A Triazole Hybrid of Neolignans as a Potential Antileishmanial Agent by Triggering Mitochondrial Dysfunction

In the search for new compounds with antileishmanial activity, we synthesized a triazole hybrid analogue of the neolignans grandisin and machilin G (LASQUIM 25), which was previously found highly active against both promastigotes and intracellular amastigote forms of Leishmania amazonensis. In this work, we investigated the leishmanicidal effects of LASQUIM 25 to identify the mechanisms involved in the cell death of L. amazonensis promastigotes. Transmission electron microscopy (TEM) analysis showed marked effects of LASQUIM 25 (IC50 = 7.2 µM) on the morphology of promastigote forms, notably on mitochondria. The direct action of the triazole derivative on the parasite was noticed over time from 2 h to 48 h, and cells displayed several ultrastructural alterations characteristic of apoptotic cells. Also, flow cytometric analysis (FACS) after TMRE staining detected changes in mitochondrial membrane potential after LASQUIM 25 treatment (64.83% labeling versus 83.38% labeling in nontreated cells). On the other hand, FACS after PI staining in 24 h-treatment showed a slight alteration in the integrity of the cell membrane, a necrotic event (16.76% necrotic cells versus 3.19% staining in live parasites). An abnormal secretion of lipids was observed, suggesting an exocytic activity. Another striking finding was the presence of autophagy-related lysosome-like vacuoles, suggesting an autophagic cell death that may arise as consequence of mitochondrial stress. Taken together, these results suggest that LASQUIM 25 leishmanicidal mechanisms involve some degree of mitochondrial dysregulation, already evidenced by the treatment with the IC50 of this compound. This effect may be due to the presence of a methylenedioxy group originated from machilin G, whose toxicity has been associated with the capacity to generate electrophilic intermediates.

Synthesis and Structure-Activity Relationships of a Series of Aporphine Derivatives with Antiarrhythmic Activities and Acute Toxicity

Some aporphine alkaloids, such as crebanine, were found to present arrhythmic activity and also higher toxicity. A series of derivatives were synthesized by using three kinds of aporphine alkaloids (crebanine, isocorydine, and stephanine) as lead compounds. Chemical methods, including ring-opening reaction, bromination, methylation, acetylation, quaternization, and dehydrogenation, were adopted. Nineteen target derivatives were evaluated for their antiarrhythmic potential in the mouse model of ventricular fibrillation (VF), induced by CHCl3, and five of the derivatives were investigated further in the rat model of arrhythmia, induced by BaCl2. Meanwhile, preliminary structure-activity/toxicity relationship analyses were carried out. Significantly, N-acetamidesecocrebanine (1d), three bromo-substituted products of crebanine (2a, 2b, 2c), N-methylcrebanine (2d), and dehydrostephanine (4a) displayedantiarrhythmic effects in the CHCl3-induced model. Among them, 7.5 mg/kg of 2b was able to significantly reduce the incidence of VF induced by CHCl3 (p<0.05), increase the number of rats that resumed sinus rhythm from arrhythmia, induced by BaCl2 (p<0.01), and the number of rats that maintained sinus rhythm for more than 20 minutes (p<0.01). Therefore, 2b showed remarkably higher antiarrhythmic activity and a lower toxicity (LD50=59.62 mg/kg, mice), simultaneously, indicating that 2b could be considered as a promising candidate in the treatment of arrhythmia. Structural-activity analysis suggested that variationsin antiarrhythmic efficacy and toxicity of aporphines were related to the C-1,C-2-methylenedioxy group on ring A, restricted ring B structural conformation, N-quaternization of ring B, levoduction of 6a in ring C, and the 8-, 9-, 10-methoxy groups on ring D on the skeleton.

Antiproliferative Aporphine Alkaloids from Litsea glutinosa and Ethnopharmacological Relevance to Kuuku I’yu Traditional Medicine

Australian Aboriginal people have a long history of relying on plants for the treatment of various ailments and illnesses. Our ongoing collaborative research project initiated by Chuulangun Aboriginal Corporation (Cape York, Australia) has recently focussed on revealing whether Kuuku I’yu plant medicines possess anticancer-related activities and the chemistry responsible for this. Here, we present results from a study of the plant Litsea glutinosa, used traditionally for the treatment of gastrointestinal disorders. Four known aporphine alkaloids N-methylactinodaphnine (1), boldine (2), N-methyllaurotetanine (3), and isoboldine (4) were isolated by activity-guided fractionation and tested for cytotoxicity against HT29, SKMEL28, and primary human keratinocytes. Compound 1 was the most cytotoxic and this observation may be explained by the presence of a 1,2-methylenedioxy group. In silico docking revealed that a plausible mechanism for the observed cytotoxicity is the stabilization of a topoisomerase II (β) DNA–enzyme complex. The ethnopharmacological relevance of this study is discussed in the context of researching and using traditional knowledge in biomolecular discovery.