The Biochemistry of Bone

Accelerated Osteogenic Response of Electrodynamically Stimulated Mg1-xCaxSi1-xZrxO3 (x = 0-0.4) Bioelectrets

MgSiO3-based biodegradable ceramics demonstrated remarkable potential for treating small-scale bone defects and temporary bone replacement. In addition, the dissolution behavior of MgSiO3 bioceramics can be tuned by doping of Ca and Zr elements at Mg and Si sites, respectively. The present study reported the influence of formation of Ca- and Zr-codoped Mg1-xCaxSi1-xZrxO3 (x = 0, 0.1, 0.2, 0.3, and 0.4) bioelectrets and electrodynamic stimulation toward improving their osteogenic response. Mg1-xCaxSi1-xZrxO3 electrets were successfully synthesized by a solid-state route. A detailed X-ray photoelectron spectroscopy (XPS) analyses revealed that the electrets produced oxygen-deficient active sites. The formation of Mg1-xCaxSi1-xZrxO3 electrets significantly increased the surface hydrophilicity. Inductively coupled plasma (ICP) analyses were used to examine the leaching behavior of Ca/Zr-codoped MgSiO3 bioceramics. In vitro cell culture analyses indicated that the osteogenesis of MG-63 cells was remarkably enhanced on the electrodynamic field-treated Mg1-xCaxSi1-xZrxO3 bioelectrets as compared to hydroxyapatite (HA). Moreover, a better osteogenic response was observed for higher concentrations of Ca (0.3 and 0.4) and Zr (0.3 and 0.4) doping in the MgSiO3 bioelectrets. Further, the mechanism of enhanced cellular functionality was revealed by the measurement of intracellular Ca2+.

Interplay of surface polarization charge, dynamic electrical stimulation and compositional modification towards accelerated osteogenic response of NaxK1-xNbO3 piezo-bioceramics

Bone remodeling processes involve endogenous bioelectrical signals such as piezoelectric charges. Moreover, external electrical stimulation helps in improving the healing capability of injured tissues by modulating the metabolic signaling pathways of cells. Towards this end, the present study reveals the influence of the combined action of electrostatic surface polarization charge and dynamic pulsed electrical stimulation alongwith compositional modification towards improving the osteogenic response of emerging piezo-bioceramics, sodium potassium niobate [Na_xK_1-xNbO₃ (x = 0.2-0.8), NKN]. The dependence of crystal structure on compositions (x) was retrieved by Rietveld refinement and X-ray peak profile analyses. The surface charge, stored in the polarized (@ 25 kV at 500 °C) Na_xK_1-xNbO₃ (x = 0.2, 0.5, 0.8) samples were measured to be 0.52, 0.50 and 0.47 μC/cm², respectively, using thermally stimulated depolarized current (TSDC). X-ray photoelectron spectroscopy (XPS) survey scan spectra revealed that the polarization process does not alter the surface chemistry of NKN. Negatively charged surfaces are observed to accelerate early-stage adhesion of osteoblast-like cells which further results in enhanced spreading of adhered cells. Subsequently, the dynamic pulsed electrical stimulation of 1 V/cm with the pulse duration of 400 μs was applied, while the cells were being adhered on electrostatically charged surfaces. The quantitative and qualitative analyses revealed that the synergistic action of electrostatic surface polarization charge and dynamic pulsed electrical stimulation further accelerates cell proliferation and differentiation on negatively charged surfaces of Na and K-rich compositions of NKN. The mechanism of augmented cellular activity was analyzed using intracellular Ca²⁺ measurement.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Chondrocyte proliferation, viability and differentiation is declined following administration of methylphenidate utilized for the treatment of attention-deficit/hyperactivity disorder

PURPOSE

Methylphenidate (MPH) derivative drugs are used because of psychostimulants effects on attention-deficit hyperactivity disorder in children and adults. As far as we know, toxic or anti-proliferative effects of MPH against cartilage tissue were not studied in the literature. The present study was carried out to investigate the possible effects of MPH on the proliferation, viability and differentiation of primary human chondrocytes, in vitro.

METHODS

Monolayer primary chondrocyte cultures were prepared using osteochondral tissue obtained from patients who underwent a total knee prosthesis operation. Stock solution of MPH was prepared and aliquots having 1-1000 µM concentrations of the drug was composed. These solutions were applied to the wells containing cultured chondrocyte samples within the well plates. Control groups were composed of pure chondrocyte culture and no solution was added into them. All groups were evaluated at 24, 48 and 72 h in order to determine the possible negative effects of the drug on the chondrocytes. The data were evaluated by Tukey's honestly significantly different test following analysis of variance.

RESULTS

In the group where MPH was applied, it was found that viability, proliferation and stage-specific embryonic antigen-1 protein expression were decreased in comparison to the control group.

CONCLUSIONS

It was emphasized that clinicians should not disregard the fact that this drug might suppress chondrocyte cell proliferation and chondrogenic differentiation.

Hierarchically biomimetic scaffold of a collagen-mesoporous bioactive glass nanofiber composite for bone tissue engineering

Mesoporous bioactive glass nanofibers (MBGNFs) were prepared by a sol-gel/electrospinning technique. Subsequently, a collagen-MBGNF (CM) composite scaffold that simultaneously possessed a macroporous structure and collagen nanofibers was fabricated by a gelation and freeze-drying process. Additionally, immersing the CM scaffold in a simulated body fluid resulted in the formation of bone-like apatite minerals on the surface. The CM scaffold provided a suitable environment for attachment to the cytoskeleton. Based on the measured alkaline phosphatase activity and protein expression levels of osteocalcin and bone sialoprotein, the CM scaffold promoted the differentiation and mineralization of MG63 osteoblast-like cells. In addition, the bone regeneration ability of the CM scaffold was examined using a rat calvarial defect model in vivo. The results revealed that CM is biodegradable and could promote bone regeneration. Therefore, a CM composite scaffold is a potential bone graft for bone tissue engineering applications.

Visceral adipose tissue is associated with insulin resistance in hemodialyzed patients

BACKGROUND

It has not been definitively established which factors affect insulin resistance (IR) and whether dialysis decreases IR. The aim of this study was to investigate factors that may have an influence on homeostasis model assessment (HOMA-IR) in hemodialyzed patients (HDpts) and to compare IR between HDpts and healthy subjects.

MATERIAL AND METHODS

We examined 33 HDpts and paired 33 subjects of the control group, matched for sex, age, and BMI. We analyzed concentrations of insulin, glucose, leptin, resistin, and total and high-molecular-weight adiponectin (HMWad) in serum. Using computed tomography in HDpts, we evaluated visceral adipose tissue (VAT), concentrations of visfatin, CRP, and IL-6.

