Quercetin exhibits a specific fluorescence in cellular milieu: a valuable tool for the study of its intracellular distribution

Diversity and function of fluorescent molecules in marine animals

Fluorescence in marine animals has mainly been studied in Cnidaria but is found in many different phyla such as Annelida, Crustacea, Mollusca, and Chordata. While many fluorescent proteins and molecules have been identified, very little information is available about the biological functions of fluorescence. In this review, we focus on describing the occurrence of fluorescence in marine animals and the behavioural and physiological functions of fluorescent molecules based on experimental approaches. These biological functions of fluorescence range from prey and symbiont attraction, photoprotection, photoenhancement, stress mitigation, mimicry, and aposematism to inter- and intraspecific communication. We provide a comprehensive list of marine taxa that utilise fluorescence, including demonstrated effects on behavioural or physiological responses. We describe the numerous known functions of fluorescence in anthozoans and their underlying molecular mechanisms. We also highlight that other marine taxa should be studied regarding the functions of fluorescence. We suggest that an increase in research effort in this field could contribute to understanding the capacity of marine animals to respond to negative effects of climate change, such as rising sea temperatures and increasing intensities of solar irradiation.

Fighting nature with nature: antiviral compounds that target retroviruses

The human immunodeficiency virus (HIV) is a type of lentivirus that targets the human immune system and leads to acquired immunodeficiency syndrome (AIDS) at a later stage. Up to 2021, there are millions still living with HIV and many have lost their lives. To date, many anti-HIV compounds have been discovered in living organisms, especially plants and marine sponges. However, no treatment can offer a complete cure, but only suppressing it with a life-long medication, known as combined antiretroviral therapy (cART) or highly active antiretroviral therapy (HAART) which are often associated with various adverse effects. Also, it takes many years for a discovered compound to be approved for clinical use. Thus, by employing advanced technologies such as automation, conducting systematic screening and testing protocols may boost the discovery and development of potent and curative therapeutics for HIV infection/AIDS. In this review, we aim to summarize the antiretroviral therapies/compounds and their associated drawbacks since the discovery of azidothymidine. Additionally, we aim to provide an updated analysis of the most recent discoveries of promising antiretroviral candidates, along with an exploration of the current limitations within antiretroviral research. Finally, we intend to glean insightful perspectives and propose future research directions in this crucial area of study.

Clearance of extracellular human amyloid-β aggregates in C. elegans by nutraceutical and pharmaceutical interventions

Numerous anti-amyloid therapies have seen recent clinical development and approval, such as the monoclonal antibodies aducanumab and lecanemab. However, in Alzheimer's disease patients, amyloid-β (Aβ) plaques are found embedded in the extracellular matrix and surrounded by collagens, which might hinder these antibodies from targeting the plaques. We reasoned that various different nutraceutical and pharmaceutical agents might induce collagen and extracellular matrix turnover and removal of these collagen-embedded amyloid-β (Aβ) plaques. To address this idea, here, we used a transgenic C. elegans strain, LSD2104 , expressing fluorescent human Aβ 1-42 as an in-vivo model for secreted amyloid aggregation in the extracellular matrix. We performed a screen of various nutraceuticals and pharmaceuticals along with different combinations, and we found that quercetin 350 µM and rifampicin 75 µM successfully cleared the extracellular amyloid plaque burden compared to the 0.2% DMSO control group, with a combination of the two agents producing the maximum effect compared to either drug alone. These results may implicate the exploration of combination therapeutics of nutraceuticals and pharmaceuticals in the clearance of amyloid-β (Aβ) plaques in Alzheimer's disease.

Analytical Methods for the Determination of Quercetin and Quercetin Glycosides in Pharmaceuticals and Biological Samples

Flavonoids are plant-derived compounds that have several health benefits, including antioxidative, anti-inflammatory, anti-mutagenic, and anti-carcinogenic effects. Quercetin is a flavonoid that is widely present in various fruits, vegetables, and drinks. Accurate determination of quercetin in different samples is of great importance for its potential health benefits. This review, is an overview of sample preparation and determination methods for quercetin in diverse matrices. Previous research on sample preparation and determination methods for quercetin are summarized, highlighting the advantages and disadvantages of each method and providing insights into recent developments in quercetin sample treatment. Various analytical techniques are discussed including spectroscopic, chromatographic, electrophoretic, and electrochemical methods for the determination of quercetin and its derivatives in different samples. UV-Vis (Ultraviolet-visible) spectrophotometry is simple and inexpensive but lacks selectivity. Chromatographic techniques (HPLC, GC) offer selectivity and sensitivity, while electrophoretic and electrochemical methods provide high resolution and low detection limits, respectively. The aim of this review is to comprehensively explore the determination methods for quercetin and quercetin glycosides in diverse matrices, with emphasis on pharmaceutical and biological samples. The review also provides a theoretical basis for method development and application for the analysis of quercetin and quercetin glycosides in real samples.

