Inhibitory effects of tetramethylpyrazine on pain transmission of trigeminal neuralgia in CCI-ION rats

The ethanol extract of Scutellaria baicalensis Georgi attenuates complete Freund's adjuvant (CFA)-induced inflammatory pain by suppression of P2X3 receptor

ETHNOPHARMACOLOGICAL RELEVANCE

Scutellaria baicalensis Georgi (SBG) is a perennial herb with anti-inflammatory, antibacterial, and antioxidant activities, which is traditionally used to treat inflammation of respiratory tract and gastrointestinal tract, abdominal cramps, bacterial and viral infections. Clinically, it is often used to treat inflammatory-related diseases. Research has shown that the ethanol extract of Scutellaria baicalensis Georgi (SGE) has anti-inflammatory effect, and its main components baicalin and baicalein have analgesic effects. However, the mechanism of SGE in relieving inflammatory pain has not been deeply studied.

AIM OF THE STUDY

This study aimed to evaluate the analgesic effect of SGE on complete Freund's adjuvant (CFA)-induced inflammatory pain rats, and to investigate whether its effect on relieving inflammatory pain is associated with regulation of P2X3 receptor.

MATERIALS AND METHODS

The analgesic effects of SGE on CFA-induced inflammatory pain rats were evaluated by measuring mechanical pain threshold, thermal pain threshold, and motor coordination ability. The mechanisms of SGE in relieving inflammatory pain were explored by detecting inflammatory factors levels, NF-κB, COX-2 and P2X3 expression, and were further verified by addition of P2X3 receptor agonist (α, β me-ATP).

RESULTS

Our results revealed that SGE can notably increase the mechanical pain threshold and thermal pain threshold of CFA-induced inflammatory pain rats, and markedly alleviate the pathological damage in DRG. SGE could suppress the release of inflammatory factors including IL-1β, IL-6, TNF-α and restrain the expression of NF-κB, COX-2 and P2X3. Moreover, α, β me-ATP further exacerbated the inflammatory pain of CFA-induced rats, while SGE could markedly raise the pain thresholds and relieve inflammatory pain. SGE could attenuate the pathological damage, inhibit P2X3 expression, inhibit the elevation of inflammatory factors caused by α, β me-ATP. SGE can also inhibit NF-κB and ERK1/2 activation caused by α, β me-ATP, and inhibit the mRNA expression of P2X3, COX-2, NF-κB, IL-1β, IL-6 and TNF-α in DRG of rats induced by CFA coupled with α, β me-ATP.

CONCLUSIONS

In summary, our research indicated that SGE could alleviate CFA-induced inflammatory pain by suppression of P2X3 receptor.

Imperatorin Improves Obesity-Induced Cardiac Sympathetic Nerve Injury Mediated by P2X4 Receptor in Stellate Sympathetic Ganglion

Obesity can activate the inflammatory signal pathway, induce in the body a state of chronic inflammation, and increase the excitability of the sympathetic nervous system, which may induce sympathetic neuropathic injury. The stellate sympathetic ganglia (SG) can express the P2X4 receptor, and the abnormal expression of the P2X4 receptor is related to inflammation. Imperatorin (IMP) is a kind of furan coumarin plant which has anti-inflammatory effects. This project aimed to investigate whether IMP can affect the expression of P2X4 receptors in the SG of obese rats to display a protective effect from high-fat-triggered cardiac sympathetic neuropathic injury. Molecular docking through homology modelling revealed that IMP had good affinity for the P2X4 receptor. Our results showed that compared with the normal group, the administration of IMP or P2X4 shRNA decreased sympathetic excitement; reduced the serum levels of triglyceride, total cholesterol, and lactate dehydrogenase; downregulated the expression of P2X4 receptors in SG; and inhibited the expression of inflammatory factors in the SG and serum of obese rats significantly. In addition, the expression of factors associated with the cell pyroptosis GSDMD, caspase-1, NLRP-3, and IL-18 in obese rats were significantly higher than those of the normal rats, and such effects were decreased after treatment with IMP or P2X4 shRNA. Furthermore, IMP significantly reduced the ATP-activated currents in HEK293 cells transfected with P2X4 receptor. Thus, the P2X4 receptor may be a key target for the treatment of obesity-induced cardiac sympathetic excitement. IMP can improve obesity-induced cardiac sympathetic excitement, and its mechanism of action may be related to the inhibition of P2X4 receptor expression and activity in the SG, suppression of cellular pyroptosis in the SG, and reduction of inflammatory factor levels.

