Tachykinins, sensory nerves, and asthma--an overview

Exposure limits for indoor volatile substances concerning the general population: The role of population-based differences in sensory irritation of the eyes and airways for assessment factors

Assessment factors (AFs) are essential in the derivation of occupational exposure limits (OELs) and indoor air quality guidelines. The factors shall accommodate differences in sensitivity between subgroups, i.e., workers, healthy and sick people, and occupational exposure versus life-long exposure for the general population. Derivation of AFs itself is based on empirical knowledge from human and animal exposure studies with immanent uncertainty in the empirical evidence due to knowledge gaps and experimental reliability. Sensory irritation in the eyes and airways constitute about 30-40% of OELs and is an abundant symptom in non-industrial buildings characterizing the indoor air quality and general health. Intraspecies differences between subgroups of the general population should be quantified for the proposal of more 'empirical' based AFs. In this review, we focus on sensitivity differences in sensory irritation about gender, age, health status, and vulnerability in people, based solely on human exposure studies. Females are more sensitive to sensory irritation than males for few volatile substances. Older people appear less sensitive than younger ones. However, impaired defense mechanisms may increase vulnerability in the long term. Empirical evidence of sensory irritation in children is rare and limited to children down to the age of six years. Studies of the nervous system in children compared to adults suggest a higher sensitivity in children; however, some defense mechanisms are more efficient in children than in adults. Usually, exposure studies are performed with healthy subjects. Exposure studies with sick people are not representative due to the deselection of subjects with moderate or severe eye or airway diseases, which likely underestimates the sensitivity of the group of people with diseases. Psychological characterization like personality factors shows that concentrations of volatile substances far below their sensory irritation thresholds may influence the sensitivity, in part biased by odor perception. Thus, the protection of people with extreme personality traits is not feasible by an AF and other mitigation strategies are required. The available empirical evidence comprising age, lifestyle, and health supports an AF of not greater than up to 2 for sensory irritation. Further, general AFs are discouraged for derivation, rather substance-specific derivation of AFs is recommended based on the risk assessment of empirical data, deposition in the airways depending on the substance's water solubility and compensating for knowledge and experimental gaps. Modeling of sensory irritation would be a better 'empirical' starting point for derivation of AFs for children, older, and sick people, as human exposure studies are not possible (due to ethical reasons) or not generalizable (due to self-selection). Dedicated AFs may be derived for environments where dry air, high room temperature, and visually demanding tasks aggravate the eyes or airways than for places in which the workload is balanced, while indoor playgrounds might need other AFs due to physical workload and affected groups of the general population.

An underlying mechanism behind interventional pulmonology techniques for refractory asthma treatment: Neuro-immunity crosstalk

Asthma is a common disease that seriously threatens public health. With significant developments in bronchoscopy, different interventional pulmonology techniques for refractory asthma treatment have been developed. These technologies achieve therapeutic purposes by targeting diverse aspects of asthma pathophysiology. However, even though these newer techniques have shown appreciable clinical effects, their differences in mechanisms and mutual commonalities still deserve to be carefully explored. Therefore, in this review, we summarized the potential mechanisms of bronchial thermoplasty, targeted lung denervation, and cryoablation, and analyzed the relationship between these different methods. Based on available evidence, we speculated that the main pathway of chronic airway inflammation and other pathophysiologic processes in asthma is sensory nerve-related neurotransmitter release that forms a "neuro-immunity crosstalk" and amplifies airway neurogenic inflammation. The mechanism of completely blocking neuro-immunity crosstalk through dual-ablation of both efferent and afferent fibers may have a leading role in the clinical efficacy of interventional pulmonology in the treatment of asthma and deserves further investigation.

Cholinergic chemosensory cells in the trachea regulate breathing

In the epithelium of the lower airways, a cell type of unknown function has been termed "brush cell" because of a distinctive ultrastructural feature, an apical tuft of microvilli. Morphologically similar cells in the nose have been identified as solitary chemosensory cells responding to taste stimuli and triggering trigeminal reflexes. Here we show that brush cells of the mouse trachea express the receptors (Tas2R105, Tas2R108), the downstream signaling molecules (α-gustducin, phospholipase C(β2)) of bitter taste transduction, the synthesis and packaging machinery for acetylcholine, and are addressed by vagal sensory nerve fibers carrying nicotinic acetylcholine receptors. Tracheal application of an nAChR agonist caused a reduction in breathing frequency. Similarly, cycloheximide, a Tas2R108 agonist, evoked a drop in respiratory rate, being sensitive to nicotinic receptor blockade and epithelium removal. This identifies brush cells as cholinergic sensors of the chemical composition of the lower airway luminal microenvironment that are directly linked to the regulation of respiration.

Involvement of preprotachykinin A gene-encoded peptides and the neurokinin 1 receptor in endotoxin-induced murine airway inflammation

Tachykinins encoded by the preprotachykinin A (TAC1) gene such as substance P (SP) and neurokinin A (NKA) are involved in neurogenic inflammatory processes via predominantly neurokinins 1 and 2 (NK1 and NK2) receptor activation, respectively. Endokinins and hemokinins encoded by the TAC4 gene also have remarkable selectivity and potency for the NK1 receptors and might participate in inflammatory cell functions. The aim of the present study was to investigate endotoxin-induced airway inflammation and consequent bronchial hyper-reactivity in TAC1(-/-), NK1(-/-) and also in double knockout (TAC1(-/-)/NK1(-/-)) mice. Sub-acute interstitial lung inflammation was evoked by intranasal Escherichia coli lipopolysaccharide (LPS) in the knockout mice and their wildtype C57BL/6 counterparts 24 h before measurement. Respiratory parameters were measured with unrestrained whole body plethysmography. Bronchoconstriction was induced by inhalation of the muscarinic receptor agonist carbachol and Penh (enhanced pause) correlating with airway resistance was calculated. Lung interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured with ELISA. Histological evaluation was performed and a composite morphological score was determined. Myeloperoxidase (MPO) activity in the lung was measured with spectrophotometry to quantify the number of infiltrating neutrophils/macrophages. Airway hyper-reactivity was significantly reduced in the TAC1(-/-) as well as the TAC1(-/-)/NK1(-/-) groups. However, LPS-induced histological inflammatory changes (perivascular/peribronchial oedema, neutrophil infiltration and goblet cell hyperplasia), MPO activity and TNF-alpha concentration were markedly diminished only in TAC1(-/-) mice. Interestingly, the concentrations of both cytokines, IL-1beta and TNF-alpha, were significantly greater in the NK1(-/-) group. These data clearly demonstrated on the basis of histology, MPO and cytokine measurements that TAC1 gene-derived tachykinins, SP and NKA, play a significant role in the development of endotoxin-induced murine airway inflammation, but not solely via NK1 receptor activation. However, in inflammatory bronchial hyper-responsiveness other tachykinins, such as hemokinin-1 acting through NK1 receptors also might be involved.

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.

