Short- and long-term efficacy of hexadecylphosphocholine against established Leishmania infantum infection in BALB/c mice

Apigenin is a promising molecule for treatment of visceral leishmaniasis

Current treatment for visceral leishmaniasis is based on drugs such as pentavalent antimony and amphotericin B. However, this treatment remains mostly ineffective and expensive, resulting in several side effects and generating resistance. Apigenin, a flavonoid present in fruits and vegetables, has demonstrated several biological functions. In the present study, we observed a concentration-dependent inhibition of the L. infantum promastigote in the presence of apigenin, exhibiting an IC₅₀ value of 29.9 µM. Its effect was also evaluated in L. infantum-infected murine peritoneal macrophages, presenting an C₅₀ value against intracellular amastigotes of 2.3 µM and a selectivity index of 34.3. In a murine model of visceral leishmaniasis, the in vivo effect of apigenin was measured using short-term and long-term treatment schemes. Treatment with apigenin demonstrated 99.7% and 94% reductions in the liver parasite load in the short-term and long-term treatment schemes, respectively. Furthermore, no alterations in serological and hematological parameters were observed. Taken together, these results suggest that apigenin is a potential candidate for visceral leishmaniasis chemotherapy by oral administration.

In vitro effect of artemether-loaded nanostructured lipid carrier (NLC) on Leishmania infantum

Visceral leishmaniasis (VL) is an acute and deadly form of leishmaniasis, caused by Leishmania infantum parasite. Due to the toxicity and side effects of conventional treatment options, such as glucantime and other pentavalent drugs, finding novel drugs with fewer adverse effects is required. Artemether (ART), is one of the derivatives of artemisinin, which was shown to be effective in treating malaria and more recently, leishmaniasis. In this fundamental-applied research, we compared the effect of ART and nanostructure loaded with artemether (NLC-ART) on Leishmania infantum promastigotes and amastigotes, at different concentrations (2.5-5-10-25-50-100 μg/ml) using the MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay method after 24 and 48 h of treatment. Inhibitory concentration (IC50) values (μg/ml) of promastigote and amastigote of L. infantum to ART/ NLC-ART, after 48 h of treatment, were found to be 37.12 / 32.1 and 16.43 / 15.42, respectively. Moreover, we found that (NLC-ART), had the lowest cytotoxicity against the J774 macrophage cell line. Conclusion: The NLC-ART can be a good candidate for the treatment of visceral leishmaniasis.

Identification of potential antileishmanial agents via structure-based molecular simulations

Leishmaniasis is a parasitic disease with frequent annual incidence. An important issue in chemotherapy is the emergence of resistance, toxicity and lack of cost-effectiveness within current drugs. Therefore, it is of utmost importance to design effective drugs against disease. Current contribution was devoted to the in-silico analysis of binding a few flavonoids/alkaloids to relevant leishmanial targets. Docking scores were used to prioritize acquired affinities and top ranked binders were subjected to subsequent 100-ns MD simulation in explicit water. Binding trajectories revealed the tightest interaction modes for two flavonoid molecules (acerosin and nevadensin) in the uracil DNA glycolase (UDG) active site. Acerosin showed less conformational changes whereas, nevadensin interacted stably during longer simulation time. Conserved interactions of Gln205 and His331 to acerosin indicated their dominant biological role in complex stability. No conserved residues were perceived for nevadensin interactions and a completely new and stable binding conformation could be retrieved after 12 ns simulation. Moreover; acerosin was subjected to DFT analysis for pairwise decomposition evaluations of interacted residues. Although primary mechanisms of action are yet to be discovered, UDG may be a promising target for developing antileishmanial flavonoids.

Leishmaniasis: where are we and where are we heading?

Leishmaniasis is a zoonotic disease in humans caused by the bite of a parasite-infected sandfly. The disease, widely referred to as "poor man's disease," affects millions of people worldwide. The clinical manifestation of the disease depends upon the species of the parasite and ranges from physical disfigurement to death if left untreated. Here, we review the past, present, and future of leishmaniasis in detail. The life cycle of Leishmania sp., along with its epidemiology, is discussed, and in addition, the line of therapeutics available for treatment currently is examined. The current status of the disease is critically evaluated, keeping emerging threats like human immunodeficiency virus (HIV) coinfection and post kala-azar dermal leishmaniasis (PKDL) into consideration. In summary, the review proposes a dire need for new therapeutics and reassessment of the measures and policies concerning emerging threats. New strategies are essential to achieve the goal of leishmaniasis eradication in the next few decades.

Antileishmanial activity of fullerol and its liposomal formulation in experimental models of visceral leishmaniasis

Visceral leishmaniasis (VL) is a systemic parasitic disease that leads to high rates of morbidity and mortality in humans worldwide. There is a great need to develop new drugs and novel strategies to make chemotherapy for this disease more efficacious and well tolerated. Recent reports on the immunomodulatory effects and the low toxicity of the spherical carbon nanostructure fullerol led us to investigate in vitro and in vivo antileishmanial activity in free and encapsulated forms in liposomes. When assayed against intramacrophagic Leishmania amastigotes, fullerol showed a dose-dependent reduction of the infection index with IC50 of 0.042 mg/mL. When given daily by i.p. route for 20 days (0.05 mg/kg/d) in a murine model of acute VL, fullerol promoted significant reduction in the liver parasite load. To improve the delivery of fullerol to the infection sites, liposomal formulations were prepared by the dehydration-rehydration method. When evaluated in the acute VL model, liposomal fullerol (Lip-Ful) formulations given i.p. at 0.05 and 0.2 mg/kg with 4-days intervals were more effective than the free form, with significant parasite reductions in both liver and spleen. Lip-Ful at 0.2 mg/kg promoted complete parasite elimination in the liver. The antileishmanial activity of Lip-Ful was further confirmed in a chronic model of VL. Lip-Ful was also found to induce secretion of pro-inflammatory TNF-α, IFN-γ and IL-1β cytokines. In conclusion, this work reports for the first time the antileishmanial activity of fullerol and introduces an innovative approach for treatment of VL based on the association of this nanostructure with liposomes.

