Matrix vesicle calcification in bones of adult rats

Hydrogenated silicene nanosheet functionalized scaffold enables immuno-bone remodeling

An ideal implant needs to have the ability to coordinate the foreign body response and tissue regeneration. Here, Hydrogenated-silicon nanosheets (H-Si NSs) with favorable biodegradability are integrated and functionalized into a β-tricalcium phosphate scaffold (H-Si TCP) for bone defect healing. H-Si TCP can greatly improve bone regeneration through osteoimmunomodulation-guided biodegradation in vivo. The spatiotemporal regulation of degradation products replenishes sufficient nutrients step by step for the entire process of bone repair. Extracellular and intracellular reactive oxygen species (ROS) are first downregulated by reaction with H-Si NSs, followed by marked M2 polarization, remodeling the micro-environment timely for immune-bone regeneration. The release of primary reaction products awakened bone marrow mesenchymal stem cells (BMSCs), which are converted into osteoblasts anchored on scaffolds. Subsequently, biomineralization is promoted by the final degradation products. The intrinsic ROS-responsive, immunoregulatory, and osteo-promotive capability of 2D H-Si NSs makes such composite H-Si TCP scaffold a highly potential alternative for the treatment of critical bone defect.

Matrix vesicles from dental follicle cells improve alveolar bone regeneration via activation of the PLC/PKC/MAPK pathway

Background

The regeneration of bone loss that occurs after periodontal diseases is a significant challenge in clinical dentistry. Extracellular vesicles (EVs)-based cell-free regenerative therapies represent a promising alternative for traditional treatments. Developmental biology suggests matrix vesicles (MVs), a subtype of EVs, contain mineralizing-related biomolecules and play an important role in osteogenesis. Thus, we explore the therapeutic benefits and expect to find an optimized strategy for MV application.

Methods

Healthy human dental follicle cells (DFCs) were cultured with the osteogenic medium to generate MVs. Media MVs (MMVs) were isolated from culture supernatant, and collagenase-released MVs (CRMVs) were acquired from collagenase-digested cell suspension. We compared the biological features of the two MVs and investigated their induction of cell proliferation, migration, mineralization, and the modulation of osteogenic genes expression. Furthermore, we investigated the long-term regenerative capacity of MMVs and CRMVs in an alveolar bone defect rat model.

Results

We found that both DFC-derived MMVs and CRMVs effectively improved the proliferation, migration, and osteogenic differentiation of DFCs. Notably, CRMVs showed better bone regeneration capabilities. Compared to MMVs, CRMVs-induced DFCs exhibited increased synthesis of osteogenic marker proteins including ALP, OCN, OPN, and MMP-2. In the treatment of murine alveolar bone defects, CRMV-loaded collagen scaffold brought more significant therapeutic outcomes with less unhealing areas and more mature bone tissues in comparison with MMVs and acquired the effects resembling DFCs-based treatment. Furthermore, the western blotting results demonstrated the activation of the PLC/PKC/MAPK pathway in CRMVs-induced DFCs, while this cascade was inhibited by MMVs.

Conclusions

In summary, our findings revealed a novel cell-free regenerative therapy for repairing alveolar bone defects by specific MV subtypes and suggest that PLC/PKC/MAPK pathways contribute to MVs-mediated alveolar bone regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02721-6.

Bioinspired mineralized collagen scaffolds for bone tissue engineering

Successful regeneration of large segmental bone defects remains a major challenge in clinical orthopedics, thus it is of important significance to fabricate a suitable alternative material to stimulate bone regeneration. Due to their excellent biocompatibility, sufficient mechanical strength, and similar structure and composition of natural bone, the mineralized collagen scaffolds (MCSs) have been increasingly used as bone substitutes via tissue engineering approaches. Herein, we thoroughly summarize the state of the art of MCSs as tissue-engineered scaffolds for acceleration of bone repair, including their fabrication methods, critical factors for osteogenesis regulation, current opportunities and challenges in the future. First, the current fabrication methods for MCSs, mainly including direct mineral composite, in-situ mineralization and 3D printing techniques, have been proposed to improve their biomimetic physical structures in this review. Meanwhile, three aspects of physical (mechanics and morphology), biological (cells and growth factors) and chemical (composition and cross-linking) cues are described as the critical factors for regulating the osteogenic feature of MCSs. Finally, the opportunities and challenges associated with MCSs as bone tissue-engineered scaffolds are also discussed to point out the future directions for building the next generation of MCSs that should be endowed with satisfactorily mimetic structures and appropriately biological characters for bone regeneration.

