Interaction of albumin with the endothelial cell surface

Effectiveness of human albumin for clinical outcome in aneurysmal subarachnoid hemorrhages: a protocol for randomized controlled (HASH) trial

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is a dreadful acute neurological condition with an overwhelmingly high rate of associated morbidities and mortality. Despite leaping advancement in neurosurgical techniques and imaging modalities, there is no substantiative improvement in the overall prognosis for aSAH. Cerebral vasospasm remains the predominant cause of associated morbidities. Human albumin has been used in different neurological conditions, including head trauma, intracerebral hemorrhages, and ischemic strokes, with favorable outcomes. However, its beneficial use in aSAH has not been sufficiently explored until recently a published systematic review by our team. In view of the scarcity of published data and lack of robust evidence, our group has designed the first-ever RCT to compare the use of human albumin-enhanced fluid management versus standard fluid therapy with crystalloids in patients with aSAH.

METHODS

This single-center open-label, prospective, parallel group randomized control trial will be conducted at Hamad General Hospital, Doha, Qatar, from August 2024 to July 2027. A sample size of 84 (42 in each arm) has been calculated to be sufficient to detect a clinically significant difference in the modified Rankin scale good score between two groups (human-albumin induced volume expansion therapy versus crystalloid only) for fluid management in aneurysmal subarachnoid hemorrhage patients. The primary outcome will be based on a dichotomized modified Rankin scale [good grades (0-2) and poor grades (3-6)], while the secondary outcome will include symptomatic vasospasm, transcranial Doppler velocities, and Pulse index Contour Cardiac Output (PiCCO) parameters.

DISCUSSION

The trial aims to provide firsthand evidence on the beneficial use of human albumin to achieve an optimal fluid management regime to explore its potential role in improving clinical outcomes in patients with aSAH.

TRIAL REGISTRATION

ClinicalTrials.gov NCT06548477. Registered on August 9, 2024. https://clinicaltrials.gov/search?term=NCT06548477 .

Glycocalyx Interactions Modulate the Cellular Uptake of Albumin-Coated Nanoparticles

Albumin-based nanoparticles (ABNPs) represent promising drug carriers in nanomedicine due to their versatility and biocompatibility, but optimizing their effectiveness in drug delivery requires understanding their interactions with and uptake by cells. Notably, albumin interacts with the cellular glycocalyx, a phenomenon particularly studied in endothelial cells. This observation suggests that the glycocalyx could modulate ABNP uptake and therapeutic efficacy, although this possibility remains unrecognized. In this study, we elucidate the critical role of the glycocalyx in the cellular uptake of a model ABNP system consisting of silica nanoparticles (NPs) coated with native, cationic, and anionic albumin variants (BSA, BSA+, and BSA-). Using various methodologies-including fluorescence anisotropy, dynamic light scattering, microscale thermophoresis, surface plasmon resonance spectroscopy, and computer simulations─we found that both BSA and BSA+, but not BSA-, interact with heparin, a model glycosaminoglycan (GAG). To explore the influence of albumin-GAG interactions on NP uptake, we performed comparative uptake studies in wild-type and GAG-mutated Chinese hamster ovary cells (CHO), along with complementary approaches such as enzymatic GAG cleavage in wild-type cells, chemical inhibition, and competition assays with exogenous heparin. We found that the glycocalyx enhances the cell uptake of NPs coated with BSA and BSA+, while serving as a barrier to the uptake of NPs coated with BSA-. Furthermore, we showed that harnessing albumin-GAG interactions increases cancer cell death induced by paclitaxel-loaded albumin-coated NPs. These findings underscore the importance of albumin-glycocalyx interactions in the rational design and optimization of albumin-based drug delivery systems.

Physiologically Based Pharmacokinetic Model of Brain Delivery of Plasma Protein Bound Drugs

INTRODUCTION

A physiologically based pharmacokinetic (PBPK) model is developed that focuses on the kinetic parameters of drug association and dissociation with albumin, alpha-1 acid glycoprotein (AGP), and brain tissue proteins, as well as drug permeability at the blood-brain barrier, drug metabolism, and brain blood flow.

