A Review on Structure, Modifications and Structure-Activity Relation of Quercetin and Its Derivatives

A Comprehensive View on the Quercetin Impact on Colorectal Cancer

Colorectal cancer (CRC) represents the third type of cancer in incidence and second in mortality worldwide, with the newly diagnosed case number on the rise. Among the diagnosed patients, approximately 70% have no hereditary germ-line mutations or family history of pathology, thus being termed sporadic CRC. Diet and environmental factors are to date considered solely responsible for the development of sporadic CRC; therefore; attention should be directed towards the discovery of preventative actions to combat the CRC initiation, promotion, and progression. Quercetin is a polyphenolic flavonoid plant secondary metabolite with a well-characterized antioxidant activity. It has been extensively reported as an anti-carcinogenic agent in the scientific literature, and the modulated targets of quercetin have been also characterized in the context of CRC, mainly in original research publications. In this fairly comprehensive review, we summarize the molecular targets of quercetin reported to date in in vivo and in vitro CRC models, while also giving background information about the signal transduction pathways that it up- and downregulates. Among the most relevant modulated pathways, the Wnt/β-catenin, PI3K/AKT, MAPK/Erk, JNK, or p38, p53, and NF-κB have been described. With this work, we hope to encourage further quests in the elucidation of quercetin anti-carcinogenic activity as single agent, as dietary component, or as pharmaconutrient delivered in the form of plant extracts.

A Review of the Potential Roles of Antioxidant and Anti-Inflammatory Pharmacological Approaches for the Management of Mild-to-Moderate Symptomatic COVID-19

In the past 2 years, the coronavirus disease 2019 (COVID-19) pandemic has driven investigational studies and controlled clinical trials on antiviral treatments and vaccines that have undergone regulatory approval. Now that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants may become endemic over time, there remains a need to identify drugs that treat the symptoms of COVID-19 and prevent progression toward severe cases, hospitalization, and death. Understanding the molecular mechanisms of SARS-CoV-2 infection is extremely important for the development of effective therapies against COVID-19. This review outlines the key pathways involved in the host response to SARS-CoV-2 infection and discusses the potential role of antioxidant and anti-inflammatory pharmacological approaches for the management of early mild-to-moderate COVID-19, using the examples of combined indomethacin, low-dose aspirin, omeprazole, hesperidin, quercetin, and vitamin C. The pharmacological targets of these substances are described here for their possible synergism in counteracting SARS-CoV-2 replication and progression of the infection from the upper respiratory airways to the blood, avoiding vascular complications and cytokine and bradykinin storms.

Biotechnological Applications and Health-Promoting Properties of Flavonols: An Updated View

Flavonols are a subclass of natural flavonoids characterized by a remarkable number of biotechnological applications and health-promoting properties. They attract researchers' attention due to many epidemiological studies supporting their usage. They are phytochemicals commonly present in our diet, being ubiquitous in the plant kingdom and, in particular, relatively very abundant in fruits and vegetables. All these aspects make flavonols candidates of choice for the valorization of products, based on the presence of a remarkable number of different chemical structures, each one characterized by specific chemical features capable of influencing biological targets inside the living organisms in very different manners. In this review, we analyzed the biochemical and physiological characteristics of flavonols focalizing our attention on the most promising compounds to shed some light on their increasing utilization in biotechnological applications in processing industries, as well as their suitable employment to improve the overall wellness of the humankind.

Polymer grafted magnetic graphene oxide as a potential nanocarrier for pH-responsive delivery of sparingly soluble quercetin against breast cancer cells

In this work, polymer grafted magnetic graphene oxide (GO-PVP-Fe3O4) was successfully synthesized for efficient delivery of anticancer drug. Firstly, GO was functionalized with the hydrophilic and biocompatible polymer polyvinylpyrrolidone (PVP) and then grafted with magnetic nanoparticles (Fe3O4) through an easy and effective chemical co-precipitation method. Quercetin (QSR) as an anticancer drug was loaded onto the surface of GO-PVP-Fe3O4 via non-covalent interactions. The drug loading capacity was as high as 1.69 mg mg-1 and the synthesized magnetic nanocarrier shows pH-responsive controlled release of QSR. The cellular cytotoxicity of the synthesized nanocarrier with and without drugs was investigated in human breast cancer MDA MB 231 cells and their effects compared on non-tumorigenic epithelial HEK 293T cells. These results reveal that the drug loaded GO-PVP-Fe3O4 nanohybrid was found to be more toxic than the free drug towards MDA MB 231 cells and exhibits biocompatibility towards HEK 293T cells. Overall, a smart drug delivery system including polymer grafted magnetic graphene oxide as a pH-responsive potential nanocarrier could be beneficial for targeted drug delivery, controlled by an external magnetic field as an advancement in chemotherapy against cancer.

