Oxidation of Quercetin and Kaempferol Markedly Amplifies Their Antioxidant, Cytoprotective, and Anti-Inflammatory Properties.

The contention that flavonoids' oxidation would necessarily lead to a loss of their antioxidant properties was recently challenged by the demonstration that quercetin oxidation leads to the formation of 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Que-BZF), a metabolite whose antioxidant potency was notably higher than that of its precursor. Here, we compared and expanded the former observation to that of the quercetin analogue kaempferol. Oxidation of kaempferol led to the formation of a mixture of metabolites that included the 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Kae-BZF). Following the chromatographic isolation of Kae-BZF from such a mixture, its antioxidant, mitochondria- and cell-protecting, and NF-kB-inhibiting effects were assessed, and compared with those of Que-BZF, in Caco-2 cells exposed to indomethacin as a source of ROS. The concentrations of Que-BZF (100 nm) and Kae-BZF (1 nm) needed to attain their maximal protection effects were 50- and 5000-fold lower than those of their respective precursors. The former differences in concentrations were also seen when the abilities of Que-BZF and Kae-BZF to inhibit the indomethacin-induced activation of NF-kB were compared. These data not only reveal that the oxidative conversion of quercetin and kaempferol into their respective 2-benzoyl-2-hydroxy-3(2H)-benzofuranones (BZF) results in a considerable amplification of their original antioxidant properties, but also that the in the case of kaempferol, such amplification is 100-fold greater than that of quercetin.

Novel Hybrid Inulin-Soy Protein Nanoparticles Simultaneously Loaded with (-)-Epicatechin and Quercetin and Their In Vitro Evaluation.

(-)-Epicatechin and quercetin have attracted considerable attention for their potential therapeutic application in non-communicable chronic diseases. A novel hybrid inulin-soy protein nanoparticle formulation was simultaneously loaded with (-)-epicatechin and quercetin (NEQs) to improve the bioavailability of these flavonoids in the human body, and NEQs were synthesized by spray drying. After process optimization, the physicochemical and functional properties of NEQs were characterized including in vitro release, in vitro gastrointestinal digestion, and cell viability assays. Results showed that NEQs are an average size of 280.17 ± 13.42 nm and have a zeta potential of -18.267 ± 0.83 mV in the organic phase. Encapsulation efficiency of (-)-epicatechin and quercetin reached 97.04 ± 0.01 and 92.05 ± 1.95%, respectively. A 3.5% soy protein content conferred controlled release characteristics to the delivery system. Furthermore, NEQs presented inhibitory effects in Caco-2, but not in HepG-2 and HDFa cell lines. These results contribute to the design and fabrication of inulin-soy protein nanoparticles for improving the bioavailability of multiple bioactive compounds with beneficial properties.

Revisiting the Oxidation of Flavonoids: Loss, Conservation or Enhancement of Their Antioxidant Properties.

Flavonoids display a broad range of health-promoting bioactivities. Among these, their capacity to act as antioxidants has remained most prominent. The canonical reactive oxygen species (ROS)-scavenging mode of the antioxidant action of flavonoids relies on the high susceptibility of their phenolic moieties to undergo oxidation. As a consequence, upon reaction with ROS, the antioxidant capacity of flavonoids is severely compromised. Other phenol-compromising reactions, such as those involved in the biotransformation of flavonoids, can also markedly affect their antioxidant properties. In recent years, however, increasing evidence has indicated that, at least for some flavonoids, the oxidation of such residues can in fact markedly enhance their original antioxidant properties. In such apparent paradoxical cases, the antioxidant activity arises from the pro-oxidant and/or electrophilic character of some of their oxidation-derived metabolites and is exerted by activating the Nrf2-Keap1 pathway, which upregulates the cell's endogenous antioxidant capacity, and/or, by preventing the activation of the pro-oxidant and pro-inflammatory NF-κB pathway. This review focuses on the effects that the oxidative and/or non-oxidative modification of the phenolic groups of flavonoids may have on the ability of the resulting metabolites to promote direct and/or indirect antioxidant actions. Considering the case of a metabolite resulting from the oxidation of quercetin, we offer a comprehensive description of the evidence that increasingly supports the concept that, in the case of certain flavonoids, the oxidation of phenolics emerges as a mechanism that markedly amplifies their original antioxidant properties. An overlooked topic of great phytomedicine potential is thus unraveled.

