Alpha- and beta-adrenergic-receptor systems in bronchial asthma and in subjects without asthma: reduced mononuclear cell beta-receptors in bronchial asthma

Platelet-Activating Factor (PAF) in Allergic Rhinitis: Clinical and Therapeutic Implications

Platelet-activating factor (PAF) is a lipid mediator involved in several allergic reactions. It is released from multiple cells of the immune system, such as eosinophils, neutrophils, and mast cells, and also exerts its effect on most of them upon specific binding to its receptor, becoming a pleiotropic mediator. PAF is considered a potential relevant mediator in allergic rhinitis, with a key role in nasal congestion and rhinorrhoea due to its effect on vascular permeability. Interestingly, despite its potential relevance as a therapeutic target, no specific PAF inhibitors have been studied in humans. However, rupatadine, a second-generation antihistamine with dual antihistamine and anti-PAF effects has shown promising results by both blocking nasal symptoms and inhibiting mast cell activation induced by PAF, in comparison to antihistamine receptor drugs. In conclusion, the inhibition of PAF may be an interesting approach in the treatment of allergic rhinitis as part of a global strategy directed at blocking as many relevant inflammatory mediators as possible.

β2-Adrenoceptor Function in Asthma

β2-adrenoceptor agonists, often used in combination with corticosteroids, have been extensively used for the treatment of asthma. However, concerns have been raised regarding their adverse effects and safety including poor asthma control, life-threatening exacerbations, exacerbations that often require hospitalization, and asthma-related deaths. The question as to whether these adverse effects relate to the loss of their bronchoprotective action remains an interesting possibility. In the chapter, we will review the experimental evidence that describes the different potential factors and associated mechanisms that can blunt the therapeutic action of β2-adrenoceptor agonists in asthma. We show here evidence that various key inflammatory cytokines, growth factors, some respiratory viruses, certain allergens, unknown factors present in serum from atopic asthmatics have the capacity to impair β2-adrenoceptor function in airway smooth muscle, the main target of these drugs. More importantly, we present our latest research describing the role played by mast cells in impairing β2-adrenoceptor function. Although no definitive conclusion could be made regarding the implication of one single mechanism, receptor uncoupling, or receptor desensitization due to phosphorylation represents the main inhibitory pathways associated with a loss of β2-adrenoceptor function in airway smooth muscle. Targeting the pathways leading to β2-adrenoceptor dysfunction will likely provide novel therapies to improve the efficacy of β2-agonists in asthma.

Recent findings on the pathogenesis of bronchial asthma. Part II. The role of hormonal predisposition, environmental influences and conditioning leading to bronchial asthma

In this second part of the review on the pathogenesis of asthma the hormonal factors and adverse external events are shortly reviewed which skew the balance of Th1 vs. Th2 CD4+ lymphocytes towards the latter ones and this way increase the probability of atopic diseases. Among other the role of transplacental priming, insulin, insulin-like and other growth factors, lack of the usual microbial infections in the early childhood (the so-called hygiene hypothesis), gender, diminished testosterone production, gastroesophageal reflux, adverse effects during pregnancy are discussed. A separate chapter deals with the role of central nervous system in the etiology and finally the most common allergizing and airway tissue damaging agents are listed in tabulated form.

A2A adenosine receptor deficiency leads to impaired tracheal relaxation via NADPH oxidase pathway in allergic mice

