasma albumin were measured on 15 occasions over 5 h. The rate of albumin disappearance from the plasma was quantitated with population kinetic methodology and reported as the half-life (T1/2).

RESULTS

No differences were observed for T1/2 between volunteers, post-burn patients, patients who underwent surgery with minor bleeding and postoperative patients. The T1/2 averaged 16.2 h, which corresponds to 3.8% of the amount infused per h. Two groups showed plasma concentrations of C-reactive protein of approximately 60 mg/L and still had a similarly long T1/2 for albumin. By contrast, patients undergoing surgery associated with major hemorrhage had a shorter T1/2, corresponding to 15% of the infused albumin per h. In addition, our analyses show that the T1/2 differ greatly depending on whether the calculations consider plasma volume changes and blood losses.

CONCLUSION

The disappearance rate of the albumin in 20% preparations was low in volunteers, in patients with moderately severe inflammation, and in postoperative patients.

Dexmedetomidine suppresses serum syndecan-1 elevation and improves survival in a rat hemorrhagic shock model

Hemorrhagic shock causes vascular endothelial glycocalyx (EGCX) damage and systemic inflammation. Dexmedetomidine (DEX) has anti-inflammatory and EGCX-protective effects, but its effect on hemorrhagic shock has not been investigated. Therefore, we investigated whether DEX reduces inflammation and protects EGCX during hemorrhagic shock. Anesthetized Sprague-Dawley rats were randomly assigned to five groups (n=7 per group): no shock (SHAM), hemorrhagic shock (HS), hemorrhagic shock with DEX (HS+DEX), hemorrhagic shock with DEX and the α7 nicotinic type acetylcholine receptor antagonist methyllycaconitine citrate (HS+DEX/MLA), and hemorrhagic shock with MLA (HS+MLA). HS was induced by shedding blood to a mean blood pressure of 25–30 mmHg, which was maintained for 30 min, after which rats were resuscitated with Ringer’s lactate solution at three times the bleeding volume. The survival rate was assessed up to 3 h after the start of fluid resuscitation. Serum tumor necrosis factor-alpha (TNF-α) and syndecan-1 concentrations, and wet-to-dry ratio of the heart were measured 90 min after the start of fluid resuscitation. The survival rate after 3 h was significantly higher in the HS+DEX group than in the HS group. Serum TNF-α and syndecan-1 concentrations, and the wet-to-dry ratio of heart were elevated by HS, but significantly decreased by DEX. These effects were antagonized by MLA. DEX suppressed the inflammatory response and serum syndecan-1 elevation, and prolonged survival in rats with HS.

Inhalation of 2% Hydrogen Improves Survival Rate and Attenuates Shedding of Vascular Endothelial Glycocalyx in Rats with Heat Stroke

ABSTRACT

Heat stroke is characterized by excessive oxidative stress and inflammatory responses, both of which are implicated in vascular endothelial glycocalyx shedding and heat-stroke mortality. Although molecular hydrogen has antioxidation and anti-inflammatory potency, its effect on the vascular endothelial glycocalyx in heat stroke has not been examined. Therefore, the aim of this study was to investigate the influence of hydrogen inhalation on the survival and thickness of the vascular endothelial glycocalyx of rats subjected to heat stroke. Altogether, 98 Wistar rats were assigned to the experiments. A heat-controlled chamber set at 40°C temperature and 60% humidity was used to induce heat stroke. After preparation, the anesthetized rats that underwent the heating process were subjected to an hour of stabilization in which 0%, 2%, or 4% hydrogen gas was inhaled and maintained until the experiment ended. In addition to survival rate assessments, blood samples and left ventricles were collected to evaluate the thickness of the vascular endothelial glycocalyx and relevant biomarkers. The results showed that 2% hydrogen gas significantly improved survival in the heat-stroked rats and partially preserved the thickness of the endothelial glycocalyx. In addition, serum levels of endotoxin, syndecan-1, malondialdehyde, and tumor necrosis factor-α decreased, whereas superoxide dismutase levels increased, indicating that inhalation of 2% hydrogen attenuated the damage to the vascular endothelial glycocalyx through its antioxidative and anti-inflammatory effects.

