Simvastatin-loaded macroporous calcium phosphate cement: preparation, in vitro characterization, and evaluation of in vivo performance

Statins-Their Role in Bone Tissue Metabolism and Local Applications with Different Carriers

Statins, widely prescribed for lipid disorders, primarily target 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase competitively and reversibly, resulting in reduced low-density lipoprotein cholesterol (LDL-C). This mechanism proves effective in lowering the risk of lipid-related diseases such as ischemic cerebrovascular and coronary artery diseases. Beyond their established use, statins are under scrutiny for potential applications in treating bone diseases. The focus of research centers mainly on simvastatin, a lipophilic statin demonstrating efficacy in preventing osteoporosis and aiding in fracture and bone defect healing. Notably, these effects manifest at elevated doses (20 mg/kg/day) of statins, posing challenges for systematic administration due to their limited bone affinity. Current investigations explore intraosseous statin delivery facilitated by specialized carriers. This paper outlines various carrier types, characterizing their structures and underscoring various statins' potential as local treatments for bone diseases.

Amorphous calcium magnesium phosphate nanocomposites with superior osteogenic activity for bone regeneration

The seek of bioactive materials for promoting bone regeneration is a challenging and long-term task. Functionalization with inorganic metal ions or drug molecules is considered effective strategies to improve the bioactivity of various existing biomaterials. Herein, amorphous calcium magnesium phosphate (ACMP) nanoparticles and simvastatin (SIM)-loaded ACMP (ACMP/SIM) nanocomposites were developed via a simple co-precipitation strategy. The physiochemical property of ACMP/SIM was explored using transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD) and high-performance liquid chromatograph (HPLC), and the role of Mg²⁺ in the formation of ACMP/SIM was revealed using X-ray absorption near-edge structure (XANES). After that, the transformation process of ACMP/SIM in simulated body fluid (SBF) was also tracked to simulate and explore the in vivo mineralization performance of materials. We find that ACMP/SIM releases ions of Ca²⁺, Mg²⁺ and PO43−, when it is immersed in SBF at 37°C, and a phase transformation occurred during which the initially amorphous ACMP turns into self-assembled hydroxyapatite (HAP). Furthermore, ACMP/SIM displays high cytocompatibility and promotes the proliferation and osteogenic differentiation of MC3T3-E1 cells. For the in vivo studies, lamellar ACMP/SIM/Collagen scaffolds with aligned pore structures were prepared and used to repair a rat defect model in calvaria. ACMP/SIM/Collagen scaffolds show a positive effect in promoting the regeneration of calvaria defect after 12 weeks. The bioactive ACMP/SIM nanocomposites are promising as bone repair materials. Considering the facile preparation process and superior in vitro/vivo bioactivity, the as-prepared ACMP/SIM would be a potential candidate for bone related biomedical applications.

Co-culture of BMSCs and HUVECs with simvastatin-loaded gelatin nanosphere/chitosan coating on Mg alloy for osteogenic differentiation and vasculogenesis

Mg alloys are increasingly being investigated as a versatile and economical alternative for developing bone repair implants because of their high mechanical strength, wide availability, adjustable structure and properties. In this study, magnesium alloy WE43 is coated on both sides with gelatin nanosphere/chitosan (GNs/CTS), a coating enhanced by incorporating simvastatin (SIM). SIM-loaded GNs/CTS coated magnesium alloy can promote the osteogenic differentiation of bone mesenchymal stem cells (BMSCs). BMSCs and human umbilical vein endothelial cells (HUVECs) are co-cultured through transwell systems. The release of SIM from the coating is found to increase the secretion of chemokine and angiogenic factors from BMSCs, which promote the migration and tube formation of HUVECs, respectively. Bone morphogenetic protein secreted by HUVECs is seen to increase by the release of SIM from the coating, promoting the osteogenic differentiation of BMSCs. The secretion of chemokines from HUVECs promote the migration of BMSCs. The coated magnesium alloy substrate loaded with SIM is found to regulate the osteogenic differentiation of BMSCs. The study of the paracrine interaction between BMSCs and HUVECs proves that the applied coating promotes both osteogenic differentiation and vascularization, thus demonstrating a new approach for the design of bone repair materials based on magnesium alloys.

