Overview of Neurological Mechanism of Pain Profile Used for Animal "Pain-Like" Behavioral Study with Proposed Analgesic Pathways

A novel animal model of tegafur-induced hand-foot syndrome

Hand-foot syndrome (HFS) is a common side effect of fluoropyrimidine anticancer drugs and often becomes a dose-limiting manifestation of toxicity once it occurs. The precise mechanism of HFS remains unclear, and effective measures to prevent or relieve it are currently limited. To investigate the pathogenesis of HFS and effective measures for treating or preventing it, establishment of animal models is crucial. Here, we gave male SD rats 170 mg/kg of tegafur (prodrug of 5-FU) daily for 35 days and evaluated their clinical and histopathological characteristics and pain-related behavioral tests. TUNEL-positive apoptotic cells and 5-FU concentrations in the plantar skin were also evaluated to investigate the mode of toxicity. Tegafur treatment induced hypersensitivity to mechanical pressure on the plantar surface beginning in Week 3, with decreased locomotor activity. Focal desquamation of the plantar skin was observed almost concomitantly and gradually worsened to palmar and plantar skin thickening with severe desquamation, cracks, or both. Histopathological lesions in the plantar skin at treatment end included desquamation and thickening, with epidermal cell swelling and spongiosis and focal inflammation in the dermis. The time-course of development and the characteristics of the tegafur-induced skin lesions were highly similar to those in human fluoropyrimidine-induced HFS, indicating that a HFS rat model was successfully established. Localized high concentrations of 5-FU in the palmar and plantar skin, with increased apoptosis, are likely involved in the mode of toxicity. Our model should clarify the pathogenesis of HFS, providing new insights into the best supportive care and prevention.

Exploring Localized Provoked Vulvodynia: Insights from Animal Model Research

Provoked vulvodynia represents a challenging chronic pain condition, characterized by its multifactorial origins. The inherent complexities of human-based studies have necessitated the use of animal models to enrich our understanding of vulvodynia's pathophysiology. This review aims to provide an exhaustive examination of the various animal models employed in this research domain. A comprehensive search was conducted on PubMed, utilizing keywords such as "vulvodynia", "chronic vulvar pain", "vulvodynia induction", and "animal models of vulvodynia" to identify pertinent studies. The search yielded three primary animal models for vulvodynia: inflammation-induced, allergy-induced, and hormone-induced. Additionally, six agents capable of triggering the condition through diverse pathways were identified, including factors contributing to hyperinnervation, mast cell proliferation, involvement of other immune cells, inflammatory cytokines, and neurotransmitters. This review systematically outlines the various animal models developed to study the pathogenesis of provoked vulvodynia. Understanding these models is crucial for the exploration of preventative measures, the development of novel treatments, and the overall advancement of research within the field.

A phenotypic screening platform for chronic pain therapeutics using all-optical electrophysiology

ABSTRACT

Chronic pain associated with osteoarthritis (OA) remains an intractable problem with few effective treatment options. New approaches are needed to model the disease biology and to drive discovery of therapeutics. We present an in vitro model of OA pain, where dorsal root ganglion (DRG) sensory neurons were sensitized by a defined mixture of disease-relevant inflammatory mediators, here called Sensitizing PAin Reagent Composition or SPARC. Osteoarthritis-SPARC components showed synergistic or additive effects when applied in combination and induced pain phenotypes in vivo. To measure the effect of OA-SPARC on neural firing in a scalable format, we used a custom system for high throughput all-optical electrophysiology. This system enabled light-based membrane voltage recordings from hundreds of neurons in parallel with single cell and single action potential resolution and a throughput of up to 500,000 neurons per day. A computational framework was developed to construct a multiparameter OA-SPARC neuronal phenotype and to quantitatively assess phenotype reversal by candidate pharmacology. We screened ∼3000 approved drugs and mechanistically focused compounds, yielding data from over 1.2 million individual neurons with detailed assessment of functional OA-SPARC phenotype rescue and orthogonal "off-target" effects. Analysis of confirmed hits revealed diverse potential analgesic mechanisms including ion channel modulators and other mechanisms including MEK inhibitors and tyrosine kinase modulators. Our results suggest that the Raf-MEK-ERK axis in DRG neurons may integrate the inputs from multiple upstream inflammatory mediators found in osteoarthritis patient joints, and MAPK pathway activation in DRG neurons may contribute to chronic pain in patients with osteoarthritis.

Selective neural inhibition via photobiomodulation alleviates behavioral hypersensitivity associated with small sensory fiber activation

OBJECTIVE

Photobiomodulation at higher irradiances has great potential as a pain-alleviating method that selectively inhibits small diameter nerve fibers and corresponding sensory experiences, such as nociception and heat sensation. The longevity and magnitude of these effects as a function of laser irradiation parameters at the nerve was explored.

