Vitamin K2 inhibits osteoclastic bone resorption by inducing osteoclast apoptosis

Beyond the Coagulation Cascade: Vitamin K and Its Multifaceted Impact on Human and Domesticated Animal Health

Vitamin K (VK) is an essential micronutrient impacting many systems in the body. This lipid-soluble vitamin is found in various plant and animal products and is absorbed via the lymphatic system. This biomolecule's importance to human health includes but is not limited to its promotion of brain, cardiovascular, bone, and immune functions. These biological properties are also necessary for maintaining domesticated animal health. The synergistic impact of both VK and vitamin D (VD) maximizes these health benefits, specifically for the circulatory and skeletal systems. This manuscript reviews VK's properties, molecular structures, nutrikinetics, mechanisms of action, daily requirements, safety in supplemental form, biomarkers used for its detection, and impacts on various organs. The purpose of synthesizing this information is to evaluate the potential uses of VK for the treatment or prevention of diseases.

Construction of microgravity biological knowledge graph and its applications in anti-osteoporosis drug prediction

Microgravity in the space environment can potentially have various negative effects on the human body, one of which is bone loss. Given the increasing frequency of human space activities, there is an urgent need to identify effective anti-osteoporosis drugs for the microgravity environment. Traditional microgravity experiments conducted in space suffer from limitations such as time-consuming procedures, high costs, and small sample sizes. In recent years, the in-silico drug discovery method has emerged as a promising strategy due to the advancements in bioinformatics and computer technology. In this study, we first collected a total of 184,915 literature articles related to microgravity and bone loss. We employed a combination of dependency path extraction and clustering techniques to extract data from the text. Afterwards, we conducted data cleaning and standardization to integrate data from several sources, including The Global Network of Biomedical Relationships (GNBR), Curated Drug-Drug Interactions Database (DDInter), Search Tool for Interacting Chemicals (STITCH), DrugBank, and Traditional Chinese Medicines Integrated Database (TCMID). Through this integration process, we constructed the Microgravity Biology Knowledge Graph (MBKG) consisting of 134,796 biological entities and 3,395,273 triplets. Subsequently, the TransE model was utilized to perform knowledge graph embedding. By calculating the distances between entities in the model space, the model successfully predicted potential drugs for treating osteoporosis and microgravity-induced bone loss. The results indicate that out of the top 10 ranked western medicines, 7 have been approved for the treatment of osteoporosis. Additionally, among the top 10 ranked traditional Chinese medicines, 5 have scientific literature supporting their effectiveness in treating bone loss. Among the top 20 predicted medicines for microgravity-induced bone loss, 15 have been studied in microgravity or simulated microgravity environments, while the remaining 5 are also applicable for treating osteoporosis. This research highlights the potential application of MBKG in the field of space drug discovery.

Can vitamins improve periodontal wound healing/regeneration?

Periodontitis is a complex inflammatory disorder of the tooth supporting structures, associated with microbial dysbiosis, and linked to a number if systemic conditions. Untreated it can result in an irreversible damage to the periodontal structures and eventually teeth loss. Regeneration of the lost periodontium requires an orchestration of a number of biological events on cellular and molecular level. In this context, a set of vitamins have been advocated, relying their beneficial physiological effects, to endorse the biological regenerative events of the periodontium on cellular and molecular levels. The aim of the present article is to elaborate on the question whether or not vitamins improve wound healing/regeneration, summarizing the current evidence from in vitro, animal and clinical studies, thereby shedding light on the knowledge gap in this field and highlighting future research needs. Although the present review demonstrates the current heterogeneity in the available evidence and knowledge gaps, findings suggest that vitamins, especially A, B, E, and CoQ10, as well as vitamin combinations, could exert positive attributes on the periodontal outcomes in adjunct to surgical or nonsurgical periodontal therapy.

The Potential of Vitamin K as a Regulatory Factor of Bone Metabolism-A Review

Vitamin K (VK), a fat-soluble vitamin, is essential for the clotting of blood because of its role in the production of clotting factors in the liver. Moreover, researchers continue to explore the role of VK as an emerging novel bioactive molecule with the potential function of improving bone health. This review focuses on the effects of VK on bone health and related mechanisms, covering VK research history, homologous analogs, dietary sources, bioavailability, recommended intake, and deficiency. The information summarized here could contribute to the basic and clinical research on VK as a natural dietary additive and drug candidate for bone health. Future research is needed to extend the dietary VK database and explore the pharmacological safety of VK and factors affecting VK bioavailability to provide more support for the bone health benefits of VK through more clinical trials.

A Case Control Study Evaluating the Relationship between Vitamin K2 Serum Level and Periodontitis

BACKGROUND AND AIM

Vitamin K2 (VK2) is an essential co-factor for bone metabolism. There is still very little data regarding possible VK2 relation to periodontitis. This study aimed to investigate any potential link between VK2 serum level and the severity of periodontitis in comparison to a control group of healthy individuals. The trial was performed on 100 patients among whom 50 were diagnosed with periodontitis. The patients underwent full clinical periodontal and radiological examination. The VK2 serum level was assessed using the ELISA kit (Gla-type osteocalcin EIA Kit, Takara, Kusatsu). Patients with periodontitis had mean serum levels of VK2 significantly lower (0.27 ± 0.06 nmol/L; p < 0.001) than the control group (0.43 ± 0.09 nmol/L; p < 0.001) regardless of the patient's age or sex. The VK2 serum level decreased with the severity of periodontitis with the lowest level in stage IV of the disease (0.19 ± 0.01 nmol/L; p < 0.001). Also, a significant drop was noticed between the grades of periodontitis. Individuals with localized forms of the disease had significantly lower VK2 levels (0.26 ± 0.006 nmol/L; p < 0.001) in comparison to subjects with generalized periodontitis (0.30 ± 0.01 nmol/L; p < 0.001). The VK2 serum levels were also associated with most of the clinical parameters such as bleeding on probing (-0.805, 95% CI: -0.894 to -0.654, p < 0.001), attachment loss (-0.752, 95% CI: -0.862 to -0.574, p < 0.001), and bone loss (-0.656, 95% CI: -0.801 to -0.439, p < 0.001). In the present study, the VK2 serum level was correlated to periodontitis, and its severity, complexity, extension, and grade. The range of VK2 was decreasing together with the worsening of all clinical parameters of periodontitis.

The additive effect of vitamin K supplementation and bisphosphonate on fracture risk in post-menopausal osteoporosis: a randomised placebo controlled trial

This study assessed whether vitamin K, given with oral bisphosphonate, calcium and/or vitamin D has an additive effect on fracture risk in post-menopausal women with osteoporosis. No difference in bone density or bone turnover was observed although vitamin K1 supplementation led to a modest effect on parameters of hip geometry.

