The analgesic effect of rolipram is associated with the inhibition of the activation of the spinal astrocytic JNK/CCL2 pathway in bone cancer pain

Discovery of a CCR2-targeting pepducin therapy for chronic pain

Targeting the CCL2/CCR2 chemokine axis has been shown to be effective at relieving pain in rodent models of inflammatory and neuropathic pain, therefore representing a promising avenue for the development of non-opioid analgesics. However, clinical trials targeting this receptor for inflammatory conditions and painful neuropathies have failed to meet expectations and have all been discontinued due to lack of efficacy. To overcome the poor selectivity of CCR2 chemokine receptor antagonists, we generated and characterized the function of intracellular cell-penetrating allosteric modulators targeting CCR2, namely pepducins. In vivo, chronic intrathecal administration of the CCR2-selective pepducin PP101 was effective in alleviating neuropathic and bone cancer pain. In the setting of bone metastases, we found that T cells infiltrate dorsal root ganglia (DRG) and induce long-lasting pain hypersensitivity. By acting on CCR2-expressing DRG neurons, PP101 attenuated the altered phenotype of sensory neurons as well as the neuroinflammatory milieu of DRGs, and reduced bone cancer pain by blocking CD4+ and CD8+ T cell infiltration. Notably, PP101 demonstrated its efficacy in targeting the neuropathic component of bone cancer pain, as evidenced by its anti-nociceptive effects in a model of chronic constriction injury of the sciatic nerve. Importantly, PP101-induced reduction of CCR2 signaling in DRGs did not result in deleterious tumor progression or adverse behavioral effects. Thus, targeting neuroimmune crosstalk through allosteric inhibition of CCR2 could represent an effective and safe avenue for the management of chronic pain.

SPOCK2 modulates neuropathic pain by interacting with MT1-MMP to regulate astrocytic MMP-2 activation in rats with chronic constriction injury

BACKGROUND

Neuropathic pain (NP) is a kind of intractable pain. The pathogenesis of NP remains a complicated issue for pain management practitioners. SPARC/osteonectin, CWCV, and Kazal-like domains proteoglycan 2 (SPOCK2) are members of the SPOCK family that play a significant role in the development of the central nervous system. In this study, we investigated the role of SPOCK2 in the development of NP in a rat model of chronic constriction injury (CCI).

METHODS

Sprague-Dawley rats were randomly grouped to establish CCI models. We examined the effects of SPOCK2 on pain hpersensitivity and spinal astrocyte activation after CCI-induced NP. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were used to reflects the pain behavioral degree. Molecular mechanisms involved in SPOCK2-mediated NP in vivo were examined by western blot analysis, immunofluorescence, immunohistochemistry, and co-immunoprecipitation. In addition, we examined the SPOCK2-mediated potential protein-protein interaction (PPI) in vitro coimmunoprecipitation (Co-IP) experiments.

RESULTS

We founded the expression level of SPOCK2 in rat spinal cord was markedly increased after CCI-induced NP, while SPOCK2 downregulation could partially relieve pain caused by CCI. Our research showed that SPOCK2 expressed significantly increase in spinal astrocytes when CCI-induced NP. In addition, SPOCK2 could act as an upstream signaling molecule to regulate the activation of matrix metalloproteinase-2 (MMP-2), thus affecting astrocytic ERK1/2 activation and interleukin (IL)-1β production in the development of NP. Moreover, in vitro coimmunoprecipitation (Co-IP) experiments showed that SPOCK2 could interact with membrane-type 1 matrix metalloproteinase (MT1-MMP/MMP14) to regulate MMP-2 activation by the SPARC extracellular (SPARC_EC) domain.

CONCLUSIONS

Research shows that SPOCK2 can interact with MT1-MMP to regulate MMP-2 activation, thus affecting astrocytic ERK1/2 activation and IL-1β production to achieve positive promotion of NP.

