Cyclooxygenase-2 inhibition delays the attainment of peak woven bone formation following four-point bending in the rat

Fracture healing is retarded in the presence of cyclooxygenase-2 (COX-2) inhibitors, demonstrating an important role of COX-2 in trauma-induced woven bone adaptation. The aim of this experiment was to determine the influence of COX-2 inhibition on the remodeling and consolidation of nontraumatic woven bone produced by mechanical loading. A periosteal woven bone callus was initiated in the right tibia of female Wistar rats following a single bout of four-point bending, applied as a haversine wave for 300 cycles at a frequency of 2 Hz and a magnitude of 65 N. Daily injections of vehicle (VEH, polyethylene glycol) or the COX-2 inhibitor 5,5-dimethyl-3-3(3 fluorophenyl)-4-(4-methylsulfonal)phenyl-2(5H)-furanone (DFU, 2.0 mg . kg(-1) and 0.02 mg . kg(-1) i.p.), commenced 7 days postloading, and tibiae were examined 2, 3, 4, and 5 weeks postloading. Tibiae were dissected, embedded in polymethylmethacrylate, and sectioned for histomorphometric analysis of periosteal woven bone. No significant difference in peak woven bone area was observed between DFU-treated and VEH rats. However, treatment with DFU resulted in a temporal defect in woven bone formation, where the achievement of peak woven bone area was delayed by 1 week. Woven bone remodeling was observed in DFU-treated rats at 21 days postloading, demonstrating that remodeling of the periosteal callus is not prevented in the presence of a COX-2 inhibitor in the rat. We conclude that COX-2 inhibition does not significantly disrupt the mechanism of woven bone remodeling but alters its timing.

ED-71, a novel vitamin D analog, promotes bone formation and angiogenesis and inhibits bone resorption after bone marrow ablation

ED-71, a novel analog of 1alpha,25-(OH)2 D3, increases bone mass to a greater extent than alfacalcidol, an 1alpha,25-(OH)2 D3 prodrug. In this study, we used a murine bone marrow ablation model to compare the effect of ED-71 on bone formation and resorption in vivo with that of 1alpha,25-(OH)2 D3. We discovered that bone matrix remodeling occurring within the first week after bone marrow ablation was enhanced by a single injection of ED-71, but not by 1alpha,25-(OH)2 D3. This enhancement was associated with an increase in bone surface. Trabecular bone resorption occurring from 1 to 2 weeks after the procedure was suppressed by a single injection of ED-71, but not 1alpha,25-(OH)2 D3, with treated mice exhibiting a reduction in osteoclast numbers, despite increases in osteoblast surface. As seen with the single injection, daily administration of ED-71 also enhanced bone modeling. Bone marrow osteoblast differentiation was also augmented by ED-71 pretreatment. Furthermore, ED-71 treatment immediately after bone marrow ablation enhanced angiogenesis within the bone marrow cavity via enhancement of VEGF(120) expression. In this paper, we clearly demonstrate that ED-71 is an orally administered small molecular weight compound with an anabolic effect on bone metabolism.

Effects of local infusion of OP-1 on particle-induced and NSAID-induced inhibition of bone ingrowth in vivo

Excessive polyethylene wear particles from joint replacements may lead to periprosthetic osteolysis and loosening. Nonsteroidal anti-inflammatory drugs (NSAIDs) decrease fracture healing and bone ingrowth. We hypothesized that continuous local infusion of OP-1 (BMP-7) would increase local bone formation in the presence of two different adverse stimuli, polyethylene particles, and an oral NSAID. The Drug Test Chamber (DTC) was implanted in the proximal tibia of mature rabbits. The tissue growing into the chamber was exposed to OP-1 solution (110 ng/day), which was infused via an osmotic pump. Infusion of OP-1 alone for 6 weeks enhanced local bone formation in the chamber by 80% (p < 0.05) over infusion of carrier alone. In the presence of polyethylene particles, infusion of OP-1 increased local bone formation by 38% (p < 0.05) over treatment with particles and carrier. Oral administration of NSAID reduced local bone formation by 58% (p < 0.05); this suppressive effect caused by NSAIDS was completely reversed by the infusion of OP-1 (p < 0.05). These findings underline a potential role for local treatment with OP-1 to increase bone formation in the presence of potentially adverse stimuli such as polyethylene wear particles or NSAID use.

Endothelin signaling in osteoblasts: global genome view and implication of the calcineurin/NFAT pathway

Patients with prostate cancer develop osteoblastic metastases when tumor cells arrive in the bone and stimulate osteoblasts by secreting growth-promoting factors. Endothelin 1 (ET-1) is believed to be a key factor in promoting osteoblastic metastasis. Selective blockade of the ET(A) receptor is an established strategy in the development of cancer therapeutics. However, the molecular mechanisms whereby prostate cancer promotes abnormal bone growth are not fully understood. In this study, we have applied genomic approaches to elucidate the molecular mechanism of stimulation of osteoblasts by ET-1. To examine the ET-1 axis, we generated genomic signatures for osteoblasts treated with ET-1, in the presence and absence of a selective ET(A) antagonist (ABT-627). The ET-1 signature was comprised of several motifs, such as osteoblastic differentiation, invasion, and suppression of apoptosis. The signature also pointed at possible activation of the calcineurin/NFAT pathway. We showed that ET-1 activates calcineurin and causes nuclear translocation of NFATc1, implicating the pathway in the ET-1-mediated stimulation of osteoblasts. We also showed that ET-1 inhibits apoptosis in osteoblasts, implying that the suppression of apoptosis may be an important factor in the promotion of osteoblastic growth by ET-1.

Efeito dos anti-inflamatórios não-esteroidais convencionais e seletivos para COX-2 sobre o reparo ósseo

Na presente revisão de literatura foram relacionados trabalhos experimentais e clínicos dos últimos 15 anos referentes aos efeitos dos antiinflamatórios não-esteroidais (AINEs) convencionais e seletivos para COX-2 sobre a formação óssea reparacional. A maioria dos trabalhos mostra que os AINEs convencionais podem atrasar o reparo de fratura de ossos longos e a fusão espinhal, em animais, e interferir negativamente com a taxa de fusão espinhal, em humanos. Apesar da importância comprovada da prostaglandina E2, sintetizada por osteoblastos sob estímulo da enzima ciclooxigenase-2 (COX-2), no controle da formação óssea, os resultados experimentais acerca dos prováveis efeitos inibitórios dos AINEs seletivos sobre o reparo ósseo além de raros são ainda controversos e não há comprovação de que eles interferem com a neoformação óssea reparacional em humanos.

Selective and nonselective cyclooxygenase-2 inhibitors and experimental fracture-healing. Reversibility of effects after short-term treatment

BACKGROUND

Cyclooxygenase-2-specific anti-inflammatory drugs (coxibs) and nonspecific nonsteroidal anti-inflammatory drugs have been shown to inhibit experimental fracture-healing. The present study tested the hypothesis that these effects are reversible after short-term treatment.

METHODS

With use of a standard model of fracture-healing, identical ED50 dosages of either a nonsteroidal anti-inflammatory drug (ketorolac), a coxib (valdecoxib), or vehicle (control) were orally administered to rats for either seven or twenty-one days and fracture-healing was assessed with biomechanical, histological, and biochemical analyses.

RESULTS

When healing was assessed at twenty-one days, the seven-day treatment produced only a trend for a higher rate of nonunion in valdecoxib and ketorolac-treated animals as compared with controls. No differences were observed at thirty-five days. The twenty-one-day treatment produced significantly more nonunions in valdecoxib-treated animals as compared with either ketorolac-treated or control animals (p < 0.05), but these differences disappeared by thirty-five days. The dose-specific inhibition of these drugs on prostaglandin E2 levels and the reversibility of the effects after drug withdrawal were assessed in fracture calluses and showed that ketorolac treatment led to twofold to threefold lower levels of prostaglandin E2 than did valdecoxib. Withdrawal of either drug after six days led to a twofold rebound in these levels by fourteen days. Histological analysis showed delayed remodeling of calcified cartilage and reduced bone formation in association with valdecoxib treatment.

CONCLUSIONS

Cyclooxygenase-2-specific drugs inhibit fracture-healing more than nonspecific nonsteroidal anti-inflammatory drugs, and the magnitude of the effect is related to the duration of treatment. However, after the discontinuation of treatment, prostaglandin E2 levels are gradually restored and the regain of strength returns to levels similar to control.

