Mast cell-derived histamine mediates cystitis pain

The role of the neuronal microenvironment in sensory function and pain pathophysiology

The high prevalence of pain and the at times low efficacy of current treatments represent a significant challenge to healthcare systems worldwide. Effective treatment strategies require consideration of the diverse pathophysiologies that underlie various pain conditions. Indeed, our understanding of the mechanisms contributing to aberrant sensory neuron function has advanced considerably. However, sensory neurons operate in a complex dynamic microenvironment that is controlled by multidirectional interactions of neurons with non-neuronal cells, including immune cells, neuronal accessory cells, fibroblasts, adipocytes, and keratinocytes. Each of these cells constitute and control the microenvironment in which neurons operate, inevitably influencing sensory function and the pathology of pain. This review highlights the importance of the neuronal microenvironment for sensory function and pain, focusing on cellular interactions in the skin, nerves, dorsal root ganglia, and spinal cord. We discuss the current understanding of the mechanisms by which neurons and non-neuronal cells communicate to promote or resolve pain, and how this knowledge could be used for the development of mechanism-based treatments.

Emodin suppresses mast cell migration via modulating the JAK2/STAT3/JMJD3/CXCR3 signaling to prevent cystitis

AIMS

This study aimed to determine the preventive effects of emodin on cyclophosphamide (CYP)-induced cystitis and to explore the molecular mechanism.

METHODS

In vivo, mice were modeled by CYP. Before a half hour of CYP treatment, Jumonji domain-containing protein-3 (JMJD3) inhibitors (GSK-J4) and emodin were used to treat CYP model mice. Bladder samples were stained for hematoxylin-eosin and toluidine blue. Next, JMJD3 was quantified by immunofluorescence staining, RT-PCR, and Western blot. CXCR3 was quantified by Western blot and ELISA. In vitro, before stimulated by lipopolysaccharide (LPS), human bladder smooth muscle cells (hBSMCs) were transfected with pcDNA3.1-JMJD3 plasmids, shRNA-JMJD3 plasmids or pretreated with emodin. Collected cells to detect JMJD3 and CXCR3 ligands again; collected supernatant of culture for Transwell assay. Finally, as the JAK2 inhibitor, AG490 was used to pretreat LPS-induced hBSMCs. Western blot was performed to quantify proteins.

RESULTS

Emodin inhibited mast cell migration and suppressed the expression of JMJD3, CXCR3, and CXCR3 ligands, not only in vivo but also in vitro. The pharmacological effects of emodin were similar to GSK-J4 or JMJD3 inhibition. In addition, emodin significantly downregulated the phosphorylation of JAK2 and STAT3, and inhibited JMJD3/CXCR3 axis transduction like AG490.

CONCLUSION

Emodin has a preventive effect on cystitis by inhibiting mast cell migration through inhibition of the JAK2/STAT3/JMJD3/CXCR3 signaling pathway.

Therapeutic Approaches for Urologic Chronic Pelvic Pain Syndrome; Management: Research Advances, Experimental Targets, and Future Directions

Urologic chronic pelvic pain syndrome (UCPPS) is a painful chronic condition with persistent pain originating from the pelvis that often leads to detrimental lifestyle changes in the affected patients. The syndrome develops in both sexes, with an estimated prevalence of 5.7% to 26.6% worldwide. This narrative review summarizes currently recommended therapies for UCPPS, followed by the latest animal model findings and clinical research advances in the field. The diagnosis of UCPPS by clinicians has room for improvement despite the changes in the past decade aiming to decrease the time to treatment. Therapeutic approaches targeting growth factors (i.e., nerve growth factor, vascular endothelial growth factor), amniotic bladder therapy, and stem cell treatments gain more attention as experimental treatment options for UCPPS. The development of novel diagnostic tests based on the latest advances in urinary biomarkers would be beneficial to assist with the clinical diagnosis of UCPPS. Future research directions should address the role of chronic psychologic stress and the mechanisms of pain refractory to conventional management strategies in UCPPS etiology. Testing the applicability of cognitive behavioral therapy in this cohort of UCPPS patients might be promising to increase their quality of life. The search for novel lead compounds and innovative drug delivery systems requires clinically relevant translational animal models. The role of autoimmune responses triggered by environmental factors is another promising research direction to clarify the impact of the immune system in UCPPS pathophysiology. SIGNIFICANCE STATEMENT: This minireview provides an up-to-date summary of the therapeutic approaches for UCPPS with a focus on recent advancements in the clinical diagnosis and treatments of the disease, pathophysiological mechanisms of UCPPS, signaling pathways, and molecular targets involved in pelvic nociception.

Mechanisms of oxidative stress in interstitial cystitis/bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is characterized by bladder and/or pelvic pain, increased urinary urgency and frequency and nocturia. The pathophysiology of IC/BPS is poorly understood, and theories include chronic inflammation, autoimmune dysregulation, bacterial cystitis, urothelial dysfunction, deficiency of the glycosaminoglycan (GAG) barrier and urine cytotoxicity. Multiple treatment options exist, including behavioural interventions, oral medications, intravesical instillations and procedures such as hydrodistension; however, many clinical trials fail, and patients experience an unsatisfactory treatment response, likely owing to IC/BPS phenotype heterogeneity and the use of non-targeted interventions. Oxidative stress is implicated in the pathogenesis of IC/BPS as reactive oxygen species impair bladder function via their involvement in multiple molecular mechanisms. Kinase signalling pathways, nociceptive receptors, mast-cell activation, urothelial dysregulation and circadian rhythm disturbance have all been linked to reactive oxygen species and IC/BPS. However, further research is necessary to fully uncover the role of oxidative stress in the pathways driving IC/BPS pathogenesis. The development of new models in which these pathways can be manipulated will aid this research and enable further investigation of promising therapeutic targets.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Recurrent infections drive persistent bladder dysfunction and pain via sensory nerve sprouting and mast cell activity

Urinary tract infections (UTIs) account for almost 25% of infections in women. Many are recurrent (rUTI), with patients frequently experiencing chronic pelvic pain and urinary frequency despite clearance of bacteriuria after antibiotics. To elucidate the basis for these bacteria-independent bladder symptoms, we examined the bladders of patients with rUTI. We noticed a notable increase in neuropeptide content in the lamina propria and indications of enhanced nociceptive activity. In mice subjected to rUTI, we observed sensory nerve sprouting that was associated with nerve growth factor (NGF) produced by recruited monocytes and tissue-resident mast cells. Treatment of rUTI mice with an NGF-neutralizing antibody prevented sprouting and alleviated pelvic sensitivity, whereas instillation of native NGF into naïve mice bladders mimicked nerve sprouting and pain behavior. Nerve activation, pain, and urinary frequency were each linked to the presence of proximal mast cells, because mast cell deficiency or treatment with antagonists against receptors of several direct or indirect mast cell products was each effective therapeutically. Thus, our findings suggest that NGF-driven sensory sprouting in the bladder coupled with chronic mast cell activation represents an underlying mechanism driving bacteria-independent pain and voiding defects experienced by patients with rUTI.

Restoring the barrier of chronically damaged urothelium using chondroitin sulfate glycosaminoglycan-replenishment therapy

PURPOSE OF REVIEW

This study aims to further understand the physiological mechanism of chondroitin sulfate treatment on the urinary bladder in cases of inflammation, by investigating the effect of chondroitin sulfate therapy on recovery of urothelial barrier in an in-vitro chronic injury model.

RECENT FINDINGS

With inflammatory bladder conditions, the urothelial barrier seems decreased. Glycosaminoglycan (GAG) replacement therapy is supposed to help restore this barrier. Clinical studies on inflammatory bladder conditions are complicated because of the heterogeneous patient population, hence the need for preclinical models.

