Stage-specific polyamine metabolism in Trypanosoma cruzi

Protists: Eukaryotic single-celled organisms and the functioning of their organelles

Organelles are membrane bound structures that compartmentalize biochemical and molecular functions. With improved molecular, biochemical and microscopy tools the diversity and function of protistan organelles has increased in recent years, providing a complex panoply of structure/function relationships. This is particularly noticeable with the description of hydrogenosomes, and the diverse array of structures that followed, having hybrid hydrogenosome/mitochondria attributes. These diverse organelles have lost the major, at one time, definitive components of the mitochondrion (tricarboxylic cycle enzymes and cytochromes), however they all contain the machinery for the assembly of Fe-S clusters, which is the single unifying feature they share. The plasticity of organelles, like the mitochondrion, is therefore evident from its ability to lose its identity as an aerobic energy generating powerhouse while retaining key ancestral functions common to both aerobes and anaerobes. It is interesting to note that the apicoplast, a non-photosynthetic plastid that is present in all apicomplexan protozoa, apart from Cryptosporidium and possibly the gregarines, is also the site of Fe-S cluster assembly proteins. It turns out that in Cryptosporidium proteins involved in Fe-S cluster biosynthesis are localized in the mitochondrial remnant organelle termed the mitosome. Hence, different organisms have solved the same problem of packaging a life-requiring set of reactions in different ways, using different ancestral organelles, discarding what is not needed and keeping what is essential. Don't judge an organelle by its cover, more by the things it does, and always be prepared for surprises.

Trypanosoma cruzi Coexpressing Ornithine Decarboxylase and Green Fluorescence Proteins as a Tool to Study the Role of Polyamines in Chagas Disease Pathology

Polyamines are essential for Trypanosoma cruzi, the causative agent of Chagas disease. As T. cruzi behaves as a natural auxotrophic organism, it relies on host polyamines biosynthesis. In this paper we obtained a double-transfected T. cruzi parasite that expresses the green fluorescent protein (GFP) and a heterologous ornithine decarboxylase (ODC), used itself as a novel selectable marker. These autotrophic and fluorescent parasites were characterized; the ODC presented an apparent Km for ornithine of 0.51 ± 0.16 mM and an estimated V_max value of 476.2 nmoles/h/mg of protein. These expressing ODC parasites showed higher metacyclogenesis capacity than the auxotrophic counterpart, supporting the idea that polyamines are engaged in this process. This double-transfected T. cruzi parasite results in a powerful tool—easy to follow by its fluorescence—to study the role of polyamines in Chagas disease pathology and in related processes such as parasite survival, invasion, proliferation, metacyclogenesis, and tissue spreading.

Polyamine metabolism in Trypanosoma cruzi: studies on the expression and regulation of heterologous genes involved in polyamine biosynthesis

Biochemical studies have shown that Trypanosoma cruzi and Toxoplasma gondii are the only eukaryotic organisms so far described which are auxotrophic for polyamines. Both parasites are unable to carry out the de novo biosynthesis of putrescine, and therefore they need the addition of exogenous polyamines to the culture medium for their normal proliferation. Further investigations at the molecular level have demonstrated that the wild-type T. cruzi genome does not contain ornithine or arginine decarboxylase-like nucleic acid sequences, and that the corresponding genes have been presumably lost during evolution. Since T. cruzi behaves as a deletion mutant for ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) genes, this parasite has been selected to study the regulation of the expression of heterologous genes involved in polyamine biosynthesis in other organisms. The resulting transgenic parasites have been useful tools to analyze the different stages of gene expression after transformation, as well as the mechanisms of drug resistance induction and the post-translational processing of enzyme precursors.

Insights into the redox biology of Trypanosoma cruzi: Trypanothione metabolism and oxidant detoxification

Trypanosoma cruzi is the etiologic agent of Chagas' disease, an infection that affects several million people in Latin America. With no immediate prospect of a vaccine and problems associated with current chemotherapies, the development of new treatments is an urgent priority. Several aspects of the redox metabolism of this parasite differ enough from those in the mammalian host to be considered targets for drug development. Here, we review the information about a trypanosomatid-specific molecule centrally involved in redox metabolism, the dithiol trypanothione, and the main effectors of cellular antioxidant defense. We focus mainly on data from T. cruzi, making comparisons with other trypanosomatids whenever possible. In these parasites trypanothione participates in crucial thiol-disulfide exchange reactions and serves as electron donor in different metabolic pathways, from synthesis of DNA precursors to oxidant detoxification. Interestingly, the levels of several enzymes involved in trypanothione metabolism and oxidant detoxification increase during the transformation of T. cruzi to its mammalian-infective form and the overexpression of some of them has been associated with increased resistance to macrophage-dependent oxidative killing. Together, the evidence suggests a central role of the trypanothione-dependent antioxidant systems in the infection process.

Polyamine transport in parasites: a potential target for new antiparasitic drug development

The metabolism of the naturally occurring polyamines-putrescine, spermidine and spermine-is a highly integrated system involving biosynthesis, uptake, degradation and interconversion. Metabolic differences in polyamine metabolism have long been considered to be a potential target to arrest proliferative processes ranging from cancer to microbial and parasitic diseases. Despite the early success of polyamine inhibitors such as alpha-difluoromethylornithine (DFMO) in treating the latter stages of African sleeping sickness, in which the central nervous system is affected, they proved to be ineffective in checking other major diseases caused by parasitic protozoa, such as Chagas' disease, leishmaniasis or malaria. In the use and design of new polyamine-based inhibitors, account must be taken of the presence of up-regulated polyamine transporters in the plasma membrane of the infectious agent that are able to circumvent the effect of the drug by providing the parasite with polyamines from the host. This review contains information on the polyamine requirements and molecular, biochemical and genetic characterization of different transport mechanisms in the parasitic agents responsible for a number of the deadly diseases that afflict underdeveloped and developing countries.