Amauroderma rugosum Extract Suppresses Inflammatory Responses in Tumor Necrosis Factor Alpha/Interferon Gamma-Induced HaCaT Keratinocytes

Keratinocytes form the physical barrier of the skin and play an important role in the inflammatory process. Amauroderma rugosum is an edible mushroom; however, its pharmacological properties have seldom been studied. Although the anti-inflammatory effect of the organic solvent extract of Amauroderma rugosum has been previously reported, it is not known whether the aqueous extract has a similar effect. In addition, the effect of Amauorderma rugosum extract on skin has never been explored. Therefore, the objectives of the present study were to evaluate the anti-inflammatory effects of the aqueous extract of Amauroderma rugosum on HaCaT keratinocytes, to explore its mechanisms of action, and to study the possible active ingredients involved. The results showed that the aqueous extract of Amauroderm rugosum at a concentration of 1.5 mg/mL was non-toxic to HaCaT cells and inhibited the release of cytokine interleukin-1β, and chemokines interleukin-8 and monocyte chemoattractant protein-1 in tumor necrosis factor (TNF)-α- and interferon (IFN)-γ-stimulated HaCaT cells. Amauroderma rugosum extract reduced the intracellular levels of reactive oxygen species. In addition, Amauroderma rugosum extract reduced the total protein expression of nuclear factor-kappa B (NF-κB) and B-cells inhibitor alpha in HaCaT keratinocytes and inhibited the phosphorylation of mitogen-activated protein kinase kinase (MEK) 1/2, extracellular signal-regulated kinase (ERK) 1/2, protein kinase B (Akt), and mammalian target of rapamycin (mTOR) in TNF-α- and INF-γ-stimulated HaCaT keratinocytes. Chemical analysis revealed that the aqueous extract of Amauroderma rugosum contains polysaccharides, triterpenes, and phenolic compounds. Anti-inflammatory compounds, such as gallic acid, guanosine, and uridine, were also present. The anti-inflammatory effect of Amauroderma rugosum could be mimicked by a combination of gallic acid, guanosine, and uridine. In conclusion, our study suggests that the aqueous extract of Amauroderma rugosum exerts anti-inflammatory effects on keratinocytes through its antioxidant and inhibitory effects on MEK/ERK-, Akt/mTOR-, and NF-κB-dependent signaling pathways.