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Antioxidant and Prooxidant Properties of Flavonoids
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Antioxidant and Prooxidant Properties of Flavonoids

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Pharmacology".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 30042

Special Issue Editor

Prof. Dr. Marian Valko

grade E-Mail Website
Guest Editor
Faculty Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava, Slovakia
Interests: biometals; oxidative stress; metallodrugs; antioxidants; EPR spectroscopy of biomolecules

Special Issue Information

Dear Colleagues,

The beneficial effects of flavonoids have been documented predominantly in the context of oxidative-stress-related diseases, such as cancer, cardiovascular diseases, and neurological disorders. Antioxidant properties of flavonoids are related primarily to the number and positions of hydroxyl groups and to their redox active metal chelating capacity. However, flavonoids cannot exclusively be considered to be antioxidants. Under certain conditions, such as a high concentration and in the presence of redox metals, flavonoids may exhibit pro-oxidant behavior. Paradoxically, the pro-oxidant activity of flavonoids may be beneficial since it may induce the pooling of antioxidant enzymes and, thus, exhibit preventive effects on various health problems. 

The aim of this Special Issue is to discuss the antioxidant and pro-oxidant properties of flavonoids, their interaction with redox metals, and their role in the prevention of a variety of disease states.

Prof. Dr. Marian Valko
Guest Editor

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Keywords

  • flavonoids
  • antioxidant
  • prooxidant
  • redox metal
  • metal chelating agents
  • free radicals
  • hydroxyl radical
  • DNA damage
  • DNA intercalation
  • signaling pathways
  • cancer
  • neurological disorders
  • cardiological diseases

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Published Papers (4 papers)

