Phytochemical analysis and trypanocidal activity of Marrubium incanum Desr.

The rationale inspiring the discovery of lead compounds for the treatment of humanparasitic protozoan diseases from natural sources is the well-established use of medicinal plantsin various systems of traditional medicine. On this basis, we decided to select an overlookedmedicinal plant growing in central Italy,Marrubium incanumDesr.(Lamiaceae), which hasbeen used as a traditional remedy against protozoan diseases, and to investigate its potentialagainst Human African trypanosomiasis (HAT). For this purpose, we assayed three extracts ofdifferent polarities obtained from the aerial parts ofM. incanum—namely, water (MarrInc-H2O),ethanol (MarrInc-EtOH) and dichloromethane (MarrInc-CH2Cl2)—againstTrypanosoma brucei(TC221),with the aim to discover lead compounds for the development of antitrypanosomal drugs. Theirselectivity index (SI) was determined on mammalian cells (BALB/3T3 mouse fibroblasts) as acounter-screen for toxicity. The preliminary screening selected the MarrInc-CH2Cl2extract as themost promising candidate against HAT, showing an IC50value of 28μg/mL. On this basis, columnchromatography coupled with the NMR spectroscopy of a MarrInc-CH2Cl2extract led to the isolationand identification of five compounds i.e. 1-α-linolenoyl-2-palmitoyl-3-stearoyl-sn- glycerol (1),1-linoleoyl-2-palmitoyl-3-stearoyl-sn-glycerol (2), stigmasterol (3), palmitic acid (4), and salvigenin(5). Notably, compounds3and5were tested onT. brucei, with the latter being five-fold more activethan the MarrInc-CH2Cl2extract (IC50=5.41±0.85 and 28±1.4μg/mL, respectively). Furthermore.the SI for salvigenin was>18.5, showing a preferential effect on target cells compared with thedichloromethane extract (>3.6). Conversely, stigmasterol was found to be inactive. To complete thework, also the more polar MarrInc-EtOH extract was analyzed, giving evidence for the presence of2”-O-allopyranosyl-cosmosiin (6), verbascoside (7), and samioside (8). Our findings shed light on thephytochemistry of this overlooked species and its antiprotozoal potential, providing evidence for thepromising role of flavonoids such as salvigenin for the treatment of protozoal diseases.