SUMMARY

In a model using porcine urothelial cells, functional barrier (TEER) and barrier markers were assessed. Chronic urothelial damage was simulated through protamine sulfate instillations with and without subsequent chondroitin sulfate instillations during 3 days. Chondroitin sulfate instillations significantly improved TEER compared to protamine sulfate treatment only (TEER difference 310 Ω.cm 2 , P  < 0.001). This consistent effect over 3 days resulted in a significant higher mean TEER value in the chondroitin sulfate treated group (difference 1855 Ω.cm 2 , P  < 0.001). Enhanced recovery of chondroitin sulfate and other barrier markers was observed.Chondroitin sulfate therapy shows promise in facilitating the recovery of the urothelial barrier in cases of chronic damage. This preclinical study lends support to the use of clinical GAG replenishment therapy for patients with a chronically impaired urothelium.

Therapeutic Effects of IL-1RA against Acute Bacterial Infections, including Antibiotic-Resistant Strains

Innate immunity is essential for the anti-microbial defense, but excessive immune activation may cause severe disease. In this study, immunotherapy was shown to prevent excessive innate immune activation and restore the anti-bacterial defense. E. coli-infected Asc-/- mice develop severe acute cystitis, defined by IL-1 hyper-activation, high bacterial counts, and extensive tissue pathology. Here, the interleukin-1 receptor antagonist (IL-1RA), which inhibits IL-1 hyper-activation in acute cystitis, was identified as a more potent inhibitor of inflammation and NK1R- and substance P-dependent pain than cefotaxime. Furthermore, IL-1RA treatment inhibited the excessive innate immune activation in the kidneys of infected Irf3-/- mice and restored tissue integrity. Unexpectedly, IL-1RA also accelerated bacterial clearance from infected bladders and kidneys, including antibiotic-resistant E. coli, where cefotaxime treatment was inefficient. The results suggest that by targeting the IL-1 response, control of the innate immune response to infection may be regained, with highly favorable treatment outcomes, including infections caused by antibiotic-resistant strains.

Obacunone alleviates chronic pelvic pain and pro-inflammatory depolarization of macrophage induced by experimental autoimmune prostatitis in mice

Chronic pelvic pain syndrome (CPPS) is a common complication of prostatitis, which was associated with the pathological depolarization of macrophage and the neuroinflammation. However, its underlying reason is far from clear and few effective treatments is applicable. In this study, we tested the effect of obacunone (Oba), a highly oxygenated triterpenoid, on CPPS. The experimental autoimmune prostatitis (EAP) was induced by subcutaneous injection of heterologous prostate homogenate in mice. We found that EAP led to prostatodynia, neuronal activation of spinal dorsal horn, and the pro-inflammatory depolarization of macrophage within prostate, which was significantly alleviated by oral administration of Oba in a dose-dependent manner. Mechanistically, EAP-induced production of IL-6 on prostatic macrophage was suppressed by Oba. Moreover, co-administration of Oba and MIF inhibitor ISO-1 did not lead to additive effect when compared with either alone. In summary, we conclude that Oba prevents the production of macrophage-derived pro-inflammatory factors by inhibiting MIF, which eventually alleviates CPPS after prostatitis.

Immune mechanisms in vulvodynia: key roles for mast cells and fibroblasts

Vulvodynia is a debilitating condition characterized by painful sensitivity to touch and pressure in the vestibular tissue surrounding the vaginal opening. It is often a "diagnosis of exclusion" of idiopathic pain made in the absence of visible inflammation or injury. However, the association between increased vulvodynia risk and a history of yeast infections and skin allergies has led researchers to explore whether immune mechanisms of dysregulated inflammation might underlie the pathophysiology of this chronic pain condition. Here we synthesize epidemiological investigations, clinical biopsies and primary cell culture studies, and mechanistic insights from several pre-clinical models of vulvar pain. Taken together, these findings suggest that altered inflammatory responses of tissue fibroblasts, and other immune changes in the genital tissues, potentially driven by the accumulation of mast cells may be key to the development of chronic vulvar pain. The association of increased numbers and function of mast cells with a wide variety of chronic pain conditions lends credence to their involvement in vulvodynia pathology and underscores their potential as an immune biomarker for chronic pain. Alongside mast cells, neutrophils, macrophages, and numerous inflammatory cytokines and mediators are associated with chronic pain suggesting immune-targeted approaches including the therapeutic administration of endogenous anti-inflammatory compounds could provide much needed new ways to treat, manage, and control the growing global pandemic of chronic pain.

The Unmet Needs for Studying Chronic Pelvic/Visceral Pain Using Animal Models

The different definitions of chronic pelvic/visceral pain used by international societies have changed over the years. These differences have a great impact on the way researchers study chronic pelvic/visceral pain. Recently, the role of systemic changes, including the role of the central nervous system, in the perpetuation and chronification of pelvic/visceral pain has gained weight. Consequently, researchers are using animal models that resemble those systemic changes rather than using models that are organ- or tissue-specific. In this review, we discuss the advantages and disadvantages of using bladder-centric and systemic models, enumerating some of the central nervous system changes and pain-related behaviors occurring in each model. We also present some drawbacks when using animal models and pain-related behavior tests and raise questions about possible, yet to be demonstrated, investigator-related bias. We also suggest new approaches to study chronic pelvic/visceral pain by refining existing animal models or using new ones.

Compound 48/80 increases murine bladder wall compliance independent of mast cells

A balance between stiffness and compliance is essential to normal bladder function, and changes in the mechanical properties of the bladder wall occur in many bladder pathologies. These changes are often associated with the release of basic secretagogues that in turn drive the release of inflammatory mediators from mast cells. Mast cell degranulation by basic secretagogues is thought to occur by activating an orphan receptor, Mas-related G protein-coupled receptor B2 (Mrgprb2). We explored the effects of the putative mast cell degranulator and Mrgprb2 agonist Compound 48/80 on urinary bladder wall mechanical compliance, smooth muscle contractility, and urodynamics, and if these effects were mast cell dependent. In wild-type mice, Mrgprb2 receptor mRNA was expressed in both the urothelium and smooth muscle layers. Intravesical instillation of Compound 48/80 decreased intermicturition interval and void volume, indicative of bladder overactivity. Compound 48/80 also increased bladder compliance while simultaneously increasing the amplitude and leading slope of transient pressure events during ex vivo filling and these effects were inhibited by the Mrgprb2 antagonist QWF. Surprisingly, all effects of Compound 48/80 persisted in mast cell-deficient mice, suggesting these effects were independent of mast cells. These findings suggest that Compound 48/80 degrades extracellular matrix and increases urinary bladder smooth muscle excitability through activation of Mrgprb2 receptors located outside of mast cells. Thus, the pharmacology and physiology of Mrgprb2 in the urinary bladder is of potential interest and importance in terms of treating lower urinary tract dysfunction.

Treatment of primary eosinophilic colitis using immunoglobulin/histamine complex

Primary eosinophilic colitis (PEC) is a primary eosinophilic gastrointestinal disorder, and immunoglobulin/histamine complex (IHC) may be an effective therapeutic for PEC. IHC has a nonallergen-specific antinociceptive effect in the treatment of histamine-mediated pain.

Targeting spinal microglia with fexofenadine-loaded nanoparticles prolongs pain relief in a rat model of neuropathic pain

Targeting microglial activation is emerging as a clinically promising drug target for neuropathic pain treatment. Fexofenadine, a histamine receptor 1 antagonist, is a clinical drug for the management of allergic reactions as well as pain and inflammation. However, the effect of fexofenadine on microglial activation and pain behaviors remains elucidated. Here, we investigated nanomedicinal approach that targets more preferentially microglia and long-term analgesics. Fexofenadine significantly abolished histamine-induced microglial activation. The fexofenadine-encapsulated poly(lactic-co-glycolic acid) nanoparticles (Fexo NPs) injection reduced the pain sensitivity of spinal nerve ligation rats in a dose-dependent manner. This alleviation was sustained for 4 days, whereas the effective period by direct fexofenadine injection was 3 h. Moreover, Fexo NPs inhibited microglial activation, inflammatory signaling, cytokine release, and a macrophage phenotype shift towards the alternative activated state in the spinal cord. These results show that Fexo NPs exhibit drug repositioning promise as a long-term treatment modality for neuropathic pain.