PURPOSE

Some clinical studies have suggested that vitamin K prevents bone loss and may improve fracture risk. The aim was to assess whether vitamin K supplementation has an additive effect on bone mineral density (BMD), hip geometry and bone turnover markers (BTMs) in post-menopausal women with osteoporosis (PMO) and sub-optimum vitamin K status receiving bisphosphonate, calcium and/or vitamin D treatment.

METHODS

We conducted a trial in 105 women aged 68.7[12.3] years with PMO and serum vitamin K1 ≤ 0.4 µg/L. They were randomised to 3 treatment arms; vitamin K1 (1 mg/day) arm, vitamin K2 arm (MK-4; 45 mg/day) or placebo for 18 months. They were on oral bisphosphonate and calcium and/or vitamin D. We measured BMD by DXA, hip geometry parameters using hip structural analysis (HSA) software and BTMs. Vitamin K1 or MK-4 supplementation was each compared to placebo. Intention to treat (ITT) and per protocol (PP) analyses were performed.

RESULTS

Changes in BMD at the total hip, femoral neck and lumbar spine and BTMs; CTX and P1NP did not differ significantly following either K1 or MK-4 supplementation compared to placebo. Following PP analysis and correction for covariates, there were significant differences in some of the HSA parameters at the intertrochanter (IT) and femoral shaft (FS): IT endocortical diameter (ED) (% change placebo:1.5 [4.1], K1 arm: -1.02 [5.07], p = 0.04), FS subperiosteal/outer diameter (OD) (placebo: 1.78 [5.3], K1 arm: 0.46 [2.23] p = 0.04), FS cross sectional area (CSA) (placebo:1.47 [4.09],K1 arm: -1.02[5.07], p = 0.03).

CONCLUSION

The addition of vitamin K1 to oral bisphosphonate with calcium and/or vitamin D treatment in PMO has a modest effect on parameters of hip geometry. Further confirmatory studies are needed.

TRIAL REGISTRATION

The study was registered at Clinicaltrial.gov:NCT01232647.

Role of Vitamin K in Bone and Muscle Metabolism

Vitamin K, a cofactor for the γ-glutamyl carboxylase enzyme, is required for the post-translational activation of osteocalcin and matrix Gla protein, which play a key role in bone and muscle homeostasis. In vivo and in vitro models for osteoporosis and sarcopenia suggest the vitamin K could exert a positive effect in both conditions. In bone, it increases osteoblastogenesis, whilst decreases osteoclast formation and function. In muscle, it is associated with increased satellite cell proliferation and migration and might play a role in energy metabolism. Observational trials suggest that high levels of vitamin K are associated with increased bone mineral density and reduced fracture risk. However, interventional studies for vitamin K supplementation yielded conflicting results. Clinical trials in sarcopenia suggest that vitamin K supplementation could improve muscle mass and function. One of the main limitations on the vitamin K studies are the technical challenges to measure its levels in serum. Thus, they are obtained from indirect sources like food questionnaires, or levels of undercarboxylated proteins, which can be affected by other environmental or biological processes. Although current research appoints to a beneficial effect of vitamin K in bone and muscle, further studies overcoming the current limitations are required in order to incorporate this supplementation in the clinical management of patients with osteosarcopenia.

The Interface between Cell Signaling Pathways and Pregnane X Receptor

Highly expressed in the enterohepatic system, pregnane X receptor (PXR, NR1I2) is a well-characterized nuclear receptor (NR) that regulates the expression of genes in the liver and intestines that encode key drug metabolizing enzymes and drug transporter proteins in mammals. The net effect of PXR activation is to increase metabolism and clear drugs and xenobiotics from the body, producing a protective effect and mediating clinically significant drug interaction in patients on combination therapy. The complete understanding of PXR biology is thus important for the development of safe and effective therapeutic strategies. Furthermore, PXR activation is now known to specifically transrepress the inflammatory- and nutrient-signaling pathways of gene expression, thereby providing a mechanism for linking these signaling pathways together with enzymatic drug biotransformation pathways in the liver and intestines. Recent research efforts highlight numerous post-translational modifications (PTMs) which significantly influence the biological function of PXR. However, this thrust of research is still in its infancy. In the context of gene-environment interactions, we present a review of the recent literature that implicates PXR PTMs in regulating its clinically relevant biology. We also provide a discussion of how these PTMs likely interface with each other to respond to extracellular cues to appropriately modify PXR activity.

Vitamin K and D Supplementation and Bone Health in Chronic Kidney Disease-Apart or Together?

Vitamin K (VK) and vitamin D (VD) deficiency/insufficiency is a common feature of chronic kidney disease (CKD), leading to impaired bone quality and a higher risk of fractures. CKD patients, with disturbances in VK and VD metabolism, do not have sufficient levels of these vitamins for maintaining normal bone formation and mineralization. So far, there has been no consensus on what serum VK and VD levels can be considered sufficient in this particular population. Moreover, there are no clear guidelines how supplementation of these vitamins should be carried out in the course of CKD. Based on the existing results of preclinical studies and clinical evidence, this review intends to discuss the effect of VK and VD on bone remodeling in CKD. Although the mechanisms of action and the effects of these vitamins on bone are distinct, we try to find evidence for synergy between them in relation to bone metabolism, to answer the question of whether combined supplementation of VK and VD will be more beneficial for bone health in the CKD population than administering each of these vitamins separately.

Effect of Vitamin K2 Alone or in Combination on Various Bone Turnover Markers Amongst Postmenopausal Females

Background

Osteoporosis is common in postmenopausal women. Some studies have demonstrated the usefulness of vitamin K through the action of bone-specific proteins and osteoblast and osteoclast activities. However, no systematic review had explored this aspect in postmenopausal women. Hence, this systematic review aimed to explore the effect of vitamin K₂ alone or in combination with other agents (vitamin D₃ or calcium) on various bone turnover markers (BTMs) and bone mineral density (BMD) in postmenopausal women.

Methods

MEDLINE, ScienceDirect, PubMed, and Google Scholar were searched to identify relevant studies using specific inclusion criteria. Data extraction and quality assessment were carried out using standardized tests, and the results were narratively synthesized and presented in the form of tables.

Results

Vitamin K₂ was beneficial in inducing an improvement or preventing deterioration, as evidenced by the BMD and osteocalcin (OC), undercarboxylated OC (ucOC), carboxylated OC (cOC), and γ-carboxylated OC levels. However, its effect was not conclusive when procollagen type 1 N-terminal propeptide, carboxyterminal propeptide of type I procollagen, C-terminal telopeptide of type I collagen, bone alkaline phosphatase, deoxypyridinoline, and N-terminal telopeptide levels (NTX) and ucOC:cOC or cOC:ucOC, and NTX:creatinine ratios were examined.

