Blocking of TRPV-1 in the parodontium relieves orthodontic pain by inhibiting the expression of TRPV-1 in the trigeminal ganglion during experimental tooth movement in rats

Nociceptor mechanisms underlying pain and bone remodeling via orthodontic forces: toward no pain, big gain

Orthodontic forces are strongly associated with pain, the primary complaint among patients wearing orthodontic braces. Compared to other side effects of orthodontic treatment, orthodontic pain is often overlooked, with limited clinical management. Orthodontic forces lead to inflammatory responses in the periodontium, which triggers bone remodeling and eventually induces tooth movement. Mechanical forces and subsequent inflammation in the periodontium activate and sensitize periodontal nociceptors and produce orthodontic pain. Nociceptive afferents expressing transient receptor potential vanilloid subtype 1 (TRPV1) play central roles in transducing nociceptive signals, leading to transcriptional changes in the trigeminal ganglia. Nociceptive molecules, such as TRPV1, transient receptor potential ankyrin subtype 1, acid-sensing ion channel 3, and the P2X3 receptor, are believed to mediate orthodontic pain. Neuropeptides such as calcitonin gene-related peptides and substance P can also regulate orthodontic pain. While periodontal nociceptors transmit nociceptive signals to the brain, they are also known to modulate alveolar bone remodeling in periodontitis. Therefore, periodontal nociceptors and nociceptive molecules may contribute to the modulation of orthodontic tooth movement, which currently remains undetermined. Future studies are needed to better understand the fundamental mechanisms underlying neuroskeletal interactions in orthodontics to improve orthodontic treatment by developing novel methods to reduce pain and accelerate orthodontic tooth movement-thereby achieving "big gains with no pain" in clinical orthodontics.

The role of TRPV1 in RA pathogenesis: worthy of attention

Transient receptor potential cation channel subfamily V member 1 (TRPV1) is a Ca2+permeable, non-selective cation channel that is found primarily in sensory nerve fibres. Previous studies focused on pain transmission. However, recent studies have found that the TRPV1 channel, in addition to being associated with pain, also plays a role in immune regulation and their dysregulation frequently affects the development of rheumatoid arthritis (RA). A thorough understanding of the mechanism will facilitate the design of new TRPV1-targeted drugs and improve the clinical efficacy of RA. Here, we provide an updated and comprehensive overview of how the TRPV1 channel intrinsically regulates neuronal and immune cells, and how alterations in the TRPV1 channel in synoviocytes or chondrocytes extrinsically affect angiogenesis and bone destruction. Rapid progress has been made in research targeting TRPV1 for the treatment of inflammatory arthritis, but there is still much-uncharted territory regarding the therapeutic role of RA. We present a strategy for targeting the TRPV1 channel in RA therapy, summarising the difficulties and promising advances in current research, with the aim of better understanding the role of the TRPV1 channel in RA pathology, which could accelerate the development of TRPV1-targeted modulators for the design and development of more effective RA therapies.

Considerations for Cannabinoids in Perioperative Care by Anesthesiologists

Increased usage of recreational and medically indicated cannabinoid compounds has been an undeniable reality for anesthesiologists in recent years. These compounds’ complicated pharmacology, composition, and biological effects result in challenging issues for anesthesiologists during different phases of perioperative care. Here, we review the existing formulation of cannabinoids and their biological activity to put them into the context of the anesthesia plan execution. Perioperative considerations should include a way to gauge the patient’s intake of cannabinoids, the ability to gain consent properly, and vigilance to the increased risk of pulmonary and airway problems. Intraoperative management in individuals with cannabinoid use is complicated by the effects cannabinoids have on general anesthetics and depth of anesthesia monitoring while simultaneously increasing the potential occurrence of intraoperative hemodynamic instability. Postoperative planning should involve higher vigilance to the risk of postoperative strokes and acute coronary syndromes. However, most of the data are not up to date, rending definite conclusions on the importance of perioperative cannabinoid intake on anesthesia management difficult.

