Chronic Neuropathic Pain Model Research Articles

Examination of the antiallodynic effect of rosmarinic acid in neuropathic pain and possible mechanisms of action

This study aimed to explore the potential antiallodynic effects of rosmarinic acid, a natural antioxidant with a demonstrated safety profile across a broad dose range. Using a chronic constriction injury-induced neuropathic pain model, the impact of rosmarinic acid on allodynia was investigated. Furthermore, the involvement of adrenergic and opioidergic mechanisms in its activity was assessed. To evaluate rosmarinic acid’s efficacy, doses of 10, 20, and 40 mg/kg were administered and the electronic von Frey test was utilized along with an activity cage apparatus. % MPE values were calculated to gauge the extent of pain relief. Mechanistic insights were obtained by pretreating animals with the β-adrenergic receptor antagonist propranolol, the α1-adrenergic receptor antagonist prazosin, α2-adrenergic receptor antagonist yohimbine, and the opioid receptor antagonist naloxone. Rosmarinic acid demonstrated a statistically significant antiallodynic effect that was independent of locomotor activity. This effect was noteworthy as it resembled both the level and duration of relief provided by pregabalin. Additionally, the %MPE value of the group treated with 40 mg/kg rosmarinic acid showed a significant difference compared to the value of the pregabalin-treated group (P<0.001). Pre-administration of the antagonists revealed that the antiallodynic activity was shown to be mediated by the stimulation of opioid and adrenergic receptors, with a primary contribution from α2-adrenergic receptor stimulation. Our findings suggest that rosmarinic acid may hold promise as a potential therapeutic agent for neuropathic pain. By elucidating the involvement of adrenergic and opioidergic mechanisms, we have provided valuable preclinical data that could inform novel treatment approaches.

Neuropeptide Y Y2 Receptors in Sensory Neurons Tonically Suppress Nociception and Itch but Facilitate Postsurgical and Neuropathic Pain Hypersensitivity.

Neuropeptide Y (NPY) Y2 receptor (Y2) antagonist BIIE0246 can both inhibit and facilitate nociception. The authors hypothesized that Y2 function depends on inflammation or nerve injury status. The authors implemented a battery of behavioral tests in mice of both sexes that received (1) no injury; (2) an incision model of postoperative pain; (3) a spared nerve injury model of neuropathic pain; and (4) a latent sensitization model of chronic postsurgical pain. In addition to Y2 gene expression assays, spinal Y2 G-protein coupling was studied with guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding assays. The authors report that intrathecal BIIE0246 increased mechanical and cold hypersensitivity, produced behavioral signs of spontaneous nociception and itch, and produced conditioned place aversion and preference in normal, uninjured mice. BIIE0246 did not change heat hypersensitivity or motor coordination. Conditional (sensory neuron-specific) Y2 deletion prevented BIIE0246-induced mechanical and cold hypersensitivity, nocifensive behaviors, and aversion. Both conditional deletion and pharmacologic blockade of Y2 reduced mechanical and thermal hypersensitivity after incision or nerve injury. SNI did not change the sensitivity of Y2 G-protein coupling with the Y2 agonist peptide YY (3-36) (PYY3-36), but increased the population of Y2 that effectively coupled G-proteins. Intrathecal PYY3-36 failed to reduce spared nerve injury- or incision-induced hypersensitivity in C57BL/6N mice. Incision did not change Npy2r gene expression in dorsal root ganglion. The authors conclude that Y2 at central terminals of primary afferent neurons provides tonic inhibition of mechanical and cold nociception and itch. This switches to the promotion of mechanical and thermal hyperalgesia in models of acute and chronic postsurgical and neuropathic pain, perhaps due to an increase in the population of Y2 that effectively couples to G-proteins. These results support the development of Y2 antagonists for the treatment of chronic postsurgical and neuropathic pain.

Role of HDAC5 Epigenetics in Chronic Craniofacial Neuropathic Pain.

