Effects of the phytoestrogen coumestrol on RANK-ligand-induced differentiation of osteoclasts

Dual regulation of phaseol on osteoclast formation and osteoblast differentiation by targeting TAK1 kinase for osteoporosis treatment

INTRODUCTION

Osteoporosis is an osteolytic disorder resulting from an inequilibrium between osteoblast-mediated osteogenesis and osteoclast-driven bone absorption. Safe and effective approaches for osteoporosis management are still highly demanded.

PURPOSE

This study aimed to examine the osteoprotective effect and the mechanisms of phaseol (PHA) in vitro and in vivo.

METHODS

Virtual screening identified the potential inhibitors of transforming growth factor-beta-activated kinase 1 (TAK1) from coumestans. The interaction between PHA and TAK1 was investigated by molecular simulation, pronase and thermal resistance assays. The maturation and function of osteoclasts were determined using tartrate-resistant acid phosphatase staining, bone absorption and F-actin ring formation assays. The differentiation and calcification of osteoblasts were assessed by alkaline phosphatase staining and Alizarin Red S staining. The activity of related targets and pathways were detected using immunoblotting, immunofluorescence and co-immunoprecipitation assays. The in vivo osteoprotective effect of PHA was evaluated using a lipopolysaccharide (LPS)-induced mouse osteoporosis model.

RESULTS

Firstly, we confirmed that TAK1 was essential in controlling bone remodeling by regulating osteogenesis and osteoclastogenesis. Moreover, PHA, a coumestan compound predominantly present in leguminous plants, was identified as a potent TAK1 inhibitor through virtual and real experiments. Subsequently, PHA was observed to enhance osteoblast differentiation and calcification, while suppress osteoclast maturation and bone resorptive function in vitro. Mechanistically, PHA remarkably inhibited the TRAF6-TAK1 complex formation, and inhibited the activation of TAK1, MAPK and NF-κB pathways by targeting TAK1. In the in vivo study, PHA strongly attenuated bone loss, inflammatory responses, and osteoclast over-activation in lipopolysaccharide-induced osteoporosis mice.

CONCLUSION

PHA had a dual-functional regulatory impact on osteogenesis and osteoclastogenesis by targeting TAK1, suppressing TRAF6-TAK1 complex generation, and modulating its associated signaling pathways, ultimately leading to mitigating osteoporosis. This study offered compelling evidence in favor of using PHA for preventing and managing osteoporosis as both a bone anabolic and anti-resorptive agent.

An ethnopharmacological, phytochemical, and pharmacological overview of onion (Allium cepa L.)

ETHNOPHARMACOLOGICAL RELEVANCE

Onion (Allium cepa L.) is one of the most widely distributed species within the Allium genus of family Amaryllidaceae. Onion has been esteemed for its medicinal properties since antiquity. It has been consumed for centuries in various indigenous cultures for the management of several ailments including microbial infections, respiratory, gastrointestinal, skin and cardio-vascular disorders, diabetes, renal colic, rheumatism, sexual impotence, menstrual pain, and headache. However, so far, there is a scarcity of recent data that compiles the plant chemistry, traditional practices, biological features, and toxicity.

AIM OF THE WORK

The aim of this review is to provide a comprehensive and analytical overview of ethnopharmacological uses, phytochemistry, pharmacology, industrial applications, quality control, and toxicology of onion, to offer new perspectives and broad scopes for future studies.

MATERIALS AND METHODS

The information gathered in this review was obtained from various sources including books, scientific databases such as Science Direct, Wiley, PubMed, Google Scholar, and other domestic and foreign literature.

RESULTS

Onion has a long history of use as a traditional medicine for management of various conditions including infectious, inflammatory, respiratory, cardiovascular diseases, diabetes, and erectile dysfunction. More than 400 compounds have been identified in onion including flavonoids, phenolic acids, amino acids, peptides, saponins and fatty acids. The plant extracts and compounds showed various pharmacological activities such as antimicrobial, antidiabetic, anti-inflammatory, anti-hyperlipidemic, anticancer, aphrodisiac, cardioprotective, and neuroprotective activities. In addition to its predominant medicinal uses, onion has found various applications in the functional food industry.