The preclinical discovery and development of oral miltefosine for the treatment of visceral leishmaniasis: a case history

INTRODUCTION

Visceral leishmaniasis (VL) is a vector-borne disease caused by Leishmania donovani or Leishmania infantum. Closely related to poverty, VL is fatal and represents one of the main burdens on public health in developing countries. Treatment of VL relies exclusively on chemotherapy, a strategy still experiencing numerous limitations. Miltefosine (MF) has been used in the chemotherapy of VL in some endemic areas, and has been expanded to other regions, being considered crucial in eradication programs.

AREAS COVERED

This article reviews the most relevant preclinical and clinical aspects of MF, its mechanism of action and resistance to Leishmania parasites, as well as its limitations. The authors also give their perspectives on the treatment of VL.

EXPERT OPINION

The discovery of MF represented an enormous advance in the chemotherapy of VL, since it was the first oral drug for this neglected disease. Beyond selection of resistant parasites due to drug pressure, several other factors can lead to treatment failure such as, for example, factors intrinsic to the host, parasite and the drug itself. Although its efficacy as a monotherapy has reduced over recent years, MF is still an important alternative in VL chemotherapy, especially when used in combination with other drugs.

Ascorbic acid reduces the genetic damage caused by miltefosine (hexadecylphosphocholine) in animals infected by Leishmania (Leishamnia) infantum without decreasing its antileishmanial activity

Leishamaniasis is a neglected disease caused by over 20 Leishmania species, occurring in more than a hundred countries. Miltefosine (hexadecylphosphocholine) is the single oral drug used in treatment for leshmaniases, including cases of infections resistant to pentavalent antimony. Our group has recently demonstrated the ability of miltefosine to cause genomic lesions by DNA oxidation. Acknowledging that antioxidant compounds can potentially modulate Reactive Oxygen Species (ROS), our study verified whether ascorbic acid reduces the genotoxic and mutagenic effects caused by miltefosine, and whether it interferes with drug efficacy. For this purpose, uninfected Swiss mice received simultaneous (single dose treatment) miltefosine and ascorbic acid (gavage and intraperitoneally), besides pre and post treatments (ascorbic acid 24 h before and after drug administration); furthermore, Balb/c mice infected with Leishmania infantum received miltefosine plus ascorbic acid (repeated doses treatment). We conducted comet assays, micronucleus tests, dosages of superoxide dismutase enzyme and parasitic burden by the limiting dilution assay. We observed that ascorbic acid administered intraperitoneally displayed a protective effect over damage caused by miltefosine. However, this effect was not not observed when the same doses were administered via gavage, possibly due to low serum levels of this antioxidant. Ascorbic acid's protective effect reinforces that miltefosine damages DNA by oxidizing its nitrogenous bases, which is reduced by ascorbic acid due to its ability of protecting genetic material from the action of ROS. Therefore, our results show that this drug is efficient in reducing parasitic burden of L. infantum.

Use of miltefosine to treat canine visceral leishmaniasis caused by Leishmania infantum in Brazil

Background

Visceral leishmaniasis (VL) is an infectious disease with a variety of clinical signs. The main form of parasite transmission to humans and other mammalian hosts is through the bite of infected arthropod females with Lutzomyia longipalpis serving as the main vector in the Americas. Dogs are the main urban domestic reservoirs of the parasite and the main source of vector infection due to their high prevalence in endemic areas and the large number of parasites in the skin of infected animals. Although miltefosine has been used in Europe since 2002 for treatment of VL infected dogs, in the Americas the treatment of dogs has not been recommended. Therefore, this study aimed to evaluate efficacy of miltefosine observing a reduction of clinical signs in infected dogs and the infectiveness to the vector by Leishmania (L.) infantum.

Methods

To our knowledge, this is the first controlled study using qPCR and xenodiagnosis to evaluate the efficacy of miltefosine (Milteforan®, Virbac) as a single treatment in Brazil. Thirty-five adult dogs with canine visceral leishmaniasis (CVL), confirmed by clinical and laboratory tests, were included in this study. They received miltefosine at a dose of 2 mg/kg every 24 h for 28 days. The dogs were observed over a three-month period, during which clinical evaluations based on a scoring system were conducted at pre-established times. Parasite load was assessed by cytology and real-time polymerase chain reaction (qPCR). Transmissibility to the vector was evaluated by xenodiagnosis.

Results

At the end of the period, the following were observed: (i) the remission of clinical signs with a reduction in clinical scores for 94.2% of the animals; (ii) a statistically significant reduction (98.7%) in parasitic load by qPCR; and (iii) a reduction in infectivity to sand flies. After treatment, 74.2% of the animals remained or had become non-infectious.

Conclusions

Our study indicates that the use of miltefosine administered orally for 4 weeks contributes to a clinical improvement and reduction in infectivity of dogs to L. infantum.

Preclinical Studies Evaluating Subacute Toxicity and Therapeutic Efficacy of LQB-118 in Experimental Visceral Leishmaniasis

Visceral leishmaniasis (VL) is the most severe form of leishmaniasis and is the second major cause of death by parasites, after malaria. The arsenal of drugs against leishmaniasis is small, and each has a disadvantage in terms of toxicity, efficacy, price, or treatment regimen. Our group has focused on studying new drug candidates as alternatives to current treatments. The pterocarpanquinone LQB-118 was designed and synthesized based on molecular hybridization, and it exhibited antiprotozoal and anti-leukemic cell line activities. Our previous work demonstrated that LQB-118 was an effective treatment for experimental cutaneous leishmaniasis. In this study, we observed that treatment with 10 mg/kg of body weight/day LQB-118 orally inhibited the development of hepatosplenomegaly with a 99% reduction in parasite load. An in vivo toxicological analysis showed no change in the clinical, biochemical, or hematological parameters. Histologically, all of the analyzed organs were normal, with the exception of the liver, where focal points of necrosis with leukocytic infiltration were observed at treatment doses 5 times higher than the therapeutic dose; however, these changes were not accompanied by an increase in transaminases. Our findings indicate that LQB-118 is effective at treating different clinical forms of leishmaniasis and presents no relevant signs of toxicity at therapeutic doses; thus, this framework is demonstrated suitable for developing promising drug candidates for the oral treatment of leishmaniasis.

Antileishmanial drug discovery: comprehensive review of the last 10 years

This review covers the current aspects of leishmaniasis including marketed drugs, new antileishmanial agents, and possible drug targets of antileishmanial agents.

