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 (IC₅₀ 4.6 - 58.6 μm) without any significant toxicity (IC₅₀ > 100 μm) which were more potent than l-NMMA (NO-production inhibitory activity, IC₅₀ 65.6 μm; cytotoxicity, IC₅₀ > 100 μm), 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 (IC₅₀ 4.6 - 29.3 μm). In particular, compounds 6 (IC₅₀ 7.3 μm), an azadirone-type limonoid, and 73 (IC₅₀ 4.6 μm), 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.

Inflammation; Limonoids; Meliaceae; NO Production-inhibitory activity; Terpenoids.