Cigarette Smoke-Induced Emphysema and Pulmonary Hypertension Can Be Prevented by Phosphodiesterase 4 and 5 Inhibition in Mice

<div><p>Rationale</p><p>Chronic obstructive pulmonary disease (COPD) is a widespread disease, with no curative therapies available. Recent findings suggest a key role of NO and sGC-cGMP signaling for the pathogenesis of the disease. Previous data suggest a downregulation/inactivation of the cGMP producing soluble guanylate cyclase, and sGC stimulation prevented cigarette smoke-induced emphysema and pulmonary hypertension (PH) in mice. We thus aimed to investigate if the inhibition of the cGMP degrading phosphodiesterase (PDE)5 has similar effects. Results were compared to the effects of a PDE 4 inhibitor (cAMP elevating) and a combination of both.</p><p>Methods</p><p>C57BL6/J mice were chronically exposed to cigarette smoke and in parallel either treated with Tadalafil (PDE5 inhibitor), Piclamilast (PDE4 inhibitor) or both. Functional measurements (lung compliance, hemodynamics) and structural investigations (alveolar and vascular morphometry) as well as the heart ratio were determined after 6 months of tobacco smoke exposure. In addition, the number of alveolar macrophages in the respective lungs was counted.</p><p>Results</p><p>Preventive treatment with Tadalafil, Piclamilast or a combination of both almost completely prevented the development of emphysema, the increase in lung compliance, tidal volume, structural remodeling of the lung vasculature, right ventricular systolic pressure, and right ventricular hypertrophy induced by cigarette smoke exposure. Single, but not combination treatment prevented or reduced smoke-induced increase in alveolar macrophages.</p><p>Conclusion</p><p>Cigarette smoke-induced emphysema and PH could be prevented by inhibition of the phosphodiesterases 4 and 5 in mice.</p></div

Effect of Piclamilast and/or Tadalafil on cigarette smoke-induced lung emphysema development assessed by structural parameters.

<p>Mice were exposed to cigarette smoke for 6 months and treated in parallel with Piclamilast (10 mg/kg body weight/day) and/or Tadalafil (10 mg/kg body weight/day). Time matched controls received solvent only. <b>(A)</b> Air space, <b>(B)</b> septal wall thickness and <b>(C)</b> mean linear intercept. <b>(D)</b> Representative histology from mice lung sections stained with hematoxylin and eosin. Data are given as mean ± SEM from n = 5–6, each. Bars indicate significant differences using ANOVA followed by Student-Newman-Keuls post hoc test (*<i>P</i><0.05;** <i>P</i><0.01; ***<i>P</i><0.001).</p

Systemic effects of smoke exposure and treatment with Piclamilast and/or Tadalafil in mice.

<p>Mice were exposed to cigarette smoke for 6 months and treated in parallel with Piclamilast (10 mg/kg body weight/day) and/or Tadalafil (10 mg/kg body weight/day). Time matched controls were received solvent only. Systemic arterial pressure determined by <i>A</i>. <i>carotis</i> catheterization and quantified in anesthetized animals. Data are given as mean ± SEM from n = 5–8, each. Bars indicate significant differences using ANOVA followed by Student-Newman-Keuls post hoc test (**<i>P</i><0.01; ***<i>P</i><0.001).</p

Effect of Piclamilast and/or Tadalafil on cigarette smoke-induced pulmonary hypertension in mice assessed by functional parameters.

<p>Mice were exposed to cigarette smoke for 6 months and treated in parallel with Piclamilast (10 mg/kg body weight/day) and/or Tadalafil (10 mg/kg body weight/day). Time matched controls received solvent only. <b>(A)</b> Right ventricular systolic pressure quantified by right heart catheterization in anesthetized animals. <b>(B)</b> Right heart hypertrophy, given as the ratio of right ventricular (RV) mass to left ventricular plus septum (LV+S) mass, from dried heart tissue; left ventricular weights did not differ between the different groups. Data are given as mean ± SEM from n = 5–8, each. Bars indicate significant differences using ANOVA followed by Student-Newman-Keuls post hoc test (**<i>P</i><0.01; ***<i>P</i><0.001).</p

Effect of Piclamilast and/or Tadalafil on cigarette smoke-induced pulmonary vascular remodeling in mice assessed by structural parameters.

<p>Mice were exposed to cigarette smoke for 6 months and treated in parallel with Piclamilast (10 mg/kg body weight/day) and/or Tadalafil (10 mg/kg body weight/day). Time matched controls received solvent only. <b>(A-C)</b> Degree of muscularization of <b>(A)</b> small pulmonary arteries (outer diameter 20–70 μm), <b>(B)</b> medium vessels (outer diameter >70 to 150 μm), and <b>(C)</b> large vessel (outer diameter >150 μm), as a percentage of total vessel count for fully muscularized (full), partially muscularized (partial), and non-muscularized (non) vessels. <b>(D-F)</b> Mean vascular lumen area of <b>(D)</b> small pulmonary vessels (outer diameter 20–70 μm), <b>(E)</b> medium vessels (outer diameter >70 to 150 μm), and <b>(F)</b> large vessel (outer diameter >150 μm). Data are given as mean ± SEM from n = 6, each. Bars indicate significant differences using ANOVA followed by Student-Newman-Keuls post hoc test (*<i>P</i><0.05; **<i>P</i><0.01; ***<i>P</i><0.001).</p

Effect of Piclamilast and/or Tadalafil on cigarette smoke-induced pulmonary vascular remodeling in mice—histology.

<p>Representative histology from lung sections stained with antibodies against α-smooth muscle actin and von Willebrand factor.</p

Effect of Piclamilast and/or Tadalafil on cigarette smoke-induced lung emphysema development assessed by <i>in vivo</i> lung functional parameters.

<p>Mice were exposed to cigarette smoke for 6 months and treated in parallel with Piclamilast (10 mg/kg body weight/day) and/or Tadalafil (10 mg/kg body weight/day). Time matched controls received solvent only. <b>(A)</b> dynamic lung compliance, <b>(B)</b> tidal volume and <b>(C)</b> airway resistance. Data are given as mean ± SEM from n = 6–9, each. Bars indicate significant differences using ANOVA followed by Student-Newman-Keuls post hoc test (* <i>P</i><0.05**; <i>P</i><0.01; ***<i>P</i><0.001).</p