A selective EP4 receptor antagonist abrogates the stimulation of osteoblast recruitment from bone marrow stromal cells by prostaglandin E2 in vivo and in vitro

FXR Activation Accelerates Early Phase of Osteoblast Differentiation Through COX-2-PGE2-EP4 Axis in BMP-2-Induced Mouse Mesenchymal Stem Cells

Farnesoid X receptor (FXR), a nuclear receptor, is expressed in calvaria and bone marrow stromal cells and plays a role in bone homeostasis. However, the mechanism of FXR-activated osteoblast differentiation remains unclear. In this study, we investigated the regulatory mechanism underlying FXR-activated osteoblast differentiation using bone morphogenetic protein-2 (BMP-2)-induced mouse ST-2 mesenchymal stem cells. We also synthesized a novel FXR agonist, FLG390, and compared its biological effects in osteoblast differentiation with a known FXR agonist, chenodeoxycholic acid (CDCA). As an FXR agonist, FLG390 accelerated osteoblast differentiation to a comparable extent with CDCA, enhancing alkaline phosphatase (ALP) activity and the expression of osteoblast differentiated-related genes such as ALP, collagen type 1 α1 chain (COL1A1), and runt-related transcription factor 2 (RUNX2). FXR activation elevated the expression of cyclooxygenase (COX)-2 and the production of prostaglandin (PG) E2 in the early phase of osteoblast differentiation. A selective COX-2 inhibitor and an antagonist of EP4 receptors, one of PGE2 receptors, partially suppressed FXR-activated osteoblast differentiation. Moreover, treatment with either inhibitor during the first 6 h after initiating osteoblast differentiation repressed FXR-activated osteoblast differentiation to the same extent as did the treatment for 6 d. Therefore, a novel FXR agonist, FLG390, exhibited potency comparable to CDCA. FXR activation promoted the early phase of osteoblast differentiation via the COX-2-PGE2-EP4 axis, representing a potential target for control of bone metabolism.

G. AR, Al Kawas S, Samsudin AR, A. C. SA. Impact of Bone Morphogenetic Protein 7 and Prostaglandin receptors on osteoblast healing and organization of collagen

PURPOSE

This study seeks to investigate the impact of co-administering either a Prostaglandin EP2 receptor agonist or an EP1 receptor antagonist alone with a low dose BMP7 on in vitro healing process, collagen content and maturation of human osteoblasts.

METHODOLOGY

Human osteoblast cells were used in this study. These cells were cultured and subjected to different concentrations of Prostaglandin EP2 receptor agonist, EP1 receptor antagonist, BMP7, Control (Ct) (Vehicle alone), and various combinations treatments. Cell viability at 24, 48 and 72 hours (h) was evaluated using the XTT assay. A wound healing assay was conducted to observe the migration ability of human osteoblast cells. Additionally, Sirius red staining and Fourier-Transform Infrared Spectroscopy Imaging (FT-IR) was employed to analyze various parameters, including total protein concentration, collagen production, mature collagen concentration, and mineral content.

RESULTS

The combination of low dose BMP7 and Prostaglandin EP2 receptor agonist resulted to the lowest cell viability when compared to both the Ct and individual treatments. In contrast, the Prostaglandin EP1 receptor antagonist alone showed the highest cellular viability at 72 h. In the wound healing assay, the combined treatment of low dose BMP7 with the Prostaglandin EP2 receptor agonist and EP1 receptor antagonist showed a decrease in human osteoblast healing after 24 h. Analysis of FT-IR data indicated a reduction in total protein content, collagen maturity, collagen concentration and mineral content in combination treatment compared to the single or Ct treatments.

CONCLUSION

The combination of a Prostaglandin EP2 receptor agonist or an EP1 receptor antagonist when combined with low dose BMP7 significantly hinders both human osteoblast healing and collagen maturity/concentration in comparison to low dose BMP7 treatment alone.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Prostaglandin E2/EP4 axis is upregulated in Spondyloarthritis and contributes to radiographic progression

Ankylosing spondylitis (AS) is an inflammatory disease leading to spine ankylosis; however, the mechanisms behind new bone formation are still not fully understood. Single Nucleotide Polymorphisms (SNPs) in PTGER4, encoding for the receptor EP4 of prostaglandin E2 (PGE2), are associated with AS. Since the PGE2-EP4 axis participates in inflammation and bone metabolism, this work aims at investigating the influence of the prostaglandin-E2 axis on radiographic progression in AS. In 185 AS (97 progressors), baseline serum PGE2 predicted progression, and PTGER4 SNP rs6896969 was more frequent in progressors. Increased EP4/PTGER4 expression was observed in AS circulating immune cells, synovial tissue, and bone marrow. CD14highEP4 + cells frequency correlated with disease activity, and when monocytes were cocultured with mesenchymal stem cells, the PGE2/EP4 axis induced bone formation. In conclusion, the Prostaglandin E2 axis is involved in bone remodelling and may contribute to the radiographic progression in AS due to genetic and environmental upregulation.

The gut-enthesis axis and the pathogenesis of Spondyloarthritis

Subclinical inflammation is associated with Spondylarthritis (SpA). SpA patients show features of dysbiosis, altered gut barrier function, and local expansion of innate and innate-like cells involved in type 3 immune response. The recirculation of intestinal primed immune cells into the bloodstream and, in some cases, in the joints and the inflamed bone marrow of SpA patients gave the basis of the gut-joint axis theory. In the light of the critical role of enthesis in the pathogenesis of SpA and the identification of mucosal-derived immune cells residing into the normal human enthesis, a gut-enthesis axis is also likely to exist. This work reviews the current knowledge on enthesis-associated innate immune cells' primary involvement in enthesitis development, questions their origin, and critically discusses the clues supporting the existence of a gut-enthesis axis contributing to SpA development.

Local dual delivery therapeutic strategies: Using biomaterials for advanced bone tissue regeneration

Bone development is a complex process involving a vast number of growth factors and chemical substances. These factors include transforming growth factor-beta, platelet-derived growth factor, insulin-like growth factor, and most importantly, the bone morphogenetic protein, which exhibits excellent therapeutic value in bone repair. However, the spatial-temporal relationship in the expression of these factors during bone formation makes the bone repair a more complicated process to address. Thus, using a single therapeutic agent to address bone formation does not seem to provide a clinically effective option. Conversely, a dual delivery approach facilitating the co-delivery of agents has proved to be a dynamic alternative since such a strategy can provide more efficient spatial-temporal action. Such delivery systems can smartly target more than one pathway or differentiation lineage and thus offer more efficient bone regeneration. This review discusses various dual delivery strategies reported in the literature employed to achieve improved bone regeneration. These include concurrent use of different therapeutic agents (including growth factors and drugs), enhancing bone formation and cell recruitment, and improving the efficiency of bone healing.

Control of osteoblast arrangement by osteocyte mechanoresponse through prostaglandin E2 signaling under oscillatory fluid flow stimuli

Anisotropic collagen/apatite microstructure is a prominent determinant of bone tissue functionalization; in particular, bone matrix modulates its anisotropic microstructure depending on the surrounding mechanical condition. Although mechanotransduction in bones is governed by osteocyte function, the precise mechanisms linking mechanical stimuli and anisotropic formation of collagen/apatite microstructure are poorly understood. Here we developed a novel anisotropic mechano-coculture system which enables the understanding of the biological mechanisms regulating the oriented bone matrix formation, which is constructed by aligned osteoblasts. The developed model provides bone-mimetic coculture platform that enables simultaneous control of mechanical condition and osteoblast-osteocyte communication with an anisotropic culture scaffold. The engineered coculture device helps in understanding the relationship between osteocyte mechanoresponses and osteoblast arrangement, which is a significant contributor to anisotropic organization of bone tissue. Our study showed that osteocyte responses to oscillatory flow stimuli regulated osteoblast arrangement through soluble molecular interactions. Importantly, we found that prostaglandin E2 is a novel determinant for oriented collagen/apatite organization of bone matrix, through controlling osteoblast arrangement.

