Akt is a direct target for myricetin to inhibit cell transformation

Fisetin is a selective adenosine triphosphate-competitive inhibitor for mitogen-activated protein kinase kinase 4 to inhibit lipopolysaccharide-stimulated inflammation

The mitogen-activated protein kinase kinase 4 (MKK4), a member of the MAP kinase kinase family, directly phosphorylates and activates the c-Jun NH2-terminal kinases (JNK), in response to proinflammatory cytokines and cellular stresses. Regulation of the MKK4 activity is considered to be a novel approach for the prevention and treatment of inflammation. The aim of this study was to identify whether fisetin, a potential anti-inflammatory compound, targets MKK4-JNK cascade to inhibit lipopolysaccharide (LPS)-stimulated inflammatory response. RAW264 macrophage pretreated with fisetin following LPS stimulation was used as a cell model to investigate the transactivation and expression of related-inflammatory genes by transient transfection assay, electrophoretic mobility shift assay (EMSA), or enzyme-linked immunosorbent assay (ELISA), and cellular signaling as well as binding of related-signal proteins by Western blot, pull-down assay and kinase assay, and molecular modeling. The transactivation and expression of cyclooxygenase-2 (COX-2) gene as well as prostaglandin E2 (PGE2) secretion induced by LPS were inhibited by fisetin in a dose-dependent manner. Signaling transduction analysis demonstrated that fisetin selectively inhibited MKK4-JNK1/2 signaling to suppress the phosphorylation of transcription factor AP-1 without affecting the NF-κB and Jak2-Stat3 signaling as well as the phosphorylation of Src, Syk, and TAK1. Furthermore, in vitro and ex vivo pull-down assay using cell lysate or purified protein demonstrated that fisetin could bind directly to MKK4. Molecular modeling using the Molecular Operating Environment™ software indicated that fisetin docked into the ATP-binding pocket of MKK4 with a binding energy of -71.75 kcal/mol and formed a 1.70 Å hydrogen bound with Asp247 residue of MKK4. The IC50 of fisetin against MKK4 was estimated as 2.899 μM in the kinase assay, and the ATP-competitive effect was confirmed by ATP titration. Taken together, our data revealed that fisetin is a potent selective ATP-competitive MKK4 inhibitor to suppress MKK4-JNK1/2-AP-1 cascade for inhibiting LPS-induced inflammation.

Myricetin, a natural inhibitor of CD147, increases sensitivity of cisplatin in ovarian cancer

BACKGROUND

Ovarian cancer (OC) is the most lethal gynecological tumor, but it currently lacks effective therapeutic targets. CD147, which is overexpressed in OC, plays a crucial role in promoting malignant progression and is associated with poor prognosis in patients. Therefore, CD147 has been identified as a potential therapeutic target. However, there is a limited amount of research on the development of CD147 inhibitors.

METHODS

Surface plasmon resonance (SPR) assay and virtual molecular docking analysis were performed to identify potential natural compounds targeting CD147. The anti‑tumor effects of myricetin were evaluated using various assays, including CCK8, Alkaline comet, immunofluorescence and xenograft mouse models. The underlying mechanism was investigated through western blot analysis and lentivirus short hairpin RNA (LV-shRNA) transfection.

RESULTS

Myricetin, a flavonoid commonly found in plants, was discovered to be a potent inhibitor of CD147. Our findings demonstrated that myricetin exhibited a strong affinity for CD147 and down-regulated the protein level of CD147 by facilitating its proteasome-dependent degradation. Additionally, we observed synergistic antitumor effects of myricetin and cisplatin both in vivo and in vitro. Mechanistically, myricetin suppressed the expression of FOXM1 and its downstream DNA damage response (DDR) genes E×O1and BRIP1, thereby enhancing the DDR induced by cisplatin.

CONCLUSION

Our data demonstrate that myricetin, a natural inhibitor of CD147, may have clinical utility in the treatment of OC due to its ability to increase genomic toxicity when combined with cisplatin.

Flavonoid Myricetin as Potent Anticancer Agent: A Possibility towards Development of Potential Anticancer Nutraceuticals

Good nutrition plays a crucial role in maintaining a balanced lifestyle. The beneficial effects of nutrition have been found to counteract nutritional disturbances with the expanded use of nutraceuticals to treat and manage cardiovascular diseases, cancer, and other developmental defects over the last decade. Flavonoids are found abundantly in plant-derived foods such as fruits, vegetables, tea, cocoa, and wine. Fruits and vegetables contain phytochemicals like flavonoids, phenolics, alkaloids, saponins, and terpenoids. Flavonoids can act as anti-inflammatory, anti-allergic, anti-microbial (antibacterial, antifungal, and antiviral) antioxidant, anti-cancer, and anti-diarrheal agents. Flavonoids are also reported to upregulate apoptotic activity in several cancers such as hepatic, pancreatic, breast, esophageal, and colon. Myricetin is a flavonol which is naturally present in fruits and vegetables and has shown possible nutraceutical value. Myricetin has been portrayed as a potent nutraceutical that may protect against cancer. The focus of the present review is to present an updated account of studies demonstrating the anticancer potential of myricetin and the molecular mechanisms involved therein. A better understanding of the molecular mechanism(s) underlying its anticancer activity would eventually help in its development as a novel anticancer nutraceutical having minimal side effects.

