Effects of tadalafil (PDE5 inhibitor) and roflumilast (PDE4 inhibitor) on airway reactivity and markers of inflammation in ovalbumin-induced airway hyperresponsiveness in guinea pigs.

Selective phosphodiesterase (PDE) 4 inhibitors have recently been introduced into the therapy of chronic obstructive pulmonary disease. However, suppression of airway reactivity and eosinophilic inflammation by increased intracellular cAMP could be beneficial in bronchial asthma as well. PDE5 inhibitors are used for the therapy of erectile dysfunction, pulmonary hypertension, and other cardiovascular diseases, but an expression of PDE5 in several immune cells suggests its perspectives in inflammation, as well. To bring a new information on the therapeutically relevant potential of PDE4 and PDE5 inhibitors in allergic inflammation, this study evaluated the effects of 7-days administration of PDE5 inhibitor tadalafil and PDE4 inhibitor roflumilast in experimentally-induced allergic inflammation and compared their action with effects of a corticosteroid dexamethasone. In the study, male adult guinea pigs were used. Control group was non-sensitized, while other animals were ovalbumin-sensitized over two weeks and thereafter treated intraperitoneally for 7 days with tadalafil or roflumilast (daily dose 1.0 mg/kg b.w. each), with their combination (0.5 mg/kg b.w. each), with dexamethasone (1.0 mg/kg b.w.), or with vehicle. Both tadalafil and roflumilast reduced the specific airway resistance after nebulization of histamine (a marker of in vivo airway reactivity), and decreased the in vitro airway reactivity to cumulative doses of histamine and acetylcholine in tracheal strips (significant for roflumilast) and in lung tissue strips (significant for both agents), analyzed by organ bath method. These changes were associated with decreased numbers of circulating leukocytes and eosinophils and lower production of interleukins 4 and 5, nuclear factor kappa B and tumor necrosis factor alpha in the lung. Similar effects were observed also for dexamethasone. Roflumilast and tadalafil, but not their combination with reduced doses, lowered lung TBARS, a marker of lipid oxidation. Selective PDE5 inhibition alleviated allergic airway inflammation, but it was less potent than PDE4 inhibition, whereas anti-inflammatory action of the PDE inhibitors was comparable to the effects of dexamethasone.

Effects of Selective Inhibition of PDE4 by YM976 on Airway Reactivity and Cough in Ovalbumin-Sensitized Guinea Pigs.

Phosphodiesterases (PDEs) are enzymes involved in the degradation of cAMP and cGMP. Selective PDE4 inhibitors (e.g., roflumilast) are effective in therapy of chronic obstructive pulmonary disease associated with neutrophil inflammation. The aim of this study was to evaluate the effects of a selective PDE4 inhibitor, YM976, on citric acid-induced cough, in vivo and in vitro airway smooth muscle reactivity to histamine, and on inflammatory mediators in ovalbumin-sensitized guinea pigs, with experimentally induced eosinophil inflammation. The YM976 was administered intraperitoneally at a dose of 1.0 mg/kg once daily for 7 days. Sensitization with ovalbumin led to a significant increase in the number of coughs, and in vivo and in vitro airway reactivity. Also, increased plasma levels of IL-4, IL-5, and PAF were observed, with a significant increase in the differential count of eosinophils in both blood and bronchoalveolar lavage fluid. The YM976 suppressed the number of coughs, the airway reactivity in tracheal tissue strips, and the IL-4 level. The findings indicate that PDE4 inhibition by YM976 exerts antitussive and anti-inflammatory effects in guinea pigs with ovalbumin-induced eosinophilic inflammation.

The Guinea Pig Sensitized by House Dust Mite: A Model of Experimental Cough Studies.

The guinea pig sensitized by ovalbumin is the most widely used model to study cough experimentally, as the neurophysiology of the vagus nerve in the guinea pig is closest to humans. Nonetheless, the choice of the antigen remains questionable, which influences the translation of results into clinical medicine. The present study seeks to develop an alternative model of cough study using house dust mite sensitization (HDM). Thirty guinea pigs were divided into the HDM group, ovalbumin (OVA) group, and control group based on their cough response to 0.4 M citric acid. In the HDM group animals were sensitized by 0.25 %HDM aerosol, which they inhaled for 5 min over 5 days, followed by inhalation of 0.5 %HDM in the same protocol. Sensitization was confirmed by a skin test. Symptoms of allergic rhinitis were induced by intranasal application of 15 µl 0.5 %HDM and cough challenges with citric acid were performed. Airway resistance was measured in vivo by Pennock's method. We found that both HDM and OVA-sensitized groups showed a significantly enhanced nasal reactivity and cough response compared with controls. The airway resistance data did not show significant differences. We conclude that the HDM cough model replicates functional aspects of the OVA model, which may make it an alternative to the latter. However, the superiority of the HDM model for experimental cough studies remains to be further explored.

