Interleukin-10 levels in rat models of nerve damage and neuropathic pain

Interactions and Trends of Interleukins, PAI-1, CRP, and TNF-α in Inflammatory Responses during the Perioperative Period of Joint Arthroplasty: Implications for Pain Management-A Narrative Review

Inflammation during the perioperative period of joint arthroplasty is a critical aspect of patient outcomes, influencing both the pathophysiology of pain and the healing process. This narrative review comprehensively evaluates the roles of specific cytokines and inflammatory biomarkers in this context and their implications for pain management. Inflammatory responses are initiated and propagated by cytokines, which are pivotal in the development of both acute and chronic postoperative pain. Pro-inflammatory cytokines play essential roles in up-regulating the inflammatory response, which, if not adequately controlled, leads to sustained pain and impaired tissue healing. Anti-inflammatory cytokines work to dampen inflammatory responses and promote resolution. Our discussion extends to the genetic and molecular influences on cytokine production, which influence pain perception and recovery rates post-surgery. Furthermore, the role of PAI-1 in modulating inflammation through its impact on the fibrinolytic system highlights its potential as a therapeutic target. The perioperative modulation of these cytokines through various analgesic and anesthetic techniques, including the fascia iliac compartment block, demonstrates a significant reduction in pain and inflammatory markers, thus underscoring the importance of targeted therapeutic strategies. Our analysis suggests that a nuanced understanding of the interplay between pro-inflammatory and anti-inflammatory cytokines is required. Future research should focus on individualized pain management strategies.

Role of Exercise on Inflammation Cytokines of Neuropathic Pain in Animal Models

Neuropathic pain (NP) resulting from a lesion or disease of the somatosensory system can lead to loss of function and reduced life quality. Neuroinflammation plays a vital role in the development and maintenance of NP. Exercise as an economical, effective, and nonpharmacological treatment, recommended by clinical practice guidelines, has been proven to alleviate chronic NP. Previous studies have shown that exercise decreases NP by modifying inflammation; however, the exact mechanisms of exercise-mediated NP are unclear. Therefore, from the perspective of neuroinflammation, this review mainly discussed the effects of exercise on inflammatory cytokines in different parts of NP conduction pathways, such as the brain, spinal cord, dorsal root ganglion, sciatic nerve, and blood in rat/mice models. Results suggested that exercise training could modulate neuroinflammation, inhibit astrocyte glial cell proliferation and microglial activation, alter the macrophage phenotype, reduce the expression of proinflammatory cytokines, increase anti-inflammatory cytokine levels, and positively modulate the state of the immune system, thereby relieving NP.

Altered serum cytokines in patients with symptomatic disk herniation and depressive symptoms

Purpose

An increasing number of studies have indicated the important role of cytokines in the development of depressive disturbances (DD). In medically ill patients, cytokines can provoked sickness behavior, the signs of which resemble DD. This results in alterations in behavior to limit energy expenditure and redirect it to cope with particular diseases. The aim of our study was to investigate the role of pro-inflammatory IL-6, TNF-α, and IL-1β and anti-inflammatory IL-10 and TGF-β in DD observed in patients suffering from pain caused by disk herniation (DH) qualified for surgery.

Patients and methods

The intensity of DD assessed by using Beck Depression Inventory, pain intensity, and functional impairment were evaluated in 70 patients with DH who were qualified for surgery. Pro-inflammatory serum levels of TNF-α, IL-1, IL-6, anti-inflammatory TGF-β, and IL-10 were measured.

Results

Elevated serum levels of TGF-β, IL-10, and IL-6 were found in the group with moderate and severe depressive symptoms (SD) compared with the groups with mild (MD) or no depressive symptoms (ND). TGF-β levels were negatively correlated with pain intensity, as assessed using the Present Pain Intensity scale in SD. Functional impairment measured using the Oswestry Disability Index was the most advanced in SD group.

Conclusion

Results of our study can suggest association between depressive disturbances and anti-inflammatory cytokines TGF-β and IL-10. Functional impairment of SD group is more severe but serum levels of TGF-β and IL-10, which are involved in the healing processes, are increased.

The Peripheral Nerve Surgeon's Role in the Management of Neuropathic Pain

Neuropathic pain (NP) underlies significant morbidity and disability worldwide. Although pharmacologic and functional therapies attempt to address this issue, they remain incompletely effective for many patients. Peripheral nerve surgeons have a range of techniques for intervening on NP. The aim of this review is to enable practitioners to identify patients with NP who might benefit from surgical intervention. The workup for NP includes patient history and specific physical examination maneuvers, as well as imaging and diagnostic nerve blocks. Once diagnosed, there is a range of options surgeons can utilize based on specific causes of NP. These techniques include nerve decompression, nerve reconstruction, nerve ablative techniques, and implantable nerve-modulating devices. In addition, there is an emerging role for preoperative involvement of peripheral nerve surgeons for cases known to carry a high risk of inducing postoperative NP. Lastly, we describe the ongoing work that will enable surgeons to expand their armamentarium to better serve patients with NP.

Systemic and Peripheral Mechanisms of Cortical Stimulation-Induced Analgesia and Refractoriness in a Rat Model of Neuropathic Pain

Epidural motor cortex stimulation (MCS) is an effective treatment for refractory neuropathic pain; however, some individuals are unresponsive. In this study, we correlated the effectiveness of MCS and refractoriness with the expression of cytokines, neurotrophins, and nociceptive mediators in the dorsal root ganglion (DRG), sciatic nerve, and plasma of rats with sciatic neuropathy. MCS inhibited hyperalgesia and allodynia in two-thirds of the animals (responsive group), and one-third did not respond (refractory group). Chronic constriction injury (CCI) increased IL-1β in the nerve and DRG, inhibited IL-4, IL-10, and IL-17A in the nerve, decreased β-endorphin, and enhanced substance P in the plasma, compared to the control. Responsive animals showed decreased NGF and increased IL-6 in the nerve, accompanied by restoration of local IL-10 and IL-17A and systemic β-endorphin. Refractory animals showed increased TNF-α and decreased IFNγ in the nerve, along with decreased TNF-α and IL-17A in the DRG, maintaining low levels of systemic β-endorphin. Our findings suggest that the effectiveness of MCS depends on local control of inflammatory and neurotrophic changes, accompanied by recovery of the opioidergic system observed in neuropathic conditions. So, understanding the refractoriness to MCS may guide an improvement in the efficacy of the technique, thus benefiting patients with persistent neuropathic pain.

The association between migraines and periodontal disease: A systematic review of clinical studies

BACKGROUND

Recent studies have postulated several hypotheses explaining the association between migraines and periodontitis. We aimed to systematically review and assess if there is an association between inflammatory mediators in migraines and periodontal disease. Indexed database search was performed from inception up to and including April 2022. Data such as study design, study grouping, participants, age, sex, migraine characteristics, assessment criteria for periodontitis and outcomes were collected. Methodological index for non-randomized studies was used to assess the risk of bias. The systematic analysis format was personalized to review the appropriate information.

HIGHLIGHTS

Levels of pro-inflammatory mediators such as serum procalcitonin, leptin, calcitonin gene related peptide and interleukin-6 were elevated in patients with chronic periodontitis and migraines.

CONCLUSION

Chronic periodontitis may be a contributing factor for migraines. However, future standardized studies are required to understand the true relationship at a clinical and molecular level. This may better help in managing patients with comorbid conditions in the future.

Suppressive role of lovastatin in intracerebral hemorrhage through repression of autophagy

Statins possess critical function in the brain. Here, we intended to investigate the role of lovastatin in brain damage after intracerebral hemorrhage (ICH). A collagenase-induced ICH rat model was established followed by lovastatin treatment. Then, the effect of lovastatin on ICH-induced brain damage was explored with cognitive function, learning and memory abilities, and neurological damage of rats analyzed. Besides, brain water content, number of degenerate neurons, Nissl's body, and apoptosis of neurons were detected. Oxidative stress levels, inflammation, and autophagy levels in ICH were measured after treatment of lovastatin. Lovastatin improved the cognitive impairment of rats, enhanced their spatial learning and memory abilities, reduced nervous system damage, lesion area, and brain water content after ICH. Lovastatin was capable of reducing the number of degenerated neurons, the apoptosis level, autophagy level, and increasing the number of Nissl's body. Lovastatin inhibited the oxidative stress response and inflammatory factors in the brain tissue after ICH, and increased the expression of anti-inflammatory factor IL-10. Lovastatin inhibited AMPK/mTOR signaling pathway after ICH. Our study highlighted the suppressive role of lovastatin in ICH-induced brain damage.

