Computational study of the supramolecular complexation of azocompounds with cucurbit[7]uril: effects on the production and release of free radicals

CONTEXT

An inclusion complex between 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), a widely employed azocompound, and cucurbit[7]util (CB[7]), has shown an increased yield of radicals derived from the homolytic cleavage of the azo bond. Aimed to get insights about the formation of complexes and their effect on the yield of radicals production, complexes of CB[7] with seven azocompounds were studied by computational methods. Molecular electrostatic surfaces and structural analysis showed that the inclusion of symmetrical azocompounds inside of CB[7] depends mainly on the charge density and position of the functional groups at the main chain of the azoderivative. Analysis of non-covalent interactions and thermodynamic outcomes revealed that positively charged azocompounds with amidinium or imidazolium groups presented strong favorable interactions (multiple hydrogen bonds) with the oxygens of CB[7] portals. Additionally, carbon-centered radicals generated from the complexes (azocompounds@CB[7]) were corroborated using the electron localization function (ELF). Results evidenced that the strength of the interactions and the level of inclusion (partial or complete) between the azocompound and CB[7] determined the final orientation of the radicals (located out- or inside of the CB[7] cavity). Obtained results could be employed to design new supramolecular systems based on the properties of azocomplound@CB[7] complexes for new scientific or industrial applications.

METHODS

First-principles calculations at B3LYP-D3BJ/6-311g(d,p) level theory in the gas phase and in solvent (PCM, water) were performed in Gaussian 16 software package. The dispersion energy correction was included through the Grimme's dispersion with Becke-Johnson damping D3(BJ). Thermodynamical data and the minimum character of all structures were obtained from vibrational frequency calculations. NBO, Multiwfn, Chemcraft, and NCIPLOT software were used to perform population analysis, analyze outcomes, visualize data, and display non-covalent interactions respectively.

General Approach to Identify, Assess, and Characterize Inhibitors of Lipid Peroxidation and Associated Cell Death

Lipid peroxidation (LPO) is associated with a variety of pathologies and drives a form of regulated necrosis called ferroptosis. There is much interest in small-molecule inhibitors of LPO as potential leads for therapeutic development for neurodegeneration, stroke, and acute organ failure, but this has been hampered by the lack of a universal high-throughput assay that can identify and assess candidates. Herein, we describe the development and validation of such an approach. Phosphatidylcholine liposomes loaded with ∼10% phospholipid hydroperoxide and STY-BODIPY, a fluorescent signal carrier that co-autoxidizes with polyunsaturated phospholipids, are shown to autoxidize at convenient and constant rates when subjected to an optimized Fe²⁺-based initiation cocktail. The use of this initiation system enables the identification of each of the various classes of LPO inhibitors which have been shown to rescue from cell death in ferroptosis: radical-trapping antioxidants (RTAs), peroxidase mimics, and iron chelators. Furthermore, a limited dose-response profile of inhibitors enables the resolution of RTA and non-RTA inhibitors─thereby providing not only relative efficacy but mechanistic information in the same microplate-based experiment. Despite this versatility, the approach can still be used to estimate rate constants for the reaction of RTAs with chain-propagating peroxyl radicals, as demonstrated for a representative panel of RTAs. To illustrate the utility of this assay, we carried out a preliminary investigation of the 'off-target' activity of several ferroptosis suppressors that have been proposed to act independently of inhibition of LPO, including lipoxygenase inhibitors, cannabinoids, and necrostatins, the archetype inhibitors of necroptosis.

Modulation of the chain-breaking antioxidant activity of phenolic organochalcogens with various co-antioxidants at various pH values

Phenolic organochalcogen chain-breaking antioxidants, i.e. 6-bromo-8 (hexadecyltellanyl)-3,3-dimethyl-1,5-dihydro-[1,3]dioxepino[5,6-c]pyridin-9-ol and 2-methyl-2,3-dihydrobenzo[b]selenophene-5-ol, have been investigated in a two-phase (chlorobenzene/water) lipid peroxidation model system as potent inhibitors of lipid peroxyl radicals with various co-antioxidants at various pH values. The pH has a significant effect on the chain-breaking antioxidant activities of phenolic organochalcogens. The key chain-breaking mechanism profile was attributed to the first oxygen atom transfer from the lipid peroxyl radicals to the Se/Te atom, followed by hydrogen atom transfer in a solvent cage from the nearby phenolic group to the resulting alkoxyl radical. Finally, regeneration of organochalcogen antioxidants could take place in the presence of aqueous-soluble co-antioxidants. Also, in the presence of aqueous soluble N-acetylcysteine at pH 1-7, both antioxidants behaved as very good inhibitors of lipid peroxyl radicals. The role of aqueous soluble mild co-antioxidants in the regeneration studies of organochalcogen antioxidants has been investigated in a two-phase lipid peroxidation model system. The importance of the phase transfer catalyst has been explored in the inhibition studies of selenium containing antioxidants using an Fe(II) source. The overall pH-dependent antioxidant activities of organochalcogens depend on their hydrogen atom transfer ability, relative stability, and distribution in the aqueous/lipid phase.

Intrinsic and Extrinsic Limitations to the Design and Optimization of Inhibitors of Lipid Peroxidation and Associated Cell Death

The archetype inhibitors of ferroptosis, ferrostatin-1 and liproxstatin-1, were identified via high-throughput screening of compound libraries for cytoprotective activity. These compounds have been shown to inhibit ferroptosis by suppressing propagation of lipid peroxidation, the radical chain reaction that drives cell death. Herein, we present the first rational design and optimization of ferroptosis inhibitors targeting this mechanism of action. Engaging the most potent radical-trapping antioxidant (RTA) scaffold known (phenoxazine, PNX), and its less reactive chalcogen cousin (phenothiazine, PTZ), we explored structure-reactivity-potency relationships to elucidate the intrinsic and extrinsic limitations of this approach. The results delineate the roles of inherent RTA activity, H-bonding interactions with phospholipid headgroups, and lipid solubility in determining activity/potency. We show that modifications which increase inherent RTA activity beyond that of the parent compounds do not substantially improve RTA kinetics in phospholipids or potency in cells, while modifications that decrease intrinsic RTA activity lead to corresponding erosions to both. The apparent "plateau" of RTA activity in phospholipid bilayers (k_inh ∼ 2 × 10⁵ M^-1 s^-1) and cell potency (EC₅₀ ∼ 4 nM) may be the result of diffusion-controlled reactivity between the RTA and lipid-peroxyl radicals and/or the potential limitations on RTA turnover/regeneration by endogenous reductants. The metabolic stability of selected derivatives was assessed to identify a candidate for in vivo experimentation as a proof-of-concept. This PNX-derivative demonstrated stability in mouse liver microsomes comparable to liproxstatin-1 and was successfully used to suppress acute renal failure in mice brought on by tissue-specific inactivation of the ferroptosis regulator GPX4.