Target discovery of bioactive natural products with native-compound-coupled CNBr-activated Sepharose 4B beads (NCCB): Applications, mechanisms and outlooks

Natural products (NPs) represent a treasure trove for drug discovery and development due to their chemical structural diversity and a broad spectrum of biological activities. Uncovering the biological targets and understanding their molecular mechanism of actions are crucial steps in the development of clinical therapeutics. However, the structural complexity of NPs and intricate nature of biological system present formidable challenges in target identification of NPs. Although significant advances have been made in the development of new chemical tools, these methods often require high levels of synthetic skills for preparing chemical probes. This can be costly and time-consuming relaying on operationally complicated procedures and instruments. In recent efforts, we and others have successfully developed an operationally simple and practical chemical tool known as native-compound-coupled CNBr-activated Sepharose 4B beads (NCCB) for NP target identification. In this approach, a native compound readily reacts with commercial CNBr-activated Sepharose 4B beads with a process that is easily performed in any biology laboratory. Based on NCCB, our group has identified the direct targets of more than 60 NPs. In this review, we will elucidate the application scopes, including flavonoids, quinones, terpenoids and others, characteristics, chemical mechanisms, procedures, advantages, disadvantages, and future directions of NCCB in specific target discovery.

Myricetin attenuates hypoxia-induced inflammation in human adipocytes

BACKGROUND

Adipose tissue hypoxia plays a crucial role in the development of chronic low-grade systemic inflammation which has been associated with the pathogenesis of obesity-related diseases. Myricetin is a natural compound present in numerous plant-based foods with presumed anti-inflammatory and beneficial health effects. The impact of this flavonoid on hypoxia-induced expression of inflammatory adipokines and hypoxia-regulated pathways is unknown so far and has been addressed in the present study.

METHODS

Differentiated human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes were cultured with or without myricetin under normoxic and hypoxic conditions for varying time periods. The effect of hypoxia and myricetin on the expression of the investigated adipokines was measured by real-time RT-PCR. Western blot analysis was used for the detection of transcription factors involved in hypoxia-regulated pathways.

RESULTS

Myricetin interfered in the hypoxia-induced regulation of adipokines and the underlying pathways, which are involved in transmitting the inflammatory response. It strongly repressed hypoxia-induced expression of apelin, leptin, chemerin, asprosin, and DPP-4 and HIF-1α accumulation in the nucleus was diminished. Furthermore, the activation of the key regulators in the inflammatory response NF-κB, Akt, and CREB was suppressed by myricetin under hypoxic conditions. Myricetin also decreased hypoxia-induced accumulation of the pro-tumorigenic transcription factors Snail and Slug in the nucleus.

CONCLUSION

Taken together, our results indicated that myricetin regulated hypoxia-induced expression of adipokines and hypoxia-regulated pathways in human adipocytes. Our study therefore provided evidence of the anti-inflammatory effects of myricetin in hypoxia-treated human adipocytes.

Myricetin: targeting signaling networks in cancer and its implication in chemotherapy

The gaps between the complex nature of cancer and therapeutics have been narrowed down due to extensive research in molecular oncology. Despite gathering massive insight into the mysteries of tumor heterogeneity and the molecular framework of tumor cells, therapy resistance and adverse side effects of current therapeutic remain the major challenge. This has shifted the attention towards therapeutics with less toxicity and high efficacy. Myricetin a natural flavonoid has been under the spotlight for its anti-cancer, anti-oxidant, and anti-inflammatory properties. The cutting-edge molecular techniques have shed light on the interplay between myricetin and dysregulated signaling cascades in cancer progression, invasion, and metastasis. However, there are limited data available regarding the nano-delivery platforms composed of myricetin in cancer. In this review, we have provided a comprehensive detail of myricetin-mediated regulation of different cellular pathways, its implications in cancer prevention, preclinical and clinical trials, and its current available nano-formulations for the treatment of various cancers.

Recent advances in research on vine tea, a potential and functional herbal tea with dihydromyricetin and myricetin as major bioactive compounds

Vine tea has been used as an herbal tea by several ethnic minorities for hundreds of years in China. Flavonoids, a kind of indispensable component in a variety of nutraceutical, pharmaceutical and cosmetic applications, are identified to be the major metabolites and bioactive ingredients in vine tea. Interestingly, vine tea exhibits a wide range of significant bioactivities including anti-oxidant, anti-inflammatory, anti-tumor, antidiabetic, neuroprotective and other activities, but no toxicity. These bioactivities, to some extent, enrich the understanding about the role of vine tea in disease prevention and therapy. The health benefits of vine tea, particularly dihydromyricetin and myricetin, are widely investigated. However, there is currently no comprehensive review available on vine tea. Therefore, this report summarizes the most recent studies investigating bioactive constituents, pharmacological effects and possible mechanisms of vine tea, which will provide a better understanding about the health benefits and preclinical assessment of novel application of vine tea.

