Inhibition of leukotriene function can modulate particulate-induced changes in bone cell differentiation and activity

Bioceramic and polycationic biopolymer nanocomposite scaffolds for improved wound self-healing and anti-inflammatory properties: an in vitro study

The development of wound healing scaffolds with high porosity, rapid healing properties, and anti-inflammatory functionality is vital in the chronic wound healing stage for the production of extracellular matrices of injured tissues. The 45S5 bioactive glass (BG) possesses good biocompatibility and provides a potential bonding resource for fibroblast cell proliferation, growth factor synthesis, and granulated tissue formation. Chitosan, a natural polymer, promotes tissue regeneration and has anti-microbial properties. BG and chitosan scaffolds were prepared by the freeze-drying (lyophilization) method. The chitosan scaffold is a semi-crystalline polymer with a random crystal structure because it contains more hydroxyl groups. Chitosan alone shows a sheet-like morphology with a porous microstructure (1.7475 nm). BG particulates were well decorated over the surface of the chitosan scaffold with a homogeneous dispersion. Cell viability was observed for L929 cells on the chitosan-BG scaffolds. Confocal images vividly depict the interaction of the L929 cells with the scaffold without causing any damage to the cell membrane. In vitro scratch assay shows the best wound healing activity (complete wound closure) for the BG-chitosan nanocomposite scaffolds at 18 h. The chitosan-BG scaffolds were combined with anti-inflammatory drugs and induced inflammatory genes at an inhibition rate of COX of (36, 28, and 30%), LOX of (20, 13, and 14%), and NO of (48, 38, and 39%) for chitosan, chitosan-BG, and chitosan-BG (Na-free) at 100 μL addition. The in vitro bioactivities proved that the chitosan-BG scaffolds could enable better cell formation, and exhibited improved biocompatibility, and anti-inflammatory and wound healing properties.

Recent development of lipoxygenase inhibitors as anti-inflammatory agents

Inflammation is favorable in most cases, because it is a kind of body defensive response to external stimuli; sometimes, inflammation is also harmful, such as attacks on the body's own tissues. It could be that inflammation is a unified process of injury and resistance to injury. Inflammation brings extreme pain to patients, showing symptoms of rubor, swelling, fever, pain and dysfunction. As the specific mechanism is not clear yet, the current anti-inflammatory agents are given priority for relieving suffering of patients. Thus it is emergent to find new anti-inflammatory agents with rapid effect. Lipoxygenase (LOX) is a kind of rate-limiting enzyme in the process of arachidonic acid metabolism into leukotriene (LT) which mediates the occurrence of inflammation. The inhibition of LOX can reduce LT, thereby producing an anti-inflammatory effect. In this review, the LOX inhibitors reported in recent years are summarized, and, in particular, their activities, structure-activity relationships and molecular docking studies are emphasized, which will provide new ideas to design novel LOX inhibitors.

The relevance of leukotrienes for bone resorption induced by mechanical loading

5-Lipoxygenase (5-LO) metabolites are important pro-inflammatory lipid mediators. However, much still remains to be understood about the role of such mediators in bone remodeling. This study aimed to investigate the effect of 5-LO metabolites, LTB4 and CysLTs, in a model of mechanical loading-induced bone remodeling. Strain-induced tooth movement and consequently alveolar bone resorption/apposition was achieved by using a coil spring placed on molar and attached to incisors of C57BL6 (wild-type-WT), 5-LO deficient mice (5-LO(-/-)) and mice treated with 5-LO inhibitor (zileuton-ZN) or with antagonist of CysLTs receptor (montelukast-MT). The amount of bone resorption and the number of osteoclasts were determined morphometrically. The expression of inflammatory and bone remodeling markers in periodontium was analyzed by qPCR. Osteoclast differentiation and TNF-α production were evaluated in vitro using RAW 264.7 cells treated with LTB4 or LTD4. Bone resorption, TRAP(+) cells and expression of Tnfa, Il10 and Runx2 were significantly diminished in 5-LO(-/-), ZN- and MT-treated mice. The expression of Rank was also reduced in 5-LO(-/-) and MT-treated mice. Accordingly, LTB4 and LTD4 in association with RANKL promoted osteoclast differentiation and increased TNF-α release in vitro. These data demonstrate that the absence of 5-LO metabolites, LTB4 and CysLTs reduces osteoclast recruitment and differentiation, consequently diminishing bone resorption induced by mechanical loading. Thus, 5-LO might be a potential target for controlling bone resorption in physiological and pathological conditions.