RESULTS

HOMA-IR (median, 1.3 vs. 1.4, P=0.19), insulin (median 6.8 vs. 6.0 µIU/mL, P=0.7), glucose (79 mg/dL vs. 93 mg/dL, P=0.001). IR in HDpts is dependent on VAT (r=0.36, P=0.04) and this relationship is stronger than the relationship of BMI and IR (r=0.3, P=0.1). In HDpts we found higher concentrations of leptin (P=0.001) and resistin (P<0.001), with no relation to IR. HMWad and its percentage in relation to total adiponectin are higher in HDpts (P=0.03 and P<0.001, respectively).

CONCLUSIONS

HOMA-IR in HDpts does not differ from the control group. In HDpts it depends on the quantity of VAT and this relationship is stronger than with BMI. In HDpts leptin and resistin do not influence IR. HMWad and its percentage in total adiponectin are significantly higher in HDpts.

Osteogenic differentiation and mineralization in fibre-reinforced tubular scaffolds: theoretical study and experimental evidences

The development of composite scaffolds with well-organized architecture and multi-scale properties (i.e. porosity, degradation) represents a valid approach for achieving a tissue-engineered construct capable of reproducing the medium- and long-term in vitro behaviour of hierarchically complex tissues such as spongy bone. To date, the implementation of scaffold design strategies able to summarize optimal scaffold architecture as well as intrinsic mechanical, chemical and fluid transport properties still remains a challenging issue. In this study, poly ε-caprolactone/polylactid acid (PCL/PLA) tubular devices (fibres of PLA in a PCL matrix) obtained by phase inversion/salt leaching and filament winding techniques were proposed as cell instructive scaffold for bone osteogenesis. Continuous fibres embedded in the polymeric matrix drastically improved the mechanical response as confirmed by compression elastic moduli, which vary from 0.214 ± 0.065 to 1.174 ± 0.143 MPa depending on the relative fibre/matrix and polymer/solvent ratios. Moreover, computational fluid dynamic simulations demonstrated the ability of composite structure to transfer hydrodynamic forces during in vitro culture, thus indicating the optimal flow rate conditions that, case by case, enables specific cellular events-i.e. osteoblast differentiation from human mesenchymal stem cells (hMSCs), mineralization, etc. Hence, we demonstrate that the hMSC differentiation preferentially occurs in the case of higher perfusion rates-over 0.05 ml min(-1)-as confirmed by the expression of alkaline phosphate and osteocalcin markers. In particular, the highest osteopontin values and a massive mineral phase precipitation of bone-like phases detected in the case of intermediate flow rates (i.e. 0.05 ml min(-1)) allows us to identify the best condition to stimulate the bone extracellular matrix in-growth, in agreement with the hydrodynamic model prediction. All these results concur to prove the succesful use of tubular composite as temporary device for long bone treatment.

Preparation and characterization of microspheres comprised of collagen, chondroitin sulfate, and apatite as carriers for the osteoblast-like cell MG63

Numerous studies about bone matrix fabrication focus on how the species and concentrations of components affect the cellular response. However, there are few studies that investigate how the related spatial arrangement of the components influences cellular activity. The aim of this work was to develop a novel method to biomimetically manufacture a three-dimensional mineral bone matrix and study the effect of apatite-collagen-chondroitin sulfate (CS) microspheres on the adhesion rate and activity of osteoblast-like cells. Although previous studies used a crosslinking agent or lyophilized methods to fabricated three-dimensional collagen microspheres, we produced beads composed of collagen and CS under mild reaction conditions. This process not only maintains collagen self-assembly into fibrils with a D-periodic pattern ability but also simultaneously introduces two major native bone matrix elements, collagen and CS, into the beads. Furthermore, we mimic the native in vivo bone matrix formation process by the direct nucleation and growth of apatite crystals on collagen fibrils. The apatite crystals are similar in composition to human bone mineral via X-ray diffraction and energy-dispersive X-ray spectrometric analysis. The cellular attachment rate of MG63 osteoblast-like cells is significantly higher for collagen-CS-apatite gel beads than for collagen-CS gel beads. In addition, with regard to the osteoblast bioactivity, we observed that alkaline phosphatase activity of MG63 cells on the collagen-CS-apatite gel beads higher than on the collagen-CS gel beads on day 14.

Biological basis of bone formation, remodeling, and repair-part I: biochemical signaling molecules

The bony biochemical environment is an active and dynamic system that permits and promotes cellular functions that lead to matrix production and ossification. Each component is capable of conveying important regulatory cues to nearby cells, thus effecting gene expression and changes at the cytostructural level. Here, we review the various signaling molecules that contribute to the active and dynamic nature of the biochemical system. These components include hormones, cytokines, and growth factors. We describe their role in regulating bone metabolism. Certain growth factors (i.e., TGF-beta, IGF-1, and VEGF) are described in greater detail because of their potential importance in developing successful tissue-engineering strategies.

In vivo evaluation of bone-bonding ability of RGD-coated porous implant using layer-by-layer electrostatic self-assembly

RGD has been demonstrated to improve implant osseointegration. However, few studies are known about an effect of RGD coating on a bone-bonding ability of screw-shaped porous implant. The aim of this study was to investigate the effect of RGD coating using the layer-by-layer self-assembly technique on the bone-bonding ability of porous implant. 60 implants of 10 mm in length (30 control and 30 RGD-coated) were inserted into femurs of 30 rabbits and 30 implants of 8 mm in length (15 control and 15 RGD-coated) were inserted into tibias of 15 rabbits. At 4, 8, and 12 weeks post-implantation, femurs and tibias were retrieved and prepared for removal torque tests (RTQ) and histomorphometric evaluation, respectively. No differences were found in the RTQ values between two implants at 4 weeks (p = 0.932). There were statistical significances in the RTQ values at 8 and 12 weeks (p = 0.002, 0.001, respectively). New bone was formed on both implant surfaces. The bone-implant contact pattern appeared to produce a broad-based direct contact in both implants. The RGD-coated implants showed a significantly greater BIC in the threads inside the cortical bone compared with the control implants at 4, 8, and 12 weeks (p = 0.024, 0.041, 0.022, respectively). No differences were found in the bone area within the same threads between two implants at 4 weeks (p = 0.806) whereas differences were found at 8 and 12 weeks (p = 0.009, 0.031, respectively). It was concluded that RGD coating using the layer-by-layer self-assembly technique has a positive effect on the bone-bonding ability of porous implant.