Roles of COX-2 and iNOS in the bony repair of the injured growth plate cartilage

Growth plate injuries often lead to bone growth defects, which primarily occur due to bony repair at injury sites. Bony repair is preceded by an injury-induced inflammatory response, which could play a role in regulating the repair process. Here, roles of two inflammatory mediators, cyclo-oxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS), in the injury responses were analysed by examining their gene expression and effects of blocking their activities, respectively, with celecoxib and aminoguanidine during 2 days prior to and until 7 days after injury in a rat tibial growth plate injury model. Quantitative RT-PCR assays revealed upregulated expression of COX-2 on days 1 and 4 and iNOS on day 1. Histological analysis of injury sites revealed significant reductions in inflammatory infiltrate (particularly neutrophils) on day 1 in treated groups compared to saline control. While bony tissue proportions at injury sites were unaffected by either treatment, mesenchymal tissue proportions were larger but cartilaginous tissue proportions were smaller on day 8 (though statistically insignificant), and bone remodelling appeared delayed with a smaller bone marrow proportion on day 14 in both treatment groups. These findings suggest that COX-2 and iNOS mediate injury-induced inflammatory response, and may play a role in enhancing mesenchymal cell differentiation to cartilaginous cells and in promoting bone remodelling during bony repair of growth plate injury sites. Furthermore, increased expression of cartilage-related (collagen-2, collagen-10, SOX-9) and bone-related molecules (osteocalcin, cbfalpha-1) suggest involvement of both endochondral and direct bone formation mechanisms during bony repair.

Fracture healing in the elderly patient

Clinical experience gives rise to the impression that there are differences in fracture healing in different age groups. It is evident that fractures heal more efficiently in children than in adults. However, minimal objective knowledge exists to evaluate this assumption. Temporal, spatial, and cellular quantitative and qualitative interrelationships, as well as signaling molecules and extracellular matrix have not been comprehensively and adequately elucidated for fracture healing in the geriatric skeleton. The biological basis of fracture healing will provide a context for revealing the pathophysiology of delayed or even impaired bone regeneration in the elderly. We will summarize experimental studies on age-related changes at the cellular and molecular level that will add to the pathophysiological understanding of the compromised bone regeneration capacity believed to exist in the elderly patient. We will suggest why this understanding would be useful for therapeutics focused on bone regeneration, in particular fracture healing at an advanced age.

Identification of adiponectin and its receptors in human osteoblast-like cells and association of T45G polymorphism in exon 2 of adiponectin gene with lumbar spine bone mineral density in Korean women

OBJECTIVE

The role of adiponectin in bone metabolism has been recently reported in in vitro and in vivo studies. There has been no report on the association of adiponectin gene polymorphism and bone mineral density (BMD). Therefore, we investigated whether two single nucleotide polymorphisms (SNPs), T45G and G276T, in the adiponectin gene were related to BMD in Koreans. We also report on the identification of adiponectin and its receptors 1 and 2 in human osteoblast-like cell lines.

PATIENTS AND MEASUREMENTS

MG-63 cells were cultured and osteogenic and adipogenic differentiations from human mesenchymal stem cells (hMSCs) were performed. RNA was then extracted from the cultured cells and reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using primers for adiponectin and for the adiponectin receptor genes. In 249 female and 80 male subjects, measurements were made of their lumbar spine and femoral neck BMDs, and biochemical markers of bone turnover. The genotyping of the T45G polymorphism in exon 2 and the G276T polymorphisms in intron 2 in the adiponectin gene was performed using an allelic discrimination assay with a TaqMan probe. Analyses were performed separately in each cohort.

RESULTS

We found that the mRNAs for adiponectin and for adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) were expressed in the MG-63 cells. Sequencing of the PCR products revealed that they were identical to human adiponectin, AdipoR1 and AdipoR2, respectively. mRNAs for adiponectin, AdipoR1 and AdipoR2 were also expressed in the osteoblastic and adipogenic cell lines differentiated from hMSCs. For the polymorphism study, the frequencies of T45G and G276T in the adiponectin gene were in compliance with Hardy-Weinberg equilibrium and the two polymorphisms were in complete linkage disequilibrium (D' = -1.0, P < 0.001). In the female cohort, subjects with G alleles at the T45G locus had significantly lower lumbar spine BMD than those subjects with the TT genotype. Although BMD levels showed no association with the G276T locus, the GT genotype group showed significantly higher urine deoxypyridinoline levels than other genotype groups. In the male cohort, no association was observed between adiponectin genotypes and BMD levels.

CONCLUSIONS

We observed the expression of adiponectin, AdipoR1 and AdipoR2 in the MG-63 cell line and the osteoblastic cell line differentiated from hMSCs. T45G polymorphism in exon 2 of the adiponectin gene is associated with lumbar spine BMD and G276T polymorphism in intron 2 of the adiponectin gene is associated with the urine deoxypyridinoline level in Korean women. Additional studies are needed to elucidate the precise contribution of adiponectin to bone mineral metabolism.

The isozyme-specific effects of cyclooxygenase-deficiency on bone in mice

Prostaglandin E(2) (PGE(2)) plays a critical role in skeletal physiology and bone loss. PGE(2) production is regulated in vivo by at least two cyclooxygenase (COX) isozymes, COX-1 and COX-2. The purpose of this study was to investigate the in vivo effects of the selective deletion of COX-1 or COX-2 on bone mineral density (BMD), bone microarchitecture and bone strength in wild type (WT), COX-1(-/-) and COX-2(-/-) mice. Using a LUNAR PIXImus, BMD was measured in 18 (WT), 18 COX-1(-/-) and 16 COX-2(-/-) mice. COX-1(-/-) mice exhibited significantly higher BMD (0.0506 g/cm(2) +/- 0.0014 g/cm(2)) than either WT (0.0493 g/cm(2) +/- 0.0019, P < or = 0.05) or COX-2(-/-) (0.0473 g/cm(2) +/- 0.0034, P < or = 0.01) mice. COX-2(-/-) mice had significantly lower BMD than WT (P < or = 0.01) or COX-1(-/-) (P < or = 0.01). Flexure stress of the femurs, determined by breaking the bones with three-point bending, correlated with bone density. Although plasma levels of both Ca(2+) and PTH were comparable in wild type and COX-1(-/-) mice, both were elevated in COX-2(-/-) mice consistent with primary hyperparathyroidism. These studies suggest that COX enzymes are important regulators of BMD and bone strength in mice. The beneficial effect of absence of the COX-1 enzyme on skeletal parameters may be secondary to decreases in PGE(2). On the other hand, primary hyperparathyroidism and lower bone magnesium content may account for the lower BMD and impairments in bone strength of COX-2(-/-) mice. Further elucidation of the effects of the COX pathway on bone remodeling may provide important information on potential therapeutic targets for preventing and/or treating osteoporosis.

Nonsteroidal anti-inflammatory drug-induced fracture nonunion: an inhibition of angiogenesis?

BACKGROUND

Approximately 5% to 10% of fractures may result in delayed union or nonunion. The results of research done over the past three decades have shown that the use of nonsteroidal anti-inflammatory drugs (NSAIDs) has an inhibitory effect on fracture repair, but the exact mechanism of action remains to be elucidated. Cancer research has identified that NSAIDs impede cell proliferation by inhibiting angiogenesis. It is proposed that a similar mechanism occurs in the induction of NSAID-induced nonunions. This hypothesis was investigated in a randomized placebo-controlled trial of the NSAID rofecoxib with use of a murine femoral fracture model.

METHODS

Two hundred and forty mice were randomized to receive either the nonsteroidal anti-inflammatory drug rofecoxib (5 mg/kg orally) in a 0.5% methylcellulose solution (the NSAID group) or the 0.5% methylcellulose solution only (the control group). Two hundred and thirty-five of the 240 mice underwent surgery to induce an open transverse middiaphyseal femoral fracture, which was then treated with use of a custom-made external fixator. Five additional animals underwent sham surgery with no fracture induced. Outcomes measures included radiographic assessment, histologic analysis, biomechanical testing, and use of laser Doppler flowmetry to assess blood flow across the fracture gap.

RESULTS

Radiography revealed similar healing patterns in both groups; however, at the later stages (day 32), the NSAID group had poorer healing. Histological analysis demonstrated that the control animals healed quicker (at days 24 and 32) and had more callus and less fibrous tissue (at days 8 and 32) than the NSAID animals did. Biomechanical testing found that the control animals were stronger at day 32. Both groups exhibited a similar pattern of blood flow; however, the NSAID group exhibited a lower median flow from day 4 onward (significant at days 4, 16, and 24). Positive correlations were demonstrated between both histological and radiographic assessments of healing and increasing blood flow. NSAID-treated animals exhibited lower blood flow and poorer healing by all parameters. Regression analysis, however, demonstrated that the negative effect of NSAIDs on fracture repair is independent of its inhibitory action on blood flow.