Antiprotozoal activity of quinonemethide triterpenes from Maytenus ilicifolia (Celastraceae)

The present study describes the leishmanicidal and trypanocidal activities of two quinonemethide triterpenes, maytenin (1) and pristimerin (2), isolated from Maytenus ilicifolia root barks (Celastraceae). The compounds were effective against the Trypanosomatidae Leishmania amazonensis and Leishmania chagasi and Trypanosoma cruzi, etiologic agents of leishmaniasis and Chagas' disease, respectively. The quinonemethide triterpenes 1 and 2 exhibited a marked in vitro leishmanicidal activity against promastigotes and amastigotes with 50% inhibitory concentration (IC(50)) values of less than 0.88 nM. Both compounds showed IC(50) lower than 0.3 nM against Trypanosoma cruzi epimastigotes. The selectivity indexes (SI) based on BALB/c macrophages for L. amazonensis and L. chagasi were 243.65 and 46.61 for (1) and 193.63 and 23.85 for (2) indicating that both compounds presented high selectivity for Leishmania sp. The data here presented suggests that these compounds should be considered in the development of new and more potent drugs for the treatment of leishmaniasis and Chagas' disease.

In vitro and in vivo efficacy of ether lipid edelfosine against Leishmania spp. and SbV-resistant parasites

Background

The leishmaniases are a complex of neglected tropical diseases caused by more than 20 Leishmania parasite species, for which available therapeutic arsenal is scarce and unsatisfactory. Pentavalent antimonials (SbV) are currently the first-line pharmacologic therapy for leishmaniasis worldwide, but resistance to these compounds is increasingly reported. Alkyl-lysophospoholipid analogs (ALPs) constitute a family of compounds with antileishmanial activity, and one of its members, miltefosine, has been approved as the first oral treatment for visceral and cutaneous leishmaniasis. However, its clinical use can be challenged by less impressive efficiency in patients infected with some Leishmania species, including L. braziliensis and L. mexicana, and by proneness to develop drug resistance in vitro.

Methodology/Principal Findings

We found that ALPs ranked edelfosine>perifosine>miltefosine>erucylphosphocholine for their antileishmanial activity and capacity to promote apoptosis-like parasitic cell death in promastigote and amastigote forms of distinct Leishmania spp., as assessed by proliferation and flow cytometry assays. Effective antileishmanial ALP concentrations were dependent on both the parasite species and their development stage. Edelfosine accumulated in and killed intracellular Leishmania parasites within macrophages. In vivo antileishmanial activity was demonstrated following oral treatment with edelfosine of mice and hamsters infected with L. major, L. panamensis or L. braziliensis, without any significant side-effect. Edelfosine also killed SbV-resistant Leishmania parasites in in vitro and in vivo assays, and required longer incubation times than miltefosine to generate drug resistance.

Conclusions/Significance

Our data reveal that edelfosine is the most potent ALP in killing different Leishmania spp., and it is less prone to lead to drug resistance development than miltefosine. Edelfosine is effective in killing Leishmania in culture and within macrophages, as well as in animal models infected with different Leishmania spp. and SbV-resistant parasites. Our results indicate that edelfosine is a promising orally administered antileishmanial drug for clinical evaluation.

Leishmaniasis represents a major international health problem, has a high morbidity and mortality rate, and is classified as an emerging and uncontrolled disease by the World Health Organization. The migration of population from endemic to nonendemic areas, and tourist activities in endemic regions are spreading the disease to new areas. Unfortunately, treatment of leishmaniasis is far from satisfactory, with only a few drugs available that show significant side-effects. Here, we show in vitro and in vivo evidence for the antileishmanial activity of the ether phospholipid edelfosine, being effective against a wide number of Leishmania spp. causing cutaneous, mucocutaneous and visceral leishmaniasis. Our experimental mouse and hamster models demonstrated not only a significant antileishmanial activity of edelfosine oral administration against different wild-type Leishmania spp., but also against parasites resistant to pentavalent antimonials, which constitute the first line of treatment worldwide. In addition, edelfosine exerted a higher antileishmanial activity and a lower proneness to generate drug resistance than miltefosine, the first drug against leishmaniasis that can be administered orally. These data, together with our previous findings, showing an anti-inflammatory action and a very low toxicity profile, suggest that edelfosine is a promising orally administered drug for leishmaniasis, thus warranting clinical evaluation.

The in vitro leishmanicidal activity of hexadecylphosphocholine (miltefosine) against four medically relevant Leishmania species of Brazil

The in vitro leishmanicidal activity of miltefosine® (Zentaris GmbH) was assessed against four medically relevant Leishmania species of Brazil: Leishmania (Leishmania) amazonensis, Leishmania (Viannia) braziliensis, Leishmania (Viannia) guyanensis and Leishmania (Leishmania) chagasi. The activity of miltefosine against these New World species was compared to its activity against the Old World strain, Leishmania (Leishmania) donovani, which is known to be sensitive to the effects of miltefosine. The IC50 and IC90 results suggested the New World species harboured similar in vitro susceptibilities to miltefosine; however, miltefosine was approximately 20 times more active against the Old World L. (L.) donovani than against the New World L. (L.) chagasi species. The selectivity index varied from 17.2-28.9 for the New World Leishmania species and up to 420.0 for L. (L.) donovani. The differences in susceptibility to miltefosine suggest that future clinical trials with this drug should include a laboratory pre-evaluation and a dose-defining step.

Luciferase-expressing Leishmania infantum allows the monitoring of amastigote population size, in vivo, ex vivo and in vitro

Here we engineered transgenic Leishmania infantum that express luciferase, the objectives being to more easily monitor in real time their establishment either in BALB/c mice—the liver and spleen being mainly studied—or in vitro. Whatever stationary phase L. infantum promastigotes population—wild type or engineered to express luciferase—the parasite burden was similar in the liver and the spleen at day 30 post the intravenous inoculation of BALB/c mice. Imaging of L. infantum hosting BALB/C mice provided sensitivity in the range of 20,000 to 40,000 amastigotes/mg tissue, two tissues—liver and spleen—being monitored. Once sampled and processed ex vivo for their luciferin-dependent bioluminescence the threshold sensitivity was shown to range from 1,000 to 6,000 amastigotes/mg tissue. This model further proved to be valuable for in vivo measurement of the efficiency of drugs such as miltefosine and may, therefore, additionally be used to evaluate vaccine-induced protection.

