The role of the sympathetic efferents in endotoxin-induced localized inflammatory hyperalgesia and cytokine upregulation

Inflammation Induces Changes in the Functional Expression of P-gp, BCRP, and MRP2: An Overview of Different Models and Consequences for Drug Disposition

The ATP-binding cassette (ABC) transporters play a key role in drug pharmacokinetics. These membrane transporters expressed within physiological barriers can be a source of pharmacokinetic variability. Changes in ABC transporter expression and functionality may consequently affect the disposition of substrate drugs, resulting in different drug exposure. Inflammation, present in several acute and chronic diseases, has been identified as a source of modulation in drug transporter expression leading to variability in drug response. Its regulation may be particularly dangerous for drugs with a narrow therapeutic index. In this context, numerous in vitro and in vivo models have shown up- or downregulation in the expression and functionality of ABC transporters under inflammatory conditions. Nevertheless, the existence of contradictory data and the lack of standardization for the models used have led to a less conclusive interpretation of these data.

Adjunctive effects of laser therapy on somatosensory function and vasomotor regulation of periodontal tissues in patients with periodontitis: A randomized controlled clinical trial

BACKGROUND

The purpose of this prospective study was to compare the changes in periodontal somatosensory function and microcirculation in patients with periodontitis following initial treatment with scaling and root planing (SRP) with or without adjuvant laser therapy.

METHODS

Twenty-four patients suffering from periodontitis were recruited and randomly allocated into a split-mouth design to either SRP combined laser therapy side (test side) or SRP only side (control side). All treatments were performed by the same investigator at a single visit. Laser Doppler Flowmetry (LDF) and Quantitative Sensory Testing (QST) were performed at baseline (W0), 1 week (1W), 2 weeks (2W), and 4 weeks (4W) after treatment on both sides of the attached gingiva of the maxillary lateral incisor. Clinical examination including probing depth (PD) and bleeding on probing (BOP) was performed at W0, 2W, and 4W on both sides. Data were analyzed with two-way analysis of variance.

RESULTS

PD and BOP significantly improved after treatment (P <0.001). LDF values were significantly decreased on both sides at all follow-up time points (P <0.001), temperature was increased only on the test side (P = 0.017) whereas there was no significant change on the control side (P = 0.792). Significantly less sensitivity was observed for all QST parameters (P <0.030) except for warmth detection after treatment.

CONCLUSION

Adjunctive use of laser therapy did not provide any significant clinical advantage or additional effects on the recovery of periodontal somatosensory function or gingival microcirculation in the present study.

Peripheral nitric oxide signaling directly blocks inflammatory pain

Pain is a classical sign of inflammation, and sensitization of primary sensory neurons (PSN) is the most important mediating mechanism. This mechanism involves direct action of inflammatory mediators such as prostaglandins and sympathetic amines. Pharmacologic control of inflammatory pain is based on two principal strategies: (i) non-steroidal anti-inflammatory drugs targeting inhibition of prostaglandin production by cyclooxygenases and preventing nociceptor sensitization in humans and animals; (ii) opioids and dipyrone that directly block nociceptor sensitization via activation of the NO signaling pathway. This review summarizes basic concepts of inflammatory pain that are necessary to understand the mechanisms of peripheral NO signaling that promote peripheral analgesia; we also discuss therapeutic perspectives based on the modulation of the NO pathway.

Bacterial cellulose membrane associated with red propolis as phytomodulator: Improved healing effects in experimental models of diabetes mellitus

Since early times, propolis has been used in folk medicine. The red propolis, collected in the northeast region of Brazil has been highlighted due to its popular use as an antimicrobial, with anti-inflammatory and healing properties, which are associated with its chemical composition. Here, we combine a bacterial membrane with red propolis to treat wounds of diabetic mice. This work aims to evaluate a biocurative from bacterial cellulose associated with red propolis in diabetic mice as wound healing model. Biocuratives from bacterial cellulose membrane and different extracts of red propolis were produced. The qualification and quantification of the presence of propolis chemical compounds in the membrane were investigated through high-resolution mass spectrometry (HRMS). Tests in vivo with biocuratives were performed on Swiss male diabetic mice induced by estroptozotocin. The animals were submitted to a surgical procedure and a single lesion was produced in the dorsal region, which was treated with the biocuratives. Macroscopic assessments were performed at 2, 7 and 14 postoperative days, and biopsies were collected on days 0, 7 and 14 for histological analysis, myeloperoxidase enzyme activity (MPO) and cytokines (TNF-α, IL-1β, and TGF-β). Altogether, ten compounds were identified in membranes and five were further quantified. The ethyl acetate extract showed more red propolis markers, and the most prevalent compound was Formononetin with 4423.00-2907.00 μg.g^-1. Macroscopic analyses demonstrated that the two groups treated with red propolis (GMEBT and GMEAE) showed significantly greater healing capabilities compared to the control groups (GS and GMS). An increase in leukocyte recruitment was observed, confirmed by the activity of the enzyme myeloperoxidase (MPO) in GMEBT and GMEAE groups. The levels of TNF-α were significantly higher in wounds stimulated with red propolis, as well as in TGF-β (GMEBT and GMEAE) on day 7. This was different from the IL-1β levels that were higher in the control groups (GS and GMS). In summary, the biocuratives produced in this work were able to accelerate the wound healing process in a diabetic mouse model. In this way, the traditional knowledge of red propolis activity helped to create a biotechnological product, which can be used for diabetic wound healing purpose.

Inhibitory effect of luminal saccharides on glucose absorption from an adjacent jejunal site in rats: a newly described intestinal neural reflex

Nutrients in the lumen of the small intestine are sensed by special cells in the epithelial lining. The ensuing neurohumoral reflexes affect gastrointestinal absorption/secretion, motility, and vascular perfusion. To study in vivo the effect of a monosaccharide (glucose) or polysaccharide (starch) present in the jejunum on glucose absorption from an adjacent part of the intestine and investigate the possible underlying mechanisms. Using the single pass intraluminal perfusion technique, a segment of jejunum (perfusion segment) was continuously perfused with 20 mM glucose to determine glucose absorption. One hour later, a bolus of a saccharide was instilled in an isolated adjacent jejunal segment and the change in glucose absorption was monitored for a further 2 h. The contribution of neural mechanisms in this process was investigated. Instillation of glucose (20 mM or 40 mM) in either distal or proximal jejunal pouch elicited immediate and sustained inhibition of glucose absorption (a decrease by 25%; P < 0.01) from the perfused jejunal segment. Comparable inhibition was obtained with instillation of other monosaccharides or starch in the jejunal pouch. This inhibition was abolished by adding tetrodotoxin to the pouch or to the perfused jejunal segment and also by pretreatment with sympathetic blockers (guanethidine or hexamethonium) and by chemical ablation of capsaicin-sensitive primary afferent fibers. Glucose absorption within the jejunum is auto-regulated through backward and forward mechanisms. This regulation is mediated by neural reflexes involving capsaicin-sensitive afferent and sympathetic efferent fibers. These reflexes might serve to protect against hyperglycemia.

Contribution of capsaicin-sensitive innervation to the continuous eruption of the rat mandibular incisors

A major component of tooth innervation is made of capsaicin-sensitive primary afferents (CSPA). These fibers play a key role in tooth pain and inflammation; little is known, however, about the role of CSPA in tooth eruption. The aim of this study was to examine the role of the capsaicin-sensitive afferents in the process of eruption of intact rat incisors. CSPA fibers in several rat groups, were subjected to one of the following experimental procedures: systemic chemical ablation, systemic ablation followed by chemical sympathectomy and localized activation. The observed effects on incisor eruption were compared to those made on controls. The total amount of eruption in control/naïve rats, measured over a total period of 144 h, was 3.18 ± 0.07 mm and decreased to 2.43 ± 0.08 mm (n = 7; p < 0.001) following systemic ablation of CSPA. Further decrease to 2.24 ± 0.08 mm (n = 7; p < 0.001) was noticed when chemical sympathectomy was added to CSPA ablation. The average rate of eruption was 1.7 ± 0.25 mm following CSPA activation, compared to an average of 0.8 ± 0.07 mm for controls (n = 7; p < 0.001). Capsaicin sensitive fibers play an important role in tooth homeostasis, and intact neural supply is required for tooth growth under normal conditions.

