Modulation of suppressive activity of lipopolysaccharide-induced nitric oxide production by glycosidation of flavonoids

Production of Four Flavonoid C-Glucosides in Escherichia coli

Flavonoid C-glucosides, which are found in several plant families, are characterized by several biological properties, including antioxidant, anticancer, anti-inflammatory, neuroprotective, hepatoprotective, cardioprotective, antibacterial, antihyperalgesic, antiviral, and antinociceptive activities. The biosynthetic pathway of flavonoid C-glucosides in plants has been elucidated. In the present study, a pathway was introduced to Escherichia coli to synthesize four flavonoid C-glucosides, namely, isovitexin, vitexin, kaempferol 6-C-glucoside, and kaempferol 8-C-glucoside. A five- or six-step metabolic pathway for synthesizing flavonoid aglycones from tyrosine was constructed and two regioselective flavonoid C-glycosyltransferases from Wasabia japonica (WjGT1) and Trollius chinensis (TcCGT) were used. Additionally, the best shikimate gene module construct was selected to maximize the titer of each C-glucoside flavonoid. Isovitexin (30.2 mg/L), vitexin (93.9 mg/L), kaempferol 6-C-glucoside (14.4 mg/L), and kaempferol 8-C-glucoside (38.6 mg/L) were synthesized using these approaches. The flavonoid C-glucosides synthesized in this study provide a basis for investigating and unraveling their novel biological properties.

Modification of flavonoids: methods and influences on biological activities

Flavonoids are important active ingredients in plant-based food, which have many beneficial effects on health. But the low solubility, poor oral bioavailability, and inferior stability of many flavonoids may limit their applications in the food, cosmetics, and pharmaceutical industries. Structural modification can overcome these shortcomings to improve and extend the application of flavonoids. The study of how to modify flavonoids and the influence of various modifications on biological activity have drawn great interest in the current literature. In this review, the working principles and operating conditions of modification methods were summarized along with their potential and limitations in terms of operational safety, cost, and productivity. The influence of various modifications on biological activities and the structure-activity relationships of flavonoids derivatives were discussed and highlighted, which may give guidance for the synthesis of highly effective active agents. In addition, the safety of flavonoids derivatives is reviewed, and future research directions of flavonoid modification research are discussed.

Isoquercetin as an Anti-Covid-19 Medication: A Potential to Realize

Isoquercetin and quercetin are secondary metabolites found in a variety of plants, including edible ones. Isoquercetin is a monoglycosylated derivative of quercetin. When ingested, isoquercetin accumulates more than quercetin in the intestinal mucosa where it is converted to quercetin; the latter is absorbed into enterocytes, transported to the liver, released in circulation, and distributed to tissues, mostly as metabolic conjugates. Physiologically, isoquercetin and quercetin exhibit antioxidant, anti-inflammatory, immuno-modulatory, and anticoagulant activities. Generally isoquercetin is less active than quercetin in vitro and ex vivo, whereas it is equally or more active in vivo, suggesting that it is primarily a more absorbable precursor to quercetin, providing more favorable pharmacokinetics to the latter. Isoquercetin, like quercetin, has shown broad-spectrum antiviral activities, significantly reducing cell infection by influenza, Zika, Ebola, dengue viruses among others. This ability, together with their other physiological properties and their safety profile, has led to the proposition that administration of these flavonols could prevent infection by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), or arrest the progression to severity and lethality of resulting coronavirus disease of 2019 (Covid-19). In silico screening of small molecules for binding affinity to proteins involved SARS-CoV-2 life cycle has repeatedly situated quercetin and isoquercetin near to top of the list of likely effectors. If experiments in cells and animals confirm these predictions, this will provide additional justifications for the conduct of clinical trials to evaluate the prophylactic and therapeutic efficacy of these flavonols in Covid-19.