Quercetin's Dual Mode of Action to Counteract the Sp1-miR-27a Axis in Colorectal Cancer Cells

Quercetin (Qc) inhibits cell proliferation and induces apoptosis in a variety of cancer cells. The molecular mechanism of action has not been fully elucidated; however, interplay with some miRNAs has been reported, specifically with miR-27a, an onco-miRNA overexpressed in several malignancies. Here, we show that Qc reduces cell viability and induces apoptosis in HCT116 and HT-29 colon cancer cells, by upregulating negative modulators of proliferation pathways such as Sprouty2, PTEN and SFRP1. These are targets of miR-27a whose high expression is reduced by Qc. Moreover, miR-23a, and miR-24-2, the two other components of the unique gene cluster, and the pri-miRNA transcript are reduced, evoking a transcriptional regulation of the entire cluster by Sp1. Mechanistically, we show that Qc is rapidly internalized and localizes in the nucleus, where it likely interacts with Sp1, inducing its proteasomal degradation. Sp1 is further repressed by ZBTB10, an Sp1 competitor for DNA binding that is an miR-27a target and whose levels increase following Qc. SP1 mRNA is also reduced, supporting the regulation of its own gene transcription. Finally, Sp1 knockdown elicits the impaired transcription of the entire cluster and the upregulation of the miR-27a targets, phenocopying the effects of Qc. Through this dual mode of action, Qc counteracts the protumoral Sp1-miR-27a axis, opening the way for novel therapies based on its association as neoadjuvant with known anticancer treatments.

Nrf2-Mediated Pathway Activated by Prunus spinosa L. (Rosaceae) Fruit Extract: Bioinformatics Analyses and Experimental Validation

In our previous studies, Prunus spinosa fruit (PSF) ethanol extract was showed to exert antioxidant, antimicrobial, anti-inflammatory and wound healing activities. In the present study, an integrated bioinformatics analysis combined with experimental validation was carried out to investigate the biological mechanism(s) that are responsible for the reported PSF beneficial effects as an antioxidant during a pro-inflammatory TLR4 insult. Bioinformatics analysis using miRNet 2.0 was carried out to address which biological process(es) the extract could be involved in. In addition, Chemprop was employed to identify the key targets of nuclear receptor (NR) signaling and stress response (SR) pathways potentially modulated. The miRNet analysis suggested that the PSF extract mostly activates the biological process of cellular senescence. The Chemprop analysis predicted three possible targets for nine phytochemicals found in the extract: (i) ARE signaling, (ii) mitochondrial membrane potential (MMP) and (iii) p53 SR pathways. The PSF extract antioxidant effect was also experimentally validated in vitro using the human monocyte U937 cell line. Our findings showed that Nrf2 is modulated by the extract with a consequent reduction of the oxidative stress level. This was confirmed by a strong decrease in the amount of reactive oxygen species (ROS) observed in the PSF-treated cells subjected to lipopolysaccharide (LPS) (6 h treatment, 1 µg/mL). No visible effects were observed on p53 and MMP modulation.

Loading and Release of Quercetin from Contact-Drawn Polyvinyl Alcohol Fiber Scaffolds

Polymeric drug releasing systems have numerous applications for the treatment of chronic diseases and traumatic injuries. In this study, a simple, cost-effective, and scalable method for dry spinning of crosslinked polyvinyl alcohol (PVA) fibers is presented. This method utilizes an entangled solution of PVA to form liquid bridges that are drawn into rapidly drying fibers through extensional flow. The fibers are crosslinked by a one-pot reaction in which glyoxal is introduced to the PVA solution prior to contact drawing. Failure analysis of fiber formation is used to understand the interplay of polymer concentration, glyoxal concentration, and crosslinking time to identify appropriate formulations for the production of glyoxal-crosslinked PVA fibers. The small molecule quercetin (an anti-inflammatory plant flavonoid) can be added to the one-pot reaction and is shown to be incorporated into the fibers in a concentration-dependent manner. Upon rehydration in an aqueous medium, the glyoxal-crosslinked PVA fiber scaffolds retain their morphology and slowly degrade, as measured over the course of 10 days. As the scaffolds degrade, they release the loaded quercetin, reaching a cumulative release of 56 ± 6% of the loaded drug after 10 days. The bioactivity of the released quercetin is verified by combining quercetin-loaded fibers with contact-drawn polyethylene oxide-type I collagen (PEO-Col) fibers and monitoring the growth of PC12 cells on the fibers. PC12 cells readily attach to the PEO-Col fibers and display increased nerve growth factor-induced elongation and neurite formation in the presence of quercetin-loaded PVA fibers relative to substrates formed from only PEO-Col fibers or PEO-Col and PVA fibers without quercetin.

pH-Sensitive Twin Liposomes Containing Quercetin and Laccase for Tumor Therapy

In this study, functional twin liposomes (TLs) were designed by linking avidin-anchored single liposomes and biotin-anchored single liposomes via avidin-biotin interactions. Here, we first punched a hole on the liposome surface using the liposome magnetoporation method to prepare functional single liposomes, which were used for safely encapsulating quercetin (QER, as a model prodrug) or laccase (LAC, as a bioactive enzyme) inside the liposomes without the use of organic solvents; the pores were then plugged by pH-sensitive glycol chitosan grafted with 3-diethylaminopropylamine (GDEAP) and avidin (or biotin). As a result, single liposomes with QER and biotin-GDEAP were efficiently coupled with other liposomes with LAC and avidin-GDEAP. We demonstrated that the TLs could accelerate QER and LAC release at acidic pH (6.8), improving the LAC-mediated oxidization of QER and significantly elevating tumor cell death, suggesting that this strategy can be used as an efficient method for the programmed action of prodrugs.