CONCLUSION

Extensive literature analysis reveals that onion extracts and bioactive constituents possess diverse pharmacological activities that can be beneficial for treating various diseases. However, the current research primarily revolves around the documentation of ethnic pharmacology and predominantly consists of in vitro studies, with relatively limited in vivo and clinical studies. Consequently, it is imperative for future investigations to prioritize and expand the scope of in vivo and clinical research. Additionally, it is strongly recommended to direct further research efforts towards toxicity studies and quality control of the plant. These studies will help bridge the current knowledge gaps and establish a solid basis for exploring the plant's potential uses in a clinical setting.

Phytoestrogens and Health Effects

Phytoestrogens are literally estrogenic substances of plant origin. Although these substances are useful for plants in many aspects, their estrogenic properties are essentially relevant to their predators. As such, phytoestrogens can be considered to be substances potentially dedicated to plant-predator interaction. Therefore, it is not surprising to note that the word phytoestrogen comes from the early discovery of estrogenic effects in grazing animals and humans. Here, several compounds whose activities have been discovered at nutritional concentrations in animals and humans are examined. The substances analyzed belong to several chemical families, i.e., the flavanones, the coumestans, the resorcylic acid lactones, the isoflavones, and the enterolignans. Following their definition and the evocation of their role in plants, their metabolic transformations and bioavailabilities are discussed. A point is then made regarding their health effects, which can either be beneficial or adverse depending on the subject studied, the sex, the age, and the physiological status. Toxicological information is given based on official data. The effects are first presented in humans. Animal models are evoked when no data are available in humans. The effects are presented with a constant reference to doses and plausible exposure.

Dietary interventions for better management of osteoporosis: An overview

Osteoporosis is a public health concern and a cause of bone loss, increased risk of skeletal fracture, and a heavy economic burden. It is common in postmenopausal women and the elderly and is impacted by dietary factors, lifestyle and some secondary factors. Although many drugs are available for the treatment of osteoporosis, these therapies are accompanied by subsequent side effects. Hence, dietary interventions are highly important to prevent osteoporosis. This review was aimed to provide a comprehensive understanding of the roles of dietary nutrients derived from natural foods and of common dietary patterns in the regulation of osteoporosis. Nutrients from daily diets, such as unsaturated fatty acids, proteins, minerals, peptides, phytoestrogens, and prebiotics, can regulate bone metabolism and reverse bone loss. Meanwhile, these nutrients generally existed in food groups and certain dietary patterns also play critical roles in skeletal health. Appropriate dietary interventions (nutrients and dietary patterns) could be primary and effective strategies to prevent and treat osteoporosis across the lifespan for the consumers and food enterprises.

Naturally occurring coumestans from plants, their biological activities and therapeutic effects on human diseases

Naturally occurring coumestans are known as a collection of plant-derived polycyclic aromatic secondary metabolites which are characterized by the presence of an oxygen heterocyclic four-ring system comprising a coumarin moiety and a benzofuran moiety sharing a C˭C bond. Recently, there is an increasing attention in excavating the medicinal potential of coumestans, particularly coumestrol, wedelolactone, psoralidin and glycyrol, in a variety of diseases. This review is a comprehensive inventory of the chemical structures of coumestans isolated from various plant sources during the period of 1956-2020, together with their reported biological activities. 120 molecules were collected and further classified as coumestans containing core skeleton, dimethylpyranocoumestans, furanocoumestans, O-glycosylated coumestans and others, which showed a wide range of pharmacological activities including estrogenic, anti-cancer, anti-inflammatory, anti-osteoporotic, organ protective, neuroprotective, anti-diabetic and anti-obesity, antimicrobial, immunosuppressive, antioxidant and skin-protective activities. Furthermore, this review focuses on the counteraction of coumestans against bone diseases and organ damages, and the involved molecular mechanisms, which could provide important information to better understand the medicinal values of these compounds. This review is intended to be instructive for the rational design and development of less toxic and more effective drugs with a coumestan scaffold.

Pharmacological Properties of Allium cepa, Preclinical and Clinical Evidences; A Review

Onion or Allium cepa (A. cepa) is one of the most important condiment plants grown and consumed all over the world. This plant has various therapeutic effects attributed to its constituents, such as quercetin, thiosulphinates and phenolic acids. In the present article, various pharmacological and therapeutic effects of A. cepa were reviewed. Different online databases using keywords such as onion, A. cepa, therapeutic effects, and pharmacological effects until the end of December 2019 were searched for this purpose. Onion has been suggested to be effective in treating a broad range of disorders, including asthma, inflammatory disorders, dysentery, wounds, scars, keloids and pain. In addition, different studies have demonstrated that onion possesses numerous pharmacological properties, including anti-cancer, anti-diabetic and anti-platelet properties as well as the effect on bone, cardiovascular, gastrointestinal, nervous, respiratory, and urogenital systems effects such as anti-osteoporosis, anti-hypertensive, antispasmodic, anti-diarrheal, neuro-protective, anti-asthmatic and diuretic effects. The present review provides detailed the various pharmacological properties of onion and its constituents and possible underlying mechanisms. The results of multiple studies suggested the therapeutic effect of onion on a wide range of disorders.

