Cardiopulmonary bypass associated acute kidney injury: better understanding and better prevention

Cardiopulmonary bypass (CPB) is a common technique in cardiac surgery but is associated with acute kidney injury (AKI), which carries considerable morbidity and mortality. In this review, we explore the range and definition of CPB-associated AKI and discuss the possible impact of different disease recognition methods on research outcomes. Furthermore, we introduce the specialized equipment and procedural intricacies associated with CPB surgeries. Based on recent research, we discuss the potential pathogenesis of AKI that may result from CPB, including compromised perfusion and oxygenation, inflammatory activation, oxidative stress, coagulopathy, hemolysis, and endothelial damage. Finally, we explore current interventions aimed at preventing and attenuating renal impairment related to CPB, and presenting these measures from three perspectives: (1) avoiding CPB to eliminate the fundamental impact on renal function; (2) optimizing CPB by adjusting equipment parameters, optimizing surgical procedures, or using improved materials to mitigate kidney damage; (3) employing pharmacological or interventional measures targeting pathogenic factors.

Promising results of a clinical feasibility study: CIRBP as a potential biomarker in pediatric cardiac surgery

Objective

Cold-inducible RNA binding Protein (CIRBP) has been shown to be a potent inflammatory mediator and could serve as a novel biomarker for inflammation. Systemic inflammatory response syndrome (SIRS) and capillary leak syndrome (CLS) are frequent complications after pediatric cardiac surgery increasing morbidity, therefore early diagnosis and therapy is crucial. As CIRBP serum levels have not been analyzed in a pediatric population, we conducted a clinical feasibility establishing a customized magnetic bead panel analyzing CIRBP in pediatric patients undergoing cardiac surgery.

Methods

A prospective hypothesis generating observational clinical study was conducted at the German Heart Center Berlin during a period of 9 months starting in May 2020 (DRKS00020885, https://drks.de/search/de/trial/DRKS00020885). Serum samples were obtained before the cardiac operation, upon arrival at the pediatric intensive care unit, 6 and 24 h after the operation in patients up to 18 years of age with congenital heart disease (CHD). Customized multiplex magnetic bead-based immunoassay panels were developed to analyze CIRBP, Interleukin-1β (IL-1β), Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), Monocyte chemotactic protein 1 (MCP-1), Syndecan-1 (SDC-1), Thrombomodulin (TM), Vascular endothelial growth factor (VEGF-A), Angiopoietin-2 (Ang-2), and Fibroblast growth factor 23 (FGF-23) in 25 µl serum using the Luminex MagPix® system.

Results

19 patients representing a broad range of CHD (10 male patients, median age 2 years, 9 female patients, median age 3 years) were included in the feasibility study. CIRBP was detectable in the whole patient cohort. Relative to individual baseline values, CIRBP concentrations increased 6 h after operation and returned to baseline levels over time. IL-6, IL-8, IL-10, and MCP-1 concentrations were significantly increased after operation and except for MCP-1 concentrations stayed upregulated over time. SDC-1, TM, Ang-2, as well as FGF-23 concentrations were also significantly increased, whereas VEGF-A concentration was significantly decreased after surgery.

Discussion

Using customized magnetic bead panels, we were able to detect CIRBP in a minimal serum volume (25 µl) in all enrolled patients. To our knowledge this is the first clinical study to assess CIRBP serum concentrations in a pediatric population.

Endothelial Dysfunction in Patients Undergoing Cardiac Surgery: A Narrative Review and Clinical Implications

Cardiac surgery is one of the highest-risk procedures, usually involving cardiopulmonary bypass and commonly inducing endothelial injury that contributes to the development of perioperative and postoperative organ dysfunction. Substantial scientific efforts are being made to unravel the complex interaction of biomolecules involved in endothelial dysfunction to find new therapeutic targets and biomarkers and to develop therapeutic strategies to protect and restore the endothelium. This review highlights the current state-of-the-art knowledge on the structure and function of the endothelial glycocalyx and mechanisms of endothelial glycocalyx shedding in cardiac surgery. Particular emphasis is placed on potential strategies to protect and restore the endothelial glycocalyx in cardiac surgery. In addition, we have summarized and elaborated the latest evidence on conventional and potential biomarkers of endothelial dysfunction to provide a comprehensive synthesis of crucial mechanisms of endothelial dysfunction in patients undergoing cardiac surgery, and to highlight their clinical implications.

Inflammatory markers calprotectin, NETs, syndecan-1 and neopterin in COVID-19 convalescent blood donors

Persisting inflammation has been discovered in lungs and other parenchymatous organs of some COVID-19 convalescents. Calprotectin, neutrophil extracellular traps (NETs), syndecan-1 and neopterin are general key inflammatory markers, and systemically enhanced levels of them may remain after the COVID-19 infection. These inflammatory markers were therefore measured in serum samples of 129 COVID-19 convalescent and 27 healthy blood donors or employees at Oslo Blood bank, Norway. Also antibodies against SARS-CoV-2 nucleocapsid antigen were measured, and timing of sampling and severity of infection noted. Whereas neopterin and NETs values remained low and those for syndecan-1 were not raised to statistically significant level, concentrations for calprotectin, as measured by a novel mixed monoclonal assay, were significantly increased in the convalescents. Antibodies against SARS-CoV-2 nucleocapsid antigen were elevated, but did not correlate with levels of inflammatory markers. Difference between the groups in only one biomarker makes evaluation of ongoing or residual inflammation in the convalescents difficult. If there is a low-grade inflammation, it would in that case involve neutrophils.