Antihyperalgesic Activity of Atomoxetine on Diabetes-Induced Neuropathic Pain: Contribution of Noradrenergic and Dopaminergic Systems

Atomoxetine is a selective noradrenaline reuptake inhibitor drug. Based on the knowledge that agents increasing monoamine levels in the central nervous system have therapeutic potential for neuropathic pain, it is planned to investigate the possible efficacy of atomoxetine on diabetes-induced hyperalgesia, in this study. Randall-Selitto (mechanical noxious stimuli) and Hargreaves (thermal noxious stimuli) tests were used to evaluate nociceptive perception of rats. Obtained data indicated that streptozotocin-induced diabetes causes significant decreases in the paw withdrawal threshold and paw withdrawal latency values of the animals, respectively. However, atomoxetine administered at 3 mg/kg/day for 7 and 14 days improved these diabetes-induced hyperalgesia responses. Furthermore, antihyperalgesic activity was antagonized with α-methyl-para-tyrosine methyl ester, phentolamine, propranolol, and sulpiride pre-treatments. The same effect was not reversed, however, by SCH 23390. These findings demonstrated, for the first time, that atomoxetine possesses significant antihyperalgesic activity on diabetes-induced neuropathic pain and this effect seems to be mediated by α- and β-adrenergic and D₂/D₃ dopaminergic receptors. Results of this present study seem to offer a new indication for an old drug; atomoxetine, but these preclinical data should first be confirmed with further well-designed clinical trials.

The effects of propranolol on heart rate variability and quantitative, mechanistic, pain profiling: a randomized placebo-controlled crossover study

Background and aims

The autonomic nervous system (ANS) is capable of modulating pain. Aberrations in heart rate variability (HRV), reflective of ANS activity, are associated with experimental pain sensitivity, chronic pain, and more recently, pain modulatory mechanisms but the underlying mechanisms are still unclear. HRV is lowered during experimental pain as well as in chronic pain conditions and HRV can be increased by propranolol, which is a non-selective β-blocker. Sensitization of central pain pathways have been observed in several chronic pain conditions and human mechanistic pain biomarkers for these central pain pathways include temporal summation of pain (TSP) and conditioned pain modulation (CPM). The current study aimed to investigate the effect of the β-blocker propranolol, and subsequently assessing the response to standardized, quantitative, mechanistic pain biomarkers.

Methods

In this placebo-controlled, double-blinded, randomized crossover study, 25 healthy male volunteers (mean age 25.6 years) were randomized to receive 40 mg propranolol and 40 mg placebo. Heart rate, blood pressure, and HRV were assessed before and during experimental pain tests. Cuff pressure pain stimulation was used for assessment of pain detection (cPDTs) and pain tolerance (cPTTs) thresholds, TSP, and CPM. Offset analgesia (OA) was assessed using heat stimulation.

Results

Propranolol significantly reduced heart rate (p<0.001), blood pressure (p<0.02) and increased HRV (p<0.01) compared with placebo. No significant differences were found comparing cPDT (p>0.70), cPTT (p>0.93), TSP (p>0.70), OA-effect (p>0.87) or CPM (p>0.65) between propranolol and placebo.

Conclusions

The current study demonstrated that propranolol increased HRV, but did not affect pressure pain sensitivity or any pain facilitatory or modulatory outcomes.

Implications

Analgesic effects of propranolol have been reported in clinical pain populations and the results from the current study could indicate that increased HRV from propranolol is not associated with peripheral and central pain pathways in healthy male subjects.

Ropivacaine and Bupivacaine prevent increased pain sensitivity without altering neuroimmune activation following repeated social defeat stress

OBJECTIVE

Mounting evidence indicates that stress influences the experience of pain. Exposure to psychosocial stress disrupts bi-directional communication pathways between the central nervous system and peripheral immune system, and can exacerbate the frequency and severity of pain experienced by stressed subjects. Repeated social defeat (RSD) is a murine model of psychosocial stress that recapitulates the immune and behavioral responses to stress observed in humans, including activation of stress-reactive neurocircuitry and increased pro-inflammatory cytokine production. It is unclear, however, how these stress-induced neuroimmune responses contribute to increased pain sensitivity in mice exposed to RSD. Here we used a technique of regional analgesia with local anesthetics in mice to block the development of mechanical allodynia during RSD. We next investigated the degree to which pain blockade altered stress-induced neuroimmune activation and depressive-like behavior.

METHODS

Following development of a mouse model of regional analgesia with discrete sensory blockade over the dorsal-caudal aspect of the spine, C57BL/6 mice were divided into experimental groups and treated with Ropivacaine (0.08%), Liposomal Bupivacaine (0.08%), or Vehicle (0.9% NaCl) prior to exposure to stress. This specific region was selected for analgesia because it is the most frequent location for aggression-associated pain due to biting during RSD. Mechanical allodynia was assessed 12 h after the first, third, and sixth day of RSD after resolution of the sensory blockade. In a separate experiment, social avoidance behavior was determined after the sixth day of RSD. Blood, bone marrow, brain, and spinal cord were collected for immunological analyses after the last day of RSD in both experiments following behavioral assessments.

RESULTS

RSD increased mechanical allodynia in an exposure-dependent manner that persisted for at least one week following cessation of the stressor. Mice treated with either Ropivacaine or Liposomal Bupivacaine did not develop mechanical allodynia following exposure to stress, but did develop social avoidance behavior. Neither drug affected stress-induced activation of monocytes in the bone marrow, blood, or brain. Neuroinflammatory responses developed in all treatment groups, as evidenced by elevated IL-1β mRNA levels in the brain and spinal cord after RSD.

CONCLUSIONS

In this study, psychosocial stress was associated with increased pain sensitivity in mice. Development of mechanical allodynia with RSD was blocked by regional analgesia with local anesthetics, Ropivacaine or Liposomal Bupivacaine. Despite blocking mechanical allodynia, these anesthetic interventions did not prevent neuroimmune activation or social avoidance associated with RSD. These data suggest that stress-induced neuroinflammatory changes are not associated with increased sensitivity to pain following RSD. Thus, blocking peripheral nociception was effective in inhibiting enhanced pain signaling without altering stress-induced immune or behavioral responses.

Repeated electroacupuncture treatment attenuated hyperalgesia through suppression of spinal glial activation in chronic neuropathic pain rats

Background

Cumulated evidence reveals that glial cells in the spinal cord play an important role in the development of chronic neuropathic pain and are also complicated in the analgesic effect of EA intervention. But the roles of microgliacytes and astrocytes of spinal cord in the process of EA analgesia remain unknown.

Methods

A total of 120 male Wistar rats were used in the present study. The neuropathic pain model was established by chronic constrictive injury (CCI) of the sciatic nerve. The rats were randomly divided into sham group, CCI group, and sham CCI + EA group, and CCI + EA group. EA was applied to bilateral Zusanli (ST36)-Yanlingquan (GB34). The mechanical (both time and force responses) and thermal pain thresholds (PTs) of the bilateral hind-paws were measured. The number of microgliacytes and activity of astrocytes in the dorsal horns (DHs) of lumbar spinal cord (L4–5) were examined by immunofluorescence staining, and the expression of glial fibrillary acidic protein (GFAP) protein was detected by western blot.

Results

Following CCI, both mechanical and thermal PTs of the ipsilateral hind-paw were significantly decreased beginning from the 3rd day after surgery (P < 0.05), and the mechanical PT of the contralateral hind-paw was considerably decreased from the 6th day on after surgery (P < 0.05). CCI also significantly upregulated the number of Iba-1 labeled microgliacytes and the fluorescence intensity of glial fibrillary acidic protein (GFAP) -labeled astrocyte in the superficial laminae of DHs on bilateral sides (P < 0.05). After repeated EA, the mechanical and thermal PTs at bilateral hind-paws were significantly relieved (P < 0.05). The increased of number of microgliacytes was markedly suppressed by 2 days’ EA intervention, and the average fluorescence intensity was suppressed by 2 weeks’ EA. The expression of GFAP protein were down-regulated by 1 and 2 weeks’ EA treatment, respectively (P < 0.05).