Flavonoids and intestinal microbes interact to alleviate depression

Flavonoids have a variety of biological activities that are beneficial to human health. However, owing to low bioavailability, most flavonoids exert beneficial effects in the intestine through metabolism by the flora into a variety of structurally different derivatives. Also, flavonoids can modulate the type and structure of intestinal microorganisms to improve human health. It has been reported that the development of depression is accompanied by changes in the type and number of intestinal microorganisms, and gut microbes can significantly improve depressive symptoms through the gut-brain axis. Therefore, the interaction between flavonoids and intestinal microbes to alleviate depression is discussed. © 2021 Society of Chemical Industry.

The Pharmacological Action of Kaempferol in Central Nervous System Diseases: A Review

Kaempferol (KPF) is a flavonoid antioxidant found in fruits and vegetables. Many studies have described the beneficial effects of dietary KPF in reducing the risk of chronic diseases, especially cancer. Nevertheless, little is known about the cellular and molecular mechanisms underlying KPF actions in the central nervous system (CNS). Also, the relationship between KPF structural properties and their glycosylation and the biological benefits of these compounds is unclear. The aim of this study was to review studies published in the PubMed database during the last 10 years (2010–2020), considering only experimental articles that addressed the isolated cell effect of KPF (C₁₅H₁₀O₆) and its derivatives in neurological diseases such as Alzheimer's disease, Parkinson, ischemia stroke, epilepsy, major depressive disorder, anxiety disorders, neuropathic pain, and glioblastoma. 27 publications were included in the present review, which presented recent advances in the effects of KPF on the nervous system. KPF has presented a multipotential neuroprotective action through the modulation of several proinflammatory signaling pathways such as the nuclear factor kappa B (NF-kB), p38 mitogen-activated protein kinases (p38MAPK), serine/threonine kinase (AKT), and β-catenin cascade. In addition, there are different biological benefits and pharmacokinetic behaviors between KPF aglycone and its glycosides. The antioxidant nature of KPF was observed in all neurological diseases through MMP2, MMP3, and MMP9 metalloproteinase inhibition; reactive oxygen species generation inhibition; endogenous antioxidants modulation as superoxide dismutase and glutathione; formation and aggregation of beta-amyloid (β-A) protein inhibition; and brain protective action through the modulation of brain-derived neurotrophic factor (BDNF), important for neural plasticity. In conclusion, we suggest that KPF and some glycosylated derivatives (KPF-3-O-rhamnoside, KPF-3-O-glucoside, KPF-7-O-rutinoside, and KPF-4′-methyl ether) have a multipotential neuroprotective action in CNS diseases, and further studies may make the KPF effect mechanisms in those pathologies clearer. Future in vivo studies are needed to clarify the mechanism of KPF action in CNS diseases as well as the impact of glycosylation on KPF bioactivity.

Comparative study of the effects of diosmin and diosmetin on fat accumulation, dyslipidemia, and glucose intolerance in mice fed a high-fat high-sucrose diet

This study compared the effects of diosmin and its aglycone, diosmetin, on body weight, liver fat, serum cholesterol, and glucose intolerance in male C57BL/6 mice fed a high-fat high-sucrose (HFHS) diet for 12 weeks. The mice were divided into four groups that received the following diets: normal diet (ND), HFHS diet, HFHS diet with 0.5% diosmin, and HFHS diet with 0.5% diosmetin. The body weight increased significantly in the HFHS diet group but decreased significantly in the HFHS diet with 0.5% diosmin group. The diosmin and diosmetin treatment inhibited fat accumulation in liver and epididymal tissues, and improved glucose intolerance by lowering glucose levels during a glucose tolerance test; these effects were greater in the diosmin group than those in the diosmetin group. Furthermore, only diosmin significantly ameliorated dyslipidemia, by reducing TC and LDL-C levels, while diosmetin had little effect on these parameters. Taken together, the results showed that diosmin and diosmetin can prevent fat accumulation and glucose intolerance; however, diosmin was more effective and also showed an antidyslipidemic effect.

