Rebalancing bone turnover in favour of formation with strontium ranelate: implications for bone strength

Exploring the role of strontium-based nanoparticles in modulating bone regeneration and antimicrobial resistance: a public health perspective

Strontium-based nanoparticles (SrNPs) have emerged as a versatile and promising class of nanomaterials with a wide range of potential applications in healthcare, particularly in the fields of bone regeneration and combating antimicrobial resistance (AMR). Recent research has highlighted the unique properties of SrNPs, including their ability to promote osteogenesis, enhance bone healing, and exhibit strong antimicrobial activity against multidrug-resistant pathogens. These attributes position SrNPs as innovative therapeutic agents with the potential to address challenges such as osteoporosis, bone infections, and the growing global AMR crisis. This comprehensive review critically examines the dual functional potential of SrNPs by analyzing their synthesis methods, physicochemical properties, biological interactions, and translational applications in orthopedic and antimicrobial therapies. Specifically, the review emphasizes SrNPs' ability to enhance bone density, accelerate fracture healing, and reduce the economic burden associated with prolonged treatment and rehabilitation for bone-related diseases. Furthermore, their novel application as antimicrobial agents is explored, highlighting their ability to target bacterial metabolic pathways and combat the rise of antibiotic resistance. The review focuses on the synthesis methods used for SrNPs, particularly co-precipitation, hydrothermal synthesis, and sol-gel techniques. Each method is explored for its ability to produce SrNPs with controlled size, shape, and functionality, while addressing their scalability, cost-effectiveness, and environmental impact. Additionally, the toxicological risks associated with SrNPs are also explored, emphasizing the need for comprehensive preclinical and clinical evaluations to ensure safety for humans and ecosystems. The regulatory and ethical landscape of SrNPs highlights the need for global safety protocols, equitable access, and international cooperation to ensure ethical nanotechnology use. Environmental fate studies address bioaccumulation risks and ecological concerns. This review identifies opportunities and challenges in advancing bone regenerative medicine and combating AMR while emphasizing sustainable and ethical SrNP development for researchers, policymakers, and stakeholders.

Strontium Functionalization of Biomaterials for Bone Tissue Engineering Purposes: A Biological Point of View

Strontium (Sr) is a trace element taken with nutrition and found in bone in close connection to native hydroxyapatite. Sr is involved in a dual mechanism of coupling the stimulation of bone formation with the inhibition of bone resorption, as reported in the literature. Interest in studying Sr has increased in the last decades due to the development of strontium ranelate (SrRan), an orally active agent acting as an anti-osteoporosis drug. However, the use of SrRan was subjected to some limitations starting from 2014 due to its negative side effects on the cardiac safety of patients. In this scenario, an interesting perspective for the administration of Sr is the introduction of Sr ions in biomaterials for bone tissue engineering (BTE) applications. This strategy has attracted attention thanks to its positive effects on bone formation, alongside the reduction of osteoclast activity, proven by in vitro and in vivo studies. The purpose of this review is to go through the classes of biomaterials most commonly used in BTE and functionalized with Sr, i.e., calcium phosphate ceramics, bioactive glasses, metal-based materials, and polymers. The works discussed in this review were selected as representative for each type of the above-mentioned categories, and the biological evaluation in vitro and/or in vivo was the main criterion for selection. The encouraging results collected from the in vitro and in vivo biological evaluations are outlined to highlight the potential applications of materials’ functionalization with Sr as an osteopromoting dopant in BTE.

