Myricetin inhibits the induction of anti-Fas IgM-, tumor necrosis factor-α- and interleukin-1β-mediated apoptosis by Fas pathway inhibition in human osteoblastic cell line MG-63

Myricetin Restores Autophagy to Attenuate Lumbar Intervertebral Disk Degeneration Via Negative Regulation of the JAK2/STAT3 Pathway

Autophagy is a critical player in lumbar intervertebral disk degeneration (IDD), and autophagy activation has been suggested to prevent the apoptosis of nucleus pulposus cells (NPCs). Myricetin has anti-cancer, anti-inflammatory, and antioxidant potentials and can activate autophagy. Thus, this study focused on the roles and mechanisms of myricetin in IDD. A puncture-induced rat IDD model was established and intraperitoneally injected with 20-mg/kg/day myricetin. Histopathological changes of intervertebral disks (IVDs) were assessed by hematoxylin and eosin staining and Safranin O/Fast Green staining. The isolated NPCs from IVDs of healthy rats were stimulated with IL-1β to mimic IDD-like conditions. The roles of myricetin in cell apoptosis, extracellular matrix (ECM) degradation, autophagy repression, and the JAK2/STAT3 pathway activation were examined by cell counting kit-8, flow cytometry, western blotting, real-time quantitative polymerase chain reaction, and immunofluorescence staining. Myricetin treatment attenuated the apoptosis and ECM degradation, and enhanced autophagy in the IL-1β-treated NPCs, whereas the myricetin-mediated protection was limited by autophagy inhibition. Mechanistically, myricetin activated autophagy through blocking the JAK2/STAT3 signaling. In vivo experiments revealed that intraperitoneal injection of myricetin activated NPC autophagy to relieve puncture injury in rats. Myricetin prevents IDD by attenuating NPC apoptosis and ECM degradation through blocking the JAK2/STAT3 pathway to enhance autophagy.

Royal Jelly Enhances the Ability of Myoblast C2C12 Cells to Differentiate into Multilineage Cells

Royal jelly (RJ) is recognized as beneficial to mammalian health. Multilineage differentiation potential is an important property of mesenchymal stem cells (MSCs). C2C12 cells have an innate ability to differentiate into myogenic cells. Like MSCs, C2C12 cells can also differentiate into osteoblast- and adipocyte-lineage cells. We recently reported that RJ enhances the myogenic differentiation of C2C12 cells. However, the effect of RJ on osteoblast or adipocyte differentiation is still unknown. Here in this study, we have examined the effect of RJ on the osteoblast and adipocyte differentiation of C2C12 cells. Protease-treated RJ was used to reduce the adverse effects caused by RJ supplementation. To induce osteoblast or adipocyte differentiation, cells were treated with bone morphogenetic proteins (BMP) or peroxisome proliferator-activated receptor γ (PPARγ) agonist, respectively. RNA-seq was used to analyze the effect of RJ on gene expression. We found that RJ stimulates osteoblast and adipocyte differentiation. RJ regulated 279 genes. RJ treatment upregulated glutathione-related genes. Glutathione, the most abundant antioxidative factor in cells, has been shown to promote osteoblast differentiation in MSC and MSC-like cells. Therefore, RJ may promote osteogenesis, at least in part, through the antioxidant effects of glutathione. RJ enhances the differentiation ability of C2C12 cells into multiple lineages, including myoblasts, osteoblasts, and adipocytes.

Rheumatoid arthritis molecular targets and their importance to flavonoid-based therapy

Rheumatoid arthritis (RA) is a progressive, chronic, autoimmune, inflammatory, and systemic condition that primarily affects the synovial joints and adjacent tissues, including bone, muscle, and tendons. The World Health Organization recognizes RA as one of the most prevalent chronic inflammatory diseases. In the last decade, there was an expansion on the available RA therapeutic options which aimed to improve patient's quality of life. Despite the extensive research and the emergence of new therapeutic approaches and drugs, there are still significant unwanted side effects associated to these drugs and still a vast number of patients that do not respond positively to the existing therapeutic strategies. Over the years, several references to the use of flavonoids in the quest for new treatments for RA have emerged. This review aimed to summarize the existing literature about the flavonoids' effects on the major pathogenic/molecular targets of RA and their potential use as lead compounds for the development of new effective molecules for RA treatment. It is demonstrated that flavonoids can modulate various players in synovial inflammation, regulate immune cell function, decrease synoviocytes proliferation and balance the apoptotic process, decrease angiogenesis, and stop/prevent bone and cartilage degradation, which are all dominant features of RA. Although further investigation is necessary to determine the effectiveness of flavonoids in humans, the available data from in vitro and in vivo models suggest their potential as new disease-modifying anti-rheumatic drugs. This review highlights the use of flavonoids as a promising avenue for future research in the treatment of RA.

