Abstract
The role of the 6″-OH (ω-OH) group in the antioxidant activity of flavonoid glycosides has been largely overlooked. Herein, we selected quercitrin (quercetin-3-O-rhamnoside) and isoquercitrin (quercetin-3-O-glucoside) as model compounds to investigate the role of the 6″-OH group in several antioxidant pathways, including Fe2+-binding, hydrogen-donating (H-donating), and electron-transfer (ET). The results revealed that quercitrin and isoquercitrin both exhibited dose-dependent antioxidant activities. However, isoquercitrin showed higher levels of activity than quercitrin in the Fe2+-binding, ET-based ferric ion reducing antioxidant power, and multi-pathways-based superoxide anion-scavenging assays. In contrast, quercitrin exhibited greater activity than isoquercitrin in an H-donating-based 1,1-diphenyl-2-picrylhydrazyl radical-scavenging assay. Finally, in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl assay based on an oxidatively damaged mesenchymal stem cell (MSC) model, isoquercitrin performed more effectively as a cytoprotector than quercitrin. Based on these results, we concluded that (1) quercitrin and isoquercitrin can both indirectly (i.e., Fe2+-chelating or Fe2+-binding) and directly participate in the scavenging of reactive oxygen species (ROS) to protect MSCs against ROS-induced oxidative damage; (2) the 6″-OH group in isoquercitrin enhanced its ET and Fe2+-chelating abilities and lowered its H-donating abilities via steric hindrance or H-bonding compared with quercitrin; and (3) isoquercitrin exhibited higher ROS scavenging activity than quercitrin, allowing it to improve protect MSCs against ROS-induced oxidative damage.
Highlights
Flavonoid glycosides can be found in a wide range of plants, especially those used in Chinese herbal medicines, and have been reported to exhibit remarkable antioxidant effects [1]
The effects of the 600 -OH group of isoquercitrin only appear to be negligible based on the analyses presented above, this group did lead to an increase in the O2 − -scavenging activity of isoquercitrin compared with quercitrin
The results revealed that quercitrin and isoquercitrin both protected the mesenchymal stem cell (MSC) from OH radical-induced damage at concentrations in the range of 0–100 μg/mL
Summary
Flavonoid glycosides can be found in a wide range of plants, especially those used in Chinese herbal medicines, and have been reported to exhibit remarkable antioxidant effects [1]. We used these compounds to conduct a mechanistic analysis of To explore this possibility, we selected quercitrin and isoquercitrin as two model compounds to compare their antioxidant effects. We selected quercitrin and isoquercitrin as two model compounds to compare their antioxidant effects We used these compounds to conduct a mechanistic analysis of the role played by the 600 -OH group in antioxidant processes. We have conducted our experiments at physiological pH 7.4 (instead of pH 8.2) to improve the reliability of our results and provide a satisfactory explanation for the effects of quercitrin and isoquercitrin
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