The Effects of Resuscitative Fluid Therapy on the Endothelial Surface Layer

The goal of resuscitative fluid therapy is to rapidly expand circulating blood volume in order to restore tissue perfusion. Although this therapy often serves to improve macrohemodynamic parameters, it can be associated with adverse effects on the microcirculation and endothelium. The endothelial surface layer (ESL) provides a protective barrier over the endothelium and is important for regulating transvascular fluid movement, vasomotor tone, coagulation, and inflammation. Shedding or thinning of the ESL can promote interstitial edema and inflammation and may cause microcirculatory dysfunction. The pathophysiologic perturbations of critical illness and rapid, large-volume fluid therapy both cause shedding or thinning of the ESL. Research suggests that restricting the volume of crystalloid, or “clear” fluid, may preserve some ESL integrity and improve outcome based on animal experimental models and preliminary clinical trials in people. This narrative review critically evaluates the evidence for the detrimental effects of resuscitative fluid therapy on the ESL and provides suggestions for future research directions in this field.

Heparan Sulfate Proteoglycans in Diabetes

Diabetes is a complex disorder responsible for the mortality and morbidity of millions of individuals worldwide. Although many approaches have been used to understand and treat diabetes, the role of proteoglycans, in particular heparan sulfate proteoglycans (HSPGs), has only recently received attention. The HSPGs are heterogeneous, highly negatively charged, and are found in all cells primarily attached to the plasma membrane or present in the extracellular matrix (ECM). HSPGs are involved in development, cell migration, signal transduction, hemostasis, inflammation, and antiviral activity, and regulate cytokines, chemokines, growth factors, and enzymes. Hyperglycemia, accompanying diabetes, increases reactive oxygen species and upregulates the enzyme heparanase that degrades HSPGs or affects the synthesis of the HSPGs altering their structure. The modified HSPGs in the endothelium and ECM in the blood vessel wall contribute to the nephropathy, cardiovascular disease, and retinopathy seen in diabetes. Besides the blood vessel, other cells and tissues in the heart, kidney, and eye are affected by diabetes. Although not well understood, the adipose tissue, intestine, and brain also reveal HSPG changes associated with diabetes. Further, HSPGs are significantly involved in protecting the β cells of the pancreas from autoimmune destruction and could be a focus of prevention of type I diabetes. In some circumstances, HSPGs may contribute to the pathology of the disease. Understanding the role of HSPGs and how they are modified by diabetes may lead to new treatments as well as preventative measures to reduce the morbidity and mortality associated with this complex condition.

Effect of volatile and total intravenous anesthesia on syndecan-1 shedding after minimally invasive gastrectomy: a randomized trial

This study aimed to compare the effects of volatile anesthesia and total intravenous anesthesia (TIVA) on syndecan-1 shedding in patients with gastric cancer undergoing minimally invasive gastrectomy. Patients were randomly assigned to either the Volatile (n = 68) or the TIVA (n = 68) group. Anesthesia was maintained with sevoflurane/remifentanil or propofol/remifentanil in the Volatile and TIVA groups, respectively. Serum syndecan-1 was evaluated at pre-operation, end of operation, and postoperative day (POD) 1. Inflammatory markers including white blood cell (WBC) count, neutrophil-to-lymphocyte ratio (NLR), and C-reactive protein (CRP), were also measured at pre-operation, end of operation, and POD 1, 2, 3, and 5. The TIVA group showed significantly lower levels of syndecan-1 at the end of the operation compared to the Volatile group; however, no difference was seen between the groups at POD 1. The WBC count and NLR were significantly lower in the TIVA group at the end of the operation than the Volatile group, but there were no differences between the groups at POD 1, 2, 3, and 5. CRP levels were similar between the groups at all time points. In conclusion, despite TIVA being superior to volatile anesthesia in protecting endothelial glycocalyx during the operation, both did not prevent postoperative syndecan-1 shedding after gastrectomy.

Clinical trial registration number: NCT04183296 (ClinicalTrial.gov, 03/12/2019).

