Clinical significance of endothelial dysfunction in children with relapsing obstructive bronchitis and bronchial asthma

Bronchial asthma (BA) is one of the most common childhood diseases. Epidemiological studies in recent years show that 5 to 10% of children suffer from this disease, and this indicator increases every year. Another serious concern is the increase in mortality from bronchial asthma and the number of hospitalizations in pediatric institutions. In recent years, the close interest of researchers in studying the mechanisms of development of bronchial asthma causes endothelial dysfunction. Endothelium is a metabolically active highly specialized monolayer of cells lining all the blood vessels of the human body. Endothelial cells, specifically reacting to different molecular signals, perform a variety of functions, including transport, barrier, participate in the metabolism of extracellular matrix, the biosynthesis of various cytokines, angiogenesis, regulate blood coagulation, vascular tone and immuno-inflammatory responses, participate in the production and metabolism of oxide nitrogen. The involvement of the endothelium in the regulation of systemic and pulmonary vascular tone is accomplished by the formation and release of vasodilator and vasoconstrictor substances, in particular endothelin-1 and endothelium-dependent relaxing factor - nitrogen oxide (NO)]. Endothelial dysfunction occurring when exposed to damaging agents (mechanical, infectious, metabolic, immunocomplex, etc.) dramatically changes the direction of its endocrine activity to the opposite: vasoconstrictors, endothelines, coagulants are formed. Endothelial dysfunction disrupts the relationship between NO (antiaggregant, anticoagulant, vasodilator) and peroxynitrate-metabolite NO, which increases the level of oxidative stress, which leads to various pathophysiological reactions. In the last decade, researchers have emphasized the damaging effect of proinflammatory cytokines (IL-1-p, TNF-a, IL-8, etc.) on the vascular endothelium, triggering a cascade of processes from local vasoconstriction and release of growth factors to vascular wall remodeling processes. In this connection, the question of the ratio of immunoinflammatory activation and the state of the vascular endothelium in patients with bronchial asthma is of particular interest. Endothelial dysfunction is considered as one of the possible pathogenetic mechanisms of the formation of bronchial asthma. Morphologically, in patients with bronchial asthma, there is an increase in the cross-section of the submucosal layer of the vessels, an increase in the number of vessels in the walls of the respiratory tract, thickening of the intima. Similar elements of remodeling are revealed already in childhood against a background of mild course of bronchial asthma.

The mechanisms of endothelial dysfunction and remodeling of the airway vessels have not been sufficiently studied, which was the prerequisite for our study.

The aim of the study was to study the endothelial function in children with relapsing obstructive bronchitis and bronchial asthma in the period of exacerbation and remission.

A total of 147 patients with children aged 1-17 years were examined. In accordance with the nosological forms and severity of the disease, the children were divided into groups: patients with relapsing obstructive bronchitis (group 1), intermittent asthma (2nd group), persistent asthma of mild degree (3rd group), persistent asthma severity, or severe (group 4) during an exacerbation of the disease (subgroups 1A, 2A, 3A, 4A, respectively) and in the remission period (subgroups 1B, 2B, 3B, 4B, respectively).

The level of endothelin-1 (ET-1) in the blood was determined by the method of enzyme immunoassay using standard DRG reagents (USA). NO in the blood was determined by the level of final metabolites (nitrites (NO2) / nitrates (NO3)) calorimetric method using Griess reagents. Doppler echocardiography of the heart and blood vessels was performed on an AU 3 Partner ultrasound from Esaote Biomedica (Italy), measuring the mean pulmonary artery pressure in the Kitobatake. The control group included 13 practically healthy children of the same age without signs of any acute or chronic diseases.

The statistical analysis of the data was carried out using the statistical packages Excel lor Windows and Statistica 7.0. For Windows.

Given the lack of data on the significance of the levels of the indicators selected for the study in healthy children, the children of the control group were examined to determine the regulatory parameters.

The period of exacerbation of bronchial asthma and recurrent obstructive bronchitis was characterized by pulmonary ventilation disorders of varying severity. As is known, ventilation disorders lead to the development of alveolar hypoxia, which can not but affect the state of endothelial function.

When assessing the indices during the exacerbation period, the level of vasoconstrictor factor ET-1 significantly increased in all groups and was highest in the group of children with severe and moderate-to-severe BA (subgroup 4A). The course of the disease in subgroup 4A was characterized by severe obstructive ventilation, leading to alveolar hypoxia, which is a potent inducer of ET-1. In addition to the hypoxia inducing role, this group of patients is characterized by pronounced immunopathologic responses both in intensity and in duration of flow, which also contribute to a greater ejection of ET-1 by the vascular endothelium.

The analysis of multiple comparisons by the Kraslak-Wallis method revealed a highly significant criterion H (H = 38.02, p = 0.0001), which gives the right to state that the statistical characteristics of the levels of ET-1 in patients of different subgroups in the exacerbation period differ significantly between themselves, and their level depends on the patient's belonging to a particular subgroup. Since patients were divided into groups according to the severity of the disease, it can be said that there is a connection between the level of ET-1 and the severity of the disease.

Thus, in subgroup 1A, endothelial dysfunction was characterized by a moderate increase in the level of ET-1 and a decrease in the level of nitrates and nitrites in the blood. In patients in subgroups 2A and 3A (mild bronchial asthma), a significant decrease in the level of nitrites (4.44-4.64 μmol / L) was observed against a background of a moderate increase in the level of ET-1 (0.1-0.13 ng / ml) in comparison with the control and equalization of indicators of NO metabolism due to a relative increase in the level of nitrates (31.54-33.48 μmol / l). This imbalance can be considered prognostically unfavorable due to the fact that the increase in nitrate levels is associated with increased lipid peroxidation, highly active free radicals and an increase in the activity of inducible NO synthase (iNOS) in smooth muscle vessels and macrophages. In patients with subgroup 4A with severe bronchial asthma, the imbalance is even greater: against a background of a high level of ET-1 (up to 0.2 ng / ml), more pronounced inhibition of endothelial NO synthetase (eNOS) was observed, which was manifested by a decrease in the level of nitrites (6 , 19 μmol / L) and pronounced activation of iNOS, which resulted in an increase in the level of nitrates and total metabolites of N0 as compared to the control group.

