Indomethacin attenuates mechanical allodynia during the organization but not the maintenance of the peripheral neuropathic pain induced by nervus ischiadicus chronic constriction injury

The neurochemical mechanisms underlying neuropathic pain (NP) are related to peripheral and central sensitization caused by the release of inflammatory mediators in the peripheral damaged tissue and ectopic discharges from the injured nerve, leading to a hyperexcitable state of spinal dorsal horn neurons. The aim of this work was to clarify the role played by cyclooxygenase (COX) in the lesioned peripheral nerve in the development and maintenance of NP by evaluating at which moment the non-steroidal anti-inflammatory drug indomethacin, a non-selective COX inhibitor, attenuated mechanical allodynia after placing one loose ligature around the nervus ischiadicus, an adaptation of Bennett and Xie's model in rodents. NP was induced in male Wistar rats by subjecting them to chronic constriction injury (CCI) of the nervus ischiadicus, placing one loose ligature around the peripheral nerve, and a sham surgery (without CCI) was used as control. Indomethacin (2 mg/kg) or vehicle was intraperitoneally and acutely administered in each group of rats and at different time windows (1, 2, 4, 7, 14, 21, and 28 days) after the CCI or sham surgical procedures, followed by von Frey's test for 30 min. The data showed that indomethacin decreased the mechanical allodynia threshold of rats on the first, second, and fourth days after CCI (P<0.05). These findings suggested that inflammatory mechanisms are involved in the induction of NP and that COX-1 and COX-2 are involved in the induction but not in the maintenance of NP.

IL-33/ST2 signalling contributes to carrageenin-induced innate inflammation and inflammatory pain: role of cytokines, endothelin-1 and prostaglandin E2

BACKGROUND AND PURPOSE

IL-33 signals through ST2 receptors and induces adaptive and innate inflammation. IL-33/ST2 is involved in adaptive inflammation-induced pain. Here, we have investigated the contribution of IL-33/ST2-triggered mechanisms to carrageenin-induced innate inflammation.

EXPERIMENTAL APPROACH

Carrageenin- and IL-33-induced inflammatory responses were assessed in BALB/c- (WT) and ST2-deficient ((-/-) ) mice as follows: oedema (plethysmometer), myeloperoxidase activity (colorimetric assay), mechanical hyperalgesia (electronic version of von Frey filaments), cytokine levels (ELISA), PGE2 (RIA), mRNA expression (quantitative PCR), drug treatments targeting leukocyte recruitment (fucoidin), TNF-α (infliximab), CXCL1 (antibody to CXCL1), IL-1 (IL-1ra), endothelin ETA (clazosentan) and ETB (BQ788) receptors and COX (indomethacin).

KEY RESULTS

Carrageenin injection increased ST2 and IL-33 mRNA expression and IL-33 production in paw skin samples. Carrageenin-induced paw oedema, hyperalgesia and myeloperoxidase activity were reduced in ST2(-/-) compared with WT mice, effects mimicked by IL-33 injection in the paw. Furthermore, IL-33-induced hyperalgesia was reduced by fucoidin suggesting a role for recruited leukocytes in its hyperalgesic effect. IL-33-induced hyperalgesia in naïve mice was reduced by treatments targeting TNF, CXCL1, IL-1, endothelin receptors and COX while carrageenin-induced ST2-dependent TNF-α, CXCL1, IL-1β, IL-10 and PGE2 production and preproET-1 mRNA expression. Combining IL-33 and carrageenin at doses that were ineffective as single treatment induced significant hyperalgesia, oedema, myeloperoxidase activity and cytokine production in a ST2-dependent manner.

CONCLUSIONS AND IMPLICATIONS

IL-33/ST2 signalling triggers the production of inflammatory mediators contributing to carrageenin-induced inflammation. These data reinforces the importance of IL-33/ST2 signalling as a target in innate inflammation and inflammatory pain.

Esthetic Rehabilitation of a Patient With Severe Oligodontia

Oligodontia, or the congenital absence of teeth, can occur in isolation or as part of a syndrome. This study describes a case of isolated oligodontia associated with conical teeth and large diastemas in the anterior region. The patient was treated using direct composite resin restorations. Recent improvements in adhesive restorative materials allow practitioners to offer this low-cost, conservative esthetic treatment, which has the advantage of preserving sound dental structures, to patients with missing teeth.

An interleukin-33/ST2 signaling deficiency reduces overt pain-like behaviors in mice

Interleukin (IL)-33, the most recent member of the IL family of cytokines, signals through the ST2 receptor. IL-33/ST2 signaling mediates antigen challenge-induced mechanical hyperalgesia in the joints and cutaneous tissues of immunized mice. The present study asked whether IL-33/ST2 signaling is relevant to overt pain-like behaviors in mice. Acetic acid and phenyl-p-benzoquinone induced significant writhing responses in wild-type (WT) mice; this overt nociceptive behavior was reduced in ST2-deficient mice. In an antigen-challenge model, ST2-deficient immunized mice had reduced induced flinch and licking overt pain-like behaviors. In the formalin test, ST2-deficient mice also presented reduced flinch and licking responses, compared with WT mice. Naive WT and ST2-deficient mice presented similar responses in the rota-rod, hot plate, and electronic von Frey tests, indicating no impairment of motor function or alteration in basal nociceptive responses. The results demonstrate that IL-33/ST2 signaling is important in the development of overt pain-like behaviors.

Neutrophils recruited by CXCR1/2 signalling mediate post-incisional pain

BACKGROUND

Neutrophil recruitment mediated by the CXCL1/KC chemokine and its receptors CXCR1/CXCR2 plays a critical role in inflammatory diseases. Recently, neutrophil migration and activation triggered by CXCL1-CXCR1/2 signalling was implicated in inflammatory nociception; however, their role in post-surgical pain has not been elucidated. In this study, we addressed the function of neutrophils in the genesis of post-incisional pain in an experimental model of post-surgical pain.

METHODS

Mechanical hyperalgesia was determined with an electronic von Frey test in a mouse hindpaw incisional model. Neutrophil accumulation and the level of CXCL1/KC in the plantar tissue were determined by myeloperoxidase activity assay and enzyme-linked immunosorbent assay, respectively.

RESULTS

An incision in the mouse hindpaw produces long-lasting mechanical hyperalgesia that persists for at least 72 h after surgery. Following surgery, there was an increase in both neutrophil accumulation and the CXCL1/KC level in the incised paws. The depletion of the mouse neutrophils by vinblastine sulphate or anti-neutrophil antibody treatments reduced the mechanical hyperalgesia after paw incision. Furthermore, the treatment of mice with ladarixin, an orally acting CXCR1/2 antagonist, also reduced both the mechanical hyperalgesia and the infiltration of neutrophils in the incised paws.

CONCLUSION

In conclusion, it appears that after surgical processes, neutrophils are recruited by CXCL1-CXCR1/2 signalling and participate in the cascade of events, leading to mechanical hyperalgesia. These results suggest that blocking neutrophil migration through the inhibition of CXCL1-CXCR1/2 signalling might be a target to control post-surgical pain.

Tumor necrosis factor, interleukin-1 and interleukin-8 mediate the nociceptive activity of the supernatant of LPS-stimulated macrophages

It has been suggested that the supernatant of LPSstimulated macrophages (macrophage nociceptive factor, MNF) promotes nociception in mice. Intraperitoneal administration of MNF induced dose-related writhing, which reached a plateau between 18 and 26 min after injection and decreased within 60 min. The release of MNF was inhibited by the pretreatment of the macrophages with cycloheximide, a protein synthesis inhibitor, or with the glucocorticoid dexamethasone. Cyclooxygenase inhibitors, such as indomethacin or paracetamol, had no effect. The MNF-induced nociception was inhibited in a dose-related manner by pretreatment of the animals with indomethacin, paracetamol or dexamethasone. Pretreatment of the animals with the sympatholytics guanethidine and atenolol partially reduced the MNF nociception, which was abolished by the combination of guanethidine or atenolol with indomethacin. The preincubation of MNF with antisera against TNF-α, IL-1 or IL-8 partially inhibited its nociceptive effect. Intraperitoneal injection of a mixture of the recombinants cytokines TNF-α, IL-1 and IL-8 mimicked MNF nociception. The individual injection of these cytokines was unable to induce the nociceptive effect. In conclusion, our data suggest that the nociceptive activity of the supernatant of LPSstimulated macrophages is explained by the presence of TNF-α, IL-1 and IL-8, the nociceptive activity of which (in mice) seems to be due to the release of cyclooxygenase and sympathetic metabolites.

