Inhibition of the compound action potentials of frog sciatic nerves by aroma oil compounds having various chemical structures

Treatment of neuropathic pain by traditional Chinese medicine: An updated review on their effect and putative mechanisms of action

Neuropathic pain (NP) is a common chronic pain with heterogeneous clinical features, and consequent lowering of quality of life. Currently, although conventional chemical drugs can effectively manage NP symptoms in the short term, their long-term efficacy is limited, and they come with significant side effects. In this regard, traditional Chinese medicine (TCM) provides a promising avenue for treating NP. Numerous pharmacological and clinical studies have substantiated the effectiveness of TCM with multiple targets and mechanisms. We aimed to outline the characteristics of TCM, including compound prescriptions, single Chinese herbs, active ingredients, and TCM physical therapy, for NP treatment and discussed their efficacy by analyzing the pathogenesis of NP. Various databases, such as PubMed, Web of Science, China National Knowledge Infrastructure, and Wanfang database, were searched. We focused on recent research progress in NP treatment by TCM. Finally, we proposed the future challenges and emerging trends in the treatment of NP. TCM demonstrates significant clinical efficacy in NP treatment, employing multi-mechanisms. Drawing from the theory of syndrome differentiation, four types of dialectical treatments for NP by compound TCM prescriptions were introduced: promoting blood circulation and removing blood stasis; promoting blood circulation and promote Qi flow; warming Yang and benefiting Qi; soothing the liver and regulating Qi. Meanwhile, 33 single Chinese herbs and 25 active ingredients were included. In addition, TCM physical therapy (e.g., acupuncture, massage, acupoint injection, and fumigation) also showed good efficacy in NP treatment. TCM, particularly through the use of compound prescriptions and acupuncture, holds bright prospects in treating NP owing to its diverse holistic effects. Nonetheless, the multi-targets of TCM may result in possible disadvantages to NP treatment, and the pharmacological mechanisms of TCM need further evaluation. Here, we provide an overview of NP treatment via TCM, based on the pathogenesis and the potential therapeutic mechanisms, thus providing a reference for further studies.

Inhibition of compound action potentials in the frog sciatic nerve by inchinkoto, a traditional Japanese medicine used for oral mucositis

OBJECTIVE

This study aimed to determine the effects of traditional Japanese (Kampo) medicines used to treat oral mucositis on nerve conduction.

METHODS

The effects of Kampo medicines, crude drugs, and chemical compounds on compound action potentials (CAPs) were analyzed using extracellular recordings in frog sciatic nerves.

RESULTS

Among the Kampo medicines, inchinkoto demonstrated the most significant reduction in CAP amplitude, with a half-maximal inhibitory concentration (IC50) of 5.4 mg/mL. Hangeshashinto, shosaikoto, hochuekkito, and juzentaihoto also showed a significant reduction. Regarding inchinkoto, Artemisiae Capillari Spica (artemisia) was the most effective crude drug, with an IC50 of 4.2 mg/mL for CAP amplitude reduction, whereas Gardeniae Fructus (gardenia) exerted no significant effect. However, the combined use of artemisia and gardenia reduced the CAP amplitude more effectively than artemisia alone, indicating a synergistic interaction. The chemical ingredient eugenol from artemisia administered at 1 and 3 mmol/L reduced CAP amplitude, whereas other chemical ingredients administered at 0.1 and 1 mmol/L had no significant effects.

CONCLUSIONS

Inchinkoto exhibited the most effective reduction in CAP amplitude in the sciatic nerve of frogs, primarily through the action of artemisia, with potential synergistic interaction between artemisia and gardenia.

Research progress on mechanism of Chinese Kaiqiao herbs in management of neuropathic pain

The Chinese herbal medicine for Kaiqiao, such as borneol, musk, grassleaf sweetflag rhizome, storax and camphor, have been prescribed in traditional Chinese medicine for thousands of years and now are widely used for neuropathic pain, the main components of which are annular compounds. Studies have shown that their analgesic mechanisms include regulating the expression of γ-aminobutyric acid, N-methyl- D-aspartic acid and other receptors; regulating ion channel function; inhibiting inflammatory response, oxidative stress and apoptosis; regulating neurotransmission and neuronal excitability; and participating in neuroprotection and neurological repair. It is suggested that the mechanisms of action of Kaiqiao herbs in central nervous system analgesia should be further explored; high-quality rapid screening of drug targets may be used, and the targeted agents using the characteristics of Kaiqiao herbs would be developed. This article reviews the research progress on the effect mechanism of traditional Kaiqiao herbs in the treatment of neuropathic pain to provide further research directions.

