Forsythia fruits, which are usually obtained from F. suspensa (Thumb) Vahl and F. viridissima Lindley, are known in Asia as diuretic, hypotensive, anti-allergic, anti-inflammatory, antipyretic, anti-infective and antidote agents. In Europe, these plants do not form fruits and, in Europe, more attention is paid to the leaves and flowers as a source of valuable compounds [1]. The present study we demonstrated that leaves and flowers of Forsythia x intermedia are source of lignans which were able to mediate pro-inflammatory function of neutrophils.
Using bio-guided fractionation, we isolated the active compounds and determined their biological activity on human neutrophil model. We examined: (I) cytotoxicity, (II) expression of adhesion molecules CD11a/CD18 and CD11b/CD18, (III) phosphorylation level of p38, ERK1/2 and JNK MAP kinases and (IV) pro-inflammatory cytokine release (IL-8, IL-1β and TNFα).
Cytotoxicity of lignans was determined by a standard flow cytometric probe using propidium iodide staining. The expression of adhesion molecules CD11a and CD11b was analyzed with flow cytometry. Phosphorylation of p38, ERK1/2 and JNK MAPK was determined by immunoblotting analysis. The effect on chemokines production was measured by enzyme-linked immunosorbent assay (ELISA).
The bio-guided fractionation led to the isolation of the following lignan aglycones: (+) pinoresinol, (+)-epipinoresinol, (-)-matairesinol, (+)-phillygenin and (-)-arctigenin. Compounds significantly decreased the surface expression of CD11a and CD11b at 50µM. Moreover all lignans significantly inhibited TNF-α and IL-1β production at 10µM, probably by attenuating the p38 and ERK kinase pathways. The lignans did not inhibit of interleukin 8 release.
Conclusion: Forsythia x intermedia is a valuable source of active lignans, which may be potential candidates for treating inflammatory diseases that are associated with the excessive production of cytokines such as TNF-α and IL-1β.
Acknowledgments
This study was financially supported by research grant 2015/17/B/NZ7/03086 from the Polish National Science Center.
[1] Tokar, M., and Klimek, B. (1998). Biologically active compounds in Forsythia flowers and leaves. Acta Pol. Pharm. 55, 499-504