Sciatic Nerve Ligation Research Articles

Activation of TGR5 in the injured nerve site according to a prevention protocol mitigates partial sciatic nerve ligation-induced neuropathic pain by alleviating neuroinflammation.

Neuropathic pain is a pervasive medical challenge currently lacking effective treatment options. Molecular changes at the site of peripheral nerve injury contribute to both peripheral and central sensitization, critical components of neuropathic pain. This study explores the role of the G-protein-coupled bile acid receptor (GPBAR1 or TGR5) in the peripheral mechanisms underlying neuropathic pain induced by partial sciatic nerve ligation in male mice. TGR5 was upregulated in the injured nerve site and predominantly colocalized with macrophages. Perisciatic nerve administration of the TGR5 agonist, INT-777 according to a prevention protocol (50 μg/μL daily from postoperative day [POD] 0 to POD6) provided sustained relief from mechanical allodynia and spontaneous pain, whereas the TGR5 antagonist, SBI-115 worsened neuropathic pain. Transcriptome sequencing linked the pain relief induced by TGR5 activation to reduced neuroinflammation, which was further evidenced by a decrease in myeloid cells and pro-inflammatory mediators (eg, CCL3, CXCL9, interleukin [IL]-6, and tumor necrosis factor [TNF] α) and an increase in CD86-CD206+ anti-inflammatory macrophages at POD7. Besides, myeloid-cell-specific TGR5 knockdown in the injured nerve site exacerbated both neuropathic pain and neuroinflammation, which was substantiated by bulk RNA-sequencing and upregulated expression levels of inflammatory mediators (including CCL3, CCL2, IL-6, TNF α, and IL-1β) and the increased number of monocytes/macrophages at POD7. Furthermore, the activation of microglia in the spinal cord on POD7 and POD14 was altered when TGR5 in the sciatic nerve was manipulated. Collectively, TGR5 activation in the injured nerve site mitigates neuropathic pain by reducing neuroinflammation, while TGR5 knockdown in myeloid cells worsens pain by enhancing neuroinflammation.

Scorpion Neurotoxin: An Analgesic Antitumor Peptide Down-Regulates VGSCs and Exhibits Local Anesthetic Potency during Sciatic Nerve Block

Background: Some neurotoxins inhibit nerves strongly. Saxitoxins and tetrodotoxin exhibit strong affinity for various voltage-gated sodium channels (VGSCs), including Nav 1.7, but low affinity for Nav 1.8. Emerging data suggests AGAP mediate analgesia by binding voltage-independently to sodium channel site-3. Objective: This study examined AGAP's mechanism and analgesic efficacy during sciatic nerve block. Methods: In rats, partial sciatic nerve ligation caused rapid and persistent mechanical hyperalgesia. Mechanical hyperalgesia after medication delivery was assessed with von Frey filaments. Western blot and immunohistochemical staining assessed VGSC expression following drug treatment. Results: The data showed that lidocaine and AGAP increased paw withdrawal threshold compared to control rats. Compared to the control group, lidocaine or AGAP inhibited VGSCs. Conclusion: This study suggested that AGAP inhibits VGSCs to elicit lidocaine-like analgesia.

Upregulation of Phosphodiesterase 7A Contributes to Concurrent Pain and Depression via Inhibition of cAMP-PKA-CREB-BDNF Signaling and Neuroinflammation in the Hippocampus of Mice.

Phosphodiesterases (PDEs) are enzymes that catalyze the hydrolysis of cyclic adenosine monophosphate AMP (cAMP) and/or cyclic guanosine monophosphate (cGMP). PDE inhibitors can mitigate chronic pain and depression when these disorders occur individually; however, there is limited understanding of their role in concurrent chronic pain and depression. We aimed to evaluate the mechanisms of action of PDE using 2 mouse models of concurrent chronic pain and depression. C57BL/6J mice were subjected to partial sciatic nerve ligation (PSNL) to induce chronic neuropathic pain or injected with complete Freund's adjuvant (CFA) to induce inflammatory pain, and both animals showed depression-like behavior. First, we determined the change in PDE expression in both animal models. Next, we determined the effect of PDE7 inhibitor BRL50481 or hippocampal PDE7A knockdown on PSNL- or CFA-induced chronic pain and depression-like behavior. We also investigated the role of cAMP-protein kinase A (PKA)-cAMP response element binding protein (CREB)-brain-derived neurotrophic factor (BDNF) signaling and neuroinflammation in the effect of PDE7A inhibition on PSNL- or CFA-induced chronic pain and depression-like behavior. This induction of chronic pain and depression in the 2 animal models upregulated hippocampal PDE7A. Oral administration of PDE7 inhibitor, BRL50481, or hippocampal PDE7A knockdown significantly reduced mechanical hypersensitivity and depression-like behavior. Hippocampal PDE7 inhibition reversed PSNL- or CFA-induced downregulation of cAMP and BDNF and the phosphorylation of PKA, CREB, and p65. cAMP agonist forskolin reversed these changes and caused milder behavioral symptoms of pain and depression. BRL50481 reversed neuroinflammation in the hippocampus in PSNL mice. Hippocampal PDE7A mediated concurrent chronic pain and depression in both mouse models by inhibiting cAMP-PKA-CREB-BDNF signaling. Inhibiting PDE7A or activating cAMP-PKA-CREB-BDNF signaling are potential strategies to treat concurrent chronic pain and depression.

