Receptors in airway disease. Beta-adrenoceptors in lung inflammation

Uncovering the Role of Oxidative Imbalance in the Development and Progression of Bronchial Asthma

Asthma is a chronic inflammatory disease of the airways related to epithelial damage, bronchial hyperresponsiveness to contractile agents, tissue remodeling, and luminal narrowing. Currently, there are many data about the pathophysiology of asthma; however, a new aspect has emerged related to the influence of reactive oxygen and nitrogen species (ROS and RNS) on the origin of this disease. Several studies have shown that an imbalance between the production of ROS and RNS and the antioxidant enzymatic and nonenzymatic systems plays an important role in the pathogenesis of this disease. Considering this aspect, this study is aimed at gathering data from the scientific literature on the role of oxidative distress in the development of inflammatory airway and lung diseases, especially bronchial asthma. For that, articles related to these themes were selected from scientific databases, including human and animal studies. The main findings of this work showed that the respiratory system works as a highly propitious place for the formation of ROS and RNS, especially superoxide anion, hydrogen peroxide, and peroxynitrite, and the epithelial damage is reflected in an important loss of antioxidant defenses that, in turn, culminates in an imbalance and formation of inflammatory and contractile mediators, such as isoprostanes, changes in the activity of protein kinases, and activation of cell proliferation signalling pathways, such as the MAP kinase pathway. Thus, the oxidative imbalance appears as a promising path for future investigations as a therapeutic target for the treatment of asthmatic patients, especially those resistant to currently available therapies.

Mitochondrial regulation of airway smooth muscle functions in health and pulmonary diseases

Mitochondria are important for airway smooth muscle physiology due to their diverse yet interconnected roles in calcium handling, redox regulation, and cellular bioenergetics. Increasing evidence indicates that mitochondria dysfunction is intimately associated with airway diseases such as asthma, IPF and COPD. In these pathological conditions, increased mitochondrial ROS, altered bioenergetics profiles, and calcium mishandling contribute collectively to changes in cellular signaling, gene expression, and ultimately changes in airway smooth muscle contractile/proliferative properties. Therefore, understanding the basic features of airway smooth muscle mitochondria and their functional contribution to airway biology and pathology are key to developing novel therapeutics for airway diseases. This review summarizes the recent findings of airway smooth muscle mitochondria focusing on calcium homeostasis and redox regulation, two key determinants of physiological and pathological functions of airway smooth muscle.

Loss of salmeterol bronchoprotection against exercise in relation to ADRB2 Arg16Gly polymorphism and exhaled nitric oxide

RATIONALE

β2-Agonists are the treatment of choice for exercise-induced bronchoconstriction (EIB) and act through specific receptors (ADRB2). Arg16Gly polymorphisms have been shown to affect responses to regular use of β2-agonists.

OBJECTIVES

To evaluate the influence of the Arg16Gly receptor polymorphism on salmeterol bronchoprotection in EIB and assess predictors of bronchoprotection.

METHODS

A prospective, genotype-blinded, randomized trial was performed in 26 subjects (12 Arg16Arg and 14 Gly16Gly) with EIB who were not on controller therapy. Subjects were administered salmeterol, 50 μg twice a day for 2 weeks, and underwent an exercise challenge 9 hours after the first and last drug dose. In addition to genotype, FEV1, response to salmeterol, degree of EIB, and exhaled nitric oxide (FE(NO)) at baseline were examined for their association with loss of bronchoprotection (LOB).

MEASUREMENTS AND MAIN RESULTS

The maximum exercise-induced FEV1 fall was 27.9 ± 1.4% during the run-in period, 8.1 ± 1.2% (70.3 ± 4.1% bronchoprotection) after the first salmeterol dose, and 22.8 ± 3.2% (18.9 ± 11.5% bronchoprotection) after 2 weeks of salmeterol (P = 0.0001). The Arg16Gly polymorphisms were not associated with the LOB in response to salmeterol. FeNO values at baseline were significantly related to the LOB (r = 0.47; P = 0.01). Mean change was a 74 ± 13% LOB in subjects with FE(NO) levels greater than 50 ppb and a 7 ± 16% gain in bronchoprotection in those with FE(NO) levels less than 25 ppb (P = 0.01).

