The hydroperoxyl and superoxide anion radical scavenging activity of anthocyanidins in physiological environments: Theoretical insights into mechanisms and kinetics

Urolithin D: A promising metabolite of ellagitannin in combatting oxidative stress

The objective of this research is to examine the function of urolithin D (UroD, 3,4,8,9-tetrahydroxy-6H-benzo[c]chromen-6-one), a metabolite obtained from ellagitannins, in the mitigation of oxidative stress. The research is based on estimating the mechanisms through which UroD acts as an antioxidant under physiological conditions, emphasizing standard antioxidant mechanisms such as formal Hydrogen Aatom Transfer (f-HAT), Radical Adduct Formation (RAF)/Radical Coupling Formation (RCF), and Single Electron Transfer followed by Proton Transfer (SET-PT). This study utilised advanced quantum mechanical techniques, specifically density functional theory (DFT) and the Quantum Mechanics-based test for Overall free Radical Scavenging activity (QM-ORSA) methodology, to assess the thermodynamic and kinetic parameters of UroD in the presence of reactive radical species HOO•, CH3OO• and CCl3OO•. The estimated overall rate constants (koverall) indicate a reactivity order of CCl3OO• (koverall = 2.06 × 1010 M-1s-1) > HOO• (koverall = 2.59 × 109 M-1s-1) > CH3OO• (koverall = 1.89 × 109 M-1s-1). The examination of the relative proportions of products (%) indicates that UroD exhibits antiradical action primarily through all examined mechanisms, with the predominant involvement of mononion and dianion acid-base species. In addition to its capacity to directly counteract ROS, UroD can restore oxidative DNA damage, specifically targeting oxidative byproducts commonly associated with 2-deoxyguanosine (2 dG), which are susceptible to oxidative stress. The UroD regenerates G-centered radical cations (2 dG•+) through the SET mechanism, C-centered radicals (2 dG•) in the sugar moiety through f-HAT, and repairs i-OH-2dG lesions through sequential hydrogen atom transfer dehydration (SHATD). Additionally, the radical products formed during antioxidant action can be regenerated in the presence of O2•- into anionic species, which are subsequently protonated into neutral species that can re-engage in antioxidant activity. These findings underscore the efficiency of UroD in scavenging free radicals and suggest its potential role in preserving cellular integrity and protecting against oxidative stress-related diseases.

A Comprehensive Experimental and Theoretical Investigation of the Antioxidant Properties of Hispidin and Isohispidin

This study provides a comprehensive analysis of the antioxidant activity of hispidin (His) and its tautomer isohispidin (IsoH) using DFT calculations, corroborated by experimental data. Under physiological conditions, both tautomers demonstrated significant scavenging capacity for the HO• radical, with koverall ranging from 4.48 × 109 to 2.06 × 1010 M-1 s-1 in lipid media and 3.24 × 1010 M-1 s-1 in water. Mechanistic analysis revealed that the radical adduct formation (RAF) mechanism is dominant in lipid environments, whereas both RAF and single electron transfer (SET) operate nonselectively in water. Hispidin also exhibited strong scavenging capacity for the HOO• radical in water (koverall = 1.40 × 108 M-1 s-1), but its reactivity in lipid environments was comparatively lower, with koverall of 1.40 × 102 M-1 s-1 for His and 1.94 × 104 M-1 s-1 for IsoH. The f-HAT mechanism was identified as the predominant pathway in lipid media, while both f-HAT and SET contribute to HOO• scavenging in water. Additionally, hispidin demonstrated a strong ability to chelate copper(II) ions, effectively inhibiting HO• radical formation via the Fenton reaction. The theoretical results align well with the experimental data from the DPPH and ABTS assays, indicating that hispidin is a potent antioxidant under physiological conditions.

