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

Benefits of Quercetin on Glycated Hemoglobin, Blood Pressure, PiKo-6 Readings, Night-Time Sleep, Anxiety, and Quality of Life in Patients with Type 2 Diabetes Mellitus: A Randomized Controlled Trial

Background: Diabetes is a rapidly growing global morbidity issue with high prevalence, and the associated dysglycemia leads to complications. Patients with type 2 diabetes mellitus (T2DM) often experience elevated anxiety levels, affecting their quality of life and diabetes management. This study investigated quercetin, a nutraceutical and potential senolytic with antioxidant activity, to detect its possible positive effect on the bio-clinical measurements and routine health of patients with T2DM. Methods: This prospective randomized controlled trial (RCT) investigated the clinical usefulness of quercetin in patients with T2DM receiving non-insulin medications. One hundred participants were stratified by age and sex (1:1) and randomized to control (n = 50) or intervention (n = 50) groups. The control received standard care only, while the intervention received 500 mg quercetin daily for 12 weeks, followed by an 8-week washout and a final consecutive 12-week supplementation period (total: 32 weeks), as adjunct to their usual care. Comprehensive health assessments, including blood analyses, were conducted at baseline and study termination. Quality of life and anxiety were assessed using the 36-item Short Form Health Survey (SF-36) and Short Anxiety Screening Test (SAST-10). Results: Eighty-eight patients with T2DM concluded the trial. Compared with the control, glycated hemoglobin (HbA1c) levels showed a significant decrease (Δ%-change: -4.0% vs. 0.1%, p = 0.011). Quercetin also significantly improved PiKo-6 readings (FEV1: 5.6% vs. -1.5%, p = 0.002), systolic blood pressure (-5.0% vs. -0.2%, p = 0.029), night-time sleep (11.6% vs. -7.3%, p < 0.001), anxiety levels (SAST-10) (-26.2% vs. 3.3%, p < 0.001), and quality of life (SF-36) (both physical and mental components, p < 0.001). Conclusions: Based on the current open-label study, quercetin appears to be a promising supplement for T2DM, providing lifestyle and care support. Further research is warranted to shift this potential from clinical usefulness and feasibility to multidisciplinary evidence.

The Impact of Three-Month Quercetin Intake on Quality of Life and Anxiety in Patients With Type II Diabetes Mellitus: An Early Data Analysis From a Randomized Controlled Trial

BACKGROUND

Diabetes is a high-prevalence, major chronic metabolic disease demanding effective interventions. Quercetin, a phytochemical with potential health benefits, has garnered interest for its therapeutic properties.

AIM

This study was designed to capture the early efficacy and clinical safety aspects following quercetin administration in patients with type II diabetes mellitus (T2DM).

METHODS

The main study involved a randomized allocation procedure to assign non-insulin-treated patients attending the 4th Health Unit of Heraklion to intervention and control groups based on age and sex. The intervention group (n=50) received 500 mg of quercetin daily for 12 + (8 free intervals) + 12 weeks, alongside their usual treatment, while the control group (n=50) did not. After randomization, for the intermediary 12-week follow-up, data from 38 patients (intervention: 20; control: 18) were analyzed in this report. All subjects provided informed consent for the collection of anthropometric measurements, vital signs, daily habits data, and PiKo-6 spirometric readings. Additionally, participants responded to the Short Anxiety Screening Test (SAST) and the 36-Item Short Form Health Survey (SF-36) questionnaires.

RESULTS

Thirty-eight participants were included (60% men and 40% women in the intervention group; 38.9% men and 61.1% women in the control group). In the treatment arm, Forced Expiratory Volume in the first second (FEV1) measured with PiKo-6 showed a Δ%- change for the intervention arm: +6.8%, control: -0.2% (p=0.059), systolic blood pressure; intervention: -7.4%, control: -3.7% (p=0.117), waist circumference; intervention: -1.5% control: -0.7% (p=0.455) and night-time sleep; intervention: +5.3%, control: +1.4% (p=0.926) were favourably influenced. The treatment group exhibited significant enhancements in both anxiety levels assessed by the anxiety symptoms scale (SAST-10, p=0.026) and quality of life evaluated by the SF-36 (p<0.001).

CONCLUSIONS

Positive evidence is emerging for a pleiotropic effect of quercetin intake in patients with T2DM, specifically in terms of anxiety reduction and amelioration of life quality, in just 12 weeks of administration and without adverse effects, indicating clinical safety and underscoring its potential for integration in T2DM supportive care.

Effect of quercetin on doxorubicin cytotoxicity in sensitive and resistant human MCF7 breast cancer cell lines

Chemoresistance is the major cause of cancer recurrence, relapse and eventual death. Doxorubicin resistance is one such challenge in breast cancer. The use of quercetin, an antioxidant, in combination with doxorubicin has been investigated for offering protection to normal cells from the toxic side effects of doxorubicin in addition to modulation of its resistance. The present study aimed to investigate the effects of quercetin in prevention of a doxorubicin-chemoresistant phenotype in both doxorubicin-sensitive and -resistant human MCF-7 breast cancer cell lines. A doxorubicin-resistant MCF-7 cell line was established. The development of resistant cells was closely monitored for changes in morphological features. Sensitivity to doxorubicin and the doxorubicin/quercetin combination was assessed using the tetrazolium assay. To determine the mechanism by which quercetin sensitizes the doxorubicin MCF-7-resistant cell line to doxorubicin, gene expression alterations in breast cancer-related genes were examined using the reverse transcription-quantitative PCR (RT-qPCR) array technology. Resistant MCF cells were successfully developed and the inhibitory concentration (IC50) value of doxorubicin increased from 0.133 to 4 µM (wild-type to resistant). The effects of the quercetin/doxorubicin combination exhibited different effects on wild-type vs. resistant cells. The IC50 of doxorubicin was reduced in wild cells, whereas resistant cells showed an increase in cell viability at lower concentrations and a potentiation of the effects of doxorubicin only at higher concentrations. Annexin V/propidium iodide staining demonstrated that quercetin drives cells into late apoptosis and necrosis, but in resistant cells, necrosis predominates. RT-qPCR results revealed that quercetin led to a reversal in doxorubicin effects via up- and downregulation of important genes such as SNAI2, PLAU and CSF1 genes. Downregulation of cell migration genes, SNAI2 (-31.23-fold) and plasminogen activator, urokinase (PLAU; -30.62-fold), and the apoptotic pathway gene, colony stimulating factor 1 (CSF1; -17.25-fold) were the most important querticin-associated events. Other gene alterations were also observed involving cell cycle arrest and DNA repair pathways. The results of the present study indicated that quercetin could lead to a reversal of doxorubicin resistance in breast cancer cells via downregulation of the expression of important genes, such as SNAI2, PLAU and CSF1. Such findings may represent a potential strategy for reversing breast cancer cell-related chemoresistance.

