Endothelial glycocalyx-the battleground for complications of sepsis and kidney injury

Endothelial dysfunction: Pathophysiology and therapeutic targets for sepsis-induced multiple organ dysfunction syndrome

Sepsis and septic shock are critical medical conditions characterized by a systemic inflammatory response to infection, significantly contributing to global mortality rates. The progression to multiple organ dysfunction syndrome (MODS) represents the most severe complication of sepsis and markedly increases clinical mortality. Central to the pathophysiology of sepsis, endothelial cells play a crucial role in regulating microcirculation and maintaining barrier integrity across various organs and tissues. Recent studies have underscored the pivotal role of endothelial function in the development of sepsis-induced MODS. This review aims to provide a comprehensive overview of the pathophysiology of sepsis-induced MODS, with a specific focus on endothelial dysfunction. It also compiles compelling evidence regarding potential small molecules that could attenuate sepsis and subsequent multi-organ damage by modulating endothelial function. Thus, this review serves as an essential resource for clinical practitioners involved in the diagnosing, managing, and providing intensive care for sepsis and associated multi-organ injuries, emphasizing the importance of targeting endothelial cells to enhance outcomes of the patients.

Changes of the serum properties and its effect on the endothelial cells restoration in patients with chronic disease treated with sulodexide

OBJECTIVE

Inflammation and endothelial dysfunction are important venous changes in patients with chronic venous disease (CVD). The use of the venoactive drugs remains an important treatment modality for patients with CVD, reducing the severity of the CVD-related symptoms and swelling but also reducing inflammation and protecting endothelial cells. In this research, the effects of the serum obtained from patients with CVD before and after sulodexide treatment were evaluated for in vivo and in vitro inflammatory markers and endothelial cell function.

METHODS

Inflammatory markers (IL-6, matrix metalloproteinase-9 [MMP-9], vascular cell adhesion molecule-1 [VCAM-1], and von Willebrand factor [vWF]) from the incompetent great saphenous veins (GSVs) and from the systemic venous circulation were studied in 10 patients with CVD (C2s) before and after 2 months of sulodexide (2 × 500 LSU/d) therapy. Serum from pretreatment and following sulodexide treated patients was evaluated for in vitro cultured human umbilical vein endothelial cell function.

RESULTS

The serum collected from lower leg incompetent GSVs had significantly elevated levels of VCAM-1 (+29%, P < .001) compared with the serum from the systemic circulation. Endothelial cells exposed to the serum from the incompetent lower leg veins of the untreated CVD patients demonstrated higher stimulated synthesis of MMP-9 (+17%, P < .01), as well as increased markers of senescence (prolongation of population doubling time, β-galactosidase activity, and expression of p21 and p53 genes). CVD serum-induced senescent endothelial cells had a higher expression of genes regulating IL-6, MMP-9, VCAM-1, and vWF synthesis. The overall proinflammatory effect on endothelial cells by the serum collected from the incompetent GSVs was stronger as compared with the serum from the systemic circulation. Serum collected from the veins after sulodexide treatment caused lower levels of endothelial cell inflammatory markers as well as respective gene expression than serum obtained at the beginning of the study (before sulodexide treatment). Sulodexide application also reduced the inflammatory secretory activity of the senescent endothelial cells. Sulodexide treatment resulted in the decrease of the majority of the studied inflammatory parameters in both lower limb incompetent vein and systemic blood.

CONCLUSIONS

In patients with CVD, there are significant differences between circulating inflammatory markers analyzed from the lower leg incompetent GSV segments compared with the systemic circulation, indicating a higher inflammatory condition in CVD. Treatment with sulodexide reduces the proinflammatory and endothelial cell activation properties of the serum from patients with CVD.

CLINICAL RELEVANCE

The study documented the significant proinflammatory human vascular endothelial cell activation when exposed to the serum collected from the varicose veins as compared with the serum from the systemic circulation in patients with chronic venous disease (CVD). The inflammatory marker expression, endothelial dysfunction, and endothelial cell senescence transformation can be successfully controlled and downregulated by patients' exposure to the glycosaminoglycan (sulodexide) treatment. Further studies are needed to confirm if glycosaminoglycan application can prevent further CVD clinical progression due to potential CVD-related pathological processes' modulation and their downregulation.