TRP channels and monoterpenes: Past and current leads on analgesic properties

The activation of the transient receptor potential (TRP) channels expressed by sensory neurons is essential to the transduction of thermal and mechanical sensory information. In the setting of chronic inflammatory conditions, the activation of the melastatin family member 8 (TRPM8), the TRP vanilloid 1 (TRPV1), and the TRP ankyrin 1 (TRPA1) is correlated with pain hypersensitivity reactions. Monoterpenes, among which pulegone and menthol, a major class of phytocompounds present in essential oils of medicinal plants, are known modulators of those TRP channels activity. In the present review, we correlate the monoterpene content of plants with their historical therapeutic properties. We then describe how monoterpenes exert their anti-inflammatory and antihyperalgesia effects through modulation of TRP channels activity. Finally, we discuss the importance and the potential of characterizing new plant extracts and reassessing studied plant extracts for the development of ethnopharmacology-based innovative treatments for chronic pain. This review suggests that monoterpene solutions, based on composition from traditional healing herbs, offer an interesting avenue for the development of new phytotherapeutic treatments to alleviate chronic inflammatory pain conditions.

Transient receptor potential channel involvement in antinociceptive effect of citral in orofacial acute and chronic pain models

This study aimed to test for the possible antinociceptive effect of the naturally occurring terpene citral in rodent models of acute and chronic orofacial pain and to test for the possible involvement of transient receptor potential (TRP) channels in this effect. Acute nociceptive behavior was induced in one series of experiments by administering formalin, cinnamaldehyde, menthol or capsaicin to the upper lip. Nociceptive behavior was assessed by orofacial rubbing, and the effects of pre-treatment with citral (0.1, 0.3 or 1.0 mg/Kg) or vehicle (control) were tested on the behavior. Nociceptive behavior was also induced by formalin injected into the temporomandibular joint or mustard oil injected into the masseter muscle, preceded by citral or vehicle (control) treatment. The chronic pain model involved infraorbital nerve transection (IONX) that induced mechanical hypersensitivity which was assessed by von Frey hair stimulation of the upper lip. Motor activity was also evaluated. Docking experiments were performed using TRPV1 and TRPM8 channels. Citral but not vehicle produced significant (p<0.01, ANOVA) antinociception on all the acute nociceptive behaviors, and these effects were attenuated by TRPV1 antagonist capsazepine, TRPM3 antagonist mefenamic acid and by TRPM8 desensitization, but not by ruthenium red and TRPA1 antagonist HC-030031. The IONX animals developed facial mechanical hypersensitivity that was significantly reduced by citral but not by vehicle. The docking experiments revealed that citral may interact with TRPV1 and TRPM8 channels. These results indicate the potential use of citral as an inhibitor of orofacial nociception in both acute and chronic pain states through TRPV1, TRPM3 and TRPM8 channels. See also Figure 1(Fig. 1).

Food Ingredients Derived from Lemongrass Byproduct Hydrodistillation: Essential Oil, Hydrolate, and Decoction

Essential oil (EO), hydrolate, and nondistilled aqueous phase (decoction) obtained from the hydrodistillation of lemongrass byproducts were studied in terms of their potential as food ingredients under a circular economy. The EO (0.21%, dry weight basis) was composed mainly of monoterpenoids (61%), the majority being citral (1.09 g/kg). The minimal inhibitory concentrations (MIC) of lemongrass EO against Escherichia coli, Salmonella enterica, and Staphylococcus aureus, were 617, 1550, and 250 μg/mL, respectively. This effect was dependent on the citral content. Particularly for Gram-negative bacteria, a synergism between citral and the remaining EO compounds enhanced the antimicrobial activity. The polymeric material obtained from the nondistilled aqueous phase was composed of phenolic compounds (25% gallic acid equivalents) and carbohydrates (22%), mainly glucose (66 mol%). This polymeric material showed high antioxidant activity due to bound phenolic compounds, allowing its application as a functional dietary fiber ingredient. Matcha green tea formulations were successfully mixed with lemongrass hydrolate containing 0.21% EO (dry weight basis) with 58% of monoterpenoids, being citral at 0.73 g/kg, minimizing matcha astringency with a citrus flavor and extending the product shelf life. This holistic approach to essential oils’ hydrodistillation of Cymbopogon citratus byproducts allows for valorizing of the essential oil, hydrolate, and decoction for use as food ingredients.

Genome-Wide Identification of BAHD Superfamily and Functional Characterization of Bornyl Acetyltransferases Involved in the Bornyl Acetate Biosynthesis in Wurfbainia villosa