Extracellular Vesicles in Musculoskeletal Pathologies and Regeneration

The incidence of musculoskeletal diseases is steadily increasing with aging of the population. In the past years, extracellular vesicles (EVs) have gained attention in musculoskeletal research. EVs have been associated with various musculoskeletal pathologies as well as suggested as treatment option. EVs play a pivotal role in communication between cells and their environment. Thereby, the EV cargo is highly dependent on their cellular origin. In this review, we summarize putative mechanisms by which EVs can contribute to musculoskeletal tissue homeostasis, regeneration and disease, in particular matrix remodeling and mineralization, pro-angiogenic effects and immunomodulatory activities. Mesenchymal stromal cells (MSCs) present the most frequently used cell source for EV generation for musculoskeletal applications, and herein we discuss how the MSC phenotype can influence the cargo and thus the regenerative potential of EVs. Induced pluripotent stem cell-derived mesenchymal progenitor cells (iMPs) may overcome current limitations of MSCs, and iMP-derived EVs are discussed as an alternative strategy. In the last part of the article, we focus on therapeutic applications of EVs and discuss both practical considerations for EV production and the current state of EV-based therapies.

Autophagy Regulates Craniofacial Bone Acquisition

Increasing evidence has demonstrated the important role of autophagy in skeletal homeostasis; however, the role of autophagy in craniofacial bone development and acquisition is largely unknown. In this study, we investigated the effect of autophagy suppression on craniofacial bone acquisition by deleting Fip200 or Atg5, two essential autophagy genes, using Osterix-Cre (Osx-Cre). We found that the Osx-Cre transgene mildly decreased the bone mass of parietal bone but not frontal bone, and did not affect cranial base bone mass in adult mice. In the cranial vault, Fip200 or Atg5 deletion similarly decreased 50% bone mass of neural crest-derived frontal bone; Atg5 deletion decreased 50% and Fip200 deletion decreased 30% bone mass of mesoderm-derived parietal bone. In the cranial base, Fip200 or Atg5 deletion similarly decreased 30% bone mass of neural crest-derived presphenoid bone; Atg5 deletion decreased 30% and Fip200 deletion decreased 16% bone mass of mesoderm-derive basioccipital bone. Lastly, we used doxycycline treatment to inhibit the Osx-Cre expression until 2 months of age and showed that postnatal Fip200 deletion led to cranial vault bone mass decrease in association with a small increase in both bone volume/tissue volume and tissue mineral density. Altogether, this study demonstrated the important role of autophagy in craniofacial bone acquisition during development and postnatal growth.

Extracellular vesicles are integral and functional components of the extracellular matrix

Extracellular vesicles (EV) are small plasma membrane-derived particles released into the extracellular space by virtually all cell types. Recently, EV have received increased interest because of their capability to carry nucleic acids, proteins, lipids and signaling molecules and to transfer their cargo into the target cells. Less attention has been paid to their role in modifying the composition of the extracellular matrix (ECM), either directly or indirectly via regulating the ability of target cells to synthesize or degrade matrix molecules. Based on recent results, EV can be considered one of the structural and functional components of the ECM that participate in matrix organization, regulation of cells within it, and in determining the physical properties of soft connective tissues, bone, cartilage and dentin. This review addresses the relevance of EV as specific modulators of the ECM, such as during the assembly and disassembly of the molecular network, signaling through the ECM and formation of niches suitable for tissue regeneration, inflammation and tumor progression. Finally, we assess the potential of these aspects of EV biology to translational medicine.

Matrix vesicles: Are they anchored exosomes?

