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

It is well known that allergic airways disease is characterized by inflammation and hyperresponsiveness, but the link between these two conditions has not been elucidated. We have previously shown that in allergic rhinitis, hyperresponsiveness is attributable to increased neural reactivity. We thus hypothesized that nerve growth factor (NGF), which is expressed by inflammatory cells and effects changes that lead to increased neural responsiveness, could be a pivotal mediator in this disease. Using reverse transcription-polymerase chain reaction (RT-PCR), Western immunoblotting, and ELISA to evaluate NGF expression and release, we found that subjects with allergic rhinitis have significantly decreased NGF mRNA in superficial nasal scrapings and significantly higher baseline concentrations of NGF protein in nasal lavage fluids, compared with control subjects. Nasal provocation with allergen significantly increased NGF protein in nasal lavage fluids of subjects with allergic rhinitis, but not of control subjects. The concentrations of NGF protein in nasal lavage fluids were not affected by provocation with the vehicle for allergen or with histamine. These data provide the first evidence of a steady state of dysregulation in mucosal NGF expression and release in allergic rhinitis, and support a role of this neurotrophin in the pathophysiology of allergic inflammatory disease of the human airways.

Neural hyperresponsiveness and nerve growth factor in allergic rhinitis.

BACKGROUND: In allergic rhinitis, symptoms are triggered not only by allergens but also by environmental irritants. Hereinafter we address the hypothesis that this is reflective of increased responsiveness of the neural apparatus which, in turn, may be attributable to upregulation of nerve growth factor (NGF) in this disease. METHODS: We compared subjects with active allergic rhinitis and healthy volunteers in terms of sensitivity and/or magnitude of three nerve-mediated responses, namely (1) the sneezing reflex induced by histamine, (2) the central or nasonasal reflex depicted by contralateral secretions induced by unilateral nasal challenge with capsaicin, and (3) the axonal reflex depicted by plasma extravasation upon capsaicin challenge. We have also measured NGF levels in nasal lavage fluids at baseline and with allergen provocation in rhinitis and healthy subjects. RESULTS: Compared to healthy individuals, subjects with active allergic rhinitis were found to have (1) significantly greater sensitivity and reactivity of the sneezing reflex, (2) significantly greater secretory responsiveness to sensory nerve stimulation, and (3) significantly greater plasma extravasation indicated by albumin leakage following capsaicin nasal challenge. We also found that subjects with active allergic rhinitis have significantly greater baseline levels of NGF in nasal lavage fluids compared to their healthy counterparts, and that these levels can be increased by allergen nasal provocation. CONCLUSION: The responsiveness of the neural apparatus of the nose is significantly greater in patients with active allergic rhinitis. The increased presence of NGF in the nasal mucosa of these patients supports the hypothesis that this neurotrophin may be implicated in neural hyperresponsiveness.

Hyperosmolar saline induces reflex nasal secretions, evincing neural hyperresponsiveness in allergic rhinitis.

We investigated whether hyperosmolar saline (HS), applied via paper disk onto the septum of one nostril, induces a nasal secretory response. Furthermore, we examined whether this response is accentuated in patients with active allergic rhinitis (AR) compared with healthy volunteers. Unilateral HS produced significant nasal secretions both ipsilateral and contralateral to the site of challenge in the AR group and only ipsilaterally in the healthy group. The HS-induced nasal secretions were significantly greater in the AR vs. the healthy subjects. In a separate study, we ascertained that the nasal response to HS is neurally mediated and found that ipsilateral nerve blockade with lidocaine significantly attenuates the HS-induced secretions bilaterally. In another group of AR subjects, we determined whether nociceptive fibers were involved in this response and found that sensory nerve desensitization with repeated application of capsaicin attenuated the HS-induced nasal secretions. Finally, we determined whether the secretory hyperresponsiveness in AR is attributable to increased reactivity of submucosal glands rather than of nerves. We found that the dose response to methacholine, which directly stimulates the glands, was identical among AR and healthy subjects. We conclude that, in AR, nasal challenge with HS induces significantly greater reflex secretions involving capsaicin-sensitive nerve fibers, consistent with the notion of neural hyperresponsiveness in this disease.

Comparison of nasal mucosal responsiveness to neuronal stimulation in non-allergic and allergic rhinitis: effects of capsaicin nasal challenge.

BACKGROUND: Neuronal involvement has been implicated in the pathophysiology of non-allergic and allergic rhinitis, contributing to the typical exacerbation of these conditions upon exposure to non-specific environmental irritants. OBJECTIVES: To determine if non-allergic and allergic rhinitis are characterized by increased responsiveness of the nasal mucosa to sensorineural stimulation. METHODS: Nasal challenges with capsaicin and its vehicle were performed in three groups of subjects -- non-allergic rhinitics, perennial allergic rhinitics, and healthy controls -- and resultant symptom scores, glandular secretion reflected by lactoferrin levels, and plasma extravasation reflected by albumin levels in nasal lavage fluid were compared. RESULTS: Capsaicin-sensitive nerve stimulation produced increases in symptom scores and lactoferrin levels which were similar among the three groups of subjects. On the other hand, only the group of subjects with allergic rhinitis demonstrated a significant capsaicin-induced increase in albumin levels and a trend in total protein levels. CONCLUSIONS: We conclude that non-allergic rhinitis is not characterized by increased responsiveness of capsaicin-sensitive nerve fibres; while allergic rhinitis is marked by hyperresponsiveness manifested as increased albumin leakage in nasal fluids. This may reflect the activity of an axonal reflex to sensorineural stimulation.