The neutrophil migration induced by tumour necrosis factor alpha in mice is unaffected by glucocorticoids

Macrophages harvested from the peritoneal cavities of rats release a neutrophil chemotactic factor (MNCF) in response to stimulation with Gram-negative bacterial lipopolysaccharide (LPS). MNCF has been shown to be active in rats treated with dexamethasone, a glucocorticoid that usually inhibits the neutrophil migration induced in this species by interleukin (IL)-1, tumour necrosis factor alpha (TNFalpha), IL-8, C5a and leukotriene B(4) (LTB(4)). Here we report that macrophages harvested from peritoneal cavities of mice, and stimulated in vitro with LPS, also release a factor that induces neutrophil migration in dexamethasone-treated animals. This chemotactic activity was neutralized by the incubation of the LPS-stimulated macrophage supernatants with a purified polyclonal IgG anti-mouse TNFalpha. In addition, significant amounts of TNF were detected in the supernatants. The neutrophil migration induced by intraperitoneal administration of recombinant murine TNFalpha was also unaffected by pretreatment of the mice with dexamethasone. Moreover, neutrophil migration induced by intraperitoneal injection of LPS was completely blocked by pretreatment of the mice with a monoclonal antibody against murine TNFalpha. In conclusion, our results support the hypothesis that, in contrast to the role of TNF in rats (where it indirectly induces neutrophil migration), in mice, it may be an important mediator in the recruitment of neutrophils to inflammatory sites.

Streptozotocin-induced mechanical hypernociception is not dependent on hyperglycemia

Since streptozotocin (STZ)-induced diabetes is a widely used model of painful diabetic neuropathy, the aim of the present study was to design a rational protocol to investigate whether the development of mechanical hypernociception induced by STZ depends exclusively on hyperglycemia. Male Wistar rats (180-200 g; N = 6-7 per group) received a single intravenous injection of STZ at three different doses (10, 20, or 40 mg/kg). Only the higher dose (40 mg/kg) induced a significant increase in blood glucose levels, glucose tolerance and deficiency in weight gain. However, all STZ-treated rats (hyperglycemic or not) developed persistent (for at least 20 days) and indistinguishable bilateral mechanical hypernociception that was not prevented by daily insulin treatment (2 IU twice a day, sc). Systemic morphine (2 mg/kg) but not local (intraplantar) morphine treatment (8 microg/paw) significantly inhibited the mechanical hypernociception induced by STZ (10 or 40 mg/kg). In addition, intraplantar injection of STZ at doses that did not cause hyperglycemia (30, 100 or 300 microg/paw) induced ipsilateral mechanical hypernociception for at least 8 h that was inhibited by local and systemic morphine treatment (8 microg/paw or 2 mg/kg, respectively), but not by dexamethasone (1 mg/kg, sc). The results of this study demonstrate that systemic administration of STZ induces mechanical hypernociception that does not depend on hyperglycemia and intraplantar STZ induces mechanical sensitization of primary sensory neurons responsive to local morphine treatment.

Fructose-1,6-bisphosphate reduces inflammatory pain-like behaviour in mice: role of adenosine acting on A1 receptors

BACKGROUND AND PURPOSE

D-Fructose-1,6-bisphosphate (FBP) is an intermediate in the glycolytic pathway, exerting pharmacological actions on inflammation by inhibiting cytokine production or interfering with adenosine production. Here, the possible antinociceptive effect of FBP and its mechanism of action in the carrageenin paw inflammation model in mice were addressed, focusing on the two mechanisms described above.

EXPERIMENTAL APPROACH

Mechanical hyperalgesia (decrease in the nociceptive threshold) was evaluated by the electronic pressure-metre test; cytokine levels were measured by elisa and adenosine was determined by high performance liquid chromatography.

KEY RESULTS

Pretreatment of mice with FBP reduced hyperalgesia induced by intraplantar injection of carrageenin (up to 54%), tumour necrosis factor alpha (40%), interleukin-1 beta (46%), CXCL1 (33%), prostaglandin E(2) (41%) or dopamine (55%). However, FBP treatment did not alter carrageenin-induced cytokine (tumour necrosis factor alpha and interleukin-1 beta) or chemokine (CXCL1) production. On the other hand, the antinociceptive effect of FBP was prevented by systemic and intraplantar treatment with an adenosine A(1) receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine), suggesting that the FBP effect is mediated by peripheral adenosine acting on A(1) receptors. Giving FBP to mice increased adenosine levels in plasma, and adenosine treatment of paw inflammation presented a similar antinociceptive mechanism to that of FBP.

CONCLUSIONS AND IMPLICATIONS

In addition to anti-inflammatory action, FBP also presents an antinociceptive effect upon inflammatory hyperalgesia. Its mechanism of action seems dependent on adenosine production but not on modulation of hyperalgesic cytokine/chemokine production. In turn, adenosine acts peripherally on its A(1) receptor inhibiting hyperalgesia. FBP may have possible therapeutic applications in reducing inflammatory pain.

The fate of circulating biologically active peptides in the lungs

The factors which regulate the disappearance of endogenous active substances during pulmonary transit are discussed. The presence of hydrolytic enzymes in the cytosol is not the only factor regulating pulmonary metabolism. An uptake-transport process is required to permit access to intracellular enzymes. No endothelial cell transport mechanism has yet been described for peptides. However, bradykinin and angiotensin I are metabolized by the pulmonary circulation because the enzyme is localized on the luminal surface of the endothelial cells. The pulmonary and extrapulmonary conversion of angiotensin in rat is still a matter of debate. Evidence is presented which supports the idea that when low doses of angiotensin I (greater than 10 ng) are given intravenously, most of the conversion is pulmonary. With higher doses, extrapulmonary conversion also contributes to the final pressor effect of angiotensin I.

Treatment with DF 2162, a non-competitive allosteric inhibitor of CXCR1/2, diminishes neutrophil influx and inflammatory hypernociception in mice

BACKGROUND AND PURPOSE

Neutrophil migration into tissues is involved in the genesis of inflammatory pain. Here, we addressed the hypothesis that the effect of CXC chemokines on CXCR1/2 is important to induce neutrophil migration and inflammatory hypernociception.

EXPERIMENTAL APPROACH

Mice were treated with a non-competitive allosteric inhibitor of CXCR1/2, DF 2162, and neutrophil influx and inflammatory hypernociception were assessed by myeloperoxidase assay and electronic pressure meter test, respectively, in various models of inflammation.

KEY RESULTS

DF 2162 inhibited neutrophil chemotaxis induced by CXCR1/2 ligands but had no effect on CXCL8 binding to neutrophils. A single mutation of the allosteric site at CXCR1 abrogated the inhibitory effect of DF 2162 on CXCL-8-induced chemotaxis. Treatment with DF 2162 prevented influx of neutrophils and inflammatory hypernociception induced by CXCL1 in a dose-dependent manner. The compound inhibited neutrophil influx and inflammatory hypernociception induced by carrageenan, lipopolysaccharide and zymosan, but not hypernociception induced by dopamine and PGE(2). DF 2162 had a synergistic effect with indomethacin or the absence of TNFR1 to abrogate carrageenan-induced hypernociception. Treatment with DF 2162 diminished neutrophil influx, oedema formation, disease score and hypernociception in collagen-induced arthritis.

CONCLUSIONS AND IMPLICATIONS

CXCR1/2 mediates neutrophil migration and is involved in the cascade of events leading to inflammatory hypernociception. In addition to modifying fundamental pathological processes, non-competitive allosteric inhibitors of CXCR1/2 may have the additional benefit of providing partial relief for pain and, hence, may be a valid therapeutic target for further studies aimed at the development of new drugs for the treatment of rheumatoid arthritis.

Role of complement C5a in mechanical inflammatory hypernociception: potential use of C5a receptor antagonists to control inflammatory pain

BACKGROUND AND PURPOSE

C5a, a complement activation product, exhibits a broad spectrum of inflammatory activities particularly neutrophil chemoattraction. Herein, the role of C5a in the genesis of inflammatory hypernociception was investigated in rats and mice using the specific C5a receptor antagonist PMX53 (AcF-[OP(D-Cha)WR]).

EXPERIMENTAL APPROACH

Mechanical hypernociception was evaluated with a modification of the Randall-Selitto test in rats and electronic pressure meter paw test in mice. Cytokines were measured by ELISA and neutrophil migration was determined by myeloperoxidase activity.

KEY RESULTS

Local pretreatment of rats with PMX53 (60-180 microg per paw) inhibited zymosan-, carrageenan-, lipopolysaccharide (LPS)- and antigen-induced hypernociception. These effects were associated with C5a receptor blockade since PMX53 also inhibited the hypernociception induced by zymosan-activated serum and C5a but not by the direct-acting hypernociceptive mediators, prostaglandin E(2) and dopamine. Underlying the C5a hypernociceptive mechanisms, PMX53 did not alter the cytokine release induced by inflammatory stimuli. However, PMX53 inhibited cytokine-induced hypernociception. PMX53 also inhibited the recruitment of neutrophils induced by zymosan but not by carrageenan or LPS, indicating an involvement of neutrophils in the hypernociceptive effect of C5a. Furthermore, the C5a-induced hypernociception was reduced in neutrophil-depleted rats. Extending these findings in rats, blocking C5a receptors also reduced zymosan-induced joint hypernociception in mice.

