Unraveling the therapeutic potential of quercetin and quercetin-3-O-glucuronide in Alzheimer's disease through network pharmacology, molecular docking, and dynamic simulations.

Quercetin is a flavonoid with notable pharmacological effects and promising therapeutic potential. Quercetin plays a significant role in neuroinflammation, which helps reduce Alzheimer's disease (AD) severity. Quercetin (Q) and quercetin 3-O-glucuronide (Q3OG) are some of the most potent antioxidants available from natural sources. However, the natural form of quercetin converted into Q3OG when reacted with intestinal microbes. The study aims to ensure the therapeutic potential of Q and Q3OG. In this study, potential molecular targets of Q and Q3OG were first identified using the Swiss Target Prediction platform and pathogenic targets of AD were identified using the DisGeNET database. Followed by compound and disease target overlapping, 77 targets were placed in that AKT1, EGFR, MMP9, TNF, PTGS2, MMP2, IGF1R, MCL1, MET and PARP1 was the top-ranked target, which was estimated by CytoHubba plug-in. The Molecular docking was performed for Q and Q3OG towards the PDB:1UNQ target. The binding score of Q and Q3OG was - 6.2 kcal/mol and - 6.58 kcal/mol respectively. Molecular dynamics simulation was conducted for Q and Q3OG towards the PDB:1UNQ target at 200 ns. This study's results help identify the multiple target sites for the bioactive compounds. Thus, synthesizing new chemical entity-based quercetin on structural modification may aid in eradicating AD complications.

Quercetin-3-O-ß-d-glucuronide in the Nuciferine Leaf Polyphenol Extract Promotes Neurogenesis Involving the Upregulation of the Tropomyosin Receptor Kinase (Trk) Receptor and AKT/Phosphoinositide 3-Kinase Signaling Pathway.

Neurogenesis is crucial during the human lifespan for the maintenance of synaptic plasticity and normal function. The impairment of hippocampal neurogenesis in adults may lead to neurodegenerative disease, such as Alzheimer's disease. Miquelianin (quercetin-3-O-ß-d-glucuronide, Q3GA) is a constituent of the nuciferine leaf polyphenol extract (NLPE), and it has protective effects against neurodegeneration. In this study, we examined the effect of the NLPE on neurogenesis and the mechanisms underlying Q3GA on neurogenesis. We fed 24-week-old male C57BL/6 mice with 0.1 or 0.25% NLPE for 2 weeks. NLPE treatment increased small spindle-shaped stem cell numbers in the subgranular zone and the number of doublecortin (DCX)- and neuron-specific nuclear protein (NeuN)-expressing neurons. HT22, a hippocampal cell line, treated with Q3GA revealed significant neurite growth and upregulated TrkR and PI3K/Akt levels. The evidence from a model of retinoic acid-induced SH-SY5Y cell differentiation showed that Q3GA or NLPE increases neurite growth significantly. Taken together, the NLPE containing Q3GA to promote neurogenesis involving the upregulation of TrkR and the PI3K/Akt signaling pathway might be potentiated as an alternative strategy for the treatment of neurodegeneration.

Flavonoid quercetin and its glucuronide and sulfate conjugates bind to 67-kDa laminin receptor and prevent neuronal cell death induced by serum starvation.

Quercetin, a dietary flavonoid, has been shown to protect against various neurodegenerative diseases with mechanisms largely unknown. After oral administration, quercetin is rapidly conjugated, and the aglycone is not detectable in the plasma and brain. However, its glucuronide and sulfate conjugates are present only at low nanomolar concentrations in the brain. Since quercetin and its conjugates have limited antioxidant capability at low nanomolar concentrations, it is crucial to determine whether they induce neuroprotection by binding to high-affinity receptors. Previously we found that (-)-epigallocatechin-3-gallate (EGCG), a polyphenol from green tea, induces neuroprotection by binding to the 67-kDa laminin receptor (67LR). Therefore, in this study, we determined whether quercetin and its conjugates bind 67LR to induce neuroprotection and compared their ability with EGCG. Based on the quenching of intrinsic tryptophan fluorescence of peptide G (residues 161-180 in 67LR), we found quercetin, quercetin-3-O-glucuronide, and quercetin-3-O-sulfate bind to this peptide with a high affinity comparable to EGCG. Molecular docking using the crystal structure of 37-kDa laminin receptor precursor supported the high-affinity binding of all these ligands to the site corresponding to peptide G. A pretreatment with quercetin (1-1000 nM) did not effectively protect Neuroscreen-1 cells from death induced by serum starvation. Contrarily, a pretreatment with low concentrations (1-10 nM) of quercetin conjugates better protected these cells than quercetin and EGCG. The 67LR-blocking antibody substantially prevented neuroprotection by all these agents, suggesting the role of 67LR in this process. Collectively, these studies reveal that quercetin induces neuroprotection primarily through its conjugates via high affinity binding to 67LR.