Conclusions

Repeated EA can relieve neuropathic pain and mirror-image pain in chronic neuropathic pain rats, which is probably associated with its effect in downregulating glial cell activation of the lumbar spinal cord, the microgliacyte first and astrocyte later.

Modulation of incisor eruption in rats by sympathetic efferents

INTRODUCTION

Intact neural supply is necessary for tooth eruption. Sympathetic denervation accelerates or decelerates the eruption rate depending on the tooth condition (intact or injured). The aim of this study is to reexamine the role of the sympathetic innervation, through the observation of the effects of pre or post ganglionic chemical sympathectomy on the eruption of intact rat incisors.

MATERIALS AND METHODS

Different groups of rats were subjected to either ganglionic or peripheral chemical sympathectomy and the observed effects on incisor eruption were compared to those made on intact/sham groups or on rats subjected to inferior alveolar nerve (IAN) lesion.

RESULTS

The total amount of eruption in control/naïve rats, measured over a total period of 144 h, was 3 ± 0.15 mm and decreased to 2.57 ± 0.06 mm (n = 8; p < 0.01) or 2.8 ± 0.10 mm (n = 8; p < 0.05) following treatment with guanethidine and hexamethonium, respectively. This amount decreased to 1.8 ± 0.14 mm (p < 0.001 vs. control, n = 7; or p < 0.01 vs. sham, n = 5) in rats subjected to IAN lesion.

CONCLUSION

Sympathectomy delayed tooth eruption. Blocking the sympathetic effectors with guanethidine exerted more potent effects than ganglionic block with hexamethonium. Intact sympathetic supply is required for tooth growth under normal conditions.

Chronic Pain in Inflammatory Arthritis: Mechanisms, Metrology, and Emerging Targets-A Focus on the JAK-STAT Pathway

Chronic pain is nowadays considered not only the mainstay symptom of rheumatic diseases but also "a disease itself." Pain is a multidimensional phenomenon, and in inflammatory arthritis, it derives from multiple mechanisms, involving both synovitis (release of a great number of cytokines) and peripheral and central pain-processing mechanisms (sensitization). In the last years, the JAK-STAT pathway has been recognized as a pivotal component both in the inflammatory process and in pain amplification in the central nervous system. This paper provides a summary on pain in inflammatory arthritis, from pathogenesis to clinimetric instruments and treatment, with a focus on the JAK-STAT pathway.

Antinociceptive Activities of the Methanolic Extract of the Stem Bark of Boswellia dalzielii Hutch. (Burseraceae) in Rats Are NO/cGMP/ATP-Sensitive-K+ Channel Activation Dependent

Boswellia dalzielii (B. dalzielii) is traditionally used in the treatment of rheumatism, pain, and inflammation. The present investigation evaluates the property and possible mechanism of action of the methanolic extract of B. dalzielii (BDME) on inflammatory and neuropathic pain models. Effects of BDME (250 and 500 mg/kg), orally administered, were verified in mechanical hypernociception induced by LPS or PGE₂. Mechanical hyperalgesia, cold allodynia, and heat hyperalgesia were used in vincristine-induced neuropathic pain. NW-nitro-L-arginine methyl ester (inhibitor of nitric oxide synthase), glibenclamide (ATP-sensitive potassium channel blocker), methylene blue (cGMP blocker), or naloxone (opioid antagonist receptor) has been used to evaluate the therapeutic effects of BDME on PGE₂-induced hyperalgesia. Chemical profile of BDME was determined by using HPLC-XESI-PDA/MS. BDME showed significant antinociceptive effects in inflammatory pain caused by LPS and PGE₂. The extract also significantly inhibited neuropathic pain induced by vincristine. The antinociceptive property of BDME in PGE₂ model was significantly blocked by L-NAME, glibenclamide, methylene blue, or naloxone. The present work reveals the antinociceptive activities of BDME both in inflammatory and in neuropathic models of pain. This plant extract may be acting firstly by binding to opioid receptors and secondly by activating the NO/cGMP/ATP-sensitive-K⁺ channel pathway.

Inhibition of NLRP3 Inflammasome Prevents LPS-Induced Inflammatory Hyperalgesia in Mice: Contribution of NF-κB, Caspase-1/11, ASC, NOX, and NOS Isoforms

The nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3), an intracellular signaling molecule that senses many environmental- and pathogen/host-derived factors, has been implicated in the pathogenesis of several diseases associated with inflammation. It has been suggested that NLRP3 inflammasome inhibitors may have a therapeutic potential in the treatment of NLRP3-related inflammatory diseases. The aim of this study was to determine whether inhibition of NLRP3 inflammasome prevents inflammatory hyperalgesia induced by lipopolysaccharide (LPS) in mice as well as changes in expression/activity of nuclear factor κB (NF-κB), caspase-1/11, nicotinamide adenine dinucleotide phosphate oxidase (NOX), and endothelial/neuronal/inducible nitric oxide synthase (eNOS/nNOS/iNOS) that may regulate NLRP3/apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC)/pro-caspase-1 inflammasome formation and activity by using a selective NLRP3 inflammasome inhibitor, MCC950. Male mice received saline (10 ml/kg; i.p.), LPS (10 mg/kg; i.p.), and/or MCC950 (3 mg/kg; i.p.). Reaction time to thermal stimuli within 1 min was evaluated after 6 h. The mice were killed and the brains, hearts, and lungs were collected for measurement of NF-κB, caspase-1, caspase-11, NLRP3, ASC, NOX subunits (gp91^phox; NOX2), and p47^phox; NOXO2), nitrotyrosine, eNOS, nNOS, iNOS, and β-actin protein expression, NOS activity, and interleukin (IL)-1β levels. LPS-induced hyperalgesia was associated with a decrease in eNOS, nNOS, and iNOS protein expression and activity as well as an increase in expression of NF-κB p65, caspase-1 p20, caspase-11 p20, NLRP3, ASC, gp91^phox, p47^phox, and nitrotyrosine proteins in addition to elevated IL-1β levels. The LPS-induced changes were prevented by MCC950. The results suggest that inhibition of NLRP3/ASC/pro-caspase-1 inflammasome formation and activity prevents inflammatory hyperalgesia induced by LPS in mice as well as changes in NF-κB, caspase-11, NOX2, NOXO2, and eNOS/nNOS/iNOS expression/activity.

Effect of subacute agomelatine treatment on painful diabetic neuropathy: involvement of catecholaminergic mechanisms

In this study, we investigated the effects of subacute agomelatine (40 and 80 mg/kg) administration on chronic hyperglycemia, metabolic parameters, and pain perception in streptozotocin-induced diabetic rats. Fasting blood glucose measurements and oral glucose tolerance tests were performed to evaluate the effect of agomelatine on glycemia, while metabolic parameters were monitored using metabolic cages. Potential effect of agomelatine on diabetes-induced mechanical and thermal allodynia was evaluated using dynamic plantar aesthesiometer and warm plate (38 °C) tests, respectively. Additionally, influence of agomelatine on hyperalgesia occurring in connection with diabetic neuropathy was examined using the Randall-Selitto (mechanical nociceptive stimulus), Hargreaves (thermal nociceptive stimulus), and cold plate (4 °C, thermal nociceptive stimulus) tests. Obtained data indicated that, in diabetic rats, agomelatine significantly improved hyperalgesia and allodynia responses, without no effect on hyperglycemia or the associated polydipsia, polyuria, and hyperphagia. Therapeutic potential of agomelatine on neuropathic pain was suppressed with α-methyl-para-tyrosine methyl ester (an inhibitor of catecholamine synthesis), phentolamine (a nonselective α-adrenoceptor antagonist), and propranolol (a nonselective β-adrenoceptor antagonist) administrations. However, p-chlorophenylalanine methyl ester (an inhibitor of serotonin synthesis) pretreatment could not be achieved to reverse these antihyperalgesic and antiallodynic effects. These results suggest that the curative effect of agomelatine on neuropathic pain is mediated through rising synaptic catecholamine levels as well as through interactions with both α- and β-adrenoceptors. To our knowledge, this is the first study to show findings that indicate catecholaminergic system mediated antihyperalgesic and antiallodynic effects of agomelatine.

