Ascorbic acid modifies the free radical scavenging behaviour of catechin: An insight into the mechanism

The ferryl generation by fenton reaction driven by catechol

The Fenton and Fenton-like reactions are based on the decomposition of hydrogen peroxide catalyzed by Fe(II), primarily producing highly oxidizing hydroxyl radicals (HO∙). While HO∙ is the main oxidizing species in these reactions, Fe(IV) (FeO2+) generation has been reported as one of the primary oxidants. FeO2+ has a longer lifetime than HO∙ and can remove two electrons from a substrate, making it a critical oxidant that may be more efficient than HO∙. It is widely accepted that the preferential generation of HO∙ or FeO2+ in the Fenton reaction depends on factors such as pH and Fe: H2O2 ratio. Reaction mechanisms have been proposed to generate FeO2+, which mainly depend on the radicals generated in the coordination sphere and the HO∙ radicals that diffuse out of the coordination sphere and react with Fe(III). As a result, some mechanisms are dependent on prior HO∙ radical production. Catechol-type ligands can induce and amplify the Fenton reaction by increasing the generation of oxidizing species. Previous studies have focused on the generation of HO∙ radicals in these systems, whereas this study investigates the generation of FeO2+ (using xylidine as a selective substrate). The findings revealed that FeO2+ production is increased compared to the classical Fenton reaction and that FeO2+ generation is mainly due to the reactivity of Fe(III) with HO∙ from outside the coordination sphere. It is proposed that the inhibition of FeO2+ generation via HO∙ generated from inside the coordination sphere is caused by the preferential reaction of HO∙ with semiquinone in the coordination sphere, favoring the formation of quinone and Fe(III) and inhibiting the generation of FeO2+ through this pathway.

Intermolecular hydrogen bonds between catechin and theanine in tea: slow release of the antioxidant capacity by a synergetic effect

The health benefits of drinking tea stem from it being rich in polyphenols and other physiologically-active substances. Thus, exploring the synergistic effect between polyphenols and a variety of physiologically-active substances can contribute to our understanding of how tea benefits health. In this work, we have studied the interactions between catechin and theanine, exploring the synergetic antioxidant mechanism of the two molecules. Electrochemical characterization results showed that the oxidation peak current of catechin decreased gradually with the concentration of theanine, which is due to theanine spontaneously binding to catechin through intermolecular hydrogen bonds and forming molecular clusters via two hydrogen bonds. The binding constant is 4.75 at room temperature. The molecular clusters reduce the diffusion coefficient of catechin in solution, leading to the slow release of its antioxidant capacity (ability to effectively inhibit free radical oxidation reactions). Density functional theory calculations were also performed and verified the binding behavior. In identifying the synergistic effect between catechin and theanine on the antioxidant capacity of tea, this study adds to our understanding of the efficacy of tea polyphenols.

The health benefits of drinking tea stem from it being rich in polyphenols and other physiologically-active substances.

Thiogenistein-Antioxidant Chemistry, Antitumor Activity, and Structure Elucidation of New Oxidation Products

Isoflavonoids such as genistein (GE) are well known antioxidants. The predictive biological activity of structurally new compounds such as thiogenistein (TGE)–a new analogue of GE–becomes an interesting way to design new drug candidates with promising properties. Two oxidation strategies were used to characterize TGE oxidation products: the first in solution and the second on the 2D surface of the Au electrode as a self-assembling TGE monolayer. The structure elucidation of products generated by different oxidation strategies was performed. The electrospray ionization mass spectrometry (ESI-MS) was used for identifying the product of electrochemical and hydrogen peroxide oxidation in the solution. Fourier transform infrared spectroscopy (FT-IR) with the ATR mode was used to identify a product after hydrogen peroxide treatment of TGE on the 2D surface. The density functional theory was used to support the experimental results for the estimation of antioxidant activity of TGE as well as for the molecular modeling of oxidation products. The biological studies were performed simultaneously to assess the suitability of TGE for antioxidant and antitumor properties. It was found that TGE was characterized by a high cytotoxic activity toward human breast cancer cells. The research was also carried out on mice macrophages, disclosing that TGE neutralized the production of the LPS-induced reactive oxygen species (ROS) and exhibits ABTS (2,2′-azino-bis-3-(ethylbenzothiazoline-6-sulphonic acid) radical scavenging ability. In the presented study, we identified the main oxidation products of TGE generated under different environmental conditions. The electroactive centers of TGE were identified and its oxidation mechanisms were proposed. TGE redox properties can be related to its various pharmacological activities. Our new thiolated analogue of genistein neutralizes the LPS-induced ROS production better than GE. Additionally, TGE shows a high cytotoxic activity against human breast cancer cells. The viability of MCF-7 (estrogen-positive cells) drops two times after a 72-h incubation with 12.5 μM TGE (viability 53.86%) compared to genistein (viability 94.46%).

