Role of albumin in the preservation of endothelial glycocalyx integrity and the microcirculation: a review

Abstract

The endothelial glycocalyx comprises a complex layer of membrane-bound proteoglycans, secreted glycosaminoglycans, glycoproteins, glycolipids and bound plasma proteins such as albumin and antithrombin associated with the endothelial surface. The glycocalyx plays an important role in vascular homeostasis, regulating vascular permeability and cell adhesion, and acts as a mechanosensor for hemodynamic shear stresses; it also has antithrombotic and anti-inflammatory functions. Plasma proteins such as albumin are physiologically bound within the glycocalyx, thus contributing to stability of the layer. Albumin is the major determinant of plasma colloid osmotic pressure. In addition, albumin transports sphingosine-1-phosphate which has protective endothelial effects, acts as a free radical scavenger, and has immunomodulatory and anti-inflammatory effects. This review examines the physiological function of the endothelial glycocalyx and the role of human albumin in preserving glycocalyx integrity and the microcirculation.

Keywords: Albumin; Endothelial cell; Glycocalyx; Microcirculation; Sepsis.

Fig. 1

Structure of the endothelial glycocalyx illustrating proteoglycans and glycosaminoglycans. Reproduced with permission from [4]. GPI glycosylphosphatidylinositol

Fig. 2

Electron micrograph of a cross-sectional image of a coronary endothelial glycocalyx (courtesy of B. van den Berg, Maastricht University). Reproduced with permission from [11]

Fig. 3

The revised Starling principle. Reproduced with permission from [2]. Jv/A filtered volume per unit area; Lp hydraulic conductance; Pc capillary hydrostatic pressure; P_is interstitial hydrostatic pressure; σ osmotic reflection co-efficient; π_p oncotic pressure in the luminal side of endothelial surface layer; π_sg oncotic pressure in the subglycocalyx space

Fig. 4

Pathologies/interventions associated with glycocalyx alterations. Reproduced with permission from [10]. ecSOD extracellular superoxide dismutase; MMP matrix metalloprotease; NO nitric oxide. Sulodexide is a highly purified glycosaminoglycan mixture of low molecular weight heparin plus dermatan sulfate [30]