Effect of lidocaine on expression of P2X7, p-p38 and IL-Iβ in the thalamus of rats with trigeminal neuralgia

We investigated whether lidocaine can increase the pain threshold of rats with trigeminal neuralgia by affecting the expression of P2X7, p-p38 and IL-Iβ proteins in the thalamus. Thirty-three male Sprague-Dawley (SD) rats were randomly divided into three groups (n = 11): Sham group, Ion-CCI (infraorbital nerve chronic constriction injury) group and Ion-CCI+L group(Ion-CCI+lidocaine 10 mg/kg/day, i.p.). The mechanical pain threshold of rats was measured preoperatively and at 1, 3, 5, 7, 9, 11 and 14days after operation with the von Frey filament sensor tester. Fourteen days after operation, the rats were dissected to collect their whole brain, thalamus and trigeminal ganglion to detect IL-1β, P2X7, p38, and p-p38 protein expression. The pain threshold of rats in Ion-CCI+L group was lower than that in Sham group (p < 0.01) and higher than that in Ion-CCI group (p < 0.01).ELISA showed that IL-1β in the thalamus and trigeminal ganglion in Ion-CCI+L group were lower than those in ion-CCI group (p < 0.05) but higher than those in Sham group (p < 0.05). Western blot showed that the expression levels of P2X7 and p-p38 in the thalamus of rats in Ion-CCI+L group were lower than those in Ion-CCI group (p < 0.01) and higher than thaose in Sham group (p < 0.01),while the expression levels of IL-1β in the thalamus in Ion-CCI+L group were lower than those in Ion-CCI group (p < 0.05) and higher than those in Sham group (p < 0.01). Immunofluorescence showed that p-p38 in the thalamus in Ion-CCI+L group was lower than that in Ion-CCI group (p < 0.05) and higher than that in Sham group (p < 0.05). Lidocaine can reduce the inflammatory response of the central nervous system and increase the pain threshold of trigeminal neuralgia rats by inhibiting p2x7-p38-IL-1β signaling pathway.This pathway play an important role in the pathogenesis of trigeminal neuralgia, and it may be one of the targets for the treatment of trigeminal neuralgia.

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-1β (IL-1β) 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.

P2Y14 receptor in trigeminal ganglion contributes to neuropathic pain in mice

Trigeminal nerve injury is a common complication of various dental and oral procedures, which could induce trigeminal neuropathic pain but lack effective treatments. P2 purinergic receptors have emerged as novel therapeutic targets for such pain. Recent reports implied that the P2Y₁₄ receptor (P2Y₁₄R) was activated and promoted orofacial inflammatory pain and migraine. However, the role and mechanism of P2Y₁₄R in trigeminal neuropathic pain remain unknown. We induced an orofacial neuropathic pain model by chronic constriction injury of the infraorbital nerve (CCI-ION). Von-Frey tests showed that CCI-ION induced orofacial mechanical hypersensitivity. The increased activating transcription factor 3 (ATF3) expression in the trigeminal ganglion (TG) measured by immunofluorescence confirmed trigeminal nerve injury. Immunofluorescence showed that P2Y₁₄R was expressed in trigeminal ganglion neurons (TGNs) and satellite glial cells (SGCs). RT-qPCR and Western blot identified increased expression of P2Y₁₄R in TG after CCI-ION. CCI-ION also upregulated interleukin-1β (IL-1β), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-α (TNF-α) in TG. Notably, CCI-ION-induced mechanical hypersensitivity and pro-inflammatory cytokines production were decreased by a P2Y₁₄R antagonist (PPTN). Trigeminal administration of P2Y₁₄R agonist (UDP-glucose) evoked orofacial mechanical hypersensitivity and increased pro-inflammatory cytokines above in TG. Furthermore, CCI-ION induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 in TG, which also were reduced by PPTN. The inhibitors of ERK1/2 (U0126) and p38 (SB203580) decreased these upregulated pro-inflammatory cytokines after CCI-ION. Collectively, this study revealed that P2Y₁₄R in TG contributed to trigeminal neuropathic pain via ERK- and p38-dependent neuroinflammation. Thus, P2Y₁₄R may be a potential drug target against trigeminal neuropathic pain.

