Effects of intermittent versus continuous parathyroid hormone administration on condylar chondrocyte proliferation and differentiation

Abaloparatide and teriparatide enhance mandibular growth in adolescent rats with site-specific and mechano-related effects

OBJECTIVE

Teriparatide (TPTD) and abaloparatide (ABL) are two osteoanabolic drugs targeting parathyroid hormone (PTH)1R signalling. This study aimed to investigate the effects of TPTD and ABL on the adolescent mandibular growth.

METHOD

In total, 70 4-week-old male Sprague-Dawley rats were randomly divided into 14 groups, treated with intermittent TPDT or ABL at various doses, accompanied by mandibular advancement (MA) or not. 3D printing was used to fabricate an innovative splint for MA. After a 4-week treatment, morphological measurement, histological and immunohistochemical analysis were performed. Mandibular condylar chondrocytes (MCCs) were treated with TPTD or ABL, followed by CCK-8 assay, alcian blue staining, real time-PCR and immunofluorescent staining.

RESULT

In vivo, TPTD or ABL alone increased the condylar length and cartilage thickness, with up-regulated SOX9 and COL II, whilst down-regulated COL X; however, when combined with MA, the promotive effects were attenuated. TPTD or ABL alone increased the mandibular body height and mandibular angle width, whilst increased the mandibular body length and alveolar bone width when combined with MA. In vitro, TPTD or ABL enhanced the MCC proliferation, glycosaminoglycan synthesis, COL II and SOX9 expression, whilst down-regulated COL X, Ihh and PTH1R expression.

CONCLUSION

Both ABL and TPTD enhance mandibular growth in adolescent rats with site-specific and mechano-related effects, including propelling chondrogenesis at the condylar cartilage and promoting bone apposition at other mechano-responsive sites. They behave as promising drugs for mandibular growth modification, and in general ABL seems more potent than TPTD in this context.

Intraflagellar transport protein 88 interacts with polycystin 2 to regulate mechanosensitive hedgehog signaling in mandibular condylar chondrocytes

OBJECTIVE

This study aimed to explore whether intraflagellar transport protein 88 (IFT88) was associated with polycystin 2 during mechanotransduction of mandibular condylar chondrocytes.

METHODS

Rat mandibular condylar chondrocytes isolated from the condylar bone-cartilage junction were subjected to cyclic tensile strain (0.1 Hz, 10% elongation). Overexpression of IFT88 was achieved by lentiviral vector-mediated transfection. Knockdown of IFT88 and polycystin 2 was achieved by small interfering RNA (siRNA). The prevalence and length of cilia were reflected by immunofluorescence staining. The activities of hedgehog signaling were evaluated by western blot analysis. The interaction between polycystin 2 and IFT88 was evaluated by conducting a co-immunoprecipitation (co-IP) assay.

RESULTS

Overexpression of IFT88 increased the length of cilia. Protein levels of polycystin 2, Indian hedgehog (Ihh), Patched 1 (Ptch1), Smoothened (Smo), and Glioma-associated oncogene homolog 1 (Gli1) were elevated in IFT88-overexpressing mandibular condylar chondrocytes under cyclic tensile strain. Knockdown of the protein level of IFT88 reduced the prevalence and length of cilia, and protein levels of polycystin 2, Ihh, Ptch1, Smo, and Gli1. A co-IP assay showed that IFT88 formed a complex with polycystin 2 under cyclic tensile strain. Knockdown of polycystin 2 decreased the protein levels of IFT88, Ihh, Ptch1, Smo, and Gli1 in mandibular condylar chondrocytes following cyclic tensile strain.

CONCLUSION

These findings highlight the vital role of an interaction between IFT88 and polycystin 2 in mechanosensitive hedgehog signaling in mandibular condylar chondrocytes following cyclic tensile strain, which suggest that therapies regulating polycystin 2 may be considered for the disorders of temporomandibular joints.

Transplantation of Parathyroid Hormone-Treated Achilles Tendon Promotes Meniscal Regeneration in a Rat Meniscal Defect Model

BACKGROUND

Autologous tendon grafts are used for meniscal reconstruction of surgically removed knee joint meniscus. However, as meniscal reconstruction cannot prevent the progression of cartilage degeneration, additional procedures that confer meniscus-like histological properties to the transplanted tendon are required for improved outcomes.

