TTX-R Na+ current-reduction by celecoxib correlates with changes in PGE2 and CGRP within rat DRG neurons during acute incisional pain

Neuroimmune Mechanisms Underlying Post-acute Sequelae of SARS-CoV-2 (PASC) Pain, Predictions from a Ligand-Receptor Interactome

PURPOSE OF REVIEW

Individuals with post-acute sequelae of SARS-CoV-2 (PASC) complain of persistent musculoskeletal pain. Determining how COVID-19 infection produces persistent pain would be valuable for the development of therapeutics aimed at alleviating these symptoms.

RECENT FINDINGS

To generate hypotheses regarding neuroimmune interactions in PASC, we used a ligand-receptor interactome to make predictions about how ligands from PBMCs in individuals with COVID-19 communicate with dorsal root ganglia (DRG) neurons to induce persistent pain. In a structured literature review of -omics COVID-19 studies, we identified ligands capable of binding to receptors on DRG neurons, which stimulate signaling pathways including immune cell activation and chemotaxis, the complement system, and type I interferon signaling. The most consistent finding across immune cell types was an upregulation of genes encoding the alarmins S100A8/9 and MHC-I. This ligand-receptor interactome, from our hypothesis-generating literature review, can be used to guide future research surrounding mechanisms of PASC-induced pain.

Unveiling Targets for Treating Postoperative Pain: The Role of the TNF-α/p38 MAPK/NF-κB/Nav1.8 and Nav1.9 Pathways in the Mouse Model of Incisional Pain

Although the mouse model of incisional pain is broadly used, the mechanisms underlying plantar incision-induced nociception are not fully understood. This work investigates the role of Na_v1.8 and Na_v1.9 sodium channels in nociceptive sensitization following plantar incision in mice and the signaling pathway modulating these channels. A surgical incision was made in the plantar hind paw of male Swiss mice. Nociceptive thresholds were assessed by von Frey filaments. Gene expression of Na_v1.8, Na_v1.9, TNF-α, and COX-2 was evaluated by Real-Time PCR in dorsal root ganglia (DRG). Knockdown mice for Na_v1.8 and Na_v1.9 were produced by antisense oligodeoxynucleotides intrathecal treatments. Local levels of TNF-α and PGE₂ were immunoenzymatically determined. Incised mice exhibited hypernociception and upregulated expression of Na_v1.8 and Na_v1.9 in DRG. Antisense oligodeoxynucleotides reduced hypernociception and downregulated Na_v1.8 and Na_v1.9. TNF-α and COX-2/PGE₂ were upregulated in DRG and plantar skin. Inhibition of TNF-α and COX-2 reduced hypernociception, but only TNF-α inhibition downregulated Na_v1.8 and Na_v1.9. Antagonizing NF-κB and p38 mitogen-activated protein kinase (MAPK), but not ERK or JNK, reduced both hypernociception and hyperexpression of Na_v1.8 and Na_v1.9. This study proposes the contribution of the TNF-α/p38/NF-κB/Na_v1.8 and Na_v1.9 pathways to the pathophysiology of the mouse model of incisional pain.

Simultaneous Determination of Tetrodotoxin in the Fresh and Heat-Processed Aquatic Products by High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Tetrodotoxin (TTX) was simultaneously detected in the fresh and heat-processed aquatic products by high-performance liquid chromatography-tandem mass spectrometry method. The detection conditions were investigated, including the chromatography column and mobile phase. Based on the optimized parameters, a sensitive determination method of TTX was established. The proposed method featured the merits of a good linear relationship between signal and TTX concentration (R2 = 0.9998), a wide detection matrix-based range of 0.2-100 ng/g, and a low detection limit of 0.2 ng/g, etc. The spiked assays evidenced its accuracy and reliability with recoveries of 90.5-107.2%. Finally, the developed method was simultaneously successfully applied in the determination of TTX in various fresh and heat-processed aquatic products.

