Effect of hydroxyapatite nanocrystals functionalized with lactoferrin in osteogenic differentiation of mesenchymal stem cells

Designing bioinspired multifunctional nanoplatforms to support wound healing and skin regeneration: Mg-hydroxyapatite meets melanins

Melanin is a multifunctional biological pigment that recently emerged as endowed with anti-inflammatory, antioxidant, and antimicrobial properties and with high potentialities in skin protection and regenerative medicine. Here, a biomimetic magnesium-doped nano-hydroxyapatite (MgHA) was synthesized and decorated with melanin molecules starting from two different monomeric precursors, i.e. 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and dopamine (DA), demonstrating to be able to polymerize on the surface of MgHA nanostructures, thus leading to a melanin coating. This functionalization was realized by a simple and green preparation method requiring mild conditions in an aqueous medium and room temperature. Complementary spectroscopy and electron imaging analyses were carried out to define the effective formation of a stable coating, the percentage of the organic compounds, and the structural properties of resulting melanin-coated nanostructures, which showed good antioxidant activity. The in vitro interaction with a cell model, i.e. mouse fibroblasts, was investigated. The excellent biocompatibility of all bioinspired nanostructures was confirmed from a suitable cell proliferation. Finally, the enhanced biological performances of the nanostructures coated with melanin from DHICA were confirmed by scratch assays. Jointly our findings indicated that low crystalline MgHA and melanin pigments can be efficiently combined, and the resulting nanostructures are promising candidates as multifunctional platforms for a more efficient approach for skin regeneration and protection.

The role of lactoferrin in bone remodeling: evaluation of its potential in targeted delivery and treatment of metabolic bone diseases and orthopedic conditions

Lactoferrin (Lf) is a multifunctional protein that is synthesized endogenously and has various biological roles including immunological regulation, antibacterial, antiviral, and anticancer properties. Recently, research has uncovered Lf's critical functions in bone remodeling, where it regulates the function of osteoblasts, chondrocytes, osteoclasts, and mesenchymal stem cells. The signaling pathways involved in Lf's signaling in osteoblasts include (low density lipoprotein receptor-related protein - 1 (LRP-1), transforming growth factor β (TGF-β), and insulin-like growth factor - 1 (IGF-1), which activate downstream pathways such as ERK, PI3K/Akt, and NF-κB. These pathways collectively stimulate osteoblast proliferation, differentiation, and mineralization while inhibiting osteoclast differentiation and activity. Additionally, Lf's inhibitory effect on nuclear factor kappa B (NF-κB) suppresses the formation and activity of osteoclasts directly. Lf also promotes chondroprogenitor proliferation and differentiation to chondrocytes by activating the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and phosphoinositide 3-kinase/protein kinase B(PI3K/Akt)signaling pathways while inhibiting the expression of matrix-degrading enzymes through the suppression of the NF-κB pathway. Lf's ability to stimulate osteoblast and chondrocyte activity and inhibit osteoclast function accelerates fracture repair, as demonstrated by its effectiveness in animal models of critical-sized long bone defects. Moreover, studies have indicated that Lf can rescue dysregulated bone remodeling in osteoporotic conditions by stimulating bone formation and suppressing bone resorption. These beneficial effects of Lf on bone health have led to its exploration in nutraceutical and pharmaceutical applications. However, due to the large size of Lf, small bioactive peptides are preferred for pharmaceutical applications. These peptides have been shown to promote bone fracture repair and reverse osteoporosis in animal studies, indicating their potential as therapeutic agents for bone-related diseases. Nonetheless, the active concentration of Lf in serum may not be sufficient at the site requiring bone regeneration, necessitating the development of various delivery strategies to enhance Lf's bioavailability and target its active concentration to the site requiring bone regeneration. This review provides a critical discussion of the issues mentioned above, providing insight into the roles of Lf in bone remodeling and the potential use of Lf as a therapeutic target for bone disorders.

