Pulmonary neuronal M2 muscarinic receptor function in asthma and animal models of hyperreactivity

Exploring the Modulatory Effect of High-Fat Nutrition on Lipopolysaccharide-Induced Acute Lung Injury in Vagotomized Rats and the Role of the Vagus Nerve

During esophagectomy, the vagus nerve is transected, which may add to the development of postoperative complications. The vagus nerve has been shown to attenuate inflammation and can be activated by a high-fat nutrition via the release of acetylcholine. This binds to α7 nicotinic acetylcholine receptors (α7nAChR) and inhibits α7nAChR-expressing inflammatory cells. This study investigates the role of the vagus nerve and the effect of high-fat nutrition on lipopolysaccharide (LPS)-induced lung injury in rats. Firstly, 48 rats were randomized in 4 groups as follows: sham (sparing vagus nerve), abdominal (selective) vagotomy, cervical vagotomy and cervical vagotomy with an α7nAChR-agonist. Secondly, 24 rats were randomized in 3 groups as follows: sham, sham with an α7nAChR-antagonist and cervical vagotomy with an α7nAChR-antagonist. Finally, 24 rats were randomized in 3 groups as follows: fasting, high-fat nutrition before sham and high-fat nutrition before selective vagotomy. Abdominal (selective) vagotomy did not impact histopathological lung injury (LIS) compared with the control (sham) group (p > 0.999). There was a trend in aggravation of LIS after cervical vagotomy (p = 0.051), even after an α7nAChR-agonist (p = 0.090). Cervical vagotomy with an α7nAChR-antagonist aggravated lung injury (p = 0.004). Furthermore, cervical vagotomy increased macrophages in bronchoalveolar lavage (BAL) fluid and negatively impacted pulmonary function. Other inflammatory cells, TNF-α and IL-6, in the BALF and serum were unaffected. High-fat nutrition reduced LIS after sham (p = 0.012) and selective vagotomy (p = 0.002) compared to fasting. vagotomy. This study underlines the role of the vagus nerve in lung injury and shows that vagus nerve stimulation using high-fat nutrition is effective in reducing lung injury, even after selective vagotomy.

2021 Guideline for the Management of COPD Exacerbations: Emergency Medicine Association of Turkey (EMAT) / Turkish Thoracic Society (TTS) Clinical Practice Guideline Task Force

Chronic obstructive pulmonary disease (COPD) is an important public health problem that manifests with exacerbations and causes serious mortality and morbidity in both developed and developing countries. COPD exacerbations usually present to emergency departments, where these patients are diagnosed and treated. Therefore, the Emergency Medicine Association of Turkey and the Turkish Thoracic Society jointly wanted to implement a guideline that evaluates the management of COPD exacerbations according to the current literature and provides evidence-based recommendations. In the management of COPD exacerbations, we aim to support the decision-making process of clinicians dealing with these patients in the emergency setting.

Pioglitazone prevents obesity-related airway hyperreactivity and neuronal M2 receptor dysfunction

Obesity-related asthma often presents with more severe symptoms than non-obesity-related asthma and responds poorly to current treatments. Both insulin resistance and hyperinsulinemia are common in obesity. We have shown that increased insulin mediates airway hyperreactivity in diet-induced obese rats by causing neuronal M2 muscarinic receptor dysfunction, which normally inhibits acetylcholine release from parasympathetic nerves. Decreasing insulin with streptozotocin prevented airway hyperreactivity and M2 receptor dysfunction. The objective of the present study was to investigate whether pioglitazone, a hypoglycemic drug, prevents airway hyperreactivity and M2 receptor dysfunction in obese rats. Male rats fed a low- or high-fat diet were treated with pioglitazone or PBS by daily gavage. Body weight, body fat, fasting insulin, and bronchoconstriction and bradycardia in response to electrical stimulation of vagus nerves and to aerosolized methacholine were recorded. Pilocarpine, a muscarinic receptor agonist, was used to measure M2 receptor function. Rats on a high-fat diet had potentiated airway responsiveness to vagal stimulation and dysfunctional neuronal M2 receptors, whereas airway responsiveness to methacholine was unaffected. Pioglitazone reduced fasting insulin and prevented airway hyperresponsiveness and M2 receptor dysfunction but did not change inflammatory cytokine mRNA expression in alveolar macrophages. High-fat diet, with and without pioglitazone, had tissue-specific effects on insulin receptor mRNA expression. In conclusion, pioglitazone prevents vagally mediated airway hyperreactivity and protects neuronal M2 muscarinic receptor function in obese rats.

Urinary Dialkyl Phosphate Concentrations and Lung Function Parameters in Adolescents and Adults: Results from the Canadian Health Measures Survey

BACKGROUND

Epidemiological studies have reported associations between lung function parameters and organophosphate (OP) pesticide exposures in agricultural occupations, but to our knowledge associations have not been evaluated in general populations.

OBJECTIVES

We examined associations between OP metabolite dialkyl phosphates (DAPs) and lung function using data from the Canadian Health Measures Survey (CHMS) Cycle 1.

METHODS

Forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), FEV1/FVC ratio, and forced expiratory flow between 25% and 75% of FVC (FEF25%-75%) were measured for 4,446 CHMS participants. Urinary concentrations of six DAP metabolites (DMP, DMTP, DMDTP, DEP, DETP, and DEDTP), smoking status, and other predictors of lung function were also measured in the CHMS-Cycle 1. Multiple linear regression analyses were used to examine the relationship between total DAP concentrations (ΣDAPs) and lung function in adolescents (12-19 years) and adults (20-79 years).

RESULTS

In adults, estimates from multiple regression analyses suggested that a 1-unit increase on natural logarithmic scale (171% increase on the original scale) in the creatinine-corrected urinary concentration (nanomoles per gram creatinine) of ΣDAP was associated with a 32.6-mL (95% CI: -57.2, -8.1) reduction in FVC, 32.6-mL (95% CI: -59.0, -6.3) reduction in FEV1, 0.2% (95% CI: -0.6, 0.2) reduction in FEV1/FVC ratio, and 53.1-mL/sec (95% CI: -113.9, 7.7) reduction in FEF25%-75%. In adolescents, associations between ΣDAP and FEV1 were closer to the null and positive for FVC, whereas associations with FEV1/FVC and FEF25%-75% were negative, as in adults. However, none of the associations were significant in adolescents.

CONCLUSIONS

The negative association between ΣDAP and lung function in adult participants suggests a detrimental effect of OP pesticides on lung function in the adult general population. Further studies using prospective designs are warranted to confirm the findings reported in this study.

CITATION

Ye M, Beach J, Martin JW, Senthilselvan A. 2016. Urinary dialkyl phosphate concentrations and lung function parameters in adolescents and adults: results from the Canadian Health Measures Survey. Environ Health Perspect 124:491-497; http://dx.doi.org/10.1289/ehp.1509745.