METHODS

In a rodent chronic pain model (spared nerve injury-SNI), light was applied directly at the sural nerve with four delivery schemes: two irradiance levels (7.64 and 2.55 W/cm2 ) for two durations each, corresponding to either 4.8 or 14.4 J total energy, and the effect on sensory hypersensitivities was evaluated.

RESULTS

At emitter irradiances of 7.64 W/cm2 (for 240 s), 2.55 W/cm2 (for 720 s), and 7.64 W/cm2 (for 80 s) the heat hypersensitivity was relieved the day following photobiomodulation (PBM) treatment by 37 ± 8.1% (statistically significant, p < 0.001), 26% ± 6% (p = 0.072), and 28 ± 6.1% (statistically significant, p = 0.032), respectively, and all three treatments reduced the hypersensitivity over the course of the experiment (13 days) at a statistically significant level (mixed-design analysis of variance, p < 0.05). The increases in tissue temperature (5.3 ± 1.0 and 1.3 ± 0.4°C from 33.3°C for the higher and lower power densities, respectively) at the neural target were well below those typically associated with permanent action potential disruption.

CONCLUSIONS

The data from this study support the use of direct PBM on nerves of interest to reduce sensitivities associated with small-diameter fiber activity.

Synthesis, molecular docking, electrochemical and fluorimetric analysis of new caffeic and cinnamic acid-conjugated hemorphin derivatives designed as potential anticonvulsant and antinociceptive agents

Based on the pharmacophore model of opioid receptors, our team recently synthesized a series of short-chain hemorphin peptide analogs containing non-natural amino acids. They demonstrated anticonvulsant and antinociceptive activity with low neurotoxicity. In the present study, a series of novel bioconjugates of N-modified hemorphin analogs containing second pharmacophore cinnamic acids (CA) or caffeic (KA) were synthesized by a traditional solid-phase Fmoc chemistry method for peptide synthesis. Electrochemical and fluorimetric analysis, in vivo anticonvulsant and antinociceptive activity in mice were conducted on the compounds. The three CA acid- (H4-CA, H5-CA, and H7-CA) and three KA acid- (H4-KA, H5-KA, and H7-KA) conjugated hemorphin derivatives exhibited potency at the highest doses of 2 µg/5 µl, administered by intracerebroventricular (icv) mode, against seizure spread in the maximal electroshock test (MES) in mice. The KA-conjugated H5-KA derivate, at the lowest dose, was the only compound that suppressed clonic seizures in the subcutaneous pentylenetetrazol (scPTZ) test. Except for the H5-CA, all tested CA acid- and KA acid-conjugated peptide derivates had the potency to increase the latency for clonic seizures in a dose-dependent mode. The activity against the psychomotor seizures in the 6-Hz test was detected only for the H4-CA (0.5 µg) and H4-KA (0.5 µg and 1 µg), respectively. All investigated peptides showed a more pronounced antinociceptive effect in the "intraplantar formalin" test compared to the "hot plate" test. Shorter chain analogs showed a better antinociceptive profile against tonic pain. The data suggest a DOR and KOR-mediated mechanism of action. According to the docking analysis, H7-CA showed a different antinociceptive profile than other investigated peptides. The novel peptide derivates did not exhibit neurotoxicity in the rotarod test. Our findings suggest that conjugated CA and KA morphine peptides can be used to develop novel morphine-related analogs with anticonvulsant and antinociceptive activity.

Himalayan Pyracantha crenulata (D.Don) M.Roem. leaf and fruit extracts alleviate algesia through COX-2 and Mu-opioid receptor mediated pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Pyracantha crenulata (D.Don) M.Roem., a plant of high nutritional and medicinal value is traditionally employed for its analgesic property in joint and body pain in the Kumaun region of Western Himalaya.

AIM OF THE STUDY

To validate the traditional claims for analgesic property of Pyracantha crenulata.

METHODS

Hydroethanolic extract of P. crenulata leaves and fruits were tested for their analgesic potential in rodent models for algesia by tail immersion test, tail flick test, Eddy's hot plate model, and formalin induced paw irritation test in Wistar rats. Molecular docking and dynamics studies were also performed to understand the possible mechanisms.

RESULTS

Both P. crenulata fruit extract and leaf extract exhibited significant amelioration in all the tested experimental models of algesia acting through central and peripheral mechanisms. The efficacy in reducing nociception was found comparable to diclofenac that was used as a reference standard. Molecular docking and dynamic simulation studies further established binding affinity of gallic acid (confirmed to be present in P. crenulata leaf extract through HPTLC profiling) with cyclooxygenase-2 (COX-2) and mu-opioid receptors, suggesting the modulatory effect of these extracts on COX-2 and mu-opioid receptors in combating algesia.

