Modification of gene expression induced in human osteogenic and osteosarcoma cells by culture on a biphasic calcium phosphate bone substitute

Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials.

Bone microenvironment signals in osteosarcoma development

The bone is a complex connective tissue composed of many different cell types such as osteoblasts, osteoclasts, chondrocytes, mesenchymal stem/progenitor cells, hematopoietic cells and endothelial cells, among others. The interaction between them is finely balanced through the processes of bone formation and bone remodeling, which regulates the production and biological activity of many soluble factors and extracellular matrix components needed to maintain the bone homeostasis in terms of cell proliferation, differentiation and apoptosis. Osteosarcoma (OS) emerges in this complex environment as a result of poorly defined oncogenic events arising in osteogenic lineage precursors. Increasing evidence supports that similar to normal development, the bone microenvironment (BME) underlies OS initiation and progression. Here, we recapitulate the physiological processes that regulate bone homeostasis and review the current knowledge about how OS cells and BME communicate and interact, describing how these interactions affect OS cell growth, metastasis, cancer stem cell fate and therapy outcome.

Response of stem cells from different origins to biphasic calcium phosphate bioceramics

Biphasic calcium phosphate (BCP) bioceramics have been successfully applied in a broad variety of presentation forms and with different ratios of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). BCPs have been loaded with stem cells from different origins for bone tissue engineering purposes, but evidence of stem cell behavior on different compositions (various HA/β-TCP ratios) and physical features of BCPs is limited. We compared the adhesion, proliferation, viability and osteogenic potential of human mesenchymal stem cells (MSCs) on granular BCPs with equal HA/β-TCP ratio of diverse particle sizes and on porous blocks which had different chemical compositions. In addition, the osteogenic differentiation of MSCs was compared to adipose-derived (ADSC) and dental pulp (DPSC) stem cells, as well as to pre-osteoblasts on a particulate BCP. MSCs growing on granular BCPs demonstrated increased number as compared to MSCs growing on blocks. Cells proliferated to a greater extent on small granular BCPs, while large granular BCPs and blocks promoted cell differentiation. Surprisingly, the expression of genes involved in osteogenesis was upregulated in MSCs on bioceramics in basal medium which indicates that BCPs may have osteoinductive potential. This was confirmed with the upregulation of osteochondrogenic markers, at different time points, when stem cells from various tissues were grown on the BCP. This study demonstrates that BCPs, depending on their physical features and chemical composition, modulate stem cell behavior, and that stem cells from different origins are inherently distinct in their gene expression profile and can be triggered toward osteochondrogenic fate by BCPs.

Bone environment is essential for osteosarcoma development from transformed mesenchymal stem cells

The cellular microenvironment plays a relevant role in cancer development. We have reported that mesenchymal stromal/stem cells (MSCs) deficient for p53 alone or together with RB (p53(-/-)RB(-/-)) originate leiomyosarcoma after subcutaneous (s.c.) inoculation. Here, we show that intrabone or periosteal inoculation of p53(-/-) or p53(-/-)RB(-/-) bone marrow- or adipose tissue-derived MSCs originated metastatic osteoblastic osteosarcoma (OS). To assess the contribution of bone environment factors to OS development, we analyzed the effect of the osteoinductive factor bone morphogenetic protein-2 (BMP-2) and calcified substrates on p53(-/-)RB(-/-) MSCs. We show that BMP-2 upregulates the expression of osteogenic markers in a WNT signaling-dependent manner. In addition, the s.c. coinfusion of p53(-/-)RB(-/-) MSCs together with BMP-2 resulted in appearance of tumoral osteoid areas. Likewise, when p53(-/-)RB(-/-) MSCs were inoculated embedded in a calcified ceramic scaffold composed of hydroxyapatite and tricalciumphosphate (HA/TCP), tumoral bone formation was observed in the surroundings of the HA/TCP scaffold. Moreover, the addition of BMP-2 to the ceramic/MSC implants further increased the tumoral osteoid matrix. Together, these data indicate that bone microenvironment signals are essential to drive OS development.

