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At least 613 records · Page 34Linked to original sources

PubMed2004

Insulin-like growth factor II induces apoptosis in osteoblasts.

The ability of insulin-like growth factor II (IGF-II) to modulate apoptosis was studied in murine osteoblasts. At 72 h of culture, 0.01, 0.1, and 1.0 nM IGF-II produced a dose-dependent increase in apoptosis assayed by TdT-mediated dUTP-biotin nick end labeling (TUNEL) and confirmed with acridine orange-ethidium bromide staining. A maximal increase of 5.0-fold above control was found with 1 nM IGF-II. A time course of treatment with 0.1 nM IGF-II demonstrated a significant increase in apoptosis compared to vehicle-treated cells by 48 h. IGF-II-induced apoptosis could not be inhibited by a blocking antibody to the IGF-I receptor. Human osteoblast cultures demonstrated a similar dose-dependent increase in apoptosis with IGF-II. No significant effect of IGF-II was found on proliferation in murine osteoblast cultures. Western blot analysis demonstrated that IGF-II decreased Bcl-2 protein levels, but not Bax, resulting in a significant reduction in the Bcl-2/Bax ratio. To determine if overexpression of Bcl-2 could block IGF-II-induced apoptosis, osteoblasts were isolated from a transgenic mouse that overexpresses human Bcl-2 in bone through a construct utilizing the 2.3 kb promoter region of the Type I collagen gene linked to a 1.8 kb region of human Bcl-2 (Col2.3Bcl-2). At 72 h, IGF-II significantly increased apoptosis in a dose-dependent manner in osteoblast cultures from the control littermates. In osteoblasts from Col2.3Bcl-2 mice, no significant effect on apoptosis was found with 0.01, 0.1, or 1.0 nM IGF-II. Western blot analysis of Bcl-2 and Bax levels demonstrated a transient decrease in the Bcl-2/Bax ratio at 24 h with no decrease in the ratio at 48 or 72 h. Thus, IGF-II appears to promote osteoblast apoptosis, and overexpression of Bcl-2 is able to block IGF-II-induced apoptosis.

Animals↗

PubMed2006

Osteoclast inhibitory lectin (OCIL) inhibits osteoblast differentiation and function in vitro.

Osteoclast inhibitory lectin (OCIL) is a type II C-type lectin and binds NK cell-associated receptor Nkrp1d and sulfated glycosaminoglycans. OCIL is expressed by several cell types found in bone and inhibits osteoclast differentiation. To determine whether OCIL may have wider effects on bone metabolism, we examined the effects of recombinant soluble OCIL on cultured osteoblasts and pre-osteoblastic KUSA O cells. Although OCIL did not affect osteoblast proliferation or apoptosis, or the formation of alkaline phosphatase positive colonies in cultured bone marrow, OCIL profoundly inhibited mineralization by primary osteoblasts and KUSA O cells in vitro. Analysis of ascorbate-treated KUSA O cells showed that addition of OCIL reduced bone sialoprotein (BSP), osterix and osteocalcin mRNA expression, as well as alkaline phosphatase activity while, in contrast, expression of markers associated with the earlier stages of osteoblast maturation or the transcription factors Runx2, ATF4 and c-fos were not affected by OCIL treatment. Indeed, osteocalcin expression was strongly inhibited within 3 days in a dose-dependent manner, although after subsequent removal of OCIL, osteocalcin mRNA levels recovered within 4 days. OCIL treatment also reduced osteocalcin expression in BMP-2 stimulated C2C12 cells. In support of a role for OCIL in mineralization, OCIL anti-sense oligonucleotide treatment of KUSA O cells increased mineralization and osteocalcin expression. In addition, insulin-, dexamethasone- and IBMX-stimulated KUSA O cells undergo adipocyte differentiation and OCIL treatment greatly suppressed this process. Consistent with this, OCIL also reduced adiponectin and resistin mRNA expression in these cells. Our data indicate that OCIL reduces osteoblastic function in vitro and this may be due to an inhibitory effect on osteoblast maturation. In addition, the reduction of adipocyte formation in KUSA O cells by OCIL indicates that OCIL may have wider effects on the mesenchymal lineage that may be important for both bone metabolism and other connective tissue functions.