Capability of core-sheath polyvinyl alcohol-polycaprolactone emulsion electrospun nanofibrous scaffolds in releasing strontium ranelate for bone regeneration

Core-sheath nanofibrous scaffolds from polyvinyl alcohol (PVA)-strontium ranelate (SrR)-Polycaprolactone (PCL) were prepared by water in oil electrospinning method. Thus, PCL (the oil phase) was used as the shell part and a mixture of PVA and SrR (the water phase) was inserted in the core. The amounts of SrR was varied from 0 to 15 wt.% Mussel-inspired dopamine-gelatin coating was done on the nanofibrous to improve their hydrophilicity and cellular attachment. The effect of the SrR content on morphology, mechanical, physicochemical, in vitro release behaviors, and biological properties as well as in vivo bone regeneration was investigated. Morphological observations revealed that continuous nanofibers with a core/shell structure were successfully obtained and the fibers diameter increased as the SrR content rose. X-ray diffraction (XRD) analysis revealed that SrR was molecularly distributed in the nanofibers and increasing the amount of the SrR decreased the crystallinity of the nanofibers. Moreover, the SrR release was regulated through the mechanism of Fickian diffusion and it was assumed as fast as possible in the samples with higher SrR content. The mesenchymal stem cell culturing showed improved cell proliferation by adding SrR and accelerating the expression of ALP, Runx2, Col I, and OCN genes. Besides, the SrR-loaded nanofibers improved bone formation of calvarial defects in a rat model as revealed by in vivo investigations.

In Vitro Effects of Strontium on Proliferation and Osteoinduction of Human Preadipocytes

Development of tools to be used for in vivo bone tissue regeneration focuses on cellular models and differentiation processes. In searching for all the optimal sources, adipose tissue-derived mesenchymal stem cells (hADSCs or preadipocytes) are able to differentiate into osteoblasts with analogous characteristics to bone marrow mesenchymal stem cells, producing alkaline phosphatase (ALP), collagen, osteocalcin, and calcified nodules, mainly composed of hydroxyapatite (HA). The possibility to influence bone differentiation of stem cells encompasses local and systemic methods, including the use of drugs administered systemically. Among the latter, strontium ranelate (SR) represents an interesting compound, acting as an uncoupling factor that stimulates bone formation and inhibits bone resorption. The aim of our study was to evaluate the in vitro effects of a wide range of strontium (Sr(2+)) concentrations on proliferation, ALP activity, and mineralization of a novel finite clonal hADSCs cell line, named PA20-h5. Sr(2+) promoted PA20-h5 cell proliferation while inducing the increase of ALP activity and gene expression as well as HA production during in vitro osteoinduction. These findings indicate a role for Sr(2+) in supporting bone regeneration during the process of skeletal repair in general, and, more specifically, when cell therapies are applied.

Epidermal closure regulates histolysis during mammalian (Mus) digit regeneration

Mammalian digit regeneration progresses through consistent stages: histolysis, inflammation, epidermal closure, blastema formation, and finally redifferentiation. What we do not yet know is how each stage can affect others. Questions of stage timing, tissue interactions, and microenvironmental states are becoming increasingly important as we look toward solutions for whole limb regeneration. This study focuses on the timing of epidermal closure which, in mammals, is delayed compared to more regenerative animals like the axolotl. We use a standard wound closure device, Dermabond (2-octyl cyanoacrylate), to induce earlier epidermal closure, and we evaluate the effect of fast epidermal closure on histolysis, blastema formation, and redifferentiation. We find that fast epidermal closure is reliant upon a hypoxic microenvironment. Additionally, early epidermal closure eliminates the histolysis stage and results in a regenerate that more closely replicates the amputated structure. We show that tools like Dermabond and oxygen are able to independently influence the various stages of regeneration enabling us to uncouple histolysis, wound closure, and other regenerative events. With this study, we start to understand how each stage of mammalian digit regeneration is controlled.

The synthesis and characterisation of strontium and calcium folates with potential osteogenic activity

New strontium derivatives based on folic acid resulted in the formation of biocompatible SrFO compounds with osteogenic activity.

