Inducible nitric oxide synthase inhibitor of the Chinese herb I. Saposhnikovia divaricata (Turcz.) Schischk

l-Arginine derived nitric oxide (NO) and its derivatives, such as nitrogen dioxide and peroxynitrite, play a role in inflammation and also possibly in the multistage process of carcinogenesis. Four furanocoumarins and eight chromones isolated from the dried root of Saposhnikovia divaricata (Fang Feng in Chinese) and evaluated for their effects on the synthesis of NO induced by lipopolysaccharide (LPS) in macrophage cell line RAW 264.7. The inhibition of nitrite production, as an index for NO released from the macrophage cells, was quantitatively analyzed by Griess reaction. The results showed that imperatorin and deltoin are potential NO production inhibitor, and their IC₅₀ values for inhibition of nitrite production were 17.3 and 11.6 μg/ml, respectively. Western-blot analysis demonstrated that iNOS enzyme activity was not inhibited by treatment with imperatorin or deltoin, but revealed that both compounds inhibited the expression of the iNOS protein.