Inquiry of the susceptibility of sanguineous forms of plasmodium falciparum to apoptosis front the stimulatons with nitric oxide, choloroquine and staurosporine.
It is known that antibodies, nitric oxide and chloroquine inhibit P. falciparum growth, even though the mechanism of parasite death was never clearly elucidated. In the studies where parasite culture was used to access cell death in presence of antiparasite compounds, apoptosis was only investigated on the basis of DNA fragmentation using electrophoresis gel or TUNEL assays. Considering that apoptosis could represent a mechanism for maintenance of species, we decided to evaluate if the in vitro P. falciparum death induced by different treatments would be marked by apoptotic events. When S-nitroso-acetyl-penicillamine (SNAP - a nitric oxide producer), chloroquine or staurosporine were added in P. falciparum in vitro cultures, we observed by light microscopic as well as by flow cytometry that these compounds besides inhibit parasite growth, were also able to decrease the parasitemia levels of 24h treated cultures, when compared with initial culture (0h). Conversely, rabbit anti-plasmodial IgGs did not have any effect on plasmodial development. Unexpectedly, when DNA integrity was verified by TUNEL staining, only a few number of positively FITC-labeling parasites was detected. Furthermore, pretreatment of P. falciparum with a general caspase inhibitor was not able to prevent the parasite death. The lack of these apoptotic events together with parasite morphology showing a vacuolization-induced process with no signal of chromatin condensation, lead us to conclude that death of P. falciparum blood forms induced by pharmacological or immune stresses is not due to an apoptotic process, but to a vacuolization process similar to autophagy. This may be true even for parasite death induced by well characterized mammalian cell apoptosis inductor such as staurosporine.
Advisor:Maria de Fátima Ferreira da Cruz
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Date of Publication:11/24/2006