Quercetin 3-O-glucuronide-rich lotus leaf extract promotes a Brown-fat-phenotype in C3H10T1/2 mesenchymal stem cells.

Lotus (Nelumbo nucifera Gaertn.) is an aquatic perennial crop planted worldwide and its leaf (also called "He-Ye") has therapeutic effects on obesity. However, whether the underlying mechanism leads to increased energy expenditure by activation of brown adipocytes has not been clarified. Here, murine C3H10T1/2 mesenchymal stem cells (MSCs) were employed to investigate the effects of ethanol extracts from lotus leaf (LLE) on brown adipocytes formation and the underlying molecular mechanisms. The results showed LLE was rich in polyphenols (383.7 mg/g) and flavonoids (178.3 mg/g), with quercetin 3-O-glucuronide (Q3G) the most abundant (128.2 µg/mg). In LLE-treated C3H10T1/2 MSCs, the expressions of lipolytic factors (e.g., ATGL, HSL, and ABHD5) and brown regulators (e.g., Sirt1, PGC-1α, Cidea, and UCP1) were significantly upregulated compared to that in the untreated MSCs. Furthermore, LLE promoted mitochondrial biogenesis and fatty acid ß-oxidation, as evidenced by increases in the expression of Tfam, Cox7A, CoxIV, Cox2, Pparα, and Adrb3. Likewise, enhanced browning and mitochondrial biogenesis were also observed in Q3G-stimulated cells. Importantly, LLE and Q3G induced phosphorylation of AMPK accompanied by a remarkable increase in the brown fat marker UCP1, while pretreatment with Compound C (an AMPK inhibitor) reversed these changes. Moreover, stimulating LLE or Q3G-treated cells with CL316243 (a beta3-AR agonist) increased p-AMPKα/AMPKα ratio and UCP1 protein expression, indicating ß3-AR/AMPK signaling may involve in this process. Collectively, these observations suggested that LLE, especially the component Q3G, stimulates thermogenesis by activating brown adipocytes, which may involve the ß3-AR/AMPK signaling pathway.

Identification of components in coriander (Coriandrum sativum L.) inhibiting degranulation of RBL-2H3 cells.

We found that a water-soluble extract of coriander (Coriandrum sativum L.) (leaves, petioles and stems) inhibits antigen-induced degranulation of RBL-2H3 cells, a rat basophil leukemia cell line. The aim of this study was to elucidate the anti-degranulation active components in the extract. The methanol-eluate fraction obtained by fractionation of the water-soluble extract using MCI gel column chromatography had strong activity, and eight components were isolated and identified. Two of them were identified as new compounds, (3S)-3-methyl-6-hydroxyisocoumarin 8-O-ß-D-glucopyranoside (compound 1) and (7S,8R)-7,8-dihydro-8-ß-D-glucopyranosyloxy-4-methoxy-7-methyl-5H-fro[2,3-g][2]benzopyran-5-one (compound 2). As a result of evaluation of anti-degranulation activity of eight components, seven of them, such as tryptophan, phenylalanine, dihydroxycoumarin glucoside, quercetin glycoside, rutin, compound 1, and compound 2, had the activity. These results indicated that the water-soluble extract of coriander contains several anti-degranulation substances.

Protective Effect of Quercetin 3-O-Glucuronide against Cisplatin Cytotoxicity in Renal Tubular Cells.

