Antiallodynic and antihyperalgesic activity of 3-[4-(3-trifluoromethyl-phenyl)-piperazin-1-yl]-dihydrofuran-2-one compared to pregabalin in chemotherapy-induced neuropathic pain in mice

Discovery and Profiling of New Multimodal Phenylglycinamide Derivatives as Potent Antiseizure and Antinociceptive Drug Candidates

We developed a focused series of original phenyl-glycinamide derivatives which showed potent activity across in vivo mouse seizure models, namely, maximal electroshock (MES) and 6 Hz (using both 32 and 44 mA current intensities) seizure models. Following intraperitoneal (i.p.) administration, compound (R)-32, which was identified as a lead molecule, demonstrated potent protection against all seizure models with ED50 values of 73.9 mg/kg (MES test), 18.8 mg/kg (6 Hz, 32 mA test), and 26.5 mg/kg (6 Hz, 44 mA test). Furthermore, (R)-32 demonstrated efficacy in both the PTZ-induced kindling paradigm and the ivPTZ seizure threshold test. The expression of neurotrophic factors, such as mature brain-derived neurotrophic factor (mBDNF) and nerve growth factor (NGF), in the hippocampus and/or cortex of mice, and the levels of glutamate and GABA were normalized after PTZ-induced kindling by (R)-32. Importantly, besides antiseizure activity, (R)-32 demonstrated potent antinociceptive efficacy in formalin-induced pain, capsaicin-induced pain, as well as oxaliplatin- and streptozotocin-induced peripheral neuropathy in mice (i.p.). No influence on muscular strength and body temperature in mice was observed. Pharmacokinetic studies and in vitro ADME-Tox data (i.e., high metabolic stability in human liver microsomes, a weak influence on CYPs, no hepatotoxicity, satisfactory passive transport, etc.) proved favorable drug-like properties of (R)-32. Thermal stability of (R)-32 shown in thermogravimetry and differential scanning calorimetry gives the opportunity to develop innovative oral solid dosage forms loaded with this compound. The in vitro binding and functional assays indicated its multimodal mechanism of action. (R)-32, beyond TRPV1 antagonism, inhibited calcium and sodium currents at a concentration of 10 μM. Therefore, the data obtained in the current studies justify a more detailed preclinical development of (R)-32 for epilepsy and pain indications.

Chemotherapy-Induced Peripheral Neuropathy: A Recent Update on Pathophysiology and Treatment

Chemotherapy-induced peripheral neuropathy (CIPN) is a major long-lasting side effect of some chemotherapy drugs, which threatens cancer survival rate. CIPN mostly affects sensory neurons and occasionally motor neurons, causing numbness, tingling, discomfort, and burning pain in the upper and lower extremities. The pathophysiology of CIPN is not completely understood; however, it is believed that chemotherapies induce peripheral neuropathy via directly damaging mitochondria, impairing the function of ion channels, triggering immunological mechanisms, and disrupting microtubules. The treatment of CIPN is a medical challenge, and there are no approved pharmacological options. Currently, duloxetine and other antidepressants, antioxidant, anti-inflammatory, and ion-channel targeted therapies are commonly used in clinics to relieve the symptoms of CIPN. Several other types of drugs, such as cannabinoids, sigma-1 receptor antagonists, and nicotinamides ribose, are being evaluated in preclinical and clinical studies. This paper summarizes the information related to the physiology of CIPN and medicines that could be used for treating this condition.

The Combination of Molecular Hydrogen and Heme Oxygenase 1 Effectively Inhibits Neuropathy Caused by Paclitaxel in Mice

Chemotherapy-provoked peripheral neuropathy and its associated affective disorders are important adverse effects in cancer patients, and its treatment is not completely resolved. A recent study reveals a positive interaction between molecular hydrogen (H2) and a heme oxygenase (HO-1) enzyme inducer, cobalt protoporphyrin IX (CoPP), in the inhibition of neuropathic pain provoked by nerve injury. Nevertheless, the efficacy of CoPP co-administered with hydrogen-rich water (HRW) on the allodynia and emotional disorders related to paclitaxel (PTX) administration has not yet been assessed. Using male C57BL/6 mice injected with PTX, we examined the effects of the co-administration of low doses of CoPP and HRW on mechanical and thermal allodynia and anxiodepressive-like behaviors triggered by PTX. Moreover, the impact of this combined treatment on the oxidative stress and inflammation caused by PTX in the amygdala (AMG) and dorsal root ganglia (DRG) were studied. Our results indicated that the antiallodynic actions of the co-administration of CoPP plus HRW are more rapid and higher than those given by each of them when independently administered. This combination inhibited anxiodepressive-like behaviors, the up-regulation of the inflammasome NLRP3 and 4-hydroxynonenal, as well as the high mRNA levels of some inflammatory mediators. This combination also increased the expression of NRF2, HO-1, superoxide dismutase 1, glutathione S-transferase mu 1, and/or the glutamate-cysteine ligase modifier subunit and decreased the protein levels of BACH1 in the DRG and/or AMG. Thus, it shows a positive interaction among HO-1 and H2 systems in controlling PTX-induced neuropathy by modulating inflammation and activating the antioxidant system. This study recommends the co-administration of CoPP plus HRW as an effective treatment for PTX-provoked neuropathy and its linked emotive deficits.

Novel Alaninamide Derivatives with Drug-like Potential for Development as Antiseizure and Antinociceptive Therapies─In Vitro and In Vivo Characterization

In the present study, a series of original alaninamide derivatives have been designed applying a combinatorial chemistry approach, synthesized, and characterized in the in vivo and in vitro assays. The obtained molecules showed potent and broad-spectrum activity in basic seizure models, namely, the maximal electroshock (MES) test, the 6 Hz (32 mA) seizure model, and notably, the 6 Hz (44 mA) model of pharmacoresistant seizures. Most potent compounds 26 and 28 displayed the following pharmacological values: ED50 = 64.3 mg/kg (MES), ED50 = 15.6 mg/kg (6 Hz, 32 mA), ED50 = 29.9 mg/kg (6 Hz, 44 mA), and ED50 = 34.9 mg/kg (MES), ED50 = 12.1 mg/kg (6 Hz, 32 mA), ED50 = 29.5 mg/kg (6 Hz, 44 mA), respectively. Additionally, 26 and 28 were effective in the ivPTZ seizure threshold test and had no influence on the grip strength. Moreover, lead compound 28 was tested in the PTZ-induced kindling model, and then, its influence on glutamate and GABA levels in the hippocampus and cortex was evaluated by the high-performance liquid chromatography (HPLC) method. In addition, 28 revealed potent efficacy in formalin-induced tonic pain, capsaicin-induced pain, and oxaliplatin- and streptozotocin-induced peripheral neuropathy. Pharmacokinetic studies and in vitro ADME-Tox data proved favorable drug-like properties of 28. The patch-clamp recordings in rat cortical neurons showed that 28 at a concentration of 10 μM significantly inhibited fast sodium currents. Therefore, 28 seems to be an interesting candidate for future preclinical development in epilepsy and pain indications.

Transient Receptor Potential Channels: Multiple Modulators of Peripheral Neuropathic Pain in Several Rodent Models

Neuropathic pain, a prevalent chronic condition in clinical settings, has attracted widespread societal attention. This condition is characterized by a persistent pain state accompanied by affective and cognitive disruptions, significantly impacting patients' quality of life. However, current clinical therapies fall short of addressing its complexity. Thus, exploring the underlying molecular mechanism of neuropathic pain and identifying potential targets for intervention is highly warranted. The transient receptor potential (TRP) receptors, a class of widely distributed channel proteins, in the nervous system, play a crucial role in sensory signaling, cellular calcium regulation, and developmental influences. TRP ion channels are also responsible for various sensory responses including heat, cold, pain, and stress. This review highlights recent advances in understanding TRPs in various rodent models of neuropathic pain, aiming to uncover potential therapeutic targets for clinical management.

Naturally Inspired Molecules for Neuropathic Pain Inhibition-Effect of Mirogabalin and Cebranopadol on Mechanical and Thermal Nociceptive Threshold in Mice

BACKGROUND

Neuropathic pain is drug-resistant to available analgesics and therefore novel treatment options for this debilitating clinical condition are urgently needed. Recently, two drug candidates, namely mirogabalin and cebranopadol have become a subject of interest because of their potential utility as analgesics for chronic pain treatment. However, they have not been investigated thoroughly in some types of neuropathic pain, both in humans and experimental animals.

