The Anti-inflammatory Effects of Lignan Glycosides from Cistanche tubulosa stems on LPS/IFN-γ-induced RAW264.7 Macrophage Cells via PI3K/ AKT Pathway

Background: Cistanche tubulosa is a tonic in traditional Chinese medicines and has a broad spectrum of biological activity, including anti-inflammatory. However, the anti-inflammatory major constituents of C. tubulosa and their underlying mechanisms are still unknown. Objective: The aim of the current study was to explore the separation and structural characterization of lignan glycosides from C. tubulosa (Schenk) Wight., their anti-inflammatory activity and the underlying mechanism. Materials and Methods: Fractionation and isolation of the 85% EtOH extract of C. tubulosa (Schenk) Wight. were carried out and the primary ingredients lignan glycosides (1-6) were structurally characterized. CCK8 methods were used to evaluate the cytotoxic effect of lignan glycosides (1-6). Effects of lignan glycosides (1-6) on NO production in LPS/IFN-γ-induced RAW264.7 macrophages cells were measured using Griess reagent by reaction with nitrite. The mRNA expression levels of iNOS, COX-2, IL-1β, IL-6, TNF-a, and TGF-β treated RAW264.7 cells with various concentrations (0, 25 and 50 μg/ml) of lignan glycosides (1, 4) in the presence of LPS (10 ng/ml) and IFN-γ (20 ng/ml) for 24 h were analyzed by quantitative RT-PCR. Also, the protein expressions of iNOS, COX-2, PI3K, AKT, p-AKT and β -actin were determined using Western blot analysis. A molecular docking study was performed to investigate the interactions between the lignan glycosides and the PI3K using Autodock vina 1.1.2 package. Results: Six lignan glycosides (1-6) were isolated from stems of C. tubulosa. Among them, (+)- pinoresinol-4-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranoside (5) and eleutheroside E (6) were firstly isolated from C. tubulosa. Of these lignans, 1 and 4 exhibited pronounced inhibitions on NO production with the values of 33.63 ± 4.78 and 39.28 ± 5.52 % at 50 μg/ml, respectively. Additionally, LPS/IFN-γ-induced expression of inducible Nitric Oxide Synthase (iNOS), Cyclooxygenase-2 (COX-2), Interleukin-1β (IL-1β), IL-6, and Tumor Necrosis Factor-a (TNF-a) was significantly suppressed by pre-treatment of 1 and 4 in a dose-dependent manner. While 1 and 4 increased the mRNA levels of anti-inflammatory cytokines (TGF-β). Furthermore, 1 and 4 significantly inhibited the protein levels of PI3K and p-AKT in a dose-dependent manner. Conclusion: Taken together, these results suggest that 1 and 4 play an important role in the attenuation of LPS/IFN-γ-induced inflammatory responses in RAW264.7 cells and that the mechanisms involve down-regulation of the PI3K/AKT pathway.