CONCLUSION

P. crenulata extracts produce analgesic effects plausibly through COX-2 and mu-opioid receptor mediated pathways.

Essential oil from leaves of Myrciaria floribunda (H. West ex Willd.) O. Berg has antinociceptive and anti-inflammatory potential

Myrciaria floribunda is a plant that is distributed across different Brazilian biomes such as the Amazon, Caatinga, Cerrado, and Atlantic Forest, and it possesses antioxidant, antimicrobial, and anticancer properties. The antinociceptive and anti-inflammatory properties of the essential oil from M. floribunda leaves (MfEO) were examined in this study using mouse models. Gas chromatography-mass spectrometry was employed to describe the oil, and the results revealed that δ-cadinene, bicyclogermacrene, α-cadinol, and epi-α-muurolol predominated in the chemical profile. The oil stimulated a decrease in nociception in the chemical and thermal models used to evaluate acute antinociceptive activity. Findings from the use of pain pathway blockers to study the presumed underlying mechanism indicated opioid pathway activity. The anti-edematogenic effect, decreased cell migration, and generation of pro-inflammatory cytokines provided evidence of the anti-inflammatory potential of the essential oil from M. floribunda. According to this research, the essential oil from M. floribunda can effectively alleviate acute pain and inflammation.

LncRNA NONRATT014888.2 contributes to cancer-induced bone pain through downregulation of natriuretic peptide receptor 3 in rats

Long noncoding RNA (lncRNA) is implicated in both cancer development and pain process. However, the role of lncRNA in the development of cancer-induced bone pain (CIBP) is unclear. LncRNA NONRATT014888.2 is highly expressed in tibia related dorsal root ganglions (DRGs) in CIBP rats which function is unknown. CIBP was induced by injection of Walker 256 mammary gland tumor cells into the tibia canal of female SD rats. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of rats were measured. Down-regulation of NONRATT014888.2 by siRNA in CIBP rats markedly attenuated hind-paw mechanical pain hypersensitivity. LncRNA-predicted target mRNAs analysis and mRNA sequencing results cued Socs3, Npr3 were related with NONRATT014888.2. Intrathecal injection of NONRATT014888.2-siR206 upregulated Npr3 both in mRNA and protein level. Npr3 was co-expressed in NONRATT014888.2-positive DRGs neurons and mainly located in cytoplasm, but not in Glial fibrillary acidic protein (GFAP)-positive cells. Intrathecal injection of ADV-Npr3 upregulated Npr3 expression and enhanced the PWT of CIBP rats. Our results suggest that upregulated lncRNA NONRATT014888.2 contributed to hyperalgesia in CIBP rats, and the mechanism may through downregulation of Npr3.

Evaluated periodontal tissues and oxidative stress in rats with neuropathic pain-like behavior

BACKGROUND

Oxidative stress has a critical effect on both persistent pain states and periodontal disease. Voltage-gated sodium NaV1.7 (SCN9A), and transient receptor potential ankyrin 1 (TRPA1) are pain genes. The goal of this study was to investigate oxidative stress markers, periodontal status, SCN9A, and TRPA1 channel expression in periodontal tissues of rats with paclitaxel-induced neuropathic pain-like behavior (NPLB).

METHODS AND RESULTS

Totally 16 male Sprague Dawley rats were used: control (n = 8) and paclitaxel-induced pain (PTX) (n = 8). The alveolar bone loss and 8-hydroxy-2-deoxyguanosine (8-OHdG) levels were analyzed histometrically and immunohistochemically. Gingival superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities (spectrophotometric assay) were measured. The relative TRPA1 and SCN9A genes expression levels were evaluated using quantitative real-time PCR (qPCR) in the tissues of gingiva and brain. The PTX group had significantly higher alveolar bone loss and 8-OHdG compared to the control. The PTX group had significantly lower gingival SOD, GPx and CAT activity than the control groups. The PTX group had significantly higher relative gene expression of SCN9A (p = 0.0002) and TRPA1 (p = 0.0002) than the control in gingival tissues. Increased nociceptive susceptibility may affect the increase in oxidative stress and periodontal destruction.

CONCLUSIONS

Chronic pain conditions may increase TRPA1 and SCN9A gene expression in the periodontium. The data of the current study may help develop novel approaches both to maintain periodontal health and alleviate pain in patients suffering from orofacial pain.