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.

Design of Quercetin-Loaded Natural Oil-Based Nanostructured Lipid Carriers for the Treatment of Bacterial Skin Infections

The biological activity of natural plant-oil-based nanostructured lipid carriers (NPO-NLCs) can be enhanced by the encapsulation of bioactive compounds, and they in turn can improve topical delivery of the drugs. Quercetin (QR), a vital plant flavonoid, expresses antibacterial properties, and we recently showed that empty NPO-NLCs also have antimicrobial activity. The main objective of this study was to evaluate the synergetic effect of loading natural plant-oil-based nanostructured lipid carriers with quercetin (QR-NPO-NLCs) as a topical delivery system for the treatment of bacterial skin infections. Five nanostructured lipid carrier systems containing different oils (sunflower, olive, corn, coconut, and castor) were engineered. The particles’ stability, structural properties, bioavailability, and antimicrobial activity were studied. NLCs with an average size of <200 nm and Z-potential of −40 mV were developed. Stable QR-NPO-NLCs were obtained with high encapsulation efficiency (>99%). The encapsulation of QR decreased cytotoxicity and increased the antioxidant effect of nanocarriers. An increase in antibacterial activity of the systems containing QR was demonstrated against Staphylococcus aureus. QR-NPO-NLCs could transport QR to an intranuclear location within HaCaT cells, indicating that QR-NPO-NLCs are promising candidates for controlled topical drug delivery.

Evidence for Multilevel Chemopreventive Activities of Natural Phenols from Functional Genomic Studies of Curcumin, Resveratrol, Genistein, Quercetin, and Luteolin

Herein, I present an updated and contextualized literature review of functional genomic studies of natural phenols in the context of cancer. I suggest multilevel chemopreventive and anticancer mechanisms of action, which are shared by multiple dietary natural phenols. Specifically, I cite evidence that curcumin and resveratrol have multilevel anti-cancer effects through: (1) inducing either p53-dependent or p53-independent apoptosis in cancer cell lines, (2) acting as potent regulators of expression of oncogenic and anti-oncogenic microRNAs, and (3) inducing complex epigenetic changes that can switch off oncogenes/switch on anti-oncogenes. There is no simple reductionist explanation for anti-cancer effects of curcumin and resveratrol. More generally, multilevel models of chemoprevention are suggested for related natural phenols and flavonoids such as genistein, quercetin, or luteolin.

A sensitive and simple HPLC-FLD-based method for the measurement of intracellular glucose uptake

Glucose is a primary source of energy used in most organisms. Thus, development of reliable approaches to measure intracellular glucose uptake is an important research issue. 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-d-glucose (2-NBDG), as a fluorescent glucose derivative, has been widely used to track intracellular glucose uptake by fluorescence imaging and measuring in mammalian cells. However, the avoid-less cross-interference of intrinsic autofluorescence background and tested fluorescent compounds limits its ability to provide trustworthy information on intracellular glucose uptake. By the extraction, separation and detection of 2-NBDG, a simple, sensitive and accurate HPLC-FLD method was established and validated for the measurement of intracellular glucose uptake in HepG2 cells. The developed method has been employed successfully to assess the glucose uptake activity of anti-diabetic drugs and fluorescent natural products. A fit-for-purpose partial validation was further performed for quantification and comparison of glucose uptake in AML12, LO2 hepatocytes, L6 myoblasts and 3T3-L1 preadipocytes.

A Preliminary Study of the Effect of Quercetin on Cytotoxicity, Apoptosis, and Stress Responses in Glioblastoma Cell Lines

A growing body of evidence indicates that dietary polyphenols show protective effects against various cancers. However, little is known yet about their activity in brain tumors. Here we investigated the interaction of dietary flavonoid quercetin (QCT) with the human glioblastoma A172 and LBC3 cell lines. We demonstrated that QCT evoked cytotoxic effect in both tested cell lines. Microscopic observations, Annexin V-FITC/PI staining, and elevated expression and activity of caspase 3/7 showed that QCT caused predominantly apoptotic death of A172 cells. Further analyses confirmed enhanced ROS generation, deregulated expression of SOD1 and SOD2, depletion of ATP levels, and an overexpression of CHOP, suggesting the activation of oxidative stress and ER stress upon QCT exposure. Finally, elevated expression and activity of caspase 9, indicative of a mitochondrial pathway of apoptosis, was detected. Conversely, in LBC3 cells the pro-apoptotic effect was observed only after 24 h incubation with QCT, and a shift towards necrotic cell death was observed after 48 h of treatment. Altogether, our data indicate that exposure to QCT evoked cell death via activation of intrinsic pathway of apoptosis in A172 cells. These findings suggest that QCT is worth further investigation as a potential pharmacological agent in therapy of brain tumors.

