Current treatment approaches to leishmaniasis

Structural Evidence of the Similarity of Sb(OH)3 and As(OH)3 with Glycerol: Implications for Their Uptake

Recent experimental results suggest that As(III) and Sb(III) transport in prokaryotes and eukaryotes might be facilitated by aquaglyceroporins. GlpF, the glycerol facilitator in Escherichia coli was the first to be identified as a trivalent metalloid transporter. Quantum calculations have been performed to study the possible existence of common structural properties between As(OH) 3 and Sb(OH) 3 and glycerol. Because the mechanism of substrate migration is primarily related to the successive formation of hydrogen bonds between the substrate and the hydrophilic part of the channel wall, this study has focused on the structural, thermodynamic, and electrostatic comparison of the main As(III) and Sb(III) compounds present in aqueous solution at physiological pH values, As(OH) 3 and Sb(OH) 3, with the glycerol conformation closest to the structures of these As- and Sb-containing compounds. This particular glycerol conformation has then been compared to three known experimental conformations of glycerol present in the protein channel. Besides their stoichiometry and electroneutral condition, As(OH) 3 and Sb(OH) 3 show very strong similarities to both each other and the studied conformation of the glycerol molecule: Namely, they show a similar charge distribution and a slightly smaller volume than glycerol. Their smaller size can be an additional advantage for the transit through the narrowest region of the GlpF channel. However, the metalloid hydroxyl groups lack the flexibility of glycerol, which probably helps this molecule to adapt its conformation to the topology of the GlpF channel.

Leishmanicidal activity of a supercritical fluid fraction obtained from Tabernaemontana catharinensis

The branches and leaves of Tabernaemontana catharinensis were extracted with supercritical fluid using a mixture of CO(2) plus ethanol (SFE), and the indole alkaloid enriched fraction (AF3) was selected for anti-Leishmania activity studies. We found that AF3 exhibits a potent effect against intracellular amastigotes of Leishmania amazonensis, a causative agent of New World cutaneous leishmaniasis. AF3 inhibits Leishmania survival in a dose-dependent manner, and reached 88% inhibition of amastigote growth at 100 microg/mL. The anti-parasite effect was independent of nitric oxide (NO), since AF3 was able to inhibit NO production induced by IFN-gamma plus LPS. In addition, AF3 inhibited TGF-beta production, which could have facilitated AF3-mediated parasite killing. The AF3 fraction obtained from SFE was nontoxic for host macrophages, as assessed by plasma membrane integrity and mitochondrial activity. We conclude that SFE is an efficient method for obtaining bioactive indole alkaloids from plant extracts. Importantly, this method preserved the alkaloid properties associated with inhibition of Leishmania growth in macrophages without toxicity to host cells.

First case of typical Old World cutaneous leishmaniasis treated with miltefosine

A 26-year-old man presented to our clinic for advice on treatment options regarding cutaneous leishmaniasis (CL) with multiple lesions. The biopsy revealed Leishmania amastigotes; Leishmania major was identified by polymerase chain reaction (PCR).(11 )Leishmania serology (indirect immunofluorescence test) was positive at 1 : 160 (normal, < or = 1 : 40). Ten weeks earlier, the patient had spent a 1-week biking holiday in central Tunisia. Two weeks after returning to Germany, he noticed the flaring up of multiple insect bites (> 40) contracted in Tunisia on both arms. The lesions increased in size and axillary lymph node enlargement occurred. Some of the nodular lesions disappeared spontaneously and some increased in size and showed central ulceration. When we first saw the patient, he had six lesions on his right arm and one on his left arm. The largest lesion was on the dorsum of the right hand (Fig. 1) and showed an indurated edge and central ulceration. Before starting systemic treatment, the patient decided to wait a few weeks in case spontaneous improvement occurred. However, 8 weeks later, the ulceration had further increased in size (Fig. 2) from a diameter of 2 cm initially to a diameter of 5 cm. Regional lymphatic spread with palpable nodules along the adjacent lymphatic vessel had occurred. With the patient's informed consent, treatment with oral miltefosine, according to his body weight of 96 kg, was started at 50 mg three times daily for 28 days. The treatment was well tolerated without any subjective side-effects reported. Liver enzymes, serum creatinine, and urea were monitored during treatment. There was a mild increase in liver enzymes during the third week of treatment: aspartate aminotransferase (AST), 49 U/L (normal, < 35 U/L); alanine aminotransferase (ALT), 107 U/L (normal, < 45 U/L); this resolved spontaneously. Ten days after completion of treatment, the rolled edge had disappeared and the central ulcer had almost healed (Fig. 3). Figure 4 shows the lesion 5 months after completion of treatment.

