CUPRAC total antioxidant capacity assay of lipophilic antioxidants in combination with hydrophilic antioxidants using the macrocyclic oligosaccharide methyl β-cyclodextrin as the solubility enhancer

Cyclodextrins and their potential applications for delivering vitamins, iron, and iodine for improving micronutrient status

Cyclodextrins (CDs) have been investigated as potential biopolymeric carriers that can form inclusion complexes with numerous bioactive ingredients. The inclusion of micronutrients (e.g. vitamins or minerals) into cyclodextrins can enhance their solubility and provide oxidative or thermal stability. It also enables the formulation of products with extended shelf-life. The designed delivery systems with CDs and their inclusion complexes including electrospun nanofibers, emulsions, liposomes, and hydrogels, show potential in enhancing the solubility and oxidative stability of micronutrients while enabling their controlled and sustained release in applications including food packaging, fortified foods and dietary supplements. Nano or micrometer-sized delivery systems capable of controlling burst release and permeation, or moderating skin hydration have been reported, which can facilitate the formulation of several personal and skin care products for topical or transdermal delivery of micronutrients. This review highlights recent developments in the application of CDs for the delivery of micronutrients, i.e. vitamins, iron, and iodine, which play key roles in the human body, emphasizing their existing and potential applications in the food, pharmaceuticals, and cosmeceuticals industries.

In Vitro and In Silico Study on the Molecular Encapsulation of α-Tocopherol in a Large-Ring Cyclodextrin

α-tocopherol is the physiologically most active form of vitamin E, with numerous biological activities, such as significant antioxidant activity, anticancer capabilities, and anti-aging properties. However, its low water solubility has limited its potential use in the food, cosmetic, and pharmaceutical industries. One possible strategy for addressing this issue is the use of a supramolecular complex with large-ring cyclodextrins (LR-CDs). In this study, the phase solubility of the CD26/α-tocopherol complex was investigated to assess the possible ratios between host and guest in the solution phase. Next, the host-guest association of the CD26/α-tocopherol complex at different ratios of 1:2, 1:4, 1:6, 2:1, 4:1, and 6:1 was studied by all-atom molecular dynamics (MD) simulations. At 1:2 ratio, two α-tocopherol units interact spontaneously with CD26, forming an inclusion complex, as supported by the experimental data. In the 2:1 ratio, a single α-tocopherol unit was encapsulated by two CD26 molecules. In comparison, increasing the number of α-tocopherol or CD26 molecules above two led to self-aggregation and consequently limited the solubility of α-tocopherol. The computational and experimental results indicate that a 1:2 ratio could be the most suitable stoichiometry to use in the CD26/α-tocopherol complex to improve α-tocopherol solubility and stability in inclusion complex formation.

Clarification of the Complexation Behaviour of 2,6-di-O-Methylated β-Cyclodextrin and Vitamin E and Radical Scavenging Ability of the Complex in Aqueous Solution

The precise understanding of the behaviour of vitamin E (α-tocopherol; Toc) complexed with cyclodextrin (CD) additives in aqueous solution is a fundamental issue for further development of their aqua-related biological applications. In this study, the solubilisation and complexation behaviours of Toc with methyl-substituted CD derivatives and the radical scavenging ability of the resulting complexes were precisely investigated in water media. Several problems were encountered upon pre-dissolving Toc in an organic solvent prior to the addition to the water media, such as enhancement of the dispersibility and decrease in the complexation capacity. Additionally, dispersions were obtained in some cases when mixing CD and Toc even in the absence of an organic solvent; therefore, to perform the measurements, a transparent solution was prepared via filtration with a nanopore filter. Consequently, unexpectedly, the addition of certain CD methylated derivatives did not always enhance the solubility of Toc significantly. However, 2,6-di-O-methylated β-CD (2,6-DMCD) formed a water-soluble inclusion complex with Toc, effectively enhancing its solubility. A phase solubility study indicated the formation of 1:2 or 1:3 Toc/CD inclusion complexes, and the interaction of 2,6-DMCD with both the chromanol head and the phytol chain of Toc was revealed by 2D ROESY nuclear magnetic resonance analysis. The interaction between 2,6-DMCD and the chromanol head was also confirmed for a 2,6-DMCD-2,2,5,7,8-pentamethyl-6-chromanol inclusion complex. Additionally, a rapid scavenging effect for molecularly dissolved Toc was demonstrated even in a system comprising a chromanol head directly encapsulated by CD. Hence, this work elucidated the precise complexation and radical scavenging ability of 2,6-DMCD-Toc in an aqueous solution, which paves the way for its biological applications.