CONCLUSIONS AND IMPLICATIONS

These results suggest that C5a is an important inflammatory hypernociceptive mediator, acting by a mechanism independent of hypernociceptive cytokine release, but dependent on the presence of neutrophils. Therefore, we suggest that inhibiting the action of C5a has therapeutic potential in the control of inflammatory pain.

Acute-phase protein alpha-1-acid glycoprotein mediates neutrophil migration failure in sepsis by a nitric oxide-dependent mechanism

The reduction of circulating neutrophil migration to infection sites is associated with a poor outcome of severe sepsis. alpha-1-Acid glycoprotein (AGP) was isolated from the sera of severely septic patients by HPLC and acrylamide gel electrophoresis and identified by mass spectrometry. Both the isolated protein and commercial AGP inhibited carrageenin-induced neutrophil migration into the rat peritoneal cavity when administered i.v. at a dose of 4.0 microg per rat (95 pmol per rat). Analysis by intravital microscopy demonstrated that both proteins inhibited the rolling and adhesion of leukocytes in the mesenteric microcirculation. The inhibitory activity was blocked by 50 mg/kg aminoguanidine, s.c., and was not demonstrable in inducible nitric oxide synthase (iNOS) knockout mice. Incubation of AGP with neutrophils from healthy subjects induced the production of NO and inhibited the neutrophil chemotaxis by an iNOS/NO/cyclic guanosine 3,5-monophosphate-dependent pathway. In addition, AGP induced the l-selectin shedding by neutrophils. The administration of AGP to rats with mild cecal ligation puncture sepsis inhibited neutrophil migration and reduced 7-day survival from approximately 80% to 20%. These data demonstrate that AGP, an acute-phase protein, inhibits neutrophil migration by an NO-dependent process and suggest that AGP also participates in human sepsis.

Peroxynitrite mediates the failure of neutrophil migration in severe polymicrobial sepsis in mice

BACKGROUND AND PURPOSE

Sepsis is a systemic inflammatory response resulting from the inability of the host to restrict local infection. The failure of neutrophil migration to the infection site is one of the mechanisms involved in this process. Recently, it was demonstrated that this event is mediated by nitric oxide (NO). The present study addresses the possibility that peroxynitrite (ONOO(-)), a NO-derived powerful oxidizing and nitrating compound, could also be involved in neutrophil migration failure.

EXPERIMENTAL APPROACH

Male C57Bl/6 mice were subjected to moderate (MSI) or severe (SSI) septic injury, both induced by cecal ligation and puncture (CLP). The leukocyte rolling and adhesion in the mesentery was evaluated by intravital microscopy. Cytokines (TNF-alpha and MIP-1alpha) were measured by ELISA and 3-nitrotyrosine (3-NT) by immunofluorescence.

KEY RESULTS

Compared with saline pretreatment of SSI mice, pre-treatment with uric acid, a ONOO(-) scavenger, partially restored the failure of neutrophil rolling, adhesion and migration to the site of infection. These mice also presented low circulating bacterial counts and diminished systemic inflammatory response. Pretreatment with uric acid reduced 3-NT labelling in leukocytes in mesenteric tissues and in neutrophils obtained from peritoneal exudates. Finally, uric acid pretreatment enhanced significantly the survival rate in the SSI mice. Similarly, treatment with FeTPPs, a more specific ONOO(-) scavenger, re-established neutrophil migration and increased mice survival rate.

CONCLUSIONS AND IMPLICATIONS

These results indicate that ONOO(-) contributed to the reduction of neutrophil/endothelium interaction and the consequent failure of neutrophil migration into infection foci and hence susceptibility to severe sepsis.

A novel technique to perform direct intraganglionar injections in rats

The present work describes a simple method for direct drug administration into the dorsal root ganglion (DRG) in anesthetized rats. This technique does not involve surgery, is easy to learn and allows behavioral testing within minutes after the injection. Based on landmarks that target the L5 DRG, an orifice was created with a guide needle through which a specially designed needle was inserted for solution injection. Its introduction into the ganglia was ensured by the triggering of an ipsilateral hindpaw reflex. The precision of the technique was checked by injections of the biological dye Pontamine Sky Blue (PSB) or C14-labeled arginine. There was no leakage of the dye to the surrounding tissues after a single 4 microl or three successive 2.5 microl injections (at 30-min intervals). Moreover, identical effects were observed with prostaglandin E2 (PGE2), morphine or glibenclamide injected intraplantarly or in the DRG, thus confirming the precision of the method and suggesting that the ganglion cells and peripheral nociceptors may display similar receptor population.

Heme oxygenase/carbon monoxide-biliverdin pathway down regulates neutrophil rolling, adhesion and migration in acute inflammation

BACKGROUND AND PURPOSE

Heme oxygenase (HO) activity is known to down-regulate inflammatory events. Here, we address the role of HO and its metabolites, carbon monoxide (CO) and biliverdin (BVD), in leukocyte rolling, adhesion and neutrophil migration during inflammatory processes.

EXPERIMENTAL APPROACH

Intravital microscopy was used to evaluate leukocyte rolling and adhesion in the mesenteric microcirculation of mice. TNFalpha and IL-1beta were determined by ELISA and HO-1 protein expression by Western blot.

KEY RESULTS

Intraperitoneal challenge with carrageenan enhanced HO-1 protein expression in mesentery and bilirubin concentration in peritoneal exudates. Pretreatment of mice with a non-specific inhibitor of HO (ZnDPBG) or with a HO-1 specific inhibitor (ZnPP IX) enhanced neutrophil migration, rolling and adhesion on endothelium induced by carrageenan. In contrast, HO substrate (hemin), CO donor (DMDC) or BVD reduced these parameters. The reduction of neutrophil recruitment promoted by HO metabolites was independent of the production of chemotactic cytokines. Inhibitory effects of CO, but not of BVD, were counteracted by treatment with a soluble guanylate cyclase (sGC) inhibitor, ODQ. Furthermore, inhibition of HO prevented the inhibitory effect of a nitric oxide (NO) donor (SNAP) upon neutrophil migration, while the blockade of NO synthase (NOS) activity by aminoguanidine did not affect the CO or BVD effects.

CONCLUSIONS AND IMPLICATIONS

Metabolites of HO decreased leukocyte rolling, adhesion and neutrophil migration to the inflammatory site by a mechanism partially dependent on sGC. Moreover, inhibition by NO of neutrophil migration was dependent on HO activity.

Atorvastatin inhibits inflammatory hypernociception

BACKGROUND AND PURPOSE

Atorvastatin is an inhibitor of the enzyme 3-hydroxyl-3-methylglutaryl coenzyme A reductase used to prevent coronary heart disease. We have studied the analgesic effect of atorvastatin in inflammatory models in which a sequential release of mediators (bradykinin, (BK), tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and the chemokine, KC/CXCL) links the stimulus with release of directly acting hypernociceptive mediators such as prostaglandin E(2) (PGE(2)).

EXPERIMENTAL APPROACH

The effects of orally administered atorvastatin on inflammatory mechanical hypernociception in mouse paws were evaluated with an electronic pressure-meter. Cytokines and PGE(2) were measured by ELISA and RIA.

KEY RESULTS

Treatment with atorvastatin for 3 days dose-dependently reduced hypernociception induced by lipopolysaccharide (LPS) or that following antigen challenge in sensitized animals. Atorvastatin pre-treatment reduced hypernociception induced by bradykinin and cytokines (TNF-alpha, IL-1beta and KC), and the release of IL-1beta and PGE(2) in paw skin, induced by lipopolysaccharide. The antinociceptive effect of atorvastatin on LPS-induced hypernociception was prevented by mevalonate co-treatment without affecting serum cholesterol levels. Hypernociception induced by PGE(2) was inhibited by atorvastatin, suggesting intracellular antinociceptive mechanisms for atorvastatin. The antinociceptive effect of atorvastatin upon LPS- or PGE(2)-induced hypernociception was prevented by non-selective inhibitors of nitric oxide synthase (NOS) but not by selective inhibition of inducible NOS or in mice lacking this enzyme.

CONCLUSIONS AND IMPLICATIONS

Antinociceptive effects of atorvastatin depend on inhibition of cytokines and prostanoid production and on stimulation of NO production by constitutive NOS. Our study suggests that statins may constitute a novel class of analgesic drugs.

