Background/Aim: Glycyrrhizin (GL) is an important derivative of certain herbal medicines used in Asian countries. Currently, GL is used to treat hepatitis and allergic disease worldwide because of its anti-viral and anti-allergy effects. In addition to these prominent functions, GL likely regulates cellular functions such as tumor cell growth and cellular immunity. However, how GL affects the keratinocyte inflammation response remains poorly understood. The current paper investigates the effect of GL on psoriasis and explores the mechanisms involved. Methods: We used an in vitro cell model of tumor necrosis factor (TNF)-a-induced keratinocyte inflammation and the topical application of imiquimod (IMQ) using an animal model (mouse skin) of IMQ-induced psoriasis-like inflammation (IPI) to investigate the effect of GL on skin inflammation. Cell viability was analyzed using the Cell Counting Kit-8 (CCK8). Carboxyfluorescein succinimidyl ester (CFSE) labeling was used to trace monocyte adherence to keratinocytes. A Western blot analysis was used to detect the expression of intercellular adhesion molecule 1 (ICAM-1) and the activation of the nuclear factor (NF)-κB/mitogen-activated protein kinase (MAPK) signaling pathway. A modified version of the Psoriasis Area Severity Index (PASI) was used to monitor disease severity. Hematoxylin and eosin (H&E) staining was used to observe pathological changes. An immunohistochemistry (IHC) analysis was used to detect ICAM-1 expression in mouse skin. Results: GL treatment significantly reduced the levels of ICAM-1 in TNF-a-stimulated HaCaT cells, inhibited subsequent monocyte adhesion to keratinocytes, and suppressed the nuclear translation and phosphorylation of p65 following the degradation of inhibitor κB (IκB). GL treatment blocked the phosphorylation of extracellular signal-regulated kinase (ERK)/p38 MAPK. GL effectively delayed the onset of IPI in mice and ameliorated ongoing IPI, thereby reducing ICAM-1 expression in epidermal tissues. Conclusions: These results demonstrate that GL treatment ameliorates skin inflammation by inhibiting ICAM-1 expression via interference with the ERK/p38 MAPK and NF-κB signaling pathways in keratinocytes. Therefore, GL can be used as an anti-psoriasis drug.

Psoriasis, characterized by circumscribed, red, thickened plaques with an overlying silver-white scale, is a common T-cell-mediated chronic inflammatory skin disease. Although hydrogen sulfide (H 2 S) has been shown to be a signaling molecule with both pro-or anti-inflammatory effects, its relationship with psoriasis has not been elucidated. In the present study, 15 patients with chronic progressive psoriasis and 15 healthy volunteers were investigated. Serum H 2 S levels in psoriasis patients were significantly lower than those of healthy controls (16.69 ± 5.47 μM vs. 34.5 ± 6.39 μM). In contrast, serum levels of tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) and interleukin-8 (IL-8) were significantly higher in psoriasis patients than healthy controls (22.88 ± 6.24 pg/ml vs. 12.07 ± 3.68 pg/ml; 61.47 ± 8.21 pg/ml vs. 31.54 ± 13.73 pg/ml; and 39.43 ± 8.56 pg/ml vs. 20.55 ± 6.45 pg/ml, respectively). The serum H 2 S levels negatively correlated with clinical disease severity. Furthermore, treatment of HaCaT human keratinocytes with TNF-α increased the levels of nitric oxide (NO), IL-6 and IL-8 (32.21 ± 5.71 μM vs. 3.22 ± 0.98 μM; 203.96 ± 13.16 pg/ml vs. 13.57 ± 3.75 pg/ml; and 301.24 ± 30.17 pg/ml vs. 29.06 ± 10.91 pg/ml, respectively) in the culture media. Exogenous H 2 S inhibited the TNF-α -mediated upregulation of NO, IL-6 and IL-8 in a dosedependent manner. In addition, H 2 S inhibited TNF-α-mediated activation of p38, extracellular-signalregulated kinase and nuclear factor kappa B. In conclusion, H 2 S may play a protective role in the pathogenesis of psoriasis. H 2 S-releasing agents may be promising therapeutics for psoriasis.

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