Physiological Changes in Subjects Exposed to Accidental Hypothermia: An Update

Background

Accidental hypothermia (AH) is an unintended decrease in body core temperature (BCT) to below 35°C. We present an update on physiological/pathophysiological changes associated with AH and rewarming from hypothermic cardiac arrest (HCA).

Temperature Regulation and Metabolism

Triggered by falling skin temperature, Thyrotropin-Releasing Hormone (TRH) from hypothalamus induces release of Thyroid-Stimulating Hormone (TSH) and Prolactin from pituitary gland anterior lobe that stimulate thyroid generation of triiodothyronine and thyroxine (T4). The latter act together with noradrenaline to induce heat production by binding to adrenergic β3-receptors in fat cells. Exposed to cold, noradrenaline prompts degradation of triglycerides from brown adipose tissue (BAT) into free fatty acids that uncouple metabolism to heat production, rather than generating adenosine triphosphate. If BAT is lacking, AH occurs more readily.

Cardiac Output

Assuming a 7% drop in metabolism per °C, a BCT decrease of 10°C can reduce metabolism by 70% paralleled by a corresponding decline in CO. Consequently, it is possible to maintain adequate oxygen delivery provided correctly performed cardiopulmonary resuscitation (CPR), which might result in approximately 30% of CO generated at normal BCT.

Liver and Coagulation

AH promotes coagulation disturbances following trauma and acidosis by reducing coagulation and platelet functions. Mean prothrombin and partial thromboplastin times might increase by 40–60% in moderate hypothermia. Rewarming might release tissue factor from damaged tissues, that triggers disseminated intravascular coagulation. Hypothermia might inhibit platelet aggregation and coagulation.

Kidneys

Renal blood flow decreases due to vasoconstriction of afferent arterioles, electrolyte and fluid disturbances and increasing blood viscosity. Severely deranged renal function occurs particularly in the presence of rhabdomyolysis induced by severe AH combined with trauma.

Conclusion

Metabolism drops 7% per °C fall in BCT, reducing CO correspondingly. Therefore, it is possible to maintain adequate oxygen delivery after 10°C drop in BCT provided correctly performed CPR. Hypothermia may facilitate rhabdomyolysis in traumatized patients. Victims suspected of HCA should be rewarmed before being pronounced dead. Rewarming avalanche victims of HCA with serum potassium > 12 mmol/L and a burial time >30 min with no air pocket, most probably be futile.

Intraoperative systemic biomarkers predict post-liver transplantation acute kidney injury

OBJECTIVE

Liver transplant (LT) is a definitive therapeutic option for patients with chronic liver disease. However, acute kidney injury after LT (post-LT AKI) is a frequent complication that may lead to graft dysfunction and decrease life expectancy. Delay in AKI detection by traditional biomarkers boosted research with new biomarkers for post-LT AKI as neutrophil gelatinase-associated lipocalin (NGAL) and syndecan-1. We aim to evaluate associations of intraoperative systemic NGAL and syndecan-1 levels with post-LT AKI.

METHODS

This is a prospective study conducted in 46 patients selected for LT. Patients were evaluated preoperatively and blood samples were collected intraoperatively: T1 (after induction of anesthesia), T2 (anhepatic phase) and T3 (2 h after reperfusion of the graft).

RESULTS

The mean age was 54 ± 12 years and 60% were male. Post-LT AKI was observed in 24 (52%) patients of which 12% needed dialysis. Serum NGAL and syndecan-1 increased along surgical phases. Mostly, increment values of serum NGAL of T2 to T3 and syndecan-1 at T3 were importantly associated with post-LT AKI. Into a multivariate model with model for end-stage liver disease score, age, gender, warm ischemia, cold ischemia and surgery time, syndecan-1 levels at T3 remains capable to predict post-LT AKI. Serum NGAL had significance only with increment values calculated by the ratio of 'T3/T2'. Finally, serum syndecan-1 at T3 had a better diagnostic performance in receiver operating characteristic curve analysis.

CONCLUSION

Serum syndecan-1 levels in 2 h after reperfusion were most useful in early post-LT AKI diagnosis and may be used to construct new risk groups in this context.