Crocetin Exerts Its Anti-inflammatory Property in LPS-Induced RAW264.7 Cells Potentially via Modulation on the Crosstalk between MEK1/JNK/NF-κB/iNOS Pathway and Nrf2/HO-1 Pathway

Crocetin is a main bioactive component with a carotenoid skeleton in Gardenia jasminoides, a typical traditional Chinese medicine with a long history in Southeast Asia. Crocetin is being commonly consumed as spices, dyes, and food colorants. Recent pharmacological studies had implied that crocetin may possess potent anti-inflammatory properties; however, the underlying molecular mechanism is not fully elucidated. In the present study, the regulatory effect of crocetin on redox balance was systematically investigated in lipopolysaccharide- (LPS-) stimulated RAW264.7 cells. The results showed that crocetin dose-dependently inhibited LPS-induced nitric oxide production and inducible nitric oxide synthase (iNOS) expression in RAW264.7 cells. Molecular data revealed that crocetin exerted its anti-inflammatory property by inhibiting the MEK1/JNK/NF-κB/iNOS pathway and activating the Nrf2/HO-1 pathway. The shRNA-knockdown (KD) of MEK1 and ERK1 confirmed that the activation of MEK1 and inhibition of JNK mediated the anti-inflammatory effect of crocetin. Moreover, the pull-down assay and computational molecule docking showed that crocetin could directly bind to MEK1 and JNK1/2. It is noticed that both KD and knockout (KO) of HO-1 gene blocked this action. More detailed data have shown that HO-1-KO blocked the inhibition of p-IκB-α by crocetin. These data indicated that crocetin exerted its anti-inflammatory property via modulating the crosstalk between the MEK1/JNK/NF-κB/iNOS pathway and the Nrf2/HO-1 pathway, highlighting HO-1 as a major player. Therefore, the present study reveals that crocetin can act as a potential candidate for redox-balancing modulation in charge of its anti-inflammatory and chemopreventive effect, which strengthens its potency in the subsequent clinic application in the near future.

Real-Time Analysis of Polyphenol-Protein Interactions by Surface Plasmon Resonance Using Surface-Bound Polyphenols

A selection of bioactive polyphenols of different structural classes, such as the ellagitannins vescalagin and vescalin, the flavanoids catechin, epicatechin, epigallocatechin gallate (EGCG), and procyanidin B2, and the stilbenoids resveratrol and piceatannol, were chemically modified to bear a biotin unit for enabling their immobilization on streptavidin-coated sensor chips. These sensor chips were used to evaluate in real time by surface plasmon resonance (SPR) the interactions of three different surface-bound polyphenolic ligands per sensor chip with various protein analytes, including human DNA topoisomerase IIα, flavonoid leucoanthocyanidin dioxygenase, B-cell lymphoma 2 apoptosis regulator protein, and bovine serum albumin. The types and levels of SPR responses unveiled major differences in the association, or lack thereof, and dissociation between a given protein analyte and different polyphenolic ligands. Thus, this multi-analysis SPR technique is a valuable methodology to rapidly screen and qualitatively compare various polyphenol-protein interactions.

Neurotoxic Effect of Flavonol Myricetin in the Presence of Excess Copper

Oxidative stress (OS) induced by the disturbed homeostasis of metal ions is one of the pivotal factors contributing to neurodegeneration. The aim of the present study was to investigate the effects of flavonoid myricetin on copper-induced toxicity in neuroblastoma SH-SY5Y cells. As determined by the MTT method, trypan blue exclusion assay and measurement of ATP production, myricetin heightened the toxic effects of copper and exacerbated cell death. It also increased copper-induced generation of reactive oxygen species, indicating the prooxidative nature of its action. Furthermore, myricetin provoked chromatin condensation and loss of membrane integrity without caspase-3 activation, suggesting the activation of both caspase-independent programmed cell death and necrosis. At the protein level, myricetin-induced upregulation of PARP-1 and decreased expression of Bcl-2, whereas copper-induced changes in the expression of p53, p73, Bax and NME1 were not further affected by myricetin. Inhibitors of ERK1/2 and JNK kinases, protein kinase A and L-type calcium channels exacerbated the toxic effects of myricetin, indicating the involvement of intracellular signaling pathways in cell death. We also employed atomic force microscopy (AFM) to evaluate the morphological and mechanical properties of SH-SY5Y cells at the nanoscale. Consistent with the cellular and molecular methods, this biophysical approach also revealed a myricetin-induced increase in cell surface roughness and reduced elasticity. Taken together, we demonstrated the adverse effects of myricetin, pointing out that caution is required when considering powerful antioxidants for adjuvant therapy in copper-related neurodegeneration.

Dual Inhibitors as a New Challenge for Cancer Multidrug Resistance Treatment

BACKGROUND

Dual-targeting in cancer treatment by a single drug is an unconventional approach in relation to drug combinations. The rationale for the development of dualtargeting agents is to overcome incomplete efficacy and drug resistance frequently present when applying individual targeting agents. Consequently, -a more favorable outcome of cancer treatment is expected with dual-targeting strategies.

METHODS

We reviewed the literature, concentrating on the association between clinically relevant and/or novel dual inhibitors with the potential to modulate multidrug resistant phenotype of cancer cells, particularly the activity of P-glycoprotein. A balanced analysis of content was performed to emphasize the most important findings and optimize the structure of this review.

RESULTS

Two-hundred and forty-five papers were included in the review. The introductory part was interpreted by 9 papers. Tyrosine kinase inhibitors' role in the inhibition of Pglycoprotein and chemosensitization was illustrated by 87 papers. The contribution of naturalbased compounds in overcoming multidrug resistance was reviewed using 92 papers, while specific dual inhibitors acting against microtubule assembling and/or topoisomerases were described with 55 papers. Eleven papers gave an insight into a novel and less explored approach with hybrid drugs. Their influence on P-glycoprotein and multidrug resistance was also evaluated.

CONCLUSION

These findings bring into focus rational anticancer strategies with dual-targeting agents. Most evaluated synthetic and natural drugs showed a great potential in chemosensitization. Further steps in this direction are needed for the optimization of anticancer treatment.

