Increased capsaicin receptor TRPV1 nerve fibres in the inflamed human oesophagus

Neuroimmune modulation in liver pathophysiology

The liver, the largest organ in the human body, plays a multifaceted role in digestion, coagulation, synthesis, metabolism, detoxification, and immune defense. Changes in liver function often coincide with disruptions in both the central and peripheral nervous systems. The intricate interplay between the nervous and immune systems is vital for maintaining tissue balance and combating diseases. Signaling molecules and pathways, including cytokines, inflammatory mediators, neuropeptides, neurotransmitters, chemoreceptors, and neural pathways, facilitate this complex communication. They establish feedback loops among diverse immune cell populations and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems within the liver. In this concise review, we provide an overview of the structural and compositional aspects of the hepatic neural and immune systems. We further explore the molecular mechanisms and pathways that govern neuroimmune communication, highlighting their significance in liver pathology. Finally, we summarize the current clinical implications of therapeutic approaches targeting neuroimmune interactions and present prospects for future research in this area.

Role of Mast Cells in Eosinophilic Gastrointestinal Diseases

Mast cells play a central role in the pathogenesis of eosinophilic gastrointestinal disorders (EGIDs), including eosinophilic esophagitis. Their interactions with immune and structural cells, involvement in tissue remodeling, and contribution to symptoms make them attractive targets for therapeutic intervention. More is being discovered regarding the intricate interplay of mast cells and eosinophils. Recent studies demonstrating that depletion of eosinophils is insufficient to improve symptoms of EGIDs have raised the question of whether other cells may play a role in symptomatology and pathogenesis of EGIDs.

Comprehensive insights into the multifaceted roles of the transient receptor potential vanilloid 1 channel in the digestive system

The transient receptor potential vanilloid (TRPV) channel, a family of calcium transporters comprising six distinct members (TRPV1-6), takes on a paramount role in maintaining intracellular Ca2+ homeostasis in mammalian cells. Notably, TRPV1, among its counterparts, has emerged as the subject of extensive scrutiny, owing to its pervasive presence in diverse cellular, tissue, and organ settings. This ubiquitous distribution underscores its fundamental involvement in the genesis of pain, making it a central focus in pain-related research. However, recent investigations have unveiled that TRPV1's functional significance transcends the realm of pain modulation, extending its influence to encompass a wide spectrum of physiological and pathological processes. The ambit of TRPV1's influence encompasses not only pain responses but also embraces the intricate domains of nervous system disorders, cancer metastasis, as well as afflictions pertaining to the skin and heart. Moreover, compelling evidence now demonstrates that TRPV1 also wields substantial sway in the domain of digestive diseases, further highlighting its versatility and far-reaching impact on human health. Therefore, this comprehensive review endeavors to delve into the multifaceted roles played by TRPV1 in the various organs constituting the digestive system.

Esophageal Reflux Hypersensitivity: A Comprehensive Review

Reflux hypersensitivity (RH) is one of the phenotypes of gastroesophageal reflux disease. The latest Rome IV defines RH as a condition with typical reflux symptoms and positive reflux-symptom association despite normal acid exposure. Subsequently, the Lyon consensus proposed detailed cutoff values for the criteria on the basis of experts' consensus. Rome IV brought a clear-cut perspective into the pathophysiology of gastroesophageal reflux disease and the importance of esophageal hypersensitivity. This perspective can be supported by the fact that other functional gastrointestinal disorders such as irritable bowel syndrome and functional dyspepsia often overlap with RH. Although several possible pathophysiological mechanisms of esophageal hypersensitivity have been identified, there is still unmet medical needs in terms of treatment for this condition. This review summarizes the current knowledge regarding RH.

Revisiting the Role of Esophageal Mucosal Dilated Intercellular Spaces in the Diagnosis and Pathophysiology of Heartburn

Background/Aims

Dilated intercellular spaces (DISs) facilitate the diffusion of noxious agents into the deep layers of the esophageal epithelium. The role of DIS in heartburn pathogenesis is still controversial. Therefore, we aim to reinvestigate DIS in an extensively evaluated group of patients and healthy controls (HCs).

Methods

We classified 149 subjects into the following groups: 15 HC, 58 mild erosive reflux disease (ERD), 17 severe ERD, 25 nonerosive reflux disease (NERD), 15 reflux hypersensitivity (RH), and 19 functional heartburn (FH). A total of 100 length measurements were performed for each patient's biopsy.

Results

The overall intercellular spaces (ISs) value of gastroesophageal reflux disease (GERD) patients was higher than that of HC (P = 0.020). In phenotypes, mild ERD (vs HC [P = 0.036], NERD [P = 0.004], RH [P = 0.014]) and severe ERD (vs HC [P = 0.002], NERD [P < 0.001], RH [P = 0.001], FH [P = 0.004]) showed significantly higher IS. There was no significant difference between the HC, NERD, RH, and FH groups. The 1.12 μm DIS cutoff value had 63.5% sensitivity and 66.7% specificity in the diagnosis of GERD. There was a weak correlation (r = 0.302) between the IS value and acid exposure time, and a weak correlation (r = -0.359) between the IS value and baseline impedance. A strong correlation was shown between acid exposure time and baseline impedance (r = -0.783).

Conclusions

Since the IS length measurement had better discrimination power only in erosive groups, it is not feasible to use in daily routine to discriminate other nonerosive phenotypes and FH. The role of DIS in heartburn in nonerosive patients should be reconsidered.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Sensory Phenotype of the Oesophageal Mucosa in Gastro-Oesophageal Reflux Disease

Gastroesophageal reflux disease (GORD) affects up to 20% of Western populations, yet sensory mechanisms underlying heartburn pathogenesis remain incompletely understood. While central mechanisms of heartburn perception have been established in earlier studies, recent studies have highlighted an important role of neurochemical, inflammatory, and cellular changes occurring in the oesophageal mucosa itself. The localization and neurochemical characterisation of sensory afferent nerve endings differ among GORD phenotypes, and could explain symptom heterogeneity among patients who are exposed to similar levels of reflux. Acid-induced stimulation of nociceptors on pain-sensing nerve endings can regulate afferent signal transmission. This review considers the role of peripheral mechanisms of sensitization in the amplification of oesophageal sensitivity in patients with GORD.

Mechanism and potential treatments for gastrointestinal dysfunction in patients with COVID-19

The global coronavirus disease 2019 (COVID-19) has become one of the biggest threats to the world since 2019. The respiratory and gastrointestinal tracts are the main targets for severe acute respiratory syndrome coronavirus 2 infection for they highly express angiotensin-converting enzyme-2 and transmembrane protease serine 2. In patients suffering from COVID-19, gastrointestinal symptoms have ranged from 12% to 61%. Anorexia, nausea and/or vomiting, diarrhea, and abdominal pain are considered to be the main gastrointestinal symptoms of COVID-19. It has been reported that the direct damage of intestinal mucosal epithelial cells, malnutrition, and intestinal flora disorders are involved in COVID-19. However, the underlying mechanisms remain unclear. Thus, in this study, we reviewed and discussed the correlated mechanisms that cause gastrointestinal symptoms in order to help to develop the treatment strategy and build an appropriate guideline for medical workers.