TRPV1 Channel Activated by the PGE2/EP4 Pathway Mediates Spinal Hypersensitivity in a Mouse Model of Vertebral Endplate Degeneration

Low back pain (LBP) is the primary cause of disability globally. There is a close relationship between Modic changes or endplate defects and LBP. Endplates undergo ossification and become highly porous during intervertebral disc (IVD) degeneration. In our study, we used a mouse model of vertebral endplate degeneration by lumbar spine instability (LSI) surgery. Safranin O and fast green staining and μCT scan showed that LSI surgery led to endplate ossification and porosity, but the endplates in the sham group were cartilaginous and homogenous. Immunofluorescent staining demonstrated the innervation of calcitonin gene-related peptide- (CGRP-) positive nerve fibers in the porous endplate of LSI mice. Behavior test experiments showed an increased spinal hypersensitivity in LSI mice. Moreover, we found an increased cyclooxygenase 2 (COX2) expression and an elevated prostaglandin E2 (PGE2) concentration in the porous endplate of LSI mice. Immunofluorescent staining showed the colocalization of E-prostanoid 4 (EP4)/transient receptor potential vanilloid 1 (TRPV1) and CGRP in the nerve endings in the endplate and in the dorsal root ganglion (DRG) neurons, and western blotting analysis demonstrated that EP4 and TRPV1 expression significantly increased in the LSI group. Our patch clamp study further showed that LSI surgery significantly enhanced the current density of the TRPV1 channel in small-size DRG neurons. A selective EP4 receptor antagonist, L161982, reduced the spinal hypersensitivity of LSI mice by blocking the PGE2/EP4 pathway. In addition, TRPV1 current and neuronal excitability in DRG neurons were also significantly decreased by L161982 treatment. In summary, the PGE2/EP4 pathway in the porous endplate could activate the TRPV1 channel in DRG neurons to cause spinal hypersensitivity in LSI mice. L161982, a selective EP4 receptor antagonist, could turn down the TRPV1 current and decrease the neuronal excitability of DRG neurons to reduce spinal pain.

RANKL/RANK/OPG Pathway: A Mechanism Involved in Exercise-Induced Bone Remodeling

Bones as an alive organ consist of about 70% mineral and 30% organic component. About 200 million people are suffering from osteopenia and osteoporosis around the world. There are multiple ways of protecting bone from endogenous and exogenous risk factors. Planned physical activity is another useful way for protecting bone health. It has been investigated that arranged exercise would effectively regulate bone metabolism. Until now, a number of systems have discovered how exercise could help bone health. Previous studies reported different mechanisms of the effect of exercise on bone health by modulation of bone remodeling. However, the regulation of RANKL/RANK/OPG pathway in exercise and physical performance as one of the most important remodeling systems is not considered comprehensive in previous evidence. Therefore, the aim of this review is to clarify exercise influence on bone modeling and remodeling, with a concentration on its role in regulating RANKL/RANK/OPG pathway.

In Vivo Bone Effects of a Novel Bisphosphonate-EP4a Conjugate Drug (C3) for Reversing Osteoporotic Bone Loss in an Ovariectomized Rat Model

Pathological bone loss is a regular feature of postmenopausal osteoporosis, and the microstructural changes along with the bone loss make the individual prone to getting hip, spine, and wrist fractures. We have developed a new conjugate drug named C3, which has a synthetic, stable EP4 agonist (EP4a) covalently linked to an inactive alendronate (ALN) that binds to bone and allows physiological remodeling. After losing bone for 12 weeks, seven groups of rats were treated for 8 weeks via tail‐vein injection. The groups were: C3 conjugate at low and high doses, vehicle‐treated ovariectomy (OVX) and sham, C1 (a similar conjugate, but with active ALN at high dose), inactive ALN alone, and a mixture of unconjugated ALN and EP4a to evaluate the conjugation effects. Bone turnover was determined by dynamic and static histomorphometry; μCT was employed to determine bone microarchitecture; and bone mechanical properties were evaluated via biomechanical testing. Treatment with C3 significantly increased trabecular bone volume and vertebral BMD versus OVX controls. There was also significant improvement in the vertebral load‐bearing abilities and stimulation of bone formation in femurs after C3 treatment. This preclinical research revealed that C3 resulted in significant anabolic effects on trabecular bone, and EP4a and ALN conjugation components are vital to conjugate anabolic efficacy. A combined therapy using an EP4 selective agonist anabolic agent linked to an inactive ALN is presented here that produces significant anabolic effects, allows bone remodeling, and has the potential for treating postmenopausal osteoporosis or other diseases where bone strengthening would be beneficial. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Inhibition of the Prostaglandin EP-1 Receptor in Periosteum Progenitor Cells Enhances Osteoblast Differentiation and Fracture Repair

Fracture healing is a complex and integrated process that involves mesenchymal progenitor cell (MPC) recruitment, proliferation and differentiation that eventually results in bone regeneration. Prostaglandin E2 (PGE2) is an important regulator of bone metabolism and has an anabolic effect on fracture healing. Prior work from our laboratory showed EP1^-/- mice have enhanced fracture healing, stronger cortical bones, higher trabecular bone volume and increased in vivo bone formation. We also showed that bone marrow MSCs from EP1^-/- mice exhibit increased osteoblastic differentiation in vitro. In this study we investigate the changes in the periosteal derived MPCs (PDMPCs), which are crucial for fracture repair, upon EP1 deletion. EP1^-/- PDMPCs exhibit increased numbers of total (CFU-F) and osteoblastic colonies (CFU-O) as well as enhanced osteoblastic and chondrogenic differentiation. Moreover, we tested the possible therapeutic application of a specific EP1 receptor antagonist to accelerate fracture repair. Our findings showed that EP1 antagonist administration to wild type mice in the early stages of repair similarly resulted in enhanced CFU-F, CFU-O, and osteoblast differentiation in PDMPCs and resulted in enhanced fracture callus formation at 10 days post fracture and increased bone volume and improved biomechanical healing of femur fractures at 21 days post fracture.

Identification of Specific Components of the Eicosanoid Biosynthetic and Signaling Pathway Involved in Pathological Inflammation during Intra-abdominal Infection with Candida albicans and Staphylococcus aureus

Polymicrobial intra-abdominal infections (IAIs) are a significant cause of morbidity and mortality, particularly when fungal pathogens are involved. Our experimental murine model of IAI involving intraperitoneal inoculation of Candida albicans and Staphylococcus aureus results in synergistic lethality (∼80%) due to exacerbated inflammation. Monomicrobial infection results in no mortality, despite a microbial burden and dissemination similar to those in a coinfection. In the coinfection model, the immunomodulatory eicosanoid prostaglandin E₂ (PGE₂) was determined to be necessary and sufficient to induce mortality, implicating PGE₂ as the central mediator of the amplified inflammatory response. The aim of this study was to identify key components of the PGE₂ biosynthetic and signaling pathway involved in the inflammatory response and explore whether these can be targeted to prevent or reduce mortality. Using selective pharmacological inhibitors of cyclooxygenases (COX) or PGE₂ receptor antagonists in the C. albicans-S. aureus IAI mouse model, we found that inhibition of COX and/or blocking of PGE₂ receptor 1 (EP1) or PGE₂ receptor 3 (EP3) signaling reduced proinflammatory cytokine production, promoted interleukin-10 production, reduced cellular damage in the peritoneal cavity, and, most importantly, significantly improved survival. The greatest effect on survival was obtained by the simultaneous inhibition of COX-1 activity and EP1 and EP3 receptor signaling. Importantly, early inhibition of PGE₂ pathways dramatically improved the survival of fluconazole-treated mice compared with that achieved with fluconazole treatment alone. These findings indicate that COX-1 and the EP1 and EP3 receptors mediate the downstream pathological effects of PGE₂ during polymicrobial IAI and may serve as effective therapeutic targets.

