Medium pH modulates matrix, mineral, and energy metabolism in cultured chick bones and osteoblast-like cells

Additively-manufactured Mg wire-reinforced PLDL-matrix composites for biomedical applications

Coupons of a medical grade PLDL polymer matrix uniaxially reinforced with a 15% volume fraction of Mg wires have been manufactured by fused filament fabrication for the first time. Two different types of Mg wires, without and with a surface treatment by plasma electrolytic oxidation were used. Both composite materials were subjected to degradation in phosphate buffer solution over a 3-week period, and their degradation and deformation micromechanisms were analysed in detail. Additionally, the materials were subjected to extensive mechanical testing under various loading conditions, and the interface strength was also analysed. It was found that the presence of the Mg wires improves the mechanical behaviour and accelerates the corrosion rate of the composite with respect that of the polymer matrix and these properties can be further tailored through the surface-modification of Mg wires by plasma electrolytic oxidation. The additive manufacturing strategy presented opens the path to fabricate multimaterial implants and scaffolds with complex shape and tailored properties provided by biodegradable polymers reinforced with either Mg and Zn particles and/or wires.

Electrical stimulation to promote osseointegration of bone anchoring implants: a topical review

Electrical stimulation has shown to be a promising approach for promoting osseointegration in bone anchoring implants, where osseointegration defines the biological bonding between the implant surface and bone tissue. Bone-anchored implants are used in the rehabilitation of hearing and limb loss, and extensively in edentulous patients. Inadequate osseointegration is one of the major factors of implant failure that could be prevented by accelerating or enhancing the osseointegration process by artificial means. In this article, we reviewed the efforts to enhance the biofunctionality at the bone-implant interface with electrical stimulation using the implant as an electrode. We reviewed articles describing different electrode configurations, power sources, and waveform-dependent stimulation parameters tested in various in vitro and in vivo models. In total 55 English-language and peer-reviewed publications were identified until April 2020 using PubMed, Google Scholar, and the Chalmers University of Technology Library discovery system using the keywords: osseointegration, electrical stimulation, direct current and titanium implant. Thirteen of those publications were within the scope of this review. We reviewed and compared studies from the last 45 years and found nonuniform protocols with disparities in cell type and animal model, implant location, experimental timeline, implant material, evaluation assays, and type of electrical stimulation. The reporting of stimulation parameters was also found to be inconsistent and incomplete throughout the literature. Studies using in vitro models showed that osteoblasts were sensitive to the magnitude of the electric field and duration of exposure, and such variables similarly affected bone quantity around implants in in vivo investigations. Most studies showed benefits of electrical stimulation in the underlying processes leading to osseointegration, and therefore we found the idea of promoting osseointegration by using electric fields to be supported by the available evidence. However, such an effect has not been demonstrated conclusively nor optimally in humans. We found that optimal stimulation parameters have not been thoroughly investigated and this remains an important step towards the clinical translation of this concept. In addition, there is a need for reporting standards to enable meta-analysis for evidence-based treatments.

Growth Rate and Bone Hydroxyproline Concentration in Turkeys Fed with a Silage-Composed Diet Modified with Different Diet Cation-Anion Differences (DCADs)

Simple Summary

In this study, we point to the possibility of using dietary cation–anion difference manipulation to improve growth rates and bone condition, especially in the last phase of poultry turkey husbandry, when birds have many bone abnormalities.

Abstract

Our goal was to determine the responses of body weight (BW) and bone hydroxyproline (Hyp) concentration in turkeys fed a corn silage (CS) diet with different values of dietary cation–anion differences (DCADs). The turkeys (n = 90) were divided into five groups and fed as follows: group A (control)—standard diet (SD) (60%) plus CS (40%); group B—SD (60%), CS (40%) plus 240 g of CaCl₂ per 100 kg of diet; group C—SD (60%), CS (40%) plus 480 g of CaCl₂ per 100 kg of diet; group D—SD (60%), CS (40%) plus 240 g of NaHCO₃ per 100 kg of diet; group E—SD (60%), CS (40%) plus 480 g NaHCO₃ per 100 kg of diet. The addition of a lesser amount of CaCl₂ lowered the DCAD, which ranged between 52.5 ± 4.19 and 91.14 ± 3.14 mEq/kg DM. An increased content of CaCl₂ led to high negative values of DCAD. NaHCO₃ supplemented in both doses resulted in a significant elevation of DCAD. Compared to each experimental group, feeding birds with a diet supplemented only with CS resulted in a lower BW. Addition of CaCl₂ or NaHCO₃ to the diet improved BW, but only CaCl₂ addition enhanced the bone Hyp amount. In conclusion, we suggest that an anionic diet with low DCAD can prevent bone abnormalities in large turkeys, especially in the final course of production.

Changes in the extracellular microenvironment and osteogenic responses of mesenchymal stem/stromal cells induced by in vitro direct electrical stimulation

Electrical stimulation (ES) has potential to be an effective tool for bone injury treatment in clinics. However, the therapeutic mechanism associated with ES is still being discussed. This study aims to investigate the initial mechanism of action by characterising the physical and chemical changes in the extracellular environment during ES and correlate them with the responses of mesenchymal stem/stromal cells (MSCs). Computational modelling was used to estimate the electrical potentials relative to the cathode and the current density across the cell monolayer. We showed expression of phosphorylated ERK1/2, c-FOS, c-JUN, and SPP1 mRNAs, as well as the increased metabolic activities of MSCs at different time points. Moreover, the average of 2.5 μM of H₂O₂ and 34 μg/L of dissolved Pt were measured from the electrically stimulated media (ES media), which also corresponded with the increases in SPP1 mRNA expression and cell metabolic activities. The addition of sodium pyruvate to the ES media as an antioxidant did not alter the SPP1 mRNA expression, but eliminated an increase in cell metabolic activities induced by ES media treatment. These findings suggest that H₂O₂ was influencing cell metabolic activity, whereas SPP1 mRNA expression was regulated by other faradic by-products. This study reveals how different electrical stimulation regime alters cellular regenerative responses and the roles of faradic by-products, that might be used as a physical tool to guide and control cell behaviour.

In vitro and in vivo evaluation of the pH-neutral bioactive glass as high performance bone grafts

Osteogenic and angiogenic properties are two most valued factors for bone grafting materials. Biomedical materials with synergistic promotion effects on these two properties would be highly desirable. In this study, we showed that a recently developed pH-neutral bioactive glass (PSC) possessed such characteristics. Compared to two classical biomaterials, 45S5 bioactive glass and beta-tricalcium phosphate (β-TCP), PSC markedly improved BMSCs' proliferation, migration and mineralization as well as their osteogenic and angiogenic differentiation. In vivo, PSC showed better performance on inducing bone regeneration than both 45S5 and β-TCP, as featured by elevated bone mineral density (BMD) and new bone areas. PSC also significantly promoted new blood vessels formation compared with those in control groups. Furthermore, we revealed that PSC induced osteogenic and angiogenic differentiation of BMSCs through the PI3K/Akt/HIF-1α pathway, which had not been reported before. This synergistic effect of the PI3K/Akt/HIF-1α pathway on osteogenesis and angiogenic differentiation of BMSCs suggested that biomedical materials may promote new bone formation through multiple signal pathways, thus shedding light on the future development of materials with better performance.

