The Effect of a Combination of Inhaled Nitric Oxide and an EndothelinA-Receptor Antagonist onHemodynamic Dysfunction in Experimental AcutePulmonary Thromboembolism

Animal models of right heart failure

Right heart failure may be the ultimate cause of death in patients with acute or chronic pulmonary hypertension (PH). As PH is often secondary to other cardiovascular diseases, the treatment goal is to target the underlying disease. We do however know, that right heart failure is an independent risk factor, and therefore, treatments that improve right heart function may improve morbidity and mortality in patients with PH. There are no therapies that directly target and support the failing right heart and translation from therapies that improve left heart failure have been unsuccessful, with the exception of mineralocorticoid receptor antagonists. To understand the underlying pathophysiology of right heart failure and to aid in the development of new treatments we need solid animal models that mimic the pathophysiology of human disease. There are several available animal models of acute and chronic PH. They range from flow induced to pressure overload induced right heart failure and have been introduced in both small and large animals. When initiating new pre-clinical or basic research studies it is key to choose the right animal model to ensure successful translation to the clinical setting. Selecting the right animal model for the right study is hence important, but may be difficult due to the plethora of different models and local availability. In this review we provide an overview of the available animal models of acute and chronic right heart failure and discuss the strengths and limitations of the different models.

Apelin/APJ system: an emerging therapeutic target for respiratory diseases

Apelin is an endogenous ligand of G protein-coupled receptor APJ. It is extensively expressed in many tissues such as heart, liver, and kidney, especially in lung tissue. A growing body of evidence suggests that apelin/APJ system is closely related to the development of respiratory diseases. Therefore, in this review, we focus on the role of apelin/APJ system in respiratory diseases, including pulmonary arterial hypertension (PAH), pulmonary embolism (PE), acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), obstructive sleep apnoea syndrome (OSAS), non-small cell lung cancer (NSCLC), pulmonary edema, asthma, and chronic obstructive pulmonary diseases. In detail, apelin/APJ system attenuates PAH by activating AMPK-KLF2-eNOS-NO signaling and miR424/503-FGF axis. Also, apelin protects against ALI/ARDS by reducing mitochondrial ROS-triggered oxidative damage, mitochondria apoptosis, and inflammatory responses induced by the activation of NF-κB and NLRP3 inflammasome. Apelin/APJ system also prevents the occurrence of pulmonary edema via activating AKT-NOS3-NO pathway. Moreover, apelin/APJ system accelerates NSCLC cells' proliferation and migration via triggering ERK1/2-cyclin D1 and PAK1-cofilin signaling, respectively. Additionally, apelin/APJ system may act as a predictor in the development of OSAS and PE. Considering the pleiotropic actions of apelin/APJ system, targeting apelin/APJ system may be a potent therapeutic avenue for respiratory diseases.

Inhaled nitric oxide has pulmonary vasodilator efficacy both in the immediate and prolonged phase of acute pulmonary embolism

BACKGROUND

Inhaled nitric oxide (iNO) effectively reduces right ventricular afterload when administered in the immediate phase of acute pulmonary embolism (PE) in preclinical animal models. In a porcine model of intermediate-risk PE, we aimed to investigate whether iNO has pulmonary vasodilator efficacy both in the immediate and prolonged phase of acute PE.

METHODS

Anesthetized pigs (n = 18) were randomized into three subgroups. An acute PE iNO-group (n = 6) received iNO at 40 ppm at one, three, six, nine and 12 hours after onset of PE. Vehicle animals (n = 6) received PE, but no active treatment. A third group of sham animals (n = 6) received neither PE nor treatment. Animals were evaluated using intravascular pressures, respiratory parameters, biochemistry and intracardiac pressure-volume measurements.

RESULTS

The administration of PE increased mean pulmonary artery pressure (mPAP) (vehicle vs sham; 33.3 vs 17.7 mmHg, p < 0.0001), pulmonary vascular resistance (vehicle vs sham; 847.5 vs 82.0 dynes, p < 0.0001) and right ventricular arterial elastance (vehicle vs sham; 1.2 vs 0.2 mmHg/ml, p < 0.0001). Significant mPAP reduction by iNO was preserved at 12 hours after the onset of acute PE (vehicle vs iNO; 0.5 vs -3.5 mmHg, p < 0.0001). However, this response was attenuated over time (p = 0.0313). iNO did not affect the systemic circulation.