HYPOTHESES

Parathyroid hormone (PTH)(1-34) induces cartilage formation in the rat tendon, and transplantation of PTH-treated tendon promotes meniscal regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rat Achilles tendon-derived cells were cultured with or without PTH for 28 days and stained with Alcian blue to determine chondrogenic differentiation. After 14 and 28 days of incubation, gene expression was assessed using quantitative real-time polymerase chain reaction. In an in vivo study, rat Achilles tendon was injected with PTH and then transplanted onto a medial meniscal defect. Macroscopic and histological assessments of the regenerated meniscus and of cartilage degeneration in the tibial plateau were performed at 4 and 8 weeks after surgery.

RESULTS

In vitro, PTH-treated cells showed better staining with Alcian blue than the control (normal medium) group. PTH1R, Col2a1, Sox9, and RUNX2 were significantly upregulated in PTH-treated cells (P < .05). Macroscopically, the in vivo results revealed more prominent meniscal coverage and lesser progression of articular cartilage degeneration in the PTH group than in the phosphate-buffered saline-injected group. Histologically, toluidine blue staining revealed metachromasia in the PTH-injected tissue at 4 and 8 weeks. The PTH-treated regenerated meniscus showed positive immunostaining for type II collagen in the area exhibiting metachromasia. Moreover, PTH-treated tendon had an enhanced histological score compared with the untreated group at 4 and 8 weeks (P < .05).

CONCLUSION

PTH(1-34) induced cartilage formation in the rat tendon. Transplantation of PTH(1-34)-treated Achilles tendon in a rat meniscal defect model induced meniscal regeneration and preserved knee articular cartilage. Macroscopically, PTH groups showed a greater coverage of the regenerated meniscus. Histologically, the regenerated meniscus had higher cartilaginous matrix content in rats transplanted with PTH-treated tendons. PTH(1-34) stimulated tendon-derived cells to promote chondrogenic differentiation.

CLINICAL RELEVANCE

Meniscal transplantation using PTH-injected autologous tendon grafts might promote meniscal regeneration and prevent progression of cartilage degeneration by stimulating chondrogenic differentiation of tendon-derived cells.

Parathyroid hormone promotes cartilage healing after free reduction of mandibular condylar fractures by upregulating Sox9

After high fractures of the mandibular condyle, the insufficient blood supply to the condyle often leads to poor bone and cartilage repair ability and poor clinical outcome. Parathyroid hormone (PTH) can promote the bone formation and mineralization of mandibular fracture, but its effects on cartilage healing after the free reduction and internal fixation of high fractures of the mandibular condyle are unknown. In this study, a rabbit model of free reduction and internal fixation of high fractures of the mandibular condyle was established, and the effects and mechanisms of PTH on condylar cartilage healing were explored. Forty-eight specific-pathogen-free (SPF) grade rabbits were randomly divided into two groups. In the experimental group, PTH was injected subcutaneously at 20 µg/kg (PTH (1-34)) every other day, and in the control group, PTH was replaced with 1 ml saline. The healing cartilages were assessed at postoperative days 7, 14, 21, and 28. Observation of gross specimens, hematoxylin eosin staining and Safranin O/fast green staining found that every-other-day subcutaneous injection of PTH at 20 µg/kg promoted healing of condylar cartilage and subchondral osteogenesis in the fracture site. Immunohistochemistry and polymerase chain reaction showed that PTH significantly upregulated the chondrogenic genes Sox9 and Col2a1 in the cartilage fracture site within 7-21 postoperative days in the experimental group than those in the control group, while it downregulated the cartilage inflammation gene matrix metalloproteinase-13 and chondrocyte terminal differentiation gene ColX. In summary, exogenous PTH can stimulate the formation of cartilage matrix by triggering Sox9 expression at the early stage of cartilage healing, and it provides a potential therapeutic protocol for high fractures of the mandibular condyle.

