Mechanism of the OH radical scavenging activity of nordihydroguaiaretic acid: a combined theoretical and experimental study

Novel Flurbiprofen Derivatives as Antioxidant and Anti-Inflammatory Agents: Synthesis, In Silico, and In Vitro Biological Evaluation

In this study, we present the synthesis of five novel compounds by combining flurbiprofen with various substituted 2-phenethylamines. The synthesized derivatives underwent comprehensive characterization using techniques such as 1H- and 13C-NMR spectroscopy, UV-Vis spectroscopy, and high-resolution mass spectrometry (HRMS). Detailed HRMS analysis was performed for each of these newly created molecules. The biological activities of these compounds were assessed through in vitro experiments to evaluate their potential as anti-inflammatory and antioxidant agents. Furthermore, the lipophilicity of these derivatives was determined, both theoretically using the cLogP method and experimentally through partition coefficient (RM) measurements. To gain insights into their binding affinity, we conducted an in silico analysis of the compounds' interactions with human serum albumin (HSA) using molecular docking studies. Our findings reveal that all of the newly synthesized compounds exhibit significant anti-inflammatory and antioxidant activities, with results statistically comparable to the reference compounds. Molecular docking studies further explain the observed in vitro results, shedding light on the molecular mechanisms behind their biological activities. Using in silico method, toxicity was calculated, resulting in LD50 values. Depending on the administration route, the novel flurbiprofen derivatives show lower toxicity compared to the standard flurbiprofen.

Mechanistic Insights on Pd-Catalyzed Three-Component Reactions of Alkynols, Methyl Orthoformate, and Salicylaldehyde Derivatives. Application to the Synthesis of Steroid Chroman Ketals and Spiroketals with Antioxidant Activity

Contrary to our previous report in which a Pd-catalyzed three-component reaction of a steroid alkynol, trimethyl orthoformate, and salicylaldehyde exclusively produced chroman ketals, the same reaction employing 2,5-dihydroxysalicylaldehyde led to a mixture of a chroman ketal and a spiroketal. Provided that both courses of the reaction imply a 4 + 2 inverse demand cycloaddition between an o-quinone methide and an enol ether, density functional theory calculations revealed that the chroman ketal/spiroketal selectivity is governed by both, the rate of the formation of the o-quinone methide and the isomerization of the initially produced exocyclic enol ether─that led to the spiroketal─to its endocyclic partner that produces the chroman ketal. Remarkably, Lewis catalysis is central to the observed reactivity, and the availability of plausible catalytic species controls the overall chemoselectivity. The methodology herein applied and scrutinized enriches the palette of reactions, leading to increased molecular complexity, as demonstrated in the obtained products, whose antioxidant activity and detailed NMR characterization are presented.

Optimization of extraction condition for platycodin D from Platycodon grandiflorum root and verification of its biological activity

Platycosides, major components of Platycodon grandiflorum (PG) extract, have been implicated in a wide range of biological effects. In particular, platycodin D (PD) is a well-known main bioactive compound of Platycosides. Despite the biological significance of PD, optimization of extract condition for PD from PG root has not been well investigated. Here, we established the optimum extraction condition as ethanol concentration of 0%, temperature of 50°C, and extraction time of 11 h to obtain PD-rich P. grandiflorum extract (PGE) by using response surface methodology (RSM) with Box-Behnken design (BBD). The 5.63 mg/g of PD was extracted from the PG root in optimum condition, and this result was close to the predicted PD content. To analyze the biological activity of PGE related to mucin production, we demonstrated the inhibitory effect of PGE on PMA-induced hyperexpression of MUC5AC as well as ERK activation, a signal mediator of MUC5AC expression. Moreover, we showed that PGE had expectorant activity in mice. These results indicated that PGE had sufficient functions as a potential mucoregulator and expectorant for treating diverse airway diseases. Additionally, we confirmed that PGE had antioxidant activity and inhibited LPS-induced proinflammatory cytokines, TNF-α, and IL-6. Taken together, PGE derived from novel optimizing conditions showed various biological effects, suggesting that PGE could be directly applied to the food industry as food material having therapeutic and preventive potential for human airway diseases.

HPLC Analysis and In Vitro and In Silico Evaluation of the Biological Activity of Polyphenolic Components Separated with Solvents of Various Polarities from Helichrysum italicum