The information provided from the papers reviewed here about the role of epigenetics in chronic craniofacial neuropathic pain is critically important because epigenetic dysregulation during the development and maintenance of chronic neuropathic pain is not yet well characterized, particularly for craniofacial pain. We have noted that gene expression changes reported vary depending on the nerve injury model and the reported sample collection time point. At a truly chronic timepoint of 10 weeks in our model of chronic neuropathic pain, functional groupings of genes examined include those potentially contributing to anti-inflammation, nerve repair/regeneration, and nociception. Genes altered after treatment with the epigenetic modulator LMK235 are discussed. All of these differentials are key in working toward the development of diagnosis-targeted therapeutics and likely for the timing of when the treatment is provided. The emphasis on the relevance of time post-injury is reiterated here.

Select Minor Cannabinoids from Cannabis sativa Are Cannabimimetic and Antinociceptive in a Mouse Model of Chronic Neuropathic Pain.

Chronic pain conditions affect nearly 20% of the population in the United States. Current medical interventions, such as opioid drugs, are effective at relieving pain but are accompanied by many undesirable side effects. This is one reason increased numbers of chronic pain patients have been turning to Cannabis for pain management. Cannabis contains many bioactive chemical compounds; however, current research looking into lesser-studied minor cannabinoids in Cannabis lacks uniformity between experimental groups and/or excludes female mice from investigation. This makes it challenging to draw conclusions between experiments done with different minor cannabinoid compounds between laboratories or parse out potential sex differences that could be present. We chose five minor cannabinoids found in lower quantities within Cannabis: cannabinol (CBN), cannabidivarin (CBDV), cannabigerol (CBG), Δ8-tetrahydrocannabinol (Δ8-THC), and Δ9-tetrahydrocannabivarin (THCV). These compounds were then tested for their cannabimimetic and pain-relieving behaviors in a cannabinoid tetrad assay and a chemotherapy-induced peripheral neuropathy (CIPN) pain model in male and female CD-1 mice. We found that the minor cannabinoids we tested differed in the cannabimimetic behaviors evoked, as well as the extent. We found that CBN, CBG, and high-dose Δ8-THC evoked some tetrad behaviors in both sexes, while THCV and low-dose Δ8-THC exhibited cannabimimetic tetrad behaviors only in females. Only CBN efficaciously relieved CIPN pain, which contrasts with reports from other researchers. Together these findings provide further clarity to the pharmacology of minor cannabinoids and suggest further investigation into their mechanism and therapeutic potential. SIGNIFICANCE STATEMENT: Minor cannabinoids are poorly studied ligands present in lower levels in Cannabis than cannabinoids like THC. In this study, we evaluated five minor cannabinoids (CBN, CBDV, CBG, THCV, and Δ8-THC) for their cannabimimetic and analgesic effects in mice. We found that four of the five minor cannabinoids showed cannabimimetic activity, while one was efficacious in relieving chronic neuropathic pain. This work is important in further evaluating the activity of these drugs, which are seeing wider public use with marijuana legalization.

Terpenes from Cannabis sativa induce antinociception in a mouse model of chronic neuropathic pain via activation of adenosine A 2A receptors.

Terpenes are small hydrocarbon compounds that impart aroma and taste to many plants, including Cannabis sativa . A number of studies have shown that terpenes can produce pain relief in various pain states in both humans and animals. However, these studies were methodologically limited and few established mechanisms of action. In our previous work, we showed that the terpenes geraniol, linalool, β-pinene, α-humulene, and β-caryophyllene produced cannabimimetic behavioral effects via multiple receptor targets. We thus expanded this work to explore the potential antinociception and mechanism of these Cannabis terpenes in a mouse model of chronic pain. We first tested for antinociception by injecting terpenes (200 mg/kg, IP) into male and female CD-1 mice with mouse models of chemotherapy-induced peripheral neuropathy (CIPN) or lipopolysaccharide-induced inflammatory pain, finding that the terpenes produced roughly equal antinociception to 10 mg/kg morphine or 3.2 mg/kg WIN55,212. We further found that none of the terpenes produced reward as measured by conditioned place preference, while low doses of terpene (100 mg/kg) combined with morphine (3.2 mg/kg) produced enhanced antinociception vs either alone. We then used the adenosine A 2A receptor (A 2A R) selective antagonist istradefylline (3.2 mg/kg, IP) and spinal cord-specific CRISPR knockdown of the A 2A R to identify this receptor as the mechanism for terpene antinociception in CIPN. In vitro cAMP and binding studies and in silico modeling studies further suggested that the terpenes act as A 2A R agonists. Together these studies identify Cannabis terpenes as potential therapeutics for chronic neuropathic pain and identify a receptor mechanism for this activity.