METHODS

This study used the von Frey test, the hot plate test and the two-plate thermal place preference test supported by image analysis and machine learning to assess the effect of intraperitoneal mirogabalin and subcutaneous cebranopadol on mechanical and thermal nociceptive threshold in mouse models of neuropathic pain induced by streptozotocin, paclitaxel and oxaliplatin.

RESULTS

Mirogabalin and cebranopadol effectively attenuated tactile allodynia in models of neuropathic pain induced by streptozotocin and paclitaxel. Cebranopadol was more effective than mirogabalin in this respect. Both drugs also elevated the heat nociceptive threshold in mice. In the oxaliplatin model, cebranopadol and mirogabalin reduced cold-exacerbated pain.

CONCLUSIONS

Since mirogabalin and cebranopadol are effective in animal models of neuropathic pain, they seem to be promising novel therapies for various types of neuropathic pain in patients, in particular those who are resistant to available analgesics.

Broad-spectrum neuroprotection exerted by DDD-028 in a mouse model of chemotherapy-induced neuropathy

ABSTRACT

Neurotoxicity of chemotherapeutics involves peculiar alterations in the structure and function, including abnormal nerve signal transmission, of both the peripheral and central nervous system. The lack of effective pharmacological approaches to prevent chemotherapy-induced neurotoxicity necessitates the identification of innovative therapies. Recent evidence suggests that repeated treatment with the pentacyclic pyridoindole derivative DDD-028 can exert both pain-relieving and glial modulatory effects in mice with paclitaxel-induced neuropathy. This work is aimed at assessing whether DDD-028 is a disease-modifying agent by protecting the peripheral nervous tissues from chemotherapy-induced damage. Neuropathy was induced in animals by paclitaxel injection (2.0 mg kg -1 i.p). DDD-028 (10 mg kg -1 ) and the reference drug, pregabalin (30 mg kg -1 ), were administered per os daily starting concomitantly with the first injection of paclitaxel and continuing 10 days after the end of paclitaxel treatment. The behavioural tests confirmed the antihyperalgesic efficacy of DDD-028 on paclitaxel-induced neuropathic pain. Furthermore, the electrophysiological analysis revealed the capacity of DDD-028 to restore near-normal sensory nerve conduction in paclitaxel-treated animals. Histopathology evidence indicated that DDD-028 was able to counteract effectively paclitaxel-induced peripheral neurotoxicity by protecting against the loss of intraepidermal nerve fibers, restoring physiological levels of neurofilament in nerve tissue and plasma, and preventing morphological alterations occurring in the sciatic nerves and dorsal root ganglia. Overall, DDD-028 is more effective than pregabalin in preventing chemotherapy-induced neurotoxicity. Thus, based on its potent antihyperalgesic and neuroprotective efficacy, DDD-028 seems to be a viable prophylactic medication to limit the development of neuropathies consequent to chemotherapy.

Cebranopadol for the Treatment of Chronic Pain

PURPOSE OF REVIEW

Regardless of the etiology, if pain persists chronically, it can detrimentally impact multiple aspects of a patient's well-being. Both physical and psychological effects are significant in many chronic pain patients. In this regard, psychological consequences can alter a patient's quality of life, functionality, and social functioning. Opioids have been the long-established gold standard for acute pain treatment in settings such as the postoperative period. An alternative to opioids in pain management has been highly sought after. Through a non-selective mechanism, cebranopadol is a first-in-class oral drug which combines agonism of the mu and nociceptin opioid peptide (NOP) receptors to provide improved analgesia, while reducing the occurrence of many typically opioid side effects. This manuscript is a narrative review of the possible use of cebranopadol in pain management.

RECENT FINDINGS

In pre-clinical studies, cebranopadol was similar to morphine in its pain control efficacy. In a phase IIa trial, cebranopadol was superior to placebo in reducing pain. In a randomized clinical trial, cebranopadol was superior to morphine. Another study concluded that cebranopadol had a lower misuse potential when compared to hydromorphone. In summary, cebranopadol offers new opportunities in treating chronic moderate to severe pain, while also countering risks of addiction. Additional studies are warranted to further evaluate the safety and efficacy of cebranopadol. In this regard, cebranopadol could prove to be a promising alternative to current pain treatment options.

Novel GPR18 Ligands in Rodent Pharmacological Tests: Effects on Mood, Pain, and Eating Disorders

The lack of selective pharmacological tools has limited the full unraveling of G protein-coupled receptor 18 (GPR18) functions. The present study was aimed at discovering the activities of three novel preferential or selective GPR18 ligands, one agonist (PSB-KK-1415) and two antagonists (PSB-CB-5 and PSB-CB-27). We investigated these ligands in several screening tests, considering the relationship between GPR18 and the cannabinoid (CB) receptor system, and the control of endoCB signaling over emotions, food intake, pain sensation, and thermoregulation. We also assessed whether the novel compounds could modulate the subjective effects evoked by Δ⁹-tetrahydrocannabinol (THC). Male mice or rats were pretreated with the GPR18 ligands, and locomotor activity, depression- and anxiety-like symptoms, pain threshold, core temperature, food intake, and THC-vehicle discrimination were measured. Our screening analyses indicated that GPR18 activation partly results in effects that are similar to those of CB receptor activation, considering the impact on emotional behavior, food intake, and pain activity. Thus, the orphan GPR18 may provide a novel therapeutic target for mood, pain, and/or eating disorders, and further investigation is warranted to better discern its function.

Rodent Animal Models of Endometriosis-Associated Pain: Unmet Needs and Resources Available for Improving Translational Research in Endometriosis

Chronic pain induced by endometriosis is a maladaptive pain experienced by half of women with this disease. The lack of pharmacological treatments suitable for the long-term relief of endometriosis-associated pain, without an impact on fertility, remains an urgent unmet need. Progress has been slowed by the absence of a reproducible rodent endometriosis model that fully replicates human physiopathological characteristics, including pain symptoms. Although pain assessment in rodents is a complicated task requiring qualified researchers, the choice of the behavioral test is no less important, since selecting inappropriate tests can cause erroneous data. Pain is usually measured with reflex tests in which hypersensitivity is evaluated by applying a noxious stimulus, yet this ignores the associated emotional component that could be evaluated via non-reflex tests. We conducted a systematic review of endometriosis models used in rodents and the number of them that studied pain. The type of behavioral test used was also analyzed and classified according to reflex and non-reflex tests. Finally, we determined the most used reflex tests for the study of endometriosis-induced pain and the main non-reflex behavioral tests utilized in visceral pain that can be extrapolated to the study of endometriosis and complement traditional reflex tests.

KM-408, a novel phenoxyalkyl derivative as a potential anticonvulsant and analgesic compound for the treatment of neuropathic pain

BACKGROUND

Epilepsy frequently coexists with neuropathic pain. Our approach is based on the search for active compounds with multitarget profiles beneficial in terms of potential side effects and on the implementation of screening for potential multidirectional central activity.

METHODS

Compounds were synthesized by means of chemical synthesis. After antiseizure and neurotoxicity screening in vivo, KM-408 and its enantiomers were chosen for analgesic activity evaluations. Further safety studies included acute toxicity in mice, the effect on normal electrocardiogram and on blood pressure in rats, whole body plethysmography in rats, and in vitro and biochemical assays. Pharmacokinetics has been studied in rats after iv and po administration. Metabolism has been studied in vivo in rat serum and urine. Radioligand binding studies were performed as part of the mechanism of action investigation.

RESULTS

Selected results for KM-408: K_i sigma = 7.2*10^-8; K_i 5-HT_1A = 8.0*10^-7; ED₅₀ MES (mice, ip) = 13.3 mg/kg; formalin test (I phase, mice, ip)-active at 30 mg/kg; SNL (rats, ip)-active at 6 mg/kg; STZ-induced pain (mice, ip)-active at 1 mg/kg (von Frey) and 10 mg/kg (hot plate); hot plate test (mice, ip)-active at 30 mg/kg; ED₅₀ capsaicin test (mice, ip) = 18.99 mg/kg; tail immersion test (mice)-active at 0.5%; corneal anesthesia (guinea pigs)-active at 0.125%; infiltration anesthesia (guinea pigs)-active at 0.125%.

CONCLUSIONS

Within the presented study a novel compound, R,S-2-((2-(2-chloro-6-methylphenoxy)ethyl)amino)butan-1-ol hydrochloride (KM-408) with dual antiseizure and analgesic activity has been developed for potential use in neuropathic pain treatment.