Targeting the chemokine ligand 2-chemokine receptor 2 axis provides the possibility of immunotherapy in chronic pain

Chronic pain affects patients' physical and psychological health and quality of life, entailing a tremendous public health challenge. Currently, drugs for chronic pain are usually associated with a large number of side effects and poor efficacy. Chemokines in the neuroimmune interface combine with their receptors to regulate inflammation or mediate neuroinflammation in the peripheral and central nervous system. Targeting chemokines and their receptor-mediated neuroinflammation is an effective means to treat chronic pain. In recent years, growing evidence has shown that the expression of chemokine ligand 2 (CCL2) and its main chemokine receptor 2 (CCR2) is involved in its occurrence, development and maintenance of chronic pain. This paper summarises the relationship between the chemokine system, CCL2/CCR2 axis, and chronic pain, and the CCL2/CCR2 axis changes under different chronic pain conditions. Targeting chemokine CCL2 and its chemokine receptor CCR2 through siRNA, blocking antibodies, or small molecule antagonists may provide new therapeutic possibilities for managing chronic pain.

Screening of potential pain genes in pancreatic ductal adenocarcinoma (PDAC) based on bioinformatics methods

Background

We aimed to identify cancer pain genes in pancreatic ductal adenocarcinoma (PDAC) using bioinformatic tools to provide evidence for pain treatment in PDAC patients.

Methods

The GSE50570 data were obtained from the high-throughput Gene Expression Omnibus (GEO) database and subsequently analyzed. A volcano map, principal component analysis (PCA) map, box plot, and heat map were drawn, and a Venn diagram was constructed by comparison with human secreted histone genes. The differentially expressed secreted histone genes in PDAC were obtained. Then, Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed, followed by protein-protein interaction (PPI) network analysis and key genetic screening.

Results

In comparison to normal samples, the expression of 81 secreted protein-related genes was downregulated, and the expression of 12 secreted protein-related genes was upregulated in PDAC. According to the GO and KEGG enrichment analysis results, these differentially expressed genes are mainly involved in the PI3K-Akt signaling pathway, protein digestion and absorption, extracellular matrix (ECM) receptor interaction, AGE-RAGE (advanced glycation endproducts-the Receptor of Advanced Glycation Endproducts) signaling pathway, relaxin signaling pathway, interleukin-17 (IL-17) signaling pathway, and transforming growth factor-β (TGF-β) signaling pathway, affecting the different manifestations of PDAC cancer pain. We used Cytoscape software to construct a protein interaction network of common differentially expressed genes and obtained three clusters with high scores. Our literature review found that several genes, including PTGS2, VCAN, and CCL2, were directly related to cancer pain occurrence.

Conclusions

By data mining the PDAC tumor expression, dozens of differentially expressed genes were identified in this study, several of which have been associated with the frequency and severity of cancer pain. This study provides an important foundation for the pain treatment of PDAC tumor patients.

The role and pharmacological properties of P2Y12 receptor in cancer and cancer pain

The G protein-coupled P2Y12 receptor (P2Y12R) was cloned in platelets and found to play a key role in maintaining platelet function in hemostasis and thrombosis, and these effects could be mediated by the P2Y12R. However, it has recently been found that P2Y12R-mediated the progression of tumor through interactions between platelets and tumor and stromal cells, as well as through products secreted by platelets. During tumor progression, tumor cells or other cells in the tumor microenvironment (such as immune cells) can secrete large amounts of ATP into the extracellular matrix, and extracellular ATP can be hydrolyzed into ADP. ADP is a P2Y12R activator and plays an important regulatory role in the proliferation and metastasis of tumor cells. P2Y12R is involved in platelet-cancer cell crosstalk and become a potential target for anticancer therapy. Moreover, tumor progression can induce pain, which seriously affects the quality of life of patients. P2Y12R is expressed in microglia and mediates the activities of microglial and participates in the occurrence of cancer pain. Conversely, inhibiting P2Y12R activation and down-regulating its expression has the effect of inhibiting tumor progression and pain. Therefore, P2Y12R can be a common therapeutic target for both. In this article, we explored the potential link between P2Y12R and cancer, discussed the intrinsic link of P2Y12R in cancer pain and the pharmacological properties of P2Y12R antagonists in the treatment of both.