Adipogenesis↗

PubMed2005

Canonical Wnt signaling in differentiated osteoblasts controls osteoclast differentiation.

Inactivation of beta-catenin in mesenchymal progenitors prevents osteoblast differentiation; inactivation of Lrp5, a gene encoding a likely Wnt coreceptor, results in low bone mass (osteopenia) by decreasing bone formation. These observations indicate that Wnt signaling controls osteoblast differentiation and suggest that it may regulate bone formation in differentiated osteoblasts. Here, we study later events and find that stabilization of beta-catenin in differentiated osteoblasts results in high bone mass, while its deletion from differentiated osteoblasts leads to osteopenia. Surprisingly, histological analysis showed that these mutations primarily affect bone resorption rather than bone formation. Cellular and molecular studies showed that beta-catenin together with TCF proteins regulates osteoblast expression of Osteoprotegerin, a major inhibitor of osteoclast differentiation. These findings demonstrate that beta-catenin, and presumably Wnt signaling, promote the ability of differentiated osteoblasts to inhibit osteoclast differentiation; thus, they broaden our knowledge of the functions Wnt proteins have at various stages of skeletogenesis.

Animals↗

PubMed2006

Calcineurin/NFAT signaling in osteoblasts regulates bone mass.

Development and repair of the vertebrate skeleton requires the precise coordination of bone-forming osteoblasts and bone-resorbing osteoclasts. In diseases such as osteoporosis, bone resorption dominates over bone formation, suggesting a failure to harmonize osteoclast and osteoblast function. Here, we show that mice expressing a constitutively nuclear NFATc1 variant (NFATc1(nuc)) in osteoblasts develop high bone mass. NFATc1(nuc) mice have massive osteoblast overgrowth, enhanced osteoblast proliferation, and coordinated changes in the expression of Wnt signaling components. In contrast, viable NFATc1-deficient mice have defects in skull bone formation in addition to impaired osteoclast development. NFATc1(nuc) mice have increased osteoclastogenesis despite normal levels of RANKL and OPG, indicating that an additional NFAT-regulated mechanism influences osteoclastogenesis in vivo. Calcineurin/NFATc signaling in osteoblasts controls the expression of chemoattractants that attract monocytic osteoclast precursors, thereby coupling bone formation and bone resorption. Our results indicate that NFATc1 regulates bone mass by functioning in both osteoblasts and osteoclasts.

Animals↗

PubMed2006

Piceatannol stimulates osteoblast differentiation that may be mediated by increased bone morphogenetic protein-2 production.

Piceatannol (3,3',4,5'-tetrahydroxy-trans-stilbene) is a polyphenol present in grapes and wine. By means of alkaline phosphatase activity and osteocalcin enzyme-linked immunosorbent assay (ELISA), we have shown that piceatannol exhibits a significant induction of differentiation in immortalized fetal osteoblasts (hFOB), and osteosarcoma cells (MG-63). Alkaline phosphatase and osteocalcin are phenotypic markers for early-stage differentiated osteoblasts and terminally differentiated osteoblasts, respectively, our results indicate that piceatannol stimulate osteoblast differentiation at various stages (from maturation to terminally differentiated osteoblasts). Induction of differentiation by piceatannol was associated with increased bone morphogenetic protein-2 (BMP-2) production. Addition of purified BMP-2 protein did not increase the upregulation of alkaline phosphatase activity and osteocalcin secretion by piceatannol, whereas the BMP-2 antagonist noggin blocked piceatannol and BMP-2-mediated alkaline phosphatase activity, and osteocalcin secretion enhancement, indicating that BMP-2 production is required in piceatannol-mediated osteoblast maturation and differentiation. In conclusion, piceatannol increased BMP-2 synthesis, and this effect may contribute to its action on the induction of osteoblasts maturation and differentiation, followed by an increase of bone mass. Decreases in new bone formation, followed by estrogen deficiency or various pathologic factors, may contribute to the mechanisms involved in postmenopausal osteoporosis.

Alkaline Phosphatase↗

PubMed2005

Osteoblastic activity and estrogenic response in the regenerating scale of goldfish, a good model of osteogenesis.

