PDE5A and Alzheimer disease: It has been repeatedly shown that increasing cGMP levels by using inhibitors of the phosphodiesterases (PDEs) that degrades it (mainly PDE5) prevents or reverses neuroinflammation in models of different pathologies including hepatic encephalopathy, hyperammonemia, focal ischemia, multiple sclerosis, Huntington’s, or Alzheimer’s diseases [53–59].