Failure of neutrophil migration to infectious focus and cardiovascular changes on sepsis in rats: Effects of the inhibition of nitric oxide production, removal of infectious focus, and antimicrobial treatment

Recently, we demonstrated that mice under lethal sepsis present failure of neutrophil migration (FNM) to infectious focus, which is mediated by nitric oxide. The aims of the present study were to investigate whether FNM is also observed in severe sepsis induced by cecal ligation and puncture in rats and the effects of the prevention of nitric oxide production and of the elimination of the infectious focus through peritoneal lavage or by antimicrobial treatment on FNM and disease outcome. Rats were submitted to several septic stimuli (low, moderate, and severe) by cecal ligation and puncture. Severe septic stimulus animals presented FNM to the peritoneal cavity that was accompanied by large numbers of bacteria in the peritoneal cavity, blood, and liver and lung tissues; high cytokines (tumor necrosis factor alpha, interleukin [IL] 1beta, IL-6, cytokine-induced neutrophil chemoattractant 1, and IL-10) concentrations in the infection site, sera, and lung tissues; marked hypotension; and high mortality rate. The exhaustive lavage of the peritoneal cavity to reduce the infectious focus did not ameliorate the disease outcome. The association of lavage procedure with aminoguanidine treatment re-established neutrophil migration, but only delayed the death of the animals. In contrast, the antimicrobial treatment of severe septic stimulus animals with sulfamethoxazole and trimethoprim significantly improved the survival rate of the severe septic stimulus but did not re-establish neutrophil migration. However, the association of aminoguanidine plus sulfamethoxazole and trimethoprim brought about a significant increase in the survival rate and re-established neutrophil migration to infectious focus; reduced the colony-forming units in the peritoneal cavity, blood, and lung tissues; and caused an improvement in the cardiovascular performance. The results showed, for the first time, that the pharmacological prevention of FNM to the infectious focus associated with the antimicrobial therapy could be a new beneficial strategy for the treatment of sepsis syndrome.

Glutathione and the redox control system trypanothione/trypanothione reductase are involved in the protection of Leishmania spp. against nitrosothiol-induced cytotoxicity

Glutathione is the major intracellular antioxidant thiol protecting mammalian cells against oxidative stress induced by oxygen- and nitrogen-derived reactive species. In trypanosomes and leishmanias, trypanothione plays a central role in parasite protection against mammalian host defence systems by recycling trypanothione disulphide by the enzyme trypanothione reductase. Although Kinetoplastida parasites lack glutathione reductase, they maintain significant levels of glutathione. The aim of this study was to use Leishmania donovani trypanothione reductase gene mutant clones and different Leishmania species to examine the role of these two individual thiol systems in the protection mechanism against S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a nitrogen-derived reactive species donor. We found that the resistance to SNAP of different species of Leishmania was inversely correlated with their glutathione concentration but not with their total low-molecular weight thiol content (about 0.18 nmol/10(7) parasites, regardless Leishmania species). The glutathione concentration in L. amazonensis, L. donovani, L. major, and L. braziliensis were 0.12, 0.10, 0.08, and 0.04 nmol/10(7) parasites, respectively. L. amazonensis, that have a higher level of glutathione, were less susceptible to SNAP (30 and 100 microM). The IC50 values of SNAP determined to L. amazonensis, L. donovani, L. major, and L. braziliensis were 207.8, 188.5, 160.9, and 83 microM, respectively. We also observed that L. donovani mutants carrying only one trypanothione reductase allele had a decreased capacity to survive (approximately 40%) in the presence of SNAP (30-150 microM). In conclusion, the present data suggest that both antioxidant systems, glutathione and trypanothione/trypanothione reductase, participate in protection of Leishmania against the toxic effect of nitrogen-derived reactive species.

Effect of various acupuncture treatment protocols upon sepsis in Wistar rats

Sepsis is a syndrome characterized by infection and generalized inflammatory response that can lead to organ failure and death. In this study we standardize a model to investigate acupuncture's effects upon sepsis. the objectives were to study the use of acupuncture in the infectious process and to formulate acupuncture's treatment protocol for sepsis. The CLP (cecal ligation and puncture) model in rats was used to induce sepsis through bacterial entrance into the peritoneal cavity. An acupuncture treatment protocol that enhanced survival and reversed the neutrophil impairment migration toward the peritoneal cavity in rats with sepsis was achieved. It seems that acupuncture can be used for the treatment of experimental infectious processes. The effects of acupuncture and related mechanisms are discussed.

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.

An electronic pressure-meter nociception paw test for rats

The objective of the present investigation was to compare the sensitivity of an electronic nociceptive mechanical paw test with classical mechanical tests to quantify the intensity variation of inflammatory nociception. The electronic pressure-meter test consists of inducing the hindpaw flexion reflex by poking the plantar region with a polypropylene pipette tip adapted to a hand-held force transducer. This method was compared with the classical von Frey filaments test and with the rat paw constant pressure test, a modification of the Randall and Selitto test developed by our group. When comparing the three methods, the electronic pressure-meter and the rat paw constant pressure test, but not the von Frey filaments test, detected time vs treatment interactions in prostaglandin E2 (PGE2)-induced hypernociception. Both methods also detected the PGE2-induced hypernociception in dose- (50-400 ng/paw) and time- (1-4 h) dependent manners, and time vs treatment interactions induced by carrageenin (25-400 microg/paw). Furthermore, the electronic pressure-meter test was more sensitive at early times, whereas the constant pressure test was more sensitive at later times. Moreover, the electronic pressure-meter test detected the dose-dependent antinociceptive effect of local indomethacin (30-300 microg/paw) and dipyrone (80-320 microg/paw) on carrageenin- (200 microg/paw) and PGE2- (100 ng/paw) induced hypernociception, respectively, and also detected the ineffectiveness of indomethacin (300 microg) on the effect of PGE2. Our results show that the electronic pressure-meter provides a sensitive, objective and quantitative mechanical nociceptive test that could be useful to characterize new nociceptive inflammatory mediators and also to evaluate new peripheral analgesic substances.

An electronic pressure-meter nociception paw test for mice

The aim of the present investigation was to describe and validate an electronic mechanical test for quantification of the intensity of inflammatory nociception in mice. The electronic pressure-meter test consists of inducing the animal hindpaw flexion reflex by poking the plantar region with a polypropylene pipette tip adapted to a hand-held force transducer. This method was compared to the classical von Frey filaments test in which pressure intensity is automatically recorded after the nociceptive hindpaw flexion reflex. The electronic pressure-meter and the von Frey filaments were used to detect time versus treatment interactions of carrageenin-induced hypernociception. In two separate experiments, the electronic pressure-meter was more sensitive than the von Frey filaments for the detection of the increase in nociception (hypernociception) induced by small doses of carrageenin (30 microg). The electronic pressure-meter detected the antinociceptive effect of non-steroidal drugs in a dose-dependent manner. Indomethacin administered intraperitoneally (1.8-15 mg/kg) or intraplantarly (30-300 microg/paw) prevented the hypersensitive effect of carrageenin (100 microg/paw). The electronic pressure-meter also detected the hypernociceptive effect of prostaglandin E2 (PGE2; 10-100 ng) in a dose-dependent manner. The hypernociceptive effect of PGE2 (100 ng) was blocked by dipyrone (160 and 320 microg/paw) but not by intraplantar administration of indomethacin (300 microg/paw). The present results validate the use of the electronic pressure-meter as more sensitive than the von Frey filaments in mice. Furthermore, it is an objective and quantitative nociceptive test for the evaluation of the peripheral antinociceptive effect of anti-inflammatory analgesic drugs, which inhibit prostaglandin synthesis (indomethacin) or directly block the ongoing hypernociception (dipyrone).

Neutrophil migration induced by IL-8-activated mast cells is mediated by CINC-1

The aim of this study was to characterize the mediators released by mast cells responsible for IL-8-induced neutrophil migration. It was observed that IL-8 induces a dose-dependent neutrophil migration into peritoneal cavity of rats, but not into air-pouch cavity in which resident mast cells are not present. The transference of peritoneal mast cells to the air-pouch renders this cavity responsive to IL-8. The neutrophil migration induced by IL-8 into the peritoneal cavity was not observed when the peritoneal-resident mast cells were depleted by compound 48/80 or distilled water treatment. Confirming the importance of mast cells, IL-8-stimulated mast cells supernatant induced significant neutrophil migration when injected into peritoneal and air-pouch cavities. The IL-8-induced neutrophil migration was observed not to be dependent on LTB(4), prostaglandins or TNF-alpha, since MK886, indomethacin or thalidomide were unable to block the IL-8-induced neutrophil accumulation 'in vivo' or the release of neutrophil chemotactic factor "in vitro" by IL-8-stimulated mast cells. However, dexamethasone, an inhibitor of the synthesis of pro-inflammatory cytokines, blocked the neutrophil migration induced by IL-8 "in vivo" and also inhibited the release of the neutrophil chemotactic factor by IL-8-stimulated mast cells. Moreover, the incubation of IL-8-stimulated mast cells supernatant with antibody against cytokine-induced neutrophil chemoattractant 1 (CINC-1), but not against TNF-alpha or IL-1beta, inhibited its neutrophil chemotactic activity. Furthermore, we found a significant amount of CINC-1 in this supernatant. In conclusion, we demonstrated that the neutrophil migration induced by IL-8 is dependent on CINC-1 release from mast cells.