Antirheumatic treatment is associated with reduced serum Syndecan-1 in Rheumatoid Arthritis

The endothelial glycocalyx (EG) is essential for proper function of the endothelium and for vascular integrity, but its role in premature atherogenesis in rheumatoid arthritis (RA) has not been studied yet. EG impairment can play a role in pathogenesis of vascular disease, and one of its characteristics is shedding of syndecan-1 from endothelial cells. Syndecan-1 shedding is mediated by matrix metalloproteinase-9 (MMP-9) and counteracted by tissue inhibitor of metalloproteinases (TIMP)-1. Cardiovascular disease risk in RA is reversible by disease modifying antirheumatic drugs (DMARDs), but the exact modes of action are still unclear. Therefore, we examined effects of DMARDs on syndecan-1, MMP-9 and TIMP-1 in RA patients, and searched for associations between these parameters and inflammatory activity. From the observational PSARA study, we examined 39 patients starting with methotrexate (MTX) monotherapy (in MTX naïve patients, n = 19) or tumor necrosis factor inhibitors (TNFi) in combination with MTX (in MTX non-responders, n = 20) due to active RA. Serum syndecan-1, MMP-9 and TIMP-1 were measured at baseline and after six weeks of treatment. Serum syndecan-1 (p = 0.008) and TIMP-1 (p<0.001) levels decreased after six weeks of anti-rheumatic treatment. Levels of MMP-9 also decreased, but the difference was not statistically significant. The improvement in syndecan-1 levels were independent of changes in inflammatory activity. There was no significant difference in changes in syndecan-1 levels from baseline to 6 weeks between the MTX and TNFi groups, however the change was significant within the MTX group. Six weeks of antirheumatic treatment was associated with reduction in serum levels of syndecan-1, which might reflect reduced syndecan-1 shedding from EG. Thus, it is possible that EG-preserving properties of DMARDs might contribute to their cardioprotective effects. These effects may be at least partly independent of their anti-inflammatory actions. Our findings do not support the notion that syndecan-1 shedding in RA is mediated mainly by increased MMP-9 or decreased TIMP-9 serum concentration.

Endothelial glycocalyx during early reperfusion in patients undergoing cardiac surgery

Background

Experimental cardiac ischemia-reperfusion injury causes degradation of the glycocalyx and coronary washout of its components syndecan-1 and heparan sulfate. Systemic elevation of syndecan-1 and heparan sulfate is well described in cardiac surgery. Still, the events during immediate reperfusion after aortic declamping are unknown both in the systemic and in the coronary circulation.

Methods

In thirty patients undergoing aortic valve replacement, arterial concentrations of syndecan-1 and heparan sulfate were measured immediately before and at one, five and ten minutes after aortic declamping (reperfusion). Parallel blood samples were drawn from the coronary sinus to calculate trans-coronary gradients (coronary sinus–artery).

Results

Compared with immediately before aortic declamping, arterial syndecan-1 increased by 18% [253.8 (151.6–372.0) ng/ml vs. 299.1 (172.0–713.7) ng/ml, p < 0.001] but arterial heparan sulfate decreased by 14% [148.1 (135.7–161.7) ng/ml vs. 128.0 (119.0–138.2) ng/ml, p < 0.001] at one minute after aortic declamping. There was no coronary washout of syndecan-1 or heparan sulfate during reperfusion. On the contrary, trans-coronary sequestration of syndecan-1 occurred at five [-12.96 ng/ml (-36.38–5.15), p = 0.007] and at ten minutes [-12.37 ng/ml (-31.80–6.62), p = 0.049] after reperfusion.

Conclusions

Aortic declamping resulted in extracardiac syndecan-1 release and extracardiac heparan sulfate sequestration. Syndecan-1 was sequestered in the coronary circulation during early reperfusion. Glycocalyx has been shown to degrade during cardiac surgery. Besides degradation, glycocalyx has propensity for regeneration. The present results of syndecan-1 and heparan sulfate sequestration may reflect endogenous restoration of the damaged glycocalyx in open heart surgery.

Elevated plasma levels of syndecan-1 and soluble thrombomodulin predict adverse outcomes in thrombotic thrombocytopenic purpura

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal blood disorder resulting from acquired deficiency of plasma ADAMTS13 activity. Despite recent advances in early diagnosis and novel therapeutics, the mortality rate of acute iTTP remains as high as 10% to 20%. Moreover, a reliable clinical and laboratory parameter that predicts disease severity and outcomes is lacking. We show in the present study that plasma levels of syndecan-1 (Sdc-1) and soluble thrombomodulin (sTM) on admission were dramatically increased in patients with acute iTTP and remained substantially elevated in a subset of patients compared with healthy controls. The elevated admission plasma levels of Sdc-1 and sTM were associated with abnormal Glasgow coma scale scores, low estimated glomerular filtration rates, the need for intensive care, and in-hospital mortality rates. Moreover, a further simultaneous increase in plasma Sdc-1 and sTM levels at the time of clinical response/remission (eg, when normalization of platelet counts and substantial reduction of serum lactate dehydrogenase activity were achieved) was highly predictive of iTTP recurrence. These results demonstrate that endothelial injury, resulting from disseminated microvascular thromboses, is severe and persistent in patients with acute iTTP. Plasma levels of Sdc-1 and sTM on admission and in remission are predictive of in-hospital mortality and recurrence of acute iTTP, respectively. Thus, an incorporation of such novel plasma biomarkers into the risk assessment in acute iTTP may help implement a more vigorous and intensive therapeutic strategy for these patients.