Response profile in a rat model of exercise-induced hypoalgesia is associated with duloxetine, pregabalin and diclofenac effect on constriction-induced neuropathy

BACKGROUND

Exercise is a known trigger of the inhibitory pain modulation system and its analgesic effect is termed exercise-induced hypoalgesia (EIH). Previous studies have demonstrated that rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury compared to rats with substantial analgesic response following exercise.

OBJECTIVES

A rat model of EIH as an indicator of the pain inhibitory system's efficiency was used to explore the association between EIH profiles and the effect of pharmacotherapy on rat's neuropathic pain.

METHODS

EIH profiles were assessed by evaluating paw responses to mechanical stimuli before and after exercise on a rotating rod. Rats with a reduction of ≤33% in responses were classified as low EIH and those with ≥67% as high EIH. Low and high EIH rats underwent sciatic nerve chronic constriction injury (CCI). Paw responses to mechanical stimuli were measured at baseline, following CCI, and after treatment with diclofenac, duloxetine or pregabalin. In a different group of low and high EIH rats, EIH was measured before and following treatment with the same medications.

RESULTS

Low EIH rats developed more significant hypersensitivity following CCI. Duloxetine and pregabalin successfully reduced hypersensitivity, although significantly more so in low EIH rats. Diclofenac had limited effects, and only on low EIH rats. Four days of duloxetine administration transformed low EIH rats' profiles to high EIH.

CONCLUSIONS

The findings of this study suggest that EIH profiles in rats can not only predict the development of hypersensitivity following injury but may also support targeted pharmacological treatment.

SIGNIFICANCE

Exercise is a known trigger of the inhibitory pain modulation. Rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury. Pain modulation profiles in rats can also support targeted pharmacological treatment; rats with deficient analgesic response following exercise benefit more from treatment with duloxetine and gabapentin. Treatment with duloxetine can improve pain modulation profile.

Effects of co-administration of vitamin E and lithium chloride on chronic constriction injury-induced neuropathy in male Wistar rats: Focus on antioxidant and anti-inflammatory mechanisms

OBJECTIVES

This study investigated the antinociceptive effects of co-administration of lithium chloride (LiCl) and vitamin E (Vit E) on chronic constriction injury (CCI)-induced peripheral neuropathy in male Wistar rats. It further explored the anti-inflammatory and neuroprotective properties of LiCl and Vit E, which may be complementary to the antinociceptive effects of the two substances.

METHODS

Thirty-six male Wistar rats, 190.00 ± 10.00 g of body weight were randomly assigned to 6 experimental groups and administered with normal saline, Vit E, LiCl, or their combination, once daily for 21 days. CCI was used to induce neuropathic pain (NP) and mechanical allodynia was assessed using von Frey filaments and pinprick test. Open field maze (OFM) was used to assess the exploratory behavior. Biochemical parameters were assessed in the dorsal root ganglion after 21 days of treatment.

RESULTS

Mechanical allodynia was developed in rats following CCI. Co-administration of LiCl and Vit E synergistically reduced mechanical hyperalgesia in rats which were significantly different compared with the single administration of either Vit E or LiCl. Combined doses of Vit E and LiCl significantly increases the explorative behavior in the OFM. CCI increased malondialdehyde (MDA), tumor necrotic factor-alpha (TNF-α), calcitonin gene-related polypeptide, calcium ion (Ca2+ ), and reduced superoxide dismutase (SOD) activities. Co-administration of LiCl and Vit E significantly reduced MDA, TNF-α, but increased SOD compared with ligated control.

DISCUSSION

The findings revealed that the synergistic effects of the co-administration of Vit E and LiCl in ameliorating NP are mediated by their anti-inflammatory and antioxidant properties.

Myofascial pain in temporomandibular disorders: Updates on etiopathogenesis and management

OBJECTIVES

Temporomandibular disorders (TMDs) are an umbrella term encompassing disorders of both the temporomandibular joint (TMJD) and masticatory musculature (MMD). The objective of this review is to provide an overview of the etiopathogenesis, clinical features and diagnosis of MMD, and to summarize the current trends in the therapeutic management.

METHODS

A review of the literature was performed from 1985 to 2020. The keywords included were "temporomandibular disorders OR temporomandibular joint disorders" AND "myofascial pain OR masticatory myofascial pain OR trigger point". A total of 983 articles were screened with abstracts and approximately 500 full text articles were included in the review based on their relevance to the topic.

RESULTS

MMD's present significant challenges in diagnosis and treatment. Effective treatment requires a clear diagnosis based on an understanding of pathophysiologic mechanisms, a detailed history with assessment of predisposing local and systemic factors, perpetuating factors, a comprehensive clinical evaluation and a diagnostic workup.

CONCLUSION

A thorough history and clinical examination are the gold standards for diagnosis of MMD. Serological testing may help identify underlying co-morbidities. Recent diagnostic modalities including ultrasound sonoelastography and magnetic resonance elastography (MRE) have shown promising results. The treatment goals for MMD are to control pain, restore mandibular function and facilitate the return to normal daily activity and improve the overall quality of life of a patient. Conservative modalities including home care regimens, pharmacotherapy, intraoral appliance therapy, local anesthetic trigger point injections, physiotherapy and complementary modalities may be beneficial in patients with MMD's.

Repetitive Transcranial Magnetic Stimulation (rTMS) Reverses the Long-term Memory Impairment and the Decrease of Hippocampal Interleukin-10 Levels, both Induced by Neuropathic Pain in Rats

Neuropathic pain (NP) is characterized by the presence of spontaneous pain, allodynia and hyperalgesia. Repetitive transcranial magnetic stimulation (rTMS) is one of neuromodulatory techniques that induces satisfactory NP relief, including that from refractory pain patients. The objective of this study was to evaluate rTMS treatment over long term memory (LTM) and hippocampal BDNF and IL-10 levels in rats submitted to a NP model. A total of 81 adult (60-days old) male Wistar rats were randomly allocated to one of the following 9 experimental groups: control, control + sham rTMS, control + rTMS, sham neuropathic pain, sham neuropathic pain + sham rTMS, sham neuropathic pain + rTMS, neuropathic pain (NP), neuropathic pain + sham rTMS and neuropathic pain + rTMS. Fourteen days after the surgery for chronic constriction injury (CCI) of the sciatic nerve, NP establishment was accomplished. Then, rats were treated with daily 5-minute sessions of rTMS for eight consecutive days. LTM was assessed by the object recognition test (ORT) twenty-four hours after the end of rTMS treatment. Biochemical assays (BDNF and IL-10 levels) were performed in hippocampus tissue homogenates. rTMS treatment reversed the reduction of the discrimination index in the ORT and the hippocampal IL-10 levels in NP rats. This result shows that rTMS reverses the impairment LTM and the increase in the hippocampal IL-10 levels, both induced by NP. Moreover, it appears to be a safe non-pharmacological therapeutic tool since it did not alter LTM and neurochemical parameters in naive animals.

Exercise induced hypoalgesia profile in rats is associated with IL-10 and IL-1 β levels and pain severity following nerve injury

BACKGROUND

Pain may undergo modulation in the central nervous system prior to reaching the primary somatosensory cortex and being perceived as pain. Faulty pain modulation mechanisms have been linked to various chronic pain conditions. Cytokines such as IL-10 and IL-1beta, are known to be involved in initiation and maintenance of neuropathic pain. In this study, we investigated the association between pain modulation profile, pain intensity and cytokines (IL-10 and IL-1beta) levels in a rat model of neuropathic pain.

METHODS

Exercise-Induced Hypoalgesia (EIH) was assessed by evaluating the percentage of responses to a train of 60g mechanical stimuli before and after 180 seconds of exercise on a rotating rod. The differences in the response rates before and after the exercise were used to divide the rats into low and high EIH responders. Rats from low and high EIH groups underwent constriction injury of the left sciatic nerve. Pain behavior (allodynia and hyperalgesia) were assessed by measuring responses to mechanical and thermal stimuli applied to the plantar surface of the foot. Serum, sciatic nerve and the related Dorsal Root Ganglia (DRG) levels of IL-10 and IL-1beta were determined by ELISA. The DRG mRNA levels of IL-10 and IL-1beta measured with PCR. A comparison between the low and high EIH rats of all measured parameters was made.

