Ginseng root extract attenuates inflammation by inhibiting the MAPK/NF-κB signaling pathway and activating autophagy and p62-Nrf2-Keap1 signaling in vitro and in vivo

Abstract

Ethnopharmacological relevance: Panax ginseng C.A. Meyer is a type of herbal plant that has frequently been used in many Asian countries to treat a variety of diseases. Ginseng is considered to exhibit anti-inflammatory and anti-oxidative pharmacological effects. However, the specific mechanism is still not entirely understood.

Aim of the study: In this study, we investigated if ginseng extract could attenuate inflammation and oxidative stress in RAW264.7 cells and in dextran sulfate sodium (DSS)-induced colitis mouse model.

Materials and methods: RAW264.7 cells and LPS were used to develop inflammatory and oxidative cell models. C57/6J male mice and DSS were used to construct the animal models. O2-, mitochondria number, and mitochondrial membrane potential were analyzed using fluorescent probes and fluorescence microscopy. Reactive oxygen species and nitric oxide generation were detected with probes and microplate readers. The secreted amounts of inflammatory cytokines were measured by enzyme-linked immunosorbent assay kits. Protein expression levels in the cytoplasm and nucleus were measured by western blotting analyses. Quantitative real-time PCR (qRT-PCR) was used to determine the changes in mRNA levels. Autophagosome accumulation was analyzed by transmission electron microscopy. A p62-specific siRNA was used to evaluate the effect of p62 on the anti-oxidative function of ginseng root extract (GRE). Asperuloside and SP600125 were used to confirm the involvement of the MAPK/NF-κB signaling pathway.

Results: We performed a systematic analysis of the anti-inflammatory, anti-oxidative, and autophagy regulatory mechanisms of GRE in LPS-treated RAW264.7 cells. GRE considerably reduced the levels of nitric oxide, TNF-α, and IL-6 secreted by LPS-treated cells. GRE treatments dose-dependently upregulated IL-10 mRNA levels and decreased IL-6 and IL-1β mRNA levels in LPS-treated cells. Similar to the NF-κB and JNK inhibitors, GRE treatment significantly inhibited NF-κB activity and phosphorylation of MAPKs (JNK, ERK-1/2, and p38). Additionally, GRE treatment remarkably decreased LPS-triggered reactive oxygen species production and mitochondrial dysfunction by motivating Nrf2 nuclear translocation by enhancing phosphorylated p62. Knockdown of p62 resulted in the loss of GRE anti-oxidative ability. Autophagy was strongly induced by GRE via the Akt-mTOR signaling pathway, relieving excessive oxidation, mitochondrial dysfunction, and inflammation, while enhancing Beclin-1, LC3 II, and Atg7 protein expression. Furthermore, GRE alleviated the degree of injury, inflammatory cytokine production, and regulated the relative signaling pathway in DSS-induced colitis.

Conclusions: GRE can exert both anti-inflammatory and anti-oxidative functions by targeting the MAPK/NF-κB and p62-Nrf2-Keap1 pathways, as well as autophagy, in vitro and vivo.

Keywords: Autophagy; Ginseng root extract; Inflammation; MAPK/NF-κB; Oxidative damage; p62-Nrf2-Keap1.