Nerve growth factor expression and release in allergic inflammatory disease of the upper airways

The pharmacotherapeutic management of allergic rhinitis in people with asthma

INTRODUCTION

Up to 90% of asthmatic patients have comorbid allergic rhinitis (AR). Although appropriate therapy of AR can improve asthma symptoms and management, AR is often underdiagnosed and under-treated in asthmatics.A non-systematic literature research was conducted on AR as a comorbidity and risk factor of asthma. Latest international publications in medical databases, international guidelines, and the Internet were reviewed.

AREAS COVERED

Based on the conducted literature research there is proved evidence of the necessity of diagnosis and treatment of AR in patients with asthma because it affects health care utilization. Therefore, it is recommended in national and global guidelines.

EXPERT OPINION

AR increases the risk of asthma development and contributes to the severity of an existing asthma. Early treatment of AR with drugs as intranasal steroids, antihistamines, leukotriene receptor antagonists, and especially allergen-specific immunotherapy can reduce the risk of asthma development and the concomitant medication use in addition to severity of symptoms in AR and asthma.

Neuroimmune communication in allergic rhinitis

The prevalence rate of allergic rhinitis (AR) is high worldwide. The inhalation of allergens induces AR, which is an immunoglobulin E-mediated and type 2 inflammation-driven disease. Recently, the role of neuroimmune communication in AR pathogenesis has piqued the interest of the scientific community. Various neuropeptides, such as substance P (SP), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), nerve growth factor (NGF), and neuromedin U (NMU), released via "axon reflexes" or "central sensitization" exert regulatory effects on immune cells to elicit "neurogenic inflammation," which contributes to nasal hyperresponsiveness (NHR) in AR. Additionally, neuropeptides can be produced in immune cells. The frequent colocalization of immune and neuronal cells at certain anatomical regions promotes the establishment of neuroimmune cell units, such as nerve-mast cells, nerve-type 2 innate lymphoid cells (ILC2s), nerve-eosinophils and nerve-basophils units. Receptors expressed both on immune cells and neurons, such as TRPV1, TRPA1, and Mas-related G protein-coupled receptor X2 (MRGPRX2) mediate AR pathogenesis. This review focused on elucidating the mechanisms underlying neuroimmune communication in AR.

[Neuroimmunology of allergic rhinitis part 2 : Interactions of neurons and immune cells and neuroimmunological units]

Allergic rhinitis is an IgE-mediated, type‑2 inflammatory disease. neuropeptides are released by neurons and interact with immune cells. Via colocalization, neuroimmune cell units such as nerve-mast cell units, nerve-type 2 innate lymphoid cell (ILC2) units, nerve-eosinophil units, and nerve-basophil units are formed. Markedly elevated tryptase levels were found in nasal lavage fluid and were strongly associated with neuropeptide levels. A close anatomical connection allows bidirectional communication between immune and neuronal cells. Transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin repeat 1 (TRPA1) are critically involved in immunological reactions in the setting of allergic rhinitis. Neuroimmunological communication plays an important role in the inflammatory process, so that allergic rhinitis can no longer be considered a purely immunological disease, but rather a combined neuroimmunological disease.

[Neuroimmunology of allergic rhinitis : Part 1: Cellular and humoral basic principles]

Allergic rhinitis (AR) is a very common disease with a high prevalence worldwide. It is an IgE-mediated type 2 inflammatory disease following exposure to inhalant allergens. A multitude of different neuropeptides including substance P, vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), nerve growth factor (NGF), and neuromedin U (NMU) can be released via peripheral axon or central reflexes, interact with immune cells, and thus contribute to neurogenic inflammation which causes the nasal hyperreactivity (NHR) characteristic of AR. Independent production of neuroendocrine hormones and neuropeptides by immune cells has also been demonstrated. Neuro-immune cell units arise when immune and neuronal cells colocalize, for which typical anatomic regions are, e.g., the mast cell-nerve functional unit. The focus of this review is the elucidation of neuroimmune communication mechanisms in AR.

Allergic rhinitis

Allergic rhinitis (AR) is caused by immunoglobulin E (IgE)-mediated reactions to inhaled allergens and is one of the most common chronic conditions globally. AR often co-occurs with asthma and conjunctivitis and is a global health problem causing major burden and disability worldwide. Risk factors include inhalant and occupational allergens, as well as genetic factors. AR impairs quality of life, affects social life, school and work, and is associated with substantial economic costs. The Allergic Rhinitis and its Impact on Asthma (ARIA) initiative classified AR into intermittent or persistent and mild or moderate/severe. The diagnosis is based on the clinical history and, if needed in patients with uncontrolled rhinitis despite medications or with long-lasting symptoms, on skin tests or the presence of serum-specific IgE antibodies to allergens. The most frequently used pharmacological treatments include oral, intranasal or ocular H₁-antihistamines, intranasal corticosteroids or a fixed combination of intranasal H₁-antihistamines and corticosteroids. Allergen immunotherapy prescribed by a specialist using high-quality extracts in stratified patients is effective in patients with persistent symptoms. Real-world data obtained by mobile technology offer new insights into AR phenotypes and management. The outlook for AR includes a better understanding of novel multimorbid phenotypes, health technology assessment and patient-centred shared decision-making.

Neurotrophic factors and nerve growth factor in ocular allergy

PURPOSE OF REVIEW

During allergic reaction, nervous and immune systems mutually interact through release of mediators, including neurotrophic factors and nerve growth factor (NGF). These mediators modulate allergic reaction through binding their receptors expressed by immune and structural cells and by stimulating neuropeptide release by nerves. The role of neuropeptides and NGF has been demonstrated in allergic asthma and rhinitis, and, to a lesser extent, in allergic conjunctivitis. The aim of this review are to elucidate the evidence of the role of NGF and neuropeptides in the pathogenesis of allergic conjunctivitis.

RECENT FINDINGS

NGF modulates allergic reaction by stimulating release of cytokines, inflammatory mediators and neuropeptides by immune and structural cells and nerve endings at the site of inflammation. Evidence showed that local and systemic NGF levels increase in patients with allergic conjunctivitis, including allergic rhinoconjuncivitis, vernal keratoconjunctivitis and atopic keratoconjunctivitis. We recently described an increase of conjunctival p75NTR expression in patients with allergic rhinoconjuncivitis, and an increase of tear levels of NGF after conjunctival provocation test with allergen.

SUMMARY

NGF modulates ocular allergic reaction. Increasing understanding of the role of neuropeptides in allergic conjunctivitis may pave the way to the development of novel therapeutic approaches and improvement of patients' management.

Immunoregulatory Effects of Neuropeptides on Endothelial Cells: Relevance to Dermatological Disorders

Many skin diseases, including psoriasis and atopic dermatitis, have a neurogenic component. In this regard, bidirectional interactions between components of the nervous system and multiple target cells in the skin and elsewhere have been receiving increasing attention. Neuropeptides released by sensory nerves that innervate the skin can directly modulate functions of keratinocytes, Langerhans cells, dermal dendritic cells, mast cells, dermal microvascular endothelial cells and infiltrating immune cells. As a result, neuropeptides and neuropeptide receptors participate in a complex, interdependent network of mediators that modulate the skin immune system, skin inflammation, and wound healing. In this review, we will focus on recent studies demonstrating the roles of α-melanocyte-stimulating hormone, calcitonin gene-related peptide, substance P, somatostatin, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, and nerve growth factor in modulating inflammation and immunity in the skin through their effects on dermal microvascular endothelial cells.

