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Open AccessArticle

Dual Effect of Glucuronidation of a Pyrogallol-Type Phytophenol Antioxidant: A Comparison between Scutellarein and Scutellarin

by Qianru Liu 1,2,†, Xican Li 1,2,*,†, Xiaojian Ouyang 1,2 and Dongfeng Chen 3,4,*
1
School of Chinese Herbal Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
2
Innovative Research & Development Laboratory of TCM, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
3
School of Basic Medical Science, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
4
The Research Center of Basic Integrative Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editors: Susana M. Cardoso and Alessia Fazio
Molecules 2018, 23(12), 3225; https://doi.org/10.3390/molecules23123225
Received: 16 November 2018 / Revised: 5 December 2018 / Accepted: 6 December 2018 / Published: 6 December 2018
(This article belongs to the Special Issue The Antioxidant Capacities of Natural Products 2019)
To explore whether and how glucuronidation affects pyrogallol-type phytophenols, scutellarein and scutellarin (scutellarein-7-O-glucuronide) were comparatively investigated using a set of antioxidant analyses, including spectrophotometric analysis, UV-vis spectra analysis, and ultra-performance liquid chromatography coupled with electrospray ionization-quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) analysis. In spectrophotometric analyses of the scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+•), and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radicals (PTIO) and the reduction of Cu2+ ions, scutellarein showed lower IC50 values than scutellarin. However, in O2-scavenging spectrophotometric analysis, scutellarein showed higher IC50 value than scutellarin. The analysis of UV-Vis spectra obtained after the Fe2+-chelating reaction of scutellarin showed a typical UV-Vis peak (λmax = 611 nm), while scutellarein showed no typical peak. In UPLC-ESI-Q-TOF-MS/MS analysis, mixing of scutellarein with DPPH yielded MS peaks (m/z 678, 632, 615, 450, 420, 381, 329, 300, 288, 227, 196, 182, 161, and 117) corresponding to the scutellarein-DPPH adduct and an MS peak (m/z 570) corresponding to the scutellarein-scutellarein dimer. Scutellarin, however, generated no MS peak. On the basis of these findings, it can be concluded that glucuronidation of pyrogallol-type phytophenol antioxidants has a dual effect. On the one hand, glucuronidation can decrease the antioxidant potentials (except for O2 scavenging) and further lower the possibility of radical adduct formation (RAF), while on the other hand, it can enhance the O2-scavenging and Fe2+-chelating potentials. View Full-Text
Keywords: scutellarein; scutellarin; pyrogallol-type phytophenol; structure-activity relationship; glucuronidation; antioxidant scutellarein; scutellarin; pyrogallol-type phytophenol; structure-activity relationship; glucuronidation; antioxidant
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Liu, Q.; Li, X.; Ouyang, X.; Chen, D. Dual Effect of Glucuronidation of a Pyrogallol-Type Phytophenol Antioxidant: A Comparison between Scutellarein and Scutellarin. Molecules 2018, 23, 3225.

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