Helichrysum italicum has piqued the interest of many researchers in recent years, mostly for its essential oil, but increasingly for its polyphenolic content as well. In the current study, we examine the polyphenolic composition of H. italicum grown in Bulgaria. The polyphenolic complex was fractionated with solvents of various polarities, including hexane, chloroform, ethyl acetate, and butanol, in order to assess the biological impact of the components. HPLC-PDA and UHPLC-MS/MS were used to examine all fractions. The green coffee fingerprint profile was employed as a "surrogate standard" in the polyphenolic components detection approach. From the UHPLC-MS/MS analysis, we identified 60 components of the polyphenolic complex such as quercetin 3-O-glucuronide, quercetin acetyl-glycoside, isorhamnetin acetyl-glycoside, isorhamnetin caffeoyl-glycoside, quercetin caffeoyl-malonyl-glycoside, isorhamnetin coumaroyl-glycoside, coumaroyl-caffeoylquinic acid, and diCQA-acetyl-derivative were first reported in the composition of H. italicum. The biological activity of the fractions was evaluated in vitro and in silico, which included the fight against oxidative stress (hydrogen peroxide scavenging activity (HPSA), hydroxyl radical scavenging activity (HRSA), metal-chelating activity (MChA)) and nitrosative (nitric oxide scavenging activity) (NOSA)), in vitro anti-inflammatory, and anti-arthritic activity. Results are presented as IC50 ± SD μg/mL. The analysis showed that the EtOAc fraction was characterized by highest HPSA (57.12 ± 1.14 μg/mL), HRSA (92.23 ± 1.10 μg/mL), MChA (5.60 ± 0.17 μg/mL), and NOSA (89.81 ± 2.09 μg/mL), while the hexane and chloroform fractions showed significantly higher in vitro anti-inflammatory activity (30.48 ± 2.33 μg/mL, 62.50 ± 1.69 μg/mL) compared to the standard ibuprofen. All three fractions showed potential anti-arthritic activity (102.93 ± 8.62 μg/mL, 108.92 ± 4.42 μg/mL, 84.19 ± 3.89 μg/mL).

Characterization of Polyphenols from Chenopodium botrys after Fractionation with Different Solvents and Study of Their In Vitro Biological Activity

In the present work, we have investigated the polyphenolic composition of Chenopodium botrys from Bulgaria. The polyphenols were fractionated with solvents of varying polarity (n-hexane, chloroform, ethyl acetate, and n-butanol). The fractions were analyzed by HPLC-PDA and UHPLC-MS. The ethyl acetate fraction contained mono- and di-glycosides of quercetin, di-glycosides of kaempferol, and isorhamnetin and monoglycosides of hispidulin and jaceosidine. We found quercetin triglycosides in the butanol fraction. The ethyl acetate and butanol fractions contained 168.82 mg/g Extr and 67.21 mg/g Extr of quercetin glycosides, respectively. The main components of the polyphenolic complex in C. botrys were 6-methoxyflavones (355.47 mg/g Extr), which were found in the chloroform fraction. The flavonoids pectolinarigenin, demethylnobiletin, and isosinensetin, and the glycosides of quercetin (triglycosides, acylglycosides), kaempferol, isorhamnetin, hispidiulin, and jaceosidine, were discovered and reported in Chenopodium botrys for the first time. We used in vitro methods to assess the biological activity against oxidative stress (hydrogen peroxide scavenging activity (HPSA) and hydroxyl radical scavenging activity (HRSA)), nitrosative stress (nitric oxide scavenging activity (NOSA)), anti-inflammatory activity (IAD inhibition), and anti-tryptic activity (ATA). Quercetin mono- and di-glycosides exhibited greater HPSA and HRSA (IC₅₀ = 39.18, 105.03 µg/mL), while 6-methoxyflavones had a greater NOSA (IC₅₀ = 146.59 µg/mL). The same components showed the highest ATA (IC₅₀ ranging from 116.23 to 202.44 µg/mL).

The effect of diphenylethane side-chain substituents on dibenzocyclohexadiene formation and their inhibition of α-synuclein aggregation in vitro

The naturally-occurring di-catechol lignan nordihydroguaiaretic acid (NDGA) and an analog without methyl groups on the butyl linker both undergo intramolecular cyclization at pH 7.4 to form dibenzocyclooctadienes. Both NDGA and these dibenzocyclooctadienes have been shown to prevent in vitro aggregation of α-synuclein, an intrinsically disordered protein associated with Parkinson's disease. NDGA possesses two vicinal methyl groups on the butyl linker and the presence of these methyl groups attenuates the rate of intramolecular cyclization versus the unsubstituted analog, in opposition to the anticipated Thorpe-Ingold effect, likely due to steric repulsions during cyclization. Numerous 1,2-bis-ethane di-catechols are known to inhibit α-synuclein aggregation in vitro and we hypothesize that these compounds undergo a similar intramolecular cyclization and the cyclized products may be responsible for the activity. To test this hypothesis we prepared a series of 1,2-bis-ethane di-catechols with 0, 2 and 4 methyl substituents on the linker. We have confirmed that these compounds undergo intramolecular cyclization to form dibenzocyclohexadienes and that steric interactions between the methyl substituents leads to an increase in the rate of intramolecular cyclization, which is in contrast to what was observed for lignan di-catechols. The rate of cyclization to form six-membered rings is 10-30 times more rapid than formation of eight membered rings and the dibenzocyclohexadienes also prevent in vitro aggregation of α-synuclein.