Novel calcium phosphate coated calcium silicate-based cement: in vitro evaluation

Calcium silicate-based cements are known for their wide applications in dentistry and orthopedics. The alkaline pH (up to 12) of these cements limits their application in other orthopedic areas. In this study, the effect of dicalcium phosphate dihydrate (DCPD) coating on set cement on pH reduction and biocompatibility improvement was examined. Samples with 0 and 10 weight ratio DCPD were prepared and characterized by XRD, FTIR, and SEM. The DCPD coating on the set cement was performed by a 7 d immersion in 1% monocalcium phosphate (MCP) solution and characterized by XRD, FTIR, SEM, and EDX. Also, the compressive strength and cytotoxicity of the samples were tested. The results showed that DCPD coating did not significantly change the compressive strength of the cement, but by decreasing the pH of the culture medium to the physiological range, it led to enhance adhesion, spreading and proliferation of human osteosarcoma cell line (Saos-2). The novel DCPD coated calcium silicate-based cement could be served as a bulk or porous bone substitute and scaffold.

Corylin, a flavonoid derived from Psoralea Fructus, induces osteoblastic differentiation via estrogen and Wnt/β-catenin signaling pathways

Corylin is a naturally occurring flavonoid isolated from the fruit of Psoralea corylifolia L. (Fabaceae), which is a Chinese medicinal herb in treating osteoporosis. Although a variety of pharmacological activities of corylin have been reported, its osteogenic action and the underlying mechanism in bone development remain unclear. In the present study, the involvement of bone-specific genes in corylininduced differentiated osteoblasts was analyzed by RT-PCR, promoter-reporter assay, and Western blotting. In cultured osteoblasts, corylin-induced cell differentiation and mineralization, as well as increased the expressions of vital biological markers for osteogenesis, such as Runx2, Osterix, Col1, and ALP. Corylin was proposed to have dual pathways in triggering the osteoblastic differentiation. First, the osteogenic function of corylin acted through the activation of Wnt/β-catenin signaling. The nuclear translocation of β-catenin of cultured osteoblasts, as determined by flow cytometry and confocal microscopy, was triggered by applied corylin, and which was blocked by DKK-1, an inhibitor of Wnt/β-catenin signaling. Second, the application of corylin-induced estrogenic response in a dose-dependent manner, and which was blocked by ICI 182 780, an antagonist of estrogen receptor. Furthermore, the activation of Runx2 promoter by corylin was abolished by both DKK-1 and ICI 182,780, indicating that the corylin exhibited its osteogenic effect via estrogen and Wnt/β-catenin signaling pathways. In addition, corylin regulated the metabolic profiles, as well as the membrane potential of mitochondria, in cultured osteoblasts. Corylin also stimulated the osteogenesis in bone micromass derived from mesenchymal progenitor cells. This study demonstrated the osteogenic activities of corylin in osteoblasts and micromass, suggesting that corylin has the potential to be developed as a novel pro-osteogenic agent in targeting for the treatment of osteoblast-mediated osteoporosis.

Direct electrical stimulation enhances osteogenesis by inducing Bmp2 and Spp1 expressions from macrophages and preosteoblasts

The capability of electrical stimulation (ES) in promoting bone regeneration has already been addressed in clinical studies. However, its mechanism is still being investigated and discussed. This study aims to investigate the responses of macrophages (J774A.1) and preosteoblasts (MC3T3-E1) to ES and the faradic by-products from ES. It is found that pH of the culture media was not significantly changed, whereas the average hydrogen peroxide concentration was increased by 3.6 and 5.4 µM after 1 and 2 hr of ES, respectively. The upregulation of Bmp2 and Spp1 messenger RNAs was observed after 3 days of stimulation, which is consistent among two cell types. It is also found that Spp1 expression of macrophages was partially enhanced by faradic by-products. Osteogenic differentiation of preosteoblasts was not observed during the early stage of ES as the level of Runx2 expression remains unchanged. However, cell proliferation was impaired by the excessive current density from the electrodes, and also faradic by-products in the case of macrophages. This study shows that macrophages could respond to ES and potentially contribute to the bone formation alongside preosteoblasts. The upregulation of Bmp2 and Spp1 expressions induced by ES could be one of the mechanisms behind the electrically stimulated osteogenesis.

Development of mussel-inspired 3D-printed poly (lactic acid) scaffold grafted with bone morphogenetic protein-2 for stimulating osteogenesis

3D printing is a versatile technique widely applied in tissue engineering due to its ability to manufacture large quantities of scaffolds or constructs with various desired architectures. In this study, we demonstrated that poly (lactic acid) (PLA) scaffolds fabricated via fused deposition not only retained the original interconnected microporous architectures, the scaffolds also exhibited lower lactic acid dissolution as compared to the freeze-PLA scaffold. The 3D-printed scaffolds were then grafted with human bone morphogenetic protein-2 (BMP-2) via the actions of polydopamine (PDA) coatings. The loading and release rate of BMP-2 were monitored for a period of 35 days. Cellular behaviors and osteogenic activities of co-cultured human mesenchymal stem cells (hMSCs) were assessed to determine for efficacies of scaffolds. In addition, we demonstrated that our fabricated scaffolds were homogenously coated with PDA and well grafted with BMP-2 (219.1 ± 20.4 ng) when treated with 250 ng/mL of BMP-2 and 741.4 ± 127.3 ng when treated with 1000 ng/mL of BMP-2. This grafting enables BMP-2 to be released in a sustained profile. From the osteogenic assay, it was shown that the ALP activity and osteocalcin of hMSCs cultured on BMP-2/PDA/PLA were significantly higher when compared with PLA and PDA/PLA scaffolds. The methodology of PDA coating employed in this study can be used as a simple model to immobilize multiple growth factors onto different 3D-printed scaffold substrates. Therefore, there is potential for generation of scaffolds with different unique modifications with different capabilities in regulating physiochemical and biological properties for future applications in bone tissue engineering.

In Vitro Uptake of Hydroxyapatite Nanoparticles and Their Effect on Osteogenic Differentiation of Human Mesenchymal Stem Cells

There have been many applications in biomedical fields based on hydroxyapatite nanoparticles (HA NPs) over the past decades. However, the biocompatibility of HANPs is affected by exposure dose, particle size, and the way of contact with cells. The objective of this study is to investigate the effect of HA NPs with different sizes on osteogenesis using human mesenchymal stem cells (hMSCs). Three different-sized HA NPs (~50, ~100, and ~150 nm, resp.) were synthesized to study the cytotoxicity, cellular uptake, and effect on osteogenic differentiation of hMSCs. The results clearly showed that each size of HA NPs had dose-dependent cytotoxicity on hMSCs. It was found that HA NPs could be uptaken into hMSCs. The osteogenic differentiation of hMSCs was evaluated through alkaline phosphatase (ALP) activity measurement, ALP staining, immunofluorescent staining for osteopontin (OPN), and real-time polymerase chain reaction (RT-PCR) examination. As expected, HA NPs of all sizes could promote the differentiation of hMSCs towards osteoblast lineage. Among the three sizes, smaller-sized HA NPs (~50 and ~100 nm) appeared to be more effective in stimulating osteogenic differentiation of hMSCs.

Systemic bone marker expression induced by grey and white mineral trioxide aggregate in normal and diabetic conditions

AIM

To investigate the relationship between diabetes mellitus and local/systemic effects of both grey and white mineral trioxide aggregate (MTA) Angelus on bone marker expression.