Role of endothelial hyaluronan in peritoneal membrane transport and disease conditions during peritoneal dialysis

Peritoneal membrane dysfunction in peritoneal dialysis (PD) is primarily attributed to angiogenesis; however, the integrity of vascular endothelial cells can affect peritoneal permeability. Hyaluronan, a component of the endothelial glycocalyx, is reportedly involved in preventing proteinuria in the normal glomerulus. One hypothesis suggests that development of encapsulating peritoneal sclerosis (EPS) is triggered by protein leakage due to vascular endothelial injury. We therefore investigated the effect of hyaluronan in the glycocalyx on peritoneal permeability and disease conditions. After hyaluronidase-mediated degradation of hyaluronan on the endothelial cells of mice, macromolecules, including albumin and β2 microglobulin, leaked into the dialysate. However, peritoneal transport of small solute molecules was not affected. Pathologically, hyaluronan expression was diminished; however, expression of vascular endothelial cadherin and heparan sulfate, a core protein of the glycocalyx, was preserved. Hyaluronan expression on endothelial cells was studied using 254 human peritoneal membrane samples. Hyaluronan expression decreased in patients undergoing long-term PD treatment and EPS patients treated with conventional solutions. Furthermore, the extent of hyaluronan loss correlated with the severity of vasculopathy. Hyaluronan on endothelial cells is involved in the peritoneal transport of macromolecules. Treatment strategies that preserve hyaluronan in the glycocalyx could prevent the leakage of macromolecules and subsequent related complications.

Research progress on microcirculatory disorders in septic shock: A narrative review

Hemodynamic coherence plays a critical role in the outcomes of septic shock. Due to the potential negative consequences of microcirculatory disorders on organ failure and clinical outcomes, the maintenance of a balance between the macrocirculation and microcirculation is a topic of significant research focus. Although physical methods and specialized imaging techniques are used in clinical practice to assess microcirculation, the use of monitoring devices is not widespread. The integration of microcirculation research tools into clinical practice poses a significant challenge for the future. Consequently, this review aims to evaluate the impact of septic shock on the microcirculation, the methods used to monitor the microcirculation and highlight the importance of microcirculation in the treatment of critically ill patients. In addition, it proposes an evaluation framework that integrates microcirculation monitoring with macrocirculatory parameters. The optimal approach should encompass dynamic, multiparametric, individualized, and continuous monitoring of both the macrocirculation and microcirculation, particularly in cases of hemodynamic separation.

Effect of 5% albumin on endothelial glycocalyx degradation during off-pump coronary artery bypass

PURPOSE

The integrity of the endothelial glycocalyx (EG), a critical player in vascular homeostasis, reportedly influences the outcomes of critically ill patients. We investigated the effect of 5% albumin, which preserved EG integrity in preclinical studies, vs balanced crystalloid solution on EG degradation in patients undergoing off-pump coronary surgery.

METHODS

Patients were randomized to receive either 5% albumin (N = 51) or balanced crystalloid solution (Plasma-Lyte [Baxter Incorporated, Seoul, Republic of Korea]; N = 53) for intravenous volume replacement during surgery (double-blinded). The primary outcome was plasma syndecan-1 concentration, a marker of EG degradation, measured after anesthetic induction (baseline), completion of grafting, and sternal closure. Secondary outcomes were atrial natriuretic peptide (ANP), tumour necrosis factor (TNF)-α, soluble thrombomodulin, and perioperative fluid balance.

RESULTS

The mean (standard deviation) fluid requirements were 833 (270) mL and 1,323 (492) mL in the albumin and Plasma-Lyte group, respectively (mean difference, -489 mL; 95% confidence interval [CI], -643 to -335; P < 0.001). Plasma syndecan-1 concentration increased after completion of grafting (median difference, 116 ng·mL-1; 95% CI, 67 to 184; P < 0.001) and sternal closure (median difference, 57 ng·mL-1; 95% CI, 36 to 80; P < 0.001) compared with those at baseline, without any intergroup differences. Atrial natriuretic peptide, TNF-α, and soluble thrombomodulin concentrations were similar between the two groups. The amount of chest tube drainage was greater in the albumin group than that in the Plasma-Lyte group (median difference, 190 mL; 95% CI, 18 to 276; P = 0.03).

