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

The annonalide diterpene extracted from Casimirella ampla (Miers) reduces inflammatory and antinociceptive events in general models of inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

The plants of the genus Casimirella ampla (Miers) (C. ampla) are extensively used in folk medicine. For a long time, rural communities have been using extracts from its roots for food and therapeutic purposes. The extract is rich in diterpenoid annonalide (Annona), which has antiophidic, anti-inflammatory and antinociceptive properties. Inflammation is the body's primary defense mechanism against cell damage and invasion by pathogens, which can trigger acute and chronic inflammatory processes. The first line of treatment for this condition consists of the use of non-steroidal anti-inflammatory drugs, but these have numerous associated collateral damages, based on scientific knowledge about diterpenoids from C. ampla, as well as their already reported antinociceptive and anti-inflammatory properties.

AIMS OF THE STUDY

Evaluate the effect of Annona in classic models of inflammation and pain.

MATERIALS AND METHODS

Animals were pretreated with Annona (0.1, 1.0 and 10 mg/kg), or Tween 80 (2%), or indomethacin (Indo) (10 mg/kg) orally in the paw edema tests induced by carrageenan (Cg), serotonin (5-HT), histamine, bradykinin, 48/80 and, prostaglandin E2 (PGE2), evaluating microscopic lesion scores, migration of leukocytes to the peritoneal cavity, concentration of myeloperoxide (MPO), malonyldialdehyde (MDA) and glutathione (GSH), abdominal contortion test by acetic acid and formalin test.

RESULTS

Treatment with Annona compound at a dose of 0.1 mg/kg was more effective in reducing inflammatory, oxidant and nociceptive parameters, as it reduced paw edema induced by carrageenan, through different mediators and migration of inflammatory cells. Furthermore, it worked by reducing the concentration of MPO, MDA, preserving GSH levels and reducing nociception caused by formalin and acetic acid.

Oral treatment with Berberine reduces peripheral nociception: Possible interaction with different nociceptive pathways activated by different allogeneic substances

ETHNOPHARMACOLOGICAL RELEVANCE

Berberine was identified in extracts of Berberis ruscifolia Lam., a plant used in traditional medicine as an analgesic. Its presence may be involved in the reported pharmacological activity of this species. However, there is still a lack of scientific research concerning its analgesic activity in the peripheral nervous system.

AIM OF THE STUDY

To investigate Berb-induced antinociception in the formalin test and to evaluate several pathways related to its pharmacological antinociceptive effects in chemical models of nociception in mice.

MATERIALS AND METHODS

The antinociceptive activity of Berb was assessed by inducing the paw licking in mice with different allodynic agents. In the formalin test, the antiedematous and antithermal effect of Berb was evaluated simultaneously in the same experiment. Other nociceptive behavior produced by endogenous [prostaglandin E2 (PGE2), histamine (His), glutamate (Glu) or bradykinin (BK)] or exogenous [capsaicin (Caps) and cinnamaldehyde (Cin)] chemical stimuli, and activators as protein kinase A (PKA) and C (PKC), were also evaluated.The in vivo doses for p.o. were 3 and 30 mg/kg.

RESULTS

Berb, at 30 mg/kg p.o., showed a significant inhibition of the nociceptive action in formalin in both phases being stronger at the inflammatory phase (59 ± 9%) and more active than Asp (positive control) considering the doses evaluated. Moreover, Berb inhibited the edema (34 ± 10%), but not the temperature in the formalin test. Regarding the different nociceptive signaling pathways evaluated, the most relevant data were that the administration of p.o. of Berb, at 30 mg/kg, caused significant inhibition of nociception induced by endogenous [His (72 ± 11%), PGE2 (78 ± 4%), and BK (51 ± 7%)], exogenous [Cap (68 ± 4%) and Cinn (57 ± 5%)] compounds, and activators of the PKA [(FSK (86 ± 3%)] and PKC [(PMA(86 ± 6%)] signaling pathway. Berb did not inhibit the nociceptive effect produced by Glu.

CONCLUSION

The present study demonstrated, for the first time, the potential of Berb in several nociceptive tests, with the compound present in B. ruscifolia contributing to the analgesic effect reported for this species.

Effect of sound-induced repeated stress on the development of pain and inflammation in the temporomandibular joint of female and male rats

Temporomandibular disorder (TMD) is a common painful condition of the temporomandibular joint (TMJ) and associated structures. Stress is a significant risk factor for developing this painful condition that predominantly affects women. This study aimed to test the hypothesis that stress increases the risk of developing TMJ pain by facilitating inflammatory mechanisms in female and male rats. To test this hypothesis, we evaluated TMJ carrageenan-induced expression of pro-inflammatory cytokines and migration of inflammatory cells and TMJ formalin-induced nociception in female and male rats submitted to a repeated stress protocol induced by sound. We found that sound-induced repeated stress facilitates TMJ inflammation and contributes to TMJ nociception development equally in females and males. We conclude that stress is a risk factor for developing painful TMJ conditions in males and females, at least in part, by favoring the inflammatory process similarly in both sexes.

Antinociceptive effect and identification of berberine alkaloid in Berberis ruscifolia extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Aerial parts (leaves and stems) of Berberis ruscifolia Lam. are a usual preparation as an analgesic, anti-inflammatory, antimalarial, antibacterial, and digestive in folk medicine. However, there were no previous studies of its chemical composition and biological activity related to analgesic effects.

THE OBJECTIVE OF THE STUDY

The evaluation of the anti-nociception of the infusion (I), the decoction (D), and the ethanolic extract (EE) obtained from aerial parts of B. ruscifolia and its main chemical constituent in them, in mouse models.

MATERIAL AND METHODS

The chemical constituent of B. ruscifolia extracts was evaluated and quantified by LC-MS and HPLC methodology. The inhibition of nociception in mice was analyzed by formalin and acetic acid-induced contortions tests. Also, when the formalin test was performed to evaluate the antinociceptive activity, the inhibition of edema formation and the antipyretic effect of each extract were simultaneously evaluated in the same experiment. For the oral administration in the in vivo assays, doses ranging from 10 to 1000 mg/kg and 10-30 mg/kg were used for extract and the chemical compound, respectively.

RESULTS

The presence of berberine (Berb) was identified in the three evaluated extracts where the EE showed the highest content of this compound getting a yield of 2%, while in the I and D, Berb is present at 0.2%. The three extracts promoted a reduction of the contortions induced by acetic acid, being observed in EE the highest activity with 63 ± 6% of significant inhibition of the nociceptive behavior at a dose of 300 mg/kg, while D significantly inhibited 32 ± 12% at the same dose and for I at a dose of 1000 mg/kg an inhibition of 44 ± 8% was observed. Likewise, in the formalin trial, I and EE reduced nociception at a dose of 1000 (31 ± 5%) and 300 (35 ± 3%) mg/kg, respectively in the neurogenic phase, while in the second phase of the experiment, all the extracts evaluated showed an antinociceptive effect, with significant inhibition of I of 54 ± 6% and D of 44 ± 5% at a dose of 1000 mg/kg and for EE showed a 63 ± 2% inhibition at a dose of 300 mg/kg being the one with the highest antinociceptive activity. These extracts showed no inhibition in temperature and formalin-injected paw edema formation when compared to the control. As for Berb, at a 30 mg/kg dose, it showed significant inhibition of 70 ± 5% in the acetic acid-induced contortion test.

CONCLUSION

Altogether, the present results evidenced the analgesic properties of B. ruscifolia, scientific information presented for the first time, and also provided important knowledge not reported so far about the chemical composition of its extracts, by identifying the presence of Berb in them. Finally, we were able to conclude that the analgesic effect demonstrated by this medicinal plant is partly due to the presence of Berb.

The Interactions of Magnesium Sulfate and Cromoglycate in a Rat Model of Orofacial Pain; The Role of Magnesium on Mast Cell Degranulation in Neuroinflammation

Mast cell degranulation impacts the development of pain and inflammation during tissue injury. We investigated the antinociceptive effect of a combination of cromoglycate and magnesium in the orofacial model of pain and the histological profile of the effect of magnesium in orofacial pain. In male Wistar rats, formalin (1.5%, 100 µL) was injected subcutaneously into the right upper lip of rats after cromoglycate and/or magnesium. Pain was measured as the total time spent on pain-related behavior. Toluidine blue staining was used to visualize mast cells under the light microscope. In the formalin test, in phase 1, magnesium antagonized the antinociceptive effect of cromoglycate, while in phase 2, it potentiated or inhibited its effect. Magnesium significantly reduced mast cell degranulation in the acute phase by about 23% and in the second phase by about 40%. Pearson’s coefficient did not show a significant correlation between mast cell degranulation and pain under treatment with magnesium. The cromoglycate–magnesium sulfate combination may prevent the development of inflammatory orofacial pain. The effect of a combination of cromoglycate–magnesium sulfate depends on the nature of the pain and the individual effects of the drugs. Magnesium reduced orofacial inflammation in the periphery, and this effect did not significantly contribute to its analgesic effect.