Construction of novel potentiometric sensors modified with biogenically synthesized metal oxide nanoparticles for sensitive detection of the opioid agonist-antagonist nalbuphine hydrochloride in its injection

Novel and sensitive potentiometric sensors were described for the assay of nalbuphine HCl (NBP) in authentic powder and injection samples. The developed sensors were modified with alumina nanoparticles (Al2O3NPs) and copper oxide nanoparticles (CuONPs). The nanoscale materials were synthesized using the extract of Salvia officinalis leaves in an environmentally friendly manner. The synthesized metal oxides were fully confirmed by various analytical techniques. Scanning electron microscope confirmed the morphology of nanosized materials with even distribution and particle size of 55.07 ± 4.15 and 59.48 ± 4.50 nm for Al2O3NPs and CuONPs, respectively. The modified sensors were prepared in three different steps. Nalbuphine hydrochloride was mixed with phosphomolybdic acid to prepare the sensor material nalbuphine phosphomolybdate (NBP-PM). It was then mixed with polyvinyl chloride in the presence of o-nitrophenyl ether and metal oxide nanoparticles to form the membrane matrix. Finally, a copper wire was coated with the sensing material. Excellent potentials of 1.0 × 10-8-1.0 × 10-2 and 1.0 × 10-9-1.0 × 10-2 mol L-1 were measured with lower assay limits of 4.8 × 10-9 and 5.0 × 10-10 mol L-1. The average detection % were 99.28 ± 0.58% and 99.52 ± 0.28% for NBP-PM-Al2O3NPs and NBP-PM-CuONPs, correspondingly. The suitability of the described sensors was investigated in terms of various validation criteria, and the modified sensors exposed excellent applicability and insurance for the quantification of nalbuphine hydrochloride in its bulk samples and injections compared with another standard sensor. It is obvious that the developed NBP-PM-Al2O3NPs and NBP-PM-CuONPs will serve as suitable sensors for the determination of NBP.

Thrombin-Induced Microglia Activation Modulated through Aryl Hydrocarbon Receptors

Thrombin is a multifunctional serine protein which is closely related to neurodegenerative disorders. The Aryl hydrocarbon receptor (AhR) is well expressed in microglia cells involving inflammatory disorders of the brain. However, it remains unclear as to how modulation of AhR expression by thrombin is related to the development of neurodegeneration disorders. In this study, we investigated the role of AhR in the development of thrombin-induced neurodegenerative processes, especially those concerning microglia. The primary culture of either wild type or AhR deleted microglia, as well as BV-2 cell lines, was used for an in vitro study. Hippocampal slice culture and animals with either wild type or with AhR deleted were used for the ex vivo and in vivo studies. Simulations of ligand protein docking showed a strong integration between the thrombin and AhR. In thrombin-triggered microglia cells, deleting AhR escalated both the NO release and iNOS expression. Such effects were abolished by the administration of the AhR agonist. In thrombin-activated microglia cells, downregulating AhR increased the following: vascular permeability, pro-inflammatory genetic expression, MMP-9 activity, and the ratio of M1/M2 phenotype. In the in vivo study, thrombin induced the activation of microglia and their volume, thereby contributing to the deterioration of neurobehavior. Deleting AhR furthermore aggravated the response in terms of impaired neurobehavior, increasing brain edema, aggregating microglia, and increasing neuronal death. In conclusion, thrombin caused the activation of microglia through increased vessel permeability, expression of inflammatory response, and phenotype of M1 microglia, as well the MMP activity. Deleting AhR augmented the above detrimental effects. These findings indicate that the modulation of AhR is essential for the regulation of thrombin-induced brain damages and that the AhR agonist may harbor the potentially therapeutic effect in thrombin-induced neurodegenerative disorder.

Rosuvastatin Synergistically Enhances the Antinociceptive Efficacy of Duloxetine in Paclitaxel-Induced Neuropathic Pain in Mice

Paclitaxel, a widely used cancer chemotherapeutic agent, has high incidence of neurotoxicity associated with the production of neuropathic pain, for which only duloxetine has shown significant but moderate analgesic effect. Since statins, classically used to reduce hypercholesterolemia, have shown antinociceptive effect in preclinical studies on neuropathic pain, we studied whether the antinociceptive efficacy of duloxetine could be synergistically potentiated by rosuvastatin in a model of paclitaxel-induced neuropathy in mice. The astrocytic and microglial responses in the spinal cord of paclitaxel-treated mice were also assessed by measuring GFAP and CD11b proteins, respectively. Paclitaxel treatment did not impair motor coordination and balance in rotarod testing. Rosuvastatin, duloxetine, and the rosuvastatin/duloxetine combination (combined at equieffective doses) dose-dependently decreased mechanical allodynia (ED₃₀, von Frey testing) and thermal hyperalgesia (ED₅₀, hot plate testing) in paclitaxel-treated mice. Isobolographic analysis showed a superadditive interaction for rosuvastatin and duloxetine, as both the ED₃₀ and ED₅₀ for the rosuvastatin/duloxetine combination contained only a quarter of each drug compared to the individual drugs. The rosuvastatin/duloxetine combination reversed paclitaxel-induced GFAP overexpression, indicating that such effects might depend in part on astrocyte inactivation. Results suggest that statins could be useful in synergistically enhancing the efficacy of duloxetine in some chemotherapy-induced neuropathic conditions.