Cardioprotective effects of phytopigments via multiple signaling pathways

BACKGROUND

Cardiovascular diseases (CVDs) are among the deadliest non-communicable diseases, and millions of dollars are spent every year to combat CVDs. Unfortunately, the multifactorial etiology of CVDs complicates the development of efficient therapeutics. Interestingly, phytopigments show significant pleiotropic cardioprotective effects both in vitro and in vivo.

PURPOSE

This review gives an overview of the cardioprotective effects of phytopigments based on in vitro and in vivo studies as well as clinical trials.

METHODS

A literature-based survey was performed to collect the available data on cardioprotective activities of phytopigments via electronic search engines such as PubMed, Google Scholar, and Scopus.

RESULTS

Different classes of phytopigments such as carotenoids, xanthophylls, flavonoids, anthocyanins, anthraquinones alleviate major CVDs (e.g., cardiac hypertrophy, atherosclerosis, hypertension, cardiotoxicities) via acting on signaling pathways related to AMPK, NF-κB, NRF2, PPARs, AKT, TLRs, MAPK, JAK/STAT, NLRP3, TNF-α, and RA.

CONCLUSION

Phytopigments represent promising candidates to develop novel and effective CVD therapeutics. More randomized, placebo-controlled clinical studies are recommended to establish the clinical efficacy of phytopigments.

Phytochemical profiles of edible flowers of medicinal plants of Dendrobium officinale and Dendrobium devonianum

The discovery of new edible flowers that are nontoxic, innocuous flowers having human health benefits, surveys of their phytochemicals and utilization are of great scientific and commercial interest. Dendrobium officinale and Dendrobium devonianum are precious Traditional Chinese Medicine. During the massive commercial cultivation, a lot of flowers were produced and certified as edible flowers, and the phytochemical profiles and bioactivities warrant evaluate. The present study aimed to investigate the phytochemicals and antioxidative activities in flowers of D. officinale (DOF) and D. devonianum (DDF). In total, 474 metabolites were identified using a widely targeted metabonomics method, 16 amino acids and 6 flavonoids were measured using high-performance liquid chromatography (HPLC), and 8 fatty acids were detected using gas chromatography-mass spectrometry (GC-MS). Both flowers contained various amino acids, including 7 essential amino acids, diverse flavonoids, especially quercetin, kaempferol and their derivatives, and high levels of methyl linoleate and methyl linolenate. The relative levels of quercetin, kaempferol and their glycosides were higher in DDF than in DOF, whereas the relative levels of several flavonoids C-glycosides were high in DOF. Ethanol extracts of both DOF and DDF showed antioxidative capacities including the scavenging of 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals. Both edible flowers contained flavonoids, amino acids, and fatty acids and have antioxidative activities, which should be explored for use in functional foods and pharmaceuticals.

Effects of quercetin on apoptosis and extracellular matrix degradation of chondrocytes induced by oxidative stress-mediated pyroptosis

Quercetin has been preliminarily proven to serve as a potential agent for the treatment of osteoarthritis (OA). However, its effects and potential mechanisms on the pathological process of OA are not very clear. This study aimed to study the protective effect of quercetin on OA. Lipopolysaccharide (LPS)-treated chondrocytes (C28/I2 cell) and anterior cruciate ligament transection with partial medial meniscectomy-treated Wistar rats were used as models of OA in vitro and in vivo. Cell counting kit-8 (CCK-8 kit), flow cytometry, enzyme-linked immunosorbent assay (ELISA) kit, western blot, dichlorodihydrofluorescein diacetate (DCFH-DA) kit, thiobarbituric acid (TBA) test, toluidine blue staining, Hematoxylin eosin (HE) staining and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining were used to evaluate cell viability, cell apoptosis, inflammatory cytokines level, protein expression, reactive oxygen species (ROS) level, malondialdehyde (MDA) content, morphological changes, and chondrocyte apoptosis of cartilage, respectively. Results showed that quercetin could reduce LPS-induced C28/I2 cell apoptosis, extracellular matrix (ECM) degradation, and cell pyroptosis, and overexpression of nucleotide-binding domain and leucine-rich-repeat-containing (NLR) family, pyrin domain-containing 3 (NLRP3) revealed that quercetin reduced chondrocyte apoptosis and ECM degradation by inhibiting NLRP3-mediated pyroptosis. Furthermore, quercetin could reduce chondrocyte apoptosis and ECM degradation, and inhibit NLRP3-mediated pyroptosis through blocking oxidative stress. It was further confirmed in the rat OA model that quercetin alleviated OA by blocking oxidative stress, reduces chondrocyte pyroptosis, apoptosis, and ECM degradation. In conclusion, quercetin inhibited OA via blocking oxidative stress-induced chondrocyte pyroptosis in models of OA in vitro and in vivo.