Involvement of NO in the failure of neutrophil migration in sepsis induced by Staphylococcus aureus

1. Sepsis induced by S. aureus was used to investigate whether neutrophil migration failure to infectious focus correlates with lethality in Gram-positive bacteria-induced sepsis in mice. 2. By contrast with the sub-lethal (SL-group), the lethal (L-group) intraperitoneal inoculum of S. aureus caused failure of neutrophil migration (92% reduction), high CFU in the exudate, bacteremia and impairment of in vitro neutrophil chemotactic activity. 3. Pre-treatments of L-group with adequate doses of aminoguanidine prevented the neutrophil migration failure and improved the survival of the animals (pre-treated: 43%; untreated: 0% survival). Thus, the impairment of neutrophil migration in the L-group appears to be mediated by nitric oxide (NO). 4. The injection of S. aureus SL-inoculum in iNOS deficient (-/-) or aminoguanidine-treated wild-type mice (pre- and post-treatment), which did not present neutrophil migration failure, paradoxically caused severe peritonitis and high mortality. This fact is explainable by the lack of NO dependent microbicidal activity in migrated neutrophils. 5. In conclusion, although the NO microbicidal mechanism is active in neutrophils, the failure of their migration to the infectious focus may be responsible for the severity and outcome of sepsis.

Peripheral analgesic sites of action of anti-inflammatory drugs

Inflammatory signs and symptoms of redness, swelling, heat and pain are due to the effects of inflammatory mediators released during the inflammatory response. Depending on the type of injurious stimuli and the tissue involved, the array of mediators may differ but eicosanoids are involved in the genesis of inflammatory pain. They are responsible for the hypersensitisation of the nociceptors (allodynialhyperalgesia). The basic mechanism of analgesic action of nonsteroidal anti-inflammatory drugs results from the inhibition of prostaglandin synthesis (prostacyclin or PGE2), thus preventing nociceptor threshold lowering. Because there is a temporal hierarchy in the release of inflammatory mediators, there are several targets for the action of peripheral acting analgesics before and after the inhibition of prostaglandin synthesis. Blockade of the release and inhibition of inducible cyclooxygenase explain the analgesic action of glucocorticoids. Nimesulide also has an inhibitory action on the cascade of hypersensitising cytokines. Some analgesics, such as dipyrone, flurbiprofen or diclofenac, act directly upon ongoing inflammatory hypersensitisation. Those analgesics restore the nociceptor by stimulating the arginine/NO/cGMP/K(ATP) channel pathway.

Sephadex induces eosinophil migration to the rat and mouse peritoneal cavity: involvement of mast cells, LTB4, TNF-alpha, IL-8 and PAF

OBJECTIVE AND DESIGN

In this study we investigated the chemotactic mediators involved in the Sephadex-induced eosinophil migration into the peritoneal cavities of rats and mice, and which resident peritoneal cells release these mediators.

MATERIALS AND METHODS

Sephadex suspension was injected into the peritoneal cavities of rats or mice which were pretreated, or not, with specific drugs that inhibit synthesis or production of the inflammatory mediators and eosinophil chemotactic activities were observed. To investigate the role of resident peritoneal cells as a source of these chemotactic factors, the macrophage population was enhanced or the mast cell population was depleted. The resident cells were also stimulated, in vitro, with Sephadex and the chemotactic activity of the supernatants was determined.

RESULTS

Sephadex induced dose and time dependent eosinophil migration in rats and mouse, which were inhibited by dexamethasone and MK 886. BN 52021 only affected the eosinophil migration into the mouse peritoneal cavity. An increase in the macrophage population did not alter the eosinophil migration induced by Sephadex in rat or mouse. However, mast cell population depletion reduced eosinophil migration in rats, but did not alter the migration in mice. Sephadex-stimulated rat mast cells released an eosinophil chemotactic factor whose release was inhibited by dexamethasone and MK 886. Anti-TNF-alpha and anti-IL-8 Abs inhibited the chemotactic activity of the mast cell supernatant.

CONCLUSION

Sephadex-induced eosinophil migration into the rat peritoneal cavity is dependent on mast cells, which release LTB4, TNF-alpha and CINC-1. Conversely, Sephadex-induced eosinophil migration into the mouse peritoneal cavity is mediated by PAF and LTB4, which are not released from resident macrophages or mast cells.

A comparative study of the antipyretic effects of indomethacin and dipyrone in rats

OBJECTIVE

Compare the antipyretic effects of dipyrone and indomethacin.

MATERIALS AND METHODS

Fever was induced in rats by i. v. LPS or i. c. v. interleukins (IL), prostaglandins (PG), arachidonic acid (AA), pre-formed pyrogenic factor (PFPF), tumour necrosis factor-alpha (TNF-alpha) or corticotrophin releasing hormone (CRH). Dipyrone and indomethacin were administered i.p., arginine vasopressin V1-receptor antagonist, d(CH2)5 Tyr(Me)AVP, into the ventral septal area. Cyclooxygenase (COX-1/-2) blocking activity was assessed in transfected COS-7 cells. CRH release from isolated hypothalami was determined by ELISA.

RESULTS

Indomethacin or dipyrone reduced LPS, IL-1beta, IL-6 or TNF-alpha induced fever and CRH release from rat hypothalamus. Only dipyrone inhibited IL-8, PFPF or PGF2alpha fever. Only indomethacin inhibited fever induced by AA or IL-1beta, plus AA. Neither antipyretic affected fever caused by PGE2 or CRH. d(CH2)5Tyr(Me)AVP only blocked antipyresis induced by indomethacin. Dipyrone at a very high concentration (10 mM) inhibited only COX-1, while indomethacin (0.1 microM) blocked COX-1 and COX-2 in COS-7 cells.

CONCLUSION

The antipyretic effect of dipyrone differs from that of indomethacin in that it does not depend on AVP release or inhibition of PG synthesis.

Tumour necrosis factor-alpha and leukotriene B(4) mediate the neutrophil migration in immune inflammation

1. We investigated the mediators responsible for neutrophil migration induced by ovalbumin (OVA) in immunized mice and the mechanisms involved in their release. 2. OVA administration promoted dose- and time-dependent neutrophil migration in immunized, but not in non-immunized mice, which was mediated by leukotriene B(4) (LTB(4)) and tumour necrosis factor (TNF)alpha, since it was inhibited by LTB(4) synthesis inhibitor (MK 886) or by LTB(4) receptor antagonist (CP 105,696), by dexamethasone and by antiserum to TNFalpha (82, 85, 63 and 87%, respectively). Confirming TNFalpha involvement, OVA challenge in immunized p55 TNF receptor deficient mice (p55(-/-)) did not promote neutrophil migration (control: 2.90 +/- 0.68; p55(-/-): 0.92+/-0.23 x 10(6) neutrophils cavity(-1)). 3. OVA-stimulated peritoneal cells from immunized mice released a neutrophil chemotactic factor which mimicked, in naive mice, neutrophil migration induced by OVA. 4. Supernatant chemotactic activity is due to TNFalpha and LTB(4), since its release was inhibited by MK 886 (93%) and dexamethasone (90%), and significant amounts of these mediators were detected. 5. TNFalpha and LTB(4) released by OVA challenge seem to act through a sequential mechanism, since MK 886 inhibited (88%) neutrophil migration induced by TNFalpha. Moreover, peritoneal cells stimulated with TNFalpha released LTB(4). 6. CD(4)(+) T cells are responsible for TNFalpha release, because the depletion of this subset prevented the release of TNFalpha (control: 400 +/- 25; immunized: 670 +/- 40; CD(4)(+) depleted: 435 +/- 18 pg ml(-1)). 7. In conclusion, neutrophil migration induced by OVA depends on TNFalpha released by CD(4)(+) cells, which acts through an LTB(4)-dependent mechanism.

Nitric oxide mediates the inhibition of neutrophil migration induced by systemic administration of LPS

To investigate the role of NO in the inhibition of neutrophil migration by circulating endotoxin, mice were pretreated with NO synthase inhibitors or with a free radical scavenger (D-penicillamine), before intravenous LPS injection. LPS dose-dependently inhibited the thioglycollate-induced neutrophil migration into the peritoneal cavities. Aminoguanidine, a selective inducible NO synthase inhibitor, abolished the inhibition of neutrophil migration and the increase in serum nitrate levels induced by a nonlethal dose of LPS. During lethal endotoxemia aminoguanidine partially abolished the neutrophil migration inhibition. Additionally, D-penicillamine prevented the inhibition of neutrophil migration caused by LPS. However, Nitro-L-Arginine, a selective constitutive NO synthase inhibitor, did not prevent neutrophil migration inhibition. Aminoguanidine treatment did not affect the systemic increased levels of TNF-alpha, IL-1beta, and IL-10, suggesting that NO is the final mediator involved in the inhibition of neutrophil migration. Our results suggest that NO released by the inducible NO synthase mediates the inhibition of neutrophil migration mediated by circulating LPS.