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.

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.

High Preoperative Serum Syndecan-1, a Marker of Endothelial Glycocalyx Degradation, and Severe Acute Kidney Injury after Valvular Heart Surgery

Degradation of endothelial glycocalyx (EG) is associated with inflammation and endothelial dysfunction, which may contribute to the development of acute kidney injury (AKI). We investigated the association between a marker of EG degradation and AKI after valvular heart surgery. Serum syndecan-1 concentrations were measured at induction of anesthesia and discontinuation of cardiopulmonary bypass in 250 patients. Severe AKI was defined as Kidney Disease: Improving Global Outcomes Criteria Stage 2 or 3. Severe AKI occurred in 13 patients (5%). Receiver operating characteristic analysis of preoperative syndecan-1 to predict severe AKI showed area under curve of 0.714 (95% confidence interval (CI), 0.575–0.853; p = 0.009). The optimal cut-off value was 90 ng/mL, with a sensitivity of 61.5% and specificity of 78.5%. In multivariable analysis, both preoperative syndecan-1 ≥ 90 ng/mL and Cleveland Clinic Foundation score independently predicted severe AKI. Severe tricuspid regurgitation was more frequent (42.4% vs. 17.8%, p < 0.001), and baseline right ventricular systolic pressure (41 (33–51) mmHg vs. 33 (27–43) mmHg, p = 0.001) and TNF-α (1.85 (1.37–2.43) pg/mL vs. 1.45 (1.14–1.92) pg/mL, p <0.001) were higher in patients with high preoperative syndecan-1. Patients with high preoperative syndecan-1 had longer hospital stay (16 (12–24) days vs. 13 (11–17) days, p = 0.001). In conclusion, a high preoperative syndecan-1 concentration greater than 90 ng/mL was able to predict severe AKI after valvular heart surgery and was associated with prolonged hospitalization.

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.

Glycocalyx Degradation in Ischemia-Reperfusion Injury

The glycocalyx is a layer coating the luminal surface of vascular endothelial cells. It is vital for endothelial function as it participates in microvascular reactivity, endothelium interaction with blood constituents, and vascular permeability. Structural and functional damage to glycocalyx occurs in various disease states. A prominent clinical situation characterized by glycocalyx derangement is ischemia-reperfusion (I/R) of the whole body as well as during selective I/R to organs such as the kidney, heart, lung, or liver. Degradation of the glycocalyx is now considered a cornerstone in I/R-related endothelial dysfunction, which further impairs local microcirculation with a feed-forward loop of organ damage, due to vasoconstriction, leukocyte adherence, and activation of the immune response. Glycocalyx damage during I/R is evidenced by rising plasma levels of its principal constituents, heparan sulfate and syndecan-1. By contrast, the concentrations of these compounds in the circulation decrease after successful protective interventions in I/R, suggesting their use as surrogate biomarkers of endothelial integrity. In light of the importance of the glycocalyx in preserving endothelial cell integrity and its involvement in pathologic conditions, several promising therapeutic strategies to restore the damaged glycocalyx and to attenuate its deleterious consequences have been suggested. This review focuses on alterations of glycocalyx during I/R injury in general (to vital organs in particular), and on maneuvers aimed at glycocalyx recovery during I/R injury.

Matrix metalloproteinase-9 mediated shedding of syndecan-4 in glomerular endothelial cells

BACKGROUND

Diabetic nephropathy is the most common cause of end-stage renal failure in the western world and Asia. The mechanisms are not fully elucidated, but disruption of glomerular endothelial glycocalyx and shedding of its components including syndecans has been implicated.

AIMS

We hypothesize that reduced glomerular filtration in diabetes is caused by disruption of endothelial glycocalyx in glomeruli, including increased shedding of syndecan-4. The aim of this study was to determine the effects of experimental diabetic conditions by means of hyperglycemia and IL-1β exposure on syndecan-4 shedding in GEnC, and to investigate regulation of shedding by sheddases.

RESULTS

We found that in GEnC the expression of syndecan-4 is higher than that of the other syndecans. In polarized GEnC, apical shedding of syndecan-4 and syndecan-4 gene expression was increased by 60% after IL-1β-stimulation, but not affected by hyperglycemic conditions. This was accompanied by a 50% increase in MMP9 gene expression in IL-1β-stimulated cells but not hyperglycemia. MMP9 knockdown reduced syndecan-4 shedding by 50%.

CONCLUSION

IL-1β but not hyperglycemia increases the shedding of syndecan-4 from GEnC in an MMP9-dependent manner. This provides a potential mechanism of GEnC damage in diabetes and other inflammatory conditions.

Perioperative implication of the endothelial glycocalyx

The endothelial glycocalyx (EG) is a gel-like layer lining the luminal surface of healthy vascular endothelium. Recently, the EG has gained extensive interest as a crucial regulator of endothelial funtction, including vascular permeability, mechanotransduction, and the interaction between endothelial and circulating blood cells. The EG is degraded by various enzymes and reactive oxygen species upon pro-inflammatory stimulus. Ischemia-reperfusion injury, oxidative stress, hypervolemia, and systemic inflammatory response are responsible for perioperative EG degradation. Perioperative damage of the EG has also been demonstrated, especially in cardiac surgery. However, the protection of the EG and its association with perioperative morbidity needs to be elucidated in future studies. In this review, the present knowledge about EG and its perioperative implication is discussed from an anesthesiologist's perspective.