Conclusions

Vitamin K₂ supplementation combined with vitamin D and calcium was found to be advantageous. However, vitamin K₂ supplementation cannot replace the existing treatment options. In addition, vitamin K₂ should be used with caution, considering its interactions with food and other drugs.

The Medical Benefits of Vitamin K2 on Calcium-Related Disorders

BACKGROUND

Due to the potentially crucial role of vitamin K2 in calcium metabolism, a deficit can disrupt many mechanisms, resulting in an array of different issues, such as broken bones, stiff arteries and poor fertility. Although there has been existing research, the potential of vitamin K2 as a treatment for conditions including cerebral palsy, parathyroid disease, heart disease and gastrointestinal disease is unknown. This review discusses the biochemistry of vitamin K and the metabolism of calcium, followed by an analysis of the current literature available on vitamin K2 and its prospects.

METHODS

Using public libraries including PubMed and Wiley, we searched for existing research on the metabolism and use of vitamin K2 that has been conducted in the preceding two decades.

RESULTS

Data indicated that vitamin K2 had a positive impact on osteoporosis, cardiovascular disease, parathyroid disorders, cerebral palsy and sperm motility.

CONCLUSION

Due to the existence of confounding variables and limitations in the quality and volume of research conducted, further investigation must be done to see whether the beneficial effects seen are reproducible and must assess the viability of vitamin K2 as treatment in isolation for these conditions.

Nutritional interventions during bed rest and spaceflight: prevention of muscle mass and strength loss, bone resorption, glucose intolerance, and cardiovascular problems

Bed rest is necessary for many medical conditions but also used as a ground-based model for space flight (along with head-down tilt to simulate fluid shifts in microgravity). The purpose of this review is to examine nutritional interventions during bed rest and spaceflight for prevention of muscle and strength loss, glucose intolerance, bone resorption, and cardiovascular problems. Increased dietary protein intake and supplementation with amino acids, β-hydroxy-β-methylbutyrate, or cofactors with antioxidant properties are effective for ameliorating bed rest-induced loss of muscle mass and strength. Previous literature involving bed rest with dietary protein/amino acid supplementation had mixed findings, likely due to differences in dosage. Although high protein intake in some studies prevents bed rest-induced muscle loss, it also increases bone resorption. High calcium intake and vitamin D supplementation are not beneficial for preventing bone degradation during bed rest or spaceflight. Very few studies investigated countermeasures to prevent glucose intolerance and cardiovascular risks during bed rest/spaceflight. Low-glycemic index diets might be beneficial for the prevention of bed rest-induced glucose intolerance and cardiovascular problems. The present evidence warrants additional studies on the exact threshold of protein/amino acid intake to prevent the loss of muscle mass and strength during bed rest/spaceflight specifically to maintain the beneficial effects of proteins on muscle mass and function without increasing bone resorption. Furthermore, it is suggested to study the effects of vitamin K supplementation on bone health during bed rest/spaceflight and determine the role of long-term low-glycemic index diets on glucose regulation and cardiovascular health during extended bed rest.

Genome-Wide Analysis of circular RNAs and validation of hsa_circ_0006719 as a potential novel diagnostic biomarker in congenital scoliosis patients

Congenital scoliosis (CS) is a form of spinal curvature resulting from anomalous development of vertebrae. Recent studies demonstrated that circRNAs could serve as potential biomarkers of disease diagnosis. Genome‐wide circRNAs expression in seven CS patients and three healthy controls was initially detected. Bioinformatics analysis was conducted to explore the potential pathological pathway of CS. Quantitative PCR (qPCR) was performed to validate the selected circRNAs in the replication cohort with 32 CS patients and 30 healthy controls. Logistic regression controlling for gender was conducted to compare the expression difference. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic value. Twenty‐two differentially expressed circRNAs were filtered from genome‐wide circRNA sequencing. Seven circRNAs were validated by qPCR. Only hsa_circ_0006719 was confirmed to have a higher expression level in the CS group than the healthy control group (P = 0.036). Receiver operating characteristic curve also suggested that hsa_circ_0006719 had significant diagnostic value for CS (AUC = 0.739, P = 0.001). We described the first study of circRNAs in CS and validated hsa_circ_0006719 as a potential novel diagnostic biomarker of CS.

Positive and negative regulators of osteoclast apoptosis

Survival and apoptosis are of major importance in the osteoclast life cycle. As osteoclasts have short lifespan, any alteration that prolongs their viability may cause enhanced osteoclast activity. Hence, the regulation of OC apoptosis has been recognized as a critical factor in bone remodeling. An imbalance in bone remodeling due to increased osteoclast activity leads to most adult bone diseases such as osteoporosis, rheumatoid arthritis and multiple myeloma. Therefore, manipulating osteoclast death would be a viable therapeutic approach in ameliorating bone diseases, with accelerated resorption. Over the last few decades we have witnessed the unraveling of many of the intracellular mechanisms responsible for osteoclast apoptosis. Thus, an understanding of the underlying mechanisms by which osteoclasts undergo programmed cell death and the regulators that modulate that activity will undoubtedly provide an insight into the development of pharmacological agents to treat such pathological bone diseases.

A comparatively study of menaquinone-7 isolated from Cheonggukjang with vitamin K1 and menaquinone-4 on osteoblastic cells differentiation and mineralization

The effect of menaquinone-7 isolated from cheonggukjang was comparatively investigated with vitamin K₁ and menaquinone-4 on cell differentiation and mineralization of the osteoblastic cell line MC3T3-E1. Results indicated that all vitamin K species significantly increased MC3T3-E1 cell proliferation, cellular alkaline phosphatase activity, osteocalcin synthesis, and calcium deposition in a dose-dependent manner. Menaquinone-4 and menaquinone-7 had more potent effects on calcium deposition than vitamin K₁, and their effects were only partly reduced by warfarin (γ-carboxylation inhibitor) treatment, while warfarin abolished the induction activity of vitamin K₁ on calcification. This suggests that vitamin K₁ and K₂ (menaquinone-4 & menaquinone-7) may have different mechanisms in stimulating osteoblast mineralization. In addition, the mRNA expression ratio of osteoprotegerin and the receptor activator of nuclear factor-kB ligand was also dramatically increased by treatment with vitamin K₁ (62%), menaquinone-4 (247%), and menaquinone-7 (329%), suggesting that vitamin K may suppress the formation of osteoclast by up-regulating the ratio of osteoprotegerin/receptor activator of nuclear factor-kB ligand in osteoblasts. These results provide compelling evidence that vitamin K₁, menaquinone-4, and menaquinone-7 all can promote bone health, which might be associated with elevations in the osteoprotegerin/receptor activator of nuclear factor-kB ligand ratio.