OXER1 mediates testosterone-induced calcium responses in prostate cancer cells

In prostate cancer, calcium homeostasis plays a significant role in the disease's development and progression. Intracellular calcium changes are an important secondary signal, triggered by a variety of extracellular stimuli, that controls many cellular functions. One of the main events affecting calcium is androgen signaling. Indeed, via calcium changes, androgens regulate cell processes like cell growth, differentiation and motility. In the present work we explored the nature of the receptor involved in calcium response induced by membrane-acting testosterone in prostate cancer cells. We report that testosterone, independently of the presence of the classical androgen receptor, can rapidly increase intracellular calcium from calcium stores, through the oxoeicosanoid receptor 1 (OXER1) and a specific signaling cascade that triggers calcium release from the endoplasmic reticulum. These findings reveal for the first time the receptor involved in the rapid calcium changes induced by androgens. Moreover, they further support the notion that androgens, even in the absence of AR, can still exert specific effects that regulate cancer cell fate.

ERα36-GPER1 Collaboration Inhibits TLR4/NFκB-Induced Pro-Inflammatory Activity in Breast Cancer Cells

Inflammation is important for the initiation and progression of breast cancer. We have previously reported that in monocytes, estrogen regulates TLR4/NFκB-mediated inflammation via the interaction of the Erα isoform ERα36 with GPER1. We therefore investigated whether a similar mechanism is present in breast cancer epithelial cells, and the effect of ERα36 expression on the classic 66 kD ERα isoform (ERα66) functions. We report that estrogen inhibits LPS-induced NFκB activity and the expression of downstream molecules TNFα and IL-6. In the absence of ERα66, ERα36 and GPER1 are both indispensable for this effect. In the presence of ERα66, ERα36 or GPER1 knock-down partially inhibits NFκB-mediated inflammation. In both cases, ERα36 overexpression enhances the inhibitory effect of estrogen on inflammation. We also verify that ERα36 and GPER1 physically interact, especially after LPS treatment, and that GPER1 interacts directly with NFκB. When both ERα66 and ERα36 are expressed, the latter acts as an inhibitor of ERα66 via its binding to estrogen response elements. We also report that the activation of ERα36 leads to the inhibition of breast cancer cell proliferation. Our data support that ERα36 is an inhibitory estrogen receptor that, in collaboration with GPER1, inhibits NFκB-mediated inflammation and ERα66 actions in breast cancer cells.

The impact of the phytotherapeutic agent quercetin on expression of genes and activity of signaling pathways

Quercetin is a flavonoid existing in different herbs, fruits, seeds, nuts and tea. It has beneficial effects on human health through mediating antioxidant activities, immune-modulatory impacts and regulating metabolic pathways. These effects are most probably induced through modulation of activity of signaling pathways and expression of genes. Several in vitro studies have verified anti-proliferative effects of quercetin and its effect on expression of apoptotic genes and cell cycle-related genes. Moreover, through modulation of a number of proteins such as NF-kB, PARP, STAT3, Bax, Bcl-2, COX2, and cytokines, quercetin has beneficial effects in neurodegenerative disorders, liver diseases and diabetes. PI3K/AKT is the mostly linked pathway with beneficial effects of quercetin. In the current manuscript, we explain the impact of quercetin on expression of genes and function of cellular signaling cascades in different contexts.

Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 Transporters

Quercetin is a flavonoid, its glycosides and aglycone are found in significant amounts in several plants and dietary supplements. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. As has been reported in previous studies, quercetin can interact with several proteins of pharmacokinetic importance. However, the interactions of its metabolites with biotransformation enzymes and drug transporters have barely been examined. In this study, the inhibitory effects of quercetin and its most relevant methyl, sulfate, and glucuronide metabolites were tested on cytochrome P450 (CYP) (2C19, 3A4, and 2D6) enzymes as well as on organic anion-transporting polypeptides (OATPs) (OATP1A2, OATP1B1, OATP1B3, and OATP2B1) and ATP (adenosine triphosphate) Binding Cassette (ABC) (BCRP and MRP2) transporters. Quercetin and its metabolites (quercetin-3'-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and 3A4, while they did not affect CYP2D6 activity. Some of the flavonoids caused weak inhibition of OATP1A2 and MRP2. However, most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. Our data demonstrate that not only quercetin but some of its conjugates, can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.

The ubiquitous flavonoid quercetin is an atypical KCNQ potassium channel activator

Many commonly consumed plants are used as folk medicines, often with unclear molecular mechanisms. Recent studies uncovered the ubiquitous and influential KCNQ family of voltage-gated potassium (Kv) channels as a therapeutic target for several medicinal plant compounds. Capers - immature flower buds of Capparis spinosa - have been consumed for food and medicinal purposes for millennia. Here, we show that caper extract hyperpolarizes cells expressing KCNQ1 or KCNQ2/3 Kv channels. Capers are the richest known natural source of quercetin, the most consumed dietary flavonoid. Quercetin potentiated KCNQ1/KCNE1, KCNQ2/3 and KCNQ4 currents but, unusually, not KCNQ5. Strikingly, quercetin augmented both activation and inactivation of KCNQ1, via a unique KCNQ activation mechanism involving sites atop the voltage sensor and in the pore. The findings uncover a novel potential molecular basis for therapeutic effects of quercetin-rich foods and a new chemical space for atypical modes of KCNQ channel modulation.

Kaitlyn E. Redford and Geoffrey W. Abbott show that quercetin, a flavonoid highly expressed in capers, potentiates KCNQ currents to varying degrees depending on the subunit composition of the channel complex. By combining in silico docking, mutagenesis, and electrophysiology they show that this flavonoid can bind KCNQ channels atop the voltage sensor and within the pore module, highlighting an atypical mode of channel modulation.

Molecular docking-assisted design and synthesis of an anti-tumor quercetin–Se(iv) complex

Design and synthesis of an anti-tumor quercetin–Se(iv) complex under the guidance of molecular docking and visualized DNA binding activity.

