Anti-inflammatory activity of diterpenes from Croton stellatopilosus on LPS-induced RAW264.7 cells

An acyclic diterpene (plaunotol; 1) and two furanoditerpenes (plaunolide, 2 and plaunol E, 3), were isolated from Croton stellatopilosus leaves, and assessed for their inhibitory activity on nitric oxide (NO) production by lipopolysaccharide (LPS)-induced RAW264.7 cells. Plaunotol, plaunolide and plaunol E exhibited inhibitory activity with IC50 values of 3.41, 17.09 and 2.79 mu M, respectively. Cytotoxic effects were observed at concentrations of a parts per thousand yen100 mu M for plaunotol and a parts per thousand yen10 mu M for plaunol E. In order to understand the mechanism of this anti-inflammatory activity, transcription profiles of the COX-1, COX-2 and iNOS genes were measured using a quantitative RT-PCR technique. The level of gene expression was expressed as a relative quantitation according to the comparative C (T) method. The results indicated that plaunotol stimulated the COX-1 and COX-2 genes, and suppressed expression of the iNOS gene. Treatment of cells with plaunolide caused a downregulation of the expressions of the COX-1, COX-2 and iNOS genes. In contrast, plaunol E inhibited the expression of the COX-2, stimulated COX-1 and iNOS expressions. In summary, the present study shows that different diterpenes from C. stellatopilosus leaves exhibit anti-inflammatory activity towards LPS-activated RAW264.7 cells by different mechanisms. Our results provide data to support further investigations into the possibility that these diterpenes could be alternatives to act as anti-inflammatory agents.