Chemogenetic Manipulation of Amygdala Kappa Opioid Receptor Neurons Modulates Amygdala Neuronal Activity and Neuropathic Pain Behaviors

Chemogenetic Manipulation of Amygdala Kappa Opioid Receptor Neurons Modulates Amygdala Neuronal Activity and Neuropathic Pain Behaviors

A next generation peripherally restricted Cavα2δ-1 ligand with inhibitory action on Cav2.2 channels and utility in neuropathic pain

The Voltage-Gated Calcium Channel (VGCC) auxiliary subunit Cavα2δ-1 (CACNA2D1) is the target/receptor of gabapentinoids which are known therapeutics in epilepsy and neuropathic pain. Following damage to the peripheral sensory nervous system, Cavα2δ-1 is upregulated in dorsal root ganglion (DRG) neurons in several animal models of chronic neuropathic pain. Gabapentinoids, such as gabapentin and pregabalin, engage with Cavα2δ-1 via binding an arginine residue (R241) within an RRR motif located at the N-terminus of human Cavα2δ-1. A novel, next generation gabapentinoid, engineered not to penetrate the brain, was able to generate a strong analgesic response in Chronic Constriction Injury animal model of chronic neuropathic pain and showed binding specificity for Cavα2δ-1 versus the Cavα2δ-2 subunit. This novel non-brain penetrant gabapentinoid, binds to R241 and a novel binding site on Cavα2δ-1, which is located within the VGCC_α2 domain, identified as a lysine residue within an IKAK amino acid motif (K634). The overall whole cell current amplitudes were diminished by the compound, with these inhibitory effects being diminished in R241A mutant Cavα2δ-1 subunits. The functional effects occurred at lower concentrations than those needed for inhibition by gabapentin or pregabalin, which apparently bound the Cavα2δ-1 subunit only on the R241 and not on the K634 residue. Our work sets the stage for the identification and characterisation of novel compounds with therapeutic properties in neuropathic pain and possibly in other disorders and conditions which require engagement of the Cavα2δ-1 target.

Ketogenic Diet Alleviates Mechanical Allodynia in the Models of Inflammatory and Neuropathic Pain in Male Mice.

Inflammation is involved in the induction of chronic inflammatory and neuropathic pain. Moreover, the ketogenic diet, a high-fat, low-carbohydrate, and adequate protein diet, has an anti-inflammatory effect. Thus, we hypothesized that a ketogenic diet has a therapeutic effect on both types of chronic pain. In the present study, we investigated the effect of a ketogenic diet on mechanical allodynia, a chronic pain symptom, in formalin-induced chronic inflammatory pain and nerve injury-induced neuropathic pain models using adult male mice. Formalin injection into the hind paw induced mechanical allodynia in both the injected and intact hind paws, and the ketogenic diet alleviated mechanical allodynia in both hind paws. In addition, the ketogenic diet prevented formalin-induced edema. Furthermore, the diet alleviated mechanical allodynia induced by peripheral nerve injury. Thus, these findings indicate that a ketogenic diet has a therapeutic effect on chronic pain induced by inflammation and nerve injury.

Substance P-Botulinum Mediates Long-term Silencing of Pain Pathways that can be Re-instated with a Second Injection of the Construct in Mice

Chronic pain presents an enormous personal and economic burden and there is an urgent need for effective treatments. In a mouse model of chronic neuropathic pain, selective silencing of key neurons in spinal pain signalling networks with botulinum constructs resulted in a reduction of pain behaviours associated with the peripheral nerve. However, to establish clinical relevance it was important to know how long this silencing period lasted. Now, we show that neuronal silencing and the concomitant reduction of neuropathic mechanical and thermal hypersensitivity lasts for up to 120d following a single injection of botulinum construct. Crucially, we show that silencing and analgesia can then be reinstated with a second injection of the botulinum conjugate. Here we demonstrate that single doses of botulinum-toxin conjugates are a powerful new way of providing long-term neuronal silencing and pain relief. PerspectiveThis research demonstrates that botulinum-toxin conjugates are a powerful new way of providing long-term neuronal silencing without toxicity following a single injection of the conjugate and have the potential for repeated dosing when silencing reverses.

