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.

Modulation of Intestinal Epithelial Glycocalyx Development by Human Milk Oligosaccharides and Non-Digestible Carbohydrates.

SCOPE: The epithelial glycocalyx development is of great importance for microbial colonization. Human milk oligosaccharides (hMOs) and non-digestible carbohydrates (NDCs) may modulate glycocalyx development. METHODS AND RESULTS: The effects of hMOs and NDCs on human gut epithelial cells (Caco2) are investigated by quantifying thickness and area coverage of adsorbed albumin, heparan sulfate (HS), and hyaluronic acid (HA) in the glycocalyx. Effects of hMOs (2'-FL and 3-FL) and NDCs [inulins with degrees of polymerization (DP) (DP3-DP10, DP10-DP60, DP30-DP60) and pectins with degrees of methylation (DM) (DM7, DM55, DM69)] are tested using immunofluorescence staining at 1 and 5 days stimulation. HMOs show a significant enhancing effect on glycocalyx development but effects are structure-dependent. 3-FL induces a stronger albumin adsorption and increases HS and HA stronger than 2'-FL. The DP3-DP10, DP30-60 inulins also increase glycocalyx development in a structure-dependent manner as DP3-DP10 selectively increases HS, while DP30-DP60 specifically increases HA. Pectins have less effects, and only increase albumin adsorption. CONCLUSION: Here, it is shown that 2'-FL and 3-FL and inulins stimulate glycocalyx development in a structure-dependent fashion. This may contribute to formulation of effective hMO and NDC formulations in infant formulas to support microbial colonization and gut barrier function.

Vascular Endothelial Growth Factor-A165b Is Protective and Restores Endothelial Glycocalyx in Diabetic Nephropathy.

Diabetic nephropathy is the leading cause of ESRD in high-income countries and a growing problem across the world. Vascular endothelial growth factor-A (VEGF-A) is thought to be a critical mediator of vascular dysfunction in diabetic nephropathy, yet VEGF-A knockout and overexpression of angiogenic VEGF-A isoforms each worsen diabetic nephropathy. We examined the vasculoprotective effects of the VEGF-A isoform VEGF-A165b in diabetic nephropathy. Renal expression of VEGF-A165b mRNA was upregulated in diabetic individuals with well preserved kidney function, but not in those with progressive disease. Reproducing this VEGF-A165b upregulation in mouse podocytes in vivo prevented functional and histologic abnormalities in diabetic nephropathy. Biweekly systemic injections of recombinant human VEGF-A165b reduced features of diabetic nephropathy when initiated during early or advanced nephropathy in a model of type 1 diabetes and when initiated during early nephropathy in a model of type 2 diabetes. VEGF-A165b normalized glomerular permeability through phosphorylation of VEGF receptor 2 in glomerular endothelial cells, and reversed diabetes-induced damage to the glomerular endothelial glycocalyx. VEGF-A165b also improved the permeability function of isolated diabetic human glomeruli. These results show that VEGF-A165b acts via the endothelium to protect blood vessels and ameliorate diabetic nephropathy.

Sodium selective erythrocyte glycocalyx and salt sensitivity in man.

Negatively charged surfaces of erythrocytes (RBC) reflect properties of the endothelial glycocalyx. Plasma electrolytes counteract these charges and thus control the repulsive forces between RBC and endothelium. Although Na(+) is supposed to exert a rather high affinity to the RBC surface, a direct comparison between Na(+) and K(+) in counteracting the RBC surface has been never made. Therefore, we measured Na(+)/K(+) selectivity of the RBC surface in 20 healthy volunteers applying the previously published salt blood test (SBT). It turned out that the Na(+)/K(+) selectivity ratio of the RBC glycocalyx is on average 6.1 ± 0.39 (ranging from 3 to 9 in different individuals). Considering standard plasma Na(+) and K(+) concentrations, binding probability of Na(+)/K(+) at the RBC surface is about 180:1. The SBT reveals that plasma K(+) counteracts only about 7% of the negative charges in the RBC glycocalyx. As an in vivo proof of principle, a volunteer's blood was continuously tested over 6 months while applying a glycocalyx protective polyphenol-rich natural compound (hawthorn extract). It turned out that RBC Na(+) sensitivity (the inverse of Na(+) buffer capacity) decreased significantly by about 25% while Na(+)/K(+) selectivity of the RBC glycocalyx declined only slightly by about 8 %. Taken together, (i) plasma Na(+) selectively buffers the negative charges of the RBC glycocalyx, (ii) the contribution of K(+) in counteracting these negative surface charges is small, and (iii) natural polyphenols applied in vivo increase RBC surface negativity. In conclusion, low plasma Na(+) is supposed to favor frictionless RBC-slipping through blood vessels.