Short-term Haze Exposure Predisposes Healthy Volunteers to Nasal Inflammation

PURPOSE

This study aimed to investigate the impact of short-term haze exposure on nasal inflammation in healthy volunteers.

METHODS

Thirty-three healthy university students were assessed for nasal symptoms, nasal patency, upper and lower respiratory tract nitric oxide (NO) as well as inflammatory mediators and neuropeptides in nasal secretions before and after a 5-day haze episode. Peripheral blood mononuclear cells (PBMCs) were stimulated with particulate matter with an aerodynamic diameter of less than 2.5 μm (PM_2.5), and cytokines in the supernatants were examined.

RESULTS

Mild nasal symptoms were reported by some participants during the haze episode. Objective measures of nasal patency demonstrated that nasal airway resistance was significantly increased from baseline levels, while nasal cavity volume and minimum cross-sectional area were significantly decreased. Similarly, the levels of nasal and exhaled NO, eotaxin, interleukin (IL)-5, chemokine (C-C motif) ligand 17, IL-8, substance P, nerve growth factor and vasoactive intestinal peptides in nasal secretions were significantly increased from baseline values following the haze episode. In contrast, the levels of interferon-γ, IL-10, transforming growth factor-β and neuropeptide Y were significantly decreased. Incubation with 0.1-10 μg/mL PM2.5 significantly increased release of IL-1β, IL-4, IL-5, IL-8 and IL-10 from PBMCs.

CONCLUSIONS

Short-term haze exposure may lead to nasal inflammation and hypersensitivity in healthy subjects predominantly by Th2 cytokine-mediated immune responses.

Neuro-immune interactions in allergic diseases: novel targets for therapeutics

Recent studies have highlighted an emerging role for neuro-immune interactions in mediating allergic diseases. Allergies are caused by an overactive immune response to a foreign antigen. The peripheral sensory and autonomic nervous system densely innervates mucosal barrier tissues including the skin, respiratory tract and gastrointestinal (GI) tract that are exposed to allergens. It is increasingly clear that neurons actively communicate with and regulate the function of mast cells, dendritic cells, eosinophils, Th2 cells and type 2 innate lymphoid cells in allergic inflammation. Several mechanisms of cross-talk between the two systems have been uncovered, with potential anatomical specificity. Immune cells release inflammatory mediators including histamine, cytokines or neurotrophins that directly activate sensory neurons to mediate itch in the skin, cough/sneezing and bronchoconstriction in the respiratory tract and motility in the GI tract. Upon activation, these peripheral neurons release neurotransmitters and neuropeptides that directly act on immune cells to modulate their function. Somatosensory and visceral afferent neurons release neuropeptides including calcitonin gene-related peptide, substance P and vasoactive intestinal peptide, which can act on type 2 immune cells to drive allergic inflammation. Autonomic neurons release neurotransmitters including acetylcholine and noradrenaline that signal to both innate and adaptive immune cells. Neuro-immune signaling may play a central role in the physiopathology of allergic diseases including atopic dermatitis, asthma and food allergies. Therefore, getting a better understanding of these cellular and molecular neuro-immune interactions could lead to novel therapeutic approaches to treat allergic diseases.

Anti-nerve growth factor antibody improves airway hyperresponsiveness by down-regulating RhoA

BACKGROUND

The pathogenesis of asthma is complex and continues to be considered as a challenging subject. Some studies have shown that nerve growth factor (NGF) participates in the pathogenesis of asthma, but the mechanism of airway contraction caused by NGF is still unclear.

OBJECTIVE

Our aim was to discuss the effect of anti-NGF antibody on RhoA expression, and further explore the role of NGF in airway hyperresponsiveness (AHR).

METHODS

Thirty female BALB/c mice were divided into three groups randomly: control group (group C, n = 10), asthma group (group A, n = 10) and anti-NGF antibody intervention group (group N, n = 10). The asthmatic mice were stimulated by OVA suspension, the intervention mice were given nasal instillation of anti-NGF antibody before the stimulation. Airway responsiveness, eosinophils, IL-13, IFN-γ were measured. The protein expression and mRNA level of NGF and RhoA were detected by immunohistochemical and Real Time-PCR (RT-PCR) analyses.

RESULTS

Airway responsiveness, eosinophils and IL-13 levels in group A were significantly increased compare with the other groups, and significantly decreased in group N than those in group A. IFN-γ level was significantly reduced in group A and increased in group N. Immunohistochemistry and RT-PCR analyses showed that the protein expression and mRNA level of NGF and RhoA were significantly increased in group A and significantly decreased in group N.

CONCLUSION

NGF participates in the pathogenesis of asthma in mice. Anti-NGF antibody can inhibit airway inflammation and alleviate AHR by down-regulating the protein expression and mRNA level of RhoA.

Nerve growth factor: a neuroimmune crosstalk mediator for all seasons

Neurotrophic factors comprise a broad family of biomolecules - most of which are peptides or small proteins - that support the growth, survival and differentiation of both developing and mature neurons. The prototypical example and best-characterized neurotrophic factor is nerve growth factor (NGF), which is widely recognized as a target-derived factor responsible for the survival and maintenance of the phenotype of specific subsets of peripheral neurons and basal forebrain cholinergic nuclei during development and maturation. In addition to being active in a wide array of non-nervous system cells, NGF is also synthesized by a range of cell types not considered as classical targets for innervation by NGF-dependent neurons; these include cells of the immune-haematopoietic lineage and populations in the brain involved in neuroendocrine functions. NGF concentrations are elevated in numerous inflammatory and autoimmune states such as multiple sclerosis, chronic arthritis, systemic lupus erythematosus and mastocytosis, in conjunction with increased accumulation of mast cells. Intriguingly, NGF seems to be linked also with diabetic pathology and insulin homeostasis. Mast cells and NGF appear involved in neuroimmune interactions and tissue inflammation. As mast cells are capable of producing and responding to NGF, this suggests that alterations in mast cell behaviour could provoke maladaptive neuroimmune tissue responses, including those of an autoimmune nature. Moreover, NGF exerts a modulatory role on sensory nociceptive nerve physiology in the adult, which appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. NGF can therefore be viewed as a multifactorial modulator of neuro-immune-endocrine functions.

Effect of melatonin supplemented at the light or dark period on recovery of sciatic nerve injury in rats

Peripheral nerve injuries can cause disabilities, social or economic problems. Melatonin, the secretory product of the pineal gland has antioxidant and anti-inflammatory actions. The aim of the present study was to investigate the effect of melatonin on the recovery of sciatic nerve after injury, comparing its effect when given in the light or the dark periods. Forty adult male Albino rats were allocated into four groups: control, nerve injury, nerve injury + melatonin given at light and nerve injury + melatonin given at dark. Nerve injury was initiated by clamping the sciatic nerve. Sciatic functional index (SFI) was measured preoperatively and postoperatively. Melatonin was given daily for six weeks. Recovery of the function was analyzed by functional analysis, electrophysiological analysis and biochemical measurement of Superoxide dismutase (SOD), Interleukin 1-beta (IL-1 β), Nerve growth factor (NGF), and bcl-2. Melatonin improved SFI, nerve conduction velocity (NCV) and the force of gastrocnemius muscle contraction as compared to the untreated rats. SOD activity, NGF, and bcl-2 were significantly increased, while IL-1β was significantly decreased after melatonin treatment as compared to the untreated injury group. SFI reached the control level; muscle contraction and IL-1B were significantly improved in the group treated with melatonin in the dark. Melatonin fastened the neural recovery and may be used in the treatment of nerve injury and it induced better nerve regeneration when the rats were treated during the dark period.