CONCLUSIONS

Following the development of a novel method of analyzing functional vascularity across a fracture gap, we have demonstrated that the cyclooxygenase-2 (COX-2) inhibitor rofecoxib has a significant negative effect on blood flow across the fracture gap as well as an inhibiting effect on fracture repair.

CLINICAL RELEVANCE

COX-2 inhibitors are marketed as having low side-effect profiles. We propose that these drugs should be used with caution in all patients following osseous trauma and, in particular, after injuries that may already predispose a fracture to a delayed union due to osseous, vascular, or patient-related factors.

Transcriptome analysis reveals an osteoblast-like phenotype for human osteotropic breast cancer cells

Metastatic breast cancer cells exhibit the selective ability to seed and grow in the skeleton. We and others have previously reported that human breast tumors which metastasize to the skeleton overexpress bone matrix extracellular proteins. In an attempt to reveal the osteoblast-like phenotype of osteotropic breast cancer cells, we performed a microarray study on a model of breast cancer bone metastasis consisting of the MDA-MB-231 human cell line and its variant B02 selected for its high capacity to form bone metastases in vivo. Analysis of B02 cells transcriptional profile revealed that 11 and 9 out of the 50 most up- and down-regulated mRNAs, respectively, corresponded to genes which expression has been previously associated with osteoblastic differentiation process. Thus, osteoblast specific cadherin 11 which mediates the differentiation of mesenchymal cells into osteoblastic cells is up-regulated in B02. While S100A4, recently described as a key negative regulator of osteoblast differentiation, is the most down-regulated gene in B02 cells. RT-PCR and western blotting experiments allowed the validation of the modulation of several genes of interest. Using immunohistochemistry, performed on human breast primary tumors and their matched liver and bone metastases, we were able to confirm that the osteoblast-like pattern of gene expression observed in our model holds true in vivo. This is the first report demonstrating a gene-expression pattern corresponding to the acquisition of an osteomimetic phenotype by bone metastatic breast cancer cells.

Alteration of femoral bone morphology and density in COX-2-/- mice

A role of COX-2 in pathological bone destruction and fracture repair has been established; however, few studies have been conducted to examine the involvement of COX-2 in maintaining bone mineral density and bone micro-architecture. In this study, we examined bone morphology in multiple trabecular and cortical regions within the distal and diaphyseal femur of 4-month-old wild-type and COX-2-/- mice using micro-computed tomography. Our results demonstrated that while COX-2-/- female mice had normal bone geometry and trabecular microarchitecture at 4 months of age, the male knockout mice displayed reduced bone volume fraction within the distal femoral metaphysis. Furthermore, male COX-2-/- mice had a significant reduction in cortical bone mineral density within the central cortical diaphysis and distal epiphysis and metaphysis. Consistent with the observed reduction in cortical mineral density, biomechanical testing via 4-point-bending showed that male COX-2-/- mice had a significant increase in postyield deformation, indicating a ductile bone phenotype in male COX-2-/- mice. In conclusion, our study suggests that genetic ablation of COX-2 may have a sex-related effect on cortical bone homeostasis and COX-2 plays a role in maintaining normal bone micro-architecture and density in mice.

Analyzing the cellular contribution of bone marrow to fracture healing using bone marrow transplantation in mice

The bone marrow is believed to play important roles during fracture healing such as providing progenitor cells for inflammation, matrix remodeling, and cartilage and bone formation. Given the complex nature of bone repair, it remains difficult to distinguish the contributions of various cell types. Here we describe a mouse model based on bone marrow transplantation and genetic labeling to track cells originating from bone marrow during fracture healing. Following lethal irradiation and engraftment of bone marrow expressing the LacZ transgene constitutively, wild type mice underwent tibial fracture. Donor bone marrow-derived cells, which originated from the hematopoietic compartment, did not participate in the chondrogenic and osteogenic lineages during fracture healing. Instead, the donor bone marrow contributed to inflammatory and bone resorbing cells. This model can be exploited in the future to investigate the role of inflammation and matrix remodeling during bone repair, independent from osteogenesis and chondrogenesis.

Parecoxib impairs early metaphyseal bone healing in rats

INTRODUCTION

Cox2 inhibitors decrease prostaglandin production and therefore influence bone healing especially in unstable long bone models. It is unclear to what extent implant fixation in stable metaphyseal bone is impaired.

METHOD

Male rats numbering 30 and female rats numbering 40 received a stainless steel screw in the metaphyseal bone of the proximal tibia. Half of the rats were treated with 6.4 mg/kg BW parecoxib by continuous release from a subcutaneous mini pump during 7 or 14 days. After treatment, the pull out force, stiffness, and pull out energy of the screw were measured.

RESULTS

No effect of parecoxib on the pull out force was found for male rats. In female rats the pull out force was decreased by 16% (P = 0.03) after 7 days treatment with parecoxib. This effect had disappeared after 14 days.

CONCLUSION

Adverse effects of parecoxib on the early phase healing of metaphyseal bone in female rats are small and were not detectable after 14 days. No effect was seen in male rats, possibly due to a faster metabolic elimination of the drug.

Perioperative medication management for the patient with rheumatoid arthritis

The treatment of rheumatoid arthritis has improved dramatically in recent years with the advent of the latest generation of disease-modifying antirheumatic drugs. Despite these advances, in some patients inflammation is not diminished sufficiently to prevent irreversible musculoskeletal damage, thus requiring surgical intervention to reduce pain and improve function. In these cases, the orthopaedic surgeon frequently encounters patients on a drug regimen consisting of nonsteroidal anti-inflammatory drugs, glucocorticoids, methotrexate, and biologic agents (disease-modifying antirheumatic drugs). Consultation with a rheumatologist is recommended, but the surgeon also should be aware of these medications that could potentially affect surgical outcome. Prudent perioperative management of these drugs is required to optimize surgical outcome. A balance must be struck between minimizing potential surgical complications and maintaining disease control to facilitate postoperative rehabilitation of patients with rheumatoid arthritis.

Three-dimensional reconstruction of fracture callus morphogenesis

Rat and mouse femur and tibia fracture calluses were collected over various time increments of healing. Serial sections were produced at spatial segments across the fracture callus. Standard histological methods and in situ hybridization to col1a1 and col2a1 mRNAs were used to define areas of cartilage and bone formation as well as tissue areas undergoing remodeling. Computer-assisted reconstructions of histological sections were used to generate three-dimensional images of the spatial morphogenesis of the fracture calluses. Endochondral bone formation occurred in an asymmetrical manner in both the femur and tibia, with cartilage tissues seen primarily proximal or distal to the fractures in the respective calluses of these bones. Remodeling of the calcified cartilage proceeded from the edges of the callus inward toward the fracture producing an inner-supporting trabecular structure over which a thin outer cortical shell forms. These data suggest that the specific developmental mechanisms that control the asymmetrical pattern of endochondral bone formation in fracture healing recapitulated the original asymmetry of development of a given bone because femur and tibia grow predominantly from their respective distal and proximal physis. These data further show that remodeling of the calcified cartilage produces a trabecular bone structure unique to fracture healing that provides the rapid regain in weight-bearing capacity to the injured bone.

High-grade slippage of the lumbar spine in a rat model of spondylolisthesis: effects of cyclooxygenase-2 inhibitor on its deformity

STUDY DESIGN

Radiographic and histologic evaluation of spondylolisthesis in a rat model.

OBJECTIVES

To investigate the effects of etodolac, a cox-2 inhibitor, on the severity of spondylolisthesis in a 4-week-old rat model.

SUMMARY OF BACKGROUND DATA

Spondylolisthesis occurs associated with spondylolysis in some pediatric patients. In such patients, the percent of forward slippage varies individually ranging between 0% and 100%. The factors determining the severity of forward slippage have not been clarified as yet. In earlier studies, we found that growth plate stress fracture was the basic lesion and that slippage was a consequence of the stress fracture. Hence, we hypothesized that the capacity of bone healing might be an important determinant of the degree of forward slippage.

METHODS

A lumbar spine slippage model was prepared in 4-week-old rats with vertebral physis fracture. To disrupt the fracture healing, the cyclooxygenase-2 (cox-2) inhibitor etodolac was used, and its effects on slippage and deformity were evaluated radiologically and histologically.

RESULTS

In the etodolac group, forward slip significantly increased (P < 0.05) to the Meyerding Grade III while in the control rats it was Grade I or II. Bone remodeling of the vertebral body was suppressed by etodolac. Histologically, epiphyseal separation with slippage was observed in all the control and etodolac-treated rats. However, in the etodolac-treated group, the epiphyseal plate was greatly separated and did not present periosteal thickening at the physis fracture site.

