Elevated levels of tumor necrosis factor-α and TNFR1 in recurrent herniated lumbar discs correlate with chronicity of postoperative sciatic pain

The role of TNF-α in osteoporosis, bone repair and inflammatory bone diseases: A review

Tumour necrosis factor alpha (TNF-α) is a pleiotropic cytokine synthesised primarily by mononuclear cells; it has a potent pro-inflammatory effect, playing a crucial role in metabolic, immune, and inflammatory diseases. This cytokine has been studied in various biological systems. In bone tissue, TNF-α plays an integral role in skeletal disorders such as osteoporosis, fracture repair and rheumatoid arthritis through its involvement in regulating the balance between osteoblasts and osteoclasts, mediating inflammatory responses, promoting angiogenesis and exacerbating synovial proliferation. The biological effect TNF-α exerts in this context is determined by a combination of the signalling pathway it activates, the type of receptor it binds, and the concentration and duration of exposure. This review summarises the participation and pathophysiological role of TNF-α in osteoporosis, bone damage repair, chronic immunoinflammatory bone disease and spinal cord injury, and discusses its main mechanisms.

TNFR1/p38αMAPK signaling in Nex + supraspinal neurons regulates estrogen-dependent chronic neuropathic pain

Upregulation of soluble tumor necrosis factor (sTNF) cytokine signaling through TNF receptor 1 (TNFR1) and subsequent neuronal hyperexcitability are observed in both animal models and human chronic neuropathic pain (CNP). Previously, we have shown that estrogen modulates sTNF/TNFR1 signaling in CNP, which may contribute to female prevalence of CNP. The estrogen-dependent role of TNFR1-mediated supraspinal neuronal circuitry in CNP remains unknown. In this study, we interrogated the intersect between supraspinal TNFR1 mediated neuronal signaling and sex specificity by selectively removing TNFR1 in Nex + neurons in adult mice (NexCreERT2::TNFR1f/f). We determined that mechanical hypersensitivity induced by chronic constriction injury (CCI) decreases over time in males, but not in females. Subsequently, we investigated two downstream pathways, p38MAPK and NF-κB, important in TNFR1 signaling and injury response. We detected p38MAPK and NF-κB activation in male cortical tissue; however, p38MAPK phosphorylation was reduced in NexCreERT2::TNFR1f/f males. We observed a similar recovery from acute pain in male mice following CCI when p38αMAPK was knocked out of supraspinal Nex + neurons (NexCreERT2::p38αMAPKf/f), while chronic pain developed in female mice. To explore the intersection between estrogen and inflammation in CNP we used a combination therapy of an estrogen receptor β (ER β) inhibitor with a sTNF/TNFR1 or general p38MAPK inhibitor. We determined both combination therapies lends therapeutic relief to females following CCI comparable to the response evaluated in male mice. These data suggest that TNFR1/p38αMAPK signaling in Nex + neurons in CNP is male-specific and lack of therapeutic efficacy following sTNF inhibition in females is due to ER β interference. These studies highlight sex-specific differences in pathways important to pain chronification and elucidate potential therapeutic strategies that would be effective in both sexes.

Biphasic release of betamethasone from an injectable HA hydrogel implant for alleviating lumbar disc herniation induced sciatica

Epidural steroid injection (ESI) is a common therapeutic approach for managing sciatica caused by lumbar disc herniation (LDH). However, the short duration of therapeutic efficacy and the need for repeated injections pose challenges in LDH treatment. The development of a controlled delivery system capable of prolonging the effectiveness of ESI and reducing the frequency of injections, is highly significant in LDH clinical practice. In this study, we utilized a thiol-ene click chemistry to create a series of injectable hyaluronic acid (HA) based release systems loaded with diphasic betamethasone, including betamethasone dipropionate (BD) and betamethasone 21-phosphate disodium (BP) (BD/BP@HA). BD/BP@HA hydrogel implants demonstrated biocompatibility and biodegradability to matched neuronal tissues, avoiding artificial compression following injection. The sustained release of betamethasone from BD/BP@HA hydrogels effectively inhibited both acute and chronic neuroinflammation by suppressing the nuclear factor kappa-B (NF-κB) pathway. In a mouse model of LDH, the epidural administration of BD/BP@HA efficiently alleviated LDH-induced sciatica for at least 10 days by inhibiting the activation of macrophages and microglia in dorsal root ganglion and spinal dorsal horn, respectively. The newly developed HA hydrogels represent a valuable platform for achieving sustained drug release. Additionally, we provide a simple paradigm for fabricating BD/BP@HA for epidural injection, demonstrating greater and sustained efficiency in alleviating LDH-induced sciatica compared to traditional ESI and displaying potentials for clinical translation. This system has the potential to revolutionize drug delivery for co-delivery of both soluble and insoluble drugs, thereby making a significant impact in the pharmaceutical industry. STATEMENT OF SIGNIFICANCE: Lumbar disc herniation (LDH) is a common degenerative disorder leading to sciatica and spine surgery. Although epidural steroid injection (ESI) is routinely used to alleviate sciatica, the efficacy is short and repeated injections are required. There remains challenging to prolong the efficacy of ESI. Herein, an injectable hyaluronic acid (HA) hydrogel implant by crosslinking acrylated-modified HA (HA-A) with thiol-modified HA (HA-SH) was designed to achieve a biphasic release of betamethasone. The hydrogel showed biocompatibility and biodegradability to match neuronal tissues. Notably, compared to traditional ESI, the hydrogel better alleviated sciatica in vivo by synergistically inhibiting the neuroinflammation in central and peripheral nervous systems. We anticipate the injectable HA hydrogel implant has the potential for clinical translation in treating LDH-induced sciatica.

