Dehydrogenase activity was evaluated by the resazurin assay. The resazurin assay measures the activity of intra-and extramitochondrial dehydrogenases. The working solution of resazurin (Merck, USA) was prepared by dilution in DPBS 1 × (pH 7; 1 mM, Merck, USA) to the concentration of 0.3 mg/mL. After cell treatment, 20 μL of resazurin solution was added to the cells in 96-well plates, and the measurement started immediately. The fluorescence intensity (Ex/Em = 530/590 nm) was measured for 20 min using a SPARK microplate reader (Tecan, Austria) while incubating at 37 °C. The dehydrogenase activity was expressed as the percentage of total cellular dehydrogenase activity relative to that in control cells (control = 100%). At the tested concentrations, no significant interference of the tested compounds was observed with any of the assays.