PROLONGED HYPOXIA ALTERS ENDOTHELIAL BARRIER FUNCTION

Background. It is well recognized that hypoxia/reoxygenation and expos ure to inflammatory mediators such as cytokines and neutrophils alter the barrier function of the vascular endothelium. The experiments we c onducted tested whether hypoxia alone could produce changes in permeab ility and whether a prolonged period of hypoxia alters the surface exp ression of cell adhesion molecules. Methods. Endothelial cells were cu ltured from human umbilical vein endothelial cells (HUVECs). Hypoxia w as 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 tensio n was measured through oxygen-quenching phosphorescence. Hypoxia was m aintained for 24 hours. Changes in endothelial permeability were measu red by transendothelial electrical resistance (TEER). Endothelial leuk ocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1) expression were assessed by flow cytometry (mean +/- stand ard error of the mean [SEM]). Results. Exposure of endothelial cells t o hypoxia resulted in increased permeability between 6 and 24 hours, w ith the greatest decrease in TEER at 18 hours (63% +/- 3%; P <.05). Pr olonged hypoxia produced no change in the surface expression of ELAM-1 or ICAM-1. Conclusions. Hypoxia alone produced a significant reversib le alteration in endothelial permeability. However this change was obs erved only under severe hypoxic conditions (eg, below 20 mm Hg); highe r oxygen tensions (25 and 35 mm Hg) had no significant effect. Unlike observations made after cytokine exposure, hypoxic breakdown of endoth elial barrier function was unassociated with up-regulation of either E LAM-1 ICAM-1.