Role of transient receptor potential vanilloid 1 receptors in endotoxin-induced airway inflammation in the mouse

Airways are densely innervated by capsaicin-sensitive sensory neurons expressing transient receptor potential vanilloid 1 (TRPV1) receptors/ion channels, which play an important regulatory role in inflammatory processes via the release of sensory neuropeptides. The aim of the present study was to investigate the role of TRPV1 receptors in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity with functional, morphological, and biochemical techniques using receptor gene-deficient mice. Inflammation was evoked by intranasal administration of Escherichia coli lipopolysaccharide (60 microl, 167 microg/ml) in TRPV1 knockout (TRPV1(-/-)) mice and their wild-type counterparts (TRPV1(+/+)) 24 h before measurement. Airway reactivity was assessed by unrestrained whole body plethysmography, and its quantitative indicator, enhanced pause (Penh), was calculated after inhalation of the bronchoconstrictor carbachol. Histological examination and spectrophotometric myeloperoxidase measurement was performed from the lung. Somatostatin concentration was measured in the lung and plasma with radioimmunoassay. Bronchial hyperreactivity, histological lesions (perivascular/peribronchial edema, neutrophil/macrophage infiltration, goblet cell hyperplasia), and myeloperoxidase activity were significantly greater in TRPV(-/-) mice. Inflammation markedly elevated lung and plasma somatostatin concentrations in TRPV1(+/+) but not TRPV1(-/-) animals. In TRPV1(-/-) mice, exogenous administration of somatostatin-14 (4 x 100 microg/kg ip) diminished inflammation and hyperreactivity. Furthermore, in wild-type mice, antagonizing somatostatin receptors by cyclo-somatostatin (4 x 250 microg/kg ip) increased these parameters. This study provides the first evidence for a novel counterregulatory mechanism during endotoxin-induced airway inflammation, which is mediated by somatostatin released from sensory nerve terminals in response to activation of TRPV1 receptors of the lung. It reaches the systemic circulation and inhibits inflammation and consequent bronchial hyperreactivity.

Role of capsaicin-sensitive afferents and sensory neuropeptides in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity in the mouse

Substance P (SP) and calcitonin gene-related peptide (CGRP) released from capsaicin-sensitive afferents induce neurogenic inflammation via NK(1), NK(2) and CGRP1 receptor activation. This study examines the role of capsaicin-sensitive fibres and sensory neuropeptides in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity with functional, morphological and biochemical techniques in mice. Carbachol-induced bronchoconstriction was measured with whole body plethysmography 24 h after intranasal lipopolysaccharide administration. SP and CGRP were determined with radioimmunoassay, myeloperoxidase activity with spectrophotometry, interleukin-1beta with ELISA and histopathological changes with semiquantitative scoring from lung samples. Treatments with resiniferatoxin for selective destruction of capsaicin-sensitive afferents, NK(1) antagonist SR 140333, NK(2) antagonist SR 48968, their combination, or CGRP1 receptor antagonist CGRP(8-37) were performed. Lipopolysaccharide significantly increased lung SP and CGRP concentrations, which was prevented by resiniferatoxin pretreatment. Resiniferatoxin-desensitization markedly enhanced inflammation, but decreased bronchoconstriction. CGRP(8-37) or combination of SR 140333 and SR 48968 diminished neutrophil accumulation, MPO levels and IL-1beta production, airway hyperresponsiveness was inhibited only by SR 48968. This is the first evidence that capsaicin-sensitive afferents exert a protective role in endotoxin-induced airway inflammation, but contribute to increased bronchoconstriction. Activation of CGRP1 receptors or NK(1)+NK(2) receptors participate in granulocyte accumulation, but NK(2) receptors play predominant role in enhanced airway resistance.

The role of neurotrophins in bronchial asthma: contribution of the pan-neurotrophin receptor p75

Allergic bronchial asthma is characterized by chronic inflammation of the airways, development of airway hyperreactivity and recurrent reversible airway obstruction. Target and effector cells responsible for airway hyperresponsiveness and airway obstruction include sensory and motor neurons as well as epithelial and smooth muscle cells. Although it is well established that the inflammatory process is controlled by T-helper-2 (Th2) cells, the mechanisms by which immune cells interact with neurons, epithelial cells or smooth muscle cells still remain uncertain. Due to growing evidence for extensive communication between neurons and immune cells, the mechanisms of this neuroimmune crosstalk in lung and airways of asthmatic patients are becoming the focus of asthma research. Neurotrophins represent molecules potentially responsible for regulating and controlling the crosstalk between the immune and peripheral nervous system. They are constitutively expressed by resident lung cells and produced in increasing concentrations by immune cells invading the airways under pathological conditions. Neurotrophins modify the functional activity of sensory and motor neurons, leading to enhanced and altered neuropeptide and tachykinin production. These effects are defined as neuronal plasticity. The consequences are the development of neurogenic inflammation.

NEUROPEPTIDES AND NEUROGENIC MECHANISMS IN ORAL AND PERIODONTAL INFLAMMATION

It is generally accepted that the nervous system contributes to the pathophysiology of peripheral inflammation, and a neurogenic component has been implicated in many inflammatory diseases, including periodontitis. Neurogenic inflammation should be regarded as a protective mechanism, which forms the first line of defense and protects tissue integrity. However, severe or prolonged noxious stimulation may result in the inflammatory response mediating injury rather than facilitating repair. This review focuses on the accumulating evidence suggesting that neuropeptides have a pivotal role in the complex cascade of chemical activity associated with periodontal inflammation. An overview of neuropeptide synthesis and release introduces the role of neuropeptides and their interactions with other inflammatory factors, which ultimately lead to neurogenic inflammation. The biological effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) are summarized, and evidence for their involvement in the localized inflammatory lesions which characterize periodontitis is presented. In this context, the role of CGRP in bone metabolism is described in more detail. Recent research highlighting the role of the nervous system in suppressing pain and inflammation is also discussed.

Nicotine inhibits voltage-dependent sodium channels and sensitizes vanilloid receptors

Nicotine is an alkaloid that is used by large numbers of people. When taken into the body, it produces a myriad of physiological actions that occur primarily through the activation of neuronal nicotinic acetylcholine receptors (nAChRs). We have explored its ability to modulate TRPV1 receptors and voltage-gated sodium channels. The reason for investigating nicotine's effect on sodium channels is to obtain a better understanding of its anti-nociceptive properties. The reasons for investigating its effects on capsaicin-activated TRPV1 channels are to understand how it may modulate this channel that is involved in pain, inflammation, and gustatory physiology. Whole cell patch-clamp recordings from rat trigeminal ganglion (TG) nociceptors revealed that nicotine exhibited anesthetic properties by decreasing the number of evoked action potentials and by inhibiting tetrodotoxin-resistant sodium currents. This anesthetic property can be produced without the necessity of activating nAChRs. Nicotine also modulates TRPV1 receptors inducing a several-fold increase in capsaicin-activated currents in both TG neurons and in cells with heterologously expressed TRPV1 receptors. This sensitizing effect does not require the activation of nAChRs. Nicotine did not alter the threshold temperature (approximately 41 degrees C) of heat-activated currents in TG neurons that were attributed to arise from the activation of TRPV1 receptors. In this regard, its effect on TRPV1 receptors differs from those of ethanol that has been shown to increase the capsaicin-activated current but decrease the threshold temperature. These studies document several new effects of nicotine on channels involved in nociception and indicate how they may impact physiological processes involving pain and gustation.

Effect of anti-nerve growth factor on early and late airway responses in allergic rats

BACKGROUND

The increased production of nerve growth factor (NGF) has been associated with allergen-induced airway hyperresponsiveness and enhanced airway inflammation in experimental models of asthma. The aim of this study was to investigate whether a local application of anti-NGF to the lungs may affect the allergen-specific early (EAR) and late (LAR) airway responses to ovalbumin (Ova) of Ova-sensitized brown Norway rats.