Bornyl acetate (BA) is known as a natural aromatic monoterpene ester with a wide range of pharmacological and biological activities. Borneol acetyltransferase (BAT), catalyzing borneol and acetyl-CoA to synthesize BA, is alcohol acetyltransferase, which belongs to the BAHD super acyltransferase family, however, BAT, responsible for the biosynthesis of BA, has not yet been characterized. The seeds of Wurfbainia villosa (homotypic synonym: Amomum villosum) are rich in BA. Here we identified 64 members of the BAHD gene family from the genome of W. villosa using both PF02458 (transferase) and PF07247 (AATase) as Hidden Markov Model (HMM) to screen the BAHD genes. A total of sixty-four WvBAHDs are distributed on 14 chromosomes and nine unanchored contigs, clustering into six clades; three WvBAHDs with PF07247 have formed a separated and novel clade: clade VI. Twelve candidate genes belonging to clade I-a, I-b, and VI were selected to clone and characterize in vitro, among which eight genes have been identified to encode BATs acetylating at least one type of borneol to synthesize BA. All eight WvBATs can utilize (-)-borneol as substrates, but only five WvBATs can catalyze (+)-borneol, which is the endogenous borneol substrate in the seeds of W. villosa; WvBAT3 and WvBAT4 present the better catalytic efficiency on (+)-borneol than the others. The temporal and spatial expression patterns of WvBATs indicate that WvBAT3 and WvBAT4 are seed-specific expression genes, and their expression levels are correlated with the accumulation of BA, suggesting WvBAT3 and WvBAT4 might be the two key BATs for BA synthesis in the seeds of W. villosa. This is the first report on BAT responsible for the last biosynthetic step of BA, which will contribute to further studies on BA biosynthesis and metabolism engineering of BA in other plants or heterologous hosts.

IN VIVO NEUROPHYSIOLOGICAL ASSESSMENT OF IN SILICO PREDICTIONS OF NEUROTOXICITY: CITRONELLAL, 3,4-DICHLORO-1-BUTENE, AND BENZYL BROMOACETATE

Neurotoxicants may be widespread in the environment and can produce serious health impacts in the human population. Screening programs that use in vitro methods have generated data for thousands of chemicals. However, these methods often do not evaluate repeated or prolonged exposures, which are required for many neurotoxic outcomes. Additionally, the data produced by such screening methods may not include mechanisms which play critical biological roles necessary for in vivo neurotoxicity. The Hard and Soft Acids and Bases (HSAB) in silico model focuses on chemical structure and electrophilic properties which are important to the formation of protein adducts. A group of structurally diverse chemicals have been evaluated with an in silico screening approach incorporating HSAB parameters. However, the predictions from the expanded chemical space have not been evaluated using in vivo methods. Three chemicals predicted to be cumulative toxicants were selected for in vivo neurotoxicological testing. Adult male Long-Evans rats were treated orally with citronellal (CIT), 3,4-dichloro-1-butene (DCB), or benzyl bromoacetate (BBA) for 8 weeks. Behavioral observations were recorded weekly to assess motor function. Peripheral neurophysiological measurements were derived from nerve excitability (NE) tests which involved compound muscle action potentials (CMAPs) in the tail and foot, and mixed nerve action potentials (MNAPs) in the tail. Compound nerve action potentials (CNAPs) and nerve conduction velocity (NCV) in the tail were also quantified. Peripheral inputs into the central nervous system were examined using somatosensory evoked potentials recorded from the cortex (SEP_CTX) and cerebellum (SEP_CEREB). CIT or BBA did not result in significant alterations to peripheral nerve or somatosensory function. DCB reduced grip-strength and altered peripheral nerve function. The MNAPs required less current to reach 50% amplitude and had a lower calculated rheobase, suggesting increased excitability. Increased CNAP amplitudes and greater NCV were also observed. Novel changes were found in the SEP_CTX with an abnormal peak forming in the early portion of the waveforms of treated rats, and decreased latencies and increased amplitudes were observed in SEP_CEREB recordings. These data contribute to testing an expanded chemical space from an in silico HSAB model for predicting cumulative neurotoxicity and may assist with prioritizing chemicals to protect human health.

Anesthetic Pharmacology of the Mint Extracts L-Carvone and Methyl Salicylate

INTRODUCTION

Hydrocarbons with sufficient water solubility allosterically modulate anesthetic-sensitive ion channels. Mint extracts L-carvone and methyl salicylate water solubility exceeds modulation cutoff values for γ-amino butyric acid type A (GABAA) receptors, N-methyl-D-aspartate (NMDA) receptors, and type-2 voltage-gated sodium (Nav1.2) channels. We hypothesized that mint extracts modulate these channels at concentrations that anesthetize rats.

METHODS

Channels were expressed separately in frog oocytes and studied using 2-electrode voltage clamp techniques at drug concentrations up to 10 mM. Normalized current effects were fit to Hill equations. Mint compounds were formulated in a lipid emulsion and administered IV to rats. When unresponsive to the tail clamp, rats were exsanguinated, and plasma drug concentrations were measured.

RESULTS

Both mint compounds caused concentration-dependent inhibition of all channels except for methyl salicylate which inhibited GABAA receptors at low concentrations and potentiated at high concentrations. Plasma drug concentrations in anesthetized rats were 7.9 mM for L-carvone and 2.7 mM for methyl salicylate. This corresponded to ≥53% NMDA receptor inhibition and ≥78% Nav1.2 channel inhibition by both compounds and 30% potentiation of GABAA receptors by methyl salicylate.

