Food-Derived Natural Compounds for Pain Relief in Neuropathic Pain

Nutraceuticals Targeting Cannabinoid Receptor 1 and Transient Receptor Potential Vanilloid 1 for Pain Relief: A Computational Screening Approach

OBJECTIVE

This study examined the binding affinities and therapeutic potential of natural products targeting pain-related receptors using molecular docking and molecular dynamics (MD) simulations. Drug-like properties and absorption, distribution, metabolism, excretion, and toxicity (ADMET) analyses were also conducted.

METHODS

AutoDock Vina (The Scripps Research Institute, La Jolla, CA, USA) was used for docking against pain-related receptors, including transient receptor potential vanilloid 1 (TRPV1), cyclooxygenase-2 (COX-2), cannabinoid receptor 1 (CB1), mu-opioid receptor, and nicotinic acetylcholine receptors. Celecoxib was included as a reference drug for docking score comparison. Protein-ligand complex stability was assessed via 100-nanosecond (ns) MD simulations using GROMACS (GROningen MAchine for Chemical Simulations; the University of Groningen, Netherlands), analyzing root mean square deviation (RMSD) and radius of gyration (Rg). Drug-likeness was evaluated by Lipinski's rule of five, and ADMET analysis was performed for pharmacokinetics and toxicity profiling.

RESULTS

Ginsenoside Rb1 exhibited a strong affinity for TRPV1 (-9.5 kcal/mol) and mu-opioid (-9.0 kcal/mol) receptors, suggesting its potential as a non-opioid analgesic candidate. Cyanidin 3-O-rutinoside demonstrated high binding to TRPV1 (-9.35 kcal/mol), COX-2 (-9.65 kcal/mol), and CB1 (-9.18 kcal/mol), surpassing the reference drug celecoxib (-7.22 kcal/mol) in COX-2 binding. MD simulations confirmed complex stability, with RMSD (~3.0 Å) and Rg (~3.0 nm) values lower than unbound proteins. Most compounds met Lipinski's criteria, indicating good oral bioavailability. ADMET analysis revealed favorable absorption and distribution with low toxicity.

CONCLUSION

Ginsenoside Rb1 and cyanidin 3-O-rutinoside exhibit high binding affinity, stability, and favorable pharmacokinetic properties, supporting their potential as non-opioid analgesic candidates. Their ability to modulate pain pathways in vitro and in vivo warrants further investigation.

A comprehensive review of traditional Chinese medicine in treating neuropathic pain

Neuropathic pain (NP) is a common, intractable chronic pain caused by nerve dysfunction and primary lesion of the nervous system. The etiology and pathogenesis of NP have not yet been clarified, so there is a lack of precise and effective clinical treatments. In recent years, traditional Chinese medicine (TCM) has shown increasing advantages in alleviating NP. Our review aimed to define the therapeutic effect of TCM (including TCM prescriptions, TCM extracts and natural products from TCM) on NP and reveal the underlying mechanisms. Literature from 2018 to 2024 was collected from databases including Web of Science, PubMed, ScienceDirect, Google academic and CNKI databases. Herbal medicine, Traditional Chinese medicines (TCM), neuropathic pain, neuralgia and peripheral neuropathy were used as the search terms. The anti-NP activity of TCM is clarified to propose strategies for discovering active compounds against NP, and provide reference to screen anti-NP drugs from TCM. We concluded that TCM has the characteristics of multi-level, multi-component, multi-target and multi-pathway, which can alleviate NP through various pathways such as anti-inflammation, anti-oxidant, anti-apoptotic pathway, regulating autophagy, regulating intestinal flora, and influencing ion channels. Based on the experimental study and anti-NP mechanism of TCM, this paper can offer analytical evidence to support the effectiveness in treating NP. These references will be helpful to the research and development of innovative TCM with multiple levels and multiple targets. TCM can be an effective treatment for NP and can serve as a treasure house for new drug development.

