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

Gross Antioxidant Capacity and Anti-Inflammatory Potential of Flavonol Oxidation Products: A Combined Experimental and Theoretical Study

This study evaluated the antioxidant capacity of the oxidation products of three flavonols using oxygen radical absorbance capacity-fluorescein assay (ORAC-FL), oxygen radical absorbance capacity-pyrogallol red assay (ORAC-PGR), and the cellular antioxidant activity (CAA) assay in human dermal fibroblast (HFF) cells, with 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) as a free radical generator under controlled pH and solvent conditions. At pH 2 in a polar aprotic solvent, BZF-OH (benzofuranone-OH) compounds were formed, while methoxylated analogs were obtained at pH 7 in a polar protic solvent. The products generated at pH 2 exhibited significantly higher antioxidant capacities, demonstrating the influence of the reaction environment on modulating antioxidant properties. The antioxidant activity was observed to reflect the combined action of the flavonol precursor and its oxidation products. This led to the proposal of the Gross Antioxidant Capacity (GAC) concept to integrate the contribution of all generated species. Since chemical assays such as ORAC do not fully capture the complexity of biological systems, they should be complemented with cellular approaches for a more accurate evaluation. Additionally, BZF-OH compounds were analyzed as potential cyclooxygenase-2 (COX-2) inhibitors through docking and molecular dynamics simulations, where BZF-Quer-OH showed binding affinities comparable to celecoxib, a selective COX-2 inhibitor. These findings were complemented by an analysis of COX-2 expression in RAW 264.7 cells treated with lipopolysaccharide (LPS), where treatment with the antioxidants significantly inhibited COX-2 expression. In the case of the oxidation products, only the oxidation product of rhamnetin showed a reduction in COX-2 expression compared to the LPS-treated control. Together, these results highlight that flavonol-derived oxidation products not only retain significant antioxidant capacity but may also possess anti-inflammatory properties, opening new perspectives for the development of innovative therapies targeting oxidative stress and chronic inflammation.

Effect of Thermal Treatment on the Extraction and Antioxidant and Antiglycation Activities of (Poly)phenols from Ribes magellanicum

Phenolic compounds have antiglycation activity, but the changes occurring during thermal treatment (TT) in these activities are not completely understood. The effects of the extraction conditions of (poly)phenols from Ribes magellanicum fruits, before and after TT, on their antioxidant and antiglycation effects were assessed. (Poly)phenol-enriched extracts (PEEs) from raw and TT (90 °C, 1 h) Ribes magellanicum were extracted using three solvent mixtures (ethanol/water/acetic acid) with increasing water content (0, 24, and 49%) and three solvent-to-solid ratios (5, 10, and 20 mL/g). PEEs of raw samples showed increased values of total (poly)phenols (TPC), TEAC, and FRAP and decreased IC50 values of fluorescent advanced glycation end products (AGEs) with increasing water content. An increase in TPC and FRAP values was observed for TT samples, but an increase in the IC50 values of fluorescent AGEs for PEEs with increasing water content was observed. Antiglycation activity (IC50 raw/IC50 TT) depended on the solvent-to-solid ratio and the extracting solvent. HPLC-DAD-MS analysis of raw and TT samples showed degradation of anthocyanins, flavonoid fragmentation, and oxidation as the main changes in the phenolic composition of TT samples. We show that TT affects the (poly)phenolic composition of R. magellanicum, producing a decrease in the antiglycation activity when extractions are performed with increasing water content, despite increasing TPC and FRAP activity.

Thermal treatment under oxidative conditions increases the antioxidant and antiglycation activity of Chilean Tórtola beans (Phaseolus vulgaris)

The influence of oxygen on the thermal treatment (TT) of secondary metabolite-enriched extracts (SMEEs) from Tórtola beans and procyanidin C1 (PC1) on the inhibition of advanced glycation end products (AGEs) generation in proteins was investigated. SMEE was incubated at 4 °C (control) or thermally treated at 60 °C for 2 h, at either 0 % O2 (I) or 20 % O2 (II). Treatments I and II increased the content of procyanidin dimers B2. Treatment II was more effective than the control or treatment I in preventing homocysteine oxidation and AGEs generation. TT of PC1 at 0 % or 20 % O2 generated procyanidin dimers and tetramers. PC1 TT at 20 % O2 exhibited higher oxidation potentials and lower IC50 values of fluorescent AGEs than those of controls or TT at 0 % O2. These findings indicate that SMEE from Tórtola beans after treatment II changes the degree of polymerization and oxidation procyanidins, thereby increasing their antiglycation activity.

Polyphenol compounds contributing to the improved bioactivities of fermented Rubus chingii Hu

This research aims to evaluate the phenolic composition, antioxidant and enzyme inhibition activities of fermented Rubus chingii Hu wine, and explore the correlation between them. TPC (Total Phenolic content) and TFC (Total Flavonoid content) increased rapidly from 0 h to 72 h, followed by a slight decrease in TPC and a significant decrease in TFC. Fermentation could significantly increase the antioxidant activity and α-amylase/α-glucosidase enzyme inhibitory activity of Rubus chingii Hu. A total of 39 polyphenols and organic acids in fermented Rubus chingii Hu were identified by UPLC-ESI-Q-TOF-MS/MS and 11 of them were quantitatively analyzed. After fermentation, the contents of all the detected polyphenol compounds, except for quercetin and ellagic acid, significantly increased (p < 0.05). Correlation analysis showed that protocatechuic acid and catechin played an important role in the antioxidant activity of fermented Rubus chingii Hu, while protocatechuic acid and hypericin played an important role in the α-amylase inhibition activity. This study indicated that Rubus chingii Hu could be applided as a potential meterial for the wine production, and has the potential to be a functional food for promoting health.