Fabrication and In Vitro/Vivo Evaluation of Drug Nanocrystals Self-Stabilized Pickering Emulsion for Oral Delivery of Quercetin

The aim of this study was to develop a new drug nanocrystals self-stabilized Pickering emulsion (NSSPE) for improving oral bioavailability of quercetin (QT). Quercetin nanocrystal (QT–NC) was fabricated by high pressure homogenization method, and QT–NSSPE was then prepared by ultrasound method with QT–NC as solid particle stabilizer and optimized by Box-Behnken design. The optimized QT–NSSPE was characterized by fluorescence microscope (FM), scanning electron micrograph (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The stability, in vitro release, and in vivo oral bioavailability of QT–NSSPE were also investigated. Results showed that the droplets of QT–NSSPE with the size of 10.29 ± 0.44 μm exhibited a core-shell structure consisting of a core of oil and a shell of QT–NC. QT–NSSPE has shown a great stability in droplets shape, size, creaming index, zeta potential, and QT content during 30 days storage at 4, 25, and 40 °C. In vitro release studies showed that QT–NSSPE performed a better dissolution behavior (65.88% within 24 h) as compared to QT–NC (50.71%) and QT coarse powder (20.15%). After oral administration, the AUC_0–t of QT–NSSPE was increased by 2.76-times and 1.38 times compared with QT coarse powder and QT–NC. It could be concluded that NSSPE is a promising oral delivery system for improving the oral bioavailability of QT.

Synthesis of 3'-O-Alkyl Homologues and a Biotin Probe of Isorhamnetin and Evaluation of Cytotoxic Efficacy on Cancer Cells

Isorhamnetin is a natural flavonoid which shows a variety of biological activities such as antioxidant, anti-inflammatory and antitumor. In order to identify the cellular binding protein of isorhamnetin as potential anti-cancer target, we first synthesized 3'-O-substituted quercetin as isorhamnetin homologues and evaluated the growth inhibitory activity of these derivatives on breast, colon and prostate cancer cell lines. The preliminary results showed that the 3'-O modification did not affect the cytotoxic activity of the scaffold. Analysis of the co-crystal structure and the docking pose of isorhamnetin with reported binding protein of isorhamnetin or quercetin indicated the 3'-O-substitution groups located outside of the binding pocket, which is in accordance with activity of 3'-O derivatives. Then a biotin conjugate of isorhamnetin with a tetraethylene glycol (PEG)₄ linker at the 3' position was synthesized and the resulting probe retained the anti-proliferative activity on cancer cell lines, while the cellular fluorescence analysis showed the distribution of probe inside the cells which indicated the probe had limited cell permeability. Finally, pull down assay both in situ inside cells and in the cell lysates indicated the isorhamnetin biotin probe was capable of protein labeling in cell lysates. These findings provide the isorhamnetin 3'-O-biotin probe as a tool to reveal the target proteins of isorhamnetin.

Quercetin in the form of a nano-antioxidant (QTiO2) provides stabilization of quercetin and maximizes its antioxidant capacity in the mouse fibroblast model

Living cells are constantly exposed to reactive oxygen species (ROS) causing them to rely on a constant supply of exogenous antioxidants. Quercetin (Q) is one of the potent exogenous antioxidants utilized in various antioxidant formulations. However, the potential application of Q is largely limited because of its poor water solubility. In this study, we employed titanium dioxide (TiO₂) nanoparticles to maximize cellular penetration and antioxidant effect of Q on mouse fibroblast cells. To accomplish this, polyethylene glycol (PEG) modified TiO₂-nanoparticle surfaces were utilized that exhibited better dispersion, with enhanced biocompatibility. Cell viability assays using Q and Q-conjugated TiO₂-nanoparticles (QTiO₂) were evaluated in terms of cell morphology as well as with an immunoblotting analysis to look for key biomarkers of apoptosis. In addition, cleavages of Cas 3 and PARP were obtained in cells treated with Q. Furthermore, antioxidant defence with QTiO₂ was validated by means of the Nrf2 upregulation pathway. We also observed increased expressions of target enzymes; HO-1, NQO1 and SOD1 in QTiO₂-treated cells. The antioxidant potency of the QTiO₂ nano-antioxidant form was successfully tested in ROS and superoxide radicals induced cells. Our results demonstrated that the QTiO₂ nano-antioxidant promoted a high quercetin bioavailability and stability, in cells with maximal antioxidant potency against ROS, with no signs of cytotoxicity.

Onion derived carbon nanodots for live cell imaging and accelerated skin wound healing

Nitrogen, sulfur, and phosphorous co-doped water-soluble carbon nanodots are synthesized from culinary waste onion peel powder (OPP) by a short microwave treatment. Onion Derived Carbon Nano Dots (OCND) that comprised hydrophilic group-decorated amorphous nano-dots exhibited bright, stable fluorescence at an excitation of 450 nm and emission wavelength at 520 nm along with a free radical scavenging property. The OCND exhibited excellent stability at different pH and UV exposure. Although extracted polyphenols degraded in the extract, interestingly it was shown to be cytocompatible and blood compatible as observed during cytotoxicity, fluorescence imaging of the cell and a hemolysis study. The present work not only focuses on the synthesis of OCND from the OPP extract but also provides an interesting fact that, even after the degradation of polyphenols in the extract, they are non-toxic to human cells (HFF & MG63) and RBCs. Moreover, OCND had no adverse effect on the migration rate of Human Foreskin-derived Fibroblasts (HFFs) as observed from a scratch assay. In addition to accelerating the migration rate of fibroblasts, the OCND altered intra- and extracellular reactive oxygen species (ROS) by enhancing the antioxidant mechanism of a fibroblast under oxidative stress. Further, OCND was observed to accelerate wound healing in a full thickness (FT) wound in a rat model for topical application, which can be attributed to its radical scavenging potential. In summary, this study leads to a new type of OCND synthesis route, which is inherently co-doped with phosphorous, sulfur and nitrogen and holds a great promise for a myriad of biological applications, including bio-imaging, free radical scavenging and wound healing.

