NAMPT expression in osteoblasts controls osteoclast recruitment in alveolar bone remodeling.

In bone remodeling, osteoclasts are recruited via increased production of RANKL (receptor activator of nuclear factor-κB ligand) and migrate to the bone surface, aided by matrix metalloproteinases (MMPs). NAMPT (nicotinamide phosphoribosyl transferase), which catalyzes the rate-limiting step in the NAD+ salvage pathway, increases during in vitro osteogenic differentiation and inhibits RANKL-induced osteoclast differentiation. Alveolar bone loss, due to disturbance of the remodeling process, is a major feature of periodontitis. Thus, we investigated the role of NAMPT in a synchronized alveolar bone remodeling rat model. NAMPT expression increased in osteogenic cells during the remodeling activation phase, in parallel with RANKL and MMP-2 expression. Inhibition of NAMPT activity, by systemic delivery of its selective inhibitor FK866, decreased the recruitment of osteoclasts, but not their activity. In vitro, NAMPT mRNA, and protein expression also increased during osteoblast differentiation in primary calvarial osteoblast cultures. Recombinant NAMPT and NMN, its direct metabolite, dose-dependently increased bone marker expression, including that of sialoprotein (BSP) and osteocalcin (OC), whereas their expression was inhibited by FK866 treatment. Recombinant NAMPT did not regulate MMP-2, -9, MMP-13, or RANKL/OPG mRNA expression in osteoblasts. Our data suggest that de novo NAMPT synthesis in osteoblasts controls cell differentiation through osteoclast recruitment during the activation of bone remodeling.

RGTA® or ReGeneraTing Agents mimic heparan sulfate in regenerative medicine: from concept to curing patients.

The importance of extracellular matrix (ECM) integrity in maintaining normal tissue function is highlighted by numerous pathologies and situations of acute and chronic injury associated with dysregulation or destruction of ECM components. Heparan sulfate (HS) is a key component of the ECM, where it fulfils important functions associated with tissue homeostasis. Its degradation following tissue injury disrupts this delicate equilibrium and may impair the wound healing process. ReGeneraTing Agents (RGTA®s) are polysaccharides specifically designed to replace degraded HS in injured tissues. The unique properties of RGTA® (resistance to degradation, binding and protection of ECM structural and signaling proteins, like HS) permit the reconstruction of the ECM, restoring both structural and biochemical functions to this essential substrate, and facilitating the processes of tissue repair and regeneration. Here, we review 25 years of research surrounding this HS mimic, supporting the mode of action, pre-clinical studies and therapeutic efficacy of RGTA® in the clinic, and discuss the potential of RGTA® in new branches of regenerative medicine.

Relevance of surgical management of patients affected by bisphosphonate-associated osteonecrosis of the jaws. A prospective clinical and radiological study.

OBJECTIVES: Actually, consensus management of osteonecrosis of the jaws (ONJ) related to nitrogen-containing bisphosphonates (NBPs) is mostly a conservative approach. It does not always control the symptoms and the progression of the disease. The aim of this study was to evaluate the clinical and radiological outcomes of three therapeutic management strategies of established ONJ. MATERIALS AND METHODS: Three treatment strategies, i.e., conservative approach, minimal invasive surgery, and extensive surgery were evaluated in 39 ONJ patients treated with NBPs for malignant diseases or osteoporosis. The patients were closely monitored, and the outcome (extension, improvement, or healing) of mucosa and bone was clinically and radiographically evaluated on a long-term period (27.05 ± 2.96 months). RESULTS: Primary pathology (osteoporosis or malignancies) and clinical severity of ONJ (mild, moderate, severe) were decisive factors. Osteoporotic patients showed more frequently complete mucosa or bone healing (p = 0.0128 and p = 0.00021, respectively) than malignant patients. Mucosa closure and bone improvement occurred more in mild ONJ patients than in severe ONJ (p = 0.0053 and p = 0.0319, respectively). Treatment strategy appeared to be a crucial factor for mucosa but not for bone healing. The rate of complete mucosa healing increased after an extensive surgical procedure (p = 0.0096). CONCLUSIONS: A surgical management of patients with ONJ positively influenced the clinical outcome by enhancing mucosa healing. CLINICAL RELEVANCE: These results deserve further investigations involving a larger cohort. However, they strongly suggest that the guidelines of management of patients with ONJ related to NBPs have to be reconsidered.