GOAL

The model evaluates the extent to which plasma protein-mediated uptake (PMU) of drugs by brain influences the concentration of free drug both within the brain capillary compartment in vivo and the brain compartment. The model also studies the effect of drug binding to brain tissue proteins on the concentration of free drug in brain.

METHODS

The steady state and non-steady state PBPK models are comprised of 11-12 variables, and 18-23 parameters, respectively. Two model drugs are analyzed: propranolol, which undergoes modest PMU from the AGP-bound pool, and imipramine, which undergoes a high degree of PMU from both the albumin-bound and AGP-bound pools in plasma.

RESULTS

The free propranolol concentration in brain is under-estimated 2- to fourfold by in vitro measurements of free plasma propranolol, and the free imipramine concentration in brain is under-estimated by 18- to 31-fold by in vitro measurements of free imipramine in plasma. The free drug concentration in brain in vivo is independent of drug binding to brain tissue proteins.

CONCLUSIONS

In vitro measurement of free drug concentration in plasma under-estimates the free drug in brain in vivo if PMU in vivo from either the albumin and/or the AGP pools in plasma takes place at the BBB surface.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

The Glomerular Endothelium Restricts Albumin Filtration

Inflammatory activation and/or dysfunction of the glomerular endothelium triggers proteinuria in many systemic and localized vascular disorders. Among them are the thrombotic microangiopathies, many forms of glomerulonephritis, and acute inflammatory episodes like sepsis and COVID-19 illness. Another example is the chronic endothelial dysfunction that develops in cardiovascular disease and in metabolic disorders like diabetes. While the glomerular endothelium is a porous sieve that filters prodigious amounts of water and small solutes, it also bars the bulk of albumin and large plasma proteins from passing into the glomerular filtrate. This endothelial barrier function is ascribed predominantly to the endothelial glycocalyx with its endothelial surface layer, that together form a relatively thick, mucinous coat composed of glycosaminoglycans, proteoglycans, glycolipids, sialomucins and other glycoproteins, as well as secreted and circulating proteins. The glycocalyx/endothelial surface layer not only covers the glomerular endothelium; it extends into the endothelial fenestrae. Some glycocalyx components span or are attached to the apical endothelial cell plasma membrane and form the formal glycocalyx. Other components, including small proteoglycans and circulating proteins like albumin and orosomucoid, form the endothelial surface layer and are bound to the glycocalyx due to weak intermolecular interactions. Indeed, bound plasma albumin is a major constituent of the endothelial surface layer and contributes to its barrier function. A role for glomerular endothelial cells in the barrier of the glomerular capillary wall to protein filtration has been demonstrated by many elegant studies. However, it can only be fully understood in the context of other components, including the glomerular basement membrane, the podocytes and reabsorption of proteins by tubule epithelial cells. Discovery of the precise mechanisms that lead to glycocalyx/endothelial surface layer disruption within glomerular capillaries will hopefully lead to pharmacological interventions that specifically target this important structure.

The glycocalyx, a novel key in understanding of mechanism of diabetic nephropathy: a commentary

Introduction

Diabetes is a chronic and progressive disease that usually causes disrupts the function of the body's organs and can eventually lead to cardiomyopathy, nephropathy, retinopathy, and neuropathy. Diabetic nephropathy (DN) is the most common cause of chronic kidney disease and causes chronic structural changes in different parts of the affected kidney. Glycocalyx layer is one of the most important components of the vascular base found in the endothelium throughout the body's arteries and it has been shown that glycocalyx is also damaged during diabetic nephropathy. Our goal is to conduct this systematic review study is to find the cause-and-effect relationship between glycocalyx and diabetic nephropathy and also to clarify the role of the endothelial renal glycocalyx in understanding of mechanism of the course of diabetic nephropathy, and to provide an accurate background for further important studies.

Methods

All databases included MEDLINE (PubMed), Science Direct, Scopus, Ovid and Google Scholar were systematically searched for related published articles. In all databases, the following search strategy was implemented and these key words (in the title/abstract) were used: "diabetes" AND "glycocalyx" OR "diabetic nephropathy" AND "glycocalyx".