The Role of Neurotrophins in Inflammation and Allergy

Allergic inflammation is the result of a specific pattern of cellular and humoral responses leading to the activation of the innate and adaptive immune system, which, in turn, results in physiological and structural changes affecting target tissues such as the airways and the skin. Eosinophil activation and the production of soluble mediators such as IgE antibodies are pivotal features in the pathophysiology of allergic diseases. In the past few years, however, convincing evidence has shown that neurons and other neurosensory structures are not only a target of the inflammatory process but also participate in the regulation of immune responses by actively releasing soluble mediators. The main products of these activated sensory neurons are a family of protein growth factors called neurotrophins. They were first isolated in the central nervous system and identified as important factors for the survival and differentiation of neurons during fetal and postnatal development as well as neuronal maintenance later in life. Four members of this family have been identified and well defined: nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, and neurotrophin 4/5. Neurotrophins play a critical role in the bidirectional signaling mechanisms between immune cells and the neurosensory network structures in the airways and the skin. Pruritus and airway hyperresponsiveness, two major features of atopic dermatitis and asthma, respectively, are associated with the disruption of the neurosensory network activities. In this chapter, we provide a comprehensive description of the neuroimmune interactions underlying the pathophysiological mechanisms of allergic and inflammatory diseases.

Side-stream tobacco smoke-induced airway hyperresponsiveness in early postnatal period is involved nerve growth factor

Epidemiological studies have shown that children are more susceptible to adverse respiratory effects of passive smoking than adults. The goal of this study is to elucidate the possible neural mechanism induced by exposure to passive smoking during early life. Postnatal day (PD) 2 and PD 21 mice were exposed to side-stream tobacco smoke (SS), a surrogate to secondhand smoke, or filtered air (FA) for 10 consecutive days. Pulmonary function, substance P (SP) airway innervation, neurotrophin gene expression in lung and nerve growth factor (NGF) release in bronchoalveolar lavage (BAL) fluid were measured at different times after the last SS or FA exposure. Exposure to SS significantly altered pulmonary function in PD2, accompanied with an enhanced SP innervation in airway. However, exposure to SS during the later developmental period (PD21) did not appear to affect pulmonary function and SP innervation of the airways. Interestingly, SS exposure in PD2 group significantly induced an increased gene expression on NGF, and decreased NGF receptor P75 in lung; parallel with high levels of NGF protein in BAL. Furthermore, pretreatment with NGF antibody significantly diminished SS-induced airway hyperresponsivenss and the increased SP airway innervation in the PD2 group. These findings suggest that enhanced NGF released in the lung contributes to SS-enhanced SP tracheal innervation and airway responsiveness in early life.

Neuroimmunity: Physiology and Pathology

Evolution has yielded multiple complex and complementary mechanisms to detect environmental danger and protect tissues from damage. The nervous system rapidly processes information and coordinates complex defense behaviors, and the immune system eliminates diverse threats by virtue of mobile, specialized cell populations. The two systems are tightly integrated, cooperating in local and systemic reflexes that restore homeostasis in response to tissue injury and infection. They further share a broad common language of cytokines, growth factors, and neuropeptides that enables bidirectional communication. However, this reciprocal cross talk permits amplification of maladaptive feedforward inflammatory loops that contribute to the development of allergy, autoimmunity, itch, and pain. Appreciating the immune and nervous systems as a holistic, coordinated defense system provides both new insights into inflammation and exciting opportunities for managing acute and chronic inflammatory diseases.

Local Effect of Neurotrophin-3 in Neuronal Inflammation of Allergic Rhinitis: Preliminary Report

BACKGROUND

Allergic rhinitis is a common inflammatory nasal mucosal disease characterized by sneezing, watery nasal discharge, nasal obstruction and itching. Although allergen-specific antibodies play a main role in the allergic airway inflammation, neuronal inflammation may also contribute to the symptoms of allergic rhinitis. Neuronal inflammation is primarily caused by the stimulation of sensory nerve endings with histamine. It has been shown that neurotrophins may also have a role in allergic reactions and neuronal inflammation. Nerve growth factor, neurotrophin 3 (NT-3), neurotrophin 4/5 and brain-derived neurotrophic factor are members of the neurotrophin family. Although nerve growth factor and brain-derived neurotrophic factor are well studied in allergic rhinitis patients, the exact role of Neurotrophin-3 is not known.

AIMS

To investigate the possible roles of neurotrophin-3 in allergic rhinitis patients.

STUDY DESIGN

Case-control study.

METHODS

Neurotrophin-3 levels were studied in the inferior turbinate and serum samples of 20 allergic rhinitis and 13 control patients. Neurotrophin-3 staining of nasal tissues was evaluated by immunohistochemistry and ELISA was used for the determination of serum Neurotrophin-3 levels.

RESULTS

Neurotrophin-3 staining scores were statistically higher in the study group than in the control patients (p=0.001). Regarding serum Neurotrophin-3 levels, no statistically significant difference could be determined between allergic rhinitis and control patients (p=0.156). When comparing the serum NT-3 levels with tissue staining scores, there were no statistically significant differences in the allergic rhinitis and control groups (p=0.254 for allergic rhinitis and p=0.624 for control groups).

CONCLUSION

We suggest that Neurotrophin-3 might affect the nasal mucosa locally without being released into the systemic circulation in allergic rhinitis patients.

Sensory nerves in lung and airways

Sensory nerves innervating the lung and airways play an important role in regulating various cardiopulmonary functions and maintaining homeostasis under both healthy and disease conditions. Their activities conducted by both vagal and sympathetic afferents are also responsible for eliciting important defense reflexes that protect the lung and body from potential health-hazardous effects of airborne particulates and chemical irritants. This article reviews the morphology, transduction properties, reflex functions, and respiratory sensations of these receptors, focusing primarily on recent findings derived from using new technologies such as neural immunochemistry, isolated airway-nerve preparation, cultured airway neurons, patch-clamp electrophysiology, transgenic mice, and other cellular and molecular approaches. Studies of the signal transduction of mechanosensitive afferents have revealed a new concept of sensory unit and cellular mechanism of activation, and identified additional types of sensory receptors in the lung. Chemosensitive properties of these lung afferents are further characterized by the expression of specific ligand-gated ion channels on nerve terminals, ganglion origin, and responses to the action of various inflammatory cells, mediators, and cytokines during acute and chronic airway inflammation and injuries. Increasing interest and extensive investigations have been focused on uncovering the mechanisms underlying hypersensitivity of these airway afferents, and their role in the manifestation of various symptoms under pathophysiological conditions. Several important and challenging questions regarding these sensory nerves are discussed. Searching for these answers will be a critical step in developing the translational research and effective treatments of airway diseases.

High-intensity focused ultrasound leads to histopathologic changes of the inferior turbinate mucosa with allergic inflammation

This study was aimed at understanding the histopathologic changes that occur in the nasal mucosa of patients with perennial allergic rhinitis after high-intensity focused ultrasound (HIFU) treatment. Biopsy specimens of the inferior turbinate mucosa were taken from 11 PAR patients before, immediately after and 1 y after HIFU treatment. Morphometric analysis revealed that the density of eosinophils and other inflammatory cells increased immediately after treatment and then were decreased significantly 1 y post-treatment. Submucosal glands were swollen and venous sinusoids were dilated, but there was no statistically significant change in their density, immediately after treatment. However, both glands and venous sinusoids significantly decreased in number 1 y after HIFU treatment. The ciliated epithelium or basement membrane of the nasal mucosa was well preserved at all stages. In conclusion, HIFU is a tolerable and effective treatment to reduce inflammation of the inferior turbinate mucosa in patients with perennial allergic rhinitis.

