(V.) peruviana

Stimulation of metacyclogenesis in Leishmania (Mundinia) orientalis for mass production of metacyclic promastigotes

Leishmania (Mundinia) orientalis is a human pathogen causing leishmaniasis and studies on the properties of metacyclic promastigotes, the parasite’s infective stage, are required for a better understanding of its transmission and infection. However, information on cultivation for mass production of L. orientalis metacyclic promastigotes and factors that stimulate their metacyclogenesis is limited. Therefore, the objective of this study was to develop a suitable methodology for generating promastigote cultures containing a high proportion and number of L. orientalis metacyclic promastigotes. Various media, i.e., Schneider’s insect medium, Medium 199 and Grace’s insect medium, supplemented with various quantities of dithiothreitol, Basal Medium Eagle vitamins, pooled human urine, and fetal bovine serum, were optimized for metacyclogenesis. The results revealed that the optimum culture medium and conditions of those tested were Schneider’s insect medium supplemented with 100 μM dithiothreitol, 1% (v/v) Basal Medium Eagle vitamins, 2% (v/v) pooled human urine, and 10% (v/v) fetal bovine serum, pH 5.0 at 26°C. We also demonstrated that L. orientalis metacyclic promastigotes could be purified and enriched by negative selection using peanut lectin. Under these culture conditions, the highest yield of metacyclic promastigotes was obtained with a significantly higher percentage of parasite survival, resistance to complement-mediated lysis, and infection index in THP-1 macrophage cells compared to parasites cultured without media supplements at neutral pH. This is the first report providing a reliable method for mass production of L. orientalis metacyclic promastigotes for in vivo infections and other experimental studies of this emerging parasite in the future.

Route map for the discovery and pre-clinical development of new drugs and treatments for cutaneous leishmaniasis

Although there have been significant advances in the treatment of visceral leishmaniasis (VL) and several novel compounds are currently in pre-clinical and clinical development for this manifestation of leishmaniasis, there have been limited advances in drug research and development (R & D) for cutaneous leishmaniasis (CL). Here we review the need for new treatments for CL, describe in vitro and in vivo assays, models and approaches taken over the past decade to establish a pathway for the discovery, and pre-clinical development of new drugs for CL. These recent advances include novel mouse models of infection using bioluminescent Leishmania, the introduction of PK/PD approaches to skin infection, and defined pre-clinical candidate profiles.

Metacyclogenesis of Leishmania (Viannia) guyanensis: a comprehensive study of the main transformation features in axenic culture and purification of metacyclic promastigotes by negative selection with Bauhinia purpurea lectin

Leishmania (Viannia) guyanensis is one species that causes cutaneous leishmaniasis in the New World. The incidence of infections with this parasite is probably underestimated and few studies exist on this species, despite its epidemiological importance. In particular, there are no studies concerning L. guyanensis metacyclogenesis and no technique for obtaining metacyclic promastigotes for this species is presently available. Here, we have studied L. guyanensis metacyclogenesis in axenic culture, describing the main changes that occur during this process, namely, in morphology and size, sensitivity to complement-mediated lysis, surface carbohydrates and infectivity to macrophages. We have shown that metacyclogenesis in L. guyanensis promastigotes is basically complete on the 4th day of culture, as determined by decreased body size, increased flagellum length, resistance to complement-mediated lysis and infectivity. We have also found that only a fraction of the parasites is agglutinated by Bauhinia purpurea lectin. The non-agglutinated parasites, which also peaked on the 4th day of culture, had all morphological traits typical of the metacyclic stage. This is the first report describing metacyclogenesis in L. guyanensis axenic promastigotes and a simple and efficient method for the purification of metacyclic forms. Furthermore, a model of human macrophage infection with L. guyanensis was established.

