Osteoclastic metabolism of 25(OH)-vitamin D3: a potential mechanism for optimization of bone resorption

A comprehensive perspective on the role of vitamin D signaling in maintaining bone homeostasis: Lessons from animal models

1,25(OH)2D3 is well known for its role in maintaining normal serum calcium levels. Through its receptor, 1,25(OH)2D3 enhances intestinal calcium absorption and renal calcium reabsorption, thereby ensuring serum calcium levels are within physiological range, which is in turn important for normal bone development and mineralization. The vitamin D receptor (VDR) achieves this via transcriptional induction of genes important in calcium transport. When intestinal and renal calcium (re)absorption is impaired, VDR-mediated signaling will stimulate bone resorption and inhibit mineralization in order to maintain normal serum calcium levels, as evidenced in mice with a systemic or intestine-specific deletion of the VDR. However, VDR signaling in bone is also reported to have anabolic effects. In this review we will discuss the effects of 1,25(OH)2D3-mediated VDR signaling on bone homeostasis and provide an overview of the in vitro experiments and various transgenic mice models that have been generated to unravel the role of VDR signaling in different bone cell types such as chondrocytes, (pre)osteoblasts, osteocytes, and (pre)osteoclasts.

Chronically increased osteoclastogenesis in adult celiac disease patients does not hinder improvement in bone health induced by gluten-free diet: Role of vitamin D, OPG and IL-6

The etiology of bone loss in celiac disease (CeD) remains a clinical challenge, with uncertainties present such as the extent of involvement of malabsorption and inflammation-induced osteoresorption processes in development of osteopenia/osteoporosis (OPN/OP), or reasons for failure to achieve healthy bone mass (BMD) even after long-term gluten-free diet (GFD) treatment. This observational prospective study explores the in vitro osteoclastogenic potential of peripheral blood precursors originating from adult active (newly diagnosed and untreated) celiac disease patients (aCeD) and describes the longitudinal changes in osteoclastogenesis after long-term adherence to GFD. To find connections between in vitro observations and in vivo bone metabolism changes, serum levels of 25(OH)D3, PTH, bCTX, PINP, CRP, IL-6, RANKL and OPG were measured before and after GFD and levels of these markers were correlated with the rate of osteoclastogenesis in vitro. OPG and IL-6 showed associations with BMD and/or presence of OPN/OP. Patients after GFD (CeD-GFD) exhibited improved BMD and increased serum 25(OH)D3 levels, alongside reduced bCTX and PINP levels. Compared to healthy donors, aCeD osteoclast genesis in vitro was higher and, surprisingly, remained elevated even in CeD-GFD patients. Negative correlation was found between osteoclastogenesis rate and serum OPG in aCeD, while osteoclastogenesis rate positively correlated with PTH in CeD-GFD. These results highlight OPG as marker for risk of OPN/OP in CeD and suggest that improvement of BMD after GFD is a result of uncoupling between bone metabolism and osteoresorptive action of osteoclasts after GFD.

Treatment of Extraosseous Giant Cell Tumor of Bone and Calcitriol-Mediated Hypercalcemia With Denosumab in Paget Disease

Extraosseous giant cell tumor of bone (GCTB) associated with Paget disease of bone (PDB) is rare. We report a patient aged in their 70s with polyostotic PDB involving the skull, spine, and pelvis, previously treated with bisphosphonates, who presented with symptomatic hypercalcemia (calcium 14.8 mg/dL [3.7 mmol/L]; reference range [RR], 8.6-10.5 mg/dL [2.1-2.6 mmol/L]), kidney injury (creatinine 2.6 mg/dL [230 μmol/L]; RR, 0.4-1.1 mg/dL [35-97 μmol/L]), and a 17.5 cm pelvic mass. Testing showed elevated calcitriol or 1,25-dihydroxyvitamin D (1,25(OH)2D) (57-108 pg/mL [137-259 pmol/L]; RR, 18-72 pg/mL [43-173 pmol/L]), but normal parathyroid hormone and bone-specific alkaline phosphatase (BSAP), arguing against parathyroid autonomy and active osseous PDB. Histopathology showed osteoclast-like giant cells and stromal mononuclear cells without atypia, necrosis, or mitoses. A one-time dose of denosumab 120 mg resulted in normalized calcium (9.0 mg/dL [2.2 mmol/L]) and 1,25(OH)2D (24 pg/mL [57 pmol/L]) and reduced tumor size. Denosumab was continued at a dose of 60 mg every 6 months. After 20 months, calcium and 1,25(OH)2D remained normal, with no tumor regrowth, and BSAP stayed low. This is the first report of 1,25(OH)2D-mediated hypercalcemia in extraosseous GCTB. It responded well to denosumab. Long-term management options are discussed in the context of existing literature.

Regulation of osteoclast-mediated bone resorption by lipids

Hyperactivation of osteoclasts has been identified as a significant etiological factor in several bone resorption-related disorders, including osteoporosis, periodontitis, arthritis, and bone metastasis of tumors. It has been demonstrated that the severity of these diseases is influenced by lipids that regulate osteoclast differentiation and activity through specific signaling pathways and cytokine levels. The regulatory mechanisms of different types of lipids on osteoclastogenesis vary across diverse disease contexts in bone resorption regulated by osteoclasts. This review presents an overview of the mechanisms underlying osteoclast formation and summarizes the pathways through which various lipids regulate osteoclastogenesis in different pathological contexts. We also discuss effective therapeutic strategies for osteolytic diseases based on modulation of lipid metabolism.

Can Vitamin D Levels Influence Bone Metabolism and Osseointegration of Dental Implants? An Umbrella Review

INTRODUCTION

Due to the large amount of scientific evidence on the subject and the limitations and incongruities in previous reviews, the primary aim of this umbrella review is to gather all the information regarding the importance of vitamin D levels in the osseointegration of dental implants.

METHODS

The literature search was performed in PubMed, Web of Science, CINAHL Plus, Cochrane Library, and Academic Search Complete throughout the search expression ["vitamin D" AND ("dental implant" OR "dental implants")].

RESULTS

The initial search yielded 351 results, but at the end of the process, only five systematic reviews were selected.

CONCLUSIONS

Vitamin D seems to have a positive effect on the osseointegration of dental implants and on the reduction of dental implant failures; however, it is recommended that future studies take into account the limitations mentioned in this study in order to increase the validity and quality of scientific evidence on the subject.

Exosomal Osteoclast-Derived miRNA in Rheumatoid Arthritis: From Their Pathogenesis in Bone Erosion to New Therapeutic Approaches

Rheumatoid arthritis (RA) is an autoimmune disease that causes inflammation, pain, and ultimately, bone erosion of the joints. The causes of this disease are multifactorial, including genetic factors, such as the presence of the human leukocyte antigen (HLA)-DRB1*04 variant, alterations in the microbiota, or immune factors including increased cytotoxic T lymphocytes (CTLs), neutrophils, or elevated M1 macrophages which, taken together, produce high levels of pro-inflammatory cytokines. In this review, we focused on the function exerted by osteoclasts on osteoblasts and other osteoclasts by means of the release of exosomal microRNAs (miRNAs). Based on a thorough revision, we classified these molecules into three categories according to their function: osteoclast inhibitors (miR-23a, miR-29b, and miR-214), osteoblast inhibitors (miR-22-3p, miR-26a, miR-27a, miR-29a, miR-125b, and miR-146a), and osteoblast enhancers (miR-20a, miR-34a, miR-96, miR-106a, miR-142, miR-199a, miR-324, and miR-486b). Finally, we analyzed potential therapeutic targets of these exosomal miRNAs, such as the use of antagomiRs, blockmiRs, agomiRs and competitive endogenous RNAs (ceRNAs), which are already being tested in murine and ex vivo models of RA. These strategies might have an important role in reestablishing the regulation of osteoclast and osteoblast differentiation making progress in the development of personalized medicine.

