Igalan from Inula helenium (L.) suppresses the atopic dermatitis-like response in stimulated HaCaT keratinocytes via JAK/STAT3 signaling

Objective This study aimed to evaluate the protective effect of igalan, a sesquiterpene lactone isolated from Inula helenium (L.), on inhibiting inflammation, regulating the epidermal differentiation gene expression, and reactive oxygen species scavenging in atopic dermatitis (AD)-like inflammatory keratinocytes. Methods HaCaT human keratinocytes were treated with igalan at indicated concentrations before being activated by a combination of TNF-α and IFN-γ or IL-4 representative for T-helper 1 and T-helper 2 cell cytokines, which are associated with AD pathogenesis. Results By inhibiting the NF-κB pathway as well as the STAT activation, igalan could downregulate several marker inflammatory genes in AD, such as TARC/CCL17, MDC/CCL22, and RANTES/CCL5. In contrast, igalan, acting as JAK inhibitor, could promote the mRNA expression levels of the genes FLG, LOR, KRT10, and DSC1, which encode for essential proteins responsible for keratinocyte differentiation, by inhibiting STAT3 signaling. Furthermore, igalan exerts its antioxidant effect through activating the Nrf2 pathway, triggering the expression of some enzymes that contribute to preventing intracellular ROS generation during inflammation. Conclusion These findings indicate that igalan, via suppressing JAK/STAT3 signaling, could impair the production of pro-inflammatory chemokines and enhance expression levels of several genes involved in keratinocyte differentiation in AD-like stimulated keratinocytes.