Strontium coating by electrochemical deposition improves implant osseointegration in osteopenic models

Osteopenia, a preclinical state of osteoporosis, restricts the application of adult orthodontic implant anchorage and tooth implantation. Strontium (Sr) is able to promote bone formation and inhibit bone absorption. The aim of the present study was to evaluate a new method for improving the success rate of dental implantation. In this study, an electrochemical deposition (ECD) method was used to prepare a Sr coating on a titanium implant. The coating composition was investigated by energy dispersive X-ray spectroscopy and X-ray diffraction, and the surface morphology of the coating was studied using scanning electron microscopy. A total of 24 Sprague-Dawley rats received bilateral ovariectomy (OVX) and an additional 12 rats underwent a sham surgery. All rats were then implanted in the bilateral tibiae with titanium mini-implants with or without a Sr coating. The results of histological examination and a fluorescence double labeling assay showed strong new bone formation with a wider zone between the double labels, a higher rate of bone mineralization and better osseointegration in the OVX rats that received Sr-coated implants compared with the OVX rats that received uncoated implants. The study indicates that Sr coatings are easily applied by an ECD method, and that Sr coatings have a promoting effect on implant osseointegration in animals with osteopenia.

Morphology, composition, and bioactivity of strontium-doped brushite coatings deposited on titanium implants via electrochemical deposition

Surface modification techniques have been applied to generate titanium implant surfaces that promote osseointegration for use in dental applications. In this study, strontium-doped brushite coatings were deposited on titanium by electrochemical deposition. The phase composition of the coating was investigated by energy dispersive X-ray spectroscopy and X-ray diffraction. The surface morphologies of the coatings were studied through scanning electron microscopy, and the cytocompatibility and bioactivity of the strontium-doped brushite coatings were evaluated using cultured osteoblasts. Osteoblast proliferation was enhanced by the addition of strontium, suggesting a possible mechanism by which strontium incorporation in brushite coatings increased bone formation surrounding the implants. Cell growth was also strongly influenced by the composition of the deposited coatings, with a 10% Sr-doped brushite coating inducing the greatest amount of bone formation among the tested materials.

Pharmacological management of osteogenesis

Osteogenesis and bone remodeling are complex biological processes that are essential for the formation of new bone tissue and its correct functioning. When the balance between bone resorption and formation is disrupted, bone diseases and disorders such as Paget's disease, fibrous dysplasia, osteoporosis and fragility fractures may result. Recent advances in bone cell biology have revealed new specific targets for the treatment of bone loss that are based on the inhibition of bone resorption by osteoclasts or the stimulation of bone formation by osteoblasts. Bisphosphonates, antiresorptive agents that reduce bone resorption, are usually recommended as first-line therapy in women with postmenopausal osteoporosis. Numerous studies have shown that bisphosphonates are able to significantly reduce the risk of femoral and vertebral fractures. Other antiresorptive agents indicated for the treatment of osteoporosis include selective estrogen receptor modulators, such as raloxifene. Denosumab, a human monoclonal antibody, is another antiresorptive agent that has been approved in Europe and the USA. This agent blocks the RANK/RANKL/OPG system, which is responsible for osteoclastic activation, thus reducing bone resorption. Other approved agents include bone anabolic agents, such as teriparatide, a recombinant parathyroid hormone that improves bone microarchitecture and strength, and strontium ranelate, considered to be a dual-action drug that acts by both osteoclastic inhibition and osteoblastic stimulation. Currently, anti-catabolic drugs that act through the Wnt-β catenin signaling pathway, serving as Dickkopf-related protein 1 inhibitors and sclerostin antagonists, are also in development. This concise review provides an overview of the drugs most commonly used for the control of osteogenesis in bone diseases.

Trajectories of Bone Remodeling Markers and Bone Mineral Density during Treatment with Strontium Ranelate in Postmenopausal Women Previously Treated with Bisphosphonates

OBJECTIVE

To evaluate the responses of C-terminal telopeptide (CTX) and serum osteocalcin after the first 4 months of treatment with strontium ranelate (SR) and demonstrate their association with long-term bone density changes.