Quercetin, a flavonoid with promising therapeutic potential, has been shown to protect from cisplatin nephrotoxicity in rats following intraperitoneal injection, but its low bioavailability curtails its prospective clinical utility in oral therapy. We recently developed a micellar formulation (P-quercetin) with enhanced solubility and bioavailability, and identical nephroprotective properties. As a first aim, we herein evaluated the oral treatment with P-quercetin in rats, which displayed no nephroprotection. In order to unravel this discrepancy, quercetin and its main metabolites were measured by HPLC in the blood and urine after intraperitoneal and oral administrations. Whilst quercetin was absorbed similarly, the profile of its metabolites was different, which led us to hypothesize that nephroprotection might be exerted in vivo by a metabolic derivate. Consequently, we then aimed to evaluate the cytoprotective capacity of quercetin and its main metabolites (quercetin 3-O-glucoside, rutin, tamarixetin, isorhamnetin and quercetin 3-O-glucuronide) against cisplatin toxicity, in HK-2 and NRK-52E tubular cell lines. Cells were incubated for 6 h with quercetin, its metabolites or vehicle (pretreatment), and subsequently 18 h in cotreatment with 10-300 µM cisplatin. Immediately after treatment, cell cultures were subject to the MTT technique as an index of cytotoxicity and photographed under light microscopy for phenotypic assessment. Quercetin afforded no direct cytoprotection and quercetin-3-O-glucuronide was the only metabolite partially preventing the effect of cisplatin in cultured tubule cells. Our results identify a metabolic derivative of quercetin contributing to its nephroprotection and prompt to further explore exogenous quercetin-3-O-glucuronide in the prophylaxis of tubular nephrotoxicity.

Quercetin-3-O-glucuronide in the Ethanol Extract of Lotus Leaf (Nelumbo nucifera) Enhances Sleep Quantity and Quality in a Rodent Model via a GABAergic Mechanism.

Current pharmacological treatments for insomnia carry several and long-term side effects. Therefore, natural products without side effects are warranted. In this study, the sleep-promoting activity of the lotus leaf (Nelumbo nucifera) extract was assessed using ICR mice and Sprague Dawley rats. A pentobarbital-induced sleep test and electroencephalogram analysis were conducted to measure sleep latency time, duration, and sleep architecture. The action mechanism of the extract was evaluated through ligand binding experiments. A high dose (300 mg/kg) of the ethanolic lotus leaf extract significantly increased sleep duration compared to the normal group (p < 0.01). Administration of low (150 mg/kg) and high doses (300 mg/kg) of the extract significantly increased sleep quality, especially the relative power of theta waves (p < 0.05), compared to the normal group. Furthermore, caffeine and lotus leaf extract administration significantly recovered caffeine-induced sleep disruption (p < 0.001), and the sleep quality was similar to that of the normal group. Additionally, ligand binding assay using [3H]-flumazenil revealed that quercetin-3-O-glucuronide contained in the lotus leaf extract (77.27 µg/mg of extract) enhanced sleep by binding to GABAA receptors. Collectively, these results indicated that the lotus leaf extract, particularly quercetin-3-O-glucuronide, exhibits sleep quantity- and quality-enhancing activity via the GABAergic pathway.

Development and Validation of a Method for Determining the Quercetin-3-O-glucuronide and Ellagic Acid Content of Common Evening Primrose (Oenothera biennis) by HPLC-UVD.

Toward the standardization of common evening primrose (Oenothera biennis) sprout extract (OBS-E), we aimed to obtain indicator compounds and use a validated method. HPLC-UVD allowed simultaneous quantification of the indicator compounds quercetin-3-O-glucuronide and ellagic acid. The method was validated in terms of specificity, linearity, precision, accuracy, and limit of detection/limit of quantification (LOD/LOQ). High specificity and linearity was demonstrated, with correlation coefficients of 1.0000 for quercetin-3-O-glucuronide and 0.9998 for ellagic acid. The LOD/LOQ values were 0.486/1.472 µg/mL for quercetin-3-O-glucuronide and 1.003/3.039 µg/mL for ellagic acid. Intra-day and inter-day variability tests produced relative standard deviation for each compound of <2%, a generally accepted precision criterion. High recovery rate were also obtained, indicating accuracy validation. The OBS-E prepared using various concentrations of ethanol were then analyzed. The 50% ethanol extract had highest content of quercetin-3-O-glucuronide, whereas the 70% ethanol extract possessed the lowest. However, the ellagic acid content was highest in the 70% ethanol extract and lowest in the 90% ethanol extract. Thus, quercetin-3-O-glucuronide and ellagic acid can be used industrially as indicator compounds for O. biennis sprout products, and our validated method can be used to establish indicator compounds for other natural products.