Beads of collagen-nanohydroxyapatite composites prepared by a biomimetic process and the effects of their surface texture on cellular behavior in MG63 osteoblast-like cells

The aim of this work was to develop a novel method for preparing a three-dimensional bone-like matrix comprising nanohydroxyapatite crystals and fibrous collagen and to apply it for bone tissue engineering. Hydroxyapatite and collagen are the major components of natural hard bone. Therefore, they have been used extensively in orthopedic surgery as bone-filling materials. According to the principle of complex coacervation, three-dimensional collagen beads can be formed by extruding collagen solution into chondroitin sulfate A (CSA) solution. Subsequently, the collagen beads thus formed are soaked in simulated body-fluid solution to biomimic the formation process of natural bone matrix via the fabrication of collagen-nanohydroxyapatite beads. We also investigate the effect of the collagen-nanohydroxyapatite matrix on the proliferation and differentiation of MG63 cells. The presence of crystalline hydroxyapatite structure on the surface of fibrous collagen was confirmed by X-ray diffraction. MG63 cells cultured on the collagen-nanohydroxyapatite beads proliferate at the normal rate. Moreover, alkaline phosphatase (ALP) activity and the expression levels of three osteogenic genes, namely, type I collagen osteopontin and osteocalcin, in MG63 cells were significantly higher when the cells were cultured on collagen-nanohydroxyapatite beads than when they were cultured on collagen alone. The results of this study reveal that, in the presence of nanohydroxyapatite, the three-dimensional cell beads not only provide a substrate for cell growth but could also enhance the osteoblast-like cell differentiation of MG63 cells.

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

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

Osteoporosis

Effective therapies are available for the patient who has arthritic osteoporosis. The approach is critical to ensure an optimal quality of life in these individuals who suffer with a disease that is clearly treatable.

ENA Actimineral Resource A restores bone loss and bone quality in ovariectomized rats

The purpose of this study was to examine the effects of ENA Actimineral Resource A (ENA-A), seaweed origin alkaline water, on postmenopausal osteoporosis in ovariectomized (OVX) rats. The 12-week old Wistar rats were divided randomly into 4 groups: ovariectomized (OVX), OVX plus 0.5% ENA-A, OVX plus 5% ENA-A and OVX plus 10% ENA-A. A histopathological analysis indicated that ENA-A could prevent OVX-induced bone loss by increasing femur trabecular bone area in a dose-dependent manner. ENA-A significantly (p<0.05) increased serum estradiol levels, decreased serum osteocalcin activity and suppressed serum pyridinoline (PYD) levels. The in vitro effects of ENA-A were also studied using MC3T3-E1 cells. ENA-A significantly stimulated cell proliferation and increased both ALP activity and calcium deposition in a dose-dependent manner. These results suggest that the treatment of ovariectomized rats with ENA-A not only prevents bone resorption but also appears to maintain the cancellous bone structure of postmenopausal osteoporosis.

Efeito da atividade física no osso normal e na prevenção e tratamento da osteoporose

A osteoporose é uma doença cada vez mais diagnosticada em mulheres e homens de todo o mundo. Embora os esteróides sexuais sejam importantes na gênese da osteoporose, a inatividade física constitui um fator de risco. O exercício físico atua no osso por efeito direto, via força mecânica, ou indireto, mediado por fatores hormonais. Mas os mecanismos pelos quais a atividade física melhora a massa óssea ainda não são totalmente conhecidos. Baseando-se nos resultados que demonstram os efeitos benéficos da atividade física no tecido ósseo, a prática de esportes vem sendo cada vez mais indicada na prevenção e até mesmo no tratamento da osteoporose. O objetivo desta revisão é descrever os efeitos da atividade física no tecido ósseo normal e na prevenção e tratamento da osteoporose.

Solution-mediated effect of bioactive glass in poly (lactic-co-glycolic acid)-bioactive glass composites on osteogenesis of marrow stromal cells

A previous study demonstrated that the incorporation of bioactive glass (BG) into poly (lactic-co-glycolic acid) (PLGA) can promote the osteoblastic differentiation of marrow stromal cells (MSCs) on PLGA by promoting the formation of a calcium-phosphate-rich layer on its surface. To further understand the mechanisms underlying the osteogenic effect of PLGA-BG composite scaffolds, whether solution-mediated factors derived from composite scaffolds/hybrids can promote osteogenesis of marrow stromal cells was tested. The dissolution product from PLGA-30%BG scaffold stimulated osteogenesis of MSCs, as was confirmed by increased mRNA expression of osteoblastic markers such as osteocalcin (OCN), alkaline phosphatase (ALP), and bone sialoprotein (BSP). The three-dimensional structure of the scaffolds may contribute to the production of cell-derived factors that promoted distant MSC differentiation. Thus PLGA-BG composites demonstrate significant potential as a bone-replacement material.

Osteoporosis

Bone is a complex organ which contains an organic matrix which serves as scaffolding, includes mineral as calcium distributed in a pattern providing structure and serves as an ion reservoir for the body. Throughout life it dynamically changes in response to changes in activity, body mass, and weight bearing. It is important to define patients at risk for bone loss, since accrued bone loss leading to osteoporosis in the older population of both men and women is unacceptable. There are many different therapies including biphosphonates which can decrease loss of bone and decrease fracture risk in patients who already have had sustained a fracture. Newer therapies such as parathyroid hormone may improve the fracture risk even more than biphosphonates over a shorter period of time.

In vitro osteogenic differentiation of marrow stromal cells encapsulated in biodegradable hydrogels

Novel hydrogel materials based on oligo(poly(ethylene glycol) fumarate) (OPF) crosslinked with a redox radical initiation system were recently developed in our laboratory as injectable cell carriers for orthopedic tissue engineering applications. The effect of OPF hydrogel material properties on in vitro osteogenic differentiation of encapsulated rat marrow stromal cells (MSCs) with and without the presence of osteogenic supplements (dexamethasone) was investigated. Two OPF formulations that resulted in hydrogels with different swelling properties were used to encapsulate rat MSCs (seeding density approximately 13 million cells/mL, samples 6 mm diameter x 0.5 mm thick before swelling) and osteogenic differentiation in these constructs over 28 days in vitro was determined via histology and biochemical assays for alkaline phosphatase, osteopontin and calcium. Evidence of MSC differentiation was apparent over the culture period for samples without dexamethasone, but there was large variability in calcium production between constructs using cells of the same source. Differentiation was also seen in samples cultured with osteogenic supplements, but calcium deposition varied depending on the source pool of MSCs. By day 28, osteopontin and calcium results suggested that, in the presence of dexamethasone, OPF hydrogels with greater swelling promoted embedded MSC differentiation over those that swelled less (43.7 +/- 16.5 microg calcium/sample and 16.4 +/- 2.8 microg calcium/sample, respectively). In histological sections, mineralized areas were apparent in all sample types many microns away from the cells. These experiments indicate that OPF hydrogels are promising materials for use as injectable MSC carriers and that hydrogel swelling properties can influence osteogenic differentiation of encapsulated progenitor cells.