Prodrugs for the treatment of neglected diseases

Recently, World Health Organization (WHO) and Medicins San Frontieres (MSF) proposed a classification of diseases as global, neglected and extremely neglected. Global diseases, such as cancer, cardiovascular and mental (CNS) diseases represent the targets of the majority of the R&D efforts of pharmaceutical companies. Neglected diseases affect millions of people in the world yet existing drug therapy is limited and often inappropriate. Furthermore, extremely neglected diseases affect people living under miserable conditions who barely have access to the bare necessities for survival. Most of these diseases are excluded from the goals of the R&D programs in the pharmaceutical industry and therefore fall outside the pharmaceutical market. About 14 million people,mainly in developing countries, die each year from infectious diseases. From 1975 to 1999,1393 new drugs were approved yet only 1% were for the treatment of neglected diseases[3]. These numbers have not changed until now, so in those countries there is an urgent need for the design and synthesis of new drugs and in this area the prodrug approach is a very interesting field. It provides, among other effects, activity improvements and toxicity decreases for current and new drugs, improving market availability. It is worth noting that it is essential in drug design to save time and money, and prodrug approaches can be considered of high interest in this respect. The present review covers 20 years of research on the design of prodrugs for the treatment of neglected and extremely neglected diseases such as Chagas' disease (American trypanosomiasis), sleeping sickness (African trypanosomiasis), malaria, sickle cell disease, tuberculosis, leishmaniasis and schistosomiasis.

Leishmaniavaccines: progress and problems

Leishmaniaare protozoan parasites spread by a sandfly insect vector and causing a spectrum of diseases collectively known as leishmaniasis. The disease is a significant health problem in many parts of the world resulting in an estimated 12 million new cases each year. Current treatment is based on chemotherapy, which is difficult to administer, expensive and becoming ineffective due to the emergence of drug resistance. Leishmaniasis is considered one of a few parasitic diseases likely to be controllable by vaccination. The relatively uncomplicated leishmanial life cycle and the fact that recovery from infection renders the host resistant to subsequent infection indicate that a successful vaccine is feasible. Extensive evidence from studies in animal models indicates that solid protection can be achieved by immunisation with protein or DNA vaccines. However, to date no such vaccine is available despite substantial efforts by many laboratories. Advances in our understanding ofLeishmaniapathogenesis and generation of host protective immunity, together with the completedLeishmaniagenome sequence open new avenues for vaccine research. The major remaining challenges are the translation of data from animal models to human disease and the transition from the laboratory to the field. This review focuses on advances in anti-leishmania vaccine development over the recent years and examines current problems hampering vaccine development and implementation.

Cholesterol: a potential therapeutic target in Leishmania infection?

Leishmania are obligate intracellular parasites that invade and survive within host macrophages and can result in visceral leishmaniasis, a major public health problem worldwide. The entry of intracellular parasites, in general, involves interaction with the plasma membrane of host cells. Cholesterol in host cell membranes was recently shown to be necessary for binding and internalization of Leishmania and for the efficient presentation of leishmanial antigens in infected macrophages. This article describes the need to explore cyclodextrin-based compounds, which modulate host membrane cholesterol levels, as a possible therapeutic strategy against leishmaniasis in addition to other intracellular parasites.