Effect of Epicatechin on Skeletal Muscle.

Loss of skeletal muscle (SkM) quality is associated with different clinical conditions such as aging, diabetes, obesity, cancer, and heart failure. Nutritional research has focused on identifying naturally occurring molecules that mitigate the loss of SkM quality induced by pathology or syndrome. In this context, although few human studies have been conducted, epicatechin (Epi) is a prime candidate that may positively affect SkM quality by its potential ability to mitigate muscle mass loss. This seems to be a consequence of its antioxidant and anti-inflammatory properties and its stimulation of mitochondrial biogenesis to increase myogenic differentiation, as well as its modulation of key proteins involved in SkM structure, function, metabolism, and growth. In conclusion, the Epi could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases. However, studies in humans are needed.

Protection against indomethacin-induced loss of intestinal epithelial barrier function by a quercetin oxidation metabolite present in onion peel: In vitro and in vivo studies.

Oxidative stress is directly implicated in the loss of intestinal epithelial barrier function (IEBF) induced by non-steroidal anti-inflammatory drugs (NSAIDs). Previous studies by our research team demonstrated that 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (BZF), a quercetin oxidation metabolite that naturally occurs in onion peels, exhibits an antioxidant potency notably higher than quercetin. Thus, we assessed the potential of BZF and a BZF-rich onion peel aqueous extract (OAE) to protect against the loss of IEBF in Caco-2 cell monolayers and in rats exposed to indomethacin. In vitro, pure BZF and OAE standardized in BZF (100 nM), protected against the drop in transepithelial electrical resistance by 70 - 73%. Likewise, it prevented the increase in fluorescein-isothiocyanate labelled dextran (FITC-dextran) paracellular transport by 74% and oxidative stress by 84 - 86%. In vivo, BZF, given orally at a dose 80 µg/Kg bw as OAE, totally abolished a 30-fold increase in FITC-dextran serum concentration induced by indomethacin. This effect was dose-dependent and largely conserved (85%) when OAE was given 180-min prior to indomethacin. The IEBF-protective effect of OAE was accompanied by a full prevention of the NF-ĸB activation, and the increases in interleukine-8 secretion and myeloperoxidase activity induced by indomethacin. The protection was also associated with a 21-fold increase in Nrf2, and a 7-fold and 9-fold increase in heme oxygenase-1 and NAD(P)H-quinone oxidoreductase 1, respectively. The IEBF-protecting effect of OAE involves, most likely, its dual capacity to activate Nrf2 while inhibiting NF-ĸB activation. The extremely low doses of BZF needed to promote such actions warrants extending its IEBF-protective effects to other NSAIDs.

Wheat and Rice beyond Phenolic Acids: Genetics, Identification Database, Antioxidant Properties, and Potential Health Effects.

Wheat and rice play a vital role in human nutrition and food security. A better understanding of the potential health benefits associated with consuming these cereals, combined with studies by plant scientists and food chemists to view the entire food value chain from the field, pre and post-harvest processing, and subsequent "fork" consumption, may provide the necessary tools to optimize wheat and rice production towards the goal of better human health improvement and food security, providing tools to better adapt to the challenges associated with climate change. Since the available literature usually focuses on only one food chain segment, this narrative review was designed to address the identities and concentration of phenolics of these cereal crops from a farm-to-fork perspective. Wheat and rice genetics, phenolic databases, antioxidant properties, and potential health effects are summarized. These cereals contain much more than phenolic acids, having significant concentrations of flavonoids (including anthocyanins) and proanthocyanidins in a cultivar-dependent manner. Their potential health benefits in vitro have been extensively studied. According to a number of in vivo studies, consumption of whole wheat, wheat bran, whole rice, and rice bran may be strategies to improve health. Likewise, anthocyanin-rich cultivars have shown to be very promising as functional foods.

Optimization of the Synthesis of Natural Polymeric Nanoparticles of Inulin Loaded with Quercetin: Characterization and Cytotoxicity Effect.

