Mechanisms of suppression of nitric oxide production by 3-O-methylquercetin in RAW 264.7 cells

Rhamnus nakaharai Hayata (Rhamnaceae) is used as a folk medicine in Taiwan for treating constipation, inflammation, tumors, and asthma. 3-O-Methylquercetin (3-MQ), a main constituent of the plant, has been reported to have potential for use in the treatment of asthma. The mechanisms of anti-inflammation of 3-MQ are still unclear. Nitric oxide (NO) production induced by lipopolysaccharide (LPS) through iNOS expression in RAW 264.7 cells, a mouse macrophage cell line, may reflect the degree of inflammation and may provide a measure for assessing the effect of drugs on the inflammatory process. Therefore, we were interested in investigating the mechanisms of suppression of NO production by 3-MQ in RAW 264.7 cells. 3-MQ (1-10 μM) concentration-dependently inhibited LPS (100 ng/mL)-induced NO production in RAW 264.7 cells. The IC₅₀ value was calculated to be 4.23 μM. 3-MQ (1-10 μM) significantly and concentration-dependently inhibited LPS (100 ng/mL)-induced iNOS protein and mRNA expressions in cells. The IC₅₀ values were calculated to be 4.36 and 6.53 μM, respectively. There was no significant difference among these three IC₅₀ values of 3-MQ. In conclusion, 3-MQ may exert its anti-inflammatory effect through the inhibition of iNOS DNA transcription.