Can chronic spontaneous urticarial produce symptoms of neuropathic pain?

BACKGROUND

Chronic spontaneous urticaria (CSU) is a condition that is associated with recurrent pruritic hives and/or angioedema lasting for more than 6 weeks and is known to affect 1% of the population. Neuropathic pain can be defined as abnormal pain in the peripheral or central nervous system following injury and results from dysfunctions in the peripheral or central nervous system without peripheral nociceptor stimulation. Histamine appears in the pathogenesis of both the CSU and diseases of the neuropathic pain spectrum.

OBJECTIVE

To evaluate the symptoms of neuropathic pain in patients with CSU using scales.

METHOD

Fifty-one patients with CSU and 47 sex- and age-matched healthy controls were included in the study.

RESULTS

The results of the short-form McGill Pain Questionnaire revealed the scores in the sensory and affective domains, Visual Analogue Scale (VAS) scores and pain indices to be significantly higher in the patient group (p < 0.05 for all cases), while the overall pain assessment and sensory assessment based on the Self-Administered Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) pain scale were also significantly higher in the patient group. Based on the assumption that scores of > 12 indicated neuropathy, 27 (53%) of the patients in the patient group and 8 (17%) in the control group were found to have neuropathy (p < 0.05).

STUDY LIMITATIONS

Cross-sectional study, small patient sample and use of self-reported scales.

CONCLUSION

In addition to itching, patients with CSU should be aware of the potential for the association of neuropathic pain. In this chronic disease that is known to affect the quality of life, using an integrated approach with the patients and identifying accompanying problems are as important as treating the dermatological disorder.

Tibouchina granulosa Leaves Present Anti-Inflammatory Effect

The ethanol extract (EE) prepared from the leaves of Tibouchina granulosa, and its fraction in ethyl acetate (fEA) were evaluated concerning their capacity to reduce inflammation in different experimental models. fEA was also studied concerning its chemical constituents. EE and fEA were assayed for their anti-inflammatory potential, using formalin-induced licking behavior and carrageenan-induced inflammation into the subcutaneous air pouch (SAP) models. Reduction in polymorphonuclear cells (PMN) activation was performed in freshly isolated PMN. Chromatographic analysis of fEA was performed by HPLC-DAD. Hispiduloside was isolated as the main constituent in fEA, and its quantity was estimated to be 39.3% in fEA. EE (30 mg/kg) significantly reduced the second phase of formalin-induced licking. fEA demonstrated a reduction in leukocyte migration into the SAP. EE and fEA drastically reduced cytokines (TNF-α, IL-1β, and IFN-γ), nitric oxide (NO) production, in vitro PMN migration induced by C5a and IL-8, and TNF-α and IL-1β gene expression. Taken together, our data indicate that either ethanol extract or its fEA fraction from leaves of T. granulosa present an anti-inflammatory effect, contributing to the pharmacological and chemical knowledge of this species and confirming the rationale behind its traditional use.

Characterization of the Dahl salt-sensitive rat as a rodent model of inherited, widespread, persistent pain

Animal models are essential for studying the pathophysiology of chronic pain disorders and as screening tools for new therapies. However, most models available do not reproduce key characteristics of clinical persistent pain. This has limited their ability to accurately predict which new medicines will be clinically effective. Here, we characterize the Dahl salt-sensitive (SS) rat strain as the first rodent model of inherited widespread hyperalgesia. We show that this strain exhibits physiological phenotypes known to contribute to chronic pain, such as neuroinflammation, defective endogenous pain modulation, dysfunctional hypothalamic-pituitary-adrenal axis, increased oxidative stress and immune cell activation. When compared with Sprague Dawley and Brown Norway rats, SS rats have lower nociceptive thresholds due to increased inflammatory mediator concentrations, lower corticosterone levels, and high oxidative stress. Treatment with dexamethasone, the reactive oxygen species scavenger tempol, or the glial inhibitor minocycline attenuated the pain sensitivity in SS rats without affecting the other strains while indomethacin and gabapentin provided less robust pain relief. Moreover, SS rats presented impaired diffuse noxious inhibitory controls and an exacerbated response to the proalgesic mediator PGE₂, features of generalized pain conditions. These data establish this strain as a novel model of spontaneous, widespread hyperalgesia that can be used to identify biomarkers for chronic pain diagnosis and treatment.

Novel Regioisomeric Analogues of Naphthyl-N-Acylhydrazone Derivatives and Their Anti-Inflammatory Effects

BACKGROUND

When homeostasis is disturbed it can result in a pathological event named inflammation. The main drugs used in the treatment consist of non-steroidal and steroidal anti-inflammatory drugs. However, the side effects remain an obstacle during the treatments. In this study, we aimed to evaluate three new regioisomers analogues of naphthyl-N-acylhydrazone derivatives.

METHODS

Acute models of inflammation in vivo (formalin-induced licking and carrageenan-induced inflammation) as well as in vitro were used to evaluate the effects of LASSBio-2039, LASSBio-2040, and LASSBio-2041.

RESULTS

All three substances (at 1, 10 or 30 µmol/kg) presented significant effects in the in vivo model reducing leukocyte migration, nitric oxide (NO) and interleukin-1β production. It was observed that only LASSBio-2039 significantly reduced cell migration in vitro. None of the LASSBios affected inducible nitric oxide synthase activity nor presented nitric oxide (NO) scavenger effect. No toxic effect was observed, either in vivo or in vitro. The new regioisomers analogues of naphthyl-N-acylhydrazone derivatives presented significant anti-inflammatory activity, suggesting LASSBio-2039 has a direct effect in leukocytes migratory capacity.

CONCLUSIONS

Taken together, the data indicate that these substances present promising effects for the development of a prototype for new drugs.

Suppression of NF-κB signaling by ECN in an arthritic model of inflammation

Background

The 7β-(3-ethyl-cis-crotonoyloxy)-1α-(2-methylbutyryloxy)-3,14-dehydro-Z-notonipetranone (ECN), a sesquiterpenoid isolated from the Tussilago farfara Linneaus (Asteraceae), was evaluated against acute Carrageenan and chronic complete Freund’s adjuvant (CFA)-induced arthritis in mice.

Methods

Acute and chronic arthritis were induced by administering Carrageenan and CFA to the intraplantar surface of the mouse paw. Edema, mechanical allodynia, mechanical hyperalgesia, and thermal hyperalgesia were assessed in the paw. Similarly, histological and immunohistological parameters were assessed following arthritis induced by CFA. Antioxidants, inflammatory cytokines, and oxidative stress markers were also studied in all the treated groups.

Results

The ECN treatment significantly attenuated edema in the paw and elevated the nocifensive threshold following induction of this inflammatory model. Furthermore, ECN treatment markedly improved the arthritis index and distress symptoms, while attenuating the CFA-induced edema in the paw. ECN treatment also improved the histological parameters in the paw tissue compared to the control. At the same time, there was a significant reduction in edema and erosion in the ECN-treated group, as measured by radiographic analysis. Using the Comet’s assay, we showed that ECN treatment protected the DNA from chronic CFA-induced arthritis. Immunohistochemistry analysis showed a marked decrease in the expression level of p-JNK (phosphorylated C-Jun N-terminal kinase), NF-κB (Nuclear factor-kappa B), COX-2 (Cyclooxygenase-2), and TNF-α (Tumour necrosis factor-alpha) compared to the CFA-treated group. Biophysical analysis involving molecular docking, molecular dynamics simulations, and binding free energies of ECN were performed to explore the underlying mechanism.

Conclusion

ECN exhibited significant anti-inflammatory and anti-arthritic activity against Carrageenan and CFA-induced models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03629-7.

Soluble epoxide hydrolase inhibition avoid formalin-induced inflammatory hyperalgesia in the temporomandibular joint

Epoxyeicosatrienoic acids (EETs) are endogenous molecules that exerts effective antinociceptive and resolutive actions. However, because of their rapid metabolism by the soluble epoxide hydrolase (sEH), EETs are unable to remain bioavailable. Therefore, the aim of this study was to investigate whether local sEH inhibition could prevent inflammatory hyperalgesia in the temporomandibular joint (TMJ) of rats. For that, rats were pre-treated with an intra-TMJ injection of TPPU, followed by the noxious stimulus (1.5% of formalin intra-articular) to evaluate nociceptive behavior. Histological analysis was conducted to explore the inflammatory exudate and mast cell degranulation. Periarticular tissue over the TMJ was used to measure inflammatory lipids and cytokines/chemokine by Enzyme-Linked Immunosorbent Assay (ELISA). We demonstrated that peripheral pretreatment with TPPU prevents formalin-induced inflammatory hyperalgesia in the TMJ, and this effect is strictly local. Moreover, TPPU mitigates the leukocyte exudate in the TMJ, as well as inflammatory lipids mediators. Mast cell number and degranulation were abrogated by TPPU, and the inflammatory cytokine levels were decreased by TPPU. On the other hand, TPPU up-regulated the release of interleukin 10 (IL-10), an anti-inflammatory cytokine. We provide evidence that locally sEH by intra-TMJ injection of TPPU produces an antinociceptive and anti-inflammatory effect on rats' TMJ.