CD206+ M2-like macrophages protect against intervertebral disc degeneration partially by targeting R-spondin-2

OBJECTIVE

This study aimed to explore the specific function of M2 macrophages in intervertebral disc degeneration (IDD).

METHODS

Intervertebral disc (IVD) samples from normal (n = 4) and IDD (n = 6) patients were collected, and the expression of M2-polarized macrophage marker, CD206, was investigated using immunohistochemical staining. Nucleus pulposus cells (NPCs) in a TNF-α environment were obtained, and a mouse caudal IVD puncture model was established. Mice with Rheb deletions, specifically in the myeloid lineage, were generated and subjected to surgery-induced IDD. IDD-induced damage and cell apoptosis were measured using histological scoring, X-ray imaging, immunohistochemical staining, and TdT-mediated dUTP nick end labeling (TUNEL) assay. Finally, mice and NPCs were treated with R-spondin-2 (Rspo2) or anti-Rspo2 to investigate the role of Rspo2 in IDD.

RESULTS

Accumulation of CD206 in human and mouse IDD tissues was detected. Rheb deletion in the myeloid lineage (RheBcKO) increased the number of CD206+ M2-like macrophages (mean difference 18.6% [15.7-21.6%], P < 0.001), decreased cell apoptosis (mean difference -15.6% [-8.9 to 22.2%], P = 0.001) and attenuated the IDD process in the mouse IDD model. NPCs treated with Rspo2 displayed increased extracellular matrix catabolism and apoptosis; co-culture with a conditioned medium derived from RheBcKO mice inhibited these changes. Anti-Rspo2 treatment in the mouse caudal IVD puncture model exerted protective effects against IDD.

CONCLUSIONS

Promoting CD206+ M2-like macrophages could reduce Rspo2 secretion, thereby alleviating experimental IDD. Rheb deletion may help M2-polarized macrophages accumulate and attenuate experimental IDD partially by inhibiting Rspo2 production. Hence, M2-polarized macrophages and Rspo2 may serve as therapeutic targets for IDD.

Transforming Growth Factor-β-Activated Kinase 1 (TAK1) Mediates Chronic Pain and Cytokine Production in Mouse Models of Inflammatory, Neuropathic, and Primary Pain

The origin of chronic pain is linked to inflammation, characterized by increased levels of proinflammatory cytokines in local tissues and systemic circulation. Transforming growth factor beta-activated kinase 1 (TAK1) is a key regulator of proinflammatory cytokine signaling that has been well characterized in the context of cancer and autoimmune disorders, yet its role in chronic pain is less clear. Here, we evaluated the ability of our TAK1 small-molecule inhibitor, takinib, to attenuate pain and inflammation in preclinical models of inflammatory, neuropathic, and primary pain. Inflammatory, neuropathic, and primary pain was modeled using intraplantar complete Freund's adjuvant (CFA), chronic constriction injury (CCI), and systemic delivery of the catechol-O-methyltransferase (COMT) inhibitor OR486, respectively. Behavioral responses evoked by mechanical and thermal stimuli were evaluated in separate groups of mice receiving takinib or vehicle prior to pain induction (baseline) and over 12 days following CFA injection, 4 weeks following CCI surgery, and 6 hours following OR486 delivery. Hindpaw edema was also measured prior to and 3 days following CFA injection. Upon termination of behavioral experiments, dorsal root ganglia (DRG) were collected to measure cytokines. We also evaluated the ability of takinib to modulate nociceptor activity via in vitro calcium imaging of neurons isolated from the DRG of Gcamp3 mice. In all 3 models, TAK1 inhibition significantly reduced hypersensitivity to mechanical and thermal stimuli and expression of proinflammatory cytokines in DRG. Furthermore, TAK1 inhibition significantly reduced the activity of tumor necrosis factor (TNF)-primed/capsaicin-evoked DRG nociceptive neurons. Overall, our results support the therapeutic potential of TAK1 as a novel drug target for the treatment of chronic pain syndromes with different etiologies. PERSPECTIVE: This article reports the therapeutic potential of TAK1 inhibitors for the treatment of chronic pain. This new treatment has the potential to provide a greater therapeutic offering to physicians and patients suffering from chronic pain as well as reduce the dependency on opioid-based pain treatments.