Neuroinflammation as a Therapeutic Target in Retinitis Pigmentosa and Quercetin as Its Potential Modulator

The retina is a multilayer neuronal tissue located in the back of the eye that transduces the environmental light into a neural impulse. Many eye diseases caused by endogenous or exogenous harm lead to retina degeneration with neuroinflammation being a major hallmark of these pathologies. One of the most prevalent retinopathies is retinitis pigmentosa (RP), a clinically and genetically heterogeneous hereditary disorder that causes a decline in vision and eventually blindness. Most RP cases are related to mutations in the rod visual receptor, rhodopsin. The mutant protein triggers inflammatory reactions resulting in the activation of microglia to clear degenerating photoreceptor cells. However, sustained insult caused by the abnormal genetic background exacerbates the inflammatory response and increases oxidative stress in the retina, leading to a decline in rod photoreceptors followed by cone photoreceptors. Thus, inhibition of inflammation in RP has received attention and has been explored as a potential therapeutic strategy. However, pharmacological modulation of the retinal inflammatory response in combination with rhodopsin small molecule chaperones would likely be a more advantageous therapeutic approach to combat RP. Flavonoids, which exhibit antioxidant and anti-inflammatory properties, and modulate the stability and folding of rod opsin, could be a valid option in developing treatment strategies against RP.

Human Sirtuin Regulators: The "Success" Stories

The human sirtuins are a group of NAD⁺-dependent protein deacylases. They “erase” acyl modifications from lysine residues in various cellular targets including histones, transcription factors, and metabolic enzymes. Through these far-reaching activities, sirtuins regulate a diverse array of biological processes ranging from gene transcription to energy metabolism. Human sirtuins have been intensely pursued by both academia and industry as therapeutic targets for a broad spectrum of diseases such as cancer, neurodegenerative diseases, and metabolic disorders. The last two decades have witnessed a flood of small molecule sirtuin regulators. However, there remain relatively few compounds targeting human sirtuins in clinical development. This reflects the inherent issues concerning the development of isoform-selective and potent molecules with good drug-like properties. In this article, small molecule sirtuin regulators that have advanced into clinical trials will be discussed in details as “successful” examples for future drug development. Special attention is given to the discovery of these compounds, the mechanism of action, pharmacokinetics analysis, formulation, as well as the clinical outcomes observed in the trials.

A review on pharmacological activities and synergistic effect of quercetin with small molecule agents

BACKGROUND

Quercetin is a natural flavonoid, which widely exists in nature, such as tea, coffee, apples, and onions. Numerous studies have showed that quercetin has multiple biological activities such as anti-oxidation, anti-inflammatory, and anti-aging. Hence, quercetin has a significant therapeutic effect on cancers, obesity, diabetes, and other diseases. In the past decades, a large number of studies have shown that quercetin combined with other agents can significantly improve the overall therapeutic effect, compared to single use.

PURPOSE

This work reviews the pharmacological activities of quercetin and its derivatives. In addition, this work also summarizes both in vivo and in vitro experimental evidence for the synergistic effect of quercetin against cancers and metabolic diseases.

METHODS

An extensive systematic search for pharmacological activities and synergistic effect of quercetin was performed considering all the relevant literatures published until August 2021 through the databases including NCBI PubMed, Scopus, Web of Science, and Google Scholar. The relevant literatures were extracted from the databases with following keyword combinations: "pharmacological activities" OR "biological activities" OR "synergistic effect" OR "combined" OR "combination" AND "quercetin" as well as free-text words.

RESULTS

Quercetin and its derivatives possess multiple pharmacological activities including anti-cancer, anti-oxidant, anti-inflammatory, anti-cardiovascular, anti-aging, and neuroprotective activities. In addition, the synergistic effect of quercetin with small molecule agents against cancers and metabolic diseases has also been confirmed.

CONCLUSION

Quercetin cooperates with agents to improve the therapeutic effect by regulating signal molecules and blocking cell cycle. Synergistic therapy can reduce the dose of agents and avoid the possible toxic and side effects in the treatment process. Although quercetin treatment has some potential side effects, it is safe under the expected use conditions. Hence, quercetin has application value and potential strength as a clinical drug. Furthermore, quercetin, as the main effective therapeutic ingredient in traditional Chinese medicine, may effectively treat and prevent coronavirus disease 2019 (COVID-19).