CONCLUSION

L-Carvone and methyl salicylate allosterically modulate cell receptor targets important to molecular actions of conventional anesthetics at concentrations that also induce general anesthesia in rats.

Anticarcinogenic Effects of Odorant Substances Citral, Citrathal R and Cyclovertal on Breast Cancer in vitro

Purpose

In 2020, breast cancer still represents the most common type of cancer in women worldwide. Depending on the specific molecular subtype, clinical breast cancer management comprises surgery, radiotherapy, chemotherapy and targeted therapy. Furthermore, there are some therapeutic approaches from the field of complementary and alternative medicine. Current research focuses on the elucidation of new therapeutic targets for treatment development. Odorant substances affect apoptosis, proliferation and cell cycle in healthy and cancerous cells. Exact signalling pathways involved are not entirely clear. The present study aims to analyse their therapeutic potential in breast cancer.

Methods

This study focuses on the effect of commonly used odorant substances (citral, citrathal R, cyclovertal, para-cymol, hexylacetat, herbavert, dihydromyrcerol and limonen) on the breast cancer cell lines MDA-MB-231, T47-D and BT474. Methodologically, this study applied cell culturing, MTT assay for detection of IC50 of the odorant substance, RNA purification followed by qRT-PCR, protein isolation and Western Blot, as well as immunocytochemistry. Further, this study investigates the role of transient receptor potential channel V1 (TRPV1), involved in the mechanisms of action for some odorant substances. Therefore, capsazepine, a TRPV1 antagonist, was used.

Results

The odorant substances citral, citrathal R and cyclovertal have significant pro-apoptotic (p < 0.001), anti-proliferative (p < 0.001) and cell cycle-arresting effects measurable in RNA expression as well as in protein levels and immunocytochemical staining. The combination of citral and capsazepine no longer showed significant pro-apoptotic, antiproliferative, and cell cycle inhibitory effects compared to the compounds alone. This indicates that TRPV1 is necessary for the signal transduction of citral.

Conclusion

This present study reveals three odorant substances with effects on cell viability, indicating their potential use in breast cancer therapy.

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Inhibition of Fast Nerve Conduction Produced by Analgesics and Analgesic Adjuvants-Possible Involvement in Pain Alleviation

Nociceptive information is transmitted from the periphery to the cerebral cortex mainly by action potential (AP) conduction in nerve fibers and chemical transmission at synapses. Although this nociceptive transmission is largely inhibited at synapses by analgesics and their adjuvants, it is possible that the antinociceptive drugs inhibit nerve AP conduction, contributing to their antinociceptive effects. Many of the drugs are reported to inhibit the nerve conduction of AP and voltage-gated Na⁺ and K⁺ channels involved in its production. Compound action potential (CAP) is a useful measure to know whether drugs act on nerve AP conduction. Clinically-used analgesics and analgesic adjuvants (opioids, non-steroidal anti-inflammatory drugs, ₂-adrenoceptor agonists, antiepileptics, antidepressants and local anesthetics) were found to inhibit fast-conducting CAPs recorded from the frog sciatic nerve by using the air-gap method. Similar actions were produced by antinociceptive plant-derived chemicals. Their inhibitory actions depended on the concentrations and chemical structures of the drugs. This review article will mention the inhibitory actions of the antinociceptive compounds on CAPs in frog and mammalian peripheral (particularly, sciatic) nerves and on voltage-gated Na⁺ and K⁺ channels involved in AP production. Nerve AP conduction inhibition produced by analgesics and analgesic adjuvants is suggested to contribute to at least a part of their antinociceptive effects.

The Preclinical Pharmacological Study of a Novel Long-Acting Local Anesthetic, a Fixed-Dose Combination of QX-OH/Levobupivacaine, in Rats

Introduction: Previous studies demonstrated that 35 mM QX-OH/10 mM Levobupivacaine (LL-1), a fixed-dose combination, produced a long-acting effect in rat local anesthesia models. All preclinical pharmacodynamic results indicated that LL-1 had potential for postsurgical pain treatment. The objective of this study was to investigate the pharmacokinetics of LL-1. Then, the possible mechanism of the extended duration by the combination was examined.

Methods and Results: All experiments were examined and approved by the Committee of Animal Care of the West China Hospital Sichuan University (Ethical approval number, 2015014A). The compound action potentials were recorded to verify the pharmacodynamic result in ex vivo. In frog sciatic nerve, LL-1 produced an effective inhibition with rapid onset time. The concentration-time profiles of LL-1 were determined in plasma and local tissues after sciatic nerve block. The maximum concentration of QX-OH and levobupivacaine were 727.22 ± 43.38 µg/g and 256.02 ± 28.52 µg/g in muscle, 634.26 ± 36.04 µg/g and 429.63 ± 48.64 µg/g in sciatic nerve, and 711.71 ± 25.14 ng/ml and 114.40 ± 10.19 ng/ml in plasma, respectively. The absorption of QX-OH into circulation was very rapid at 0.71 ± 0.06 h, which was faster than that of levobupivacaine (4.11 ± 0.39 h, p = 0.003). The half-time of QX-OH in plasma and local tissues had no significant difference (p = 0.329), with the values of 2.64 h, 3.20 h, and 3.79 h in plasma, muscle, and sciatic nerve, respectively. The elimination profile of levobupivacaine differed from that of QX-OH, which was slower eliminated from plasma (4.89 ± 1.77 h, p = 0.036) than from muscle (1.38 ± 0.60 h) or sciatic nerve (1.28 ± 0.74 h). When levobupivacaine was used alone, the Tmax in plasma was 1.07 ± 0.16 h. Interestingly, the Tmax of levobupivacaine in the plasma was increased by four times in combination with QX-OH (4.11 ± 0.39 h). Levobupivacaine promotes cellular QX-OH uptake.