Histamine promotes osteoclastogenesis through the differential expression of histamine receptors on osteoclasts and osteoblasts.

In addition to the numerous roles of histamine in both the immune and nervous systems, previous studies have suggested that this bioamine might also be involved in bone metabolism. Following our observations of impaired bone resorption in ovariectomized rats after histamine receptor antagonist treatment, we focused in this study on osteoclasts and osteoclast precursors. We looked for a direct action of histamine on these cells using both in vivo and in vitro approaches. In vivo, we triggered a remodeling sequence in rat mandibular bone and treated the animals with either histamine or histamine receptor antagonists. Histamine was shown to increase the number of osteoclasts and osteoclast precursors whereas antagonists of histamine receptor-1 and -2 decreased both osteoclast recruitment and resorption. In vitro, spleen cells from histamine-deficient mice were treated with receptor activator for nuclear factor kappa B ligand and macrophage colony stimulating factor, giving rise to both reduced numbers of osteoclasts and decreased resorption on dentin slices. Histamine enhanced resorption in these cultures in a dose-dependent manner. In addition, we identified osteoclast precursors as a source of histamine. In contrast, histamine increased the receptor activator for nuclear factor kappa B ligand/osteoprotegerin ratio in primary osteoblasts that did not secrete histamine. We observed a differential expression of histamine receptor-1 and -2 mRNAs in both primary osteoclasts and osteoblasts, confirming their functional roles with selective antagonists. Thus, histamine acts directly on osteoclasts, osteoclast precursors, and osteoblasts, promoting osteoclastogenesis through autocrine/paracrine mechanisms.

Periodontal reconstruction by heparan sulfate mimetic-based matrix therapy in Porphyromonas gingivalis-infected mice.

BACKGROUND: Periodontitis is a set of chronic inflammatory diseases affecting the supporting structures of the teeth, during which a persistent release of lytic enzymes and inflammatory mediators causes a self-perpetuating vicious cycle of tissue destruction and repair. A matrix-based therapy using a heparan sulfate (HS) analogue called ReGeneraTing Agent (RGTA) replaces destroyed HS by binding to available heparin-binding sites of structural molecules, leading to restoration of tissue homeostasis in several inflammatory tissue injuries, including a hamster periodontitis model. METHODS: The ability of RGTA to restore the periodontium was tested in a model of Porphyromonas gingivalis-infected Balb/cByJ mice. After 12 weeks of disease induction, mice were treated weekly with saline or RGTA (1.5 mg/kg) for 8 weeks. Data were analyzed by histomorphometry. RESULTS: RGTA treatment restored macroscopic bone loss. This was related to (1) a significant reduction in gingival inflammation assessed by a decrease in infiltrated connective tissue, particularly in cells expressing interleukin 1ß, an inflammatory mediator selected as a marker of inflammation; (2) a normalization of bone resorption parameters, i.e. number, activation and activity of osteoclasts, and number of preosteoclasts; (3) a powerful bone formation reaction. The Sharpey's fibers of the periodontal ligament recovered their alkaline phosphatase coating. This was obtained while P. gingivalis infection was maintained throughout the treatment period. CONCLUSIONS: RGTA treatment was able to control the chronic inflammation characteristic of periodontitis and blocked destruction of periodontal structures. It ensured tissue regeneration with recovery of the periodontium's anatomy.

Coordination of early cellular reactions during activation of bone resorption in the rat mandible periosteum: An immunohistochemical study.