Scorpion Neurotoxin Syb-prII-1 Exerts Analgesic Effect through Nav1.8 Channel and MAPKs Pathway

Trigeminal neuralgia (TN) is a common type of peripheral neuralgia in clinical practice, which is usually difficult to cure. Common analgesic drugs are difficult for achieving the desired analgesic effect. Syb-prII-1 is a β-type scorpion neurotoxin isolated from the scorpion venom of Buthus martensi Karsch (BmK). It has an important influence on the voltage-gated sodium channel (VGSCs), especially closely related to Nav1.8 and Nav1.9. To explore whether Syb-prII-1 has a good analgesic effect on TN, we established the Sprague Dawley (SD) rats’ chronic constriction injury of the infraorbital nerve (IoN-CCI) model. Behavioral, electrophysiological, Western blot, and other methods were used to verify the model. It was found that Syb-prII-1 could significantly relieve the pain behavior of IoN-CCI rats. After Syb-prII-1 was given, the phosphorylation level of the mitogen-activated protein kinases (MAPKs) pathway showed a dose-dependent decrease after IoN-CCI injury. Moreover, Syb-prII-1(4.0 mg/kg) could significantly change the steady-state activation and inactivation curves of Nav1.8. The steady-state activation and inactivation curves of Nav1.9 were similar to those of Nav1.8, but there was no significant difference. It was speculated that it might play an auxiliary role. The binding mode, critical residues, and specific interaction type of Syb-prII-1 and VSD2^rNav1.8 were clarified with computational simulation methods. Our results indicated that Syb-prII-1 could provide a potential treatment for TN by acting on the Nav1.8 target.

Anti-nociceptive effects of ECa 233 a standardized extract of Centella asiatica (L.) Urban on chronic neuropathic orofacial pain in mice

ETHNOPHARMACOLOGICAL RELEVANCE

ECa 233 is a standardized extract of Centella asiatica (L.) Urban, a herb traditionally used to treat a number of diseases including neurological disorders. Accordingly, ECa 233 showed benefits on animal models of cognitive deficits, chronic stress and Parkinson's disease. Analgesic activity of ECa 233 was shown in Tail's flick test in rodent and relieving aphthous ulcer pain in man. Moreover, acute and sub-chronic toxicity testing in rodents and pharmacokinetic study in healthy volunteers, clinical trial phase I demonstrated good safety profiles of ECa 233.

AIM OF THE STUDY

This study aims to evaluate the anti-nociceptive effects of ECa 233 and its synergistic effect with gabapentin on chronic neuropathic orofacial pain after 3 weeks infraorbital nerve chronic constriction injury in mice. The peripheral and central nociceptive activities are also examined.

MATERIALS AND METHODS

Chronic neuropathic orofacial pain was induced by 3 weeks infraorbital nerve chronic constriction injury. Mice were treated with ECa 233 (30, 100 and 300 mg/kg) and gabapentin (10 mg/kg) by oral gavage starting on day 21 and going on for 14 consecutive days. Mechanical hyperalgesia and allodynia were measured on day 7, 14, 21, 28 and 35 after infraorbital nerve chronic constriction injury. At the end of the experiment, mice were observed for the sedative effect using the locomotor activity, the calcitonin gen-related peptide in trigeminal ganglion and c-fos expression in trigeminal nucleus caudalis were investigated after euthanasia.

RESULTS

Infraorbital nerve chronic constriction injury gradually induced marked ipsilateral mechanical hyperalgesia and allodynia. The maximum hyperalgesia and allodynia response presented on day 21 and the response was remained constant until day 35. Treatment with either 300 mg/kg ECa 233 or 10 mg/kg gabapentin were able to attenuate mechanical hyperalgesia and allodynia. The downregulation of calcitonin gen-related peptide on ipsilateral trigeminal ganglion were observed in ECa 233 at 100 and 300 mg/kg and 10 mg/kg gabapentin-treated groups. The c-fos expression on ipsilateral trigeminal nucleus caudalis was also decreased in 300 mg/kg ECa 233 and 10 mg/kg gabapentin-treated groups.

CONCLUSION

ECa 233 reduced hyperalgesia and allodynia by modulating the peripheral calcitonin gen-related peptide expression consequently alleviate the nociceptive activity in trigeminal nucleus caudalis. Further clinical trial to proof ECa 233's efficacy in neuropathic pain in man as well as possible attributable mechanism of action should be further investigated.