Development of Water-Insoluble Vehicle Comprising Natural Cyclodextrin-Vitamin E Complex

Development of a novel antioxidant-delivery vehicle exerting biosafety has been attracting a great deal of interest. In this study, a vehicle comprising a natural composite consisting of vitamin E (α-tocopherol; Toc) and cyclodextrin (CD) additives was developed, directed toward aqua-related biological applications. Not only β-CD, but also γ-CD, tended to form a water-insoluble aggregate with Toc in aqueous media. The aggregated vehicle, in particular the γ-CD-added system, showed a remarkable sustained effect because of slow dynamics. Furthermore, a prominent cytoprotective effect by the γ-CD-Toc vehicle under the oxidative stress condition was confirmed. Thus, the novel vitamin E vehicle motif using γ-CD as a stabilizer was proposed, widening the usability of Toc for biological applications.

Comparison of Different Dietary Indices as Predictors of Inflammation, Oxidative Stress and Intestinal Microbiota in Middle-Aged and Elderly Subjects

During the last decades the gut microbiota has been identified as a key mediator in the diet-health interaction. However, our understanding on the impact of general diet upon microbiota is still limited. Dietary indices represent an essential approach for addressing the link between diet and health from a holistic point of view. Our aim was to test the predictive potential of seven dietary ratings on biomarkers of inflammation, oxidative stress and on the composition and metabolic activity of the intestinal microbiota. A cross-sectional descriptive study was conducted on a sample of 73 subjects aged >50 years with non-declared pathologies. Dietary inflammatory index (DII), Empirical Dietary Inflammatory Index (EDII), Healthy Eating Index (HEI), Alternative Healthy Eating Index (AHEI), Mediterranean adapted Diet Quality Index-International (DQI-I), Modified Mediterranean Diet Score (MMDS) and relative Mediterranean Diet Score (rMED) were calculated based on a Food Frequency Questionnaire. Major phylogenetic types of the intestinal microbiota were determined by real time polymerase chain reaction (qPCR) and fecal short chain fatty acids (SCFAs) by gas chromatography. While DII, HEI, DQI-I and MMDS were identified as predictors of Faecalibacterium prausnitzii levels, AHEI and MMDS were negatively associated with Lactobacillus group. HEI, AHEI and MMDS were positively associated with fecal SCFAs. In addition, DII and EDII explained lipoperoxidation level and Mediterranean scores the serum IL-8 concentrations. The lower detection of IL-8 in individuals with higher scores on Mediterranean indices may be partially explained by the increased levels of the anti-inflammatory bacterium F. prausnitzii in such individuals.

Propyl gallate/cyclodextrin supramolecular complexes with enhanced solubility and radical scavenging capacity

This study prepared and investigated the inclusion complexes of propyl gallate (PG) with beta-cyclodextrin (β-CD) and its water-soluble derivatives dimethyl-beta-cyclodextrin (DM-β-CD), hydroxypropyl-beta-cyclodextrin (HP-β-CD), and sulfobutylether-beta-cyclodextrin (SBE-β-CD). Phase solubility studies indicated that the formed complexes were in 1:1 stoichiometry. FT-IR, PXRD, DSC, ¹H-NMR, ROESY-NMR, and SEM analysis results confirmed the formation of the complexes. The NMR results indicated that the aromatic ring of PG was embedded into the CD cavity. The aqueous solubility of PG was markedly improved, and that of the PG/DM-β-CD complex increased by 365.3 times. In addition, the results of the antioxidant activity assay showed that the hydroxyl radical and superoxide radical scavenging capacities of the complexes increased by 3-11 times and 1-6.5 times, respectively, compared with those of PG under the same concentration. Therefore, CD/PG inclusion complexes with improved solubility and radical scavenging capacity can be used as water-soluble antioxidants in the food industry.