Isolation and Identification of Antiarthritic Constituents from Glycine tabacina and Network Pharmacology-Based Prediction of Their Protective Mechanisms against Rheumatoid Arthritis

Glycine tabacina (Labill.) Benth is an edible medicinal herb for rheumatoid arthritis (RA) treatment in folk medicine. Current phytochemical research on this dried herb led to the isolation of eight new coumestans, named glytabastan A-H (1-8), and twenty-three known compounds 9-31. Their structures were elucidated using spectroscopic methods. The antiarthritic activities of all isolates were evaluated, and the results showed that coumestans 1-6 and 8-10 could inhibit arthritic inflammation in vitro, while coumestans 1, 2, 9, and 10 significantly blocked the osteoclastogenesis induced by receptor activator of nuclear factor (NF) κB ligand (RANKL). Moreover, network pharmacological analysis revealed that the anti-RA effect of G. tabacina involved multitargets, multipathways such as PI3K/Akt and MAPK signaling pathways, and various biological processes such as inflammatory response and cytokine-mediated signaling pathways. These results suggested that this species and its novel coumestans could serve as potential antiarthritic agents for functional food or medicinal use.

The Role of Matrix Metalloproteinases in Periodontal Disease

This review provides a detailed description of matrix metalloproteinases (MMPs), focusing on those that are known to have critical roles in bone and periodontal disease. Periodontal disease is an inflammatory process initiated by anaerobic bacteria, which promote the host immune response in the form of a complex network of molecular pathways involving proinflammatory mediators such as cytokines, growth factors, and MMPs. MMPs are a family of 23 endopeptidases, collectively capable of degrading virtually all extracellular matrix (ECM) components. This study critically discusses the available research concerning the involvement of the MMPs in periodontal disease development and progression and presents possible therapeutic strategies. MMPs participate in morphogenesis, physiological tissue turnover, and pathological tissue destruction. Alterations in the regulation of MMP activity are implicated in the manifestation of oral diseases, and MMPs comprise the most important pathway in tissue destruction associated with periodontal disease. MMPs can be considered a risk factor for periodontal disease, and measurements of MMP levels may be useful markers for early detection of periodontitis and as a tool to assess prognostic follow-ups. Detection and inhibition of MMPs could, therefore, be useful in periodontal disease prevention or be an essential part of periodontal disease therapy, which, considering the huge incidence of the disease, may greatly improve oral health globally.

Coumestrol modulates Akt and Wnt/β-catenin signaling during the attenuation of adipogenesis

Coumestrol is a natural phytochemical present in plants such as red clover and soy, and has been reported to stimulate the estrogen receptor as a major phytoestrogen. While the molecular mechanisms responsible for the anti-adipogenic effects of phytoestrogens such as genistein and daidzein have been previously investigated, the effects of coumestrol on adipogenesis remain to be elucidated. We observed that coumestrol dose-dependently attenuates MDI (mixture of 3-isobutyl-1-methylxanthine, dexamethasone, and insulin)-induced lipid accumulation, consistent with an earlier study, while significantly inhibiting MDI-induced adipogenesis in the first 48 hours of differentiation, a critical time window for anti-adipogenic effects. Coumestrol treatment suppressed MDI-induced protein expression of PPARγ and C/EBPα in adipocytes, leading to the subsequent downregulation of FAS and aP2 expression. Akt and GSK3β were phosphorylated shortly after MDI stimulation, and these responses were inhibited by coumestrol treatment. Coumestrol also increased LRP6 protein expression, resulting in the recovery of β-catenin downregulation by MDI, while attenuating MDI-induced downregulation of Wnt10b. In addition, mRNA and protein expression of c-Myc and cyclin D1, target genes of β-catenin, were both recovered by coumestrol treatment. These results suggest that coumestrol inhibits adipocyte differentiation via regulation of Akt and Wnt/β-catenin signaling and may have potential for development as an agent to prevent adipogenesis.

