Parasite polyamine metabolism: targets for chemotherapy

Proteomic profile approach of effect of putrescine depletion over Trichomonas vaginalis

Infection with Trichomonas vaginalis produces a malodorous seropurulent vaginal discharge due to several chemicals, including polyamines. The presence of 1,4-diamino-2-butanone (DAB) reduces the amount of intracellular putrescine by 90%, preventing the cotransport of exogenous spermine. DAB-treated parasites present morphological changes, which are restored by adding exogenous putrescine into the culture medium. However, the effect of polyamines over the trichomonad proteomic profile is unknown. In this study, we used a proteomic approach to analyze the polyamine-depletion and restoration effect by exogenous putrescine on T. vaginalis proteome. In the presence of inhibitor DAB, we obtained 369 spots in polyamine-depleted condition and observed 499 spots in the normal culture media. With DAB treatment, the intensity of 43 spots was increased but was found to be reduced in 39 spots, as compared to normal conditions. Interestingly, in DAB-treated parasites restored with a medium with added exogenous putrescine, 472 spots were found, of which 33 were upregulated and 63 were downregulated in protein intensity. Some of these downregulated proteins in DAB-treated parasites are involved in several cellular pathways such as glycolysis, glycolytic fermentation, arginine dihydrolase pathway, redox homeostasis, host cell binding mediated by carbohydrate, chaperone function, and cytoskeletal remodeling. Interestingly, the intensity of some of the proteins was restored by adding exogenous putrescine. In conclusion, the presence of DAB altered the proteomic profile of T. vaginalis, resulting in a decrease in the intensity of 130 proteins and an increase in the intensity of 43 proteins that was restored by the addition of putrescine.

Bifunctional activity of deoxyhypusine synthase/hydroxylase from Trichomonas vaginalis

The Trichomonas vaginalis genome analysis suggested the presence of a putative deoxyhypusine synthase (TvDHS) that catalyzes the posttranslational modification of eIF-5A. Herein, we expressed and purified the recombinant TvDHS (rTvDHS) protein (43 kDa) and the recombinant TveIF-5A (rTveIF-5A) precursor protein (46 kDa). A 41 kDa band of the native TvDHS was recognized by western blot analysis in T. vaginalis total protein extract by a mouse polyclonal anti-rTvDHS antibody. The enzymatic activity of rTvDHS was determined by in vitro rTveIF-5A precursor modification. The modification reaction was performed by using ((3)H)-spermidine, and the biochemical analysis showed that rTvDHS exhibited Km value of 0.6 μM. The rTvDHS activity was inhibited by the spermidine analog, N″-guanyl-1,7-diamino-heptane (GC7). Native gel electrophoresis analysis showed two bands corresponding to an rTvDHS-rTveIF-5A complex and an intermediate form of rTveIF-5A. The two forms were subsequently separated by ion exchange chromatography to identify the hypusine residue by MS/MS analysis. Moreover, mutations in TvDHS showed that the putative HE motif present in this enzyme is involved in the hydroxylation of TveIF-5A. We observed that only hypusine-containing TveIF-5A was bound to an RNA hairpin ERE structure from the cox-2 gene, which contains the AAAUGUCACAC consensus sequence. Interestingly, 2DE-WB assays, using parasites that were grown in DAB-culture conditions and transferred to exogenous putrescine, showed the new isoform of TveIF-5A. In summary, our results indicate that T. vaginalis contains an active TvDHS capable of modifying the precursor TveIF-5A protein, which subsequently exhibits RNA binding activity.

Putrescine-dependent re-localization of TvCP39, a cysteine proteinase involved in Trichomonas vaginalis cytotoxicity