Antioxidant Vitamin E/Cyclodextrin Inclusion Complex Electrospun Nanofibers: Enhanced Water Solubility, Prolonged Shelf Life, and Photostability of Vitamin E

Here, we demonstrated the electrospinning of polymer-free nanofibrous webs from inclusion complex (IC) between hydroxypropyl-β-cyclodextrin (HPβCD) and Vitamin E (Vitamin E/HPβCD-IC NF). The inclusion complexation between HPβCD and Vitamin E was prepared by using two different molar ratios (Vitamin E/HPβCD; 1:2 and 1:1), which correspond to theoretical value of ∼13% (w/w) and 26% (w/w) loading of Vitamin E in the nanofiber (NF) matrix. After electrospinning and storage, a very high loading of Vitamin E (up to ∼11% w/w, with respect to fiber matrix) was preserved in Vitamin E/HPβCD-IC NF. Because of the cyclodextrin inclusion complexation, only a minimal weight loss (only ∼2% w/w) was observed. While pure Vitamin E is insoluble in water, Vitamin E/HPβCD-IC NF web has displayed fast-dissolving behavior. Because of the greatly enhanced water-solubility of Vitamin E, Vitamin E/HPβCD-IC NF web has shown effective antioxidant activity. Additionally, Vitamin E/HPβCD-IC NF web has provided enhanced photostability for the sensitive Vitamin E by the inclusion complexation in which Vitamin E/HPβCD-IC NF still kept its antioxidant activity even after exposure to UV-light. Moreover, a 3 year-old Vitamin E/HPβCD-IC NF sample has shown very similar antioxidant efficiency when compared with freshly prepared Vitamin E/HPβCD-IC NF indicating that long-term stability was achieved for Vitamin E in the CD-IC fiber matrix. In brief, our results suggested that polymer-free electrospun Vitamin E/HPβCD-IC nanofibrous webs could have potential applications in food, pharmaceuticals, and healthcare thanks to its efficient antioxidant activity along with enhanced water-solubility, prolonged shelf life, and high photostability of Vitamin E.

Antioxidative and cardioprotective properties of anthocyanins from defatted dabai extracts

This study aimed to determine anthocyanins and their antioxidative and cardioprotective properties in defatted dabai parts. Anthocyanins in crude extracts and extract fractions of defatted dabai peel and pericarp were quantified using UHPLC, while their antioxidant capacity and oxidative stress inhibition ability were evaluated by using DPPH and CUPRAC assays as well as linoleic acid oxidation system, hemoglobin oxidation, and PARP-1 inhibition ELISA. Cardioprotective effect of the defatted dabai peel extract was evaluated using hypercholesterolemic-induced New Zealand white rabbits. Six anthocyanins were detected in the defatted dabai peel, with the highest antioxidant capacities and oxidative stress inhibition effect compared to the other part. The defatted dabai peel extract has also inhibited lipid peroxidation (plasma MDA) and elevated cellular antioxidant enzymes (SOD and GPx) in the tested animal model. Major anthocyanin (cyanidin-3-glucoside) and other anthocyanins (pelargonidin-3-glucoside, malvidin-3-glucoside, cyanidin-3-galactoside, cyanidin-3-arabinoside, and peonidin-3-glucoside) detected in the defatted dabai peel are potential future nutraceuticals with promising medicinal properties.