Phytochemistry and Biological Activities of Hedeoma piperita Benth. (Quiensabe)

Hedeoma piperita Benth. (Lamiaceae) is a native medicinal plant from Mexico. It grows in pine, oak, and oyamel forests, as well as grasslands. In the Purépecha Plateau of Michoacán, it is called quiensabe and traditionally used to treat stomach pain, colic, cough, and low blood pressure, among other ailments. This study aimed to determine the phytochemical profile of infusions and ethanolic extracts of the stems and green and purple leaves of H. piperita collected in Cherán, Michoacán. Total phenols, flavonoids, anthocyanins, and terpenoids were analyzed using UV-visible spectrophotometry; specific phenolic acids and flavonoids were detected by high performance thin layer chromatography (HPTLC); and the volatile profile of stems, green and purple leaves was determined by solid phase microextraction in GC-MS. Biological activities such as antioxidant activities (via DPPH and ABTS methods), antihypertensive activities (angiotensin converting enzyme (ACE) inhibition), antibacterial activities (minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC), anti-inflammatory activities (xanthine oxidase enzyme (XOD) inhibition) and antidiabetic activities (α-glucosidase enzyme inhibition) were evaluated in vitro. Results showed key compounds like rosmarinic acid, luteolin, menthone, menthol, and pulegone were identified using HPTLC and SPME/GC-MS, with organ-specific variations. Green and purple leaves infusions inhibited DPPH and ABTS+ by 90-99% (IC50 3.3-3.8 and 7.4-11.5 µg/mL, respectively) and purple leaves infusion showed a 69.88% XOD enzyme inhibition (IC50 47.991 µg/mL) and an 85.12% α-glucosidase enzyme inhibition (IC50 72.49 µg/mL). Purple leaves ethanolic extract exhibited the lowest MIC and MBC against Shigella flexneri and ACE inhibition at 97.25% (IC50 11.19 µg/mL). These results demonstrate the biological potential of H. piperita in the development of natural drugs and expand its use as an herbal remedy.

Comparative Study of pH-Responsive and Aggregation Stability of Bosutinib-Loaded Nanogels Comprising Gelatin Methacryloyl, Carboxymethyl Dextran, and Hyaluronic Acid for Controlled Drug Delivery in Colorectal Cancer: An Extensive In Vitro Investigation

This study investigates the use of pH-responsive nanogels for delivering Bosutinib (BOSU) in colon cancer treatment. Nanogels were formulated using three polymers: hyaluronic acid (HA), carboxymethyl dextran (CMD), and gelatin methacryloyl (GelMA). These nanogels achieved high drug entrapment efficiencies (80-90%) through polymer mixing with BOSU, followed by EDC/NHS cross-linking and sonication. The nanogels were stable, with negative zeta potentials (-20 to -30 mV) and particle sizes between 100 and 200 nm. Fourier-transform infrared analysis confirmed successful methacrylation in GelMA nanogels. Sustained BOSU release at pH 5.0 was observed, resembling tumor environments, compared to slower release at normal pH (7.4). Cytotoxicity tests showed 70-80% cell survival reduction in HCT116 colon cancer cells at higher doses, and GelMA-BOSU nanogels notably reduced cell migration. Antiangiogenic effects were confirmed in a chick chorioallantoic membrane model, highlighting the potential of these nanogels for targeted BOSU delivery in colon cancer therapy.

Antioxidant Activity of Anthocyanins and Anthocyanidins: A Critical Review

Anthocyanins are the main plant pigments responsible for the color of flowers, fruits, and vegetative organs of many plants, and are applied also as safe food colorants. They are efficient antioxidants. In this review, the reactivity of anthocyanins and their aglycones, anthocyanidins, in the main antioxidant assays, and their reactions with reactive oxygen and nitrogen species, effects of interactions with other compounds and metal ions on the antioxidant activity of anthocyanins and the electrochemical properties of anthocyanins are presented. Numerous cases of attenuation of oxidative stress at the cellular and organismal levels by anthocyanins are cited. The direct and indirect antioxidant action of anthocyanins, the question of the specificity of anthocyanin action in complex extracts, as well as limitations of cellular in vitro assays and biomarkers used for the detection of antioxidant effects of anthocyanins, are critically discussed.

