Peptic ulcers are currently treated with various drugs, all having serious side effects. The aim of this study was to evaluate the gastroprotective activity of calein D (from Calea urticifolia), a sesquiterpene lactone with a germacrane skeleton. Gastric lesions were induced in mice by administering ethanol (0.2 mL) after oral treatment with calein D at 3, 10 and 30 mg/kg, resulting in 13.15 ± 3.44%, 77.65 ± 7.38% and 95.76 ± 2.18% gastroprotection, respectively, to be compared with that of the control group. The effect found for 30 mg/kg of calein D was not reversed by pretreatment with N^G-nitro-l-arginine methyl ester (l-NAME, 70 mg/kg, ip), indomethacin (10 mg/kg, sc) or N-ethylmaleimide (NEM, 10 mg/kg, sc). Hence, the mechanism of action of calein D does not involve NO, prostaglandins or sulfhydryl compounds. Calein D was more potent than carbenoxolone, the reference drug. The findings for the latter are in agreement with previous reports.

Linearolactone (LL) is a neo-clerodane type diterpene that has been shown to exert giardicidal effects; however, its mechanism of action is unknown. This work analyzes the cytotoxic effect of LL on Giardia intestinalis trophozoites and identifies proteins that could be targeted by this active natural product. Increasing concentrations of LL and albendazole (ABZ) were used as test and reference drugs, respectively. Cell cycle progression, determination of reactive oxygen species (ROS) and apoptosis/necrosis events were evaluated by flow cytometry (FCM). Ultrastructural alterations were analyzed by transmission electron microscopy (TEM). Ligand–protein docking analyses were carried out using the LL structure raised from a drug library and the crystal structure of an aldose reductase homologue (GdAldRed) from G. intestinalis. LL induced partial arrest at the S phase of trophozoite cell cycle without evidence of ROS production. LL induced pronecrotic death in addition to inducing ultrastructural alterations as changes in vacuole abundances, appearance of perinuclear and periplasmic spaces, and deposition of glycogen granules. On the other hand, the in silico study predicted that GdAldRed is a likely target of LL because it showed a favored change in Gibbs free energy for this complex.

Linearolactone (LL) isolated from Salvia polystachya presents antiparasitic activity against E. histolytica and G. lamblia through ROS production, an apoptosis-like process, and alteration of the actin cytoskeleton. This effect limits the invasion and spread of parasites during host infection. However, the possible toxicological effects or the molecular mechanisms by which LL affects the E. histolytica mobility are still not understood. LL could act as an inhibitor of accessory cytoskeletal proteins, such as myosin, calreticulin, and calpain to achieve this end. The aim of this study was to determine the pharmacological and toxicological properties of LL via bioinformatic analyses to find therapeutic targets and to understand the action mechanism on the actin cytoskeleton against E. histolytica. The pharmacological activities, toxicological risks, and molecular targets of LL were determined using free software such as Molsoft© to define the bioactivity through comparison with standard drugs [¹], Molinspiration© to calculate physicochemical properties [²], ToxiM© to determine possible intestinal permeability [³,⁴], SuperCYPsPred© to predict drug metabolism via the cytochrome-P450 system [⁵,⁶], and SEA© to find proteins with binding sites for the active compounds through an inverse protein–ligand approach [⁷,⁸]. Molecular docking with key proteins for the pathogenic activity of E. histolytica trophozoites, such as myosin-II and calreticulin, was performed with AutoDock-Vina and UCSF-Chimera. Results revealed that LL presents a drug-likeness of −0.55 and ToxiM of 0.958 due to medium toxicity associated with interactions in nuclear receptors (0.66), GPCR ligands (0.65), and enzymatic inhibitions (0.47) related to the cytochrome-P450 system (CYP3A4, low). Results indicate that LL is a hydrophobic molecule (LogP: 1.59) with intermediate intestinal absorption (TPSA: 65.75, CACO-2 permeability) and medium blood–brain barrier penetration (3.86). SEA analysis demonstrated that the potential target pharmacophores are OPRK1 (p-Value: 6.49 × 10⁻³⁷, Max TC: 0.49) and NLRP3 (p-Value: 3.90 × 10⁻¹⁹, Max TC: 0.36) in humans. Molecular docking of LL with E. histolytica proteins showed high affinity to ATP-binding catalytic sites in the heavy-chain (GLU-187.A, THR-186.A, ASN-234.B) of myosin-II (−8.30 Kcal/mol), as well as in chain A and C (LYS-199.A, LYS-152.C) of calreticulin (−8.77 Kcal/mol). As for conclusions, LL is a compound with possible moderate toxicity, sedative effects on CNS, and anti-inflammatory properties. In addition, LL has antiparasitic activity involving the immobilization of E. histolytica trophozoites through interactions with accessory proteins from the actin cytoskeleton such as myosin-II and calreticulin. These proteins are present in the parasite and are fundamental to amoebic liver abscess formation during host infection. Therefore, LL could be a therapeutic alternative to the amoebiasis treatment and provide a leading compound for drug discovery against parasitic diseases, but in-depth studies are necessary to confirm these claims.