Ultrastructural Alteration of Pulmonary Capillary Endothelial Glycocalyx During Endotoxemia.

BACKGROUND: The most recent diagnostic criteria for sepsis include organ failure. Microvascular endothelial injury is believed to lead to the multiple organ failure seen in sepsis, although the precise mechanism is still controversial. ARDS is the primary complication during the sequential development of multiple organ dysfunction in sepsis, and endothelial injury is deeply involved. Sugar-protein glycocalyx coats all healthy vascular endothelium, and its disruption is one factor believed to contribute to microvascular endothelial dysfunction during sepsis. The goal of this study was to observe the three-dimensional ultrastructural alterations in the pulmonary capillary endothelium, including the glycocalyx, during sepsis-induced pulmonary vasculitis. METHODS: This study investigated the three-dimensional ultrastructure of pulmonary vascular endothelial glycocalyx in a mouse lipopolysaccharide-induced endotoxemia model. Lungs were fixed with lanthanum-containing alkaline fixative to preserve the glycocalyx. RESULTS: On both scanning and transmission electron microscopic imaging, the capillary endothelial glycocalyx appeared as a moss-like structure entirely covering the endothelial cell surface in normal mice. In the septic lung following liposaccharide injection, however, this structure was severely disrupted; it appeared to be peeling away and coagulated. In addition, syndecan-1 levels were significantly reduced in the septic lung, and numerous spherical structures containing glycocalyx were observed on the endothelial surface. CONCLUSIONS: It appears that endothelial glycocalyx in the lung is markedly disrupted under experimental endotoxemia conditions. This finding supports the notion that disruption of the glycocalyx is causally related to the microvascular endothelial dysfunction that is characteristic of sepsis-induced ARDS.

Three-dimensional ultrastructure of capillary endothelial glycocalyx under normal and experimental endotoxemic conditions.

BACKGROUND: Sugar-protein glycocalyx coats healthy endothelium, but its ultrastructure is not well described. Our aim was to determine the three-dimensional ultrastructure of capillary endothelial glycocalyx in the heart, kidney, and liver, where capillaries are, respectively, continuous, fenestrated, and sinusoidal. METHODS: Tissue samples were processed with lanthanum-containing alkaline fixative, which preserves the structure of glycocalyx. RESULTS: Scanning and transmission electron microscopy revealed that the endothelial glycocalyx layer in continuous and fenestrated capillaries was substantially thicker than in sinusoids. In the heart, the endothelial glycocalyx presented as moss- or broccoli-like and covered the entire luminal endothelial cell surface. In the kidney, the glycocalyx appeared to nearly occlude the endothelial pores of the fenestrated capillaries and was also present on the surface of the renal podocytes. In sinusoids of the liver, glycocalyx covered not only the luminal side but also the opposite side, facing the space of Disse. In a mouse lipopolysaccharide-induced experimental endotoxemia model, the capillary endothelial glycocalyx was severely disrupted; that is, it appeared to be peeling off the cells and clumping. Serum concentrations of syndecan-1, a marker of glycocalyx damage, were significantly increased 24 h after administration of lipopolysaccharide. CONCLUSIONS: In the present study, we visualized the three-dimensional ultrastructure of endothelial glycocalyx in healthy continuous, fenestrated, and sinusoidal capillaries, and we also showed their disruption under experimental endotoxemic conditions. The latter may provide a morphological basis for the microvascular endothelial dysfunction associated with septic injury to organs.