Perspective on skeletal health in inflammatory bowel disease.

Osteopenia and osteoporosis are common features in inflammatory bowel disease (IBD), comprising both Crohn's disease and ulcerative colitis. Moreover, Crohn's disease is associated with increased fracture risk. The etiology of bone loss in IBD is multifactorial. It includes insufficient intake or absorption of calcium, vitamin D, and potassium; smoking; a low peak bone mass; a low body mass index; and decreased physical activity. In several studies, it has been shown that elevated concentrations of systemic and local pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interferon-γ (IFNγ), interleukin (IL)-1ß, IL-4, IL-5, IL-6, IL-13, and IL-17, present in IBD patients are potentially detrimental for bone metabolism and may be responsible for bone loss and increased fracture risk. This perspective aims to review the current literature on the role of inflammatory factors in the pathophysiology of skeletal problems in IBD and to suggest potential treatment to improve bone health, based on a combination of evidence and clinical and pathophysiological reasoning.

Effects of 1,25(OH)2 D3 and 25(OH)D3 on C2C12 Myoblast Proliferation, Differentiation, and Myotube Hypertrophy.

An adequate vitamin D status is essential to optimize muscle strength. However, whether vitamin D directly reduces muscle fiber atrophy or stimulates muscle fiber hypertrophy remains subject of debate. A mechanism that may affect the role of vitamin D in the regulation of muscle fiber size is the local conversion of 25(OH)D to 1,25(OH)2 D by 1α-hydroxylase. Therefore, we investigated in a murine C2C12 myoblast culture whether both 1,25(OH)2 D3 and 25(OH)D3 affect myoblast proliferation, differentiation, and myotube size and whether these cells are able to metabolize 25(OH)D3 and 1,25(OH)2 D3 . We show that myoblasts not only responded to 1,25(OH)2 D3 , but also to the precursor 25(OH)D3 by increasing their VDR mRNA expression and reducing their proliferation. In differentiating myoblasts and myotubes 1,25(OH)2 D3 as well as 25(OH)D3 stimulated VDR mRNA expression and in myotubes 1,25(OH)2 D3 also stimulated MHC mRNA expression. However, this occurred without notable effects on myotube size. Moreover, no effects on the Akt/mTOR signaling pathway as well as MyoD and myogenin mRNA levels were observed. Interestingly, both myoblasts and myotubes expressed CYP27B1 and CYP24 mRNA which are required for vitamin D3 metabolism. Although 1α-hydroxylase activity could not be shown in myotubes, after treatment with 1,25(OH)2 D3 or 25(OH)D3 myotubes showed strongly elevated CYP24 mRNA levels compared to untreated cells. Moreover, myotubes were able to convert 25(OH)D3 to 24R,25(OH)2 D3 which may play a role in myoblast proliferation and differentiation. These data suggest that skeletal muscle is not only a direct target for vitamin D3 metabolites, but is also able to metabolize 25(OH)D3 and 1,25(OH)2 D3 . J. Cell. Physiol. 231: 2517-2528, 2016. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Regulation of CYP27B1 mRNA Expression in Primary Human Osteoblasts.

The enzyme 1α-hydroxylase (gene CYP27B1) catalyzes the synthesis of 1,25(OH)2D in both renal and bone cells. While renal 1α-hydroxylase is tightly regulated by hormones and 1,25(OH)2D itself, the regulation of 1α-hydroxylase in bone cells is poorly understood. The aim of this study was to investigate in a primary human osteoblast culture whether parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), calcitonin, calcium, phosphate, or MEPE affect mRNA levels of CYP27B1. Our results show that primary human osteoblasts in the presence of high calcium concentrations increase their CYP27B1 mRNA levels by 1.3-fold. CYP27B1 mRNA levels were not affected by PTH1-34, rhFGF23, calcitonin, phosphate, and rhMEPE. Our results suggest that the regulation of bone 1α-hydroxylase is different from renal 1α-hydroxylase. High calcium concentrations in bone may result in an increased local synthesis of 1,25(OH)2D leading to an enhanced matrix mineralization. In this way, the local synthesis of 1,25(OH)2D may contribute to the stimulatory effect of calcium on matrix mineralization.

Mechanical loading reduces inflammation-induced human osteocyte-to-osteoclast communication.

