Glycyrrhiza glabra L. Extract Inhibits LPS-Induced Inflammation in RAW Macrophages

Glycyrrhiza glabra has been used in medicine for thousands of years. Our previous study revealed that the methanolic extract of Glycyrrhiza glabra L. (EGGR) exhibits significant nitric oxide (NO) inhibitory effect on lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages among 100 other extracts. Accordingly, the aim of the present study was to investigate the potential anti-inflammatory effect of EGGR. The anti-inflammatory effect of EGGR on LPS-stimulated RAW 264.7 macrophages was measured by MTT assay, NO content analysis, reactive oxygen species (ROS) level analysis, RT-PCR, Western blot analysis, and ELISA assay. Low doses of EGGR were non-toxic to macrophages and imparted protective effect against LPS induced cell death. Incubation of LPS-treated macrophages with 100 μg/mL EGGR led to an increase in cell viability from 66.6 to 99%. Moreover, EGGR led to down regulation of NO (NO2+NO3) and ROS productions in a dose-dependent manner. In particular, 100 μg/mL EGGR led to a reduction in NO2+NO3 level from 336.2 to 24.1 pM/mL, and ROS level from 483.5 to 128.4%. Consistent with the result related to NO production, EGGR suppressed the ability of LPS to induce mRNA and protein expressions of nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) cytokines, tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), and IL-6 productions which were analyzed by an ELISA assay. These results provide a comprehensive approach into the anti-inflammatory effect of EGGR on LPS-stimulated macrophages; however, efforts are underway on gaining detailed insight into anti-inflammatory signaling pathways.