METHODOLOGY

Wistar rats were divided into two groups: healthy and diabetic (Alloxan induced), which were further divided into three subgroups (control, GMTA Angelus and WMTA Angelus). Polyethylene tubes filled with MTA materials or empty tubes were implanted in dorsal connective tissue. On days 7 and 30, blood samples were collected for calcium, phosphorus and ALP measurement. The animals were euthanized; implanted tubes were removed and processed for immunohistochemical analysis of osteocalcin (OCN) and osteopontin (OPN). Kruskal-Wallis followed by Dunn's multiple comparison test was performed for nonparametric data, and anova followed by Tukey's test for parametric data.

RESULTS

No difference in systemic serum calcium levels between both groups was observed. On day 7, serum phosphorus levels within the WMTA healthy group were higher than that of the diabetic group. On day 30, healthy rats exhibited lower phosphorus levels than diabetic ones. At both time points, the diabetic group was associated with more ALP activity than the healthy group. Immunohistochemical analyses of the healthy group revealed OCN- and OPN-positive cells in the presence of both MTA materials. However, under diabetic conditions, both OCN and OPN were absent.

CONCLUSION

Both MTA materials were associated with an increase in serum calcium, phosphorus and ALP, suggesting a potential systemic effect, along with triggered differentiation of OCN- and OPN-positive cells. Moreover, in diabetic conditions, an inhibitory effect on MTA-induced differentiation of OCN- and OPN-positive cells was detected.

Increased osteoblast viability at alkaline pH in vitro provides a new perspective on bone regeneration

We investigated the effects of alkaline pH on developing osteoblasts. Cells of the osteoblast-like cell line MC3T3-E1 were initially cultured for six days in HEPES-buffered media with pH ranging from 7.2 to 9.0. Cell count, cellular WST-1 metabolism, and ATP content were analyzed. The three parameters showed a pH optimum around pH 8.4, exceeding the recommended buffer range of HEPES at the alkaline flank. Therefore, only pH 7.2, 7.4, 7.8, and 8.4 media were used in more elaborate, daily investigations to reduce the effects of pH change within the pH control intervals of 24 h. All parameters exhibited similar pH behaviors, roughly showing increases to 130% and 230% at pH 7.8 and 8.4, as well as decreases to 70% at pH 7.2 when using the pH 7.4 data for reference. To characterize cell differentiation and osteoblastic cell function, cells were cultured at pH 7.4 and under alkaline conditions at pH 7.8 and 8.4 for 14 days. Gene expression and mineralization were evaluated using microarray technology and Alizarin staining. Under alkaline conditions, ATF4, a regulator for terminal differentiation and function as well as DMP1, a potential marker for the transition of osteoblasts into osteocytes, were significantly upregulated, hinting at an accelerated differentiation process. After 21 days, significant mineralization was only detected at alkaline pH. We conclude that elevated pH is beneficial for the cultivation of bone cells and may also provide therapeutic value in bone regeneration therapies.

Direct ink writing of silica-bonded calcite scaffolds from preceramic polymers and fillers

Silica-bonded calcite scaffolds have been successfully 3D-printed by direct ink writing, starting from a paste comprising a silicone polymer and calcite powders, calibrated in order to match a SiO₂/CaCO₃ weight balance of 35/65. The scaffolds, fabricated with two slightly different geometries, were first cross-linked at 350 °C, then fired at 600 °C, in air. The low temperature adopted for the conversion of the polymer into amorphous silica, by thermo-oxidative decomposition, prevented the decomposition of calcite. The obtained silica-bonded calcite scaffolds featured open porosity of about 56%-64% and compressive strength of about 2.9-5.5 MPa, depending on the geometry. Dissolution studies in SBF and preliminary cell culture tests, with bone marrow stromal cells, confirmed the in vitro bioactivity of the scaffolds and their biocompatibility. The seeded cells were found to be alive, well anchored and spread on the samples surface. The new silica-calcite composites are expected to be suitable candidates as tissue-engineering 3D scaffolds for regeneration of cancellous bone defects.

Primary stability and osseointegration of dental implants in polylactide modified bone - A pilot study in Goettingen minipigs

The present study aimed to evaluate primary stability (PS) and osseointegration of dental implants in polylactide [70/30 poly(l-lactide-co-d, l-lactide); (PLDLA)] modified bone in 30 Goettingen minipigs. Each animal received three implants per jaw quadrant. In a split-mouth design, one side of the maxilla and mandible was randomly allocated to the experimental treatment (PLDLA applied into the drill hole before implantation), while the contralateral sides served as intraindividual controls (no PLDLA applied). The required insertion torque and the implant stability quotient (ISQ) were measured during implantation. ISQ, volume density (VD) of new bone formation (NBF), and the bone-implant contact (BIC) were evaluated at the end of the observation period (1, 3, 6, 12, and 24 months, respectively) in six animals each. Across all study groups, the PLDLA treatment resulted in a) a comparable insertion torque, b) an equivalent ISQ, c) a reduced BIC, and d) a reduced VD of NBF, as opposed to the untreated controls. In conclusion, the PLDLA treatment did not affect the PS, but rather led to an impaired osseointegration, which was particularly strong in the compact mandibular bone, and decreased in the spongious maxillary bone. PLDLA induced anchoring in spongious bone should be evaluated in further investigations.

A neglected requirement for optimizing treatment of age-related osteoporosis: Replenishing the skeleton's base reservoir with net base-producing diets

Osteoporosis is a disorder of bone in which the mass of the bone is reduced and the bone's architecture at the microscopic level is disordered. Together those abnormalities predispose affected individuals to experience fractures despite only minimal trauma (i.e., fragility fractures). Age related osteoporosis is a common type of osteoporosis that occurs with aging in both men and women usually beginning after the age of peak bone mass. Research has found that the disorder can be partially reversed by reducing the net amount of acid that is produced when consuming typical Western diets. However, the amelioration that results has not been so dramatic or so consistent that physicians have adopted the procedure as part of the standard treatment for age-related osteoporosis. We propose that reducing the net acid load from the diet is not sufficient to reverse age related osteoporosis because it fails to supply base needed to restore the large amount of base in bone that had been lost by reacting with the net acid load of the diet that had been consumed for years or decades. Reducing the net acid load from the diet might be expected to have little ameliorative effect or merely slow the progression of the disorder. We hypothesize that both to restore osteoporotic bone to, or nearly to, its pre-disease state, as well as to eliminate the risk of fragility fractures, requires consuming diets that produce net amounts of base to restore the base lost from years to decades of consuming diets that produce net amounts of acid. We hypothesize also that the excess base and attendant subclinical metabolic alkalosis will both stimulate the cellular process of bone formation and suppress the cellular process of bone resorption, and thereby implement the restorative process.

Mesenchymal stem cell proliferation and mineralization but not osteogenic differentiation are strongly affected by extracellular pH

Osteomyelitis is a serious complication in oral and maxillofacial surgery affecting bone healing. Bone remodeling is not only controlled by cellular components but also by ionic and molecular composition of the extracellular fluids in which calcium phosphate salts are precipitated in a pH dependent manner.

OBJECTIVE

To determine the effect of pH on self-renewal, osteogenic differentiation and matrix mineralization of mesenchymal stem cells (MSCs).

METHODS

We selected three different pH values; acidic (6.3, 6.7), physiological (7.0-8.0) and severe alkaline (8.5). MSCs were cultured at different pH ranges, cell viability measured by WST-1, apoptosis detected by JC-1, senescence was analyzed by β-galactosidase whereas mineralization was detected by Alizarin Red and osteogenic differentiation analyzed by Real-time PCR.

