Abstract
Glycyrrhizin (GL) is known to have various immunomodulating activities and has long been used clinically as an anti-allergic and anti-hepatitis agent. While the potency of GL against lung inflammatory diseases has been expected, the effect of GL on the lung has been poorly understood. Lung fibroblasts are known as a potent producer of inflammatory chemokines, IL-8 and eotaxin 1, by which neutrophils and eosinophils are strongly attracted during inflammation. Therefore, we studied the effects of GL on the production of these chemokines using a human fetal lung fibroblast cell line, HFL-1, stimulated with TNF-α and IL-4. Moreover, we examined the structure–activity relationships of GL to explore more beneficial compounds. 18α,β-GL inhibited IL-8 dose-dependently and inhibited eotaxin 1 slightly. 18α,β-Glycyrrhetic acid (GA) did not inhibit IL-8 but inhibited eotaxin 1. The effect of 18α,β-glycyrrhetic acid monoglucuronide (MGA) resembled that of 18α,β-GL but was weaker. Both 3β-[(2- O-β- d-glucopyranuronosyl-β- d-glucopyranuronosyl)oxy]-18β-11-deoxo-olean-12-en-30-oic acid (11-deoxo-GL) and 3β-[(2- O-β- d-glucopyranuronosyl-β- d-glucopyranuronosyl)oxy]-olean-11,13,(18)-dien-30-oic acid (hetero-GL) exhibited inhibitory activity with significant cytotoxicity. 3β-[(2- O-β- d-Glucopyranuronosyl-β- d-glucopyranuronosyl)oxy]-18β-olean-9,12-dien-30-oic acid (homo-GL) did not have cytotoxicity but its activity was mild like that of 18α,β-GL. 3β-[(2- O-β- d-Glucopyranuronosyl-β- d-glucopyranuronosyl)oxy]-olean-11,13(18)-dien-30-ol (hetero-30-OH-GL) and 3β-[(2- O-β- d-glucopyranuronosyl-β- d-glucopyranuronosyl)oxy]-18β-olean-9,12-dien-30-ol (homo-30-OH-GL) showed potent inhibitory effects, at concentrations lower than 18α,β-GL with no significant cytotoxicity. These results suggest that GL-related compounds are effective in reducing chemokine production and that GL-modified compounds including hetero-30-OH-GL and homo-30-OH-GL appear most beneficial in view of their inhibitory capacity with less cytotoxicity.
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