Atenolol Reduces Leishmania major-Induced Hyperalgesia and TNF-α Without Affecting IL-1β or Keratinocyte Derived Chemokines (KC)

Infection with a high dose of the intracellular parasitic protozoan Leishmania major induces a sustained hyperalgesia in susceptible BALB/c mice accompanied by up-regulation of the pro-inflammatory cytokines IL-1β and IL-6. Interleukin-13 (IL-13) has been shown to reduce this hyperalgesia (despite increased levels of IL-6) and the levels of IL-1β during and after the treatment period. These findings favor the cytokine cascade leading to the production of sympathetic amines (involving TNF-α and KC) over prostaglandins (involving IL-lβ and IL-6) as the final mediators of hyperalgesia. The aim of this study was to investigate the effect of daily treatment with the β-blockers atenolol on L. major-induced inflammation in mice with respect to hyperalgesia as well as the levels of TNF-α and KC (the analog of IL-8 in mice). Our data demonstrates that atenolol is able to reduce the L. major induced sustained peripheral hyperalgesia, which does not seem to involve a direct role for neither IL-lβ nor KC. Moreover, our results show that TNF-α may play a pivotal and direct role in sensitizing the peripheral nerve endings (nociceptors) since its level was reduced during the period of atenolol treatment, which correlates well with the reduction of the observed peripheral, but not central, hyperalgesia. These findings contribute to a better understanding of the cytokine cascade leading to hyperalgesia and may lead to the development of new and more efficient medications for many types of pain.

Chronic CRF1 receptor blockade reduces heroin intake escalation and dependence-induced hyperalgesia

Opioids represent effective drugs for the relief of pain, yet chronic opioid use often leads to a state of increased sensitivity to pain that is exacerbated during withdrawal. A sensitization of pain-related negative affect has been hypothesized to closely interact with addiction mechanisms. Neuro-adaptive changes occur as a consequence of excessive opioid exposure, including a recruitment of corticotropin-releasing factor (CRF) and norepinephrine (NE) brain stress systems. To better understand the mechanisms underlying the transition to dependence, we determined the effects of functional antagonism within these two systems on hyperalgesia-like behavior during heroin withdrawal utilizing models of both acute and chronic dependence. We found that passive or self-administered heroin produced a significant mechanical hypersensitivity. During acute opioid dependence, systemic administration of the CRF1 receptor antagonist MPZP (20 mg/kg) alleviated withdrawal-induced mechanical hypersensitivity. In contrast, several functional adrenergic system antagonists (clonidine, prazosin, propranolol) failed to alter mechanical hypersensitivity in this state. We then determined the effects of chronic MPZP or clonidine treatment on extended access heroin self-administration and found that MPZP, but not clonidine, attenuated escalation of heroin intake, whereas both drugs alleviated chronic dependence-associated hyperalgesia. These findings suggest that an early potentiation of CRF signaling occurs following opioid exposure that begins to drive both opioid-induced hyperalgesia and eventually intake escalation.

Impact of β-adrenoceptor blockade on systemic inflammation and coagulation disturbances in rats with acute traumatic coagulopathy

BACKGROUND

Sympathetic hyperactivity occurs early in acute traumatic coagulopathy (ATC) and is closely related to its development. β-adrenoceptor antagonists are known to alleviate adverse sympathetic effects and improve outcome in various diseases. We investigated whether β-blockers have protective effects against inflammation and endothelial and hemostatic disorders in ATC.

MATERIAL AND METHODS

ATC was induced in male Sprague-Dawley rats by trauma and hemorrhagic shock. Rats were randomly assigned to the sham, ATCC (ATC control), and ATCB (ATC with beta-adrenoceptor blockade) groups. Rats were injected intraperitoneally with propranolol or vehicle at baseline. Heart rate variability (HRV) and markers of inflammation, coagulation, and endothelial activation were measured, and Western blotting analysis of nuclear factor (NF)-κB was done after shock. Separate ATCC and ATCB groups were observed to compare overall mortality.

RESULTS

HRV showed enhanced sympathetic tone in the ATCC group, which was reversed by propranolol. Propranolol attenuated the induction of pro-inflammatory cytokines TNF-α and IL-6, as well as fibrinolysis markers plasmin antiplasmin complex and tissue-type plasminogen activator. The increased serum syndecan-1 and soluble thrombomodulin were inhibited by propranolol, and the NF-κB expression was also decreased by propranolol pretreatment. But propranolol did not alter overall mortality in rats with ATC after shock.

CONCLUSIONS

Beta-adrenoceptor blockade can alleviate sympathetic hyperactivity and exert anti-inflammatory, anti-fibrinolysis, and endothelial protective effects, confirming its pivotal role in the pathogenesis of ATC. Its mechanism in ATC should be explored further.

Association between albuminuria, kidney function, and inflammatory biomarker profile in CKD in CRIC

BACKGROUND AND OBJECTIVES

Increased risk of mortality in patients with CKD has been attributed to inflammation. However, the association between kidney function, albuminuria, and biomarkers of inflammation has not been examined in a large cohort of CKD patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study measured the plasma levels of IL-1β, IL-1 receptor antagonist (IL-1RA), IL-6, TNF-α, TGF-β, high-sensitivity C-reactive protein (hs-CRP), fibrinogen, and serum albumin in 3939 participants enrolled in the Chronic Renal Insufficiency Cohort study between June 2003 and September 2008. An inflammation score was established based on plasma levels of IL-1β, IL-6, TNF-α, hs-CRP, and fibrinogen. Estimated GFR (eGFR) and serum cystatin C were used as measures of kidney function. Albuminuria was quantitated by urine albumin to creatinine ratio (UACR).

RESULTS

Plasma levels of IL-1β, IL-1RA, IL-6, TNF-α, hs-CRP, and fibrinogen were higher among participants with lower levels of eGFR. Inflammation score was higher among those with lower eGFR and higher UACR. In regression analysis adjusted for multiple covariates, eGFR, cystatin C, and UACR were strongly associated with fibrinogen, serum albumin, IL-6, and TNF-α. Each unit increase in eGFR, cystatin C, and UACR was associated with a -1.2% (95% confidence interval, -1.4, -1), 64.9% (56.8, 73.3) and 0.6% (0.4, 0.8) change in IL-6, respectively (P<0.001).

CONCLUSIONS

Biomarkers of inflammation were inversely associated with measures of kidney function and positively with albuminuria.

Sex effects on neurodevelopmental outcomes of innate immune activation during prenatal and neonatal life

Humans are exposed to potentially harmful agents (bacteria, viruses, toxins) throughout our lifespan; the consequences of such exposure can alter central nervous system development. Exposure to immunogens during pregnancy increases the risk of developing neurological disorders such as schizophrenia and autism. Further, sex hormones, such as estrogen, have strong modulatory effects on immune function and have also been implicated in the development of neuropathologies (e.g., schizophrenia and depression). Similarly, animal studies have demonstrated that immunogen exposure in utero or during the neonatal period, at a time when the brain is undergoing maturation, can induce changes in learning and memory, as well as dopamine-mediated behaviors in a sex-specific manner. Literature that covers the effects of immunogens on innate immune activation and ultimately the development of the adult brain and behavior is riddled with contradictory findings, and the addition of sex as a factor only adds to the complexity. This review provides evidence that innate immune activation during critical periods of development may have effects on the adult brain in a sex-specific manner. Issues regarding sex bias in research as well as variability in animal models of immune function are discussed.

Interleukin-13 reduces hyperalgesia and the level of interleukin-1β in BALB/c mice infected with Leishmania major with an up-regulation of interleukin-6

The anti-inflammatory cytokines interleukin-10 (IL-10) and interleukin-13 (IL-13) were shown to reduce hyperalgesia in some models such as rats exposed to UV rays. In addition, IL-10 was also shown to reduce hyperalgesia in high dose of Leishmania major-induced inflammation in BALB/c mice accompanied by a significant decrease in the levels of interleukin-1β (IL-1β) in the paws of infected mice, while no effect on the levels of IL-6 was observed. In this study, we injected BALB/c mice with a high dose of L. major and treated them with IL-13 (15 ng/animal) for twelve days (excluding the weekends) and hyperalgesia was assessed using thermal pain tests. Furthermore, the levels of IL-1β and IL-6 were also assessed at different post-infection days. Our results show that IL-6 and more importantly IL-1β don't play a direct role in the L. major-induced hyperalgesia and that IL-13 induces this hyperalgesia through the down-regulation of IL-1β and another proinflammatory cytokine (most probably TNF-α). Furthermore, our data show that IL-13 leads to the upregulation of the level IL-6 which initially seems to have no direct role in the induced hyperalgesia. Therefore, we suggest that the L. major-induced hyperalgesia is mainly mediated by the cytokine cascade leading to the production of sympathetic amines.