The major role of peripheral release of histamine and 5-hydroxytryptamine in formalin-induced nociception

Formalin injected subcutaneously into the paw is a widely used model of pain. This procedure evokes a short-lasting period of flinching (phase 1) and a long-lasting period of intense flinching (phase 2) following a very short period of quiescence. Phase 2 has been extensively used to support the involvement of central (spinal cord) sensitization in inflammatory hyperalgesia. The present study evaluated the contribution of stimulation of peripheral nociceptors by the release of endogenous mediators at the site of lesion. The participation of histamine and 5-hydroxytryptamine was demonstrated by the treatment of the rat hindpaws with selective histamine H1 (pyrilamine and meclizine) and histamine H2 (cimetidine) receptor antagonists or selective 5-hydroxytryptamine(1A) (WAY100,135) and 5-hydroxytryptamine(4/3) (tropisetron) receptor antagonists. The co-administration of pyrilamine or meclizine with formalin (1%) significantly reduced phases 1 and 2, while cimetidine had no effect. Pyrilamine administration during the period of quiescence (10min after formalin administration) caused strong dose-related inhibition of phase 2. The co-administration of tropisetron with formalin caused a blockade of both phases, while with WAY100,135 caused only inhibition of the phase 2. In contrast, tropisetron administrated during the period of quiescence did not cause antinociception. Histamine and 5-hydroxytryptamine receptors could be strongly activated in naïve animals by administration of a mixture of both agonists or compound 48/80 (2microg/paw) which is known to release both mediators from mast cells. Pretreatment of the paws with a mast cell stabilizer, sodium cromoglycate, significantly reduced the second phase of the formalin injection model. From these results we suggest that phases 1 and 2 of the formalin test are dependent upon the ongoing afferent input. Furthermore, while histamine H1 participates in both phases, 5-hydroxytryptamine(4/3) participates in phase 1 and 5-hydroxytryptamine(1A) in phase 2.

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-13

The effect of interleukin-13 (IL-13) on hyperalgesic responses to intraplantar (i.pl.) injection of carrageenin, E. coli endotoxin (LPS), bradykinin, tumour necrosis factor a (TNF-alpha), interleukin-1 beta (IL-1 beta), interleukin-8 (IL-8) and prostaglandin E(2) (PGE(2)) was investigated in a model of mechanical hyperalgesia in rats. Also, the cellular source of the IL-13 was investigated. IL-13, administered 30 min before the stimulus, inhibited responses to carrageenin, LPS, bradykinin, and TNF-alpha, but not responses to IL-1 beta, IL-8 and PGE2. IL-13, administered 2 hours before the injection of IL-1b, did not affect the response to IL-1b, whereas IL-13, administered 12 hours or 12 + 2 hours before the IL-1 beta, inhibited the hyperalgesia (- 35%, - 77%, respectively). In murine peritoneal macrophages, IL-13 administered 2 hours before stimulation with LPS, inhibited the production of IL-1 beta (- 67%) and PGE(2) (- 56%). IL-13 administered 12 hours before stimulation with LPS inhibited LPS-stimulated PGE(2) but not IL-1 beta. An anti-IL-13 serum potentiated responses to carrageenin, LPS, bradykinin and TNF-alpha (but not IL-1 beta and IL-8), as well as responses to bradykinin in rats depleted of mast cells with compound 40/80, but not in athymic rats. These data suggest that IL-13, released by lymphocytes, limits inflammatory hyperalgesia by the inhibition of the production TNF-alpha, IL-1 beta, IL-8 and PGs.

Role of the haeme oxygenase/carbon monoxide pathway in mechanical nociceptor hypersensitivity

The cleavage of haeme by haeme oxygenase (HO) yields carbon monoxide (CO), a biologically active molecule which exerts most of its effects via activation of soluble guanylate cyclase (sGC). In the present study, we tested the hypothesis that endogenous CO could modulate inflammatory hyperalgesia. The intensity of hyperalgesia was investigated in a model of mechanical nociceptor hypersensitivity in rats. The intra-plantar (i.pl.) administration of the HO inhibitor, ZnDPBG (Zinc deuteroporphyrin 2,4-bis glycol), potentiated in a dose-dependent manner the mechanical nociceptor hypersensitivity evoked by i.pl. administration of carrageenan. The mechanical hypersensitivity evoked by i.pl. injection of interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha), but not interleukin-8 (IL-8), prostaglandin E(2) (PGE(2)) or dopamine, was also enhanced by ZNDPBG: Moreover, the haeme (HO substrate) injection in the paws reduced the hypersensitivity evoked by IL-1beta, but not PGE(2). Furthermore, i.pl. administration of the gas CO reduced the hypersensitivity elicited by PGE(2). The inhibitory effect of haeme and CO upon mechanical nociceptor hypersensitivity were counteracted by a soluble guanylate cyclase (sGC) inhibitor, ODQ (1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one), suggesting that this effect of CO is mediated via cyclic GMP. Finally, the inhibitory effect of CO upon mechanical nociceptor hypersensitivity was prevented by the NO synthase blocker, L-NMMA (N(G)-monomethyl L-arginine), suggesting that the impairment of mechanical hypersensitivity elicited by CO depends on the integrity of the NO pathway. In conclusion, the results presented in this paper imply that endogenously CO produced by HO plays an anti-hyperalgesic role in inflamed paws, probably by increasing the intracellular levels of cyclic GMP in the primary afferent neurone.

Chronic intrathecal cannulation enhances nociceptive responses in rats

The influence of a chronically implanted spinal cannula on the nociceptive response induced by mechanical, chemical or thermal stimuli was evaluated. The hyperalgesia in response to mechanical stimulation induced by carrageenin or prostaglandin E2 (PGE2) was significantly increased in cannulated (Cn) rats, compared with naive (Nv) or sham-operated (Sh) rats. Only Cn animals presented an enhanced nociceptive response in the first phase of the formalin test when low doses were used (0.3 and 1%). The withdrawal latency to thermal stimulation of a paw inflamed by carrageenin was significantly reduced in Cn rats but not in Nv or Sh rats. In contrast to Nv and Sh rats, injection in Cn animals of a standard non-steroid anti-inflammatory drug, indomethacin, either intraperitoneally or into the spinal cord via an implanted cannula or by direct puncture of the intrathecal space significantly blocked the intensity of the hyperalgesia induced by PGE2. Cannulated animals treated with indomethacin also showed a significant inhibition of second phase formalin-induced paw flinches. Histopathological analysis of the spinal cord showed an increased frequency of mononuclear inflammatory cells in the Cn groups. Thus, the presence of a chronically implanted cannula seems to cause nociceptive spinal sensitization to mechanical, chemical and thermal stimulation, which can be blocked by indomethacin, thus suggesting that it may result from the spinal release of prostaglandins due to an ongoing mild inflammation.

Role of nitric oxide in the failure of neutrophil migration in sepsis

The cecal ligation and puncture (CLP) model was used to investigate whether failure of neutrophil migration occurs in sepsis and whether it correlates with disease outcome. It was observed that the severity of sepsis correlates with the number of punctures in the cecum: mice with 2 punctures (sublethal [SL]-CLP) developed mild peritonitis (100% survived), whereas mice with 12 punctures (lethal [L]-CLP) developed severe peritonitis and bacteremia that evolved to sepsis (none survived). The production of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-10 was higher in L-CLP than in SL-CLP mice. The impairment of neutrophil migration to the peritoneum and to the cecum wall was observed only in L-CLP mice. This phenomenon was shown to be mediated by nitric oxide, because aminoguanidine prevented the failure of neutrophil migration and improved the survival of L-CLP animals. In conclusion, impairment of neutrophil migration is a crucial event in the worsening of sepsis, and nitric oxide seems to be responsible for the phenomenon.

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-1 receptor antagonist

1. The effect of IL-1ra on response to intraplantar (i.pl.) injection of LPS, carrageenin, bradykinin, TNFalpha, IL-1beta, IL-8, PGE(2) and dopamine was investigated in a model of mechanical hyperalgesia in rats. 2. IL-1ra inhibited hyperalgesic response to LPS, carrageenin, bradykinin, TNFalpha, and IL-1beta, but not responses to IL-8, PGE(2) and dopamine. 3. A sheep anti-rat IL-1ra serum potentiated response to LPS, carrageenin, bradykinin, TNFalpha and IL-1beta but not IL-8. 4. Carrageenin and LPS stimulated and production of immunoreactive TNFalpha, IL-1beta and IL-1ra in the skin of injected paws. 5. The inhibition by IL-1ra of the hyperalgesic response to carrageenin was not affected by antibodies neutralizing IL-4 and IL-10. 6. In mice, IL-1ra inhibited the nociceptive response to i.p. injection of acetic acid. 7. These data suggest that IL-1ra, released at sites of inflammation, limits inflammatory hyperalgesia. This effect is independent of (IL-1ra-induced) IL-4 and IL-10 and appears to be the result of antagonism by IL-1ra of IL-1beta-stimulated eicosanoid production.