Method to Improve Azo-Compound (AAPH)-Induced Hemolysis of Erythrocytes for Assessing Antioxidant Activity of Lipophilic Compounds

We examined the method of oxidative hemolysis for assessment of antioxidant activity of various compounds, especially lipophilic compounds. 2,2'-Azobis(amidinopropane) dihydrochloride (AAPH) was used as the source of free radicals for the oxidative hemolysis of horse erythrocytes. We found that absorbance at 540 nm is not appropriate for monitoring AAPH-induced hemolysis. Instead, we should use absorbance at 523 nm (an isosbestic point), because AAPH oxidizes the oxygenated hemoglobin to methemoglobin and absorbance at 540 nm does not correctly reflect the amount of released hemoglobin by AAPH-induced hemolysis. The corrected method of AAPH-induced hemolysis was applicable to assess the antioxidant activity of various hydrophilic compounds such as ascorbic acid, (-)-epicatechin, and edaravone. For the assessment of antioxidant activity of lipophilic compounds, we need appropriate dispersing agents for these lipophilic compounds. Among several agents tested, 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC) liposome at a concentration of 0.34 mM was found to be useful. Exogenous α-tocopherol incorporated using DMPC liposome as a dispersing agent was shown to protect erythrocytes from AAPH-induced hemolysis in a concentration-dependent manner.

Azocompounds as generators of defined radical species: Contributions and challenges for free radical research

Peroxyl radicals participate in multiple processes involved in critical changes to cells, tissues, pharmacueticals and foods. Some of these reactions explain their association with degenerative pathologies, including cardiovascular and neurological diseases, as well as cancer development. Azocompounds, and particularly AAPH (2,2'-Azobis(2-methylpropionamidine) dihydrochloride), a cationic water-soluble derivative, have been employed extensively as sources of model peroxyl radicals. A considerable number of studies have reported mechanistic data on the oxidation of biologically-relevant targets, the scavenging activity of foods and natural products, and the reactions with, and responses of, cultured cells. However, despite the (supposed) experimental simplicity of using azocompounds, the chemistry of peroxyl radical production and subsequent reactions is complicated, and not always considered in sufficient depth when analyzing experimental data. The present work discusses the chemical aspects of azocompounds as generators of peroxyl (and other) radicals, together with their contribution to our understanding of biochemistry, pharmaceutical and food chemistry research. The evidence supporting a role for the formation of alkoxyl (RO•) and other radicals during thermal and photochemical decomposition of azocompounds is assessed, together with the potential influence of such species on the reactions under study.

Veiled Extra Virgin Olive Oils: Role of Emulsion, Water and Antioxidants

This review traces the current knowledge on the effects of various factors and phenomena that occur at interface, and the role of dispersed phase on the physicochemical, sensorial and nutritional characteristics of veiled extra virgin olive oil (VVOO). Since 1994 there have been numerous articles in the literature regarding the peculiar characteristic of unfiltered olive oil, so-called veiled or cloud virgin olive oil. It is a colloidal system (emulsion–sol), where the continuous lipidic phase dispreads mini droplets of milling water, fragments of cells and biotic fraction obtained from oil processing. During storage, the dispersed phase collapses and determines the quality of the virgin olive oil (VOO). The observed phenomena lead to worsening the quality of the product by causing defects such as oxidation of phenols, triacylglycerols hydrolysis and off-flavor formation. The addition of bioactive compounds, such as vitamins, on product based on VVOO, must take into account the eventual synergistic effect of individual substances. The role of the interphase is crucial to the synergic activity of bioactive molecules in improving oxidative stability, sensorial and health characteristics of VVOO.

Antioxidant Effect of Vitamins in Olive Oil Emulsion

In this study, water-in-extra virgin olive oil emulsions were enriched with vitamins. Water-in oil emulsions are heterogeneous systems able to solubilize both hydrophilic and hydrophobic compounds. Thus, hydrophilic vitamin C and lipophilic vitamin E were loaded separately or together in emulsion. A suitable emulsion composition was selected after considering different surfactant (mono and diglycerides of fatty acids, E471; sorbitan monooleate, Span 80; polyoxyethylene sorbitan monooleate, Tween 80) and water concentrations. The most appropriate emulsion, for the high stability, resulted the one containing concentrations of Span 80 1% w/w and water 1% w/w. The antioxidant effect of vitamins in emulsions was studied considering the variation of the peroxide values during storage. The oxidation reaction was slowed down in emulsions containing vitamin C, but it was quickened by the loading of vitamin E for its high concentration. In emulsions containing vitamin E, indeed, the peroxide values were higher than in emulsions prepared in the absence of vitamins or in oil. The antioxidant activity generated by the co-loading of vitamin C and E was very effective to the point that in presence of high amounts of vitamins the peroxide values did not change in about 40 days of storage, due to the vitamin E regeneration by vitamin C.