Myricetin: a Multifunctional Flavonol in Biomedicine

PURPOSE OF REVEIW

The root cause of many diseases like CVD, cancer, and aging is free radicals which exert their effect by interfering with different metabolic pathways. The sources of free radicals can be exogenous, like UV rays from sunlight, and endogenous due to different metabolic by-products.In our body, there are defense mechanisms present, such as antioxidant enzymes and antioxidant molecules to combat these free radicals, but if there is an overload of these free radicals in our body, the defense system may not be sufficient to neutralize these free radicals. In such situations, we are exposed to a chronic low dose of oxidants creating oxidative stress, which is responsible for eliciting different diseases.

RECENT FINDINGS

Pubmed and Google Scholar are the search engines used to sort out relevant papers on myricetin and its role in combating many diseases. Myricetin is present in many fruits and vegetables and is a known antioxidant. It can elevate the antioxidant enzyme levels; reduces the lipid peroxidation; and is known to protect against cancer. In the case of myocardial dysfunction, myricetin has been shown to suppress the inflammatory cytokines and reduced the mortality rate. Myricetin has also been found to reduce platelet aggregation and control the viral infections by interfering in the DNA replication pathways.

SUMMARY

In this paper, we have briefly reviewed about the different type and site of free radicals and the role of myricetin in addressing the ROS and different diseases.

Flavonoids: Classification, Function, and Molecular Mechanisms Involved in Bone Remodelling

Flavonoids are polyphenolic compounds spotted in various fruits, vegetables, barks, tea plants, and stems and many more natural commodities. They have a multitude of applications through their anti-inflammatory, anti-oxidative, anti-carcinogenic properties, along with the ability to assist in the stimulation of bone formation. Bone, a rigid connective body tissue made up of cells embedded in a mineralised matrix is maintained by an assemblage of pathways assisting osteoblastogenesis and osteoclastogenesis. These have a significant impact on a plethora of bone diseases. The homeostasis between osteoblast and osteoclast formation decides the integrity and structure of the bone. The flavonoids discussed here are quercetin, kaempferol, icariin, myricetin, naringin, daidzein, luteolin, genistein, hesperidin, apigenin and several other flavonoids. The effects these flavonoids have on the mitogen activated protein kinase (MAPK), nuclear factor kappa β (NF-kβ), Wnt/β-catenin and bone morphogenetic protein 2/SMAD (BMP2/SMAD) signalling pathways, and apoptotic pathways lead to impacts on bone remodelling. In addition, these polyphenols regulate angiogenesis, decrease the levels of inflammatory cytokines and play a crucial role in scavenging reactive oxygen species (ROS). Considering these important effects of flavonoids, they may be regarded as a promising agent in treating bone-related ailments in the future.

Application of Ligature-Induced Periodontitis in Mice to Explore the Molecular Mechanism of Periodontal Disease

Periodontitis is an inflammatory disease characterized by the destruction of the periodontium. In the last decade, a new murine model of periodontitis has been widely used to simulate alveolar bone resorption and periodontal soft tissue destruction by ligation. Typically, 3-0 to 9-0 silks are selected for ligation around the molars in mice, and significant bone loss and inflammatory infiltration are observed within a week. The ligature-maintained period can vary according to specific aims. We reviewed the findings on the interaction of systemic diseases with periodontitis, periodontal tissue destruction, the immunological and bacteriological responses, and new treatments. In these studies, the activation of osteoclasts, upregulation of pro-inflammatory factors, and excessive immune response have been considered as major factors in periodontal disruption. Multiple genes identified in periodontal tissues partly reflect the complexity of the pathogenesis of periodontitis. The effects of novel treatment methods on periodontitis have also been evaluated in a ligature-induced periodontitis model in mice. This model cannot completely represent all aspects of periodontitis in humans but is considered an effective method for the exploration of its mechanisms. Through this review, we aimed to provide evidence and enlightenment for future studies planning to use this model.