Numerous studies have documented that matrix vesicles are unique extracellular membrane-bound microparticles that serve as initial sites for mineral formation in the growth plate and most other vertebrate mineralizing tissues. Microparticle generation is not confined to hard tissues, as cells in soft tissues generate similar structures; numerous studies have shown that a common type of extracellular particle, termed an exosome, a product of the endosomal pathway, shares many characteristics of matrix vesicles. Indeed, analyses of size, morphology and lipid and protein content indicate that matrix vesicles and exosomes are homologous structures. Such a possibility impacts our understanding of the biogenesis, processing and function of matrix vesicles (exosomes) in vertebrate hard tissues and explains in part how cells control the earliest stages of mineral deposition. Moreover, since exosomes influence a spectrum of functions, including cell-cell communication, it is suggested that this type of microparticle may provide a mechanism for the transfer of signaling molecules between cells within the growth plate and thereby regulate endochondral bone development and formation.

Autophagy in osteoblasts is involved in mineralization and bone homeostasis

Bone remodeling is a tightly controlled mechanism in which osteoblasts (OB), the cells responsible for bone formation, osteoclasts (OC), the cells specialized for bone resorption, and osteocytes, the multifunctional mechanosensing cells embedded in the bone matrix, are the main actors. Increased oxidative stress in OB, the cells producing and mineralizing bone matrix, has been associated with osteoporosis development but the role of autophagy in OB has not yet been addressed. This is the goal of the present study. We first show that the autophagic process is induced in OB during mineralization. Then, using knockdown of autophagy-essential genes and OB-specific autophagy-deficient mice, we demonstrate that autophagy deficiency reduces mineralization capacity. Moreover, our data suggest that autophagic vacuoles could be used as vehicles in OB to secrete apatite crystals. In addition, autophagy-deficient OB exhibit increased oxidative stress and secretion of the receptor activator of NFKB1 (TNFSF11/RANKL), favoring generation of OC, the cells specialized in bone resorption. In vivo, we observed a 50% reduction in trabecular bone mass in OB-specific autophagy-deficient mice. Taken together, our results show for the first time that autophagy in OB is involved both in the mineralization process and in bone homeostasis. These findings are of importance for mineralized tissues which extend from corals to vertebrates and uncover new therapeutic targets for calcified tissue-related metabolic pathologies.

The role of intracellular calcium phosphate in osteoblast-mediated bone apatite formation

Mineralization is a ubiquitous process in the animal kingdom and is fundamental to human development and health. Dysfunctional or aberrant mineralization leads to a variety of medical problems, and so an understanding of these processes is essential to their mitigation. Osteoblasts create the nano-composite structure of bone by secreting a collagenous extracellular matrix (ECM) on which apatite crystals subsequently form. However, despite their requisite function in building bone and decades of observations describing intracellular calcium phosphate, the precise role osteoblasts play in mediating bone apatite formation remains largely unknown. To better understand the relationship between intracellular and extracellular mineralization, we combined a sample-preparation method that simultaneously preserved mineral, ions, and ECM with nano-analytical electron microscopy techniques to examine osteoblasts in an in vitro model of bone formation. We identified calcium phosphate both within osteoblast mitochondrial granules and intracellular vesicles that transported material to the ECM. Moreover, we observed calcium-containing vesicles conjoining mitochondria, which also contained calcium, suggesting a storage and transport mechanism. Our observations further highlight the important relationship between intracellular calcium phosphate in osteoblasts and their role in mineralizing the ECM. These observations may have important implications in deciphering both how normal bone forms and in understanding pathological mineralization.

Tooth dentin defects reflect genetic disorders affecting bone mineralization

Several genetic disorders affecting bone mineralization may manifest during dentin mineralization. Dentin and bone are similar in several aspects, especially pertaining to the composition of the extracellular matrix (ECM) which is secreted by well-differentiated odontoblasts and osteoblasts, respectively. However, unlike bone, dentin is not remodelled and is not involved in the regulation of calcium and phosphate metabolism. In contrast to bone, teeth are accessible tissues with the shedding of deciduous teeth and the extractions of premolars and third molars for orthodontic treatment. The feasibility of obtaining dentin makes this a good model to study biomineralization in physiological and pathological conditions. In this review, we focus on two genetic diseases that disrupt both bone and dentin mineralization. Hypophosphatemic rickets is related to abnormal secretory proteins involved in the ECM organization of both bone and dentin, as well as in the calcium and phosphate metabolism. Osteogenesis imperfecta affects proteins involved in the local organization of the ECM. In addition, dentin examination permits evaluation of the effects of the systemic treatment prescribed to hypophosphatemic patients during growth. In conclusion, dentin constitutes a valuable tool for better understanding of the pathological processes affecting biomineralization.