Can Rice Growth Substrate Substitute Rapeseed Growth Substrate in Rapeseed Blanket Seedling Technology? Lesson from Reactive Oxygen Species Production and Scavenging Analysis

Rapeseed (Brassica napus L.) seedlings suffering from inappropriate growth substrate stress will present poor seedling quality. However, the regulatory mechanism for the production and scavenging of reactive oxygen species (ROS) caused by this type of stress remains unclear. In the current study, a split plot experiment design was implemented with two crop growth substrates-a rice growth substrate (RIS) and rapeseed growth substrate (RAS)-as the main plot and two genotypes-a hybrid and an open-pollinated variety (Zheyouza 1510 and Zheyou 51, respectively)-as the sub-plot. The seedling quality was assessed, and the ROS production/scavenging capacity was evaluated. Enzymatic and non-enzymatic systems, including ascorbic acid and glutathione metabolism, and RNA-seq data were analyzed under the two growth substrate treatments. The results revealed that rapeseed seedling quality decreased under RIS, with the plant height, maximum leaf length and width, and aboveground dry matter being reduced by 187.7%, 64.6%, 73.2%, and 63.8% on average, respectively, as compared to RAS. The main type of ROS accumulated in rapeseed plants was hydrogen peroxide, which was 47.8% and 14.1% higher under RIS than under RAS in the two genotypes, respectively. The scavenging of hydrogen peroxide in Zheyouza 1510 was the result of a combination of enzymatic systems, with significantly higher peroxidase (POD) and catalase (CAT) activity as well as glutathione metabolism, with significantly higher reduced glutathione (GSH) content, under RAS, while higher oxidized glutathione (GSSH) was observed under RIS. However, the scavenging of hydrogen peroxide in Zheyou 51 was the result of a combination of elevated oxidized ascorbic acid (DHA) under RIS and higher GSH content under RAS. The identified gene expression levels were in accordance with the observed enzyme expression levels. The results suggest that the cost of substituting RAS with RIS is a reduction in rapeseed seedling quality contributing to excessive ROS production and a reduction in ROS scavenging capacity.

The inhibitory potential of 4,7-dihydroxycoumarin derivatives on ROS-producing enzymes and direct HOO•/o2• - radical scavenging activity - a comprehensive kinetic DFT study

This study examined the antiradical activity of three synthesized coumarin derivatives: (E)-3-(1-((2-hydroxyphenyl)amino)ethylidene)-2,4-dioxochroman-7-yl acetate (A1-OH), (E)-3-(1-((3-hydroxyphenyl)amino)ethylidene)-2,4-dioxochroman-7-yl acetate (A2-OH), and (E)-3-(1-((4-hydroxyphenyl)amino)ethylidene)-2,4-dioxochroman-7-yl acetate (A3-OH) against HOO•/O2•- radical species. The investigation included electron spin resonance (ESR) measurements and a DFT kinetic study. Thermodynamic and kinetic parameters of antiradical mechanisms-Formal Hydrogen Atom Transfer (f-HAT), Radical Adduct Formation (RAF), Sequential Proton Loss followed by Electron Transfer (SPLET), and Single-Electron Transfer followed by Proton Transfer (SET-PT)-were evaluated using the Quantum Mechanics-based test for Overall Free Radical Scavenging Activity (QM-ORSA) under physiological conditions. ESR results indicated antiradical activity decreased in the sequence A1-OH (58.7%) > A2-OH (57.5%) > A3-OH (53.1%). Kinetic analysis revealed the f-HAT mechanism dominated HOO• inactivation. A newly formulated Sequential Proton Loss followed by Radical Adduct Formation (SPL-RAF) mechanism described interactions with O2•-. The activity toward O2•- was A2-OH (1.26 × 106 M-1s-1) > A3-OH (7.71 × 105 M-1s-1) > A1-OH (4.22 × 105 M-1s-1). Molecular docking and dynamics studies tested inhibitory capability against enzymes producing reactive species: Lipoxygenase (LOX), Myeloperoxidase (MPO), NAD(P)H oxidase (NOX), and Xanthine Oxidase (XOD). Affinity to enzymes decreased in the order: XOD > LOX > NOX > MPO.

