Mechanism and therapeutic effectiveness of nerve growth factor in osteoarthritis pain

N-Acetylcysteine Antagonizes NGF Activation of TrkA through Disulfide Bridge Interaction, an Effect Which May Contribute to Its Analgesic Activity

N-acetylcysteine (NAC), a mucolytic agent and an antidote to acetaminophen intoxication, has been studied in experimental conditions and trials exploring its analgesic activity based on its antioxidant and anti-inflammatory properties. The purpose of this study is to investigate additional mechanisms, namely, the inhibition of nerve growth factor (NGF) and the activation of the Tropomyosin receptor kinase A (TrkA) receptor, which is responsible for nociception. In silico studies were conducted to evaluate dithiothreitol and NAC's interaction with TrkA. We also measured the autophosphorylation of TrkA in SH-SY5Y cells via ELISA to assess NAC's in vitro activity against NGF-induced TrkA activation. The in silico and in vitro tests show that NAC interferes with NGF-induced TrkA activation. In particular, NAC breaks the disulfide-bound Cys 300-345 of TrkA, perturbing the NGF-TrkA interaction and producing a rearrangement of the binding site, inducing a consequent loss of their molecular recognition and spatial reorganization, which are necessary for the induction of the autophosphorylation process. The latter was inhibited by 40% using 20 mM NAC. These findings suggest that NAC could have a role as a TrkA antagonist, an action that may contribute to the activity and use of NAC in various pain states (acute, chronic, nociplastic) sustained by NGF hyperactivity and/or accompanied by spinal cord sensitization.

TissueGene-C induces long-term analgesic effects through regulation of pain mediators and neuronal sensitization in a rat monoiodoacetate-induced model of osteoarthritis pain

OBJECTIVE

TissueGene-C (TG-C), a combination of human allogeneic chondrocytes and irradiated GP2-293 cells engineered to overexpress transforming growth factor-β1 (TGF-β1), has been developed as a novel cell-based gene therapy and a candidate for disease modifying osteoarthritis drug (DMOAD). We aim to investigate analgesic mechanism of TG-C in a pre-clinical animal model with monoiodoacetate (MIA)-induced pain.

DESIGN

We used a rat MIA model of osteoarthritis (OA) pain. We examined that TG-C can regulate pain by inhibiting the upregulation of various pain mediators in both knee joint tissue and dorsal root ganglia (DRG) (n = 112) and alleviating pain behavior (n = 41) and neuronal hyperexcitability in DRG (n = 60), afferent nerve fiber (n = 24), and spinal cord (n = 35).

RESULTS

TG-C significantly alleviated pain-related behavior by restoring altered dynamic weight bearing and reduced mechanical threshold of the affected hindlimb. TG-C significantly suppressed the expression of nerve growth factor (NGF) and calcitonin gene-related peptide (CGRP) in inflamed joint tissue. TG-C significantly suppressed the upregulation of tropomyosin receptor kinase A (TrkA) and nerve injury/regeneration protein (GAP43) and activation of Iba1-positive microglial cells in DRG. TG-C significantly recovered neuronal hyperexcitability by restoring RMP and firing threshold and frequency of DRG neurons, attenuating firing rates of mechanosensitive C- or Aδ-nerve fiber innervating knee joint, and lowering increased miniature and evoked excitatory postsynaptic currents (mEPSCs and eEPSCs) in the spinal cord.

CONCLUSION

Our results demonstrated that TG-C exerted potent analgesic effects in a rat MIA model of OA pain by inhibiting the upregulation of pain mediators and modulating neuronal sensitization.

The multifaceted role of mast cells in joint inflammation and arthritis

OBJECTIVE

To review current knowledge surrounding the role of mast cells in joint inflammation and arthritis.

METHOD

Narrative review.

RESULTS

Mast cells (MCs) are commonly observed in the synovium of the joint, particularly surrounding blood vessels and nerve endings. Some studies have reported increased MC number and degranulation in patients with osteoarthritis (OA). In two studies, MCs were the only immune cell type found in higher concentrations in synovium of OA patients compared to rheumatoid arthritis patients. Activation of MCs in OA includes signaling pathways such as immunoglobulin E/Fc epsilon Receptor 1 (IgE/FcεR1), immunoglobulin G/Fc gamma receptor (IgG/FcγR), complement, and toll-like cell surface receptor-mediated signaling, resulting in context-dependent release of either pro-inflammatory and/or anti-inflammatory mediators within the joint. Activation of MCs results in the release of pro-inflammatory mediators that ultimately contribute to inflammation of the synovium, bone remodeling, and cartilage damage. However, some studies have proposed that MCs can also exhibit anti-inflammatory effects by secreting mediators that inactivate pro-inflammatory cytokines such as interleukin 6 (IL-6).

