Nitric Oxide Production‐Inhibitory Activity of Limonoids from Azadirachta indica and Melia azedarach

Seventy‐three limonoids isolated from three Meliaceae plants, Azadirachta indica , A . indica var. siamensis , and Melia azedarach , or semi‐synthesized from the Meliaceae limonoids, were evaluated for their inhibitory activity against nitric oxide ( NO ) production in mouse macrophage RAW 264.7 cells induced by lipopolysaccharide ( LPS ), as a primary screening test for anti‐inflammatory agents. Of the compounds tested, 21 compounds exhibited inhibitory activity ( IC 50 4.6 – 58.6 μ m ) without any significant toxicity ( IC 50 > 100 μ m ) which were more potent than l ‐ NMMA ( NO ‐production inhibitory activity, IC 50 65.6 μ m ; cytotoxicity, IC 50 > 100 μ m ), and among which, nine compounds, i.e ., 17‐hydroxy‐15‐methoxynimbocinol ( 6 ), ohchinin ( 20 ), 1‐ cis ‐cinnamoyl‐1‐decinnamoylohchinin ( 24 ), salannin ( 27 ), methyl nimbidate ( 32 ), isosalannin ( 55 ), nimbolinin D ( 58 ), mesendanin E ( 69 ), and 7‐deacetylgedunin ( 73 ) exhibited potent inhibitory activity ( IC 50 4.6 – 29.3 μ m ). In particular, compounds 6 ( IC 50 7.3 μ m ), an azadirone‐type limonoid, and 73 ( IC 50 4.6 μ m ), a gedunin‐type limonoid, exhibited remarkable activity. Western blot analysis revealed that 27 and 73 reduced the expression levels of the inducible NO synthase and cyclooxygenase‐2 proteins in a concentration‐dependent manner. These findings suggest that limonoids of A . indica , A . indica var. siamensis , and M . azedarach , and their semi‐synthetic derivatives may be effective against inflammation.