CONCLUSION

Off-pump coronary surgery was associated with significant EG degradation. Yet, intraoperative fluid therapy with 5% albumin could not ameliorate EG degradation when compared with balanced crystalloid solution.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT03699462); first posted 9 October 2018.

Increased R-spondin 3 contributes to aerobic exercise-induced protection against renal vascular endothelial hyperpermeability and acute kidney injury

AIM

Exercise training exerts protective effects against sepsis-associated multiple organ dysfunction. This study aimed to investigate whether aerobic exercise protected against sepsis-associated acute kidney injury (AKI) via modulating R-spondin 3 (RSPO3) expression.

METHODS

To investigate the effects of aerobic exercise on lipopolysaccharide (LPS)-induced AKI, LPS (20 mg/kg) was intraperitoneally injected after six weeks of treadmill training. To investigate the role of RSPO3 in LPS-induced AKI, wild-type (WT) or inducible endothelial cell-specific RSPO3 knockout (RSPO3EC-/- ) mice were intraperitoneally injected with 12 mg/kg LPS. RSPO3 was intraperitoneally injected 30 min before LPS treatment.

RESULTS

Aerobic exercise-trained mice were more resistant to LPS-induced body weight loss and hypothermia and had a significant higher survival rate than sedentary mice exposed to LPS. Exercise training restored the LPS-induced decreases in serum and renal RSPO3 levels. Exercise or RSPO3 attenuated, whereas inducible endothelial cell-specific RSPO3 knockout exacerbated LPS-induced renal glycocalyx loss, endothelial hyperpermeability, inflammation, and AKI. Bioinformatics analysis results revealed significant increases in the expression of matrix metalloproteinases (MMPs) in kidney tissues of mice exposed to sepsis or endotoxaemia, which was validated in renal tissue from LPS-exposed mice and LPS-treated human microvascular endothelial cells (HMVECs). Both RSPO3 and MMPs inhibitor restored LPS-induced downregulation of tight junction protein, adherens junction protein, and glycocalyx components, thus ameliorating LPS-induced endothelial leakage. Exercise or RSPO3 reversed LPS-induced upregulation of MMPs in renal tissues.

CONCLUSION

Increased renal expression of RSPO3 contributes to aerobic exercise-induced protection against LPS-induced renal endothelial hyperpermeability and AKI by suppressing MMPs-mediated disruption of glycocalyx and tight and adherens junctions.

Liposomal nanocarriers of preassembled glycocalyx expeditiously restore endothelial glycocalyx in endotoxemia

The endothelial glycocalyx (EG) is degraded early during sepsis, and currently available treatments are not effective in promptly restoring it. Here, we created liposomal nanocarriers of preassembled glycocalyx (LNPG) by synthesizing glycosylated syndecan-1 and inserting it into the lipid membrane of unilamellar liposomes. We hypothesized that LNPG would fuse with the endothelial cells where EG is degraded and restore EG in sepsis. We induced endotoxemia in C57BL/6J mice using lipopolysaccharides (LPS) and treated them with LNPG, saline, syndecan-1, or liposomes. LNPG significantly prolonged the survival time of LPS-treated mice compared with the other treatments. Immunostaining of en face mesenteric arteries of LPS-treated mice showed that syndecan-1 was fully restored after LNPG administration. In addition, EG height in microvasculature of mouse cremaster muscle was monitored using sidestream dark field imaging. LNPG restored the perfused boundary region (PBR), which is inversely related to EG dimensions, to the control level after LPS administration. Furthermore, flow-induced dilation in isolated mouse mesenteric arterioles was fully recovered after LNPG treatment in LPS-treated mice. In summary, our findings provide evidence of the therapeutic efficacy of LNPG in the LPS-induced mouse model of sepsis, achieved by expeditiously restoring EG through fusion of LNPG with the endothelial plasma membrane and recovery of endothelial function.NEW & NOTEWORTHY Vascular endothelial cells represent the first line of exposure to bacterial endotoxins. Here, we propose a novel therapeutic strategy using liposomes to deliver preassembled glycocalyx to vascular endothelial cell surface and consequently restore endothelial glycocalyx (EG). We tested liposomal nanocarriers of preassembled glycocalyx (LNPG) in vivo and ex vivo to establish for the first time their expeditious therapeutic efficacy in improving survival of lipopolysaccharides (LPS)-treated mice, as achieved by the restoration of EG and recovery of endothelial function.

