15d-prostaglandin J2 inhibits inflammatory hypernociception: involvement of peripheral opioid receptor

Improved Local Anesthesia at Inflamed Tissue Using the Association of Articaine and Copaiba Oil in Avocado Butter Nanostructured Lipid Carriers

Unsuccessful anesthesia often occurs under an inflammatory tissue environment, making dentistry treatment extremely painful and challenging. Articaine (ATC) is a local anesthetic used at high (4%) concentrations. Since nanopharmaceutical formulations may improve the pharmacokinetics and pharmacodynamics of drugs, we encapsulated ATC in nanostructured lipid carriers (NLCs) aiming to increase the anesthetic effect on the inflamed tissue. Moreover, the lipid nanoparticles were prepared with natural lipids (copaiba (Copaifera langsdorffii) oil and avocado (Persia gratissima) butter) that added functional activity to the nanosystem. NLC-CO-A particles (~217 nm) showed an amorphous lipid core structure according to DSC and XDR. In an inflammatory pain model induced by λ-carrageenan in rats, NLC-CO-A improved (30%) the anesthetic efficacy and prolonged anesthesia (3 h) in relation to free ATC. In a PGE2-induced pain model, the natural lipid formulation significantly reduced (~20%) the mechanical pain when compared to synthetic lipid NLC. Opioid receptors were involved in the detected analgesia effect since their blockage resulted in pain restoration. The pharmacokinetic evaluation of the inflamed tissue showed that NLC-CO-A decreased tissue ATC elimination rate (ke) by half and doubled ATC’s half-life. These results present NLC-CO-A as an innovative system to break the impasse of anesthesia failure in inflamed tissue by preventing ATC accelerated systemic removal by the inflammatory process and improving anesthesia by its association with copaiba oil.

Mechanisms of Transmission and Processing of Pain: A Narrative Review

Knowledge about the mechanisms of transmission and the processing of nociceptive information, both in healthy and pathological states, has greatly expanded in recent years. This rapid progress is due to a multidisciplinary approach involving the simultaneous use of different branches of study, such as systems neurobiology, behavioral analysis, genetics, and cell and molecular techniques. This narrative review aims to clarify the mechanisms of transmission and the processing of pain while also taking into account the characteristics and properties of nociceptors and how the immune system influences pain perception. Moreover, several important aspects of this crucial theme of human life will be discussed. Nociceptor neurons and the immune system play a key role in pain and inflammation. The interactions between the immune system and nociceptors occur within peripheral sites of injury and the central nervous system. The modulation of nociceptor activity or chemical mediators may provide promising novel approaches to the treatment of pain and chronic inflammatory disease. The sensory nervous system is fundamental in the modulation of the host's protective response, and understanding its interactions is pivotal in the process of revealing new strategies for the treatment of pain.

Peroxisome proliferator-activated receptor-gamma (PPARγ) and its immunomodulation function: current understanding and future therapeutic implications

INTRODUCTION

: Pain is a multidimensional experience involving the biological, psychological, and social dimensions of each individual. Particularly, the biological aspects of pain conditions are a response of the neuroimmunology system and the control of painful conditions is a worldwide challenge for researchers. Although years of investigation on pain experience and treatment exist, the high prevalence of chronic pain is still a fact.

AREAS COVERED

: Peroxisome proliferator-activated receptor-gamma (PPARγ) is a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily. It regulates several metabolic pathways, including lipid biosynthesis and glucose metabolism, when activated. However, PPARγ activation also has a critical immunomodulatory and neuroprotective effect.

EXPERT OPINION

: This review summarizes the evidence of synthetic or natural PPARγ ligands such as 15d-PGJ₂, epoxyeicosatrienoic acids, thiazolidinediones, and specialized pro-resolving mediators, representing an interesting therapeutic tool for pain control.

The PPARγ agonist pioglitazone produces a female-predominant inhibition of hyperalgesia associated with surgical incision, peripheral nerve injury, and painful diabetic neuropathy

Pioglitazone, an agonist at peroxisome proliferator-activated receptor gamma, is FDA-approved for the treatment of insulin resistance in type 2 diabetes. Numerous studies in male rodents suggest that pioglitazone inhibits inflammatory and neuropathic pain, but few included female subjects. To address this gap, we compared the effects of pioglitazone in both sexes in the intraplantar methylglyoxal model (MG) model of chemical pain and painful diabetic neuropathy (PDN), the plantar incision model (PIM) of postoperative pain, the spared nerve injury (SNI) model of traumatic nerve injury, and the ZDF rat and db/db mouse models of PDN. We administered pioglitazone by one-time intrathecal or intraperitoneal injection or by adding it to chow for 6 weeks, followed by measurement of hypersensitivity to non-noxious mechanical, noxious mechanical, heat, and/or cold stimuli. In all mouse models, injection of pioglitazone decreased pain-like behaviors with greater potency and/or efficacy in females as compared to males: heat and mechanical hypersensitivity in the MG model (0.1-10 mg/kg); mechanical hypersensitivity in the PIM model (10 μg); mechanical and cold hypersensitivity in the SNI model (100 mg/kg); and heat hypersensitivity in the db/db model (100 mg/kg). Furthermore, co-administration of low doses of morphine (1 mg/kg) and pioglitazone (10 mg/kg) decreased SNI-induced mechanical and cold hypersensitivity in female but not male mice. In the ZDF rat, pioglitazone (100 mg/kg) decreased heat and mechanical hypersensitivity with no sex difference. In the db/db model, pioglitazone had no effect when given into chow for 6 weeks at 0.3, 3 or 30 mg/kg doses. We conclude that females exhibit greater anti-hyperalgesic responses to pioglitazone in mouse models of chemical-induced nociception, postsurgical pain, neuropathic pain, and PDN. These findings set the stage for clinical trials to determine whether pioglitazone has analgesic properties across a broad spectrum of chronic pain conditions, particularly in women.

Topical Administration of 15-Deoxy-Δ 12,14-Prostaglandin J2 Using a Nonionic Cream: Effect on UVB-Induced Skin Oxidative, Inflammatory, and Histopathological Modifications in Mice

UVB radiation is certainly one of the most important environmental threats to which we are subjected to. This fact highlights the crucial protective role of the skin. However, the skin itself may not be capable of protecting against UVB depending on irradiation intensity and time of exposition. Sun blockers are used to protect our skin, but they fail to fully protect it against oxidative and inflammatory injuries initiated by UVB. To solve this issue, topical administration of active molecules is an option. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an arachidonic acid-derived lipid with proresolution and anti-inflammatory actions. However, as far as we are aware, there is no evidence of its therapeutic use in a topical formulation to treat the deleterious events initiated by UVB, which was the aim of the present study. We used a nonionic cream to vehiculate 15d-PGJ₂ (30, 90, and 300 ng/mouse) (TFcPGJ₂) in the skin of hairless mice. UVB increased skin edema, myeloperoxidase activity, metalloproteinase-9 activity, lipid peroxidation, superoxide anion production, gp91^phox and COX-2 mRNA expression, cytokine production, sunburn and mast cells, thickening of the epidermis, and collagen degradation. UVB also diminished skin ability to reduce iron and scavenge free radicals, reduced glutathione (GSH), sulfhydryl proteins, and catalase activity. TFcPGJ₂ inhibited all these pathological alterations in the skin caused by UVB. No activity was observed with the unloaded topical formulation. The protective outcome of TFcPGJ₂ indicates it is a promising therapeutic approach against cutaneous inflammatory and oxidative pathological alterations.

