Avaliação do efeito de drogas sobre o processo de diferenciação de Giardia lamblia e na interação com células epiteliais intestinais in vitro

Abstract

The protozoan of the genus Giardia are considered the most primitive eukaryotic cells in evolutive scale. The main charactheristics are the ability to differentiate in two forms, the infective and inert cyst, and the motil and vegetative trophozoite in which its adhesion to gut epithelium charactherizes the parasitism. Its life cycle comprises the encystation, that is the transformation of the trophozoite in cyst, whereas the excystation is characterized by the inverse. Giardiasis is one of the main parasitic diseases that affect children from regions with precarious basic sanitation in Brazil. Current treatment in humans mainly involves the benzimidazole family drugs. Other drugs such as pyrantel pamoate (PP) and metronidazole (MZ) are more commonly used in veterinary treatments, the latter one being rarely used because it causes side effects, i.e. inflammation of the intestinal mucosa. Most drugs act on giardia trophozoites and bind primarily to the microtubule structures of the giardia cytoskeleton. Regarding treatment, the main questions about the effectiveness are based on healing, and secondarily, on the removal of cysts. There are in the literature, no data evaluating how infective Giardia cysts are when eliminated during treatment, or even a study to evaluate possible synergistic activities of the major anti-parasitic drugs for the treatment against Giardia. Thus, this study evaluated these two questions in an in vitro model with the main drugs used in human and veterinary clinical treatment. In the first study, we analyzed the effects on the differentiation benzimidazoles Giardia and their viability after treatment. In the second work, on the trophozoite form the MZ and PP were combined or not, in order to verify synergistic action against the parasite but having focus to not reduce the viability of the intestinal cells in co-culture. The results demonstrated that although albendazole (AB) did not completely inhibit encystation, even at low doses there was 100% inhibition of excystation. Transmission electron microscopy results revealed that the ultrastructure of the ventral disc as well as the flagella depolymerized in amorphous bodies in the cystic form. This was probably the main factor that prevented the reorganization of the ventral disc and associated structures during the excystation. The inability to excyst described herein has made AB as the main candidate drug in order to be effective in both treatment and environment, taking it free of contamination. In the second study, according to the isobolograms generated from the trophozoites count under the effects of drugs, it revealed that there was a synergistic effect between the MZ and PP, i.e., the lowest concentration of MZ potentiated the effect of PP, leading to inviability of the trophozoites with no effects in host cells under the co-culture. The results indicated that in addition to the excellent prognosis for the treatment of giardia, the drugs tested in vitro have the potential both to treat giardiasis and to inhibit their spread by host during treatment. In addition, on trophozoites, MZ when combined with the PP has the desired properties for an effective treatment with fewer adverse effects on intestinal cells.