Antinociceptive activities of a novel diarylpentanoid analogue, 2-benzoyl-6-(3-bromo-4-hydroxybenzylidene)cyclohexen-1-ol, and its possible mechanisms of action in mice

A novel synthetic compound from the 2-benzoyl-6-benzylidenecyclohexanone analogue, namely 2-benzoyl-6-(3-bromo-4-hydroxybenzylidene)cyclohexen-1-ol (BBHC), showed pronounced nitric oxide inhibition in IFN-γ/LPS-induced RAW 264.7 cells. Based on this previous finding, our present study aimed to investigate the antinociceptive effects of BBHC via chemical and thermal stimuli in vivo. The investigation of the antinociceptive activity of BBHC (0.1, 0.3, 1.0 and 3.0 mg/kg, i.p.) was initiated with 3 preliminary screening tests, then BBHC was subjected to investigate its possible involvement with excitatory neurotransmitters and opioid receptors. The potential acute toxicity of BBHC administration was also studied. Administration of BBHC significantly inhibited acetic acid-induced abdominal constrictions, formalin-induced paw licking activity and developed notable increment in the latency time. BBHC’s ability to suppress capsaicin- and glutamate-induced paw licking activities, as well as to antagonise the effect of naloxone, had indicated the possible involvement of its antinociception with TRPV1, glutamate and opioid receptors, respectively. The antinociceptive activities of BBHC was not related to any sedative action and no evidence of acute toxic effect was detected. The present study showed that BBHC possessed significant peripheral and central antinociceptive activities via chemical- and thermal-induced nociceptive murine models without any locomotor alteration and acute toxicity.

Chemical diversity analysis and biological activities evaluation of different polyphenolic extracts of Marrubium deserti De Noé from Algeria

ETHNOPHARMACOLOGICAL RELEVANCE

Marrubium deserti De Noé (Lamiaceae) commonly known as desert horehound, is a small perennial herb distributed in arid climates. This plant has been used in Algeria for the treatment of cold, cough, fever and inflammation.

AIM OF THE STUDY

This study aimed to perform a phytochemical analysis and to evaluate the effect of diethyl ether (ExDiEth), n-butanol (ExBut) and hydroalcoholic (ExHyD) extracts of the aerial parts of M. deserti De Noé on inflammation, nociceptive response and fever in animal models.

MATERIALS AND METHODS

The total phenolic content and the different phenolic fraction (flavones-flavonols, free aglycones, anthocyanidins, C-glycosides and flavonic heterosides) were quantified in order to study the chemical diversity. The anti-inflammatory effect was evaluated using carrageenan-induced paw oedema test and the nociceptive response was determined by the chemical method using acetic acid-induced writhing response and formalin-induced paw licking tests and by the thermal method using the hot plate in mice. In addition, anti-fever was investigated using yeast-induced pyrexia in rats.

RESULTS

Quantitative analysis revealed that among all extracts, ExBut had a higher phenolic content and the aerial parts of M. deserti De Noé collected from two different sites (Biskra and Tamanresset) had a significant difference in the contents of flavonic heterosids and flavones-flavonols. PCA and CA showed a strong intra-specific variability of M. deserti De Noé individuals. Our results showed that the ExDiEth, ExBut and ExHyD treatments prevented the increase of paw oedema by 56.25%, 66.65% and 45.56% inhibition percent, respectively. Moreover, treatments with these extracts significantly (p<0.05) decreased the number of writhing and increased the reaction time to thermal stimulation as well as demonstrated reduction in paw licking time both at early and late phases. Likewise, they also showed a significant reduction of yeast-induced pyrexia till 4 h of treatment.

CONCLUSION

Results from this study show that M. deserti De Noé aerial parts exhibited anti-inflammatory, analgesic with central and peripheral actions and antipyretic activities which could be associated with the presence of some phytochemicals as flavones, flavonols, flavonic heterosids and phenolic acids.

Characterization of βN-Octadecanoyl-5-hydroxytryptamide Anti-Inflammatory Effect

Background: N-octadecanoyl-5-hydroxytryptamide (C₁₈-5HT) is an amide that can be obtained by the coupling of serotonin and octadecanoic acid. This study aims to characterize the in vivo and in vitro anti-inflammatory activity of C₁₈-5HT. Methods: A subcutaneous air pouch model (SAP) was used. The exudates were collected from SAP after carrageenan injection to assess cell migration and inflammatory mediators production. RAW 264.7 cells were used for in vitro assays. Results: C₁₈-5HT significantly inhibited leukocyte migration into the SAP as well as nitric oxide (NO) and cytokines production and protein extravasation. We also observed an reduction in some cytokines and an increase in IL-10 production. Assays conducted with RAW 264.7 cells indicated that C₁₈-5HT inhibited NO and cytokine produced. Conclusions: Taken together, our data suggest that C₁₈-5HT presents a significant effect in different cell types (leukocytes collected from exudate, mainly polumorphonuclear leukocytes and cell culture macrophages) and is a promising compound for further studies for the development of a new anti-inflammatory drug.

Chemical Profiling, Pharmacological Insights and In Silico Studies of Methanol Seed Extract of Sterculia foetida

Sterculia foetida, also known as jangli badam in Bangladesh, is a traditionally used plant that has pharmacological activities. A qualitative phytochemical analysis was performed to assess the metabolites in a methanolic extract of S. foetida seeds (MESF), and the cytotoxic, thrombolytic, anti-arthritics, analgesic, and antipyretic activities were examined using in vitro, in vivo, and in silico experiments. Quantitative studies were performed through gas chromatography-mass spectroscopy (GC-MS) analysis. The brine shrimp lethality bioassays and clot lysis were performed to investigate the cytotoxic and thrombolytic activities, respectively. The anti-arthritics activity was assessed using the albumin denaturation assay. Analgesic activity was determined using the acetic acid-induced writhing test and the formalin-induced paw-licking test. A molecular docking study was performed, and an online tool was used to perform ADME/T (absorption, distribution, metabolism, and excretion/toxicity) and PASS (Prediction of Activity Spectra for Substances). GC-MS analysis identified 29 compounds in MESF, consisting primarily of phenols, terpenoids, esters, and other organic compounds. MESF showed moderate cytotoxic activity against brine shrimp and significant thrombolytic and anti-arthritics activities compared with the relative standards. The extract also showed a dose-dependent and significant analgesic and antipyretic activities. Docking studies showed that 1-azuleneethanol, acetate returned the best scores for the tested enzymes. These findings suggested that MESF represents a potent source of thrombolytic, anti-arthritic, analgesic, antipyretic agents with moderate cytotoxic effects.

Synthesis of Novel Esters of Mefenamic Acid with Pronounced Anti-nociceptive Effects and a Proposed Activity on GABA, Opioid and Glutamate Receptors

BACKGROUND

Mefenamic acid (MFA), a commonly prescribed non-steroidal anti-inflammatory drug (NSAID), possesses a greater risk of dose-related central nervous system (CNS) toxicity than other NSAIDs. In this study, α-tocopherol and α-tocopherol acetate were selected as prodrug moieties for MFA in an attempt to reduce the CNS toxicity and enhance the therapeutic efficacy.

METHOD

α-tocopherol monoester of MFA (TMMA) and α-tocopherol di-ester of MFA (TDMA) were synthesized by esterification reaction and were subjected to various in vivo characterizations.

RESULTS

Masking of the carboxylate group of MFA with the proposed pro-moieties significantly (p<0.05) delayed the onset of tonic-clonic seizure in mice. Besides, the intraperitoneal administration of TMMA and TDMA in mice produced significantly (p<0.05) stronger anti-inflammatory effects in the carrageenan-induced paw edema test and greater anti-nociceptive effect in the acetic acid-induced writhing test than MFA at an equimolar dose of 20 mg/kg. Treatment with TMMA and TDMA caused a significant (p<0.05) inhibition of pain at 1st and 2nd phases of formalin-induced licking test in mice, whereas treatment with MFA inhibited the 2nd phase only. Pretreatment with naloxone and flumazenil significantly (p<0.05) reversed the anti-nociceptive effect of MFA, TMMA and TDMA in the acetic acid-induced writhing test. In addition, treatment with TMMA and TDMA caused significantly (p<0.05) a higher inhibition of pain in the glutamate-induced licking response in mice than MFA.

