Erika L. Poitras, Stephen L. Gust, Paul M. Kerr and Frances Plane* Pages 2418 - 2437 ( 20 )
Nitric oxide (NO), an important endogenous signaling molecule released from vascular endothelial cells and nerves, activates the enzyme soluble guanylate cyclase to catalyze the production of cyclic guanosine monophosphate (cGMP) from guanosine triphosphate. cGMP, in turn, activates protein kinase G to phosphorylate a range of effector proteins in smooth muscle cells that reduce intracellular Ca2+ levels to inhibit both contractility and proliferation. The enzyme phosphodiesterase type 5 (PDE5) curtails the actions of cGMP by hydrolyzing it into inactive 5’-GMP. Small molecule PDE5 inhibitors (PDE5is), such as sildenafil, prolong the availability of cGMP and therefore, enhance NO-mediated signaling. PDE5is are the first-line treatment for erectile dysfunction but are also now approved for the treatment of pulmonary arterial hypertension (PAH) in adults. Persistent pulmonary hypertension in neonates (PPHN) is currently treated with inhaled NO, but this is an expensive option and around 1/3 of newborns are unresponsive, resulting in the need for alternative approaches. Here the development, chemistry and pharmacology of PDE5is, the use of sildenafil for erectile dysfunction and PAH, are summarized and then current evidence for the utility of further repurposing of sildenafil, as a treatment for PPHN, is critically reviewed.
Sildenafil, nitric oxide, pulmonary hypertension, phosphodiesterase inhibitor, cyclic GMP, neonate.
Department of Pharmacology, University of Alberta, Edmonton, Alberta T6G 2H7, Department of Pharmacology, University of Alberta, Edmonton, Alberta T6G 2H7, Faculty of Nursing, Robbins Health Learning Centre, MacEwan University, Edmonton, Alberta T5J 4S2, Department of Pharmacology, University of Alberta, Edmonton, Alberta T6G 2H7