Flavonoid Oxidation Potentials and Antioxidant Activities-Theoretical Models Based on Oxidation Mechanisms and Related Changes in Electronic Structure

Herein, I will review our efforts to develop a comprehensive and robust model for the estimation of the first oxidation potential, Ep1, and antioxidant activity, AA, of flavonoids that would, besides enabling fast and cheap prediction of Ep1 and AA for a flavonoid of interest, help us explain the relationship between Ep1, AA and electronic structure. The model development went forward with enlarging the set of flavonoids and, that way, we had to learn how to deal with the structural peculiarities of some of the 35 flavonoids from the final calibration set, for which the Ep1 measurements were all made in our laboratory. The developed models were simple quadratic models based either on atomic spin densities or differences in the atomic charges of the species involved in any of the three main oxidation mechanisms. The best model takes into account all three mechanisms of oxidation, single electron transfer-proton transfer (SET-PT), sequential proton loss electron transfer (SPLET) and hydrogen atom transfer (HAT), yielding excellent statistics (R2 = 0.970, S.E. = 0.043).

Amplification of the antioxidant properties of myricetin, fisetin, and morin following their oxidation

Quercetin oxidation leads to the formation of a metabolite, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone, whose antioxidant potency was recently reported to be a 1000-fold higher than that of its precursor. The formation of similar metabolites (BZF) is limited to certain flavonols (FL), among which are myricetin, fisetin, and morin. Here we addressed the consequences of inducing the auto-oxidation of these flavonols in terms of their antioxidant properties (assessed in ROS-exposed Caco-2 cells). The mixtures that result from their oxidation (FLox) exhibited antioxidant activities 10-to-50-fold higher than those of their precursors. Such amplification was fully attributable to the presence of BZF in each FLox (established by HPLC-ESI-MS/MS and chemical subtraction techniques). An identical amplification was also found when the antioxidant activities of BZF, isolated from each FLox, and FL were compared. These findings warrant the search of these BZF in edible plants and their subsequent evaluation as a new type of functional food ingredients.

Enhancing effect of the coexisting alpha-tocopherol on quercetin absorption and metabolism

The aim of this study is to investigate the modulating effect of coexisting food components on the absorption and metabolism of quercetin and blood plasma antioxidant potentials. The combination of quercetin with α-tocopherol (αT), cellulose, or a commercially available vegetable beverage containing αT and dietary fiber was orally administered to mice. Compared to the single administration of quercetin aglycone, the coadministration of αT with quercetin significantly increased the plasma quercetin concentration at 0.5 h, whereas the combination of quercetin and cellulose decreased it. Interestingly, the administration of quercetin mixed with the vegetable beverage showed no significant change in the quercetin concentration in the mice plasma. The treatment of the cells with the blood plasma after the coadministration of αT with quercetin significantly upregulated the gene expression of the antioxidant enzyme (heme oxygenase-1), whereas the quercetin and cellulose combination did not. In the plasma of the quercetin-administered mice, eight types of quercetin metabolites were detected, and their quantities were affected by the combination with αT. The potentials of the heme oxygenase-1 gene expression by these metabolites were very limited, although several metabolites showed radical scavenging activities comparable to aglycone in the in vitro assays. These results suggested that the combination of αT potentiates the quercetin absorption and metabolism and thus the plasma antioxidant potentials, at least in part, by the quantitative changes in the quercetin metabolites.

Insights in Electrochemical Determination of Quercetin in Peach Vinegar by the Hexagonal Platinum Nanocrystal

Peach vinegar is a popular condiment that is thought to have various health benefits. However, the low levels of quercetin and complex detection environment in peach vinegar make it difficult to detect using traditional methods. Electrochemical detection is a promising solution because it is sensitive, inexpensive, and provides real-time results. Herein, a hexagonal Pt nanocrystal was developed as an electrocatalyst for selective detection of quercetin in peach vinegar, and a comprehensive examination was given of the electrochemical characteristics of quercetin when applied to electrodes modified with platinum. The morphology and crystal properties of Pt nanocrystals were analyzed, and the Pt-modified electrode was found to exhibit strong electrocatalytic effects toward quercetin in peach vinegar with a high sensitivity of 58 μA μM-1. Furthermore, the investigation showcased exceptional specificity, consistency, sustained durability, and replicability of the Pt-modified electrode in identifying quercetin. The detection result of the Pt-modified electrode tested in three different peach vinegar samples demonstrated its practical utility in real-world applications. Overall, the findings of this study may have important implications for the development of more efficient and sensitive electrochemical sensors for the detection of quercetin and other analytes in vinegar.

Quercetin ameliorates acute acrylamide induced spleen injury

Acrylamide is used for industrial and laboratory purposes; it also is produced during cooking of carbohydrate-rich food at high temperature. We investigated the therapeutic potential of quercetin for treatment of acute acrylamide induced injury to the spleen. We used female albino rats treated with acrylamide for 10 days followed by oral administration of quercetin in three doses for 5 days. We observed significantly reduced total body weight, spleen weight, red blood cells, total proteins, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glucose-6-phophate dehydrogenase, reduced glutathione, concentration of serum IgG and IgM after acrylamide induced toxicity compared to controls. We also found that white blood cells, triglycerides, cholesterol and lipid oxidation were increased significantly after acrylamide induced toxicity in rats compared to controls. Histoarchitecture of spleen was affected adversely by acrylamide toxicity. Administration of quercetin ameliorated adverse effects of acrylamide in a dose-dependent manner. Quercetin appears to ameliorate acrylamide induced injury to the spleen by increasing endogenous antioxidants and improving histoarchitecture and immune function.

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.

The potential of functionalized dressing releasing flavonoids facilitates scar-free healing

Scars are pathological marks left after an injury heals that inflict physical and psychological harm, especially the great threat to development and aesthetics posed by oral and maxillofacial scars. The differential expression of genes such as transforming growth factor-β, local adherent plaque kinase, and yes-related transcriptional regulators at infancy or the oral mucosa is thought to be the reason of scarless regenerative capacity after tissue defects. Currently, tissue engineering products for defect repair frequently overlook the management of postoperative scars, and inhibitors of important genes alone have negative consequences for the organism. Natural flavonoids have hemostatic, anti-inflammatory, antioxidant, and antibacterial properties, which promote wound healing and have anti-scar properties by interfering with the transmission of key signaling pathways involved in scar formation. The combination of flavonoid-rich drug dressings provides a platform for clinical translation of compounds that aid in drug disintegration, prolonged release, and targeted delivery. Therefore, we present a review of the mechanisms and effects of flavonoids in promoting scar-free regeneration and the application of flavonoid-laden dressings.