Effects of Physical Cues on Stem Cell-Derived Extracellular Vesicles toward Neuropathy Applications

The peripheral nervous system undergoes sufficient stress when affected by diabetic conditions, chemotherapeutic drugs, and personal injury. Consequently, peripheral neuropathy arises as the most common complication, leading to debilitating symptoms that significantly alter the quality and way of life. The resulting chronic pain requires a treatment approach that does not simply mask the accompanying symptoms but provides the necessary external environment and neurotrophic factors that will effectively facilitate nerve regeneration. Under normal conditions, the peripheral nervous system self-regenerates very slowly. The rate of progression is further hindered by the development of fibrosis and scar tissue formation, which does not allow sufficient neurite outgrowth to the target site. By incorporating scaffolding supplemented with secretome derived from human mesenchymal stem cells, it is hypothesized that neurotrophic factors and cellular signaling can facilitate the optimal microenvironment for nerve reinnervation. However, conventional methods of secretory vesicle production are low yield, thus requiring improved methods to enhance paracrine secretions. This report highlights the state-of-the-art methods of neuropathy treatment as well as methods to optimize the clinical application of stem cells and derived secretory vesicles for nerve regeneration.

Effects of Natural Product-Derived Compounds on Inflammatory Pain via Regulation of Microglial Activation

Inflammatory pain is a type of pain caused by tissue damage associated with inflammation and is characterized by hypersensitivity to pain and neuroinflammation in the spinal cord. Neuroinflammation is significantly increased by various neurotransmitters and cytokines that are expressed in activated primary afferent neurons, and it plays a pivotal role in the development of inflammatory pain. The activation of microglia and elevated levels of pro-inflammatory cytokines are the hallmark features of neuroinflammation. During the development of neuroinflammation, various intracellular signaling pathways are activated or inhibited in microglia, leading to the regulation of inflammatory proteins and cytokines. Numerous attempts have been conducted to alleviate inflammatory pain by inhibiting microglial activation. Natural products and their compounds have gained attention as potential candidates for suppressing inflammatory pain due to verified safety through centuries of use. Many studies have also shown that natural product-derived compounds have the potential to suppress microglial activation and alleviate inflammatory pain. Herein, we review the literature on inflammatory mediators and intracellular signaling involved in microglial activation in inflammatory pain, as well as natural product-derived compounds that have been found to suppress microglial activation. This review suggests that natural product-derived compounds have the potential to alleviate inflammatory pain through the suppression of microglial activation.

Utilizing network pharmacological analysis to investigate the key targets and mechanisms of kaempferol against oxaliplatin-induced neurotoxicity

This study investigated the pharmacological mechanism of kaempferol in the treatment of oxaliplatin-induced neuropathic pain by network pharmacological method and cells experiment. The kaempferol and disease target genes were obtained from several databases, including TCMSP, SwissTargetPrediction, GeneCards, and CTD. Then, the common target genes of drugs and diseases were obtained using Venny online tools. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional analyses were carried out to obtain the enriched molecular pathways associated with the kaempferol and disease. Finally, we constructed a neuropathic pain cell experiment to confirm the findings. 138 intersection targets were identified between targets of kaempferol and oxaliplatin-induced neurotoxicity. Enrichment analyses revealed that the IL-17 signaling pathway was associated with the therapeutic effects of kaempferol. Kaempferol down-regulated the mRNA expression levels of TNF-α, IL-6, and CCL2 in oxaliplatin-treated astrocytes. Our findings showed that kaempferol alleviated oxaliplatin-induced neurotoxicity via regulation of inflammation-related genes.

The Effectiveness of Aloe Vera on Relief of Irritation and Nipple Pain in Lactating Women: Systematic Review and Meta-Analysis

