Serum levels of BCAAs were determined by method of capillary electrophoresis (CE) with contactless conductivity detection, which has been already described in details [18]. Shortly: CE measurements were carried out using HP3DCE system (Agilent Technologies, Waldbronn, Germany) equipped with a built-in contactless conductivity detector. Separation took place in a fused-silica capillary (31.4 cm in total length, 14.7 cm to detector, 25 μm inside diameter, 363 μm outside diameter, Composite Metal Services, UK) at the controlled temperature of 25 °C. The inner surface of the capillary is covered using INST coating solution (Biotaq, U.S.A.) to prevent electro-osmotic flow before its first use [19]. The CE separation is performed in an optimized background electrolyte with composition 3.2 mol/l acetic acid in 20% v/v methanol, pH 2.0. The achieved separation time was 125 s at electric field intensity of 0.96 kV/cm and simultaneous application of a hydrodynamic pressure of 50 mbar. The separation efficiency in blood serum equaled 461,000 plates/m for valine and isoleucine, and 455,000 plates/m for leucine; the detection limits are equal to 0.4 µM for all three amino acids. The relative standard deviation values for repeatability of the migration time equaled 0.1% for measurements during a single day and 0.3% for measurements on different days; the relative standard deviation values for repeatability of the peak areas equaled 2.3 - 2.6% for measurements during a single day and 2.7 - 4.6% for measurements on different days. Blood samples were collected in test tubes containing ethylenediaminetetraacetic acid (EDTA). The obtained serum samples were stored in a freezer at -20 °C until the analysis. Prior to the analysis, the unfrozen serum samples were deproteinized by mixing 250 µl of serum with 750 µL of acetonitrile. Deproteinization was performed in an Eppendorf tube after shaking for 30s. Then the serum samples were centrifuged at an acceleration of 4 g for 45 s; 800 µL of the obtained supernatant were taken for CE analysis.