The Endocannabinoid Analgesic Entourage Effect: Investigations in Cultured DRG Neurons

BACKGROUND

The endocannabinoid 2-Arachidonyl glycerol (2-AG) exerts dose-related anti-nociceptive effects, which are potentiated by the related but inactive 2-palmitoyl glycerol (2-PG) and 2-linoleoyl glycerol (2-LG). This potentiation of analgesia and other in vivo measures was described as the "entourage effect". We investigated this effect on TRPV1 signalling in cultured dorsal root ganglion (DRG) nociceptors.

METHODS

Adult rat DRG neurons were cultured in medium containing NGF and GDNF at 37°C. 48 h later cultures were loaded with 2 µM Fura2AM for calcium imaging, and treated with 2-AG, 2-PG and 2-LG, individually or combined, for 5 min, followed by 1 µMol capsaicin. The amplitude and latency of capsaicin responses were measured (N=3-7 rats, controls N=16), and analysed.

RESULTS

In controls, 1 µMol capsaicin elicited immediate calcium influx in a subset of neurons, with average latency of 1.27 ± 0.2 s and amplitude of 0.15 ± 0.01 Units. 2-AG (10-100 µMol) elicited calcium influx in some neurons. In the presence of 2-AG (0.001-100 µMol), capsaicin responses were markedly delayed in 64% neurons by up to 320 s (P<0.001). 2-PG increased capsaicin response latency at 0.1 nMol-100 µMol (P<0.001), in 60% neurons, as did 2-LG at 0.1-100 µMol (P<0.001), in 76% neurons. Increased capsaicin response latency due to 2-AG and 2-PG was sensitive to the CB2 but not to the CB1 receptor antagonist. Combined application of 1 µMol 2-AG, 5 µMol 2-PG and 10 µMol 2-LG, also resulted in significantly increased capsaicin response latency up to 281.5 ± 41.5 s (P<0.001), in 96% neurons, that was partially restored by the CB2, but not the CB1 antagonist.

CONCLUSION

2-AG, 2-LG and 2-PG significantly delayed TRPV1 signalling in the majority of capsaicin-sensitive DRG neurons, that was markedly increased following combined application. Further studies of these endocannabinoids are required to identify the underlying mechanisms.

Physiological and Pathological Significance of Esophageal TRP Channels: Special Focus on TRPV4 in Esophageal Epithelial Cells

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel that is broadly expressed in different human tissues, including the digestive system, where it acts as a molecular sensor and a transducer that regulates a variety of functional activities. Despite the extensive research to determine the role of this channel in the physiology and pathophysiology of different organs, the unique morphological and functional features of TRPV4 in the esophagus remain largely unknown. Ten years ago, TRPV4 was shown to be highly expressed in esophageal epithelial cells where its activation induces Ca²⁺-dependent ATP release, which, in turn, mediates several functions, ranging from mechanosensation to wound healing. This review summarizes the research progress on TRPV4, and focuses on the functional expression of TRPV4 in esophageal epithelium and its possible role in different esophageal diseases that would support TRPV4 as a candidate target for future therapeutic approaches to treat patients with these conditions.

Pathophysiology of Pediatric Gastroesophageal Reflux Disease: Similarities and Differences With Adults

Gastroesophageal reflux (GOR) is defined as "the passage of gastric contents into the esophagus with or without regurgitation and vomiting" and gastroesophageal reflux disease (GORD) is defined "when GOR leads to troublesome symptoms affecting the daily functioning and/or complications." This definition was first developed in 2006 by the Montreal consensus group (1) and later on adopted by pediatric gastroenterology societies such as ESPGHAN and NASPGHAN in 2009 (2). The definition of gastroesophageal reflux reveals little about its pathophysiology and is focused on symptomatology. In this way, it acts as an umbrella term for the multifactorial causes of the disease and the various phenotypes encountered; from functional heartburn to hypersensitive esophagus and nonerosive reflux disease, to erosive esophagitis and Barrett's esophagus. This article is devoted to the pathophysiology of pediatric GORD in comparison to adult GORD and is divided in 2 parts. In the first part, we will systematically describe the different mechanisms for the generation and clearance of reflux events, while on the second part we will discuss the mechanisms involved in symptoms generation. Finally, we will discuss the similarities and differences between pediatric and adult GORD.

Analgesic effects of Phα1β toxin: a review of mechanisms of action involving pain pathways

Phα1β is a neurotoxin purified from spider venom that acts as a high-voltage-activated (HVA) calcium channel blocker. This spider peptide has shown a high selectivity for N-type HVA calcium channels (NVACC) and an analgesic effect in several animal models of pain. Its activity was associated with a reduction in calcium transients, glutamate release, and reactive oxygen species production from the spinal cord tissue and dorsal ganglia root (DRG) in rats and mice. It has been reported that intrathecal (i.t.) administration of Phα1β to treat chronic pain reverted opioid tolerance with a safer profile than ω-conotoxin MVIIA, a highly selective NVACC blocker. Following a recent development of recombinant Phα1β (CTK 01512-2), a new molecular target, TRPA1, the structural arrangement of disulphide bridges, and an effect on glial plasticity have been identified. CTK 01512-2 reproduced the antinociceptive effects of the native toxin not only after the intrathecal but also after the intravenous administration. Herein, we review the Phα1β antinociceptive activity in the most relevant pain models and its mechanisms of action, highlighting the impact of CTK 01512-2 synthesis and its potential for multimodal analgesia.

The Dilemma of Persistent Irritable Bowel Syndrome Symptoms in Patients with Quiescent Inflammatory Bowel Disease

Irritable bowel syndrome and inflammatory bowel disease differ in their natural evolution, etiopathogenesis, diagnostic criteria, and therapeutic approach. However, recent evidence has suggested some similarities in mechanisms underlying symptom development and progression. There is a relevant role for alterations in the microbiome-brain-gut axis in both diseases. The presence of irritable bowel syndrome symptoms in patients with quiescent inflammatory bowel disease is common in clinical practice. To determine the cause of irritable bowel syndrome symptoms in patients with quiescent inflammatory bowel disease is a clinical challenge. This review aims to illustrate possible causes and solutions for these patients.

Esophageal Mucosa Innervation in Children With Nonerosive Reflux Disease

INTRODUCTION

Esophageal mucosa innervation in adults with nonerosive reflux disease (NERD) is more superficial compared with healthy volunteers. We delineated the esophageal mucosal innervation in pediatric NERD and controls.

METHODS

Distal and proximal pediatric esophageal biopsies were immunohistochemically stained with calcitonin gene-related peptide and transient receptor potential cation channel subfamily V member 1.