흰 쥐의 만성 통증모델에서 구강건조증이 c-fos 발현에 미치는 영향

Objectives: The purpose of this study was to determine whether xerostomia could improve the level of neuropathic pain. To conduct the study, the change in c-fos expression level in the medulla oblongata was confirmed by xerostomia induction using the chronic neuropathic facial pain model. Methods: mal-positioned dental implant surgery was performed on the extraction site of the mandibular second molar of rats, and 4-diphenylacetoxy-N- methylpiperidine (4-DAMP) (30mg/kg) was injected intraperitoneally after a pain test on the 4th day after surgery. c-fos was counted only in the lamina I and II regions. Results: A significant increase in c-fos expression was observed when the maxilla was stimulated compared to the mandible in the group induced both neuropathy and xerostomia. Conclusions: Therefore, it is considered that xerostomia in the facial area is the cause of the expression of chronic pain and the improvement of pain sensation.

Ninety-Hz Spinal Cord Stimulation–Induced Analgesia Is Dependent on Active Charge Balance and Is Nonlinearly Related to Amplitude: A Sham-Controlled Behavioral Study in a Rodent Model of Chronic Neuropathic Pain

BackgroundNinety-Hz active-recharge spinal cord stimulation (SCS) applied at below sensory-threshold intensity, as used with fast-acting subperception therapy spinal cord stimulation, has been shown clinically to produce significant analgesia, but additional characterization is required to better understand the therapy. This preclinical study investigates the behavioral effect of multiple 90-Hz SCS variants in a rodent model of neuropathic pain, focusing on charge balance and the relationship between 90-Hz efficacy and stimulation intensity. Materials and MethodsRats (n = 24) received a unilateral partial sciatic nerve ligation to induce neuropathic pain and were implanted with a quadripolar lead at T13. Mechanical hypersensitivity was assessed before, during, and after 60 minutes of SCS. After a prescreen with 50-Hz SCS 67% motor threshold ([MT], the positive control), rats underwent a randomized-crossover study including sham SCS and several 90-Hz SCS paradigms (at 40% MT or 60% MT, either using active or pseudopassive recharge) (experiment 1, n = 16). A second, identical experiment (experiment 2) was performed to supplement data with 90-Hz SCS at 20% and 80% MT (experiment 2, n = 8). ResultsExperiment 1: At 40% MT, 90-Hz active-recharge SCS produced a significantly larger recovery to baseline than did 90-Hz pseudopassive SCS at both tested intensities and sham SCS. Experiment 2: Only the 90-Hz SCS active recharge at 40% MT and 50-Hz SCS positive control caused mean recovery to baseline that was statistically better than that of sham SCS. ConclusionsThe degree to which 90-Hz SCS reduced mechanical hypersensitivity during stimulation depended on the nature of charge balance, with 90-Hz active-recharge SCS generating better responses than did 90-Hz pseudopassive recharge SCS. In addition, our findings suggest that the amplitude of 90-Hz active-recharge SCS must be carefully configured for efficacy.

