Ligustilide covalently binds to Cys703 in the pre-S1 helix of TRPA1, blocking the opening of channel and relieving pain in rats with acute soft tissue injury.

ETHNOPHARMACOLOGICAL RELEVANCE: The natural anodyne Ligustilide (Lig), derived from Angelica sinensis (Oliv.) Diels and Ligusticum chuanxiong Hort., has been traditionally employed for its analgesic properties in the treatment of dysmenorrhea and migraine, and rheumatoid arthritis pain. Despite the existing reports on the correlation between TRP channels and the analgesic effects of Lig, a comprehensive understanding of their underlying mechanisms of action remains elusive. AIM OF THE STUDY: The objective of this study is to elucidate the mechanism of action of Lig on the analgesic target TRPA1 channel. METHODS: The therapeutic effect of Lig was evaluated in a rat acute soft tissue injury model. The analgesic target was identified through competitive inhibition of TRP channel agonists at the animal level, followed by Fluo-4/Ca2+ imaging on live cells overexpressing TRP proteins. The potential target was verified through in-gel imaging, colocalization using a Lig-derived molecular probe, and a drug affinity response target stability assay. The binding site of Lig was identified through protein spectrometry and further analyzed using molecular docking, site-specific mutation, and multidisciplinary approaches. RESULTS: The administration of Lig effectively ameliorated pain and attenuated oxidative stress and inflammatory responses in rats with soft tissue injuries. Moreover, the analgesic effects of Lig were specifically attributed to TRPA1. Mechanistic studies have revealed that Lig directly activates TRPA1 by interacting with the linker domain in the pre-S1 region of TRPA1. Through metabolic transformation, 6,7-epoxyligustilide (EM-Lig) forms a covalent bond with Cys703 of TRPA1 at high concentrations and prolonged exposure time. This irreversible binding prevents endogenous electrophilic products from entering the cysteine active center of ligand-binding pocket of TRPA1, thereby inhibiting Ca2+ influx through the channel opening and ultimately relieving pain. CONCLUSIONS: Lig selectively modulates the TRPA1 channel in a bimodal manner via non-electrophilic/electrophilic metabolic conversion. The epoxidized metabolic intermediate EM-Lig exerts analgesic effects by irreversibly inhibiting the activation of TRPA1 on sensory neurons. These findings not only highlight the analgesic mechanism of Lig but also offer a novel nucleophilic attack site for the development of TRPA1 antagonists in the pre-S1 region.

MicroRNA let-7b enhances spinal cord nociceptive synaptic transmission and induces acute and persistent pain through neuronal and microglial signaling.

ABSTRACT: Secreted microRNAs (miRNAs) have been detected in various body fluids including the cerebrospinal fluid, yet their direct role in regulating synaptic transmission remains uncertain. We found that intrathecal injection of low dose of let-7b (1 µg) induced short-term (<24 hours) mechanical allodynia and heat hyperalgesia, a response that is compromised in Tlr7-/- or Trpa1-/- mice. Ex vivo and in vivo calcium imaging in GCaMP6-report mice revealed increased calcium signal in spinal cord afferent terminals and doral root ganglion/dorsal root ganglia neurons following spinal perfusion and intraplantar injection of let-7b. Patch-clamp recordings also demonstrated enhanced excitatory synaptic transmission (miniature excitatory postsynaptic currents [EPSCs]) in spinal nociceptive neurons following let-7b perfusion or optogenetic activation of axonal terminals. The elevation in spinal calcium signaling and EPSCs was dependent on the presence of toll-like receptor-7 (TLR7) and transient receptor potential ion channel subtype A1 (TRPA1). In addition, endogenous let-7b is enriched in spinal cord synaptosome, and peripheral inflammation increased let-7b in doral root ganglion/dorsal root ganglia neurons, spinal cord tissue, and the cerebrospinal fluid. Notably, let-7b antagomir inhibited inflammatory pain and inflammation-induced synaptic plasticity (EPSC increase), suggesting an endogenous role of let-7b in regulating pain and synaptic transmission. Furthermore, intrathecal injection of let-7b, at a higher dose (10 µg), induced persistent mechanical allodynia for >2 weeks, which was abolished in Tlr7-/- mice. The high dose of let-7b also induced microgliosis in the spinal cord. Of interest, intrathecal minocycline only inhibited let-7b-induced mechanical allodynia in male but not female mice. Our findings indicate that the secreted microRNA let-7b has the capacity to provoke pain through both neuronal and glial signaling, thereby establishing miRNA as an emerging neuromodulator.

Zhisou powder suppresses airway inflammation in LPS and CS-induced post-infectious cough model mice via TRPA1/TRPV1 channels.