Microvascular permeability to water is independent of shear stress, but dependent on flow direction.

Endothelial cells in a cultured monolayer change from a "cobblestone" configuration when grown under static conditions to a more elongated shape, aligned with the direction of flow, after exposure to sustained uniform shear stress. Sustained blood flow acts to protect regions of large arteries from injury. We tested the hypothesis that the stable permeability state of individually perfused microvessels is also characteristic of flow conditioning. In individually perfused rat mesenteric venular microvessels, microvascular permeability, measured as hydraulic conductivity (Lp), was stable [mean 1.0 × 10(-7) cm/(s × cmH2O)] and independent of shear stress (3-14 dyn/cm(2)) for up to 3 h. Vessels perfused opposite to the direction of normal blood flow exhibited a delayed Lp increase [ΔLp was 7.6 × 10(-7) cm/(s × cmH2O)], but the increase was independent of wall shear stress. Addition of chondroitin sulfate and hyaluronic acid to perfusates increased the shear stress range, but did not modify the asymmetry in response to flow direction. Increased Lp in reverse-perfused vessels was associated with numerous discontinuities of VE-cadherin and occludin, while both proteins were continuous around the periphery of forward-perfused vessels. The results are not consistent with a general mechanism for graded shear-dependent permeability increase, but they are consistent with the idea that a stable Lp under normal flow contributes to prevention of edema formation and also enables physiological regulation of shear-dependent small solute permeabilities (e.g., glucose). The responses during reverse flow are consistent with reports that disturbed flows result in a less stable endothelial barrier in venular microvessels.

Sevoflurane preserves the endothelial glycocalyx against ischaemia-reperfusion injury.

BACKGROUND: Healthy vascular endothelium is coated by the glycocalyx, important in multiple endothelial functions, but destroyed by ischaemia-reperfusion. The impact of volatile anaesthetics on this fragile structure has not been investigated. We evaluated the effect of cardiac pre- and post-conditioning with sevoflurane on integrity of the endothelial glycocalyx in conjunction with coronary vascular function. METHODS: Isolated guinea pig hearts perfused with Krebs-Henseleit buffer underwent 20 min stopped-flow ischaemia (37 degrees C), either without or with 1 MAC sevoflurane. This was applied for 15 min before, for 20 min after, or both before and after ischaemia. Transudate was collected for assessing coronary net fluid extravasation and histamine release by mast cells. Coronary release of syndecan-1 and heparan sulphate was measured. In additional experiments with and without continuous sevoflurane, cathepsin B and tryptase beta-like protease activity were measured in effluent. Hearts were perfusion-fixed to visualize the endothelial glycocalyx. RESULTS: Ischaemia led to a significant (P<0.05) increase by 70% in transudate formation during reperfusion only in hearts without sevoflurane. This was accompanied by significant (P<0.05) increases in heparan sulphate (four-fold) and syndecan release (6.5-fold), with electron microscopy revealing massive degradation of glycocalyx. After ischaemia, histamine was released into transudate, and cathepsin B activity increased in effluent (P<0.05). Sevoflurane application attenuated all these changes, except for histamine release. CONCLUSIONS: Sevoflurane protects the endothelial glycocalyx from ischaemia-reperfusion-induced degradation, with both preconditioning and rapid post-conditioning being successful. The mechanism seems to involve attenuation of lysosomal cathepsin B release and to be independent from tissue mast cell degranulation.