PDE4A and chronic obstructive pulmonary disease: Noteworthy, the use of selective phosphodiesterase 4 (PDE4) inhibitors (which promote increased intracellular cAMP levels) for the treatment of predominantly inflammatory diseases, such as Alzheimer, psoriasis, arthritis, chronic obstructive pulmonary disease (COPD), and asthma has been widely studied [41,42,43], and roflumilast, an active oral PDE4 inhibitor, was approved by the FDA aiming to reduce COPD exacerbations [43].