ETHNOPHARMACOLOGICAL RELEVANCE: Zhisou Powder (ZSP), a traditional Chinese medicine (TCM) prescription, has been widely used in the clinic for the treatment of post-infectious cough (PIC). However, the exact mechanism is not clear. AIM OF THE STUDY: The aim of this study was to investigate the ameliorative effect of ZSP on PIC in mice. The possible mechanisms of action were screened based on network pharmacology, and the potential mechanisms were explored through molecular docking and in vivo experimental validation. MATERIALS AND METHODS: Lipopolysaccharide (LPS) (80µg/50 µL) was used to induce PIC in mice, followed by daily exposure to cigarette smoke (CS) for 30 min for 30 d to establish PIC model. The effects of ZSP on PIC mice were observed by detecting the number of coughs and cough latency, peripheral blood and bronchoalveolar lavage fluid (BALF) inflammatory cell counts, enzyme-linked immunosorbent assay (ELISA), and histological analysis. The core targets and key pathways of ZSP on PIC were analyzed using network pharmacology, and TRPA1 and TRPV1 were validated using RT-qPCR and western blotting assays. RESULTS: ZSP effectively reduced the number of coughs and prolonged the cough latency in PIC mice. Airway inflammation was alleviated by reducing the expression levels of the inflammatory mediators TNF-α and IL-1ß. ZSP modulated the expression of Substance P, Calcitonin gene-related peptide (CGRP), and nerve growth factor (NGF) in BALF. Based on the results of network pharmacology, the mechanism of action of ZSP may exert anti-neurogenic airway-derived inflammation by regulating the expression of TRPA1 and TRPV1 through the natural active ingredients α-spinastero, shionone and didehydrotuberostemonine. CONCLUSION: ZSP exerts anti-airway inflammatory effects through inhibition of TRPA1/TRPV1 channels regulating neuropeptides to alleviate cough hypersensitivity and has a favorable therapeutic effect on PIC model mice. It provides theoretical evidence for the clinical application of ZSP.

Borneol exerts its antipruritic effects by inhibiting TRPA1 and activating TRPM8.

ETHNOPHARMACOLOGICAL RELEVANCE: Borneol is a long-established traditional Chinese medicine that has been found to be effective in treating pain and itchy skin. However, whether borneol has a therapeutic effect on chronic itch and its related mechanisms remain unclear. AIM OF THE STUDY: To investigate the antipruritic effect of borneol and its molecular mechanism. MATERIALS AND METHODS: DrugBAN framework and molecular docking were applied to predict the targets of borneol, and the calcium imaging or patch-clamp recording analysis were used to detect the effects of borneol on TRPA1, TRPM8 or TRPV3 channels in HEK293T cells. In addition, various mouse models of acute itch and chronic itch were established to evaluate the antipruritic effects of borneol on C57BL/6J mice. Then, the borneol-induced pruritic relief was further investigated in Trpa1-/-, Trpm8-/-, or Trpa1-/-/Trpm8-/- mice. The effects of borneol on the activation of TRPM8 and the inhibition of TRPA1 were also measured in dorsal root ganglia neurons of wild-type (WT), Trpm8-/- and Trpv1-/- mice. Lastly, a randomized, double-blind study of adult patients was conducted to evaluate the clinical antipruritic effect of borneol. RESULTS: TRPA1, TRPV3 and TRPM8 are the potential targets of borneol according to the results of DrugBAN algorithm and molecular docking. Calcium imaging and patch-clamp recording analysis demonstrated that borneol activates TRPM8 channel-induced cell excitability and inhibits TRPA1 channel-mediated cell excitability in transfected HEK293T cells. Animal behavior analysis showed that borneol can significantly reduce acute and chronic itch behavior in C57BL/6J mice, but this effect was eliminated in Trpa1-/-, Trpm8-/- mice, or at least in Trpa1-/-/Trpm8-/- mice. Borneol elicits TRPM8 channel induced [Ca2+]i responses but inhibits AITC or SADBE-induced activation of TRPA1 channels in dorsal root ganglia neurons of WT and Trpv1-/- mice, respectively. Furthermore, the clinical results indicated that borneol could reduce itching symptoms in patients and its efficacy is similar to that of menthol. CONCLUSION: Borneol has therapeutic effects on multiple pruritus models in mice and patients with chronic itch, and the mechanism may be through inhibiting TRPA1 and activating TRPM8.

The potent analgesia of intrathecal 2R, 6R-HNK via TRPA1 inhibition in LF-PENS-induced chronic primary pain model.