Characterization of the calcification process modeled in rat embryonic calvarial culture

An organ culture system to model the physiological calcification process was designed using rat embryonic calvaria as a device for analyzing its mechanism. Standardized calvarial explants were dissected from rat embryos aged 18 and 20 days (E18 and E20) and cultured for 1, 3 and 5 days. The calcium content of the cultured explants was quantified by atomic absorption spectrophotometry. Equivalent explants were fixed, embedded in paraffin, sectioned and stained with von Kossa stain combined with hematoxylin-eosin or processed for energy-dispersive X-ray spectroscopy to determine the concentrations of calcium, phosphorus and carbon in the tissue. The total calcium content increased significantly in E18 and E20 cultured calvaria (E18cc and E20cc) over 5 days of culture. All cultured calvaria were von Kossa-positive, whereas the staining was intensified, and sound osteoblasts and osteocytes were observed in the bone matrix only in E18cc during the 5-day culture period. Concentrations of calcium and carbon increased significantly in E18cc over 5 days, whereas E20 showed little increase. Physiological calcification proceeded in E18cc, but not in E20cc. These results indicate that the organ culture system using E18 calvaria is useful for modeling the physiological calcification process in vitro.

In vitro calcification of chemically functionalized carbon nanotubes

Bone is composed of two phases. The organic phase is made of collagen fibrils assembled in broad fibers acting as a template for mineralization. The mineral phase comprises hydroxyapatite (HAP) crystals grown between and inside the collagen fibers. We have developed a biomimetic material using functionalized carbon nanotubes as scaffold to initiate in vitro mineralization. Biomimetic formation of HAP was performed on single-walled carbon nanotubes (SWCNTs) which have been grafted with carboxylic groups. Two types of nanotubes, HiPco(R) and Carbon Solutions(R), were oxidized via various acidic processes, leading to five different groups of carboxylated nanotubes, fully characterized by physical methods (thermogravimetric analysis, attenuated total reflectance infrared spectroscopy and X-ray photoelectron spectroscopy). All samples were dispersed in ultra-pure water and incubated for 2weeks in a synthetic body fluid, in order to induce the calcification of the SWCNTs. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis studies showed that Ca(2+) and PO(4)(3-) ions were deposited as round-shaped nodules (calcospherites) on the carboxylated SWCNTs. Fourier transform infrared and Raman spectroscopic studies confirmed the HAP formation, and image analysis made on SEM pictures showed that calcospherites and carboxylated SWCNTs were packed together. The size of calcospherites thus obtained in vitro from the HiPco(R) series was close to that issued from calcospherites observed in vivo. Functionalization of SWCNTs with carboxylic groups confers the capacity to induce calcification similar to woven bone.

Dietary ungerminated and germinated soybean supplementation improves bone mineralization and strength in growing male rats

It has been thought that soybean products rich in phytoestrogenic isoflavones are effective in promoting bone metabolism in ovariectomized rats. However, it is not clear if such an effect can be changed by germination of soybean and can be observed in growing males. The present study was undertaken to determine the effects of different concentrations of dietary ungerminated and germinated soybean (UGS and GS, respectively) on bone metabolism in young male rats. Forty-nine 6-week-old male Sprague-Dawley rats were assigned to seven dietary treatment groups: AIN 93G (control); control with UGS powder at 3% (UGS-L), 15% (UGS-M), or 30% (UGS-H); and control with GS powder at 3% (GS-L), 15% (GS-M), or 30% (GS-H). The biomarkers of bone metabolism (plasma and urinary Ca and P) and the physical properties and mineral content of bones were measured. Plasma osteocalcin and urinary deoxypyridinoline levels were not affected by soybean diets. The plasma P level was significantly elevated by dietary soybeans (P < .001). However, there was a negative correlation (r = -0.555) between plasma P level and dietary UGS level (P < .01). Between the UGS and GS groups, the P level of the GS-M group was significantly higher than that of the UGS-M group (P < .001). The tibial weight was decreased with low to medium doses of soybeans, but not with higher levels. Femoral bone strength was improved in the UGS-H, GS-M, and GS-H groups. The P contents of femoral and tibial bones were increased in all UGS groups as well as in GS-M and GS-H groups. In conclusion, soybean supplementation in young growing male rats improved bone mineralization and bone strength.