A(2A) adenosine receptor (A(2A)AR) has been shown to suppress superoxide generation in leukocytes via the cAMP-protein kinase A (PKA) pathway. However, no study has yet explored the role of A(2A)AR in relation to NADPH oxidase in murine tracheas in vitro, which may lead to altered smooth muscle relaxation in asthma. Therefore, the present study evaluated the effects of A(2A)AR deficiency on the NADPH oxidase pathway in tracheas of A(2A) wild-type (WT) and A(2A) knockout (KO) mice. A(2A)WT mice were sensitized with ovalbumin (30 microg i.p.) on days 1 and 6, followed by 5% ovalbumin aerosol challenge on days 11, 12, and 13. A(2A)AR (gene and protein expression), cAMP, and phosphorylated PKA (p-PKA) levels were decreased in A(2A)WT sensitized mice compared with controls. A(2A)KO mice also showed decreased cAMP and p-PKA levels. A(2A)WT sensitized and A(2A)KO control mice had increased gene and protein expression of NADPH oxidase subunits (p47phox and gp91phox) compared with the controls. Tracheal relaxation to specific A(2A)AR agonist, 4-[2-[[6-amino-9-(N-ethyl-beta-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680), decreased in A(2A)WT sensitized mice compared with the controls, although it was absent in A(2A)KO mice. Pretreatment with NADPH oxidase inhibitors apocyanin/diphenyliodonium reversed the attenuated relaxation to CGS 21680 in A(2A)WT sensitized tracheas, whereas specific PKA inhibitor (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i] [1,6]benzodiazocine-10-carboxylic acid hexyl ester (KT 5720) blocked CGS 21680-induced relaxation. Tracheal reactive oxygen species (ROS) generation was also increased in A(2A)WT sensitized and A(2A)KO control mice compared with the controls. In conclusion, this study shows that A(2A)AR deficiency causes increased NADPH oxidase activation leading to decreased tracheal relaxation via altered cAMP-PKA signaling and ROS generation.

Interleukin 13 and the beta-adrenergic blockade theory of asthma revisited 40 years later

BACKGROUND

Beta2-Adrenergic agonists are the most potent agents clinically used in inhibiting and preventing the immediate response to bronchoconstricting agents and in inhibiting mast cell mediator release. This raises the possibility that an abnormality in beta-adrenergic receptor function or circulating catecholamine levels could contribute to airway hyperresponsiveness.

OBJECTIVE

To link interleukin 13 (IL-13) to the pathogenesis of asthma.

METHODS

Almost 4 decades ago, Andor Szentivanyi published a beta-adrenergic theory of atopic abnormality in bronchial asthma. He proposed 9 characteristics to define bronchial asthma. Because he published these 9 tenets of the beta-adrenergic blockade theory of asthma in 1968, it is appropriate and important to evaluate their relevance in light of advances in pharmacology, inflammation, and immunology.

RESULTS

We describe the effects of the allergic reaction on beta-adrenergic responses and airway responsiveness. Both IL-1beta and tumor necrosis factor a have been detected in increased amounts in bronchial lavage fluids in allergic airway inflammation. Both IL-13 and the proinflammatory cytokines IL-1beta and tumor necrosis factor a have been demonstrated in airway smooth muscle to cause a decreased relaxation response to beta-adrenergic agonist. However, IL-13 has been shown to be necessary and sufficient to produce the characteristics of asthma.

CONCLUSION

The decreased adrenergic bronchodilator activity and associated hypersensitivity to mediators put forth by Szentivanyi can be elicited with IL-13 and support its role in the pathogenesis of asthma.

Effects of ciclamilast, a new PDE 4 PDE4 inhibitor, on airway hyperresponsiveness, PDE4D expression and airway inflammation in a murine model of asthma

PDE4 (phosphodiesterase-4) plays a critical role in pathogenesis of allergic asthma and chronic obstructive pulmonary disease (COPD). PDE4 inhibitors are presently under clinical development for the treatment of asthma and/or COPD. Ciclamilast, a new PDE4 inhibitor, is a piclamilast (RP 73401) structural analogue, but has a more potent inhibitory effect on PDE4 and inflammation in the airway tissues and less side effects than that of piclamilast. In this study, we elucidate primarily on the roles of compound on PDE4 enzyme in physiological and pathological processes in a mouse model of asthma. The sensitized/challenged mice were reexposed to ovalbumin and airway response to inhaled methacholine was monitored. Orally administration of ciclamilast, in a dose-dependent manner, significantly inhibited changes in lung resistance and lung dynamic compliance, as well as upregulation of cAMP-PDE activity, increase of PDE4D mRNA expression, but not PDE4B from lung tissue in the murine model. In addition, the compound dose-dependently reduced mRNA expression of eotaxin, tumor necrosis factor (TNF)-alpha and interleukin (IL)-4, but slightly increased mRNA expression of interferon (IFN)-gamma from lung tissue. Further, levels of eotaxin, TNF-alpha and IL-4, and eosinophil and neutrophil accumulation in bronchoalveolar lavage fluid were also significantly reduced. Pathological examination, goblet cell hyperplasia and inflammatory cells infiltration in lung tissue were suppressed by treatment with ciclamilast. A significant correlation was observed between the increases in PDE4D mRNA expression and airway hyperresponsiveness. These studies confirm that inhibitory effect of ciclamilast on airway hyperresponsiveness includes its inhibiting PDE4D mRNA expression, down-modulating PDE4 activity, anti-inflammation and anti-mucus hypersecretion, and ciclamilast may have therapeutic potential for the treatment of asthma.