Antioxidants and antioxidant methods: an updated overview

Antioxidants had a growing interest owing to their protective roles in food and pharmaceutical products against oxidative deterioration and in the body and against oxidative stress-mediated pathological processes. Screening of antioxidant properties of plants and plant-derived compounds requires appropriate methods, which address the mechanism of antioxidant activity and focus on the kinetics of the reactions including the antioxidants. Many studies evaluating the antioxidant activity of various samples of research interest using different methods in food and human health have been conducted. These methods are classified, described, and discussed in this review. Methods based on inhibited autoxidation are the most suited for termination-enhancing antioxidants and for chain-breaking antioxidants, while different specific studies are needed for preventive antioxidants. For this purpose, the most common methods used in vitro determination of antioxidant capacity of food constituents were examined. Also, a selection of chemical testing methods was critically reviewed and highlighted. In addition, their advantages, disadvantages, limitations and usefulness were discussed and investigated for pure molecules and raw extracts. The effect and influence of the reaction medium on the performance of antioxidants are also addressed. Hence, this overview provides a basis and rationale for developing standardized antioxidant methods for the food, nutraceuticals, and dietary supplement industries. In addition, the most important advantages and shortcomings of each method were detected and highlighted. The chemical principles of these methods are outlined and critically discussed. The chemical principles of methods of 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical (ABTS^·+) scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radical scavenging, Fe³⁺-Fe²⁺ transformation assay, ferric reducing antioxidant power (FRAP) assay, cupric ions (Cu²⁺) reducing power assay (Cuprac), Folin-Ciocalteu reducing capacity (FCR assay), peroxyl radical (ROO·), superoxide radical anion (O₂^·-), hydrogen peroxide (H₂O₂) scavenging assay, hydroxyl radical (OH·) scavenging assay, singlet oxygen (¹O₂) quenching assay, nitric oxide radical (NO·) scavenging assay and chemiluminescence assay are outlined and critically discussed. Also, the general antioxidant aspects of main food components were discussed by a number of methods, which are currently used for the detection of antioxidant properties of food components. This review consists of two main sections. The first section is devoted to the main components in the food and pharmaceutical applications. The second general section comprises some definitions of the main antioxidant methods commonly used for the determination of the antioxidant activity of components. In addition, some chemical, mechanistic and kinetic basis, and technical details of the used methods are given.

The impact of prenatal environment on postnatal life and performance: Future perspectives for prevention and treatment

The present review aims to offer a non-comprehensive outline of the current state-of-the-art and future perspectives on management and therapeutic tools for intrauterine growth restriction (IUGR) and associated prenatal programming in both human and animal species. Animals are used as models for the study of phenomena related to IUGR, but also for research on prenatal therapies with the main objective of designing and developing preventive and therapeutic strategies. The research is currently paying attention on maternal-focused pharmacological treatments and nutritional strategies but also on fetal-focused treatments. Fetal-focused treatments, administered either directly at the fetus or by using infusion of umbilical cord, amniotic sac or placenta, which avoids the administration of substances at high doses to the mother for allowing their availability at the fetoplacental level. The results obtained in this area of research using large animals (rabbits, pigs and ruminants) have a dual interest, for translational biomedicine and for veterinary medicine and animal production.

Key nutritional factors and interactions during larval development of pikeperch (Sander lucioperca)

The effects of 8 nutritional variables (Ca/P, Eicosapentaenoic acid (20:5n-3) + Docosahexaenoic acid (22:6n − 3) (EPA + DHA), Arachidonic acid (20:4n − 6) (ARA), Se, vitamins E, C, D and A) were investigated to identify their respective importance and interactions in pikeperch larval development. In this respect, two modalities (low and high levels) of each variable were tested through a fractional factorial experimental design allowing a reduction from 256 (2⁸) to 16 (2^8 – 4) experimental units. Survival was significantly higher in larvae fed a high Ca/P diet while larval growth was significantly lower in larvae fed the same diet variant, associated with a higher incidence of kyphosis and pectoral anomalies in these larvae. Lordosis and scoliosis seemed to be mostly affected by dietary long chain polyunsaturated fatty acids (LC-PUFAs). A significant interaction was shown between n-3 LC-PUFA and vitamin C on jaw anomalies, while myocyte-specific enhancer factor 2C (mef2c) gene expression correlated positively with dietary vitamin C increment. Results also demonstrated an effect of the different nutrients and their interactions on the activity levels of digestive enzymatic activities. The results of the present study highlight the importance of the interactions between Ca/P, LC-PUFAs and vitamins C and E, suggesting their essential roles as key nutritional factors influencing pikeperch larval development.

Effects of Ergothioneine-Rich Mushroom Extract on the Oxidative Stability of Astaxanthin in Liposomes

Ergothioneine-rich crude extracts of Pleurotus cornucopiae were used as a source of antioxidative components to control the effects of lipid oxidation in astaxanthin-containing liposomes. This study aimed to elucidate the interactions of liposomal astaxanthin and lipids with ergothioneine-rich mushroom extract (ME) under radical oxidation-induced conditions to provide a better understanding of the agricultural and postharvest applications of this strategy. Azo compounds (2,2'-azobis(2-methylpropionamidine) dihydrochloride and 2,2'-azobis(2,4-dimethylvaleronitrile) were used as hydrophilic and lipophilic radical initiators, respectively. Results of this study demonstrate that the presence of ME significantly delayed the oxidative degradation of astaxanthin and controlled the progress of lipid oxidation in a liposomal system. The lipid hydroperoxide formation was significantly suppressed, while polyunsaturated fatty acids were protected from degradation. In addition, Crude ME also demonstrated more potent DPPH radical scavenging activities and EC₅₀ than the equimolar concentrations of ergothioneine alone, which suggested the presence of additional compounds with antioxidative properties.

Chain-Breaking Phenolic 2,3-Dihydrobenzo[b]selenophene Antioxidants: Proximity Effects and Regeneration Studies

Phenolic 2,3-dihydrobenzo[b]selenophene antioxidants bearing an OH-group ortho (9), meta (10, 11) and para (8) to the Se were prepared by seleno-Claisen rearrangement/intramolecular hydroselenation. meta-Isomer (11) was studied by X-ray crystallography. The radical-trapping activity and regenerability of compounds 8-11 were evaluated using a two-phase system in which linoleic acid was undergoing peroxidation in the lipid phase while regeneration of the antioxidant by co-antioxidants (N-acetylcysteine, glutathione, dithiothreitol, ascorbic acid, tris(carboxyethyl)phosphine hydrochloride) was ongoing in the aqueous layer. Compound 9 quenched peroxyl radicals more efficiently than α-tocopherol. It also provided the most long-lasting antioxidant protection. With thiol co-antioxidants it could inhibit peroxidation for more than five-fold longer than the natural product. Regeneration was more efficient when the aqueous phase pH was slightly acidic. Since calculated O-H bond dissociation energies for 8-11 were substantially larger than for α-tocopherol, an antioxidant mechanism involving O-atom transfer from peroxyl to selenium was proposed. The resulting phenolic selenoxide/alkoxyl radical would then exchange a hydrogen atom in a solvent cage before antioxidant regeneration at the aqueous lipid interphase.