The activation step of bone remodeling remains poorly characterized. Activation comprises determination of the site to be remodeled, osteoclast precursor recruitment, their migration to the site of remodeling, and differentiation. These actions involve different compartments and cell types. The aim of this study was to investigate events and cell types involved during activation. We used a bone remodeling model in rats where extractions of the upper jaw molars initiate remodeling of the antagonist lower jaw (mandible) cortex along the periosteum. In this model osteoclastic resorption peaks 4 days after extractions. We previously reported that mast cell activation in the periosteum fibrous compartment is an early event of activation, associated with recruitment of circulating monocyte osteoclast precursors. By using immunohistochemistry, we observed 9 hours after induction a spatially oriented expression of InterCellular Adhesion Molecule-1 in the vessels that was inhibited by antagonists of histamine receptors 1 and 2. It was followed at 12 hours by the recruitment of ED1+ monocytes. In parallel, at 9 hours, Vascular Cellular Adhesion Molecule-1+ fibroblast-like cells scattered in the fibrous compartment of the periosteum between the vessels and the osteogenic compartment increased; these cells may be implicated in osteoclast precursor migration. Receptor Activator of NF KappaB Ligand+ cells increased at 12 hours in the osteogenic compartment and reached a peak at 18 hours. At 24 hours the numbers of osteogenic cells and subjacent osteocytes expressing semaphorin 3a, a repulsive for osteoclast precursors, decreased before returning to baseline at 48 hours. These data show that during activation the two periosteum compartments and several cell types are coordinated to recruit and guide osteoclast precursors towards the bone surface.

RGTA®-based matrix therapy - A new branch of regenerative medicine in locomotion.

Matrix therapy is an innovative, minimally invasive approach in the field of regenerative medicine, that aims to promote tissue regeneration by reconstructing the cellular microenvironment following tissue injury. This approach has significant therapeutic potential in the treatment of pathologies characterized by tissue inflammation and damage, or following injury, conditions which can be incapacitating and cost-consuming. Heparan sulfate mimics, termed ReGeneraTing Agents (RGTA®s) have emerged as a unifying approach to treat these diverse pathologies. Today, skin and corneal healing topical products have already been used in clinics, demonstrating a proof of concept in humans. In this review, we present key evidence that RGTA®s regenerate damaged tissue in bone, muscle, tendon and nerve, with astonishing results. In animal models of bone surgical defects and inflammatory bone loss, RGTA® induced healing of injured bones by controlling inflammation and bone resorption, and stimulated bone formation by coordinating vascularization, recruitment and differentiation of competent cells from specific niches, restoring tissue quality to that of uninjured tissue, evoking true regeneration. In models of muscle injury, RGTA® had marked effects on healing speed and quality, evidenced by increased muscle fiber density, maturation, vascularization and reduced fibrosis, more mature motor endplates and functional recovery. Applications merging RGTA®-based matrix therapy and cell therapy, combining Extra-Cellular Matrix reconstruction with cells required for optimal tissue repair show significant promise. Hence restoration of the proper microenvironment is a new paradigm in regenerative medicine. Harnessing the potential of RGTA® in this brave, new vision of regenerative therapy will therefore be the focus of future studies.

'Pre-prosthetic use of poly(lactic-co-glycolic acid) membranes treated with oxygen plasma and TiO2 nanocomposite particles for guided bone regeneration processes'.

OBJECTIVES: Guided bone regeneration (GBR) processes are frequently necessary to achieve appropriate substrates before the restoration of edentulous areas. This study aimed to evaluate the bone regeneration reliability of a new poly-lactic-co-glycolic acid (PLGA) membrane after treatment with oxygen plasma (PO2) and titanium dioxide (TiO2) composite nanoparticles. METHODS: Circumferential bone defects (diameter: 10mm; depth: 3mm) were created on the parietal bones of eight experimentation rabbits and were randomly covered with control membranes (Group 1: PLGA) or experimental membranes (Group 2: PLGA/PO2/TiO2). The animals were euthanized two months afterwards, and a morphologic study was then performed under microscope using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone formed in the grown defects, concentration of osteoclasts, and intensity of osteosynthetic activity were assessed. Comparisons among the groups and with the original bone tissue were made using the Kruskal-Wallis test. The level of significance was set in advance at a=0.05. RESULTS: The experimental group recorded higher values for new bone formation, mineralised bone length, and osteoclast concentration; this group also registered the highest osteosynthetic activity. Bone layers in advanced formation stages and low proportions of immature tissue were observed in the study group. CONCLUSIONS: The functionalised membranes showed the best efficacy for bone regeneration. CLINICAL SIGNIFICANCE: The addition of TiO2 nanoparticles onto PLGA/PO2 membranes for GBR processes may be a promising technique to restore bone dimensions and anatomic contours as a prerequisite to well-supported and natural-appearing prosthetic rehabilitations.

