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. Moreover, the plant material is listed by the Chinese, Japanese and Korean Pharmacopoeias [1]. In Europe, F. x intermedia, F. suspensa and F. viridissima are naturalized and cultivated as decorative shrubs. In temperate climates, these plants do not form fruits and, in Europe, more attention is paid to the leaves and flowers as a source of valuable compounds [2]. 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
[2] Tokar, M., and Klimek, B. (2004). The content of lignan glycosides in Forsythia flowers and leaves. Acta Pol. Pharm. 61, 273-278