RESULTS

The low EIH rats developed significantly more severe allodynia and hyperalgesia in the affected paw and allodynia in the contralateral paw compared to the high EIH rats, 7 days following the injury. The low EIH rats had higher IL-1beta protein levels in serum prior to and following injury, higher affected and contralateral sciatic nerve IL-1beta levels following injury and higher IL-1beta levels in the contralateral DRG (protein and mRNA) following injury when compared to high EIH rats. The high EIH rats had higher affected sciatic nerve IL-10 levels following nerve injury and higher IL-10 levels of both protein and mRNA in the affected and contralateral DRG at baseline and following injury.

CONCLUSION

EIH profile was found to be predictive of pain behavior following nerve injury, low EIH rats developed more severe allodynia and hyperalgesia. IL-1beta may be associated with painful neuropathy developed in rats with low EIH while the anti-inflammatory cytokine IL-10 may have a protective role, inhibiting the development of painful.

Association of Self-Rated Pain with Clinical Peri-Implant Parameters and Cytokine Profile in Smokers and Never Smokers with and without Peri-Implantitis

To examine the association between self-perceived pain (SPP), clinical and radiographic peri-implant parameters, and biomarker levels among smokers and never smokers with and without peri-implantitis. Sixty individuals (20 smokers with peri-implantitis [group-1], 20 never smokers with peri-implantitis [group-2] and 20 never smokers without peri-implantitis [control-group]) were included. SPP was evaluated using a numeric pain rating scale (NPRS). Peri-implant plaque index (PI), probing depth (PD), and bleeding on probing (BOP) were recorded. After obtaining the samples, the levels of TNF-α, MMP-1, and IL-8 were measured. The mean SPP score in group-1, group-2, and the control group was 1.3 ± 1, 3.4 ± 1, and zero, respectively. The peri-implant mean PD (p < 0.05), BOP (p < 0.05), PI (p < 0.05), and crestal bone loss (CBL) (p < 0.05) were significantly higher among test groups than the control group. The levels of TNF-α, MMP-1, and IL-8 were significantly raised among group-1 and group-2 than the control group. A significant correlation between increasing SPP and PICF TNF-α, MMP-1, and IL-8 levels was observed based on regression analysis. Proinflammatory biomarkers were higher in smokers with peri-implantitis than never smokers with and without peri-implantitis, with a significant association between the proinflammatory cytokines and SPP.

Whole Genomic DNA Methylation Profiling of CpG Sites in Promoter Regions of Dorsal Root Ganglion in Diabetic Neuropathic Pain Mice

DNA methylation and demethylation play an important role in neuropathic pain. In general, DNA methylation of CpG sites in the promoter region impedes gene expression, whereas DNA demethylation contributes to gene expression. Here, we evaluated the methylation status of CpG sites in genomic DNA promoter regions in dorsal root ganglions (DRGs) of diabetic neuropathic pain (DNP) mice. In our research, streptozotocin (STZ) was intraperitoneally injected into mice to construct DNP models. The DNP mice showed higher fasting blood glucose (above 11.1 mmol/L), lower body weight, and mechanical allodynia than control mice. Whole-genome bisulfite sequencing (WGBS) revealed an altered methylation pattern in CpG sites in the DNA promoter regions in DRGs of DNP mice. The results showed 376 promoter regions with hypermethylated CpG sites and 336 promoter regions with hypomethylated CpG sites. In addition, our data indicated that altered DNA methylation occurs primarily on CpG sites in DNA promoter regions. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that differentially methylated CpG sites annotated genes were involved in activities of the nervous and sensory systems. Enrichment analysis indicated that genes in these pathways contributed to diabetes or pain. In conclusion, our study enriched the role of DNA methylation in DNP.

Adenosine A3 agonists reverse neuropathic pain via T cell-mediated production of IL-10

The A3 adenosine receptor (A3AR) has emerged as a therapeutic target with A3AR agonists to tackle the global challenge of neuropathic pain, and investigation into its mode of action is essential for ongoing clinical development. Immune cell A3ARs, and their activation during pathology, modulate cytokine release. Thus, the use of immune cells as a cellular substrate for the pharmacological action of A3AR agonists is enticing, but unknown. The present study discovered that Rag-KO mice lacking T and B cells, as compared with WT mice, are insensitive to the anti-allodynic effects of A3AR agonists. Similar findings were observed in interleukin-10 and interleukin-10 receptor knockout mice. Adoptive transfer of CD4+ T cells from WT mice infiltrated the dorsal root ganglion (DRG) and restored A3AR agonist-mediated anti-allodynia in Rag-KO mice. CD4+ T cells from Adora3-KO or Il10-KO mice did not. Transfer of CD4+ T cells from WT mice, but not Il10-KO mice, into Il10-KO mice or Adora3-KO mice fully reinstated the anti-allodynic effects of A3AR activation. Notably, A3AR agonism reduced DRG neuron excitability when cocultured with CD4+ T cells in an IL-10-dependent manner. A3AR action on CD4+ T cells infiltrated in the DRG decreased phosphorylation of GluN2B-containing N-methyl-D-aspartate receptors at Tyr1472, a modification associated with regulating neuronal hypersensitivity. Our findings establish that activation of A3AR on CD4+ T cells to release IL-10 is required and sufficient evidence for the use of A3AR agonists as therapeutics.

Sensory neuron-associated macrophages as novel modulators of neuropathic pain

The peripheral nervous system comprises an infinity of neural networks that act in the communication between the central nervous system and the most diverse tissues of the body. Along with the extension of the primary sensory neurons (axons and cell bodies), a population of resident macrophages has been described. These newly called sensory neuron-associated macrophages (sNAMs) seem to play an essential role in physiological and pathophysiological processes, including infection, autoimmunity, nerve degeneration/regeneration, and chronic neuropathic pain. After different types of peripheral nerve injury, there is an increase in the number and activation of sNAMs in the sciatic nerve and sensory ganglia. The activation of sNAMs and their participation in neuropathic pain development depends on the stimulation of pattern recognition receptors such as Toll-like receptors and Nod-like receptors, chemokines/cytokines, and microRNAs. On activation, sNAMs trigger the production of critical inflammatory mediators such as proinflammatory cytokines (eg, TNF and IL-1β) and reactive oxygen species that can act in the amplification of primary sensory neurons sensitization. On the other hand, there is evidence that sNAMs can produce antinociceptive mediators (eg, IL-10) that counteract neuropathic pain development. This review will present the cellular and molecular mechanisms behind the participation of sNAMs in peripheral nerve injury-induced neuropathic pain development. Understanding how sNAMs are activated and responding to nerve injury can help set novel targets for the control of neuropathic pain.

tDCS and exercise improve anxiety-like behavior and locomotion in chronic pain rats via modulation of neurotrophins and inflammatory mediators

Anxiety disorders cause distress and are commonly found to be comorbid with chronic pain. Both are difficult-to-treat conditions for which alternative treatment options are being pursued. This study aimed to evaluate the effects of transcranial direct current stimulation (tDCS), treadmill exercise, or both, on anxiety-like behavior and associated growth factors and inflammatory markers in the hippocampus and sciatic nerve of rats with neuropathic pain. Male Wistar rats (n = 216) were subjected to sham-surgery or sciatic nerve constriction for pain induction. Fourteen days following neuropathic pain establishment, either bimodal tDCS, treadmill exercise, or a combination of both was used for 20 min a day for 8 consecutive days. The elevated plus-maze test was used to assess anxiety-like behavior and locomotor activity during the early (24 h) or late (7 days) phase after the end of treatment. BDNF, TNF-ɑ, and IL-10 levels in the hippocampus, and BDNF, NGF, and IL-10 levels in the sciatic nerve were assessed 48 h or 7 days after the end of treatment. Rats from the pain groups developed an anxiety-like state. Both tDCS and treadmill exercise provided ethological and neurochemical alterations induced by pain in the early and/or late phase, and a modest synergic effect between tDCS and exercise was observed. These results indicate that non-invasive neuromodulatory approaches can attenuate both anxiety-like status and locomotor activity and alter the biochemical profile in the hippocampus and sciatic nerve of rats with neuropathic pain and that combined interventions may be considered as a treatment option.