Preparation of Quercetin Loaded Microparticles and their Antitumor Activity against Human Lung Cancer Cells (A549) in vitro

BACKGROUND

Novel quercetin-loaded microparticles (QM) were fabricated using coaxial electrospraying, characterized for surface morphology and release profile, and evaluated for antitumor activity in vitro.

METHODS

QM exhibited an average diameter of 1.69 ±1.13 mm, which was an appropriate size suitable for respiratory delivery. X-ray diffraction patterns showed that the components in QM existed in an amorphous physical form, leading to favorable interactions between the drug (quercetin), the polymer matrix (polyvinylpyrrolidone, PVP) and other excipients (sodium dodecyl sulfate and sucralose).

RESULTS

QM performed much faster release rate compared with free quercetin powder (Q) in vitro. Furthermore, QM also showed more potent inhibitory effects on A549 cell growth with reduced cell viability, decreased cell migration and induced more G0/G1 phase cell cycle arrest than Q.

CONCLUSION

Thus, the quercetin loaded microparticles exhibited more potent inhibitory effects than free quercetin on A549 cell. The increased antitumor activity could be attributed to the enhanced accumulation of quercetin in the A549 cells with the QM. However, further studies are necessary to elucidate the exact mechanisms.

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.

Impact of Red Wine Consumption on Cardiovascular Health

BACKGROUND

The devastating effects of heavy alcohol drinking have been long time recognized. In the last decades, potential benefits of modest red wine drinking were suggested. In European countries in which red wide intake is not negligible (such as France), the association between cholesterol and cardiovascular (CV) risk was less evident, suggesting the action of some protective molecules in red wine or other foods and drinks.

METHODS

This narrative review is based on the material searched for and obtained via PubMed up to May 2016. The search terms we used were: "red wine, cardiovascular, alcohol" in combination with "polyphenols, heart failure, infarction".

RESULTS

Epidemiological and mechanistic evidence of a J-shaped relationship between red wine intake and CV risk further supported the "French paradox". Specific components of red wine both in vitro and in animal models were discovered. Polyphenols and especially resveratrol largely contribute to CV prevention mainly through antioxidant properties. They exert beneficial effects on endothelial dysfunction and hypertension, dyslipidemia, metabolic diseases, thus reducing the risk of adverse CV events such as myocardial infarction ischemic stroke and heart failure. Of interest, recent studies pointed out the role of ethanol itself as a potential cardioprotective agent, but a clear epidemiological evidence is still missing. The aim of this narrative review is to update current knowledge on the intracellular mechanism underlying the cardioprotective effects of polyphenols and ethanol. Furthermore, we summarized the results of epidemiological studies, emphasizing their methodological criticisms and the need for randomized clinical trials able to clarify the potential role of red wine consumption in reducing CV risk.

CONCLUSION

Caution in avowing underestimation of the global burden of alcohol-related diseases was particularly used.

Differential Impact of Flavonoids on Redox Modulation, Bioenergetics, and Cell Signaling in Normal and Tumor Cells: A Comprehensive Review

SIGNIFICANCE

Flavonoids can interact with multiple molecular targets to elicit their cellular effects, leading to changes in signal transduction, gene expression, and/or metabolism, which can, subsequently, affect the entire cell and organism. Immortalized cell lines, derived from tumors, are routinely employed as a surrogate for mechanistic studies, with the results extrapolated to tissues in vivo. Recent Advances: We review the activities of selected flavonoids on cultured tumor cells derived from various tissues in comparison to corresponding primary cells or tissues in vivo, mainly using quercetin and flavanols (epicatechin and (-)-epigallocatechin gallate) as exemplars. Several studies have indicated that flavonoids could retard cancer progression in vivo in animal models as well as in tumor cell models.

CRITICAL ISSUES

Extrapolation from in vitro and animal models to humans is not straightforward given both the extensive conjugation and complex microbiota-dependent metabolism of flavonoids after consumption, as well as the heterogeneous metabolism of different tumors.

FUTURE DIRECTIONS

Comparison of data from studies on primary cells or in vivo are essential not only to validate results obtained from cultured cell models, but also to highlight whether any differences may be further exploited in the clinical setting for chemoprevention. Tumor cell models can provide a useful mechanistic tool to study the effects of flavonoids, provided that the limitations of each model are understood and taken into account in interpretation of the data.

Atomic force microscopy reveals new biophysical markers for monitoring subcellular changes in oxidative injury: Neuroprotective effects of quercetin at the nanoscale

Oxidative stress has been recognised as an important pathological mechanism underlying the development of neurodegenerative diseases. The biomarkers for assessing the degree of oxidative stress have been attracting much interest because of their potential clinical relevance in understanding the cellular effects of free radicals and evaluation of the efficacy of drug treatment. Here, an interdisciplinary approach using atomic force microscopy (AFM) and cellular and biological molecular methods were used to investigate oxidative damage in P19 neurons and to reveal the underlying mechanism of protective action of quercetin. Biological methods demonstrated the oxidative damage of P19 neurons and showed that quercetin improved neuronal survival by preventing H2O2-induced p53 and Bcl-2 down-regulation and modulated Akt and ERK1/2 signalling pathways. For the first time, AFM was employed to evaluate morphologically (roughness, height, Feret dimension) and nanomechanical (elasticity) properties in H2O2-induced neuronal damage. The AFM analysis revealed that quercetin suppressed H2O2-provoked changes in cell membrane elasticity and morphological properties, thus confirming its neuroprotective activity. The obtained results indicate the potential of AFM-measured parameters as a biophysical markers of oxidative stress-induced neurodegeneration. In general, our study suggests that AFM can be used as a highly valuable tool in other biomedical applications aimed at screening and monitoring of drug-induced effects at cellular level.