Intra-Articular Slow-Release Triamcinolone Acetonide from Polyesteramide Microspheres as a Treatment for Osteoarthritis

Osteoarthritis (OA) is a common cause of pain and disability. Local corticosteroid injections are effective in treating OA pain and inflammation but are short-acting. Prolonged intra-articular (IA) corticosteroid exposure may even lead to cartilage deterioration. The aim of this prospective study was to assess safety and provide proof-of-concept of IA-applied biodegradable polyesteramide-based microspheres (PEAMs) gradually releasing triamcinolone acetonide (TA). Mimicking continuous exposure associated with local drug delivery in canine articular chondrocytes cultured in the continuous presence of TA tissue regeneration was not affected, whereas intermittent exposure reduced proteoglycan production. In this respect, TA-PEAMs administered IA in a proof-of-concept study in 12 client-owned dogs with established OA also showed safety by radiographic examination, without changes in OA severity and in glycosaminoglycan synovial fluid levels. Treatment also resulted in clinical improvement in 10 out of 11 dogs during the two-month follow-up period, which persisted in 6 out of 10 dogs after 6 months, based on objective gait analysis and owner questionnaires. Synovial prostaglandin E₂, a pro-inflammatory marker, was decreased two months after treatment. This study showed safety and proof-of-concept of IA-administered TA-PEAMs in dogs with OA, as a first step towards translation into the veterinary and human clinic.

Lysophosphatidic Acid Analogue rather than Lysophosphatidic Acid Promoted the Bone Formation In Vivo

Lysophosphatidic acid (LPA), a bioactive lipid molecule, has recently emerged as physiological and pathophysiological regulator in skeletal biology. Here we evaluate the effects of LPA on bone formation in vivo in murine femoral critical defect model. Primary femoral osteoblasts were isolated and treated with osteogenic induction conditional media supplemented with 20 μM LPA or LPA analogue. Mineralized nodules were visualized by Alizarin Red S staining. Forty-five C57BL/6 mice underwent unilateral osteotomy. The femoral osteotomy gap was filled with porous scaffolds of degradable chitosan/beta-tricalcium phosphate containing PBS, LPA, or LPA analogue. 2, 5, and 10 weeks after surgery, mice were sacrificed and femurs were harvested and prepared for Micro-Computed Tomography (Micro-CT) and histological analysis. Alizarin Red S staining showed that LPA and LPA analogue significantly enhanced the mineral deposition in osteoblasts. Micro-CT 3D reconstruction images and HE staining revealed that significantly more newly formed bone in osteotomy was treated with LPA analogue when compared to control and LPA group, which was verified by histological analysis and biomechanical characterization testing. In summary, our study demonstrated that although LPA promotes mineralized matrix formation in vitro, the locally administrated LPA was not effective in promoting bone formation in vivo. And bone formation was enhanced by LPA analogue, administrated locally in vivo. LPA analogue was a potent stimulating factor for bone formation in vivo due to its excellent stability.

Teriparatide treatment in an adult patient with hypophosphatasia exposed to bisphosphonate and revealed by bilateral atypical fractures

Atypical femoral fractures are defined as atraumatic fractures located in the subtrochanteric region or femoral shaft. They have been mainly reported in patients taking bisphosphonates. We report the case of a 67-year-old female with osteoporosis treated by alendronate during ten years. Radiographies showed atypical femoral fractures. Serum levels of total and bone-specific alkaline phosphatase were low. In order to accelerate bone healing, teriparatide was introduced. After one year of teriparatide treatment, pain and functional difficulty have decreased, and alkaline phosphatase levels were normalized. In view of this history of recurrent fractures, of atypical femoral fractures, of early spontaneous loss of teeth, and of low serum total and bone-specific alkaline phosphatase levels, the diagnosis of hypophosphatasia has been considered and confirmed by genetic research. Other conditions than exposure to anti-resorptive therapies may promote atypical femoral fractures, such as in conditions associated with abnormal bone structures, as hypophosphatasia, a rare inherited bone metabolism disorder. A few case reports have reported adult hypophosphatasia treated by teriparatide with a good efficacy on bone pain and consolidation but with mixed results on biological markers. Teriparatide may be therefore a treatment option in adult hypophosphatasia. ALP levels should be carefully checked among osteoporotic patients and specially before introducing a bone resorption inhibitor. Low alkaline phosphatase levels have to be taken into account and an evocative history of hypophosphatasia has to be sought because this condition may expose patients to develop atypical femoral fractures during bisphosphonate treatment.