Biospectroscopy, biospectrometry and imaging of Ilex paraguariensis. Basis for non-destructive quality evaluation using artificial vision

Optical indicators related to the nutraceutical content derived from fluorescence, reflectance and imaging ofIlex paraguariensishave been developed. The results are complemented with mass spectrometry analysis.

Can Invalid Bioactives Undermine Natural Product-Based Drug Discovery?

High-throughput biology has contributed a wealth of data on chemicals, including natural products (NPs). Recently, attention was drawn to certain, predominantly synthetic, compounds that are responsible for disproportionate percentages of hits but are false actives. Spurious bioassay interference led to their designation as pan-assay interference compounds (PAINS). NPs lack comparable scrutiny, which this study aims to rectify. Systematic mining of 80+ years of the phytochemistry and biology literature, using the NAPRALERT database, revealed that only 39 compounds represent the NPs most reported by occurrence, activity, and distinct activity. Over 50% are not explained by phenomena known for synthetic libraries, and all had manifold ascribed bioactivities, designating them as invalid metabolic panaceas (IMPs). Cumulative distributions of ∼200,000 NPs uncovered that NP research follows power-law characteristics typical for behavioral phenomena. Projection into occurrence–bioactivity–effort space produces the hyperbolic black hole of NPs, where IMPs populate the high-effort base.

Bioinspired Quercitrin Nanocoatings: A Fluorescence-Based Method for Their Surface Quantification, and Their Effect on Stem Cell Adhesion and Differentiation to the Osteoblastic Lineage

Polyphenol-based coatings have several potential applications in medical devices, such as cardiovascular stents, contrast agents, drug delivery systems, or bone implants, due to the multiple bioactive functionalities of these compounds. In a previous study, we fabricated titanium surfaces functionalized with flavonoids through covalent chemistry, and observed their osteogenic, anti-inflammatory, and antifibrotic properties in vitro. In this work, we report a fluorescence-based method for the quantification of the amount of flavonoid grafted onto the surfaces, using 2-aminoethyl diphenylborinate, a boronic ester that spontaneously forms a fluorescent complex with flavonoids. The method is sensitive, simple, rapid, and easy to perform with routine equipment, and could be applied to determine the surface coverage of other plant-derived polyphenol-based coatings. Besides, we evaluated an approach based on reductive amination to covalently graft the flavonoid quercitrin to Ti substrates, and optimized the grafting conditions. Depending on the reaction conditions, the amount of quercitrin grafted was between 64 ± 10 and 842 ± 361 nmol on 6.2 mm Ti coins. Finally, we evaluated the in vitro behavior of bone-marrow-derived human mesenchymal stem cells cultured on the quercitrin nanocoated Ti surfaces. The surfaces functionalized with quercitrin showed a faster stem cell adhesion than control surfaces, probably due to the presence of the catechol groups of quercitrin on the surfaces. A rapid cell adhesion is crucial for the successful performance of an implant. Furthermore, quercitrin-nanocoated surfaces enhanced the mineralization of the cells after 21 days of cell culture. These results indicate that quercitrin nanocoatings could promote the rapid osteointegration of bone implants.

Quercetin-POM (pivaloxymethyl) conjugates: Modulatory activity for P-glycoprotein-based multidrug resistance

BACKGROUND

We previously demonstrated that the bioactivity of quercetin could be improved through conjugation with a hydrolysable pivaloxymethyl (POM) group.

PURPOSE

Present study aimed to evaluate MDR (multidrug resistance)-modulatory activity of the quercetin-POM conjugates.

STUDY DESIGN/METHODS

MDR-modulatory activity was determined by measuring cytotoxicity of various anticancer agents to MDR MES-SA/Dx5 cell lines upon combination with the quercetin-POM conjugates.

RESULTS

The quercetin-7-O-POM conjugate (7-O-POM-Q) was significantly more potent than quercetin in reversing MDR, which recovered the cytotoxicity of various anticancer agents with EC50 values of 1.1-1.3 µM. A series of mechanistic studies revealed that 7-O-POM-Q competes with verapamil in binding to the same drug-binding site of the major MDR target, Pgp (P-glycoprotein), and inhibits Pgp-mediated drug efflux with a similar potency as verapamil. The physicochemical properties of 7-O-POM-Q were then evaluated, which confirmed that 7-O-POM-Q has remarkably enhanced cellular uptake and intracellular localization compared with quercetin. Additionally, it is noteworthy that 7-O-POM-Q undergoes slow hydrolysis to quercetin over a prolonged period of time.

CONCLUSION

The quercetin-POM conjugate showed significantly improved MDR-reversing activity compared with quercetin, which could be attributed to its capacity to maintain high intracellular concentrations.