Gabapentin Increases Intra-Epidermal and Peptidergic Nerve Fibers Density and Alleviates Allodynia and Thermal Hyperalgesia in a Mouse Model of Acute Taxol-Induced Peripheral Neuropathy

The clinical pathology of Taxol-induced peripheral neuropathy (TIPN), characterized by loss of sensory sensitivity and pain, is mirrored in a preclinical pharmacological mice model in which Gabapentin, produced anti-thermal hyperalgesia and anti-allodynia effects. The study aimed to investigate the hypothesis that gabapentin may protect against Taxol-induced neuropathic pain in association with an effect on intra-epidermal nerve fibers density in the TIPN mice model. A TIPN study schedule was induced in mice by daily injection of Taxol during the first week of the experiment. Gabapentin therapy was performed during the 2nd and 3rd weeks. The neuropathic pain was evaluated during the whole experiment by the Von Frey, tail flick, and hot plate tests. Intra-epidermal nerve fibers (IENF) density in skin biopsies was measured at the end of the experiment by immunohistochemistry of ubiquitin carboxyl-terminal hydrolase PGP9.5 pan-neuronal and calcitonin gene-related (CGRP) peptides-I/II- peptidergic markers. Taxol-induced neuropathy was expressed by 80% and 73% reduction in the paw density of IENFs and CGPR, and gabapentin treatment corrected by 83% and 46% this reduction, respectively. Gabapentin-induced increase in the IENF and CGRP nerve fibers density, thus proposing these evaluations as an additional objective end-point tool in TIPN model studies using gabapentin as a reference compound.

Evaluation of analgesic and anti-inflammatory activity of purine-2,6-dione-based TRPA1 antagonists with PDE4/7 inhibitory activity

Background

To verify the validity of the proposed pain treatment approach, which is based on concomitant blocking of the Transient Receptor Potential Ankyrin 1 (TRPA1) channel and phosphodiesterases (PDEs) 4B/7A activity, we continued our pharmacological studies on 8-alkoxypurine-2,6-diones selected based on previous in vitro screening.

Methods

Derivatives 17, 31, and 36 were pharmacologically evaluated in vivo using the formalin test and oxaliplatin-induced neuropathic pain: the von Frey and the cold plate tests, and in the carrageenan-induced edema model. Compound 36, which turned out to be the most promising, was further evaluated in the collagen-induced arthritis model. The pharmacokinetic parameters of this compound were also estimated.

Results

All the tested compounds exhibited significant analgesic and anti-inflammatory activities. Compound 36 was additionally characterized by an antiarthritic effect and showed a favorable pharmacokinetic profile in rats.

Conclusion

The compounds evaluated in this study represent a new class of derivatives with analgesic and anti-inflammatory activities that involve TRPA1 antagonism and PDE4/7 inhibition.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-022-00397-6.

Antinociceptive and Antiallodynic Activity of Some 3-(3-Methylthiophen-2-yl)pyrrolidine-2,5-dione Derivatives in Mouse Models of Tonic and Neuropathic Pain

Antiseizure drugs (ASDs) are commonly used to treat a wide range of nonepileptic conditions, including pain. In this context, the analgesic effect of four pyrrolidine-2,5-dione derivatives (compounds 3, 4, 6, and 9), with previously confirmed anticonvulsant and preliminary antinociceptive activity, was assessed in established pain models. Consequently, antinociceptive activity was examined in a mouse model of tonic pain (the formalin test). In turn, antiallodynic and antihyperalgesic activity were examined in the oxaliplatin-induced model of peripheral neuropathy as well as in the streptozotocin-induced model of painful diabetic neuropathy in mice. In order to assess potential sedative properties (drug safety evaluation), the influence on locomotor activity was also investigated. As a result, three compounds, namely 3, 6, and 9, demonstrated a significant antinociceptive effect in the formalin-induced model of tonic pain. Furthermore, these substances also revealed antiallodynic properties in the model of oxaliplatin-induced peripheral neuropathy, while compound 3 attenuated tactile allodynia in the model of diabetic streptozotocin-induced peripheral neuropathy. Apart from favorable analgesic properties, the most active compound 3 did not induce any sedative effects at the active dose of 30 mg/kg after intraperitoneal (i.p.) injection.

Novel Functionalized Amino Acids as Inhibitors of GABA Transporters with Analgesic Activity

Neuropathic pain resistance to pharmacotherapy has encouraged researchers to develop effective therapies for its treatment. γ-Aminobutyric acid (GABA) transporters 1 and 4 (mGAT1 and mGAT4) have been increasingly recognized as promising drug targets for neuropathic pain (NP) associated with imbalances in inhibitory neurotransmission. In this context, we designed and synthesized new functionalized amino acids as inhibitors of GABA uptake and assessed their activities toward all four mouse GAT subtypes (mGAT1–4). According to the obtained results, compounds 2RS,4RS-39c (pIC₅₀ (mGAT4) = 5.36), 50a (pIC₅₀ (mGAT2) = 5.43), and 56a (with moderate subtype selectivity that favored mGAT4, pIC₅₀ (mGAT4) = 5.04) were of particular interest and were therefore evaluated for their cytotoxic and hepatotoxic effects. In a set of in vivo experiments, both compounds 50a and 56a showed antinociceptive properties in three rodent models of NP, namely, chemotherapy-induced neuropathic pain models (the oxaliplatin model and the paclitaxel model) and the diabetic neuropathic pain model induced by streptozotocin; however compound 56a demonstrated predominant activity. Since impaired motor coordination is also observed in neuropathic pain conditions, we have pointed out that none of the test compounds induced motor deficits in the rotarod test.

Corydalis saxicola Bunting total alkaloids attenuate paclitaxel-induced peripheral neuropathy through PKCε/p38 MAPK/TRPV1 signaling pathway

Background

Corydalis saxicola Bunting, affiliated with the Papaveraceae Juss., has been proven to work well in anti-inflammation, hemostasis, and analgesia. This study was designed to observe the effect and potential mechanism of Corydalis saxicola Bunting total alkaloids (CSBTA) on paclitaxel-induced peripheral neuropathy (PIPN).

Materials and methods

Rats were injected 2 mg/kg paclitaxel 4 times and administrated with 30 or 120 mg/kg CSBTA. Mechanical and thermal allodynia and hyperalgesia were tested. After 40 days, serum was collected to detect PGE2, TNF-α, and IL-1β by ELISA. The L4-L6 segment spinal cord, DRG, and plantar skin were harvested, and Western-blot or RT-qPCR analyzed protein and gene levels of pro-inflammatory cytokines, p38 MAPK, PKCε, and TRPV1. The PIPN cell model was established with paclitaxel (300 nM, 5 d) in primary DRG neurons. We examined the effect of CSBTA (25 μg/ml or 50 μg/ml) by measuring the mRNA levels in PGE2, TNF-α and CGRP, and the protein expression on the PKCε/p38 MAPK/TRPV1 signaling pathway in the PIPN cell model.

Results

The results showed that CSBTA effectively ameliorated allodynia and hyperalgesia, and regulated cytokines' contents (PGE2, TNF-α, and IL-1β) and neuropeptides (CGRP and SP) in different tissues in vivo. In addition, CSBTA significantly decreased cytokine gene levels of DRG neurons (PGE2, TNF-α, and CGRP) and the protein expressions of PKCε/p38 MAPK/TRPV1 signaling pathway in vivo and in vitro.

Conclusion

Therefore, CSBTA has a perspective therapeutic effect on the treatment of paclitaxel-induced peripheral neuropathy.

Wide-Range Measurement of Thermal Preference-A Novel Method for Detecting Analgesics Reducing Thermally-Evoked Pain in Mice

Background: Wide use of oxaliplatin as an antitumor drug is limited by severe neuropathy with pharmacoresistant cold hypersensitivity as the main symptom. Novel analgesics to attenuate cold hyperalgesia and new methods to detect drug candidates are needed. Methods: We developed a method to study thermal preference of oxaliplatin-treated mice and assessed analgesic activity of intraperitoneal duloxetine and pregabalin used at 30 mg/kg. A prototype analgesiameter and a broad range of temperatures (0–45 °C) were used. Advanced methods of image analysis (deep learning and machine learning) enabled us to determine the effectiveness of analgesics. The loss or reversal of thermal preference of oxaliplatin-treated mice was a measure of analgesia. Results: Duloxetine selectively attenuated cold-induced pain at temperatures between 0 and 10 °C. Pregabalin-treated mice showed preference towards a colder plate of the two used at temperatures between 0 and 45 °C. Conclusion: Unlike duloxetine, pregabalin was not selective for temperatures below thermal preferendum. It influenced pain sensation at a much wider range of temperatures applied. Therefore, for the attenuation of cold hypersensitivity duloxetine seems to be a better than pregabalin therapeutic option. We propose wide-range measurements of thermal preference as a novel method for the assessment of analgesic activity in mice.

