High-resolution neuraminidase inhibition profiling of Arnebia euchroma (Royle) IM Johnst. based on HR-MS and target isolation: An example study of anti-infectious constituents in traditional Chinese medicine

Ethnopharmacological relevance: Traditional Chinese Medicines (TCMs) are an important source to discover new anti-infectious drugs. Neuraminidases (NAs) not only play a key role on human health, but also are promising targets for anti-infectious drugs. Arnebia euchroma which is a widely used traditional Chinese medicine with the effect of cooling blood and detoxifying showed potential inhibitory activities on both bacterial NA and virus NA, suggesting that the material basis of A. euchroma deserves in-depth study. Aim of the study: To investigate the anti-infectious constituents of A. euchroma based on NA inhibition. Material and methods: A HPLC-DAD system incorporated an auto-sampler was used for micro-fractionation. A nanoliter liquid handler and a high sensitive multimode plate reader system were used for high throughput NA inhibition screening. Thus a high-resolution NA inhibition profiling platform was constructed. The structures of potential active components in A. euchroma obtained by the high-resolution bioassay profiling were identified by DAD and MS in parallel. Then, a target and rapid isolation of NAIs from A. euchroma was achieved under the guidance of the spectrum-effect relationship obtained above. Finally, the isolated compounds were elucidated by extensive spectroscopic methods and their bioactivities were validated by in vitro assay and molecular docking. Results: 16 potential active ingredients in A. euchroma were isolated and identified, including a new meromonoterpenoid. The in vitro bioassay results revealed that 12 out of the 16 isolated compounds showed potent inhibitory activities on bacterial NA (IC50s = 1-6 mu M) and five of them exhibited potent anti-microbial activities on methicillin-resistant Staphylococccus aureus (MRSA) with MICs in the range of 0.5-4 mu g/mL. Furthermore, some isolated compounds showed equal or even better inhibitory activities on oseltamivir resistant viral NA than oseltamivir sensitive NA. The mechanism study in silicon revealed that these natural compounds possessed absolutely different binding modes on the bacterial and viral NAs. Conclusions: Our study gave a clear spectrum-effect relationship of A. euchroma, providing a scientific evidence for future study of the multi-components synergistic effect of TCMs.