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

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.

Cyclooxygenase-2 deficiency impairs muscle-derived stem cell-mediated bone regeneration via cellular autonomous and non-autonomous mechanisms

This study investigated the role of cyclooxygenase-2 (COX-2) expression by donor and host cells in muscle-derived stem cell (MDSC)-mediated bone regeneration utilizing a critical size calvarial defect model. We found that BMP4/green fluorescent protein (GFP)-transduced MDSCs formed significantly less bone in COX-2 knock-out (Cox-2KO) than in COX-2 wild-type (WT) mice. BMP4/GFP-transduced Cox-2KO MDSCs also formed significantly less bone than transduced WT MDSCs when transplanted into calvarial defects created in CD-1 nude mice. The impaired bone regeneration in the Cox-2KO MDSCBMP4/GFP group is associated with downregulation of BMP4-pSMAD1/5 signaling, decreased osteogenic differentiation and lowered proliferation capacity after transplantation, compared with WT MDSCBMP4/GFP cells. The Cox-2KO MDSCBMP4/GFP group demonstrated a reduction in cell survival and direct osteogenic differentiation in vitro These effects were mediated in part by the downregulation of Igf1 and Igf2. In addition, the Cox-2KO MDSCBMP4/GFP cells recruited fewer macrophages than the WT MDSC/BMP4/GFP cells in the early phase after injury. We concluded that the bone regeneration capacity of Cox-2KO MDSCs was impaired because of a reduction in cell proliferation and survival capacities, reduction in osteogenic differentiation and a decrease in the ability of the cells to recruit host cells to the injury site.

Effects of Diclofenac Sodium on BMP-induced Inflammation in a Rodent Model

STUDY DESIGN

Prospective in vivo rodent model of bone morphogenetic protein (BMP)-induced inflammation.

OBJECTIVE

To evaluate the effects of the coadministration of the nonsteroidal anti-inflammatory drug, diclofenac, on BMP-induced inflammation using our rodent model.

SUMMARY OF BACKGROUND DATA

The use of BMP-2 is associated with inflammation in the neck and back. We have previously reported on a rodent model of BMP-2-induced inflammation.

METHODS

Seven treatment groups were: Surgery alone; absorbable collagen sponges (ACS) alone; 20 μg rhBMP-2 on ACS with no diclofenac; 20 μg rhBMP-2 on ACS+50 mg diclofenac injections; 20 μg rhBMP-2 on ACS+75 mg diclofenac; 20 μg rhBMP-2 on ACS+100 mg diclofenac; and 20 μg rhBMP-2 on ACS+125 mg diclofenac. Using magnetic resonance imaging, inflammation (soft tissue edema volume) was assessed at 3 hours and at 2, 7, and 14 days after implantation. Western blot analysis, histology, and immunohistochemical staining were performed to compare the inflammatory response between groups. The mass size and tissue density of bone formation were compared between groups using plain radiography.

RESULTS

Soft-tissue edema volumes in all diclofenac-treated groups were significantly lower than those observed in the rhBMP-2 alone. There was no significant difference in soft tissue edema volumes between 4 diclofenac-treated groups. The expression of NF-κB signaling pathway related proteins (p65 and p-p65) were increased in the rhBMP-2+ACS group and decreased in diclofenac treatment groups. Histological findings and immunohistochemical staining were consistent with the Western blot results. There was no significant difference between the rhBMP-2+ACS group and diclofenac treatment groups in terms of the mass size and tissue density of bone formation.

CONCLUSION

Coadministration of diclofenac sodium can reduce the inflammatory response to BMP-2 without impairing heterotopic bone formation in our rodent model of BMP-2-induced inflammation.

LEVEL OF EVIDENCE

N/A.

The Effect of Cyclooxygenase Inhibition on Tendon-Bone Healing in an In Vitro Coculture Model

The effects of cyclooxygenase (COX) inhibition following the reconstruction of the anterior cruciate ligament remain unclear. We examined the effects of selective COX-2 and nonselective COX inhibition on bone-tendon integration in an in vitro model. We measured the dose-dependent effects of ibuprofen and parecoxib on the viability of lipopolysaccharide- (LPS-) stimulated and unstimulated mouse MC3T3-E1 and 3T3 cells, the influence on gene expression at the osteoblast, interface, and fibroblast regions measured by quantitative PCR, and cellular outgrowth assessed on histological sections. Ibuprofen led to a dose-dependent suppression of MC3T3 cell viability, while parecoxib reduced the viability of 3T3 cultures. Exposure to ibuprofen significantly suppressed expression of Alpl (P < 0.01), Bglap (P < 0.001), and Runx2 (P < 0.01), and although parecoxib reduced expression of Alpl (P < 0.001), Fmod (P < 0.001), and Runx2 (P < 0.01), the expression of Bglap was increased (P < 0.01). Microscopic analysis showed a reduction in cellular outgrowth in LPS-stimulated cultures following exposure to ibuprofen and parecoxib. Nonselective COX inhibition and the specific inhibition of COX-2 led to region-specific reductions in markers of calcification and cell viability. We suggest further in vitro and in vivo studies examining the biologic and biomechanical effects of selective and nonselective COX inhibition.