Leishmania infantum/L. chagasi parasites are inoculated in the skin of mammals by sand flies. Though most often these L. infantum-mammal interactions are asymptomatic, they can proceed, in some individuals, to a systemic disease known as visceral leishmaniasis. If left untreated this disease is fatal. The lack of protective or curative vaccines and the limited number of parasite-targeting drugs were incentive to set up experimental conditions that could allow easy monitoring of the fluctuation of the population size of parasites in living laboratory animals. Thus, in the present report, we depict two distinct readout assays that rely on a population of L. infantum we genetically engineered for stably expressing the firefly luciferase gene. These transgenic parasites were either inoculated to BALB/c mice or added to a culture of monocytic cells. Post intravenous inoculation, BALB/c mice were imaged over time, with special attention being given to the liver and the spleen. The sensitivity of this technique ranged from 20,000 to 40,000 parasites/mg of tissue and from 1,000 to 6,000 parasites/mg tissue, for in vivo and ex vivo measurements, respectively. Though preliminary, the data, relying on monocytic cells, are promising for further in vitro screening of small compound libraries.

Multicentric, controlled clinical study to evaluate effectiveness and safety of miltefosine and allopurinol for canine leishmaniosis

The aim of this trial was to evaluate the effectiveness and safety of miltefosine-allopurinol combination therapy vs. the current reference combination therapy, meglumine antimoniate-allopurinol, for canine leishmaniosis. Dogs included in the study exhibited clinical signs of the disease, were positive by PCR and serologically positive by immunofluorescent antibody test for leishmaniosis, and negative for ehrlichiosis. Dogs were divided into two groups: Group 1 was treated with 2 mg/kg of miltefosine orally once daily for 28 days and 10 mg/kg of allopurinol orally twice daily for 7 months; Group 2 was treated with 50 mg/kg of meglumine antimoniate sub-cutaneously twice daily for 28 days and allopurinol (same dose as Group 1) for 7 months. Dogs were examined according to the following schedule: pre-inclusion, Day 0 (D0), D14, D28, D84, D140 and D196. At each visit, blood, urine and bone marrow samples were collected. Parameters monitored included haematology, biochemistry, protein electrophoresis, serology, urinary protein/creatinine ratio and RTQ-PCR performed on bone marrow aspirates. A significant reduction in total clinical score and parasite load was observed in both groups over the 7-month study period (P < 0.0001), with no significant difference between groups (P = 0.3). The safety of miltefosine-allopurinol combination therapy was confirmed by lack of effect on renal and hepatic parameters and adverse reactions. Miltefosine, in combination with allopurinol, offers a safe, convenient and effective alternative treatment option for canine leishmaniosis compared to the reference therapy.

Long term failure of miltefosine in the treatment of refractory visceral leishmaniasis in AIDS patients

We carried out a retrospective and descriptive study of 4 HIV infected patients with relapsing visceral leishmaniasis (VL) seen at 2 tertiary-care hospitals in Spain during the last 6 y, in whom miltefosine was used as a compassionate use treatment at a dosage of 50 mg b.i.d. Patients had a medium CD4 lymphocyte count of 69 cells/microl and were C stage. All patients received at least 2 different anti-leishmanial drugs and had at least 3 relapses before miltefosine treatment (range 3-7). Three patients were treated with miltefosine at a standard dose of 50 mg b.i.d. for 28 d, and the other during 12 months. Despite an initial symptomatic improvement, miltefosine treatment failed to eradicate the infection in all cases. We conclude that the use of miltefosine alone is not strong enough to cure relapsing VL in HIV-1 controlled infected patients.

The reformulation of amphotericin B for oral administration to treat systemic fungal infections and visceral leishmaniasis

Amphotericin B (AmB) is a parenterally administered broad-spectrum antifungal and leishmanicidal drug that has been on the market for over sixty years. Unfortunately, significant infusion-related side effects and renal toxicity often accompany treatment, limiting its clinical applications. Lipid-based formulations have somewhat ameliorated the associated toxicity, but the increased cost of formulations restricts widespread use. AmB is amphipathic and exhibits low solubility and permeability, resulting in negligible absorption when administered orally. Advances in drug delivery systems have overcome some of the solubility issues that prevent oral bioavailability and new formulations are currently in development. The existence of an effective, safe and inexpensive oral formulation of amphotericin B would have significant applications for the treatment of disseminated fungal infections and would dramatically expand access to treatment of visceral leishmaniasis by introducing a readily available highly tolerated oral formulation of a drug with known efficacy.

Selection and phenotype characterisation of sitamaquine-resistant promastigotes of Leishmania donovani

A Leishmania donovani promastigote line resistant to 160microM sitamaquine, named SITA-160R, was selected in vitro by continuous stepwise drug pressure. SITA-160R line was able to infect murine peritoneal macrophages in vitro in the same manner as the wild-type line (WT) but was less infective for Balb/c mice than its parent WT clone. This line was about five and three times more resistant to sitamaquine than the WT line on promastigote and intramacrophage amastigote forms, respectively. No cross-resistance with other antileishmanial agents was observed and this resistance was stable when parasites were subcultured in drug-free medium for a long time or after in vivo passage.

Recent strategies for the chemotherapy of visceral leishmaniasis

Visceral leishmaniasis is a widespread and deadly disease. First-line drugs are antimonials, but amphotericin B and its lipid formulations B is used for treating visceral leishmaniasis that is unresponsive to antimony. New therapeutic approaches are being actively developed, including the following: use of drug carriers targeted specifically to the parasite location, thus reduce adverse effects of drug; use of immunomodulating drugs; evaluation of natural products; pharmacokinetic studies; and drug combinations. Recent clinical trials with paromomycin and miltefosine were successful and these drugs appear to be promising for the future therapy of visceral leishmaniasis. Furthermore, identification and therapeutic evaluation of specific targets in the Leishmania organism could lead to new compounds, such as antileishmanial drugs and reversal agents of drug resistance.