Background. Aloe vera is one of the herbal products with anti-inflammatory, antioxidant, moisturizing, bactericidal, anti-viral, and anti-fungal effects that were used to relieve pain and irritation. The aim of the current systematic review and meta-analysis is to determine the effect of Aloe vera on the relief of irritation and nipple pain in lactating women. Methods. A search was carried out in four English electronic databases including Scopus, Embase, PubMed, and Web of Science until November 2021. All clinical trials that assessed the effect of Aloe vera on the relief of irritation and nipple pain in lactating women were included. The study’s risk of bias was assessed using the Cochrane risk of bias checklist. Study heterogeneity was determined using the I2 statistic and publication bias using Begg’s and Egger’s tests. Results of the random-effects meta-analysis were presented using standard mean difference (SMD) with 95% confidence intervals (CIs). Data were analyzed using STATA software version 16 MP. Results. In total, 7 articles with 1670 subjects were included in the meta-analysis. Overall, we found a positive impact of Aloe vera on reducing breast pain (pooled SMD= −0.45; CI= −0.83, −0.07, $P$ value <0.02) and irritation (pooled SMD= −0.48; CI= −0.64, −0.32, $P$ value<0.001) in lactating women. There is a high heterogeneity among pain studies (I2= 86%) but was low within irritation studies (I2= 26%). Conclusion. Our result showed that Aloe vera can be considered a choice for relieving breast pain or irritation in lactating women compared with routine care or another treatment. Considering the limited number of studies conducted on this topic and the low sample size, future studies with a larger sample will be required to draw better conclusions.

Bioactive compounds for neuropathic pain: An update on preclinical studies and future perspectives

Among different types of chronic pain, neuropathic pain (NP), arising from damage to the nervous system, including peripheral fibers and central neurons, is notoriously difficult to treat and affects 7-10% of the general population. Currently available treatment options for NP are limited and opioid analgesics have severe side effects and can result in opioid use disorder. Recent studies have exhibited the role of dietary bioactive compounds in the mitigation of NP. Here, we assessed the effects of commonly consumed bioactive compounds (ginger, curcumin, omega-3 polyunsaturated fatty acids, epigallocatechin gallate, resveratrol, soy isoflavones, lycopene, and naringin) on NP and NP-related neuroinflammation. Cellular studies demonstrated that these bioactive compounds reduce inflammation via suppression of NF-κB and MAPK signaling pathways that regulate apoptosis/cell survival, antioxidant, and anti-inflammatory responses. Animal studies strongly suggest that these regularly consumed bioactive compounds have a pronounced anti-NP effect as shown by decreased mechanical allodynia, mechanical hyperalgesia, thermal hyperalgesia, and cold hyperalgesia. The proposed molecular mechanisms include (1) the enhancement of neuron survival, (2) the reduction of neuronal hyperexcitability by activation of antinociceptive cannabinoid 1 receptors and opioid receptors, (3) the suppression of sodium channel current, and (4) enhancing a potassium outward current in NP-affected animals, triggering a cascade of chemical changes within, and between neurons for pain relief. Human studies administered in this area have been limited. Future randomized controlled trials are warranted to confirm the findings of preclinical efficacies using bioactive compounds in patients with NP.

NLRP3 Inflammasome Mediates Neurodegeneration in Rats with Chronic Neuropathic Pain

ABSTRACT

Patients with chronic neuropathic pain (NP) have a significantly increased risk of central nervous degeneration. Trigeminal neuralgia (TN) is a typical NP, and this manifestation is more obvious. In addition to severe pain, patients with TN are often accompanied by cognitive dysfunction and have a higher risk of central nervous system degeneration, but the mechanism is not clear. The NOD-like receptor 3 (NLRP3) inflammasome assembles inside of microglia on activation, which plays an important role in neurodegeneration such as Alzheimer disease. MCC950 is a specific blocker of NLRP3 inflammasome, which can improve the performance of degenerative diseases. Although NLRP3 inflammasome assembles inside of microglia on activation has been shown to be essential for the development and progression of amyloid pathology, its whether it mediates the neurodegeneration caused by NP is currently unclear. By constructing a rat model of chronic TN, we found that as the course of the disease progresses, TN rats have obvious cognitive and memory deficit. In addition, Tau hyperphosphorylation and Aβ expression increase in the cortex and hippocampus of the brain. At the same time, we found that NLRP3 expression increased significantly in model rats. Interestingly, NLRP3 specific blocker MCC950 can alleviate the neurodegeneration of trigeminal neuralgia rats to a certain extent. It is suggested that our NLRP3 inflammasome plays an important role in the neurodegeneration of trigeminal neuralgia rats. And it is related to the activation of central nervous system inflammation.