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Research

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14 pages, 2422 KiB  
Article
The Oxidation of Equol by Tyrosinase Produces a Unique Di-ortho-Quinone: Possible Implications for Melanocyte Toxicity
by Hitomi Tanaka, Shosuke Ito, Makoto Ojika, Tomoko Nishimaki-Mogami, Kazunari Kondo and Kazumasa Wakamatsu
Int. J. Mol. Sci. 2021, 22(17), 9145; https://doi.org/10.3390/ijms22179145 - 24 Aug 2021
Cited by 7 | Viewed by 2802
Abstract
Equol (7-hydroxy-3-(4′-hydroxyphenyl)-chroman, EQ), one of the major intestinally derived metabolites of daidzein, the principal isoflavane found in soybeans and most soy foods, has recently attracted increased interest as a health-beneficial compound for estrogen-dependent diseases. However, based on its structure with two p-substituted [...] Read more.
Equol (7-hydroxy-3-(4′-hydroxyphenyl)-chroman, EQ), one of the major intestinally derived metabolites of daidzein, the principal isoflavane found in soybeans and most soy foods, has recently attracted increased interest as a health-beneficial compound for estrogen-dependent diseases. However, based on its structure with two p-substituted phenols, this study aimed to examine whether EQ is a substrate for tyrosinase and whether it produces o-quinone metabolites that are highly cytotoxic to melanocyte. First, the tyrosinase-catalyzed oxidation of EQ was performed, which yielded three EQ-quinones. They were identified after being reduced to their corresponding catechols with NaBH4 or L-ascorbic acid. The binding of the EQ-quinones to N-acetyl-L-cysteine (NAC), glutathione (GSH), and bovine serum albumin via their cysteine residues was then examined. NAC and GSH afforded two mono-adducts and one di-adduct, which were identified by NMR and MS analysis. It was also found that EQ was oxidized to EQ-di-quinone in cells expressing human tyrosinase. Finally, it was confirmed that the EQ-oligomer, the EQ oxidation product, exerted potent pro-oxidant activity by oxidizing GSH to the oxidized GSSG and concomitantly producing H2O2. These results suggest that EQ-quinones could be cytotoxic to melanocytes due to their binding to cellular proteins. Full article
(This article belongs to the Special Issue Antioxidant and Prooxidant Properties of Flavonoids)
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17 pages, 2563 KiB  
Article
Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study
by Miriama Simunkova, Zuzana Barbierikova, Klaudia Jomova, Lenka Hudecova, Peter Lauro, Saleh H. Alwasel, Ibrahim Alhazza, Christopher J. Rhodes and Marian Valko
Int. J. Mol. Sci. 2021, 22(4), 1619; https://doi.org/10.3390/ijms22041619 - 5 Feb 2021
Cited by 99 | Viewed by 9391
Abstract
Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which [...] Read more.
Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways. Indeed, this matter has already been the focus of a number of published studies and reviews. The aim of the present study was to elucidate the antioxidant vs. prooxidant properties of flavonoids in the presence of the redox-active metal, copper (II) ion, by means of the Fenton reaction. The specific motivation of this work is that, since an increased level of Cu(II) ions is known to be associated with many disease states such as neurological conditions (Alzheimer’s disease) and cancer, any interaction between these ions and flavonoids might affect the outcome of therapeutic uses of the latter. The structure of the Cu-kaempferol complex in DMSO was investigated by means of low temperature EPR spectroscopy, which confirmed the existence of at least two distinct coordination environments around the copper (II) ion. UV vis-spectra of kaempferol and its Cu(II) complex in DMSO revealed an interaction between the 5-OH (A ring) group and the 4-CO (C ring) group of kaempferol with Cu(II) ions. An ABTS assay confirmed that kaempferol acted as an effective radical scavenger, and that this effect was further enhanced in the form of the Cu(II)-kaempferol complex. Quantitative EPR spin trapping experiments, using DMPO as the spin trap, confirmed suppression of the formation of a mixture of hydroxyl, superoxide, and methyl radicals, in a Fenton reaction system, upon coordination of kaempferol to the redox-active Cu(II) ions, by 80% with respect to the free Cu(II) ions. A viscometric study revealed a better DNA-intercalating ability of the Cu-kaempferol complex than for free kaempferol, essential for conferring anticancer activity of these substances. The results of the viscometric measurements were compared with those from a DNA damage study of Cu-kaempferol complexes in a Fenton reaction system, using gel electrophoresis. At low concentrations of kaempferol (Cu–kaempferol ratios of 1:1 and 1:2), a very weak protective effect on DNA was noted, whereas when kaempferol was present in excess, a significant DNA-protective effect was found. This can be explained if the weakly intercalated kaempferol molecules present at the surface of DNA provide protection against attack by ROS that originate from the Fenton reaction involving intercalated Cu(II)-kaempferol complexes. Following the application of ROS scavengers, L-histidine, DMSO, and SOD, gel electrophoresis confirmed the formation of singlet oxygen, hydroxyl radicals, and superoxide radical anions, respectively. We propose that the prooxidant properties of Cu-kaempferol complexes may provide anticancer activity of these substances. When present in excess, kaempferol displays antioxidant properties under Cu-Fenton conditions. This suggests that kaempferol might prove a suitable candidate for the prevention or treatment of oxidative stress related medical conditions that involve a disturbed metabolism of redox metals such as copper, for example, Menkes disease, and neurological disorders, including Alzheimer’s disease. For the potential use of kaempferol in clinical practice, it will be necessary to optimize the dose size and critical age of the patient so that this flavonoid may be beneficial as a preventive drug against cancer and neurological disorders. Full article
(This article belongs to the Special Issue Antioxidant and Prooxidant Properties of Flavonoids)
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18 pages, 9110 KiB  
Article
Anti-Inflammatory and Proliferative Properties of Luteolin-7-O-Glucoside
by Alessandro De Stefano, Sabrina Caporali, Nicola Di Daniele, Valentina Rovella, Carmine Cardillo, Francesca Schinzari, Marilena Minieri, Massimo Pieri, Eleonora Candi, Sergio Bernardini, Manfredi Tesauro and Alessandro Terrinoni
Int. J. Mol. Sci. 2021, 22(3), 1321; https://doi.org/10.3390/ijms22031321 - 28 Jan 2021
Cited by 79 | Viewed by 5745
Abstract
Flavonoids display a broad range of structures and are responsible for the major organoleptic characteristics of plant-derived foods and beverages. Recent data showed their activity, and in particular of luteolin-7-O-glucoside (LUT-7G), in reduction of oxidative stress and inflammatory mechanisms in different physiological systems. [...] Read more.
Flavonoids display a broad range of structures and are responsible for the major organoleptic characteristics of plant-derived foods and beverages. Recent data showed their activity, and in particular of luteolin-7-O-glucoside (LUT-7G), in reduction of oxidative stress and inflammatory mechanisms in different physiological systems. In this paper, we tried to elucidate how LUT-7G could exert both antioxidant and anti-inflammatory effects in endothelial cells cultured in vitro. Here, we showed that LUT-7G is able to inhibit the STAT3 pathway, to have an antiproliferative action, and an important antioxidant property in HUVEC cells. These properties are exerted by the flavone in endothelial through the transcriptional repression of a number of inflammatory cytokines and their receptors, and by the inhibition of ROS generation. ROS and STAT3 activation has been correlated with the production of oxysterols and other hydroxylated fatty acids, and they have been recognized important as players of atherogenesis and cardiocirculatory system diseases. The analysis of the general production pathway of these hydroxylated species, showed a strong decrease of cholesterol hydroxylated species such as 7-alpha-hydroxicholesterol, 7-beta-hydroxicholesterol by the treatment with LUT-7G. This confirms the anti-inflammatory properties of LUT-7G also in the endothelial district, showing for the first time the molecular pathway that verify previous postulated cardiovascular benefits of this flavone. Full article
(This article belongs to the Special Issue Antioxidant and Prooxidant Properties of Flavonoids)
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Review

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20 pages, 1372 KiB  
Review
Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond
by Zdeněk Kejík, Robert Kaplánek, Michal Masařík, Petr Babula, Adam Matkowski, Petr Filipenský, Kateřina Veselá, Jakub Gburek, David Sýkora, Pavel Martásek and Milan Jakubek
Int. J. Mol. Sci. 2021, 22(2), 646; https://doi.org/10.3390/ijms22020646 - 11 Jan 2021
Cited by 111 | Viewed by 10313
Abstract
Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its [...] Read more.
Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review. Full article
(This article belongs to the Special Issue Antioxidant and Prooxidant Properties of Flavonoids)
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