Inhibition of neutrophil superoxide production by adenosine released from vascular endothelial cells

Abstract

To investigate the inhibitory effect of adenosine released by endothelium on neutrophil Superoxide (O ₂ ⁻) production, we treated confluent monolayers of cultured human umbilical vein endothelial cells with the enzyme adenosine deaminase, and then added human neutrophils. Superoxide (O₂ ⁻) production by human neutrophils stimulated with 10⁻⁶ M formyl-methionyl-leucyl-phenylalanine was inhibited by 49% in the presence of a confluent monolayer of human umbilical vein endothelial cells (5.1 ± 0.1 versus 2.6 ± 0.3 nmols O₂ ⁻/10⁶ neutrophils). Addition of 0.25 U/ml adenosine deaminase to neutrophils plus endothelial cells restored formyl-methionyl-leucyl-phenylalanine-stimulated neutrophil Superoxide production to the level seen with neutrophils alone. Deoxycoformycin (10⁻⁴ M), an inhibitor of adenosine deaminase activity, prevented the increase in Superoxide production associated with adenosine deaminase addition. The adenosine analogue 5′-(N-ethylcarboxamido)-adenosine (3 × 10⁻⁴ M) caused increased inhibition of formyl-methionyl-leucylphenylalanine-stimulated superoxide release by neutrophils in the presence of endothelial cells and prevented neutrophil-mediated endothelial cell damage, as measured by release of³H-2-deoxy-D-glucose. Pairing 2-chloroadenosine (10⁻⁵ M) or 5′-(N-ethylcarboxamido)-adenosine (3 × 10⁻⁴ M) with a cyclic adenosine monophosphate phosphodiesterase inhibitor, 3-isobutyl-l-methyl-xanthine (10⁻⁴ M), produced greater inhibition of neutrophil superoxide production than occurred with either compound alone. The results support the hypothesis that vascular endothelial cells protect themselves from neutrophil attack by releasing adenosine to inhibit superoxide production.