Syndecan-1 and Glypican-1 Knockout Alters Body Water Balance and Urine Response to Fluid Challenge in Mice

Syndecan-1 (Sdc-1) and glypican-1 (Gpc-1) are 2 important proteoglycans found in the glycocalyx and believed to govern transvascular distribution of fluid and protein. In this translational study, we assessed Sdc-1 and Gpc-1 knockout (KO) on whole body water balance after an intravenous volume challenge. Sdc-1 and Gpc-1 KO mice had higher starting blood water content versus strain-matched controls. Sdc-1 KO mice exhibited a significantly higher diuretic response (87%; p < 0.05), higher excreted volume/infusion volume ratio (p < 0.01), higher extravascular/infused ratio, and greater tissue water concentration (60 vs. 52%). Collectively, these suggest differences in kidney response and greater fluid efflux from peripheral vessels. The CD1 strain and Gpc-1 KO had a 2-3-fold larger urine output relative to C57 strain, but Gpc-1 KO reduced the excreted/infused ratio relative to controls (p < 0.01) and they maintained plasma dilution longer. Thus, genetic KO of Sdc-1 and Gpc-1 resulted in markedly different phenotypes. This work establishes the feasibility of performing fluid balance studies in mice.

Intravenous lidocaine to prevent endothelial dysfunction after major abdominal surgery: a randomized controlled pilot trial

Background

Major abdominal surgery is associated with endothelial glycocalyx disruption. The anti-inflammatory effects of lidocaine were recently associated with endothelial barrier protection.

Methods

This was a single-centre, parallel group, randomized, controlled, double blind, pilot trial. Forty adult patients scheduled for major abdominal surgery were included between December 2016 and March 2017 in the setting of a University Hospital in Brussels (Belgium); reasons for non-inclusion were planned liver resection and conditions associated to increased risk of local anesthetics systemic toxicity. Patients were randomized to receive either lidocaine by continuous intravenous administration or an equivalent volume of 0.9% saline.

The primary endpoint was the postoperative syndecan-1 concentration (difference between groups). Near-infrared spectroscopy of the thenar eminence in association with the vascular occlusion test, and contemporary analysis of flow-mediated dilation of the brachial artery were the secondary outcomes, along with haemodynamic data. Blood samples and data were collected before surgery (T0), and at 1–3 h (T1) and 24 h (T2) post-surgery.

Results

Syndecan-1 concentration increased significantly post-surgery (P < 0.001), but without any difference between groups. The near-infrared spectroscopy-derived and flow-mediated dilation-derived variables showed minor changes unrelated to group assignment. Compared with the placebo group, the intervention group had a significantly lower peri-operative mean arterial pressure and cardiac index, despite equally conducted goal-directed haemodynamic management. Postoperative lactate concentrations were similar between groups.

Conclusions

Lidocaine failed to have any effect on endothelial function. Since in comparisons to other types of clinical situations, syndecan-1 was only slightly upregulated, endothelial dysfunction after major abdominal surgery might be overestimated.

Trial registration

« ISRCTN Registry » identifier: ISRCTN63417725. Date: 15/06/2020. Retrospectively registered.

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).

Plasma volume expansion and capillary leakage of 20% albumin in burned patients and volunteers

Background

Burn injury is associated with a long-standing inflammatory reaction. The use of albumin solutions for plasma volume support is controversial because of concerns of increased capillary leakage, which could aggravate the commonly seen interstitial oedema.

Methods

In the present open controlled clinical trial, an intravenous infusion of 20% albumin at 3 mL/kg was given over 30 min to 15 burn patients and 15 healthy volunteers. Blood samples and urine were collected for 5 h. Plasma dilution, plasma albumin and colloid osmotic pressure were compared. Mass balance calculations were used to estimate plasma volume expansion and capillary leakage of fluid and albumin.