Comparative study of the efficacy of formulations containing fluconazole or paromomycin for topical treatment of infections by Leishmania (Leishmania) major and Leishmania (Leishmania) amazonensis

The development of alternative therapeutic approaches for cutaneous leishmaniasis (CL) has received considerable attention in recent research, including the identification of formulations for topical treatment. In the present study, the activity of two formulations was evaluated in BALB/c mice experimentally infected with either Leishmania (Leishmania) major or L. (L.) amazonensis, a hydrophilic gel containing 10% paromomycin (PAHG) and a cream containing 1% fluconazole (FLUC). After development of ulcerated lesions, infected mice were divided into three groups of five animals each: (1) PA group: Lesions were covered with 50 microl of PAHG; (2) FLUC group: Lesions were covered with 50 microl of FLUC, and (3) placebo group: treated with gel without paromomycin. During and after treatment, the size of lesions was determined weekly using a caliper. The efficacy of PAHG was significantly higher than that observed for FLUC for both Leishmania species. The PAHG formulation was effective in promoting the healing of ulcers in all animals 28 days after the beginning of treatment, whereas none of the animals was cured by FLUC. These results suggest that the PAHG formulation could be suitable for clinical studies and may represent an alternative formulation for the topical treatment of CL.

The role of splenectomy in HIV-infected patients with relapsing visceral leishmaniasis

The treatment of visceral leishmaniasis (VL) in HIV-infected patients is characterized by having a protracted course and frequent relapses, despite the use of adequate anti-leishmanial drugs and effective anti-retroviral therapy. A small subset of patients with significant splenomegaly develops severe cytopaenias and chronic leishmania infection. The use of elective splenectomy is effective for restoring the haematological parameters and reduces the need for blood transfusions but it does not avoid relapsing visceral leishmaniasis.

Leishmania-derived murine monocyte chemoattractant protein 1 enhances the recruitment of a restrictive population of CC chemokine receptor 2-positive macrophages

Transgenic Leishmania parasites that encode the murine chemokine monocyte chemoattractant protein 1 (MCP-1) were generated. These parasites transcribed MCP-1 mRNA and secreted MCP-1 protein. Infection of BALB/c, C57BL/6, or MCP-1 knockout (KO) mice with these parasites resulted in minimal lesion development with fewer parasites in the infected foot, lymph node, and spleen compared to wild-type-infected mice. In contrast, transgenic parasites caused substantial lesions with relatively high numbers of parasites in CC chemokine receptor 2 (CCR2) KO mice, indicating that the parasites are viable and healthy and that the lack of lesion development is CCR2 dependent. Prior infection of mice with transgenic parasites offered no protection to subsequent wild-type L. major challenge, suggesting that the transgenic parasites are controlled by an early innate immune response. Consistent with innate immunity, flow cytometry of cells from the ears of mice infected with transgenic parasites revealed an increase in the number of CCR2-positive macrophages by day 7 postinfection. The enumeration of transgenic parasites in ear lesions demonstrated a significant reduction in parasite numbers, which coincided with the increased CCR2-positive macrophage migration. CCR2-positive macrophages isolated from ears of mice infected with transgenic parasites contained virtually no parasites. In vitro studies revealed that optimal parasite killing required the recruitment of CCR2-positive macrophages, followed by stimulation with a combination of both MCP-1 and gamma interferon (IFN-gamma). This work suggests that the parasite-derived MCP-1 can recruit a restrictive population of CCR2-positive macrophages into lesions that can be optimally stimulated by MCP-1 and IFN-gamma to efficiently kill Leishmania parasites.

