Ultrastructural characterization and immunolocalization of osteopontin in rat calvarial osteoblast primary cultures

Osteogenic potential of laser modified and conditioned titanium zirconium surfaces

Statement of Problem:

The osseointegration of dental implant is related to their composition and surface treatment. Titanium zirconium (TiZr) has been introduced as an alternative to the commercially pure titanium and its alloys as dental implant material, which is attributed to its superior mechanical and biological properties. Surface treatments of TiZr have been introduced to enhance their osseointegration ability; however, reliable, easy to use surface modification technique has not been established.

Purpose:

The purpose of this study was to evaluate and compare the effect of neodymium-doped yttrium aluminum garnet (Nd-YAG) laser surface treatment of TiZr implant alloy on their osteogenic potential.

Materials and Methods:

Twenty disc-shaped samples of 5 mm diameter and 2 mm height were milled from the TiZr alloy ingot. The polished discs were ultrasonically cleaned in distilled water. Ten samples each were randomly selected as Group A control samples and Group B consisted of Nd-YAG laser surface etched and conditioned test samples. These were evaluated for cellular response. Cellular adhesion and proliferation were quantified, and the results were statistically analyzed using nonparametric analysis. Cellular morphology was observed using electron and epiflurosence microscopy.

Results:

Nd-YAG laser surface modified and conditioned TiZr samples increased the osteogenic potential.

Conclusion:

Nd-YAG laser surface modification of TiZr, improves the cellular activity, surface roughness, and wettability, thereby increasing the osteogenic potential.

Effects of TGF-β1 on mineralization mediated by rat calvaria-derived osteogenic cells

In this study, we have analyzed the viability and cell growth, as well as, the mineralization of extracellular matrix (ECM) by alizarin red and von Kossa staining of calvaria-derived osteogenic cultures, treated with TGF-β1 alone or associated with Dex comparing with acid ascorbic (AA) + β-glicerophosphate (βGP) (positive mineralization control). The expression of the noncollagenous proteins bone sialoprotein (BSP), osteopontin (OPN) and fibronectin (FN) were evaluated by indirect immunofluorescence. In addition, the main ultrastructural morphological findings were assessed by transmission electron microscopy. Osteogenic cells were isolated of calvaria bone from newborn (2-day-old) Wistar rats were treated with TGF-β1 alone or with dexamethasone for 7, 10, and 14 days. As positive mineralization control, the cells were supplemented only with AA+ βGP. As negative control, the cells were cultured with basal medium (α-MEM + 10%FBS + 1%gentamicin). The treatment with TGF-β1, even when combined with Dex, decreased the viability and cell growth when compared with the positive control. Osteoblastic cell cultures were positive to alizarin red and von Kossa stainings after AA + βGP and Dex alone treatments. Positive immunoreaction was found for BSP, OPN and FN in all studied treatments. Otherwise, when the cell cultures were supplemented with TGF-β1 and TGF-β1 + Dex, no mineralization was observed in any of the studied periods. These present findings suggest that TGF-β1, in the studied in vitro doses, inhibits the proliferation and differentiation of osteoblastic cells by impairment of nodule formation.

Microwave Irradiation of Ethanol-fixed Bone Improves Preservation, Reduces Processing Time, and Allows Both Light and Electron Microscopy on the Same Sample

Methylmethacrylate (MMA) embedding is routinely used for histomorphometry of undecalcified bone preserved by prolonged immersion in ethanol, a procedure that yields poor ultrastructural detail. Because microwave irradiation (MWI) facilitates penetration of fixatives, we have investigated whether it can improve preservation by ethanol. Rat tibiae, some labeled with tetracycline, and a human iliac crest biopsy were immersed in 70% ethanol and dehydrated, both under MWI, for a total processing time of ~7 hr. Controls were not irradiated, and all specimens were embedded in MMA at 4C. They were then processed for histomorphometry, histochemistry, structural analysis, and immunolabeling. The results showed that histological preservation was improved with MWI. Static bone formation and resorption parameters and rate of mineral apposition were similar to those of conventionally processed specimens. Mineral distribution, as visualized by von Kossa staining and backscattered electron imaging, was not affected. Alkaline phosphatase and tartrate-resistant acid phosphatase activity, as well as immunolocalization of bone sialoprotein and osteopontin, were readily visualized. Ultrastructurally, osteopontin exhibited a typical distribution in mineralization foci, between calcified collagen fibrils, and at cement lines. These data show that MWI improves preservation and permits application of a broad spectrum of analytical methodologies on the same bone sample while considerably reducing processing time.

Single-walled carbon nanotubes functionalized with sodium hyaluronate enhance bone mineralization

The aim of this study was to evaluate the effects of sodium hyaluronate (HY), single-walled carbon nanotubes (SWCNTs) and HY-functionalized SWCNTs (HY-SWCNTs) on the behavior of primary osteoblasts, as well as to investigate the deposition of inorganic crystals on titanium surfaces coated with these biocomposites. Primary osteoblasts were obtained from the calvarial bones of male newborn Wistar rats (5 rats for each cell extraction). We assessed cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay and by double-staining with propidium iodide and Hoechst. We also assessed the formation of mineralized bone nodules by von Kossa staining, the mRNA expression of bone repair proteins, and the deposition of inorganic crystals on titanium surfaces coated with HY, SWCNTs, or HY-SWCNTs. The results showed that treatment with these biocomposites did not alter the viability of primary osteoblasts. Furthermore, deposition of mineralized bone nodules was significantly increased by cells treated with HY and HY-SWCNTs. This can be partly explained by an increase in the mRNA expression of type I and III collagen, osteocalcin, and bone morphogenetic proteins 2 and 4. Additionally, the titanium surface treated with HY-SWCNTs showed a significant increase in the deposition of inorganic crystals. Thus, our data indicate that HY, SWCNTs, and HY-SWCNTs are potentially useful for the development of new strategies for bone tissue engineering.

Changes in actin and tubulin expression in osteogenic cells cultured on bioactive glass-based surfaces

The present study evaluated whether the changes in the labeling pattern of cytoskeletal proteins in osteogenic cells cultured on bioactive glass-based materials are due to altered mRNA and protein levels. Primary rat-derived osteogenic cells were plated on Bioglass® 45S5, Biosilicate®, and borosilicate (bioinert control). The following parameters were assayed: (i) qualitative epifluorescence analysis of actin and tubulin; (ii) quantitative mRNA and protein expression for actin and tubulin by real-time PCR and ELISA, respectively, and (iii) qualitative analysis of cell morphology by scanning electron microscopy (SEM). At days 3 and 7, the cells grown on borosilicate showed typical actin and tubulin labeling patterns, whereas those on the bioactive materials showed roundish areas devoid of fluorescence signals. The cultures grown on bioactive materials showed significant changes in actin and tubulin mRNA expression that were not reflected in the corresponding protein levels. A positive correlation between the mRNA and protein as well as an association between epifluorescence imaging and quantitative data were only detected for the borosilicate. SEM imaging of the cultures on the bioactive surfaces revealed cells partly or totally coated with material aggregates, whose characteristics resembled the substrate topography. The culturing of osteogenic cells on Bioglass® 45S5 and Biosilicate® affect actin and tubulin mRNA expression but not the corresponding protein levels. Changes in the labeling pattern of these proteins should then be attributed, at least in part, to the presence of a physical barrier on the cell surface as a result of the material surface reactions, thus limiting fluorescence signals.