The Search for New Anticonvulsants in a Group of (2,5-Dioxopyrrolidin-1-yl)(phenyl)Acetamides with Hybrid Structure-Synthesis and In Vivo/In Vitro Studies

Epilepsy belongs to the most common and debilitating neurological disorders with multifactorial pathophysiology and a high level of drug resistance. Therefore, with the aim of searching for new, more effective, and/or safer therapeutics, we discovered a focused series of original hybrid pyrrolidine-2,5-dione derivatives with potent anticonvulsant properties. We applied an optimized coupling reaction yielding several hybrid compounds that showed broad-spectrum activity in widely accepted animal seizure models, namely, the maximal electroshock (MES) test and the psychomotor 6 Hz (32 mA) seizure model in mice. The most potent anticonvulsant activity and favorable safety profile was demonstrated for compound 30 (median effective dose (ED₅₀) MES = 45.6 mg/kg, ED₅₀ 6 Hz (32 mA) = 39.5 mg/kg, median toxic dose (TD₅₀) (rotarod test) = 162.4 mg/kg). Anticonvulsant drugs often show activity in pain models, and compound 30 was also proven effective in the formalin test of tonic pain, the capsaicin-induced pain model, and the oxaliplatin (OXPT)-induced neuropathic pain model in mice. Our studies showed that the most plausible mechanism of action of 30 involves inhibition of calcium currents mediated by Cav_1.2 (L-type) channels. Importantly, 30 revealed high metabolic stability on human liver microsomes, negligible hepatotoxicity, and relatively weak inhibition of CYP3A4, CYP2D6, and CYP2C9 isoforms of cytochrome P450, compared to reference compounds. The promising in vivo activity profile and drug-like properties of compound 30 make it an interesting candidate for further preclinical development.

KM-416, a novel phenoxyalkylaminoalkanol derivative with anticonvulsant properties exerts analgesic, local anesthetic, and antidepressant-like activities. Pharmacodynamic, pharmacokinetic, and forced degradation studies

Anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic, neuropathic pain. We obtained a phenoxyalkylaminoalkanol derivative, KM-416 which had previously demonstrated a significant anticonvulsant activity and had also been shown to bind to 5-HT_1A, α₂-receptors and SERT and not to exhibit mutagenic properties. As KM-416 is a promising compound in our search for drug candidates, in the present study we further assessed its pharmacological profile (analgesic, local anesthetic, and antidepressant-like activities) accompanied with patch-clamp studies. Considering the importance of drug safety, its influence on the cardiovascular system was also evaluated. Moreover, KM-416 was subjected to forced degradation and pharmacokinetic studies to examine its stability and pharmacokinetic parameters. KM-416 revealed a significant antinociceptive activity in the tonic - the formalin test, neurogenic - the capsaicin test, and neuropathic pain model - streptozotocin-induced peripheral neuropathy. Moreover, it exerted a local anesthetic effect. In addition, KM-416 exhibited anti-depressant like activity. The results from the patch-clamp studies indicated that KM-416 can inhibit currents elicited by activation of NMDA receptors, while it also exhibited a voltage-dependent inhibition of Na⁺ currents. KM-416 did not influence ventricular depolarization and repolarization. Following oral administration, pharmacokinetics of KM-416 was characterized by a rapid absorption in the rat. The brain-to-plasma AUC ratio was 6.7, indicating that KM-416 was well distributed to brain. The forced degradation studies showed that KM-416 was very stable under stress conditions. All these features made KM-416 a promising drug candidate for further development against neuropathic pain and epilepsy.

Comparison of Bromhexine and its Active Metabolite - Ambroxol as Potential Analgesics Reducing Oxaliplatin-induced Neuropathic Pain - Pharmacodynamic and Molecular Docking Studies

BACKGROUND

Painful peripheral neuropathy is a dose-limiting adverse effect of the antitumor drug oxaliplatin. The main symptoms of neuropathy: tactile allodynia and cold hyperalgesia, appear in more than 80% of patients on oxaliplatin therapy and are due to the overexpression of neuronal sodium channels (Navs) and neuroinflammation.

OBJECTIVE

This study assessed antiallodynic and antihyperalgesic properties of two repurposed drugs with antiinflammatory and Nav-blocking properties (bromhexine and its pharmacologically active metabolite - ambroxol) in a mouse model of neuropathic pain induced by oxaliplatin. Using molecular docking techniques, we predicted targets implicated in the observed in vivo activity of bromhexine.

METHODS

Oxaliplatin (a single intraperitoneal dose of 10 mg/kg) induced tactile allodynia and cold hyperalgesia in CD-1 mice and the effectiveness of single-dose or repeated-dose bromhexine and ambroxol to attenuate pain hypersensitivity was assessed in von Frey and cold plate tests. Additionally, Veber analysis and molecular docking experiments of bromhexine on mouse (m) and human (h) Nav1.6-1.9 were carried out.

RESULTS

At the corresponding doses, ambroxol was more effective than bromhexine as an antiallodynic agent. However, at the dose of 150 mg/kg, ambroxol induced motor impairments in mice. Repeated-dose bromhexine and ambroxol partially attenuated the development of late-phase tactile allodynia in oxaliplatin-treated mice. Only 7-day administration of bromhexine attenuated the development of late-phase cold hyperalgesia. Bromhexine was predicted to be a strong inhibitor of mNav1.6, mNav1.7, mNav1.9, and hNav1.7-hNav1.9.

CONCLUSION

The conversion of bromhexine to other than ambroxol active metabolites should be considered when interpreting some of its in vivo effects. Nav-blocking properties of bromhexine (and previously also predicted for ambroxol) might underlie its ability to attenuate pain caused by oxaliplatin.

KA-104, a new multitargeted anticonvulsant with potent antinociceptive activity in preclinical models

OBJECTIVE

The main objective of the present work was to assess the utility of KA-104 as potential therapy for drug-resistant seizures and neuropathic pain, and to characterize its druglike properties in a series of absorption, distribution, metabolism, excretion and toxicity (ADME-Tox) studies. We also aimed to establish its mechanism of action in electrophysiological studies.

METHODS

The activity of KA-104 against drug-resistant seizures was tested in the mouse 6-Hz (44-mA) model, whereas the antinociceptive activity was assessed with the capsaicin- and oxaliplatin-induced pain models in mice. The patch-clamp technique was used to study the influence of KA-104 on fast voltage-gated sodium currents in rat prefrontal cortex pyramidal neurons. The pharmacokinetic profile was determined after intraperitoneal (ip) injection in mice. The in vitro ADME-Tox properties were studied by applying routine testing procedures.

RESULTS

KA-104 was effective in the 6-Hz (44-mA) model (median effective dose [ED₅₀ ] = 73.2 mg/kg) and revealed high efficacy in capsaicin-induced neurogenic pain as well as in oxaliplatin-induced neuropathic pain in mice. Patch-clamp technique showed that KA-104 reversibly inhibits voltage-gated sodium currents. KA-104 was rapidly absorbed after the ip injection and showed relatively good penetration through the blood-brain barrier. This molecule was also characterized by high passive permeability, moderate influence on CYP2C9, and negligible hepatotoxicity on HepG2 cells.

SIGNIFICANCE

The results reported herein indicate that KA-104 is a new wide-spectrum multitargeted anticonvulsant with favorable in vitro ADME-Tox properties. Importantly, this compound may also prove to become an interesting and hopefully more effective therapeutic option for treatment of neuropathic pain.

Chemotherapy-induced peripheral neuropathy: part 1-current state of knowledge and perspectives for pharmacotherapy

Background

Despite the increasing knowledge of the etiology of neuropathic pain, this type of chronic pain is resistant to available analgesics in approximately 50% of patients and therefore is continuously a subject of considerable interest for physiologists, neurologists, medicinal chemists, pharmacologists and others searching for more effective treatment options for this debilitating condition.

Materials and methods

The present review article is the first of the two articles focused on chemotherapy-induced peripheral neuropathy (CIPN).

Results

CIPN is regarded as one of the most common drug-induced neuropathies and is highly pharmacoresistant. The lack of efficacious pharmacological methods for treating CIPN and preventing its development makes CIPN-related neuropathic pain a serious therapeutic gap in current medicine and pharmacotherapy. In this paper, the most recent advances in the field of studies on CIPN caused by platinum compounds (namely oxaliplatin and cisplatin), taxanes, vinca alkaloids and bortezomib are summarized.