METHODS

Rats were sensitized systemically with Ova and were boosted twice intratracheally with Ova aerosol using a microsprayer. Two hours before every boost, the animals were pretreated either with aerosolized anti-NGF or with a control antibody. On day 21, all animals were challenged with inhalational Ova aerosol and pulmonary resistance was recorded in anesthetized, orotracheally intubated animals during the early and late asthmatic responses. In addition, differential cell counts from bronchoalveolar lavage and serum immunoglobulin E (IgE) levels were determined 48 h post-Ova challenge.

RESULTS

Pretreatment with anti-NGF significantly attenuated the EAR but had no significant effect on the LAR. Serum IgE levels and inflammatory cell influx into the lungs were not affected by anti-NGF pretreatment.

CONCLUSION

The data from this study suggest that NGF is directly involved in the development of the EAR without affecting the inflammatory airway response or LAR.

Immediate sensory nerve-mediated respiratory responses to irritants in healthy and allergic airway-diseased mice

The immediate responses of the upper respiratory tract (URT) to the irritants acrolein and acetic acid were examined in healthy and allergic airway-diseased C57Bl/6J mice. Acrolein (1.1 ppm) and acetic acid (330 ppm) vapors induced an immediate increase in flow resistance, as measured in the surgically isolated URT of urethane-anesthetized healthy animals. Acrolein, but not acetic acid, induced a small URT vasodilatory response. In awake spontaneously breathing mice, both vapors induced a prolonged pause at the start of expiration (a response mediated via stimulation of nasal trigeminal nerves) and an increase in total respiratory specific airway flow resistance, the magnitude of which was similar to that observed in the isolated URT. Both responses were significantly reduced in animals pretreated with large doses of capsaicin to defunctionalize sensory nerves, strongly suggesting a role for sensory nerves in development of these responses. The breathing pattern and/or obstructive responses were enhanced in mice with ovalbumin-induced allergic airway disease. These results suggest that the primary responses to acrolein and acetic acid vapors are altered breathing patterns and airway obstruction, that sensory nerves play an important role in these responses, and that these responses are enhanced in animals with allergic airway disease.

Pan-neurotrophin receptor p75 contributes to neuronal hyperreactivity and airway inflammation in a murine model of experimental asthma

Bronchial asthma represents a severe chronic inflammatory disease with increasing prevalence. The pathogenesis is characterized by complex neuroimmune dysregulation. Although the immunopathogenesis of the disease has been extensively studied, the nature of neuronal dysfunction still remains poorly understood. Recent data indicate that neurotrophins contribute to airway inflammation, broncho-obstruction and airway hyperresponsiveness. Using an established murine model of allergic bronchial asthma, the contribution of the pan-neurotrophin receptor p75(NTR) was defined. This receptor is expressed both in normal and asthmatic lungs and airways. Analysis of p75(NTR-/-) mice, as well as in vivo blocking of p75(NTR), revealed that airway inflammation is to a large extent dependent upon functional receptor expression. Furthermore, neuronal hyperreactivity depends entirely on this receptor. Based on these data, a novel molecular pathway in the neuroimmune pathogenesis of bronchial asthma could be defined.

Neurogenic inflammation of the bladder

Current evidence suggests multiple and redundant pathways through which the nervous system can initiate, amplify, and perpetuate inflammation. Many of the processes initiated by neurogenic inflammation have the capacity to recruit the participation of additional sensory nerves. These observations indicate that effective strategies for prevention or treatment of neurogenic inflammation of the bladder will entail or require intervention at multiple points. It has been observed that pain management in the future will be based on selective intervention tailored to the specific processes modulating pain perception in individual patients. It is exciting to contemplate the same approach to prevention and treatment of neurogenic bladder inflammation.

Augmentation of allergic early-phase reaction by nerve growth factor

The allergic early-phase reaction, a hallmark of allergic bronchial asthma, is caused by allergen and immunoglobulin E-dependent mediator release from mast cells. It was previously shown that nerve growth factor (NGF) contributes to acute airway inflammation. This study further investigates the role of NGF in the allergic early-phase reaction using a well-established mouse model of ovalbumin-induced allergic airway inflammation. Treatment of sensitized and aerosol challenged BALB/c mice with blocking anti-NGF antibodies inhibited allergen-induced early-phase reaction and suppressed airway inflammation. Transgenic mice constitutively overexpressing NGF in the airways (Clara-cell secretory protein promoter [CCSP]-NGF-tg) were employed and compared with wild-type animals. In sensitized and challenged CCSP-NGF-tg mice, early-phase reaction, airway inflammation, as well as percental relative increases in serotonin levels were augmented compared with wild-type mice. These effects were paralleled by increased serotonin levels in the airways, whereas immunoglobulin E levels remained unaffected. Furthermore, CCSP-NGF-tg mice developed an increased reactivity of sensory neurons in response to inhaled capsaicin demonstrating NGF-mediated neuronal plasticity. These data provide evidence for the functional role of NGF in the development of allergic early phase responses in the airways and the lung.

Mechanisms underlying tissue selectivity of anandamide and other vanilloid receptor agonists

Anandamide acts as a full vanilloid receptor agonist in many bioassay systems, but it is a weak activator of primary afferents in the airways. To address this discrepancy, we compared the effect of different vanilloid receptor agonists in isolated airways and mesenteric arteries of guinea pig using preparations containing different phenotypes of the capsaicin-sensitive sensory nerve. We found that anandamide is a powerful vasodilator of mesenteric arteries but a weak constrictor of main bronchi. These effects of anandamide are mediated by vanilloid receptors on primary afferents and do not involve cannabinoid receptors. Anandamide also contracts isolated lung strips, an effect caused by the hydrolysis of anandamide and subsequent formation of cyclooxygenase products. Although capsaicin is equally potent in bronchi and mesenteric arteries, anandamide, resiniferatoxin, and particularly olvanil are significantly less potent in bronchi. Competition experiments with the vanilloid receptor antagonist capsazepine did not provide evidence of vanilloid receptor heterogeneity. Arachidonoyl-5-methoxytryptamine (VDM13), an inhibitor of the anandamide membrane transporter, attenuates responses to olvanil and anandamide, but not capsaicin and resiniferatoxin, in mesenteric arteries. VDM13 did not affect responses to these agonists in bronchi, suggesting that the anandamide membrane transporter is absent in this phenotype of the sensory nerve. Computer simulations using an operational model of agonism were consistent, with differences in intrinsic efficacy and receptor content being responsible for the remaining differences in agonist potency between the tissues. This study describes differences between vanilloid receptor agonists regarding tissue selectivity and provides a conceptual framework for developing tissue-selective vanilloid receptor agonists devoid of bronchoconstrictor activity.