Results

The patients were studied between 4 and 14 (median, 7) days after the burn injury, which spread over 7–48% (median, 15%) of the total body surface area. The albumin solution expanded the plasma volume by almost 15%, equivalent to twice the infused volume, in both groups. The urinary excretion exceeded the infused volume by a factor of 2.5. Capillary leakage of albumin occurred at a rate of 3.4 ± 1.5 g/h in burn patients and 3.7 ± 1.6 g/h in the volunteers (P = 0.61), which corresponded to 2.4 ± 1.0% and 2.5 ± 1.2% per hour of the intravascular pool (P = 0.85). The median half-life of the plasma volume expansion was 5.9 (25th–75th percentiles 2.7–11.7) h in the burn patients and 6.9 (3.4–8.5) h in the volunteers (P = 0.56).

Conclusions

Albumin 20% was an effective volume expander in patients at 1 week post-burn. No relevant differences were found between burn patients and healthy volunteers.

Trial registration

EudraCT 2016-000996-26 on May 31, 2016.

Long Intravascular Persistence of 20% Albumin in Postoperative Patients

BACKGROUND

Albumin may persist intravascularly for a shorter time in patients after major surgery than in healthy volunteers due to a surgery-induced breakdown (shedding) of the endothelial glycocalyx layer.

METHODS

In this nonrandomized clinical trial, an IV infusion of 3 mL/kg of 20% albumin was given at a constant rate during 30 minutes to 15 patients on the first day after major open abdominal surgery (mean operating time 5.9 h) and to 15 conscious volunteers. Blood samples and urine were collected during 5 h and mass balance calculations used to estimate the half-lives of the administered albumin molecules and the induced plasma volume expansion, based on measurements of hemodilution and the plasma albumin concentration.

RESULTS

At the end of the infusions, albumin had diluted the plasma volume by 13.3% ± 4.9% (mean ± SD) in the postoperative patients and by 14.2% ± 4.8% in the volunteers (mean difference -0.9, 95% CI, -4.7 to 2.9; 1-way ANOVA P = .61), which amounted to twice the infused volume. The intravascular half-life of the infused albumin molecules was 9.1 (5.7-11.2) h in the surgical patients and 6.0 (5.1-9.0) h in the volunteers (Mann-Whitney U test, P = .26; geometric mean difference 1.2, 95% CI, 0.8-2.0). The half-life of the plasma volume expansion was 10.3 (5.3-17.6; median and interquartile range) h in the surgical patients and 7.6 (3.5-9.0) h in the volunteers (P = .10; geometric mean difference 1.5, 95% CI, 0.8-2.8). All of these parameters correlated positively with the body mass index (correlation coefficients being 0.42-0.47) while age and sex did not affect the results.

CONCLUSIONS

Twenty percent albumin caused a long-lasting plasma volume expansion of similar magnitude in postoperative patients and volunteers.

The association of endothelial injury and systemic inflammation with perioperative myocardial infarction

Background

Major surgery predisposes to endothelial glycocalyx injury. Endothelial glycocalyx injury associates with cardiac morbidity, including spontaneous myocardial infarction. However, the relation between endothelial glycocalyx injury and the development of perioperative myocardial infarction remains unknown.

Methods

Fifteen perioperative myocardial infarction patients and 60 propensity-matched controls were investigated in this prospective study. The diagnosis of perioperative myocardial infarction was based on repeated cardiac troponin T measurements, electrocardiographs and recordings of ischaemic signs and symptoms. We measured endothelial glycocalyx markers – soluble thrombomodulin, syndecan-1 and vascular adhesion protein 1 – and an inflammatory marker, namely interleukin-6, preoperatively and 6 h and 24 h postoperatively. We calculated the areas under the receiver operating characteristics curves (AUCs) to compare the performances of the different markers in predicting perioperative myocardial infarction. The highest value of each marker was used in the analysis.

Results

The interleukin-6 concentrations of perioperative myocardial infarction patients were significantly higher preoperatively and 6 and 24 h postoperatively ( P =  0.002, P =  0.002 and P =  0.001, respectively). The AUCs (95% confidence intervals) for the detection of perioperative myocardial infarction were 0.51 (0.34–0.69) for soluble thrombomodulin, 0.63 (0.47–0.79) for syndecan-1, 0.54 (0.37–0.70) for vascular adhesion protein 1 and 0.69 (0.54–0.85) for interleukin-6.

