Leishmania mexicana: proteinase activities and megasomes in axenically cultivated amastigote-like forms

Three types of Leishmania mexicana amastigotes: Proteome comparison by quantitative proteomic analysis

Leishmania is the unicellular parasite transmitted by phlebotomine sand fly bite. It exists in two different forms; extracellular promastigotes, occurring in the gut of sand flies, and intracellular, round-shaped amastigotes residing mainly in vertebrate macrophages. As amastigotes originating from infected animals are often present in insufficient quality and quantity, two alternative types of amastigotes were introduced for laboratory experiments: axenic amastigotes and amastigotes from macrophages infected in vitro. Nevertheless, there is very little information about the degree of similarity/difference among these three types of amastigotes on proteomic level, whose comparison is crucial for assessing the suitability of using alternative types of amastigotes in experiments. In this study, L. mexicana amastigotes obtained from lesion of infected BALB/c mice were proteomically compared with alternatively cultivated amastigotes (axenic and macrophage-derived ones). Amastigotes of all three types were isolated, individually treated and analysed by LC-MS/MS proteomic analysis with quantification using TMT10-plex isobaric labeling. Significant differences were observed in the abundance of metabolic enzymes, virulence factors and proteins involved in translation and condensation of DNA. The most pronounced differences were observed between axenic amastigotes and lesion-derived amastigotes, macrophage-derived amastigotes were mostly intermediate between axenic and lesion-derived ones.

Insights into Leishmania Molecules and Their Potential Contribution to the Virulence of the Parasite

Neglected parasitic diseases affect millions of people worldwide, resulting in high morbidity and mortality. Among other parasitic diseases, leishmaniasis remains an important public health problem caused by the protozoa of the genus Leishmania, transmitted by the bite of the female sand fly. The disease has also been linked to tropical and subtropical regions, in addition to being an endemic disease in many areas around the world, including the Mediterranean basin and South America. Although recent years have witnessed marked advances in Leishmania-related research in various directions, many issues have yet to be elucidated. The intention of the present review is to give an overview of the major virulence factors contributing to the pathogenicity of the parasite. We aimed to provide a concise picture of the factors influencing the reaction of the parasite in its host that might help to develop novel chemotherapeutic and vaccine strategies.

Cysteine peptidases of kinetoplastid parasites

We review Clan CA Family C1 peptidases of kinetoplastid parasites (Trypanosoma and Leishmania) with respect to biochemical and genetic diversity, genomic organization and stage-specificity and control of expression. We discuss their contributions to parasite metabolism, virulence and pathogenesis and modulation of the host's immune response. Their applications as vaccine candidates and diagnostic markers as well as their chemical and genetic validation as drug targets are also summarized.

Leishmania amazonensis: early proteinase activities during promastigote-amastigote differentiation in vitro

Leishmania proteinase activity is known as parasite differentiation marker, and has been considered relevant for leishmanial survival and virulence. These properties suggest that Leishmania proteinases can be promising targets for development of anti-leishmania drugs. Here, we analyze the activities of four proteinases during the early phase of the Leishmania amazonensis promastigotes differentiation into amastigotes induced by heat shock. We have examined activities of cysteine-, metallo-, serine-, and aspartic-proteinase by hydrolysis of specific chromogenic substrates at pH 5.0 and at the optimal pH for each enzyme. Our results show that metallo-, serine-, and aspartic-proteinases activities were down-regulated during the shock-induced transformation of promastigotes into amastigotes. In contrast, cysteine-proteinase activity increased concomitantly with the promastigote differentiation. Immunocytochemical localization using two anti-cysteine-proteinase monospecific rabbit antibodies detected the enzyme in several cell compartments of both parasite stages. Our results show different proteinase activity modulation and expression during the early phases of the shock-induced parasite transformation.

