Dual effect of nitric oxide in articular inflammatory pain in zymosan-induced arthritis in rats

The role of nitric oxide and neuroendocrine system in pain generation

Previous studies have indicated a complex interplay between the nitric oxide (NO) pain signaling pathways and hormonal signaling pathways in the body. This article delineates the role of nitric oxide signaling in neuropathic and inflammatory pain generation and subsequently discusses how the neuroendocrine system is involved in pain generation. Hormonal systems including the hypothalamic-pituitary axis (HPA) generation of cortisol, the renin-angiotensin-aldosterone system, calcitonin, melatonin, and sex hormones could potentially contribute to the generation of nitric oxide involved in the sensation of pain. Further research is necessary to clarify this relationship and may reveal therapeutic targets involving NO signaling that alleviate neuropathic and inflammatory pain.

A clindamycin acetylated derivative with reduced antibacterial activity inhibits articular hyperalgesia and edema by attenuating neutrophil recruitment, NF-κB activation and tumor necrosis factor-α production

We recently demonstrated that clindamycin exhibits activities in acute and chronic models of pain and inflammation. In the present study, we investigated the effects of clindamycin and a clindamycin acetylated derivative (CAD) in models of acute joint inflammation and in a microbiological assay. Joint inflammation was induced in mice by intraarticular (i.a.) injection of zymosan or lipopolysaccharide (LPS). Clindamycin or CAD were administered via the intraperitoneal route 1 h before zymosan or LPS. Paw withdrawal threshold, joint diameter, histological changes, neutrophil recruitment, tumor necrosis factor-α (TNF-α) production and phosphorylation of the IκBα and NF-κB/p65 were evaluated. In vitro assays were used to measure the antibacterial activity of clindamycin and CAD and also their effects on zymosan-induced TNF-α production by RAW264.7 macrophages. Clindamycin exhibited activity against Staphylococcus aureus and Salmonella Typhimurium ATCC® strains at much lower concentrations than CAD. Intraarticular injection of zymosan or LPS induced articular hyperalgesia, edema and neutrophil infiltration in the joints. Zymosan also induced histological changes, NF-κB activation and TNF-α production. Responses induced by zymosan and LPS were inhibited by clindamycin (200 and 400 mg/kg) or CAD (436 mg/kg). Both clindamycin and CAD inhibited in vitro TNF-α production by macrophages. In summary, we provided additional insights of the clindamycin immunomodulatory effects, whose mechanism was associated with NF-κB inhibition and reduced TNF-α production. Such effects were extended to a clindamycin derivative with reduced antibacterial activity, indicating that clindamycin derivatives should be investigated as candidates to drugs that could be useful in the management of inflammatory and painful conditions.

Sulfatide-selectin signaling in the spinal cord induces mechanical allodynia

Sulfatide is a sulfated glycosphingolipid that is present abundantly in myelin sheaths of the brain and spinal cord. It is synthesized by a cerebroside sulfotransferase encoded by Gal3st1, which catalyzes the transfer of sulfate from 3'-phosphoadenylylsulfate to galactosylceramide. We previously reported that Gal3st1 gene expression in the spinal cord is up-regulated 1 day after intraplantar injection of complete Freund's adjuvant (CFA), indicating that sulfatide is involved in inflammatory pain. In the present study, we found that intrathecal injection of sulfatide led to mechanical allodynia. Sulfatide caused levels of glial fibrillary acidic protein (GFAP) and nitric oxide in the spinal cord to increase. Mechanical allodynia induced by intrathecal injection of sulfatide was blocked by nitric oxide synthase inhibitors and by suppression of astrocyte activation by L-α-aminoadipate. These results suggest that sulfatide-induced mechanical allodynia involved glial activation and nitric oxide production. Blocking selectin, a sulfatide-binding protein, with bimosiamose attenuated sulfatide-induced allodynia and ameliorated CFA-induced mechanical allodynia during inflammatory pain. Finally, elevated levels of sulfatide concentration in the spinal cord were observed during CFA-induced inflammatory pain. The elevated sulfatide levels enhanced selectin activation in the spinal cord, resulting in mechanical allodynia. Our data suggest that sulfatide-selectin interaction plays a key role in inflammatory pain.

The Lectin Isolated from the Alga Hypnea cervicornis Promotes Antinociception in Rats Subjected to Zymosan-Induced Arthritis: Involvement of cGMP Signalization and Cytokine Expression

This study investigated the effects of the alga lectin Hypnea cervicornis agglutinin (HCA) on rat zymosan-induced arthritis (ZyA). Zymosan (50-500 μg/25 μL) or sterile saline (Sham) was injected into the tibio-tarsal joint of female Wistar rats (180-200 g). Arthritic animals received morphine (4 mg/kg, intraperitoneal), indomethacin (5 mg/kg, intraperitoneal), or 2% lidocaine (100 μL, subcutaneous). HCA (0.3-3 mg/kg) was administered by intravenous route 30 min before or 2 h after zymosan. 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (ODQ, 4 μg, intra-articular) was given 30 min prior HCA. Hypernociception was measured every hour until 6 h, time in which animals were sacrificed for evaluation of leukocytes of the intra articular fluid and gene expression of TNF-α, IL-1, IL-10, and iNOS in the joint tissues using PCR techniques. Hypernociception was responsive to morphine and indomethacin, and its threshold was not altered by lidocaine. The post-treatment of HCA reduced both hypernociception and leukocyte influx. This antinociceptive effect was abolished either by ODQ and glibenclamide. HCA also reduced gene expression of iNOS and TNF-α. In conclusion, the antinociceptive effect of HCA in ZyA involves cyclic GMP signalization and selective modulation of cytokine expression.

In Vitro Anti-Inflammatory and In Vivo Antiarthritic Activities of Aqueous and Ethanolic Extracts of Dissotis thollonii Cogn. (Melastomataceae) in Rats

Dissotis thollonii Cogn. (Melastomataceae) is a tropical plant widely used in traditional Cameroonian medicine to relieve and treat many pathologies. It is widespread in the western region where it is used to treat typhoid fever, gastrointestinal disorders, and inflammatory diseases. The purpose of this study is to scientifically demonstrate the anti-inflammatory and antiarthritic properties of the aqueous and ethanolic extracts of the leaves of Dissotis thollonii. The anti-inflammatory properties were evaluated in vitro by inhibition tests for cyclooxygenase, 5-lipoxygenase, protein denaturation, extracellular ROS production, and cell proliferation; while antiarthritic properties were evaluated in vivo in rats using the zymosan A-induced monoarthritis test and the CFA-induced polyarthritis model. This study shows that aqueous and ethanolic extracts at a concentration of 1000 μg/ml inhibit the activity of cyclooxygenase (47.07% and 63.36%) and 5-lipoxygenase (66.79% and 77.7%) and protein denaturation (42.51% and 44.44%). Similarly, both extracts inhibited extracellular ROS production (IC₅₀ = 5.74 μg/ml and 2.96 μg/ml for polymorphonuclear leukocytes, 7.47 μg/ml and 3.28 μg ml for peritoneal macrophages of mouse) and cell proliferation (IC₅₀ = 16.89 μg/ml and 3.29 μg/ml). At a dose of 500 mg/kg, aqueous and ethanolic extracts significantly reduce edema induced by zymosan A (69.30% and 81.80%) and CFA (71.85% and 79.03%). At the same dose, both extracts decreased sensitivity to mechanical hyperalgesia with 69.00% and 70.35% inhibition, respectively. Systemic and histological analyzes show that both extracts maintain the studied parameters very close to normal and greatly restored the normal architecture of the joint in animals. Dissotis thollonii would therefore be a very promising source for the treatment of inflammatory diseases.