Modulation of the vitamin D/vitamin D receptor system in osteoporosis pathogenesis: insights and therapeutic approaches

Osteoporosis is a prevalent bone disorder characterized by low bone mineral density (BMD) and deteriorated bone microarchitecture, leading to an increased risk of fractures. Vitamin D (VD), an essential nutrient for skeletal health, plays a vital role in maintaining bone homeostasis. The biological effects of VD are primarily mediated through the vitamin D receptor (VDR), a nuclear receptor that regulates the transcription of target genes involved in calcium and phosphate metabolism, bone mineralization, and bone remodeling. In this review article, we conduct a thorough literature search of the PubMed and EMBASE databases, spanning from January 2000 to September 2023. Utilizing the keywords "vitamin D," "vitamin D receptor," "osteoporosis," and "therapy," we aim to provide an exhaustive overview of the role of the VD/VDR system in osteoporosis pathogenesis, highlighting the most recent findings in this field. We explore the molecular mechanisms underlying VDR's effects on bone cells, including osteoblasts and osteoclasts, and discuss the impact of VDR polymorphisms on BMD and fracture risk. Additionally, we examine the interplay between VDR and other factors, such as hormonal regulation, genetic variants, and epigenetic modifications, that contribute to osteoporosis susceptibility. The therapeutic implications of targeting the VDR pathway for osteoporosis management are also discussed. By bringing together these diverse aspects, this review enhances our understanding of the VD/VDR system's critical role in the pathogenesis of osteoporosis and highlights its significance as a potential therapeutic target.

A parathyroid hormone/salt-inducible kinase signaling axis controls renal vitamin D activation and organismal calcium homeostasis

The renal actions of parathyroid hormone (PTH) promote 1,25-vitamin D generation; however, the signaling mechanisms that control PTH-dependent vitamin D activation remain unknown. Here, we demonstrated that salt-inducible kinases (SIKs) orchestrated renal 1,25-vitamin D production downstream of PTH signaling. PTH inhibited SIK cellular activity by cAMP-dependent PKA phosphorylation. Whole-tissue and single-cell transcriptomics demonstrated that both PTH and pharmacologic SIK inhibitors regulated a vitamin D gene module in the proximal tubule. SIK inhibitors increased 1,25-vitamin D production and renal Cyp27b1 mRNA expression in mice and in human embryonic stem cell-derived kidney organoids. Global- and kidney-specific Sik2/Sik3 mutant mice showed Cyp27b1 upregulation, elevated serum 1,25-vitamin D, and PTH-independent hypercalcemia. The SIK substrate CRTC2 showed PTH and SIK inhibitor-inducible binding to key Cyp27b1 regulatory enhancers in the kidney, which were also required for SIK inhibitors to increase Cyp27b1 in vivo. Finally, in a podocyte injury model of chronic kidney disease-mineral bone disorder (CKD-MBD), SIK inhibitor treatment stimulated renal Cyp27b1 expression and 1,25-vitamin D production. Together, these results demonstrated a PTH/SIK/CRTC signaling axis in the kidney that controls Cyp27b1 expression and 1,25-vitamin D synthesis. These findings indicate that SIK inhibitors might be helpful for stimulation of 1,25-vitamin D production in CKD-MBD.

Role of nutritional vitamin D in chronic kidney disease-mineral and bone disorder: A narrative review

Chronic kidney disease-mineral and bone disorder has complex and diverse clinical manifestations, including the simplest abnormalities of calcium, phosphorus and parathyroid hormone detected in blood, abnormalities of bone transformation and mineralization in bone, and calcification of blood vessels or other soft tissues detected on imaging. Patients with CKD-MBD combined low bone mineral density and fragility fractures are referred to as CKD-MBD with low bone mineral density. Vascular calcification refers to ectopic deposition of calcium phosphate in the blood vessel walls and heart valves. The degree of vascular calcification was inversely proportional to bone mineral density. The more severe the degree of vascular calcification, the lower the bone mineral density, and the higher the risk of death, indicating that the bone-vascular axis exists. Activation and alteration of the Wnt signaling pathway are central to the treatment of vascular diseases in uremia. Vitamin D supplementation can prevent secondary hyperparathyroidism, activate osteoblasts, relieve muscle weakness and myalgia, and reduce vascular calcification. Nutritional vitamin D may improve vascular calcification in uremia patients by regulating Wnt signaling pathway.

Integrated Transcriptome and Microbiota Reveal the Regulatory Effect of 25-Hydroxyvitamin D Supplementation in Antler Growth of Sika Deer

The level of plasma 25-hydroxyvitamin D (25(OH)D) is associated with the growth of the antler, a fast-growing bone organ of Cervidae. However, the benefits of 25(OH)D supplementation on antler growth and the underlying mechanisms remain unclear. Here, the antler growth profile and transcriptome, plasma parameters, rumen bacteria, and metabolites (volatile fatty acids and amino acids) were determined in sika deer in a 25(OH)D supplementation group (25(OH)D, n = 8) and a control group (Ctrl, n = 8). 25(OH)D supplementation significantly increased the antler weight and growth rate. The levels of IGF-1,25(OH)D and 1,25-dihydroxyvitamin D were significantly higher in the 25(OH)D group than in the Ctrl group, while the levels of LDL-C were lower. The levels of valerate and branched-chain amino acids in the rumen fluid were significantly different between the 25(OH)D and Ctrl groups. The bacterial diversity indices were not significantly different between the two groups. However, the relative abundances of the butyrate-producing bacteria (families Lachnospiraceae and Succinivibrionaceae) and the pyruvate metabolism pathway were higher in the 25(OH)D group. The transcriptomic profile of the antler was significantly different between the 25(OH)D and Ctrl groups, with 356 up- and 668 down-regulated differentially expressed genes (DEGs) in the 25(OH)D group. The up-regulated DEGs were enriched in the proteinaceous extracellular matrix and collagen, while the down-regulated DEGs were enriched in the immune system and lipid metabolism pathways. Overall, these results provide novel insights into the effects of 25(OH)D supplementation on the host metabolism, rumen microbiota, and antler transcriptome of sika deer.

Vitamin D and the Kidney: Two Players, One Console

Vitamin D belongs to the group of liposoluble steroids mainly involved in bone metabolism by modulating calcium and phosphorus absorption or reabsorption at various levels, as well as parathyroid hormone production. Recent evidence has shown the extra-bone effects of vitamin D, including glucose homeostasis, cardiovascular protection, and anti-inflammatory and antiproliferative effects. This narrative review provides an overall view of vitamin D’s role in different settings, with a special focus on chronic kidney disease and kidney transplant.

Does vitamin D have an effect on osseointegration of dental implants? A systematic review

Purpose

The aim of this study was to systematically review the available evidence to evaluate the efficacy of vitamin D supplementation or vitamin D depletion on the osseointegration of implants in animals and humans.

Methods

The focus questions addressed were “Do vitamin D deficient subjects treated with (dental) implants have an inferior osseointegration than subjects with adequate serum vitamin D level?” and “Do vitamin D supplemented subjects treated with (dental) implants have a superior osseointegration than subjects with adequate serum vitamin D level?” Humans and animals were considered as subjects in this study. Databases were searched from 1969 up to and including March 2021 using different combination of the following terms: “implant”, “bone to implant contact”, “vitamin D” and “osseointegration”. Letters to the editor, historic reviews, commentaries and articles published in languages other than English and German were excluded. The pattern of the present systematic review was customize to primarily summarize the pertinent data.

Results

Thirteen experimental studies with animals as subject, two clinical studies and three case reports, with humans as subjects, were included. The amount of inserted titanium implants ranged between 24 and 1740. Results from three animal studies showed that vitamin D deficiency has a negative effect on new bone formation and/or bone to implant contact (BIC). Eight animal studies showed that vitamin D supplementation has a enhancing effect on BIC and/or new bone formation around implants. Furthermore, enhancing the impact of vitamin D supplementation on the osseointegration of implants in subjects with diabetes mellitus, osteoporosis and chronic kidney disease (CKD) were assessed. Studies and case reports involving human subjects showed that patients with a low serum vitamin D level have a higher tendency to exhibit an early dental implant failure. When supplemented with vitamin D the osseointegration was successful in the case reports and a beneficial impact on the changes in the bone level during the osseointegration were determined.

Conclusions

Vitamin D deficiency seems to have a negative effect on the osseointegration of implants in animals. The supplementation of vitamin D appears to improve the osseointegration in animals with systemic diseases, such as vitamin D deficiency, diabetes mellitus, osteoporosis, and CKD. Slight evidence supports the hypothesis that humans similarly benefit from vitamin D supplementation in terms of osseointegration. Further investigation is required to maintain these assumptions.