Conclusion: The preclinical pharmacokinetic study of LL-1 in the rat plasma, muscle, and sciatic nerve was accomplished. Then, the possible mechanism of the prolonged duration was that QX-OH delayed the absorption of levobupivacaine from the injection site into circulation, and levobupivacaine accelerated QX-OH to accumulate into cells.

Natural products as a perspective for cancer pain management: A systematic review

BACKGROUND

Cancer is the leading cause of death in the world and one of the main symptoms affecting these individuals is chronic pain, which must be evaluated and treated in its various components. Several drugs are currently used, but beyond the high cost, they have harmful side effects to patients or are transitorily effective. Ergo, there is a need to look for new options for cancer pain relief. Natural products (NPs) present themselves as strong candidates for the development of new drugs for the treatment of chronic pain, such as cancer pain.

PURPOSE

This systematic review aimed to summarize current knowledge about the analgesic profile of NPs in cancer pain.

METHODS

The search included PubMed, Scopus and Web of Science (from inception to June 2018) sought to summarize the articles studying new proposals with NPs for the management of oncological pain. Two independent reviewers extracted data on study characteristics, methods and outcomes.

RESULTS

After an extensive survey, 21 articles were selected, which described the analgesic potential of 15 natural compounds to relieve cancer pain. After analyzing the data, it can be suggested that these NPs, which have targets in central and peripheral mechanisms, are interesting candidates for the treatment of cancer pain for addressing different pharmacological mechanisms (even innovative), but ensuring the safety of these compounds is still a challenge. Likewise, the cannabinoids compounds leave the front as the most promising compounds for direct applicability due to the clinical studies that have already been developed and the background already established about these effects on chronic pain.

CONCLUSION

Regarding these findings, it can be concluded that the variability of possible biological sites of action is strategic for new perspectives in the development of therapeutic proposals different from those available in the current market.

Inhibition by general anesthetic propofol of compound action potentials in the frog sciatic nerve and its chemical structure

Although the intravenous general anesthetic propofol (2,6-diisopropylphenol) has an ability to inhibit nerve conduction, this has not been fully examined. Various agents inhibit compound action potentials (CAPs) in a manner dependent on their chemical structures. To determine propofol's chemical structure that is important in nerve conduction inhibition, we examined the effects of propofol and its related compounds on fast-conducting CAPs recorded from the frog sciatic nerve by using the air-gap method. Propofol concentration-dependently reduced the peak amplitude of the CAP with a half-maximal inhibitory concentration (IC₅₀) value of 0.14 mM. A similar inhibition was produced by other phenols, 4-sec-butylphenol and 4-amylphenol (IC₅₀ values: 0.33 and 0.20 mM, respectively). IC₅₀ values for these and more phenols (4-isopropylphenol, 4-tert-butylphenol, and 4-ter-amylphenol; data published previously) were correlated with the logarithm of their octanol-water partition coefficients. A phenol having ketone group (raspberry ketone) and alcohols (3-phenyl-1-propanol and 2-phenylethylalcohol) inhibited CAPs less effectively than the above-mentioned phenols. The local anesthetic (LA) benzocaine reduced CAP peak amplitudes with an IC₅₀ of 0.80 mM, a value larger than that of propofol. When compared with other LAs, propofol activity was close to those of ropivacaine, levobupivacaine, and pramoxine, while benzocaine activity was similar to those of cocaine and lidocaine. It is concluded that propofol inhibits nerve conduction, possibly owing to isopropyl and hydroxyl groups bound to the benzene ring of propofol and to its lipophilicity; propofol's efficacy is comparable to those of some LAs. These results could serve to develop propofol-related agents exhibiting analgesia when applied topically.

