Effects of Diabetes on Elemental Levels and Nanostructure of Root Canal Dentin.

INTRODUCTION: This study evaluated the effects of diabetes mellitus (DM) on the nanostructure of root canal dentin using high-resolution transmission electron microscopy (HRTEM) and inductively coupled plasma mass spectrometry (ICP-MS). METHODS: Twenty extracted human premolars from diabetic and nondiabetic patients (n = 10 in each group) were decoronated and sectioned horizontally into 40 2-mm-thick dentin discs, with each disc designated for a specific test. ICP-MS was used to determine the different elemental levels of copper, lithium, zinc, selenium, strontium, manganese, and magnesium in diabetic and nondiabetic specimens. HRTEM was used to analyze the shape and quantity of the apatite crystals in diabetic and nondiabetic dentin at the nanostructural level. Statistical analysis was performed using Kolmogorov-Smirnov and Student t test (P < .05). RESULTS: ICP-MS revealed significant differences in trace element concentrations between the diabetic and nondiabetic specimens (P < .05), with lower levels of magnesium, zinc, strontium, lithium, manganese, and selenium (P < .05), and higher levels of copper in diabetic specimens (P < .05). HRTEM revealed that diabetic dentin exhibited a less compact structure with smaller crystallites and significantly more crystals in the 2500 nm2 area (P < .05). CONCLUSION: Diabetic dentin exhibited smaller crystallites and altered elemental levels more than nondiabetic dentin, which could explain the higher root canal treatment failure rate in diabetic patients.

Effect of pectin on the crystallization of strontium substituted HA for bone reconstruction application.

The biomacropolymers of bone extracellular matrix (ECM) guide the growth of hydroxyapatite (HA) with various ionic substitutions. Pectin, a plant polysaccharide with chemical similarities to ECM, was investigated for its potential to promote the crystallization of strontium-substituted HA (SH). The influence of pectin (0.5 and 1.0 wt%) on the in situ mineralization of SH (10 and 30 mol% calcium substitution with strontium) was studied. The preferential affinity of pectin to strontium over calcium favoured the incorporation of strontium in apatite, decreased crystal size (18.85-26.22 nm) and retained more pectin residues (8-16%). The residual pectin strongly interacted with small SH particles, resulting in high microhardness (0.43-0.85 GPa) and high surface charge (-32.1 to -30.3 mV), while weak interaction with large HA particles resulted in low microhardness (0.15-0.25 GPa) and low surface charge (-35.4 to -34.6 mV). The in vitro cellular study using human osteoblast-like MG-63 cells demonstrated that inorganic size and material crystallinity play a vital role in regulating osteogenesis. The study suggests that the synchronization of low pectin concentration (0.5 wt%) and high strontium substitution in HA (30 mol%) offers the desired microhardness and in vitro osteogenic properties to emulate natural bone.

Strontium and simvastatin dual loaded hydroxyapatite microsphere reinforced poly(ε-caprolactone) scaffolds promote vascularized bone regeneration.

The promotion of vascular network formation in the early stages of implantation is considered a prerequisite for successful functional bone regeneration. In this study, we successfully constructed 3D printed scaffolds with strong mechanical strength and a controllable pore structure that can sustainably release strontium (Sr) ions and simvastatin (SIM) for up to 28 days by incorporation of Sr2+ and SIM-loaded hydroxyapatite microspheres (MHA) into a poly(ε-caprolactone) (PCL) matrix. In vitro cell experiments showed that Sr-doped scaffolds were beneficial to the proliferation and osteogenic differentiation of bone mesenchymal stem cells (BMSCs), an appropriate dose of SIM was beneficial to cell proliferation and angiogenesis, and a high dose of SIM was cytotoxic. The Sr- and SIM-dual-loaded scaffolds with an appropriate dose significantly induced osteogenic differentiation of BMSCs and tube formation of human umbilical vein endothelial cells (HUVECs) in vitro and promoted vascular network and functional bone formation in vivo. Ribose nucleic acid (RNA) sequencing analysis suggested that the mechanism of promotion of vascularized bone regeneration by fabricated scaffolds is that dual-loaded Sr2+ and SIM can upregulate osteogenic and vasculogenic-related genes and downregulate osteoclast-related genes, which is beneficial for vascular and new bone regeneration. The 3D printed composite scaffolds loaded with high-stability and low-cost inorganic Sr2+ ions and SIM small-molecule drugs hold great promise in the field of promoting vascularized bone regeneration.