Pregnancy ameliorates neuropathic pain through suppression of microglia and upregulation of the δ-opioid receptor in the anterior cingulate cortex in late-pregnant mice.

Pregnancy-induced analgesia develops in late pregnancy, but its mechanisms are unclear. The anterior cingulate cortex (ACC) plays a key role in the pathogenesis of neuropathic pain. The authors hypothesized that pregnancy-induced analgesia ameliorates neuropathic pain by suppressing activation of microglia and the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and by upregulating opioid receptors in the ACC in late-pregnant mice. Neuropathic pain was induced in non-pregnant (NP) or pregnant (P) C57BL/6JJmsSlc female mice by partial sciatic nerve ligation (PSNL). The nociceptive response was evaluated by mechanical allodynia and activation of microglia in the ACC was evaluated by immunohistochemistry. The expressions of phosphorylated AMPA receptors and opioid receptors in the ACC were evaluated by immunoblotting. In von Frey reflex tests, NP-PSNL-treated mice showed a lower 50% paw-withdrawal threshold than NP-Naïve mice on experimental day 9. No difference in 50% paw-withdrawal threshold was found among the NP-Naïve, NP-Sham, P-Sham, and P-PSNL-treated mice. The number of microglia in the ACC was significantly increased in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting showed significantly increased expression of phosphorylated AMPA receptor subunit GluR1 at Ser831 in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting also showed significantly increased δ-opioid receptor in the ACC in P-Sham and P-PSNL-treated mice compared to NP-Sham mice. Pregnancy-induced analgesia ameliorated neuropathic pain by suppressing activation of microglia and the expression of phosphorylated AMPA receptor subunit GluR1 at Ser831, and by upregulation of the δ-opioid receptor in the ACC in late-pregnant mice.

Electroacupuncture alleviates neuropathic pain by regulating hippocampal SP/NK1R/ARRB1 pathway.

To observe the effect of electroacupuncture (EA) on pain, anxiety like behavior, and substance P(SP) /neurokinin-1 receptor (NK1R) /β -arrestin 1(ARRB1) pathway related protein expression in hippocampus of chronic constriction injury (CCI) rats, so as to explore its mechanisms underlying improvement of neuropathic pain. Twenty-seven male SD rats were randomly divided into sham operation, model and EA groups, with 9 rats in each group. The CCI model was established by ligature of the left sciatic nerve. On the 8th day following modeling, EA (2 Hz, 0.5-1.5 mA) was applied to the left "Huantiao" (GB34) and "Yanglingquan" (GB34) for 30 min, once every other day for 13 times. Mechanical paw withdrawal threshold (MWT), thermal paw withdrawal threshold (TWL) and difference of the weight distribution of the hind limbs were detected before operation and at the 5th, 9th, 17th, 25th and 33rd days after operation. Open field test was used to evaluate the anxiety-like behavior of rats. The content of SP in hippocampus was determined by ELISA. The protein expression of NK1R and ARRB1 in hippocampus was detected by Western blot. Compared with the sham operation group, the MWT and TWL of the left hind limb at the 5th, 9th, 17th, 25th and 33rd days after operation, the time of entering the central area and the total distance of movement, and the content of SP in the hippocampus were significantly decreased (P<0.001, P<0.01), while the difference of the weight distribution of the hind limbs at the 5th, 9th, 17th, 25th and 33rd days after operation and the protein expression of NK1R and ARRB1 were significantly increased (P<0.001, P<0.05) in the model group. After EA intervention, the MWT and TWL of the left hind limb, the time of entering the central area and the total moving distance, and the expression of SP in the hippocampus were significantly increased (P<0.01, P<0.001, P<0.05), while the difference in the weight distribution of the hind limbs was significantly reduced, and the expression of NK1R and ARRB1 protein in the hippocampus were significantly decreased (P<0.001, P<0.05) in the EA group. EA can effectively improve the pain and anxiety behaviors in CCI rats, and reverse the abnormal expression of SP, NK1R and ARRB1 proteins in the hippocampus, which may be related to its effects in regulating the SP/NK1R/ARRB1 pathway in the hippocampus.