Micronutrients: Essential Treatment for Inflammatory Arthritis?

PURPOSE OF REVIEW

Synovial inflammation is characteristic of inflammatory chronic arthropathies and can cause progressive articular damage, chronic pain, and functional loss. Scientific research has increasingly focused on investigating anti-inflammatory micronutrients present in fruits, vegetables, spices, seeds, tea, and wine. This review aims to examine the anti-inflammatory effect of polyphenols (phytonutrients present in plants) and other micronutrients described in randomized clinical trials conducted in patients with chronic inflammatory arthropathies.

RECENT FINDINGS

There is an increasing evidence that differences in micronutrient intake might play an essential role in pathogenesis, therapeutic response, and remission of synovitis. Randomized clinical trials with specific micronutrient- or nutrient-enriched food intake show improvement of symptoms and modulation of both pro- and anti-inflammatory mediators. We found convincing evidence of the anti-inflammatory effect of several micronutrients in arthritis symptoms and inflammation. Although in clinical practice nutritional recommendations to patients with chronic joint inflammation are not consistently prescribed, the addition of these nutrients to day-to-day eating habits could potentially change the natural history of inflammatory arthritis. Future research is needed for a consensus on the specific nutritional recommendations for patients with chronic synovial inflammation.

DMY protects the knee joints of rats with collagen-induced arthritis by inhibition of NF-κB signaling and osteoclastic bone resorption

Collagen-induced arthritis (CIA) is a widely used animal model for studying rheumatoid arthritis (RA), which manifests serious joint dysfunction, progressive bone erosion and articular cartilage destruction. Considering that joint damage in RA is caused by systemic inflammation and dihydromyricetin (DMY), the main flavonoid of Ampelopsis Michx, possesses anti-inflammatory properties, in the present study we have investigated the potential capability of DMY to inhibit inflammation-mediated joint damage and explore the underlying mechanisms. A rat model of RA induced by CIA was administered with DMY for 5 weeks. Prior to histological analysis, the knee joints were scanned by microcomputed tomography (μCT) to detect bone damage. Articular cartilage destruction was assessed by Alcian blue and Toluidine blue staining and the pathological alteration of osteoblasts and osteoclasts in joints was evaluated by hematoxylin-eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining, respectively. The effects of DMY on osteoblast differentiation and osteoclast formation in vitro were investigated. Consistent with the in vivo results, DMY had no significant effect on osteoblast differentiation but an inhibitory effect on osteoclast formation. Furthermore, we determined that the mechanism of the DMY-suppressed osteoclast formation was blocking the phosphorylation of I-κB kinase (IKK) so as to hinder the activation of nuclear factor-κB (NF-κB). Collectively, DMY could ameliorate knee joint damage, especially in articular cartilage, which is the weight-bearing region, by inhibiting osteoclast formation through NF-κB signaling.

EDACO, a derivative of myricetin, inhibits the differentiation of Gaoyou duck embryonic osteoclasts in vitro

1. This study determined the effects of (E)-3-(2-(4-(3-(2,4-dimethoxyphenyl)acryloyl)phenoxy)ethoxy)-5,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-4H-chromen-4-one (EDACO) on the differentiation of Gaoyou duck embryonic osteoclasts cultured in vitro. 2. Bone marrow mononuclear cells (BM-MNC) were collected from 23-d-old Gaoyou duck embryos and induced by macrophage colony-stimulating factor and receptor activator of nuclear factor κB ligand in the presence of EDACO at different concentrations (i.e. 10, 20, 40, 80 and 160 µM). Tartrate-resistant acid phosphatase (TRAP) staining and resorption ability determination were conducted. 3. Results suggested that EDACO suppressed the shaping of positive multinucleated cells and the number of TRAP-positive cells in the 20, 40, 80 and 160 μM EDACO groups was significantly decreased (P < 0.05 or P < 0.01). Besides, the absorption activity of differentiated duck embryonic osteoclasts was significantly inhibited (P < 0.05) in both 80 and 160 μM EDACO groups. 4. Overall, EDACO can inhibit the differentiation of BM-MNC into mature osteoclasts in duck embryos.1.