BACKGROUND: Chronic primary pain (CPP) is an intractable pain of unknown cause with significant emotional distress and/or dysfunction that is a leading factor of disability globally. The lack of a suitable animal model that mimic CPP in humans has frustrated efforts to curb disease progression. 2R, 6R-hydroxynorketamine (2R, 6R-HNK) is the major antidepressant metabolite of ketamine and also exerts antinociceptive action. However, the analgesic mechanism and whether it is effective for CPP are still unknown. METHODS: Based on nociplastic pain is evoked by long-term potentiation (LTP)-inducible high- or low-frequency electrical stimulation (HFS/LFS), we wanted to develop a novel CPP mouse model with mood and cognitive comorbidities by noninvasive low-frequency percutaneous electrical nerve stimulation (LF-PENS). Single/repeated 2R, 6R-HNK or other drug was intraperitoneally (i.p.) or intrathecally (i.t.) injected into naïve or CPP mice to investigate their analgesic effect in CPP model. A variety of behavioral tests were used to detect the changes in pain, mood and memory. Immunofluorescent staining, western blot, reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) and calcium imaging of in cultured dorsal root ganglia (DRG) neurons by Fluo-8-AM were used to elucidate the role and mechanisms of 2R, 6R-HNK in vivo or in vitro. RESULTS: Intrathecal 2R, 6R-HNK, rather than intraperitoneal 2R, 6R-HNK or intrathecal S-Ketamine, successfully mitigated HFS-induced pain. Importantly, intrathecal 2R, 6R-HNK displayed effective relief of bilateral pain hypersensitivity and depressive and cognitive comorbidities in a dose-dependent manner in LF-PENS-induced CPP model. Mechanically, 2R, 6R-HNK markedly attenuated neuronal hyperexcitability and the upregulation of calcitonin gene-related peptide (CGRP), transient receptor potential ankyrin 1 (TRPA1) or vanilloid-1 (TRPV1), and vesicular glutamate transporter-2 (VGLUT2) in peripheral nociceptive pathway. In addition, 2R, 6R-HNK suppressed calcium responses and CGRP overexpression in cultured DRG neurons elicited by the agonists of TRPA1 or/and TRPV1. Strikingly, the inhibitory effects of 2R, 6R-HNK on these pain-related molecules and mechanical allodynia were substantially occluded by TRPA1 antagonist menthol. CONCLUSIONS: In the newly designed CPP model, our findings highlighted the potential utility of intrathecal 2R, 6R-HNK for preventing and therapeutic modality of CPP. TRPA1-mediated uprgulation of CGRP and neuronal hyperexcitability in nociceptive pathways may undertake both unique characteristics and solving process of CPP.

Targeting TRPV1 and TRPA1: A feasible strategy for natural herbal medicines to combat postoperative ileus.

Under physiological or pathological conditions, transient receptor potential (TRP) channel vanilloid type 1 (TRPV1) and TRP ankyrin 1 (TRPA1) possess the ability to detect a vast array of stimuli and execute diverse functions. Interestingly, increasing works have reported that activation of TRPV1 and TRPA1 could also be beneficial for ameliorating postoperative ileus (POI). Increasing research has revealed that the gastrointestinal (GI) tract is rich in TRPV1/TRPA1, which can be stimulated by capsaicin, allicin and other compounds. This activation stimulates a variety of neurotransmitters, leading to increased intestinal motility and providing protective effects against GI injury. POI is the most common emergent complication following abdominal and pelvic surgery, and is characterized by postoperative bowel dysfunction, pain, and inflammatory responses. It is noteworthy that natural herbs are gradually gaining recognition as a potential therapeutic option for POI due to the lack of effective pharmacological interventions. Therefore, the focus of this paper is on the TRPV1/TRPA1 channel, and an analysis and summary of the processes and mechanism by which natural herbs activate TRPV1/TRPA1 to enhance GI motility and relieve pain are provided, which will lay the foundation for the development of natural herb treatments for this disease.

Neuropathic-like Nociception and Spinal Cord Neuroinflammation Are Dependent on the TRPA1 Channel in Multiple Sclerosis Models in Mice.

Background: Transient receptor potential ankyrin 1 (TRPA1) activation is implicated in neuropathic pain-like symptoms. However, whether TRPA1 is solely implicated in pain-signaling or contributes to neuroinflammation in multiple sclerosis (MS) is unknown. Here, we evaluated the TRPA1 role in neuroinflammation underlying pain-like symptoms using two different models of MS. Methods: Using a myelin antigen, Trpa1+/+ or Trpa1-/- female mice developed relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE) (Quil A as adjuvant) or progressive experimental autoimmune encephalomyelitis (PMS)-EAE (complete Freund's adjuvant). The locomotor performance, clinical scores, mechanical/cold allodynia, and neuroinflammatory MS markers were evaluated. Results: Mechanical and cold allodynia detected in RR-EAE, or PMS-EAE Trpa1+/+ mice, were not observed in Trpa1-/- mice. The increased number of cells labeled for ionized calcium-binding adapter molecule 1 (Iba1) or glial fibrillary acidic protein (GFAP), two neuroinflammatory markers in the spinal cord observed in both RR-EAE or PMS-EAE Trpa1+/+ mice, was reduced in Trpa1-/- mice. By Olig2 marker and luxol fast blue staining, prevention of the demyelinating process in Trpa1-/- induced mice was also detected. Conclusions: Present results indicate that the proalgesic role of TRPA1 in EAE mouse models is primarily mediated by its ability to promote spinal neuroinflammation and further strengthen the channel inhibition to treat neuropathic pain in MS.

Topical borneol relieves nonhistaminergic pruritus via targeting TRPA1 and TRPM8 channels in peripheral nerve terminals of mice.

