Glycyrrhizic Acid Suppress Post-inflammatory Hyperpigmentation via MAPK p38/NF-κB Singalling Pathway

OBJECTIVE To investigate the inhibitory effect of glycyrrhizic acid(GA) on LPS-induced expression of COX-2/PGE₂ in keratinocytes and the melanin production in co-cultured melanocytes explore its possible mechanism. METHODS Human cutaneous keratinocytes were treated with GA of different concentration(0, 2, 5 and 10 μmol·L^-1) and LPS. The level of cytokine PGE₂ in the culture medium was determined using ELISA kit. The expression of COX-2, NF-κB p-p65, p-IKKα/β and MAPK p-p38 were studied by Western blotting. The melanin content in co-cultured melanocytes was measured by colorimetric method. RESULTS The expression of COX-2, NF-κB p-p65, p-IKKα/β and MAPK p-p38 in LPS-treated keratinocytes were significantly raised compared to that in control group. LPS also elevated PGE₂ levels in the culture medium. The melanin content in co-cultured melanocytes increased after LPS stimulation. GA decreased COX-2, NF-κB p-p65, p-IKKα/β and MAPK p-p38 expression in LPS-treated keratinocytes in a dose-dependent manner(P<0.05). GA decreased PGE₂ levels in the culture medium of keratinocytes dose-dependently (P<0.05). GA also decreased melanin production in co-cultured melanocytes dose-dependently(P<0.05). CONCLUSION GA decreases LPS-induced expression of COX-2/PGE₂ in keratinocytes and melanin production in co-cultured melanocytes through suppressing MAPK p38/NF-κB signal pathway.