Bromelain reduced pro-inflammatory mediators as a common pathway that mediate antinociceptive and anti-anxiety effects in sciatic nerve ligated Wistar rats

The involvement of pro-inflammatory mediators complicates the complex mechanism in neuropathic pain (NP). This study investigated the roles of bromelain against pro-inflammatory mediators as a mechanism that underpins its antinociceptive and anti-anxiety effects in the peripheral model of NP. Sixty-four male Wistar rats randomly divided into eight groups, were used for the study. A chronic constriction injury model of peripheral neuropathy was used to induce NP. Tail-immersion and von Frey filaments tests were used to assess hyperalgesia while open field and elevated plus mazes were used to assess anxiety-like behaviour. NF-кB, iNOS, nitrate, and pro-inflammatory cytokines were investigated in the plasma, sciatic nerve, and brain tissues using ELISA, spectrophotometer, and immunohistochemistry techniques after twenty-one days of treatment. Bromelain significantly (p < 0.05) improved the cardinal signs of NP and inhibited anxiety-like behaviours in ligated Wistar rats. It mitigated the increases in cerebral cortex interleukin (IL) -1β, IL-6, and PGE₂ levels. Bromelain reduced NF-кB, IL-1β, IL-6, TNF-α, PGE_2, and nitrate concentrations as well as the expression of iNOS in the sciatic nerve. Hence, the antinociceptive and anxiolytic effects of bromelain in the sciatic nerve ligation model of NP is in part due to its ability to reduce nitrosative and inflammatory activities.

Mesenchymal stem cells reduce the oxaliplatin-induced sensory neuropathy through the reestablishment of redox homeostasis in the spinal cord

AIMS

The present study was designed to investigate whether the antinociceptive effect of bone marrow-derived mesenchymal stem/stromal cells (MSC) during oxaliplatin (OXL)-induced sensory neuropathy is related to antioxidant properties.

MAIN METHODS

Male mice C57BL/6 were submitted to repeated intravenous administration of OXL (1 mg/kg, 9 administrations). After the establishment of sensory neuropathy, mice were treated with a single intravenous administration of MSC (1 × 10⁶), vehicle or gabapentin. Paw mechanical and thermal nociceptive thresholds were evaluated through von Frey filaments and cold plate test, respectively. Motor performance was evaluated in the rota-rod test. Gene expression profile, cytokine levels, and oxidative stress markers in the spinal cord were evaluated by real-time PCR, ELISA and biochemical assays, respectively.

KEY FINDINGS

OXL-treated mice presented behavioral signs of sensory neuropathy, such as mechanical allodynia and thermal hyperalgesia, which were completely reverted by a single administration of MSC. Repeated oral treatment with gabapentin (70 mg/kg) induced only transient antinociception. The IL-1β and TNF-α spinal levels did not differ between mice with or without sensory neuropathy. MSC increased the levels of anti-inflammatory cytokines, IL-10 and TGF-β, in the spinal cord of neuropathic mice, in addition to increasing the gene expression of antioxidant factors SOD and Nrf-2. Additionally, nitrite and MDA spinal levels were reduced by the MSC treatment.

SIGNIFICANCE

MSC induce reversion of sensory neuropathy induced by OXL possibly by activation of anti-inflammatory and antioxidant pathways, leading to reestablishment of redox homeostasis in the spinal cord.

LOW-DOSE NALTREXONE REVERSES FACIAL MECHANICAL ALLODYNIA IN A RAT MODEL OF TRIGEMINAL NEURALGIA

Trigeminal neuralgia (TN) is a type of neuropathic pain characterized by intense pain; although anticonvulsants are used as an option to relieve pain, adverse side effects can decrease patient adherence. In this context, a low dose of naltrexone is effective in relieving pain in other pain conditions. Thus, the objective of the present study was to evaluate the analgesic effect of low-dose naltrexone on facial mechanical allodynia in a rat model of TN, as well as its effect(s) on biomarkers in the central nervous system (tumor necrosis factor-alpha, brain-derived neurotrophic factor [BDNF], interleukin [IL]-10, and toll-like receptor-4). Fifty-nine adult male Wistar rats (CEUA-HCPA#2017-0575) were allocated to following groups: control; sham-pain + vehicle; sham-pain + carbamazepine (100 mg/kg); sham-pain + naltrexone (0.5 mg/kg); pain + vehicle; pain + carbamazepine; and pain + naltrexone. TN was induced using chronic constriction of the infraorbital nerve. Facial allodynia was assessed using von Frey test. Drugs were administered by gavage 14 days after surgery for 10 days. At baseline, the mechanical threshold was similar between groups (P > 0.05; generalized estimating equation). Seven days after surgery, facial allodynia was observed in sham-TN and pain-TN groups (P < 0.05). Fourteen days after surgery, only pain-TN groups exhibited facial allodynia. The first dose of low-dose naltrexone or carbamazepine partially reversed facial allodynia. After 10 days of treatment, both drugs completely reversed it. Spinal cord levels of BDNF and IL-10 were modulated by low-dose naltrexone. Thus, low-dose naltrexone may be suitable to relieve TN; however, the exact mechanisms need to be clarified.

The LFA-1 antagonist BIRT377 reverses neuropathic pain in prenatal alcohol-exposed female rats via actions on peripheral and central neuroimmune function in discrete pain-relevant tissue regions

Previous reports show that moderate prenatal alcohol exposure (PAE) poses a risk factor for developing neuropathic pain following adult-onset peripheral nerve injury in male rats. Recently, evidence suggests that immune-related mechanisms underlying neuropathic pain in females are different compared to males despite the fact that both sexes develop neuropathy of similar magnitude and duration following chronic constriction injury (CCI) of the sciatic nerve. Data suggest that the actions of peripheral T cells play a greater role in mediating neuropathy in females. The goal of the current study is to identify specificity of immune cell and cytokine changes between PAE and non-PAE neuropathic females by utilizing a well-characterized rodent model of sciatic nerve damage, in an effort to unmask unique signatures of immune-related factors underlying the risk of neuropathy from PAE. Cytokines typically associated with myeloid cell actions such as interleukin (IL)-1β, tumor necrosis factor (TNF), IL-6, IL-4 and IL-10 as well as the neutrophil chemoattractant CXCL1, are examined. In addition, transcription factors and cytokines associated with various differentiated T cell subtypes are examined (anti-inflammatory FOXP3, proinflammatory IL-17A, IL-21, ROR-γt, interferon (IFN)-γ and T-bet). Lymphocyte function associated antigen 1 (LFA-1) is an adhesion molecule expressed on peripheral immune cells including T cells, and regulates T cell activation and extravasation into inflamed tissue regions. A potential therapeutic approach was explored with the goal of controlling proinflammatory responses in neuroanatomical regions critical for CCI-induced allodynia by blocking LFA-1 actions using BIRT377. The data show profound development of hindpaw allodynia in adult non-PAE control females following standard CCI, but not following minor CCI, while minor CCI generated allodynia in PAE females. The data also show substantial increases in T cell-associated proinflammatory cytokine mRNA and proteins, along with evidence of augmented myeloid/glial activation (mRNA) and induction of myeloid/glial-related proinflammatory cytokines, CCL2, IL-1β and TNF in discrete regions along the pain pathway (damaged sciatic nerve, dorsal root ganglia; DRG, and spinal cord). Interestingly, the characteristic anti-inflammatory IL-10 protein response to nerve damage is blunted in neuropathic PAE females. Moreover, T cell profiles are predominantly proinflammatory in neuropathic Sac and PAE females, augmented levels of Th17-specific proinflammatory cytokines IL-17A and IL-21, as well as the Th1-specific factor, T-bet, are observed. Similarly, the expression of RORγt, a critical transcription factor for Th17 cells, is detected in the spinal cord of neuropathic females. Blocking peripheral LFA-1 actions with intravenous (i.v.) BIRT377 reverses allodynia in Sac and PAE rats, dampens myeloid (IL-1β, TNF, CXCL1)- and T cell-associated proinflammatory factors (IL-17A and RORγt) and spinal glial activation. Moreover, i.v. BIRT377 treatment reverses the blunted IL-10 response to CCI observed only in neuropathic PAE rats and elevates FOXP3 in pain-reversed Sac rats. Unexpectedly, intrathecal BIRT377 treatment is unable to alter allodynia in either Sac or PAE neuropathic females. Together, these data provide evidence that: 1) fully differentiated proinflammatory Th17 cells recruited at the sciatic nerve, DRGs and lumbar spinal cord may interact with the local environment to shape the immune responses underlying neuropathy in female rats, and, 2) PAE primes peripheral and spinal immune responses in adult females. PAE is a risk factor in females for developing peripheral neuropathy after minor nerve injury.