Mind the gap: mechanisms regulating the endothelial barrier

The endothelial barrier consists of intercellular contacts localized in the cleft between endothelial cells, which is covered by the glycocalyx in a sievelike manner. Both types of barrier-forming junctions, i.e. the adherens junction (AJ) serving mechanical anchorage and mechanotransduction and the tight junction (TJ) sealing the intercellular space to limit paracellular permeability, are tethered to the actin cytoskeleton. Under resting conditions, the endothelium thereby builds a selective layer controlling the exchange of fluid and solutes with the surrounding tissue. However, in the situation of an inflammatory response such as in anaphylaxis or sepsis intercellular contacts disintegrate in post-capillary venules leading to intercellular gap formation. The resulting oedema can cause shock and multi-organ failure. Therefore, maintenance as well as coordinated opening and closure of interendothelial junctions is tightly regulated. The two principle underlying mechanisms comprise spatiotemporal activity control of the small GTPases Rac1 and RhoA and the balance of the phosphorylation state of AJ proteins. In the resting state, junctional Rac1 and RhoA activity is enhanced by junctional components, actin-binding proteins, cAMP signalling and extracellular cues such as sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang-1). In addition, phosphorylation of AJ components is prevented by junction-associated phosphatases including vascular endothelial protein tyrosine phosphatase (VE-PTP). In contrast, inflammatory mediators inhibiting cAMP/Rac1 signalling cause strong activation of RhoA and induce AJ phosphorylation finally leading to endocytosis and cleavage of VE-cadherin. This results in dissolution of TJs the outcome of which is endothelial barrier breakdown.

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.

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.

The Biomechanical Effects of Resuscitation Colloids on the Compromised Lung Endothelial Glycocalyx

BACKGROUND

The endothelial glycocalyx is an important component of the vascular permeability barrier, forming a scaffold that allows serum proteins to create a gel-like layer on the endothelial surface and transmitting mechanosensing and mechanotransduction information that influences permeability. During acute inflammation, the glycocalyx is degraded, changing how it interacts with serum proteins and colloids used during resuscitation and altering its barrier properties and biomechanical characteristics. We quantified changes in the biomechanical properties of lung endothelial glycocalyx during control conditions and after degradation by hyaluronidase using biophysical techniques that can probe mechanics at (1) the aqueous/glycocalyx interface and (2) inside the glycocalyx. Our goal was to discern the location-specific effects of albumin and hydroxyethyl starch (HES) on glycocalyx function.

METHODS

The effects of albumin and HES on the mechanical properties of bovine lung endothelial glycocalyx were studied using a combination of atomic force microscopy and reflectance interference contrast microscopy. Logistic regression was used to determine the odds ratios for comparing the effects of varying concentrations of albumin and HES on the glycocalyx with and without hyaluronidase.

RESULTS

Atomic force microscopy measurements demonstrated that both 0.1% and 4% albumin increased the thickness and reduced the stiffness of glycocalyx when compared with 1% albumin. The effect of HES on glycocalyx thickness was similar to albumin, with thickness increasing significantly between 0.1% and 1% HES and a trend toward a softer glycocalyx at 4% HES. Reflectance interference contrast microscopy revealed a concentration-dependent softening of the glycocalyx in the presence of albumin, but a concentration-dependent increase in stiffness with HES. After glycocalyx degradation with hyaluronidase, stiffness was increased only at 4% albumin and 1% HES.

CONCLUSIONS

Albumin and HES induced markedly different effects on glycocalyx mechanics and had notably different effects after glycocalyx degradation by hyaluronidase. We conclude that HES is not comparable with albumin for studies of vascular permeability and glycocalyx-dependent signaling. Characterizing the molecular and biomechanical effects of resuscitation colloids on the glycocalyx should clarify their indicated uses and permit a better understanding of how HES and albumin affect vascular function.

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.

Inhibition of inflammation induced shedding of the endothelial glycocalyx with low molecular weight heparin

The endothelial surface layer (ESL) consists of the endothelial cell (EC) glycocalyx and adsorbed proteins, and forms a barrier between blood and the EC. Enzymatic shedding of the ESL in response to cytokines may expose receptors for leukocyte (WBC) adhesion and increase vascular permeability. Thus, intravital microscopy was used to explore stabilization of the ESL with low molecular weight heparin (LMWH) to mitigate structural changes with inflammation. Following bolus infusions (i.v.) of LMWH (0.12-1.6mg/kg), shedding of glycans in response to 10^-7M fMLP was measured by loss of fluorescently labeled lectins bound to the EC and WBC-EC adhesion was monitored in post-capillary venules of rat mesentery. During a 30min exposure to fMLP, a 50% reduction in fluorescence (indicative of glycan shedding) occurred at the lowest dose of LMWH whereas a 50% increase occurred (indicative of ESL compaction) at the highest dose. Shedding was reduced by LMWH in a dose dependent manner with an EC50 of 0.6mg/kg. Concomitant WBC-EC adhesion increased over 3-fold for all doses of LMWH. However, at a dose of 1.6mg/kg, WBC-EC adhesion did not rise significantly during the initial 10min exposure to fMLP. Correlation of WBC adhesion with intensity of the lectin stain for all measurements revealed a significant 40% reduction in adhesion as intensity increased 50%. This relationship was attributed to LMWH inhibition of heparanase and/or binding to components of the glycocalyx that resulted in mitigation of glycan shedding, compaction of the lectin stain and stabilization of the glycocalyx.