Gemcitabine alters sialic acid binding of the glycocalyx and induces inflammatory cytokine production in cultured endothelial cells

Gemcitabine (GEM) is an anticancer drug inhibiting DNA synthesis. Glomerular thrombotic microangiopathy (TMA) has been reported as an adverse effect. However, the precise mechanism of GEM-induced endothelial injury remains unknown. Cultured human umbilical vein endothelial cells (HUVECs) in the confluent phase were exposed to GEM (5-100 μM) for 48 h and evaluated cell viability and morphology, lectin binding concerning sialic acid of endothelial glycocalyx (GCX), and immunofluorescent staining of platelet-endothelial cell adhesion molecule (PECAM) and vascular endothelial growth factor receptor 2 (VEGFR2). The mRNA expression of α2,6-sialyltransferase (ST6Gal1), sialidase (neuraminidase-1: NEU-1), and interleukin (IL)-1β and IL-6 was also evaluated. GEM exposure at 5 μM induced cellular shrinkage and intercellular dissociation, accompanied by slight attenuation of PECAM and VEGFR2 immunostaining, although cell viability was still preserved. At this concentration, lectin binding showed a reduction of terminal sialic acids in endothelial GCX, probably associated with reduced ST6Gal1 mRNA expression. IL-1β and IL-6 mRNA expression was significantly increased after GEM exposure. GEM reduced terminal sialic acids in endothelial GCX through mRNA suppression of ST6Gal1 and induced inflammatory cytokine production in HUVECs. This phenomenon could be associated with the mechanism of GEM-induced TMA.

Pericyte-mediated constriction of renal capillaries evokes no-reflow and kidney injury following ischaemia

Acute kidney injury is common, with ~13 million cases and 1.7 million deaths/year worldwide. A major cause is renal ischaemia, typically following cardiac surgery, renal transplant or severe haemorrhage. We examined the cause of the sustained reduction in renal blood flow ('no-reflow'), which exacerbates kidney injury even after an initial cause of compromised blood supply is removed. Adult male Sprague-Dawley rats, or NG2-dsRed male mice were used in this study. After 60 min kidney ischaemia and 30-60 min reperfusion, renal blood flow remained reduced, especially in the medulla, and kidney tubule damage was detected as Kim-1 expression. Constriction of the medullary descending vasa recta and cortical peritubular capillaries occurred near pericyte somata, and led to capillary blockages, yet glomerular arterioles and perfusion were unaffected, implying that the long-lasting decrease of renal blood flow contributing to kidney damage was generated by pericytes. Blocking Rho kinase to decrease pericyte contractility from the start of reperfusion increased the post-ischaemic diameter of the descending vasa recta capillaries at pericytes, reduced the percentage of capillaries that remained blocked, increased medullary blood flow and reduced kidney injury. Thus, post-ischaemic renal no-reflow, contributing to acute kidney injury, reflects pericytes constricting the descending vasa recta and peritubular capillaries. Pericytes are therefore an important therapeutic target for treating acute kidney injury.

Is the Endothelium the Missing Link in the Pathophysiology and Treatment of COVID-19 Complications?