Involvement of a neutrophil-mast cell axis in the effects of Piper malacophyllum (C. PESL) C. DC extract and its isolated compounds in a mouse model of dysmenorrhoea

The effects of Piper malacophyllum (C. Pesl) C. DC extracts and its isolated compounds were analysed in a mouse model of primary dysmenorrhoea (PD). Female Swiss mice (6-8 weeks old) on proestrus were intraperitoneally treated with estradiol benzoate for 3 days, to induce PD. Twenty-four hours later, animals were treated 24 h later with vehicle, plant extract, gibbilimbol B, 4,6-dimethoxy-5-E-phenylbutenolide, mixture of 4,6-dimethoxy-5-E-phenylbutenolide and 4,6-dimethoxy-5-Z-phenylbutenolide, or ibuprofen. One hour later, oxytocin was injected and the numbers of abdominal writhing were counted. Then, mice were euthanized and uteri were collected for morphometrical and histological analyses. The effects of P. malacophyllum in inflammation were investigated in mouse peritoneal neutrophils culture stimulated with LPS or fMLP (chemotaxis and mediator release). Finally, uterus contractile and relaxing responses were assessed. Similar to ibuprofen, P. malacophyllum extract and isolated compounds reduced abdominal writhing in mice with PD. Histology indicated a marked neutrophil and mast cell infiltrate in the uterus of PD animals which was attenuated by the extract. The compounds and the extract reduced neutrophil chemotaxis and inflammatory mediator release by these cells. Reduced TNF levels were also observed in uteri of PD mice treated with P. malacophyllum. The extract did not affect spontaneous uterine contractions nor those induced by carbachol or KCl. However, it caused relaxation of oxytocin-induced uterine contraction, an effect blunted by H1 receptor antagonist. Overall the results indicate that P. malacophyllum may represent interesting natural tools for reliving PD symptoms, reducing the triad of pain, inflammation and spasmodic uterus behaviour.

Protective Effect of Purinergic P2X7 Receptor Inhibition on Acrolein-Induced Urothelial Cell Damage

Patients undergoing chemotherapy with cyclophosphamide experience cystitis due to excretion of a toxic metabolite, acrolein. Cystitis, an inflammation of the bladder, is associated with damage to the integrity of the urothelial barrier. The purinergic P2X7 receptor (P2X7R) is increasingly recognized for its role in inflammation and cell death. P2X7R is expressed abundantly on the bladder urothelium. The aim of this study was to investigate the role of P2X7R in acrolein-induced inflammatory damage in primary cultured porcine bladder urothelial cells. Confluent urothelial cells in culture were treated with acrolein to induce damage; also, with the P2X7R selective antagonist, A804598. Cell viability assay, immunocytochemistry, and trans-epithelial electrical resistance (TEER) studies were carried out to investigate the effect of treatments on urothelial cell function. Acrolein induced a significant reduction in urothelial cell viability, which was protected by the presence of A804598 (10 µM). The urothelial barrier function, indicated by TEER values, was also significantly reduced by acrolein, whereas pre-incubation with P2X7R antagonist significantly protected the urothelial cell barrier from acrolein-induced TEER reduction. The structure of urothelial cell tight junctions was similarly impacted by acrolein treatment, showing the fragmentation of zona occludens-1 (ZO-1) immunoreactivity. Pre-treatment of cells with A804598 countered against the actions of acrolein and maintained ZO-1 expression level and cell structure. The damaging effect of acrolein on urothelial cells integrity could be impaired by inhibition of P2X7R, therefore P2X7R blockade may be a possible therapy in patients with bladder cystitis caused by cyclophosphamide treatment.

Histamine receptors rapidly desensitize without altering nerve-evoked contractions in murine urinary bladder smooth muscle

Histamine has been implicated in urinary bladder dysfunction as an inflammatory mediator driving sensory nerve hypersensitivity. However, the direct influence of histamine on smooth muscle has not been thoroughly investigated. We hypothesized that histamine directly contracts urinary bladder smooth muscle (UBSM) independent of effects on nerves. Single cell quantitative RT-PCR determined that only histamine H1 and H2 receptors were expressed on UBSM cells. In isolated tissue bath experiments, histamine (200 µM) caused a highly variable and rapidly desensitizing contraction that was completely abolished by the H1 receptor antagonist fexofenadine (5 µM) and the Gq/11 inhibitor YM254890 (1 µM). Neither the muscarinic receptor antagonist atropine (1 µM), the Na+ channel blocker tetrodotoxin (1 µM), nor the transient receptor potential vanilloid type 1 antagonist capsazepine (10 µM) altered responses to histamine, suggesting that nerve activation was not involved. UBSM desensitization to histamine was not due to receptor internalization, as neither the cholesterol-depleting agent methyl-β-cyclodextrin (10 mM), the dynamin-mediated endocytosis inhibitor dynasore (100 µM), nor the clathrin-mediated endocytosis inhibitor pitstop2 (15 µM) augmented or prolonged histamine contractions. Buffer from desensitized tissues still contracted histamine-naïve tissues, revealing that histamine was not metabolized. Prolonged exposure to histamine also had no effect on contractions due to electrical field stimulation, suggesting that both efferent nerve and UBSM excitability were unchanged. Together, these data suggest that histamine, although able to transiently contract UBSM, does not have a lasting effect on UBSM excitability or responses to efferent nerve input. Thus, any acute effects of histamine directly on UBSM contractility are unlikely to alter urinary bladder function.NEW & NOTEWORTHY Histamine is commonly associated with inflammatory bladder pathologies. We sought to investigate the role of histamine on urinary bladder contractility. Histamine contracts the bladder, but this response is highly variable and desensitizes completely in minutes. This desensitization is not due to internalization of the receptor or metabolism of histamine. Because nerve-evoked contractions are also not increased in the presence of histamine, our findings suggest that histamine is not directly acting to change contractility.

Neuronal Dual Leucine Zipper Kinase Mediates Inflammatory and Nociceptive Responses in Cyclophosphamide-Induced Cystitis

Interstitial cystitis is associated with neurogenic inflammation and neuropathic bladder pain. Dual leucine zipper kinase (DLK) expressed in sensory neurons is implicated in neuropathic pain. We hypothesized that neuronal DLK is involved in the regulation of inflammation and nociceptive behavior in cystitis. Mice deficient in DLK in sensory neurons (cKO) were generated by crossing DLK floxed mice with mice expressing Cre recombinase under Advillin promoter. Cystitis was induced by cyclophosphamide (CYP) administration in mice. Nociceptive behavior, bladder inflammation, and pathology were assessed following cystitis induction in control and cKO mice. The role of DLK in CYP-induced cystitis was further determined by pharmacological inhibition of DLK with GNE-3511. Deletion of neuronal DLK attenuated CYP-induced pain-like nociceptive behavior and suppressed histamine release from mast cells, neuronal activation in the spinal cord, and bladder pathology. Mice deficient in neuronal DLK also showed reduced inflammation induced by CYP and reduced c-Jun activation in the dorsal root ganglia (DRG). Pharmacological inhibition of DLK with GNE-3511 recapitulated the effects of neuronal DLK depletion in CYP treatment mice. Our study suggests that DLK is a potential target for the treatment of neuropathic pain and bladder pathology associated with cystitis.

Involvement of Mast Cells in the Pathophysiology of Pain

Mast cells (MCs) are immune cells and are widely distributed throughout the body. MCs are not only classically viewed as effector cells of some allergic diseases but also participate in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. Mounting evidence indicates that activation of MCs releasing numerous vasoactive and inflammatory mediators has effects on the nervous system and has been involved in different pain conditions. Here, we review the latest advances made about the implication of MCs in pain. Possible cellular and molecular mechanisms regarding the crosstalk between MC and the nervous system in the initiation and maintenance of pain are also discussed.

Mast cell stabilizer ketotifen fumarate reverses inflammatory but not neuropathic-induced mechanical pain in mice

Supplemental Digital Content is Available in the Text.

Our preclinical findings indicate that ketotifen fumarate's analgesic effects are MC-dependent, and the case series report presented supports its use for the treatment of chronic pain.

Introduction:

Mast cell (MC) activation could establish a positive feedback loop that perpetuates inflammation and maintains pain. Stabilizing MCs with ketotifen fumarate (KF) may disrupt this loop and relieve pain.