Iron-Related Genes and Proteins in Mesenchymal Stem Cell Detection and Therapy

Mesenchymal stem cells (MSCs) are located in various tissues of the body. These cells exhibit regenerative and reparative properties, which makes them highly valuable for cell-based therapy. Despite this, majority of MSC-related studies remain to be translated for regular clinical use. This is partly because there are methodical challenges in pre-administration MSC labelling, post-administration detection and tracking of cells, and in retention of maximal therapeutic potential in-vivo. This calls for exploration of alternative or adjunctive approaches that would enable better detection of transplanted MSCs via non-invasive methods and enhance MSC therapeutic potential in-vivo. Interestingly, these attributes have been demonstrated by some iron-related genes and proteins.Accordingly, this unique forward-looking article integrates the apparently distinct fields of iron metabolism and MSC biology, and reviews the utility of iron-related genes and iron-related proteins in facilitating MSC detection and therapy, respectively. Effects of genetic overexpression of the iron-related proteins ferritin, transferrin receptor-1 and MagA in MSCs and their utilisation as reporter genes for improving MSC detection in-vivo are critically evaluated. In addition, the beneficial effects of the iron chelator deferoxamine and the iron-related proteins haem oxygenase-1, lipocalin-2, lactoferrin, bone morphogenetic protein-2 and hepcidin in enhancing MSC therapeutics are highlighted with the consequent intracellular alterations in MSCs. This review aims to inform both regenerative and translational medicine. It can aid in formulating better methodical approaches that will improve, complement, or provide alternatives to the current pre-transplantation MSC labelling procedures, and enhance MSC detection or augment the post-transplantation MSC therapeutic potential.

Nanoparticular and other carriers to deliver lactoferrin for antimicrobial, antibiofilm and bone-regenerating effects: a review

Bone and joint infections are a rare but serious problem worldwide. Lactoferrin’s antimicrobial and antibiofilm activity coupled with its bone-regenerating effects may make it suitable for improving bone and joint infection treatment. However, free lactoferrin (LF) has highly variable oral bioavailability in humans due to potential for degradation in the stomach and small intestine. It also has a short half-life in blood plasma. Therefore, encapsulating LF in nanocarriers may slow degradation in the gastrointestinal tract and enhance LF absorption, stability, permeability and oral bioavailability. This review will summarize the literature on the encapsulation of LF into liposomes, solid lipid nanoparticles, nanostructured lipid carriers, polymeric micro and nanoparticles and hydroxyapatite nanocrystals. The fabrication, characterization, advantages, disadvantages and applications of each system will be discussed and compared.

Multifunctional Titanium Surfaces for Orthopedic Implants: Antimicrobial Activity and Enhanced Osseointegration

The use of implants in orthopedics and dental practice is a widespread surgical procedure to treat diverse diseases. However, peri-implantitis due to infections and/or poor osseointegration can lead to metallic implant failure. The aim of this study was to develop a multifunctional coating on titanium (Ti) surfaces, to simultaneously deal with both issues, by combining antibacterial silver nanoparticles (AgNPs) and regenerative properties of lactoferrin (Lf). A simple and cost-effective methodology that allows the direct multifunctionalization of Ti surfaces was developed. The modified surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and contact angle measurements. Additionally, in vitro preosteoblast cell adhesion, cell viability, and differentiation were evaluated. The antibacterial capability of the surfaces was tested against Staphylococcus aureus as a prosthesis infection model strain. Our results showed that Lf adsorbed on both Ti surfaces and Ti surfaces with adsorbed AgNPs. Simultaneously, the presence of Lf and AgNPs notably improved preosteoblast adhesion, proliferation, and differentiation, whereas it reduced the bacterial colonization by 97.7%. Our findings indicate that this simple method may have potential applications in medical devices to both improve osseointegration and reduce bacterial infection risk, enhancing successful implantation and patients' quality of life.

Lactoferrin as a regenerative agent: The old-new panacea?

Lactoferrin (Lf) possesses various biological properties and therapeutic potentials being a perspective anti-inflammatory, antibacterial, antiviral, antioxidant, antitumor, and immunomodulatory agent. A significant body of literature has also demonstrated that Lf modulates regenerative processes in different anatomical structures, such as bone, cartilage, skin, mucosa, cornea, tendon, vasculature, and adipose tissue. Hence, this review collected and analyzed the data on the regenerative effects of Lf, as well as paid specific attention to their molecular basis. Furthermore, tissue and condition-specific activities of different Lf types as well as problems of their delivery to the targeted organs were discussed. The authors strongly hope that this review will stimulate researchers to focus on the highlighted topics thus accelerating the progress of Lf's wider clinical application.