CONCLUSION

Masking the carboxylate moiety of MFA by α-tocopherol and α-tocopherol acetate has a great potential for reducing CNS toxicity, enhancing the therapeutic efficacy and altering the mode of anti-nociceptive action.

Two New βN-Alkanoyl-5-Hydroxytryptamides with Relevant Antinociceptive Activity

In this work, we describe a new route for the synthesis and the antinociceptive effects of two new ^βN-alkanoyl-5-hydroxytryptamides (named C_20:0-5HT and C_22:0-5HT). The antinociceptive activities were evaluated using well-known models of thermal-induced (reaction to a heated plate, the hot plate model) or chemical-induced (licking response to paw injection of formalin, capsaicin, or glutamate) nociception. The mechanism of action for C_20:0-5HT and C_22:0-5HT was evaluated using naloxone (opioid receptor antagonist, 1 mg/kg), atropine (muscarinic receptor antagonist, 1 mg/kg), AM251 (cannabinoid CB1 receptor antagonist, 1 mg/kg), or ondansetron (5-HT3 serotoninergic receptor antagonist, 0.5 mg/kg) 30 min prior to C_20:0-5HT or C_22:0-5HT. The substances both presented significant effects by reducing licking behavior induced by formalin, capsaicin, and glutamate and increasing the latency time in the hot plate model. Opioidergic, muscarinic, cannabinoid, and serotoninergic pathways seem to be involved in the antinociceptive activity since their antagonists reversed the observed effect. Opioid receptors are partially involved due to tolerant mice demonstrating less antinociception when treated with both compounds. Our data showed a quicker and simpler route for the synthesis of the new ^βN-alkanoyl-5-hydroxytryptamides. Both compounds demonstrated significant antinociceptive effects. These new compounds could be used as a scaffold for the synthesis of analogues with promising antinociceptive effects.

Role of peripheral 5-HT1D, 5-HT3 and 5-HT7 receptors in the mechanical allodynia induced by serotonin in mice

Serotonin (5-HT) acts as a neurotransmitter in the central nervous system (CNS) and as a mediator released by enterochromaffin cells to regulate intestinal motility. However, this amine also plays an important role as an inflammatory mediator and induces phenotypic changes of nociceptors. Despite the wide knowledge of the role of 5-HT in nociception, most studies have focused on its role in the CNS, while a clear information about its role in peripheral tissues is still lacking. In the present study, we investigated the role of peripheral 5-HT receptors in the nociceptive response induced by 5-HT or carrageenan in mice by using antagonists that target different 5-HT receptors. Mechanical nociceptive threshold was measured with an analgesimeter and evaluated after intraplantar (i.pl.) injection of 5-HT or carrageenan. 5-HT antagonists were injected via the i.pl. route. 5-HT (10, 20, 40 or 80 μg/paw) or carrageenan (100 μg/paw) induced mechanical allodynia. Pretreatment with isamoltane (5 μg; 5-HT_1B antagonist) or ketanserine (1 μg; 5-HT_2A antagonist) did not affect the mechanical allodynia induced by 5-HT. This response was inhibited by BRL 15572 (10 μg; 5-HT_1D antagonist) or SB 269970 (25 μg; 5-HT₇ antagonist). On the other hand, mechanical allodynia induced by 5-HT or carrageenan was exacerbated by ondansetron (10, 20 or 40 μg; 5-HT₃ antagonist). The results indicate that activation of 5-HT_1D and 5-HT₇ receptors plays a role in the mechanical allodynia induced by 5-HT in mice. This study also demonstrates the inhibitory role of peripheral 5-HT₃ receptors in the nociceptive response induced by 5-HT or carrageenan.

[Pain in rheumatic diseases : What can biologics and JAK inhibitors offer?]

Persistent pain despite adequate inflammation control poses a big challenge in many rheumatic diseases for patients as well as physicians. The focus of drug development over the past years was on anti-inflammatory therapies. Enormous progress has been made and several treatment options have been added. It has been observed that pain triggered by inflammation can be effectively treated by inflammation control; however, the chronic pain component remains a problem, is little studied and specific treatment options are missing. Pain is influenced by inflammatory mediators, such as cytokines, which act on peripheral nociceptors and lead to peripheral sensitization. If inflammation continues, this can potentially lead to central sensitization and chronification of pain via immigration of immune cells and/or local activation of e.g. microglia. This leads to increasing autonomization and uncoupling of pain from the actual inflammatory process. The present review deals with the question if bDMARD or tsDMARD also show benefits concerning pain processes in addition to the profound inhibitory effects on inflammation. There are preclinical data that show an influence on sensitization following the use of cytokine inhibitors. On the other hand, so far clinical data show that bDMARDs as well as tsDMARDs consistently rapidly and reliably reduce nociceptive inflammatory pain across disease entities. An effect especially on the process of central sensitization and therefore on chronification of pain cannot be finally evaluated based on the currently available data.

Dual-Acting Peripherally Restricted Delta/Kappa Opioid (CAV1001) Produces Antinociception in Animal Models of Sub-Acute and Chronic Pain

Background

The development of highly efficacious alternatives to mu-opioid analgesics represents an urgent unmet medical and public health need. In the presence of inflammation both delta- and kappa-opioid agonists, acting on peripheral sensory neurons, mediate analgesia. The dual-acting, peripherally restricted kappa/delta-opioid agonist, CAV1001, was tested in four rodent pain models.

Methods

Experiment 1 – Formalin testing in mice. Three doses (1–10 mg/kg) of CAV1001 or ICI204448 at 30 minutes were tested after formalin injection. Spontaneous nocifensive responses were video recorded. Experiment 2 – Complete Freund’s Adjuvant (CFA)-induced arthritis. CFA was injected into the ankle joint of rats. Joint compression thresholds (JCT) were measured. CAV1001 was compared to celecoxib. Experiment 3 – Spinal nerve ligation (SNL) in rats. Paw compression thresholds (PCT) were measured. CAV1001 was compared to gabapentin. Experiment 4 – MMRT-1 bone cancer implantation into the rat tibia. Weight-bearing was assessed. CAV1001 was compared to morphine.

Results

In Phase 2 of the formalin model, CAV1001 (1 mg/kg) significantly reduced pain behaviors to a degree comparable to the peripherally restricted kappa-opioid agonist, ICI204448 (10 mg/kg). CAV1001 (10 mg/kg) effectively eliminated pain behaviors associated with phase 2. In the CFA-induced arthritis model, a significant increase in JCTs, similar to the comparator celecoxib, was observed with CAV1001 at 1 mg/kg at 2 hours; CAV1001 (10 mg/kg) was effective at 1 hour. In the SNL model, both the comparator gabapentin and CAV1001 (5 mg/kg) significantly reduced PCT at 2 hours, but at 4 hours, the CAV1001 thresholds improved to baseline. CAV1001 10 mg/kg significantly improved weight bearing at 4-hour post-dosing compared to baseline following MMRT-1 implantation.

Conclusion

CAV1001 demonstrated efficacy in several different preclinical pain models. Time- and dose-dependent differences in the efficacy of CAV1001 amongst these rodent pain models parallel the degree of underlying inflammation.

Evaluation of Efficacy of Mirtazapine on Pruritus and Serum Histamine and Serotonin Levels in Patients Undergoing Hemodialysis: A Before-After Pilot Clinical Trial

Background

Although chronic kidney disease-associated pruritus (CKD-aP) remains a frequent and frustrating symptom in patients with advanced kidney diseases, its optimal treatments are not well defined. Based on its mechanism of action, as a histamine-1 (H1), 5-(hydroxytryptamine) HT2, and 5HT3-receptor blocker, mirtazapine may be effective in the treatment of CKD-aP. Hence, this study aimed to investigate the efficacy of mirtazapine for the treatment of pruritus in patients undergoing hemodialysis (HD).

Methods

A before-after clinical trial was conducted from September 2018 until March 2019, on 30 HD-patients that had been referred to the HD ward of a tertiary hospital, in Hamadan, Iran. After the 2-week washout period, mirtazapine was administered with a dosage of 15 mg/day for an additional 2 weeks. At baseline and at each dialysis session, the effects of the mirtazapine on the pruritus severity based on the visual analogue scale (VAS) and degree of sleep interference resulting from the pruritus were asked and recorded. Additionally, at the baseline and the end of 2 weeks of treatment, the serum histamine and serotonin levels, as the main chemical pruritogens evoking pruritus symptoms, were also determined.

Results

Twenty-seven patients completed the entire course of the study. Based on the general linear model analysis, a progressive decline in the mean VAS score was observed over time during the study. The mean VAS score decreased from 8.48 ± 1.01 at baseline to 1.04 ±0.79 at the end of treatment (P-value<0.001). Similarly, the mean sleep interference scores were also significantly improved throughout treatment (decreased from 8.07±1.43 to 2.81± 0.74; P-value<0.001). Further, at the end of the treatment, a noticeable decrement in the serum histamine level was also seen (P-value = 0.006). The drug was acceptably well-tolerated and a majority of the patients were satisfied with this treatment.