In vitro osteogenic differentiation of human mesenchymal stem cells photoencapsulated in PEG hydrogels

Much research has focused on the differentiation of human mesenchymal stem cells (hMSCs) in monolayer culture; however, little is known about their differentiation potential in three-dimensional culture conditions. In this research, hMSCs were encapsulated in a photocrosslinkable, injectable scaffolding system based on poly(ethylene glycol) (PEG) hydrogels. To demonstrate the ability of hMSCs to differentiate in PEG hydrogels, cell/polymer constructs were cultured in osteogenic differentiation media to elicit an osteoblastic response. First, viability of encapsulated hMSCs up to 4 weeks in culture was investigated using a membrane integrity assay. Second, gene expression of encapsulated cells was determined with reverse transcription polymerase chain reaction (RT-PCR) as a function of media composition. After 1 week in osteogenic differentiation media, encapsulated hMSCs expressed osteonectin, osteopontin, and alkaline phosphatase, which are all characteristic of osteoblasts. Finally, von Kossa staining was used to evaluate mineralization of the PEG gels. Results support the hypothesis that hMSCs photoencapsulated in PEG hydrogels and cultured in the presence of osteogenic differentiation media are able to differentiate to osteoblasts inside the gel and mineralize the matrix. These experiments demonstrate the feasibility of using a PEG-based, photocrosslinkable system to culture and deliver human mesenchymal stem cells for bone tissue regeneration and repair.

PTH-related protein enhances MCF-7 breast cancer cell adhesion, migration, and invasion via an intracrine pathway

Breast cancer is the most common carcinoma that metastasizes to the bone. Parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption, is a major mediator of the osteolytic process in breast cancer. PTHrP overexpression increases mitogenesis and decreases apoptosis in the human breast cancer cell line MCF-7. In this study, MCF-7 cells were used as a model system to study the effects of PTHrP on breast cancer cell adhesion, migration, and invasion. Clones of MCF-7 cells were established that overexpress wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Wild-type PTHrP-overexpressing cells showed significantly higher laminin adhesion and migration, and Matrigel invasion than empty vector-transfectants or cells overexpressing NLS-mutated PTHrP. Wild-type PTHrP also increased the cell surface expression of the pro-invasive integrins alpha6 and beta4; deletion of the NLS negated these effects. Exogenous PTHrP (1-34), (67-86), (107-139), and (140-173) had no effect on integrin expression, or on cell adhesion, migration, and invasion. These results indicate that PTHrP exerts its effects on cell adhesion, migration, invasion, and integrin expression via an intracrine pathway. PTHrP may play a role in breast cancer metastasis by upregulating proinvasive integrin expression, and controlling PTHrP production in breast cancer may provide therapeutic benefit.

Thermally Cross-Linked Oligo(poly(ethylene glycol) fumarate) Hydrogels Support Osteogenic Differentiation of Encapsulated Marrow Stromal Cells In Vitro

A novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF), cross-linked with a thermal radical initiation system has recently been developed in our laboratory as an injectable, biodegradable cell carrier for regeneration of orthopaedic tissues. The cross-linking, swelling, and degradative properties of hydrogels prepared from OPF with poly(ethylene glycol) of two different chain lengths were assessed. The two OPF types had similar gelation onset times ( approximately 3.6 min) but, when cross-linked for 8 min at 37 degrees C, exhibited significantly different swelling characteristics (fold swelling: 17.5 +/- 0.2 vs 13.4 +/- 0.4). Rat marrow stromal cells (MSCs) were then directly combined with the hydrogel precursors and encapsulated in a model OPF formulation at approximately 14 million cells/mL, cultured in vitro in the presence of osteogenic supplements (dexamethasone), and monitored over 28 days via histology. MSC differentiation in these samples (6 mm diameter x 0.5 mm thick before swelling), as determined by Von Kossa staining for calcified matrix, was apparent by day 21. At day 28, mineralized matrix could be seen throughout the samples, many microns away from the cells. These experiments strongly support the usefulness of thermally cross-linked OPF hydrogels as injectable cell carriers for bone regeneration.

Effect of fibronectin- and collagen I-coated titanium fiber mesh on proliferation and differentiation of osteogenic cells

The objective of this study was to evaluate the effects of fibronectin and collagen I coatings on titanium fiber mesh on the proliferation and osteogenic differentiation of rat bone marrow cells. Three main treatment groups were investigated in addition to uncoated titanium fiber meshes: meshes coated with fibronectin, meshes coated with collagen I, and meshes coated first with collagen I and then subsequently with fibronectin. Rat bone marrow cells were cultured for 1, 4, 8, and 16 days in plain and coated titanium fiber meshes. In addition, a portion of each of these coating treatment groups was cultured in the presence of antibodies against fibronectin and collagen I integrins. To evaluate cellular proliferation and differentiation, constructs were examined for DNA, osteocalcin, and calcium content and alkaline phosphatase activity. There were no significant effects of the coatings on cellular proliferation as indicated by the DNA quantification analysis. When antibodies against fibronectin and collagen I integrins were used, a significant reduction (p < 0.05) in cell proliferation was observed for the uncoated titanium meshes, meshes coated with collagen, and meshes coated with collagen and fibronectin. The different coatings also did not affect the alkaline phosphatase activity of the cells seeded on the coated meshes. However, the presence of antibodies against fibronectin or collagen I integrins resulted in significantly delayed expression of alkaline phosphatase activity for uncoated titanium meshes, meshes coated with collagen, and meshes coated with collagen and fibronectin. Calcium measurements did not reveal a significant effect of fibronectin or collagen I coating on calcium deposition in the meshes. Also, no difference in calcium content was observed in the uncoated titanium meshes and meshes coated with fibronectin when antibodies against fibronectin or collagen I integrins were present. Meshes coated with both collagen I and fibronectin showed significantly higher calcium content when cultured in the presence of antibodies to collagen and fibronectin integrins. A similar phenomenon was also observed for collagen-coated meshes cultured in the presence of antibodies to fibronectin integrins. No significant differences in osteocalcin content were observed between the treatment groups. However, all groups exposed to antibodies against fibronectin integrins showed a significant decrease in osteocalcin content on day 16. These results show that a fibronectin or collagen I coating does not stimulate the differentiation of rat bone marrow cells seeded in a titanium fiber mesh.