Electrospun polylactic acid scaffolds with strontium- and cobalt-doped bioglass for potential use in bone tissue engineering applications.

The development of nanoscale biomaterials associated with polymers has been growing over the years, due to their important structural characteristics for applications in biological systems. The present study aimed to produce and test polymeric scaffolds composed of polylactic acid (PLA) fibers associated with a 58S bioglass doped with therapeutic ions for use in tissue engineering. Three 58S Bioglass was obtained by the sol-gel route, pure and doped with 5% strontium and cobalt ions. Solutions of 7% PLA was used as control and added the three different bioglass, 4% of 58S bioglass (PLA-BG), 4% bioglass-doped strontium (PLA-BGSr) and 4% bioglass-doped cobalt (PLA-BGCo). Scaffolds were produced through electrospinning process, and was characterized chemical and morphologically. The in vitro tests were performed using mesenchymal cells cultures from femurs of nine rats, grown in osteogenic supplemented total culture medium. After osteoblastic differentiation induction cell viability, alkaline phosphatase activity, total protein content quantification, and visualization of mineralization nodule tests were performed. Analysis of normal distribution used the Shapiro-Wilk test (nanofibers diameter and biological assay). Data were compared using the Kruskal-Wallis nonparametric test (p = 0.05). The bioglasses produced proved to be free of nitrate, chlorinated and nano-sized, with effective incorporation of therapeutic ions in their structure. All materials showed cell viability (>70%), total protein production, and alkaline phosphatase activity. It was possible to develop polylactic acid scaffolds associated with 58S bioglass doped with therapeutic ions without cytotoxicity. Scaffolds characteristics appear to sustain its application in bone tissue engineering.

Strontium Ranelate and Strontium Chloride Supplementation Influence on Bone Microarchitecture and Bone Turnover Markers-A Preliminary Study.

Despite strontium ranelate use in osteoporosis management being one of the promising concepts in disease treatment, there is no clear evidence that strontium organic compounds are more effective than inorganic ones. The aim of this study was to compare strontium chlorate and strontium ranelate influence on the mice bone microarchitecture. We investigated whether strontium chlorate (7.532 mmol/L) and strontium ranelate (7.78 mmol/L) solutions fed to healthy SWISS growing mice (n = 42) had an influence on the percent of bone volume (BV/TV), trabecular thickness (Tb.Th), number of trabeculae (Tb.N), and separation between each trabecula (Tb.Sp) in the chosen ROI (region of interest) in the distal metaphysis of the left femurs. The cortical bone surface was examined close to the ROI proximal scan. There was an increase in each examined parameter compared with the control group. There were no statistical differences between strontium ranelate and strontium chlorate parameters. Our study indicates that organic and inorganic strontium compounds similarly affect the bone microarchitecture and strength.

Fabrication of strontium carbonate-based composite bioceramics as potential bone regenerative biomaterials.

Strontium carbonate (SrC) bioceramics are proposed as potential biomaterials to efficaciously repair the bone defects. However, the development of SrC bioceramics is restricted by their intrinsic low mechanical strength. In this study, SrC-based composite bioceramics (SrC-SrP) were fabricated by incorporating strontium-containing phosphate glass (SrP). The results indicated that aside from the main crystalline phase SrC, new compounds were generated in the SrC-SrP bioceramics. Incorporating 10 wt% SrP promoted densification, thus dramatically improving compressive strength of SrC-SrP bioceramics. The SrC-SrP bioceramics facilitated apatite precipitation on their surface, and sustainedly released strontium, phosphorus and sodium ions. Compared with the well-known ß-tricalcium phosphate bioceramics, the SrC-SrP bioceramics with certain amounts of SrP enhanced proliferation, alkaline phosphatase activity and osteogenesis-related gene expressions of mouse bone mesenchymal stem cells. The SrC-SrP bioceramics with appropriate constituent can serve as novel bone regenerative biomaterials.