Extracellular matrix mineralization in murine MC3T3-E1 osteoblast cultures: an ultrastructural, compositional and comparative analysis with mouse bone

Bone cell culture systems are essential tools for the study of the molecular mechanisms regulating extracellular matrix mineralization. MC3T3-E1 osteoblast cell cultures are the most commonly used in vitro model of bone matrix mineralization. Despite the widespread use of this cell line to study biomineralization, there is as yet no systematic characterization of the mineral phase produced in these cultures. Here we provide a comprehensive, multi-technique biophysical characterization of this cell culture mineral and extracellular matrix, and compare it to mouse bone and synthetic apatite mineral standards, to determine the suitability of MC3T3-E1 cultures for biomineralization studies. Elemental compositional analysis by energy-dispersive X-ray spectroscopy (EDS) showed calcium and phosphorus, and trace amounts of sodium and magnesium, in both biological samples. X-ray diffraction (XRD) on resin-embedded intact cultures demonstrated that similar to 1-month-old mouse bone, apatite crystals grew with preferential orientations along the (100), (101) and (111) mineral planes indicative of guided biogenic growth as opposed to dystrophic calcification. XRD of crystals isolated from the cultures revealed that the mineral phase was poorly crystalline hydroxyapatite with 10 to 20nm-sized nanocrystallites. Consistent with the XRD observations, electron diffraction patterns indicated that culture mineral had low crystallinity typical of biological apatites. Fourier-transform infrared spectroscopy (FTIR) confirmed apatitic carbonate and phosphate within the biological samples. With all techniques utilized, cell culture mineral and mouse bone mineral were remarkably similar. Scanning (SEM) and transmission (TEM) electron microscopy showed that the cultures had a dense fibrillar collagen matrix with small, 100nm-sized, collagen fibril-associated mineralization foci which coalesced to form larger mineral aggregates, and where mineralized sites showed the accumulation of the mineral-binding protein osteopontin. Light microscopy, confocal microscopy and three-dimensional reconstructions showed that some cells had dendritic processes and became embedded within the mineral in an osteocyte-like manner. In conclusion, we have documented characteristics of the mineral and matrix phases of MC3T3-E1 osteoblast cultures, and have determined that the structural and compositional properties of the mineral are highly similar to that of mouse bone.

In Vitro Cytotoxicity of a Ti-35Nb-7Zr-5Ta Alloy Doped with Different Oxygen Contents

Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these alloys are directly related to its microstructure and the presence of interstitial elements, such as oxygen, carbon, nitrogen and hydrogen. In this study, the in vitro cytotoxicity of Ti-35Nb-7Zr-5Ta (TNZT) alloys was analyzed in the as-received condition and after being doped with several small quantities of oxygen on a cultured osteogenic cell. The cell’s morphology was also examined by scanning electron microscopy (SEM). The TNZT alloy presented no cytotoxic effects on osteoblastic cells in the studied conditions.

Influence of Oxygen Content and Microstructure on the Mechanical Properties and Biocompatibility of Ti-15 wt%Mo Alloy Used for Biomedical Applications

The Ti-15Mo alloy has its mechanical properties strongly altered by heat treatments and by addition of interstitial elements, such as, oxygen, for example. In this sense, the objective of this paper is to analyze the effect of the introduction of oxygen in selected mechanical properties and the biocompatibility of Ti-15Mo alloy. The samples used in this study were prepared by arc-melting and characterized by density measurements, X-ray diffraction, scanning electron microscopy, microhardness, modulus of elasticity, and biocompatibility tests. Hardness measurements were shown to be sensitive to concentration of oxygen. The modulus results showed interstitial influence in value; this was verified under several conditions to which the samples were exposed. Cytotoxicity tests conducted in vitro showed that the various processing conditions did not alter the biocompatibility of the material.

Multifunctional role of osteopontin in directing intrafibrillar mineralization of collagen and activation of osteoclasts

Mineralized collagen composites are of interest because they have the potential to provide a bone-like scaffold that stimulates the natural processes of resorption and remodeling. Working towards this goal, our group has previously shown that the nanostructure of bone can be reproduced using a polymer-induced liquid-precursor (PILP) process, which enables intrafibrillar mineralization of collagen with hydroxyapatite to be achieved. This prior work used polyaspartic acid (pASP), a simple mimic for acidic non-collagenous proteins, to generate nanodroplets/nanoparticles of an amorphous mineral precursor which can infiltrate the interstices of type-I collagen fibrils. In this study we show that osteopontin (OPN) can similarly serve as a process-directing agent for the intrafibrillar mineralization of collagen, even though OPN is generally considered a mineralization inhibitor. We also found that inclusion of OPN in the mineralization process promotes the interaction of mouse marrow-derived osteoclasts with PILP-remineralized bone that was previously demineralized, as measured by actin ring formation. While osteoclast activation occurred when pASP was used as the process-directing agent, using OPN resulted in a dramatic effect on osteoclast activation, presumably because of the inherent arginine-glycine-aspartate acid ligands of OPN. By capitalizing on the multifunctionality of OPN, these studies may lead the way to producing biomimetic bone substitutes with the capability of tailorable bioresorption rates.

Association of calcium and phosphate ions with collagen in the mineralization of vertebrate tissues

Among the vertebrate species, collagen is the most abundant protein and is associated with mineralization of their skeleton and dentition in all tissues except enamel. In such tissues, bones, calcifying tendon, dentin, and cementum are comprised principally of type I collagen, which has been proposed as a template for apatite mineral formation. Recent considerations of the interaction between type I collagen and calcium and phosphate ions as the major constituents of apatite have suggested that collagen polypeptide stereochemistry underlies binding of these ions at sites within collagen hole and overlap regions and leads to nucleation of crystals. The concept is fundamental to understanding both normal and abnormal mineralization, and it is reviewed in this article. Given this background, avenues for additional research studies in vertebrate mineralization will also be described. The latter include, for instance, how mineralization events subsequent to nucleation, that is, crystal growth and development, occur and whether they, too, are directed by collagen stereochemical parameters; whether mineralization can be expected in all spaces between collagen molecules; whether the side chains of charged amino acid residues actually point toward and into the hole and overlap collagen spaces to provide putative binding sites for calcium and phosphate ions; and what phenomena may be responsible for mineralization beyond hole and overlap zones and into extracellular tissue regions between collagen structural units. These questions will be discussed to provide a broader understanding of collagen contributions to potential mechanisms of vertebrate mineralization.

Imaging analysis of osteogenic transformation of Meckel's chondrocytes from green fluorescent protein-transgenic mice during intrasplenic transplantation

Our previous studies demonstrated that Meckel's chondrocytes, which are derived from ectomesenchyme, have the potential to transform into osteogenic phenotypes. The present study aimed to clarify the role of cell origin in the phenotypic transformation of chondrocytes. Cell pellets from ectomesenchyme-derived Meckel's cartilage and mesoderm-derived costal cartilage from green fluorescent protein (GFP)-transgenic mice were transplanted into the spleen for up to 4 weeks. Chondrocyte pellets from both cartilages adapted well to the splenic tissues and formed an alizarin red-positive calcified matrix, with increasing duration of transplantation. Following the production of cartilage-specific type II and type X collagens, newly-formed type I collagen appeared in the chondrocyte pellets from Meckel's cartilage during the late stage of transplantation. Although the bone-marker proteins: osteocalcin, osteopontin, osteonectin and bone morphogenetic protein-2, were detected in pellets from both Meckel's and costal cartilage, only type I collagen in Meckel's cartilage was a significant marker protein for detecting transformation. These bone-type protein-producing cells represented osteogenic cells transformed from GFP-expressing cells, rather than from recipient cells. These results indicate that neural crest-derived Meckel's cartilage displays a higher potential for phenotypic switching than mesoderm-derived costal chondrocytes under in vivo conditions.