Vitamin K1 Supplementation Did Not Alter Inflammatory Markers and Clinical Status in Patients with Rheumatoid Arthritis

Background: Rheumatoid arthritis (RA) is an inflammatory disorder in which the disease severity might be decreased by anti-inflammatory agents. There are several lines of evidence which support anti-inflammatory effects of vitamin K. The aim of this study was to examine whether vitamin K is a useful strategy for reducing inflammation in RA subjects. Materials and methods: In this double-blind placebo controlled trial, 58 patients with definitive RA were randomly allocated into two groups to receive vitamin K₁ as phylloquinone [10 mg/day] or placebo pills for 8 weeks. Clinical status using disease activity score-28 (DAS-28) and serum concentrations of some inflammatory markers (IL-6, hs-CRP, TNFα) were assessed at baseline and at the end of intervention. Results: There were no significant differences between the two groups regarding any of the baseline characteristics. In the vitamin K₁ group, a 27 % decrease in serum levels of IL-6 (P = 0.006) and a 13 % decrease in DAS-28 (P = 0.041) were observed. However, after adjusting for relevant confounders, i. e.; duration of RA, intake of folic acid supplements, energy intake, weight and baseline values of each variable, by comparing the two groups, we found no significant reduction in these markers. Conclusion: Vitamin K₁ supplementation at 10 mg/day for 8 weeks had no significant effects on blood biomarkers of inflammation and disease severity of patients with rheumatoid arthritis compared with the placebo group.

Vitamin K and Bone Metabolism: A Review of the Latest Evidence in Preclinical Studies

Bone is a metabolically active tissue that renews itself throughout one's life. Cytokines along with several hormonal, nutritional, and growth factors are involved in tightly regulated bone remodeling. Accordingly, vitamin K as a multifunctional vitamin has been recently deemed appreciable as a topic of research as it plays a pivotal role in maintenance of the bone strength, and it has been proved to have a positive impact on the bone metabolism. Vitamin K exerts its anabolic effect on the bone turnover in different ways such as promoting osteoblast differentiation, upregulating transcription of specific genes in osteoblasts, and activating the bone-associated vitamin k dependent proteins which play critical roles in extracellular bone matrix mineralization. There is also credible evidence to support the effects of vitamin k2 on differentiation of other mesenchymal stem cells into osteoblast. The main objective of the present paper is to comprehensively outline the preclinical studies on the properties of vitamin K and its effects on the bone metabolism. The evidence could shed light on further clinical studies to improve osteogenesis in bone graft surgeries.

Effect of vitamin K in bone metabolism and vascular calcification: A review of mechanisms of action and evidences

Osteoporosis is a public health concern associated with an increased risk of bone fractures and vascular calcification. Vitamin K presents unique benefits on these issues, although understudied. The two main forms of vitamin K are phylloquinone (vitamin K₁) and menaquinone (vitamin K₂). In this study, it was especially investigated the action of vitamin K₂ in bones and vessels. Vitamin K₂ has shown to stimulate bone formation by promoting osteoblast differentiation and carboxylation of osteocalcin, and increasing alkaline phosphatase, insulin-like growth factor-1, growth differentiation factor-15, and stanniocalcin 2 levels. Furthermore, vitamin K₂ reduces the pro-apoptotic proteins Fas and Bax in osteoblasts, and decreases osteoclast differentiation by increasing osteoprotegerin and reducing the receptor activator of nuclear factor kappa-B ligand. In blood vessels, vitamin K₂ reduces the formation of hydroxyapatite, through the carboxylation of matrix Gla protein and Gla rich protein, inhibits the apoptosis of vascular smooth muscle cells, by increasing growth arrest-specific gene 6, and reduces the transdifferentiation of vascular smooth muscle cells to osteoblasts. The commonly used dosage of vitamin K₂ in human studies is 45 mg/day and its application can be an interesting strategy in benefitting bone and vascular health, especially to osteoporotic post-menopausal women.

Euphorbia factor L1 inhibits osteoclastogenesis by regulating cellular redox status and induces Fas-mediated apoptosis in osteoclast

Excessive bone resorption caused by increased osteoclast number or activity leads to a variety of bone diseases including osteoporosis, rheumatoid arthritis and periodontitis. Thus, the therapeutic strategy for these diseases has been focused primarily on the inhibition of osteoclast formation and function. This study shows that euphorbia factor L1 (EFL1), a diterpenoid isolated from Euphorbia lathyris, inhibited osteoclastogenesis and induced osteoclast apoptosis. EFL1 suppressed osteoclast formation and bone resorption at both initial and terminal differentiation stages. EFL1 inhibited receptor activator of NF-κB ligand (RANKL)-induced NFATc1 induction with attenuated NF-κB activation and c-Fos expression. EFL1 decreased the level of reactive oxygen species by scavenging them or activating Nrf2, and inhibited PGC-1β that regulates mitochondria biogenesis. In addition, EFL1 induced apoptosis in differentiated osteoclasts by increasing Fas ligand expression followed by caspase activation. Moreover, EFL1 inhibited inflammation-induced bone erosion and ovariectomy-induced bone loss in mice. These findings suggest that EFL1 inhibits osteoclast differentiation by regulating cellular redox status and induces Fas-mediated apoptosis in osteoclast, and may provide therapeutic potential for preventing or treating bone-related diseases caused by excessive osteoclast.

Regulation of bone remodeling by vitamin K2

All living tissues require essential nutrients such as amino acids, fatty acids, carbohydrates, minerals, vitamins, and water. The skeleton requires nutrients for development, maintaining bone mass and density. If the skeletal nutritional requirements are not met, the consequences can be quite severe. In recent years, there has been growing interest in promotion of bone health and inhibition of vascular calcification by vitamin K2. This vitamin regulates bone remodeling, an important process necessary to maintain adult bone. Bone remodeling involves removal of old or damaged bone by osteoclasts and its replacement by new bone formed by osteoblasts. The remodeling process is tightly regulated, when the balance between bone resorption and bone formation shifts to a net bone loss results in the development of osteoporosis in both men and women. In this review, we focus on our current understanding of the effects of vitamin K2 on bone cells and its role in prevention and treatment of osteoporosis.

Bone Health and Osteoporosis: The Role of Vitamin K and Potential Antagonism by Anticoagulants

BACKGROUND

Vitamin K's effects extend beyond blood clotting to include a role in bone metabolism and potential protection against osteoporosis. Vitamin K is required for the gamma-carboxylation of osteocalcin. Likewise, this gamma-carboxylation also occurs in the liver for several coagulation proteins. This mechanism is interrupted by coumarin-based anticoagulants in both the liver and bone.