RESULTS

Mucosal innervation was assessed in 18 controls (9M:9F, median age: 9 years) and 11 NERD patients (6M:5F, median age: 5 years). Calcitonin gene-related peptide positive nerve fibers were lying deep in the mucosa in both groups, P > 0.05 and did not coexpress transient receptor potential cation channel subfamily V member 1.

DISCUSSION

The pediatric esophageal mucosa in NERD displays deep lying nerve fibers, in contrast to adults.

Esophageal afferent innervation and its role in gastro-esophageal reflux disease symptoms

PURPOSE OF REVIEW

Despite the wide prevalence of gastro-esophageal reflux disease (GERD), the neurophysiological mechanisms underlying heartburn perception in the esophagus of patients with GERD remains incompletely understood. Recent studies have highlighted the potential influence sensory afferent nerves innervating the oesophageal epithelium may have on heartburn pathogenesis. The purpose of this review is to consider the current understanding of esophageal afferent neuronal innervation, including the nociceptive role of acid-sensing receptors expressed on these sensory nerves, in relation to pain perception in the esophagus of GERD patients.

RECENT FINDINGS

Central and peripheral pathways of sensitization following noxious stimulation of nociceptive receptors expressed on afferent nerves can regulate the strength of sensory nerve activation in the esophagus, which can result in the amplification or suppression of afferent signal transmission. The localization and characterization of mucosal sensory afferent nerves vary between GERD phenotypes and may explain the heterogeneity of symptom perception in patients with apparently similar levels of reflux.

SUMMARY

In this review, we discuss the relevance of afferent esophageal innervation in heartburn perception, with a particular focus on the pathways of reflux-induced activation of nociceptive nerves.

Capsaicin-Sensitive Vagal Afferent Nerve-Mediated Interoceptive Signals in the Esophagus

Heartburn and non-cardiac chest pain are the predominant symptoms in many esophageal disorders, such as gastroesophageal reflux disease (GERD), non-erosive reflux disease (NERD), functional heartburn and chest pain, and eosinophilic esophagitis (EoE). At present, neuronal mechanisms underlying the process of interoceptive signals in the esophagus are still less clear. Noxious stimuli can activate a subpopulation of primary afferent neurons at their nerve terminals in the esophagus. The evoked action potentials are transmitted through both the spinal and vagal pathways to their central terminals, which synapse with the neurons in the central nervous system to induce esophageal nociception. Over the last few decades, progress has been made in our understanding on the peripheral and central neuronal mechanisms of esophageal nociception. In this review, we focus on the roles of capsaicin-sensitive vagal primary afferent nodose and jugular C-fiber neurons in processing nociceptive signals in the esophagus. We briefly compare their distinctive phenotypic features and functional responses to mechanical and chemical stimulations in the esophagus. Then, we summarize activation and/or sensitization effects of acid, inflammatory cells (eosinophils and mast cells), and mediators (ATP, 5-HT, bradykinin, adenosine, S1P) on these two nociceptive C-fiber subtypes. Lastly, we discuss the potential roles of capsaicin-sensitive esophageal afferent nerves in processing esophageal sensation and nociception. A better knowledge of the mechanism of nociceptive signal processes in primary afferent nerves in the esophagus will help to develop novel treatment approaches to relieve esophageal nociceptive symptoms, especially those that are refractory to proton pump inhibitors.

TRP channels in COVID-19 disease: Potential targets for prevention and treatment

Coronavirus disease 2019 [COVID-19] is a global health threat caused by severe acute respiratory syndrome coronavirus 2 [SARS-CoV2] that requires two proteins for entry: angiotensin-converting enzyme 2 [ACE2] and -membrane protease serine 2 [TMPRSS2]. Many patients complain from pneumonia, cough, fever, and gastrointestinal (GI) problems. Notably, different TRP channels are expressed in various tissues infected by SARS-CoV-2. TRP channels are cation channels that show a common architecture with high permeability to calcium [Ca²⁺] in most sub-families. Literature review shed light on the possible role of TRP channels in COVID-19 disease. TRP channels may take part in inflammation, pain, fever, anosmia, ageusia, respiratory, cardiovascular, GI and neurological complications related to COVID-19. Also, TRP channels could be the targets for many active compounds that showed effectiveness against SARS-CoV-2. Desensitization or blocking TRP channels by antibodies, aptamers, small molecules or venoms can be an option for COVID-19 prevention and future treatment. This review provides insights into the involvement of TRP channels in different symptoms and mechanisms of SARS-CoV-2 , potential treatments targeting these channels and highlights missing gaps in literature.

Irritable Bowel Syndrome in Inflammatory Bowel Disease. Synergy in alterations of the gut-brain axis?

The presence of digestive symptoms associated with irritable bowel syndrome (IBS) in patients with inflammatory bowel disease (IBD) in remission is a topic of growing interest. Although there is heterogeneity in clinical studies regarding the use of IBD remission criteria and the diagnosis of IBS, the available data indicate that the IBD-IBS overlap would affect up to one third of patients in remission, and they agree on the finding of a negative impact on the mental health and quality of life of the individuals who suffer from it. The pathophysiological bases that would explain this potential overlap are not completely elucidated; however, an alteration in the gut-brain axis associated with an increase in intestinal permeability, neuroimmune activation and dysbiosis would be common to both conditions. The hypothesis of a new clinical entity or syndrome of "Irritable Inflammatory Bowel Disease" or "Post-inflammatory IBS" is the subject of intense investigation. The clinical approach is based on certifying the remission of IBD activity and ruling out other non-inflammatory causes of potentially treatable persistent functional digestive symptoms. In the case of symptoms associated with IBS and in the absence of sufficient evidence, comprehensive and personalized management of the clinical picture (dietary, pharmacological and psychotherapeutic measures) should be carried out, similar to a genuine IBS.

Heartburn sensation in nonerosive reflux disease: pattern of superficial sensory nerves expressing TRPV1 and epithelial cells expressing ASIC3 receptors