Rutin derivatives obtained by transesterification reactions catalyzed by Novozym 435: Antioxidant properties and absence of toxicity in mammalian cells

Flavonoids are one of the most important and diversified phenolic groups among products of natural origin. An important property of this metabolite class is the antioxidant action. This study evaluated the antioxidant and cytotoxic activities and oxidative stress of transesterification products of the flavonoid rutin, catalyzed by Novozym^® 435. The presence of monoacetate and diacetate was confirmed by quantitative evaluation of the retention times (rutin, 15.68 min; rutin monoacetate, 18.14 min; and rutin diacetate, 18.57 min) and by the data from LC-MS and NMR ¹H and ¹³C. The experiment showed excellent conversion values of 96% in total acetates (rutin monoacetate and diacetate). These results confirmed that rutin derivatives have antioxidant potential, as evaluated by the ORAC method (rutin standard: 0.53 ± 0.08 μM Trolox/g and rutin derivatives: 2.33 ± 1.08 μM Trolox/g) and also show low cytotoxicity in human and animal cells. Rutin derivatives reduced the production of reactive oxygen species in RAW macrophages as well. Many qualities attributed to rutin derivatives make them promising potential candidates for use as nutraceuticals, including their high amounts of antioxidants, biological potential and low toxicity, which contribute to the reduction of oxidative stress.

Substance P and IL-33 administered together stimulate a marked secretion of IL-1β from human mast cells, inhibited by methoxyluteolin

Mast cells are critical for allergic and inflammatory responses in which the peptide substance P (SP) and the cytokine IL-33 are involved. SP (0.01-1 μM) administered together with IL-33 (30 ng/mL) to human cultured LAD2 mast cells stimulates a marked increase (P < 0.0001) in secretion of the proinflammatory cytokine IL-1β. Preincubation of LAD2 (30 min) with the SP receptor (NK-1) antagonists L-733,060 (10 μM) or CP-96345 (10 µM) inhibits (P < 0.001) secretion of IL-1β stimulated by either SP (1 μM) or SP together with IL-33 (30 ng/mL). Surprisingly, secretion of IL-1β stimulated by IL-33 is inhibited (P < 0.001) by each NK-1 antagonist. Preincubation with an antibody against the IL-33 receptor ST2 inhibits (P < 0.0001) secretion of IL-1β stimulated either by IL-33 or together with SP. The combination of SP (1 μM) with IL-33 (30 ng/mL) increases IL-1β gene expression by 90-fold in LAD2 cells and by 200-fold in primary cultured mast cells from human umbilical cord blood. The combination of SP and IL-33 increases intracellular levels of IL-1β in LAD2 by 100-fold and gene expression of IL-1β and procaspase-1 by fivefold and pro-IL-1β by twofold. Active caspase-1 is present even in unstimulated cells and is detected extracellularly. Preincubation of LAD2 cells with the natural flavonoid methoxyluteolin (1-100 mM) inhibits (P < 0.0001) secretion and gene expression of IL-1β, procaspase-1, and pro-IL-1β. Mast cell secretion of IL-1β in response to SP and IL-33 reveals targets for the development of antiinflammatory therapies.

Antiproliferative and antimetastatic action of quercetin on A549 non-small cell lung cancer cells through its effect on the cytoskeleton

To our knowledge, this study is the first to investigate the effect of the dietary flavonoid quercetin on the main cytoskeletal elements, namely microfilaments, microtubules and vimentin intermediate filaments, as well as cytoskeleton-driven processes in A549 non-small cell lung cancer cells. The methyl-thiazol-diphenyl-tetrazolium assay, annexin V/propidium iodide test, electron microscopic examination, cell cycle analysis based on DNA content, real-time PCR assays, in vitro scratch wound-healing assay, fluorescence staining of F-actin, β-tubulin and vimentin were performed to assess the effects of quercetin on A549 cells. Our results showed that quercetin triggered BCL2/BAX-mediated apoptosis, as well as necrosis and mitotic catastrophe, and inhibited the migratory potential of A549 cells. The disassembling effect of quercetin on microfilaments, microtubules and vimentin filaments along with its inhibitory impact on vimentin and N-cadherin expression might account for the decreased migration of A549 cells in response to quercetin treatment. We also suggest that the possible mechanism underlying quercetin-induced mitotic catastrophe involves the perturbation of mitotic microtubules leading to monopolar spindle formation, and, consequently, to the failure of cytokinesis. We further propose that cytokinesis failure could also be a result of the depletion of actin filaments by quercetin. These findings are important to our further understanding of the detailed mechanism of the antitumor activity of quercetin and render this flavonoid a potentially useful candidate for combination therapy with conventional antimicrotubule drugs, nucleic acid-directed agents or novel cytoskeletal-directed agents.

Flow Cytometric Method for the Detection of Flavonoids in Cell Lines

Here, we describe an easy-to-use flow cytometric method using diphenylboric acid 2-amino ethyl ester (DPBA) stain for the detection of flavonoids in cells from human/animal origin. Flavonoid bioavailability and bioactivity depend on structure, conjugation and the cell type to which they are presented. We have studied cellular uptake of five flavonoids with different structures and conjugation forms. First, parameters including fixation method, technical and batch variability, and concentration were optimized. Second, uptake of two aglycones—quercetin and hesperetin—and their corresponding glycosides—rutin and hesperidin—in Caco-2 cells was compared. Third, the aglycone quercetin, glycoside rutin, and glucuronide baicalin were added to the Caco-2, HepG2, and CHO-K1 cell lines at 1, 10, and 20 µM concentrations and cellular uptake was measured after 1, 4, and 7 h. We conclude that quercetin was taken up by cells in a dose-dependent way, and that HepG2 cells had the highest uptake factors, followed by CHO-K1 and Caco-2 cells. Confocal microscopy showed cell type–dependent localization of quercetin in the cell membrane and cytoplasm. No uptake of flavonoid glycosides was detected. This flow cytometric method can be used for future research unravelling mechanisms behind flavonoid bioactivity in health and disease at the cellular level.