Calcium Phosphate Carrying Simvastatin Enhances Bone Regeneration: A Systematic Review

Several studies have aimed to develop alternative therapeutic biomaterials for bone repair. The purpose of this systematic review was to evaluate how statins carried by calcium phosphate affect the formation and regeneration of bone tissue in animal models when compared to other biomaterials or spontaneous healing. This systematic review followed the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions, the PRISMA guidelines, and the Preclinical Systematic Review & Meta-analysis Facility (SyRF). The protocol of this systematic review was registered in PROSPERO (CRD42018091112) and in CAMARADES. In addition, ARRIVE checklists were followed in order to increase the quality and transparency of the search. An electronic search was performed using the MEDLINE/PubMed, Scopus, SciELO, and PROSPERO library databases. The authors used a specific search strategy for each database, and they also conducted a search in the grey literature and cross-references. The eligibility criteria were animal studies, which evaluated bone repair treated with calcium phosphate as a simvastatin carrier. The selection process yielded 8 studies from the 657 retrieved. All manuscripts concluded that locally applied simvastatin carried by calcium phosphate is biocompatible, enhanced bone repair and induced statistically greater bone formation than cloth or calcium phosphate alone. In conclusion, the pertinent pre-clinical studies evidenced the calcium phosphate biocompatibility and its effectiveness in delivering SIM to improve the repair of bone defects. So, clinical trials are encouraged to investigate the impact of SIM associated with calcium phosphate bone graft in repairing bone defect in humans.

Mimicking growth factors: role of small molecule scaffold additives in promoting tissue regeneration and repair

The primary aim of tissue engineering scaffolds is to mimic the in vivo environment and promote tissue growth. In this quest, a number of strategies have been developed such as enhancing cell-material interactions through modulation of scaffold physico-chemical parameters. However, more is required for scaffolds to relate to the cell natural environment. Growth factors (GFs) secreted by cells and extracellular matrix (ECM) are involved in both normal repair and abnormal remodeling. The direct use of GFs on their own or when incorporated within scaffolds represent a number of challenges such as release rate, stability and shelf-life. Small molecules have been proposed as promising alternatives to GFs as they are able to minimize or overcome many shortcomings of GFs, in particular immune response and instability. Despite the promise of small molecules in various TE applications, their direct use is limited by nonspecific adverse effects on non-target tissues and organs. Hence, they have been incorporated within scaffolds to localize their actions and control their release to target sites. However, scanty rationale is available which links the chemical structure of these molecules with their mode of action. We herewith review various small molecules either when used on their own or when incorporated within polymeric carriers/scaffolds for bone, cartilage, neural, adipose and skin tissue regeneration.

Targeted delivery as key for the success of small osteoinductive molecules

Molecules such as growth factors, peptides and small molecules can guide cellular behavior and are thus important for tissue engineering. They are rapidly emerging as promising compounds for the regeneration of tissues of the musculoskeletal system. Growth factors have disadvantages such as high cost, short half-life, supraphysiological amounts needed, etc. Therefore, small molecules may be an alternative. These molecules have been discovered using high throughput screening. Small osteoinductive molecules exhibit several advantages over growth factors owing to their small sizes, such as high stability and non-immunogenicity. These molecules may stimulate directly signaling pathways that are important for osteogenesis. However, systemic application doesn't induce osteogenesis in most cases. Therefore, local administration is needed. This may be achieved by using a bone graft material providing additional osteoconductive properties. These graft materials can also act by themselves as a delivery matrix for targeted and local delivery. Furthermore, vascularization is necessary in the process of osteogenesis. Many of the small molecules are also capable of promoting vascularization of the tissue to be regenerated. Thus, in this review, special attention is given to molecules that are capable of inducing both angiogenesis and osteogenesis simultaneously. Finally, more recent preclinical and clinical uses in bone regeneration of those molecules are described, highlighting the needs for the clinical translation of these promising compounds.