Pharmacological profile of (2R-trans)-4-[1-[3,5-bis(trifluoromethyl)benzoyl]-2-(phenylmethyl)-4-piperidinyl]-N-(2,6-dimethylphenyl)-1-acetamide (S)-Hydroxybutanedioate (R116301), an orally and centrally active neurokinin-1 receptor antagonist

In comparison with a series of reference compounds, (2R-trans)-4-[1-[3,5-bis(trifluoromethyl)benzoyl]-2-(phenylmethyl)-4-piperidinyl]-N-(2,6-dimethylphenyl)-1-acetamide (S)-Hydroxybutanedioate (R116301) was characterized as a specific, orally, and centrally active neurokinin-1 (NK(1)) receptor antagonist with subnanomolar affinity for the human NK(1) receptor (K(i): 0.45 nM) and over 200-fold selectivity toward NK(2) and NK(3) receptors. R116301 inhibited substance P (SP)-induced peripheral effects (skin reactions and plasma extravasation in guinea pigs) and a central effect (thumping in gerbils) at low doses (0.08-0.16 mg/kg, s.c. or i.p.), reflecting its high potency as an NK(1) receptor antagonist and excellent brain disposition. Higher doses blocked various emetic stimuli in ferrets, cats, and dogs (ED(50) values: 3.2 mg/kg, s.c.; 0.72-2.5 mg/kg, p.o.). Even higher doses (11-25 mg/kg, s.c.) were required in mice (capsaicin-induced ear edema) and rats (SP-induced extravasation and salivation), consistent with lower affinity for the rodent NK(1) receptor and known species differences in NK(1) receptor interactions. R116301 inhibited the ocular discharge (0.034 mg/kg) but not the dyspnoea, lethality, or cough (>40 mg/kg, s.c.) induced by [betaALA(8)]-neurokinin A (NKA) (4-10) in guinea pigs, attesting to NK(1) over NK(2) selectivity. R116301 did not affect senktide-induced miosis (>5 mg/kg, s.c.) in rabbits, confirming the absence of an interaction with the NK(3) receptor. R116301 was inactive in guinea pigs against skin reactions induced by histamine, platelet-aggregating factor, bradykinin, or Ascaris allergens (>10 mg/kg, s.c.). In all species, R116301 showed excellent oral over parenteral activity (ratio, 0.22-2.7) and a relatively long duration (6.5-16 h, p.o.). The data attest to the specificity and sensitivity of the animal models and support a role of NK(1) receptors in various diseases.

Expression of tachykinins in nonnociceptive vagal afferent neurons during respiratory viral infection in guinea pigs

Immunohistochemistry was combined with retrograde labeling to characterize the effect of respiratory infection with Sendai virus on the number of Substance P/Neurokinin A-containing vagal afferent neurons whose cell bodies resided in the nodose ganglia and whose receptive fields were located in guinea pig trachea. Of the neurons labeled from the trachea of vehicle-inoculated guinea pigs, few stained positively for Substance P/Neurokinin A (approximately 3% of total labeled neurons). These neurons had small diameter cell bodies (mode = 16-20 microm), a feature of nociceptive-like C-fibers. Viral infection (Day 4 after inoculation) was associated with a significantly greater number of labeled neurons containing Substance P/Neurokinin A (approximately 20% of total labeled neurons). The majority of these had a relatively large cell body diameter (mode = 36- 40 microm), a feature of nonnociceptive afferent neurons. This induction appeared to be reversible as there were significantly fewer Substance P/Neurokinin A positive neurons in nodose ganglia from virus-inoculated guinea pigs at Day 28 after inoculation, a time point when virus-induced airway inflammation had all but resolved. These findings support the hypothesis that viral infection leads to a qualitative change in the vagal afferent innervation of guinea pig airways such that both small diameter nociceptive-like neurons and large diameter nonnociceptive neurons express tachykinins.

Antibodies directed against nerve growth factor inhibit the acute bronchoconstriction due to allergen challenge in guinea-pigs

BACKGROUND

We have previously demonstrated that the administration of nerve growth factor (NGF) to guinea-pigs results in airway hyper-responsiveness within 1 h.

OBJECTIVE

In the present study we document the involvement of NGF in the acute allergic airway response.

METHODS

Guinea-pigs that are sensitized to ovalbumin show an acute bronchoconstriction directly after challenge with ovalbumin.

RESULTS

Intratracheal application of 10 microg of antibodies directed against NGF (anti-NGF) 1 h before the challenge reduces the acute severe bronchoconstriction to approximately 40% and the sustained bronchoconstriction to approximately 20% of the reaction in controls. This shows a high potency of anti-NGF in diminishing the direct bronchoconstriction. Inhibition of the tyrosine kinases of the tyrosine kinase receptor A, the high-affinity receptor for NGF, has no effect on the bronchoconstriction. Therefore, we postulate that the p75, the low-affinity receptor for neurotrophins, is responsible for the acute bronchoconstriction. Our findings suggest a role for NGF in the induction of the acute asthmatic reaction.

CONCLUSION

These findings offer a new potential therapeutic strategy for the treatment of allergic asthma.

Neurogenic inflammation and particulate matter (PM) air pollutants

Exposure to a class of airborne pollutants known as particulate matter (PM) is an environmental health risk of global proportions. PM is thought to initiate and/or exacerbate respiratory disorders, such as asthma and airway hyper-responsiveness and is epidemiologically associated with causing death in the elderly and those with pre-existing respiratory, or cardiopulmonary disease. Plausible mechanisms of action to explain PM inflammation and its susceptible sub-population component are lacking. This review describes a series of published studies which indicate that PM initiates airway inflammation through sensory neural pathways, specifically by activation of capsaicin-sensitive vanilloid (e.g. VRI) irritant receptors. These acid-sensitive receptors are located on the sensory C nerve fibers that innervate the airways as well as on various immune and non-immune airway target cells. The activation of these receptors results in the release of neuropeptides from the sensory terminals that innervate the airways. Their interactions with airway target cells, result in signs of inflammation (e.g. bronchoconstriction, vasodilation, histamine release, mucous secretion etc.). Our data have linked the activation of the VR1 receptors to the surface charge carried on the colloidal particulates which constitute PM pollution. Related studies have examined how genetic and non-genetic factors modify the sensitivity of these irritant receptors and enhance the inflammatory responsiveness to PM. In summary, this review proposes a mechanism by which neurogenic elements initiate and sustain PM-mediated airway inflammation. Although neurogenic influences have been appreciated in normal airway homeostasis, they have not, until now, been associated with PM toxicity. The sensitivity of the sensory nervous system to irritants and its interactions with pulmonary target tissues, should encourage neuroscientists to explore the relevance of neurogenic influences to toxic disorders involving other peripheral target systems.

The role of sensory nerve endings in nerve growth factor-induced airway hyperresponsiveness to histamine in guinea-pigs

1. Nerve growth factor induces an airway hyperresponsiveness in vivo in guinea-pigs, as we have shown previously. Since antagonizing the neurokinin-1 (NK(1)) receptor can prevent this NGF-induced airway hyperresponsiveness and since sensory nerves release tachykinins, we investigated the role of sensory nerves in the NGF-induced airway hyperresponsiveness. 2. We used isolated tracheal rings from guinea-pigs to measure tracheal contractility. In these rings sensory nerve endings are present, but these endings lack any contact with their cell bodies. 3. In this in vitro system, NGF dose-dependently induced a tracheal hyperresponsiveness to histamine. The NK(1) receptor antagonist SR140333 could block the induction of tracheal hyperresponsiveness. 4. To further investigate the involvement of sensory nerve endings we used the cannabinoid receptor 1 (CB(1)) agonist R-methanandamide to inhibit excitatory events at the nerve terminal. The CB(1) receptor agonist was capable of blocking the tracheal hyperresponsiveness to NGF in the isolated system, as well as the airway hyperresponsiveness to NGF in vivo. 5. This indicates that NGF can induce an increase in airway responsiveness in the absence of sensory nerve cell bodies. NGF may act by increasing substance P release from sensory nerve endings, without upregulation of substance P in the neurons. Substance P in its turn is responsible for the induction of the NGF-induced airway hyperresponsiveness.