Growth phase and medium ph modulate the expression of proteinase activities and the development of megasomes in axenically cultivated Leishmania (Leishmania) amazonensis amastigote-like organisms

Leishmania (Leishmania) amazonensis LV79 (MPRO/BR/72/M1841) has been adapted to grow at 33 C as amastigote-like (AL) organisms in modified UM-54 medium initially adjusted to a pH of 4.8-5.0. Axenic cultures could be routinely restarted from parasites recovered from footpad lesions obtained by inoculation of BALB/c mice with preadapted culture stages. Morphological features, proteinase activities, and infectivity of AL organisms were examined during the in vitro growth cycle, and differences were found between log- and stationary-phase parasites. Stationary-phase AL organisms were morphologically similar to lesion amastigotes, did not react with a paraflagellar rod-specific monoclonal antibody in western blots, and contained proteinase activities resolving identically to the enzymes of lesion amastigotes in gelatin gels. Whereas typical megasomes could be identified in about a third of the stationary-phase AL population, the organelles were rarely seen in log-phase organisms. Azocaseinolytic activity progressively increased during the exponential growth phase and reached its highest values (approximately 65-70% of those determined in lesion amastigotes) at the stationary phase; the association of total proteinase activity with increased expression of cysteine proteinases was indicated by the strong inhibition of azocasein hydrolysis by E-64, the intensified banding of the 28-, 31-, and 35-kDa proteinases in gelatin gels, and the higher susceptibility of stationary-phase AL organisms to L-leucine methyl ester. Although overall axenic amastigotes were less infective to BALB/c mice than were lesion-derived parasites, stationary-phase AL organisms were more infective than were log-phase parasites. Medium pH increased during the exponential growth phase, but dropped in the stationary phase, when the observed morphological, biochemical, and biological changes became apparent.

Bioactivity of crude extracts and some constituents of Blutaparon portulacoides (Amaranthaceae)

Crude extracts (aerial parts and roots, both dried), methylenedioxyflavonol, and a mixture of acyl steryl glycosides isolated from Blutaparon portulacoides, were assayed for their toxicity against Trypanosoma cruzi trypomastigotes and Leishmania amazonensis amastigotes from axenic cultures. The antimicrobial activity was also investigated, in a screening conducted using fifteen strains of Gram-positive and Gram-negative bacteria, along with the yeasts, Candida albicans and Candida tropicalis. To assess the antibacterial activity of the isolated compounds, the minimum inhibitory concentrations (MICs) were determined. There are no reports of acyl steryl glycosides in the genus Blutaparon and their biological activities are being evaluated for the first time.

Biochemical and biological characterization of the protective Leishmania pifanoi amastigote antigen P-8

The Leishmania pifanoi amastigote antigen P-8 has been previously shown to induce protective immunity in a murine model of cutaneous leishmaniasis (L. Soong, S. M. Duboise, P. Kima, and D. McMahon-Pratt, Infect. Immun. 63:3559-3566, 1995). As this antigen is of interest for further vaccine studies, the biochemical characterization of P-8 was undertaken. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western-blot analysis, and gel filtration chromatography revealed that P-8 antigen consisted of two proteoglycolipid complexes. The P-8 epitope is associated with the L. pifanoi amastigote-specific glycolipid components found in the two complexes. The P-8 complex 1 (P-8c1) consists of a 56-kDa serine metalloproteinase, apolipoprotein E (derived from fetal bovine serum), and amastigote-specific glycolipids. The P-8 complex 2 (P-8c2) consists of a 31-kDa cysteine proteinase associated with amastigote glycolipids. Biochemical analyses suggest that the P-8 antigenic glycolipids may be distinct from previously described Leishmania glycolipids (glycosylinositol-phospholipids and sphingoglycolipids). Protective immunity studies revealed that P-8c1 (serine metalloproteinase-glycolipid complex) confers comparable protection against infection as immunopurified P-8. The isolated P-8c2 (cysteine proteinase-glycolipid complex) does not provide significant protection, nor does stimulation with P-8c2 result in significant T-cell activation in P-8- or P-8c2-vaccinated mice. Consequently, the P-8c1 complex appears to be the immunodominant component of P-8.

In vitro cultivation and characterization of axenic amastigotes of Leishmania

The establishment of axenic cultures of the amastigote stage of Leishmania is important to understand the mechanisms regulating the differentiation, survival and pathogenicity of the parasite with a view to develop and identify molecular and chemotherapeutic targets. Recent developments in axenic culture and the characterization of amastigotes of different species of Leishmania are discussed.