Miltefosine – discovery of the antileishmanial activity of phospholipid derivatives

Miltefosine (hexadecylphosphocholine, Impavidotrade mark), a novel antiprotozoal drug used for the treatment of visceral and cutaneous leishmaniasis, was identified and evaluated independently in the early 1980s as a potential anticancer drug in Germany and as an antileishmanial drug in the UK. Although miltefosine is not the most active compound of its class against Leishmania parasites in vitro, the early demonstration of activity after oral administration in experimental models of visceral leishmaniasis helped to bring this compound to the attention of WHO TDR for further development in a unique collaboration model with the pharmaceutical industry (Zentaris GmbH). Miltefosine is active against most Leishmania species, including those that cause cutaneous disease.

Imprinting of BALB/c mice with low Leishmania infantum parasite dose markedly protects spleen against high-dose challenge

In this study, we investigated in the BALB/c model, the dose-dependent protective potential of previous infection with Leishmania infantum parasites, against a high-dose challenge and showed for the first time that low-dose imprinting conferred substantial spleen resistance. Mice were immunized for 1 month or 5 months by IV route with parasite inocula ranging from 10(4) to 10(7) and from 10(3) to 10(5), respectively, and challenged for 1 month with 3 x 10(7) parasites. Liver protection was directly proportional to the parasite dose used for infection and reached 90-95% whereas, only low doses (< or =10(5)) protected spleen. Maximal spleen resistance (80%) was reached in mice infected for 5 months with 10(5) parasites. In most cases, protection was accompanied in spleen, by restored in vitro responses to Leishmania antigens. Analysis of anti L. infantum isotype responses and in vitro antigen-induced cytokine production, indicated that the acquired protection was irrespective of a Th1/Th2 imbalance.

Animal models of depression: navigating through the clinical fog

Animal models of human disease have proven of considerable value in elucidating basic pathophysiological mechanisms and in developing novel treatments. However, modelling human mental disorders in experimental animals is fraught with difficulties. Depression models generally lack both clinical and scientific credibility and have, thus far, failed to inform treatment strategies previously acquired through serendipity. The complexity and heterogeneity of the clinical states labelled 'depression' dictate that we continue to work with a crude and uninformative taxonomy within which 'core' clinical and pathophysiological features of depression are not clearly identified. Consequently, much of the neuroscience of animal modelling is framed around physiological and neurobiological phenomena that may be of relevance to only a minority of patients. Additionally, inferring pathophysiology from apparent treatment responses overestimates the efficacy of existing treatments and tends to ignore reliable demonstrations of the 'antidepressant effects' of non-pharmacological interventions. Whilst animal modelling remains a potentially important approach towards understanding neurobiological mechanisms in depression, we need to address the poverty of reliable clinical science that should inform model development.

The overexpression of an intracellular ABCA-like transporter alters phospholipid trafficking in Leishmania

In parasites, ATP-binding cassette (ABC) transporters represent an important family of proteins related to drug resistance and other biological activities. Here we report the characterization of LtrABCA2, a new ABC transporter of the ABCA subfamily in the protozoan parasite Leishmania tropica, localized at the flagellar pocket region and in internal vesicles. The overexpression of this transporter reduced the accumulation of fluorescent glycerophospholipid analogs, increased the exocytic activity, and decreased infectivity of macrophage, but did not confer resistance to drugs. Together, these results suggest that this new ABC transporter plays a role in phospholipid trafficking, which may be modifying the vesicular trafficking and the infectivity of the parasite.

Challenges and new discoveries in the treatment of leishmaniasis

Leishmaniasis is a parasitic disease caused by a hemoflagellate, Leishmania spp. The parasite is transmitted by the bite of an infected female phlebotomine sandfly. The disease is prevalent throughout the world and in at least 88 countries. Human leishmanial infections may manifest in any of the four most common forms. Depending on the causative species, it can manifest as cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL), diffused cutaneous leishmaniasis (DCL), or visceral leishmaniasis (VL). Although there are nearly 25 compounds having antileishmanial effects, only a few are used for humans and most of these are parenteral. The oldest was urea stibamine, developed in India in 1922. The original drug had severe toxic effects, and later on its pentavalent compounds were prepared, which remained the sole treatment modality for several decades and saved millions of lives. However, reports of unresponsiveness to pentavalent sodium antimony gluconate (SAG) started in the 1970s, and in some parts of India about a quarter of kala-azar cases are reported to have developed resistance even to its higher doses. This development led to successful clinical trials of pentamidine and amphotericine B. The latter, an antifungal compound, was also found to be highly nephrotoxic, and to minimize these side effects various colloidal and lipid formulations have been prepared. These preparations are comparatively safe but are exorbitantly costly. In the past two decades, more focus has been given to finding oral drugs to minimize injection-associated complications, including blood-borne infection. Various drugs were reported effective, including antifungal ketoconazole. However, the most promising drug found is an anticancer compound, miltefosine, that belongs to the alkylphosphocholine group. The drug has undergone experimental and clinical trials and found to be 94%-97% effective. However, the drug cannot be given during pregnancy and shows severe gastrointestinal side effects. Moreover, its cost will be another limiting factor. Other drugs such as paromomycin, allopurinol, and sitamaquine have been reported with variable cure rates. Because of these limitations, a combination therapy, preferably coupled with specific parasite enzyme inhibitors, is the only hope.

Effect of the lysophospholipid analogues edelfosine, ilmofosine and miltefosine against Leishmania amazonensis

OBJECTIVES

Analysis of the effect of edelfosine, ilmofosine and miltefosine on Leishmania amazonensis and of potential targets of these lysophospholipid analogues.

METHODS

Quantification and ultrastructural analysis of the effect of lysophospholipid analogues on promastigote forms and on infected peritoneal macrophages, and flow cytometry analysis of treated promastigotes labelled with propidium iodide and rhodamine 123 (Rh123).

RESULTS

The lysophospholipid analogues presented potent antiproliferative activity with IC50/3 days of 1.9-3.4 microM for promastigotes and 4.2-9.0 microM for intracellular amastigotes. Treatment with these analogues in Schneider medium for 1 day led to a dose-dependent decrease in Rh123 fluorescence, an effect more accentuated in edelfosine-treated parasites, suggesting interference with the potential of the mitochondrial membrane. In both forms of L. amazonensis, edelfosine induced extensive mitochondrial damage, multinucleation and, in promastigotes, also led to plasma membrane alterations, formation of autophagic structures and membranous arrangements inside the flagellar pocket.