RESULTS

Self-renewal was affected by pH as well as matrix mineralization in which pH other than physiologic inhibited the deposition of extracellular matrix but did not affect MSCs differentiation as osteoblast markers were upregulated. The expression of osteocalcin and alkaline phosphatase activity was upregulated whereas osteopontin was downregulated under acidic pH.

CONCLUSION

pH affected MSCs self-renewal and mineralization without influencing osteogenic differentiation. Thus, future therapies, based on shifting acid-base balance toward the alkaline direction might be beneficial for prevention or treatment of osteomyelitis.

Acidosis is a key regulator of osteoblast ecto-nucleotidase pyrophosphatase/phosphodiesterase 1 (NPP1) expression and activity

Previous work has shown that acidosis prevents bone nodule formation by osteoblasts in vitro by inhibiting mineralisation of the collagenous matrix. The ratio of phosphate (P_i) to pyrophosphate (PP_i) in the bone microenvironment is a fundamental regulator of bone mineralisation. Both P_i and PP_i, a potent inhibitor of mineralisation, are generated from extracellular nucleotides by the actions of ecto‐nucleotidases. This study investigated the expression and activity of ecto‐nucleotidases by osteoblasts under normal and acid conditions. We found that osteoblasts express mRNA for a number of ecto‐nucleotidases including NTPdase 1–6 (ecto‐nucleoside triphosphate diphosphohydrolase) and NPP1‐3 (ecto‐nucleotide pyrophosphatase/phosphodiesterase). The rank order of mRNA expression in differentiating rat osteoblasts (day 7) was Enpp1 > NTPdase 4 > NTPdase 6 > NTPdase 5 > alkaline phosphatase > ecto‐5‐nucleotidase > Enpp3 > NTPdase 1 > NTPdase 3 > Enpp2 > NTPdase 2. Acidosis (pH 6.9) upregulated NPP1 mRNA (2.8‐fold) and protein expression at all stages of osteoblast differentiation compared to physiological pH (pH 7.4); expression of other ecto‐nucleotidases was unaffected. Furthermore, total NPP activity was increased up to 53% in osteoblasts cultured in acid conditions (P < 0.001). Release of ATP, one of the key substrates for NPP1, from osteoblasts, was unaffected by acidosis. Further studies showed that mineralised bone formation by osteoblasts cultured from NPP1 knockout mice was increased compared with wildtypes (2.5‐fold, P < 0.001) and was partially resistant to the inhibitory effect of acidosis. These results indicate that increased NPP1 expression and activity might contribute to the decreased mineralisation observed when osteoblasts are exposed to acid conditions. J. Cell. Physiol. 230: 3049–3056, 2015. © 2015 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Preparation and Characterization of Low Temperature Heat-Treated 45S5 Bioactive Glass-Ceramic Analogues

The 45S5 Bioglassr and its sintered bioactive glass-ceramic (BGC) have been widely investigated as bone implants, mainly for its ability to bond to hard tissues. However, high temperature treatment is not enough to improve its poor mechanical properties, but compromise its biologically relevant performances. The innovative BGC compositions based on the thermally treated 45S5 Bioglassr were developed by decreasing the P2O5 quantity and adding B2O3 (0-6%) into the Na2O–2CaO–3SiO2- based bioactive glasses (BG). The thermally treated BGCs were fully characterized from the microstructural and mechanical points of view and compared to each other. Their bioactivity and bio-dissolutionwere established by means of in vitro soaking tests. The new B2O3-added 45S5 BG analogues, named NCS-xB, can be transformed to crystalline phase (Na2Ca2Si3O9)-based BGCs of high compactness and bioactivity at a relatively low temperature heat treatment (≤ 900ºC), since their bioactivity is preserved. Our experimental results suggest that the new 45S5 BGC analogues with optimized composition exhibit improved micro- structural and mechanical properties, and are beneficial for making specific products such as porous scaffolds or composites for bone defect repair.

Stem cell differentiation-induced calcium silicate cement with bacteriostatic activity

The calcium silicate cement (CSC) on osteogenic differentiation of hMSCs and bacteriostatic abilities was more effective than calcium phosphate cement (CPC).

In vitro and in vivo biocompatibility of multi-walled carbon nanotube/biodegradable polymer nanocomposite for bone defects repair

Biomaterials are extensively used in bone defect recovery caused by bone diseases. Multi-walled carbon nanotubes have been reported to reinforce synthetic polymeric materials. The aim of the study is to test poly(3-hydroxybutyrate- co-3-hydroxyvalerate) loaded with different amounts of multi-walled carbon nanotubes to fabricate nanocomposites. Mechanical, mineralization, and degradation properties were studied in vitro. The proliferation and differentiation of rat bone marrow stem cells were studied to determine biocompatibility in vivo. The incorporation of multi-walled carbon nanotubes greatly increased the mechanical properties of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) and the strongest composite obtained was at 2% multi-walled carbon nanotubes. The 2% nanocomposite also had higher rat bone marrow stem cell adhesion, proliferation, and differentiation characteristics compared to the pure poly(3-hydroxybutyrate- co-3-hydroxyvalerate). The apoptosis in the later stage of rat bone marrow stem cells decreased in the 2% nanocomposites group at different time points. Based on histology and micro-computed tomography tests 6 weeks after in vivo implantation, the 2% multi-walled carbon nanotubes/poly(3-hydroxybutyrate- co-3-hydroxyvalerate) treated animals had a higher volume of bone formation compared to the pure poly(3-hydroxybutyrate- co-3-hydroxyvalerate) group. Thus, the presence of multi-walled carbon nanotubes has an apparent positive effect on poly(3-hydroxybutyrate- co-3-hydroxyvalerate) in assisting osteogenesis.

Electrical polarization of titanium surfaces for the enhancement of osteoblast differentiation

Electrical stimulation has been used clinically to promote bone regeneration in cases of fractures with delayed union or nonunion, with several in vitro and in vivo reports suggesting its beneficial effects on bone formation. However, the use of electrical stimulation of titanium (Ti) implants to enhance osseointegration is less understood, in part because of the few in vitro models that attempt to represent the in vivo environment. In this article, the design of a new in vitro system that allows direct electrical stimulation of osteoblasts through their Ti substrates without the flow of exogenous currents through the media is presented, and the effect of applied electrical polarization on osteoblast differentiation and local factor production was evaluated. A custom-made polycarbonate tissue culture plate was designed to allow electrical connections directly underneath Ti disks placed inside the wells, which were supplied with electrical polarization ranging from 100 to 500 mV to stimulate MG63 osteoblasts. Our results show that electrical polarization applied directly through Ti substrates on which the cells are growing in the absence of applied electrical currents may increase osteoblast differentiation and local factor production in a voltage-dependent manner.

In vitro physicochemical properties, osteogenic activity, and immunocompatibility of calcium silicate-gelatin bone grafts for load-bearing applications

The use of a composite made of natural polymer gelatin and bioactive calcium silicate resembling the morphology and properties of natural bone may provide a solution to the problem of ceramic brittleness for load-bearing applications. The in vitro bioactivity, degradability, osteogenic activity, and immunocompatibility of three types of calcium silicate-gelatin composite bone grafts were characterized. The osteogenic activity and immunocompatibility were evaluated by incubating the bone grafts with human dental pulp cells. After soaking in a simulated body fluid (SBF) for 1 day, all materials were covered with clusters of "bone-like" apatite spherulites. The control material without gelatin exhibited an insignificant change in strength, degradability, and porosity and a small weight loss of 6% after 180 days of soaking in the SBF solution. In contrast, the soaking time imposed in this study did have a statistically significant effect on compressive strength, porosity, and weight loss of the gelatin-containing composites. After 180 days of soaking, the composite with 10 wt % gelatin lost 47% and 10% in compressive strength and weight, respectively, with a porosity of 23%. However, the presence of gelatin promoted greater cell attachment and proliferation on the composite bone grafts. Pulp cells on the calcium silicate-gelatin bone grafts expressed higher levels of osteocalcin, osteopontin, and bone sialoprotein. The inhibition of inducible nitric oxide synthase and interleukin-1 expression and the activation of interleukin-10 were increased with increasing gelatin content. Overall, these findings provide evidence that composite bone grafts containing 10 wt % gelatin with a high initial strength were bioactive, nontoxic, and osteogenic and may be able to promote bone healing for load-bearing applications.