CONCLUSION

Vertebral forward slippage occurred in young rats after epiphyseal separation. In the etodolac group, slippage increased as deterioration of the bone healing capacity increased. Poor bony healing is suggested as one of the determinants of high-grade spondylolisthesis in children and adolescents.

Inhibitors of cyclo-oxygenase-2 and secretory phospholipase A2 preserve bone architecture following ovariectomy in adult rats

Epidemiological evidence and in vitro data suggest that COX-2 is a key regulator of accelerated remodeling. Accelerated states of osteoblast and osteoclast activity are regulated by prostaglandins in vitro, but experimental evidence for specific roles of cyclooxygenase-2 (COX-2) and secretory phospholipase A2 (sPLA2) in activated states of remodeling in vivo is lacking. The aim of this study was to determine the effect of specific inhibitors of sPLA2-IIa and COX-2 on bone remodeling activated by estrogen deficiency in adult female rats. One hundred and twenty-four adult female Wistar rats were ovariectomized (OVX) or sham-operated. Rats commenced treatment 14 days after surgery with either vehicle, a COX-2 inhibitor (DFU at 0.02 mg/kg/day and 2.0 mg/kg/day) or a sPLA2-group-IIa inhibitor (KH064 at 0.4 mg/kg/day and 4.0 mg/kg/day). Treatment continued daily until rats were sacrificed at 70 days or 98 days post-OVX. The right tibiae were harvested, fixed and embedded in methylmethacrylate for structural histomorphometric bone analysis at the proximal tibial metaphysis. The specific COX-2 or sPLA2 inhibitors prevented ovariectomy-induced (OVX-induced) decreases in trabecular connectivity (P<0.05); suppressed the acceleration of bone resorption; and maintained bone turnover at SHAM levels following OVX in the rat. The sPLA2 inhibitor significantly suppressed increases in osteoclast surface induced by OVX (P<0.05), while the effect of COX-2 inhibition was less marked. These findings demonstrate that inhibitors of COX-2 and sPLA2-IIa can effectively suppress OVX-induced bone loss in the adult rat by conserving trabecular bone mass and architecture through reduced bone remodeling and decreased resorptive activity. Moreover, we report an important role of sPLA2-IIa in osteoclastogenesis that may be independent of the COX-2 metabolic pathway in the OVX rat in vivo.

Low-intensity pulsed ultrasound accelerates and a nonsteroidal anti-inflammatory drug delays knee ligament healing

BACKGROUND

Low-intensity pulsed ultrasound and nonsteroidal anti-inflammatory drugs are used to treat ligament injuries; however, their individual and combined effects are not established.

HYPOTHESES

Low-intensity pulsed ultrasound accelerates ligament healing, a nonsteroidal anti-inflammatory drug delays healing, and the nonsteroidal anti-inflammatory drug inhibits the beneficial effect of low-intensity pulsed ultrasound.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty adult rats underwent bilateral transection of their knee medial collateral ligaments. Animals were divided into 2 drug groups and treated 5 d/wk with celecoxib (5 mg/kg) mixed in a vehicle solution (NSAID group) or vehicle alone (VEH group). One to 3 hours after drug administration, all animals were treated with unilateral active low-intensity pulsed ultrasound and contralateral inactive low-intensity pulsed ultrasound. Equal numbers of animals from each drug group were mechanically tested at 2 weeks (n = 14/group), 4 weeks (n = 8/group), and 12 weeks (n = 8/group) after injury.

RESULTS

Ultrasound and drug intervention did not interact to influence ligament mechanical properties at any time point. After 2 weeks of intervention, ligaments treated with active low-intensity pulsed ultrasound were 34.2% stronger, 27.0% stiffer, and could absorb 54.4% more energy before failure than could ligaments treated with inactive low-intensity pulsed ultrasound, whereas ligaments from the NSAID group could absorb 33.3% less energy than could ligaments from the VEH group. There were no ultrasound or drug effects after 4 and 12 weeks of intervention.

CONCLUSIONS

Low-intensity pulsed ultrasound accelerated but did not improve ligament healing, whereas the nonsteroidal anti-inflammatory drug delayed but did not impair healing. When used in combination, the beneficial low-intensity pulsed ultrasound effect was cancelled by the detrimental nonsteroidal anti-inflammatory drug effect.

CLINICAL RELEVANCE

Low-intensity pulsed ultrasound after ligament injury may facilitate earlier return to activity, whereas non-steroidal anti-inflammatory drugs may elevate early reinjury risk.

Experimental study of the action of COX-2 selective nonsteroidal anti-inflammatory drugs and traditional anti-inflammatory drugs in bone regeneration

OBJECTIVE

The aim of this study is to compare the effects of traditional nonsteroidal anti-inflammatory drugs with nonsteroidal anti-inflammatory drugs that are selective cyclooxygenase-2 (COX-2) inhibitors in the process of bone regeneration in a rat model.

MATERIALS AND METHODS

Forty-four Wistar strain rats were subjected to osteotomy of the right femur and randomly divided into 3 groups according to the drug to be given (diclofenac, rofecoxib, or placebo). Each group was divided into 2 subgroups according to the time to euthanasia after the surgery. The animals of Subgroup 1 were submitted to euthanasia 2 weeks after surgery, and those of Subgroup 2, underwent euthanasia 4 weeks after surgery. Radiographic examinations and bone callus histomorphometry were analyzed.

RESULTS

No intergroup statistical difference was found in the bone callus area or in bone formation area 2 and 4 weeks after surgery. Intra-group analysis concerning the bone neoformation area inside the callus showed a significant difference within the diclofenac group, which presented less tissue.

CONCLUSIONS

Fracture consolidation in Wistar rats occurs within less than 2 weeks, and the use of nonsteroidal anti-inflammatory drugs does not significantly influence this process.

Histone deacetylase 1-mediated histone modification regulates osteoblast differentiation

Osteogenesis is a complex process associated with dramatic changes in gene expression. To elucidate whether modifications in chromatin structure are involved in osteoblast differentiation, we examined the expression levels of histone deacetylases (HDACs) and the degree of histone acetylation at the promoter regions of osteogenic genes. During osteogenesis, total HDAC enzymatic activity was decreased with significant reduction in HDAC1 expression. Consistently, recruitment of HDAC1 to the promoters of osteoblast marker genes, including osterix and osteocalcin, was down-regulated, whereas histone H3 and H4 were hyperacetylated at those promoters during osteoblast differentiation. Moreover, suppression of HDAC activity with a HDAC inhibitor, sodium butyrate, accelerated osteogenesis by inducing osteoblast marker genes including osteopontin and alkaline phosphatase. Consistently, knockdown of HDAC1 by the short interference RNA system stimulated osteoblast differentiation. Taken together, these data propose that down-regulation of HDAC1 is an important process for osteogenesis.

Pharmacologic agents in fracture healing

Bone fractures are a known risk of athletic participation and can result in significant lost playing time. A variety of medications have been investigated in animal studies regarding their effects on fracture healing. Parathyroid hormone and the bisphosphonates may have future uses in the prevention and treatment of athletic-related stress fractures and acute fractures. Nonsteroidal anti-inflammatory drugs have been implicated in effecting fracture healing in some animal models, but little clinical evidence supports these findings. Large randomized clinical trials are needed to further delineate the role of these and other drugs and their effects on fracture healing.

Role of the different isoforms of cyclooxygenase and nitric oxide synthase during gastric ulcer healing in cyclooxygenase-1 and -2 knockout mice

Traditional NSAIDs, selective cyclooxygenase (COX)-2 inhibitors, and inhibitors of nitric oxide synthase (NOS) impair the healing of preexisting gastric ulcers. However, the role of COX-1 (with or without impairment of COX-2) and the interaction between COX and NOS isoforms during healing are less clear. Thus we investigated healing and regulation of COX and NOS isoforms during ulcer healing in COX-1 and COX-2 deficiency and inhibition mouse models. In this study, female wild-type COX-1(-/-) and COX-2(-/-) mice with gastric ulcers induced by cryoprobe were treated intragastrically with vehicle, selective COX-1 (SC-560), COX-2 (celecoxib, rofecoxib, and valdedoxib), and unselective COX (piroxicam) inhibitors. Ulcer healing parameters, mRNA expression, and activity of COX and NOS were quantified. Gene disruption or inhibition of COX-1 did not impair ulcer healing. In contrast, COX-2 gene disruption and COX-2 inhibitors moderately impaired wound healing. More severe healing impairment was found in dual (SC-560 + rofecoxib) and unselective (piroxicam) COX inhibition and combined COX impairment (in COX-1(-/-) mice with COX-2 inhibition and COX-2(-/-) mice with COX-1 inhibition). In the ulcerated repair tissue, COX-2 mRNA in COX-1(-/-) mice, COX-1 mRNA in COX-2(-/-) mice, and, remarkably, NOS-2 and NOS-3 mRNA in COX-impaired mice were more upregulated than in wild-type mice. This study demonstrates that COX-2 is a key mediator in gastric wound healing. In contrast, COX-1 has no significant role in healing when COX-2 is unimpaired but becomes important when COX-2 is impaired. As counterregulatory mechanisms, mRNA of COX and NOS isoforms were increased during healing in COX-impaired mice.