The Effect of Melatonin on Radicular Pain in a Rat Model of Lumbar Disc Herniation

STUDY DESIGN

Controlled, randomized, animal study.

OBJECTIVE

To investigate the effect of melatonin and its receptors on radicular pain and the possible mechanisms.

SUMMARY OF BACKGROUND DATA

Lumbar disc herniation (LDH) may induce radicular pain, but the mechanism is not clear and therapeutic effect is still poor. Previously we report central sensitization meaning potentiation of spinal nociceptive synaptic transmission is the critical cause of radicular pain. Melatonin (Mel) has been reported to promote hippocampal synaptic transmission and thus improve learning ability. But the effect of Mel on spinal synaptic transmission and radicular pain are not clear.

METHODS

Rat LDH model was induced by autologous nucleus pulposus (NP) implantation. Melatonin was delivered intraperitoneally four times a day, from day 1 to day 3 after surgery. Melatonin receptor agonist and antagonists were delivered intrathecally for 3 days as well. Mechanical and thermal pain thresholds were assessed by von Frey filaments and hotplate test respectively. Electrophysiological recording was employed for survey C-fiber evoked field potentials. The protein level of N- methyl-D-aspartate submit 2A (NR2A), NR2B, melatonin receptor 1 (MT1), and receptor 2 (MT2) was evaluated by western blotting. Spinal expression of calcitonin gene related peptides (CGRP), isolectin b4 (IB4), and neurofilament-200 (NF200) was displayed by immunofluorescence staining.

RESULTS

Melatonin significantly increased mechanical and thermal pain thresholds, lasting at least to day 5 after surgery. Melatonin decreased C-fiber evoked field potentials; decreased spinal NR2B protein level; reduced spinal CGRP, and IB4 expression. MT2 was upregulated after NP implantation and was co-localized with neuron and microglia. MT2 receptor agonist simulated the effect of Mel, and both MT receptor broadspectrum antagonist and MT2 specific antagonist abolished the effect of MT2 receptor agonist.

CONCLUSION

Melatonin alleviates radicular pain from LDH by inhibiting central sensitization via binding with its receptor 2, decreasing spinal CGRP, IB4, and NR2B expression.

TNF-ɑ Induces Methylglyoxal Accumulation in Lumbar Herniated Disc of Patients With Radicular Pain

Lumbar disc herniation (LDH) with radicular pain is a common and complicated musculoskeletal disorder. Our previous study showed that LDH-induced methylglyoxal (MG) accumulation contributed to radicular pain. The underlying mechanisms through which MG accumulates are poorly understood. In the present study, we found that both MG and tumor necrosis factor-alpha (TNF-ɑ) levels in the herniated disc of patients with radicular pain were significantly increased, and the activity of Glyoxalase 1 (GLO1), the rate-limiting enzyme that metabolizes MG, was decreased. In rats, the LDH model was mimicked by implantation of autologous nucleus pulposus (NP) to the left lumbar five spinal nerve root. The mechanical allodynia was observed in LDH rats. Besides, MG and TNF-ɑ levels were increased, and GLO1 activity was significantly decreased in the implanted NP. In cultured rat NP cells, stimulation with the inflammatory mediator TNF-ɑ reduced GLO1 activity and expression. These results suggested that TNF-ɑ-induced GLO1 activity decrease contributed to MG accumulation in the herniated disc of patients with radicular pain.

Network Pharmacological Dissection of the Mechanisms of Eucommiae Cortex-Achyranthis Radix Combination for Intervertebral Disc Herniation Treatment

Eucommiae cortex (EC) and Achyranthis radix (AR) are herbal medicines widely used in combination for the treatment of intervertebral disc herniation (IDH). The mechanisms of action of the herbal combination have not been understood from integrative and comprehensive points of view. By adopting network pharmacological methodology, we aimed to investigate the pharmacological properties of the EC-AR combination as a therapeutic agent for IDH at a systematic molecular level. Using the pharmacokinetic information for the chemical ingredients of the EC-AR combination obtained from the comprehensive herbal drug-associated databases, we determined its 31 bioactive ingredients and 68 IDH-related therapeutic targets. By analyzing their enrichment for biological functions, we observed that the targets of the EC-AR combination were associated with the regulation of angiogenesis; cytokine and chemokine activity; oxidative and inflammatory stress responses; extracellular matrix organization; immune response; and cellular processes such as proliferation, apoptosis, autophagy, differentiation, migration, and activation. Pathway enrichment investigation revealed that the EC-AR combination may target IDH-pathology-associated signaling pathways, such as those of cellular senescence and chemokine, neurotrophin, TNF, MAPK, toll-like receptor, and VEGF signaling, to exhibit its therapeutic effects. Collectively, these data provide mechanistic insights into the pharmacological activity of herbal medicines for the treatment of musculoskeletal diseases such as IDH.

