The release of nitric oxide and superoxide anion by neutrophils and mononuclear cells from patients with sickle cell anaemia

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Abstract
The aim of this work was to investigate the release of nitric oxide and superoxide by neutrophils and mononuclear cells from patients with sickle cell anaemia. Nitric oxide release was assayed by the ability of leucocytes to inhibit thrombin-induced washed platelet aggregation. Superoxide release was assessed by a cytochrome c reduction assay. Neutrophils from sickle cell anaemia patients released nitric oxide in a similar manner to those from healthy controls, because inhibition of platelet aggregation by neutrophils from sickle cell anaemia or from healthy controls was blocked by the inhibitor of nitric oxide synthesis N ω-nitro-l-arginine methyl ester (300 μm), but not by N ω-nitro-d-arginine methyl ester (300 μm) and was reversed by l-arginine (1 mm). Additionally, a similar number of neutrophils from sickle cell anaemia patients and from healthy controls was required to inhibit platelet aggregation. Mononuclear cells from sickle cell anaemia patients inhibited platelet aggregation only in the presence of superoxide dismutase (60 U ml−1). Phorbol 12-myristate 13-acetate (PMA, 30 nm)- or zymosan (100 particles/cell)-induced release of superoxide by mononuclear cells from sickle cell anaemia patients was significantly higher than that observed in mononuclear cells from healthy controls (P < 0.001 and P < 0.01 respectively, Mann-Whitney test). The levels of superoxide released by neutrophils from sickle cell anaemia patients were similar to those from healthy controls. We conclude that mononuclear cells from sickle cell anaemia patients release more superoxide than those from healthy controls, when stimulated with PMA or zymosan in vitro. Considering that superoxide inactivates nitric oxide, that nitric oxide is an important endogenous vasodilator, and that superoxide produces oxidant damage, this greater production of superoxide by mononuclear cells from sickle cell anaemia patients may represent an additional risk factor for the obstruction of the microcirculation and tissue damage in these patients.

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