Synthesis of 16-mercaptohexadecylphosphocholine, a miltefosine analog with leishmanicidal activity

The alkylphosphocholine miltefosine (n-hexadecylphosphocholine, MT) has been introduced recently as a very effective drug for the oral treatment of human leishmaniasis. However, the parasiticidal mechanism of MT at a molecular level is far from being understood. Here we report the synthesis and biological characterization of 16-mercaptohexadecylphosphocholine, a thiol analog of MT which was designed to facilitate the search of MT interacting targets within the parasite by a variety of analytical methods. This analog presents the same leishmanicidal effect as the parent drug against Leishmania donovani promastigotes and Leishmania pifanoi axenic amastigotes, and has been used to develop an affinity chromatography method to attempt the isolation of putative Leishmania proteins that bind to the phosphocholine part of the molecule.

2H-Benzimidazole 1,3-Dioxide Derivatives: A New Family of Water-Soluble Anti-Trypanosomatid Agents†

Three series of benzimidazole N-oxide derivatives were developed and were examined for their activity against trypanosomatid parasites (Trypanosoma cruzi and Leishmania spp.). 2H-benzimidazole 1,3-dioxides displayed remarkable in vitro activities against both parasites, with derivatives 28, 29, and 32 being the most potent (IC50 < 5 microM) against the epimastigote form of T. cruzi and 28, 33, and 35 the most potent against the promastigote form of Leishmania spp. Unspecific cytotoxicity was evaluated using murine macrophages, and derivative 33 was not toxic at a concentration 30 times that of its IC50 against T. cruzi that was completely toxic for Leishmania spp., implying that the series of 2H-benzimidazole 1,3-dioxides is selective toward both trypanosomatid parasites. Derivatives 33 and 35 were submitted to an in vivo assay using an acute model of Chagas' disease and a short-term treatment (30 mg/kg/day orally administrated as aqueous solution, during 10 days). While in the control (untreated) and Benznidazole (50 mg/kg/day) groups survival fraction was 60.0% and 87.5%, respectively, none of the animals treated with derivatives 33 and 35 died. From the preliminary structure-activity relationship studies reduction potential and electrophilicity were found relevant to anti-T. cruzi activity. Active compounds are better electrophiles and more easily reduced than inactive ones.

Unresponsiveness to AmBisome in some Sudanese patients with kala-azar

In Sudan, two treatments are currently registered for visceral leishmaniasis: sodium stibogluconate (SSG) as first line and liposomal amphotericin B (AmBisome) as second line. We present 64 patients (52 relapse cases to SSG, 12 new but complicated cases) treated with AmBisome in eastern Sudan. AmBisome was administered at 2.5-8.2mg/kg (15-49mg/kg in total) per dose six times (days 1, 2, 3, 5, 10, 15) as an intravenous infusion. We measured outcome according to clinical response and parasitological clearance (lymph node aspiration). Patient outcomes fell into three groups: group 1, clinical responders (cured) with a negative test of cure (n=35); group 2, clinical responders with a positive test of cure (n=19); group 3, clinical non-responders (failures) with a positive test of cure (n=10). Of the 10 failures, six were already relapse cases. All of group 3, and 15 from group 2, were also treated with additional SSG (20mg/kg intramuscularly daily for 30-50 d) with resulting clinical and parasitological improvement. Parasite persistence and clinical failure were associated with a higher parasite density on admission (P<0.002) and underlying immunosuppressive disease: tuberculosis (three cases) or HIV (two cases). Because AmBisome monotherapy may fail in Sudan, a combination of AmBisome and SSG is recommended for relapse cases.

Cutaneous leishmaniasis in soldiers from Fort Campbell, Kentucky returning from Operation Iraqi Freedom highlights diagnostic and therapeutic options

BACKGROUND

Cutaneous leishmaniasis (CL), rare in the first Gulf War, is common in American troops serving in Operation Iraqi Freedom. Awareness of the clinical features and treatment options of CL would benefit clinicians who may encounter soldiers, as well as civilians, returning from the Middle East with skin lesions.