Modified expression of peripheral blood lymphocyte muscarinic cholinergic receptors in asthmatic children

Lymphocytes possess an independent cholinergic system. We assessed the expression of muscarinic cholinergic receptors in lymphocytes from 49 asthmatic children and 10 age matched controls using Western blot. We demonstrated that CD4+ and CD8+ T cells expressed M2 and M4 muscarinic receptors which density were significantly increased in asthmatic children in comparison with controls. M2 and M4 receptor increase was strictly related with IgE and fraction of exhaled nitric oxide (FeNO) measurements and with impairment in objective measurements of airway obstruction. Increased lymphocyte muscarinic cholinergic receptor expression may concur with lung cholinergic dysfunction and with inflammatory molecular framework in asthma.

Acetylcholine beyond bronchoconstriction: roles in inflammation and remodeling

Acetylcholine is the primary parasympathetic neurotransmitter in the airways, where it not only induces bronchoconstriction and mucus secretion, but also regulates airway inflammation and remodeling. In this review, we propose that these effects are all primarily mediated via the muscarinic M3 receptor. Acetylcholine promotes inflammation and remodeling via direct effects on airway cells, and via mechanical stress applied to the airways sequential to bronchoconstriction. The effects on inflammation and remodeling are regulated by both neuronal and non-neuronal acetylcholine. Taken together, we believe that the combined effects of anticholinergic therapy on M3-mediated bronchoconstriction, mucus secretion, inflammation, and remodeling may account for the positive outcome of treatment with these drugs for patients with chronic pulmonary obstructive disease (COPD) or asthma.

Crosstalk between beta-2-adrenoceptor and muscarinic acetylcholine receptors in the airway

The M3 and M2 muscarinic acetylcholine receptors (mAChRs) and beta-2-adrenoceptors (β2ARs) are important regulators of airway cell function, and drugs targeting these receptors are among the first line drugs in the treatment of the obstructive lung diseases asthma and chronic obstructive lung disease (COPD). Cross-regulation or crosstalk between mAChRs and β2ARs in airway smooth muscle (ASM) helps determine the contractile state of the muscle, thus airway diameter and resistance to airflow. In this review we will detail mAChR and β2AR-signaling and crosstalk, focusing on events in the ASM cell but also addressing the function of these receptors in other cell types that impact airway physiology. We conclude by discussing how recent advances in GPCR pharmacology offer a unique opportunity to fine tune mAChR and β2AR signaling and their crosstalk, and thereby produce superior therapeutics for obstructive lung and other diseases.

Cholinergic connectivity: it's implications for psychiatric disorders

Acetylcholine has been implicated in both the pathophysiology and treatment of a number of psychiatric disorders, with most of the data related to its role and therapeutic potential focusing on schizophrenia. However, there is little thought given to the consequences of the documented changes in the cholinergic system and how they may affect the functioning of the brain. This review looks at the cholinergic system and its interactions with the intrinsic neurotransmitters glutamate and gamma-amino butyric acid as well as those with the projection neurotransmitters most implicated in the pathophysiologies of psychiatric disorders; dopamine and serotonin. In addition, with the recent focus on the role of factors normally associated with inflammation in the pathophysiologies of psychiatric disorders, links between the cholinergic system and these factors will also be examined. These interfaces are put into context, primarily for schizophrenia, by looking at the changes in each of these systems in the disorder and exploring, theoretically, whether the changes are interconnected with those seen in the cholinergic system. Thus, this review will provide a comprehensive overview of the connectivity between the cholinergic system and some of the major areas of research into the pathophysiologies of psychiatric disorders, resulting in a critical appraisal of the potential outcomes of a dysregulated central cholinergic system.

β₂ long-acting and anticholinergic drugs control TGF-β1-mediated neutrophilic inflammation in COPD

We quantified TGF-β1 and acetylcholine (ACh) concentrations in induced sputum supernatants (ISSs) from 18 healthy controls (HC), 22 healthy smokers (HS) and 21 COPDs. ISSs from HC, HS and COPD as well as rhTGF-β1 were also tested in neutrophil adhesion and in mAChR2, mAChR3 and ChAT expression experiments in human bronchial epithelial cells (16-HBE). Finally, we evaluated the effects of Olodaterol (a novel inhaled β(2)-adrenoceptor agonist) and Tiotropium Spiriva®, alone or in combination, on neutrophil adhesion and mAChRs and ChAT expression in stimulated 16-HBE. The results showed that 1) TGF-β1 and ACh concentrations are increased in ISSs from COPD in comparison to HC and HS, and TGF-β1 in HS is higher than in HC; 2) ISSs from COPD and HS caused increased neutrophil adhesion to 16-HBE when compared to ISSs from HC. The effect of ISSs from COPD was significantly reduced by TGF-β1 depletion or by the pretreatment with Olodaterol or Tiotropium alone or in combination, while the effect of ISSs from HS was significantly reduced by the pretreatment with Olodaterol alone; 3) mAChR2, mAChR3 and ChAT expression was increased in 16-HBE stimulated with ISSs from COPD and TGF-β1 depletion significantly reduced this effect on mAChR3 and ChAT expression; 4) rhTGF-β1 increased mAChR2, mAChR3 and ChAT expression in 16-HBE; 5) Olodaterol did not affect the expression of mAChRs and ChAT in 16-HBE. Our findings support the use of β₂ long-acting and anticholinergic drugs to control the bronchoconstriction and TGF-β1-mediated neutrophilic inflammation in COPD.

Role of eosinophils and their clinical significance in allergic inflammation

Eosinophils are believed to play roles in the pathophysiology of allergic inflammation, such as bronchial asthma. However, recent studies on anti-interleukin-5 monoclonal antibody treatment of asthmatic patients raised the possibility that eosinophils may play only a limited role. More recent studies established that eosinophils are essentially involved in the development of airway remodeling. Moreover, it is theoretically conceivable that eosinophils are a cellular source of lipid mediators, such as cysteinyl leukotrienes or platelet-activating factor in asthma. Even in the absence of interleukin-5, it is likely that the 'T-helper Type 2 network', including a cascade of vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, CC chemokines, granulocyte-macrophage colony-stimulating factor, for example, can maintain sufficient eosinophilic infiltration and effector functions, such as superoxide anion generation and degranulation. Long-term studies, wherein tissue eosinophils are eliminated effectively will be required to establish the exact roles of these cells in asthma. Finally, the authors will demonstrate that eosinophils have the potential for not only playing detrimental roles but also beneficial ones.