Acute and persistent nociceptive paw sensitisation in mice: the involvement of distinct signalling pathways

AIMS

Many fundamental pharmacological studies in pain and inflammation have been performed on rats. However, the pharmacological findings were generally not extended to other species in order to increase their predictive therapeutic value. We studied acute and chronic inflammatory nociceptive sensitisation of mouse hind paws by prostaglandin E(2) (PGE(2)) or dopamine (DA), as previously described in rats. We also investigated the participation of the signalling pathways in acute and persistent sensitisation.

MAIN METHODS

Mechanical sensitisation (hypernociception) induced by intraplantar administrations of PGE(2) or DA was evaluated with an electronic pressure meter. The signalling pathways were pharmacologically investigated with the pre-administration of adenylyl cyclase (AC), cAMP-dependent protein kinase (PKA), protein kinase Cepsilon (PKCepsilon), and the extracellular signal-related kinase (ERK) inhibitors.

KEY FINDINGS

Single or 14days of successive intraplantar injections of PGE(2) or DA-induced acute and persistent hypernociception (lasting for more than 30days), respectively. The involvement of AC, PKA or PKCepsilon was observed in the acute hypernociception induced by PGE(2), while PKA or PKCepsilon were continuously activated during the period of persistent hypernociception. The acute hypernociception induced by DA involves activation of ERK, PKCepsilon, AC or PKA, while persistent hypernociception implicated ERK activation, but not PKA, PKCepsilon or AC.

SIGNIFICANCE

In mice, acute and persistent paw sensitisation involves the different activation of kinases, as previously described for rats. This study opens the possibility of comparing pharmacological approaches in both species to further understand acute and chronic inflammatory sensitisation, and possibly associated genetic manipulations.

Propolis effect on Th1/Th2 cytokines production by acutely stressed mice

AIM OF THE STUDY

Propolis has gained special attention due to its biological properties, however, little is known about its immunomodulatory effects in stress conditions. The purpose of this study was to investigate propolis effect on Th1/Th2 cytokines production by spleen cells of acutely stressed mice. Serum corticosterone concentration was determined as a stress indicator.

MATERIALS AND METHODS

Male BALB/c mice were submitted to restraint stress and treated with propolis (200mg/kg) for 3 days. Supernatants of splenocytes cultures were assessed for Th1/Th2 cytokines determination.

RESULTS

Regarding Th1 cytokines production, no alterations were seen in IL-2 production; however, IFN-gamma production was inhibited in stressed mice, even when treated with propolis. As to Th2 cytokines, IL-4 was inhibited in stressed mice, but normal levels were seen when these animals were treated with propolis. No significant differences were found in IL-10 production between the experimental groups. Stressed groups (treated or not with propolis) showed higher corticosterone concentrations in comparison to control group.

CONCLUSIONS

Data suggest that propolis treatment was not able to counteract the stress-induced immunosuppressive effect on IFN-gamma production; however, propolis showed an immunorestorative role, increasing IL-4 production in stressed mice, favoring humoral immune response during stress. Since the exact mechanisms of this natural product on immune system are still unclear, further studies are still required for a better comprehension of propolis use as a therapeutic alternative against the stress-induced negative effects that could lead to the development of various diseases.

Propolis effects on pro-inflammatory cytokine production and Toll-like receptor 2 and 4 expression in stressed mice

INTRODUCTION

Propolis is a beehive product and its immunomodulatory action has been well documented; however, little is known concerning its activity on the immune system of stressed mice. This work investigated a possible role of propolis against the immunosuppressive effects induced by stress in mice, assessing the pro-inflammatory cytokine (IL-1beta and IL-6) production and Toll-like receptor (TLR-2 and TLR-4) expression by spleen cells.

METHODS

BALB/c mice were divided into 3 groups: G1 was considered control; G2 was submitted to restraint stress for 3 days, and G3 was treated with propolis and immediately submitted to stress. After sacrifice, spleens were removed and TLR-2 and TLR-4 gene expression was analyzed, as well as the pro-inflammatory cytokine production. Serum corticosterone levels were determined by radioimmunoassay as a stress indicator.

RESULTS

Stressed mice, treated or not with propolis, produced higher corticosterone levels, whereas IL-1beta and IL-6 production was inhibited. TLR-2 and TLR-4 expression was inhibited in stressed mice, while propolis exerted an immunorestorative role in TLR-4 expression. The immunosuppressive effects on IL-1beta and IL-6 production and on TLR expression by stressed mice might have occurred due to a higher corticosterone production during stress.

CONCLUSION

Propolis treatment did not antagonize the inhibitory effects on pro-inflammatory cytokine production, however it restored at least partially TLR2 mRNA expression and counteracted the inhibition on TLR-4 expression in stressed animals, contributing to the recognition of microorganisms during stressful conditions.

[Effect of local anesthetics on the postoperative inflammatory response]

Current knowledge suggests that peripheral inflammation following surgery activates and sensitizes both peripheral and central nervous system. These phenomena involved in the maintenance of the inflammatory response lead to hypersensibility, hyperalgesia and allodynia. Hyperalgesia participates in the general experience of postoperative pain and ALo in the development of chronic pain. A correlation between the ability of treatments to reduce areas of hypersensitivity surrounding the wound after surgery and their ability to reduce the incidence of chronic pain has been shown. For a long time, local anaesthetics have been used for their capacity to block nociceptive input. They can ALo modulate the inflammatory response following a surgical trauma. By inhibiting the nervous conductivity at the site of the trauma, local anesthetics attenuate the sensitization of the nervous system and therefore the inflammatory phenomena. They ALo exert intrinsic anti-inflammatory properties by modulating the local and systemic liberation of inflammatory mediators. The mechanisms involved are not clearly elucidated. Local, systemic, and spinal inflammatory mechanisms may be influenced by local anesthetics through multiple different mechanisms. The therapeutic implications of effects of local anesthetics on local, systemic, and spinal inflammatory responses merit further study.

Role of interleukin-1beta during pain and inflammation

The cytokine cascade in pain and inflammatory processes is a tremendously complex system, involving glial, immune, and neuronal cell interactions. IL-1beta is a pro-inflammatory cytokine that has been implicated in pain, inflammation and autoimmune conditions. This review will focus on studies that shed light on the critical role of IL-1beta in various pain states, including the role of the intracellular complex, the inflammasome, which regulates IL-1beta production. Evidence will be presented demonstrating the importance of IL-1beta in both the induction of pain and in the maintenance of pain in chronic states, such as after nerve injury. Additionally, the involvement of IL-1beta as a key mediator in the interaction between glia and neurons in pain states will be discussed. Taken together, the evidence presented in the current review showing the importance of IL-1beta in animal and human pain states, suggests that blockade of IL-1beta be considered as a therapeutic opportunity.

On the mechanisms and putative pathways involving neuroimmune interactions

Bidirectional interdependence between the immune system and the CNS involves the intervention of common cofactors. Cytokines are endogenous to the brain, endocrine and immune systems. These shared ligands are used as a chemical language for communication. Such interaction suggests an immunoregulatory role for the brain, and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is associated with effects of stress on immunity. Cytokines are thus capable of modulating responses in the CNS, while neuropeptides can exert their effects over cellular groups in the immune system. One way is controlled by the HPA axis, a coordinator of neuroimmune interactions that is essential to unravel in order to elucidate vital communications in a manner that this crosstalk remains a cornerstone in perpetuating a stance of homeostasis.