Mechanism of (−)-epigallocatechin gallate (EGCG) dimerization by low-temperature plasma

The efficient dimerization of (−)-Epigallocatechin gallate (EGCG), which is the major bioactive constituent isolated from the leaves of Camellia sinensis, was initially reported without changes in its stereochemistry using low-temperature plasma. The contribution of plasma during the dimerization of EGCG in a methanolic solution was quantified using a major factor, with the major factor demonstrated based on the contents of newly generated products, in this case the sum of oolonghomobisflavans A and B depending on the plasma treatment method. Samples were treated in three methods: plasma direct treatment, an indirect treatment using only reactive species, and an indirect treatment using effects other than those by reactive species. Ozone was identified as a major factor during the plasma treatment, and the operating ranges of the ozone concentration for regulated dimerization were evaluated. The mechanism by which EGCG synthesizes dimers A and B during the treatment process using low-temperature plasma was investigated using the derived major factor and prior literature. The ozone generated by the plasma reacted with methanol to form formaldehyde, and dimers A and B were synthesized by oligomers through a methylene-bridge by the formaldehyde. A plausible pathway of regulated dimerization was deduced based on these results, and the mechanism of EGCG dimerization by plasma is described using this pathway.

Recent insights into oxidative metabolism of quercetin: catabolic profiles, degradation pathways, catalyzing metalloenzymes and molecular mechanisms

Quercetin is the most abundant polyphenolic flavonoid (flavonol subclass) in vegetal foods and medicinal plants. This dietary chemopreventive agent has drawn significant interest for its multiple beneficial health effects ("polypharmacology") largely associated with the well-documented antioxidant properties. However, controversies exist in the literature due to its dual anti-/pro-oxidant character, poor stability/bioavailability but multifaceted bioactivities, leaving much confusion as to its exact roles in vivo. Increasing evidence indicates that a prior oxidation of quercetin to generate an array of chemical diverse products with redox-active/electrophilic moieties is emerging as a new linkage to its versatile actions. The present review aims to provide a comprehensive overview of the oxidative conversion of quercetin by systematically analyzing the current quercetin-related knowledge, with a particular focus on the complete spectrum of metabolite products, the enzymes involved in the catabolism and the underlying molecular mechanisms. Herein we review and compare the oxidation pathways, protein structures and catalytic patterns of the related metalloenzymes (phenol oxidases, heme enzymes and specially quercetinases), aiming for a deeper mechanistic understanding of the unusual biotransformation behaviors of quercetin and its seemingly controversial biological functions.

Advances on nanoformulation approaches for delivering plant-derived antioxidants: A case of quercetin

Oxidative stress has been implicated in tumorigenic, cardiovascular, neuro-, and age-related degenerative changes. Antioxidants minimize the oxidative damage through neutralization of reactive oxygen species (ROS) and other causative agents. Ever since the emergence of COVID-19, plant-derived antioxidants have received enormous attention, particularly in the Indian subcontinent. Quercetin (QCT), a bio-flavonoid, exists in the glycosylated form in fruits, berries and vegetables. The antioxidant potential of QCT analogs relates to the number of free hydroxyl groups in their structure. Despite presence of these groups, QCT exhibits substantial hydrophobicity. Formulation scientists have tested nanotechnology-based approaches for its improved solubilization and delivery to the intended site of action. By the virtue of its hydrophobicity, QCT gets encapsulated in nanocarriers carrying hydrophobic domains. Apart from passive accumulation, active uptake of such formulations into the target cells can be facilitated through well-studied functionalization strategies. In this review, we have discussed the approaches of improving solubilization and bioavailability of QCT with the use of nanoformulations.

Actinidia deliciosa Mitigates Oxidative Stress and Changes in Pancreatic α-, β-, and δ-Cells and Immunohistochemical and Histological Architecture in Diabetic Rats

The present study evaluated the antioxidant capacity and antidiabetic effect of Actinidia deliciosa in diabetic rats. Rats were grouped as follows: control, Actinidia deliciosa aqueous extract (ADAE, 1 g/kg, daily and orally), streptozotocin (STZ, 50 mg/kg BW, single intraperitoneal dose), and STZ plus ADAE, respectively. Twenty-eight components were detected by GC-MS analysis with high phenolic contents and high DPPH scavenging activity. In vivo results revealed that rats treated with STZ showed a highly significant elevation in blood glucose and a decrease in insulin hormone levels. Thiobarbituric acid-reactive substances and hydrogen peroxide levels were elevated, while bodyweight, enzymatic, and nonenzymatic antioxidants were significantly decreased. Furthermore, histopathological and immunohistochemical insulin expression, besides ultrastructure microscopic variations (β-cells, α-cells, and δ-cells), were seen in pancreas sections supporting the obtained biochemical changes. Otherwise, rats supplemented with ADAE alone showed an improved antioxidant status and declined lipid peroxidation. Moreover, diabetic rats augmented with ADAE showed significant modulation in oxidative stress markers and different pancreatic tissue investigations compared to diabetic ones. Conclusively, ADAE has a potent antioxidant and hypoglycemic influence that may be utilized as a health-promoting complementary therapy in diabetes mellitus.