Effects of connective tissue growth factor (CTGF/CCN2) on condylar chondrocyte proliferation, migration, maturation, differentiation and signalling pathway

CCN2, also known as connective tissue growth factor (CTGF), is a 38 kDa cysteine-rich extracellular matrix protein that regulates a sequence of cellular functions and participates in multiple complex biological processes, such as chondrogenesis and osteogenesis. In the present study, we provided the first evidence describing the physiological role of CCN2 in condylar chondrocyte proliferation, migration, maturation and differentiation. CCN2 was widely expressed throughout the whole layers of condylar cartilage and predominantly distributed in the proliferative zone. Recombinant CCN2 promoted the proliferation, migration, proteoglycan synthesis and differentiation capacity of isolated condylar chondrocytes. The stimulatory effect of CCN2 on chondrocyte proliferation was associated with the activation of phosphatidylinositol 3-kinase/Akt signalling pathway. The blocking of this pathway by its inhibitor LY294002 impaired the proliferative effect of CCN2 on chondrocytes. These results suggested a novel physiological role of CCN2 in the development of condylar cartilage.

Intermittent Administration of Parathyroid Hormone 1-34 Enhances Osteogenesis of Human Mesenchymal Stem Cells by Regulating Protein Kinase Cδ

Human mesenchymal stem cells (hMSCs) can differentiate into osteoblasts and are regulated by chemical cues. The recombinant N-terminal (1–34 amino acids) fragment of the parathyroid hormone (PTH (1–34)) is identified to promote osteogenesis. The osteoanabolic effects of intermittent PTH (1–34) treatment are linked to a complex consisting of signaling pathways; additionally, protein kinase C (PKC) act as mediators of multifunctional signaling transduction pathways, but the role of PKC δ (PKCδ), a downstream target in regulating osteoblast differentiation during intermittent administration of PTH (1–34) is less studied and still remains elusive. The purpose of this study is to examine the role of PKCδ during intermittent and continuous PTH (1–34) administration using osteoblast-lineage-committed hMSCs. Relative gene expression of osteoblast-specific genes demonstrated significant upregulation of RUNX2, type I Collagen, ALP, and Osterix and increased alkaline phosphatase activity in the presence of PTH (1–34). Intermittent PTH (1–34) administration increased PKC activity at day 7 of osteogenic differentiation, whereas inhibition of PKC activity attenuated these effects. In addition, the specific isoform PKCδ was activated upon treatment. These findings demonstrate that intermittent PTH (1–34) treatment enhances the osteogenesis of hMSCs by upregulating osteoblast-specific genes via PKCδ activation.

Sialoglycoprotein isolated from the eggs of Gadus morhua enhances fracture healing in osteoporotic mice

Osteoporosis is a common disease in the elderly, which is related to fracture healing delay. In this study, the effects of treatment with sialoglycoprotein isolated from the eggs of Gadus morhua (Gm-SGP) on tibial fracture healing in ovariectomized (OVX) osteoporotic female C57BL/6J mice for 56 days post-fracture were investigated. The result showed that Gm-SGP treatment significantly increased serum angiogenic factors and bone formation markers on day 5 and 11 post-fracture when compared with the OVX group. In addition, histological results in the Gm-SGP group showed a stronger endochondral ossification, a stronger bony consolidation and a stronger bony callus remodeling capability on day 11, 24 and 35 post-fracture, respectively, in comparison with the OVX group. Meanwhile, micro-computerized tomography revealed that the Gm-SGP group had stronger bony callus remodeling capability as evidenced by higher BV/TV and Tb.N but lower Tb.Sp and shorter lengths of callus maximum cross section than the OVX group on day 24 post-fracture. Besides, the tibial callus bending stiffness was significantly enhanced in the Gm-SGP group as compared with the OVX group on day 56 post-fracture. Moreover, gene expression suggested that Gm-SGP promoted vascular invasion and endochondral ossification on day 11 post-fracture as well as bone formation on day 11 and 24 post-fracture via up-regulating the expression of angiogenesis factors (including VEGF, PDGF and Ang1), entochondrostosis factors (including Col2a1, Aggrecan, Col10a1 and MMP-13) and osteogenesis markers (including Col1a1, BMP-2 and OCN). This research suggests that Gm-SGP significantly improve fracture healing which is delayed by OVX-induced osteoporosis. The present study may contribute to providing important implications for the utilization of Gm-SGP from fish eggs as a functional food to enhance fracture healing.