Evaluation of the effects of the herbal product Catuama in inflammatory and neuropathic models of nociception in rats

Here we evaluated the antinociceptive effects of the herbal drug Catuama in rat inflammatory and neuropathic models of pain, in order to assess some of the mechanisms involved in its actions. Catuama given orally, in both acute and chronic schedules of treatment, consistently inhibited the mechanical allodynia induced by the intraplantar (i.pl.) injection of complete Freund's adjuvant (CFA). The same treatment with Catuama failed to significantly affect CFA-caused thermal hyperalgesia. In addition, Catuama did not significantly modify the mechanical allodynia or hyperalgesia observed following the partial ligation of the sciatic nerve or the diabetic polyneuropathy, respectively. In another series of experiments, Catuama caused a striking reduction of the mechanical allodynia induced by LPS. Oral treatment with Catuama was not, however, effective in altering the production of the pro-inflammatory mediators IL-1beta, TNFalpha, PGE(2) or LTB(4) following i.pl. administration of LPS in the rat paw. Of high interest, the antinociceptive effects of Catuama in the LPS model were reversed significantly by the non-selective dopamine antagonist haloperidol, but not by serotonin methysergide or adrenergic yohimbine receptor antagonists. Our results indicate that the herbal drug Catuama diminishes inflammatory, but not neuropathic, nociceptive responses in rats, by mechanisms involving an interference with dopaminergic pathways. Catuama might represent a potential therapeutic tool for the management of persistent inflammatory pain.

Ultra violet-induced localized inflammatory hyperalgesia in awake rats and the role of sensory and sympathetic innervation of the skin

Exposure to mid range ultrat violet radiations (UVBs) has been shown to produce systemic inflammation and hyperalgesia in mice [Saadé, N.E., Nasr, I.W., Massaad, C.A., Safieh-Garabedian, B., Jabbur, S.J., Kanaan, S.A., 2000. Modulation of ultraviolet-induced hyperalgesia and cytokine upregulation by interleukins 10 and 13. Br. J. Pharmacol. 131, 1317-1324]. Our aim was to characterize a new rat model of localized exposure to UVB and to determine the role of skin innervation in the observed hyperalgesia and cytokine upregulation. In several groups of rats one hindpaw was exposed to UVB (250-350 mJ/cm(2)) and this was followed by the application, to the plantar area of the paw, of either Von Frey hairs or a few acetone drops to measure tactile and cold allodynia, respectively. Thermal hyperalgesia was assessed by the paw withdrawal latency and duration. Cytokine levels were determined, by ELISA, in processed samples of skin tissue isolated from the exposed and non-exposed paws. UVB induced a biphasic thermal hyperalgesia and cold and tactile allodynia with an early phase that peaked at 3-6h and disappeared at 24h and a late phase with a peak at 48 h and recovery at 72-h post-exposure. Tumor necrosis factor, interleukins 1 beta, 6, 8, 10 and NGF levels were significantly increased following the same biphasic temporal pattern. Chemical ablation of capsaicin sensitive afferents and guanethidine injection produced significant alteration of the hyperalgesia and allodynia. The increase in cytokine levels by UVB was also altered by both treatments. The present study describes a new animal model for localized UVB-induced inflammatory hyperalgesia and provides evidence about the involvement of neurogenic mechanisms in the observed hyperalgesia and upregulation of proinflammatory mediators.

Pronociceptive response elicited by TRPA1 receptor activation in mice

Ankyrin-repeat transient receptor potential 1 (TRPA1) is a member of the transient receptor potential (TRP) channel family and it is found in sensory neurons. In the present study, we found that TRPA1 receptor activation with allyl isothiocyanate or cinnamaldehyde caused dose-dependent spontaneous nociception when injected into the mouse hind paw. Very similar results were obtained when stimulating transient receptor potential vanilloid 1 (TRPV1) receptors with capsaicin. Pretreatment with the TRP receptor antagonist Ruthenium Red (1 nmol/paw) inhibited capsaicin-(0.1 nmol/paw) and allyl isothiocyanate-(1 nmol/paw) induced nociceptive responses. However, the nonselective TRPV1 receptor antagonist capsazepine (1 nmol/paw) and the selective TRPV1 receptor antagonist SB 366791 (1 nmol/paw) only attenuated capsaicin-induced nociception. In contrast, the intrathecal treatment with TRPA1 antisense oligodeoxynucleotide (2.5 nmol/site) and the degeneration of the subset of primary afferent fibers sensitive to capsaicin significantly reduced allyl isothiocyanate-induced nociception. Consequently to TRPA1 antisense oligodeoxynucleotide treatment there was a marked decrease of the expression of TRPA1 receptor in both sciatic nervous and spinal cord segments. Moreover, capsaicin and allyl isothiocyanate-induced nociception were not significantly changed by chemical sympathectomy produced by guanethidine. The previous degranulation of mast cells by compound 48/80 and treatment with antagonist H(1) receptor antagonist pyrilamine (400 microg/paw) both significantly inhibited the capsaicin- and allyl isothiocyanate-induced nociception. The selective NK(1) receptor antagonist N(2)-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl) carbony-1-L-prolyl]-N-methyl-N-phenylmethyl-3-2-(2-naphtyl)-L-alaninamide (10 nmol/paw) reduced either capsaicin- or allyl isothiocyanate-induced nociception. Collectively, the present findings demonstrate that the TRPA1 agonist allyl isothiocyanate produces a consistent nociceptive response when injected into the mouse paw, an effect that seems to be mediated via activation of TRPA1 receptor and dependent on the capsaicin-sensitive fibers, release of histamine by mast cells and participation of tachykinins. Thus, the TRPA1 receptor has an apparently relevant role in nociceptive processes and the selective TRPA1 antagonist might possess a potential antinociceptive property.

Low-frequency electroacupuncture suppresses zymosan-induced peripheral inflammation via activation of sympathetic post-ganglionic neurons

Electroacupuncture (EA) is used to treat a variety of inflammatory diseases; however, the neurophysiological mechanisms underlying EA's anti-inflammatory effect remain unclear. Accumulating evidence suggests that the sympathetic nervous system regulates immunologic and inflammatory responses and thus we hypothesized that this system could be involved in EA's anti-inflammatory effect (EA-AI). The goal of the present study was to evaluate whether the sympathetic nervous system plays a critical role in EA-AI using a mouse air pouch inflammation model. We found that bilateral low-frequency (1 Hz) EA applied to the Zusanli acupoint significantly suppressed the number of zymosan-induced leukocytes migrating into the air pouch. Furthermore, double-labeling immunohistochemical experiments showed that EA stimulation increased Fos expression in choline acetyltransferase (ChAT)-positive sympathetic pre-ganglionic neurons in the intermediolateral region of thoracic spinal cord segments. Chemical sympathetic denervation by intraperitoneal injection of 6-hydroxydopamine (which spares sympathetic adrenal medullary innervation) significantly inhibited EA-AI. In contrast, adrenalectomy did not alter EA-AI. Finally, systemic propranolol administration significantly inhibited EA's anti-inflammatory effect, suggesting that beta-adrenoceptors are involved. Collectively, these results suggest that EA produces an anti-inflammatory effect in this mouse air pouch model by activating the sympathetic nervous system leading to the release of catecholamines from post-ganglionic nerve terminals, which act on beta-adrenoceptors on immune cells to inhibit their migration.

On the enigma of pain and hyperalgesia: A molecular perspective

Pain is a common symptom of injuries and inflammatory-related conditions. The perception of pain, commonly known as nociception, depends on integrated receptors and molecular pathways. Inflammatory mediators are involved in the genesis, persistence, and severity of pain. Noxious stimuli can trigger a cascade of inflammatory loops that feedback onto sensory modalities and domains of the CNS, in an attempt to alert the brain of deregulated homeostasis. Understanding the mechanisms of pain continue to make nociception and hyperalgesia a burgeoning field of research.

