Enhancement of nitric oxide synthesis by the aqueous extract of Spiraea prunifolia var. simpliciflora's root in RAW 264.7 cells

The effects of aqueous extract of Spiraea prunifolia var. simpliciflora's r oot, a traditional medicine for the treatment of malaria in Chinese medicin e, on the generation of nitric oxide (NO) are investigated in RAW 264.7 cel ls. NO generation from IFN-gamma primed RAW 264.7 cells is markedly increas ed by the addition of aqueous extract in a dose-dependent manner. The enhan cement of NO generation by the aqueous extract is accompanied by a signific antly increased expression of inducible nitric oxide synthase (iNOS). Howev er, the aqueous extract of Spiraea prunifolia var, simpliciflora's root doe s not affect the viability of RAW 264.7 cells, as assessed by MTT assay. Po lymyxin B does not inhibit NO generation by the aqueous extract in IFN-gamm a primed RAW 264.7 cells. However, polymyxin B significantly decreases NO g eneration by lipopolysaccharide (LPS) in IFN-y primed RAW 264.7 cells. Thes e data indicate that the signaling pathway of the aqueous extract-induced N O generation is not dependent on PKC. These results strongly support the me chanism by which the aqueous extract may exert anti-malarial effect via dir ect cytotoxicity of NO as well as NO-mediated modulation of immune function s.