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Background   Pyrola decorata  H. Andres, is exclusively distributed in China and a source of traditional Chinese herbal medicine  Luxiancao  for more than 2000 years .  Here, we evaluated the antioxidant and cytoprotective effects of  P. decorata  and its five phenolic components (protocatechuic acid, gallic acid, hyperoside, 2′′- O -galloylhyperin, and quercetin), and discussed their antioxidant chemistry.    Methods  A lyophilized aqueous extract of  P. decorata  ( LAEP ) was prepared and analyzed with high-performance liquid chromatography (HPLC).  LAEP  and its five phenolic components were comparatively investigated using five antioxidant assays, including ferric-reducing antioxidant power, cupric ion-reducing antioxidant capacity, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical (PTIO • )-scavenging, 1,1-diphenyl-2-picryl-hydrazl radical (DPPH • )-scavenging, and 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) radical (ABTS +• )-scavenging activities. The reaction products of the five phenolic components with 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (4-methoxy-TEMPO • ) were determined with ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) analysis.  LAEP  and its five phenolic components were incubated with bone marrow-derived mesenchymal stem cells (bmMSCs) subjected to oxidative stress to demonstrate their cytoprotective effects with a flow cytometry assay.    Results  In the five antioxidant assays,  LAEP  and its five phenolic components dose-dependently increased the radical-scavenging (or reducing power) activities. However, the IC 50  values of hyperoside were consistently higher than those of 2′′- O -galloylhyperin. UPLC-ESI-Q-TOF-MS/MS analysis results indicated that the five phenolics could yield dimer products in the presence of 4-methoxy-TEMPO •  via the radical adduct formation (RAF) pathway. Flow cytometry assay results confirmed the cytoprotective activity of  LAEP  and its five phenolic components toward stressed bmMSCs. In particular, 2′′- O -galloylhyperin could more effectively reduce the percentage of damaged bmMSCs than hyperoside.    Conclusion   LAEP  and its five phenolic components may undergo redox-based pathways (such as electron transfer and H +  transfer) and covalent-based pathway (i.e., RAF) to exhibit antioxidant activity. One consequence of RAF is the generation of phenolic-phenolic dimer. In both organic and aqueous media, 2′′- O -galloylhyperin exhibited higher redox-based antioxidant levels (or cytoprotective levels) than those with hyperoside. The differences could be attributed to 2′′- O -galloylation reaction.

Antioxidant and Cytoprotective effects of Pyrola decorata H. Andres and its five phenolic components