Analgesic effect of thalidomide on inflammatory pain

Tumor necrosis factor alpha (TNF-alpha) may have a pivotal role in the genesis of mechanical inflammatory hyperalgesia in rats and in the nociceptive writhing response in mice. Thalidomide has been shown to selectively inhibit TNF-alpha production. We therefore investigated the effect of thalidomide on these responses as well as on the hot plate response in mice. Hyperalgesic responses to intraplantar (i.pl.) injections of carrageenin or bradykinin, which act by stimulating TNF-alpha release, but not responses to TNF-alpha or prostaglandin E(2), were inhibited in a dose-dependent manner by pretreatment of the animals with thalidomide. The nociceptive writhing responses induced by intraperitoneal (i.p.) injections of zymosan or acetic acid were also inhibited in a dose-dependent manner by pretreatment of mice with thalidomide. Moreover, the thalidomide pretreatment also reduced the TNF-alpha mRNA levels in the peritoneal cells induced by injection of zymosan in mice. The analgesic effect of thalidomide is not due to a central effect, since the drug had no effect in the hot plate test. The demonstration that thalidomide is able to inhibit inflammatory hyperalgesia in rats and the writhing nociceptive response in mice suggests that these analgesic effects seem to be a consequence of the inhibition of TNF-alpha production, and indicates the need for investigations on the possibility of the use of thalidomide for the treatment of pain refractory to classical non-narcotic analgesics.

Angiotensin converting enzyme: history and relevance

The renin angiotensin system (RAS) is now recognized as the body's most powerful hormone system for controlling renal hemodynamics and sodium excretion and, therefore, body fluid volumes and arterial pressure. The discovery of angiotensin converting enzyme inhibitors (ACEi) was a keystone for the understanding of the significance of the RAS since ACEi proved to be effective in controlling hypertension and heart failure and in preventing the development of the vascular injury of chronic diseases like scleroderma and diabetes mellitus. The success of ACEi stimulated the research into inhibitors of other actors of the RAS like renin or angiotensin receptor antagonists. It is not often realized that the discovery of ACEi owes a great deal to basic research in which the venom of a Brazilian viper, Bothrops Jararaca, was instrumental for the discovery of bradykinin by Rocha e Silva and the bradykinin potentiating factor. This article reviews the contribution of the converting enzyme inhibitors for the demonstration of the relevance of the RAS to several human pathologies.

Involvement of resident macrophages and mast cells in the writhing nociceptive response induced by zymosan and acetic acid in mice

Intraperitoneal administration of zymosan and acetic acid induced a dose-dependent nociceptive writhing response in mice. Lavage of the peritoneal cavities with saline reduced the number of total resident peritoneal cells and caused a proportional decrease in the nociceptive responses induced by these stimuli. Furthermore, the specific reduction of the peritoneal mast cell population by intraperitoneal administration of compound 48/80 also reduced the nociceptive responses induced by zymosan and acetic acid. In contrast, enhancement of the peritoneal macrophage population by pretreatment of the cavities with thioglycollate caused an increase in the number of writhes induced by both stimuli. These data suggest that the nociceptive responses induced by zymosan and acetic acid are dependent upon the peritoneal resident macrophages and mast cells. These cells modulate the nociceptive response induced by zymosan and acetic acid via release of tumour necrosis factor alpha (TNF-alpha), interleukin 1beta and interleukin 8. This suggestion is supported by the following observations: (a) pretreatment of the peritoneal cavities with antisera against these cytokines reduced the nociceptive responses induced by these stimuli; (b) peritoneal cells harvested from cavities injected with zymosan or acetic acid released both interleukin 1beta and TNF-alpha; (c) although individual injection of TNF-alpha, interleukin 1beta or interleukin 8 did not induce the nociceptive effect, intraperitoneal injection of a mixture of these three recombinant cytokines caused a significant nociceptive writhing response. In conclusion, our results suggest that the nociceptive activity of zymosan and acetic acid in the writhing model is due to the release of TNF-alpha, interleukin 1beta and interleukin 8 by resident peritoneal macrophages and mast cells.

L-NAME causes antinociception by stimulation of the arginine-NO-cGMP pathway

NG-nitro-L-arginine methyl ester (L-NAME) has been used extensively as a paradigmatic inhibitor of NO synthase and has been shown to cause antinociception in several experimental models. We describe here how L-NAME produced a dose-dependent antinociceptive effect when injected intraperitoneally in the mouse after acetic acid induced writhings, or intraplantarly in the rat paw pressure hyperalgesia induced by carrageenin or prostaglandin E2. In contrast another NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), had no significant effect per se but inhibited L-NAME systemic induced antinociception in mice and local induced antinociception in the rat paw hyperalgesia test. D-NAME had no antinociceptive effect upon carrageenin-induced hyperalgesia. Pretreatment of the paws with two inhibitors of guanylate cyclase, methylene blue (MB) and 1H-:[1,2,4]-oxadiazolo-:[4,3-a] quinoxalin-1-one (ODQ) abolished the antinociceptive effect of L-NAME. L-Arginine and the cGMP phosphodiesterase inhibitor, MY 5445 significantly enhanced the L-NAME antinociceptive effect. The central antinociceptive effect of L-NAME was blocked by co-administration of L-NMMA, ODQ and MB. The present series of experiments shows that L-NAME, but not L-NMMA, has an antinociceptive effect. It can be suggested that L-NAME causes the antinociceptive effect by stimulation of the arginine/ NO/ cGMP pathway, since the antinociceptive effect of L-NAME can be antagonized by L-NMMA and abolished by the guanylate cyclase inhibitors (MB and ODQ). In addition, the NO synthase substrate, L-arginine and the cGMP phosphodiesterase inhibitor, MY5445 were seen to potentiate the effects of L-NAME. Thus, L-NAME used alone, has limitations as a specific inhibitor of the arginine-NO-cGMP pathway and may therefore be a poor pharmacological tool for use in characterising participation in pathophysiological processes.

Glutathione protects macrophages and Leishmania major against nitric oxide-mediated cytotoxicity

The aim of this investigation was to examine whether macrophage and Leishmania major glutathione were involved in either host or parasite protection against NO cytotoxicity. Buthionine sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthase, caused a complete and irreversible depletion of macrophage glutathione, but only a 20% and reversible decrease in L. major glutathione. Glutathione-depleted macrophages, when activated with IFN-gamma/LPS, released less than 60% of the NO produced by untreated macrophages, resulting in a corresponding decrease in their leishmanicidal activity. BSO-treated macrophages were more susceptible to the cytotoxic effects of the NO donor SNAP. Treatment of macrophages with 1,3-bis(chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase and trypanothione reductase or with Br-Octane, a glutathione-S-transferase substrate, resulted in a transient decrease in glutathione levels and did not increase the susceptibility of the macrophages to SNAP. Treatment of the promastigote forms of L. major with BCNU resulted in an 80% decrease in total glutathione concentration with no concomitant change in viability. However, this treatment rendered the parasites more susceptible to SNAP. Finally, macrophage glutathione protected the internalized L. major from SNAP. Overall, these results demonstrate that glutathione is an essential protective component against NO cytotoxicity on both macrophages and parasites.

Pharmacological modulation of secondary mediator systems--cyclic AMP and cyclic GMP--on inflammatory hyperalgesia

1. The objective of the present paper was to evaluate the relevance of neuronal balance of cyclic AMP and cyclic GMP concentration for functional regulation of nociceptor sensitivity during inflammation. 2. Injection of PGE2 (10-100 ng paw-1) evoked a dose-dependent hyperalgesic effect which was mediated via a cyclic AMP-activated protein kinase (PKA) inasmuch as hyperalgesia was blocked by the PKA inhibitor H89. 3. The PDE4 inhibitor rolipram and RP73401, but not PDE3 and PDE5 inhibitors potentiated the hyperalgesic effects of PGE2. The hyperalgesic effect of dopamine was also enhanced by rolipram. Moreover, rolipram significantly potentiated hyperalgesia induced by carrageenan, bradykinin, TNF alpha, IL-1 beta, IL-6 and IL-8. This suggests that neuronal cyclic AMP mediates the prostanoid and sympathetic components of mechanical hyperalgesia. Moreover, in the neuron cyclic AMP is mainly metabolized by PDE4. 4. To examine the role of the NO/cyclic GMP pathway in modulating mechanical hyperalgesia, we tested the effects of the soluble guanylate cyclase inhibitor, ODQ. This substance counteracts the inhibitory effects of the NO donor, SNAP, on the hyperalgesia induced by PGE2. 5. The ODQ potentiated hyperalgesia induced by carrageenan, bradykinin, TNF alpha, IL-1 beta, IL-6 and IL-8. In contrast, ODQ had no significant effect on the hyperalgesia induced by PGE2 and dopamine. This indicates that the hyperalgesic cytokines may activate soluble guanylate cyclase, which down-regulate the ability of these substances to cause hyperalgesia. This event appears not to be mediated by prostaglandin or dopamine. 6. In conclusion, the results presented in this paper confirm an association between (i) hyperalgesia and elevated levels of cyclic AMP as well as (ii) antinociception and elevated levels of cyclic GMP. The intracellular levels of cyclic AMP that enhance hyperalgesia are controlled by the PDE4 isoform and appear to result in activation of protein kinase A whereas the intracellular levels of cyclic GMP results from activation of a soluble guanylate cyclase.