Patients with COVID-19 present a wide spectrum of disease severity, from asymptomatic cases in the majority to serious disease leading to critical care and even death. Clinically, four different scenarios occur within the typical disease timeline: first, an incubation and asymptomatic period; second, a stage with mild symptoms due mainly to the virus itself; third, in up to 20% of the patients, a stage with severe symptoms where a hyperinflammatory response with a cytokine storm driven by host immunity induces acute respiratory distress syndrome; and finally, a post-acute sequelae (PASC) phase, which present symptoms that can range from mild or annoying to actually quite incapacitating. Although the most common manifestation is acute respiratory failure of the lungs, other organs are also frequently involved. The clinical manifestations of the COVID-19 infection support a key role for endothelial dysfunction in the pathobiology of this condition. The virus enters into the organism via its interaction with angiotensin-converting enzyme 2-receptor that is present prominently in the alveoli, but also in endothelial cells, which can be directly infected by the virus. Cytokine release syndrome can also drive endothelial damage independently. Consequently, a distinctive feature of SARS-CoV-2 infection is vascular harm, with severe endothelial injury, widespread thrombosis, microangiopathy, and neo-angiogenesis in response to endothelial damage. Therefore, endothelial dysfunction seems to be the pathophysiological substrate for severe COVID-19 complications. Biomarkers of endothelial injury could constitute strong indicators of disease progression and severity. In addition, the endothelium could represent a very attractive target to both prevent and treat these complications. To establish an adequate therapy, the underlying pathophysiology and corresponding clinical stage should be clearly identified. In this review, the clinical features of COVID-19, the central role of the endothelium in COVID-19 and in other pathologies, and the potential of specific therapies aimed at protecting the endothelium in COVID-19 patients are addressed.

Roles of glomerular endothelial hyaluronan in the development of proteinuria

Vascular endothelial cells are covered with glycocalyx comprising heparan sulfate, hyaluronan, chondroitin sulfate, and associated proteins. Glomerular endothelial glycocalyx is involved in protecting against induction of proteinuria and structural damage, but the specific components in glycocalyx that represent therapeutic targets remain unclear. Anti-vascular endothelial growth factor (VEGF) therapy is associated with an increased risk of glomerular endothelial injury. This study investigated whether hyaluronan could provide a therapeutic target to protect against proteinuria. We conducted ex vivo and in vivo experiments to explore the effects of degrading glomerular hyaluronan by administering hyaluronidase and of supplementation with hyaluronan. We investigated hyaluronan expression using biotin-labeled hyaluronan-binding protein (HABP) in human kidney specimens or serum hyaluronan in endothelial injuries under inhibition of VEGF signaling. We directly demonstrated hyaluronan in glomerular endothelial layers using HABP staining. Ex vivo and in vivo experiments showed the development of proteinuria after digestion of hyaluronan in glomerular capillaries. Supplementation with hyaluronan after hyaluronidase treatment suppressed proteinuria. Mice in the in vivo study developed albuminuria after intraperitoneal injection of hyaluronidase with decreased glomerular hyaluronan and increased serum hyaluronan. In human kidneys with endothelial cell dysfunction and proteinuria due to inhibition of VEGF, glomerular expression of hyaluronan was reduced even in normal-appearing glomeruli. Serum hyaluronan levels were elevated in patients with pre-eclampsia with VEGF signaling inhibition. Our data suggest that hyaluronan itself plays crucial roles in preventing proteinuria and preserving the integrity of endothelial cells. Hyaluronan could provide a therapeutic target for preventing glomerular endothelial glycocalyx damage, including VEGF signaling inhibition.

Selenocompounds and Sepsis: Redox Bypass Hypothesis for Early Diagnosis and Treatment: Part A-Early Acute Phase of Sepsis: An Extraordinary Redox Situation (Leukocyte/Endothelium Interaction Leading to Endothelial Damage)

Significance: Sepsis is a health disaster. In sepsis, an initial, beneficial local immune response against infection evolves rapidly into a generalized, dysregulated response or a state of chaos, leading to multiple organ failure. Use of life-sustaining supportive therapies creates an unnatural condition, enabling the complex cascades of the sepsis response to develop in patients who would otherwise die. Multiple attempts to control sepsis at an early stage have been unsuccessful. Recent Advances: Major events in early sepsis include activation and binding of leukocytes and endothelial cells in the microcirculation, damage of the endothelial surface layer (ESL), and a decrease in the plasma concentration of the antioxidant enzyme, selenoprotein-P. These events induce an increase in intracellular redox potential and lymphocyte apoptosis, whereas apoptosis is delayed in monocytes and neutrophils. They also induce endothelial mitochondrial and cell damage. Critical Issues: Neutrophil production increases dramatically, and aggressive immature forms are released. Leukocyte cross talk with other leukocytes and with damaged endothelial cells amplifies the inflammatory response. The release of large quantities of reactive oxygen, halogen, and nitrogen species as a result of the leukocyte respiratory burst, endothelial mitochondrial damage, and ischemia/reperfusion processes, along with the marked decrease in selenoprotein-P concentrations, leads to peroxynitrite damage of the ESL, reducing flow and damaging the endothelial barrier. Future Directions: Endothelial barrier damage by activated leukocytes is a time-sensitive event in sepsis, occurring within hours and representing the first step toward organ failure and death. Reducing or stopping this event is necessary before irreversible damage occurs.