Potentiation of Imipramine-Induced Anti-hyperalgesic and Anti-Nociceptive Effects by Citicoline in the Sciatic Nerve Ligated Mice.

Peripheral neuropathic pain is a result of damage/illness of the peripheral nerves. The mechanisms caused by its pathophysiology are not completely understood. Imipramine is a tricyclic antidepressant that is sometimes used to treat neuropathic pain. Moreover, citicoline is considered a novel adjuvant for painful disorders such as neuropathic pain. So, a possible interaction between imipramine and citicoline on pain behavior was examined in nerve-ligated mice using tail-flick and hot plate tests. The results indicated that induction of neuropathic pain by sciatic nerve ligation caused hyperalgesia in nerve-ligated mice. On the other hand, intraperitoneal (i.p.) administration of citicoline (50, 75, and 100 mg/kg), and imipramine (2.5 and 5 mg/kg) induced anti-hyperalgesic and anti-nociceptive effects in nerve-ligated mice. Furthermore, citicoline potentiated the anti-hyperalgesic and anti-nociceptive effects of imipramine when they were co-administrated in nerve-ligated mice. Interestingly, there was an additive effect between imipramine and citicoline upon induction of anti-hyperalgesic and anti-nociceptive effects in nerve-ligated mice. Therefore, it can be concluded that citicoline (as an adjuvant substance) enhanced the efficacy of imipramine for the modulation of pain behavior in nerve-ligated mice.

Descending facilitation from rostral ventromedial medulla mu opioid receptor-expressing neurons is necessary for maintenance of sensory and affective dimensions of chronic neuropathic pain.

Pharmacological ablation of rostral ventromedial medulla (RVM) mu opioid receptor-expressing cells before peripheral nerve injury prevents the development of neuropathic pain. However, whether these neurons are required for the expression of established neuropathic pain is not known. Male Oprm1Cre heterozygous (MORCre) or wild-type (MORWT) mice received AAV8-hSyn-DIO-hM4D(Gi)-mCherry in the RVM. After partial sciatic nerve ligation (PSNL), we evaluated pain behaviors and descending control of nociception in response to acute or sustained chemogenetic inhibition of RVM-MOR cells expressing hM4D(Gi). A single systemic administration of hM4D(Gi) agonist clozapine-N-oxide (CNO) reversibly inhibited hind paw tactile allodynia and produced conditioned place preference only in MORCre mice with PSNL. Intrathecal CNO also reversibly inhibited PSNL-induced hind paw allodynia, suggesting that the spinal projections from these RVM-MOR cells are critical for manifestation of pain behaviors. Consistent with enhanced descending facilitation from RVM-MOR cells, MORCre-hM4D(Gi) mice with PSNL showed diminished descending control of nociception that was restored by systemic CNO. Sustained CNO in drinking water before PSNL prevented expression of chronic pain without affecting acute surgical pain; however, relief of chronic pain required sustained CNO treatment. Thus, in male mice, activity of spinally projecting RVM-MOR cells is required (1) for expression and manifestation of both sensory and affective dimensions of established neuropathic pain and (2) to promote descending facilitation that overcomes apparently intact descending inhibition to maintain chronic pain. Enhanced descending facilitation likely regulates the output signal from the spinal cord to the brain to shape the pain experience and may provide a mechanism for nonopioid management of pain.

The additive effect between bupropion and citicoline upon induction of anti-nociceptive effect in nerve-ligated mice

ABSTRACT Objectives Bupropion is an atypical antidepressant that shows robust efficacy in the regulation of neuropathic pain. Citicoline is a dietary supplement which is used as a neuroprotective agent for central nervous system (CNS) disorders. The probable interaction between bupropion and citicoline on neuropathic pain was assessed in male mice. Methods Neuropathic pain was induced by sciatic nerve ligation. Neuropathic pain was examined in nerve-ligated mice using tail-flick and hot-plate tests. Results The results indicated that intraperitoneal (i.p.) administration of citicoline (50 and 100 mg/kg) induced an anti-nociceptive effect in nerve-ligated animals. Similarly, i.p. injection of bupropion (2.5 and 5 mg/kg) induced anti-nociceptive effects in nerve-ligated mice. Co-administration of different doses of bupropion (2.5 and 5 mg/kg) along with a low dose of citicoline (25 mg/kg) caused an anti-nociceptive effect by enhancement of tail-flick and hot plate latencies. Interestingly, there is an additive effect between bupropion and citicoline upon the induction of the anti-nociceptive effect. Conclusions Based on these results, it can be concluded that there is an interaction between bupropion and citicoline upon induction of an anti-nociceptive effect in nerve-ligated mice.