Quercetin is a bioactive component that is capable of having therapeutic potential in the prevention of different noncommunicable chronic diseases (NCDs). However, it presents instability in the gastrointestinal tract in addition to low bioavailability. One way to overcome the limitations of quercetin lies in using nanotechnology for the development of nanoparticles, based on biopolymers, that are capable of being ingestible. Inulin, a fructan-type polysaccharide, acts as a delivery system for the release of quercetin in a target cell, guaranteeing the stability of the molecule. Inulin-coated quercetin nanoparticles were synthesized by the spray dryer method, and four variables were evaluated, namely inulin concentration (5-10% w/v), feed temperature (40-60 °C), inlet temperature (100-200 °C) and outlet temperature (60-100 °C). The optimal conditions were obtained at 10% w/v inulin concentration, with 45 °C feed temperature, 120 °C inlet temperature and 60 °C outlet temperature, and the nanoparticle size was 289.75 ± 16.3 nm in water. Fluorescence microscopy indicated quercetin loading in the inulin nanoparticles, with an encapsulation efficiency of approximately 73.33 ± 7.86%. Inulin-coated quercetin nanoparticles presented effects of inhibition in Caco-2 and HepG2 cells, but not in HDFa cells. The experimental data showed the potential of inulin nanoparticles as transport materials for unstable molecules, in oral administration systems, for the encapsulation, protection and release of quercetin.

Vitamin E as an essential micronutrient for human health: Common, novel, and unexplored dietary sources.

Vitamin E comprises a group of vitamers that includes tocopherols and tocotrienols. They occur in four homologues according to the number and position of methyl groups attached to the chromanol ring. Vitamin E, a liposoluble antioxidant, may participate as an adjuvant in the prevention and treatment of cardiovascular, neurological, and aging-related diseases. Furthermore, vitamin E has applications in the food industry as a natural additive. In this contribution, the most recent information on the dietary sources of vitamin E, including common, novel, and unexplored sources, is presented. Common edible oils, such as those of corn, olive, palm, rice bran, and peanut, represent the most prominent sources of vitamin E. However, specialty and underutilized oils such as those obtained from tree nuts, fruit seeds, and by-products, emerge as novel sources of this important micronutrient. Complementary studies should examine the tocotrienol content of vitamin E dietary sources to better understand the different biological functions of these vitamers.

Quercetin Oxidation Metabolite Present in Onion Peel Protects Caco-2 Cells against the Oxidative Stress, NF-kB Activation, and Loss of Epithelial Barrier Function Induced by NSAIDs.

The potential of 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (BZF), a quercetin oxidation metabolite, and that of a BZF-rich onion peel aqueous extract (OAE) to protect Caco-2 monolayers against the oxidative stress (OS) and an increased permeability (IP) induced by five nonsteroidal anti-inflammatory drugs (NSAIDs) (indomethacin, diclofenac, piroxicam, ibuprofen, and metamizole) were investigated. Under identical OS conditions, the NSAIDs substantially differed in their ability to induce an IP and/or NF-kB activation. The OAE (100 nM BZF) protected in identical magnitude (84-86%) against OS but in a highly dissimilar manner against the IP (18-73%). While all NSAIDs activated NF-kB, the OAE prevented only that induced by indomethacin. Results reveal that the IP has no direct relationship with the OS and that with the exception of indomethacin, the prevention of NSAIDs-induced OS and/or NF-kB activation plays no fundamental role in the IP-protecting effect of OAE. These results warrant the in vivo evaluation of OAE against indomethacin-induced loss of intestinal barrier function.

Nanotechnology as a Key to Enhance the Benefits and Improve the Bioavailability of Flavonoids in the Food Industry.

Nanotechnology has impacted the food industry, mainly on developing healthier, safer, and high-quality functional food. Flavonoids are valuable compounds present in plants, fruits, grains, roots, stems, tea, and wine, among others; they possess many benefits for health due to their antioxidant properties toward reactive oxygen species, anti-inflammatory, and antiproliferative, among others. These characteristics make flavonoids attractive in various industrial areas such as medicine, nutraceutical, cosmetology, and pharmaceutical. Unfortunately, flavonoids lack long-term stability, are sensitive to light, long periods of darkness with low oxygen concentration, and often present a low water solubility and poor bioavailability. Nanoencapsulation is an alternative to improve bioavailability and sensitivity in the manufacturing process, based on encapsulating substances on a nanoscale. Nanocapsules are a promising strategy in significantly enhancing the delivery of compounds to various sites in the body. The development of biopolymers to encapsulate sensitive compounds is increasing, as well as the search for the non-toxic, biodegradable, natural and biocompatible characteristics of polymers, is fundamental. The present review describes the recent techniques and technologies for the nanoencapsulation of flavonoids. It discusses their potential advantages and possible limitations, compares natural and synthetic biopolymers, and finally, details nanoparticle regulation.