CONCLUSIONS

The LOB that occurs with chronic long-acting β2-agonists use is not affected by ADRB2 Arg16Gly polymorphisms. High FE(NO) was associated with marked LOB. Use of long-acting β2-agonists before achieving a reduction in FeNO may need to be avoided. Clinical trial registered with www.clinicaltrials.gov (NCT 00595361).

Characterization of bovine neutrophil beta2-adrenergic receptor function

This study compares bovine leukocyte beta-adrenergic receptor densities to that of the rat, demonstrates for the first time a functional beta(2)-adrenergic receptor signaling pathway in steer neutrophils, and investigates the effect of an inflammatory stimulus on that signaling pathway. The beta(1)-/beta(2)-adrenergic antagonist ([3H])CGP-12177 demonstrated that rat lymphocyte specific binding-site density was highest, followed by steer and dairy cow lymphocytes, and lastly steer and dairy cow neutrophils. The beta(2)-adrenergic agonist terbutaline stimulated steer neutrophil adenosine 3,5-cyclic monophosphate (cAMP) production, an effect increased by inclusion of > or = 1 x 10(-8) M phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C. Both terbutaline and the nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) independently decreased steer neutrophil superoxide anion production in a concentration-dependent manner, with 1 x 10(-4) M IBMX enhancing both the potency and efficacy of the terbutaline effect (up to 74% reduction in superoxide anion production). Superoxide anion production was also reduced by the synthetic cAMP analog 8-bromo-cAMP, which increased the potency of the IBMX effect on superoxide anion production. Taken together, these data demonstrate the presence of a beta(2)-adrenergic receptor signaling pathway in bovine neutrophils much like that described in other animal species, as well as the potential for an inflammatory stimulus to alter its function.

Biochemical markers as a response guide for steroid therapy in asthma

BACKGROUND

Exhaled breath condensate pH and hydrogen peroxide concentration is a non-invasive, simple and inexpensive assay that can be performed for monitoring in patients with asthma.

OBJECTIVE

To evaluate the possibility of usefulness of expired breath condensate pH and H(2)O(2) concentration as well as serum total antioxidant capacity and malondialdehyde as markers for steroid treatment response.

PATIENTS AND METHODS

A total of 153 patients were included in this study (age range 18 to 64 years). Asthmatic patients, regularly followed for at least 3 months, were randomly recruited for the study over a period of one month. All patients received inhaled beclomethasone dipropionate (1,000 microg daily in four divided doses) and salbutamol inhalers (800 microg daily in four divided doses) for 4 weeks. Expired breath condensate was collected at the end of the study to determine hydrogen peroxide concentration and pH. Venous blood samples were collected for determination of total antioxidant capacity and malondialdehyde as markers of peroxidation.

RESULTS

In asthmatic patients with poorly controlled asthma, expired breath condensate hydrogen peroxide concentration was higher and the pH was lower than stable asthma. Serum malondialdehyde concentration in poorly controlled asthma was higher (6.98 micromol/L), and total antioxidant capacity was lower (589 micromol/L) than in stable asthma.

CONCLUSION

Exhaled hydrogen peroxide concentration and pH can be used as predictors for monitoring of nonresponse to asthma treatment.

Small molecule receptors as imaging targets

The aberrant expression and function of certain receptors in tumours and other diseased tissues make them preferable targets for molecular imaging. PET and SPECT radionuclides can be used to label specific ligands with high affinity for the target receptors. The functional information obtained from imaging these receptors can be used to better understand the systems under investigation and for diagnostic and therapeutic applications. This review discusses some of the aspects of receptor imaging with small molecule tracers by PET and SPECT and reviews some of the tracers for the receptor imaging of tumours and brain, heart and lung disorders.

beta-Adrenoceptor signaling in regenerating skeletal muscle after beta-agonist administration

