Abstract
We investigated the effect of γ-mangostin purified from the fruit hull of the medicinal plant Garcinia mangostana on spontaneous prostaglandin E2 (PGE2) genase release and inducible cyclooxy-2 (COX-2) gene expression in C6 rat glioma cells. An 18-h treatment with γ-mangostin potently inhibited spontaneous PGE2 release in a concentration-dependent manner with the IC50 value of approximately 2 μM, without affecting the cell viability even at 30 μM. By immunoblotting and reverse-transcription polymerase chain reaction, we showed that γ-mangostin concentration-dependently inhibited lipopolysaccharide (LPS)-induced expression of COX-2 protein and its mRNA, but not those of constitutive COX-1 cyclooxygenase. Because LPS is known to stimulate inhibitor κB (IκB) kinase (IKK)-mediated phosphorylation of IκB followed by its degradation, which in turn induces nuclear factor (NF)-κB nuclear translocation leading to transcriptional activation of COX-2 gene, the effect of γ-mangostin on the IKK/IκB cascade controlling the NF-κB activation was examined. An in vitro IKK assay using IKK protein immunoprecipitated from C6 cell extract showed that this compound inhibited IKK activity in a concentration-dependent manner, with the IC50 value of approximately 10 μM. Consistently γ-mangostin was also observed to decrease the LPS-induced IκB degradation and phosphorylation in a concentration-dependent manner, as assayed by immunoblotting. Furthermore, luciferase reporter assays showed that γ-mangostin reduced the LPS-inducible activation of NF-κB–and human COX-2 gene promoter region-dependent transcription. γ-Mangostin also inhibited rat carrageenan-induced paw edema. These results suggest that γ-mangostin directly inhibits IKK activity and thereby prevents COX-2 gene transcription, an NF-κB target gene, probably to decrease the inflammatory agent-stimulated PGE2 production in vivo, and is a new useful lead compound for anti-inflammatory drug development.
- Received May 11, 2004.
- Accepted June 18, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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