Borneol has been used successfully for the treatment of itchy skin in traditional Chinese medicine. However, the antipruritic effect of borneol has rarely been studied, and the mechanism is unclear. Here, we showed that topical application of borneol on skin substantially suppressed pruritogen chloroquine- and compound 48/80-induced itching in mice. The potential targets of borneol, including transient receptor potential cation channel subfamily V member 3 (TRPV3), transient receptor potential cation channel subfamily A member 1 (TRPA1), transient receptor potential cation channel subfamily M member 8 (TRPM8), and gamma-aminobutyric acid type A (GABAA) receptor were pharmacologically inhibited or genetically knocked out one by one in mouse. Itching behavior studies demonstrated that the antipruritic effect of borneol is largely independent of TRPV3 and GABAA receptor, and TRPA1 and TRPM8 channels are responsible for a major portion of the effect of borneol on chloroquine-induced nonhistaminergic itching. Borneol activates TRPM8 and inhibits TRPA1 in sensory neurons of mice. Topical co-application of TRPA1 antagonist and TRPM8 agonist mimicked the effect of borneol on chloroquine-induced itching. Intrathecal injection of a group II metabotropic glutamate receptor antagonist partially attenuated the effect of borneol and completely abolished the effect of TRPM8 agonist on chloroquine-induced itching, suggesting that a spinal glutamatergic mechanism is involved. In contrast, the effect of borneol on compound 48/80-induced histaminergic itching occurs through TRPA1-and TRPM8-independent mechanisms. Our work demonstrates that borneol is an effective topical itch reliever, and TRPA1 inhibition and TRPM8 activation in peripheral nerve terminals account for its antipruritic effect.

The traditional herbal medicines mixture, Banhasasim-tang, relieves the symptoms of irritable bowel syndrome via modulation of TRPA1, NaV1.5 and NaV1.7 channels.

ETHNOPHARMACOLOGICAL RELEVANCE: The cause of irritable bowel syndrome (IBS), a functional gastrointestinal (GI) disorder, remains unclear. Banhasasim-tang (BHSST), a traditional herbal medicines mixture, mainly used to treat GI-related diseases, may have a potential in IBS treatment. IBS is characterized by abdominal pain as the main clinical symptom, which seriously affects the quality of life. AIM OF THE STUDY: We conducted a study to evaluate the effectiveness of BHSST and its mechanisms of action in treating IBS. MATERIALS AND METHODS: We evaluated the efficacy of BHSST in a zymosan-induced diarrhea-predominant animal model of IBS. Electrophysiological methods were used to confirm modulation of transient receptor potential (TRP) and voltage-gated Na+ (NaV) ion channels, which are associated mechanisms of action. RESULTS: Oral administration of BHSST decreased colon length, increased stool scores, and increased colon weight. Weight loss was also minimized without affecting food intake. In mice administered with BHSST, the mucosal thickness was suppressed, making it similar to that of normal mice, and the degree of tumor necrosis factor-α was severely reduced. These effects were similar to those of the anti-inflammatory drug-sulfasalazine-and antidepressant-amitriptyline. Moreover, pain-related behaviors were substantially reduced. Additionally, BHSST inhibited TRPA1, NaV1.5, and NaV1.7 ion channels associated with IBS-mediated visceral hypersensitivity. CONCLUSIONS: In summary, the findings suggest that BHSST has potential beneficial effects on IBS and diarrhea through the modulation of ion channels.

Expression of Trpa1 and Trpv1 Genes in the Hypothalamus and Blood Pressure in Normotensive and Hypertensive Rats. Effect of Losartan and Captopril.

Analysis of the role of genomic regulation of systolic BP (SBP) in normal and hypertensive rats showed the presence of an inverse relationship between the level of Trpa1 gene expression in the anterior hypothalamus and SBP. Losartan, an antagonist of angiotensin II type 1 receptors, shifts it to the region of lower SBP and greater expression of the Trpa1 gene, which can attest to interaction of the TRPA1 ion channel in the anterior hypothalamus with angiotensin II type 1 receptors. No association was found between the expression of the Trpv1 gene in the hypothalamus and SBP. We have previously shown that activation of the peripheral ion channel TRPA1 in the skin also contributes to SBP decrease in hypertensive animals. Hence, activation of the TRPA1 ion channel both in the brain and at the periphery has similar effects on SBP and leads to its decrease.

Aconitine - A promising candidate for treating cold and mechanical allodynia in cancer induced bone pain.

BACKGROUND AND AIMS: Patients suffering from cancer induced bone pain (CIBP) have a poor quality of life that is exacerbated by the lack of effective therapeutic drugs. Monkshood is a flowering plant that has been used in traditional Chinese medicine where it has been used to relieve cold pain. Aconitine is the active component of monkshood, but the molecular mechanism for how this compound reduces pain is unclear. METHODS AND RESULTS: In this study, we employed molecular and behavioral experiments to explore the analgesic effect of aconitine. We observed aconitine alleviated cold hyperalgesia and AITC (allyl-isothiocyanate, TRPA1 agonist) induced pain. Interestingly, we found aconitine directly inhibits TRPA1 activity in calcium imaging studies. More importantly, we found aconitine alleviated cold and mechanical allodynia in CIBP mice. Both the activity and expression of TRPA1 in L4 and L5 DRG (Dorsal Root Ganglion) neurons were reduced with the treatment of aconitine in the CIBP model. Moreover, we observed aconiti radix (AR) and aconiti kusnezoffii radix (AKR), both components of monkshood that contain aconitine, alleviated cold hyperalgesia and AITC induced pain. Furthermore, both AR and AKR alleviated CIBP induced cold allodynia and mechanical allodynia. CONCLUSIONS: Taken together, aconitine alleviates both cold and mechanical allodynia in cancer induced bone pain via the regulation of TRPA1. This research on the analgesic effect of aconitine in cancer induced bone pain highlights a component of a traditional Chinese medicine may have clinical applications for pain.