Objective:

We aimed to test the effect of treatment with KF in pain assays in mice and in a case series of patients with chronic widespread pain.

Methods:

The analgesic effect of KF was tested in CD-1 mice injected with formalin, complete Freund's adjuvant, or subjected to spared nerve injury. In addition, wild-type (C57BL/6) and MC-deficient (C57BL/6-Kit^W-sh/W-sh) mice were injected with formalin or complete Freund's adjuvant and treated with KF. Patients with chronic widespread pain (n = 5; age: 13–16 years) who failed to respond to standard of care participated in a 16-week treatment trial with KF (6 mg/d). Ketotifen fumarate's therapeutic effect was evaluated using the patient global impression of change.

Results:

In the mouse experiments, KF produced dose- and MC-dependent analgesic effects against mechanical allodynia in the acute and chronic inflammatory pain but not neuropathic pain assays. In the patient case series, 4 patients reported that activity limitations, symptoms, emotions, and overall quality of life related to their pain condition were “better” or “a great deal better” since beginning treatment with KF. This was accompanied by improvements in pain comorbid symptoms.

Conclusion:

Treatment with KF is capable of reducing established inflammatory-induced mechanical nociception in an MC-dependent manner in mice, and it may be beneficial for the treatment of chronic pain conditions.

Immune Actions on the Peripheral Nervous System in Pain

Pain can be induced by tissue injuries, diseases and infections. The interactions between the peripheral nervous system (PNS) and immune system are primary actions in pain sensitizations. In response to stimuli, nociceptors release various mediators from their terminals that potently activate and recruit immune cells, whereas infiltrated immune cells further promote sensitization of nociceptors and the transition from acute to chronic pain by producing cytokines, chemokines, lipid mediators and growth factors. Immune cells not only play roles in pain production but also contribute to PNS repair and pain resolution by secreting anti-inflammatory or analgesic effectors. Here, we discuss the distinct roles of four major types of immune cells (monocyte/macrophage, neutrophil, mast cell, and T cell) acting on the PNS during pain process. Integration of this current knowledge will enhance our understanding of cellular changes and molecular mechanisms underlying pain pathogenies, providing insights for developing new therapeutic strategies.

Biomaterial-assisted drug delivery for interstitial cystitis/bladder pain syndrome treatment

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic and painful bladder condition afflicting patients with increased urinary urgency and frequency as well as incontinence. Owing to the elusive pathogenesis of IC/BPS, obtaining effective therapeutic outcomes remains challenging. Current administrational routes such as intravesical-bladder injection improve the treatment efficacy and reduce systemic side effects. However, the bladder permeability barrier hinders drug penetration into the bladder wall to meet the desired therapeutic expectation. These issues can be addressed by encapsulating drugs into biomaterials. When appropriately exploited, they would increase the drug dwelling time in the bladder, enhance the penetration of mucosa and improve the therapeutic response of IC/BPS. In this review, we first elucidate the pathogenesis and animal models of IC/BPS. Then, we highlight recent representative biomaterial-assisted drug delivery systems for IC/BPS treatment. Finally, we discuss the challenges and outlook for further developing biomaterial-based delivery systems for IC/BPS management.

AOAH remodels arachidonic acid-containing phospholipid pools in a model of interstitial cystitis pain: A MAPP Network study

Interstitial cystitis/bladder pain syndrome (IC) is a debilitating condition of chronic pelvic pain with unknown etiology. Recently, we used a genetic approach in a murine model of IC to identify the lipase acyloxyacyl hydrolase (AOAH) as a modulator of pelvic pain. We found that AOAH-deficient mice have elevated pelvic pain responses, and AOAH immunoreactivity was detected along the bladder-brain axis. Lipidomic analyses identified arachidonic acid (AA) and its metabolite PGE₂ as significantly elevated in the sacral spinal cord of AOAH-deficient mice, suggesting AA is a substrate for AOAH. Here, we quantified the effects of AOAH on phospholipids containing AA. Spinal cord lipidomics revealed increased AA-containing phosphatidylcholine in AOAH-deficient mice and concomitantly decreased AA-phosphatidylethanolamine, consistent with decreased CoA-independent transferase activity (CoIT). Overexpression of AOAH in cell cultures similarly altered distribution of AA in phospholipid pools, promoted AA incorporation, and resulted in decreased membrane fluidity. Finally, administration of a PGE₂ receptor antagonist reduced pelvic pain in AOAH-deficient mice. Together, these findings suggest that AOAH represents a potential CoA-independent AA transferase that modulates CNS pain pathways at the level of phospholipid metabolism.

Nerve Growth Factor Signaling and Its Contribution to Pain

Nerve growth factor (NGF) is a neurotrophic protein essential for the growth, differentiation, and survival of sympathetic and sensory afferent neurons during development. A substantial body of evidence, based on both animal and human studies, demonstrates that NGF plays a pivotal role in modulation of nociception in adulthood. This has spurred development of a variety of novel analgesics that target the NGF signaling pathway. Here, we present a narrative review designed to summarize how NGF receptor activation and downstream signaling alters nociception through direct sensitization of nociceptors at the site of injury and changes in gene expression in the dorsal root ganglion that collectively increase nociceptive signaling from the periphery to the central nervous system. This review illustrates that NGF has a well-known and multifunctional role in nociceptive processing, although the precise signaling pathways downstream of NGF receptor activation that mediate nociception are complex and not completely understood. Additionally, much of the existing knowledge derives from studies performed in animal models and may not accurately represent the human condition. However, available data establish a role for NGF in the modulation of nociception through effects on the release of inflammatory mediators, nociceptive ion channel/receptor activity, nociceptive gene expression, and local neuronal sprouting. The role of NGF in nociception and the generation and/or maintenance of chronic pain has led to it becoming a novel and attractive target of pain therapeutics for the treatment of chronic pain conditions.

Histamine induces peripheral and central hypersensitivity to bladder distension via the histamine H1 receptor and TRPV1

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a common chronic pelvic disorder with sensory symptoms of urinary urgency, frequency, and pain, indicating a key role for hypersensitivity of bladder-innervating sensory neurons. The inflammatory mast cell mediator histamine has long been implicated in IC/BPS, yet the direct interactions between histamine and bladder afferents remain unclear. In the present study, we show, using a mouse ex vivo bladder afferent preparation, that intravesical histamine enhanced the mechanosensitivity of subpopulations of afferents to bladder distension. Histamine also recruited “silent afferents” that were previously unresponsive to bladder distension. Furthermore, in vivo intravesical histamine enhanced activation of dorsal horn neurons within the lumbosacral spinal cord, indicating increased afferent signaling in the central nervous system. Quantitative RT-PCR revealed significant expression of histamine receptor subtypes ( Hrh1– Hrh3) in mouse lumbosacral dorsal root ganglia (DRG), bladder detrusor smooth muscle, mucosa, and isolated urothelial cells. In DRG, Hrh1 was the most abundantly expressed. Acute histamine exposure evoked Ca2+ influx in select populations of DRG neurons but did not elicit calcium transients in isolated primary urothelial cells. Histamine-induced mechanical hypersensitivity ex vivo was abolished in the presence of the histamine H1 receptor antagonist pyrilamine and was not present in preparations from mice lacking transient receptor potential vanilloid 1 (TRPV1). Together, these results indicate that histamine enhances the sensitivity of bladder afferents to distension via interactions with histamine H1 receptor and TRPV1. This hypersensitivity translates to increased sensory input and activation in the spinal cord, which may underlie the symptoms of bladder hypersensitivity and pain experienced in IC/BPS.

Painful interactions: Microbial compounds and visceral pain

Visceral pain, characterized by abdominal discomfort, originates from organs in the abdominal cavity and is a characteristic symptom in patients suffering from irritable bowel syndrome, vulvodynia or interstitial cystitis. Most organs in which visceral pain originates are in contact with the external milieu and continuously exposed to microbes. In order to maintain homeostasis and prevent infections, the immune- and nervous system in these organs cooperate to sense and eliminate (harmful) microbes. Recognition of microbial components or products by receptors expressed on cells from the immune and nervous system can activate immune responses but may also cause pain. We review the microbial compounds and their receptors that could be involved in visceral pain development.