Antimicrobial, antioxidant, volatile and phenolic profiles of cabbage-stalk and pineapple-crown flour revealed by GC-MS and UPLC-MSE.

Unconventional parts of vegetables represent a rich source of health-promoting phytochemicals. The phenolic profile of cabbage-stalk flour (CSF), pineapple-crown flour (PCF), and their essential oils were characterized via UPLC-ESI-QTOF-MSE and GC-FID/MS. Antimicrobial activity was tested against five strains, and antioxidant activities were determined in free and bound extracts. Globally, 177 phenolics were tentatively identified in PCF (major p-coumaric acid, ferulic acid, and 4-hydroxybenzaldehyde) and 56 in CSF (major chlorogenicacid, quercetin 3-O-glucuronide, and p-coumaric acid). PCF exhibited a distinguished profile (lignans, stilbenes) and antioxidant capacity, especially in bound extracts (1.3 g GAE.100 g-1; 0.6 g catechin eq.100 g-1; DPPH: 244.7; ABTS: 467.8; FRAP: 762.6 µg TE.g-1, ORAC: 40.9 mg TE.g-1). The main classes of volatile compounds were fatty acids, their esters, and terpenes in CSF (30) and PCF (41). A comprehensive metabolomic approach revealed CSF and PCF as a promising source of PC, showing great antioxidant and discrete antimicrobial activities.

Quercetin-3-O-Glucuronide Alleviates Cognitive Deficit and Toxicity in Aß1-42 -Induced AD-Like Mice and SH-SY5Y Cells.

SCOPE: Alzheimer's disease (AD) is characterized by amyloid-ß (Aß) related imbalance, Tau-hyperphosphorylation, and neuroinflammation, in which Aß and neuroinflammation can induce brain insulin resistance (IR). Gut microbiome disorder is correlated with inflammation in AD. As of yet, there are no effective treatments clinically. Thus, it is focused on the potential benefit of quercetin-3-O-glucuronide (Q3G), a pharmacologically active flavonol glucuronide, on AD treatment by regulating brain IR and the gut microbiome. METHODS AND RESULTS: AD mice model built through intracerebroventricular injection of Aß1-42 and AD cell model developed through the SH-SY5Y cell line and Aß1-42 are used to explore the protective effects of Q3G on AD. Neurobehavioral test, brain insulin signaling pathway, and high-throughput pyrosequencing of 16S rRNA are assessed. Data show that Q3G attenuates neuroinflammation and brain IR in Aß1-42 -injected mice and relieves apoptosis in Aß1-42 -treated SH-SY5Y cells by interrupting the downstream insulin signaling. Q3G ameliorates Aß accumulation and Tau phosphorylation, restores CREB and BDNF levels in the hippocampus , and reverses Aß1-42 -induced cognitive impairment. Besides, Q3G restores Aß1-42 -induced reduction of short-chain fatty acids (SCFAs) and gut microbiota dysbiosis. CONCLUSION: Q3G can alleviate brain IR through directly acting on the brain or modulating the gut-brain axis, ultimately to relieve Aß1-42 -induced cognitive dysfunction.

[Quality evaluation methods for standard decoction of Nelumbinis Folium].