Evaluating Pain Behaviours: Widely Used Mechanical and Thermal Methods in Rodents

Globally, over 300 million surgical procedures are performed annually, with pain being one of the most common post-operative side effects. During the onset of injury, acute pain plays a protective role in alerting the individual to remove noxious stimuli, while long-lasting chronic pain without any physiological reason is detrimental to the recovery process. Hence, it created an urgent need to better understand the pain mechanism and explore therapeutic targets. Despite the hardship in performing human pain studies due to ethical considerations, clinically relevant rodent pain models provide an excellent opportunity to perform pain studies. Several neurobehavioural tests are used to assess the drug efficacy in rodents to determine avoidance behaviour latency and threshold. This review article provides a methodological overview of mechanical (i.e. von Frey, Mechanical Conflict System) and thermal (i.e. Hargreaves Assay, Hot and Cold Plate, Temperature Place Preference) tests to assess pain in clinically relevant pain rodent models. We further discussed the current modifications of those tests along with their use in literature, the impact of confounding variables, advantages and disadvantages.

Neoline, fuziline, songorine and 10-OH mesaconitine are potential quality markers of Fuzi: In vitro and in vivo explorations as well as pharmacokinetics, efficacy and toxicity evaluations

ETHNOPHARMACOLOGICAL RELEVANCE

Fuzi, the lateral roots of Aconitum carmichaelii Debx, plays an irreplaceable role in treating Yang deficiency and cold coagulation syndromes. However, Fuzi has a narrow margin of safety since its pharmacological constituents, Aconitum alkaloids, have potential cardiotoxicity and neurotoxicity. The current quality markers (Q-markers) for the control of Fuzi's efficacy and toxicity are 3 monoester-diterpenoid alkaloids, namely, benzoylaconine (BAC), benzoylhypaconine and benzoylmesaconine (BMA) and 3 diester-diterpenoid alkaloids, namely, aconitine (AC), hypaconitine and mesaconitine (MA). However, mounting evidence indicates that the current 6 Q-markers may not be efficacy- or toxicity-specific enough for Fuzi.

AIM OF THE STUDY

The aim of this study was to explore and evaluate efficacy- or toxicity-specific potential quality markers (PQ-markers) of Fuzi.

MATERIALS AND METHODS

PQ-markers were explored by analyzing 30 medicinal samples and alkaloids exposed in mouse. Pharmacokinetics of PQ-markers on C57BL/6J mice were determined. Anti-inflammatory effects of PQ-markers were evaluated by λ-carrageenan-induced paw edema model and lipopolysaccharide-induced RAW264.7 cell inflammatory model, while analgesic effects were assessed by acetic acid-induced pain model and Hargreaves test. Cardiotoxicity and neurotoxicity of PQ-markers were assessed by histological and biochemical analyses, while acute toxicity was evaluated by modified Kirschner method.

RESULTS

After in vitro and in vivo explorations, 7 PQ-markers, namely, neoline (NE), fuziline (FE), songorine (SE), 10-OH mesaconitine (10-OH MA), talatizamine, isotalatizidine and 16β-OH cardiopetalline, were found. In the herbal medicines, NE, FE, SE and 10-OH MA were found in greater abundance than many other alkaloids. Specifically, the amounts of NE, FE and SE in the Fuzi samples were all far higher than that of BAC, and the contents of 10-OH MA in 56.67% of the samples were higher than that of AC. In mouse plasma and tissues, NE, FE, SE, talatizamine, isotalatizidine and 16β-OH cardiopetalline had higher contents than the other alkaloids, including the 6 current Q-markers. The pharmacokinetics, efficacy and toxicity of NE, FE, SE and 10-OH MA were further evaluated. The average oral bioavailabilities of NE (63.82%), FE (18.14%) and SE (49.51%) were higher than that of BMA (3.05%). Additionally, NE, FE and SE produced dose-dependent anti-inflammatory and analgesic effects, and their actions were greater than those of BMA. Concurrently, the toxicities of NE, FE and SE were lower than those of BMA, since no cardiotoxicity or neurotoxicity was found in mice after NE, FE and SE treatment, while BMA treatment notably increased the creatine kinase activity and matrix metalloproteinase 9 level in mice. The average oral bioavailability of 10-OH MA (7.02%) was higher than that of MA (1.88%). The median lethal dose (LD₅₀) of 10-OH MA in mice (0.11 mg/kg) after intravenous injection was close to that of MA (0.13 mg/kg). Moreover, 10-OH MA produced significant cardiotoxicity and neurotoxicity, and notable anti-inflammatory and analgesic effects that were comparable to those of MA.