Analgesic potency of intrathecally administered punicalagin in rat neuropathic and inflammatory pain models

Punicalagin, a natural polyphenolic compound classified as an ellagitannin, is a major ingredient of pomegranate (Punica granatum L.). Punicalagin has potent antioxidant and anti-inflammatory effects. Although the antinociceptive effects of orally administered pomegranate extracts have been reported, little is known about the effect of punicalagin on nociceptive transmission in the central nervous system. We examined whether punicalagin ameliorates neuropathic pain and inflammatory pain in the spinal cord. Male Sprague-Dawley rats were subjected to chronic constriction injury (CCI) of the sciatic nerve, and an intrathecal catheter was implanted for drug administration. The electronic von Frey test and cold-plate test were performed in CCI rats to evaluate mechanical and cold hyperalgesia in neuropathic pain, and the formalin test was performed in normal rats to evaluate acute and persistent inflammatory pain. An open-field test was conducted to explore whether punicalagin affects locomotor activity in CCI rats. Punicalagin administered intrathecally attenuated mechanical and cold hyperalgesia to the same degree as gabapentin in CCI rats and reduced pain-related behaviors in both the early and late phases in formalin-injected rats. Punicalagin did not affect motor function. These results suggest that punicalagin exerts an antinociceptive effect in the spinal cord without motor deficit, thus showing therapeutic potential for neuropathic pain and inflammatory pain.

Effects of Curcumin and Its Different Formulations in Preclinical and Clinical Studies of Peripheral Neuropathic and Postoperative Pain: A Comprehensive Review

Lesion or disease of the somatosensory system leads to the development of neuropathic pain. Peripheral neuropathic pain encompasses damage or injury of the peripheral nervous system. On the other hand, 10–15% of individuals suffer from acute postoperative pain followed by persistent pain after undergoing surgeries. Antidepressants, anticonvulsants, baclofen, and clonidine are used to treat peripheral neuropathy, whereas opioids are used to treat postoperative pain. The negative effects associated with these drugs emphasize the search for alternative therapeutics with better efficacy and fewer side effects. Curcumin, a polyphenol isolated from the roots of Curcuma longa, possesses antibacterial, antioxidant, and anti-inflammatory properties. Furthermore, the low bioavailability and fast metabolism of curcumin have led to the advent of various curcumin formulations. The present review provides a comprehensive analysis on the effects of curcumin and its formulations in preclinical and clinical studies of neuropathic and postoperative pain. Based on the positive outcomes from both preclinical and clinical studies, curcumin holds the promise of mitigating or preventing neuropathic and postoperative pain conditions. However, more clinical studies with improved curcumin formulations are required to involve its use as adjuvant to neuropathic and postoperative drugs.

Topical Capsaicin for the Treatment of Neuropathic Pain

BACKGROUND

Neuropathic pain (NP) is an egregious problem worldwide. Due to the side-effects of oral drugs, drugs delivered directly to the affected area of pain are preferred.

OBJECTIVE

Capsaicin, a chemical compound isolated from chili peppers, is used as an analgesic in topical ointments and dermal patches to alleviate pain. Objective of the study is to review the application and functionality of topical capsaicin in treatment of neuropathic pain.

DATA SOURCES

To systematically review capsaicin's functions on NP, we retrieved articles from the PubMed database published in the last ten years.

STUDY ELIGIBILITY CRITERIA

The inclusion criteria were capsaicin and the use of capsaicin for the treatment of NP; on the other hand, articles were excluded according to the mentioned criteria such as abstracts, articles written in any language other than English, incomplete articles, and conference papers.

PARTICIPANTS AND INTERVENTIONS

Out of 265 articles, 108 articles were selected after filtering through the inclusion and exclusion criteria. The data and knowledge currently existing for capsaicin treatment in NP are summarized.

RESULTS

This review indicates that capsaicin effectively improves NP treatment without affecting the motor and large nerve fibres involved in sensory function. Transient receptor potential channel vanilloid type 1 (TRPV1) is the capsaicin receptor expressed in central and peripheral terminals of a sensitive primary nerve cell. Conclusions and implications of key findings: Topical capsaicin has a sensible safety profile and is effective in reducing NP. Therefore, studies over the last decade suggest that capsaicin might be a potential drug for NP treatment.