Prevention of Chronic Rejection of Marginal Kidney Graft by Using a Hydrogen Gas-Containing Preservation Solution and Adequate Immunosuppression in a Miniature Pig Model

In clinical kidney transplantation, the marginal kidney donors are known to develop chronic allograft rejection more frequently than living kidney donors. In our previous study, we have reported that the hydrogen gas-containing organ preservation solution prevented the development of acute injuries in the kidney of the donor after cardiac death by using preclinical miniature pig model. In the present study, we verified the impact of hydrogen gas treatment in transplantation with the optimal immunosuppressive protocol based on human clinical setting by using the miniature pig model. Marginal kidney processed by hydrogen gas-containing preservation solution has been engrafted for long-term (longer than 100 days). A few cases showed chronic rejection reaction; however, most were found to be free of chronic rejection such as graft tissue fibrosis or renal vasculitis. We concluded that marginal kidney graft from donor after cardiac death is an acceptable model for chronic rejection and that if the transplantation is carried out using a strict immunosuppressive protocol, chronic rejection may be alleviated even with the marginal kidney.

The role of endothelial shear stress on haemodynamics, inflammation, coagulation and glycocalyx during sepsis

Sepsis is a multifactorial syndrome primarily determined by the host response to an invading pathogen. It is common, with over 48 million cases worldwide in 2017, and often lethal. The sequence of events in sepsis begins with the damage of endothelium within the microvasculature, as a consequence of the inflammatory and coagulopathic responses to the pathogen that can progress to multiple organ failure and death. Most therapeutic interventions target the inflammation and coagulation pathways that act as an auto-amplified vicious cycle, which, if unchecked can be fatal. Normal blood flow and shear stress acting on a healthy endothelium and intact glycocalyx have anti-inflammatory, anticoagulant and self-repairing effects. During early stages of sepsis, the vascular endothelium and its glycocalyx become dysfunctional, yet they are essential components of resuscitation and recovery from sepsis. The effects of shear forces on sepsis-induced endothelial dysfunction, including inflammation, coagulation, complement activation and microcirculatory breakdown are reviewed. It is suggested that early therapeutic strategies should prioritize on the restoration of shear forces and endothelial function and on the preservation of the endothelial-glycocalyx barrier.

Correlation of D-xylose with severity and morbidity-related factors of COVID-19 and possible therapeutic use of D-xylose and antibiotics for COVID-19

The SARS-Cov-2 pandemic that currently affects the entire world has been shown to be especially dangerous in the elderly (≥65 years) and in smokers, with notably strong comorbidity in patients already suffering from chronic diseases, such as Type 2 diabetes, cancers, chronic respiratory diseases, obesity, and hypertension. Inflammation of the lungs is the main factor leading to respiratory distress in patients with chronic respiratory disease and in patients with severe COVID-19. Several studies have shown that inflammation of the lungs in general and Type 2 diabetes are accompanied by the degradation of glycosaminoglycans (GAGs), especially heparan sulfate (HS). Several studies have also shown the importance of countering the degradation of HS in lung infections and Type 2 diabetes. D-xylose, which is the initiating element for different sulfate GAG chains (especially HS), has shown regeneration properties for GAGs. D-xylose and xylitol have demonstrated anti-inflammatory, antiglycemic, antiviral, and antibacterial properties in lung infections, alone or in combination with antibiotics. Considering the existing research on COVID-19 and related to D-xylose/xylitol, this review offers a perspective on why the association between D-xylose and antibiotics may contribute to significantly reducing the duration of treatment of COVID-19 patients and why some anti-inflammatory drugs may increase the severity of COVID-19. A strong correlation with scurvy, based on gender, age, ethnicity, smoking status, and obesity status, is also reviewed. Related to this, the effects of treatment with plants such as Artemisia are also addressed. CHEMICAL COMPOUNDS: D-xylose; xylitol; l-ascorbic Acid; D-glucuronic acid; N-acetylglucosamine; D-N-acetylglucosamine; N-acetylgalactosamine; galactose.