G protein-coupled receptors as anabolic drug targets in osteoporosis

Osteoporosis is a progressive bone disorder characterised by imbalance between bone building (anabolism) and resorption (catabolism). Most therapeutics target inhibition of osteoclast-mediated bone resorption, but more recent attention in early drug discovery has focussed on anabolic targets in osteoblasts or their precursors. Two marketed agents that display anabolic properties, strontium ranelate and teriparatide, mediate their actions via the G protein-coupled calcium-sensing and parathyroid hormone-1 receptors, respectively. This review explores their activity, the potential for improved therapeutics targeting these receptors and other putative anabolic GPCR targets, including Smoothened, Wnt/Frizzled, relaxin family peptide, adenosine, cannabinoid, prostaglandin and sphingosine-1-phosphate receptors.

Expression of Prostaglandin E2 Receptors in Acquired Middle Ear Cholesteatoma

Objectives

To investigate the expression of prostaglandin E₂ receptor subtypes, E-prostanoid (EP) 1–4 receptors, in acquired cholesteatoma and its possible role in the pathologic process of this disorder.

Methods

Specimens of human acquired cholesteatoma were obtained from 29 patients and 19 skin biopsies of normal external auditory canal were as controls. The mRNA and protein expression of EP receptors was assessed by quantitative real-time polymerase chain reaction, immunohistochemistry and Western blot.

Results

In acquired cholesteatoma, EP1–EP4 receptors were mainly expressed on squamous epithelium and subepithelial infiltrated inflammatory cells. In external auditory canal skin, EP1–EP4 receptors were mainly expressed on squamous epithelium and glandular epithelium. The expression of EP4 receptor on mRNA and protein levels were significant lower in acquired cholesteatoma compared with controls. EP1–EP3 receptors had no significant difference between the experimental and control group.

Conclusion

Low expression of EP4 may play a crucial role in the pathologic process of inflammation reaction and bone destruction in acquired cholesteatoma, but not EP1, EP2, or EP3 receptors.

PGE2 Receptor Subtype 1 (EP1) Regulates Mesenchymal Stromal Cell Osteogenic Differentiation by Modulating Cellular Energy Metabolism

Mesenchymal stromal cells (MSCs) are multipotent progenitors capable of differentiation into osteoblasts and can potentially serve as a source for cell-based therapies for bone repair. Many factors have been shown to regulate MSC differentiation into the osteogenic lineage such as the Cyclooxygenase-2 (COX2)/Prostaglandin E2 (PGE2) signaling pathway that is critical for bone repair. PGE2 binds four different receptors EP1-4. While most studies focus on the role PGE2 receptors EP2 and EP4 in MSC differentiation, our study focuses on the less studied, receptor subtype 1 (EP1) in MSC function. Recent work from our laboratory showed that EP1^-/- mice have enhanced fracture healing, stronger cortical bones, higher trabecular bone volume and increased in vivo bone formation, suggesting that EP1 is a negative regulator of bone formation. In this study, the regulation of MSC osteogenic differentiation by EP1 receptor was investigated using EP1 genetic deletion in EP1^-/- mice. The data suggest that EP1 receptor functions to maintain MSCs in an undifferentiated state. Loss of the EP1 receptor changes MSC characteristics and permits stem cells to undergo more rapid osteogenic differentiation. Notably, our studies suggest that EP1 receptor regulates MSC differentiation by modulating MSC bioenergetics, preventing the shift to mitochondrial oxidative phosphorylation by maintaining high Hif1α activity. Loss of EP1 results in inactivation of Hif1α, increased oxygen consumption rate and thus increased osteoblast differentiation. J. Cell. Biochem. 118: 4383-4393, 2017. © 2017 Wiley Periodicals, Inc.

G-CSF-induced sympathetic tone provokes fever and primes antimobilizing functions of neutrophils via PGE2

Granulocyte colony-stimulating factor (G-CSF) is widely used for peripheral blood stem/progenitor mobilization. G-CSF causes low-grade fever that is ameliorated by nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting the activation of arachidonic acid (AA) cascade. How G-CSF regulated this reaction was assessed. G-CSF treatment in mice resulted in fever, which was canceled in prostaglandin E synthase (mPGES-1)-deficient mice. Mobilization efficiency was twice as high in chimeric mice lacking mPGES-1, specifically in hematopoietic cells, suggesting that prostaglandin E₂ (PGE₂) from hematopoietic cells modulated the bone marrow (BM) microenvironment. Neutrophils from steady-state BM constitutively expressed mPGES-1 and significantly enhanced PGE₂ production in vitro by β-adrenergic stimulation, but not by G-CSF, which was inhibited by an NSAID. Although neutrophils expressed all β-adrenergic receptors, only β3-agonist induced this phenomenon. Liquid chromatography-tandem mass spectrometry traced β-agonist-induced PGE₂ synthesis from exogenous deuterium-labeled AA. Spontaneous PGE₂ production was highly efficient in Gr-1^high neutrophils among BM cells from G-CSF-treated mice. In addition to these in vitro data, the in vivo depletion of Gr-1^high neutrophils disrupted G-CSF-induced fever. Furthermore, sympathetic denervation eliminated both neutrophil priming for PGE₂ production and fever during G-CSF treatment. Thus, sympathetic tone-primed BM neutrophils were identified as one of the major PGE₂ producers. PGE₂ upregulated osteopontin, specifically in preosteoblasts, to retain progenitors in the BM via EP4 receptor. Thus, the sympathetic nervous system regulated neutrophils as an indispensable PGE₂ source to modulate BM microenvironment and body temperature. This study provided a novel mechanistic insight into the communication of the nervous system, BM niche components, and hematopoietic cells.

Pathophysiological mechanisms of diarrhea caused by the Vibrio cholerae O1 El Tor variant: an in vivo study in mice

Cholera is caused by infection with Vibrio cholerae. This study aimed to investigate the pathophysiology of diarrhea caused by the V. cholerae O1 El Tor variant (EL), a major epidemic strain causing severe diarrhea in several regions. In the ligated ileal loop model of EL-induced diarrhea in the ICR mice, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a calcium-activated chloride channel (CaCC) inhibitor similarly inhibited intestinal fluid secretion. In addition, barrier disruption and NF-κB-mediated inflammatory responses, e.g., iNOS and COX-2 expression, were observed in the infected ileal loops. Interestingly, intestinal fluid secretion and barrier disruption were suppressed by NF-κB and COX-2 inhibitors, whereas an iNOS inhibitor suppressed barrier disruption without affecting fluid secretion. Furthermore, EP2 and EP4 PGE2 receptor antagonists ameliorated the fluid secretion in the infected ileal loops. The amount of cholera toxin (CT) produced in the ileal loops by the EL was ∼2.4-fold of the classical biotype. The CT transcription inhibitor virstatin, a toll-like receptor-4 (TLR-4) antibody and a CT antibody suppressed the EL-induced intestinal fluid secretion, barrier disruption and COX-2 expression. The CT at levels detected during EL infection induced mild intestinal barrier disruption without inducing inflammatory responses in mouse intestine. Collectively, this study indicates that CT-induced intestinal barrier disruption and subsequent TLR-4-NF-κB-mediated COX-2 expression are involved in the pathogenesis of EL-induced diarrhea and represent promising novel therapeutic targets of cholera.