Multiple factors contribute to bone loss in inflammatory diseases such as rheumatoid arthritis (RA), but circulating inflammatory factors and immobilization play a crucial role. Mechanical loading prevents bone loss in the general population, but the effects of mechanical loading in patients with RA are less clear. Therefore, we aimed to investigate whether mechanical stimuli reverse the stimulatory effect of RA serum on osteocyte-to-osteoclast communication. Human primary osteocytes were pretreated with 10 % RA serum or healthy control serum for 7 days, followed by 1 h ± mechanical loading by pulsating fluid flow (PFF). Nitric oxide (NO) and prostaglandin E2 were measured in the medium. Receptor activator of nuclear factor-kappaB ligand (RANKL), osteoprotegerin (OPG), interleukin-6 (IL-6), cyclooxygenase-2 (COX2), matrix-extracellular phosphoglycoprotein (MEPE), cysteine-rich protein 61 (CYR61), and SOST gene expression was quantified by qPCR. Osteoclast precursors were cultured with PFF-conditioned medium (PFF-CM) or static-conditioned medium (stat-CM), and osteoclast formation was assessed. RA serum alone did not affect IL-6, CYR61, COX2, MEPE, or SOST gene expression in osteocytes. However, RA serum enhanced the RANKL/OPG expression ratio by 3.4-fold, while PFF nullified this effect. PFF enhanced NO production to the same extent in control serum (2.6-3.5-fold) and RA serum-pretreated (2.7-3.6-fold) osteocytes. Stat-CM from RA serum-pretreated osteocytes enhanced osteoclastogenesis compared with stat-CM from control serum-pretreated osteocytes, while PFF nullified this effect. In conclusion, RA serum, containing inflammatory factors, did not alter the intrinsic capacity of osteocytes to sense mechanical stimuli, but upregulated osteocyte-to-osteoclast communication. Mechanical loading nullified this upregulation, suggesting that mechanical stimuli could contribute to the prevention of osteoporosis in inflammatory disease.

Heterogeneous pattern of bone disease in adult type 1 Gaucher disease: clinical and pathological correlates.

Gaucher disease (GD) is a lysosomal storage disorder characterized by accumulation of glucosylceramide in macrophages, so-called Gaucher cells, as a result of a deficiency of the lysosomal enzyme glucocerebrosidase. Bone complications are an important cause of morbidity of GD and are thought to result from imbalance in bone remodeling. Bone manifestations among GD patients demonstrate a large variation including increased osteoclastic bone resorption, low bone formation and osteonecrosis. The purpose of the current case series is to describe the histological features observed in undecalcified bone samples, obtained from three GD patients, and evaluate the relationship with clinical features in these patients. Bone fragments were obtained from three adult type 1 GD patients with variable degrees of bone disease during orthopedic surgery. Specimens were embedded without prior decalcification in methylmethacrylate and prepared for histology according to standardized laboratory procedures. Histology revealed a heterogeneous pattern of bone involvement. High cellularity of bone marrow, abundant presence of Gaucher cells (GCs) and high turnover were observed in a patient with a history of multiple bone complications, while minimal bone turnover and few GCs were detected in the mildest affected patient in this series. An intermediate picture with relatively low bone turnover and a substantial amount of Gaucher cells was demonstrated in the third, moderately affected patient. No gross abnormalities in three biochemical markers of bone turnover (osteocalcin, N-terminal propeptide of type 1 procollagen and type 1 collagen C-terminal telopeptide) were noted. Plastic embedding and subsequent Goldner and TRAP staining offered a unique possibility to study bone histological findings in GD. Our data show that bone manifestations in GD may vary both clinically as well as histologically and bone disease in GD will likely require a personalized approach.

Inflammatory factors in the circulation of patients with active rheumatoid arthritis stimulate osteoclastogenesis via endogenous cytokine production by osteoblasts.

SUMMARY: The combination of cytokines present in the circulation of patients with active rheumatoid arthritis might contribute to the generalized bone loss that commonly occurs in these patients, by directly inhibiting osteoblast proliferation and differentiation, but especially by enhancing endogenous cytokine (i.e., receptor activator of nuclear factor-kappa B ligand (RANKL) and interleukin-6 (IL)-6) production by osteoblasts, thereby stimulating osteoclastogenesis. INTRODUCTION: Generalized bone loss, as occurs in patients with rheumatoid arthritis (RA), is related to elevated levels of circulating cytokines. Individual cytokines have deleterious effects on proliferation and differentiation of osteoblast cell lines, but little is known about the effect of the interaction between inflammatory factors in the circulation of patients with active RA on human osteoblast function, including their communication towards other bone cells. We investigated whether serum from patients with active RA enhances cytokine production by osteoblasts, thereby effectively altering osteoblast-stimulated osteoclastogenesis. METHODS: Serum was obtained from 20 patients with active RA (active RA sera) and from the same patients in clinical remission (remission RA sera). To determine osteoclastogenesis, RA serum-pretreated primary human osteoblast cultures were established in direct contact with human osteoclast precursors in the presence or absence of osteoprotegerin (OPG) or IL-6 inhibitor. RESULTS: Compared to remission RA sera, active RA sera inhibited osteoblast proliferation and differentiation in vitro as demonstrated by a reduced DNA content and gene expression of KI-67, collagen type 1, osteopontin, and osteocalcin. Active RA sera inhibited OPG expression and enhanced RANKL and IL-6 expression but did not alter IL-8 expression in osteoblasts. IL-1ß, IL-17, and tumor necrosis factor-α (TNF-α) expression were undetectable. In coculture, active RA sera treatment of osteoblasts stimulated while addition of OPG or IL-6 inhibitory antibodies significantly reduced the number of osteoclasts. CONCLUSION: Active RA sera contain circulating factors, likely cytokines and chemokines, that might contribute to bone loss by directly inhibiting osteoblast proliferation and differentiation, but especially, these factors modulate endogenous cytokine production by osteoblasts, thereby affecting osteoclastogenesis.