Reviewing the relevance of fluorescence in biological systems

Fluorescence is emitted by diverse living organisms. The analysis and interpretation of these signals may give information about their physiological state, ways of communication among species and the presence of specific chemicals. In this manuscript we review the state of the art in the research on the fluorescence emitted by plant leaves, fruits, flowers, avians, butterflies, beetles, dragonflies, millipedes, cockroaches, bees, spiders, scorpions and sea organisms and discuss its relevance in nature.

Modulation of nitric oxide by flavonoids

One of the main mechanisms by which dietary flavonoids are thought to influence cardiovascular disease is via protection of the bioactivity of the endothelium-derived nitric oxide (NO). Additionally, flavonoids may also interfere with the signalling cascades of inflammation and prevent overproduction of NO and its deleterious consequences in shock and ischemia-reperfusion injury. In the present paper we review the evidence of the effects of flavonoids on NO. Flavonoids exert complex actions on the synthesis and bioavailability of NO which may result both in enhanced or decreased NO levels: (1) in cell free systems, several flavonoids may scavenge NO via its pro-oxidant properties by increasing superoxide. However, under conditions of oxidative stress, flavonoids may also protect NO from superoxide-driven inactivation. (2) In intact healthy tissues, some flavonoids increase eNOS activity in endothelial cells. Paradoxically this effect involves a pro-oxidant effect which results in Ca(2+)-dependent activation of eNOS. As inhibitors of PI3K, flavonoids may potentially inhibit the PI3K/Akt-dependent activation of eNOS. (3) Under conditions of inflammation and oxidative stress, flavonoids may prevent the inflammatory signalling cascades via inhibition of NFκB and thereby downregulate iNOS. On the other hand, they also prevent the overexpression of ROS generating enzymes, reducing superoxide and peroxynitrite levels, and hence preventing superoxide-induced NO inactivation and eNOS uncoupling. Therefore, the final effect of flavonoids on NO levels will depend on the flavonoid structure and the concentrations used, on the cell type under study and particularly on the presence of inflammatory/oxidative conditions.

Quercetin delivery to porcine cornea and sclera by solid lipid nanoparticles and nanoemulsion

Two potential nanocarriers including nanoemulsions and solid lipid nanoparticles have been demonstrated as vehicles for quercetin encapsulation and ocular delivery.

Water-soluble and cleavable quercetin-amino acid conjugates as safe modulators for P-glycoprotein-based multidrug resistance

Quercetin-amino acid conjugates with alanine or glutamic acid moiety attached at 7-O and/or 3-O position of quercetin were prepared, and their multidrug resistance (MDR)-modulatory effects were evaluated. A quercetin-glutamic acid conjugate, 7-O-Glu-Q (3a), was as potent as verapamil in reversing MDR and sensitized MDR MES-SA/Dx5 cells to various anticancer drugs with EC50 values of 0.8-0.9 μM. Analysis on Rh-123 accumulation confirmed that 3a inhibits drug efflux by Pgp, and Pgp ATPase assay showed that 3a interacts with the drug-binding site of Pgp to stimulate its ATPase activity. Physicochemical analysis of 3a revealed that solubility, stability, and cellular uptake of quercetin were significantly improved by the glutamic acid promoiety, which eventually dissociates from 3a to produce quercetin and quercetin metabolites in intracellular milieu. Taken together, potent MDR-modulating activity along with intracellular conversion into the natural flavonoid quercetin warrants development of the quercetin-amino acid conjugates as safe MDR modulators.

Phenolic promiscuity in the cell nucleus--epigallocatechingallate (EGCG) and theaflavin-3,3'-digallate from green and black tea bind to model cell nuclear structures including histone proteins, double stranded DNA and telomeric quadruplex DNA

Flavanols from tea have been reported to accumulate in the cell nucleus in considerable concentrations. The nature of this phenomenon, which could provide novel approaches in understanding the well-known beneficial health effects of tea phenols, is investigated in this contribution. The interaction between epigallocatechin gallate (EGCG) from green tea and a selection of theaflavins from black tea with selected cell nuclear structures such as model histone proteins, double stranded DNA and quadruplex DNA was investigated using mass spectrometry, Circular Dichroism spectroscopy and fluorescent assays. The selected polyphenols were shown to display affinity to all of the selected cell nuclear structures, thereby demonstrating a degree of unexpected molecular promiscuity. Most interestingly theaflavin-digallate was shown to display the highest affinity to quadruplex DNA reported for any naturally occurring molecule reported so far. This finding has immediate implications in rationalising the chemopreventive effect of the tea beverage against cancer and possibly the role of tea phenolics as "life span essentials".

Immunolocalisation of spermidine synthase in Solanum tuberosum

Spermidine synthase (SPDS) catalyses the formation of spermidine, which is an essential polyamine and widespread in living organisms. Spermidine is formed from putrescine by transfer of an aminopropyl group from decarboxylated S-adenosylmethionine. Spermidine is also a precursor to further polyamines, such as spermine and thermospermine, most of which contribute to tolerance against drought and salinity in plants. Thermospermine is indispensible for vascular tissue growth. Plant spermidine synthases have been cloned from several angiosperms; organ-specific gene expression levels are known for Arabidopsis only. In this study, immunolocalisation of SPDS in potato (Solanum tuberosum) organs is presented. Polyclonal antibodies for SPDS from potato produced in rabbits were purified by affinity chromatography. Cross-reaction with potato putrescine N-methyltransferase was eliminated. Accumulation of SPDS protein in the phloem region of vascular tissues throughout the potato plant is demonstrated.