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5′-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn’s disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

Anti-interleukin-6 receptor antibody improves allodynia and cognitive impairment in mice with neuropathic pain following partial sciatic nerve ligation

Neuropathic pain caused by nerve injury presents with severe spontaneous pain and a range of comorbidities, including deficits in higher executive functioning, none of which are adequately treated with current analgesics. Interleukin-6 (IL-6), a proinflammatory cytokine, is critically involved in the development and maintenance of central sensitization. However, the roles of IL-6 in neuropathic pain and related comorbidities have yet to be fully clarified. The present study examined the effect of MR16-1, an anti-IL-6 receptor antibody and inhibits IL-6 activity, on allodynia and cognitive impairment in mice with neuropathic pain following partial sciatic nerve ligation (PSNL). Significant upregulation of IL-6 expression was observed in the hippocampus in PSNL mice. Intranasal administration of MR16-1 significantly improved cognitive impairment but not allodynia in PSNL mice. Intranasal MR16-1 blocked PSNL-induced degenerative effects on hippocampal neurons. Intraperitoneal administration of MR16-1 suppressed allodynia but not cognitive impairment of PSNL mice. The findings suggest that cognitive impairment associated with neuropathic pain is mediated through changes in hippocampus induced by IL-6. These data also suggest that IL-6 mediated peripheral inflammation underlies allodynia, and IL-6 mediated inflammation in the central nervous system underlies cognitive impairment associated with neuropathic pain, and further suggest the therapeutic potential of blocking IL-6 functioning by blocking its receptor.

Corydalis decumbens Can Exert Analgesic Effects in a Mouse Neuropathic Pain Model by Modulating MAPK Signaling

Objectives

This study is aimed at investigating the analgesic effect of the administration of Corydalis decumbens (CD) in a mouse model of postherpetic neuralgia (PHN) and at elucidating its mechanism of analgesic action.

Methods

Adult Kunming (KM) mice were randomly divided into control, CD, and vehicle-treated groups. Neuropathic pain was induced with a single intraperitoneal injection of resiniferatoxin (RTX). Thermal hyperalgesia was assessed with a hot/cold plate test, and mechanical allodynia was evaluated using von Frey filaments. The activation states of astrocytes, microglia, and the mitogen-activated protein kinase (MAPK) pathway in the spinal cord were determined by immunofluorescence staining and Western blot analysis of Iba-1, GFAP, phospho-p38, and phospho-Jun N-terminal kinase (JNK).

Results

RTX diminished thermal sensitivity and gradually increased sensitivity to tactile stimulation. The expression of Iba-1, GFAP, phospho-p38 MAPK, and phospho-JNK was upregulated in the RTX-induced postherpetic neuralgia mouse model. Systemic treatment with CD significantly ameliorated thermal sensitivity and mechanical hyperalgesia and was accompanied by a reduction in the expression of Iba-1 and GFAP and reduced phosphorylation of p38 and JNK.

Conclusions

This study suggests that CD is effective at ameliorating mechanical hyperalgesia in PHN mice and that its mechanism of action may involve modulation of MAPK phosphorylation and glial cell activation. Thus, CD may be a promising alternative therapy for PHN.

Inhibition of phosphodiesterase-4 in the spinal dorsal horn ameliorates neuropathic pain via cAMP-cytokine-Cx43 signaling in mice

Background

The spinal phosphodiesterase‐4 (PDE4) plays an important role in chronic pain. Inhibition of PDE4, an enzyme catalyzing the hydrolysis of cyclic adenosine monophosphate AMP (cAMP), produces potent antinociceptive activity. However, the antinociceptive mechanism remains largely unknown. Connexin43 (Cx43), a gap junction protein, has been shown to be involved in controlling pain transduction at the spinal level; restoration of Cx43 expression in spinal astrocytes to the normal levels reduces nerve injury‐induced pain. Here, we evaluate the novel mechanisms involving spinal cAMP‐Cx43 signaling by which PDE4 inhibitors produce antinociceptive activity.