Tachykinin-induced bronchoconstriction in sheep is NK-1 receptor mediated and exhibits tachyphylaxis

OBJECTIVE

Tachykinins are mediators of airway hyper-reactivity and inflammation. There is in vitro evidence that ovine responses to tachykinins correlate closely to human responses. This study was designed to characterize the effect of intravenously administered tachykinins on sheep lung resistance in vivo to determine the effect of dose timing on reproducibility of responses and the induction of tachyphylaxis. We then used this information to help further characterize the response with several pharmacological agents.

METHODOLOGY

Substance P (SP) was administered by infusion to conscious merino ewes and lung resistance (RL) was measured. Infusions were given at 30, 60, 120 min and 24 h intervals. The effect of various agents on the response to SP was then assessed.

RESULTS

Substance P led to a transient increase in RL, mean (+/- SEM) 754.8 (+/- 139)% of baseline, with marked tachyphylaxis at 30, 60 and 120 min. Phosphoramidon increased the peak response to 1151.5 +/- 196%. Atropine and CP 96 345 abolished the response to SP, while indomethacin, sodium cromoglycate and pyrilamine had no significant effect. Substance P had a greater effect on RL than did neurokinin A.

CONCLUSIONS

Substance P increases RL in sheep via a cholinergic mechanism which is mediated by NK-1 receptors, and is subject to tachyphylaxis. These findings have implications for the design of studies using the ovine model in the evaluation of tachykinin antagonists as potential therapeutic agents.

Role of vagal C-fiber afferents in the bronchomotor response to lactic acid in the newborn dog

We addressed the hypothesis that vagal C-fiber afferents and cyclooxygenase products are the mechanisms responsible for lactic acid (LA)-induced bronchoconstriction in the newborn dog. Perineural capsaicin and indomethacin were used to block conduction of vagal C fibers and production of cyclooxygenase products, respectively. Perineural capsaicin eliminated (85%) the increase in lung resistance (Rl; 45 ± 5.6%) due to capsaicin (25 μg/kg), whereas the increase in Rl (54 ± 6.9%) due to LA (0.4 mmol/kg) was only inhibited by 37 ± 4.7% ( P < 0.05). Atropine reduced LA-induced bronchoconstriction (42 ± 2.1%) by an amount similar to that obtained with perineural capsaicin. However, inhibition was significantly increased when atropine was combined with indomethacin (61 ± 2.7%; P < 0.05), implicating cyclooxygenase products in the LA-induced bronchoconstrictor response. We conclude that the mechanisms responsible for LA-induced bronchoconstriction in the newborn are 1) activation of vagal C-fibers, which, through projections to medullary respiratory centers, leads to activation of vagal cholinergic efferents; 2) production of cyclooxygenase products, which cause bronchoconstriction independent of medullary involvement; and 3) an unknown bronchoconstrictor mechanism, putatively tachykinin mediated. On the basis of our data, pharmaceutical targeting of pulmonary afferents would prevent multiple downstream mechanisms that lead to airway narrowing due to inflammatory lung disease.

NK1 receptor stimulation causes contraction and inositol phosphate increase in medium-size human isolated bronchi

Although contraction of human isolated bronchi is mediated mainly by tachykinin NK2 receptors, NK1 receptors, via prostanoid release, contract small-size (approximately 1 mm in diameter) bronchi. Here, we have investigated the presence and biological responses of NK1 receptors in medium-size (2-5 mm in diameter) human isolated bronchi. Specific staining was seen in bronchial sections with an antibody directed against the human NK1 receptor. The selective NK1 receptor agonist, [Sar(9), Met(O2)(11)]SP, contracted about 60% of human isolated bronchial rings. This effect was reduced by two different NK1 receptor antagonists, CP-99,994 and SR 140333. Contraction induced by [Sar(9), Met(O2)(11)]SP was independent of acetylcholine and histamine release and epithelium removal, and was not affected by nitric oxide synthase and cyclooxygenase (COX) inhibition. [Sar(9), Met(O2)(11)]SP increased inositol phosphate (IP) levels, and SR 140333 blocked this increase, in segments of medium- and small-size (approximately 1 mm in diameter) human bronchi. COX inhibition blocked the IP increase induced by [Sar(9), Met(O2)(11)]SP in small-size, but not in medium-size, bronchi. NK1 receptors mediated bronchoconstriction in a large proportion of medium-size human bronchi. Unlike small-size bronchi this effect is independent of prostanoid release, and the results are suggestive of a direct activation of smooth muscle receptors and IP release.

Sensory pathways and cyclooxygenase regulate mucus gel thickness in rat duodenum

We previously showed that the duodenal hyperemic response to acid occurs through activation of capsaicin-sensitive afferent nerves with subsequent release of vasodilatory substances such as calcitonin gene-related peptide (CGRP) and nitric oxide. We then tested the hypothesis that similar factors regulate duodenal mucus gel thickness. Gel thickness was optically measured using in vivo microscopy in anesthetized rats. Duodenal mucosae were superfused with pH 7.0 buffer with vanilloid receptor agonist capsaicin, bradykinin, or PGE(2) injection or were challenged with pH 2.2 solution, with or without the vanilloid antagonist capsazepine, human CGRP-(8-37), N(G)-nitro-L-arginine methyl ester, and indomethacin. Other rats underwent sensory ablation with high-dose capsaicin pretreatment. Acid, bradykinin, capsaicin, and PGE(2) all quickly thickened the gel. Antagonism of vanilloid and CGRP receptors, inhibition of nitric oxide synthase, and sensory deafferentation delayed gel thickening, suggesting that the capsaicin pathway mediated the initial burst of mucus secretion that thickened the gel. Indomethacin abolished gel thickening due to acid, bradykinin, and capsaicin. Inhibition of gel thickening by indomethacin in response to multiple agonists suggests that cyclooxygenase activity is essential for duodenal gel thickness regulation. Duodenal afferent neural pathways play an important role in the modulation of cyclooxygenase-mediated physiological control of gel thickness.

Neurotrophins and asthma

The neurotrophins are a family of peptides that promote survival, growth, and differentiation of neurons. Neurotrophins may also influence the function of nonneuronal cell types, including immune cells. The development and maintenance of asthma is thought to involve the nervous system and the immune system, but the role that neurotrophins play in asthma is unknown. The cellular sources of the neurotrophins include mast cells, lymphocytes, macrophages, epithelial cells, smooth muscle cells, and eosinophils. The activation of neurotrophin receptors in immune cells and neurons involves ligand-induced homodimerization, which leads to activation of intrinsic Trk receptor kinase. The exact consequences of activating these receptors on immune cells is unknown, but rather than having unique actions on immune cells, the neurotrophins appear to act in concert with known immune regulating factors to modulate the maturation, accumulation, proliferation, and activation of immune cells. Neurotrophins can modulate afferent nerve function by stimulating the production of neuropeptides within airway afferent neurons. These neuropeptides may be released from the central terminals of airway afferent neurons, which leads to heightened autonomic reflex activity, and increased reactivity in the airways.

Neurotrophins in bronchial asthma

Allergic bronchial asthma (BA) is characterized by chronic airway inflammation, development of airway hyperreactivity and recurrent reversible airway obstruction. T-helper 2 cells and their products have been shown to play an important role in this process. In contrast, the mechanisms by which immune cells interact with the cells residing in lung and airways, such as neurons, epithelial or smooth muscle cells, still remains uncertain. Sensory and motor neurons innervating the lung exhibit a great degree of functional plasticity in BA defined as "neuronal plasticity". These neurons control development of airway hyperresponsiveness and acute inflammatory responses, resulting in the concept of "neurogenic inflammation". Such quantitative and/or qualitative changes in neuronal functions are mediated to a great extent by a family of cytokines, the neurotrophins, which in turn are produced by activated immune cells, among others in BA. We have therefore developed the concept that neurotrophins such as nerve growth factor and brain-derived neurotrophic factor link pathogenic events in BA to dysfunctions of the immune and nervous system.

