Morphine activates neuroinflammation in a manner parallel to endotoxin

TLR4 elimination prevents synaptic and myelin alterations and long-term cognitive dysfunctions in adolescent mice with intermittent ethanol treatment

The adolescent brain undergoes important dynamic and plastic cell changes, including overproduction of axons and synapses, followed by rapid pruning along with ongoing axon myelination. These developmental changes make the adolescent brain particularly vulnerable to neurotoxic and behavioral effects of alcohol. Although the mechanisms of these effects are largely unknown, we demonstrated that ethanol by activating innate immune receptors toll-like receptor 4 (TLR4), induces neuroinflammation and brain damage in adult mice. The present study aims to evaluate whether intermittent ethanol treatment in adolescence promotes TLR4-dependent pro-inflammatory processes, leading to myelin and synaptic dysfunctions, and long-term cognitive impairments. Using wild-type (WT) and TLR4-deficient (TLR4-KO) adolescent mice treated intermittently with ethanol (3.0g/kg) for 2weeks, we show that binge-like ethanol treatment activates TLR4 signaling pathways (MAPK, NFκB) leading to the up-regulation of cytokines and pro-inflammatory mediators (COX-2, iNOS, HMGB1), impairing synaptic and myelin protein levels and causing ultrastructural alterations. These changes were associated with long-lasting cognitive dysfunctions in young adult mice, as demonstrated with the object recognition, passive avoidance and olfactory behavior tests. Notably, elimination of TLR4 receptors prevented neuroinflammation along with synaptic and myelin derangements, as well as long-term cognitive alterations. These results support the role of the neuroimmune response and TLR4 signaling in the neurotoxic and behavioral effects of ethanol in adolescence.

Alcohol-induced sedation and synergistic interactions between alcohol and morphine: a key mechanistic role for Toll-like receptors and MyD88-dependent signaling

Increasing evidence demonstrates induction of proinflammatory Toll-like receptor (TLR) 2 and TLR4 signaling by morphine and, TLR4 signaling by alcohol; thus indicating a common site of drug action and a potential novel innate immune-dependent hypothesis for opioid and alcohol drug interactions. Hence, the current study aimed to assess the role of TLR2, TLR4, MyD88 (as a critical TLR-signaling participant), NF-κB, Interleukin-1β (IL-1β; as a downstream proinflammatory effector molecule) and the μ opioid receptor (MOR; as a classical site for morphine action) in acute alcohol-induced sedation (4.5g/kg) and alcohol (2.5g/kg) interaction with morphine (5mg/kg) by assessing the loss of righting reflex (LORR) as a measure of sedation. Wild-type male Balb/c mice and matched genetically-deficient TLR2, TLR4, and MyD88 strains were utilized, together with pharmacological manipulation of MOR, NF-κB, TLR4 and Interleukin-1β. Alcohol induced significant LORR in wild-type mice; this was halved by MyD88 and TLR4 deficiency, and surprisingly nearly completely eliminated by TLR2 deficiency. In contrast, the interaction between morphine and alcohol was found to be MOR-, NF-κB-, TLR2- and MyD88-dependent, but did not involve TLR4 or Interleukin-1β. Morphine-alcohol interactions caused acute elevations in microglial cell counts and NF-κB-p65 positive cells in the motor cortex in concordance with wild-type and TLR2 deficient mouse behavioral data, implicating neuroimmunopharmacological signaling as a pivotal mechanism in this clinically problematic drug-drug interaction.

Morphine for the treatment of pain in sickle cell disease

Pain is a hallmark of sickle cell disease (SCD) and its treatment remains challenging. Opioids are the major family of analgesics that are commonly used for treating severe pain. However, these are not always effective and are associated with the liabilities of their own. The pharmacology and multiorgan side effects of opioids are rapidly emerging areas of investigation, but there remains a scarcity of clinical studies. Due to opioid-induced endothelial-, mast cell-, renal mesangial-, and epithelial-cell-specific effects and proinflammatory as well as growth influencing signaling, it is likely that when used for analgesia, opioids may have organ specific pathological effects. Experimental and clinical studies, even though extremely few, suggest that opioids may exacerbate existent organ damage and also stimulate pathologies of their own. Because of the recurrent and/or chronic use of large doses of opioids in SCD, it is critical to evaluate the role and contribution of opioids in many complications of SCD. The aim of this review is to initiate inquiry to develop strategies that may prevent the inadvertent effect of opioids on organ function in SCD, should it occur, without compromising analgesia.

Pain in children--are we accomplishing the optimal pain treatment?

Morphine, paracetamol and local anesthetics have for a long time been the foremost used analgesics in the pediatric patient by tradition but not always enough effective and associated with side effects. The purpose with this article is to propose alternative approaches in pain management, not always supported up by substantial scientific work but from a combination of science and clinical experience in the field. The scientific literature has been reviewed in parts regarding different aspects of pain assessment and analgesics used for treatment of diverse pain conditions with focus on procedural and acute pain. Clinical experience has been added to form the suggested improvements in accomplishing an improved pain management in pediatric patients. The aim with pain management in children should be a tailored analgesic medication with an individual acceptable pain level and optimal degree of mobilization with as little side effects as possible. Simple techniques of pain control are as effective as and complex techniques in pediatrics but the technique used is not of the highest importance in achieving a good pain management. Increased interest and improved education of the doctors prescribing analgesics is important in accomplishing a better pain management. The optimal treatment with analgesics is depending on the analysis of pain origin and analgesics used should be adjusted thereafter. A multimodal treatment regime is advocated for optimal analgesic effect.

The relationship between opioids and immune signalling in the spinal cord

Opioids are considered the gold standard for the treatment of moderate to severe pain. However, heterogeneity in analgesic efficacy, poor potency and side effects are associated with opioid use, resulting in dose limitations and suboptimal pain management. Traditionally thought to exhibit their analgesic actions via the activation of the neuronal G-protein-coupled opioid receptors, it is now widely accepted that neuronal activity of opioids cannot fully explain the initiation and maintenance of opioid tolerance, hyperalgesia and allodynia. In this review we will highlight the evidence supporting the role of non-neuronal mechanisms in opioid signalling, paying particular attention to the relationship of opioids and immune signalling.

Chronic morphine-induced microRNA-124 promotes microglial immunosuppression by modulating P65 and TRAF6

Opioids have been widely applied in clinics as one of the most potent pain relievers for centuries, but their abuse has deleterious physiological effects including immunosuppression. However, the mechanisms are unclear. TLRs and acetylcholine are widely expressed in the immune and nervous systems, and play critical roles in immune responses. In this article, we show that morphine suppresses the innate immunity in microglia and bone marrow-derived macrophages through differential regulation of TLRs and acetylcholinesterase. Either morphine or inhibition of acetylcholine significantly promotes upregulation of microRNA-124 (miR-124) in microglia, bone marrow-derived macrophages, and the mouse brain, where miR-124 mediates morphine inhibition of the innate immunity by directly targeting a subunit of NF-κB p65 and TNFR-associated factor 6 (TRAF6). Furthermore, transcription factors AP-1 and CREB inhibited miR-124, whereas p65 bound directly to promoters of miR-124, thereby enhancing miR-124 transcription. Moreover, acute morphine treatment transiently upregulated the expression of p65 and phospho-p65 in both nucleus and cytoplasm priming the expression of miR-124, whereas long exposure of morphine maintained miR-124 expression, which inhibited p65- and TRAF6-dependent TLR signaling. These data suggest that modulation of miRs is capable of preventing opioid-induced damage to microglia.