Periosteum Metabolism and Nerve Fiber Positioning Depend on Interactions between Osteoblasts and Peripheral Innervation in Rat Mandible.

The sympathetic nervous system controls bone remodeling by regulating bone formation and resorption. How nerves and bone cells influence each other remains elusive. Here we modulated the content or activity of the neuropeptide Vasoactive Intestinal Peptide to investigate nerve-bone cell interplays in the mandible periosteum by assessing factors involved in nerve and bone behaviors. Young adult rats were chemically sympathectomized or treated with Vasoactive Intestinal Peptide or Vasoactive Intestinal Peptide10-28, a receptor antagonist. Sympathectomy depleted the osteogenic layer of the periosteum in neurotrophic proNerve Growth Factor and neurorepulsive semaphorin3a; sensory Calcitonin-Gene Related Peptide-positive fibers invaded this layer physiologically devoid of sensory fibers. In the periosteum non-osteogenic layer, sympathectomy activated mast cells to release mature Nerve Growth Factor while Calcitonin-Gene Related Peptide-positive fibers increased. Vasoactive Intestinal Peptide treatment reversed sympathectomy effects. Treating intact animals with Vasoactive Intestinal Peptide increased proNerve Growth Factor expression and stabilized mast cells. Vasoactive Intestinal Peptide10-28 treatment mimicked sympathectomy effects. Our data suggest that sympathetic Vasoactive Intestinal Peptide modulate the interactions between nervous fibers and bone cells by tuning expressions by osteogenic cells of factors responsible for mandible periosteum maintenance while osteogenic cells keep nervous fibers at a distance from the bone surface.

Zoledronate effects on systemic and jaw osteopenias in ovariectomized periostin-deficient mice.

Osteoporosis and periodontal disease (PD) are frequently associated in the elderly, both concurring to the loss of jaw alveolar bone and finally of teeth. Bisphosphonates improve alveolar bone loss but have also been associated with osteonecrosis of the jaw (ONJ), particularly using oncological doses of zoledronate. The effects and therapeutic margin of zoledronate on jaw bone therefore remain uncertain. We reappraised the efficacy and safety of Zoledronate (Zol) in ovariectomized (OVX) periostin (Postn)-deficient mice, a unique genetic model of systemic and jaw osteopenia. Compared to vehicle, Zol 1M (100 µg/kg/month) and Zol 1W (100 µg/kg/week) for 3 months both significantly improved femur BMD, trabecular bone volume on tissue volume (BV/TV) and cortical bone volume in both OVX Postn(+/+) and Postn(-/-) (all p<0.01). Zol 1M and Zol 1W also improved jaw alveolar and basal BV/TV, although the highest dose (Zol 1W) was less efficient, particularly in Postn(-/-). Zol decreased osteoclast number and bone formation indices, i.e. MAR, MPm/BPm and BFR, independently in Postn(-/-) and Postn(+/+), both in the long bones and in deep jaw alveolar bone, without differences between Zol doses. Zol 1M and Zol 1W did not reactivate inflammation nor increase fibrous tissue in the bone marrow of the jaw, whereas the distance between the root and the enamel of the incisor (DRI) remained high in Postn(-/-) vs Postn(+/+) confirming latent inflammation and lack of crestal alveolar bone. Zol 1W and Zol 1M decreased osteocyte numbers in Postn(-/-) and Postn(+/+) mandible, and Zol 1W increased the number of empty lacunae in Postn(-/-), however no areas of necrotic bone were observed. These results demonstrate that zoledronate improves jaw osteopenia and suggest that in Postn(-/-) mice, zoledronate is not sufficient to induce bone necrosis.

