In Vitro Metabolism of Helenalin Acetate and 11α,13-Dihydrohelenalin Acetate: Natural Sesquiterpene Lactones from Arnica

Abstract

Arnica tincture is a herbal medicinal preparation with anti-inflammatory activity which is used traditionally for the topical treatment of blunt injuries as well as rheumatic muscle and joint complaints. Its main bioactive constituents are sesquiterpene lactones (STLs) of the helenalin and 11α,13-dihydrohelenalin types. Besides the mentioned activity, the tincture and its isolated STLs have antileishmanial activity. In a recent in vivo study, a treatment with Arnica tincture cured cutaneous Leishmaniasis (CL) in a golden hamster model. CL is a neglected tropical disease affecting more than two million people every year, for which new treatments are urgently needed. In order to use Arnica tincture on open CL lesions of human patients, it is important to know how the constituents are metabolized. Therefore, in vitro metabolism experiments with liver microsomes of different species (rat, pig and human) were performed with the Arnica STLs helenalin acetate and 11α,13-dihydrohelenalin acetate. Phase I and phase II metabolism experiments were performed, as well as a combination of both. Glutathione conjugation plays a major role in the metabolism of these STLs, as could be expected based on previous reports on their reactivity. Besides glutathione conjugates, several other metabolites were formed, e.g., water conjugates and hydroxides. Our results show for the first time a detailed picture of the metabolism of Arnica STLs. The fast and extensive formation of glutathione conjugates makes it unlikely that low absorbed levels of these compounds, as expected after dermal absorption from Arnica tincture, which could be of toxicological concern.

Therapeutic Efficacy of Arnica in Hamsters with Cutaneous Leishmaniasis Caused by Leishmania braziliensis and L. tropica

“…The analytical details of this method have been published very recently [ 23 ]. The STLs were isolated based on the description in [ 24 ] and with a purity of >95% (determined by 1 H-NMR spectroscopy, see Figures S13–S19, Supplementary Materials ).…”

“…For the LC-MS analysis, all SPE eluates (receptor fluid samples and skin wash solution samples) and methanolic extracts (adhesive tape with stratum corneum samples and the remaining skin samples) were dried and the residues were dissolved in 250 µL of water/acetonitrile (95/5, v / v ). The LC-MS parameters are described in [ 24 ]. An injection volume of 20 µL was used.…”

Fungal Biotransformation of Chlordiazepoxide and Evaluation of Type and Kinetics of Fungal Enzyme

“…Fungal metabolism studies were proved as potential suitable methods because of their inherent enzymatic systems which can produce variety of chemical compounds when compared to synthetic procedures. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] In this context, fungal biotransformation studies are essential to produce active metabolite of chlordiazepoxide by fungi and also to develop microbial model for 3A4 enzyme. Hence, in present study, screening of fungi for their ability to biotransform chlordiazepoxide was conducted to identify the fungi which could be able to biotransform the chlordiazepoxide.…”