Dose and time-dependent effects of cyclooxygenase-2 inhibition on fracture-healing

Basal bone phenotype and increased anabolic responses to intermittent parathyroid hormone in healthy male COX-2 knockout mice

Cyclooxygenase-2 (COX-2) knockout (KO) mice in inbred strains can have renal dysfunction with secondary hyperparathyroidism (HPTH), making direct effects of COX-2 KO on bone difficult to assess. COX-2 KO mice in an outbred CD-1 background did not have renal dysfunction but still had two-fold elevated PTH compared to wild type (WT) mice. Compared to WT mice, KO mice had increased serum markers of bone turnover, decreased femoral bone mineral density (BMD) and cortical bone thickness, but no differences in trabecular bone volume by microCT or dynamic histomorphometry. Because PTH is a potent inducer of COX-2 and prostaglandin (PG) production, we examined the effects of COX-2 KO on bone responses after 3 weeks of intermittent PTH. Intermittent PTH increased femoral BMD and cortical bone area more in KO mice than in WT mice and increased trabecular bone volume in the distal femur in both WT and KO mice. Although not statistically significant, PTH-stimulated increases in trabecular bone tended to be greater in KO mice than in WT mice. PTH increased serum markers of bone formation and resorption more in KO than in WT mice but increased the ratio of osteoblastic surface-to-osteoclastic surface only in KO mice. PTH also increased femoral mineral apposition rates and bone formation rates in KO mice more than in WT mice. Acute mRNA responses to PTH of genes that might mediate some anabolic and catabolic effects of PTH tended to be greater in KO than WT mice. We conclude that (1) the basal bone phenotype in male COX-2 KO mice might reflect HPTH, COX-2 deficiency or both, and (2) increased responses to intermittent PTH in COX-2 KO mice, despite the presence of chronic HPTH, suggest that absence of COX-2 increased sensitivity to PTH. It is possible that manipulation of endogenous PGs could have important clinical implications for anabolic therapy with PTH.

BMP-7-induced ectopic bone formation and fracture healing is impaired by systemic NSAID application in C57BL/6-mice

Nonsteroidal antiinflammatory drugs (NSAIDs) are known to potentially impair the fracture healing process. The aim of the present study was to determine if the impairment of bone healing by systemic NSAID application is, at least in part, due to an interaction of NSAIDs with the bone anabolic BMP-7 pathway. Therefore, we first analyzed fracture healing in control and diclofenac-treated mice, where we not only found a significant impairment of fracture healing due to diclofenac treatment as assessed by biomechanical testing and microCT imaging, but also found high coexpression of bone morphogenetic protein-7 (BMP-7) and cyclooxygenase-2 (COX-2) within the fracture callus of both groups. To experimentally address the possible interaction between BMP-7 and COX-2, we then induced ectopic bone formation in control (n = 10) and diclofenac-treated mice (n = 10) by application of BMP-7 (recombinant human OP-1, rhOP-1) into the hamstring muscles. After 20 days of treatment, each ectopic bone nodule was analyzed by contact-radiography, microCT, histology, and histomorphometry. Diclofenac application decreased the trabecular number and bone mass in the ectopic bone nodules significantly due to reduced osteoblast number and activity. These data demonstrate that the bone anabolic effect of BMP-7 and fracture healing is impaired by diclofenac application, and suggest that the potential negative impact of NSAIDs on fracture healing is, at least in part, due to interference with BMP-7 signaling.

Comparison of two carbonated apatite ceramics in vivo

Carbonated apatite ceramics, with a composition similar to that of bone mineral, are potentially interesting synthetic bone graft substitutes. In the present study, two porous carbonated apatite ceramics were developed, characterized and tested for their bone repair capacity and osteoinductive potential in a goat model. Although the two ceramics were prepared from a similar starting powder, their physico-chemical and structural characteristics differed as a consequence of different preparation methods. Both ceramics had an open and interconnected porous structure with a porosity of about 80%. The morphology of the surface of CA-A and CA-B at the submicron level differed significantly: CA-A consisted of irregular grains with a size of 5-20microm, with 1-10microm large micropores among the grains, whereas CA-B surface consisted of much smaller and regular shaped grains (0.05-0.5microm), with most micropores smaller than 1microm. The specific surface area of CA-B was about 10 times larger than that of CA-A due to its significantly smaller grain size. CA-A and CA-B ceramics contained 3 and 5 wt.% of B-type carbonated apatite, respectively. Although neither ceramic succeeded in completely bridging the 17mm iliac wing defect with new bone after 12weeks of implantation, CA-A showed significantly more bone formation in the pores of the implant than CA-B. The total area percentage of new bone in the total defect area was 12.7+/-1.81 and 5.51+/-1.37 (mean+/-SEM) for CA-A and CA-B, respectively. Intramuscular implantation of the ceramics led to ectopic bone formation by CA-A in all three implanted specimens, in contrast to CA-B, where no new bone was observed in any of the 11 animals. CA-A showed a more pronounced degradation than CA-B both in vitro and in vivo at both implantation sites, which was unexpected based on the physico-chemical and structural properties of the two ceramics. Both physico-chemical and structural properties of the ceramics could, dependently or independently, have affected their in vivo behaviour, emphasizing the importance to control individual parameters for successful bone repair.

Effects of nonsteroidal anti-inflammatory drugs on flexor tendon adhesion

PURPOSE

Besides its anti-inflammatory effects, nonsteroidal anti-inflammatory drug therapy may affect tendon healing and the development of peritendinous adhesions. The purpose of this study was to compare the effect of nonselective (ibuprofen) and COX-2 selective (rofecoxib) nonsteroidal anti-inflammatory drugs on the adhesion formation after tendon repair.

METHODS

We assigned 67 rabbits to one of 3 (placebo, ibuprofen, or rofecoxib) groups. The deep flexor tendon was transected, followed by a primary repair. Dosing of the medication began the day after surgery and continued for 27 days. The animals were immobilized in a cast for the first 14 days. Postoperatively, tendon adhesion formation was assessed histologically by calculating the total adhesion in serial axial tendon sections at 3 and 6 weeks and by range of motion measurements at 6 and 12 weeks. We measured range of motion by fixing the metacarpal, applying increasing weight to the free end of the flexor digitorum profundus, and measuring the flexion angle between the metacarpal and the proximal phalanx. Comparison was performed between the treatment groups, as well as to the unoperated forepaws.