Fabrication and characterization of sol-gel derived 45S5 Bioglass®-ceramic scaffolds

Although Bioglass® has existed for nearly half a century its ability to trigger bone formation and tuneable degradability is vastly superior to other bioceramics, such as SiO(2)-CaO bioactive glasses. The sol-gel process of producing glass foams is well established for SiO(2)-CaO compositions, but not yet established for 45S5 composites containing Na(2)O. In this work the sol-gel derived 45S5 Bioglass® has for the first time been foamed into highly porous three-dimensional scaffolds using a surfactant, combined with vigorous mechanical stirring and subsequent sintering at 1000°C for 2 h. It was found that the mechanical strength of the sintered sol-gel derived Bioglass® scaffolds was significantly improved, attributable to the small fraction of material on the pore walls. More importantly, the compressive strength of the three-dimensional scaffolds produced by this surfactant foaming method could be predicted using Gibson and Ashby's closed cell model of porous networks. A comparative experiment revealed that ion release from the sol-gel derived Bioglass® foams was faster than that of counterparts produced by the replication technique. In vitro evaluation using osteoblast-like cells demonstrated that the sol-gel derived 45S5 Bioglass foams supported the proliferation of viable cell populations on the surface of the scaffolds, although few cells were observed to migrate into the virtually closed pores within the foams. Further work should be focused on modifications of the reaction conditions or alternative foaming techniques to improve pore interconnection.

UV-killed Staphylococcus aureus enhances adhesion and differentiation of osteoblasts on bone-associated biomaterials

Titanium alloys (Ti) are the preferred material for orthopedic applications. However, very often, these metallic implants loosen over a long period and mandate revision surgery. For implant success, osteoblasts must adhere to the implant surface and deposit a mineralized extracellular matrix (ECM). Here, we utilized UV-killed Staphylococcus aureus as a novel osteoconductive coating for Ti surfaces. S. aureus expresses surface adhesins capable of binding to bone and biomaterials directly. Furthermore, interaction of S. aureus with osteoblasts activates growth factor-related pathways that potentiate osteogenesis. Although UV-killed S. aureus cells retain their bone-adhesive ability, they do not stimulate significant immune modulator expression. All of the abovementioned properties were utilized for a novel implant coating so as to promote osteoblast recruitment and subsequent cell functions on the bone-implant interface. In this study, osteoblast adhesion, proliferation, and mineralized ECM synthesis were measured on Ti surfaces coated with fibronectin with and without UV-killed bacteria. Osteoblast adhesion was enhanced on Ti alloy surfaces coated with bacteria compared to uncoated surfaces, while cell proliferation was sustained comparably on both surfaces. Osteoblast markers such as collagen, osteocalcin, alkaline phosphatase activity, and mineralized nodule formation were increased on Ti alloy coated with bacteria compared to uncoated surfaces.

An electronic device for accelerating bone formation in tissues surrounding a dental implant

A dental implant is a unique structure which can be used with a noninvasive method because it is inserted into the bone in part and extended extracorporally. This study presents an electronic device that is temporarily connected with the dental implant, and reports its effect on accelerating bone formation in the surrounding tissues in a canine mandibular model. A small sized and low power consumption biphasic electrical current (BEC) stimulator ASIC was developed and the surrounding tissue was exposed to continuous BEC stimulation for 7 days with the parameters of 20 microA/cm(2), 125 micros duration, and 100 pulses/s. After 2 (n = 5) and 5 weeks (n = 5), animals were sacrificed and the specimens were histomorphometrically evaluated. The newly formed bone area (BA) was 1.30 times (3 weeks, P < 0.05) and 1.35 times (5 weeks, P < 0.05) higher in the experimental group compared to the control group, respectively. Bone-implant contact (BIC) in 3-week specimens was 1.62 times (P < 0.05) greater in the experimental group, while there was no statistically significant difference in 5-week specimens. Based on these results showing accelerated bone formation on and around the dental implant, it could be suggested that the latent time for osseointegration in dental implants can be reduced, and the success rate of implants in poor quality bone can be increased by using our device with BEC.

TNAP, TrAP, ecto-purinergic signaling, and bone remodeling

Bone remodeling is a process of continuous resorption and formation/mineralization carried out by osteoclasts and osteoblasts, which, along with osteocytes, comprise the bone multicellular unit (BMU). A key component of the BMU is the bone remodeling compartment (BRC), isolated from the marrow by a canopy of osteoblast-like lining cells. Although much progress has been made regarding the cytokine-dependent and hormonal regulation of bone remodeling, less attention has been placed on the role of extracellular pH (pH(e)). Osteoclastic bone resorption occurs at acidic pH(e). Furthermore, osteoclasts can be regarded as epithelial-like cells, due to their polarized structure and ability to form a seal against bone, isolating the lacunar space. The major ecto-phosphatases of osteoclasts and osteoblasts, acid and alkaline phosphatases, both have ATPase activity with pH optima several units different from neutrality. Furthermore, osteoclasts and osteoblasts express plasma membrane purinergic P2 receptors that, upon activation by ATP, accelerate bone osteoclast resorption and impair osteoblast mineralization. We hypothesize that these ecto-phosphatases help regulate [ATP](e) and localized pH(e) at the sites of bone resorption and mineralization by pH-dependent ATP hydrolysis coupled with P2Y-dependent regulation of osteoclast and osteoblast function. Furthermore, osteoclast cellular HCO3(-), formed as a product of lacunar V-ATPase H(+) secretion, is secreted into the BRC, which could elevate BRC pH(e), in turn affecting osteoblast function. We will review the existing data addressing regulation of BRC pH(e), present a hypothesis regarding its regulation, and discuss the hypothesis in the context of the function of proteins that regulate pH(e).

Staphylococcus aureus induces expression of receptor activator of NF-kappaB ligand and prostaglandin E2 in infected murine osteoblasts

Osteomyelitis is an inflammatory disease of the bone that is characterized by the presence of necrotic bone tissue and increased osteoclast activity. Staphylococcus aureus is responsible for approximately 80% of all cases of human osteomyelitis. While the disease is especially difficult to treat, the pathogenesis of S. aureus-induced osteomyelitis is poorly understood. Elucidating the molecular mechanisms by which S. aureus induces osteomyelitis could lead to a better understanding of the disease and its progression and development of new treatments. Osteoblasts can produce several soluble factors that serve to modulate the activity or formation of osteoclasts. Receptor activator of NF-kappaB ligand (RANK-L) and prostaglandin E(2) (PGE(2)) are two such molecules which can promote osteoclastogenesis and stimulate bone resorption. In addition, previous studies in our laboratory have shown that osteoblasts produce inflammatory cytokines, such as interleukin 6, following infection with S. aureus, which could induce COX-2 and in turn PGE(2), further modulating osteoclast recruitment and differentiation. Therefore, we hypothesized that following infection with S. aureus, osteoblasts will express increased levels of RANK-L and PGE(2). The results presented in this study provide evidence for the first time that RANK-L mRNA and protein and PGE(2) expression are upregulated in S. aureus-infected primary osteoblasts. In addition, through the use of the specific COX-2 inhibitor NS 398, we show that when PGE(2) production is inhibited, RANK-L production is decreased. These data suggest a mechanism whereby osteoblasts regulate the production of RANK-L during infection.