Narrow-Band Red-Emitting Phosphors with High Color Purity, Trifling Thermal and Concentration Quenching for Hybrid White LEDs and Li3Y3BaSr(MoO4)8:Sm3+, Eu3+-Based Deep-Red LEDs for Plant Growth Applications.

Trivalent europium-based monochromatic red light-emitting phosphors are an essential component to realize high-performance smart lighting devices; however, the concentration and thermal quenching restrict their usage. Here, we report a series of efficient Eu3+-substituted Li3Y3BaSr(MoO4)8 red-emitting phosphors based on a stratified scheelite structure with negligible concentration and thermal quenching. All of the host and phosphor compositions crystallize in monoclinic crystal structure (space group C2/c). All of the phosphor compositions produce narrow-band red emission (FWHM ∼6 nm), which is highly apparent to the human eyes, and lead to exceptional chromatic saturation of the red spectral window. Concurrently, detailed investigations were carried out to comprehend the concentration and thermal quenching mechanism. Absolute quantum yields as high as 88.5% were obtained for Li3Y0.3Eu2.7BaSr(MoO4)8 phosphor with virtuous thermal stability (at 400 K, retaining 87% of its emission intensity). The light-emitting diodes were constructed by coupling Li3BaSrY0.3Eu2.7(MoO4)8 red phosphor with a near-UV LED chip (395 nm) operated at 20 mA forward bias, and the hybrid white LED (an organic yellow dye + red Li3Y3BaSr(MoO4)8:Eu3+ phosphor integrated with an NUV LED chip) showed a low CCT (6645 K), high CRI (83) values, and CIE values of x = 0.303; y = 0.368, which indicated that the synthesized phosphors can be a suitable red component for white LEDs. In addition, we have systematically investigated the Sm3+ and Sm3+, Eu3+ activation in Li3Y3BaSr(MoO4)8 to display the latent use of the system in plant growth applications and establish that the phosphor exhibits orange red emission with an intense deep-red emission (645 nm (4G5/2 → 6H9/2)). The phytochrome (Pr) absorption spectrum well matched the fabricated deep-red LED (by integrating a NUV LED + Li3Y3BaSr(MoO4)8:Sm3+ and Eu3+ phosphor) spectral lines.

Nanofibrous scaffolds ofϵ-polycaprolactone containing Sr/Se-hydroxyapatite/graphene oxide for tissue engineering applications.

For wound healing applications, a scaffold of biocompatible/porous networks is crucial to support cell proliferation and spreading. Therefore,ϵ-polycaprolactone (PCL) nanofibrous scaffolds containing co-dopants of strontium/selenium in hydroxyapatite (HAP) were modified with different contributions of graphene oxide (GO) via the laser ablation technique. The obtained compositions were investigated using XRD, TEM and FESEM. It was evident that fiber diameters were in the range of 0.15-0.30µm and 0.35-0.83µm at the lowest and highest concentration of GO respectively, while the maximum height of the roughness progressed to 393 nm. The toughness behavior was promoted from 5.77 ± 0.21 to 9.16 ± 0.29 MJ m-3upon GO from the lowest to the highest contribution, while the maximum strain at break reached 148.1% ± 0.49% at the highest concentration of GO. The cell viability indicated that the fibrous scaffold was biocompatible. The investigation of the HFB4 cell attachments towards the fibrous compositions showed that with the increase of GO, cells tended to grow intensively through the scaffolds. Furthermore, the proliferation of cells was observed to be rooted in the porous structure and spreading on the surface of the scaffold. This progression of cells with an increase in GO content may provide a simple strategy not only to enhance the mechanical properties, but also to manipulate a nanofibrous scaffold with proper behaviors for biomedical applications.

Strontium enhances BMP-2 mediated bone regeneration in a femoral murine bone defect model.

