Targeting invading macrophage-derived PGE2, IL-6 and calcitonin gene-related peptide in injured nerve to treat neuropathic pain

Inflammation in the Peripheral Nervous System after Injury

Nerve injury is a common condition that occurs as a result of trauma, iatrogenic injury, or long-lasting stimulation. Unlike the central nervous system (CNS), the peripheral nervous system (PNS) has a strong capacity for self-repair and regeneration. Peripheral nerve injury results in the degeneration of distal axons and myelin sheaths. Macrophages and Schwann cells (SCs) can phagocytose damaged cells. Wallerian degeneration (WD) makes the whole axon structure degenerate, creating a favorable regenerative environment for new axons. After nerve injury, macrophages, neutrophils and other cells are mobilized and recruited to the injury site to phagocytose necrotic cells and myelin debris. Pro-inflammatory and anti-inflammatory factors involved in the inflammatory response provide a favorable microenvironment for peripheral nerve regeneration and regulate the effects of inflammation on the body through relevant signaling pathways. Previously, inflammation was thought to be detrimental to the body, but further research has shown that appropriate inflammation promotes nerve regeneration, axon regeneration, and myelin formation. On the contrary, excessive inflammation can cause nerve tissue damage and pathological changes, and even lead to neurological diseases. Therefore, after nerve injury, various cells in the body interact with cytokines and chemokines to promote peripheral nerve repair and regeneration by inhibiting the negative effects of inflammation and harnessing the positive effects of inflammation in specific ways and at specific times. Understanding the interaction between neuroinflammation and nerve regeneration provides several therapeutic ideas to improve the inflammatory microenvironment and promote nerve regeneration.

Ziyuglycoside II attenuated OVX mice bone loss via inflammatory responses and regulation of gut microbiota and SCFAs

BACKGROUND AND PURPOSE

Osteoporosis (OP) is a frequent clinical problem for the elderly. Traditional Chinese Medicine (TCM) has achieved beneficial results in the treatment of OP. Ziyuglycoside II (ZGS II) is a major active compound of Sanguisorba officinalis L. that has shown anti-inflammation and antioxidation properties, but little information concerning its anti-OP potential is available. Our research aims to investigate the mechanism of ZGS II in ameliorating bone loss by inflammatory responses and regulation of gut microbiota and short chain fatty acids (SCFAs) in ovariectomized (OVX) mice.

METHODS

We predicted the mode of ZGS II action on OP through network pharmacology and molecular docking, and an OVX mouse model was employed to validate its anti-OP efficacy. Then we analyzed its impact on bone microstructure, the levels of inflammatory cytokines and pain mediators in serum, inflammation in colon, intestinal barrier, gut microbiota composition and SCFAs in feces.

RESULTS

Network pharmacology identified 55 intersecting targets of ZGS II related to OP. Of these, we predicted IGF1 may be the core target, which was successfully docked with ZGS II and showed excellent binding ability. Our in vivo results showed that ZGS II alleviated bone loss in OVX mice, attenuated systemic inflammation, enhanced intestinal barrier, reduced the pain threshold, modulated the abundance of gut microbiota involving norank_f__Muribaculaceae and Dubosiella, and increased the content of acetic acid and propanoic acid in SCFAs.

CONCLUSIONS

Our data indicated that ZGS II attenuated bone loss in OVX mice by relieving inflammation and regulating gut microbiota and SCFAs.

Histological evaluation of mouse tongue incisions after Er:YAG laser surgery with different pulse energies versus after conventional scalpel surgery

PURPOSE

To identify the surgical instrument that allows for optimal healing of tongue incisions.

METHODS

An Er:YAG laser was compared with different pulse energies to a conventional scalpel for the incision of mouse tongue tissues. Mice were sacrificed through cervical dislocation at 24, 48, and 72 h postoperatively, followed by extraction of their tongues for incision experiments. The healing of the incisions and expression of inflammation- and pain-related factors in the tongues were compared between the surgical procedure groups.