PTH-related protein modulates PC-3 prostate cancer cell adhesion and integrin subunit profile

Parathyroid hormone-related protein (PTHrP), which has been localized in prostate cancer tissue and cell lines, plays a role in the development of bone metastases, a frequent complication in prostate cancer patients. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. The present experiments examined the ability of PTHrP to influence adhesion of the human prostate cancer cell line PC-3 to several ECM proteins found in normal tissues. Clonal PC-3 cells induced to overexpress PTHrP by stable transfection with PTHrP complementary DNA showed significantly higher adhesion to collagen type 1, fibronectin, and laminin than control (empty vector-transfected) cells. PTHrP-overexpressing cells also exhibited higher expression of the alpha1, alpha5, alpha6, and beta4 integrin subunits. These results suggest that PTHrP may play a role in prostate tumor invasion and metastasis by influencing cell adhesion to the ECM via upregulation of specific integrin subunits.

Incadronate inhibits osteoporosis in ovariectomized rats

Incadronate is a highly effective inhibitor of stimulated bone resorption as demonstrated in a hypercalcemia model in rats, bone metastasis models in mice and rats, and an osteoporosis model in dogs. In this study, the effect of incadronate on osteoporosis in ovariectomized rats was examined. Incadronate dose-dependently inhibited decreases in second lumbar vertebrae bone mineral density (BMD) following oral administration for 4 or 12 weeks. Significant inhibition was observed at doses of more than 0.3 mg/kg. Incadronate dose-dependently inhibited the loss of distal femur metaphyseal compressive strength following 12 weeks of oral administration, and this was significant at a 3 mg/kg daily dose. Incadronate also dose-dependently inhibited the increases in urinary deoxypyridinoline levels after 4-or 12-week oral administrations. While incadronate had no effect on serum osteocalcin levels after 4 weeks of oral administration, it did dose-dependently reduce levels after 12 weeks of oral administration. These results suggested that incadronate may be a useful drug for osteoporosis due to stimulated bone resorption.

Biomaterials and bone mechanotransduction

Bone is an extremely complex tissue that provides many essential functions in the body. Bone tissue engineering holds great promise in providing strategies that will result in complete regeneration of bone and restoration of its function. Currently, such strategies include the transplantation of highly porous scaffolds seeded with cells. Prior to transplantation the seeded cells are cultured in vitro in order for the cells to proliferate, differentiate and generate extracellular matrix. Factors that can affect cellular function include the cell-biomaterial interaction, as well as the biochemical and the mechanical environment. To optimize culture conditions, good understanding of these parameters is necessary. The new developments in bone biology, bone cell mechanotransduction, and cell-surface interactions are reviewed here to demonstrate that bone mechanotransduction is strongly influenced by the biomaterial properties.

Malignant phyllodes tumor of the breast with expression of osteonectin and vinculin

Phyllodes tumor is a very rare neoplasm which accounts for 2.5% of all fibroepithelial lesions of the breast. The mesenchymal component of a malignant phyllodes tumor frequently contains heterologous components. We report a case of malignant phyllodes tumor. The patient was a 40-year-old woman with a lump on the left breast. Histological examination revealed the lump to be a malignant phyllodes tumor with foci of liposarcomatous differentiation. The mesenchymal tumor cells, including those in the liposarcomatous components, were found to express vimentin, osteonectin and vinculin. However, they showed no immunoreaction to CAM 5.2, desmin, alpha-smooth muscle actin (ASMA), neuron-specific enolase (NSE) nor S-100. Ultrastructurally, the mesenchymal tumor cells were found to have abundant cytoplasmic organelles, but there was no evidence showing their differentiation to myofibroblasts. Further studies will be necessary to elucidate the significance of vinculin and osteonectin expression in malignant phyllodes tumor.

Relationships between bone protein and mineral in developing porcine long bone and calvaria

Several proteins in the bone matrix have been implicated in the regulation of mineral crystal formation and growth. To investigate the relationships between these proteins and the mineral phase at various stages of mineral maturation, fetal porcine calvariae and long bones were fragmented and the particles (20 microm) separated by density gradient sedimentation into fractions of increasing density (1.8 to >2.2 g/cm3). Samples from each fraction were analyzed by X-ray diffraction to obtain the average crystal size/strain and chemical composition. Other samples were sequentially extracted, first with 4.0 mol/L guanidium hydrochloride (GuHCl) (G1), then with 0.5 mol/L ethylene-diamine tetraacetic acid (EDTA) (E), and again with 4.0 mol/L Gu-HCI (G2), for analysis of proteins in different tissue compartments. Based on the mineral density distribution and crystal size, fetal porcine bone protein content was determined for tissue residue and each extract and the protein composition analyzed by sodium dodecyl-polyacrylamide gel electrophoresis (SDS-PAGE). Although the insoluble organic matrix decreased with mineral density the collagen and protein content remained fairly constant, representing approximately 10% of the tissue weight, except in the highest density fraction. Whereas the total extractable protein, representing predominantly noncollagenous proteins, did not show density-related differences, differences were observed for individual proteins on SDS-PAGE. Consistent with their presence in osteoid, the content of bone sialoprotein (BSP), tyrosine-rich acidic matrix protein (TRAMP), and a series of small proteins with cell attachment properties in the G1 extract decreased with mineral density, whereas TRAMP and BSP were increased in G2 extracts. Mineral-associated proteins, including alpha2HS-glycoprotein, BSP, osteopontin (OPN), and osteocalcin, increased with mineral density, whereas secreted protein acidic and rich in cysteine (SPARC)/osteonectin, and some minor proteins, appeared to decrease. Differences of individual proteins within and between the calvarial and long bones could be related to the role of these proteins in the formation and maturation of hydroxyapatite crystals. Collectively, these studies demonstrate mineral density-associated changes in protein composition that reflect a rapid maturation of mineral crystals in embryonic porcine bones.

Tumour progression and angiogenesis in bone metastasis from breast cancer: new approaches to an old problem

Breast cancer metastasizes frequently to the skeleton and causes considerable morbidity and deterioration of the quality of life. The clinical consequences of skeletal metastases are bone pain, pathological fractures, hypercalcaemia and nerve compression syndromes. From the moment breast cancer cells are located in the bone microenvironment, they may release factors which stimulate bone resorption and angiogenesis leading to growth of skeletal metastases and a subsequent selective increase in the attraction of new cancer cells to bone. In this review, emerging new concepts of breast cancer-bone interactions, in particular the involvement of angiogenesis, proteolysis and the role of cancer-induced bone resorption in skeletal metastasis are discussed. Better understanding of the processes involved in the metastasis of cancer cells to bone, local tumour growth and subsequent destruction of skeletal architecture can lead to optimal methods for the prevention and treatment of metastatic bone disease.

