Characterization of Nociceptive Behaviors Induced by Formalin in the Glabrous and Hairy Skin of Rats

Antinociceptive effects of bupivacaine and its sulfobutylether-β-cyclodextrin inclusion complex in orofacial pain

Bupivacaine hydrochloride (BVC) represents an option to produce long-lasting analgesia, and complexation in cyclodextrins has shown improvements in biopharmaceutical properties. This study aimed to characterize and test the cytotoxicity and antinociceptive effects of BVC complexed in sulfobutylether-β-cyclodextrin (SBEβCD). The kinetics and stoichiometry of complexation and BVC-SBEβCD association constant were evaluated by phase solubility study and Job's plot. Evidence of the BVC-SBEβCD complex formation was obtained from scanning electron microscopy (SEM), infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The cytotoxicity was evaluated in keratinocyte (HaCaT) and neuroblastoma (SH-SY5Y). Antinociceptive effects were registered via orofacial pain models: the formalin test, carrageenan-induced hyperalgesia, and postoperative pain (intraoral incision). The complex formation occurred at a 1:1 BVC-SBEβCD molar ratio, with a low association constant (13.2 M^-1). SEM, DSC, and FTIR results demonstrated the host-guest interaction. The IC_50% values determined in SH-SY5Y were 216 µM and 149 µM for BVC and BVC-SBEβCD, respectively (p < 0.05). There was no difference in HaCaT IC_50%. In orofacial pain model, BVC-SBEβCD significantly prolonged antinociceptive effect, in about 2 h, compared to plain BVC. SBEβCD can be used as a drug delivery system for bupivacaine, whereas the complex showed long-lasting analgesic effects.

PA-Int5: An isatin-thiosemicarbazone derivative that exhibits anti-nociceptive and anti-inflammatory effects in Swiss mice

Pain and inflammation are symptoms of various diseases, and they can be modulated by different pathways, thus highlighting the importance of investigating the therapeutic effects of novel compounds. Previous studies have shown that isatin-thiosemicarbazone exhibits antitumor, antifungal antibacterial and other biological properties. Based on the wide range of biological effects of these compounds, the aim of the present study was to investigate the central nervous system (CNS) performance, and the anti-nociceptive and anti-inflammatory activity of (Z)-2-(5-nitro-2-oxoindolin-3-ilidene)-N-hydroazinecarbothioamide (PA-Int5) in treated mice. Three doses of PA-Int5 were tested orally (1.0, 2.5 and 5.0 mg/kg) in the nociceptive and inflammatory animal models. Additionally, the potential sedative effects of PA-Int5 (5 mg/kg, oral gavage) were investigated using an open field and rotarod tests, to exclude any possible unspecific effects of the nociceptive assays. Anti-nociceptive activity was assessed using the acetic acid-induced abdominal contortion and formalin tests, whereas anti-inflammatory activity was assessed using a carrageenan-induced paw edema and zymosan-induced air-pouch models. PA-Int5 (5 mg/kg) induced anti-nociceptive activity in the abdominal contortion model. In the formalin test, PA-Int5 (at 2.5 and 5 mg/kg) reduced nociception in the second phase. At the higher dose tested, PA-Int5 did not affect spontaneous locomotion or motor coordination. The data revealed that at all doses tested, the compound significantly reduced paw edema following carrageenan administration. In the zymosan-induced air-pouch model, PA-Int5 potently inhibited leukocyte migration and protein levels at the site of inflammation. When combined, the results revealed, for the first time, that PA-Int5 exhibited anti-nociceptive and anti-inflammatory activities, and highlights its potential, as well that of other derivatives, as novel candidates for pain relief.

Anti-hyperalgesic properties of a flavanone derivative Poncirin in acute and chronic inflammatory pain models in mice

BACKGROUND

Poncirin is flavanone derivative (isolated from Poncirus trifoliata) with known pharmacological activities such as anti-tumor, anti-osteoporotic, anti-inflammatory and anti-colitic. The present study aimed to explore the anti-allodynic and anti-hyperalgesic potentials of poncirin in murine models of inflammatory pain.

METHODS

The analgesic potential of poncirin was evaluated in formalin-, acetic acid-, carrageenan- and Complete Freund's Adjuvant (CFA)-induced inflammatory pain models in mice. Anti-allodynic and anti-hyperalgesic activities were measured using Von Frey filaments, Randall Selitto, hotplate and cold acetone tests. The serum nitrite levels were determined using Griess reagent. The Quantitative Real-time PCR (qRT-PCR) was performed to assess the effect of poncirin on mRNA expression levels of inflammatory cytokines and anti-oxidant enzymes.

RESULTS

Intraperitoneal administration of poncirin (30 mg/kg) markedly reduced the pain behavior in both acetic acid-induced visceral pain and formalin-induced tonic pain models used as preliminary screening tools. The poncirin (30 mg/kg) treatment considerably inhibited the mechanical hyperalgesia and allodynia as well as thermal hyperalgesia and cold allodynia. The qRT-PCR analysis showed noticeable inhibition of pro-inflammatory cytokines (mRNA expression levels of TNF-α, IL-1β and IL-6) (p < 0.05) in poncirin treated group. Similarly, poncirin treatment also enhanced the mRNA expressions levels of anti-oxidant enzymes such as transcription factor such as nuclear factor (erythroid-derived 2)-like 2 (Nrf2) (p < 0.05), heme oxygenase (HO-1) (p < 0.05) and superoxide dismutase (SOD2) (p < 0.05). Chronic treatment of poncirin for 6 days did not confer any significant hepatic and renal toxicity. Furthermore, poncirin treatment did not altered the motor coordination and muscle strength in CFA-induced chronic inflammatory pain model.