Myricetin inhibits panel of kinases implicated in tumorigenesis

Myricetin is a flavonoid with several biological properties, including antioxidant and anti-inflammatory features. Its protective effect in chronic diseases may occur through the inhibition of protein kinases that trigger inflammation and carcinogenesis pathways. Considering the influence of kinases on such pathological disorders, it is crucial to study compounds that inhibit these proteins. This study aims to evaluate the inhibitory potential of 14 flavonoids on TNF-α release in human whole blood as well as the inhibitory potential of myricetin towards kinases involved in tumorigenesis. Our results showed that, out of all flavonoids, myricetin had the highest inhibitory effect on TNF-α level. In addition, myricetin showed potential as a multi-anti-kinase compound, reducing the activity of 7 kinases by >70% and of 9 kinases by >90%. Together these data demonstrate the great inhibitory activity of myricetin on tumorigenic kinases and potential for the development of new therapeutics.

The protective effect of some Thai plants and their bioactive compounds in UV light-induced skin carcinogenesis

Skin cancer, represents a major public health concern. While the vast majority is non-melanoma skin cancers, melanomas are mostly responsible for mortality. Solar UVB radiation is mutagenic and carcinogenic. It is primarily responsible for both non-melanoma and melanoma skin cancers via excessive production of reactive oxygen species (ROS), which mediate changes in inflammation and immunity, and have been implicated in all three stages of skin cancer development. Due to their regulatory role in numerous functions of cells, signaling pathways are targets for chemoprevention. The current standards in melanoma therapy are targeted and combination therapies, which, albeit prolong survival responses, are still prone to development of drug resistance. To this extent, drugs of natural origin continue to spark great interest. Thailand has a rich biodiversity of indigenous flora, which have traditionally been used to treat a variety of pathologies. The active components in plant extracts that have medicinal properties, termed 'bioactive compounds,' are efficient chemopreventive agents due to their antioxidant, antimutagenic, anticarcinogenic, and carcinogen detoxification properties. Thai plants and their bioactive compounds have shown protective effects on UV light-induced skin cancer in different experimental models. This warrants further in vivo investigations and translation to clinical studies to determine efficacy and safety, for use as lead compounds in targeted/combination therapy or adjuvant therapy with existing regimes. Coupled with a strategy for prevention, this offers a promising outlook for protection against photocarcinogenesis.

Quercetin: A functional dietary flavonoid with potential chemo-preventive properties in colorectal cancer

Recently, an intense attention has been paid to the application of natural compounds as a novel therapeutic strategy for cancer treatment. Quercetin, a natural flavonol present in many commonly consumed food items, is widely demonstrated to exert inhibitory effects on cancer progression through various mechanisms. Since there is a strong association with diets containing abundant vegetables, fruits, and grains, and significant decline in the risk of colon cancer, accumulation studies have focused on the anticancer potential of quercetin in colorectal cancer. Cell cycle arrest, increase in apoptosis, antioxidant replication, modulation of estrogen receptors, regulation of signaling pathways, inhibition of and metastasis and angiogenesis are among various mechanisms underlying the chemo-preventive effects of quercetin in colorectal cancer. This review covers various therapeutic interactions of Quercetin as to how targets cellular involved in cancer treatment.

Kinase-targeted cancer therapies: progress, challenges and future directions

The human genome encodes 538 protein kinases that transfer a γ-phosphate group from ATP to serine, threonine, or tyrosine residues. Many of these kinases are associated with human cancer initiation and progression. The recent development of small-molecule kinase inhibitors for the treatment of diverse types of cancer has proven successful in clinical therapy. Significantly, protein kinases are the second most targeted group of drug targets, after the G-protein-coupled receptors. Since the development of the first protein kinase inhibitor, in the early 1980s, 37 kinase inhibitors have received FDA approval for treatment of malignancies such as breast and lung cancer. Furthermore, about 150 kinase-targeted drugs are in clinical phase trials, and many kinase-specific inhibitors are in the preclinical stage of drug development. Nevertheless, many factors confound the clinical efficacy of these molecules. Specific tumor genetics, tumor microenvironment, drug resistance, and pharmacogenomics determine how useful a compound will be in the treatment of a given cancer. This review provides an overview of kinase-targeted drug discovery and development in relation to oncology and highlights the challenges and future potential for kinase-targeted cancer therapies.

Molecular Targets Underlying the Anticancer Effects of Quercetin: An Update

Quercetin, a medicinally important member of the flavonoid family, is one of the most prominent dietary antioxidants. It is present in a variety of foods-including fruits, vegetables, tea, wine, as well as other dietary supplements-and is responsible for various health benefits. Numerous pharmacological effects of quercetin include protection against diseases, such as osteoporosis, certain forms of malignant tumors, and pulmonary and cardiovascular disorders. Quercetin has the special ability of scavenging highly reactive species, such as hydrogen peroxide, superoxide anion, and hydroxyl radicals. These oxygen radicals are called reactive oxygen species, which can cause oxidative damage to cellular components, such as proteins, lipids, and deoxyribonucleic acid. Various oxygen radicals play important roles in pathophysiological and degenerative processes, such as aging. Subsequently, several studies have been performed to evaluate possible advantageous health effects of quercetin and to collect scientific evidence for these beneficial health claims. These studies also gather data in order to evaluate the exact mechanism(s) of action and toxicological effects of quercetin. The purpose of this review is to present and critically analyze molecular pathways underlying the anticancer effects of quercetin. Current limitations and future directions of research on this bioactive dietary polyphenol are also critically discussed.