Results and discussion

A total of 19 articles were retrieved from all databases using search strategy. After screening based on the title and abstract, number of 17 of them selected for full text assessment. Finally, after extracting the key points and making connections between the articles, we came up with new points to consider. It can be said that diabetes with the action of reactive oxygen species through oxidative stress, increases ICAM-1 and TNF-α and decreases heparanase enzyme, it affects the glomerular endothelium and eventually leads to albuminuria and destruction of the Glx layer.

Conclusion

Diabetes causes super-structural changes in the kidney nephrons at the glomerular level. The glomerular filter barrier, which includes the epithelial cell called the podocyte, endothelial pore cells, and basal membrane of the glomerulus, plays a major role in stabilizing the selective glomerular function in healthy individuals. Diabetic nephropathy also causes changes in endothelial glycocalyx.

Exploring the mechanism of hyperpermeability following glycocalyx degradation: Beyond the glycocalyx as a structural barrier

Pathological hyperpermeability is a morbidity involved in various systemic diseases, including sepsis. The endothelial glycocalyx layer (GCX) plays a key role in controlling vascular permeability and could be a useful therapeutic target. The purpose of the present study was to analyze the functional role of the GCX in vascular permeability and to elucidate its role in pathological conditions. First, male C57BL/6J wild-type mice were used as in vivo models to study the effects of sepsis and the pharmacological digestion of glycosaminoglycans (GAGs) on the GCX. Vascular permeability was evaluated using fluorescein isothiocyanate (FITC)-labeled dextran. Second, the changes in gene expression in vascular endothelial cells after GAGs digestion were compared between a control and a septic model using RNA sequencing. In the in vivo study, the glycocalyx was depleted in both the septic model and the group with pharmacological GAGs digestion. FITC-labeled dextran had leaked into the interstitium in the septic group, but not in the other groups. In the in vitro study, histamine decreased the transendothelial electrical resistance (TEER), indicating an increase in permeability. GAGs digestion alone did not change the TEER, and the effect of histamine on the TEER was not enhanced by GAGs digestion. The gene expression profiles after GAGs digestion differed from the control condition, indicating the initiation of signal transduction. In conclusion, we demonstrated that the structural barrier of the GCX does not solely determine the fluid permeability of the endothelial layer, since enzymatic depletion of the GCX did not increase the permeability. The gene expression findings suggest that the digestion of GAGs alone did not induce hyperpermeability either in vitro or in vivo, although sepsis did induce hyperpermeability. While GAGs degradation by itself does not appear to induce hyperpermeability, it may play an important role in initiating signal transductions.

A Novel Experimental and Theoretical Method for Estimating Albumin-Mediated Hepatic Uptake Based on the Albumin Binding Fraction in Plasma and Human PK Prediction Using a Physiologically-Based Pharmacokinetic Approach

Recently, protein-facilitated uptake has been suggested to be an important factor in the precise prediction of the pharmacokinetic (PK) profiles of drugs. In our previous study, a physiologically-based pharmacokinetic (PBPK) approach considering the mechanism of albumin-mediated hepatic uptake was developed for predicting human PK profiles. It was assumed that drugs affected by albumin-mediated hepatic uptake would bind only to albumin, which means that there would be over-estimation of the contribution of protein-facilitated uptake for a drug that could bind to multiple proteins. In this study, we developed a method that can evaluate the albumin binding fraction in plasma considering the affinity for other proteins. Based on the albumin binding fraction, the contribution of albumin-mediated hepatic uptake was theoretically estimated, and then the human PK profiles were predicted by our proposed PBPK approach incorporating this mechanism. As a result, the predicted human PK profiles agreed well with the observed ones, and the absolute average fold error of PK parameters was almost within a 1.5-fold error on average. These findings show the importance of considering protein-facilitated uptake and also suggest that our proposed PBPK approach can be useful in scientific discussions with regulatory authorities.

Clinical features and outcome of septic shock in dogs: 37 Cases (2008-2015)

OBJECTIVES

To describe patient characteristics of dogs with septic shock, investigate markers of disease severity, and assess treatment impact on outcome.