OBJECTIVE

Our purpose was to describe our clinical experience in treating soldiers with CL.

METHODS

From December 2003 through June 2004, approximately 360 of an estimated 20,000 soldiers returning from a yearlong deployment in Iraq with skin lesions suspected of being CL were examined by dermatologists. We summarized CL diagnoses, laboratory evaluations, and treatments, including localized heat therapy (ThermoMed model 1.8; ThermoSurgery Technologies, Inc, Phoenix, Ariz), oral fluconazole, cryotherapy, and itraconazole.

RESULTS

Among 237 soldiers diagnosed with CL, 181 had one or more laboratory confirmations, most by Giemsa-stained lesion smears and polymerase chain reaction (PCR). PCR was positive for all 122 smear-positive and 26 biopsy-positive lesions and all 34 smear negative and all 3 biopsy-negative cases. Primary outpatient treatments, including ThermoMed (n = 26), oral fluconazole (n = 15), cryotherapy (n = 4), and itraconazole (n = 2), were safe and tolerable. Treatment failure occurred in 2 fluconazole recipients and was suspected in 1 ThermoMed and 2 fluconazole recipients. Seventy-two soldiers elected no treatment.

LIMITATION

This was a retrospective study.

CONCLUSION

Approximately 1% of Ft Campbell troops returning from Iraq were diagnosed with CL, most by laboratory confirmation. PCR appeared to be the most useful diagnostic technique. Among outpatient treatments, ThermoMed and cryotherapy had favorable safety and efficacy profiles.

Mechanism of metalloid-induced death in Leishmania spp.: role of iron, reactive oxygen species, Ca2+, and glutathione

There is growing evidence that metalloid-induced cell death in protozoan parasites is due to oxidative injury; however, the biochemical changes related to this event are not fully understood. Leishmania spp. demonstrated cross-resistance to two related metalloids, arsenic and antimony, and both metalloids induced cell death accompanied by cell shrinkage and DNA fragmentation that was preceded by an increase in reactive oxygen species. Both drugs caused mitochondrial dysfunction in terms of loss of membrane potential and a drop in ATP levels. Arsenic treatment resulted in an elevation of intracellular Ca2+ levels that did not occur with antimony exposure. Cellular glutathione level was reduced after antimony treatment but arsenic did not affect glutathione. Inhibition of Ca2+ influx during arsenic treatment reduced cell death, whereas supplementation of glutathione during antimony treatment rescued cell loss. Under iron-depleted conditions, the cytotoxic effects of arsenic and antimony did not occur and cell survival increased; in contrast, the presence of excess iron resulted in higher cell death. Therefore, this study provides a new possibility that iron can potentiate parasite death induced by metalloids like arsenic and antimony. In addition, an important observation is that the two similar metalloids produce toxicity by very different mechanisms.

Arylanthranilodinitriles: A new biaryl class of antileishmanial agents

A series of anthranilodinitrile-based biaryls were synthesized and evaluated in vitro against extracellular promastigotes and intracellular amastigotes of Leishmania donovani. Among various screened compounds, a biaryl with trifluoromethyl group 5f showed 83% inhibition against promastigotes and 70% inhibition against amastigotes of L. donovani at 8 and 20microg/mL concentrations, respectively.

Hyperbaric oxygen therapy reduces the size of Leishmania amazonensis-induced soft tissue lesions in mice

In this study we determined whether exposing mice to hyperbaric oxygen (HBO) would alter various disease parameters of a susceptible mouse strain infected with Leishmania amazonensis. BALB/c mice exposed to HBO (100% O2 at a pressure of 2.5 ATA, 1h before parasite inoculation and subsequently for 20 days) showed significant delay in lesion development and reduction in lesion parasite burdens compared with HBO-unexposed mice. Circulating levels of interferon gamma (IFN-gamma) and tumor necrosis factor (TNF-alpha) were significantly elevated in HBO-exposed as compared to HBO-unexposed mice. Concanavalin A-stimulated lymph nodes cultures from HBO-exposed mice released significantly more IFN-gamma and less interleukin 10 (IL-10) than cultures from HBO-unexposed mice, consistent with a skewed Th1 response. These results demonstrate, for the first time, that HBO can play a pathogen control role during leishmaniasis. Further studies are needed to elucidate whether hyperoxia alone or increased atmospheric pressure alone can exert a similar effect.