IL-27 Counteracts Neuropathic Pain Development Through Induction of IL-10

Neuroimmune–glia interactions have been implicated in the development of neuropathic pain. Interleukin-27 (IL-27) is a cytokine that presents regulatory activity in inflammatory conditions of the central nervous system. Thus, we hypothesized that IL-27 would participate in the neuropathic pain process. Here, we found that neuropathic pain caused by peripheral nerve injury (spared nerve injury model; SNI), was enhanced in IL-27-deficient^(−/−) mice, whereas nociceptive pain is similar to that of wild-type mice. SNI induced an increase in the expression of IL-27 and its receptor subunit (Wsx1) in the sensory ganglia and spinal cord. IL-27 receptor was expressed mainly in resident macrophage, microglia, and astrocytes of the sensory ganglia and spinal cord, respectively. Finally, we identify that the antinociceptive effect of IL-27 was not observed in IL-10^−/− mice. These results provided evidence that IL-27 is a cytokine produced after peripheral nerve injury that counteracts neuropathic pain development through induction of the antinociceptive cytokine IL-10. In summary, our study unraveled the role of IL-27 as a regulatory cytokine that counteracts the development of neuropathic pain after peripheral nerve damage. In conclusion, they indicate that immunotherapies based on IL-27 could emerge as possible therapeutic approaches for the prevention of neuropathic pain development after peripheral nerve injury.

Cytokines in Pain: Harnessing Endogenous Anti-Inflammatory Signaling for Improved Pain Management

Current pain therapeutics offer inadequate relief to patients with chronic pain. A growing literature supports that pro-inflammatory cytokine signaling between immune, glial, and neural cells is integral to the development of pathological pain. Modulation of these communications may hold the key to improved pain management. In this review we first offer an overview of the relationships between pro-inflammatory cytokine and chemokine signaling and pathological pain, with a focus on the actions of cytokines and chemokines in communication between glia (astrocytes and microglia), immune cells (macrophages and T cells), and neurons. These interactions will be discussed in relation to both peripheral and central nervous system locations. Several novel non-neuronal drug targets for controlling pain are emerging as highly promising, including non-viral IL-10 gene therapy, which offer the potential for substantial pain relief through localized modulation of targeted cytokine pathways. Preclinical investigation of the mechanisms underlying the success of IL-10 gene therapy revealed the unexpected discovery of the powerful anti-nociceptive anti-inflammatory properties of D-mannose, an adjuvant in the non-viral gene therapeutic formulation. This review will include gene therapeutic approaches showing the most promise in controlling pro-inflammatory signaling via increased expression of anti-inflammatory cytokines like interleukin-10 (IL-10) or IL-4, or by directly limiting the bioavailability of specific pro-inflammatory cytokines, as with tumor necrosis factor (TNF) by the TNF soluble receptor (TNFSR). Approaches that increase endogenous anti-inflammatory signaling may offer additional opportunities for pain therapeutic development in patients not candidates for gene therapy. Promising novel avenues discussed here include the disruption of lymphocyte function-associated antigen (LFA-1) activity, antagonism at the cannabinoid 2 receptor (CB2R), and toll-like receptor 4 (TLR4) antagonism. Given the partial efficacy of current drugs, new strategies to manipulate neuroimmune and cytokine interactions hold considerable promise.

LFA-1 antagonist (BIRT377) similarly reverses peripheral neuropathic pain in male and female mice with underlying sex divergent peripheral immune proinflammatory phenotypes

Aim:

The majority of preclinical studies investigating aberrant glial-neuroimmune actions underlying neuropathic pain have focused on male rodent models. Recently, studies have shown peripheral immune cells play a more prominent role than glial cells in mediating pathological pain in females. Here, we compared the onset and duration of allodynia in males and females, and the anti-allodynic action of a potentially novel therapeutic drug (BIRT377) that not only antagonizes the action of lymphocyte function-associated antigen-1 (LFA-1) to reduce cell migration in the periphery, but may also directly alter the cellular inflammatory bias.

Methods:

Male and female mice were subjected to peripheral nerve injury chronic constriction injury (CCI) applying two methods, using either 4–0 or 5–0 chromic gut suture material, to examine potential sex differences in the onset, magnitude and duration of allodynia. Hindpaw sensitivity before and after CCI and application of intravenous BIRT377 was assessed. Peripheral and spinal tissues were analyzed for protein (multiplex electrochemiluminescence technology) and mRNA expression (quantitative real-time PCR). The phenotype of peripheral T cells was determined using flow cytometry.

Results:

Sex differences in proinflammatory CCL2 and IL-1β and the anti-inflammatory IL-10 were observed from a set of cytokines analyzed. A profound proinflammatory T cell (Th17) response in the periphery and spinal cord was also observed in neuropathic females. BIRT377 reversed pain, reduced IL-1β and TNF, and increased IL-10 and transforming growth factor (TGF)-β1, also an anti-inflammatory cytokine, in both sexes. However, female-derived T cell cytokines are transcriptionally regulated by BIRT377, as demonstrated by reducing proinflammatory IL-17A production with concurrent increases in IL-10, TGF-β1 and the anti-inflammatory regulatory T cell-related factor, FOXP3.

Conclusion:

This study supports that divergent peripheral immune and neuroimmune responses during neuropathy exists between males and females. Moreover, the modulatory actions of BIRT377 on T cells during neuropathy are predominantly specific to females. These data highlight the necessity of including both sexes for studying drug efficacy and mechanisms of action in preclinical studies and clinical trials.

The anti-nociceptive effects of Porphyromonas gingivalis lipopolysaccharide

OBJECTIVE

The objective of this study was to assess the effect of Porphyromonas gingivalis lipopolysaccharide (PG LPS) on acute pain-related behaviour induced in rats and to measure its impact on the levels of pro-inflammatory cytokines (IL-1β, IL-6) and anti-inflammatory (IL-10) cytokines.

DESIGN

The Brennan model was used to induce acute pain like signs in rats' hind paw. Twenty-four hours following the surgery the rats were divided into 5 groups and the affected paws were injected with 0.2 m l of one of three commercialized forms PG LPS doses (high - 1 mg/ml, medium - 0.6 mg/m l and low - 0.2 mg/m l), diclofenac sodium (1 mg/kg) or saline. Tactile allodynia, mechanical hyperalgesia, body temperature and paw swelling were assessed at baseline, 24 h postoperatively and 2 h after the paw injection. The affected and contra-lateral paw tissue was assessed for the mentioned above cytokines levels employing enzyme-linked immunosorbent assay.

RESULTS

This study may suggest that PG LPS can reduce pain like behaviour via increased levels of anti-inflammatory cytokine IL-10 (5900 ± 748, p < 0.05). The high PG LPS dose and diclofenac reduced the tactile allodynia and mechanical hyperalgesia significantly (42.2 ± 4 and1.6 ± 0.3, p < 0.05). PG LPS high dose increase IL-10 levels while diclofenac reduces IL-1β levels significantly (5900 ± 748 and 1760 ± 271.2). The LPS administration had no effect on paw swelling and did not increase rat's body temperature.

CONCLUSION

The results demonstrated that PG LPS local application could possess anti- nociceptive properties, which at least in part is mediated by an increase in IL-10 levels.

Targeting the β2-integrin LFA-1, reduces adverse neuroimmune actions in neuropathic susceptibility caused by prenatal alcohol exposure

Recently, moderate prenatal alcohol exposure (PAE) was shown to be a risk factor for peripheral neuropathy following minor nerve injury. This effect coincides with elevated spinal cord astrocyte activation and ex vivo immune cell reactivity assessed by proinflammatory cytokine interleukin (IL) -1β protein expression. Additionally, the β2-integrin adhesion molecule, lymphocyte function-associated antigen-1 (LFA-1), a factor that influences the expression of the proinflammatory/anti-inflammatory cytokine network is upregulated. Here, we examine whether PAE increases the proinflammatory immune environment at specific anatomical sites critical in the pain pathway of chronic sciatic neuropathy; the damaged sciatic nerve (SCN), the dorsal root ganglia (DRG), and the spinal cord. Additionally, we examine whether inhibiting LFA-1 or IL-1β actions in the spinal cord (intrathecal; i.t., route) could alleviate chronic neuropathic pain and reduce spinal and DRG glial activation markers, proinflammatory cytokines, and elevate anti-inflammatory cytokines. Results show that blocking the actions of spinal LFA-1 using BIRT-377 abolishes allodynia in PAE rats with sciatic neuropathy (CCI) of a 10 or 28-day duration. This effect is observed (utilizing immunohistochemistry; IHC, with microscopy analysis and protein quantification) in parallel with reduced spinal glial activation, IL-1β and TNFα expression. DRG from PAE rats with neuropathy reveal significant increases in satellite glial activation and IL-1β, while IL-10 immunoreactivity is reduced by half in PAE rats under basal and neuropathic conditions. Further, blocking spinal IL-1β with i.t. IL-1RA transiently abolishes allodynia in PAE rats, suggesting that IL-1β is in part, necessary for the susceptibility of adult-onset peripheral neuropathy caused by PAE. Chemokine mRNA analyses from SCN, DRG and spinal cord reveal that increased CCL2 occurs following CCI injury regardless of PAE and BIRT-377 treatment. These data demonstrate that PAE creates dysregulated proinflammatory IL-1β and TNFα /IL-10 responses to minor injury in the sciatic-DRG-spinal pain pathway. PAE creates a risk for developing peripheral neuropathies, and LFA-1 may be a novel therapeutic target for controlling dysregulated neuroimmune actions as a consequence of PAE.

