Luteolin and Chicoric Acid, Two Major Constituents of Dandelion Leaf, Inhibit Nitric Oxide and Lipid Peroxide Formation in Lipopolysaccharide-Stimulated RAW 264.7 Cells

Luteolin and chicoric acid are the most abundant phytochemicals in dandelion (Taraxacum officinale) leaf. In this study, four kinds of extraction methods [hot water, ambient temperature (AT) water, ethanol, and methanol] were applied to analyze the contents of both phytochemicals and verify their anti-inflammatory and antioxidative activities. The methanol extract showed the most potent nitric oxide (NO) inhibitory effect. The luteolin and chicoric acid concentrations were 3.42 and $12.86\;{\mu}g/g$ dandelion leaf in the methanol extract. The NO-suppressive effect of luteolin and chicoric acid was identified in a dose-dependent manner with $IC_{50}$ values of $21.2\;{\mu}M$ and $283.6\;{\mu}M$, respectively, in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells without cytotoxicity. Malondialdehyde (MDA) concentration, as an index for free radical injury on cell membrane, was also dose-dependently inhibited by the two compounds. The suppressive effect was further examined using mRNA and protein expression levels, which were attributable to the inhibition of inducible nitric oxide synthase (iNOS). These results suggest that two phytochemicals in dandelion leaf, luteolin and chicoric acid, may play an important role in the amelioration of LPS-induced oxidative stress and inflammation.