Effect of polyphenols from Syringa vulgaris on blood stasis syndrome

In this study, we employed a previously developed in vivo assay system to determine whether the flowers and leaves of Syringa vulgaris (S. vulgaris; commonly known as "lilac") can prevent blood stasis syndrome, known as oketsu in Japanese. This syndrome is considered an important pathology in traditional Chinese and Japanese medicine, and is related to diseases such as peripheral vascular disorders, blood vessel inflammation, and platelet aggregation, whose severities are augmented owing to lipid peroxidation, free radicals, and oxidative stress. The assay system employed in this study monitored the blood flow decrease in the tail vein of mice subjected to sensitization with hen egg white lysozyme. Through bioassay-guided fractionation of different S. vulgaris extracts, five polyphenols were isolated and identified. Among them, quercetine 3-glucoside, quercetin 3-rutinoside, and acteoside were identified as active compounds, as they significantly mitigated blood flow reduction. These findings indicate that the polyphenols obtained from S. vulgaris could be useful for preventing oketsu and improve the quality of life of individuals with disorders and diseases such as gynecopathy, cold sensitivity, poor circulation, allergy, and lifestyle-related diseases.

Enhanced antioxidant, anti-inflammatory and α-glucosidase inhibitory activities of citrus hesperidin by acid-catalyzed hydrolysis

Hesperidin hydrolysates (HHS) was produced by the hydrolysis of hesperidin (HDN) in previous studies. The potential components in HHS were identified by LC-MS, and minor components (MCS) in HHS were isolated. Antioxidant activities by radical-scavenging capacities, reducing capacity and β-carotene-linoleate assay, anti-inflammatory effects by inhibiting NO production of RAW 264.7 cells, and α-glucosidase inhibitory effects of HDN, HHS, MCS and henperetin (HTN) were investigated in present study. HHS showed higher radical scavenging activities, higher reducing capacity, and higher inhibitory activity in the β-carotene-linoleate assay than HDN. HHS inhibited the production of NO and pro-inflammatory cytokines of RAW 264.7 cells more strongly than HDN. HHS also intensively inhibited α-glucosidase activity whereas HDN showed little activity. In addition, the effects of MCS on above activities showed it play a synergistic part with HTN. This work suggested that hydrolyzation of HDN enhance the activities, and provided valuable information on effective utilization of HDN.

Identification of secondary metabolites in Averrhoa carambola L. bark by high-resolution mass spectrometry and evaluation for α-glucosidase, tyrosinase, elastase, and antioxidant potential

In this study, paper spray ionization (PSI) coupled to high-resolution mass spectrometry has been used to identify secondary metabolites from ethanol extracts of Averrhoa carambola L. bark (ABE). Various phytoconstituents including phenolic acids, flavonoids, xanthones and terpenoids were identified from the bark. ABE shows potential antioxidant activity as well as markedly inhibited α-glucosidase, elastase, and tyrosinase enzyme activities in a concentration-dependent fashion, respectively. ABE significantly inhibited α-glucosidase at lower concentration (IC₅₀: 7.15 ± 0.06 μg/mL). Identified compounds were tested to understand the biological activity of ABE. Experimental results suggest that norathyriol, one of the identified compounds, has significant α-glucosidase (IC₅₀: 0.81 ± 0.01 μg/mL) inhibition and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities (IC₅₀: 4.90 ± 0.09 μg/mL). At a dose of 100 mg/kg, ABE significantly decreased the postprandial blood glucose level in oral glucose tolerance test (OGTT). This study shows that carambola bark can be a potential source of bioactive compounds.

Effect of polyphenols from Syringa vulgaris on blood stasis syndrome

In this study, we employed a previously developed in vivo assay system to determine whether the flowers and leaves of Syringa vulgaris (S. vulgaris; commonly known as "lilac") can prevent blood stasis syndrome, known as oketsu in Japanese. This syndrome is considered an important pathology in traditional Chinese and Japanese medicine, and is related to diseases such as peripheral vascular disorders, blood vessel inflammation, and platelet aggregation, whose severities are augmented owing to lipid peroxidation, free radicals, and oxidative stress. The assay system employed in this study monitored the blood flow decrease in the tail vein of mice subjected to sensitization with hen egg white lysozyme. Through bioassay-guided fractionation of different S. vulgaris extracts, five polyphenols were isolated and identified. Among them, quercetine 3-glucoside, quercetin 3-rutinoside, and acteoside were identified as active compounds, as they significantly mitigated blood flow reduction. These findings indicate that the polyphenols obtained from S. vulgaris could be useful for preventing oketsu and improve the quality of life of individuals with disorders and diseases such as gynecopathy, cold sensitivity, poor circulation, allergy, and lifestyle-related diseases.