The application of strontium is one option for the clinical treatment of osteoporosis-a disease characterized by reduced bone density and quality-in order to reduce the risk of vertebral and nonvertebral fractures. Unlike other drugs used in osteoporosis therapy, strontium shows a dual effect on bone metabolism by attenuating cellular resorption and simultaneously enhancing new bone tissue formation. Current concerns regarding the systemic application of highly dosed strontium ranelate led to the development of strontium-modified scaffolds based on mineralized collagen (MCM) capable to release biologically active Sr2+ ions directly at the fracture site. In this study, we investigated the regenerative potential of these scaffolds. For in vitro investigations, human mesenchymal stromal cells were cultivated on the scaffolds for 21 days (w/ and w/o osteogenic supplements). Biochemical analysis revealed a significant promoting effect on proliferation rate and osteogenic differentiation on strontium-modified scaffolds. In vivo, scaffolds were implanted in a murine segmental bone defect model-partly additionally functionalized with the osteogenic growth factor bone morphogenetic protein 2 (BMP-2). After 6 weeks, bridging calluses were obtained in BMP-2 functionalized scaffolds; the quality of the newly formed bone tissue by means of morphological scores was clearly enhanced in strontium-modified scaffolds. Histological analysis revealed increased numbers of osteoblasts and blood vessels, decreased numbers of osteoclasts, and significantly enhanced mechanical properties. These results indicate that the combined release of Sr2+ ions and BMP-2 from the biomimetic scaffolds is a promising strategy to enhance bone regeneration, especially in patients suffering from osteoporosis. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:174-182, 2020.

The Impact of Long-and Short-Term Strontium Treatment on Metabolites and Minerals in Glycine max.

The impact of long-term exposure to Sr2+ (LTE, four doses, 43.5 mg Sr2+ per pot, with a total of 174 mg Sr2+ per pot during the entire period of cultivation) and short-term exposure to Sr2+ (STE, one dose, 870 mg Sr2+ per pot four days before harvest) on the content of phytoestrogens and allantoin in soybeans were compared. Sr2+ accumulation, the effect on the concentration of macroelements, and basic physiology were also analyzed. LTE reduced the content of malonyldaidzin and malonylgenistin in the roots (58% and 50% compared to the control, respectively). STE increased the amount of all isoflavones in the stem and genistein in the leaves and decreased the content of malonyldaidzin and malonylgenistin in the leaves (55% and 48% compared to the control, respectively) and roots (69% and 62% of the control, respectively) as well as genistein and coumestrol in the roots (both 50% compared to the control). Sr2+ presence stimulated the accumulation of allantoin in the roots (three-fold higher than in the control), but only STE had similar effects on the shoots. In contrast to LTE, Sr2+ was transported extensively from the roots to the leaves under STE. In comparison to the control, LTE resulted in an increase in the Ca content in the stem by 36%, whereas Ca2+ accumulation in the leaves, stems, and roots increased by 60%, 80%, and 36%, respectively, under STE. Additionally, a significant accumulation of K was found only in the roots of the LTE group. The chlorophyll content did not differ between the treatments. Overall, the production of phytoestrogens and Sr accumulation were affected by both the applied dose and the duration of exposure to Sr.

Antibacterial, angiogenic, and osteogenic activities of Ca, P, Co, F, and Sr compound doped titania coatings with different Sr content.

Titanium implants are often combined with microporous titania coatings simultaneously doped with various elements to enhance their antibacterial, angiogenic and osteogenic activities. To evaluate how Sr doping levels affect properties of titania coatings simultaneously doped with Ca, P, Co and F (TiCPCF coatings), we prepared coatings with Sr contents equal to 6, 11 and 18 wt% (TiCPCF-S6, TiCPCF-S11 and TiCPCF-S18, respectively) using micro-arc oxidation of titanium. Sr presence in TiCPCF coatings did not affect their phase compositions, microstructure, surface wettability, roughness, and adhesion to titanium. Antibacterial, angio- and osteo-genic activities of all the coatings were evaluated. Sr incorporation improved mesenchymal stem cell proliferation, osteogenic differentiation and implant osseointegration. TiCPCF-S11 showed the most optimum Sr content judging by its enhanced osteogenic activity. While Sr incorporation did not weaken angiogenic and antibacterial abilities of TiCPCF. Thus TiCPCF-S11 coating is a very strong candidate to be used as a next-generation bone implant material.

Human mesenchymal stem cells differentiate into an osteogenic lineage in presence of strontium containing bioactive glass nanoparticles.