CONCLUSIONS

iNO is a safe and effective pulmonary vasodilator both in the immediate and prolonged phase of acute PE in an in-vivo porcine model of intermediate-risk PE.

Riociguat, sildenafil and inhaled nitric oxide reduces pulmonary vascular resistance and improves right ventricular function in a porcine model of acute pulmonary embolism

BACKGROUND

Pulmonary vasodilators as add-on to current treatment strategies in acute pulmonary embolism may improve right ventricular unloading and hence improve patient outcome. We aimed to investigate whether stimulation of the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway with riociguat, sildenafil or inhaled NO causes pulmonary vasodilation and improves right ventricular function in a porcine model of acute intermediate risk pulmonary embolism.

METHODS

Two large autologous blood clots were administered to the pulmonary circulation of 28 pigs (60 kg). Animals were randomized to four increasing, clinically equivalent doses of riociguat (n=6), sildenafil (n=6), inhaled NO (n=6) or vehicle (n=6). Sham animals (n=4) did not receive pulmonary embolism or treatment. Haemodynamic responses were evaluated at baseline, after pulmonary embolism and after each dose using invasive pressure measurements, transoesophageal echocardiography, respiratory parameters and blood analysis.

RESULTS

Pulmonary embolism caused a three-fold increase in pulmonary vascular resistance compared with baseline (pulmonary embolism: 352±29 vs. baseline: 107±6 dynes, p<0.0001). All treatments lowered pulmonary vascular resistance compared with vehicle (riociguat: -158±35, sildenafil: -224±35, inhaled NO: -156±35 dynes, p<0.0001). Sildenafil, but neither inhaled NO nor riociguat, caused a decrease in systemic vascular resistance (sildenafil 678±41 vs. vehicle 1081±93 dynes, p=0.02) and increased cardiac output (sildenafil 8.8±0.8 vs. vehicle: 5.9±0.2 L/min, p<0.001). Systemic blood pressure was unaltered in all treatment groups.

CONCLUSION

Stimulation of the NO-sGC-cGMP pathway by riociguat, sildenafil and inhaled NO reduces pulmonary vascular resistance in a porcine model of acute pulmonary embolism without lowering systemic blood pressure.

Pulmonary vasodilation in acute pulmonary embolism - a systematic review

Acute pulmonary embolism is the third most common cause of cardiovascular death. Pulmonary embolism increases right ventricular afterload, which causes right ventricular failure, circulatory collapse and death. Most treatments focus on removal of the mechanical obstruction caused by the embolism, but pulmonary vasoconstriction is a significant contributor to the increased right ventricular afterload and is often left untreated. Pulmonary thromboembolism causes mechanical obstruction of the pulmonary vasculature coupled with a complex interaction between humoral factors from the activated platelets, endothelial effects, reflexes and hypoxia to cause pulmonary vasoconstriction that worsens right ventricular afterload. Vasoconstrictors include serotonin, thromboxane, prostaglandins and endothelins, counterbalanced by vasodilators such as nitric oxide and prostacyclins. Exogenous administration of pulmonary vasodilators in acute pulmonary embolism seems attractive but all come with a risk of systemic vasodilation or worsening of pulmonary ventilation-perfusion mismatch. In animal models of acute pulmonary embolism, modulators of the nitric oxide-cyclic guanosine monophosphate-protein kinase G pathway, endothelin pathway and prostaglandin pathway have been investigated. But only a small number of clinical case reports and prospective clinical trials exist. The aim of this review is to give an overview of the causes of pulmonary embolism-induced pulmonary vasoconstriction and of experimental and human investigations of pulmonary vasodilation in acute pulmonary embolism.

