Sesquiterpenoids from Inula britannica and their potential mechanism for immunomodulation

The immune system serves as a role of diseases, such as Parkinson's disease, and acute lung injury. An immunoregulatory activity-directed separation depended on phorbol 12-myristate 13-acetate (PMA) plus ionomycin (Ion)-mediated Jurkat leukemic T cells was used for studying chemical constituents from Inula britannica L. in depth. Five previously undescribed aromatic sesquiterpenoid dimers inulabritanoids J-N (1-5) and a previously undescribed germacrane-type sesquiterpenoid britanicafanin F (6) were afforded from I. britannica as well as eight known sesquiterpenoids (7-14). Their structures were elucidated through 1D and 2D NMR, HRMS, and ECD spectra along with quantum chemical calculations. Immunomodulatory effects of compounds 1-14 were assayed in PMA plus Ion-mediated Jurkat cells, and indicated that compounds 8, 9, and 13 displayed significantly inhibitory effects toward IL-2 and IFN-γ. Further investigation of mechanism of action revealed that compound 13 inhibited phosphorylations of p38, ERK, and JNK to suppress c-Jun and c-Fos expressions, resulting in blocking the nuclear translocation of AP-1 (a complex of c-Jun and c-Fos) to regulate mRNA expressions of IL-2 and IFN-γ. Molecular docking analysis demonstrated that compound 13 could enter into the cavity of p38, ERK, and JNK, and from hydrogen bond interactions with Gly33, Lys53 Ser154, and Asp168 for p38, Lys54, Glu71, Ser153, and Asp167 for ERK, and Met149 and Asn152 for JNK, which supported the abovementioned results. These findings suggested that sesquiterpenoids from the genus Inula served as immunomodulators for treating diseases involved in immune and inflammatory responses.