'Respiratory epilepsy'--does it exist?

Past literature suggests a possible relationship between two recurrent illnesses: bronchial asthma and epilepsy. Only one preliminary study, performed 30 years ago, demonstrated epileptiform EEG activity in patients with bronchial asthma who were treated successfully for their asthma with antiepileptic drugs. We demonstrated epileptiform activity in six out of 24 (25%) children with bronchial asthma who had no history of neurological illnesses or epilepsy, compared to one out of 24 (4.2%) children in the control group. This relatively high percentage of EEG abnormalities raises the possibility that there is a subgroup of patients with bronchial asthma, in whom the asthma might be considered as an 'epileptic equivalent'. These patients possibly deserve a different, unique therapeutic approach.

Defect in potentiation of adenylyl cyclase correlates with bronchial hyperreactivity

BACKGROUND

Adenylyl cyclase is a transmembrane signaling system involved in the inhibition of cellular responses. Recently, we showed that the activity of adenylyl cyclase may be potentiated by stimuli that induce an increase of cellular responses but that do not activate adenylyl cyclase. This is probably an important physiologic feedback mechanism that prevents cells from becoming "overstimulated."

OBJECTIVE

Because increased cellular activities are frequently observed in persons with asthma, we hypothesized that a defect in potentiation of adenylyl cyclase might be involved.

METHODS

Potentiation of isoprenaline-induced adenosine cyclic monophosphate (cAMP) production with the mitogen phytohemagglutin (PHA; 45 micrograms/ml) or the calcium ionophore A23187 (1 mumol/L) was studied in peripheral blood mononuclear cells taken from patients with asthma (n = 8) and healthy control subjects (n = 11).

RESULTS

Isoprenaline-induced cAMP production was potentiated significantly in the healthy control subjects (PHA, 110% +/- 15%; A23187, 92% +/- 25%). In contrast, potentiation was not seen with PHA or A23187 in the total group of patients with asthma. However, some patients showed weak potentiation, whereas in others PHA decreased isoprenaline-induced cAMP production. Moreover, the effect of PHA on isoprenaline-induced cAMP production correlated significantly with the degree of bronchial hyperreactivity in patients with asthma (r = 0.96; p = 0.0001).

CONCLUSIONS

The observed defect in signal transduction could play an important part in bronchial hyperresponsiveness.

Corticosteroid effect on early beta-adrenergic down-regulation during circulatory shock: hemodynamic study and beta-adrenergic receptor assay

OBJECTIVES

The steroid effect on critically ill patients remains controversial. The aim of this study is to characterize the effect of methylprednisolone on the heart in a beta-adrenergically down-regulated condition.

DESIGN

A prospective hemodynamic study and retrospective receptor assay.

SETTING

Multidisciplinary ICU in a university hospital.

SUBJECTS

42 patients who required pulmonary arterial catheters and an additional 4 corpses who were available for study within 3 h of their deaths.

INTERVENTION

Intravenous methylprednisolone (10 mg/kg).

MEASUREMENTS AND RESULTS

We pursued a hemodynamic study following a glucocorticoid administration. In patients who had undergone a long term (> 72 h) catecholamine treatment, the cardiac index increased. In patients who had undergone a short term (1-72 h) catecholamine treatment and in patients with no record of catecholamine administration, the cardiac index showed no remarkable change. Among the corpses, who died soon after their arrival, and the patients, who later died in the ward and were available for further study, we measured beta-adrenergic receptor density in the left ventricular myocardium. It was found that receptor density was decreased after long term catecholamine treatment. Methylprednisolone, on the other hand increased the receptor density.

CONCLUSION

Methylprednisolone improved the cardiac index, intriguingly, in patients with long term catecholamine treatment in circulatory shock. Myocardial beta-adrenergic receptor also increased in number after the administration of methylprednisolone. However, the hemodynamic improvement caused by methylprednisolone was not observed in patients without beta-adrenergic down-regulation.