Differential osteogenic activity of osteoprogenitor cells on HA and TCP/HA scaffold of tissue engineered bone

Biomaterial, an essential component of tissue engineering, serves as a scaffold for cell attachment, proliferation, and differentiation; provides the three dimensional (3D) structure and, in some applications, the mechanical strength required for the engineered tissue. Both synthetic and naturally occurring calcium phosphate based biomaterial have been used as bone fillers or bone extenders in orthopedic and reconstructive surgeries. This study aims to evaluate two popular calcium phosphate based biomaterial i.e., hydroxyapatite (HA) and tricalcium phosphate/hydroxyapatite (TCP/HA) granules as scaffold materials in bone tissue engineering. In our strategy for constructing tissue engineered bone, human osteoprogenitor cells derived from periosteum were incorporated with human plasma-derived fibrin and seeded onto HA or TCP/HA forming 3D tissue constructs and further maintained in osteogenic medium for 4 weeks to induce osteogenic differentiation. Constructs were subsequently implanted intramuscularly in nude mice for 8 weeks after which mice were euthanized and constructs harvested for evaluation. The differential cell response to the biomaterial (HA or TCP/HA) adopted as scaffold was illustrated by the histology of undecalcified constructs and evaluation using SEM and TEM. Both HA and TCP/HA constructs showed evidence of cell proliferation, calcium deposition, and collagen bundle formation albeit lesser in the former. Our findings demonstrated that TCP/HA is superior between the two in early bone formation and hence is the scaffold material of choice in bone tissue engineering.

Effect of bone sialoprotein and collagen coating on cell attachment to TICER and pure titanium implant surfaces

To improve integration between implants and biological tissues, this study compared bone sialoprotein (BSP) as a surface-coating material against the major organic and inorganic components of bone, collagen type I and hydroxyapatite (TICER). The expression of osteocalcin, osteonectin and transforming growth factor ss was evaluated using immunohistochemical staining procedures. The distribution patterns of osteoblasts on the surface of pure titanium with a smooth machined surface and a rough surface (TICER) were determined by image processing using confocal laser scanning microscopy. The results compared to uncoated control materials showed that, at all times investigated, the number of cells on the surface of the TICER and pure titanium samples differed significantly (P<0.1), demonstrating the superiority of TICER over pure titanium in this respect. For pure titanium implants, collagen-precoated surfaces were not beneficial for the attachment of bone-derived cells with the exception of day 3 in vitro (P<0.01). BSP-precoated implant surfaces displayed non-significantly higher numbers of settled cells. BSP-precoated implant surfaces were beneficial for osteoinduction as revealed by osteocalcin and osteonectin expression. BSP precoating of the rough TICER implant surface enhanced the osteoinductive effect much more than did collagen precoating. These results contribute to the consideration of at least two distinct pathways of osseointegration.

A new class of bioactive and biodegradable soybean-based bone fillers

The reconstruction of large bone defects in periodontal, maxillofacial, and orthopedic surgery relies on the implantation of biomaterials able to support the growth of new tissue. None of the materials currently available is able to combine all the properties required, which are (i) easy handling, (ii) biodegradation, (iii) low immunogenicity, and more importantly, (iv) induction of tissue regeneration. A new class of biodegradable biomaterials has been obtained by simple thermosetting of defatted soybean curd. The final material can be processed into films, porous scaffolds, and granules for different surgical needs. When incubated in physiological solutions the material shows water uptake of 80%, elongation at break of 0.9 mm/mm, and 25% (w/w) degradation in 7 days. Soybean-based biomaterial granules are shown to reduce the activity of the monocytes/macrophages and of the osteoclasts and to induce osteoblast differentiation in vitro, thus demonstrating a bone regeneration potential suitable for many clinical applications.