CONCLUSIONS

MCs may play a role in mediating synovial inflammation and OA progression. However, the mechanisms governing MC activation, the downstream pro- and/or anti-inflammatory effects, and their impact on osteoarthritis pathogenesis remains to be elucidated and requires extensive further study. Furthermore, it is important to establish the pathways of MC activation in OA to determine whether MCs exhibit varying phenotypes as a function of disease stage. Ultimately, such research is needed before understanding whether MCs could be targeted in OA treatments.

Therapeutic Effects of Live Lactobacillus plantarum GKD7 in a Rat Model of Knee Osteoarthritis

Osteoarthritis (OA) is a painful, progressive chronic inflammatory disease marked by cartilage destruction. Certain synovial inflammatory cytokines, such as IL-1β and TNF-α, promote OA inflammation and pain. Lactobacillus spp. is a well-known probiotic with anti-inflammatory, analgesic, antioxidant, and antiosteoporotic properties. This study evaluated the therapeutic effects of a live L. plantarum strain (GKD7) in the anterior cruciate ligament transection (ACLT)-induced OA rat model. The results show that oral administration of live L. plantarum GKD7 improved weight-bearing asymmetry after ACLT surgery. Moreover, micro-computed tomography images and histopathological analysis show that oral live L. plantarum GKD7 improved subchondral bone architecture, protected articular cartilage against ACLT-induced damage, and reduced synovial inflammation. L. plantarum GKD7 also reduced IL-1β and TNF-α production in OA cartilage and synovium. Thus, orally administered live L. plantarum GKD7 appears to effectively slow the progression of OA.

Connection between Mesenchymal Stem Cells Therapy and Osteoclasts in Osteoarthritis

The use of mesenchymal stem cells constitutes a promising therapeutic approach, as it has shown beneficial effects in different pathologies. Numerous in vitro, pre-clinical, and, to a lesser extent, clinical trials have been published for osteoarthritis. Osteoarthritis is a type of arthritis that affects diarthritic joints in which the most common and studied effect is cartilage degradation. Nowadays, it is known that osteoarthritis is a disease with a very powerful inflammatory component that affects the subchondral bone and the rest of the tissues that make up the joint. This inflammatory component may induce the differentiation of osteoclasts, the bone-resorbing cells. Subchondral bone degradation has been suggested as a key process in the pathogenesis of osteoarthritis. However, very few published studies directly focus on the activity of mesenchymal stem cells on osteoclasts, contrary to what happens with other cell types of the joint, such as chondrocytes, synoviocytes, and osteoblasts. In this review, we try to gather the published bibliography in relation to the effects of mesenchymal stem cells on osteoclastogenesis. Although we find promising results, we point out the need for further studies that can support mesenchymal stem cells as a therapeutic tool for osteoclasts and their consequences on the osteoarthritic joint.

Nerve Growth Factor (NGF) Inhibitors and Related Agents for Chronic Musculoskeletal Pain: A Comprehensive Review

Musculoskeletal pain such as osteoarthritis (OA) and low back pain (LBP) are very common and contribute to enormous burden and societal costs, despite dramatic therapeutic advances over recent decades. Novel approaches and targeted therapies are required to satisfy the urgent unmet medical need of musculoskeletal pain relief in both conditions. Nerve growth factor (NGF) inhibitors have utilized novel mechanisms different from conventional drugs, which have a variety of gastrointestinal, cardiac, or renal adverse effects. Several phase 2/3 studies have been accomplished for these drugs, such as tanezumab, fasinumab, and tyrosine receptor kinase A (TrkA) inhibitors. We searched the literature using the PubMed database and clinical trials using ClinicalTrials.gov to identify original papers, meta-analyses as well as ongoing clinical trials assessing the efficacy and safety profile of these drugs. In this narrative review, we briefly overview the disease burden of musculoskeletal pain, the role of NGF signaling and its receptors in the genesis of pain, and the mechanisms of action of inhibitors of NGF signaling and downstream pathways, and then discuss the efficacy and safety of each investigational drug in OA and LBP. Finally, we briefly review two serious adverse effects of NGF inhibitors, namely rapidly progressive OA and sympathetic system effects, and conclude with possible barriers and potential research directions to overcome these.