Regulatory effects of non-steroidal anti-inflammatory drugs on cardiac ion channels Nav1.5 and Kv11.1

Non-steroidal Anti-inflammatory Drugs (NSAIDs) are widely used because of their excellent anti-inflammatory and analgesic effects. However, NSAIDs could cause certain cardiac side effects, such as myocardial infarction, heart failure, atrial fibrillation, arrhythmia and sudden cardiac death. Therefore, meloxicam, nimesulide, piroxicam, and diclofenac were selected and the whole cell patch clamp technique was used to investigate the electrophysiological regulatory effects of them on the sodium channel hNav1.5 and potassium channel hKv11.1, which were closely associated to the biotoxicity of cardiac, and to explore the potential cardiac risk mechanism. The results showed that the four NSAIDs could inhibit the peak currents of hNav1.5 and hKv11.1. Furthermore, the four NSAIDs could affect both the activation and inactivation processes of hNav1.5 with I-V curves left-shifted to hyperpolarized direction in activation phase. These data indicate that the inhibition effects of Nav1.5 and Kv11.1 by meloxicam, nimesulide, piroxicam, and diclofenac might contribute to their potential cardiac risk. These findings provide a basis for the discovery of other potential cardiac risk targets for NSAIDs.

Molecular mechanisms underlying the actions of arachidonic acid-derived prostaglandins on peripheral nociception

Arachidonic acid-derived prostaglandins not only contribute to the development of inflammation as intercellular pro-inflammatory mediators, but also promote the excitability of the peripheral somatosensory system, contributing to pain exacerbation. Peripheral tissues undergo many forms of diseases that are frequently accompanied by inflammation. The somatosensory nerves innervating the inflamed areas experience heightened excitability and generate and transmit pain signals. Extensive studies have been carried out to elucidate how prostaglandins play their roles for such signaling at the cellular and molecular levels. Here, we briefly summarize the roles of arachidonic acid-derived prostaglandins, focusing on four prostaglandins and one thromboxane, particularly in terms of their actions on afferent nociceptors. We discuss the biosynthesis of the prostaglandins, their specific action sites, the pathological alteration of the expression levels of related proteins, the neuronal outcomes of receptor stimulation, their correlation with behavioral nociception, and the pharmacological efficacy of their regulators. This overview will help to a better understanding of the pathological roles that prostaglandins play in the somatosensory system and to a finding of critical molecular contributors to normalizing pain.

Selective inhibition of CaV3.2 channels reverses hyperexcitability of peripheral nociceptors and alleviates postsurgical pain

Pain-sensing sensory neurons of the dorsal root ganglion (DRG) can become sensitized or hyperexcitable in response to surgically induced peripheral tissue injury. We investigated the potential role and molecular mechanisms of nociceptive ion channel dysregulation in acute pain conditions such as those resulting from skin and soft tissue incision. We used selective pharmacology, electrophysiology, and mouse genetics to link increased current densities arising from the Ca_V3.2 isoform of T-type calcium channels (T-channels) to nociceptive sensitization using a clinically relevant rodent model of skin and deep tissue incision. Furthermore, knockdown of the Ca_V3.2-targeting deubiquitinating enzyme USP5 or disruption of USP5 binding to Ca_V3.2 channels in peripheral nociceptors resulted in a robust antihyperalgesic effect in vivo and substantial T-current reduction in vitro. Our study provides mechanistic insight into the role of plasticity in Ca_V3.2 channel activity after surgical incision and identifies potential targets for perioperative pain that may greatly decrease the need for narcotics and potential for drug abuse.

The effect of a coix seed oil injection on cancer pain relief

BACKGROUND

Pain is one of the most commonly reported symptoms in patients with advanced cancer, but is still less than optimally treated. The effect of traditional Chinese medicine in cancer pain treatment is nowadays getting more and more attention.

OBJECTIVE

To investigate the effect of a coix seed oil injection on cancer pain relief in a cancer center in a tertiary hospital in China.

METHODS

Patients in the treatment group received a coix seed oil injection for 2 weeks, while patients in the control group received equivalent 0.9% saline. The numeric rating scale was used to assess the pain level. The Quality of Life Questionnaire-Core 30 was used to assess life quality. The adverse drug reactions during the treatment process were observed.