SUBJECTS AND METHODS

A sample of 13 postmenopausal women with osteoporosis was analyzed (mean age 65 ± 7.7 years), who were treated with SR for an average of 2.56 ± 0.86 years. All patients had undergone previous treatment with bisphosphonates for an average period of 4.88 ± 2.27 years. Serum CTX and osteocalcin levels were determined before and after four months of treatment with SR. Bone mineral density in the lumbar spine and femoral neck were obtained before and after treatment with SR.

RESULTS

We observed an average increase of 53.7% in the CTX levels, and 30.7% in the osteocalcin levels. The increase in bone markers was associated with a mean 4.8% increase in lumbar spine bone mineral density (BMD) from 0.820 to 0.860 g/cm² (T-score from −2.67 to −1.92; P = 0.001), after 2.5 years of treatment with SR.

CONCLUSION

These data suggest an anabolic effect of SR on postmenopausal women who were previously treated with long-term bisphosphonates.

Strontium ranelate reduces cartilage degeneration and subchondral bone remodeling in rat osteoarthritis model

AIM

To investigate whether strontium ranelate (SR), a new antiosteoporotic agent, could attenuate cartilage degeneration and subchondral bone remodeling in osteoarthritis (OA).

METHODS

Medial meniscal tear (MMT) operation was performed in adult SD rats to induce OA. SR (625 or 1800 mg·kg(-1)·d(-1)) was administered via gavage for 3 or 6 weeks. After the animals were sacrificed, articular cartilage degeneration was evaluated using toluidine blue O staining, SOX9 immunohistochemistry and TUNEL assay. The changes in microarchitecture indices and tissue mineral density (TMD), chemical composition (mineral-to-collagen ratio), and intrinsic mechanical properties of the subchondral bones were measured using micro-CT scanning, confocal Raman microspectroscopy and nanoindentation testing, respectively.

RESULTS

The high-dose SR significantly attenuated cartilage matrix and chondrocyte loss at 6 weeks, and decreased chondrocyte apoptosis, improved the expression of SOX9, a critical transcription factor responsible for the expression of anabolic genes type II collagen and aggrecan, at both 3 and 6 weeks. Meanwhile, the high-dose SR also significantly attenuated the subchondral bone remodeling at both 3 and 6 weeks, as shown by the improved microarchitecture indices, TMD, mineral-to-collagen ratio and intrinsic mechanical properties. In contrast, the low-dose SR did not significantly change all the detection indices of cartilage and bone at both 3 and 6 weeks.

CONCLUSION

The high-dose SR treatment can reduce articular cartilage degeneration and subchondral bone remodeling in the rat MMT model of OA.

Strontium ranelate prevents bone loss in a rat model of localized muscle paralysis

Twenty-one 3.5-month-old female Sprague-Dawley rats were randomly assigned to three groups: BTX group, in which each rat received a single intramuscular injection of 2 U of Clostridium botulinum toxin (BTX) in the quadriceps femoris muscle of the right hind limb; BTX + SR group, in which each rat received a BTX injection and a dose of strontium ranelate (dose level of 625 mg/kg/day); and the control group. All the rats were killed at 9 weeks post-treatment. It was showed that BTX-induced rats a rapid loss of body weight in the first 3 weeks, after which their body weight showed a slow increase similar to that observed in the control rats. The net body weight loss was mainly attributed to muscle atrophy. BTX caused remarkable bone degradation in either the trabecular bone or the cortical bone of the disuse femur. The deteriorations in the bone mass and bone microstructure were locally limited and could be prevented by strontium ranelate treatment. Biomechanical analysis showed that strontium ranelate treatment improved the mechanical performance of the tibia in BTX-treated rats. It was showed that a clinical-corresponding dose of strontium ranelate could prevent bone loss in long-term immobilized rats.