Biosynthesis of a rosavin natural product in Escherichia coli by glycosyltransferase rational design and artificial pathway construction

Phytochemicals are rich resources for pharmaceutical and nutraceutical agents. A key challenge of accessing these precious compounds can present significant bottlenecks for development. The cinnamyl alcohol disaccharides also known as rosavins are the major bioactive ingredients of the notable medicinal plant Rhodiola rosea L. Cinnamyl-(6'-O-β-xylopyranosyl)-O-β-glucopyranoside (rosavin E) is a natural rosavin analogue with the arabinopyranose unit being replaced by its diastereomer xylose, which was only isolated in minute quantity from R. rosea. Herein, we described the de novo production of rosavin E in Escherichia coli. The 1,6-glucosyltransferase CaUGT3 was engineered into a xylosyltransferase converting cinnamyl alcohol monoglucoside (rosin) into rosavin E by replacing the residue T145 with valine. The enzyme activity was further elevated 2.9 times by adding the mutation N375Q. The synthesis of rosavin E from glucose was achieved with a titer of 92.9 mg/L by combining the variant CaUGT3^T145V/N375Q, the UDP-xylose synthase from Sinorhizobium meliloti 1021 (SmUXS) and enzymes for rosin biosynthesis into a phenylalanine overproducing E. coli strain. The production of rosavin E was further elevated by co-overexpressing UDP-xylose synthase from Arabidopsis thaliana (AtUXS3) and SmUXS, and the titer in a 5 L bioreactor with fed-batch fermentation reached 782.0 mg/L. This work represents an excellent example of producing a natural product with a disaccharide chain by glycosyltransferase engineering and artificial pathway construction.

SIRT5-Related Desuccinylation Modification Contributes to Quercetin-Induced Protection against Heart Failure and High-Glucose-Prompted Cardiomyocytes Injured through Regulation of Mitochondrial Quality Surveillance

Myocardial fibrosis represents the primary pathological change associated with diabetic cardiomyopathy and heart failure, and it leads to decreased myocardial compliance with impaired cardiac diastolic and systolic function. Quercetin, an active ingredient in various medicinal plants, exerts therapeutic effects against cardiovascular diseases. Here, we investigate whether SIRT5- and IDH2-related desuccinylation is involved in the underlying mechanism of myocardial fibrosis in heart failure while exploring related therapeutic drugs for mitochondrial quality surveillance. Mouse models of myocardial fibrosis and heart failure, established by transverse aortic constriction (TAC), were administered with quercetin (50 mg/kg) daily for 4 weeks. HL-1 cells were pretreated with quercetin and treated with high glucose (30 mM) in vitro. Cardiac function, western blotting, quantitative PCR, enzyme-linked immunosorbent assay, and immunofluorescence analysis were employed to analyze mitochondrial quality surveillance, oxidative stress, and inflammatory response in myocardial cells, whereas IDH2 succinylation levels were detected using immunoprecipitation. Myocardial fibrosis and heart failure incidence increased after TAC, with abnormal cardiac ejection function. Following high-glucose treatment, HL-1 cell activity was inhibited, causing excess production of reactive oxygen species and inhibition of mitochondrial respiratory complex I/III activity and mitochondrial antioxidant enzyme activity, as well as increased oxidative stress and inflammatory response, imbalanced mitochondrial quality surveillance and homeostasis, and increased apoptosis. Quercetin inhibited myocardial fibrosis and improved cardiac function by increasing mitochondrial energy metabolism and regulating mitochondrial fusion/fission and mitochondrial biosynthesis while inhibiting the inflammatory response and oxidative stress injury. Additionally, TAC inhibited SIRT5 expression at the mitochondrial level and increased IDH2 succinylation. However, quercetin promoted the desuccinylation of IDH2 by increasing SIRT5 expression. Moreover, treatment with si-SIRT5 abolished the protective effect of quercetin on cell viability. Hence, quercetin may promote the desuccinylation of IDH2 through SIRT5, maintain mitochondrial homeostasis, protect mouse cardiomyocytes under inflammatory conditions, and improve myocardial fibrosis, thereby reducing the incidence of heart failure.

The role of quercetin in plants

Flavonoids are a special category of hydroxylated phenolic compounds having an aromatic ring structure. Quercetin is aspecial subclass of flavonoid. It is a bioactive natural compound built upon the flavon structure nC6(ring A)-C3(ring C)-C6(ring B). Quercetin facilitates several plant physiological processes, such as seed germination, pollen growth, antioxidant machinery, and photosynthesis, as well as induces proper plant growth and development. Quercetin is a powerful antioxidant, so it potently provides plant tolerance against several biotic and abiotic stresses. This review highlights quercetin's role in increasing several physiological and biochemical processes under stress and non-stress environments. Additionally, this review briefly assesses quercetin's role in mitigating biotic and abiotic stresses (e.g., salt, heavy metal, and UV stress). The biosynthesis of flavonoids, their signaling pathways, and quercetin's role in plant signaling are also discussed.