Characterization and in vitro evaluation of bacterial cellulose membranes functionalized with osteogenic growth peptide for bone tissue engineering

The aim of this study was to characterize the physicochemical properties of bacterial cellulose (BC) membranes functionalized with osteogenic growth peptide (OGP) and its C-terminal pentapeptide OGP[10-14], and to evaluate in vitro osteoinductive potential in early osteogenesis, besides, to evaluate cytotoxic, genotoxic and/or mutagenic effects. Peptide incorporation into the BC membranes did not change the morphology of BC nanofibers and BC crystallinity pattern. The characterization was complemented by Raman scattering, swelling ratio and mechanical tests. In vitro assays demonstrated no cytotoxic, genotoxic or mutagenic effects for any of the studied BC membranes. Culture with osteogenic cells revealed no difference in cell morphology among all the membranes tested. Cell viability/proliferation, total protein content, alkaline phosphatase activity and mineralization assays indicated that BC-OGP membranes enabled the highest development of the osteoblastic phenotype in vitro. In conclusion, the negative results of cytotoxicity, genotoxicity and mutagenicity indicated that all the membranes can be employed for medical supplies, mainly in bone tissue engineering/regeneration, due to their osteoinductive properties.

Extracellular matrix mineralization promotes E11/gp38 glycoprotein expression and drives osteocytic differentiation

Osteocytes are terminally differentiated osteoblasts which reside in a mineralized extracellular matrix (ECM). The factors that regulate this differentiation process are unknown. We have investigated whether ECM mineralization could promote osteocyte formation. To do this we have utilised MLO-A5 pre-osteocyte-like cells and western blotting and comparative RT-PCR to examine whether the expression of osteocyte-selective markers is elevated concurrently with the onset of ECM mineralization. Secondly, if mineralization of the ECM is indeed a driver of osteocyte formation, we reasoned that impairment of ECM mineralization would result in a reversible inhibition of osteocyte formation. Supplementation of MLO-A5 cell cultures with ascorbic acid and phosphate promoted progressive ECM mineralization as well as temporally associated increases in expression of the osteocyte-selective markers, E11/gp38 glycoprotein and sclerostin. Consistent with a primary role for ECM mineralization in osteocyte formation, we also found that inhibition of ECM mineralization, by omitting phosphate or adding sodium pyrophosphate, a recognized inhibitor of hydroxyapatite formation, resulted in a 15-fold decrease in mineral deposition that was closely accompanied by lower expression of E11 and other osteocyte markers such as Dmp1, Cd44 and Sost whilst expression of osteoblast markers Ocn and Col1a increased. To rule out the possibility that such restriction of ECM mineralization may produce an irreversible modification in osteoblast behaviour to limit E11 expression and osteocytogenesis, we also measured the capacity of MLO-A5 cells to re-enter the osteocyte differentiation programme. We found that the mineralisation process was re-initiated and closely allied to increased expression of E11 protein after re-administration of phosphate or omission of sodium pyrophosphate, indicating an ECM mineralization-induced restoration in osteocyte formation. These results emphasise the importance of cell-ECM interactions in regulating osteoblast behaviour and, more importantly, suggest that ECM mineralization exerts pivotal control during terminal osteoblast differentiation and acquisition of the osteocyte phenotype.

Giemsa as a fluorescent dye for mineralizing bone-like nodules in vitro

Giemsa was first used as a fluorescent dye for mineralized bone and cartilage in tissue sections. The aim of this study was to establish the use of Giemsa as a fluorescent dye for mineralizing bone-like nodules produced in cell cultures. Osteoblasts were grown under mineralizing conditions for 14 days, producing typical bone-like nodules. Upon staining with Giemsa stock solution for 1 min, the mineralizing nodules could be selectively visualized emitting intense green and red fluorescence when observed under blue and green illumination, respectively. The textural details of the nodules were clearly observed under fluorescence microscopy, allowing to identify regions with different degrees of mineralization. The mineralized nature of the nodules was confirmed using von Kossa's method, Alizarin Red S staining and x-ray mapping for Ca and P in a scanning electron microscope, showing a strong correlation between the mineralizing and the fluorescent nodules. The selective fluorescence was related to the mineral phase, being absent in decalcified samples. The use of Giemsa as a fluorescent dye for mineralizing bone-like nodules presents a simple alternative method to quickly analyze biomineralization assays in vitro under fluorescence microscopy, particularly in the biological evaluation of biomaterials.

Ultrastructural and mineral phase characterization of the bone-like matrix assembled in F-OST osteoblast cultures

Cell cultures are often used to study bone mineralization; however, not all systems achieve a bone-like matrix formation. In this study, the mineralized matrix assembled in F-OST osteoblast cultures was analyzed, with the aim of establishing a novel model for bone mineralization. The ultrastructure of the cultures was investigated using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy (TEM). The mineral phase was characterized using conventional and high-resolution TEM, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and solid-state (31)P and (1)H nuclear magnetic resonance. F-OST osteoblast cultures presented a clear nodular mineralization pattern. The chief features of the mineralizing nodules were globular accretions ranging from about 100 nm to 1.5 μm in diameter, loaded with needle-shaped crystallites. Accretions seemed to bud from the cell membrane, increase in size, and coalesce into larger ones. Arrays of loosely packed, randomly oriented collagen fibrils were seen along with the accretions. Mineralized fibrils were often observed, sometimes in close association with accretions. The mineral phase was characterized as a poorly crystalline hydroxyapatite. The Ca/P atomic ratio was 1.49 ± 0.06. The presence of OH was evident. The lattice parameters were a = 9.435 Å and c = 6.860 Å. The average crystallite size was 20 nm long and 10 nm wide. Carbonate substitutions were seen in phosphate and OH sites. Water was also found within the apatitic core. In conclusion, F-OST osteoblast cultures produce a bone-like matrix and may provide a good model for bone mineralization studies.

Osteogenic differentiation of rat bone marrow stromal cells by various intensities of low-intensity pulsed ultrasound

Bone growth and repair are under the control of biochemical and mechanical signals. Low-intensity pulsed ultrasound (LIPUS) stimulation at 30mW/cm(2) is an established, widely used and FDA approved intervention for accelerating bone healing in fractures and non-unions. Although this LIPUS signal accelerates mineralization and bone regeneration, the actual intensity experienced by the cells at the target site might be lower, due to the possible attenuation caused by the overlying soft tissue. The aim of this study was to investigate whether LIPUS intensities below 30mW/cm(2) are able to provoke phenotypic responses in bone cells. Rat bone marrow stromal cells were cultured under defined conditions and the effect of 2, 15, 30mW/cm(2) and sham treatments were studied at early (cell activation), middle (differentiation into osteogenic cells) and late (biological mineralization) stages of osteogenic differentiation. We observed that not only 30mW/cm(2) but also 2 and 15mW/cm(2), modulated ERK1/2 and p38 intracellular signaling pathways as compared to the sham treatment. After 5 days with daily treatments of 2, 15 and 30mW/cm(2), alkaline phosphatase activity, an early indicator of osteoblast differentiation, increased by 79%, 147% and 209%, respectively, compared to sham, indicating that various intensities of LIPUS were able to initiate osteogenic differentiation. While all LIPUS treatments showed higher mineralization, interestingly, the highest increase of 225% was observed in cells treated with 2mW/cm(2). As the intensity increased to 15 and 30mW/cm(2), the increase in the level of mineralization dropped to 120% and 82%. Our data show that LIPUS intensities lower than the current clinical standard have a positive effect on osteogenic differentiation of rat bone marrow stromal cells. Although Exogen™ at 30mW/cm(2) continues to be effective and should be used as a clinical therapy for fracture healing, if confirmed in vivo, the increased mineralization at lower intensities might be the first step towards redefining the most effective LIPUS intensity for clinical use.