Epigenetic HDAC5 Inhibitor Reverses Craniofacial Neuropathic Pain in Mice

Identifying and resolving molecular complexities underlying chronic neuropathic pain is a significant challenge. Among the numerous classes of histone deacetylases, Class I (HDAC 1–3) and Class III (sirtuins) have been best studied in experimental pain models where inhibitor pre-treatments but not post-treatments abrogate the development of pain-related behaviors. Post-treatment here in week 3 with less well-studied Class IIa HDAC4/5 selective inhibitor LMK235 diminishes the trigeminal ganglia increases of HDAC5 RNA and protein in two chronic orofacial neuropathic pain models to levels measured in naïve mice at week 10 post-model induction. HDAC4 RNA reported in lower limb inflammatory pain models is not evident in the trigeminal models. Many other gene alterations persisting at week 10 in the trigeminal ganglia (TG) are restored to naïve levels in mice treated with LMK235. Important pain-related upregulated genes Hoxc8,b9,d8; P2rx4, Cckbr, growth hormone (Gh), and schlafen (Slfn4) are greatly reduced in LMK235-treated mice. Fold increase in axon regeneration/repair genes Sostdc1, TTr, and Folr1 after injury are doubled by LMK235 treatment. LMK235 reduces the excitability of trigeminal ganglia neurons in culture isolated from nerve injured mice compared to vehicle-treated controls, with no effect on neurons from naïve mice. Electrophysiological characterization profile includes a shift where ∼20% of the small neurons recorded under LMK235-treated conditions are high threshold, whereas none of the neurons under control conditions have high thresholds. LMK235 reverses long-standing mechanical and cold hypersensitivity in chronic trigeminal neuropathic pain models in males and females (5,10 mg/kg), preventing development of anxiety- and depression-like behaviors. PerspectiveData here support HDAC5 as key epigenetic factor in chronic trigeminal neuropathic pain persistence, validated with the study of RNA alterations, TG neuronal excitability, and pain-related behaviors. HDAC5 inhibitor given in week 3 restores RNA balance at 10 weeks, while upregulation remains for response to wound healing and chronic inflammation RNAs.

Evaluation of novel epibatidine analogs in the rat nicotine drug discrimination assay and in the rat chronic constriction injury neuropathic pain model.

Nicotine is the primary psychoactive component responsible for maintaining tobacco dependence in humans. Chronic pain is often a consequence of tobacco-related pathologies, and the development of a dual therapeutic that could treat chronic pain and tobacco dependence would be advantageous. Epibatidine reliably substitutes for nicotine in the drug discrimination assay, and is a potent analgesic, but has a side-effect profile that limits its therapeutic potential. Thus, considerable efforts to produce epibatidine derivatives are underway. Here we tested three epibatidine derivatives, 2'-fluoro-3'-(4-nitrophenyl)deschloroepibatidine (RTI-7527-102; i.e., RTI-102), 2'-fluorodeschloroepibatidine (RTI-7527-36; i.e., RTI-36), and 3'-(3″-dimethylaminophenyl)-epibatidine (RTI-7527-76; i.e., RTI-76) in both the rat nicotine drug discrimination assay as well as in the rat chronic constriction injury (CCI) of the sciatic nerve neuropathic pain model. Male and female Sprague-Dawley rats were trained on a fixed-ratio 10 schedule to discriminate nicotine (0.32mg/kg base) from vehicle. All compounds dose-dependently substituted for nicotine, without significant decreases in response rates. In the discrimination assay the rank order potency was RTI-36 > nicotine > RTI-102 > RTI-76. Evidence suggests the α4β2* subtype is particularly important to nicotine-related abuse potential. Thus, here we utilized the antagonist dihydro-β-erythroidine (DHβE) to examine relative β2 subunit contribution. DHβE (3.2mg/kg, s.c.) antagonized the discriminative stimulus effects of nicotine. However, relative to antagonism of nicotine, DHβE produced less antagonism of RTI-102 and RTI-76 and greater antagonism of RTI-36. It is likely that at nicotinic receptor subunits RTI-102, RTI-76 and RTI-36 possess differing activity. To confirm that the full discriminative stimulus of these compounds was due to nAChR activity beyond the β2 subunit, we examined these compounds in the presence of the non-selective nicotinic receptor antagonist mecamylamine. Mecamylamine (0.56mg/kg, s.c.) pretreatment abolished nicotine-paired lever responding for all compounds. In a separate cohort, male and female Sprague-Dawley rats underwent CCI surgery and tested for CCI-induced mechanical allodynia via the von Frey assay. Each compound produced CCI-induced mechanical allodynia reversal. RTI-36 displayed higher potency than either RTI-102 or RTI-76. These novel epibatidine analogs may prove to be useful tools in the fight against nicotine dependence as well as novel neuropathic pain analgesics.

Rapid Generation and Molecular Docking Analysis of Single-Chain Fragment Variable (scFv) Antibody Selected by Ribosome Display Targeting Cholecystokinin B Receptor (CCK-BR) for Reduction of Chronic Neuropathic Pain.