Use of In Vivo Imaging System Technology in Leishmania major BALB/c Mouse Ear Infection Studies

Novel treatments for cutaneous leishmaniasis (CL) are needed, due to current lack of effective universal treatments, increasing resistance among the parasite, and toxic effects or impracticality of the current therapeutics. Models of direct infection with high number of Leishmania parasites in the current research of CL involving the BALB/c mouse or Golden Syrian Hamster are considered not suitable for the assessment of antileishmanial drug efficacy because of the lack of disease similarities with humans. The saliva of the sand fly vector is known to affect the host response to infection by the Leishmania parasite. Here, we build upon a previous BALB/c model infected with luciferase-expressing Leishmania major parasites. In the present study, we infect the ear dermis instead of the foot pad or base of the tail, and compare multiple methods of infection, using parasites alone or mixed with either bites from uninfected sand flies (Phlebotomus duboscqi Diptera Psychodidae:Neveu-Lemaire) or salivary gland sonicate from sand flies. Our data show a dose-response of bioluminescent signal (which represents the parasite load at the infection site), dermal lesion development, and Leishmania Donovan Units in liver and spleen. This in vivo L. major ear infection model, once optimized, can be used for assessing the efficacy of drug compounds that have been determined as very effective in the other, high inoculum CL models.

Andean cutaneous leishmaniasis (Andean-CL, uta) in Peru and Ecuador: the causative Leishmania parasites and clinico-epidemiological features

This study provides comprehensive information on the past and current status of the Andean cutaneous leishmaniasis (Andean-CL, uta) in Peru and Ecuador, mainly focusing on the causative Leishmania parasites and clinico-epidemiological features. Available information and data including our unpublished works were analyzed thoroughly. Endemic regions of the Andean-CL (uta) in Peru run from the north Piura/Cajamarca to the south Ayacucho at a wide range of the Pacific watersheds of the Andes through several departments, while in Ecuador those exist at limited and spotted areas in the country's mid-southwestern two provinces, Azuay and Chimborazo. The principal species of the genus Leishmania are completely different at subgenus level, L. (Viannia) peruviana in Peru, and L. (Leishmania) mexicana and L. (L.) major-like (infrequent occurrence) in Ecuador. The Peruvian uta is now prevalent in different age and sex groups, being not clearly defined as found in the past. The precise reasons are not known and should be elucidated further, though probable factors, such as emergence of other Leishmania parasites, non-immune peoples' migration into the areas, etc., were discussed briefly in the text. The Andean-CL cases in Ecuador are more rural than before, probably because of a rapid development of the Leishmania-positive communities and towns, and the change of life-styles of the inhabitants, including newly constructed houses and roads in the endemic areas. Such information is helpful for future management of the disease, not only for Leishmania-endemic areas in the Andes but also for other endemic areas.

Use of Optical Imaging Technology in the Validation of a New, Rapid, Cost-Effective Drug Screen as Part of a Tiered In Vivo Screening Paradigm for Development of Drugs To Treat Cutaneous Leishmaniasis

In any drug discovery and development effort, a reduction in the time of the lead optimization cycle is critical to decrease the time to license and reduce costs. In addition, ethical guidelines call for the more ethical use of animals to minimize the number of animals used and decrease their suffering. Therefore, any effort to develop drugs to treat cutaneous leishmaniasis requires multiple tiers of in vivo testing that start with higher-throughput efficacy assessments and progress to lower-throughput models with the most clinical relevance. Here, we describe the validation of a high-throughput, first-tier, noninvasive model of lesion suppression that uses an in vivo optical imaging technology for the initial screening of compounds. A strong correlation between luciferase activity and the parasite load at up to 18 days postinfection was found. This correlation allows the direct assessment of the effects of drug treatment on parasite burden. We demonstrate that there is a strong correlation between drug efficacy measured on day 18 postinfection and the suppression of lesion size by day 60 postinfection, which allows us to reach an accurate conclusion on drug efficacy in only 18 days. Compounds demonstrating a significant reduction in the bioluminescence signal compared to that in control animals can be tested in lower-throughput, more definitive tests of lesion cure in BALB/c mice and Golden Syrian hamsters (GSH) using Old World and New World parasites.