Myricetin inhibits NLRP3 inflammasome activation via reduction of ROS-dependent ubiquitination of ASC and promotion of ROS-independent NLRP3 ubiquitination

Myricetin is a plant-derived flavonoid that exhibits diverse pharmacological properties. The NLRP3 (NLR family, pyrin domain-containing 3 protein) inflammasome is a cytosolic multiprotein complex that plays a critical role in the innate immune response and pathogenesis of multiple inflammatory disorders. The present study found that myricetin inhibited NLRP3 inflammasome assembly via promotion of reactive oxygen species (ROS)-independent ubiquitination of NLRP3 and reduction of ROS-dependent ubiquitination of ASC (apoptosis-associated speck-like protein containing a CARD), which disrupted the interaction between ASC and NLRP3 and inhibited ASC oligomerization. This effect was further confirmed in vivo using mouse models of lipopolysaccharide (LPS)-induced sepsis and alum-induced peritonitis. These results suggest the therapeutic value of myricetin by targeting NLRP3-driven inflammatory diseases.

Polyphenol uses in biomaterials engineering

Polyphenols are micronutrients obtained from diet that have been suggested to play an important role in health. The health benefits of polyphenols and their protective effects in food systems as antioxidant compounds are well known and have been extensively investigated. However, their functional roles as a "processing cofactor" in tissue engineering applications are less widely known. This review focuses on the functionality of polyphenols and their application in biomaterials. Polyphenols have been used to stabilize collagen and to improve its resistance to degradation in biological systems. Therefore, they have been proposed to improve the performance of biomedical devices used in cardiovascular systems by improving the mechanical properties of grafted heart valves, enhancing microcirculation through the relaxation of the arterial walls and improving the capillary blood flow and pressure resistance. Polyphenols have been found to stimulate bone formation, mineralization, as well as the proliferation, differentiation, and the survival of osteoblasts. These effects are brought about by the stimulatory effect of polyphenols on osteoblast cells and their protective effect against oxidative stress and inflammatory cytokines. In addition, polyphenols inhibit the differentiation of the osteoclast cells. Collectively, these actions lead to promote bone formation and to reduce bone resorption, respectively. Moreover, polyphenols can increase the cross-linking of dentine and hence its mechanical stability. Overall, polyphenols provide interesting properties that will stimulate further research in the bioengineering field.

Molecular signaling mechanisms behind polyphenol-induced bone anabolism

For millennia, in the different cultures all over the world, plants have been extensively used as a source of therapeutic agents with wide-ranging medicinal applications, thus becoming part of a rational clinical and pharmacological investigation over the years. As bioactive molecules, plant-derived polyphenols have been demonstrated to exert many effects on human health by acting on different biological systems, thus their therapeutic potential would represent a novel approach on which natural product-based drug discovery and development could be based in the future. Many reports have provided evidence for the benefits derived from the dietary supplementation of polyphenols in the prevention and treatment of osteoporosis. Polyphenols are able to protect the bone, thanks to their antioxidant properties, as well as their anti-inflammatory actions by involving diverse signaling pathways, thus leading to bone anabolic effects and decreased bone resorption. This review is meant to summarize the research works performed so far, by elucidating the molecular mechanisms of action of polyphenols in a bone regeneration context, aiming at a better understanding of a possible application in the development of medical devices for bone tissue regeneration.

Myricetin Prevents Alveolar Bone Loss in an Experimental Ovariectomized Mouse Model of Periodontitis

Periodontitis is a common chronic inflammatory disease, which leads to alveolar bone resorption. Healthy and functional alveolar bone, which can support the teeth and enable their movement, is very important for orthodontic treatment. Myricetin inhibited osteoclastogenesis by suppressing the expression of some genes, signaling pathways, and cytokines. This study aimed to investigate the effects of myricetin on alveolar bone loss in an ovariectomized (OVX) mouse model of periodontitis as well as in vitro osteoclast formation and bone resorption. Twenty-four healthy eight-week-old C57BL/J6 female mice were assigned randomly to four groups: phosphate-buffered saline (PBS) control (sham) OVX + ligature + PBS (vehicle), and OVX + ligature + low or high (2 or 5 mg∙kg⁻¹∙day⁻¹, respectively) doses of myricetin. Myricetin or PBS was injected intraperitoneally (i.p.) every other day for 30 days. The maxillae were collected and subjected to further examination, including micro-computed tomography (micro-CT), hematoxylin and eosin (H&E) staining, and tartrate-resistant acid phosphatase (TRAP) staining; a resorption pit assay was also performed in vitro to evaluate the effects of myricetin on receptor activator of nuclear factor κ-B ligand (RANKL)-induced osteoclastogenesis. Myricetin, at both high and low doses, prevented alveolar bone resorption and increased alveolar crest height in the mouse model and inhibited osteoclast formation and bone resorption in vitro. However, myricetin was more effective at high dose than at low dose. Our study demonstrated that myricetin had a positive effect on alveolar bone resorption in an OVX mouse model of periodontitis and, therefore, may be a potential agent for the treatment of periodontitis and osteoporosis.

