Vascular Medicine cAMP Phosphodiesterase Inhibitors Increases Nitric Oxide Production by Modulating Dimethylarginine Dimethylaminohydrolases

Background—Pulmonary arterial hypertension is characterized by a progressive increase in pulmonary vascular resistance caused by endothelial dysfunction, inward vascular remodeling, and severe loss of precapillary pulmonary vessel cross-sectional area. Asymmetrical dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, and its metabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) play important roles in endothelial dysfunc-tion. We investigated whether combined phosphodiesterase (PDE) 3 and 4 inhibition ameliorates endothelial function by regulating the ADMA-DDAH axis. Methods and Results—We investigated the effects of the PDE3/4 inhibitor tolafentrine in vitro on endothelial cell survival, proliferation, and apoptosis. Effects of tolafentrine on the endothelial nitric oxide synthase/nitric oxide pathway, DDAH expression, DDAH promoter activity, and cytokine release from endothelial cells and their subsequent influence on DDAH expression were investigated. In monocrotaline-induced pulmonary arterial hypertension in rats, the effects of inhaled tolafentrine on DDAH expression and activity were investigated. Real-time-polymerase chain reaction, immunocytochemistry, and PDE activity assays suggested high expression of PDE3 and PDE4 isoforms in endothelial cells. Treatment of endothelial cells with PDE3/4 inhibitor significantly decreased ADMA-induced apoptosis via a cAMP/PKA-dependent pathway by induction of DDAH2. Chronic nebulization of PDE3/4 inhibitor significantly attenuated monocrotaline-induced hemodynamic, gas exchange abnormalities, vascular remodeling, and right heart hypertrophy. Interestingly, PDE3/4 inhibitor treatment reduced ADMA and elevated nitric oxide/cGMP levels. Mechanistically, this could be attributed to direct modulatory effects of cAMP on the promoter region of DDAH2, which was consequently found to be increased in expression and activity. Furthermore, PDE3/4 inhibitor suppressed apoptosis in endothelial cells and increased vascularization in the lung. Conclusion—Combined inhibition of PDE3 and 4 regresses development of pulmonary hypertension and promotes endothelial regeneration by modulating the ADMA-DDAH axis. Key Words: dimethylarginine dimethylaminohydrolase (DDAH) Ⅲ endothelial regeneration Ⅲ hypertension, pulmonary Ⅲ nitric oxide synthase Ⅲ phosphodiesterase (PDE) P ulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive pulmonary vascular remodeling leading to right ventricular (RV) failure and death. 1 The pathogenesis of PAH is complex and arises from a combination of pulmonary vasoconstriction, vascular wall remodeling, and thrombosis, resulting in severe loss of vessel cross-sectional area. 2 Intimal changes in the vessel walls include endothelial injury, endothelial cell (EC) proliferation, invasion of the intima by (myo)fibroblast-like cells, enhanced matrix deposition, and in some cases obstruction of the vascular lumen by unique plexiform lesions. 3 Despite the uncertainty of exact mechanisms causing pulmonary arteriolar obstructions, a growing body of evidence implicates EC apoptosis as the initiator of microvascular degeneration or …