Medium nitrite was measured as an indicator of NO production [40 (link)]. In brief, 50 μl of supernatant was mixed with an equal volume of Griess reagent I, followed by the addition of 50 μl of Griess reagent II (S0021, Beyotime, Shanghai, China) at room temperature. Absorbance was immediately measured at 540 nm. The concentration of each sample was calculated from a standard curve generated using sodium nitrite.
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