Serum levels of endothelial glycocalyx constituents in women at 20 weeks' gestation who later develop gestational diabetes mellitus compared to matched controls: a pilot study

OBJECTIVES

The aim of this pilot study was to determine the serum concentration of heparan sulfate, hyaluronan, chondroitin sulfate and syndecan-1 and if these serum concentrations can be used to identify women at 20 weeks' gestation who later develop gestational diabetes mellitus (GDM).

DESIGN

Nested case-control study from Auckland, New Zealand participants in the prospective cohort Screening for Pregnancy Endpoints study.

SETTING

Auckland, New Zealand.

PARTICIPANTS

20 pregnant women (70% European, 15% Indian, 10% Asian, 5% Pacific Islander) at 20 weeks' gestation without any hypertensive complications who developed GDM by existing New Zealand criteria defined as a fasting glucose ≥5.5 mmol/L and/or 2 hours ≥9.0 mmol/L after a 75 g Oral Glucose Tolerance Test. Women not meeting these criteria were excluded from this study. The patients with GDM were matched with 20 women who had uncomplicated pregnancies and negative screening for GDM and matched for ethnicity, maternal age and BMI.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary measures were the serum concentrations of syndecan-1, heparan sulfate, hyaluronan and chondroitin sulfate determined by quantitative ELISA. There were no secondary outcome measures.

RESULTS

Binary logistic regression was performed to determine if serum concentrations of endothelial glycocalyx layer constituents in women at 20 weeks' gestation would be useful in predicting the subsequent diagnosis of GDM. The model was not statistically significant χ²=12.5, df=8, p=0.13, which indicates that the model was unable to distinguish between pregnant women at 20 weeks' gestation who later developed GDM and those who did not.

CONCLUSIONS

Serum concentrations of syndecan-1, heparan sulfate, hyaluronan and chondroitin sulfate in pregnant women at 20 weeks' gestation were not associated with later development of GDM. To further explore whether there is any relationship between endothelial glycocalyx constituents and GDM, the next step is to evaluate serum concentrations at the time diagnosis of GDM.

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.

Incipient renal transplant dysfunction associates with tubular syndecan-1 expression and shedding

Syndecan-1 is a transmembrane heparan sulfate proteoglycan involved in regenerative growth and cellular adhesion. We hypothesized that the induction of tubular syndecan-1 is a repair response to incipient renal damage in apparently stable, uncomplicated renal transplant recipients. We quantified tubular syndecan-1 in unselected renal protocol biopsies taken 1 yr after transplantation. Spearman rank correlation analysis revealed an inverse correlation between tubular syndecan-1 expression and creatinine clearance at the time of biopsy ( r = −0.483, P < 0.03). In a larger panel of protocol and indication biopsies from renal transplant recipients, tubular syndecan-1 correlated with tubular proliferation marker Ki67 ( r = 0.518, P < 0.0001). In a rat renal transplantation model, 2 mo after transplantation, mRNA expression of syndecan-1 and its major sheddase, A disintegrin and metalloproteinase-17, were upregulated (both P < 0.03). Since shed syndecan-1 might end up in the circulation, in a stable cross-sectional human renal transplant population ( n = 510), we measured plasma syndecan-1. By multivariate regression analysis, we showed robust independent associations of plasma syndecan-1 with renal (plasma creatinine and plasma urea) and endothelial function parameters (plasma VEGF-A, all P < 0.01). By various approaches, we were not able to localize syndecan-1 in vessel wall or endothelial cells, which makes shedding of syndecan-1 from the endothelial glycocalyx unlikely. Our data suggest that early damage in transplanted kidneys induces repair mechanisms within the graft, namely, tubular syndecan-1 expression for tubular regeneration and VEGF production for endothelial repair. Elevated plasma syndecan-1 levels in renal transplantation patients might be interpreted as repair/survival factor related to loss of tubular and endothelial function in transplanted kidneys.