Inhibitory Effects of Palmatine on P2X7 Receptor Expression in Trigeminal Ganglion and Facial Pain in Trigeminal Neuralgia Rats

Trigeminal Neuralgia (TN) refers to recurrent severe paroxysmal pain in the distribution area of the trigeminal nerve, which seriously affects the quality of life of patients. This research applied the chronic constriction injury of the infraorbital nerve (CCI—ION) approach to induce an animal model of TN in rats. The mechanical pain threshold of each group of rats was determined postoperatively; the expression of P2X7 receptor in trigeminal ganglion (TG) was assessed by qRT-PCR, immunofluorescence and Western blot; and the changes of the proinflammatory cytokines IL-1β and TNF-α in serum of rats were detected by ELISA. The results showed that the administration of palmatine in the TN rats could reduce the mechanical pain threshold, significantly decrease the expression of P2X7 receptor in TG, and lower the serum concentrations of IL-1β and TNF-α, compared to the sham group. In addition, the phosphorylation level of p38 in TG of TN rats was significantly decreased after treatment with palmatine. Likewise, inhibition of P2X7 expression by shRNA treatment could effectively counteract the adversary changes of pain sensitivity, IL-1β and TNF-α production, and p38 phosphorylation in TN rats. Our data suggest that palmatine may alleviate mechanical facial pain in TN rats possibly by reducing the expression of P2X7 receptor in TG of TN rats, which may be attributable to inhibiting p38 phosphorylation and reducing the release of IL-1β and TNF-α.

Potential Molecular Targets for Treating Neuropathic Orofacial Pain Based on Current Findings in Animal Models

This review highlights potential molecular targets for treating neuropathic orofacial pain based on current findings in animal models. Preclinical research is currently elucidating the pathophysiology of the disease and identifying the molecular targets for better therapies using animal models that mimic this category of orofacial pain, especially post-traumatic trigeminal neuropathic pain (PTNP) and primary trigeminal neuralgia (PTN). Animal models of PTNP and PTN simulate their etiologies, that is, trauma to the trigeminal nerve branch and compression of the trigeminal root entry zone, respectively. Investigations in these animal models have suggested that biological processes, including inflammation, enhanced neuropeptide-mediated pain signal transmission, axonal ectopic discharges, and enhancement of interactions between neurons and glial cells in the trigeminal pathway, are underlying orofacial pain phenotypes. The molecules associated with biological processes, whose expressions are substantially altered following trigeminal nerve damage or compression of the trigeminal nerve root, are potentially involved in the generation and/or exacerbation of neuropathic orofacial pain and can be potential molecular targets for the discovery of better therapies. Application of therapeutic candidates, which act on the molecular targets and modulate biological processes, attenuates pain-associated behaviors in animal models. Such therapeutic candidates including calcitonin gene-related peptide receptor antagonists that have a reasonable mechanism for ameliorating neuropathic orofacial pain and meet the requirements for safe administration to humans seem worth to be evaluated in clinical trials. Such prospective translation of the efficacy of therapeutic candidates from animal models to human patients would help develop better therapies for neuropathic orofacial pain.

Targeting P2 receptors in purinergic signaling: a new strategy of active ingredients in traditional Chinese herbals for diseases treatment

Adenosine triphosphate (ATP) and its metabolites adenosine diphosphate, adenosine monophosphate, and adenosine in purinergic signaling pathway play important roles in many diseases. Activation of P2 receptors (P2R) channels and subsequent membrane depolarization can induce accumulation of extracellular ATP, and furtherly cause kinds of diseases, such as pain- and immune-related diseases, cardiac dysfunction, and tumorigenesis. Active ingredients of traditional Chinese herbals which exhibit superior pharmacological activities on diversified P2R channels have been considered as an alternative strategy of disease treatment. Experimental evidence of potential ingredients in Chinese herbs targeting P2R and their pharmacological activities were outlined in the study.

