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Xu Y, Li Z, Wang Y, Li C, Zhang M, Chen H, Chen W, Zhong Q, Pei J, Chen W, Haenen GRMM, Moalin M. Unraveling the Antioxidant Activity of 2R, 3R-dihydroquercetin. Int J Mol Sci 2023; 24:14220. [PMID: 37762525 PMCID: PMC10532074 DOI: 10.3390/ijms241814220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 09/07/2023] [Accepted: 09/15/2023] [Indexed: 09/29/2023] Open
Abstract
It has been reported that in an oxidative environment, the flavonoid 2R,3R-dihydroquercetin (2R,3R-DHQ) oxidizes into a product that rearranges to form quercetin. As quercetin is a very potent antioxidant, much better than 2R,3R-DHQ, this would be an intriguing form of targeting the antioxidant quercetin. The aim of the present study is to further elaborate on this targeting. We can confirm the previous observation that 2R,3R-DHQ is oxidized by horseradish peroxidase (HRP), with H2O2 as the oxidant. However, HPLC analysis revealed that no quercetin was formed, but instead an unstable oxidation product. The inclusion of glutathione (GSH) during the oxidation process resulted in the formation of a 2R,3R-DHQ-GSH adduct, as was identified using HPLC with IT-TOF/MS detection. GSH adducts appeared on the B-ring of the 2R,3R-DHQ quinone, indicating that during oxidation, the B-ring is oxidized from a catechol to form a quinone group. Ascorbate could reduce the quinone back to 2R,3R-DHQ. No 2S,3R-DHQ was detected after the reduction by ascorbate, indicating that a possible epimerization of 2R,3R-DHQ quinone to 2S,3R-DHQ quinone does not occur. The fact that no epimerization of the oxidized product of 2R,3R-DHQ is observed, and that GSH adducts the oxidized product of 2R,3R-DHQ on the B-ring, led us to conclude that the redox-modulating activity of 2R,3R-DHQ quinone resides in its B-ring. This could be confirmed by chemical calculation. Apparently, the administration of 2R,3R-DHQ in an oxidative environment does not result in 'biotargeting' quercetin.
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Affiliation(s)
- Yaping Xu
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Zhengwen Li
- School of Pharmacy, Chengdu University, 2025 Chengluo Avenue, Chengdu 610106, China;
| | - Yue Wang
- Department of Pharmacology and Personalized Medicine, School of Nutrition and Translational Research in Metabolism (NUTRIM), Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine and Life Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands; (Y.W.); (C.L.); (G.R.M.M.H.)
| | - Chujie Li
- Department of Pharmacology and Personalized Medicine, School of Nutrition and Translational Research in Metabolism (NUTRIM), Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine and Life Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands; (Y.W.); (C.L.); (G.R.M.M.H.)
| | - Ming Zhang
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Haiming Chen
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Wenxue Chen
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Qiuping Zhong
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Jianfei Pei
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Weijun Chen
- College of Food Science and Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China; (Y.X.); (H.C.); (W.C.); (Q.Z.); (J.P.)
| | - Guido R. M. M. Haenen
- Department of Pharmacology and Personalized Medicine, School of Nutrition and Translational Research in Metabolism (NUTRIM), Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine and Life Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands; (Y.W.); (C.L.); (G.R.M.M.H.)
| | - Mohamed Moalin
- Research Centre Material Sciences, Zuyd University of Applied Science, 6400 AN Heerlen, The Netherlands;
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Webster RD. Electrochemical and Spectroscopic Characterization of Oxidized Intermediate Forms of Vitamin E. Molecules 2022; 27:molecules27196194. [PMID: 36234726 PMCID: PMC9571374 DOI: 10.3390/molecules27196194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Revised: 09/12/2022] [Accepted: 09/15/2022] [Indexed: 11/16/2022] Open
Abstract
Vitamin E, a collection of lipophilic phenolic compounds based on chroman-6-ol, has a rich and fascinating oxidative chemistry involving a range of intermediate forms, some of which are proposed to be important in its biological functions. In this review, the available electrochemical and spectroscopic data on these oxidized intermediates are summarized, along with a discussion on how their lifetimes and chemical stability are either typical of similar phenolic and chroman-6-ol derived compounds, or atypical and unique to the specific oxidized isomeric form of vitamin E. The overall electrochemical oxidation mechanism for vitamin E can be summarized as involving the loss of two-electrons and one-proton, although the electron transfer and chemical steps can be controlled to progress along different pathways to prolong the lifetimes of discreet intermediates by modifying the experimental conditions (applied electrochemical potential, aqueous or non-aqueous solvent, and pH). Depending on the environment, the electrochemical reactions can involve single electron transfer (SET), proton-coupled electron transfer (PCET), as well as homogeneous disproportionation and comproportionation steps. The intermediate species produced via chemical or electrochemical oxidation include phenolates, phenol cation radicals, phenoxyl neutral radicals, dications, diamagnetic cations (phenoxeniums) and para–quinone methides. The cation radicals of all the tocopherols are atypically long-lived compared to the cation radicals of other phenols, due to their relatively weak acidity. The diamagnetic cation derived from α–tocopherol is exceptionally long-lived compared to the diamagnetic cations from the other β–, γ– and δ–isomers of vitamin E and compared with other phenoxenium cations derived from phenolic compounds. In contrast, the lifetime of the phenoxyl radical derived from α–tocopherol, which is considered to be critical in biological reactions, is typical for what is expected for a compound with its structural features. Over longer times via hydrolysis reactions, hydroxy para–quinone hemiketals and quinones can be formed from the oxidized intermediates, which can themselves undergo reduction processes to form intermediate anion radicals and dianions. Methods for generating the oxidized intermediates by chemical, photochemical and electrochemical methods are discussed, along with a summary of how the final products vary depending on the method used for oxidation. Since the intermediates mainly only survive in solution, they are most often monitored using UV-vis spectroscopy, FTIR or Raman spectroscopies, and EPR spectroscopy, with the spectroscopic techniques sometimes combined with fast photoinitiated excitation and time-resolved spectroscopy for detection of short-lived species.
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Affiliation(s)
- Richard D. Webster
- School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore;
- Environmental Chemistry and Materials Centre, Nanyang Environment & Water Research Institute (NEWRI), Nanyang Technological University, 1 Cleantech Loop, Clean Tech One, Singapore 637141, Singapore
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