Combination of vitamin E and vitamin C alleviates renal function in hyperoxaluric rats via antioxidant activity

Hyperoxaluria and oxidative stress are risk factors in calcium oxalate (CaOx) stone formation. Supplement with antioxidant could be effective in prevention of recurrent stone formation. The present study aims to evaluate the protective effects of vitamin E and vitamin C in hyperoxaluric rat. The experiment was performed in rats for 21 days. Rats were divided into 5 groups as follows: control (group 1, n=8), hyperoxaluric rats (group 2, n=8), hyperoxaluric rats with vitamin E supplement (group 3, n=7), hyperoxaluric rats with vitamin C supplement (group 4, n=7) and hyperoxaluric rats with vitamin E and C supplement (group 5, n=7). Hyperoxaluria was induced by feeding hydroxyl L-proline (HLP) 2% w/v dissolved in drinking water. Intraperitoneal 200 mg/kg of vitamin E was given in groups 3 and 5 on days 1, 6, 11 and 16, while 500 mg of vitamin C was injected intravenously in groups 4 and 5 on days 1 and 11. Renal functions and oxidative status were measured. The urinary oxalate excretion was increased in HLP supplement rats, while glomerular filtration rate, proximal water and sodium reabsorption were significantly lower in group 2 compared with a control (P<0.05). Giving antioxidants significantly lower urinary calcium oxalate crystals (P<0.05). Hyperoxaluric rats had higher plasma malondialdehyde (PMDA) and lower urinary total antioxidant status (UTAS), which were alleviated by vitamin E and/or vitamin C supplement. In conclusion, giving combination of vitamin E and vitamin C exerts a protective role against HLP-induced oxalate nephropathy.

Assessing Interactions between Lipophilic and Hydrophilic Antioxidants in Food Emulsions

Dietary lipids containing high concentrations of polyunsaturated fatty acids are considered to be beneficial to human health, yet their incorporation within formulated foods is complicated by their susceptibility to oxidation. Lipid oxidation in foods is inhibited through the incorporation of antioxidants, yet the list of antioxidants approved for food use is small, and consumers frequently demand foods without synthetic additives. As a consequence, food processors are now tasked with improving the efficacy of approved, "natural" (i.e., nonsynthetic) antioxidants; a rational strategy for doing so involves localizing the antioxidants at the interface where oxidation usually occurs and regenerating the consumed antioxidants after the oxidation event has occurred. The present study describes a procedure to evaluate antioxidant interactions in oil-in-water food emulsions, which is based on controlled oxidation reactions induced in the dispersed oil phase by the lipophilic radical generator, 2,2'-azobis(2,4-dimethylvaleronitrile). The extent of lipid oxidation is measured spectroscopically by following the loss of an oxidatively labile, lipophilic probe (methyl eleostearate), the synthesis of which is described here. Using this procedure, the ability of various aqueous phase solvated antioxidants (ascorbic acid, gallic acid, (-)-epicatechin, (-)-epigallocatechin-3-gallate) to regenerate lipid phase solvated α-tocopherol was evaluated. In all cases, the test compounds were able to inhibit oxidation reactions; however, these effects were not profoundly synergistic, and the maximum synergistic interaction observed was only ∼ 3% using ascorbic acid.

A new approach to elucidating repair reactions of resveratrol

The repair by co-antioxidants of the phenoxy radical of resveratrol, the famous health-preserving ingredient of red wine, is a key step of radical scavenging cascades in nature. To generate that radical, we employed 355 nm photoionization as a direct and selective access that reduces the chemical complexity and is equally applicable in organized phases; to monitor it, we used its hitherto unreported absorption in the red where no other species in our systems interfere. With this novel approach, we measured rate constants and H/D kinetic isotope effects for the repairs by ascorbate, trolox (a vitamin E analogue) and 4-aminophenol, and identified the mechanisms as one-step hydrogen abstractions. Cysteine and glutathione are unreactive. In micellar solution (SDS), the repair by ascorbate is much slower and involves only the hydrophilic phenoxy moieties protruding from the micelles. The new experimental strategy also led to a reevaluation of extinction coefficients, rate constants and mechanisms.

Effects of vitamin C, vitamin E, zinc gluconate, and selenomethionine supplementation on muscle function and oxidative stress biomarkers in patients with facioscapulohumeral dystrophy: a double-blind randomized controlled clinical trial

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disease characterized by progressive weakness and atrophy of specific skeletal muscles. As growing evidence suggests that oxidative stress may contribute to FSHD pathology, antioxidants that might modulate or delay oxidative insults could help in maintaining FSHD muscle function. Our primary objective was to test whether oral administration of vitamin C, vitamin E, zinc gluconate, and selenomethionine could improve the physical performance of patients with FSHD. Adult patients with FSHD (n=53) were enrolled at Montpellier University Hospital (France) in a randomized, double-blind, placebo-controlled pilot clinical trial. Patients were randomly assigned to receive 500 mg vitamin C, 400mg vitamin E, 25mg zinc gluconate and 200 μg selenomethionine (n=26), or matching placebo (n=27) once a day for 17 weeks. Primary outcomes were changes in the two-minute walking test (2-MWT), maximal voluntary contraction, and endurance limit time of the dominant and nondominant quadriceps (MVCQD, MVCQND, TlimQD, and TlimQND, respectively) after 17 weeks of treatment. Secondary outcomes were changes in the antioxidant status and oxidative stress markers. Although 2-MWT, MVCQ, and TlimQ were all significantly improved in the supplemented group at the end of the treatment compared to baseline, only MVCQ and TlimQ variations were significantly different between groups (MVCQD: P=0.011; MVCQND: P=0.004; TlimQD: P=0.028; TlimQND: P=0.011). Similarly, the vitamin C (P<0.001), vitamin E as α-tocopherol (P<0.001), vitamin C/vitamin E ratio (P=0.017), vitamin E γ/α ratio (P=0.022) and lipid peroxides (P<0.001) variations were significantly different between groups. In conclusion, vitamin E, vitamin C, zinc, and selenium supplementation has no significant effect on the 2-MWT, but improves MVCQ and TlimQ of both quadriceps by enhancing the antioxidant defenses and reducing oxidative stress. This trial was registered at clinicaltrials.gov (number: NCT01596803).

T cell lipid peroxidation induces ferroptosis and prevents immunity to infection

Matsushita et al. investigated the role of the selenoenzyme glutathione peroxidae 4 (Gpx4) in T cell responses and found that loss of Gpx4 results in an intrinsic T cell developmental defect in the periphery, which leads to a failure to expand and protect from acute viral and parasitic infection.The defects were rescued with dietary supplementation of vitamin E. The Gp4^−/− T cells accumulate membrane lipid peroxides and undergo cell death by ferroptosis.