CONCLUSION

The present study demonstrated that poncirin treatment significantly reduced pain behaviors in all experimental models of inflammatory pain, suggesting the promising analgesic potential of poncirin in inflammatory pain conditions.

A refinement to the formalin test in mice

The constant refinement of tests used in animal research is crucial for the scientific community. This is particularly true for the field of pain research, where ethical standards are notably sensitive. The formalin test is widely used in pain research and some of its mechanisms resemble those underlying clinical pain in humans. Immediately upon injection, formalin triggers two waves (an early and a late phase) of strong, nociceptive behaviour, characterised by licking, biting, lifting and shaking the injected paw of the animal. Although well characterised at the behaviour level, since its proposal over four decades ago, there has not been any significant refinement to the formalin test, especially those combining minimisation of animal distress and preservation of behavioural outcomes of the test.  Here, we propose a modified and improved method for the formalin test. We show that anaesthetising the animal with the inhalable anaesthetic sevoflurane at the time of the injection can produce reliable, robust and reproducible results whilst animal distress during the initial phase is reduced. Importantly, our results were validated by pharmacological suppression of the behaviour during the late phase of the test with gabapentin, the anaesthetic showing no interference with the drug. In addition, we demonstrate that this is also a useful method to screen for changes in pain behaviour in response to formalin in transgenic lines.

A refinement to the formalin test in mice

The constant refinement of tests used in animal research is crucial for the scientific community. This is particularly true for the field of pain research, where ethical standards are notably sensitive. The formalin test is widely used in pain research and some of its mechanisms resemble those underlying clinical pain in humans. Immediately upon injection, formalin triggers two waves (an early and a late phase) of strong, nociceptive behaviour, characterised by licking, biting, lifting and shaking the injected paw of the animal. Although well characterised at the behaviour level, since its proposal over four decades ago, there has not been any significant refinement to the formalin test, especially those combining minimisation of animal distress and preservation of behavioural outcomes of the test.  Here, we propose a modified and improved method for the formalin test. We show that anaesthetising the animal with the inhalable anaesthetic sevoflurane at the time of the injection can produce reliable, robust and reproducible results whilst animal distress during the initial phase is reduced. Importantly, our results were validated by pharmacological suppression of the behaviour during the late phase of the test with gabapentin, the anaesthetic showing no interference with the drug. In addition, we demonstrate that this is also a useful method to screen for changes in pain behaviour in response to formalin in transgenic lines.

Chemical Composition and Role of Opioidergic System in Antinociceptive Effect of Ziziphora Clinopodioides Essential Oil

Introduction:

Ziziphora Clinopodioides has been used widely for various therapeutic purposes in Iranian folk medicine. The current study aimed to determine interaction of antinociceptive effect of the Essential Oil of Ziziphora Clinopodioides (EOZC) and opioidergic system in male rats using formalin test.

Methods:

Sixty-four male Wistar rats were divided into eight groups. The groups 1 to 7 were injected with normal saline, vehicle (Tween-80, 0.5%), 10, 20, 40 mg/kg of the EOZC, morphine (5 mg/kg) and naloxone (2 mg/kg), respectively. Thirty minutes later, the formalin test was performed by intraplantar injection of formalin (50 μL, 2%). In group 8, naloxone (2 mg/kg) was injected 15 min before injection of EOZC (20 mg/kg), followed by formalin at 15 min later. The formalin test was done as time spent for licking and biting of the injected paw. Formalin induced a biphasic pain reaction. The chemical composition of EOZC was identified using Gas Chromatography-Mass Spectrometry (GC-MS).

Results:

EOZC (10, 20, and 40 mg/kg) dose dependently and morphine (5 mg/kg) reduced pain responses in the both phases of pain (P<0.05). Naloxone (2 mg/kg) alone had no effect on the severity of pain (P>0.05) but pretreatment with naloxone inhibited EOZC-induced antinociception activity (P<0.05). Based on the GC-MS results, EOZC comprised 65.22% carvacrol, 19.51% thymol, 4.86% p-cymene and 4.63% γ-terpinene.

Conclusion:

These results demonstrate that EOZC has antinociceptive effect and this effect might mediate via opioidergic pathways.

Analgesic, anti-inflammatory and anticancer activities of Combretin A and Combretin B isolated from Combretum fragrans F. HOFFM (Combretaceae) leaves

Previous pharmacological and phytochemical studies showed that, Combretum fragrans F. HOFFM (Combretaceae) is a Cameroonian medicinal plant possessing numerous therapeutic virtues and rich in various active secondary metabolites. In this study, we investigate in vivo anti-nociceptive and anti-inflammatory activity and, in vitro anticancer, anti-TNFα, ROS and NO-inhibitory activities of Combretum A and Combretin B, two triterpenes cycloartane-type isolated from the leaves of Combretum fragrans. The effect on ROS, TNF-α and NO production, anticancer activity and cytotoxicity assay were done using chemiluminescence technique, ELISA kit, colorimetric method, MCF-7 cells and MTT assay, respectively. Antinociceptive and anti-inflammatory activities were estimated using a model of acetic acid, formalin and carrageenan. Combretin A and Combretin B significantly (p < 0.001) inhibited extracellular ROS production. These compounds also significantly (p < 0.001) reduced TNF-α and NO production. Moreover, these compounds decreased cell viability of MCF-7 cell lines. For acetic acid- or formalin-induced pain, as well as carrageenan-induced acute inflammation, Combretin A and Combretin B exhibited significant (p < 0.001) anti-nociceptive and anti-inflammatory activities. Anti-nociceptive, anti-inflammatory and anticancer potential associated with inhibitory effects on ROS, TNFα and NO production in this study show that, Combretin A and Combretin B could be considered as the promising chemotherapeutic agents in breast cancer treatment and inflammatory disease.