Immunosuppressive constituents from Urtica dentata Hand.

A novel biscoumarin, 6,6',7,7'-tetramethoxyl-8,8'-biscoumarin (1), was isolated from the ethyl acetate extract of Urtica dentata Hand, together with five known compounds named as 7,7'-dihydroxy-6,6'-dimethoxy-8,8'-biscoumarin (2), 7,7'-dimethoxy-6,6'-biscoumarin (3), scoparone (4), vanillic acid (5), and daucosterol (6). Structures of the isolated compounds were elucidated on the basis of spectroscopic analysis including 2D NMR experiments. Compounds 1 and 2 were confirmed to be a rare carbon-carbon linked symmetrical biscoumarin. Compounds 1-4, especially 1 (IC50=8.18x10-5mol/l), showed potent immunosuppressive activities as determined by the Cell Counting Kit-8 assay for lymphocyte proliferation. Also, in the FACS analysis, 1 (IC50=5.19x10-4mol/l) promoted the differentiation of CD4+CD25+Foxp3+T regulatory cells distinctly compared to the normal control. Thus, 1 possessed specific immunosuppressive property by eliciting T regulatory cells, which may provide a potential treatment strategy for autoimmune diseases.