Anti-inflammatory effects and molecular mechanisms of 8-prenyl quercetin

SCOPE

8-prenyl quercetin (PQ) is a typical prenylflavonoid distributed in plant foods. It shows higher potential bioactivity than its parent quercetin (Q) although the mechanisms are not fully understood. This study aims to clarify the anti-inflammatory effects and molecular mechanisms of PQ in cell and animal models, compared to Q.

METHODS AND RESULTS

RAW264.7 cells were treated with PQ or Q to investigate the influence on the production of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and protein kinases by Western blotting. Nitric oxide (NO) and prostaglandin E2 (PGE2 ) were measured by the Griess method and ELISA, respectively. Cytokines were assayed by the multiplex technology. Mouse paw edema was induced by LPS. The results revealed that PQ had stronger inhibition on the production of iNOS, COX-2, NO, PGE2 , and 12 kinds of cytokines, than Q. PQ also showed in vivo anti-inflammatory effect by attenuating mouse paw edema. Molecular data revealed that PQ had no competitive binding to Toll-like receptor 4 with LPS, but directly targeted SEK1-JNK1/2 (where SEK is stress-activated protein kinase and JNK1/2 is Jun-N-terminal kinase 1/2) and MEK1-ERK1/2 (where ERK is extracellular signal regulated kinase).

CONCLUSION

PQ as a potential inhibitor revealed anti-inflammatory effect in both cell and animal models at least by targeting SEK1-JNK1/2 and MEK1-ERK1/2.

Myricetin: A Dietary Molecule with Diverse Biological Activities

Myricetin is a common plant-derived flavonoid and is well recognised for its nutraceuticals value. It is one of the key ingredients of various foods and beverages. The compound exhibits a wide range of activities that include strong anti-oxidant, anticancer, antidiabetic and anti-inflammatory activities. It displays several activities that are related to the central nervous system and numerous studies have suggested that the compound may be beneficial to protect against diseases such as Parkinson's and Alzheimer's. The use of myricetin as a preserving agent to extend the shelf life of foods containing oils and fats is attributed to the compound's ability to protect lipids against oxidation. A detailed search of existing literature revealed that there is currently no comprehensive review available on this important molecule. Hence, the present work includes the history, synthesis, pharmaceutical applications and toxicity studies of myricetin. This report also highlights structure-activity relationships and mechanisms of action for various biological activities.

Molecular mechanisms underlying anticancer effects of myricetin

Dietary guidelines published in the past two decades have acknowledged the beneficial effects of myricetin, an important and common type of herbal flavonoid, against several human diseases such as inflammation, cardiovascular pathologies, and cancer. An increasing number of studies have shown the beneficial effects of myricetin against different types of cancer by modifying several cancer hallmarks including aberrant cell proliferation, signaling pathways, apoptosis, angiogenesis, and tumor metastasis. Most importantly, myricetin interacts with oncoproteins such as protein kinase B (PKB) (Akt), Fyn, MEK1, and JAK1-STAT3 (Janus kinase-signal transducer and activator of transcription 3), and it attenuates the neoplastic transformation of cancer cells. In addition, myricetin exerts antimitotic effects by targeting the overexpression of cyclin-dependent kinase 1 (CDK1) in liver cancer. Moreover, it also targets the mitochondria and promotes different kinds of cell death in various cancer cells. In the present paper, a critical review of the available literature is presented to identify the molecular targets underlying the anticancer effects of myricetin.

Anti-inflammatory activity and molecular mechanism of Oolong tea theasinensin

Oolong tea theasinensins are a group of tea polyphenols different from green tea catechins and black tea theaflavins, and they are considered as bioactive compounds in Oolong tea. In the present study, based on the properties of theasinensin and information about inflammatory processes, we investigated the anti-inflammatory activity and molecular mechanisms of theasinensin A (TSA) in both cell and animal models. In the cell model, TSA reduced the levels of pro-inflammatory mediators including inducible nitric oxide synthase (iNOS), nitric oxide (NO), interleukin-12 (IL-12) (p70), tumor necrosis factor alpha (TNF-α), and monocyte chemotactic protein-1 (MCP-1) induced by lipopolysaccharide (LPS). Cellular signaling analysis revealed that TSA downregulated MAPK/ERK kinase (MEK)-extracellular signal-regulated kinase (ERK) signaling. Pull-down assay and affinity data revealed that TSA might directly bind to MEK-ERK for the inhibitory action. In the animal model, TSA suppressed the production of IL-12 (p70), TNF-α, and MCP-1 and attenuated mouse paw edema induced by LPS.

Development of an HTS-compatible assay for the discovery of ASK1 signalosome inhibitors using alphascreen technology

Genetic target validation studies have demonstrated that the apoptosis signal-regulating kinase 1 (ASK1) represents an important target for the treatment of rheumatoid arthritis, cardiac diseases, and several neurodegenerative disorders. To identify small-molecule inhibitors of ASK1, we have developed a high-throughput screening-compatible, homogenous, biochemical assay using AlphaScreen technology. This novel assay design utilizes purified stress-activated ASK1 signalosome complex, and it monitors phosphorylation of its full-length native substrate, MKK6. The assay has been optimized in a 384-well format and validated by screening the Sigma LOPAC library. The results presented here demonstrate that the assay is sensitive and robust with a Z' factor value of 0.88±0.04 and a signal-to-background ratio of 11, indicating that this assay can be used to screen large chemical libraries to discover novel inhibitors of ASK1.