Gantacurium and CW002 do not potentiate muscarinic receptor-mediated airway smooth muscle constriction in guinea pigs

BACKGROUND

Neuromuscular blocking agents are an integral component of general anesthesia. In addition to their intended pharmacologic target on skeletal muscle nicotinic receptors, undesirable airway effects (i.e., bronchoconstriction) can result from neuromuscular blocking agents' affinity for airway muscarinic receptors. We questioned whether two new members of a bisquaternary nondepolarizing muscle relaxant family, gantacurium and CW002, demonstrated detrimental effects of airway muscarinic receptors using an in vivo model in guinea pig airways.

METHODS

Urethane-anesthetized male guinea pigs were ventilated through a tracheostomy with continuous digital recordings of pulmonary inflation pressure and heart rate. The dose for 95% twitch suppression for gantacurium, CW002, cisatracurium, and rapacuronium was defined in the guinea pig. Transient and reproducible changes in pulmonary inflation pressure and heart rate were recorded after vagal nerve stimulation or intravenous injection of acetylcholine before and after pretreatment with cumulatively increasing concentrations of gantacurium, CW002, cisatracurium or a single concentration of rapacuronium.

RESULTS

The doses for 95% twitch suppression for gantacurium, CW002, cisatracurium, and rapacuronium were 0.064 +/- 0.006, 0.012 +/- 0.0006, 0.10 +/- 0.003, and 0.31 +/- 0.05 mg/kg, respectively. Gantacurium, CW002, and cisatracurium were without effects on baseline pulmonary inflation pressures and were devoid of significant interactions with M2 and M3 muscarinic receptors in vivo.

CONCLUSION

These findings suggest that gantacurium and CW002 are devoid of significant effects at airway muscarinic receptors particularly M3 receptors on bronchial smooth musculature at doses several fold higher than those required for functional muscle paralysis.

Role of 5-HT2A, 5-HT4 and 5-HT7 receptors in the antigen-induced airway hyperresponsiveness in guinea-pigs

BACKGROUND

A possible role of 5-hydroxytryptamine (5-HT) in the origin of antigen-induced airway hyperresponsiveness (AI-AHR) has been scarcely investigated.

OBJECTIVE

To explore the participation of different 5-HT receptors in the development of AI-AHR in guinea-pigs.

METHODS

Lung resistance was measured in anaesthetized guinea-pigs sensitized to ovalbumin (OVA). Dose-response curves to intravenous (i.v.) acetylcholine (ACh) were performed before and 1 h after antigenic challenge and expressed as the 200% provocative dose (PD(200)). Organ bath experiments, confocal microscopy and RT-PCR were additionally used. The 5-HT content in lung homogenates was measured by HPLC.

RESULTS

Antigenic challenge significantly decreased PD(200), indicating the development of AI-AHR. This hyperresponsiveness was abolished by a combination of methiothepin (5-HT(1)/5-HT(2)/5-HT(5)/5-HT(6)/5-HT(7) receptors antagonist) and tropisetron (5-HT(3)/5-HT(4) antagonist). Other 5-HT receptor antagonists showed three different patterns of response. Firstly, WAY100135 (5-HT(1A) antagonist) and ondansetron (5-HT(3) antagonist) did not modify the AI-AHR. Secondly, SB269970 (5-HT(7) antagonist), GR113808 (5-HT(4) antagonist), tropisetron or methiothepin abolished the AI-AHR. Thirdly, ketanserin (5-HT(2A) antagonist) produced airway hyporresponsiveness. Animals with bilateral vagotomy did not develop AI-AHR. Experiments in tracheal rings showed that pre-incubation with LP44 or cisapride (agonists of 5-HT(7) and 5-HT(4) receptors, respectively) induced a significant increase of the cholinergic contractile response to the electrical field stimulation. In sensitized lung parenchyma strips, ketanserin diminished the contractile responses to ACh. Sensitization was associated with a ninefold increase in the 5-HT content of lung homogenates. Confocal microscopy showed that sensitization enhanced the immunolabelling and co-localization of nicotinic receptor and 5-HT in airway epithelium, probably located in pulmonary neuroendocrine cells (PNECs). RT-PCR demonstrated that neither sensitization nor antigen challenge modified the 5-HT(2A) receptor mRNA levels.

CONCLUSIONS

Our results suggested that 5-HT was involved in the development of AI-AHR to ACh in guinea-pigs. Specifically, 5-HT(2A), 5-HT(4) and 5-HT(7) receptors seem to be particularly involved in this phenomenon. Participation of 5-HT might probably be favoured by the enhancement of the PNECs 5-HT content observed after sensitization.

Suitability of muscarinic acetylcholine receptor antibodies for immunohistochemistry evaluated on tissue sections of receptor gene-deficient mice

Acetylcholine (ACh) is a major regulator of visceral function exerting pharmacologically relevant effects upon smooth muscle tone and epithelial function via five types of muscarinic receptors (M1R-M5R). In this paper, we assessed the specificity of muscarinic receptor (MR) antibodies in immunohistochemical labelling on tissue sections by analysing specimens from wild-type and respective gene-deficient mice. Of 24 antibodies evaluated in this study, 16 were tested at 18 different conditions each, and eight of them in 21 different protocols, resulting in a total number of 456 antibody/protocol combinations. Each of them was tested at four antibody dilutions at minimum, so that finally, at least 1,824 conditions were evaluated. For each of them, dorsal root ganglia, urinary bladder and cross-sections through all thoracic viscera were investigated. In all cases where the antigen was available, at least one incubation condition was identified in which only select cell types were immunolabelled in the positive control but remained unlabelled in the pre-absorption control. With two exceptions (M2R antibodies), however, all antibodies produced identical immunohistochemical labelling patterns in tissues taken from corresponding gene-deficient mice even when the pre-absorption control in wild-type mice suggested specificity. Hence, the present data demonstrate the unpleasant fact that reliable immunohistochemical localisation of MR subtypes with antibodies is the exception rather than the rule. Immunohistochemical detection of MR subtype localisation in tissue sections of peripheral organs is limited to the M2R subtype utilising the most commonly used methodological approaches.

Isocapnic cold air challenge in patients with COPD: are there any predisposing factors?