Interactive HIV-1 Tat and morphine-induced synaptodendritic injury is triggered through focal disruptions in Na⁺ influx, mitochondrial instability, and Ca²⁺ overload

Synaptodendritic injury is thought to underlie HIV-associated neurocognitive disorders and contributes to exaggerated inflammation and cognitive impairment seen in opioid abusers with HIV-1. To examine events triggering combined transactivator of transcription (Tat)- and morphine-induced synaptodendritic injury systematically, striatal neuron imaging studies were conducted in vitro. These studies demonstrated nearly identical pathologic increases in dendritic varicosities as seen in Tat transgenic mice in vivo. Tat caused significant focal increases in intracellular sodium ([Na(+)]i) and calcium ([Ca(2+)]i) in dendrites that were accompanied by the emergence of dendritic varicosities. These effects were largely, but not entirely, attenuated by the NMDA and AMPA receptor antagonists MK-801 and CNQX, respectively. Concurrent morphine treatment accelerated Tat-induced focal varicosities, which were accompanied by localized increases in [Ca(2+)]i and exaggerated instability in mitochondrial inner membrane potential. Importantly, morphine's effects were prevented by the μ-opioid receptor antagonist CTAP and were not observed in neurons cultured from μ-opioid receptor knock-out mice. Combined Tat- and morphine-induced initial losses in ion homeostasis and increases in [Ca(2+)]i were attenuated by the ryanodine receptor inhibitor ryanodine, as well as pyruvate. In summary, Tat induced increases in [Na(+)]i, mitochondrial instability, excessive Ca(2+) influx through glutamatergic receptors, and swelling along dendrites. Morphine, acting via μ-opioid receptors, exacerbates these excitotoxic Tat effects at the same subcellular locations by mobilizing additional [Ca(2+)]i and by further disrupting [Ca(2+)]i homeostasis. We hypothesize that the spatiotemporal relationship of μ-opioid and aberrant AMPA/NMDA glutamate receptor signaling is critical in defining the location and degree to which opiates exacerbate the synaptodendritic injury commonly observed in neuroAIDS.

Dissociation of immunosuppressive and nociceptive effects of fentanyl, but not morphine, after repeated administration in mice: fentanyl-induced sensitization to LPS

Immunosuppressive morphine actions are well characterized, but other opiates are less studied. The objectives of this work were: (a) to compare the acute effects of morphine and fentanyl to inhibit early peritoneal LPS-induced TNFα release; (b) to find if, as in the case of morphine, intraperitoneal mast cells (MCs) are the target of fentanyl's immunosuppressive actions; and (c) to analyze if repeated opiate administration induces tolerance to opiate immunosuppressive effects. Independent groups of mice received a single i.p. injection of morphine (0.1-10mg/kg) or fentanyl (0.001-0.1mg/kg) 10min prior to LPS (1mg/kg). Peritoneal TNFα levels were determined 1h later. The effects of fentanyl were analyzed in MC-deficient mice (W-sh) and in W-sh mice reconstituted with bone marrow-derived MCs. Other animals received 6 or 10 doses of morphine (10mg/kg, 3×/day) or fentanyl (0.1mg/kg 3×/day) and were then challenged with LPS. Fentanyl was equally effective and 1000× more potent than morphine to inhibit i.p. LPS-induced TNFα release and this was dependent on intraperitoneal MCs. Repeated morphine administration induced tolerance to both antinociception and inhibition of response to endotoxin. Repeated fentanyl injection did not induce significant antinociceptive tolerance, but, interestingly, produced sensitization to LPS.

IN CONCLUSION

(1) opiates with different analgesic potency also differ in their potency to induce immunosuppression; (2) MCs are the cellular target of the immunosuppressive actions of fentanyl here studied; (3) in contrast with morphine, tolerance to fentanyl's immunosuppressive actions can be dissociated from tolerance to its antinociceptive effects.

TLR9 and MyD88 are crucial for the maturation and activation of dendritic cells by paromomycin-miltefosine combination therapy in visceral leishmaniasis

BACKGROUND AND PURPOSE

The combination of paromomycin-miltefosine is a successful anti-leishmanial therapy in visceral leishmaniasis (VL). This encouraged us to study its effect on Toll-like receptor (TLR)-mediated immunomodulation of dendritic cells (DC), as DC maturation and activation is crucial for anti-leishmanial activity.

EXPERIMENTAL APPROACH

In silico protein-ligand interaction and biophysical characterization of TLR9-drug interaction was performed. Interaction assays of HEK293 cells with different concentrations of miltefosine and/or paromomycin were performed, and NF-κB promoter activity measured. The role of TLR9 and MyD88 in paromomycin/miltefosine-induced maturation and activation of DCs was evaluated through RNA interference techniques. The effect of drugs on DCs was measured in terms of counter-regulatory production of IL-12 over IL-10, and characterized by chromatin immunoprecipitation assay at the molecular level.

KEY RESULTS

Computational and biophysical studies revealed that paromomycin/miltefosine interact with TLR9. Both drugs, as a monotherapy/combination, induced TLR9-dependent NF-κB promoter activity through MyD88. Moreover, the drug combination induced TLR9/MyD88-dependent functional maturation of DCs, evident as an up-regulation of co-stimulatory markers, enhanced antigen presentation by increasing MHC II expression, and increased stimulation of naive T-cells to produce IFN-γ. Both drugs, by modifying histone H3 at the promoter level, increased the release of IL-12, but down-regulated IL-10 in a TLR9-dependent manner.

CONCLUSIONS AND IMPLICATIONS

These results provide the first evidence that the combination of paromomycin-miltefosine critically modifies the maturation, activation and development of host DCs through a mechanism dependent on TLR9 and MyD88. This has implications for evaluating the success of other combination anti-leishmanial therapies that act by targeting host DCs.