Osteogenesis in the teleost was morphologically observed using regenerating scales of goldfish. Histological observations indicated that osteoblasts around the regenerating scales on days 7 to 10 were greater in size and number than those at other stages. Therefore, further experiments were carried out to examine the activity of osteoblasts in the regenerating period. To quantify their osteoblastic activities, scales on the left side of the body were taken, and the regenerating scales were then used to measure the activities of alkaline phosphatase (ALP), a marker of osteoblasts, on days 7, 10, and 15. The ontogenic scales on the right side of the body were also collected and used to measure ALP activity on the same days. Osteoblasts at all stages of regenerating scales were more active than those in the remaining ontogenic scales. The regenerating scales on day 10 had the highest activity. Furthermore, we found that estrogen receptor (ER) mRNA was expressed in the regenerating scales because estrogen participates in osteoblastic growth and differentiation in mammals. Therefore, using a scale culture system reported previously, the estrogenic response was examined in the ontogenic and regenerating scales on day 10. The reactivity was much higher in regenerating scales, although estrogen treatment significantly activated the osteoblastic activities in both scales. We are the first to demonstrate that ER is expressed in regenerating scales and that estrogen participates in osteogenesis as it does in mammalian bone. Our findings strongly suggest that regenerating scales can be used as a model of osteogenesis in vertebrates.

Alkaline Phosphatase↗

PubMed2005

Molecular mechanism of nitric oxide-induced osteoblast apoptosis.

Nitric oxide (NO) can regulate osteoblast activities. Our previous study showed that NO induced osteoblast apoptosis. This study was further aimed to evaluate the mechanism of NO-induced osteoblast apoptosis from the viewpoints of mitochondrial functions, intracellular oxidative stress, and the anti-apoptotic Bcl-2 protein using neonatal rat calvarial osteoblasts as the experimental model. Exposure of osteoblasts to sodium nitroprusside (SNP), an NO donor, significantly increased amounts of lactate dehydrogenase in the culture medium, and decreased cell viability in concentration- and time-dependent manners. Administration of SNP in osteoblasts time-dependently led to DNA fragmentation. The mitochondrial membrane potential was significantly reduced following SNP administration. SNP decreased complex I NADH dehydrogenase activity in a time-dependent manner. Levels of cellular adenosine triphosphate (ATP) were suppressed by SNP. In parallel with the mitochondrial dysfunction, SNP time-dependently increased levels of intracellular reactive oxygen species. Immunoblotting analysis revealed that SNP reduced Bcl-2 protein levels. Exposure to lipopolysaccharide (LPS) and IFN-gamma significant increased endogenous nitrite production. In parallel with the increase in endogenous NO, administration of LPS and IFN-gamma suppressed cell viability, mitochondrial membrane potential, and ATP synthesis. Results of this study show that NO released from SNP can induce osteoblast insults and apoptosis, and the mechanism may involve the modulation of mitochondrial functions, intracellular reactive oxygen species, and Bcl-2 protein.

Adenosine Triphosphate↗

PubMed2005

The effects of RANK blockade and osteoclast depletion in a model of pure osteoblastic prostate cancer metastasis in bone.

Adenocarcinoma of the prostate exhibits a clear propensity for bone and is associated with the formation of osteoblastic metastases. It has previously been suggested that osteoclast activity may be necessary for the development of these osteoblastic metastases based on data from lytic and mixed lytic-blastic tumors. Here we investigate the effects of complete in vivo osteoclast depletion via the blockade of receptor activator of NF:kappaB (RANK) on the establishment and progression of purely osteoblastic (LAPC-9 cells) bone lesions induced by human prostate cancer cells using a SCID mouse intratibial injection model. The subcutaneous administration of the RANK antagonist (15 mg/kg) RANK:Fc did not prevent the formation of purely osteoblastic lesions, indicating that osteoclasts may not be essential to the initial development of osteoblastic metastases. However, RANK:Fc protein appeared to inhibit the progression of established osteoblastic lesions, suggesting that osteoclasts may be involved in the subsequent growth of these tumors once they are already present. In contrast, RANK:Fc treatment effectively blocked the establishment and progression of purely osteolytic lesions formed by PC-3 cells, which served as a positive control. These results indicate that in vivo RANK blockade may not be effective for the prevention of osteoblastic metastasis but may potentially represent a novel therapy that limits the growth of established metastatic CaP lesions in bone.

Animals↗

PubMed2004

Electrical responses to 1alpha,25(OH)2-Vitamin D3 and their physiological significance in osteoblasts.