Anti-inflammatory and Hepatoprotective Effects of Quercetin in an Experimental Model of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammation in the joints. Although methotrexate (MX) is the first-line treatment, side effects are common. This study aimed to investigate the effects of quercetin (QT) and/or MX on inflammation and systemic toxicity in a rat model of RA. Male Wistar rats were divided into control (C), RA, QT, MX, and QT + MX groups (n=6). The RA induction consisted of three intra-articular injections of methylated bovine serum albumin (1×/week) in the temporomandibular joint (TMJ). QT (25 mg/kg) and/or MX (0.75 mg) administration occurred by oral gavage daily. We performed mechanical hyperalgesia in TMJ, leukocyte recruitment in synovial fluid, histopathology, and immunohistochemistry (TNF-α, IL-17, and IL-10) in synovial membrane and toxicity parameters. The RA showed a reduction in the nociceptive threshold (p<0.001), increase in leukocyte recruitment in synovial fluid (p<0.001), intense inflammatory infiltrate (p<0.001), and intense immunoexpression of TNF-α, IL-17, and IL-10 in the synovial membrane (p<0.001) compared to C (p<0.001). QT and/or MX therapy reduced inflammatory parameters (p<0.001). However, downregulation of IL-10 was observed only in the groups that received MX (p<0.001). Leukocytosis was seen in RA (p<0.05), but QT and/or MX reversed it (p<0.05). MX was associated with pathological changes in the liver and higher levels of transaminases when compared to the other groups (p<0.05). QT co-administered with MX reversed this hepatotoxicity (p<0.05). There were no alterations in the kidney between the groups (p>0.05). QT has potential to support MX therapy, showing anti-inflammatory and hepatoprotective effects in this model.

Nitric Oxide and Electrophilic Cyclopentenone Prostaglandins in Redox signaling, Regulation of Cytoskeleton Dynamics and Intercellular Communication

Nitric oxide (NO) and electrophilic cyclopentenone prostaglandins (CyPG) are local mediators that modulate cellular response to oxidative stress in different pathophysiological processes. In particular, there is increasing evidence about their functional role during inflammation and immune responses. Although the mechanistic details about their relationship and functional interactions are still far from resolved, NO and CyPG share the ability to promote redox-based post-translational modification (PTM) of proteins that play key roles in cellular homeostasis, signal transduction and transcription. NO-induced S-nitrosylation and S-glutathionylation as well as cyclopentenone-mediated adduct formation, are a few of the main PTMs by which intra- and inter-cellular signaling are regulated. There is a growing body of evidence indicating that actin and actin-binding proteins are susceptible to covalent PTM by these agents. It is well known that the actin cytoskeleton is key for the establishment of interactions among leukocytes, endothelial and muscle cells, enabling cellular activation and migration. In this review we analyze the current knowledge about the actions exerted by NO and CyPG electrophilic lipids on the regulation of actin dynamics and cytoskeleton organization, and discuss some open questions regarding their functional relevance in the regulation of intercellular communication.

Peripherally Acting Opioids in Orofacial Pain

The activation of opioid receptors by exogenous or endogenous opioids can produce significant analgesic effects in peripheral tissues. Numerous researchers have demonstrated the expression of peripheral opioid receptors (PORs) and endogenous opioid peptides (EOPs) in the orofacial region. Growing evidence has shown the involvement of PORs and immune cell-derived EOPs in the modulation of orofacial pain. In this review, we discuss the role of PORs and EOPs in orofacial pain and the possible cellular mechanisms involved. Furthermore, the potential development of therapeutic strategies for orofacial pain is also summarized.

Prostaglandin 15d-PGJ2 targets PPARγ and opioid receptors to prevent muscle hyperalgesia in rats

Pharmacological agents directed to either opioid receptors or peroxisome proliferator-activated receptor gamma (PPARγ) at peripheral tissues reduce behavioral signs of persistent pain. Both receptors are expressed in muscle tissue, but the contribution of PPARγ activation to muscle pain and its modulation by opioid receptors remains unknown. To address this question, we first tested whether the endogenous PPARγ ligand 15d-PGJ2 would decrease mechanical hyperalgesia induced by carrageenan administration into the gastrocnemius muscle of rats. Next, we used receptor antagonists to determine whether the antihyperalgesic effect of 15-deoxyΔ-12,14-prostaglandin J2 (15d-PGJ2) was PPARγ- or opioid receptor-dependent. Three hours after carrageenan, muscle hyperalgesia was quantified with the Randall-Selitto test. 15d-PGJ2 prevented carrageenan-induced muscle hyperalgesia in a dose-dependent manner. The antihyperalgesic effect of 15d-PGJ2 was dose-dependently inhibited by either the PPARγ antagonist, 2-chloro-5-nitro-N-phenylbenzamide, or by the opioid receptor antagonist, naloxone. We conclude that 15d-PGJ2 targets PPARγ and opioid receptors to prevent muscle hyperalgesia. We suggest that local PPARγ receptors are important pharmacological targets for inflammatory muscle pain.

Celecoxib inhibits acute edema and inflammatory biomarkers through peroxisome proliferator-activated receptor-γ in rats

Objective(s):

Celecoxib (CLX), a selective cyclooxygenase-II (COX-2) inhibitor, has been used for management of several inflammatory disorders. The present study aimed to explore the role of peroxisome proliferator-activated receptor-gamma (PPARγ) in CLX induced anti-inflammatory response in rats.

Materials and Methods:

Carrageenan-induced paw edema was used as an acute inflammation model. Rats were treated with various intra-peritoneal (IP) doses of CLX (0.3–30 mg/kg) and pioglitazone (PGL; PPARγ agonist, 1–20 mg/kg) alone or in combination. Amounts of PPARγ, COX-2, and prostaglandin E2 (PGE2) in paw tissue, and extents of TNF-α and IL-10 in serum were measured. Moreover, levels of oxidative stress parameters as malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase (GPx) activity in the cortex, hippocampus, and paw tissues were also determined.

Results:

CLX and PGL dose-dependent administration (IP), alone or in combination reduced carrageenan-induced paw edema. Further, both agents, alone or in combination, reduced either the amounts of COX-2, PGE2, and MDA in the inflamed paw, and the levels of TNF-α in serum which were elevated by carrageenan. Both drugs also increased both levels of PPARγ, GSH, GPx activity in paws, and serum levels of IL-10 that were decreased by carrageenan. Intraplantar injection of GW-9662 (IPL), a selective PPARγ antagonist, inhibited all biochemical modifications caused by both single and combined drug treatments.

Conclusion:

CLX produced its anti-inflammatory effects probably through PPARγ receptor activation. Besides, increased anti-inflammatory effects of CLX with PGL suggest that their combination might be applied for the clinical management of inflammation especially in patients suffering from diabetes.