Low nanomolar concentrations of a quercetin oxidation product, which naturally occurs in onion peel, protect cells against oxidative damage.

The occurrence of the quercetin oxidation metabolite 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (BZF), whose antioxidant potency is notably higher than the antioxidant potency of quercetin, was investigated in twenty quercetin-rich plant foods. BZF was identified (HPLC-DAD-ESI-MS/MS) only in the dry outer scales of onions and shallots. Aqueous extracts of onions (OAE) and shallots (SAE) were evaluated for their antioxidant and cytoprotective properties. OAE, whose potency did not differ from SAE, protected ROS-exposed Caco2 cells against oxidative (78%) and cellular (90%) damage at a 3 µg/L concentration (corresponding to 0.03 nM of BZF). After chromatographic resolution of OAE, the BZF peak accounted fully and exclusively for its antioxidant effect. The antioxidant effects of OAE and of a pure BZF were described by two perfectly overlapping curves whose concentration-dependence was within the 3 × 10-4 to 102 nM BZF range. Such unprecedented low concentrations place BZF-containing plants on the frontier of the search for novel sources of antioxidants.

Quercetin and related flavonoids conserve their antioxidant properties despite undergoing chemical or enzymatic oxidation.

Oxidation of a phenolic group in quercetin is assumed to compromise its antioxidant properties. To address this assumption, the ROS-scavenging, Folin-Ciocalteau- and Fe-reducing capacities of quercetin and thirteen structurally related flavonoids were assessed and compared with those of mixtures of metabolites resulting from their chemical and enzymatic oxidation. Regardless of the oxidation mode, the metabolites mixtures largely conserved the antioxidant properties of the parent molecules. For quercetin, 95% of its ROS-scavenging and over 77% of its Folin-Ciocalteau- and Fe-reducing capacities were retained. The susceptibility of flavonoids to oxidative disappearance (monitored by HPLC-DAD) and that of the mixtures to retain their antioxidant capacity was favourably influenced by the presence of a catechol (ring-B) and enol (ring C) function. This is the first study to report that mixtures resulting from the oxidation of quercetin and its analogues largely conserve their antioxidant properties.

Quercetin Oxidation Paradoxically Enhances its Antioxidant and Cytoprotective Properties.

Quercetin oxidation is generally believed to ultimately result in the loss of its antioxidant properties. To test this assertion, quercetin oxidation was induced, and after each of its major metabolites was identified and isolated by HPLC-DAD-ESI-MS/MS, the antioxidant (dichlorodihydrofluorescein oxidation-inhibiting) and cytoprotective (LDH leakage-preventing) properties were evaluated in Hs68 and Caco2 cells exposed to indomethacin. Compared to quercetin, the whole mixture of metabolites (QOX) displayed a 20-fold greater potency. After resolution of QOX into 12 major peaks, only one (peak 8), identified as 2,5,7,3',4'-pentahydroxy-3,4-flavandione or its 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone tautomer, could account for the antioxidant and cytoprotective effects afforded QOX. Peak 8 exerted such effects at a 50 nM concentration, revealing a potency 200-fold higher than that of quercetin. The effects of peak 8 were seen regardless of whether it was added to the cells 40 min before or simultaneously with the oxygen-reactive species-generating agent, suggesting an intracellular ability to trigger early antioxidant responses. Thus, the present study is the first to reveal that in regard to the intracellular actions of quercetin, attention should be extended toward some of its oxidation products.

Molecular mechanisms of gastrointestinal protection by quercetin against indomethacin-induced damage: role of NF-κB and Nrf2.