DESIGN

Retrospective study.

SETTING

Single center, university veterinary teaching intensive care unit.

ANIMALS

Thirty-seven dogs with septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Mean number of organ dysfunction was 3.24 ± 1.0, and included cardiovascular (100%), respiratory (73%), hematologic (68%), renal (49%), and hepatic (32%) dysfunction. The gastrointestinal tract was the most common source of sepsis. Mean blood pressure prior to resuscitation was 50 ± 8 mm Hg. All dogs were given IV fluids before vasopressor therapy with a mean rate of 12.1 ± 11.0 mL/kg/h. All dogs were given antimicrobials, administered within a mean of 4.3 ± 5.7 hours after diagnosis. Dopamine or norepinephrine was administered IV, respectively in 51.3% and 37.8% of dogs, with a mean duration of hypotension of 2.6 ± 3.0 hours. Mortality rate was 81.1%. Survivors were more likely to have a feeding tube (P = 0.007) and to have gastrointestinal sepsis (P = 0.012), and less likely to have respiratory dysfunction (P < 0.001). APPLE_Full scores (P = 0.014) and time to antimicrobial therapy (P = 0.047) were identified as predictors of mortality. Treatment bundles consisting of 7 interventions that may improve outcomes in people with septic shock were evaluated. Survivors received 4.1 ± 1.3 interventions, whereas nonsurvivors received 2.4 ± 1.4 (P = 0.003).

CONCLUSIONS

Septic shock in dogs confers a guarded prognosis. Early antimicrobial therapy and the utilization of treatment bundles may increase survivability in dogs with septic shock. More research is warranted to investigate the impact of specific interventions on survival.

Toward an artificial endothelium: Development of blood-compatible surfaces for extracorporeal life support

A new generation of extracorporeal artificial organ support technologies, collectively known as extracorporeal life support (ECLS) devices, is being developed for diverse applications to include acute support for trauma-induced organ failure, transitional support for bridge to organ transplant, and terminal support for chronic diseases. Across applications, one significant complication limits the use of these life-saving devices: thrombosis, bleeding, and inflammation caused by foreign surface-induced blood interactions. To address this challenge, transdisciplinary scientists and clinicians look to the vascular endothelium as inspiration for development of new biocompatible materials for ECLS. Here, we describe clinically approved and new investigational biomaterial solutions for thrombosis, such as immobilized heparin, nitric oxide-functionalized polymers, "slippery" nonadhesive coatings, and surface endothelialization. We describe how hemocompatible materials could abrogate the use of anticoagulant drugs during ECLS and by doing so radically change treatments in critical care. Additionally, we examine several special considerations for the design of biomaterials for ECLS, including: (1) preserving function of the artificial organ, (2) longevity of use, and (3) multifaceted approaches for the diversity of device functions and applications.

The need to freeze-Dehydration during specimen preparation for electron microscopy collapses the endothelial glycocalyx regardless of fixation method

OBJECTIVE

The endothelial glycocalyx covers the luminal surface of the endothelium and plays key roles in vascular function. Despite its biological importance, ideal visualization techniques are lacking. The current study aimed to improve the preservation and subsequent imaging quality of the endothelial glycocalyx.

METHODS

In mice, the endothelial glycocalyx was contrasted with a mixture of lanthanum and dysprosium (LaDy). Standard chemical fixation was compared with high-pressure frozen specimens processed with freeze substitution. Also, isolated brain microvessels and cultured endothelial cells were high-pressure frozen and by transmission soft x-rays, imaged under cryogenic conditions.

RESULTS

The endothelial glycocalyx was in some tissues significantly more voluminous from chemically fixed specimens compared with high-pressure frozen specimens. LaDy labeling introduced excessive absorption contrast, which impeded glycocalyx measurements in isolated brain microvessels when using transmission soft x-rays. In non-contrasted vessels, the glycocalyx was not resolved. LaDy-contrasted, cultured brain endothelial cells allowed to assess glycocalyx volume in vitro.