The role of peripheral opioid receptors in orofacial pain

Opioid receptors are widely distributed in the central and peripheral nervous systems and non-neuronal tissues. Numerous researchers have noted the pivotal role of peripheral opioid receptors (PORs) in analgesia. Accumulating evidence has shown the existence of PORs in the trigeminal nerve system, indicating that PORs may be involved in the modulation of orofacial pain. In this review, we summarise the recent evidence for the role of PORs in orofacial pain and discuss the possible cellular mechanisms.

Redox regulation of soluble epoxide hydrolase does not affect pain behavior in mice

Signaling mediated by soluble epoxide hydrolase (sEH) has been reported to play an important role in pain processing. Previous studies revealed that sEH activity is inhibited by specific binding of electrophiles to a redox-sensitive thiol (Cys521) adjacent to the catalytic center of the hydrolase. Here, we investigated if this redox-dependent modification of sEH is involved in pain processing using "redox-dead" knockin-mice (sEH-KI), in which the redox-sensitive cysteine is replaced by serine. However, behavioral characterization of sEH-KI mice in various animal models revealed that acute nociceptive, inflammatory, neuropathic, and visceral pain processing is not altered in sEH-KI mice. Thus, our results suggest that redox-dependent modifications of sEH are not critically involved in endogenous pain signaling in mice.

Molecular mechanisms underlying the actions of arachidonic acid-derived prostaglandins on peripheral nociception

Arachidonic acid-derived prostaglandins not only contribute to the development of inflammation as intercellular pro-inflammatory mediators, but also promote the excitability of the peripheral somatosensory system, contributing to pain exacerbation. Peripheral tissues undergo many forms of diseases that are frequently accompanied by inflammation. The somatosensory nerves innervating the inflamed areas experience heightened excitability and generate and transmit pain signals. Extensive studies have been carried out to elucidate how prostaglandins play their roles for such signaling at the cellular and molecular levels. Here, we briefly summarize the roles of arachidonic acid-derived prostaglandins, focusing on four prostaglandins and one thromboxane, particularly in terms of their actions on afferent nociceptors. We discuss the biosynthesis of the prostaglandins, their specific action sites, the pathological alteration of the expression levels of related proteins, the neuronal outcomes of receptor stimulation, their correlation with behavioral nociception, and the pharmacological efficacy of their regulators. This overview will help to a better understanding of the pathological roles that prostaglandins play in the somatosensory system and to a finding of critical molecular contributors to normalizing pain.

Improved efficacy of naproxen-loaded NLC for temporomandibular joint administration

Inflammatory conditions of the temporomandibular joint (TMJ) and peripheral tissues affect many people around the world and are commonly treated with non-steroidal anti-inflammatory drugs (NSAIDs). However, in order to get desirable results, treatments with NSAIDs may take weeks, causing undesirable side effects and requiring repeated administration. In this sense, this work describes the development of an optimized nanostructured lipid carrier (NLC) formulation for intra-articular administration of naproxen (NPX). An experimental design (2³) selected the best formulation in terms of its physicochemical and structural properties, elucidated by different methods (DLS, NTA, TEM, DSC, and ATR-FTIR). The chosen formulation (NLC-NPX) was tested on acute inflammatory TMJ nociception, in a rat model. The optimized excipients composition provided higher NPX encapsulation efficiency (99.8%) and the nanoparticles were found stable during 1 year of storage at 25 °C. In vivo results demonstrated that the sustained delivery of NPX directly in the TMJ significantly reduced leukocytes migration and levels of pro-inflammatory cytokines (IL-1β and TNF-α), for more than a week. These results point out the NLC-NPX formulation as a promising candidate for the safe treatment of inflammatory pain conditions of TMJ or other joints.

Topical atorvastatin 1% for prevention of skin toxicity in patients receiving radiation therapy for breast cancer: a randomized, double-blind, placebo-controlled trial

BACKGROUND AND PURPOSE

The purpose of this randomized, placebo-controlled, double-blind study was to investigate the preventive effect of topical administration of atorvastatin (ATV) on the acute radiation-induced skin toxicity in patients with breast cancer.

PATIENTS AND METHODS

Seventy breast cancer patients were randomly assigned to use topical ATV 1% or placebo gels during radiotherapy twice daily. Radiation-induced dermatitis was classified according to the radiation therapy oncology group (RTOG) criteria, as well as pain and itching were scored according to VAS (visual analogue scale) for 6 weeks of treatment.

RESULTS

Topical administration of ATV gel during radiotherapy reduced significantly radiation-induced breast swelling, itching, and pain in breast cancer patients by factors of 1.8, 1.7, and 1.5, respectively. ATV reduced the redness caused by radiotherapy in patients as compared with placebo; however, this difference was statistically not significant.

CONCLUSION

ATV was able to reduce significantly itching, breast edema, and pain in patients during radiotherapy.

15d-PGJ2-loaded nanocapsules ameliorate experimental gout arthritis by reducing pain and inflammation in a PPAR-gamma-sensitive manner in mice

Gout arthritis (GA) is a painful inflammatory disease in response to monosodium urate (MSU) crystals in the joints. 15deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is a natural activator of PPAR-γ with analgesic, anti-inflammatory, and pro-resolution properties. Thus, we aimed to evaluate the effect and mechanisms of action of 15d-PGJ₂ nanocapsules (NC) in the model of GA in mice, since a reduction of 33-fold in the dose of 15d-PGJ₂ has been reported. Mice were treated with 15d-PGJ₂-loaded NC, inert NC, free 15d-PGJ₂ (without NC), or 15d-PGJ₂-loaded NC+ GW9662, a PPAR-γ inhibitor. We show that 15d-PGJ₂-loaded NC provided analgesic effect in a dose that the free 15d-PGJ₂ failed to inhibiting pain and inflammation. Hence, 15d-PGJ₂-loaded NC reduced MSU-induced IL-1β, TNF-α, IL-6, IL-17, and IL-33 release and oxidative stress. Also, 15d-PGJ₂-loaded NC decreased the maturation of IL-1β in LPS-primed BMDM triggered by MSU. Further, 15d-PGJ₂-loaded NC decreased the expression of the components of the inflammasome Nlrp3, Asc, and Pro-caspase-1, as consequence of inhibiting NF-κB activation. All effects were PPAR-γ-sensitive. Therefore, we demonstrated that 15d-PGJ₂-loaded NC present analgesic and anti-inflammatory properties in a PPAR-γ-dependent manner inhibiting IL-1β release and NF-κB activation in GA. Concluding, 15d-PGJ₂-loaded NC ameliorates MSU-induced GA in a PPAR-γ-sensitive manner.

