cGMP-Hydrolytic Activity and Its Inhibition by Sildenafil in Normal and Failing Human and Mouse Myocardium

Abstract

In mouse models of cardiac disease, the type 5 (PDE5)-selective cyclic nucleotide phosphodiesterase inhibitor sildenafil has antihypertrophic and cardioprotective effects attributable to the inhibition of cGMP hydrolysis. To investigate the relevance of these findings to humans, we quantified cGMP-hydrolytic activity and its inhibition by sildenafil in cytosolic and microsomal preparations from the left ventricular myocardium of normal and failing human hearts. The vast majority of cGMP-hydrolytic activity was attributable to PDE1 and PDE3. Sildenafil had no measurable effect on cGMP hydrolysis at 10 nM, at which it is selective for PDE5, but it had a marked effect on cGMP and cAMP hydrolysis at 1 M, at which it inhibits PDE1. In contrast, in preparations from the left ventricles of normal mice and mice with heart failure resulting from coronary artery ligation, the effects of sildenafil on cGMP hydrolysis were attributable to inhibition of both PDE5 and PDE1; PDE5 comprised ϳ22 and ϳ43% of the cytosolic cGMP-hydrolytic activity in preparations from normal and failing mouse hearts, respectively. These differences in PDE5 activities in human and mouse hearts call into question the extent to which the effects of sildenafil in mouse models are likely to be applicable in humans and raise the possibility of PDE1 as an alternative therapeutic target.The PDE5-selective cyclic nucleotide phosphodiesterase inhibitor sildenafil is used in the treatment of erectile dysfunction and pulmonary hypertension. Its actions in these diseases result from its inhibition of cGMP-hydrolytic activity in vascular smooth muscle myocytes and the consequent increases in intracellular cGMP content and the potentiation of protein kinase G-mediated vasodilatory responses (Francis and Corbin, 2005;Kass et al., 2007;Movsesian et al., 2008).

Cardiac hypertrophy is not amplified by deletion of cGMP-dependent protein kinase I in cardiomyocytes

“…S5E). In addition, direct measurement of cardiac cGMP concentration showed a 3-to 4-fold increase in response to ISO (59,60) (Fig. S5F).…”

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

“…A PDE1-selective inhibitor (IC86340) blunts the hypertrophic response. These results are highly relevant since PDE1 provides the majority of cGMP-hydrolyzing activity in the heart (259,388,389,395) and acts to counter the cytoprotective effects of cGMP signaling through cGMP-dependent protein kinase (PKG).…”

“…In a model of pressure overload, sildenafil blocks cardiac hypertrophy, dilatation, and fibrosis (370) and reverses established hypertrophy. These latter findings are controversial (225,259,388), but a clinical trial ["PDE-5 Inhibition to Improve Clinical Status and Exercise Capacity in Diastolic Heart Failure (RELAX)"] will soon assess the usefulness of PDE5 inhibitors in treating heart failure.…”

“…Vinpocetine, the best known PDE1 inhibitor, has been used clinically in some places but has poor cell penetration properties and a significant toxicity profile. Most PDE5-selective inhibitors also inhibit PDE1, which becomes problematic when high extracellular concentrations are used (388,389). ICOS Corporation (now a part of Eli Lilly Corporation) has produced two selective and potent PDE1 inhibitors (IC229 and IC224 with IC 50 values of 560 and 800 nM, respectively) (249, 388, 389).…”

Phosphodiesterase-5 and Retargeting of Subcellular cGMP Signaling During Pathological Hypertrophy

“…This large difference in the relative levels of PDE5 in mouse and human myocardium raises some questions as to whether PDE5 inhibition is as likely to be as beneficial in humans as in mouse models. 17 NO also induces cardioprotection, particularly during acute ischemia/reperfusion injury, through several protection strategies such as the ischemic and pharmacological preconditioning (reviewed previously 18 ). However, if NOS becomes uncoupled, the formation of reactive oxygen species in combination with low NO bioavailability predisposes the heart to damage during pathophysiological conditions.…”