Catechol-O-methyltransferase inhibition increases pain sensitivity through activation of both beta2- and beta3-adrenergic receptors

Catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, has recently been implicated in the modulation of pain. Our group demonstrated that human genetic variants of COMT are predictive for the development of Temporomandibular Joint Disorder (TMJD) and are associated with heightened experimental pain sensitivity [Diatchenko, L, Slade, GD, Nackley, AG, Bhalang, K, Sigurdsson, A, Belfer, I, et al., Genetic basis for individual variations in pain perception and the development of a chronic pain condition, Hum Mol Genet 2005;14:135-43.]. Variants associated with heightened pain sensitivity produce lower COMT activity. Here we report the mechanisms underlying COMT-dependent pain sensitivity. To characterize the means whereby elevated catecholamine levels, resulting from reduced COMT activity, modulate heightened pain sensitivity, we administered a COMT inhibitor to rats and measured behavioral responsiveness to mechanical and thermal stimuli. We show that depressed COMT activity results in enhanced mechanical and thermal pain sensitivity. This phenomenon is completely blocked by the nonselective beta-adrenergic antagonist propranolol or by the combined administration of selective beta(2)- and beta(3)-adrenergic antagonists, while administration of beta(1)-adrenergic, alpha-adrenergic, or dopaminergic receptor antagonists fail to alter COMT-dependent pain sensitivity. These data provide the first direct evidence that low COMT activity leads to increased pain sensitivity via a beta(2/3)-adrenergic mechanism. These findings are of considerable clinical importance, suggesting that pain conditions resulting from low COMT activity and/or elevated catecholamine levels can be treated with pharmacological agents that block both beta(2)- and beta(3)-adrenergic receptors.

Hypernociceptive role of cytokines and chemokines: targets for analgesic drug development?

Pain is one of the classical signs of the inflammatory process in which sensitization of the nociceptors is the common denominator. This sensitization causes hyperalgesia or allodynia in humans, phenomena that involve pain perception (emotional component+nociceptive sensation). As this review focuses mainly on animal models, which don't allow discrimination of the emotional component, the terms nociception and hypernociception are used to describe overt behavior induced by mechanical stimulation and increase of nociceptor sensitivity, respectively. Pro- and anti-inflammatory cytokines and chemokines are endogenous small protein mediators released by local or migrating cells whose balance modulates the intensity of inflammatory response. The inflammatory stimuli or tissue injuries stimulate the release of characteristic cytokine cascades, which ultimately trigger the release of final mediators responsible for inflammatory pain. These final mediators, such as prostanoids or sympathetic amines, act directly on the nociceptors to cause hypernociception, which results from the lowering of threshold due to modulation of specific voltage-dependent sodium channels. Furthermore, a direct effect of cytokines on nociceptors is also described. On the other hand, there are also anti-inflammatory cytokines, such as interleukin (IL)-10, IL-4 and IL-13, and IL-1 receptor antagonists (IL-1ra), which inhibit the production of hypernociceptive cytokines and/or the final hypernociceptive mediators, preventing the installation of or the increase in the hypernociception. This review highlights the importance of the direct and indirect actions of cytokines and chemokines in inflammatory and neuropathic hypernociception, emphasizing the evidence suggesting these molecules are potential targets to develop novel drugs and therapies for the treatment of pain.

Prolactin modulates the functions of murine spleen CD11c-positive dendritic cells

Prolactin (PRL), an anterior pituitary polypeptide hormone, has been shown to have a role in the immunomodulation. Some reports have shown the importance of PRL in activating lymphocytes and macrophages. To further investigate the effect of PRL on the immune system in vitro, murine spleen CD11c-positive dendritic cells (SDCs) were treated with various concentrations of PRL for 24 h, then their viability, phenotype, nuclear factor kappa B p65 (NF-kappaBp65), endocytosis, stimulatory capacity, and cytokine expression were analyzed. The results showed that PRL increased the viability and stimulatory capacity of SDCs, up-regulated the expressions of MHC-11 and CD40 while decreased the level of CD54 on SDCs. Furthermore, PRL decreased the level of NF-kappaBp65 and the endocytosis of SDCs. In addition, PRL increased the expressions of IL-6, IL-10, IL-12 and TNF-alpha in SDCs. These data suggested that PRL might regulate the physiological and pathological immune responses by changing the viability, phenotype, NF-kappaBp65, endocytosis, stimulatory capacity, and cytokine expression of SDCs.

Mechanisms involved in the nociception produced by peripheral protein kinase c activation in mice

Protein kinase C (PKC) is able to phosphorylate several cellular components that serve as key regulatory components in signal transduction pathways of nociceptor excitation and sensitisation. Therefore, the present study attempted to assess some of the mechanisms involved in the overt nociception elicited by peripheral administration of the PKC activator, phorbol 12-myristate 13-acetate (PMA), in mice. The intraplantar (i.pl.) injection of PMA (16-1600 pmol/paw), but not its inactive analogue alpha-PMA, produced a long-lasting overt nociception (up to 45 min), as well as the activation of PKCalpha and PKCepsilon isoforms in treated paws. Indeed, the local administration of the PKC inhibitor GF109203X completely blocked PMA-induced nociception. The blockade of NK1, CGRP, NMDA, beta1-adrenergic, B2 or TRPV1 receptors with selective antagonists partially decreased PMA-induced nociception. Similarly, COX-1, COX-2, MEK or p38 MAP kinase inhibitors reduced the nociceptive effect produced by PMA. Notably, the nociceptive effect promoted by PMA was diminished in animals treated with an antagonist of IL-1beta receptor or with antibodies against TNFalpha, NGF or BDNF, but not against GDNF. Finally, mast cells as well as capsaicin-sensitive and sympathetic fibres, but not neutrophil influx, mediated the nociceptive effect produced by PMA. Collectively, the results of the present study have shown that PMA injection into the mouse paw results in PKC activation as well as a relatively delayed, but long-lasting, overt nociceptive behaviour in mice. Moreover, these results demonstrate that PKC activation exerts a critical role in modulating the excitability of sensory neurons.

A cascade of cytokines mediates mechanical inflammatory hypernociception in mice

The hypernociceptive effects of cytokines [TNF-alpha, keratinocyte-derived chemokine (KC), and IL-1beta] and their participation in carrageenan (Cg)-induced inflammatory hypernociception in mice were investigated. Nociceptor sensitization (hypernociception) was quantified with an electronic version of the von Frey filament test in WT and TNF receptor type 1 knockout mice (TNF-R1-/-). TNF-alpha-induced hypernociception was abolished in TNF-R1-/- mice, partially inhibited by pretreatment with IL-1 receptor antagonist (IL-1ra) or indomethacin and unaffected by Ab against KC (AbKC) or guanethidine. IL-1ra and indomethacin pretreatment strongly inhibited the hypernociception induced by IL-1beta, which was not altered by AbKC or guanethidine or by knocking out TNF-R1. KC-induced hypernociception was abolished by AbKC, inhibited by pretreatment with indomethacin plus guanethidine, and partially inhibited by IL-1ra, indomethacin, or guanethidine. In contrast, KC-induced hypernociception was not altered by knocking out TNF-R1. Cg-induced hypernociception was abolished by administration of indomethacin plus guanethidine, diminished in TNF-R1-/- mice, and partially inhibited in WT mice pretreated with AbKC, IL-1ra, indomethacin, or guanethidine. TNF-alpha, KC, and IL-1beta concentrations were elevated in the skin of Cg-injected paws. The TNF-alpha and KC concentrations rose concomitantly and peaked before that of IL-1beta. In mice, the cytokine cascade begins with the release of TNF-alpha (acting on TNF-R1 receptor) and KC, which stimulate the release of IL-1beta. As in rats, the final mediators of this cascade were prostaglandins released by IL-1beta and sympathetic amines released by KC. These results extend to mice the concept that the release of primary mediators responsible for hypernociception is preceded by a cascade of cytokines.