PPARs and pain

Chronic pain is a common cause of disability worldwide and remains a global health and socio-economic challenge. Current analgesics are either ineffective in a significant proportion of patients with chronic pain or associated with significant adverse side effects. The PPARs, a family of nuclear hormone transcription factors, have emerged as important modulators of pain in preclinical studies and therefore a potential therapeutic target for the treatment of pain. Modulation of nociceptive processing by PPARs is likely to involve both transcription-dependent and transcription-independent mechanisms. This review presents a comprehensive overview of preclinical studies investigating the contribution of PPAR signalling to nociceptive processing in animal models of inflammatory and neuropathic pain. We examine current evidence from anatomical, molecular and pharmacological studies demonstrating a role for PPARs in pain control. We also discuss the limited evidence available from relevant clinical studies and identify areas that warrant further research. LINKED ARTICLES: This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Microneedles enhance topical delivery of 15-deoxy-Δ12,14-prostaglandin J2 and reduce nociception in temporomandibular joint of rats

The pain arising from temporomandibular disorders is often treated with opioids and agents that inhibit the immune response and are associated with substantial adverse effects and long-term risks. Thus, the development of new therapies that are safer and more effective is of great interest to patients and clinicians. 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is naturally produced in the human body and has anti-inflammatory properties. We have previously shown in a rat temporomandibular joint (TMJ) model that injection of 15d-PGJ₂ into the rat TMJ can provide antinociceptive relief against a subsequent noxious challenge from formalin injection into the same TMJ. However, intra-TMJ injections are painful. Thus, to make the treatment patient friendly, this study aimed to evaluate whether the antinociceptive property of 15d-PGJ₂ cream can be enhanced with microneedles (MNs). We found that topical application of 15d-PGJ₂ cream for 15min directly on the rat TMJ skin did not induce any significant antinociceptive effect. However, if MNs were inserted in the skin for 5min, removed, and then 15d-PGJ₂ cream was applied, a significant reduction in formalin-induced nociceptive behavior was observed. This reduction in nociception was comparable to an intra-TMJ injection of 15d-PGJ₂. A concentration-dependent effect of 15d-PGJ₂ was observed, with higher concentrations of 15d-PGJ₂ in the cream showing a more durable effect up to 8h. 15d-PGJ₂ cream associated with MNs also significantly reduced the release of tumor necrosis factor-α and interleukin-1 beta, which are pro-inflammatory cytokines. Our findings suggest that 15d-PGJ₂ cream associated with MNs provides antinociceptive and anti-inflammatory effect, and can offer a potential patient-friendly therapeutic option for pain control related to inflammatory disorders of the TMJ.

Nociceptor Sensory Neuron-Immune Interactions in Pain and Inflammation

Nociceptor sensory neurons protect organisms from danger by eliciting pain and driving avoidance. Pain also accompanies many types of inflammation and injury. It is increasingly clear that active crosstalk occurs between nociceptor neurons and the immune system to regulate pain, host defense, and inflammatory diseases. Immune cells at peripheral nerve terminals and within the spinal cord release mediators that modulate mechanical and thermal sensitivity. In turn, nociceptor neurons release neuropeptides and neurotransmitters from nerve terminals that regulate vascular, innate, and adaptive immune cell responses. Therefore, the dialog between nociceptor neurons and the immune system is a fundamental aspect of inflammation, both acute and chronic. A better understanding of these interactions could produce approaches to treat chronic pain and inflammatory diseases.

Adoptive transfer of M2 macrophages reduces neuropathic pain via opioid peptides

Background

During the inflammation which occurs following nerve damage, macrophages are recruited to the site of injury. Phenotypic diversity is a hallmark of the macrophage lineage and includes pro-inflammatory M1 and anti-inflammatory M2 populations. Our aim in this study was to investigate the ability of polarized M0, M1, and M2 macrophages to secrete opioid peptides and to examine their relative contribution to the modulation of neuropathic pain.

Methods

Mouse bone marrow-derived cells were cultured as unstimulated M0 macrophages or were stimulated into an M1 phenotype using lipopolysaccharide and interferon-γ or into an M2 phenotype using interleukin-4. The macrophage phenotypes were verified using flow cytometry for surface marker analysis and cytokine bead array for cytokine profile assessment. Opioid peptide levels were measured by radioimmunoassay and enzyme immunoassay. As a model of neuropathic pain, a chronic constriction injury (CCI) of the sciatic nerve was employed. Polarized M0, M1, and M2 macrophages (5 × 10⁵ cells) were injected perineurally twice, on days 14 and 15 following CCI or sham surgery. Mechanical and heat sensitivity were measured using the von Frey and Hargreaves tests, respectively. To track the injected macrophages, we also transferred fluorescently stained polarized cells and analyzed the surface marker profile of endogenous and injected cells in the nerves ex vivo.

Results

Compared to M0 and M1 cells, M2 macrophages contained and released higher amounts of opioid peptides, including Met-enkephalin, dynorphin A (1–17), and β-endorphin. M2 cells transferred perineurally at the nerve injury site reduced mechanical, but not heat hypersensitivity following the second injection. The analgesic effect was reversed by the perineurally applied opioid receptor antagonist naloxone methiodide. M2 cells did not affect sensitivity following sham surgery. Neither M0 nor M1 cells altered mechanical and heat sensitivity in CCI or sham-operated animals. Tracing the fluorescently labeled M0, M1, and M2 cells ex vivo showed that they remained in the nerve and preserved their phenotype.

Conclusions

Perineural transplantation of M2 macrophages resulted in opioid-mediated amelioration of neuropathy-induced mechanical hypersensitivity, while M1 macrophages did not exacerbate pain. Therefore, rather than focusing on macrophage-induced pain generation, promoting opioid-mediated M2 actions may be more relevant for pain control.

15d-PGJ2-Loaded Solid Lipid Nanoparticles: Physicochemical Characterization and Evaluation of Pharmacological Effects on Inflammation

15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, has physiological properties including pronounced anti-inflammatory activity, though it binds strongly to serum albumin. The use of solid lipid nanoparticles (SLN) can improve therapeutic properties increasing drug efficiency and availability. 15d-PGJ2-SLN was therefore developed and investigated in terms of its immunomodulatory potential. 15d-PGJ2-SLN and unloaded SLN were physicochemically characterized and experiments in vivo were performed. Animals were pretreated with 15d-PGJ2-SLN at concentrations of 3, 10 or 30 μg·kg-1 before inflammatory stimulus with carrageenan (Cg), lipopolysaccharide (LPS) or mBSA (immune response). Interleukins (IL-1β, IL-10 and IL-17) levels were also evaluated in exudates. The 15d-PGJ2-SLN system showed good colloidal parameters and encapsulation efficiency of 96%. The results showed that the formulation was stable for up to 120 days with low hemolytic effects. The 15d-PGJ2-SLN formulation was able to reduce neutrophil migration in three inflammation models tested using low concentrations of 15d-PGJ2. Additionally, 15d-PGJ2-SLN increased IL-10 levels and reduced IL-1β as well as IL-17 in peritoneal fluid. The new 15d-PGJ2-SLN formulation highlights perspectives of a potent anti-inflammatory system using low concentrations of 15d-PGJ2.