Cluster analysis and gene expression profiles: a cDNA microarray system-based comparison between human dental pulp stem cells (hDPSCs) and human mesenchymal stem cells (hMSCs) for tissue engineering cell therapy

We investigated gene expression patterns and functional classifications regarding the clusters of human dental pulp stem cells (hDPSCs) and human mesenchymal stem cells (hMSCs)--which possess a multipotent ability--because little is known about the precise moleculobiological clues by which these cells activate their differentiating ability or functionality to eventually form dentin and bone, respectively. We first verified the expressions of the alkaline phosphatase (ALP) gene, dentin matrix protein 1 (DMP-1), and dentinsialophosphoprotein (DSPP) by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and consequently discovered the high expressions of these genes. Total RNA was also followed by hybridization with a human microarray system consisting of 12,814 genes. Analyses of gene expression patterns indicated several genes which encode extracellular matrix components, cell adhesion molecules, growth factors, and transcription regulators. Functional and clustering analyses of differences in gene expression levels revealed cell signaling, cell communication, or cell metabolism. In the future, information on the gene expression patterns of hDPSCs and hMSCs might be useful in determining the detailed functional roles of the relevant genes and applicable to stem cell therapies, and these cells could also be used as multipotent cell sources for gene technology and tissue engineering technology.

Indomethacin and celecoxib impair rotator cuff tendon-to-bone healing

BACKGROUND

Nonsteroidal anti-inflammatory drugs are commonly prescribed after rotator cuff repair. These agents can impair bone formation, but no studies have evaluated their impact on tendon-to-bone healing.

HYPOTHESIS

Traditional nonselective nonsteroidal anti-inflammatory drugs and cyclooxygenase-2-specific nonsteroidal anti-inflammatory drugs interfere with tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

One hundred eighty Sprague-Dawley rats underwent acute rotator cuff repairs. Postoperatively, 60 rats received 14 days of celecoxib, a cyclooxygenase-2-specific nonsteroidal anti-inflammatory drug; 60 received indomethacin, a traditional nonselective nonsteroidal anti-inflammatory drug; and 60 received standard rat chow. Animals were sacrificed at 2, 4, and 8 weeks and evaluated by gross inspection, biomechanical testing, histologic analysis, and polarized light microscopy to quantify collagen formation and maturation.

RESULTS

Five tendons completely failed to heal (4 celecoxib, 1 indomethacin). There were significantly lower failure loads in the celecoxib and indomethacin groups compared with the control groups at 2, 4, and 8 weeks (P < .001), with no significant difference between nonsteroidal anti-inflammatory drug groups. There were significant differences in collagen organization and maturation between the controls and both nonsteroidal anti-inflammatory drug groups at 4 and 8 weeks (P < .001). Controls demonstrated progressively increasing collagen organization during the course of the study (P < .001), whereas the nonsteroidal anti-inflammatory drug groups did not.

CONCLUSION

Traditional and cyclooxygenase-2-specific nonsteroidal anti-inflammatory drugs significantly inhibited tendon-to-bone healing. This inhibition appears linked to cyclooxygenase-2.

CLINICAL RELEVANCE

If the results of this study are verified in a larger animal model, the common practice of administering non-steroidal anti-inflammatory drugs after rotator cuff repair should be reconsidered.

Effects of perioperative antiinflammatory and immunomodulating therapy on surgical wound healing

Patients with various rheumatologic and inflammatory disease states commonly require drugs known to decrease the inflammatory or autoimmune response for adequate control of their condition. Such drugs include nonsteroidal antiinflammatory drugs (NSAIDs), cyclooxygenase (COX)-2 inhibitors, corticosteroids, disease-modifying antirheumatic drugs (DMARDs), and biologic response modifiers. These drugs affect inflammation and local immune responses, which are necessary for proper wound healing in the perioperative setting, thereby potentially resulting in undesirable postoperative complications. Such complications include wound dehiscence, infection, and impaired collagen synthesis. The end result is delayed healing of soft tissue and bone wounds. The current literature provides insight into the effect of some of these drugs on wound healing. For certain drugs, such as methotrexate, trials have been conducted in humans and direct us on what to do during the perioperative period. Whereas with other drugs, we must rely on either small-animal studies or extrapolation of data from human studies that did not specifically look at wound healing. Unfortunately, no clear consensus exists on the need and optimum time for withholding therapy before surgery. Likewise, clinicians are often uncertain of the appropriate time to resume therapy after the procedure. For those drugs with limited or no data in this setting, the use of pharmacokinetic properties and biologic effects of each drug should be considered individually. In some cases, discontinuation of therapy may be required up to 4 weeks before surgery because of the long half-lives of the drugs. In doing so, patients may experience an exacerbation or worsening of disease. Clinicians must carefully evaluate individual patient risk factors, disease severity, and the pharmacokinetics of available therapies when weighing the risks and benefits of discontinuing therapy in the perioperative setting.

COX-2 is necessary for venous ligation-mediated bone adaptation in mice

In osteoblasts, cyclooxygenase 2 (COX-2) is the major isozyme responsible for production of prostaglandins. Prostaglandins are local mediators of bone resorption and formation and are known to be involved in bone's adaptive response to fluid shear stress (FSS). We have previously described a model of trabecular bone loss in hindlimb-suspended mice and rats and demonstrated partial protection from osteopenia by ligation of the femoral vein. The increased FSS resulting from this ligation drove bone adaptation in the absence of mechanical loading. In this study, we investigated the role of COX-2 in this adaptive response to FSS by use of COX-2 knockout mice. COX-2 knockout ("KO"), COX-2 heterozygote ("HET"), and COX-2 wild-type ("WT") animals all lost comparable amounts of trabecular bone from sham-operated limbs as a result of suspension. In WT mice, loss of trabecular BMD in the venous-ligated limb was significantly less than that of the sham-operated limb; this effect, however, was not seen in KO or HET mice. Percentage gain in femoral periosteal circumference was greater in the ligated limb than the sham-operated limb for WT mice. KO and HET mice already possess femora of larger periosteal circumference than their WT littermates and ligation in these bones did not result in an increase in perimeter relative to sham. Histomorphometry on embedded bones revealed thinner cortices and less mineralizing perimeter in KO femora than controls. In conclusion, this is the first in vivo study to show that fluid-flow-mediated bone adaptation, independent of mechanical strain, is COX-2 dependent.

Hyperbilirubinemia is not a major contributing factor to altered bone mineral density in patients with chronic liver disease

Reduced bone density is commonly encountered in patients with chronic liver disease. Prior studies have shown that unconjugated bilirubin inhibits osteoblast activity and function in vitro and in animal models of bone mineralization. To determine whether hyperbilirubinemia promotes the development of hepatic osteodystrophy, bone mineral density (BMD) was measured by dual energy X-ray absorptiometry in a cohort of 86 consecutive patients with chronic liver disease referred for liver transplant evaluation. The mean age of the study population was 52 years (range, 22-73), in which 52% were female and 90% were white. Average bone density values were significantly lower than expected for age, race, and sex, with Z-scores for the femoral neck and spine of -0.50 (95% confidence interval [CI] -0.63 to -0.37; p=0.0003) and -0.69 (95% CI -0.85 to -0.52; p=0.0001), respectively. Sixty-one subjects (71%) exhibited reduced BMD (T-score of femoral neck or spine<or=-1 standard deviation [SD] below the young-adult mean), and 18 subjects (21%) met criteria for osteoporosis (T-score<-2.5 SD). Stepwise logistic regression analyses identified significant associations between BMD and serum creatinine, alkaline phosphatase, age, and gender. On the other hand, neither unconjugated, nor conjugated, nor total serum bilirubin levels were found to predict diminished BMD. The lack of association between serum unconjugated bilirubin levels and bone mineralization was validated in hyperbilirubinemic Gunn rats, in which BMD and serum osteocalcin levels were no different than in wild-type rodents. In conclusion, the finding that serum bilirubin levels do not correlate with reduced BMD in patients with end-stage liver disease, and that chronic unconjugated hyperbilirubinemia does not lead to alterations in bone mineralization in Gunn rats, suggests that bilirubin is not a major contributing factor to hepatic osteodystrophy.