ClC-3 chloride channel mediates the role of parathyroid hormone [1-34] on osteogenic differentiation of osteoblasts

INTRODUCTION

Different concentrations of parathyroid hormone [1-34] (PTH [1-34]) can have totally opposite effects on osteoblasts. Intermittent stimulation with PTH can significantly increase bone mineral density in vitro, mainly through the protein kinase A (PKA) signaling pathway, which phosphorylates runt-related transcription factor 2 (Runx2). The ClC-3 chloride channel, an important anion channel, can also promote osteogenesis via the Runx2 pathway based on recent studies. The purpose of our study, therefore, is to research whether the ClC-3 chloride channel has an effect on PTH osteodifferentiation in MC3T3-E1 cells.

METHODS AND RESULTS

A cell counting kit (CCK-8) and real-time PCR were used to investigate the impact of different PTH stimulation modes on MC3T3-E1 cell proliferation and osteogenesis-related gene expression, respectively. We found that the minimum inhibitory concentration of PTH was 10-9 M, and the expression of alkaline phosphatase (Alpl) and Runx2 were at the highest levels when treated with 10-9 M PTH. Next, we used real-time PCR and immunofluorescence technique to detect changes in ClC-3 in MC3T3-E1 cells under PTH treatment. The results showed higher expression of the ClC-3 chloride channel at 10-9 M intermittent PTH administration than in the other groups. Finally, we used the ClC-3 siRNA technique to examine the role of the ClC-3 chloride channel in the effect of PTH on the osteogenesis of osteoblasts, and we found an obvious decrease in the expression of bone sialoprotein (Ibsp), osteocalcin (Bglap), osterix (Sp7), Alpl and Runx2, the formation of mineralization nodules as well.

CONCLUSIONS

From the above data, we conclude that the expression of ClC-3 chloride channels in osteoblasts helps them respond to PTH stimulation, which mediates osteogenic differentiation.

Parathyroid Hormone-Induced Bone Marrow Mesenchymal Stem Cell Chondrogenic Differentiation and its Repair of Articular Cartilage Injury in Rabbits

Background

We explored the effect of parathyroid hormone (PTH)-induced bone marrow stem cells (BMSCs) complexed with fibrin glue (FG) in the repair of articular cartilage injury in rabbits.

Material/Methods

Forty-eight rabbits randomized into four groups were subjected to articular surgery (cartilage loss). The PTH and non-PTH intervention groups included transplantation with PTH/BMSC/FG xenogeneic and BMSC/FG xenogeneic complexes, respectively, into the injured area. The injured group contained no transplant while the control group comprised rabbits without any articular injury. Samples were monitored for cartilage repair up to three months post-surgery. Immunohistochemistry as well as real-time fluorescent quantitative PCR and Western blot were used to analyze the expression of type II collagen and aggrecan in the repaired tissue.

Results

At 12 weeks post-surgery, the loss of articular cartilage in the PTH group was fully repaired by hyaline tissue. Typical cartilage lacunae and intact subchondral bone were found. The boundary separating the surrounding normal cartilage tissue disappeared. The gross and International Cartilage Repair Society (ICRS) histological ranking of the repaired tissue was significantly higher in the PTH intervention group than in the non-PTH intervention and injury groups (p<0.05) without any significant difference compared to the control group (p>0.05). Type II collagen and aggrecan stained positive and the average optical density, relative mRNA expression and protein-integrated optical density in the PTH group were higher than in non-PTH and injured groups (p<0.05) but not significantly different from the control group (p>0.05).

Conclusions

PTH/BMSC/FG xenogeneic complexes effectively repaired the loss of cartilage in rabbit knee injury.

The Expression of PHOSPHO1, nSMase2 and TNAP is Coordinately Regulated by Continuous PTH Exposure in Mineralising Osteoblast Cultures