The Effect of Vitamin D3 on the Alignment of Mandibular Anterior Teeth: A Randomized Controlled Clinical Trial

Objectives

To investigate the effect of vitamin D₃ level on the alignment of mandibular anterior teeth in adults and explore the associated root resorption and pain perception. Trial Design. Multicentre, double blinded randomized clinical trial. Subjects and Methods. Adult patients aged 18–30 years, with moderate mandibular incisor crowding [Little's Irregularity index (LII) 3–6 mm], needing nonextraction treatment with fixed orthodontic appliance, were randomly allocated into two groups with 1 : 1 allocation ratio. In the 1^st group (normal vitamin D₃ level group [ND₃G]), vitamin D level was measured and corrected to normal before starting orthodontic treatment, while in the 2^nd group [control group (CG)] the vitamin D level was kept unknown until completion of the alignment phase. Outcome measures included mandibular incisor crowding using LII, orthodontically induced root resorption (OIRR), and pain perception. Independent sample t-test was used to compare the duration of treatment, the effectiveness of alignment, and OIRR between groups, while differences in pain perception were analysed by Mann–Whitney U-test (P < 0.05).

Results

Out of 87 patients recruited from four centres, 33 patients were randomly allocated into two groups (17 patients to ND₃G and 16 patients to CG). Time elapsed for the complete alignment of the mandibular incisor crowding was one month shorter in ND₃G (23.532% faster), and the improvement percentage was significantly higher in all periods when compared to the CG. The amount of OIRR was not significantly different between groups; however, pain during the first three days of alignment was significantly less in ND₃G.

Conclusions

Having optimal vitamin D₃ level reduced the alignment time and pain associated with orthodontic treatment, but it had no role in reducing OIRR. Registration. The trial was registered with ClinicalTrials.gov on 12^th April 2021 (registration number: NCT04837781).

Circulating osteogenic progenitors and osteoclast precursors are associated with long-term glycemic control, sex steroids, and visceral adipose tissue in men with type 2 diabetes mellitus

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is well-known to be associated with normal bone density but, concurrently, low bone turnover and increased risk for fracture. One of the proposed mechanisms is possible derangement in bone precursor cells, which could be represented by deficiencies in circulating osteogenic progenitor (COP) cells and osteoclast precursors (OCP). The objective of our study is to understand whether extent of glycemic control has an impact on these cells, and to identify other factors that may as well.

METHODS

This was a secondary analysis of baseline data from 51 male participants, aged 37-65 in an ongoing clinical trial at Michael E. DeBakey VA Medical Center, Houston, Texas, USA. At study entry serum Hemoglobin A1c was measured by high-performance liquid chromatography osteocalcin (OCN) and C-terminal telopeptide of type 1 collagen (CTx) were measured by ELISA, and testosterone and estradiol by liquid-chromatography/mass-spectrometry. Areal bone mineral density (BMD), trabecular bone score and body composition were measured by dual energy x-ray absorptiometry, while COP and OCP were measured by flow cytometry.

RESULTS

When adjusted for serum testosterone, parathyroid hormone, and 25-hydroxyvitamin D, those with poor long-term glycemic control had significantly higher percentage of COP (p = 0.04). COP correlated positively with visceral adipose tissue (VAT) volume (r = 0.37, p = 0.01) and negatively with free testosterone (r = -0.28, p = 0.05) and OCN (r = -0.28, p = 0.07), although only borderline for the latter. OCP correlated positively with age, FSH, lumbar spine BMD, and COP levels, and negatively with glucose, triglycerides, and free estradiol. Multivariable regression analyses revealed that, in addition to being predictors for each other, another independent predictor for COP was VAT volume while age, glucose, and vitamin D for OCP.

CONCLUSION

Our results suggest that high COP could be a marker of poor metabolic control. However, given the complex nature and the multitude of factors influencing osteoblastogenesis/adipogenesis, it is possible that the increase in COP is a physiologic response of the bone marrow to increased osteoblast apoptosis from poor glycemic control. Alternatively, it is also likely that a metabolically unhealthy profile may retard the development of osteogenic precursors to fully mature osteoblastic cells.

Anti-Osteoporotic Effects of n-trans-Hibiscusamide and Its Derivative Alleviate Ovariectomy-Induced Bone Loss in Mice by Regulating RANKL-Induced Signaling

Osteoporosis is characterized by the deterioration of bone structures and decreased bone mass, leading to an increased risk of fracture. Estrogen deficiency in postmenopausal women and aging are major factors of osteoporosis and are some of the reasons for reduced quality of life. In this study, we investigated the effects of n-trans-hibiscusamide (NHA) and its derivative 4-O-(E)-feruloyl-N-(E)-hibiscusamide (HAD) on receptor activator of nuclear factor kappa-Β (NF-κB) ligand (RANKL)-induced osteoclast differentiation and an ovariectomized osteoporosis mouse model. NHA and HAD significantly inhibited the differentiation of osteoclasts from bone marrow-derived macrophages (BMMs) and the expression of osteoclast differentiation-related genes. At the molecular level, NHA and HAD significantly downregulated the phosphorylation of mitogen-activated protein kinase (MAPK) signaling molecules. However, Akt and NF-κB phosphorylation was inhibited only after NHA or HAD treatment. In the ovariectomy (OVX)-induced osteoporosis model, both NHA and HAD effectively improved trabecular bone structure. C-terminal telopeptide (CTX), a bone resorption marker, and RANKL, an osteoclast stimulation factor, were significantly reduced by NHA and HAD. The tartrate-resistant acid phosphatase (TRAP)-stained area, which indicates the osteoclast area, was also decreased by these compounds. These results show the potential of NHA and HAD as therapeutic agents for osteoporosis.

Dietary phosphorus level regulates appetite through modulation of gut and hypothalamic expression of anorexigenic genes in broiler chickens

Two experiments were designed to elucidate gut and hypothalamic molecular regulation of appetite by dietary phosphorus (P) concentration in broiler chickens. Birds (192 Cobb-500 broiler chickens) were randomly assigned to 3 experimental diets in experiment 1 (Exp. 1) and 24 broiler chickens were randomly assigned to 3 treatment groups in Exp. 2. Each diet comprised 8 replicate cages, with either 8 birds (Exp. 1) or 1 bird (Exp. 2) per replicate cage. In Exp. 1, diets contained 1.2 (P-deficient), 2.8 (P-marginal) or 4.4 (P-adequate) g/kg non-phytate P (nPP). In Exp. 2, birds fed the P-adequate diet were pair-fed (PF) to the feed consumption levels of birds fed the P-deficient diet. Feed intake and BW gain (P < 0.001) decreased in birds fed the P-deficient diet in Exp. 1. Birds fed the P-deficient diet had similar feed intake and BW gain with PF group fed the P-adequate diet (Exp. 2) but was significantly lower (P < 0.001) than birds fed the P-adequate diets. Sodium-phosphate cotransporter (NaPi-IIb) mRNA was upregulated (P < 0.05) in both experiments. Conversely, cholecystokinin (CCK) mRNA was downregulated (P < 0.01) in birds fed P-deficient diets. Anorexia-related hypothalamic cholecystokinin receptor (CCKAR) and melanocortin receptors (MC3R and MC4R) were upregulated (P < 0.05) in birds fed P-deficient diets, in both experiments. The current data show that dietary P deficiency decreases feed intake in broiler chickens by altering the expression of anorexigenic genes in the gut and hypothalamus of broiler chickens.