Bradykinin B1 and B2 receptors, tumour necrosis factor alpha and inflammatory hyperalgesia

The effects of BK agonists and antagonists, and other hyperalgesic/antihyperalgesic drugs were measured (3 h after injection of hyperalgesic drugs) in a model of mechanical hyperalgesia (the end-point of which was indicated by a brief apnoea, the retraction of the head and forepaws, and muscular tremor). DALBK inhibited responses to carrageenin, bradykinin, DABK, and kallidin. Responses to kallidin and DABK were inhibited by indomethacin or atenolol and abolished by the combination of indomethacin + atenolol. DALBK or HOE 140, given 30 min before, but not 2 h after, carrageenin, BK, DABK and kallidin reduced hyperalgesic responses to these agents. A small dose of DABK+ a small dose of BK evoked a response similar to the response to a much larger dose of DABK or BK, given alone. Responses to BK were antagonized by HOE 140 whereas DALBK antagonized only responses to larger doses of BK. The combination of a small dose of DALBK with a small dose of HOE 140 abolished the response to BK. The hyperalgesic response to LPS (1 microg) was inhibited by DALBK or HOE 140 and abolished by DALBK + HOE 140. The hyperalgesic response to LPS (5 microg) was not antagonized by DALBK + HOE 140. These data suggest: (a) a predominant role for B2 receptors in mediating hyperalgesic responses to BK and to drugs that stimulate BK release, and (b) activation of the hyperalgesic cytokine cascade independently of both B1 and B2 receptors if the hyperalgesic stimulus is of sufficient magnitude.

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-4

1. The effect of IL-4 on responses to intraplantar (i.pl.) carrageenin, bradykinin, TNFalpha, IL-1beta, IL-8 and PGE2 was investigated in a model of mechanical hyperalgesia in rats. Also, the cellular source of the IL-4 was investigated. 2. IL-4, 30 min before the stimulus, inhibited responses to carrageenin, bradykinin, and TNFalpha, but not responses to IL-1beta, IL-8 and PGE2. 3. IL-4, 2 h before the injection of IL-1beta, did not affect the response to IL-1beta, whereas IL-4, 12 or 12+2 h before the IL-1beta, inhibited the hyperalgesia (-30%, -74%, respectively). 4. In murine peritoneal macrophages, murine IL-4 for 2 h before stimulation with LPS, inhibited (-40%) the production of IL-1beta but not PGE2. Murine IL-4 (for 16 h before stimulation with LPS) inhibited LPS-stimulated PGE2 but not IL-1beta. 5. Anti-murine IL-4 antibodies potentiated responses to carrageenin, bradykinin and TNFalpha, but not IL-1beta and IL-8, as well as responses to bradykinin in athymic rats but not in rats depleted of mast cells with compound 40/80. 6. These data suggest that IL-4 released by mast cells limits inflammatory hyperalgesia. During the early phase of the inflammatory response the mode of action of the IL-4 appears to be inhibition of the production TNFalpha, IL-1beta and IL-8. In the later phase of the response, in addition to inhibiting the production of pro-inflammatory cytokines, IL-4 also may inhibit the release of PGs.

Microbicidal activity of eosinophils is associated with activation of the arginine-NO pathway

In order to investigate the ability of rat peritoneal eosinophils to produce nitric oxide (NO) induced by cytokines in vitro, these cells were activated with several cytokines (IL-5, IL-8, Rantes, TNF-alpha, IFN-gamma) in association or not with LPS. Under these conditions, we were able to detect nitrite in the incubation medium when the eosinophils were stimulated with IFN-gamma or IL-8 in the presence of LPS. LPS alone also induced nitrite production. Significant levels of nitrite in the medium were already present after 12 h of stimulation and increased steadily within the next 48 h. Regarding NO synthase, its highest activity was achieved at 12 h after IFN-gamma/LPS stimulation. After this peak, the enzymatic activity reduced gradually to control levels 48 h after the stimulation. The simultaneous addition of the NO synthase inhibitor L-NIO (100 microM) to the eosinophil suspension blocked nitrite production and NO synthase activity. On the other hand, neither IL-5, Rantes nor TNF-alpha were able to induce the release of nitrite in the presence or absence of LPS. To evaluate the microbicidal effect of these cells against the Leishmania parasite, eosinophils were infected with Leishmania major. It was observed that these cells were able to produce nitrite and to kill the parasite after activation with LPS/IFN-gamma. Moreover, L-NIO blocked this leishmanicidal activity and the nitrite production. Our results suggest that activated eosinophils release NO which is involved in their microbicidal activity against Leishmania major.

Nitric oxide mediates the microbicidal activity of eosinophils

There are several experimental evidences that nitric oxide (NO) is involved in the microbicidal activity of macrophages against a number of intracellular pathogens including Leishmania major, Trypanozoma cruzi, Toxoplasma gondii. It is also well known that eosinophils (EO) have microbicidal activity against many parasites such as Schistosoma mansoni, Trichinella spiralis, T. cruzi and L. amazonensis. The purpose of this study was to investigate if NO is involved in the microbicidal activity of EO against L. major. Eosinophils harvested from peritoneal cavity of rats released spontaneously after 24 and 48 hr a small amount of nitrite. This release was enhanced by the treatment of cells with IFN-gamma (200 IU/ml). This release was blocked by addition of the NO synthase inhibitor, L-NIO (100 microM) into the culture. To determinate the leishmanicidal activity of eosinophils the parasites were incubated with activated eosinophils with IFN-gamma and the ability of surviving parasites to incorporate [(3)H] thymidine was evaluated. IFN-gamma-activated eosinophils were able to kill L. major and to release high levels of nitrite. The ability to destroy L. major and the release of NO were completely blocked by L-NIO. These results indicate that activated eosinophils release NO which is involved in the microbicidal activity of these cells against L. major.

Participation of interleukin-5, interleukin-8 and leukotriene B4 in eosinophil accumulation in two different experimental models

There are several experimental models describing in vivo eosinophil (EO) migration, including ip injection of a large volume of saline (SAL) or Sephadex beads (SEP). The aim of this study was to investigate the mechanisms involved in the EO migration in these two models. Two consecutive injections of SAL given 48 hr apart, induced a selective recruitment of EO into peritoneal cavity of rats, which peaked 48 hr after the last injection. SEP, when injected ip, promoted EO accumulation in rats. The phenomenon was dose-related and peaked 48 hr after SEP injection. To investigate the mediators involved in this process we showed that BW A4C, MK 886 and dexamethasone (DXA) inhibited the EO migration induced by SAL and SEP. To investigate the source of the EO chemotactic factor we showed that mast cells, macrophages (MO), but not lymphocytes, incubated in vitro in presence of SAL released a factor which induced EO migration. With SEP, only mast cells release a factor that induced EO migration, which was inhibited by BW A4c, MK 886 and DXA. Furthermore, the chemotactic activity of SAL-stimulated mast cells was inhibited by antisera against IL-5 and IL-8 (interleukins). SAL-stimulated MO were only inhibited by anti-IL-8 antibodies as well SEP-stimulated mast cells. These results suggest that the EO migration induced by SAL may be dependent on resident mast cells and MO and mediated by LTB4, IL-5 and IL-8. SEP-induced EO migration was dependent on mast cells and may be mediated by LTB4 and IL-8. Furthermore, IL-5 and IL-8 induced EO migration, which was also dependent on resident cells and mediated by LTB4. In conclusion, EO migration induced by SAL is dependent on mast cells and MO, whereas that induced by SEP is dependent on mast cells alone. Stimulated mast cells release LTB4, IL-5 and IL-8 while MO release LTB4 and IL-8. The IL-5 and IL-8 release by the SAL or SEP-stimulated resident cells may act in an autocrine fashion, thus potentiating LTB4 release.