Vitamin A increases nerve growth factor and retinoic acid receptor beta and improves diabetic neuropathy in rats

All-trans retinoic acid (ATRA) promotes the endogenous expression of both nerve growth factor (NGF) and retinoic acid receptor beta (RAR-β). We have previously shown that the administration of ATRA partly reverts the damage induced by diabetic neuropathy (DN). In this investigation, we evaluated the effects of vitamin A, a commercial, inexpensive compound of retinoic acid, on the therapy of DN. A total of 70 rats were randomized into 4 groups. Group A was the control, and groups B, C, and D received a total dose of 60 mg/kg streptozotocin intraperitoneally. When signs of DN developed, groups C and D were treated either with vitamin A (20,000 IU) or with ATRA 25 mg/kg for 60 days. Plasma glucose, contents of NGF, thermal and nociceptive tests, and RAR-β expression were evaluated. All diabetic rats developed neuropathy. The treatment with vitamin A and ATRA reverted similarly the sensorial disturbances, which was associated with increased contents of NGF and RAR-β expression. Our results indicate that the administration of vitamin A has the same therapeutic effect as ATRA on peripheral neuropathy and suggest its potential therapeutic use in patients with diabetes.

Expression of neuronal protein Kidins220/ARMS in the spleen and peripheral blood of mice following airway allergen challenge

Nerve growth factor (NGF), combined with the high-affinity tyrosine kinase receptor A (TrkA), has been reported to be involved in the pathogenesis of asthma. Ankyrin-rich membrane spanning/transmembrane substrate of protein kinase D (ARMS/Kidins220), a TrkA‑binding protein, modulates the NGF signaling pathway. The aim of the present study was to investigate the expression of Kidins220/ARMS and the effect NGF has on the protein in the spleen and peripheral blood, following airway allergen challenge in mice. BALB/c mice were sensitized and challenged with ovalbumin. The effects of NGF on Kidins220/ARMS in the spleen and peripheral blood of mice were assessed by administering anti-NGF antibody. Expression of ARMS, interleukin (IL)-1β and IL-4 in the spleen and peripheral blood was observed by reverse transcription-polymerase chain reaction, western blot analysis and immunohistochemistry. Pathological changes in the bronchi and lung tissues were examined by hematoxylin and eosin staining. Results showed that Kidins220/ARMS, IL-1β and IL-4 were overexpressed in the spleen and peripheral blood following allergen challenge, compared with the control mice. Moreover, following treatment with anti-NGF, the levels of Kidins220/ARMS, IL-1β and IL-4 in the mice were downregulated. Therefore, the results of the present study showed that Kidins220/ARMS is expressed in the spleen and peripheral blood of normal BALB/c mice and may participate in the immuno-inflammation of asthma through the NGF-mediated signaling pathway.

Enhanced nerve growth factor expression by mast cells does not differ significantly between idiopathic and allergic rhinitis

BACKGROUND

The role of neurotrophins in allergic rhinitis (AR) has been well studied, but it has not been evaluated in idiopathic rhinitis (IR).

OBJECTIVE

We aimed to evaluate the nasal β-nerve growth factor (β-NGF) expressions of mast cells in patients with AR and IR.

METHODS

Seventeen patients with house dust mites-induced persistent moderate/severe allergic rhinitis (mean age: 29.7 ± 11.96), 14 patients with idiopathic rhinitis (mean age, 29.3 ± 10.62), and 16 healthy controls (29.9 ± 11.57) were included in the study. Nasal biopsy specimens were taken from the posterior part of the inferior turbinate from all of the study subjects. Nasal β-nerve growth factor and its receptors, pan-neurotrophin receptor p75, and tyrosine kinase A (trkA) were assessed with an immunofluorescence assay. Mast cells were determined by both an immunofluorescence assay and immunohistochemistry as tryptase-positive cells.

RESULTS

The β-NGF, trkA, and p75 receptor counts were significantly higher in AR and IR patients than in the control group (P < .001, for each), but they were not different between AR and IR patients. Similarly, the ratio of β-NGF+ mast cells/total mast cells and the ratio of β-NGF+ mast cells/total β-NGF+ cells in AR and IR patients was found to be elevated when compared with the control group (P < .001, P < .001, P < .001, and P = .046, respectively); furthermore, the 2 ratios were not statistically different between the 2 patient groups.

CONCLUSION

The increase in β-NGF-expressing mast cells does not differ between idiopathic and allergic rhinitis. Therefore, we propose that mast cells do play a role in the pathogenesis of IR as important as in that of AR.

Investigation of the antiallergic activity of olopatadine on rhinitis induced by intranasal instillation of antigen in sensitized rats using thermography

Background

The main symptoms of allergic rhinitis (AR) are sneezing, rhinorrhea and nasal obstruction. It was reported that the nasal skin temperature after intranasal administration of histamine or grass pollen rose. In patients with AR, the levels of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) have increased in nasal fluids and mucosa.

Objective

The present study were to determine the temperature changes of the nose in rat allergic rhinitis model, and if olopatadine, an antiallergic agent with histamine H1 receptor antagonistic action, proved to be effective, were studied the productions of NGF and VEGF in nasal lavage fluids (NALF). In the present study, we used ovalbumin (OVA)-sensitized rats as an animal model of nasal allergy and examined the effects of olopatadine on the skin temperature of the nose area, and the productions of NGF and VEGF in NALF.

Methods

The temperature changes of the nose area were carried out with thermo tracer in rat passively sensitized with OVA antiserum. The numbers of sneezing episodes were counted and, NGF and VEGF levels in NALF were examined using the specific ELISA.

Results

In OVA-sensitized rats, the number of sneezing episodes increase and the nasal skin temperature rise were provoked after OVA challenge. The levels of NGF and VEGF in NALF also were increased. Olopatadine reduced the increased frequency of sneezing and the nasal skin temperature rise. It also inhibited the increased NGF and VEGF productions in NALF.

Conclusion

The nasal skin temperature after OVA challenge rose even in OVA-sensitized rats. These results suggest that the suppression of the increased NGF and VEGF levels might partially be involved in the improvement of allergy-like behavior (sneezing and nasal skin temperature rise) by the treatment of olopatadine.

Allergic rhinitis: an update on disease, present treatments and future prospects

Allergic rhinitis (AR) is an inflammation of nasal mucosa mediated by IgE-associated processes occurring independently, or concurrently with asthma. AR is characterized by sensitization-formation and expression of antigen specific IgE, followed by inflammation in two phases. The early phase response involves cross linking of IgE molecules leading to degranulation of mast cells and release of preformed mediators such as histamine and tryptase, or newly synthesized mediators such as prostaglandins and leukotrienes. The late phase response is predominated by the presence of eosinophils, lymphocytes, cytokines, and adhesion molecules. Newer insights reveal that the whole phenomenon of immunological inflammation is intricately knit with neural pathways, which strongly influence the process. Furthermore, AR can impact psychological health and vice versa. Classical pharmacotherapy of AR includes use of oral or topical antihistamines, oral antileukotrienes, topical corticosteroids, mast cell stabilizers, decongestants, and an anticholinergic agent. Among immunomodulatory treatments, immunotherapy is gaining widespread use, while antibody treatment is restricted mainly to resistant cases. Several small molecules with improved safety profile, or targeting novel mechanisms are in the clinical research. Newer antihistamines and corticosteroids with improved safety profile and antagonists of the prostaglandin D(2) (CRTH2) receptors are likely to be available for clinical use in the near future. Lack of properly validated animal models and complexities associated with clinical evaluation are some of the challenges facing the researchers in AR. Comprehensive understanding of immunological and neurological processes in AR would facilitate the future quest for more effective and safer management of this disease.