Cold air hyperventilation is an indirect challenge (cold air challenge, CACh) with high specificity and low sensitivity in defining asthmatic subjects. A small proportion of chronic obstructive pulmonary disease (COPD) patients present with positive CACh. The aim of this prospective study was to investigate the presence of factors related to cold air challenge (CACh) in COPD patients. Factors examined were FEV(1), FEV(1)/FVC, reversibility after bronchodilation, eosinophils in induced sputum, bronchial hyperresponsiveness to methacholine and the spirometric response to tiotropium compared to placebo. We studied 92 consecutive COPD patients in order to retrieve 15 CACh positive + patients. Fifteen COPD patients with negative CACh [CACh(-)], randomly selected from the initial group, were added in order to retrieve a group of 30 patients. Spearman's correlation coefficient was used in order to evaluate possible significant correlations between CACh values and study parameters. Sixteen percent of our subjects presented CACh+. CACh values were repeatable with an intraclass correlation coefficient between the two measurements 0.980 (95% CI 0.940-0.993). The only significant correlation observed was between Delta FEV(1) after CACh [Delta(C)FEV(1)] and trough FEV(1) values post tiotropium inhalation (r(2) = 0.62, p < 0.0001). When we analyzed the response to tiotropium in the 2 separate groups we found that patients with CACh+ presented significantly lower values of trough FEV(1) compared to those with CACh(-). In conclusion, a small proportion of COPD patients present with bronchial hyperresponsiveness to CACh. The only parameter related to CACh + in our study was a smaller bronchodilating effect of tiotropium.

Microarray profiling of lymphocytes in internal diseases with an altered immune response: potential and methodology

Recently it has become possible to investigate expression of all human genes with microarray technique. The authors provide arguments to consider peripheral white blood cells and in particular lymphocytes as a model for the investigation of pathophysiology of asthma, RA, and SLE diseases in which inflammation is a major component. Lymphocytes are an alternative to tissue biopsies that are most often difficult to collect systematically. Lymphocytes express more than 75% of the human genome, and, being an important part of the immune system, they play a central role in the pathogenesis of asthma, RA, and SLE. Here we review alterations of gene expression in lymphocytes and methodological aspects of the microarray technique in these diseases. Lymphocytic genes may become activated because of a general nonspecific versus disease-specific mechanism. The authors suppose that in these diseases microarray profiles of gene expression in lymphocytes can be disease specific, rather than inflammation specific. Some potentials and pitfalls of the array technologies are discussed. Optimal clinical designs aimed to identify disease-specific genes are proposed. Lymphocytes can be explored for research, diagnostic, and possible treatment purposes in these diseases, but their precise value should be clarified in future investigation.

Muscarinic receptors, leukotriene B4 production and neutrophilic inflammation in COPD patients

BACKGROUND

Acetylcholine (ACh) plays an important role in smooth muscle contraction and in the development of airway narrowing; preliminary evidences led us to hypothesize that ACh might also play a role in the development of airways inflammation in chronic obstructive pulmonary disease (COPD).

METHODS

We evaluated the concentrations of leukotriene B4 (LTB4) in induced sputum, and the expression of Ach M1, M2, and M3 receptors in sputum cells (SC) obtained from 16 patients with COPD, 11 smokers, and 14 control subjects. The SC were also treated with ACh and the production of LTB4 assessed in the presence or absence of a muscarinic antagonist (oxitropium). In blood monocytes, we evaluated LTB4 release and activation of the extracellular signal-regulated kinases (ERK) pathway after treatment with Ach.

RESULTS

The LTB4 concentrations were higher in COPD than in controls (P < 0.01) and correlated with the number of neutrophil (P < 0.01). The M3 receptors expression was increased in COPD subjects when compared to smokers and control (P < 0.05 and 0.0001, respectively), while M2 expression resulted decreased (P < 0.05 and 0.01). The ACh-induced LTB(4) production was observed in peripheral blood monocytes, and was sensitive to ERK inhibition. Similarly, ACh significantly increased neutrophil chemotactic activity and LTB4 released from SC of COPD patients only, and these effects were blocked by pretreatment with the inhibitor of ERK pathway PD98059.

CONCLUSIONS

The results obtained show that muscarinic receptors may be involved in airway inflammation in COPD subjects through ACh-induced, ERK1/2-dependent LTB4 release. Muscarinic antagonism may contribute to reduce neutrophil infiltration and activation in COPD.

Beta2-agonist eutomers: a rational option for the treatment of asthma?

Beta2-adrenoceptor agonists (beta2-agonists) such as albuterol (salbutamol) and terbutaline and their long-acting analogs salmeterol and formoterol are widely used as bronchodilators in the treatment of asthma. They are chiral drugs historically marketed as racemic mixtures of an active (eutomer) and essentially inactive (distomer) stereoisomer. Despite their obvious therapeutic value and widespread use, beta2-agonists have been implicated, somewhat controversially, in causing an increase in asthma mortality and a deterioration of asthma control by a mechanism that remains elusive. Inherent toxicity of the distomers has been widely touted as an explanation and has given rise to pressure for the replacement of the racemates with pure eutomer formulations (the so-called chiral or racemic switch). This has culminated in the recent introduction into clinical practice of the single active stereoisomer of albuterol (levalbuterol) and the promise of other pure beta2-agonist eutomer formulations to follow. This article examines the evidence on which these chiral switches are based. Clinical studies designed to reveal negative effects of beta2-agonists have searched for reductions in lung function, increases in airway responsiveness to bronchoconstrictor mediators and worsening of asthma control. Crossover studies administering the pure stereoisomers and racemate of albuterol have not shown a clear superiority of the pure eutomer formulation over the racemate in terms of either bronchial hyperresponsiveness, tachyphylaxis to bronchoprotective effects or improvements in lung function. Clinical toxicity of beta2-agonist distomers on any aspect of asthmatic lung function has also not been demonstrated in the relatively short-term inhalational studies (single dose or repeated dose studies <1 week) that have been carried out. In animal studies, the administration of beta2-agonist racemates and distomers has been shown to enhance bronchial hyperresponsiveness but only in ovalbumin-sensitized animals where the relevance to humans is questionable. The pharmacokinetics and metabolism of beta(2)-agonist stereoisomers appear to be essentially similar whether administered as single stereoisomers or as racemates. Levalbuterol may be slightly more potent than an equivalent dose given as racemate, but there is some evidence that it forms a small amount of the distomer in vivo which detracts somewhat from its purported benefits over use of the racemate. Whilst there remains a clear need for studies of longer duration with sensitive clinical endpoints to evaluate the benefits of beta2-agonist eutomers and to investigate distomer toxicity, the chiral switch for beta2-agonists in general, and for albuterol in particular, does not appear to be justified on the basis of the evidence available to date.