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.

Galangin, a novel dietary flavonoid, attenuates metastatic feature via PKC/ERK signaling pathway in TPA-treated liver cancer HepG2 cells

Background

Galangin (3,5,7-trihydroxyflavone) is a flavonoid compound found in high concentration in lesser galangal. The objective of this study was to investigate the ability of galangin to inhibit 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced the invasion and metastasis of HepG2 liver cancer cells.

Results

First, using a cell-matrix adhesion assay, immunofluorescence assay, transwell-chamber invasion/migration assay, and wound healing assay, we observed that galangin exerted an inhibitory effect on TPA-induced cell adhesion, morphology/actin cytoskeleton arrangement, invasion and migration. Furthermore, the results of gelatin zymography and reverse transcriptase polymerase chain reaction (RT-PCR) assays showed that galangin reduced the TPA-induced enzyme activity of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in HepG2 cells; moreover, the messenger RNA level was downregulated. We also observed through a Western blotting assay that galangin strongly inhibited the TPA-induced protein expressions of protein kinase Cα (PKCα), protein kinase Cδ (PKCδ), phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), the phospho-inhibitor of kappaBα (phospho-IκBα), c-Fos, c-Jun, and nuclear factor kappa B (NF-κB). Next, galangin dose-dependently inhibited the binding ability of NF-κB and activator protein 1 (AP-1) to MMP-2/MMP-9 promoters, respectively, resulting in the suppression of MMP-2/MMP-9 enzyme activity.

Conclusions

The results revealed that galangin effectively inhibited the TPA-induced invasion and migration of HepG2 cells through a protein kinase C/extracellular signal-regulated kinase (PKC/ERK) pathway. Thus, galangin may have widespread applications in clinical therapy as an anti-metastatic medicament.

Systems pharmacology dissection of multi-scale mechanisms of action for herbal medicines in stroke treatment and prevention

Annually, tens of millions of first-ever strokes occur in the world; however, currently there is lack of effective and widely applicable pharmacological treatments for stroke patients. Herbal medicines, characterized as multi-constituent, multi-target and multi-effect, have been acknowledged with conspicuous effects in treating stroke, and attract extensive interest of researchers although the mechanism of action is yet unclear. In this work, we introduce an innovative systems-pharmacology method that combines pharmacokinetic prescreening, target fishing and network analysis to decipher the mechanisms of action of 10 herbal medicines like Salvia miltiorrhizae, Ginkgo biloba and Ephedrae herba which are efficient in stroke treatment and prevention. Our systematic analysis results display that, in these anti-stroke herbal medicines, 168 out of 1285 constituents with the favorable pharmacokinetic profiles might be implicated in stroke therapy, and the systematic use of these compounds probably acts through multiple mechanisms to synergistically benefit patients with stroke, which can roughly be classified as preventing ischemic inflammatory response, scavenging free radicals and inhibiting neuronal apoptosis against ischemic cerebral damage, as well as exhibiting lipid-lowering, anti-diabetic, anti-thrombotic and antiplatelet effects to decrease recurrent strokes. Relying on systems biology-based analysis, we speculate that herbal medicines, being characterized as the classical combination therapies, might be not only engaged in multiple mechanisms of action to synergistically improve the stroke outcomes, but also might be participated in reducing the risk factors for recurrent strokes.

