Inhibitory effect of α-amyrin acetate isolated from Fraxinus rhynchophylla on Th17 polarization

Abstract

Background: T helper 17 (Th17) cells, which are differentiated from CD4+ T cells, drive inflammation, leading to autoimmune diseases such as psoriasis, rheumatoid arthritis, and inflammatory bowel disease. Therefore, inhibiting Th17 polarization could be a therapeutic target for inflammatory diseases. Purpose: We investigated the inhibitory effect of Fraxinus rhynchophylla (Oleaceae) on Th17 differentiation and found its active component. Study design: The activity of F. rhynchophylla and its active constituent was verified using CD4+ cells extracted from C57BL/6 mice. Methods: Micro-environment for Th17 polarization was provided to CD4+ cells and the effect of treatment with samples was measured by enzyme linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and Western blot. Results: The extract of F. rhynchophylla Hance and its chemical constituent, α-amyrin acetate, which was isolated via bioassay-guided isolation, significantly inhibited Th17 polarization as revealed when interleukin (IL)-17, a characteristic cytokine produced by Th17 cells, was measured. Furthermore, the inhibitory effect of α-amyrin acetate was compared to the amyrin derivatives, α-amyrin and β-amyrin. All displayed a suppressive effect on Th17 polarization and all reduced the expression of single transducer and activator of transcription 3 (STAT3) and retinoic acid receptor-related orphan receptor γt (RORγt), which are crucial transcription factors regulating Th17 differentiation. α-Amyrin acetate, however, exhibited the most prominent effects, which indicates that the functional group, acetate, might strengthen the inhibitory effect on Th17 differentiation. Conclusion: Taken together, these results suggest that the extract of F. rhynchophylla and its active constituent, α-amyrin acetate, could be applied as a potential therapeutic agent for autoimmune disorders such as rheumatoid arthritis. © 2019