Conclusions

The prevalence of CIPN, potential causes, risk factors, symptoms and molecular mechanisms underlying this pharmacoresistant condition are discussed.

Graphic abstract

Antinociceptive, antiedematous, and antiallodynic activity of 1H-pyrrolo[3,4-c]pyridine-1,3(2H)-dione derivatives in experimental models of pain

The aim of the presented study was to examine the potential antinociceptive, antiedematous (anti-inflammatory), and antiallodynic activities of two 1H-pyrrolo[3,4-c]pyridine-1,3(2H)-dione derivatives (DSZ 1 and DSZ 3) in various experimental models of pain. For this purpose, the hot plate test, the capsaicin test, the formalin test, the carrageenan model, and oxaliplatin-induced allodynia tests were performed. In the hot plate test, only DSZ 1 in the highest dose (20 mg/kg) was active but its effects appear to be due to sedatation rather than antinociceptiveness. In capsaicin-induced neurogenic pain model, both compounds displayed a significant antinociceptive activity. In the formalin test, DSZ 1 and DSZ 3 (5-20 mg/kg) revealed antinociceptive activity in both phases but it was more pronounced in the second phase of the test. In this test, pretreatment with caffeine, DPCPX reversed the antinociceptive effect of DSZ 3. On the other hand, pretreatment with L-NAME diminished the antinociceptive effect of DSZ 1. Pretreatment with naloxone did not affect antinociceptive activity of both compounds. Similar to ketoprofen, DSZ 1 and DSZ 3 showed antiedematous (antiinflammatory) and antihyperalgesic activity, and similar to lidocaine local anesthetic activity. Furthermore, both compounds (5 and 10 mg/kg) reduced tactile allodynia in acute and chronic phases of neuropathic pain. In the in vitro studies, DSZ 1 and DSZ 3 reduced the COX-2 level in LPS-activated RAW 264.7 cells, which suggests their anti-inflammatory activity. In conclusion, both DSZ 1 and DSZ 3 displayed broad spectrum of activity in several pain models, including neurogenic, tonic, inflammatory, and chemotherapy-induced peripheral neuropathic pain.

Searching for analgesic drug candidates alleviating oxaliplatin-induced cold hypersensitivity in mice

Oxaliplatin is a third-generation, platinum-based derivative used to treat advanced colorectal cancer. Within the patient population on oxaliplatin therapy, a lower incidence of hematological adverse effects and gastrointestinal toxicity is noted, but severe neuropathic pain episodes characterized by increased cold and tactile hypersensitivity are present in ~95% of patients. This drug is also used to induce a rodent model of chemotherapy-induced peripheral neuropathy (CIPN)-related neuropathic pain which is widely used in the search for novel therapies for CIPN prevention and treatment. This paper provides a step-by-step, detailed description of the prevention and intervention protocols used in our laboratory for the assessment of oxaliplatin-induced cold allodynia in mice. To establish cold sensitivity in mice, the cold plate test was used. Latencies to pain reaction in response to cold stimulus (2.5°C) for vehicle-treated non-neuropathic mice, vehicle-treated mice injected with oxaliplatin (neuropathic control), and oxaliplatin-treated mice treated additionally with duloxetine are compared. Duloxetine is a serotonin/noradrenaline reuptake inhibitor which was found to produce significant pain relief in patients with CIPN symptoms. In our present study, duloxetine administered intraperitoneally at the dose of 30 mg/kg served as a model antiallodynic drug which attenuated or partially prevented cold allodynia caused by oxaliplatin.

KA-11, a Novel Pyrrolidine-2,5-dione Derived Broad-Spectrum Anticonvulsant: Its Antiepileptogenic, Antinociceptive Properties and in Vitro Characterization

Recently, compound KA-11 was identified as a promising candidate for a new broad-spectrum anticonvulsant. This compound revealed wide protective activity across the most important animal models of seizures such as the maximal electroshock test (MES), the subcutaneous pentylenetetrazole test ( scPTZ), and the six-hertz test (6 Hz, 32 mA). Importantly, KA-11 was devoid of acute neurological activity, which was assessed by applying the chimney test (TD₅₀ value higher than 1500 mg/kg). The preliminary in vivo results confirmed favorable anticonvulsant and safety properties of KA-11. With the aim of further biological characterization of KA-11, in the current studies we evaluated its antiepileptogenic activity in the kindling model of epilepsy induced by repeated injection of PTZ in mice. Furthermore, we assessed the antinociceptive activity of KA-11 in several animal pain models. As a result, KA-11 (at all doses applied: 25, 50, and 100 mg/kg) significantly delayed the progression of kindling induced by repeated injection of PTZ in mice. Additionally, KA-11 revealed potent antinociceptive activity in the formalin-induced tonic pain and, importantly, in the oxaliplatin-induced neuropathic pain model in mice. Moreover, KA-11 did not induce motor deficits in the rotarod test. Patch-clamp experiments revealed that one of the mechanisms of action of KA-11 is inhibition of voltage-gated sodium currents. Compound KA-11 appeared to be safe in relation to hepatotoxic properties as no phospholipidosis induction was determined in HepG2 cells at 50 μM, and a small, statistically significant decrease of cell viability was observed only at the highest used dose of 100 μM. Moreover, KA-11 did not affect the function of CYP2D6. The aforementioned hybrid substance proved to penetrate the biological membranes in the in vitro permeability assays.

Interventional and preventive effects of aripiprazole and ceftriaxone used alone or in combination on oxaliplatin-induced tactile and cold allodynia in mice

BACKGROUND AND PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is a pharmacoresistant neurological complication induced by some antitumor drugs. This study aimed to assess antiallodynic properties of aripiprazole and ceftriaxone used alone or in combination to attenuate neuropathic pain related to CIPN caused by oxaliplatin.

METHODS

Neuropathic pain was induced in mice by a single intraperitoneal dose of oxaliplatin (10 mg/kg). Aripiprazole and ceftriaxone were used in a single- or repeated dosing protocol. Their antiallodynic activity was assessed using von Frey and cold plate tests on the day of oxaliplatin injection and after 7 days. The influence of aripiprazole and ceftriaxone on animals' locomotor activity and motor coordination was also assessed.

RESULTS

Single-dose and repeated-dose aripiprazole 10 mg/kg and ceftriaxone 200 mg/kg used alone and in combination attenuated early-phase and late-phase tactile allodynia in oxaliplatin-treated mice. Repeated administrations of ceftriaxone 200 mg/kg prevented the development of late-phase tactile allodynia. Both drugs showed no antiallodynic properties in the cold plate test. Single-dose aripiprazole 1 and 10 mg/kg but not its repeated administration significantly decreased locomotor activity of oxaliplatin-treated mice. Single-dose aripiprazole 1 and 10 mg/kg, aripiprazole 1 mg/kg + ceftriaxone 50 mg/kg and aripiprazole 1 mg/kg + ceftriaxone 200 mg/kg impaired motor coordination in the rotarod test.

CONCLUSIONS

In mice, neither ceftriaxone nor aripiprazole attenuated cold allodynia. Ceftriaxone alone could attenuate tactile allodynia caused by oxaliplatin without inducing motor adverse effects. Although the administration of aripiprazole reduced tactile allodynia, this effect seems to be limited considering severe motor deficits induced by this drug.

Novel amide derivatives of 1,3-dimethyl-2,6-dioxopurin-7-yl-alkylcarboxylic acids as multifunctional TRPA1 antagonists and PDE4/7 inhibitors: A new approach for the treatment of pain

A series of novel amide derivatives of 1,3-dimethyl-2,6-dioxopurin-7-yl-alkylcarboxylic acids designed using a structure-based computational approach was synthesized and assayed to evaluate their ability to block human TRPA1 channel and inhibit PDE4B/7A activity. We identified compounds 16 and 27 which showed higher potency against TRPA1 compared to HC-030031. In turn, compound 36 was the most promising multifunctional TRPA1 antagonist and PDE4B/7A dual inhibitor with IC₅₀ values in the range of that of the reference rolipram and BRL-50481, respectively. Compound 36 as a combined TRPA1/PDE4B/PDE7A ligand was characterized by a distinct binding mode in comparison to 16 and 27, in the given protein targets. The inhibition of both cAMP-specific PDE isoenzymes resulted in a strong anti-TNF-α effect of 36in vivo. Moreover, the potent anti-inflammatory and analgesic efficacy of 36 was observed in animal models of pain and inflammation (formalin test in mice and carrageenan-induced paw edema in rats). This compound also displayed significant antiallodynic properties in the early phase of chemotherapy-induced peripheral neuropathy in mice. In turn, the pure TRPA1 antagonists 16 and 27 revealed a statistically significant antiallodynic effect in the formalin test and in the von Frey test performed in both phases of oxaliplatin-induced allodynia. Antiallodynic activity of the test compounds 16, 27 and 36 was observed at a dose range comparable to that of the reference drug - pregabalin. In conclusion, the proposed approach of pain treatment based on the concomitant blocking of TRPA1 channel and PDE4B/7A inhibitory activity appears to be interesting research direction for the future search for novel analgesics.