Use of 25-hydroxyvitamin D3 in diets for sows: A review

Dietary supplementation with 25-hydroxyvitamin D₃ (25OHD₃), as an alternative source of vitamin D, is becoming increasingly popular due to its commercialization and more efficient absorbability. The addition of 25OHD₃ rather than its precursor vitamin D₃ can circumvent the 25-hydroxylation reaction in the liver, indicating that supplementation of 25OHD₃ can rapidly improve the circulating vitamin D status of animals. Emerging experiments have reported that maternal 25OHD₃ supplementation could increase sow performances and birth outcomes and promote circulating vitamin D status of sows and their offspring. Increased milk fat content was observed in many experiments; however, others demonstrated that adding 25OHD₃ to lactating sow diets increased the contents of milk protein and lactose. Although an inconsistency between the results of different experiments exists, these studies suggested that maternal 25OHD₃ supplementation could alter milk composition via its effects on the mammary gland. Previous studies have demonstrated that adding 25OHD₃ to sow diets could improve the mRNA expressions of insulin-induced gene 1 (INSIG1) and sterol regulatory element-binding protein 1 (SREBP1) in the mammary gland cells from milk and increase the mRNA expressions of acetyl-CoA carboxylase α (ACCα) and fatty acid synthase (FAS) in the mammary gland tissue. Maternal 25OHD₃ supplementation promotes skeletal muscle development of piglets before and after parturition, and improves bone properties including bone density and bone breaking force in lactating sows and their piglets. Interestingly, 25OHD₃ supplementation in sow diets could improve neonatal bone development via regulation of milk fatty acid composition related to bone metabolism and mineralization. In this review, we also discuss the effects of adding 25OHD₃ to sow diets on the gut bacterial metabolites of suckling piglets, and propose that butyrate production may be associated with bone health. Therefore, to better understand the nutritional functions of maternal 25OHD₃ supplementation, this paper reviews advances in the studies of 25OHD₃ for sow nutrition and provides references for practical application.

Vitamin D receptor expression in mature osteoclasts reduces bone loss due to low dietary calcium intake in male mice

Mature osteoclasts express the vitamin D receptor (VDR) and are able to respond to active vitamin D (1α, 25-dihydroxyvitamin D3; 1,25(OH)2D3) by regulating cell maturation and activity. However, the in vivo consequences of vitamin D signalling directly within functionally mature osteoclasts is only partially understood. To investigate the in vivo role of VDR in mature osteoclasts, conditional deletion of the VDR under control of the cathepsin K promoter (CtskCre/Vdr-/-), was assessed in 6 and 12-week-old mice, either under normal dietary conditions (NormCaP) or when fed a low calcium (0.03 %), low phosphorous (0.08 %) diet (LowCaP). Splenocytes from CtskCre/Vdr-/- mice were co-cultured with MLO-Y4 osteocyte-like cells to assess the effect on osteoclastogenesis. Six-week-old CtskCre/Vdr-/- mice demonstrated a 10 % decrease in vertebral bone volume (p < 0.05), which was associated with increased osteoclast size (p < 0.05) when compared to Vdrfl/fl control mice. Control mice fed a LowCaP diet exhibited extensive trabecular bone loss associated with increased osteoclast surface, number and size (p < 0.0001). Interestingly, CtskCre/Vdr-/- mice fed a LowCaP diet showed exacerbated loss of bone volume fraction (BV/TV%) and trabecular number (Tb.N), by a further 22 % and 21 %, respectively (p < 0.05), suggesting increased osteoclastic bone resorption activity with the loss of VDR in mature osteoclasts under these conditions. Co-culture of CtskCre/Vdr-/- splenocytes with MLO-Y4 cells increased resulting osteoclast numbers 2.5-fold, which were greater in nuclei density and exhibited increased resorption of dentine compared to osteoclasts derived from Vdrfl/fl splenocyte cultures. These data suggest that in addition to RANKL-mediated osteoclastogenesis, intact VDR signalling is required for the direct regulation of the differentiation and activity of osteoclasts in both in vivo and ex vivo settings.

Association between vitamin D supplementation or serum vitamin D level and susceptibility to SARS-CoV-2 infection or COVID-19 including clinical course, morbidity and mortality outcomes? A systematic review

OBJECTIVE

To systemically review and critically appraise published studies of the association between vitamin D supplementation or serum vitamin D level and susceptibility to SARS-CoV-2 infection or COVID-19, including clinical course, morbidity and mortality outcomes.

DESIGN

Systematic review.

DATA SOURCES

MEDLINE (OVID), Embase (OVID), Cochrane Central Register of Controlled Trials, MedRxiv and BioRxiv preprint databases. COVID-19 databases of the WHO, Cochrane, CEBM Oxford and Bern University up to 10 June 2020.

STUDY SELECTION

Studies that assessed vitamin D supplementation and/or low serum vitamin D in patients acutely ill with, or at risk of, severe betacoronavirus infection (SARS-CoV, MERS-CoV, SARS-CoV-2).

DATA EXTRACTION

Two authors independently extracted data using a predefined data extraction form and assessed risk of bias using the Downs and Black Quality Assessment Checklist.

RESULTS

Searches elicited 449 papers, 59 studies were eligible full-text assessment and 4 met the eligibility criteria of this review. The four studies were narratively synthesised and included (1) a cross-sectional study (n=107) suggesting an inverse association between serum vitamin D and SARS-CoV-2; (2) a retrospective cohort study (348 598 participants, 449 cases) in which univariable analysis showed that vitamin D protects against COVID-19; (3) an ecological country level study demonstrating a negative correlation between vitamin D and COVID-19 case numbers and mortality; and (4) a case-control survey (n=1486) showing cases with confirmed/probable COVID-19 reported lower vitamin D supplementation. All studies were at high/unclear risk of bias.

CONCLUSION

There is no robust evidence of a negative association between vitamin D and COVID-19. No relevant randomised controlled trials were identified and there is no robust peer-reviewed published evidence of association between vitamin D levels and severity of symptoms or mortality due to COVID-19. Guideline producers should acknowledge that benefits of vitamin D supplementation in COVID-19 are as yet unproven despite increasing interest.

Vitamin D Effects on Bone Homeostasis and Cardiovascular System in Patients with Chronic Kidney Disease and Renal Transplant Recipients

Poor vitamin D status is common in patients with impaired renal function and represents one main component of the complex scenario of chronic kidney disease-mineral and bone disorder (CKD-MBD). Therapeutic and dietary efforts to limit the consequences of uremia-associated vitamin D deficiency are a current hot topic for researchers and clinicians in the nephrology area. Evidence indicates that the low levels of vitamin D in patients with CKD stage above 4 (GFR < 15 mL/min) have a multifactorial origin, mainly related to uremic malnutrition, namely impaired gastrointestinal absorption, dietary restrictions (low-protein and low-phosphate diets), and proteinuria. This condition is further worsened by the compromised response of CKD patients to high-dose cholecalciferol supplementation due to the defective activation of renal hydroxylation of vitamin D. Currently, the literature lacks large and interventional studies on the so-called non-calcemic activities of vitamin D and, above all, the modulation of renal and cardiovascular functions and immune response. Here, we review the current state of the art of the benefits of supplementation with native vitamin D in various clinical settings of nephrological interest: CKD, dialysis, and renal transplant, with a special focus on the effects on bone homeostasis and cardiovascular outcomes.

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.

The role of autophagy in bone homeostasis

Autophagy is an evolutionarily conserved intracellular process and is considered one of the main catabolism pathways. In the process of autophagy, cells are digested nonselectively or selectively to recover nutrients and energy, so it is regarded as an antiaging process. In addition to the essential role of autophagy in cellular homeostasis, autophagy is a stress response mechanism for cell survival. Here, we review recent literature describing the pathway of autophagy and its role in different bone cell types, including osteoblasts, osteoclasts, and osteocytes. Also discussed is the mechanism of autophagy in bone diseases associated with bone homeostasis, including osteoporosis and Paget's disease. Finally, we discuss the application of autophagy regulators in bone diseases. This review aims to introduce autophagy, summarize the understanding of its relevance in bone physiology, and discuss its role and therapeutic potential in the pathogenesis of bone diseases such as osteoporosis.

The Role of Cannabinoid Receptor Type 2 in the Bone Loss Associated With Pediatric Celiac Disease

OBJECTIVES

In this study, we investigated the role of the cannabinoid receptor type 2 (CB2) in the bone loss associated with celiac disease (CD) evaluating the effect of its pharmacological modulation on osteoclast activity. We previously demonstrated a significant association between the CB2 Q63R variant and CD, suggesting it as a possible disease biomarker. Moreover, CB2 stimulation is beneficial for reducing osteoclast activity in several bone pathologic conditions.