CONCLUSIONS

The alkylglycerophosphocholines edelfosine and ilmofosine were more active than the alkylphosphocholine miltefosine against promastigotes and intracellular amastigotes of L. amazonensis, and ultrastructural and flow cytometry data indicate the mitochondrion as a target of edelfosine.

Possible mechanism of miltefosine-mediated death of Leishmania donovani

Miltefosine causes leishmanial death, but the possible mechanism(s) of action is not known. The mode of action of miltefosine was investigated in vitro in Leishmania donovani promastigotes as well as in extra- and intracellular amastigotes. Here, we demonstrate that miltefosine induces apoptosis-like death in L. donovani based on observed phenomena such as nuclear DNA condensation, DNA fragmentation with accompanying ladder formation, and in situ labeling of DNA fragments by the terminal deoxyribonucleotidyltransferase-mediated dUTP-biotin nick end labeling method. Understanding of miltefosine-mediated death will facilitate the design of new therapeutic strategies against Leishmania parasites.

Miltefosine induces apoptosis-like death in Leishmania donovani promastigotes

Miltefosine (hexadecylphosphocholine [HePC]) has proved to be a potent oral treatment for human visceral leishmaniasis due to Leishmania donovani. The molecular mechanisms that contribute to the antileishmanial activity of HePC are still unknown. We report that in wild-type promastigotes of Leishmania donovani HePC is able to induce a cell death process with numerous cytoplasmic, nuclear, and membrane features of metazoan apoptosis, including cell shrinkage, DNA fragmentation into oligonucleosome-sized fragments, and phosphatidylserine exposure. None of these changes were detected in an HePC-resistant clone treated with the same drug concentration. Therefore, HePC does not appear to kill L. donovani promastigotes by a direct toxic mechanism but, rather, kills the promastigotes by an indirect one. Pretreatment of wild-type promastigotes with two broad caspase inhibitors, z-Val-Ala-DL-Asp(methoxy)-fluoromethylketone and Boc-Asp(methoxy)-fluoromethylketone, as well as a broad protease inhibitor, calpain inhibitor I, prior to drug exposure interfered with DNA fragmentation but did not prevent cell shrinkage or phosphatidylserine externalization. These data suggest that at least part of the apoptotic machinery operating in wild-type promastigotes involves proteases. Identification of the death-signaling pathways activated in HePC-sensitive parasites appears to be essential for a better understanding of the molecular mechanisms of action and resistance in these parasites.

Canine Leishmaniasis

Canine leishmaniasis is caused by Leishmania infantum (syn. L. chagasi, in America) and is transmitted by the bite of phlebotomine sand flies. Infected dogs constitute the main domestic reservoir of the parasite and play a key role in transmission to humans, in which the parasite produces visceral leishmaniasis. The increasing awareness that control of the human disease depends on effective control of canine leishmaniasis has promoted, in the last few years, research into leishmanial infection in dogs. Newly available specific reagents and molecular tools have been applied to the detailed investigation of canine leishmaniasis and important advances have been made in elucidating the epidemiology and pathology of the disease. These new findings have led to better understanding of the disease, and have also helped in the development of new diagnostic methods and control measures against the infection, such as insecticide-impregnated collars for dogs, new drugs and treatment protocols, and second generation vaccines, with the hope of not only reducing the heavy burden of the disease among dogs but also reducing the incidence of human visceral leishmaniasis.

Miltefosine (Impavido): the first oral treatment against leishmaniasis

Miltefosine is a novel antileishmanial drug that has significant selectivity in both in vitro and in vivo models. Clinical efficacy was demonstrated for the treatment of visceral leishmaniasis with the advantage of oral administration over the currently recommended antileishmanial drugs that require parenteral administration. Miltefosine produces high cure rates also in patients resistant to the standard antimonial therapy.

Antiprotozoal activities of phospholipid analogues

The antiprotozoal activity of phospholipid analogues, originally developed as anti-cancer drugs, has been determined in the past decade. The most susceptible parasites are Leishmania spp. and Trypanosoma cruzi with activity also shown against Trypanosoma brucei spp., Entamoeba histolytica and Acanthamoeba spp. Miltefosine, an alkylphosphocholine, was registered for the oral treatment of visceral leishmaniasis (VL) in India in March 2002. This review will focus on the biological activities of phospholipid analogues. Biochemical and molecular targets and mechanism(s) of action have been studied extensively in tumor cells but have not been determined in protozoa.

Choline transport in Leishmania major promastigotes and its inhibition by choline and phosphocholine analogs

Phosphatidylcholine is the most abundant phospholipid in the membranes of the human parasite Leishmania. The metabolic pathways leading to its biosynthesis are likely to play a critical role in parasite development and survival and may offer a good target for antileishmanial chemotherapy. Phosphatidylcholine synthesis via the CDP-choline pathway requires transport of the choline precursor from the host. Here, we report the first characterization of choline transport in this parasite, which is carrier-mediated and exhibits Michaelis-Menten kinetics with an apparent K(m) value of 2.5 microM for choline. This process is Na(+)-independent and requires an intact proton gradient to be fully functional. Choline transport into Leishmania is highly specific for choline and is inhibited by the choline carrier inhibitor hemicholinium-3, the channel blocker quinacrine, the antimalarial aminoquinolines quinine and quinidine, the antileishmanial phosphocholine analogs, miltefosine and edelfosine, and by choline analogs, most of which have antimalarial activities. Most importantly, choline analogs kill the promastigote form of the parasite in vitro in the low micromolar range. These results set the stage for the use of choline analogs in antileishmanial chemotherapy and shed new lights on the mechanism of action of the leishmanicidal phosphocholine analogs.

Treatment of visceral leishmaniasis: a review of current treatment practices

Visceral leishmaniasis (VL) is a systemic protozoan infection that infects a million people living in subtropical and tropical areas. Once established, the clinical course of untreated disease leads to death. Recent, large-scale epidemics in east Africa and India and the emergence of a new epidemic in patients infected with HIV makes VL a priority for the World Health Organization. Pentavalent antimonials have been the mainstay of the treatment for > 60years. The progressive appearance of antimonial resistance, the developments of lipid formulations of amphotericin B and a new oral administered drug (miltefosine) have changed the pattern of VL treatment. The prohibitive cost of new therapies leads to different treatment practices according to the socioeconomic and cultural status of each region.