Involvement of the BNP/NPR-A/BKCa pathway in rat trigeminal ganglia following chronic constriction injury

Accumulating evidence indicates that the brain natriuretic peptide (BNP) and its receptor (natriuretic peptide receptor, NPR) are widely distributed in a variety of tissues including trigeminal ganglion (TG). Furthermore, recent studies support the involvement of the BNP-NPR-A pathway in acute and chronic pain. To investigate the role of this pathway in chronic pain, an infraorbital nerve-chronic constriction injury (ION-CCI) model of trigeminal neuralgia (TN) was produced in the rat. The time course of changes in mechanical pain threshold was examined. We observed an upregulation of BNP and NPR-A and a downregulation of large-conductance Ca²⁺-activated K⁺ (BKCa) mRNA and protein in rats subjected to ION-CCI. Patch clamping experiments in vitro found that BKCa currents were significantly reduced in rats subjected to ION-CCI. BNP increased BKCa currents in ION-CCI rats. These results suggest that BNP and NPR-A might serve as endogenous pain relievers in ION-CCI rats. Modulation of the BNP/NPR-A/BKCa channel pathway in TG may be a viable strategy for the treatment of TN.NEW & NOTEWORTHY BNP has been known to activate its receptor, NPR-A, to modulate inflammatory pain. However, the potential modulatory roles of BNP in TN have not been investigated in detail. We established an ION-CCI model of TN in the rat and observed an upregulation of BNP and NPR-A and a downregulation of BKCa in rats subjected to ION-CCI. Moreover, BNP can increase BKCa currents in ION-CCI rats. Thus, BNP and NPR-A might have inhibitory effects on trigeminal neuralgia through activating the BNP/NPR-A/BKCa channel pathway.

SNI and CFA induce similar changes in TRPV1 and P2X3 expressions in the acute phase but not in the chronic phase of pain

Peripheral inflammation and nerve injury usually accompany each other. However, whether inflammatory and neuropathic pain share similar mechanisms at all stages is unknown. TRPV1 and P2X3 are two major ion channels in dorsal root ganglia (DRGs) and are involved in chronic pain. Here, their function and expression in DRGs at different phases of the two types of pain were investigated. Both the paw withdrawal threshold (PWT) and paw withdrawal latency were decreased in rats injected with complete Freud's adjuvant (CFA). However, only the PWT was decreased in rats with spared nerve injury (SNI). CFA increased the magnitude of the TRPV1-mediated Ca²⁺ response but not the P2X3-mediated Ca²⁺ response 14 days after injection. Consistent with this result, the P2X3 expression level in CFA rats was increased only at 3 days after injection. SNI surgery increased the magnitudes of the TRPV1- and P2X3-mediated Ca²⁺ responses and upregulated both TRPV1 and P2X3 expression in lumbar DRGs. The distributions of TRPV1 and P2X3 in DRGs after modeling were observed, and TRPV1 was found to be highly expressed mainly in the L4-L5 DRGs in CFA rats and in the L5-L6 DRGs in SNI rats. P2X3 was highly expressed in the L4-L6 DRGs in CFA rats 3 days after injection but was only highly expressed in the L4 DRG 14 days after modeling. On the other hand, SNI promoted the P2X3 expression L4-L5 DRGs 3 days after surgery, but only L6 DRG 14 days after modeling. All the results indicate that P2X3 and TPRV1 are involved in inflammatory and neuropathic pain by different expression levels and distributions in the lumbar DRG in the chronic stage.

Neferine alleviates P2X3 receptor in rat dorsal root ganglia mediated neuropathic pain

Chronic neuropathic pain is caused by tissue damage or nervous system inflammation and is characterized by sensitivity to painful stimuli. P2X3 receptors play an important role in facilitating pain transmission. Neferine is a bisbenzylisoquinline alkaloid isolated from seed embryos of lotus, which has anti-inflammatory and anti-oxidation pharmacological functions. The present research investigated whether neferine relieves neuropathic pain related to the P2X3 receptor in rat dorsal root ganglia (DRGs). Chronic contraction injury (CCI) in rats was used as a model for neuropathic pain. The results indicated that the expression of P2X3 receptor was significantly increased in the DRGs of CCI rats and that mechanical allodynia and thermal hyperalgesia were also enhanced in CCI rats. Neferine markedly lowered the upregulated P2X3 receptor and interleukin-1beta, inhibited the phosphorylation and activation of ERK1/2 in the DRGs of CCI rats, and relieved neuropathic pain. Therefore, neferine alleviates neuropathic pain by downregulating the expression of P2X3 receptor.

P2X receptors and trigeminal neuralgia

There is currently no effective cure for trigeminal neuralgia (TN) - a relatively common disease that causes long-term pain in patients. Previous research has shown that ionotropic ATP signaling through excitatory and calcium-permeable P2X receptor channels plays a critical role in pathological pain generation and maintenance. In this paper, we review several hypotheses on the pathogenic mechanisms underlying TN. We further discuss pathways or agents that can target P2X expression in TN, thereby affecting pain induction and maintenance.