Effect of Extract and Synthesized Derivatives of Isolated Compound from Symplocos chinensis f. Pilosa Ohwi on Neuropathic Pain in Mice

Neuropathic pain is described as the "most terrible of all tortures that a nerve wound may inflict." The aim of the present study was to demonstrate the antinociceptive effect of Symplocos chinensis f. pilosa Ohwi water extract (SCW) and synthesized derivatives of the isolated compound. The antinociceptive effect was tested using the acetic acid-induced writhing and 5% formalin tests. Antinociceptive effects on neuropathic pain were evaluated using the von Frey test with chronic constriction injury (CCI) and surgical nerve injury (SNI) models and tail-flick test with a vincristine-induced pain model. An Ames test was also conducted. 5-hydroxymethylfurfural (5-HMF) was isolated and derivatives were synthesized with various acid groups. Among the plant water extracts, SCW showed significantly effective activity. Additionally, SCW presented antinociceptive effects in the neuropathic pain models. The SCW water fraction resulted in fewer writhes than the other fractions, and isolated 5-HMF was identified as an effective compound. Because 5-HMF revealed a positive response in the Ames test, derivatives were synthesized. Among the synthesized derivations, 5-succinoxymethylfurfural (5-SMF) showed the best effect in the neuropathic pain model. Our data suggest that SCW and the synthesized compound, 5-SMF, possess effective antinociceptive activity against neuropathic pain.

Important Flavonoids and Their Role as a Therapeutic Agent

Flavonoids are phytochemical compounds present in many plants, fruits, vegetables, and leaves, with potential applications in medicinal chemistry. Flavonoids possess a number of medicinal benefits, including anticancer, antioxidant, anti-inflammatory, and antiviral properties. They also have neuroprotective and cardio-protective effects. These biological activities depend upon the type of flavonoid, its (possible) mode of action, and its bioavailability. These cost-effective medicinal components have significant biological activities, and their effectiveness has been proved for a variety of diseases. The most recent work is focused on their isolation, synthesis of their analogs, and their effects on human health using a variety of techniques and animal models. Thousands of flavonoids have been successfully isolated, and this number increases steadily. We have therefore made an effort to summarize the isolated flavonoids with useful activities in order to gain a better understanding of their effects on human health.

Umbelliprenin relieves paclitaxel-induced neuropathy

OBJECTIVES

Umbelliprenin (UMB) is a prenylated coumarin that acts as an in vitro antioxidant and inhibits lipoxygenase managing the inflammation pathways, while in vivo it exerts anti-inflammatory activities.

METHODS

In this study, neuropathic pain was induced by four intraperitoneal doses of 2 mg/kg per day of paclitaxel (PTX) on days 1, 3, 5 and 7. Here, 49 male mice were randomly divided in the following groups: sham (not treated animals), negative control (PTX-treated receiving normal saline), single-dose UMB 6.25, 12.5 and 25 mg/kg groups (PTX-treated receiving UMB 6.25, 12.5 and 25 mg/kg, respectively), prevention (PTX-treated receiving PTX along with UMB 12.5 mg/kg on days 1, 3, 5 and 7) and positive control group (PTX-treated receiving imipramine 10 mg/kg as acute treatment). Hot-plate test was done to assess response to heat. Finally, interleukin (IL)-6 levels in the sciatic nerve and lipid peroxidation in sera were assessed.

KEY FINDINGS

Umbelliprenin was found equally effective for acute treatment with imipramine, when comparing the prevention group and the positive control group. Single, 25 mg/kg UMB effectively attenuated hyperalgesia, lipid peroxidation and IL-6 levels.

CONCLUSIONS

Umbelliprenin alleviated neuropathic pain, and decreased serum IL-6 levels and oxidative stress. UMB deserves further investigations, especially in clinical settings.