Quercetin against MCF7 and CAL51 breast cancer cell lines: apoptosis, gene expression and cytotoxicity of nano-quercetin

Aims: To evaluate the anti breast-cancer activity, biocompatibility and toxicity of poly(d,l)-lactic-co-glycolic acid (PLGA)-encapsulated quercetin nanoparticles (Q-PLGA-NPs). Materials & methods: Quercetin was nano-encapsulated by an emulsion-diffusion process, and the nanoparticles were fully characterized through Fourier transform infrared spectroscopy, x-ray diffractions, FESEM and zeta-sizer analysis. Activity against CAL51 and MCF7 cell lines were assessed by DNA fragmentation assays, fluorescence microscopy, and acridine-orange, and propidium-iodide double-stainings. Biocompatibility towards red blood cells and toxicity towards mice were also explored. Results: The Q-PLGA-NPs exhibited apoptotic activity against the cell lines. The murine in vivo studies showed no significant alterations in the liver and kidney's functional biomarkers, and no apparent abnormalities, or tissue damages were observed in the histological images of the liver, spleen, lungs, heart and kidneys. Conclusion: The study established the preliminary in vitro efficacy and in vivo safety of Q-PLGA-NPs as a potential anti-breast cancer formulation.

ASCs -derived exosomes loaded with vitamin A and quercetin inhibit rapid senescence-like response after acute liver injury

Acute liver injury is a short-term burst of liver cell damage, which has many causes and complex mechanisms. Despite the unique ability of the liver to heal itself, there is still no effective treatment except liver transplantation for chronic liver injury or even liver failure caused by acute liver injury. Stem cell-derived exosomes are ideal drug carriers due to their unique immunomodulatory effects and structural characteristics. In this study, quercetin and vitamin A loaded adipose mesenchymal stem cells (ASCs)-derived exosomes were constructed and used to treat acute liver injury induced by CCl4 in mice. Quercetin enhances the therapeutic efficacy of exosomes, while vitamin A enhances the liver targeting of exosomes, and it was found that quercetin and vitamin A loaded mesenchymal stem cell exosomes reduce rapid senescence-like response induced by acute liver injury.

2-Hydroxy-5-(3,5,7-trihydroxy-4-oxo-4H-chromen-2-yl)phenyl (E)-3-(4-hydroxy-3-methoxyphenyl)acrylate: Synthesis, In Silico Analysis and In Vitro Pharmacological Evaluation

Quercetin and ferulic acid are two phytochemicals extensively represented in the plant kingdom and daily consumed in considerable amounts through diets. Due to a common phenolic structure, these two molecules share several pharmacological properties, e.g., antioxidant and free radical scavenging, anti-cancer, anti-inflammatory, anti-arrhythmic, and vasorelaxant. The aim of the present work was the combination of the two molecules in a single chemical entity, conceivably endowed with more efficacious vasorelaxant activity. Preliminary in silico studies herein described suggested that the new hybrid compound bound spontaneously and with high affinity on the KCa1.1 channel. Thus, the synthesis of the 3′-ferulic ester derivative of quercetin was achieved and its structure confirmed by 1H- and 13C-NMR spectra, HSQC and HMBC experiments, mass spectrometry, and elementary analysis. The effect of the new hybrid compound on vascular KCa1.1 and CaV1.2 channels revealed a partial loss of the stimulatory activity that characterizes the parent compound quercetin. Therefore, further studies are necessary to identify a better strategy to improve the vascular properties of this flavonoid.

Rutin and Quercetin Decrease Cholesterol in HepG2 Cells but Not Plasma Cholesterol in Hamsters by Oral Administration

Rutin (R) and quercetin (Q) are two widespread dietary flavonoids. Previous studies regarding the plasma cholesterol-lowering activity of R and Q generated inconsistent results. The present study was therefore carried out to investigate the effects of R and Q on cholesterol metabolism in both HepG2 cells and hypercholesterolemia hamsters. Results from HepG2 cell experiments demonstrate that both R and Q decreased cholesterol at doses of 5 and 10 µM. R and Q up-regulated both the mRNA and protein expression of sterol regulatory element binding protein 2 (SREBP2), low-density lipoprotein receptor (LDLR), and liver X receptor alpha (LXRα). The immunofluorescence study revealed that R and Q increased the LDLR expression, while only Q improved LDL-C uptake in HepG2 cells. Results from hypercholesterolemia hamsters fed diets containing R (5.5 g/kg diet) and Q (2.5 g/kg diet) for 8 weeks demonstrate that both R and Q had no effect on plasma total cholesterol. In the liver, only Q reduced cholesterol significantly. The discrepancy between the in vitro and in vivo studies was probably due to a poor bioavailability of flavonoids in the intestine. It was therefore concluded that R and Q were effective in reducing cholesterol in HepG2 cells in vitro, whereas in vivo, the oral administration of the two flavonoids had little effect on plasma cholesterol in hamsters.