Involvement of the modulation of cancer cell redox status in the anti-tumoral effect of phenolic compounds

The association between the anti-tumoral properties of phenolics, the generation of ROS in culture medium and modulation of redox homeostasis was analyzed. In AGS cells, the anti-proliferative effect of quercetin was not reverted by catalase or SOD.

Myricetin blocks lipoteichoic acid-induced COX-2 expression in human gingival fibroblasts

Periodontitis is an infectious disease caused by microorganisms present in dental bacterial plaque. Lipoteichoic acid (LTA) is a component of the external membrane of Gram-positive bacteria. It causes septic shock. Ingested flavonoids have been reported to directly affect the regulation of cyclooxygenase-2 (COX-2) expression induced by bacterial toxins. In this study, we examined the effects of four flavonoids (luteolin, fisetin, morin and myricetin) on the activation of ERK1/2, p38 and AKT, and on the synthesis of COX-2 in human gingival fibroblasts treated with LTA from Streptococcus sanguinis. We found that luteolin and myricetin blocked AKT and p38 activation and that myricetin blocked LTA-induced COX-2 expression. The results of our study are important for elucidating the mechanism of action of flavonoid regulation of inflammatory responses.

Signal transduction and molecular targets of selected flavonoids

SIGNIFICANCE

Diet exerts a major influence on the risk for developing cancer and heart disease. Food factors such as flavonoids are alleged to protect cells from premature aging and disease by shielding DNA, proteins, and lipids from oxidative damage.

RECENT ADVANCES

Our work has focused on clarifying the effects of dietary components on cancer cell proliferation and tumor growth, discovering mechanisms to explain the effects, and identifying the specific molecular targets of these compounds. Our strategy for identifying specific molecular targets of phytochemicals involves the use of supercomputer technology combined with protein crystallography, molecular biology, and experimental laboratory verification.

CRITICAL ISSUES

One of the greatest challenges for scientists is to reduce the accumulation of distortion and half truths reported in the popular media regarding the health benefits of certain foods or food supplements. The use of these is not new, but interest has increased dramatically because of perceived health benefits that are presumably acquired without unpleasant side effects. Flavonoids are touted to exert many beneficial effects in vitro. However, whether they can produce these effects in vivo is disputed.

FUTURE DIRECTIONS

The World Health Organization indicates that one third of all cancer deaths are preventable and that diet is closely linked to prevention. Based on this idea and epidemiological findings, attention has centered on dietary phytochemicals as an effective intervention in cancer development. However, an unequivocal link between diet and cancer has not been established. Thus, identifying cancer preventive dietary agents with specific molecular targets is essential to move forward toward successful cancer prevention.

Myricetin attenuates lipopolysaccharide-stimulated activation of mouse bone marrow-derived dendritic cells through suppression of IKK/NF-κB and MAPK signalling pathways

BACKGROUND

Myricetin is a naturally occurring flavonoid that is found in many fruits, vegetables, teas and medicinal herbs. It has been demonstrated to have anti-inflammatory properties, but, to date, no studies have described the immunomodulatory effects of myricetin on the functions of dendritic cells (DCs). The aim of this study was to evaluate the potential for myricetin to modulate lipopolysaccharide (LPS)-stimulated activation of mouse bone marrow-derived DCs.

RESULTS

Our experimental data showed that treatment with myricetin up to 10 µg mL(-1) does not cause cytotoxicity in cells. Myricetin significantly decreased the secretion of tumour necrosis factor-α, interleukin-6 and interleukin-12p70 by LPS-stimulated DCs. The expression of LPS-induced major histocompatibility class II, CD40 and CD86 on DCs was also inhibited by myricetin, and the endocytic and migratory capacity of LPS-stimulated DCs was blocked by myricentin. In addition, LPS-stimulated DC-elicited allogeneic T-cell proliferation was reduced by myricetin. Moreover, our results confirmed that myricetin attenuates the responses of LPS-stimulated activation of DCs via suppression of IκB kinase/nuclear factor-κB and mitogen-activated protein kinase-dependent pathways.

CONCLUSION

Myricetin has novel immunopharmacological activity, and modulation of DCs by myricetin may be an attractive strategy for the treatment of inflammatory and autoimmune disorders, and for transplantation.

Target molecules of food phytochemicals: food science bound for the next dimension

Phytochemicals are generally defined as secondary metabolites in plants that play crucial roles in their adaptation to a variety of environmental stressors. There is a great body of compelling evidence showing that these metabolites have pronounced potentials for regulating and modulating human health and disease onset, as shown by both experimental and epidemiological approaches. Concurrently, enormous efforts have been made to elucidate the mechanism of actions underlying their biological and physiological functions. For example, the pioneering work of Tachibana et al. uncovered the receptor for (-)-epigallocatechin-3-gallate (EGCg) as the 67 kDa laminin receptor, which was shown to partially mediate the functions of EGCg, such as anti-inflammatory, anti-allergic, and anti-proliferative activities. Thereafter, several protein kinases were identified as binding proteins of flavonoids, including myricetin, quercetin, and kaempferol. Isothiocyanates, sulfur-containing phytochemicals present in cruciferous plants, are well known to target Keap1 for activating the transcription factor Nrf2 for inducing self-defensive and anti-oxidative gene expression. In addition, we recently identified CD36 as a cell surface receptor for ursolic acid, a triterpenoid ubiquitously occurring in plants. Importantly, the above mentioned target proteins are indispensable for phytochemicals to exhibit, at least in part, their bioactivities. Nevertheless, it is reasonable to assume that some of the activities and potential toxicities of metabolites are exerted via their interactions with unidentified, off-target proteins. This notion may be supported by the fact that even rationally designed drugs occasionally display off-target effects and induce unexpected outcomes, including toxicity. Here we update the current status and future directions of research related to target molecules of food phytochemicals.

