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Abstract

Arnica montana L. (Arnica) has a long tradition of use in treating inflammation and promoting tissue regeneration after blunt injuries such as contusions or bruises. Various immune cell types, including T cells, were shown to be critically involved in the normal muscle healing process in response to trauma. They invade the injured site in a spatiotemporally controlled manner and rapidly induce a proinflammatory milieu, which is necessary for proper wound healing. Prolonged presence of T cells, however, was found to be a hallmark of delayed muscle healing. Therefore, investigating the effects of Arnica preparations on T cell functions offers the possibility to gain novel insights and explanations regarding Arnica’s mode of action. In this thesis, differentially prepared Arnica extracts and the lead compounds Thymol and Helenalin were directly compared for their immunomodulatory potential using primary human T cells. The three selected Arnica extracts as well as the lead compounds inhibited T cell activation, measured by analyzing CD25 surface expression. Similarly, all test drugs diminished the proliferative capacity of T cells. Both, a reduced production of the growth factor IL-2 as well as limited affinity of the IL-2 receptor (IL-2R) due to lacking IL-2Ra chain (CD25) can explain the decreased cell division rate. Despite similar functional effects, different molecular mechanisms underlying drug action were identified. While the tested root extract specifically inhibited DNA binding of the transcription factor NFkB (p65), the fermented aqueous extract prepared from the whole plant interfered with NFAT-dependent gene expression. In contrast, the hydroalcoholic whole plant extract diminished NFkB DNA binding as well as NFAT-dependent gene expression without reaching statistical significance. The molecular mode of action identified for the lead compounds was again different. Thymol interfered with intracellular signaling at various steps, including NFkB nuclear translocation and transcriptional activity as well as calcium signaling and NFAT-dependent gene expression. Helenalin specifically inhibited nuclear translocation of NFkB (p50). In order to draw conclusions about which phytochemical compounds might mediate the extracts’ effects, the plant extracts were analyzed by HPLC-MS/MS followed by tentative identification of extract components. This analysis provided interesting results, since Helenalin was not found at detectable levels in any of the three Arnica extracts. Instead, Caffeoylquinic acid derivatives constituted the main identified substance group. Testing isolated (Mono-, di-, and tri-) Caffeoylquinic acids, however, revealed that the effects observed upon treating T cells with Arnica extract were not mimicked by Caffeoylquinic acids. Given the inhibitory effect on T cell functions identified in this thesis, Arnica preparations might indeed have a positive influence on restoring the normal muscle healing process in the setting of delayed tissue repair. In contrast, interfering with T cell activity too early during normal muscle regeneration might rather have detrimental effects by inhibiting the initial inflammatory phase, which is essential for normal healing.