Stimulating the beta-adrenoceptor (beta-AR) signaling pathway can enhance the functional repair of skeletal muscle after injury, but long-term use of beta-AR agonists causes beta-AR downregulation, which may limit their therapeutic effectiveness. The aim was to examine beta-AR signaling during early regeneration in rat fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles after bupivacaine injury and test the hypothesis that, during regeneration, beta-agonist administration does not cause beta-AR desensitization. Rats received either the beta-AR agonist fenoterol (1.4 mgxkg(-1)xday(-1) ip) or saline for 7 days postinjury. Fenoterol reduced beta-AR density in regenerating soleus muscles by 42%. Regenerating EDL muscles showed a threefold increase in beta-AR density, and, again, these values were 43% lower with fenoterol treatment. An amplified adenylate cyclase (AC) response to isoproterenol was observed in cell membrane fragments from EDL and soleus muscles 7 days postinjury. Fenoterol attenuated this increase in regenerating EDL muscles but not soleus muscles. beta-AR signaling mechanisms were assessed using AC stimulants (NaF, forskolin, and Mn(2+)). Although beta-agonist treatment reduces beta-AR density in regenerating muscles, these muscles can produce large cAMP responses relative to healthy (uninjured) muscles. Desensitization of beta-AR signaling in regenerating muscles is prevented by altered rates of beta-AR synthesis and/or degradation, changes in G protein populations and coupling efficiency, and altered AC activity. These mechanisms have important therapeutic implications for modulating beta-AR signaling to enhance muscle repair after injury.

Cooperative inhibitory effects of budesonide and formoterol on eosinophil superoxide production stimulated by bronchial epithelial cell conditioned medium

BACKGROUND

Improved asthma control by combinations of inhaled glucocorticosteroids (GCs) and long-acting beta(2)-agonists (LABAs) includes a reduced frequency and severity of exacerbations. In view of the association of exacerbations with increased airway inflammation, the question has arisen as to whether LABAs are able to complement the known anti-inflammatory activity of GCs. To address this, we studied the effects of a LABA, formoterol (FORM), and a GC, budesonide (BUD), alone and in combination, on bronchial epithelial cell-mediated eosinophil superoxide production in vitro.

METHODS

We employed 2 experimental approaches. First, superoxide production by human eosinophils incubated with conditioned medium (CM) from human bronchial epithelial cells cultured for 24 h with vehicle, BUD, FORM or BUD + FORM was measured (Epi/Eos assay). Second, eosinophils were stimulated with vehicle-CM to which the drugs were added (Eos assay). Superoxide production was determined as the superoxide dismutase-inhibitable reduction of ferricytochrome C.

RESULTS

CM increased eosinophil superoxide generation (p < 0.01) and epithelial-derived granulocyte macrophage colony-stimulating factor was the mediator responsible. In both assays, FORM dose-dependently inhibited eosinophil superoxide similarly and in the same concentration range as BUD. The BUD + FORM combination was more effective than BUD alone, and it completely inhibited CM-induced superoxide production in the Epi/Eos assay, suggesting complementary effects of both drugs on bronchial epithelial cells and eosinophils.

CONCLUSIONS

The cooperative, inhibitory effects of BUD and FORM on eosinophils and bronchial epithelial cells, in terms of their effects on eosinophil superoxide production, may represent a possible mechanism for the enhanced anti-inflammatory efficacy of BUD and FORM combination therapy of asthma.

Pollen NAD(P)H Oxidases and Their Contribution to Allergic Inflammation

This article provides an overview of NADPH oxidase and its role in allergic inflammation. A background and historical perspectives of NADPH oxidase are first provided, followed by a detailed overview of mammalian NADPH oxidase subunits and their functional organization. Plant NADPH oxidase, the authors' discovery of NADPH oxidase in pollens, and their contribution to allergic inflammation are then discussed, concluding with a discussion of future directions and outstanding questions that require attention.

Disruption of Nrf2 enhances susceptibility to severe airway inflammation and asthma in mice

Oxidative stress has been postulated to play an important role in the pathogenesis of asthma; although a defect in antioxidant responses has been speculated to exacerbate asthma severity, this has been difficult to demonstrate with certainty. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a redox-sensitive basic leucine zipper transcription factor that is involved in the transcriptional regulation of many antioxidant genes. We show that disruption of the Nrf2 gene leads to severe allergen-driven airway inflammation and hyperresponsiveness in mice. Enhanced asthmatic response as a result of ovalbumin sensitization and challenge in Nrf2-disrupted mice was associated with more pronounced mucus cell hyperplasia and infiltration of eosinophils into the lungs than seen in wild-type littermates. Nrf2 disruption resulted in an increased expression of the T helper type 2 cytokines interleukin (IL)-4 and IL-13 in bronchoalveolar lavage fluid and in splenocytes after allergen challenge. The enhanced severity of the asthmatic response from disruption of the Nrf2 pathway was a result of a lowered antioxidant status of the lungs caused by lower basal expression, as well as marked attenuation, of the transcriptional induction of multiple antioxidant genes. Our studies suggest that the responsiveness of Nrf2-directed antioxidant pathways may act as a major determinant of susceptibility to allergen-mediated asthma.