Compensatory cellular reactions to nonsteroidal anti-inflammatory drugs on osteogenic differentiation in canine bone marrow-derived mesenchymal stem cells

The suppressive effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on the bone healing process have remained controversial, since no clinical data have clearly shown the relationship between NSAIDs and bone healing. The aim of this study was to assess the compensatory response of canine bone marrow-derived mesenchymal stem cells (BMSCs) to several classes of NSAIDs, including carprofen, meloxicam, indomethacin and robenacoxib, on osteogenic differentiation. Each of the NSAIDs (10 µM) was administered during 20 days of the osteogenic process with human recombinant IL-1β (1 ng/ml) as an inflammatory stimulator. Gene expression of osteoblast differentiation markers (alkaline phosphatase and osteocalcin), receptors of PGE₂ (EP2 and EP4) and enzymes for prostaglandin (PG) E2 synthesis (COX-1, COX-2, cPGES and mPGES-1) was measured by using quantitative reverse transcription-polymerase chain reaction. Protein production levels of alkaline phosphatase, osteocalcin and PGE₂ were quantified using an alkaline phosphatase activity assay, osteocalcin immunoassay and PGE₂ immunoassay, respectively. Histologic analysis was performed using alkaline phosphatase staining, von Kossa staining and alizarin red staining. Alkaline phosphatase and calcium deposition were suppressed by all NSAIDs. However, osteocalcin production showed no significant suppression by NSAIDs. Gene expression levels of PGE₂-related receptors and enzymes were upregulated during continuous treatment with NSAIDs, while certain channels for PGE₂ synthesis were utilized differently depending on the kind of NSAIDs. These data suggest that canine BMSCs have a compensatory mechanism to restore PGE₂ synthesis, which would be an intrinsic regulator to maintain differentiation of osteoblasts under NSAID treatment.

Selective and non-selective cyclooxygenase inhibitors delay stress fracture healing in the rat ulna

Anti-inflammatory drugs are widely used to manage pain associated with stress fractures (SFxs), but little is known about their effects on healing of those injuries. We hypothesized that selective and non-selective anti-inflammatory treatments would retard the healing of SFx in the rat ulna. SFxs were created by cyclic loading of the ulna in Wistar rats. Ulnae were harvested 2, 4 or 6 weeks following loading. Rats were treated with non-selective NSAID, ibuprofen (30 mg/kg/day); selective COX-2 inhibition, [5,5-dimethyl-3-3 (3 fluorophenyl)-4-(4 methylsulfonal) phenyl-2 (5H)-furanone] (DFU) (2.0 mg/kg/day); or the novel c5a anatagonist PMX53 (10 mg/kg/day, 4 and 6 weeks only); with appropriate vehicle as control. Quantitative histomorphometric measurements of SFx healing were undertaken. Treatment with the selective COX-2 inhibitor, DFU, reduced the area of resorption along the fracture line at 2 weeks, without affecting bone formation at later stages. Treatment with the non-selective, NSAID, ibuprofen decreased both bone resorption and bone formation so that there was significantly reduced length and area of remodeling and lamellar bone formation within the remodeling unit at 6 weeks after fracture. The C5a receptor antagonist PMX53 had no effect on SFx healing at 4 or 6 weeks after loading, suggesting that PMX53 would not delay SFx healing. Both selective COX-2 inhibitors and non-selective NSAIDs have the potential to compromise SFx healing, and should be used with caution when SFx is diagnosed or suspected.

Effects of interleukin-6 ablation on fracture healing in mice

This study examined the impact of an interleukin-6 (IL-6) knockout on fracture healing in terms of histological and biomechanical responses. Following IACUC approval, tibial fractures were produced in 4- to 6-week-old IL-6 knockouts (n = 35) and wild-type mice (n = 36) and harvested along with contralateral limbs at 2 and 6 weeks postsurgery. Histology quantified stage of healing, lymphocyte infiltration, TRAP+ cells, and osteocalcin deposition. Bend testing established maximum load and stiffness. Based on normality assessments, Mann-Whitney U or independent t-tests were used for data analysis using a p-value threshold of 0.05. Stage of healing, lymphocyte infiltration, and osteocalcin deposition were similar for all time points (p ≥ 0.243). TRAP+ cell counts were reduced approximately 10-fold in the knockout at 2 weeks (p = 0.015) but were similar at 6 weeks (p = 0.689). Force-to-failure in knockouts was approximately 40% that of wild-type mice at 2 weeks (p = 0.040) but similar at 6 weeks (p = 0.735). Knockout bone was about 25% less stiff at 2 weeks but approximately 60% stiffer at 6 weeks (p ≥ 0.110). The absence of IL-6 during early fracture healing significantly reduced osteoclastogenesis and impaired callus strength. By 6 weeks, most histological and biomechanical parameters were similar to fractures in wild-type bone.

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.

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.

Potential applications of pulsating joint loading in sports medicine

Because bone is responsive to mechanical loading, pulsating joint loading (PJL), which laterally applies oscillatory mechanical loads to joints, can be explored for preventive conditioning and therapeutic treatments. Herein, the general features of PJL are reviewed, and its potential usage for sports medicine is discussed.