Targeting nitric oxide as a key modulator of sepsis, arthritis and pain

Nitric oxide (NO) is produced by enzymatic activity of neuronal (nNOS), endothelial (eNOS), and inducible nitric oxide synthase (iNOS) and modulates a broad spectrum of physiological and pathophysiological conditions. The iNOS isoform is positively regulated at transcriptional level and produces high levels of NO in response to inflammatory mediators and/or to pattern recognition receptor signaling, such as Toll-like receptors. In this review, we compiled the main contributions of our group for understanding of the role of NO in sepsis and arthritis outcome and the peripheral contributions of NO to inflammatory pain development. Although neutrophil iNOS-derived NO is necessary for bacterial killing, systemic production of high levels of NO impairs neutrophil migration to infections through inhibiting neutrophil adhesion on microcirculation and their locomotion. Moreover, neutrophil-derived NO contributes to multiple organ dysfunction in sepsis. In arthritis, NO is chief for bacterial clearance in staphylococcal-induced arthritis; however, it contributes to articular damage and bone mass degradation. NO produced in inflammatory sites also downmodulates pain. The mechanism involved in analgesic effect and inhibition of neutrophil migration is dependent on the activation of the classical sGC/cGMP/PKG pathway. Despite the increasing number of studies performed after the identification of NO as an endothelium-derived relaxing factor, the underlying mechanisms of NO in inflammatory diseases remain unclear.

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

NEW FINDINGS

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

ABSTRACT

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

Anti-inflammatory Effect of Methyl Gallate on Experimental Arthritis: Inhibition of Neutrophil Recruitment, Production of Inflammatory Mediators, and Activation of Macrophages

Methyl gallate (MG) is a prevalent phenolic acid in the plant kingdom, and its presence in herbal medicines might be related to its remarkable biological effects, such as its antioxidant, antitumor, and antimicrobial activities. Although some indirect evidence suggests anti-inflammatory activity for MG, there are no studies demonstrating this effect in animal models. Herein, we demonstrated that MG (0.7-70 mg/kg) inhibited zymosan-induced experimental arthritis in a dose-dependent manner. The oral administration of MG (7 mg/kg) attenuates arthritis induced by zymosan, affecting edema formation, leukocyte migration, and the production of inflammatory mediators (IL-1β, IL-6, TNF-α, CXCL-1, LTB4, and PGE2). Pretreatment with MG inhibited in vitro neutrophil chemotaxis elicited by CXCL-1, as well as the adhesion of these cells to TNF-α-primed endothelial cells. MG also impaired zymosan-stimulated macrophages by inhibiting IL-6 and NO production, COX-2 and iNOS expression, and intracellular calcium mobilization. Thus, MG is likely to present an anti-inflammatory effect by targeting multiple cellular events such as the production of various inflammatory mediators, as well as leukocyte activation and migration.

Methylglyoxal mediates streptozotocin-induced diabetic neuropathic pain via activation of the peripheral TRPA1 and Nav1.8 channels

OBJECTIVE

Methylglyoxal is known to be associated with the development of nephropathy, retinopathy, and other complications in diabetes. The present study tested the hypothesis that endogenously increased levels of methylglyoxal in diabetes are causally associated with the induction of neuropathic pain.

MATERIALS AND METHODS

Streptozotocin- and methylglyoxal-induced pain models were established in rats, and the anti-nociceptive effects of the methylglyoxal scavenging agents, selective transient receptor potential channel ankyrin 1 (TRPA1) antagonist, and Nav1.8 antagonist were tested.

RESULTS

Systemic injection of streptozotocin in rats induced a prolonged increase in plasma methylglyoxal by approximately 60%, which was correlated with the progressive development of mechanical allodynia and thermal hyperalgesia. Local subcutaneous injection of methylglyoxal into the hindpaw produced dose-dependent and biphasic flinching nociceptive responses, which resembled formaldehyde (formalin)-induced nociception. The local methylglyoxal nociception was significantly blocked by co-injection into the hindpaw of the selective transient receptor potential channel ankyrin 1 (TRPA1) antagonist, A967079, and the Nav1.8 antagonist, A803467. Co-incubation with the methylglyoxal scavengers, aminoguanidine, d-arginine, and metformin, reduced the level of free methylglyoxal by more than 90%, and injection of their incubation solutions into the hindpaw produced negligible (3-17%) nociception. Like the clinically effective anti-diabetic neuropathic pain drug gabapentin, systemic injection of aminoguanidine, d-arginine, and metformin at doses that effectively inhibit paw-injected methylglyoxal-induced nociception significantly blocked streptozotocin-induced mechanical allodynia.

CONCLUSION

Endogenously increased methylglyoxal may mediate diabetic neuropathic pain via activation of both TRPA1 and Nav1.8 expressed on primary afferent sensory neurons, and injection of methylglyoxal into the hindpaw may serve as a simple and robust model for testing the anti-diabetic pain drugs.

Synthesis and biological evaluation of new 1,3-thiazolidine-4-one derivatives of nitro-l-arginine methyl ester

BACKGROUND

l-Arginine is a semi-essential aminoacid with important role in regulation of physiological processes in humans. It serves as precursor for the synthesis of proteins and is also substrate for different enzymes such as nitric oxide synthase. This amino-acid act as free radical scavenger, inhibits the activity of pro-oxidant enzymes and thus acts as an antioxidant and has also bactericidal effect against a broad spectrum of bacteria.

RESULTS

New thiazolidine-4-one derivatives of nitro-l-arginine methyl ester (NO2-Arg-OMe) have been synthesized and biologically evaluated in terms of antioxidant and antibacterial/antifungal activity. The structures of the synthesized compounds were confirmed by (1)H, (13)C NMR, Mass and IR spectral data. The antioxidant potential was investigated using in vitro methods based on ferric/phosphomolybdenum reducing antioxidant power and DPPH/ABTS radical scavenging assay. The antibacterial effect was investigated against Gram positive (Staphylococcus aureus ATCC 25923, Sarcina lutea ATCC 9341) and Gram negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) bacterial strains. The antifungal activity was also investigated against Candida spp. (Candida albicans ATCC 10231, Candida glabrata ATCC MYA 2950, Candida parapsilosis ATCC 22019).

CONCLUSIONS

Synthesized compounds showed a good antioxidant activity in comparison with the NO2-Arg-OMe. The antimicrobial results support the selectivity of tested compounds especially on P. aeruginosa as bacterial strain and C. parapsilosis as fungal strain. The most proper compounds were 6g (R = 3-OCH3) and 6h (R = 2-OCH3) which showed a high free radical (DPPH, ABTS) scavenging ability and 6j (R = 2-NO2) that was the most active on both bacterial and fungal strains and also it showed the highest ABTS radical scavenging ability.Graphical abstract1: ethyl 3-aminopropionate hydrochloride, 2a-j: aromatic aldehydes, 3: thioglycolic acid, 4a-j: thiazolidine-propionic acid derivatives , 5: Nω-nitro-L-arginine methyl ester hydrochloride, 6a-j: thiazolidine-propionyl-nitro-L-arginine methyl ester derivatives.