The Effect of Gu-Sui-Bu (Drynaria fortunei) on Bone Cell Activity

We investigated the effects of Gu-Sui-Bu using in vitro bone cell cultures. Primary rabbit and mouse marrow cells were cultured with or without five different concentrations of Gu-Sui-Bu extract. Osteoclast numbers were assessed using tartrate-resistant acid phosphatase (TRAP) positive cell counts and for function, osteoclast resorption pits on bovine bone slices were performed. Alkaline phosphatase (AP) positive cell counts and mineralized nodule formation were examined to assess osteoblast function with Gu-Sui-Bu. TRAP+ osteoclast numbers increased, as did the number and size of resorption pits with 0.001 mg/ml of extract. Low doses of extract did not alter AP+ colony number or mineralized nodule formation, but both were inhibited by doses of 0.1 mg/ml or higher. The highest dose of extract (10 mg/ml) inhibited proliferation of all cell types. At 0.01 and 0.001 mg/ml doses, RANKL increased over time; however, osteoprotegerin levels only increased at doses ≥0.1 mg/ml. Resorption pit formation was decreased without alteration in mature multinucleated (TRAP+) cell counts only at the highest dose of the putative active ingredient of Gu-Sui-Bu. In summary, lower concentrations of Gu-Sui-Bu extract had positive effects on osteoclast proliferation, survival and resorptive activity that may be mediated through enhanced prostaglandin secretion. However, high doses of extract proved detrimental to osteoclast and osteoblast survival. No effect of low doses of Gu-Sui-Bu extract was seen in osteoblast cultures. High doses of the putative active ingredient of Gu-Sui-Bu showed mild inhibition of mouse osteoclast function.

Runx2 promotes both osteoblastogenesis and novel osteoclastogenic signals in ST2 mesenchymal progenitor cells

We profiled the global gene expression of a bone marrow-derived mesenchymal pluripotent cell line in response to Runx2 expression. Besides osteoblast differentiation, Runx2 promoted the osteoclastogenesis of co-cultured splenocytes. This was attributable to the upregulation of many novel osteoclastogenic genes and the downregulation of anti-osteoclastogenic genes.

INTRODUCTION

In addition to being a master regulator for osteoblast differentiation, Runx2 controls osteoblast-driven osteoclastogenesis. Previous studies profiling gene expression during osteoblast differentiation had limited focus on Runx2 or paid little attention to its role in mediating osteoblast-driven osteoclastogenesis.

METHODS

ST2/Rx2(dox), a bone marrow-derived mesenchymal pluripotent cell line that expresses Runx2 in response to Doxycycline (Dox), was used to profile Runx2-induced gene expression changes. Runx2-induced osteoblast differentiation was assessed based on alkaline phosphatase staining and expression of classical marker genes. Osteoclastogenic potential was evaluated by TRAP staining of osteoclasts that differentiated from primary murine splenocytes co-cultured with the ST2/Rx2(dox) cells. The BeadChip™ platform (Illumina) was used to interrogate genome-wide expression changes in ST2/Rx2(dox) cultures after treatment with Dox or vehicle for 24 or 48 h. Expression of selected genes was also measured by RT-qPCR.

RESULTS

Dox-mediated Runx2 induction in ST2 cells stimulated their own differentiation along the osteoblast lineage and the differentiation of co-cultured splenocytes into osteoclasts. The latter was attributable to the stimulation of osteoclastogenic genes such as Sema7a, Ltc4s, Efnb1, Apcdd1, and Tnc as well as the inhibition of anti-osteoclastogenic genes such as Tnfrsf11b (OPG), Sema3a, Slco2b1, Ogn, Clec2d (Ocil), Il1rn, and Rspo2.