The quality evaluation method for standard decoction of Chinese herbal slices is the basis for the quality evaluation of granules and preparations of classical formula(decoction)of traditional Chinese medicine. This study aimed to establish a method for the determination of quercetin-3-O-glucuronic acid in Nelumbinis Folium(NF)and its standard decoction, so as to provide reference for the quality control of NF and its standard decoction. Fifteen batches of representative NF were collected to prepare standard decoction, and the parameters of dry extract rate, transfer rate of index component, and pH value were calculated. HPLC was used to establish the content determination method for quercetin-3-O-glucuronic acid in NF and its standard decoction. The concentration range of quercetin-3-O-glucuronic acid in the standard decoction of NF was 1.09-3.06 g·L~(-1), while the concentration range of nuciferine was 0.01-0.17 g·L~(-1). The average extraction rate of NF standard decoction was(14.4±2.6)%, the average transfer rate of quercetin-3-O-glucuronic acid was(70.7±18.6)%, and the average transfer rate of nuciferine was(9.6±5.4)%. Compared with Nuciferine, quercetin-3-O-glucuronic acid had a high content and stable transfer rate in standard decoction, and was recommended to be the quality control marker for NF and its standard decoction. This paper establishes a quality evaluation method for NF standard decoction, and can provide reference for the quality control of all preparations derived from NF and its decoction.

Polyphenolic profile of Cichorium intybus L. endemic varieties from the Veneto region of Italy.

The present study was aimed at the investigation, through HPLCDAD-ESI-MS/MS, of polyphenols in seven autochthonous C. intybus varieties, already known from literature to contain various substances with antioxidant properties, from the Veneto region of Italy, namely 'Castelfranco', 'Chioggia', 'Rosa di Gorizia', 'Rosa di Verona', 'Treviso Precoce', 'Treviso Tardivo' and 'Verdon da Cortèl'. Thirteen polyphenols, belonging to hydroxycinnamic acid, flavone, flavonol and anthocyanin classes, were detected in most samples. The developed analytical method was validated in agreement with ICH guidelines. The total amount of polyphenols ranged from 52 to 386 (mean: 254) mg/100g fresh weight (F.W.). The results were further confirmed by Principal Composition Analysis (PCA), which highlighted peculiar features and similarities among analysed samples for each variety (except for 'Chioggia' samples). The developed method is suitable for routine analyses, as well as geographical characterization, selection of different C. intybus varieties and for the determination of related polyphenols dietary recommended intakes.

Polyphenolic profile of butterhead lettuce cultivar by ultrahigh performance liquid chromatography coupled online to UV-visible spectrophotometry and quadrupole time-of-flight mass spectrometry.

In the present study, the butterhead lettuce cultivar was analyzed by ultrahigh performance liquid chromatography (UHPLC) coupled online to diode array detection (DAD), electrospray ionization (ESI) and quadrupole time-of-flight mass spectrometry (QToF/MS) in the positive and negative ion mode in order to characterize its polyphenolic profile for the first time. The instrument acquisition mode MSE was used to collect automatic and simultaneous information of exact mass at high and low collision energies of precursor ions as well as other ions produced as a result of their fragmentation. One hundred eleven phenolic compounds were identified in the acidified hydromethanolic extract of freeze-dried leaves of butterhead lettuce cultivar: 40 hydroxycinnamic acid derivatives, 21 hydroxybenzoic acid derivatives, 2 hydroxyphenylacetic acid derivatives, 18 flavonols, 9 flavones, one flavanone, 7 coumarins, one hydrolysable tannin and 12 lignans. Forty-seven of these compounds have been tentatively identified for the first time in lettuce.

Comparison of the Impact of Two Molecules on Plant Defense and on Efficacy against Botrytis cinerea in the Vineyard: A Plant Defense Inducer (Benzothiadiazole) and a Fungicide (Pyrimethanil).

Grapevine is subject to diseases that affect yield and wine quality caused by various pathogens including Botrytis cinerea. To limit the use of fungicides, an alternative is to use plant elicitors such as benzothiadiazole (BTH). We investigated the effect of a fungicide (Pyrimethanil) and an elicitor (benzothiadiazole) on plant defenses. Applications for two consecutive years in the vineyard significantly reduced gray mold. Two and seven days after treatments, the expressions of 48 genes involved in defenses showed differential modulation (up- or down-regulation) depending on treatment. Some genes were identified as potential markers of protection and were linked to an increase in total polyphenols (TP) in leaves. Surprisingly, the fungicide also induced the expression of defense genes and increased the polyphenol content. This suggests that BTH acts as an efficient elicitor in the vineyard and that Pyrimethanil may act, in part, as a defense-inducing agent on the vine.