Sustained exposure to high levels of parathyroid hormone (PTH), as observed in hyperparathyroidism, is catabolic to bone. The increase in the RANKL/OPG ratio in response to continuous PTH, resulting in increased osteoclastogenesis, is well established. However, the effects of prolonged PTH exposure on key regulators of skeletal mineralisation have yet to be investigated. This study sought to examine the temporal expression of PHOSPHO1, TNAP and nSMase2 in mineralising osteoblast-like cell cultures and to investigate the effects of continuous PTH exposure on the expression of these enzymes in vitro. PHOSPHO1, nSMase2 and TNAP expression in cultured MC3T3-C14 cells significantly increased from day 0 to day 10. PTH induced a rapid downregulation of Phospho1 and Smpd3 gene expression in MC3T3-C14 cells and cultured hemi-calvariae. Alpl was differentially regulated by PTH, displaying upregulation in cultured MC3T3-C14 cells and downregulation in hemi-calvariae. PTH was also able to abolish the stimulatory effects of bone morphogenic protein 2 (BMP-2) on Smpd3 and Phospho1 expression. The effects of PTH on Phospho1 expression were mimicked with the cAMP agonist forskolin and blocked by the PKA inhibitor PKI (5-24), highlighting a role for the cAMP/PKA pathway in this regulation. The potent down-regulation of Phospho1 and Smpd3 in osteoblasts in response to continuous PTH may provide a novel explanation for the catabolic effects on the skeleton of such an exposure. Furthermore, our findings support the hypothesis that PHOSPHO1, nSMase2 and TNAP function cooperatively in the initiation of skeletal mineralisation.

Effects of Intermittent Administration of Parathyroid Hormone (1-34) on Bone Differentiation in Stromal Precursor Antigen-1 Positive Human Periodontal Ligament Stem Cells

Periodontitis is the most common cause of tooth loss and bone destruction in adults worldwide. Human periodontal ligament stem cells (hPDLSCs) may represent promising new therapeutic biomaterials for tissue engineering applications. Stromal precursor antigen-1 (STRO-1) has been shown to have roles in adherence, proliferation, and multipotency. Parathyroid hormone (PTH) has been shown to enhance proliferation in osteoblasts. Therefore, in this study, we aimed to compare the functions of STRO-1(+) and STRO-1(-) hPDLSCs and to investigate the effects of PTH on the osteogenic capacity of STRO-1(+) hPDLSCs in order to evaluate their potential applications in the treatment of periodontitis. Our data showed that STRO-1(+) hPDLSCs expressed higher levels of the PTH-1 receptor (PTH1R) than STRO-1(-) hPDLSCs. In addition, intermittent PTH treatment enhanced the expression of PTH1R and osteogenesis-related genes in STRO-1(+) hPDLSCs. PTH-treated cells also exhibited increased alkaline phosphatase activity and mineralization ability. Therefore, STRO-1(+) hPDLSCs represented a more promising cell resource for biomaterials and tissue engineering applications. Intermittent PTH treatment improved the capacity for STRO-1(+) hPDLSCs to repair damaged tissue and ameliorate the symptoms of periodontitis.

Roles of the kidney in the formation, remodeling and repair of bone

The relationship between the kidney and bone is highly complex, and the kidney plays an important role in the regulation of bone development and metabolism. The kidney is the major organ involved in the regulation of calcium and phosphate homeostasis, which is essential for bone mineralization and development. Many substances synthesized by the kidney, such as 1,25(OH)2D3, Klotho, bone morphogenetic protein-7, and erythropoietin, are involved in different stages of bone formation, remodeling and repair. In addition, some cytokines which can be affected by the kidney, such as osteoprotegerin, sclerostin, fibroblast growth factor -23 and parathyroid hormone, also play important roles in bone metabolism. In this paper, we summarize the possible effects of these kidney-related cytokines on bone and their possible mechanisms. Most of these cytokines can interact with one another, constituting an intricate network between the kidney and bone. Therefore, kidney diseases should be considered among patients presenting with osteodystrophy and disturbances in bone and mineral metabolism, and treatment for renal dysfunction may accelerate their recovery.

Simulated Interventions to Ameliorate Age-Related Bone Loss Indicate the Importance of Timing

Bone remodeling is the continuous process of bone resorption by osteoclasts and bone formation by osteoblasts, in order to maintain homeostasis. The activity of osteoclasts and osteoblasts is regulated by a network of signaling pathways, including Wnt, parathyroid hormone (PTH), RANK ligand/osteoprotegrin, and TGF-β, in response to stimuli, such as mechanical loading. During aging there is a gradual loss of bone mass due to dysregulation of signaling pathways. This may be due to a decline in physical activity with age and/or changes in hormones and other signaling molecules. In particular, hormones, such as PTH, have a circadian rhythm, which may be disrupted in aging. Due to the complexity of the molecular and cellular networks involved in bone remodeling, several mathematical models have been proposed to aid understanding of the processes involved. However, to date, there are no models, which explicitly consider the effects of mechanical loading, the circadian rhythm of PTH, and the dynamics of signaling molecules on bone remodeling. Therefore, we have constructed a network model of the system using a modular approach, which will allow further modifications as required in future research. The model was used to simulate the effects of mechanical loading and also the effects of different interventions, such as continuous or intermittent administration of PTH. Our model predicts that the absence of regular mechanical loading and/or an impaired PTH circadian rhythm leads to a gradual decrease in bone mass over time, which can be restored by simulated interventions and that the effectiveness of some interventions may depend on their timing.