Biocompatible glass-ceramic materials for bone substitution

A new bioactive glass composition (CEL2) in the SiO(2)-P(2)O(5)-CaO-MgO-K(2)O-Na(2)O system was tailored to control pH variations due to ion leaching phenomena when the glass is in contact with physiological fluids. CEL2 was prepared by a traditional melting-quenching process obtaining slices that were heat-treated to obtain a glass-ceramic material (CEL2GC) that was characterized thorough SEM analysis. Pre-treatment of CEL2GC with SBF was found to enhance its biocompatibility, as assessed by in vitro tests. CEL2 powder was then used to synthesize macroporous glass-ceramic scaffolds. To this end, CEL2 powders were mixed with polyethylene particles within the 300-600 microm size-range and then pressed to obtain crack-free compacted powders (green). This was heat-treated to remove the organic phase and to sinter the inorganic phase, leaving a porous structure. The biomaterial thus obtained was characterized by X-ray diffraction, SEM equipped with EDS, density measurement, image analysis, mechanical testing and in vitro evaluation, and found to be a glass-ceramic macroporous scaffold with uniformly distributed and highly interconnected porosity. The extent and size-range of the porosity can be tailored by varying the amount and size of the polyethylene particles.

TRAIL expression is induced in both osteoblasts containing intracellular Staphylococcus aureus and uninfected osteoblasts in infected cultures

Staphylococcus aureus is the principal etiological agent of osteomyelitis (bone infection), which is characterized by a progressive inflammatory response resulting in extensive damage to bone tissue. Recent studies have demonstrated the ability of S. aureus to invade and persist inside osteoblasts (bone matrix-forming cells) and other eukaryotic cells. The presence of intracellular S. aureus in bone tissue may be relevant to the pathology of osteomyelitis, a disease often refractory to antibiotic treatment and subject to recurrence months and even years after apparently successful therapy. The present study examined the production of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) following S. aureus infection, and whether expression of the molecule was induced by those osteoblasts containing intracellular S. aureus. Results from this study suggest that osteoblasts containing intracellular S. aureus induce TRAIL expression in uninfected osteoblasts present in infected cultures.

Biphasic electric current stimulates proliferation and induces VEGF production in osteoblasts

This study investigated biphasic electric current (BEC) functions as a new type of electrical stimulation to induce rat calvarial osteoblasts to proliferate, differentiate and synthesize cytokines. The culture system was designed so that biphasic current flowed between upper and lower gold plates. BEC helps to minimize the net charge accumulation during cell exposure to the electrical stimulation. Osteoblasts were exposed to electrical stimulation of 1.5 microA/cm2 at 3000 Hz, and the effect of BEC was assessed in the interrupted mode (6 h daily) and in the continuous mode (24 h daily), depending on the interval of stimulation. Whereas proliferation increased by 31% after stimulation in the continuous mode for 2 days, it was unaffected in the interrupted mode. The transcriptional expression of osteogenesis-related genes such as alkaline phosphatase (ALP), osteopontin, and type I collagen was unchanged 4 days after stimulation in both modes, while cbfa1 was decreased under the same conditions. There was no detectable change in mRNA expression of growth factors (BMP-2, -4, IGF-2 and TGF-beta1) that promote osteoblast differentiation. However, real-time RT-PCR and ELISA demonstrated that vascular endothelial growth factor (VEGF) was markedly up-regulated by BEC. Induction of VEGF by BEC was not hypoxia driven. In conclusion, the present in vitro study demonstrates that BEC increases cell proliferation and induces the production of VEGF. The BEC was more effective with continuous stimulation than with interrupted stimulation. To confirm whether BEC can enhance osteogenesis, further in vivo studies are needed.

Acidosis inhibits bone formation by osteoblasts in vitro by preventing mineralization

The negative effect of acidosis on the skeleton has been known for almost a century. Bone mineral serves an important pathophysiologic role as a reserve of hydroxyl ions to buffer systemic protons if the kidneys and lungs are unable to maintain acid-base balance within narrow physiologic limits. Extracellular hydrogen ions are now thought to be the primary activation signal for osteoclastic bone resorption, and osteoclasts are very sensitive to small changes in pH within the pathophysiologic range. Herein, we investigated the effects of acidosis on osteoblast function by using mineralized bone nodule-forming primary osteoblast cultures. Osteoblasts harvested from neonatal rat calvariae were cultured up to 21 days in serum-containing medium, with ascorbate, beta-glycerophosphate and dexamethasone. pH was manipulated by addition of 5 to 30 mmol/L HCl and monitored by blood gas analyzer. Abundant, matrix-containing mineralized nodules formed in osteoblast cultures at pH 7.4, but acidification progressively reduced mineralization of bone nodules, with complete abolition at pH 6.9. Osteoblast proliferation and collagen synthesis, assessed by 3H-thymidine and 3H-proline incorporation, respectively, were unaffected by pH in the range 7.4 to 6.9; no effect of acidification on collagen ultrastructure and organization was evident. The apoptosis rate of osteoblasts, assessed by the enrichment of nucleosomes in cell lysates, was also unaffected by pH within this range. However, osteoblast alkaline phosphatase activity, which peaked strongly near pH 7.4, was reduced eight-fold at pH 6.9. Reducing pH to 6.9 also downregulated messenger ribonucleic acid (mRNA) for alkaline phosphatase, but upregulated mRNA for matrix Gla protein, an inhibitor of mineralization. The same pH reduction is associated with two-and four-fold increases in Ca2+ and PO4(3-) solubility for hydroxyapatite, respectively. Our results show that acidosis exerts a selective, inhibitory action on matrix mineralization that is reciprocal with the osteoclast activation response. Thus, in uncorrected acidosis, the deposition of alkaline mineral in bone by osteoblasts is reduced, and osteoclast resorptive activity is increased in order to maximize the availability of hydroxyl ions in solution to buffer protons.

Long-term intermittent compressive stimulation improves the composition and mechanical properties of tissue-engineered cartilage

Tissue engineering of articular cartilage is a promising alternative for cartilage repair. However, it has been difficult to develop tissue in vitro that mimicks native cartilage. Cartilaginous tissue formed in vitro does not accumulate enough extracellular matrix, is deficient in collagen, and possesses only a fraction of the mechanical properties of native cartilage. In this study, we investigated whether long-term intermittent compressive stimulation would improve the quality of the generated tissue. Chondrocyte cultures were established on the surface of porous calcium polyphosphate substrates and allowed to form cartilaginous tissue. In vitro-formed tissues were subjected to different stimulation protocols for 1 week. The optimal mechanical stimulation parameters identified in this short-term study were then applied to the cultures for up to 4 weeks. Mechanical stimulation applied at a 5% compressive amplitude at a frequency of 1 Hz for 400 cycles every second day resulted in the greatest increase in collagen synthesis (37 +/- 9% over control) while not significantly affecting proteoglycan synthesis (2 +/- 8% over control). This condition, applied to the chondrocyte cultures for 4 weeks, resulted in a significant increase in the amount of tissue that formed (stimulated, 2.4 +/- 0.2 mg dry wt; unstimulated, 1.61 +/- 0.08 mg dry wt). Stimulated tissues contained approximately 40% more collagen (stimulated, 590 +/- 58 microg; unstimulated, 420 +/- 42 microg), and 30% more proteoglycans (stimulated, 393 +/- 34 microg; unstimulated, 302 +/- 32 microg) as well as displaying a 2- to 3-fold increase in compressive mechanical properties (maximal equilibrium stress: stimulated, 10 +/- 1 kPa; unstimulated, 5 +/- 1 kPa; maximal equilibrium modulus: stimulated, 80 +/- 23 kPa; unstimulated, 24 +/- 6 kPa). The results of this study demonstrate that intermittent mechanical stimulation can increase collagen synthesis and, when applied over a 4-week period, can accelerate extracellular matrix accumulation as well as improve the material properties of the developed tissue. Interestingly, only short periods of mechanical stimulation (6 min every second day) were needed to affect the quality of cartilaginous tissue formed in vitro.