RESULTS

Based on histology, we found no difference between the treatment groups when determining the percentage of adhesion between the flexor tendon and its sheath. Control unoperated forepaws had a significantly greater range of metacarpophalangeal joint flexion than the surgically repaired groups. At 12 weeks, range of motion in the ibuprofen group was significantly better than the placebo (p=.009) and rofecoxib (p=.009) groups.

CONCLUSIONS

Ibuprofen has a more important effect in limiting adhesion formation compared with rofecoxib after flexor tendon repair. Because ibuprofen inhibits both COX-1 and COX-2, whereas rofecoxib only inhibits COX-2, ibuprofen therapy appears to offer a greater beneficial effect on tendon repair by reducing formation of adhesions.

Effect of Non-Steroidal Anti-Inflammatory Drugs on Bone Healing

Nonspecific and COX-2 selective nonsteroidal anti-inflammatory drugs (NSAIDs) function by inhibiting the cyclooxygenase isoenzymes and effectively reduce pain and inflammation attributed to acute or chronic musculoskeletal pathologies. However, use of NSAIDs as an analgesic is thought to negatively contribute to bone healing. This review strived to provide a thorough unbiased analysis of the current research conducted on animals and humans regarding NSAIDs and their effect on bone healing. Specifically, this review discusses the role of animal models, dosing regiments, and outcome parameters when examining discrepancies about NSAIDS and their effects on bone regeneration. The role of COX-2 in bone regeneration needs to be better defined in order to further elucidate the impact of NSAIDs on bone healing.

Prostaglandins in bone: bad cop, good cop?

Prostaglandins (PGs) are multifunctional regulators of bone metabolism that stimulate both bone resorption and formation. PGs have been implicated in bone resorption associated with inflammation and metastatic bone disease, and also in bone formation associated with fracture healing and heterotopic ossification. Recent studies have identified roles for inducible cyclooxygenase (COX)-2 and PGE(2) receptors in these processes. Although the effects of PGs have been most often associated with cAMP production and protein kinase A activation, PGs can engage an extensive G-protein signaling network. Further analysis of COX-2 and PG receptors and their downstream G-protein signaling in bone could provide important clues to the regulation of skeletal cell growth in both health and disease.

Prophylactic use of NSAIDs by athletes: a risk/benefit assessment

Athletes often seek artificial means to gain advantage and prolong participation when competing. This often involves taking naturally occurring or chemically synthesized compounds. The World Anti-Doping Agency does not prohibit the use of nonsteroidal anti-inflammatory drugs (NSAIDs) because these agents are not performance enhancing, and their analgesic and anti-inflammatory effects are at best performance enabling. Consequently, athletes have relatively unrestricted access to NSAIDs, which are readily available as over-the-counter drugs. However, concern has been raised on athletes' prophylactic use of these agents. Data from many sporting fields have consistently demonstrated that many individuals self-administer NSAIDs prior to athletic participation to prevent pain and inflammation before it occurs. However, scientific evidence for this approach is currently lacking, and athletes should be aware of the potential risks in using NSAIDs as a prophylactic agent. These agents are not benign, and can produce significant side effects, including gastrointestinal and cardiovascular conditions, as well as musculoskeletal and renal side effects. The latter side effects appear paradoxical to the rationale for prophylactic use of NSAIDs. This article discusses current observations regarding athlete use of NSAIDs, and the possible benefits and potential risks of their use.

Multiple roles for CCR2 during fracture healing

Bone injury induces an inflammatory response that involves neutrophils, macrophages and other inflammatory cells. The recruitment of inflammatory cells to sites of injury occurs in response to specific signaling pathways. The CC chemokine receptor type 2 (CCR2) is crucial for recruiting macrophages, as well as regulating osteoclast function. In this study, we examined fracture healing in Ccr2-/- mice. We first demonstrated that the expression of Ccr2 transcripts and the filtration of macrophages into fracture calluses were most robust during the early phases of fracture healing. We then determined that the number of macrophages at the fracture site was significantly lower in Ccr2-/- mice compared with wild-type controls at 3 days after injury. As a result, impaired vascularization, decreased formation of callus, and delayed maturation of cartilage were observed at 7 days after injury in mutant mice. At day 14, Ccr2-/- mice had less bone in their calluses. At day 21, Ccr2-/- mice had larger calluses and more bone compared with wild-type mice, suggesting a delayed remodeling. In addition, we examined the effect of Ccr2 mutation on osteoclasts. We found that a lack of Ccr2 did not affect the number of osteoclasts within fracture calluses at 21 days after injury. However, Ccr2-/- osteoclasts exhibited a decreased ability to resorb bone compared with wild-type cells, which could contribute to the delayed remodeling of fracture calluses observed in Ccr2-/- mice. Collectively, these results indicate that a deficiency of Ccr2 reduces the infiltration of macrophages and impairs the function of osteoclasts, leading to delayed fracture healing.

Vascular endothelial growth factor: an essential component of angiogenesis and fracture healing

Fractures require adequate stability and blood supply to heal. The vascular supply to long bones is compromised in a fracture, and the ability to heal hinges on the ability of new blood vessels to proliferate from surrounding vessels in a process known as angiogenesis. This process is largely driven by the growth factor, vascular endothelial growth factor (VEGF), whose levels are increased locally and systemically during fracture healing. VEGF is involved in many steps throughout the fracture healing cascade, from initially being concentrated in fracture hematoma, to the promotion of bone turnover during the final remodeling phase. This article reviews the current literature surrounding the role of VEGF and other growth factors in reestablishing vascular supply to fractured bone, as well as medications and surgical techniques that may inhibit this process.

Pharmacological inhibition of 5-lipoxygenase accelerates and enhances fracture-healing

BACKGROUND

Loss of cyclooxygenase-2 activity is known to impair fracture-healing in animal models and to inhibit heterotopic ossification in humans. Cyclooxygenase-2 is the rate-limiting enzyme involved in the conversion of arachidonic acid into prostaglandins. Arachidonic acid also is a substrate for 5-lipoxygenase, which catalyzes the initial steps in leukotriene synthesis. In contrast to cyclooxygenase-2, genetic ablation of 5-lipoxygenase accelerates and enhances fracture-healing in mice. The goal of this study was to determine if systemic inhibition of 5-lipoxygenase with an orally delivered drug could accelerate fracture-healing.

