Modulation of arachidonic acid metabolism and nitric oxide synthesis by garcinol and its derivatives

Garcinol, a polyisoprenylated benzophenone, from the fruit rind of Garcinia spp., has been shown to have anti-inflammatory and anticarcinogenic activities. To study its mechanism of action, we analyzed the effects of garcinol and its derivatives, including cambogin, garcim-1 and garcim-2, on arachidonic acid metabolism and nitric oxide (NO) synthesis in lipopolysaccharide (LPS)-stimulated RAW264.7 murine macrophages as well as in three intestinal cell lines. We also examined the effect of garcinol on cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase-2 (COX-2), inducible NO synthase (iNOS), and related upstream signaling. At 1 μM, garcinol and its derivatives, added 1 h after LPS stimulation, significantly inhibited the release of arachidonic acid and its metabolites in macrophages; garcinol was the most effective, showing >50% inhibition. Similar inhibitory activity was also observed in intestinal cells, HT-29, HCT-116 and IEC-6 cells, showing 40-50% inhibition by 1 μM garcinol. In LPS-stimulated macrophages, garcinol inhibited the phosphorylation of cPLA₂ without altering its protein level, and the effect was related to the inhibition of ERK1/2 phosphorylation. Garcinol inhibited NFκB activation and COX-2 expression only when it was added to the cells before LPS stimulation. Garcinol (1 μM) also significantly decreased iNOS expression and NO release from LPS-stimulated macrophages; this is probably due to the inhibition of the signal transducer and activator of transcription-1 (STAT-1), an upstream event in the activation of iNOS synthesis. The results suggest that garcinol modulates arachidonic acid metabolism by blocking the phosphorylation of cPLA₂ and decreases iNOS protein level by inhibiting STAT-1 activation. These activities may contribute to the anti-inflammatory and anticarcinogenic actions of garcinol and its derivatives.