Study protocol: effect of infection, Modic and inflammation on clinical outcomes in surgery for radiculopathy (EIMICOR)

BACKGROUND

Evidence indicates that inflammatory processes are involved in radicular pain as well as in resorption of herniated disc tissue. Furthermore there are indications that the presence of vertebral end plate pathology (Modic changes; MC) is associated with a negative effect on inflammation. It is hypothesized that in patients with MC, the (possibly bacterial induced) inflammation will be accompanied by pro inflammatory cytokines that worsen the outcome, and that in patients without MC, the inflammation is accompanied by cytokines that induce a resorption process to accelerate recovery.

METHODS

This prospective cohort study will include 160 lumbar and 160 cervical patients (total of 320), which are scheduled for surgery for either a lumbar or cervical herniated disc with ages between 18 and 75. The main and interaction effects of local bacterial infection (culture), inflammatory cells in disc material (immunohistology), MC (MRI), and blood biomarkers indicating inflammation or infection (blood sample evaluation) will be evaluated. Clinical parameters to be evaluated are leg pain on the 11 point NRS pain scale, Oswestry (lumbar spine) or Neck (cervical spine) Disability Index, Global Perceived Recovery, Womac Questionnaire, and medication status, at baseline, and after 6, 16, 26 and 52 weeks.

DISCUSSION

Gaining insight in the aetiology of pain and discomfort in radiculopathy caused by a herniated disc could lead to more effective management of patients. If the type of inflammatory cells shows to be of major influence on the rate of recovery, new immunomodulating treatment strategies can be developed to decrease the duration and intensity of symptoms. Moreover, identifying a beneficial inflammatory response in the disc through a biomarker in blood could lead to early identification of patients whose herniations will resorb spontaneously versus those that require surgery.

TRIAL REGISTRATION

prospectively enrolled at trialregister.nl, ID: NL8464 .

Sod2 and catalase improve pathological conditions of intervertebral disc degeneration by modifying human adipose-derived mesenchymal stem cells

OBJECTIVE

To investigate if the modification of human adipose-derived mesenchymal stem cells (hADSCs) by the antioxidants superoxide dismutase 2 (Sod2) and catalase (Cat) can attenuate the pathological conditions of intervertebral disc degeneration (IVD).

METHODS

In vitro, MTT assay and qRT-PCR was used to detect cell proliferation and gene expressions in hADSCs transduced with Ad-null (an adenovirus vector containing no transgene expression cassette), Ad-Sod2 (recombinant adenovirus Sod2) and Ad-Cat. IVD mouse models were generated by needle puncture and treated with hADSCs with/without Ad-null/Ad-Sod2/Ad-Cat. X-ray evaluation, magnetic resonance imaging (MRI) analysis, histological analysis, immunohistochemistry, Western blots, ELISAs and qRT-PCR were performed.

RESULTS

hADSCs transduced with Ad-Sod2 and Ad-Cat showed enhanced cell proliferation with the upregulation of SOX9, ACAN, and COL2. In vivo, IVD mice injected with hADSCs showed increased disc height index, MRI index and mean T2 intensities, as well as the attenuated histologic grading of the annulus fibrosus (AF) and NP accompanied by the upregulation of GAG and COL2, which were further improved in the Ad-Sod2 hADSC + IVD and Ad-Cat hADSC + IVD groups. Furthermore, the increased expression of IL-1β, IL-6 and TNF-α was reduced in IVD mice injected with hADSCs. Compared with the hADSC + IVD group, the Ad-Sod2 hADSC/Ad-Cat hADSC + IVD groups had lower expression of pro-inflammatory factors.

CONCLUSION

Modification of hADSCs by the antioxidants Sod2 and Cat improved the pathological condition of intervertebral disc tissues with increased GAG and COL2 expression, as well as reduced inflammation, thereby demonstrating a therapeutic effect in IVD.

Inflammation in the intervertebral disc herniation

Up until fairly recently, it was thought that sciatic pain in the lumbar herniated disc was caused by compression on the nerve root. However, the lumbar herniated disc shows mixed pictures which are difficult to explain by simple mechanical compromise. In recent years various immunology, immunohistochemistry and molecular biology studies have shown that the herniated tissue is not an inert material, but rather it Is biologically very active with the capability of expressing a series of inflammatory mediators: cytokines such as interleukin-1, interleukin-6, interleuquin-8 and tumor necrosis factor being the ones which stand out. The inflammation is not only induced by the chemical irritation of the bioactive substances released by the nucleus pulposus but also by an autoimmune response against itself. Thus, in addition to the mechanical factor, the biomechanical mediation plays an important role in the pathophysiology of sciatic pain and of radiculopathy. Through a review of a wide range of literature, we researched the cellular molecular mediators involved in this inflammatory process around the lumbar herniated disc and its involvement in sciatic pain.

