INHIBITORY EFFECT OF CYCLOSPORINE-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 lipopolysacch aride (LPS), and the effect of cyclosporin A (CsA) and FK 506 on NO2- production (due technical difficulties NO2- was taken as the index for NO) was analysed. We observed an inhibitory effect of CsA and FK 506 on NO2- production, The IC50 for NO2- production by casein-elicited ma crophages was 0.1 mu g/ml for CsA and 0.3 mu g/ml FK 506. The effect o f both drugs was dose-dependent and was more clear in non-stimulated m acrophages. The presence of IFN-gamma and LPS in the culture increased NO2- production by casein-elicited macrophages and partially eliminat ed the inhibition exerted by CsA and FK 506. Both drugs acted directly on the nitric oxide synthase (NOS), since CsA and FK 506 reduced by 3 5% and by 17%, respectively, NOS activity in the crude cytosolic fract ion, However, CsA and FK 506 did not alter (CO2)-C-14 production from [I-C-14]glucose, suggesting that the pentose monophosphate pathway act ivity was not modified, These data add new insight into the interpreta tion of the immunosuppressive properties of both drugs.