Cultivation and identification of rat bone marrow-derived mesenchymal stem cells

Bone marrow‑derived mesenchymal stem cells (BMSCs) have the potential to form a variety of mesenchymal tissue types, which are a source of cells for bone tissue engineering applications. The present study attempted to establish an effective and convenient method for culturing BMSCs. Total bone marrow cells, which were harvested from rat femurs, were cultured and BMSCs were selected and expanded through passaging in vitro. Furthermore, the biological properties of BMSCs were investigated, specific surface antigen expression was assessed using flow cytometry and the multipotent differentiation potential characteristics were demonstrated using standard in vitro conditions. Monoptychial heterogeneous cells were obtained. A total of 98.4% of cells at passage 3 expressed cluster of differentiation (CD)29 and CD90, but not CD45. The cells were able to differentiate into osteogenic and adipogenic cells. In conclusion, BMSCs that are isolated from the rat bone marrow and exhibit the identified characteristics may be used as seed cells in bone tissue engineering.

Bioactive glass incorporation in calcium phosphate cement-based injectable bone substitute for improved in vitro biocompatibility and in vivo bone regeneration

In this work, we fabricated injectable bone substitutes modified with the addition of bioactive glass powders synthesized via ultrasonic energy-assisted hydrothermal method to the calcium phosphate-based bone cement to improve its biocompatibility. The injectable bone substitutes was initially composed of a powder component (tetracalcium phosphate, dicalcium phosphate dihydrate and calcium sulfate dehydrate) and a liquid component (citric acid, chitosan and hydroxyl-propyl-methyl-cellulose) upon which various concentrations of bioactive glass were added: 0%, 10%, 20% and 30%. Setting time and compressive strength of the injectable bone substitutes were evaluated and observed to improve with the increase of bioactive glass content. Surface morphologies were observed via scanning electron microscope before and after submersion of the samples to simulated body fluid and increase in apatite formation was detected using x-ray diffraction machine. In vitro biocompatibility of the injectable bone substitutes was observed to improve with the addition of bioactive glass as the proliferation/adhesion behavior of cells on the material increased. Human gene markers were successfully expressed using real time-polymerase chain reaction and the samples were found to promote cell viability and be more biocompatible as the concentration of bioactive glass increases. In vivo biocompatibility of the samples containing 0% and 30% bioactive glass were evaluated using Micro-CT and histological staining after 3 months of implantation in male rabbits’ femurs. No inflammatory reaction was observed and significant bone formation was promoted by the addition of bioactive glass to the injectable bone substitute system.

In vitro assay for osteoinductive activity of different demineralized freeze-dried bone allograft

PURPOSE

Various bone graft materials have been used for periodontal tissue regeneration. Demineralized freeze-dried bone allograft (DFDBA) is a widely used bone substitute. The current widespread use of DFDBA is based on its potential osteoinductive ability. Due to the lack of verifiable data, the purpose of this study was to assess the osteoinductive activity of different DFDBAs in vitro.

METHODS

Sarcoma osteogenic (SaOS-2) cells (human osteoblast-like cells) were exposed to 8 mg/mL and 16 mg/mL concentrations of three commercial types of DFDBA: Osseo+, AlloOss, and Cenobone. The effect of these materials on cell proliferation was determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The osteoinductive ability was evaluated using alizarin red staining, and the results were confirmed by evaluating osteogenic gene expression using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

In the SaOS-2 cells, an 8 mg/mL concentration of Osseo+ and Cenobone significantly increased cell proliferation in 48 hours after exposure (P<0.001); however, in these two bone materials, the proliferation of cells was significantly decreased after 48 hours of exposure with a 16 mg/mL concentration (P<0.001). The alizarin red staining results demonstrated that the 16 mg/mL concentration of all three tested DFDBA induced complete morphologic differentiation and mineralized nodule production of the SaOS-2 cells. The RT-PCR results revealed osteopontin gene expression at a 16 mg/mL concentration of all three test groups, but not at an 8 mg/mL concentration.

CONCLUSIONS

These commercial types of DFDBA are capable of decreasing proliferation and increasing osteogenic differentiation of the SaOS-2 cell line and have osteoinductive activity in vitro.