Preclinical ex-vivo Testing of Anti-inflammatory Drugs in a Bovine Intervertebral Degenerative Disc Model

Discogenic low back pain (LBP) is a main cause of disability and inflammation is presumed to be a major driver of symptomatic intervertebral disc degeneration (IDD). Anti-inflammatory agents are currently under investigation as they demonstrated to alleviate symptoms in patients having IDD. However, their underlying anti-inflammatory and regenerative activity is poorly explored. The present study sought to investigate the potential of Etanercept and Tofacitinib for maintaining disc homeostasis in a preclinical intervertebral disc (IVD) organ culture model within IVD bioreactors allowing for dynamic loading and nutrient exchange. Bovine caudal IVDs were cultured in a bioreactor system for 4 days to simulate physiological or degenerative conditions: (1) Phy—physiological loading (0.02–0.2 MPa; 0.2 Hz; 2 h/day) and high glucose DMEM medium (4.5 g/L); (2) Deg+Tumor necrosis factor α (TNF-α)—degenerative loading (0.32–0.5 MPa; 5 Hz; 2 h/day) and low glucose DMEM medium (2 g/L), with TNF-α injection. Etanercept was injected intradiscally while Tofacitinib was supplemented into the culture medium. Gene expression in the IVD tissue was measured by RT-qPCR. Release of nitric oxide (NO), interleukin 8 (IL-8) and glycosaminoglycan (GAG) into the IVD conditioned medium were analyzed. Cell viability in the IVD was assessed using lactate dehydrogenase and ethidium homodimer-1 staining. Immunohistochemistry was performed to assess protein expression of IL-1β, IL-6, IL-8, and collagen type II in the IVD tissue. Etanercept and Tofacitinib downregulated the expression of IL-1β, IL-6, IL-8, Matrix metalloproteinase 1 (MMP1), and MMP3 in the nucleus pulposus (NP) tissue and IL-1β, MMP3, Cyclooxygenase-2 (COX2), and Nerve growth factor (NGF) in the annulus fibrosus (AF) tissue. Furthermore, Etanercept significantly reduced the IL-1β positively stained cells in the outer AF and NP regions. Tofacitinib significantly reduced IL-1β and IL-8 positively stained cells in the inner AF region. Both, Etanercept and Tofacitinib reduced the GAG loss to the level under physiological culture condition. Etanercept and Tofacitinib are able to neutralize the proinflammatory and catabolic environment in the IDD organ culture model. However, combined anti-inflammatory and anabolic treatment may be required to constrain accelerated IDD and relieving inflammation-induced back pain.

The contradictory effect of macrophage-related cytokine expression in lumbar disc herniations: a systematic review

PURPOSE

Sciatic symptoms due to lumbar disc herniation are likely to be caused not solely by mechanical compression of the nerve root, but also by pain-inducing elements from inflammatory processes. Key components in the inflammatory reaction are M1 and M2 macrophages, with the M1 type being associated with pro-inflammatory processes and M2 with anti-inflammatory-processes.

METHOD

The present systematic review summarizes all studies on associations between M1 and M2 macrophages and their related inflammation factors and pain symptoms in lumbar disc herniations. Literature search was performed using an optimally sensitive search string. Studies were selected for inclusion by means of predefined inclusion and exclusion criteria and subsequently graded for risk of bias. A total of 14 studies were included. Overall risk of bias was moderate (8/14), and three studies had high risk of bias and three has low risk of bias.

RESULTS

Regarding M1-related cytokines, high levels of TNF-α, TNFR1, IL-6, IL-8, and IFN-γ were all associated high VAS scores. In contrast, high levels of TNFR2 were associated with lower VAS scores. Moreover, no associations were found for IL-1a and IL-1β. Results regarding M2-related cytokines revealed the opposite: high levels of both IL-4 and IL-10 were associated with lower VAS scores. No associations were established for TGF-β. Moreover, the presence of macrophages (CD68) was negatively associated with VAS scores.

CONCLUSION

While M1-related pro-inflammatory cytokines worsen pain symptoms, M2-related anti-inflammatory cytokines alleviate pain symptoms. Nevertheless, the present evidence is limited, and further research on the underlying pathophysiological mechanism in sciatica is required. These slides can be retrieved under Electronic Supplementary Material.

SFKs/p38 Pathway is Involved in Radicular Pain by Promoting Spinal Expression of Pro-Inflammatory Cytokines in a Rat Model of Lumbar Disc Herniation

STUDY DESIGN

A controlled, randomized, animal study.

OBJECTIVE

The aim of this study was to investigate the role of src-family kinases/p38 pathway in a rat model of lumbar disc herniation (LDH).