Synthesis and pharmacological activity of various organic and inorganic salts of phenyl derivatives of imidazobenzimidazole

Introduction: The creation of new opioid analgesics that are devoid of the main undesirable effects – euphoria, respiratory depression, tolerance – is an important task for the treatment of pain syndrome. Eighteen salts of 9-pyrrolidinoethyl-(1a), 9-piperidinoethyl-(1b), and 9-morpholinoethyl-2-(4-fluorophenyl)benzo[d]imidazo[1,2-a]imidazole (1c) were synthesized and tested for kappa agonist and analgesic activity. Materials and Methods: Specific analgesic activity studies were conducted using models of nociceptive pain in the “Hot/Cold-plate” and ”Plantar Test” tests, and in neuropathic pain against the background of sciatic nerve ligation. The relationship between the physicochemical and pharmacological properties of the compounds was studied in silico using quantum chemistry methods and artificial neural network technology. Results: The most active compound identified was 4-(2-(2-(4-fluorophenyl)-benzo[d]imidazo[1,2-a]imidazol-9-yl)ethyl)morpholine dihydrochloride (1c.2HCl). EC50, acute toxicity, and conditional therapeutic index values were calculated, which were 38.8 times superior to the kappa agonist U50488. It was established that compound 1c.2HCl exhibits a dose-dependent analgesic effect in the “Hot/Cold-plate” test, which is six times superior to that of butorphanol, maintaining a statistically significant effect for six hours in the “Plantar test” and without causing the formation of tolerance with a ten-day administration. In models of neuropathic pain syndrome, 1c.2HCl with a fourteen-day administration significantly reduced tactile and cold allodynia by three and 1.6 times, respectively, and was not inferior in activity to gabapentin. The kappa-opioidergic mechanism of the antinociceptive action of 1c.2HCl compound was confirmed. Quantum chemistry methods and artificial neural network technologies have shown that the high level of kappa-opioid agonist activity of hydrochlorides, in contrast to other salts, results in lower total energy production; therefore, there is a significant increase in energy during the formation of a salt supramolecular complex. Conclusion: The most active compound was identified – 1c.2HCl, for which kappa-opioid activity in vitro and analgesic properties were revealed in various in vivo models. It has been shown that the compound does not cause the formation of tolerance and is not toxic.

Intravenous application of human umbilical cord mesenchymal stem cells alleviate neuropathic pain by suppressing microglia activation in rats

ObjectiveNeuropathic pain has been considered as one of the most serious chronic pain subtypes and causes intolerable suffering to patients physically and mentally. This study aimed to verify the analgesic effect of intravenous administration of human umbilical cord mesenchymal stem cells (HUC-MSCs) upon rats with chronic constriction injury (CCI)-induced neuropathic pain and the concomitant mechanism via modulating microglia. Methods30 male SD rats were randomized divided into three groups (n = 10 per group): Sham + Saline group (S&S group), CCI + Saline group (C&S group) and CCI + HUC-MSCs group (C&U group). Rats were injected with either saline or HUC-MSCs via the caudal vein on the 7th day after modelling. The paw mechanical withdrawal threshold (PMWT) and thermal withdrawal latency (TWL) of the ligation side were measured before (day 0) and after (day 1, 3, 5, 7, 9, 11, 13, and 15) modelling. On day 15 after modelling, western-blotting and immunofluorescent staining were used to assess the expressive abundance of Iba-1 (a typical biomarker of activated microglia) in the ligation side of the spinal cord dorsal horn, and ultrastructural changes of the ligation of sciatic nerve were evaluated by transmission electron microscope (TEM). ResultsCompared with the S&S group, PMWT and TWL in the C&S group were significantly decreased on day 5 and then persisted to day 15 after modelling (C&S vs S&S, P < 0.05), while a significant amelioration of mechanical hyperalgesia (day 13, day 15) and thermal allodynia (day 9, day 11, day 15) was observed in the C&U group (C&U vs C&S, P < 0.05). Meanwhile, the expression of Iba-1 was significantly suppressed by systemic infusion of HUC-MSCs in the C&U group according to western-blotting and immunofluorescent staining analyses (P < 0.05). With the aid of TEM detection, we intuitively noticed the efficacious reconstruction of the laminate structure of the sciatic nerve ligation, elimination of mitochondrial swelling, and formation of new myelination were noted on day 15 after modelling in the C&U group. ConclusionsOverall, intravenous administration of HUC-MSCs systemically revealed an ameliorative effect upon CCI-induced neuropathic pain in SD rats by inhibiting microglia activation in the dorsal horn of the impaired spinal cord and alleviating sciatic nerve injury. Our findings supply new references for the further development of HUC-MSCs-based cytotherapy for neuropathic pain administration.