Co-encapsulation of biodegradable nanoparticles with silicon quantum dots and quercetin for monitored delivery

Polymer nanoparticles have emerged as a promising new strategy for the efficient delivery of drugs. They have several advantages when used as drug carriers, such as high stability, high capacity, improvement of drug bioavailability, as well as allowing for sustained drug release. Quercetin has therapeutic potential as an anticancer drug, but has poor solubility and low bioavailability. In this study it is shown that co-encapsulation of quercetin and fluorescent Silicon quantum dots (SiQDs) in poly (ethylene glycol)-block-polylactide (PEG-PLA) nanoparticles can be used for simultaneous in vitro imaging and to improve the biocompatibility of quercetin. Fluorescent imaging with SiQDs can provide a new concept to monitor the delivery of anti-cancer drugs. The nanoparticles are synthesized based on the double emulsion method and are extensively characterized and assayed for cytotoxicity in vitro. HepG2 cells are incubated with quercetin and SiQDs dual-loaded PEG-PLA nanoparticles, resulting in a red fluorescent staining which can be detected with a confocal microscope. PEG-PLA nanoparticle encapsulated quercetin suppresses human hepatoma HepG2 cell proliferation more effectively than the free-standing form. In addition, nanoparticle-encapsulated quercetin significantly inhibits hydrogen peroxide-induced DNA damage in HepG2 cells. These data show that nanocapsulated quercetin possesses the potential bioactivity to reduce the drug dosage frequency, as well as increase patient compliance. The combination of polymeric nanoparticles and semiconductor quantum dots can allow monitoring of delivery, improve aqueous solubility, and enhance biocompatibility. Such nanoparticulated systems could shape the future of drug delivery.

Any colour you like. Excited state and ground state proton transfer in flavonols and applications

The photoinduced and ground state proton transfer processes occurring in flavonols are responsible for their multi-wavelength emission. This peculiar behavior has touched on a wide range of research areas, ranging from biology to chemistry of materials leading, among others, to the development of fluorescent probes for physical and biophysical parameters, laser dyes, and wavelentgh shifting devices. This account aims to be a brief introduction to the multi-faceted applications of flavonols.

Quercetin modulates Nrf2 and glutathione-related defenses in HepG2 cells: Involvement of p38

Dietary flavonoid quercetin has been suggested as a cancer chemopreventive agent, but the mechanisms of action remain unclear. This study investigated the influence of quercetin on p38-MAPK and the potential regulation of the nuclear transcription factor erythroid-2p45-related factor (Nrf2) and the cellular antioxidant/detoxifying defense system related to glutathione (GSH) by p38 in HepG2 cells. Incubation of HepG2 cells with quercetin at a range of concentrations (5-50μM) for 4 or 18h induced a differential effect on the modulation of p38 and Nrf2 in HepG2 cells, 50μM quercetin showed the highest activation of p38 at 4h of treatment and values of p38 similar to those of control cells after 18 h of incubation, together with the inhibition of Nrf2 at both incubation times. Quercetin (50μM) induced a time-dependent activation of p38, which was in concert with a transient stimulation of Nrf2 to provoke its inhibition afterward. Quercetin also increased GSH content, mRNA levels of glutamylcysteine-synthetase (GCS) and expression and/or activity of glutathione-peroxidase, glutathione-reductase and GCS after 4h of incubation, and glutathione-S-transferase after 18h of exposure. Further studies with the p38 specific inhibitor SB203580 showed that the p38 blockage restored the inhibited Nrf2 transcription factor and the enzymatic expression and activity of antioxidant/detoxificant enzymes after 4h exposure. In conclusion, p38-MAPK is involved in the mechanisms of the cell response to quercetin through the modulation of Nrf2 and glutathione-related enzymes in HepG2 cells.

125I-labeled quercetin as a novel DNA-targeted radiotracer

Quercetin is a major flavonoid that is found in most plants; it can intercalate with DNA. The purpose of this study was to investigate radiolabeling of qurecetin with (125)I, DNA binding and cellular process. In this work, quercetin was labeled with Auger emitting nuclide (125)I using chloramine-T. DNA binding of (125)I-quercetin ((125)I-Q) was investigated using cell-free in vitro assay with naked human genomic DNA in agarose plugs. Cellular uptake and nuclei accumulation were evaluated in human prostate cancer cell lines (DU 145). The internalization of (125)I-Q was evaluated with fluorescence microscopy. Cellular damage was monitored by using apoptosis assay. Quercetin was successfully labeled with (125)I, and it was taken up rapidly with cells and accumulated in the cellular nuclei. (125)I-Q-DNA binding was tight with long retention time, and it potentially induced DNA damage. These findings provide for using of (125)I-labeled quercetin as a carrier of Auger electron emitting radionuclide to the cell nuclei for targeted radiotherapy.

