Treating skeletal pain: limitations of conventional anti-inflammatory drugs, and anti-neurotrophic factor as a possible alternative

Dual aldehyde cross-linked hyaluronic acid hydrogels loaded with PRP and NGF biofunctionalized PEEK interfaces to enhance osteogenesis and vascularization

Polyetheretherketone (PEEK) material has become a potential bone replacement material due to its elastic modulus, which is close to that of human bone, and stable chemical properties. However, its biological inertness has hindered its clinical application. To improve the biological inertia of PEEK material, a hyaluronic acid (HA) hydrogel coating loaded with platelet-rich plasma (PRP) and nerve growth factor (NGF) was constructed on the surface of PEEK material in this study. After the hybrid hydrogel coating was constructed, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), degradation tests, and enzyme-linked immunosorbent assays (ELISAs) were used to evaluate its characteristics and biological properties. The osteogenic and angiogenic potentials were also investigated in vitro and in vivo. Our results showed that the HA hydrogel loaded with RPP and NGF on the PEEK surface degraded slowly and could sustainably release various growth factors, including NGF. The results of in vitro tests showed that the hybrid hydrogel on the surface of PEEK effectively promoted osteogenesis and angiogenesis. The in vivo experiment also confirmed that the PEEK surface hydrogel could promote osseointegration of the implant and the integration of new bone and neovascularization. Our results suggest that the cross-linked hyaluronic acid hydrogel loaded with PRP and NGF can significantly improve the biological inertia of PEEK material, endowing PEEK material with good osteogenic and angiogenic ability.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

Ibuprofen does not impair skeletal muscle regeneration upon cardiotoxin-induced injury

Muscle regeneration is regulated through interaction between muscle and immune cells. Studies showed that treatment with supra-physiological doses of Non-Steroidal Anti-Inflammatory Drug (NSAID) abolished inflammatory signaling and impaired muscle recovery. The present study examines the effects of pharmacologically-relevant NSAID treatment on muscle regeneration. C57BL/6 mice were injected in the tibialis anterior (TA) with either PBS or cardiotoxin (CTX). CTX-injected mice received ibuprofen (CTX-IBU) or were untreated (CTX-PLAC). After 2 days, Il-1beta and Il-6 expression was upregulated in the TA of CTX-IBU and CTX-PL vs. PBS. However, Cox-2 expression and macrophage infiltration were higher in CTX-PL vs. PBS, but not in CTX-IBU. At the same time, anabolic markers were higher in CTX-IBU vs. PBS, but not in CTX-PL. Nevertheless, ibuprofen did not affect muscle mass or muscle fiber regeneration. In conclusion, mild ibuprofen doses did not worsen muscle regeneration. There were even signs of a transient improvement in anabolic signaling and attenuation of inflammatory signaling.

How faithfully does intramembranous bone regeneration recapitulate embryonic skeletal development?

Postnatal intramembranous bone regeneration plays an important role during a wide variety of musculoskeletal regeneration processes such as fracture healing, joint replacement and dental implant surgery, distraction osteogenesis, stress fracture healing, and repair of skeletal defects caused by trauma or resection of tumors. The molecular basis of intramembranous bone regeneration has been interrogated using rodent models of most of these conditions. These studies reveal that signaling pathways such as Wnt, TGFβ/BMP, FGF, VEGF, and Notch are invoked, reminiscent of embryonic development of membranous bone. Discoveries of several skeletal stem cell/progenitor populations using mouse genetic models also reveal the potential sources of postnatal intramembranous bone regeneration. The purpose of this review is to compare the underlying molecular signals and progenitor cells that characterize embryonic development of membranous bone and postnatal intramembranous bone regeneration.

Osteoblast derived-neurotrophin‑3 induces cartilage removal proteases and osteoclast-mediated function at injured growth plate in rats