Expression of RANKL in breast cancer tissue in patients with fibrous dysplasia/McCune-Albright syndrome.

BACKGROUND: In fibrous dysplasia/McCune-Albright syndrome (FD/MAS), mosaic mutations in the GNAS gene lead to locally abnormal bone turnover. Additionally, patients with FD/MAS, particularly with thoracic lesions, have an increased risk for breast cancer. Development and progression of breast cancer has been associated with expression of Receptor Activator of NF-κB ligand (RANKL) in mammary tissue, and due to the GNAS mutation, RANKL is systemically increased in patients with FD/MAS. Yet it is unknown whether breast cancer in FD/MAS is also dependent on RANKL. We hypothesized that the GNAS mutation might induce RANKL overproduction and an oncogenic niche in mammary tissue, and examined RANKL expression in breast cancer tissue of patients with FD/MAS compared to controls. METHODS: Nine patients with FD/MAS and breast cancer were included and clinical data were retrieved. Patients were matched to controls with breast cancer without FD/MAS based on age and tumor type. Three pregnant breast cancer patients were included as positive controls. Immunohistochemical detection of RANKL was performed on formalin-fixed paraffin-embedded breast cancer specimens. Staining intensity was classified as weak, moderate or intense. The area of positive RANKL staining divided by the total ductal-lobular area was assessed (positive area percentage, PAP). Number of patients with RANKL expression was compared between FD/MAS and control group by chi-square (χ2) test, the PAP by Mann-Whitney U test (MWU). RESULTS: RANKL expression was observed in 3 patients with FD/MAS (38 %), mainly in healthy tissue, and none of the control patients (χ2p = 0.055). The FD/MAS group demonstrated considerably more intense staining than the control group, comparable to positive controls. The median PAP was 0.64 % (range 0.14-2.04 %) in the 3 FD/MAS patients with RANKL expression, 0.01 % (Q1-Q3: 0.0003-0.514 %) in the entire FD/MAS group, 0.006 % (Q1-Q3: 0.001-0.012 %) in the control group (MWU = 0.574), and 0.19 % (0.08-0.32 %) in the pregnant patients. All patients with FD/MAS and RANKL expression had thoracic bone lesions, but no correlation was observed between RANKL expression and presence of the GNAS mutation or FD disease burden. CONCLUSIONS: The triad of a higher number of patients, higher positive area percentage and stronger intensity in the FD/MAS compared to the control group indicates that RANKL may be upregulated in mammary tissue in a subset of patients with FD/MAS, which may explain the increased risk for breast cancer, although the clinical significance remains unclear. Further research is needed to establish risk profiles for the development of RANKL-positive breast cancer and to improve early screening and treatment.

Clinical value of RANKL, OPG, IL-6 and sclerostin as biomarkers for fibrous dysplasia/McCune-Albright syndrome.

