Objective: Many endogenous or exogenous factors, isolated or combined, can trigger dry skin disorder, leading to a water/lipids-depleted stratum corneum concomitant with uncomfortable rough and scaly skin surface. In a defensive reaction, the alteration of the skin barrier stimulates the production of cytokines to initiate homeostasis restoration but this can also induce an inflammatory response that further weakens the barrier. The two phenomena intertwining one another lead to the creation of a vicious circle, here called Inflamm'dryness, that maintains dry skin state. It is thus very important to investigate biological mechanisms involved in Inflamm'dryness to better manage dry skin.Methods: A 3D model mimicking dry skin has been developed. Adjustment of tape stripping level allowed to reproduce skin barrier alterations and resulting inflammation involved in dry skin. The effect of Helichrysum stoechas extract on this downward spiral was then investigated to validate the concept.Results: Tape-stripping permitted to successively remove the cell layers of the stratum corneum: the barrier function was altered and skin was inflamed creating a vicious circle, mimicking very dry skin prone to Inflamm'dryness. Helichrysum stoechas extract was not only able to resolve inflammation but also to reverse concurrently adverse tape-stripping effects and imparted significant structural and functional recovery of the barrier (e.g. on NMF and ceramides levels, TEWL, tissue organization). Conclusion: This 3D model reproduces Inflamm'dryness vicious circle presentin dry skin and highlights the importance of breaking this process to improve dry skin conditions. Helichrysum stoechas extract is a promising active ingredient for the management of dry skin.

Helichrysum stoechas (L.) Moench cell suspensions were analyzed by LC-ESI-QTOF, which highlighted the predominance of 3,5-O-dicaffeoylquinic acid (3,5-diCQA). Elicitation of H. stoechas cells with methyl jasmonate (200 mM) led to a massive rise in 3,5-diCQA, up to 5-fold-increase compared with control, reaching the concentration of 10.2 mg. g-1dry weight after 14 days of culture. Previous data showed that diCQA isomers are potent allelopathic compounds, thus the methanolic extracts of control and MeJa-elicited H. stoechas cells were tested for their phytotoxicity. With this in mind, activity on the seed germination and seedling growth of the model plant Lepidium sativum were tested. Phytotoxicity of both extracts occurred in a dose-dependent manner, with a greater activity of elicited cells extract. Indeed, in the concentration range from 0.31 to 0.83 mg. mL-1, the latter showed a significantly higher inhibition rate of L. sativum seedlings root growth, when compared to control cells extract. The data presented may contribute to explore new strategies towards the conception of bioherbicides from plant origin. To our knowledge, this study is the first report of the use of elicited plant cells grown in vitro as a raw material for the production of allelopathic metabolites.

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