Increased relaxation of immature airways to β2-adrenoceptor agonists is related to attenuated expression of postjunctional smooth muscle muscarinic M2 receptors

Spontaneous or agonist-induced contraction of airway smooth muscle can be observed very early in fetal life, thus explaining the possible occurrence of bronchospasm in very low birth weight infants within the first days of life. In an attempt to better manage such bronchospasms, the aim of the present study was to investigate the age-specific modifications in airway smooth muscle relaxation to β2-agonists and muscarinic antagonists using a combination of functional and molecular techniques. In the rat, isometric relaxation to the β2-agonist salbutamol was examined in tracheae; we also examined muscarinic receptor expression (M2R and M3R mRNA levels) in airway smooth muscle by immunochemistry, Western blotting, and real-time PCR. Compared with adults, salbutamol-induced relaxation was twofold greater in immature rat isolated tracheae preconstricted by carbachol. This effect was associated with a lower expression of M2R in the smooth muscle of immature animals (sixfold and almost twofold as assessed by immunochemistry and Western blotting, respectively). Real-time PCR data indicate that changes in M2R expression according to age occurred at a posttranscriptional level. In adult airways, there was a significantly greater functional efficacy of M2R blockade by methoctramine compared with that shown in immature rats. Because of the limited availability of human neonate lung tissue, only the molecular part of the study was performed, and we observed a qualitatively similar effect, i.e., a lower M2R expression in the neonatal airway smooth muscle, although this was quantitatively smaller. We conclude that β2-agonist-induced relaxation is enhanced in immature compared with adult airways as a result of greater postjunctional M2R expression in adult airway smooth muscle. This finding may be of importance in the clinical management of bronchoconstriction in neonates.

Parasympathetic airway response and heart rate variability before and at the end of methacholine challenge

BACKGROUND

The autonomic nervous system plays a primary role in regulating airway caliber, and its dysfunction is likely to contribute to the pathogenesis of airways diseases. Moreover, some findings support the hypothesis that autonomic dysfunction and/or dysregulation contributes to the pathogenesis of airway hyperresponsiveness (AHR). Heart rate variability (HRV) spectral analysis allows identifying noninvasively perturbations of the autonomic system.

PURPOSES

We tested the relationship between AHR and cardiac parasympathetic tone assessed by HRV spectral analysis in patients submitted to a diagnostic methacholine bronchial challenge (MBC).

METHODS

Fifteen women and 38 men (age range, 18 to 56 years) participated in the study. The principal indications for MBC were suspected asthma, chronic cough, unexplained exercise-induced dyspnea, or cough. The R-R intervals were continuously recorded during the MBC. Autoregressive method was performed on two series of 256 R-R intervals extracted before and after the MBC to obtain low-frequency (LF) and high-frequency (HF) components.

RESULTS

The MBC distinguished 29 subjects without airway responsiveness (R-) and 24 responder or hyperresponsive subjects (R+): mean provocative dose of methacholine causing a 20% reduction in mean (+/- SD) FEV1 of 467 +/- 351 microg (range, 70 to 1,426 microg). The HF component expressed in normalized units (n.u.) [the index of parasympathetic modulation] was significantly higher in R+ than in R- at baseline, before MBC (21 +/- 21 n.u. vs 11 +/- 9 n.u., p < 0.05). Interestingly, R+ showed a significant increase of HF component after MBC (243 +/- 30 to 567 +/- 620 ms2 and 21 +/- 21 to 34 +/- 30 n.u., p < 0.01). For all subjects, HF (n.u.) calculated at baseline and after MBC were significantly influenced by the bronchial responsiveness (r2 = -0.28 and -0.51, respectively; p < 0.001).

CONCLUSION

In summary, we found that R+ had a significantly higher parasympathetic tone than R- at baseline, and that R+ showed a significant increase in cardiac reactivity after bronchial challenge. These findings demonstrate that the autonomic nervous system, which contributes to the pathogenesis of AHR, is closely linked to cardiac modulation.

The role of anticholinergics in chronic obstructive pulmonary disease

Anticholinergics are the bronchodilators of choice in the management of chronic obstructive pulmonary disease (COPD). They work by blocking muscarinic receptors in airway smooth muscle. Cholinergic tone appears to be the only reversible component of COPD. With the discovery of different muscarinic receptor subtypes, the development of more selective anticholinergics is possible. A major advance in this therapeutic area has been the discovery of tiotropium bromide, which has kinetic selectivity for M3 receptors as well as a duration of action of >24 hours. Once-daily administration of tiotropium is well tolerated and has shown significant advantages over ipratropium bromide, given 4 times daily, in the control of COPD.

Eosinophil adhesion to cholinergic IMR-32 cells protects against induced neuronal apoptosis

Eosinophils release a number of mediators that are potentially toxic to nerve cells. However, in a number of inflammatory conditions, such as asthma and inflammatory bowel disease, it has been shown that eosinophils localize to nerves, and this is associated with enhanced nerve activity. In in vitro studies, we have shown that eosinophil adhesion via neuronal ICAM-1 leads to activation of neuronal NF-kappaB via an ERK1/2-dependent pathway. In this study, we tested the hypothesis that eosinophil adhesion to nerves promotes neural survival by protection from inflammation-associated apoptosis. Exposure of differentiated IMR-32 cholinergic nerve cells to IL-1beta, TNF-alpha, and IFN-gamma, or culture in serum-deprived medium, induced neuronal apoptosis, as detected by annexin V staining, caspase-3 activation, and DNA laddering. Addition of human eosinophils to IMR-32 nerve cells completely prevented all these features of apoptosis. The mechanism of protection by eosinophils was by an adhesion-dependent activation of ERK1/2, which led to the induced expression of the antiapoptotic gene bfl-1. Adhesion to nerve cells did not influence the expression of the related genes bax and bad. Thus, prevention of apoptosis by eosinophils may be a mechanism by which these cells regulate neural plasticity in the peripheral nervous system.

Retinoic acid reverses the airway hyperresponsiveness but not the parenchymal defect that is associated with vitamin A deficiency

Airway hyperresponsiveness (AHR) is influenced by structural components of the bronchial wall, including the smooth muscle and connective tissue elements and the neuromuscular function. AHR is also influenced by parenchymally derived tethering forces on the bronchial wall, which maintain airway caliber by producing outward radial traction. Our previous work has shown that vitamin A-deficient (VAD) rats exhibit cholinergic hyperresponsiveness and a decrease in the expression and function of the muscarinic-2 receptors (M2R). We hypothesized that if decreases in radial traction from airway or parenchymal structures contributed to the VAD-related increase in AHR, then the radial traction would normalize more slowly than VAD-related alterations in neurotransmitter signaling. Rats remained vitamin A sufficient (VAS) or were rendered VAD and then maintained on the VAD diet in the presence or absence of supplementation with all-trans retinoic acid (RA). VAD was associated with an approximately twofold increase in respiratory resistance and elastance compared with VAS rats. Exposure to RA for 12 days but not 4 days restored resistance and elastance to control (VAS) levels. In VAD rats, AHR was accompanied by decreases in bronchial M2R gene expression and function, which were restored after 12 days of RA supplementation. Subepithelial bronchial elastic fibers were decreased by approximately 50% in VAD rats and were significantly restored by RA. The increase in AHR that is associated with VAD is accompanied by decreases in M2R expression and function that can be restored by RA and a reduction in airway elastic fibers that can be partially restored by RA.