METHODS

A thorough review of the literature on vitamin K, osteocalcin and their role in bone metabolism and osteoporosis, as well as the potential bone effects of anticoagulant therapy was conducted.

CONCLUSIONS

Epidemiological studies and clinical trials consistently indicate that vitamin K has a positive effect on bone mineral density and decreases fracture risk. Typical dietary intakes of vitamin K are below the levels associated with better BMD and reduced fracture risk; thus issues of increasing dietary intakes, supplementation, and/or fortification arise. To effectively address these issues, large-scale, intervention trials of vitamin K are needed. The effects of coumarin-based anticoagulants on bone health are more ambiguous, with retrospective studies suggesting that long-term therapy adversely affects vertebral BMD and fracture risk. Anticoagulants that do not affect vitamin K metabolism are now available and make clinical trials feasible to answer the question of whether coumarins adversely affect bone. The research suggests that at a minimum, clinicians should carefully assess anticoagulated patients for osteoporosis risk, monitor BMD, and refer them to dietitians for dietary and supplement advice on bone health. Further research is needed to make more efficacious decisions about vitamin K intake, anticoagulant therapy, and bone health.

Pregnane X Receptor and Cancer: Context-Specificity is Key

Pregnane X receptor (PXR) is an adopted orphan nuclear receptor that is activated by a wide-range of endobiotics and xenobiotics, including chemotherapy drugs. PXR plays a major role in the metabolism and clearance of xenobiotics and endobiotics in liver and intestine via induction of drug-metabolizing enzymes and drug-transporting proteins. However, PXR is expressed in several cancer tissues and the accumulating evidence strongly points to the differential role of PXR in cancer growth and progression as well as in chemotherapy outcome. In cancer cells, besides regulating the gene expression of enzymes and proteins involved in drug metabolism and transport, PXR also regulates other genes involved in proliferation, metastasis, apoptosis, anti-apoptosis, inflammation, and oxidative stress. In this review, we focus on the differential role of PXR in a variety of cancers, including prostate, breast, ovarian, endometrial, and colon. We also discuss the future directions to further understand the differential role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators to target PXR in PXR-expressing cancers.

Osteoprotegerin Induces Apoptosis of Osteoclasts and Osteoclast Precursor Cells via the Fas/Fas Ligand Pathway

Osteoprotegerin (OPG) is known to inhibit differentiation and activation of osteoclasts (OCs) by functioning as a decoy receptor blocking interactions between RANK and RANKL. However, the exact role of OPG in the survival/apoptosis of OCs remains unclear. OPG caused increased rates of apoptosis of both OCs and osteoclast precursor cells (OPCs). The expression of Fas and activated caspase-8 was increased by both 20 ng/mL and 40 ng/mL of OPG, but was markedly decreased at 80 ng/mL. Interestingly, we noted that while levels of Fas ligand (FasL) increased with increasing doses of OPG, the soluble form of FasL in the supernatant decreased. The results of a co-immunoprecipitation assay suggested that the decrease of sFasL might be caused by the binding of OPG. This would block the inhibition of the apoptosis of OCs and OPCs. Furthermore, changes in expression levels of Bax/Bcl-2, cleaved-caspase-9, cleaved-caspased-3 and the translocation of cytochrome c, illustrated that OPG induced apoptosis of OCs and OPCs via the classic Fas/FasL apoptosis pathway, and was mediated by mitochondria. Altogether, our results demonstrate that OPG induces OCs and OPCs apoptosis partly by the Fas/FasL signaling pathway.

Pregnane xenobiotic receptor in cancer pathogenesis and therapeutic response

Pregnane xenobiotic receptor (PXR) is an orphan nuclear receptor that regulates the metabolism of endobiotics and xenobiotics. PXR is promiscuous and unique in that it is activated by a diverse group of xenochemicals, including therapeutic anticancer drugs and naturally-occurring endocrine disruptors. PXR has been predominantly studied to understand its regulatory role in xenobiotic clearance in liver and intestine via induction of drug metabolizing enzymes and drug transporters. PXR, however, is widely expressed and has functional implications in other normal and malignant tissues, including breast, prostate, ovary, endometrium and bone. The differential expression of PXR and its target genes in cancer tissues has been suggested to determine the prognosis of chemotherapeutic outcome. In addition, the emerging evidence points to the implications of PXR in regulating apoptotic and antiapoptotic as well as growth factor signaling that promote tumor proliferation and metastasis. In this review, we highlight the recent progress made in understanding the role of PXR in cancer, discuss the future directions to further understand the mechanistic role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators.

Changes in parameters of bone metabolism in postmenopausal women following a 12-month intervention period using dairy products enriched with calcium, vitamin D, and phylloquinone (vitamin K(1)) or menaquinone-7 (vitamin K (2)): the Postmenopausal Health Study II

The objective of the present study was to examine the effect of dairy products enriched with calcium, vitamin D(3), and phylloquinone (vitamin K(1)) or menaquinone-7 (vitamin K(2)) on parameters of bone metabolism in postmenopausal women following a 12-month intervention. Postmenopausal women were divided into three intervention groups and a control group (CG). All three intervention groups attended biweekly sessions and received fortified dairy products providing daily 800 mg of calcium and 10 μg of vitamin D(3) (CaD). Furthermore, in two of the three intervention groups the dairy products were also enriched with vitamin K, providing daily 100 μg of either phylloquinone (CaDK1) or menaquinone-7 (CaDK2). The increase observed for serum 25(OH)D levels in all intervention groups and the increase observed for serum IGF-I levels in the CaDK2 group differed significantly compared to the changes observed in CG (P = 0.010 and P = 0.028, respectively). Furthermore, both the CaDK1 and CaDK2 groups had a significantly lower mean serum undercarboxylated osteocalcin to osteocalcin ratio and urine deoxypyridinoline levels at follow-up compared to the CaD and CG groups (P = 0.001 and P = 0.047, respectively). Significant increases in total-body BMD were observed in all intervention groups compared to CG (P < 0.05), while significant increases in lumbar spine BMD were observed only for CaDK1 and CaDK2 compared to CG (P < 0.05) after controlling for changes in serum 25(OH)D levels and dietary calcium intake. In conclusion, the present study revealed more favorable changes in bone metabolism and bone mass indices for the two vitamin K-supplemented groups, mainly reflected in the suppression of serum levels of bone remodeling indices and in the more positive changes in lumbar spine BMD for these two study groups.