Tetramethylpyrazine ameliorates hepatic fibrosis through autophagy-mediated inflammation

BACKGROUND

Imbalanced immune response and hepatic fibrosis are key factors related to the progression of chronic liver diseases. Tetramethylpyrazine (TMP), a natural alkaloid, has been widely used for treating liver injury. In this study, we explored the effect of TMP on hepatic fibrosis and the related mechanisms regulating autophagy.

METHODS

A rat model of hepatic fibrosis and a model using an hepatic stellate cell line (HSC-T6) were created using CCl₄ and platelet-derived growth factor (PDGF). Staining with haematoxylin and eosin (HE), Masson's stain, and TUNEL were performed for pathological diagnosis. ELISA, Western blotting, and immunofluorescence analyses were conducted to determine the expression levels of the specific markers for fibrosis, autophagy, inflammation, and signalling pathways.

RESULTS

TMP treatment significantly rescued pathological injury and hepatic fibrosis. It also alleviated imbalances in the immune system, accumulation of extracellular matrix, and autophagy signals in hepatic fibrosis. At the same time, we found that application of the autophagy inducer rapamycin enhanced the therapeutic effect of TMP, whereas the autophagy inhibitor 3-methyladenine, PI3K pathway inhibitor LY294002, and AKT pathway agonist SC79 did the opposite.

CONCLUSIONS

TMP exerts therapeutic effects in hepatic fibrosis mainly through promoting autophagy to ameliorate inflammation by inhibiting the AKT-mTOR signalling pathway, providing a new perspective for the treatment of chronic liver diseases.

Palmatine alleviates hyperalgesia by inhibiting the expression of calcitonin gene-related peptide in the trigeminal ganglion of rats with chronic constriction injury of the infraorbital nerve

Trigeminal neuralgia is one of the most common of the neuropathic pains, and it can seriously influence patients' quality of life. Calcitonin gene-related peptide (CGRP) is a type of nociceptive neurotransmitter that is expressed in neurons of the trigeminal ganglion and plays a major part in transmitting pain. The rat model of trigeminal neuralgia was established by causing a chronic constriction injury of the infraorbital nerve (CCI-ION). Male Sprague-Dawley rats (n=24) were randomly divided into a sham control group (sham, n=6), sham-treated with palmatine group (sham+palmatine, n=6), trigeminal nerve model group (TN, n=6), and trigeminal nerve treated with palmatine group (TN+palmatine, n=6). Fifteen days after the operation the mechanical response threshold was decreased in the TN group compared with the sham group. From postoperative day 7 to day 15, the mechanical response threshold in the TN+palmatine group significantly increased compared with the TN group. On postoperative day 15 the results of quantitative polymerase chain reaction (qPCR), immunohistochemical staining, and western blotting showed an obvious increase in expression of CGRP and its receptors, serum concentrations of interleukin-1β (IL-1β), and tumour necrosis factor-α (TNF-α), and phosphorylation of protein kinase C (PKC) in the trigeminal ganglia of the TN group compared with the sham group, but these increases could be down-regulated by treatment with palmatine. Palmatine might therefore have therapeutic potential for the treatment of trigeminal neuralgia by inhibiting the expression of CGRP and its receptors in trigeminal ganglia, suppressing the serum concentrations of IL-1β and TNF-α, and decreasing the phosphorylation of PKC in the trigeminal ganglia of affected rats.

Effects of long non-coding RNA Gm14461 on pain transmission in trigeminal neuralgia

Background

This study aims to investigate the role of long non-coding RNA Gm14461 in regulating pain transmission in trigeminal neuralgia (TN). The mouse TN model was produced by chronic constriction injury of the infraorbital nerve (CCI-ION). The values of mechanical withdrawal threshold (MWT) were measured to assess the nociception of mice at different times after CCI-ION surgery (0, 1, 3, 5, 7, 9, 11, 13, 15 d). The primary mouse trigeminal ganglion neurons (TGNs) were isolated from C57BL/6 J mice and treated with TNF-α to mimic a TN cellular model. The expression of Gm14461, TNF-α, IL-1β, and IL-6 was examined using qRT-PCR. The protein levels of CGRP and P2X3/7 receptor were measured using western blot.