Cystitis-induced bladder pain is Toll-like receptor 4 dependent in a transgenic autoimmune cystitis murine model: a MAPP Research Network animal study

Altered Toll-like receptor (TLR)4 activation has been identified in several chronic pain conditions but has not been well studied in interstitial cystitis/bladder pain syndrome (IC/BPS). Our previously published human studies indicated that patients with IC/BPS present altered systemic TLR4-mediated inflammatory responses, which were significantly correlated with reported pain severity. In the present study, we sought to determine whether altered TLR4 activation plays a role in pelvic/bladder pain seen in patients with IC/BPS using our validated IC/BPS-like transgenic autoimmune cystitis model (URO-OVA). URO-OVA mice developed responses consistent with pelvic and bladder pain after cystitis induction, which was associated with increased splenocyte production of TLR4-mediated proinflammatory cytokines IL-1β, IL-6, and TNF-α. Increased spinal expression of mRNAs for proinflammatory cytokines IL-6 and TNF-α, glial activation markers CD11b and glial fibrillary acidic protein, and endogenous TLR4 ligand high mobility group box 1 was also observed after cystitis induction. Compared with URO-OVA mice, TLR4-deficient URO-OVA mice developed significantly reduced nociceptive responses, although similar bladder inflammation and voiding dysfunction, after cystitis induction. Intravenous administration of TAK-242 (a TLR4-selective antagonist) significantly attenuated nociceptive responses in cystitis-induced URO-OVA mice, which was associated with reduced splenocyte production of TLR4-mediated IL-1β, IL-6, and TNF-α as well as reduced spinal expression of mRNAs for IL-6, TNF-α, CD11b, glial fibrillary acidic protein, and high mobility group box 1. Our results indicate that altered TLR4 activation plays a critical role in bladder nociception independent of inflammation and voiding dysfunction in the URO-OVA model, providing a potential mechanistic insight and therapeutic target for IC/BPS pain.

Mast cell stabilizer ketotifen reduces hyperalgesia in a rodent model of surgically induced endometriosis

Purpose: This study aimed to investigate the effect of oral treatment with ketotifen, a mast cell (MC) stabilizer, in a rat model of surgically induced endometriosis. Methods: At 14 days after Sprague-Dawley rats had surgery, they were treated with ketotifen (1 or 10 mg/kg/day). Pain behaviors were evaluated 3 days prior to surgery and then at 7, 14, 21, and 28 days after surgery. At day 28, rats were sacrificed and all samples were then processed for biochemical studies. Results: We found that ketotifen-treated rats showed significantly shorter duration of hyperalgesia (p<0.05); smaller cyst diameter (p<0.05) and lower histopathologic score (p<0.001); significantly lower MC number and degranulation (p<0.001), blood vessel number (p<0.001), lower expression levels of nerve growth factor (p<0.001), cyclooxygenase-2 (p<0.001), intercellular cell adhesion molecule-1 (p<0.001), and vascular endothelial growth factor (p<0.05) in cysts, and nerve growth factor (p<0.001) and transient receptor potential cation channel, subfamily V, member 1 (p<0.001) in dorsal root ganglia; and lower histamine (p<0.05) and tumor necrosis factor-alpha (p<0.05) concentrations in serum compared with placebo-treated animal subjects. Conclusion: Oral treatment with ketotifen significantly suppressed the development of hyperalgesia, probably by modulating MC activity in cysts, thereby reducing peripheral sensitization due to noxious signals from endometriotic lesions. Our results suggest that ketotifen may inhibit the development of endometriotic lesions and hyperalgesia in rats.

The potential role of folate metabolism in interstitial cystitis

The topic of interstitial cystitis (IC), also known as painful bladder syndrome (PBS), and folate/one carbon metabolism has previously been unaddressed in research. This narrative review highlights a potential connection for those with mast cell-related IC and histamine-mediated pain that is explored through four conceptual sections. The first section focuses on the nature of mast cell involvement and histamine-mediated pain in some interstitial cystitis patients. The second section reviews the literature on folate status in wider allergic conditions. The third section addresses the role of folate and methylation in general in histamine excretion. Finally, folate metabolism and vascular function are addressed because of the vascular abnormalities present in some IC bladders.

IL-33 mast cell axis is central in LL-37 induced bladder inflammation and pain in a murine interstitial cystitis model

Interstitial cystitis (IC), also known as painful bladder syndrome (PBS), is a debilitating chronic condition that afflicts over 3 million women above the age of 18 in the U.S., and most patients fail to respond to current treatment options. Mast cells have previously been implicated as both a diagnostic and prognostic marker in IC/PBS. Patients with IC/PBS have been shown to have elevated levels of IL-33, a cytokine released in response to tissue insult, in their urine. We hypothesize that mast cell-mediated inflammation induced from IL-33 may play an important role in initiating pain and inflammation in IC/PBS. A human cathelicidin, LL-37, which is found at elevated levels in IC/PBS patients, was used to induce an IC/PBS-like state of inflammation and bladder pain in mast cell deficient C-kit (-/-) and wild type C57Bl/6 (WT) mice. Inflammation was quantified using myeloperoxidase (MPO) expression in bladder tissues measured via ELISA. Response rate to suprapubic stimulation from von Frey filaments was used to assess the relative pain and discomfort. Both types of mice increased IL-33 expression in response to LL-37 exposure. However, mast cell deficient mice demonstrated significantly lower levels of inflammation (p < 0.001) and reduced pain response (p < 0.001) compared to WT mice. These findings implicate an IL-33-mast cell dependent axis with a potential etiology of pain and inflammation in IC/PBS. Future therapeutics aimed at targeting the IL-33 - mast cell axis could potentially serve as useful targets for treating IC/PBS.

Evaluation of different classes of histamine H1 and H2 receptor antagonist effects on neuropathic nociceptive behavior following tibial nerve transection in rats

It seems that histamine release in the site of neuronal injury could contribute to the neuropathic pain mechanism. In the present study, we investigated the anti-allodynic effects of chronic administration of different classes of histamine H₁ and H₂ receptor antagonists on neuropathic nociceptive behavior following tibial nerve transection (TNT) in rats. Peripheral neuropathy was induced by TNT surgery. We performed acetone tests (AT) to record cold allodynia, Von Frey tests (VFT) to measure mechanical allodynia, double plate test (DPT) to evaluate thermal place preference/avoidance and open field test (OFT) for evaluation of animal activity. TNT rats showed a significant mechanical and cold allodynia compared to the sham group. Chlorpheniramine (5 and 15 mg/kg, i.p) significantly attenuated cold allodynia and prevented cold plate avoidance behavior and at the dose of 15 mg/kg remarkably decreased mechanical allodynia. Fexofenadine (10 and 30 mg/kg, p.o) significantly attenuated the mechanical allodynia and prevented cold plate avoidance. Ranitidine (5 and 15 mg/kg, i.p) significantly prevented cold plate avoidance behavior and at the dose of 15 mg/kg notably improved mechanical and cold allodynia. Famotidine (1 and 3 mg/kg, p.o) was ineffective on all nociceptive tests. Gabapantin (100 mg/kg, p.o) significantly improved all types of nociceptive behaviors. These results indicate that both blood brain barrier penetrating (chlorpheniramine) and poorly penetrating (fexofenadine) histamine H₁ receptor antagonists could improve the neuropathic pain sign, but only the blood brain barrier penetrating histamine H₂ receptor antagonist (ranitidine) could produce anti-allodynic effects in the TNT model of neuropathic pain in rats.