METHODS

In vitro osteoclasts (OCs) were differentiated from peripheral blood mononuclear cells of healthy donors, CD children at diagnosis and after 1 year of gluten-free diet (GFD) and characterized by real-time PCR and western blot for the expression of CB2 and specific osteoclastic markers, TRAP and Cathepsin K. TRAP assay and Bone Resorption assay were performed to evaluate osteoclast activity before and after 48 h exposure to CB2 selective drugs (JWH-133 and AM630) and Vitamin D.

RESULTS

We found in CD patients an osteoclast hyperactivation and low levels of CB2. CB2 stimulation with JWH-133 agonist is more effective than Vitamin D in reducing osteoclast activity whereas CB2 blockade with AM630 increases osteoclast activation. The anti-osteoporotic effect of JWH-133 decreases when used in co-treatment with vitamin D. GFD reduces osteoclast activity without restore CB2 expression.

CONCLUSIONS

CB2 could be a molecular marker to predict the risk of bone alterations in CD and a pharmacological target to reduce bone mass loss in patients who need a direct intervention on bone metabolism, in addition to the GFD.

Pleiotropic actions of Vitamin D in composite musculoskeletal trauma

Composite tissue injuries are the result of high energy impacts caused by motor vehicle accidents, gunshot wounds or blasts. These are highly traumatic injuries characterized by wide-spread, penetrating wounds affecting the entire musculoskeletal system, and are generally defined by frank volumetric muscle loss with concomitant segmental bone defects. At the tissue level, the breadth of damage to multiple tissue systems, and potential for infection from penetration, have been shown to lead to an exaggerated, often chronic inflammatory response with subsequent dysregulation of normal musculoskeletal healing mechanisms. Aside from the direct effects of inflammation on myogenesis and osteogenesis, frank muscle loss has been shown to directly impair fracture union and ultimately contribute to failed wound regeneration. Care for these injuries requires extensive surgical intervention and acute care strategies. However, often these interventions do not adequately mitigate inflammation or promote proper musculoskeletal injury repair and force amputation of the limb. Therefore, identification of factors that can promote tissue regeneration and mitigate inflammation could be key to restoring wound healing after composite tissue injury. One such factor that may directly affect both inflammation and tissue regeneration in response to these multi-tissue injuries may be Vitamin D. Beyond traditional roles, the pleiotropic and localized actions of Vitamin D are increasingly being recognized in most aspects of wound healing in complex tissue injuries - e.g., regulation of inflammation, myogenesis, fracture callus mineralization and remodeling. Conversely, pre-existing Vitamin D deficiency leads to musculoskeletal dysfunction, increased fracture risk or fracture non-unions, decreased strength/function and reduced capacity to heal wounds through increased inflammation. This Vitamin D deficient state requires acute supplementation in order to quickly restore circulating levels to an optimal level, thereby facilitating a robust wound healing response. Herein, the purpose of this review is to address the roles and critical functions of Vitamin D throughout the wound healing process. Findings from this review suggest that careful monitoring and/or supplementation of Vitamin D may be critical for wound regeneration in composite tissue injuries.

Vitamin D and Periodontitis: A Systematic Review and Meta-Analysis

To explore the vitamin D levels of periodontitis patients in comparison with periodontally healthy ones, and to assess the influence of vitamin D supplementation as an adjunctive during nonsurgical periodontal treatment (NSPT). Five databases (Pubmed, Embase, Scholar, Web of Sciences, and Cochrane Library) were searched until May 2020. Mean difference (MD) meta-analysis with corresponding 95% confidence interval (95% CI) and sensitivity tests via meta-regression were used. We followed Strength of Recommendation Taxonomy (SORT) to appraise the strength and quality of the evidence. Sixteen articles were included, fourteen case-control and two intervention studies, all reporting 25-hydroxyvitamin D (25(OH)D) levels. Compared with the healthy controls, the circulating 25(OH)D levels were significantly lower in chronic periodontitis patients (pooled MD = -6.80, 95% CI: -10.59 to -3.02). Subgroup analysis revealed differences among 25(OH)D measurements, with liquid chromatography-mass spectrometry being the most homogeneous method (pooled MD = -2.05, 95% CI: -3.40 to -0.71). Salivary levels of 25(OH)D showed no differences between groups. Due to the low number of studies, conclusions on aggressive periodontitis and in the effect of vitamin D supplementation after NSPT were not possible to ascribe. Compared with healthy controls, 25(OH)D serum levels are significantly lower in chronic periodontitis patients, with an overall SORT A recommendation. Future studies are needed to clarify the effect of vitamin D supplementation and the biological mechanisms linking vitamin D to the periodontium.

BISPHOSPHONATES FOR THE TREATMENT OF CALCITRIOL-INDUCED HYPERCALCEMIA

Objective

Calcitriol excess is a less common cause of hypercalcemia than hyperparathyroidism. Hypercalcemia due to calcitriol excess is usually managed acutely with intravenous (IV) fluid administration and dietary calcium restriction. Steroids and ketoconazole are second-line agents. There is evidence supporting the role of bone resorption in the genesis of hypercalcemia in vitamin D intoxication and for a rapid response of hypercalcemia to treatment with bisphosphonates. We seek to demonstrate the utility of bisphosphonates in calcitriol-induced hypercalcemia (CIH).

Methods

We present the case of a patient with recurrent CIH from a follicular lymphoma who achieved normalization and subsequent stabilization of serum calcium levels following bisphosphonate administration.

Results

A 77-year-old woman with a history of non-small cell lung cancer was admitted with dry mouth, polyuria, weight loss, and fatigue. She was found to have a calcium level of 14.7 mg/dL (normal range is 8.5 to 10.2 mg/dL), 25-hydroxyvitamin D of 47 ng/mL (normal range is 30 to 60 ng/mL), 1,25-dihydroxyvitamin D of 89 pg/mL (normal range is 18 to 72 pg/mL), and parathyroid hormone of 19 pg/mL (normal range is 15 to 65 pg/mL), which recurred despite treatment with IV fluids and strict low-calcium diet. She received 5 mg of IV zoledronic acid and normocalcemia was maintained thereafter, without any diagnosis-specific treatment for >3 months. Positron emission tomography with computed tomography eventually showed new innumerable foci of increased uptake in the skeleton and lymph node biopsy revealed grade 3A follicular lymphoma.

Conclusion

The first choice for CIH is treating the underlying cause. Bisphosphonates are, however, useful until a diagnosis is made, as they may be safer than steroids and can provide rapid relief even with a single treatment with minimal side effects.

Effect of dietary 25-hydroxycholecalciferol on the sternal mass of meat ducks under different vitamin regimens

Genetic selection and intensive nutrition for increased growth rate in meat-type ducks has resulted in an imbalance between pectorales increment and sternal mass, which is detrimental to productivity and welfare. Reducing body weight and increasing sternal mass probably reverses these adverse effects. Therefore, 2 experiments (Expt.) were conducted to investigate the effects of 25-hydroxycholecalciferol (25-OH-D3), a vitamin D3 metabolites, on sternal mass. In Expt. 1, 512 1-day-old male ducks were randomly assigned to 4 low-nutrient density diets and received following treatments in a 2 × 2 factorial arrangement: (i) NRC or China Agricultural industry standards (NY/T) vitamin premixes and (ii) 0.069 mg/kg 25-HyD in feed or not. At 49 D of age, regardless of 25-OH-D3, NY/T vitamin regimen inhibited bone turnover and consequently increased sternal trabecular bone volume and mineral deposition compared with NRC vitamin premix. Supplementing 25-OH-D3 to NRC but not NY/T vitamin regimen significantly improved sternal microarchitecture and mineral content, which companied by decreased serum bone resorption markers concentration, as well as downregulation of the gene expressions of osteoclast differentiation and activity. In Expt. 2, 256 1-day-old male ducks were fed a standard nutrient density diet contained NRC vitamin premix with 0 or 0.069 mg/kg of 25-OH-D3. Results also showed that 25-OH-D3 treatment significantly improved sternal mineral accumulation and microarchitecture, along with decreasing osteoblast and osteoclast numbers in bone surface, declining serum bone turnover markers levels, and increasing serum Ca concentration. Collectively, these findings indicated that the dietary administration of 25-OH-D3 increased sternal mass in NRC vitamin diet by suppressing bone resorption in 49-day-old meat duck.