To determine the existence of a functional relationship between the level of ET-1 and the parameters characterizing the course of chronic obstructive pulmonary diseases, a multiple linear regression procedure was used with step-by-step exclusion of insignificant variables. As a result of the analysis, a mathematical model was obtained:

ET-1 = -0.00368+ (0.0142 x disease duration) + (0.00532 x PLA), with R = 0.672; R2 = 0.525; dbf = 2; F = 8,408; p = 0.001.

The multiple regression coefficient R reflects the presence of a statistically significant relationship between the level of ET-1 and independent variables (the duration of the disease), as well as the average pulmonary artery pressure (PLA). At the same time, the determination coefficient R2 makes it possible to assert that the increase in the level of ET-1 by 52.5% is due to a change in the level of the independent variables of this equation, namely the duration of the disease (p = 0.008) and PLA (p = 0.022).

Estimating the metabolism of NO by its final metabolites (nitrites, nitrates) in children in subgroups, it can be noted that it changed in different directions. In patients with subgroup 1A with exacerbation of relapsing obstructive bronchitis, there was a decrease in the level of NO metabolites, both nitrites and nitrates, which indicated a deficiency in the NO-dependent function of the endothelium, with the most pronounced decrease in the level of nitrites. At the present stage, the level of blood nitrite is regarded as a predictor of endothelial eNOS activity. This indicates a pronounced inhibition of eNO synthetase, a weak iNO reaction.

In the remission period in all groups, the level of ET-1 remained moderately elevated in the range 0.05-0.15 ng / ml compared to the control group and was most elevated in subgroup 4B to a level of 0.15 ng / ml. Similar levels of ET-1 indicate that in the subgroup 4B, in comparison with other subgroups, the highest metabolism of vasoconstrictor factors (ET-1) remains in the vascular endothelium. Perhaps this is due to the fact that patients with severe BA continue to have latent obstructive changes in the function of external respiration, alveolar hypoxia, which stimulates the highest release of ET-1 by endothelial cells.

The highly significant Kraslk-Wallis criterion H (H = 34.68, ^ = 0.0001), established as a result of multiple comparisons, gives the right to state that the statistical characteristics of the indices of ET-1 of different subgroups differ significantly, and their level depends on the patient's belonging to a particular group. Thus, as in the period of exacerbation, we can talk about the existence of a connection between the level of ET-1 and the severity of the disease.

An additional analysis of the correlation between ET-1 levels and the rates of chronic obstructive pulmonary disease revealed a reliable direct relationship between ET-1 and PLA levels (r = +0.38, p <0.014) in the remission period.

The NO metabolism in the studied groups behaves differently. In the group of children with recurrent obstructive bronchitis (subgroup 1B), an increase in the level of nitrite in the blood to 5.48 μmol / L is noted, although they remain lower compared to the control group and a marked increase in the nitrate level to 41.45 μmol / l, which can be regarded as a compensatory response to a deficiency of endothelial NO. In groups of children with mild asthma, there was a moderate increase in nitrite to 5.6-6.45 μmol / L (lower than in the control group). This can be regarded as an increase in the activity of eNOS and the protective action of NO metabolites. The most pronounced imbalance of NO metabolism was noted in children of subgroup 4B, which manifested itself in a decrease in the level of nitrites compared with the phase of exacerbation and an increase in the level of nitrates. These data may indicate pronounced oppression of eNOS even during remission and the continuing pathological activity of iNOS.

As a result of the study, the following conclusions can be drawn.

Changes in the levels of endothelium-dependent factors (ET-1 and NO metabolites) were found in patients with relapsing obstructive bronchitis and bronchial asthma, depending on the stage and severity of the disease.

In the phase of exacerbation of the disease in patients of all subgroups, unidirectional changes were established in the form of an increase in the level of ET-1, the most pronounced in patients with severe and moderate bronchial asthma up to 0.2 ng / ml.

The presence of a functional relationship between the level of ET-1 and indicators characterizing the course of chronic obstructive pulmonary disease (duration of the disease) and the level of mean pulmonary artery pressure in patients with relapsing obstructive bronchitis and bronchial asthma in the period of exacerbation of the disease has been proved.

The change in the levels of NO metabolites (nitrates, nitrites) was multidirectional in the form of persistent reduction of nitrites in the phase of exacerbation and remission and an increase in the level of nitrates, especially in severe bronchial asthma.

In patients with relapsing obstructive bronchitis and bronchial asthma, the presence of endothelial dysfunction was found, which was more pronounced in patients in the acute stage, which manifested itself in the form of vasoconstriction, increase in the average PLA and the level of ET-1, the inducer of synthesis of which was hypoxia and pathoimmunological reactions. At the same time, a low level of NO metabolite (nitrite) is associated with oppression of endothelial NO synthetase, and an increase in the level of nitrates is associated with the development of pathogenic NO (inducible NO), which could serve as a factor leading to endothelial destruction and maintenance of the pathological process in the lungs.

V. V. Polyakov, prof. AS Senatorov. Clinical significance of endothelial dysfunction in children with relapsing obstructive bronchitis and bronchial asthma // International Medical Journal №4 2012

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