Osteogenic oxysterols inhibit the adverse effects of oxidative stress on osteogenic differentiation of marrow stromal cells

The osteoporosis that occurs with aging is associated with reduced number and activity of osteoblastic cells. Aging, menopause, and osteoporosis are correlated with increased oxidative stress and reduced antioxidant defense mechanisms. We previously demonstrated that oxidative stress induced by a variety of compounds such as xanthine/xanthine oxidase (XXO) and minimally oxidized LDL (MM-LDL) inhibit the osteogenic differentiation of osteoprogenitor cells. Oxysterols are a family of products derived from cholesterol oxidation that have important biological activities. Recently, we reported that a specific oxysterol combination consisting of 22(S)- or 22(R)-hydroxycholesterol and 20(S)-hydroxycholesterol has potent osteogenic properties in vitro when applied to osteoprogenitor cells including M2-10B4 (M2) marrow stromal cells. We now demonstrate that this osteogenic combination of oxysterols prevents the adverse effects of oxidative stress on differentiation of M2 cells into mature osteoblastic cells. XXO and MM-LDL inhibited the osteogenic differentiation of M2 cells, demonstrated by the inhibition of markers of osteogenic differentiation: alkaline phosphatase activity, osteocalcin expression and mineralization. Treatment of M2 cells with osteogenic oxysterol combination 22(S)- and 20(S)-hydroxycholesterol both blocked and reversed the inhibition of osteogenic differentiation produced by XXO and MM-LDL in these cells. The protective effect of the oxysterols against oxidative stress was dependent on cyclooxygenase 1 and was associated with the osteogenic property of the oxysterols. These findings further demonstrate the ability of the osteogenic oxysterols to positively regulate osteogenic differentiation of cells, and suggests that the use of these compounds may be a novel strategy to prevent the adverse effects of oxidative stress on osteogenesis.

Biological effects of rAAV-caAlk2 coating on structural allograft healing

Structural bone allografts often fracture due to their lack of osteogenic and remodeling potential. To overcome these limitations, we utilized allografts coated with recombinant adeno-associated virus (rAAV) that mediate in vivo gene transfer. Using beta-galactosidase as a reporter gene, we show that 4-mm murine femoral allografts coated with rAAV-LacZ are capable of transducing adjacent inflammatory cells and osteoblasts in the fracture callus following transplantation. While this LacZ vector had no effect on allograft healing, bone morphogenetic protein signals delivered via rAAV-caAlk2 coating induced endochondral bone formation directly on the cortical surface of the allograft by day 14. By day 28 there was evidence of remodeling of the new woven bone and massive osteoclastic resorption of the cortical surface of the rAAV-caAlk2-coated allografts only. Micro-CT analysis of rAAV-LacZ- vs rAAV-caAlk2-coated allografts after 42 days of healing demonstrated a significant increase in new bone formation (0.67 +/- 0.21 vs 2.49 +/- 0.40 mm(3); P < 0.005). Furthermore, the 3D micro-CT images of femurs grafted with rAAV-Alk2-coated allografts provided the first evidence that complete bridging of bone around a cortical allograft is possible. These results indicate that cell-free, rAAV-coated allografts have the potential to revitalize in vivo following transplantation.

The role of cyclooxygenase-2 inhibition in foot and ankle arthrodesis

Cyclooxygenase-2 (COX-2) inhibitors are an important adjunct in controlling postoperative pain. Concerns exist regarding the use of NSAIDs for postoperative pain management because of the possible deleterious impact on bone healing in patients undergoing hindfoot arthrodesis. Orthopedic surgeons are concerned with: (1) a multimodal approach for postoperative pain control, and (2) bone healing following arthrodesis, fracture repair with rigid internal fixation, and cementless implants. The use of COX-2 inhibitors has been shown to be an important component of a pain control strategy but questions about their effects on bone healing have inhibited their use. This article discusses the laboratory and clinical data available on the use of COX-2 inhibitors on bone healing and their effects on foot and ankle arthrodesis procedures.

Periosteal progenitor cell fate in segmental cortical bone graft transplantations: implications for functional tissue engineering

A murine segmental femoral bone graft model was used to show the essential role of donor periosteal progenitor cells in bone graft healing. Transplantation of live bone graft harvested from Rosa 26A mice showed that approximately 70% of osteogenesis on the graft was attributed to the expansion and differentiation of donor periosteal progenitor cells. Furthermore, engraftment of BMP-2-producing bone marrow stromal cells on nonvital allografts showed marked increases in cortical graft incorporation and neovascularization, suggesting that gene-enhanced, tissue engineered functional periosteum may improve allograft incorporation and repair.

INTRODUCTION

The loss of cellular activity in a structural bone allograft markedly reduces its healing potential compared with a live autograft. To further understand the cellular mechanisms for structural bone graft healing and repair and to devise a therapeutic strategy aimed at enhancing the performance of allograft, we established a segmental femoral structural bone graft model in mice that permits qualitative and quantitative analyses of graft healing and neovascularization.

MATERIALS AND METHODS

Using this segmental femoral bone graft model, we transplanted live isografts harvested from Rosa 26A mice that constitutively express beta-galactosidase into their wildtype control mice. In an attempt to emulate the osteogenic and angiogenic properties of periosteum, we applied a cell-based, adenovirus-mediated gene therapy approach to engraft BMP-2-producing bone marrow stromal cells onto devitalized allografts.

RESULTS

X-gal staining for donor cells allowed monitoring the progression of periosteal progenitor cell fate and showed that 70% of osteogenesis was attributed to cellular proliferation and differentiation of donor progenitor cells on the surface of the live bone graft. Quantitative muCT analyses showed a 3-fold increase in new bone callus formation and a 6.8-fold increase in neovascularization for BMP-2/stromal cell-treated allograft compared with control acellular allografts. Histologic analyses showed the key features of autograft healing in the BMP-2/stromal cell-treated allografts, including the formation of a mineralized bone callus completely bridging the segmental defects, abundant neovascularization, and extensive resorption of bone graft.

CONCLUSIONS

The marked improvement of healing in these cellularized allografts suggests a clinical strategy for engineering a functional periosteum to improve the osteogenic and angiogenic properties of processed allografts.

A comparison between the effects of acetaminophen and celecoxib on bone fracture healing in rats

OBJECTIVES

This study compared the acute treatment effects of systemic analgesics with (celecoxib) and without anti-inflammatory activity (acetaminophen) on bone fracture healing.

STUDY DESIGN

Longitudinal time study of fracture healing in rats.

METHODS

Closed, mid diaphyseal femur fractures were produced in female Sprague-Dawley rats. The rats were treated for 10 days after fracture with 60 or 300 mg/kg of acetaminophen, 3 or 6 mg/kg of celecoxib, or vehicle by once-daily oral dosing. Fracture healing was measured after 8 weeks by radiographic examination, mechanical testing, and histology.

RESULTS

Radiographic scoring indicated that acute celecoxib treatment significantly impaired fracture healing; acetaminophen treatment had no negative effect. Mechanical testing supported the radiographic observations. No negative effects of celecoxib or acetaminophen treatment on the structural properties (peak torque and torsional rigidity) of the healing femurs were detected. In contrast, celecoxib treatment, but not acetaminophen treatment, significantly reduced the material properties (maximum shear stress and shear modulus) of the healing femurs (P < 0.001). Post-mechanical testing examination of the healing femurs found that 73% of the vehicle-treated or acetaminophen-treated femurs had healed as unions (30/41), 27% failed as incomplete unions (11/41), and none failed as nonunions (0%). In contrast, only 21% of the fractured femurs from the celecoxib treated rats had healed as unions (7/34), 53% failed as incomplete unions (18/34), and 26% failed as nonunions (9/34). The proportion of nonunions among the celecoxib-treated rats was significantly higher compared with the control and acetaminophen-treated rats (P < 0.001). Histologic examination indicated that similar to previous studies, celecoxib treatment, but not acetaminophen treatment, altered normal fracture callus morphology in which cartilage rather than new bone abuts the fracture site.

CONCLUSIONS

No negative effect from acute acetaminophen treatment on fracture healing was detected. In contrast, acute treatment with celecoxib, a selective cyclooxygenase-2 inhibitor with anti-inflammatory activity, significantly impaired fracture healing.