Honeybee Pollen From Southern Chile: Phenolic Profile, Antioxidant Capacity, Bioaccessibility, and Inhibition of DNA Damage

Honeybee pollen (HBP) chemical composition is highly variable conforming to the floral and geographical origin of the pollen grains. The beneficial effects and functional properties of the HBP are well-known and have been mainly attributed to their high content of antioxidant polyphenols. In this work, twelve HBPs samples from the Southern region of Chile (X Región de Los Lagos) were characterized for the first time according to their botanical origin, phenolic composition, and antioxidant activity. The in vitro gastrointestinal digestion assay was done to simulate the human upper digestive tract. Selected honeybee pollen extracts (HBPEs) were assessed as bioaccessible fractions during an in vitro gastrointestinal digestion. Contents of phenolic compounds, antioxidant capacity, and recovery index of quercetin, myricetin, and cinnamic acid were monitored in different steps of gastrointestinal digestion. Furthermore, the protective effect of in vitro digested HBP towards DNA damage induced by peroxyl radicals was evaluated. The introduced species Brassica rapa L. (Brassicaceae), Lotus pedunculatus Cav. (Fabaceae), and Ulex europaeus L. (Fabaceae) predominated in all the HBPs analyzed, while the native species Buddleja globosa Hope (Scrophulariaceae), Luma apiculata (DC.) Burret (Myrtaceae), Embothrium coccineum J.R. Forst. & G. Forst. (Proteaceae) and Eucryphia cordifolia Cav. (Cunoniaceae) appeared less frequently. The content of polyphenols and antioxidant capacity in HBPEs achieved full bioaccessibility at the end of the intestinal digestion step. However, results obtained by a state-of-the-art technique (i.e. HPLC-DAD) demonstrated relatively low values of bioaccessible quercetin and cinnamic acid after the digestion process. In contrast, myricetin showed a high bioaccessibility in the intestinal digestion steps. The protective effect of in vitro digested HBP towards DNA damage induced by peroxyl radicals showed promising results (up to 91.2% protection). In conclusion, HBPs from the X Region de Los Lagos are rich sources of phenolic antioxidants that protect DNA from strand breakage. Therefore, the potential of HBPEs in preventing gastric and/or intestinal cancer should be further considered.

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.

Evaluation of the antioxidative and genotoxic effects of sodium butyrate on breast cancer cells

Oncogenic stimulation shows a rise in reactive oxygen species (ROS), and ROS can eventually induce carcinogenesis by causing DNA damage. In this context, this study aims to evaluate some biochemical and genotoxic changes in the control of cell death caused by NaBu (Sodium butyrate). treatment in breast cancer cells. NaBu’s impact on cell proliferation was determined via WST-1 assay. The lipid peroxidation (MDA), reduced glutathione (GSH), Nitric Oxide (NO), hydrogen peroxide (H₂O₂), and superoxide dismutase (SOD) enzyme levels were determined biochemically. NaBu-induced genotoxic damage was estimated via single-cell gel electrophoresis (SCGE). NaBu reduced cell viability and potentially induced GSH, but decreased SOD enzyme activity and the level of MDA and NO decreased also H₂O₂ decreased at different times and NaBu concentrations. Higher NaBu concentrations amplified DNA damage in MCF-7 cells compared to the control group. NaBu shows anticancer and genotoxic effects, especially through antioxidant enzymes, one of the oxidative stress parameters in breast cancer. However, the anticancer and genotoxic effects of NaBu is changed in the oxidative stress parameters with time and treatment concentration of NaBu in MCF-7 cells. Furthermore, his oxidative stress-dependent effect changes need to be clarified by further evaluation with molecular and more biochemical parameters.

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.

A detailed DFT-based study of the free radical scavenging activity and mechanism of daphnetin in physiological environments

Daphnetin, a biologically active coumarin derivative found in plants of the genus Daphne, is a potent antioxidant phenolic compound. The present work describes the mechanisms and kinetics of the HO, NO, HOO, and NO₂ scavenging activities of daphnetin in physiological environments using quantum chemistry calculations. The main antiradical mechanisms have been studied: formal hydrogen transfer (FHT), sequential electron transfer proton transfer (SETPT), sequential proton loss electron transfer (SPLET), and radical adduct formation (RAF). Besides its good HO scavenging activity in physiological environments, daphnetin is expected to exhibit good HOO and NO₂ scavenging activities in water with k_overall = 1.51 × 10⁷ and 4.79 × 10⁸ M^-1s^-1, respectively. The FHT mechanism decides the HO scavenging activity in aqueous solution, as well as HO, HOO, and NO₂ scavenging activities in lipid media, while SPLET is the primary mechanism in water for HOO and NO₂ scavenging activities. The theoretical predictions were found to be in good agreement with the available experimental data, which supports the reliability of the calculations.

Natural product-based Radiopharmaceuticals:Focus on curcumin and its analogs, flavonoids, and marine peptides

Natural products provide a bountiful supply of pharmacologically relevant precursors for the development of various drug-related molecules, including radiopharmaceuticals. However, current knowledge regarding the importance of natural products in developing new radiopharmaceuticals remains limited. To date, several radionuclides, including gallium-68, technetium-99m, fluorine-18, iodine-131, and iodine-125, have been extensively studied for the synthesis of diagnostic and therapeutic radiopharmaceuticals. The availability of various radiolabeling methods allows the incorporation of these radionuclides into bioactive molecules in a practical and efficient manner. Of the radiolabeling methods, direct radioiodination, radiometal complexation, and halogenation are generally suitable for natural products owing to their simplicity and robustness. This review highlights the pharmacological benefits of curcumin and its analogs, flavonoids, and marine peptides in treating human pathologies and provides a perspective on the potential use of these bioactive compounds as molecular templates for the design and development of new radiopharmaceuticals. Additionally, this review provides insights into the current strategies for labeling natural products with various radionuclides using either direct or indirect methods.

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Potential use of natural products for the development of diagnostic and therapeutic radiopharmaceuticals.

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Profile of potential natural products as molecular templates for the synthesis of new radiopharmaceuticals: Focus on curcumin and its closely related substances, flavonoids, and marine peptides.

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Radiolabeling strategies, challenges, and examples of natural product-based radiopharmaceuticals under investigation.

