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Antioxidant Activity of Natural Samwirin A: Theoretical and Experimental Insights.

ABSTRACT: Samwirin A (SW), a natural compound isolated from Sambucus williamsii or Rourea harmandiana, is known to exhibit potent antiosteoporosis activity and promote cell proliferation in rat osteoblast-like UMR 106 cells. Antiosteoporosis activity suggests that the compound must also exhibit antioxidant activity but this has not been studied thus far. In the present study, the antioxidant activity of SW was examined by experimental and computational studies. It was found that SW exhibits good hydroperoxyl scavenging activity, particularly in water at physiological pH (k _overall = 1.01 × 10⁷ M^-1 s^-1). The single-electron transfer mechanism defines the HOO^• + SW reaction in water, while the activity in the lipid medium is moderate and it follows the formal hydrogen transfer mechanism. The rate constant of the HOO^• scavenging reaction in the aqueous solution is about 78 times higher than the reference compound Trolox. The computational results are in line with experimental data underscoring that SW is a promising radical scavenger in aqueous media at physiological pH.

SUBMITTER: Dinh Ngoc T

PROVIDER: S-EPMC8529648 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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Antioxidant Activity of Natural Samwirin A: Theoretical and Experimental Insights.

Dinh Ngoc Thuc T Ha Mai Vu Thi MVT Nguyen Le Thanh T Nguyen Thi Van Anh TVA Mechler Adam A Hoa Nguyen Thi NT Vo Quan V QV

ACS omega 20211004 41

Samwirin A (SW), a natural compound isolated from Sambucus williamsii or Rourea harmandiana, is known to exhibit potent antiosteoporosis activity and promote cell proliferation in rat osteoblast-like UMR 106 cells. Antiosteoporosis activity suggests that the compound must also exhibit antioxidant activity but this has not been studied thus far. In the present study, the antioxidant activity of SW was examined by experimental and computational studies. It was found tha ...[more]

PMID: 34693175

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Project description:It was recently shown that, when tested in cellular systems, quercetin oxidized products (Qox) have significantly better antioxidant activity than quercetin (Q) itself. The main Qox identified in the experiments are either 2,5,7,3',4'-pentahydroxy-3,4-flavandione (Fl) or its tautomer, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Bf). We have now performed a theoretical evaluation of different physicochemical properties using density functional theory (DFT) calculations on Q and its main Qox species. The most stable structures (for Q and Qox) were identified after a structural search on their potential energy surface. Since proton affinities (PAs) are much lower than the bond dissociation enthalpies (BDEs) of phenolic hydrogens, we consider that direct antioxidant activity in these species is mainly due to the sequential proton loss electron transfer (SPLET) mechanism. Moreover, our kinetic studies, according to transition state theory, show that Q is more favored by this mechanism. However, Qox have lower PAs than Q, suggesting that antioxidant activity by the SPLET mechanism should be a result of a balance between proclivity to transfer protons (which favors Qox) and the reaction kinetics of the conjugated base in the sequential electron transfer mechanism (which favors Q). Therefore, our results support the idea that Q is a better direct antioxidant than its oxidized derivatives due to its kinetically favored SPLET reactions. Moreover, our molecular docking calculations indicate a stabilizing interaction between either Q or Qox and the kelch-like ECH-associated protein-1 (Keap1), in the nuclear factor erythroid 2-related factor 2 (Nrf2)-binding site. This should favor the release of the Nrf2 factor, the master regulator of anti-oxidative responses, promoting the expression of the antioxidant responsive element (ARE)-dependent genes. Interestingly, the computed Keap1-metabolite interaction energy is most favored for the Bf compound, which in turn is the most stable oxidized tautomer, according to their computed energies. These results provide further support for the hypothesis that Qox species may be better indirect antioxidants than Q, reducing reactive oxygen species in animal cells by activating endogenous antioxidants.

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Antioxidant Activity of Natural Samwirin A: Theoretical and Experimental Insights.

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Antioxidant Activity of Natural Samwirin A: Theoretical and Experimental Insights.

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