SUMMARY OF BACKGROUND DATA

LDH always generates radicular pain, and the mechanism remains unclear. We have reported that spinal src-family kinases (SFKs) may be involved in the process, but the downstream mechanism needs further investigation.

METHODS

LDH was induced by implantation of autologous nucleus pulposus (NP), harvest from the tail, in lumbar 4/5 spinal nerve roots of rat. Von Frey filaments and radiant heat tests were performed to determine mechanical and thermal pain threshold respectively. Basso, Beattie, and Bresnahan (BBB) scale was assessed to test the locomotor function. The protein level of p-SFKs, t-SFKs, p-p38, t-p38 in spinal cord was examined by western blotting analysis. Cellular location of p-p38 was determined by immunochemistry staining. Spinal tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-6 levels were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Rats with NP implantation showed persistent ipsilateral mechanical allodynia and thermal hyperalgesia, which manifested as obvious decrease of paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). BBB scale indicated the locomotor function of hindpaws in rats with NP implantation kept intact. Western blotting and immunohistochemistry staining revealed that phosphorylated SFKs (p-SFKs) and phosphorylated p38 MAPK (p-p38) were sequentially upregulated in ipsilateral spinal dorsal horn, but not in contralateral side of rats with NP. Intrathecal delivery of SFKs inhibitor reduced spinal p-p38 expression. Both SFKs and p38 inhibitors alleviated pain behaviors in a dose-responsive manner without disturbing locomotor function and reduced spinal expression of TNF-α, IL-1β, and IL-6 in rats with NP.

CONCLUSION

Spinal SFKs contribute to radicular pain by activation of p38 MAPK and increasing pro-inflammatory cytokines expression in rats with NP implantation. Targeting SFKs/p38 pathway may be helpful for alleviating radicular pain.

LEVEL OF EVIDENCE

N/A.

Up-regulation of circulating microRNA-17 is associated with lumbar radicular pain following disc herniation

Background

Previous studies suggest that regulatory microRNAs (miRs) may modulate neuro-inflammatory processes. The purpose of the present study was to examine the role of miR-17 following intervertebral disc herniation.

Methods

In a cohort of 97 patients with leg pain and disc herniation verified on MRI, we investigated the association between circulating miR-17 and leg pain intensity. A rat model was used to examine possible changes in miR-17 expression in nucleus pulposus (NP) associated with leak of NP tissue out of the herniated disc. The functional role of miR-17 was addressed by transfection of miR-17 into THP-1 cells (human monocyte cell line).

Results

An association between the level of miR-17 in serum and the intensity of lumbar radicular pain was shown. Up-regulation of miR-17 in the rat NP tissue when applied onto spinal nerve roots and increased release of TNF following transfection of miR-17 into THP-1 cells were also observed. Hence, our data suggest that miR-17 may be involved in the pathophysiology underlying lumbar radicular pain after disc herniation.

Conclusions

We conclude that miR-17 may be associated with the intensity of lumbar radicular pain after disc herniation, possibly through a TNF-driven pro-inflammatory mechanism.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1967-y) contains supplementary material, which is available to authorized users.

Tumor necrosis factor receptor 1 inhibition is therapeutic for neuropathic pain in males but not in females

Tumor necrosis factor (TNF) is a proinflammatory cytokine, which is involved in physiological and pathological processes and has been found to be crucial for pain development. In the current study, we were interested in the effects of blocking Tumor necrosis factor receptor 1 (TNFR1) signaling on neuropathic pain after peripheral nerve injury with the use of transgenic mice and pharmacological inhibition. We have previously shown that TNFR1 mice failed to develop neuropathic pain and depressive symptoms after chronic constriction injury (CCI). To investigate the therapeutic effects of inhibiting TNFR1 signaling after injury, we delivered a drug that inactivates soluble TNF (XPro1595). Inhibition of solTNF signaling resulted in an accelerated recovery from neuropathic pain in males, but not in females. To begin exploring a mechanism, we investigated changes in N-methyl-D-aspartate (NMDA) receptors because neuropathic pain has been shown to invoke an increase in glutamatergic signaling. In male mice, XPro1595 treatment reduces elevated NMDA receptor levels in the brain after injury, whereas in female mice, NMDA receptor levels decrease after CCI. We further show that estrogen inhibits the therapeutic response of XPro1595 in females. Our results suggest that TNFR1 signaling plays an essential role in pain induction after CCI in males but not in females.