Bioaccessibility and Absorption of Flavonoid C-glycosides from Abrus mollis Using Simulated Digestion, Caco-2 Cell, and In Situ Single-pass Perfusion Models

Abrus mollis is commonly used as a traditional Chinese medicine for the treatment of liver diseases due to its hepatoprotection and anti-inflammation, but the absorption properties of its main bioactive ingredients remain unclear. Our previous studies verified that the flavonoid C-glycosides, including vicenin-2 (1: ), isoschaftoside (2: ), and schaftoside (3: ), were the major active components in A. mollis for hepatic protection against nonalcoholic fatty liver disease, hepatitis, and hepatic fibrosis. This study investigated the bioaccessibility and transport mechanisms of total flavonoid C-glycoside, as well as vicenin-2 (1: ), isoschaftoside (2: ), and schaftoside (3: ), in A. mollis by simulated digestion and use of the Caco-2 cell model. Moreover, this study attempted to verify their absorption properties by in situ gastrointestinal perfusion in rats. Total flavonoid C-glycoside and 1, 2: , and 3: exhibited similar bioaccessibility of 84.58%, 85.13%, 83.05%, and 81.65% respectively after simulated digestion. The transport of total flavonoid C-glycoside in the Caco-2 cell model increased with the concentration, and the transport showed saturation characteristics with the time and concentration of total flavonoid C-glycoside to a certain degree. The Papp values of total flavonoid C-glycoside and the 3 flavonoid C-glycosides were significantly improved by verapamil, probenecid, and EDTA-Na₂. Their absorption properties in the gastrointestinal tract were consistent with that found in Caco-2 cells, and superior absorption rates were observed in the duodenum and jejunum. The absorption pattern of total flavonoid C-glycoside may involve multiple transport pathways, including active transport, passive diffusion, and the paracellular pathway. TFC was actively pumped out by P-glycoprotein and multidrug resistance-associated protein. These results revealed that the bioaccessibility and intestinal absorption characteristic of total flavonoid C-glycoside were consistent with the 3 major flavonoids.

Prenylated Flavonoids with Potential Antimicrobial Activity: Synthesis, Biological Activity, and In Silico Study

Prenylated flavonoids are an important class of naturally occurring flavonoids with important biological activity, but their low abundance in nature limits their application in medicines. Here, we showed the hemisynthesis and the determination of various biological activities of seven prenylated flavonoids, named 7–13, with an emphasis on antimicrobial ones. Compounds 9, 11, and 12 showed inhibitory activity against human pathogenic fungi. Compounds 11, 12 (flavanones) and 13 (isoflavone) were the most active against clinical isolated Staphylococcus aureus MRSA, showing that structural requirements as prenylation at position C-6 or C-8 and OH at positions C-5, 7, and 4′ are key to the antibacterial activity. The combination of 11 or 12 with commercial antibiotics synergistically enhanced the antibacterial activity of vancomycin, ciprofloxacin, and methicillin in a factor of 10 to 100 times against drug-resistant bacteria. Compound 11 combined with ciprofloxacin was able to decrease the levels of ROS generated by ciprofloxacin. According to docking results of S enantiomer of 11 with ATP-binding cassette transporter showed the most favorable binding energy; however, more studies are needed to support this result.

Empirical Kinetic Modelling and Mechanisms of Quercetin Thermal Degradation in Aqueous Model Systems: Effect of pH and Addition of Antioxidants

Quercetin (Qt) is a natural flavonoid of high biological significance, and it occurs in a wide variety of plant foods. Although its oxidation by various means has been extensively studied, its behavior with regard to thermal treatments remains a challenge. The study described herein aimed at investigating Qt thermal decomposition, by proposing an empirical sigmoidal model for tracing degradation kinetics. This model was employed to examine the effect of addition of antioxidants on Qt thermal degradation, including ascorbic acid, L-cysteine, and sulfite. Furthermore, degradation pathways were proposed by performing liquid chromatography-tandem mass spectrometry analyses. Upon addition of any antioxidant used, the sigmoidal course of Qt thermal degradation was pronounced, evidencing the validity of the empirical model used in the study of similar cases. The antioxidants retarded Qt degradation in a manner that appeared to depend on Qt/antioxidant molar ratio. No major differentiation in the degradation mechanism was observed in response to the addition of various antioxidants, and in all cases protocatechuic acid and phloroglucinol carboxylic acid were typical degradation products identified. Furthermore, in all cases tested the solutions resulted after thermal treatment possessed inferior antioxidant properties compared to the initial Qt solutions, and this demonstrated the detrimental effects of heating on Qt. The empirical model proposed could be of assistance in interpreting the degradation behavior of other polyphenols, but its validity merits further investigation.

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.

A Potential Quorum-Sensing Inhibitor for Bronchiectasis Therapy: Quercetin-Chitosan Nanoparticle Complex Exhibiting Superior Inhibition of Biofilm Formation and Swimming Motility of Pseudomonas aeruginosa to the Native Quercetin

Quercetin (QUE)—a plant-derived flavonoid, is recently established as an effective quorum sensing (QS) inhibiting agent in Pseudomonas aeruginosa—the main bacterial pathogen in bronchiectasis lungs. Successful clinical application of QUE, however, is hindered by its low solubility in physiological fluids. Herein we developed a solubility enhancement strategy of QUE in the form of a stable amorphous nanoparticle complex (nanoplex) of QUE and chitosan (CHI), which was prepared by electrostatically driven complexation between ionized QUE molecules and oppositely charged CHI. At its optimal preparation condition, the QUE–CHI nanoplex exhibited a size of roughly 150 nm with a 25% QUE payload and 60% complexation efficiency. The complexation with CHI had no adverse effect on the antibacterial and anticancer activities of QUE, signifying the preservation of QUE’s bioactivities in the nanoplex. Compared to the native QUE, the QUE–CHI nanoplex exhibited superior QS inhibition in suppressing the QS-regulated swimming motility and biofilm formation of P. aeruginosa, but not in suppressing the virulence factor production. The superior inhibitions of the biofilm formation and swimming motility afforded by the nanoplex were attributed to (1) its higher kinetic solubility (5-times higher) that led to higher QUE exposures, and (2) the synergistic QS inhibition attributed to its CHI fraction.