Receptor imaging in the thorax with PET

This review focuses on positron emission tomography (PET)-imaging of receptors in the sympathetic and the parasympathetic systems of heart and lung and highlights the human applications of PET. For the alpha-adrenoceptor, only [11C]GB67 (N2-[6-[(4-amino-6,7-dimethoxy-2-quinazolinyl)(methyl)amino]hexyl]-N2-[11C]methyl-2-furamide hydrochloride) has been developed. Its potential for application in patients needs to be assessed. For both the beta-adrenergic and the muscarinic systems, potent PET radioligands have been prepared and evaluated in patients. It has been possible to measure receptor densities quantitatively in human heart [[11C]MQNB: [11C]methylquinuclidinyl benzilate, [11C]CGP12177: S-(3'-t-butylamino-2'-hydroxypropoxy)-benzimidazol-2-[11C]one and [11C]CGP12388: (S)-4-(3-(2'-[11C]isopropylamino)-2-hydroxypropoxy)-2H-benzimidazol-2-one] and qualitatively in lung [[11C]VC002: N-[11C]-methyl-piperidin-4-yl-2-cyclohexyl-2-hydroxy-2-phenylacetate and [11C]CGP12177]. Besides these subtype nonselective radioligands, the development of compounds that are selective for one subtype are ongoing and have not found successful application in humans yet.

Oxidative stress in the pathogenesis of asthma

Asthma affects 5% to 10% of the population of the United States. In asthmatics, oxidative stress occurs not only as a result of inflammation but also from environmental exposure to air pollution. The specific localization of antioxidants in the lung and the adaptive changes during asthma underscore the importance of oxidative stress, and therapeutic interventions that decrease exposure to environmental reactive oxygen species or augment endogenous antioxidant defenses might be beneficial as adjunctive therapies in asthmatic patients.

Oxidative stress in allergic respiratory diseases

There is ample evidence that allergic disorders, such as asthma, rhinitis, and atopic dermatitis, are mediated by oxidative stress. Excessive exposure to reactive oxygen and nitrogen species is the hallmark of oxidative stress and leads to damage of proteins, lipids, and DNA. Oxidative stress occurs not only as a result of inflammation but also from environmental exposure to air pollution and cigarette smoke. The specific localization of antioxidant enzymes in the lung and the rapid reaction of nitric oxide with reactive oxygen species, such as superoxide, suggest that antioxidant enzymes might also function as cell-signaling agents or regulators of cell signaling. Therapeutic interventions that decrease exposure to environmental reactive oxygen species or augment endogenous antioxidant defenses might be beneficial as adjunctive therapies for allergic respiratory disorders.

Reactive oxygen species as mediators in asthma

This review describes production and effects of reactive oxygen species (ROS) on airway function. ROS are important in many physiological processes but can also have detrimental effects on airway cells and tissues when produced in high quantities or during the absence of sufficient amounts of anti-oxidants. Therefore, these mediators play a prominent role in the pathogenesis of various inflammatory airway disorders, including asthma. Effects of ROS on airway function in asthma have been studied with isolated airway cells and tissues and with animal models and patients. With the use of inhibitors, transgenic animals and measurements of the release of ROS within the airways, it became clear that oxidative stress contributes to the initiation and worsening of inflammatory respiratory disorders.

Safety considerations in treating concomitant diseases in patients with asthma

The treatment for asthma usually involves a combination of drugs used for bronchodilation and to treat underlying airway inflammation. When asthma is severe, the regimen used to treat asthma can become quite complicated, often using as many as 3 or 4 separate pharmacological agents. As patients with asthma get older, their medication regimen can become even more complex with the development of numerous other age-related diseases requiring their own list of medications. Diseases of the joints, diseases of the eye, cardiovascular disease, neurological disease and urological problems represent the most common conditions that patients develop, at times needing medications which might interfere with asthma management. Many of these diseases require the use of nonsteroidal anti-inflammatory agents, well known to provoke wheezing in patients with intrinsic asthma, and diseases of the eye and cardiovascular system frequently require use of beta-blockers which can cause or exacerbate asthma. Managing patients with asthma who have other diseases requires constant supervision of their medication usage and careful and cautious review of the entire list of medications at each presentation.