Tailored sequential drug release from bilayered calcium sulfate composites

The current standard for treating infected bony defects, such as those caused by periodontal disease, requires multiple time-consuming steps and often multiple procedures to fight the infection and recover lost tissue. Releasing an antibiotic followed by an osteogenic agent from a synthetic bone graft substitute could allow for a streamlined treatment, reducing the need for multiple surgeries and thereby shortening recovery time. Tailorable bilayered calcium sulfate (CS) bone graft substitutes were developed with the ability to sequentially release multiple therapeutic agents. Bilayered composite samples having a shell and core geometry were fabricated with varying amounts (1 or 10 wt.%) of metronidazole-loaded poly(lactic-co-glycolic acid) (PLGA) particles embedded in the shell and simvastatin directly loaded into either the shell, core, or both. Microcomputed tomography showed the overall layered geometry as well as the uniform distribution of PLGA within the shells. Dissolution studies demonstrated that the amount of PLGA particles (i.e., 1 vs. 10 wt.%) had a small but significant effect on the erosion rate (3% vs. 3.4%/d). Mechanical testing determined that introducing a layered geometry had a significant effect on the compressive strength, with an average reduction of 35%, but properties were comparable to those of mandibular trabecular bone. Sustained release of simvastatin directly loaded into CS demonstrated that changing the shell to core volume ratio dictates the duration of drug release from each layer. When loaded together in the shell or in separate layers, sequential release of metronidazole and simvastatin was achieved. By introducing a tunable, layered geometry capable of releasing multiple drugs, CS-based bone graft substitutes could be tailored in order to help streamline the multiple steps needed to regenerate tissue in infected defects.

Novel applications of statins for bone regeneration

The use of statins for bone regeneration is a promising and growing area of research. Statins, originally developed to treat high cholesterol, are inhibitors of the enzyme 3-hydroxy-3-methylglutaryl, the rate-limiting enzyme of the mevalonate pathway. Because the mevalonate pathway is responsible for the synthesis of a wide variety of important biochemical molecules, including cholesterol and other isoprenoids, the effects of statins are pleiotropic. In particular, statins can greatly affect the process of bone turnover and regeneration via effects on important cell types, including mesenchymal stem cells, osteoblasts, endothelial cells, and osteoclasts. Statins have also been shown to have anti-inflammatory and antimicrobial properties that may be useful since infection can derail normal bone healing. This review will explore the pleiotropic effects of statins, discuss the current use of statins for bone regeneration, particularly with regard to biomaterials-based controlled delivery, and offer perspectives on the challenges and future directions of this emerging area of bone tissue engineering.

Drug release from calcium sulfate-based composites

To help reduce the need for autografts, calcium sulfate (CS)-based bone graft substitutes are being developed to provide a stable platform to aid augmentation while having the ability to release a broad range of bioactive agents. CS has an excellent reputation as a biocompatible and osteoconductive substance, but addition of bioactive agents may further enhance these properties. Samples were produced with either directly loaded small, hydrophobic molecule (i.e., simvastatin), directly loaded hydrophilic protein (i.e., lysozyme), or 1 and 10 wt % of fast-degrading poly(β-amino ester) (PBAE) particles containing protein. Although sustained release of directly loaded simvastatin was achieved, direct loading of small amounts of lysozyme resulted in highly variable release. Direct loading of a larger amount of protein generated a large burst, 65% of total loading, followed by sustained release of protein. Release of lysozyme from 1 wt % of PBAE particles embedded into CS was more controllable than when directly loaded, and for 10 wt % of protein-loaded PBAE particles, a higher burst was followed by sustained release, comparable to the results for the high direct loading. Compression testing determined that incorporation of directly loaded drug or drug-loaded PBAE particles weakened CS. In particular, PBAE particles had a significant effect on the strength of the composites, with a 25 and 80% decrease in strength for 1 and 10 wt % particle loadings, respectively. CS-based composites demonstrated the ability to sustainably release both macromolecules and small molecules, supporting the potential for these materials to release a range of therapeutic agents.

Direct and interactive influence of explanatory variables on properties of a calcium phosphate cement for vertebral body augmentation

We used the response surface methodology to investigate the direct and interactive effects of three explanatory variables on three properties of a calcium phosphate cement (CPC) for use in vertebroplasty (VP) and balloon kyphoplasty (BKP). The variables were poly(ethylene glycol) content of the cement liquid (PEG), powder-to-liquid ratio (PLR), and the amount of Na2HPO4 added to an aqueous solution of 4 wt/wt% poly(acrylic acid) (as the cement liquid) (SPC). The properties were injectability (I), final setting time (F), and 5-day compressive strength (UCS). We found that (1) there was an interactive effect between the variables on I and F but not on UCS; (2) the maximum I (98%) was obtained with PEG = 20 wt/wt% and PLR = 2 g mL(-1); (3) F = 15 min (the proposed optimum value for a CPC for use in VP and BKP) was obtained with PEG = 4 wt/wt% and PLR = 2.9 g mL(-1); and (4) the maximum UCS (39 MPa) was obtained with SPC = 0 and PLR = 3.5 g mL(-1).