Modulation of Oxidative Stress and Hemostasis by Flavonoids from Lentil Aerial Parts

While specific metabolites of lentil (Lens culinaris L.) seeds and their biological activity have been well described, other organs of this plant have attracted little scientific attention. In recent years, green parts of lentils have been shown to contain diverse acylated flavonoids. This work presents the results of the research on the effect of the crude extract, the phenolic fraction, and seven flavonoids obtained from aerial parts of lentils on oxidative damage induced by H₂O₂/Fe to lipid and protein constituents of human plasma. Another goal was to determine their effect on hemostasis parameters of human plasma in vitro. Most of the purified lentil flavonoids had antioxidant and anticoagulant properties. The crude extract and the phenolic fraction of lentil aerial parts showed antioxidant activity, only at the highest tested concentration (50 μg/mL). Our results indicate that aerial parts of lentils may be recommended as a source of bioactive substances.

Structure–antioxidant activity relationships in boldine and glaucine: a DFT study

DFT calculations indicate that boldine and glaucine exhibit direct antioxidant activity through the HAT and SPLET (at high pH values) mechanisms.

Laser Access to Quercetin Radicals and Their Repair by Co-antioxidants

We have demonstrated the feasibility and ease of producing quercetin radicals by photoionization with a pulsed 355 nm laser. A conversion efficiency into radicals of 0.4 is routinely achieved throughout the pH range investigated (pH 2-9), and the radical generation is completed within a few ns. No precursor other than the parent compound is needed, and the ionization by-products do not interfere with the further fate of the radicals. With this generation method, we have characterized the quercetin radicals and studied the kinetics of their repairs by co-antioxidants such as ascorbate and 4-aminophenol. Bell-shaped pH dependences of the observed rate constants reflect opposite trends in the availability of the reacting protonation forms of radical and co-antioxidant and even at their maxima mask the much higher true rate constants. Kinetic isotope effects identify the repairs as proton-coupled electron transfers. An examination of which co-antioxidants are capable of repairing the quercetin radicals and which are not confines the bond dissociation energies of quercetin and its monoanion experimentally to 75-77 kcal mol-1 and 72-75 kcal mol-1 , a much narrower interval in the case of the former than previously estimated by theoretical calculations.

Effects of dietary mulberry leaf powder on growth performance, blood metabolites, meat quality, and antioxidant enzyme-related gene expression of fattening Hu lambs

This study was conducted to investigate the effects of the mulberry [Morus alba var. multicaulis (Perrott.) Loud.] leaf powder (MLP) supplementation in dietary concentrates on growth performance, blood metabolites, meat quality, and antioxidant enzyme (AOE) gene expression in fattening Hu lambs. Forty approximately 3-mo-old Hu lambs (16.5 ± 0.6 kg) were randomly allocated to five groups and fed with concentrates containing 0%, 15%, 30%, 45%, or 60% MLP (control, T15, T30, T45, and T60, respectively). The results showed that 15%–30% MLP supplementation maintained growth and carcass performance, and the weight of total stomach, especially of rumen in T15 and T30, were higher than those of the control. Dietary MLP supplementation decreased serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, cholesterol, and triglyceride levels, but increased the high-density lipoprotein levels. Moreover, MLP supplementation improved the longissimus lumborum muscle color (redness), tenderness, and water-holding capacity. It was further observed that 15% MLP supplementation enhanced all AOE mRNA levels apart from that of EPHX1. In summary, dietary MLP supplementation could partially improve the blood metabolites, meat quality, and AOE mRNA levels in the liver of fattening Hu lamb, and the level of 15% supplementation was the most promising.

HPLC-DAD analysis of Hyssopus Cuspidatus Boriss extract and mensuration of its antioxygenation property

BACKGROUND

Hyssopus cuspidatus Boriss has been used as an important ethnomedicinal plant for long to eliminate phlegm, relieve cough and as well as having antibacterial, antioxygenation, and antitumor activities. In this study, the polyphenol contents, flavonoid contents, free radical scavenging assay and animal antioxygenation property assay of ethanol extract of H. cuspidatus were measured.

METHODS

This study determined the total polyphenol and flavonoid contents in H. cuspidatus by UV-VIS. Caffeic, ferulic, and rosmarinic acids were measured using HPLC-DAD. Free radical scavenging assay of H. cuspidatus was studied by colorimetric method. Animal antioxygenation property assay of H. cuspidatus was studied with mice by biochemical assay kits.

RESULTS

The total polyphenol and flavonoid contents of H. cuspidatus in 2017, 2018, 2019 were determined and the contents of H. cuspidatus in 2019 was the highest. In addition, rosmarinic acid was the phenolic acid with the highest content in H. cuspidatus. Compared with those of DPPH free radical, hydroxyl free radical, and superoxide anion free radical, the scavenging ability of H. cuspidatus of ABTS free radical was stronger, the average IC50 value was 0.0245 mg/mL. In animal antioxygenation property experiment, the model group was successfully established with decreased activities of SOD, CAT, and GSH-px and increased content of MDA. The ethanol extract of H. cuspidatus increased the activities of SOD, CAT, and GSH-px and reduced the content of MDA. Each group of samples and the ascorbic acid positive control group showed significant differences in the results of free radical scavenging and animal antioxygenation property experiments (P < 0.05).

CONCLUSIONS

These results suggest that H. cuspidatus exerts an antioxygenation property, which can be attributed to the contents of total polyphenol and flavonoid. Given its strong antioxygenation property, H. cuspidatus can be used as a new natural antioxidant in food preservation and disease treatment.

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.