Myricetin protects against cytokine-induced cell death in RIN-m5f β cells

Cytokine-induced cell death is recognized as a major cause of progressive β-cell loss. Tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and interferon γ (IFN-γ) in combination trigger a series of events that lead to β-cell death. In the past few decades, the use of myricetin as an anti-inflammatory and cytoprotective agent has gained much attention. The present study focused on the protective roles of myricetin against cytokine-induced cell death in insulin-secreting RIN-m5f β cells. The results showed that myricetin (especially at concentrations of 10 μM and 20 μM) increased cell viability and decreased cell apoptosis induced by the cytokine mixture of TNF-α (10 ng/mL), IL-1β (5 ng/mL), and IFN-γ (1000 IU/mL) for 3 days. Moreover, the cytokines increased the total and p65 subunit levels of nuclear factor κB, decreased inhibitor κB α levels, stimulated the accumulation of nitric oxide, increased cytochrome c release from mitochondria, and induced reactive oxygen species generation; myricetin (especially at the concentration of 20 μM) abolished all of these parameters. These results suggest that myricetin might have therapeutic value for preventing β-cell death.

Effects of flavonoids and other polyphenols on inflammation

Flavonoids are a family of polyphenolic compounds which are widespread in nature (vegetables) and are consumed as part of the human diet in significant amounts. There are other types of polyphenols, including, for example, tannins and resveratrol. Flavonoids and related polyphenolic compounds have significant antiinflammatory activity, among others. This short review summarizes the current knowledge on the effects of flavonoids and related polyphenolic compounds on inflammation, with a focus on structural requirements, the mechanisms involved, and pharmacokinetic considerations. Different molecular (cyclooxygenase, lipoxygenase) and cellular targets (macrophages, lymphocytes, epithelial cells, endothelium) have been identified. In addition, many flavonoids display significant antioxidant/radical scavenging properties. There is substantial structural variation in these compounds, which is bound to have an impact on their biological profile, and specifically on their effects on inflammatory conditions. However, in general terms there is substantial consistency in the effects of these compounds despite considerable structural variations. The mechanisms have been studied mainly in myeloid cells, where the predominant effect is an inhibition of NF-κB signaling and the downregulation of the expression of proinflammatory markers. At present there is a gap in knowledge of in vitro and in vivo effects, although the pharmacokinetics of flavonoids has advanced considerably in the last decade. Many flavonoids have been studied for their intestinal antiinflammatory activity which is only logical, since the gastrointestinal tract is naturally exposed to them. However, their potential therapeutic application in inflammation is not restricted to this organ and extends to other sites and conditions, including arthritis, asthma, encephalomyelitis, and atherosclerosis, among others.

Fas receptor is required for estrogen deficiency-induced bone loss in mice

Bone mass is determined by bone cell differentiation, activity, and death, which mainly occur through apoptosis. Apoptosis can be triggered by death receptor Fas (CD95), expressed on osteoblasts and osteoclasts and may be regulated by estrogen. We have previously shown that signaling through Fas inhibits osteoblast differentiation. In this study we analyzed Fas as a possible mediator of bone loss induced by estrogen withdrawal. At 4 weeks after ovariectomy (OVX), Fas gene expression was greater in osteoblasts and lower in osteoclasts in ovariectomized C57BL/6J (wild type (wt)) mice compared with sham-operated animals. OVX was unable to induce bone loss in mice with a gene knockout for Fas (Fas -/- mice). The number of osteoclasts increased in wt mice after OVX, whereas it remained unchanged in Fas -/- mice. OVX induced greater stimulation of osteoblastogenesis in Fas -/- than in wt mice, with higher expression of osteoblast-specific genes. Direct effects on bone cell differentiation and apoptosis in vivo were confirmed in vitro, in which addition of estradiol decreased Fas expression and partially abrogated the apoptotic and differentiation-inhibitory effect of Fas in osteoblast lineage cells, while having no effect on Fas-induced apoptosis in osteoclast lineage cells. In conclusion, the Fas receptor has an important role in the pathogenesis of postmenopausal osteoporosis by mediating apoptosis and inhibiting differentiation of osteoblast lineage cells. Modulation of Fas effects on bone cells may be used as a therapeutic target in the treatment of osteoresorptive disorders.

Akt is a direct target for myricetin to inhibit cell transformation

Akt, a serine/threonine kinase, is a critical regulator in many cellular processes including cell growth, proliferation, and apoptosis. In this study, we found that myricetin, a typical flavonol existing in many fruits and vegetables, could directly target Akt to inhibit cell transformation. Binding assay revealed that myricetin bound to Akt directly by competing with ATP. In vitro and ex vivo data confirmed that myricetin inhibited the phosphorylation and kinase activity of Akt. Molecular modeling suggested that myricetin easily docks to the ATP-binding site of Akt with hydrogen bonds. Signaling analysis data further demonstrated that myricetin inhibited Akt-mediated activator protein-1 (AP-1) transactivation, cyclin D1 expression and cell transformation. Overall, our results indicate that Akt is a direct target for myricetin to inhibit cell transformation.