While bioactive glass and ions released during its dissolution are known to stimulate osteoblast cells, the effect bioactive glass has on human stem cells is not clear. Here, we show that spherical monodispersed strontium containing bioactive nanoparticles (Sr-BGNPs) of composition 90.6 mol% SiO2, 5.0 mol% CaO, 4.4% mol% SrO (4.4%Sr-BGNPs) and 88.8 mol% SiO2, 1.8 mol% CaO, and 9.4 mol% SrO (9.4%Sr-BGNPs) stimulate bone marrow derived human stem cell (hMSC) differentiation down an osteogenic pathway without osteogenic supplements. The particles were synthesised using a modified StÓ§ber process and had diameters of 90 ±â€¯10 nm. Previous work on similar particles that did not contain Sr (80 mol% SiO2, 20 mol% CaO) showed stem cells did not differentiate when exposed to the particles. Here, both compositions of the Sr-BGNPs (up to concentration of 250 µg/mL) stimulated the early-, mid-, and late-stage markers of osteogenic differentiation and accelerated mineralisation in the absence of osteogenic supplements. Sr ions play a key role in osteogenic stem cell differentiation. Sr-BGNP dissolution products did not adversely affect hMSC viability and no significant differences in viability were measured between each particle composition. Confocal and transmission electron microscopy (TEM) demonstrated that monodispersed Sr-BGNPs were internalised and localised within vesicles in the cytoplasm of hMSCs. Degradation of particles inside the cells was observed, whilst maintaining effective cations (Ca and Sr) in their silica network after 24 h in culture. The uptake of Sr-BGNPs by hMSCs was reduced by inhibitors of specific routes of endocytosis, indicating that the Sr-BGNPs uptake by hMSCs was probably via mixed endocytosis mechanisms. Sr-BGNPs have potential as injectable therapeutic devices for bone regeneration or treatment of conditions such as osteoporosis, because of their ability deliver a sustained release of osteogenic inorganic cations, e.g. calcium (Ca) or and strontium (Sr), through particle degradation locally to cells. STATEMENT OF SIGNIFICANCE: Here, we show that 90 nm spherical strontium containing bioactive nanoparticles of stimulate bone marrow derived human stem cell (hMSC) differentiation down an osteogenic pathway without the use of osteogenic supplements. While bioactive glass and its dissolution products are known to promote excellent bone regeneration in vivo and to stimulate osteoblast cells to produce bone matrix in vitro, their effect on human stem cells is not clear. Previously our nanoparticles that contained only SiO2 and CaO did not provoke human bone marrow or adipose derived stem cell differentiation.

Study on MgxSr3-x(PO4)2 bioceramics as potential bone grafts.

Magnesium (Mg) and strontium (Sr), which are essential nutrient elements in the natural bone, positively affect the osteogenic activity even in wide ranges of ion concentrations. However, it remains unknown whether magnesium-strontium phosphates [MgxSr3-x(PO4)2] are potential bone grafts for accelerating bone regeneration. Herein, a serial of MgxSr3-x(PO4)2, including Mg3(PO4)2, Mg2Sr(PO4)2, Mg1.5Sr1.5(PO4)2, MgSr2(PO4)2 and Sr3(PO4)2, were synthesized using a solid-state reaction approach. The physicochemical properties and cell behaviors of MgxSr3-x(PO4)2 bioceramics were characterized and compared with the common bone graft ß-tricalcium phosphate (ß-TCP). The results indicated that various MgxSr3-x(PO4)2 bioceramics differed in compressive strength and in vitro degradation rate. All the MgxSr3-x(PO4)2 bioceramics had excellent biocompatibility. In contrast to ß-TCP, the MgxSr3-x(PO4)2 enhanced alkaline phosphatase activity of mouse bone mesenchymal stem cells (mBMSCs), and inhibited osteoclastogenesis-related gene expression of RAW264.7 cells, but did not enhance osteogenesis-related gene expression of mBMSCs which were treated with osteogenesis induction supplements. However, Mg3(PO4)2 stimulated osteogenesis-related gene expression of mBMSCs without the treatment of osteogenesis induction supplements. This work contributes to the design of bone graft and may open a new avenue for the bone regeneration field.

In vitro evaluation of MgSr and MgCaSr alloys via direct culture with bone marrow derived mesenchymal stem cells.