Effect of vitamin K on bone mineral density: a meta-analysis of randomized controlled trials

A number of randomized controlled trials (RCTs) examining the role of vitamin K on bone mineral density (BMD) have yielded inconsistent results. We performed a meta-analysis of these trials to assess the effect of vitamin K on BMD. We searched MEDLINE, EMBASE and CENTRAL for relevant studies of RCTs examining the role of vitamin K on BMD. Data on participants, interventions, and outcomes were extracted and the quality of all included trials assessed. Primary outcomes for analysis were absolute changes in BMD (mg/cm(2)) at the lumbar spine and femoral neck. Relative changes (percentage change) in BMD at the lumbar spine were also assessed. Vitamin K supplementation was shown to be efficacious in increasing BMD at the lumbar spine but not the femoral neck. The weighted mean difference (WMD) in BMD absolute change was 21.60 mg/cm(2) [95% confidence interval (CI) 3.63, 39.56] at the lumbar spine and 0.25 mg/cm(2) (95% CI -2.64, 3.14) at the femoral neck. The WMD in BMD relative change was 1.27% (95% CI 0.47, 2.06) at the lumbar spine and 0.17 (95% CI -0.21, 0.54) at the femoral neck. Subgroup analysis revealed that ethnic difference, gender, and vitamin K type were associated with variable effects on BMD at the lumbar spine. The modest overall treatment effects for vitamin K on BMD observed in this review may be biased and should be interpreted with caution. Further studies are required to address factors relating to the observed effects of vitamin K on BMD.

Menaquinone-4 enhances testosterone production in rats and testis-derived tumor cells

Background

Vitamin K is essential for the posttranslational modification of various Gla proteins. Although it is widespread in several organs, including the testis, the function of vitamin K in these organs is not well characterized. In this study, we investigated the function of vitamin K in the testis and analyzed its role in steroidogenesis.

Methods

Eight-week-old male Wistar rats were fed a diet supplemented with menaquinone-4 (MK-4, 75 mg/kg diet), one of the predominant K₂ vitamins present in the testis, for 5 weeks. In vivo testosterone levels of the rats' plasma and testes were measured by enzyme-linked immunosorbent assay, and in vitro testosterone levels of testis-derived tumor cells (I-10 cells) maintained in Ham's F-10 medium with 10% fetal bovine serum were measured following treatment with MK-4 (0 to 100 μM) at several time points. Testosterone and cellular protein levels were analyzed with respect to their effects on steroidogenesis.

Results

Testosterone levels in the plasma and testes of MK-4-fed rats were significantly increased compared to those of control rats, with no obvious differences in plasma luteinizing hormone levels. Secreted testosterone levels from I-10 cells were elevated by MK-4, but not by vitamin K₁, in a dose-dependent manner independent of cAMP treatment. Western blot analysis revealed that expression of CYP11A, the rate-limiting enzyme in steroidogenesis, and phosphorylation levels of protein kinase A (PKA) and the cAMP response element-binding protein were all stimulated by the presence of MK-4. Enhancement of testosterone production was inhibited by H89, a specific inhibitor of PKA, but not by warfarin, an inhibitor of γ-glutamylcarboxylation.

Conclusions

MK-4 stimulates testosterone production in rats and testis-derived tumor cells via activation of PKA. MK-4 may be involved in steroidogenesis in the testis, and its supplementation could reverse the downregulation of testosterone production in elders.

Effect of GGCX gene polymorphism on the responses of serum undercarboxylated osteocalcin and bone turnover markers after treatment with vitamin K2 (menatetrenone) among postmenopausal Thai women

The purpose of this study was to evaluate the influence of gamma-glutamyl transferase (GGCX) gene polymorphisms on the response of serum undercarboxylated osteocalcin (ucOC) and bone turnover markers 3 months after treatment with menatetrenone. One hundred and forty postmenopausal Thai women were enrolled and assigned to receive 45 mg/day treatment of menatetrenone (MK-4) concurrently with calcium 1.2 g and vitamin D 400 IU for 3 months. Demographic characteristics, GGCX genotyping, serum bone turnover markers and ucOC levels were obtained from all participants at baseline. We evaluated the reduction of ucOC at 3 months and the reduction of beta-CTx and P1NP at 1 and 3 months. The responses were compared between the different genotypes of GG and GA + AA groups. There was a significant reduction of serum ucOC, beta-CTx and P1NP from the baseline at 3 months (p < 0.001) though there was no significant difference between genotypes (GG vs. GA + AA; p > 0.05). Nonetheless, a subgroup analysis of postmenopausal women who 65 years of age or over (N = 37) revealed a significant difference between the two groups in the reduction of ucOC. Menatetrenone significantly reduced serum ucOC as well as beta-CTX and P1NP from the baseline. GGCX polymorphism appeared to have an influence over the reduction of ucOC especially in older women (age ≥65). Furthermore, the groups which have "A" allele trend to being more efficient in reducing the serum ucOC level than the group which does not have it.

Prospective evaluation of Vitamin K2, Raloxifene and their co-administration in osteoporotic rats

In this study, therapeutic effects of Vitamin K2, Raloxifene and their co-administration on bone, uterus, blood and weight profiles were investigated with an ovariectomized rat model. Forty Wistar rats were divided into five groups (n=8): Raloxifene (R), Vitamin K2 (K), Raloxifene+Vitamin K2 (R+K), ovariectomized controls (OVX) and Sham-operated controls (Sham). Treatment began 3 months after ovariectomy. Vitamin K2 and Raloxifene were administered 30 and 1.5 mg/kg/day separately and in combination five times per week for 12 weeks. All treatment groups had significantly higher ultimate strength and energy absorption capacity (P<0.05) than ovariectomized controls in both femur and tibia. Histological results showed that treatment groups had healthy lumen structure, whereas OVX had degeneration. Adverse effects which were seen in individual treatments (myometrium weakening in K, endometrium weakening in R, and ALP increase in group R) were not observed in the R+K group implying a synergistic effect of these two agents when they are co-administered. According to blood analysis, ALP values were significantly high in Raloxifene-only group (P<0.0001). This effect is suppressed in the co-administered group. In summary, the groups R, K and R+K had significantly higher ultimate strength and less susceptibility to fracture than ovariectomized controls. In summation, Vitamin K2 treated groups (either in single or combined with Raloxifene) had considerable biomechanical performance and reproductive tissue profile indicating that this agent is prospectively effective in osteoporosis management.

Relationships between undercarboxylated osteocalcin and vitamin K intakes, bone turnover, and bone mineral density in healthy women

BACKGROUND & AIMS

Low vitamin K intakes and high levels of undercarboxylated osteocalcin (ucOC) are risk factors for hip fractures. However, the relationship between ucOC and vitamin K intakes, bone mineral density (BMD) and bone biochemical markers is not clarified.