Emerging and New Treatment Options for Knee Osteoarthritis

Osteoarthritis (OA) is the most prevalent type of arthritis worldwide, resulting in pain and often chronic disability and a significant burden on healthcare systems globally. Non-steroidal anti-inflammatory drugs (NSAIDs), analgesics, intra-articular corticosteroid injections are of little value in the long term, and opioids may have ominous consequences. Radiotherapy of knee OA has no added value. Physical therapy, exercises, weight loss, and lifestyle modifications may give pain relief, improve physical functioning and quality of life. However, no single treatment has regenerating potential for damaged articular cartilage. Due to a better understanding of osteoarthritis, innovative new treatment options have been developed. In this narrative review, we focus on emerging OA knee treatments, relieving symptoms, and regenerating damaged articular cartilage that includes intra-articular human serum albumin, conventional disease-modifying anti-rheumatic drugs (DMARDs), lipid-lowering agents (statin), nerve growth factors antagonists, bone morphogenetic protein, fibroblast growth factors, Platelet-Rich Plasma (PRP), Mesenchymal Stem Cells (MSC), exosomes, interleukin-1 blockers, gene-based therapy, and bisphosphonate.

Targeting Nerve Growth Factor for Pain Management in Osteoarthritis-Clinical Efficacy and Safety

Nerve growth factor (NGF) is a neurotrophin that mediates pain sensitization in pathologic states, including osteoarthritis. In clinical trials, antibodies to NGF reduce pain and improve physical function due to osteoarthritis of the knee or hip and have a long duration of action. Rapidly progressive osteoarthritis is a dose-dependent adverse event with these agents, and additional joint safety signals, such as subchondral insufficiency fractures and increased rates of total joint replacement, are reported. The effects on pain and potential mechanisms behind these joint events both are of considerable importance in the consideration of future use of anti-NGF therapies for osteoarthritis.

Nerve growth factor (NGF) and NGF receptors in mesenchymal stem/stromal cells: Impact on potential therapies

Mesenchymal stem/stromal cells (MSCs) are promising for the treatment of degenerative diseases and traumatic injuries. However, MSC engraftment is not always successful and requires a strong comprehension of the cytokines and their receptors that mediate the biological behaviors of MSCs. The effects of nerve growth factor (NGF) and its two receptors, TrkA and p75NTR, on neural cells are well studied. Increasing evidence shows that NGF, TrkA, and p75NTR are also involved in various aspects of MSC function, including their survival, growth, differentiation, and angiogenesis. The regulatory effect of NGF on MSCs is thought to be achieved mainly through its binding to TrkA. p75NTR, another receptor of NGF, is regarded as a novel surface marker of MSCs. This review provides an overview of advances in understanding the roles of NGF and its receptors in MSCs as well as the effects of MSC‐derived NGF on other cell types, which will provide new insight for the optimization of MSC‐based therapy.

Contribution of nerves within osteochondral channels to osteoarthritis knee pain in humans and rats

OBJECTIVES

Subchondral bone may contribute to knee osteoarthritis (OA) pain. Nerve growth factor (NGF) can stimulate nerve growth through TrkA. We aimed to identify how sensory nerve growth at the osteochondral junction in human and rat knees associates with OA pain.

METHODS

Eleven symptomatic chondropathy cases were selected from people undergoing total knee replacement for OA. Twelve asymptomatic chondropathy cases who had not presented with knee pain were selected post-mortem. OA was induced in rat knees by meniscal transection (MNX) and sham-operated rats were used as controls. Twice-daily oral doses (30 mg/kg) of TrkA inhibitor (AR786) or vehicle were administered from before and up to 28 days after OA induction. Joints were analysed for macroscopic appearances of articular surfaces, OA histopathology and calcitonin gene-related peptide-immunoreactive (CGRP-IR) sensory nerves in medial tibial plateaux, and rats were assessed for pain behaviors.

RESULTS

The percentage of osteochondral channels containing CGRP-IR nerves in symptomatic chondropathy was higher than in asymptomatic chondropathy (difference: 2.5% [95% CI: 1.1-3.7]), and in MNX-than in sham-operated rat knees (difference: 7.8% [95%CI: 1.7-15.0]). Osteochondral CGRP-IR innervation was significantly associated with pain behavior in rats. Treatment with AR786 prevented the increase in CGRP-IR nerves in osteochondral channels and reduced pain behavior in MNX-operated rats. Structural OA was not significantly affected by AR786 treatment.

CONCLUSIONS

CGRP-IR sensory nerves within osteochondral channels are associated with pain in human and rat knee OA. Reduced pathological innervation of the osteochondral junction might contribute to analgesic effects of reduced NGF activity achieved by blocking TrkA.

