Comparative studies of nifurtimox uptake and metabolism by drug-resistant and susceptible strains of Trypanosoma cruzi.

1. Nifurtimox uptake and metabolism by epimastigote forms of three strains of Trypanosoma cruzi (Basileu, Y, YuYu) with different drug responsiveness in mice experimental infections were compared. 2. Statistical analysis of the results demonstrated no correlation between the ability of the strains to catalyze nifurtimox redox-cycling (Basileu = Y = YuYu) nor nifurtimox multiple electron reduction (Basileu = Y greater than Y) and drug susceptibility (Basileu greater than Y greater than YuYu). 3. A partial correlation however, was observed between drug responsiveness and nifurtimox uptake (Basileu greater than Y = YuYu). 4. The results suggest that drug uptake may be more important than drug metabolism in modulating resistance to nifurtimox in T. cruzi strains.

Effect of the host specific treatment in the phagocytosis of Trypanosoma cruzi blood forms by mouse peritoneal macrophages.

Single doses of drugs active against Trypanosoma cruzi (megazol, nifurtimox and benznidazole) induce a rapid clearance of the blood parasites in experimentally infected mice. Furthermore, the in vitro phagocytosis and intracellular destruction by mouse peritoneal macrophage of blood forms collected from the treated animals is strongly enhanced as compared with parasites from untreated controls. The uptake of the blood forms by macrophages is significantly higher with megazol than with benznidazole and nifurtimox, a finding that concurs with data showing that megazol is also the most active compound in the living host. The possibility that macrophages participate in a synergic effect between the host immune response and chemotherapeutic effect is discussed.

Susceptibility and natural resistance of Trypanosoma cruzi strains to drugs used clinically in Chagas disease.

The susceptibility and natural resistance to two nitroheterocyclic derivatives used clinically in Chagas disease (nifurtimox and benznidazole) were investigated in 47 Trypanosoma cruzi strains isolated from human patients, domestic vectors and sylvatic reservoirs or vectors. A large gradient of drug efficacy from 0% to 100% was detected. Drug susceptibility apparently related to geographical distribution of some T. cruzi strains was also observed. Drug resistance was identified among T. cruzi populations isolated from sylvatic vectors from an area where autochthonous human Chagas disease does not exist. Thus, natural drug-resistance of sylvatic strains might be a way of introducing this character into a T. cruzi domestic cycle. Most of the 47 studied strains were either sensitive or resistant to both compounds, an intriguing finding considering that nifurtimox and benznidazole apparently have different mechanisms of action against T. cruzi.

Primaquine can mediate hydroxyl radical generation by Trypanosoma cruzi extracts.

Primaquine increases the NAD(P)H dependent oxygen consumption and hydroxyl radical generation by extracts of Trypanosoma cruzi, the causative agent of Chagas' disease. Spin-trapping studies show that hydroxyl radical yield is completely inhibited by catalase and slightly increased by SOD, indicating that radical generation is dependent on the pair primaquine-NAD(P)H and their interaction product, H2O2. Primaquine effects upon Trypanosoma cruzi extracts are compared with those obtained with nifurtimox, a compound effective in the treatment of Chagas' disease. The observed similarity suggests that hydroxyl radical may be involved in the antiprotozoan activity of primaquine.

A rapid method for testing in vivo the susceptibility of different strains of Trypanosoma cruzi to active chemotherapeutic agents.

A method is described which permits to determine in vivo and in a short period of time (4-6 hours) the sensitivity of T. cruzi strains to known active chemotherapeutic agents. By using resistant- and sensitive T. cruzi strains a fairly good correlation was observed between the results obtained with this rapid method (which detects activity against the circulating blood forms) and those obtained with long-term schedules which involve drug administration for at least 20 consecutive days and a prolonged period of assessment. This method may be used to characterize susceptibility to active drugs used clinically, provide information on the specific action against circulating trypomastigotes and screen active compounds.

Ultrastructural alterations of intracellular stages and effects of blood forms of Trypanosoma cruzi induced in vivo by 2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4- thiadiazole.

Um estudo com microscopia eletronica mostrou que a administracao de dose unica (500 mg/kg, p.o.) do composto 2-amino-5-1-metil-5-nitro-2-imidazolil)-1,3,4- tiadiazole induz, em camundongos inoculados com T. cruzi, lesoes degenerativas das formas intracelulares do parasita. Alteracoes ultra estruturais sao observadas 6 ho ras apos a administracao da droga e destruicao ocorre em 18-36 horas. Tripamastigotas tambem desaparecem do sangue circulante dos animais 4-6 horas apos o tratamento. O efeito em ambos os estagios evolutivos do T. cruzi e aparentemente responsavel pelos efeitos in vivo desse derivado que e o mais ativo composto ja testado em nosso laboratorio na doenca de Chagas

A rapid method for testing in vivo the susceptibility of different strains of Trypanosoma cruzi to active chemotherapeutic agents.

No presente trabalho descreve-se um metodo que permite determinar in vivo e em curto espaco de tempo (4-6 horas) a sensibilidade de cepas de T. cruzi a agentes terapeuticos ativos na doenca de Chagas.Usando-se cepas sensiveis e resistentes aos medicamentos foi possivel observar uma boa correlacao entre os resultados obtidos com o metodo rapido (que detecta atividade contra as formas circulantes do parasita) e aqueles obtidos com esquema de acao prolongada que envolve a administracao da droga por 20 dias e posterior avaliacao.Esse metodo pode ser usado para caracterizar a sensibilidade de cepas a drogas ativas usadas clinicamente, fornecer informacoes especificas sobre a acao medicamentosa em tripomastigotas sanguineos e, eventualmente, para triagem de novos composto

Cryopreservation of Trypanosoma cruzi bloodstream forms.

Recovery rates of T. cruzi bloodstream forms subjected to several methods of cryopreservation in liquid nitrogen and at -73 C are reported. Inoculations of animals with cryopreserved and nonpreserved trypomastigotes revealed that prolonged storage at -196 C apparently did not change the biologic characteristics of different T. cruzi strains. The reproducibility and consistency of results suggest that "cryobanks" or "reference centers" may be established.