Vdr expression in osteoclast precursors is not critical in bone homeostasis

The long-recognized role of the vitamin D endocrine system is to maintain stable serum calcium concentrations, which are ensured by a complex interplay between parathyroid gland, kidney, intestine, and bone. However, although VDR is expressed in osteoclastogenic cells, the contribution of VDR-mediated signaling to osteoclast differentiation and activity remains undefined. We therefore deleted Vdr expression efficiently and specifically in myeloid cells by use of M lysozyme-driven Cre expression, which targets granulocytes, monocytes, macrophages and osteoclasts (Vdr^myel- mice). Bone and calcium homeostasis were investigated under basal conditions and in conditions of increased bone remodeling, by feeding Vdr^myel- and Vdr^myel+ (wildtype) mice either a normal (1%) or a low (0.02%) calcium diet from weaning onwards. Vdr^myel- mice developed normally and were normocalcemic at the age of 8 weeks, both at the normal and the low calcium diet. No differences in trabecular or cortical bone mass were observed between Vdr^myel- mice and their wildtype littermates. Dietary calcium restriction resulted in a comparable reduction of trabecular bone mass (40%) and cortical thickness (48%) in Vdr^myel- and Vdr^myel+ mice, pointing to a massive transfer of calcium from the bone to the serum. In agreement with these results, osteoclastic differentiation of hematopoietic cells of Vdr^myel- mice, either induced by M-CSF and RANKL, or cocultured with osteoblasts, occurred as efficiently as osteoclastogenesis from Vdr^myel+ mice. In conclusion, our data do not support a role for osteoclastic Vdr signaling in the control of bone homeostasis.

Nutritional vitamin D in CKD: Should we measure? Should we treat?

Vitamin Ddeficiency is frequently present in patients affected by chronic kidney disease (CKD). Experimental studies demonstrated that Vitamin D may play a role in the pathophysiology of diseases beyond mineral bone disorders in CKD (CKD-MBD). Unfortunately, the lack of large and interventional studies focused on the so called "non-classic" effects of 25(OH) Vitamin D supplementation in CKD patients, doesn't permit to conclude definitely about the beneficial effects of this supplementation in clinical practice. In conclusion, treatment of nutritional vitamin D deficiency in CKD may play a central role in both bone homeostasis and cardiovascular outcomes, but there is not clear evidence to support one formulation of nutritional vitamin D over another in CKD.

Elevated Serum 25-Hydroxyvitamin D Levels Are Associated with Improved Bone Formation and Micro-Structural Measures in Elderly Hip Fracture Patients

Vitamin D, along with calcium, is generally considered necessary for bone health and reduction of fractures. However, he effects of improving vitamin D status have not always been observed to improve bone mineral density (BMD). We have investigated whether varying vitamin D status in humans, as measured by serum 25(OH)D levels, relate to micro-structural and histomorphetric measures of bone quality and quantity, rather than density. Intertrochanteric trabecular bone biopsies and serum samples were collected from patients undergoing hip arthroplasty (65 females, 38 males, mean age 84.8 ± 8.3 years) at Royal Adelaide Hospital. Estimated GFR, serum ionized calcium, alkaline phosphatase, albumin, supplement and medication intake prior to surgery were taken from patient case records. Serum 25(OH)D, 1,25(OH)2D, and parathyroid hormone (PTH) levels were measured by immunoassays. Trabecular bone structural indices were determined by high-resolution micro-CT. Mean wall thickness (MWT) was measured on toluidine blue-stained histological sections. Bone mRNA levels for vitamin D metabolising enzymes CYP27B1 and CYP24A1 were measured by qRT-PCR. While serum 25(OH)D levels did not associate with bone volume/tissue volume (BV/TV%), serum 25(OH)D levels were strongly and independently associated with MWT (r = 0.81 p < 0.0001) with values significantly greater in patients with higher serum 25(OH)D levels. Furthermore, serum 25(OH)D levels were negatively associated with Bone Surface/Bone Volume (BS/BV) (r = −0.206, p < 0.05) and together with bone CYP27B1 and CYP24A1 mRNA accounted for 10% of the variability of BS/BV (p = 0.001). These data demonstrate that serum 25(OH)D is an independent positive predictor of micro-structural and bone formation measures and may be dependent, in part, on its metabolism within the bone.

Responses of primary osteoblasts and osteoclasts from hemizygous β-globin knockout thalassemic mice with elevated plasma glucose to 1,25-dihydroxyvitamin D3

β-thalassemia is often associated with hyperglycemia, osteoporosis and increased fracture risk. However, the underlying mechanisms of the thalassemia-associated bone loss remain unclear. It might result from abnormal activities of osteoblasts and osteoclasts, and perhaps prolonged exposure to high extracellular glucose. Herein, we determined the rate of duodenal calcium transport in hemizygous β-globin knockout thalassemic (BKO) mice. Their bones were collected for primary osteoblast and osteoclast culture. We found that BKO mice had lower calcium absorption than their wild-type (WT) littermates. Osteoblasts from BKO mice showed aberrant expression of osteoblast-specific genes, e.g., Runx2, alkaline phosphatase and osteocalcin, which could be partially restored by 1,25(OH)₂D₃ treatment. However, the mRNA expression levels of RANK, calcitonin receptor (Calcr), c-Fos, NFATc1, cathepsin K and DMT1 were similar in both BKO and WT groups. Exposure to high extracellular glucose modestly but significantly affected the expression of osteoclast-specific markers in WT osteoclasts with no significant effect on osteoblast-specific genes in WT osteoblasts. Thus, high glucose alone was unable to convert WT bone cells to BKO-like bone cells. In conclusion, the impaired calcium absorption and mutation-related aberrant bone cell function rather than exposure to high blood glucose were likely to be the principal causes of thalassemic bone loss.

Evaluation of FGF-23 and 25(OH)D3 levels in peri-implant sulcus fluid in peri-implant health and diseases

BACKGROUND

There are limited studies to date investigating vitamin D and fibroblast growth factor (FGF)-23 in different peri-implant conditions.

PURPOSE

To evaluate the peri-implant sulcus fluid (PISF) FGF-23 and 25-hydroxy-vitamin D₃ (25(OH)D₃ ) levels in peri-implant health and diseases.

MATERIALS AND METHODS

A total of 90 dental implant sites (peri-implant healthy group [n = 30], peri-implant mucositis group [n = 30], and peri-implantitis group [n = 30]) in 53 participants were included in the study. Probing depth (PD), clinical attachment level (CAL), suppuration (S), modified plaque index (mPI), gingival index (GI), modified sulcus bleeding index (mSBI), and keratinized mucosa width (KMW) were recorded as clinical parameters, and PISF samples were obtained. FGF-23 and 25(OH)D₃ levels were analyzed by enzyme-linked immunosorbent assay.

RESULTS

There were no statistically significant differences in FGF-23 concentrations among the groups (P > .05). The 25(OH)D₃ concentration was significantly lower in peri-implantitis group compared with the other two groups (P < .05). The mean total amount of FGF-23 in the peri-implantitis group was significantly higher than the peri-implant healthy group whereas 25(OH)D₃ total amount was significantly lower in the peri-implantitis group than the peri-implant healthy group. The 25(OH)D₃ concentration was significantly negatively correlated with CAL, PD, mPI, S, GI, and mSBI and statistically significant relationship was found between FGF-23 total amount and these clinical parameters (P < .05). There was a negligible positive correlation between 25(OH)D₃ and FGF-23 concentrations (τ = 0.169; P = .018).

CONCLUSION

Within the limitations of this study, it can be concluded that FGF-23 and vitamin D seems to affect peri-implant bone health, and further studies are needed to explain the association between FGF-23 and 25(OH)D₃ in peri-implant conditions.

Hypophosphatemic Rickets

Hypophosphatemic rickets, mostly of the X-linked dominant form caused by pathogenic variants of the PHEX gene, poses therapeutic challenges with consequences for growth and bone development and portends a high risk of fractions and poor bone healing, dental problems and nephrolithiasis/nephrocalcinosis. Conventional treatment consists of PO4 supplements and calcitriol requiring monitoring for treatment-emergent adverse effects. FGF23 measurement, where available, has implications for the differential diagnosis of hypophosphatemia syndromes and, potentially, treatment monitoring. Newer therapeutic modalities include calcium sensing receptor modulation (cinacalcet) and biological molecules targeting FGF23 or its receptors. Their long-term effects must be compared with those of conventional treatments.