Influence of reverse signaling via membrane TNF-alpha on cytotoxicity of NK92 cells

Membrane tumor necrosis factor-alpha (mTNF-alpha) serves as a receptor transducing signals into mTNF-alpha-bearing cells. Among human peripheral blood mononuclear cells, natural killer (NK) cells have been reported to be the only cell type constitutively expressing mTNF-alpha, which is involved in the cytotoxicity of resting NK cells. Using an IL-2-dependent human NK cell line, NK92, which constitutively expresses mTNF-alpha, we examined the effect of reverse signaling via mTNF-alpha on cellular activities. When the cells were prestimulated with soluble TNFR1 (sTNFR1) which activated mTNF-alpha-mediated reverse signaling, the cytotoxicity of NK92 cells was significantly increased. Further investigation demonstrated that prestimulation with sTNFR1 augmented exocytosis and mRNA transcription of two cytotoxic molecules, perforin and granzyme B, which could serve as underlying molecular mechanisms by which mTNF-alpha-mediated reverse signaling promoted cytotoxicity of NK cells toward K562 cells. On the other hand, pretreatment of NK92 with sTNFR1 boosted the expression of FasL and TNF-alpha, including both the secretory and membrane forms. These molecules also contribute to the NK-mediated cytotoxicity, although K562 cells are Fas-negative and sTNF-alpha-resistant. Interestingly, the mTNF-alpha reverse signaling was found to act synergistically with IL-2 on NK-mediated cytotoxicity. This synergy markedly promoted the production of secretory as well as membrane cytotoxic molecules which may be responsible for the enhanced NK92-mediated cytotoxicity. Our observations suggest that, via reverse signaling, constitutively expressed mTNF-alpha may sensitize NK cells to activating stimuli, such as IL-2, resulting in increased NK-mediated cytotoxicity through promoting the production of multiple cytotoxic effector molecules.

Myricetin, a naturally occurring flavonoid, prevents 2-deoxy-D-ribose induced dysfunction and oxidative damage in osteoblastic MC3T3-E1 cells

Myricetin, a naturally occurring flavonoid, was investigated to determine whether it could protect osteoblasts from 2-deoxy-d-ribose induced dysfunction and oxidative damage in the MC3T3-E1 cells. MC3T3-E1 cells were incubated with 2-deoxy-d-ribose and/or myricetin, and markers of osteoblast function and oxidative damage were examined. Compared with control incubation, 2-deoxy-d-ribose significantly (P<0.05) inhibited alkaline phosphatase (ALP) activity, collagen content, and calcium deposition at the concentration of 20 mM. Cellular malondialdehyde (MDA), protein carbonyl, and advanced oxidation protein products contents were significantly (P<0.05) increased in the presence of 2-deoxy-d-ribose (20 mM). Myricetin significantly (P<0.05) increased cell survival, ALP activity, collagen, osteocalcin, osteoprotegerin, and calcium deposition and decreased MDA, protein carbonyl, and advanced oxidation protein products contents of osteoblastic MC3T3-E1 cells in the presence of 20 mM 2-deoxy-d-ribose. These results demonstrate that myricetin attenuates 2-deoxy-d-ribose induced damage, suggesting that myricetin may be a useful dietary supplement for minimizing oxidative injury in diabetes related bone diseases.

Walnut extract (Juglans regia L.) and its component ellagic acid exhibit anti-inflammatory activity in human aorta endothelial cells and osteoblastic activity in the cell line KS483