Antimetastatic Potential of Quercetin Analogues with Improved Pharmacokinetic Profile: Pharmacoinformatic Preliminary Study

BACKGROUND

Urokinase-type plasminogen activator (uPA) system is a crucial pathway for tumor invasion and metastasis. Recently, multiple anticancer effects of quercetin have been described, including inhibitory activity against uPA. However, the clinical use of this flavonoid has been limited due to its low oral bioavailability.

OBJECTIVE

The objectives of the study were to assess the antimetastatic potential of quercetin analogues by analyzing their binding affinity for uPA and to select the compounds with improved pharmacological profiles.

METHODS

Binding affinities of structural analogues of quercetin to uPA receptor were determined by molecular docking analysis using Molegro Virtual Docker software, and molecular descriptors relevant for estimating pharmacological profile were calculated from ligand structures using computational models.

RESULTS

Among 44 quercetin analogues, only one quercetin analogue (3,6,2',4',5'-pentahydroxyflavone) was found to possess both higher aqueous solubility and membrane permeability, and a stronger affinity for uPA than quercetin, which makes it the potential lead compound for anticancer drug development. Like quercetin, this compound has five hydroxyl groups but is arranged differently, which contributes to the higher aqueous solubility and higher amphiphilic moment compared to quercetin. Since membrane permeability is not recognized as the limiting factor for quercetin absorption, analogues with higher aqueous solubility and retained or stronger uPA inhibitory activity should also be further experimentally validated for potential therapeutic use.

CONCLUSION

Identified quercetin analogues with better physicochemical and pharmacological properties have a high potential to succeed in later stages of research in biological systems as potential anticancer agents with antimetastatic activity.

Selective separation of main flavonoids by combinational use of ionic liquid-loaded microcapsules from crude extract of Tartary buckwheat

For selective adsorption of main flavonoids from crude Tartary buckwheat extract (rutin, 0.021 mg/mL; quercetin, 0.030 mg/mL; and kaempferol, 0.011 mg/mL), new ionic liquid-based sorbents were successfully prepared by encapsulating [Bmim]Br and [Bmim]Pro in regular spherical non-magnetic and magnetic microcapsules with polysulfone content of 8%, respectively. After appropriate loading process, the microcapsules were comprehensively characterized by infrared spectroscopy, thermogravimetry analysis and scanning electron microscopy. Then the separation strategy was designed to separate rutin and quercetin from kaempferol by combinational use of two kinds of IL-loaded microcapsules (ILLMs). The effects of solid-liquid ratio of ILLMs and extract, pH, time and adsorption temperature were all investigated. The experimental data fit well with the quasi-second-order kinetics model and Langmuir model. After desorption, target flavonoids were well recovered and the ILLMs showed good stability. As the result, a new IL-based separation technology for main flavonoids from food crop was developed for the first time.

Selective β-Mono-Glycosylation of a C15-Hydroxylated Metabolite of the Agricultural Herbicide Cinmethylin Using Leloir Glycosyltransferases

Cinmethylin is a well-known benzyl-ether derivative of the natural terpene 1,4-cineole that is used industrially as a pre-emergence herbicide in grass weed control for crop protection. Cinmethylin detoxification in plants has not been reported, but in animals, it prominently involves hydroxylation at the benzylic C15 methyl group. Here, we show enzymatic β-glycosylation of synthetic 15-hydroxy-cinmethylin to prepare a putative phase II detoxification metabolite of the cinmethylin in plants. We examined eight Leloir glycosyltransferases for reactivity with 15-hydroxy cinmethylin and revealed the selective formation of 15-hydroxy cinmethylin β-d-glucoside from uridine 5'-diphosphate (UDP)-glucose by the UGT71E5 from safflower (Carthamus tinctorius). The UGT71E5 showed a specific activity of 431 mU/mg, about 300-fold higher than that of apple (Malus domestica) UGT71A15 that also performed the desired 15-hydroxy cinmethylin mono-glycosylation. Bacterial glycosyltransferases (OleD from Streptomyces antibioticus, 2.9 mU/mg; GT1 from Bacillus cereus, 60 mU/mg) produced mixtures of 15-hydroxy cinmethylin mono- and disaccharide glycosides. Using UDP-glucose recycling with sucrose synthase, 15-hydroxy cinmethylin conversion with UGT71E5 efficiently provided the β-mono-glucoside (≥95% yield; ∼9 mM) suitable for biological studies.