Osteoblasts are a main target for the steroid 1alpha,25(OH)2-Vitamin D3 (1,25D3), where a major outcome is the modulation of the bone remodeling process. 1,25D3 deficiency leads to clinical disorders such as osteomalacia and osteoporosis, characterized by a state of insufficiently calcified tissue and bone loss, respectively. In the osteoblast nucleus, 1,25D3 modulates gene transcription for the synthesis of bone matrix proteins via the Vitamin D receptor (VDR). At the plasma membrane level, 1,25D3 potentiates ion channel functions, activates signal transduction pathways, and increases cytoplasmic calcium concentrations. So far, no clear physiological significance has been attributed to membrane-initiated 1,25D3 actions in single cells. To investigate if (a) 1,25D3 is a modulatory agent of secretion in osteoblasts and (b) the classical VDR is involved in rapid electrical events in the cell membrane, we studied hormone effects on ion channel activities in relation to exocytosis in osteoblasts isolated from VDR knockout (KO) and wild-type (WT) mice. This paper is a retrospect of the electrophysiological studies done in our laboratory to date. We found that 1,25D3-promoted ion channel responses are coupled to secretion in calvarial osteoblasts, and develop only in the presence of a functional nuclear steroid VDR. This 1,25D3-regulated exocytosis in osteoblasts, which takes place within minutes of hormone application, seems to be the natural complement of genomic actions that evolve at a longer time scale. The absence of both 1,25D3 membrane and nuclear effects in VDR KO osteoblasts may explain bone abnormalities typically found in VDR KO mice.

Animals↗

PubMed2004

Fibroblast growth factor-2 induces osteoblast survival through a phosphatidylinositol 3-kinase-dependent, -beta-catenin-independent signaling pathway.

Fibroblast growth factor-2 (FGF-2) is an important molecule that controls bone formation through activation of osteoblastic cell replication and differentiation. The role of FGF-2 on human osteoblast survival and the signaling pathway that mediates its effect are not known. We studied the effect of FGF-2 on apoptosis induced by low serum concentration and the signal transduction pathway involved in this effect in human primary calvaria osteoblasts and immortalized osteoblastic cells. Treatment with FGF-2 for 24-48 h protected against osteoblast apoptosis induced by low serum concentration, through specific inhibition of caspase-2 and caspase-3 activity. Pharmacological inhibition of MEK-1 and p38 MAPK had no effect on the inhibition of caspases-2 and -3 induced by FGF-2. In contrast, inhibition of PI3K with LY294002 abolished the FGF-2-induced inhibition of caspases-2 and -3. FGF-2 increased PI3K activity but did not induce phosphorylation of Akt or the downstream effector p70 S6 kinase. FGF-2 also induced GSK-3alpha and beta phosphorylation in osteoblastic cells, which however did not result in beta-catenin accumulation or Lef/Tcf transcriptional activity. In contrast, lithium induced beta-catenin accumulation, Lef/Tcf transcriptional activation and increased caspase-2 and -3 activity. The results indicate that the immediate protective effect of FGF-2 on human osteoblastic cell apoptosis involves PI3K and inhibition of downstream caspases, independently of GSK-3 and beta-catenin-Lef/Tcf-mediated transcription.

Apoptosis↗

PubMed2005

Adiponectin stimulates human osteoblasts proliferation and differentiation via the MAPK signaling pathway.

Adipocytes can highly and specifically express adiponectin, and the adiponectin receptor (AdipoR) has been detected in bone-forming cells. The present study was undertaken to investigate the action of adiponectin on osteoblast proliferation and differentiation. AdipoR1 protein was detected in human osteoblasts. Adiponectin promoted osteoblast proliferation and resulted in a dose- and time-dependent increase in alkaline phosphatase (ALP) activity, osteocalcin and type I collagen production, and an increase in mineralized matrix. Suppression of AdipoR1 with small-interfering RNA (siRNA) abolished the adiponectin-induced cell proliferation and ALP expression. Adiponectin induces activation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal Kinase (JNK), but not ERK1/2 in osteoblasts, and these effects were blocked by suppression of AdipoR1 with siRNA. Furthermore, pretreatment of osteoblasts with the JNK inhibitor SP600125 abolished the adiponectin-induced cell proliferation. p38 inhibitor SB203580 blocked the adiponectin-induced ALP activity. These data indicate that adiponectin induces human osteoblast proliferation and differentiation, and the proliferation response is mediated by the AdipoR/JNK pathway, while the differentiation response is mediated via the AdipoR/p38 pathway. These findings suggest that osteoblasts are the direct targets of adiponectin.