Mechanistic Insights into the Antioxidant and Pro-oxidant Activities of Bromophenols from Marine Algae: A DFT Investigation

Marine algae are a rich source of aromatic secondary metabolites, with bromophenols (BPs) receiving particular attention due to their health benefits. Despite extensive research on BPs, the understanding of their antioxidant potential, as well as their mechanisms of action at the molecular level, remains incomplete. This study utilized density functional theory (DFT) to systematically elucidate the antioxidant and pro-oxidant mechanisms of the main BP scaffolds under physiological conditions. It was found that BPs exhibit potent antioxidant capacity in both polar and lipid environments. In lipid media, the formal hydrogen transfer mechanism has been identified as the exclusive antiradical pathway. The position of bromine atoms significantly influenced the activity, particularly in scaffolds containing one hydroxyl group. However, no significant effect was observed in scaffolds with two hydroxyl groups. In water, monodeprotonated BPs showed key radical scavenging activity, with different mechanisms favored depending on the configuration of the hydroxyl groups. Additionally, BPs, particularly those bearing a catechol moiety, exhibit secondary antioxidant activity by reducing the production of hydroxyl radicals via the ascorbic acid anion pathway. These findings provide further validation of the potent antioxidant properties of BPs and shed light on their mechanism of action in physiological environments.

Enhancing the Antioxidant Potential of Weissella confusa PP29 Probiotic Media through Incorporation of Hibiscus sabdariffa L. Anthocyanin Extract

Lactic acid bacteria (LAB) produce important metabolites during fermentation processes, such as exopolysaccharides (EPS), which represent powerful natural antioxidants. On the other hand, H. sabdariffa L. anthocyanin extracts protect LAB and support their development. This study uncovers for the first time, the antioxidant profile of Weissella confusa PP29 probiotic media and focuses on elevating its impressive antioxidant attributes by synergistically integrating H. sabdariffa L. anthocyanin extract. The multifaceted potential of this innovative approach is explored and the results are remarkable, allowing us to understand the protective capacity of the fermented product on the intestinal mucosa. The total phenolic content was much lower at the end of the fermentation process compared to the initial amount, confirming their LAB processing. The DPPH radical scavenging and FRAP of the fermented products were higher compared to ascorbic acid and antioxidant extracts, while superoxide anion radical scavenging and lipid peroxidation inhibitory activity were comparable to that of ascorbic acid. The antioxidant properties of the fermented products were correlated with the initial inoculum and anthocyanin concentrations. All these properties were preserved for 6 months, demonstrating the promising efficacy of this enriched medium, underlining its potential as a complex functional food with enhanced health benefits.

The radical scavenging activity of monocaffeoylquinic acids: the role of neighboring hydroxyl groups and pH levels