In vitro metacyclogenesis of Leishmania (Viannia) braziliensis and Leishmania (Leishmania) amazonensis clinical field isolates, as evaluated by morphology, complement resistance, and infectivity to human macrophages

This study was designed to assess in vitro metacyclogenesis of Leishmania (Viannia) braziliensis and Leishmania (Leishmania) amazonensis clinical field isolates obtained from patient lesions (L. braziliensis IMG3 and PPS6m; L. amazonensis MAB6). Metacyclogenesis was evaluated by different criteria, namely, promastigote size (morphometric analysis and flow cytometry), surface modifications (loss of lectin or monoclonal antibody (mAb) binding, complement resistance), and infectivity to human macrophages. Growth curves were similar for all parasites evaluated. The various features analyzed were expressed in a high percentage of promastigotes at 6th and 10th days of culture and a low percentage at the 2nd day. However, in most isolates, these features, considered as markers of metacyclogenesis, seemed to develop with different time courses, since the percentages of metacyclic forms detected with each technique were usually different. Parasites from 6th or 10th day and those negatively selected with lectin or mAb similarly infected human macrophages. From all isolates analyzed, L. amazonensis PH8 and MAB6 showed the highest and the lowest levels of susceptibility, respectively, to leishmanicidal activity of IFN-γ/LPS-activated macrophages. Our results showed that by using different techniques to evaluate different aspects of metacyclogenesis (morphological and biochemical modifications) different percentages of metacyclic promastigotes can be detected in each isolate culture.

Comparative evaluation of lesion development, tissue damage, and cytokine expression in golden hamsters (Mesocricetus auratus) infected by inocula with different Leishmania (Viannia) braziliensis concentrations

The golden hamster (Mesocricetus auratus) is a susceptible model to Leishmania (Viannia) spp.; however, available studies employ different infection protocols, which account for clinical and pathological presentation differences. Herein, L. (V.) braziliensis preparations were standardized to contain 10(4), 10(5), or 10(6) parasites to determine an optimal inoculum that ensured cutaneous lesions without causing a disseminated infection in hamsters. Lesion development was followed for 105 days by size measurements, and skin, draining lymph node, spleen, and sera were investigated to check parasite load, spleen visceralization, cytokine expression, histopathological changes, and anti-Leishmania IgG levels. The lesion emergence time was inversely proportional to the parasite concentration in the inocula. Animals infected by 10(4) parasites presented nodular lesions, while those infected with 10(6) parasites often exhibited ulcerated lesions. The differences in the final lesion sizes were observed between 10(4) and 10(5) inocula or 10(4) and 10(6) inocula. High IFNG expression, anti-Leishmania IgG levels, and parasite load occurred independently of the inoculum used. A mild inflammatory skin involvement was observed in animals infected with 10(4) parasites, while extensive tissue damage and parasite spleen visceralization occurred with 10(5) and 10(6) parasites. These results indicate that inocula with different concentrations of parasites generate differences in the time of lesion emergence, clinical presentation, and systemic commitment, despite high and similar IFNG expression and parasite load. This suggests that a modulation in the immune response to different parasite numbers occurs in an early phase of the infection, which could dictate the establishment and magnitude of the chronic phase of the disease.

Golden hamster (Mesocricetus auratus) as an experimental model for Leishmania (Viannia) braziliensis infection

The lack of an adequate model for Leishmania (Viannia) braziliensis infection is a limiting factor for studying American tegumentary leishmaniasis (ATL). The golden hamster (Mesocricetus auratus) is a promising model because besides being highly susceptible to dermotropic Leishmania infection, the lesions are very similar to cutaneous leishmaniasis (CL) in humans. However, different Leishmania isolates or species and/or protocols have resulted in different outcomes, whereas no study has evaluated the reproducibility of L. braziliensis infection in this model. The natural history of L. braziliensis infection in 34 hamsters was evaluated by using a single parasite isolate in 8 independent experiments under similar experimental conditions. Clinical, histological and immunological analyses were performed. The hamsters presented skin ulcers similar to those observed in ATL. The intra-experiment lesion increment tended to show an intermediary variance. Histological analysis of infected skins showed granulomatous reaction, scarce amastigotes, and Schaumann's bodies. Blood lymphocytes proliferated in response to leishmanial antigens. The severity of the infection was positively correlated to spleen weight, and the titres of anti-Leishmania IgG antibodies. Our findings indicate that the hamster is an appropriate model for immunopathogenesis studies of CL caused by L. braziliensis, supporting its use in clinical, vaccine and chemotherapy experimental protocols.