The tiliroside derivative, 3-O-[(E)-(2-oxo-4-(p-tolyl) but-3-en-1-yl] kaempferol produced inhibition of neuroinflammation and activation of AMPK and Nrf2/HO-1 pathways in BV-2 microglia

Neuroinflammation is now widely accepted as an important pathophysiological mechanism in neurodegenerative disorders, thus providing a critical target for novel compounds. In this study, 3-O-[(E)-(2-oxo-4-(p-tolyl)but-3-en-1-yl] kaempferol (OTBK) prevented the production of pro-inflammatory mediators TNFα, IL-6, PGE₂ and nitrite from BV-2 microglia activated with LPS and IFNγ. These effects were accompanied by reduction in the levels of pro-inflammatory proteins COX-2 and iNOS. Involvement of NF-κB in the anti-inflammatory activity of OTBK was evaluated in experiments showing that the compound prevented phosphorylation, nuclear accumulation and DNA binding of p65 sub-unit induced by stimulation of BV-2 microglia with LPS and IFNγ. Exposure of mouse hippocampal HT22 neurons to conditioned media from LPS + IFNγ-stimulated BV-2 cells resulted in reduced cell viability and generation of cellular reactive oxygen species. Interestingly, conditioned media from LPS/IFNγ-stimulated BV-2 cells which were treated with OTBK did not induce neuronal damage or oxidative stress. OTBK was shown to increase protein levels of phospho-AMPKα, Nrf2 and HO-1 in BV-2 microglia. It was further revealed that OTBK treatment increased Nrf2 DNA binding in BV-2 microglia. The actions of the compound on AMPKα and Nrf2 were shown to contribute to its anti-inflammatory activity as demonstrated by diminished activity in the presence of the AMPK antagonist dorsomorphin and Nrf2 inhibitor trigonelline. These results suggest that OTBK inhibits neuroinflammation through mechanisms that may involve activation of AMPKα and Nrf2 in BV-2 microglia.

Structural characterization and screening of chemical markers of flavonoids in Lysimachiae Herba and Desmodii Styracifolii Herba by ultra high-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry based metabolomics approach

In traditional Chinese medicine, Lysimachiae Herba (LH) and Desmodii Styracifolii Herba (DSH) have been widely used for the treatment of calculi, but there is a certain focus in clinical application. Flavonoids as their pharmacologically active substances were focusly studied to make clear of their chemical compositions and reveal the similarities and differences between LH and DHS by analysis of characteristic marker components at the molecular level. An ultra high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS/MS) approach based on metabolite profiling was established. The high-resolution data was acquired through data dependent acquisition (DDA) mode. Based on the targeted and untargeted analytical strategies, a total of 113 compounds were identified, of which 80 compounds existed in LH and 61 in DSH. Then multivariate statistical analysis was applied to further find the characteristic marker components, and a total number of 21 variables were screened as the valuable variables for discrimination. By matching with identified flavonoids, these 21 variables were corresponding to 15 flavonoids (including 6 from LH and 9 from DSH) which were firstly identified as the marker compounds. These results indicated that the UPLC-QTOF-MS/MS method with analysis strategy was a powerful tool for rapidly identification and screening of marker compounds of flavonoids between LH and DSH, and the 15 screened marker compounds provide a chemical basis for the further researches on the mechanisms of LH and DSH in the treatment of cholelithiasis and nephrolithiasis respectively.

Dietary flavonoid aglycones and their glycosides: Which show better biological significance?