Conclusion

This pilot study suggests that mirtazapine may be an effective treatment option for the management of CKD-aP. However, further studies would be needed to confirm these results.

Curculigo recurvata W.T.Aiton exhibits anti-nociceptive and anti-diarrheal effects in Albino mice and an in silico model

BACKGROUND

Curculigo recurvata (C. recurvata) is an enthnomedicinally important herb reported to have significant medicinal values. The present study aimed to explore the in vivo and in silico anti-nociceptive and anti-diarrheal effects of a C. recurvate rhizome methanol extract (Me-RCR).

METHODS

The analgesic effects of Me-RCR were assessed using acetic acid-induced writhing and the formalin-induced flicking test. The drugs were administered intraperitoneally (IP) at doses of 200 and 400 mg/kg body weight (bw). Anti-diarrheal activity was evaluated by assessing intestinal motility, hypersecretion, and fecal score in mice at oral doses of 200 and 400 mg/kg·bw. Computer facilitated analyses for anti-nociceptive and anti-diarrheal activities of three isolated compounds from C. recurvata were undertaken to identify the best-fit phytoconstituents.

RESULTS

The Me-RCR showed significant (P < .05) peripheral anti-nociception at the highest dose. The extract inhibited both early and late phases of nociception in the formalin-induced writhing test. In the castor oil-induced diarrhoea model, the extract significantly (P < .05) prolonged the onset time of diarrhoea, inhibited percentage of diarrhoea, and decreased both the volume and weight of intestinal contents. Rates of intestinal fluid accumulation inhibition were (33.61 ± 1.00)% and (46.44 ± 0.89)% at Me-RCR doses of 200 and 400 mg/kg·bw, respectively. Moreover, a significant (P < .05) reduction in gastrointestinal motility was observed. An absorption, distribution, metabolism, excretion and/or toxicity (ADME/T) test showed that the selected compounds yielded promising results, satisfying Lipinski's rule of five for predicting drug-like potential. Notably, of the three phytoconstituents curculigine and isocurculigine possessed the highest affinity for the COX-1 and COX-2. Isocurculigine was also identified as the most effective anti-diarrheal compound in the computer-facilitated model.

CONCLUSION

An extract of the plant C. recurvata showed potential analgesic and anti-diarrheal activity due to the presence of one or more active secondary metabolite(s).

Aristolochia trilobata: Identification of the Anti-Inflammatory and Antinociceptive Effects

Aristolochia trilobata, popularly known as “mil-homens,” is widely used for treatment of stomach aches, colic, asthma, pulmonary diseases, diabetes, and skin affection. We evaluated the antinociceptive and anti-inflammatory activities of the essential oil (EO) and the main constituent, 6-methyl-5-hepten-2-yl acetate (sulcatyl acetate, SA). EO and SA (1, 10, and 100 mg/kg, p.o.) were evaluated using chemical (formalin-induced licking) and thermal (hot-plate) models of nociception or inflammation (carrageenan-induced cell migration into the subcutaneous air pouch, SAP). The mechanism of antinociceptive activity was evaluated using opioid, cholinergic receptor antagonists (naloxone and atropine), or nitric oxide synthase inhibitor (L-NAME). EO and SA presented a central antinociceptive effect (the hot-plate model). In formalin-induced licking response, higher doses of EO and SA also reduced 1st and 2nd phases. None of the antagonists and enzyme inhibitor reversed antinociceptive effects. EO and SA reduced the leukocyte migration into the SAP, and the cytokines tumor necrosis factor and interleukin-1 (TNF-α and IL-1β, respectively) produced in the exudate. Our results are indicative that EO and SA present peripheral and central antinociceptive and anti-inflammatory effects.

Establishing GPCR Targets of hMAO Active Anthraquinones from Cassia obtusifolia Linn Seeds Using In Silico and In Vitro Methods

The present study examines the effect of human monoamine oxidase active anthraquinones emodin, alaternin (=7-hydroxyemodin), aloe-emodin, and questin from Cassia obtusifolia Linn seeds in modulating human dopamine (hD₁R, hD₃R, and hD₄R), serotonin (h5-HT_1AR), and vasopressin (hV_1AR) receptors that were predicted as prime targets from proteocheminformatics modeling via in vitro cell-based functional assays, and explores the possible mechanisms of action via in silico modeling. Emodin and alaternin showed a concentration-dependent agonist effect on hD₃R with EC₅₀ values of 21.85 ± 2.66 and 56.85 ± 4.59 μM, respectively. On hV_1AR, emodin and alaternin showed an antagonist effect with IC₅₀ values of 10.25 ± 1.97 and 11.51 ± 1.08 μM, respectively. Interestingly, questin and aloe-emodin did not have any observable effect on hV_1AR. Only alaternin was effective in antagonizing h5-HT_1AR (IC₅₀: 84.23 ± 4.12 μM). In silico studies revealed that a hydroxyl group at C1, C3, and C8 and a methyl group at C6 of anthraquinone structure are essential for hD₃R agonist and hV_1AR antagonist effects, as well as for the H-bond interaction of 1-OH group with Ser192 at a proximity of 2.0 Å. Thus, based on in silico and in vitro results, hV_1AR, hD₃R, and h5-HT_1AR appear to be prime targets of the tested anthraquinones.

Altered morphology and function of the peripheral nociceptive system in the offspring of diabetic rats

The aim of this study was to determine whether maternal diabetes induced by alloxan injection in the first gestational day of female Wistar rats interferes with the development of the nociceptive peripheral system of the offspring. Behavioral and histologic analysis was performed using the adult offspring of diabetic and control rats. It was found that the offspring of diabetic rats were more sensitive to thermal stimulation and showed an altered response to carrageenan-induced inflammatory hyperalgesia. The histological analysis showed an increased proportion of nociceptive neurons, while the population of non-nociceptive myelinated neurons was reduced. Therefore, exposition to hyperglycemia and/or hyperinsulinemia in uterus, caused by a diabetic mother, might result in altered nociceptive sensations in the offspring throughout life.

Analgesic activity and mechanism of action of a Beta vulgaris dye enriched in betalains in inflammatory models in mice

Evidence demonstrates the pronounced anti-inflammatory activity of a beetroot (Beta vulgaris) dye enriched in betalains obtained using precipitation with ethanol. Herein, we expand upon our previous observations and demonstrate the analgesic and antioxidant effect of betalains. Betalains [10-1000 mg/kg; intraperitoneal route (i.p.)] diminished acetic acid- and PBQ-induced abdominal contortions, and the overt pain-like behaviour induced by complete Freund`s adjuvant (CFA) and formalin (intraplantar; i.pl.) injection. Moreover, betalains (100 mg/kg) administered by various routes [i.p. or subcutaneous (s.c.)] or as a post-treatment reduced carrageenin- or CFA-induced hyperalgesia. Mechanistically, betalains mitigated carrageenin-induced tumour necrosis factor-alpha (TNF-α), interleukin (IL)-1β, superoxide anion levels, and lipid peroxidation. Betalains also stopped the depletion of reduced glutathione (GSH) levels and ferric reducing ability produced by carrageenin, as well as upregulated Nrf2 and Ho1 transcript expression in the plantar tissue of mice. Furthermore, betalains showed hydroxyl radical, 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulphonic acid) radical (ABTS⁺), and 2,2-diphenyl-1-picryl-hydrazyl radical (DPPH•) scavenging ability and iron-chelating activity (bathophenantroline assay), and inhibited iron-independent and iron-dependent lipid peroxidation (LPO) in vitro. Finally, betalains-treated bone marrow-derived macrophages exhibited lower levels of cytokines (TNF-α and IL-1β), and superoxide anion levels and nuclear factor kappa B (NF-κB) activation following lipopolysaccharide (LPS) stimulation. Therefore, this betalain-rich dye extracted using a novel precipitation approach presents prominent analgesic effect in varied models of pain by mechanisms targeting cytokines and oxidative stress.

Mechanisms for Reducing Neuropathic Pain

Injury typically results in the development of neuropathic pain, but the pain normally decreases and disappears in paralleled with wound healing. The pain results from cells resident at, and recruited to, the injury site releasing pro-inflammatory cytokines and other mediators leading to the development of pro-inflammatory environment and causing nociceptive neurons to develop chronic ectopic electrical activity, which underlies neuropathic pain. The pain decreases as some of the cells that induce pro-inflammation, changing their phenotype leading to the blocking the release of pro-inflammatory mediators while releasing anti-inflammatory mediators, and blocking nociceptive neuron chronic spontaneous electrical activity. Often, despite apparent wound healing, the neuropathic pain becomes chronic. This raises the question of how chronic pain can be eliminated. While many of the cells and mediators contributing to the development and maintenance of neuropathic pain are known, a better understanding is required of how the injury site environment can be controlled to permanently eliminate the pro-inflammatory environment and silence the chronically electrically active nociceptive neurons. This paper examines how methods that can promote the transition of the pro-inflammatory injury site to an anti-inflammatory state, by changing the composition of local cell types, modifying the activity of pro- and anti-inflammatory receptors, inducing the release of anti-inflammatory mediators, and silencing the chronically electrically active nociceptive neurons. It also examines the hypothesis that factors released from platelet-rich plasma applied to chronic pain sites can permanently eliminate chronic inflammation and its associated chronic pain.