Expression of osteogenic proteins during the intrasplenic transplantation of Meckel's chondrocytes: A histochemical and immunohistochemical study

Meckel's chondrocytes, derived from the ectomesenchyme, have the potential to transform into other phenotypes. In this study, we transplanted cell pellets of Meckel's chondrocytes into isogenic mouse spleens and analyzed their phenotypic transformation into osteogenic cells using histological and immunohistochemical methods. With the increasing duration of transplantation, chondrocytes were incorporated into splenic tissues and formed a von Kossa-positive calcified matrix containing calcium and phosphoric acid, similar to that of intact bone. Type I, II, and X collagens, and the bone-marker proteins osteocalcin, osteopontin, osteonectin, and bone morphogenetic protein-2 (BMP-2) were immunolocalized in the matrix formed by the transplanted chondrocytes. Osteopontin and osteonectin were detected in the calcified matrix at earlier stages than osteocalcin and BMP-2. Type II collagen was expressed during the first week of transplantation, and type X collagen-positive cells appeared scattered during the initial stage of calcification, these collagens being later replaced by type I collagen formed by osteocyte-like cells. Electron microscopic observations revealed that chondrocytes surrounded by the calcified matrix transformed into spindle-shaped osteocytic cells accompanying the formation of bone-type thick-banded collagen fibrils. These results suggest that phenotypic switching of Meckel's chondrocytes can occur under in vivo conditions at a cellular morphological level.

Treatment with a growth factor-protein mixture inhibits formation of mineralized nodules in osteogenic cell cultures grown on titanium

Despite wide clinical application, the efficacy of platelet-rich plasma (PRP) for repairing bone defects and enhancing osseointegration of metal implants is still subject of debate. This study aimed to evaluate the effects of a well-defined PRP-like mixture containing platelet-derived growth factor-BB, transforming growth factor (TGF)-beta1, TGF-beta2, albumin, fibronectin, and thrombospondin [growth factors (GFs) + proteins] on the development of the osteogenic phenotype on titanium (Ti) in vitro. Human alveolar bone-derived osteoblastic cells were subcultured on Ti discs and exposed during the first 7 days to osteogenic medium supplemented with GFs + proteins and to osteogenic medium alone thereafter up to 14 days. Control cultures were exposed to only osteogenic medium. Dose-response experiments were carried out using rat primary calvarial cells exposed to GFs + proteins and 1:10 or 1:100 dilutions of the mixture. Treated human-derived cell cultures exhibited a significantly higher number of cycling cells at days 1 and 4 and of total cells at days 4 and 7, significantly reduced alkaline phosphatase (ALP) activity at days 4, 7, and 10, and no Alizarin red-stained areas (calcium deposits) at day 14, indicating an impairment in osteoblast differentiation. Although the 1:10 and 1:100 dilutions of the mixture restored the proliferative activity of rat-derived osteogenic cells to control levels and promoted a significant increase in ALP activity at day 10 compared with GFs + proteins, mineralized nodule formation was only observed with the 1:100 dilution ( approximately 50% of the control). These results showed that a PRP-like protein mixture inhibits development of the osteogenic phenotype in both human and rat osteoblastic cell cultures grown on Ti.

Effects of the association between a calcium hydroxide paste and 0.4% chlorhexidine on the development of the osteogenic phenotype in vitro

The present study aimed to evaluate whether the association between a calcium hydroxide paste (Calen paste) and 0.4% chlorhexidine (CHX) affects the development of the osteogenic phenotype in vitro. With rat calvarial osteogenic cell cultures, the following parameters were assayed: cell morphology and viability, alkaline phosphatase activity, total protein content, bone sialoprotein immunolocalization, and mineralized nodule formation. Comparisons were carried out by using the nonparametric Kruskal-Wallis test (level of significance, 5%). The results showed that the association between Calen paste and 0.4% CHX did not affect the development of the osteogenic phenotype. No significant changes were observed in terms of cell shape, cell viability, alkaline phosphatase activity, and the total amount of bone-like nodule formation among control, Calen, or Calen + CHX groups. The strategy to combine Ca(OH)(2) and CHX to promote a desirable synergistic antibacterial effect during endodontic treatment in vivo might not significantly affect osteoblastic cell biology.

The response of mineralizing culture systems to microtextured and polished titanium surfaces

The surface texture of titanium has a predictable effect on peri-implant tissue formation in vivo. When implanted in an osseous environment, smooth surfaces (R(a) < 0.5 mm) are generally apposed by fibrous tissue and textured surfaces (R(a) > 1.0 mm) are generally apposed by osseous tissue. Thus in vitro study assessed the mineralization and proliferation response of TF274, MC3T3-E1, murine femoral stromal cells and canine stromal cells to tissue culture plastic (R(a) = 0.001 mm), polished (R(a) = 0.01 mm) and irregularly textured (R(a) = 3.26 mm) titanium surfaces. Amongst all culture systems, proliferation was significantly decreased on textured vs. smooth surfaces. Midway through the culture of the canine marrow cells, the cell layer detached from the tissue culture plastic and polished titanium surfaces. The TF274, MC3T3-E1, murine femoral stromal cell systems formed a mineralized matrix on the tissue culture plastic and polished titanium surfaces which was not observed with the canine stromal cell system. Compared to the tissue culture plastic and polished titanium surfaces, matrix mineralization was significantly reduced on the textured titanium surfaces for the TF274, MC3T3-E1, murine femoral stromal systems, a result which was differed significantly in comparison to the canine stromal system. These results were surprising given the large number of reports concerning the in vivo response to titanium in clinical and pre-clinical studies. Further work is required to determine if the TF274, MC3T3-E1 and murine femoral stromal systems are suitable for the in vitro investigation of the effects of titanium surface texture on osteoblast activity.

MEPE-ASARM peptides control extracellular matrix mineralization by binding to hydroxyapatite: an inhibition regulated by PHEX cleavage of ASARM

Hyp mice having an inactivating mutation of the phosphate-regulating gene with homologies to endopeptidases on the X-chromosome (Phex) gene have bones with increased matrix extracellular phosphoglycoprotein (MEPE). An acidic, serine- and aspartic acid-rich motif (ASARM) is located in the C terminus of MEPE and other mineralized tissue matrix proteins. We studied the effects of ASARM peptides on mineralization and how PHEX and MEPE interactions contribute to X-linked hypophosphatemia (XLH). ASARM immunoreactivity was observed in the osteoid of wildtype bone and in the increased osteoid of Hyp mice. In wildtype bone, PHEX immunostaining was found particularly in osteoid osteocytes and their surrounding matrix. Treatment of MC3T3-E1 osteoblasts with triphosphorylated (3 phosphoserines) ASARM peptide (pASARM) caused a dose-dependent inhibition of mineralization. pASARM did not affect collagen deposition or osteoblast differentiation, suggesting that pASARM inhibits mineralization by direct binding to hydroxyapatite crystals. Binding of pASARM to mineralization foci in pASARM-treated cultures and to synthetic hydroxyapatite crystals was confirmed by colloidal-gold immunolabeling. Nonphosphorylated ASARM peptide showed little or no binding to hydroxyapatite and did not inhibit mineralization, showing the importance of ASARM phosphorylation in regulating mineralization. PHEX rescued the inhibition of osteoblast culture mineralization by pASARM, and mass spectrometry of cleaved peptides obtained after pASARM-PHEX incubations identified pASARM as a substrate for PHEX. These results, showing that pASARM inhibits mineralization by binding to hydroxyapatite and that this inhibitor can be cleaved by PHEX, provide a mechanism explaining how loss of PHEX activity can lead to extracellular matrix accumulation of ASARM resulting in the osteomalacia of XLH.