Serum Apelin 13 Levels in Patients With Pulmonary Embolism

Introduction and Aim:

Expression and peptide immunoreactivity of apelin messenger RNA have been described in a variety of tissues, including gastrointestinal tract, adipose tissue, brain, kidney, liver, cardiovascular system, and lungs. This study aimed to investigate the possible involvement of the endogenous apelin in the pathophysiological events that occur in patients with pulmonary embolism (PE).

Materials and Methods:

In total, 53 patients with PE and 35 healthy volunteers were included the study. This cross-sectional study was conducted at a tertiary care university hospital and among patients diagnosed as having PE. The control group consisted of healthy volunteers who applied to hospital for a routine checkup examination. Serum apelin 13 levels were measured in both the groups and their results were compared.

Results:

The median ages were 57 and 53 years, and female–male ratios were 30/23 and 20/15, in the PE and control groups, respectively. The mean serum apelin 13 levels were found to be significantly higher in the PE group (76.94 ± 10.70 ng/mL) than in the control group (50.01 ± 7.13 ng/mL; P < .001).

Conclusion:

This study demonstrated that apelin 13 levels are elevated in patients with PE. These results suggest that apelin may be a novel biomarker and a potential therapeutic target in patients with acute PE in the future.

A soluble guanylate cyclase stimulator, BAY 41-8543, preserves right ventricular function in experimental pulmonary embolism

Pulmonary embolism (PE) increases pulmonary vascular resistance, causing right ventricular (RV) dysfunction, and poor clinical outcome. Present studies test if the soluble guanylate cyclase stimulator BAY 41-8543 reduces pulmonary vascular resistance and protects RV function. Experimental PE was induced in anesthetized, male Sprague-Dawley rats by infusing 25 μm polystyrene microspheres (1.95 million/100 g body wt, right jugular vein) producing moderate PE. Pulmonary artery vascular resistance, estimated as RVPSP/CO, increased 3-fold after 5 h of PE. Treatment with BAY 41-8543 (50 μg/kg, I.V.; given at the time of PE induction) normalized this index by reducing RVPSP and markedly increasing CO, via preservation of heart rate and stroke volume. Ex vivo RV heart function showed minimal changes at 5 h of PE, but decreased significantly after 18 h of PE, including peak systolic pressure (PSP, Control 39 ± 1 mmHg vs. 19 ± 3 PE), +dP/dt (1192 ± 93 mmHg/s vs. 444 ± 64) and -dP/dt (-576 ± 60 mmHg/s vs. -278 ± 40). BAY 41-8543 significantly improved all three indices of RV heart function (PSP 35 ± 3.5, +dP/dt 1129 ± 100, -dP/dt -568 ± 87). Experimental PE produced increased PVR and RV dysfunction, which were ameliorated by treatment with BAY 41-8543. Thus, there is vasodilator reserve in this model of experimental PE that can be exploited to reduce the stress upon the heart and preserve RV contractile function.

Hemodynamic effect of apelin in a canine model of acute pulmonary thromboembolism

The peptide apelin is expressed in the pulmonary vasculature and is involved in the pathogenesis of many cardiovascular diseases. It has a biphasic role in the regulation of vasomotor tone related to the vascular endothelium. In this study, we induced acute pulmonary embolism (APE) in dogs with autologous blood clots to assess the effect of apelin on pulmonary and systemic circulation in the acute phase of APE. The expression of apelin mRNA was found to be upregulated in the lung tissue in the early several hours after APE induction and decreased at 24 h. The expression of apelin protein in the pulmonary arteries did not change within 24 h after APE, but significantly increased in the bronchial epithelial cells as early as 1h and decreased at 24 h. In normal anesthetized dogs, intravenous bolus administration of apelin significantly reduced the mean arterial pressure (MAP), but did not significantly affect the mean pulmonary arterial pressure (MPAP). In the dogs with APE, apelin decreased MPAP, whereas its impact on MAP was not significantly different from that in the control group. Taken together, the level of endogenous apelin did not change significantly in the pulmonary arterial wall, whereas its expression in the bronchial epithelium was upregulated in the early stage of APE. The effect of exogenous apelin on vasomotor tone was complicated: it resulted in differential changes in the pulmonary and systemic arterial pressures under different physiological and pathological conditions.