CONCLUSIONS

Seven PQ-markers of Fuzi were found after in vitro and in vivo explorations. Among them, NE, FE and SE were found to be more efficacy-specific than BMA, and 10-OH MA was as toxicity-specific as MA.

Increased nociceptive sensitivity is associated with periodontal inflammation and expression of chronic pain genes in gingival tissues of male rats

OBJECTIVE

This study aimed to evaluate the inflammatory response, hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2), and voltage-gated potassium (Kv) 9.1 channel expression in rats with paclitaxel-induced neuropathic pain-like behavior.

METHODS

Sixteen male Sprague Dawley rats were divided equally into two groups: control and paclitaxel-induced pain (PTX). The attachment loss and inflammatory cell infiltrate levels were analyzed histometrically and immunohistochemically. The gene expression of HCN2 and KCNS1 was analyzed by qPCR in the brain and gingival tissues.

RESULTS

The attachment loss and prominent infiltration of inflammatory cells were significantly higher in the PTX group than in the control groups. In gingival tissues; the expression levels of HCN2 (p = 0,0011) were significantly higher and KCNS1 (p = 0,0003) were significantly lower in the PTX group than in the control groups.

CONCLUSION

Increased nociceptive sensitivity, may play a role in periodontal inflammation. KCNS1 may decrease and HCN2 expression may increase in periodontium in permanent chronic pain states. The results of the present study may be helpful in developing new approaches to alleviate pain and maintain periodontal health in patients suffering from orofacial pain.

Anti-nociceptive Activity of Quebracho tannin Extract on Pain Induced by Formalin and Writhing Tests in Mice

Background: Based on positive role of the tannins for pain relief, there is no report for possible antinociceptive activity of the Quebracho tannin. Objectives: This study aimed to determine the anti-nociceptive activity of the Quebracho tannin extract (QTE) on pain in mice. Materials and Methods: For this purpose, 340 mice were used for formalin and writhing tests each including 4 experiments with 4 sub-groups. In experiment 1, mice were injected with saline, QTE (100 mg/kg), QTE (200 mg/kg), QTE (400 mg/kg), and morphine (5 mg/kg). In the second experiment, injections included saline, QTE (400 mg/kg), naloxone (2 mg/kg), and QTE + naloxone. Experiments 3 and 4 were similar to experiment 2, except that mice injected were with NG-nitro arginine methyl ester (L-NAME, 10 mg/kg) and cyproheptadine (4 mg/kg) instead of naloxone. Then, formalin (1%) was injected, and time spent for licking the injected paw was recorded until 30 minutes following injection in the first and second phases. Finally, injections in 4 experiment groups were the same, and animals were intraperitoneally injected with acetic acid, and contractions were recorded in the writhing test category. Results: According to the results, QTE (100, 200, and 400 mg/kg) decreased pain in the injected paw (P=0.001) and inhibited the pain response by 59.37% (P=0.001). Moreover, the injection of naloxone + QTE significantly decreased pain in the injected paw (P=0.021). Eventually, the injection of the L-NAME + QTE significantly reduced the anti-nociception effect of the QTE on the formalin test (P=0.031) and writhing contractions (55.75%, P=0.033). Conclusion: These findings suggested anti-nociceptive properties of the QTE mediated by opioidergic and nitrergic systems.

Neuroprotective effects of Olea europaea L. fruit extract against cigarette smoke-induced depressive-like behaviors in Sprague-Dawley rats