To flourish or perish: evolutionary TRiPs into the sensory biology of plant-herbivore interactions

The interactions between plants and their herbivores are highly complex systems generating on one side an extraordinary diversity of plant protection mechanisms and on the other side sophisticated consumer feeding strategies. Herbivores have evolved complex, integrative sensory systems that allow them to distinguish between food sources having mere bad flavors from the actually toxic ones. These systems are based on the senses of taste, olfaction and somatosensation in the oral and nasal cavities, and on post-ingestive chemosensory mechanisms. The potential ability of plant defensive chemical traits to induce tissue damage in foragers is mainly encoded in the latter through chemesthetic sensations such as burning, pain, itch, irritation, tingling, and numbness, all of which induce innate aversive behavioral responses. Here, we discuss the involvement of transient receptor potential (TRP) channels in the chemosensory mechanisms that are at the core of complex and fascinating plant-herbivore ecological networks. We review how "sensory" TRPs are activated by a myriad of plant-derived compounds, leading to cation influx, membrane depolarization, and excitation of sensory nerve fibers of the oronasal cavities in mammals and bitter-sensing cells in insects. We also illustrate how TRP channel expression patterns and functionalities vary between species, leading to intriguing evolutionary adaptations to the specific habitats and life cycles of individual organisms.

The essential oil of Lippia alba and its components affect Drosophila behavior and synaptic physiology

Lippia alba is a flowering shrub in the verbena family and its essential oil (EO) is known for its sedative, antidepressant and analgesic properties. In the Amazon region of Brazil, it is used in aquaculture to anesthetize fish during transport. Many of the specialized metabolites found in EOs presumably evolved to protect plants from herbivores, especially insects. We used Drosophila to test the behavioral and physiological actions of this EO and its components. We found that a 150 min exposure to the EO vapors resulted in immobilization of adult flies. Gas chromatography-mass spectrometry identified the major components of the EO as the monoterpenes citral (59%), carvone (7%) and limonene (7%). Fly immobilization by the EO was due to citral and carvone, with citral producing more rapid effects than carvone. We tested whether the EO affected synaptic physiology by applying it to the larval neuromuscular junction. The EO delivered at 0.012% (v/v) produced over a 50% reduction in excitatory postsynaptic potential (EPSP) amplitude within 3-4 min. When the EO components were applied at 0.4 mmol l^-1, citral and carvone produced a significant reduction in EPSP amplitude, with citral producing the largest effect. Measurement of miniature EPSP amplitudes demonstrated that citral produced over a 50% reduction in transmitter release. Calcium imaging experiments showed that citral produced about 30% reduction in presynaptic Ca²⁺ influx, which likely resulted in the decrease in transmitter release. Thus, the EO blocks synaptic transmission, largely due to citral, and this likely contributes to its behavioral effects.

α-Terpineol reduces cancer pain via modulation of oxidative stress and inhibition of iNOS

α-Terpineol (TP) is present in a wide range of essential oils of the genus Eucalyptus, with recognized potential for a range of biological effects, such as analgesic. Hence, our study aimed to investigate the effect of TP on cancer pain induced by sarcoma 180 in Swiss mice. Our results showed that TP reduced significantly mechanical hyperalgesia and spontaneous and palpation-induced nociception, improved paw use without reducing tumor growth and grip strength. Importantly, no evident biochemical and hematological toxicity was oberved. Furthermore, TP increased the tissue antioxidant capacity due to ferric-reducing antioxidant power (FRAP) and glutathione (GSH). TP also reduced inducible nitric oxide synthase (iNOS) immunocontent in the tumors. Molecular docking estimated that TP binds within the same range of iNOS regions (other iNOS inhibitors), such as N-Nitroarginine methyl ester (L-NAME). These data provide strong evidence that TP may be an interesting candidate for the development of new safe analgesic drugs that are effective for cancer pain control.

Inhibition by non-steroidal anti-inflammatory drugs of compound action potentials in frog sciatic nerve fibers

AIMS

Although antinociception produced by non-steroidal anti-inflammatory drugs (NSAIDs) is partly attributed to nerve conduction inhibition, this has not been thoroughly examined yet. The aim of the present study was to reveal quantitatively how various types of NSAIDs affect compound action potentials (CAPs), a measure of nerve conduction.

MAIN METHODS

CAPs were recorded from the frog sciatic nerve by using the air-gap method.

KEY FINDINGS

Soaking the sciatic nerve with acetic acid-based NSAIDs (diclofenac and aceclofenac) reduced the peak amplitude of CAP in a concentration-dependent manner; their IC₅₀ values were 0.94 and 0.47 mM, respectively. Other acetic acid-based NSAIDs (indomethacin, acemetacin and etodolac) also inhibited CAPs [the extent of inhibition: some 40% (1 mM), 40% (0.5 mM) and 15% (1 mM), respectively], except for sulindac and felbinac at 1 mM that had no effects on CAP peak amplitudes. A similar inhibition was produced by fenamic acid-based NSAIDs [tolfenamic acid (IC₅₀ = 0.29 mM), meclofenamic acid (0.19 mM), flufenamic acid (0.22 mM) and mefenamic acid] which are similar in chemical structure to diclofenac and aceclofenac; their derivatives (2,6-dichlorodiphenylamine and N-phenylanthranilic acid) also inhibited. On the other hand, salicylic acid-based (aspirin), propionic acid-based (ketoprofen, naproxen, ibuprofen, loxoprofen and flurbiprofen) and enolic acid-based (meloxicam and piroxicam) NSAIDs had no effects on CAP peak amplitudes.