Adiponectin↗

PubMed2006

Hypoxia inhibits the growth, differentiation and bone-forming capacity of rat osteoblasts.

We investigated the effect of hypoxia on rat osteoblast function in long-term primary cultures. Reduction of pO2 from 20% to 5% and 2% decreased formation of mineralized bone nodules 1.7-fold and 11-fold, respectively. When pO2 was reduced further to 0.2%, bone nodule formation was almost abolished. The inhibitory effect of hypoxia on bone formation was partly due to decreased osteoblast proliferation, as measured by 3H-thymidine incorporation. Hypoxia also sharply reduced osteoblast alkaline phosphatase (ALP) activity and expression of mRNAs for ALP and osteocalcin, suggesting inhibition of differentiation to the osteogenic phenotype. Hypoxia did not increase the apoptosis of osteoblasts but induced a reversible state of quiescence. Transmission electron microscopy revealed that collagen fibrils deposited by osteoblasts cultured in 2% O2 were less organized and much less abundant than in 20% O2 cultures. Furthermore, collagen produced by hypoxic osteoblasts contained a lower percentage of hydroxylysine residues and exhibited an increased sensitivity to pepsin degradation. These data demonstrate the absolute oxygen requirement of osteoblasts for successful bone formation and emphasize the importance of the vasculature in maintaining bone health. We recently showed that hypoxia also acts in a reciprocal manner as a powerful stimulator of osteoclast formation. Considered together, our results help to explain the bone loss that occurs at the sites of fracture, tumors, inflammation and infection, and in individuals with vascular disease or anemia.

Alkaline Phosphatase↗

PubMed1999

Decreased proliferation and altered differentiation in osteoblasts from genetically and clinically distinct craniosynostotic disorders.

Craniosynostoses are a heterogeneous group of disorders characterized by premature fusion of cranial sutures. Mutations in fibroblast growth factor receptors (FGFRs) have been associated with a number of such conditions. Nevertheless, the cellular mechanism(s) involved remain unknown. We analyzed cell proliferation and differentiation in osteoblasts obtained from patients with three genetically and clinically distinct craniosynostoses: Pfeiffer syndrome carrying the FGFR2 C342R substitution, Apert syndrome with FGFR2 P253R change, and a nonsyndromic craniosynostosis without FGFR canonic mutations, as compared with control osteoblasts. Osteoblasts from craniosynostotic patients exhibited a lower proliferation rate than control osteoblasts. P253R and nonsyndromic craniosynostosis osteoblasts showed a marked differentiated phenotype, characterized by high alkaline phosphatase activity, increased mineralization and expression of noncollagenous matrix proteins, associated with high expression and activation of protein kinase Calpha and protein kinase Cepsilon isoenzymes. By contrast, the low proliferation rate of C342R osteoblasts was not associated with a differentiated phenotype. Although they showed higher alkaline phosphatase activity than control, C342R osteoblasts failed to mineralize and expressed low levels of osteopontin and osteonectin and high protein kinase Czeta levels. Stimulation of proliferation and inhibition of differentiation were observed in all cultures on FGF2 treatment. Our results suggest that an anticipated proliferative/differentiative switch, associated with alterations of the FGFR transduction pathways, could be the causative common feature in craniosynostosis and that mutations in distinct FGFR2 domains are associated with an in vitro heterogeneous differentiative phenotype.

Acrocephalosyndactylia↗

PubMed2000

The effect of bone morphogenetic protein-7 on the expression of type I inositol 1,4,5-trisphosphate receptor in G-292 osteosarcoma cells and primary osteoblast cultures.