Modulation of excitatory synaptic transmissions by TRPV1 in the spinal trigeminal subnucleus caudalis neurons of neuropathic pain rats

The present study examined contribution of the transient receptor potential vanilloid 1 channel (TRPV1) to the chronic orofacial pain. Bilateral partial nerve ligation (PNL) of the mental nerve, a branch of trigeminal nerve, was performed to induce neuropathic pain. The withdrawal threshold in response to mechanical stimulation of the lower lip skin was substantially reduced after the surgery in the PNL rats while it remained unchanged in the sham rats. This reduction in the PNL rats was alleviated by pregabalin injected intraperitoneally (10 mg/kg) and intracisternally (10, 30, 100 μg). Furthermore, an intracisternal injection of AMG9810, an antagonist of TRPV1, (1.5, 5.0 μg) attenuated the reduction of withdrawal threshold. Spontaneous and miniature excitatory postsynaptic currents (sEPSCs and mEPSCs) were recorded from the spinal trigeminal subnucleus caudalis (Vc) neurons in the brainstem slice, which receive the orofacial nociceptive signals. In the PNL rats, superfusion of capsaicin (0.03, 0.1 μM) enhanced their frequency without effect on the amplitude and the highest concentration (0.3 μM) increased both the frequency and amplitude. In the sham rats, only 0.3 μM capsaicin increased their frequency. Thus, capsaicin-induced facilitation of sEPSCs and mEPSCs in the PNL rats was significantly stronger than that in the sham rats. AMG9810 (0.1 μM) attenuated the capsaicin's effect. Capsaicin was ineffective on the trigeminal tract-evoked EPSCs in the PNL and sham rats. These results suggest that the chronic orofacial pain in the PNL model results from facilitation of the spontaneous excitatory synaptic transmission in the Vc region through TRPV1 at least partly.

Molecular mechanism in trigeminal nerve and treatment methods related to orthodontic pain

BACKGROUND

Orthodontic treatment is the main treatment approach for malocclusion. Orthodontic pain is an inevitable undesirable adverse reaction during orthodontic treatment. It is reported orthodontic pain has become one of the most common reason that patients withdraw from orthodontic treatment. Therefore, understanding the underlying mechanism and finding treatment of orthodontic pain are in urgent need.

AIMS

This article aims to sort out the mechanisms and treatments of orthodontic pain, hoping to provide some ideas for future orthodontic pain relief.

MATERIALS

Tooth movement will cause local inflammation. Certain inflammatory factors and cytokines stimulating the trigeminal nerve and further generating pain perception, as well as drugs and molecular targeted therapy blocking nerve conduction pathways, will be reviewed in this article.

METHOD

We review and summaries current studies related to molecular mechanisms and treatment approaches in orthodontic pain control.

RESULTS

Orthodontics pain related influencing factors and molecular mechanisms has been introduced. Commonly used clinical methods in orthodontic pain control has been evaluated.

DISCUSSION

With the clarification of more molecular mechanisms, the direction of orthodontic pain treatment will shift to targeted drugs.

Orthodontic force induces nerve injury-like transcriptomic changes driven by TRPV1-expressing afferents in mouse trigeminal ganglia

Orthodontic force produces mechanical irritation and localized inflammation in the periodontium, which causes pain in most patients. Nocifensive behaviors resulting from orthodontic force in mice can be substantially attenuated by intraganglionic injection of resiniferatoxin (RTX), a neurotoxin that specifically ablates a subset of neurons expressing transient receptor potential vanilloid 1 (TRPV1). In the current study, we determined changes in the transcriptomic profiles in the trigeminal ganglia (TG) following the application of orthodontic force, and assessed the roles of TRPV1-expressing afferents in these transcriptomic changes. RTX or vehicle was injected into the TG of mice a week before the placement of an orthodontic spring exerting 10 g of force. After 2 days, the TG were collected for RNA sequencing. The application of orthodontic force resulted in 1279 differentially expressed genes (DEGs) in the TG. Gene ontology analysis showed downregulation of gliogenesis and ion channel activities, especially of voltage-gated potassium channels. DEGs produced by orthodontic force correlated more strongly with DEGs resulting from nerve injury than from inflammation. Orthodontic force resulted in the differential expression of multiple genes involved in pain regulation, including upregulation of Atf3, Adcyap1, Bdnf, and Csf1, and downregulation of Scn10a, Kcna2, Kcnj10, and P2ry1. Orthodontic force-induced DEGs correlated with DEGs specific to multiple neuronal and non-neuronal subtypes following nerve injury. These transcriptomic changes were abolished in the mice that received the RTX injection. These results suggest that orthodontic force produces transcriptomic changes resembling nerve injury in the TG and that nociceptive inputs through TRPV1-expressing afferents leads to subsequent changes in gene expression not only in TRPV1-positive neurons, but also in TRPV1-negative neurons and non-neuronal cells throughout the ganglia. Orthodontic force-induced transcriptomic changes might be an active regenerative program of trigeminal ganglia in response to axonal injury following orthodontic force.