The dietary flavonoids, especially their glycosides, are the most vital phytochemicals in diets and are of great general interest due to their diverse bioactivity. The natural flavonoids almost all exist as their O-glycoside or C-glycoside forms in plants. In this review, we summarized the existing knowledge on the different biological benefits and pharmacokinetic behaviors between flavonoid aglycones and their glycosides. Due to various conclusions from different flavonoid types and health/disease conditions, it is very difficult to draw general or universally applicable comments regarding the impact of glycosylation on the biological benefits of flavonoids. It seems as though O-glycosylation generally reduces the bioactivity of these compounds - this has been observed for diverse properties including antioxidant activity, antidiabetes activity, anti-inflammation activity, antibacterial, antifungal activity, antitumor activity, anticoagulant activity, antiplatelet activity, antidegranulating activity, antitrypanosomal activity, influenza virus neuraminidase inhibition, aldehyde oxidase inhibition, immunomodulatory, and antitubercular activity. However, O-glycosylation can enhance certain types of biological benefits including anti-HIV activity, tyrosinase inhibition, antirotavirus activity, antistress activity, antiobesity activity, anticholinesterase potential, antiadipogenic activity, and antiallergic activity. However, there is a lack of data for most flavonoids, and their structures vary widely. There is also a profound lack of data on the impact of C-glycosylation on flavonoid biological benefits, although it has been demonstrated that in at least some cases C-glycosylation has positive effects on properties that may be useful in human healthcare such as antioxidant and antidiabetes activity. Furthermore, there is a lack of in vivo data that would make it possible to make broad generalizations concerning the influence of glycosylation on the benefits of flavonoids for human health. It is possible that the effects of glycosylation on flavonoid bioactivity in vitro may differ from that seen in vivo. With in vivo (oral) treatment, flavonoid glycosides showed similar or even higher antidiabetes, anti-inflammatory, antidegranulating, antistress, and antiallergic activity than their flavonoid aglycones. Flavonoid glycosides keep higher plasma levels and have a longer mean residence time than those of aglycones. We should pay more attention to in vivo benefits of flavonoid glycosides, especially C-glycosides.

Chemical basis for the disparate neuroprotective effects of the anthocyanins, callistephin and kuromanin, against nitrosative stress

Oxidative and nitrosative stress are major factors in neuronal cell death underlying neurodegenerative disease. Thus, supplementation of antioxidant defenses may be an effective therapeutic strategy for diseases such as amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease. In this regard, treatment with nutraceutical antioxidants has garnered increasing attention; however, the differential neuroprotective effects of structurally similar nutraceuticals, which may affect their suitability as therapeutic agents, has not been directly examined. In this study we compare the ability of two anthocyanins, callistephin (pelargonidin-3-O-glucoside) and kuromanin (cyanidin-3-O-glucoside) to protect cerebellar granule neurons from damage induced by either oxidative or nitrosative stress. These anthocyanins differ by the presence of a single hydroxyl group on the B-ring of kuromanin, forming a catechol moiety. While both compounds protected neurons from oxidative stress induced by glutamate excitotoxicity, a stark contrast was observed under conditions of nitrosative stress. Only kuromanin displayed the capacity to defend neurons from nitric oxide (NO)-induced apoptosis. This protective effect was blocked by addition of Cu, Zn-superoxide dismutase, indicating that the neuroprotective mechanism is superoxide dependent. Based on these observations, we suggest a unique mechanism by which slight structural variances, specifically the absence or presence of a catechol moiety, lend kuromanin the unique ability to generate superoxide, which acts as a scavenger of NO. These findings indicate that kuromanin and compounds that share similar chemical characteristics may be more effective therapeutic agents for treating neurodegenerative diseases than callistephin and related (non-catechol) compounds.