At the interface of antioxidant signalling and cellular function: Key polyphenol effects

The hypothesis that dietary (poly)phenols promote well‐being by improving chronic disease‐risk biomarkers, such as endothelial dysfunction, chronic inflammation and plasma uric acid, is the subject of intense current research, involving human interventions studies, animal models and in vitro mechanistic work. The original claim that benefits were due to the direct antioxidant properties of (poly)phenols has been mostly superseded by detailed mechanistic studies on specific molecular targets. Nevertheless, many proposed mechanisms in vivo and in vitro are due to modulation of oxidative processes, often involving binding to specific proteins and effects on cell signalling. We review the molecular mechanisms for 3 actions of (poly)phenols on oxidative processes where there is evidence in vivo from human intervention or animal studies. (1) Effects of (poly) phenols on pathways of chronic inflammation leading to prevention of some of the damaging effects associated with the metabolic syndrome. (2) Interaction of (poly)phenols with endothelial cells and smooth muscle cells, leading to effects on blood pressure and endothelial dysfunction, and consequent reduction in cardiovascular disease risk. (3) The inhibition of xanthine oxidoreductase leading to modulation of intracellular superoxide and plasma uric acid, a risk factor for developing type 2 diabetes.

Quercetin and the mitochondria: A mechanistic view

Quercetin is an important flavonoid that is ubiquitously present in the diet in a variety of fruits and vegetables. It has been traditionally viewed as a potent antioxidant and anti-inflammatory molecule. However, recent studies have suggested that quercetin may exert its beneficial effects independent of its free radical-scavenging properties. Attention has been placed on the effect of quercetin on an array of mitochondrial processes. Quercetin is now recognized as a phytochemical that can modulate pathways associated with mitochondrial biogenesis, mitochondrial membrane potential, oxidative respiration and ATP anabolism, intra-mitochondrial redox status, and subsequently, mitochondria-induced apoptosis. The present review evaluates recent evidence on the ability of quercetin to interact with the abovementioned pathways, and critically analyses how, such interactions can exert protection against mitochondrial damage in response to toxicity induced by several exogenously and endogenously-produced cellular stressors, and oxidative stress in particular.

Estrogen anti-inflammatory activity on human monocytes is mediated through cross-talk between estrogen receptor ERα36 and GPR30/GPER1

Estrogens are known modulators of monocyte/macrophage functions; however, the underlying mechanism has not been clearly defined. Recently, a number of estrogen receptor molecules and splice variants were identified that exert different and sometimes opposing actions. We assessed the expression of estrogen receptors and explored their role in mediating estrogenic anti-inflammatory effects on human primary monocytes. We report that the only estrogen receptors expressed are estrogen receptor-α 36-kDa splice variant and G-protein coupled receptor 30/G-protein estrogen receptor 1, in a sex-independent manner. 17-β-Estradiol inhibits the LPS-induced IL-6 inflammatory response, resulting in inhibition of NF-κB transcriptional activity. This is achieved via a direct physical interaction of ligand-activated estrogen receptor-α 36-kDa splice variant with the p65 component of NF-κB in the nucleus. G-protein coupled receptor 30/G-protein estrogen receptor 1, which also physically interacts with estrogen receptor-α 36-kDa splice variant, acts a coregulator in this process, because its inhibition blocks the effect of estrogens on IL-6 expression. However, its activation does not mimic the effect of estrogens, on neither IL-6 nor NF-κB activity. Finally, we show that the estrogen receptor profile observed in monocytes is not modified during their differentiation to macrophages or dendritic cells in vitro and is shared in vivo by macrophages present in atherosclerotic plaques. These results position estrogen receptor-α 36-kDa splice variant and G-protein coupled receptor 30 as important players and potential therapeutic targets in monocyte/macrophage-dependent inflammatory processes.

Efficacy of quercetin against chemically induced murine oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most common form of head and neck cancer, and oxidative damage is associated with the development of OSCCs. Antioxidants have therefore been proposed for use as chemoprotective agents against different types of cancer. In the present study, the effect of the antioxidant quercetin, administered at doses of 10 and 100 mg/kg/day, was investigated in an experimental murine model of 4-nitroquinoline 1-oxide (4-NQO)-induced carcinogenesis. The survival of the treated animals, the plasmatic levels of reduced glutathione and the type and severity of lesions (according the International Histological Classification of Tumors and Bryne's Multifactorial Grading System for the Invasive Tumor Front) were assessed. Additionally, the organization of the extracellular matrix was analyzed by carbohydrate and collagen histochemistry, and immunohistochemistry was used to assess the expression of the tumor markers proliferating cell nuclear antigen and mutated p53. The results indicate that, despite the promising effect of quercetin in other studies, this drug is ineffective as a chemoprotective agent against 4-NQO-induced OSCC in mice at the assayed doses.

Effects of flavonoid quercetin on survival of motor neuron gene expression

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disease that results in muscle weakness and atrophy. To attenuate disease severity, drug development studies have been applied mainly to target the Survival of Motor Neuron 2 (SMN2) gene, which is an important modifier of SMA. Although several compounds have been tested, there is still no cure for SMA. In this study, SMN2-inducing effects of quercetin, an abundant flavonoid polyphenol in human diet, was investigated in the fibroblast cell lines of two SMA type I patients. Gene expression studies showed that quercetin upregulates SMN2 mRNA up to fourfold, but not the SMN protein level.