Conclusions

Systemic inflammation, reflected by interleukin-6, associates with cardiac troponin T release and perioperative myocardial infarction. Circulating interleukin-6 demonstrated some potential to predict perioperative myocardial infarction, whereas endothelial glycocalyx markers did not.

Fluid volume kinetics of 20% albumin

AIMS

A population kinetic model was developed for the body fluid shifts occurring when 20% albumin is given by intravenous infusion. The aim was to study whether its efficacy to expand the plasma volume is impaired after major surgery.

METHODS

An intravenous infusion of 3 mL/kg 20% albumin over 30 minutes was given to 15 volunteers and to 15 patients on the 1^st day after major open abdominal surgery. Blood samples and urine were collected during 5 hours. Mixed-effect modelling software was used to develop a fluid volume kinetic model, using blood haemoglobin and urine excretion the estimate body fluid shifts, to which individual-specific covariates were added in sequence.

RESULTS

The rise in plasma albumin expanded the plasma volume in excess of the infused volume by relocating noncirculating fluid (rate constant k₂₁ ), but it also increased losses of fluid from the kinetic system (k_b ). The balance between k₂₁ and k_b maintained the rise in plasma albumin and plasma volume at a virtual steady-state for almost 2 hours. The rate constant for urinary excretion (k₁₀ ) was slightly reduced by the preceding surgery, by a marked rise in plasma albumin, and by a high preinfusion urinary concentration of creatinine. The arterial pressure, body weight, and plasma concentrations of C-reactive protein and shedding products of the endothelial glycocalyx layer (syndecan-1, heparan sulfate, and hyaluronic acid) did not serve as statistically significant covariates.

CONCLUSIONS

There were no clinically relevant differences in the kinetics of 20% albumin between postoperative patients and volunteers.

Dexmedetomidine preserves the endothelial glycocalyx and improves survival in a rat heatstroke model

PURPOSE

Heatstroke causes systemic inflammation, followed by vascular endothelial damage. The normal vascular endothelium is coated by endothelial glycocalyx (EGCX). Dexmedetomidine (DEX) has an anti-inflammatory effect, but there has been little investigation on the influence of heatstroke on EGCX and the effect of DEX on this condition. Therefore, we examined whether EGCX was disrupted in heatstroke and if DEX improved survival and preserves EGCX.

METHODS

Anesthetized Wistar rats were randomly assigned to three groups: a DEX group treated with DEX (5 µg/kg/h) and 0.9% saline infused continuously at 10 ml/kg/h during heat exposure; a NSS group given 0.9% saline during heat exposure; and a SHAM group given 0.9% saline alone without heat exposure. Heatstroke was induced by exposure to an ambient temperature of 40 °C with relative humidity of 60%. The survival rate was assessed up to 2 h after the start of heat exposure. Plasma levels of syndecan-1 and the thickness of EGCX using electron microscopy were measured when the systolic blood pressure fell to less than 80 mmHg.

RESULTS

The survival rate after 2 h of heat exposure was significantly higher in the DEX group compared to the NSS group (89% vs. 22%, P = 0.004). Plasma levels of syndecan-1 were 0.6 ± 1.3, 9.7 ± 5.9, and 2.1 ± 3.4 ng/ml in the SHAM, NSS and DEX groups, respectively (P = 0.013). The thickness of EGCX was significantly higher in the DEX group compared with the NSS group (P = 0.001).

CONCLUSIONS

EGCX was disrupted in heatstroke, and DEX improved survival and preserved EGCX.

Endothelial Glycocalyx Layer: A Possible Therapeutic Target for Acute Lung Injury during Lung Resection

Background

Shedding of the endothelial glycocalyx layer (EGL) is known to occur during major surgery, but its degradation associated with minimally invasive video-assisted thoracoscopy (VATS) remains unclear. We investigated if serum biomarkers of EGL disruption were elevated during VATS lobectomy, and whether the urinary trypsin inhibitor (UTI) ulinastatin exerted a protective effect during this procedure.