A model of the early mineralization process of mantle dentin

The aim of this study was to investigate the relationship between proteoglycans (PGs) and collagen fibrils at the early mineralization process of mantle dentin. Ten first molar dental germs of rats were removed and fixed in glutaraldehyde/formaldehyde in cacodylate buffer and post-fixed in osmium tetroxide. The samples were dehydrated and embedded in epoxy resin. Ultrathin sections were contrasted and analyzed in TEM before and after treatment with EDTA, chondroitinases AC and ABC. After EDTA treatment, a electrondense substance associated with collagen fibril was removed, and did not stain again. A high magnification of these areas showed globular structures with 15 nm diameter surrounding collagen fibrils. In advanced mineralization areas, collagen fibrils showed a banded pattern and at high magnification the fibrils presented a light 10 nm ring inside and a dark 10 nm ring outside. After chondroitinase treatment, the electrondense substance associated with collagen fibrils was removed, showing a banded pattern of clear and dark areas along them. From morphological data, the authors proposed a model of interaction between PGs and collagen fibrils, where glicosaminoglycans chains are inside the fibrils, while the protein core remains outside. That stereochemical arrangement would start the crystal nucleation.

Soluble factors released by ATDC5 cells affect the formation of calcium phosphate crystals

During biomineralization the organism controls the nature, orientation, size and shape of the mineral phase. The aim of this study was to investigate whether proteins or vesicles that are constitutively released by growing ATDC5 cells have the ability to affect the formation of the calcium phosphate crystal. Therefore, subconfluent cultured ATDC5 cells were incubated for 1 h in medium without serum. Subsequently, medium was harvested and incubated for 24 h in the presence of additional Pi. This resulted in the formation of flat mineralizing structures (FMS), consisting of complex irregularly shaped flat crystals, which occasionally contained fiber-like structures ( approximately 40 microm in size). Without pre-incubation of medium with cells, only small punctate (dot like) calcium phosphate precipitates were observed. The formation of FMS was shown to be caused by soluble factors released by subconfluent ATDC5 cells. Proteomic analysis by mass spectrometry showed that FMS contained a specific set intracellular proteins, serum proteins, and extracellular matrix proteins. Bulk cytosolic proteins derived from homogenized cells or serum proteins did, however, not induce the formation of FMS. Conditioned medium from HeLa, CHO K1, RAW 264.7 and MDCK cells was also capable to form FMS under our experimental conditions. Therefore the formation of FMS seems to be caused by specific soluble factors constitutively released by ADTC5 and other cells. This in vitro model system can be used as a tool to identify factors that affect the shape of the biomineral phase.

Contribution of matrix vesicles and alkaline phosphatase to ectopic bone formation

Endochondral calcification involves the participation of matrix vesicles (MVs), but it remains unclear whether calcification ectopically induced by implants of demineralized bone matrix also proceeds via MVs. Ectopic bone formation was induced by implanting rat demineralized diaphyseal bone matrix into the dorsal subcutaneous tissue of Wistar rats and was examined histologically and biochemically. Budding of MVs from chondrocytes was observed to serve as nucleation sites for mineralization during induced ectopic osteogenesis, presenting a diameter with Gaussian distribution with a median of 306 +/- 103 nm. While the role of tissue-nonspecific alkaline phosphatase (TNAP) during mineralization involves hydrolysis of inorganic pyrophosphate (PPi), it is unclear how the microenvironment of MV may affect the ability of TNAP to hydrolyze the variety of substrates present at sites of mineralization. We show that the implants contain high levels of TNAP capable of hydrolyzing p-nitrophenylphosphate (pNPP), ATP and PPi. The catalytic properties of glycosyl phosphatidylinositol-anchored, polidocanol-solubilized and phosphatidylinositol-specific phospholipase C-released TNAP were compared using pNPP, ATP and PPi as substrates. While the enzymatic efficiency (k cat/Km) remained comparable between polidocanol-solubilized and membrane-bound TNAP for all three substrates, the k cat/Km for the phosphatidylinositol-specific phospholipase C-solubilized enzyme increased approximately 108-, 56-, and 556-fold for pNPP, ATP and PPi, respectively, compared to the membrane-bound enzyme. Our data are consistent with the involvement of MVs during ectopic calcification and also suggest that the location of TNAP on the membrane of MVs may play a role in determining substrate selectivity in this micro-compartment.