Functional polymorphisms within the TNFRSF11B (osteoprotegerin) gene increase the risk for low bone mineral density

Polymorphisms within the TNFRSF11B gene have been studied and associated with osteoporosis and fracture risk. Osteoprotegerin (OPG), the product of this gene, is a key negative regulator of osteoclastogenesis and is secreted by osteoblasts/stromal cells. A previous study in Maltese postmenopausal women showed positive association of low bone mineral density (BMD) with a polymorphism found within the promoter region of this gene (C950T). In this study, direct DNA sequencing revealed 12 variants with polymorphisms C950T, G1181C and rs4876869 observed to be in strong linkage disequilibrium. The constructed haplotype T-G-T was found to increase the risk for a low BMD, while C-G-T and C-C-C have a protective role; thus, we investigated the functional role of both C950T and rs4876869 in vitro. The promoter region, including the C950T alleles, was amplified by PCR, cloned into pGL3 enhancer vector and transfected into HeLa, COS-7 and RAW264.7 cell lines. After incubation, luciferase activity was measured. The T/C (rs4876869) change was tested for its possible effect on pre-mRNA splicing, using an exon-trapping vector. A statistical significant difference in gene expression was observed between the alleles for T950C, with the T allele showing a lower luciferase expression in all cell lines (P<0.01). For rs4876869, exon skipping was observed for the C allele, while only one transcript harbouring the whole exon was observed for the T allele. Our findings suggest that the T-G-T haplotype might be increasing the risk for osteoporosis due to lower quantities of the full OPG transcript being expressed resulting in a higher bone resorption.

Systematic strontium substitution in hydroxyapatite coatings on titanium via micro-arc treatment and their osteoblast/osteoclast responses

This study attempts to enhance the osseointegration of titanium implants by adopting a micro-arc treatment (MAT) capable of replacing calcium (Ca) with different percentages of strontium (Sr) in order to fabricate strontium-containing hydroxyapatite (Sr-HAp) coatings. Sr, regarded as a significant therapy promoting bone mass and bone strength, has a dual mechanism, enhancing osteoblast differentiation and inhibiting osteoclast differentiation. This study also investigates how Sr content affects the microstructure of and osteoblast/osteoclast growth on the coatings. Experimental results indicate that an increase in the Sr content in the electrolyte bath results in a greater degree of Sr substitution at Ca sites within the HAp phase, facilitating the formation of Sr-HAp coatings with Sr fully solid soluble in the HAp phase. Irrespective of the Sr content, most coatings are similar in porous morphology and pore size. Additionally, the Sr-HAp coating shows higher osteoblast compatibility than raw titanium metal and the HAp coating. Moreover, cell adhesion and proliferation after 48 h was greater than that after 4 h, indicating that Sr can stimulate osteoblast adhesion and proliferation. Further, Sr significantly inhibits osteoclast differentiation when the Sr-HAp coatings exceed 38.9 at.% Sr.

Impact of treatments for postmenopausal osteoporosis (bisphosphonates, parathyroid hormone, strontium ranelate, and denosumab) on bone quality: a systematic review

The objective of this systematic review was to examine the influence of treatments for postmenopausal osteoporosis (parathyroid hormone [PTH], bisphosphonates, strontium ranelate, and denosumab) on bone quality and discuss the clinical implications. Most bone-quality data for PTH is from teriparatide. Teriparatide results in a rapid increase in bone-formation markers, followed by increases in bone-resorption markers, opening an "anabolic window," a period of time when PTH is maximally anabolic. Teriparatide reverses the structural damage seen in osteoporosis and restores the structure of trabecular bone. It has a positive effect on cortical bone, and any early increases in cortical porosity appear to be offset by increases in cortical thickness and diameter. Bisphosphonates are antiresorptive agents which reduce bone turnover, improve trabecular microarchitecture, and mineralization. Concerns have been raised that the prolonged antiresorptive action of bisphosphonates may lead to failure to repair microdamage, resulting in microcracks and atypical fragility. Strontium ranelate is thought to have a mixed mode of action, increasing bone formation and decreasing bone resorption. Strontium ranelate improves cortical thickness, trabecular number, and connectivity, with no change in cortical porosity. Denosumab exerts rapid, marked, and sustained effects on bone resorption, resulting in falls in the markers of bone turnover. Evidence from bone-quality studies suggests that treatment-naive women, aged 60-65 years, with very low BMD T scores may benefit from PTH as primary therapy to improve bone substrate and build bone. Post-PTH treatment with bisphosphonates will maintain improvements in bone quality and reduce the risk of fracture.