Quercetin-3-O-glucuronide promotes the proliferation and migration of neural stem cells.

Quercetin is a bioactive compound exerting therapeutic effects on in vivo animal models of neurodegeneration or neurotoxicity. However, the narrow therapeutic dose-range of quercetin has been a point of concern since previous studies have demonstrated that quercetin induces cytotoxicity in vitro. Quercetin is metabolized to quercetin glucuronates such as quercetin-3-O-glucuronide (Q3GA), primarily detected in the plasma and the brain. Here, we examined whether and how quercetin or Q3GA regulates neural stem cells (NSCs) in vivo and in vitro. Immunohistochemistry showed that oral administration of quercetin increased nestin-, DCX-, BrdU/DCX-, and BrdU/NeuN-positive cells in the dentate gyrus of mice. However, quercetin decreased the viability of human embryonic NSCs in culture, accompanied by decreased Akt phosphorylation and increased cleavage of caspase-3 and PARP. In contrast, Q3GA increased BrdU-positive cell proliferation, Akt phosphorylation, and cyclin D1 expression. PI3K/Akt inhibitor LY294002 reversed Q3GA-induced Akt phosphorylation and cyclin D1 expression, thereby reducing Q3GA-induced proliferation. Furthermore, Q3GA increased the protein secretion of BDNF and its blockade using anti-BDNF antibody reversed Q3GA-induced proliferation. Under differentiation state, Q3GA promotes NSC migration, along with increased mRNA expression of CXCR4. Moreover, Q3GA significantly reversed scopolamine-induced reduction of Akt phosphorylation in the mouse hippocampus and ameliorated scopolamine-induced memory impairments. Our results demonstrate that quercetin and its metabolite Q3GA control NSC viability in a converse manner through contrary regulation of Akt, accounting for the conflicting effects of quercetin in vivo and in vitro. This study provides a novel mechanism for the positive effects of Q3GA on neurogenesis and suggests its therapeutic potential in neurodegenerative diseases.

The UDP-glycosyltransferase (UGT) superfamily expressed in humans, insects and plants: Animal-plant arms-race and co-evolution.

UDP-glycosyltransferases (UGTs) are major phase II enzymes of a detoxification system evolved in all kingdoms of life. Lipophilic endobiotics such as hormones and xenobiotics including phytoalexins and drugs are conjugated by vertebrates mainly with glucuronic acid, by invertebrates and plants mainly with glucose. Plant-herbivore arms-race has been the major driving force for evolution of large UGT and other enzyme superfamilies. The UGT superfamily is defined by a common protein structure and signature sequence of 44 amino acids responsible for binding the UDP moiety of the sugar donor. Plants developed toxic phytoalexins stored as glucosides. Upon herbivore attack these conjugates are converted to highly reactive compounds. In turn, animals developed large families of UGTs in their intestine and liver to detoxify these phytoalexins. Interestingly, phytoalexins, exemplified by quercetin glucuronides and glucosinolate-derived isocyanates, are known insect attractant pigments in plants, and antioxidants, anti-inflammatory and chemopreventive compounds of humans. It is to be anticipated that phytochemicals may provide a rich source in beneficial drugs.

Quercetin Metabolites Up-Regulate the Antioxidant Response in Osteoblasts Isolated From Fetal Rat Calvaria.