Dietary vitamin D during pregnancy has dose-dependent effects on long bone density and architecture in guinea pig offspring but not the sows

BACKGROUND

The effects of vitamin D during pregnancy on maternal and neonatal bone health remain unclear.

OBJECTIVE

This study was designed to test whether dietary vitamin D dose-dependently affects maternal and neonatal bone health.

METHODS

Female guinea pigs (n = 45; 4 mo old) were randomly assigned at mating to receive 1 of 5 doses of vitamin D3 (cholecalciferol; 0, 0.25, 0.5, 1, or 2 IU/g diet) throughout pregnancy. Plasma vitamin D metabolites, mineral homeostasis, bone biomarkers, and bone mass were tested in sows throughout pregnancy and in 2-d-old pups. Microarchitecture and histology of excised bone were conducted postpartum.

RESULTS

By 3 wk of pregnancy, plasma 25-hydroxyvitamin D [25(OH)D] followed a positive dose-response, whereas 1,25-dihydroxyvitamin D [1,25(OH)2D] reached a plateau if vitamin D was ≥0.5 IU/g diet. Weight gain, areal bone mineral density (aBMD), volumetic bone mineral density (vBMD), and bone biomarkers did not differ among maternal groups. A positive dose-response was observed for mean ± SEM pup plasma concentrations of 25(OH)D (10.5 ± 1.50 to 113 ±11.6 nmol/L) and 1,25(OH)2D (123 ± 13.8 to 544 ± 53.3 pmol/L). Pup weight, plasma minerals, and osteocalcin were not different; plasma deoxypyridinoline was lower in the 1- and 0.25-IU/g groups than in all other groups. Pup femur aBMD was higher (9.2-13%; P = 0.04) in the 2-IU/g group than in all other groups except for the 0-IU/g group. Tibia and femur vBMD of pups responded to maternal diet in a U-shaped pattern. The femoral growth plate was 7.9% wider in the 0-IU/g group than in the 1-IU/g group.

CONCLUSIONS

Maternal vitamin D supplementation dose-dependently altered pup long bone architecture and mineral density in a manner similar to vitamin D deficient rickets whereas maternal bone was stable. These data reinforce that inadequate maternal vitamin D intake may compromise neonatal bone health and that exceeding recommendations is not advantageous.

Effects of parathyroid hormone 1-34 on osteogenic and chondrogenic differentiation of human fracture haematoma-derived cells in vitro

Parathyroid hormone (PTH) 1-34 has been shown to accelerate fracture healing. Previously, we reported that progenitor cells with osteogenic and chondrogenic potential exist in human fracture haematoma, suggesting that the fracture haematoma-derived progenitor cells (HCs) contribute to fracture healing. However, there has been no study investigating the effect of PTH on HCs. We investigated the effect of pulsatile and continuous PTH treatment on human fracture HCs in vitro. HCs were isolated from seven patients. The HCs were divided into four groups: growth medium; control [osteogenic medium (OM) without PTH]; PTH-C (OM with continuous PTH); and PTH-P (OM with pulsatile PTH) groups. Osteogenic differentiation potential and proliferation of HCs were compared among the four groups. For chondrogenesis, the HCs were divided into two groups: control [chondrogenic medium (CM) without PTH]; and PTH-C (CM with continuous PTH) groups, and chondrogenic differentiation potential was analysed. PTH treatment did not affect cell proliferation, regardless of the mode of administration. Osteogenic activity was also not significantly affected by continuous PTH treatment but significantly inhibited by pulsatile PTH treatment. Conversely, chondrogenic differentiation was significantly inhibited by continuous PTH treatment. Our results revealed that PTH treatment on HCs, either continuous or pulsatile, does not exhibit any positive effect, and indicates that exogenous PTH administration after fracture has no effect on HCs. PTH may not have a positive effect at the fracture site during the early stage of fracture healing in which haematoma formation occurs. Copyright © 2013 John Wiley & Sons, Ltd.