Renal Research Fellow, Monash University
Patients with kidney disease have disorders of their blood vessels. It has recently been discovered that all blood vessels are lined by the endothelial glycocalyx (EG). This mesh-like layer plays important roles in maintaining the health of the circulation and has been shown to be damaged in various conditions. In kidney disease, damage to this layer is linked with disorders of the blood vessels. Therefore we think the EG may be a new marker of blood vessel damage, and EG damage may be linked with disordered blood vessel function. We studied healthy participants (with normal kidney function), people with chronic kidney disease, and people who have had kidney transplants. We compared their EG levels and their markers of blood vessel function. We found that people who have chronic kidney disease have higher levels of EG damage and abnormal blood vessel function compared to healthy participants and to those who have had a kidney transplant. We also found that damage to the EG correlates with markers of abnormal blood vessel function. Therefore, the EG is an important marker of blood vessel damage in kidney disease.
Abstract: Glycocalyx, composed of glycoproteins including proteoglycans, coats the luminal surface of the glomerular capillaries. Human heparanase degrades heparan sulphate glycosaminoglycans and is up-regulated in proteinuric states. In this study, we analyze the structure of the human glomerular endothelial cell glycocalyx in vitro and examine its functional relevance, especially after treatment with human heparanase. Electron microscopy of conditionally immortalized glomerular endothelial cells revealed a 200-nm thick glycocalyx over the plasma membrane, which was also demonstrated by confocal microscopy. Neuraminidase treatment removed the majority of glycocalyx, reduced trans-endothelial electrical resistance by 59%, and increased albumin flux by 207%. Heparinase III and human heparanase specifically cleaved heparan sulphate: this caused no change in trans-endothelial electrical resistance, but increased the albumin passage across the monolayers by 40% and 39%, respectively. Therefore, we have characterized the glomerular endothelial cell glycocalyx and have shown that it contributes to the barrier to flux of albumin across the cell layer. These results suggest an important role for this glycocalyx in the restriction of glomerular protein passage in vivo and suggest ways in which human heparanase levels may be linked to proteinuria in clinical disease.
Pub.: 19 Oct '07, Pinned: 26 Aug '17
Abstract: The endothelial glycocalyx (eGC), a mesh of anionic biopolymers covering the luminal surface of endothelial cells, is considered as an intravascular compartment that protects the vessel wall against pathogenic insults in cardiovascular disease. We hypothesized that chronic kidney disease (CKD) is associated with reduced eGC integrity and subsequent endothelial dysfunction.Shedding of two major components of the eGC, namely syndecan-1 (Syn-1) and hyaluronan (HA), was measured by ELISA in 95 patients with CKD (stages 3-5) and 31 apparently healthy controls. Plasma levels of Syn-1 and HA increased steadily across CKD stages (5- and 5.5-fold, respectively P < 0.001) and were independently associated with impaired renal function after multivariate adjustment. Furthermore, Syn-1 and HA correlated tightly with plasma markers of endothelial dysfunction such as soluble fms-like tyrosine kinase-1 (sFlt-1), soluble vascular adhesion molecule-1 (sVCAM-1), von-Willebrand-Factor (vWF) and angiopoietin-2 (P < 0.001). Experimentally, excessive shedding of the eGC, evidenced by 11-fold increased Syn-1 plasma levels, was also observed in an established rat model of CKD, the 5/6-nephrectomized rats. Consistently, an atomic force microscopy-based approach evidenced a significant decrease in eGC thickness (360 ± 79 vs. 157 ± 29 nm, P = 0.001) and stiffness (0.33 ± 0.02 vs. 0.22 ± 0.01 pN/nm, P < 0.001) of aorta endothelial cell explants isolated from CKD rats.Our findings provide evidence for damage of the atheroprotective eGC as a consequence of CKD and potentially open a new avenue to pathophysiology and treatment of cardiovascular disease in renal patients.
Pub.: 15 Apr '14, Pinned: 26 Aug '17
Abstract: Damage to the endothelial glycocalyx, which helps maintain vascular homeostasis, heightens the sensitivity of the vasculature to atherogenic stimuli. Patients with renal failure have endothelial dysfunction and increased risk for cardiovascular morbidity and mortality, but the state of the endothelial glycocalyx in these patients is unknown. Here, we used Sidestream Darkfield imaging to detect changes in glycocalyx dimension in dialysis patients and healthy controls from in vivo recordings of the sublingual microcirculation. Dialysis patients had increased perfused boundary region and perfused diameters, consistent with deeper penetration of erythrocytes into glycocalyx, indicating a loss of glycocalyx barrier properties. These patients also had higher serum levels of the glycocalyx constituents hyaluronan and syndecan-1 and increased hyaluronidase activity, suggesting the shedding of these components. Loss of residual renal function had no influence on the imaging parameters but did associate with greater shedding of hyaluronan in blood. Furthermore, patients with higher levels of inflammation had more significant damage to the glycocalyx barrier. In conclusion, these data suggest that dialysis patients have an impaired glycocalyx barrier and shed its constituents into blood, likely contributing to the sustained endothelial cell activation observed in ESRD.