Methods

First, we determined the effect of PDE4 inhibitors rolipram and roflumilast on partial sciatic nerve ligation (PSNL)‐induced mechanical hypersensitivity. Next, we observed the role of cAMP‐Cx43 signaling in the effect of PDE4 inhibitors on PSNL‐induced mechanical hypersensitivity.

Results

Single or repeated, intraperitoneal or intrathecal administration of rolipram or roflumilast significantly reduced mechanical hypersensitivity in mice following PSNL. In addition, repeated intrathecal treatment with either of PDE4 inhibitors reduced PSNL‐induced downregulation of cAMP and Cx43, and upregulation of proinflammatory cytokines tumor necrosis factor‐α (TNF‐α) and interleukin‐1β. Furthermore, the antinociceptive effects of PDE4 inhibitors were attenuated by the protein kinase A (PKA) inhibitor H89, TNF‐α, or Cx43 antagonist carbenoxolone. Finally, PSNL‐induced upregulation of PDE4B and PDE4D, especially the PDE4B subtype, was reduced by treatment with either of the PDE4 inhibitors.

Conclusions

The results suggest that the antinociceptive effect of PDE4 inhibitors is contributed by increasing Cx43 expression via cAMP‐PKA‐cytokine signaling in the spinal dorsal horn.

Antiallodynic action of phosphodiesterase inhibitors in a mouse model of peripheral nerve injury

Neuropathic pain arises as a consequence of a lesion or disease affecting the somatosensory nervous system. It is accompanied by neuronal and non-neuronal alterations, including alterations in intracellular second messenger pathways. Cellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) are regulated by phosphodiesterase (PDE) enzymes. Here, we studied the impact of PDE inhibitors (PDEi) in a mouse model of peripheral nerve injury induced by placing a cuff around the main branch of the sciatic nerve. Mechanical hypersensitivity, evaluated using von Frey filaments, was relieved by sustained treatment with the non-selective PDEi theophylline and ibudilast (AV-411), with PDE4i rolipram, etazolate and YM-976, and with PDE5i sildenafil, zaprinast and MY-5445, but not by treatments with PDE1i vinpocetine, PDE2i EHNA or PDE3i milrinone. Using pharmacological and knock-out approaches, we show a preferential implication of delta opioid receptors in the action of the PDE4i rolipram and of both mu and delta opioid receptors in the action of the PDE5i sildenafil. Calcium imaging highlighted a preferential action of rolipram on dorsal root ganglia non-neuronal cells, through PDE4B and PDE4D inhibition. Rolipram had anti-neuroimmune action, as shown by its impact on levels of the pro-inflammatory cytokine tumor necrosis factor-α (TNFα) in the dorsal root ganglia of mice with peripheral nerve injury, as well as in human peripheral blood mononuclear cells (PBMCs) stimulated with lipopolysaccharides. This study suggests that PDEs, especially PDE4 and 5, may be targets of interest in the treatment of neuropathic pain.