IL-10 and CXCL2 in trigeminal ganglia in neuropathic pain

Many trigeminal neuropathic pain patients suffer severe chronic pain. The neuropathic pain might be related with cross-excitation of the neighboring neurons and satellite glial cells (SGCs) in the sensory ganglia and increasing the pain signals from the peripheral tissue to the central nervous system. We induced trigeminal neuropathic pain by infraorbital nerve constriction injury (IONC) in Sprague-Dawley rats. We tested cytokine (CXCL2 and IL-10) levels in trigeminal ganglia (TGs) after trigeminal neuropathic pain induction, and the effect of direct injection of the anti-CXCL2 and recombinant IL-10 into TG. We found that IONC induced pain behavior. Additionally, IONC induced satellite glial cell activation in TG and cytokine levels of TGs were changed after IONC. CXCL2 levels increased on day 1 of neuropathic pain induction and decreased gradually, with IL-10 levels showing the opposite trend. Recombinant IL-10 or anti-CXCL2 injection into TG decreased pain behavior. Our results show that IL-10 or anti-CXCL2 are therapy options for neuropathic pain.

The Elevated Serum Level of IFN-γ in Patients with Failed Back Surgery Syndrome Remains Unchanged after Spinal Cord Stimulation

Objectives

We investigated the influence of spinal cord stimulation (SCS) on IFN-γ, IL-1β, IL-6, TNF-α, IL-10, and TGF-β serum levels in failed back surgery syndrome (FBSS) patients. The study will try to give new insights into the mechanism of SCS action and the role of IFN-γ and other cytokines in neuropathic pain (NP) development.

Materials and Methods

Clinical and biochemical assessment was conducted in four groups of patients: group 0 consisted of 24 FBSS patients qualified to SCS therapy, group 1 included 17 patients who were one month after implantation, group 2 featured 12 patients who were 3 months after the implantation, and group C (the control group) with no NP. Clinical status was assessed with the use of Numeric Rating Scale (NRS), the Pain Rating Index of McGill Pain Questionnaire (SF-MPQ), the Oswestry Disability Index (ODI), and Beck Depression Inventory (BDI). The plasma concentrations of IFN-γ were ascertained by an immunoenzymatic method.

Results

We found a significant difference between the patients before SCS and controls' serum level of IFN-γ. Similarly, a significantly higher level of TNF-α and significantly lower level of IL-10 in FBSS patients than controls were observed. The significant differences were not observed between SCS patients 3 months after the procedure and controls' serum level of IFN-γ and other cytokines. We noticed a positive correlation between IFN-γ concentration with NRS back value before SCS and positive correlation between IFN-γ concentration after SCS with NRS leg value before SCS. Higher IFN-γ concentrations accompanied higher NRS values. Levels of TGF-β and IL-10 may correlate with physical ability and depressive behavior.

Conclusions

SCS did not influence serum cytokine levels significantly. Serum concentration of IFN-γ may be recognized as an occasional pain factor because of its significantly higher level in FBSS patients versus controls and higher IFN-γ value accompanying higher pain intensity.

Inducible nitric oxide synthase inhibition by 1400W limits pain hypersensitivity in a neuropathic pain rat model

NEW FINDINGS

What is the central question of this study? Can modulation of inducible NO synthase reduce pain behaviour and pro-inflammatory cytokine signalling in a rat model of neuropathic pain? What is the main finding and its importance? Nitric oxide synthase-based therapies could be effective for the treatment of peripheral neuropathic pain.

ABSTRACT

Peripheral neuropathic pain (PNP), resulting from injury to or dysfunction of a peripheral nerve, is a major health problem that affects 7-8% of the population. It is inadequately controlled by current drugs and is characterized by pain hypersensitivity, which is believed to be attributable to sensitization of peripheral and CNS neurons by various inflammatory mediators. Here we examined, in a rat model of PNP: (i) whether reducing levels of nitric oxide (NO) with 1400W, a highly selective inhibitor of inducible NO synthase (iNOS), would prevent or attenuate pain hypersensitivity; and (ii) the effects of 1400W on plasma concentrations of several cytokines that are secreted after iNOS upregulation during chronic pain states. The L5 spinal nerve axotomy (SNA) model of PNP was used, and 1400W (20 mg kg^-1 ) was administered i.p. at 8 h intervals for 3 days starting at 18 h post-SNA. Changes in plasma concentrations of 12 cytokines in SNA rats treated with 1400W were examined using multiplex enzyme-linked immunosorbent assay. The SNA rats developed behavioural signs of mechanical and heat hypersensitivity. Compared with the vehicle/control, 1400W significantly: (i) limited development of mechanical hypersensitivity at 66 h post-SNA and of heat hypersensitivity at 42 h and at several time points tested thereafter; and (ii) increased the plasma concentrations of interleukin (IL)-1α, IL-1β and IL-10 in the SNA rats. The findings suggest that 1400W might exert its analgesic effects by reducing iNOS and altering the balance between the pro-inflammatory (IL-1β and IL-1α) and anti-inflammatory (IL-10) cytokines and that therapies targeting NO or its enzymes might be effective for the treatment of PNP.

Effects of spinal non-viral interleukin-10 gene therapy formulated with d-mannose in neuropathic interleukin-10 deficient mice: Behavioral characterization, mRNA and protein analysis in pain relevant tissues

Studies show that spinal (intrathecal; i.t.) interleukin-10 (IL-10) gene therapy reverses neuropathic pain in animal models, and co-administration with the mannose receptor (MR; CD206) ligand d-mannose (DM) greatly improves therapeutic efficacy. However, the actions of endogenous IL-10 may be required for enduring pain control observed following i.t. IL-10 gene therapy, potentially narrowing the application of this non-viral transgene delivery approach. Here, we show that i.t. application of naked plasmid DNA expressing the IL-10 transgene co-injected with DM (DM/pDNA-IL-10) for the treatment of peripheral neuropathic pain in IL-10 deficient (IL-10 KO) mice results in a profound and prolonged bilateral pain suppression. Neuropathic pain is induced by unilateral sciatic chronic constriction injury (CCI), and while enduring relief of light touch sensitivity (mechanical allodynia) in both wild type (WT) and IL-10 KO mice was observed following DM/pDNA-IL-10 co-therapy, transient reversal from allodynia was observed following i.t. DM alone. In stably pain-relieved IL-10 KO mice given DM/pDNA-IL-10, mRNA for the IL-10 transgene is detected in the cauda equina and ipsilateral dorsal root ganglia (DRG), but not the lumbar spinal cord. Further, DM/pDNA-IL-10 application increases anti-inflammatory TGF-β1 and decreases pro-inflammatory TNF mRNA in the ipsilateral DRG compared to allodynic controls. Additionally, DM/pDNA-IL-10 treated mice exhibit decreased spinal pro-inflammatory mRNA expression for TNF, CCL2 (MCP-1), and for the microglial-specific marker TMEM119. Similarly, DM/pDNA-IL-10 treatment decreases immunoreactivity for the astrocyte activation marker GFAP in lumbar spinal cord dorsal horn. Despite transient reversal and early return to allodynia in DM-treated mice, lumbar spinal cord revealed elevated TNF, CCL2 and TMEM119 mRNA levels. Both MR (CD206) and IL-10 receptor mRNAs are increased in the DRG following CCI manipulation independent of injection treatment, suggesting that pathological conditions stimulate upregulation and availability of relevant receptors in critical anatomical regions required for the therapeutic actions of the DM/pDNA-IL-10 co-therapy. Taken together, the current report demonstrates that non-viral DM/pDNA-IL-10 gene therapy does not require endogenous IL-10 for enduring relief of peripheral neuropathic pain and does not require direct contact with the spinal cord dorsal horn for robust and enduring relief of neuropathic pain. Spinal non-viral DM/pDNA-IL-10 co-therapy may offer a framework for the development of non-viral gene therapeutic approaches for other diseases of the central nervous system.