Activation of adult rat CNS endothelial cells by opioid-induced toll-like receptor 4 (TLR4) signaling induces proinflammatory, biochemical, morphological, and behavioral sequelae

CNS immune signaling contributes to deleterious opioid effects including hyperalgesia, tolerance, reward, and dependence/withdrawal. Such effects are mediated by opioid signaling at toll-like receptor 4 (TLR4), presumptively of glial origin. Whether CNS endothelial cells express TLR4 is controversial. If so, they would be well positioned for activation by blood-borne opioids, contributing to opioid-induced pro-inflammatory responses. These studies examined adult primary rat CNS endothelial cell responses to (-)-morphine or its mu opioid receptor (MOR)-inactive metabolite morphine-3-glucuronide (M3G), both known TLR4 agonists. We demonstrate that adult rat CNS endothelial cells express functional TLR4. M3G activated nuclear factor kappaB (NF-κB), increased tumor necrosis factor-α (TNFα) and cyclooxygenase-2 (COX2) mRNAs, and released prostaglandin E2 (PGE2) from these cells. (-)-Morphine-induced upregulation of TNFα mRNA and PGE2 release were unmasked by pre-treatment with nalmefene, a MOR antagonist without TLR4 activity (unlike CTAP, shown to have both MOR- and TLR4-activity), suggestive of an interplay between MOR and TLR4 co-activation by (-)-morphine. In support, MOR-dependent Protein Kinase A (PKA) opposed TLR4 signaling, as PKA inhibition (H-89) also unmasked (-)-morphine-induced TNFα and COX2 mRNA upregulation. Intrathecal injection of CNS endothelial cells, stimulated in vitro with M3G, produced TLR4-dependent tactile allodynia. Further, cortical suffusion with M3G in vivo induced TLR4-dependent vasodilation. Finally, endothelial cell TLR4 activation by lipopolysaccharide and/or M3G was blocked by the glial inhibitors AV1013 and propentofylline, demonstrating endothelial cells as a new target of such drugs. These data indicate that (-)-morphine and M3G can activate CNS endothelial cells via TLR4, inducing proinflammatory, biochemical, morphological, and behavioral sequelae. CNS endothelial cells may have previously unanticipated roles in opioid-induced effects, in phenomena blocked by presumptive glial inhibitors, as well as TLR4-mediated phenomena more broadly.

Carbamazepine potentiates the effectiveness of morphine in a rodent model of neuropathic pain

Approximately 60% of morphine is glucuronidated to morphine-3-glucuronide (M3G) which may aggravate preexisting pain conditions. Accumulating evidence indicates that M3G signaling through neuronal Toll-like receptor 4 (TLR4) may be central to this proalgesic signaling event. These events are known to include elevated neuronal excitability, increased voltage-gated sodium (NaV) current, tactile allodynia and decreased opioid analgesic efficacy. Using an in vitro ratiometric-based calcium influx analysis of acutely dissociated small and medium-diameter neurons derived from lumbar dorsal root ganglion (DRG), we observed that M3G-sensitive neurons responded to lipopolysaccharide (LPS) and over 35% of these M3G/LPS-responsive cells exhibited sensitivity to capsaicin. In addition, M3G-exposed sensory neurons significantly increased excitatory activity and potentiated NaV current as measured by current and voltage clamp, when compared to baseline level measurements. The M3G-dependent excitability and potentiation of NaV current in these sensory neurons could be reversed by the addition of carbamazepine (CBZ), a known inhibitor of several NaV currents. We then compared the efficacy between CBZ and morphine as independent agents, to the combined treatment of both drugs simultaneously, in the tibial nerve injury (TNI) model of neuropathic pain. The potent anti-nociceptive effects of morphine (5 mg/kg, i.p.) were observed in TNI rodents at post-injury day (PID) 7–14 and absent at PID21–28, while administration of CBZ (10 mg/kg, i.p.) alone failed to produce anti-nociceptive effects at any time following TNI (PID 7–28). In contrast to either drug alone at PID28, the combination of morphine and CBZ completely attenuated tactile hyperalgesia in the rodent TNI model. The basis for the potentiation of morphine in combination with CBZ may be due to the effects of a latent upregulation of NaV1.7 in the DRG following TNI. Taken together, our observations demonstrate a potential therapeutic use of morphine and CBZ as a combinational treatment for neuropathic pain.

Assessment of morphine-induced hyperalgesia and analgesic tolerance in mice using thermal and mechanical nociceptive modalities

Opioid-induced hyperalgesia and tolerance severely impact the clinical efficacy of opiates as pain relievers in animals and humans. The molecular mechanisms underlying both phenomena are not well understood and their elucidation should benefit from the study of animal models and from the design of appropriate experimental protocols.

We describe here a methodological approach for inducing, recording and quantifying morphine-induced hyperalgesia as well as for evidencing analgesic tolerance, using the tail-immersion and tail pressure tests in wild-type mice. As shown in the video, the protocol is divided into five sequential steps. Handling and habituation phases allow a safe determination of the basal nociceptive response of the animals. Chronic morphine administration induces significant hyperalgesia as shown by an increase in both thermal and mechanical sensitivity, whereas the comparison of analgesia time-courses after acute or repeated morphine treatment clearly indicates the development of tolerance manifested by a decline in analgesic response amplitude. This protocol may be similarly adapted to genetically modified mice in order to evaluate the role of individual genes in the modulation of nociception and morphine analgesia. It also provides a model system to investigate the effectiveness of potential therapeutic agents to improve opiate analgesic efficacy.

Comparison and analysis of the animal models used to study the effect of morphine on tumour growth and metastasis

The effect of opioids on tumour growth and metastasis has been debated for many years, with recent emphasis on the possibility that they might influence the rate of disease-free survival after tumour resection when used in the perioperative pain management of cancer surgery patients. The literature presents conflicting and inconclusive in vitro and in vivo data about the potential effect of opioids, especially morphine, on tumour growth and metastasis. To inform clinical practice, appropriate animal models are needed to test whether opioids alter the course of tumour growth and metastasis. Here, we review the literature on animal-based studies testing the effect of morphine on cancer so far, and analyse differences between the models used that may explain the discrepancies in published results. Such analysis should elucidate the role of opioids in cancer and help define ideal pre-clinical models to provide definitive answers.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Diagnosis and treatment of narcotic bowel syndrome

With increased prescription of opioids has come increased recognition of adverse consequences, including narcotic bowel syndrome (NBS). Characterized by incompletely controlled abdominal pain despite continued or increasing doses of opioids, NBS is estimated to occur in 4.2-6.4% of patients chronically taking opioids. Patients with NBS have a high degree of comorbid psychiatric illness, catastrophizing and disability; comorbid substance abuse must also be considered among this population. NBS should be distinguished from opioid-induced bowel disorder, which results from the effects of opioids on gastrointestinal motility and secretion. By contrast, the mechanisms of NBS are probably centrally mediated and include glial cell activation, bimodal opioid modulation in the dorsal horn, descending facilitation of pain and the glutaminergic system. Few treatments have been rigorously studied. A trial of opioid detoxification resulted in complete detoxification for the vast majority of patients with reduction in pain symptoms; however, despite improvement in pain, approximately half of patients returned to opioid use within 3 months. Improved strategies are needed to identify patients who will respond to detoxification and remain off opioids. Comorbid psychiatric and substance abuse disorders are barriers to durable response after detoxification and should be actively sought out and treated accordingly. An effective patient-physician relationship is essential.