Caffeoylquinic acids (CQAs) are well-known antioxidants. However, a key aspect of their radical scavenging activity - the mechanism of action - has not been addressed in detail thus far. Here we report on a computational study of the mechanism of activity of CQAs in scavenging hydroperoxyl radicals. In water at physiological pH, the CQAs demonstrated ≈ 104 times higher HOO˙ antiradical activity than in lipid medium (k(lipid) ≈ 104 M-1 s-1). The activity in the aqueous solution was determined by the hydrogen transfer mechanism of the adjacent hydroxyl group (O6'-H) of the dianion states (Γ = 93.2-95.2%), while the single electron transfer reaction of these species contributed 4.8-6.8% to the total rate constants. The kinetics estimated by the calculations are consistent with experimental findings in water (pH = 7.5), yielding a kcalculated/kexperimental = 2.4, reinforcing the reliability and precision of the computational method and demonstrating its utility for evaluating radical reactions in silico. The results also revealed the pH dependence of the HOO˙ scavenging activity of the CQAs; activity was comparable for all compounds below pH 3, however at higher pH values 5CQA reacted with the HOO˙ with lower activity than 3CQA or 4CQA. It was also found that CQAs are less active than Trolox below pH 4.7, however over pH 5.0 they showed higher activity than the reference. The CQAs had the best HOO˙ antiradical activity at pH values between 5.0 and 8.6. Therefore, in the physiological environment, the hydroperoxyl antiradical capacity of CQAs exhibits similarity to renowned natural antioxidants including resveratrol, ascorbic acid, and Trolox.

Antiradical Activity of Lignans from Cleistanthus sumatranus: Theoretical Insights into the Mechanism, Kinetics, and Solvent Effects

Sumatranus lignans (SL) isolated from Cleistanthus sumatranus have demonstrated bioactivities, e.g., they were shown to exhibit immunosuppressive properties in previous research. Their structure suggests potential antioxidant activity that has not attracted any attention thus far. Consistently, a comprehensive analysis of the antioxidant activity of these compounds is highly desirable with the view of prospective medical applications. In this work, the mechanism and kinetics of the antiradical properties of SL against hydroperoxyl radicals were studied by using calculations based on density functional theory (DFT). In the lipid medium, it was discovered that SL reacted with HOO• through the formal hydrogen transfer mechanism with a rate constant of 101-105 M-1 s-1, whereas in aqueous media, the activity primarily occurred through the sequential proton loss electron transfer mechanism with rate constants of 102-108 M-1 s-1. In both lipidic and aqueous environments, the antiradical activity of compounds 6 and 7 exceeds that of resveratrol, ascorbic acid, and Trolox. These substances are therefore predicted to be good radical scavengers in physiological environments.

Exploring the Antioxidant Properties of Caffeoylquinic and Feruloylquinic Acids: A Computational Study on Hydroperoxyl Radical Scavenging and Xanthine Oxidase Inhibition

Caffeoylquinic (5-CQA) and feruloylquinic (5-FQA) acids, found in coffee and other plant sources, are known to exhibit diverse biological activities, including potential antioxidant effects. However, the underlying mechanisms of these phenolic compounds remain elusive. This paper investigates the capacity and mode of action of 5-CQA and 5-FQA as natural antioxidants acting as hydroperoxyl radical scavengers and xanthine oxidase (XO) inhibitors. The hydroperoxyl radical scavenging potential was investigated using thermodynamic and kinetic calculations based on the DFT method, taking into account the influence of physiological conditions. Blind docking and molecular dynamics simulations were used to investigate the inhibition capacity toward the XO enzyme. The results showed that 5-CQA and 5-FQA exhibit potent hydroperoxyl radical scavenging capacity in both polar and lipidic physiological media, with rate constants higher than those of common antioxidants, such as Trolox and BHT. 5-CQA carrying catechol moiety was found to be more potent than 5-FQA in both physiological environments. Furthermore, both compounds show good affinity with the active site of the XO enzyme and form stable complexes. The hydrogen atom transfer (HAT) mechanism was found to be exclusive in lipid media, while both HAT and SET (single electron transfer) mechanisms are possible in water. 5-CQA and 5-FQA may, therefore, be considered potent natural antioxidants with potential health benefits.