Antinociceptive effect of 1400 W, an inhibitor of inducible nitric oxide synthase, following hind paw incision in rats

Acute tissue damage is accompanied by synthesis of nitric oxide (NO) in the inflamed tissue as well as in the spinal cord. NO release at the spinal level is likely involved in the neuroplastic changes contributing to pain. Also, previous studies indicate that this could be due to the inducible isoform of the nitric oxide synthase (iNOS) enzyme. Though, the role of NO has been investigated in several animal models of nociception, the precise contribution of NO to nociception arising from hind paw incision is unknown, which is a rodent model of postoperative pain. In the present work, we have estimated the formation of NO in Sprague-Dawley rats, both at the site of incision and the corresponding spinal cord levels by Griess assay. Subsequently, naive rats were implanted with chronic indwelling intrathecal (i.t.) catheters. Fixed quantity (30 μg) of 1400 W, an iNOS inhibitor, was either administered locally into the wound at the time of incision or into the i.t. space, 15 min before hind paw incision. In a different set, i.t. 1400 W was administered, 20 h after incision. Control group received i.t. saline. Nociception was evaluated by guarding score, mechanical allodynia and thermal hyperalgesia. NO level was significantly increased between 4 h - day 1 locally and at 4 h at the spinal level after incision. Local inhibition of iNOS produced transient decrease of guarding (4-12 h) whereas pronounced decrease of guarding and allodynia was evident after spinal inhibition of iNOS. Also, spinal NO level decreased after i.t. drug administration. Post-incision drug treatment resulted in greater antinociceptive effect at day 1 though not on day 2. These results indicate involvement of NO in postincisional nociception in rats.

Activities of 2-phthalimidethanol and 2-phthalimidethyl nitrate, phthalimide analogs devoid of the glutarimide moiety, in experimental models of inflammatory pain and edema

The reintroduction of thalidomide in the pharmacotherapy greatly stimulated the interest in the synthesis and pharmacological evaluation of phthalimide analogs with new and improved activities and also greater safety. In the present study, we evaluated the activities of two phthalimide analogs devoid of the glutarimide ring, namely 2-phthalimidethanol (PTD-OH) and 2-phthalimidethyl nitrate (PTD-NO), in experimental models of inflammatory pain and edema in male C57BL/6J mice. Intraplantar (i.pl.) injection of carrageenan (300 μg) induced mechanical allodynia and this response was inhibited by previous per os (p.o.) administration of PTD-OH and PTD-NO (750 mg/kg) and also by thalidomide (500 or 750 mg/kg). The edema induced by carrageenan was also inhibited by previous p.o. administration of PTD-OH (500 and 750 mg/kg) and PTD-NO (125, 250, 500 or 750 mg/kg), but not by thalidomide. Carrageenan increased tumor necrosis factor (TNF)-α and CXCL1 concentrations and also the number of neutrophils in the paw tissue. Previous p.o. administration of PTD-NO (500 mg/kg) reduced all the parameters, while PTD-OH (500 mg/kg) reduced only the accumulation of neutrophils. Thalidomide, on the other hand, was devoid of effect on these biochemical parameters. Plasma concentrations of nitrite were increased after p.o. administration of the phthalimide analog coupled to a NO donor, PTD-NO (500 mg/kg), but not after administration of PTD-OH or thalidomide. In conclusion, our results show that small molecules, structurally much simpler than thalidomide or many of its analogs under investigation, exhibit similar activities in experimental models of pain and inflammation. Finally, as there is evidence that the glutarimide moiety contributes to the teratogenic effect of many thalidomide analogs, our results indicate that phthalimide analogs devoid of this functional group could represent a new class of analgesic and anti-inflammatory candidates with potential greater safety.

Nitroxyl inhibits overt pain-like behavior in mice: role of cGMP/PKG/ATP-sensitive potassium channel signaling pathway

BACKGROUND

Several lines of evidence have indicated that nitric oxide (NO) plays complex and diverse roles in modulation of pain/analgesia. However, the roles of charged and uncharged congeners of NO are less well understood. In the present study, the antinociceptive effect of the nitroxyl (HNO) donor, Angeli's salt (Na2N2O3; AS) was investigated in models of overt pain-like behavior. Moreover, whether the antinociceptive effect of nitroxyl was dependent on the activation of cGMP (cyclic guanosine monophosphate)/PKG (protein kinase G)/ATP-sensitive potassium channels was addressed.

METHODS

The antinociceptive effect of AS was evaluated on phenyl-p-benzoquinone (PBQ)- and acetic acid-induced writhings and via the formalin test. In addition, pharmacological treatments targeting guanylate cyclase (ODQ), PKG (KT5923) and ATP-sensitive potassium channel (glybenclamide) were used.

RESULTS

PBQ and acetic acid induced significant writhing responses over 20min. The nociceptive response in these models were significantly reduced in a dose-dependent manner by subcutaneous pre-treatment with AS. Furthermore, AS also inhibited both phases of the formalin test. Subsequently, the inhibitory effect of AS in writhing and flinching responses were prevented by ODQ, KT5823 and glybenclamide, although these inhibitors alone did not alter the writhing score. Furthermore, pretreatment with L-cysteine, an HNO scavenger, confirmed that the antinociceptive effect of AS depends on HNO.

CONCLUSION

The present study demonstrates the efficacy of a nitroxyl donor and its analgesic mechanisms in overt pain-like behavior by activating the cGMP/PKG/ATP-sensitive potassium channel (K(+)) signaling pathway.

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

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

Tadalafil analgesia in experimental arthritis involves suppression of intra-articular TNF release

BACKGROUND AND PURPOSE

We investigated the effect of the phosphodiesterase-5 inhibitor, tadalafil, on the acute hypernociception in rat models of arthritis.

EXPERIMENTAL APPROACH

Rats were treated with either an intra-articular injection of zymosan (1 mg) or surgical transection of the anterior cruciate ligament (as an osteoarthritis model). Controls received saline intra-articular or sham operation respectively. Joint pain was evaluated using the articular incapacitation test measured over 6 h following zymosan or between 4 and 7 days after anterior cruciate ligament transection. Cell counts, tumour necrosis factor-α (TNF-α), interleukin-1 (IL-1), and the chemokine, cytokine-induced neutrophil chemoattractant-1 (CINC-1) were measured in joint exudates 6 h after zymosan. Groups received tadalafil (0.02-0.5 mg·kg⁻¹ per os) or saline 2 h after intra-articular zymosan. Other groups received the µ-opioid receptor antagonist naloxone or the cGMP inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) before tadalafil.

KEY RESULTS

Tadalafil dose-dependently inhibited hypernociception in zymosan and osteoarthritis models. In zymosan-induced arthritis, tadalafil significantly decreased cell influx and TNF-α release but did not alter IL-1 or CINC-1 levels. Pretreatment with ODQ but not with naloxone prevented the anti-inflammatory effects of tadalafil.

CONCLUSIONS AND IMPLICATIONS

Therapeutic oral administration of tadalafil provided analgesia mediated by guanylyl cyclase and was independent of the release of endogenous opioids. This effect of tadalafil was associated with a decrease in neutrophil influx and TNF-α release in inflamed joints.

Experimental model of zymosan-induced arthritis in the rat temporomandibular joint: role of nitric oxide and neutrophils

AIMS

To establish a new model of zymosan-induced temporomandibular joint (TMJ) arthritis in the rat and to investigate the role of nitric oxide.

METHODS

Inflammation was induced by an intra-articular injection of zymosan into the left TMJ. Mechanical hypernociception, cell influx, vascular permeability, myeloperoxidase activity, nitrite levels, and histological changes were measured in TMJ lavages or tissues at selected time points. These parameters were also evaluated after treatment with the nitric oxide synthase (NOS) inhibitors L-NAME or 1400 W.