Lactoferrin/Calcium Phosphate-Modified Porous Ti by Biomimetic Mineralization: Effective Infection Prevention and Excellent Osteoinduction

The surface modification of titanium (Ti) can enhance the osseointegration and antibacterial properties of implants. In this study, we modified porous Ti discs with calcium phosphate (CaP) and different concentrations of Lactoferrin (LF) by biomimetic mineralization and examined their antibacterial effects and osteogenic bioactivity. Firstly, scanning electron microscopy (SEM), the fluorescent tracing method, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and the releasing kinetics of LF were utilized to characterize the modified Ti surface. Then, the antibacterial properties against S. sanguis and S. aureus were investigated. Finally, in vitro cytological examination was performed, including evaluations of cell adhesion, cell differentiation, extracellular matrix mineralization, and cytotoxicity. The results showed that the porous Ti discs were successfully modified with CaP and LF, and that the LF-M group (200 μg/mL LF in simulated body fluid) could mildly release LF under control. Further, the LF-M group could effectively inhibit the adhesion and proliferation of S. sanguis and S. aureus and enhance the osteogenic differentiation in vitro with a good biocompatibility. Consequently, LF-M-modified Ti may have potential applications in the field of dental implants to promote osseointegration and prevent the occurrence of peri-implantitis.

Scaffold-based 3D cellular models mimicking the heterogeneity of osteosarcoma stem cell niche

The failure of the osteosarcoma conventional therapies leads to the growing need for novel therapeutic strategies. The lack of specificity for the Cancer Stem Cells (CSCs) population has been recently identified as the main limitation in the current therapies. Moreover, the traditional two-dimensional (2D) in vitro models, employed in the drug testing and screening as well as in the study of cell and molecular biology, are affected by a poor in vitro-in vivo translation ability. To overcome these limitations, this work provides two tumour engineering approaches as new tools to address osteosarcoma and improve therapy outcomes. In detail, two different hydroxyapatite-based bone-mimicking scaffolds were used to recapitulate aspects of the in vivo tumour microenvironment, focusing on CSCs niche. The biological performance of human osteosarcoma cell lines (MG63 and SAOS-2) and enriched-CSCs were deeply analysed in these complex cell culture models. The results highlight the fundamental role of the tumour microenvironment proving the mimicry of osteosarcoma stem cell niche by the use of CSCs together with the biomimetic scaffolds, compared to conventional 2D culture systems. These advanced 3D cell culture in vitro tumour models could improve the predictivity of preclinical studies and strongly enhance the clinical translation.

Lactoferrin coated or conjugated nanomaterials as an active targeting approach in nanomedicine

A successful drug delivery to a specific site relies on two essential factors including; efficient entrapment of the drug within the carrier and successful delivery of drug- loaded nanocarrier to the target site without opsonisation or drug release in the circulation before reaching the organ of interest. Lactoferrin (LF) is a glycoprotein belonging to the transferrin (TF) family which can bind to TF receptors (TFRs) and LF membrane internalization receptors (LFRs) highly expressed on the cell surface of both highly proliferating cancer cells and blood brain barrier (BBB), which in turn can facilitate its accessibility to the cell nucleus. This merit could be exploited to develop actively targeted drug delivery systems that can easily cross the BBB or internalize into tumor cells. In this review, the most recent advances of utilizing LF as an active targeting ligand for different types of nanocarriers including: inorganic nanoparticles, dendrimers, synthetic biodegradable polymers, lipid nanocarriers, natural polymers, and nanoemulstions will be highlighted. Collectively, LF seems to be a promising targeting ligand in the field of nanomedicine.