RESULTS

Patients in the coix seed treatment group had significantly superior efficacy on pain control over those in the control group. Coix seed therapy significantly improved patients' scores reflecting by the Quality of Life Questionnaire-Core 30 (QLQ-C30) scale. In addition, the occurrence of adverse reactions such as constipation and nausea in the treatment group was significantly lower than that in the control group.

CONCLUSION

The coix seed oil injection effectively reduced the pain level of cancer patients, significantly improved their life quality, and had no obvious adverse effects.

Effect of Rhizoma Paridis saponin on the pain behavior in a mouse model of cancer pain

Rhizoma Paridis saponins (RPS) as active parts of P. polyphylla Smith var. yunnanensis has been used as an anti-cancer drug in traditional Chinese medicine. In this study, RPS was first found to demonstrate a potent effect on markedly reducing the pain induced by cancer. Therefore, the aim of this study was to further explore the analgesic effect of RPS and its possible reaction pathway on H22 hepatocarcinoma cells inoculated in the hind right paw of mice. Cancer-induced pain model mice were randomly divided into 5 groups (n = 10) and orally administered with RPS (50–200 mg kg⁻¹) for 2 weeks. On the last day of treatment, the pain behavior of mice was measured using hot-plate test and open field test, and brain tissues were sampled for detection of biochemical indices, malondialdehyde (MDA), superoxide dismutase (SOD), prostaglandin E2 (PGE2), serotonin (5-HT) and β-endorphin (β-EP). Moreover, the concentrations of NF-κB and IL-1β in the blood serum were measured by ELISA reagent kits. In addition, naloxone, the non-selective antagonist of opioid receptors, was used to identify the opioid receptors involved in RPS's action. It has been found that RPS alleviates cancer pain mainly via the suppression of inflammatory pain induced by oxidative damage, such as decreasing MDA and PGE2 levels, renewing activity of SOD, as well as increasing 5-HT and β-EP in the brain and suppressing the expression of NF-κB and IL-1β in the serum in a concentration-dependent manner. Overall, the current study highlights that RPS has widespread potential antinociceptive effects on a mouse model of chronic cancer pain, which may be associated with the peripheral nervous system and the central nervous system.

Rhizoma Paridis saponins (RPS) as active parts of P. polyphylla Smith var. yunnanensis has been used as an anti-cancer drug in traditional Chinese medicine.

Local knockdown of Nav1.6 relieves pain behaviors induced by BmK I

Voltage-gated sodium channels (VGSCs) in peripheral nociceptive sensory neurons are critical to transmit pain signals. BmK I purified from the venom of scorpion Buthus martensi Karsch (BmK) has been demonstrated to be the primary contributor of envenomation-associated pain. However, the role of distinct VGSCs such as Nav1.6 in the induction and maintenance of pain behaviors induced by BmK I was ambiguous. Herein, using molecular and behavioral approaches we investigated the mRNA and protein expression profiles of Nav1.6 in rat DRG after intraplantar injection of BmK I and tested the pain behaviors after knockdown of Nav1.6 in BmK I-treated rats. It was shown that during induction and maintenance of pain responses induced by BmK I, the expression of Nav1.6 in DRG was found to be significantly increased at both mRNA and protein levels. The percentage of co-localization of Nav1.6 and Isolectin B4, a molecular marker of small diameter non-peptidergic DRG neurons, was increased at the maintenance phase of pain responses. Furthermore, spontaneous pain and mechanical allodynia, but not thermal hyperalgesia induced by BmK I, were significantly alleviated after knockdown of Nav1.6. These data strongly suggest that Nav1.6 plays an indispensable role in the peripheral pain hypersensitivity induced by BmK I.