Neuroepithelial control of mucosal inflammation in acute cystitis

The nervous system is engaged by infection, indirectly through inflammatory cascades or directly, by bacterial attack on nerve cells. Here we identify a neuro-epithelial activation loop that participates in the control of mucosal inflammation and pain in acute cystitis. We show that infection activates Neurokinin-1 receptor (NK1R) and Substance P (SP) expression in nerve cells and bladder epithelial cells in vitro and in vivo in the urinary bladder mucosa. Specific innate immune response genes regulated this mucosal response, and single gene deletions resulted either in protection (Tlr4^−/− and Il1b^−/− mice) or in accentuated bladder pathology (Asc^−/− and Nlrp3^−/− mice), compared to controls. NK1R/SP expression was lower in Tlr4^−/− and Il1b^−/− mice than in C56BL/6WT controls but in Asc^−/− and Nlrp3^−/− mice, NK1R over-activation accompanied the exaggerated disease phenotype, due, in part to transcriptional de-repression of Tacr1. Pharmacologic NK1R inhibitors attenuated acute cystitis in susceptible mice, supporting a role in disease pathogenesis. Clinical relevance was suggested by elevated urine SP levels in patients with acute cystitis, compared to patients with asymptomatic bacteriuria identifying NK1R/SP as potential therapeutic targets. We propose that NK1R and SP influence the severity of acute cystitis through a neuro-epithelial activation loop that controls pain and mucosal inflammation.

Treatment of Bladder Urothelium Injury

The management of patients with cystitis-related symptoms due to urinary tract infection, bladder pain syndrome (BPS) or radio/chemo-induced cystitis remains challenging. A component in the pathophysiology of these symptoms relates to the fact that the urothelium is a highly metabolically active structure and that alterations in this structure can give rise to a variety of symptoms.

A MAPP Network study: overexpression of tumor necrosis factor-α in mouse urothelium mimics interstitial cystitis

Interstitial cystitis/bladder pain syndrome is a chronic bladder condition associated with pain and voiding dysfunction that is often regarded as a neurogenic cystitis. Patient symptoms are correlated with the presence of urothelial lesions. We previously characterized a murine neurogenic cystitis model that recapitulates mast cell accumulation and urothelial lesions, and these events were dependent on TNF. To further explore the role of TNF in bladder inflammation and function, we generated a transgenic mouse model with chronic TNF overexpression in urothelium under the control of the uroplakin II (UPII) promoter. Transgenic mouse lines were maintained by backcross onto wild-type C57BL/6J mice and evaluated for pelvic tactile allodynia as a measure of visceral pain, urinary function, and urothelial lesions. TNF mRNA and protein were expressed at greater levels in bladders of UPII-TNF mice than in those of wild-type mice. UPII-TNF mice showed significantly increased urinary frequency and decreased void volume. UPII-TNF mice had increased urothelial apoptosis and loss of urothelial integrity consistent with urothelial lesions. Overexpression of TNF was also associated with pelvic tactile allodynia. Consistent with these findings, UPII-TNF mice exhibited increased bladder afferent activity in response to stretch ex vivo. In summary, UPII-TNF mice display significant pelvic pain, voiding dysfunction, urothelial lesions, and sensory input. Thus UPII-TNF mice are a model for characterizing mechanisms of interstitial cystitis symptoms and evaluating therapies.

Ameliorative effects of type-A procyanidins polyphenols from cinnamon bark in compound 48/80-induced mast cell degranulation

Allergic diseases are a significant health concern in developing countries. Type-A procyanidin polyphenols from cinnamon (Cinnamomum zeylanicum Blume) bark (TAPP-CZ) possesses antiasthmatic and antiallergic potential. The present study was aimed at the possible anti-allergic mechanism of TAPP-CZ against the compound 48/80 (C48/80)–induced mast cell degranulation in isolated rat peritoneal mast cells (RPMCs). TAPP-CZ (1, 3, 10, and 30 µg/ml) was incubated for 3 hours with isolated, purified RPMCs. The C48/80 (1 µg/ml) was used to induce mast cell degranulation. The mast cell viability was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay whereas histamine, β-hexosaminidase (β-HEX), and interleukin-4 (IL-4) levels were determined in RPMCs. TAPP-CZ (3, 10, and 30 µg/ml) showed significant and dose-dependent decrease in a number of degranulated cells and levels of markers (histamine, β-HEX, and IL-4) as compared with C48/80 control. In conclusion, TAPP-CZ stabilizes mast cell and cause inhibition of the allergic markers such as histamine, IL-4, and β-HEX in IgE-mediated manner. The present study supports mast cell stabilization as a possible mechanism of action of TAPP-CZ against immune respiratory disorders such as asthma and allergic rhinitis.

Lymphocyte opioid receptors as innovative biomarkers of osteoarthritic pain, for the assessment and risk management of opioid tailored therapy, before hip surgery, to prevent chronic pain and opioid tolerance/addiction development: OpMarkArt (Opioids-Markers-Arthroprosthesis) study protocol for a randomized controlled trial

BACKGROUND

The incidence of post-surgical chronic pain ranges between 20% and 40% in Europe. Osteoarthritis pain after prosthesis implantation is one of the most severe secondary syndromes, depending not only on surgery but also on organic changes before and after joints replacement. No data are available about risk factors. An excessive inflammatory response plays a central role but a best therapy is not defined yet. It is not clear whether opioid administration could influence post-surgical pain and lead to tolerance or addiction. Interestingly, the immune system, together with the nervous and peptidergic ones, is involved in hypersensibility. The connection across the three biological systems lies in the presence of opioid receptors on immune cells surface. Here, we show a method to analyze whether opioids could modulate lymphocytes, by proposing opioid receptors as biological markers to prevent chronic pain and opioid tolerance or addiction after hip surgery.

METHODS/DESIGN

After institutional independent ethics committee approval, 60 patients, in pain and undergoing hip surgery, will be enrolled in a single-blind, randomized, phase IV, pilot study. Pain treatment will be selected inside a class of non-steroidal anti-inflammatory drugs (NAISDs) or paracetamol or a class of opioids, into three medication arms: 25 mg tapentadol twice daily; 75 mg tapentadol twice daily; NSAIDs or paracetamol in accordance with surgeon's custom. For each group, we will collect blood samples before, during and after surgery, to apply molecular analysis. We will perform lymphocyte opioid receptors genes and proteins expression and functional analysis. Data will be statistically analyzed.

DISCUSSION

This project has the potential to obtain a personalized diagnostic kit, by considering lymphocyte opioid receptors as biological markers. Starting from a simple blood sample, it will be possible to decide the best therapy for a single patient. Using a noninvasive approach, we expect to fix a daily standard dose and timing, before and after surgery, to bypass hip chronic pain and the insurgence of tolerance or addiction. The analysis of opioid receptors sensitivity will help to identify the best drug administration in each specific case (tailored therapy).

TRIAL REGISTRATION

ISRCTN, ISRCTN12559751 . Retrospectively registered on 23 May 2017.

Acyloxyacyl hydrolase modulates pelvic pain severity

Chronic pelvic pain causes significant patient morbidity and is a challenge to clinicians. Using a murine neurogenic cystitis model that recapitulates key aspects of interstitial cystitis/bladder pain syndrome (IC), we recently showed that pseudorabies virus (PRV) induces severe pelvic allodynia in BALB/c mice relative to C57BL/6 mice. Here, we report that a quantitative trait locus (QTL) analysis of PRV-induced allodynia in F2_CxB progeny identified a polymorphism on chromosome 13, rs6314295 , significantly associated with allodynia (logarithm of odds = 3.11). The nearby gene encoding acyloxyacyl hydrolase ( Aoah) was induced in the sacral spinal cord of PRV-infected mice. AOAH-deficient mice exhibited increased vesicomotor reflex in response to bladder distension, consistent with spontaneous bladder hypersensitivity, and increased pelvic allodynia in neurogenic cystitis and postbacterial chronic pain models. AOAH deficiency resulted in greater bladder pathology and tumor necrosis factor production in PRV neurogenic cystitis, markers of increased bladder mast cell activation. AOAH immunoreactivity was detectable along the bladder-brain axis, including in brain sites previously correlated with human chronic pelvic pain. Finally, AOAH-deficient mice had significantly higher levels of bladder vascular endothelial growth factor, an emerging marker of chronic pelvic pain in humans. These findings indicate that AOAH modulates pelvic pain severity, suggesting that allelic variation in Aoah influences pelvic pain in IC.

Repeated hapten exposure induces persistent tactile sensitivity in mice modeling localized provoked vulvodynia

Background

Vulvodynia is a remarkably prevalent chronic pain condition of unknown etiology. Epidemiologic studies associate the risk of vulvodynia with a history of atopic disease. We used an established model of hapten-driven contact hypersensitivity to investigate the underlying mechanisms of allergy-provoked prolonged sensitivity to pressure.