Loss of vagally mediated bradycardia and bronchoconstriction in mice lacking M2 or M3 muscarinic acetylcholine receptors

The presence of multiple muscarinic acetylcholine receptor (mAChR) subtypes in the heart and lung, combined with the lack of mAChR subtype-selective ligands, have complicated the task of identifying the mAChR subtypes mediating cardiac slowing (bradycardia) and airway narrowing (bronchoconstriction) due to vagal innervation. To determine which of the five mAChRs are responsible for the cholinergic control of heart rate and airway caliber in vivo, we performed experiments on mutant mice lacking the two prime candidates for such control, the M2 or M3 mAChR. Here, we report that in vivo, bradycardia caused by vagal stimulation or administration of the muscarinic agonist methacholine (MCh) was abolished in mice lacking functional M2 mAChRs (M2-/- mice). In contrast, heart rate responses remained unchanged in M3 receptor-deficient mice (M3-/- mice). The reduced hypotensive response of M3-/- mice to MCh suggests M3 mAChRs contribute to peripheral vasodilation. The M2-/- mice showed significantly enhanced in vivo bronchoconstrictor responses to vagal stimulation or MCh administration. In contrast, bronchoconstrictor responses were totally abolished in M3-/- mice. Because altered cardiac or pulmonary vagal tone is involved in a number of pathophysiological conditions, including cardiac arrhythmias, chronic obstructive pulmonary disease and asthma, these results should be of considerable therapeutic relevance.

Interactions of eosinophil granule proteins with skin: limits of detection, persistence, and vasopermeabilization

BACKGROUND

Eosinophil granule proteins, including eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), eosinophil peroxidase (EPO), and major basic protein (MBP), are prominently deposited in skin in several cutaneous disorders and likely contribute to disease pathology.

OBJECTIVE

We sought to determine the limit of detection, persistence, and vasopermeabilization activity of the eosinophil granule proteins in skin.

METHODS

The eosinophil granule proteins were injected intradermally. Their minimum detectable concentrations in human surgical waste skin and their persistence in guinea pig skin were determined by indirect immunofluorescence. Vasopermeabilization activity in the guinea pig without and with H1 antihistamine (pyrilamine maleate) pretreatment was assessed by extrusion of Evans blue dye-treated plasma.

RESULTS

The lowest detectable cutaneous concentrations were 0.05 micromol/L EPO, 0.1 micromol/L MBP, 0.25 micromol/L ECP, and 1 micromol/L EDN. Granule proteins persisted in guinea pig skin in vivo for 1 week (EPO), 2 weeks (ECP), 2.5 weeks (EDN), and 6 weeks (MBP). Each of the eosinophil granule proteins increased cutaneous vasopermeability in a concentration-dependent manner. The potency of vasopermeabilization induced by each granule protein was comparable with that of histamine. Pyrilamine maleate pretreatment of guinea pigs did not alter increased vasopermeability induced by ECP and EDN but significantly inhibited that induced by EPO and MBP.

CONCLUSIONS

Micromolar concentrations of eosinophil granule proteins are often deposited in skin in eosinophil-associated cutaneous disorders such as atopic dermatitis. These pathophysiologically relevant concentrations of eosinophil granule proteins cause increased cutaneous vasopermeability (both by means of histamine-independent and histamine-dependent mechanisms) and might alter cutaneous function for days to weeks.

Eosinophil-induced release of acetylcholine from differentiated cholinergic nerve cells

One immunological component of asthma is believed to be the interaction of eosinophils with parasympathetic cholinergic nerves and a consequent inhibition of acetylcholine muscarinic M2 receptor activity, leading to enhanced acetylcholine release and bronchoconstriction. Here we have used an in vitro model of cholinergic nerve function, the human IMR32 cell line, to study this interaction. IMR32 cells, differentiated in culture for 7 days, expressed M2 receptors. Cells were radiolabeled with [3H]choline and electrically stimulated. The stimulation-induced release of acetylcholine was prevented by the removal of Ca2+. The muscarinic M1/M2 receptor agonist arecaidine reduced the release of acetylcholine after stimulation (to 82 +/- 2% of control at 10(-7) M), and the M2 receptor antagonist AF-DX 116 increased it (to 175 +/- 23% of control at 10(-5) M), indicating the presence of a functional M2 receptor that modulated acetylcholine release. When human eosinophils were added to IMR32 cells, they enhanced acetylcholine release by 36 +/- 10%. This effect was prevented by inhibitors of adhesion of the eosinophils to the IMR32 cells. Pretreatment of IMR32 cells with 10 mM carbachol, to desensitize acetylcholine receptors, prevented the potentiation of acetylcholine release by eosinophils or AF-DX 116. Acetylcholine release was similarly potentiated (by up to 45 +/- 7%) by degranulation products from eosinophils that had been treated with N-formyl-methionyl-leucyl-phenylalanine or that had been in contact with IMR32 cells. Contact between eosinophils and IMR32 cells led to an initial increase in expression of M2 receptors, whereas prolonged exposure reduced M2 receptor expression.

CD8+ T lymphocytes in viral hyperreactivity and M2 muscarinic receptor dysfunction

In the airways, inhibitory M2 muscarinic receptors (M2Rs) on parasympathetic nerves limit acetylcholine release. Viral infection causes M2R dysfunction, which increases acetylcholine release and leads to airway hyperreactivity. In these studies we tested the role of CD8+ T cells in parainfluenza virus-induced hyperreactivity and M2R dysfunction in normal guinea pigs and in guinea pigs previously sensitized to ovalbumin. Depleting CD8+ T cells prevented virus-induced M2R dysfunction and hyperreactivity in sensitized animals, but not in nonsensitized animals. Sensitization increased the number of eosinophils in close relation to the airway nerves where, when activated, they release major basic protein, which binds to and blocks the M2Rs. Regardless of sensitization, viral infection decreased the number of visible tissue eosinophils, likely reflecting eosinophil degranulation via cytolysis. Depleting CD8+ T cells prevented this virus-induced eosinophil degranulation. In addition, an antiviral effect of sensitization, which we previously showed to be eosinophil mediated, was again seen. This was prevented by depletion of CD8+ Tcells. Thus, CD8+ T cells play a role in airway hyperreactivity and M2R dysfunction of sensitized virus-infected guinea pigs by mediating eosinophil degranulation near airway nerves. In contrast, CD8+ T cells are not necessary for virus-induced hyperreactivity and M2R dysfunction in nonsensitized guinea pigs.