Magnesium (Mg) and its alloys have been widely investigated as the most promising biodegradable metals to replace conventional non-degradable metals for temporary medical implant applications. New Mg alloys have been developed for medical applications in recent years; and the concept of alloying Mg with less-toxic elements have aroused tremendous interests due to the promise to address the problems associated with rapid degradation of Mg without compromising its cytocompatibility and biocompatibility. Of particular interests for orthopedic/spinal implant applications are the additions of calcium (Ca) and strontium (Sr) into Mg matrix because of their beneficial properties for bone regeneration. In this study, degradation and cytocompatibility of four binary MgSr alloys (Mg-xSr, x = 0.2, 0.5, 1 and 2 wt%) and four ternary MgCaSr alloys (Mg-1Ca-xSr, x = 0.2, 0.5, 1 and 2 wt%) were investigated and compared via direct culture with bone marrow-derived mesenchymal stem cells (BMSCs). The influence of the alloy composition on the degradation rates were studied and compared. Moreover, the cellular responses to the binary MgSr alloys and the ternary MgCaSr alloys were comparatively evaluated; and the critical factors influencing BMSC behaviors were discussed. This study screened the degradability and in vitro cytocompatibility of the binary MgSr alloys and the ternary MgCaSr alloys. Mg-1Sr, Mg-1Ca-0.5Sr and Mg-1Ca-1Sr alloys are recommended for further in vivo studies toward clinical translation due to their best overall performances in terms of degradation and cytocompatibility among all the alloys studied in the present work. STATEMENT OF SIGNIFICANCE: Traditional Mg alloys with slower degradation often contain aluminum or rare earth elements as alloying components, which raised safety and regulatory concerns. To circumvent unsafe elements, nutrient elements such as calcium (Ca) and strontium (Sr) were selected to create Mg-Sr binary alloys and Mg-Ca-Sr ternary alloys to improve the safety and biocompatibility of bioresorbable Mg alloys for medical implant applications. In this study, in vitro degradation and cellular responses to four binary Mg-xSr alloys and four ternary Mg-1Ca-xSr alloys with increasing Sr content (up to 2 wt%) were evaluated in direct culture with bone marrow derived mesenchymal stem cells (BMSCs). The roles of Sr and Ca in tuning the alloy microstructure, degradation behaviors, and BMSC responses were collectively compared in the BMSC direct culture system for the first time. The most promising alloys were identified and recommended for further in vivo studies toward clinical translation.

In vitro osteogenesis by intracellular uptake of strontium containing bioactive glass nanoparticles.

Monodispersed strontium containing bioactive glass nanoparticles (Sr-BGNPs) with two compositions were synthesised, through a modified sol-gel Stöber process, wherein silica nanoparticles (SiO2-NPs) were formed prior to incorporation of calcium and strontium, with diameters of 90 ±â€¯10 nm. The osteogenic response of a murine preosteoblast cell line, MC3T3-E1, was investigated in vitro for a nanoparticle concentration of 250 µg/mL with compositions of 87 mol% SiO2, 7 mol% CaO, 6 mol% SrO and 83 mol% SiO2, 3 mol% CaO, 14 mol% SrO. Dissolution studies in minimum essential media (α-MEM) at pH 7.4 and artificial lysosomal fluid (ALF) at pH 4.5 showed that the particles dissolved and that Sr2+ ions were released from Sr-BGNPs in both environments. Both particle compositions and their ionic dissolution products enhanced the alkaline phosphatase (ALP) activity of the cells and calcium deposition. Immunohistochemistry (IHC) staining of Col1a1, osteocalcin (OSC) and osteopontin (OSP) showed that these proteins were expressed in the MC3T3-E1 cells following three weeks of culture. In the basal condition, the late osteogenic differentiation markers, OSC and OSP, were more overtly expressed by cells cultured with Sr-BGNPs with 14 mol% SrO and their ionic release products than in the control condition. Col1a1 expression was only slightly enhanced in the basal condition, but was enhanced further by the osteogenic supplements. These data demonstrate that Sr-BGNPs accelerate mineralisation without osteogenic supplements. Sr-BGNPs were internalised into MC3T3-E1 cells by endocytosis and stimulated osteogenic differentiation of the pre-osteoblast cell line. Sr-BGNPs are likely to be beneficial for bone regeneration and the observed osteogenic effects of these particles can be attributed to their ionic release products. STATEMENT OF SIGNIFICANCE: We report, for the first time, that monodispersed bioactive glass nanoparticles (∼90 nm) are internalised into preosteoblast cells by endocytosis but by unspecific mechanisms. The bioactive nanoparticles and their dissolution products (without the particles present) stimulated the expression of osteogenic markers from preosteoblast cells without the addition of other osteogenic supplements. Incorporating Sr into the bioactive glass nanoparticle composition, in addition to Ca, increased the total cation content (and therefore dissolution rate) of the nanoparticles, even though nominal total cation addition was constant, without changing size or morphology. Increasing Sr content in the nanoparticles and in their dissolution products enhanced osteogenesis in vitro. The particles therefore have great potential as an injectable therapeutic for bone regeneration, particularly in patients with osteoporosis, for which Sr is known to be therapeutic agent.