Methods

We sensitized female ND4 Swiss mice to the hapten oxazolone on their flanks, and subsequently challenged them four days later with oxazolone or vehicle for ten consecutive days on the labia. We evaluated labiar sensitivity to touch, local mast cell accumulation, and hyperinnervation after ten challenges.

Results

Oxazolone-challenged mice developed significant tactile sensitivity that persisted for over three weeks after labiar allergen exposures ceased. Allergic sites were characterized by mast cell accumulation, sensory hyper-innervation and infiltration of regulatory CD4⁺CD25⁺FoxP3⁺ T cells as well as localized early increases in transcripts encoding Nerve Growth Factor and nerve-mast cell synapse marker Cell Adhesion Molecule 1. Local depletion of mast cells by intra-labiar administration of secretagogue compound 48/80 led to a reduction in both nerve density and tactile sensitivity.

Conclusions

Mast cells regulate allergy-provoked persistent sensitivity to touch. Mast cell-targeted therapeutic strategies may provide novel means to manage and limit chronic pain conditions associated with atopic disease.

Evidence for the Role of Mast Cells in Cystitis-Associated Lower Urinary Tract Dysfunction: A Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network Animal Model Study

Bladder inflammation frequently causes cystitis pain and lower urinary tract dysfunction (LUTD) such as urinary frequency and urgency. Although mast cells have been identified to play a critical role in bladder inflammation and pain, the role of mast cells in cystitis-associated LUTD has not been demonstrated. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic and debilitating inflammatory condition of the urinary bladder characterized by the hallmark symptoms of pelvic pain and LUTD. In this study we investigated the role of mast cells in LUTD using a transgenic autoimmune cystitis model (URO-OVA) that reproduces many clinical correlates of IC/BPS. URO-OVA mice express the membrane form of the model antigen ovalbumin (OVA) as a self-antigen on the urothelium and develop bladder inflammation upon introduction of OVA-specific T cells. To investigate the role of mast cells, we crossed URO-OVA mice with mast cell-deficient Kit^W-sh mice to generate URO-OVA/Kit^W-sh mice that retained urothelial OVA expression but lacked endogenous mast cells. We compared URO-OVA mice with URO-OVA/Kit^W-sh mice with and without mast cell reconstitution in response to cystitis induction. URO-OVA mice developed profound bladder inflammation with increased mast cell counts and LUTD, including increased total number of voids, decreased mean volume voided per micturition, and decreased maximum volume voided per micturition, after cystitis induction. In contrast, similarly cystitis-induced URO-OVA/Kit^W-sh mice developed reduced bladder inflammation with no mast cells and LUTD detected. However, after mast cell reconstitution URO-OVA/Kit^W-sh mice restored the ability to develop bladder inflammation and LUTD following cystitis induction. We further treated URO-OVA mice with cromolyn, a mast cell membrane stabilizer, and found that cromolyn treatment reversed bladder inflammation and LUTD in the animal model. Our results provide direct evidence for the role of mast cells in cystitis-associated LUTD, supporting the use of mast cell inhibitors for treatment of certain forms of IC/BPS.

Host Responses to Urinary Tract Infections and Emerging Therapeutics: Sensation and Pain within the Urinary Tract

Urinary tract infection (UTI) pathogenesis is understood increasingly at the level of the uropathogens and the cellular and molecular mediators of host inflammatory responses. However, little is known about the mediators of symptoms during UTI and what distinguishes symptomatic events from asymptomatic bacteriuria. Here, we review bladder physiology and sensory pathways in the context of an emerging literature from murine models dissecting the host and pathogen factors mediating pain responses during UTI. The bladder urothelium is considered a mediator of sensory responses and appears to play a role in UTI pain responses. Virulence factors of uropathogens induce urothelial damage that could trigger pain due to compromised bladder-barrier function. Instead, bacterial glycolipids are the major determinants of UTI pain independent of urothelial damage, and the O-antigen of lipopolysaccharide modulates pain responses. The extent of pain modulation by O-antigen can have profound effects, from abolishing pain responses to inducing chronic pain that results in central nervous system features reminiscent of neuropathic pain. Although these effects are largely dependent upon Toll-like receptors, pain is independent of inflammation. Surprisingly, some bacteria even possess analgesic properties, suggesting that bacteria exhibit a wide range of pain phenotypes in the bladder. In summary, UTI pain is a complex form of visceral pain that has significant potential to inform our understanding of bacterial pathogenesis and raises the specter of chronic pain resulting from transient infection, as well as novel approaches to treating pain.

Botulinum Toxin A and Lower Urinary Tract Dysfunction: Pathophysiology and Mechanisms of Action

The use of onabotulinumtoxinA (BoNT-A) for the treatment of lower urinary tract diseases (LUTD) has increased markedly in recent years. The indications for BoNT-A treatment of LUTD now include neurogenic or idiopathic detrusor overactivity, interstitial cystitis/bladder pain syndrome and voiding dysfunction. The mechanisms of BoNT-A action on LUTDs affect many different aspects. Traditionally, the effects of BoNT-A were believed to be attributable to inhibition of acetylcholine release from the presynaptic efferent nerves at the neuromuscular junctions in the detrusor or urethral sphincter. BoNT-A injection in the bladder also regulated sensory nerve function by blocking neurotransmitter release and reducing receptor expression in the urothelium. In addition, recent studies revealed an anti-inflammatory effect for BoNT-A. Substance P and nerve growth factor in the urine and bladder tissue decreased after BoNT-A injection. Mast cell activation in the bladder also decreased. BoNT-A-induced improvement of urothelium function plays an important mitigating role in bladder dysfunction. Vascular endothelial growth factor expression in urothelium decreased after BoNT-A injection, as did apoptosis. Studies also revealed increased apoptosis in the prostate after BoNT-A injection. Although BoNT-A injection has been widely used to treat different LUTDs refractory to conventional treatment, currently, onabotulinumtoxinA has been proven effective only on urinary incontinence due to IDO and NDO in several large-scale clinical trials. The effects of onabotulinumtoxinA on other LUTDs such as interstitial cystitis, benign prostatic hyperplasia, dysfunctional voiding or detrusor sphincter dyssynergia have not been well demonstrated.

Sympathetic nervous system and chronic bladder pain: a new tune for an old song

Chronic bladder pain (CBP) patients present with pelvic pain or discomfort during bladder filling, for at least a period of 6 months, which may be accompanied by lower urinary tract symptoms such as frequency, nocturia, and urgency. However, both the etiology of CBP and pathophysiological mechanisms are not well described. A number of clinical and basic animal model findings support involvement of sympathetic nervous system in chronic pain syndromes such as CBP. Examples include sympathetic overactivity and high plasma or urinary catecholamine levels that have a high correlation with nociceptive symptoms. In this review, we explored the current evidence in support of the involvement of sympathetic overactivity in CBP. As bladder inflammation often occurs among subgroups of CBP patients, we discuss the possible role of sympathetic nervous system in mastocytosis as well examples examples of animal models that further support the involvement of sympathetic dysfunction in CBP. As there is substantive evidence for cross-organ sensitization in the pelvis can lead to co-morbidity of genitourinary and gastrointestinal dysfunctions, we also include how sympathetic dysfunction may play a role in a number of co-morbid chronic pain syndromes.

Mast Cell-Mediated Mechanisms of Nociception

Mast cells are tissue-resident immune cells that release immuno-modulators, chemo-attractants, vasoactive compounds, neuropeptides and growth factors in response to allergens and pathogens constituting a first line of host defense. The neuroimmune interface of immune cells modulating synaptic responses has been of increasing interest, and mast cells have been proposed as key players in orchestrating inflammation-associated pain pathobiology due to their proximity to both vasculature and nerve fibers. Molecular underpinnings of mast cell-mediated pain can be disease-specific. Understanding such mechanisms is critical for developing disease-specific targeted therapeutics to improve analgesic outcomes. We review molecular mechanisms that may contribute to nociception in a disease-specific manner.

