Ultrafiltration LC-ESI-MSn screening of 5-lipoxygenase inhibitors from selected Chinese medicinal herbs Saposhnikovia divaricata, Smilax glabra, Pueraria lobata and Carthamus tinctorius

• First application of ultrafiltration LC-ESI-MSn to screening of 5-lipoxygenase inhibitors.
• Identified sec-O-glucosylhamaudol, resveratrol, daidzin and anhydrosafflor yellow B to be main 5-LOX inhibitors.
• Highly efficient tool for pinpointing potential enzyme inhibitors in a mixture.
• Resveratrol and daidzein are also found in foods, thus findings have broader significance.

Ultrafiltration liquid chromatography coupled to electrospray ionization tandem mass spectrometry (ultrafiltration LC-ESI-MSn) was used to screen 5-lipoxygenase (5-LOX) inhibitors from selected Chinese medicinal herbs Saposhnikovia divaricata (Turcz.) Schischk, Smilax glabra Roxb., Pueraria lobata and Carthamus tinctorius L. for the first time. The phytochemical compositions of the four medicinal herbs were analysed and the major components identified. The potency of the 5-LOX inhibitors identified in ultrafiltration LC-ESI-MSn was compared to the IC50's obtained from in vitro enzyme inhibition assay. As a result, sec-O-glucosylhamaudol, resveratrol, daidzin and anhydrosafflor yellow B had the highest binding ability to 5-LOX, and were the main contributors to the 5-LOX inhibitory activities of S. divaricata, S. glabra, P. lobata and C. tinctorius extracts, respectively. These strong 5-LOX inhibitors were not necessarily the major components. The high inhibitory activity of resveratrol and daidzin indicates foods such as grapes and soybean may be beneficial to 5-LOX mediated diseases.