Yangonin, one of the kavalactones isolated from Piper methysticum G. Forst, acts through cannabinoid 1 (CB1) receptors to induce an intrathecal anti-hyperalgesia

Ethnopharmacological relevancePiper methysticum G. Forst (Piperaceae) is traditionally consumed in Polynesian culture. The roots are used to produce an entheogenic drink and traditional medicine with sedative and anxiolytic properties. There is also evidence that it functions as a pain reliever. Kavalactones, its main active ingredients, exhibit psychoactive effects on the central nervous system. However, the active ingredients and pharmacological mechanisms underlying the analgesic effect of kavalactones are unclear. Aim of the studyThis study investigated the effects of kavain and yangonin on nociception, inflammatory hyperalgesia, and neuropathic mechanical allodynia at the spinal level. Materials and methodsMale Sprague–Dawley rats were administered kavain and yangonin (27.14 and 19.36 nmol/rat) via intrathecal injection. Tail-flick tests were performed to evaluate the anti-nociceptive properties. The efficacy of kavain and yangonin on inflammatory hyperalgesia was examined using a plantar test in rats with carrageenan-induced paw inflammation. The von Frey test was used to assess mechanical allodynia induced by partial sciatic nerve ligation. ResultsIntrathecal injection of yangonin demonstrated a relatively potent anti-nociceptive effect and attenuated carrageenan-induced hyperalgesia. These effects were completely reversed by the co-administration of PF 514273, a cannabinoid 1 (CB1) receptor antagonist. However, yangonin did not affect mechanical allodynia at the spinal level. Kavain, another abundant kavalactone, did not affect nociception, hyperalgesia, or mechanical allodynia at the spinal level. ConclusionsOverall, our study demonstrated that yangonin exerts anti-nociception and anti-inflammatory hyperalgesia effects via CB1 receptors at the spinal level. We identified a single kavalactone, yangonin, extracted from kava as a promising treatment for pain.

Formulation of Phytosomes Containing Rubia cordifolia Extract for Neuropathic Pain: In Vitro and In Vivo Evaluation.

This study aimed to develop a delivery system for the dried aqueous extract of Rubia cordifolia leaves (RCE) that could improve the neuroprotective potential of RCE by improving the bioavailability of the chief chemical constituent rubiadin. Rubiadin, an anthraquinone chemically, is a biomarker phytoconstituent of RCE. Rubiadin is reported to have strong antioxidant and neuroprotective activity but demonstrates poor bioavailability. In order to resolve the problem related to bioavailability, RCE and phospholipids were reacted in disparate ratios of 1:1, 1:2, and 1:3 to prepare phytosome formulations PC1, PC2, and PC3, respectively. The formulation PC2 showed particle size of 289.1 ± 0.21 nm, ζ potential of -6.92 ± 0.10 mV, entrapment efficiency of 72.12%, and in vitro release of rubiadin of 89.42% at pH 7.4 for a period up to 48 h. The oral bioavailability and neuroprotective potential of PC2 and RCE were assessed to evaluate the benefit of PC2 formulation over the crude extract RCE. Formulation PC2 showed a relative bioavailability of 134.14% with a higher neuroprotective potential and significantly (p < 0.05) augmented the nociceptive threshold against neuropathic pain induced by partial sciatic nerve ligation method. Antioxidant enzyme levels and histopathological studies of the sciatic nerves in various treatment groups significantly divulged that PC2 has enough potential to reverse the damaged nerves into a normal state. Finally, it was concluded that encapsulated RCE as a phytosome is a potential carrier system for enhancing the delivery of RCE for the efficient treatment of neuropathic pain.

ESRRG-controlled downregulation of KCNN1 in primary sensory neurons is required for neuropathic pain.