Phloroglucinol protects the urinary bladder via inhibition of oxidative stress and inflammation in a rat model of cyclophosphamide-induced interstitial cystitis

Background:

Phloroglucinol plays an important role in oxidative stress and inflammatory responses. The effects of phloroglucinol have been proven in various disease models. The aim of the present study was to investigate the efficacy and possible mechanisms of phloroglucinol in the treatment of interstitial cystitis (IC).

Methods:

Thirty-two female Sprague-Dawley (SD) rats were used in this study. IC was induced by intraperitoneal injection of cyclophosphamide (CYP). Rats were randomly allocated to one of four groups (n = 8 per group): A control group, which was injected with saline (75 mg/kg; i.p.) instead of CYP on days 1, 4, and 7; a chronic IC group, which was injected with CYP (75 mg/kg; i.p.) on days 1, 4, and 7; a high-dose (30 mg/kg) phloroglucinol-treated group; and a low-dose (15 mg/kg) phloroglucinol-treated group. On day 8, the rats in each group underwent cystometrography (CMG), and the bladders were examined for evidence of oxidative stress and inflammation. Statistical analysis was performed by analysis of variance (ANOVA) followed by least square difference multiple comparison post-hoc test.

Results:

Histological evaluation showed that bladder inflammation in CYP-treated rats was suppressed by phloroglucinol. CMG revealed that the CYP treatment induced overactive bladder in rats that was reversed by phloroglucinol. Up-regulated tumor necrosis factor-α and interleukin-6 expression in the CYP-treated rats were also suppressed in the phloroglucinol treated rats. CYP treatment significantly increased myeloperoxidase activity as well as the decreased activities of catalase of the bladder, which was reversed by treatment with phloroglucinol.

Conclusions:

The application of phloroglucinol suppressed oxidative stress, inflammation, and overactivity in the bladder. This may provide a new treatment strategy for IC.

Animal Models of Urologic Chronic Pelvic Pain Syndromes: Findings From the Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network

OBJECTIVE

To describe the approach taken by the Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network investigators to advance the utility of urologic chronic pelvic pain syndromes (UCPPS) animal models.

METHODS

A multidisciplinary team of investigators representing basic science and clinical expertise defined key phenotypic criteria for rodent models of UCPPS. UCPPS symptoms were prioritized based on their clinical significance. Methods for quantifying animal correlates to patient symptoms were developed. The methods were implemented across proposed rodent models for evaluation and comparison of animals for phenotypic characteristics relevant to human symptomatology.

RESULTS

Pelvic pain and urinary frequency were deemed primary features of human UCPPS and were prioritized for assessment in animals. Nociception was quantified using visceromotor response to bladder distention and by applying von Frey filaments to the lower abdomen (referred tactile allodynia). Micturition activity was assessed as free voiding using micturition cages or blotting pad assays and in response to bladder filling by cystometry. Models varied in both depth of characterization and degree of recapitulating pelvic pain and urinary frequency characteristics of UCPPS.

CONCLUSION

Rodent models that reflect multiple key characteristics of human UCPPS may be identified and provide enhanced clinical significance to mechanistic studies. We have developed a strategy for evaluating current and future animal models of UCPPS based on human symptomatology. This approach provides a foundation for improved translation between mechanistic studies in animals and clinical research and serves as a validation strategy for assessing validity of models for symptom-driven disorders of unknown etiology.

Mechanisms of pain from urinary tract infection

The pain response to urinary tract infection is largely uncharacterized, but the symptomatic response to urinary tract infection contrasts with the lack of pain response among individuals with asymptomatic bacteriuria. Quantifying pelvic pain in a murine urinary tract infection model, uropathogenic Escerichia coli induces transient pelvic pain, whereas an asymptomatic bacteriuria E. coli isolate causes no pain, thus recapitulating the spectrum of clinical responses to intravesical E. coli. These differential pain responses are not correlated with bladder colonization or inflammation, but instead are intrinsic to E. coli lipopolysaccharide and dependent on the lipopolysaccharide receptor, TLR4. Epidemiological data suggest a link between interstitial cystitis and a history of urinary tract infection, so it was evaluated whether repetitive uropathogenic E. coli instillation would result in chronic pain through central sensitization. Although repeated infection with wild type uropathogenic E. coli results in only transient episodes of acute pain, a uropathogenic E. coli mutant lacking O-antigen causes chronic, post-urinary tract infection pelvic pain. Similarly, a K-12 E. coli strain lacking O-antigen induces chronic pain that persisted long after bacterial clearance, and expressing O-antigen nullified the pain phenotype. Spinal cords isolated from mice with post-urinary tract infection chronic pain showed deficits in short-term depression consistent with central sensitization. Deleting O-antigen gene complex from a uropathogenic E. coli strain and subsequent heterologous expression of O-antigen gene clusters shows that a single bacterial isolate can exhibit pain phenotypes ranging from a null phenotype, an acute pain phenotype, to a chronic pain phenotype. Post-urinary tract infection chronic pain is also associated with voiding dysfunction and anxious/depressive behavior. These effects are also mediated by TRPV1 at the level of pain establishment and CCR2 at the level of pain maintenance. Together, these findings show that transient infection with E. coli might result in chronic visceral pain with the hallmarks of neuropathic pain. This pattern of behaviors mimics the spectrum of interstitial cystitis symptoms, thus supporting the possibility of an infectious etiology of interstitial cystitis.

Mast cells infiltration and decreased E-cadherin expression in ketamine-induced cystitis

Background

Ketamine is a controlled substance and often illegally used as a recreational drug primarily by young adults. Increasing ketamine abusers associated with lower urinary tract symptoms have been reported at hospitals in recent years. Here we used a murine model to explore the changes of bladder in order to elucidate its pathogenesis.

Methods

ICR mice were randomly distributed into control and ketamine groups and received daily intraperitoneal injection of saline and ketamine (30 mg/kg), respectively. The bladders were excised and processed for histology at 4, 8 and 12 weeks. Tryptase and E-cadherin were investigated by immunohistochemistry in bladder tissues from ketamine-treated and control mice to assess the mast cell activation and junction protein expression.

Results

After ketamine treatment, the bladder changed to be hyperemic, inflamed, and with more fissures in mucosa. Compared with control group, the number of tryptase-positive mast cells significantly increased, which was 6.98 ± 2.89 and 23.00 ± 6.48 cells per field (100×) at 8 and 12 weeks, respectively (P = 0.016 and P = 0.003, respectively). Additionally, the expression of E-cadherin in ketamine-treated mice bladder tissue was significantly lower than that in the control tissues, P < 0.001.

Conclusions

Increased mast cells in bladder wall and downregulated expression of E-cadherin junction protein in epithelial cells were probably associated with interstitial inflammation and fissures in mucosa. It implied that ketamine induced an interstitial cystitis.

Asymptomatic bacteriuria Escherichia coli are live biotherapeutics for UTI

Urinary tract infections (UTI) account for approximately 8 million clinic visits annually with symptoms that include acute pelvic pain, dysuria, and irritative voiding. Empiric UTI management with antimicrobials is complicated by increasing antimicrobial resistance among uropathogens, but live biotherapeutics products (LBPs), such as asymptomatic bacteriuria (ASB) strains of E. coli, offer the potential to circumvent antimicrobial resistance. Here we evaluated ASB E. coli as LBPs, relative to ciprofloxacin, for efficacy against infection and visceral pain in a murine UTI model. Visceral pain was quantified as tactile allodynia of the pelvic region in response to mechanical stimulation with von Frey filaments. Whereas ciprofloxacin promoted clearance of uropathogenic E. coli (UPEC), it did not reduce pelvic tactile allodynia, a measure of visceral pain. In contrast, ASB E. coli administered intravesically or intravaginally provided comparable reduction of allodynia similar to intravesical lidocaine. Moreover, ASB E. coli were similarly effective against UTI allodynia induced by Proteus mirabilis, Enterococccus faecalis and Klebsiella pneumoniae. Therefore, ASB E. coli have anti-infective activity comparable to the current standard of care yet also provide superior analgesia. These studies suggest that ASB E. coli represent novel LBPs for UTI symptoms.