Elucidation of reactive oxygen species scavenging pathways of norbergenin utilizing DFT approaches

Bergenin is a polyphenolic compound that contains isocoumarin skeletal derived from C-glycosylated 4-O-methylgallic acid. The biological activities of this compound and its derivatives are quite diverse. Recent studies reveal neuroprotective effects in vitro and in vivo in Alzheimer's. Norbergenin is a demethylated form of bergenin, known for better antioxidant capacity and associated with neuroprotective properties through oxidative stress inhibition. This study focused on investigating the scavenging mechanism of norbergenin with the ^•OH, ^•OOH, and O 2 ∙ - as a radical model under physiological and lipid environments. The thermodynamic and kinetic parameters of the hydrogen transfer (HT), single electron transfer (SET), sequential proton lost-electron transfer (SPLET) and radical adduct formation (RAF) mechanisms were determined theoretically by the density functional theory (DFT) at M06-2X/6-311 + + G(d,p) level of theory. Based on the computational results, this compound has proved as an excellent ^•OOH and ^•OH scavenger under physiological conditions better than Trolox and vitamin C, whereas its radical demonstrated as an efficient O 2 ∙ - scavenger.

Lignans as Pharmacological Agents in Disorders Related to Oxidative Stress and Inflammation: Chemical Synthesis Approaches and Biological Activities

Plant lignans exhibit a wide range of biological activities, which makes them the research objects of potential use as therapeutic agents. They provide diverse naturally-occurring pharmacophores and are available for production by chemical synthesis. A large amount of accumulated data indicates that lignans of different structural groups are apt to demonstrate both anti-inflammatory and antioxidant effects, in many cases, simultaneously. In this review, we summarize the comprehensive knowledge about lignan use as a bioactive agent in disorders associated with oxidative stress and inflammation, pharmacological effects in vitro and in vivo, molecular mechanisms underlying these effects, and chemical synthesis approaches. This article provides an up-to-date overview of the current data in this area, available in PubMed, Scopus, and Web of Science databases, screened from 2000 to 2022.

Effect of Fe3+ on Na,K-ATPase: Unexpected activation of ATP hydrolysis

Iron is a key element in cell function; however, its excess in iron overload conditions can be harmful through the generation of reactive oxygen species (ROS) and cell oxidative stress. Activity of Na,K-ATPase has been shown to be implicated in cellular iron uptake and iron modulates the Na,K-ATPase function from different tissues. In this study, we determined the effect of iron overload on Na,K-ATPase activity and established the role that isoforms and conformational states of this enzyme has on this effect. Total blood and membrane preparations from erythrocytes (ghost cells), as well as pig kidney and rat brain cortex, and enterocytes cells (Caco-2) were used. In E1-related subconformations, an enzyme activation effect by iron was observed, and in the E2-related subconformations enzyme inhibition was observed. The enzyme's kinetic parameters were significantly changed only in the Na⁺ curve in ghost cells. In contrast to Na,K-ATPase α2 and α3 isoforms, activation was not observed for the α1 isoform. In Caco-2 cells, which only contain Na,K-ATPase α1 isoform, the FeCl₃ increased the intracellular storage of iron, catalase activity, the production of H₂O₂ and the expression levels of the α1 isoform. In contrast, iron did not affect lipid peroxidation, GSH content, superoxide dismutase and Na,K-ATPase activities. These results suggest that iron itself modulates Na,K-ATPase and that one or more E1-related subconformations seems to be determinant for the sensitivity of iron modulation through a mechanism in which the involvement of the Na, K-ATPase α3 isoform needs to be further investigated.

Synthesis of New 1,2,3,4-Tetrahydroquinoline Hybrid of Ibuprofen and Its Biological Evaluation

Herein we report the obtaining of 1-(3,4-dihydroquinolin-1(2H)-yl)-2- (4-isobutylphenyl)propan-1-one and its characterization. The newly obtained hybrid and its derivatives (hybrids of ibuprofen with 1,2,3,4-tetrahydroisoquinoline, and piperidine) were screened for their in vitro antioxidant, antitryptic, and inhibition of albumin denaturation activity. The lipophilicity was established using both reversed-phase thin layer chromatography and in silico calculations.

On the Antioxidant Properties of L-Kynurenine: An Efficient ROS Scavenger and Enhancer of Rat Brain Antioxidant Defense