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.

Genome-wide coexpression of steroid receptors in the mouse brain: Identifying signaling pathways and functionally coordinated regions

Steroid receptors are pleiotropic transcription factors that coordinate adaptation to different physiological states. An important target organ is the brain, but even though their effects are well studied in specific regions, brain-wide steroid receptor targets and mediators remain largely unknown due to the complexity of the brain. Here, we tested the idea that novel aspects of steroid action can be identified through spatial correlation of steroid receptors with genome-wide mRNA expression across different regions in the mouse brain. First, we observed significant coexpression of six nuclear receptors (NRs) [androgen receptor (Ar), estrogen receptor alpha (Esr1), estrogen receptor beta (Esr2), glucocorticoid receptor (Gr), mineralocorticoid receptor (Mr), and progesterone receptor (Pgr)] with sets of steroid target genes that were identified in single brain regions. These coexpression relationships were also present in distinct other brain regions, suggestive of as yet unidentified coordinate regulation of brain regions by, for example, glucocorticoids and estrogens. Second, coexpression of a set of 62 known NR coregulators and the six steroid receptors in 12 nonoverlapping mouse brain regions revealed selective downstream pathways, such as Pak6 as a mediator for the effects of Ar and Gr on dopaminergic transmission. Third, Magel2 and Irs4 were identified and validated as strongly responsive targets to the estrogen diethylstilbestrol in the mouse hypothalamus. The brain- and genome-wide correlations of mRNA expression levels of six steroid receptors that we provide constitute a rich resource for further predictions and understanding of brain modulation by steroid hormones.

Consumption of onion juice modulates oxidative stress and attenuates the risk of bone disorders in middle-aged and post-menopausal healthy subjects

Osteoporosis is a chronic inflammatory condition that is characterized by the loss of bone mineral density (BMD).

Inhibition of Osteoclast Differentiation by Ginsenoside Rg3 in RAW264.7 Cells via RANKL, JNK and p38 MAPK Pathways Through a Modulation of Cathepsin K: An In Silico and In Vitro Study

Various studies have demonstrated that overexpression of cathepsin K (Cat-K) causes excessive bone loss, which ultimately leads to a variety of bone diseases including osteoporosis. Therefore, inhibition of Cat-K signifies a potential therapeutic target in osteoporosis treatment. Ginsenoside Rg3 is one of the most promising compound of Panax ginseng Meyer (P. ginseng) with numerous biological activities. Thus, in recent study the inhibitory effect of Rg3 isolated from P. ginseng was investigated in order to impede the osteoclast activity by an in silico approach followed by in vitro study validation using RAW264.7 cells through the investigation of different biological activity prediction such as absorption distribution metabolism and excretion (ADMET) properties against Cat-K protein. The docking results of our study showed that Rg3 is a non-toxic compound and may act as a drug-like molecule. Additionally, the molecular interaction of Rg3 with the active residues of Cat-K markedly describes its inhibitory effects on osteoclastogenesis. Findings of the present study exhibited that Rg3 significantly reduced receptor activator of nuclear factor kappa B ligand (RANKL)-induced tartrate-resistant acid phosphatase (TRAP) activity, pit formation (actin rings), and TRAP-positive multinucleated cells development in RAW264.7 cells. Furthermore, Rg3 dose-dependently reduced the mRNA expression levels of osteoclast-specific markers such as RANK, TRAP, and Cat-K induced by RANKL through the down regulation of p38, extracellular signal-regulated kinase, and c-Jun N-terminal kinase (JNK) pathways. In conclusion, in silico docking study and in vitro validation together suggested that Rg3 inhibits osteoclastogenesis and reduces bone resorption through the inhibition of Cat-K. Therefore, Rg3 might be a useful therapeutic agent for the treatment of osteoporosis and proper bone formation. Copyright © 2015 John Wiley & Sons, Ltd.

Phytoestrogens as alternative hormone replacement therapy in menopause: What is real, what is unknown

Menopause is characterized by an altered hormonal status and by a decrease in life quality due to the appearance of uncomfortable symptoms. Nowadays, with increasing life span, women spend one-third of their lifetime under menopause. Understanding menopause-associated pathophysiology and developing new strategies to improve the treatment of menopausal-associated symptoms is an important topic in the clinic. This review describes physiological and hormone alterations observed during menopause and therapeutic strategies used during this period. We critically address the benefits and doubts associated with estrogen/progesterone-based hormone replacement therapy (HRT) and discuss the use of phytoestrogens (PEs) as a possible alternative. These relevant plant-derived compounds have structural similarities to estradiol, interacting with cell proteins and organelles, presenting several advantages and disadvantages versus traditional HRT in the context of menopause. However, a better assessment of PEs safety/efficacy would warrant a possible widespread clinical use.

