Interleukin-1 represses COLIA1 promoter activity in calvarial bones of transgenic ColCAT mice in vitro and in vivo

The osteoimmunomodulatory effect of nanostructured TiFx/TiOxcoating on osteogenesis induction

Macrophages play a central role in the host response and the integration of implant materials. The nanostructured TiF_x/TiO_xcoating (FOTi) on titanium surfaces has shown multiple properties, including antibacterial properties and bioactivity. However, little is known about the effects of these coatings on the regulation of macrophage activity and the subsequent immunomodulatory effects on osteogenesis. In this study, the behavior of macrophages on the FOTi samples was evaluated, and conditioned medium was collected and used to stimulate MC3T3-E1 cellsin vitro. The results showed that the FOTi samples stimulated macrophage elongation and promoted the production of proinflammatory cytokines at 24 h, while induced macrophage polarization to the anti-inflammatory M2 phenotype at 72 h. Furthermore, the immune microenvironment generated by macrophage/ FOTi samples interactions effectively promoted the osteogenic differentiation of MC3T3-E1 cells, as evidenced by improved cell adhesion, enhanced alkaline phosphatase activity and extracellular matrix mineralization, and upregulated osteogenesis-related gene expression. In summary, the FOTi samples mediated macrophage phenotype behaviors and induced beneficial immunomodulatory effects on osteogenesis, which could be a potential strategy for the surface modification of bone biomaterials.

Anti-inflammatory and antimicrobial activity of bioactive hydroxyapatite/silver nanocomposites

Biomaterials are often used in orthopedic surgery like cavity fillings. However, related complications often require long-term systemic antibiotics, device removal, and extended rehabilitation. Hydroxyapatite/silver (HA/Ag) composites have been proposed as implantation biomaterials owing to the osteogenic properties of hydroxyapatite and to the antimicrobial efficiency of silver. Nevertheless, higher silver concentrations induce cytotoxic effects. The aim of this study was to synthesize and characterize HA/Ag nanocomposites that will allow us to use lower concentrations of silver nanoparticles with better antimicrobial efficiency and anti-inflammatory properties. The characterization of HA/Ag was performed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier-transform infrared spectra, X-ray photoelectron spectroscopy, and laser diffraction. Bioactivity was evaluated under a simulated body fluid. The viability of osteoblast like-cells (MG-63) was determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) and the antimicrobial activity was evaluated by the standard McFarland method. The detection of nitric oxide was measured by a colorimetric assay and the inflammatory cytokines by flow cytometry. We obtained particulate composites of calcium phosphates identified as hydroxyapatite and silver nanoparticles. The bioactivity of the HA/Ag nanocomposites on SFB was confirmed by apatite formations. The viability of MG-63 cells was not affected. We also found antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans owing to the presence of silver nanoparticles at non-cytotoxic concentrations. HA/Ag reduced the release of nitric oxide and decreased the secretion of IL-1 and TNF-α in cells stimulated with Lipopolysaccharide (LPS). In conclusion, the inflammatory and antimicrobial capacity of the HA/Ag nanocomposites, as well as its bioactivity and low cytotoxicity make it a candidate as an implantation biomaterial for bone tissues engineering and clinical practices in orthopedic, oral and maxillofacial surgery.

Early Healing Events after Periodontal Surgery: Observations on Soft Tissue Healing, Microcirculation, and Wound Fluid Cytokine Levels

Early wound healing after periodontal surgery with or without enamel matrix derivative/biphasic calcium phosphate (EMD/BCP) was characterized in terms of soft tissue closure, changes of microcirculation, and expression of pro- and anti-inflammatory cytokines in gingival crevicular fluid/wound fluid (GCF/WF). Periodontal surgery was carried out in 30 patients (18 patients: application of EMD/BCP for regeneration of bony defects; 12 patients: surgical crown lengthening (SCL)). Healthy sites were observed as untreated controls. GCF/WF samples were collected during two post-surgical weeks. Flap microcirculation was measured using laser Doppler flowmetry (LDF). Soft tissue healing was evaluated after two weeks. GCF/WF levels of interleukin 1β (IL-1β), tumour necrosis factor (TNF-α), IL-6, and IL-10 were determined using a multiplex immunoassay. Surgery caused similar reductions of flap microcirculation followed by recovery within two weeks in both EMD/BCP and SCL groups. GCF/WF and pro-inflammatory cytokine levels were immediately increased after surgery, and returned only partially to baseline levels within the two-week observation period. Levels of IL-10 were temporarily reduced in all surgical sites. Flap dehiscence caused prolonged elevated levels of GCF/WF, IL-1β, and TNF-α. These findings show that periodontal surgery triggers an immediate inflammatory reaction corresponding to the early inflammatory phase of wound healing, and these inflammation measures are temporary in case of maintained closure of the flap. However, flap dehiscence causes prolonged inflammatory exudation from the periodontal wound. If the biological pre-conditions for periodontal wound healing are considered important for the clinical outcome, care should be taken to maintain primary closure of the flap.