Sensitivities of Leishmania species to hexadecylphosphocholine (miltefosine), ET-18-OCH(3) (edelfosine) and amphotericin B

The sensitivities of both promastigote and amastigote stages of six species of Leishmania, L. donovani, L. major, L. tropica, L. aethiopica, L. mexicana and L. panamensis, were determined in vitro to the phospholipid drugs hexadecylphosphocholine (HPC, miltefosine) and ET-18-OCH(3) (edelfosine). In all assays L. donovani was the most sensitive species, with ED(50) values in the range of 0.12-1.32 microM against promastigotes and 1.2-4.6 microM against amastigotes. L. major was the least sensitive species in the majority of assays with ED(50) values for HPC in the range of 4.8-13.1 microM against promastigotes and for HPC and ET-18-OCH(3) in the range of 7.5-37.1 microM against amastigotes. Amphotericin B deoxycholate was used as the standard drug and gave submicromolar ED(50) values in all assays; L. mexicana was the least sensitive species to this drug.

Quantitation of Leishmania infantum in tissues of infected BALB/c mouse by sandwich ELISA

In this report, a sandwhich ELISA was developed to quantify spleen and liver burdens from L. infantum-infected BALB/c mice. Amastigote antigens obtained following Nonidet P40 extraction of parasite-harbouring tissues were captured by anti-L. infantum human IgG insolubilized onto microtiter plate and subsequently revealed with anti-L. infantum F(ab)' fragments labelled with peroxidase. The method was easy to perform, precise and capable to specifically and accurately detect 5 x 10(4) amastigotes/100 mg tissue. Parasite burdens from infected BALB/c mice, in various conditions, were measured by ELISA and Giemsa-stained touch imprint reference methods, and compared. Both techniques agreed well with close values for liver burdens, but the spleen loads measured by the ELISA were, on average, 10.7 times higher than those calculated from imprints. This difference was attributed partly to the underestimation brought by Stauber's formula. However, it did not preclude the usefulness of this newly developed test, since results obtained in kinetics studies and evaluation of the efficiency of leishmanicidal drugs allowed us to draw identical conclusions.

Specific treatment of Chagas disease: current status and new developments

The current situation regarding specific chemotherapy for Chagas disease (American trypanosomiasis), and new developments in this field, are reviewed. Despite previous controversy on the autoimmune origin of Chagas disease pathology, available knowledge supports the notion that this condition should be treated as a parasitic, not an autoimmune, disease. Currently available drugs (nitrofurans and nitroimidazoles) are active in acute or short-term chronic infections, but have very low antiparasitic activity against the prevalent chronic form of the disease, and toxic side-effects are frequently encountered. The nitroimidazole benznidazole has also shown significant activity in the treatment of reactivated Trypanosoma cruzi infections in patients with acquired immune deficiency syndrome and in other immunosuppressed patients with underlying chronic Chagas disease. Although the etiological agent, T. (Schizotrypanum) cruzi, requires specific endogenous sterols for cell viability and proliferation, the currently available antifungal sterol biosynthesis inhibitors are not powerful enough to induce parasitological cures of human or experimental infections. However, new triazole antifungal compounds, which are potent inhibitors of the sterol C14alpha demethylase of the parasite and have special pharmacokinetic properties, are capable of inducing parasitological cures in murine models of both acute and chronic Chagas disease. They are currently the most advanced candidates for clinical trials in patients with Chagas disease. Other potential chemotherapeutic agents against T. cruzi currently in development include antiproliferative lysophospholipid analogs (already in clinical trials as the first oral treatment for visceral leishmaniasis), cysteine proteinase (cruzipain) inhibitors, and compounds that interfere with purine salvage and inositol metabolism.

Expression of green fluorescent protein as a marker for effects of antileishmanial compounds in vitro

Transgenic Leishmania infantum promastigotes, which constitutively express green fluorescent protein (GFP) in their cytoplasm, were used to monitor the effects of antileishmanial compounds in real time. The GFP-based assay provided a reliable measure of drug-induced inhibitory effects on protein expression, resulting in a dynamic picture of the responses of leishmanial promastigotes to the compounds tested.

Activities of hexadecylphosphocholine (miltefosine), AmBisome, and sodium stibogluconate (Pentostam) against Leishmania donovani in immunodeficient scid mice

In both scid and BALB/c mouse-Leishmania donovani models, hexadecyphosphocholine (miltefosine) and AmBisome had similar levels of activity. In contrast, sodium stibogluconate (Pentostam) was significantly less active against L. donovani in scid mice than in BALB/c mice. The in vitro anti-leishmanial activity of miltefosine was similar in peritoneal macrophages derived from both scid and BALB/c mice, whereas Pentostam and AmBisome were significantly more active in the latter.

Alkyl-lysophospholipid resistance in multidrug-resistant Leishmania tropica and chemosensitization by a novel P-glycoprotein-like transporter modulator

Drug resistance has emerged as a major impediment in the treatment of leishmaniasis. Alkyl-lysophospholipids (ALP), originally developed as anticancer drugs, are considered to be the most promising antileishmanial agents. In order to anticipate probable clinical failure in the near future, we have investigated possible mechanisms of resistance to these drugs in Leishmania spp. The results presented here support the involvement of a member of the ATP-binding cassette (ABC) superfamily, the Leishmania P-glycoprotein-like transporter, in the resistance to ALP. (i) First, a multidrug resistance (MDR) Leishmania tropica line overexpressing a P-glycoprotein-like transporter displays significant cross-resistance to the ALP miltefosine and edelfosine, with resistant indices of 9.2- and 7.1-fold, respectively. (ii) Reduced expression of P-glycoprotein in the MDR line correlates with a significant decrease in ALP resistance. (iii) The ALP were able to modulate the P-glycoprotein-mediated resistance to daunomycin in the MDR line. (iv) We have found a new inhibitor of this transporter, the sesquiterpene C-3, that completely sensitizes MDR parasites to ALP. (v) Finally, the MDR line exhibits a lower accumulation than the wild-type line of bodipy-C(5)-PC, a fluorescent analogue of phosphatidylcholine that has a structure resembling that of edelfosine. Also, C-3 significantly increases the accumulation of the fluorescent analogue to levels similar to those of wild-type parasites. The involvement of the Leishmania P-glycoprotein-like transporter in resistance to drugs used in the treatment of leishmaniasis also supports the importance of developing new specific inhibitors of this ABC transporter.