Potassium ion channels and allergic asthma.

High-conductive calcium-sensitive potassium channels (BK+Ca) and ATP-sensitive potassium (K+ATP) channels play a significant role in the airway smooth muscle cell and goblet cell function, and cytokine production. The present study evaluated the therapeutic potential of BK+Ca and K+ATP openers, NS 1619 and pinacidil, respectively, in an experimental model of allergic inflammation. Airway allergic inflammation was induced with ovalbumine in guinea pigs during 21 days, which was followed by a 14-day treatment with BK+Ca and K+ATP openers. The outcome measures were airway smooth muscle cells reactivity in vivo and in vitro, cilia beating frequency and the level of exhaled NO (ENO), and the level of pro-inflammatory cytokines in the plasma and bronchoalveolar lavage fluid. The openers of both channels decreased airway smooth muscle cells reactivity, cilia beating frequency, and cytokine levels in the serum. Furthermore, NS1619 reduced ENO and inflammatory cells infiltration. The findings confirmed the presence of beneficial effects of BK+Ca and K+ATP openers on airway defence mechanisms. Although both openers dampened pro-inflammatory cytokines and mast cells infiltration, an evident anti-inflammatory effect was provided only by NS1619. Therefore, we conclude that particularly BK+Ca channels represent a promising new drug target in treatment of airway's allergic inflammation.

The influence of L-NAME on iNOS expression and markers of oxidative stress in allergen-induced airway hyperreactivity.

Nitric oxide (NO) effects in airways are influenced by the activity of NO-synthase isoforms and NO metabolism. Inducible NO-synthase (iNOS), which produces large amounts of NO, is active during the inflammatory process. NO quickly reacts, producing reactive oxygen species (ROS). In this study we attempted to detect the expression of iNOS and markers of ROS in the airway hyperreactivity (AHR) condition. The study was performed in guinea pigs, divided into four groups. Two groups were treated with the non-selective inhibitor of NO-synthase L-NAME. The other two groups were used as controls. Exhaled NO was monitored in vivo, AHR was assessed both in vivo and in vitro, and the expression of iNOS in lung homogenate, and oxidative stress markers were measured in the venous blood. L-NAME significantly affected the AHR only in in vitro condition, blocked the expression of iNOS in control but not in sensitized animals, and decreased the level of exhaled NO. The results concerning the oxidative stress markers are equivocal. The study confirmed that NO is involved in the regulation of AHR; the effects being mediated via iNOS and ROS activity.

Influence of roflumilast on airway reactivity and apoptosis in ovalbumin-sensitized Guinea pigs.

Chronic inflammatory diseases, associated with airway obstruction and cough, are usually treated with bronchodilating and anti-inflammatory drugs. Inhibition of phosphodiesterases (PDE) leads to both of these effects and influences apoptosis of immune cells. In chronic obstructive pulmonary disease, roflumilast, a selective PDE4 inhibitor, has been recently approved for pharmacotherapy. The aim of this study was to evaluate the effect of long-term administration of roflumilast in experimental allergic inflammation in guinea pigs. Male adult guinea pigs were used in the study. There were four experimental groups sensitized with ovalbumin for 14 days and thereafter treated per os, by inhalation, and intraperitoneally for 7 days with roflumilast or vehicle. A control group was left without sensitization. Roflumilast reduced specific airway resistance after nebulization of histamine, as measured in a double-chamber whole-body plethysmograph. This effect was confirmed in in vitro organ bath, with significant decreases in tracheal and lung smooth muscle contractility after cumulative doses of histamine. Suppression of hematological and immunological markers of inflammation and enhanced apoptosis in animals treated with roflumilast points to the possibility of a beneficial effect of roflumilast in allergic inflammation.