Challenges for opioid receptor nomenclature: IUPHAR Review 9

Recent developments in the study of the structure and function of opioid receptors raise significant challenges for the definition of individual receptor types and the development of a nomenclature that precisely describes isoforms that may subserve different functions in vivo. Presentations at the 2013 meeting of the International Narcotics Research Conference in Cairns, Australia, considered some of the new discoveries that are now unravelling the complexities of opioid receptor signalling. Variable processing of opioid receptor messenger RNAs may lead to the presence of several isoforms of the μ receptor. Each opioid receptor type can function either as a monomer or as part of a homo- or heterodimer or higher multimer. Additionally, recent evidence points to the existence of agonist bias in the signal transduction pathways activated through μ receptors, and to the presence of regulatory allosteric sites on the receptors. This brief review summarizes the recent discoveries that raise challenges for receptor definition and the characterization of signal transduction pathways activated by specific receptor forms.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Interactions between glia, the immune system and pain processes during early development

Pain is a serious problem for infants and children and treatment options are limited. Moreover, infants born prematurely or hospitalized for illness likely have concurrent infection that activates the immune system. It is now recognized that the immune system in general and glia in particular influence neurotransmission and that the neural bases of pain are intimately connected to immune function. We know that injuries that induce pain activate immune function and suppressing the immune system alleviates pain. Despite this advance in our understanding, virtually nothing is known of the role that the immune system plays in pain processing in infants and children, even though pain is a serious clinical issue in pediatric medicine. This brief review summarizes the existing data on immune-neural interactions in infants, providing evidence for the immaturity of these interactions.

Impact of lifetime opioid exposure on arterial stiffness and vascular age: cross-sectional and longitudinal studies in men and women

OBJECTIVE

To characterise and compare the potentiation of arterial stiffness and vascular ageing by opioids in men and women.

DESIGN

Cross-sectional and longitudinal studies of 576 clinical controls and 687 opioid-dependent patients (ODP) on 710 and 1305 occasions, respectively, over a total of 2382 days (6.52 years), 2006-2011. Methodology Radial pulse wave analysis with Atcor SphygmoCor system (Sydney).

SETTING

Primary care.

CONTROLS

General practice patients with non-cardiovascular disorders, and university student controls. ODP: Patients undergoing clinical management of their opioid dependence. CONTROLS had lower chronological ages (CAs) than ODP (30.0±0.5 vs 34.5±0.3, mean±SEM, p<0.0001). 69.6% and 67.7% participants were men, and 16% and 92.3% were smokers (p<0.0001) for controls and ODP, respectively. 86.3%, 10.3% and 3.4% of ODP were treated with buprenorphine (6.98±0.21 mg), methadone (63.04±4.01 mg) or implant naltrexone, respectively. Body mass index (BMI) was depressed in ODP.

INTERVENTIONS

Nil.

PRIMARY OUTCOME MEASURES

Vascular Reference Age (RA) and the ratio of vascular age to chronological age (RA/CA).

SECONDARY OUTCOME MEASURES

Arterial stiffness including Augmentation Index.

RESULTS

After BMI adjustment, RA in ODP was higher as a function of CA and of time (both p<0.05). Modelled mean RA in control and ODP was 35.6 and 36.3 years (+1.97%) in men, and 34.5 and 39.2 years (+13.43%) in women, respectively. Changes in RA and major arterial stiffness indices were worse in women both as a factor (p = 0.0036) and in interaction with CA (p = 0.0040). Quadratic, cubic and quartic functions of opioid exposure duration outperformed linear models with RA/CA over CA and over time. The opioid dose-response relationship persisted longitudinally after multiple adjustments from p=0.0013 in men and p=0.0073 in women.

CONCLUSIONS

Data show that lifetime opioid exposure, an interactive cardiovascular risk factor, particularly in women, is related to linear, quadratic, cubic and quartic functions of treatment duration and is consistent with other literature of accelerated ageing in patients with OD.

Allergen ligands in the initiation of allergic sensitization

As investigations into the innate immune responses that lead to allergic sensitization become better defined, there is a need to determine how allergens could interact with pattern recognition receptors that bind non-proteinaceous moieties. Many important allergens are not covalently bound to lipid or carbohydrate, but have structures belonging to lipid, glycan and glycolipid-binding families. These include ML-domain proteins, lipopolysaccharide-binding/cell permeability-increasing proteins, von Ebner gland lipocalins, salivary lipocalins/major urinary proteins, plant pathogenesis-related proteins PR-5 and -10, uteroglobins, non-specific lipid transfer proteins, large lipid transfer proteins and proteins with chitin and other carbohydrate-binding modules. The binding expected is overviewed with regard to importance of the allergens and their ability to elicit responses proposed from experimental models. The evidence compiled showing that allergens from the same source sensitize for different types of adaptive immune responses supports the concept that individual allergens within these sources have their own distinctive interactions with innate immunity.

Toll-like receptor 4 mutant and null mice retain morphine-induced tolerance, hyperalgesia, and physical dependence

The innate immune system modulates opioid-induced effects within the central nervous system and one target that has received considerable attention is the toll-like receptor 4 (TLR4). Here, we examined the contribution of TLR4 in the development of morphine tolerance, hyperalgesia, and physical dependence in two inbred mouse strains: C3H/HeJ mice which have a dominant negative point mutation in the Tlr4 gene rendering the receptor non-functional, and B10ScNJ mice which are TLR4 null mutants. We found that neither acute antinociceptive response to a single dose of morphine, nor the development of analgesic tolerance to repeated morphine treatment, was affected by TLR4 genotype. Likewise, opioid induced hyperalgesia and opioid physical dependence (assessed by naloxone precipitated withdrawal) were not altered in TLR4 mutant or null mice. We also examined the behavioural consequence of two stereoisomers of naloxone: (-) naloxone, an opioid receptor antagonist, and (+) naloxone, a purported antagonist of TLR4. Both stereoisomers of naloxone suppressed opioid induced hyperalgesia in wild-type control, TLR4 mutant, and TLR4 null mice. Collectively, our data suggest that TLR4 is not required for opioid-induced analgesic tolerance, hyperalgesia, or physical dependence.

Effect of currently approved carriers and adjuvants on the pre-clinical efficacy of a conjugate vaccine against oxycodone in mice and rats

Vaccination against the highly abused prescription opioid oxycodone has shown pre-clinical efficacy for blocking oxycodone effects. The current study further evaluated a candidate vaccine composed of oxycodone derivatized at the C6 position (6OXY) conjugated to the native keyhole limpet hemocyanin (nKLH) carrier protein. To provide an oxycodone vaccine formulation suitable for human studies, we studied the effect of alternative carriers and adjuvants on the generation of oxycodone-specific serum antibody and B cell responses, and the effect of immunization on oxycodone distribution and oxycodone-induced antinociception in mice and rats. 6OXY conjugated to tetanus toxoid (TT) or a GMP grade KLH dimer (dKLH) was as effective as 6OXY conjugated to the nKLH decamer in mice and rats, while the 6OXY hapten conjugated to a TT-derived peptide was not effective in preventing oxycodone-induced antinociception in mice. Immunization with 6OXY-TT s.c. absorbed on alum adjuvant provided similar protection to 6OXY-TT administered i.p. with Freund's adjuvant in rats. The toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPLA) adjuvant, alone or in combination with alum, offered no advantage over alum alone for generating oxycodone-specific serum antibodies or 6OXY-specific antibody secreting B cells in mice vaccinated with 6OXY-nKLH or 6OXY-TT. The immunogenicity of oxycodone vaccines may be modulated by TLR4 signaling since responses to 6OXY-nKLH in alum were decreased in TLR4-deficient mice. These data suggest that TT, nKLH and dKLH carriers provide consistent 6OXY conjugate vaccine immunogenicity across species, strains and via different routes of administration, while adjuvant formulations may need to be tailored to individual immunogens or patient populations.