Results

Gm14461 expression was increased in trigeminal ganglia (TGs) of TN mice on the operation side. Furthermore, Gm14461 knockdown in TGs increased, whereas Gm14461 overexpression decreased MWT in TN mice. Moreover, Gm14461 knockdown downregulated, whereas Gm14461 overexpression upregulated mRNA levels of TNF-α, IL-1β, and IL-6 and protein levels of CGRP and P2X3/7 receptor in TGs from TN mice. In vitro assay showed that Gm14461 was upregulated by TNF-α, IL-1β, and IL-6. Additionally, Gm14461 knockdown decreased protein levels of CGRP and P2X3/7 receptor in TNF-α-treated TGNs, whereas Gm14461 overexpression exerted the opposite effect.

Conclusion

Gm14461 promoted pain transmission (reduced MWT value) in a CCI-ION-induced mouse TN model. The underlying mechanisms might involve the regulation of pro-inflammatory cytokines, CGRP and P2X3/7 receptor.

The P2Y14 receptor in the trigeminal ganglion contributes to the maintenance of inflammatory pain

P2Y purinergic receptors expressed in neurons and satellite glial cells (SGCs) of the trigeminal ganglion (TG) contribute to inflammatory and neuropathic pain. P2Y₁₄ receptor expression is reported in the spinal cord, dorsal root ganglion (DRG), and TG. In present study, the role of P2Y₁₄ receptor in the TG in inflammatory orofacial pain of Sprague-Dawley (SD) rats was investigated. Peripheral injection of complete Freund's adjuvant (CFA) induced mechanical hyperalgesia with the rapid upregulation of P2Y₁₄ receptor, glial fibrillary acidic protein (GFAP), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), C-C chemokine CCL2, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), and phosphorylated p38 (p-p38) proteins in the TG. Furthermore, immunofluorescence staining confirmed the CFA-induced upregulation of P2Y₁₄ receptor. Double immunostaining showed that P2Y₁₄ receptor colocalized with glutamine synthetase (GS) and neuronal nuclei (NeuN). Finally, trigeminal injection of a selective antagonist (PPTN) of P2Y₁₄ receptor attenuated CFA-induced mechanical hyperalgesia. PPTN also decreased the upregulation of the GFAP, IL-1β, TNF-α, CCL2, p-ERK1/2, and p-p38 proteins. Our findings showed that P2Y₁₄ receptor in TG may contribute to orofacial inflammatory pain via regulating SGCs activation, releasing cytokines (IL-1β, TNF-α, and CCL2), and phosphorylating ERK1/2 and p38.

Chinese herbal medicine for headache: A systematic review and meta-analysis of high-quality randomized controlled trials

BACKGROUND

Chinese herbal medicines (CHMs) are widely used to relieve headache in Asia. However, it is uncertain whether there is robust evidence on the effects of CHMs for headache.

PURPOSE

To assess the effectiveness and safety of CHMs for headache using systematic review of high-quality randomized controlled trials (RCTs).

METHODS

Electronic search was conducted on six databases from inception to January 2018. We included the RCTs that met the requirement of at least 4 out of the 7 domains according to the Cochrane risk of bias tool.

RESULTS

Thirty RCTs with 3447 subjects were ultimately included for analysis and all trials were conducted in Asia. Meta-analysis showed that CHMs monotherapy were superior to placebo in reducing headache frequency [SMD -0.48 (95% CI -0.76, -0.20); p < 0.01], headache days [SMD -0.29 (95% CI -0.45, -0.13); p < 0.01], headache duration[SMD -0.58 (95% CI -0.81, -0.36); p < 0.01], headache intensity [SMD -0.42 (95% CI -0.62, -0.23); p < 0.01] and analgesic consumption [SMD -0.36 (95% CI -0.52, -0.21); p < 0.01] and improving clinical efficacy rate (p < 0.01). Similarly, CHMs monotherapy were superior to western conventional medicines (WCMs) in headache frequency [SMD -0.57 (95% CI -0.84, -0.29); p < 0.01], headache days (p < 0.01), analgesic consumption [SMD -1.63 (95% CI -1.98, -1.28); p < 0.01], headache intensity [SMD -0.81 (95% CI -1.06, -0.57); p < 0.01], and clinical efficacy rate [RR 1.24 (95% CI 1.18, 1.31); p < 0.01], except reducing headache duration (p > 0.05). CHMs adjunct therapy can improve clinical efficacy rate compared with WCMs alone [RR 1.15 (95% CI 1.09, 1.22); p < 0.01]. Meanwhile, CHMs had fewer adverse events than that of controls.