Mechanism for Inhibition of Folic Acid Photodecomposition by Various Antioxidants

Folic acid, a synthetic form of folate, is a water-soluble vitamin that is essential during periods of rapid cell division and growth. However, it decomposes upon ultraviolet irradiation to form inactive photoproducts. In this study, the protective effect and mechanisms of antioxidants, including cinnamic acids, flavonoids, catechol and its derivatives, stilbenes, p-benzoquinone and its derivatives, isoprenoids, curcumin, oleic acid, and linoleic acid, against folic acid photodecomposition were investigated by using fluorescence and absorbance spectroscopy, high-performance liquid chromatography, and antioxidant assay. It was found that antioxidants could inhibit or delay the folic acid decomposition in varying degrees, among which caffeic acid was the most effective. The increase in its remarkable antioxidant efficiency and absorbance in the UVA region during irradiation contributed to its effective protection. This finding could be useful for the protection of photolabile components in food and other uses.

Quercetin modulates hyperglycemia by improving the pancreatic antioxidant status and enzymes activities linked with glucose metabolism in type 2 diabetes model of rats: In silico studies of molecular interaction of quercetin with hexokinase and catalase

Quercetin was assessed for its antihyperglycemic effect in fructose-streptozotocin (STZ) induced diabetic rats. The oral administration of quercetin at the dosage of 25 and 50 mg/kg for 28 days remarkably reduced the level of blood glucose, glycosylated hemoglobin (Hb), and hepatic glycogen but enhanced plasma Hb concentration. The altered activities of glucose-6-phosphatase and hexokinase in diabetic rats were significantly improved upon quercetin treatment. Furthermore, the antioxidant activity of pancreatic superoxide dismutase, catalase (CAT), and reduced glutathione was effectively increased while the value for thiobarbituric acid reactive species was decreased. A significant reduction of glycemia was observed in the glucose tolerance test, 120 min after the glucose pulse. Also, the damage caused by fructose-STZ in the liver and pancreas of diabetic animals were restored to near normal. Molecular docking of quercetin showed a high affinity for hexokinase and CAT with a binding energy of -7.82 and -9.83 kcal/mol, respectively, more elevated than the standard drugs. PRACTICAL APPLICATIONS: Functional foods and nutraceuticals have increasingly interested the consumers in terms of health benefits and have started focussing on the prevention or cure of disease by the foods and their health-enhancing phytochemicals. Quercetin is one of the most potent naturally occurring antioxidants within the flavonoid subclasses, mostly distributed as a secondary metabolite in fruits, vegetables, and black tea. Based on the results exhibited in the present study, we proposed that the consumption of foods rich in quercetin could be a cheap and affordable nutraceutical that can be developed for the treatment of T2DM and its complications. Further studies on the safety aspects of quercetin in long-term usage are strongly recommended before implementing for the treatment of human diseases.

Structure-Dependent Modulation of Substrate Binding and Biodegradation Activity of Pirin Proteins toward Plant Flavonols

Pirin is a nonheme metalloprotein that occurs widely in human tissues and is highly conserved across all taxa. Pirin proteins typically function as nuclear transcription regulators, but two Pirin orthologs, YhhW (from Escherichia coli) and hPirin (from humans) were revealed to possess enzymatic activity of degrading quercetin. The exact role of Pirin homologues and their catalytic specificity remain poorly understood. In this work, by screening against a panel of plant flavonoids, we found that both Pirins catalyze the oxidative degradation of a wide spectrum of flavonol analogues and release carbon monoxide (CO) in the process. This shows that Pirin acts on a broad range of substrates and could represent a novel dietary source of CO in vivo. Although the kinetic profiles differ substantially between two Pirins, the identified substrate structures all share a 2,3-double bond and 3-hydroxyl and 4-oxo groups on their "flavonol backbone," which contribute to the specific enzyme-substrate interaction. While hPirin is iron-dependent, YhhW is identified as a novel nickel-containing dioxygenase member of the bicupin family. Besides the expanded Pirin activity, we present the crystal structures of the native Ni-YhhW and tag-free Fe-hPirin, revealing the distinctive differences occurring at the metal-binding site. In addition, YhhW features a flexible Ω-loop near the catalytic cavity, which may help stabilize the reaction intermediates via a Ni-flavonol complex. The structure-dependent modulation of substrate binding to the catalytic cavity adds to understanding the differential dispositions of natural flavonols by human and bacterial Pirins.

Theoretical Study of the Antioxidant Activity of Quercetin Oxidation Products

It was recently shown that, when tested in cellular systems, quercetin oxidized products (Qox) have significantly better antioxidant activity than quercetin (Q) itself. The main Qox identified in the experiments are either 2,5,7,3',4'-pentahydroxy-3,4-flavandione (Fl) or its tautomer, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (Bf). We have now performed a theoretical evaluation of different physicochemical properties using density functional theory (DFT) calculations on Q and its main Qox species. The most stable structures (for Q and Qox) were identified after a structural search on their potential energy surface. Since proton affinities (PAs) are much lower than the bond dissociation enthalpies (BDEs) of phenolic hydrogens, we consider that direct antioxidant activity in these species is mainly due to the sequential proton loss electron transfer (SPLET) mechanism. Moreover, our kinetic studies, according to transition state theory, show that Q is more favored by this mechanism. However, Qox have lower PAs than Q, suggesting that antioxidant activity by the SPLET mechanism should be a result of a balance between proclivity to transfer protons (which favors Qox) and the reaction kinetics of the conjugated base in the sequential electron transfer mechanism (which favors Q). Therefore, our results support the idea that Q is a better direct antioxidant than its oxidized derivatives due to its kinetically favored SPLET reactions. Moreover, our molecular docking calculations indicate a stabilizing interaction between either Q or Qox and the kelch-like ECH-associated protein-1 (Keap1), in the nuclear factor erythroid 2-related factor 2 (Nrf2)-binding site. This should favor the release of the Nrf2 factor, the master regulator of anti-oxidative responses, promoting the expression of the antioxidant responsive element (ARE)-dependent genes. Interestingly, the computed Keap1-metabolite interaction energy is most favored for the Bf compound, which in turn is the most stable oxidized tautomer, according to their computed energies. These results provide further support for the hypothesis that Qox species may be better indirect antioxidants than Q, reducing reactive oxygen species in animal cells by activating endogenous antioxidants.