Antihyperalgesic effect of pentoxifylline on experimental inflammatory pain

The antihyperalgesic effect of pentoxifylline was investigated in three experimental pain models. Pentoxifylline (0.5-1.6 mg kg(-1)) given 30 min before the stimulus significantly inhibited the writhing response induced by the intraperitoneal (i.p.) administration of either acetic acid (-90%) or zymosan (-83%), but not that of iloprost, in mice, as well as the zymosan-induced articular hyperalgesia in the zymosan arthritis in rats (-50%). Pentoxifylline also inhibited the mechanical hypernociception in rats induced by the intraplantar injection of either carrageenin (-81%), bradykinin (-56%) or tumor necrosis factor alpha (TNF-alpha; -46%), but not that induced by interleukin-1beta (IL-1beta) or prostaglandin E(2) (PGE(2)). Pentoxifylline did not inhibit the nociceptive response in the hot plate test in mice. Further, the antinociceptive effect of pentoxifylline in the writhing test in mice and the zymosan-induced articular hyperalgesia were not reversed by the coadministration of the opioid receptor antagonist naloxone. Thus, pentoxifylline antinociceptive effect is probably not mediated at a central level. Pentoxifylline significantly reduced TNF-alpha (-43%) and IL-1beta (-42%) concentrations in the joint exudates of rats stimulated by intra-articular injection of zymosan and the production of both cytokines (-66 and -86%, respectively) by mouse peritoneal macrophages stimulated in vivo with zymosan as well as the expression of TNF-alpha at the tissue level in carrageenin-injected rat paws. In conclusion, the antinociceptive activity of pentoxifylline is associated with the inhibition of the release of both TNF-alpha and IL-1beta.

Involvement of bradykinin, cytokines, sympathetic amines and prostaglandins in formalin-induced orofacial nociception in rats

1. This study characterises some of the mechanisms and mediators involved in the orofacial nociception triggered by injection of formalin into the upper lip of the rat, by assessing the influence of various treatments on behavioural nociceptive responses (duration of facial rubbing) elicited either by a low subthreshold (i.e. non-nociceptive; 0.63%) or a higher concentration of the algogen (2.5%). 2. The kininase II inhibitor captopril (5 mg kg(-1), s.c.) and prostaglandin(PG) E(2) (100 ng lip(-1)) potentiated both phases of the response to 0.63% formalin, whereas tumour necrosis factor (TNF alpha; 5 pg lip(-1)), interleukin(IL)-1 beta (0.5 pg lip(-1)), IL-6 (2 ng lip(-1)) and IL-8 (200 pg lip(-1)), or the indirectly acting sympathomimetic drug tyramine (200 microg lip(-1)), each augmented only the second phase of nociception. 3. Conversely, both phases of nociception induced by 2.5% formalin were inhibited by the bradykinin (BK) B(2) receptor antagonist HOE140 (5 microg lip(-1)) or the selective beta(1)-adrenoceptor antagonist atenolol (100 microg lip(-1)). However, the BK B(1) receptor antagonist des-Arg(9)-Leu(8)-BK (1 and 2 microg lip(-1)), antibody and/or antiserum against each of the cytokines, the adrenergic neurone blocker guanethidine (30 mg kg(-1) day(-1), s.c., for 3 days) and the cyclooxygenase(COX)-2 inhibitor celecoxib (50 and 200 microg lip(-1), s.c.; or 1 and 3 mg kg(-1), i.p.) reduced only the second phase of the response. The nonselective COX inhibitor indomethacin and the 5-lipoxygenase activating protein inhibitor MK886 did not change formalin-induced nociception. 4. Our results indicate that BK, TNF-alpha, IL-1 beta, IL-6, IL-8, sympathetic amines and PGs (but not leukotrienes) contribute significantly to formalin-induced orofacial nociception in the rat and the response seems to be more susceptible to inhibition by B(2) receptor antagonist and selective COX-2 inhibitor than by B(1) receptor antagonist or nonselective COX inhibitor.

Functional consequence of exposure to dieldrin on mammary development and function

The effect of dieldrin (Dln) on the development of the mammary gland and on functional parameters of CID-9 mammary cells in culture was investigated. One-month-old Sprague-Dawley female rats were bred and received intraperitoneal injection with 2.5 or 15 microM Dln during the last trimester of their gestation. Mammary glands of 15-microM Dln-treated rats showed immature alveolar structures by day 18 of gestation and abundant adipose tissue. Dln-treated rats had a lower number of pups, and the weight of pups between days 14 and 31 of age compared with non-treated rats was significantly lower. Long-term exposure of CID-9 mammary cells, cultured under non-differentiation conditions, on plastic, or under differentiation permissive conditions, dripped with EHS-matrix, to 5 or 25 microM Dln was detrimental to cell growth. The short-term effect of Dln exposure (up to 9 h) on CID-9 cells, under the same culture conditions, did not affect their beta-casein mRNA levels, but induced apoptosis, down regulated gap junction intracellular communication and induced IL-6 and TNF-alpha expression.

The critical role of leukotriene B4 in antigen-induced mechanical hyperalgesia in immunised rats

1. We investigated the mediators responsible for mechanical hypersensitivity induced by antigen challenge in rats immunised with ovalbumin (OVA). 2. Challenge with OVA (12.5-100 micro g, intraplantar) caused a dose- and time-dependent mechanical hypersensitivity, which peaked 3 h after, decreased thereafter and reached control levels 24 h later. 3. Levels of TNFalpha, IL-1beta and cytokine-induced neutrophil chemoattractant 1 (CINC-1) were increased in paw skin after antigen challenge. 4. OVA-evoked hypersensitivity was partially inhibited (about 51%) by pretreatment with anti-TNFalpha, IL-1beta and IL-8 sera or with IL-1 receptor antagonist (IL-1ra), but not anti-NGF serum. Pretreatment with thalidomide (45 mg kg(-1)) or pentoxifylline (100 mg kg(-1)) also partially inhibited the hypersensitivity at 1-3 h after challenge. 5. Pretreatment with indomethacin (5 mg kg(-1)) or atenolol (1 mg kg(-1)) reduced the OVA-induced hypersensitivity at 1 and 3 h, but not at 5 h after challenge, while the combination of B(1) and B(2) bradykinin receptor antagonists was ineffective over the same times. 6. Pretreatment with MK886 (5-lipoxygenase-activating protein inhibitor, 3 mg kg(-1)), CP 105696 (LTB(4) receptor antagonist; 3 mg kg(-1)) or dexamethasone (0.5 mg kg(-1)) inhibited the hypersensitivity from 1 to 5 h. Furthermore, LTB(4) levels were increased in the paw skin of challenged rats. 7. In conclusion, our results suggest that the TNFalpha-, IL-1beta- and CINC-1-driven release of prostaglandins, sympathetic amines and LTB(4) mediates the first 3 h of mechanical hypersensitivity induced by antigen challenge in rats. At 5 h after OVA administration, although TNFalpha has some role, LTB(4) is the critical nociceptive mediator.

Cytokines and neuro-immune-endocrine interactions: a role for the hypothalamic-pituitary-adrenal revolving axis

Cytokines, peptide hormones and neurotransmitters, as well as their receptors/ligands, are endogenous to the brain, endocrine and immune systems. These shared ligands and receptors are used as a common chemical language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is most commonly associated with the pronounced effects of stress on immunity. The hypothalamic-pituitary-adrenal (HPA) axis is the key player in stress responses; it is well established that both external and internal stressors activate the HPA axis. Cytokines are chemical messengers that stimulate the HPA axis when the body is under stress or experiencing an infection. This review discusses current knowledge of cytokine signaling pathways in neuro-immune-endocrine interactions as viewed through the triplet HPA axis. In addition, we elaborate on HPA/cytokine interactions in oxidative stress within the context of nuclear factor-kappaB transcriptional regulation and the role of oxidative markers and related gaseous transmitters.

Redox- and oxidant-mediated regulation of interleukin-10: an anti-inflammatory, antioxidant cytokine?

Reduction-oxidation (redox) state constitutes such a potential signaling mechanism for the regulation of an inflammatory signal associated with oxidative stress. Interleukin (IL)-10 has recently emerged as an anti-inflammatory cytokine with antioxidant properties. Interestingly, redox- and oxidant-mediated pathways positively and/or negatively regulate the expression, distribution, and functional properties of IL-10, thus, allowing the evolution of what is known as an anti-inflammatory redox-oxidant revolving axis. This axis is directly involved in regulating phosphorylation mechanisms, which eventually control gene expression and the biosynthesis of oxidative stress-related cofactors, such as reactive species and inflammatory cytokines. The association between IL-10, an anti-inflammatory antioxidant, with redox- and oxidant-related pathways governing the regulation of inflammatory and closely dependent processes is thereafter discussed.