Glial and neuroimmune cell choreography in sexually dimorphic pain signaling

Chronic pain is a major global health issue that affects all populations regardless of sex, age, ethnicity/race, or country of origin, leading to persistent physical and emotional distress and to the loss of patients' autonomy and quality of life. Despite tremendous efforts in the elucidation of the mechanisms contributing to the pathogenesis of chronic pain, the identification of new potential pain targets, and the development of novel analgesics, the pharmacological treatment options available for pain management remain limited, and most novel pain medications have failed to achieve advanced clinical development, leaving many patients with unbearable and undermanaged pain. Sex-specific susceptibility to chronic pain conditions as well as sex differences in pain sensitivity, pain tolerance and analgesic efficacy are increasingly recognized in the literature and have thus prompted scientists to seek mechanistic explanations. Hence, recent findings have highlighted that the signaling mechanisms underlying pain hypersensitivity are sexually dimorphic, which sheds light on the importance of conducting preclinical and clinical pain research on both sexes and of developing sex-specific pain medications. This review thus focuses on the clinical and preclinical evidence supporting the existence of sex differences in pain neurobiology. Attention is drawn to the sexually dimorphic role of glial and immune cells, which are both recognized as key players in neuroglial maladaptive plasticity at the origin of the transition from acute pain to chronic pathological pain. Growing evidence notably attributes to microglial cells a pivotal role in the sexually dimorphic pain phenotype and in the sexually dimorphic analgesic efficacy of opioids. This review also summarizes the recent advances in understanding the pathobiology underpinning the development of pain hypersensitivity in both males and females in different types of pain conditions, with particular emphasis on the mechanistic signaling pathways driving sexually dimorphic pain responses.

Rolipram Protects Mice from Gram-negative Bacterium Escherichia coli-induced Inflammation and Septic Shock

Sepsis is typically triggered by an overwhelming systemic inflammatory response to pathogens, and may lead to severe organ dysfunction and/or death. Sepsis consequently has a high mortality rate and a high rate of complications for survivors, despite modern medical advances. Therefore, drug identification and validation for the treatment of sepsis is of the utmost importance. As a selective phosphodiesterase-4 inhibitor, rolipram also exhibits the abilities of inhibiting multiple pro-inflammatory cytokines production in macrophages and toxin-induced inflammation in mice. However, this drug has never been studied as a sepsis treatment method. We found that rolipram significantly improves survival in mice challenged with gram-negative bacterium E. coli, CLP, or E. coli derived lipopolysaccharide. We have also found that rolipram inhibits organ damage, pro-inflammatory cytokine production, and intracellular migration of early-stage inflammatory elements. Our results also show that rolipram increases anti-inflammatory cytokine production. The protective effects of rolipram on septic mice may result from inhibition of the MAP kinase and NF-κB signaling pathways. Rolipram may therefore be a potential novel sepsis treatment, one that would bypass the time-consuming and costly drug-discovery process.

Astrocyte activation in the periaqueductal gray promotes descending facilitation to cancer-induced bone pain through the JNK MAPK signaling pathway

Descending nociceptive modulation from the supraspinal structures has an important role in cancer-induced bone pain (CIBP). Midbrain ventrolateral periaqueductal gray (vlPAG) is a critical component of descending nociceptive circuits; nevertheless, its precise cellular and molecular mechanisms involved in descending facilitation remain elusive. Our previous study has shown that the activation of p38 MAPK in vlPAG microglia is essential for the neuropathic pain sensitization. However, the existence of potential connection between astrocytes and c-Jun N-terminal kinase (JNK) pathway in CIBP has not yet been elucidated. The following study examines the involvement of astrocyte activation and upregulation of p-JNK in vlPAG, using a CIBP rat model. Briefly, CIBP was mimicked by an intramedullary injection of Walker 256 mammary gland carcinoma cells into the animal tibia. A significant increase in expression levels of astrocytes in the vlPAG of CIBP rats was observed. Furthermore, stereotaxic microinjection of the astrocytic cytotoxin L-α-aminoadipic acid decreased the mechanical allodynia as well as established and reversed the astrocyte activation in CIBP rats. A significant increase in expression levels of p-JNK in astrocytes in vlPAG of CIBP rats was also observed. Moreover, the intrathecal administration of JNK inhibitors SP600125 reduced the expression of glial fibrillary acidic protein, while microinjection of the SP600125 decreased the mechanical allodynia of CIBP rats. These results suggested that CIBP is associated with astrocyte activation in the vlPAG that probably participates in driving descending pain facilitation through the JNK MAPK signaling pathway. To sum up, these findings reveal a novel site of astrocytes modulation of CIBP.