Influence of the Physical State of Spray-Dried Flavonoid-Inulin Microparticles on Oxidative Stability of Lipid Matrices

The effect of the physical state of flavonoid-inulin microparticles (semi-crystalline/amorphous) on the oxidative stability of lipid matrices was studied. Epicatechin (E) and quercetin (Q) microparticles with inulin were formulated at two infeed temperatures (15 °C and 90 °C) by spray drying. X-ray diffraction analyses showed that flavonoid-inulin microparticles obtained at feed temperature of 15 °C were semi-crystalline (E-In-15, 61.2% and Q-In-15, 60%), whereas those at 90 °C were amorphous (Q-In-90, 1.73 and Q-In-90 2.30%). Semi-crystalline state of flavonoid-inulin microparticles enhanced the EE (68.8 and 67.8% for E and Q, respectively) compared to amorphous state (41.6 and 51.1% for E and Q, respectively). However, amorphous Q-microparticles showed the highest antioxidant activity both in methyl linoleate and sunflower oil, increasing the induction period and decreasing the polar compounds and polymer triglyceride formation during long-term oxidation study. Therefore, the physical state of spray-dried flavonoid-inulin microparticles may determine their antioxidant activity in lipid matrices.

Exposure of tomato (Lycopersicon esculentum) to silver nanoparticles and silver nitrate: physiological and molecular response

Silver nanoparticles (AgNPs) are among the most widely used nanomaterials, with applications in sectors as diverse as communications, energy, medicine, and agriculture. This diverse application of AgNPs increases the risk of the release of these materials into the environment and raises the potential for transfer into plants and, subsequently, the human body. To better understand the effects of NPs in agricultural systems, this study investigates plant physiological and molecular responses upon exposure to AgNPs in comparison to silver nitrate (AgNO₃). Tomato seedlings (Lycopersison esculentum) were exposed to 10, 20, or 30 mg/L silver (Ag), AgNO₃, or AgNPs in hydroponic media for 7 days. A number of endpoints were measured, including plant growth, photosynthetic pigments, oxidative and antioxidant responses. The results showed 2-7 times lower growth rate in plants exposed to silver compared to the control. H₂O₂ and malondialdehyde as oxidative stress indicators were, respectively, 1.7 and 4 times higher in plants exposed to all forms of silver compared to the control. The antioxidative responses increased significantly in plants exposed to Ag and AgNPs compared to the control. However, plants exposed to AgNO₃ showed up to 50% lower enzymatic antioxidant activity. At the molecular level, the expression of genes involved in defense responses, including ethylene-inducing xylanase (EIX), peroxidase 51 (POX), and phenylalanine ammonia lyase, were significantly upregulated upon exposure to silver. The molecular and physiological data showed exposure to all forms of silver resulted in oxidative stress and exposure to AgNPs induced antioxidative and defense responses. However, exposure to AgNO₃ resulted in phytotoxicity and failure in antioxidative responses. It indicates the higher reactivity and phytotoxicity of the ionic form of silver compared to NPs. The findings of this study add important information to efforts in attempting to characterize the exposure and risk associated with the release of nanomaterials in the environment.

Structure affinity relationship and docking studies of flavonoids as substrates of multidrug-resistant associated protein 2 (MRP2) in MDCK/MRP2 cells

This study was aimed to determine the relationship of flavonoid structures to their affinity for an important efflux transporter, multidrug-resistant associated protein 2 (MRP2). The cellular uptake (CU) of 35 flavonoids was investigated in MRP2 overexpression MDCK/MRP2 cells. Resulting data identified 8 flavonoids as MRP2 substrates based on their high CU_MK with MK-571 in MDCK/MRP2 cells. Also, three substrates showed better CU_MD in MDCK cells than did CU_MRP in MDCK/MRP2 cells. Docking analyses showed a good correlation (R = 0.926, p = 0.003) between efflux-fold of flavonoid substrates and their docking S_scoring with the MRP2 model, indicating consistency between in silico and in vitro approaches. A structure affinity relationship (SAR) study indicated that 3-OH, 5-OH, 6-OH, 3'-OH, and 4'-OCH₃ substituents were favourable while, 8-OCH₃, 2'-OH, 3'-OCH₃, 4'-OH and 5'-OH were unfavourable for flavonoid affinity to MRP2. Our study provides valuable information for dietary application of flavonoids with specific structures for high absorption.

Flavones hydroxylated at 5, 7, 3' and 4' ameliorate skin fibrosis via inhibiting activin receptor-like kinase 5 kinase activity

Skin fibrosis is mainly characterized by excessive collagen deposition. Studies have recently identified a number of flavonoids with variable structures that have the potency of inhibiting collagen synthesis and thus attenuating organ fibrosis. In this study, we found that flavones with 5, 7, 3', 4' hydroxy substitution reduced collagen expression most efficiently. Among those flavones, luteolin, quercetin, and myricetin were selected for follow-up. In vivo, the three compounds ameliorated skin fibrosis and reduced collagen deposition. Further analysis showed the compounds had significant inhibition on the proliferation, activation and contractile ability of dermal fibroblasts in vitro and in vivo. More importantly, we revealed that luteolin, quercetin, and myricetin selectively downregulated the phosphorylation of Smad2/3 in TGF-β/Smads signaling via binding to activin receptor-like kinase 5 (ALK5) and impairing its catalytic activity. We also found flavones with 5, 7, 3', 4' hydroxy substitution showed stronger affinity with ALK5 compared with other flavonoids. Herein, we identified at least in part the underlying molecular basis as well as the critical structures that contribute to the antifibrotic bioactivity of flavones, which might benefit drug design and modification.