The sterol-binding antibiotic nystatin inhibits entry of non-opsonized Leishmania donovani into macrophages

Leishmania donovani is an obligate intracellular parasite that infects macrophages of the vertebrate host resulting in visceral leishmaniasis in humans, a major public health problem worldwide. The molecular mechanisms involved in internalization of Leishmania are still poorly characterized. We report here that cholesterol sequestration by the sterol-binding antifungal polyene antibiotic nystatin markedly inhibits binding and entry of non-opsonized L. donovani promastigotes into macrophages. Interestingly, these effects are not observed when serum-opsonized L. donovani are used for infectivity studies thus pointing the essential role of cholesterol in mediating entry of the parasite via the non-opsonic pathway. Based on our earlier results where leishmanial infectivity was shown to be sensitive to physical depletion of cholesterol from macrophages, these results indicate that the mere sequestration of cholesterol in the host plasma membrane is sufficient to inhibit the binding and entry of non-opsonized L. donovani. These results represent the first report on the effect of a cholesterol-sequestering agent on the entry of Leishmania parasites to host macrophages. More importantly, these findings offer the possibility of reevaluating the mechanism behind the effectiveness of current therapeutic strategies to treat leishmaniasis.

Synthesis and in vitro antileishmanial activity of 5-substituted-2′-deoxyuridine derivatives

We report herein the synthesis and the in vitro antileishmanial evaluation of 5-substituted-2'-deoxyuridine nucleosides. The most active compound against Leishmania donovani promastigotes was Thia-dU (3a) with an IC50 =3 microM. This compound exhibited the same activity as zidovudine (3'-azido-2'-deoxythymidine) used as nucleoside reference compound. Considering the cytotoxicity of synthetic compounds on peritoneal murine macrophages, the most toxic compound was MeThio-dU (3d) with a MTC at 10 microM. Only Methia-dU (3b) was active against intramacrophagic amastigotes with an IC50 =6.5 microM. This latter can now be evaluated in vivo, for further investigations through structure-based drug design.

Successful treatment of post-kala-azar dermal leishmaniasis (PKDL) in a HIV infected patient with multiple relapsing leishmaniasis from Western Europe

We present a 42-year-old man who was admitted with worsening of his general condition and facial skin lesions. He had previously been diagnosed with HIV infection and visceral leishmaniasis (VL). Diagnostic work-up revealed a new relapse of VL paralleled by the diagnosis of post-kala-azar dermal leishmaniasis (PKDL). The patient was treated with IV liposomal amphotericin B as well as sodium stibogluconate followed by oral hexadecylphosphocholine (miltefosine) over a period of 9 months. PKDL lesions began to disappear after 8 months of treatment. In addition, severe and relapsing VL so far remains in remission. This case demonstrates successful treatment of PKDL and relapsing VL in a Western European patient with HIV infection.

Prokaryotic expression, purification, and polyclonal antibody production against a novel drug resistance gene of Leishmania donovani clinical isolate

Diseases produced by protozoan parasites are one of the main causes of morbidity and mortality around the world, affecting millions of people. Among these, leishmaniasis has become the second most common cause of death and the problem is further complicated by the expansion of parasite resistance to the conventional drugs. The high rate of therapeutic failure thus calls for new rational approaches to develop alternative drugs. Understanding resistance mechanisms may help identify new targets for drug development. So we present here the cloning, expression, purification, and antibody production of a gene implicated in imparting resistance to pentavalent antimony (SbV) in clinical isolates of kala azar with a view to gain insight into the novel mechanism of its drug resistance.