Peripheral nerve injury-induced neuronal hyperactivity in the dorsal root ganglion (DRG) participates in neuropathic pain. The calcium-activated potassium channel subfamily N member 1 (KCNN1) mediates action potential afterhyperpolarization (AHP) and gates neuronal excitability. However, the specific contribution of DRG KCNN1 to neuropathic pain is not yet clear. We report that chronic constriction injury (CCI) of the unilateral sciatic nerve or unilateral ligation of the fourth lumbar nerve produced the downregulation of Kcnn1 mRNA and KCNN1 protein in the injured DRG. This downregulation was partially attributed to a decrease in DRG estrogen-related receptor gamma (ESRRG), a transcription factor, which led to reduced binding to the Kcnn1 promoter. Rescuing this downregulation prevented CCI-induced decreases in total potassium voltage currents and AHP currents, reduced excitability in the injured DRG neurons, and alleviated CCI-induced development and maintenance of nociceptive hypersensitivities, without affecting locomotor function and acute pain. Mimicking the CCI-induced DRG KCNN1 downregulation resulted in augmented responses to mechanical, heat, and cold stimuli in naive mice. Our findings indicate that ESRRG-controlled downregulation of DRG KCNN1 is likely essential for the development and maintenance of neuropathic pain. Thus, KCNN1 may serve as a potential target for managing this disorder.

Efficacy assessment of novel methanimine derivatives in chronic constriction injury-induced neuropathic model: An in-vivo, ex-vivo and In-Silico approach

The multicomponent etiology, complex clinical implications, dose-based side effect and degree of pain mitigation associated with the current pharmacological therapy is incapable in complete resolution of chronic neuropathic pain patients which necessitates the perpetual requirement of novel medication therapy. Therefore, this study explored the ameliorative aptitude of two novel methanimine imitative like (E)-N-(4-nitrobenzylidene)-4‑chloro-2-iodobenzamine (KB 09) and (E)-N-(4-methylbenzylidene)-4‑chloro-2-iodobenzamine (KB 10) in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in rat model. Standard behavioral tests like dynamic and static allodynia, cold, thermal and mechanical hyperalgesia along with rotarod activity were performed at various experimental days like 0, 3, 7, 14 and 21. Enzyme linked immunosorbent assay (ELISA) on spinal tissue and antioxidant assays on sciatic nerve were executed accompanied by molecular docking and simulation studies. Prolonged ligation of sciatic nerve expressively induced hyperalgesia as well as allodynia in rats. KB 09 and KB 10 substantially attenuated the CCI elicited hyperalgesia and allodynia. They significantly reduced the biomarkers of pain and inflammation like Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in ELISA and while enhanced the GSH, SOD and CAT and diminished the MDA levels during antioxidant assays. KB 09 displayed -9.62 kcal/mol with TNF-α and -7.68 kcal/mol binding energy with IL-6 whereas KB 10 exhibited binding energy of -8.20 kcal/mol with IL-6 while -11.68 kcal/mol with TNF-α and hence both trial compounds ensured stable interaction with IL-6 and TNF-α during computational analysis. The results advocated that both methanimine derivatives might be novel candidates for attenuation of CCI-induced neuropathic pain prospects via anti-nociceptive, anti-inflammatory and antioxidant mechanisms.

Implication of system xc− in neuroinflammation during the onset and maintenance of neuropathic pain

BackgroundDespite the high prevalence of neuropathic pain, treating this neurological disease remains challenging, given the limited efficacy and numerous side effects associated with current therapies. The complexity in patient management is largely attributed to an incomplete understanding of the underlying pathological mechanisms. Central sensitization, that refers to the adaptation of the central nervous system to persistent inflammation and heightened excitatory transmission within pain pathways, stands as a significant contributor to persistent pain. Considering the role of the cystine/glutamate exchanger (also designated as system xc−) in modulating glutamate transmission and in supporting neuroinflammatory responses, we investigated the contribution of this exchanger in the development of neuropathic pain.MethodsWe examined the implication of system xc− by evaluating changes in the expression/activity of this exchanger in the dorsal spinal cord of mice after unilateral partial sciatic nerve ligation. In this surgical model of neuropathic pain, we also examined the consequence of the genetic suppression of system xc− (using mice lacking the system xc− specific subunit xCT) or its pharmacological manipulation (using the pharmacological inhibitor sulfasalazine) on the pain-associated behavioral responses. Finally, we assessed the glial activation and the inflammatory response in the spinal cord by measuring mRNA and protein levels of GFAP and selected M1 and M2 microglial markers.ResultsThe sciatic nerve lesion was found to upregulate system xc− at the spinal level. The genetic deletion of xCT attenuated both the amplitude and the duration of the pain sensitization after nerve surgery, as evidenced by reduced responses to mechanical and thermal stimuli, and this was accompanied by reduced glial activation. Consistently, pharmacological inhibition of system xc− had an analgesic effect in lesioned mice.ConclusionTogether, these observations provide evidence for a role of system xc− in the biochemical processes underlying central sensitization. We propose that the reduced hypersensitivity observed in the transgenic mice lacking xCT or in sulfasalazine-treated mice is mediated by a reduced gliosis in the lumbar spinal cord and/or a shift in microglial M1/M2 polarization towards an anti-inflammatory phenotype in the absence of system xc−. These findings suggest that drugs targeting system xc− could contribute to prevent or reduce neuropathic pain.

