Tamoxifen is effective against Leishmania and induces a rapid alkalinization of parasitophorous vacuoles harbouring Leishmania (Leishmania) amazonensis amastigotes

OBJECTIVES

This study was performed to investigate the activity of tamoxifen, an antioestrogen widely used in the treatment of breast cancer, against Leishmania.

METHODS

Drug activity was assessed in vitro against axenically grown promastigotes and amastigotes through cell counting or by measuring the cleavage of MTT, and against intracellular amastigotes by treating infected macrophage cultures and evaluating the number of intracellular parasites. Intravacuolar pH changes induced inside parasitophorous vacuoles of Leishmania (Leishmania) amazonensis-infected macrophages were evaluated using the fluorescent probes SNAFL-calcein and Acridine Orange.

RESULTS

Tamoxifen killed L. (L.) amazonensis promastigotes and amastigotes with 50% inhibitory concentrations (IC50) of 16.4 +/- 0.2 and 11.1 +/- 0.2 microM, respectively. The drug was also effective against Leishmania (Viannia) braziliensis, Leishmania (Leishmania) major, Leishmania (Leishmania) chagasi and Leishmania (Leishmania) donovani with IC(50) values ranging from 9.0 to 20.2 microM. Tamoxifen induced a rapid and long-lasting alkalinization of the vacuolar environment. We also provide evidence that tamoxifen is more effective against promastigotes and amastigotes at pH 7.5 when compared with cultures at pH 4.5.

CONCLUSIONS

Tamoxifen effectively kills several Leishmania species and its activity against the parasite is increased by a modulation of the host cell intravacuolar pH induced by the drug.

Survival of Trypanosoma cruzi metacyclic trypomastigotes within Coxiella burnetii vacuoles: differentiation and replication within an acidic milieu

Coxiella burnetii, the etiological agent of Q fever, is an obligate intracellular bacterium that resides within acidified vacuoles with secondary lysosomal characteristics. Infective stages of Trypanosoma cruzi, the causative agent of Chagas' disease, actively invade a wide variety of cells, a process followed by lysosomal recruitment. Recently, we have investigated and characterized early events that occur in Vero cells persistently colonized with C. burnetii when doubly infected with T. cruzi trypomastigote forms. Kinetic studies of trypomastigote transfer indicated that parasitophorous vacuoles (PV) of metacyclic trypomastigotes are rapidly and efficiently fused to C. burnetii vacuoles. Based on these observations we have investigated the behavior of metacyclic trypomastigotes within C. burnetii vacuoles beyond 12 h of co-infection inside Vero cells. Using indirect immunofluorescence with MAb against different developmental stages, it was possible to follow the T. cruzi differentiation process within C. burnetii vacuoles after up to 96 h post-invasion. We observed that metacyclic trypomastigotes began to differentiate after 12 h of infection, and 24 h later amastigotes were the prevailing forms within C. burnetii vacuoles. T. cruzi amastigote replication within C. burnetii vacuoles was confirmed using video and time-lapse confocal microscopy and around 36 h of co-infection, cytokinesis took about 70 min to occur. After 72 h, we observed that amastigote forms seemed to escape from C. burnetii vacuoles. Labeling of amastigotes within C. burnetii vacuoles using a polyclonal antibody to C9 complement protein suggested that TcTOX (T. cruzi hemolysin) could play a role in parasite escape from C. burnetii. We concluded that T. cruzi has an outstanding adaptation capability and can survive within a hostile milieu such as C. burnetii vacuoles.

Disruption of myofibrillar proteins in cardiac muscle of Calomys callosus chronically infected with Trypanosoma cruzi and treated with immunosuppressive agent

Calomys callosus (Rodentia: Cricetidae) chronically infected with CL strain of Trypanosoma cruzi undergo recrudescence of the acute phase when treated with the immunosuppressor cyclophosphamide. The distribution of cytoskeletal proteins in cardiac tissue of immunosuppressed animals was mapped by immunofluorescence and electron microscopy to evaluate myofibrillar distribution during the intracellular life cycle of T. cruzi. Cardiac muscle sections showed enhancement of myocarditis and parasite proliferation after immunosuppression. Immunofluorescence using monoclonal antibodies against myosin, actin, desmin, titin, tropomyosin, and troponin T demonstrated disruption and loss of contractile proteins, such as myosin and actin. Desmin and titin were irregularly distributed in close proximity to parasite nests. Ultrastructural observations confirmed alterations of cardiac cells with Z-line fragmentation, indistinguishable I-bands and A-bands, and loss of myofibrillar elements. The disruption of the muscle cell architecture was greater as infection progressed, probably as a result of increased myocarditis and physical displacement due to the activity of flagellated parasites.