Rebamipide delivered by brushite cement enhances osteoblast and macrophage proliferation

Many of the bioactive agents capable of stimulating osseous regeneration, such as bone morphogenetic protein-2 (BMP-2) or prostaglandin E2 (PGE2), are limited by rapid degradation, a short bioactive half-life at the target site in vivo, or are prohibitively expensive to obtain in large quantities. Rebamipide, an amino acid modified hydroxylquinoline, can alter the expression of key mediators of bone anabolism, cyclo-oxygenase 2 (COX-2), BMP-2 and vascular endothelial growth factor (VEGF), in diverse cell types such as mucosal and endothelial cells or chondrocytes. The present study investigates whether Rebamipide enhances proliferation and differentiation of osteoblasts when delivered from brushite cement. The reactive oxygen species (ROS) quenching ability of Rebampide was tested in macrophages as a measure of bioactivity following drug release incubation times, up to 14 days. Rebamipide release from brushite occurs via non-fickian diffusion, with a rapid linear release of 9.70% ± 0.37% of drug per day for the first 5 days, and an average of 0.5%-1% per day thereafter for 30 days. Rebamipide slows the initial and final cement setting time by up to 3 and 1 minute, respectively, but does not significantly reduce the mechanical strength below 4% (weight percentage). Pre-osteoblast proliferation increases by 24% upon exposure to 0.4 uM Rebamipide, and by up to 73% when Rebamipide is delivered via brushite cement. Low doses of Rebamipide do not adversely affect peak alkaline phosphatase activity in differentiating pre-osteoblasts. Rebamipide weakly stimulates proliferation in macrophages at low concentrations (118 ± 7.4% at 1 uM), and quenches ROS by 40-60%. This is the first investigation of Rebamipide in osteoblasts.

Novel EP4 receptor agonist-bisphosphonate conjugate drug (C1) promotes bone formation and improves vertebral mechanical properties in the ovariectomized rat model of postmenopausal bone loss

Current treatments for postmenopausal osteoporosis aim to either promote bone formation or inhibit bone resorption. The C1 conjugate drug represents a new treatment approach by chemically linking the antiresorptive compound alendronate (ALN) with the anabolic agent prostanoid EP4 receptor agonist (EP4a) through a linker molecule (LK) to form a conjugate compound. This enables the bone-targeting ability of ALN to deliver EP4a to bone sites and mitigate the systemic side effects of EP4a, while also facilitating dual antiresorptive and anabolic effects. In vivo hydrolysis is required to release the EP4a and ALN components for pharmacological activity. Our study investigated the in vivo efficacy of this drug in treating established bone loss using an ovariectomized (OVX) rat model of postmenopausal osteopenia. In a curative experiment, 3-month-old female Sprague-Dawley rats were OVX, allowed to lose bone for 7 weeks, then treated for 6 weeks. Treatment groups consisted of C1 conjugate at low and high doses, vehicle-treated OVX and sham, prostaglandin E2 (PGE2 ), and mixture of unconjugated ALN-LK and EP4a to assess the effect of conjugation. Results showed that weekly administration of C1 conjugate dose-dependently increased bone volume in trabecular bone, which partially or completely reversed OVX-induced bone loss in the lumbar vertebra and improved vertebral mechanical strength. The conjugate also dose-dependently stimulated endocortical woven bone formation and intracortical resorption in cortical bone, with high-dose treatment increasing the mechanical strength but compromising the material properties. Conjugation between the EP4a and ALN-LK components was crucial to the drug's anabolic efficacy. To our knowledge, the C1 conjugate represents the first time that a combined therapy using an anabolic agent and the antiresorptive compound ALN has shown significant anabolic effects which reversed established osteopenia.

Comparison of the effects of dexketoprofen trometamol, meloxicam and diclofenac sodium on fibular fracture healing, kidney and liver: an experimental rat model

OBJECTIVES

Nonsteroidal anti-inflammatory drugs (NSAIDs) are particularly used in patients with bone fractures, but there are limited studies on whether one NSAID is superior to another. In this study, we used histopathological and biochemical parameters to determine whether there are differences between the effects of the administration of clinical doses of dexketoprofen trometamol (DEXT), meloxicam (MEL) and diclofenac sodium (DIC) on the healing of closed fibular fractures and the toxicity of both the liver and kidney.

METHODS

Twenty-eight male Sprague-Dawley rats were randomly divided into four groups of seven each. Closed diaphyseal fractures were formed in the left fibulas of all of the rats. The NSAIDs dexketoprofen trometamol (DEXT) (Arveles(®)), meloxicam (MEL) (Melox(®)) and diclofenac sodium (DIC) (Voltaren(®)) were intramuscularly administered to Groups I, II, and III, respectively, for a period of 10 days after the fibular fractures were performed. No pharmacological agents were administered to Group IV (Control group). Blood samples were collected from all of the rats after the fractures were performed, and the rats were sacrificed on day 28. The histopathological findings were compared, and the blood samples were evaluated to determine any differences between the levels of superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA).

RESULTS

Our results suggest that DEXT and MEL impair the healing of bone fractures and that DIC does not histopathologically affect the healing process of bone fractures. We also found that DEXT, MEL, and DIC impaired the renal histopathology compared with the control group. However, the liver histopathological analysis showed that DEXT and MEL caused a higher degree of parenchymal necrosis compared with DIC.

CONCLUSION

Based on our results, DIC can be considered a relatively safe medication in patients with fractures.

The prostanoid EP4 receptor and its signaling pathway

The EP4 prostanoid receptor is one of four receptor subtypes for prostaglandin E2. It belongs to the family of G protein-coupled receptors. It was originally identified, similar to the EP2 receptor as a G(s)α-coupled, adenylyl cyclase-stimulating receptor. EP4 signaling plays a variety of roles through cAMP effectors, i.e., protein kinase A and exchange protein activated by cAMP. However, emerging evidence from studies using pharmacological approaches and genetically modified mice suggests that EP4, unlike EP2, can also be coupled to G(i)α, phosphatidylinositol 3-kinase, β-arrestin, or β-catenin. These signaling pathways constitute unique roles for the EP4 receptor. EP4 is widely distributed in the body and thus plays various physiologic and pathophysiologic roles. In particular, EP4 signaling is closely related to carcinogenesis, cardiac hypertrophy, vasodilation, vascular remodeling, bone remodeling, gastrointestinal homeostasis, renal function, and female reproductive function. In addition to the classic anti-inflammatory action of EP4 on mononuclear cells and T cells, recent evidence has shown that EP4 signaling contributes to proinflammatory action as well. The aim of this review is to present current findings on the biologic functions of the EP4 receptor. In particular, we will discuss its diversity from the standpoint of EP4-mediated signaling.

Physical activity improves age-related decline in the osteogenic potential of rats' bone marrow-derived mesenchymal stem cells

AIM

To examine whether physical activity increases osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs) from adult rats compared with young rats.

METHODS

Eighteen female Wistar rats were divided into three groups and the following cells isolated: (1) differentiated BMMSCs from young donors, (2) differentiated BMMSCs from sedentary adult donors and (3) differentiated BMMSCs from active adult donors. We analysed MTT conversion, percentage of cells per field, mineralized nodule number and gene expression for telomerase reverse transcriptase (TERT), alkaline phosphatase, caspase 3, osteocalcin, bone sialoprotein and collagen I.

RESULTS

Telomerase reverse transcriptase expression and the percentage of cells per field in BMMSCs cultures from adult rats were smaller than those observed in young donors. However, levels of caspase 3 expression were higher in BMMSCs from adult donors (P < 0.05). Despite the fact that physical activity was associated with an increase in expression of caspase 3 (P < 0.05), there was no difference in the percentage of cells per field between groups of adult BMMSCs (active or sedentary). However, physical activity increased the number of mineralized nodules and osteocalcin expression after 21 days, and alkaline phosphatase expression at 7, 14 and 21 days in the BMMSCs of adult donors (P < 0.05). However, those values were smaller when compared with young donors BMMSCs (P < 0.05). Only the expression levels of alkaline phosphatase were similar to young donors BMMSCs (P ≥ 0.05).