Pinus koraiensis polyphenols: structural identification, in vitro antioxidant activity, immune function and inhibition of cancer cell proliferation

Herein, polyphenols were extracted from Pinus koraiensis bark and characterized. Besides, the in vitro antioxidant activity, inhibition effect on cancer cells and the activity of the immune system were investigated. The results showed that the main component of Pinus koraiensis bark was 3,5,7,3',5'-pentahydroxydihydroflavone. PKB polyphenols demonstrated a high antioxidant activity during in vitro investigation. In vivo immunological function studies on oxidatively injured mice revealed that Pinus koraiensis bark polyphenols effectively improved the survival status of irradiated mice. PKBP also increased the spleen and thymus index of mouse immunoregulatory organs. The results indicated that the phagocytic ability of mononuclear macrophages was increased. Comparing the cell distribution of the PKBP administered group and the model group, the PKBP-administered group reduced the cells arrested in the G1 phase, while the number of cells increased in the S and G2 phases. PKBP effectively protected the mouse immune system and reduced the immune suppression caused by radiation. These findings also confirmed that oxidative damaged cells induced by radiation could be repaired. PKBP had the highest inhibitory activity on colon cancer cells HT29, breast cancer cells MFC-7, gastric cancer cells BGC-823 and cervical cancer HeLa and HT29 cancer cells. PKB polyphenols could effectively induce the production of DNA-Ladder fragments and cause DNA damage in cancer cells. PKBP also blocked the cycle of cancer cells in the G2 phase, stopped cell division and induced cancer cell apoptosis. Analysis of cell apoptosis by Annexin V-FTIC/PI double staining indicated that PKBP inhibited HT29 cancer cell proliferation.

Antioxidant Motifs in Flavonoids: O-H versus C-H Bond Dissociation

Flavonoids provide potential health benefits due to their antioxidant properties. The antioxidant activity of natural flavonoids is primarily exerted by phenolic hydroxyl groups; however, C-H bonds also contribute to these properties. In this study, the contributions of phenolic groups and C-H bonds to the antioxidant properties of 13 flavonoids were investigated by using the (RO)B3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) model chemistry in the gas phase and water and ethanol solvents. It was found that the C-H bonds have lower bond dissociation energies than O-H bonds in the 4-carbonyl and/or 3-hydroxyl group containing flavonoids and hence define antioxidant activity. The HOO· radical scavenging of the selected flavonoids is also investigated in detail through the potential energy surface, natural bond orbitals, and kinetic calculations. It was found that the favored radical scavenging mechanism of the flavonoids is hydrogen atom transfer, with the gas phase rate constants in the range of 7.23 × 103-2.07 × 109 L·mol-1·s-1. The results suggest that the flavonoids, isomelacacidin, isoteracacidin, melacacidin, and teracacidin, have antioxidant properties as high as typical phenolic compounds such as quercetin, trans-resveratrol, trolox, and ascorbic acid.

