Rationale: Most patients with pulmonary arterial hypertension (PAH) die from right heart failure. β-Adrenergic receptor blockade reduces mortality by about 30% in patients with left-sided systolic heart failure, but is not used in PAH. Objectives: To assess the effect of the adrenergic receptor blocker carvedilol on the pulmonary circulation and right heart in experimental pulmonary hypertension in rats. Methods: Angioproliferative pulmonary hypertension was induced in rats by combined exposure to the vascular endothelial growth factor–receptor antagonist SU5416 and hypoxia. Carvedilol treatment was started after establishment of pulmonary hypertension and right heart dysfunction. Measurements and Main Results: Compared with vehicle-treated animals, treatment with carvedilol resulted in increased exercise endurance; improved right ventricular (RV) function (increased tricuspid annular plane systolic excursion and decreased RV dilatation); and an increased cardiac output. The morphology of the pulmonary vessels and the RV afterload were not affected by carvedilol. Carvedilol treatment was associated with enhancement of RV fetal gene reactivation, increased protein kinase G (PKG) activity, and a reduction in capillary rarefaction and fibrosis. Metoprolol had similar but less pronounced effects in the SU5416 and hypoxia model. Cardioprotective effects were noted of both carvedilol and metoprolol in the monocrotaline model. In the case of carvedilol, but not metoprolol, part of these effects resulted from a prevention of monocrotaline-induced lung remodeling. Conclusions: Adrenergic receptor blockade reverses RV remodeling and improves RV function in experimental pulmonary hypertension. β-Adrenergic receptor blockers are not recommended in humans with PAH before their safety and efficacy are assessed in well-designed clinical trials.

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-γ-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. Conclusion— PKG activation with tadalafil limits myocardial infarction and preserves LV function through H ₂ S signaling.

Background—: Maintaining physiological levels of hydrogen sulfide during ischemia is necessary to limit injury to the heart. Because of the anti-inflammatory effects of hydrogen sulfide, we proposed that the hydrogen sulfide donor, sodium sulfide (Na ₂ S), would attenuate myocardial injury through upregulation of protective microRNA-21 (miR-21) and suppression of the inflammasome, a macromolecular structure that amplifies inflammation and mediates further injury. Methods and Results—: Na ₂ S-induced miR-21 expression was measured by quantitative polymerase chain reaction in adult primary rat cardiomyocytes and in the mouse heart. We measured inflammasome formation and activity in cardiomyocytes challenged with lipopolysaccharide and ATP or simulated ischemia/reoxygenation and in the heart after regional myocardial ischemia/reperfusion, in the presence or absence of Na ₂ S. To assess the direct anti-inflammatory effects of hydrogen sulfide in vivo, we used a peritonitis model by way of intraperitoneal injection of zymosan A. Na ₂ S attenuated inflammasome formation and activity, measured by counting cytoplasmic aggregates of the scaffold protein apoptosis speck-like protein containing a caspase-recruitment domain (−57%) and caspase-1 activity (−50%) in isolated cardiomyocytes and in the mouse heart (all P <0.05). Na ₂ S also inhibited apoptosis (−38%) and necrosis (−43%) in cardiomyocytes in vitro and reduced myocardial infarct size (−63%) after ischemia/reperfusion injury in vivo (all P <0.05). These protective effects were absent in cells treated with the miR-21 eraser, antagomiR-21, and in miR-21 knockout mice. Na ₂ S also limited the severity of inflammasome-dependent inflammation in the model of peritonitis ( P <0.05) in wild-type but not in miR-21 knockout mice. Conclusions—: Na ₂ S induces cardioprotective effects through miR-21–dependent attenuation of ischemic and inflammatory injury in cardiomyocytes.

Cinaciguat (BAY 58–2667) is a novel nitric oxide (NO)-independent activator of soluble guanylate cyclase (sGC), which induces cGMP-generation and vasodilation in diseased vessels. We tested the hypothesis that cinaciguat might trigger protection against ischemia/reperfusion (I/R) in the heart and adult cardiomyocytes through cGMP/protein kinase G (PKG)-dependent generation of hydrogen sulfide (H₂S). Adult New Zealand White rabbits were pretreated with 1 or 10 μg/kg cinaciguat (iv) or 10% DMSO (vehicle) 15 min before I/R or with 10 μg/kg cinaciguat (iv) at reperfusion. Additionally, adult male ICR mice were treated with either cinaciguat (10 μg/kg ip) or vehicle 30 min before I/R or at the onset of reperfusion (10 μg/kg iv). The PKG inhibitor KT5283 (KT; 1 mg/kg ip) or dl-propargylglycine (PAG; 50 mg/kg ip) the inhibitor of the H₂S-producing enzyme cystathionine-γ-lyase (CSE) were given 10 and 30 min before cinaciguat. Cardiac function and infarct size were assessed by echocardiography and tetrazolium staining, respectively. Primary adult mouse cardiomyocytes were isolated and treated with cinaciguat before simulated ischemia/reoxygenation. Cinaciguat caused 63 and 41% reduction of infarct size when given before I/R and at reperfusion in rabbits, respectively. In mice, cinaciguat pretreatment caused a more robust 80% reduction in infarct size vs. 63% reduction when given at reperfusion and preserved cardiac function following I/R, which were blocked by KT and PAG. Cinaciguat also caused an increase in myocardial PKG activity and CSE expression. In cardiomyocytes, cinaciguat (50 nM) reduced necrosis and apoptosis and increased H₂S levels, which was abrogated by KT. Cinaciguat is a novel molecule to induce H₂S generation and a powerful protection against I/R injury in heart.