TRPA1 is involved in the inhibitory effect of Ke-teng-zi on allergic contact dermatitis via MAPK and JAK/STAT3 signaling pathways.

ETHNOPHARMACOLOGICAL RELEVANCE: The seeds of Entada phaseoloides (Linn.) Merr. commonly named "Ke-teng-zi" is a traditional Chinese folk medicine and reported to treat dermatitis, spasm, and headache. However, the exact effect and the mechanism of Ke-teng-zi on the treatment of dermatitis is unclear. AIM OF THE STUDY: To elucidate the antipruritic effect and molecular mechanisms of Ke-teng-zi on the treatment of allergic contact dermatitis (ACD). MATERIALS AND METHODS: The main components of the n-butanol fraction of 70% ethanol extract from Ke-teng-zi (abbreviated as KB) were analyzed by HPLC. The chloroquine (CQ)-induced acute itch and squaraine dibutyl ester (SADBE)-induced ACD chronic itch in mice was established, and the TNF-α/IFN-γ stimulated Human keratinocytes (HaCaT) were used to evaluate the antipruritic and anti-inflammatory effects of KB. Behavioral tests, lesion scoring, and histology were also examined. The expression levels of molecules in MAPK and JAK/STAT3 pathways, the mRNA levels of chemokines and cytokines in both the skin of ACD mice and the HaCaT cells were detected by western blot and qPCR. Furthermore, whole-cell patch-clamp recordings in TRPA1-tranfected HEK293T cells were used to elucidate the effect of KB on TRPA1 channels. TRPA1 siRNA was used to evaluate the role of TRPA1 in the anti-inflammatory effect of KB in keratinocytes. RESULTS: The main compounds in KB could bind to the active sites of TRPA1 mainly through hydrogen bond and hydrophobic bond interactions. KB could inhibit the scratching behavior in CQ-induced acute itch, and the inhibitory effect of KB was blocked by TRPA1 inhibitor HC-030031. In addition, KB significantly decreased the scratching bouts of ACD mice, reduced the skin lesion scores, mast cells degranulation, and epidermal thickening, inhibited the production of inflammatory chemokines/cytokines and CGRP, and down-regulated the levels of p-ERK1/2, p-p38, and p-STAT3, compared to the ACD mice. Moreover, continuous application of KB induced the desensitization of TRPA1 channels. Also, KB inhibited the expression of p-ERK1/2, p-p38, and p-STAT3, and down-regulated the expression of inflammatory chemokines and cytokines in vitro, which were reversed by the TRPA1 siRNA. CONCLUSIONS: KB alleviated the pruritus and skin inflammation in ACD mice through TRPA1 channels desensitization and down-regulation of intracellular MAPK and JAK/STAT3 signaling pathways. Our results suggested that Ke-teng-zi is a potential drug for the treatment of inflammatory skin diseases such as ACD.

Water extract of Notopterygium incisum alleviates cold allodynia in neuropathic pain by regulation of TRPA1.

ETHNOPHARMACOLOGICAL RELEVANCE: Neuropathic pain can be debilitating and drastically affects the quality of life of those patients suffering from this condition. The Chinese herb Notopterygium incisum Ting ex H.T. Chang has long been used to disperse "cold". One under examined clinical feature of neuropathic pain is sensitivity to cold. Patients with neuropathic pain or arthritis usually describe a worsening of symptoms during the winter. AIMS OF THIS STUDY: We proposed to test the hypothesis that Notopterygium incisum has a positive effect on the cold sensitivity found in neuropathic pain. MATERIALS AND METHODS: In this study, we established chronic constriction injury (CCI) and cisplatin induced neuropathic pain mice models. Behavioral experiments and physiological examination methods were employed to investigate the effect of water extract of Notopterygium incisum (WN) on cold pain. RESULTS: We found WN reduced cold pain and allyl isothiocyanate (AITC, Transient Receptor Potential A1 (TRPA1 agonist)) induced pain. WN inhibited AITC induced calcium response in HEK 293 cells transfected with TRPA1 and dorsal root ganglion (DRG) neurons. Moreover, we found that oral administration of WN reduced cold allodynia and mechanical allodynia caused by (CCI) and cisplatin induced neuropathic pain. We also observed that oral administration of WN decreased responses to AITC in DRG neurons as well as expression of TRPA1 in the WN treated neuropathic pain model. CONCLUSIONS: The present study provide evidence that Notopterygium incisum alleviates cold allodynia in CCI and cisplatin induced neuropathic pain mouse models. WN alleviated neuropathic pain induced cold allodynia via directly modulating TRPA1. Our findings identify WN as a promising candidate for treating neuropathic pain that highlights a new mechanism of Notopterygium incisum on 'disperse cold'.