The underlying causes of heartburn, characteristic symptom of gastroesophageal reflux disease (GERD), remain incompletely understood. Superficial afferent innervation of the esophageal mucosa in nonerosive reflux disease (NERD) may drive nociceptive reflux perception, but its acid-sensing role has not yet been established. Transient receptor potential vanilloid subfamily member-1 (TRPV1), transient receptor potential melastatin 8 (TRPM8), and acid-sensing ion channel 3 (ASIC3) are regulators of sensory nerve activity and could be important reflux-sensing receptors within the esophageal mucosa. We characterized TRPV1, TRPM8, and ASIC3 expression in esophageal mucosa of patients with GERD. We studied 10 patients with NERD, 10 with erosive reflux disease (ERD), 7 with functional heartburn (FH), and 8 with Barrett's esophagus (BE). Biopsies obtained from the distal esophageal mucosa were costained with TRPV1, TRPM8, or ASIC3, and CGRP, CD45, or E-cadherin. RNA expression of TRPV1, TRPM8, and ASIC3 was assessed using qPCR. Patients with NERD had significantly increased expression of TRPV1 on superficial sensory nerves compared with ERD (P = 0.028) or BE (P = 0.017). Deep intrapapillary nerve endings did not express TRPV1 in all phenotypes studied. ASIC3 was exclusively expressed on epithelial cells most significantly in patients with NERD and ERD (P ≤0.0001). TRPM8 was expressed on submucosal CD45+ leukocytes. Superficial localization of TRPV1-immunoreactive nerves in NERD, and increased ASIC3 coexpression on epithelial cells in NERD and ERD, suggests a mechanism for heartburn sensation. Esophageal epithelial cells may play a sensory role in acid reflux perception and act interdependently with TRPV1-expressing mucosal nerves to augment hypersensitivity in patients with NERD, raising the enticing possibility of topical antagonists for these ion channels as a therapeutic option.NEW & NOTEWORTHY We demonstrate for the first time that increased pain perception in patients with nonerosive reflux disease likely results from expression of acid-sensitive channels on superficial mucosal afferents and esophageal epithelial cells, raising the potential for topical therapy.

Effect of dural inflammatory soup application on activation and sensitization markers in the caudal trigeminal nucleus of the rat and the modulatory effects of sumatriptan and kynurenic acid

Background

The topical inflammatory soup can model the inflammation of the dura mater causing hypersensitivity and activation of the trigeminal system, a phenomenon present in migraineurs. Calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase are important in the sensitization process there.

5-HT_1B/1D receptor agonists, triptans are used as a treatment of migraine. Kynurenic acid an NMDA antagonist can act on structures involved in trigeminal activation.

Aim

We investigated the effect of inflammatory soup induced dural inflammation on the calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase levels in the caudal trigeminal nucleus. We also tested whether pretreatment with a well-known antimigraine drug, such as sumatriptan and kynurenic acid, a compound with a different mechanism of action, can affect these changes and if their modulatory effects are comparable.

Material and methods

After subcutaneous sumatriptan or intraperitoneal kynurenic acid the dura mater of adult male Sprague-Dawley rats (n = 72) was treated with inflammatory soup or its vehicle (synthetic interstitial fluid). Two and a half or four hours later perfusion was performed and the caudal trigeminal nucleus was removed for immunohistochemistry.

Results and conclusion

Inflammatory soup increased calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase in the caudal trigeminal nucleus compared to placebo, which was attenuated by sumatriptan and kynurenic acid. This suggests the involvement of 5-HT_1B/1D and NMDA receptors in neurogenic inflammation development of the dura and thus in migraine attacks.

Capsaicin 8% patch Qutenza and other current treatments for neuropathic pain in chemotherapy-induced peripheral neuropathy (CIPN)

PURPOSE OF REVIEW

Current oral treatments for neuropathic pain associated with chemotherapy-induced peripheral neuropathy (CIPN) have limited clinical efficacy, and undesirable side-effects. Topically delivered treatments have the advantage of avoiding CNS side-effects, while relieving pain. We have reviewed treatments of neuropathic pain associated with CIPN, focusing on the Capsaicin 8% patch, which can provide pain relief for up to 3 months or longer after a single 30-60-min application.

RECENT FINDINGS

Capsaicin 8% patch is a licensed treatment in the EU/UK for neuropathic pain and shown to be safe and effective in providing pain relief for patients with CIPN. Repeated daily oral or topical administrations are not required, as with other current treatments. The side-effects are transient and restricted to the time around patch application. New evidence suggests the Capsaicin 8% patch can promote the regeneration and restoration of skin nerve fibres in CIPN, in addition to the pain relief.

SUMMARY

The Capsaicin 8% patch is now often a preferred a treatment option for localised neuropathic pain conditions, including the feet and hands in patients with CIPN. Capsaicin 8% patch can be repeated three-monthly, if needed, for a year. In addition to pain relief, it may have a disease-modifying effect.

Gain of Function of Ion Channel TRPV1 Exacerbates Experimental Colitis by Promoting Dendritic Cell Activation

Dysregulated mucosal immunity plays an essential role in the pathophysiology of inflammatory bowel disease (IBD). Transient receptor potential vanilloid 1 (TRPV1) is a Ca²⁺-permeable ion channel that is implicated in modulating immune responses. However, its role in the pathogenesis of intestinal inflammation remains elusive. Here, we found that TRPV1 gain of function significantly increased the susceptibility of mice to experimental colitis, and that was associated with excessive recruitment of dendritic cells and enhanced Th17 immune responses in the lamina propria of colon. TRPV1 gain of function promoted dendritic cell activation and cytokine production upon inflammatory stimuli, and consequently enhanced dendritic cell-mediated Th17 cell differentiation. Further mechanistic studies showed that TRPV1 gain of function in dendritic cells enhanced activation of calcineurin/nuclear factor of activated T cells (NFATc2) signaling induced by inflammatory stimuli. Moreover, in patients with IBD, TRPV1 expression was increased in lamina propria cells of inflamed colon compared with healthy controls. Our findings identify an important role for TRPV1 in modulating dendritic cell activation and sustaining Th17 responses to inflammatory stimuli, which suggest that TRPV1 might be a potential therapeutic target in controlling mucosal immunity and IBD.

Neural control of gut homeostasis

The gut-brain axis is a coordinated communication system that not only maintains homeostasis, but significantly influences higher cognitive functions and emotions, as well as neurological and behavioral disorders. Among the large populations of sensory and motor neurons that innervate the gut, insights into the function of primary afferent nociceptors, whose cell bodies reside in the dorsal root ganglia and nodose ganglia, have revealed their multiple crosstalk with several cell types within the gut wall, including epithelial, vascular, and immune cells. These bidirectional communications have immunoregulatory functions, control host response to pathogens, and modulate sensations associated with gastrointestinal disorders, through activation of immune cells and glia in the peripheral and central nervous system, respectively. Here, we will review the cellular and neurochemical basis of these interactions at the periphery, in dorsal root ganglia, and in the spinal cord. We will discuss the research gaps that should be addressed to get a better understanding of the multifunctional role of sensory neurons in maintaining gut homeostasis and regulating visceral sensitivity.

Mucosal pathogenesis in gastro-esophageal reflux disease

BACKGROUND

Despite gastro-esophageal reflux disease affecting up to 20% of Western populations, relatively little is known about the molecular mechanisms underlying its most troublesome symptom: heartburn. Recent findings have unveiled the role of components of the esophageal mucosa in the pathogenesis of GERD including sensory nociceptive nerves and inflammatory mediators. Erosive esophagitis was long believed to develop as a result of acid injury at the esophageal lumen, but novel concepts suggest the generation of reflux-induced esophageal injury as a result of cytokine-mediated inflammation. Moreover, the localization and characterization of mucosal afferent nerves vary between GERD phenotypes and could explain the heterogeneity of symptom perception between patients who experience similar levels of acid reflux.

