THE TRITERPENOID QUINONEMETHIDE PRISTIMERIN INHIBITS INDUCTION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN MURINE MACROPHAGES

Inducible nitric oxide synthase dependent production of nitric oxide ( NO) plays an important role in inflammation. We investigated whether p ristimerin ((20 oxo-24-nor-friedela-1(10),3,5,7-tetraen-carboxylic aci d-(29)-methylester), an antitumoral, antimicrobial as well as anti-inf lammatory plant compound, has an effect on the inducible NO synthase s ystem in lipopolysaccharide-activated RAW 264.7 macrophages. Pristimer in dose dependently (IC50: 0.2-0.3 mu M) reduces nitrite accumulation, a parameter for NO synthesis, in supernatants of lipopolysaccharide-s timulated (1 mu g/ml, 20 h) macrophages. This effect correlates with a reduced inducible NO synthase enzyme activity measured by conversion of [H-3]L-arginine to [H-3]L-citrulline and significantly lower levels of enzyme protein (Western blotting) in homogenates of cells cotreate d with lipopolysaccharide and pristimerin (12 h). Northern blot analys is and polymerase chain reaction (PCR) showed decreased inducible NO s ynthase mRNA levels in activated macrophages exposed to pristimerin (4 h). Electrophoretic mobility shift assay (EMSA) demonstrated a marked ly reduced binding activity of nuclear factor-kappa B (NF kappa B) mec hanism which involves inhibition of NF kappa B activation. This featur e of pristimerin is likely to contribute to its anti-inflammatory acti vity. (C) 1997 Elsevier Science B.V.