Total sesquiterpene lactones isolated from Inula helenium L. attenuates 2,4-dinitrochlorobenzene-induced atopic dermatitis-like skin lesions in mice

Background: Inula helenium L. is an herb whose anti-inflammatory properties are attributed to its active components, the sesquiterpene lactones (SLs). Our previous study demonstrated that the total sesquiterpene lactones isolated from Inula helenium L. (TSL-IHL), consisting mainly of alantolactone (AL) and isoalantolactone (IAL), may have potential in the prevention and treatment of rheumatoid arthritis (RA). However, the effect of TSL-IHL on atopic dermatitis (AD) has not been studied yet.

Aim of the study: The present study evaluates the potential of TSL-IHL as a treatment for AD.

Methods/study designs: The effects of TSL-IHL on the expression of inflammatory genes and the activation of NF-κB signaling pathway in HaCat cells were examined by quantitative real-time PCR and western blotting, respectively, and compared with those of AL and IAL. The protective effect of TSL-IHL against AD was tested in a mouse model induced by 2,4-dinitrochlorobenzene (DNCB), in which AD-like skin lesions were induced in ICR mice by sensitizing once with 100 µl of 7% DNCB painted on their shaved back skin and then challenging with 20 µl of 0.2% DNCB five times on their right ears at 3 day intervals starting on day 5 post-sensitization.

Results: TSL-IHL, as well as AL and IAL, could all inhibit TNF-α-induced activation of NF-κB and the expression of TNF-α, IL-1, and IL-4 in HaCat cells in a dose-dependent manner in the range of 0.6-2.4 µg/ml. The topical application of TSL-IHL (1% W/W in emollient cream) attenuated DNCB-induced dermatitis severity and right ear swelling. The serum levels of IgE, TNF-α and IFN-γ in TSL-IHL-treated mice were reduced by 81.39%, 89.69%, and 87.85%, respectively, while the mRNA levels of IL-4, IL-5 and IL-13, in the back-skin lesions of TSL-IHL-treated mice were reduced by 39.21%, 40.62% and 48.12%, respectively, compared with the untreated controls. Histopathological examination showed that TSL-IHL treatment reduced epidermis/dermis thickening and dermal inflammatory infiltration in both ear and back skins.

Conclusions: We suggest that TSL-IHL inhibited the development of AD-like skin symptoms by regulating cytokine expression and may be an effective alternative therapy for AD.