The effect of polymeric chemistry on the expression of bone-related mRNAs and proteins by human bone-derived cells in vitro

This study used human bone-derived cells (HBDC) grown on two defined polymeric substrata to examine the effect of substrata chemistry on the expression of mRNAs and proteins characteristic of the osteoblastic phenotype. The growth profile of cells grown on tissue culture polystyrene (TCP) was exponential whereas for those seeded on polyethyleneterephthalate (PET) there was a pronounced lag period before cellular multiplication. The temporal expression pattern of mRNAs in HBDC cultured on TCP was similar to that of cells on PET. On TCP, the levels of several mRNAs peaked at day 4, as cellular proliferation slowed. In contrast, the induction in mRNA levels in cells grown on PET corresponded to maximum mitotic activity. There appears to be sequential cascade in protein expression in cells grown on TCP with overlapping peaks of thrombospondin (Tsp), osteocalcin (OC) and osteopontin (OP) expression. In contrast, peak intracellular protein expression levels for Tsp, OC and OP did not overlap when cells were grown on PET.

Biologic determinants of bone formation for osseointegration: clues for future clinical improvements

STATEMENT OF PROBLEM

Further improvement in and expansion of the application of dental implants requires control and improvement of bone mass for implant support.

PURPOSE

Although osseointegration involves both the formation and the maintenance of bone at implant surfaces, the aim of this article is to identify cellular and molecular determinants of bone formation that may be used in clinical attempts to enhance or expand the application of endosseous implants for dental and craniofacial prosthetics.

METHODS

A review of bone biology and dental and orthopedic implant literature was performed using Medline and published monographs.

RESULTS

This spectrum of information indicates that molecular and cellular approaches to creating and maintaining bone mass may be used to expand the application of dental implants and to improve dental implant success in bone-deficient sites.

The ubiquitin-proteasome system and cellular proliferation and regulation in osteoblastic cells

The 26S proteasome is the macromolecular assembly that mediates ATP- and ubiquitin-dependent extralysosomal intracellular protein degradation in eukaryotes. However, its contribution to the regulation of osteoblast proliferation and hormonal regulation remains poorly defined. Treating osteoblasts with MG-132 or lactacystin (membrane-permeable proteasome inhibitors) attenuates proliferation. Three proteasome activities (peptidylglutamyl-peptide bond hydrolase-, chymotrypsin-, and trypsin-like) were detected in osteoblasts. Catabolic doses of PTH stim-ulated these activities, and cotreatment with PTH and MG-132 blocked stimulation. The proteasome alpha- and beta-subunits, polyubiquitins, and large ubiquitin-protein conjugates were detected by Western blotting. A 90-min treatment with 10 nM PTH had no effect on the amount of proteasome alpha or beta subunit protein, but increased the relative amount of large ubiquitin-protein conjugates by 200%. MG-132 inhibited deubiquitination of large ubiquitin-protein conjugates. The protein kinase A inhibitor SQ22536 blocked much of the PTH-induced stimulation of MCP activities, while dibutyryl cAMP stimulated it, suggesting that protein kinase A-dependent phosphorylation is important in PTH stimulation of proteasome activities. In conclusion, the ubiquitin-proteasome system is essential for osteoblast proliferation under control and PTH-treated conditions. PTH mediates its metabolic effects on the osteoblast, in part, by enhancing ubiquitinylation of protein substrates and stimulating three major proteasome activities by a cAMP-dependent mechanism.

Activation of MMP-2 by human GCT23 giant cell tumour cells induced by osteopontin, bone sialoprotein and GRGDSP peptides is RGD and cell shape change dependent

We show that osteopontin (OPN), bone sialoprotein (BSP) and GRGDSP peptides, in solution, induce activation of metalloproteinase-2 (MMP-2) secreted by human GCT23 giant cell tumour cells. Activation of MMP-2 is RGD sequence dependent, possibly involves anti-alphaVbeta3 integrins, is preceded by a change from spread to rounded cell morphology and is mimicked by the actin depolymerising agent cytochalasin B. Cells that had spread on OPN, BSP and GRGDSP substrata failed to activate MMP-2, but subsequent addition of soluble GRGDSP induced rounding and MMP-2 activation. Activation induced by GRGDSP and cytochalasin B was cell mediated, inhibited by EDTA, tissue inhibitor of metalloproteinase-2 (TIMP-2) and carboxyl terminal MMP-2 consistent with a role for membrane type (MT)-MMP but did not involve urokinase, plasmin or thrombin activity. Activation induced by GRGDSP and cytochalasin B, but not cell rounding, was inhibited by herbimycin A, cycloheximide and actinomycin D, suggesting a role for tyrosine kinases, protein and RNA synthesis, but was not associated with changes in mRNA for MT-MMP-1, MMP-1, MMP-2, TIMP-1 or TIMP-2. GRGDSP and cytochalasin B enhanced levels of membrane-associated pro- and active form MMP-1 and MMP-2 but not MT-MMP-1, stimulated cell surface MMP-1 staining and induced that of MT-MMP-1, MMP-2 and TIMP-2. This was consistent with the possible relocation of constitutive MT-MMP-1 to the cell surface as a prerequisite for subsequent cell surface MMP-2/TIMP-2/MT-MMP-1 complex formation and to the potential induction of conditions favourable for reciprocal cell surface MMP-1/MMP-2 activation. Our data provide a novel insight into interactions between RGD containing bone matrices, GCT cells and MMPs of potential relevance to GCT pathology.

Casein kinase 2 phosphorylation of recombinant rat osteopontin enhances adhesion of osteoclasts but not osteoblasts

Osteopontin (OP) is a highly phosphorylated bone matrix protein and contains the RGD cell-binding motif, which mediates cell adhesion through integrin receptors that include alpha(v)beta3. Casein kinase 2 (CK2) is a factor-independent serine/threonine kinase, which may be the predominant physiologically relevant kinase for OP phosphorylation. This study was designed to examine the effects of unphosphorylated recombinant rat OP, and CK2-phosphorylated OP (P-OP), on the adhesion and function of mouse osteoclasts (OC) and osteoblast-like cells (UMR 201-10B and UMR 106-06) in vitro. OP significantly increased OC adhesion compared to plastic alone, and cell attachment was further increased at least twofold on OP phosphorylated with CK2. Attachment was dependent on the integrity of the RGD domain and was completely abolished in the presence of 1 mM RGD peptide. Neither CK2 phosphorylation of mutant OP, in which the RGD was converted to RGE or RAD, nor protein kinase C (PKC) phosphorylation of wild-type OP enhanced OC attachment. An antibody to the beta3 integrin subunit, but not anti-mouse CD44 antibody, specifically blocked the proportion of attachment due to phosphorylation of OP. Actin ring formation in OC was increased by plating cells onto OP, with no further increase by phosphorylation. Both OP and CK2-phosphorylated OP enhanced attachment of the two osteoblastic cell lines, compared to plastic, but in contrast to OCs, there was no significant difference with phosphorylation. Osteoblast attachment was totally blocked by 1 mM RGD peptide, but was not influenced by the beta3 integrin antibody. Plating of UMR 201-10B cells onto OP further increased retinoic acid-induced alkaline phosphatase expression. The results suggest that specific phosphorylation of OP is important for interaction with OCs, compared with osteoblastic cells, and that alternative integrins may be important in the interaction between osteoblastic cells and OP compared with OCs.