CONCLUSION

Physical activity increases osteogenic differentiation of BMMSCs from adult donors but does not increase the differentiation to the levels observed in BMMSCs from young donor rats.

Clinical Correlates of Urolithiasis in Ankylosing Spondylitis

Objective.

To determine the association between urolithiasis and syndesmophyte formation and the effect of urolithiasis on ankylosing spondylitis (AS) disease activity.

Methods.

In a longitudinal cohort of 504 patients with AS, we conducted an analysis of all patients with AS who have a history of urolithiasis. All patients met the modified New York criteria for AS. Demographics, clinical characteristics, extraarticular features, and comorbidities are systematically recorded in the database. We compared disease activity, functional indices, medical therapy and radiographic damage between AS patients with (Uro+) and without urolithiasis (Uro–) using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS).

Results.

Thirty-eight patients with AS (7.5%) had a history of urolithiasis in our cohort. Seventy-six patients with AS who did not have urolithiasis, matched for age, sex, and ethnicity, were selected as controls. Patients who were Uro+ were more likely to have more functional disability, based on the Bath AS Functional Index (BASFI; mean 5.3 vs 3.6 in control group, p = 0.003). Trends were noted in the Uro+ group toward higher Bath AS Disease Activity Index (BASDAI; mean 4.9 vs 4.0, p = 0.09), more peripheral joint involvement (p = 0.075), and higher frequency of biologic therapy (p = 0.09). No significant difference was detected in mSASSS or the Bath AS Metrology Index (BASMI). Significant association with diabetes mellitus (DM; p = 0.016) and Crohn’s disease (p = 0.006) was noted in the Uro+ group.

Conclusion.

Although there is no acceleration of syndesmophyte formation or spinal mobility restriction, more functional disability was detected in the urolithiasis group. The higher risk with concomitant DM or Crohn’s disease should alert clinicians to these comorbidities in Uro+ patients with AS.

Sustained morphine treatment augments prostaglandin E2-evoked calcitonin gene-related peptide release from primary sensory neurons in a PKA-dependent manner

Tissue damage leads to pain sensitization due to peripheral and central release of excitatory mediators such as prostaglandin E₂ (PGE₂). PGE₂ sensitizes spinal pain neurotransmitter such as calcitonin gene-related peptide (CGRP) release via activation of cyclic AMP (cAMP)/protein kinase A (PKA)-dependent signaling mechanisms. Our previous data demonstrate that sustained morphine pretreatment sensitizes adenylyl cyclase(s) (AC) toward the direct stimulator, forskolin, in cultured primary sensory neurons (AC superactivation). In the present work we investigated the hypothesis that morphine pretreatment also sensitizes ACs toward Gs-protein-coupled excitatory modulators (such as PGE₂), leading to augmented PKA-dependent CGRP release from PGE₂-stimulated primary sensory dorsal root ganglion (DRG) neurons. Our results show that sustained morphine treatment potentiated PGE₂-mediated cAMP formation and augmented PGE₂-evoked CGRP release from cultured primary sensory neurons in a PKA-dependent manner. Our data suggest that attenuation of AC superactivation in primary sensory neurons may prevent the development of opioid-induced hyperalgesia.

EP2 and EP4 receptors differentially mediate MAPK pathways underlying anabolic actions of prostaglandin E2 on bone formation in rat calvaria cell cultures

Of the four prostaglandin (PG) E receptor subtypes (EP1-EP4), EP2 and EP4 have been proposed to mediate the anabolic action of PGE(2) on bone formation but comparative evaluation studies of EPs on bone formation do not necessarily share a common mechanism, implying that their additional features including downstream MAPK pathways may be beneficial to resolve this issue. We systematically assessed the roles of EPs in the rat calvaria (RC) cell culture model by using four selective EP agonists (EPAs). Consistent with relative expression levels of the respective receptors, multiple phenotypic traits of bone formation in vitro, including proliferation of nodule-associated cells, osteoblast marker expression and mineralized nodule formation were upregulated not only by PGE(2) but equally by EP2A and EP4A, but not by EP1A and EP3A. EP2A and EP4A were effective when cells were treated chronically or pulse-treated during nascent nodule formation. EP2A and EP4A equally stimulated the endogenous PGE(2) production, while EP2A caused a greater increase in cAMP production and c-Fos gene expression compared to EP4A. EP2A and EP4A activated predominantly p38 MAPK and ERK respectively, while c-Jun N-terminal kinase (JNK) was equally activated by both agonists. SB203580 (p38 MAPK inhibitor) blocked the PGE(2) effect on mineralized nodule formation, while U0126 (ERK inhibitor) and dicumarol (JNK inhibitor) were less effective. PGE(2)-dependent phosphorylation of the MAPKs was affected not only by protein kinase (PK)A and PKC inhibitors but also by adenylate cyclase and PKC activators. Co-treatment of RC cells with EP2A or EP4A and bone morphogenetic protein (BMP)2, whose effects on bone nodule formation is known to be, in part, mediated through the PKA and p38 MAPK pathways, resulted in an additive effect on mineralized nodule formation. Further, PGE(2), EP2A and EP4A did not increase BMP2/4 mRNA levels in RC cells, and EP2-induced phosphorylation of p38 MAPK was not eliminated by Noggin. These results suggest that, in the RC cell model, the anabolic actions of PGE(2) on mineralized nodule formation are mediated at least in part by activation of the EP2 and EP4 receptor subtype-specific MAPK pathways, independently of BMP signaling, in cells associated with nascent bone nodules.

Reduced COX-2 expression in aged mice is associated with impaired fracture healing

The cellular and molecular events responsible for reduced fracture healing with aging are unknown. Cyclooxygenase 2 (COX-2), the inducible regulator of prostaglandin E(2) (PGE(2)) synthesis, is critical for normal bone repair. A femoral fracture repair model was used in mice at either 7-9 or 52-56 wk of age, and healing was evaluated by imaging, histology, and gene expression studies. Aging was associated with a decreased rate of chondrogenesis, decreased bone formation, reduced callus vascularization, delayed remodeling, and altered expression of genes involved in repair and remodeling. COX-2 expression in young mice peaked at 5 days, coinciding with the transition of mesenchymal progenitors to cartilage and the onset of expression of early cartilage markers. In situ hybridization and immunohistochemistry showed that COX-2 is expressed primarily in early cartilage precursors that co-express col-2. COX-2 expression was reduced by 75% and 65% in fractures from aged mice compared with young mice on days 5 and 7, respectively. Local administration of an EP4 agonist to the fracture repair site in aged mice enhanced the rate of chondrogenesis and bone formation to levels observed in young mice, suggesting that the expression of COX-2 during the early inflammatory phase of repair regulates critical subsequent events including chondrogenesis, bone formation, and remodeling. The findings suggest that COX-2/EP4 agonists may compensate for deficient molecular signals that result in the reduced fracture healing associated with aging.

ASARM-truncated MEPE and AC-100 enhance osteogenesis by promoting osteoprogenitor adhesion

Matrix extracellular phosphoglycoprotein (MEPE) is a member of the SIBLING (Small Integrin-Binding Ligand, N-linked Glycoprotein) family of secreted glycophosphoproteins. Several previous studies have demonstrated that MEPE and its peptide motif, AC-100, may regulate bone mass and influence osteoblast activity, suggesting its potential for inclusion in novel therapeutic strategies aimed at increasing osteogenesis. Our study uses in vitro approaches to assess how adhesion of nonadherent cells is influenced by MEPE and whether response to MEPE is dependent on the maturity of osteoblastic cells. Truncated MEPE (ASARM removed) or AC-100 enhanced the adhesion, spreading, and focal complex formation of unadhered osteoblastic cells leading to increased differentiation and bone formation after 28 days of culture. Furthermore, addition of truncated MEPE or AC-100 to mature osteoblasts had no significant effect on bone formation. Our data supports an action for truncated MEPE and AC-100 in altering the physiology of immature poorly adherent cells which subsequently influences the way in which these cells interact with a substrate to facilitate their survival and/or commitment to the osteoblast lineage.