Structural features and bioavailability of four flavonoids and their implications for lifespan-extending and antioxidant actions in C. elegans

Various studies have demonstrated longevity effects of flavonoids, a major sub-group of plant polyphenolic compounds, in Caenorhabditis elegans. To better understand their structure-activity relationship in vivo we have used a comparative approach by exposing C. elegans to the structurally related flavonoids myricetin, quercetin, kaempferol and naringenin, and assessed their impact on lifespan and on putative modes of action. The bioavailability of the tested flavonoids was demonstrated by high-performance liquid chromatography with diode-array detection (HPLC/DAD) and a 2-aminoethyl diphenyl borate-based in vivo approach. While all flavonols increased lifespan in wild-type, only myricetin elongated the mev-1(kn1) lifespan, suggesting that the flavonols antioxidant action alone is not sufficient for longevity. Structural prerequisites of high antioxidant action in vitro were also essential to reduce the reactive oxygen species (ROS) load in vivo in C. elegans and were tested in isolated mouse muscle mitochondria. Since the insulin/IGF-like signaling (IIS) cascade is a key regulator of lifespan, all compounds were tested for the ability to cause nuclear translocation of the FOXO transcription factor DAF-16 and changes in target gene expression. An increased DAF-16 translocation and sod-3 promoter activity were observed with all flavonoids but was independent of their ROS scavenging capability and their effects on lifespan.

Influence of five potential anticancer drugs on wnt pathway and cell survival in human biliary tract cancer cells

BACKGROUND

The role of Wnt signalling in carcinogenesis suggests compounds targeting this pathway as potential anti-cancer drugs. Several studies report activation of Wnt signalling in biliary tract cancer (BTC) thus rendering Wnt inhibitory drugs as potential candidates for targeted therapy of this highly chemoresistant disease.

METHODS

In this study we analysed five compounds with suggested inhibitory effects on Wnt signalling (DMAT, FH535, myricetin, quercetin, and TBB) for their cytotoxic efficiency, mode of cell death, time- and cell line-dependent characteristics as well as their effects on Wnt pathway activity in nine different BTC cell lines.

RESULTS

Exposure of cancer cells to different concentrations of the compounds results in a clear dose-dependent reduction of viability for all drugs in the order FH535 > DMAT > TBB > myricetin > quercetin. The first three substances show high cytotoxicity in all tested cell lines, cause a direct cytotoxic effect by induction of apoptosis and inhibit pathway-specific signal transduction in a Wnt transcription factor reporter activity assay. Selected target genes such as growth-promoting cyclin D1 and the cell cycle progression inhibitor p27 are down- and up-regulated after treatment, respectively.

CONCLUSIONS

Taken together, these data demonstrate that the small molecular weight inhibitors DMAT, F535 and TBB have a considerable cytotoxic and possibly Wnt-specific effect on BTC cell lines in vitro. Further in vivo investigation of these drugs as well as of new Wnt inhibitors may provide a promising approach for targeted therapy of this difficult-to-treat tumour.

Myricetin is a potent chemopreventive phytochemical in skin carcinogenesis

Myricetin is a widely distributed flavonol that is found in many plants, including tea, berries, fruits, vegetables, and medicinal herbs. Abundant sources provide interesting insights into the multiple mechanisms by which myricetin mediates chemopreventive effects on skin cancer. Myricetin strongly inhibited tumor promoter-induced neoplastic cell transformation by inhibiting MEK, JAK1, Akt, and MKK4 kinase activity directly. In a mouse skin model, myricetin attenuated the ultraviolet B (UVB)-induced COX-2 expression and skin tumor formation by regulating Fyn. Myricetin-mediated inactivation of Akt in the UVB response plays a role in regulating UVB-induced carcinogenesis. Recently, myricetin was found to inhibit UVB-induced angiogenesis by targeting PI3-K in an SKH-1 hairless mouse skin tumorigenesis model. Raf kinase is a critical target for myricetin in inhibiting the UVB-induced formation of wrinkles and suppression of type I procollagen and collagen levels in mouse skin. Accumulated data suggest that myricetin acts as a promising agent for the chemoprevention of skin cancer.

Plant polyphenols: chemical properties, biological activities, and synthesis

Eating five servings of fruits and vegetables per day! This is what is highly recommended and heavily advertised nowadays to the general public to stay fit and healthy! Drinking green tea on a regular basis, eating chocolate from time to time, as well as savoring a couple of glasses of red wine per day have been claimed to increase life expectancy even further! Why? The answer is in fact still under scientific scrutiny, but a particular class of compounds naturally occurring in fruits and vegetables is considered to be crucial for the expression of such human health benefits: the polyphenols! What are these plant products really? What are their physicochemical properties? How do they express their biological activity? Are they really valuable for disease prevention? Can they be used to develop new pharmaceutical drugs? What recent progress has been made toward their preparation by organic synthesis? This Review gives answers from a chemical perspective, summarizes the state of the art, and highlights the most significant advances in the field of polyphenol research.

