Inhibition of extracellular nucleotides hydrolysis intensifies the allergic bronchospasm. A novel protective role of ectonucleotidases.

BACKGROUND: Nucleotides released to the extracellular space stimulate purinergic receptors, and their effects are modulated by ectonucleotidases. The role of ATP in the allergic bronchospasm has been scantly studied. METHODS: We used several techniques (plethysmography, organ baths, confocal microscopy, RT-PCR, ATP measurement) to explore the role of nucleotides and ectonucleotidases in the allergic bronchospasm in guinea pigs. RESULTS: While allergenic challenge with a low-dose ovalbumin (OVA) only produced a small bronchospasm (~2-fold the basal lung resistance), previous inhibition of ectonucleotidases by ARL-67156 greatly intensified this response (~11-fold the basal lung resistance, with 44% mortality). Bronchoalveolar lavage fluid obtained during this bronchospasm contained increased ATP concentration. This potentiation was abolished by antagonism of purinergic receptors (suramin+RB2) or TXA2 receptor (SQ29548), or by intratracheal apyrase. In tracheal rings and lung parenchyma strips, OVA caused a concentration-dependent contraction. Suramin+RB2 or levamisole produced a significant rightward displacement of this response, and ARL-67156 did not modify it. Platelets stimulated with OVA released ATP. Confocal images of nonsensitized tracheas showed slight fluorescence for P2Y6 receptors in epithelium and none for P2Y4 . Sensitized animals showed strong fluorescence to both receptors and to alkaline phosphatase in the airway epithelium. This correlated with a large increment in mRNA for P2Y4 and P2Y6 receptors in sensitized animals. CONCLUSIONS: Nucleotides greatly potentiate the allergic bronchospasm when ectonucleotidases activity is diminished, and this effect is probably favored by the upregulation of P2Y4 and P2Y6 receptors in airway epithelium during sensitization. These results prompt for further research on these mechanisms in human asthma.

Lyn-deficient mice develop severe, persistent asthma: Lyn is a critical negative regulator of Th2 immunity.

The etiology of asthma, a chronic inflammatory disorder of the airways, remains obscure, although T cells appear to be central disease mediators. Lyn tyrosine kinase has been implicated as both a facilitator and inhibitor of signaling pathways that play a role in allergic inflammation, although its role in asthma is unclear because Lyn is not expressed in T cells. We show in the present study that Lyn-/- mice develop a severe, persistent inflammatory asthma-like syndrome with lung eosinophilia, mast cell hyperdegranulation, intensified bronchospasm, hyper IgE, and Th2-polarizing dendritic cells. Dendritic cells from Lyn-/- mice have a more immature phenotype, exhibit defective inhibitory signaling pathways, produce less IL-12, and can transfer disease when adoptively transferred into wild-type recipients. Our results show that Lyn regulates the intensity and duration of multiple asthmatic traits and indicate that Lyn is an important negative regulator of Th2 immune responses.

Comparison of phosphodiesterase III, IV and dual III/IV inhibitors on bronchospasm and pulmonary eosinophil influx in guinea pigs.