17β-Estradiol Exacerbated Experimental Occlusal Interference-Induced Chronic Masseter Hyperalgesia by Increasing the Neuronal Excitability and TRPV1 Function of Trigeminal Ganglion in Ovariectomized Rats

Pain symptoms in temporomandibular disorders (TMD) predominantly affect reproductive women, suggesting that estrogen regulates pain perception. However, how estrogen contributes to chronic TMD pain remains largely unclear. In the present study, we performed behavioral tests, electrophysiology, Western blot and immunofluorescence to investigate the role and underlying mechanisms of estrogen in dental experimental occlusal interference (EOI)-induced chronic masseter mechanical hyperalgesia in rats. We found that long-term 17β-estradiol (E2) replacement exacerbated EOI-induced masseter hyperalgesia in a dose-dependent manner in ovariectomized (OVX) rats. Whole-cell patch-clamp recordings demonstrated that E2 (100 nM) treatment enhanced the excitability of isolated trigeminal ganglion (TG) neurons in OVX and OVX EOI rats, and EOI increased the functional expression of transient receptor potential vanilloid-1 (TRPV1). In addition, E2 replacement upregulated the protein expression of TRPV1 in EOI-treated OVX rats. Importantly, intraganglionic administration of the TRPV1 antagonist AMG-9810 strongly attenuated the facilitatory effect of E2 on EOI-induced masseter mechanical sensitivity. These results demonstrate that E2 exacerbated EOI-induced chronic masseter mechanical hyperalgesia by increasing TG neuronal excitability and TRPV1 function. Our study helps to elucidate the E2 actions in chronic myogenic TMD pain and may provide new therapeutic targets for relieving estrogen-sensitive pain.

Interval Vibration Reduces Orthodontic Pain Via a Mechanism Involving Down-regulation of TRPV1 and CGRP

BACKGROUND/AIM

The transient receptor potential vanilloid 1 (TRPV1) ion receptor is involved in the release of calcitonin gene-related peptide (CGRP), a major contributor to orthodontic pain. Approaches that attenuate expression of TRPV1 and CGRP may reduce orthodontic pain. We explored the ability of high-frequency interval vibration to reduce orthodontic pain.

MATERIALS AND METHODS

Orthodontic force (50 g) was applied to both maxillary first molars in 8-week-old Wistar rats (n=72). Vibration was applied at 125 Hz for 15 min/day. Duration of face grooming was assessed as a measure of orthodontic pain. Immunofluorescence and western blotting were used to assess TRPV1 and CGRP in the trigeminal ganglia.

RESULTS

Compared to orthodontic force alone, application of vibration significantly decreased the duration of face grooming at 24 h and day 3 and reduced expression of TRPV1 and CGRP at 24 h.

CONCLUSION

Vibration represents a promising mechanical approach to reduce orthodontic pain.

Electroacupuncture reduces cold stress-induced pain through microglial inactivation and transient receptor potential V1 in mice

Background

The treatment, and efficacy thereof, is considered to be inadequate with specificity to alleviation of Fibromyalgia and its associated pain. Fibromyalgia patients suffer from chronic and persistent widespread pain and generalized tenderness. Transient receptor potential V1 (TRPV1), which is reported as a Ca²⁺ permeable ion channel that can be activated by inflammation, is reported to be involved in the development of fibromyalgia pain.

Methods

The current study explored the TRPV1 channel functions as a noxious sensory input in mice cold stress model. It remains unknown whether electroacupuncture (EA) attenuates fibromyalgia pain or affects the TRPV1 pathway.

Results

We show that cold stress increases mechanical and thermal pain (day 7: mechanical: 1.69 ± 0.41 g; thermal: 4.68 ± 0.56 s), and that EA and Trpv1 deletion counter this increase. EA and Trpv1 deletion reduced the cold stress-induced increase in inflammatory mediators and TRPV1-related molecules in the hypothalamus, periaqueductal gray (PAG), and cerebellum of mice.