Low-dose strontium stimulates osteogenesis but high-dose doses cause apoptosis in human adipose-derived stem cells via regulation of the ERK1/2 signaling pathway.

BACKGROUND: Strontium is a widely used anti-osteoporotic agent due to its dual effects on inhibiting bone resorption and stimulating bone formation. Thus, we studied the dose response of strontium on osteo-inductive efficiency in human adipose-derived stem cells (hASCs). METHOD: Qualitative alkaline phosphatase (ALP) staining, quantitative ALP activity, Alizarin Red staining, real-time polymerase chain reaction and Western blot were used to investigate the in vitro effects of a range of strontium concentrations on hASC osteogenesis and associated signaling pathways. RESULTS: In vitro work revealed that strontium (25-500 µM) promoted osteogenic differentiation of hASCs according to ALP activity, extracellular calcium deposition, and expression of osteogenic genes such as runt-related transcription factor 2, ALP, collagen-1, and osteocalcin. However, osteogenic differentiation of hASCs was significantly inhibited with higher doses of strontium (1000-3000 µM). These latter doses of strontium promoted apoptosis, and phosphorylation of ERK1/2 signaling was increased and accompanied by the downregulation of Bcl-2 and increased phosphorylation of BAX. The inhibition of ERK1/2 decreased apoptosis in hASCs. CONCLUSION: Lower concentrations of strontium facilitate osteogenic differentiation of hASCs up to a point; higher doses cause apoptosis of hASCs, with activation of the ERK1/2 signaling pathway contributing to this process.

Strontium-doped hydroxyapatite polysaccharide materials effect on ectopic bone formation.

Previous studies performed using polysaccharide-based matrices supplemented with hydroxyapatite (HA) particles showed their ability to form in subcutaneous and intramuscular sites a mineralized and osteoid tissue. Our objectives are to optimize the HA content in the matrix and to test the combination of HA with strontium (Sr-HA) to increase the matrix bioactivity. First, non-doped Sr-HA powders were combined to the matrix at three different ratios and were implanted subcutaneously for 2 and 4 weeks. Interestingly, matrices showed radiolucent properties before implantation. Quantitative analysis of micro-CT data evidenced a significant increase of mineralized tissue formed ectopically with time of implantation and allowed us to select the best ratio of HA to polysaccharides of 30% (w/w). Then, two Sr-substitution of 8% and 50% were incorporated in the HA powders (8Sr-HA and 50Sr-HA). Both Sr-HA were chemically characterized and dispersed in matrices. In vitro studies performed with human mesenchymal stem cells (MSCs) demonstrated the absence of cytotoxicity of the Sr-doped matrices whatever the amount of incorporated Sr. They also supported osteoblastic differentiation and activated the expression of one late osteoblastic marker involved in the mineralization process i.e. osteopontin. In vivo, subcutaneous implantation of these Sr-doped matrices induced osteoid tissue and blood vessels formation.

Effect of strontium citrate on bone consolidation during mandibular distraction osteogenesis.