RESULTS

Zymosan-induced TMJ arthritis caused a time-dependent leucocyte migration, plasma extravasation, mechanical hypernociception, and neutrophil accumulation between 4 and 24 h. TMJ immunohistochemical analyses showed increased inducible NOS expression. Treatment with L-NAME or 1400 W inhibited these parameters.

CONCLUSION

Zymosan-induced TMJ arthritis is a reproducible model that may be used to assess both the mechanisms underlying TMJ inflammation and the potential tools for therapies. Nitric oxide may participate in the inflammatory temporomandibular dysfunction mechanisms.

Inhibition of nNOS prevents and inhibition of iNOS reverses α,β-meATP-induced facilitation of neck muscle nociception in mice

Infusion of α,β-methylene ATP (α,β-meATP) into murine neck muscle facilitates brainstem nociception. Unspecific nitric oxide synthase (NOS) inhibition prevents and reverses this sensitization. It is unclear whether neuronal (nNOS), inducible (iNOS) or endothelial NOS isoenzymes are involved in this α,β-meATP effect. Hypothesized involvement of nNOS isoenzyme was addressed by preceding (0.5, 1, and 2 mg/kg) and subsequent (2 mg/kg) intraperitoneal injection of the nNOS-inhibitor NPLA. iNOS involvement was addressed by subsequent, intraperitoneal administration of the iNOS-inhibitor 1400 W (2 mg/kg). Brainstem nociception was monitored by the jaw-opening reflex elicited via electrical tongue stimulation in 45 anesthetized mice. Preceding NPLA dose-dependently prevented α,β-meATP-induced reflex facilitation. Whereas subsequent inhibition of nNOS showed no effect, iNOS inhibition by 1400 W significantly reversed reflex facilitation. Data provide evidence that nNOS plays a major role in induction and iNOS in maintenance of facilitation in neck muscle nociception. Divergent roles of NOS isoenzymes may promote research on target specific treatment for headache and neck muscle pain.

Investigation of the role of tumour necrosis factor-α, interleukin-1β, interleukin-10, nitric oxide and rheumatoid factor-immunoglobulin M in a rat model of arthritis

Collagen-induced arthritis (CIA) in rats is a widely used preclinical animal model of rheumatoid arthritis (RA). However, CIA development in Sprague-Dawley (SD) rats is less severe in terms of inflammatory response compared with other strains. Therefore, a modified CIA model called MCIA, using N-acetylmuramyl dipeptide (MDP), has been developed in the less sensitive SD rat strains. This work was conducted to better understand the immunopathological role and contributions of the pro-inflammatory T-helper type 1 (Th-1) cytokines and inflammatory mediators, interleukin-1 (IL-1 β), tumour necrosis factor-alpha (TNF- α) and nitric oxide (NO); the anti-inflammatory T-helper type 2 (Th-2) cytokine, IL-10 and autoantibodies such as rheumatoid factor (RF)-immunoglobulin M (IgM) in this newly developed RA model. TNF-α, NO and RF-IgM levels were significantly increased, while IL-1 β levels were not affected in this MCIA rat model. The levels of IL-10 were lower than the baseline when compared with controls. In conclusion: (1) the immunological features represented in the MCIA rat model favour the Th-1 cytokine profile over Th-2 and (2) RF-IgM can be used as a diagnostic test in preclinical RA models.

Effects of nitric oxide on neutrophil influx depends on the tissue: role of leukotriene B4 and adhesion molecules

BACKGROUND AND PURPOSE

We investigated the effect of nitric oxide synthase (NOS) inhibition on polymorphonuclear cell (PMN) influx in zymosan or lipopolysaccharide (LPS)-induced arthritis and peritonitis.

EXPERIMENTAL APPROACH

Wistar rats received intra-articular (i.art.) zymosan (30-1000 microg) or LPS (1-10 microg). Swiss C57/Bl6 mice genetically deficient in intercellular adhesion molecule-1 (ICAM-1(-/-)) or in beta(2)-integrin (beta(2)-integrin(-/-)) received zymosan either i.art. or i.p. PMN counts, leukotriene B(4) (LTB(4)), tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) levels were measured in joint and peritoneal exudates. Groups received the NOS inhibitors N(G)-nitro-L-arginine methyl ester (LN), nitro-L-arginine, N-[3-(aminomemethyl)benzyl] acetamide or aminoguanidine, prior to zymosan or LPS, given i.p. or s.c. in the arthritis and peritonitis experiments respectively. A group of rats received LN locally (i.art. or i.p.), 30 min prior to 1 mg zymosan i.art.

KEY RESULTS

Systemic or local NOS inhibition significantly prevented PMN migration in arthritis while increasing it in peritonitis, regardless of stimuli, concentration of NOS inhibitors and species. NOS inhibition did not alter TNF-alpha and IL-10 but decreased LTB(4) in zymosan-induced arthritis. LN administration significantly inhibited PMN influx into the joints of ICAM-1(-/-) and beta(2)-integrin(-/-) mice with zymosan-arthritis, while not altering PMN influx into the peritoneum of mice with zymosan-peritonitis.

CONCLUSIONS AND IMPLICATIONS

Nitric oxide has a dual modulatory role on PMN influx into joint and peritoneal cavities that is stimulus- and species-independent. Differences in local release of LTB(4) and in expression of ICAM-1 and beta(2)-integrin account for this dual role of NO on PMN migration.

Antinociceptive effects of St. John's wort, Harpagophytum procumbens extract and Grape seed proanthocyanidins extract in mice

Hypericum perforatum extract (St. John's wort, SJW), Harpagophytum procumbens extract (HPE) and Grape seed proanthocyanidin extract (GSPE) have a broad spectrum of biological activities including antidepressant, anti-inflammatory or anti-oxidant effects. The aim of this study was to clarify antinociceptive properties of SJW, HPE and GSPE in mice with mechanisms that might potentially underlie these activities. Also, the effects of these herbal extracts on the antinociception and plasma and brain concentrations of morphine were examined. Oral pretreatment with SJW (100-1000 mg/kg) and HPE (30-300 mg/kg) attenuated significantly times of licking/biting both first and second phases of formalin injection in mice in the dose-dependent manner, and GSPE (10-300 mg/kg) suppressed second phase. Naloxone (5 mg/kg, s.c.) significantly attenuated antinociceptive effect of HPE but not SJW and GSPE. Formalin injection resulted in significant increase in the content of nitrites/nitrates (NO(x)) in mouse spinal cord. The rise of spinal NO(x) content by formalin was significantly attenuated by HPE and SJW. The pretreatment with SJW significantly potentiated an antinociceptive effect of morphine (0.3 mg/kg, s.c.), although concentrations of morphine in plasma and brain were not significantly changed by these herbal extracts. In conclusion, the present study has shown that SJW, HPE and GSPE exert significant antinociceptive effects in the formalin test of mice. In addition, opioidergic system seems to be involved in the antinociceptive effect of HPE but not SJW and GSPE. Furthermore, SJW potentiates morphine-induced antinociception possibly by pharmacodynamic interaction.

