Evidence for generation of a large amount of nitric oxide-like vascular smooth muscle relaxant by cholesterol-rich neutrophils

To determine the effect of cholesterol incorporation on the ability of neutrophils to generate superoxide radicals and nitric oxide-like vasorelaxant material, isolated human neutrophils were incubated with cholesterol-rich liposomes, which increased total cholesterol content by 141% and esterified cholesterol content by 523%. Cholesterol loading resulted in 5 to 7 fold increase in cytosolic calcium in resting as well as in PMA or f-MLP-stimulated cells, but a marked (P<0.01) reduction in both PMA- and f-MLP-stimulated superoxide radical generation by these cells. Nitric oxide-like activity measured as relaxation of rat aortic rings was more pronounced (P<0.02) in cholesterol-rich than in cholesterol-poor cells. The greater relaxation of aortic rings in response to cholesterol-rich neutrophils was observed in rings with or without intact endothelium, and was potentiated by superoxide dismutase and inhibited by oxyhemoglobin as well as l -NMMA, thus suggesting that the vasorelaxant material was nitric oxide. The greater generation of nitric oxide by cholesterol-rich neutrophils occurs perhaps in response to increased cytosolic calcium.