Polyamines are involved in the regulation of some Trichomonas vaginalis virulence factors such as the transcript, proteolytic activity, and cytotoxicity of TvCP65, a cysteine proteinase (CP) involved in the trichomonal cytotoxicity. In this work, we reported the putrescine effect on TvCP39, other CP that also participate in the trichomonal cytotoxicity. Parasites treated with 1,4-diamino-2-butanone (DAB) (an inhibitor of putrescine biosynthesis), diminished the amount and proteolytic activity of TvCP39 as compared with untreated parasites. Inhibition of putrescine biosynthesis also reduced ∼80% the tvcp39 mRNA levels according to RT-PCR and qRT-PCR assays. Additionally, actinomycin D-treatment showed that the tvcp39 mRNA half-life decreased in the absence of putrescine. However, this reduction was restored by exogenous putrescine addition, suggesting that putrescine is necessary for tvcp39 mRNA stability. TvCP39 was localized in the cytoplasm but, in DAB treated parasites transferred into exogenous putrescine culture media, TvCP39 was re-localized to the nucleus and nuclear periphery of trichomonads. Interestingly, the amount and proteolytic activity of TvCP39 was recovered as well as the tvcp39 mRNA levels were restored when putrescine exogenous was added to the DAB-treated parasites. In conclusion, our data show that putrescine regulate the TvCP39 expression, protein amount, proteolytic activity, and cellular localization.

Putrescine is required for the expression of eif-5a in Trichomonas vaginalis

Recently, we found that Trichomonas vaginalis contains a eukaryotic translation initiation factor 5A (TveIF-5A) with unknown function in this parasite. eIF-5A is the only cellular protein dependent of polyamines to form a hypusine residue, an unusual basic amino acid that is post-translationally formed by modification of a single specific lysine residue in an eIF-5A precursor protein. The purpose of this study was to determine the effect of a putrescine analogue, 1,4-diamino-2-butanone (DAB), on tveif-5a mRNA and TveIF-5A protein expression. TveIF-5A protein expression was reduced by inhibition of putrescine biosynthesis, and tveif-5a mRNA levels were reduced ∼90%, as shown by western blot and immunofluorescence assays. Cycloheximide treatment reduced the amount of mature TveIF-5A protein at 4h and decreased the tveif-5a transcript level at 2h, according to western blot, RT-PCR and qRT-PCR analyses. Actinomycin D treatment showed that the tveif-5a mRNA had half-life of ∼2.5h in DAB-treated parasites. The half-life of tveif-5a mRNA was ∼4.5h under exogenous putrescine conditions. These results suggest that putrescine is required for tveif-5a mRNA stability, and it is necessary for the expression, stability and maturation of TveIF-5A protein.

Trichomonas vaginalis polyamine metabolism is linked to host cell adherence and cytotoxicity

Trichomonas vaginalis secretes putrescine that is readily detected in vaginal secretions. We wanted to examine the effect of decreased putrescine synthesis by inhibition of ornithine decarboxylase (ODC) on T. vaginalis. One reason is because inhibition of Tritrichomonas foetus ODC results in growth arrest, destruction of hydrogenosomes, and decreased amounts of hydrogenosomal enzymes. Treatment of T. vaginalis T016 with >/=20 mM 1,4-diamino-2-butanone (DAB) to inhibit ODC resulted in growth arrest, which was reversed by addition of exogenous putrescine. No similar reversal of growth arrest was achieved with the polyamines spermine or spermidine or with iron. Electron microscopic examination of control versus DAB-treated trichomonads did not reveal any adverse effects on the number and integrity of hydrogenosomes. Further, the adhesins AP65, AP51, and AP33 mediating binding to immortalized vaginal epithelial cells (VECs) share identity to enzymes of the hydrogenosome organelle, and there was no difference in amounts of adhesins between control versus DAB-treated T. vaginalis parasites. Likewise, similar patterns and extent of fluorescence were evident for the prominent AP65 adhesin. Surprisingly, DAB treatment increased by 4- to 20-fold above untreated trichomonads handled identically the level of adherence mediated by adhesins. Interestingly, the enhanced attachment to VECs was reversed by exogenous putrescine added to DAB-treated trichomonads. Equally noteworthy was that DAB-treated T. vaginalis with enhanced adherence did not possess the previously reported ability to kill host cells in a contact-dependent fashion mediated by cysteine proteinases, and total cysteine proteinase activity patterns were identical between control and DAB-treated trichomonads. Overall, these data suggest that polyamine metabolism and secreted putrescine are linked to host cell adherence and cytotoxicity.

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.