Aging of mouse intervertebral disc and association with back pain

With the increased burden of low back pain (LBP) in our globally aging population there is a need to develop preclinical models of LBP that capture clinically relevant features of physiological aging, degeneration, and disability. Here we assess the validity of using a mouse model system for age-related LBP by characterizing aging mice for features of intervertebral disc (IVD) degeneration, molecular markers of peripheral sensitization, and behavioral signs of pain. Compared to three-month-old and one-year-old mice, two-year-old mice show features typical of IVD degeneration including loss of disc height, bulging, innervation and vascularization in the caudal lumbar IVDs. Aging is also associated with the loss of whole-body bone mineral density in both male and female mice, but not associated with percent lean mass or body fat. Additionally, two-year-old mice have an accumulation of TRPA1 channels and sodium channels NaV1.8 and NaV1.9 in the L4 and L5 lumbar dorsal root ganglia consistent with changes in nociceptive signaling. Lastly, the effect of age, sex, and weight on mobility, axial stretching and radiating pain measures was assessed in male and female mice ranging from two months to two years in a general linear model. The model revealed that regardless of sex or weight, increased age was a predictor of greater reluctance to perform axial stretching and sensitivity to cold, but not heat in mice.

Puerarin alleviate radicular pain from lumbar disc herniation by inhibiting ERK-dependent spinal microglia activation

Lumbar disc herniation is a common cause of radicular pain, but the mechanism remains ambiguous and the treatment stays unsatisfied. Many studies revealed a traditional Chinese medicine puerarin may moderate chronic pain from diabetes and nerve injury. Thus far, the role and mechanism of puerarin in radicular pain is still unknown. In this study, by using a rat model of lumbar disc herniation, which was induced by autologous nucleus pulposus (NP) implantation, the analgesic effect of puerarin on radicular pain was tested. Puerarin was delivered intraperitoneally form 1 h before surgery, and once daily for 7 days. The results demonstrated that NP implantation induced long-lasting pain, characterized by decrease of paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) in ipsilateral hindpaws, as long as day 20 after surgery. Spinal phosphorylated extracellular signal-regulated kinase (p-ERK) was up-regulated from day 5 to day 20 after surgery in ipsilateral but not contralateral side, and p-ERK was mainly co-localized with microglia. Puerarin decreased p-ERK expression from day 7 to day 20 after surgery. Puerarin or ERK inhibitor PD98059 alleviated pain behaviors, decreased expression of microglia marker ionized calcium-binding adaptor molecule 1 (Iba-1) in rats with NP implantation. The results suggested puerarin may alleviate radicular pain by inhibiting ERK-dependent or accompanied spinal microglia activation.

An intervertebral disc whole organ culture system to investigate proinflammatory and degenerative disc disease condition

The aim of this study was to compare the effect of different disease initiators of degenerative disc disease (DDD) within an intervertebral disc (IVD) organ culture system and to understand the interplay between inflammation and degeneration in the early stage of DDD. Bovine caudal IVDs were cultured within a bioreactor for up to 11 days. Control group was cultured under physiological loading (0.02-0.2 MPa; 0.2 Hz; 2 hr/day) and high glucose (4.5 g/L) medium. Detrimental loading (0.32-0.5 MPa, 5 Hz; 2 hr/day) and low glucose (2 g/L) medium were applied to mimic the condition of abnormal mechanical stress and limited nutrition supply. Tumour necrosis factor alpha (TNF-α) was injected into the nucleus pulposus (100 ng per IVD) as a proinflammatory trigger. TNF-α combined with detrimental loading and low glucose medium up-regulated interleukin 1β (IL-1β), IL-6, and IL-8 gene expression in disc tissue, nitric oxide, and IL-8 release from IVD, which indicate a proinflammatory effect. The combined initiators up-regulated matrix metalloproteinase 1 gene expression, down-regulated gene expression of Type I collagen in annulus fibrosus and Type II collagen in nucleus pulposus, and reduced the cell viability. Furthermore, the combined initiators induced a degradative effect, as indicated by markedly higher glycosaminoglycan release into conditioned medium. The combination of detrimental dynamic loading, nutrient deficiency, and TNF-α intradiscal injection can synergistically simulate the proinflammatory and degenerative disease condition within DDD. This model will be of high interest to screen therapeutic agents in further preclinical studies for early intervention and treatment of DDD.

Phenylpyridine-2-ylguanidines and rigid mimetics as novel inhibitors of TNFα overproduction: Beneficial action in models of neuropathic pain and of acute lung inflammation

4-phenylpyridin-2-yl-guanidine (5b): a new inhibitor of the overproduction of pro-inflammatory cytokines (TNFα and Il1β) was identified from a high-throughput screening of a chemical library on human peripheral blood mononuclear cells (PBMCs) after LPS stimulation. Derivatives, homologues and rigid mimetics of 5b were designed and synthesized, and their cytotoxicity and ability to inhibit TNFα overproduction were evaluated. Among them, compound 5b and its mimetic 12 (2-aminodihydroquinazoline) showed similar inhibitory activities, and were evaluated in vivo in models of lung inflammation and neuropathic pain in mice. In particular, compound 12 proved to be active (5 mg/kg, ip) in both models.