Resveratrol reduces morphine tolerance by inhibiting microglial activation via AMPK signalling

BACKGROUND

Evidence has accumulated indicating that microglia within the spinal cord play a critical role in morphine tolerance. The present study investigated the effects and possible mechanisms of 5' adenosine monophosphate-activated protein kinase (AMPK) activator resveratrol and AICAR to inhibit microglial activation and to limit the decrease in antinociceptive effects of morphine.

METHODS

The microglial cell line BV-2 was used. Cytokine expression was measured using quantitative polymerase chain reaction. Cell signalling was assayed by Western blot and immunohistochemistry. The antinociception and morphine tolerance were assessed in CD-1 mice using the hot plate and tail-flick tests.

RESULTS

(1) Morphine induces robust BV-2 cell activation, as evidenced by increased p38 mitogen-activated protein kinase phosphorylation, nuclear factor-κB translocation and mRNA expression of pro-inflammatory cytokines [including interleukin-1β (IL-1β), IL-6 and tumour necrosis factor-α], inducible nitric oxide synthase and Toll-like receptor-4, and these changes are inhibited by resveratrol. (2) Resveratrol activates AMPK to suppress morphine-induced BV-2 cell activation. AICAR, another AMPK activator, can mimic the effects of resveratrol, whereas compound C, an AMPK inhibitor, reverses the inhibitory effects of resveratrol treatment. (3) Systemic or spinal administration of resveratrol with morphine significantly blocks microglial activation in the spinal cord and then attenuates the development of acute and chronic morphine tolerance in both male and female mice.

CONCLUSION

Resveratrol directly suppresses morphine-induced microglial activation through activating AMPK, resulting in significant attenuation of morphine antinociceptive tolerance.

A monoclonal antibody specific for 6-monoacetylmorphine reduces acute heroin effects in mice

Immunotherapy against drugs of abuse is being studied as an alternative treatment option in addiction medicine and is based on antibodies sequestering the drug in the bloodstream and blocking its entry into the brain. Producing an efficient vaccine against heroin has been considered particularly challenging because of the rapid metabolism of heroin to multiple psychoactive molecules. We have previously reported that heroin's first metabolite, 6-monoacetylmorphine (6-MAM), is the predominant mediator for heroin's acute behavioral effects and that heroin is metabolized to 6-MAM primarily prior to brain entry. On this basis, we hypothesized that antibody sequestration of 6-MAM is sufficient to impair heroin-induced effects and therefore examined the effects of a monoclonal antibody (mAb) specific for 6-MAM. In vitro experiments in human and rat blood revealed that the antibody was able to bind 6-MAM and block the metabolism to morphine almost completely, whereas the conversion of heroin to 6-MAM remained unaffected. Mice pretreated with the mAb toward 6-MAM displayed a reduction in heroin-induced locomotor activity that corresponded closely to the reduction in brain 6-MAM levels. Intraperitoneal and intravenous administration of the anti-6-MAM mAb gave equivalent protection against heroin effects, and the mAb was estimated to have a functional half-life of 8 to 9 days in mice. Our study implies that an antibody against 6-MAM is effective in counteracting heroin effects.

Pathological pain and the neuroimmune interface

Reciprocal signalling between immunocompetent cells in the central nervous system (CNS) has emerged as a key phenomenon underpinning pathological and chronic pain mechanisms. Neuronal excitability can be powerfully enhanced both by classical neurotransmitters derived from neurons, and by immune mediators released from CNS-resident microglia and astrocytes, and from infiltrating cells such as T cells. In this Review, we discuss the current understanding of the contribution of central immune mechanisms to pathological pain, and how the heterogeneous immune functions of different cells in the CNS could be harnessed to develop new therapeutics for pain control. Given the prevalence of chronic pain and the incomplete efficacy of current drugs--which focus on suppressing aberrant neuronal activity--new strategies to manipulate neuroimmune pain transmission hold considerable promise.

Toll like receptor (TLR)-4 as a regulator of peripheral endogenous opioid-mediated analgesia in inflammation

BACKGROUND

Leukocytes containing opioid peptides locally control inflammatory pain. In the early phase of complete Freund's adjuvant (CFA)-induced hind paw inflammation, formyl peptides (derived e.g. from Mycobacterium butyricum) trigger the release of opioid peptides from neutrophils contributing to tonic basal antinociception. In the later phase we hypothesized that toll-like-receptor-(TLR)-4 activation of monocytes/macrophages triggers opioid peptide release and thereby stimulates peripheral opioid-dependent antinociception.

RESULTS

In Wistar rats with CFA hind paw inflammation in the later inflammatory phase (48-96 h) systemic leukocyte depletion by cyclophosphamide (CTX) or locally injected naloxone (NLX) further decreased mechanical and thermal nociceptive thresholds. In vitro β-endorphin (β-END) content increased during human monocyte differentiation as well as in anti-inflammatory CD14+CD16- or non-classical M2 macrophages. Monocytes expressing TLR4 dose-dependently released β-END after stimulation with lipopolysaccharide (LPS) dependent on intracellular calcium. Despite TLR4 expression proinflammatory M1 and anti-inflammatory M2 macrophages only secreted opioid peptides in response to ionomycin, a calcium ionophore. Intraplantar injection of LPS as a TLR4 agonist into the inflamed paw elicited an immediate opioid- and dose-dependent antinociception, which was blocked by TAK-242, a small-molecule inhibitor of TLR4, or by peripheral applied NLX. In the later phase LPS lowered mechanical and thermal nociceptive thresholds. Furthermore, local peripheral TLR4 blockade worsened thermal and mechanical nociceptive pain thresholds in CFA inflammation.

CONCLUSION

Endogenous opioids from monocytes/macrophages mediate endogenous antinociception in the late phase of inflammation. Peripheral TLR4 stimulation acts as a transient counter-regulatory mechanism for inflammatory pain in vivo, and increases the release of opioid peptides from monocytes in vitro. TLR4 antagonists as new treatments for sepsis and neuropathic pain might unexpectedly transiently enhance pain by impairing peripheral opioid analgesia.

Differential expression of the alternatively spliced OPRM1 isoform μ-opioid receptor-1K in HIV-infected individuals

OBJECTIVE

We previously examined the expression of specific C-terminal μ-opioid receptor (MOR) splice variants in human central nervous system cell types and HIV-infected brain tissue from individuals with neurocognitive impairment ± HIV encephalitis (HIVE). In the present study, we examined the N-terminal splice variant MOR-1K, which mediates excitatory cellular signaling.