Faulty bony repair causes dysrepair of injured growth plate cartilage and bone growth defects in children; however, the underlying mechanisms are unclear. Recently, we observed the prominent induction of neurotrophin‑3 (NT-3) and its important roles as an osteogenic and angiogenic factor promoting the bony repair. The current study investigated its roles in regulating injury site remodelling. In a rat tibial growth plate drill-hole injury repair model, NT-3 was expressed prominently in osteoblasts at the injury site. Recombinant NT-3 (rhNT-3) systemic treatment enhanced, but NT-3 immunoneutralization attenuated, expression of cartilage-removal proteases (MMP-9 and MMP-13), presence of bone-resorbing osteoclasts and expression of osteoclast protease cathepsin K, and remodelling at the injury site. NT-3 was also highly induced in cultured mineralizing rat bone marrow stromal cells, and the conditioned medium augmented osteoclast formation and resorptive activity, an ability that was blocked by presence of anti-NT-3 antibody. Moreover, NT-3 and receptor TrkC were induced during osteoclastogenesis, and rhNT-3 treatment activated TrkC downstream kinase Erk1/2 in differentiating osteoclasts although rhNT-3 alone did not affect activation of osteoclastogenic transcription factors NF-κB or NFAT in RAW_264.7 osteoclast precursor cells. Furthermore, rhNT-3 treatment increased, but NT-3 neutralization reduced, expression of osteoclastogenic cytokines (RANKL, TNF-α, and IL-1) in mineralizing osteoblasts and in growth plate injury site, and rhNT-3 augmented the induction of these cytokines caused by RANKL treatment in RAW_264.7 cells. Thus, injury site osteoblast-derived NT-3 is important in promoting growth plate injury site remodelling, as it induces cartilage proteases for cartilage removal and augments osteoclastogenesis and resorption both directly (involving activing Erk1/2 and substantiating RANKL-induced increased expression of osteoclastogenic signals in differentiating osteoclasts) and indirectly (inducing osteoclastogenic signals in osteoblasts).

Nonsteroidal Anti-Inflammatory Drugs and Bone-Healing: A Systematic Review of Research Quality

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are often avoided by orthopaedic surgeons because of their possible influence on bone-healing. This belief stems from multiple studies, in particular animal studies, that show delayed bone-healing or nonunions associated with NSAID exposure. The purpose of this review was to critically analyze the quality of published literature that evaluates the impact of NSAIDs on clinical bone-healing.

METHODS

A MEDLINE and Embase search was conducted to identify all articles relating to bone and fracture-healing and the utilization of NSAIDs. All human studies, including review articles, were identified for further analysis. Non-English-language manuscripts and in vitro and animal studies were excluded. A total of twelve clinical articles and twenty-four literature reviews were selected for analysis. The quality of the clinical studies was assessed with a modified Coleman Methodology Score with emphasis on the NSAID utilization. Review articles were analyzed with regard to variability in the cited literature and final conclusions.

RESULTS

The mean modified Coleman Methodology Score (and standard deviation) was significantly lower (p = 0.032) in clinical studies that demonstrated a negative effect of NSAIDs on bone-healing (40.0 ± 14.3 points) compared with those that concluded that NSAIDs were safe (58.8 ± 10.3 points). Review articles also demonstrated substantial variability in the number of cited clinical studies and overall conclusions. There were only two meta-analyses and twenty-two narrative reviews. The mean number (and standard deviation) of clinical studies cited was significantly greater (p = 0.008) for reviews that concluded that NSAIDs were safe (8.0 ± 4.8) compared with those that recommended avoiding them (2.1 ± 2.1). Unanimously, all reviews admitted to the need for prospective randomized controlled trials to help clarify the effects of NSAIDs on bone-healing.

CONCLUSIONS

This systematic literature review highlights the great variability in the interpretation of the literature addressing the impact of NSAIDs on bone-healing. Unfortunately, there is no consensus regarding the safety of NSAIDs following orthopaedic procedures, and future studies should aim for appropriate methodological designs to help to clarify existing discrepancies to improve the quality of care for orthopaedic patients.

CLINICAL RELEVANCE

This systematic review highlights the limitations in the current understanding of the effects of NSAIDs on bone healing. Thus, withholding these medications does not have any proven scientific benefit to patients and may even cause harm by increasing narcotic requirements in cases in which they could be beneficial for pain management. This review should encourage further basic-science and clinical studies to clarify the risks and benefits of anti-inflammatory medications in the postoperative period, with the aim of improving patient outcomes.