Lactoferrin, a multi-functional glycoprotein: Active therapeutic, drug nanocarrier & targeting ligand

Recent progress in protein-based nanomedicine, inspired by the success of Abraxane® albumin-paclitaxel nanoparticles, have resulted in novel therapeutics used for treatment of challenging diseases like cancer and viral infections. However, absence of specific drug targeting, poor pharmacokinetics, premature drug release, and off-target toxicity are still formidable challenges in the clinic. Therefore, alternative protein-based nanomedicines were developed to overcome those challenges. In this regard, lactoferrin (Lf), a glycoprotein of transferrin family, offers a promising biodegradable well tolerated material that could be exploited both as an active therapeutic and drug nanocarrier. This review highlights the major pharmacological actions of Lf including anti-cancer, antiviral, and immunomodulatory actions. Delivery technologies of Lf to improve its pries and enhance its efficacy were also reviewed. Moreover, different nano-engineering strategies used for fabrication of drug-loaded Lf nanocarriers were discussed. In addition, the use of Lf for functionalization of drug nanocarriers with emphasis on tumor-targeted drug delivery was illustrated. Besides its wide application in oncology nano-therapeutics, we discussed the recent advances of Lf-based nanocarriers as efficient platforms for delivery of anti-parkinsonian, anti-Alzheimer, anti-viral drugs, immunomodulatory and bone engineering applications.

Nanomaterials-based Cell Osteogenic Differentiation and Bone Regeneration

With the rapid development of nanotechnology, various nanomaterials have been applied to bone repair and regeneration. Due to the unique chemical, physical and mechanical properties, nanomaterials could promote stem cells osteogenic differentiation, which has great potentials in bone tissue engineering and exploiting nanomaterials-based bone regeneration strategies. In this review, we summarized current nanomaterials with osteo-induction ability, which could be potentially applied to bone tissue engineering. Meanwhile, the unique properties of these nanomaterials and their effects on stem cell osteogenic differentiation are also discussed. Furthermore, possible signaling pathways involved in the nanomaterials- induced cell osteogenic differentiation are also highlighted in this review.

Lactoferrin in Bone Tissue Regeneration

Among the multiple properties exhibited by lactoferrin (Lf), its involvement in bone regeneration processes is of great interest at the present time. A series of in vitro and in vivo studies have revealed the ability of Lf to promote survival, proliferation and differentiation of osteoblast cells and to inhibit bone resorption mediated by osteoclasts. Although the mechanism underlying the action of Lf in bone cells is still not fully elucidated, it has been shown that its mode of action leading to the survival of osteoblasts is complemented by its mitogenic effect. Activation of several signalling pathways and gene expression, in an LRPdependent or independent manner, has been identified. Unlike the effects on osteoblasts, the action on osteoclasts is different, with Lf leading to a total arrest of osteoclastogenesis. Due to the positive effect of Lf on osteoblasts, the potential use of Lf alone or in combination with different biologically active compounds in bone tissue regeneration and the treatment of bone diseases is of great interest. Since the bioavailability of Lf in vivo is poor, a nanotechnology- based strategy to improve the biological properties of Lf was developed. The investigated formulations include incorporation of Lf into collagen membranes, gelatin hydrogel, liposomes, loading onto nanofibers, porous microspheres, or coating onto silica/titan based implants. Lf has also been coupled with other biologically active compounds such as biomimetic hydroxyapatite, in order to improve the efficacy of biomaterials used in the regulation of bone homeostasis. This review aims to provide an up-to-date review of research on the involvement of Lf in bone growth and healing and on its use as a potential therapeutic factor in bone tissue regeneration.

Urinary Metabolic Profiling via LC-MS/MS Reveals Impact of Bovine Lactoferrin on Bone Formation in Growing SD Rats

Lactoferrin (LF) exerts a promoting bone health function. The effects of LF on bone formation at the metabolic level have been less explored. Urinary metabolic profiling of growing Sprague-Dawley (SD) rats LF-supplemented (1000 mg/kg bw) for four weeks were explored by Liquid chromatography–tandem mass spectrometry (LC-MS/MS). The serum markers of bone formation and bone resorption, the bone mass, and the osteogenesis markers of femur were measured by an enzyme-linked immunosorbent assay, micro-computerized tomography, and immunohistochemistry, respectively. Compared with the control, LF supplementation improved bone formation (p < 0.05), reduced bone resorption (p < 0.05), enhanced femoral bone mineral density and microarchitecture (p < 0.05), and upregulated osteocalcin, osterix, and Runx-2 expression (p < 0.05) of femur. LF upregulated 69 urinary metabolites. KEGG and pathway enrichment analyses of those urinary metabolites, and the Person’s correlation analyses among those urinary metabolites and bone status revealed that LF impacted on bone formation via regulatory comprehensive pathways including taurine and hypotaurine metabolism, arginine and proline metabolism, cyanoamino acid metabolism, nitrogen metabolism, nicotinate and nicotinamide metabolism, and fatty acid biosynthesis. The present study indicated the metabolomics is a useful and practical tool to elucidate the mechanisms by which LF augments bone mass formation in growing animals.