Histopathological Signatures of the Femoral Head in Patients with Osteonecrosis and Potential Applications in a Multi-Targeted Approach: A Pilot Study

(1) Background: Osteonecrosis (ON) of the femoral head is a disabling disease for which limited treatment options exist. Identifying therapeutic targets of its evolution could provide crucial insights into multi-targeted approaches. The aim of this pilot study was to assess the histopathological features of patients with non-traumatic femoral head (NTFH) and post-traumatic femoral head (PTFH) ON to produce a fresh vision for clinical use. (2) Methods: We got biopsies from patients with different ON stages, according to the ARCO system. Samples from multi-organ donors were used as controls. Histological and immunohistochemical evaluations were performed on the osteochondral unit. (3) Results: The PTFH group displayed several fibrotic reactions, a small stem cell pool and a lower international cartilage repair society (ICRS)-I score than NTFH, which instead presented intact cartilage similar to the controls. Immunostaining for collagen I and autotaxin confirmed these features in the PTFH group, which displayed top levels of MMP-13 involved in cartilage loss and reduced CB-2 in the underlying bone. Both groups manifested a similar pattern of apoptotic and pain mediators. (4) Conclusions: The different histopathological features suggest a multi-disciplinary and multi-targeted approach for ON. Further studies are necessary to measure the effect size to gain clinical evidence.

Noninvasive Mechanical Joint Loading as an Alternative Model for Osteoarthritic Pain

Objective

Mechanisms responsible for osteoarthritic (OA) pain remain poorly understood, and current analgesic therapies are often insufficient. This study was undertaken to characterize and pharmacologically test the pain phenotype of a noninvasive mechanical joint loading model of OA, thus providing an alternative murine model for OA pain.

Methods

The right knees of 12‐week‐old male C57BL/6 mice were loaded at 9N or 11N (40 cycles, 3 times per week for 2 weeks). Behavioral measurements of limb disuse and mechanical and thermal hypersensitivity were acquired before mechanical joint loading and monitored for 6 weeks postloading. The severity of articular cartilage lesions was determined postmortem with the Osteoarthritis Research Society International scoring system. To assess efficacy of various treatments for pain, 9N‐loaded mice were treated for 4 weeks with diclofenac (10 mg/kg), gabapentin (100 mg/kg), or anti–nerve growth factor (anti‐NGF) (3 mg/kg).

Results

Mechanical hypersensitivity and weight bearing worsened significantly in 9N‐loaded mice (n = 8) and 11N‐loaded mice (n = 8) 2 weeks postloading, compared to baseline values and nonloaded controls. Maximum OA scores of ipsilateral knees confirmed increased cartilage lesions in 9N‐loaded mice (mean ± SEM 2.8 ± 0.2; P < 0.001) and 11N‐loaded mice (5.3 ± 0.3; P < 0.001), compared to nonloaded controls (1.0 ± 0.0). Gabapentin and diclofenac restored pain behaviors to baseline values after 2 weeks of daily treatment, and gabapentin was more effective than diclofenac. A single injection of anti‐NGF alleviated nociception 2 days after treatment and remained effective for 2 weeks, with a second dose inducing stronger and more prolonged analgesia.

Conclusion

Our findings show that mechanical joint loading induces OA lesions in mice and a robust pain phenotype that can be reversed using analgesics known to alleviate OA pain in patients. This establishes the use of mechanical joint loading as an alternative model for the study of OA pain.

Contribution of Infrapatellar Fat Pad and Synovial Membrane to Knee Osteoarthritis Pain

Osteoarthritis (OA) is the most common form of joint disease and a major cause of pain and disability in the adult population. Interestingly, there are patients with symptomatic OA displaying pain, while patients with asymptomatic OA that do not experience pain but show radiographic signs of joint damage. Pain is a complex experience integrating sensory, affective, and cognitive processes related to several peripheral and central nociceptive factors besides inflammation. During the last years, the role of infrapatellar fat pad (IFP), other than the synovial membrane, has been investigated as a potential source of pain in OA. Interestingly, new findings suggest that IFP and synovial membrane might act as a functional unit in OA pathogenesis and pain. The present review discuss the role of IFP and synovial membrane in the development of OA, with a particular focus on pain onset and the possible involved mediators that may play a role in OA pathology and pain mechanisms. Inflammation of IFP and synovial membrane may drive peripheral and central sensitization in KOA. Since sensitization is associated with pain severity in knee OA and may potentially contribute to the transition from acute to chronic, persistent pain in knee OA, preventing sensitization would be a potentially effective and novel means of preventing worsening of pain in knee OA.