The effect of autoclaving on the physical and biological properties of dicalcium phosphate dihydrate bioceramics: brushite vs. monetite

Dicalcium phosphate dihydrate (brushite) is an osteoconductive biomaterial with great potential as a bioresorbable cement for bone regeneration. Preset brushite cement can be dehydrated into dicalcium phosphate anhydrous (monetite) bioceramics by autoclaving. This heat treatment results in changes in the physical characteristics of the material, improving in vivo bioresorption. This property is a great advantage in bone regeneration; however, it is not known how autoclaving brushite preset cement might improve its capacity to regenerate bone. This study was designed to compare brushite bioceramics with monetite bioceramics in terms of physical characteristics in vitro, and in vivo performance upon bone implantation. In this study we observed that monetite bioceramics prepared by autoclaving preset brushite cements had higher porosity, interconnected porosity and specific surface area than their brushite precursors. In vitro cell culture experiments revealed that bone marrow cells expressed higher levels of osteogenic genes Runx2, Opn, and Alp when the cells were cultured on monetite ceramics rather than on brushite ones. In vivo experiments revealed that monetite bioceramics resorbed faster than brushite ones and were more infiltrated with newly formed bone. In summary, autoclaving preset brushite cements results in a material with improved properties for bone regeneration procedures.

Biphasic, triphasic and multiphasic calcium orthophosphates

Biphasic, triphasic and multiphasic (polyphasic) calcium orthophosphates have been sought as biomaterials for reconstruction of bone defects in maxillofacial, dental and orthopedic applications. In general, this concept is determined by advantageous balances of more stable (frequently hydroxyapatite) and more resorbable (typically tricalcium orthophosphates) phases of calcium orthophosphates, while the optimum ratios depend on the particular applications. Therefore, all currently known biphasic, triphasic and multiphasic formulations of calcium orthophosphate bioceramics are sparingly soluble in water and, thus, after being implanted they are gradually resorbed inside the body, releasing calcium and orthophosphate ions into the biological medium and, hence, seeding new bone formation. The available formulations have already demonstrated proven biocompatibility, osteoconductivity, safety and predictability in vitro, in vivo, as well as in clinical models. More recently, in vitro and in vivo studies have shown that some of them might possess osteoinductive properties. Hence, in the field of tissue engineering biphasic, triphasic and multiphasic calcium orthophosphates represent promising biomaterials to construct various scaffolds capable of carrying and/or modulating the behavior of cells. Furthermore, such scaffolds are also suitable for drug delivery applications. This review summarizes the available information on biphasic, triphasic and multiphasic calcium orthophosphates, including their biomedical applications. New formulations are also proposed.

Biphasic calcium phosphate bioceramics for orthopaedic reconstructions: clinical outcomes

BCP are considered the most promising biomaterials for bone reconstruction. This study aims at analyzing the outcomes of patients who received BCP as bone substitutes in orthopaedic surgeries. Sixty-six patients were categorized according to the etiology and morphology of the bone defects and received scores after clinical and radiographic evaluations. The final results corresponded to the combination of both parameters and varied from 5 (excellent result) to 2 or lower (poor result). Most of the patients who presented cavitary defects or bone losses due to prosthesis placement or revision, osteotomies, or arthrodesis showed good results, and some of them excellent results. However, patients with segmental defects equal or larger than 3 cm in length were classified as moderate results. This study established clinical parameters where the BCP alone can successfully support the osteogenic process and where the association with other tissue engineering strategies may be considered.

Biphasic Calcium Phosphate Ceramics for Bone Regeneration and Tissue Engineering Applications

Biphasic calcium phosphates (BCP) have been sought after as biomaterials for the reconstruction of bone defects in maxillofacial, dental and orthopaedic applications. They have demonstrated proven biocompatibility, osteoconductivity, safety and predictability in in vitro, in vivo and clinical models. More recently, in vitro and in vivo studies have shown that BCP can be osteoinductive. In the field of tissue engineering, they represent promising scaffolds capable of carrying and modulating the behavior of stem cells. This review article will highlight the latest advancements in the use of BCP and the characteristics that create a unique microenvironment that favors bone regeneration.

