Screening 5-lipoxygenase inhibitors from selected traditional Chinese medicines and isolation of the active compounds from Polygoni Cuspidati Rhizoma by an on-line bioactivity evaluation system.

To identify natural products as new prototypes for 5-lipoxygenase (5-LOX), 12 traditional Chinese medicines (TCMs) were selected for screening their 5-LOX inhibition activities. The results showed that the methanol extracts of all selected TCMs (n = 12) possessed inhibitory activities against 5-LOX at 200 µg/mL, of which six extracts of the TCMs showed significant inhibitory effects with IC50 values in the range from 33.2 ± 1.4 µg/mL to 153.5 ± 1.7 µg/mL, and the extract of Polygoni Cuspidati Rhizoma (RPC) was the most active sample. An on-line ultra-performance liquid chromatography-photodiode array-MSn -5-LOX-fluorescence detector (UPLC-PDA-MSn -5-LOX-FLD) method was applied to further identify the potential 5-LOX inhibitory constituents in RPC extracts, which resulted in the identification of seven components with 5-LOX-binding activities. Finally, four compounds (polydatin, resveratrol, emodin-8-O-glucoside, and emodin) were successfully purified from RPC extracts. The 5-LOX inhibition action was assayed in vitro, and the results showed that these compounds possessed potent inhibitory effects against 5-LOX with IC50 values of 15.3 ± 2.1, 4.5 ± 1.2, 23.8 ± 0.4, and 11.8 ± 1.5 µg/mL, respectively. This was the first study to reveal the 5-LOX inhibitory constituents of RPC, and the present investigation might provide a valuable approach for the rapid discovery of natural inhibitors from TCMs.