Beyond the classic eicosanoids: Peripherally-acting oxygenated metabolites of polyunsaturated fatty acids mediate pain associated with tissue injury and inflammation

Pain is a complex sensation that may be protective or cause undue suffering and loss of function, depending on the circumstances. Peripheral nociceptor neurons (PNs) innervate most tissues, and express ion channels, nocisensors, which depolarize the cell in response to intense stimuli and numerous substances. Inflamed tissues manifest inflammatory hyperalgesia in which the threshold for pain and the response to painful stimuli are decreased and increased, respectively. Constituents of the inflammatory milieu sensitize PNs, thereby contributing to hyperalgesia. Polyunsaturated fatty acids undergo enzymatic and free radical-mediated oxygenation into an array of bioactive metabolites, oxygenated polyunsaturated fatty acids (oxy-PUFAs), including the classic eicosanoids. Oxy-PUFA production is enhanced during inflammation. Pioneering studies by Vane and colleagues from the early 1970s first implicated classic eicosanoids in the pain associated with inflammation. Here, we review the production and action of oxy-PUFAs that are not classic eicosanoids, but nevertheless are produced in injured/ inflamed tissues and activate or sensitize PNs. In general, oxy-PUFAs that sensitize PNs may do so directly, by activation of nocisensors, ion channels or GPCRs expressed on the surface of PNs, or indirectly, by increasing the production of inflammatory mediators that activate or sensitize PNs. We focus on oxy-PUFAs that act directly on PNs. Specifically, we discuss the role of arachidonic acid-derived 12S-HpETE, HNE, ONE, PGA2, iso-PGA2 and 15d-PGJ2, 5,6-and 8,9-EET, PGE2-G and 8R,15S-diHETE, as well as the linoleic acid-derived 9-and 13-HODE in inducing acute nocifensive behavior and/or inflammatory hyperalgesia in rodents. The nocisensors TRPV1, TRPV4 and TRPA1, and putative Gαs-type GPCRs are the PN targets of these oxy-PUFAs.

Potentiation of indomethacin-induced anti-inflammatory response by pioglitazone in carrageenan-induced acute inflammation in rats: Role of PPARγ receptors

This study aimed to assess the interaction between anti-inflammatory effects of pioglitazone (peroxysome proliferator activated receptor-gamma (PPARγ) agonist, PGL), and indomethacin (cyclooxygenase (COX) inhibitor, IND) and to evaluate the possible underlying mechanisms. Paw edema induced by carrageenan was used to induce inflammation. Different doses of IND (0.3-10mg/kg) and PGL (1-20mg/kg) alone or in combination were administered intraperitoneally to rats. Paw tissue levels of PPARγ, COX-2, and prostaglandin E2 and serum levels of TNF-α and IL-10 were also estimated. Doses of IND and PGL showed a statistically significant anti-inflammatory effect. Combination of a non-effective dose of IND (0.3mg/kg) with increasing doses of PGL (1-10mg/kg) resulted in potentiated anti-inflammation and vise versa. IND, PGL and the combination were able to reduce the COX-2, PGE2 contents and TNF-α level. Moreover, all these treatments caused elevation in PPARγ levels and IL-10 levels. However, when the rats were pre-treated with GW-9662 (a selective PPARγ antagonist), all the anti-inflammation and alterations in the biochemical factors were antagonized. These results showed that PGL markedly enhanced the anti-inflammatory activity of IND and this effect mediated partly at least, through PPARγ. Possible mechanisms of the interaction were that PGL stimulates the PPARγ and inhibits COX-2 by those cytokines that trigger the PPARγ and also inhibit COX-2. This study suggests that combination therapy with pioglitazone and indomethacin may provide an alternative for the clinical control of inflammation especially in patients with diabetes.

The role of endogenous opioid peptides in the antinociceptive effect of 15-deoxy(Δ12,14)-prostaglandin J2 in the temporomandibular joint

We have previously demonstrated that peripheral administration of 15d-PGJ2 in the Temporomandibular joint (TMJ) of rats can prevent nociceptor sensitization, mediated by peroxisome proliferator activated receptor-γ (PPAR-γ), and κ- and δ- opioid receptors. However, the mechanism that underlies the signaling of PPAR-γ (upon activation by 15d-PGJ2) to induce antinociception, and how the opioid receptors are activated via 15d-PGJ2 are not fully understood. This study demonstrates that peripheral antinociceptive effect of 15d-PGJ2 is mediated by PPAR-γ expressed in the inflammatory cells of TMJ tissues. Once activated by 15d-PGJ2, PPAR-γ induces the release of β-endorphin and dynorphin, which activates κ- and δ-opioid receptors in primary sensory neurons to induce the antinociceptive effect.

Antinociceptive and antidiarrheal effects of pioglitazone in a rat model of diarrhoea-predominant irritable bowel syndrome: role of nitric oxide

Irritable bowel syndrome (IBS) is a prevalent disease characterized by abdominal pain and abnormal bowel habits. Pioglitazone is a peroxisome proliferator-activated receptor (PPAR) γ agonist and, although it is mostly used as an antidiabetic agent, it has been reported to have analgesic effects. Nitric oxide (NO), a gaseous molecule that mediates many of the effects of pioglitazone, has been implicated in the pathophysiology of IBS. The aim of the present study was to investigate the effects of pioglitazone on symptoms in a rat model of diarrhoea-predominant IBS (D-IBS).and to determine the role of NO in these effects. Diarrhoea-predominant IBS was induced by intracolonic instillation of acetic acid. Pioglitazone (2 mg/kg, i.p.) was administered on Days 7, 9 and 11 after acetic acid instillation. To investigate the mechanism involved in pioglitazone action, rats were also administered either the PPARγ antagonist GW9662 (3 mg/kg, i.p.), the NO synthase (NOS) inhibitor N(G) -nitro-l-arginine methyl ester (l-NAME; 10 mg/kg, i.p.) or the NO precursor l-arginine (250 mg/kg, i.p.) along with pioglitazone. Visceral hypersensitivity, nociceptive thresholds, defecation frequency, stool form, serum and colon NO production and inducible (i) NOS activity were assessed 1 h after the final injection of pioglitazone or dimethylsulphoxide (used as the vehicle). Pioglitazone reduced visceral hypersensitivity and defecation frequency, increased nociceptive thresholds, NO production and iNOS activity and shifted stool form towards hard stools in D-IBS rats. These effects of pioglitazone were significantly reversed by l-NAME, but not GW9662. l-Arginine augmented the effects of pioglitazone. In conclusion, pioglitazone alleviates symptoms in a rat model of D-IBS through an NO-dependent mechanism.

15-deoxy-Δ12,14-prostaglandin J2 reduces albumin-induced arthritis in temporomandibular joint of rats

The aim of this study was to evaluate the peripheral effect of 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) in albumin-induced arthritis in temporomandibular joint (TMJ) of rats. Antigen-induced arthritis (AIA) was generated in rats with methylated bovine serum albumin (mBSA) diluted in complete Freund׳s adjuvant. Pretreatment with an intra-articular injection of 15d-PGJ2 (100 ng/TMJ) before mBSA intra-articular injection (10 µg/TMJ) (challenge) in immunized rats significantly reduced the albumin-induced arthritis inflammation. The results demonstrated that 15d-PGJ2 was able to inhibit plasma extravasation, leukocyte migration and the release of inflammatory cytokines IL-6, IL-12, IL-18 and the chemokine CINC-1 in the TMJ tissues. In addition, 15d-PGJ2 was able to increase the expression of the anti-adhesive molecule CD55 and the anti-inflammatory cytokine IL-10. Taken together, it is possible to suggest that 15d-PGJ2 inhibit leukocyte infiltration and subsequently inflammatory process, through a shift in the balance of the pro- and anti-adhesive properties. Thus, 15d-PGJ2 might be used as a potential anti-inflammatory drug to treat arthritis-induced inflammation of the temporomandibular joint.