Proliferation and differentiation of osteoblasts on Biocement D modified with collagen type I and citric acid

In this study, the proliferation and differentiation of rat calvarial osteoblasts cultured on either (1) calcium-phosphate bone cement Biocement D, (2) Biocement D with 2.5% (w/w) mineralized collagen type I, or (3) Biocement D with 2.5% (w/w) mineralized collagen type I and 3% (w/w) citric acid were investigated. Incubation of the composites in cell-culture medium resulted in a fast decrease of pH and calcium concentration as well as in an increase of phosphate concentration. Although these effects occurred with all investigated materials, the lowest extent could be observed for the citric-acid-containing composites. As shown by scanning-electron microscopy, osteoblasts adhered to the composite surfaces. Proliferation and differentiation of the cells grown on the composites were found to be reduced compared to cells grown on tissue-culture polystyrene. Cells cultured in the vicinity of the composites but without direct contact also exhibited a reduced rate of proliferation, reduced alkaline phosphatase activity, and reduced mineralization. Simulating the changes in calcium and phosphate concentration occasioned by the composites through exposing cells to EGTA and phosphate gives rise to the same effects of reducing proliferation, ALP activity, and mineralization. No indication for apoptosis in cells exposed to low calcium and high phosphate concentrations was found. The number of necrotic cells, however, increased after incubation with EGTA and phosphate. For assessment of cell-composite interactions and the success of the composites in vivo, as well as for more effective material development, it seems to be important to know how changes in microenvironmental pH and ion composition of the material affect cellular proliferation and differentiation.

Skeletal affinity of Tc(V)-DMS is bone cell mediated and pH dependent

In spite of recent advances in bone cellular and molecular biology, there is still a poor correlation between these parameters and data obtained from bone scintigraphy. Diphosphonate derivatives radiolabelled with technetium-99m (Tc-BPs) have long been recognised as bone-seeking agents with an affinity for areas of active mineralisation. However, during clinical trials with a pH-sensitive tumour agent, the pentavalent technetium complex of dimercaptosuccinic acid [Tc(V)-DMS] showed a noticeable osteotropic character only in bone pathologies (bone metastases, Paget's diseases) and lacked accumulation in normal mature bone. To decipher the osteotropic character of Tc(V)-DMS, a study at the cellular level was considered necessary. Moreover, to learn more about the role of Tc bone agents, acid-base regulation by bone tissue or cells was studied. First, biological parameters in body fluid were measured under systemic acidosis, induced by glucose administration, in normal and Ehrlich ascites tumour (EAT)-bearing mice. Then, in vivo biodistribution studies using Tc(V)-DMS or a conventional Tc-BP agent were carried out. The effect of glucose-mediated acidification on the skeletal distribution of the Tc agents in the mice provided valuable hints regarding the differential mediation of bone cells in skeletal tissue affinity for the agents. Thereafter, in vitro studies on osteoblast and osteoclast cells were performed and the comparative affinity of Tc(V)-DMS and Tc-BP was screened under diverse acidification conditions. Moreover, studies were also carried out on acid-base parameters related to the cellular uptake mechanism. Very specific pH-sensitive Tc(V)-DMS accumulation only in the osteoclastic system was detected, and use of Tc(V)-DMS in the differential detection of osteoblastic and osteoclastic metastases is discussed.

Influence of physicochemical reactions of bioactive glass on the behavior and activity of human osteoblastsin vitro

Bioactive glasses are characterized by a bond to bone with a hydroxyl carbonate apatite layer. They enhance bone tissue formation and for this purpose are used in orthopedic surgery and in dental implantology. In the current work, we studied the biological response of human osteoblasts with a bioactive glass. This bioactive glass is based on 50% Si0(2), 20% Na(2)O, 16% CaO, 6% P(2)O(5), 5% K(2)0, 2% Al(2)O(3) and 1% MgO and designated A9. Cracks and irregularities were observed on the material surface when it was immersed in the culture medium. In addition, energy dispersive X-ray analyses highlighted a selective release of the elements at the surface of the bioactive glass, such as Na(+) and K(+) ions, released from the first day, contrary to the Si, Al, Ca, P, and Mg elements, which were released more slowly. Cell proliferation kinetics, total protein synthesis, and DNA content of the osteoblasts in contact with bioactive glass were similar to control cells. The morphological studies by light and scanning electron microscopy revealed an increasing cellular density in culture with bioactive glass without contact inhibition. The immunohistochemical studies highlighted the expression of types I, III, and V collagens by osteoblasts cultured in the presence of bioactive glass. The pH measurement of the culture medium in the presence of bioactive glass demonstrated a slight alkalinization. We thus conclude that human osteoblasts preserve their properties in the presence of bioactive glass (A9).

Mechanism of pH regulation of connexin 43 expression in MC3T3-E1 cells

Gap junction (GJ) expression and function allowing cell-cell communication among osteoblasts may be important in new bone formation. An alkaline milieu stimulates mineralization, while extracellular acidification leads to demineralization of bone. It was previously demonstrated that alkaline pH increases, while acid pH decreases GJ intercellular communication by an increase in steady-state GJ connexin 43 (Cx43) mRNA and protein expression. At pH 7.6, transcription of new Cx43 mRNA was significantly higher than that at pH 6.9 but not significantly different at pH 7.2, as assessed by nuclear run-on assay. Transcription of new Cx43 mRNA was higher at pH 7.2 compared to that at pH 6.9. Although Cx43 mRNA half-life tended to be longer at pH 7.6, analysis of variance did not yield a significant difference of the Cx43 mRNA half-life at any of the pHs tested. Likewise, the half-life of Cx43 protein at pHs of 6.9, 7.2, and 7.6 was not significantly different. Plasma membrane and cytosolic Cx43 fractions were proportionately similar at pH 7.2 and 6.9. Thus, the decrease in Cx43 mRNA at low pH compared to high pH is due to a decrease in the transcription rate of Cx43 but not due to an alteration of message stability. The early uncoupling of gap junctions by low pH found previously does not appear to be due to changes in the half-life nor distribution of Cx43 protein between cytosolic and plasma membrane compartments.

Staphylococcus aureus - induced tumor necrosis factor - related apoptosis - inducing ligand expression mediates apoptosis and caspase-8 activation in infected osteoblasts

BACKGROUND

Staphylococcus aureus infection of normal osteoblasts induces expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL).

