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.

Bronchodilator and Anti-Inflammatory Action of Theophylline in a Model of Ovalbumin-Induced Allergic Inflammation.

Phosphodiesterases (PDEs) represent a super-family of 11 enzymes hydrolyzing cyclic nucleotides into inactive 5' monophosphates. Inhibition of PDEs leads to a variety of cellular effects, including airway smooth muscle relaxation, inhibition of cellular inflammation, and immune responses. In this study we focused on theophylline, a known non-selective inhibitor of PDEs. Theophylline has been used for decades in the treatment of chronic inflammatory airway diseases. It has a narrow therapeutic window and belongs to the drugs whose plasma concentration should be monitored. Therefore, the main goal of this study was to evaluate the plasma theophylline concentration and to determine its relevance to pharmacological effects after single and longer term (7 days) administration of theophylline at different doses (5, 10, 20, and 50 mg/kg) in guinea pigs. Airway hyperresponsiveness was assessed by repeated exposure to ovalbumin. Theophylline reduced specific airway resistance in response to histamine nebulization, measured in a double chamber body plethysmograph. A decrease in tracheal smooth muscle contractility after cumulative doses of histamine and acetylcholine was confirmed in vitro. A greater efficacy of theophylline after seven days long treatment indicates the predominance of its anti-inflammatory activity, which may be involved in the bronchodilating action.

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.