Sensitivity to environmental irritants and capsaicin cough reaction in patients with a positive methacholine provocation test before and after treatment with inhaled corticosteroids

BACKGROUND

Increasing evidence points to a potential role for members of the transient receptor potential family of cation channels on several features of asthmatic disease. The cough sensitivity to inhaled capsaicin is known to reflect the reactivity of these airway sensory nerves.

OBJECTIVE

The aim was to study, among patients having a positive methacholine provocation and diagnosed with asthma, capsaicin cough sensitivity, sensitivity to methacholine, and levels of exhaled nitric oxide before and after treatment with inhaled steroids, and further, to measure the self-reported impact from environmental irritants.

METHODS

Eighteen steroid-naïve patients with a positive methacholine test underwent capsaicin inhalation provocation on two occasions, before and after regular use of inhaled steroids over at least 3 months. Comparisons were made to 21 healthy controls. Sensitivity to methacholine and levels of exhaled nitric oxide were measured before and after the treatment. The participants also answered a validated questionnaire regarding environmental irritants.

RESULTS

The patients displayed higher capsaicin cough sensitivity than the controls before the treatment period, but not afterward. Before treatment, capsaicin cough answer correlated significantly with levels of exhaled nitric oxide, but not with methacholine sensitivity. After treatment with inhaled corticosteroids, the capsaicin cough sensitivity and the inflammatory parameters were normalized. In comparison to the control group, the patients reported more affective reactions to and behavioral disruptions induced by environmental irritants.

CONCLUSIONS

In steroid-naïve patients with a positive methacholine test, there is a link between that part of the airway inflammation that is reflected by exhaled nitric oxide and that followed by an augmented reactivity of capsaicin-sensitive sensory nerves. This association disappears after steroid treatment.

Mucosal expression of nerve growth factor and brain-derived neurotrophic factor in chronic rhinosinusitis

BACKGROUND

Allergic rhinitis (AR) is characterized in part by hyperresponsiveness to nonspecific stimuli, a phenomenon that reflects the fundamental role of nasal neural pathways in chronic airway inflammation. Neurotrophins may serve pivotal roles in mediating hyperresponsiveness in allergic airway disease, although the role of such neurogenic mediators in chronic rhinosinusitis (CRS) is not well understood. This study was designed to examine the expression of two potent neurotrophins, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), in CRS.

METHODS

Inferior turbinate and sinus mucosa were obtained from CRS patients with and without nasal polyps (NPs) and from nonallergic controls. Enzyme-linked immunosorbent assay was used for quantitative determination of tissue concentrations of NGF and BDNF.

RESULTS

Ninety-four tissue samples from 48 patients were included. Mean concentration of NGF in sinus mucosa was significantly higher in CRS than controls. CRS without NPs was associated with a 60% increase in sinus NGF over controls (p < 0.05), and CRS with NPs was associated with a 140% increase (p < 0.05). Mean sinus NGF concentration was significantly elevated in allergic subjects compared with controls (p < 0.01). A similar trend was noted in subjects with nonallergic CRS, although this did not reach significance. Mean BDNF concentration was decreased in CRS compared with controls, with the most significant decrease in patients with polyps (p < 0.05). Mean turbinate concentration of both NGF and BDNF were similar in controls and CRS.

CONCLUSION

Increased expression of NGF may contribute to neural hyperresponsiveness in CRS sinus mucosa, particularly those patients with NP and/or allergies. BDNF expression is decreased in CRS sinus mucosa. Alterations in neurogenic inflammation may contribute to the pathophysiology of CRS and provide alternative therapeutic targets.

The role of neurotrophins in the pathophysiology of allergic rhinitis

PURPOSE OF REVIEW

Allergic rhinitis is characterized by allergic airway inflammation and a hyperresponsiveness to nonspecific stimuli which is partly neuronally controlled. In this regard, neurotrophins are prime candidates as mediators of neuronal and immunological plasticity and they will be the focus of the current review.

RECENT FINDINGS

Neurotrophins including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are expressed in the nasal mucosa. The majority of NGF expression has been found in eosinophil granulocytes, the glandular apparatus and peripheral nerves. As shown recently, nasal allergen provocation upregulates BDNF expression in nasal mucosa and NGF expression on peripheral nerves and nasal lavage in patients with allergic rhinitis. In this regard, increased BDNF expression positively correlates with the maximum increase in total nasal symptom score. The neurotrophin receptors including pan-neurotrophin receptor p75, tyrosine kinase A (trkA) and trkB are expressed in nasal tissue. TrkA is expressed on endothelial, p75 on peripheral nerves and trkB on nasal mucosa mast cells that decreases after allergen provocation. The expression of these neurotrophin receptors is increased on peripheral blood eosinophils in allergic rhinitis compared with nonatopic controls. Further, BDNF and NGF exert immunomodulatory functions on eosinophils of patients with allergic rhinitis. Finally, eosinophils of patients with allergic rhinitis are capable of BDNF and NGF production.

SUMMARY

Neurotrophins represent prime candidates in upper airway pathophysiology in allergic rhinitis. Research on neurotrophins in allergic rhinitis is thus becoming a progressively more exciting field and may reveal new and promising therapeutic options for the future.

Modulation of sensory nerve function and the cough reflex: understanding disease pathogenesis

To cough is a protective defence mechanism that is vital to remove foreign material and secretions from the airways and which in the normal state serves its function appropriately. Modulation of the cough reflex pathway in disease can lead to inappropriate chronic coughing and an augmented cough response. Chronic cough is a symptom that can present in conjunction with a number of diseases including chronic obstructive pulmonary disease (COPD) and asthma, although often the cause of chronic cough may be unknown. As current treatments for cough have proved to exhibit little efficacy and are largely ineffective, there is a need to develop novel, efficacious and safe antitussive therapies. The underlying mechanisms of the cough reflex are complex and involve a network of events, which are not fully understood. It is accepted that the cough reflex is initiated following activation of airway sensory nerves. Therefore, in the hope of identifying novel antitussives, much research has focused on understanding the neural mechanisms of cough provocation. Experimentally this has been undertaken using chemical or mechanical tussive stimuli in conjunction with animal models of cough and clinical cough assessments. This review will discuss the neural mechanisms involved in the cough, changes that occur under pathophysiological conditions and and how current research may lead to novel therapeutic opportunities for the treatment of cough.

Effect of resection of the posterior nasal nerve on functional and morphological changes in the inferior turbinate mucosa

CONCLUSIONS

The underlying pathophysiological mechanisms of the posterior nasal nerve (PNN) resection involved the suppression of the secretogogue motor and the inhibition of neurogenic inflammation induced by parasympathetic and sensory denervation.

OBJECTIVE

The study was designed to clarify the underlying mechanisms of the resection of the PNN.