METHODS AND RESULTS

We found segregation of expression ranging from undetectable to seemingly exclusive across nervous system cell types compared to the pool of C-terminal MOR splice variants using the real-time polymerase chain reaction (RT-PCR). Expression of MOR-1K mRNA was also increased in HIV-infected individuals with combined neurocognitive impairment and HIVE compared with the other groups. MOR-1K expression correlated with the level of patient neurocognitive impairment, whereas the pool of C-terminal MOR splice variants did not. HIVE was also associated with increased expression of the inflammatory mediators MCP-1, MCP-2, and RANTES, but not the host HIV coreceptors CXCR4 and CCR5 or the CD4 receptor using qRT-PCR. Network analysis of microarray data from these same patients revealed filamin A (FLNA) as a possible interaction partner with MOR-1K, and FLNA gene expression was also found to be upregulated in HIVE using qRT-PCR. Overexpression of FLNA in HEK293 cells redistributed MOR-1K from intracellular compartments to the cell surface.

CONCLUSION

These results suggest that HIVE, and neurocognitive impairment depending on its severity, are associated with enhanced MOR-1K signaling through both increased expression and trafficking to the cell surface, which may alter the contribution of MOR receptor isoforms and exacerbate the effects of MOR activation in neuroAIDS.

Glial modulators as potential treatments of psychostimulant abuse

Glia (including astrocytes, microglia, and oligodendrocytes), which constitute the majority of cells in the brain, have many of the same receptors as neurons, secrete neurotransmitters and neurotrophic and neuroinflammatory factors, control clearance of neurotransmitters from synaptic clefts, and are intimately involved in synaptic plasticity. Despite their prevalence and spectrum of functions, appreciation of their potential general importance has been elusive since their identification in the mid-1800s, and only relatively recently have they been gaining their due respect. This development of appreciation has been nurtured by the growing awareness that drugs of abuse, including the psychostimulants, affect glial activity, and glial activity, in turn, has been found to modulate the effects of the psychostimulants. This developing awareness has begun to illuminate novel pharmacotherapeutic targets for treating psychostimulant abuse, for which targeting more conventional neuronal targets has not yet resulted in a single, approved medication. In this chapter, we discuss the molecular pharmacology, physiology, and functional relationships that the glia have especially in the light in which they present themselves as targets for pharmacotherapeutics intended to treat psychostimulant abuse disorders. We then review a cross section of preclinical studies that have manipulated glial processes whose behavioral effects have been supportive of considering the glia as drug targets for psychostimulant-abuse medications. We then close with comments regarding the current clinical evaluation of relevant compounds for treating psychostimulant abuse, as well as the likelihood of future prospects.

Targeting Toll-like receptors with small molecule agents

Toll-like receptors (TLRs) are type I transmembrane proteins that are key regulators of both innate and adaptive immune responses. To protect the host from viral and bacterial threats, TLRs trigger a pro-inflammatory immune response by detecting pathogen and danger associated molecular patterns. Considerable evidence has accumulated to show that the dysregulation of TLR signaling contributes to the development and progression of numerous diseases. Therefore, TLRs are emerging as important drug discovery targets. Currently, there is great interest in the development of TLR small molecule modulators for interrogating TLR signaling and treating diseases caused by TLR signaling malfunctions. In this tutorial review, we will outline methods for the discovery of TLR small molecule modulators and the up-to-date progress in this field. Small molecules targeting TLRs not only provide an opportunity to identify promising drug candidates, but also unveil knowledge regarding TLR signaling pathways.

FACS analysis of neuronal-glial interactions in the nucleus accumbens following morphine administration

RATIONALE

Glia, including astrocytes and microglia, can profoundly modulate neuronal function and behavior; however, very little is known about the signaling molecules that govern neuronal-glial communication and in turn affect behavior. Morphine treatment activates microglia and astrocytes in the nucleus accumbens (NAcc) to induce the synthesis of cytokines and chemokines, and this has important implications for addictive behavior. Blocking morphine-induced glial activation using the nonspecific glial inhibitor, ibudilast, has no effect on the initial rewarding properties of morphine, but completely prevents the relapse of drug-seeking behavior months later.

OBJECTIVES

We sought to determine the cellular source of these cytokines and chemokines in the NAcc in response to morphine, and the cell-type-specific expression pattern of their receptors to determine whether neurons have the capacity to respond to these immune signals directly.

METHODS

We used fluorescence-activated cell sorting of neurons (Thy1+), astrocytes (GLT1+), and microglia (CD11b+) from the NAcc for the analysis of cell type specific gene expression following morphine or saline treatment.

RESULTS

The results indicate that microglia and neurons each produce a subset of chemokines in response to morphine and that neurons have the capacity to respond directly to a select group of these chemokines via their receptors. In addition, we provide evidence that microglia are capable of responding directly to dopamine release in the NAcc.

CONCLUSIONS

Future studies will examine the mechanism(s) by which neurons respond to these immune signals produced by microglia in an effort to understand their effect on addictive behaviors.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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).

Toll-like receptor 4 (TLR4) modulation by synthetic and natural compounds: an update

Toll-like receptor 4 (TLR4), together with MD-2, binds bacterial endotoxins (E) with high affinity, triggering formation of the activated homodimer (E.MD-2.TLR4)2. Activated TLR4 induces intracellular signaling leading to activation of transcription factors that result in cytokine and chemokine production and initiation of inflammatory and immune responses. TLR4 also responds to endogenous ligands called danger associated molecular patterns (DAMPs). Increased sensitivity to infection and a variety of immune pathologies have been associated with either too little or too much TLR4 activation. We review here the molecular mechanisms of TLR4 activation (agonism) or inhibition (antagonism) by small organic molecules of both natural and synthetic origin. The role of co-receptors MD-2 and CD14 in the TLR4 modulation process is also discussed. Recent achievements in the field of chemical TLR4 modulation are reviewed, with special focus on nonclassical TLR4 ligands with a chemical structure different from that of lipid A.

CCL5 and cytokine expression in the rat brain: differential modulation by chronic morphine and morphine withdrawal

Opioids have been shown to influence the immune system and to promote the expression of pro-inflammatory cytokines in the central nervous system. However, recent data have shown that activation of opioid receptors increases the expression and release of the neuroprotective chemokine CCL5 from astrocytes in vitro. To further define the interaction between CCL5 and inflammation in response to opioids, we have examined the effect of chronic morphine and morphine withdrawal on the in vivo expression of CCL5 as well as of pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Rats undergoing a chronic morphine paradigm (10 mg/kg increasing to 30 mg/kg, twice a day for 5 days) showed a twofold increase of CCL5 protein and mRNA within the cortex and striatum. No changes were observed in the levels of IL-1β and TNF-α. Naltrexone blocked the effect of morphine. A chronic morphine paradigm with no escalating doses (10 mg/kg, twice a day) did not alter CCL5 levels compared to saline-treated animals. On the contrary, rats undergoing spontaneous morphine withdrawal exhibited lower levels of CCL5 within the cortex as well as increased levels of pro-inflammatory cytokines and Iba-1 positive cells than saline-treated rats. Overall, these data suggest that morphine withdrawal may promote cytokines and other inflammatory responses that have the potential of exacerbating neuronal damage.