Injury-Induced Effectors of Neuropathic Pain

Injuries typically result in the development of neuropathic pain, which decreases in parallel with wound healing. However, the pain may remain after the injury appears to have healed, which is generally associated with an ongoing underlying pro-inflammatory state. Injury induces many cells to release factors that contribute to the development of a pro-inflammatory state, which is considered an essential first step towards wound healing. However, pain elimination requires a transition of the injury site from pro- to anti-inflammatory. Therefore, developing techniques that eliminate chronic pain require an understanding of the cells resident at and recruited to injury sites, the factors they release, that promote a pro-inflammatory state, and promote the subsequent transition of that site to be anti-inflammatory. Although a relatively large number of cells, factors, and gene expression changes are involved in these processes, it may be possible to control a relatively small number of them leading to the reduction and elimination of chronic neuropathic pain. This first of two papers examines the roles of the most salient cells and mediators associated with the development and maintenance of chronic neuropathic pain. The following paper examines the cells and mediators involved in reducing and eliminating chronic neuropathic pain.

A new cationic palladium(II) dithiocarbamate exhibits anti-inflammatory, analgesic, and antipyretic activities through inhibition of inflammatory mediators in in vivo models

Inflammation is being a protective mechanism of the body towards the injury. However, chronic and progressive inflammation may lead to some chronic diseases. Due to the serious unwanted effects associated with available drugs, new and safe anti-inflammatory agents are still required. Therefore, the present study was designed to investigate the anti-inflammatory, analgesics, and antipyretic properties of a new compound (4-benzylpiperidine-1-carbodithioato-κ2S,S')(1,4-bis-(diphenylphosphino)butane)palladium(II)chloride monohydrate (compound-1) in albino mice models. Compound-1 was characterized by elemental analysis, FT-IR, and multinuclear NMR spectroscopy. Initially, compound-1 was evaluated for cytotoxicity, anti-inflammatory, and analgesic activities by performing MTT assay, carrageenan-, histamine-, serotonin-, and CFA-induced paw edema, mechanical hyperalgesia, thermal hyperalgesia, and mechanical allodynia (0.1, 1, and 10 mg/kg, b.w). Antipyretic activity was evaluated in brewer's yeast-induced model. The pro-inflammatory cytokines were measured by using commercially available ELISA kits. Additionally, nitrite production, antioxidant enzymes, H&E staining, muscle activity and motor coordination, and kidney and liver function tests were also determined. The results demonstrated that compound-1 significantly inhibited inflammation, pain, and febrile responses in all models at a dose of 10 mg/kg without effecting viability of cells in vitro at concentrations up to 100 μM. Similarly, the data clearly demonstrated significant reduction in the pro-inflammatory cytokines and nitrite production while enhancing antioxidant enzymes. Furthermore, pretreatment with compound-1 did not produce any prominent side effect on kidney, liver, stomach, and muscles. These findings suggest that compound-1 has potent anti-inflammatory-, pain-, and pyrexia-relieving properties. Hence, compound-1 might be a potential candidate for the therapeutic management of chronic inflammation and pain.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Effects of hydroalcoholic extract of Solidago chilensis Meyen on nociception and hypernociception in rodents

Background

Solidago chilensis (syn. microglossa) is a plant from the Asteraceae family widely distributed in South America and used to treat inflammatory diseases. In 2009, it was listed as one of the native medicinal herbal plants used in the Brazilian public health system. In addition to its anti-inflammatory properties, a recent clinical study has shown antinociceptive effects of S. chilensis, introducing a new potential medical use for this plant. The aim of the present study was to investigate the antinociceptive activity of the hydroalcoholic extract of Solidago chilensis (HESc) in rodent models of pain.

Methods

The dried plant extract was obtained from its aerial parts, maintained in ethanol (100 g/l) and filtered. Rats or mice were treated with intraperitoneal injections of HESc (3, 10 or 30 mg/kg) 30 min before being submitted to writhing, 0.2%-formaline or hot-plate tests or prostaglandin E₂ (PGE₂) administration in the hind paw. Mechanical hypernociception and motor impairment were evaluated by electronic von Frey and rota-rod, respectively.

Results

HESc dose-dependently inhibited abdominal contortions in the writhing test and attenuated phases I and II formalin-induced nociceptive behavior. Treatment with HESc also increased thermal threshold and decreased PGE₂-induced hypernociception without promoting motor impairment.

Conclusions

Our data suggest that, when systemically administered, HESc decreases nociception without inducing a sedative effect. Importantly, this effect was observed in both inflammatory and non-inflammatory models of pain and nociception, suggesting a specific non-inflammatory mechanism of HESc on pain. Our findings indicate that S. chilensis might be an important adjuvant in pain management.

Characterization of sensory neuronal subtypes innervating mouse tongue

The tongue is uniquely exposed to water-soluble environmental chemicals that may lead to injury or tumorigenesis. However, comparatively little research has focused on the molecular and functional organization of trigeminal ganglia (TG) afferent neurons innervating the tongue. The current study identified and characterized lingual sensory neurons based on a neuronal subtype classification previously characterized in the dorsal root ganglion (DRG) neurons. We employed immunohistochemistry on transgenic reporter mouse lines as well as single-cell PCR of known markers of neuronal subtypes to characterize neuronal subtypes innervating the tongue. Markers expressed in retrogradely labeled TG neurons were evaluated for the proportion of neurons expressing each marker, intensity of expression, and overlapping genes. We found that tongue-innervating sensory neurons primarily expressed CGRP, TRPV1, TrkC, 5HT3A and Parvalbumin. These markers correspond to peptidergic and a subgroup of non-peptidergic C-nociceptors, peptidergic A nociceptors, proprioceptors and myelinated low-threshold mechanoreceptors (LTMRs). Interestingly, as reported previously, we also found several differences between TG and DRG neurons indicating the need for single-cell sequencing of neuronal types based on tissue type within all TG as well as DRG neurons.

Evaluation of different classes of histamine H1 and H2 receptor antagonist effects on neuropathic nociceptive behavior following tibial nerve transection in rats

It seems that histamine release in the site of neuronal injury could contribute to the neuropathic pain mechanism. In the present study, we investigated the anti-allodynic effects of chronic administration of different classes of histamine H₁ and H₂ receptor antagonists on neuropathic nociceptive behavior following tibial nerve transection (TNT) in rats. Peripheral neuropathy was induced by TNT surgery. We performed acetone tests (AT) to record cold allodynia, Von Frey tests (VFT) to measure mechanical allodynia, double plate test (DPT) to evaluate thermal place preference/avoidance and open field test (OFT) for evaluation of animal activity. TNT rats showed a significant mechanical and cold allodynia compared to the sham group. Chlorpheniramine (5 and 15 mg/kg, i.p) significantly attenuated cold allodynia and prevented cold plate avoidance behavior and at the dose of 15 mg/kg remarkably decreased mechanical allodynia. Fexofenadine (10 and 30 mg/kg, p.o) significantly attenuated the mechanical allodynia and prevented cold plate avoidance. Ranitidine (5 and 15 mg/kg, i.p) significantly prevented cold plate avoidance behavior and at the dose of 15 mg/kg notably improved mechanical and cold allodynia. Famotidine (1 and 3 mg/kg, p.o) was ineffective on all nociceptive tests. Gabapantin (100 mg/kg, p.o) significantly improved all types of nociceptive behaviors. These results indicate that both blood brain barrier penetrating (chlorpheniramine) and poorly penetrating (fexofenadine) histamine H₁ receptor antagonists could improve the neuropathic pain sign, but only the blood brain barrier penetrating histamine H₂ receptor antagonist (ranitidine) could produce anti-allodynic effects in the TNT model of neuropathic pain in rats.