Vanilloid (capsaicin) receptors influence inflammatory sensitivity in response to particulate matter

The signs of airway inflammation and hyperresponsiveness that occur in animals exposed to air pollutants are often strain- and species-specific. To investigate the underlying causes of this phenomenon, BALB/c and C57bl/6 mice were exposed intratracheally to residual oil fly ash (ROFA, 3 mg/kg) and examined after 24 h for signs of airway inflammation. BALB/c showed significantly higher numbers of neutrophils and increased airway hyperresponsiveness in response to methacholine challenge, whereas B6 mice showed no significant change in either inflammatory endpoint. To determine the underlying cause of this strain specificity, cultures of dorsal root ganglion (DRG) sensory neurons, which innervate the upper airways in situ, were explanted from both BALB/c and B6 fetal mice. After 5-7 days in culture, they were exposed to ROFA, other urban and industrial particulate matter (PM; e.g., oil fly ash, woodstove, Mt. St. Helen, St. Louis, Ottawa, coal fly ash) or to prototype irritants (e.g., capsaicin 3-10 microM, pH 5.0 and 6.5). In all instances (except for woodstove), DRG neurons from BALB/c mice released significantly higher levels of the pro-inflammatory cytokine IL-6 into their nutrient media relative to neurons from B6 mice. This cytokine release could be significantly reduced for all PM treated cultures (except woodstove) by pretreatment of cultures with capsazepine (CPZ), a competitive antagonist of vanilloid receptors. DRG neurons, cultured from BALB/c and B6 neonates, were loaded with Fluo-3 AM and exposed to the prototype irritants, acid pH (5.0, 6.5), or capsaicin (3, 10 microM). Analysis of their increases in intracellular calcium showed that significantly higher numbers of BALB/c neurons responded to these prototype irritants, relative to B6 neurons. Morphometric analysis of BALB/c neurons, histochemically stained with cobalt to label neurons bearing capsaicin-sensitive receptors, showed a significantly higher level of stained neurons relative to B6 neurons. Finally, semiquantitative RT-PCR showed a higher expression of VR1 receptor mRNA in DRG and spinal cord taken from neonatal BALB/c mice relative to B6 mice. Taken together, these data suggest that capsaicin and acid-sensitive irritant receptors, located on somatosensory cell bodies and their nerve fiber terminals, subserve PM-induced airway inflammation and are quantitatively different in responsive and nonresponsive mouse strains.

Neurokinin mediation of edema and inflammation

The aim of this article is to furnish a brief review of the role played by neurokinins in the inflammatory process. Further attention is given to the mechanisms, as well as to the receptor subtypes involved in neurokinin-mediated inflammation, in an attempt to clarify the participation of neurokinins in different models of acute and chronic inflammation. The involvement of SP, NKA and NKB is also examined in relation to the major signs of inflammation, including edema formation, protein plasma extravasation and vasodilatation. Finally, we provide a general overview on the potential clinical applications of neurokinin antagonists, along with the involvement of neurokinins in human diseases.

Substance P in the nucleus of the solitary tract augments bronchopulmonary C fiber reflex output

Bronchopulmonary C fibers defend the lungs against injury from inhaled agents by a central nervous system reflex consisting of apnea, cough, bronchoconstriction, hypotension, and bradycardia. Glutamate is the putative neurotransmitter at the first central synapses in the nucleus of the solitary tract (NTS), but substance P, also released in the NTS, may modulate the transmission. To test the hypothesis that substance P in the NTS augments bronchopulmonary C fiber input and hence reflex output, we stimulated the C fibers with left atrial capsaicin (LA CAP) injections and compared the changes in phrenic nerve discharge, tracheal pressure (TP), arterial blood pressure (ABP), and heart rate (HR) in guinea pigs before and after substance P injections (200 microM, 25 nl) in the NTS. Substance P significantly augmented LA CAP-evoked increases in expiratory time by 10-fold and increases in TP and decreases in ABP and HR by threefold, effects prevented by neurokinin-1 (NK1) receptor antagonism. Thus substance P acting at NTS NK1 receptors can exaggerate bronchopulmonary C fiber reflex output. Because substance P synthesis in vagal airway C fibers may be enhanced in pathological conditions such as allergic asthma, the findings may help explain some of the associated respiratory symptoms including cough and bronchoconstriction.

Distribution of neuropeptides, histamine content, and inflammatory cells in the ureter

OBJECTIVES

To determine the anatomic distribution of select neuropeptides (neurokinin A [NKA], substance P [SP], and bradykinin [BK]), of inflammatory cells (leukocytes and mast cells), and the histamine content in the normal swine ureter and compare the findings with regions of increased ureteral contractility.

METHODS

Ureters from 10 pigs were obtained and cut into eight segments, proximally to distally. A portion of each ureteral segment was suspended in Krebs buffer (37 degrees C) and attached to force displacement transducers, and spontaneous contractility was measured for 30 minutes. A second portion was assayed for histamine, NKA, SP, and BK using enzyme-linked immunosorbent assay. A third portion was fixed in 10% buffered formalin, stained with hematoxylin-eosin, and evaluated histologically.

RESULTS

Ureteral contractility was found to be highest in the most proximal and most distal regions of the ureter. Similarly, SP content was three times greater in the proximal ureter and two times greater in the distal ureter than in the midureter (P <0.05, n = 10). The total NKA and BK content were also higher in the proximal and distal ureter than in the midureter. Conversely, the histamine content was consistent throughout the ureter. Moreover, no significant difference in the distribution of inflammatory cells was identified throughout the ureter.

CONCLUSIONS

The anatomic distribution of NKA, SP, and BK in the ureter corresponded to regions of increased spontaneous ureteral contractility, more specifically the proximal and distal ureter. Neuropeptides may play a significant role in ureteral contractility and may be a target for pharmacologic mediation during obstruction and stone passage.

Residual oil fly ash and charged polymers activate epithelial cells and nociceptive sensory neurons

Residual oil fly ash (ROFA) is an industrial pollutant that contains metals, acids, and unknown materials complexed to a particulate core. The heterogeneous composition of ROFA hampers finding the mechanism(s) by which it and other particulate pollutants cause airway toxicity. To distinguish culpable factors contributing to the effects of ROFA, synthetic polymer microsphere (SPM) analogs were synthesized that resembled ROFA in particle size (2 and 6 microm in diameter) and zeta potential (-29 mV). BEAS-2B human bronchial epithelial cells and dorsal root ganglion neurons responded to both ROFA and charged SPMs with an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and the release of the proinflammatory cytokine interleukin-6, whereas neutral SPMs bound with polyethylene glycol (0-mV zeta potential) were relatively ineffective. In dorsal root ganglion neurons, the SPM-induced increases in [Ca(2+)](i) were correlated with the presence of acid- and/or capsaicin-sensitive pathways. We hypothesized that the acidic microenvironment associated with negatively charged colloids like ROFA and SPMs activate irritant receptors in airway target cells. This causes subsequent cytokine release, which mediates the pathophysiology of neurogenic airway inflammation.