The healing potential of the periosteum molecular aspects

The presence of pluripotential mesenchymal cells in the under surface of the periosteum in combination with growth factors regularly produced or released after injury, provide this unique tissue with an important role in the healing of bone and cartilage. The periosteum contributes in the secondary callus formation with cells and growth factors and should always be preserved and protected when surgery is performed for the management of a fracture. The current evidence about the cellular interactions, the stimulants and the signalling pathways related to osteogenesis and chondrogenesis is described. An essential knowledge of the basics related to the contribution of the periosteum in the healing of fractures, osteotomies, during the process of distraction osteogenesis and in some degree in the repair of cartilagenous defects, provides the surgeons with a better insight to understand the upcoming "biological" interventions in the management of skeletal injuries.

Cyclooxygenase-2 inhibition selectively attenuates bone morphogenetic protein-6 synthesis and bone formation during guided tissue regeneration in a rat model

OBJECTIVES

Bone formation during guided tissue regeneration is a tightly regulated process involving cells, extracellular matrix and growth factors. The aims of this study were (i) to examine the expression of cyclooxygenase-2 (COX-2) during bone regeneration and (ii) the effects of selective COX-2 inhibition on osseous regeneration and growth factor expression in the rodent femur model.

MATERIAL AND METHODS

A standardized transcortical defect of 5 x 1.5 mm was prepared in the femur of 12 male rats and a closed half-cylindrical titanium chamber was placed over the defect. The expression of COX-2 and of platelet-derived growth factor-B (PDGF-B), bone morphogenetic protein-6 (BMP-6) and insulin-like growth factor-I/II (IGF-I/II) was analyzed at Days 3, 7, 21 and 28 semiquantitatively by reverse transcriptase-polymerase chain reaction and immunohistochemistry. The effects of COX-2 inhibition by intraperitoneal injection of NS-398 (3 mg/kg/day) were analyzed in five additional animals sacrificed at Day 14.

RESULTS

Histomorphometry revealed that new bone formation occurred in the cortical defect area as well as in the supracortical region, i.e. region within the chamber by Day 7 and increased through Day 28. Immunohistochemical evidence of COX-2 and PDGF-B levels were observed early (i.e. Day 3) and decreased rapidly by Day 7. BMP-6 expression was maximal at Day 3 and slowly declined by Day 28. In contrast, IGF-I/II expression gradually increased during the 28-day period. Systemic administration NS-398 caused a statistically significant reduction (P<0.05) in new bone formation (25-30%) and was associated with a statistically significant reduction in BMP-6 protein and mRNA expression (50% and 65% at P<0.05 and P<0.01, respectively). PDGF-B mRNA or protein expression was not affected by NS-398 treatment.

CONCLUSION

COX-2 inhibition resulted in reduced BMP-6 expression and impaired osseous regeneration suggesting an important role for COX-2-induced signaling in BMP synthesis and new bone formation.

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.

Application of histomorphometric methods to the study of bone repair

Standardized methods for the histomorphometric assessment of bone are essential features of most studies of metabolic bone diseases and their treatments. These methodologies were developed to assess coupled remodeling, focusing primarily on osteoblasts and osteoclasts, the anabolic and catabolic rates of these cells, and structural features of mature bone. Research studies on bone healing and the development of new therapeutic approaches for the enhancement of bone repair also require a comprehensive understanding of the basic cellular and tissue level mechanisms that underlie these processes. However, the histological methods developed for metabolic bone disease studies are not completely suitable for studies of bone repair because they are based on assumptions that there is little variation in tissue composition within a sample of bone and not generally designed to quantify other types of tissues, such as cartilage, that contribute to bone healing. These techniques also do not provide tissue-based structural measurements that are relatable to the specific types of biomechanical and radiographic structural assessments that are used to determine rates of bone healing. These deficiencies in current histological approaches therefore point to the need to establish standardized criteria for the histomorphometric assessments that are specifically adapted for the study of bone repair in models of fracture healing and bone regeneration. In this Perspective, we outline what we believe to be the specific structural, tissue. and cellular aspects that need to be addressed to establish these standardized criteria for the histomorphometric assessment of bone repair. We present the specific technical considerations that need to be addressed to appropriately sample repair tissues to obtain statistically meaningful results and suggest specific procedures and definitions of nomenclatures for the application of this technology to bone repair. Finally, we present how aspects of histomorphometric measurements of bone repair can be related to biomechanical and radiographic imaging properties that functionally define rates of bone healing, and thus, how these tools can be used to provide corroborating data.

Nonsteroidal antiinflammatory drugs reduce radiographic progression in patients with ankylosing spondylitis: a randomized clinical trial

OBJECTIVE

A 2-year randomized controlled trial was performed to test the hypothesis that long-term, continuous treatment with nonsteroidal antiinflammatory drugs (NSAIDs), in comparison with NSAID treatment on demand only, influences radiographic progression in patients with ankylosing spondylitis (AS).

METHODS

Patients with AS (n = 215), who had previously participated in a 6-week, randomized, double-blind clinical trial that compared celecoxib, ketoprofen, and placebo, were randomly allocated to receive either continuous treatment with NSAIDs or on-demand treatment with NSAIDs for a period of 2 years. All patients began treatment with celecoxib, at a starting dosage of 100 mg twice daily; patients could increase this dosage to 200 mg twice daily or could switch to another NSAID while maintaining the same treatment strategy. Structural changes were assessed by radiographs of the lumbar and cervical spine and scored according to the modified Stoke Ankylosing Spondylitis Spine Score by one observer who was blinded to the treatment strategy and temporal order of the radiographs. Statistical analyses included a between-group comparison of 1) radiographic progression scores (by Mann-Whitney U test), 2) time-averaged values of variables reflecting signs and symptoms of AS (by linear regression analysis), and 3) the frequency of reported site-specific adverse events (by chi-square test or Fisher's exact test, as appropriate).

RESULTS

Complete sets of radiographs were available for 76 of the 111 patients in the continuous-treatment group and for 74 of the 104 patients in the on-demand group. The mean +/- SD scores for radiographic progression were 0.4 +/- 1.7 in the continuous-treatment group and 1.5 +/- 2.5 in the on-demand treatment group (P = 0.002). Parameters reflecting signs and symptoms were not statistically significantly different between groups. The between-group difference in radiographic progression did not disappear after adjusting for baseline values of radiographic damage or disease activity variables and for time-averaged values of disease activity variables, nor after input of missing data. Relevant adverse events tended to occur more frequently in the continuous-treatment group than in the on-demand group (for hypertension, 9% versus 3%; for abdominal pain, 11% versus 6%; for dyspepsia, 41% versus 38%), but the differences were not statistically significant.

CONCLUSION

A strategy of continuous use of NSAIDs reduces radiographic progression in symptomatic patients with AS, without increasing toxicity substantially.

Transcriptional induction of cyclooxygenase-2 in osteoclast precursors is involved in RANKL-induced osteoclastogenesis

Regulation of osteoclast differentiation is key to understanding the pathogenesis and to developing treatments for bone diseases such as osteoporosis. To gain insight into the mechanism of the receptor activator of nuclear factor (NF)–κB ligand (RANKL)–specific induction of the osteoclast differentiation program, we took a suppression-subtractive hybridization screening approach to identify genes specifically induced via the RANKL-Rac1 signaling pathway. Among identified targets, we show that RANKL selectively induces cyclooxygenase (COX) 2 expression via Rac1 that results in turn in production of prostaglandin E2 (PGE2) in RAW 264.7 cells. By using transient transfection assays, we found that the –233/–206 region of the COX-2 promoter gene was critical for RANKL-induced promoter activity. This RANKL-responsive region contained an NF-κB site that, when mutated, completely abolished the induction of NF-κB DNA-binding activity by RANKL. Blockade of COX-2 by celecoxib inhibits differentiation of bone marrow-derived monocyte/macrophage precursor cells (BMMs) into tartrate-resistant acid phosphatase-positive (TRAP+) osteoclastic cells. This inhibition can be rescued by the addition of exogenous PGE2, suggesting that COX-2–dependent PGE2 induction by RANKL in osteoclast precursors is required for osteoclast differentiation.

Cyclooxygenase-2 inhibitor delays fracture healing in rats

BACKGROUND

Cyclooxigenase-2 (COX-2) inhibitors have been reported to delay fracture healing. To investigate the major inhibitory period of COX-2 inhibitors in fracture healing, we administrated etodolac, a COX-2-specific inhibitor, to a rat fracture model by altering the period of administration from early to late.