Epidemiological studies suggest that the incidence of CVD and postmenopausal osteoporosis is low in the Mediterranean area, where herbs and nuts, among others, play an important role in nutrition. In the present study, we sought a role of walnuts (Juglans regia L.) in endothelial and bone-cell function. As the endothelial cell expression of adhesion molecules has been recognised as an early step in inflammation and atherogenesis, we examined the effect of walnut methanolic extract and ellagic acid, one of its major polyphenolic components (as shown by HPLC analysis), on the expression of vascular cell adhesion molecule (VCAM)-1 and intracellular adhesion molecule (ICAM)-1 in human aortic endothelial cells. After incubating the cells with TNF-α (1 ng/ml) in the absence and in the presence of walnut extract (10–200 μg/ml) or ellagic acid (10− 7–10− 5m), the VCAM-1 and ICAM-1 expression was quantified by cell-ELISA. We further evaluated the effect of walnut extract (10–50 μg/ml), in comparison with ellagic acid (10− 9–10− 6m), on nodule formation in the osteoblastic cell line KS483.Walnut extract and ellagic acid decreased significantly the TNF-α-induced endothelial expression of both VCAM-1 and ICAM-1 (P < 0·01; P < 0·001). Both walnut extract (at 10–25 μg/ml) and ellagic acid (at 10− 9–10− 8m) induced nodule formation in KS483 osteoblasts. The present results suggest that the walnut extract has a high anti-atherogenic potential and a remarkable osteoblastic activity, an effect mediated, at least in part, by its major component ellagic acid. Such findings implicate the beneficial effect of a walnut-enriched diet on cardioprotection and bone loss.

Effects of flavonoid on calcium content in femoral tissue culture and parathyroid hormone-stimulated osteoclastogenesis in bone marrow culture in vitro

The effect of various flavonoids, which are present in food and plants, on bone calcium content and osteoclastogenesis were investigated to compare action of flavonoid on bone formation and bone resorption in vitro. Rat femoral-diaphyseal (cortical bone) and -metaphyseal (trabecular bone) tissues were cultured for 48 h in Dulbecco's modified Eagle's medium (high glucose) supplemented with antibiotics and bovine serum albumin. Amoung quercetin, myricetin, kaempferol, isorhamnetin, curcumin, hesperidin, or astaxanthin in the range of 10(-7)-10(-5)M, culture with quercetin (10(-6) or 10(-5)M) caused a significant increase in diaphyseal calcium content. Such an effect was not seen in other compounds. Mouse bone marrow cells were cultured for 7 days in the presence of parathyroid hormone (PTH; 10(-7)M), a bone-resorbing factor, in vitro. Culture with PTH caused a significant increase in osteoclast-like cell formation. This increase was significantly inhibited in the presence of quercetin, myricetin, kaempferol, isorhamnetin, or curcumin in the range of 10(-8)-10(-6)M. Such an effect was not seen in the case of hesperidin or astaxanthin. In addition, culture with PTH (10(-7)M) caused a significant decrease in diaphyseal calcium content. This decrease was completely prevented in the presence of quercetin, myricetin, kaempferal, or isorhamnetin of 10(-6)M. This study demonstrates that various flavonoids have a potent inhibitory effect on osteoclastogenesis and bone resorption rather than bone formation in vitro. Among various flavonoids, quercetin had a stimulatory effect on bone formation and an inhibitory effect on bone resorption in vitro.

Myricetin induces human osteoblast differentiation through bone morphogenetic protein-2/p38 mitogen-activated protein kinase pathway

Myricetin (3,3',4',5,5',7-hexahydroxyflavone), a flavonoid compound, is present in vegetables and fruits. By means of alkaline phosphatase (ALP) activity, osteocalcin, and type I collagen enzyme-linked immunosorbent assay (ELISA), we have shown that myricetin exhibits a significant induction of differentiation in MG-63 and hFOB human osteoblasts. Alkaline phosphatase and osteocalcin are phenotypic markers for early-stage differentiated osteoblasts and terminally differentiated osteoblasts, respectively. Our results indicate that myricetin stimulates osteoblast differentiation at various stages, from maturation to terminally differentiated osteoblasts. Induction of differentiation by myricetin is associated with increased bone morphogenetic protein-2 (BMP-2) production. The BMP-2 antagonist noggin blocked myricetin-mediated ALP activity and osteocalcin secretion enhancement, indicating that BMP-2 production is required in myricetin-mediated osteoblast maturation and differentiation. Induction of differentiation by myricetin is associated with increased activation of SMAD1/5/8 and p38 mitogen-activated protein kinases. Cotreatment of p38 inhibitor SB203580 inhibited myricetin-mediated ALP upregulation and osteocalcin production. In conclusion, myricetin increased BMP-2 synthesis, and subsequently activated SMAD1/5/8 and p38 MAPK, and this effect may contribute to its action on the induction of osteoblast maturation and differentiation, followed by an increase of bone mass.