Sulfur-Containing Amino Acid Metabolism in Parasitic Protozoa

Sulfur-containing amino acids play indispensable roles in a wide variety of biological activities including protein synthesis, methylation, and biosynthesis of polyamines and glutathione. Biosynthesis and catabolism of these amino acids need to be carefully regulated to achieve the requirement of the above-mentioned activities and also to eliminate toxicity attributable to the amino acids. Genome-wide analyses of enzymes involved in the metabolic pathways of sulfur-containing amino acids, including transsulfuration, sulfur assimilatory de novo cysteine biosynthesis, methionine cycle, and degradation, using genome databases available from a variety of parasitic protozoa, reveal remarkable diversity between protozoan parasites and their mammalian hosts. Thus, the sulfur-containing amino acid metabolic pathways are a rational target for the development of novel chemotherapeutic and prophylactic agents against diseases caused by protozoan parasites. These pathways also demonstrate notable heterogeneity among parasites, suggesting that the metabolism of sulfur-containing amino acids reflects the diversity of parasitism among parasite species, and probably influences their biology and pathophysiology such as virulence competence and stress defense.

Enhanced replication of Leishmania amazonensis amastigotes in gamma interferon-stimulated murine macrophages: implications for the pathogenesis of cutaneous leishmaniasis

During Leishmania major infection in mice, gamma interferon (IFN-gamma) plays an essential role in controlling parasite growth and disease progression. In studies designed to ascertain the role of IFN-gamma in Leishmania amazonensis infection, we were surprised to find that IFN-gamma could promote L. amazonensis amastigote replication in macrophages (Mphis), although it activated Mphis to kill promastigotes. The replication-promoting effect of IFN-gamma on amastigotes was independent of the source and genetic background of Mphis, was apparently not affected by surface opsonization of amastigotes, was not mediated by interleukin-10 or transforming growth factor beta, and was observed at different temperatures. Consistent with the different fates of promastigotes and amastigotes in IFN-gamma-stimulated Mphis, L. amazonensis-specific Th1 transfer helped recipient mice control L. amazonensis infection established by promastigotes but not L. amazonensis infection established by amastigotes. On the other hand, IFN-gamma could stimulate Mphis to limit amastigote replication when it was coupled with lipopolysaccharides but not when it was coupled with tumor necrosis factor alpha. Thus, IFN-gamma may play a bidirectional role at the level of parasite-Mphi interactions; when it is optimally coupled with other factors, it has a protective effect against infection, and in the absence of such synergy it promotes amastigote growth. These results reveal a quite unexpected aspect of the L. amazonensis parasite and have important implications for understanding the pathogenesis of the disease and for developing vaccines and immunotherapies.

Novel alkylpolyamine analogues that possess both antitrypanosomal and antimicrosporidial activity

A novel series of alkyl- or aralkyl-substituted polyamine analogues was synthesized containing a 3-7-3 polyamine backbone. These analogues were evaluated in vitro, and in one case in vivo, for activity as antitrypanosomal agents, and for activity against opportunistic infection caused by Microsporidia. Compound 21 inhibits trypanosomal growth with an IC(50) as low as 31nM, while compound 24 shows promising activity in vitro against trypanosomes, and against Microsporidia in vitro and in vivo.

Dependence of Trichomonas vaginalis upon polyamine backconversion

Trichomonas vaginalis grown for 16 h in the presence of [(14)C]spermine formed a high intracellular pool of [(14)C]spermidine and a small but detectable pool of [(14)C]putrescine. When [(3)H]putrescine was added to the growth medium, a large intracellular pool of [(3)H]putrescine was found, but it was not further metabolized, confirming previous studies suggesting the absence of a forward-directed polyamine synthetic pathway in T. vaginalis. Spermidine:spermineN:(1)-acetyltransferase (SSAT) and polyamine oxidase enzyme activities were detected which collectively converted spermine to spermidine. Polyamine oxidase was localized in the hydrogenosome-enriched fraction, whereas SSAT was found predominantly in the cytosolic fraction. In the presence of saturating substrate, the trichomonad SSAT had an activity of 0. 39+/-0.09 nmol min(-1) (mg protein)(-1) (the mean of five analyses) and an apparent K:(m) for spermine of 1.7 microM. The enzyme was competitively inhibited by di(ethyl)norspermine with a K:(i) of 28 microM. Growth studies indicated that 50 microM di(ethyl)norspermine caused a 68% and 84% reduction in the intracellular concentrations of spermidine and spermine, respectively. The trichomonad polyamine oxidase required FAD as a cofactor and had an apparent K:(m) of 6.0 microM for N(1)-acetylspermine. The potential of bis(alkyl) polyamine analogues as antitrichomonad agents is discussed.