RESULTS

In laser-treated mice, tongue incisions healed the fastest when the laser output energy was 60 MJ per pulse. Macrophage chemotaxis toward the incisional area was triggered on the first postoperative day for the 60-MJ group, while the time for macrophage chemotaxis to the surgical area was later in the 80-MJ group. Tumor necrosis factor-alpha expression increased and then decreased in the 80-MJ group; however, it gradually decreased in the 60-MJ and conventional scalpel groups. Prostaglandin E2 expression increased and then decreased in the 80-MJ and conventional scalpel groups but gradually decreased in the 60-MJ group. The expression of transforming growth factor beta 1 gradually decreased in the 60-MJ and 80-MJ groups but gradually increased in the conventional scalpel group.

CONCLUSION

Compared with surgical procedures using conventional scalpels, those using an Er:YAG laser with appropriate pulse energies can inhibit inflammation in the incisional area and promote incision healing. The use of an Er:YAG laser with appropriate pulse energies can alleviate intraoperative and postoperative pain in the incisional area.

Mediators of Neuropathic Pain; Focus on Spinal Microglia, CSF-1, BDNF, CCL21, TNF-α, Wnt Ligands, and Interleukin 1β

Intractable neuropathic pain is a frequent consequence of nerve injury or disease. When peripheral nerves are injured, damaged axons undergo Wallerian degeneration. Schwann cells, mast cells, fibroblasts, keratinocytes and epithelial cells are activated leading to the generation of an “inflammatory soup” containing cytokines, chemokines and growth factors. These primary mediators sensitize sensory nerve endings, attract macrophages, neutrophils and lymphocytes, alter gene expression, promote post-translational modification of proteins, and alter ion channel function in primary afferent neurons. This leads to increased excitability and spontaneous activity and the generation of secondary mediators including colony stimulating factor 1 (CSF-1), chemokine C-C motif ligand 21 (CCL-21), Wnt3a, and Wnt5a. Release of these mediators from primary afferent neurons alters the properties of spinal microglial cells causing them to release tertiary mediators, in many situations via ATP-dependent mechanisms. Tertiary mediators such as BDNF, tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and other Wnt ligands facilitate the generation and transmission of nociceptive information by increasing excitatory glutamatergic transmission and attenuating inhibitory GABA and glycinergic transmission in the spinal dorsal horn. This review focusses on activation of microglia by secondary mediators, release of tertiary mediators from microglia and a description of their actions in the spinal dorsal horn. Attention is drawn to the substantial differences in the precise roles of various mediators in males compared to females. At least 25 different mediators have been identified but the similarity of their actions at sensory nerve endings, in the dorsal root ganglia and in the spinal cord means there is considerable redundancy in the available mechanisms. Despite this, behavioral studies show that interruption of the actions of any single mediator can relieve signs of pain in experimental animals. We draw attention this paradox. It is difficult to explain how inactivation of one mediator can relieve pain when so many parallel pathways are available.

Phosphorylation at Ser 727 Increases STAT3 Interaction with PKCε Regulating Neuron–Glia Crosstalk via IL-6-Mediated Hyperalgesia In Vivo and In Vitro

Methods

A rat hyperalgesia model was induced using an intraplantar injection of Freund's complete adjuvant (FCA) or an intrathecal injection of IL-6. Mechanical allodynia was evaluated using von Frey filament tests after intrathecal injections of T-5224 (c-Fos/AP-1 inhibitor), minocycline (Mino, a specific microglia inhibitor), L-2-aminoadipic acid (LAA, an astroglial toxin), PKCε inhibitor peptide, APTSTAT3-9R (STAT3 inhibitor), or anti-IL-6 antibody. The c-Fos, GFAP, Iba-1, PKCε, STAT3, pSTAT3^Tyr705 and pSTAT3^Ser727, and IL-6 expression at the spinal cord level was assessed by Western blot analysis. The interactive effects of PKCε and STAT3 were determined using immunofluorescence staining and immunoprecipitation in vivo and in vitro. Interleukin-6 promoter activity was examined using luciferase assays.

