Prolonged hypoxia alters endothelial barrier function

Background. It is well recognized that hypoxia/reoxygenation and exposure to inflammatory mediators such as cytokines and neutrophils alter the barrier function of the vascular endothelium. The experiments we conducted tested whether hypoxia alone could produce changes in permeability and whether a prolonged period of hypoxia alters the surface expression of cell adhesion molecules. Methods. Endothelial cells were cultured from human umbilical vein endothelial cells (HUVECs). Hypoxia was created by isolating the cells in a chamber through which 1% O-2, 5% CO2, and 94% N-2 were insufflated (30 min at 1 L/min). Oxygen tension was measured through oxygen-quenching phosphorescence. Hypoxia was maintained for 24 hours. Changes in endothelial permeability were measured by transendothelial electrical resistance (TEER). Endothelial leukocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1) expression were assessed by flow cytometry (mean +/- standard error of the mean [SEM]). Results. Exposure of endothelial cells to hypoxia resulted in increased permeability between 6 and 24 hours, with the greatest decrease in TEER at 18 hours (63% +/- 3%; P <.05). Prolonged hypoxia produced no change in the surface expression of ELAM-1 or ICAM-1. Conclusions. Hypoxia alone produced a significant reversible alteration in endothelial permeability. However this change was observed only under severe hypoxic conditions (eg, below 20 mm Hg); higher oxygen tensions (25 and 35 mm Hg) had no significant effect. Unlike observations made after cytokine exposure, hypoxic breakdown of endothelial barrier function was unassociated with up-regulation of either ELAM-1 ICAM-1.