The selenoenzyme glutathione peroxidase 4 (Gpx4) is a major scavenger of phospholipid hydroperoxides. Although Gpx4 represents a key component of the reactive oxygen species-scavenging network, its relevance in the immune system is yet to be defined. Here, we investigated the importance of Gpx4 for physiological T cell responses by using T cell–specific Gpx4-deficient mice. Our results revealed that, despite normal thymic T cell development, CD8⁺ T cells from T^{ΔGpx4/ΔGpx4} mice had an intrinsic defect in maintaining homeostatic balance in the periphery. Moreover, both antigen-specific CD8⁺ and CD4⁺ T cells lacking Gpx4 failed to expand and to protect from acute lymphocytic choriomeningitis virus and Leishmania major parasite infections, which were rescued with diet supplementation of high dosage of vitamin E. Notably, depletion of the Gpx4 gene in the memory phase of viral infection did not affect T cell recall responses upon secondary infection. Ex vivo, Gpx4-deficient T cells rapidly accumulated membrane lipid peroxides and concomitantly underwent cell death driven by ferroptosis but not necroptosis. These studies unveil an essential role of Gpx4 for T cell immunity.

A modified method for studying behavioral paradox of antioxidants and their disproportionate competitive kinetic effect to scavenge the peroxyl radical formation

We have described a modified method for evaluating inhibitor of peroxyl radicals, a well-recognized and -documented radical involved in cancer initiation and promotion as well as diseases related to oxidative stress and ageing. We are reporting hydrophilic and lipophilic as well as natural and synthetic forms of antioxidants revealing a diversified behaviour to peroxyl radical in a dose-dependent manner (1 nM–10 μM). A simple kinetic model for the competitive oxidation of an indicator molecule (ABTS) and a various antioxidant by a radical (ROO^•) is described. The influences of both the concentration of antioxidant and duration of reaction (70 min) on the inhibition of the radical cation absorption are taken into account while determining the activity. The induction time of the reaction was also proposed as a parameter enabling determination of antioxidant content by optimizing and introducing other kinetic parameters in 96-well plate assays. The test evidently improves the original PRTC (peroxyl radical trapping capacity) assay in terms of the amount of chemical used, simultaneous tracking, that is, the generation of the radical taking place continually and the kinetic reduction technique (area under curve, peak value, slope, and V_max).

Role of vitamin E as a lipid-soluble peroxyl radical scavenger: in vitro and in vivo evidence

Multiple reactive oxygen/nitrogen species induce oxidative stress. Mammals have evolved with an elaborate defense network against oxidative stress, in which multiple antioxidant compounds and enzymes with different functions exert their respective roles. Radical scavenging is one of the essential roles of antioxidants and vitamin E is the most abundant and important lipophilic radical-scavenging antioxidant in vivo. The kinetic data and physiological molar ratio of vitamin E to substrates show that the peroxyl radicals are the only radicals that vitamin E can scavenge to break chain propagation efficiently and that vitamin E is unable to act as a potent scavenger of hydroxyl, alkoxyl, nitrogen dioxide, and thiyl radicals in vivo. The preventive effect of vitamin E against the oxidation mediated by nonradical oxidants such as hypochlorite, singlet oxygen, ozone, and enzymes may be limited in vivo. The synergistic interaction of vitamin E and vitamin C is effective for enhancing the antioxidant capacity of vitamin E. The in vitro and in vivo evidence of the function of vitamin E as a peroxyl radical-scavenging antioxidant and inhibitor of lipid peroxidation is presented.

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

The incorporation of nitrogen atoms into the aromatic ring of phenolic compounds has enabled the development of some of the most potent radical-trapping antioxidants ever reported. These compounds, 3-pyridinols and 5-pyrimidinols, have stronger O-H bonds than equivalently substituted phenols, but possess similar reactivities toward autoxidation chain-carrying peroxyl radicals. These attributes suggest that 3-pyridinols and 5-pyrimidinols will be particularly effectiveco-antioxidants when used in combination with more common, but less reactive, phenolic antioxidants such as 2,6-di-tert-butyl-4-methylphenol (BHT), which we demonstrate herein. The antioxidants function in a synergistic manner to inhibit autoxidation; taking advantage of the higher reactivity of the 3-pyridinols/5-pyrimidinols to trap peroxyl radicals and using the less reactive phenols to regenerate them from their corresponding aryloxyl radicals. The present investigations were carried out in chlorobenzene and acetonitrile in order to provide some insight into the medium dependence of the synergism and the results, considered with some from our earlier work, prompt a revision of the H-bonding basicity value of acetonitrile to β2 (H) of 0.39. Overall, the thermodynamic and kinetic data presented here enable the design of co-antioxidant systems comprising lower loadings of the more expensive 3-pyridinol/5-pyrimidinol antioxidants and higher loadings of the less expensive phenolic antioxidants, but which are equally efficacious as the 3-pyridinol/5-pyrimidinol antioxidants alone at higher loadings.

The effect of dietary supplementation of vitamins C and E on the α-tocopherol content of muscles, liver and kidney, on the stability of lipids, and on certain meat quality parameters of the longissimus dorsi of rabbits

The trial was carried out to investigate the effects of adding to the diet of rabbits vitamin E (40; 300; 500 ppm) and C (0; 500 ppm), on vitamin E deposition in the muscles and organs, on the oxidative stability of muscular lipids, and on various meat quality characteristics. The α-tocopherol content in muscles and organs was roughly doubled by feeding the highest levels of vitamin E; it was also increased by giving 500 ppm of vitamin C, but only in those muscles of rabbits receiving 40 ppm of vitamin E. The α-tocopherol content in tissues was negatively correlated with TBARS values of the longissimus dorsi (LD) at days 6 and 8 post mortem (p.m.). Five hundred parts per million (ppm) of vitamin C increased lipid stability of the LD at both 6 and 8 days p.m., though its effect was significant only with 40 ppm of vitamin E. Moreover, 500 ppm of vitamin C resulted in the lowest L(*) and highest pH values at all p.m. times, when the dietary vitamin E was equal to 40 ppm, and in the highest L(*) and lowest pH values when the vitamin E was equal to 300 ppm. Conversely, weight losses of the LD were the lowest, at days 6 and 8 p.m., in the group fed the highest levels of both vitamins.