Spectroscopic study and antioxidant properties of the inclusion complexes of rosmarinic acid with natural and derivative cyclodextrins

Measurement of total antioxidant activity/capacity of polyphenols in various solvent media necessitates the use of cyclodextrins to solubilize lipophilic antioxidants of poor aqueous solubility. The inclusion complexes of the slightly water soluble antioxidant, rosmarinic acid (RA), with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), 2-hydroxyethyl-β-cyclodextrin (HE-β-CD), and methyl-β-cyclodextrin (M-β-CD) were investigated for the first time. The effect of cyclodextrins (CDs) on the spectral features of RA was measured in aqueous medium using UV-vis and steady-state fluorescence techniques by varying the concentrations of CDs. The molar stoichiometry of RA-CD inclusion complexes was verified as 1:1, and the formation constants of the complexes were determined from Benesi-Hildebrand equation using fluorescence spectroscopic data. Among the CDs, maximum inclusion ability was measured in the case of M-β-CD followed by HP-β-CD, HE-β-CD, β-CD and α-CD. Solid inclusion complexes were prepared by freeze drying, and their functional groups were analyzed by IR spectroscopy. Antioxidant capacity of CD-complexed rosmarinic acid was measured to be higher than that of the lone hydroxycinnamic acid by the CUPric Reducing Antioxidant Capacity (CUPRAC) method. The mechanism of the TAC increase was interpreted as the stabilization of the 1-e oxidized o-catechol moiety of RA by enhanced intramolecular H-bonding in a hydrophobic environment provided by CDs, mostly by M-β-CD.

Cupric ion reducing antioxidant capacity assay for antioxidants in human serum and for hydroxyl radical scavengers

Tests measuring the combined antioxidant effect of the nonenzymatic defenses in biological fluids may be useful in providing an index of the organism's capability to counteract reactive species known as pro-oxidants, resist oxidative damage, and combat oxidative stress-related diseases. The selected chromogenic redox reagent for the assay of human serum should be easily accessible, stable, selective, and respond to all types of biologically important antioxidants such as ascorbic acid, alpha-tocopherol, beta-carotene, reduced glutathione (GSH), uric acid, and bilirubin, regardless of chemical type or hydrophilicity. Our recently developed cupric reducing antioxidant capacity (CUPRAC) spectrophotometric method for a number of polyphenols and flavonoids using the copper(II)-neocuproine reagent in ammonium acetate buffer is now applied to a complete series of plasma antioxidants for the assay of total antioxidant capacity of serum, and the resulting absorbance at 450 nm is recorded either directly (e.g., for ascorbic acid, alpha-tocopherol, and glutathione) or after incubation at 50 degrees C for 20 min (e.g., for uric acid, bilirubin, and albumin), quantitation being made by means of a calibration curve. The lipophilic antioxidants, alpha-tocopherol and beta-carotene, are assayed in dichloromethane. Lipophilic antioxidants of serum are extracted with n-hexane from an ethanolic solution of serum subjected to centrifugation. Hydrophilic antioxidants of serum are assayed in the centrifugate after perchloric acid precipitation of proteins. The CUPRAC molar absorptivities, linear ranges, and TEAC (trolox equivalent antioxidant capacity) coefficients of the serum antioxidants are established, and the results are evaluated in comparison with the findings of the ABTS/TEAC reference method. The intra- and inter-assay coefficients of variation (CVs) are 0.7 and 1.5%, respectively, for serum. The CUPRAC assay proved to be efficient for glutathione and thiol-type antioxidants, for which the FRAP (ferric reducing antioxidant potency) test is basically nonresponsive. The additivity of absorbances of all the tested antioxidants confirmed that antioxidants in the CUPRAC test do not chemically interact among each other so as to cause an intensification or quenching of the theoretically expected absorbance, and that a total antioxidant capacity (TAC) assay of serum is possible. As a distinct advantage over other electron-transfer based assays (e.g., Folin, FRAP, ABTS, DPPH), CUPRAC is superior in regard to its realistic pH close to the physiological pH, favorable redox potential, accessibility and stability of reagents, and applicability to lipophilic antioxidants as well as hydrophilic ones. The CUPRAC procedure can also assay hydroxyl radicals, being the most reactive oxygen species (ROS). As a more convenient, efficient, and less costly alternative to HPLC/electrochemical detection techniques and to the nonspecific, low-yield TBARS test, we use p-aminobenzoate, 2,4- and 3,5-dimethoxybenzoate probes for detecting hydroxyl radicals generated from an equivalent mixture of [Fe(II)+EDTA] with hydrogen peroxide. The produced hydroxyl radicals attack both the probe and the water-soluble antioxidants in 37 degrees C-incubated solutions for 2 h. The CUPRAC absorbance of the ethylacetate extract due to the reduction of Cu(II)-neocuproine reagent by the hydroxylated probe decreases in the presence of (.)OH scavengers, the difference being proportional to the scavenging ability of the tested compound. The developed method is less lengthy, more specific, and of a higher yield than the classical TBARS assay.