In vitro and in vivo behaviour of sympatric Leishmania (V.) braziliensis, L. (V.) peruviana and their hybrids

Leishmania (Viannia) braziliensis is the main cause of highly disfiguring mucocutaneous leishmaniasis (MCL) in South America. The related species L. (V.) peruviana has only been identified in simple cutaneous lesions (CL). Hybrids between L. braziliensis and L. peruviana have been reported although genetic exchange in Leishmania is considered to be rare. Here we compared growth in vitro, adaptive capacity under thermal and oxidative stress and behaviour in a hamster model, of L. braziliensis, L. peruviana, and their putative hybrids. At 24°C, the optimal temperature for in vitro growth, L. braziliensis had the highest growth rate. In in vitro studies hybrid clones presented heterogeneous phenotypes, from slower growth rates, similar to L. peruviana, to higher growth rates, as observed in L. braziliensis. Hamsters infected with hybrid strains, presented the highest parasite densities and aggressive relapses at a later stage of infection. Hybrids generally presented higher plasticity and phenotypic diversity than the putative parental species, with potential eco-epidemiological implications, including an impact on the success of disease control.

Increased metacyclogenesis of antimony-resistant Leishmania donovani clinical lines

Mathematical models predict that the future of epidemics of drug-resistant pathogens depends in part on the competitive fitness of drug-resistant strains. Considering metacyclogenesis (differentiation process essential for infectivity) as a major contributor to the fitness of Leishmania donovani, we tested its relationship with pentavalent antimony (SbV) resistance in clinical lines. Different methods for the assessment of metacyclogenesis were cross-validated: gene expression profiling (META1 and SHERP), morphometry (microscopy and FACS), in vitro infectivity to macrophages and resistance to complement lysis. This was done on a model constituted by 2 pairs of reference strains cloned from a SbV-resistant and -sensitive isolate. We selected the most adequate parameter and extended the analysis of metacyclogenesis diversity to a sample of 20 clinical lines with different in vitro susceptibility to the drug. The capacity of metacyclogenesis, as measured by the complement lysis test, was shown to be significantly higher in SbV-resistant clinical lines of L. donovani than in SbV-sensitive lines. Together with other lines of evidence, it is concluded that L. donovani constitutes a unique example and model of drug-resistant pathogens with traits of increased fitness. These findings raise a fundamental question about the potential risks of selecting more virulent pathogens through massive chemotherapeutic interventions.

Comparative gene expression analysis throughout the life cycle of Leishmania braziliensis: diversity of expression profiles among clinical isolates

Background

Most of the Leishmania genome is reported to be constitutively expressed during the life cycle of the parasite, with a few regulated genes. Inter-species comparative transcriptomics evidenced a low number of species-specific differences related to differentially distributed genes or the differential regulation of conserved genes. It is of uppermost importance to ensure that the observed differences are indeed species-specific and not simply specific of the strains selected for representing the species. The relevance of this concern is illustrated by current study.

Methodology/Principal Findings

We selected 5 clinical isolates of L. braziliensis characterized by their diversity of clinical and in vitro phenotypes. Real-time quantitative PCR was performed on promastigote and amastigote life stages to assess gene expression profiles at seven time points covering the whole life cycle. We tested 12 genes encoding proteins with roles in transport, thiol-based redox metabolism, cellular reduction, RNA poly(A)-tail metabolism, cytoskeleton function and ribosomal function. The general trend of expression profiles showed that regulation of gene expression essentially occurs around the stationary phase of promastigotes. However, the genes involved in this phenomenon appeared to vary significantly among the isolates considered.

Conclusion/Significance

Our results clearly illustrate the unique character of each isolate in terms of gene expression dynamics. Results obtained on an individual strain are not necessarily representative of a given species. Therefore, extreme care should be taken when comparing the profiles of different species and extrapolating functional differences between them.

Leishmania is a group of parasites (Protozoa, Trypanosomatidae) responsible for a wide spectrum of clinical forms. Among the factors explaining this phenotypic polymorphism, parasite features are important contributors. One approach to identify them consists in characterizing the gene expression profiles throughout the life cycle. In a recent study, the transcriptome of 3 Leishmania species was compared and this revealed species-specific differences, albeit in a low number. A key issue, however, is to ensure that the observed differences are indeed species-specific and not specific of the strains selected for representing the species. In order to illustrate the relevance of this concern, we analyzed here the gene expression profiles of 5 clinical isolates of L. braziliensis at seven time points of the life cycle. Our results clearly illustrate the unique character of each isolate in terms of gene expression dynamics: one Leishmania strain is not necessarily representative of a given species.