SIGNIFICANCE

At least a part of antinociception produced by NSAIDs used as a dermatological drug to alleviate pain may be attributed to their inhibitory effects on nerve conduction, which depend on the chemical structures of NSAIDs.

Acupuncture with or without combined auricular acupuncture for insomnia: a randomised, waitlist-controlled trial

BACKGROUND

Few high-quality, large-scale, controlled trials comparing the effectiveness and safety of acupuncture, auricular acupuncture and combined acupuncture treatment for insomnia are available.

OBJECTIVE

To carry out a randomised, assessor-blinded, waitlist-controlled trial to test the superiority of combination treatment.

METHODS

After in-person and polysomnography screening, 224 subjects (mean age 53.4 years; 75.4% female) with DSM-5 insomnia disorder, who were free from major psychiatric disorders and with sleep-diary-derived sleep efficiency averaged over 1 week of <85%, were randomised to acupuncture alone, acupuncture plus auricular acupuncture (combination treatment), or a waitlist in a 3:3:1 ratio. Standardised acupuncture and combination treatment were provided three times weekly for 3 weeks. The primary outcome was sleep-diary-derived sleep efficiency. Secondary outcomes included wrist actigraphy and self-reported scales on insomnia, anxiety and depression, fatigue, sleepiness and functioning. Assessments were conducted at baseline, 1 week, 4 weeks and 13 weeks after treatment. Participants on the waitlist were re-randomised to receive acupuncture or combination treatment after the second post-baseline assessment.

RESULTS

There was no significant difference between acupuncture and combination treatment in the primary outcome and most secondary outcomes at all time points. However, both treatments were better than waitlist in reducing insomnia, anxiety/depressive symptoms and fatigue, and improving function. Within-group improvements were maintained at 13 weeks after treatment. Of 260 adverse events, 243 were mild (93.5%). Discontinuation due to adverse events was 2.1% and 3.1% for acupuncture and combination treatment, respectively.

CONCLUSIONS

Limited by short-term treatment and follow-up, the attempt to augment acupuncture by auricular acupuncture was not supported. Acupuncture and combination treatment were safe and had mild hypnotic effects, which lasted for at least 13 weeks.

TRIAL REGISTRATION NUMBER

NCT01891097; Results.

Anesthetic Agents of Plant Origin: A Review of Phytochemicals with Anesthetic Activity

The majority of currently used anesthetic agents are derived from or associated with natural products, especially plants, as evidenced by cocaine that was isolated from coca (Erythroxylum coca, Erythroxylaceae) and became a prototype of modern local anesthetics and by thymol and eugenol contained in thyme (Thymus vulgaris, Lamiaceae) and clove (Syzygium aromaticum, Myrtaceae), respectively, both of which are structurally and mechanistically similar to intravenous phenolic anesthetics. This paper reviews different classes of phytochemicals with the anesthetic activity and their characteristic molecular structures that could be lead compounds for anesthetics and anesthesia-related drugs. Phytochemicals in research papers published between 1996 and 2016 were retrieved from the point of view of well-known modes of anesthetic action, that is, the mechanistic interactions with Na⁺ channels, γ-aminobutyric acid type A receptors, N-methyl-d-aspartate receptors and lipid membranes. The searched phytochemicals include terpenoids, alkaloids and flavonoids because they have been frequently reported to possess local anesthetic, general anesthetic, antinociceptive, analgesic or sedative property. Clinical applicability of phytochemicals to local and general anesthesia is discussed by referring to animal in vivo experiments and human pre-clinical trials. This review will give structural suggestions for novel anesthetic agents of plant origin.

Myrcene, an Aromatic Volatile Compound, Ameliorates Human Skin Extrinsic Aging via Regulation of MMPs Production

Myrcene is an aromatic volatile compound that is commercially well-known as a flavor ingredient in the food industry and a fragrance in the soap and detergent industry. Given the worldwide interest in natural antiphotoaging products, we investigated the protective effects of myrcene in UVB-irradiated human dermal fibroblasts (NHDFs). NHDFs were subjected to 144[Formula: see text]mJ/cm2of UVB irradiation. The expression of intracellular reactive oxygen species (ROS), matrix metalloproteinase-1 (MMP-1), MMP-3, interleukin-6 (IL-6), transforming growth factor (TGF-[Formula: see text]1) and type I procollagen were examined. We showed that myrcene decreased the production of ROS, MMP-1, MMP-3, and IL-6, and increased TGF-[Formula: see text]1 and type I procollagen secretions. Furthermore, myrcene treatment (0.1–10[Formula: see text][Formula: see text]M) dramatically reduced the activation of MAPK-related signaling molecules such as p-ERK, p-p38, and p-JNK and AP-1 including p-c-Jun and p-c-Fos. Our data indicate that myrcene has a potential protective effect on UVB-induced human skin photoaging. Therefore, myrcene might have applications in the skincare industry.