Curcumin suppresses cell proliferation and reduces cholesterol absorption in Caco-2 cells by activating the TRPA1 channel.

BACKGROUND: Curcumin (Cur) is a bioactive dietary polyphenol of turmeric with various biological activities against several cancers. Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths. Intestinal cholesterol homeostasis is associated with CRC. Chemotherapy for CRC is related to varied adverse effects. Therefore, natural products with anti-cancer properties represent a potential strategy for primary prevention of CRC. METHODS: The present study used Cur as a therapeutic approach against CRC using the Caco-2 cell line. The cells were treated with different concentrations of Cur for different duration of time and then the proliferation ability of cells was assessed using Cell Counting Kit-8 and 5-Ethynyl-2'-deoxyuridine assays. Oil red O staining and cholesterol assay kit were used to evaluate cellular lipid content and cholesterol outward transportation. Finally, the protein expressions of cholesterol transport-related protein and signal transduction molecules were assessed using Western blot assay. RESULTS: Cur inhibited cell proliferation in Caco-2 cells in a dose- and time-dependent manner by activating the transient receptor potential cation channel subfamily A member 1 (TRPA1) channel. Activation of the TRPA1 channel led to increased intracellular calcium, peroxisome proliferator-activated receptor gamma (PPARγ) upregulation, and the subsequent downregulation of the specificity protein-1 (SP-1)/sterol regulatory element-binding protein-2 (SREBP-2)/Niemann-Pick C1-like 1 (NPC1L1) signaling pathway-related proteins, and finally reduced cholesterol absorption in Caco-2 cells. CONCLUSIONS: Cur inhibits cell proliferation and reduces cholesterol absorption in Caco-2 cells through the Ca2+/PPARγ/SP-1/SREBP-2/NPC1L1 signaling by activating the TRPA1 channel, suggesting that Cur can be used as a dietary supplement for the primary prevention of CRC. In Caco-2 cells, Cur first stimulates calcium influx by activating the TRPA1 channel, further upregulates PPARγ and downregulates SP-1/SREBP-2/NPC1L1 signaling pathway, and finally inhibits the absorption of cholesterol. TRPA1, transient receptor potential cation channel subfamily A member 1; NPC1L1, Niemann-Pick C1-like 1; PPARγ, peroxisome proliferator-activated receptor gamma; SP-1, specificity protein-1; SREBP-2, sterol regulatory element-binding protein-2; Cur, curcumin.

Ligustrazine mitigates chronic venous disease-induced pain hyperalgesia through desensitization of inflammation-associated TRPA1 activity in DRG.

ETHNOPHARMACOLOGICAL RELEVANCE: Ligustrazine, an important active ingredient extracted from Ligusticum chuanxiong hort, has been widely used to cure cardiovascular diseases and exerts an analgesic effect. AIMS OF THIS STUDY: The aim of this study is to investigate whether ligustrazine mitigates chronic venous disease (CVeD)-induced pain and to explore its underlying mechanisms. MATERIALS AND METHODS: A mouse model of CVeD was established by vein ligature. Ligustrazine was administered intraperitoneally to CVeD mice for a single injection (20 mg/kg, 100 mg/kg, and 200 mg/kg) or once a day for three weeks (100 mg/kg and 200 mg/kg), and TRPA1 overexpressed HEK 293 cells were treated with ligustrazine (600 µM) in the presence of mustard oil (100 µM) for 2 min. Patch clamp and calcium imaging were used to measure the inhibitory response of ligustrazine on DRG neurons and TRPA1 transfected HEK293 cells. RESULTS: The present results showed that mice receiving vein ligature surgery exhibited obvious pain hypersensitivity to mechanical, cold and thermal stimuli, whereas ligustrazine significantly reversed the pain hyperalgesia in CVeD mice. Furthermore, ligustrazine desensitized transient receptor potential ankyrin 1 (TRPA1) activity in the dorsal root ganglion (DRG) neurons, resulting in suppressing the DRG neuronal excitability in the CVeD mice. However, ligustrazine could not directly inhibit the response of TRPA1 transfected HEK293 cells to mustard oil. Strikingly, ligustrazine restricted the macrophage infiltration and decreased the mRNA levels of Interleukin-1ß (IL-1ß) and NOD-like receptor protein 3 (NLRP3) in the DRG neurons of the CVeD mice. CONCLUSIONS: The present study provided evidence that ligustrazine alleviated pain hypersensitivity to mechanical, cold and thermal stimuli in CVeD mice. Ligustrazine could weaken the activity of TRPA1 in the DRG to mitigate CVeD-induced pain hyperalgesia mainly through inhibition of inflammation. Our findings identify that ligustrazine may be a new therapeutic agent for the treatment of CVeD-induced pain.