Roles of neurotrophins in skeletal tissue formation and healing

Neurotrophins and their receptors are key molecules that are known to be critical in regulating nervous system development and maintenance and have been recognized to be also involved in regulating tissue formation and healing in skeletal tissues. Studies have shown that neurotrophins and their receptors are widely expressed in skeletal tissues, implicated in chondrogenesis, osteoblastogenesis, and osteoclastogenesis, and are also involved in regulating tissue formation and healing events in skeletal tissue. Increased mRNA expression for neurotrophins NGF, BDNF, NT-3, and NT-4, and their Trk receptors has been observed in injured bone tissues, and NT-3 and its receptor, TrkC, have been identified to have the highest induction at the injury site in a drill-hole injury repair model in both bone and the growth plate. In addition, NT-3 has also recently been shown to be both an osteogenic and angiogenic factor, and this neurotrophin can also enhance expression of the key osteogenic factor, BMP-2, as well as the major angiogenic factor, VEGF, to promote bone formation, vascularization, and healing of the injury site. Further studies, however, are needed to investigate if different neurotrophins have differential roles in skeletal repair, and if NT-3 can be a potential target of intervention for promoting bone fracture healing.

Neurotrophin-3 Induces BMP-2 and VEGF Activities and Promotes the Bony Repair of Injured Growth Plate Cartilage and Bone in Rats

Injured growth plate is often repaired by bony tissue causing bone growth defects, for which the mechanisms remain unclear. Because neurotrophins have been implicated in bone fracture repair, here we investigated their potential roles in growth plate bony repair in rats. After a drill-hole injury was made in the tibial growth plate and bone, increased injury site mRNA expression was observed for neurotrophins NGF, BDNF, NT-3, and NT-4 and their Trk receptors. NT-3 and its receptor TrkC showed the highest induction. NT-3 was localized to repairing cells, whereas TrkC was observed in stromal cells, osteoblasts, and blood vessel cells at the injury site. Moreover, systemic NT-3 immunoneutralization reduced bone volume at injury sites and also reduced vascularization at the injured growth plate, whereas recombinant NT-3 treatment promoted bony repair with elevated levels of mRNA for osteogenic markers and bone morphogenetic protein (BMP-2) and increased vascularization and mRNA for vascular endothelial growth factor (VEGF) and endothelial cell marker CD31 at the injured growth plate. When examined in vitro, NT-3 promoted osteogenesis in rat bone marrow stromal cells, induced Erk1/2 and Akt phosphorylation, and enhanced expression of BMPs (particularly BMP-2) and VEGF in the mineralizing cells. It also induced CD31 and VEGF mRNA in rat primary endothelial cell culture. BMP activity appears critical for NT-3 osteogenic effect in vitro because it can be almost completely abrogated by co-addition of the BMP inhibitor noggin. Consistent with its angiogenic effect in vivo, NT-3 promoted angiogenesis in metatarsal bone explants, an effect abolished by co-treatment with anti-VEGF. This study suggests that NT-3 may be an osteogenic and angiogenic factor upstream of BMP-2 and VEGF in bony repair, and further studies are required to investigate whether NT-3 may be a potential target for preventing growth plate faulty bony repair or for promoting bone fracture healing. © 2016 American Society for Bone and Mineral Research.

Inhibition of COX1/2 alters the host response and reduces ECM scaffold mediated constructive tissue remodeling in a rodent model of skeletal muscle injury

Extracellular matrix (ECM) has been used as a biologic scaffold material to both reinforce the surgical repair of soft tissue and serve as an inductive template to promote a constructive tissue remodeling response. Success of such an approach is dependent on macrophage-mediated degradation and remodeling of the biologic scaffold. Macrophage phenotype during these processes is a predictive factor of the eventual remodeling outcome. ECM scaffolds have been shown to promote an anti-inflammatory or M2-like macrophage phenotype in vitro that includes secretion of downstream products of cycolooxygenases 1 and 2 (COX1/2). The present study investigated the effect of a common COX1/2 inhibitor (Aspirin) on macrophage phenotype and tissue remodeling in a rodent model of ECM scaffold treated skeletal muscle injury. Inhibition of COX1/2 reduced the constructive remodeling response by hindering myogenesis and collagen deposition in the defect area. The inhibited response was correlated with a reduction in M2-like macrophages in the defect area. The effects of Aspirin on macrophage phenotype were corroborated using an established in vitro macrophage model which showed a reduction in both ECM induced prostaglandin secretion and expression of a marker of M2-like macrophages (CD206). These results raise questions regarding the common peri-surgical administration of COX1/2 inhibitors when biologic scaffold materials are used to facilitate muscle repair/regeneration.

