Inhibitory effect of cyclosporin A and FK506 on nitric oxide production by cultured macrophages. Evidence of a direct effect on nitric oxide synthase activity.

Casein-elicited peritoneal macrophages from mice were cultured either alone or with interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS), and the effect of cyclosporin A (CsA) and FK506 on NO2- production (due technical difficulties NO2- was taken as the index for NO) was analysed. We observed an inhibitory effect of CsA and FK506 on NO2- production. The IC50 for NO2- production by casein-elicited macrophages was 0.1 microgram/ml for CsA and 0.3 microgram/ml FK506. The effect of both drugs was dose-dependent and was more clear in non-stimulated macrophages. The presence of IFN-gamma and LPS in the culture increased NO2- production by casein-elicited macrophages and partially eliminated the inhibition exerted by CsA and FK506. Both drugs acted directly on the nitric oxide synthase (NOS), since CsA and FK506 reduced by 35% and by 17%, respectively, NOS activity in the crude cytosolic fraction. However, CsA and FK506 did not alter 14CO2 production from [1-14C]glucose, suggesting that the pentose monophosphate pathway activity was not modified. These data add new insight into the interpretation of the immunosuppressive properties of both drugs.