METHODS

Closed femoral fractures were made in Sprague-Dawley rats. The rats were treated with oral doses of vehicle (ninety-five rats), celecoxib (fifty-nine rats), or AA-861 (a 5-lipoxygenase inhibitor; eighty-nine rats). Fracture-healing was measured with use of radiographs, histomorphometry, and biomechanical testing. Effects of drug treatments on callus cell proliferation and gene expression were determined by incorporation of bromodeoxyuridine and quantitative polymerase chain reactions, respectively.

RESULTS

AA-861 treatment decreased fracture-bridging time, significantly increased early callus cartilage (5.6-fold; p < 0.001) and bone formation (4.2-fold; p = 0.015), and significantly increased callus mechanical properties compared with the vehicle-treated rat fractures. Callus cell proliferation rate was increased by AA-861 treatment, compared with vehicle, at day 2 after fracture (3.68% compared with 2.08%; p < 0.001; 95% confidence interval, -2.81 to -0.039) but was reduced by celecoxib treatment at day 4 after fracture (4.22% compared with 1.84%; p < 0.001; 95% confidence interval, 2.27 to 4.07). At day 10 after fracture, AA-861 and celecoxib treatment increased Type-II collagen mRNA levels (16.0-fold and 6.1-fold, respectively; p < 0.001 for both), but only AA-861 treatment caused an increase in Type-X collagen mRNA (6.3-fold; p < 0.001). AA-861 treatment significantly increased cyclooxygenase-2 (4.0-fold at day 10; p < 0.001) and osteopontin mRNA levels (3.6-fold at day 7; p = 0.024), while decreasing 5-lipoxygenase mRNA levels (5.6-fold at day 4; p < 0.001).

CONCLUSIONS

Systemic inhibition of 5-lipoxygenase with an orally delivered drug significantly accelerated and enhanced fracture-healing in this rat model. Gene expression analysis indicates that cyclooxygenase-2 is necessary for callus chondrocytes to progress into hypertrophy so as to complete endochondral ossification. Conversely, inhibition of 5-lipoxygenase alters the inflammatory response, which enhances callus chondrocyte hypertrophy and accelerates endochondral ossification.

Selective COX-2 inhibitor versus nonselective COX-1 and COX-2 inhibitor in the prevention of heterotopic ossification after total hip arthroplasty: a meta-analysis of randomised trials

Whether selective cyclo-oxygenase-2 (COX-2) inhibitors are equally effective compared to nonselective NSAIDs for the prevention of heterotopic ossification (HO) after total hip arthroplasty (THA) is still unclear. We carried out a comprehensive search strategy, in which only randomised controlled trials were included. Two reviewers independently assessed methodological quality and extracted outcome data. Analyses were performed using Stata version 10.0. Four eligible randomised controlled trials totalling 808 patients were included. Meta-analysis results showed that no statistically significant difference was found in overall incidence of HO (RR 1.08; 95% CI 0.71-1.64), incidence of moderate severe HO (Brooker II and III) (RR 0.83; 95% CI 0.48-1.42) and any grade of Brooker classification between two groups. In summary, the selective COX-2 inhibitors are equally effective as nonselective NSAIDs for the prevention of HO after THA. Considering the gastrointestinal side effects of nonselective NSAIDs, we recommend selective COX-2 inhibitors for the prevention of HO after THA. However, future well-designed, randomised controlled trials are still needed to further confirm our results.

A comparison of the effects of ibuprofen and rofecoxib on rabbit fibula osteotomy healing

BACKGROUND AND PURPOSE

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX) activity, which is the rate-limiting enzyme in the synthesis of prostaglandins. Previous studies have indicated that NSAID therapy, and in particular NSAIDs that specifically target the inflammatory cyclooxygenase (COX-2), impair bone healing. We compared the effects of ibuprofen and rofecoxib on fibula osteotomy healing in rabbits to determine whether nominal, continuous inhibition of COX-2 with rofecoxib would differentially affect fracture healing more than cyclical inhibition of COX-2 using ibuprofen, which inhibits COX-1 and COX-2 and has a short half-life in vivo.

METHODS

Bilateral fibula osteotomies were done in 67 skeletally mature male New Zealand white rabbits. The rabbits were treated with placebo, rofecoxib (12.5 mg once a day), or ibuprofen (50 mg 3 times a day) for 28 days after surgery. Plasma ibuprofen levels were measured by HPLC analysis. Bone healing was assessed by histomorphometry at 3 and 6 weeks after osteotomy, and at 6 and 12 weeks by torsional mechanical testing.

RESULTS

Plasma ibuprofen levels peaked and declined between successive doses. Fracture callus morphology was abnormal in the rofecoxib-treated rabbits and torsional mechanical testing showed that fracture healing was impaired. Ibuprofen treatment caused persistence of cartilage within the fracture callus and reduced peak torque at 6 weeks after osteotomy as compared to the fibulas from the placebo-treated rabbits. In the specimens allowed to progress to possible healing, non-union was seen in 5 of the 26 fibulas from the rofecoxib-treated animals as compared to 1 of 24 in the placebo group and 1 of 30 in the ibuprofen treatment group.

INTERPRETATION

Continuous COX-2 inhibition as modeled by rofecoxib treatment appears to be more deleterious to fracture repair than cyclical cyclooxygenase inhibition as modeled by ibuprofen treatment. Ibuprofen treatment appeared to delay bone healing based upon the persistence of cartilage within the fracture callus and diminished shear modulus. Despite the ibuprofen-induced delay, rofecoxib treatment produced worse fracture (osteotomy) healing than ibuprofen treatment.