Saikosaponin a increases interleukin-10 expression and inhibits scar formation after sciatic nerve injury

Nerve scarring after peripheral nerve injury can severely hamper nerve regeneration and functional recovery. Further, the anti-inflammatory cytokine, interleukin-10, can inhibit nerve scar formation. Saikosaponin a (SSa) is a monomer molecule extracted from the Chinese medicine, Bupleurum. SSa can exert anti-inflammatory effects in spinal cord injury and traumatic brain injury. However, it has not been shown whether SSa can play a role in peripheral nerve injury. In this study, rats were randomly assigned to three groups. In the sham group, the left sciatic nerve was directly sutured after exposure. In the sciatic nerve injury (SNI) + SSa and SNI groups, the left sciatic nerve was sutured and continuously injected daily with SSa (10 mg/kg) or an equivalent volume of saline for 7 days. Enzyme linked immunosorbent assay results demonstrated that at 7 days after injury, interleukin-10 level was considerably higher in the SNI + SSa group than in the SNI group. Masson staining and western blot assay demonstrated that at 8 weeks after injury, type I and III collagen content was lower and nerve scar formation was visibly less in the SNI + SSa group compared with the SNI group. Simultaneously, sciatic functional index and nerve conduction velocity were improved in the SNI + SSa group compared with the SNI group. These results confirm that SSa can increase the expression of the anti-inflammatory factor, interleukin-10, and reduce nerve scar formation to promote functional recovery of injured sciatic nerve.

Effect of Pregabalin and Diclofenac on tactile allodynia, mechanical hyperalgesia and pro inflammatory cytokine levels (IL-6, IL-1β) induced by chronic constriction injury of the infraorbital nerve in rats

The present study evaluated the effects of systemic pregabalin (PG) and diclofenac (Dic) on neuropathic orofacial pain induced by chronic constriction injury (CCI) of the infraorbital nerve (ION) and on the pro-inflammatory cytokines levels in the affected nerve. Fifty-four rats underwent left infra orbital nerve CCI, and 7 days after the procedure as the pain developed, the rats were randomly assigned to one of the treatment groups: PG 300, 30 or 10 mg/kg, Dic 10, 5 or 1 mg/kg or saline group (Sal) (n/group = 8). Addiitonal 8 rats served as naïve control group. Tactile-allodynia and Mechano-hyperalgesia were tested before the surgical procedure and at days 7, 8, and 9 postoperatively. On the 9th day, the rats were euthanized and the affected and contralateral sciatic nerves were harvested to assess IL-6 and IL-1β nerve levels employing enzyme linked immunosorbent assay (ELISA). Daily injection of PG (all doses) significantly reduced tactile-allodynia and mechano-hyperalgesia (p < .05) while Dic did not. On the 9th day, the ipsilateral nerve IL-6 levels were significantly decreased (p < .05) in the PG and DIC groups compared to the Sal group. IL-1β levels demonstrated a significant reduction (p < .05) in the PG group when compared to saline. These results suggest that PG but not Dic may be effective in reducing neuropathic orofacial pain. The mechanisms of action may be associated to some extent with reduction in IL-1β levels in the affected nerve.

Immune modulation by curcumin: The role of interleukin-10

Cytokines are small secreted proteins released by different types of cells with specific effects on cellular signaling and communication via binding to their receptors on the cell surface. IL-10 is known to be a pleiotropic and potent anti-inflammatory and immunosuppressive cytokine that is produced by both innate and adaptive immunity cells including dendritic cells, macrophages, mast cells, natural killer cells, eosinophils, neutrophils, B cells, CD8⁺ T cells, and T_H1, T_H2, and T_H17 and regulatory T cells. Both direct and indirect activation of the stress axis promotes IL-10 secretion. IL-10 deregulation plays a role in the development of a large number of inflammatory diseases such as neuropathic pain, Parkinson's disease, Alzheimer's disease, osteoarthritis, rheumatoid arthritis, psoriasis, systemic lupus erythematosus, type 1 diabetes, inflammatory bowel disease, and allergy. Curcumin is a natural anti-inflammatory compound able to induce the expression and production of IL-10 and enhancing its action on a large number of tissues. In vitro and in pre-clinical models curcumin is able to modulate the disease pathophysiology of conditions such as pain and neurodegenerative diseases, bowel inflammation, and allergy, but also of infections and cancer through its effect on IL-10 secretion. In humans, at least one part of the positive effects of curcumin on health could be related to its ability to enhance IL-10 -mediated effects.

Targeting cytokines for treatment of neuropathic pain

BACKGROUND

Neuropathic pain is a challenging condition often refractory to existing therapies. An increasing number of studies have indicated that the immune system plays a crucial role in the mediation of neuropathic pain. Exploration of the various functions of individual cytokines in neuropathic pain will provide greater insight into the mechanisms of neuropathic pain and suggest potential opportunities to expand the repertoire of treatment options.

METHODS

A literature review was performed to assess the role of pro-inflammatory and anti-inflammatory cytokines in the development of neuropathic pain. Both direct and indirect therapeutic approaches that target various cytokines for pain were reviewed. The current understanding based on preclinical and clinical studies is summarized.

RESULTS AND CONCLUSIONS

In both human and animal studies, neuropathic pain has been associated with a pro-inflammatory state. Analgesic therapies involving direct manipulation of various cytokines and indirect methods to alter the balance of the immune system have been explored, although there have been few large-scale clinical trials evaluating the efficacy of immune modulators in the treatment of neuropathic pain. TNF-α is perhaps the widely studied pro-inflammatory cytokine in the context of neuropathic pain, but other pro-inflammatory (IL-1β, IL-6, and IL-17) and anti-inflammatory (IL-4, IL-10, TGF-β) signaling molecules are garnering increased interest. With better appreciation and understanding of the interaction between the immune system and neuropathic pain, novel therapies may be developed to target this condition.

Interleukin-8 levels in rat models of nerve damage and neuropathic pain

Interleukin-8 (IL-8) is a pro-inflammatory cytokine that has been shown to play a role in inflammatory and autoimmune disorders. The objective of the present study was to assess the levels of IL-8 in rat serum, dorsal root ganglion (DRG) and the sciatic nerve following four different forms of sciatic nerve injury. The models used to induce the injury included partial sciatic ligation (PSL), chronic constriction injury (CCI), perineural inflammation (neuritis) and complete sciatic transection (CST). Mechanical and thermal hyperalgesia were detected by measuring withdrawal responses from a mechanical stimulus and withdrawal latency from thermal stimulation. Enzyme-linked immunosorbent assays (ELISA) was used to assess the IL-8 levels in the affected and contralateral sciatic nerves. Rats exposed to PSL and neuritis developed significant nociceptive response (mechanical and thermal hyperalgesia) in the affected side at three days post-surgery whereas the CCI group at eight days post-surgery. No mechanical or thermal hyperalgesia was observed in rats exposed to CST at either three or eight days postsurgery. Additionally, IL-8 levels were significantly increased in the injured sciatic nerve at 3 and 8days following PSL and neuritis as well as at 8days following CCI when compared to naïve animals. A significant up regulation of IL-8 levels was observed in the ipsilateral DRG at 3 and 8days following CST compared to naïve animals. The serum IL-8 levels remained unchanged in all models of nerve damage. The results of this study suggest that IL-8's role in the neuropathic pain etiology may be specific to nerve injury type.

Presence of caffeine reversibly interferes with efficacy of acupuncture-induced analgesia

Acupuncture is an alternative treatment for wide spectrum chronic pain. However, its validity remains controversial due to the disputed efficacy assessed in various clinical studies. Moreover, variability amongst individuals complicates the predictability of outcome, which impedes the integration of acupuncture into mainstream pain management programs. In light of our previous finding that the analgesic effect of acupuncture is mediated by adenosine A1 receptor activation at the acupuncture point, we here report that in acute and chronic animal pain models, oral intake of caffeine, a potent adenosine receptor antagonist, interferes with acupuncture analgesia, even at a low dose. Local administration of caffeine at the acupuncture point was sufficient to eliminate the analgesic effect, dismissing the systemic action of caffeine. Such interference was reversible, as caffeine withdrawal fully restored the efficacy of acupuncture by the next day, and long-term exposure to caffeine did not alter A1 receptor expression at the acupuncture point. Combined, these data indicate that a trace amount of caffeine can reversibly block the analgesic effects of acupuncture, and controlling caffeine consumption during acupuncture may improve pain management outcomes.

