Igalan from Inula helenium modulates the immune response and inflammation in RAW 264.7 macrophages and HaCaT keratinocytes

Abstract

Inula helenium L. is a herb belonging to the Asteraceae family and contains an abundant amount of sesquiterpene lactones, which show the potential on the treatment of inflammatory diseases. Although igalan is one of the main sesquiterpene lactones found in I. helenium, there have been very few studies conducted to evaluate its biological activities. This study aimed to assess the anti-inflammatory capacity of igalan in vitro, specifically on the atopic dermatitis-like skin inflammation model, using the RAW 264.7 macrophages and HaCaT keratinocytes. RAW 264.7 cells were pre-treated with igalan in two hours then activated by lipopolysaccharide (LPS) in additional 18 hours. HaCaT cells, after 2 h-pretreatment with igalan, were stimulated with interleukin-4 (IL-4) or combination of tumor necrosis alpha (TNF-α) and interferon gamma (IFN-γ) in different periods. The results demonstrated the suppression of igalan on the NF-κB activation by inhibiting the degradation of IκB as well as the subsequent translocation of the p65 subunit to the nucleus in both models. By suppressing the expression of the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), igalan reduced the nitric oxide (NO) production in LPS-stimulated RAW 264.7 cells. In TNF-α/IFN-γ stimulated HaCaT cells, igalan effectively down-regulated the expression of several T helper 2 (Th2) chemokine genes, such as thymus-and activation-regulated chemokine (TARC/CCL17), macrophage-derived chemokine (MDC/CCL22) and regulated upon activation, normal T cell expressed and secreted (RANTES/CCL5), which are considered as biomarkers in the severity of atopic dermatitis. In addition, igalan suppressed the activation of both JAK/STAT3 and p44/42 MAPK signaling pathway, thus improved skin barrier function by regulating the IL-4-mediated changes in the mRNA expression levels of following genes: filaggrin (FLG), loricrin (LOR), keratin (KRT10) and desmocollin (DSC1), which encode for the essential structural components in keratinocyte differentiation. To conclude, this study revealed the potent anti-inflammatory and anti-atopic dermatitis activities of igalan, thus suggesting its promising effect on the treatment of inflammatory skin diseases.