Organic anion transporting polypeptides and organic cation transporter 1 contribute to the cellular uptake of the flavonoid quercetin

Flavonoids such as quercetin and kaempferol mediate several health protective effects, e.g., anticancer effects. They are inhibitors of organic anion transporting polypeptides (OATP) and organic cation transporters (e.g., OCT2). However, little is known whether such transporters contribute to the cellular uptake of flavonoids. Therefore, we investigated the cellular uptake of kaempferol and quercetin using HEK293 cell lines stably expressing different human OATPs or OCT1. Kaempferol was not a substrate of any of the investigated transporters (OATP1A2, OATP1B1, OATP1B3, OATP2A1, OATP2B1, OATP3A1, OATP4A1, OATP5A1, and OCT1). Quercetin showed a significantly higher uptake into the HEK293-OATP1A2, HEK293-OATP2A1, HEK293-OATP2B1, and HEK293-OCT1 cells compared to control cells. The OATP1A2-, OATP2B1-, and OCT1-mediated quercetin uptake was inhibited by known inhibitors such as naringin, cyclosporin A, and quinidine, respectively. The cellular accumulation of quercetin into HEK293-OATP2A1 cells was not inhibited by prostaglandin E2 and diclofenac. The ionophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) reduced the net uptake of quercetin by increasing the uptake in the HEK293-control cells and causing no significant change in the HEK293-OATP2B1 cells indicating that quercetin follows the FCCP-driven proton flux through the plasma membrane. In addition to passive diffusion, the SLC transporters OATP1A2, OATP2B1, and OCT1 contribute to cellular accumulation of quercetin.

Fluorescence enhancement of quercetin complexes by silver nanoparticles and its analytical application

It is found that the plasmon effect of silver nanoparticles (AgNPs) helps to enhance the fluorescence intensity of the quercetin (Qu) and nucleic acids system. Qu exhibited strong fluorescence enhancement when it bound to nucleic acids in the presence of AgNPs. Based on this, a sensitive method for the determination of nucleic acids was developed. The detection limits for the nucleic acids (S/N=3) were reduced to the ng mL(-1) level. The interaction mechanism of the AgNPs-fish sperm DNA (fsDNA)-Qu system was also investigated in this paper. This complex system of Qu and AgNPs was also successfully used for the detection of nucleic acids in agarose gel electrophoresis analysis. Preliminary results indicated that AgNPs also helped to improve sensitivity in the fluorescence image analysis of Qu combined with cellular contents in Arabidopsis thaliana protoplasts.

Luteolin inhibits human keratinocyte activation and decreases NF-κB induction that is increased in psoriatic skin

Psoriasis (Ps) is an autoimmune disease characterized by keratinocyte hyperproliferation and chronic inflammation, with increased expression of tumor necrosis factor (TNF) and vascular endothelial growth factor (VEGF). Anti-TNF biologic agents are effective in treating Ps, but are associated with increased risk of infections and blood malignancies. Moreover, keratinocyte hyperproliferation and activation have yet to be addressed. Flavonoids, such as luteolin, are natural compounds with potent anti-inflammatory properties, but their actions on keratinocytes remain unknown. We show that TNF (50 ng/mL) triggers significant production of inflammatory mediators interleukin-6, interleukin-8 and VEGF from both human HaCaT and primary keratinocytes. Pretreatment with the flavonoid luteolin (10–100 µM) significantly inhibits mRNA expression and release of all three mediators in a concentration-dependent manner. More importantly, luteolin decreases TNF-induced phosphorylation, nuclear translocation and DNA binding of the nuclear factor-kappa B (NF-κB) typically involved in inflammatory mediator transcription. We also report that luteolin reduces TNF-induced mRNA expression of two genes (NFKB1 and RELA) encoding two NF-κB subunits (NF-κB p50 and NF-κB p65, respectively). Interestingly, we show that gene expression of RELA is increased in human psoriatic skin. Keratinocyte proliferation, which is a characteristic feature of psoriatic skin, is effectively reduced by luteolin in HaCaT cells, but not in primary keratinocytes. Finally, luteolin does not affect intracellular ATP production or viability. Appropriate formulations of luteolin and related flavones may be promising candidates to be developed into local and systemic treatments for Ps and other inflammatory skin diseases.

Investigations on the membrane interactions of naringin and its complexes with copper and iron: implications for their cytotoxicity

Flavonoid glycosides are a group of polyphenols with different glycoside substituents that possess diverse pharmacological activities albeit with lesser potency than their aglycone counterparts.

Modulation of paraoxonase 2 (PON2) in mouse brain by the polyphenol quercetin: a mechanism of neuroprotection?

Quercetin is a common flavonoid polyphenol which has been shown to exert neuroprotective actions in vitro and in vivo. Though quercetin has antioxidant properties, it has been suggested that neuroprotection may be ascribed to its ability of inducing the cell's own defense mechanisms. The present study investigated whether quercetin could increase the levels of paraoxonase 2 (PON2), a mitochondrial enzyme expressed in brain cells, which has been shown to have potent antioxidant properties. PON2 protein, mRNA, and lactonase activity were highest in mouse striatal astrocytes. Quercetin increased PON2 levels, possibly by activating the JNK/AP-1 pathway. The increased PON2 levels induced by quercetin resulted in decreased oxidative stress and ensuing toxicity induced by two oxidants. The neuroprotective effect of quercetin was significantly diminished in cells from PON2 knockout mice. These findings suggest that induction of PON2 by quercetin represents an important mechanism by which this polyphenol may exert its neuroprotective action.