Conclusions

Our results imply that EA has an analgesic effect associated with TRPV1 downregulation. We provide novel evidence that these inflammatory mediators can modulate the TRPV1 signaling pathway and suggest new potential therapeutic targets for fibromyalgia pain.

Functional characterization of nociceptive mechanisms involved in fibromyalgia and electroacupuncture

The diagnosis and treatment of chronic pain in diseases such as fibromyalgia (FM) are lacking effective standardised protocols that can be widely accessed and implemented by healthcare professionals across the globe. Persistent hyperalgesia and allodynia are characteristic symptoms of FM. This disease has indicated a refractory tendency to conventional treatment ventures, largely resultant from a lack of etiological and pathogenic understanding of the disease development. Emerging evidence indicates that the central nervous system (CNS) plays a critical role in the amplification of pain signals and the neurotransmitters associated therewith. We examined the contribution of the transient receptor potential vanilloid 1 (TRPV1) channel and the major nociceptive components in response to fibromyalgia-like pain in an intermittent cold-stress (ICS) model, in the prefrontal cortex, somatosensory cortex, hippocampus and thalamus areas of the brain. The use of TRPV1 gene deletion mice served to elucidate the role of the TRPV1 receptor in the development and expression of FM-like pain. The results suggest that TRPV1 upregulation is central to the sustained sensation of FM related hyperalgesia. Furthermore, the potential therapeutic benefits of electroacupuncture (EA) at bilateral ST36 acupoint were analysed in order to identify the analgesic effects and mechanism associated with this therapy. The findings indicate that EA treatment successfully attenuated both mechanical and thermal hyperalgesia and suggests that a definitive underlying mechanism of neuromodulation through EA is responsible for providing analgesic benefits to patients suffering from FM.

Orthodontic force-induced oxidative stress in the periodontal tissue and dental pulp elicits nociception via activation/sensitization of TRPA1 on nociceptive fibers

Orthodontic patients complain of pain for the first few days after insertion of appliances. Mechanical force has been reported to produce oxidants in periodontal ligament (PDL) cells. It has not been studied whether orthodontic force-induced oxidative stress elicits nociception. Herein, we focused on the role of the oxidant-sensitive channel TRPA1 on nociception in orthodontic pain. In a rat model of loaded orthodontic force between the maxillary first molar and incisor, the behavioral signs of orofacial nociception, facial rubbing and wiping, increased to a peak on day 1 and gradually diminished to the control level on day 5. Administration of free radical scavengers (Tempol and PBN) and TRPA1 antagonist (HC-030031) inhibited nociceptive behaviors on day 1. In the PDL, the oxidative stress marker 8-OHdG was highly detected on day 1 and recovered on day 5 to the sham-operated level. The dental pulp showed similar results as the PDL. TRPA1 mRNA was abundantly expressed in the trigeminal ganglion relative to PDL tissue, and there were TRPA1-immunopositive neuronal fibers in the PDL and pulp. In dissociated trigeminal ganglion neurons, H₂O₂ at 5 mM induced a Ca²⁺ response that was inhibited by HC-030031. Although H₂O₂ at 100 μM did not yield any response, it enhanced the mechanically activated TRPA1-dependent Ca²⁺ response. These results suggest that oxidative stress in the PDL and dental pulp following orthodontic force activates and/or mechanically sensitizes TRPA1 on nociceptive fibers, resulting in orthodontic nociception. Later, the disappearance of nociception seems to be related to a decrease in oxidative stress, probably due to tissue remodeling.

TRPV1 and TRPV1-Expressing Nociceptors Mediate Orofacial Pain Behaviors in a Mouse Model of Orthodontic Tooth Movement