The Analgesic Potential of Litsea Species: A Systematic Review.

Various plant species from the Litsea genus have been claimed to be beneficial for pain relief. The PRISMA approach was adopted to identify studies that reported analgesic properties of plants from the Litsea genus. Out of 450 records returned, 19 primary studies revealed the analgesic potential of nine Litsea species including (1) Litsea cubeba, (2) Litsea elliptibacea, (3) Litsea japonica, (4) Litsea glutinosa, (5) Litsea glaucescens, (6) Litsea guatemalensis, (7) Litsea lancifolia, (8) Litsea liyuyingi and (9) Litsea monopetala. Six of the species, 1, 3, 4, 7, 8 and 9, demonstrated peripheral antinociceptive properties as they inhibited acetic-acid-induced writhing in animal models. Species 1, 3, 4, 8 and 9 further showed effects via the central analgesic route at the spinal level by increasing the latencies of heat stimulated-nocifensive responses in the tail flick assay. The hot plate assay also revealed the efficacies of 4 and 9 at the supraspinal level. Species 6 was reported to ameliorate hyperalgesia induced via partial sciatic nerve ligation (PSNL). The antinociceptive effects of 1 and 3 were attributed to the regulatory effects of their bioactive compounds on inflammatory mediators. As for 2 and 5, their analgesic effect may be a result of their activity with the 5-hydroxytryptamine 1A receptor (5-HT1AR) which disrupted the pain-stimulating actions of 5-HT. Antinociceptive activities were documented for various major compounds of the Litsea plants. Overall, the findings suggested Litsea species as good sources of antinociceptive compounds that can be further developed to complement or substitute prescription drugs for pain management.

Sexually dimorphic effects of pexidartinib on nerve injury-induced neuropathic pain in mice.

It is well-established that spinal microglia and peripheral macrophages play critical roles in the etiology of neuropathic pain; however, growing evidence suggests sex differences in pain hypersensitivity owing to microglia and macrophages. Therefore, it is crucial to understand sex- and androgen-dependent characteristics of pain-related myeloid cells in mice with nerve injury-induced neuropathic pain. To deplete microglia and macrophages, pexidartinib (PLX3397), an inhibitor of the colony-stimulating factor 1 receptor, was orally administered, and mice were subjected to partial sciatic nerve ligation (PSL). Following PSL induction, healthy male and female mice and male gonadectomized (GDX) mice exhibited similar levels of spinal microglial activation, peripheral macrophage accumulation, and mechanical allodynia. Treatment with PLX3397 significantly suppressed mechanical allodynia in normal males; this was not observed in female and GDX male mice. Sex- and androgen-dependent differences in the PLX3397-mediated preventive effects were observed on spinal microglia and dorsal root ganglia (DRG) macrophages, as well as in expression patterns of pain-related inflammatory mediators in these cells. Conversely, no sex- or androgen-dependent differences were detected in sciatic nerve macrophages, and inhibition of peripheral CC-chemokine receptor 5 prevented neuropathic pain in both sexes. Collectively, these findings demonstrate the presence of considerable sex- and androgen-dependent differences in the etiology of neuropathic pain in spinal microglia and DRG macrophages but not in sciatic nerve macrophages. Given that the mechanisms of neuropathic pain may differ among experimental models and clinical conditions, accumulating several lines of evidence is crucial to comprehensively clarifying the sex-dependent regulatory mechanisms of pain.