CONCLUSION

Direct control of osteoblast differentiation and concomitant indirect control of osteoclast differentiation, both through the activity of Runx2 in pre-osteoblasts, constitute a novel mechanism of coordination with a potential crucial role in coupling bone formation and resorption.

Effects of platelet factors on biodegradation and osteogenesis in metaphyseal defects filled with nanoparticular hydroxyapatite--an experimental study in minipigs

There are no studies on the cellular activity in the early phase of biodegradation and bone healing of bone substitutes loaded with platelet factors (PLF). The purpose of this study was to evaluate the cellular effects of PLF in combination with nanoparticulate hydroxyapatite (HA) on the biodegradation and bone formation after 20 days. Autogenous PLFs were obtained by centrifugation of miniature pig blood samples and subsequent degranulation of platelets by calcium and thrombin. A cylindrical bone defect with a diameter of 8.9 mm was created in the distal femoral condyle of 20 miniature pigs. Four of the defects were left empty, 8 were filled with HA with loading and 8 with HA loaded with PLF. The distal femur was harvested after 20 days and TRAP-staining, cathepsin-K and CD44 staining and scanning electron microscopy were performed for cellular assessment of biodegradation was done. Histomorphometry of new bone formation and of biodegradation of HA material was performed. PLF loading of HA led to statistically significant more TRAP-positive cells with enhanced biodegradation of the nanoparticulate HA but no statistically enhanced new bone formation compared to unloaded HA. Furthermore, there was a higher number of CD44 and cathepsin-K positive cells by PLF-loading. In summary, PLF led to stimulation of the cellular process of the biodegradation of HA.

Adsorption of bisphosphonate onto hydroxyapatite using a novel co-precipitation technique for bone growth enhancement

Premature bone resorption and remodeling by osteoclasts can limit the longevity of implant fixation and recovery time. Orally administered bisphosphonates (BPs) have been used to inhibit osteoclast action at the implant/bone interface. Ideally, these should be delivered at the interface with the osteoblast-active hydroxyapatite (HA) for maximum effect. This investigation introduces a novel BP loading technique to achieve improved BP release from a simulated body fluid-grown HA (SBF-HA) with the aim of improving implant fixation. A solution co-precipitation technique incorporates the BP (pamidronate) into a thin SBF-HA coating. Surface analysis, using X-ray photoelectron spectroscopy (XPS), of the resultant coating was employed to confirm the presence of the adsorbed BP on the surface of SBF-HA. XPS analysis was also used to determine the optimal adsorption process. Osteoclast cell culture experiments confirmed the biological effectiveness of BP adsorption and proved that the pamidronate was biologically active, causing both decreased osteoclast numbers and decreased resorption.

Osteoimmunology

Osteoimmunology is an interdisciplinary research field combining the exciting fields of osteology and immunology. An observation that contributed enormously to the emergence of osteoimmunology was the accelerated bone loss caused by inflammatory diseases such as rheumatoid arthritis. Receptor activator of nuclear factor kappaB ligand (RANKL), which is the main regulator of osteoclastogenesis, was found to be the primary culprit responsible for the enhanced activation of osteoclasts: activated T cells directly and indirectly increased the expression of RANKL, and thereby promoted osteoclastic activity. Excessive bone loss is not only present in inflammatory diseases but also in autoimmune diseases and cancer. Furthermore, there is accumulating evidence that the very prevalent skeletal disorder osteoporosis is associated with alterations in the immune system. Meanwhile, numerous connections have been discovered in osteoimmunology beyond merely the actions of RANKL. These include the importance of osteoblasts in the maintenance of the hematopoietic stem cell niche and in lymphocyte development as well as the functions of immune cells participating in osteoblast and osteoclast development. Furthermore, research is being done investigating cytokines, chemokines, transcription factors and co-stimulatory molecules which are shared by both systems. Research in osteoimmunology promises the discovery of new strategies and the development of innovative therapeutics to cure or alleviate bone loss in inflammatory and autoimmune diseases as well as in osteoporosis. This review gives an introduction to bone remodeling and the cells governing that process and summarizes the most recent discoveries in the interdisciplinary field of osteoimmunology. Furthermore, an alternative large animal model will be discussed and the pathophysiological alterations of the immune system in osteoporosis will be highlighted.

