Effects of Natural Products on the Inhibition of Lipopolysaccharide-Inducible Nitric Oxide Synthase Activity in RAW 264.7 Cell Culture System

다국어 초록 (Multilingual Abstract)

Nitric oxide (NO) is a free radical synthesized from L-arginine by nitric oxide synthase (NOS). It is believed that NO is an important mediator in numerous physiological and inflammatory responses. Particularly, a large amount of NO released from the inducible nitric oxide synthase (iNOS) is mostly associated with inflammatory processes. Overproduction of NO in these processes including sepsis and autoimmune diseases can have deleterious consequences and pathophysiologic relevance. Therefore, for the discovery of new inhibitory agents against iNOS activity, we have evaluated about 100 kinds of natural products after partition into three layers (n-hexane, ethyl acetate and aqueous) from 100% methanol extracts to study inhibitory effects on iNOS activity induced by lipopalysaccharide (LPS) in RAW264.7 cells culture system. As a positive control, curcumin, which is known as an anti-tumor promotor, anti-inflammatory agent as an iNOS inhibitor, was used and showed the dose-dependent inhibitory effect (IC₅₀, 2.5 ㎍/㎖). Among tested fractions, the n-hexane fraction of Cimicifuga heracleifolia (IC₅₀: 9.65 ㎍/㎖), Forsythiae fructus (IC₅₀: 6.36 ㎍/㎖), Saposhnikovia divaricata (IC₅₀: 5.92 ㎍/㎖), and the ethyl acetate fraction of Chrysanthemum sibiricum (IC₅₀: 2.56 ㎍/㎖), Gastrodia edata (IC₅₀: 3.46 ㎍/㎖), and the aqueous fraction of Dianthus chinensis (IC₅₀: 6.73 ㎍/㎖), Euonymus alatus (IC₅₀: 6.78 ㎍/㎖), Mechania urticifodoria (IC₅₀: 8.01 ㎍/㎖) showed strong inhibitory activity against LPSstimulated iNOS. Especially, the ethyl acetate fraction of Chrysanthemum sibiricum (IC₅₀: 2.56 ㎍/㎖), which exhibited the strongest inhibition against iNOS, was fractionated with silica-gel column chromatography. These subfracdons exhibited dose-dependent inhibition against iNOS activity in the range of 2.59-5.6 ㎍/㎖ except for fraction No. 3, 4, 5, 6, 8, 9, and 16. Our study shows that Chrysanthemum sibiricum has the strongest inhibitory effect against iNOS activity and has similar effect to curcumin. Therefore, further studies for the identification of active principles from Chrysanthemum sibiricum and investigation for the mechanism of the inhibition of iNOS by active principles will be performed.