Production of hydroxyl radicals and their relationship with phenolic compounds in white wines

Exposure of white wine to oxygen can cause detrimental effects, such as loss of sensorial characteristics. New antecedents, to the oxidation of wine, establish the importance of the formation of metallic complexes with compounds with adjacent hydroxyls. These complexes could reduce iron, promoting the formation of radicals through the Fenton reaction. The formation of hydroxyl radical (OH) induced by air was found in all 18 white wines analysed by electronic paramagnetic resonance (EPR) spectroscopy. The variation in the OH production was related to the phenolic composition of the wines. The amount of these radicals was linearly related to 5 phenolic compounds (caffeic acid, protocatechuic acid, p-coumaric acid, gentisic acid and syringic acid). Therefore, in this study, the relationship between certain phenolic compounds and the induction and amplification of the OH production was established and was postulated to be a chemical oxidation pathway to the Fenton reaction.

Density functional theory study of the role of benzylic hydrogen atoms in the antioxidant properties of lignans

Antioxidants are a diverse group of chemicals with proven health benefits and thus potential preventive medicine and therapeutic applications. While most of these compounds are natural products, determining their mechanism of radical scavenging and common motifs that contribute to antioxidant activity would allow the rational design of novel antioxidants. Here the origins of the antioxidant properties of ten natural products of the lignan family were studied in silico by calculating their thermochemical properties by using ROB3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) model chemistry. Three conditions were modelled: gas phase, ethanol and water solvents. The results allowed assigning the antioxidant activity to specific moieties and structural features of these compounds. It was found that the benzylic hydrogen atoms are the most likely to be abstracted to form radicals and hence define antioxidant properties in most of the studied compounds. The results also suggested that the most likely mechanism of HOO^• radical scavenging differs by the key moiety: it is hydrogen atom transfer in case the benzylic C-H bonds, however it is proton coupled electron transfer in case of the compounds where O-H bonds are responsible for radical scavenging.

Co-delivery of hydrophobic curcumin and hydrophilic catechin by a water-in-oil-in-water double emulsion

Curcumin and catechin are naturally occurring phytochemicals with extreme sensitivity to oxidation and low bioavailability. We fabricated a water-in-oil-in-water (W/O/W) double emulsion encapsulating hydrophilic catechin and hydrophobic curcumin simultaneously. The co-loaded emulsion was fabricated using a two-step emulsification method, and its physicochemical properties were characterised. Volume-weighted mean size (d43) of emulsion droplets was ≈3.88 μm for blank emulsions, whereas it decreased to ≈2.8-3.0 μm for curcumin and/or catechin-loaded emulsions, which was attributed to their capacity to act as emulsifiers. High entrapment efficiency was observed for curcumin and/or catechin-loaded emulsions (88-97%). Encapsulation of catechin and curcumin within an emulsion increased their stability significantly in simulated gastrointestinal fluid, which resulted in a four-fold augmentation in their bioaccessibility compared to that of freely suspended curcumin and catechin solutions. Co-loading of curcumin and catechin did not have adverse effects on either compound's stability or bioaccessibility.

Toward a new philosophy of preventive nutrition: from a reductionist to a holistic paradigm to improve nutritional recommendations

The reductionist approach has been predominant to date in human nutrition research and has unraveled some of the fundamental mechanisms at the basis of food nutrients (e.g., those that involve deficiency diseases). In Western countries, along with progress in medicine and pharmacology, the reductionist approach helped to increase life expectancy. However, despite 40 y of research in nutrition, epidemics of obesity and diabetes are growing each year worldwide, both in developed and developing countries, leading to a decrease in healthy life years. Yet, interactions between nutrition-health relations cannot be modeled on the basis of a linear cause-effect relation between 1 food compound and 1 physiologic effect but rather from multicausal nonlinear relations. In other words, explaining the whole from the specific by a bottom-up reductionist approach has its limits. A top-down approach becomes necessary to investigate complex issues through a holistic view before addressing any specific question to explain the whole. However, it appears that both approaches are necessary and mutually reinforcing. In this review, Eastern and Western research perspectives are first presented, laying out bases for what could be the consequences of applying a reductionist versus holistic approach to research in nutrition vis-à-vis public health, environmental sustainability, breeding, biodiversity, food science and processing, and physiology for improving nutritional recommendations. Therefore, research that replaces reductionism with a more holistic approach will reveal global and efficient solutions to the problems encountered from the field to the plate. Preventive human nutrition can no longer be considered as "pharmacology" or foods as "drugs."