Depression is broadly acclaimed as a mental health anomaly and despite advancements in the development of antidepressant drugs, they are linked with side effects. Dietary modifications and medicinal plants like olives can be used as effective strategies due to their antioxidant, immune-modulatory, antiinflammatory, and anticonvulsant properties. Considering the compositional alterations in olive fruits during ripening, the antidepressant potential of olive fruits at different degrees of ripeness, that is, un-ripened (green) and ripened (black) was investigated. Rats were randomly divided into five groups: G₀ (Normal diet), G₁ (Normal diet + smoke exposure (SE), G₂ (Normal diet + SE + Citalopram), G₃ (Normal diet + SE + Green olive extract), and G₄ (Normal diet + SE + Black olive extract). Depressive-like behaviors were induced in all groups through cigarette smoke exposure except G₀ . Green and black olive extracts prevented depressive behaviors by reducing the immobility time of rats in forced swim test and tail suspension test while increased the latency to respond in hot plate assay. Moreover, lipid peroxidation in brain tissue was reduced with citalopram, green, and black olive extracts. Additionally, treatments also enhanced the antioxidant pool of brain tissues. Histological examination revealed that olive extracts and citalopram prevented cigarette smoke-induced moderate to severe necrosis and congestion in the brain parenchyma and elucidated antidepressant potential by improving the expression of monoamine oxidase-A, solute carrier family 6 member 4, and brain-derived neurotrophic factor genes. Conclusively, olives may act as a promising antidepressant agent in ameliorating cigarette smoke-induced depressive-like behaviors. PRACTICAL APPLICATIONS: Olive extracts at both ripening stages revealed an antidepressant-like effect almost similar to the standard antidepressant drug and also prevented oxidative damages. Therefore, from the current findings, it can be recommended that food ingredients with antidepressant potential like olives should be incorporated in future interventions to combat depression/psychiatric anomalies and diet therapy should be encouraged to alleviate lifestyle-related disorders.

Limonene from Agastache mexicana essential oil produces antinociceptive effects, gastrointestinal protection and improves experimental ulcerative colitis

ETHNOPHARMACOLOGY RELEVANCE

Agastache mexicana is a popular plant of great demand in folk medicine, essentially due to its calming properties and for alleviating arthritic, muscular and abdominal pain. Despite its spectrum for pain relief, pharmacological studies of its bioactive constituents have been barely investigated.

AIM OF THE STUDY

To evaluate protective properties of the A. mexicana and bioactive compounds improving pathological gastrointestinal conditions in rodents.

MATERIAL AND METHODS

Different doses of the essential oil of A. mexicana ssp. mexicana and ssp. xolocotziana (30-562.2 mg/kg, i.p.) and individual monoterpenes (3-300 mg/kg, i.p.) were evaluated in an abdominal pain model. The most active monoterpene limonene and sulfasalazine (reference drug, 100 mg/kg, p.o.) were also evaluated in the oxazolone-induced colitis model using an oral gavage, where some inflammatory cytokines were analyzed by enzyme-linked immunosorbent assays. Finally, colonic histological assessment and gastroprotection in the absolute ethanol-induced ulcer model were explored.

RESULTS

Our results demonstrated that the essential oil of both subspecies produced a significant reduction in the abdominal writhes, where monoterpenes limonene and pulegone were partially responsible bioactive metabolites. Limonene showed the major antinociceptive efficacy in the writhing test. It also significantly decreased hyperalgesia, pathological biomarkers, and colonic inflammatory cytokines in the oxazolone-induced colitis model, as well as prevention in gastric damage.

CONCLUSIONS

Present results provide scientific evidence to reinforce the use of A. mexicana in the traditional medicine for gastrointestinal conditions, mainly related to pain and inflammation, demonstrating the potential of monoterpenes as natural products in the therapeutics of gastrointestinal affections such as ulcer, colitis, and abdominal pain.

Involvement of opioidergic and GABAergic systems in the anti-nociceptive activity of the methanolic extract of Cuscuta Epithymum Murr. in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cuscuta epithymum Murr. (CE) is a parasitic plant used as a traditional medicine to treat various diseases such as muscle and joint pains and headache different parts of the world, Europe in the north, Asia in the east.

AIM OF THE STUDY

In this study, we aimed to investigate the anti-nociceptive effect of the methanolic extract of the aerial parts of CE and its probable mechanism(s) in mice.

MATERIALS AND METHODS

The anti-nociceptive activity of different doses of CE methanolic extract (2.5, 5, 10, 25, 50 and 100 mg/kg, i.p.) was assessed using tail flick, formalin and writhing tests. Morphine (5 mg/kg, s.c.) was used as positive control drug. The possible mechanisms were evaluated by using naloxone (4 mg/kg, i.p.), ondansetron (4 mg/kg, i.p.), picrotoxin (0.6 mg/kg, i.p.) and MK-801 (0.03 mg/kg, i.p.).

RESULTS

GC-MS analysis indicated that one of the main components of CE extract was terpenoid compounds. The CE extract (25-100 mg/kg), like morphine, reduced tail flick latency and nociceptive response in both phases of the formalin test. We also observed that the extract significantly decreased the number of abdominal contractions dose-dependently from 5 to 100 mg/kg. The results of tail flick and the first phase of formalin test proved that unlike ondansetron and MK-801, naloxone and picotroxin were able to reverse the anti-nociceptive effect of CE extract.

CONCLUSION

Our observations showed the anti-nociceptive potential of the CE extract, which may be mediated by opioidergic and GABAergic systems.