Improved implant osseointegration of a nanostructured titanium surface via mediation of macrophage polarization

The use of endosseous implanted materials is often limited by undesirable effects that may be due to macrophage-related inflammation. The purpose of this study was to fabricate a nanostructured surface on a titanium implant to regulate the macrophage inflammatory response and improve the performance of the implant. Anodization at 5 and 20 V as well as UV irradiation were used to generate hydrophilic, nanostructured TiO2 surfaces (denoted as NT5 and NT20, respectively). Their surface characteristics and in vivo osseointegration as well as the inflammatory response they elicit were analyzed. In addition, the behavior of macrophages in vitro was evaluated. Although the in vitro osteogenic activity on the two surfaces was similar, the NT5 surface was associated with more bone formation, less inflammation, and a reduced CD68(+) macrophage distribution in vivo compared to the NT20 and polished Ti surfaces. Consistently, further experiments revealed that the NT5 surface induced healing-associated M2 polarization in vitro and in vivo. By contrast, the NT20 surface promoted the pro-inflammatory M1 polarization, which could further impair bone regeneration. The results demonstrate the dominant role of macrophage-related inflammation in bone healing around implants and that surface nanotopography can be designed to have an immune-regulating effect in support of the success of implants.

Infection, inflammation, and bone regeneration: a paradoxical relationship

Various strategies have been developed to promote bone regeneration in the craniofacial region. Most of these interventions utilize implantable materials or devices. Infections resulting from colonization of these implants may result in local tissue destruction in a manner analogous to periodontitis. This destruction is mediated via the expression of various inflammatory mediators and tissue-destructive enzymes. Given the well-documented association among microbial biofilms, inflammatory mediators, and tissue destruction, it seems reasonable to assume that inflammation may interfere with bone healing and regeneration. Paradoxically, recent evidence also suggests that the presence of certain pro-inflammatory mediators is actually required for bone healing. Bone injury (e.g., subsequent to a fracture or surgical intervention) is followed by a choreographed cascade of events, some of which are dependent upon the presence of pro-inflammatory mediators. If inflammation resolves promptly, then proper bone healing may occur. However, if inflammation persists (which might occur in the presence of an infected implant or graft material), then the continued inflammatory response may result in suboptimal bone formation. Thus, the effect of a given mediator is dependent upon the temporal context in which it is expressed. Better understanding of this temporal sequence may be used to optimize regenerative outcomes.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.

Skeletal homeostasis in tissue-engineered bone

Tissue-engineering strategies to stimulate bone regeneration may offer an alternative approach to conventional orthopaedic and maxillofacial surgical therapies. Over the last decade, significant advances have been accomplished in developing biomimetic matrices, growth factors, cell transplantation and gene delivery therapeutics to support new bone growth. However, it is not known if tissue-engineered bone recapitulates the biology of normal skeletal tissue in response to physiologic cues. Here, we report that bone formed by the differentiation of transplanted murine bone marrow stromal cells (BMSCs) responds to a systemically delivered calciotropic hormone. Ectopic ossicles in mice exposed to catabolic doses of parathyroid hormone (PTH) had increased numbers of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts as compared to control mice. In contrast, treatment with anabolic doses of PTH promoted a marked increase in trabecular bone mass as analyzed by microcomputed tomography and histomorphometry. Our findings demonstrate that bone formed from transplanted BMSCs is responsive to normal physiologic signals, and can be augmented by the addition of a systemic anabolic agent. Because multiple and distinct ossicles can be generated in a single animal, this versatile system may be used to: (a) elucidate cellular/molecular mechanisms in bone regeneration; (b) study cell-to-cell interactions in the bone marrow microenvironment in health and disease; and (c) evaluate the efficacy of osteotropic agents that modulate bone turnover in vivo.