STATEMENT OF SIGNIFICANCE

COX1/2 inhibitors such as nonsteroidal anti-inflammatory drugs (NSAIDs) are routinely administered post-surgically for analgesic purposes. While COX1/2 inhibitors are important in pain management, they have also been shown to delay or diminish the healing process, which calls to question their clinical use for treating musculotendinous injuries. The present study aimed to investigate the influence of a common NSAID, Aspirin, on the constructive remodeling response mediated by an ECM scaffold (UBM) in a rat skeletal muscle injury model. The COX1/2 inhibitor, Aspirin, was found to mitigate the ECM scaffold-mediated constructive remodeling response both in an in vitro co-culture system and an in vivo rat model of skeletal muscle injury. The results presented herein provide data showing that NSAIDs may significantly alter tissue remodeling outcomes when a biomaterial is used in a regenerative medicine/tissue engineering application. Thus, the decision to prescribe NSAIDs to manage the symptoms of inflammation post-ECM scaffold implantation should be carefully considered.

NGF/TrkA Signaling as a Therapeutic Target for Pain

Nerve growth factor (NGF) was first discovered approximately 60 years ago by Rita Levi-Montalcini as a protein that induces the growth of nerves. It is now known that NGF is also associated with Alzheimer's disease and intractable pain, and hence, it, along with its high-affinity receptor, tropomyosin receptor kinase (Trk) A, is considered to be 1 of the new targets for therapies being developed to treat these diseases. Anti-NGF antibody and TrkA inhibitors are known drugs that suppress NGF/TrkA signaling, and many drugs of these classes have been developed thus far. Interestingly, local anesthetics also possess TrkA inhibitory effects. This manuscript describes the development of an analgesic that suppresses NGF/TrkA signaling, which is anticipated to be 1 of the new methods to treat intractable pain.

NSAIDs and fracture healing

PURPOSE OF REVIEW

Published data raise concerns about the use of nonselective NSAIDs and selective cyclo-oxygenase (COX)-2 inhibitors as anti-inflammatory or analgesic drugs in patients after a recent fracture or who are undergoing (uncemented) arthroplasty or osteotomy. However, clinical reports on the effect of COX-2 inhibition on fracture healing in humans have been variable and inconclusive. This review gives an overview of the published data and an advice when to avoid NSAIDs.

RECENT FINDINGS

Prostaglandins play an important role as mediators of inflammation and COX are required for their production. Inflammation is an essential step in the fracture healing process in which prostaglandin production by COX-2 is involved. Data from animal studies suggest that NSAIDs, which inhibit COX-2, can impair fracture healing due to the inhibition of the endochondral ossification pathway. Animal data suggest that the effects of COX-2 inhibitors are dependent on the timing, duration, and dose, and that these effects are reversible.

SUMMARY

These animal data, together with the view of limited scientifically robust clinical evidence in humans, indicate that physicians consider only short-term administration of COX-2 inhibitors or other drugs in the pain management of patients who are in the phase of fracture or other bone defect healing. COX-2-inhibitors should be considered a potential risk factor for fracture healing, and therefore to be avoided in patients at risk for delayed fracture healing.

Potential benefits of green tea polyphenol EGCG in the prevention and treatment of vascular inflammation in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the joints in which systemic overproduction of pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) may accelerate cardiovascular (CV) complications. Synovial inflammation in RA spreads systemically and transforms silently into chronic inflammation manifested by increased cytokine release and abnormally high levels of acute reactive proteins (ARPs) such as C-reactive protein (CRP), suggesting inflammation as a connecting link between RA and CV dysfunction. While the treatment to improve CV function in RA patients is being validated, it is timely to propose and test two-pronged therapies that ameliorate arthritis concomitant to improving CV functions. In this review, we summarized the pre-clinical and clinical studies validating the cardiovascular and anti-rheumatic activities of epigallocatechin-3 gallate (EGCG), a potent anti-inflammatory molecule found in green tea. The review also draws many parallels that have emerged between the paradigm of cytokine-driven inflammation in the pathogenesis of RA and its CV complications. Finally, based on extensive clinical evidence of the 'synovial inflammation-systemic inflammation' link and the benefits of EGCG in regulating these two pathologies via common driving factors, authors put forward an argument that EGCG may be tested for its potential CV benefit along with anti-rheumatic activity in animal models of human RA.