Pub.: 23 Oct '12, Pinned: 26 Aug '17
Abstract: ESRD is accompanied by endothelial dysfunction. Because the endothelial glycocalyx (endothelial surface layer) governs interactions between flowing blood and the vessel wall, perturbation could influence disease progression. This study used a novel noninvasive sidestream-darkfield imaging method, which measures the accessibility of red blood cells to the endothelial surface layer in the microcirculation (perfused boundary region), to investigate whether renal function is associated with endothelial surface layer dimensions.Perfused boundary region was measured in control participants (n=10), patients with ESRD (n=23), participants with normal kidney function after successful living donor kidney transplantation (n=12), and patients who developed interstitial fibrosis/tubular atrophy after kidney transplantation (n=10). In addition, the endothelial activation marker angiopoietin-2 and shed endothelial surface layer components syndecan-1 and soluble thrombomodulin were measured using ELISA.Compared with healthy controls (1.82 ± 0.16 µm), ESRD patients had a larger perfused boundary region (+0.23; 95% confidence interval, 0.46 to <0.01; P<0.05), which signifies loss of endothelial surface layer dimensions. This large perfused boundary region was accompanied by higher circulating levels of syndecan-1 (+57.71; 95% confidence interval, 17.38 to 98.04; P<0.01) and soluble thrombomodulin (+12.88; 95% confidence interval, 0.29 to 25.46; P<0.001). After successful transplantation, the perfused boundary region was indistinguishable from healthy controls (without elevated levels of soluble thrombomodulin or syndecan-1). In contrast, however, patients who developed interstitial fibrosis and tubular atrophy showed a large perfused boundary region (+0.36; 95% confidence interval, 0.09 to 0.63; P<0.01) and higher levels of endothelial activation markers. In addition, a significant correlation between perfused boundary region, angiopoietin-2, and eGFR was observed (perfused boundary region versus GFR: Spearman's ρ=0.31; P<0.05; perfused boundary region versus angiopoietin-2: Spearman's ρ=-0.33; P<0.05).Reduced renal function is strongly associated with low endothelial surface layer dimensions. After successful kidney transplantation, the endothelial surface layer is indistinguishable from control.
Pub.: 25 Jan '14, Pinned: 24 Aug '17
Abstract: Endothelial cells perform key homeostatic functions such as regulating blood flow, permeability, and aiding immune surveillance for pathogens. While endothelial activation serves normal physiological adaptation, maladaptation of these endothelial functions has been identified as an important effector mechanism in the progression of renal disease as well as the associated development of cardiovascular disease. The primary interface between blood and the endothelium is the glycocalyx. This carbohydrate-rich gel-like structure with its associated proteins mediates most of the regulatory functions of the endothelium. Because the endothelial glycocalyx is a highly dynamic and fragile structure ex vivo, and traditional tissue processing for staining and perfusion-fixation usually results in a partial or complete loss of the glycocalyx, studying its dimensions and function has proven to be challenging. In this review, we will outline the core functions of the glycocalyx and focus on different techniques to study structure-function relationships in kidney and vasculature.
Pub.: 13 Feb '15, Pinned: 24 Aug '17
Abstract: After briefly discussing endothelial glycocalyx and its role in vascular physiology and renal disease, this overview focuses on its degradation very early in the course of microbial sepsis. We describe our recently proposed mechanism for glycocalyx degradation induced by exocytosis of lysosome-related organelles and release of their cargo. Notably, an intermediate in nitric oxide synthesis, NG-hydroxy-l-arginine, shows efficacy in curtailing exocytosis of these organelles and improvement in animal survival. These data not only depict a novel mechanism responsible for very early glycocalyx degradation, but may also outline a potential preventive therapy. The second issue discussed in this article is related to the therapeutic acceleration of restoration of already degraded endothelial glycocalyx. Here, using as an example our recent findings obtained with sulodexide, we illustrate the importance of the expedited repair of degraded endothelial glycocalyx for the survival of animals with severe sepsis. These two focal points of the review on glycocalyx may not only have broader disease applicability, but they may also provide additional evidence to buttress the idea of the importance of endothelial glycocalyx and its maintenance and repair in the prevention and treatment of an array of renal and nonrenal diseases.
Pub.: 24 May '17, Pinned: 24 Aug '17