Ulinastatin Exhibits Antinociception in Rat Models of Acute Somatic and Visceral Pain Through Inhibiting the Local and Central Inflammation

Introduction

Ulinastatin, a broad-spectrum serine protease inhibitor, has been widely used to treat various diseases clinically. However, so far, the antinociceptive effect of ulinastatin remains less studied experimentally and the underlying mechanisms of ulinastatin for pain relief remain unclear. This study aimed to find evidence of the analgesic effect of ulinastatin on acute somatic and visceral pain.

Methods

The analgesic effect of ulinastatin on acute somatic and visceral pain was evaluated by using formalin and acetic acid-induced writhing test. The analgesic mechanism of ulinastatin was verified by detecting the peripheral inflammatory cell infiltration and spinal glial activation with hematoxylin-eosin (H&E) and immunohistochemistry staining.

Results

We found that both of intraperitoneal (i.p.) pre-administration and post-administration of ulinastatin could reduce the total number of flinching and the licking duration following intraplantar formalin injection in a dose-related manner. However, the inhibitory effect of ulinastatin existed only in the second phase (Phase 2) of formalin-induced spontaneous pain response, with no effect in the first phase (Phase 1). The formalin-induced edema and ulcer were also improved by i.p. administration of ulinastatin. Moreover, i.p. administration of ulinastatin was also able to delay the occurrence of acetic acid-induced writhing and reduced the total number of writhes dose-dependently. We further demonstrated that ulinastatin significantly decreased the local inflammatory cell infiltration in injured paw and peritoneum tissue under formalin and acetic acid test separately. The microglial and astrocytic activation in the spinal dorsal horn induced by intraplantar formalin and i.p. acetic acid injection were also dramatically inhibited by i.p. administration of ulinastatin.

Conclusion

Our results for the first time provided a new line of evidence showing that ulinastatin could attenuate acute somatic and visceral pain by inhibiting the peripheral and spinal inflammatory reaction.

Evaluation of Antinociceptive Effects of Chitosan-Coated Liposomes Entrapping the Selective Kappa Opioid Receptor Agonist U50,488 in Mice

Background and Objectives: The selective kappa opioid receptor agonist U50,488 was reported to have analgesic, cough suppressant, diuretic and other beneficial properties. The aim of our study was to analyze the effects of some original chitosan-coated liposomes entrapping U50,488 in somatic and visceral nociceptive sensitivity in mice. Materials and Methods: The influence on the somatic pain was assessed using a tail flick test by counting the tail reactivity to thermal noxious stimulation. The nociceptive visceral estimation was performed using the writhing test in order to evaluate the behavioral manifestations occurring as a reaction to the chemical noxious peritoneal irritation with 0.6% acetic acid (10 mL/kbw). The animals were treated orally, at the same time, with a single dose of: distilled water 0.1 mL/10 gbw; 50 mg/kbw U50,488; 50 mg/kbw U50,488 entrapped in chitosan-coated liposomes, according to the group they were randomly assigned. Results: The use of chitosan-coated liposomesas carriers for U50,488 induced antinociceptive effects that began to manifest after 2 h, andwere prolonged but with a lower intensity than those caused by the free selective kappa opioid in both tests. Conclusion: In this experimental model, the oral administration of nanovesicles containing the selective kappa opioid agonist U50,488 determined a prolonged analgesic outcome in the tail flick test, as well as in the writhing test.

Synergistic interaction between trazodone and gabapentin in rodent models of neuropathic pain

Neuropathic pain is a chronic debilitating condition caused by injury or disease of the nerves of the somatosensory system. Although several therapeutic approaches are recommended, none has emerged as an optimal treatment leaving a need for developing more effective therapies. Given the small number of approved drugs and their limited clinical efficacy, combining drugs with different mechanisms of action is frequently used to yield greater efficacy. We demonstrate that the combination of trazodone, a multifunctional drug for the treatment of major depressive disorders, and gabapentin, a GABA analogue approved for neuropathic pain relief, results in a synergistic antinociceptive effect in the mice writhing test. To explore the potential relevance of this finding in chronic neuropathic pain, pharmacodynamic interactions between low doses of trazodone (0.3 mg/kg) and gabapentin (3 mg/kg) were evaluated in the chronic constriction injury (CCI) rat model, measuring the effects of the two drugs both on evoked and spontaneous nociception and on general well being components. Two innate behaviors, burrowing and nest building, were used to assess these aspects. Besides exerting a significant antinociceptive effect on hyperalgesia and on spontaneous pain, combined inactive doses of trazodone and gabapentin restored in CCI rats innate behaviors that are strongly reduced or even abolished during persistent nociception, suggesting that the combination may have an impact also on pain components different from somatosensory perception. Our results support the development of a trazodone and gabapentin low doses combination product for optimal multimodal analgesia treatment.