Detection of cysteine-proteinases in Leishmania amazonensis promastigotes using a cross-reactive antiserum

Rabbit serum against the cysteine-proteinases papain has been employed for the cellular localization of cysteine-proteinases of in Leishmania amazonensis promastigotes. By immunocytochemistry, immune complexes were found in the plasma membrane and in the flagella pocket of the parasite. The antiserum immunoprecipitated major iodinated proteins with molecular masses of 66, 45, 28 and 24 kDa and a wide partitioning of the Triton X-114 detergent phase. The presence of cysteine-proteinase at the cell surface membrane was also suggested by the detection of proteolytic activity in living cells (19.0 microg azocasein min(-1) 10(-7) promastigotes (1.0 S.D. )).

The cytostome of Trypanosoma cruzi epimastigotes is associated with the flagellar complex

Okuda, K., Esteva, M., Segura, E. L., and Bijovsky, A. T. 1999. The cytostome of Trypanosoma cruzi epimastigotes is associated with the flagellar complex. Experimental Parasitology 92, 223-231. Proliferative forms of Trypanosoma cruzi, amastigotes and epimastigotes, have a cytostome, a specialized structure formed by an invagination of the flagellar pocket's membrane surrounded by microtubules and frequently followed by a row of vesicles. All this assemblage penetrates deeply into the cytoplasm overpassing the nucleus. This structure, together with the flagellar pocket, appears to play an important role in the nutrition of the parasite. We demonstrated that the monoclonal antibody 2C4, made-up against isolated flagellar complex of T. cruzi epimastigotes, recognizes a protein doublet of 76 and 87 kDa in total epimastigotes homogenate. The 76-kDa polypeptide is enriched in the detergent-soluble fraction whereas the 87-kDa polypeptide is highly represented in the insoluble fractions and the purified flagella. Immuno-fluorescence assays show the antigen as a small spot at the flagellar pocket region. Immunogold labeling of ultrathin sections of epimastigote forms reveals gold particles at the opening of flagellar pocket, concentrated in the cytostome region. Immunocytochemistry of epimastigote whole-mount cytoskeletons reveals the labeling on an array of three to four microtubules that appears attached to flagellum, running in the direction of the nucleus. Ultrastructural observations have shown that the posterior region of isolated flagella, corresponding to the level of the flagellar pocket, possesses a microtubular structure compatible with that from the cytostome. The relationship between the cytostome, an endocytic organelle, and the flagellum is here described for the first time.

Proteases of protozoan parasites

Proteolytic enzymes seem to play important roles in the life cycles of all medically important protozoan parasites, including the organisms that cause malaria, trypanosomiasis, leishmaniasis, amebiasis, toxoplasmosis, giardiasis, cryptosporidiosis and trichomoniasis. Proteases from all four major proteolytic classes are utilized by protozoans for diverse functions, including the invasion of host cells and tissues, the degradation of mediators of the immune response and the hydrolysis of host proteins for nutritional purposes. The biochemical and molecular characterization of protozoan proteases is providing tools to improve our understanding of the functions of these enzymes. In addition, studies in multiple systems suggest that inhibitors of protozoan proteases have potent antiparasitic effects. This review will discuss recent advances in the identification and characterization of protozoan proteases, in the determination of the function of these enzymes, and in the evaluation of protease inhibitors as potential antiprotozoan drugs.

Insulin-like growth factor I is a growth-promoting factor for Leishmania promastigotes and amastigotes

Leishmaniases are diseases caused by protozoa of the genus Leishmania that affect more than 20 million people in the world. The initial phase of the infection is fundamental for either the progression or control of the disease. The Leishmania parasites are injected in the skin as promastigotes and then, after been phagocytized by the host macrophages, rapidly transform into amastigotes. In this phase different nonspecific cellular and humoral elements participate. We have shown previously that insulin-like growth factor (IGF)-I that is constitutively present in the skin induces growth of Leishmania promastigotes. In the present paper we show further evidence for the importance of this factor: (i) IGF-I also can induce a growth response in Leishmania (Leishmania) mexicana amastigotes; (ii) IGF-I binds specifically to a putative single-site receptor on both promastigotes and amastigotes; (iii) IGF-I induces a rapid tyrosine phosphorylation of parasite proteins with different molecular mass in promastigotes and amastigotes of L. (L.) mexicana; and, finally, (iv) the cutaneous lesion in the mice when challenged by IGF-I-preactivated Leishmania (Viannia) panamensis is increased significantly because of inflammatory process and growth of parasites. We thus suggest that IGF-I is another important host factor participating in the Leishmania-host interplay in the early stage during the establishment of the infection and presumably also in the later stages.