In vivo involvement of polymorphonuclear neutrophils in Leishmania infantum infection

BACKGROUND

The role of lymphocytes in the specific defence against L. infantum has been well established, but the part played by polynuclear neutrophil (PN) cells in controlling visceral leishmaniasis was much less studied. In this report we examine in vivo the participation of PN in early and late phases of infection by L. infantum.

RESULTS

Promastigote phagocytosis and killing occurs very early after infection, as demonstrated by electron microscopy analyses which show in BALB/c mouse spleen, but not in liver, numerous PN harbouring ultrastructurally degraded parasites. It is shown, using mAb RB6-8C5 directed against mature mouse granulocytes, that in chronically infected mice, long-term PN depletion did not enhance parasite counts neither in liver nor in spleen, indicating that these cells are not involved in the late phase of L. infantum infection. In acute stage of infection, in mouse liver, where L. infantum load is initially larger than that in spleen but resolves spontaneously, there was no significant effect of neutrophils depletion. By contrast, early in infection the neutrophil cells crucially contributed to parasite killing in spleen, since PN depletion, performed before and up to 7 days after the parasite inoculation, resulted in a ten-fold increase of parasite burden.

CONCLUSIONS

Taken together these data show that neutrophil cells contribute to the early control of the parasite growth in spleen but not in liver and that these cells have no significant effect late in infection in either of these target organs.

Treatment of visceral leishmaniasis (kala-azar): a decade of progress and future approaches

In 1990, there was essentially one treatment regimen in use for visceral leishmaniasis (kala-azar) around the world: 20 to 28 days of daily injections of pentavalent antimony (Sb). During the past 10 years, however, new agents have been tested alone or in combination, in more than 50 studies carried out worldwide. This renewed clinical effort was spurred by a variety of factors, including the emergence of large-scale Sb unresponsiveness in India, where up to one-half of the world's cases of kala-azar now are found. As this new decade opens, the success of this clinical research effort is tangible: three additional, highly effective parenteral regimens now are available (amphotericin B, lipid formulations of amphotericin B, aminosidine), and an active oral agent, a long sought after objective in kala-azar, has been identified (miltefosine). This report reviews the evolution of treatment of visceral leishmaniasis, considers the interaction of the immune response and chemotherapy, highlights therapeutic successes and failures, examines advantages and disadvantages of current treatments, and looks at future therapeutic approaches to the management of this disseminated intracellular protozoal infection.

Mechanism of action of anti-proliferative lysophospholipid analogues against the protozoan parasite Trypanosoma cruzi: potentiation of in vitro activity by the sterol biosynthesis inhibitor ketoconazole

We investigated the mechanism of action of metabolically stable lysophospholipid analogues (LPAs), with potent anti-tumour and anti-protozoal activity against Trypanosoma cruzi, the causative agent of Chagas' disease. Against the axenically grown epimastigote form of the parasite, the IC(50)s after 120 h for ET-18-OCH(3), miltefosine and ilmofosine were 3, 1 and 3 microM, respectively; at higher concentrations immediate lytic effects were observed. Eradication of the intracellular amastigote, grown inside Vero cells, was achieved at 0.1, 0.1 and 1 microM for ET-18-OCH(3), miltefosine and ilmofosine, respectively. Analysis of the lipid composition of epimastigotes exposed to LPAs at their IC(50) for 120 h showed that the ratio of phosphatidyl-choline (PC) to phosphatidylethanolamine (PE) changed from 1.5 in control cells to c. 0.67 in those treated with the analogues. A significant increase in the content of phosphatidylserine was also observed in treated cells. Intact epimastigotes efficiently incorporated radioactivity from L-[methyl-(14)C]methionine into PC, but not from [methyl-(14)C]choline. ET-18-OCH(3) inhibited the incorporation of L-[methyl-(14)C]methionine into PC with an IC(50) of 2 microM, suggesting that inhibition of the de novo synthesis through the Greenberg's pathway was a primary effect underlying the selective anti-parasitic activity of this compound. Antiproliferative synergism was observed as a consequence of combined treatment of epimastigotes with ET-18-OCH(3) and ketoconazole, a sterol biosynthesis inhibitor, probably due to the fact that a secondary effect of the latter is also a blockade of PC synthesis at the level of PE-PC-N-methyl-transferase.

Flow cytometry analysis of the effect of allopurinol and the dinitroaniline compound (Chloralin) on the viability and proliferation of Leishmania infantum promastigotes

BACKGROUND

Leishmaniasis is a major parasitic disease in the tropical regions. However, Leishmania infantum has recently emerged as a very important cause of opportunistic infections for individuals positive for human immunodeficiency virus (HIV). However, there is a lack of in vitro tests for assessing the effect of anti-parasitic drugs on the viability and proliferation of Leishmania infantum. The aim of this study is to assess the efficacy of anti-parasitic drugs like allopurinol and Chloralin on the viability and proliferation of L. infantum promastigotes by utilizing two complementary flow cytometric approaches after exposure of the promastigotes to various concentrations of the drugs.

RESULTS

The density of the cultures in the presence and absence of allopurinol was determined by haemocytometer enumeration. The two flow cytometric approaches used to monitor the drug effect were: (i) a quantitative method to measure cell division using 5-,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) staining and (ii) evaluation of cell viability by dual-staining with the membrane-permeable nuclear stain, SBRY-14 and propidium iodide. It was found that concentrations of allopurinol above 50 microg/ml yielded a clear decrease in the proliferation rate of the promastigotes. However, the viability results showed that about 46.8% of the promastigotes incubated in the presence of 800 microg/ml of allopurinol were still alive after 96 hours. In sharp contrast, more than 90% of promastigotes treated with Chloralin 10 microM (2.7 microg/ml) were dead after 48 hours of treatment. These flow cytometric findings suggest that allopurinol has a leishmaniostatic effect while the dinitroaniline compound (Chloralin) has a leishmaniocidal effect against promastigotes.

CONCLUSIONS

The flow cytometric data on proliferation and viability were consistent with results obtained from haemocytometer counts and allowed us to develop a model for assessing in vitro the effects of medicaments like allopurinol and chloralin on L. infantum promastigotes on a cellular level.