Helenalin

Helenalin is a natural sesquiterpene lactone with antiphlogistic and antitumor effects that occurs in arnica species(Arnica chamissonis, Arnica montana) and other Asteraceae (nasturtium, elecampane).
Helenalin selectively inhibits the transcription factor NF-κB. In vitro, helenalin has been shown to inhibit telomerase gene expression; the substance also exhibits anti-trypanosomal and antimicrobial activity. Experimentally, the substance inhibits melanin productionin melanocytes.
Helenalin is highly toxic and has considerable allergenic potency. Helenalin is the actual cause of arnica sensitization (see arnica below) and has a cardiotoxic effect in high doses.

1. Hausen BM et al. (1978) The sensitizing capacity of Compositae plants. I. Occupational contact dermatitis from Arnica longifolia Eaton. Contact Dermatitis 4:3-10.
2. Jimenez V et al. (2014) Natural sesquiterpene lactones induce programmed cell death in Trypanosoma cruzi: a new therapeutic target? Phytomedicine 21:1411-1418.
3. Kordi S et al. (2016) A comparison of the inhibitory effect of nano-encapsulated helenalin and free helenalin on telomerase gene expression in the breast cancer cell line, by real-time PCR. Artif Cells Nanomed Biotechnol 44:695-703.
4. Merfort I (2011)Perspectives on sesquiterpene lactones in inflammation and cancer. Curr Drug Targets 12:1560-1573.
5. Song FN et al. (2014) RANKL promotes migration and invasion of hepatocellular carcinoma cells via NF-κB-mediated epithelial-mesenchymal transition. PLoS One 9:e108507.
6. Usui K et al.(2015) Identification of HSP70-inducing activity in Arnica montana extract and purification and characterization of HSP70-inducers. J Dermatol Sci 78:67-75.
7. Zhang Z et al.(2014) The inhibitory effect of helenalin on telomerase activity is attributed to the alkylation of the CYS445 residue: evidence from QM/MM simulations. J Mol Graph Model 51:97-103.
8. https://www.bundessortenamt.de/bsa/media/Files/BSL/bsl_arznei_2002.pdf