Effects of a mixture of growth factors and proteins on the development of the osteogenic phenotype in human alveolar bone cell cultures

Strategies to promote bone repair have included exposure of cells to growth factor (GF) preparations from blood that generally include proteins as part of a complex mixture. This study aimed to evaluate the effects of such a mixture on different parameters of the development of the osteogenic phenotype in vitro. Osteoblastic cells were obtained by enzymatic digestion of human alveolar bone and cultured under standard osteogenic conditions until subconfluence. They were subcultured on Thermanox coverslips up to 14 days. Treated cultures were exposed during the first 7 days to osteogenic medium supplemented with a GFs + proteins mixture containing the major components found in platelet extracts [platelet-derived growth factor-BB, transforming growth factor (TGF)-beta1, TGF-beta2, albumin, fibronectin, and thrombospondin] and to osteogenic medium alone thereafter. Control cultures were exposed only to the osteogenic medium. Treated cultures exhibited a significantly higher number of adherent cells from day 4 onward and of cycling cells at days 1 and 4, weak alkaline phosphatase (ALP) labeling, and significantly decreased levels of ALP activity and mRNA expression. At day 14, no Alizarin red-stained nodular areas were detected in cultures treated with GFs + proteins. Results were confirmed in the rat calvaria-derived osteogenic cell culture model. The addition of bone morphogenetic protein 7 or growth and differentiation factor 5 to treated cultures upregulated Runx2 and ALP mRNA expression, but surprisingly, ALP activity was not restored. These results showed that a mixture of GFs + proteins affects the development of the osteogenic phenotype both in human and rat cultures, leading to an increase in the number of cells, but expressed a less differentiated state.

Effects of alendronate on tooth eruption and molar root formation in young growing rats

Tooth eruption consists of the movement of teeth from the bony crypt in which they initiate their development to the occlusal plane in the oral cavity. Interactions between the tooth germ and its surrounding alveolar bone occur in order to offer spatial conditions for its development and eruption. This involves bone remodeling during which resorption is a key event. Bisphosphonates are a group of drugs that interfere with the resorption of mineralized tissues. With the purpose of investigating the effects of sodium alendronate (a potent bisphosphonate inhibitor of osteoclast activity) on alveolar bone during tooth development and eruption, we gave newborn rats daily doses of this drug for 4, 14, and 30 days. Samples of the maxillary alveolar process containing the tooth germs were processed for light, transmission, and scanning electron microscopy and were also submitted to tartrate-resistant acid phosphatase histochemistry and high-resolution colloidal-gold immunolabeling for osteopontin. Inhibition of osteoclast activity by sodium alendronate caused the absence of tooth eruption. The lack of alveolar bone remodeling resulted in primary bone with the presence of latent osteoclasts and abundant osteopontin at the interfibrillar regions. The developing bone trabeculae invaded the dental follicle and reached the molar tooth germs, provoking deformities in enamel surfaces. No root formation was observed. These findings suggested that alendronate effectively inhibited tooth eruption by interfering with the activation of osteoclasts, which remained in a latent stage.

Ultrastructural and immunocytochemical analyses of osteopontin in reactionary and reparative dentine formed after extrusion of upper rat incisors

Reactionary dentine and reparative dentine are two strategies used by the dentine-pulp complex to respond to injury. The reactionary dentine is secreted by original odontoblasts, while the reparative dentine is formed by odontoblast-like cells. Osteopontin (OPN) is a non-collagenous protein usually present in the repair of mineralized tissues. It is likely to be present in newly formed dentine but there are no studies attempting to detect it in reactionary and reparative dentine. The aim of the present study was to examine the ultrastructural characteristics, as well as the presence and distribution of OPN in reactionary and reparative dentine by provoking extrusion of the rat incisor. The right upper incisors of 3-month-old male rats were extruded 3 mm and then repositioned into their original sockets. At 3, 7, 10, 15, 20, 30 and 60 days after surgery, the incisors were fixed in glutaraldehyde-formaldehyde and then processed for scanning and transmission electron microscopy and for immunocytochemistry for OPN. After extrusive trauma, the dentine-pulp interface showed the presence of reactionary and reparative dentine, which varied in aspect, thickness and related cells. OPN was not detected in the physiological and reactionary dentine, while it was strongly immunoreactive in the matrix that surrounded the entrapped cells of reparative dentine. In addition, original odontoblasts subjacent to the physiological dentine contained OPN in their Golgi region. The present findings showed that reparative dentine shares some structural characteristics with primary bone, especially in relation to its OPN content. The odontoblast-like cells resemble osteoblasts rather than odontoblasts.

In vitro osteogenesis on a microstructured titanium surface with additional submicron-scale topography

The present study aimed to evaluate key parameters of in vitro osteogenesis on (1) commercially pure titanium (cpTi) discs with 20-200-microm-scale microtopography patterned with additional micron- and submicron-scale topography (0.5-20 microm; Plus surface, Dentsply Friadent), (2) control cpTi discs with 20-200-microm-scale microtopography (DPS, Deep Profile Surface, Dentsply Friadent), and (3) a machined surface. Using calvaria-derived osteogenic cultures, the following parameters were assessed: cell adhesion and spreading, growth curve and cell viability, alkaline phosphatase (ALP) activity and total protein content, immunolocalization of fibronectin, bone sialoprotein (BSP) and osteopontin (OPN), and bone-like tissue formation. The results showed no major differences between surfaces in terms of cell adhesion, growth curve, cell viability (days 4 and 11), ALP activity, or total protein content (days 11 and 17). At day 11, cultures grown on Plus exhibited small, well-defined nodular areas of calcified matrix, which were only rarely observed on DPS and absent on the machined surface. Such areas were larger at day 17 and were not associated with the typical mineralized bone-like nodules (with BSP- and OPN-positive osteoblastic cells on top). At day 17, the total mineralized area was significantly larger on DPS than on a Plus or machined surface (DPS>Plus>machined; Kruskal-Wallis test, P<0.05). Direct fluorescence allowed the straightforward observation of higher amounts of apoptotic bodies associated with mineralized nodules for Plus. The results suggested the occurrence of an additional, early pattern of matrix mineralization mostly for the Plus microstructured surface, which did not necessarily translate into larger bone-like tissue formation in vitro.

Pyrophosphate inhibits mineralization of osteoblast cultures by binding to mineral, up-regulating osteopontin, and inhibiting alkaline phosphatase activity

Inorganic pyrophosphate (PP(i)) produced by cells inhibits mineralization by binding to crystals. Its ubiquitous presence is thought to prevent "soft" tissues from mineralizing, whereas its degradation to P(i) in bones and teeth by tissue-nonspecific alkaline phosphatase (Tnap, Tnsalp, Alpl, Akp2) may facilitate crystal growth. Whereas the crystal binding properties of PP(i) are largely understood, less is known about its effects on osteoblast activity. We have used MC3T3-E1 osteoblast cultures to investigate the effect of PP(i) on osteoblast function and matrix mineralization. Mineralization in the cultures was dose-dependently inhibited by PP(i). This inhibition could be reversed by Tnap, but not if PP(i) was bound to mineral. PP(i) also led to increased levels of osteopontin (Opn) induced via the Erk1/2 and p38 MAPK signaling pathways. Opn regulation by PP(i) was also insensitive to foscarnet (an inhibitor of phosphate uptake) and levamisole (an inhibitor of Tnap enzymatic activity), suggesting that increased Opn levels did not result from changes in phosphate. Exogenous OPN inhibited mineralization, but dephosphorylation by Tnap reversed this effect, suggesting that OPN inhibits mineralization via its negatively charged phosphate residues and that like PP(i), hydrolysis by Tnap reduces its mineral inhibiting potency. Using enzyme kinetic studies, we have shown that PP(i) inhibits Tnap-mediated P(i) release from beta-glycerophosphate (a commonly used source of organic phosphate for culture mineralization studies) through a mixed type of inhibition. In summary, PP(i) prevents mineralization in MC3T3-E1 osteoblast cultures by at least three different mechanisms that include direct binding to growing crystals, induction of Opn expression, and inhibition of Tnap activity.