The soybean isoflavone genistein induces differentiation of MG63 human osteosarcoma osteoblasts

A soybean-rich diet was shown to reduce the incidence of osteoporosis in Eastern countries; its effect on bone metabolism was ascribed to the action of the soybean isoflavones such as genistein. Although many studies have shown isoflavone-induced osteoblast differentiation, its preventative action on bone mass loss has not been clarified. Here, the osteogenetic effects of genistein on human cell line MG63 osteoblasts were elucidated using a variety of approaches. In particular, phalloidin-rhodamine staining revealed that genistein-treated osteoblasts possessed a more organized cytoskeleton, and genistein's inhibitory effect upon cell proliferation was associated with exposure of phosphatidylserines on the external plasmalemma surface. Although this phosphatidylserine exposure is considered a typical apoptotic marker, scanning and transmission electron microscopy revealed that genistein-treated osteoblasts released matrix vesicles and showed no evidence of chromatin condensation. Assays, stainings, and scanning electron microscopy showed that genistein-treated osteoblasts synthesized relatively high levels of collagen and alkaline phosphatase and, even in a nonosteogenic growth medium, formed mineralized bone noduli. A clear pattern of genistein-induced osteoblast activation therefore emerges, in which all of the essential components required for the rapid production of mineralized bone extracellular matrix are stimulated by this soybean isoflavone.

Effects of phosphatidylserine coatings on titanium on inflammatory cells and cell-induced mineralisation in vitro

Ideally an active bone biomaterial should increase the mineralisation rate at the bone healing sites, keeping at the same time the inflammation process to levels required for tissue regeneration. Our studies suggest that in addition to improving the nucleation process for new bone formation, coating titanium with phospholipids may reduce the inflammatory response, which was shown to vary depending on the formulation employed. As phosphatidylserine reduced the inflammatory response to the greatest extent, in the second part of this study we examined its effect on osteoblast mineralisation. These studies demonstrated that phosphatidylserine improves the nucleation process for bone formation, by promoting the formation of bone-like tissue, so the high mineralisation potential of phosphatidylserine-coated titanium, together with the lower level of inflammatory response, supports the further development of this technology for coating osteointegrative devices.

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.

Quantitation of soluble and skeletal alkaline phosphatase, and insoluble alkaline phosphatase anchor-hydrolase activities in human serum

BACKGROUND

The current studies were intended to compare the circulating levels of total and anchorless (soluble) skeletal and hepatic ALP isoenzyme activities, and insoluble ALP anchor-hydrolase activity in serum of postmenopausal women.

METHODS

Preliminary studies of the insoluble ALP anchor-hydrolase activity in serum revealed a pH optimum of pH 5-6.5, a sensitivity to inactivation by heat at temperatures >45 degrees C (t(1/2)=8-9 min at 60 degrees C), and an apparent K(M) (at pH 7.5) of 40-45 mU/ml of insoluble skeletal ALP activity.

RESULTS

Serum analyses showed that 94.5+/-0.5% (mean+/-SEM) of the ALP activity in serum was in the anchorless, soluble form. The data were also consistent with the notion that the amount of insoluble ALP anchor-hydrolase activity in serum, 52.8+/-0.8 U/l (mean+/-SEM), was sufficient for the conversion of anchor-intact (insoluble) ALP into the anchorless, soluble form, assuming activation by serum lipids and/or bile salts. Distributions of results for total, skeletal, hepatic, and insoluble ALP anchor-hydrolase activity were skewed toward the higher range and leptokurtotic (p<0.01 for each). Total ALP activity ranged from 42% to 208% of the group mean value; skeletal, hepatic, and insoluble ALP anchor-hydrolase activities ranged from 5% to 306%, 33% to 277%, and 2% to 325%, respectively. In contrast, the soluble ALP fraction only ranged from 71% to 106% of the group mean value.

CONCLUSIONS

The correlations between the total and both skeletal (r=0.711, p<0.001) and hepatic (r=0.782, p<0.001) ALP isoform activities were predictive. Although correlations were also observed between insoluble ALP anchor-hydrolase activity and total (r=0.197, p<0.001), hepatic (r=0.184, p<0.001) and skeletal ALP activities (r=0.118, p<0.05), those relationships were not predictive (r(2)<0.04).