Coumestrol induces mitochondrial biogenesis by activating Sirt1 in cultured skeletal muscle cells

The mitochondrion is a central organelle in cellular energy homeostasis; thus, reduced mitochondrial activity has been associated with aging and metabolic disorders. This paper provides biological evidence that coumestrol, which is a natural isoflavone, activates mitochondrial biogenesis. In cultured myocytes, coumestrol activated the silent information regulator two ortholog 1 (Sirt1) through the elevation of the intracellular NAD(+)/NADH ratio. Coumestrol also increased the mitochondrial contents and induced the expression of key proteins in the mitochondrial electron transfer chain in cultured myocytes. A Sirt1 inhibitor and Sirt1-targeting siRNAs abolished the effect of coumestrol on mitochondrial biogenesis. Similar to an increase in mitochondrial content, coumestrol improved myocyte function with increased ATP concentration. Taken together, the data suggest that coumestrol is a novel inducer of mitochondrial biogenesis through the activation of Sirt1.

Tools to evaluate estrogenic potency of dietary phytoestrogens:A consensus paper from the EU Thematic Network "Phytohealth" (QLKI-2002-2453)

Phytoestrogens are naturally occurring plantderived polyphenols with estrogenic potency. They are ubiquitous in diet and therefore, generally consumed. Among Europeans, the diet is rich in multiple putative phytoestrogens including flavonoids, tannins, stilbenoids, and lignans. These compounds have been suggested to provide beneficial effects on multiple menopause-related conditions as well as on development of hormone-dependent cancers, which has increased the interest in products and foods with high phytoestrogen content. However, phytoestrogens may as well have adverse estrogenicity related effects similar to any estrogen. Therefore, the assessment of estrogenic potency of dietary compounds is of critical importance. Due to the complex nature of estrogenicity, no single comprehensive test approach is available. Instead, several in vitro and in vivo assays are applied to evaluate estrogenic potency. In vitro estrogen receptor (ER) binding assays provide information on the ability of the compound to I) interact with ERs, II) bind to estrogen responsive element on promoter of the target gene as ligand-ER complex, and III) interact between the co-activator and ERs in ligand-dependent manner. In addition, transactivation assays in cells screen for ligand-induced ERmediated gene activation. Biochemical in vitro analysis can be used to test for possible effects on protein activities and E-screen assays to measure (anti)proliferative response in estrogen responsive cells. However, for assessment of estrogenicity in organs and tissues, in vivo approaches are essential. In females, the uterotrophic assay is applicable for testing ERa agonistic and antagonistic dietary compounds in immature or adult ovariectomized animals. In addition, mammary gland targeted estrogenicity can be detected as stimulated ductal elongation and altered formation of terminal end buds in immature or peripubertal animals. In males, Hershberger assay in peri-pubertal castrated rats can be used to detect (anti)androgenic/ (anti)estrogenic responses in accessory sex glands and other hormone regulated tissues. In addition to these short-term assays, sub-acute and chronic reproductive toxicity assays as well as two-generation studies can be applied for phytoestrogens to confirm their safety in long-term use. For reliable assessment of estrogenicity of dietary phytoestrogens in vivo, special emphasis should be focused on selection of the basal diet, route and doses of administration, and possible metabolic differences between the species used and humans. In conclusion, further development and standardization of the estrogenicity test methods are needed for better interpretation of both the potential benefits and risks of increasing consumption of phytoestrogens from diets and supplements.

Effects of bisphenol A administration to pregnant mice on serum Ca and intestinal Ca absorption

Bisphenol A (BPA) is a xenoestrogen commonly used in food storage plastics. The present study was conducted to clarify the effects of BPA administration to pregnant mice on serum calcium (Ca) and Ca metabolism of the gut and kidney. From 6.5 to 16.5 days post coitus (dpc), pregnant mice were administered at 2 mg or 20 mg/kg body weight/day of BPA. Serum Ca was decreased in mice treated with 20 mg BPA at 17.5 dpc, but no remarkable differences were detected in the alkaline phosphatase activity and vitamin D receptor protein expression in the duodenum and jejunum. The messenger RNA (mRNA) expressions of calcium binding protein (CaBP-9k) and active vitamin D synthesis enzyme (CYP27B1) in the kidney were increased in mice treated with 20 mg BPA. The mRNA expressions of occludin and junction adherence molecular A (JAM-A) in the duodenum and ileum, which regulate paracellular transport, were increased in mice treated with 20 mg BPA. However, the administration of 2 mg BPA had no effect on serum Ca and mRNA expressions of relative genes in Ca metabolism. These results imply that BPA administration at 20 mg/kg body weight/day during pregnancy decreases serum Ca in pre-delivery mice, which may be partly due to decreased paracellular Ca absorption.