Quercetin accumulates in nuclear structures and triggers specific gene expression in epithelial cells

Quercetin is a flavonol modifying a number of cell processes in different cell lines. Here, we present evidence that nonconjugated quercetin enters cells possibly via organic anion transporter polypeptides and quickly accumulates in the nucleus where it concentrates at distinct foci. Furthermore, it induces major transcriptional events with a high number of transcripts being modified over time and about 2200 transcripts being continuously influenced by the agent. The latter transcripts are related to cell cycle and adhesion, xenobiotic metabolism, immune-related factors and transcription. In addition, quercetin up-regulates the expression of estrogen receptors α and β. The overall outcome on cell fate is reflected by an inhibition of cell proliferation, cell cycle arrest in the G1 phase and reduction of the cells' migratory potential due to actin cytoskeleton disorganization. Finally, we report that the flavonol modifies the transcription and/or activity of numerous transcription factors. In conclusion, our data support the idea that quercetin may actively accumulate in discrete cell structures and exert more than just antioxidant actions on epithelial cells by regulating mechanisms related to gene transcription.

Protic equilibria as the key factor of quercetin emission in solution. Relevance to biochemical and analytical studies

A detailed spectrofluorimetric study on quercetin in aqueous solution proves that its anionic forms are responsible for a strong fluorescence enhancement observed at pH > 6. Anion fluorescence is also observed in organic solvents with strong hydrogen bond acceptor properties. The results provide a new interpretation of biophysical and analytical literature data where the fluorescence of the anionic forms of quercetin has never been explicitly taken into account. In particular, comparison with published binding studies strongly suggests that quercetin deprotonation and consequent fluorescence enhancement takes place when the flavonoid binds to several biological macromolecules. This observation can be very helpful in the understanding at a molecular level of the interaction between quercetin and the biomolecule.

Enhanced stability and intracellular accumulation of quercetin by protection of the chemically or metabolically susceptible hydroxyl groups with a pivaloxymethyl (POM) promoiety

In order to increase stability of quercetin, its metabolically and chemically susceptible hydroxyl groups 7-OH and 3-OH respectively were transiently blocked with a pivaloxymethyl (POM) promoiety to provide two novel quercetin conjugates [7-O-POM-Q, 3-O-POM-Q]. In the absence of stabilizer (ascorbic acid), the synthesized conjugates showed significantly increased stability in cell culture media [t(½) = 4 h, 52 h] compared with quercetin (t(½) < 30 min) and quercetin prodrug 1 (t(½) = 0.8 h). In addition, the quercetin conjugate 2 underwent efficient cellular uptake and intracellular levels of its hydrolysis product, quercetin, were maintained up to 12 h. Stability and intracellular accumulation of were demonstrated by its stabilizer-independent cytostatic effect and induction of apoptotic cell death. Even though was more stable than, it failed to penetrate cell membranes. However, the remarkable stability of warrants further investigation of quercetin conjugates with various promoieties at the 3-OH position.

Flavonols and cardiovascular disease

Flavonols, and specially quercetin, are widely distributed in plants and are present in considerable amounts in fruits and vegetables. In addition to their anti-oxidant effect, flavonols interfere with a large number of biochemical signaling pathways and, therefore, physiological and pathological processes. There is solid evidence that, in vitro, quercetin and related flavonols exert endothelium-independent vasodilator effects, protective effect on nitric oxide and endothelial function under conditions of oxidative stress, platelet antiaggregant effects, inhibition of LDL oxidation, reduction of adhesion molecules and other inflammatory markers and prevention of neuronal oxidative and inflammatory damage. The metabolites of quercetin show partial protective effects on endothelial function and LDL oxidation. Quercetin produces undisputed antihypertensive and antiatherogenic effects, prevents endothelial dysfunction and protects the myocardium from ischemic damage. It has no clear effects on serum lipid profile and on insulin resistance. Human intervention trials with isolated flavonols demonstrate an antihypertensive effect. The meta-analysis of epidemiological studies show an inverse association between flavonol (together with flavone) intake and coronary heart disease and stroke. Therefore, although there is no solid proof yet, a substantial body of evidence suggests that quercetin may prevent the most common forms of cardiovascular disease contributing to the protective effects afforded by fruits and vegetables.

The Photodynamic Effect of Different Size ZnO Nanoparticles on Cancer Cell Proliferation In Vitro

Nanomaterials have widely been used in the field of biological and biomedicine, such as tissue imaging, diagnosis and cancer therapy. In this study, we explored the cytotoxicity and photodynamic effect of different-sized ZnO nanoparticles to target cells. Our observations demonstrated that ZnO nanoparticles exerted dose-dependent and time-dependent cytotoxicity for cancer cells like hepatocellular carcinoma SMMC-7721 cells in vitro. Meanwhile, it was observed that UV irradiation could enhance the suppression ability of ZnO nanoparticles on cancer cells proliferation, and these effects were in the size-dependent manner. Furthermore, when ZnO nanoparticles combined with daunorubicin, the related cytotoxicity of anticancer agents on cancer cells was evidently enhanced, suggesting that ZnO nanoparticles could play an important role in drug delivery. This may offer the possibility of the great potential and promising applications of the ZnO nanoparticles in clinical and biomedical areas like photodynamic cancer therapy and others.

Mesophyll distribution of 'antioxidant' flavonoid glycosides in Ligustrum vulgare leaves under contrasting sunlight irradiance

BACKGROUND AND AIMS

Flavonoids have the potential to serve as antioxidants in addition to their function of UV screening in photoprotective mechanisms. However, flavonoids have long been reported to accumulate mostly in epidermal cells and surface organs in response to high sunlight. Therefore, how leaf flavonoids actually carry out their antioxidant functions is still a matter of debate. Here, the distribution of flavonoids with effective antioxidant properties, i.e. the orthodihydroxy B-ring-substituted quercetin and luteolin glycosides, was investigated in the mesophyll of Ligustrum vulgare leaves acclimated to contrasting sunlight irradiance.