Results

T-5224, Mino, and LAA attenuated FCA- or IL-6-mediated inflammatory pain, with a decrease in c-Fos, GFAP, Iba-1, PKCε, and IL-6 expression. PKCε inhibitor peptide and APTSTAT3-9R reversed FCA-induced nociceptive behavior, while decreasing pSTAT3^Ser727, IL-6, c-Fos, GFAP, and Iba-1 expression and PKCε and STAT3 coexpression. Interleukin-6 promoter activity increased in the presence of PKCε and STAT3. The interaction with PKCε increased on phosphorylating STAT3 at Ser727 but not at Tyr705.

Conclusion

STAT3 phosphorylation at Ser 727 and the interaction with PKCε contribute to hyperalgesia via the IL-6-mediated signaling pathway, thus regulating neuron–glia crosstalk during inflammatory pain.

Targeting Neuroimmune Interactions in Diabetic Neuropathy with Nanomedicine

Significance: Diabetes is a major source of neuropathy and neuropathic pain that is set to continue growing in prevalence. Diabetic peripheral neuropathy (DPN) and pain associated with diabetes are not adequately managed by current treatment regimens. Perhaps the greatest difficulty in treating DPN is the complex pathophysiology, which involves aspects of metabolic disruption and neurotrophic deficits, along with neuroimmune interactions. There is, therefore, an urgent need to pursue novel therapeutic options targeting the key cellular and molecular players. Recent Advances: To that end, cellular targeting becomes an increasingly compelling drug delivery option as our knowledge of neuroimmune interactions continues to mount. These nanomedicine-based approaches afford a potentially unparalleled specificity and longevity of drug targeting, using novel or established compounds, all while minimizing off-target effects. Critical Issues: The DPN therapeutics directly targeted at the nervous system make up the bulk of currently available treatment options. However, there are significant opportunities based on the targeting of non-neuronal cells and neuroimmune interactions in DPN. Future Directions: Nanomedicine-based agents represent an exciting opportunity for the treatment of DPN with the goals of improving the efficacy and safety profile of analgesia, as well as restoring peripheral neuroregenerative capacity. Antioxid. Redox Signal. 36, 122-143.

Evaluation of Associated Genes with Traumatic Pain: A Systematic Review

OBJECTIVES

The knowledge about the molecular pathway of traumatic pain relief is less documented. This systematic review study aimed to identify the genes and molecular pathways associated with various traumatic pains.

METHODS

The online databases such as EMBASE, MEDLINE, PubMed, Cochrane Library, International Clinical Trials Registry Platform, Clinical Trials, Google Scholar, Wiley, ISI Web of Knowledge, and Scopus were searched. Two review authors searched and screened all records' titles and abstracts, and the third expert reviewer author resolved their disagreement. The study's design, various trauma injuries, types of genes, and molecular pathways were recorded. The genes and molecular pathways data were obtained via GeneCards®: The Human Gene Database (https://www.genecards.org).

RESULTS

Studies on a variety of trauma injuries regarding nerve and Spinal Cord Injuries (SCIs) (12 records), Hypertrophic scar with Severe Pain (one record), severe post-traumatic musculoskeletal pain (MSP) (one record), and orthopedic trauma (one record) were included. The main molecular pathways such as the immune system, apoptosis, and death receptor signaling, T-cell antigen receptor (TCR) signaling pathway, oxidative stress, interleukin(s) mediated signaling pathway, biological oxidations, metabolic pathways (especially amino acid metabolism and amino group), focal adhesion, the proliferation of vascular, epithelial, and connective tissue cells, angiogenesis and neural development were identified.

CONCLUSION

The immune system, apoptosis, and metabolic pathways are crucial for understanding the roles of genes in traumatic pain. It is recommended that these identified pathways and related genes be considered therapeutical targets for pain management in patients with trauma injuries. In addition, different forms of trauma injuries require different pathways and related genes to be considered.

Role of IL-6 in the regulation of neuronal development, survival and function

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Low-dose NSAIDs reduce pain via macrophage targeted nanoemulsion delivery to neuroinflammation of the sciatic nerve in rat

Neuroinflammation involving macrophages elevates Prostaglandin E₂, associated with neuropathic pain. Treatment with non-steroidal anti-inflammatory drugs (NSAIDs) inhibits cyclooxygenase, reducing PGE₂. However, NSAIDs cause physiological complications. We developed nanoemulsions incorporating celecoxib and near infrared dye. Intravenous injected nanoemulsion is incorporated into monocytes that accumulate at the injury; revealed in live animals by fluorescence. A single dose (celecoxib 0.24 mg/kg) provides targeted delivery in chronic constriction injury rats, resulting in significant reduction in the visualized inflammation, infiltration of macrophages, COX-2 and PGE₂. Animals exhibit relief from hypersensitivity persisting at least four-days. The total body burden of drug is reduced by >2000 fold over oral drug delivery.