Assessment of antioxidant capacity for scavenging free radicals in vitro: a rational basis and practical application

With increasing evidence showing the involvement of oxidative stress induced by free radicals in the development of various diseases, the role of radical-scavenging antioxidants has received much attention. Although many randomized controlled clinical trials do not support the beneficial effects of indiscriminate supplementation of antioxidants, more recent studies suggest that antioxidants such as vitamin E may be effective for prevention and treatment of some diseases when given to the right subjects at the right time. Many studies on the antioxidant capacity assessed by various available methods showed inconsistent results and the assessment of antioxidant capacity has been the subject of extensive studies and arguments. This study was performed to elucidate the basic chemistry required for the development of a reliable method for the assessment of antioxidant capacity for radical scavenging in vitro. In this study, the capacity of α-tocopherol and its related compounds, ascorbic acid, and uric acid for scavenging radicals was assessed from their effects on the rate of decay of hydrophilic and lipophilic probes with various reactivities toward free radicals induced by hydrophilic and lipophilic radicals in homogeneous solution and heterogeneous micelle systems. Fluorescein, pyranine, and pyrogallol red were used as hydrophilic probes, and BODIPY and N,N-diphenyl-p-phenylenediamine were used as lipophilic probes. We show that the rate and amount of radical scavenging by antioxidants, termed the antioxidant radical absorbance capacity, could be assessed by an appropriate combination of radical initiator and probe. This method was applied to the assessment of radical-scavenging capacity of human plasma, wine, and green tea powder.

Interplay between structure and fluidity of model lipid membranes under oxidative attack

A proper regulation of membrane fluidity is critical for cellular activities such as communication between cells, mitosis, and endocytosis. Unsaturated lipids, a main component of biological membranes, are particularly susceptible to oxidative attack of reactive oxygen species. The oxidation of lipids can produce structural derangement of membranes and eventually alter the membrane fluidity. We have applied fluorescence correlation spectroscopy (FCS) and Raman spectroscopy to investigate the fluidity and structure of model membranes subject to oxidative attack. Hydrogen peroxide has little effect on the lateral fluidity of membranes, whereas hydroxyl radical causes a significantly increased fluidity. The latter is rationalized with the cleavage of the acyl chains of lipids caused by hydroxyl radical; this interpretation is founded on the diminished intensities of lines in Raman spectra associated with -CH(2) and C═C moieties in lipids and supported by mass-spectral measurements. The same approach provides a mechanistic account of the inhibitory capability of vitamins C and E against the increased membrane fluidity resulting from an oxidative attack. Membranes with much cholesterol exhibit a novel resistance against altered membrane fluidity induced with oxidative attack; this finding has biological implications. Our approach combining FCS and Raman measurements reveals the interplay between the structure and fluidity of membranes and provides insight into the pathophysiology of cellular oxidative injury.

The location and behavior of alpha-tocopherol in membranes

Vitamin E (alpha-tocopherol) has long been recognized as the major antioxidant in biological membranes, and yet many structurally related questions persist of how the vitamin functions. For example, the very low levels of alpha-tocopherol reported for whole cell extracts question how this molecule can successfully protect the comparatively enormous quantities of PUFA-containing phospholipids found in membranes that are highly susceptible to oxidative attack. The contemporary realization that membranes laterally segregate into regions of distinct lipid composition (domains), we propose, provides the answer. We hypothesize alpha-tocopherol partitions into domains that are enriched in polyunsaturated phospholipids, amplifying the concentration of the vitamin in the place where it is most needed. These highly disordered domains depleted in cholesterol are analogous, but organizationally antithetical, to the well-studied lipid rafts. We review here the ideas that led to our hypothesis. Experimental evidence in support of the formation of PUFA-rich domains in model membranes is presented, focusing upon docosahexaenoic acid that is the most unsaturated fatty acid commonly found. Physical methodologies are then described to elucidate the nature of the interaction of alpha-tocopherol with PUFA and to establish that the vitamin and PUFA-containing phospholipids co-localize in non-raft domains.

Catalytic chain-breaking pyridinol antioxidants

The synthesis of 3-pyridinols carrying alkyltelluro, alkylseleno, and alkylthio groups is described together with a detailed kinetic, thermodynamic, and mechanistic study of their antioxidant activity. When assayed for their capacity to inhibit azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system, tellurium-containing 3-pyridinols were readily regenerable by N-acetylcysteine contained in the aqueous phase. The best inhibitors quenched peroxyl radicals more efficiently than alpha-tocopherol, and the duration of inhibition was limited only by the availability of the thiol reducing agent. In homogeneous phase, inhibition of styrene autoxidation absolute rate constants k(inh) for quenching of peroxyl radical were as large as 1 x 10(7) M(-1) s(-1), thus outperforming the best phenolic antioxidants including alpha-tocopherol. Tellurium-containing 3-pyridinols could be quantitatively regenerated in homogeneous phase by N-tert-butoxycarbonyl cysteine methyl ester, a lipid-soluble analogue of N-acetylcysteine. In the presence of an excess of the thiol, a catalytic mode of action was observed, similar to the one in the two-phase system. Overall, compounds bearing the alkyltelluro moiety ortho to the OH group were much more effective antioxidants than the corresponding para isomers. The origin of the high reactivity of these compounds was explored using pulse-radiolysis thermodynamic measurements, and a mechanism for their unusual antioxidant activity was proposed. The tellurium-containing 3-pyridinols were also found to catalyze reduction of hydrogen peroxide in the presence of thiol reducing agents, thereby acting as multifunctional (preventive and chain-breaking) catalytic antioxidants.

Application of Water-Soluble Radical Initiator, 2,2′-Azobis-[2-(2-imidazolin-2-yl)propane] Dihydrochloride, to a Study of Oxidative Stress

It is essential to generate free radicals at a controled and constant rate for specific duration and at specific site to study the dynamics of oxidation and also antioxidation. Both hydrophilic and lipophilic azo compounds have been used for such purpose. In the present work, the action of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) was examined and compared with those of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (AMHP). The rate constant of free radical formation (ek(d)) for AIPH was 2.6 x 10(-6)/s at 37 degrees C in PBS (pH 7.4) solution, indicating that AIPH gives 3.8 times more free radicals than AAPH under the same conditions. It was found that the dynamics of oxidation and antioxidation induced by AIPH can be studied satisfactorily in the oxidation in micelles, LDL and erythrocyte suspensions, plasma, and cultured cells. The extent of cell death induced by AIPH and AAPH was directly proportional to the total free radicals formed. Interestingly, it was found that rats would not drink water containing AAPH, but they drank water containing AIPH. The levels of 8-iso-prostaglandin F2alpha (8-isoPs), 7-hydroxycholesterol (FCOH), lysophosphatidylcholine in the plasma of rats given water containing 50 mM AIPH for 1 month increased compared with those of control rats which drank water without AIPH. It may be concluded that AIPH is useful for kinetic and mechanistic studies on oxidative stress to membranes, lipoproteins, cells, and even animal models.