Compounds of traditional Chinese medicine and neuropathic pain

Neuropathic pain (NP) has become a serious global health issue and a huge clinical challenge without available effective treatment. P2 receptors family is involved in pain transmission and represents a promising target for pharmacological intervention. Traditional Chinese medicine (TCM) contains multiple components which are effective in targeting different pathological mechanisms involved in NP. Different from traditional analgesics, which target a single pathway, TCMs take the advantage of multiple components and multiple targets, and can significantly improve the efficacy of treatment and contribute to the prediction of the risks of NP. Compounds of TCM acting at nucleotide P2 receptors in neurons and glial cells could be considered as a potential research direction for moderating neuropathic pain. This review summarized the recently published data and highlighted several TCMs that relieved NP by acting at P2 receptors.

In silico analysis of polyphenols and flavonoids for design of human Nav1.7 inhibitors

Neuropathic pain is commonly associated with lesion or disease of the somatosensory system and often reflected as indicator of impaired life. Although the central nervous system is main regulator of pain but for initiation and maintenance of the neuropathic pain is regulated by peripheral nervous system. Sodium channels particularly Nav1.7, Nav1.8, Nav 1.9 are key stake holders in the peripheral neuropathy, activation of these sodium channels might lead to genesis and propagation. Flavonoids and polyphenols showed promising effects in neuropathic pain. Here we are reporting In silico analysis of some selected flavonoids and polyphenols on sodium activated voltage channel 1.7 to explore the structural fragments required for binding. Results indicated Baicalin, Butrin, Dihydromonospermoside, Icariin, Isocoreopsin and Isosaponarin are showing promising docking score with sodium activated voltage channel 1.7 than other compounds. Structural modification of these promising leads keeping pharamcophoric requirement intact may yield potent Nav1.7 inhibitors for peripheral pain management.Communicated by Ramaswamy H. Sarma.

Hydroxy-epoxide and keto-epoxide derivatives of linoleic acid activate trigeminal neurons

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11-hydroxy- and 11-keto-epoxide-LA derivatives elicit Ca²⁺ transients in trigeminal neuron subpopulations.

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11H-12,13E-LA, 11 K-12,13E-LA, and 11H-9,10E-LA produce Ca²⁺ responses in higher proportions of neurons than linoleic acid or 9-HODE.

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11-hydroxy-epoxide- and 11-keto-epoxide derivatives of linoleic acid potentially contribute to nociception.

Endogenous lipid mediators are proposed to contribute to headache and facial pain by activating trigeminal neurons (TN). We recently identified 11-hydroxy-epoxide- and 11-keto-epoxide derivatives of linoleic acid (LA) that are present in human skin and plasma and potentially contribute to nociception. Here we expand upon initial findings by examining the effects of 11-hydroxy- and 11-keto-epoxide-LA derivatives on TN activation in comparison to LA, the LA derivative [9-hydroxy-octadecadienoic acid (9-HODE)] and prostaglandin E₂ (PGE₂). 11-hydroxy- and 11-keto-epoxide-LA derivatives elicited Ca²⁺ transients in TN subpopulations. The proportion of neurons responding to test compounds (5 μM, 5 min) ranged from 16.2 ± 3.8 cells (11 K-9,10E-LA) to 34.1 ± 2.4 cells (11H-12,13E-LA). LA and 9-HODE (5 μM, 5 min) elicited responses in 11.6 ± 3.1% and 9.7 ± 3.4% of neurons, respectively. 11H-12,13E-LA, 11K-12,13E-LA, and 11H-9,10E-LA produced Ca²⁺ responses in significantly higher proportions of neurons compared to either LA or 9-HODE (F (6, 36) = 5.12, P = 0.0007). 11H-12,13E-LA and 11H-9,10E-LA increased proportions of responsive neurons in a concentration-dependent fashion, similar to PGE₂. Most sensitive neurons responded to additional algesic agents (32.9% to capsaicin, 40.1% to PGE₂, 58.0% to AITC), however 20.6% did not respond to any other agent. In summary, 11-hydroxy-epoxide derivatives of LA increase trigeminal neuron excitability, suggesting a potential role in headache or facial pain.

Postoperative pain pathophysiology and treatment strategies after CRS + HIPEC for peritoneal cancer

Background

Cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) is a treatment choice for peritoneal cancer. However, patients commonly suffer from severe postoperative pain. The pathophysiology of postoperative pain is considered to be from both nociceptive and neuropathic origins.