Analgesic effect of a cholinergic agonist (carbachol) in a sural nerve ligation-induced hypersensitivity mouse model

ABSTRACT Objectives Neuropathic pain is characterized by long-lasting, intractable pain. Sciatic nerve ligation is often used as an animal model of neuropathic pain, and the spared nerve injury (SNI) model, in which the common peroneal nerve (CPN) and tibial nerve (TN) are ligated, is widely used. In the present study, we evaluated the analgesic effect of a cholinergic agonist, carbachol, on a neuropathic pain model prepared by sural nerve (SN) ligation in mice. Methods The SN was tightly ligated as a branch of the sciatic nerve. Mechanical and thermal allodynia, and hyperalgesia were assessed using von Frey filaments and heat from a hot plate. The analgesic effects of intracerebroventricularly-administered morphine and carbachol were compared. Results SN ligation resulted in a significant decrease in pain threshold for mechanical stimulation 1 day after ligation. In response to thermal stimulation, allodynia was observed at 50°C and hyperalgesia at 53 and 56°C 3 days after ligation. Content of thiobarbituric acid reactive substances (TBARS) in the spinal cord increased significantly at 6 and 12 h after ligation. Acetylcholine content of the spinal cord also increased at 5 and 7 days after ligation. Intracerebroventricular administration of carbachol at 7 days after ligation produced a marked analgesic effect against mechanical and thermal stimuli, which was stronger and longer-lasting than morphine at all experimental time points. Conclusion These findings suggest that cholinergic nerves are involved in allodynia and hyperalgesia of the SN ligation neuropathic pain model.

Health Benefits of Electrolyzed Hydrogen Water: Antioxidant and Anti-Inflammatory Effects in Living Organisms.

Molecular hydrogen, the smallest and lightest molecule, serves as an intense reducing agent. Its distinct characteristics, including minimal size and neutral charge, enhance bioavailability and facilitate significant biological effects. Previously considered physiologically inert, hydrogen has gained recognition as a powerful therapeutic agent, known for its antioxidative and anti-inflammatory properties. Electrolyzed hydrogen water (EHW), enriched with molecular hydrogen, demonstrates remarkable antioxidative capabilities, indicating potential benefits for various diseases. Inflammation-induced reactive oxygen species (ROS) amplify inflammation, leading to secondary oxidative stress and creating a crosstalk between ROS and inflammatory responses. This crosstalk contributes to the pathogenesis and progression of chronic diseases. EHW interrupts this crosstalk, reducing inflammatory cytokines and oxidative stress across various disease models, suggesting therapeutic potential. EHW is also known for its anti-inflammatory effects, extending to pain management, as evidenced in models like sciatic nerve ligation and inflammatory pain. In an inflammatory bowel disease (IBD) model, EHW effectively alleviates abdominal pain, mitigating 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced inflammation and oxidative stress, offering insights for clinical applications. Additionally, hydrogen selectively targets harmful radicals, and EHW intake helps balance stress-induced hormonal dysregulation, potentially easing disorders associated with chronic stress.

Intrathecal Injections of Angiotensin IV and Oxytocin Conjugates Induce Antihyperalgesia and Antiallodynia in Both Sexes of Rats

Our previous studies have established that intrathecal oxytocin (OT) and angiotensin IV (Ang IV) injections induce antihyperalgesia and antiallodynia in rodents. Ang IV, a renin-angiotensin system hexapeptide, acts as an endogenous inhibitor that inhibits the oxytocin-degrading enzyme insulin-regulated aminopeptidase (IRAP). The pain inhibitory effects by Ang IV were found to be through its inhibition on IRAP to potentiate the effect of OT. However, these effects were found to be with a significant sex difference, which could be partially due to the higher expression of IRAP at the spinal cords of female. Therefore, we synthesized Ang IV and OT conjugates connected with a peptide bond and tested for their effects on hyperalgesia and allodynia. Carrageenan-induced hyperalgesia and partial sciatic nerve ligation (PSNL) were performed using rat models. Conjugates Ang IV-OT (Ang IV at the N-terminal) and OT-Ang IV (OT at the N-terminal) were synthesized and intrathecally injected into male and female rats. Our results showed that Ang IV-OT exhibited prominent antihyperalgesia in male rats, particularly during hyperalgesia recovery, whereas OT-Ang IV was more effective during development stage. Ang IV-OT showed clear antihyperalgesia in female rats, but OT-Ang IV had no significant effect. Notably, both conjugates alleviated neuropathic allodynia in male rats; however, OT-Ang IV had no effect in female rats, whereas Ang IV-OT induced significant antiallodynia. In conclusion, Ang IV-OT has greater therapeutic potential for treating hyperalgesia and allodynia than OT-Ang IV. Its effects were not affected by sex, unlike those of OT and OT-Ang IV, extending its possible clinical applications.