Abstract
An effective and previously demonstrated screening method for active constituents in natural products using LC-MS coupled with a bioassay was reported in our earlier studies. With this, the current investigation attempted to identify bioactive constituents of Scutellaria baicalensis through LC-MS coupled with a bioassay. Peaks at broadly 17–20 and 24–25 min on the MS chromatogram displayed an inhibitory effect on NO production in lipopolysaccharide-induced BV2 microglia cells. Similarly, peaks at roughly 17–19 and 22 min showed antioxidant activity with an 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)/2,2-diphenyl-1- picrylhydrazyl (DPPH) assay. For confirmation of LC-MS coupled with a bioassay, nine compounds (1–9) were isolated from an MeOH extract of S. baicalensis. As we predicted, compounds 1, 8, and 9 significantly reduced lipopolysaccharide (LPS)-induced NO production in BV2 cells. Likewise, compounds 5, 6, and 8 exhibited free radical-scavenging activities with the ABTS/DPPH assay. In addition, the structural similarity of the main components was confirmed by analyzing the total extract and EtOAc fractions through molecular networking. Overall, the results suggest that the method comprised of LC-MS coupled with a bioassay can effectively predict active compounds without an isolation process, and the results of molecular networking predicted that other components around the active compound node may also be active.
Highlights
IntroductionNatural products, which have a variety of chemical structures and are produced by diverse organisms (microorganisms, plants, animals, and humans), possess potential therapeutic properties and are fascinating drug leads [1]
Natural products, which have a variety of chemical structures and are produced by diverse organisms, possess potential therapeutic properties and are fascinating drug leads [1]
For LC-Quadrupole Time of Flight (QTOF) MS/MS coupled with bioassay, the first phase was to obtain the chemical profile of the MeOH extract of S. baicalensis (Figure 1A,B, Figure S1 and Table 1), and the second phase was to collect the eluent through the column for 30 s per well in a 96-well plate
Summary
Natural products, which have a variety of chemical structures and are produced by diverse organisms (microorganisms, plants, animals, and humans), possess potential therapeutic properties and are fascinating drug leads [1]. The isolation of active components from natural products is normally achieved by bioassay-guided purification methodologies, but this often results in higher rates of unnecessary reisolation and dissipation of bioactive compounds from repeated processes [1,2]. Liquid chromatography-mass spectrometry (LC-MS) or nuclear magnetic resonance (LC-NMR) methods were applied as dereplication tools to determine known compounds before beginning any isolation step [2]. MS/MS molecular networking was described as an effective tool in visualizing for dereplication [7]. Molecular networking is established through networking the chemical and structural similarity relationships between metabolites based on the similarity of their MS/MS fragments. Metabolites with similar scaffolds can be grouped into clusters, confirming structural similarity [2,3,6]
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