Visual authentication of steroidal saponins in Allium macrostemon Bge. and Allium chinense G. Don using MALDI-TOF imaging mass spectrometry and their structure activity relationship

Allium macrostemon Bge. (AMB) and Allium chinense G. Don (ACGD), both named Allii Macrostemonis Bulbus or Xiebai in Chinese, belong to the same genus. They are both used as edible vegetables and medicinal herbs for the treatment of atherosclerosis. So far, comparative analysis of the spatial metabolomes and platelet aggregation function of steroidal saponins has rarely been performed. In this study, high mass resolution matrix-assisted laser desorption/ionization time-of-flight imaging mass spectrometry (MALDI-TOF MSI) were performed on the fresh bulbs of these two herbs for the spatial distribution of steroidal saponins, and ultra-high-performance liquid chromatography tandem triple quadrupole mass spectrometry (UHPLC/TQD-MS) was used to quantify their content levels. Platelet inhibitory activity induced by arachidonic acid, adenosine diphosphate and collagen were fully investigated. A total of 53 differential variables with compounds were identified or tentatively characterized between AMB and ACGD samples by UHPLC/TQD-MS. Furthermore, these steroidal saponins were almost distributed in tunic and outer scale regions of AMB, while they were rich in tunic and whole leaf scale, and rarely in developing flower bud of ACGD bulbs. Quantitative results demonstrated several saponins were the unique components for AMB (macrostemonoside I, timosaponin B-II, macrostemonoside F, etc.) and ACGD (chinenoside I, chinenoside II, chinenoside IV, etc.). Moreover, spirostanol saponins exhibited stronger inhibitory platelet activity than furostanol saponins, and the structure activity relationship was further summarized. In conclusion, high-mass resolution MALDI full-scan MSI provides abundant spatial distribution information of steroidal saponins in AMB and ACGD. And we finished the discussion of their activity characteristics. These findings would benefit the understanding of safety and effectiveness for their edible and medicinal use.