Glycosaminoglycan mimetic associated to human mesenchymal stem cell-based scaffolds inhibit ectopic bone formation, but induce angiogenesis in vivo.

Tissue engineering approaches to stimulate bone formation currently combine bioactive scaffolds with osteocompetent human mesenchymal stem cells (hMSC). Moreover, osteogenic and angiogenic factors are required to promote differentiation and survival of hMSC through improved vascularization through the damaged extracellular matrix (ECM). Glycosaminoglycans (GAGs) are ECM compounds acting as modulators of heparin-binding protein activities during bone development and regenerative processes. GAG mimetics have been proposed as ECM stabilizers and were previously described for their positive effects on bone formation and angiogenesis after local treatment. Here, we developed a strategy associating the GAG mimetic [OTR4120] with bone substitutes to optimize stem cell-based therapeutic products. We showed that [OTR4120] was able to potentiate proliferation, migration, and osteogenic differentiation of hMSC in vitro. Its link to tricalcium phosphate/hydroxyapatite scaffolds improved their colonization by hMSC. Surprisingly, when these combinations were tested in an ectopic model of bone formation in immunodeficient mice, the GAG mimetics inhibit bone formation induced by hMSC and promoted an osteoclastic activity. Moreover, the inflammatory response was modulated, and the peri-implant vascularization stimulated. All together, these findings further support the ability of GAG mimetics to organize the local ECM to coordinate the host response toward the implanted biomaterial, and to inhibit the abnormal bone formation process on a subcutaneous ectopic site.

Different sympathetic pathways control the metabolism of distinct bone envelopes.

Bone remodeling, the mechanism that modulates bone mass adaptation, is controlled by the sympathetic nervous system through the catecholaminergic pathway. However, resorption in the mandible periosteum envelope is associated with cholinergic Vasoactive Intestinal Peptide (VIP)-positive nerve fibers sensitive to sympathetic neurotoxics, suggesting that different sympathetic pathways may control distinct bone envelopes. In this study, we assessed the role of distinct sympathetic pathways on rat femur and mandible envelopes. To this goal, adult male Wistar rats were chemically sympathectomized or treated with agonists/antagonists of the catecholaminergic and cholinergic pathways; femora and mandibles were sampled. Histomorphometric analysis showed that sympathectomy decreased the number of preosteoclasts and RANKL-expressing osteoblasts in mandible periosteum but had no effect on femur trabecular bone. In contrast, pharmacological stimulation or repression of the catecholaminergic cell receptors impacted the femur trabecular bone and mandible endosteal retromolar zone. VIP treatment of sympathectomized rats rescued the disturbances of the mandible periosteum and alveolar wall whereas the cholinergic pathway had no effect on the catecholaminergic-dependent envelopes. We also found that VIP receptor-1 was weakly expressed in periosteal osteoblasts in the mandible and was increased by VIP treatment, whereas osteoblasts of the retromolar envelope that was innervated only by tyrosine hydroxylase-immunoreactive fibers, constitutively expressed beta-2 adrenergic receptors. These data highlight the complexity of the sympathetic control of bone metabolism. Both the embryological origin of the bone (endochondral for the femur, membranous for the mandibular periosteum and the socket wall) and environmental factors specific to the innervated envelope may influence the phenotype of the sympathetic innervation. We suggest that an origin-dependent imprint of bone cells through osteoblast-nerve interactions determines the type of autonomous system innervating a particular bone envelope.

Dense fibrillar collagen matrices sustain osteoblast phenotype in vitro and promote bone formation in rat calvaria defect.