Evaluation of cebranopadol, a dually acting nociceptin/orphanin FQ and opioid receptor agonist in mouse models of acute, tonic, and chemotherapy-induced neuropathic pain

BACKGROUND

Cebranopadol (a.k.a. GRT-6005) is a dually acting nociceptin/orphanin FQ and opioid receptor agonist that has been recently developed in Phase 2 clinical trials for painful diabetic neuropathy or cancer pain. It also showed analgesic properties in various rat models of pain and had a better safety profile as compared to equi-analgesic doses of morphine. Since antinociceptive properties of cebranopadol have been studied mainly in rat models, in the present study, we assessed analgesic activity of subcutaneous cebranopadol (10 mg/kg) in various mouse pain models.

METHODS

We used models of acute, tonic, and chronic pain induced by thermal and chemical stimuli, with a particular emphasis on pharmacoresistant chronic neuropathic pain evoked by oxaliplatin in which cebranopadol was used alone or in combination with simvastatin.

KEY RESULTS

As shown in the hot plate test, the analgesic activity of cebranopadol developed more slowly as compared to morphine (90-120 min vs. 60 min). Cebranopadol displayed a significant antinociceptive activity in acute pain models, i.e., the hot plate, writhing, and capsaicin tests. It attenuated nocifensive responses in both phases of the formalin test and reduced cold allodynia in oxaliplatin-induced neuropathic pain model. Its efficacy was similar to that of morphine. Used in combination and administered simultaneously, 4 or 6 h after simvastatin, cebranopadol did not potentiate antiallodynic activity of this cholesterol-lowering drug. Cebranopadol did not induce any motor deficits in the rotarod test.

CONCLUSION

Cebranopadol may have significant potential for the treatment of various pain types, including inflammatory and chemotherapy-induced neuropathic pain.

Evaluation of anticonvulsant and analgesic activity of new hybrid compounds derived from N-phenyl-2-(2,5-dioxopyrrolidin-1-yl)-propanamides and -butanamides

Epilepsy is a chronic neurological disorder that is associated with various types of recurrent seizures, which are drug-resistant in about one third of patients. Moreover, anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic pain. Here, we investigated the anticonvulsant activity of six new hybrid compounds based on the pyrrolidine-2,5-dione scaffold in the 6 Hz corneal stimulation test with 44 mA stimulus intensity in mice, which is the model of pharmacoresistant seizures. We demonstrated that two molecules, DK-10 (11) and DK-14 (14) show higher anticonvulsant activity and similar safety profile in comparison with valproic acid and much higher in comparison with levetiracetam in the aforementioned test. The second aim of this study was to examine analgesic activity of these compounds. For this purpose, the hot plate test, the formalin test, and the oxaliplatin-induced peripheral neuropathy model were performed. Among tested agents DK-11 (12) revealed prominent antinociceptive activity at non-sedative doses in the second (inflammatory) phase of the formalin test, which is the model of tonic pain and antiallodynic activity in the oxaliplatin-induced neuropathic pain, the model of painful chemotherapy-induced peripheral neuropathy. No cytotoxic effect on hepatoma cells was observed. Compound DK-10 (11) had high affinity for voltage-gated sodium channels, whereas compound DK-11 (12) showed weak binding toward sodium and calcium voltage-gated channels and the NMDA receptor. As a result, hybrid compounds reported herein seem to be very promising broad spectrum anticonvulsant molecules with collateral analgesic activity.

Antiallodynic and antihyperalgesic activity of new 3,3-diphenyl-propionamides with anticonvulsant activity in models of pain in mice

Anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic pain. The aim of the present experiments was to examine analgesic activity of three new 3,3-diphenyl-propionamides, which had previously demonstrated anticonvulsant activity in the MES (maximal electroshock seizure), scPTZ (subcutaneous pentylenetetrazole) and/or 6Hz (psychomotor seizure) tests in mice. Antinociceptive activity was examined in mouse models of acute pain (the hot plate test) and tonic pain (the formalin test) in mice. Antiallodynic and antihyperalgesic activity was estimated in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy and in the streptozotocin-induced model of painful diabetic neuropathy in mice. Considering the drug safety evaluation, the influence on locomotor activity was checked. Moreover, using in vitro methods, selected compound was tested for potential hepatotoxicity on human hepatocellular carcinoma cell line and for metabolic stability. To determine the plausible mechanism of anticonvulsant and antinociceptive action, in vitro binding and functional assays were carried out. Among tested molecules two of them JOA 122 (3p) and JOA 123 (3q) revealed significant antinociceptive activity in the model of tonic pain - the formalin test and neuropathic pain models - the oxaliplatin and streptozotocin-induced peripheral neuropathy. In the binding studies JOA 122 (3p) revealed the high affinity to voltage-gated sodium channels (Na_v1.2), as well as for 5-HT_1A receptors. Metabolism studies in mouse liver microsomes showed a low metabolic stability of this compound.

Zinc Inhibits TRPV1 to Alleviate Chemotherapy-Induced Neuropathic Pain

Zinc is a transition metal that has a long history of use as an anti-inflammatory agent. It also soothes pain sensations in a number of animal models. However, the effects and mechanisms of zinc on chemotherapy-induced peripheral neuropathy remain unknown. Here we show that locally injected zinc markedly reduces neuropathic pain in male and female mice induced by paclitaxel, a chemotherapy drug, in a TRPV1-dependent manner. Extracellularly applied zinc also inhibits the function of TRPV1 expressed in HEK293 cells and mouse DRG neurons, which requires the presence of zinc-permeable TRPA1 to mediate entry of zinc into the cytoplasm. Moreover, TRPA1 is required for zinc-induced inhibition of TRPV1-mediated acute nociception. Unexpectedly, zinc transporters, but not TRPA1, are required for zinc-induced inhibition of TRPV1-dependent chronic neuropathic pain produced by paclitaxel. Together, our study demonstrates a novel mechanism underlying the analgesic effect of zinc on paclitaxel-induced neuropathic pain that relies on the function of TRPV1.SIGNIFICANCE STATEMENT The chemotherapy-induced peripheral neuropathy is a major limiting factor affecting the chemotherapy patients. There is no effective treatment available currently. We demonstrate that zinc prevents paclitaxel-induced mechanical hypersensitivity via inhibiting the TRPV1 channel, which is involved in the sensitization of peripheral nociceptors in chemotherapy. Zinc transporters in DRG neurons are required for the entry of zinc into the intracellular side, where it inhibits TRPV1. Our study provides insight into the mechanism underlying the pain-soothing effect of zinc and suggests that zinc could be developed to therapeutics for the treatment of chemotherapy-induced peripheral neuropathy.

The use of antioxidant agents for chemotherapy-induced peripheral neuropathy treatment in animal models

Antineoplastic drugs such as cisplatin, oxaliplatin, paclitaxel and vincristin are widely used in the treatment of several solid and blood tumours. However, the severity of peripheral neuropathy caused by these agents can affect the patient's quality of life. The major symptoms of chemotherapy-induced peripheral neuropathy (CIPN) involve: sensory loss, paresthesia, dysesthaesia, numbness, tingling, temperature sensitivity, allodynia and hyperalgesia, in a "stocking and glove" distribution. Why many different chemotherapeutic agents result in similar neuropathy profiles is unclear. Many drug classes such as antidepressants, anticonvulsants, antispastic agents and others have been used in clinical practice, but there is no scientific evidence to prove their effectiveness. But drugs as the antioxidant have shown a protective effect against free radical damage. In order to find out a successful treatment for CIPN, animal studies (ie pharmacological and mechanical tests and histopathological immunohistochemical analyses) have been developed to try to determinate the action of the antioxidant agents. This review provides an overview of the major antioxidant agents recently investigated to treat CIPN and the animal models used for this purpose.