Effect of modulating dietary vitamin D on the general bone health of rats during posterolateral spinal fusion

Vitamin D plays a significant role in musculoskeletal health by regulating calcium, phosphate, and promoting new bone mineralization. The purpose of this study was to understand the effect of dietary vitamin D on general bone health during peri-operative bone healing via an in vivo dosing study of vitamin D in a rat posterolateral fusion model using autograft. Vitamin D Deficient (DD), vitamin D Insufficient (ID), Control vitamin D (CD), and Hyper-vitamin D (HD) groups were studied. Increasing dietary vitamin D improved quantitative measures of femoral geometry, including femoral strength, stiffness, and density. Femoral biomechanics, cortical thickness, moment of inertia, cross-sectional area, and measures from bone ashing were all greater in the HD group versus the CD. This suggests that additional dietary vitamin D above normal levels during spinal fusion may lead to improvement in bone health. Serum vitamin D levels were also observed to decrease during fusion healing. These results demonstrate that dietary vitamin D improves general bone health in the femur of a rat model during posterolateral spinal fusion. This suggests a role for further clinical evaluation of vitamin D dietary intake during the peri-operative period, with the possibility of avoiding adverse consequences to general bone health. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1435-1443, 2018.

Transglutaminase activity regulates differentiation, migration and fusion of osteoclasts via affecting actin dynamics

Osteoclasts, bone resorbing cells, derive from monocyte/macrophage cell lineage. Increased osteoclast activity is responsible for bone destruction in diseases such as osteoporosis, periodontitis and rheumatoid arthritis. Transglutaminases (TGs), protein crosslinking enzymes, were recently found involved in osteoclastogenesis in vivo, however their mechanisms of action have remained unknown. In this study, we have investigated the role of TG activity in osteoclastogenesis in vitro using four TG inhibitors, NC9, Z006, T101, and monodansyl cadaverine. Our results showed that all TG inhibitors were capable of blocking the entire osteoclastogenesis process. The most potent of the inhibitors, NC9 when added to cultures at different phases of osteoclastogenesis, inhibited differentiation, migration, and fusion of pre-osteoclasts as well as resorption activity of mature osteoclasts. Further investigation into the mechanisms revealed that NC9 increased RhoA levels and blocked podosome belt formation suggesting that TG activity regulates actin dynamics in pre-osteoclasts. The inhibitory effect of NC9 on osteoclastogenesis as well as podosome belt formation was completely reversed with a Rho-family inhibitor Exoenzyme C3. Microtubule architecture, acetylation, and detyrosination of α-tubulin were not affected. Finally, we demonstrated that macrophages and osteoclasts expressed mRNA of three TGs:TG1, TG2, and Factor XIII-A which were all differentially regulated in these cells during differentiation. Immunofluoresence microscopic analysis showed that all three enzymes co-localized to podosomes in osteoclasts. Taken together, our data suggests that TG activity regulates differentiation, migration and fusion of osteoclasts via affecting actin dynamics and that this may involve contribution from all three TG enzymes.

Absence of vitamin D receptor in mature osteoclasts results in altered osteoclastic activity and bone loss

Mature osteoclasts express the vitamin D receptor (VDR) and are able to synthesise and respond to 1,25(OH)₂D₃ via CYP27B1 enzyme activity. Whether vitamin D signalling within osteoclasts is necessary for the regulation of osteoclastic bone resorption in an in vivo setting is unclear. To determine the requirement for the VDR- and CYP27B1-mediated activity in mature osteoclasts, conditional deletion mouse models were created whereby either Vdr or Cyp27b1 gene was inactivated by breeding either Vdr^fl/fl or Cyp27b1^fl/fl mice with Cathepsin K-Cre transgenic mice (Cstk^Cre) to generate Ctsk^Cre/Vdr^-/- and Ctsk^Cre/Cyp27b1^-/- mice respectively. To account for potential Ctsk^Cre-meaited off-target deletion of Vdr, Dmp1^Cre were also used determine the effect of Vdr deletion in osteocytes. Furthermore, Ctsk^Cre/Vdr^-/- mice were ovariectomised (OVX) to assess the role of VDR in osteoclasts under bone-loss conditions and bone marrow precursor cells were cultured under osteoclastogenic conditions to assess osteoclast formation. Six-week-old Ctsk^Cre/Vdr^-/- female mice demonstrated a 15% decrease in femoral BV/TV (p<0.05). In contrast, BV/TV remained unchanged in Ctsk^Cre/Cyp27b1^-/- mice as well as in Dmp1^Cre/VDR^-/- mice. When Ctsk^Cre/Vdr^-/- mice were subjected to OVX, the bone loss that occurred in Ctsk^Cre/Vdr^-/- was predominantly due to a diminished volume of thinner trabeculae when compared to control levels. These changes in bone volume in Ctsk^Cre/Vdr^-/- mice occurred without an observable histological change in osteoclast numbers or size. However, while cultured bone marrow-derived osteoclasts from Ctsk^Cre/Vdr^-/- mice were marginally increased when compared to VDR^fl/fl mice, elevated expression of genes such as Cathepsin K, Nfatc1 and VATPase was observed. Collectively, these data indicate that the absence of VDR in mature osteoclasts causes exacerbated bone loss in young mice and during OVX which is associated with enhanced osteoclastic activity and without increased osteoclastogenesis.

Evidence for altered osteoclastogenesis in splenocyte cultures from VDR knockout mice

The indirect action of 1α,25(OH)₂-vitamin-D₃ (1,25D) on the osteoclast through stromal signalling is well established. The role of vitamin D in osteoclasts through direct 1,25D-VDR signalling is less well known. We showed previously that local 1,25D synthesis in osteoclasts modified osteoclastogenesis and osteoclastic resorptive activity. In this study, we hypothesised that osteoclasts lacking VDR expression would display an enhanced resorptive capacity due to the loss of 1,25D signalling. Splenocytes were cultured under osteoclast-differentiating conditions from mice with global deletion of the Vdr gene (VDRKO) and this was compared with age-matched wild-type littermate controls (WT). In VDRKO cultures, osteoclastogenesis was reduced, as indicated by fewer TRAP-positive multinucleated cells at all time points measured (p<0.05) compared to WT levels. However, VDRKO osteoclasts demonstrated greater resorption on a per cell basis than their WT counterparts. VDRKO cultures expressed greatly increased c-Fos mRNA compared to WT. In addition, the ratio of expression of the pro-apoptotic gene Bax to the pro-survival gene Bcl-2 was decreased in VDRKO cultures, implying that these osteoclasts may survive longer than WT osteoclasts. Our data indicate abnormal osteoclastogenesis due to the absence of Vdr expression, consistent with direct effects of vitamin D signalling being important for regulating the maturation and resorptive activities of osteoclasts.

Physiologic and pathophysiologic roles of extra renal CYP27b1: Case report and review

Although the kidney was initially thought to be the sole organ responsible for the production of 1,25(OH)₂D via the enzyme CYP27b1, it is now appreciated that the expression of CYP27b1 in tissues other than the kidney is wide spread. However, the kidney is the major source for circulating 1,25(OH)₂D. Only in certain granulomatous diseases such as sarcoidosis does the extra renal tissue produce sufficient 1,25(OH)₂D to contribute to the circulating levels, generally associated with hypercalcemia, as illustrated by the case report preceding the review. Therefore the expression of CYP27b1 outside the kidney under normal circumstances begs the question why, and in particular whether the extra renal production of 1,25(OH)₂D has physiologic importance. In this chapter this question will be discussed. First we discuss the sites for extra renal 1,25(OH)₂D production. This is followed by a discussion of the regulation of CYP27b1 expression and activity in extra renal tissues, pointing out that such regulation is tissue specific and different from that of CYP27b1 in the kidney. Finally the physiologic significance of extra renal 1,25(OH)₂D₃ production is examined, with special focus on the role of CYP27b1 in regulation of cellular proliferation and differentiation, hormone secretion, and immune function. At this point the data do not clearly demonstrate an essential role for CYP27b1 expression in any tissue outside the kidney, but several examples pointing in this direction are provided. With the availability of the mouse enabling tissue specific deletion of CYP27b1, the role of extra renal CYP27b1 expression in normal and pathologic states can now be addressed definitively.