Coumestrol promotes proliferation and osteoblastic differentiation in rat bone marrow stromal cells

Although the effects of coumestrol on osteoblasts and osteoclasts can be summarized as increasing the bone density and preventing bone resorption, direct and detailed effects of coumestrol on bone marrow stromal cells remain obscure. In the present study, the effects of coumestrol on proliferation and osteoblastic differentiation of rat bone marrow stromal cells (BMSCs) have been investigated; the regulative effect of coumestrol on BMSCs and skeletal system has also been discussed. The results showed that treatment with coumestrol increased cellular activities (analyzed by MTT assay), alkaline phosphatase (ALP), type I collagen and osteocalcin (OCN) activity as well as the protein and gene expression of OPG, gene expression ratio of OPG/RANKL and gene expression of estrogen receptor alpha(ERalpha). These results demonstrate that phytoestrogen coumestrol has a direct enhancing effect on the proliferation and osteogenic differentiation of bone marrow stromal cells, which would lead to stimulation of bone formation, and it can also protect the whole skeletal system by regulating OPG/RANKL expression, and these effects may be mediated by ERalpha.

Genistein and a soy extract differentially affect three-dimensional bone parameters and bone-specific gene expression in ovariectomized mice

Soy isoflavone preparations, such as purified genistein and a soy extract (Novasoy), were reported previously to exert beneficial effects on bones. Our purpose in this study was to compare the effects of genistein and Novasoy on 3-dimensional trabecular bone parameters and the expression of bone-specific genes in ovariectomized (OVX) mice. The sham-operated mice were fed the control diet and OVX mice were fed diets containing genistein or Novasoy or the control diet, with or without 17beta-estradiol treatment, for 5 wk. Trabecular bone parameters of tibias were measured by microcomputed tomography and gene expression was assayed by real-time PCR. Consumption of diets containing genistein or Novasoy partially prevented the ovariectomy-induced increase in body weight but did not alter the uterus weight of the OVX mice. Novasoy, but not purified genistein, significantly preserved trabecular bone mass, bone volume, and trabecular bone separation in the proximal tibial metaphysis. Purified genistein decreased mRNA expression of receptor activator of nuclear factor-kappaB ligand (RANKL), carbonic anhydrase II, and cathepsin K and enhanced the ratio of osteoprotegrin:RANKL mRNA expression in the tibial head of the OVX mice. In contrast, the diet containing Novasoy suppressed the OVX-induced increase in serum alkaline phosphatase but did not alter bone-specific gene expression of tibia. Our study demonstrated that a soy extract containing a similar level of genistein in the form of Novasoy is more effective than purified genistein in improving tibial trabecular bone quality in OVX mice, but the mechanism of action might be distinct from that of genistein.

Mitogen-activated protein kinase (MAPK) pathway mediates the oestrogen-like activities of ginsenoside Rg1 in human breast cancer (MCF-7) cells

BACKGROUND AND PURPOSE

The present study was designed to determine how ginsenoside Rg1, an active ingredient in ginseng root, exerts its oestrogenic effects. We hypothesize that Rg1 may exert oestrogen-like actions in MCF-7 cells by activating the mitogen-activated protein kinase (MAPK) pathway in a ligand-independent manner.

EXPERIMENTAL APPROACH

MCF-7 cells were co-incubated with the MAPK inhibitor PD98059 to determine whether the stimulant effects of Rg1 on cell proliferation, the induction of IGF-IR and pS2, the functional transactivation of oestrogen receptor-alpha (ERalpha), as well as ERalpha phosphorylation are dependent on MAPK. The time-dependent responses of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated protein kinase (ERK) to Rg1 in MCF-7 cells were studied. The responses of MEK phosphorylation to Rg1 in oestrogen receptor (ER)-negative HEK293 cells were also determined. The effects of Rg1 on cell proliferation and IGF-IR protein expression were studied in the presence of tyrosine kinase inhibitor genistein to elucidate the involvement of tyrosine kinase in mediating these effects.