CXCL1/CXCR2 signaling in pathological pain: Role in peripheral and central sensitization

Pathological pain conditions can be triggered after peripheral nerve injury and/or inflammation. It is associated with plasticity of nociceptive pathway in which pain is prolonged even after healing of the injured tissue. Generally combinations of analgesic drugs are not sufficient to achieve selective palliation from chronic pain, besides causing a greater number of side effects. In order to identify novel alternatives for more effective treatments, it is necessary to clarify the underlying mechanisms of pathological pain. It is well established that there are two main components in pathological pain development and maintenance: (i) primary sensory neuron sensitization (peripheral sensitization), and (ii) central sensitization. In both components cytokines and chemokines act as key mediators in pain modulation. CXCL1 is a chemokine that promote both nociceptor and central sensitization via its main receptor CXCR2, which is a promising target for novel analgesic drugs. Here, we reviewed and discussed the role of the CXCL1/CXCR2 signaling axis in pathological pain conditions triggered by either peripheral inflammation or nerve injury.

Dynamic response to peripheral nerve injury detected by in situ hybridization of IL-6 and its receptor mRNAs in the dorsal root ganglia is not strictly correlated with signs of neuropathic pain

Background

IL-6 is a typical injury-induced mediator. Together with its receptors, IL-6 contributes to both induction and maintenance of neuropathic pain deriving from changes in activity of primary sensory neurons in dorsal root ganglia (DRG). We used in situ hybridization to provide evidence of IL-6 and IL-6 receptors (IL-6R and gp130) synthesis in DRG along the neuraxis after unilateral chronic constriction injury (CCI) of the sciatic nerve as an experimental model of neuropathic pain.

Results

All rats operated upon to create unilateral CCI displayed mechanical allodynia and thermal hyperalgesia in ipsilateral hind paws. Contralateral hind paws and forepaws of both sides exhibited only temporal and nonsignificant changes of sensitivity. Very low levels of IL-6 and IL-6R mRNAs were detected in naïve DRG. IL-6 mRNA was bilaterally increased not only in DRG neurons but also in satellite glial cells (SGC) activated by unilateral CCI. In addition to IL-6 mRNA, substantial increase of IL-6R mRNA expression occurred in DRG neurons and SGC following CCI, while the level of gp130 mRNA remained similar to that of DRG from naïve rats.

Conclusions

Here we evidence for the first time increased synthesis of IL-6 and IL-6R in remote cervical DRG nonassociated with the nerve injury. Our results suggest that unilateral CCI of the sciatic nerve induced not only bilateral elevation of IL-6 and IL-6R mRNAs in L4–L5 DRG but also their propagation along the neuraxis to remote cervical DRG as a general neuroinflammatory reaction of the nervous system to local nerve injury without correlation with signs of neuropathic pain. Possible functional involvement of IL-6 signaling is discussed.

Multiple mechanisms of microglia: a gatekeeper's contribution to pain states

Microglia are gatekeepers in the CNS for a wide range of pathological stimuli and they blow the whistle when things go wrong. Collectively, microglia form a CNS tissue alarm system (Kreutzberg's "sensor of pathology"), and their involvement in physiological pain is in line with this function. However, pathological neuropathic pain is characterized by microglial activation that is unwanted and considered to contribute to or even cause tactile allodynia, hyperalgesia and spontaneous pain. Such abnormal microglial behavior seems likely due to an as yet ill-understood disturbance of microglial functions unrelated to inflammation. The idea that microglia have roles in the CNS that differ from those of peripheral macrophages has gained momentum with the discovery of their separate, pre-hematopoietic lineage during embryonic development and their direct interactions with synapses.