Each type of cause that initiates rheumatoid arthritis or RA flares differentially affects the response to therapy

The autoimmune disease rheumatoid arthritis (RA) presents difficulty in diagnosis, commonly observed flare ups, polycyclical nature of RA progression, and variable response to therapies. Congruent with multiple causes, literature has documented various infectious agents, environmental factors, physical trauma, silica and food sensitivities as potential causes of RA or RA flares in different populations. We propose that these>36 events can initiate RA or RA flares which complicates treatment decisions. Each pharmaceutical medicine benefits 15-82% of RA patients. Predictive factors are needed. Because the initiating cause of RA or RA flare affects the type of joint damage, initial inflammatory response, adaptive immune response, and potential molecular mimicry, we propose the "RA cause affects response to therapy" (RACART) theory. The potential cause combined with confounding factors such as genetic risk factors, nutritional status, epigenetic status, inflammatory levels, and detoxification ability may help predict responses to various therapies.

Harnessing and modulating inflammation in strategies for bone regeneration

Inflammation is an immediate response that plays a critical role in healing after fracture or injury to bone. However, in certain clinical contexts, such as in inflammatory diseases or in response to the implantation of a biomedical device, the inflammatory response may become chronic and result in destructive catabolic effects on the bone tissue. Since our previous review 3 years ago, which identified inflammatory signals critical for bone regeneration and described the inhibitory effects of anti-inflammatory agents on bone healing, a multitude of studies have been published exploring various aspects of this emerging field. In this review, we distinguish between regenerative and damaging inflammatory processes in bone, update our discussion of the effects of anti-inflammatory agents on bone healing, summarize recent in vitro and in vivo studies demonstrating how inflammation can be modulated to stimulate bone regeneration, and identify key future directions in the field.

Sustained blockade of neurotrophin receptors TrkA, TrkB and TrkC reduces non-malignant skeletal pain but not the maintenance of sensory and sympathetic nerve fibers

Current therapies for treating skeletal pain have significant limitations as available drugs (non-steroidal anti-inflammatory drugs and opiates) have significant unwanted side effects. Targeting nerve growth factor (NGF) or its cognate receptor tropomysin receptor kinase A (TrkA) has recently become an attractive target for inhibition of adult skeletal pain. Here we explore whether sustained administration of a selective small molecule Trk inhibitor that blocks TrkA, TrkB and TrkC kinase activity with nanomolar affinity reduces skeletal pain while allowing the maintenance of sensory and sympathetic neurons in the adult mouse. Twice-daily administration of a Trk inhibitor was begun 1 day post fracture and within 8 h of acute administration fracture pain-related behaviors were reduced by 50% without significant sedation, weight gain or inhibition of fracture healing. Following administration of the Trk inhibitor for 7 weeks, there was no significant decline in the density of unmyelinated or myelinated sensory nerve fibers, sympathetic nerve fibers, measures of acute thermal pain, acute mechanical pain, or general neuromuscular function. The present results suggest that sustained administration of a peripherally selective TrkA, B and C inhibitor significantly reduces skeletal pain without having any obvious detrimental effects on adult sensory and sympathetic nerve fibers or early fracture healing. As with any potential therapeutic advance, understanding whether the benefits of Trk blockade are associated with any risks or unexpected effects will be required to fully appreciate the patient populations that may benefit from this therapeutic approach.

Administration of a tropomyosin receptor kinase inhibitor attenuates sarcoma-induced nerve sprouting, neuroma formation and bone cancer pain

Pain often accompanies cancer and most current therapies for treating cancer pain have significant unwanted side effects. Targeting nerve growth factor (NGF) or its cognate receptor tropomyosin receptor kinase A (TrkA) has become an attractive target for attenuating chronic pain.

In the present report, we use a mouse model of bone cancer pain and examine whether oral administration of a selective small molecule Trk inhibitor (ARRY-470, which blocks TrkA, TrkB and TrkC kinase activity at low nm concentrations) has a significant effect on cancer-induced pain behaviors, tumor-induced remodeling of sensory nerve fibers, tumor growth and tumor-induced bone remodeling. Early/sustained (initiated day 6 post cancer cell injection), but not late/acute (initiated day 18 post cancer cell injection) administration of ARRY-470 markedly attenuated bone cancer pain and significantly blocked the ectopic sprouting of sensory nerve fibers and the formation of neuroma-like structures in the tumor bearing bone, but did not have a significant effect on tumor growth or bone remodeling.

These data suggest that, like therapies that target the cancer itself, the earlier that the blockade of TrkA occurs, the more effective the control of cancer pain and the tumor-induced remodeling of sensory nerve fibers. Developing targeted therapies that relieve cancer pain without the side effects of current analgesics has the potential to significantly improve the quality of life and functional status of cancer patients.