THE RELEASE OF NITRIC-OXIDE AND SUPEROXIDE ANION BY NEUTROPHILS AND MONONUCLEAR-CELLS FROM PATIENTS WITH SICKLE-CELL-ANEMIA

The aim of this work. was to investigate the release of nitric oxide a nd superoxide by neutrophils and mononuclear cells from patients with sickle cell anaemia, Nitric oxide release was assayed by the ability o f leucocytes to inhibit thrombin-induced washed platelet aggregation, Superoxide release was assessed by a cytochrome c reduction assay, Neu trophils from sickle cell anaemia patients released nitric oxide in a similar manner to those from healthy controls, because inhibition of p latelet aggregation by neutrophils from sickle cell anaemia or from he althy controls was blocked by the inhibitor of nitric oxide synthesis N-omega-nitro-L-arginine methyl ester (300 mu M), but not by N-omega-n itro-D-arginine methyl ester (300 mu M) and was reversed by L-arginine (1 mM), Additionally, a similar number of neutrophils from sickle cel l anaemia patients and from healthy controls was required to inhibit p latelet aggregation. Mononuclear cells from sickle cell anaemia patien ts inhibited platelet aggregation only in the presence of superoxide d ismutase (60 U ml(-1)). Phorbol 12-myristate 13-acetate (PMA, 30 nM)- or zymosan (100 particles/cell)-induced release of superoxide by monon uclear cells from sickle cell anaemia patients was significantly highe r than that observed in mononuclear cells from healthy controls (P < 0 .001 and P < 0.01 respectively, Mann-Whitney test). The levels of supe roxide released by neutrophils from sickle cell anaemia patients were similar to those from healthy controls. We conclude that mononuclear c ells from sickle cell anaemia patients release more superoxide than th ose from healthy controls, when stimulated with PMA or zymosan in vitr o, Considering that superoxide inactivates nitric oxide, that nitric o xide is an important endogenous vasodilator, and that superoxide produ ces oxidant damage, this greater production of superoxide by mononucle ar cells from sickle cell anaemia patients may represent an additional risk factor for the obstruction of the microcirculation and tissue da mage in these patients.