An Experimental Animal Model of Postobstructive Pulmonary Hypertension

Study of Morphological Changes in Rat Liver Caused by Occlusion of Inferior Vena Cava

Background/objectives

Up to date, there are no reports on animal survival rate and morphological changes in the liver caused by the impairment of blood outflow from the liver and its time dependence. Moreover, the impact of duration and degree of occlusion of inferior vena cava on pathological changes was not investigated yet. This study aimed at the assessment of the survival rate and morphological changes in the liver with varying degrees of occlusion of inferior vena cava. The exact timing of the reversibility of pathological processes was determined.

Methods

Rats (n = 160) were randomly divided into five groups: I - control group (CG) (n = 20); II - sham group (SG) (n = 20); III - intervention group (IG-1) (narrowing of the lumen of the inferior vena cava by 25%) (n = 40); IV intervention group (IG-2) (narrowing by 50%) (n = 40); and intervention group V (IG-3) (narrowing by 75%) (n = 40). The level of postoperative pain, the body and liver weight of the animals, histological examination, morphometry, and macroscopic evaluation of abdominal organs were carried out on the 1, 3, 7, 14, and 30 days following the surgical intervention. The survival rate of animals was assessed using the Kaplan-Meier method.

Results

On the 30th day, the rat grimace scale indices in the IG-1 (P ≤ 0.05), IG-2, and IG-3 (P ≤ 0.001) groups were higher. By body weight, this indicator on the 30th day was lower in the IG-1 (P ≤ 0.05), IG-2, and IG-3 (P ≤ 0.001) groups compared to the CG and SG groups. In the IG1 and IG2 groups, the survival rates were 72.5% and 65.0%, respectively. The lowest survival rate was observed in the IG3 group (22.5%).

Conclusions

Compression of the inferior vena cava by 75% led to an increase in animal mortality and the development of persistent morphological changes in the liver. At the same time, the survival rate of animals and the extent of changes in the liver with narrowing of the inferior vena cava by 25% and 50% had similar results. The results acquired possess scientific and practical importance.

Rodent models of pulmonary embolism and chronic thromboembolic pulmonary hypertension

Pulmonary embolism (PE) is the third most prevalent cardiovascular disease. It is associated with high in-hospital mortality and the development of acute and chronic complications. New approaches aimed at improving the prognosis of patients with PE are largely dependent on reliable animal models. Mice, rats, hamsters, and rabbits, are currently most commonly used for PE modeling because of their ethical acceptability and economic feasibility. This article provides an overview of the main approaches to PE modeling, and the advantages and disadvantages of each method. Special attention is paid to experimental endpoints, including morphological, functional, and molecular endpoints. All approaches to PE modeling can be broadly divided into three main groups: 1) induction of thromboembolism, either by thrombus formation in vivo or by injection of in vitro prepared blood clots; 2) introduction of particles of non-thrombotic origin; and 3) surgical procedures. The choice of a specific model and animal species is determined based on the objectives of the study. Rodent models of chronic thromboembolic pulmonary hypertension (CTEPH), which is the most devastating complication of PE, are also described. CTEPH models are especially challenging because of insufficient knowledge about the pathogenesis and high fibrinolytic activity of rodent plasma. The CTEPH model should demonstrate a persistent increase in pulmonary artery pressure and stable reduction of the vascular bed due to recurrent embolism. Based on the analysis of available evidence, one might conclude that currently, there is no single optimal method for modeling PE and CTEPH.

Challenges in the development of chronic pulmonary hypertension models in large animals

Pulmonary hypertension (PH) results in significant morbidity and mortality. Chronic PH animal models may advance the study of PH's mechanisms, evolution, and therapy. In this report, we describe the challenges and successes in developing three models of chronic PH in large animals: two models (one canine and one swine) utilized repeated infusions of ceramic microspheres into the pulmonary vascular bed, and the third model employed a surgical aorto-pulmonary shunt. In the canine model, seven dogs underwent microsphere infusions that resulted in progressive elevation of pulmonary arterial pressure over a few months. In this model, pulmonary endoarterial tissue was obtained for histology. In the aorto-pulmonary shunt swine model, 17 pigs developed systemic level pulmonary pressures after 2-3 months. In this model, pulmonary endoarterial tissue was sequentially obtained to assess for changes in gene and microRNA expression. In the swine microsphere infusion model, three pigs developed only a modest chronic increase in pulmonary arterial pressure, despite repeated infusions of microspheres (up to 40 in one animal). The main purpose of this model was for vasodilator testing, which was performed successfully immediately after acute microsphere infusions. Chronic PH in large animal models can be successfully created; however, a model's characteristics need to match the investigational goals.