PURPOSE

The purpose of this review is to consider the crosstalk of different factors of the esophageal mucosa in the pathogenesis of GERD, with a particular focus on mucosal innervation and molecular basis of acid-induced cytokine response. We discuss the current understanding of the mucosal response to acid injury, the nociceptive role of acid-sensitive receptors expressed in the esophageal mucosa, and the role of esophageal epithelial cells in initiating the onset of erosive esophagitis.

Involvement of Neural Transient Receptor Potential Channels in Peripheral Inflammation

Transient receptor potential (TRP) channels are a superfamily of non-selective cation channels that act as polymodal sensors in many tissues throughout mammalian organisms. In the context of ion channels, they are unique for their broad diversity of activation mechanisms and their cation selectivity. TRP channels are involved in a diverse range of physiological processes including chemical sensing, nociception, and mediating cytokine release. They also play an important role in the regulation of inflammation through sensory function and the release of neuropeptides. In this review, we discuss the functional contribution of a subset of TRP channels (TRPV1, TRPV4, TRPM3, TRPM8, and TRPA1) that are involved in the body’s immune responses, particularly in relation to inflammation. We focus on these five TRP channels because, in addition to being expressed in many somatic cell types, these channels are also expressed on peripheral ganglia and nerves that innervate visceral organs and tissues throughout the body. Activation of these neural TRP channels enables crosstalk between neurons, immune cells, and epithelial cells to regulate a wide range of inflammatory actions. TRP channels act either through direct effects on cation levels or through indirect modulation of intracellular pathways to trigger pro- or anti-inflammatory mechanisms, depending on the inflammatory disease context. The expression of TRP channels on both neural and immune cells has made them an attractive drug target in diseases involving inflammation. Future work in this domain will likely yield important new pathways and therapies for the treatment of a broad range of disorders including colitis, dermatitis, sepsis, asthma, and pain.

Vagus Nerves Provide a Robust Afferent Innervation of the Mucosa Throughout the Body of the Esophagus in the Mouse

The vagal afferent nerves regulate swallowing and esophageal motor reflexes. However, there are still gaps in the understanding of vagal afferent innervation of the esophageal mucosa. Anatomical studies found that the vagal afferent mucosal innervation is dense in the upper esophageal sphincter area but rare in more distal segments of the esophagus. In contrast, electrophysiological studies concluded that the vagal afferent nerve fibers also densely innervate mucosa in more distal esophagus. We hypothesized that the transfection of vagal afferent neurons with adeno-associated virus vector encoding green fluorescent protein (AAV-GFP) allows to visualize vagal afferent nerve fibers in the esophageal mucosa in the mouse. AAV-GFP was injected into the vagal jugular/nodose ganglia in vivo to sparsely label vagal afferent nerve fibers. The esophageal tissue was harvested 4-6 weeks later, the GFP signal was amplified by immunostaining, and confocal optical sections of the entire esophagi were obtained. We found numerous GFP-labeled fibers in the mucosa throughout the whole body of the esophagus. The GFP-labeled mucosal fibers were located just beneath the epithelium, branched repeatedly, had mostly longitudinal orientation, and terminated abruptly without forming terminal structures. The GFP-labeled mucosal fibers were concentrated in random areas of various sizes in which many fibers could be traced to a single parental axon. We conclude that the vagus nerves provide a robust afferent innervation of the mucosa throughout the whole body of the esophagus in the mouse. Vagal mucosal fibers may contribute to the sensing of intraluminal content and regulation of swallowing and other reflexes.

Mechanism and Pathophysiology of Gastroesophageal Reflux Disease

Gastroesophageal reflux (GER) describes a process in which gastric contents travel retrograde into the esophagus. GER can be either a physiologic phenomenon that occurs in asymptomatic individuals or can potentially cause symptoms. When the latter occurs, this represents GER disease (GERD). The process by which GER transforms into GERD begins at the esophagogastric junction. Impaired clearance of the refluxate also contributes to GERD. Reflux causes degradation of esophageal mucosal defense. The refluxate triggers sensory afferents leading to symptom generation.

Novel Therapies for Gastroesophageal Reflux Disease: Beyond Proton Pump Inhibitors

PURPOSE OF REVIEW

Despite the many areas of unmet needs in gastroesophageal reflux disease (GERD), proton pump inhibitors (PPIs) remain the cornerstone of medical therapy. However, since their introduction, the therapeutic limitations of PPIs in GERD management have been increasingly recognized.

RECENT FINDINGS

In this review we discuss the new medical, endoscopic, and surgical therapeutic modalities that have been developed over the last decade. They include the potassium-competitive acid blockers (P-CABs) which provide a rapid onset, prolonged, and profound acid suppression, mucosal protectants which promote the physiological protective barrier of the esophageal mucosa, new prokinetics and neuromodulators. There are growing numbers of novel therapeutic endoscopic techniques that are under investigation or were recently introduced into the market, further expanding our therapeutic armamentarium for GERD. The development of diverse therapeutic modalities for GERD, despite the availability of PPIs, suggests that there are many areas of unmet need in GERD that will continue and drive future exploration for novel therapies.

The infusion of menthol into the esophagus evokes cold sensations in healthy subjects but induces heartburn in patients with gastroesophageal reflux disease (GERD)

Recent studies in animal models have reported that some afferent fibers innervating the esophagus express the cold receptor TRPM8. In the somatosensory system the stimulation of TRPM8 leads to cold sensations and in certain circumstances alleviates pain. It is therefore hypothesized in this paper that the esophageal infusion of the TRPM8 activator menthol evokes cold sensations from the esophagus and alleviates heartburn in humans. The esophageal infusion of menthol (3 mM, 20 min) evoked cold sensations in 11 of 12 healthy subjects. In striking contrast, the esophageal infusion of menthol evoked heartburn in 10 of 10 patients with gastroesophageal reflux disease (GERD). In healthy subjects the cold sensation evoked by menthol was perceived only as a minor discomfort as evaluated by the visual analog scale (VAS score 1.9 ± 0.3 on the scale 1-10). However, in patients with GERD the menthol-induced heartburn was perceived as painful (VAS score 5.6 ± 0.6, P < 0.01 compared to healthy subjects). It is concluded that the sensations evoked by esophageal infusion of menthol change from relatively nonpainful cold sensations in healthy subjects to painful heartburn sensations in patients with GERD. These qualitative and quantitative changes indicate substantial alterations in afferent signaling mediating sensations from the esophagus in patients with GERD.