New βN-octadecanoyl-5-hydroxytryptamide: antinociceptive effect and possible mechanism of action in mice

The present study examined the potential antinociceptive activity of C18 5-HT (^βN-octadecanoyl-5-hydroxytryptamide) using chemical and thermal nociception models in mice. Orally administered C18 5-HT (0.1, 1 and 10 mg/kg) produced significant dose-dependent antinociceptive effects in formalin-, capsaicin- and glutamate-induced licking models. This compound also induced a significant increase in the response to thermal stimuli in the hot plate test, and its antinociceptive effect was not related to muscle relaxant or sedative actions. In a thermal hyperalgesia model, C18 5-HT presented an anti-hyperalgesic profile as evidenced by the increase in the response time of the animals. Furthermore, intraperitoneal (i.p) pretreatment with naloxone (a non-selective opioid receptor antagonist, 1 mg/kg), ondansetron (serotoninergic receptor antagonist (5-HT3 subtype), 0.5 mg/kg) or AM241 (CB1 cannabinoid receptor antagonist, 1 mg/kg) reversed the antinociceptive effects of C18 5-HT in the hot plate model. In the formalin-induced licking model, pretreatment with naloxone reversed the antinociceptive effects of C18 5-HT, as demonstrated by an increase in the paw licking response when compared with the C18 5-HT-treated group. These findings suggest that C18 5-HT has peripheral and central antinociceptive effects and that its mechanism of action involves, ate least in part, opioid, serotoninergic and cannabinoid pathways.

Potamotrygon motoro stingray venom induces both neurogenic and inflammatory pain behavior in rodents

Freshwater stingray accidents cause an immediate, intense, and unrelieved pain which is followed by edema, erythema and necrosis formation. Treatment for stingray envenomation is based on administration of analgesic, antipyretic and anti-inflammatory drugs. Concerning pain control, it is prescribed to immerse punctured limb on hot water to alleviate pain. There are no studies demonstrating specific targets on which stingray venom acts to promote pain. Therefore, the aim of this work was to investigate some mechanisms of Potamotrygon motoro venom (PmV) that contribute to nociception induction. Evaluating spontaneous pain behavior in mice injected i.pl. with PmV, it was seen that PmV induced both neurogenic and inflammatory pain. PmV also induced hyperalgesia in both mice and rats, evaluated through electronic von Frey and rat paw pressure test, respectively. Partial inhibition of hyperalgesia was observed in mice treated with cromolyn or promethazine, which indicated that mast cell and histamine via H1 receptor participate in the inflammatory pain. To search for some targets involved in PmVinduced hyperalgesia, the participation of TRPV1, calcium channels, neurokinins, CGRP, and norepinephrine, was evaluated in rats. It was seen that PmV-induced hyperalgesia occurs with the participation of neurokinins, mainly via NK1 receptor, CGRP, and calcium influx, through both P/Q and L-type voltage-dependent calcium channels, besides TRPV1 activation. The data presented herein indicate that PmV causes hyperalgesia in rodents which is dependent on the participation of several neuroinflammatory mediators.

Sex Differences and Estrous Cycle Effects of Peripheral Serotonin-Evoked Rodent Pain Behaviors

Many persistent pain conditions occur predominantly in women making pain a major women's health issue. One theory for the prevalence in females is hormone modulation of pain mechanisms. The peripheral release of the neurotransmitter serotonin (5HT) has been implicated in various sexually dimorphic pain conditions; yet no studies have examined the effect of ovarian hormones on peripheral 5HT-evoked pain behaviors. We hypothesized that peripheral 5HT evokes greater pain behaviors in female rodents during estrus and/or proestrus, stages of the estrous cycle where ovarian hormones are greatly fluctuating. Female Sprague-Dawley rats (250-350 g) from each stage of the estrous cycle, ovariectomized females, and intact males received an intraplantar hindpaw injection of 5HT (2 μg/100 μL) or saline (n = 6 per group) and thermal hyperalgesia, mechanical allodynia, or edema was measured at 0, 10, 20 and 30 min post-injection. A separate group of rats received an ipsilateral injection of the selective 5HT_2A antagonist, M100907, 15 min prior to 5HT injection. We report that females in proestrus and estrus exhibited significantly greater and/or longer lasting pain behaviors compared to males, females in diestrus, and ovariectomized females. There were no significant sex differences or estrous cycle effects on 5HT-evoked edema or 5HT content in inflamed hindpaws. Local pretreatment with the 5HT_2A receptor antagonist blocked 5HT-evoked thermal hyperalgesia and edema. These data provide evidence of a modulatory role of hormones on peripheral 5HT-evoked pain occurring via the 5HT_2A receptor.

Eugenia brasiliensis leaves extract attenuates visceral and somatic inflammatory pain in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Eugenia brasiliensis Lam. (Myrtaceae) is a Brazilian tree distributed throughout Atlantic rain forest, since Bahia until Santa Catarina state, and is popularly known as "grumixaba, grumixameira, cumbixaba, ibaporoiti, and cereja-brasileira". The bark and leaves of Eugenia brasiliensis are used in folk medicine as adstringent, diuretic, energizing, anti-rheumatic and anti-inflammatory. This study aimed at investigating the chemical composition, antinociceptive and anti-inflammatory effect of the hydroalcoholic extract of Eugenia brasiliensis (HEEb).

MATERIAL AND METHODS

Chemical composition of the HEEb was determined by High Performance Liquid Chromatography/ESI-Mass Spectrometry (HPLC-ESI-MS/MS). The antinociceptive and anti-inflammatory effects of HEEb (30-300 mg/kg) was verified in mice after oral administration by intra-gastric gavage (i.g.) 60 min prior to experimentation. It was investigated whether HEEb decreases visceral pain and leukocyte migration induced by an intraperitoneal (i.p.) injection of acetic acid (0.6%). We also evaluated whether HEEb decreases nociceptive behavior induced by formalin (including paw edema and temperature), prostaglandin E₂ (PGE₂), histamine, and compound 48/80. Finally, we evaluated the effect of HEEb in the chronic inflammatory (mechanical and thermal hypersensitivity) pain induced by complete Freund's adjuvant (CFA), as well as quantifying the concentration of the pro-inflammatory cytokines TNF-α and IL-6 in the paw by ELISA method.

RESULTS

Seven polyphenols were identified in HEEb by HPLC-ESI-MS/MS analysis. HEEb treatment alleviated nocifensive behavior and leukocyte migration caused by acetic acid. Moreover, HEEb also reduced the inflammatory pain and paw temperature induced by formalin, as well as it decreased nociceptive behavior induced by histamine and compound 48/80. Finally, acute and repeated treatment of animals with HEEb (100 mg/kg, i.g.) markedly reduced the mechanical and thermal (heat) hypersensitivity, besides decrease paw edema and temperature induced by CFA, and this effect was evident until the day 7. Moreover, repeated treatment with HEEb (100 mg/kg, i.g.) significantly reduced the levels of IL-6 and TNF-α in the paw when compared to the CFA group.

CONCLUSIONS

This is the first report showing that HEEb presents antinociceptive and anti-inflammatory effects in the visceral and somatic inflammatory pain in mice, possibly involving the inhibition of histamine receptors and pro-inflammatory cytokines activated pathways. Our results are of interest because they support the use of Eugenia brasiliensis as a potential source of phytomedicine for inflammatory diseases and pain.

Pruritus: Progress toward Pathogenesis and Treatment

Pruritus, the most common cutaneous symptom, is widely seen in many skin complaints. It is an uncomfortable feeling on the skin and sometimes impairs patients' quality of life. At present, the specific mechanism of pruritus still remains unclear. Antihistamines, which are usually used to relieve pruritus, ineffectively work in some patients with itching. Recent evidence has suggested that, apart from histamine, many mediators and signaling pathways are involved in the pathogenesis of pruritus. Various therapeutic options for itching correspondingly have been developed. In this review, we summarize the updated pathogenesis and therapeutic strategies for pruritus.

Mast cells in neuropathic pain: an increasing spectrum of their involvement in pathophysiology

Mast cells are immunological cells that are diversely distributed in different parts of the body. Their role in various pathological conditions such as hypersensitivity, atherosclerosis, pulmonary hypertension, and male infertility has been reported by different scientists. Apart from these, a number of studies have shown their important role in pathogenesis of neuropathic pain of diverse aetiology. They have been found to release active mediators, primarily histamine and serotonin on degranulation in response to different stimuli including chemical, nerve damage, toxin or disease-related conditions. The mast cells stabilizer has shown pain attenuating effects by preventing degranulation of mast cells. Similarly, compound 48/80 (first dose 200 μg/100 g and after 6-h interval, second dose of 500 μg/100 g) caused the degranulation of the accumulated endoneurial histamine and 5-HT antagonists have shown pain relieving effects by attenuating the effects of histamine and serotonin, respectively. On the other hand, the mast cell degranulator compound 48/80 has shown dual action depending on its time of administration. The present review discusses the critical role of mast cells in the generation and maintenance of neuropathic pain in experimental models.

