Anti-inflammatory activity of the synthetic C-C biflavonoids

To find anti-inflammatory agents based on plant constituents, the effects of six synthetic C-C biflavonoids connecting with different positions of C-C bond between flavone monomers (a: 4'-4', b: 4'-3', c: 4'-6, d: 3'-6, e: 6-6, f: 4'-3) were examined on PGE(2) and nitric oxide (NO) production from lipopolysaccharide (LPS)-treated macrophages, RAW 264.7. Among the compounds tested, the biflavonoids d, e, and f showed a considerable inhibition of cyclooxygenase-2 (COX-2)-mediated PGE(2) production at concentrations up to 50 microM, while the derivative c exerted cytotoxic effects on RAW cells. Especially, the biflavonoid e possessed the most potent inhibitory activity of PGE(2) production with an IC50 of 3.7 microM, compared with an IC50 of 8.2-20.7 microM by ginkgetin (natural biflavonoid). Western blot and reverse transcriptase-polymerase chain reaction analyses have shown that the inhibition of PGE(2) production by these synthetic derivatives was mediated at least in part by COX-2 inhibition, but not by COX-2 down-regulation. Meanwhile, these synthetic biflavonoids did not considerably inhibit inducible nitric oxide synthase-mediated NO production at concentrations up to 50 microM. When intraperitoneally administered, the biflavonoid e showed a significant anti-inflammatory activity (22.2% inhibition) against rat carrageenan-induced paw oedema at 5 mg kg(-1). The biflavonoid e may be used as a synthetic lead for developing new anti-inflammatory agents.