Quercetin-3-O-β-D-Glucuronide Suppresses Lipopolysaccharide-Induced JNK and ERK Phosphorylation in LPS-Challenged RAW264.7 Cells

Quercetin, a flavonol, has been reported to exhibit a wide range of biological properties including anti-oxidant and anti-inflammatory activities. However, pharmacological properties of quercetin-3-O-β-D-glucuronide (QG), a glycoside derivative of quercetin, have not been extensively examined. The objective of this study is to elucidate the anti-inflammatory property and underlying mechanism of QG in lipopolysaccharide (LPS)-challenged RAW264.7 macrophage cells in comparison with quercetin. QG significantly suppressed LPS-induced extracellular secretion of pro-inflammatory mediators such as nitric oxide (NO) and PGE₂, and pro-inflammatory protein expressions of iNOS and COX-2. To elucidate the underlying mechanism of the anti-inflammatory property of QG, involvement of MAPK signaling pathways was examined. QG significantly attenuated LPS-induced activation of JNK and ERK in concentration-dependent manners with a negligible effect on p38. In conclusion, the present study demonstrates QG exerts anti-inflammatory activity through the suppression of JNK and ERK signaling pathways in LPS-challenged RAW264.7 macrophage cells.

WITHDRAWN: The paradox of natural flavonoid C-glycosides and health benefits: When more occurrence is less research

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Flavonoids are inhibitors of human organic anion transporter 1 (OAT1)-mediated transport

Organic anion transporter 1 (OAT1) has been reported to be involved in the nephrotoxicity of many anionic xenobiotics. As current clinically used OAT1 inhibitors are often associated with safety issues, identifying potent OAT1 inhibitors with little toxicity is of great value in reducing OAT1-mediated drug nephrotoxicity. Flavonoids are a class of polyphenolic compounds with exceptional safety records. Our objective was to evaluate the effects of 18 naturally occurring flavonoids, and some of their glycosides, on the uptake of para-aminohippuric acid (PAH) in both OAT1-expressing and OAT1-negative LLC-PK1 cells. Most flavonoid aglycones produced substantial decreases in PAH uptake in OAT1-expressing cells. Among the flavonoids screened, fisetin, luteolin, morin, and quercetin exhibited the strongest effect and produced complete inhibition of OAT1-mediated PAH uptake at a concentration of 50 μM. Further concentration-dependent studies revealed that both morin and luteolin are potent OAT1 inhibitors, with IC50 values of <0.3 and 0.47 μM, respectively. In contrast to the tested flavonoid aglycones, all flavonoid glycosides had negligible or small effects on OAT1. In addition, the role of OAT1 in the uptake of fisetin, luteolin, morin, and quercetin was investigated and fisetin was found to be a substrate of OAT1. Taken together, our results indicate that flavonoids are a novel class of OAT1 modulators. Considering the high consumption of flavonoids in the diet and in herbal products, OAT1-mediated flavonoid-drug interactions may be clinically relevant. Further investigation is warranted to evaluate the nephroprotective role of flavonoids in relation to drug-induced nephrotoxicity mediated by the OAT1 pathway.

WITHDRAWN: Flavonoid glycosylation and biological benefits

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Avicularin Inhibits Lipopolysaccharide-Induced Inflammatory Response by Suppressing ERK Phosphorylation in RAW 264.7 Macrophages

suppresAvicularin, quercetin-3-α-L-arabinofuranoside, has been reported to possess diverse pharmacological properties such as anti-inflammatory and anti-infectious effects. However, the underlying mechanism by which avicularin exerts its anti-inflammatory activity has not been clearly demonstrated. This study aimed to elucidate the anti-inflammatory mechanism of avicularin in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells. Avicularin significantly inhibited LPS-induced excessive production of pro-inflammatory mediators such as nitric oxide (NO) and PGE₂ and the protein levels of iNOS and COX-2, which are responsible for the production of NO and PGE₂, respectively. Avicularin also suppressed LPS-induced overproduction of pro-inflammatory cytokine IL-1β. Furthermore, avicularin significantly suppressed LPS-induced degradation of IκB, which retains NF-κB in the cytoplasm, consequently inhibiting the transcription of pro-inflammatory genes by NF-κB in the nucleus. To understand the underlying signaling mechanism of anti-inflammatory activity of avicularin, involvement of multiple kinases was examined. Avicularin significantly attenuated LPS-induced activation of ERK signaling pathway in a concentration-dependent manner. Taken together, the present study clearly demonstrates that avicularin exhibits anti-inflammatory activity through the suppression of ERK signaling pathway in LPS-stimulated RAW 264.7 macrophage cells.