Putrescine and spermidine transport in Leishmania

The transport of putrescine and spermidine into Leishmnania donovani promastigotes and Leishmania mexicana promastigotes and amastigotes has been characterised. Polyamine transport was shown to be saturable and temperature-sensitive for both developmental stages of Leishmania. Transport was pH-dependent with pH optima of 7.4 and 5.5 for promastigotes and amastigotes, respectively. The uptake process was independent of extracellular Na+, but inhibited by protonophores and H+-ATPase inhibitors. Kinetic analyses of polyamine transport showed that Km and Vmax differed between promastigotes of the two species and between promastigotes and amastigotes of L. mexicana. Inhibition data suggest that putrescine and spermidine use different transporters. The aromatic diamidine pentamidine, the drug of choice for treatment of antimonial-resistant cases of leishmaniasis, inhibited both putrescine and spermidine transport non-competitively.

Elevated levels of polyamines and trypanothione resulting from overexpression of the ornithine decarboxylase gene in arsenite-resistant Leishmania

The levels of trypanothione, a glutathione-spermidine conjugate, are increased in the protozoan parasite Leishmania selected for resistance to the heavy metal arsenite. The levels of putrescine and spermidine were increased in resistant mutants. This increase is mediated by overexpression of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. Gene overexpression is generally mediated by gene amplification in Leishmania but, here, the mRNA and the enzymatic activity of ODC are increased without gene amplification. This RNA overexpression is stable when cells are grown in the absence of the drug and does not result from gene rearrangements or from an increased rate of RNA synthesis. Transient transfections suggest that mutations in the revertant cells contribute to these elevated levels of RNA. Stable transfection of the ODC gene increases the level of trypanothione, which can contribute to arsenite resistance. In addition to ODC overexpression, the gene for the ABC transporter PGPA is amplified in the mutants. The co-transfection of the ODC and PGPA genes confers resistance in a synergistic fashion in partial revertants, also suggesting that PGPA recognizes metals conjugated to trypanothione.

Inhibition of polyamine synthesis arrests trichomonad growth and induces destruction of hydrogenosomes

Trichomonad parasites such as Tritrichomonas foetus produce large amounts of putrescine (1,4-diaminobutane), which is transported out of the cell via an antiport mechanism which results in the uptake of a molecule of spermine. The importance of putrescine to the survival of the parasite and its role in the biology of T. foetus was investigated by use of the putrescine analogue 1, 4-diamino-2-butanone (DAB). Growth of T. foetus in vitro was significantly inhibited by 20 mM DAB, which was reversed by the addition of exogenous 40 mM putrescine. High-performance liquid chromatography analysis of 20 mM DAB-treated T. foetus revealed that putrescine, spermidine, and spermine levels were reduced by 89, 52, and 43%, respectively, compared to those in control cells. The DAB treatment induced several ultrastructural alterations, which were primarily observed in the redox organelles termed hydrogenosomes. These organelles were progressively degraded, giving rise to large vesicles that displayed material immunoreactive with an antibody to beta-succinyl-coenzyme A synthetase, a hydrogenosomal enzyme. A protective role for polyamines as stabilizing agents in the trichomonad hydrogenosomal membrane is proposed.

Polyamine transport systems of Leishmania donovani promastigotes

The following observations are conjointly indicative of the presence of distinct energy-dependent, saturable and multiple polyamine transport systems in Leishmania donovani promastigotes, the causative agent for visceral leishmaniasis. Spermidine was influxed with as much as seven times higher rate than putrescine, while both spermidine and putrescine transporters exhibited equally high affinity for the respective polyamine. N-Ethylmaleimide arrested the complete functionality of both the transporters which could be restored by reduced glutathione. Putrescine transporter did not recognize spermine but spermidine was recognized to some extent, while spermidine transporter significantly recognized spermine but putrescine was absolutely spared. A few aromatic diamines viz., diaminobiphenyl and the analogs as well as aliphatic diamines viz., cadaverine and agmatine were selectively recognized by the putrescine transporter only. L. donovani promastigotes grown in presence of alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, registered marked upregulation of putrescine transport while spermidine transport was only marginally induced. PA transport systems provide the alternative pool of polyamines in L. donovani promastigotes in the absence of an adequate intracellular PA repertoire.