Enhancement ofin vitro osteogenesis on titanium by chemically produced nanotopography

The surface characteristics of biomaterials can influence protein adsorption, cellular functions, and ultimately tissue formation. Controlled chemical oxidation of titanium-based surfaces with a mixture of H(2)SO(4)/H(2)O(2) creates a nanopatterned surface that has been shown to affect early osteogenic events. The objective of this study was to evaluate the effect over time of this nanopattern on various key parameters of osteogenesis, and determine whether these effects ultimately translate into more mineralized matrix production. Osteogenic cells were obtained by enzymatic digestion of newborn rat calvaria and grown on treated and untreated titanium discs for periods of up to 14 days. Alkaline phosphatase activity peaked earlier and cell number was higher as of day 7 on the nanopatterned discs. Immunofluorescence showed that the treated surface favored early bone sialoprotein and osteopontin secretion, and fibronectin accumulation. Alizarin red staining revealed that, at days 10 and 14, there were significantly more mineralized nodules on treated than on untreated discs. These results demonstrate that simple chemical treatment of titanium with H(2)SO(4)/H(2)O(2) accelerates the in vitro osteogenic potential of calvaria-derived cells. They also suggest that this treatment may represent an advantageous approach for producing "intelligent surfaces" that stimulate bone formation and enhance bone-implant contact.

In vitro osteogenesis on a highly bioactive glass-ceramic (Biosilicate®)

One of the strategies to improve the mechanical performance of bioactive glasses for load-bearing implant devices has been the development of glass-ceramic materials. The present study aimed to evaluate the effect of a highly bioactive, fully-crystallized glass-ceramic (Biosilicate) of the system P(2)O(5)-Na(2)O-CaO-SiO(2) on various key parameters of in vitro osteogenesis. Surface characterization was carried out by scanning electron microscopy and Fourier transform infrared spectroscopy. Osteogenic cells were obtained by enzymatic digestion of newborn rat calvarial bone and by growing on Biosilicate discs and on control bioactive glass surfaces (Biosilicate) parent glass and Bioglass(R) 45S5) for periods of up to 17 days. All materials developed an apatite layer in simulated body fluid for 24h. Additionally, as early as 12 h under culture conditions and in the absence of cells, all surfaces developed a layer of silica-gel that was gradually covered by amorphous calcium phosphate deposits, which remained amorphous up to 72 h. During the proliferative phase of osteogenic cultures, the majority of cells exhibited disassembly of the actin cytoskeleton, whereas reassembly of actin stress fibers took place only in areas of cell multilayering by day 5. Although no significant differences were detected in terms of total protein content and alkaline phosphatase activity at days 11 and 17, Biosilicate supported significantly larger areas of calcified matrix at day 17. The results indicate that full crystallization of bioactive glasses in a range of compositions of the system P(2)O(5)-Na(2)O-CaO-SiO(2) may promote enhancement of in vitro bone-like tissue formation in an osteogenic cell culture system.

Mechanism by which MLO-A5 late osteoblasts/early osteocytes mineralize in culture: similarities with mineralization of lamellar bone

The mechanisms whereby bone mineralizes are unclear. To study this process, we used a cell line, MLO-A5, which has highly elevated expression of markers of the late osteoblast such as alkaline phosphatase, bone sialoprotein, parathyroid hormone type 1 receptor, and osteocalcin and will mineralize in sheets, not nodules. In culture, markers of osteocytes and dendricity increase with time, features of differentiation from a late osteoblast to an early osteocyte. Mineral formation was examined using transmission electron microscopy, scanning electron microscopy with energy-dispersive X-ray analysis, and atomic force microscopy. At 3-4 days of culture, spheres of approximately 20-50 nm containing calcium and phosphorus were observed budding from and associated with developing cellular projections. By 5-6 days, these calcified spheres were associated with collagen fibrils, where over time they continued to enlarge and to engulf the collagen network. Coalescence of these mineralized spheres and collagen-mediated mineralization were responsible for the mineralization of the matrix. Similar calcified spheres were observed in cultured fetal rat calvarial cells and in murine lamellar bone. We propose that osteoid-osteocytes generate spherical structures that calcify during the budding process and are fully mineralized on their developing cellular processes. As the cellular process narrows in diameter, these mineralized structures become associated with and initiate collagen-mediated mineralization.

Cilia-like structures and polycystin-1 in osteoblasts/osteocytes and associated abnormalities in skeletogenesis and Runx2 expression

We examined the osteoblast/osteocyte expression and function of polycystin-1 (PC1), a transmembrane protein that is a component of the polycystin-2 (PC2)-ciliary mechano-sensor complex in renal epithelial cells. We found that MC3T3-E1 osteoblasts and MLO-Y4 osteocytes express transcripts for PC1, PC2, and the ciliary proteins Tg737 and Kif3a. Immunohistochemical analysis detected cilia-like structures in MC3T3-E1 osteoblastic and MLO-Y4 osteocyte-like cell lines as well as primary osteocytes and osteoblasts from calvaria. Pkd1m1Bei mice have inactivating missense mutations of Pkd1 gene that encode PC1. Pkd1m1Bei homozygous mutant mice demonstrated delayed endochondral and intramembranous bone formation, whereas heterozygous Pkd1m1Bei mutant mice had osteopenia caused by reduced osteoblastic function. Heterozygous and homozygous Pkd1m1Bei mutant mice displayed a gene dose-dependent decrease in the expression of Runx2 and osteoblast-related genes. In addition, overexpression of constitutively active PC1 C-terminal constructs in MC3T3-E1 osteoblasts resulted in an increase in Runx2 P1 promoter activity and endogenous Runx2 expression as well as an increase in osteoblast differentiation markers. Conversely, osteoblasts derived from Pkd1m1Bei homozygous mutant mice had significant reductions in endogenous Runx2 expression, osteoblastic markers, and differentiation capacity ex vivo. Co-expression of constitutively active PC1 C-terminal construct into Pkd1m1Bei homozygous osteoblasts was sufficient to normalize Runx2 P1 promoter activity. These findings are consistent with a possible functional role of cilia and PC1 in anabolic signaling in osteoblasts/osteocytes.

Local gene transfer to calcified tissue cells using prolonged infusion of a lentiviral vector

Gene transfer using viral vectors offers the potential for the sustained expression of proteins in specific target tissues. However, in the case of calcified tissues, in vivo delivery remains problematic because of limited accessibility. The aim of this study was to test the efficiency of lentiviral vectors (LVs) on osteogenic cells in vitro, and determine the feasibility of directly transducing resident bone cells in vivo. LVs encoding for green fluorescent protein (GFP) and ameloblastin (AMBN), a protein associated with mineralization not reported in bone, were generated. The transduction efficiency of the LVs was evaluated using the MC3T3 cell line and primary calvaria-derived osteogenic cells. For in vivo delivery, the LVs were infused using osmotic minipumps through holes created in the bone of the rat hemimandible and tibia. The production of GFP and AMBN in vitro and in vivo was monitored using fluorescence microscopy. Both transgenes were expressed in MC3T3 and primary osteogenic cells. In vivo, GFP was detected at the infusion site and fibroblast-like cells, osteoblasts, osteocytes and osteoclasts expressed AMBN. Our data demonstrate, for the first time, that primary osteogenic cells are efficiently transduced with LVs and that their infusion is advantageous for locally delivering DNA to bone cells.