Retroviral-based gene therapy with cyclooxygenase-2 promotes the union of bony callus tissues and accelerates fracture healing in the rat

BACKGROUND

An in vivo gene therapy strategy was developed to accelerate bone fracture repair.

METHODS

Direct injection of a murine leukemia virus-based vector targeted transgene expression to the proliferating periosteal cells arising shortly after fracture. Cyclooxygenase-2 (Cox-2) was selected because the transgene for its prostaglandin products that promote angiogenesis, bone formation and bone resorption, are all required for fracture healing. The human (h) Cox-2 transgene was modified to remove AU-rich elements in the 3'-untranslated region and to improve protein translation.

RESULTS

In vitro studies revealed robust and sustained Cox-2 protein expression, prostaglandin E(2) and alkaline phosphatase production in rat bone marrow stromal cells and osteoblasts transgenic for the hCox-2 gene. In vivo studies in the rat femur fracture revealed that Cox-2 transgene expression produced bony union of the fracture by 21 days post-fracture, a time when cartilage persisted within the fracture tissues of control animals and approximately 1 week earlier than the healing normally observed in this model. None of the ectopic bone formation associated with bone morphogenetic protein gene therapy was observed.

CONCLUSIONS

This study represents the first demonstration that a single local application of a retroviral vector expressing a single osteoinductive transgene consistently accelerated fracture repair.

Prostaglandins differentially affect osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) are currently used for bone tissue engineering. AT-MSCs undergoing osteogenic differentiation respond to mechanical loading with increased cyclooxygenase-2 gene expression, a key enzyme in prostaglandin (PG) synthesis. PGs are potent multifunctional regulators in bone, exhibiting stimulatory and inhibitory effects on bone formation and resorption. PGE(2), but not PGI(2) or PGF(2), recruits osteoprogenitors from the bone marrow space and influences their differentiation. We hypothesize that PGE(2), PGI(2), and PGF(2) may differentially regulate osteogenic differentiation of human AT-MSCs. PGE(2), PGI(2), and PGF(2) (0.01-10 microM) affected osteogenic differentiation, but not proliferation of AT-MSCs after 4-14 days. Only PGF(2) (0.01-10 microM) increased alkaline phosphatase (ALP) activity at day 4. PGE(2) (10 microM), PGI(2) (0.01-10 microM), and PGF(2) (10 microM) decreased ALP activity, whereas PGF(2) (0.1 microM) increased ALP activity at day 14. PGF(2) (0.01-0.1 microM) and PGI(2) (0.01 microM) upregulated osteopontin gene expression, and PGF(2) (0.01 microM) upregulated alpha1(I)procollagen gene expression at day 4. PGE(2) and PGF(2) (10 microM) at day 4 and PGF(2) (1 microM) at day 14 downregulated runt-related transcription factor-2 gene expression. We conclude that PGE(2), PGI(2), and PGF(2) differentially affect osteogenic differentiation of AT-MSCs, with PGF(2) being the most potent. Thus, locally produced PGF(2) might be most beneficial in promoting osteogenic differentiation of AT-MSCs, resulting in enhanced bone formation for bone tissue engineering.

Bone formation and tooth movement are synergistically enhanced by administration of EP4 agonist

INTRODUCTION

Stimulation of the prostaglandin receptor EP4 induces bone anabolic responses to external loading. The aim of this study was to determine the possibility of synergistic enhancement of tooth movement along with bone formation in vivo through the stimulation of the prostaglandin receptor EP4.

METHODS

The sample consisted of 25 male rats, 6 to 7 weeks old. Experimental tooth movement was induced in the maxillary right molars with a split-mouth design. During the 7-day experimental period, some rats were injected periodically with a specific EP4 agonist (ONO-AE1-329), a drug that binds to the EP4 receptor to mimic the actions of ligand binding; the injection site was on the tension side in the interproximal region between the first and second molars. Other rats received vehicle injection (saline solution only). For control, EP4 agonist or vehicle was injected into some rats, but tooth movement was not initiated. The amounts of tooth movement and bone volume of the paradental region were evaluated by using soft x-ray and micro-computed tomography.

RESULTS

The injection of EP4 agonist alone did not induce notable changes in body weight, macro-structures, or bone volume compared with the vehicle-treated group or the untouched control side. EP4 agonist injection in conjunction with tooth movement significantly enhanced the amounts of tooth movement and regional bone volume in the tension side compared with the vehicle-treated group (P <.05).

CONCLUSIONS

Our preliminary study suggests the possibilities of synergistic enhancement of the rates of tooth movement and bone formation during tooth movement through the local injection of a specific EP4 receptor agonist. However, more study on the synergistic effect on tooth movement and bone formation in response to an EP4 agonist is needed to determine its mechanisms.

Prostaglandin E2 EP4 agonist (ONO-4819) accelerates BMP-induced osteoblastic differentiation

Bone morphogenetic proteins (BMPs) were originally isolated based on their ability to induce ectopic cartilage and bone formation. The agents to promote the local bone formation with BMP would be beneficial to promote bone repair and to shorten the treatment period. For this purpose, we have examined ONO-4819, which is a prostaglandin (PG) E2 EP4 receptor selective agonist (EP4A), as a positive modulators for the efficacy of BMPs. In our previous study, the systemic and local (with biodegradable synthetic polymers) administration of EP4A led to a significant augmentation of ossicle mass. But the mechanisms how EP4A accelerates the BMP-mediated bone formation are still unknown. In this study, we have examined how EP4A facilitates the BMP signaling using in vitro system with pluripotent stromal cell line, ST2. The mRNA expressions of Osterix and ALP (a marker enzyme of osteoblastic differentiation) and enzymatic activity of ALP in the ST2 cells were elevated significantly by BMP treatment. This elevation was further elevated by addition of the EP4A. The accelerated BMP action by the EP4A was abolished by pre-treatment with PKA inhibitor. This study suggests that ONO-4819 accelerates BMP-induced osteoblastic differentiation of ST2 cells by stimulating the commitment for osteoblastic lineage. Thus PKA signaling pathway would be the main intracellular signaling pathway of the EP4 for the anabolic effect of bone and mineral metabolisms.

Enhancing effects of a prostaglandin EP4 receptor agonist on recombinant human bone morphogenetic protein-2 mediated spine fusion in a rabbit model

STUDY DESIGN

An experimental animal study aimed at achieving posterolateral intertransverse process fusion with rhBMP-2 in combination with the local delivery of an EP4 receptor agonist.

OBJECTIVE

To determine whether an EP4 receptor agonist (EP4A) can reduce the amount of BMP required to achieve posterolateral spinal fusion in rabbits.

SUMMARY OF BACKGROUND DATA

In the clinic, BMP retaining implants are used for spinal fusion and the treatment of pseudarthrosis after long bone fracture. However, the requirement of high doses of BMP-2 for bone formation in humans makes the implants expensive and limits their use in the clinic. Previous studies in our laboratory using a new delivery system involving a synthetic polymer/beta-TCP powder composite had shown it was possible to reduce the total BMP-2 amount to 30 microg per fusion in a rabbit model. To further reduce the dose of BMP required for a successful fusion, we explored the use of a chemical compound to enhance the bone-inducing action of BMP-2.

