A conformational study of hydroxyflavones by vibrational spectroscopy coupled to DFT calculations

Differences in in vitro bioavailability, bioaccessibility, and antioxidant capacity depending on linkage type of luteolin 4'-O-glucosides

This study investigated the effect of glycosylation on the antioxidant capacities of luteolin by analyzing the differences in in vitro bioaccessibility, bioavailability, and bioactivity based on glucose anomers. Luteolin, luteolin 4'-O-alpha-glucoside (L4αG), and luteolin 4'-O-beta-glucoside (L4βG) were used to obtain clear and direct research results, excluding the influence of complex food matrices. L4αG exhibited lower water solubility, digestive stability, and aglycone-releasing ability compared to L4βG. However, L4αG most effectively alleviated intracellular oxidative stress in H2O2-induced Caco-2 cells by inhibiting the mitogen-activated protein kinases and activating nuclear factor erythroid-2-related factor signaling pathways. The findings suggested that the alpha-anomer of glucose in L4αG significantly (p < 0.05) enhanced intracellular antioxidant capacity by activating the cellular antioxidant enzyme systems rather than acting as an exogenous scavenger compared to L4βG. This study highlights a new approach for exploring natural antioxidants based on flavonoid aglycones with high cell affinity and electron-donating capacity.

Glycosylation of flavonoids by sucrose- and starch-utilizing glycoside hydrolases: A practical approach to enhance glycodiversification

Flavonoids are ubiquitous and diverse in plants and inseparable from the human diet. However, in terms of human health, their further research and application in functional food and pharmaceutical industries are hindered by their low water solubility. Therefore, flavonoid glycosylation has recently attracted research attention because it can modulate the physicochemical and biochemical properties of flavonoids. This review represents a comprehensive overview of the O-glycosylation of flavonoids catalyzed by sucrose- and starch-utilizing glycoside hydrolases (GHs). The characteristics of this feasible biosynthesis approach are systematically summarized, including catalytic mechanism, specificity, reaction conditions, and yields of the enzymatic reaction, as well as the physicochemical properties and bioactivities of the product flavonoid glycosides. The cheap glycosyl donor substrates and high yields undoubtedly make it a practical flavonoid modification approach to enhance glycodiversification.

Anticancer effect of novel luteolin capped gold nanoparticles selectively cytotoxic towards human cervical adenocarcinoma HeLa cells: An in vitro approach

BACKGROUND

Although luteolin has been confirmed as potent anticancer agent, its potential application as therapeutic is limited by its water solubility. To overcome this shortcoming nanoparticle technology approach was applied. Owing to their proven low toxicity and the possibility to be easily functionalized gold nanoparticles (AuNP) were the nanosystem of choice used in this study. Novel luteolin capped gold nanoparticles (AuNPL) were synthesized and their anticancer effect towards human cervical adenocarcinoma HeLa cells was investigated in vitro.

METHODS

AuNPL were synthesized by reducing chloroauric acid by trisodium citrate with subsequent addition of luteoline during synthesis and their physicochemical characterization was done. AuNPL cytotoxicity against HeLa, human malignant melanoma A375, and normal human keratinocytes HaCaT cells was tested by MTT cell survival assay, and their IC50 values were determined. The capability of AuNPL to induce cell cycle arrest and apoptosis in HeLa cells were demonstrated by flow cytometry. The antioxidant activity of AuNPL was assessed by DPPH· and ABTS·+ scavenging assays. Cytoprotective properties of AuNPL towards HaCaT cells were examined by measuring the physiological and H2O2 induced intracellular reactive oxygen species (ROS) levels using flow cytometry. Also, genotoxicity of AuNPL in HaCaT cells was investigated by the single cell alkaline comet assay.

RESULTS

Spherical AuNPL, stable in aqueous solution up to six months at 4 °C were obtained in the synthesis. The selectivity in the cytotoxic action of AuNPL on HeLa and A375 cancer cells compared with their cytotoxicity on normal keratinocytes HaCaT was observed. AuNPL exerted their cytotoxic activity against HeLa cells through accumulation of the cells in the subG1 phase of the cell cycle, inducing the apoptotic cell death mediated by the activation of caspase-3 - 8, and - 9. AuNPL antioxidative potential was confirmed by DPPH· and ABTS·+ scavenging assays. IC50 concentration of AuNPL exerted cytoprotective effect against HaCaT cells by the significant reduction of the physiological intracellular ROS level. Additionally, AuNPL were shown as more cytoprotective towards HaCaT cells then luteolin due to the more successful elimination of H2O2 induced intracellular ROS. Moreover, nontoxic concentrations of AuNPL did not cause considerable DNA damage of HaCaT cells, indicating low genotoxicity of the nanoparticles.

CONCLUSION

Synthesized AuNPL showed selective cytotoxic activity against HeLa cells, while being nontoxic and cytoprotective against HaCaT cells. The observed findings encourage further investigation of AuNPL as a promising novel anticancer agent.

Synthesis of Alpha-Linked Glucosides from Soybean Isoflavone Aglycones Using Amylosucrase from Deinococcus geothermalis

Soybean isoflavone aglycones (SIAs) have many biological activities but are poorly water-soluble in the human body. Glycosylation provides structural diversity to SIAs and can alter their physicochemical properties, including water solubility. An alpha-linked glucosylation of SIA was achieved using amylosucrase from Deinococcus geothermalis. A total of 13 alpha-linked glucosyl SIAs were obtained, and their colors in solution were confirmed. The structures of the isolated compounds were identified by mass spectrometry and multidimensional nuclear magnetic resonance spectroscopy. The amylosucrase transglycosylation formed new isoflavone glycosides with alpha glycosidic bonds at C-7 and/or C-4' of SIAs, followed by the production of isoflavone glycosides with alpha (1 → 6) glycosidic bonds. The products with a glucosyl moiety attached to the C-4' of SIAs were found to be more water-soluble than their counterparts attached to the C-7 and/or beta-linkages. This study suggests a strategy for the synthesis of bioactive compounds with enhanced water solubility through alpha-linked glucosylation.