BACKGROUND: Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare genetic bone disease caused by a somatic mutation in the GNAS gene. Currently used bone turnover markers (BTMs) do not correlate with the clinical picture and are not useful to predict or monitor therapy success. This study assessed the correlation of RANKL, OPG, RANKL/OPG ratio, IL-6 and sclerostin with the classic BTMs alkaline phosphatase (ALP), procollagen type 1 propeptide (P1NP) and beta crosslaps (CTX), with pain, skeletal burden score (SBS) and response to bisphosphonate or denosumab treatment. METHODS: Ninety-six serum samples of adult patients >18 years of age with any subtype of FD/MAS were included from the biobank facility of the Leiden University Medical Center, Center for Bone Quality between 2015 and 2021. Standard laboratory assessments were assessed as part of usual care. The concentrations of potential biomarkers RANKL, OPG, sclerostin, IL-6 were analyzed. Data on FD/MAS subtype, age, pain, treatment history and treatment response were retrieved from the electronic patient files. Baseline characteristics were summarized by descriptive statistics. Correlations of the concentrations of the potential biomarkers with classic bone turnover markers, SBS and pain scores were cross-sectionally assessed by Spearman rank order correlation. Correction for multiple testing was performed by Benjamini and Hochberg False Discovery Rate. A sensitivity analyses was performed by excluding patients with SBS below 15 and patients using antiresorptive medication at the time of blood withdrawal or within the wash-out period. In patients treated with bisphosphonates or denosumab after blood withdrawal, pre-treatment concentrations were compared in patients with and without therapy response by Mann Whitney U test. RESULTS: The median age of the patients was 41.2 (Q1-Q3 25.9-52.2) years, 62.5 % was female. Median SBS was 2.5 (Q1-Q3 0.5-7.8). RANKL level correlated weakly with ALP (Spearman rho 0.309, p = 0.004, n = 84), but not with P1NP or CTX. The RANKL/OPG ratio, OPG, IL-6 and sclerostin did not correlate with ALP, P1NP or CTX. None of the potential biomarkers correlated with SBS or pain. Results of the sensitivity analyses were comparable. Pre-treatment biomarker levels were similar in patients with and without improvement in pain scores following bisphosphonate therapy. Pre-treatment RANKL and sclerostin were comparable between patients with and without improvement in pain scores after denosumab therapy. Pre-treatment IL-6 level and the RANKL/OPG ratio seemed to be higher in patients with response to denosumab (IL-6: median 0.64 (Q1-Q3 0.53-0.74) pg/mL, n = 6, RANKL/OPG: median 0.062 (Q1-Q3 0.016-0.331), n = 5) compared to patients without response (IL-6: median 0.35 (0.20-0.54) pg/mL, n = 5, RANKL/OPG: 0.027 (0.024-0.046), n = 4). Pre-treatment IL-6 correlated with the improvement in maximum pain scores (rho 0.962, p < 0.001, n = 9) and average pain scores (rho 0.895, p = 0.001, n = 9) reported during denosumab therapy. CONCLUSION: Increased concentrations of RANKL, IL-6, sclerostin and of the RANKL/OPG ratio do not indicate severity of FD/MAS, as no correlation was observed of these potential biomarkers with the classic BTMs and SBS. Biomarker levels did not correlate with pain and had no value in predicting bisphosphonate treatment response. These biomarkers are not superior over the currently used methods of assessing ALP, P1NP and CTX or evaluating SBS to establish disease extent or activity and provide no reliable results. Yet, possibly pre-treatment IL-6 and the RANKL/OPG ratio may have some predictive value for clinical response to denosumab. Therefore, studies investigating disease activity and treatment response should include lesional imaging and patient-reported outcome measures.

The use of Straumann Bone Ceramic in a maxillary sinus floor elevation procedure: a clinical, radiological, histological and histomorphometric evaluation with a 6-month healing period.

OBJECTIVES: In this study, we evaluated the quality and quantity of bone formation in maxillary sinus floor elevation procedure using a new fully synthetic biphasic calcium phosphate (BCP) consisting of a mixture of 60% hydroxyapatite and 40% of beta-tricalcium phosphate (Straumann Bone Ceramic). MATERIAL AND METHODS: A unilateral maxillary sinus floor elevation procedure was performed in six patients using 100% BCP. Biopsy retrieval for histological and histomorphometric analysis was carried out before implant placement after a 6-month healing period. RESULTS: In this study, the maxillary sinus floor elevation procedure with the use of BCP showed uneventful healing. Radiological evaluation after 6 months showed maintenance of vertical height gained immediately after surgery. Primary stability was achieved with all Straumann SLA dental implants of 4.1 mm diameter and 10 or 12 mm length. The implants appeared to be osseointegrated well after a 3-month healing period. Histological investigation showed no signs of inflammation. Cranial from the native alveolar bone, newly formed mineralized tissue was observed. Also, osteoid islands as well as connective tissue were seen around the BCP particles, cranial from the front of newly formed mineralized tissue. Close bone-to-substitute contact was observed. Histomorphometric analysis showed an average bone volume/total volume (BV/TV) of 27.3% [standard deviation (SD) 4.9], bone surface/total volume (BS/TV) 4.5 mm(2)/mm(3) (SD 1.1), trabecula-thickness (TbTh) 132.1 mum (SD 38.4), osteoid-volume/bone volume (OV/BV) 7.5% (SD 4.3), osteoid surface/bone surface (OS/BS) 41.3% (SD 28.5), osteoid thickness (O.Th) 13.3 mum (SD 4.7) and number of osteoclasts/total area (N.Oc/Tar) 4.4 1/mm (SD 5.7). CONCLUSIONS: Although a small number of patients were treated, this study provides radiological and histological evidence in humans confirming the suitability of this new BCP for vertical augmentation of the atrophied maxilla by means of a maxillary sinus floor elevation procedure allowing subsequent dental implant placement after a 6-month healing period. The newly formed bone had a trabecular structure and was in intimate contact with the substitute material, outlining the osteoconductive properties of the BCP material. Bone maturation was evident by the presence of lamellar bone.

Bone microarchitecture and turnover in the irradiated human mandible.