CONCLUSIONS

Both chemical and cryogenic fixation followed by dehydration lead to substantial collapse of the glycocalyx. Cryogenic fixation without freeze substitution could be a way forward although transmission soft x-ray tomography based solely on amplitude contrast seems unsuitable.

Implications Enzymatic Degradation of the Endothelial Glycocalyx on the Microvascular Hemodynamics and the Arteriolar Red Cell Free Layer of the Rat Cremaster Muscle

The endothelial glycocalyx is a complex network of glycoproteins, proteoglycans, and glycosaminoglycans; it lines the vascular endothelial cells facing the lumen of blood vessels forming the endothelial glycocalyx layer (EGL). This study aims to investigate the microvascular hemodynamics implications of the EGL by quantifying changes in blood flow hydrodynamics post-enzymatic degradation of the glycocalyx layer. High-speed intravital microscopy videos of small arteries (around 35 μm) of the rat cremaster muscle were recorded at various time points after enzymatic degradation of the EGL. The thickness of the cell free layer (CFL), blood flow velocity profiles, and volumetric flow rates were quantified. Hydrodynamic effects of the presence of the EGL were observed in the differences between the thickness of CFL in microvessels with an intact EGL and glass tubes of similar diameters. Maximal changes in the thickness of CFL were observed 40 min post-enzymatic degradation of the EGL. Analysis of the frequency distribution of the thickness of CFL allows for estimation of the thickness of the endothelial surface layer (ESL), the plasma layer, and the glycocalyx. Peak flow, maximum velocity, and mean velocity were found to statistically increase by 24, 27, and 25%, respectively, after enzymatic degradation of the glycocalyx. The change in peak-to-peak maximum velocity and mean velocity were found to statistically increase by 39 and 32%, respectively, after 40 min post-enzymatic degradation of the EGL. The bluntness of blood flow velocity profiles was found to be reduced post-degradation of the EGL, as the exclusion volume occupied by the EGL increased the effective volume impermeable to RBCs in microvessels. This study presents the effects of the EGL on microvascular hemodynamics. Enzymatic degradation of the EGL resulted in a decrease in the thickness of CFL, an increase in blood velocity, blood flow, and decrease of the bluntness of the blood flow velocity profile in small arterioles. In summary, the EGL functions as a molecular sieve to solute transport and as a lubrication layer to protect the endothelium from red blood cell (RBC) motion near the vessel wall, determining wall shear stress.

Effect of acute hyaluronidase treatment of the glycocalyx on tracer-based whole body vascular volume estimates in mice

The endothelial glycocalyx forms a hyaluronan-containing interface between the flowing blood and the endothelium throughout the body. By comparing the systemic distribution of a small glycocalyx-accessible tracer vs. a large circulating plasma tracer, the size-selective barrier properties of the glycocalyx have recently been utilized to estimate whole body glycocalyx volumes in humans and animals, but a comprehensive validation of this approach has been lacking at the moment. In the present study, we compared, in anesthetized, ventilated C57Bl/6 mice, the whole body distribution of small (40 kDa) dextrans (Texas Red labeled; Dex40) vs. that of intermediate (70 kDa) and large (500 kDa) dextrans (both FITC labeled; Dex70 and Dex500, respectively) using tracer dilution and vs. that of circulating plasma, as derived from the dilution of fluorescein-labeled red blood cells and large-vessel hematocrit. The contribution of the glycocalyx was evaluated by intravenous infusion of a bolus of the enzyme hyaluronidase. In saline-treated control mice, distribution volume (in ml) differed between tracers ( P < 0.05; ANOVA) in the following order: Dex40 (0.97 ± 0.04) > Dex70 (0.90 ± 0.04) > Dex500 (0.81 ± 0.10) > plasma (0.71 ± 0.02), resulting in an inaccessible vascular volume, i.e., compared with the distribution volume of Dex40, of 0.03 ± 0.01, 0.15 ± 0.04, and 0.31 ± 0.05 ml for Dex70, Dex500, and plasma, respectively. In hyaluronidase-treated mice, Dex70 and Dex40 volumes were not different from each other, and inaccessible vascular volumes for Dex500 (0.03 ± 0.03) and plasma (0.14 ± 0.05) were smaller ( P < 0.05) than those in control animals. Clearance of Dex70 and Dex500 from the circulation was enhanced ( P < 0.05) in hyaluronidase-treated vs. control mice. These results indicate that the glycocalyx contributes to size-dependent differences in whole body vascular distribution of plasma solutes in mice. Whole body vascular volume measurements based on the differential distribution of glycocalyx-selective tracers appear appropriate for the detection of generalized glycocalyx degradation in experimental animals and humans.