Osteoblastic response to the defective matrix in the osteogenesis imperfecta murine (oim) mouse

This work examines the cellular pathophysiology associated with the weakened bone matrix found in a murine model of osteogenesis imperfecta murine (oim). Histomorphometric analysis of oim/oim bone showed significantly diminished bone mass, and the osteoblast and osteoclast histomorphometric parameters were increased in the oim/oim mice, compared with wild-type (+/+) mice. To assess osteoblast activity, a rat Col1a1 promoter linked to the chloramphenicol acetyltransferase reporter transgene was bred into the oim model. At 8 d and 1 month of age, no difference in transgene activity between oim and control mice was observed. However, at 3 months of age, chloramphenicol acetyl transferase activity was elevated in oim/oim;Tg/Tg, compared with +/+;Tg/Tg and oim/+;Tg/Tg. High levels of urinary pyridinoline crosslinks in the oim/oim;Tg/Tg mice were present at all ages, reflecting continuing high bone resorption. Our data portray a state of ineffective osteogenesis in which the mutant mouse never accumulates a normal quantity of bone matrix. However, it is only after the completion of the rapid growth phase that the high activity of the oim/oim osteoblast can compensate for the high rate of bone resorption. This relationship between bone formation and resorption may explain why the severity of osteogenesis imperfecta decreases after puberty is completed. The ability to quantify high bone turnover and advantages of using a transgene that reflects osteoblast lineage activity make this a useful model for studying interventions designed to improve the bone strength in osteogenesis imperfecta.

Involvement of CCAAT enhancer binding protein transcription factors in the regulation of prostaglandin G/H synthase 2 expression by interleukin-1 in osteoblastic MC3T3-E1 cells

Interleukin-1 (IL-1) stimulates prostaglandin production in bone by a rapid and transient activation of prostaglandin G/H synthase 2 (PGHS-2) gene expression. In osteoblastic MC3T3-E1 cells, IL-1 caused a transient increase in PGHS-2 messenger RNA (mRNA), which peaked at 2 h. IL-1 caused a 2- to 4-fold activation of a 371-base pair (bp) murine PGHS-2 promoter/luciferase construct in stable transfectants. This response mapped to a proximal promoter element(s) located between -150 and -40 bp. This region contains a putative CCAAT enhancer binding protein (C/EBP) site (centered at -135 bp), which shows enhanced binding of C/EBPbeta and C/EBPdelta by mobility shift analysis after IL-1 treatment. A transient cotransfection approach was used to examine the effects of C/EBPbeta and C/EBPdelta overexpression. IL-1 caused a maximal 3- to 7-fold stimulation of PGHS-2 promoter activity after 2.5 h. Overexpression of murine C/EBPbeta and C/EBPdelta caused a dose-dependent increase in basal and IL-1-stimulated luciferase activity. C/EBPdelta caused a greater enhancement of basal and IL-1-stimulated promoter activity than C/EBPbeta, suggesting that C/EBPdelta is a stronger transactivator. Overexpression of p20C/EBPbeta, a dominant negative inhibitor of C/EBP function, blocked the stimulation of PGHS-2 promoter activity by IL-1 and blocked the ability of overexpressed C/EBPbeta and C/EBPdelta to increase basal and IL-1-stimulated promoter activity. Mutagenesis of the C/EBP site reduced, but did not abolish, the stimulation of PGHS-2 promoter activity by IL-1 and blunted the effect of overexpressed C/EBPdelta on basal and IL-1-stimulated promoter activity. These results suggest an essential role for C/EBPbeta and C/EBPdelta in the induction of PGHS-2 gene expression by IL-1 in osteoblastic cells.

Parathyroid hormone inhibits collagen synthesis and the activity of rat col1a1 transgenes mainly by a cAMP-mediated pathway in mouse calvariae

We examined the effect of parathyroid hormone and various signaling molecules on collagen synthesis and chloramphenicol acetyltransferase activity in cultured transgenic mouse calvariae carrying fusion genes of the rat Col1a1 promoter and the chloramphenicol acetyltransferase reporter. After 48 h of culture, parathyroid hormone, forskolin, dibutyryl cAMP, 8-bromo cAMP, and phorbol myristate acetate inhibited transgene activity, while the calcium ionophore ionomycin had no effect. Pretreatment of calvariae with the phosphodiesterase inhibitor isobutylmethylxanthine potentiated the inhibitory effect of 1 nM parathyroid hormone on transgene activity and collagen synthesis. Parathyroid hormone further inhibited transgene activity and collagen synthesis in the presence of phorbol myristate acetate. Parathyroid hormone inhibition of transgene activity and collagen synthesis was not affected by indomethacin or interleukin-6. After 48 h of culture, parathyroid hormone inhibited chloramphenicol acetyltransferase activity by 50-85% in cultured calvariae carrying transgenes having progressive 5' upstream deletions of promoter DNA down to -1683 bp. These data show that the inhibitory effect of parathyroid hormone on Col1a1 expression in mouse calvariae is mediated mainly by the cAMP signaling pathway. Prostaglandins and IL-6 are not local mediators of the parathyroid hormone response in this model. Finally, regions of the Col1a1 promoter downstream of -1683 bp are sufficient for parathyroid hormone inhibition of the Col1a1 promoter.