A robust cell-free platform technology, ribosome display in combination with cloning, expression, and purification was utilized to develop single chain Fragment variable (scFv) antibody variants as pain therapy directed at the mouse cholecystokinin B (CCK-B) receptor. Three effective CCK-B peptide-specific scFvs were generated through ribosomal display technology. Soluble expression and ELISA analysis showed that one antibody, scFv77-2 had the highest binding and could be purified from bacterial cells in large quantities. Octet measurements further revealed that the CCK-B scFv77-2 antibody had binding kinetics of KD = 1.794 × 10-8 M. Molecular modeling and docking analyses suggested that the scFv77-2 antibody shaped a proper cavity to embed the whole CCK-B peptide molecule and that a steady-state complex was formed relying on intermolecular forces, including hydrogen bonding, electrostatic force, and hydrophobic interactions. Thus, the scFv antibody can be applied for mechanistic intermolecular interactions and functional in vivo studies of CCK-BR. The high affinity scFv77-2 antibody showed good efficacy with binding to CCK-BR tested in a chronic pain model. In vivo studies validated the efficacy of the CCK-B receptor (CCK-BR) scFv77-2 antibody as a potential therapy for chronic trigeminal nerve injury-induced pain. Mice were given a single dose of the CCK-B receptor (CCK-BR) scFv antibody 3 weeks after induction of a chronic trigeminal neuropathic pain model, during the transition from acute to chronic pain. The long-term effectiveness for the reduction of mechanical hypersensitivity was evident, persisting for months. The anxiety- and depression-related behaviors typically accompanying persisting hypersensitivity subsequently never developed in the mice given CCK-BR scFv. The effectiveness of the antibody is the basis for further development of the lead CCK-BR scFv as a promising non-opioid therapeutic for chronic pain and the long-term reduction of chronic pain- and anxiety-related behaviors.

The effect of dexmedetomidine on expression of neuronal nitric oxide synthase in spinal dorsal cord in a rat model with chronic neuropathic pain.

Neuropathic pain typically refers to the pain caused by somatosensory system injury or diseases, which is usually characterized by ambulatory pain, allodynia, and hyperalgesia. Nitric oxide produced by neuronal nitric oxide synthase (nNOS) in the spinal dorsal cord might serve a predominant role in regulating the algesia of neuropathic pain. The high efficacy and safety, as well as the plausible ability in providing comfort, entitle dexmedetomidine (DEX) to an effective anesthetic adjuvant. The aim of this study was to investigate the effect of DEX on the expression of nNOS in spinal dorsal cord in a rat model with chronic neuropathic pain. Male Sprague Dawley (SD) rats were randomly assigned into three groups: sham operation group (sham), (of the sciatic nerve) operation (CCI) group, and dexmedetomidine (DEX) group. Chronic neuropathic pain models in the CCI and DEX groups were established by sciatic nerve ligation. The thermal withdrawal latency (TWL) was measured on day 1 before operation and on day 1, 3, 7 and 14 after operation. Six animals were sacrificed after TWL measurement on day 7, and 14 days after operation, in each group, the L4-6 segment of the spinal cords was extracted for determination of nNOS expression by immunohistochemistry. Compared with the sham group, the TWL threshold was significantly decreased and the expression of nNOS was up-regulated after operation in the CCI and DEX groups. Compared with the CCI grou[, the TWL threshold was significantly increased and the expression of nNOS was significantly down-regulated on day 7 and 14 days after operation in the DEX group. Down-regulated nNOS in the spinal dorsal cord is involved in the attenuation of neuropathic pain by DEX.

The heptapeptide somatostatin analogue TT-232 exerts analgesic and anti-inflammatory actions via SST4 receptor activation: In silico, in vitro and in vivo evidence in mice