Endothelial barrier dysfunction in diabetic conduit arteries: a novel method to quantify filtration

The endothelial barrier plays an important role in atherosclerosis, hyperglycemia, and hypercholesterolemia. In the present study, an accurate, reproducible, and user-friendly method was used to further understand endothelial barrier function of conduit arteries. An isovolumic method was used to measure the hydraulic conductivity (L(p)) of the intact vessel wall and medial-adventitial layer. Normal arterial segments with diameters from 0.2 to 5.5 mm were used to validate the method, and femoral arteries of diabetic rats were studied as an example of pathological specimens. Various arterial segments confirmed that the volume flux of water per unit surface area was linearly related to intraluminal pressure, as confirmed in microvessels. L(p) of the intact wall varied from 3.5 to 22.1 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 7-180 mmHg. Over the same pressure range, L(p) of the endothelial barrier changed from 4.4 to 25.1 × 10(-7) cm·s(-1)·cmH(2)O(-1). During perfusion with albumin-free solution, L(p) of rat femoral arteries increased from 6.1 to 13.2 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 10-180 mmHg. Hyperglycemia increased L(p) of the femoral artery in diabetic rats from 2.9 to 5.5 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 20-135 mmHg. In conclusion, the L(p) of a conduit artery can be accurately and reproducibly measured using a novel isovolumic method, which in diabetic rats is hyperpermeable. This is likely due to disruption of the endothelial glycocalyx.

Transmembrane diffusion of gemcitabine by a nanoparticulate squalenoyl prodrug: an original drug delivery pathway

We have designed an amphiphilic prodrug of gemcitabine (dFdC) by its covalent coupling to a derivative of squalene, a natural lipid. The resulting bioconjugate self-assembled spontaneously in water as nanoparticles that displayed a promising in vivo anticancer activity. The aim of the present study was to provide further insight into the in vitro subcellular localization and on the metabolization pathway of the prodrug. Cells treated with radiolabelled squalenoyl gemcitabine (SQdFdC) were studied by differential detergent permeation, and microautography coupled to fluorescent immunolabeling and confocal microscopy. This revealed that the bioconjugate accumulated within cellular membranes, especially in those of the endoplasmic reticulum. Radio-chromatography analysis proved that SQdFdC delivered dFdC directly in the cell cytoplasm. Mass spectrometry studies confirmed that gemcitabine was then either converted into its biologically active triphosphate metabolite or exported from the cells through membrane transporters. To our knowledge, this is the first description of such an intracellular drug delivery pathway. In vitro cytotoxicity assays revealed that SQdFdC was more active than dFdC on a transporter-deficient human resistant leukemia model, which was explained by the subcellular distribution of the drugs and their metabolites. The squalenoylation drug delivery strategy might, therefore, dramatically improve the efficacy of gemcitabine on transporter-deficient resistant cancer in the clinical context.

New aspects of glomerular filtration barrier structure and function: five layers (at least) not three

PURPOSE OF REVIEW

Three structures (glomerular endothelial fenestrae, glomerular basement membrane and podocyte interfoot process/slit diaphragms) have traditionally been considered as the major determinants of glomerular permeability. We review recent work demonstrating the functional importance of two additional layers: the endothelial surface layer (ESL) and the subpodocyte space (SPS).