Preserved bronchial dilatation after salbutamol does not guarantee protection against bronchial hyperresponsiveness

Racemic salbutamol, a beta2-adrenoceptor agonist used for dilatation of airways, has recently been shown to induce lessened relaxation of bronchial smooth muscle and partial loss of bronchoprotection, seen as increased hyperresponsiveness, after regular treatment. The racemate undergoes stereo-selective disposition, giving higher plasma levels of S-salbutamol than that of bronchodilating R-salbutamol, thus raising S : R ratios after repeated administration. Our aim was to evaluate whether increased bronchial hyperresponsiveness (BHR) could be found even after 1 day of repeated salbutamol inhalations, with beta2-receptor-induced bronchial smooth muscle relaxation remaining and whether this would be associated with plasma levels of either enantiomer. Fifteen patients with stable asthma, aged 19-54 years, were included in a randomized, cross-over study. An indirect bronchial challenge method was used [voluntary isocapnic hyperventilation of cold air (IHCA)], and airway condition tested by means of impulse oscillometry. Racemic salbutamol was inhaled three times during a 6-h period. IHCA was performed and plasma concentrations of enantiomers were measured 4 h after the last dose. Tests were also performed without preceding drug treatment. beta2-Agonist-produced bronchial dilatation and protection persisted in the majority of the 15 patients 4 h after repeated inhalations of salbutamol during 1 day. In only two of the 15 patients we could trace increased BHR after salbutamol. Neither dilatation nor protection could be linked to plasma levels of either R- or S-salbutamol. The underlying mechanisms of BHR remain unknown and are dissociated from beta2-receptor-mediated dilatation.

Management of acute pediatric asthma

Pediatric asthma prevalence, morbidity, and severity are increasing. Direct costs associated with providing emergency department and inpatient care account for more than 40% of overall dollars spent for this disease in the United States. Physicians in many health care settings may be required to treat a child in severe respiratory distress caused by acute asthma. This article reviews the pathophysiology, evaluation, and treatment of severe asthma exacerbations, or status asthmaticus.

Expression of peripheral blood lymphocyte muscarinic cholinergic receptor subtypes in airway hyperresponsiveness

The expression of muscarinic cholinergic receptor subtypes was investigated in peripheral blood lymphocytes (PBL) of bronchial asthma patients by a combined kinetic and equilibrium labeling technique for radioligand binding assay of muscarinic cholinergic receptor subtypes and by receptor immunochemistry and immunocytochemistry. An increased expression of M2 and to a lesser extent of M5 receptors and no changes of M4 receptor were observed in PBL of asthmatics compared to control individuals. The increase was related to bronchial hyperresponsiveness detected by methacholine challenge test. Analysis of M3 receptor expression revealed biphasic changes, with a decreased receptor density in patients with normal, mild and moderate responses to methacholine test and a recovery to levels similar to those found in healthy individuals in severe responders to methacholine test. The demonstration of a different expression of lymphocyte muscarinic receptors in asthma suggests that cholinergic system may participate to a molecular framework influencing immune functions in asthma.

Characterization of contractile function and expression of muscarinic receptors, G proteins and adenylate cyclase in cultured tracheal smooth muscle of Swine

Smooth muscle cells lose their contractile function and phenotype very rapidly when placed in culture. During organ culture of smooth muscle strips, phenotype is lost more slowly. In the present studies, we established an organ culture model to study contractile function and expression of muscarinic receptors, G proteins and adenylyl cyclase in different serum concentrations in tracheal smooth muscle from swine. The results show that contractile function and the amounts of M(3) receptors, G proteins and adenylyl cyclase were maintained for up to 5 days in culture. The expression of M(2) receptors was significantly decreased in culture when compared to freshly isolated muscles. Maximal isometric tension was significantly increased in cultured muscles compared with freshly isolated muscles. Different serum concentrations did not significantly affect contractile function and expression of muscarinic receptors, G proteins and adenylyl cyclase. In conclusion, our studies suggest that cultured smooth muscle might be used as a model to study the regulation of contractile function of smooth muscle by various signal transduction pathways.

Vitamin A deficiency promotes bronchial hyperreactivity in rats by altering muscarinic M(2) receptor function

Vitamin A deficiency (VAD) remains an important health problem among children in developing countries. Children living in these areas have a higher mortality from respiratory infections, which likely results in part from suboptimal nutrition, including VAD. Bronchial hyperreactivity can follow viral respiratory infections and may complicate the recovery. To investigate whether VAD promotes bronchial hyperreactivity, we have assessed methacholine-induced bronchoconstriction in VAD and vitamin A-sufficient rats. Bronchial constriction developed at lower concentrations of inhaled methacholine in VAD than in vitamin A-sufficient rats. This did not result from an increase in the bronchial wall thickness or the clearance of a small molecule (with a size similar to methacholine) from the air space. The function and abundance of the muscarinic M(2) receptors in bronchial tissue were reduced in VAD rats, suggesting that this receptor may contribute to these animals' diminished ability to limit cholinergic-mediated bronchoconstriction. A similar reduction in muscarinic M(2) receptor function has been observed in asthma. Vitamin A (retinol) and its congeners (retinoids) may be required to regulate bronchial responsiveness in addition to maintaining a normal bronchial epithelium.

Airway hyperresponsiveness, late allergic response, and eosinophilia are reversed with mycobacterial antigens in ovalbumin-presensitized mice

Pretreatment with mycobacterial Ags has been shown to be effective in preventing allergic airway inflammation from occurring in a mouse model. Because most asthmatics are treated after the development of asthma, it is crucial to determine whether mycobacterial Ags can reverse established allergic airway inflammation in the presensitized state. Our hypothesis, based upon our previous findings, is that mycobacteria treatment in presensitized mice will suppress the allergic airway inflammation with associated clinical correlates of established asthma, with the noted exception of factors associated with the early allergic response (EAR). BALB/c mice sensitized and challenged with OVA were evaluated for pulmonary functions during both the EAR and late allergic response, and airway hyperresponsiveness to methacholine. Following this, sensitized mice were randomized and treated with placebo or a single dose (1 x 10(5) CFUs) of bacillus Calmette-Guérin (BCG) or Mycobacterium vaccae via nasal or peritoneal injection. One week later, the mice were rechallenged with OVA and methacholine, followed by bronchoalveolar lavage (BAL) and tissue collection. Mice treated with intranasal BCG were most significantly protected from the late allergic response (p < 0.02), airway hypersensitivity (p < 0.001) and hyperreactivity (p < 0.05) to methacholine, BAL (p < 0.05) and peribronchial (p < 0.01) eosinophilia, and BAL fluid IL-5 levels (p < 0.01) as compared with vehicle-treated, sensitized controls. Intranasal M. vaccae treatment was less effective, suppressing airway hypersensitivity (p < 0.01) and BAL eosinophilia (p < 0.05). No changes were observed in the EAR, BAL fluid IL-4 levels, or serum total and Ag-specific IgE. These data suggest that mycobacterial Ags (BCG>>M. vaccae) are effective in attenuating allergic airway inflammation and associated changes in pulmonary functions in an allergen-presensitized state.