Since the conventional and adjuvant analgesics have limited effectiveness frequently accompanied by serious side effects, development of novel, potent pain killers for chronic neuropathic and inflammatory pain conditions is a big challenge. Somatostatin (SS) regulates endocrine, vascular, immune and neuronal functions, cell proliferation through 5 Gi protein-coupled receptors (SST1-SST5). SS released from the capsaicin-sensitive peptidergic sensory nerves mediates anti-inflammatory and antinociceptive effects without endocrine actions via SST4. The therapeutic use of the native SS is limited by its diverse biological actions and short plasma elimination half-life. Therefore, SST4 selective SS analogues could be promising analgesic and anti-inflammatory drug candidates with new mode of action. TT-232 is a cyclic heptapeptide showing great affinity to SST4 and SST1. Here, we report the in silico SST4 receptor binding mechanism, in vitro binding (competition assay) and cAMP- decreasing effect of TT-232 in SST4-expressing CHO cells, as well as its analgesic and anti-inflammatory actions in chronic neuropathic pain and arthritis models using wildtype and SST4-deficient mice. TT-232 binds to SST4 with similar interaction energy (-11.03 kcal/mol) to the superagonist J-2156, displaces somatostatin from SST4 binding (10 nM to 30 µM) and inhibits forskolin-stimulated cAMP accumulation (EC50: 371.6 ± 58.03 nmol; Emax: 78.63 ± 2.636 %). Its i.p. injection (100, 200 µg/kg) results in significant, 35.7 % and 50.4 %, analgesic effects upon single administration in chronic neuropathic pain and repeated injection in arthritis models in wildtype, but not in SST4-deficient mice. These results provide evidence that the analgesic effect of TT-232 is mediated by SST4 activation, which might open novel drug developmental potentials.Chemical compoundsChemical compounds studied in this article TT-232 (PubChem CID: 74053735).

Inhibition effect of choline and parecoxib sodium on chronic constriction nerve injury-induced neuropathic pain in rats

PurposeThe simultaneous use of drugs with different mechanisms of analgesic action is a strategy for achieving effective pain control while minimizing dose-related side effects. Choline was described to potentiate the analgesic action of parecoxib sodium at small doses in several inflammatory pain models. However, these findings are still very limited, and more associated data are required to confirm the effectiveness of the combined choline and parecoxib sodium therapy against inflammatory pain.MethodsAdult rats were randomly divided into 9 groups (N = 6/group). The sham surgery group received an intraperitoneal (i.p.) injection of saline. Rats with chronic constriction injury (CCI) of the sciatic nerve received saline, choline (cho, 6, 12 and 24 mg/kg), parecoxib sodium (pare, 3, 6, and 12 mg/kg), or a combination of choline 6 mg/kg and parecoxib sodium 3 mg/kg. Mechanical and heat pain thresholds were measured at 30 min after drug treatment at Days 3, 5, 7, 10, and 14 after CCI. Another 30 rats were divided into 5 groups (N = 6/group): the sham, CCI + saline, CCI + cho-6 mg/kg, CCI + pare-3 mg/kg, and CCI + cho-6 mg/kg + pare-3 mg/kg groups. After repeated drug treatment for 7 days, five rats were randomly selected from each group, and the lumbar dorsal root ganglia (DRGs) (L4–6) were harvested for western blot analysis.ResultsCholine significantly attenuated mechanical and heat hypersensitivity in CCI rats at 12 and 24 mg/kg doses (P < 0.05) but was not effective at the 6 mg/kg dose. Parecoxib sodium exerted significant pain inhibitory effects at the 6 and 12 mg/kg doses (P < 0.05) but not at the 3 mg/kg dose. Combining a low dose of choline (6 mg/kg) and parecoxib sodium (3 mg/kg) produced significant pain inhibition in CCI rats and reduced the expression of high mobility group protein 1 (HMGB1) and nuclear factor-kappa Bp65 (NF-κBp65) in L4–6 DRGs.Conclusion1. In a rat model of chronic neuropathic pain (CCI), at a certain dose, choline or parecoxib sodium can alleviate mechanical pain and thermal hyperalgesia caused by CCI. 2. The combination of choline and parecoxib sodium in nonanalgesic doses can effectively relieve neuropathic pain, and its mechanism may be related to the inhibition of the high mobility group protein 1 (HMGB1)/Toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) pathway.

Targeting the vascular endothelial growth factor A/neuropilin 1 axis for relief of neuropathic pain.