Asthma mortality: another opinion--is it a matter of life and ... bread?

There is a general consensus that the mortality rates for asthma in much of the developed world have been increasing for the past 10-15 years. This has occurred despite an improved information base regarding diagnosis and management as well as the development of novel and more effective therapeutic modalities. Several explanations have been proposed for this increase, including a statistical artifact based on a change in the coding criteria for asthma from the International Classification of Diseases Version 8 (ICD-8) to ICD-9, worsened pollution, delays in seeking medical help, behavioral changes, deficits in asthma education of both patients and primary care providers, toxicity of beta agonists, and noncompliance with medications. We suggest that although all of these are potential etiological factors, there may exist still another major etiological risk. There have been dramatic changes in our eating habits and food preparation. In general, we eat less total calories, more meals outside the home, and more refined or prepared foods. With the emphasis on reducing the intake of saturated fats and cholesterol, we eat more polyunsaturated fats both by choice and secondary to manufacturers' attempts to improve the appeal of foods to health-conscious government and the public. The drive to remove animal fats and cholesterol from our diet has resulted in the replacement of animal fats with vegetable oil in food manufacture, fast-food frying, and even home preparation. One result of these dietary habits has been a doubling from 8 to 15% of the percentage of the polyunsaturated linoleic acid in body fat. We postulate that this, and other nutritional changes, will render asthma a more difficult syndrome to manage and will contribute adversely to the inflammatory abnormalities in airways.

Pharmacologic modulation of Th1- and Th2-associated lymphokine production

Murine helper T cells can be divided into at least two groups, Th1 and Th2, based on the patterns of lymphokine secretion after antigenic or mitogenic stimulation. Recently, a similar subdivision was proposed in the human situation. Interestingly, the different patterns of lymphokine production correlate with different effector functions of the Th subpopulations. Th1 cells appear to dominate delayed type hypersensitivity reactions. Conversely, Th2 cells dominate the immune response to allergens and probably play an important role in allergic disorders. One of the clinical manifestations in which Th2 cells appear to dominate the immune response is allergic asthma. The mainstay of therapy in asthmatic persons is formed by glucocorticoid and beta-adrenoceptor agonist treatment. A differential pharmacological modulation of the lymphokine production by Th1 and Th2 cells can be of therapeutic relevance in allergic diseases in which an inappropriate balance between Th1 and Th2 cells exists. Such a differential modulation may underlie the beneficial usage of glucocorticoids and beta-adrenoceptor agonists in the treatment of asthma. The present report summarizes the effects of glucocorticoids and cAMP modulating agents on the activation and lymphokine production of T lymphocytes and Th subsets. Additionally, the effect of other steroid hormones is evaluated.

Stimulation of cyclic AMP production in human alveolar macrophages induced by inflammatory mediators and beta-sympathicomimetics

We have investigated the effects of inflammatory mediators and beta-adrenoceptor agonists on the adenylyl cyclase responsiveness in alveolar macrophages from control subjects, patients suffering from chronic obstructive pulmonary disease (COPD) and asthmatics. Basal cyclic AMP (cAMP) levels in alveolar macrophages from COPD patients were significantly elevated (plus 42%) as compared to controls. In addition, the adenylyl cyclase responsiveness to prostaglandin E2, histamine and the beta-adrenoceptor agonist salbutamol was significantly impaired in alveolar macrophages from COPD patients and asthmatics. The lipid mediator platelet activating factor showed no effect on cAMP production in all three alveolar macrophage populations. Furthermore, the cAMP-enhancing effects of isoprenaline, salbutamol and histamine appeared to be mediated via beta 2-adrenoceptors and histamine H2-receptor subtypes respectively. Taken together, these data suggest an intrinsic desensitization phenomenon in alveolar macrophages from COPD patients and asthmatics.