Anti-inflammatory and anti-hyperalgesic effect of all-trans retinoic acid in carrageenan-induced paw edema in Wistar rats: involvement of peroxisome proliferator-activated receptor-β/δ receptors

Objective:

In this study, we investigated the role of peroxisome proliferator-activated receptors (PPAR)-β/δ receptors in carrageenan-induced inflammation and in the anti-inflammatory effects of all-trans retinoic acid (ATRA).

Materials and Methods:

The λ-carrageenan (0.1 ml of 1% w/v) was injected into intra-plantar (i.pl.) region of the hind paw to produce acute inflammation. Paw volume was measured by using the mercury plethysmography. Further, mechanical and thermal hyperalgesia (TH) were assessed by using the dynamic plantar aesthesiometer and plantar test apparatus, respectively. In addition, markers of oxido-nitrosative stress were assessed spectrophotometrically in the hind paw tissue 5 h post-carrageenan.

Results:

An i.pl injection of carrageenan has produced a marked mechanical hyperalgesia (MH) and TH in ipsilateral paw, which was associated with significant elevated oxido-nitrosative stress. Treatment with ATRA (5 mg/kg/p.o/4 days) and GW0742, a selective PPAR-β/δ receptor agonist (0.1 mg/kg/i.p/4 days), significantly decreased the paw volume, mechanical and TH as compared to vehicle control. Administration of GSK0660, selective PPAR-β/δ receptor antagonist, at a dose of (0.3 mg/kg/i.p/4 days), did not produce a significant effect on carrageenan-induced paw edema, MH and TH. However, co-administration of GSK0660 (0.3 mg/kg/i.p/4 days) along with both ATRA (5 mg/kg/p.o/4 days) and GW0742 (0.1 mg/kg/i.p/4 days), significantly reverse the decreased paw edema, MH, and TH. These observed ameliorative effects on inflammatory pain symptoms are correlated with the extent of reduction of oxido-nitrosative stress.

Conclusion:

From above findings, it can be concluded that ATRA exerts anti-inflammatory and anti-hyperalgesic effect, possibly through activation of PPAR-β/δ and subsequent reduction of oxido-nitrosative stress.

Peroxisome proliferator-activated receptor-gamma agonist rosiglitazone attenuates inflammatory pain through the induction of heme oxygenase-1 in macrophages

Macrophage infiltration to inflammatory sites promotes tissue repair and may be involved in pain hypersensitivity. Peroxisome proliferator-activated receptor (PPAR)γ signaling is known to regulate polarity of macrophages, which are often referred to as proinflammatory (M1) and antiinflammatory (M2) macrophages. We recently showed that the PPARγ agonist rosiglitazone ameliorated the development of postincisional hyperalgesia by increasing the influx of M2 macrophages to inflamed sites. It has been suggested that heme oxygenase (HO)-1, upregulated by PPARγ signaling, promotes differentiation of macrophages to M2 phenotype. In this study, we investigated how rosiglitazone alters pain hypersensitivity by a PPARγHO-1-dependent mechanism during the course of inflammation induced by complete Freund's adjuvant. Local administration of rosiglitazone alleviated mechanical hyperalgesia, with increased gene induction of HO-1. Phenotype switching of infiltrated macrophages to M2 by rosiglitazone was reversed by an HO-1 inhibitor, tin protoporphyrin, at the inflamed sites. Direct stimulation of peritoneal macrophages with rosiglitazone also increased HO-1 induction in the presence of lipopolysaccharide/interferon-γ. Moreover, rosiglitazone increased gene induction of endogenous opioid proenkephalin, both at inflamed sites and in isolated macrophages. Administration of naloxone blocked the analgesic effects of rosiglitazone. We speculate that rosiglitazone alleviated the development of inflammatory pain, possibly through regulating the M1/M2 balance at the inflamed site by a PPARγ/HO-1-dependent mechanism. PPARγ signaling in macrophages may be a potential therapeutic target for the treatment of acute pain development.

The nitroxyl donor, Angeli's salt, inhibits inflammatory hyperalgesia in rats

Nitric oxide modulates pain development. However, there is no evidence on the effect of nitroxyl (HNO/NO⁻) in nociception. Therefore, we addressed whether nitroxyl inhibits inflammatory hyperalgesia and its mechanism using the nitroxyl donor Angeli's salt (AS; Na₂N₂O₃). Mechanical hyperalgesia was evaluated using a modified Randall and Selitto method in rats, cytokine production by ELISA and nitroxyl was determined by confocal microscopy in DAF (a cell permeable reagent that is converted into a fluorescent molecule by nitrogen oxides)-treated dorsal root ganglia neurons in culture. Local pre-treatment with AS (17-450 μg/paw, 30 min) inhibited the carrageenin-induced mechanical hyperalgesia in a dose- and time-dependent manner with maximum inhibition of 97%. AS also inhibited carrageenin-induced cytokine production. AS inhibited the hyperalgesia induced by other inflammatory stimuli including lipopolysaccharide, tumor necrosis factor-α, interleukin-1β and prostaglandin E2. Furthermore, the analgesic effect of AS was prevented by treatment with ODQ (a soluble guanylate cyclase inhibitor), KT5823 (a protein kinase G [PKG] inhibitor) or glybenclamide (an ATP-sensitive K⁺ channel blocker), but not with naloxone (an opioid receptor antagonist). AS induced concentration-dependent increase in fluorescence intensity of DAF-treated neurons in a l-cysteine (nitroxyl scavenger) sensitive manner. l-cysteine did not affect the NO⁺ donor S-Nitroso-N-acetyl-DL- penicillamine (SNAP)-induced anti-hyperalgesia or fluorescence of DAF-treated neurons. This is the first study to demonstrate that nitroxyl inhibits inflammatory hyperalgesia by reducing cytokine production and activating the cGMP/PKG/ATP-sensitive K⁺ channel signaling pathway in vivo.

The ruthenium NO donor, [Ru(bpy)2(NO)SO3](PF6), inhibits inflammatory pain: involvement of TRPV1 and cGMP/PKG/ATP-sensitive potassium channel signaling pathway

The activation of nitric oxide (NO) production is an analgesic mechanism shared by drugs such as morphine and diclofenac. Therefore, the controlled release of low amounts of NO seems to be a promising analgesic approach. In the present study, the antinociceptive effect of the ruthenium NO donor [Ru(bpy)2(NO)SO3](PF6) (complex I) was investigated. It was observed that complex I inhibited in a dose (0.3-10mg/kg)-dependent manner the acetic acid-induced writhing response. At the dose of 1mg/kg, complex I inhibited the phenyl-p-benzoquinone-induced writhing response and formalin- and complete Freund's adjuvant-induced licking and flinch responses. Additionally, complex I also inhibited transient receptor potential cation channel subfamily V member 1 (TRPV1)-dependent overt pain-like behavior induced by capsaicin. Complex I also inhibited the carrageenin-induced mechanical hyperalgesia and increase of myeloperoxidase activity (MPO) in paw skin samples. The inhibitory effect of complex I in the carrageenin-induced hyperalgesia, MPO activity and formalin was prevented by the treatment with ODQ, KT5823 and glybenclamide, indicating that complex I inhibits inflammatory hyperalgesia by activating the cGMP/PKG/ATP-sensitive potassium channel signaling pathway. The present study demonstrates the efficacy of a novel ruthenium NO donor and its analgesic mechanisms.