Interactions of total bone marrow cells with increasing quantities of macroporous calcium phosphate ceramic granules

The biological properties of synthetic calcium phosphate bioceramics have made them the third choice of material for bone reconstructive surgery, after autologous bone and allografts. Nevertheless, bioceramics lack the osteogenic properties that would allow them to repair large bone defects. One strategy in bone tissue engineering consists of associating a synthetic scaffold with osteogenic cells. Mesenchymal stem cells (MSC) are usually isolated from bone marrow cultured for several weeks and seeded on to a small quantity of bioceramic. We have studied the association of total bone marrow cells, harvested from femurs of rats, with increasing amounts of calcium phosphate ceramic granules (50-250 mg). A cell viability test indicated that a little quantity of bioceramics granules (50 mg) was less detrimental for culturing 1 million nucleated cells from the whole bone marrow population. Cell morphology, viability, adhesion and differentiation were studied after different culture periods. Among the heterogeneous population of bone marrow cells, only a limited amount of cells attached and differentiated on the bioceramics. To explain the influence of the amount of synthetic scaffold on cell viability, media calcium concentrations were measured. Low cell viability could be explained by calcium phosphate precipitation leading to a decrease in calcium concentrations observed with relatively large amounts of scaffold. This study showed that the chemical stability of the ceramic plays a critical role in the viability of bone marrow cells.

Comparison of Human alveolar osteoblasts cultured on polymer-ceramic composite scaffolds and tissue culture plates

The effects of medical grade polycaprolactone-tricalcium phosphate (mPCL-TCP) (80:20) scaffolds on primary human alveolar osteoblasts (AOs) were compared with standard tissue-culture plates. Of the seeded AOs, 70% adhered to and proliferated on the scaffold surface and within open and interconnected pores; they formed multi-layered sheets and collagen fibers with uniform distribution within 28 days. Elevation of alkaline phosphatase activity occurred in scaffold-cell constructs independent of osteogenic induction. AO proliferation rate increased and significant decrease in calcium concentration of the medium for both scaffolds and plates under induction conditions were seen. mPCL-TCP scaffolds significantly influenced the AO expression pattern of osterix and osteocalcin (OCN). Osteogenic induction down-regulated OCN at both RNA and protein level on scaffolds (3D) by day 7, and up-regulated OCN in cell-culture plates (2D) by day 14, but OCN levels on scaffolds were higher than on cell-culture plates. Immunocytochemical signals for type I collagen, osteopontin and osteocalcin were detected at the outer parts of scaffold-cell constructs. More mineral nodules were found in induced than in non-induced constructs. Only induced 2D cultures showed nodule formation. mPCL-TCP scaffolds appear to stimulate osteogenesis in vitro by activating a cellular response in AO's to form mineralized tissue. There is a fundamental difference between culturing AOs on 2D and 3D environments that should be considered when studying osteogenesis in vitro.

Does seeding density affectin vitro mineral nodules formation in novel composite scaffolds?

This study investigated the human alveolar osteoblasts (AOs) proliferation and extracellular matrix formation at seeding density of 0.05, 0.1, 0.2, 0.4, and 0.8 million (M) per 3x4x4 mm3 on medical grade polycaprolactone-tricalcium phosphate (mPCL-TCP) scaffolds designed for bone regeneration. Over 80-90% of the initial seeded cells were retained in the scaffolds after 24 h. AOs bridged over pores at density of 0.2M/scaffold and below, but formed cell balls at density of 0.4M/scaffold and above. At seeding density of 0.2M and below, cell proliferation increased with time having DNA content peaked to 1600 ng/scaffold at day 21 and 28, respectively, whereas at 0.4 and 0.8M, the corresponding DNA content decreased to 1600 ng in 28 days. At day 7, higher alkaline phosphatase (ALP) activity and higher osteocalcin (OCN) secretion were detected at 0.2M/scaffold and below. After 28 days, multilayered cell-sheet formation and collagen fibers were observed at all densities. ALP and OCN in matrix and mineral nodules were found mainly at the border of AOs-scaffold construct. These findings demonstrated that the density of 0.2M and below per 3 x 4 x 4 mm(3) scaffold resulted in better cell proliferation and extracellular matrix synthesis, potentially resulting in better mineralized tissue formation.