OBJECTIVES: The aim of this study was to assess the microarchitecture and turnover in irradiated cancellous mandibular bone and the relation with radiation dose, to elucidate the effects of radiotherapy on the mandible. PATIENTS AND METHODS: Mandibular cancellous bone biopsies were taken from irradiated patients and controls. Micro-CT scanning was performed to analyze microstructural bone parameters. Bone turnover was assessed by histomorphometry. Local radiation dose at the biopsy site (Dmax) was estimated from radiotherapy plans. RESULTS: Twenty-seven irradiated patients and 35 controls were included. Osteoid volume (Osteoid Volume/Bone Volume, OV/BV) [0.066/0.168 (median/interquartile range (IQR), OV/BV; %), P < 0.001], osteoid surface (Osteoid Surface/Bone Surface, OS/BS) [0.772/2.17 (median/IQR, OS/BS; %), P < 0.001] and osteoclasts number (Osteoclasts per millimetre bone surface, Ocl/mmBS; mm2) [0.026/0.123 (median/IQR, Ocl/mmBS; mm2), P < 0.001] were decreased; trabecular number (Tb.N) was lower [1.63/0.63 (median/IQR, Tb.N; 1/mm-1), P = 0.012] and trabecular separation (Tb.Sp) [0.626/0.24 (median/IQR, Tb.Sp; µm), P = 0.038] was higher in irradiated mandibular bone. With higher Dmax, trabecular number increases (Spearman's correlation R = 0.470, P = 0.018) and trabecular separation decreases (Spearman's correlation R = -0.526, P = 0.007). Bone mineral density (BMD, milligrams hydroxyappetite per cubic centimetre, mgHA/cm3) [1016/99 (median/IQR, BMD; mgHA/cm3), P = 0.03] and trabecular separation [0.739/0.21 (median/IQR, Tb.Sp; µm), P = 0.005] are higher whereas connectivity density (Conn Dens) [3.94/6.71 (median/IQR, Conn Dens), P = 0.047] and trabecular number [1.48/0.44 (median/IQR, Tb.N; 1/mm-1), P = 0.002] are lower in Dmax ≤50 Gy compared to controls. CONCLUSIONS: Radiotherapy dramatically impairs bone turnover in the mandible. Deterioration in microarchitecture only affects bone irradiated with a Dmax of <50 Gy. The 50 Gy value seems to be a critical threshold to where the effects of the radiation is more detrimental.

Generation of Fibrodysplasia ossificans progressiva and control integration free iPSC lines from periodontal ligament fibroblasts.

Fibrodysplasia ossificans progressiva (FOP) is a very rare devastating heterotopic ossification disorder, classically caused by a heterozygous single point mutation (c.617G>A) in the ACVR1gene, encoding the Bone morphogenetic protein (BMP) type I receptor, also termed activin receptor-like kinase (ALK)2. FOP patients develop heterotopic ossification episodically in response to inflammatory insults, thereby compromising tissue sampling and the development of in vitro surrogate models for FOP. Here we describe the generation and characterization of a control and a classical FOP induced pluripotent stem cell (iPSC) line derived from periodontal ligament fibroblast cells using Sendai virus vectors.

The irradiated human mandible: A quantitative study on bone vascularity.

OBJECTIVES: Hypovascularisation is thought to play an important role in the pathogenesis of osteoradionecrosis. The objective of this study was to assess the microvascular system in the irradiated mandibular bone marrow. MATERIALS AND METHODS: Mandibular bone biopsies were taken from 20 irradiated patients and 24 controls. Blood vessels were visualized using CD34 antibody stain to detect endothelial cells. The vascular density (VD) and vascular area fraction (VAF) were measured. Mean vessel lumen area, perimeter and diameter of the vessels were calculated for each vessel. A distinction was made between large and small vessels (cut-off point <400 µm2). RESULTS: Vascular density and vascular area fraction were lower in the irradiated group. The mean vascular perimeter and mean vascular diameter were higher in samples with a local radiation dose of ≥50 Gy, whereas the percentage of small vessels was lower. Larger vessel perimeter is associated with higher radiation dose. A longer interval between biopsy and radiotherapy is associated with a larger mean vessel perimeter and a lower percentage of small vessels. CONCLUSIONS: Radiation dosages higher than 50 Gy mainly affect the smaller vessels. With increased time after irradiation, the share of smaller vessels in the mandibular bone marrow seems to decrease. In search of the exact mechanisms of irradiation damage and osteoradionecrosis of the mandible, the role of the microvascular system in the mandibular bone marrow should be further explored.

Ground reaction forces during walking with different load and slope combinations in rats.