Materials and Methods

Sixty ASA II-III lung cancer patients undergoing elective VATS lobectomy were divided equally into UTI and control groups. UTI group patients received intravenous UTI during surgery. Serum levels of syndecan-1 and heparan sulfate were examined before (T0) and at the end of surgery (T1). Serum albumin and hemoglobin were measured before surgery (BOD) and on the first postoperative day (POD1).

Results

In control group, syndecan-1 levels were significantly elevated at T1 compared with T0 (3.77 ± 3.15 versus 4.28 ± 3.30, P = 0.022^⁎) and increased even more significantly in patients whose surgery lasted >3 h (3.28 ± 2.84 versus 4.31 ± 3.39, P = 0.003^⁎⁎). Serum albumin levels on POD1 were significantly lower in control group compared with UTI group (32.63 ± 4.57 versus 35.76 ± 2.99, P = 0.031^⁎).

Conclusion

EGL degradation occurs following VATS lobectomy. UTI can alleviate this shedding, thus helping preserve normal vascular permeability.

Trail Registration

This trial is registered with ChiCTR-IOC-17010416 (January 13, 2017).

Targeting the endothelial glycocalyx in acute critical illness as a challenge for clinical and laboratory medicine

The purpose of this manuscript is to review the role of endothelial glycocalyx (EG) in the field of critical and perioperative medicine and to discuss possible future directions for investigations in this area. Under physiological conditions, EG has several well-defined functions aimed to prevent the disruption of vessel wall integrity. Under pathological conditions, the EG represent one of the earliest sites of injury during inflammation. EG structure and function distortion contribute to organ dysfunction related to sepsis, trauma, or global ischemia of any origin. Discovering new therapeutic approaches (either pharmacological or non-pharmacological) aimed to protect the EG against injury represents a promising direction in clinical medicine. Further, the currently-used common interventions in the acutely ill - fluids, blood products, nutritional support, organ-supporting techniques (e.g. continuous renal replacement therapy, extracorporeal circulation), temperature modulation and many others - should be re-evaluated during acute illness in terms of their EG "friendliness". To assess new therapies that protect the EG, or to evaluate the effect of currently-used interventions on EG integrity, a relevant marker or method to determine EG damage is needed. Such marker or method should be available to clinicians within hours, preferably in the form of a point-of-care test at the bedside. Collaborative research between clinical disciplines and laboratory medicine is warranted, and targeting the EG represents major challenges for both.

Structural Behavior of the Endothelial Glycocalyx Is Associated With Pathophysiologic Status in Septic Mice: An Integrated Approach to Analyzing the Behavior and Function of the Glycocalyx Using Both Electron and Fluorescence Intravital Microscopy

BACKGROUND

The endothelial surface layer (ESL) regulates vascular permeability to maintain fluid homeostasis. The glycocalyx (GCX), which has a complex and fragile ultrastructure, is an important component of the ESL. Abnormalities of the GCX have been hypothesized to trigger pathological hyperpermeability. Here, we report an integrated in vivo analysis of the morphological and functional properties of the GCX in a vital organ.

METHODS

We examined the behavior of the ESL and GCX, using both electron microscopy (EM) and intravital microscopy (IVM). We also compared morphological changes in the ESL of mouse skin in a glycosidase-treated and control group. Combined approaches were also used to examine both morphology and function in a lipopolysaccharide-induced septic model and the pathophysiological features of leukocyte-endothelial interactions and in vivo vascular permeability.

RESULTS

Using IVM, we identified an illuminated part of the ESL as the GCX and confirmed our observation using morphological and biochemical means. In septic mice, we found that the GCX was thinner than in nonseptic controls in both an EM image analysis (0.98 ± 2.08 nm vs 70.68 ± 36.36 nm, P< .001) and an IVM image analysis (0.36 ± 0.15 μm vs 1.07 ± 0.39 μm, P< .001). Under septic conditions, syndecan-1, a representative core protein of the GCX, was released into the blood serum at a higher rate in septic animals (7.33 ± 3.46 ng/mL) when compared with controls (below the limit of detection, P< .001). Significant increases in leukocyte-endothelial interactions, defined as the numbers of rolling or firm-sticking leukocytes, and molecular hyperpermeability to the interstitium were also observed after GCX shedding in vivo.