Pioglitazone potentiates development of morphine-dependence in mice: possible role of NO/cGMP pathway

Peroxizome proliferator-activated receptor gamma (PPARγ) is highly expressed in the central nervous system where it modulates numerous gene transcriptions. Nitric oxide synthase (NOS) expression could be modified by simulation of PPARγ which in turn activates nitric oxide (NO)/soluble guanylyl-cyclase (sGC)/cyclic guanosine mono phosphate (cGMP) pathway. It is well known that NO/cGMP pathway possesses pivotal role in the development of opioid dependence and this study is aimed to investigate the effect of PPARγ stimulation on opioid dependence in mice as well as human glioblastoma cell line. Pioglitazone potentiated naloxone-induced withdrawal syndrome in morphine dependent mice in vivo. While selective inhibition of PPARγ, neuronal NOS or GC could reverse the pioglitazone-induced potentiation of morphine withdrawal signs; sildenafil, a phosphodiesterase-5 inhibitor amplified its effect. We also showed that nitrite levels in the hippocampus were significantly elevated in pioglitazone-treated morphine dependent mice. In the human glioblastoma (U87) cell line, rendered dependent to morphine, cAMP levels did not show any alteration after chronic pioglitazone administration while cGMP measurement revealed a significant rise. We were unable to show a significant alteration in neuronal NOS mRNA expressions by pioglitazone in mice hippocampus or U87 cells. Our results suggest that pioglitazone has the ability to enhance morphine-dependence and to augment morphine withdrawal signs. The possible pathway underlying this effect is through activation of NO/GC/cGMP pathway.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

Hypernociception and wound healing after application of cyanoacrylate ester as a tissue adhesive in rats

OBJECTIVE

The present study assessed and compared postoperative hypernociception and skin healing after cyanoacrylate and classic suture as well as analyzed morphologic features of the tissue repair.

STUDY DESIGN

The intensity of hypernociception was measured with an electronic pressure-meter test. Rats were given an incised wound in the middle of the palms of the right and left paws. The left side was treated with a silk suture, and the right with cyanoacrylate. Control groups were treated locally with dipyrone or received a systemic pretreatment with valdecoxib.

RESULTS

Cyanoacrylate was associated with less inflammation (first week), and the healing wound site was rich in collagenous extracellular matrix and neovascularization. Dipyrone in combination with cyanoacrylate greatly increased the antinociceptive effect. These results were not repeated after systemic treatment with valdecoxib, suggesting that the antinociceptive effect seen in the tissue adhesive was due to formation of a physical barrier.

Prostaglandin metabolite induces inhibition of TRPA1 and channel-dependent nociception

Background

The Transient Receptor Potential (TRP) ion channel TRPA1 is a key player in pain pathways. Irritant chemicals activate ion channel TRPA1 via covalent modification of N-terminal cysteines. We and others have shown that 15-Deoxy-Δ12, 14-prostaglandin J₂ (15d-PGJ₂) similarly activates TRPA1 and causes channel-dependent nociception. Paradoxically, 15d-PGJ₂ can also be anti-nociceptive in several pain models. Here we hypothesized that activation and subsequent desensitization of TRPA1 in dorsal root ganglion (DRG) neurons underlies the anti-nociceptive property of 15d-PGJ₂. To investigate this, we utilized a battery of behavioral assays and intracellular Ca²⁺ imaging in DRG neurons to test if pre-treatment with 15d-PGJ₂ inhibited TRPA1 to subsequent stimulation.

Results

Intraplantar pre-injection of 15d-PGJ₂, in contrast to mustard oil (AITC), attenuated acute nocifensive responses to subsequent injections of 15d-PGJ₂ and AITC, but not capsaicin (CAP). Intraplantar 15d-PGJ₂—administered after the induction of inflammation—reduced mechanical hypersensitivity in the Complete Freund’s Adjuvant (CFA) model for up to 2 h post-injection. The 15d-PGJ₂-mediated reduction in mechanical hypersensitivity is dependent on TRPA1, as this effect was absent in TRPA1 knockout mice. Ca²⁺ imaging studies of DRG neurons demonstrated that 15d-PGJ₂ pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP. AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ₂ combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ₂ depend on TRPA1 activation. Single daily doses of 15d-PGJ₂, administered during the course of 4 days in the CFA model, effectively reversed mechanical hypersensitivity without apparent tolerance or toxicity.

Conclusions

Taken together, our data support the hypothesis that 15d-PGJ₂ induces activation followed by persistent inhibition of TRPA1 channels in DRG sensory neurons in vitro and in vivo. Moreover, we demonstrate novel evidence that 15d-PGJ₂ is analgesic in mouse models of pain via a TRPA1-dependent mechanism. Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

15d-PGJ2-loaded in nanocapsules enhance the antinociceptive properties into rat temporomandibular hypernociception

AIMS

To verify whether the nanoencapsulation of 15d-PGJ(2) in poly(D,L-lactide-co-glycolide) (PLGA) nanocapsules (15d-PGJ(2)-NC) might potentialize its antinociceptive activity into rats' temporomandibular joint (TMJ).

MAIN METHODS

Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to evaluate the morphology and suspension of the PLGA nanocapsules. Rats were pretreated (15 min) with an intra-TMJ injection of unloaded 15d-PGJ(2) or 15d-PGJ(2)-NC at concentrations of 10, 100 or 1000 pg followed by an ipsilateral intra-TMJ injection of 1.5% formalin. The nociceptive behavioral response was observed during 45 min; animals were then sacrificed and the periarticular tissue was removed for IL-1β measurements.

KEY FINDING

TEM and AFM analyses showed that 15d-PGJ(2)-NC is spherical without any aggregates or adhesion confirming that this formulation is a good drug carrier system for 15d-PGJ(2). Pretreatment with 15d-PGJ(2)-NC (100 and 1000 pg/TMJ), but not unloaded 15d-PGJ(2), was found to significantly decrease the release of IL-1β cytokine and the animals' nociceptive behavioral response induced by intra-TMJ injection of formalin.

SIGNIFICANCE

The compound 15d-PGJ(2)-NC might be used as a potential antinociceptive and anti-inflammatory agent to treat temporomandibular disorders in clinical practice.