Bisphenol A inhibits compound action potentials in the frog sciatic nerve in a manner independent of estrogen receptors

Although the endocrine disruptor bisphenol A (BPA) is reported to inhibit nerve conduction, the underlying mechanisms are unclear. Therefore, in the present study, we examined the effect of BPA on compound action potentials (CAPs) recorded from the frog sciatic nerve using the air-gap method. Treatment of the sciatic nerve with BPA (0.5 mM) for 20 min reduced the peak amplitude of the CAP by approximately 60% in a partially reversible manner. The reduction in the CAP peak amplitude was concentration-dependent, with a half-maximal inhibitory concentration (IC₅₀) value of 0.31 mM. This effect of BPA was unaffected by an estrogen-receptor antagonist, 4-hydroxytamoxifen, which by itself reduced CAP peak amplitude, with an IC₅₀ value of 0.26 mM (comparable to that of BPA). The natural estrogen 17β-estradiol, at the highest dissolvable concentration (0.05 mM), had an effect similar to that of BPA. The IC₅₀ value of BPA was comparable to those of some local anesthetics in inhibiting frog CAPs. Our findings suggest that BPA inhibits nerve conduction in a manner independent of estrogen receptors. This action of BPA may underlie, at least in part, the neurotoxicity of the compound.

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Bisphenol A acutely inhibits compound action potentials in nerve fibers.

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The effect of bisphenol A is not mediated by estrogen receptors.

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The effect of bisphenol A is comparable to those of local anesthetics.

Enhancement by citral of glutamatergic spontaneous excitatory transmission in adult rat substantia gelatinosa neurons

Although citral, which is abundantly present in lemongrass, has various actions including antinociception, how citral affects synaptic transmission has not been examined as yet. Citral activates in heterologous cells transient receptor potential vanilloid-1, ankyrin-1, and melastatin-8 (TRPV1, TRPA1, and TRPM8, respectively) channels, the activation of which in the spinal lamina II [substantia gelatinosa (SG)] increases the spontaneous release of L-glutamate from nerve terminals. It remains to be examined what types of transient receptor potential channel in native neurons are activated by citral. With a focus on transient receptor potential activation, we examined the effect of citral on glutamatergic spontaneous excitatory transmission using the whole-cell patch-clamp technique to SG neurons in adult rat spinal cord slices. Bath-applied citral for 3 min increased the frequency of spontaneous excitatory postsynaptic current in a concentration-dependent manner (half-maximal effective concentration=0.58 mM), with a small increase in its amplitude. The spontaneous excitatory postsynaptic current frequency increase produced by citral was repeated at a time interval of 30 min, albeit this action recovered with a slow time course after washout. The presynaptic effect of citral was inhibited by TRPA1 antagonist HC-030031, but not by voltage-gated Na-channel blocker tetrodotoxin, TRPV1 antagonist capsazepine, and TRPM8 antagonist BCTC. It is concluded that citral increases spontaneous L-glutamate release in SG neurons by activating TRPA1 channels. Considering that the SG plays a pivotal role in modulating nociceptive transmission from the periphery, the citral activity could contribute toward at least a part of the modulation.

Traditional Japanese medicines inhibit compound action potentials in the frog sciatic nerve

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Japanese (Kampo) medicines have a variety of clinical effects including pain alleviation, but evidence for a mechanism for their pain relief has not yet been elucidated fully. Considering that Kampo medicine contains many plant-derived chemicals having an ability to inhibit nerve action potential conduction, it is possible that this medicine inhibits nerve conduction. The purpose of the present study was to know how various Kampo medicines affect nerve conduction.

MATERIALS AND METHODS

We examined the effects of Kampo and crude medicines on compound action potentials (CAPs) recorded from the frog sciatic nerve by using the air-gap method.

RESULTS

Daikenchuto, rikkosan, kikyoto, rikkunshito, shakuyakukanzoto and kakkonto concentration-dependently reduced the peak amplitude of the CAP. Among the Kampo medicines, daikenchuto was the most effective in inhibiting CAPs. Daikenchuto is composed of three kinds of crude medicine, Japanese pepper, processed ginger and ginseng radix. When the crude medicines were tested, Japanese pepper and processed ginger reduced CAP peak amplitudes, while ginseng radix hardly affected CAPs. Moreover, there was an interaction between the Japanese pepper and processed ginger activities in such that one medicine at low but not high concentrations increased the extent of the inhibition by the other one that was co-applied.

CONCLUSIONS

Kampo medicines have an ability to inhibit nerve conduction. This action of daikenchuto is due to Japanese pepper and processed ginger but not ginseng radix, probably through an interaction between Japanese pepper and processed ginger in a manner dependent on their concentrations. Nerve conduction inhibition could contribute to at least a part of Kampo medicine's clinical effects such as pain alleviation.