Accelerated Osteogenic Differentiation of MC3T3-E1 Cells by Lactoferrin-Conjugated Nanodiamonds through Enhanced Anti-Oxidant and Anti-Inflammatory Effects

The purpose of this study was to investigate the effects of lactoferrin (LF)-conjugated nanodiamonds (NDs) in vitro on both anti-oxidant and anti-inflammation activity as well as osteogenic promotion. The application of LF-NDs resulted in sustained release of LF for up to 7 days. In vitro anti-oxidant analyses performed using Dichlorofluorescin diacetate (DCF-DA) assay and cell proliferation studies showed that LF (50 μg)-NDs effectively scavenged the reactive oxygen species (ROS) in MC3T3-E1 cells (osteoblast-like cells) after H₂O₂ treatment and increased proliferation of cells after H₂O₂ treatment. Treatment of lipopolysaccharide (LPS)-induced MC3T3-E1 cells with LF-NDs suppressed levels of pro-inflammatory cytokines, including interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). In addition, LF-NDs were associated with outstanding enhancement of osteogenic activity of MC3T3-E1 cells due to increased alkaline phosphatase (ALP) and calcium deposition. Our findings suggest that LF-NDs are an important substrate for alleviating ROS effects and inflammation, as well as promoting osteogenic differentiation of cells.

Human Mesenchymal Stem Cell Response to Lactoferrin-based Composite Coatings

The potential of mesenchymal stem cells (MSCs) for implantology and cell-based therapy represents one of the major ongoing research subjects within the last decades. In bone regeneration applications, the various environmental factors including bioactive compounds such as growth factors, chemicals and physical characteristics of biointerfaces are the key factors in controlling and regulating osteogenic differentiation from MSCs. In our study, we have investigated the influence of Lactoferrin (Lf) and Hydroxyapatite (HA) embedded within a biodegradable PEG-PCL copolymer on the osteogenic fate of MSCs, previous studies revealing an anti-inflammatory potential of the coating and osteogenic differentiation of murine pre-osteoblast cells. The copolymer matrix was obtained by the Matrix Assisted Pulsed Laser Evaporation technique (MAPLE) and the composite layers containing the bioactive compounds (Lf, HA, and Lf-HA) were characterised by Scanning Electron Microscopy and Atomic Force Microscopy. Energy-dispersive X-ray spectroscopy contact angle and surface energy of the analysed coatings were also measured. The characteristics of the composite surfaces were correlated with the viability, proliferation, and morphology of human MSCs (hMSCs) cultured on the developed coatings. All surfaces were found not to exhibit toxicity, as confirmed by the LIVE/DEAD assay. The Lf-HA composite exhibited an increase in osteogenic differentiation of hMSCs, results supported by alkaline phosphatase and mineralisation assays. This is the first report of the capacity of biodegradable composite layers containing Lf to induce osteogenic differentiation from hMSCs, a property revealing its potential for application in bone regeneration.