Membrane lipidomics and the geometry of unsaturated fatty acids from biomimetic models to biological consequences

In the last decades, free radical processes delineated an interdisciplinary field linking chemistry to biology and medicine. Free radical mechanisms became of importance as molecular basis of physiological and pathological conditions. Lipids, in particular, unsaturated fatty acids, are susceptible of free radical attack. The reactivity of the double bond toward free radicals is well known, in particular the reversible addition of radical species to this functionality determines the cis-trans double bond isomerization. Since the prevalent geometry displayed by unsaturated fatty acids in eukaryotes is cis, the occurrence of the cis-trans isomerization by free radicals corresponds to the loss of an important structural information linked to biological activity. The formation of trans isomers can have important meaning and consequences connected to radical stress. Free radical isomerization of membrane fatty acids has been the subject of research coupling the top-down approach by model studies, such as biomimetic chemistry in liposomes, with the bottom-up approach dealing with the examination of cell membrane lipidome in living systems under several physiopathological conditions. Methodologies and molecular libraries have been settled, for both liposome experiments and the examination of the radical stress in biological membranes. This chapter will give an overview of the current procedures used for liposome models and the cis-trans isomerization experiments, in order to build-up a library of trans geometrical fatty acid isomers.

Evaluation of the ability of antioxidants to counteract lipid oxidation: Existing methods, new trends and challenges

Oxidative degradation of lipids, especially that induced by reactive oxygen species (ROS), leads to quality deterioration of foods and cosmetics and could have harmful effects on health. Currently, a very promising way to overcome this is to use vegetable antioxidants for nutritional, therapeutic or food quality preservation purposes. A major challenge is to develop tools to assess the antioxidant capacity and real efficacy of these molecules. Many rapid in vitro tests are now available, but they are often performed in dissimilar conditions and different properties are thus frequently measured. The so-called 'direct' methods, which use oxidizable substrates, seem to be the only ones capable of measuring real antioxidant power. Some oxidizable substrates correspond to molecules or natural extracts exhibiting biological activity, such as lipids, proteins or nucleic acids, while others are model substrates that are not encountered in biological systems or foods. Only lipid oxidation and direct methods using lipid-like substrates will be discussed in this review. The main mechanisms of autoxidation and antioxidation are recapitulated, then the four components of a standard test (oxidizable substrate, medium, oxidation conditions and antioxidant) applied to a single antioxidant or complex mixtures are dealt with successively. The study is focused particularly on model lipids, but also on dietary and biological lipids isolated from their natural environment, including lipoproteins and phospholipidic membranes. Then the advantages and drawbacks of existing methods and new approaches are compared according to the context. Finally, recent trends based on the chemometric strategy are introduced as a highly promising prospect for harmonizing in vitro methods.

Bilirubin as an antioxidant in micelles and lipid bilayers: its contribution to the total antioxidant capacity of human blood plasma

The antioxidant capacities, antioxidant activities, k(inh), and stoichiometric factors, n, of water-soluble derivatives of bilirubin (BR), BR-human serum albumin (BR-HSA), and BR-ditaurate disodium conjugate (BRC) were determined in aqueous/lipid dispersions of sodium dodecyl sulfate (SDS) micelles/methyl linoleate and in bilayers of dilinoleoylphosphatidylcholine (DLPC) during initiation by water-soluble azo-bis-amidinopropane dihydrochloride (ABAP). The inhibition rate constants for BRC and BR-HSA were similar in micelles (k(inh) approximately 1.3 x 10(4) M(-1) s(-1)), where n approximately 2, whereas the k(inh) for BR-HSA dropped by (1/2) in bilayers. The dimethyl ester of bilirubin (BRDE) gave a k(inh) only one-tenth that of the vitamin E analog, pentamethylhydroxychroman (PMHC) in SDS micelles/methyl linoleate when initiated by lipid-soluble azo-bis-2,4-dimethylvaleronitrile (DMVN). Biliverdin hydrochloride (BVHCl) was NOT an effective peroxyl radical-trapping agent in the micellar phase during initiation by ABAP or DMVN containing methyl linoleate but it inhibited oxygen uptake in the aqueous phase. Both BRC and BR-HSA extended the total radical antioxidant parameter (TRAP) of human blood plasma and their contribution to TRAP was in the range of 5-10% of the natural TRAP of blood plasma, depending on the BR content determined in the blood plasma.