Enhanced fracture repair by leukotriene antagonism is characterized by increased chondrocyte proliferation and early bone formation: a novel role of the cysteinyl LT-1 receptor

Inflammatory mediators and drugs which affect inflammation can influence the healing of injured tissues. Leukotrienes are potent inflammatory mediators, and similar to prostaglandins, are metabolites of arachidonic acid which can have positive or negative effects on bone and cartilage tissues. Here we tested the hypothesis that blocking the negative regulation of leukotrienes, would lead to enhanced endochondral bone formation during fracture repair. A closed femoral fracture was created in mice. Animals were divided into three groups for treatment with either montelukast sodium, a cysteinyl leukotriene type 1 receptor antagonist (trade name Singulair), zileuton, a 5-lipoxygenase enzyme inhibitor (trade name Zyflo), or carrier alone. The fractures were analyzed using radiographs, quantitative gene expression, histology and histomorphometry, and immunohistochemistry. Both the montelukast sodium group and the zileuton group exhibited enhanced fracture repair when compared with controls. Both treatment groups exhibited increased callous size and earlier bone formation when compared to controls as early as day 7. Gene expression analysis of treatment groups showed increased markers of chondrocyte proliferation and differentiation, and increased early bone formation markers when compared with controls. Treatment with montelukast sodium directly targeted the cysteinyl leukotriene type 1 receptor, leading to increased chondrocyte proliferation at early time points. These novel findings suggests a potential mechanism by which the cysteinyl leukotriene type 1 receptor acts as a negative regulator of chondrocyte proliferation, with important and previously unrecognized implications for both fracture repair, and in a broader context, systemic chondrocyte growth and differentiation.

Modulation of the inflammatory response for enhanced bone tissue regeneration

Proinflammatory cytokines are infamous for their catabolic effects on tissues and joints in both inflammatory diseases and following the implantation of biomedical devices. However, recent studies indicate that many of these same molecules are critical for triggering tissue regeneration following injury. This review will discuss the role of inflammatory signals in regulating bone regeneration and the impact of both immunomodulatory and antiinflammatory pharmacologic agents on fracture healing, to demonstrate the importance of incorporating rational control of inflammation into the design of tissue engineering strategies.

The use of NSAIDs in pediatric scoliosis surgery - a survey of physicians' prescribing practice

BACKGROUND

Pediatric scoliosis surgery is associated with considerable postoperative pain requiring opioids for analgesia. Nonsteroidal antiinflammatory drugs (NSAIDs) can be used as adjuvants for analgesia; however, the potential of these agents to affect bone healing raises concerns. No large-scale prospective studies have been performed to evaluate the benefit-to-risk ratio of NSAID use after pediatric scoliosis surgery. Given the lack of evidence in the literature, a survey of practice patterns of anesthesiologists from around the world was conducted with respect to the use of NSAIDs after pediatric spinal fusion surgery for scoliosis.

METHODS

One hundred and fourteen anesthesiologists from international academic pediatric hospitals were asked to complete an online survey. After 1 month, nonresponders were sent a second e-mail asking for their participation. All questions were developed specifically for this study.

RESULTS

Out of 80 anesthesiologists who responded 61 were included in the final analysis. Fifty-nine percent routinely use NSAIDs, the most common agents being intravenous ketorolac and oral ibuprofen. The majority of respondents begin to administer NSAIDs within the first three postoperative days for a duration of four or more days. The primary reason for not routinely prescribing NSAIDs was the risk of bone nonunion.

CONCLUSIONS

This survey demonstrates that the practice patterns of pediatric anesthesiologists from around the world with respect to the administration of NSAIDs for the management of postoperative pain after pediatric spinal fusion reflects the conflicting evidence in the literature and the lack of high-quality studies in humans.

Parecoxib and indomethacin delay early fracture healing: a study in rats

Nonsteroidal antiinflammatory drugs (NSAIDs) are used to reduce inflammatory response and pain. These drugs have been reported to impair bone metabolism. Parecoxib, a specific COX-2 inhibitor, exerts an inhibitory effect on the mineralization of fracture callus after a tibial fracture in rats. Decreased bone mineral density (BMD) at a fracture site may indicate impairment of early healing, casting doubt on the safety of using COX-2 inhibitors during the early treatment of diaphyseal fractures. Forty-two female Wistar rats were randomly allocated to three groups. They were given parecoxib, indomethacin, or saline intraperitoneally for 7 days after being subjected to a closed tibial fracture stabilized with an intramedullary nail. Two and 3 weeks after surgery, the bone density at the fracture site was measured using dual energy xray absorptiometry (DEXA). Three weeks after the operation the rats were euthanized and the healing fractures were mechanically tested in three-point cantilever bending. Parecoxib decreased BMD at the fracture site for 3 weeks after fracture, indomethacin for 2 weeks. Both parecoxib and indomethacin reduced the ultimate bending moment and the bending stiffness of the healing fractures after 3 weeks. These results suggest COX inhibitors should be avoided in the early phase after fractures.

Relevance of bone graft viability in a goat transverse process model

Little is known about the mechanism by which autologous bone grafts are so successful. The relevance of viable osteogenic cells, which is a prominent difference between autologous bone graft and conventional alternatives, is especially controversial. With the emergence of bone tissue engineering, knowledge of the exact role of these cells has become crucial. The most obvious question to answer is whether viability of the graft has an effect on bone formation. In the current study, we investigated this effect of bone graft viability in a transverse process model that represents the initial bone formation in posterolateral spinal fusion. Eight goats received viable and devitalized autologous bone grafts in chambers mounted on the decorticated lumbar transverse processes. In addition, five goats received empty chambers. Histology and histomorphometry were performed after a 12-week implantation, and the dynamics of bone formation was monitored by sequential fluorochrome labeling. An obvious qualitative effect of viability was demonstrated by the presence of early onset osteogenesis distant from the transverse process bone in the viable grafts only. Quantitative analysis indicated about 30% more bone in the viable grafts, however, this difference was not statistically significant. In the empty chambers, bone was found in comparable quantities. We conclude that there is a qualitative advantage of graft viability in terms of early graft-derived osteogenesis. However, this advantage did not lead to significantly more bone formation in the viable bone grafts.