RESULTS

Normal osteoblasts were incubated in the presence of purified bacterial products over a range of concentrations. Results demonstrate that purified surface structures and a selected superantigen present in the extracellular environment are not capable of inducing TRAIL expression by osteoblasts. Osteoblasts were co-cultured with S. aureus at various multiplicities of infection utilizing cell culture chamber inserts. Results of those experiments suggest that direct contact between bacteria and osteoblasts is necessary for optimal TRAIL induction. Finally, S. aureus infection of osteoblasts in the presence of anti-TRAIL antibody demonstrates that TRAIL mediates caspase-8 activation and apoptosis of infected cells.

CONCLUSIONS

Collectively, these findings suggest a mechanism whereby S. aureus mediates bone destruction via induction of osteoblast apoptosis.

The effect of extracellular calcium ion on gene expression of bone-related proteins in human pulp cells

Calcium hydroxide is often used for induction of reparative dentin formation in endodontic treatment. However, little is known about the mechanism by which calcium hydroxide works. The calcium ion (Ca2+) is an important regulator of cell functions. In this study, we examined the effect of extracellular Ca2+ on gene expression of bone-related proteins in human cultured pulp cells in serum-free conditions. A Ca2+ level elevated by 0.7 mM induced an increase in mRNA expression of osteopontin and bone morphogenetic protein (BMP)-2. However, mRNA levels of BMP-4 and alkaline phosphatase decreased under the elevated Ca2+ culture condition. The same concentration of additional magnesium ions had little effect on expressions of the examined bone-related protein mRNAs. These findings suggest that Ca2+ in Ca(OH)2 specifically modulates osteopontin and BMP-2 levels during calcification in pulp.

Factors that modulate the effects of bone morphogenetic protein-induced periodontal regeneration: a critical review

The healing process initiated by a single molecular species of bone morphogenetic protein (BMP) such as BMP-2 or BMP-7 sets in motion a cascade of cellular events resulting in differentiation of progenitor cells into phenotypes involved in periodontal regeneration. For example, animal studies show that a single dose of recombinant human (rh) BMP-2 increases the rate of normal intramembranous bone formation and enhanced cementum formation during periodontal wound healing. However, the optimal effects of BMPs are modulated by a range of factors that need careful evaluation in clinical studies. These factors include the influence of root conditioning, occlusal loading, BMP dose, and the release characteristics of the carrier as well as the suitability of the model to evaluate the efficacy of BMPs. Each of these factors may affect the rate of BMP-induced osteogenesis and cementogenesis and subsequent periodontal ligament (PDL) formation during the early and late stages of periodontal wound healing. Although BMP-2 initiates stem cells along an osteogenic pathway, the dose may have to be of sufficient concentration to ensure other growth and differentiation factors do not redirect or retard the osteogenic potential of the cell. Understanding when to manipulate the cell's differentiation pathway with the application of single or multiple doses of BMPs at the appropriate concentration is required to optimize the effect of BMPs in periodontal wound healing. Therefore, different release profiles from the same carrier may be particularly important in tissues with mixed cell populations such as in the periodontium, where similar tissues like bone and cementum grow at different rates. Furthermore, treatment of intrabony defects with BMPs are likely to not only require appropriate temporal release of the BMP(s), but also a carrier that can serve as a template for new tissue formation providing space maintenance and supporting the mucoperiosteal flap. Many of these issues have not been adequately addressed from a periodontal standpoint; therefore the purpose of this review is to clarify our current understanding of the factors that are likely to modulate the effects of BMP-induced periodontal regeneration. Moreover, assessing the importance of these factors is essential prior to conducting expensive human clinical trials.

Effects of pH on human bone marrow stromal cells in vitro: implications for tissue engineering of bone

The objective of this study was to address the hypothesis that changes in extracellular pH alter collagen gene expression, collagen synthesis, and alkaline phosphatase activity in bone marrow stromal cells (BMSCs). Potential effects of pH on cell function are of particular importance for tissue engineering because considerable effort is being placed on engineering biodegradable polymers that may generate a local acidic microenvironment on degradation. Human and murine single-cell marrow suspensions were plated at a density of 2 x 10(4) cells/cm(2). After 7 days in culture, the pH of the culture medium was adjusted to one of six ranges: > or = 7.8, 7.5.-7.7, 7.2-7.4, 6.9-7.1, 6.6-6.8, or < or = 6.5. After 48 h of exposure to an altered pH, alkaline phosphatase activity and collagen synthesis decreased significantly with decreasing pH. This decrease was two-to threefold as pH decreased from 7.5 to 6.6. In contrast, alpha1(I) procollagen mRNA levels increased two- to threefold as pH was decreased. The trend in osteocalcin mRNA expression was opposite to that of collagen. Small shifts in extracellular pH led to significant changes in the ability of BMSCs to express markers of the osteoblast phenotype. These pH effects potentially relate to the microenvironment supplied by a tissue-engineering scaffold and suggest that degrading polymer scaffolds may influence the biologic activity of the cells in the immediate environment.

Involvement of mitogen-activated protein kinase pathways in Staphylococcus aureus invasion of normal osteoblasts

Staphylococcus aureus invades osteoblasts and can persist in the intracellular environment. The present study examined the role of osteoblast mitogen-activated protein kinase (MAPK) pathways in bacterial invasion. S. aureus infection of normal human and mouse osteoblasts resulted in an increase in the phosphorylation of the extracellular signal-regulated protein kinases (ERK 1 and 2). This stimulation of ERK 1 and 2 correlated with the time course of S. aureus invasion, and bacterial adherence induced the MAPK pathway. ERK 1 and 2 phosphorylation was time and dose dependent and required active S. aureus gene expression for maximal induction. The nonpathogenic Staphylococcus carnosus was also able to induce ERK 1 and 2 phosphorylation, albeit at lower levels than S. aureus. Phosphorylation of the stress-activated protein kinases was increased in both infected human and mouse osteoblasts; however, the p38 MAPK pathway was not activated in response to S. aureus. Finally, the transcription factor c-Jun, but not Elk-1 or ATF-2, was phosphorylated in response to S. aureus infection.

Staphylococcus aureus and Salmonella enterica serovar Dublin induce tumor necrosis factor-related apoptosis-inducing ligand expression by normal mouse and human osteoblasts

Staphylococcus aureus and Salmonella enterica serovar Dublin invade osteoblasts and are causative agents of human bone disease. In the present study, we examined the ability of S. aureus and Salmonella serovar Dublin to induce the production of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by normal osteoblasts. Normal mouse and human osteoblasts were cocultured with S. aureus or Salmonella serovar Dublin at different multiplicities of infection. Following initial incubation and examination of TRAIL expression, extracellular bacteria were killed by the addition of media containing the antibiotic gentamicin. Lysates and conditioned media from osteoblast cultures were then collected at various times following invasion and analyzed. The results demonstrated that S. aureus and Salmonella serovar Dublin are potent inducers of TRAIL expression by osteoblasts. Mouse and human TRAIL mRNA expression was induced by bacterial infection and demonstrated a dose-dependent response. Analysis of kinetics suggested that TRAIL mRNA was induced within 30 min after exposure to bacteria and that its level of expression remained relatively constant over the time period examined. mRNA molecules encoding TRAIL receptors were constitutively expressed by osteoblasts. Furthermore, TRAIL protein was detected as early as 45 min and up to 24 h following infection. The quantity of TRAIL protein produced also increased in a dose-dependent manner. Collectively, these findings suggest a mechanism whereby bacterial pathogens mediate bone destruction via osteoblast apoptosis.