BACKGROUND: Treadmill animal models are commonly used to study effects of exercise on bone. Since mechanical loading induces bone strain, resulting in bone formation, exercise that induces higher strains is likely to cause more bone formation. Our aim was to investigate the effect of slope and additional load on limb bone strain. METHODS: Horizontal and vertical ground reaction forces on left fore-limb (FL) and hind-limb (HL) of twenty 23-week old female Wistar rats (weight 279 ± 26 g) were measured for six combinations of SLOPE (-10°, 0°, +10°) and LOAD (0 to 23% of body mass). Peak force (Fmax), rate of force rise (RC), stance time (Tstance) and impulse (Fint) on FLs and HLs were analyzed. RESULTS: For the FL, peak ground reaction forces and rate of force rise were highest when walking downward -10° with load (Fmax = 2.09±0.05 N, FLRC = 34±2 N/s) For the HL, ground reaction forces and rate of force rise were highest when walking upward +10°, without load (Fmax = 2.20±0.05 N, HLRC = 34±1 N/s). Load increased stance time. Without additional load, estimates for the highest FL loading (slope is -10°) were larger than for the highest HL loading (slope is +10°) relative to level walking. CONCLUSIONS: Thus, walking downward has a higher impact on FL bones, while walking upward is a more optimal HL exercise. Additional load may have a small effect on FL loading.

The use of a biphasic calcium phosphate in a maxillary sinus floor elevation procedure: a clinical, radiological, histological, and histomorphometric evaluation with 9- and 12-month healing times.

BACKGROUND: This study evaluates the clinical, radiological, histological, and histomorphometric aspects of a fully synthetic biphasic calcium phosphate (BCP) (60% hydroxyapatite and 40% ß-tricalcium phosphate), used in a human maxillary sinus floor elevation (MSFE) procedure with 9- and 12-month healing time. METHODS: A unilateral MSFE procedure, using 100% BCP, was performed in two series of five patients with healing times of 9 and 12 months respectively. Clinical and radiological parameters were measured up to 5 years postoperatively. Biopsy retrieval was carried out during dental implants placement. Histology and histomorphometry were performed on 5-µm sections of undecalcified bone biopsies. RESULTS: The MSFE procedure with BCP showed uneventful healing in all cases. All dental implants appeared to be well osseointegrated after 3 months. Radiological evaluation showed less than 1 mm tissue height loss from MSFE to the 5-year follow-up examination. No signs of inflammation were detected on histological examination. Newly formed mineralized tissue was found cranially from the native bone. The BCP particles were surrounded by connective tissue, osteoid islands, and newly formed bone. Mineralized bone tissue was in intimate contact with the BCP particles. After 12 months, remnants of BCP were still present. The newly formed bone had a trabecular structure. Bone maturation was demonstrated by the presence of lamellar bone. Histomorphometric analysis showed at 9 and 12 months respectively an average vital bone volume/total volume of 35.2 and 28.2%, bone surface/total volume of 4.2 mm2/mm3 and 8.3 mm2/mm3, trabecular thickness of 224.7 and 66.7 µm, osteoid volume/bone volume of 8.8 and 3.4%, osteoid surface/bone surface (OS/BS) of 42.4 and 8.2%, and osteoid thickness of 93.9 and 13.6 µm. CONCLUSIONS: MFSE with BCP resulted in new bone formation within the augmented sinus floor and allowed the osseointegration of dental implants in both groups. From a histological and histomorphometric perspective, a 9-month healing time for this type of BCP may be the optimal time for placement of dental implants.

Mechanical loading and the synthesis of 1,25(OH)2D in primary human osteoblasts.

The metabolite 1,25-dihydroxyvitamin D (1,25(OH)2D) is synthesized from its precursor 25-hydroxyvitamin D (25(OH)D) by human osteoblasts leading to stimulation of osteoblast differentiation in an autocrine or paracrine way. Osteoblast differentiation is also stimulated by mechanical loading through activation of various responses in bone cells such as nitric oxide signaling. Whether mechanical loading affects osteoblast differentiation through an enhanced synthesis of 1,25(OH)2D by human osteoblasts is still unknown. We hypothesized that mechanical loading stimulates the synthesis of 1,25(OH)2D from 25(OH)D in primary human osteoblasts. Since the responsiveness of bone to mechanical stimuli can be altered by various endocrine factors, we also investigated whether 1,25(OH)2D or 25(OH)D affect the response of primary human osteoblasts to mechanical loading. Primary human osteoblasts were pre-incubated in medium with/without 25(OH)D3 (400 nM) or 1,25(OH)2D3 (100 nM) for 24h and subjected to mechanical loading by pulsatile fluid flow (PFF). The response of osteoblasts to PFF was quantified by measuring nitric oxide, and by PCR analysis. The effect of PFF on the synthesis of 1,25(OH)2D3 was determined by subjecting osteoblasts to PFF followed by 24h post-incubation in medium with/without 25(OH)D3 (400 nM). We showed that 1,25(OH)2D3 reduced the PFF-induced NO response in primary human osteoblasts. 25(OH)D3 did not significantly alter the NO response of primary human osteoblasts to PFF, but 25(OH)D3 increased osteocalcin and RANKL mRNA levels, similar to 1,25(OH)2D3. PFF did not increase 1,25(OH)2D3 amounts in our model, even though PFF did increase CYP27B1 mRNA levels and reduced VDR mRNA levels. CYP24 mRNA levels were not affected by PFF, but were strongly increased by both 25(OH)D3 and 1,25(OH)2D3. In conclusion, 1,25(OH)2D3 may affect the response of primary human osteoblasts to mechanical stimuli, at least with respect to NO production. Mechanical stimuli may affect local vitamin D metabolism in primary human osteoblasts. Our results suggest that 1,25(OH)2D3 and mechanical loading, both stimuli of the differentiation of osteoblasts, interact at the cellular level.