Plasma extravasation through neuronal stimulation in human nasal mucosa in the setting of allergic rhinitis.

We have previously shown that capsaicin nasal challenge in subjects with allergic rhinitis produces a dose-dependent increase in the albumin content of nasal lavage fluids. In the present set of studies, we determined whether this observation represents plasma extravasation that is neuronally mediated. To evaluate whether glandular secretions contribute to the albumin increase in nasal lavage fluids, volunteers with allergic rhinitis were pretreated with atropine or placebo before capsaicin challenge. Atropine significantly reduced the volume of returned lavage fluids and their lysozyme content but increased their albumin and fibrinogen content. To assess the contribution of sensory nerve stimulation, subjects with allergic rhinitis were pretreated in a second study with lidocaine or placebo before capsaicin challenge. Lidocaine significantly attenuated the capsaicin-induced increases in the volume of nasal lavage fluids, as well as their lysozyme and albumin content. To rule out the possibility of a direct effect of lidocaine on blood vessels rather than on nerves, healthy subjects were pretreated in a third study with lidocaine or placebo before bradykinin nasal challenge. Lidocaine did not affect the bradykinin-induced increase in the albumin content of nasal fluids. We conclude that, in allergic rhinitis, high-dose capsaicin induces plasma extravasation in the human nose and that this effect is neuronally mediated. This provides more definitive evidence that neurogenic inflammation can occur in vivo in the human upper airway.

Dose-dependent effects of capsaicin nasal challenge: in vivo evidence of human airway neurogenic inflammation.

BACKGROUND: Nerve involvement has been implicated in the pathophysiology of chronic respiratory inflammatory diseases. Peptidergic nerve stimulation has been shown to induce leukocyte activation and plasma extravasation in the airways of various animal species. The occurrence of this phenomenon of neurogenic inflammation in the human airway, however, has not been established. OBJECTIVE: We conducted this study to determine whether neuronal stimulation can induce reproducible and dose-dependent inflammatory changes in the human upper airway. METHODS: Ten volunteers with active allergic rhinitis participated in the study. Capsaicin, the pungent component of hot pepper that specifically stimulates afferent nerve fibers, was administered by means of nasal spray in doses of 1 microg, 10 microg, and 100 microg in a double-blind, randomized, crossover manner with 1 week between doses. Symptom scores before and after capsaicin nasal challenge were recorded by using visual analog scales. Nasal lavage fluids collected before and at 30 minutes, 1 hour, and 4 hours after capsaicin challenge were analyzed for leukocyte counts; albumin and lysozyme levels were measured to evaluate effects on plasma leakage and gland secretion, respectively. RESULTS: Capsaicin nasal challenge produced symptoms of burning, congestion, and rhinorrhea. Leukocyte counts or albumin and lysozyme levels were not significantly increased after administration of 1 microg of capsaicin at any time point. On the other hand, there were significant increases in leukocyte counts 1 hour (p < 0.05) and 4 hours (p = 0.008) after 10 microg of capsaicin and 30 minutes (p = 0.009), 1 hour (p = 0.007), and 4 hours (p = 0.007) after 100 microg of capsaicin. Albumin and lysozyme levels were both significantly increased 30 minutes after 10 microg and 100 microg of capsaicin (p = 0.005 for both). Comparison of changes in symptom scores, leukocyte counts, and albumin and lysozyme levels among the three capsaicin challenges indicated generally increasing effects with higher capsaicin doses. CONCLUSION: Capsaicin-sensitive nerve stimulation in subjects with active allergic rhinitis produces reproducible and dose-dependent leukocyte influx, albumin leakage, and glandular secretion. These results provide in vivo evidence for the occurrence of neurogenic inflammation in the human upper airway with active allergic disease.

Inflammatory cellular influx follows capsaicin nasal challenge.

Capsaicin is a specific activator of sensory nerve endings. In rodents, mucosal application of capsaicin causes cells to infiltrate the tissue. To examine whether inflammatory-cell influx follows sensory-nerve activation in human airways, we delivered capsaicin (200 microM) nasal spray into the nares of 20 subjects (10 with allergic rhinitis and 10 normal), and measured the total leukocyte content of nasal lavage fluid obtained from 10 min to 4 h after the capsaicin challenge. Vehicle spray (1% EtOH in 0.9% saline) served as a control. Capsaicin challenge caused significant increases from prechallenge leukocyte counts at 10 min (p<0.03), 30 min (p<0.01), and 4 h (p<0.03) after challenge, but not at 1 h after challenge (p = 0.68). Vehicle challenge did not increase leukocyte counts. Differential counts (performed on the 13 of 20 subjects from whom adequate specimens for differential counts were obtained) showed that neutrophils, eosinophils, and mononuclear cells increased at 10 min, 30 min, and 4 h (all p < 0.04), but not at 1 h after capsaicin challenge. Comparing the rhinitic to the normal subjects, we found no significant differences in the cellular response to capsaicin. These data support a nonspecific inflammatory effect of sensory nerve activation in the human nose. Consequently, this work provides evidence that neurogenic inflammation can be induced in the human airway in vivo.