Suppression of Aseptic Inflammation Reduces the Severity of Remodeling of the Pulmonary Artery Branches and Improves Progressing of Experimental Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a complication of pulmonary embolism, characterized by increased pressure in the pulmonary artery and impaired lysis of thromboemboli. Previously, the presence of aseptic inflammation in CTEPH was identified in the wall of the pulmonary artery branches and perivascularly. However, the role of this inflammation in the CTEPH formation is unknown. The aim of the work was to study the effect of aseptic inflammation on the CTEPH formation and progression. The experiments were performed on 54 male rats. The CTEPH model was reproduced by repeated intravenous administration of partially biodegradable microspheres (MS). Immediately after the last administration of MS, all animals were divided into groups: control CTEPH (c.CTEPH) – saline solution was administered intramuscularly (i/m) for 6 weeks; low dose of prednisolone (LD) – prednisolone was administered i/m at a dose of 1.5 mg/kg; high dose (HD) – prednisolone was administered i/m at a dose of 6 mg/kg; healthy animals. After 6 weeks, the following was performed: treadmill test, TTE, cardiac catheterization with manometry, and histological examination of the lungs. In a separate series of experiments, the severity of inflammatory infiltration of the vascular wall and perivascular zone was assessed by immunohistochemical studies (IHC). In the LD group, there was the decreasing of hypertrophy index (HI) and the percentage of collagen fibers in the vascular wall compared to c.CTEPH. There was a significantly greater reduction in HI compared to HD. In the HD group, there was positive effect on the percentage of collagen fibers in the vascular wall, this parameter did not significantly differ from healthy animals. According to IHC data, prednisolone in low dose effectively suppressed inflammatory infiltration of the vascular wall and perivascular space. The results of the study revealed the ability of prednisolone, by suppressing aseptic inflammation, to reduce the severity of remodeling of the pulmonary artery branches.