Vitamin D Deficiency and Its Influence on Bone Metabolism and Density in a Brazilian Population of Healthy Men

Vitamin D supplementation is universal for postmenopausal women, but not for elderly men, in whom osteoporosis is also commonly neglected. This study aimed to evaluate vitamin D deficiency and its association with secondary hyperparathyroidism, bone resorption, and bone density in Brazilian men. A total of 120 men, 20-93 years, were evaluated for serum calcium, phosphorus, creatinine, 25-hydroxyvitamin D (25(OH)D), parathyroid hormone, biochemical markers of bone resorption (carboxy-terminal telopeptide, carboxy-terminal peptide of type I collagen), and bone mineral density (dual-energy X-ray absorptiometry). Glomerular filtration rate (GFR) below 30 mL/min/1.73 m², chronic diseases, and medications affecting bone were the exclusion criteria. No participant reported previous low-impact fractures. In the overall population, 25(OH)D levels were below 30 ng/mL in 46.7%, and below 20 ng/mL in 27.6%. Among the 93 patients 50 years and older, 28 had osteoporosis. In those 70 years and older, the prevalence of vitamin D deficiency (42.1%), secondary hyperparathyroidism (46.4%), high bone resorption (39.6%), decreased GFR (39.2%), and osteoporosis (41.4%) was significantly higher than in the younger subjects (p < 0.005 for all comparisons). Serum parathyroid hormone increased with aging and declining GFR, but was not significantly associated with 25(OH)D or bone mineral density. There was a clear contribution of vitamin D deficiency to increased bone resorption and osteoporosis. Binary logistic regression model considering age, 25(OH)D, and bone resorption identified age ≥70 years as the main determinant of osteoporosis. Our data demonstrate a high prevalence of vitamin D deficiency in a male population living in Rio de Janeiro, and emphasize its participation on the pathogenesis of age-related bone loss. (Vitamin D deficiency and osteoporosis are common in elderly Brazilian men.).

The effect of high-dose vitamin D3 supplementation on bone mineral density in subjects with prediabetes

The rationale of this study was to determine the effect of high-dose vitamin D₃ supplementation on bone mineral density (BMD). Prediabetic males given vitamin D had significantly less reduction in BMD at the femoral neck compared to the controls. The clinical implications of our findings require further investigation.

INTRODUCTION

Type 2 diabetes mellitus is associated with increased fracture risk, and recent studies show crosstalk between bone and glucose metabolism. Few studies have investigated the effect of vitamin D supplementation on the bone without additional calcium. In the present study, we aimed to determine whether a high dose of vitamin D₃ could improve bone mass density (BMD) in prediabetic subjects.

METHODS

The current study was conducted as a secondary research on a previously performed trial, in which 511 subjects with prediabetes were randomized to vitamin D₃ (20,000 IU per week) versus placebo for 5 years. BMD was measured using dual-energy X-ray absorptiometry (DEXA).

RESULTS

Two hundred and fifty-six subjects were randomized to vitamin D and 255 to placebo. Mean baseline serum 25-hydroxyvitamin D (25(OH)D) level was 60 nmol/L. Two hundred and two and 214 in the vitamin D and placebo groups, respectively, completed BMD measurements, whereas one in each group was excluded due to use of bisphosphonates. Males given vitamin D had significantly less reduction in BMD at the femoral neck measurement site compared to the controls (0.000 versus - 0.010 g/cm², p = 0.008). No significant differences between intervention groups were seen at the total hip measurement site, regarding both males and females.

CONCLUSIONS

Vitamin D₃ supplementation alone may be beneficial in males with prediabetes, but confirmatory studies are needed.

Pharmacologic Calcitriol Inhibits Osteoclast Lineage Commitment via the BMP-Smad1 and IκB-NF-κB Pathways

Vitamin D is involved in a range of physiological processes and its active form and analogs have been used to treat diseases such as osteoporosis. Yet how vitamin D executes its function remains unsolved. Here we show that the active form of vitamin D calcitriol increases the peak bone mass in mice by inhibiting osteoclastogenesis and bone resorption. Although calcitriol modestly promoted osteoclast maturation, it strongly inhibited osteoclast lineage commitment from its progenitor monocyte by increasing Smad1 transcription via the vitamin D receptor and enhancing BMP-Smad1 activation, which in turn led to increased IκBα expression and decreased NF-κB activation and NFATc1 expression, with IκBα being a Smad1 target gene. Inhibition of BMP type I receptor or ablation of Bmpr1a in monocytes alleviated the inhibitory effects of calcitriol on osteoclast commitment, bone resorption, and bone mass augmentation. These findings uncover crosstalk between the BMP-Smad1 and RANKL-NF-κB pathways during osteoclastogenesis that underlies the action of active vitamin D on bone health. © 2017 American Society for Bone and Mineral Research.

1,25(OH)2 vitamin D(3) contributes to osteoclast-like trans-differentiation of malignant plasma cells

1,25-dihydroxyvitamin D (1,25(OH)₂D) exerts pleiotropic effects including bone turnover and immune system regulation. It inhibits both T and B cell proliferation while decreasing the secretion of inflammatory cytokines and immunoglobulins. 1,25(OH)₂D also modulates monocyte-macrophage and osteoclast (OC) maturation. Since we have previously described that malignant plasma cells may trans-differentiate towards the myeloid lineage participating to skeletal devastation in multiple myeloma (MM), we here evaluated in vitro the role of 1,25(OH)₂D in this lineage switch. We investigated the gene and protein expression of vitamin D receptor (VDR) in MM cell lines. Thus, after cell treatment with 1,25(OH)₂D, we analyzed their morphology and the expression of myeloid and OC markers. Finally, we assessed their bone resorption property on calcium phosphate slices. All MM cells expressed VDR in nuclear and perinuclear sites. Treatment with 1,25(OH)₂D altered their morphology from round to fusiform, while inducing paxillin focalization. 1,25(OH)₂D administration also up-regulated myeloid and OC genes, including C/EBPα, RANK, M-CSFR and V-ATPase, whose promoters contain potential 1,25(OH)₂D responsive elements. Finally, 1,25(OH)₂D increased MM cell capability to generate pits of erosion on calcium phosphate discs. This data suggest that myeloma cells may undergo a functional trans-differentiation into OCs and, under appropriate experimental conditions, 1,25(OH)₂D triggers this lineage switch.

Simvastatin and MBCD Inhibit Breast Cancer-Induced Osteoclast Activity by Targeting Osteoclastogenic Factors

Previous reports have documented that cholesterol-lowering simvastatin prevented osteolytic metastasis of breast cancer in animal model in which cancer cells were placed into blood circulation. Thus, simvastatin treatment might have a preventive effect in inhibiting osteoclast activity of metastatic bone microenvironment. This study documented that both simvastatin and MBCD (cholesterol depleting drug) blocked the breast cancer-induced TRAP and MMP activity, and expressions of various osteoclastogenic genes (TRAP, Cathepsin K, and NFATc1) in pre-osteoclast RAW264.7 cells, and osteoclastogenic CSF-1 and RANKL expressions in breast cancer MCF-7 cells. Thus, these findings unravel a molecular mechanism of simvastatin-/MBCD-mediated inhibition of breast cancer-driven osteoclast activity.

The effects of different intensities of exercise and active vitamin D on mouse bone mass and bone strength

Physical exercise is beneficial to bone health. However, little is known how different intensities of exercise affect bone mass and strength. In the present study, we used young mice to study the effects of different intensities of exercise on bone mass and bone strength in comparison to pharmacological doses of active vitamin D (calcitriol). We found that only the medium level of exercise tested showed a positive effect on bone mineral density, trabecular bone volume, and bone strength, which are attributable to a decrease in bone resorption and an increase in bone formation, with the latter being accompanied by an increase in the number of osteogenic mesenchymal stem cells in the bone marrow. Calcitriol increases bone volume and bone strength, yet the combination of calcitriol and medium-intensity exercise did not further improve bone mass or strength. Moreover, calcitriol also showed some protective effect on the bone in mice with high levels of exercise. These results indicate that exercise at medium intensity increases bone mass and strength via affecting both bone formation and resorption and that its beneficial effects on bone mass cannot be further improved by calcitriol.