Maxillary sinus augmentation with Bio-Oss particles: a light, scanning, and transmission electron microscopy study in man

Biological interactions occurring at the bone-biomaterial interface are critical for long-term clinical success. Bio-Oss is a deproteinized, sterilized bovine bone that has been extensively used in bone regeneration procedures. The aim of the present study was a comparative light, scanning, and electron microscopy evaluation of the interface between Bio-Oss and bone in specimens retrieved after sinus augmentation procedures. Under light microscopy, most of the particles were surrounded by newly formed bone, while in a few cases, at the interface of some particles it was possible to observe marrow spaces and biological fluids. Under scanning electron microscopy, in most cases, the particle perimeter appeared lined by bone that was tightly adherent to the biomaterial surface. Transmission electron microscopy showed that the bone tissue around the biomaterial showed all the phases of the bone healing process. In some areas, randomly organized collagen fibers were present, while in other areas, newly formed compact bone was present. In the first bone lamella collagen fibers contacting the Bio-Oss surface were oriented at 243.73 +/- 7.12 degrees (mean +/- SD), while in the rest of the lamella they were oriented at 288.05 +/- 4.86 degrees (mean +/- SD) with a statistically significant difference of 44.32 degrees (p < 0.001). In the same areas the intensity of gray value was 172.56 +/- 18.15 (mean +/- SD) near the biomaterial surface and 158.71 +/- 21.95 (mean +/- SD) in the other part of the lamella with an unstatistically significant difference of 13.79 (p = 0.071). At the bone-biomaterial interface there was also an electron-dense layer similar to cement lines. This layer had a variable morphology being, in some areas, a thin line, and in other areas, a thick irregular band. The analyses showed that Bio-Oss particles do not interfere with the normal osseous healing process after sinus lift procedures and promote new bone formation. In conclusion, this study serves as a better understanding of the morphologic characteristics of Bio-Oss and its interaction with the surrounding tissues.

Sequence of protein expression of bone sialoprotein and osteopontin at the developing interface between repair cementum and dentin in human deciduous teeth

Experimental periodontal regeneration studies have revealed the weak binding of repair cementum to the root surface, whereas attachment of cementum to dentin preconditioned by odontoclasts appears to be superior. The aim of this study has been, therefore, to analyze the structural and partial biochemical nature of the interface that develops between resorbed dentin and repair cementum by using human deciduous teeth as a model. Aldehyde-fixed and decalcified tooth samples were embedded in acrylic or epoxy resins and sectioned for light and transmission electron microscopy. Antibodies against bone sialoprotein (BSP) and osteopontin (OPN), two noncollagenous proteins accumulating at hard tissue interfaces in bone and teeth, were used for protein A-gold immunocytochemistry. Light microscopy revealed a gradually increasing staining intensity of the external dentin matrix starting after the withdrawal of the odontoclast. Labeling for both BSP and OPN was first detected among the exposed collagen fibrils and in the intratubular dentin matrix when odontoclasts had withdrawn but mesenchymal cells were present. Subsequently, collagen fibrils of the repair cementum were deposited concomitantly with the appearance of labeling for BSP and OPN over the intratubular, intertubular, and peritubular dentin matrix. Labeled mineralization foci indicated the advancing mineralization front, and the collagenous repair matrix became integrated in an electron-dense organic material that showed labeling for BSP and OPN. Thus, no distinct planar interfacial matrix layer lies between the resorbed dentin and the repair cementum. The results suggest that odontoclasts precondition the dentin matrix such that the repair cementum becomes firmly attached.

Nanotexturing of titanium-based surfaces upregulates expression of bone sialoprotein and osteopontin by cultured osteogenic cells

Bone formation around implants is influenced by surface geometry. Since cell/matrix/substrate interactions associated with cell signaling occur in the nanoscale dimension, we have evaluated the influence of nanotexturing of titanium-based surfaces on the expression of matrix proteins by cultured osteogenic cells at initial time points. Cells were obtained by enzymatic digestion of newborn rat calvaria and grown on titanium and titanium alloy discs with nanotextured or machined surfaces, and on glass coverslips for periods of 6 h, 1 day, and 3 days, under standard culture conditions. Cultures were processed for single or dual immunolabeling with monoclonal and/or polyclonal antibodies against bone sialoprotein (BSP), fibronectin (FN), osteopontin (OPN), type-I pro-collagen, or tubulin, followed by corresponding fluorophore-conjugated secondary antibodies. Some samples were processed for scanning electron microscope analysis of morphology and immunogold labeling. After 6 h, nanotextured surfaces exhibited up to a nine-fold increase in the proportion of cells with peripheral OPN labeling. At day 3, the proportion of OPN and BSP labeled cells was higher, and the intensity of immunoreactivity dramatically increased. No significant differences were observed in the expression pattern and the proportion of cells immunoreactive for FN or type-I pro-collagen. Our results demonstrate that nanotexturing of titanium-based surfaces upregulates the early expression of BSP and OPN in osteogenic cell cultures.

Origin-associated features of chondrocytes in mouse Meckel's cartilage and costal cartilage: an in vitro study

Using a cell culture method, we histochemically and immunohistochemically investigated whether chondrocytes deriving from different origins, such as Meckel's or costal cartilages, express similar phenotypic characteristics. Chondrocytes isolated enzymatically from Meckel's and costal cartilages of 17-day embryonic mice both actively proliferated and formed cartilage nodules consisting of toluidine blue-positive proteoglycans and type II collagen. Both deposited calcified cartilaginous matrix as revealed by alkaline phosphatase (ALPase) activity and alizarin red staining throughout 3 weeks in culture. Immunostaining for osteopontin (OP), osteocalcin (OC), and osteonectin (ON) revealed that chondrocytes from both cartilages were positive for their proteins, but type I collagen was detected only in cells transforming from Meckel's chondrocytes late in the culture. Electron microscopy demonstrated that although costal and Meckel's chondrocytes had typical chondrocytic features during 2 weeks in culture, Meckel's chondrocytes transformed into osteocytic cells that produced thick, banded type I collagen fibrils. In contrast, costal chondrocytes maintained typical hypertrophic morphology throughout the final stage of culture. The present study suggests that Meckel's chondrocytes derived from neural crest-ectomesenchyme retain osteogenic potential, and differ from costal chondrocytes originating from mesoderm.

The attachment and growth behavior of osteoblast-like cells on microtextured surfaces

In previous studies, we showed that the application of microgrooves on a surface can direct cellular morphology and the deposition of mineralized matrix of osteoblast-like cells (Biomaterials 20 (1999) 1293; Clin. Oral Impl Res. 11 (2000) 325). In this study, we evaluated the attachment and growth behavior of these cells, using scanning- and transmission electron microscopy (SEM/TEM). Smooth and microgrooved polystyrene substrates were made (groove depth 0.5-1.5 microm, groove- and ridge width 1-10 microm). On these substrates, osteoblast-like cells were cultured for periods up to 16 days. SEM showed that the cells, and their extensions, closely followed the surface on smooth and wider grooved (>5 microm) substrates. In contrast, narrow grooves (<2 microm) were bridged. After 16 days of incubation, the matrix showed extensive deposition of collagen fibrils, and the formation of calcified nodules. With TEM it was shown that on the smooth and wider grooved substrates, focal adhesions were spread throughout the surface. However, on narrow grooves focal adhesions were always positioned on the edges of surface ridges only. Apparently, most extracellular matrix (ECM) was produced by the cells that directly adhered to the substrate. Deposition of ECM was seen in the surface grooves, as well as in between the cell layers. On basis of the current study and previous experiments, we conclude that microgrooves are able to influence bone cell behavior by (1) determining the alignment of cells and cellular extensions, (2) altering the formation and placement of cell focal adhesions, and (3) altering ECM production. Therefore, microgrooved surfaces seem interesting to be applied on bone-anchored implants.