Long-term vitamin D deficiency in older adult C57BL/6 mice does not affect bone structure, remodeling and mineralization.

Animal models show that vitamin D deficiency may have severe consequences for skeletal health. However, most studies have been performed in young rodents for a relatively short period, while in older adult rodents the effects of long-term vitamin D deficiency on skeletal health have not been extensively studied. Therefore, the first aim of this study was to determine the effects of long-term vitamin D deficiency on bone structure, remodeling and mineralization in bones from older adult mice. The second aim was to determine the effects of long-term vitamin D deficiency on mRNA levels of genes involved in vitamin D metabolism in bones from older adult mice. Ten months old male C57BL/6 mice were fed a diet containing 0.5% calcium, 0.2% phosphate and 0 (n=8) or 1 (n=9) IU vitamin D3/gram for 14 months. At an age of 24 months, mice were sacrificed for histomorphometric and micro-computed tomography (micro-CT) analysis of humeri as well as analysis of CYP27B1, CYP24 and VDR mRNA levels in tibiae and kidneys using RT-qPCR. Plasma samples, obtained at 17 and 24 months of age, were used for measurements of 25-hydroxyvitamin D (25(OH)D) (all samples), phosphate and parathyroid hormone (PTH) (terminal samples) concentrations. At the age of 17 and 24 months, mean plasma 25(OH)D concentrations were below the detection limit (<4nmol/L) in mice receiving vitamin D deficient diets. Plasma phosphate and PTH concentrations did not differ between both groups. Micro-CT and histomorphometric analysis of bone mineral density, structure and remodeling did not reveal differences between control and vitamin D deficient mice. Long-term vitamin D deficiency did also not affect CYP27B1 mRNA levels in tibiae, while CYP24 mRNA levels in tibiae were below the detection threshold in both groups. VDR mRNA levels in tibiae from vitamin D deficient mice were 0.7 fold lower than those in control mice. In conclusion, long-term vitamin D deficiency in older adult C57BL/6 mice, accompanied by normal plasma PTH and phosphate concentrations, does not affect bone structure, remodeling and mineralization. In bone, expression levels of CYP27B1 are also not affected by long-term vitamin D deficiency in older adult C57BL/6 mice. Our results suggest that mice at old age have a low or absent response to vitamin D deficiency probably due to factors such as a decreased bone formation rate or a reduced response of bone cells to 25(OH)D and 1,25(OH)2D. Older adult mice may therefore be less useful for the study of the effects of vitamin D deficiency on bone health in older people.

(18)F-fluoride-PET for dynamic in vivo monitoring of bone formation in multiple myeloma.

BACKGROUND: Bone disease in multiple myeloma is characterized by reduced bone formation. The gold standard of bone formation is the mineral apposition rate (MAR), an invasive technique reflecting bone formation at a single site. We compared (18)F-fluoride-PET with the MAR in myeloma patients. METHODS: Bone formation was measured before and after bortezomib treatment by determination of the MAR in iliac bone marrow biopsies and the measurement of (18)F-uptake. RESULTS: The inter- and intra-individual variations in (18)F-uptake (SUVA50%) were pronounced as 33.50 (range 4.42 to 37.92) and 27.18 (range 4.00 to 31.18), respectively. A significant correlation between the MAR and (18)F-uptake was found (r = 0.80, p = 0.017). There was a heterogeneous response after treatment varying from -2.20 to 4.53. CONCLUSIONS: Iliac (18)F-uptake was associated with the local MAR in myeloma patients. Furthermore, (18)F-fluoride-PET demonstrated the heterogeneity of in vivo bone formation, enabling monitoring during treatment.

Effects of Chronic Estrogen Administration in the Ventromedial Nucleus of the Hypothalamus (VMH) on Fat and Bone Metabolism in Ovariectomized Rats.