L-kynurenine (L-KYN) is an endogenous metabolite, that has been used as a neuroprotective strategy in experimental models. The protective effects of L-KYN have been attributed mainly to kynurenic acid (KYNA). However, considering that L-KYN is prone to oxidation, this redox property may play a substantial role in its protective effects. The aim of this work was to characterize the potential impact of the redox properties of L-KYN, in both synthetic and biological systems. First, we determined whether L-KYN scavenges reactive oxygen species (ROS) and prevents DNA and protein oxidative degradation in synthetic systems. The effect of L-KYN and KYNA (0.1–100 µM) on redox markers (ROS production, lipoperoxidation and cellular function) was compared in rat brain homogenates when exposed to FeSO₄ (10 µM). Then, the effect of L-KYN administration (75 mg/kg/day for 5 days) on the GSH content and the enzymatic activity of glutathione reductase (GR) and glutathione peroxidase (GPx) was determined in rat brain tissue. Finally, brain homogenates from rats pretreated with L-KYN were exposed to pro-oxidants and oxidative markers were evaluated. The results show that L-KYN is an efficient scavenger of ^●OH and ONOO⁻, but not O₂^●– or H₂O₂ and that it prevents DNA and protein oxidative degradation in synthetic systems. L-KYN diminishes the oxidative effect induced by FeSO₄ on brain homogenates at lower concentrations (1 µM) when compared to KYNA (100 µM). Furthermore, the sub-chronic administration of L-KYN increased the GSH content and the activity of both GR and GPx, and also prevented the oxidative damage induced by the ex vivo exposure to pro-oxidants. Altogether, these findings strongly suggest that L-KYN can be considered as a potential endogenous antioxidant.

Lipid Nanoparticles Containing Mixtures of Antioxidants to Improve Skin Care and Cancer Prevention

Oxidative stress, triggered by UV radiation, is one of the major causes of free radical-associated disorders, such as skin cancer. The application of natural compounds (NCs) with antioxidant effects can attenuate free radicals’ accumulation and, therefore, provide a strategy for skin care and cancer prevention. In this work, three natural compounds, naringenin, nordihydroguaiaretic acid (NDGA), and kaempferol, were encapsulated into nanostructured lipid carriers (NLCs) aiming for the development of a formulation for cutaneous application with antioxidant properties. For the experiments, different formulation parameters were evaluated to optimize the NLCs that showed a diameter around 200 nm, which is an adequate particle size for incorporation in cosmetics. Transmission electron microscopy (TEM) analysis confirmed the NLCs’ typical spherical morphology. Encapsulation efficiency (EE) and loading capacity (LC) values revealed an effective production process, with EEs over 90% and LCs near the maximum value. The developed NLCs revealed a prolonged in vitro release of the natural compounds. The NLCs were stable under storage conditions, maintaining their psychochemical characteristics for 30 days. Additionally, they did not show any physical instability in accelerated stability studies, which also suggests long-term stability. Finally, the NCs antioxidant activity was evaluated. Interestingly, the NDGA and kaempferol mixture provided an antioxidant synergic effect. The NLC formulations’ cytotoxicity was tested in vitro in immortalized human keratinocytes (HaCaT). In addition, putative antioxidant effects of the developed NLC formulations against tert-butyl hydroperoxide (t-BHP)-induced oxidative stress were studied, and the NDGA-loaded NLC was revealed to be the one with the most protective effect. Therefore, we concluded that the naringenin, NDGA, and kaempferol incorporation into NLCs constitutes a promising strategy to increase their bioavailability and delivery to the skin.

Free radical scavenging activity of newly designed sesamol derivatives

Recently proposed derivatives of sesamol as better oxidants than the parent molecule are predicted to react faster, with several orders larger rate constants than sesamol itself.

Radical scavenging activity of hydroxycinnamic acids in polar and nonpolar solvents: A computational investigation

The aim of this work is to perform a computational study of the radical scavenging activity of a series of common hydroxycinnamic acids (HCAs) in polar and nonpolar solvents in order to rationalize the experimental order obtained in ethanol and to analyze the solvent effect on mechanism and radical scavenging capacity. The thermodynamics of the main mechanisms, namely, hydrogen atom transfer (HAT), sequential proton loss followed by electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) were investigated at the M05-2X/6-31[Formula: see text]G([Formula: see text]) level of theory using the SMD solvation model. This study shows that the SET-PT mechanism is disfavored in all media, whereas HAT is the most thermodynamically favored mechanism in gas phase and SPLET is the preferred reaction pathway in pentyl ethanoate, ethanol and water. The thermodynamically preferred site of antioxidant action and the radical scavenging order are predicted using the BDE[Formula: see text] and (PA[Formula: see text]ETE)[Formula: see text] descriptors corresponding to the HAT and SPLET mechanisms, respectively. The obtained results point out that the mechanism and the radical scavenging potency are influenced by solvent polarity and our predictions are in agreement with the experimental measurements performed in ethanol giving the following descending order: caffeic [Formula: see text] [Formula: see text] [Formula: see text]-coumaric acid. Our results also show that the ortho substitution of caffeic acid by strong electron donating groups leads to a notable increase of their radical scavenging activity and new potent HCA derivatives are designed.