PATIENTS AND METHODS

Ten patients with allergic rhinitis and non-allergic chronic rhinitis were enrolled in the study. Clinical symptoms were evaluated before and after administration of oxitropium bromide aerosol, and after the PNN resection. Biopsy specimens from the inferior turbinate mucosa obtained from five patients before and after resection of the PNN were examined.

RESULTS

The application of oxitropium bromide resulted in a significant reduction of both watery rhinorrhea and nasal obstruction, but not sneezing or postnasal drip. Resection of the PNN also significantly improved both rhinorrhea and nasal obstruction. Morphometric analysis of the density of the nasal gland showed a significant reduction, whereas no significant change was recognized in the density of the vessels. A significant reduction in the number of infiltrating neutrophils, eosinophils, and lymphocytes was recognized.

Brain-derived neurotrophic factor gene polymorphisms and serum levels in Chinese atopic dermatitis patients

BACKGROUND

Brain-derived neurotrophic factor (BDNF) plays an important role in the pathogenesis of atopic dermatitis (AD). Whether BDNF gene polymorphisms are associated with Chinese AD remains totally unknown.

OBJECTIVE

The aim is to determine if BDNF gene C270T and G196A polymorphisms are associated with Chinese AD, and analyse the clinical relevance of BDNF gene polymorphisms and BDNF serum levels. Methods We conducted a case-control association analysis (160 patients and 169 controls) in Northern Chinese subjects. Genotyping was performed by restriction fragment length polymorphism, and serum levels of BDNF were measured using enzyme-linked immunosorbent assay.

RESULTS

For C270T, there were significant differences in C/T genotype distribution (P = 0.003) and T allele frequencies (P = 0.004) between AD patients and controls in the whole dataset. Higher C/T genotype frequencies were found in male AD (10.6% vs. 1.1%, P = 0.018) and in intrinsic AD (IAD; 15.79% vs. 2.91%, P = 0.008). No association between G196A polymorphism and AD was observed in the whole cohort, while A allele was much more frequent in AD patients with atopy in first-degree relatives (65.8% vs. 34.2%, P = 0.038). Serum BDNF levels were correlated with IAD severity as measured by Scoring Atopic Dermatitis index (r = 0.576, P < 0.001).

CONCLUSION

T allele in C270T may be a risk factor for AD, especially in IAD and male AD. A allele in G196A may be a risk factor in AD patients with atopy in first-degree relatives. Serum BDNF levels were correlated with the severity of IAD.

Nerve growth factor localization in the nasal mucosa of patients with persistent allergic rhinitis

BACKGROUND AND OBJECTIVES

Nerve growth factor (NGF) and NGF receptors have been shown to be expressed by structural and infiltrating inflammatory cells in the human allergic bronchial mucosa and conjunctiva. In the nose, a positive immunostaining for NGF was recently reported in biopsies of subjects undergoing surgery for refractory nasal obstruction. This study was aimed at studying by immunohistochemistry NGF expression and localization in the nasal mucosa from subjects with moderate/severe persistent allergic rhinitis and natural allergen exposure.

METHODS

Immunostaining for NGF, tryptase and eosinophil cationic protein was performed in human nasal turbinate sections of 25 patients affected by persistent allergic rhinitis and sensitization to Dermatophagoides pteronyssinus.

RESULTS

NGF was consistently expressed in the epithelium and in the submucosa of allergic rhinitic subjects, preferentially localized in eosinophils and mast cells. A strong NGF immunostaining was found in mucous cells of the epithelial lining and in the submucosal glands.

CONCLUSIONS

As previously shown for allergic asthma and allergic conjunctivitis, NGF is also detectable in the nasal mucosa of patients with persistent allergic rhinitis. The preferential NGF localization in mucous cells of the epithelial lining and in the submucosal glands suggests a possible role for NGF in modulating secretion in allergic rhinitis and possibly other allergic diseases.

Peripheral mechanisms I: plasticity of peripheral pathways

Cough plays a vital role in protecting the lower airways from inhaled irritants, pollutants, and infectious agents. The cough reflex exhibits remarkable plasticity, such that in the context of infectious or inflammatory respiratory diseases such as asthma, chronic bronchitis, and idiopathic pulmonary fibrosis the cough reflex can become dysregulated, leading to a chronic cough. A chronic, nonproductive (dry) cough can rob sufferers of quality of life. Plasticity of the cough reflex likely involves multiple intersecting pathways within the airways, the peripheral nerves that supply them, and the central nervous system. While further studies are needed to determine the presence and relevance of many of these specific pathways in cough associated with chronic respiratory disease, the last decade has yielded unprecedented insight into the molecular identity of the ion channels and associated proteins that initiate and conduct action potentials in the primary sensory nerves involved in reflexes such as cough. We now know, for instance, that members of the transient receptor potential superfamily of nonselective cation channels function as transducers that convert specific external stimuli into neuronal activation. We also know that certain Na+ and K+ channels play specialized roles in regulating action potential discharge in irritant-sensing afferent nerves. In this chapter, we summarize the available information regarding factors that may modulate afferent neuron function acutely, via posttranslational modifications and over the longer term through neurotrophin-dependent alterations of the transcriptional programs of adult sensory neurons.

Important research questions in allergy and related diseases: nonallergic rhinitis: a GA2LEN paper

Nonallergic rhinitis (NAR) can be defined as a chronic nasal inflammation which is not caused by systemic IgE-dependent mechanisms. It is common and probably affects far more than 200 million people worldwide. Both children and adults are affected. However, its exact prevalence is unknown and its phenotypes need to be evaluated using appropriate methods to better understand its pathophysiology, diagnosis and management. It is important to differentiate between infectious rhinitis, allergic/NAR and chronic rhinosinusitis, as management differs for each of these cases. Characterization of the phenotype, mechanisms and management of NAR represents one of the major unmet needs in allergic and nonallergic diseases. Studies on children and adults are required in order to appreciate the prevalence, phenotype, severity and co-morbidities of NAR. These studies should compare allergic and NAR and consider different age group populations including elderly subjects. Mechanistic studies should be carried out to better understand the disease(s) and risk factors and to guide towards an improved diagnosis and therapy. These studies need to take the heterogeneity of NAR into account. It is likely that neuronal mechanisms, T cells, innate immunity and possibly auto-immune responses all play a role in NAR and may also contribute to the symptoms of allergic rhinitis.

Overexpression of functional TrkA receptors after internalisation in human airway smooth muscle cells

Trafficking of the TrkA receptor after stimulation by NGF is of emerging importance in structural cells in the context of airway inflammatory diseases. We have recently reported the expression of functional TrkA receptors in human airway smooth muscle cells (HASMC). We have here studied the TrkA trafficking mechanisms in these cells. TrkA disappearance from the cell membrane was induced within 5 min of NGF (3pM) stimulation. Co-immunoprecipitation of clathrin-TrkA was revealed, and TrkA internalisation inhibited either by clathrin inhibitors or by siRNA inducing downregulation of endogenous clathrin. TrkA internalised receptors were totally degraded in lysosomes, with no recycling phenomenon. Newly synthesized TrkA receptors were thereafter re-expressed at the cell membrane within 10 h. TrkA re-synthesis was inhibited by blockade of clathrin-dependent internalisation, but not of TrkA receptors lysosomal degradation. Finally, we observed that NGF multiple stimulations progressively increased TrkA expression in HASMC, which was associated with an increase in NGF/TrkA-dependent proliferation. In conclusion, we show here the occurrence of clathrin-dependent TrkA internalisation and lysosomal degradation in the airway smooth muscle, followed by upregulated re-synthesis of functional TrkA receptors and increased proliferative effect in the human airway smooth muscle. This may have pathophysiological consequences in airway inflammatory diseases.