Regenerable Chain-Breaking 2,3-Dihydrobenzo[b]selenophene-5-ol Antioxidants

A series of 2,3-dihydrobenzo[b]selenophene-5-ol antioxidants was prepared by subjecting suitably substituted allyl 4-methoxyphenyl selenides to microwave-induced seleno-Claisen rearrangement/intramolecular Markovnikov hydroselenation followed by boron tribromide-induced O-demethylation. The novel antioxidants were assayed for their capacity to inhibit azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system containing N-acetylcysteine as a thiol reducing agent in the aqueous phase. Antioxidant efficiency as determined by the inhibited rate of peroxidation, Rinh, increased with increasing methyl substitution (Rinh=46-26 microM/h), but none of the compounds could match alpha-tocopherol (Rinh=22 microM/h). Regenerability as determined by the inhibition time, Tinh, in the presence of the thiol regenerating agent decreased with increasing methyl substitution. Thus, under conditions where the unsubstituted compound 5a inhibited peroxidation for more than 320 min, alpha-tocopherol worked for 90 min and the trimethylated antioxidant 5g for 60 min only. Sampling of the aqueous phase at intervals during peroxidation using antioxidant 5a showed that N-acetylcysteine was continuously oxidized with time to the corresponding disulfide. In the absence of the regenerating agent, compounds 5 inhibited peroxidation for 50-60 min only. A (RO)B3LYP/LANL2DZdp//B3LYP/LANL2DZ model was used for the calculation of homolytic O-H bond dissociation enthalpies (BDE) and adiabatic ionization potentials (IP) of phenolic antioxidants 5. Both BDE (80.6-76.3 kcal/mol) and IP (163.2-156.0 kcal/mol) decrease with increasing methyl substitution. The phenoxyl radical corresponding to phenol 5g gave an intense ESR signal centered at g=2.0099. The H-O bond dissociation enthalpy of the phenol was determined by a radical equilibration method using BHA as an equilibration partner. The observed BDE (77.6+/-0.5 kcal/mol) is in reasonable agreement with calculations (76.3 kcal/mol). As judged by calculated log P values, the lipophilicity of compounds 5 increased slightly when methyl groups were introduced into the phenolic moiety (2.9>C log P<4.2). The capacity of compounds 5a (kinh=3.8x10(5) M-1 s-1) and 5g (kinh=1.5x10(6) M-1 s-1) to inhibit azo-initiated autoxidation of styrene in the homogeneous phase (chlorobenzene) was also studied. More efficient regeneration at the lipid-aqueous interphase is the most likely explanation why the intrinsically poorest antioxidant 5a can outperform its analogues as well as alpha-TOC in the two-phase system. Possible mechanisms of regeneration are discussed and evaluated.

Ascorbate uptake and antioxidant function in peritoneal macrophages

Since activated macrophages generate potentially deleterious reactive oxygen species, we studied whether ascorbic acid might function as an antioxidant in these cells. Thioglycollate-elicited murine peritoneal macrophages contained about 3 mM ascorbate that was halved by culture in ascorbate-free medium. However, the cells took up added ascorbate to concentrations of 6-8 mM by a high-affinity sodium-dependent transport mechanism. This likely reflected the activity of the SVCT2 ascorbate transporter, since its message and protein were present in the cells. Activation of the cells by phagocytosis of latex particles depleted intracellular ascorbate, although not below the basal levels present in the cells in culture. Glutathione (GSH) was unaffected by phagocytosis, suggesting that ascorbate was more sensitive to the oxidant stress of phagocytosis than GSH. Phagocytosis induced a modest increase in reactive oxygen species as well as a progressive loss of alpha-tocopherol, both of which were prevented in cells loaded with ascorbate. These results suggest that activated macrophages can use ascorbate to lessen self-generated oxidant stress and spare alpha-tocopherol, which may protect these long-lived cells from necrosis or apoptosis.

Effect of Temperature, Cholesterol Content, and Antioxidant Structure on the Mobility of Vitamin E Constituents in Biomembrane Models Studied by Laterally Diffusion-Controlled Fluorescence Quenching

Kinetic parameters relevant for the antioxidant activity of the vitamin E constituents (alpha, beta, gamma, and delta homologues of tocopherols and tocotrienols) and of an amphiphilic vitamin C derivative, l-ascorbyl 6-palmitate, were determined. Fluorescence quenching experiments of 2,3-diazabicyclo[2.2.2]oct-2-ene in homogeneous acetonitrile-water mixtures afforded reactivity trends in terms of intermolecular quenching rate constants, while the quenching of Fluorazophore-L in liposomes provided the lateral diffusion coefficients relevant for understanding their biological activity in membranes. The reactivity in homogeneous solution was not influenced by the nature of the isoprenoid tail (tocopherol versus tocotrienol), but was dependent on the methylation pattern. The resulting order (alpha > beta = gamma > delta) was found to be in line with their reactivities toward peroxyl radicals as well as the phenolic O-H bond dissociation energies. The mutual lateral diffusion coefficient in POPC liposomes was the same, within error, for different tocopherols and tocotrienols (D(L) = (1.6 +/- 0.2) x 10(-7) cm(2) s(-1)). l-Ascorbyl 6-palmitate exhibited a reactivity similar to that of delta-tocopherol in homogeneous solution, but displayed a 1 order of magnitude lower fluorescence quenching efficiency in liposomes than the vitamin E constituents. Temperature effects on the laterally diffusion-controlled fluorescence quenching were large, with activation energies of 44 +/- 6 kJ mol(-1). The addition of cholesterol (0-30%) to POPC liposomes resulted only in slightly reduced diffusion coefficients. The combined results demonstrate that Fluorazophore-L can provide important physicochemical parameters for the understanding of antioxidant activity in biological environments.

Lipid peroxidation: mechanisms, inhibition, and biological effects

In the last 50 years, lipid peroxidation has been the subject of extensive studies from the viewpoints of mechanisms, dynamics, product analysis, involvement in diseases, inhibition, and biological signaling. Lipids are oxidized by three distinct mechanisms; enzymatic oxidation, non-enzymatic, free radical-mediated oxidation, and non-enzymatic, non-radical oxidation. Each oxidation mechanism yields specific products. The oxidation of linoleates and cholesterol is discussed in some detail. The relative susceptibilities of lipids to oxidation depend on the reaction milieu as well as their inherent structure. Lipid hydroperoxides are formed as the major primary products, however they are substrates for various enzymes and they also undergo various secondary reactions. Phospholipid hydroperoxides, for example, are reduced to the corresponding hydroxides by selenoproteins in vivo. Various kinds of antioxidants with different functions inhibit lipid peroxidation and the deleterious effects caused by the lipid peroxidation products. Furthermore, the biological role of lipid peroxidation products has recently received a great deal of attention, but its physiological significance must be demonstrated in future studies.

Ultraviolet B-induced DNA damage in human epidermis is modified by the antioxidants ascorbic acid and D-alpha-tocopherol

DNA damage caused by ultraviolet (UV) irradiation is considered the main etiologic factor contributing to the development of skin cancer. Systemic or topical application of antioxidants has been suggested as a protective measure against UV-induced skin damage. We investigated the effect of long-term oral administration of a combination of the antioxidants ascorbic acid (vitamin C) and D-alpha-tocopherol (vitamin E) in human volunteers on UVB-induced epidermal damage. The intake of vitamins C and E for a period of 3 mo significantly reduced the sunburn reaction to UVB irradiation. Detection of thymine dimers in the skin using a specific antibody revealed a significant increase of this type of DNA damage following UVB exposure. After 3 mo of antioxidant administration, significantly less thymine dimers were induced by the UVB challenge, suggesting that antioxidant treatment protected against DNA damage.