OBJECTIVES/HYPOTHESIS: Mandibular distraction osteogenesis (MDO) involves a lengthy consolidation phase where complications can occur. Strontium is an element that has been shown to improve bone healing. The objective of this study was to determine whether strontium citrate can be used to enhance bone healing during MDO in a rabbit model. STUDY DESIGN: Prospective animal model study. METHODS: Custom-made MDO devices were placed on 20 New Zealand White rabbits. After a 7-day latency period, distraction was performed at 1 mm/day for 5 days. The study group rabbits (n = 10) received oral strontium citrate; the other 10 rabbits served as controls. Mandibles were removed at the end of the consolidation period (4 weeks). Formation and healing of new bone were evaluated with microcomputed tomography, histology, and a three-point bending mechanical test. RESULTS: New bone formed in all animals, but the consolidation process was enhanced in rabbits that received strontium. The histological analysis showed that study group rabbits had more mature bone. Microcomputed tomographic images demonstrated significantly higher bone density for study group animals, and the three-point bending test results demonstrated that the maximum load of the study group specimens was significantly greater than that of the control group mandibles. CONCLUSIONS: Strontium citrate improved the formation of new bone in the current rabbit model of MDO. The prolonged consolidation period may be shortened with strontium citrate, which may also have the potential to reduce complications. LEVEL OF EVIDENCE: NA Laryngoscope, 127:E212-E218, 2017.

Synthesis and characterization of strontium-substituted hydroxyapatite nanoparticles for bone regeneration.

The production of stable suspensions of strontium-substituted hydroxyapatite (Sr-HA) nanopowders, as Sr ions vector for bone tissue regeneration, was carried out in the present work. Sr-HA nanopowders were synthesized via aqueous precipitation methods using Sr2+ amount from 0 to 100mol% and were characterized by several complementary techniques such as solid-state Nuclear Magnetic Resonance spectroscopy, X-ray diffraction, Infrared spectroscopy, N2 physisorption and Transmission Electron Microscopy. The substitution of Ca2+ with Sr2+ in HA is always isomorphic with gradual evolution between the two limit compositions (containing 100% Ca and 100% Sr), this pointing out the homogeneity of the synthesized nanopowders and the complete solubility of strontium in HA lattice. Strontium addition is responsible for an increasing c/a ratio in the triclinic unit cell. A significant variation of the nanopowders shape and dimension is also observed, a preferential growth along the c-axis direction being evident at higher strontium loads. Modifications in the local chemical environment of phosphate and hydroxyl groups in the apatite lattice are also observed. Stable suspensions were produced by dispersing the synthesized nanopowders in bovine serum albumin. Characterization by Dynamic Light Scattering and ζ-potential determination allowed to show that Ca2+→Sr2+ substitution influences the hydrodynamic diameter, which is always twice the particles size determined by TEM, the nanoparticles being always negatively charged as a result from the albumin rearrangement upon the interaction with nanoparticles surface. The biocompatibility of the suspensions was studied in terms of cell viability, apoptosis, proliferation and morphology, using osteosarcoma cell line SAOS-2. The data pointed out an increased cell proliferation for HA nanoparticles containing larger Sr2+ load, the cells morphology remaining essentially unaffected.

The Stimulatory Effect of Strontium Ions on Phytoestrogens Content in Glycine max (L.) Merr.

The amount of secondary metabolites in plants can be enhanced or reduced by various external factors. In this study, the effect of strontium ions on the production of phytoestrogens in soybeans was investigated. The plants were treated with Hoagland's solution, modified with Sr(2+) with concentrations ranging from 0.5 to 3.0 mM, and were grown for 14 days in hydroponic cultivation. After harvest, soybean plants were separated into roots and shoots, dried, and pulverized. The plant material was extracted with methanol and hydrolyzed. Phytoestrogens were quantified by HPLC. The significant increase in the concentration of the compounds of interest was observed for all tested concentrations of strontium ions when compared to control. Sr(2+) at a concentration of 2 mM was the strongest elicitor, and the amount of phytoestrogens in plant increased ca. 2.70, 1.92, 3.77 and 2.88-fold, for daidzein, coumestrol, genistein and formononetin, respectively. Moreover, no cytotoxic effects were observed in HepG2 liver cell models after treatment with extracts from 2 mM Sr(2+)-stressed soybean plants when compared to extracts from non-stressed plants. Our results indicate that the addition of strontium ions to the culture media may be used to functionalize soybean plants with enhanced phytoestrogen content.