Respiratory syncytial virus infection and G and/or SH protein expression contribute to substance P, which mediates inflammation and enhanced pulmonary disease in BALB/c mice

A distinct clinical presentation of respiratory syncytial virus (RSV) infection of humans is bronchiolitis, which has clinical features similar to those of asthma. Substance P (SP), a tachykinin neuropeptide, has been associated with neurogenic inflammation and asthma; therefore, we chose to examine SP-induced inflammation with RSV infection. In this study, we examined the production of pulmonary SP associated with RSV infection of BALB/c mice and the effect of anti-SP F(ab)(2) antibodies on the pulmonary inflammatory response. The peak production of pulmonary SP occurred between days 3 and 5 following primary RSV infection and day 1 after secondary infection. Treatment of RSV-infected mice with anti-SP F(ab)(2) antibodies suggested that SP may alter the natural killer cell response to primary and secondary infection. In mice challenged after formalin-inactivated RSV vaccination, SP appears to markedly enhance pulmonary eosinophilia as well as increase polymorphonuclear cell trafficking to the lung. Based on studies with a strain of RSV that lacks the G and SH genes, the SP response to RSV infection appears to be associated with G and/or SH protein expression. These data suggest that SP may be an important contributor to the inflammatory response to RSV infection and that anti-SP F(ab)(2) antibodies might be used to ameliorate RSV-associated disease.

The role of protease-activated receptor-2 (PAR2) in the modulation of beating of the mouse isolated ureter: lack of involvement of mast cells or sensory nerves

1 The localization of protease-activated receptor-2 (PAR2) and the effects of PAR2 activators were investigated in the mouse isolated ureter in order to test the hypothesis that PAR2 activation may initiate neuropeptide release from sensory nerve fibres and hence contribute to inflammation. 2 PAR2 was localized by fluorescence immunohistochemistry to both the smooth muscle and epithelium of the ureter. Macrophage-like cells in the adventitia of the ureter were also PAR2-immunoreactive. PAR2-immunoreactivity was not observed in mast cells or nerve fibres. 3 In circular muscle preparations of the ureter in which continuous rhythmic beating was induced by KCl (20 mM) and the thromboxane A2 mimetic U46619 (0.3 microM), trypsin (0.3 U ml-1) reduced beat frequency to 84.6+/-2.0% of control rates. The PAR2-selective peptide agonist SLIGRL-NH2 concentration-dependently (0.1-3.0 microM) slowed beat frequency to a maximum of 72.7+/-2.0%. 4 Histamine (1-300 microM) was more efficacious than SLIGRL-NH2 in inhibiting ureter beat frequency in a concentration-dependent manner to a maximum (at 300 microM) of 7.9+/-2.5% of the control rate. 5 Pretreatment of preparations with capsaicin (10 microM for 30 min) markedly attenuated the inhibitory effect of histamine, but not that of SLIGRL-NH2, indicating a role for sensory nerves in the inhibitory effect of histamine only. 6 The inhibitory effect of SLIGRL-NH2 on ureter beat frequency was unaffected by the nitric oxide (NO) synthase inhibitor, L-NOARG (100 microM) or the cyclo-oxygenase inhibitor, indomethacin (3 microM). 7 In conclusion, PAR2 activation causes inhibition of beating in the mouse ureter that is not mediated by axon reflex release of inhibitory neuropeptides. This inhibitory effect of PAR2 appears to be mediated directly on smooth muscle cells, although the contribution of non-NO, non-prostanoid epithelium-derived factors cannot be ruled out.

Nerve growth factor induces a neurokinin-1 receptor- mediated airway hyperresponsiveness in guinea pigs

Because asthmatic patients show increased nerve growth factor (NGF) serum levels, we examined the effect of NGF on airway function. Intravenously administered NGF potentiates the histamine- induced bronchoconstriction with a maximum of over 200% in anesthetized spontaneously breathing guinea pigs. Doses of 8 ng and 80 ng NGF/kg body weight induce a significant hyperresponsiveness to histamine. NGF itself does not affect airway reactivity. Airway hyperresponsiveness is observed 30 min and 3 h after NGF administration, and has disappeared after 24 h. The neurokinin-1 receptor antagonist SR 140333 completely blocks the NGF-induced hyperresponsiveness, pointing to a role for tachykinins. This is the first report showing a direct relation between peripherally administered NGF and airway hyperresponsiveness. Taking into consideration that plasma NGF levels have been shown to be elevated in asthmatic patients, our result points to an important role for NGF in the pathogenesis of asthma.

NK-2 is the predominant tachykinin receptor subtype in the swine ureter

OBJECTIVE

To determine which of the known tachykinin receptor subtypes is predominant in the swine ureter.

MATERIALS AND METHODS

Ureters from adult pigs were harvested, cut into longitudinal strips and placed in 10 mL tissue baths containing Krebs buffer, under 4 g of initial tension. The magnitude and frequency of contractions were recorded. Tissues were incubated with 1 micromol/L solutions of peptidase inhibitors (phosphoramidon and captopril) for 1 h to inhibit degradation of peptides and treated with either CP 96,345 (NK-1 receptor antagonist), SR 48,968 (NK-2 receptor antagonist) or saline (control). Concentration-response curves to the tachykinins substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were determined.

RESULTS

Ureteric segments showed a concentration-dependent response to all tachykinins; NKA stimulated increased contractions at a lower concentration than either SP or NKB (P<0.05). This was reflected by the difference in the effective concentration required to obtain half the maximal response (EC50 ) for each of the peptides. The mean (sd) EC50 values were (micromol/L): NKA, 0.2 (0.02); SP, 3.5 (0.7); and NKB, 4.5 (1.7). In addition, the selective NK-2 antagonist (SR 48,968) significantly reduced contractile responses to all peptides, as indicated by a 10-fold rightward shift of the concentration-response curves (P<0. 05), whereas the NK-1 antagonist (CP 96,345) had no significant effect.

CONCLUSION

These results indicate that NK-2 is the predominant tachykinin receptor subtype responsible for contraction of ureteric smooth muscle. The use of mediators which act on NK-2 receptors may have clinical applications for the treatment of ureteric disease.

Particulate matter initiates inflammatory cytokine release by activation of capsaicin and acid receptors in a human bronchial epithelial cell line

Recent experiments have shown that human bronchial epithelial cells (i.e., BEAS-2B) release pro-inflammatory cytokines (i.e., IL-6 and TNFalpha) in a receptor-mediated fashion in response to the neuropeptides, substance P (SP), calcitonin gene-related protein (CGRP), and the prototype botanical irritant capsaicin. In the present experiments, we examined the relevance of these receptors to particulate matter (PM)-associated cellular inflammation. BEAS-2B cells, exposed to residual oil fly ash particles (ROFA), responded with an immediate (<30 s) increase in intracellular calcium levels ([Ca2+]i), increases of key inflammatory cytokine transcripts (i.e., IL-6, IL-8, TNFalpha) within 2 h exposure, and subsequent release of IL-6 and IL-8 cytokine protein after 4 h exposure. Pretreatment of BEAS-2B cells with pharmacological antagonists selective for the SP or CGRP receptors reduced the ROFA-stimulated IL-6 cytokine production by approximately 25 and 50%, respectively. However, pretreatment of these cells with capsazepine (CPZ), an antagonist for capsaicin (i.e., vanilloid) receptors, inhibited the immediate increases in [Ca2+]i, diminished transcript (i.e., IL-6, IL-8, TNFalpha) levels and reduced IL-6 cytokine release to control levels. BEAS-2B cells exposed to ROFA in calcium-free media failed to demonstrate increases of [Ca2+]i and showed reduced levels of cytokine transcript (i.e., IL-6, IL-8, TNFalpha) and IL-6 release, suggesting that ROFA-stimulated cytokine formation was partially dependent on extracellular calcium sources. A final set of experiments compared the inflammatory properties of the soluble and acidic insoluble components of ROFA. BEAS-2B cells, exposed to ROFA or ROFA that had been filtered through a 0.2-micrometer pore filter, produced equivocal IL-6. BEAS-2B cells exposed to pH 5.0 media for 15 min released moderate amounts of IL-6, 4 h later. This cytokine release could be blocked by amiloride, a pH receptor antagonist, but not by CPZ. BEAS-2B cells, pretreated with amiloride before ROFA exposure, showed a partial (approximately 25%) reduction of IL-6. Together, these data indicate that the acidic, soluble components of ROFA initiate cytokine release in BEAS-2B cells through activation of both capsaicin- and pH-sensitive irritant receptors.