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.

Sirtuin 1 and endothelial glycocalyx

Sirtuin1 deficiency or reduced activity comprises one of the hallmarks of diseases as diverse as chronic cardiovascular, renal, and metabolic, some malignancies, and infections, as well as aging-associated diseases. In a mouse model of endothelium-limited defect in sirtuin 1 deacetylase activity, we found a dramatic reduction in the volume of endothelial glycocalyx. This was associated with the surge in the levels of one of key scaffolding heparan sulfate proteoglycans of endothelial glycocalyx, syndecan-4, and specifically, its extracellular domain (ectodomain). We found that the defect in endothelial sirtuin 1 deacetylase activity is associated with (a) elevated basal and stimulated levels of superoxide generation (via the FoxO1 over-acetylation mechanism) and (b) increased nuclear translocation of NF-kB (via p65 over-acetylation mechanism). These findings laid the foundation for the proposed novel function of sirtuin 1, namely, the maintenance of endothelial glycocalyx, particularly manifest in conditions associated with sirtuin 1 depletion. In the forthcoming review, we summarize the emerging conceptual framework of the enhanced glycocalyx degradation in the states of defective endothelial sirtuin 1 function, thus explaining a broad footprint of the syndrome of endothelial dysfunction, from impaired flow-induced nitric oxide production, deterrent leukocytes infiltration, increased endothelial permeability, coagulation, and pro-inflammatory changes to development of microvascular rarefaction and progression of an underlying disease.

Glycocalyx breakdown is increased in African children with cerebral and uncomplicated falciparum malaria

Cerebral malaria (CM) from Plasmodium falciparum infection is associated with endothelial dysfunction and parasite sequestration. The glycocalyx (GCX), a carbohydrate-rich layer lining the endothelium, is crucial in vascular homeostasis. To evaluate the role of its loss in the pathogenesis of pediatric CM, we measured GCX degradation in Tanzanian children with World Health Organization-defined CM (n = 55), uncomplicated malaria (UM; n = 20), and healthy controls (HCs; n = 25). Urine GCX breakdown products [glycosaminoglycans (GAGs)] were quantified using dimethylmethylene blue (DMMB) and liquid chromatography-tandem mass spectrometry assays. DMMB-GAG and mass spectrometry (MS)-GAG (g/mol creatinine) were increased in CM and UM compared with HCs (P < 0.001), with no differences in DMMB-GAG and MS-GAG between CM and UM children or between those with and without a fatal outcome. In CM survivors, urinary GCX DMMB-GAG normalized by d 3. After adjusting for disease severity, DMMB-GAG was significantly associated with parasitemia [partial correlation coefficient (P_corr) = 0.34; P = 0.01] and plasma TNF (P_corr = 0.26; P = 0.04) and inversely with plasma and urine NO oxidation products [P_corr = -0.31 (P = 0.01) and P_corr = -0.26 (P = 0.03), respectively]. GCX breakdown is increased in children with falciparum malaria, with similar elevations in CM and UM. Endothelial GCX degradation may impair endothelial NO production, exacerbate adhesion-molecule expression, exposure, and parasite sequestration, and contribute to malaria pathogenesis.-Yeo, T. W., Bush, P. A., Chen, Y., Young, S. P., Zhang, H., Millington, D. S., Granger, D. L., Mwaikambo, E. D., Anstey, N. M., Weinberg, J. B. Glycocalyx breakdown is increased in African children with cerebral and uncomplicated falciparum malaria.