METHOD

After closed fractures had been created at the middle of the femoral shafts in 12-week-old Wister rats, a standardized dose of etodolac was administrated in three ways: group I received it for 3 weeks, group II for just the first week after operation, and group III for just the third (final) week. Group IV was the vehicle control group. Bone maturation was estimated by radiographic scoring system, and mechanically by a three-point bending test.

RESULTS AND INTERPRETATION

In both the radiographic and mechanical studies, groups I and II showed lower scores than group IV, indicating that even a short period of administration of a COX-2-specific inhibitor in the early phase of fracture healing creates a risk of delayed healing. blacksquare, square, filled.

Lead exposure inhibits fracture healing and is associated with increased chondrogenesis, delay in cartilage mineralization, and a decrease in osteoprogenitor frequency

Lead exposure continues to be a significant public health problem. In addition to acute toxicity, Pb has an extremely long half-life in bone. Individuals with past exposure develop increased blood Pb levels during periods of high bone turnover or resorption. Pb is known to affect osteoblasts, osteoclasts, and chondrocytes and has been associated with osteoporosis. However, its effects on skeletal repair have not been studied. We exposed C57/B6 mice to various concentrations of Pb acetate in their drinking water to achieve environmentally relevant blood Pb levels, measured by atomic absorption. After exposure for 6 weeks, each mouse underwent closed tibia fracture. Radiographs were followed and histologic analysis was performed at 7, 14, and 21 days. In mice exposed to low Pb concentrations, fracture healing was characterized by a delay in bridging cartilage formation, decreased collagen type II and type X expression at 7 days, a 5-fold increase in cartilage formation at day 14 associated with delayed maturation and calcification, and a persistence of cartilage at day 21. Fibrous nonunions at 21 days were prevalent in mice receiving very high Pb exposures. Pb significantly inhibited ex vivo bone nodule formation but had no effect on osteoclasts isolated from Pb-exposed animals. No significant effects on osteoclast number or activity were observed. We conclude that Pb delays fracture healing at environmentally relevant doses and induces fibrous nonunions at higher doses by inhibiting the progression of endochondral ossification.

[In vivo and in vitro bone regeneration from cord blood derived mesenchymal stem cells]

BACKGROUND

Mesenchymal stem cells with an osteoblastic differentiating potency are investigated in regard of probable tissue engineering for further clinical application. The following report describes the use of cord blood derived stem cells as an alternative to other stem cell populations for bone regenerating tissue engineering.

METHODS

To demonstrate the multipotency of cord blood derived mesenchymal stem cells, unrestringated somatic stem cells (USSC) were isolated from cord blood and underwent an osteo-, chondro- and adipoblastic in vitro stimulation. To evaluate the osteoinductive potency of a porcine collagen I/III cell carrier USSC were incubated on this matrix. To investigate the in vivo effects of human USSC an athymic rat model was developed. These cells were transplanted into a femoral defect.

RESULTS

Cord blood derived mesenchymal stem cells (USSC) have an in vitro multipotency and show adipo-, chondro- and osteogenic differentiation. The porcine collagen I/III carrier promoted an osteoblastic differentiation. USSC survived after xenotransplantation in an athymic rat and differentiated into osteoblasts filling the bony defect zone.

CONCLUSION

Human USSC are a mesenchymal multipotent stem cell population that shows osteoblastic differentiation onto a collagen I/III carrier in vitro as well as in an athymic rat in vivo.

Differential regulation of EP receptor isoforms during chondrogenesis and chondrocyte maturation

Regulation of chondrogenesis and chondrocyte maturation by prostaglandins has been a topic of interest during recent years. Particular focus on this area derives from the realization that inhibition of prostaglandin synthesis with non-steroidal anti-inflammatory drugs could impact these cartilage-related processes which are important in skeletal development and are recapitulated during bone healing either post-trauma or post-surgery. In addition to reviewing the relevant literature focused on prostaglandin synthesis and signaling through the G-protein coupled EP receptors, we present novel findings that establish the expression profile of EP receptors in chondroprogenitors and chondrocytes. Further, we begin to examine the signaling that may be involved with the transduction of PGE2 effects in these cells. Our findings suggest that EP2 and EP4 receptor activation of cAMP metabolism may represent a central axis of events that facilitate the impact of PGE2 on the processes of mesenchymal stem cell commitment to chondrogenesis and ultimate chondrocyte maturation.

Do cyclooxygenase-2 knockout mice have primary hyperparathyroidism?

The absence of cyclooxygenase-2 (COX-2) activity in vitro reduces differentiation of both bone-forming and bone-resorbing cells. To examine the balance of COX-2 effects on bone in vivo, we studied COX-2 knockout (KO) and wild-type (WT) mice. After weaning, KO mice died 4 times faster than WT mice, consistent with reports of progressive renal failure in KO mice. Among KO mice killed at 4 months of age, some had renal failure with marked secondary hyperparathyroidism, but others appeared healthy. On the assumption that renal failure was not inevitable in COX-2 KO mice and that phenotypic differences might increase with age, we studied KO mice surviving to 10 months of age with serum creatinine levels similar to those of WT mice. In 10-month-old male KO mice, serum calcium and PTH, but not phosphorus, levels were increased compared with those in WT mice. 1,25-Dihydroxyvitamin D(3) levels were markedly elevated in KO mice. Skeletal analysis showed small nonsignificant decreases in cortical bone density by BMD and either an increase (distal femur, by microcomputed tomography) or no difference (distal femur, by static histomorphometry) in trabecular bone density in KO mice. There was a trend toward increased percent osteoblastic and osteoclastic surfaces, and on dynamic histomorphometry, the rates of trabecular bone formation and mineral apposition were increased in KO mice relative to WT mice. Similar trends were observed for most parameters in 10-month-old female COX-2 KO mice. However, rates of trabecular bone formation and mineral apposition were increased in 10-month-old WT females compared with males and did not increase further in female KO mice. These data suggest that COX-2 KO mice with intact renal function have primary hyperparathyroidism, and that effects of increased PTH and 1,25-dihydroxyvitamin D(3) to increase bone turnover may compensate for the absence of COX-2.

Production of prostaglandin D(2) by human osteoblasts and modulation of osteoprotegerin, RANKL, and cellular migration by DP and CRTH2 receptors

Human osteoblasts produce PGD(2), which acts on the DP receptor to decrease osteoprotegerin production and on the CRTH2 receptor to decrease RANKL expression and to induce osteoblast chemotaxis. These results indicate that activation of CRTH2 may lead to an anabolic response in bone.

INTRODUCTION

Whereas the actions of prostaglandin (PG)E(2) as a modulator of bone and osteoblast function are relatively well characterized, little is known about PGD(2) and bone metabolism. The objectives of this study were to determine if human osteoblasts can produce PGD(2), which prostaglandin D(2) synthases are implicated in this synthesis, to identify the PGD(2) receptors (DP and CRTH2) on these cells and to characterize the biological effects resulting from their activation.

MATERIALS AND METHODS

RT-PCR analysis and immunohistochemistry were used to detect PGD(2) receptor and synthases in cultured human osteoblasts. Immunohistochemistry was used to identify the synthases and receptors in human bone tissue. Intracellular cAMP and calcium levels were determined to verify receptor activation. The cells were stimulated with PGD(2) or the specific agonists BW 245C (DP) and DK-PGD(2) (CRTH2), and the resulting effects on osteoprotegerin (OPG) secretion, RANKL expression, and chemotaxis were determined. Osteoblast production of PGD(2) was evaluated by measuring PGD(2) in the culture supernatants after stimulation with interleukin (IL)-1, TNF-alpha, PTH, vascular endothelial growth factor (VEGF), and insulin-like growth factor I (IGF-I).

RESULTS

Human osteoblasts in culture generated PGD(2) when stimulated. Both osteoblasts in culture and in situ present the lipocalin-type PGD(2) synthase only. Both DP and CRTH2 receptors were present in human osteoblasts in culture and in situ. Stimulation of DP resulted in an increase in cAMP, whereas CRTH2 increased the intracellular calcium level. OPG production was reduced by 60% after DP receptor stimulation, whereas CRTH2 receptor stimulation decreased RANKL expression on human osteoblasts. As reported for other cell types, CRTH2 was a potent inducer of chemotaxis for human osteoblasts in culture.

CONCLUSIONS

Human osteoblasts in culture produce PGD(2) under biologically relevant stimuli through the lipocalin-type PGD(2) synthase (L-PGDS) pathway. As an autacoid, PGD(2) can act on DP and CRTH2 receptors, both present on these cells. Specific activation of CRTH2 could lead directly and indirectly to an anabolic response in bone.