In the present study, we investigated the inhibitory effect of the known oxycoumarins poncitrin (3), osthol (4), and xanthoxyletin (5), newly isolated from Clausena guillauminii (Rutaceae), together with the known carbazoles heptaphylline (1) and 7-methoxyheptaphylline (2) on inducible-nitric oxide synthase (iNOS) expression induced by lipopolysaccharide (LPS) and the NO generation in RAW 264.7 mouse macrophages. Isolation of active oxycoumarins was guided by Western blot analysis of iNOS protein expression. These oxycoumarins showed an inhibitory effect on iNOS protein expression at 10 μM. Further examination of the inhibitory effects of these compounds on inflammation mediators revealed that the synthesis of nitric oxide (NO) and the protein expression of tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2) were inhibited by 5. It was expected that these compounds show anti-inflammatory activities.
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