Response Surface Optimization for Investigating Antioxidant Potential of Camellia Sinensis and Withania Somnifera in Synergistic Manner

The paper highlights the synergistic potential of the novel combination of Camellia sinensis (Kangra green tea) and Withania somnifera (Ashwagandha). One variable at a time approach was used to find antioxidant potential of C. sinensis and W. somnifera alone and in combination. Optimization of antioxidant potential was done by using different plant concentrations of C. sinensis and W. somnifera using a statistical approach of central composite design (CCD) of RSM (response surface methodology). Initial antioxidant activity during optimization of the solvent system was observed in methanol for C. sinensis with DPPH, superoxide radical scavenging assay and hydrogen peroxide scavenging assay (44.9 ± 0.62, 43.77 ± 0.10, 43.88 ± 0.10% scavenging) and for W. somnifera (40.22 ± 0.39, 43.29 ± 1.12, 41.88 ± 0.11% scavenging), respectively. Initially, IC50 has been calculated for C. sinensis (235.26 ± 0.012 μg/mL) and W. somnifera (256.39 ± 0.43 μg/mL) in methanol. Before statistical optimization, the maximum synergistic antioxidant potential of C. sinensis (200 μg/mL) and W. somnifera (150 μg/mL) with DPPH assay, superoxide radical scavenging and hydrogen peroxide scavenging assay was found to be 56.57 ± 0.62, 56.99 ± 0.42, 55.44 ± 0.53% scavenging, respectively. IC50 value has been calculated for C. sinensis + W. somnifera (IC50 = 215.47 ± 0.06 μg/mL). Optimization of plant concentration using CCD of RSM resulted in enhancement of antioxidant potential of C. sinensis (200.5 μg/mL) and W. somnifera (200.5 μg/mL) was found to be 78.01 ± 0.01% scavenging when compared to the initial antioxidant potential, i.e., 56.57 ± 0.62% scavenging shows a 1.37-fold increase from initial antioxidant potential. Research unveils that using various combination of C. sinensis and W. somnifera enhance the antioxidant potential in vitro.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40011-022-01423-6.

The hydroperoxyl radical scavenging activity of natural hydroxybenzoic acids in oil and aqueous environments: Insights into the mechanism and kinetics

Foods that contain hydroxybenzoic acid derivatives (HBA) include red fruits, black radish, onion, and potato peel. HBA are widely known for their anti-inflammatory, anti-cancer, and especially antioxidant capabilities; however, a comprehensive study of the mechanism and kinetics of the antiradical action of these compounds has not been performed. Here, we report a study on the mechanisms and kinetics of hydroperoxyl radical scavenging activity of HBA by density functional theory (DFT) calculations. According to the results, HBA exert low HOO^• antiradical activity in the nonpolar environment with overall rate constants in the range of k_overall = 5.90 × 10^-6 - 4.10 × 10³ M^-1 s^-1. However, most HBA exhibit significant HOO^• antiradical activity (k_overall = 10⁵ - 10⁸ M^-1 s^-1) by the single electron transfer (SET) reaction of the phenoxide anions in water at physiological pH. The overall rate constant increases with increasing pH values in the majority of the substances studied. At pH ≤ 4, gentisic acid had the best HOO^• antiradical activity (log(k_overall) = 3.7-4.8), however at pH > 4, the largest HOO^• radical scavenging activity (log(k_overall) = 4.8-9.8) was almost exclusively found for gallic and syringic acids. Salicylic and 5-sulphosalicylic acids have the lowest antiradical activity across most of the pH range. The activities of the majority of the acids in this study are faster than the reference compound Trolox. Thus, in the aqueous physiological environment, these HBA are good natural antioxidants.

The hydroperoxyl antiradical activity of natural hydroxycinnamic acid derivatives in physiological environments: the effects of pH values on rate constants

Quantum chemistry calculations suggest that hydroxycinnamic acid derivatives are good natural antioxidants in aqueous solutions.

Insights on the kinetics and mechanisms of the peroxyl radical scavenging capacity of caftaric acid: the important role of the acid–base equilibrium

Considering the acid–base equilibrium, caftaric acid has been shown to be one of the best antioxidants among phenolic acids in the aqueous physiological environment.