Norepinephrine-induced nociception and vasoconstrictor hypersensitivity in rats with chronic post-ischemia pain

Painful hypersensitivity to norepinephrine (NE) has been reported in various chronic pain conditions that exhibit sympathetically-maintained pain (SMP), particularly CRPS-I and II. We investigated the parallels between the nociceptive and vascular sensitivity to NE in rats with chronic post-ischemia pain (CPIP), an animal model of CRPS-I induced by hind paw ischemia-reperfusion injury. Intradermal injections of NE to the affected hind paw induced dose-dependent nociceptive behaviours in CPIP rats, but not sham animals. These behaviours were blocked by alpha(1)- and alpha(2)-adrenergic receptor antagonists, or a nitric oxide (NO) donor. Using laser Doppler flowmetry, we detected vasoconstrictor hypersensitivity in the ipsilateral CPIP hind paw, as compared to responses in sham animals or the contralateral hind paw. The vasoconstrictor hypersensitivity was also attenuated by adrenergic antagonists. Intradermal injection of [Arg(8)] vasopressin (AVP) or the endothelial NO synthase (eNOS) inhibitor, L-NIO, to the affected paw also induced nociceptive behaviours in CPIP rats, but not sham rats. These results suggest CPIP rats display abnormal nociceptive responses to adrenergic and non-adrenergic vasoconstrictive agents. Furthermore, the nociceptive responses to NE in CPIP rats are paralleled by enhanced vasoconstrictive responses to NE, and are relieved by alpha-adrenergic antagonists or a vasodilator. We conclude that persistent tissue ischemia and hypersensitivity to sympathetic vasoconstriction are important mechanisms for pain in CPIP rats, and that either reducing vasoconstriction or enhancing vasodilatation may be effective methods of relieving the pain of CRPS-I.

Low-level laser therapy for zymosan-induced arthritis in rats: Importance of illumination time

BACKGROUND

It has been proposed for many years that low-level laser (or light) therapy (LLLT) can ameliorate the pain, swelling, and inflammation associated with various forms of arthritis. Light is thought to be absorbed by mitochondrial chromophores leading to an increase in adenosine triphosphate (ATP), reactive oxygen species and/or cyclic AMP production and consequent gene transcription via activation of transcription factors. However, despite many reports about the positive effects of LLLT in arthritis and in medicine in general, its use remains controversial. For all indications (including arthritis) the optimum optical parameters have been difficult to establish and so far are unknown.

METHODS

We tested LLLT on rats that had zymosan injected into their knee joints to induce inflammatory arthritis. We compared illumination regimens consisting of a high and low fluence (3 and 30 J/cm(2)), delivered at high and low irradiance (5 and 50 mW/cm(2)) using 810-nm laser light daily for 5 days, with the positive control of conventional corticosteroid (dexamethasone) therapy.

RESULTS

Illumination with 810-nm laser was highly effective (almost as good as dexamethasone) at reducing swelling and a longer illumination time (10 or 100 minutes compared to 1 minute) was more important in determining effectiveness than either the total fluence delivered or the irradiance. LLLT induced reduction of joint swelling correlated with reduction in the inflammatory marker serum prostaglandin E2 (PGE2).

CONCLUSION

LLLT with 810-nm laser is highly effective in treating inflammatory arthritis in this model. Longer illumination times were more effective than short times regardless of total fluence or irradiance. These data will be of value in designing clinical trials of LLLT for various arthritides.

Inhibition of spinal constitutive NOS-2 by 1400W attenuates tissue injury and inflammation-induced hyperalgesia and spinal p38 activation

Nitric oxide (NO) and its synthesizing enzymes, including NO synthase-2 (NOS-2, also called inducible NOS, iNOS), have been implicated in spinal nociception. 1400W is a highly selective NOS-2 inhibitor, as compared with either NOS-1 (neuronal NOS, nNOS) or NOS-3 (endothelial NOS). Here we examined the anti-nociceptive effects of intrathecal (IT) administration of 1400W in two experimental models of hyperalgesia (formalin and carrageenan models), in addition to the effect of 1400W on stimulation-induced activation of spinal p38 mitogen-activated protein kinase (p38). IT treatment of rats with 1400W produced a dose-dependent inhibition of paw formalin-induced phase II flinches, and attenuated carrageenan-induced thermal hyperalgesia. In contrast, IT injection of a selective inhibitor of NOS-1, nNOS inhibitor-I, had no effect in either model. Furthermore, 1400W at a dose that suppressed formalin-induced flinching behavior also blocked formalin-evoked p38 phosphorylation (activation) in the spinal cord, while nNOS inhibitor-I displayed no activity. The prompt effects of IT 1400W suggest involvement of constitutively expressed NOS-2 in spinal nociception. The NOS-2 protein in rat spinal cords was undetectable by Western blotting. However, when the protein was immunoprecipitated prior to Western blotting, NOS-2-immunoreactive bands were detected in the tissues, including naïve spinal cords. The presence of constitutive spinal NOS-2 was further confirmed by reverse transcriptase-polymerase chain reaction. Taken together, the present studies suggest that constitutively expressed spinal NOS-2 mediates tissue injury and inflammation-induced hyperalgesia, and that activation of p38 is one of the downstream factors in NO-mediated signaling in the initial processing of spinal nociception.

Zymosan-induced inflammation stimulates neo-adipogenesis

OBJECTIVE

To investigate the potential of inflammation to induce new adipose tissue formation in the in vivo environment.

METHODS AND RESULTS

Using an established model of in vivo adipogenesis, a silicone chamber containing a Matrigel and fibroblast growth factor 2 (1 microg/ml) matrix was implanted into each groin of an adult male C57Bl6 mouse and vascularized with the inferior epigastric vessels. Sterile inflammation was induced in one of the two chambers by suspending Zymosan-A (ZA) (200-0.02 microg/ml) in the matrix at implantation. Adipose tissue formation was assessed at 6, 8, 12 and 24 weeks. ZA induced significant adipogenesis in an inverse dose-dependent manner (P<0.001). At 6 weeks adipose tissue formation was greatest with the lowest concentrations of ZA and least with the highest. Adipogenesis occurred both locally in the chamber containing ZA and in the ZA-free chamber in the contralateral groin of the same animal. ZA induced a systemic inflammatory response characterized by elevated serum tumour necrosis factor-alpha levels at early time points. Aminoguanidine (40 microg/ml) inhibited the adipogenic response to ZA-induced inflammation. Adipose tissue formed in response to ZA remained stable for 24 weeks, even when exposed to the normal tissue environment.

CONCLUSIONS

These results demonstrate that inflammation can drive neo-adipogenesis in vivo. This suggests the existence of a positive feedback mechanism in obesity, whereby the state of chronic, low-grade inflammation, characteristic of the condition, may promote further adipogenesis. The mobilization and recruitment of a circulating population of adipose precursor cells is likely to be implicated in this mechanism.

The snake venom metalloproteinase BaP1 induces joint hypernociception through TNF-alpha and PGE2-dependent mechanisms

BACKGROUND AND PURPOSE

Matrix metalloproteinases (MMPs) have been implicated in joint tissue destruction in arthritis. However, MMPs have not been assigned a role in joint pain. We investigated the ability of BaP1, a metalloproteinase from Bothrops asper snake venom, with structural homology to MMPs, to induce joint hypernociception.

EXPERIMENTAL APPROACH

Animals received intra-articular (i.art.) BaP1. Hypernociception was assessed using the rat-knee joint articular incapacitation test. Cell influx, prostaglandin E(2) (PGE(2)), and TNF-alpha levels were assessed in joint exudates following BaP1 injection.

KEY RESULTS

BaP1 (5 microg per joint) provoked hypernociception between 1 and 6 h after i.art. injection. Cell influx, mostly neutrophils, was maximal 3 h after BaP1 i.art. injection. BaP1 also led to increase in PGE(2) and TNF-alpha levels in the joint exudates. Pretreatment with either indomethacin (4 mg.kg(-1) i.p.) or with an anti-TNF-alpha antiserum (i.art.) significantly inhibited both BaP1-induced joint hypernociception and cell influx. In isolated rat peritoneal macrophages, BaP1 increased cyclooxygenase (COX)-2 expression, while not altering that of COX-1.