Therapeutic options for 5-lipoxygenase inhibitors

5-Lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid (AA) into leukotriene (LT) A(4) and 5-hydroperoxyeicosatetraenoic acid. LTA(4) can then be converted into LTB(4) by LTA(4) hydrolase or into LTC(4) by LTC(4) synthase and the LTC(4) synthase isoenzymes MGST2 and MGST3. LTB(4) is a potent chemoattractant for neutrophils, eosinophils and monocytes leading to adherence of phagocytes to vessel walls, neutrophil degranulation and release of superoxide anions. LTC(4) and its metabolite, LTD(4), are potent bronchoconstrictors that increase vascular permeability and stimulate mucus secretion from airways. Recent data also suggest that LT have an immunomodulatory role. Due to these properties, the increased biosynthesis of LT in asthma, and based upon clinical data obtained with CysLT(1) receptor antagonists in asthma patients, there is a consensus that CysLT play a prominent role in asthma. In this review, we summarize the knowledge on possible functions of the 5-LO pathway in various diseases like asthma, cancer and cardiovascular events and review the corresponding potential therapeutic roles of 5-LO inhibitors.

The effects of titanium and polymethylmethacrylate particles on osteoblast phenotypic stability

Wear particles generated following total joint arthroplasty interact with cells at the periprosthetic margin and induce an inflammatory response that contributes to osteolysis, aseptic loosening, and implant failure. This study examined the long-term effects of particles from two commonly implanted materials, titanium (Ti) and polymethylmethacrylate (PMMA), on cell viability and metabolism over a 21-day time course, using the human osteoblast-like cell line MG-63. Addition of particles was not associated with increased cell death or nitric oxide production at the particle concentration chosen. Collagen production was increased with exposure to titanium particles, whereas alkaline phosphatase and osteocalcin expression remained unchanged following exposure to both types of particles. The data show that titanium but not PMMA particles shifts bone cell metabolism to preferentially produce fibrous tissue rather than bone.

The effect of bisphosphonates and titanium particles on osteoblasts

In an attempt to increase the life of cementless prostheses, an hydroxyapatite-coated implant which releases a bisphosphonate has been suggested as a drug-delivery system. Our in vitro study was designed to determine the maximum dose to which osteoblasts could be safely exposed.

Our findings demonstrated that zoledronate did not impair the proliferation of human osteoblasts when used at concentrations below 1 μm. Murine cells can be exposed to concentrations as high as 10 μm.

A concentration of 0.01% of titanium particles did not impair the proliferation of either cell line. Zoledronate affected the alkaline phosphatase activity of murine osteoblasts through a chelation phenomenon. The presence of titanium particles strongly decreased the alkaline phosphatase activity of murine osteoblasts. We did not detect any synergic effect of zoledronate and titanium particles on the behaviour of both human and murine osteoblasts.

Alendronate inhibits bone resorption at the bone-screw interface

In the current study, we investigated whether the systemic administration of alendronate, a third-generation bisphosphonate, suppressed the loosening of screws at the bone-screw interface. We systemically administered alendronate to rats fitted with external fixators. External fixators with two half pins were applied to the right femurs of rats, and alendronate was administrated once a week during a 5-week postoperative period. Radiographic, histologic, and immunohistochemical findings subsequently were analyzed. Treatment with alendronate reduced the width of the fibrous loosening membrane and the number of osteoclasts at the bone-screw interface. These findings indicate that systemic treatment with alendronate exerts an inhibitory effect on local bone resorption at the bone-screw interface.