Modulation of neurotrophin and neurotrophin receptor expression in nasal mucosa after nasal allergen provocation in allergic rhinitis

BACKGROUND

Patients with allergic rhinitis (AR) feature both allergic airway inflammation and a hyperresponsiveness to nonspecific stimuli which is partly neuronally controlled. Still, it is unclear whether or not neurotrophins are involved in airway pathophysiology of AR and in nasobronchial interaction.

METHODS

Nine AR patients with mono-allergy to grass pollen and nine healthy controls underwent nasal allergen provocation (NP). Serum samples, nasal and bronchial biopsies were taken before (T(0)) and 24 h after (T(24)) NP. Pan-neurotrophin receptor p75(NTR), tyrosine kinase A (trkA), trkB, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) were assessed with immunohistochemistry, and NGF and BDNF levels with ELISA.

RESULTS

At T(24), BDNF and NGF were upregulated in nasal mucosa (P < 0.05) and increased in the peripheral blood of AR compared with T(0). The increase in nasal BDNF expression correlated positively with the maximum increase in total nasal symptom score in AR (P = 0.02). p75(NTR) was expressed on peripheral nerves and epithelial layer, trkA on endothelial cells, and trkB on mast cells. trkB + mast cells significantly decreased after NP in AR (P < 0.01). NP did not modulate p75(NTR) and trkA expression in nasal mucosa and had no effect on the expression of neurotrophins and receptors in bronchial mucosa.

CONCLUSION

This study shows that neurotrophins and their receptors are expressed in human airways. Allergic rhinitis was characterized by a modulation of BDNF, NGF, and trkB in nasal mucosa after NP and a correlation of nasal BDNF with the maximal increase of total nasal symptom score. Therefore, our data suggest that neurotrophins participate in upper-airway pathophysiology in AR, whereas their role in nasobronchial interaction remains unclear.

Granule formation in NGF-cultured mast cells is associated with expressions of pyruvate kinase type M2 and annexin I proteins

BACKGROUND

Nerve growth factor (NGF) is a potent mediator, which regulates characteristics of mast cells, but its biological function is not well characterized. This study aimed to screen proteins associated with the maturation of human mast cells-1 (HMC-1) or mouse bone marrow-derived mast cells (BMMCs) cultured with NGF, and to examine the functions of proteins involved.

METHODS

NGF (10 ng/ml) was added to cell culture medium every other day for 10 days for HMC-1 or twice a week for 5 weeks for BMMCs. Granule formation was determined by electron microscopy or May-Grunwald-Giemsa staining, TNF-alpha by ELISA, expressions of various proteins by two-dimensional gel electrophoresis (2-DE), siRNA transfection by Lipofectamine 2000, and the expressions of pyruvate kinase and annexin I by immunoblotting.

RESULTS

After NGF treatment, granule formation and total amounts of granular mediator, TNF-alpha increased in both mast cells. This TNF-alpha was released by calcium ionophore or by antigen/antibody reaction. Expressions of pyruvate kinase and annexin I obtained by 2-DE were confirmed by immunoblotting and siRNA-transfected HMC-1 cells. Expressions of proteins, granule formation and TNF-alpha content were blocked by both the TrkA inhibitor, K252a, and the ERK inhibitor, PD98059, but not by the PI3 kinase inhibitors, LY294002 and wortmannin.

CONCLUSION

These data suggest that pyruvate kinase and annexin I expressed by NGF contribute to granule formation containing TNF-alpha as well as other mediators in mast cells, which play a major role in allergic diseases via a TrkA/ERK pathway.

The mast cell and allergic diseases: role in pathogenesis and implications for therapy

Mast cells have long been recognized for their role in the genesis of allergic inflammation; and more recently for their participation in innate and acquired immune responses. Mast cells reside within tissues including the skin and mucosal membranes, which interface with the external environment; as well as being found within vascularized tissues next to nerves, blood vessels and glandular structures. Mast cells have the capability of reacting both within minutes and over hours to specific stimuli, with local and systemic effects. Mast cells express the high affinity IgE receptor (FcepsilonRI) and upon aggregation of FcepsilonRI by allergen-specific IgE, mast cells release and generate biologically active preformed and newly synthesized mediators which are involved in many aspects of allergic inflammation. While mast cells have been well documented to be essential for acute allergic reactions, more recently the importance of mast cells in reacting through pattern recognition receptors in innate immune responses has become recognized. Moreover, as our molecular understanding of the mast cell has evolved, novel targets for modulation have been identified with promising therapeutic potential.

The nerve growth factor and its receptors in airway inflammatory diseases

The nerve growth factor (NGF) belongs to the neurotrophin family and induces its effects through activation of 2 distinct receptor types: the tropomyosin-related kinase A (TrkA) receptor, carrying an intrinsic tyrosine kinase activity in its intracellular domain, and the receptor p75 for neurotrophins (p75NTR), belonging to the death receptor family. Through activation of its TrkA receptor, NGF activates signalling pathways, including phospholipase Cgamma (PLCgamma), phosphatidyl-inositol 3-kinase (PI3K), the small G protein Ras, and mitogen-activated protein kinases (MAPK). Through its p75NTR receptor, NGF activates proapoptotic signalling pathways including the MAPK c-Jun N-terminal kinase (JNK), ceramides, and the small G protein Rac, but also activates pathways promoting cell survival through the transcription factor nuclear factor-kappaB (NF-kappaB). NGF was first described by Rita Levi-Montalcini and collaborators as an important factor involved in nerve differentiation and survival. Another role for NGF has since been established in inflammation, in particular of the airways, with increased NGF levels in chronic inflammatory diseases. In this review, we will first describe NGF structure and synthesis and NGF receptors and their signalling pathways. We will then provide information about NGF in the airways, describing its expression and regulation, as well as pointing out its potential role in inflammation, hyperresponsiveness, and remodelling process observed in airway inflammatory diseases, in particular in asthma.

Airway hyper-responsiveness in allergic asthma in guinea-pigs is mediated by nerve growth factor via the induction of substance P: a potential role for trkA

BACKGROUND

The neurotrophin nerve growth factor (NGF) has been implicated as a mediator in allergic asthma. Direct evidence that inhibition of NGF-induced activation of neurotrophin receptors leads to improvement of airway symptoms is lacking. We therefore studied the effects of inhibitors of NGF signal transduction on the development of airway hyper-responsiveness (AHR) and pulmonary inflammation in a guinea-pig model for allergic asthma.

METHODS

Airway responsiveness to the contractile agonist histamine was measured in vivo in guinea-pigs that were sensitized and challenged with ovalbumin (OVA). Inflammatory cell influx and NGF levels were determined in bronchoalveolar lavage fluid (BALF). Substance P, a key mediator of inflammation, was measured in lung tissue by radioimmunoassay, while substance P immunoreactive neurons in nodose ganglia were measured by immunohistochemistry.

