NO regulates LPS-stimulated cyclooxygenase gene expression and activity in pulmonary artery endothelium.

We examined whether nitric oxide (NO) inhibits prostanoid synthesis through actions on cyclooxygenase (COX) gene expression and activity. Bovine pulmonary artery endothelial cells were pretreated for 30 min with the NO donors 1 mM S-nitroso-N-acetylpenicillamine (SNAP), 0.5 mM sodium nitroprusside (SNP), or 0.2 microM spermine NONOate; controls included cells pretreated with either 1 mM N-acetyl-D-penicillamine or the NO synthase (NOS) inhibitor 1 mM N(G)-nitro-L-arginine methyl ester with and without addition of lipopolysaccharide (LPS; 0.1 microg/ml) for 8 h. COX-1 and COX-2 gene and protein expression were examined by RT-PCR and Western analysis, respectively; prostanoid measurements were made by gas chromatography-mass spectrometry, and COX activity was studied after a 30-min incubation with 30 microM arachidonic acid. LPS induced COX-2 gene and protein expression and caused an increase in COX activity and an eightfold increase in 6-keto-PGF(1alpha) release. LPS-stimulated COX-2 gene expression was decreased by approximately 50% by the NO donors. In contrast, LPS caused a significant reduction in COX-1 gene expression and treatment with NO donors had little effect. SNAP, SNP, and NONOate significantly suppressed LPS-stimulated COX activity and 6-keto-PGF(1alpha) release. Our data indicate that increased generation of NO attenuates LPS-stimulated COX-2 gene expression and activity, whereas inhibition of endogenous NOS has little effect.