Flavonoids as protein kinase inhibitors for cancer chemoprevention: direct binding and molecular modeling

Protein kinases play crucial roles in the regulation of multiple cell signaling pathways and cellular functions. Deregulation of protein kinase function has been implicated in carcinogenesis. The inhibition of protein kinases has emerged as an important target for cancer chemoprevention and therapy. Accumulated data revealed that flavonoids exert chemopreventive effects through acting at protein kinase signaling pathways, more than as conventional hydrogen-donating antioxidants. Recent studies show that flavonoids can bind directly to some protein kinases, including Akt/protein kinase B (Akt/PKB), Fyn, Janus kinase 1 (JAK1), mitogen-activated protein kinase kinase 1 (MEK1), phosphoinositide 3-kinase (PI3K), mitogen-activated protein (MAP) kinase kinase 4 (MKK4), Raf1, and zeta chain-associated 70-kDa protein (ZAP-70) kinase, and then alter their phosphorylation state to regulate multiple cell signaling pathways in carcinogenesis processes. In this review, we report recent results on the interactions of flavonoids and protein kinases, especially their direct binding and molecular modeling. The data suggest that flavonoids act as protein kinase inhibitors for cancer chemoprevention that were thought previously as conventional hydrogen-donating antioxidant. Moreover, the molecular modeling data show some hints for creating natural compound-based protein kinase inhibitors for cancer chemoprevention and therapy.

Myricetin reduces voltage activated potassium channel currents in DRG neurons by a p38 dependent mechanism

Myricetin is a naturally occurring flavonoid known for its anti-neoplastic, anti-oxidant and anti-inflammatory effects. Currently, potential analgesic effects are proposed for several animal models of acute and chronic pain. Pilot studies show a flavonoid-induced modulation of intracellular mitogen-activated protein kinases (MAPK) as p38 and interactions with voltage activated potassium channel currents (I(K(V))). The aim of this study was to investigate the underlying modulation of I(K(V)) and the influence of MAPK phosphorylation in an in vitro cell model. Whole cell patch-clamp recordings of rat dorsal root ganglion neurons were performed and I(K(V)) isolated. I(K(V)) were concentration-dependently reduced by myricetin (1-75μM myricetin; reduction range 18-78%) with no voltage dependency (-80 to +60mV). The reduction of I(K(V)) was enhanced by blocking p38 with the p38 inhibitor SB203580 (40±20% without SB203580 vs. 62±5% with 5μM SB203580 or 83±7% with 10μM SB203580), but abolished by activation of p38 using anisomycin (40±20% without anisomycin vs. 0.73±17% with 5μM anisomycin). We conclude that myricetin reduces I(K(V)) by p38 dependent mechanisms in sensory neurons. Since a reduction of I(K(V)) rather increases neuronal excitability, it is unlikely that this effect of myricetin contributes to its analgesic effects.

Relationships between structures of hydroxyflavones and their antioxidative effects

Even hydroxyflavones show diverse biological functions, they have two common features such as showing antioxidative effects and containing hydroxyl groups. The authors tested the antioxidative effects of thirty hydroxyflavones using 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay. While the scavenging activity of galangin, 3,5,7-trihydroxyflavone was 52.5%, fisetin, 3,7,3',4'-tetrahydroxyflavone showed 85.2%. To investigate the relationships between the structures of hydroxyflavones and their antioxidative effects, the three-dimensional quantitative structure-activity relationships were examined.

Myricetin inhibits Akt survival signaling and induces Bad-mediated apoptosis in a low dose ultraviolet (UV)-B-irradiated HaCaT human immortalized keratinocytes

Deregulation of cell survival pathways and resistance to apoptosis are generally accepted as crucial aspects of tumorigenesis. As in many tumors, increasing occurrence of human skin cancer and other conflicting effects of solar ultraviolet (UV) radiation enhance the demand for novel chemoprevention agents. Myricetin, a naturally occurring phytochemical, is potent in anti-cancer promoting activity and affords to the chemopreventive potential of several healthy-foods, including fruits and vegetables. We demonstrate here that myricetin inhibits Akt activity to induce apoptosis in a low dose ('repairable dose') UVB-irradiated keratinocytes. Treatment of UVB-irradiated HaCaT cells with an apoptosis-inducing concentration of myricetin (20 microM) resulted in a decrease in phosphorylation of Akt leading to inhibition of its kinase activity. Myricetin treatment also caused a decrease in phosphorylation of Bad (a pro-apoptotic protein), a direct target of Akt in signaling pathway. Interaction between Bad and 14-3-3beta was reduced markedly in UVB-irradiated cells upon a treatment with myricetin. Comparable to these results, myricetin treatment promoted mitochondrial translocation of Bad, loss of the mitochondrial membrane potential, and release of the mitochondrial apoptotic proteins including cytochrome c, Smac, and AIF. Ectopic expression of constitutively active Akt granted statistically significant protection against myricetin-induced apoptosis. In addition, myricetin-induced apoptosis in UVB-irradiated cells was notably attenuated in the presence of caspase inhibitors. Together, these results indicate that myricetin might take on potent chemopreventive activity by inhibiting the Akt-mediated survival signaling axis in UVB-induced skin carcinogenesis.