CONCLUSIONS

Using IVM, we visualized an illuminated part of the ESL layer that was subsequently confirmed as the GCX using EM. Severe sepsis induced morphological degradation of the GCX, accompanied by shedding of the syndecan-1 core protein and an increase in leukocyte-endothelial interactions affecting the vascular permeability. Our in vivo model describes a new approach to deciphering the relationship between structural and functional behaviors of the GCX.

Minimal shedding of the glycocalyx layer during abdominal hysterectomy

Background

Surgery with and without hypervolaemia may cause shedding (breakdown) of the endothelial glycocalyx layer, but the severity of this problem is unclear.

Methods

In this preliminary report of a larger clinical trial, the plasma and urine concentrations of three biomarkers of glycocalyx shedding (syndecan-1, hyaluronic acid and heparan sulfate) were measured in seven patients before, during, and after open hysterectomy. The fluid therapy consisted of 25 ml/kg (approximately 2 l) of Ringer’s lactate, which was infused over 30 min when the surgery started. The resulting plasma volume expansion at the end of the infusion was estimated from the haemodilution.

Results

The mean plasma concentration of syndecan-1 was 21.7 ng/ml before surgery and averaged 19.7 ng/ml during and after the surgery. The plasma concentration of hyaluronic acid decreased from 38.0 to 27.7 ng/ml (P < 0.05), while heparan sulfate increased from 3.4 to 5.5 μg/ml (P < 0.05). The urine concentrations of syndecan-1 decreased significantly, while they increased for hyaluronic acid and heparan sulfate. Despite the vigorous fluid load, the urine flow did not exceed 1 ml/min.

Conclusions

No clear evidence was found for shedding of the endothelial glycocalyx layer when 2 l of Ringer’s lactate was infused over 30 min during abdominal hysterectomy. Urine analyses yielded patterns of changes that differed from those in plasma.

Trial registration

ISRCTN81005631. Registered May 17, 2016.

Glycocalyx and its involvement in clinical pathophysiologies

Vascular hyperpermeability is a frequent intractable feature involved in a wide range of diseases in the intensive care unit. The glycocalyx (GCX) seemingly plays a key role to control vascular permeability. The GCX has attracted the attention of clinicians working on vascular permeability involving angiopathies, and several clinical approaches to examine the involvement of the GCX have been attempted. The GCX is a major constituent of the endothelial surface layer (ESL), which covers most of the surface of the endothelial cells and reduces the access of cellular and macromolecular components of the blood to the surface of the endothelium. It has become evident that this structure is not just a barrier for vascular permeability but contributes to various functions including signal sensing and transmission to the endothelium. Because GCX is a highly fragile and unstable layer, the image had been only obtained by conventional transmission electron microscopy. Recently, advanced microscopy techniques have enabled direct visualization of the GCX in vivo, most of which use fluorescent-labeled lectins that bind to specific disaccharide moieties of glycosaminoglycan (GAG) chains. Fluorescent-labeled solutes also enabled to demonstrate vascular leakage under the in vivo microscope. Thus, functional analysis of GCX is advancing. A biomarker of GCX degradation has been clinically applied as a marker of vascular damage caused by surgery. Fragments of the GCX, such as syndecan-1 and/or hyaluronan (HA), have been examined, and their validity is now being examined. It is expected that GCX fragments can be a reliable diagnostic or prognostic indicator in various pathological conditions. Since GCX degradation is strongly correlated with disease progression, pharmacological intervention to prevent GCX degradation has been widely considered. HA and other GAGs are candidates to repair GCX; further studies are needed to establish pharmacological intervention. Recent advancement of GCX research has demonstrated that vascular permeability is not regulated by simple Starling’s law. Biological regulation of vascular permeability by GCX opens the way to develop medical intervention to control vascular permeability in critical care patients.