RESULTS

OVA challenge induced an AHR after 24 h in OVA-sensitized guinea-pigs. This coincided with an increase in the amount of NGF in BALF. Simultaneously, an increase in the percentage of substance P immunoreactive neurons in the nodose ganglia and an increase in the amount of substance P in lung tissue were found. We used tyrosine kinase inhibitors to block the signal transduction of the high-affinity NGF receptor, tyrosine kinase A (trkA). Treatment with the tyrosine kinase inhibitors (K252a or tyrphostin AG879) both inhibited the development of AHR, and prevented the increase in substance P in the nodose ganglia and lung tissue completely whereas both inhibitors had no effect on baseline airway resistance. Neither treatment with K252a or tyrphostin AG879 changed the influx of inflammatory cells in the BALF due to allergen challenge.

CONCLUSIONS

We conclude that substance P plays a role in the induction of AHR in our model for allergic asthma which is most likely mediated by NGF. As both tyrosine kinase inhibitors AG879 and K252a show a similar inhibitory effect on airway function after allergen challenge, although both tyrosine kinase inhibitors exhibit different non-specific inhibitory effects on targets other than trkA tyrosine kinases, it is likely that the induction of substance P derived from sensory nerves is mediated by NGF via its high-affinity receptor trkA.

Circulating levels of brain-derived neurotrophic factor correlate with disease severity in the intrinsic type of atopic dermatitis

BACKGROUND

Recent studies have shed light on the complex regulation of genetic, environmental, immunologic and pharmacologic factors, which contribute to the development of atopic dermatitis (AD). However, it is still unclear to which extent neuroimmune mediators have a role in AD.

AIMS OF THE STUDY

To assess peripheral neurotrophin levels and their correlation with scoring atopic dermatitis (SCORAD) scores in both the intrinsic and extrinsic types of AD compared with patients with psoriasis and nonatopic healthy subjects.

METHODS

Levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were assessed in peripheral blood with enzyme-linked immunosorbent assay. Based on IgE-mediated sensitization, AD was divided into the extrinsic and intrinsic type. Severity of AD was assessed with SCORAD score and with psoriasis area and severity index (PASI) in patients with psoriasis.

RESULTS

Brain-derived neurotrophic factor and NGF were detectable in all the subjects studied. However, the levels of both neurotrophins were significantly higher in patients with extrinsic and intrinsic types of AD compared with patients with psoriasis and nonatopic healthy subjects (NGF: P < 0.001, BDNF: P < 0.001). NGF and BDNF levels were similar in the intrinsic and extrinsic type of AD. There was a significant correlation between BDNF and SCORAD score only in patients with the intrinsic type of AD (r = 0.57, P < 0.05).

CONCLUSIONS

This study shows for the first time that NGF and BDNF are increased in both, the extrinsic type and the intrinsic type of AD. This finding points to a similar pathophysiologic background implicating a neuroimmune network in both variants of this chronic inflammatory skin disease. Future studies are needed to show the direct mechanisms of neurotrophin action in chronic inflammatory skin.

Allergic bronchial airway inflammation in nerve growth factor (NGF)-deprived rats: evidence suggesting a neuroimmunomodulatory role of NGF

In the present study, ovalbumin-sensitized/challenged rats were characterized by an nerve growth factor (NGF) increase in both serum and bronchial alveolar lavage fluid (BALF), but not in the lung. Exogenous administration of NGF or NGF-neutralizing antibodies did not modify immunoglobulin (IgE) and eosinophil parameters. In control rats, NGF administration did not induce increase of IgE or eosinophils in both BALF and lung. The present findings suggest that at least NGF does not act as a proper proinflammatory factor but most probably as a neuroimmune modulator molecule of the allergic state.

The role of inflammatory mediators in the synergistic toxicity of ozone and 1-nitronaphthalene in rat airways

Ambient air is polluted with a mixture of pulmonary toxicants. Previous studies indicate that prior exposure to atmospheric oxidant pollutants such as ozone may significantly alter the response to other pollutants, such as 1-nitronaphthalene (1-NN) . 1-NN, a component of the particulate exhaust from diesel engines, has been found at low concentrations in ambient air. Using a metabolomic approach, we investigated inflammatory responses in arachidonic and linoleic acid biochemical cascades (35 metabolites) and the expression of 19 cytokines/chemokines at three time points (2, 6, and 24 hr) following exposure to 1-NN with and without prior long-term O3 exposure. Long-term O3 exposure is associated with biochemical changes that have been shown to render the lung resistant to further O3 exposure. This study indicates that airways of O3-tolerant rats exhibited a low level of chronic inflammation, rendering the lungs more susceptible to other environmental pollutants such as 1-NN. Specifically, a 12.5-mg/kg dose of 1-NN to O3-tolerant rats produced significantly higher levels of cysteinyl-leukotrienes in bronchiolar lavage fluid even when compared to a 50-mg/kg dose of 1-NN in rats exposed to filtered air. Collectively, these results indicate that the combination of exposures as encountered in polluted ambient air are considerably more injurious to the lung than would be anticipated from previous studies employing single exposures. The observed synergism between O3 and 1-NN may be causally related to a shift in a T-helper 1 to T-helper 2 immune response in the airways.

Plasticity of peripheral mechanisms of cough

The cough reflex pathway is characterized by a remarkable plasticity often resulting in a persistent and uncontrollable urge to cough during airway inflammation. In many instances cough becomes up regulated to the extent that ceases to fulfill its defensive role in protecting the airways. The exact mechanisms underlying this plasticity are unknown and likely involves a variety of factors influencing the function of the peripheral and central nervous system. This review outlines the evidence of increased cough sensitivity during airway disease. This is followed by a discussion of the peripheral mechanisms involved including the potential role of inflammatory mediators, neutrophins and changes in the airway mucosal structure. A greater understanding of the mechanisms leading to enhanced cough should lead to the development of more effective therapeutic strategies.

Neurotrophins in allergic diseases: From neuronal growth factors to intercellular signaling molecules

Understanding the complex pathophysiology of allergic diseases has been a main challenge of clinical and experimental research for many years. It is well known that the allergic inflammation triggers neuronal dysfunction and structural changes in the diseased tissues such as the airways or the skin. Recent evidence has emerged that the inflammatory response is also controlled by resident tissue cells such as neurons and structural cells. Therefore, signaling molecules that mediate inflammatory interactions among immune, neuronal, and structural cells are becoming a focus of allergy research. Neurotrophins, a family of homologous growth factors initially discovered in the nervous system, display such bidirectional signaling. The expression of neurotrophins, such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), is highly upregulated during allergic inflammation. Neurons, structural cells, and invading immune cells were now identified not only as sources but also as targets of neurotrophins within the inflamed tissue. In this review, we provide an actual overview of the role of neurotrophins in the pathobiology of allergic diseases. We discuss recent findings in human and animal studies such as the regulation of neurotrophin expression during allergic inflammation and the effect of neurotrophins on the development and magnitude of allergic reactions.

Nerve growth factor: the central hub in the development of allergic asthma?

Neurotrophins like nerve growth factor (NGF), originally described as nerve growth factors in neuronal development, have been implicated in many physiological processes in the last years. They are now regarded as important factors involved in the resolution of pathological conditions. NGF has profound effects on inflammation, repair and remodeling of tissues. However, in the lung these beneficial effects can transact into disease promoting actions, e.g., in allergic inflammation or respiratory syncytial virus (RSV) infection. Overproduction of NGF then enhances inflammation, and promotes (neuronal) airway hyperreactivity and neurogenic inflammation. We hypothesize that NGF overexpression in certain vulnerable time windows during infancy could be a major risk factor for the development of asthma symptoms.