Marine Toxins and Nociception: Potential Therapeutic Use in the Treatment of Visceral Pain Associated with Gastrointestinal Disorders

Visceral pain, of which the pathogenic basis is currently largely unknown, is a hallmark symptom of both functional disorders, such as irritable bowel syndrome, and inflammatory bowel disease. Intrinsic sensory neurons in the enteric nervous system and afferent sensory neurons of the dorsal root ganglia, connecting with the central nervous system, represent the primary neuronal pathways transducing gut visceral pain. Current pharmacological therapies have several limitations, owing to their partial efficacy and the generation of severe adverse effects. Numerous cellular targets of visceral nociception have been recognized, including, among others, channels (i.e., voltage-gated sodium channels, VGSCs, voltage-gated calcium channels, VGCCs, Transient Receptor Potential, TRP, and Acid-sensing ion channels, ASICs) and neurotransmitter pathways (i.e., GABAergic pathways), which represent attractive targets for the discovery of novel drugs. Natural biologically active compounds, such as marine toxins, able to bind with high affinity and selectivity to different visceral pain molecular mediators, may represent a useful tool (1) to improve our knowledge of the physiological and pathological relevance of each nociceptive target, and (2) to discover therapeutically valuable molecules. In this review we report the most recent literature describing the effects of marine toxin on gastrointestinal visceral pain pathways and the possible clinical implications in the treatment of chronic pain associated with gut diseases.

Chronic stress augments esophageal inflammation, and alters the expression of transient receptor potential vanilloid 1 and protease‑activated receptor 2 in a murine model

Stress is a pivotal factor for inflammation, reactive oxygen species (ROS) production and formation of visceral hypersensitivity (VH) in the process of gastroesophageal reflux disease (GERD). In the present study, the effects of stress on esophageal inflammation, oxidative stress and VH were investigated in a chronic restraint stress mouse model. C57BL/6J male mice were subjected to 2 weeks of intermittent restraint stress, and histopathological analysis revealed that stress induced esophageal inflammation and fibrosis, while no distinct changes were detected in non‑stressed control mice. In addition, increased NADPH oxidase 4 expression was observed in the plasma and esophagus of stressed mice, indicating accumulation of ROS. The expression levels of antioxidants, including Mn‑superoxide dismutase (MnSOD), Cu/Zn‑SOD, catalase and glutathione peroxidase, were also analyzed using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). In addition, transient receptor potential vanilloid 1 (TRPV‑1) and protease‑activated receptor 2 (PAR‑2), which are crucial receptors for VH, were measured by immunohistochemistry and RT‑qPCR. The results demonstrated that stress markedly reduced antioxidant expression, while it significantly upregulated TRPV‑1 and PAR‑2 expression levels in the mouse esophagus. Finally, 2 weeks of restraint stress significantly increased the esophageal and plasma levels of inflammatory cytokines, including interleukin (IL)‑6, IL‑8, interferon‑γ and tumor necrosis factor‑α. Taken together, the present study results indicated that stress‑induced esophageal inflammation and ROS generation involves VH.

QX-314 inhibits acid-induced activation of esophageal nociceptive C fiber neurons

INTRODUCTION

Acid reflux in the esophagus can induce painful sensations such as heartburn and non-cardiac chest pain. These nociceptive symptoms are initiated by activation of TRPV1-positive afferent C fibers in the esophagus. The present study aimed to explore a novel C fiber inhibition approach. We hypothesized that activation of TRPV1 by acid enabled QX-314, a membrane impermeable sodium channel blocker, to inhibit acid-induced activation of esophageal nociceptive C fiber neurons.

METHOD

We determined the inhibitory effect of QX-314 in the presence of acid in guinea pig esophageal nociceptive vagal jugular C fiber neurons by both patch clamp recording in neuron soma and by extra-cellular recording at nerve terminals.

KEY RESULTS

Our data demonstrated QX-314 alone did not inhibit sodium currents. However, when applied along with capsaicin to activate TRPV1, QX-314 was able to block sodium currents in esophageal-specific jugular C fiber neurons. We then showed that in the presence of acid, QX-314 significantly blocked acid-evoked activation of jugular C fiber neurons. This effect was attenuated by TRPV1 antagonist AMG9810, suggesting acid-mediated inhibitory effect of QX-314 was TRPV1-dependent. Finally, we provided evidence at nerve endings that acid-evoked action potential discharges in esophageal jugular C fibers were inhibited by QX-314 when applied in the presence of acid.

CONCLUSION AND INFERENCES

Our data demonstrated that activation of TRPV1 by acid enabled membrane impermeable sodium channel blocker QX-314 to inhibit acid-induced activation in esophageal nociceptive C fibers. This supports a localized application of QX-314 in the esophagus to block esophageal nociception in acid reflux disorders.

Pathophysiology of Gastroesophageal Reflux Disease

The pathogenesis of gastroesophageal reflux disease (GERD) is complex and involves changes in reflux exposure, epithelial resistance, and visceral sensitivity. The gastric refluxate is a noxious material that injures the esophagus and elicits symptoms. Esophageal exposure to gastric refluxate is the primary determinant of disease severity. This exposure arises via compromise of the anti-reflux barrier and reduced ability of the esophagus to clear and buffer the refluxate, leading to reflux disease. However, complications and symptoms also occur in the context of normal reflux burden, when there is either poor epithelial resistance or increased visceral sensitivity. Reflux therefore develops via alterations in the balance of aggressive and defensive forces.

Pharmacokinetics and Safety of Mavatrep (JNJ-39439335), a TRPV1 Antagonist in Healthy Japanese and Caucasian Men: A Double-Blind, Randomized, Placebo-Controlled, Sequential-Group Phase 1 Study

This single-center, double-blind, placebo-controlled, sequential-group phase 1 study evaluated the safety, tolerability, and pharmacokinetics (PK) of mavatrep (JNJ-39439335), a transient receptor potential vanilloid 1 antagonist, in healthy Japanese and caucasian subjects. In part 1, a single-ascending-dose study, 50 subjects (25 each healthy Japanese and caucasians) were enrolled and received a single oral dose of 10, 25, or 50 mg mavatrep. Caucasian subjects were matched to Japanese subjects with respect to age (±5 years) and body mass index (±5 kg/m² ). In part 2, a multiple-ascending-dose study, 36 Japanese subjects were enrolled and received once-daily oral doses of 10, 25, or 50 mg of mavatrep for 21 days. The single-dose PK of mavatrep and its metabolites was similar in the Japanese and caucasian subjects after adjustment of body weight. Following multiple dosing in Japanese subjects, a steady-state condition was reached in approximately 14 days. M2 and M3 are major circulating metabolites with mean exposure > 10% of mavatrep. Nonrenal clearance was the major route of elimination for mavatrep, M2, and M3. Mavatrep exhibited a long half-life, ranging from 68 to 101 and 82-130 hours for Japanese and caucasian subjects, respectively. After single and multiple dosing, mavatrep was well tolerated. The most common adverse events observed were thermohypoesthesia, feeling cold, chills, and feeling hot. Mavatrep and its metabolites exhibited similar PK profiles after single ascending doses in healthy Japanese and caucasian men.