KEY RESULTS

The oestrogenic effects of Rg1 in MCF-7 cells were abolished in the presence of PD98059. Rg1 could induce MEK protein expression and the phosphorylation level of MEK and ERK significantly in a time- and dose-dependent manner. Rg1 activated MEK phosphorylation in ER-negative HEK293 cells in a time- and dose-dependent manner. Rg1 induction of cell proliferation and IGF-IR protein expression was abolished by co-treatment with genistein.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results show that the MAPK pathway is involved in mediating the oestrogen-like actions of Rg1 in MCF-7 cells and suggest that Rg1 may activate ERalpha via MEK/ERK in a ligand-independent manner.

Water solution of onion crude powder inhibits RANKL-induced osteoclastogenesis through ERK, p38 and NF-kappaB pathways

Onion powder has been reported to decrease the ovariectomy-induced bone resorption of rats. However, the molecular mechanism of onion powder on the bone cells has not been reported. Here, we report that water solution of onion crude powder decreases the osteoclastogenesis from co-cultures of bone marrow stromal cells and macrophage cells. Additionally, water solution of onion crude powder inhibits the RANKL-induced ERK, p38 and NF-kappaB activation in macrophages. In summary, our data showed that onion powder may benefit bone through an anti-resorption effect on the osteoclasts.

INTRODUCTION

A nutritional approach is important for both prevention and treatment of osteoporosis. Onion has been reported to decrease the ovariectomy-induced bone resorption. However, the functional effects of onion on the cultured osteoclasts and osteoblasts remain largely unknown. Here, we found that water solution of onion crude powder markedly inhibited the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis through ERK, p38 and NF-kappaB pathways. Other studies were also designed to investigate the potential signaling pathways involved in onion-induced decrease in osteoclastogenesis.

METHODS

The osteoclastogenesis was examined using the TRAP staining method. The MAPKs and NF-kappaB pathways were measured using Western blot analysis. A transfection protocol was used to examine NF-kappaB activity.

RESULTS

Water solution of onion crude powder inhibited the RANKL plus M-CSF-induced osteoclastic differentiation from either bone marrow stromal cells or from RAW264.7 macrophage cells. Treatment of RAW264.7 macrophages with RANKL could induce the activation of ERK, p38 and NF-kappaB that was inhibited by water solution of onion crude powder. On the other hand, it did not affect the cell proliferation and differentiation of human cultured osteoblasts.

CONCLUSIONS

Our data suggest that water solution of onion crude powder inhibits osteoclastogenesis from co-cultures of bone marrow stromal cells and macrophage cells via attenuation of RANKL-induced ERK, p38 and NF-kappaB activation.

Baicalein inhibits osteoclast differentiation and induces mature osteoclast apoptosis

In bone remodeling, an imbalance caused by increased bone resorption over bone formation leads to adult skeletal diseases such as osteoporosis. Therefore, the development of anti-resorptive agents has still gained more interest. In this study, using cell-based assay systems in RAW264.7 murine macrophage cells, we found that baicalein significantly inhibited the receptor activator of NF-kappaB ligand (RANKL)-induced tartrate-resistance acid phosphatase (TRAP) activity and the formation of multinucleated osteoclasts in a dose-dependent manner. Interestingly, baicalein inhibited RANKL-induced activation of signaling molecules (Akt, ERK/MAP kinase and NF-kappaB) and mRNA expression of osteoclast-associated genes (TRAP, matrix metalloproteinase 9 and c-Src) and another transcription factors (c-Fos, Fra-2 and NFATc1). In addition, baicalein inhibited the bone resorptive activity of mature osteoclasts by inducing apoptosis. The inhibitory effects of baicalein on the formation of mouse bone marrow macrophage-derived osteoclasts and their bone resorptive activity were also observed. In conclusion, although further studies are needed to determine its biological efficacy and precise mechanism in bone, the present results demonstrated that baicalein has a potential to inhibit osteoclast differentiation and induce mature osteoclast apoptosis.