IRMPD Spectroscopy of Bare Monodeprotonated Genistein, an Antioxidant Flavonoid

Genistein is a naturally occurring polyphenol belonging to the family of flavonoids with estrogenic properties and proven antioxidant, anti-inflammatory, and hormonal effects. Genistein and its derivatives are involved in radical scavenging activity by way of mechanisms based on sequential proton-loss electron transfer. In view of this role, a detailed structural characterization of its bare deprotonated form, [geni-H]^-, generated by electrospray ionization, has been performed by tandem mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy in the 800-1800 cm^-1 spectral range. Quantum chemical calculations at the B3LYP/6-311+G(d,p) level of theory were carried out to determine geometries, thermochemical data, and anharmonic vibrational properties of low-lying isomers, enabling to interpret the experimental spectrum. Evidence is gathered that the conjugate base of genistein exists as a single isomeric form, which is deprotonated at the most acidic site (7-OH) and benefits from a strong intramolecular H-bond interaction between 5-OH and the adjacent carbonyl oxygen in the most stable arrangement.

Effects of nitro- and amino-group on the antioxidant activity of genistein: A theoretical study

Five novel compounds (Gen-NO₂, Gen-2NO₂, Gen-NH₂, Gen-2NH₂ and Gen-6NH₂) have been designed via introducing an electron-withdrawing group -NO₂ and an electron-donating group -NH₂ into the structure of genistein. The effects of -NO₂ and -NH₂ groups on the antioxidant ability of genistein were investigated via quantum chemistry method in gas and methanol phases. The crucial parameters related to three antioxidant mechanisms were calculated. Moreover, the frontier molecular orbital, natural bond orbital and global descriptive parameters were calculated to evaluate the reactivity of genistein and its derivatives. Calculated results indicate the antioxidant process of genistein and its derivatives inclines to the hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms in gas and methanol phases, respectively. Moreover, introducing -NH₂ group into genistein can improve its antioxidant activity owing to the outstanding activities of amino-substituents of genistein, which will provide valuable guidance for the synthesis of new antioxidants experimentally.

Addressing Facts and Gaps in the Phenolics Chemistry of Winery By-Products

Grape and wine phenolics display a noticeable structural diversity, encompassing distinct compounds ranging from simple molecules to oligomers, as well as polymers usually designated as tannins. Since these compounds contribute critically to the organoleptic properties of wines, their analysis and quantification are of primordial importance for winery industry operators. Besides, the occurrence of these compounds has been also extensively described in winery residues, which have been pointed as a valuable source of bioactive phytochemicals presenting potential for the development of new added value products that could fit the current market demands. Therefore, the cumulative knowledge generated during the last decades has allowed the identification of the most promising compounds displaying interesting biological functions, as well as the chemical features responsible for the observed bioactivities. In this regard, the present review explores the scope of the existing knowledge, concerning the compounds found in these winery by-products, as well as the chemical features presumably responsible for the biological functions already identified. Moreover, the present work will hopefully pave the way for further actions to develop new powerful applications to these materials, thus, contributing to more sustainable valorization procedures and the development of newly obtained compounds with enhanced biological properties.

Raman microspectroscopy for probing the impact of a dietary antioxidant on human breast cancer cells

Breast cancer is the second most common type of cancer worldwide and the most frequent among women, being the fifth cause of death from neoplastic disease. Since this is an oxidative-stress related neoplasia, it is largely preventable. A dietary isoflavone abundant in soybean - daidzein - is currently being investigated owing to its chemopreventive and/or chemotherapeutic properties towards the human MDA-MB-231 (metastatic, estrogen-unresponsive) and MCF-7 (estrogen-responsive) breast cancer cell lines. Biological assays for evaluation of antitumour and anti-invasive activities were combined with state-of-the-art vibrational microspectroscopy techniques. At 50 and 100 μM concentrations and 48 h incubation time, daidzein was found to induce a marked decrease in cell viability (ca. 50%) for MDA-MB-231 and MCF-7 cells (respectively ca. 50% and 42%) and 40% inhibition of cell migration. MicroRaman analysis of fixed cells upon exposure to this isoflavone unveiled its metabolic impact on both cell lines. Multivariate data analysis (unsupervised PCA) led to a clear discrimination between the control and DAID-exposed cells, with distinctive effects on their biochemical profile, particularly regarding DNA, lipids and protein components, in a cell-dependent way. This is the first reported study on the impact of dietary antioxidants on cancer cells by microRaman techniques.

Vibrational analysis of α-cyanohydroxycinnamic acid

In the present study, a comparative Raman vibrational analysis of alpha-cyano-4-hydroxycinnamic acid (4CHCA) and its derivative, alpha-cyano-3-hydroxycinnamic acid (3CHCA), was performed. The Raman spectra of the 4CHCA and 3CHCA in solid form were obtained and analyzed to determine differences between the two structurally similar derivatives. For comparison, the CHCA derivatives cyanocinnamic acid (CCA) and coumaric acid (CA) were also studied. The plausible vibrational assignments were made and matched with those obtained theoretically using density functional theory (DFT) based method employing a 6-31 g basis set. The computational wavenumbers obtained were in good agreement with the observed experimental results. This was the first reported Raman study of CCA, 3CHCA and 4CHCA.