Successful liposomal amphotericin B treatment of Leishmania braziliensis cutaneous leishmaniasis

Existing systemic treatments for New World cutaneous leishmaniasis (CL) caused by Leishmania (vianna) braziliensis are unsatisfactory. Liposomal amphotericin B has been used extensively for the treatment of visceral leishmaniasis, but in few cases of CL, and an appropriate regimen for CL has not been described. We successfully treated a patient with multiple L. braziliensis CL lesions acquired in Belize. Liposomal amphotericin B (AmBisome) was given to our patient as an inpatient for seven daily doses of 3 mg kg(-1) day(-1) and then as an outpatient at 3 mg kg(-1) twice weekly for a further three weeks, a total of 40 mg kg(-1). Liposomal amphotericin offers a well-tolerated alternative to pentavalent antimony or amphotericin B deoxycholate for the systemic treatment of New World CL.

Complexation of antimony (Sb(V)) with guanosine 5'-monophosphate and guanosine 5'-diphospho-D-mannose: formation of both mono- and bis-adducts

In spite of the extensive use of pentavalent antimony chemotherapy, the mechanism of its anti-leishmania action is still not clear. Here, we report the interactions of Sb(V), including the clinically used drug stibogluconate, with guanosine 5'-monophosphate (5'-GMP) and guanosine 5'-diphospho-d-mannose (5'-GDP-mannose) in aqueous solution. The deprotonated hydroxyl groups (-OH) of the ribose ring are shown to be the binding site for Sb(V), probably via chelation. Both mono- and bis-adducts were formed as determined by NMR, high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS), and both of them are stable in the pH range of 4 to around 9.5. The formation of the mono-adduct (k(1)=1.67x10(-3) and 3.43x10(-3) mM(-1) min(-1) for Sb(5'-GMP) and Sb(5'-GDP-mannose), respectively, at 298 K) was 10-fold faster than that of the bis-adduct (k(2)=0.16x10(-3) and 0.21x10(-3) mM(-1) min(-1), for Sb(5'-GMP)(2) and Sb(5'-GDP-mannose)(2), respectively), and the mono-adduct was the major species in solution with the [bis-adduct]/[mono-adduct]<0.5. The reactions of stibogluconate with 5'-GMP and 5'-GDP-mannose were slower than that of antimonate under similar conditions.

A role for IgG immune complexes during infection with the intracellular pathogen Leishmania

We examined the role of immunoglobulin (Ig)G antibodies in mediating host defense to the intracellular parasite, Leishmania. We show that IgG not only fails to provide protection against this intracellular pathogen, but it actually contributes to disease progression. The J_H strain of BALB/c mice, which lack IgG because they have a targeted deletion in the Ig heavy chain (J) locus, were more resistant to infection with Leishmania major than were normal BALB/c mice. However, the passive administration of anti-Leishmania IgG caused J_H mice to develop large lesions containing high numbers of parasites. Antibody administration correlated with an increase in interleukin (IL) 10 production in lesions, and blocking the murine IL-10 receptor prevented antibody-mediated disease exacerbation. In human patients with active visceral leishmaniasis, high IgG levels are predictive of disease. Patients with ongoing disease had high IgG antibody titers and no delayed-type hypersensitivity (DTH) responses to Leishmania antigens. This pattern was reversed upon disease resolution after treatment, resulting in a decrease in total IgG, which was accompanied by a progressive increase in DTH responsiveness. We conclude that IgG can cause a novel form of immune enhancement due to its ability to induce IL-10 production from macrophages.