Two pure collagen materials were prepared from acidic collagen solutions at 5 and 40 mg/mL. Benefits of collagen concentration on bone repair were evaluated in vitro with human calvaria cells and in vivo in a rat cranial defect. Both materials exhibited specific structures, 5 mg/mL was soft with an open porous network of fibrils; 40 mg/mL was stiffer with a plugged surface and bundles of collagen fibrils. Osteoblasts seeded on 5 mg/mL formed an epithelioid layer with ultrastructural characteristics of mature osteoblasts and induced mineralization. Numerous osteoblasts migrated inside 5 mg/mL, triggering reorganization of their actin cytoskeleton, whereas on 40 mg/mL osteoblasts remained in a resting state. In rat calvaria defects, both materials induced active bone formation. Dual-energy X-ray absorption bone area measures after 4 weeks averaged 84.0% with 5 mg/mL, 88.4% with 40 mg/mL, and 36.7% in the controls (p < 0.05). Tartrate-resistant acid phosphatase-positive giant cells releasing amounts of metalloproteinase-2 progressively degraded the implants at 76.5% with 5 mg/mL and 38.2% with 40 mg/mL (p < 0.05), whereas alkaline phosphatase-positive osteoprogenitors invaded collagen remnant. Hence, the dense structure of collagen materials allowed cell invasion and raise their mechanical behavior without addition of chemical cross-linkers. Collagen concentration can be tuned to form 3D matrices for in vitro investigations or to fit degradation rate to different bone repair purposes.

ReGeneraTing agents matrix therapy regenerates a functional root attachment in hamsters with periodontitis.

Matrix-based therapy restoring the cell microenvironment is a new approach in regenerative medicine successfully treating human chronic pathologies by using a heparan sulfate mimetic (ReGeneraTing agents [RGTA]). Periodontitis are inflammatory diseases destroying the tooth-supporting tissues with no satisfactory therapy. We studied in vivo RGTA ability to fully restore the tooth-supporting tissues. After periodontitis induction, hamsters were treated with RGTA (1.5 mg kg(-1) w(-1)) or saline. Bone loss was evaluated and immunohistochemical labeling of molecules expressed during cementum development was performed. RGTA treatment restored alveolar bone and the attachment apparatus where fibers were inserted in acellular decorin-negative cementum. RGTA treatment increased the epithelial rests of Malassez, previously depleted by periodontitis. Bone morphogenetic protein (BMP) expressions were compartmentalized: BMP-3 was strongly expressed by epithelial rests of Malassez; BMP-7 was expressed by cells lying on the cementum and BMP-2 by osteoprogenitors around bone formation sites but not at the root-bone interface. Cells near the cementum and bone expressed the ALK2 receptor. This is the first evidence that reconstructing the extracellular matrix scaffold with a heparan sulfate mimetic regenerated the root interface despite the persistence of the bacteria responsible for the disease The improved cellular microenvironment led to the sequential recruitment of cell populations involved in attachment apparatus regeneration.

Structure and remodelling of the human parietal bone: an age and gender histomorphometric study.

OBJECTIVE: Despite its clinical usefulness, the internal structure and remodelling of parietal bone remained poorly documented. The aim of this study was to gain reliable information on parietal bone remodelling in living humans. MATERIALS AND METHODS: This study provided a site-specific analysis of static indices of turnover in relation to gender and age by using leftovers of parietal bone sampled in 100 patients (78 females; 22 males, aged 16-79 years). RESULTS: The bone architecture, cortical thickness, trabecular volume and cortical volume (C.Th, BV/TV, BV/CV) did not vary with gender. The number of osteoclasts (N.Oc/BPm) and the resorption surface (Oc.S/BS) were higher in females (p<0.05) when osteoclast resorbing activity did not vary with gender. Bone formation, osteoid surface (OS/BS) and surface covered by alkaline phosphatase-positive osteogenic cells (ALPS/BS) were higher in females (p<0.05 and p<0.01 respectively). All these parameters remained stable with aging. The osteocytic parameters, number of osteocytes (Ot.N/B.Ar) and number of osteocyte lacunae (T.L.N/B.Ar) were higher in females (p<0.05) and decreased with age in both genders (p<0.01). CONCLUSION: This study highlights the low and stable remodelling in the parietal bone. It appears to be higher in women. This stability probably reflects the low mechanical strains applied to the skull, particularly to the parietal bone.

Bisphosphonate-associated osteonecrosis of the jaw: a key role of inflammation?