The attenuation of pain behaviour and serum interleukin-6 concentration by nimesulide in a rat model of neuropathic pain

Background

Evidence for a role of immune system in hyperalgesic pain states is increasing. Recent work in neuroimmunology suggests that the immune system does more than simply perform its well known functions of recognizing and removing invading pathogens and tumors. Interest in neuroinflammation and neuroimmune activation has grown rapidly in recent years with the recognition of the role of central nervous system inflammatiom and immune responses in the aetiology of pain states. Among various theories, the role of inflammatory responses of the injured nerve has recently received attention. Cytokines are heterogenous group of polypeptides that activate the immune system and mediate inflammatory responses, acting on a variety of tissue, including the peripheral and central nervous system. Interleukin-6 (IL-6) a pro-inflammatory cytokine, is potentially important in pain aetiology, have pronociceptive actions. Neuropathic pain may be due to a primary insult to the peripheral or central nervous system. Substances released during inflammation from immune cells play an important role in the development and maintenance of chronic pain. Nimesulide, a highly selective cox-2 inhibitor, effectively reduces hyperalgesia due to peripherally administration of inflammatory agents like formalin. The safety of nimesulide was reported for some conditions in which other NSAIDs are contraindicated. Here we have determined the effect of nimesulide on pain behaviour and serum IL-6 level in chronic constriction injury (CCI) model of neuropathic pain.

Methods

Experiments were carried out on male Wistar rats, (weight 150–200 g, n = 8). Rats were divided into 3 different groups: 1-CCI + saline 0.9% 2Sham + saline 0.9% (control) 3CCI + drug. Nimesulide (1.25, 2.5, 5 mg/kg, i.p.) was injected 1h before surgery and continued daily to day 14 post-ligation. 42 °C water for thermal hyperalgesia, von Frey filaments for mechanical allodynia, acetone test for cool allodynia and 10 °C water for cold hyperalgesia were respectively used as pain behavioural tests. Behavioural tests were recorded before surgery and on postoperative days 1, 3, 5, 7, 10, 14 and the serum concentration of IL-6 was determined at the day 14.

Results

The results of this study showed a decrease in hyperalgesia and allodynia following nimesulide administration.

Conclusions

It appears that nimesulide was able to reduce pain behaviour due to nerve inflammation and a parallel decrease in the serum IL-6 concentration was observed.

Implications

The immune system is an important mediator in the cascade of events that ultimately results in hyperalgesia. Cytokines contribute to the patheogenesis of neuropathic pain, therefore drugs that inhibit cytokine release from immune cells may reduce inflammatory pain states.

Novel insights on diagnosis, cause and treatment of diabetic neuropathy: focus on painful diabetic neuropathy

Diabetic neuropathy is common, under or misdiagnosed, and causes substantial morbidity with increased mortality. Defining and developing sensitive diagnostic tests for diabetic neuropathy is not only key to implementing earlier interventions but also to ensure that the most appropriate endpoints are employed in clinical intervention trials. This is critical as many potentially effective therapies may never progress to the clinic, not due to a lack of therapeutic effect, but because the endpoints were not sufficiently sensitive or robust to identify benefit. Apart from improving glycaemic control, there is no licensed treatment for diabetic neuropathy, however, a number of pathogenetic pathways remain under active study. Painful diabetic neuropathy is a cause of considerable morbidity and whilst many pharmacological and nonpharmacological interventions are currently used, only two are approved by the US Food and Drug Administration. We address the important issue of the 'placebo effect' and also consider potential new pharmacological therapies as well as nonpharmacological interventions in the treatment of painful diabetic neuropathy.

Differential regulation of immune responses and macrophage/neuron interactions in the dorsal root ganglion in young and adult rats following nerve injury

BACKGROUND

Neuropathic pain is an apparently spontaneous experience triggered by abnormal physiology of the peripheral or central nervous system, which evolves with time. Neuropathic pain arising from peripheral nerve injury is characterized by a combination of spontaneous pain, hyperalgesia and allodynia. There is no evidence of this type of pain in human infants or rat pups; brachial plexus avulsion, which causes intense neuropathic pain in adults, is not painful when the injury is sustained at birth. Since infants are capable of nociception from before birth and display both acute and chronic inflammatory pain behaviour from an early neonatal age, it appears that the mechanisms underlying neuropathic pain are differentially regulated over a prolonged postnatal period.