Cytokines, chaperones and neuroinflammatory responses in heroin-related death: what can we learn from different patterns of cellular expression?

Heroin (3,6-diacetylmorphine) has various effects on the central nervous system with several neuropathological alterations including hypoxic-ischemic brain damage from respiratory depressing effects and neuroinflammatory response. Both of these mechanisms induce the release of cytokines, chemokines and other inflammatory mediators by the activation of many cell types such as leucocytes and endothelial and glial cells, especially microglia, the predominant immunocompetent cell type within the central nervous system. The aim of this study is to clarify the correlation between intravenous heroin administration in heroin related death and the neuroinflammatory response. We selected 45 cases among autopsies executed for heroin-related death (358 total cases); immunohistochemical studies and Western blotting analyses were used to investigate the expression of brain markers such as tumor necrosis factor-α, oxygen-regulated protein 150, (interleukins) IL-1β, IL-6, IL-8, IL-10, IL-15, cyclooxygenase-2, heat shock protein 70, and CD68 (MAC387). Findings demonstrated that morphine induces inflammatory response and cytokine release. In particular, oxygen-regulated protein 150, cyclooxygenase-2, heat shock protein 70, IL-6 and IL-15 cytokines were over-expressed with different patterns of cellular expression.

Pharmacological characterization of LPS and opioid interactions at the toll-like receptor 4

BACKGROUND AND PURPOSE

Previous work in our laboratory showed opioid agents inhibit cytokine expression in astrocytes. Recently, Watkins and colleagues hypothesized that opioid agonists activate toll-like receptor 4 (TLR4) signalling, which leads to neuroinflammation. To test this hypothesis, we characterized LPS and opioid effects on TLR4 signalling in reporter cells.

EXPERIMENTAL APPROACH

NF-κB reporter cells expressing high levels of TLR4 were used to compare LPS and opioid effects on NF-κB activation, a pathway activated by TLR4 stimulation.

KEY RESULTS

LPS increased TLR4 signalling in a concentration-dependent manner and was antagonized by LPS antagonist (LPS-RS, from Rhodobacter sphaeroides). A concentration ratio analysis showed that LPS-RS was a competitive antagonist. The opioid agonists, morphine and fentanyl, produced minor activation of TLR4 signalling when given alone. When tested following LPS stimulation, opioid agonists inhibited NF-κB activation but this inhibition was not blocked by the general opioid antagonist, naloxone, nor by the selective μ opioid receptor antagonist, β-FNA. Indeed, both naloxone and β-FNA also inhibited NF-κB activation in reporter cells. Further examination of fentanyl and β-FNA effects revealed that both opioid agents inhibited LPS signalling in a non-competitive fashion.

CONCLUSIONS AND IMPLICATIONS

These results show that LPS-RS is a competitive antagonist at the TLR4 complex, and that both opioid agonists and antagonists inhibit LPS signalling in a non-competitive fashion through a non-GPCR, opioid site(s) in the TLR4 signalling pathway. If confirmed, existing opioid agents or other drug molecules more selective at this novel site may provide a new therapeutic approach to the treatment of neuroinflammation.

Traditional medicines and globalization: current and future perspectives in ethnopharmacology

The ethnopharmacological approach toward the understanding and appraisal of traditional and herbal medicines is characterized by the inclusions of the social as well as the natural sciences. Anthropological field-observations describing the local use of nature-derived medicines are the basis for ethnopharmacological enquiries. The multidisciplinary scientific validation of indigenous drugs is of relevance to modern societies at large and helps to sustain local health care practices. Especially with respect to therapies related to aging related, chronic and infectious diseases traditional medicines offer promising alternatives to biomedicine. Bioassays applied in ethnopharmacology represent the molecular characteristics and complexities of the disease or symptoms for which an indigenous drug is used in “traditional” medicine to variable depth and extent. One-dimensional in vitro approaches rarely cope with the complexity of human diseases and ignore the concept of polypharmacological synergies. The recent focus on holistic approaches and systems biology in medicinal plant research represents the trend toward the description and the understanding of complex multi-parameter systems. Ethnopharmacopoeias are non-static cultural constructs shaped by belief and knowledge systems. Intensified globalization and economic liberalism currently accelerates the interchange between local and global pharmacopoeias via international trade, television, the World Wide Web and print media. The increased infiltration of newly generated biomedical knowledge and introduction of “foreign” medicines into local pharmacopoeias leads to syncretic developments and generates a feedback loop. While modern and post-modern cultures and knowledge systems adapt and transform the global impact, they become more relevant for ethnopharmacology. Moreover, what is traditional, alternative or complementary medicine depends on the adopted historic-cultural perspective.

Morphine stimulates platelet-derived growth factor receptor-β signalling in mesangial cells in vitro and transgenic sickle mouse kidney in vivo

BACKGROUND

Pain and renal dysfunction occur in sickle cell disease. Morphine used to treat pain also co-activates platelet-derived growth factor receptor-β (PDGFR-β), which can adversely affect renal disease. We examined the influence of morphine in mesangial cells in vitro and in mouse kidneys in vivo.

METHODS

> Mouse mesangial cells treated with 1 μM morphine in vitro or kidneys of transgenic homozygous or hemizygous sickle or control mice (n=3 for each), treated with morphine (0.75, 1.4, 2.14, 2.8, 3.6, and 4.3 mg kg(-1) day(-1) in two divided doses during the first, second, third, fourth, fifth, and sixth weeks, respectively), were used. Western blotting, bromylated deoxy uridine incorporation-based cell proliferation assay, reverse transcriptase-polymerase chain reaction, immunofluorescent microscopy, and blood/urine chemistry were used to analyse signalling, cell proliferation, opioid receptor (OP) expression, and renal function.

RESULTS

Morphine stimulated phosphorylation of PDGFR-β and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) to the same extent as induced by platelet-derived growth factor-BB (PDGF-BB) and promoted a two-fold increase in mesangial cell proliferation. The PDGFR-β inhibitor, AG1296, OP antagonists, and silencing of μ- and κ-OP abrogated morphine-induced MAPK/ERK phosphorylation and proliferation by ~100%. Morphine treatment of transgenic mice resulted in phosphorylation of PDGFR-β, MAPK/ERK, and signal transducer and activator of transcription 3 (Stat3) in the kidneys. Morphine inhibited micturition and blood urea nitrogen (BUN) clearance and increased BUN and urinary protein in sickle mice.

CONCLUSION

Morphine stimulates mitogenic signalling leading to mesangial cell proliferation and promotes renal dysfunction in sickle mice.