Vascular endothelial growth factor A (VEGF-A) is a pronociceptive factor that causes neuronal sensitization and pain. We reported that blocking the interaction between the membrane receptor neuropilin 1 (NRP1) and VEGF-A-blocked VEGF-A-mediated sensory neuron hyperexcitability and reduced mechanical hypersensitivity in a rodent chronic neuropathic pain model. These findings identified the NRP1-VEGF-A signaling axis for therapeutic targeting of chronic pain. In an in-silico screening of approximately 480 K small molecules binding to the extracellular b1b2 pocket of NRP1, we identified 9 chemical series, with 6 compounds disrupting VEGF-A binding to NRP1. The small molecule with greatest efficacy, 4'-methyl-2'-morpholino-2-(phenylamino)-[4,5'-bipyrimidin]-6(1H)-one, designated NRP1-4, was selected for further evaluation. In cultured primary sensory neurons, VEGF-A enhanced excitability and decreased firing threshold, which was blocked by NRP1-4. In addition, NaV1.7 and CaV2.2 currents and membrane expression were potentiated by treatment with VEGF-A, and this potentiation was blocked by NRP1-4 cotreatment. Neuropilin 1-4 reduced VEGF-A-mediated increases in the frequency and amplitude of spontaneous excitatory postsynaptic currents in dorsal horn of the spinal cord. Neuropilin 1-4 did not bind to more than 300 G-protein-coupled receptors and receptors including human opioids receptors, indicating a favorable safety profile. In rats with spared nerve injury-induced neuropathic pain, intrathecal administration of NRP1-4 significantly attenuated mechanical allodynia. Intravenous treatment with NRP1-4 reversed both mechanical allodynia and thermal hyperalgesia in rats with L5/L6 spinal nerve ligation-induced neuropathic pain. Collectively, our findings show that NRP1-4 is a first-in-class compound targeting the NRP1-VEGF-A signaling axis to control voltage-gated ion channel function, neuronal excitability, and synaptic activity that curb chronic pain.

Pharmacological Profile of MP-101, a Novel Non-racemic Mixture of R- and S-dimiracetam with Increased Potency in Rat Models of Cognition, Depression and Neuropathic Pain.

The racemic mixture dimiracetam negatively modulates NMDA-induced glutamate release in rat spinal cord synaptosomal preparations and is orally effective in models of neuropathic pain. In this study, we compared the effects of dimiracetam, its R- or S-enantiomers, and the R:S 3:1 non-racemic mixture (MP-101). In vitro, dimiracetam was more potent than its R- or S-enantiomers in reducing the NMDA-induced [3H]D-aspartate release in rat spinal cord synaptosomes. Similarly, acute oral administration of dimiracetam was more effective than a single enantiomer in the sodium monoiodoacetate (MIA) paradigm of painful osteoarthritis. Then, we compared the in vitro effects of a broad range of non-racemic enantiomeric mixtures on the NMDA-induced [3H]D-aspartate release. Dimiracetam was a more potent blocker than each isolated enantiomer but the R:S 3:1 non-racemic mixture (MP-101) was even more potent than dimiracetam, with an IC50 in the picomolar range. In the chronic oxaliplatin-induced neuropathic pain model, MP-101 showed a significantly improved anti-neuropathic profile, and its effect continued one week after treatment suspension. MP-101 also performed better than dimiracetam in animal models of cognition and depression. Based on the benign safety and tolerability profile previously observed with racemic dimiracetam, MP-101 appears to be a novel, promising clinical candidate for the prevention and treatment of several neuropathic and neurological disorders.

Neuropathic pain treatment with xenon

THE AIM: This study aimed to evaluate the effects of xenon on neuropathic pain during parapulmonal injections in the rat model. Xenon is a drug for inhalation anesthesia that is assumed to have an analgesic effect when administered parapulmonary (similar to nitrous oxide and cyclopropane) and can later be used as an alternative analgesic drug in patients with pain syndrome that is not controlled by standard methods.&#x0D; MATERIALS AND METHODS: The experiment used in vivo model of neuropathic pain by Bennet and Xie (1988) on rats with sciatic nerve transection. Additionally, a special scoring was adopted based on known behavioral changes of experimental animals (self-harm of limbs, neatness, activity, and bedding conditions). The control group was subcutaneously administered air daily for 5 days, and the experimental group received medical xenon at 40 ml/kg. The pain was assessed with the subcutaneous introduction of air and xenon in the experimental and control groups.&#x0D; RESULTS: Study results revealed that rats from the experimental group (xenon) showed fewer signs of neuropathic pain syndrome development compared to the control group (air).&#x0D; CONCLUSION: Therefore, parapulmonal injections of xenon showed a high analgesia effect in animal models of chronic neuropathic pain.