RESULTS

We have performed a microarray analysis of the rat L4/L5 dorsal root ganglia (DRG), 7 days post spared nerve injury, a model of neuropathic pain. Genes that are regulated in adult rats displaying neuropathic behaviour were compared to those regulated in young rats (10 days old) that did not show the same neuropathic behaviour. The results show a set of genes, differentially regulated in the adult DRG, that are principally involved in immune system modulation. A functional consequence of this different immune response to injury is that resident macrophages cluster around the large A sensory neuron bodies in the adult DRG seven days post injury, whereas the macrophages in young DRG remain scattered evenly throughout the ganglion, as in controls.

CONCLUSIONS

The results show, for the first time, a major difference in the neuroimmune response to nerve injury in the dorsal root ganglion of young and adult rats. Differential analysis reveals a new set of immune related genes in the ganglia, that are differentially regulated in adult neuropathic pain, and that are consistent with the selective activation of macrophages around adult, but not young large A sensory neurons post injury. These differences may contribute to the reduced incidence of neuropathic pain in infants.

Cytokine and chemokine regulation of sensory neuron function

Pain normally subserves a vital role in the survival of the organism, prompting the avoidance of situations associated with tissue damage. However, the sensation of pain can become dissociated from its normal physiological role. In conditions of neuropathic pain, spontaneous or hypersensitive pain behavior occurs in the absence of the appropriate stimuli. Our incomplete understanding of the mechanisms underlying chronic pain hypersensitivity accounts for the general ineffectiveness of currently available options for the treatment of chronic pain syndromes. Despite its complex pathophysiological nature, it is clear that neuropathic pain is associated with short- and long-term changes in the excitability of sensory neurons in the dorsal root ganglia (DRG) as well as their central connections. Recent evidence suggests that the upregulated expression of inflammatory cytokines in association with tissue damage or infection triggers the observed hyperexcitability of pain sensory neurons. The actions of inflammatory cytokines synthesized by DRG neurons and associated glial cells, as well as by astrocytes and microglia in the spinal cord, can produce changes in the excitability of nociceptive sensory neurons. These changes include rapid alterations in the properties of ion channels expressed by these neurons, as well as longer-term changes resulting from new gene transcription. In this chapter we review the diverse changes produced by inflammatory cytokines in the behavior of sensory neurons in the context of chronic pain syndromes.

The role of IL-6 and IL-1beta in painful perineural inflammatory neuritis

Inflammation along a nerve trunk (perineural inflammation), without detectable axonal damage, has been shown to induce transient pain in the organ supplied by the nerve. The aims of the present study were to study the role IL-6 and IL-1beta, in pain induced by perineural inflammation.

METHODS

IL-6 and IL-1beta secretion from rat's sciatic nerves, L-5 Dorsal Root Ganglia (DRG), and the hind paw skin, 3 and 8 days following exposure of the nerve to Complete Freund's Adjuvant (CFA), were measured using ELISA method. Hind paw tactile-allodynia, mechano-hyperalgesia, heat-allodynia and electrical detection thresholds were tested up to 8 days following the application of CFA, IL-6 or IL-1beta adjacent to the sciatic nerve trunk. Employing electrophysiological recording, saphenous nerve spontaneous activity, nerve trunk mechano-sensitivity and paw tactile detection threshold (determined by recording action potential induced by the lowest mechanical stimulus) were assessed 3 and 8 days following exposure of the nerve trunk to CFA, IL-6, or IL-1beta.