CONCLUSIONS AND IMPLICATIONS

This is the first demonstration that a metalloproteinase promotes joint hypernociception. This effect involves local release of PGE(2) and TNF-alpha. BaP1-induced increase in PGE(2) is associated to increased COX-2 expression in macrophages. Blocking PGE(2) or TNF-alpha inhibits BaP1-induced hypernociception. In addition to unravelling a hitherto unknown mechanism whereby TNF blockade provides analgesia in arthritis, the data show, for the first time that MMPs are involved in inflammatory joint hypernociception and induce COX-2 expression.

Techniques for assessing knee joint pain in arthritis

The assessment of pain is of critical importance for mechanistic studies as well as for the validation of drug targets. This review will focus on knee joint pain associated with arthritis. Different animal models have been developed for the study of knee joint arthritis. Behavioral tests in animal models of knee joint arthritis typically measure knee joint pain rather indirectly. In recent years, however, progress has been made in the development of tests that actually evaluate the sensitivity of the knee joint in arthritis models. They include measurements of the knee extension angle struggle threshold, hind limb withdrawal reflex threshold of knee compression force, and vocalizations in response to stimulation of the knee. A discussion of pain assessment in humans with arthritis pain conditions concludes this review.

Analgesic activity of a polysaccharide in experimental osteoarthritis in rats

Viscosupplementation efficacy has been related to the high molecular weight of hyaluronic acid-like compounds, as well as to gel formulation. We evaluated the effect of a galactomannan polysaccharide derived from Guar gum (GG) in joint pain in an osteoarthritis (OA) model. Wistar rats (six animals/group) were subjected to anterior cruciate ligament transection (ACLT-OA group). The OA group was compared to a false-operated group (sham). Joint pain was recorded daily, using the articular incapacitation test, until 7 days after ACLT. Solutions or gel preparations of GG (100 microg) or Hylan G-F 20 (100 microg), used as a comparator, were given intraarticularly (i.a.) at day 4 after ACLT. Controls received saline i.a. The OA group had significantly increased joint pain as compared to sham (P<0.001). GG, either as a gel or solution, significantly inhibited joint pain similar to the inhibition achieved with Hylan G-F20. This is the first demonstration that a galactomannan derived from GG reduces joint pain in experimental OA. This analgesia is independent of the colloidal state. We propose that the analgesic benefit of viscosupplementation may be due to an intrinsic carbohydrate-mediated mechanism rather than to the rheologic properties of the material.

Analgesic effects by electroacupuncture were decreased in inducible nitric oxide synthase knockout mice

BACKGROUND

This study was designed to investigate the involvement of inducible nitric oxide synthase (iNOS) in electroacupuncture (EA)-induced analgesia.

METHODS

Two and 100 Hz EA stimulation were applied at acupoint ST 36 (Zusanli) in iNOS knockout mice (n = 28). Needles were inserted 5 mm in depth in ST36. After insertion, the needles were fixed in situ with adhesive tape. EA was applied after the basal threshold determination. The EA parameters were set as follows: constant square wave current output (pulse width: 0.6 ms at 2 Hz and 0.2 ms at 100 Hz) and 2 mA intensities. EA was performed for 30 minutes and tail-flick latencies (TFLs) were evaluated every 15 minutes for 1 hour.

RESULTS

In 2 Hz EA stimulation, the tail-flick response (TFR) of wild-type mice for durations of 0, 15, 30, 45 and 60 minutes were 2.70 +/- 0.26, 4.19 +/- 0.37, 4.17 +/- 0.34, 3.57 +/- 0.27 and 3.39 +/- 0.32 seconds of TFLs. Meanwhile, iNOS -/- mice showed 4.10 +/- 0.33, 4.77 +/- 0.24, 5.26 +/- 0.30, 4.48 +/- 0.33 and 5.00 +/- 0.41 seconds of TFLs. In 100 Hz EA stimulation, the TFR of wild-type mice were 3.01 +/- 0.24, 4.67 +/- 0.31, 4.76 +/- 0.25, 4.04 +/- 0.45 and 4.26 +/- 0.30 seconds of TFLs. The iNOS -/- mice were 4.33 +/- 0.16, 5.29 +/- 0.28, 5.06 +/- 0.35, 4.52 +/- 0.17 and 4.80 +/- 0.28 seconds of TFLs. Wild-type mice exhibited 63.9% increase in TFL compared to the baseline after 2 Hz EA, whereas the iNOS knockout mice exhibited 32.9% increase in TFL. The TFL after 100 Hz EA showed similar trends: 66.5% increase in TFL in wildtype mice and 18.3% increase in the iNOS knockout mice.

CONCLUSION

The present findings suggested that iNOS may play a crucial role in both low- and high-frequency EA-induced analgesic effects.

Neutrophils-derived peroxynitrite contributes to acute hyperalgesia and cell influx in zymosan arthritis

We investigated the contribution of neutrophils to joint hyperalgesia and peroxynitrite formation in zymosan arthritis. Rats received 1 mg zymosan intra-articular, and joint hyperalgesia was measured using the rat knee-joint articular incapacitation test. After 6 h, joint exudates were collected by aspiration for the assessment of cell influx, myeloperoxidase activity, and nitrite (as an index of nitric oxide formation) levels. Nitrotyrosine content, used as an index of peroxynitrite formation, was measured in joint exudates, using enzyme-linked immunosorbent assay. A group of rats was rendered neutropenic through the administration of a rabbit anti-rat neutrophil antibody (2 ml kg(-1), i.p.) 30 min before injection of 1 mg zymosan intra-articular. Other groups received uric acid (100 or 250 mg kg(-1), i.p.), the peroxynitrite scavenger, 30 min before 1 mg zymosan intra-articular. Controls received the vehicle. The significant inhibition of joint hyperalgesia in neutropenic animals was associated to significantly decreased cell influx, myeloperoxidase activity, nitric oxide, and nitrotyrosine levels in the joint exudates, as compared to naive rats. Uric acid administration inhibited both hyperalgesia and cell influx, as compared to controls. Neutrophils are involved in both nitric oxide and peroxynitrite formation in zymosan arthritis, thereby contributing to acute joint hyperalgesia. Scavenging of reactive nitrogen species (e.g. peroxynitrite) inhibits neutrophil migration and joint hyperalgesia in the acute phase of zymosan arthritis in rats.

Role of nitric oxide on pathogenesis of 5-fluorouracil induced experimental oral mucositis in hamster

INTRODUCTION

Mucositis induced by antineoplastic drugs is an important, dose-limiting, and costly side effect of cancer therapy.

AIM

To investigate the role of nitric oxide (NO) on the pathogenesis of 5-fluorouracil (5-FU)-induced oral mucositis.

MATERIALS AND METHODS

Oral mucositis was induced by two intraperitoneal (i.p) administrations of 5-FU on the first and second days of the experiment (60 and 40 mg/kg, respectively) in male hamsters. Animals were treated subcutaneously with saline (0.4 ml), 1,400 W (1 mg/kg), aminoguanidine (5 or 10 mg/kg) or Nphi-Nitro-L-Arginine Methyl Ester (L-NAME) (5, 10, or 20 mg/kg) 1 h before the injections of 5-FU and daily until sacrifice, on the tenth day. Macroscopic and histopathological analyses were evaluated and graded. Tissues from the cheek pouches were harvested for measurement of myeloperoxidase (MPO) activity, nitrite level, and immunohistochemistry for induced nitric oxide synthase (iNOS).