Pharmacologic modulation of periprosthetic osteolysis

Wear and periprosthetic osteolysis of total joint replacements continue to be the most important problems in arthroplasty surgery. Despite the introduction of improved technologies including alternative bearing surfaces for TJRs, wear is inevitable because of relative movement at different interfaces and processes such as electrolysis and material degradation. Worn, clinically failing implants need to be followed closely and revised when appropriate. However, early wear and minor osteolysis do not result necessarily in progressive failure of the prosthesis. Indeed such cases may be followed up clinically and radiographically to establish the functional and biologic sequelae of wear and the timeline of these events. This scenario provides an opportunity to modulate the adverse biologic reaction associated with wear particles that includes chronic inflammation, the foreign body response, and periprosthetic bone destruction. Currently, immunological events associated with wear particles are becoming understood more clearly. Strategies to mitigate adverse processes associated with wear debris include local or systemic administration of immune modulators, signaling molecules, anti-inflammatory agents and growth factors, and altering osteoclast function. Ultimately, prevention of accelerated wear and periprosthetic osteolysis will be achieved with improved bearing surfaces and prosthetic designs.

Regulation of osteoclast activity in peri-implant tissues

Implants, particularly joint replacement prostheses, are one of the great success stories of modern medicine. However, too many implants fail prematurely, mainly due to aseptic bone loss around the implant. This paper reviews our current understanding of the role of osteoclasts in this peri-implant bone lysis. Prosthetic particles, often produced by articulating prostheses, are one of the major causes of elevated osteoclast lysis of peri-implant bone. Over the past decade there have been major advances in our understanding of the factors that regulate osteoclast activity, many of which were found to be important in osteoclast formation and activity in the peri-implant tissues. These factors are targets of a number of recently developed drugs that have been used successfully to prevent and treat peri-implant bone lysis in experimental models. Treatments such as these are being used in a number of bone loss pathologies in humans and have the potential for successful treatment of peri-implant osteolysis. In addition, understanding how different biomaterials influence the expression of key osteoclastogenic factors may allow us to select biomaterials for implantation that will last the lifetime of the recipient.

Regulation of osteoclast activity in peri-implant tissues

Implants, particularly joint replacement prostheses, are one of the great success stories of modern medicine. However, too many implants fail prematurely, mainly due to aseptic bone loss around the implant. This paper reviews our current understanding of the role of osteoclasts in this peri-implant bone lysis. Prosthetic particles, often produced by articulating prostheses, are one of the major causes of elevated osteoclast lysis of peri-implant bone. Over the past decade there have been major advances in our understanding of the factors that regulate osteoclast activity, many of which were found to be important in osteoclast formation and activity in the peri-implant tissues. These factors are targets of a number of recently developed drugs that have been used successfully to prevent and treat peri-implant bone lysis in experimental models. Treatments such as these are being used in a number of bone loss pathologies in humans and have the potential for successful treatment of peri-implant osteolysis. In addition, understanding how different biomaterials influence the expression of key osteoclastogenic factors may allow us to select biomaterials for implantation that will last the lifetime of the recipient.

Wear-particle-induced osteoclast osteolysis: the role of particulates and mechanical strain

Periprosthetic osteolysis involves osteoclast activation by wear particulates and their exposure to mechanical perturbation through exposure to shear forces generated by periprosthetic fluid as well as interface micromotion. This study aimed to determine the interactions between wear particulates, mechanical stimulation, and osteoclasts. In static cultures, wear particulates increased osteoclast differentiation. Addition of neutralizing antibodies to RANKL (receptor activator of nuclear factor kappa ligand) inhibited the particle-induced increase in osteoclast numbers. Cyclic 5000 microstrains were applied with the use of a custom-built device to marrow-derived cultures to assess the effect on osteoclast differentiation. Mechanical strain application alone decreased osteoclast differentiation, which was further decreased by the addition of particles despite increases in the soluble RANKL to osteoprotegerin (OPG) ratio. Mechanical strain alone induced mature osteoclast apoptosis in a dose-dependent manner. In contrast, in the mature osteoclast model, the addition of nonmetal particulates protected the osteoclasts from becoming apoptopic. Titanium (Ti) and cobalt chromium (CoCr) particles, however, induced osteoclast apoptosis, whereas polyethylene (PE) and polymethylmethacrylate (PMMA) did not. Wear particulates and mechanical stimulation interact via an eicosanoid-dependent pathway to alter osteoclast function and survival. The addition of mechanical perturbation to a particle-laden system thus appears to enhance the potential for osteolytic activity by enhancing osteoclast survival.