Dibenzylbutane neolignans from Saururus cernuus L. (Saururaceae) displayed anti-Trypanosoma cruzi activity via alterations in the mitochondrial membrane potential

Saururus cernuus L. (Saururaceae) is one of the perennial freshwater Angiosperms, distributed throughout the Southeastern of United States and introduced in other regions of America, including Brazil [1]. This species has been widely used in folk medicine for the treatment of inflammation of the breasts, bladder, kidneys, and as a sedative [1-2]. Chemically, S. cernuus accumulates lignans, alkaloids, and terpenoids with several biological activities including antitumor, anti-inflammatory and antiviral [3-9]. The MeOH extract from the leaves of S. cernuus displayed in vitro activity against trypomastigote forms of T. cruzi (100% of parasite death at 30 200 µg/mL), suggesting the presence of bioactive compounds. Thus, the bioactivity-guided fractionation was carried out, leading to the isolation of three related neolignan derivatives, identified as threo-austrobailignan-5 (1), threo-austrobailignan-6 (2) and threo-dihydroguaiaretic acid (3). Anti-T. cruzi activity of compounds 1 – 3 was performed against cell-derived trypomastigotes and intracellular amastigotes. Additionally, the mammalian cytotoxicity was investigated using NCTC cells. Compound 2 was the most effective against extracellular trypomastigotes with IC50 of 3.7 μM, while compound 3 showed activity in both clinically relevant forms of the parasite, trypomastigotes and amastigotes, with IC50 values of 7.0 and 16.2 μM, respectively. However, the structurally related compound 1 was inactive. Based on these results, compounds 2 and 3 were selected to evaluate the mechanism of cellular death. Compound 2 induced alteration in the plasma membrane permeability and consequently in the ROS levels after 120 min of incubation. By using flow cytometry and fluorescence microscopy, compound 3 showed alterations in the mitochondrial membrane potential (ΔΨm) of trypomastigotes. Considering the promising chemical and biological properties of the isolated neolignans, these compounds could be used as starting points to develop new lead compounds for Chagas disease.