Strontium ranelate: a review of its use in the treatment of postmenopausal osteoporosis

This is a review of the pharmacology of strontium ranelate (Protelos, Protos, Protaxos, Bivalos, Osseor), and its efficacy and tolerability in the treatment of patients with postmenopausal osteoporosis. Strontium ranelate is a divalent strontium salt of ranelic acid that is capable of increasing bone formation and reducing bone resorption, thereby uncoupling and rebalancing bone turnover in favour of bone formation. The drug is effective in reducing the risk of fractures, including both vertebral and nonvertebral fractures, in patients with postmenopausal osteoporosis, according to data from two large, double-blind, placebo-controlled, multicentre trials of 5 years' duration, and reduced the risk of hip fracture in high-risk patients in a post hoc analysis of one trial. Moreover, data from patients who continued to receive the drug during the 3-year extension phases of these trials indicate that strontium ranelate continues to provide protection against new vertebral fractures and nonvertebral fractures for up to 8 years of therapy. It also improves bone mineral density at numerous sites and both increases markers of bone formation and decreases markers of bone resorption. Strontium ranelate is administered orally as a suspension and is generally well tolerated. The nature of adverse events was generally similar regardless of treatment duration in clinical trials, with the most commonly reported being nausea and diarrhoea over 5 years of treatment, and memory loss and diarrhoea during longer-term treatment. Although an increased risk of venous thromboembolism was associated with strontium ranelate relative to placebo over 5 years of treatment in a pooled analysis of clinical trials, postmarketing data have not confirmed this finding. Overall, the clinical data available suggest that strontium ranelate is an effective and generally well tolerated option for the first-line treatment of postmenopausal osteoporosis.

Osteoblast response and osseointegration of a Ti-6Al-4V alloy implant incorporating strontium

This study investigated the surface characteristics, in vitro and in vivo biocompatibility of Ti-6Al-4V alloy implants incorporating strontium ions (Sr), produced by hydrothermal treatment using a Sr-containing solution, for future biomedical applications. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry, contact angle and surface energy measurement and inductively coupled plasma-mass spectroscopy (ICP-MS). Human osteoblast-like cell (MG63) attachment, proliferation, alkaline phosphatase (ALP) activity, and quantitative analysis of osteoblastic gene expression on Sr-containing Ti-6Al-4V surfaces were compared with untreated Ti-6Al-4V surfaces. Fifty-six screw implants (28 control and 28 experimental) were placed in the tibiae and femoral condyles of seven New Zealand White rabbits. The osteoconductivity of Sr-containing Ti-6Al-4V implants was evaluated by removal torque testing and histomorphometric analysis after 4weeks implantation. Hydrothermal treatment produced a crystalline SrTiO(3) layer. ICP-MS analysis showed that Sr ions were released from treated surfaces into the solution. Significant increases in ALP activity (P=0.000), mRNA expressions of key osteoblast genes (osterix, bone sialoprotein, and osteocalcin), removal torque values (P<0.05) and bone-implant contact percentages (P<0.05) in both cortical and cancellous bone were observed for Sr-containing Ti-6Al-4V surfaces. The results indicate that the Sr-containing oxide layer produced by hydrothermal treatment may be effective in improving the osseointegration of Ti-6Al-4V alloy implants by enhancing differentiation of osteoblastic cells, removal torque forces and bone apposition in both cortical and cancellous bone.

Methyl 5-[N,N-bis(methoxycarbonylmethyl)amino]-4-cyano-2-methoxycarbonyl-3-thiopheneethanoate

In the title compound, C₁₆H₁₈N₂O₈S, derived from ranelic acid, there is a highly substituted thio­phene ring. The crystal structure involves inter­molecular C—H⋯O and C—H⋯S hydrogen bonds.