Celecoxib and ion channels: a story of unexpected discoveries

Celecoxib (Celebrex), a highly popular selective inhibitor of cyclooxygenase-2, can modulate ion channels and alter functioning of neurons and myocytes at clinically relevant concentrations independently of cyclooxygenase inhibition. In experimental systems varying from Drosophila to primary mammalian and human cell lines, celecoxib inhibits many voltage-activated Na(+), Ca(2+), and K(+) channels, including NaV1.5, L- and T-type Ca(2+) channels, KV1.5, KV2.1, KV4.3, KV7.1, KV11.1 (hERG), while stimulating other K(+) channels-KV7.2-5 and, possibly, KV11.1 (hERG) channels under certain conditions. In this review, we summarize the information currently available on the effects of celecoxib on ion channels, examine mechanistic aspects of drug action and the concomitant changes at the cellular and organ levels, and discuss these findings in the therapeutic context.

The role of potassium channel activation in celecoxib-induced analgesic action

BACKGROUND AND PURPOSE

Celecoxib (CXB) is a widely prescribed COX-2 inhibitor used clinically to treat pain and inflammation. Recently, COX-2 independent mechanisms have been described to be the targets of CXB. For instance, ion channels such as the voltage-gated sodium channel, L-type calcium channel, Kv2.1, Kv1.5, Kv4.3 and HERG potassium channel were all reported to be inhibited by CXB. Our recent study revealed that CXB is a potent activator of Kv7/M channels. M currents expressed in dorsal root ganglia play an important role in nociception. Our study was aimed at establishing the role of COX-2 independent M current activation in the analgesic action of CXB.

METHODS AND RESULTS

We compared the effects of CXB and its two structural analogues, unmethylated CXB (UMC) and 2,5-dimethyl-CXB (DMC), on Kv7/M currents and pain behavior in animal models. UMC is a more potent inhibitor of COX-2 than CXB while DMC has no COX-2 inhibiting activity. We found that CXB, UMC and DMC concentration-dependently activated Kv7.2/7.3 channels expressed in HEK293 cells and the M-type current in dorsal root ganglia neurons, negatively shifted I-V curve of Kv7.2/7.3 channels, with a potency and efficiency inverse to their COX-2 inhibitory potential. Furthermore, CXB, UMC and DMC greatly reduced inflammatory pain behavior induced by bradykinin, mechanical pain behavior induced by stimulation with von Frey filaments and thermal pain behavior in the Hargreaves test. CXB and DMC also significantly attenuated hyperalgesia in chronic constriction injury neuropathic pain.

CONCLUSION

CXB, DMC and UMC are openers of Kv7/M K(+) channels with effects independent of COX-2 inhibition. The analgesic effects of CXBs on pain behaviors, especially those of DMC, suggest that activation of Kv7/M K(+) channels may play an important role in the analgesic action of CXB. This study strengthens the notion that Kv7/M K(+) channels are a potential target for pain treatment.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

Colonic inflammation up-regulates voltage-gated sodium channels in bladder sensory neurons via activation of peripheral transient potential vanilloid 1 receptors

BACKGROUND

Primary sensory neurons express several types of ion channels including transient receptor potential vanilloid 1 (TRPV1) and voltage-gated Na(+) channels. Our previous studies showed an increased excitability of bladder primary sensory and spinal neurons triggered by inflammation in the distal colon as a result of pelvic organ cross-sensitization. The goal of this work was to determine the effects of TRPV1 receptor activation by potent agonists and/or colonic inflammation on voltage-gated Na(+) channels expressed in bladder sensory neurons.

METHODS

Sprague-Dawley rats were treated with intracolonic saline (control), resiniferatoxin (RTX, 10(-7 ) mol L(-1)), TNBS (colonic irritant) or double treatment (RTX followed by TNBS).

KEY RESULTS

TNBS-induced colitis increased the amplitude of total Na(+) current by two-fold and of tetrodotoxin resistant (TTX-R) Na(+) current by 78% (P ≤ 0.05 to control) in lumbosacral bladder neurons during acute phase (3 days post-TNBS). Instillation of RTX in the distal colon caused an enhancement in the amplitude of total Na(+) current at -20 mV from -112.1 ± 18.7 pA/pF (control) to -183.6 ± 27.8 pA/pF (3 days post-RTX, P ≤ 0.05) without changes in TTX resistant component. The amplitude of net Na(+) current was also increased by 119% at day 3 in the group with double treatment (RTX followed by TNBS, P ≤ 0.05 to control) which was significantly higher than in either group with a single treatment.