The aim of this study was to determine the gastrointestinal protection by quercetin against indomethacin-induced oxidative stress and inflammation, with specific interest in studying the underlying molecular mechanisms. We hypothesized that the quercetin-protective effect relies on its antioxidant and antiinflammatory properties. Rats were pretreated with quercetin (50- or 100-mg/kg, ig single dose), 30 min before INDO administration (40-mg/kg ig single dose). Caco-2 cells were treated with INDO (250 and 500 µM) in the absence or presence of quercetin (10 µg/ml). Quercetin prevented the decrease in nuclear translocation of Nrf2, a key regulator of the antioxidant response, and the increase in reactive oxygen species levels induced by INDO by inhibiting the enhancement of NADPH oxidase and xanthine oxidase activities as well as the reduction in superoxide dismutase and glutathione peroxidase activities in gastric and ileal tissues. Quercetin also prevented INDO-induced ICAM-1 and P-selectin expressions and the increase of myeloperoxidase activity in gastric and ileal tissues and NF-κB activation and IL-8 production in Caco-2 cells. Quercetin did not affect the inhibition of TNFα-mediated production of prostaglandin E2 induced by INDO in Caco-2 cells. The protective effects of quercetin observed in the gastric and ileal mucosa of rats as well as in Caco-2 cells relied on the ability of this flavonol to prevent NF-κB activation and increase Nrf2 translocation. This study supports the concept that quercetin may be useful in the prevention and/or treatment of nonsteroidal antiinflammatory drug-associated side effects, without interfering with their therapeutic efficacy.

Cu(II)-disulfide complexes with superoxide dismutase- and catalase-like activities protect mitochondria and whole cells against oxidative stress.

Mitochondria are a major subcellular site of superoxide (O2(-)) formation. Conditions leading to an uncontrolled production, accumulation and/or conversion of O2(-) into hydrogen peroxide result in an increment in the intramitochondrial oxidative tone which, ultimately leads to the loss of cell viability. Recently, we reported on the ability of a series of Cu(II)-disulfide complexes to act simultaneously as SOD- and catalase-like molecules. In the present study, we addressed the potential of such compounds to protect mitochondria and cells against the oxidative stress and the cytolytic damage induced by diclofenac. Exposure of Caco-2 cells to diclofenac (250µM, 20min) led to a near 80% inhibition of mitochondrial complex I activity and almost doubled the rate of mitochondrial O2(-) production (assessed by Mitosox). A comparable increment was seen in whole cells when the oxidative tone was assessed through the largely hydrogen peroxide-dependent dichlorofluorescein (DCFH) oxidation. The increment in mitochondrial O2(-) production was totally and concentration-dependently prevented by the addition of the complexes formed between Cu(II) and the disulfides of glutathione, homocysteine, or a-dehydro-lipoic acid (20µM each); comparatively, the Cu(II)-cystine complex exerted a weaker protection. A comparable protection pattern was seen at the whole cell level, as these complexes were also effective in preventing the increment in DCFH oxidation. The mitochondrial and whole cell antioxidant protection also translated into a full protection against the cytolytic effects of diclofenac (45min). Results from the present study indicate that the here-tested Cu(II)-disulfides complexes are able to effectively protect cells against the oxidative and the lytic effects of O2(-)-overproducing mitochondria, suggesting a potential for these type of compounds to act as SOD- and catalase-like molecules under oxidative-stress conditions. Supported by FONDECYT #1110018.

First web-based database on total phenolics and oxygen radical absorbance capacity (ORAC) of fruits produced and consumed within the south Andes region of South America.

This paper reports the first database on antioxidants contained in fruits produced and consumed within the south Andes region of South America. The database ( www.portalantioxidantes.com ) contains over 500 total phenolics (TP) and ORAC values for more than 120 species/varieties of fruits. All analyses were conducted by a single ISO/IEC 17025-certified laboratory. The characterization comprised native berries such as maqui ( Aristotelia chilensis ), murtilla ( Ugni molinae ), and calafate ( Barberis microphylla ), which largely outscored all other studied fruits. Major differences in TP and ORAC were observed as a function of the fruit variety in berries, avocado, cherries, and apples. In fruits such as pears, apples, apricots, and peaches, a significant part of the TP and ORAC was accounted for by the antioxidants present in the peel. These data should be useful to estimate the fruit-based intake of TP and, through the ORAC data, their antioxidant-related contribution to the diet of south Andes populations.