Ultrastructural and proapoptotic-like effects of kaempferol in Giardia duodenalis trophozoites and bioinformatics prediction of its potential protein target

BACKGROUND: Kaempferol (KPF) is a flavonoid with antiparasitic activity including experimental giardiasis which mechanism of action is unknown. OBJECTIVE: To analyse the cytotoxic effects of KPF on Giardia duodenalis trophozoites and to identify a likely parasite target of this compound. METHODS: We used inhibitory concentrations of KPF (IC(25), IC(50) and IC(100)) and albendazole (ABZ) as reference drug. The ultrastructure of the trophozoites was analysed by transmission electron microscopy (TEM) whilst apoptosis/necrosis, production of reactive oxygen species (ROS) and cell cycle progression were assessed by flow cytometry (FCM) and confocal laser microscopy (CLM). Ligand-protein docking analyses were carried out using KPF structure from a drug library and crystal structure of a G. duodenalis aldose reductase (GdAldRed) homolog. RESULTS: KPF provoked appearance of perinuclear and periplasmic spaces devoid of cytosolic content and multilamellar structures. KPF induced proapoptotic death associated with partial arrest in the S phase without ROS production. Bioinformatics approaches predicted that GdAldRed is a viable KPF target (ΔG = -7.09 kCal/mol), exhibiting 92% structural identity and a similar coupling pattern as its human homolog. CONCLUSIONS: KPF exerted a proapoptotic effect on G. duodenalis trophozoites involving partial interruption of DNA synthesis without oxidative stress or structure damage to chromatin and cytoskeletal structures. GdAldRed is a likely target underlying its antigiardial activity.