Leishmania phagolysosome: drug trafficking and protein sorting across the compartment

Survival or destruction of intramacrophage pathogen Leishmania depends in part on modulation of their host cell phagosome, capabilities of the infected macrophages to present parasite antigen to the host's immune system. Macrophages house these parasites as amastigotes in the acidic phagolysosomal compartment. Leishmania phagolysosome is the potential site for processing and presentation of its antigen as well as being the target site for chemotherapy in leishmaniasis. It is thought that the parasites are killed from macrophage activation by lymphokines secreted from either helper T1 cells or CD8+ T cells. Characterization of both the host and parasite molecules in the compartment in the context of biogenesis of Leishmania-phagolysosome and processing of the parasite antigen by this compartment are discussed. Trafficking of different drugs and new agents through this compartment and their role in chemotherapy and necessity of developing new drug carrier are also stressed.

An axenic amastigote system for drug screening

Currently available primary screens for selection of candidate antileishmanial compounds are not ideal. The choices include screens that are designed to closely reflect the situation in vivo but are labor-intensive and expensive (intracellular amastigotes and animal models) and screens that are designed to facilitate rapid testing of a large number of drugs but do not use the clinically relevant parasite stage (promastigote model). The advent of successful in vitro culture of axenic amastigotes permits the development of a primary screen which is quick and easy like the promastigote screen but still representative of the situation in vivo, since it uses the relevant parasite stage. We have established an axenic amastigote drug screening system using a Leishmania mexicana strain (strain M379). A comparison of the 50% inhibitory concentration (IC50) drug sensitivity profiles of M379 promastigotes, intracellular amastigotes, and axenic amastigotes for six clinically relevant antileishmanial drugs (sodium stibogluconate, meglumine antimoniate, pentamidine, paromomycin, amphotericin B, WR6026) showed that M379 axenic amastigotes are a good model for a primary drug screen. Promastigote and intracellular amastigote IC50s differed for four of the six drugs tested by threefold or more; axenic amastigote and intracellular amastigote IC50s differed by twofold for only one drug. This shows that the axenic amastigote susceptibility to clinically used reference drugs is comparable to the susceptibility of amastigotes in macrophages. These data also suggest that for the compounds tested, susceptibility is intrinsic to the parasite stage. This contradicts previous hypotheses that suggested that the activities of antimonial agents against intracellular amastigotes were solely a function of the macrophage.

A radioiodinated peptidyl diazomethane detects similar cysteine proteinases in amastigotes and promastigotes of Leishmania (L.) mexicana and L. (L.) amazonensis

Cysteine proteinase activities were examined in lesion amastigotes as well as in stationary-phase promastigotes of Leishmania (L.) mexicana and Leishmania (L.) amazonensis isolates. Enzyme detection in gelatin gels revealed that amastigotes of three L. (L.) mexicana isolates (M379, IOC-0561, and IP) shared similar proteinases, including the multiple low-molecular-weight (25-35 kDa) cysteine proteinases. High cysteine proteinase activity was also observed in L. (L.) amazonensis amastigotes, but the banding profile was different in two of the isolates examined. Promastigotes displayed fewer low-molecular-weight proteinase bands, and these were much less intense as compared with those of lesion amastigotes. Independently of the Leishmania isolates and developmental stages examined, incubation of the parasites for 2 h with 0.2 microM radioiodinated N-benzyl-oxycarbonyl-tyrosyl-alanyl diazomethane (Z-Tyr[125I]-AlaCHN2) markedly and selectively labeled bands comigrating with the 28- and 31-kDa cysteine proteinases. Under reducing conditions, labeling was associated with four similar polypeptides (29-34 kDa), which were also detected when incubation with Z-Tyr[125I]-AlaCHN2 was carried out after cell lysis. Labeling was completely abolished if lysates were first incubated with 20 microM E-64 and then exposed to the 125I-tagged inhibitor, thus confirming the specificity of the compound toward cysteine proteinases.