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.

A Comprehensive Analysis into the Therapeutic Application of Natural Products as SIRT6 Modulators in Alzheimer's Disease, Aging, Cancer, Inflammation, and Diabetes

Natural products have long been used as drugs to treat a wide array of human diseases. The lead compounds discovered from natural sources are used as novel templates for developing more potent and safer drugs. Natural products produce biological activity by binding with biological macromolecules, since natural products complement the protein-binding sites and natural product-protein interactions are already optimized in nature. Sirtuin 6 (SIRT6) is an NAD+ dependent histone deacetylase enzyme and a unique Sirtuin family member. It plays a crucial role in different molecular pathways linked to DNA repair, tumorigenesis, glycolysis, gluconeogenesis, neurodegeneration, cardiac hypertrophic responses, etc. Thus, it has emerged as an exciting target of several diseases such as cancer, neurodegenerative diseases, aging, diabetes, metabolic disorder, and heart disease. Recent studies have shown that natural compounds can act as modulators of SIRT6. In the current review, a list of natural products, their sources, and their mechanisms of SIRT6 activity modulation has been compiled. The potential application of these naturally occurring SIRT6 modulators in the amelioration of major human diseases such as Alzheimer's disease, aging, diabetes, inflammation, and cancer has also been delineated. Natural products such as isoquercetin, luteolin, and cyanidin act as SIRT6 activators, whereas vitexin, catechin, scutellarin, fucoidan, etc. work as SIRT6 inhibitors. It is noteworthy to mention that quercetin acts as both SIRT6 activator and inhibitor depending on its concentration used. Although none of them were found as highly selective and potent modulators of SIRT6, they could serve as the starting point for developing selective and highly potent scaffolds for SIRT6.

Rutin: A Potential Antiviral for Repurposing as a SARS-CoV-2 Main Protease (Mpro) Inhibitor

Various computational studies, including in silico ones, have identified several existing compounds that could serve as effective inhibitors of the SARS-CoV-2 main protease (Mpro), and thus preventing replication of the virus. Among these, rutin has been identified as a potential hit, having prominent binding affinity to the virus. Moreover, its presence in several traditional antiviral medicines prescribed in China to infected patients with mild to moderate symptoms of COVID-19 justify its promise as a repurposed bioactive secondary metabolite against SARS-CoV-2.

Rutin Is a Low Micromolar Inhibitor of SARS-CoV-2 Main Protease 3CLpro: Implications for Drug Design of Quercetin Analogs

The pandemic, due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has stimulated the search for antivirals to tackle COVID-19 infection. Molecules with known pharmacokinetics and already approved for human use have been demonstrated or predicted to be suitable to be used either directly or as a base for a scaffold-based drug design. Among these substances, quercetin is known to be a potent in vitro inhibitor of 3CLpro, the SARS-CoV-2 main protease. However, its low in vivo bioavailability calls for modifications to its molecular structure. In this work, this issue is addressed by using rutin, a natural flavonoid that is the most common glycosylated conjugate of quercetin, as a model. Combining experimental (spectroscopy and calorimetry) and simulation techniques (docking and molecular dynamics simulations), we demonstrate that the sugar adduct does not hamper rutin binding to 3CLpro, and the conjugated compound preserves a high potency (inhibition constant in the low micromolar range, K_i = 11 μM). Although showing a disruption of the pseudo-symmetry in the chemical structure, a larger steric volume and molecular weight, and a higher solubility compared to quercetin, rutin is able to associate in the active site of 3CLpro, interacting with the catalytic dyad (His41/Cys145). The overall results have implications in the drug-design of quercetin analogs, and possibly other antivirals, to target the catalytic site of the SARS-CoV-2 3CLpro.