Orthodontic force produces mechanical irritation and inflammation in the periodontium, which is inevitably accompanied by pain. Despite its prevalence, treatment of orthodontic pain is ineffective. Elucidating underlying neural mechanisms is critical to improving the management of orthodontic pain. We have assessed the contribution of transient receptor potential vanilloid subtype 1 (TRPV1) and the TRPV1-expressing subset of nociceptive afferents to pain behaviors induced by orthodontic force in mice. Microfocus X-ray computed tomography analysis showed that application of an orthodontic force of 10 g to the maxillary first molar produced reliable tooth movement in mice. Mouse grimace scale (MGS) was evaluated as an indication of non-evoked spontaneous pain and bite force (BF) was measured for assessing bite-evoked nocifensive behaviors. Orthodontic force increased MGS and decreased BF, both of which were interpreted as increased levels of pain. These behaviors peaked at 1d and returned near to the sham level at 7d. Retrograde labeling and immunohistochemical assays showed TRPV1-expressing peptidergic afferents are abundantly projected to the periodontium. Direct injection of resiniferatoxin into trigeminal ganglia (TG) decreased TRPV1-expressing afferents by half in the targeted region of TG. The chemical ablation of TRPV1-expressing afferents significantly attenuated orthodontic pain behaviors assessed by MGS and BF. Consistently, the knockout of TRPV1 also attenuated orthodontic force-induced changes in MGS and BF. These results suggest that TRPV1 and TRPV1-expressing trigeminal nociceptors constitute a primary pathway mediating orthodontic pain behaviors in mice. This model will be useful for mechanistic studies on orthodontic pain aimed at developing novel approaches for painless orthodontics.

Transient receptor potential Vanilloid 1-based gene therapy alleviates orthodontic pain in rats

Orthodontic pain that is induced by tooth movement is an important sequela of orthodontic treatment and has a significant effect on patient quality of life. Studies have shown that the high expression of transient receptor potential vanilloid 1 (TRPV1) in trigeminal ganglions plays a vital role in the transmission and modulation of orofacial pain. However, little is known about the role of TRPV1 in orthodontic pain. In this study, male Sprague-Dawley rats were randomly assigned to six groups to study the role of TRPV1 in the modulation of tooth-movement pain. The expression levels of TRPV1 mRNA and protein were determined by real-time PCR and western blot, respectively. Moreover, pain levels were assessed using the rat grimace scale (RGS). The role of TRPV1 in modulating tooth-movement pain was examined by injecting a TRPV1 antagonist into the trigeminal ganglia of rats. A lentivirus containing a TRPV1 shRNA sequence was constructed and transduced into the rats' trigeminal ganglia. The results showed that the expression levels of TRPV1 protein and mRNA were elevated following tooth-movement pain. Pain levels increased rapidly on the 1st day, peaked on the 3rd day and returned to baseline on the 14th day. The TRPV1 antagonist significantly reduced tooth-movement pain. The lentivirus containing a TRPV1 shRNA sequence was able to inhibit the expression of TRPV1 and relieved tooth-movement pain. In conclusion, TRPV1-based gene therapy may be a treatment strategy for the relief of orthodontic pain.

Role of peripheral and central TRPV1 receptors in facial heat hyperalgesia in streptozotocin-induced diabetic rats

There is increasing evidence that diabetes may be related to sensory changes in the trigeminal system. Long lasting facial heat hyperalgesia has been described in diabetic rats, but the mechanisms remain to be elucidated. Herein, the contribution of peripheral and central TRPV1 receptors to facial heat hyperalgesia in diabeticrats was investigated. Diabetes was induced in male Wistar rats by streptozotocin (60mg/kg, i.p) and facial heat hyperalgesia was assessed once a week up to four weeks. The role of TRPV1 receptors in the heat hyperalgesia in diabetic rats was evaluated through: 1) the ablation of TRPV1 receptors by resiniferatoxin (RTX) treatment and 2) injection of the TRPV1 antagonist, capsazepine, into the upper lip, trigeminal ganglion or medullary subarachnoid space, at doses that completed prevented the heat hyperalgesia induced by capsaicin in naïve rats. Western blot was used to estimate the changes in TRPV1 expression in diabetic rats. Diabetic rats exhibited facial heat hyperalgesia from the first up to the fourth week after streptozotocin injection, which was prevented by insulin treatment. Ablation of TRPV1-expressing fibers prevented facial hyperalgesia in diabetic rats. Capsazepine injection in all sites resulted in significant reduction of facial heat hyperalgesia in diabetic rats. Diabetic rats exhibited a significant decrease in TRPV1 expression in the trigeminal nerve, increased expression in the trigeminal ganglion and no changes in subnucleus caudalis when compared to normoglycemic ones. In conclusion, our results suggest that facial heat hyperalgesia in diabetic rats is maintained by peripheral and central TRPV1 receptors activation.