Functional expression of a multidrug P-glycoprotein transporter of Leishmania

P-glycoprotein (Pgp) transporters play an important role in multidrug resistance in eukaryotic cells and in protozoan parasites such as Leishmania. To search for new reversal agents of the Leishmania tropica Pgp, we developed a screening assay using the Baculovirus-insect cell expression system. We demonstrated a MgATP-dependent, vanadate-sensitive transport of Hoechst 33342 in membrane preparations of Sf9 insect cells expressing Pgp. We have found that dihydro-beta-agarofuran sesquiterpenes from Maytenus cuzcoina inhibited Hoechst 33342 transport that correlates with their reversal effect in a multidrug-resistant L. tropica line overexpressing Pgp. The results suggest that Sf9 cell membrane Hoechst 33342 transport system represents an efficient tool for examining the interactions of Leishmania Pgp with pharmacological agents.

Activity of a paromomycin hydrophilic formulation for topical treatment of infections by Leishmania (Leishmania) amazonensis and Leishmania (Viannia) braziliensis

Studies on in vitro skin permeation and in vivo anti-leishmanial activity in mice experimentally infected with Leishmania (Leishmania) major pointed out to the potential of a new paromomycin (PA) formulation (hydrophilic gel) for treatment of cutaneous leishmaniasis (CL). In this study, the activity of this formulation was evaluated in animals experimentally infected by Leishmania species that prevail in the New World. PA gel activity was compared to antimony treatment, since it is still the first choice treatment to the different clinical forms of leishmaniasis. The topical treatment activity with 10% PA gel in BALB/c mice infected by Leishmania (Leishmania) amazonensis was higher than that observed for parenteral antimony treatment, while the efficacy of these two regimes in hamsters infected by Leishmania (Viannia) braziliensis was similar. These results suggest that this formulation could be suitable for clinical studies and may represent an alternative novel formulation for topical treatment of CL.

RNA interference for analysis of gene function in trypanosomatids

Gene-specific silencing by RNA interference is a valuable tool for analysis of gene function in the protozoan parasite Trypanosoma brucei. The development of tetracycline-regulated vectors for production of double-stranded RNA has facilitated its widespread use. RNA interference provides a fast and efficient method for determining whether a gene is essential for growth and viability, reveals mechanistic information on gene function, and has greatly enhanced our understanding of complex biological processes. Finally, the creation of an RNA interference-based library has allowed, for the first time, an approach for conducting forward genetic experiments in this organism.

In vitro assays for evaluation of drug activity against Leishmania spp

Leishmania is a parasitic protozoan which causes severe disease in humans and dogs. Screening of new compounds against leishmaniasis is particularly needed to determine the toxicity of some existing drugs and the appearance of drug-resistant strains. Reliable and simple in vitro models are required for large-scale initial screenings. In this review different methods for in vitro evaluation of drug activity against Leishmania spp. are summarized.

The heat shock protein HSP70 and heat shock cognate protein HSC70 contribute to antimony tolerance in the protozoan parasite leishmania

Antimony-containing drugs are still the drugs of choice in the treatment of infections caused by the parasite Leishmania. Resistance to antimony is now common in some parts of the world, and several mechanisms of resistance have been described. By transfecting cosmid banks and selecting with potassium antimonyl tartrate (SbIII), we have isolated a cosmid associated with resistance. This cosmid contains 2 copies of the heat shock protein 70 (HSP70) and 1 copy of the heat shock cognate protein 70 (HSC70). Several data linked HSP70 to antimony response and resistance. First, several Leishmania species, both as promastigotes and amastigotes, increased the expression of their HSP70 proteins when grown in the presence of 1 or 2 times the Effect Concentration 50% of SbIII. In several mutants selected for resistance to either SbIII or to the related metal arsenite, the HSP70 proteins were found to be overexpressed. This increase was also observed in revertant cells grown for several passages in the absence of SbIII, suggesting that this increased production of HSP70 is stable. Transfection of HSP70 or HSC70 in Leishmania cells does not confer resistance directly, though these transfectants were better able to tolerate a shock with SbIII. Our results are consistent with HSP70 and HSC70 being a first line of defense against SbIII until more specific and efficient resistance mechanisms take over.