Osteonecrosis of the jaw (ONJ) can be associated with nitrogen-containing bisphosphonates (NBPs) therapy. Various mechanisms of NBP-associated ONJ have been proposed and there is currently no consensus of the underlying pathogenesis. The detailed medical and dental histories of 30 ONJ patients treated with NBPs for malignant diseases (24) or osteoporosis (6) were analyzed. The necrotic bone was resected and analyzed histologically after demineralization. In 10 patients the perinecrotic bone was also resected and processed without demineralization. Alveolar bone samples from 5 healthy patients were used as controls. In 14 ONJ patients, serial technetium-99m-methylene diphosphonate scintigraphic scans were also available and confronted to the other data. Strong radionuclide uptake was detected in some patients several months before clinical diagnosis of ONJ. The medullary spaces of the necrotic bone were filled with bacterial aggregates. In the perinecrotic bone, the bacteria-free bone marrow characteristically showed an inflammatory reaction. The number of medullary inflammatory cells taken as an index of inflammation allowed us to discriminate two inflammation grades in the ONJ samples. Low-grade inflammation, characterized by marrow fibrosis and low inflammatory cells infiltration, increased numbers of TRAP(+) mono- and multineacleated cells was seen in patients with bone exposure<2 cm(2). High-grade inflammation, associated with larger lesions, showed amounts of tartrate-resistant acid phosphatase(+)/calcitonin receptor(-) mono- and multinucleated cells, osteocyte apoptosis, hypervascularization and high inflammatory cell infiltration. The clinical extent of ONJ was statistically linked to the numbers of inflammatory cell. Taken together these data suggest that bone necrosis precedes clinical onset and is an inflammation-associated process. We hypothesize that from an initial focus, bone damage spreads centrifugally, both deeper into the jaw and towards the mucosa before the oral bone exposure and the clinical diagnosis of ONJ.

Prostaglandin E2 synthesis in cartilage explants under compression: mPGES-1 is a mechanosensitive gene.

Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE2) is one of the main catabolic factors involved in OA. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE2. For both COX and PGES, three isoforms have been described: in cartilage, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. COX-3 (a variant of COX-1) and mPGES-2 have been recently cloned but little is known about their expression and regulation in cartilage, as is also the case for 15-PGDH. We investigated the regulation of the genes encoding COX and PGES isoforms during mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) for 2 to 24 hours. After determination of the amount of PGE2 released in the media (enzyme immunoassay), mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blotting respectively. Mechanical compression of cartilage explants significantly increased PGE2 production in a time-dependent manner. This was not due to the synthesis of IL-1, since pretreatment with interleukin 1 receptor antagonist (IL1-Ra) did not alter the PGE2 synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression, whereas COX-3 and mPGES-2 mRNA expression was not modified. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE2 synthesis after 18 hours, suggesting that PGE2 synthesis could be altered by the induction of 15-PGDH expression. We conclude that, along with COX-2, dynamic compression induces mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.

An engineered biopolymer prevents mucositis induced by 5-fluorouracil in hamsters.

Oral mucositis is a common, treatment-limiting, and costly side effect of cancer treatments whose biological underpinnings remain poorly understood. In this study, mucositis induced in hamsters by 5-fluorouracil (5-FU) was observed after cheek-pouch scarifications, with and without administration of RGTA (RG1503), a polymer engineered to mimic the protective effects of heparan sulfate. RG1503 had no effects on 5-FU-induced decreases in body weight, blood cell counts, or cheek-pouch and jejunum epithelium proliferation rates, suggesting absence of interference with the cytotoxic effects of 5-FU. Extensive mucositis occurred in all of the untreated animals, and consisted of severe damage to cheek pouch tissues (epithelium, underlying connective tissue, and muscle bundles). Only half of the RG1503-treated animals had mucositis, over a mean area 70% smaller than in the untreated animals. Basement membranes were almost completely destroyed in the untreated group but was preserved in the RG1503 group. RG1503 blunted or abolished the following 5-FU-induced effects: increases in matrix metalloproteinase (MMP)-2, MMP-9, and plasmin, and decreases in tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. These data indicate that mucositis lesions are related to massive release of proteolytic enzymes and are improved by RG1503 treatment, this effect being ascribable in part to restoration of the MMP-TIMP balance. RG1503 given with cancer treatment might protect patients from mucositis.