ENDOTHELIAL-CELL RESPONSE TO HYPOXIA REOXYGENATION IS MEDIATED BY IL-1

Reperfusion injury involves the adhesion and activation of neutrophils (PMN) both in affected tissues and distant organs. Cell adhesion molecules (CAM) such as endothelial-leukocyte adhesion molecule-1 (ELAM-1) and intercellular adhesion molecule-1 (ICAM-1) are known to mediate, at least in part, the adherence of activated PMN to the endothelium. To characterize the cellular mechanisms of this phenomenon, we exposed cultured human umbilical vein endothelial cells (HUVEC) to hypoxia and reoxygenation (H/R) using an incubator chamber purged of oxygen with 100% nitrogen. Confluent monolayers of HUVEC were subjected to 60 min of hypoxia followed by variable periods of reoxygenation (120 and 240 min). Flow cytometry was utilized to assess the expression of ELAM-1 and ICAM-1, expressed as percent shift from baseline expression. To determine what role endothelium-derived cytokines such as IL-1 play in the expression of CAM after H/R, we performed additional experiments in the presence of recombinant IL-1 receptor antagonist (IL-1RA). ICAM-1 was present on unstimulated HUVEC while ELAM-1 was not constituitively expressed. Following exposure of cells to hypoxia and reoxygenation, significant increases in ELAM expression were seen (8.4 +/- 2.4% at 120 min; 19.1 +/- 7.4%, P < 0.05). While there was similar trend in ICAM expression, this did not achieve statistical significance (0.10 < P < 0.05). The addition of IL-1RA (10 ng/ml) to hypoxic HUVEC consistently attenuated ELAM-1 upregulation during reoxygenation (0.8 +/- 0.7% at 120 min and 5.9 +/- 4.1% at 240 min) such that expression was not significantly greater than baseline. This in vitro model of ischemia/reperfusion demonstrated reproducible increases in the expression of ELAM-1, an adhesion molecule important in the initial PMN rolling and adhesion to endothelial cells in the microcirculation. The data also suggest that the cytokine IL-1 plays a central role in the endothelial cell response to H/R. (C) 1995 Academic Press, Inc.