CONCLUSIONS & INFERENCES

These results provide evidence that colonic inflammation activates TRPV1 receptors at the peripheral sensory terminals leading to an up-regulation of voltage gated Na(+) channels on the cell soma of bladder sensory neurons. This mechanism may underlie the occurrence of peripheral cross-sensitization in the pelvis and functional chronic pelvic pain.

Drug management of visceral pain: concepts from basic research

Visceral pain is experienced by 40% of the population, and 28% of cancer patients suffer from pain arising from intra- abdominal metastasis or from treatment. Neuroanatomy of visceral nociception and neurotransmitters, receptors, and ion channels that modulate visceral pain are qualitatively or quantitatively different from those that modulate somatic and neuropathic pain. Visceral pain should be recognized as distinct pain phenotype. TRPV1, Na 1.8, and ASIC3 ion channels and peripheral kappa opioid receptors are important mediators of visceral pain. Mu agonists, gabapentinoids, and GABAB agonists reduce pain by binding to central receptors and channels. Combinations of analgesics and adjuvants in animal models have supra-additive antinociception and should be considered in clinical trials. This paper will discuss the neuroanatomy, receptors, ion channels, and neurotransmitters important to visceral pain and provide a basic science rationale for analgesic trials and management.

Insights into the effects of diclofenac and other non-steroidal anti-inflammatory agents on ion channels

OBJECTIVES

Diclofenac and other non-steroidal anti-inflammatory drugs (NSAIDs) are widely used in the treatment of inflammation and pain. Most effects of NSAIDs are attributed to the inhibition of cyclooxygenases (COX). However, many NSAIDs may have other effects not related to COX, including the modulation of various ion channels. The clinical implications of the effects on channels are not fully understood. This review outlines the effects of NSAIDs, with special attention to diclofenac, on ion channels and highlights the possible underlying mechanisms.

KEY FINDINGS

NSAIDs have effects on channels such as inhibition, activation or changes in expression patterns. The channels affected include voltage-gated Na(+) , Ca(2+) , or K(+) channels, ligand-gated K(+) channels, transient receptor potential and other cation channels as well as chloride channels in several types of cells. The mechanisms of drug actions not related to COX inhibition may involve drug-channel interactions, interference with the generation of second messengers, changes in channel expression, or synergistic/antagonist interactions with other channel modulators.

SUMMARY

The effects on ion channels may account for novel therapeutic actions of NSAIDs or for adverse effects. Among the NSAIDs, diclofenac may serve as a template for developing new channel modulators and as a tool for investigating the actions of other drugs.

Targeting voltage-gated sodium channels for treatment for chronic visceral pain

Voltage-gated sodium channels (VGSCs) play a fundamental role in controlling cellular excitability, and their abnormal activity is related to several pathological processes, including cardiac arrhythmias, epilepsy, neurodegenerative diseases, spasticity and chronic pain. In particular, chronic visceral pain, the central symptom of functional gastrointestinal disorders such as irritable bowel syndrome, is a serious clinical problem that affects a high percentage of the world population. In spite of intense research efforts and after the dedicated decade of pain control and research, there are not many options to treat chronic pain conditions. However, there is a wealth of evidence emerging to give hope that a more refined approach may be achievable. By using electronic databases, available data on structural and functional properties of VGSCs in chronic pain, particularly functional gastrointestinal hypersensitivity, were reviewed. We summarize the involvement and molecular bases of action of VGSCs in the pathophysiology of several organic and functional gastrointestinal disorders. We also describe the efficacy of VGSC blockers in the treatment of these neurological diseases, and outline future developments that may extend the therapeutic use of compounds that target VGSCs. Overall, clinical and experimental data indicate that isoform-specific blockers of these channels or targeting of their modulators may provide effective and novel approaches for visceral pain therapy.