Phyto-oestrogens and bone health

As oestrogen deficiency is the main cause in the pathogenesis of osteoporosis hormone-replacement therapy remains the mainstay for prevention. However, prophylaxis by hormone-replacement therapy is limited. Phyto-oestrogens, which are weakly-oestrogenic compounds present in plants, deserve particular mention because emerging data support the suggestion that they may prevent bone loss associated with the menopause. In the past few years extensive research using animal models has provided convincing data to indicate a significant improvement in bone mass or other end points following feeding with soyabean. Moreover, observational studies relate the lower incidence of osteoporosis among women in the Eastern world to a diet rich in phyto-oestrogens. However, it is not valid to extrapolate to the Western situation. The varied clinical trials that have been published suggest that isoflavones reduce bone loss in women in the early period post menopause, but a definitive result requires more investigations of the effect of phyto-oestrogens on bone health that have substantial sample size and are of long duration. In addition, the clinical efficacy of soya foods in preventing osteopenia depends on their intestinal metabolism. Thus, phyto-oestrogens are a source for putative innovative dietary health intervention for post-menopausal women. However, more data are necessary, particularly in relation to their effect on the risk of fracture.

Phenethyl isothiocyanate suppresses receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis by blocking activation of ERK1/2 and p38 MAPK in RAW264.7 macrophages

Osteoclastogenesis is induced by differentiation of hemopoietic cells of monocyte-macrophage lineage into bone-resorbing osteoclasts. The process is initiated by receptor activator of NF-kappaB ligand (RANKL) and resultant activation of mitogen-activated protein kinases (MAPK), including extracellular signal-regulated kinase (ERK)1/2, as well as the NFkappaB pathway. Phenethyl isothiocyanate (PEITC), a phytochemical present in various cruciferous plants, has been shown to disrupt those signaling pathways in several cell types. In this study, we examined the efficacy of PEITC for suppressing RANKL-induced osteoclastogenesis in RAW264.7 murine macrophages and addressed the underlying molecular mechanisms. PEITC (2-10 microM) suppressed osteoclastogenesis in a concentration dependent manner, as detected by tartarate-resistant acid phosphatase (TRAP) activity and microscopic observations. RANKL-up-regulated extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) activities were attenuated by PEITC, whereas c-Jun N-terminal kinase (JNK1/2) activation was increased. PEITC also abrogated the RANKL-induced degradation of IkappaB-alpha, a suppressive partner of nuclear factor kappaB (NFkappaB), thereby inhibiting transcription activity, as detected by a reporter assay. In addition, PEITC reduced the level of NFkappaB-dependent mRNA expression of nuclear factor of activated T cell (NFAT)c1, a master regulator of osteoclastogenesis. Our results indicate that PEITC is a promising agent for treatment of osteoclastogenesis with a reasonable action mechanism.

Homocysteine enhances bone resorption by stimulation of osteoclast formation and activity through increased intracellular ROS generation

Hyperhomocystinemia is a modifiable risk factor for osteoporosis and fracture. Physiologic concentrations of Hcy directly activate osteoclast formation and activity through stimulation of p38 MAPK and integrin beta3. The effects of Hcy were mediated by generation of intracellular ROS.

INTRODUCTION

Hyperhomocysteinemia is a modifiable risk factor for osteoporosis and its related bone fractures. It has been reported that bone resorption and turnover rate were increased in hyperhomocystinemia. Using mouse bone marrow cells, we examined the direct effects of homocysteine (Hcy) on osteoclast formation and activity.

MATERIALS AND METHODS

Osteoclast formation was determined by TRACP staining and TRACP activity. Intracellular reactive oxygen species (ROS) generation was measured using a fluorescent probe, dichlorodihydrofluorescein diacetate. Intracellular signaling cascades of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-kappaB were measured by Western blotting. Integrin beta3 mRNA levels were measured by RT-PCR. Actin ring formation and bone resorption assays were also performed.

RESULTS

Physiologic concentrations of Hcy upregulated TRACP+ multinucleated cells and TRACP activity, stimulated actin ring formation, and increased the number of nuclei per cell and the level of expression of integrin beta3 mRNA. In addition, Hcy increased bone resorption and stimulated p38 MAPK activity and intracellular reactive oxygen species (ROS) generation. All of these Hcy-induced changes were blocked by pretreatment with the antioxidant, N-acetyl cysteine.

CONCLUSIONS

Hcy directly activates osteoclast formation and activity through increased generation of intracellular ROS. These findings suggest that, in individuals with mild to moderate hyperhomocystinemia, increased bone resorption by osteoclasts may contribute to osteoporosis and that an antioxidant may attenuate bone loss in these individuals.