Status asthmaticus in children: a review

About 10% of American children have asthma, and its prevalence, morbidity, and mortality have been increasing. Asthma is an inflammatory disease with edema, bronchial constriction, and mucous plugging. Status asthmaticus in children requires aggressive treatment with beta-agonists, anticholinergics, and corticosteroids. Intubation and mechanical ventilation should be avoided if at all possible, as the underlying dynamic hyperinflation will worsen with positive-pressure ventilation. If mechanical ventilation becomes necessary, controlled hypoventilation with low tidal volume and long expiratory time may lessen the risk of barotrauma and hypotension. Unusual and nonestablished therapies for severe asthma are discussed.

Mutation screening of the muscarinic M(2) and M(3) receptor genes in normal and asthmatic subjects

1. Muscarinic receptors are important in the development of airway hyperresponsiveness, and dysfunction of these receptors has been suggested to be present in asthma. 2. The human muscarinic M(2) and M(3) receptor genes were screened for polymorphic variation using single-stranded conformation polymorphism (SSCP) analysis, complemented by direct fluorescent sequencing. Forty-six random DNA samples and 46 respiratory physician diagnosed asthmatic samples were used as a template for analysis. 3. Within the muscarinic M(2) receptor gene, we identified two degenerate single base substitutions (1197T-->C, Thr-->Thr and 976A-->C, Arg-->Arg) in one random and one asthmatic sample respectively. Analysis of the 3' UTR region revealed an additional 'A' at bp 1793 (c.f. ATG). This was present in all of 49 samples analysed by sequencing or BsmI digest, suggesting that the published sequence (GenBank Accession NO: M16404) is incorrect. A common 3' UTR polymorphism (T-->A) was found at bp 1696 (c.f. ATG) (allelic frequency=65%, n=60), but this does not alter transcription factor recognition sites. 4. We were unable to identify any polymorphic variation within the muscarinic M(3) coding region or the flanking regions investigated, using the methods described. 5. The coding regions for the human muscarinic M(2) and M(3) receptor genes are both highly conserved. These data suggest that polymorphic variation within these coding sequences is unlikely to account for inter-individual variability in response to methacholine or anticholinergic therapy. The potential functional significance of the muscarinic M(2) receptor 3' UTR polymorphism (bp 1696) remains to be determined.

The role of neuroeffector mechanisms in the pathogenesis of asthma

Neural regulation of the airways consists of cholinergic excitatory, adrenergic inhibitory nerves and nonadrenergic, noncholinergic (NANC) nerves. NANC nerves can be either inhibitory or excitatory. Cholinergic nerves form the predominant bronchoconstrictor neural pathway in human airways. Acetylcholine controls neuronal and nonneuronal target cells via a short-lived action at nicotinic and muscarinic receptors. The most important control over acetylcholine release from postganglionic cholinergic nerves is exerted by acetylcholine itself. The M2 autoreceptor is located prejunctionally on postganglionic nerves. Its stimulation limits the further release of acetylcholine. A loss of function in the neuronal muscarinic M2 autoreceptor occurs after exposure to allergen, ozone, or viruses. In human airways, inhibitory NANC (i-NANC) mechanisms are the only neural bronchodilatory mechanisms. The presumed neurotransmitters of the i-NANC system are vasoactive intestinal peptide and nitric oxide. Substance P and neurokinin A have been implicated as the neurotransmitters mediating the excitatory part of the NANC nervous system. NK2 receptors are present on smooth muscle of both large and small airways and mediate part of the bronchoconstrictor effect of tachykinins. Most of the proinflammatory effects of substance P are mediated by the NK1 receptor. Tachykinin receptor antagonists are currently being developed as a possible anti-asthma treatment. An extensive cross-talk exists between nerves and the immune system. The complexity of the picture has increased further as it has become clear that classical neurotransmitters, such as acetylcholine and neuropeptides, are produced by nonneuronal cells.

Enhanced expression of the leukotriene C(4) synthase due to overactive transcription of an allelic variant associated with aspirin-intolerant asthma

Aspirin-intolerant asthma (AIA), a distinct clinical syndrome affecting about 10% of adult asthmatics, appears to be unusually dependent on cysteine leukotriene (cys-LT) overproduction by pulmonary eosinophils. The gene coding for leukotriene (LT) C(4) synthase (LTC(4)S), the enzyme controlling cys-LT biosynthesis, exists as two common alleles distinguished by an A to C transversion at a site 444 nucleotides upstream of the translation start. We tested the hypothesis that this single nucleotide polymorphism (SNP) affects binding of transcription factors and influences the transcription rate, predisposing to AIA. Gel shift assay studies revealed that the (-444)C allele, conferring an activator protein-2 binding sequence, is an additional target for a transcription factor of histone H4 consensus. Introduction of the H4TF-2 decoy oligonucleotide into LTC(4)S-positive, differentiated HL-60 cells decreased accumulation of LTC(4) to 68%. Transfection of COS-7 with promoter construct increased expression of beta-galactosidase reporter for the (-444)C variant. The (-444)C allelic frequency was significantly higher in AIA patients (n = 76) as compared with matched aspirin-tolerant asthmatics (n = 110) and healthy controls (n = 75). Patients with AIA had also upregulated LTC(4)S messenger RNA expression in peripheral blood eosinophils. An inhaled provocation test with lysine-aspirin led to an increase in urinary output of LTE(4), which reached statistical significance only in carriers of the (-444)C allele. Our results suggest that a transcription factor, present in dividing and bone marrow resident progenitors of eosinophils, triggers LTC(4)S transcription in carriers of a common (-444)C allele due to binding with the histone H4 promoter element of the gene. Genetic predisposition to cys-LT pathway upregulation, a hallmark of AIA, can be related to overactive expression of the LTC(4)S (-444)C allele.

Absence of muscarinic cholinergic airway responses in mice deficient in the cyclic nucleotide phosphodiesterase PDE4D

Muscarinic cholinergic signaling plays an essential role in the control of the normal airway functions and in the development of pulmonary pathologies including asthma. In this paper we demonstrate that the airways of mice deficient in a cAMP-specific phosphodiesterase (PDE4D) are no longer responsive to cholinergic stimulation. Airway hyperreactivity that follows exposure to antigen was also abolished in PDE4D(-/-) mice, despite an apparently normal lung inflammatory infiltration. The loss of cholinergic responsiveness was specific to the airway, not observed in the heart, and was associated with a loss of signaling through muscarinic receptors with an inability to decrease cAMP accumulation. These findings demonstrate that the PDE4D gene plays an essential role in cAMP homeostasis and cholinergic stimulation of the airway, and in the development of hyperreactivity. In view of the therapeutic potentials of PDE4 inhibitors, our findings provide the rationale for novel strategies that target a single PDE isoenzyme.