Post-COVID syndrome is associated with increased extracellular purine bases and neutrophil extracellular traps in the blood plasma

Post-COVID syndrome is characterized by fatigue, reduced exercise tolerance, muscle and joint pain, and psychoemotional disorders. In the development of a generalized body response in a viral infection, abnormal defense responses are of great importance. We studied neutrophils, neutrophil extracellular traps (NETs), DNA degradation products (purine nitrogenous bases, PNBs), and traditional biochemical parameters.

Aim. To determine biochemical parameters and the number of NETs and PNBs in the peripheral blood of patients with post-COVID syndrome.

Materials and methods. The study included outpatients (n = 21) aged 18–59 years (36 [27 ÷ 50]). The control group consisted of 20 individuals aged 18–59 years (38.5 [29 ÷ 51.5]) without a past medical history of the coronavirus infection. All patients underwent a physical examination, their medical history was assessed, and the level of NETs and PNBs in the venous blood was determined.

Results. 11 patients had a mild form of the disease in their past medical history, 7 – moderate, and 3 – severe. The most common symptoms in the patients were fatigue, headache, epigastric pain, dizziness, and joint pain. Hair loss and dyspnea were less common. The concentration of NETs and PNBs was higher in the patients with post-COVID syndrome than in the control group (p < 0.05). We detected NETs in the patients with post-COVID syndrome only in the form of filamentous structures. The concentration of extracellular purine bases in the blood of the patients with post-COVID syndrome was the highest in patients with moderate and severe acute periods. In patients with a mild acute period, the concentration of PNBs was 7.38 [0.0 ÷ 60.7] mg / ml, and in patients with moderate and severe acute periods – 19.15 [0.0 ÷ 33.5] and 34.19 [3.35 ÷ 70.0] mg / ml, respectively.

Conclusion. Extracellular purine bases in concentrations capable of causing secondary alteration of cells are found in the peripheral blood of patients with post-COVID syndrome. Post-COVID syndrome is accompanied by the formation of filamentous NETs in the blood of patients.

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