Identification of anti-inflammatory components in Dioscorea nipponica Makino based on HPLC-MS/MS, quantitative analysis of multiple components by single marker and chemometric methods

The rhizome of Dioscorea nipponica Makino (RDN) is a widely used herbal medicine, which has significant anti-inflammatory activities on various inflammatory diseases. However, the bioactive compositions responsible for the anti-inflammatory activity of RDN are still unknown. This study aimed to identify the anti-inflammatory bioactive compounds in RDN using high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q/TOF-MS), quantitative analysis of multiple components by single marker (QAMS) and chemometric methods. Firstly, an HPLC-Q/TOF-MS method was employed for identification of bioactive steroidal saponins in RND, and a total of twelve steroid saponins were identified. Then, QAMS method was employed to determine the contents of seven bioactive steroidal saponins, including protodioscin, protogracillin, methyl protodioscin, pseudoprotodioscin, pseudoprogracillin, dioscin and gracillin in RND samples using dioscin as the reference analyte. The anti-inflammatory effects of RDN samples were then evaluated by inhibition of NO production in LPS-induced RAW264.7 cells. Furthermore, chemometric methods, including Pearson correlation analysis and partial least squares regression (PLSR) were employed to investigate the correlations between chemical components and anti-inflammatory activities, and explore the potential anti-inflammatory bioactive compounds of RDN. The results indicated that protodioscin, dioscin and gracillin were selected as the major anti-inflammatory compounds in RND. The further verification experiments showed that protodioscin, dioscin and gracillin exhibited great inhibition on NO production with IC50 values (the half maximal inhibitory concentration) of 0.712 μM, 0.469 μM and 0.815 μM, respectively. They also significantly reduced the levels of TNF-α, IL-1β, and IL-6 in LPS-induced RAW264.7 cells. The present study provided evidences for the anti-inflammatory activity of RND and identification of the anti-inflammatory components in RDN.