ALDH7A1 and chronic obstructive pulmonary disease: The compartmentalized intracellular localization of individual PDEs, their cell-specific expression, as well as the fact that the expression of individual PDEs may change in response to substances and irritants to which patients may be exposed, including those that cause exacerbations in asthma and COPD, such as smoking tobacco and potentially also COVID-19, are in favor of molecules able to affect multiple simultaneous targets and, at the same time, multiple specific PDE subtypes [40].