RESULTS

Treatment with 1,400 W or aminoguanidine reduced macroscopic and histological parameters of oral mucositis, and reduced the inflammatory cell infiltration as detected by histopathology and by MPO activity. In contrast, the administration of L-NAME did not significantly reverse the inflammatory alterations induced by experimental mucositis. Increased NOS activity, nitrite level and immunostaining for iNOS were detected on the check pouch tissue of animals submitted to 5-FU-induced oral mucositis on the tenth day.

CONCLUSION

These results suggest an important role of NO produced by iNOS in the pathogenesis of oral mucositis induced by 5-FU.

A quantitative approach to measure joint pain in experimental osteoarthritis--evidence of a role for nitric oxide

OBJECTIVES

To describe a method to study joint pain in experimental osteoarthritis (OA) and to study nitric oxide (NO) participation in experimental OA.

DESIGN

Rats were subjected to anterior cruciate ligament transection (ACLT) (OA group) of the right knee and evaluated during 28 days. A sham group was false operated and a naive group received no manipulation. Joint pain was measured by recording the time the right hind paw fails to touch the surface while walking. Cell influx (CI) and nitrite levels were measured in joint exudates. Expression of inducible NO synthase (iNOS) in synovia was detected by immunostaining. For the specific purpose of pharmacological manipulation, groups received either indomethacin (2 mg/kg/day s.c. (subcutaneous)), meloxicam (6 mg/kg/day s.c.), morphine (200 microg intra-articularly), the non-selective NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME; 30 mg/kg/bid i.p. (intra-peritoneal)) or the selective iNOS inhibitor 1400W (0.5 mg/kg/day s.c.), given 30 min prior (prophylactic) or 4 days after (therapeutic) ACLT, until sacrifice, at 7 days. The respective non-treated groups received the vehicles.

RESULTS

The OA group developed joint pain, as compared to sham and control groups (P<0.05). Significantly increased nitrite levels and iNOS immunostaining were seen in the OA group. Both indomethacin and meloxicam inhibited joint pain (P<0.05). Morphine inhibited joint pain, whereas this effect was blocked by co-administration of the mu-opioid receptor naloxone. CI was similar among all groups. Prophylactic but not therapeutic L-NAME or 1400W reduced joint pain.

CONCLUSION

We describe a method to quantitate joint pain associated to weight bearing in the ACLT model. The joint pain is sensitive to classical antinociceptive compounds. NO release is associated to joint pain though NOS inhibition does not inhibit ongoing pain.

Anti-nociceptive effect of thalidomide on zymosan-induced experimental articular incapacitation

The anti-nociceptive effect of thalidomide on zymosan-induced articular knee joint incapacitation in rats was investigated. Thalidomide (5-45 mg/kg), given 30 min before but not 2 h after the intra-articular injection of zymosan, inhibited the nociceptive response in a dose-dependent manner. Furthermore, thalidomide pretreatment significantly reduced the concentration of tumor necrosis factor-alpha (TNF-alpha, -68.4%) in the exudate of zymosan-injected joints, but not those of interleukin-1beta, interleukin-6, CINC-1 or interleukin-10. The expression of TNF-alpha, determined by immunohistochemical staining, in synovial tissues obtained from articular joints injected with zymosan was also inhibited by thalidomide pretreatment. The anti-nociceptive effect of thalidomide was not reversed by the co-administration of an opioid receptor antagonist, naloxone, suggesting that endogenous opioids do not mediate the anti-nociceptive effect of thalidomide in this model. In conclusion, the anti-nociceptive activity of thalidomide in zymosan-induced articular incapacitation is associated with the inhibition of TNF-alpha by resident synovial cells.

Nitric oxide inhibition and the impact on renal nerve-mediated antinatriuresis and antidiuresis in the anaesthetized rat

The contribution of nitric oxide (NO) to the antinatriuresis and antidiuresis caused by low-level electrical stimulation of the renal sympathetic nerves (RNS) was investigated in rats anaesthetized with chloralose-urethane. Groups of rats, n= 6, were given i.v. infusions of vehicle, l-NAME (10 microg kg(-1) min(-1)), 1400W (20 microg kg(-1) min(-1)), or S-methyl-thiocitrulline (SMTC) (20 microg kg(-1) min(-1)) to inhibit NO synthesis non-selectively or selectively to block the inducible or neuronal NOS isoforms (iNOS and nNOS, respectively). Following baseline measurements of blood pressure (BP), renal blood flow (RBF), glomerular filtration rate (GFR), urine flow (UV) and sodium excretion (U(Na)V), RNS was performed at 15 V, 2 ms duration with a frequency between 0.5 and 1.0 Hz. RNS did not cause measurable changes in BP, RBF or GFR in any of the groups. In untreated rats, RNS decreased UV and U(Na)V by 40-50% (both P < 0.01), but these excretory responses were prevented in l-NAME-treated rats. In the presence of 1400W i.v., RNS caused reversible reductions in both UV and U(Na)V of 40-50% (both P < 0.01), while in SMTC-treated rats, RNS caused an inconsistent fall in UV, but a significant reduction (P < 0.05) in U(Na)V of 21%. These data demonstrated that the renal nerve-mediated antinatriuresis and antidiuresis was dependent on the presence of NO, generated in part by nNOS. The findings suggest that NO importantly modulates the neural control of fluid reabsorption; the control may be facilitatory at a presynaptic level but inhibitory on tubular reabsorptive processes.

Blockade of leukotriene B4 prevents articular incapacitation in rat zymosan-induced arthritis

We investigated whether leukotrienes mediate cell influx and articular incapacitation in zymosan-induced arthritis. Rats received 1 mg zymosan intra-articularly (i.a.). The hyperalgesia was measured using the rat articular incapacitation test. Cell influx, leukotriene B(4) and prostaglandin E(2) levels were assessed in the joint exudate, at 6 h. Groups received either the leukotriene B(4) synthesis inhibitor MK 886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl)]-2,2-dimethylpropanoic acid 30 min before or 2 h after the zymosan; 0.3-3 mg kg(-1) i.p.), the leukotrienes synthesis inhibitor BWA(4)C (N-(3-phenoxycinnamyl)-acetohydroxamic acid--2 h after the zymosan; 10 microg i.a.) or the peptido-leukotrienes antagonist sodium montelukast (30 min before and 2 h after the zymosan; 10 mg kg(-1) per os). MK 886 inhibited the articular incapacitation and cell influx, while reducing leukotriene B(4), but not prostaglandin E(2) levels. BWA(4)C inhibited the articular incapacitation. Sodium montelukast did not affect either of the parameters. The data suggest that leukotriene B(4) is involved in cell influx and articular incapacitation in zymosan arthritis.