Selective inhibition of phosphodiesterase (PDE) isozymes has been shown to inhibit inflammatory cell function and relax airway smooth muscle and, thus, may be useful in the therapy of asthma. In guinea pigs sensitized to ovalbumin (OA), the effects of three PDE inhibitors were compared: siguazodan (PDE III selective, IC50 = 0.7 microM), rolipram (PDE IV selective, IC50 = 0.8 microM) and zardaverine (dual PDE III/IV, IC50S = 2.5 microM and 1.1 microM, respectively) against histamine-, leukotriene (LT) D4- and OA-induced bronchospasm in vitro and in vivo. Rolipram or zardaverine (0.1-10 microM), but not siguazodan, inhibited OA-induced contraction of the isolated trachea in a concentration-dependent manner. Rolipram or siguazodan alone (10 microM) were ineffective against histamine- or LTD4-induced contractions. Zardaverine alone (10 microM) or the combination of rolipram and siguazodan (10 microM each) markedly antagonized the contractions elicited by both spasmogens. In anesthesized, ventilated guinea pigs, the i.v. ID50S against OA-induced bronchospasm were: rolipram = 0.2 mg/kg, siguazodan > 10 mg/kg and zardaverine = 2.4 mg/kg. When administered at doses up to 7.5 mg/kg, i.v., rolipram or siguazodan were markedly less effective (i.e., < or = 50% inhibition) than zardaverine (ID50S = 2.4 and 1.7 mg/kg, respectively) at blocking exogenous histamine- or LTD4-induced bronchospasm. However, when administered in combination with siguazodan (5.4 mg/kg, i.v.), rolipram (0.4-5.4 mg/kg) abolished histamine- and LTD4-induced bronchoconstriction. In conscious guinea pigs, zardaverine (5 mg/kg, intragastrically (i.g.) or the combination of rolipram and siguazodan (5 mg/kg each) were substantially more effective than rolipram or siguazodan alone at inhibiting aerosol histamine- or LTD4-induced bronchospasm. In the same animals, rolipram or zardaverine (5 mg/kg, i.g.) but not siguazodan (5 mg/kg, i.g.) markedly inhibited aerosol OA-induced bronchoconstriction. The OA-induced pulmonary eosinophil infiltration in these animals was attenuated by all treatments with zardaverine producing the greatest degree of inhibition. These results indicate that 1) PDE IV inhibitors but not PDE III inhibitors are effective at blocking antigen-induced bronchospasm, 2) compounds that selectively inhibit either PDE III or PDE IV are poor inhibitors of bronchoconstriction elicited by exogenously administered spasmogens, and 3) the combined inhibition of both PDE III and PDE IV isozymes acts in an additive or synergistic manner to inhibit bronchospasm in the guinea pig.

[Serum angiotensin converting enzyme (SACE) in patients with atopic bronchial asthma]. / Surowicza aktywnosc enzymu konwertujacego angiotensyne (SACE) u chorych z atopowa astma oskrzelowa.

The aim of the study was to assess serum ACE (S-ACE) activity in atopic bronchial asthma. S-ACE activity values were determined in 50 subjects (11 blood donors, 39 asthmatics) using the radioenzymatic method with Ventrex Laboratories kits. The authors did not find any differences between asthmatics in clinical remission, not receiving therapy, patients receiving prednisone (mean daily dose 10.0 +/- 2.5 mg) and healthy blood donors. In subjects with exacerbations of bronchospasm (not receiving steroids) S-ACE activity was significantly higher.

Membrane IgE and adenyl cyclase activity in the dynamics of bronchospasm. Ketotifen as a blocker of antigen action.

A continuous exposition to antigen provokes an increase of IgE synthesis in individuals sensitized to that antigen. This increase in the synthesis is hardly seen to be reflected in seric levels; however, it is clearly seen in the quantity of IgE associated with membranes as this value increases considerably. This fact is due to the characteristic of IgE which tends to fix itself to basophil membrane. On the other hand, although no difference exists in basal adenyl cyclase activity of asthmatic and healthy individuals, the sensitivity of this enzyme to isoproterenol (beta-agonist) is greater in healthy than in asthmatic individuals. The antigenic stimulus makes adenyl cyclase activity descend in these individuals; this does not happen when the cells are treated with ketotifen before stimulating them with the antigen.

Activity of a novel hydroquinone inhibitor of leukotriene synthesis (U-66,858) in the rhesus monkey Ascaris reactor.

The IgE-mediated hypersensitivity to Ascaris antigen in reactor rhesus primates was used to assess the pharmacologic profile of U-66,858 (1-acetoxy-2-n-butyl-4-methoxy-naphthalene). When the compound was given by the oral route, it showed dose-related inhibition of resistance (RL) and compliance (Cdyn) changes. When the compound was given by the aerosol route, it showed dose independent inhibition. In 15 animals, aerosols (52 +/- 32 to 53 +/- 10% for RL, p = 0.05 and 45 +/- 19 to 28 +/- 19% Cdyn inhibitions, p = 0.05) for 5.0-0.1% aerosol. By the oral route, inhibition was seen at 1-4 h following administration. In 5 animals, oral doses of 10 and 5 mg/kg inhibited (RL by 98 +/- 2 to 78 +/- 1.5%, p = 0.01 and Cdyn by 75 +/- 17 to 60.9 +/- 9.1%, p = 0.05) by 10 and 5 mg/kg U-66,858, respectively. The in vivo demonstration of inhibition of pulmonary bronchoconstriction by this compound, in a model known to be leukotriene sensitive, coupled with its potent in vitro inhibition of 5-lipoxygenase enzymes, suggests this compound may be of use in 5-lypoxygenase-mediated models of asthma.