RECENT FINDINGS

Removing glomerular endothelial cell monolayer ESL in vitro significantly alters monolayer permeability, supporting previous in-vivo demonstrations of the importance of the ESL in determining glomerular permeability. Whether fenestral diaphragms are present to support the ESL in healthy adult glomeruli has been examined in a recent report. On the downstream side of the glomerular filtration barrier, the SPS is a recently described structure that covers approximately two-thirds of the barrier, has highly restrictive dimensions and contributes to the hydraulic resistance and ultrafiltration characteristics of the glomerulus. Different layers of the barrier have also been shown to influence the permeability characteristics of one another, either through biophysical interactions, or through the activities of ligand-receptor axes that cross the various layers of the barrier.

SUMMARY

The structure and function of the glomerular filtration barrier remains an area of significant new discovery, and recent work continues to highlight the complexity of this dynamic multilayered watershed.

The Structure and Function of the Endothelial Glycocalyx Layer

Over the past decade, since it was first observed in vivo, there has been an explosion in interest in the thin (approximately 500 nm), gel-like endothelial glycocalyx layer (EGL) that coats the luminal surface of blood vessels. In this review, we examine the mechanical and biochemical properties of the EGL and the latest studies on the interactions of this layer with red and white blood cells. This includes its deformation owing to fluid shear stress, its penetration by leukocyte microvilli, and its restorative response after the passage of a white cell in a tightly fitting capillary. We also examine recently discovered functions of the EGL in modulating the oncotic forces that regulate the exchange of water in microvessels and the role of the EGL in transducing fluid shear stress into the intracellular cytoskeleton of endothelial cells, in the initiation of intracellular signaling, and in the inflammatory response.

Mechanotransduction and the glycocalyx

Endothelial cells (ECs) line all blood vessel walls and are exposed to the mechanical forces of blood flow which modulate their function and play a role in vascular regulation, remodelling and disease. The principal mechanical forces sensed by ECs are the shear stress of flowing blood on their apical surface, and the circumferential stress resisting blood pressure, which induces stretch in the cell body. 'Mechanotransduction' refers to the mechanisms by which these forces are transduced into biomolecular responses of the cells. Given the importance of endothelial mechanotransduction in cardiovascular physiology and pathology, numerous research efforts have been dedicated to identifying the mechanosensory component(s) of ECs. This review focuses on mechanotransduction of shear stress by ECs and considers the evidence in support of the surface glycocalyx acting as a mechanotransducer.

Effect of human albumin administration on clinical outcome and hospital cost in patients with subarachnoid hemorrhage

OBJECT

Human albumin is used to induce hypervolemia (central venous pressure [CVP] > 8 mm Hg) after subarachnoid hemorrhage (SAH). Unfortunately, human albumin may increase the mortality rate in critically ill patients; because of this, its use became restricted in the authors' hospital in May 1999. The goal of this study was to determine the effect of human albumin on outcome and cost in patients with SAH before and after this restriction was put into place.

METHODS

All patients with aneurysmal SAH who were admitted to the authors' institution between May 1998 and May 2000 were studied. Basic demographic information, dosage of human albumin given, length of stay, and the incidence of in-hospital deaths and complications were collected. The authors obtained Glasgow Outcome Scale (GOS) scores at 3 months after SAH (good outcome, GOS > or = 4). Data were analyzed using t-test and chi-square analysis. Logistic regression was used to identify independent associations between use of human albumin and outcome. The authors studied 140 patients: 63 who were admitted between May 1998 and May 1999 (Group 1) and 77 treated between June 1999 and May 2000 (Group 2). Two subgroups of patients were further analyzed. Group 1 patients who received human albumin (albumin subgroup, 37 patients) and Group 2 patients who would have received albumin under the old protocol (that is, those who failed to achieve CVP > 8 mm Hg after normal saline administration; nonalbumin subgroup, 47 patients). Patients in the nonalbumin subgroup were more likely to be male (38% compared with 16%), to experience hypertension (55% compared with 30%), to suffer from hypomagnesemia (49% compared with 5.4%), and to have hydrocephalus (47% compared with 27%). There was a trend for these patients to have more vasospasm (28% compared with 19%, p = 0.2). Patients in the albumin subgroup were more likely to have a good outcome at 3 months.

CONCLUSIONS

Administration of human albumin after SAH may improve clinical outcome and reduce hospital cost.