NONSTEROIDAL ANTIINFLAMMATORY AGENTS INHIBIT STIMULATED NEUTROPHIL ADHESION TO ENDOTHELIUM - ADENOSINE-DEPENDENT AND INDEPENDENT MECHANISMS

All nonsteroidal antiinflammatory drugs (NSAIDs) inhibit neutrophil ag gregation (homotypic cell-cell adhesion) and do so without affecting e xpression of CD11b/CD18. Since the first step in acute inflammation is a critical interaction between neutrophils and the vascular endotheli um (heterotypic cell-cell adhesion), we determined whether NSAIDs dimi nish the adherence of neutrophils to the endothelium. At antiinflammat ory concentrations (0.5-5 mM) sodium salicylate, an NSAID that does no t inhibit prostaglandin synthesis, inhibited stimulated but not unstim ulated neutrophil adherence to endothelial cells (IC50 < 1 mM, P < 0.0 0001). Salicylates have previously been shown to inhibit oxidative pho sphorylation and, predictably, sodium salicylate inhibited oxidative p hosphorylation, as evidenced by depletion of ATP stores (875 +/- 75 pm ol/10(6) PMN, [2.92 +/- 0.25 mM]) in stimulated (FMLP, 0.1 mu M) but n ot resting neutrophils treated with antiinflammatory doses of sodium s alicylate (EC(50) = 1 mM, P < 0.00001). Indomethacin and piroxicam (10 and 30 mu M) only minimally decreased ATP concentrations in stimulate d and resting neutrophils. ATP is metabolized to adenosine, and we hav e previously demonstrated that both endogenously released (180-200 nM) and exogenous adenosine (IC50 = 250 nM) inhibit stimulated neutrophil adherence to endothelial cells. To determine whether the increased me tabolism of ATP and the resultant increase in adenosine release were r esponsible for inhibition of neutrophil adhesion to endothelium, we de termined whether addition of adenosine deaminase (ADA, 0.125 IU/ml), a n enzyme that converts extracellular adenosine to its inactive metabol ite, inosine, affected inhibition of neutrophil adhesion to endotheliu m by stimulated neutrophils. ADA significantly reversed inhibition of neutrophil adherence to endothelium by sodium salicylate (0.5-5 mM, P < 0.00001). This suggests that sodium salicylate inhibits neutrophil a dherence by increasing adenosine release. Whereas indomethacin and pir oxicam (10-50 mu M) also inhibited stimulated neutrophil adherence to endothelial cells, ADA did not affect their inhibition of adherence. T hese studies demonstrate a heretofore unexpected antiinflammatory mech anism for salicylates: salicylates increase ATP hydrolysis and thereby enhance release of adenosine. Moreover, these data are consistent wit h the hypothesis that NSAIDs differ from one another with respect to t heir mechanisms of action.