Degradation of the endothelial glycocalyx in clinical settings: searching for the sheddases

The endothelial glycocalyx has a profound influence at the vascular wall on the transmission of shear stress, on the maintenance of a selective permeability barrier and a low hydraulic conductivity, and on attenuating firm adhesion of blood leukocytes and platelets. Major constituents of the glycocalyx, including syndecans, heparan sulphates and hyaluronan, are shed from the endothelial surface under various acute and chronic clinical conditions, the best characterized being ischaemia and hypoxia, sepsis and inflammation, atherosclerosis, diabetes, renal disease and haemorrhagic viral infections. Damage has also been detected by in vivo microscopic techniques. Matrix metalloproteases may shed syndecans and heparanase, released from activated mast cells, cleaves heparan sulphates from core proteins. According to new data, not only hyaluronidase but also the serine proteases thrombin, elastase, proteinase 3 and plasminogen, as well as cathepsin B lead to loss of hyaluronan from the endothelial surface layer, suggesting a wide array of potentially destructive conditions. Appropriately, pharmacological agents such as inhibitors of inflammation, antithrombin and inhibitors of metalloproteases display potential to attenuate shedding of the glycocalyx in various experimental models. Also, plasma components, especially albumin, stabilize the glycocalyx and contribute to the endothelial surface layer. Though symptoms of the above listed diseases and conditions correlate with sequelae expected from disturbance of the endothelial glycocalyx (oedema, inflammation, leukocyte and platelet adhesion, low reflow), therapeutic studies to prove a causal connection have yet to be designed. With respect to studies on humans, some clinical evidence exists for benefits from application of sulodexide, a preparation delivering precursors of the glycocalyx constituent heparan sulphate. At present, the simplest option for protecting the glycocalyx seems to be to ensure an adequate level of albumin. However, also in this case, definite proof of causality needs to be delivered.

Syndecan-4 is a major syndecan in primary human endothelial cells in vitro, modulated by inflammatory stimuli and involved in wound healing

Syndecans are important cell surface proteoglycans with many functions; yet, they have not been studied to a very large extent in primary human endothelial cells. The purpose of this study was to investigate syndecan-4 expression in cultured human umbilical vein endothelial cells (HUVECs) and assess its role in inflammatory reactions and experimental wound healing. qRT-PCR analysis revealed that syndecan-3 and syndecan-4 were highly expressed in HUVECs, whereas the expression of syndecan-1 and -2 was low. HUVECs were cultured with the inflammatory mediators lipopolysaccharide (LPS) and interleukin 1β (IL-1β). As a result, syndecan-4 expression showed a rapid and strong increase. Syndecan-1 and -2 expressions decreased, whereas syndecan-3 was unaffected. Knockdown of syndecan-4 using siRNA resulted in changes in cellular morphology and focal adhesion sites, delayed wound healing and tube formation, and increased secretion of the pro-inflammatory and angiogenic chemokine, CXCL8. These data suggest functions for syndecan-4 in inflammatory reactions, wound healing and angiogenesis in primary human endothelial cells.

Sphingosine-1-phosphate protects endothelial glycocalyx by inhibiting syndecan-1 shedding

Endothelial cells (ECs) are covered by a surface glycocalyx layer that forms part of the barrier and mechanosensing functions of the blood-tissue interface. Removal of albumin in bathing media induces collapse or shedding of the glycocalyx. The electrostatic interaction between arginine residues on albumin, and negatively charged glycosaminoglycans (GAGs) in the glycocalyx have been hypothesized to stabilize the glycocalyx structure. Because albumin is one of the primary carriers of the phospholipid sphingosine-1-phosphate (S1P), we evaluated the alternate hypothesis that S1P, acting via S1P1 receptors, plays the primary role in stabilizing the endothelial glycocalyx. Using confocal microscopy on rat fat-pad ECs, we demonstrated that heparan sulfate (HS), chondroitin sulfate (CS), and ectodomain of syndecan-1 were shed from the endothelial cell surface after removal of plasma protein but were retained in the presence of S1P at concentrations of >100 nM. S1P1 receptor antagonism abolished the protection of the glycocalyx by S1P and plasma proteins. S1P reduced GAGs released after removal of plasma protein. The mechanism of protection from loss of glycocalyx components by S1P-dependent pathways was shown to be suppression of metalloproteinase (MMP) activity. General inhibition of MMPs protected against loss of CS and syndecan-1. Specific inhibition of MMP-9 and MMP-13 protected against CS loss. We conclude that S1P plays a critical role in protecting the glycocalyx via S1P1 and inhibits the protease activity-dependent shedding of CS, HS, and the syndecan-1 ectodomain. Our results provide new insight into the role for S1P in protecting the glycocalyx and maintaining vascular homeostasis.

The effect of doxycycline on shedding of the glycocalyx due to reactive oxygen species