Antinociceptive, antiallodynic and antihyperalgesic effects of the 5-HT1A receptor selective agonist, NLX-112 in mouse models of pain

BACKGROUND AND PURPOSE

NLX-112 (a.k.a. befiradol, F13640) is a drug candidate intended for the treatment of l-DOPA-induced dyskinesia. It is a highly selective serotonin 5-HT_1A receptor full agonist which has been previously tested in a variety of models of CNS effects including analgesic activity in rat. Its activity in mouse models of pain has not been previously investigated.

EXPERIMENTAL APPROACH

The activity of NLX-112 was tested in mouse models of acute pain (hot plate), tonic pain (intraplantar formalin test), in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy and in the streptozotocin (STZ)-induced model of painful diabetic neuropathy.

KEY RESULTS

The main findings indicate that (i) NLX-112 was markedly active in the formalin test with potent reduction of paw licking in both phases of the test (minimal effective dose (MED) 0.5 mg/kg i.p. and p.o. in acute phase, and 0.1 mg/kg i.p. and 1 mg/kg p.o. in late phase). The effects of NLX-112 in this test were completely abolished by the selective 5-HT_1A receptor antagonist, WAY100635; (ii) NLX-112 was active in the hot plate test and in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy, but at markedly higher doses (MED 2.5 mg/kg i.p.); (iii) NLX-112 was least active in the STZ-induced model of painful diabetic neuropathy (MED 5 mg/kg i.p.); (iv) NLX-112 did not affect locomotor activity.

CONCLUSIONS AND IMPLICATIONS

NLX-112 may have significant potential for treatment of tonic pain but may be less promising as a candidate for treatment of chemotherapy-induced or diabetic neuropathic pain.

Bioactive Fraction of Annona reticulata Bark (or) Ziziphus jujuba Root Bark along with Insulin Attenuates Painful Diabetic Neuropathy through Inhibiting NF-κB Inflammatory Cascade

The present study explains the neuroprotective ability of bioactive fractions of Annona reticulata bark (ARB) and Ziziphus jujuba root bark (ZJ) along with insulin against diabetic neuropathy. By using different solvents of increasing polarity ARB and ZJ were undergone for bioactive guided fractionation. The neuroprotective ability of the all the plant fractions were tested against H₂O₂ induced toxicity in SHSY5Y neuroblastoma cell lines and DRG neuronal cells. Among all the fractions tested, the methanol extract of ARB and ZJ (ARBME and ZJME) and its water fractions (ARBWF and ZJWF) exhibited significant neuroprotection against H₂O₂ induced toxicity in SHSY5Y cells and DRG neuronal cells. Further both the active fractions were tested against streptozotocin (55 mg/kg i.p.) induced diabetic neuropathy in male Wistar rats. Body weight changes, blood glucose levels and pain threshold through hot plate, tail immersion, cold plate and Randall-Sillitto methods were measured throughout the study at weekly interval. After completion of the drug treatment period, all the animals were sacrificed to measure the sciatic nerve lipid peroxidation, antioxidative enzyme levels (SOD, catalase, and GSH) and cytokine levels (IL-1β, IL-6, IL-10, TNF-α, iNOS, and NFκB) through ELISA and western blotting analysis. Results of this study explain that ARBME, ZJME, ARBWF, and ZJWF along with insulin potentially attenuate the thermal, mechanical hyperalgesia and cold allodynia in diabetic neuropathic rats, where insulin treatment alone failed to diminish the same. Reduction of sciatic nerve oxidative stress, NF-κB and iNOS mediated inflammatory cascade and normalization of abnormal cytokine release confirms the possible mechanism of action. The present study confirms the neuroprotective ability of ARB and ZJ against painful diabetic neuropathy through inhibiting oxidative stress and NF-κB inflammatory cascade.

Analgesic, antiallodynic, and anticonvulsant activity of novel hybrid molecules derived from N-benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide and 2-(2,5-dioxopyrrolidin-1-yl)butanamide in animal models of pain and epilepsy

The purpose of the present study was to examine the analgesic activity of six novel hybrid molecules, which demonstrated in the previous research anticonvulsant activity in the maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole seizure (scPTZ) tests in mice. The antinociceptive properties were estimated in three models of pain in mice—the hot plate test, the formalin test, and in the oxaliplatin-induced neuropathy. Moreover, extended anticonvulsant studies were carried out and the antiseizure activity was investigated in the 6-Hz test. Considering drug safety evaluation, the influence of compounds on locomotor activity and contextual memory were checked. Furthermore, chosen molecules were tested in vitro for potential hepatotoxicity. To explain the probable mechanism of action, the radioligand binding assays were performed. In both phases of formalin test, analgesic activity demonstrated compounds 4, 8, and 9. These agents relieved also mechanical allodynia in oxaliplatin-induced model of neuropathic pain. At active doses, they did not influence locomotor activity of mice. Moreover, for compounds 8 and 9, no deleterious effect on memory was observed, but compound 4 might induce memory deficits. All tested compounds (4, 5, 8, 9, 15, and 16) inhibited psychomotor seizures with the ED₅₀ values = 24.66–47.21 mg/kg. The binding studies showed that compound 4 only at the high concentrations revealed the effective binding to the neuronal sodium channels and moderately binding to the L-type calcium (verapamil site) channels and NMDA receptors. The present preclinical results proved that novel hybrid molecules demonstrate very promising anticonvulsant and analgesic activity.

Effect of pregabalin on fear-based conditioned avoidance learning and spatial learning in a mouse model of scopolamine-induced amnesia

OBJECTIVES

Cognitive deficits are one of the frequent symptoms accompanying epilepsy or its treatment.

METHODS

In this study, the effect on cognition of intraperitoneally administered antiepileptic drug, pregabalin (10 mg/kg), was investigated in scopolamine-induced memory-impaired mice in the passive avoidance task and Morris water maze task. The effect of scopolamine and pregabalin on animals' locomotor activity was also studied.

RESULTS

In the retention phase of the passive avoidance task, pregabalin reversed memory deficits induced by scopolamine (p < 0.05). During the acquisition phase of the Morris water maze pregabalin-treated memory-impaired mice performed the test with longer escape latencies than the vehicle-treated mice (significant at p < 0.05 on Day 5, and at p < 0.001 on Day 6). There were no differences in this parameter between the scopolamine-treated control group and pregabalin-treated memory-impaired mice, which indicated that pregabalin had no influence on spatial learning in this task. During the probe trial a significant difference (p < 0.05) was observed in terms of the mean number of target crossings between vehicle-treated mice and pregabalin-treated memory-impaired mice but there was no difference between the scopolamine-treated control group and mice treated with pregabalin + scopolamine. Pregabalin did not influence locomotor activity increased by scopolamine.

DISCUSSION

In passive avoidance task, pregabalin reversed learning deficits induced by scopolamine. In the Morris water maze, pregabalin did not influence spatial learning deficits induced by scopolamine. These results are relevant for epileptic patients treated with pregabalin and those who use it for other therapeutic indications (anxiety, pain).

Aryl-1,3,5-triazine ligands of histamine H4 receptor attenuate inflammatory and nociceptive response to carrageen, zymosan and lipopolysaccharide

Objective and design

Histamine H₄ receptor (H₄R) offers a great potential for new therapeutic strategies for the treatment of inflammation-based diseases. The aim of this study is to present the pharmacological profile of two recently synthesized ligands of H₄R with particular reference to their anti-inflammatory and analgesic activity.

Materials and subjects

We used mice and rats in the in vivo tests. We also used murine RAW 264.7 cells and isolated guinea-pig ileum in in vitro test.

Treatments

In the in vivo tests, animals were pre-treated with the increasing doses of investigated compounds (12.5, 25 and 50 mg/kg) and reference compounds: JNJ7777120 (25 mg/kg), indomethacin (10 mg/kg). Macrophages were pre-treated with two concentrations of tested compounds 100 and 10 µM.

Methods

We examined anti-inflammatory and analgesic effects of the new H₄R antagonists in the in vivo models of inflammation induced by carrageenan or zymosan. We assessed the level of cAMP and release of cytokines, ROS and NO in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Moreover, we assessed the affinity of the investigated compounds for histamine H₁ receptor in functional studies.