METHODS

We enrolled 221 healthy women, and examined BMD, urinary type-I collagen cross-linked-N-telopeptide (uNTX), and nutrient intakes. BMD was measured at the lumbar spine and femoral neck.

RESULTS

Vitamin K intakes were significantly and negatively correlated with ucOC after adjustment for age, height, and body weight (r=-0.305, p<0.0001). ucOC was negatively associated with lumbar BMD (r=-0.147, p<0.05), but not femoral neck BMD (r=-0.099, p=0.095) after adjustment for age, height, and body weight. In multiple regression analysis, even after adjustment for age, height, body weight, and vitamin K intake, a significant and positive correlation remained between ucOC and urinary NTX (r=0.493, p<0.0001). Moreover, in postmenopausal women, ucOC levels were positively correlated with urinary NTX, but not BMD.

CONCLUSION

Dietary vitamin K intakes influence serum levels of ucOC in healthy women. Furthermore, ucOC may be linked to bone biochemical markers.

Vitamin K suppresses the lipopolysaccharide-induced expression of inflammatory cytokines in cultured macrophage-like cells via the inhibition of the activation of nuclear factor κB through the repression of IKKα/β phosphorylation

Vitamin K is essential for blood coagulation and bone metabolism in mammals. This vitamin functions as a cofactor in the posttranslational synthesis of γ-carboxyglutamic acid (Gla) from glutamic acid residues. However, other functions of vitamin K have been reported recently. We previously found that vitamin K suppresses the inflammatory reaction induced by lipopolysaccharide (LPS) in rats and human macrophage-like THP-1 cells. In this study, we further investigated the mechanism underlying the anti-inflammatory effect of vitamin K by using cultures of LPS-treated human- and mouse-derived cells. All the vitamin K analogues analyzed in our study exhibited varied levels of anti-inflammatory activity. The isoprenyl side chain structures, except geranylgeraniol, of these analogues did not show such activity; warfarin did not interfere with this activity. The results of our study suggest that the 2-methyl-1,4-naphtoquinone ring structure contributes to express the anti-inflammatory activity, which is independent of the Gla formation activity of vitamin K. Furthermore, menaquinone-4, a form of vitamin K₂, reduced the activation of nuclear factor κB (NFκB) and inhibited the phosphorylation of IKKα/β after treatment of cells with LPS. These results clearly show that the anti-inflammatory activity of vitamin K is mediated via the inactivation of the NFκB signaling pathway.

Response of serum carboxylated and undercarboxylated osteocalcin to risedronate monotherapy and combined therapy with vitamin K(2) in corticosteroid-treated patients: a pilot study

OBJECTIVE

The aim of this study was to investigate the responses of serum osteocalcin (OC), undercarboxylated osteocalcin (ucOC) and N-terminal telopeptide of type I collagen (NTx) to corticosteroids, and to examine the effects of risedronate therapy with or without vitamin K(2) supplementation on bone metabolic markers in corticosteroid-treated patients.

METHODS

Sixteen patients on corticosteroid therapy for neuromuscular disorders were assigned randomly to 2 groups (A: risedronate monotherapy, n=8; B: combined risedronate and vitamin K(2) therapy, n=8) and treated for 1 year. Another 6 patients who received intravenous steroid pulse therapy were assigned to group C for investigation of the effects of corticosteroids on OC and ucOC 1 month after pulse therapy.

RESULTS

Serial measurements revealed that significant decreases of OC, ucOC and NTx persisted with a similar time course profile during 1 year of treatment in groups A and B, and between-group analysis failed to demonstrate any additional effects of vitamin K(2) on risedronate therapy. Intravenous steroid pulse therapy induced a transient depression of OC and ucOC within 1 week in group C.

CONCLUSION

These results indicate that serum concentrations of OC and ucOC become consistently low during corticosteroid administration despite risedronate therapy with or without vitamin K(2) supplementation, and the serum ucOC level may not be a reliable indicator of vitamin K status under corticosteroid administration.

Roles for vitamin K beyond coagulation

Recent interest in vitamin K has been motivated by evidence of physiological roles beyond that of coagulation. Vitamin K and vitamin K-dependent (VKD) proteins may be involved in regulation of calcification, energy metabolism, and inflammation. However, the evidence for many of these proposed roles in the maintenance of health is equivocal. There is also an emerging viewpoint that the biochemical function of vitamin K may extend beyond that of a cofactor for the VKD carboxylation of glutamyl residues (Glus) to carboxylated Glus in VKD proteins.

Assessment of bone mineral density and markers of bone turnover in children under long-term oral anticoagulant therapy

Oral anticoagulants antagonize vitamin K action and potentially impair the carboxylation of osteocalcin, a protein essential for normal bone matrix formation. In the present study, bone mineral density (BMD) and bone turnover markers were evaluated in 23 children under long-term oral anticoagulant therapy. BMD of the lumbar spine was assessed (Dual Energy x-ray Absorptiometry) and reported as z score. Osteoblast [bone alkaline phosphatase, osteocalcin (Gla-Oc), amino-terminal procollagen 1 extension peptide] and osteoclast (urinary calcium and deoxypyridinoline, serum cross-linked C telopeptide) activity markers were measured. Vitamin D {[25(OH) D], parathormone, calcium, phosphorus, magnesium} and vitamin K status [factors II, VII, IX, X, protein C, protein S, undercarboxylated osteocalcin (Glu-Oc)] were determined. The above parameters were also evaluated in 25 healthy controls. Patients presented with higher levels in Glu-Oc, parathormone, and bone resorption markers, lower levels in bone formation markers and 25(OH) D, whereas 52% of them showed signs of osteopenia (-1>BMD z score>-2.5). Statistical analysis demonstrated that anticoagulant therapy was an independent predictor of alterations in Glu-Oc, Gla-Oc, bone alkaline phosphatase, amino-terminal procollagen 1 extension peptide, and serum cross-linked C telopeptide levels. It seems that long-term use of coumarin derivatives may cause osteopenia in children with the risk of developing osteoporosis later in life.