The structure and composition of the endothelial cell (EC) glycocalyx reflect a balance of the biosynthesis of glycans and their shear dependent removal. Shedding of glycans from the EC surface has been shown to occur in response to reactive oxygen species (ROS) and inflammatory mediators. Using sub-antimicrobial doses of doxycycline, a broad spectrum matrix metalloprotease (MMP) inhibitor, inhibition of chemoattractant induced glycan shedding has suggested that MMPs may be a major effector of the loss of glycans. However, it has also been reported that doxycycline is a scavenger of ROS that may also activate MMPs. To clarify the basis for doxycycline as an inhibitor of glycan shedding, the present studies were undertaken to determine its effect on ROS induced shedding in post-capillary venules of the exteriorized mesentery of the rat. To this end, hypoxanthine (HX) and xanthine oxidase (XO) were rapidly mixed on the mesenteric surface for a 2min period to generate superoxide anion (O2(-)·) and the time course of glycan shedding was monitored in post-capillary venules over a 30min period. Glycan shedding was quantitated by loss of adherent fluorescently labeled lectin coated microspheres (FLMs, 0.1μm diameter) that were systemically infused. It was found that HX/XO caused FLM adhesion to decrease 45% within 30min. This effect could be inhibited in a dose dependent manner by the addition of superoxide dismutase to the superfusion solution, thus confirming the role of O2(-)·. In contrast, 0.5μM doxycycline had no effect on FLM shedding in response to HX/XO, contrary to its ability to attenuate shedding in response to the chemoattractant fMLP. Thus it is suggested that the efficacy of doxycycline as an inhibitor of glycan shedding during inflammation arises from its ability to inhibit MMP activation.

Diabetic nephropathy and extracellular matrix

Diabetic nephropathy (DN) is a serious complication in diabetes. Major typical morphological changes are the result of changes in the extracellular matrix (ECM). Thus, basement membranes are thickened and the glomerular mesangial matrix and the tubulointerstitial space are expanded, due to increased amounts of ECM. One important ECM component, the proteoglycans (PGs), shows a more complex pattern of changes in DN. PGs in basement membranes are decreased but increased in the mesangium and the tubulointerstitial space. The amounts and structures of heparan sulfate chains are changed, and such changes affect levels of growth factors regulating cell proliferation and ECM synthesis, with cell attachment affecting endothelial cells and podocytes. Enzymes modulating heparan sulfate structures, such as heparanase and sulfatases, are implicated in DN. Other enzyme classes also modulate ECM proteins and PGs, such as matrix metalloproteinases (MMPs) and serine proteases, such as plasminogen activator, as well as their corresponding inhibitors. The levels of these enzymes and inhibitors are changed in plasma and in the kidneys in DN. Several growth factors, signaling pathways, and hyperglycemia per se affect ECM synthesis and turnover in DN. Whether ECM components can be used as markers for early kidney changes is an important research topic, whereas at present, the clinical use remains to be established.

Vascular adhesion protein-1 and syndecan-1 in septic shock

BACKGROUND

Constituents of vascular endothelial surface layer (glycocalyx), e.g. an anchor protein syndecan-1 (SDC-1), can be detected in plasma in many inflammatory conditions. In inflammation, vascular adhesion protein-1 (VAP-1) is rapidly translocated to the apical side of the endothelial cells and may be released to plasma in a soluble form. We hypothesized that glycocalyx injury coincides with VAP-1 activation on endothelial cells. To test the hypothesis, we measured SDC-1 and VAP-1 levels in 20 patients with septic shock.

METHODS

A prospective observational study was conducted in two multidisciplinary critical care units in two tertiary academic teaching hospitals with 20 mechanically ventilated adult patients with septic shock, on days 1 and 4 of treatment. Twenty healthy adults were enrolled as a control group. Plasma SDC-1 content, serum VAP-1 activity, platelets, and leukocyte count were measured in septic shock group at baseline and at 72 h and compared with those of healthy controls.

RESULTS

VAP-1 activity and SDC-1 content were significantly increased in septic patients' group (P < 0.01) in comparison with controls. VAP-1 activity and SDC-1 content correlated positively to each other, and negatively to platelet count. In the septic shock group SDC-1 correlated on day 1 to SOFA score.

CONCLUSIONS

We found increased VAP-1 activity and SDC-1 content in critically ill patients with septic shock. Based on our results, the role of VAP-1 in shock pathogenesis should be studied with semicarbazide-sensitive amine oxidase activity blocking agents and substrate affinity testing.

The endothelial glycocalyx as a barrier to leukocyte adhesion and its mediation by extracellular proteases

The endothelial cell (EC) surface is coated with a layer of polysaccharides linked to membrane-bound and trans-membrane proteoglycans that comprise the glycocalyx, which is augmented by adsorbed proteins derived from the blood stream. This surface layer has been shown to affect hemodynamics in small blood vessels of the microcirculation, the resistance to flow, and leukocyte (WBC) to EC adhesion. Parallel studies of WBC-EC adhesion in response to chemoattractants and cytokines, and shedding of constituents of the glycocalyx, have suggested a role for activation of extracellular proteases in mediating the dynamics of WBC adhesion in response to inflammatory and ischemic stimuli. Likely candidates among the many proteases present are the matrix metalloproteases (MMPs). Inhibition of MMP activation with sub-antimicrobial doses of doxycycline, or zinc chelators, has also inhibited WBC adhesion and shedding of glycans from the EC surface in response to the chemoattractant fMLP. Taken together, these studies suggest that shedding of the EC glycocalyx exposes adhesion receptors and thus enhances WBC-EC adhesion. Future therapeutic strategies for treating pathologies such as the low flow state and inflammation may benefit by further exploration of the mechanics of the glycocalyx in light of protease activation and shear-dependent effects.