Main body

The recent advances on the etiology of postoperative pain after CRS + HIPEC treatment were described, and the treatment strategy and outcomes were summarized.

Conclusion

Conventional analgesics could provide short-term symptomatic relief. Thoracic epidural analgesia combined with opioids administration could be an effective treatment choice. In addition, a transversus abdominis plane block could also be an alternative option, although further studies should be performed.

Organic Isothiocyanates as Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H₂S), the "new entry" in the series of endogenous gasotransmitters, plays a fundamental role in regulating the biological functions of various organs and systems. Consequently, the lack of adequate levels of H₂S may represent the etiopathogenetic factor of multiple pathological alterations. In these diseases, the use of H₂S donors represents a precious and innovative opportunity. Recent Advances: Natural isothiocyanates (ITCs), sulfur compounds typical of some botanical species, have long been investigated because of their intriguing pharmacological profile. Recently, the ITC moiety has been proposed as a new H₂S-donor chemotype (with a l-cysteine-mediated reaction). Based on this recent discovery, we can clearly observe that almost all the effects of natural ITCs can be explained by the H₂S release. Consistently, the ITC function was also used as an original H₂S-releasing moiety for the design of synthetic H₂S donors and original "pharmacological hybrids." Very recently, the chemical mechanism of H₂S release, resulting from the reaction between l-cysteine and some ITCs, has been elucidated. Critical Issues: Available literature gives convincing demonstration that H₂S is the real player in ITC pharmacology. Further, countless studies have been carried out on natural ITCs, but this versatile moiety has been used only rarely for the design of synthetic H₂S donors with optimal drug-like properties. Future Directions: The development of more ITC-based synthetic H₂S donors with optimal drug-like properties and selectivity toward specific tissues/pathologies seem to represent a stimulating and indispensable prospect of future experimental activities.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

Analgesic Effects of Cnidium officinale Extracts on Postoperative, Neuropathic, and Menopausal Pain in Rat Models

Cnidium officinale, widely cultivated in East Asia, has been reported to exhibit pharmacological efficacy in various disorders. However, little has been reported on its role as a pain killer. In this study, we reveal that the C. officinale extract (COE) has great efficacy as a novel analgesic in various in vivo pain models. Administration of COE attenuated hypersensitivity in all postoperative, neuropathic, and menopausal pain models. Decreased hyperalgesia was confirmed by a mechanical withdrawal threshold assay and ultrasonic vocalization call analysis. In addition, application of COE inhibited the induction of the proinflammatory cytokines and calpain-3 on dorsal root ganglion neurons in a spared nerve injury rat model. Treatment with ferulic acid, which was identified as one of the components of COE by HPLC analysis, alleviated nociceptive behaviors. Our findings suggest that ferulic acid is an active compound from COE, and COE is a potential phytomedical source for pain relief by inhibiting the process of inflammation.

The role of orphan G protein-coupled receptors in the modulation of pain: A review

G protein-coupled receptors (GPCRs) comprise a large number of receptors. Orphan GPCRs are divided into six families. These groups contain orphan receptors for which the endogenous ligands are unclear. They have various physiological effects in the body and have the potential to be used in the treatment of different diseases. Considering their important role in the central and peripheral nervous system, their role in the treatment of pain has been the subject of some recent studies. At present, there are effective therapeutics for the treatment of pain including opioid medications and non-steroidal anti-inflammatory drugs. However, the side effects of these drugs and the risks of tolerance and dependence remain a major problem. In addition, neuropathic pain is a condition that does not respond to currently available analgesic medications well. In the present review article, we aimed to review the most recent findings regarding the role of orphan GPCRs in the treatment of pain. Accordingly, based on the preclinical findings, the role of GPR3, GPR7, GPR8, GPR18, GPR30, GPR35, GPR40, GPR55, GPR74, and GPR147 in the treatment of pain was discussed. The present study highlights the role of orphan GPCRs in the modulation of pain and implies that these receptors are potential new targets for finding better and more efficient therapeutics for the management of pain particularly neuropathic pain.