METHODS

In the first experiment, plants were grown at 20 % (shade) or 100% (sun) natural sunlight. Plants were exposed to 100 % sunlight irradiance in the presence or absence of UV wavelengths, in a second experiment. Fluorescence microspectroscopy and multispectral fluorescence microimaging were used in both cross sections and intact leaf pieces to visualize orthodihydroxy B-ring-substituted flavonoids at inter- and intracellular levels. Identification and quantification of individual hydroxycinnamates and flavonoid glycosides were performed via HPLC-DAD.

KEY RESULTS

Quercetin and luteolin derivatives accumulated to a great extent in both the epidermal and mesophyll cells in response to high sunlight. Tissue fluorescence signatures and leaf flavonoid concentrations were strongly related. Monohydroxyflavone glycosides, namely luteolin 4'-O-glucoside and two apigenin 7-O-glycosides were unresponsive to changes in sunlight irradiance. Quercetin and luteolin derivatives accumulated in the vacuoles of mesophyll cells in leaves growing under 100 % natural sunlight in the absence of UV wavelengths.

CONCLUSIONS

The above findings lead to the hypothesis that flavonoids play a key role in countering light-induced oxidative stress, and not only in avoiding the penetration of short solar wavelengths in the leaf.

Synergistic Effect of Functionalized Nickel Nanoparticles and Quercetin on Inhibition of the SMMC-7721 Cells Proliferation

The effect of functionalized nickel (Ni) nanoparticles capped with positively charged tetraheptylammonium on cellular uptake of drug quercetin into hepatocellular carcinoma cells (SMMC-7721) has been explored in this study via microscopy and electrochemical characterization as well as MTT assay. Meanwhile, the influence of Ni nanoparticles and/or quercetin on cell proliferation has been further evaluated by the real-time cell electronic sensing (RT-CES) study. Our observations indicate that Ni nanoparticles could efficiently improve the permeability of cancer cell membrane, and remarkably enhance the accumulation of quercetin in SMMC-7721 cells, suggesting that Ni nanoparticles and quercetin would facilitate the synergistic effect on inhibiting proliferation of cancer cells.

Mitochondria accumulate large amounts of quercetin: prevention of mitochondrial damage and release upon oxidation of the extramitochondrial fraction of the flavonoid

Quercetin uptake in Jurkat cells is extremely rapid and associated with a remarkable accumulation of the flavonoid, dependent on its binding to intracellular components. Cell-associated quercetin is biologically active, quantitatively consumed to promote survival in the presence of reactive species, such as peroxynitrite (ONOO(-)), or reduction of extracellular oxidants via activation of plasma membrane oxidoreductases. In alternative, quercetin is very slowly released upon post-incubation in drug-free medium, an event significantly accelerated by extracellular albumin. Quercetin uptake is also observed in isolated mitochondria, resulting in an enormous accumulation of the flavonoid, consumed under conditions associated with prevention of lipid peroxidation induced by ONOO(-). Interestingly, remarkable quercetin accumulation is also detected in the mitochondria isolated from quercetin-pre-loaded cells, and exposure to either ONOO(-) or extracellular oxidants caused the parallel loss of both the mitochondrial and cytosolic fractions of the flavonoid. In conclusion, Jurkat cells accumulate large amounts of quercetin and even larger amounts of the flavonoid further accumulate in their mitochondria. Intramitochondrial quercetin appears to be functional for prevention of mitochondrial damage as well as for redistribution to the cytosol, when the fraction of the flavonoid therein retained is progressively consumed either by cell-permeant oxidants or by activation of plasma membrane oxidoreductases.

The nutritional flavanone naringenin triggers antiestrogenic effects by regulating estrogen receptor alpha-palmitoylation

Naringenin (Nar) is a component of fruits and vegetables associated with healthful benefits, such as in osteoporosis, cancer, and cardiovascular diseases. These protective effects have been linked with Nar antiestrogenic as well as estrogenic activities. Previous studies indicate that Nar impaired estrogen receptor (ER) alpha signaling by interfering with ERalpha-mediated activation of ERK and phosphoinositide 3-kinase signaling pathways in the absence of effects at the transcriptional level. The present studies evaluated the hypothesis that these Nar antagonistic effects occur at the level of the plasma membrane. Our results indicate that Nar induces ERalpha depalmitoylation faster than 17beta-estradiol, which results in receptor rapid dissociation from caveolin-1. Furthermore, Nar impedes ERalpha to bind adaptor (modulator of nongenomic actions of the ER) and signaling (c-Src) proteins involved in the activation of the mitogenic signaling cascades (i.e. ERK and phosphoinositide 3-kinase). On the other hand, Nar induces the ER-dependent, but palmitoylation-independent, activation of p38 kinase, which in turn is responsible for Nar-mediated antiproliferative effects in cancer cells. Altogether, these data highlight new ER-dependent mechanisms on the root of antiproliferative and antiestrogenic effects of Nar. Moreover, the different modulation of ERalpha palmitoylation exerted by different ligands represents a pivotal mechanism that drives cancer cell to proliferation or apoptosis.