Specificity of RGS10A as a key component in the RANKL signaling mechanism for osteoclast differentiation

Significant progress has been made in studies of the mechanisms by which RANKL induces terminal osteoclast differentiation. However, many crucial details in the RANKL-evoked signaling pathway for osteoclast differentiation remain to be defined. We characterized genes specifically expressed in osteoclasts by differential screening of a human osteoclastoma cDNA library, and found that the regulator of G-protein signaling 10A (RGS10A), but not the RGS10B isoform, was specifically expressed in human osteoclasts. The expression of RGS10A is also induced by RANKL in osteoclast precursors and is prominently expressed in mouse osteoclast-like cells. RGS10A silencing by RNA interference blocked intracellular [Ca2+]i oscillations, the expression of NFAT2, and osteoclast terminal differentiation in both bone marrow cells and osteoclast precursor cell lines. Reintroduction of RGS10A rescued the impaired osteoclast differentiation. RGS10A silencing also resulted in premature osteoclast apoptosis. RGS10A silencing affected the RANKL-[Ca2+]i oscillation-NFAT2 signaling pathway but not other RANKL-induced responses. Our data demonstrate that target components of RGS10A are distinct from those of RGS12 in the RANKL signaling mechanism. Our results thus show the specificity of RGS10A as a key component in the RANKL-evoked signaling pathway for osteoclast differentiation, which may present a promising target for therapeutic intervention.

Response of serum carboxylated and undercarboxylated osteocalcin to alendronate monotherapy and combined therapy with vitamin K2 in postmenopausal women

Alendronate decreases the risk of femoral neck fracture by suppressing bone turnover, and also decreases the serum total osteocalcin level. A low serum carboxylated osteocalcin level or high undercarboxylated osteocalcin level could be risk factors for femoral neck fracture. Vitamin K mediates the carboxylation of osteocalcin, but the effect of alendronate therapy with or without vitamin K(2) supplementation remains unknown. Forty-eight postmenopausal women were enrolled in a 1-year prospective randomized trial and assigned to alendronate monotherapy (5 mg/day) (group A, n = 26) or vitamin K(2) (45 mg/day) plus alendronate (5 mg/day) (group AK, n = 22). Bone mineral density was measured by dual-energy X-ray absorptiometry at 0 and 12 months; bone turnover parameters were measured at 0, 3, and 12 months. Four patients discontinued alendronate therapy, and we analyzed the remaining 44 patients (23 in group A and 21 in group AK) who completed 1 year of treatment. Alendronate decreased undercarboxylated osteocalcin; carboxylated osteocalcin was not affected. Addition of vitamin K(2) enhanced the decrease of undercarboxylated osteocalcin levels and led to a greater increase of femoral neck bone mineral density. Alendronate monotherapy does not decrease carboxylation of osteocalcin, and combination of vitamin K(2) and alendronate brings further benefits on both osteocalcin carboxylation and BMD of femoral neck in postmenopausal women with osteoporosis.

Vitamin K deficiency inhibits mineralization and enhances deformity in vertebrae of haddock (Melanogrammus aeglefinus L.)

Vitamin K has been known to regulate bone formation through osteocalcin synthesis by osteoblasts, which is important for mineralization and bone structure. The mechanism underlying the relationship of vitamin K with the changes of microanatomy is not fully understood, and our goal is to test whether bone deformities develop in association with vitamin K deficiency. Fish were fed a semi-purified diet containing either devoid (0.00 mg/kg diet) or adequate (40.0 mg/kg diet supplemented but 20.8 mg/kg analyzed) levels of vitamin K (menadione sodium bisulphite) for 20 weeks. At the end of 8 and 20 weeks, fish were subjected to gross examination and X-ray, and mineral content of the vertebrae was measured. The vertebrae were also subjected to histological, histomorphometric and enzyme histochemical examinations to determine the bone formation and resorption. Vitamin K deficiency primarily decreased bone mineralization and subsequently a decrease in bone mass thus resulted in an increased susceptibility to bone deformity. The occurrence of bone deformities coincided with an increased amount of osteoid tissue and decreased bone mineral content. Number of osteoblasts and osteoclasts were not affected by dietary vitamin K. In conclusion, vitamin K deficiency can impair bone mineralization and enhances bone deformities.

From space to Earth: advances in human physiology from 20 years of bed rest studies (1986-2006)

Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body's upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10-15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures--exercise (aerobic, resistive, vibration), nutritional and pharmacological--are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.

Anti-arthritis effects of vitamin K(2) (menaquinone-4)--a new potential therapeutic strategy for rheumatoid arthritis

Vitamin K(2) (menaquinone-4, MK-4) has been reported to induce apoptosis in hepatocellular carcinoma, leukemia and myelodysplastic syndrome cell lines. The effects of MK-4 on the development of arthritis have never been addressed thus far. In the present study, we investigated the effect of MK-4 upon the proliferation of rheumatoid synovial cells and the development of arthritis in collagen-induced arthritis. We analyzed the effect of MK-4 on the proliferation of fibroblast-like synoviocytes using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The pro-apoptotic effect of MK-4 upon fibroblast-like synoviocytes was investigated with annexin V staining and DNA fragmentation and caspase 3/7 assays. Moreover, we analyzed the effect of MK-4 on the development of collagen-induced arthritis in female dark agouti rats. Our results indicated that MK-4 inhibited the proliferation of fibroblast-like synoviocytes and the development of collagen-induced arthritis in a dose-dependent manner. We conclude that MK-4 may represent a new agent for the treatment of rheumatoid arthritis in the setting of combination therapy with other disease-modifying antirheumatic drugs.

RGS10-null mutation impairs osteoclast differentiation resulting from the loss of [Ca2+]i oscillation regulation

Increased osteoclastic resorption leads to many bone diseases, including osteoporosis and rheumatoid arthritis. While rapid progress has been made in characterizing osteoclast differentiation signaling pathways, how receptor activator of nuclear factor kappaB (NF-kappaB) ligand (RANKL) evokes essential [Ca2+]i oscillation signaling remains unknown. Here, we characterized RANKL-induced signaling proteins and found regulator of G-protein signaling 10 (RGS10) is predominantly expressed in osteoclasts. We generated RGS10-deficient (RGS10-/-) mice that exhibited severe osteopetrosis and impaired osteoclast differentiation. Our data demonstrated that ectopic expression of RGS10 dramatically increased the sensitivity of osteoclast differentiation to RANKL signaling; the deficiency of RGS10 resulted in the absence of [Ca2+]i oscillations and loss of NFATc1; ectopic NFATc1 expression rescues impaired osteoclast differentiation from deletion of RGS10; phosphatidylinositol 3,4,5-trisphosphate (PIP3) is essential to PLCgamma activation; and RGS10 competitively interacts with Ca2+/calmodulin and PIP3 in a [Ca2+]i-dependent manner to mediate PLCgamma activation and [Ca2+]i oscillations. Our results revealed a mechanism through which RGS10 specifically regulates the RANKL-evoked RGS10/calmodulin-[Ca2+]i oscillation-calcineurin-NFATc1 signaling pathway in osteoclast differentiation using an in vivo model. RGS10 provides a potential therapeutic target for the treatment of bone diseases.