Natural phenylethanoid glycosides isolated from Callicarpa kwangtungensis suppressed lipopolysaccharide-mediated inflammatory response via activating Keap1/Nrf2/HO-1 pathway in RAW 264.7 macrophages cell

Ethnopharmacological relevance: Callicarpa kwangtungensis, as a characteristic traditional herb in China, has been widely used as indigenous medicine for thousands of years in the treatment of upper respiratory tract Infection, tonsillitis, pneumonia and traumatic bleeding in China. Phenylethanoid glycosides (PhGs), as natural Polyphenols, are especially abundant in this herb and can be regarded as the representative active ingredients in C. kwangtungensis.

Aim of this study: This study was performed to investigate the anti-inflammatory pharmacodynamic basis of six PhGs (acteoside, forsythoside B, poliumoside, alyssonoside, parvifloroside A, and syringalide A 3'-α-L-rhanmnopyranoside) isolated from C. kwangtungensis from the perspective of antioxidation.

Materials and methods: Six PhGs were isolated from the anti-inflammatory extracts of C. kwangtungensis by various chromatographic techniques and their anti-inflammatory activity on RAW 264.7 murine macrophages induced by LPS was investigated by measuring the release of tumor necrosis factor (TNF-α), the colonic interleukin-6 (IL-6), nitric oxide (NO) and Reactive Oxygen Species (ROS). Further, the underlying anti-inflammatory mechanism of two PhGs (forsythoside B and alyssonoside) was explored by determining the expression of Kelch-like ECH-association protein 1 (Keap1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (OH-1) and quinone oxidoreductase 1 (NQO1). Besides, molecular simulation was also employed to evaluate the binding capacity of two PhGs with Keap1.

Results: Compared with the model group, six PhGs revealed obviously inhibitory effects on TNF-α, IL-6, NO and the generation of ROS in RAW 264.7 macrophages. Moreover, forsythoside B and alyssonoside could act as the inhibitors of Keap1-Nrf2 interaction, then activated the nuclear translocation of Nrf2 and promoted the upregulated protein expression of HO-1 and NQO1, finally suppressed LPS-induced inflammatory response in RAW 264.7 macrophages. Molecular modeling exhibited hydrogen bonds played a crucial role for the binding of PhGs with the Nrf2 binding site in Keap1 protein.

Conclusions: Natural PhGs-induced protection against LPS-induced inflammatory response via activating Keap1/Nrf2/HO-1 signaling pathway in RAW 264.7 macrophages were confirmed, which provided experimental and theoretical basis for the deeper use of C. Kwangtungensis in the treatment and prevention of diseases related to inflammation and oxidative stress.