The effect of altered functional forces on the expression of bone-matrix proteins in developing mouse mandibular condyle

Mechanical forces are known to have an effect on bone formation, maintenance and remodelling, and there is evidence that the development of the mandibular condyle in the rat is influenced by the consistency of the diet. Here a mouse model was used to investigate the relation between food, condylar development and the expression of bone sialoprotein (BSP), osteopontin (OPN), osteocalcin (OC) and type 1 collagen (COL I). Twenty-four 19-day-old male mice were randomly divided into three groups. Groups 1 and 2 were fed hard pellets and soft powdered food, respectively, for 2 weeks. Group 3 mice were fed soft food for 1 week followed by a week of hard pellets. Incisors of mice in groups 2 and 3 were trimmed twice a week to reduce occlusal forces. After killing the animals, mandibular condyles were collected for RNA extraction, in situ hybridization and immunohistochemical analyses. Histological sections showed that the condyles of mice in group 2 were underdeveloped, with a thinner layer of cartilage and fewer bone trabeculae. Northern hybridization of total RNA of the condyle from mice in this soft-food group also exhibited a significant decrease in the amounts of BSP, OPN, OC and COL I, representing 79%, 75%, 77% and 79% respectively, of that from mice fed hard food. In situ hybridization of these bone-matrix proteins demonstrated signals in bone-forming cells and BSP mRNA was also seen in the hypertrophic cartilage cells in the developing condyle. Immunohistochemical study demonstrated an obvious difference in the intensity of staining, especially for BSP. Results from group 3 were similar to those from group 1. The observed decrease in bone matrix-protein expression confirms that the consistency of the diet affects the development of the mouse mandibular condyle and that a soft diet diminishes the rate of bone formation.

Role of integrins in the attachment of metastatic follicular thyroid carcinoma cell lines to bone

One of the principle targets for metastasis of follicular thyroid carcinoma (FTC) is the skeleton. Because no data are available on the role of the integrin adhesion molecule family in the attachment of FTC to bone, we studied the attachment characteristics of three FTC cell lines to bone and the role of integrins. Three cell lines were used from the same patient, one (FTC-133) from the primary tumor and two (FTC-236 and FTC-238) from metastases. Attachment of FTC cell lines to bone was assessed on conditioned medium of an osteoblastic cell line, coated onto plastic, as an in vitro model of bone matrix. The synthetic RGD (Arg-Gly-Asp) peptide GRGDS impaired attachment of the FTC cell lines to bone matrix, demonstrating the role of integrins in the attachment of FTC to bone. Attachment of FTC-133 to bone matrix was blocked completely by GRGDS, whereas attachment of FTC-236 and FTC-238 could not be impaired completely. Semiquantitative polymerase chain reaction (PCR) of cDNA from the cell lines indicated stronger expression of alpha5 integrin mRNA in FTC-133 than in the other cell lines. In line with this, attachment of FTC-133 to bone matrix could be inhibited almost completely by anti alpha5 and beta1 integrin antibodies, indicating the importance of the fibronectin receptor in the attachment of FTC-133 to bone. Binding of FTC-236 and FTC-238 to bone matrix could not be inhibited completely by anti-integrin antibodies, suggesting an additional role of nonintegrin adhesion molecules in the attachment of FTC-236 and FTC-238 to bone. The synthetic bone sialoprotein cyclic peptide, CNB, revealed antiadhesive effects in the binding of FTC to bone. In conclusion, integrins play an important role in the attachment of metastatic FTC to bone. Differences in the functional involvement of integrins in the attachment to bone are observed between the three cell lines studied. From the present results, antiadhesive interventions with synthetic RGD peptides in FTC may be designed.

Influence of vitamin D and retinoids on the gammacarboxylation of osteocalcin in human osteosarcoma MG63 cells

Osteocalcin (OC) is a bone matrix protein, synthesized by osteoblasts, which contains three residues of gammacarboxyglutamic acid (GLA). A fraction of circulating OC, which is not fully carboxylated and does not bind to hydroxyapatite, is called undercarboxylated OC (ucOC). In elderly institutionalized women, we have shown an increase of circulating ucOC level which may result not only from vitamin K deficiency but also from vitamin D deficiency (Szulc et al., J Clin Invest 91:1769; 1993). This intriguing finding prompted us to study the effect of vitamin D on the secretion of ucOC by osteoblastic cells in vitro in the presence of warfarin, an inhibitor of gammacarboxylation of GLA-containing proteins. The potential influence of retinoic acid (RA) was also studied, because its mechanism of action involves pathways that are similar to vitamin D. In the presence of warfarin (0.05 microg/mL), 1alpha,25(OH)2D (10(-8)-10(-6) mol/L) decreased dose dependently ucOC secretion by human osteosarcoma MG63 cells (from 3.87 +/- 0.96 to 2.12 +/- 0.13 ng/10(6) cells). When expressed as a fraction of total OC, secretion ucOC decreased from 47.4 +/- 1.4% to 24.8 +/- 3.2% in the MG63 cells. The secretion of total OC was stimulated by RA and by Ro 13-7410, which is a specific ligand of retinoic acid receptor (RAR), but not by 9-cis retinoic acid (9-cisRA), which is a physiologic ligand of retinoid X receptor (RXR). RA and Ro 13-7410 decreased ucOC secretion and ucOC% in warfarin-treated MG63 cells (RA: from 50.4 +/- 13.3% to 13.5 +/- 2.8%; Ro 13-7410: from 28.4 +/- 8.2% to 11.3 +/- 8.4%). 9-cisRA had no effect on OC gammacarboxylation. These results show that vitamin D, RA, and Ro 13-7410, but not 9-cisRA, may modify the gammacarboxylation of OC in human MG63 cells.

Expression of bone sialoprotein in primary human breast cancer is associated with poor survival

We have recently demonstrated that bone sialoprotein (BSP), a bone-matrix protein involved in hydroxyapatite crystal formation, is ectopically expressed in human breast cancers. We explored a possible association between expression of BSP in primary breast cancer and patients' survival. We analyzed BSP expression in 454 breast-cancer patients by immunohistochemistry on archival paraffin-embedded material using an anti-BSP polyclonal antibody. BSP expression was correlated to survival, tumor size, axillary lymph-node status and first site of distant metastasis. Of the breast cancers analyzed, 89% expressed detectable amounts of BSP. We found a statistical association between expression of BSP and poor prognosis as indicated by survival curves analyzed using the log rank and the Gehan methods. BSP expression was significantly higher in breast-cancer patients with axillary lymph-node involvement. Interestingly, survival of patients with positive lymph nodes but BSP-negative tumors was significantly higher than that of patients with no lymph-node involvement but BSP-positive cancers. The frequency of bone metastases was higher in the group of patients with BSP-positive tumors (22%) than in the group with BSP-negative cancers (7%). There was a significant increase in the incidence of lung metastases in patients whose tumors were negative for BSP. Our data show that bone sialoprotein expression in breast cancer is associated with poor prognosis. BSP detection also appears to be a valuable marker with which to identify, among the lymph-node-negative patients, those who have high risk of disease progression.