Effect of Houpo-Mahuang Decoction on aggravated asthma induced by cigarette smoke and the expression of TRPA1 and tight junctions in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Cigarette smoke (CS) is a common environmental irritant and a risk factor for asthma, as it induces as well as aggravates asthmatic attacks. The injured airway epithelial tight junctions (TJs) aggravate asthma. CS can aggravate asthma by activating the transient receptor potential ankyrin A1 (TRPA1) channel and enhancing TJs destruction. Houpo Mahuang decoction (HPMHD) is a classic traditional Chinese prescription for the treatment of asthma. However, its underlying action mechanism is unclear. AIM OF THE STUDY: The present study aimed to evaluate the effect of HPMHD on the asthma phenotype and the regulation of TRPA1 and TJs in a CS-induced mouse model of aggravated asthma. MATERIALS AND METHODS: Under optimized chromatographic and mass spectrometry conditions, the ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) technique was used to detect and analyze the major chemical components of HPMHD. C57BL/6 female mice were randomly divided into seven groups, viz, normal saline (NS) group, ovalbumin (OVA) + CS group, dexamethasone group, HPMHD high-dose group and low-dose groups, n-butanol extract group, and ethyl acetate extract group, with 10 mice in each group. OVA sensitization and challenge, and CS exposure were used to establish the aggravated asthma model. As the main indices to evaluate the protective effect of HPMHD, the eosinophils count in peripheral blood, percentages of inflammatory cells classified and the levels of interleukin (IL)-4, IL-5, IL-13 in the bronchoalveolar lavage fluid (BALF), airway responsiveness enhanced pause (Penh), and changes in lung histopathology were determined and compared among the groups. The mRNA and protein expression of TRPA1 and TJs in lung tissue was also examined. RESULTS: Using UPLC-QTOF-MS, the chemical components of HPMHD, including ephedrine, pseudoephedrine, laetrile, and amygdalin amide, were identified by 51 signal peaks. Compared with those in the NS group, the eosinophil number in the peripheral blood and the eosinophils and neutrophils percentages in BALF of the OVA + CS group were remarkably increased. Following the inhalation of 50 µl of acetylcholine chloride (ACH) at doses of 25 and 50 mg/mL, the Penh increased significantly (p < 0.01). Moreover, in the OVA + CS group, hematoxylin and eosin (H&E) staining of lung tissue showed a significant number of infiltrated inflammatory cells, increased mucus secretion in the lumen, damaged bronchial mucosa, increased thickness of tracheal wall, and increased score of lung damage (p < 0.01). The IL-4/5/13 levels were also remarkably increased (p < 0.01). The protein as well as gene expression of both ZO-1 and occludin decreased markedly in the lung tissue, while the expression of TRPA1 and claudin-2 was increased (p < 0.05, p < 0.01). Next, the OVA + CS group and the treatment groups were compared. The inflammatory cells, Penh value, and levels of IL-4/5/13 were significantly reduced, and less lung injury was observed in the treatment groups. The gene and protein levels of TRPA1 and TJs were corrected (p < 0.05, p < 0.01); the effects on the HPMHD high-dose and ethyl acetate extract groups were particularly remarkable. CONCLUSIONS: HPMHD reduced airway hyperresponsiveness, inflammatory cell recruitment and Th2 cytokine secretion in CS-induced aggravated asthma mice, in a manner potentially dependent on regulation of the expression of TRPA1 and TJ proteins. Both the n-butanol and ethyl acetate extracts contained the active ingredients, especially the ethyl acetate extract.

Lycium barbarum Polysaccharides and Capsaicin Inhibit Oxidative Stress, Inflammatory Responses, and Pain Signaling in Rats with Dextran Sulfate Sodium-Induced Colitis.

Ulcerative colitis (UC) is an inflammatory disease with chronic relapsing symptoms. This study investigated the effects of Lycium barbarum polysaccharides (LBP) and capsaicin (CAP) in dextran sulfate sodium (DSS)-induced UC rats. Rats were divided into normal, DSS-induced UC, and UC treated with 100 mg LBP/kg bw, 12 mg CAP/kg bw, or 50 mg LBP/kg bw and 6 mg CAP/kg bw. Rats were fed LBP or CAP orally by gavage for 4 weeks, and UC model was established by feeding 5% DSS in drinking water for 6 days during week 3. Oral CAP and mixture significantly reduced disease activity index. Oral LBP significantly decreased serum malondialdehyde, interleukin (IL)-6, colonic tumor necrosis factor (TNF)-α levels, and protein expression of transient receptor potential cation channel V1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1), but increased serum catalase activity. Oral CAP significantly suppressed serum IL-6, colonic TRPV1 and TRPA1 protein expression, but elevated IL-10 levels, serum superoxide dismutase and catalase activities. The mixture of LBP and CAP significantly reduced serum IL-6, colonic TNF-α and TRPA1 protein. In conclusion, administration of LBP and/or CAP attenuate DSS-induced UC symptoms through inhibiting oxidative stress, proinflammatory cytokines, and protein expression of TRPV1 and TRPA1.

Common bacterial metabolite indole directly activates nociceptive neuron through transient receptor potential ankyrin 1 channel.