METHODS

In order to prepare 1 implant to bridge the unilateral L5 and L6 transverse processes, 300 mg of polymer gel (PLA-DX-PEG block copolymer), 300 mg of beta-TCP powder, rhBMP-2 (7.5, 3.75, or 0 microg), with or without EP4A (45 microg) were mixed and manually shaped to resemble a rod. Through a posterolateral approach, 2 implants were placed on both sides (1 per side) by surgery in order to bridge the transverse processes of adult New Zealand white rabbits (n = 48). The lumbar vertebrae were recovered 6 weeks after surgery. The posterolateral fusion was examined by manual palpation, radiography, biomechanical testing, and histology.

RESULTS

All of 8 rabbits that received 7.5 microg of BMP-2 and EP4A consistently showed fusion by significant amount of new bone formation. However, solid fusion was seen in only 3 of 8 rabbits that received 7.5 microg of BMP-2 without the EP4 receptor agonist.

CONCLUSION

Local administration of an EP4 receptor agonist enhanced the bone-inducing activity of BMP-2 in a rabbit posterolateral lumbar spinal fusion model and as a result, the dose of BMP-2 required for this outcome was reduced by 50% compared with our previous report. The coadministration of this compound via a local delivery system may help to reduce the costs of spine fusion with use of BMP-2 in the clinic.

The non-steroidal anti-inflammatory drug diclofenac reduces appearance of osteoblasts in bone defect healing in rats

INTRODUCTION

Non-steroidal anti-inflammatory drug (NSAID) is well known to significantly delay fracture healing. Results from in vitro studies implicate an impairment of osteoblast proliferation due to NSAIDs during the initial stages of healing. We studied whether diclofenac, a non-selective NSAID, also impairs appearance of osteoblasts in vivo during the early phase of healing (at 10 days).

MATERIALS AND METHODS

Two defects (Ø 1.1 mm) were drilled within distal femurs of 20 male Wistar rats. Ten rats received diclofenac continuously; the other obtained a placebo until sacrificing at 10 days. Osteoblast proliferation was assessed by cell counting using light microscopy, and bone mineral density (BMD) was measured using pQCT.

RESULTS

Osteoblast counts from the centre of bone defect were significantly reduced in the diclofenac group (median 73.5 +/- 8.4 cells/grid) compared to animals fed with placebo (median 171.5 +/- 13.9 cells/grid). BMD within the defect showed a significant reduction after diclofenac administration (median 111.5 +/- 9.3 mg/cm(3)) compared to the placebo group (median 177 +/- 45.4 mg/cm(3)).

CONCLUSION

The reduced appearance of osteoblasts in vivo implicates an inhibiting effect of diclofenac on osteoblasts at a very early level of bone healing. The inhibition of proliferation and migration of osteoblasts, or differentiation from progenitor cells, is implicated in the delay of fracture healing after NSAID application.

Administration of Cyclooxygenase-2 Inhibitor Reduces Joint Inflammation but Exacerbates Osteopenia in IL-1α Transgenic Mice Due to GM-CSF Overproduction

IL-1alpha transgenic (Tg) mice exhibit chronic inflammatory arthritis and subsequent osteopenia, with IL-1-induced GM-CSF playing an important role in the pathogenesis. This study analyzed the mechanisms underlying osteopenia in Tg mice, and the therapeutic effects of the cyclooxygenase-2 inhibitor celecoxib on such osteopenia. Inhibited osteoclast formation was observed in RANKL-treated bone marrow cell (BMC) cultures from Tg mice and coculture of Tg-derived BMCs and wild-type-derived primary osteoblasts (POBs). FACS analysis indicated that this inhibition was attributable to a decreased number of osteoclast precursors within Tg-derived BMCs. Moreover, in coculture of Tg-derived POBs and either Tg- or wild-type-derived BMCs, osteoclast formation was markedly inhibited because Tg-derived POBs produced abundant GM-CSF, known as a potent inhibitor of osteoclast differentiation. Histomorphometric analysis of Tg mice revealed that both bone formation and resorption were decreased, with bone formation decreased more prominently. Interestingly, administration of celecoxib resulted in further deterioration of osteopenia where bone formation was markedly suppressed, whereas bone resorption remained unchanged. These results were explained by our in vitro observation that celecoxib dose-dependently and dramatically decreased osteogenesis by Tg mouse-derived POBs in culture, whereas mRNA expressions of GM-CSF and M-CSF remained unchanged. Consequently, blockade of PGE(2) may exert positive effects on excessively enhanced bone resorption observed in inflammatory bone disease, whereas negative effects may occur mainly through reduced bone formation, when bone resorption is constitutively down-regulated as seen in Tg mice.

Anabolic agents and the bone morphogenetic protein pathway

A major unmet need in the medical field today is the availability of suitable treatments for the ever-increasing incidence of osteoporosis and the treatment of bone deficit conditions. Although therapies exist which prevent bone loss, the options are extremely limited for patients once a substantial loss of skeletal bone mass has occurred. Patients who have reduced bone mass are predisposed to fractures and further morbidity. The FDA recently approved PTH (1-34) (Teriparatide) for the treatment of postmenopausal osteoporosis after both preclinical animal and clinical human studies indicated it induces bone formation. This is the only approved bone anabolic agent available but unfortunately it has limited use, it is relatively expensive and difficult to administer. Consequently, the discovery of low cost orally available bone anabolic agents is critical for the future treatment of bone loss conditions. The intricate process of bone formation is co-ordinated by the action of many different bone growth factors, some stored in bone matrix and others released into the bone microenvironment from surrounding cells. Although all these factors play important roles, the bone morphogenetic proteins (BMPs) clearly play a central role in both bone cartilage formation and repair. Recent research into the regulation of the BMP pathway has led to the discovery of a number of small molecular weight compounds as candidate bone anabolic agents. These agents may usher in a new wave of more innovative and versatile treatments for osteoporosis as well as orthopedic and dental indications.

Lipopolysaccharide stimulates the production of prostaglandin E2 and the receptor Ep4 in osteoblasts

Previous studies have indicated that one of the causes of alveolar bone destruction with periodontitis is lipopolysaccharide (LPS) from the cell wall of gram-negative bacteria in plaque, and that prostaglandin E(2) (PGE(2)) is one of the bone resorption factors that stimulate osteoclast formation through an intercellular interaction between osteoblasts and osteoclast precursors. The present study was undertaken to determine the effect of LPS on cell growth, alkaline phosphatase (ALPase) activity, the production of PGE(2), and the expression of receptors by PGE(2), cyclooxygenase (COX)-1, and COX-2, using human osteosarcoma cell line Saos-2 as osteoblasts. The cells were cultured with 0, 1, or 10 microg mL(-1) of LPS for up to 14 days. The production of PGE(2) and the gene expression of COX-1, COX-2, and PGE(2) receptors, including Ep1, Ep2, Ep3, and Ep4, were determined using enzyme-linked immunosorbent assay (ELISA) and real-time reverse transcription-polymerase chain reaction (real-time RT-PCR), respectively. With the addition of LPS, cell growth and ALPase activity decreased by day 5 of the culture, while PGE(2) production increased in a dose-dependent manner throughout the entire 14-day culture period. LPS-reduced ALP activity and LPS-induced PGE(2) production returned to the control level by the addition simultaneously with indomethacin. The expression of COX-1, Ep1, Ep2, and Ep3 receptors decreased on day 14 of the culture, whereas the expression of COX-2 and Ep4 receptors increased significantly with the addition of LPS. These results suggest that LPS promotes PGE(2) production by increasing the expression of COX-2, and that LPS promotes the production of Ep4 receptors in osteoblasts. These results also indicate that LPS-induced PGE(2) may combine with osteoblast Ep4 receptors in autocrine or paracrine modes, and may promote the formation of osteoclasts.