A single seed treatment mediated through reactive oxygen species increases germination, growth performance, and abiotic stress tolerance in Arabidopsis and rice

Hydroxyl radical (•OH) is considered to be the most damaging among reactive oxygen species. Although afew studies have reported on its effects on growth and stress adaptation of plants, no detailed studies have been performed using •OH in germination and early seedling growth under abiotic stresses. Here we report a single seed treatment with •OH on germination and seedling growth of Arabidopsis and rice under non-stressed (ambient) and various abiotic-stressed conditions (chilling, high temperature, heat, and salinity). The treatment resulted in faster seed germination and early seedling growth under non-stressed conditions, and, interestingly, these effects were more prominent under abiotic stresses. In addition, Arabidopsis seedlings from treated seeds showed faster root growth and developed more lateral roots. These results show apositive and potential practical use for •OH in model and crop plants for direct seeding in the field, as well as improvement of tolerance against emerging stresses. Abbreviations: AUC: area under curve; MGT: mean germination time; t50: time to reach 50% germination; U₇₅₂₅: time for uniform germination from 25% to 75%; ROS: reactive oxygen species; GSI: germination speed index; SI: stress index; DI: dormancy index.

ROS systems are a new integrated network for sensing homeostasis and alarming stresses in organelle metabolic processes

Reactive oxygen species (ROS) are critical for the progression of cardiovascular diseases, inflammations and tumors. However, the mechanisms of how ROS sense metabolic stress, regulate metabolic pathways and initiate proliferation, inflammation and cell death responses remain poorly characterized. In this analytic review, we concluded that: 1) Based on different features and functions, eleven types of ROS can be classified into seven functional groups: metabolic stress-sensing, chemical connecting, organelle communication, stress branch-out, inflammasome-activating, dual functions and triple functions ROS. 2) Among the ROS generation systems, mitochondria consume the most amount of oxygen; and nine types of ROS are generated; thus, mitochondrial ROS systems serve as the central hub for connecting ROS with inflammasome activation, trained immunity and immunometabolic pathways. 3) Increased nuclear ROS production significantly promotes cell death in comparison to that in other organelles. Nuclear ROS systems serve as a convergent hub and decision-makers to connect unbearable and alarming metabolic stresses to inflammation and cell death. 4) Balanced ROS levels indicate physiological homeostasis of various metabolic processes in subcellular organelles and cytosol, while imbalanced ROS levels present alarms for pathological organelle stresses in metabolic processes. Based on these analyses, we propose a working model that ROS systems are a new integrated network for sensing homeostasis and alarming stress in metabolic processes in various subcellular organelles. Our model provides novel insights on the roles of the ROS systems in bridging metabolic stress to inflammation, cell death and tumorigenesis; and provide novel therapeutic targets for treating those diseases. (Word count: 246).

Monoalkylated Epigallocatechin-3-gallate (C18-EGCG) as Novel Lipophilic EGCG Derivative: Characterization and Antioxidant Evaluation

Epigallocatechin-3-gallate (EGCG) has the highest antioxidant activity compared to the others catechins of green tea. However, the beneficial effects are mainly limited by its poor membrane permeability. A derivatization strategy to increase the EGCG interaction with lipid membranes is considered as one feasible approach to expand its application in lipophilic media, in particular the cellular absorption. At this purpose the hydrophilic EGCG was modified by inserting an aliphatic C18 chain linked to the gallate ring by an ethereal bond, the structure determined by NMR (Nuclear Magnetic Resonance) and confirmed by Density Functional Theory (DFT) calculations. The in vitro antioxidant activity of the mono-alkylated EGCG (C18-EGCG) was studied by the DPPH and Thiobarbituric Acid Reactive Substances (TBARS) assays, and its ability to protect cells towards oxidative stress was evaluated in Adult Retinal Pigmented Epithelium (ARPE-19) cells. Molecular Dynamics (MD) simulation and liposomal/buffer partition were used to study the interaction of the modified and unmodified antioxidants with a cell membrane model: the combined experimental-in silico approach shed light on the higher affinity of C18-EGCG toward lipid bilayer. Although the DPPH assay stated that the functionalization decreases the EGCG activity against free radicals, from cellular experiments it resulted that the lipid moiety increases the antioxidant protection of the new lipophilic derivative.

Synthesis, Characterization and Antioxidant Properties of a New Lipophilic Derivative of Edaravone

As part of a program aimed to obtain antioxidants able to interact with cell membrane, edaravone (EdV, 3-methyl-1-phenyl-2-pyrazolin-5-one), a well-known free radical scavenger, has been modified by alkylation at its allylic position (4) with a C-18 hydrocarbon chain, and the increased lipophilicity has been determined towards the interaction with liposomes. The obtained derivative has been studied by means of density functional theory (DFT) methods in order to characterize its lowest energy conformers and predict its antioxidant properties with respect to the parent compound EdV. The in vitro antioxidant activity of C18-edaravone was studied by means of the α,α-diphenyl-β-picrylhydrazyl (DPPH) assay and in lipid peroxidation experiments performed on artificial lipid membranes using water-soluble as well as lipid-soluble radical initiators. Moreover, since oxidative stress is involved in numerous retinal degenerative diseases, the ability of C18-edaravone to contrast 2,2-azobis (2-amidinopropane hydrochloride) (AAPH)-induced cell death was assessed in adult retinal pigmented epithelium (ARPE-19) cells. Overall, the results demonstrated that the newly synthesized molecule has a high affinity for lipid membrane, increasing the efficacy of the unmodified edaravone under stress conditions.