15-Deoxy-Δ¹²,¹⁴-prostaglandin J₂, an electrophilic lipid mediator of anti-inflammatory and pro-resolving signaling

15-deoxy-Δ(12,14)-prostagandin J(2) (15d-PGJ2) is produced in the inflamed cells and tissues as a consequence of upregulation of cyclooxygenase-2 (COX-2). 15d-PGJ2 is known to be the endogenous ligand of peroxisome proliferator-activated receptor gamma (PPARγ) with multiple physiological properties. Though one of the terminal products of the COX-2-catalyzed reactions, this cyclopentenone prostaglandin exerts potent anti-inflammatory actions, in part, by antagonizing the activities of pro-inflammatory transcription factors, such as NF-κB, STAT3, and AP-1, while stimulating the anti-inflammatory transcription factor Nrf2. These effects are not necessarily dependent on its activation of PPARγ, but often involves direct interaction with the above signaling molecules and their regulators. The locally produced 15d-PGJ2 is also involved in the resolution of inflammatory responses. Thus, 15d-PGJ2, especially formed during the late phase of inflammation, might inhibit cytokine secretion and other events by antigen-presenting cells like dendritic cells or macrophages. 15d-PGJ2 can also affect the priming and effector functions of T lymphocytes and induce their apoptotic cell death. These represent a negative feedback explaining how once-initiated immunologic and inflammatory responses are switched off and terminated. In this context, 15d-PGJ2 and its synthetic derivatives have therapeutic potential for the treatment of inflammatory disorders.

Effects of 15d-PGJ₂-loaded poly(D,L-lactide-co-glycolide) nanocapsules on inflammation

BACKGROUND AND PURPOSE

The PPAR-γ agonist 15d-PGJ₂ is a potent anti-inflammatory agent but only at high doses. To improve the efficiency of 15d-PGJ₂, we used poly(D,L-lactide-co-glycolide) nanocapsules to encapsulate it, and function as a drug carrier system. The effects of these loaded nanocapsules (15d-PGJ₂-NC) on inflammation induced by different stimuli were compared with those of free 15d-PGJ₂.

EXPERIMENTAL APPROACH

Mice were pretreated (s.c.) with either 15d-PGJ₂-NC or unloaded 15d-PGJ₂ (3, 10 or 30 µg·kg⁻¹), before induction of an inflammatory response by i.p. injection of either endotoxin (LPS), carrageenan (Cg) or mBSA (immune response).

KEY RESULTS

The 15d-PGJ₂-NC complex did not display changes in physico-chemical parameters or drug association efficiency over time, and was stable for up to 60 days of storage. Neutrophil migration induced by i.p. administration of LPS, Cg or mBSA was inhibited by 15d-PGJ₂-NC, but not by unloaded 15d-PGJ₂. In the Cg model, 15d-PGJ₂-NC markedly inhibited serum levels of the pro-inflammatory cytokines TNF-α, IL-1β and IL-12p70. Importantly, 15d-PGJ₂-NC released high amounts of 15d-PGJ₂, reaching a peak between 2 and 8 h after administration. 15d-PGJ ₂ was detected in mouse serum after 24 h, indicating sustained release from the carrier. When the same concentration of unloaded 15d-PGJ₂ was administered, only small amounts of 15d-PGJ₂ were found in the serum after a few hours.

CONCLUSIONS AND IMPLICATIONS

The present findings clearly indicate the potential of the novel anti-inflammatory 15d-PGJ₂ carrier formulation, administered systemically. The formulation enables the use of a much smaller drug dose, and is significantly more effective compared with unloaded 15d-PGJ₂.

Using the Phenogen website for 'in silico' analysis of morphine-induced analgesia: identifying candidate genes

The identification of genes that contribute to polygenic (complex) behavioral phenotypes is a key goal of current genetic research. One approach to this goal is to combine gene expression information with genetic information, i.e. to map chromosomal regions that regulate gene expression levels. This approach has been termed 'genetical genomics', and, when used in conjunction with the identification of genomic regions (QTLs) that regulate the complex physiological trait under investigation, provides a strong basis for candidate gene discovery. In this paper, we describe the implementation of the genetical genomic/phenotypic approach to identify candidate genes for sensitivity to the analgesic effect of morphine in BXD recombinant inbred mice. Our analysis was performed 'in silico', using an online interactive resource called PhenoGen (http://phenogen.ucdenver.edu). We describe in detail the use of this resource, which identified a set of candidate genes, some of whose products regulate the cellular localization and activity of the mu opiate receptor. The results demonstrate how PhenoGen can be used to identify a novel set of genes that can be further investigated for their potential role in pain, morphine analgesia and/or morphine tolerance.

Influence of naloxone and methysergide on the analgesic effects of low-level laser in an experimental pain model

BACKGROUND AND OBJECTIVES

Although the mechanism of action of laser phototherapy (LPT) is not known, it is a promising analgesic method. The aim of this study was to evaluate whether the action of LPT depends on the activation of peripheral opioid or serotonergic receptors.

METHOD

Inflammatory pain was induced through the injection of carrageenin in the left posterior paw of male Wistar rats. The InGaAIP visible laser diode (660 nm) with fluency of 2.5 J*cm(-2) was used. Von Frey filaments were used to analyze mechanical hyperalgesia. Animals were separated into five groups: Carrageenin; Laser (LPT); Non-coherent light; LPT + Naloxone; and LPT + Methysergide.

RESULTS

Low-Level Laser phototherapy proved to be an effective analgesic method, while non-coherent light did not show a similar effect. The use of naloxone blocked the analgesic effect of LPT, while methysergide did not affect LPT-induced analgesia.

CONCLUSIONS

According to the parameter used in this study, LPT produced analgesia. Analgesia induced by laser phototherapy is mediated by peripheral opioid receptors. Laser phototherapy does not seem to interact with peripheral serotonergic receptors.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Activation of peroxisome proliferator-activated receptor gamma in brain inhibits inflammatory pain, dorsal horn expression of Fos, and local edema

Systemic administration of thiazolidinediones reduces peripheral inflammation in vivo, presumably by acting at peroxisome proliferator-activated receptor gamma (PPARgamma) in peripheral tissues. Based on a rapidly growing body of literature indicating the CNS as a functional target of PPARgamma actions, we postulated that brain PPARgamma modulates peripheral edema and the processing of inflammatory pain signals in the dorsal horn of the spinal cord. To test this in the plantar carrageenan model of inflammatory pain, we measured paw edema, heat hyperalgesia, and dorsal horn expression of the immediate-early gene c-fos after intracerebroventricular (ICV) administration of PPARgamma ligands or vehicle. We found that ICV rosiglitazone (0.5-50 microg) or 15d-PGJ(2) (50-200 microg), but not vehicle, dose-dependently reduced paw thickness, paw volume and behavioral withdrawal responses to noxious heat. These anti-inflammatory and anti-hyperalgesia effects result from direct actions in the brain and not diffusion to other sites, because intraperitoneal and intrathecal administration of rosiglitazone (50 microg) and 15d-PGJ(2) (200 microg) had no effect. PPARgamma agonists changed neither overt behavior nor motor coordination, indicating that non-specific behavioral effects do not contribute to PPAR ligand-induced anti-hyperalgesia. ICV administration of structurally dissimilar PPARgamma antagonists (either GW9662 or BADGE) reversed the anti-inflammatory and anti-hyperalgesic actions of both rosiglitazone and 15d-PGJ(2). To evaluate the effects of PPARgamma agonists on a classic marker of noxious stimulus-evoked gene expression, we quantified Fos protein expression in the dorsal horn. The number of carrageenan-induced Fos-like immunoreactive profiles was less in rosiglitazone-treated rats as compared to vehicle controls. We conclude that pharmacological activation of PPARgamma in the brain rapidly inhibits local edema and the spinal transmission of noxious inflammatory signals.