Bone morphogenetic protein-7 (BMP-7) affects differentiation of preosteoblasts enabling the resultant cells to respond optimally to acutely acting regulators. As the phosphoinositide cascade and, particularly, the calcium-mobilizing inositol 1,4,5-trisphosphate (InsP3) receptor are integral to stimulus-secretion coupling in osteoblasts, the hypothesis that BMP-7 affects InsP3 receptor expression was examined in the G-292 human osteosarcoma cell line and in primary cultures of human osteoblasts. G-292 osteosarcoma cells were found to be a valid experimental model for primary human osteoblasts, expressing osteoblastic mRNAs encoding osteocalcin, bone sialoprotein, alkaline phosphatase, alpha1-collagen, epidermal growth-factor receptor, and BMP type II receptor. When cultured long term in the presence of ascorbic acid and beta-glycerophosphate, G-292 cells underwent further osteoblastic differentiation, forming nodules and exhibiting restricted mineralization. G-292 cells responded to BMP-7 with an increase in InsP3 receptor density. Ligand-binding studies established that BMP-7 (50 ng/ml) treatment of G-292 cells increased InsP3 receptor density 2.4-fold with no apparent change in affinity. Immunoblot analysis with antibodies specific for type I, type II, and type III InsP3 receptors revealed that BMP-7 (50 ng/ml) treatment resulted in a specific increase (206+/-8%) in the type I receptor. Reverse transcription-polymerase chain reaction and Northern blot analyses of G-292 and primary human osteoblasts confirmed an increase in type I InsP3 receptor mRNA upon BMP-7 treatment. These results demonstrate that G-292 cells respond to BMP-7 with an increase InsP3 receptor density, consistent with the enhanced capacity of these cells to respond to Ca2+-mobilizing secretory hormones during osteoblast differentiation.

Alkaline Phosphatase↗

PubMed2001

Behavior of osteoblasts on a type I atelocollagen grafted ozone oxidized poly L-lactic acid membrane.

With oxidizing poly-L-lactic acid (PLLA) surface by ozone, peroxide groups are easily generated on the surface. Those peroxides are broken down by redox-coupling reaction, and provide active species that initiate grafting by reaction with the collagen molecules. The surface density of generated peroxide on a PLLA surface was determined by an iodide method. The maximum concentration of peroxide was about 2.87 x 10(-8) mol/cm2 when ozone oxidation was performed at 60 V for 60 min. After the surface oxidation, type I atelocollagen was grafted onto PLLA surface. All physical measurements on the collagen-grafted surface indicated that the PLLA surface was effectively grafted with type I atelocollagen. Behavior of rat calvaria osteoblasts on type I atelocollagen grafted PLLA (PLLA + COL) surface was observed. Initial attachment of osteoblasts on the surface was significantly enhanced, and it is assumed that the atelocollagen matrix supported the initial attachment and growth of cells. Collagenous protein synthesis of osteoblasts was maintained at relatively low level in the early stage of proliferation due to the primarily existing grafted type I atelocollagen, and then increased in 7 days as the osteoblast differentiated. After 7 days, collagenous protein synthesis in osteoblasts was activated. Alkaline phosphatase (ALPase) activity and mineralization by osteoblasts were promoted on PLLA + COL surface. In comparison with PLLA + COL, non-treated PLLA and tissue culture plate (TCPS) did not show any feature expressed in osteoblasts' maturation up to 9 days in this experiment. The grafted type I atelocollagen provided a favorable matrix for cell migration in relation with collagenase expression. Ozone oxidation might be a favorable method for surface modification of PLLA membranes by collagen grafting, and cell behavior could be modulated by the grafted collagen.

Animals↗

PubMed2004

Attachment, proliferation, and migration of marrow stromal osteoblasts cultured on biomimetic hydrogels modified with an osteopontin-derived peptide.

