Phosphodiesterase-5 inhibitor, tadalafil, protects against myocardial ischemia/reperfusion through protein-kinase g-dependent generation of hydrogen sulfide

Abstract

Background: Tadalafil is a novel long-acting inhibitor of phosphodiesterase-5. Because cGMP-dependent protein kinase (PKG) signaling plays a key role in cardioprotection, we hypothesized that PKG activation with tadalafil would limit myocardial ischemia/reperfusion (I/R) injury and dysfunction. Additionally, we contemplated that cardioprotection with tadalafil is mediated by hydrogen sulfide (H(2)S) signaling in a PKG-dependent fashion.

Methods and results: After baseline transthoracic echocardiography (TTE), adult ICR mice were injected i.p. with vehicle (10% DMSO) or tadalafil (1 mg/kg) with or without KT5823 (KT, PKG blocker, 1 mg/kg) or dl-propargylglycine (PAG, Cystathionine-gamma-lyase [CSE, H(2)S-producing enzyme] blocker; 50 mg/kg) 1 hour before coronary artery ligation for 30 minutes and reperfusion for 24 hours, whereas C57BL wild-type and CSE-knockout mice were treated with either vehicle or tadalafil. After reperfusion, TTE was performed and hearts were collected for infarct size (IS) measurement using TTC staining. Survival was increased with tadalafil (95%) compared with control (65%, P<0.05). Infarct size was reduced with tadalafil (13.2+/-1.7%) compared to vehicle (40.6+/-2.5%; P<0.05). KT and PAG abolished tadalafil-induced protection (IS: 39.2+/-1% and 51.2+/-2.4%, respectively) similar to genetic deletion of CSE (47.2+/-5.1%). Moreover, tadalafil preserved fractional shortening (FS: 31+/-1.5%) compared to control (FS: 22+/-4.8%, P<0.05). Baseline FS was 44+/-1.7%. KT and PAG abrogated the preservation of LV function with tadalafil by decline in FS to 17+/-1% and 23+/-3%, respectively. Compared to vehicle, myocardial H(2)S production was significantly increased with tadalafil and was abolished with KT.

Conclusions: PKG activation with tadalafil limits myocardial infarction and preserves LV function through H(2)S signaling.

Figure 1

Experimental protocol. Arrows indicate time points for treatment, performance of surgical procedures and measurement of various parameters.

Figure 2

Survival of mice following I/R in the various treatment groups at 24 h post-MI. Note that tadalafil-treated mice exhibited a significant increase in survival compared with animals treated with vehicle or PKG and CSE blockers (P<0.05).

Figure 3

A. Myocardial infarct size (% of RA) measured 24 h post-MI in the various groups. Note that infarct size was significantly reduced with tadalafil, which was blocked by KT and PAG. B. The area-at-risk, expressed as percent of the left ventricle, was similar in all groups. C. Myocardial infarct size measured 24 h post-MI in C57BL wild-type mice, mice treated with DMSO or tadalafil, and in CSE-knockout mice. Note that genetic deletion of CSE abrogated the infarct-sparing effect of tadalafil. D. The area-at-risk was similar in C57BL wild-type mice, mice treated with DMSO or tadalafil, and in CSE-knockout mice.

Figure 4

PKG activity 1 h following treatment with tadalafil or 10% DMSO compared with sham hearts. Note that tadalafil increases PKG activity compared with DMSO (P<0.05).

Figure 5

H₂S tissue levels assessed in hearts harvested 1 h after treatment. Note that tadalafil caused an increase in cardiac H₂S compared with DMSO (P<0.05). Interestingly, KT abrogated the increase in H₂S caused by tadalafil (P<0.05).

Figure 6

A. Representative M-mode images demonstrating the preservation of LV contractility with tadalafil compared with vehicle. KT and PAG abolished this preservation in LV function. B. LV End-Diastolic Diameter, End-Systolic Diameter and Fractional Shortening measured in the various treatment groups.

Figure 7

Proposed scheme outlining the pathway by which tadalafil may lead to PKG-dependent generation of H₂S and protection against ischemia/reperfusion injury, LV dysfunction as well as ischemic cardiomyopathy.