Heparanase-2 protects from LPS-mediated endothelial injury by inhibiting TLR4 signalling

The endothelial glycocalyx and its regulated shedding are important to vascular health. Endo-β-D-glucuronidase heparanase-1 (HPSE1) is the only enzyme that can shed heparan sulfate. However, the mechanisms are not well understood. We show that HPSE1 activity aggravated Toll-like receptor 4 (TLR4)-mediated response of endothelial cells to LPS. On the contrary, overexpression of its endogenous inhibitor, heparanase-2 (HPSE2) was protective. The microfluidic chip flow model confirmed that HPSE2 prevented heparan sulfate shedding by HPSE1. Furthermore, heparan sulfate did not interfere with cluster of differentiation-14 (CD14)-dependent LPS binding, but instead reduced the presentation of the LPS to TLR4. HPSE2 reduced LPS-mediated TLR4 activation, subsequent cell signalling, and cytokine expression. HPSE2-overexpressing endothelial cells remained protected against LPS-mediated loss of cell-cell contacts. In vivo, expression of HPSE2 in plasma and kidney medullary capillaries was decreased in mouse sepsis model. We next applied purified HPSE2 in mice and observed decreases in TNFα and IL-6 plasma concentrations after intravenous LPS injections. Our data demonstrate the important role of heparan sulfate and the glycocalyx in endothelial cell activation and suggest a protective role of HPSE2 in microvascular inflammation. HPSE2 offers new options for protection against HPSE1-mediated endothelial damage and preventing microvascular disease.

Investigation of Endothelial Surface Glycocalyx Components and Ultrastructure by Single Molecule Localization Microscopy: Stochastic Optical Reconstruction Microscopy (STORM)

On the luminal surface of our blood vessels, there is a thin layer called endothelial surface glycocalyx (ESG) which consists of proteoglycans, glycosaminoglycans (GAGs), and glycoproteins. The GAGs in the ESG are heparan sulfate (HS), hyaluronic acid (HA), chondroitin sulfate (CS), and sialic acid (SA). In order to play important roles in regulating vascular functions, such as being a mechanosensor and transducer for the endothelial cells (ECs) to sense the blood flow, a molecular sieve to maintain normal microvessel permeability and a barrier between the circulating cells and endothelial cells forming the vessel wall, the ESG should have an organized structure at the molecular level. Due to the limitations of conventional optical and electrical microscopy, the ultrastructure of ESG, in the order of 10 to 100 nanometers, has not been revealed until recent development of a super resolution fluorescence optical microscope, Stochastic Optical Reconstruction Microscope (STORM), which is one type of single molecule localization microscopy. This short review describes how the STORM can overcome the diffraction barrier in the conventional fluorescence microscopy to identify the chemical components of the ESG at a high spatial resolution. Examples of the organized ultrastructure of the ESG on the in vitro EC monolayer revealed by the Nikon-STORM system are given as well as how its components get lost during the onset of sepsis, a systemic inflammatory syndrome induced by bacterial infection, which demonstrate that this new technique can be applied to discover the structural and molecular mechanisms at nanometer scales in the native cellular environment for the cellular functions under normal and disease conditions.

The Role of Endothelial Surface Glycocalyx in Mechanosensing and Transduction

The endothelial cells (ECs) forming the inner wall of every blood vessel are constantly exposed to the mechanical forces generated by blood flow. The EC responses to these hemodynamic forces play a critical role in the homeostasis of the circulatory system. A variety of mechanosensors and transducers, locating on the EC surface, intra- and trans-EC membrane, and within the EC cytoskeleton, have thus been identified to ensure proper functions of ECs. Among them, the most recent candidate is the endothelial surface glycocalyx (ESG), which is a matrix-like thin layer covering the luminal surface of the EC. It consists of various proteoglycans, glycosaminoglycans, and plasma proteins and is close to other prominent EC mechanosensors and transducers. This chapter summarizes the ESG composition, thickness, and structure observed by different labeling and visualization techniques and in different types of vessels. It also presents the literature in determining the ESG mechanical properties by atomic force microscopy and optical tweezers. The molecular mechanisms by which the ESG plays the role in EC mechanosensing and transduction are described as well as the ESG remodeling by shear stress, the actin cytoskeleton, the membrane rafts, the angiogenic factors, and the sphingosine-1-phosphate.