Estrogen deficiency after ovariectomy (OVX) results in increased adiposity and bone loss, which can be prevented by systemic 17-ß estradiol (E2) replacement. Studies in transgenic mice suggested that in addition to direct actions of estrogen in peripheral tissues, also estrogen signaling in the hypothalamus regulates fat distribution and bone metabolism. We hypothesized that the protective effect of systemic E2 on fat and bone metabolism in the OVX model is partly mediated through the ventromedial nucleus of the hypothalamus (VMH). To test this hypothesis, we determined the effect of systemic, central, and targeted VMH administration of E2 on fat and bone metabolism in OVX rats. Subcutaneous administration of E2 for 4 weeks decreased body weight, gonadal and perirenal fat, and bone formation rate in OVX rats. This effect was completely mimicked by intracerebroventricular injections of E2, once every 4 days for 4 weeks. Administration of E2 locally in the VMH by retromicrodialysis (3 h) acutely increased expression of the lipolytic gene hormone-sensitive lipase in gonadal and perirenal fat. Finally, chronic administration of E2 in the VMH for 8 weeks decreased perirenal fat but did not affect body weight, trabecular bone volume, or cortical thickness. In conclusion, we demonstrated that intracerebroventricular E2 replacement reduces body weight gain, ameliorates intraabdominal fat accumulation, and reduces bone formation in the OVX rats. E2 administration selectively in the VMH also reduced intraabdominal fat but did not affect bone metabolism.

Bone structure in patients with low bone mineral density with or without vertebral fractures.

Vertebral fractures (VFX) are caused by low bone mass and microstructural deterioration of bone tissue. The latter is not well defined. We investigated bone structure in transiliac biopsy specimens from 88 volunteers. Biopsy specimens were obtained at baseline in the Multiple Outcomes of Raloxifene Evaluation trail, a prospective study in osteoporotic (BMD < or = -2.5 T score) postmenopausal women without or with VFX on standardized lateral spinal radiographs. Bone biopsy specimens were embedded in methylmethacrylate (MMA). Histomorphometry was done in 8 microns (U.S.A.) or 5 microns (Europe) Goldner stained sections. Vertebral fracture status (yes/no) was the outcome variable in logistic regression models adjusted for age and biopsy specimen origin (U.S.A. vs. Europe). Patients with and without VFX (26/62) were similar regarding age (69.2 +/- 5.2 years vs. 67.3 +/- 6.7 years), bone volume (BV/TV; 17.7 +/- 4.7% vs. 19.0 +/- 5.8%), and bone surface (BS/TV; 2.7 +/- 0.6 mm2/mm3 vs. 2.8 +/- 0.6 mm2/mm3). A lower cortical thickness (C.Th; 652 +/- 267 microns vs. 822 +/- 325 microns), total strut length (TSL; 826 +/- 226 microns/mm2 vs. 922 +/- 256 microns/mm2), node-to-loop (Nd-Lp) strut length (10.1 +/- 10.3% vs. 15.0 +/- 13.6%), together with a higher node-to-terminus (Nd-Tm) strut length (45.6 +/- 9.7% vs. 39.1 +/- 9.3%) were each associated with prevalent VFX (0.01 < p < 0.10). Differences in BV/TV did not explain these associations. In conclusion, cortical thinning and disruption of trabecular lattice are possible pathogenic mechanisms in patients with VFX.

The effect of growth hormone (GH) on histomorphometric indices of bone structure and bone turnover in GH-deficient men.

We investigated the effects of GH on bone structure and turnover by histomorphometry in GH-deficient adults. Therefore, transiliac bone biopsies were obtained before and after 1 yr of treatment in 36 GH-deficient men (mean age, 28 +/- 4 yr). Thirteen patients had isolated GH deficiency and 23 patients had multiple pituitary hormone deficiencies. Patients were randomly assigned to four treatment groups. Groups 1, 2, and 3 received 1, 2, and 3 IU/m2/day (0.35, 0.69, and 1.3 mg/m2/day) [corrected] GH, respectively, and the fourth group received placebo for the first 6 months and 2 IU/m2/day (5.8 mg/m2/day) GH for the subsequent 6 months. GH treatment resulted in an increase of cortical thickness from 0.98 +/- 0.27 to 1.20 +/- 0.35 mm (P = 0.005), but trabecular bone volume did not change. Bone formation variables increased significantly: osteoid surface increased from 8.5 +/- 5.3 to 15.5 +/- 6.1% (P = 0.0002), mineralizing surface increased from 6.7 +/- 2.5 to 10.8 +/- 4.4% (P = 0.0002), and bone formation rate increased from 0.04 +/- 0.02 to 0.08 +/- 0.04 mm3/mm2/day (P = 0.0001). Eroded surface did not change, but osteoclast number increased from 0.6 +/- 0.5 to 1.25 +/- 0.5 Oc/mm2 (P = 0.0001). The relative formation period increased significantly (P = 0.001), whereas the resorption period, including reversal phase, decreased from 65 to 40 days (P = 0.02). Activation frequency increased from 0.39 +/- 0.17 to 0.74 +/- 0.34 y(-1) (P = 0.0001). These data indicate a stimulated bone turnover as a result of GH treatment and a shorter resorption and reversal time. The increased turnover did not result in an increased trabecular bone volume, but the cortical thickness increased significantly.