ABSTRACT: Nociceptors are known to directly recognize bacterial cell wall components or secreted toxins, thereby leading to pain induced by bacterial infection. However, direct activation of nociceptors by bacterial metabolites remains unclear although bacteria produce numerous metabolites related to health and disease. In this study, we investigated whether and how a common bacterial metabolite, indole, which is produced by normal microflora of the gastrointestinal tract and oral cavity, can directly activate nociceptive sensory neurons. We found that indole elicits calcium response and evokes inward currents in subsets of dorsal root ganglia (DRG) neurons. Intraplantar (i.pl.) injection of indole produced nocifensive behaviors in adult mice, which were enhanced in complete Freund's adjuvant-induced chronic inflammatory condition. Indole increased calcitonin gene-related peptide release in DRG neurons, and i.pl. injection of indole increased hind paw thickness, suggesting its role in generation of neurogenic inflammation. These in vitro and in vivo indole-induced responses were pharmacologically blocked by transient receptor potential ankyrin 1 (TRPA1) antagonist, HC-030031, and significantly abolished in TRPA1 knockout (KO) mice, indicating that indole targets TRPA1 for its action in DRG neurons. Nocifensive licking behavior induced by the injection of live Escherichia coli was significantly decreased in tryptophanase mutant (TnaA KO) E. coli- injected mice that lack indole production, further supporting the idea that bacteria-derived indole can induce pain during infection. Identifying the mechanism of action of indole through TRPA1 provides insights into bacteria-neuron interactions and the role of bacterial metabolites in pain signaling, especially in inflammation-accompanied bacterial infection.

Sanse Powder Essential Oil Nanoemulsion Negatively Regulates TRPA1 by AMPK/mTOR Signaling in Synovitis: Knee Osteoarthritis Rat Model and Fibroblast-Like Synoviocyte Isolates.

Synovitis is the primary driving factor for the occurrence and development of knee osteoarthritis (KOA) and fibroblast-like synoviocytes (FLSs) and plays a crucial role during this process. Our previous works revealed that transient receptor potential ankyrin 1 (TRPA1) ion channels mediate the amplification of KOA synovitis. In recent years, essential oils have been proved to have blocking effect on transient receptor potential channels. Meanwhile, the therapeutic effect of Sanse Powder on KOA synovitis has been confirmed in clinical trials and basic studies; although, the mechanism remains unclear. In the present study, Sanse Powder essential oil nanoemulsion (SP-NEs) was prepared, and then chemical composition, physicochemical properties, and stability were investigated. Besides, both in MIA-induced KOA rats and in LPS-stimulated FLSs, we investigated whether SP-NES could alleviate KOA synovitis by interfering with AMP-activated protein kinase- (AMPK-) mammalian target of rapamycin (mTOR), an energy sensing pathway proved to negatively regulate the TRPA1. Our research shows that the top three substances in SP-NEs were tumerone, delta-cadinene, and Ar-tumerone, which accounted for 51.62% of the total, and should be considered as the main pharmacodynamic ingredient. Less inflammatory cell infiltration and type I collagen deposition were found in the synovial tissue of KOA rats treated with SP-NEs, as well as the downregulated expressions of interleukin (IL)-1ß, IL-18, and TRPA1. Besides, SP-NEs increased the phosphorylation level of AMPK and decreased the phosphorylation level of mTOR in the KOA model, and SP-NEs also upregulated expressions of peroxisome proliferator-activated receptor-gamma (PPARγ) and PPARγ coactivator-1α and downstream signaling molecules of AMPK-mTOR in vivo and in vitro. To conclude, a kind of Chinese herbal medicine for external use which is effective in treating synovitis of KOA was extracted and prepared into essential oil nanoemulsion with stable properties in the present study. It may alleviate synovitis in experimental KOA through the negative regulation of TRPA1 by AMPK-mTOR signaling.

Oxymatrine screened from Sophora flavescens by cell membrane immobilized chromatography relieves histamine-independent itch.

OBJECTIVES: This study aimed to discover the active compounds of Sophora flavescens Ait. (SF), the anti-itch effects and underlying mechanisms of oxymatrine (OMT), one of the bioactive compounds from SF. METHODS: Dorsal root ganglion cell membrane immobilized chromatography was used to screen potential anti-pruritic active compounds from SF. The scratching behaviour was analysed to systematically study the anti-pruritic effects of OMT in chloroquine- (CQ), peptide Ser-Leu-Ile-Gly-Arg-Leu- (SLIGRL), histamine- (HIS) and allyl-isothiocyanate-(AITC)-induced itch mice models. Real-time quantitative PCR, in-vivo study and molecular docking were employed to explore the underlying mechanisms. KEY FINDINGS: All in all, 21 compounds of SF were identified and 5 potential bioactive compounds were discovered. OMT significantly reduced scratching bouts in two HIS-independent itch models induced by CQ and SLIGRL but was not effective in the HIS-induced itch model. OMT reduced scratching bouts in a dose-dependent manner and decreased the messenger RNA (mRNA) expression of transient receptor potential ankyrin 1 (TRPA1) channel in two HIS-independent itch models; in addition, OMT reduced the wipes and scratching bouts induced by AITC. CONCLUSIONS: This study discovered five potential anti-pruritic compounds including OMT in the SF extract, and OMT has strong anti-pruritic effects in HIS-independent itch via TRPA1 channel.