Mammalian cell invasion and intracellular trafficking by Trypanosoma cruzi infective forms

Trypanosoma cruzi, the etiological agent of Chagas’ disease, occurs as different strains or isolates that may be grouped in two major phylogenetic lineages: T. cruzi I, associated with the sylvatic cycle and T. cruzi II, linked to the human disease. In the mammalian host the parasite has to invade cells and many studies implicated the flagellated trypomastigotes in this process. Several parasite surface components and some of host cell receptors with which they interact have been identified. Our work focused on how amastigotes, usually found growing in the cytoplasm, can invade mammalian cells with infectivities comparable to that of trypomastigotes. We found differences in cellular responses induced by amastigotes and trypomastigotes regarding cytoskeletal components and actin-rich projections. Extracellularly generated amastigotes of T. cruzi I strains may display greater infectivity than metacyclic trypomastigotes towards cultured cell lines as well as target cells that have modified expression of different classes of cellular components. Cultured host cells harboring the bacterium Coxiella burnetii allowed us to gain new insights into the trafficking properties of the different infective forms of T. cruzi, disclosing unexpected requirements for the parasite to transit between the parasitophorous vacuole to its final destination in the host cell cytoplasm.

Parameters affecting cellular invasion and escape from the parasitophorous vacuole by different infective forms of Trypanosoma cruzi

In this study we have examined certain aspects of the process of cell invasion and parasitophorous vacuole escape by metacyclic trypomastigotes and extracellular amastigote forms of Trypanosoma cruzi (G strain). Using Vero (and HeLa) cells as targets, we detected differences in the kinetics of vacuole escape by the two forms. Alcalinization of intercellular pH influenced both invasion as well as the escape from the parasitophorous vacuole by metacyclic trypomastigotes, but not the escape kinetics of extracellular amastigotes. We used sialic acid mutants as target cells and observed that the deficiency of this molecule facilitated the escape of both infective forms. Hemolysin activity was only detected in extracellular amastigotes and neither form presented detectable transialidase activity. Invasion of extracellular amastigotes and trypomastigotes in Vero cells was affected in different ways by drugs that interfere with host cell Ca2+ mobilization. These results are in line with previous results that indicate that metacyclic trypomastigotes and extracellular amastigote forms utilize mechanisms with particular features to invade host cells and to escape from their parasitophorous vacuoles.

Acidification modulates the traffic of Trypanosoma cruzi trypomastigotes in Vero cells harbouring Coxiella burnetii vacuoles

We studied the fate of different Trypanosoma cruzi trypomastigote forms after they invade Vero cells persistently colonised with Coxiella burnetii. When the invasion step was examined we found that persistent C. burnetii infection per se reduced only tissue-culture trypomastigote invasion, whereas raising vacuolar pH with Bafilomycin A1 and related drugs, increased invasion of both metacyclic and tissue-culture trypomastigotes when compared with control Vero cells. Kinetic studies of trypomastigote transfer indicated that metacyclic trypomastigotes parasitophorous vacuoles are more efficiently fused to C. burnetii vacuoles. The higher tissue-culture trypomastigote hemolysin and transialidase activities appear to facilitate their faster escape from the parasitophorous vacuole. Sialic acid deficient Lec-2 cells facilitate the escape of both forms. Endosomal-lysosomal sequential labelling with EEA1, LAMP-1, and Rab7 of the parasitophorous vacuoles formed during the entry of each infective form revealed that the phagosome maturation processes are also distinct. Measurements of C. burnetii vacuolar pH disclosed a marked preference for trypomastigote fusion with more acidic rickettsia vacuoles. Our results thus suggest that intravacuolar pH modulates the traffic of trypomastigote parasitophorous vacuoles in these doubly infected cells.

Features of host cell invasion by different infective forms of Trypanosoma cruzi

Through its life cycle from the insect vector to mammalian hosts Trypanosoma cruzi has developed clever strategies to reach the intracellular milieu where it grows sheltered from the hosts' immune system. We have been interested in several aspects of in vitro interactions of different infective forms of the parasite with cultured mammalian cells. We have observed that not only the classically infective trypomastigotes but also amastigotes, originated from the extracellular differentiation of trypomastigotes, can infect cultured cells. Interestingly, the process of invasion of different parasite infective forms is remarkably distinct and also highly dependent on the host cell type.