Nanofilm generated non-pharmacological anabolic bone stimulus

Stimulus-responsive nanomaterials have mainly been employed to ablate or destroy tissues or to facilitate controlled release of drugs or biologics. Herein, we demonstrate the potential of stimulus-responsive nanomaterials to promote tissue regeneration via a non-pharmacological and noninvasive strategy. Thin nanofilms of an optically-absorbing organic dye or nanoparticle (single-walled graphene nanoribbons [SWOGNR]) were placed over (without touching the skin) a rodent femoral fracture site. A nanosecond pulsed near-infrared laser diode was employed to generate photoacoustic (PA) signals from the nanofilms. X-ray micro-computed tomography (microCT), histology, and mechanical testing results showed that daily PA stimulations of upto 45 min for 6 weeks (complete fracture healing) do not adversely affect bone regeneration and quality. Further, microCT and histological analysis showed 10 min daily stimulation for 2 weeks significantly increases bone quantity at the fracture sites of rats exposed to the nanoparticle-generated PA signals. In these rats, up to threefold increase in bone volume to callus volume ratio and twofold increase in bone mineral density within the callus were noted, compared to rats that were not exposed to the photoacoustic signals. The results taken together indicate that nanofilm-generated photoacoustic signals serve as an anabolic stimulus for bone regeneration. The results, in conjugation with the ability of these nanofilms to serve as PA contrast agents, present opportunities toward the development of integrated noninvasive imaging and noninvasive or invasive treatment strategies for bone loss due to disease or trauma.

Effect of Lactoferrin on the Expression Profiles of Long Non-coding RNA during Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Lactoferrin (LF) has demonstrated stimulation of osteogenic differentiation of mesenchymal stem cells (MSCs). Long non-coding RNAs (lncRNAs) participate in regulating the osteogenic differentiation processes. However, the impact of LF on lncRNA expression in MSC osteogenic differentiation is poorly understood. Our aim was to investigate the effects of LF on lncRNAs expression profiles, during osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs), by RNA sequencing. A total number of 1331 putative lncRNAs were identified in rBMSCs during osteogenic differentiation in the study. LF influenced the expression of 120 lncRNAs (differentially expressed lncRNAs [DELs], Fold change > 1.5 or < −1.5; p < 0.05) in rBMSCs on day 14 of osteogenic differentiation, consisted of 60 upregulated and 60 down-regulated. Furthermore, the potential functions of DELs were of prediction by searching their target cis- and trans-regulated protein-coding genes. The bioinformatic analysis of DELs target gene revealed that LF led to the disfunction of transforming growth factor beta stimulus (TGF-β) and positive regulation of I-κappa B kinase/NF-κappa B signaling pathway, which may relate to osteogenic differentiation of rBMSCs. Our work is the first profiling of lncRNA in osteogenic differentiation of rBMSCs induced by LF, and provides valuable insights into the potential mechanisms for LF promoting osteogenic activity.

Lactoferrin-Hydroxyapatite Containing Spongy-Like Hydrogels for Bone Tissue Engineering

The development of bioactive and cell-responsive materials has fastened the field of bone tissue engineering. Gellan gum (GG) spongy-like hydrogels present high attractive properties for the tissue engineering field, especially due to their wide microarchitecture and tunable mechanical properties, as well as their ability to entrap the responsive cells. Lactoferrin (Lf) and Hydroxyapatite (HAp) are bioactive factors that are known to potentiate faster bone regeneration. Thus, we developed an advanced three-dimensional (3D) biomaterial by integrating these bioactive factors within GG spongy-like hydrogels. Lf-HAp spongy-like hydrogels were characterized in terms of microstructure, water uptake, degradation, and concomitant release of Lf along the time. Human adipose-derived stem cells (hASCs) were seeded and the capacity of these materials to support hASCs in culture for 21 days was assessed. Lf addition within GG spongy-like hydrogels did not change the main features of GG spongy-like hydrogels in terms of porosity, pore size, degradation, and water uptake commitment. Nevertheless, HAp addition promoted an increase of the pore wall thickness (from ~13 to 28 µm) and a decrease on porosity (from ~87% to 64%) and mean pore size (from ~12 to 20 µm), as well as on the degradability and water retention capabilities. A sustained release of Lf was observed for all the formulations up to 30 days. Cell viability assays showed that hASCs were viable during the culture period regarding cell-laden spongy-like hydrogels. Altogether, we demonstrate that GG spongy-like hydrogels containing HAp and Lf in high concentrations gathered favorable 3D bone-like microenvironment with an increased hASCs viability with the presented results.