Efficacy and safety of etanercept in the treatment of sciatica: A systematic review and meta-analysis

Etanercept might be promising to alleviate sciatica caused by lumbar disc herniation and spinal stenosis. However, the results remained controversial. We conducted a systematic review and meta-analysis to evaluate the efficacy of etanercept in patients with sciatica. PubMed, EMbase, Web of science, EBSCO, and Cochrane library databases were systematically searched. Randomized controlled trials (RCTs) and Controlled clinical trials (CCT) assessing the efficacy of etanercept on sciatica caused by lumbar disc herniation and spinal stenosis were included. Two investigators independently searched articles, extracted data, and assessed the quality of included studies. The primary outcome was leg pain scores. Meta-analysis was performed using random-effect model. Four RCTs and one CCT involving 184 patients were included in the meta-analysis. Overall, compared with placebo, etanercept could significantly reduce leg pain (Std. mean difference=-0.83; 95% CI=-1.59 to -0.06; P=0.03) and back pain (Std. mean difference=-1.89; 95% CI=-3.34 to -0.43; P=0.01). However, when comparing etanercept to steroids there was no significant difference in the relief of leg pain (Std. mean difference=-1.18; 95% CI=-3.21 to 0.84; P=0.25) and back pain (Std. mean difference=-0.29; 95% CI=-1.26 to 0.67; P=0.55). Etanercept showed no increase in Oswestry Disability Index (ODI) compared with placebo (Std. mean difference=-0.83; 95% CI=-2.03 to 0.37; P=0.18) and steroids (Std. mean difference=-0.19; 95% CI=-1.15 to 0.77; P=0.70). Etanercept treatment was associated with a significantly reduced pain in leg and back compared to placebo and may possibly improve leg pain relief compared to steroids, but failed to improve ODI. Etanercept should be recommended for sciatica with caution because of heterogeneity.

Tumor necrosis factor-α: a key contributor to intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most common cause leading to low back pain (LBP), which is a highly prevalent, costly, and crippling condition worldwide. Current treatments for IDD are limited to treat the symptoms and do not target the pathophysiology. Tumor necrosis factor-α (TNF-α) is one of the most potent pro-inflammatory cytokines and signals through its receptors TNFR1 and TNFR2. TNF-α is highly expressed in degenerative IVD tissues, and it is deeply involved in multiple pathological processes of disc degeneration, including matrix destruction, inflammatory responses, apoptosis, autophagy, and cell proliferation. Importantly, anti-TNF-α therapy has shown promise for mitigating disc degeneration and relieving LBP. In this review, following a brief description of TNF-α signal transduction, we mainly focus on the expression pattern and roles of TNF-α in IDD, and summarize the emerging progress regarding its inhibition as a promising biological therapeutic approach to disc degeneration and associated LBP. A better understanding will help to develop novel TNF-α-centered therapeutic interventions for degenerative disc disease.

17β-Estradiol Inhibites Tumor Necrosis Factor-α Induced Apoptosis of Human Nucleus Pulposus Cells via the PI3K/Akt Pathway

Background

Tumor necrosis factor-α (TNF-α) has been widely known to induce degeneration of nucleus pulposus cells (NPCs). 17β-estradiol (17β-E2) has been broadly proven for its function of suppressing cell apoptosis. The aim of this study is to explore whether 17β-E2 protects apoptosis of human NPCs induced by TNF-α via the PI3K/AKT pathway.

Material/Methods

NPCs were divided into four groups: control, TNF-α (100 ng/mL), TNF-α (100 ng/mL) with pretreated 17β-E2 (10 um/L), TNF-α (100 ng/mL) with pretreated 17β-E2 (10 um/L) and MK2206 (10 um/L, inhibitor of the PI3K/AKT pathway). Flow cytometry was used to measure the apoptotic incidence. Inverted phase-contrast microscopy was used to accomplish the morphological observation for apoptosis of treated cells. Additionally, Cell Counting Kit 8 (CCK-8) assay was used to detected cell proliferation. Western blot and quantitative real-time PCR (qRT-PCR) were applied to explore the expression of pro-caspase-3, caspase-3/p17, cleaved PARP, PARP, Akt, and phospho-Akt (p-Akt).

Results

First, inverted phase-contrast microscopy, CCK-8, and flow cytometry showed that TNF-α induced marked apoptosis, which was abolished by 17β-E2. Furthermore, Western blot and qRT-PCR showed that 17β-E2 protects TNF-α which can induced apoptosis by upregulating p-Akt, whereas Akt was essentially constant. Our data revealed that p-Akt expression peaked at 24 hours in a time-dependent manner (0–48 hours) after treating with TNF-α; and the p-Akt expression generally increased in a time-dependent manner (0–48 hours) after treating with TNF-α and 17β-E2.

Conclusions

17β-E2 is shown to protect NPCs against TNF-α induced apoptosis by upregulating p-Akt in the PI3K/AKT pathway. 17β-E2 generally increases expression of p-Akt.