Thalidomide alleviates bone cancer pain by down-regulating expressions of NF-κB and GFAP in spinal astrocytes in a mouse model

Aim: Thalidomide is one of the first line therapies in cancer pain management. Previous study has shown that thalidomide decreases the expression of tumor necrosis factor alpha in the mouse spinal cord. However, the exact cellular and molecular mechanism underlying the effect of thalidomide remains unclear. Here, we investigated the effect of thalidomide on the expression level of NF-κB as well as glial fibrillary acidic protein (GFAP) in the spinal cord astrocyte in a mice model. Materials and methods: MC57G fibrosarcoma cells were intramedullary injected into the right femurs of C57/BL mice to induce behaviors related to bone cancer pain. Postoperative thalidomide was administered intraperitoneally to the mice at dose of 100 mg/kg/day for 7 days. The effect of thalidomide on pain hypersensitivity was checked by behavioral testing. The expression levels of NF-κB and GFAP in spinal cord were evaluated by using Western blotting and Immunohistochemistry. Results: Compared with the controls, the tumor-bearing mice showed substantial pain-related behaviors. Furthermore, the expression levels of both NF-κB and GFAP increased significantly in the spinal cord astrocytes of the tumor-bearing mice. Treating the tumor-bearing mice with thalidomide results in a dramatic reduction in pain behaviors and a significant decrease of NF-κB and GFAP expressions. Conclusions: Thalidomide alleviates the pain behaviors probably by down-regulating the expression of NF-κB and GFAP.

Phosphodiesterase 4 and 7 inhibitors produce protective effects against high glucose-induced neurotoxicity in PC12 cells via modulation of the oxidative stress, apoptosis and inflammation pathways

Diabetic neuropathy (DN) is the most common diabetic complication. It is estimated diabetic population will increase to 592 million by the year 2035. This is while at least 50-60% of all diabetic patients will suffer from neuropathy in their lifetime. Oxidative stress, mitochondrial dysfunction, apoptosis, and inflammation are crucial pathways in development and progression of DN. Since there is also no selective and effective therapeutic agent to prevent or treat high glucose (HG)-induced neuronal cell injury, it is crucial to explore tools by which one can reduce factors related to these pathways. Phosphodiesterase 4 and 7 (PDE 4 and 7) regulate oxidative damage, neurodegenaration, and inflammatory responses through modulation of cyclic adenosine monophosphate (cAMP) level, and thus can be as important drug targets for regulating DN. The aim of this study was to evaluate the protective effects of inhibitors of PDE 4 and 7, named rolipram and BRL5048, on HG-induced neurotoxicity in PC12 cells as an in vitro cellular model for DN and determine the possible mechanisms for theirs effects. We report that the PC12 cells pre-treatment with rolipram (2 μM) and/or BRL5048 (0.2 μM) for 60 min and then exposing the cells to HG (4.5 g/L for 72 h) or normal glucose (NG) (1 g/L for 72 h) condition show: (1) significant attenuation in ROS, MDA and TNF-a levels, Bax/Bcl-2 ratio, expression of caspase 3 and UCP2 proteins; (2) significant increase in viability, GSH/GSSG ratio, MMP and ATP levels. All these data together led us to propose PDE 4 and 7 inhibitors, and specifically, rolipram and BRL5048, as potential drugs candidate to be further studied for the prevention and treatment of DN.