Peripheral and spinal TRPA1 channels contribute to formalin-induced long-lasting mechanical hypersensitivity

Background

Transient receptor potential ankyrin 1 (TRPA1) is a non-selective cation channel expressed by a subset of nociceptive neurons that acts as a multimodal receptor. Its activity contributes to modulate nociceptive transmission in acute inflammatory pain. However, the role of this channel in chronic pain has been less studied. The purpose of this study was to investigate the local peripheral and spinal participation of TRPA1 channels in formalin-induced long-lasting hypersensitivity.

Materials and methods

Formalin (1%)-induced chronic hypersensitivity was determined by the application of von Frey filaments to ipsilateral and contralateral paws and through pharmacological testing using a selective TRPA1 blocker (A-967079). TRPA1 expression in the dorsal root ganglion (DRG) and spinal cord was analyzed by Western blotting.

Results

Formalin (1%) injection produced acute flinching behavior (1 h) as well as secondary allodynia and hyperalgesia (12 days). Local peripheral pretreatment (10 min before) or posttreatment (6 days later) with A-967079 (1–100 µM) partially prevented and reversed, respectively, in a dose-dependent manner, long-lasting secondary mechanical allodynia and hyperalgesia evoked by 1% formalin. Likewise, intrathecal pretreatment or posttreatment with A-967079 partially prevented and reversed, respectively, formalin-induced long-lasting hypersensitivity. A-967079 (100 µM) completely abolished the pro-nociceptive effect of formalin (adjusted to pH 7.4). Finally, formalin injection increased TRPA1 protein expression in the DRG and spinal cord.

Conclusion

Results indicate that TRPA1 expressed in the DRG and spinal cord plays a relevant role in formalin-induced long-lasting secondary nociceptive hypersensitivity.

Peripheral 5-HT3 Receptors Are Involved in the Antinociceptive Effect of Bunodosine 391

Bunodosine 391 (BDS 391), a low molecular weight compound isolated from the sea anemone Bunodosoma cangicum, increases the nociceptive threshold and inhibits inflammatory hyperalgesia. Serotonin receptors are involved in those effects. In this study, we have expanded the characterization of the antinociceptive effect of BDS 391 demonstrating that, in rats: (a) the compound inhibits (1.2–12 ng/paw) overt pain, in the formalin test, and mechanical hyperalgesia (0.6–6.0 ng/paw) detected in a model of neuropathic pain; (b) intraplantar administration of ondansetron, a selective 5-HT3 receptor antagonist, blocks the effect of BDS 391, whereas ketanserin, a 5-HT2 receptor antagonist, partially reversed this effect, indicating the involvement of peripheral 5-HT2 and 5-HT3 receptors in BDS 391 antinociception; and (c) in binding assay studies, BDS 391 was not able to displace the selective 5-HT receptor antagonists, suggesting that this compound does not directly bind to these receptors. The effect of biguanide, a selective 5-HT3 receptor agonist, was also evaluated. The agonist inhibited the formalin’s nociceptive response, supporting an antinociceptive role for 5-HT3 receptors. Our study is the first one to show that a non-peptidic low molecular weight compound obtained from a sea anemone is able to induce antinociception and that activation of peripheral 5-HT3 receptors contributes to this effect.

Chronic Monosodium Glutamate Administration Induced Hyperalgesia in Mice

Monosodium glutamate (MSG) is a widely used food additive. Although it is generally considered safe, some questions regarding the impact of its use on general health have arisen. Several reports correlate MSG consumption with a series of unwanted reactions, including headaches and mechanical sensitivity in pericranial muscles. Endogenous glutamate plays a significant role in nociceptive processing, this neurotransmitter being associated with hyperalgesia and central sensitization. One of the mechanisms underlying these phenomena is the stimulation of Ca2+/calmodulin sensitive nitric oxide synthase, and a subsequent increase in nitric oxide production. This molecule is a key player in nociceptive processing, with implications in acute and chronic pain states. Our purpose was to investigate the effect of this food additive on the nociceptive threshold when given orally to mice. Hot-plate and formalin tests were used to assess nociceptive behaviour. We also tried to determine if a correlation between chronic administration of MSG and variations in central nitric oxide (NO) concentration could be established. We found that a dose of 300 mg/kg MSG given for 21 days reduces the pain threshold and is associated with a significant increase in brain NO level. The implications of these findings on food additive-drug interaction, and on pain perception in healthy humans, as well as in those suffering from affections involving chronic pain, are still to be investigated.

Antihyperalgesic effect of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol: participation of the NO/cGMP/KATP pathway and κ-opioid receptor

The present study used behavioral analyses to investigate the involvement of the NO/cGMP/KATP pathway, serotoninergic, and opioid systems in the antinociceptive action of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol (CTHP) in mice. Oral administration of CTHP (1, 5, 10, and 30 mg/kg) exerted effects at higher doses in chemical models of nociception (the acetic acid writhing and formalin tests) as well as a thermal model (the tail-flick test). It was also found that pretreatment with L-N-nitroarginine methyl ester (nonselective nitric oxide synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (selective inhibitor of nitric oxide-sensitive guanosyl cyclase), glibenclamide (selective ATP-sensitive K channel blocker), naloxone (nonselective opioid receptor blocker), and nor-binaltorphimine (selective κ-opioid receptor blocker), but not methylnaltrexone (peripheral μ-opioid receptor blocker) or naltrindole (selective δ-opioid receptor blocker), reversed the antinociceptive effect of CTHP. In addition, CTHP induced the development of tolerance in the tail-flick test: the tolerance appeared later compared with morphine, and was only observed with a higher dose. Taken together, the present study showed that the systemic administration of CTHP reduced pain induced by chemical and thermal stimuli. We also suggest that the possible mechanisms include the involvement of the NO/cGMP/KATP pathway and the κ-opioid receptor.

Pharmacological investigations on mast cell stabilizer and histamine receptor antagonists in vincristine-induced neuropathic pain

The present study was designed to investigate the role of mast cells and mast cell-derived histamine in vincristine-induced neuropathic pain. Neuropathic pain was induced by administration of vincristine (100 μg/kg, i.p.) over a period of 10 days, with a break of 2 days, and pain behavioural estimations including pin prick, hot plate and acetone spray tests were performed to assess mechanical and heat hyperalgesia and cold allodynia, respectively, on days 0, 14 and 28. Mast cell stabilizer, sodium cromoglycate, H₁ receptor antagonist promethazine and H₂ receptor antagonist ranitidine were administered over a period of 12 days. Administration of vincristine resulted in significant development of heat and mechanical hyperalgesia as well as cold allodynia. Furthermore, the pain observed was markedly elevated on the 28th day in comparison to the 14th day. Administration of sodium cromoglycate, promethazine and ranitidine significantly reduced mechanical and heat hyperalgesia and cold allodynia. However, the pain-attenuating effects of ranitidine were significantly less as compared to sodium cromoglycate and promethazine, which suggests that H₁ receptors play a more important role than H₂ receptors in vincristine-induced neuropathic pain. It may be concluded that vincristine may degranulate mast cells to release inflammatory mediators, particularly histamine which may act through H₁ (primarily H₁) and H₂ receptors to induce neuropathic pain.

Evidence for the modulation of nociception in mice by central mast cells

BACKGROUND

Hyperalgesia that develops following nerve ligation corresponds temporally and in magnitude with the number of thalamic mast cells located contralateral to the ligature. We tested the possibility that mast cells modulate nociception centrally, similar to their role in the periphery.

METHODS

We examined the central effect of two hyperalgesic compounds that induce mast cell degranulation and of stabilized mast cells using cromolyn.

RESULTS

Thermal hyperalgesia (tail flick) induced by nerve growth factor (NGF, a neurotrophic compound) and mechanical hyperalgesia (von Frey) induced by dynorphin A (1-17) (opioid compound) each correlated with the per cent of thalamic mast cells that were degranulated. Degranulation of these mast cells by the central injection of compound 48/80, devoid of neurotrophic or opioid activity, was sufficient to recapitulate thermal hyperalgesia. Stabilization of mast cells by central injections of cromolyn produced no analgesic effect on baseline tail flick or von Frey fibre sensitivity, but inhibited thermal hyperalgesia produced by compound 48/80 and tactile hyperalgesia induced by dynorphin and by Freund's complete adjuvant. Finally, chemical nociception produced by the direct activation of nociceptors by formalin (phase I) was not inhibited by centrally injected cromolyn whereas chemical nociception dependent on central sensitization (formalin-phase II and acetic acid-induced abdominal stretches) was.

CONCLUSIONS

These convergent lines of evidence suggest that degranulation of centrally located mast cells sensitizes central nociceptive pathways leading to hyperalgesia and tonic chemical sensitivity.

SIGNIFICANCE

Hyperalgesia induced by spinal nerve ligation corresponds temporally and in magnitude with degranulation of thalamic mast cells. Here, we provide evidence that hyperalgesia induced by NGF, formalin and dynorphin also may depend on mast cell degranulation in the CNS whereas cromolyn, a mast cell stabilizer, blocks these effects in mice.