Results

Both investigated compounds reduced paw edema, mechanical and thermal hyperalgesia in the carrageenan-induced acute inflammation. Moreover, administration of the investigated compounds resulted in decreased granulocyte influx and attenuated nociceptive reaction in the zymosan-induced peritonitis model. In the same model of inflammation, the investigated compounds reduced vascular permeability; however, this effect was observed only after the highest applied dose. Furthermore, the test compounds had no impact on cell viability in the experiments on RAW 264.7 macrophages. In these cells, stimulated with LPS, the test compounds decreased reactive oxygen species (ROS) production. They increased the cellular concentration of cAMP and attenuated the production of inflammatory cytokines such as TNFα and IL-1β. All results were comparable to those obtained for the reference compound JNJ7777120 with the exception of the impact on NO production. Nevertheless, this effect was similar to that obtained for the other reference compound rolipram, which is a phosphodiesterase 4 (PDE 4) inhibitor. Further experiments revealed that both of the investigated compounds possessed relatively low affinity for histamine H₁ receptor and do not inhibit the activity of the PDE 4B1 enzyme. In addition, all the effects of the investigated compounds in in vivo experiments were observed at doses that did not cause neurologic deficits in rotarod test and did not reduce spontaneous locomotor activity.

Conclusions

Our results demonstrate the anti-inflammatory and analgesic activity of the new aryl-1,3,5-triazine derivatives, which are primarily H₄R–dependent.

Potential role of selected antiepileptics used in neuropathic pain as human GABA transporter isoform 1 (GAT1) inhibitors-Molecular docking and pharmacodynamic studies

The chemical interaction of nine antiepileptic drugs (tiagabine, gabapentin, pregabalin, lamotrigine, zonisamide, valproic acid, valpromide, vigabatrin, progabide) and two endogenous metabolites (4-aminobutanoic acid, 4-hydroxybutanoic acid) with a model of human GABA transporter 1 (hGAT1) is described using the molecular docking method. To establish the role of hGAT1 in chronic pain, tiagabine, a selective hGAT1 inhibitor, was assessed in the in vivo experiments for its antiallodynic properties in two mouse models of neuropathic pain. Docking analyses performed in this study provided the complex binding energies, specific hydrogen bond components, and hydrogen bond properties such as energies, distances and angles. The data of the docking studies strongly support the assumption that the antiepileptic and analgesic actions of the studied drugs can be at least in part related to the strength of their chemical interactions with hGAT1. In vivo experiments with tiagabine confirmed the involvement of hGAT1 in the regulation of the mechanical nociceptive threshold in neuropathic pain.

Chemotherapy-induced painful neuropathy: pain-like behaviours in rodent models and their response to commonly used analgesics

PURPOSE OF REVIEW

Chemotherapy-induced painful neuropathy (CIPN) is a major dose-limiting side-effect of several widely used chemotherapeutics. Rodent models of CIPN have been developed using a range of dosing regimens to reproduce pain-like behaviours akin to patient-reported symptoms. This review aims to connect recent evidence-based suggestions for clinical treatment to preclinical data.

RECENT FINDINGS

We will discuss CIPN models evoked by systemic administration of taxanes (paclitaxel and docetaxel), platinum-based agents (oxaliplatin and cisplatin), and the proteasome-inhibitor - bortezomib. We present an overview of dosing regimens to produce CIPN models and their phenotype of pain-like behaviours. In addition, we will discuss how potential, clinically available treatments affect pain-like behaviours in these rodent models, relating those effects to clinical trial data wherever possible. We have focussed on antidepressants, opioids, and gabapentinoids given their broad usage.

SUMMARY

The review outlines the latest description of the most-relevant rodent models of CIPN enabling comparison between chemotherapeutics, dosing regimen, rodent strain, and sex. Preclinical data support many of the recent suggestions for clinical management of established CIPN and provides evidence for potential treatments warranting clinical investigation. Continued research using rodent CIPN models will provide much needed understanding of the causal mechanisms of CIPN, leading to new treatments for this major clinical problem.

Anticonvulsant and antinociceptive activity of new amides derived from 3-phenyl-2,5-dioxo-pyrrolidine-1-yl-acetic acid in mice

The aim of the present experiments was to examine the anticonvulsant and antinociceptive activity of five new amides derived from 3-phenyl-2,5-dioxo-pyrrolidine-1-yl-acetic acid in animal models of seizures and pain. The antiseizure activity was investigated in three acute models of seizures, namely, the maximal electroshock (MES), the subcutaneous pentylenetetrazole (scPTZ), and 6Hz psychomotor seizure tests in mice. The antinociceptive properties were estimated in the formalin model of tonic pain, and in the oxaliplatin-induced neuropathic pain model in mice. Considering drug safety evaluation, acute neurological toxicity was determined in the rotarod test. Three tested compounds (3, 4, and 7) displayed a broad spectrum of anticonvulsant activity and showed better protective indices than those obtained for MES/scPTZ/6Hz active reference drug - valproic acid. Furthermore, three compounds (3, 4, and 6) demonstrated a significant antinociceptive effect in the formalin test, as well as antiallodynic activity in the oxaliplatin-induced neuropathic pain model. Among the tested agents, compounds 3 and 4 displayed not only antiseizure properties, but also collateral prominent analgesic properties. The in vitro binding study indicated that the plausible mechanism of action of chosen compound (4) was the influence on neuronal voltage-sensitive sodium (site 2) and L-type calcium channels.

Effect of pregabalin on contextual memory deficits and inflammatory state-related protein expression in streptozotocin-induced diabetic mice

Diabetes mellitus is a metabolic disease characterized by hyperglycemia due to defects in insulin secretion or its action. Complications from long-term diabetes consist of numerous biochemical, molecular, and functional tissue alterations, including inflammation, oxidative stress, and neuropathic pain. There is also a link between diabetes mellitus and vascular dementia or Alzheimer’s disease. Hence, it is important to treat diabetic complications using drugs which do not aggravate symptoms induced by the disease itself. Pregabalin is widely used for the treatment of diabetic neuropathic pain, but little is known about its impact on cognition or inflammation-related proteins in diabetic patients. Thus, this study aimed to evaluate the effect of intraperitoneal (ip) pregabalin on contextual memory and the expression of inflammatory state-related proteins in the brains of diabetic, streptozotocin (STZ)-treated mice. STZ (200 mg/kg, ip) was used to induce diabetes mellitus. To assess the impact of pregabalin (10 mg/kg) on contextual memory, a passive avoidance task was applied. Locomotor and exploratory activities in pregabalin-treated diabetic mice were assessed by using activity cages. Using Western blot analysis, the expression of cyclooxygenase-2 (COX-2), cytosolic prostaglandin E synthase (cPGES), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), nuclear factor-ĸB (NF-ĸB) p50 and p65, aryl hydrocarbon receptor (AhR), as well as glucose transporter type-4 (GLUT4) was assessed in mouse brains after pregabalin treatment. Pregabalin did not aggravate STZ-induced learning deficits in vivo or influence animals’ locomotor activity. We observed significantly lower expression of COX-2, cPGES, and NF-κB p50 subunit, and higher expression of AhR and Nrf2 in the brains of pregabalin-treated mice in comparison to STZ-treated controls, which suggested immunomodulatory and anti-inflammatory effects of pregabalin. Antioxidant properties of pregabalin in the brains of diabetic animals were also demonstrated. Pregabalin does not potentiate STZ-induced cognitive decline, and it has antioxidant, immunomodulatory, and anti-inflammatory properties in mice. These results confirm the validity of its use in diabetic patients.

Graphical abstract

Evaluation of anticonvulsant and antinociceptive properties of new N-Mannich bases derived from pyrrolidine-2,5-dione and 3-methylpyrrolidine-2,5-dione

The aim of the present experiments was to examine anticonvulsant activity of new pyrrolidine-2,5-dione and 3-methylpyrrolidine-2,5-dione derivatives in animal models of epilepsy. In addition, the possible collateral antinociceptive activity was assessed. Anticonvulsant activity was investigated in the electroconvulsive threshold (MEST) test and the pilocarpine-induced seizure models in mice. Antinociceptive activity was examined in the hot plate and the formalin tests in mice. Considering the drug safety evaluation, the Vibrio harveyi test was used to estimate anti/mutagenic activity. To determine the plausible mechanism of anticonvulsant action, for two chosen compounds (12 and 23), in vitro binding assays were carried out. All of the tested compounds revealed significant anticonvulsant activity in the MEST test. Compounds 12 and 23 displayed anticonvulsant effect also in pilocarpine-induced seizures. Four of the tested compounds (12, 13, 15, and 24) revealed analgesic activity in the hot plate test as well as in the first phase of the formalin test, and all of them were active in the second phase of the formalin test. The possible mechanism of action of compounds 12 and 23 is the influence on the neuronal voltage-sensitive sodium and L-type calcium channels. The obtained results indicate that in the group of pyrrolidine-2,5-diones, new anticonvulsants with collateral analgesic properties can be found.