A Theoretical Study on the Antioxidant Activity of Piceatannol and Isorhapontigenin Scavenging Nitric Oxide and Nitrogen Dioxide Radicals

The antioxidant activity of naturally occurring stilbene compounds piceatannol (PIC) and isorhapontigenin (ISO) scavenging two free radicals (NO and NO₂) were studied using density functional theory (DFT) method. Four reaction mechanisms have been considered: hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer (SET), and sequential proton loss electron transfer (SPLET). The reaction channels in water solution were traced independently, and the respective thermodynamic and kinetic parameters were obtained. We found PIC and ISO scavenge NO mainly through RAF mechanism, and scavenge NO₂ through HAT mechanism. The capacity of PIC scavenging NO₂ is much higher than ISO, but the reactivity of scavenging NO is lower than ISO.

Free Radical Scavenging Potency of Dihydroxybenzoic Acids

In order to evaluate the free radical scavenging potency of dihydroxybenzoic acids (DHBAs) the Density Functional Theory (DFT) was used. The M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) theoretical models were applied. Three possible antioxidant mechanisms were examined: hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms. All of these mechanisms have been studied in nonpolar (benzene and pentylethanoate) and polar solvents (water) using an implicit solvation model (SMD). The following thermodynamic quantities related to these mechanisms were calculated: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). The obtained results indicated the HAT mechanism as the most favourable reaction pathway for antioxidative action of DHBAs in benzene. On the other hand, SPLET is indicated as predominant reaction mechanism in polar solvent. The SET-PT mechanism was not favourable reaction path for antioxidative action in any of the solvents under investigation.

Reactive oxygen species and antioxidant defense in human gastrointestinal diseases

Crohn's disease and ulcerative colitis, known together as inflammatory bowel diseases (IBDs), and celiac disease are the most common disorders affecting not only adults but also children. Both IBDs and celiac disease are associated with oxidative stress, which may play a significant role in their etiologies. Reactive oxygen species (ROS) such as superoxide radicals (O2•-), hydroxyl radicals (•OH), hydrogen peroxide (H2O2), and singlet oxygen (1O2) are responsible for cell death via oxidation of DNA, proteins, lipids, and almost any other cellular constituent. To protect biological systems from free radical toxicity, several cellular antioxidant defense mechanisms exist to regulate the production of ROS, including enzymatic and nonenzymatic pathways. Superoxide dismutase catalyzes the dismutation of O2•- to H2O2 and oxygen. The glutathione redox cycle involves two enzymes: glutathione peroxidase, which uses glutathione to reduce organic peroxides and H2O2; and glutathione reductase, which reduces the oxidized form of glutathione with concomitant oxidation of nicotinamide adenine dinucleotide phosphate. In addition to this cycle, GSH can react directly with free radicals. Studies into the effects of free radicals and antioxidant status in patients with IBDs and celiac disease are scarce, especially in pediatric patients. It is therefore very necessary to conduct additional research studies to confirm previous data about ROS status and antioxidant activities in patients with IBDs and celiac disease, especially in children.

Ring substitution influences oxidative cyclisation and reactive metabolite formation of nordihydroguaiaretic acid analogues

Nordihydroguaiaretic acid (NDGA) is a natural polyphenol with a broad spectrum of pharmacological properties. However, its usefulness is hindered by the lack of understanding of its pharmacological and toxicological pathways. Previously we showed that oxidative cyclisation of NDGA at physiological pH forms a dibenzocyclooctadiene that may have therapeutic benefits whilst oxidation to an ortho-quinone likely mediates toxicological properties. NDGA analogues with higher propensity to cyclise under physiologically relevant conditions might have pharmacological implications, which motivated this study. We synthesized a series of NDGA analogues which were designed to investigate the structural features which influence the intramolecular cyclisation process and help to understand the mechanism of NDGA's autoxidative conversion to a dibenzocyclooctadiene lignan. We determined the ability of the NDGA analogues investigated to form dibenzocyclooctadienes and evaluated the oxidative stability at pH 7.4 of the analogues and the stability of any dibenzocyclooctadienes formed from the NDGA analogues. We found among our group of analogues the catechols were less stable than phenols, a single catechol-substituted ring is insufficient to form a dibenzocyclooctadiene lignan, and only compounds possessing a di-catechol could form dibenzocyclooctadienes. This suggests that quinone formation may not be necessary for cyclisation to occur and the intramolecular cyclisation likely involves a radical-mediated rather than an electrophilic substitution process. We also determined that the catechol dibenzocyclooctadienes autoxidised at comparable rates to the parent catechol. This suggests that assigning in vitro biological activity to the NDGA dibenzocyclooctadiene is premature and requires additional study.