Implications of cellular and molecular biology advances in periodontal regeneration

BACKGROUND

The mechanisms by which new periodontium is established on root surfaces previously exposed to periodontal disease has been an area of active research interest for the past decade.

METHODS

Recently, histological examination of periodontal regeneration has revealed a complex process orchestrated by temporo-spatial specific cell-matrix interactions.

RESULTS

Advances in cell and molecular biology techniques have provided invaluable tools to begin investigating the cascade of events occurring periodontal regeneration.

CONCLUSION

This report summarizes current understanding of the cellular and molecular aspects of periodontal regeneration and determines the clinical relevance of these findings.

Osteopontin at mineralized tissue interfaces in bone, teeth, and osseointegrated implants: ultrastructural distribution and implications for mineralized tissue formation, turnover, and repair

Currently available data describing the gene expression and regulation, secretion, distribution, and protein chemistry of osteopontin (OPN) all are consistent with the notions of this protein functioning as an inhibitor of mineralization and/or as a mediator of cell-matrix and matrix-matrix/mineral adhesion (cohesion) during the formation, turnover, and repair of normal and pathological mineralized tissues. The properties and overall integrity of mineralized tissues are in part dictated by the nature of their interfaces--sites where organic and inorganic components of the extracellular matrix interact to provide biomechanical strength, regulate mineral ion homeostasis, and influence cellular events involved in mineralized tissue modeling, remodeling, and repair. High-resolution, colloidal-gold immunocytochemistry has been used to characterize the proteinaceous composition of these interfaces and to establish that the phosphorylated sialoprotein, OPN, is a major component found at these sites where it accumulates as a dense, planar "coating" of organic material termed either a cement line or a lamina limitans. Structural/functional features of OPN predict an ability of this protein to regulate calcification in the matrix proper of mineralized tissues and to participate, more specifically, in cell-matrix and matrix-matrix/mineral adhesion in laminae limitantes and cement lines, respectively. From the ultrastructural immunocytochemical data presented herein for OPN illustrating the cellular expression and extracellular matrix distribution of this protein, it is demonstrated that the production of OPN is one of the earliest, and latest, secretory activities of the osteoblast lineage and that this activity manifests itself morphologically as a cement line or a lamina limitans, respectively, at bone matrix interfaces. In laminae limitantes at bone surfaces, OPN appears to be involved in osteoclast adhesion and possibly haptotaxis. An OPN-containing cement line is also present at hard tissue interfaces in rat tooth, against osseointegrated titanium and hydroxyapatite implants and at the margins of surgically created bone defects--and there may influence biological adhesion in a manner similar to that proposed for normal bone. It is suggested, therefore, that in addition to its potential for influencing cell adhesion/dynamics in bones and teeth, OPN in cement lines may act as an interfacial adhesion promoter between apposing substrates, therein maintaining the overall integrity of bone during the bone remodeling sequence and "bonding" dissimilar tissues (or biocompatible materials) together in biological composites such as teeth and osseointegrated implants.

Monoclonal antibodies as tools for studying the osteoblast lineage

Knowledge of the number and kinds of differentiation steps characterizing cells of the osteoblast lineage is inadequate. To analyze further osteoblast differentiation, a number of labs have generated monoclonal antibodies to osteogenic cells, derived from both normal bone and osteosarcomas. A variety of immunolabelling patterns on primary cell cultures, cell lines, and tissue sections has been reported, including cell surface, cytoplasmic, and extracellular matrix-associated patterns. Most of the antibodies selected recognize predominantly the mature osteoblast and osteocyte; in addition, however, antibodies have been generated that recognize pre-osteoblasts. Some recognize cells of both the osteoblast and chondroblast lineages and may contribute to a better understanding of the lineage and phenotypic relationships between these two cell types. In addition to recognition in vivo of cell subpopulations of discrete maturational stages, changes in the immunolabelling patterns in vitro have also documented a differentiation sequence in cells undergoing osteogenesis in cell and tissue cultures. In at least two cases, the antibodies have been used to isolate subpopulations of cells from bone, including relatively pure populations of osteocytes. With the exception of several antibodies that are against alkaline phosphatase or known matrix proteins including osteocalcin, the nature of the macromolecular species recognized by most of the antibodies generated to date are unknown. Recently, however, one antibody was used to clone the cDNA for the beta-galactoside-binding lectin, galectin 3 or epsilon binding protein (epsilon BP; IgE-binding protein; Mac-2), from a lambda gt11 osteoblast expression library; another was used to clone from an ROS 17/2.8-COS cell expression library the cDNA for OTS-8, a putative target gene of early response genes stimulated in response to phorbol esters in MC3T3-E1 cells. Neither of these macromolecules had previously been identified in bone cells, but the recent molecular and cellular analyses have shown them to be developmentally and/or hormonally regulated in osteoblastic cells. These antibodies extend the available markers and support earlier observations that a variety of molecules are differentially expressed by cells at different stages of the osteoblast lineage. This chapter will not be an exhaustive survey of all immunocytochemical and immunohistochemical analyses of osteogenic cells and tissues but will focus on the approach of eliciting novel monoclonal antibodies by the injection of osteogenic cells or crude bone extracts and its potential for establishing new markers of the osteoblast lineage. We have not included a large number of studies documenting the use of antibodies raised against several known bone matrix proteins; while these have been crucial in developing our current understanding of osteogenic differentiation, we sought rather to highlight the potential of the "random" injection approach.

Cytokine regulation of bone cell differentiation

Systemic hormones and cytokines play important roles in regulating both osteoblast and osteoclast activity. These cytokines can have either positive or negative effects on the growth and differentiation of bone cells. These effects appear to be dependent on the model systems use to assess them, as well as the species tested. In the near future, other autocrine-paracrine factors will be identified that enhance osteoblast and osteoclast activity, and model systems should be available to further delineate their effects on cells in the osteoblast lineage. Use of transgenic mice with genes targeted to the osteoblast and osteoclast may further reveal the mechanisms responsible for the growth and differentiation of these cells, as well as produce immortalized cell lines that more accurately reflect the cell biology of the osteoclast and osteoblast in vivo.