Emerging therapeutic agents in osteoarthritis

Osteoarthritis (OA) is the most common joint disorder and a leading cause of disability. Current treatments for OA can improve symptoms but do not delay the progression of disease. In the last years, much effort has been devoted to developing new treatments for OA focused on pain control, inflammatory mediators or degradation of articular tissues. Although promising results have been obtained in ex vivo studies and animal models of OA, few of these agents have completed clinical trials. Available clinical data support the interest of nerve growth factor as a target in pain control as well as the disease-modifying potential of inhibitors of Wnt signaling or catabolic enzymes such as aggrecanases and cathepsin K, and anabolic strategies like fibroblast growth factor-18 or cellular therapies. Carefully controlled studies in patients selected according to OA phenotypes and with a long follow-up will help to confirm the relevance of these new approaches as emerging therapeutic treatments in OA.

Proceedings of the signature series symposium "cellular therapies for orthopaedics and musculoskeletal disease proven and unproven therapies-promise, facts and fantasy," international society for cellular therapies, montreal, canada, may 2, 2018

The Signature Series Symposium "Cellular Therapies for Orthopaedics and Musculoskeletal Disease Proven and Unproven Therapies-Promise, Facts and Fantasy" was held as a pre-meeting of the 26^th International Society for Cellular Therapy (ISCT) annual congress in Montreal, Canada, May 2, 2018. This was the first ISCT program that was entirely dedicated to the advancement of cell-based therapies for musculoskeletal diseases. Cellular therapies in musculoskeletal medicine are a source of great promise and opportunity. They are also the source of public controversy, confusion and misinformation. Patients, clinicians, scientists, industry and government share a commitment to clear communication and responsible development of the field. Therefore, this symposium convened thought leaders from around the world in a forum designed to catalyze communication and collaboration to bring the greatest possible innovation and value to patients with musculoskeletal conditions.

Novel treatments for osteoarthritis: an update

Osteoarthritis is the most prevalent chronic joint condition worldwide. The principles of osteoarthritis treatment are to alleviate pain and stiffness as well as maintain function, with current consensus guidelines recommending the use of a combination of conservative measures including physical therapy, analgesia, and surgical interventions such as arthroplasty. In recent years, several pharmacological therapies have emerged as potential alternatives. Although a disease-modifying osteoarthritis drug has yet to be identified, promising results have been reported in recent trials especially with serotonin-norepinephrine reuptake inhibitors, IL-1 antagonists, and antibodies to nerve growth factor. The present review aims to summarize and discuss the latest results of novel treatments for osteoarthritis and potential targets for future research.

Synovial fluid-derived exosomal lncRNA PCGEM1 as biomarker for the different stages of osteoarthritis

OBJECTS

The purpose of this study is to investigate the role of exosomal lncRNAs from plasma and from synovial fluid in patients with osteoarthritis (OA) and to determine their diagnostic value in distinguishing the early stage of OA from progressive stage of OA.

METHODS

Participants were divided into three groups. The control  group included 20 pre-arthritic patients, early OA group included 20 patients in the early OA, and late-stage OA group included 22 patients in the late-stage OA. For all subjects, blood sample from cubital vein and synovial fluid sample from knee joint were collected. Exosomes were extracted by ultracentrifugation. LncRNAs were extracted from exosomes using RNeasy kit, and the expression of several exosomal lncRNAs, including HOTAIR, PCGEM1, and GAS5, was measured using quantitative real-time polymerase chain reaction (qPCR). Also, Spearman's correlation test was performed to determine the correlation between exosomal lncRNA PCGEM1 and WOMAC index. Last, the receiver operating characteristic (ROC) curve was performed to determine the diagnostic value of exosomal lncRNA PCGEM1 in distinguishing the different stages of OA.

RESULTS

First, for plasma, both the expression of exosomes in three groups and the relative expression of exosomal lncRNAs chosen showed no significant difference among three groups, while for synovial fluid sample, the expression of exosomes in early OA and late-stage OA was much markedly higher than that in controls; and the expression of exosomal lncRNA PCGEM1 was markedly higher in late-stage OA than in early OA, and markedly higher in early OA than controls. Both the expression of exosomal lncRNA HOTAIR and GAS5 showed no significant difference among these groups. Second, there was a positive relationship between exosomal lncRNA PCGEM1 and WOMAC Index. Last, ROC curve showed that the area values under the curve of exosomal lncRNA PCGEM1 were 0.879, 0.757, and 0.593, respectively.

CONCLUSION

Our study demonstrated that exosomal lncRNA PCGEM1 might be a powerful indicator in distinguishing the early OA from the late-stage OA.