Rescue of impaired fracture healing in COX-2-/- mice via activation of prostaglandin E2 receptor subtype 4

Although the essential role of cyclooxygenase (COX)-2 in fracture healing is known, the targeted genes and molecular pathways remain unclear. Using prostaglandin E2 receptor (EP)2 and EP4 agonists, we examined the effects of EP receptor activation in compensation for the lack of COX-2 during fracture healing. In a fracture-healing model, COX-2(-/-) mice showed delayed initiation and impaired endochondral bone repair, accompanied by a severe angiogenesis deficiency. The EP4 agonist markedly improved the impaired healing in COX-2(-/-) mice, as evidenced by restoration of bony callus formation on day 14, a near complete reversal of bone formation, and an approximately 70% improvement of angiogenesis in the COX-2(-/-) callus. In comparison, the EP2 agonist only marginally enhanced bone formation in COX-2(-/-) mice. To determine the differential roles of EP2 and EP4 receptors on COX-2-mediated fracture repair, the effects of selective EP agonists on chondrogenesis were examined in E11.5 long-term limb bud micromass cultures. Only the EP4 agonist significantly increased cartilage nodule formation similar to that observed during prostaglandin E2 treatment. The prostaglandin E2/EP4 agonist also stimulated MMP-9 expression in bone marrow stromal cell cultures. The EP4 agonist further restored the reduction of MMP-9 expression in the COX-2(-/-) fracture callus. Taken together, our studies demonstrate that EP2 and EP4 have differential functions during endochondral bone repair. Activation of EP4, but not EP2 rescued impaired bone fracture healing in COX-2(-/-) mice.

Prostaglandin E2 inhibits BMP signaling and delays chondrocyte maturation

While cyclooxygenases are important in endochondral bone formation during fracture healing, mechanisms involved in prostaglandin E2 (PGE2) regulation of chondrocyte maturation are incompletely understood. The present study was undertaken to determine if PGE2 effects on chondrocyte differentiation are related to modulation of the bone morphogenetic protein (BMP) signaling pathway. In primary murine sternal chondrocytes, PGE2 differentially regulated genes involved in differentiation. PGE2 induced type II collagen and MMP-13, had minimal effects on alkaline phosphatase, and inhibited the expression of the maturational marker, type X collagen. In BMP-2-treated cultures, PGE2 blocked the induction of type X collagen. All four EP receptors were expressed in chondrocytes and tended to be inhibited by BMP-2 treatment. RCJ3.1C5.18 chondrocytes transfected with the protein kinase A (PKA) responsive reporter, CRE-luciferase, showed luciferase induction following exposure to PGE2, consistent with activation of PKA signaling and the presence of the EP2 and EP4 receptors. Both PGE2 and the PKA agonist, dibutyryl cAMP, blocked the induction of the BMP-responsive reporter, 12XSBE, by BMP-2 in RCJ3.1C5.18 chondrocytes. In contrast, PGE2 increased the ability of TGF-beta to activate the TGF-beta-responsive reporter, 4XSBE. Finally, PGE2 down-regulated BMP-mediated phosphorylation of Smads 1, 5, and 8 in RCJ3.1C5.18 cells and in primary murine sternal chondrocytes. Altogether, the findings show that PGE2 regulates chondrocyte maturation in part by targeting BMP/Smad signaling and suggest an important role for PGE2 in endochondral bone formation.

Capsaicin-sensitive sensory nerve fibers contribute to the generation and maintenance of skeletal fracture pain

Although skeletal pain can have a marked impact on a patient's functional status and quality of life, relatively little is known about the specific populations of peripheral nerve fibers that drive non-malignant bone pain. In the present report, neonatal male Sprague-Dawley rats were treated with capsaicin or vehicle and femoral fracture was produced when the animals were young adults (15-16 weeks old). Capsaicin treatment, but not vehicle, resulted in a significant (>70%) depletion in the density of calcitonin-gene related peptide positive (CGRP(+)) sensory nerve fibers, but not 200 kDa neurofilament H positive (NF200(+)) sensory nerve fibers in the periosteum. The periosteum is a thin, cellular and fibrous tissue that tightly adheres to the outer surface of all but the articulated surface of bone and appears to play a pivotal role in driving fracture pain. In animals treated with capsaicin, but not vehicle, there was a 50% reduction in the severity, but no change in the time course, of fracture-induced skeletal pain-related behaviors as measured by spontaneous flinching, guarding and weight bearing. These results suggest that both capsaicin-sensitive (primarily CGRP(+) C-fibers) and capsaicin-insensitive (primarily NF200(+) A-delta fibers) sensory nerve fibers participate in driving skeletal fracture pain. Skeletal pain can be a significant impediment to functional recovery following trauma-induced fracture, osteoporosis-induced fracture and orthopedic surgery procedures such as knee and hip replacement. Understanding the specific populations of sensory nerve fibers that need to be targeted to inhibit the generation and maintenance of skeletal pain may allow the development of more specific mechanism-based therapies that can effectively attenuate acute and chronic skeletal pain.

The effect of newer anti-rheumatic drugs on osteogenic cell proliferation: an in-vitro study

Background

Disease modifying anti-rheumatic drugs (DMARDs) may interfere with bone healing. Previous studies give conflicting advice regarding discontinuation of these drugs in the peri-operative setting. No consensus exists in current practice especially with the newer DMARDs such as Leflunomide, Etanercept, and Infliximab. The aim of this study was to assess the in-vitro effect of these drugs alone and in relevant clinical combinations on Osteoblast activity.

Methods

Osteoblasts were cultured from femoral heads obtained from five young otherwise healthy patients undergoing total hip replacement. The cells were cultured using techniques that have been previously described. A full factorial design was used to set up the experiment on samples obtained from the five donors. Normal therapeutic concentrations of the various DMARDs were added alone and in combination to the media. The cell proliferation was estimated after two weeks using spectrophotometric technique using Roche Cell proliferation Kit. Multilevel regression analysis was used to estimate which drugs or combination of drugs significantly affected cell proliferation.

Results

Infliximab and Leflunomide had an overall significant inhibitory effect (p < 0.05). Dexamethasone had a small stimulatory effect that was however strongly donor-dependent. The cox-2 inhibitor Etoricoxib was found to negate or increase the action of two other drugs (Leflunomide and Dexamethasone). Methotrexate and Etanercept had no discernable donor-dependant or donor-independent effect on osteoblast proliferation.

Conclusion

Our study indicates that in-vitro osteoblast proliferation can be inhibited by the presence of certain DMARDs. Combinations of drugs had an influence and could negate the action of a drug on osteoblast proliferation. The response to drugs may be donor-dependent.