We prepared oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels modified with a rat osteopontin-derived peptide (ODP), Asp-Val-Asp-Val-Pro-Asp-Gly-Arg-Gly-Asp-Ser-Leu-Ala-Try-Gly (DVDVPDGRGDSLAYG), as well as Gly-Arg-Gly-Asp-Ser (GRGDS) and investigated the modulation of marrow stromal osteoblast function on the peptide-modified hydrogels. Osteoblast attachment was competitively inhibited by a soluble peptide suggesting that the interaction of osteoblasts with the hydrogel was ligand specific. The proliferation index of osteoblasts relative to the initial seeding density was similar on the hydrogels modified with ODP (1.18+/-0.13) and GRGDS (1.27+/-0.12). However, fibroblasts proliferated faster on GRGDS-modified hydrogels than on ODP-modified hydrogels as evidenced by the proliferation indices of 4.89+/-0.03 and 2.42+/-0.16, respectively. A megacolony migration assay conducted for 3 days with a seeding density of 53,000 cells/cm(2) showed that osteoblasts migrated to a longer distance on ODP-modified hydrogels (0.23+/-0.06 mm/day) than on hydrogels modified with GRGDS (0.15+/-0.02 mm/day). In addition, osteoblasts migrated faster than fibroblasts seeded at the same density on ODP-modified hydrogels (0.15+/-0.11 mm/day). The migration of osteoblasts on the peptide-modified hydrogels was dependent on the peptide concentration of the hydrogels resulting in an increased migration distance with increasing the peptide concentration for the concentrations tested. These results show that OPF-based biomimetic hydrogels hold promise for modulating cell proliferation and migration for specific applications by altering the specific ligand and its concentration in the hydrogels.

Animals↗

PubMed1999

Osteoblast adhesion on nanophase ceramics.

Osteoblast adhesion on nanophase alumina (Al2O3) and titania (TiO2) was investigated in vitro. Osteoblast adhesion to nanophase alumina and titania in the absence of serum from Dulbecco's modified Eagle medium (DMEM) was significantly (P < 0.01) less than osteoblast adhesion to alumina and titania in the presence of serum. In the presence of 10% fetal bovine serum in DMEM osteoblast adhesion on nanophase alumina (23 nm grain size) and titania (32 nm grain size) was significantly (P < 0.05) greater than on conventional alumina (177 nm grain size) and titania (2.12 microm grain size), respectively, after 1, 2, and 4 h. Further investigation of the dependence of osteoblast adhesion on alumina and titania grain size indicated the presence of a critical grain size for osteoblast adhesion between 49 and 67 nm for alumina and 32 and 56 nm for titania. The present study provides evidence of the ability of nanophase alumina and titania to simulate material characteristics (such as surface grain size) of physiological bone that enhance protein interactions (such as adsorption, configuration, bioactivity, etc.) and subsequent osteoblast adhesion.

Aluminum Oxide↗

PubMed1994

Interleukin-1 beta induces cyclic AMP formation in isolated human osteoblasts: a signalling mechanism that is not related to enhanced prostaglandin formation.

Interleukin-1 (IL-1) is a potent stimulator of bone resorption. Induction of osteoclastic bone resorption by various endocrine or paracrine factors is mediated via the osteoblasts. We have therefore investigated the effects of IL-1 beta on cell signalling in isolated human osteoblasts. Special interest was focused on prostaglandin synthesis, since indomethacin, an inhibitor of prostaglandin synthesis, partly inhibits IL-1-induced bone resorption. IL-1 beta, at and above 0.3 pM, dose dependently stimulated PGE2 formation in isolated human osteoblasts, with half maximal stimulation, EC50, at 3 pM. Treatment with the calcium ionophore A23187 (1 microM), or with forskolin (30 microM), also stimulated PGE2 formation in human osteoblasts. The time-course for IL-1 beta-induced PGE2 formation was similar to that of forskolin, with a significant increase in the formation of PGE2 seen after 1 h. In contrast, A23187-induced PGE2 formation was seen within minutes. IL-1 beta stimulated the accumulation of cyclic AMP in isolated human osteoblasts incubated for 15 min. This increase in cyclic AMP formation was not secondary to PGE2 formation since it was not blocked by the addition of indomethacin (1 microM). Pretreatment with the phosphodiesterase inhibitor IBMX did not augment IL-1 beta-induced PGE2 formation, nor did the protein kinase A inhibitor Rp-cAMPs inhibit IL-1 beta-induced PGE2 formation, suggesting that cyclic AMP does not mediate the stimulatory effect of IL-1 on PGE2 formation. We conclude that IL-1 beta enhances the formation of cyclic AMP as well as PGE2 in primary cultures of isolated human osteoblasts. The IL-1 beta-induced cyclic AMP formation is, however, not related to the enhanced prostaglandin formation. The findings implicate that both cyclic AMP- and PGE2-formation in osteoblasts might be involved as independent mediators of IL-1 beta-induced bone resorption.

1-Methyl-3-isobutylxanthine↗