Therapeutic Potential of Quercetin to Alleviate Endothelial Dysfunction in Age-Related Cardiovascular Diseases

The vascular endothelium occupies a catalog of functions that contribute to the homeostasis of the cardiovascular system. It is a physically active barrier between circulating blood and tissue, a regulator of the vascular tone, a biochemical processor and a modulator of coagulation, inflammation, and immunity. Given these essential roles, it comes to no surprise that endothelial dysfunction is prodromal to chronic age-related diseases of the heart and arteries, globally termed cardiovascular diseases (CVD). An example would be ischemic heart disease (IHD), which is the main cause of death from CVD. We have made phenomenal advances in treating CVD, but the aging endothelium, as it senesces, always seems to out-run the benefits of medical and surgical therapies. Remarkably, many epidemiological studies have detected a correlation between a flavonoid-rich diet and a lower incidence of mortality from CVD. Quercetin, a member of the flavonoid class, is a natural compound ubiquitously found in various food sources such as fruits, vegetables, seeds, nuts, and wine. It has been reported to have a wide range of health promoting effects and has gained significant attention over the years. A growing body of evidence suggests quercetin could lower the risk of IHD by mitigating endothelial dysfunction and its risk factors, such as hypertension, atherosclerosis, accumulation of senescent endothelial cells, and endothelial-mesenchymal transition (EndoMT). In this review, we will explore these pathophysiological cascades and their interrelation with endothelial dysfunction. We will then present the scientific evidence to quercetin's anti-atherosclerotic, anti-hypertensive, senolytic, and anti-EndoMT effects. Finally, we will discuss the prospect for its clinical use in alleviating myocardial ischemic injuries in IHD.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.

Global Gene Expression Profiling Reveals Isorhamnetin Induces Hepatic-Lineage Specific Differentiation in Human Amniotic Epithelial Cells

Human amnion epithelial cells (hAECs), derived from discarded term placenta, is anticipated as a new stem cell resource because of their advantages over embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), such as no risk of tumorigenicity and minimal ethical issue. hAECs have been reported to differentiate into hepatic-like cells (HLCs) with variable functionalities suitable for cell-based therapy of end-stage liver diseases, drug screening, and drug toxicity tests. On the other hand, a new research stream has been evolving to use natural compounds as stimulants of stem cell differentiation because of their high availability and minimum side effects. Isorhamnetin is a naturally occurring flavonoid commonly found in fruits and vegetables and has been reported to improve hepatic fibrosis and steatosis. In this present study, we have screened the differentiation potential of isorhamnetin in hAECs. The cells were grown on 3D cell culture and were treated with 20 μM of synthesized isorhamnetin for 10 days without adding any additional growth factors. DNA microarray global gene expression analysis was conducted for differentially expressed genes between isorhamnetin-treated and untreated control cells, gene expression validation was carried out using RT-qPCR method, and finally, several hepatic functions were assessed. Microarray analysis showed that isorhamnetin could activate essential biological processes, molecular functions, and signaling pathways for hepatic differentiation. Hepatic progenitor markers, EPCAM and DLK1, were upregulated in the isorhamnetin-treated hAECs. AFP was downregulated, while ALB was upregulated on Day 10. Furthermore, isorhamnetin-treated cells could show increased CYP enzyme mRNA levels, ICG uptake and release, glycogen storage activity, and urea secretion. Additionally, isorhamnetin-treated cells did not show any trace of transdifferentiation evident by significant downregulation of several colon- and cholangiocyte-specific markers. However, longer treatment with isorhamnetin did not promote hepatic maturation. Altogether, our findings indicate that isorhamnetin has a promising effect on directing the hepatic-lineage specific differentiation in hAECs.

The Pharmacological Activity, Biochemical Properties, and Pharmacokinetics of the Major Natural Polyphenolic Flavonoid: Quercetin

Flavonoids are a class of natural substances present in plants, fruits, vegetables, wine, bulbs, bark, stems, roots, and tea. Several attempts are being made to isolate such natural products, which are popular for their health benefits. Flavonoids are now seen as an essential component in a number of cosmetic, pharmaceutical, and medicinal formulations. Quercetin is the major polyphenolic flavonoid found in food products, including berries, apples, cauliflower, tea, cabbage, nuts, and onions that have traditionally been treated as anticancer and antiviral, and used for the treatment of allergic, metabolic, and inflammatory disorders, eye and cardiovascular diseases, and arthritis. Pharmacologically, quercetin has been examined against various microorganisms and parasites, including pathogenic bacteria, viruses, and Plasmodium, Babesia, and Theileria parasites. Additionally, it has shown beneficial effects against Alzheimer’s disease (AD), and this activity is due to its inhibitory effect against acetylcholinesterase. It has also been documented to possess antioxidant, antifungal, anti-carcinogenic, hepatoprotective, and cytotoxic activity. Quercetin has been documented to accumulate in the lungs, liver, kidneys, and small intestines, with lower levels seen in the brain, heart, and spleen, and it is extracted through the renal, fecal, and respiratory systems. The current review examines the pharmacokinetics, as well as the toxic and biological activities of quercetin.