Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare and life-threatening complication of pulmonary embolism. As existing animal models of CTEPH do not fully recapitulate complex disease pathophysiology, we report a new rat model for CTEPH evoked by repetitive embolization of the distal pulmonary artery branches with partially biodegradable alginate microspheres (MSs). MSs (180 ± 28 μm) were intravenously administered eight times at 4-day intervals; control animals received saline. The validity of the model was confirmed using transthoracic echocardiography, exercise testing, catheterization of the right ventricle, and histological examination of the lung and heart. The animals in the CTEPH group demonstrated a stable increase in right ventricular systolic pressure (RVSP) and decreased exercise tolerance. Histopathological examination revealed advanced medial hypertrophy in the small pulmonary arteries associated with fibrosis. The diameter of the main pulmonary artery was significantly larger in the CTEPH group than in the control group. Marinobufagenin and endothelin-1 serum levels were significantly elevated in rats with CTEPH. In conclusion, repetitive administration of alginate MSs in rats resulted in CTEPH development characterized by specific lung vasculature remodeling, reduced exercise tolerance, and a persistent rise in RVSP. The developed model can be used for pre-clinical testing of promising drug candidates.

Summary A major translational barrier to the use of stem cell (SC)‐based therapy in patients with myocardial infarction (MI) is the lack of a clear understanding of the mechanism(s) underlying the cardioprotective effect of SCs. Numerous paracrine factors from SCs may account for reduction in infarct size, but myocardial salvage associated with transdifferentiation of SCs into vascular cells as well as cardiomyocyte‐like cells may be involved too. In this study, bone marrow‐derived rat mesenchymal SC (MSCs) were microencapsulated in alginate preventing viable cell release while supporting their secretory phenotype. The hypothesis on the key role of paracrine factors from MSCs in their cardioprotective activity was tested by comparison of the effect of encapsulated vs free MSCs in the rat model of MI. Intramyocardial administration of both free and encapsulated MSCs after MI caused reduction in scar size (12.1 ± 6.83 and 14.7 ± 4.26%, respectively, vs 21.7 ± 6.88% in controls, P = 0.015 and P = 0.03 respectively). Scar size was not different in animals treated with free and encapsulated MSC (P = 0.637). These data provide evidence that MSC‐derived growth factors and cytokines are crucial for cardioprotection elicited by MSC. Administration of either free or encapsulated MSCs was not arrhythmogenic in non‐infarcted rats. The consistency of our data with the results of other studies on the major role of MSC secretome components in cardiac protection further support the theory that the use of live, though encapsulated, cells for MI therapy may be replaced with heart‐targeted‐sustained delivery of growth factors/cytokines.

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Introduction. Chronic thromboembolic pulmonary hypertension (CTEPH) is one of the most severe complications of pulmonary embolism (PE), characterized by poor prognosis and insuffcient effectiveness of standard treatment approaches. A small number of representative models of CTEPH make it diffcult to conduct preclinical studies of promising pharmacological substances.Objective – development and validation of the experimental model of CTEPH in rats by embolization of the distal branches of the pulmonary artery with biodegradable microspheres.Material and methods. Male Wistar rats were used for the experiments. Biodegradable microspheres (MS) based on sodium alginate and autologous blood clots (AT) were used as embolizing particles. The animals were divided into groups: control: saline solution was injected 4 times with an interval of 8 days into the tail vein; AT: according to the above protocol, 50 μL of AT was injected; MS was administered intravenously in a volume of 50 μl of MS according to two protocols: MS4: 4 times with an interval of 8 days; MS8: 8 times with an interval of 4 days. After 2 and 6 weeks after the last injection, a histological examination of the lungs was performed; after 6 weeks: echocardiographic study (TTE), right ventricular catheterization (RV) with measurement of right ventricular systolic pressure (RVSP), treadmill test, assessment of serum endothelin­1 levels by the immunoassay method.Results. During the experiments, the survival rate in the MS8 group was 50 %. In the other groups, there were no animal losses. According to the treadmill test 6 weeks after the modeling of PE, exercise tolerance was signifcantly reduced in the MC4 and MC8 groups compared with the control group. TTE data indicate a signifcant increase in the diameter of the pulmonary trunk and the right ventricular outflow tract in the MC8 compared with the control and AT. There were signifcant increase in RVSP and the level of endothelin­1 compared with the control only in the MS8. After 6 weeks, the index of hypertrophy of vessel wall of the pulmonary artery in the MC4 and MC8 was signifcantly higher compared with the control and AT groups.Conclusion. Based on the use of MS, administered under the MS 8 protocol, a new representative model of CTEPH has been created, which can be used to test promising pharmacological substances.

Introduction Chronic thromboembolic pulmonary hypertension (CTEPH) is life-threatening complication of pulmonary embolism (PE) with insufficiently understood mechanisms. Several rodent CTEPH models based on i.v. administration of non-biodegradable microparticles have been validated for preclinical studies. Major limitation of these models is the lack of partial dissolution of emboli following their entrapment in the lung vasculature. Purpose The study was aimed at development and validation of rat CTEPH model based on recurrent embolization of (sub)segmental pulmonary artery branches with biodegradable microspheres. Methods Male Wistar rats were used for the experiments. Pulmonary vasculature was embolized either with sodium alginate microspheres (MS) or with autologous blood clots (AT). The animals were randomized into the following groups: i) controls: saline at a volume of 50 μL was injected 4 times with 8-day interval into the tail vein; the same regimen was used in two next groups; ii) AT; iii) MS4; iv) MS8: MS were administered 8 times with 4-day interval. Histological examination of the lungs was performed after 2 and 6 weeks after the last injection. 6 weeks after the last injection the following analyses were performed: treadmill test, transthoracic echocardiography (TTE), right ventricular catheterization with measurement of right ventricular systolic pressure (RVSP), determination of serum endothelin-1 level. Results The survival rate in the MS8 group was 50%. In the other groups, there were no animal deaths. Multiple emboli were found in the lumen of (sub)segmental pulmonary artery branches 2 weeks after the last injection in MS4 and MS8 groups. Increased diameter and thickening of the bronchial arterial wall were also registered. After 6 weeks, the index of hypertrophy of vessel wall in MS4 and MS8 groups was significantly higher than in controls (p=0.041 and p=0.006, respectively) (Fig. 1). No sign of vascular remodeling was identified in the branches of the pulmonary artery in the AT group. Exercise tolerance was significantly reduced in both MS4 and MS8 groups compared with the controls (p=0.025 and p=0.008, respectively). There were no significant differences in exercise tolerance between the AT and control groups. TTE data indicate a significant increase in the diameter of the pulmonary trunk and the right ventricular outflow tract in the MS8 group compared with controls and AT (p<0.05). Significant increase in RVSP as well as in endothelin-1 level versus controls was found only in the MS8 group. Figure 1. Histological changes in the branches of the pulmonary artery 6 weeks after the last injection of emboli. Conclusion Recurrent (×8) intravenous administration of MS in rats resulted in CTEPH development characterized by specific lung vasculature remodelling, reduced exercise tolerance, and persistent rise in RVSP. The model developed can be used for preclinical testing of promising drug candidates.