The multiple faces of quercetin in neuroprotection

This review discusses the most recent data on the potential of quercetin to confer neuroprotection. Unfortunately, most of the in vitro studies have used quercetin aglycone, which is not detectable in the plasma or in the brain after oral intake. Moreover, quercetin metabolites and glycosides seem to be less neuroprotective and penetrate the BBB less efficiently than aglycone. Surprisingly, quercetin has beneficial effects on various in vivo models of neural disorders, particularly in cerebrovascular insults; contrasting data also do exist. This may be due to an increase of BBB permeability, described in many of these animal models, which would facilitate quercetin brain penetration. Although quercetin causes no significant toxicity in several animal studies, the risk for neurotoxicity is not negligible because of its narrow therapeutic dose-range in vitro. Notably, this risk may be even higher in the case of increased quercetin access to the brain, which may occur pathologically or artificially (e.g., by liposomal preparations). Based on the referred literature, we doubt that quercetin possesses any significant efficacy in neurodegenerative disorders. Instead, therapeutic trials should focus more on the quercetin efficacy in cerebrovascular insults rather than neurodegeneration.

Neuroprotection of nicotiflorin in permanent focal cerebral ischemia and in neuronal cultures

Nicotiflorin is a single component extracted from traditional Chinese medicine Flos Carthami. In this study, we investigated its neuroprotection in permanent focal cerebral ischemia model in rats, and in an in vitro model of ischemia. At doses of 2.5, 5 and 10 mg/kg, nicotiflorin administered immediately after the onset of ischemia markedly reduced brain infarct volume and neurological deficits. For primarily cultured neurons suffered 2 h hypoxia followed by 24 h reoxygenation, nicotiflorin significantly attenuated cell death and reduced LDH release. Morphological observation also directly confirmed its protective effect on neuron. These results provided strong pharmacological basis for its potential therapeutic role in cerebral ischemic illness.

Flavonoids as a novel class of human organic anion-transporting polypeptide OATP1B1 (OATP-C) modulators

Flavonoids are a class of polyphenolic compounds widely present in the diet and herbal products. The interactions of flavonoids with some major efflux transporters [e.g., P-glycoprotein, multidrug resistance-associated protein 1 (MRP1), and breast cancer resistance protein] have been reported; however, their interactions with uptake transporters are largely unknown. Organic anion-transporting polypeptide OATP1B1 is a liver-specific uptake transporter important in hepatic drug disposition. Our objective was to evaluate the effects of 20 naturally occurring flavonoids, and some of their corresponding glycosides, on the uptake of [3H]dehydroepiandrosterone sulfate (DHEAS) in OATP1B1-expressing and OATP1B1-negative HeLa cells. Many of the tested flavonoids (including biochanin A, genistein, and epigallocatechin-3-gallate) significantly inhibited [3H]DHEAS uptake in a concentration-dependent manner in OATP1B1-expressing cells, with biochanin A being one of the most potent inhibitors with an IC50 of 11.3 +/- 3.22 microM. The flavonoids had negligible or small effects in OATP1B1-negative cells. Four of the eight pairs of tested flavonoids and their glycosides, namely, genistein/genistin, diosmetin/diosmin, epigallocatechin/epigallocatechin-3-gallate, and quercetin/rutin, exhibited distinct effects on [3H]DHEAS uptake. For example, genistin did not inhibit DHEAS uptake, whereas genistein did, and rutin stimulated uptake, whereas quercetin had no effect. [3H]Biochanin A uptake was similar in OATP1B1-expressing and OATP1B1-negative cells, suggesting that it is not a substrate for OATP1B1. A kinetic study revealed that biochanin A inhibited [3H]DHEAS uptake in a noncompetitive manner, with a Ki of 10.2 +/- 1.89 microM. Taken together, these results indicate that flavonoids are a novel class of OATP1B1 modulators, suggesting the potential for diet-drug interactions.