The inflammation influence on pathological remodeling of pulmonary arteries in monocrotaline-induced pulmonary hypertension in rats
Authors: Adzerikho I , Yatsevich O , Vladimirskaja T , Semenkova G , Amaegberi N 
Published: October 2021

Abstract

Aim
To investigate the inflammation role on pathological remodeling of pulmonary arteries (PA) in monocrotaline-induced pulmonary hypertension (mPAH) in rats with joint assessment serum and tissue inflammatory biomarkers and the morphological arteries changes.

Methods
The mPAH was induced by a subcutaneous monocrotaline injection (60 mg/kg) in male rats and control group received a single saline solution. Baseline and every 2, 4, 6, 8 weeks after the serum concentrations of interleukin-6 (IL-6), interleukin-10 (IL-10) were measured by enzyme-linked immunosorbent assay; matrix metalloproteinase-9 (MMP-9), interleukin-1β (IL-1β), collagen type 1 and 3, smooth muscle actin α (SMA-α) in lung tissue were investigated immunohistochemically and quantitative measurements of intima and media thickness were done by planimetry. The functional activity neutrophil changes measured by chemiluminescence and fluorescent methods.

Results
The IL-10 increased after 2 weeks of mPAH (5,9 vs 0,6 pg/ml, p&lt;0,05) vs control and then it decreased to initial values by 8 weeks (0,06 vs 0,62 pg/ml, p&gt;0,05). The increasing IL-6 (30,3 vs 0,01 pg/ml, p&lt;0,05) and the maximum expression of IL-1β in the lung tissue (0,119 vs 0,099 index of expression (IE), p&lt;0,05) we observed 4 weeks after mPAH. The SMA-α (29,4 vs 40,2 IE, p&lt;0,05) and MMP-9 (1,6 vs 0,8 IE, p&lt;0,05) expression level significantly raised 4 weeks later vs control and remained in a high level until 8 week. A significant increase of type 1 collagen expression was observed at all phases of the experiment, and high level type 3 collagen expression was observed from 4 to 8 weeks (7,0 vs 10,4 IE, p&lt;0,05). The histological characteristics of remodeling these were a thickening of the media (30,6 vs 56,0 μm, p&lt;0,05) and the subintimal layer (1,6 vs 10,9 μm, p&lt;0,05) of the PA.
2 weeks after mPAH cell priming occurred which manifested by modification ROS generation systems, decrease NADPH oxidase activity, increase of myeloperoxidase secretion (MPO), enhance of unbound cytosolic calcium ions, mitochondrial potential reduction. From 4 to 8 weeks an increase NADPH oxidase activity and MPO secretion was revealed into the extracellular environment which leads to overproduction of hypochlorous acid. This functional activity reprogramming of circulating neutrophils indicate associated with time-development of mPAH.

Conclusion
The inflammation is the most important mediator of pathological remodeling processes in mPA. The monocrotaline launches a neutrophil reaction at an early stage of PAH with changes their functional activity which leads to immune cells recruitment into the lung tissue, producing inflammation and proliferation biomarkers. The hyperplasia of smooth muscle cells and reconstruction of the extracellular matrix are the result of this process and leads to increase intima and media thickness. The high MMP-9, SMA-α, IL-6 activity in 6–8 weeks reflects maintenance local inflammatory potential.

Funding Acknowledgement
Type of funding sources: Public Institution(s). Main funding source(s): Basic and applied sciences - medicine, subprogram “Diagnostics and therapy of diseases” on the assignment “To establish the molecular-cellular mechanisms of the development of irreversible remodeling of pulmonary vessels in pulmonary arterial hypertension in an experiment in vivo.”