Influence of GABA-B Agonist Baclofen on Capsaicin-Induced Excitation of Secondary Peristalsis in Humans

OBJECTIVES

Esophageal instillation of capsaicin enhances secondary peristalsis, but the γ-aminobutyric acid receptor type B (GABA-B) agonist baclofen inhibits secondary peristalsis. This study aimed to investigate whether baclofen could influence heartburn perception and secondary peristalsis subsequent to capsaicin infusion in healthy adults.

METHODS

Secondary peristalsis was performed by slow and rapid mid-esophagus air injections in 15 healthy subjects. Two different sessions including esophageal infusion of capsaicin-containing red pepper sauce (0.84 mg) following pre-treatment with placebo or baclofen were randomly performed to test the effects on heartburn perception and secondary peristalsis.

RESULTS

The intensity of heartburn symptom subsequent to capsaicin infusion was significantly greater after pre-treatment of baclofen as compared with the placebo (P=0.03). Baclofen significantly increased the threshold volume of secondary peristalsis to slow air injections subsequent to esophageal capsaicin infusion (P<0.001). Baclofen significantly increased the threshold volume of secondary peristalsis to rapid air injections subsequent to esophageal capsaicin infusion (P<0.01). The frequency of secondary peristalsis subsequent to capsaicin infusion was significantly decreased with baclofen as compared with the placebo (P<0.002). Baclofen had no effect on any of the peristaltic parameters of secondary peristalsis subsequent to capsaicin infusion.

CONCLUSIONS

The GABA-B agonist baclofen appears to attenuate the esophagus to capsaicin-induced excitation of secondary peristalsis in healthy adults. Our study suggests the inhibitory modulation for GABA-B receptors on capsaicin-sensitive afferents mediating secondary peristalsis in human esophagus.

The Role of Esophageal Hypersensitivity in Functional Heartburn

Functional heartburn (FH) is defined as a functional esophageal disorder characterized by symptoms of chronic heartburn with no apparent correlation to acid or nonacid reflux. In addition, its symptoms persist despite the lack of organic abnormalities or inflammation, esophageal motility disorders, or metabolic disorders. Although conditions presenting with esophageal symptoms without endoscopic abnormalities were previously categorized as nonerosive reflux disease, such conditions are now classified into 3 categories under Rome IV criteria: nonerosive reflux disease, reflux hypersensitivity, and FH. Although many aspects of FH remain unclear, its onset mechanism is considered to be strongly associated with peripheral or central sensitization, given the fact that its symptoms seem to be unrelated to gastroesophageal reflux. In addition, the cause of such hypersensitivity is an interesting topic in itself, and psychological factors, such as stress followed by increasing esophageal permeability are gaining attention as factors that can potentially influence this condition. There is a great unmet clinical need for therapeutic drugs that can be used to treat FH, and the development of novel drugs, diagnostic tests and biomarkers is eagerly awaited.

Exploration of the Esophageal Mucosal Barrier in Non-Erosive Reflux Disease

In the absence of visible mucosal damage, it is hypothesized that the esophageal mucosal barrier is functionally impaired in patients with non-erosive reflux disease (NERD). The aim of the present study was to perform an exploratory analysis of the mucosal barrier in NERD compared to erosive esophagitis (EE) and controls. A second aim was to explore TRPV1 gene transcription in relation to the mucosal barrier function and heartburn symptoms. In this prospective study, 10 NERD patients, 11 patients with active erosive esophagitis and 10 healthy volunteers were included. Biopsies from non-eroded mucosa were obtained for (1) ex vivo analyses (Ussing chamber) of transepithelial electrical resistance (TEER) and permeability (2) gene transcription of tight-junction proteins and transient receptor potential vanilloid subfamily member 1 (TRPV1). No differences in TEER or permeability were found between NERD and healthy volunteers, whereas TEER was lower in patients with erosive esophagitis. TRPV1 gene transcription was not significantly different between EE, NERD and controls. Conclusions: esophageal mucosal barrier function and TRPV1 transcription is not significantly altered in NERD patients. Future research is needed to explore other potential mechanisms that may account for the high symptom burden in these patients.

Sleep disturbance and enhanced esophageal capsaicin sensitivity in patients with gastroesophageal reflux disease

BACKGROUND AND AIM

Esophageal infusion of capsaicin-containing red pepper sauce induced heartburn symptoms in patients with gastroesophageal reflux disease (GERD). We aimed to test the hypothesis whether sleep disturbance modulates esophageal sensitivity to capsaicin infusion in patients with GERD.

METHODS

We enrolled 40 patients with their sleep quality measured by the Pittsburg Sleep Quality Index with > 5 indicating sleep disturbance. Esophageal sensation to capsaicin infusion was documented via measures of lag time to initial heartburn perception, heartburn intensity rating, and sensitivity score by esophageal infusion of capsaicin-containing red pepper sauce. Objective sleep measures were assessed by ambulatory actigraphy.

RESULTS

We found 22 patients with sleep disturbance. The patients with sleep disturbance had shorter lag time to initial heartburn perception (P = 0.03) and greater sensory intensity rating (P = 0.02). The sensitivity score for capsaicin infusion was greater in patients with sleep disturbance when compared with those without sleep disturbance (P = 0.04). Actigraphy measures revealed that patients with sleep disturbance also had poor sleep efficiency (P = 0.04), longer average awakening time (P = 0.03), and greater total activity account (P = 0.04). The lag time for perceiving capsaicin infusion was positively correlated with total sleep time (r = 0.43, P = 0.03).

CONCLUSIONS

We have shown that GERD patients with sleep disturbance have significantly enhanced heartburn perception to capsaicin infusion as compared with those with normal sleep. Our findings suggest that sleep disturbance is associated with esophageal hypersensitivity to capsaicin infusion in patients with GERD.

TRP channels: potential drug target for neuropathic pain

Neuropathic pain is a debilitating disease which affects central as well as peripheral nervous system. Transient receptor potential (TRP) channels are ligand-gated ion channels that detect physical and chemical stimuli and promote painful sensations via nociceptor activation. TRP channels have physiological role in the mechanisms controlling several physiological responses like temperature and mechanical sensations, response to painful stimuli, taste, and pheromones. TRP channel family involves six different TRPs (TRPV1, TRPV2, TRPV3, TRPV4, TRPM8, and TRPA1) which are expressed in pain sensing neurons and primary afferent nociceptors. They function as transducers for mechanical, chemical, and thermal stimuli into inward currents, an essential first step for provoking pain sensations. TRP ion channels activated by temperature (thermo TRPs) are important molecular players in acute, inflammatory, and chronic pain states. Different degree of heat activates four TRP channels (TRPV1-4), while cold temperature ranging from affable to painful activate two indistinctly related thermo TRP channels (TRPM8 and TRPA1). Targeting primary afferent nociceptive neurons containing TRP channels that play pivotal role in revealing physical stimuli may be an effective target for the development of successful pharmacotherapeutics for clinical pain syndromes. In this review, we highlighted the potential role of various TRP channels in different types of neuropathic pain. We also discussed the pharmacological activity of naturally and synthetically originated TRP channel modulators for pharmacotherapeutics of nociception and neuropathic pain.