Early expression of bone matrix proteins in osteogenic cell cultures

Osteogenic cells express some matrix proteins at early culture intervals. The aim of this study was to determine if, and in what proportion, cells used for plating contain bone sialoprotein (BSP) and osteopontin (OPN), two matrix proteins associated with initial events in bone formation. Their pattern of expression, as well as that of fibronectin (FN) and type I pro-collagen, was also examined at 6 hr and at 1 and 3 days. The cells were obtained by enzymatic digestion of newborn rat calvariae, and grown on glass coverslips. Cytocentrifuge preparations of isolated cells and coverslips were processed for single or dual immunolabeling with monoclonal and/or polyclonal primary antibodies, followed by fluorochrome-conjugated antibodies. The cell labeling was mainly associated with perinuclear elements. OPN was also distinctively found at peripheral cytoplasmic sites. About 31% of isolated cells were OPN-positive and 18% were BSP-positive. After 1 day, almost 50% of cells were immunoreactive for OPN and for type I pro-collagen, and still less than 20% reacted for BSP. Approximately 7% exhibited peripheral staining for OPN. Almost all cells were associated with extracellular FN. However, only 15% showed intracellular labeling. These results indicate that an important proportion of cells used for plating contain BSP and OPN, a situation that should be taken into consideration in experimental analyses of osteoblast activity in vitro.

Quantitative immunogold labeling of bone sialoprotein and osteopontin in methylmethacrylate-embedded rat bone

Methylmethacrylate (MMA) embedding of undecalcified bone is routinely employed for histomorphometric analyses. Although MMA-embedded bone has been used for immunolabeling at the light microscopic level after removal of the resin, there are no such reports for electron microscopy. The aim of the present study was to determine whether MMA embedding can be used for ultrastructural immunolabeling and how it compares to LR White (LRW), an acrylic resin frequently used for immunocytochemistry of bone. Rat tibiae were fixed by vascular perfusion with aldehyde and embedded either in MMA or LRW resin. Thin sections were processed for postembedding protein A-gold immunolabeling with antibodies to rat bone sialoprotein (BSP) and osteopontin (OPN). The density of gold particles over bone was quantified. The density and distribution of immunolabeling for BSP and OPN respectively, were comparable between MMA and LRW. These results indicate that MMA performs as well as LRW for the ultrastructural immunolabeling of noncollagenous bone matrix proteins.

Immunodetection of osteopontin at sites of resorption in the pulp of rat molars

Osteopontin (OPN) has been proposed to act as a substrate for osteoclast adhesion during bone resorption. The aim of the present study was to examine the presence and distribution of OPN at sites of resorption in traumatized radicular pulp. The upper first molars of 6-week-old male Sprague-Dawley rats were luxated and then repositioned in the original sockets. The animals were sacrificed by intracardiac perfusion at 10 and 14 days after tooth reimplantation. The teeth were decalcified in EDTA and then processed for embedding in paraffin for histochemistry or LR White resin for immunocytochemistry. Odontoclasts were identified by their multinucleated morphology and expression of tartrate-resistant acid phosphatase (TRAP). Osteopontin was immunolocalized using postembedding colloidal gold labeling with a chicken egg yolk anti-rat OPN antibody. After reimplantation of the teeth, TRAP-positive cells were present along the pulp dentin wall. Osteopontin was not consistently detected at exposed predentin/dentin surfaces. However, gold particles were often found at the margin of resorption lacunae. Labeling was also seen over the Golgi region and cytoplasmic vesicles of odontoclasts and of neutrophils and fibroblast-like cells. The results suggest that accumulation of OPN at the predentin/dentin surface is not a prerequisite for adhesion of odontoclasts to the wall substance and that recruited odontoclasts produce OPN locally to mediate cell and/or matrix events within the resorption lacuna.

High-resolution immunocytochemistry of noncollagenous matrix proteins in rat mandibles processed with microwave irradiation

The mineral phase in calcified tissues represents an additional factor to be considered during their preservation for ultrastructural analyses. Microwave (MW) irradiation has been shown to facilitate fixative penetration and to improve structural preservation and immunolabeling in a variety of soft tissues. The aim of the present study was to determine whether MW processing could offer similar advantages for hard tissues. Rat hemimandibles were immersed in 4% formaldehyde + 0.1% glutaraldehyde buffered with 0.1 M sodium cacodylate, pH 7.2, and exposed to MWs for three periods of 5 min at temperatures not exceeding 37C. They were then decalcified in 4.13% EDTA, pH 7.2, for 15 hr, also under MW irradiation. Osmicated and non-osmicated samples were dehydrated in graded concentrations of ethanol and embedded in LR White resin. Sections of incisor, molars, and alveolar bone were processed for postembedding colloidal gold immunolabeling using antibodies against ameloblastin, amelogenin, bone sialoprotein, or osteopontin. Ultrastructural preservation of tissues was in most cases comparable to that obtained by perfusion-fixation, and there was no difference in distribution of labeling with those previously reported for the antibodies used. However, the immunoreactivities obtained were generally more intense, particularly at early stages of tooth formation. Amelogenin was abundant between differentiating ameloblasts and labeling for osteopontin appeared over the Golgi apparatus of odontoblasts after initiation of dentine mineralization. We conclude that MW irradiation represents a simple method that can accelerate the processing of calcified tissues while yielding good structural preservation and antigen retention. (J Histochem Cytochem 49:1099-1109, 2001)

A histomorphometric, structural, and immunocytochemical study of the effects of diet-induced hypocalcemia on bone in growing rats

Despite several studies on the effect of calcium deficiency on bone status, there is relatively little information on the ensuing histological alterations. To investigate bone changes during chronic hypocalcemia, weanling rats were kept on a calcium-free diet and deionized water for 28 days while control animals were fed normal chow. The epiphyseal-metaphyseal region of the tibiae were processed for histomorphometric, histochemical, and structural analyses. The distribution of bone sialoprotein (BSP), osteocalcin (OC), and osteopontin (OPN), three noncollagenous bone matrix proteins implicated in cell-matrix interactions and regulation of mineral deposition, was examined using postembedding colloidal gold immunocytochemistry. The experimental regimen resulted in serum calcium levels almost half those of control rats. Trabecular bone volume showed no change but osteoid exhibited a significant increase in all its variables. There were a multitude of mineralization foci in the widened osteoid seam, and intact matrix vesicles were observed in the forming bone. Many of the osteoblasts apposed to osteoid were tartrate-resistant acid phosphatase (TRAP)- and alkaline phosphatase-positive, whereas controls showed few such TRAP-reactive cells. Osteoclasts in hypocalcemic rats generally exhibited poorly developed ruffled borders and were inconsistently apposed to bony surfaces showing a lamina limitans. Sometimes osteoclasts were in contact with osteoid, suggesting that they may resorb uncalcified matrix. Cement lines at the bone-calcified cartilage interface in some cases were thickened but generally did not appear affected at bone-bone interfaces. As in controls, electron-dense portions of the mineralized matrix showed labeling for BSP, OC, and OPN but, in contrast, there was an abundance of immunoreactive mineralization foci in osteoid of hypocalcemic rats. These data suggest that chronic hypocalcemia affects both bone formation and resorption.