Pathophysiology of cyclooxygenase inhibition in animal models

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins (PGs), which play a significant role in health and disease in the gastrointestinal tract (GI) and in the renal, skeletal, and ocular systems. COX-1 is constitutively expressed and found in most normal tissues, whereas COX-2 can be expressed at low levels in normal tissues and is highly induced by pro-inflammatory mediators. Inhibitors of COX activity include: (1) conventional nonselective, nonsteroidal anti-inflammatory drugs (ns-NSAIDs) and (2) COX-2 selective nonsteroidal anti-inflammatory drugs (COX-2 s-NSAIDs). Inhibition of COX-1 often elicits GI toxicity in animals and humans. Therefore, COX-2 s-NSAIDs were developed to provide a selective COX-2 agent, while minimizing the attendant COX-1-mediated GI toxicities. Rats and dogs overpredict COX inhibition for renal effects such as renal handling of electrolytes in humans. COX inhibitors are shown to have both beneficial and detrimental effects, such as on healing of ligament or tendon tears, on the skeletal system in animal models. Certain ophthalmic conditions such as glaucoma and keratitis are associated with increased COX-2 expression, suggesting a potential role in their pathophysiology.

Influence of nonsteroidal anti-inflammatory drugs on osseointegration

This paper reviews contemporary literature concerning the possible influence of nonsteroidal anti-inflammatory drugs (NSAIDs) on osseointegration. In vitro studies concerning the effect of NSAIDs on growth factors and bone-generating cells are the primary source of data pertaining to this issue because relatively few in vivo studies have been conducted. It is concluded that prescribing NSAIDs during the early postoperative period is likely not without negative effect, although any negative influence appears to be temporary and does not affect the final outcome of osseointegration.

New advances in musculoskeletal pain

Non-malignant musculoskeletal pain is the most common clinical symptom that causes patients to seek medical attention and is a major cause of disability in the world. Musculoskeletal pain can arise from a variety of common conditions including osteoarthritis, rheumatoid arthritis, osteoporosis, surgery, low back pain and bone fracture. A major problem in designing new therapies to treat musculoskeletal pain is that the underlying mechanisms driving musculoskeletal pain are not well understood. This lack of knowledge is largely due to the scarcity of animal models that closely mirror the human condition which would allow the development of a mechanistic understanding and novel therapies to treat this pain. To begin to develop a mechanism-based understanding of the factors involved in generating musculoskeletal pain, in this review we present recent advances in preclinical models of osteoarthritis, post-surgical pain and bone fracture pain. The models discussed appear to offer an attractive platform for understanding the factors that drive this pain and the preclinical screening of novel therapies to treat musculoskeletal pain. Developing both an understanding of the mechanisms that drive persistent musculoskeletal pain and novel mechanism-based therapies to treat these unique pain states would address a major unmet clinical need and have significant clinical, economic and societal benefits.

COX-2 from the injury milieu is critical for the initiation of periosteal progenitor cell mediated bone healing

Although a critical role of COX-2 in bone repair has been established, the mechanism involved remains unclear. During early inflammatory phase of bone healing, COX-2 is produced by the surrounding inflammatory cells as well as bone/cartilage progenitors. Based on the temporal and spatial expression of COX-2 during the early phase of fracture healing, we hypothesize that COX-2 from both sources is critical for progenitor cell activation, proliferation and differentiation. To directly test this we utilized a murine femoral grafting model, in which live segmental grafts from the same strains were transplanted and donor versus host cell involvement in healing was assessed. Specifically, fresh femur cortical bone grafts of 4 mm in length from COX-2(-/-) (KO) mice were transplanted into wild type (WT) mice with the same sized segmental defect in femurs. Similarly, grafts from WT were transplanted into the defects in KO mice. As controls, transplantations between wild types, and transplantations between KO were also performed. Histologic analyses showed that WT-to-WT transplantation resulted in normal endochondral bone healing as evidenced by markedly induction of neovascularization and periosteal bone formation on donor graft. In contrast, transplantation of KO graft into KO host led to 96% reduction of bone formation and near elimination of donor cell-initiated periosteal bone formation. Similarly, transplantation of WT graft into a KO host resulted in 87% reduction of bone formation (n=8, p>0.05), indicating that KO host impaired WT donor progenitor cell expansion and differentiation. When a KO graft was transplanted into WT host, KO donor periosteal cell-initiated endochondral bone formation was restored. Histomorphometric analyses demonstrated 10-fold increase in bone formation and 3-fold increase in cartilage formation compared to KO-to-KO transplantation (n=8, p<0.05), suggesting that COX-2 deficient donor cells were capable to differentiate and form bone when placed in a WT host. Taken together, our data strongly suggest that COX-2 is critical for initiation of periosteal cortical bone healing. The early induction of COX-2 constitutes a crucial host-healing environment for activation and differentiation of donor periosteal progenitors. Elimination of COX-2 at the early stage of healing could lead to detrimental effects on periosteal progenitor cell-initiated cortical bone repair.

Comparative in vivo study of six hydroxyapatite-based bone graft substitutes

Improvement of synthetic bone graft substitutes as suitable alternatives to a patient's own bone graft remains a challenge in biomaterials research. Our goal was to answer the question of whether improved osteoinductivity of a material would also translate to better bone-healing orthotopically. Three porous biphasic calcium phosphate (BCP) ceramics (BCPA, BCPB, and BCPC), consisting of hydroxyapatite and beta-tricalcium phosphate, a porous biphasic calcium phosphate ceramic reinforced with a bioresorbable polylactic acid to improve its mechanical properties (BCPC+), a pure hydroxyapatite ceramic (HA), and a carbonated apatite ceramic (CA) were implanted intramuscularly and orthotopically by using a transverse process model in 11 goats for 12 weeks. BCPA and BCPB had similar chemical composition but differed in their microstructure. BCPB was not osteoinductive at all, but BCPA induced ectopic bone formation in 9 of 11 animals. Orthotopically, BCPA performed better than BCPB in both the amount and rate of bone formation. BCPC, similar to BCPA structurally and physicochemically, showed comparable results ectopically and orthotopically. Addition of resorbable polymer to BCPC made the material less osteoinductive (4 of 11 animals) and delayed bone formation orthotopically. Neither HA nor CA were osteoinductive, and their orthotopic performance was inferior to the osteoinductive ceramics. The results of the present study showed that material-derived osteoinduction significantly enhanced bone healing orthotopically, and that this material property appeared more sensitive for predicting orthotopic performance than physicochemical and structural characteristics.