Understanding the sensory irregularities of esophageal disease

Symptoms relating to esophageal sensory abnormalities can be encountered in the clinical environment. Such sensory abnormalities may be present in demonstrable disease, such as erosive esophagitis, and in the ostensibly normal esophagus, such as non-erosive reflux disease or functional chest pain. In this review, the authors discuss esophageal sensation and the esophageal pain system. In addition, the authors provide a primer concerning the techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of esophageal sensory function. Such technological advances, whilst not readily available in the clinic may facilitate the stratification and individualization of therapy in disorders of esophageal sensation in the future.

Safety, Tolerability and Pharmacokinetic and Pharmacodynamic Learnings from a Double-Blind, Randomized, Placebo-Controlled, Sequential Group First-in-Human Study of the TRPV1 Antagonist, JNJ-38893777, in Healthy Men

BACKGROUND AND OBJECTIVE

Nociceptive and neuropathic pain, one of common reasons of disability and loss of quality life, are often undertreated due to safety concerns with current therapies. This study assessed the safety, tolerability, pharmacokinetics and pharmacodynamics of JNJ-38893777, a potent and selective transient receptor potential vanilloid 1 (TRPV1) channel antagonist in healthy men.

METHODS

In a single-center, double-blind, placebo-controlled, sequential group, single-ascending-dose phase 1 study, 80 healthy men (18-45 years old; body mass index 18.5 to <30 kg/m(2)), randomized to two groups, received either JNJ-38893777 (n = 6) or placebo (n = 2) in a dose-escalation manner. The study was designed in two parts: Part 1, an early tablet formulation was administered under fasting conditions at 5, 15, 45, 125, 250, or 500 mg; Part 2, a new tablet formulation was administered in a fasting state (250 mg) and a high-fat fed state (250 mg, 375 mg, or 500 mg). Serial plasma and urine samples (collected over 120 h post-dose) were analyzed using LC-MS/MS for pharmacokinetic evaluations.

RESULTS

JNJ-38893777 concentrations peaked from 3.0 to 5.5 h (median) post-administration, and then declined multi-exponentially with a prolonged terminal phase. Renal clearance was negligible. Maximum concentration (C max) and area under the concentration-time curve from time zero to infinity (AUC∞) of the early formulation increased with increasing doses but less than dose-proportionally over 5-500 mg (fasted) doses. The new tablet formulation showed no improvements in the fasting state but showed an 11- to 22-fold increase in JNJ-38893777 exposure; interindividual variability reduced from 73-85% to 23-24%, and a significant increase (P < 0.05) in heat pain detection threshold (~3 °C) was observed in the fed state. Mild to moderate adverse events were observed, with no evidence of exposure dependence up to 500 mg (fed). Concentration-related increases in body temperature or changes in Fridericia-corrected QT interval (QTcF) were not observed.

CONCLUSION

JNJ-38893777 was tolerated at single doses up to 500 mg (fed) and is suitable for further clinical development.

Esophageal Submucosal Injection of Capsaicin but Not Acid Induces Symptoms in Normal Subjects

Background/Aims

Transient receptor potential vanilloid-1 (TRPV1) is a candidate for mediating acid-induced symptoms in the esophagus. We conducted studies to determine if the presence of acid in the mucosa/submucosa and direct activation of TRPV1 by capsaicin elicited symptoms in normal healthy subjects. We also studied the presence of TRPV1 receptors in the esophagus.

Methods

Unsedated endoscopy was performed on healthy subjects with no symptoms. Using a sclerotherapy needle, normal saline (pH 2.0–7.5) was injected into the mucosa/submucosa, 5 cm above the Z line. In a separate group of healthy subjects, injection of capsaicin and vehicle was also studied. Quality of symptoms was reported using the McGill Pain Questionnaire, and symptom intensity using the visual analogue scale (VAS). Immunohistochemistry was performed on 8 surgical esophagus specimens using TRPV1 antibody.

Results

Acid injection either did not elicit or elicited mild symptoms in subjects at all pH solutions. Capsaicin but not the vehicle elicited severe heartburn/chest pain in all subjects. Mean VAS for capsaicin was 91 ± 3 and symptoms lasted for 25 ± 1 minutes. Immunohistochemistry revealed a linear TRPV1 staining pattern between the epithelial layer and the submucosa that extended into the papillae. Eighty-five percent of papillae stained positive for TRPV1 with a mean 1.1 positive papillae per high-powered field.

Conclusions

The mechanism of acid-induced heartburn and chest pain is not the simple interaction of hydrogen ions with afferents located in the esophageal mucosa and submucosa. TRPV1 receptors are present in the lamina propria and their activation induces heartburn and chest pain.

Capsaicin, Nociception and Pain

Capsaicin, the pungent ingredient of the hot chili pepper, is known to act on the transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1). TRPV1 is involved in somatic and visceral peripheral inflammation, in the modulation of nociceptive inputs to spinal cord and brain stem centers, as well as the integration of diverse painful stimuli. In this review, we first describe the chemical and pharmacological properties of capsaicin and its derivatives in relation to their analgesic properties. We then consider the biochemical and functional characteristics of TRPV1, focusing on its distribution and biological effects within the somatosensory and viscerosensory nociceptive systems. Finally, we discuss the use of capsaicin as an agonist of TRPV1 to model acute inflammation in slices and other ex vivo preparations.

Upregulation of Vanilloid Receptor-1 in Functional Dyspepsia With or Without Helicobacter pylori Infection

The etiological basis of functional dyspepsia (FD) is incompletely understood. The aim of this study was to evaluate the involvement of nociceptor-related genes and Helicobacter pylori (HP) in the pathogenesis of FD. The expression of nociceptor-related genes was measured in gastric cell lines that were co-cultured with HP. FD patients (n = 117) and controls (n = 55) were enrolled from a tertiary hospital gastroenterology clinic. Expression of the genes nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), and transient receptor potential cation channel subfamily V member 1 (TRPV1) in the gastric mucosa were detected by reverse transcription polymerase chain reaction (RT-PCR), and immunohistochemical staining of TRPV1 was analyzed. These measurements were repeated after 1 year. TRPV1, GDNF, and NGF expression was elevated in gastric cell lines co-cultured with HP. TRPV1 immunostaining was stronger in HP-positive than HP-negative subjects. The FD group showed higher expression levels of TRPV1, GDNF, and NGF and increased TRPV1 immunostaining compared with those of the control group (all P < 0.05). Among 61 subjects who were followed up at 1 year, controls with successful HP eradication and patients whose symptoms had improved both showed significant reductions in the expression of TRPV1 and NGF (all P < 0.05) compared with controls without HP eradication and patients whose symptoms had not improved, respectively. The expression of NGF, GDNF, and TRPV1 may be associated with the pathogenesis of FD. Since HP infection may induce the increased expression of these genes, anti-HP therapy could be beneficial for HP-positive patients with FD.