RESULTS

IL-6 and IL-1beta secretion from the nerve was significantly elevated on the 3rd day post-operation (DPO). On the 8th DPO, IL-6 levels returned to baseline while IL-1beta levels remained significantly elevated. The DRG cytokine's level was increased on the 3rd and 8th DPOs, contralateral cytokine's level was increased on the 3rd DPO. The skin IL-6 level was increased bilaterally on the 3rd DPO and returned to baseline on the 8th DPO. IL-1beta levels increased in the affected side on the 3rd and bilaterally on the 8th DPO. Direct application of IL-6 or CFA on the sciatic nerve induced significant hind paw tactile-allodynia from the 1st to 5th DPOs, reduced electrical detection threshold from the 1st to 3rd DPOs, mechano-hyperalgesia from 3rd to 5th DPOs and heat-allodynia on the 3rd DPO. Direct application of IL-1beta induced paw tactile and heat-allodynia on the 7-8th DPOs and mechano-hyperalgesia on the 5-8th DPOs. Perineural inflammation significantly increased spontaneous activity myelinated fibres 3 and 8 days following the application. Direct application of IL-6 induced elevation of spontaneous activity on the 3rd while IL-1beta on the 8th DPO. Nerve mechano-sensitivity was significantly increased on the 3rd day following exposure to CFA and IL-6 and on the 8th following CFA application. The rat's paw lowest mechanical force necessary for induction of action potential, was significantly reduced 3 days following CFA application.

CONCLUSION

IL-6 and IL-1beta play an important role in pain induced by perineural inflammation. IL-6 activity is more prominent immediately following application (2-5th DPOs), while IL-1beta, activity is more significant in a later stage (5-8th DPOs).

Nutrition and age-associated inflammation: implications for disease prevention

Accumulating evidence suggests that aging is associated with dysregulated immune and inflammatory responses. Investigation into the cellular and molecular mechanisms underlying this phenomenon suggests that an up-regulated cyclooxygenase (COX)-2 expression, and resulting increase in production of prostaglandin E(2) (PGE(2)), is a critical factor. Macrophages from old mice have significantly higher levels of PGE(2) production compared with those from young mice, a result of increased COX-2 expression and protein levels leading to increased COX enzyme activity. Furthermore, studies suggest that the age-associated increase in macrophage PGE(2) production is due to ceramide-induced up-regulation of nuclear factor-kappa B activation. Such processes may also occur in cell types other than macrophages, lending further insight into potential mechanisms of age-related diseases. Moreover, the excess PGE(2) induces harmful effects in other cell types such as T cells and adipocytes through the negative crosstalk between macrophages with other cells, resulting in further increased susceptibility to diseases. Nutrient/dietary medications, such as antioxidants and certain lipids have suggested a promising route to reduce the age-related increase in COX activity and PGE(2) production that is associated with several disease states.

Age-associated inflammatory changes: role of nutritional intervention

Accumulating evidence suggests that aging is associated with dysregulated immune and inflammatory responses. Investigation into the cellular and molecular mechanisms underlying this phenomenon suggests that an up-regulated cyclooxygenase (COX)-2 expression, and resulting increase in production of prostaglandin E2 (PGE2), is a critical factor. Macrophages from old mice have significantly higher levels of PGE2 production compared with those from young mice, a result of increased COX-2 expression and protein levels leading to increased COX enzyme activity. Further, it is possible that the age-associated increase in macrophage PGE2 production is due to ceramide-induced up-regulation of nuclear factor-kappa B activation. Such processes may also occur in cell types other than macrophages, lending further insight into potential mechanisms of age-related disease. More research is necessary to determine the efficacy of nutrient/dietary modifications, such as antioxidants and lipids, for reducing the age-related increase in COX activity and PGE2 production that are associated with several disease states.

"Listening" and "talking" to neurons: implications of immune activation for pain control and increasing the efficacy of opioids

It is recently become clear that activated immune cells and immune-like glial cells can dramatically alter neuronal function. By increasing neuronal excitability, these non-neuronal cells are now implicated in the creation and maintenance of pathological pain, such as occurs in response to peripheral nerve injury. Such effects are exerted at multiple sites along the pain pathway, including at peripheral nerves, dorsal root ganglia, and spinal cord. In addition, activated glial cells are now recognized as disrupting the pain suppressive effects of opioid drugs and contributing to opioid tolerance and opioid dependence/withdrawal. While this review focuses on regulation of pain and opioid actions, such immune-neuronal interactions are broad in their implications. Such changes in neuronal function would be expected to occur wherever immune-derived substances come in close contact with neurons.