No effect of ketoprofen and meloxicam on bone graft ingrowth: a bone chamber study in goats

BACKGROUND AND PURPOSE

There is increasing awareness that non-steroidal anti-inflammatory drugs (NSAIDs), and especially the cyclooxygenase-2 (COX-2) selective ones, may retard bone healing. We have used NSAIDs (indomethacin for at least 7 days) to prevent heterotopic ossification after acetabular reconstructions using impacted bone grafts. The long-term clinical results have been satisfying, making it difficult to believe that there is an important negative effect of NSAIDs on graft incorporation. We studied the effect of two different NSAIDs on bone and tissue ingrowth in a bone chamber model in goats, using autograft, rinsed allograft, and allograft that had been rinsed and subsequently irradiated.

METHODS

9 goats received no NSAIDs, 9 received ketoprofen, and 9 received meloxicam--all for 6 weeks. In each goat 6 bone chambers were implanted: 2 filled with autograft, 2 with rinsed allograft, and 2 with allograft that had been rinsed and irradiated. The amount of bone ingrowth and total tissue ingrowth was compared between the groups.

RESULTS

There were no statistically significant differences in bone ingrowth between the different groups. Also, no differences in bone ingrowth were found with respect to the type of graft used. Furthermore, there was no statistically significant difference in the total amount of ingrowth of fibrous tissue between the treatment groups.

INTERPRETATION

No differences in bone ingrowth in titanium bone chambers could be detected with both ketoprofen and meloxicam compared to untreated control animals. This confirms our hypothesis that the effect of NSAIDs on the incorporation and ingrowth of bone graft is limited.

Nonsteroidal antiinflammatory drugs for postoperative pain management after lumbar spine surgery: a meta-analysis of randomized controlled trials

OBJECT

The authors undertook this meta-analysis to assess the efficacy and safety of nonsteroidal antiinflammatory drugs (NSAIDs) in addition to opioid analgesics on perioperative pain management in lumbar spine surgery.

METHODS

The authors searched MEDLINE, Excerpta Medica (EMBASE), The Cochrane Library, CINAHL, PsycINFO, Allied and Complementary Medicine (AMED), and Science Citation Index Expanded databases. In addition, they manually searched key journals and their references. They included randomized trials comparing the use of NSAIDs in addition to opioid analgesics versus opioid analgesics alone after posterior lumbar discectomy, laminectomy, or spinal fusion. Two independent reviewers performed an assessment of the quality of the methods.

RESULTS

Seventeen studies comprising 400 patients who received NSAIDs in addition to opioid analgesics and 389 patients receiving opioid analgesics alone were included. Patients receiving NSAIDs in addition to opioid analgesics had lower pain scores and consumed fewer opioids than the group receiving opioid analgesics alone. There was no difference in the incidence of adverse effects.

CONCLUSIONS

This meta-analysis provides evidence that the addition of NSAIDs to opioid analgesics in lumbar spine surgery provided better pain control than opioid analgesics alone.

Negative effect of parecoxib on bone mineral during fracture healing in rats

BACKGROUND AND PURPOSE

Non-steroidal anti-inflammatory drugs (NSAIDs) are conventional cyclooxygen-ase (cox) inhibitors commonly used in musculoskeletal trauma to reduce the inflammatory response and pain, but they also seem to affect bone metabolism. Parecoxib is a cox inhibitor that selectively inhibits cox-2. Through their selective mechanism of action, these newer drugs are supposed to reduce the gastrointestinal side effects of conventional cox inhibitors. The effects on bone metabolism and healing have, however, not been fully elucidated. Thus, there are reasons for concern regarding the potential negative effects of these drugs on bone metabolism and bone repair. We investigated the effects of short-term administration of parecoxib on bone mineral formation and bone healing in rats.

ANIMALS AND METHODS

26 female Wistar rats were given parecoxib intraperitoneally for 7 days after a closed tibial fracture that was stabilized with an intra-medullary nail, and 26 animals were given saline. At 2, 3, and 6 weeks after surgery bone mineral density (BMD) at the fracture site was measured using dualenergy X-ray absorptiometry (DEXA). 6 weeks after the fracture, 14 rats from the parecoxib group and 16 rats from the placebo group were killed for mechanical testing, and the rest of the animals were killed for tissue analysis. The healing fractures and the intact contralateral tibias were mechanically tested by three-point cantilever bending.

RESULTS

The BMD at the fracture site was calculated as the average of the results after 2,3, and 6 weeks. Mean BMD was lower in the parecoxib group, 0.23 (SD 0.06) g/ cm2, than in the control group, 0.27 (SD 0.05) g/cm2 (p = 0.01). There were no statistically significant differences in mechanical properties of the healing fractures after 6 weeks. However, the study may have lacked sufficient statistical power to determine whether a negative effect on healing had occurred.

INTERPRETATION

No mechanical differences were detected between the control and treatment groups after 6 weeks, but they may have been present earlier in the fracture healing process. Our findings do, however, indicate that parecoxib given postoperatively for a week has a negative effect on mineralization during the early phase of fracture healing.

Comparison of fracture healing among different inbred mouse strains

Quantitative trait locus analysis can be used to identify genes critically involved in biological processes. No such analysis has been applied to identifying genes that control bone fracture healing. To determine the feasibility of such an approach, healing of femur fractures was measured between C57BL/6, DBA/2, and C3H inbred strains of mice. Healing was assessed by radiography and histology and measured by histomorphometry and biomechanical testing. In all strains, radiographic bridging of the fracture was apparent after 3 weeks of healing. Histology showed that healing occurred through endochondral ossification in all strains. Histomorphometric measurements found more bone in the C57BL/6 fracture calluses 7 and 10 days after fracture. In contrast, more cartilage was present after 7 days in the C3H callus, which rapidly declined to levels less than those of C57BL/6 or DBA/2 mice by 14 days after fracture. An endochondral ossification index was calculated by multiplying the callus percent cartilage and bone areas as a measure of endochondral ossification. At 7 and 10 days after fracture, this value was higher in C57BL/6 mice. Using torsional mechanical testing, normalized structural and material properties of the C57BL/6 healing femurs were higher than values from the DBA/2 or C3H mice 4 weeks after fracture. The data indicate that fracture healing proceeds more rapidly in C57BL/6 mice and demonstrate that genetic variability significantly contributes to the process of bone regeneration. Large enough differences exist between C57BL/6 and DBA/2 or C3H mice to permit a quantitative trait locus analysis to identify genes controlling bone regeneration.