Simultaneous total antioxidant capacity assay of lipophilic and hydrophilic antioxidants in the same acetone-water solution containing 2% methyl-beta-cyclodextrin using the cupric reducing antioxidant capacity (CUPRAC) method

Antioxidants are health beneficial compounds that can protect cells from the damage caused by unstable molecules known as reactive oxygen species (ROS). This work reports the capacity assay of both lipophilic and hydrophilic antioxidants simultaneously, by making use of their 'host-guest' complexes with methyl-beta-cyclodextrin (M-beta-CD), a cyclic oligosaccharide, in acetonated aqueous medium using the cupric reducing antioxidant capacity (CUPRAC) method. Thus the order of antioxidant potency of various compounds irrespective of their lipophilicity could be established in the same solvent medium. M-beta-CD was introduced as the water solubility enhancer for lipophilic antioxidants. Two percent M-beta-CD (w/v) in an acetone-H(2)O (9:1, v/v) mixture was found to sufficiently solubilize beta-carotene, lycopene, vitamin E, vitamin C, synthetic antioxidants and other phenolic antioxidants. This assay was validated through linearity, additivity, precision, and recovery. The validation results demonstrate that the CUPRAC assay is reliable and robust. In acetonated aqueous solution of M-beta-CD, only CUPRAC and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays were capable of measuring carotenoids together with hydrophilic antioxidants. The CUPRAC antioxidant capacities of a wide range of polyphenolics and flavonoids were experimentally reported in this work as trolox equivalent antioxidant capacity (TEAC) in the CUPRAC assay, and compared to those found by reference methods, ABTS/horseradish peroxidase (HRP)-H(2)O(2) and ferric reducing antioxidant power (FRAP) assays.

Comparative evaluation of various total antioxidant capacity assays applied to phenolic compounds with the CUPRAC assay

It would be desirable to establish and standardize methods that can measure the total antioxidant capacity level directly from vegetable extracts containing phenolics. Antioxidant capacity assays may be broadly classified as electron transfer (ET)- and hydrogen atom transfer (HAT)-based assays. The majority of HAT assays are kinetics-based, and involve a competitive reaction scheme in which antioxidant and substrate compete for peroxyl radicals thermally generated through the decomposition of azo compounds. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes colour when reduced. ET assays include the ABTS/TEAC, CUPRAC, DPPH, Folin-Ciocalteu and FRAP methods, each using different chromogenic redox reagents with different standard potentials. This review intends to offer a critical evaluation of existing antioxidant assays applied to phenolics, and reports the development by our research group of a simple and low-cost antioxidant capacity assay for dietary polyphenols, vitamins C and E, and human serum antioxidants, utilizing the copper(II)-neocuproine reagent as the chromogenic oxidizing agent, which we haved named the CUPRAC (cupric ion reducing antioxidant capacity) method. This method offers distinct advantages over other ET-based assays, namely the selection of working pH at physiological pH (as opposed to the Folin and FRAP methods, which work at alkaline and acidic pHs, respectively), applicability to both hydrophilic and lipophilic antioxidants (unlike Folin and DPPH), completion of the redox reactions for most common flavonoids (unlike FRAP), selective oxidation of antioxidant compounds without affecting sugars and citric acid commonly contained in foodstuffs and the capability to assay -SH bearing antioxidants (unlike FRAP). Other similar ET-based antioxidant assays that we have developed or modified for phenolics are the Fe(III)- and Ce(IV)-reducing capacity methods.