Mast cell activation contributes to sickle cell pathobiology and pain in mice

Sickle cell anemia (SCA) is an inherited disorder associated with severe lifelong pain and significant morbidity. The mechanisms of pain in SCA remain poorly understood. We show that mast cell activation/degranulation contributes to sickle pain pathophysiology by promoting neurogenic inflammation and nociceptor activation via the release of substance P in the skin and dorsal root ganglion. Mast cell inhibition with imatinib ameliorated cytokine release from skin biopsies and led to a correlative decrease in granulocyte-macrophage colony-stimulating factor and white blood cells in transgenic sickle mice. Targeting mast cells by genetic mutation or pharmacologic inhibition with imatinib ameliorates tonic hyperalgesia and prevents hypoxia/reoxygenation-induced hyperalgesia in sickle mice. Pretreatment with the mast cell stabilizer cromolyn sodium improved analgesia following low doses of morphine that were otherwise ineffective. Mast cell activation therefore underlies sickle pathophysiology leading to inflammation, vascular dysfunction, pain, and requirement for high doses of morphine. Pharmacological targeting of mast cells with imatinib may be a suitable approach to address pain and perhaps treat SCA.

Innate immunity and neuroinflammation

Inflammation of central nervous system (CNS) is usually associated with trauma and infection. Neuroinflammation occurs in close relation to trauma, infection, and neurodegenerative diseases. Low-level neuroinflammation is considered to have beneficial effects whereas chronic neuroinflammation can be harmful. Innate immune system consisting of pattern-recognition receptors, macrophages, and complement system plays a key role in CNS homeostasis following injury and infection. Here, we discuss how innate immune components can also contribute to neuroinflammation and neurodegeneration.

Why is neuroimmunopharmacology crucial for the future of addiction research?

A major development in drug addiction research in recent years has been the discovery that immune signaling within the central nervous system contributes significantly to mesolimbic dopamine reward signaling induced by drugs of abuse, and hence is involved in the presentation of reward behaviors. Additionally, in the case of opioids, these hypotheses have advanced through to the discovery of the novel site of opioid action at the innate immune pattern recognition receptor Toll-like receptor 4 as the necessary triggering event that engages this reward facilitating central immune signaling. Thus, the hypothesis of major proinflammatory contributions to drug abuse was born. This review will examine these key discoveries, but also address several key lingering questions of how central immune signaling is able to contribute in this fashion to the pharmacodynamics of drugs of abuse. It is hoped that by combining the collective wisdom of neuroscience, immunology and pharmacology, into Neuroimmunopharmacology, we may more fully understanding the neuronal and immune complexities of how drugs of abuse, such as opioids, create their rewarding and addiction states. Such discoveries will point us in the direction such that one day soon we might successfully intervene to successfully treat drug addiction. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Glucuronic acid and the ethanol metabolite ethyl-glucuronide cause toll-like receptor 4 activation and enhanced pain

We have previously observed that the non-opioid morphine metabolite, morphine-3-glucuronide, enhances pain via a toll-like receptor 4 (TLR4) dependent mechanism. The present studies were undertaken to determine whether TLR4-dependent pain enhancement generalizes to other classes of glucuronide metabolites. In silico modeling predicted that glucuronic acid alone and ethyl glucuronide, a minor but long-lasting ethanol metabolite, would dock to the same MD-2 portion of the TLR4 receptor complex previously characterized as the docking site for morphine-3-glucuronide. Glucuronic acid, ethyl glucuronide and ethanol all caused an increase in TLR4-dependent reporter protein expression in a cell line transfected with TLR4 and associated co-signaling molecules. Glucuronic acid-, ethyl glucuronide-, and ethanol-induced increases in TLR4 signaling were blocked by the TLR4 antagonists LPS-RS and (+)-naloxone. Glucuronic acid and ethyl glucuronide both caused allodynia following intrathecal injection in rats, which was blocked by intrathecal co-administration of the TLR4 antagonist LPS-RS. The finding that ethyl glucuronide can cause TLR4-dependent pain could have implications for human conditions such as hangover headache and alcohol withdrawal hyperalgesia, as well as suggesting that other classes of glucuronide metabolites could have similar effects.

Effect of chronic delivery of the Toll-like receptor 4 antagonist (+)-naltrexone on incubation of heroin craving

BACKGROUND

Recent evidence implicates toll-like receptor 4 (TLR4) in opioid analgesia, tolerance, conditioned place preference, and self-administration. Here, we determined the effect of the TLR4 antagonist (+)-naltrexone (a μ-opioid receptor inactive isomer) on the time-dependent increases in cue-induced heroin seeking after withdrawal (incubation of heroin craving).

METHODS

In an initial experiment, we trained rats for 9 hours per day to self-administer heroin (.1 mg/kg/infusion) for 9 days; lever presses were paired with a 5-second tone-light cue. We then assessed cue-induced heroin seeking in 30-minute extinction sessions on withdrawal day 1; immediately after testing, we surgically implanted rats with Alzet minipumps delivering (+)-naltrexone (0, 7.5, 15, 30 mg/kg/day, subcutaneous) for 14 days. We then tested the rats for incubated cue-induced heroin seeking in 3-hour extinction tests on withdrawal day 13.

RESULTS

We found that chronic delivery of (+)-naltrexone via minipumps during the withdrawal phase decreased incubated cue-induced heroin seeking. In follow-up experiments, we found that acute injections of (+)-naltrexone immediately before withdrawal day 13 extinction tests had no effect on incubated cue-induced heroin seeking. Furthermore, chronic delivery of (+)-naltrexone (15 or 30 mg/kg/day) or acute systemic injections (15 or 30 mg/kg) had no effect on ongoing extended access heroin self-administration. Finally, in rats trained to self-administer methamphetamine (.1 mg/kg/infusion, 9 hours/day, 9 days), chronic delivery of (+)-naltrexone (30 mg/kg/day) during the withdrawal phase had no effect on incubated cue-induced methamphetamine seeking.

CONCLUSIONS

The present results suggest a critical role of TLR4 in the development of incubation of heroin, but not methamphetamine, craving.

Rifampin inhibits Toll-like receptor 4 signaling by targeting myeloid differentiation protein 2 and attenuates neuropathic pain

Rifampin has been used for the treatment of bacterial infections for many years. Clinically, rifampin has been found to possess immunomodulatory effects. However, the molecular target responsible for the immunosuppressive effects of rifampin is not known. Herein, we show that rifampin binds to myeloid differentiation protein 2 (MD-2), the key coreceptor for innate immune TLR4. Rifampin blocked TLR4 signaling induced by LPS, including NF-κB activation and the overproduction of proinflammatory mediators nitric oxide, interleukin 1β, and tumor necrosis factor α in mouse microglia BV-2 cells and macrophage RAW 264.7 cells. Rifampin's inhibition of TLR4 signaling was also observed in immunocompetent rat primary macrophage, microglia, and astrocytes. Further, we show that rifampin (75 or 100 mg/kg b.i.d. for 3 d, intraperitoneal) suppressed allodynia induced by chronic constriction injury of the sciatic nerve and suppressed nerve injury-induced activation of microglia. Our findings indicate that MD-2 is a important target of rifampin in its inhibition of innate immune function and contributes to its clinically observed immune-suppressive effect. The results also suggest that rifampin may be repositioned as an agent for the treatment of neuropathic pain.