Pro and anti-inflammatory cytokine levels (TNF-α, IL-1β, IL-6 and IL-10) in rat model of neuroma

Traumatic neuroma is neuronal tissue proliferation developed in a nerve injury site, often associated with increased sensitivity and spontaneous or evoked neuropathic pain. The mechanisms leading to the disorganized nerve proliferation are not completely understood, though inflammation in the injured nerve vicinity most likely has a role in the process. Inflammatory cytokines are also known to be involved in the maintenance and development of post-traumatic and neuropathic pain. The goal of this study was to quantify and compare pro and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10) levels in nerves that formed neuromas and nerves that did not, following sciatic nerve transection. A total of 30 rats were used in this study. Twenty rats underwent sciatic nerve transection and 10 underwent sham surgery. Six weeks post-surgery nerve sections were collected and histologically evaluated for neuroma formation. The samples were then classified as neuroma, non-neuroma and sham groups. TNF-α, IL-1β, IL-6 and IL-10 levels were measured in the nerves employing ELISA. TNF-α levels were significantly higher in both neuroma and non-neuroma-forming injured nerves compared to the sham group. IL-1β and IL-6 levels were significantly higher in the neuroma-forming nerves compared to the sham group. IL-10 levels were significantly higher in the non-neuroma group compared to the sham group. In conclusion IL-6, and IL-1 β may have a role in the formation of traumatic neuroma while IL-10 may inhibit neuroma formation.

Bupivacaine effectively relieves inflammation-induced pain by suppressing activation of the NF-κB signalling pathway and inhibiting the activation of spinal microglia and astrocytes

The pain induced by local acute inflammation results in mild to severe discomfort, in addition to the possibility of physiological dysfunction and psychiatric disorders, such as sleep disorders and depression. However, the pathogenesis of pain is yet to be fully elucidated. In the present study, the effects of bupivacaine were explored in rat models inflammatory pain in order to investigate the anti-pain mechanism of bupivacaine. Complete Freund's adjuvant (CFA) was injected into the right rear foot of the rats to establish a model of transient inflammation-induced pain. Rats were randomly divided into four groups (n=8): CFA, CFA plus bupivacaine, CFA plus saline and untreated. The mechanical withdrawal threshold (MWT) of the rats was detected prior to and following CFA injection, and the results demonstrated that the MWT in the right rear foot significantly decreased from the 1st day of CFA injection (P<0.01; n=8), as compared with the untreated controls. Bupivacaine treatment was demonstrated to significantly increase the MWT of rats treated with CFA stimulation, as compared with the CFA group (P<0.01). Rotarod testing was performed to assess the motor activity of the rats, and the results demonstrated no significant differences among the four groups (P>0.05). Furthermore, the respective body weights of the rats were determined every two days before and after CFA injection, and no significant differences were detected among the four groups (P>0.05). Western blot analysis was performed to analyze expression levels of IκB and nuclear factor (NF)-κB, and the results demonstrated that bupivacaine increased the expression of IκB and decreased the expression levels of NF-κB, as compared with the rats with CFA-induced inflammatory responses, suggesting that bupivacaine inhibited NF-κB activation in the dorsal horn of the lumbar spinal cord of the model rats. Furthermore, reverse transcription-quantitative polymerase chain reaction analysis was performed to analyze the expression levels of inflammatory cytokines, which demonstrated that bupivacaine significantly inhibited the expression of TNF-α, IL-1β and IL-6, as compared with the untreated group (P<0.01). Moreover, bupivacaine treatment significantly decreased the expression of spinal microglial marker OX42 and astrocyte marker-glial fibrillary acidic protein, as compared with the rats in the CFA group (P<0.01). The present findings demonstrated that treatment with bupivacaine significantly decreased the activation of microglia and astrocytes in rat models of inflammatory pain. Therefore, the present results may provide clarification of the pathogenesis and mechanism of inflammation-induced pain and may provide novel therapeutic strategies for the clinical treatment of pain.

Mesoporous Silica Particles as a Multifunctional Delivery System for Pain Relief in Experimental Neuropathy

The long-term use of potent analgesics is often needed to treat chronic pain. However, it has been greatly hindered by their side effects such as addiction and withdrawal reactions. The study seeks to circumvent these drawbacks by taking advantage of a multifunctional delivery system based on nanoparticles to target on pathological neuroinflammation. A drug delivery system is designed and generated using mesoporous silica nanoparticles (MSNs) that are loaded with Δ9-THC (Δ9-tetrahydrocannabinol, a cannabinoid) and ARA290 (an erythropoietin-derived polypeptide), both of which possess analgesic and anti-inflammatory functions. The actions of such THC-MSN-ARA290 nanocomplexes depend on the enhanced permeability and retention of THC through nanosized carriers, and a redox-sensitive release of conjugated ARA290 peptide into the local inflammatory milieu. The biosafety and anti-inflammatory effects of the nanocomplexes are first evaluated in primary microglia in vitro, and further in a mouse model of chronic constriction injury. It is found that the nanocomplexes attenuate in vitro and in vivo inflammation, and achieve a sustained relief of neuropathic pain in injured animals induced by both thermal hyperalgesia and mechanical allodynia. Thus, a nanoparticle-based carrier system can be useful for the amelioration of chronic neuropathic pain through combinatorial drug delivery.

Resolvin D1 Inhibits Mechanical Hypersensitivity in Sciatica by Modulating the Expression of Nuclear Factor-κB, Phospho-extracellular Signal–regulated Kinase, and Pro- and Antiinflammatory Cytokines in the Spinal Cord and Dorsal Root Ganglion

Background

Accumulating evidence indicates that spinal inflammatory and immune responses play an important role in the process of radicular pain caused by intervertebral disk herniation. Resolvin D1 (RvD1) has been shown to have potent antiinflammatory and antinociceptive effects. The current study was undertaken to investigate the analgesic effect of RvD1 and its underlying mechanism in rat models of noncompressive lumbar disk herniation.

Methods

Rat models of noncompressive lumber disk herniation were established, and mechanical thresholds were evaluated using the von Frey test during an observation period of 21 days (n = 8/group). Intrathecal injection of vehicle or RvD1 (10 or 100 ng) was performed for three successive postoperative days. On day 7, the ipsilateral spinal dorsal horns and L5 dorsal root ganglions (DRGs) were removed to assess the expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-10, and transforming growth factor-β1 (TGF-β1) and the activation of nuclear factor-κB (NF-κB)/p65 and phospho-extracellular signal–regulated kinase (p-ERK) signaling (n = 30/group).

Results

The application of nucleus pulposus to L5 DRG induced prolonged mechanical allodynia, inhibited the production of IL-10 and TGF-β1, and up-regulated the expression of TNF-α, IL-1β, NF-κB/p65, and p-ERK in the spinal dorsal horns and DRGs. Intrathecal injection of RvD1 showed a potent analgesic effect, inhibited the up-regulation of TNF-α and IL-1β, increased the release of IL-10 and TGF-β1, and attenuated the expression of NF-κB/p65 and p-ERK in a dose-dependent manner.

Conclusions

The current study showed that RvD1 might alleviate neuropathic pain via regulating inflammatory mediators and NF-κB/p65 and p-ERK pathways. Its antiinflammatory and proresolution properties may offer novel therapeutic approaches for the management of neuropathic pain.

Atorvastatin prevents neuroinflammation in chronic constriction injury rats through nuclear NFκB downregulation in the dorsal root ganglion and spinal cord

Atorvastatin, traditionally used to treat hyperlipidemia, belongs to a class of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors. This study investigated the antineuroinflammatory and antihyperalgesic effects of atorvastatin in dorsal root ganglia (DRG) and spinal cord for chronic constriction injury (CCI) neuropathic pain in rats. Fifty-four Sprague-Dawley rats were divided into three groups including sham, CCI, and CCI+atorvastatin. Rats were orally administered atorvastatin (10 mg/kg/day) once daily for 2 weeks after surgery and sacrificed at days 3, 7, and 14. All animals were assessed for mechanical allodynia and thermal hyperalgesia in both hindpaws. Western blotting, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA) were used to detect inflammatory proteins and proinflammatory cytokines at day 7 after surgery. Pain behaviors were significantly reduced in the CCI+atorvastatin group compared to the CCI group. Atorvastatin attenuated CCI-induced inflammatory mediators (pAkt/Akt, COX-2, iNOS, EP1, and EP4) and reduced proinflammatory cytokines TNF-α and IL-1β levels in DRG and spinal cord. Atorvastatin also inhibited nuclear pNFκB activation. Double immunofluorescent staining further demonstrated that pNFκB proteins were decreased by atorvastatin in DRG satellite cells and spinal microglia. Atorvastatin may primarily inhibit the nuclear translocation of pNFκB to prevent CCI-induced peripheral neuropathic pain. Atorvastatin exhibits antineuroinflammatory and antinociceptive properties in the central and peripheral nerve systems.