Quantum Chemical Study on the Antioxidation Mechanism of Piceatannol and Isorhapontigenin toward Hydroxyl and Hydroperoxyl Radicals

A systematic study of the antioxidation mechanisms behind hydroxyl (•OH) and hydroperoxyl (•OOH) radical scavenging activity of piceatannol (PIC) and isorhapontigenin (ISO) was carried out using density functional theory (DFT) method. Two reaction mechanisms, abstraction (ABS) and radical adduct formation (RAF), were discussed. A total of 24 reaction pathways of scavenging •OH and •OOH with PIC and ISO were investigated in the gas phase and solution. The thermodynamic and kinetic properties of all pathways were calculated. Based on these results, we evaluated the antioxidant activity of every active site of PIC and ISO and compared the abilities of PIC and ISO to scavenge radicals. According to our results, PIC and ISO may act as effective •OH and •OOH scavengers in organism. A4-hydroxyl group is a very important active site for PIC and ISO to scavenge radicals. The introducing of -OH or -OCH₃ group to the ortho-position of A4-hydroxyl group would increase its antioxidant activity. Meanwhile, the conformational effect was researched, the results suggest that the presence and pattern of intramolecular hydrogen bond (IHB) are considerable in determining the antioxidant activity of PIC and ISO.

Synthesis and radical scavenger properties of novel spirochromenes derived from steroid sapogenins

Tandem aldol condensation between steroid sapogenins and hydroxylated benzaldehydes afforded steroidal spirochromenes. Compounds that bear a phenolic hydroxyl group at position C-6', obtained by a reaction with 2,5-dihydroxybenzaldehyde, showed approximately 80% of maximal radical scavenging activity in the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) assay at 288 nM. In contrast, the starting steroid sapogenins and the spirochromenes without a phenolic group in the side chain proved to be inactive.

Experimental and theoretical study of antioxidative properties of some salicylaldehyde and vanillic Schiff bases

A set of ten phenolic Schiff bases was evaluated for their antioxidative properties. Two of them, one salicylaldehyde and one vanillic, showed high activity. Parameters obtained by DFT supported the experimental findings.

Mechanistic and kinetic study on the reactions of coumaric acids with reactive oxygen species: a DFT approach

The mechanism and kinetics of reactions between coumaric acids and a series of reactive oxygen species ((•)OX) was studied through the density functional theory (DFT). H atom abstraction from -OH and -COOH groups and addition to the nonaromatic double bond were the most representative reaction pathways chosen for which free energy barriers and rate constants were calculated within the transition state theory (TST) framework. From these calculations, it was estimated that (•)OH > (•)OCH3 > (•)OOH > (•)OOCH3 is the order of reactivity of (•)OX with any coumaric acid. The highest rate constant was estimated for p-coumaric acid + (•)OH reaction, whereas the rest of the (•)OX species are more reactive with o-coumaric acid. On the basis of the calculated rate constants, H abstraction from a -OH group should be the main mechanism for the reactions involving (•)OCH3, (•)OOH, and (•)OOCH3 radicals. Nevertheless, the addition mechanism, which sometimes is not considered in theoretical studies on reactions of phenolic compounds with electrophilic species, could play a relevant role in the global mechanism of coumaric acid + (•)OH reactions.

Influence of different free radicals on scavenging potency of gallic acid

The M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) models are used to evaluate scavenging potency of gallic acid. The hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) mechanisms of gallic acid with some radicals ((•)OO(-), (•)OH, and CH3OO(•)) were investigated using the corresponding thermodynamic quantities: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). Namely, the ΔHBDE, ΔHIP, and ΔHPA values of the corresponding reactions in some solvents (water, DMSO, pentylethanoate, and benzene) are investigated using an implicit solvation model (SMD). An approach based on the reactions enthalpies related to the examined mechanisms is applied. This approach shows that a thermodynamically favored mechanism depends on the polarity of reaction media and properties of free radical reactive species. The most acidic 4-OH group of gallic acid is the active site for radical inactivation. The results of this investigation indicate that the SPLET mechanism can be a favored reaction pathway for all three radicals in all solvents, except for (•)OH in the aqueous solution. In water, gallic acid can inactivate (•)OH by the HAT mechanism.

The preferred radical scavenging mechanisms of fisetin and baicalein towards oxygen-centred radicals in polar protic and polar aprotic solvents

The flavonoids fisetin and baicalein have been investigated for their ability to scavenge certain anion radicals.