BALB/c mice infected with antimony treatment refractory isolate of Leishmania braziliensis present severe lesions due to IL-4 production

Background

Leishmania braziliensis is the main causative agent of cutaneous leishmaniasis in Brazil. Protection against infection is related to development of Th1 responses, but the mechanisms that mediate susceptibility are still poorly understood. Murine models have been the most important tools in understanding the immunopathogenesis of L. major infection and have shown that Th2 responses favor parasite survival. In contrast, L. braziliensis–infected mice develop strong Th1 responses and easily resolve the infection, thus making the study of factors affecting susceptibility to this parasite difficult.

Methodology/Principal Findings

Here, we describe an experimental model for the evaluation of the mechanisms mediating susceptibility to L. braziliensis infection. BALB/c mice were inoculated with stationary phase promastigotes of L. braziliensis, isolates LTCP393(R) and LTCP15171(S), which are resistant and susceptible to antimony and nitric oxide (NO), respectively. Mice inoculated with LTCP393(R) presented larger lesions that healed more slowly and contained higher parasite loads than lesions caused by LTCP15171(S). Inflammatory infiltrates in the lesions and production of IFN-γ, TNF-α, IL-10 and TGF-β were similar in mice inoculated with either isolate, indicating that these factors did not contribute to the different disease manifestations observed. In contrast, IL-4 production was strongly increased in LTCP393(R)-inoculated animals and also arginase I (Arg I) expression. Moreover, anti-IL-4 monoclonal antibody (mAb) treatment resulted in decreased lesion thickness and parasite burden in animals inoculated with LTCP393(R), but not in those inoculated with LTCP15171(S).

Conclusion/Significance

We conclude that the ability of L. braziliensis isolates to induce Th2 responses affects the susceptibility to infection with these isolates and contributes to the increased virulence and severity of disease associated with them. Since these data reflect what happens in human infection, this model could be useful to study the pathogenesis of the L. braziliensis infection, as well as to design new strategies of therapeutic intervention.

Leishmaniasis is a neglected disease that affects more than 12 million people worldwide. In Brazil, the cutaneous disease is more prevalent with about 28,000 new cases reported each year, and L. braziliensis is the main causative agent. The interesting data about the infection with this parasite is the wide variety of clinical manifestations that ranges from single ulcerated lesions to mucocutaneous and disseminated disease. However, experimental models to study the infection with this parasite are difficult to develop due to high resistance of most mouse strains to the infection, and the mechanisms underlying the distinct manifestations remain poorly understood. Here, the authors use a mouse experimental model of infection with different L. braziliensis isolates, known to induce diseases with distinct severity in the human hosts, to elucidate immune mechanisms that may be involved in the different manifestations. They showed that distinct parasite isolates may modulate host response, and increased IL-4 production and Arg I expression was related to more severe disease, resulting in longer length of disease with larger lesions and reduced parasite clearance. These findings may be useful in the identification of immunological targets to control L. braziliensis infection and potential clinical markers of disease progression.

Leishmania infantum and Toxoplasma gondii: Mixed infection of macrophages in vitro and in vivo

Although macrophages have a microbicidal role in the immune system they themselves can be infected by pathogens. Often a simultaneous infection by more than one microbe may occur in a single cell. This is the first report of coinfection of macrophages with Toxoplasma gondii and Leishmania infantum, in vitro and in vivo. L. infantum does not cause severe disease in mice but T. gondii, RH strain, is lethal. Cell culture studies using THP-1 macrophages dually infected in vitro revealed that 4.3% harbored both parasites 24h after infection. When mice were infected with both parasites on the same day 7.3% of the infected cells carried both parasites 7 days later. Yet, if mice were first infected with L. infantum and then with Toxoplasma (5 days post-infection) 18.7% of the macrophages hosted either parasite but concomitant infection could not be found and mice, already harboring L. infantum, survived Toxoplasma's lethal effect.