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Background. Cystic fibrosis is a hereditary multi-organ disease. The involvement of the respiratory system due to chronic inflammation and a chronic infectious process is the main cause of death in 90% of cases. Currently, chronic inflammation in the respiratory tract in cystic fibrosis is being actively studied and new approaches to therapy are being developed. Circulating extracellular DNA/cell-free DNA (eDNA/cf DNA) is present in the bloodstream and other biological fluids of both healthy and sick individuals. The eDNA concentration is increased during exacerbation of several illnesses and in cases of exposure to damaging factors. The eDNA concentration is regulated by the endonucleases activity.
Objectives. Study of the eDNA concentration and endonuclease activity in the plasma of children with cystic fibrosis.
Methods. The concentration of eDNA was determined in 115 children, and nuclease activity was determined in 117 children. The control group included 49 healthy children of the same age and sex. The eDNA was extracted by phenolic extraction. The concentration of extracellular DNA was measured by fluorescence with an intercalating dye PicoGreen (Invitrogen). The DNAse 1 activity in plasma samples was measured by means of radial diffusion. The data are presented as a median (Me) and quartiles (Q1 - Q3). Statistical analysis was performed using a nonparametric Mann-Whitney U test to compare the eDNA concentration and nuclease activity in groups of children with cystic fibrosis and control, and also to analyze the relationship between the eDNA concentration and the nuclease activity with the clinical characteristics of patients.
Results. The eDNA concentration was lower than that of healthy children (p<0.05). The nuclease activity in CF patients did not differ from that of the control group. There was a trend to decrease of the eDNA concentration with the age. Nuclease activity decreased significantly with the age (p<0.05). In patients with exacerbation of the bronchopulmonary process, a decrease in nuclease activity was demostrated (p <0.05). The eDNA concentration in patients with FEV1> 80% does not differ from the control group. The eDNA concentration decreased along with a decrease of lung function (FEV1 <80%). Patients with deteriorated lung function and increased requirement for bronchodilators had low nuclease activity.
Conclusion. Children with cystic fibrosis had lower eDNA concentration in comparison with the control. In patients with normal spirometry parameters, eDNA probably plays a metabolic role and its composition differs from that of the eDNA of patients with impaired lung function. The nuclease activity of blood plasma in patients with cystic fibrosis decreased with age, and at the same time the progression of the disease was observed. Changes of the eDNA concentration and composition, as well as the nuclease activity in CF patients, can be important for predicting the course and severity of the disease. The interpretation of the qualitative composition of the eDNA requires further study to determine its role in the development of the chronic inflammatory process in CF. The study of eDNA and nuclease activity in CF can be used for development of new pathogenetic treatment modalities
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