Macrophage in vitro Response on Hybrid Coatings Obtained by Matrix Assisted Pulsed Laser Evaporation

The improvement in the research area of the implant by surface functionalization when correlated with the biological response is of major interest in the biomedical field. Based on the fact that the inflammatory response is directly involved in the ultimate response of the implant within the body, it is essential to study the macrophage-material interactions. Within this context, we have investigated the composite material-macrophage cell interactions and the inflammatory response to these composites with amorphous hydroxyapatite (HA), Lactoferrin (Lf), and polyethylene glycol-polycaprolactone (PEG-PCL) copolymer. All materials are obtained by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique and characterized by Atomic Force Microscopy and Scanning Electron Microscopy. Macrophage-differentiated THP-1 cells proliferation and metabolic activity were assessed by qualitative and quantitative methods. The secretion of tumor necrosis factor alpha (TNF-α) and interleukin 10 (IL-10) cytokine, in the presence and absence of the inflammatory stimuli (bacterial endotoxin; lipopolysaccharide (LPS)), was measured using an ELISA assay. Our results revealed that the cellular response depended on the physical-chemical characteristics of the coatings. Copolymer-HA-Lf coatings led to low level of pro-inflammatory TNF-α, the increased level of anti-inflammatory IL-10, and the polarization of THP-1 cells towards an M2 pro-reparative phenotype in the presence of LPS. These findings could have important potential for the development of composite coatings in implant applications.

Small Molecules Enhance Scaffold-Based Bone Grafts via Purinergic Receptor Signaling in Stem Cells

The need for bone grafts is high, due to age-related diseases, such as tumor resections, but also accidents, risky sports, and military conflicts. The gold standard for bone grafting is the use of autografts from the iliac crest, but the limited amount of accessible material demands new sources of bone replacement. The use of mesenchymal stem cells or their descendant cells, namely osteoblast, the bone-building cells and endothelial cells for angiogenesis, combined with artificial scaffolds, is a new approach. Mesenchymal stem cells (MSCs) can be obtained from the patient themselves, or from donors, as they barely cause an immune response in the recipient. However, MSCs never fully differentiate in vitro which might lead to unwanted effects in vivo. Interestingly, purinergic receptors can positively influence the differentiation of both osteoblasts and endothelial cells, using specific artificial ligands. An overview is given on purinergic receptor signaling in the most-needed cell types involved in bone metabolism-namely osteoblasts, osteoclasts, and endothelial cells. Furthermore, different types of scaffolds and their production methods will be elucidated. Finally, recent patents on scaffold materials, as wells as purinergic receptor-influencing molecules which might impact bone grafting, are discussed.

Ultrastructural characteristics of ovine bone marrow-derived mesenchymal stromal cells cultured with a silicon stabilized tricalcium phosphate bioceramic

Bioceramics are being used in experimental bone engineering application in association with bone marrow derived mesenchymal stem cells (BM-MSCs) as a new therapeutic tool, but their effects on the ultrastructure of BM-MSCs are yet unknown. In this study we report the morphological features of ovine (o)BM-MSCs cultured with Skelite, a resorbable bioceramic based on silicon stabilized tricalcium phosphate (SiTCP), able to promote the repair of induced bone defect in sheep model. oBM-MSCs were isolated from the iliac crest, cultured until they reached near-confluence and incubated with SiTCP. After 48 hr the monolayers were highly damaged and only few cells adhered to the plastic. Thus, SiTCP was removed, and after washing the cells were cultured until they became confluent. Then, they were trypsinizated and processed for transmission electron microscopy (TEM) and RT-PCR analysis. RT-PCR displayed that oBM-MSCs express typical surface marker for MSCs. TEM revealed the presence of electron-lucent cells and electron-dense cells, both expressing the CD90 surface antigen. The prominent feature of electron-lucent cells was the concentration of cytoplasmic organelles around the nucleus as well as large surface blebs containing glycogen or profiles of endoplasmic reticulum. The dark cells had a multilocular appearance by the presence of peripheral vacuoles. Some dark cells contained endocytic vesicles, lysosomes, and glycogen aggregates. oBM-MSCs showed different types of specialized interconnections. The comparison with ultrastructural features of untreated oBM-MSCs suggests the light and dark cells are two distinct cell types which were differently affected by SiTCP bioceramic. Skelite cultured ovine BM-MSCs display electron-dense and electron-lucent cells which are differently affected by this bioceramic. This suggests that they could play a different role in bioceramic based therapy.