Quantitative kinetic analysis of gene expression during human osteoblastic adhesion on orthopaedic materials

Little information was found in the literature about the expression on hydroxyapatite (HA) materials of genes specific of cellular adhesion molecules although more were found on titanium-based substrates. Hence, the goal of this work was to study by a kinetic approach from 30 min to 4 days the adhesion of Saos-2 cells on microporous (mHA) and non-microporous hydroxyapatite (pHA) in comparison to polished titanium. Our strategy associated the visualization of adhesion proteins inside the cells by immunohistochemistry and the quantitative expression of genes at mRNA level by real-time PCR. The cell morphology was assessed using scanning electron microscopy and the number of cells thanks to biochemical techniques. The cellular attachment was the highest on mHA from 30 min to 24 h although the cell growth on mHA was the lowest after 4 days. Generally, the Saos-2 osteoblastic cells morphology on mHA was radically different than on other surfaces with the particularity of the cytoplasmic edge, which appeared un-distinguishable from the surface. The revelation by specific antibodies of proteins of the cytoskeleton (actin) and the focal adhesions (FAK, phosphotyrosine) confirmed that adhesion and spreading were different on the 3 materials. The actin stress fibres were less numerous and shorter on mHA ceramics. Cells had more focal contacts after 4 h on mHA compared to other substrates but less after 24 h. The highest values of total proteins were extracted from mHA at 0.5 and 24 h and from pHA at 1, 4, and 96 h. The alphav and beta1 integrin, actin, FAK, and ERK gene expression were found to be different with adhesion time and with materials. C-jun expression was comparable on mHA, titanium and plastic but was largely higher than on pHA at 0.5 and 1 h. On the contrary, c-fos expression was the highest on pHA after 0.5 h and the lowest after 1h. This difference between c-fos and c-jun expression on pHA after 0.5 h could be related to the fact that these two genes may differ in their signalling pathways. The expression of the alkaline phosphatase gene after 4 days was lower on mHA compared to other materials demonstrating that the microstructure of the mHA ceramic was not favourable to Saos-2 cells differentiation. Finally, it was demonstrated in this study that HA and titanium surfaces influence as well gene expression at early times of adhesion as the synthesis of adhesion proteins but also proliferation and differentiation phases. Indeed, the signal transduction pathways involved in adhesion of Saos-2 cells on HA and titanium were confirmed by the sequential expression of alphav and beta1 integrins, FAK, and ERK genes followed by the expression of c-jun and c-fos genes for proliferation and alkaline phosphatase gene for differentiation.

A Novel Injectable Poly(ɛ-caprolactone)/Calcium Sulfate System for Bone Regeneration: Synthesis and Characterization

A novel poly(epsilon-caprolactone)/calcium sulfate system was prepared and characterized in order to enhance calcium sulfate (gypsum) performance as bone graft substitute overcoming its brittleness and fast resorption rate. A poly(epsilon-caprolactone) (PCL) photo-crosslinkable derivative (PCLf) was synthesized by reaction of a low molecular weight PCL diol with methacryloyl chloride and confirmed by FT-IR and 1H NMR analyses. An injectable and easy mouldable mixture of PCLf and calcium sulfate hemi-hydrate (PCLf/CHS) was obtained. Thermal analyses and solvent extraction proved the occurrence of PCLf photo-crosslinking, even in the presence of CHS, in a time suitable for clinical applications. Swelling studies demonstrated that the encapsulation of the inorganic filler increases network hydrophilicity making it more permeable to water. Scanning electron microscopy, performed on crosslinked PCLf/CHS and on the same material after incubation in a PBS solution, showed the feasibility to obtain, in situ, gypsum entrapped into a degradable polymeric network. In vitro cytotoxicity tests, performed according to ISO 10993-5, proved that the developed system was not cytotoxic supporting its potential use in tissue engineering as a new, injectable, photocurable bone graft material. SEM micrograph of calcium sulfate di-hydrate (gypsum) entrapped in the PCL network.