Phytochemical composition, antioxidant, anti-tyrosinase, anti-cholinesterase, and anti-inflammatory activities of Rhynchanthus beesianus rhizome extracts

Rhynchanthus beesianus is a medicine food homology plant, and its rhizome is a food spice and traditional Chinese medicine used to treat inflammation-related disorders. Still, little research has been done on its phytochemicals and biological activities. Therefore, this study firstly reported the phytochemical analysis by UHPLC-Q-Orbitrap-MS, antioxidant, anti-enzymatic, and anti-inflammatory effects of R. beesianus rhizome water extract (WE) and 70% ethanol extract (EE). For phytochemical analysis, WE and EE had high total phenolic (25.57–28.19 mg GAE/g extract) and flavonoid (10.57–28.08 mg RE/g extract) contents, and further UHPLC-Q-Orbitrap-MS test identified sixty-one compounds, including twelve phenolic compounds and six flavonoids. In the antioxidant assay, WE and EE showed significant DPPH (IC50: 83.93 ± 5.90 and 69.48 ± 1.57 μg/mL, respectively) and ABTS (IC50: 73.46 ± 0.69 and 40.72 ± 0.67 μg/mL, respectively) radical scavenging ability, especially the efficacy of EE was superior or equivalent to that of positive control BHT. Moreover, the WE and EE exhibited poor inhibition on acetylcholinesterase (IC50: 3.31 ± 0.16 and 3.53 ± 0.14 mg/mL, respectively), butyrylcholinesterase (IC50: 1.29 ± 0.02 and 0.75 ± 0.08 mg/mL, respectively), and tyrosinase (IC50: 5.91 ± 0.63 and 21.30 ± 1.52 mg/mL, respectively). Interestingly, EE showed remarkable inhibition on NO, PGE2, IL-6, and TNF-α produced by LPS stimulation without cytotoxicity. It reduced ROS generation and down-regulated mRNA and protein levels of iNOS and COX-2 in LPS-stimulated RAW264.7 macrophages. Besides, EE decreased LPS-stimulated MAPKs (ERK, p38, and JNK) phosphorylation and inhibited NF-κB p65 nuclear translocation by suppressing the phosphorylation and degradation of IκBα. Therefore, R. beesianus can be used as a promising natural antioxidant, enzyme inhibitor, and anti-inflammatory agent with great exploitation potential in functional food and pharmaceuticals.