Nitrite Test
Since nitric oxide (NO) was unstable and easy to form nitrates and
nitrites in cells, the nitrite in the supernatant was measured as an
indicator of NO production using an oxidized nitrite kit (Beyotime
Institute of Biotechnology, Jiangsu, China). Briefly, according to the
instructions, the supernatant was sequentially mixed with an equal
volume of Gris reagent I and Gris reagent II, and then the concentration
of nitrites was calculated according to the optical density (OD) value
at 540 nm measured using a smart-spec plus spectrophotometer (Bio Rad
laboratories, Hercules, CA, USA) (Stepuro, Chaikovskaya, 1997).