Chronic effects of pulmonary artery stenosis on hemodynamic and structural development of the lungs

Pulmonary artery (PA) stenosis is a difficult obstructive defect to manage since clinicians cannot know a priori which obstructions to treat and when. Prognosis of PA stenosis and its chronic effects on lung development are poorly understood. This study aimed to characterize the hemodynamic and structural effects of PA stenosis during development. Fourteen male Sprague-Dawley rats underwent left PA (LPA) banding at age 21 days, and 13 underwent sham operation. Hemodynamic and structural impacts were studied longitudinally at 20, 36, 52, 100, and 160 days. Chronic LPA banding resulted in a significant reduction in LPA flow ( P < 0.0001) and size of both proximal LPA ( P < 0.0001) and distal LPA ( P < 0.01), as well as a significant increase in flow and size of the right PA ( P < 0.05) throughout development. Flows and sizes adapted such that normal levels of wall shear were restored after banding. At 160 days, LPA banding resulted in a significant decrease in left lung volume and an increase in right lung volume but no significant differences in total lung volume. There was an elevation of proximal LPA pressure as well as right ventricular hypertrophy in the banded animals. The banded lung exhibited arterial disorganization, loss of vessels, and enlargement of its bronchial arteries, whereas the contralateral lung showed signs of vascular pathology. There are consequences on development of both lungs in the presence of an LPA stenosis at young age. These results suggest that early intervention may be necessary to optimize left lung growth and minimize right lung vascular pathology.

Mesenchymal Stem Cells Restore Lung Function by Recruiting Resident and Nonresident Proteins

Because human lungs are unlikely to repair or regenerate beyond the cellular level, cell therapy has not previously been considered for chronic irreversible obstructive lung diseases. To explore whether cell therapy can restore lung function, we administered allogenic intratracheal mesenchymal stem cells (MSCs) in the trachea of rats with chronic thromboembolic pulmonary hypertension (CTEPH), a disease characterized by single or recurrent pulmonary thromboembolic obliteration and progressive pulmonary vascular remodeling. MSCs were retrieved only in high pressure-exposed lungs recruited via a homing stromal derived factor-1α/ CXCR4 pathway. After MSC administration, a marked and long-lasting improvement of all clinical parameters and a significant change of the proteome level were detected. Beside a variation of liver proteome, such as caspase-3, NF-κB, collagen1A1, and α-SMA, we also identified more than 300 resident and nonresident lung proteins [e.g., myosin light chain 3 (P16409) or mitochondrial ATP synthase subunit alpha (P15999)]. These results suggest that cell therapy restores lung function and the therapeutic effects of MSCs may be related to protein-based tissue reconstituting effects.

Delayed activin A administration attenuates tissue death after transient focal cerebral ischemia and is associated with decreased stress-responsive kinase activation

Focal cerebral ischemia and reperfusion initiates complex cellular and molecular interactions that lead to either cell repair or destruction. In earlier work, we found that activin A is an early gene response to cerebral ischemia and supports cortical neuron survival in vitro. In this study, the ability of exogenous activin A to attenuate injury from transient middle cerebral artery occlusion was tested in adult mice. Intracerebroventricular administration of activin A prior to middle cerebral artery occlusion reduced infarct volume apparent 1 day after experimental stroke. A single activin A administration at 6 h following ischemia/reperfusion reduced lesion volumes at 1 and 3 days and led to improved neurobehavior. Moreover, activin A treatment spared neurons within the ischemic hemisphere and led to a concomitant reduction in microglial activation. Activation of the stress-responsive kinases p38 and c-jun N-terminal kinase implicated in neuronal apoptosis after stroke was reduced following activin A treatment. Together these findings suggest that activin A promotes tissue survival after focal cerebral ischemia/reperfusion with an extended therapeutic window.

Endothelin receptor blockade combined with phosphodiesterase-5 inhibition increases right ventricular mitochondrial capacity in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is often treated with endothelin (ET) receptor blockade or phosphodiesterase-5 (PDE5) inhibition. Little is known about the specific effects on right ventricular (RV) function and metabolism. We determined the effects of single and combination treatment with Bosentan [an ET type A (ET(A))/type B (ET(B)) receptor blocker] and Sildenafil (a PDE5 inhibitor) on RV function and oxidative metabolism in monocrotaline (MCT)-induced PAH. Fourteen days after MCT injection, male Wistar rats were orally treated for 10 days with Bosentan, Sildenafil, or both. RV catheterization and echocardiography showed that MCT clearly induced PAH. This was evidenced by increased RV systolic pressure, reduced cardiac output, increased pulmonary vascular resistance (PVR), and reduced RV fractional shortening. Quantitative histochemistry showed marked RV hypertrophy and fibrosis. Monotreatment with Bosentan or Sildenafil had no effect on RV systolic pressure or cardiac function, but RV fibrosis was reduced and RV capillarization increased. Combination treatment did not reduce RV systolic pressure, but significantly lowered PVR, and normalized cardiac output, RV fractional shortening, and fibrosis. Only combination treatment increased the mitochondrial capacity of the RV, as reflected by increased succinate dehydrogenase and cytochrome c oxidase activities, associated with an activation of PKG, as indicated by increased VASP phosphorylation. Moreover, significant interactions were found between Bosentan and Sildenafil on PVR, cardiac output, RV contractility, PKG activity, and mitochondrial capacity. These data indicate that the combination of Bosentan and Sildenafil may beneficially contribute to RV adaptation in PAH, not only by reducing PVR but also by acting on the mitochondria in the heart.