Serum Levels of Substance P Are Elevated in Patients With Sickle Cell Disease and Increase Further During Vaso-Occlusive Crisis

As a mediator of neurogenic inflammation and pain, we hypothesized that levels of the neuropeptide Substance P (SP) would be elevated in patients with sickle cell disease (SCD) with vaso-occlusive pain crisis. SP is a known stimulator of tumor necrosis factor- (TNF-) release and a promoter of interleukin-8 (IL-8), which are reported to be increased in SCD. These cytokines enhance adhesion of leukocytes to endothelium and may play a role in vaso-occlusive events. Serum levels of IL-8, TNF, and SP were studied in three groups of children aged 2 to 18 years: 30 well children with SCD, 21 with SCD in pain crisis, and 20 healthy age-matched controls. Serum levels of SP were elevated in all SCD patients and were highest in patients in pain crisis. The percentage of sera with detectable levels of IL-8 (&gt;5.0 pmol/L) was increased in SCD patients as compared with the control group. IL-8 levels were similar for well SCD patients and those with pain. TNF levels were not significantly different among the three groups. In three children with SCD, SP was measured at baseline and again during pain crisis. In each case, serum levels during pain crisis were higher than they were when the patient was well. We conclude that levels of SP are high in patients with SCD and increase during pain crisis. These results imply that SP plays a prominent role in the pain and inflammation of SCD and may be a measurable laboratory marker of vaso-occlusive crisis. We speculate that neurokinin receptor antagonists may have a therapeutic potential in the treatment of crisis pain.

© 1998 by The American Society of Hematology.

Serum Levels of Substance P Are Elevated in Patients With Sickle Cell Disease and Increase Further During Vaso-Occlusive Crisis

As a mediator of neurogenic inflammation and pain, we hypothesized that levels of the neuropeptide Substance P (SP) would be elevated in patients with sickle cell disease (SCD) with vaso-occlusive pain crisis. SP is a known stimulator of tumor necrosis factor- (TNF-) release and a promoter of interleukin-8 (IL-8), which are reported to be increased in SCD. These cytokines enhance adhesion of leukocytes to endothelium and may play a role in vaso-occlusive events. Serum levels of IL-8, TNF, and SP were studied in three groups of children aged 2 to 18 years: 30 well children with SCD, 21 with SCD in pain crisis, and 20 healthy age-matched controls. Serum levels of SP were elevated in all SCD patients and were highest in patients in pain crisis. The percentage of sera with detectable levels of IL-8 (>5.0 pmol/L) was increased in SCD patients as compared with the control group. IL-8 levels were similar for well SCD patients and those with pain. TNF levels were not significantly different among the three groups. In three children with SCD, SP was measured at baseline and again during pain crisis. In each case, serum levels during pain crisis were higher than they were when the patient was well. We conclude that levels of SP are high in patients with SCD and increase during pain crisis. These results imply that SP plays a prominent role in the pain and inflammation of SCD and may be a measurable laboratory marker of vaso-occlusive crisis. We speculate that neurokinin receptor antagonists may have a therapeutic potential in the treatment of crisis pain.

© 1998 by The American Society of Hematology.

L-tryptophan urea amides as NK1/NK2 dual antagonists

We report that a systematic modification of an NK1 receptor selective antagonist resulted in the identification of novel compounds, 4c and 4d, with high affinity for both NK1 and NK2 receptors.

Endocrine and vagal controls of sympathetically dependent neurogenic inflammation

Recently the very significant role of the postganglionic sympathetic neuron (PGSN) terminal in the production of neurogenic inflammation has been appreciated. An important model of this sympathetically dependent inflammation is venular plasma extravasation (PE) and neutrophil attraction produced by local intra-articular injection of the potent inflammatory mediator bradykinin (BK). Sympathetic-dependent PE in the synovium has been proposed as a protective mechanism in arthritis. In a recent series of studies, a novel mechanism has been discovered by which activation of primary afferent nociceptors exerts a potent feedback inhibition of PGSN-dependent PE. Activation of nociceptive afferents was shown to be involved in this feedback system. Such a negative feedback control of the acute inflammatory response would have survival value; the inflammatory response, as initiated by a high degree of positive feedback, and the inflammatory process itself when persisting can result in significant tissue injury. If indeed HPA axis activity plays a significant physiological role in the modulation of neurogenic inflammation, then physiological processes that modulate the HPA axis would be expected to influence neurogenic inflammation. A dramatic effect of this kind has been demonstrated, in the rat, for vagal afferent activity. In the presence of subdiaphragmatic (or celiac branch) vagotomy, the potency of nociceptive afferent activity to inhibit sympathetically dependent, BK-induced PE was increased by four orders of magnitude compared to vagus-intact animal. Hypoactivity or hyperactivity of these vagally mediated mechanisms could contribute to diseases characterized by either an inadequate or an exaggerated inflammatory response.

Allergic inflammation in isolated vagal sensory ganglia unmasks silent NK-2 tachykinin receptors

Neuroplastic changes in vagal afferents inflicted by allergic inflammation were examined in nodose ganglia (NG) removed from guinea pigs immunized to chick ovalbumin. In control NG neurons, substance P (SP; 0.1-10 microM) produces no discernable changes in membrane electrophysiological properties or [Ca2+]i. After exposing NG from immunized animals to the sensitizing antigen in vitro, 83% of the neurons were depolarized by 100 nM SP. SP also produces an inward current, an increase in membrane conductance, and an elevation of [Ca2+]i. Buffering [Ca2+]i with BAPTA blocked the [Ca2+]i rise and the SP depolarization, indicating that internal stores of Ca2+ are required. When protein synthesis was inhibited >96% (as determined by [3H] leucine incorporation), antigen challenge still unmasked SP responses. The SP response was maximal 30 min after antigen challenge, and it was evident for at least 8 hr in intact ganglia and for 3.5 d in isolated neurons. [beta-Ala8]Neurokinin A ([beta-Ala8]NKA; 10 nM), an NK-2 selective agonist, mimicked SP; selective NK-1 and NK-3 agonists were ineffective. The EC50 values for SP and [beta-Ala8]NKA membrane currents were 78 and 33 nM, respectively. Additionally, SR48968, an NK-2 receptor antagonist, blocked these responses. Thus, antigen challenge appears to unmask an NK-2 tachykinin receptor. These data further support the hypothesis that inflammatory mediators released during immediate hypersensitivity (allergic) reactions can produce profound effects on the excitability of sensory nerves. Unmasked NK-2 receptors may serve an excitatory autoreceptor function, provide a pathway for paracrine signaling between NG neurons, and contribute to ectopic sensory nerve activity.