Sinomenine attenuates cancer-induced bone pain via suppressing microglial JAK2/STAT3 and neuronal CAMKII/CREB cascades in rat models

Cancer-induced bone pain is one of the most severe types of pathological pain, which often occurs in patients with advanced prostate, breast, and lung cancer. It is of great significance to improve the therapies of cancer-induced bone pain due to the opioids' side effects including addiction, sedation, pruritus, and vomiting. Sinomenine, a traditional Chinese medicine, showed obvious analgesic effects on a rat model of chronic inflammatory pain, but has never been proven to treat cancer-induced bone pain. In the present study, we investigated the analgesic effect of sinomenine after tumor cell implantation and specific cellular mechanisms in cancer-induced bone pain. Our results indicated that single administration of sinomenine significantly and dose-dependently alleviated mechanical allodynia in rats with cancer-induced bone pain and the effect lasted for 4 h. After tumor cell implantation, the protein levels of phosphorylated-Janus family tyrosine kinase 2 (p-JAK2), phosphorylated-signal transducers and activators of transcription 3 (p-STAT3), phosphorylated-Ca2+/calmodulin-dependent protein kinase II (p-CAMKII), and phosphorylated-cyclic adenosine monophosphate response element-binding protein (p-CREB) were persistently up-regulated in the spinal cord horn. Chronic intraperitoneal treatment with sinomenine markedly suppressed the activation of microglia and effectively inhibited the expression of JAK2/STAT3 and CAMKII/CREB signaling pathways. We are the first to reveal that up-regulation of microglial JAK2/STAT3 pathway are involved in the development and maintenance of cancer-induced bone pain. Moreover, our investigation provides the first evidence that sinomenine alleviates cancer-induced bone pain by inhibiting microglial JAK2/STAT3 and neuronal CAMKII/CREB cascades.

Mice with cancer-induced bone pain show a marked decline in day/night activity

INTRODUCTION

Cancer-induced bone pain (CIBP) is the most common type of pain with cancer. In humans, this pain can be difficult to control and highly disabling. A major problem with CIBP in humans is that it increases on weight-bearing and/or movement of a tumor-bearing bone limiting the activity and functional status of the patient. Currently, there is less data concerning whether similar negative changes in activity occur in rodent models of CIBP.

OBJECTIVES

To determine whether there are marked changes in activity in a rodent model of CIBP and compare this to changes in skin hypersensitivity.

METHODS

Osteosarcoma cells were injected and confined to 1 femur of the adult male mouse. Every 7 days, spontaneous horizontal and vertical activities were assessed over a 20-hour day and night period using automated activity boxes. Mechanical hypersensitivity of the hind paw skin was assessed using von Frey testing.

RESULTS

As the tumor cells grew within the femur, there was a significant decline in horizontal and vertical activity during the times of the day/night when the mice are normally most active. Mice also developed significant hypersensitivity in the skin of the hind paw in the tumor-bearing limb.

CONCLUSION

Even when the tumor is confined to a single load-bearing bone, CIBP drives a significant loss of activity, which increases with disease progression. Understanding the mechanisms that drive this reduction in activity may allow the development of therapies that allow CIBP patients to better maintain their activity and functional status.

Inhibition of interleukin-6 function attenuates the central sensitization and pain behavior induced by osteoarthritis

Chronic pain is the most prominent and disabling symptom in the patients with osteoarthritis (OA), and the underlying mechanism largely remains unclear. Interleukin-6 (IL-6), a proinflammatory cytokine, is critically involved in the development and maintenance of central sensitization in several rodent models of chronic pain. The present study aims to elucidate the IL-6 mediated neurological adaptation in dorsal horn in the rat with monosodium iodoacetate (MIA) - induced OA. Significant upregulation of IL-6 expression was detected in the dorsal horn in the modeled rats. Blockade of IL-6 function by tocilizumab markedly suppressed the activation of astrocytes and microglia in the ipsilateral dorsal horn, reduced c-Fos immunoreactivity in dorsal horn neurons, and attenuated the upregulation of glutamate receptor subunits GluR1 and NR2B in dorsal horn in the rats with MIA-induced OA. It was further reported that administration of tocilizumab significantly improved the performance in weight-bearing test and mitigated the mechanical allodynia in the modeled rats. These data illustrated spinal IL-6 mediated mechanism underlying the chronic pain, and proposed the potential therapeutic effect of tocilizumab on the chronic pain in the setting of OA.