Effects of anti-inflammatory drugs on proliferation, cytotoxicity and osteogenesis in bone marrow mesenchymal stem cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) were found to suppress proliferation and induce cell death in cultured osteoblasts, and steroids were found to decrease the osteogenesis potential of mesenchymal stem cells. In this study, we further tested the effects of anti-inflammatory drugs (AIDs) on the functions of bone marrow mesenchymal stem cells (BMSCs). The BMSCs from mice (D1-cells) and humans (hBMSCs) were treated with dexamethasone (10(-7) to 10(-6) M), cyclooxygenase-2 (COX-2) selective NSAIDs (10(-6) to 10(-5) M) and non-selective NSAIDs (10(-5) to 10(-4) M). Drug effects on proliferation, cell cycle kinetics, cytotoxicity and mRNA and protein expressions of cell cycle regulators were tested. The osteogenesis potential of D1-cells were evaluated by testing mRNA expressions of type Ialpha collagen and osteocalcin 2-8 days after treatments, and testing mineralization 1-3 weeks after treatments. The results showed that all the tested drugs suppressed proliferation and arrested cell cycle of D1-cells, but no significant cytotoxic effects was found. Prostaglandin E1, E2 and F2alpha couldn't rescue the effects of AIDs on proliferation. The p27kip1 expression was up-regulated by indomethacin, celecoxib and dexamethasone in both D1-cells and hBMSCs. Higher concentrations of indomethacin and dexamethasone also up-regulated p21Cip1/Waf1 expression in hBMSCs, and so did celecoxib on D1-cells. Expressions of cyclin E1 and E2 were down-regulated by these AIDs in D-cells, while only cyclin E2 was down-regulated by dexamethasone in hBMSCs. All the tested NSAIDs revealed no obvious detrimental effects on osteogenic differentiation of D1-cells. These results suggest that the proliferation suppression of AIDs on BMSCs may act via affecting expressions of cell cycle regulators, but not prostaglandin-related mechanisms.

Effects of a monoclonal antibody raised against nerve growth factor on skeletal pain and bone healing after fracture of the C57BL/6J mouse femur

A closed femur fracture pain model was developed in the C57BL/6J mouse. One day after fracture, a monoclonal antibody raised against nerve growth factor (anti-NGF) was delivered intraperitoneally and resulted in a reduction in fracture pain-related behaviors of approximately 50%. Anti-NGF therapy did not interfere with bone healing as assessed by mechanical testing and histomorphometric analysis.

INTRODUCTION

Current therapies to treat skeletal fracture pain are limited. This is because of the side effect profile of available analgesics and the scarcity of animal models that can be used to understand the mechanisms that drive this pain. Whereas previous studies have shown that mineralized bone, marrow, and periosteum are innervated by sensory and sympathetic fibers, it is not understood how skeletal pain is generated and maintained even in common conditions such as osteoarthritis, low back pain, or fracture.

MATERIALS AND METHODS

In this study, we characterized the pain-related behaviors after a closed femur fracture in the C57BL/6J mouse. Additionally, we assessed the effect of a monoclonal antibody that binds to and sequesters nerve growth factor (anti-NGF) on pain-related behaviors and bone healing (mechanical properties and histomorphometric analysis) after fracture.

RESULTS

Administration of anti-NGF therapy (10 mg/kg, days 1, 6, and 11 after fracture) resulted in a reduction of fracture pain-related behaviors of approximately 50%. Attenuation of fracture pain was evident as early as 24 h after the initial dosing and remained efficacious throughout the course of fracture pain. Anti-NGF therapy did not modify biomechanical properties of the femur or histomorphometric indices of bone healing.

CONCLUSIONS

These findings suggest that therapies that target NGF or its cognate receptor(s) may be effective in attenuating nonmalignant fracture pain without interfering with bone healing.

Non-steroidal anti-inflammatory drugs, cyclooxygenase-2 and the bone healing process

Traditional non-steroidal anti-inflammatory drugs (NSAID) and selective cyclooxygenase-2 (COX-2) inhibitors are widely used in the treatment of pain, including bone fracture pain and orthopaedic post-operative pain. The gastrointestinal and cardiovascular adverse effects of NSAIDs are acknowledged, but their effects on bone are less widely known. Prostaglandins play an important role in the regulation of osteoblast and osteoclast functions, and inhibition of prostaglandin production retards bone formation. Therefore, NSAIDs could be expected to have significant consequences in divergent clinical situations where bone formation or remodelling is a contributing factor. The present survey reviews current experimental and clinical evidence related to two of those conditions (i.e. on ectopic bone formation and on bone fracture healing). NSAIDs are used clinically to prevent ectopic bone formation (also known as heterotopic ossification) (e.g. after total hip arthroplasty or trauma). The efficacy of NSAIDs in the avoidance of heterotopic ossification has been documented in controlled clinical trials, but the inherent risks (e.g. on healing processes and on loosening of prostheses) need further studies. At the same time, NSAIDs are widely used in the treatment of fracture pain, and their inhibitory effects on the ongoing bone healing process have raised concerns. Results of fracture healing studies in animals treated with NSAIDs or in mice lacking COX-2 gene show that inhibition or deficiency of COX-2 impairs the bone healing process. The limited clinical data also support the assumption that inhibition of COX-2 by non-selective or COX-2-selective NSAIDs delays fracture healing. However, the clinical significance of the effect in various patient groups needs to be carefully assessed and further investigations are needed to characterize the patients at the highest risk for NSAID-induced delayed fracture healing and its complications. In the meantime, use of NSAIDs in fracture patients should be cautious, keeping in mind the benefits of pain relief and inhibition of ectopic bone formation on one hand, and the risks of non-union and retarded union on the other hand.