APRIL binding to BCMA activates a JNK2-FOXO3-GADD45 pathway and induces a G2/M cell growth arrest in liver cells

The TNF superfamily ligands APRIL and BAFF bind with different affinity to two receptors, BCMA and TACI, and induce cell survival and/or proliferation, whereas BAFF also binds specifically to BAFFR. These molecules were considered specific for the immune system. Recently, however, they were also found in epithelial and mesenchymal noncancerous and cancerous tissues and cell lines. In this article, we report that hepatocellular carcinoma (HCC) cell lines HepG2 and Hep3B and HCC specimens express APRIL and BAFF and their receptors BCMA and BAFFR, but not TACI; APRIL/BCMA is enhanced in HCC, compared with normal liver tissue. In contrast to previous reports, APRIL binding to BCMA decreases cell proliferation by inducing G(2)/M cell cycle arrest, whereas BAFF has no effect on cell growth. HCC cells therefore represent a rare system in which these two ligands (APRIL and BAFF) exert a differential effect and may serve as a model for specific APRIL/BCMA actions. We show that the effect of APRIL is mediated via BCMA, which does not activate the classical NF-κB pathway, whereas it induces a novel signaling pathway, which involves JNK2 phosphorylation, FOXO3A activation, and GADD45 transcription. In addition, JNK2 mediates the phosphorylation of Akt, which is activated but does not participate in the antiproliferative effect of APRIL. Furthermore, transcriptome analysis revealed that APRIL modifies genes specifically related to cell cycle modulation, including MCM2/4/5/6, CDC6, PCNA, and POLE2. Our data, therefore, identify a novel APRIL/BCMA signaling pathway in HCC and suggest that APRIL could have a pleiotropic role in tumor biology.

Influence of berry polyphenols on receptor signaling and cell-death pathways: implications for breast cancer prevention

Breast cancer is the most commonly diagnosed cancer among women worldwide. Many women have become more aware of the benefits of increasing fruit consumption, as part of a healthy lifestyle, for the prevention of cancer. The mechanisms by which fruits, including berries, prevent breast cancer can be partially explained by exploring their interactions with pathways known to influence cell proliferation and evasion of cell-death. Two receptor pathways, estrogen receptor (ER) and tyrosine kinase receptors, especially the epidermal growth factor receptor (EGFR) family, are drivers of cell proliferation and play a significant role in the development of both primary and recurrent breast cancer. There is strong evidence to show that several phytochemicals present in berries such as cyanidin, delphinidin, quercetin, kaempferol, ellagic acid, resveratrol, and pterostilbene interact with and alter the effects of these pathways. Furthermore, they also induce cell death (apoptosis and autophagy) via their influence on kinase signaling. This review summarizes in vitro data regarding the interaction of berry polyphenols with the specific receptors and the mechanisms by which they induce cell death. This paper also presents in vivo data of primary breast cancer prevention by individual compounds and whole berries. Finally, a possible role for berries and berry compounds in the prevention of breast cancer and a perspective on the areas that require further research are presented.

TWEAK affects keratinocyte G2/M growth arrest and induces apoptosis through the translocation of the AIF protein to the nucleus

The soluble TNF-like weak inducer of apoptosis (TWEAK, TNFSF12) binds to the fibroblast growth factor-inducible 14 receptor (FN14, TNFRSF12A) on the cell membrane and induces multiple biological responses, such as proliferation, migration, differentiation, angiogenesis and apoptosis. Previous reports show that TWEAK, which does not contain a death domain in its cytoplasmic tail, induces the apoptosis of tumor cell lines through the induction of TNFα secretion. TWEAK induces apoptosis in human keratinocytes. Our experiments clearly demonstrate that TWEAK does not induce the secretion of TNFα or TRAIL proteins. The use of specific inhibitors and the absence of procaspase-3 cleavage suggest that the apoptosis of keratinocytes follows a caspase- and cathepsin B-independent pathway. Further investigation showed that TWEAK induces a decrease in the mitochondrial membrane potential of keratinocytes. Confocal microscopy showed that TWEAK induces the cleavage and the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus, thus initiating caspase-independent apoptosis. Moreover, TWEAK induces FOXO3 and GADD45 expression, cdc2 phosphorylation and cdc2 and cyclinB1 degradation, resulting in the arrest of cell growth at the G2/M phase. Finally, we report that TWEAK and FN14 are normally expressed in the basal layer of the physiological epidermis and are greatly enhanced in benign (psoriasis) and malignant (squamous cell carcinoma) skin pathologies that are characterized by an inflammatory component. TWEAK might play an essential role in skin homeostasis and pathology.

Kaempferol protects against doxorubicin-induced cardiotoxicity in vivo and in vitro

The long-term clinical usefulness of doxorubicin (DOX), an anthracycline with potent antitumor activity, is limited by DOX-induced cardiotoxicity. Kaempferol, one of the most common dietary flavonoids, is known to have anti-apoptotic, anti-oxidative, and anti-inflammatory properties. The current study aimed to investigate the possible protective effect of kaempferol against DOX-induced cardiotoxicity and the underlying mechanisms. Rats were intraperitoneally (i.p.) treated with DOX (3 mg/kg) every other day for a cumulative dose of 9 mg/kg. After 28 days, DOX caused retarded body and heart growth, oxidative stress, apoptotic damage, mitochondrial dysfunction, and Bcl-2 expression disturbance. In contrast, kaempferol pretreatment (10 mg/kg i.p. before DOX administration) attenuated the DOX-induced apoptotic damage in heart tissues. In vitro studies also indicated that kaempferol may have used the mitochondrion-dependent pathway to counteract the DOX-induced cardiotoxicity. This counteraction was achieved by inhibiting p53 expression and its binding to the promoter region of the Bax proapoptotic gene, but not to the Bcl-2 antiapoptotic gene. Kaempferol also effectively suppressed DOX-induced extracellular signal-regulated kinase (ERK) 1/2 activation, but had no effect on p38 and JNK. Therefore, kaempferol protected against DOX-induced cardiotoxicity, at least, partially, by inhibiting the activation of p53-mediated, mitochondrion-dependent apoptotic signaling, and by being involved in an ERK-dependent mitogen-activated protein kinase pathway. These findings elucidated the potential of kaempferol as a promising reagent for treating DOX-induced cardiotoxicity, and may have implications in the long-term clinical usefulness of DOX.