J, Viana RB, Baetas AC, Orestes E, Andrade MA, Honório KM, da Silva ABF. Understanding the molecular aspects of tetrahydrocannabinol and cannabidiol as antioxidants

An antioxidant mechanism of tetrahydrocannabinol (THC) and cannabidiol (CBD) were compared with a simplified model of α-tocopherol, butylhydroxytoluene and hydroxytoluene in order to understand the antioxidant nature of THC and CBD molecules using DFT. The following electronic properties were evaluated: frontier orbitals nature, ionization potential, O-H bond dissociation energy (BDE_OH), stabilization energy, and spin density distribution. An important factor that shows an influence in the antioxidant property of THC is the electron abstraction at the phenol position. Our data indicate that the decrease of the HOMO values and the highest ionization potential values are related to phenol, ether, and alkyl moieties. On the other hand, BDE_OH in molecules with the cyclohexenyl group at ortho position of phenol are formed from lower energies than the molecules with an ether group at the meta position. In the light of our results, the properties calculated here predict that THC has a sightly higher antioxidant potential than CBD.

Antioxidant properties of xanthones from Calophyllum brasiliense: prevention of oxidative damage induced by FeSO₄

Background

Reactive oxygen species (ROS) are important mediators in a number of degenerative diseases. Oxidative stress refers to the imbalance between the production of ROS and the ability to scavenge these species through endogenous antioxidant systems. Since antioxidants can inhibit oxidative processes, it becomes relevant to describe natural compounds with antioxidant properties which may be designed as therapies to decrease oxidative damage and stimulate endogenous cytoprotective systems. The present study tested the protective effect of two xanthones isolated from the heartwood of Calophyllum brasilienses against FeSO₄-induced toxicity.

Methods

Through combinatory chemistry assays, we evaluated the superoxide (O₂^●—), hydroxyl radical (OH^●), hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO^—) scavenging capacity of jacareubin (xanthone III) and 2-(3,3-dimethylallyl)-1,3,5,6-tetrahydroxyxanthone (xanthone V). The effect of these xanthones on murine DNA and bovine serum albumin degradation induced by an OH• generator system was also evaluated. Additionally, we investigated the effect of these xanthones on ROS production, lipid peroxidation and glutathione reductase (GR) activity in FeSO₄-exposed brain, liver and lung rat homogenates.

Results

Xanthone V exhibited a better scavenging capacity for O₂^●—, ONOO^- and OH^● than xanthone III, although both xanthones were unable to trap H₂O₂. Additionally, xanthones III and V prevented the albumin and DNA degradation induced by the OH^● generator system. Lipid peroxidation and ROS production evoked by FeSO₄ were decreased by both xanthones in all tissues tested. Xanthones III and V also prevented the GR activity depletion induced by pro-oxidant activity only in the brain.

Conclusions

Altogether, the collected evidence suggests that xanthones can play a role as potential agents to attenuate the oxidative damage produced by different pro-oxidants.

Nordihydroguaiaretic acid induces Nrf2 nuclear translocation in vivo and attenuates renal damage and apoptosis in the ischemia and reperfusion model

It has been shown that the pretreatment with nordihydroguaiaretic acid (NDGA), a lignan with direct and indirect antioxidant properties, protects against the ischemia-reperfusion (I/R)-induced renal oxidant damage. Although it has been shown that NDGA induces Nrf2 nuclear translocation in renal epithelial LLC-PK1 cells in culture, it is unknown if NDGA may induce Nrf2 translocation in vivo. In this work was explored if NDGA is able to induce in vivo Nrf2 nuclear translocation in kidneys of rats submitted to uni-nephrectomy (U-NX) or I/R injury. Four groups of male Wistar rats were used: U-NX, NDGA, I/R, and I/R+NDGA. NDGA was injected i.p. (10mg/kg/day) starting 48 h before I/R. Kidney samples were obtained at 3 h of reperfusion after to measure Nrf2 translocation. Additional groups of rats were studied at 24 h of reperfusion to measure histological damage and apoptosis. NDGA was able to induce Nrf2 translocation in vivo in kidneys of rats submitted to both U-NX and I/R injury and to protect against renal histological damage and apoptosis. It is concluded that the pretreatment of NDGA is able to induce in vivo nuclear Nrf2 translocation in kidney of rats suggesting that this may be involved in the renoprotection against I/R.

Nordihydroguaiaretic acid attenuates the oxidative stress-induced decrease of CD33 expression in human monocytes

Nordihydroguaiaretic acid (NDGA) is a natural lignan with recognized antioxidant and beneficial properties that is isolated from Larrea tridentata. In this study, we evaluated the effect of NDGA on the downregulation of oxidant stress-induced CD33 in human monocytes (MNs). Oxidative stress was induced by iodoacetate (IAA) or hydrogen peroxide (H₂O₂) and was evaluated using reactive oxygen species (ROS) production, and cell viability. NDGA attenuates toxicity, ROS production and the oxidative stress-induced decrease of CD33 expression secondary to IAA or H₂O₂ in human MNs. It was also shown that NDGA (20 μM) attenuates cell death in the THP-1 cell line that is caused by treatment with either IAA or H₂O₂. These results suggest that NDGA has a protective effect on CD33 expression, which is associated with its antioxidant activity in human MNs.