Oxidative stress contributes to osteoporosis by suppressing differentiation of osteoblasts, suggesting the osteoblast antioxidant response may be a viable strategy for osteoporosis prevention. Quercetin, an antioxidant flavonol, up-regulates the antioxidant response in many cell types, but studies are needed to understand the effects of quercetin plasma metabolites on the osteoblast antioxidant response. The first specific aim was to examine antioxidant response genes and proteins in osteoblasts exposed to plasma quercetin metabolites. The second specific aim was to identify potential signaling pathways in the osteoblast antioxidant response that mediate the effect of quercetin, specifically Nrf2, ERK1/2, and NFκB p65. Osteoblasts isolated from fetal rat calvaria were treated with doses up to 20 µM of three different quercetin metabolites found in blood plasma after consumption of quercetin-rich foods or supplements: quercetin aglycone (QRC), isorhamnetin (ISO), or quercetin 3-O-glucuronide (Q3G). Alternatively, some cells received a 2:1:1 mixture of all three metabolites (10 µM Q3G: 5 µM ISO: 5 µM QRC) to evaluate synergistic effects. Antioxidant response genes and proteins known to be up-regulated by quercetin were analyzed along with Nrf2, ERK1/2, and NFκB proteins. Both QRC and ISO, but not Q3G, up-regulated heme oxygenase-1 (HO-1) and γ-glutamate cysteine ligase catalytic subunit (GCLC) at the mRNA and protein level. Synergistic effects of metabolites were not observed. Up-regulation of HO-1 and GCLC was associated with suppression of phosphorylated ERK1/2 and NFκB, but no alterations in Nrf2 protein levels were observed. This study shows that the antioxidant response of osteoblasts is differentially stimulated by quercetin metabolites.

Quercetin-3-O-glucuronide inhibits noradrenaline-promoted invasion of MDA-MB-231 human breast cancer cells by blocking ß2-adrenergic signaling.

Endogenous catecholamines such as adrenaline (A) and noradrenaline (NA) are released from the adrenal gland and sympathetic nervous system during exposure to stress. The adrenergic system plays a central role in stress signaling, and excessive stress was found to be associated with increased production of reactive oxygen species (ROS). Overproduction of ROS induces oxidative damage in tissues and causes the development of diseases such as cancer. In this study, we investigated the effects of quercetin-3-O-glucuronide (Q3G), a circulating metabolite of quercetin, which is a type of natural flavonoid, on the catecholamine-induced ß2-adrenergic receptor (ß2-AR)-mediated response in MDA-MB-231 human breast cancer cells expressing ß2-AR. Treatment with A or NA at concentrations above 1µM generated significant levels of ROS, and NA treatment induced the gene expression of heme oxygenase-1 (HMOX1), and matrix metalloproteinase-2 (MMP-2) and -9 (MMP9). Inhibitors of p38 MAP kinase (SB203580), cAMP-dependent protein kinase (PKA) (H-89), activator protein-1 (AP-1) transcription factor (SR11302), and NF-κB and AP-1 (Tanshinone IIA) decreased MMP2 and MMP9 gene expression. NA also enhanced cAMP induction, RAS activation and phosphorylation of ERK1/2. These results suggested that the cAMP-PKA, MAPK, and ROS-NF-κB pathways are involved in ß2-AR signaling. Treatment with 0.1µM Q3G suppressed ROS generation, cAMP and RAS activation, phosphorylation of ERK1/2 and the expression of HMOX1, MMP2, and MMP9 genes. Furthermore, Q3G (0.1µM) suppressed invasion of MDA-MB-231 breast cancer cells and MMP-9 induction, and inhibited the binding of [(3)H]-NA to ß2-AR. These results suggest that Q3G may function to suppress invasion of breast cancer cells by controlling ß2-adrenergic signaling, and may be a dietary chemopreventive factor for stress-related breast cancer.

Quercetin-3-O-glucuronide induces ABCA1 expression by LXRα activation in murine macrophages.

Reverse cholesterol transport (RCT) removes excess cholesterol from macrophages to prevent atherosclerosis. ATP-binding cassette, subfamily A, member 1 (ABCA1) is a crucial cholesterol transporter involved in RCT to produce high density lipoprotein-cholesterol (HDLC), and is transcriptionally regulated by liver X receptor alpha (LXRα), a nuclear receptor. Quercetin is a widely distributed flavonoid in edible plants which prevented atherosclerosis in an animal model. We found that quercetin-3-O-glucuronide (Q3GA), a major quercetin metabolite after absorption from the digestive tract, enhanced ABCA1 expression, in vitro, via LXRα in macrophages. In addition, leaf extracts of a traditional Asian edible plant, Nelumbo nucifera (NNE), which contained abundant amounts of quercetin glycosides, significantly elevated plasma HDLC in mice. We are the first to present experimental evidence that Q3GA induced ABCA1 in macrophages, and to provide an alternative explanation to previous studies on arteriosclerosis prevention by quercetin.