Fe-Doping-Induced Magnetism in Nano-Hydroxyapatites

Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising strategies for the development of advanced magnetic biomaterials. However, especially in the case of iron-doped magnetic hydroxyapatites, it is not clear if the magnetic features come merely from the magnetic phases/ions used as dopants or from complex mechanisms involving interactions at the nanoscale. Here, we report an extensive chemical-physical and magnetic investigation of three hydroxyapatite nanocrystals doped with different iron species and containing small or no amounts of maghemite as a secondary phase. The association of several investigation techniques such as X-ray absorption spectroscopy, Mössbauer, magnetometry, and TEM allowed us to determine that the unusual magnetic properties of Fe^2+/3+-doped hydroxyapatites (FeHA) occur by a synergy of two different phenomena: i.e., (i) interacting superparamagnetism due to the interplay between iron-doped apatite and iron oxide nanoparticles as well as to the occurrence of dipolar interactions and (ii) interacting paramagnetism due to Fe³⁺ ions present in the superficial hydrated layer of the apatite nanophase and, to a lesser extent, paramagnetism due to isolated Fe³⁺ ions in the apatite lattice. We also show that a major player in the activation of the above phenomena is the oxidation of Fe²⁺ into Fe³⁺, as induced by the synthesis process, and their consequent specific positioning in the FeHA structure.

Coupling Hydroxyapatite Nanocrystals with Lactoferrin as a Promising Strategy to Fine Regulate Bone Homeostasis

Lactoferrin (LF) is an interesting glycoprotein in the field of bone biology for its regulatory effect on cells involved in bone remodeling, that results compromised in several pathological conditions, as osteoporosis. In a previous study we observed that the coupling of LF and biomimetic hydroxyapatite nanocrystals (HA), a material well-known for its bioactivity and osteoconductive properties, leads to a combined effect in the induction of osteogenic differentiation of mesenchymal stem cells. On the basis of this evidence, the present study is an extension of our previous work aiming to investigate the synergistic effect of the coupling of HA and LF on bone homeostasis. Biomimetic HA nanocrystals were synthesized and functionalized with LF (HA-LF) and then pre-osteoblasts (MC3T3-E1) and monocyte/macrophage cells lines (RAW 264.7), using as osteoclastogenesis in vitro model, were cultured separately or in co-culture in presence of HA-LF. The results clearly revealed that HA and LF act in synergism in the regulation of the bone homeostasis, working as anabolic factor for osteoblasts differentiation and bone matrix deposition, and as inhibitor of the osteoclast formation and activity.

A rabbit maxillary sinus model with simultaneous customized-implant placement: Comparative microscopic analysis for the evaluation of surface-treated implants

We describe the use of a rabbit maxillary sinus model, characterized by thin osseous tissue and low bone density, for the evaluation of surface-treated implants by histologically and histomorphometrically comparing the osseointegration patterns depending on the surface treatment methods. Twenty rabbits were randomly assigned to two groups of 10 animals, one receiving 5 × 3 mm customized implants (machined, MA or sandblasted and acid etched, SLA) placed in sinus and the other receiving implants placed in a tibia. Histological observation of the implant placed in sinus shows relatively more active new bone formation, characterized by trabecular bone pattern underneath the cortical bone in sinus as compared with that in tibia. Histomorphometric analysis in the rabbits receiving implants in a tibia, the NBIC (%) associated with the SLA surface implant was greater than that associated with the MA implant at 2 weeks (55.63 ± 8.65% vs. 47.87 ± 10.01%; P > 0.05) and at 4 weeks (61.76 ± 9.49% vs. 42.69 ± 10.97%; P < 0.05). Among rabbits receiving implants in a sinus, the NBIC (%) associated with the SLA surface implant was significantly greater than that associated with the MA surface implant both at 2 weeks (37.25 ± 7.27% vs. 20.98 ± 6.42%; P < 0.05) and at 4 weeks (48.82 ± 6.77% vs. 31.51 ± 9.14%; P < 0.05). As a result, we suggest that the maxillary sinus model is an appropriate animal model for assessing surface-treated implants and may be utilized for the evaluation of surface-treated implants in poor bone quality environment. Microsc. Res. Tech. 78:697-706, 2015.