Systemic bone loss and induction of coronary vessel disease in a rat model of chronic inflammation

Clinically, osteopenia or low bone mass has been observed in a variety of chronic inflammatory diseases, and elevated proinflammatory mediators have implicated this process. The purpose of this study was to develop an in vivo model of bone loss induced by chronic systemic inflammation. Time-release pellets designed to deliver one of three doses of LPS: Low (3.3 microg/day), High (33.3 microg/day), or Placebo over 90 days, were implanted subcutaneously in 3-month-old male Sprague-Dawley rats (n = 8/group). Neutrophil counts, indicative of ongoing inflammation, were elevated (P < 0.05) in both LPS groups at 30 days post-implant and remained significantly elevated in the High dose throughout the 90-day study period. At the end of the study, bone loss occurred in the femur as indicated by decreased bone mineral density (BMD) in both LPS-treated groups, but vertebral BMD was reduced in the High dose animals only. Microcomputed tomography revealed that trabecular bone volume (BV/TV) of the proximal tibial metaphysis tended to be reduced in the High dose LPS group. Deleterious effects on trabecular number (TbN) and trabecular separation (TbSp) were observed in both LPS-treated groups, but only the High dose group reached statistical significance. These alterations in trabecular microarchitecture resulted in compromised biomechanical properties. No changes in cortical thickness, porosity, or area of the tibia midshaft were evident at either dose of LPS. Up-regulation of the proinflammatory mediators, cyclooxygenase (COX)-2, interleukin (IL)-1, and tumor necrosis factor (TNF)-alpha was demonstrated in the metaphyseal region where the deleterious effects of LPS were observed. In addition to these alterations in bone, trichrome staining indicated changes in the coronary arterioles, consistent with vascular disease. Utilization of a LPS time-release pellet appears to provide an in vivo model of chronic inflammation-induced bone loss and a potentially novel system to study concurrent development of osteopenia and vascular disease.

Local simvastatin effects on mandibular bone growth and inflammation

BACKGROUND

Simvastatin has been shown to increase bone growth when applied topically to murine bone; however, it causes considerable soft tissue inflammation at high doses (2.2 mg), making future clinical use problematic. This study evaluated the effect of lower simvastatin doses and cyclooxygenase (COX) synthase inhibitors on tissue inflammation and bone growth in rats and gene expression in mice.

METHODS

Adult female rats were untreated or treated with a single dose of 0.1, 0.5, 1.0, 1.5, or 2.2 mg simvastatin in methylcellulose gel in a polylactic acid membrane (SIM) on the lateral aspect of the mandible. The contralateral mandible side was implanted with methylcellulose gel/polylactic acid membrane alone (GEL), and five rats in each dose pairing were evaluated histomorphometrically after 3, 7, and 24 days. Subsequent rats were similarly treated with 0.5 mg simvastatin (optimal dose) and daily intraperitoneal injections of COX-2 inhibitor (NS-398; 1 mg/kg x 7 days; N = 16), general COX inhibitor (indomethacin; 1 mg/kg x 7 days; N = 16), or no inhibitor (N = 10) and evaluated histomorphometrically after 7 or 24 days by analysis of variance (ANOVA). Gene arrays were also used to evaluate osteogenic gene expression from 0.5 mg simvastatin in murine calvaria (N = 12).

RESULTS

There was a 45% increase in bone area with 0.5 mg simvastatin versus gel control (P <0.001; similar to the 2.2-mg dose), and clinical swelling was reduced compared to the high simvastatin dose (P <0.05). The 0.1-mg simvastatin dose failed to stimulate significant bone growth. NS-398 and indomethacin reduced inflammation and bone growth. Simvastatin significantly upregulated procollagen, fibronectin, and matrix metalloproteinase-13 genes.

CONCLUSION

Reducing the simvastatin dose from 2.2 to 0.5 mg reduced inflammation to a more clinically acceptable level without sacrificing bone-growth potential, but COX-associated inflammation appears to be necessary for in vivo bone growth.

Augmentation of bone morphogenetic protein-induced bone mass by local delivery of a prostaglandin E EP4 receptor agonist

Recombinant human bone morphogenetic protein (rhBMP) is viewed as a therapeutic cytokine because of its ability to induce bone. However, the high doses of rhBMP required for bone induction in humans remain a major hurdle for the therapeutic application of this protein. The development of a methodology that would effectively overcome the weak responsiveness to human BMP is highly desired. In the present study, we investigate the ability of a prostaglandin E EP4 receptor selective agonist (EP4A) to augment the bone-inducing ability of BMP in a biodegradable delivery system. A block copolymer composed of poly-D,L-lactic acid with random insertion of p-dioxanone and polyethylene glycol (PLA-DX-PEG, polymer) was used as the delivery system. Polymer discs containing rhBMP-2 and EP4A were implanted into the left dorsal muscle pouch of mice to examine the dose-dependent effects of EP4A. Fifty mice were divided into 5 groups based on the contents of rhBMP and EP4 in the polymer (group 1; BMP 5 microg EP4A 0 microg, group 2; BMP 5 microg EP4 3 microg, group 3; BMP 5 microg EP4 30 microg, group 4; BMP 5 microg EP4 300 microg, group 5; BMP 0 microg EP4 30 microg, n=10 each). All implants were harvested, examined radiologically, and processed for histological analysis 3 weeks after surgery. On dual-energy X-ray absorptiometry (DXA) analysis, the bone mineral content (BMC) of the ossicles was 6.52+/-0.80 (mg), 9.36+/-1.89, 14.21+/-1.27, and 18.75+/-2.31 in groups 1, 2, 3, and 4 respectively. In terms of BMC, the values of groups 3 and 4 were significantly higher than those of group 1. The mean BMC value of group 4 was approximately 3 times higher than that of group 1. No significant difference in body weight was noted among the groups during the experimental period. In summary, the presence of a prostaglandin E EP4 receptor selective agonist in the carrier polymer enhanced the bone-inducing capacity of rhBMP-2 with no apparent systemic adverse effects.

Effect of a selective agonist for prostaglandin E receptor subtype EP4 (ONO-4819) on the cortical bone response to mechanical loading

The influence of a selective agonist for prostaglandin E receptor subtype EP4 (ONO-4819) on the bone response to mechanical loading was evaluated. Six-month-old female Wistar rats were used and assigned to three groups (n = 12/group): Vehicle administration (EP4-V), low-dose ONO-4819 administration (EP4-L, 3 microg/kg BW), and high-dose ONO-4819 administration (EP4-H, 30 microg/kg BW). ONO-4819 was subcutaneously injected in the back twice a day for 3 weeks. Loads on the right tibia at 39.4 N for 36 cycles at 2 Hz were applied in vivo by 4-point bending every other day for 3 weeks. Whole-body bone mineral content showed a significant difference between EP4-V and EP4-H (P < 0.05). Bone mineral density (BMD) of the total and regional tibia (the region with maximal bending at the central diaphysis) was higher in EP4-H than EP4-V, showing a significant effect of loading (P < 0.001) and ONO-4819 (P < 0.05). BMD of the total femur was higher in EP4-H than EP4-V (P < 0.01) and that of the distal femur was higher in EP4-H than EP4-V (P < 0.001). Histomorphometry of the cortical bone showed that loading increased formation surface (FS/BS), mineral appositional rate (MAR), and bone formation rate (BFR/BS) significantly at the lateral periosteal surface (P < 0.001); however, the effect of ONO-4819 was not significant. At the medial periosteal surface, loading increased the three parameters (P < 0.001) and ONO-4819 increased FS/BS (P < 0.001) and MAR (P < 0.05) significantly. At the endocortical surface, the effects of both loading and ONO-4819 were significant on all three parameters (for loading; FS/BS P < 0.01, MAR P < 0.05, BFR/BS P < 0.03, for ONO-4819 all P < 0.001). It was concluded that ONO-4819 increased cortical bone formation in rats and there was an additive effect on the bone response to external loading by 4-point bending.