CONCLUSION

The findings supported, at least to an extent, the use of CHM for headache patients; however, we should treat the results cautiously because the clinical heterogeneity.

Effects of long non-coding RNA uc.48+ on pain transmission in trigeminal neuralgia

Trigeminal neuralgia (TN) is the most common neuropathic pain in the facial area, for which the effective therapy is unavailable. Long non-coding RNA (lncRNA) such as lncRNA uc.48+ is involved in diabetic neuropathic pain and may affect purinergic signaling in ganglia of diabetic rats. In this research, chronic constriction injury of the infraorbital nerve (CCI-ION) was applied to establish a rat model of TN. Five days after local injection of siRNA targeting the lncRNA uc.48+ in trigeminal ganglia (TGs), the upregulated uc.48+ expression and the reduced mechanical withdrawal threshold (MWT) in the TN rats were significantly reversed. The expression of P2X₇ receptor in TGs was increased in the TN group compared with the sham group, but uc.48+ siRNA treatment mitigated this effect. The phosphorylation of ERK1/2 in TGs of TN rats was significantly enhanced compared with the sham group, while uc.48+ siRNA treatment reversed this change. In addition, injection of the lncRNA uc.48+ overexpression plasmid in TGs of control rats significantly reduced the MWT but elevated the expression of P2X₇ in TGs; the phosphorylation of ERK1/2 in TGs in these uc.48+-overexpressed rats was significantly higher, similar to the observations in rats of TN model. The interaction between uc.48+ and the P2X₇ receptor was detected by RNA binding protein immunoprecipitation (RIP), indicating that P2X₇ receptor could specifically bind to uc.48 + . In summary, knockdown of lncRNA uc.48+ by siRNA could inhibit transduction of TN signals, whereas uc.48+ overexpression promoted TN signal transduction. LncRNA uc.48+ may interact with P2X₇ receptor to upregulate expression of P2X₇ receptor and furthermore enhance the phosphorylation of ERK1/2 in TGs, thereby participating in pain transmission in TN.

Natural compounds acting at P2 receptors alleviate peripheral neuropathy

Neuropathic pain is generally resistant to currently available treatments, and it is often a consequence of nerve injury due to surgery, diabetes or infection. Myocardial ischemic nociceptive signaling increases the sympathoexcitatory reflex to aggravate myocardial injury. Elucidation of the pathogenetic factors might provide a target for optimal treatment. Abundant evidence in the literature suggests that P2X and P2Y receptors play important roles in signal transmission. Traditional Chinese medicines, such as emodin, puerarin and resveratrol, antagonize nociceptive transmission mediated by purinergic 2 (P2) receptors in primary afferent neurons. This review summarizes recently published data on P2 receptor-mediated neuropathic pain and myocardial ischemia in dorsal root ganglia (DRG), superior cervical ganglia (SCG) and stellate ganglia (SG), with a special focus on the beneficial role of natural compounds.

Chuanxiong Formulae for Migraine: A Systematic Review and Meta-Analysis of High-Quality Randomized Controlled Trials

Objective: Migraine is a complex, prevalent and disabling neurological disorder characterized by recurrent episodes of headache without ideal treatment. We aim to assess the current available evidence of herbal Chuanxiong (Ligusticum chuanxiong Hort. root) formulae for the treatment of migraine according to the high-quality randomized controlled trials (RCTs). Methods: English and Chinese electronic databases were searched from their inceptions until March 2017. The methodological quality of included study was assessed by the Cochrane Collaboration risk of bias tool. RCTs with Cochrane risk of bias (RoB) score ≥4 were included in the analyses. Meta-analysis was conducted using RevMan 5.3 software. Publication bias was assessed by funnel plot analysis and Egger's test. Results: Nineteen RCTs with 1832 participants were identified. The studies investigated the Chuanxiong formulae vs. placebo (n = 5), Chuanxiong formulae vs. conventional pharmacotherapy (CP) (n = 13 with 15 comparisons), and Chuanxiong formulae plus CP vs. CP (n = 1). Meta-analysis indicated that Chuanxiong formulae could reduce frequency, duration, days and pain severity of migraine and improve the total clinical efficacy rate (P < 0.05). Adverse event monitoring was reported in 16 out of 19 studies and occurrence rate of adverse event was low. Conclusion: The findings of present study indicated that Chuanxiong formulae exerted the symptom reliefs of for migraine.