Interaction of inducible nitric oxide synthase and cyclooxygenase-2 inhibitors in formalin-induced nociception in mice

Studies with inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 inhibitor were conducted to assess their synergistic antinociceptive effect and possible therapeutic advantage. The antinociceptive interaction of rofecoxib, a selective cyclooxygenase-2 inhibitor, with aminoguanidine hydrochloride, a selective iNOS inhibitor, was examined in the formalin-induced paw-licking model in mice. Analysis of variance (ANOVA) and the isobolographic method were used to identify the nature of the antinociceptive interaction. Different doses of rofecoxib (1, 3, 10 and 30 mg/kg) and aminoguanidine hydrochloride (10, 30, 100 and 300 mg/kg) alone were administered orally to adult male albino mice (20-30 g). Only high doses of rofecoxib (10 and 30 mg/kg) and aminoguanidine hydrochloride (100 and 300 mg/kg) showed a statistically significant antinociceptive effect. Combination of a subthreshold dose of rofecoxib (1 mg/kg) with increasing doses of aminoguanidine hydrochloride (30, 100 and 300 mg/kg) resulted in potentiated antinociception (P<0.05). Combined therapy with a subthreshold dose of aminoguanidine hydrochloride (30 mg/kg) with increasing doses of rofecoxib (1, 3, 10 and 30 mg/kg) also resulted in significant antinociception (P<0.05). These results suggest that rofecoxib and aminoguanidine hydrochloride act synergistically in their antinociceptive action in mice. A possible mechanism of interaction is that nitric oxide (NO) stimulates the activity of cyclooxygenase-2 by combining with its heme component. Furthermore, the present results suggest that combination therapy with rofecoxib and aminoguanidine hydrochloride may provide an alternative for the clinical control of pain.

PAF is involved in the Mycoplasma arthritidis superantigen-triggering pathway for iNOS and COX-2 expression in murine peritoneal cells

We investigated the capacity of Mycoplasma arthritidis mitogen (MAM) to induce (a) expression of the inducible enzymes cyclo-oxygenase (COX-2) and nitric oxide synthase (iNOS), (b) production of prostaglandin E2 (PGE2) and nitric oxide (NO), and (c) involvement of platelet-activating factor (PAF) in the MAM-induced activation pathway. Resident peritoneal cells from C3H/HePas mice were incubated with MAM in the presence or absence of a PAF-antagonist (WEB2170) or COX-2 inhibitors (nimesulide or NS398). Enzyme expression was evaluated by immunoblotting, PGE2 by EIA, and NO by Griess reaction. Following MAM-stimulation of peritoneal cells, expression of COX-2 was detected at 3 h (peak levels at 12 h) and of iNOS at 6 h (peak levels at 20 h). PGE2 increased till 20 h, decreasing thereafter, whereas NO increased with time. WEB2170 (5 x 10(-5) M) treatment caused 44% inhibition of NO output and reduced iNOS expression (48% at the peak of expression). Concomitant treatment with WEB2170 and nimesulide (10(-5) M) reversed these inhibitory effects. WEB2170 reduced COX-2 expression (43% at the peak of expression) and prevented the decline in PGE2 levels after 20 h. These results suggest the involvement of PAF in the signaling pathway triggered by MAM that leads to expression of iNOS and COX-2, and show that PAF regulates the production of NO, possibly by controlling levels of PGE2.

Intrathecal interleukin-1β administration induces thermal hyperalgesia by activating inducible nitric oxide synthase expression in the rat spinal cord

The effect of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) on the inducible nitric oxide synthase-nitric oxide (iNOS-NO) cascade in nociceptive signal transduction was examined in the intact rat spinal cord. All rats were implanted with an intrathecal (i.t.) catheter; some were also implanted with an i.t. microdialysis probe. The paw withdrawal latency to radiant heat was used to assess thermal hyperalgesia. The iNOS protein expression in the spinal cord dorsal horn was examined by western blot analysis and NOS activity assay. NO production in the CSF dialysate was also measured. IL-1beta i.t. (100 ng) produced thermal hyperalgesia from 4 to 24 h after i.t. injection. The iNOS protein expression was induced at 4 h after i.t. IL-1beta injection, peaked at the 6th hour, and disappeared at 24 h. The iNOS activity showed a similar time-dependent change as the iNOS protein expression. NO release increased by 1.1- to 1.9-fold between 4 and 12 h, also with a peak at the 6th hour, after i.t. IL-1beta administration. Pretreatment with the iNOS inhibitor 1400W (10 microg, i.t.) 1 h before i.t. IL-1beta injection prevented all the responses of IL-1beta. Neither 1400W nor artificial CSF (aCSF) affected the thermal nociceptive threshold and NO production. These results demonstrate that i.t. administration of IL-1beta induced thermal hyperalgesia by activating the iNOS-NO cascade in the rat spinal cord. On the basis of the present findings, we suggest that i.t. administration of iNOS inhibitors may have potential in the treatment of inflammatory and neuropathic pain syndromes.

Reactive nitrogen species scavenging, rather than nitric oxide inhibition, protects from articular cartilage damage in rat zymosan-induced arthritis

1. The contribution of nitric oxide (NO) and peroxynitrite (PN) to inflammation in a zymosan-induced (1 mg, intra-articular, i.art.) rat model of arthritis was assessed by histopathology and by measuring the glycosaminoglycan (GAG) content of the articular cartilage. 2. Progression of the chronic synovitis in zymosan-induced arthritis (ZYA) was associated with increased nitrite and nitrotyrosine (3-NT) levels in the joint exudates that paralleled a progressive loss of the GAG content. An increase in 3-NT was also observed after i.art. PN. 3. The nonselective nitric oxide synthase (NOS) inhibitor l-N(G)-nitroarginine methyl ester (25-75 mg x kg(-1)day(-1)) or the selective inducible NOS inhibitor aminoguanidine (50-100 mg x kg(-1)day(-1)) given 1 h before (prophylactic) or 3 days after (therapeutic) injection of the zymosan ameliorated the synovitis, but worsened the GAG loss, as measured at the end of the experiment (day 7). 4. The PN scavenger uric acid (100-250 mg x kg(-1) i.p. four times daily) given prophylactically until the end of the experiment (day 14), in a dose compatible with its PN scavenging activity, significantly decreased both the synovitis and the GAG loss. 5. In conclusion, PN formation is associated with cartilage damage in addition to proinflammatory activity in ZYA. NOS inhibitors and a PN scavenger were able to reduce the cellular infiltration, while displaying opposite effects on cartilage homeostasis either by enhancing or ameliorating the damage, respectively.

Nitric oxide and cyclooxygenase may participate in the analgesic and anti-inflammatory effect of the cucurbitacins fraction from Wilbrandia ebracteata

Wilbrandia ebracteata is a medicinal plant from South America used in folk medicine for the treatment of chronic rheumatic diseases. We have shown that the high performance liquid chromatography-characterized (HPLC) dichloromethane fraction isolated from Wilbrandia ebracteata (WEDC) inhibits the parameters observed in experimental models of inflammation in vivo and in vitro. In the present study, we extend our previous observations on the analgesic effects of WEDC by investigating its actions using the hot plate test and zymosan-induced writhing test in mice, as well as zymosan-induced arthritis in rats evaluating articular inflammatory pain, cell migration and determination of NO release into the joint exudate. The effect of WEDC on the activity of COX-1 and COX-2 in vitro and its ulcerogenic capacity in vivo were also investigated. The oral treatment of the animals with WEDC (1-10 mg/kg) produced a significant, dose-dependent reduction of articular incapacitation and abdominal contortions in the writhing test. The same effect was not observed in the hot plate and rota-rod tests. WEDC also reduced nitrite release into the zymosan-inflamed joints. In the evaluation of COX activity, we observed that WEDC was able to selectively inhibit COX-2 but not COX-1 activity in COS-7 cells. Moreover, WEDC treatment did not show gastrointestinal toxicity. Our data confirm the anti-nociceptive activities of the WEDC and indicate that this effect could be associated with inhibition of cyclooxygenase-2 (COX-2) and nitric oxide release. The effects could be attributed to cucurbitacins since several of these were isolated from the WEDC.