Leishmania spp.: development of pentostam-resistant clones in vitro by discontinuous drug exposure

Genotypic profiles of Leishmania (Viannia) braziliensis strains from cutaneous leishmaniasis patients and their relationship with the response to meglumine antimoniate treatment: a pilot study

Background: Forty-four strains isolated from a cohort of cutaneous leishmaniasis (CL) patients who did or did not respond to one course of treatment with meglumine antimoniate were investigated to explore genetic polymorphisms in parasite kinetoplast DNA minicircles. Leishmania (Viannia) braziliensis strains isolated from responder (R) and non-responder (NR) patients who acquired infection in Rio de Janeiro or in other Brazilian states were studied using low-stringency single-specific primer polymerase chain reaction (LSSP-PCR) to identify genetic polymorphisms. Results: Polymorphisms were observed in parasites recovered from patient lesions. No association was found between a specific genotype and R or NR patients. Phenetic analysis grouped the genotypes into three main clusters, with similarity indices varying from 0.72 to 1.00. Although no specific genotype association was detected, at least one group of L. (V.) braziliensis genotypes that circulates in Rio de Janeiro was discriminated in clusters I and III, showing phenotypes of good and poor responses to treatment, respectively. Cluster I comprised parasite profiles recovered from R patients from Rio de Janeiro and in cluster III, NR samples were prevalent. Cluster II comprised 24 isolates, with 21 from Rio de Janeiro and three from other states, equally distributed between R and NR patients. Additionally, we found that parasites sharing all common genetic characteristics acted differently in response to treatment. Conclusions: These results are of clinical-epidemiological importance since they demonstrate that populations of L. (V.) braziliensis that exhibit high levels of genetic similarity also display different phenotypes associated with meglumine antimoniate responses in cutaneous leishmaniasis patients.

In Vitro Sensitivity of Cutaneous Leishmania Promastigote Isolates Circulating in French Guiana to a Set of Drugs

AbstractAnti-leishmaniasis drug resistance is a common problem worldwide. The aim of this study was to inventory the general in vitro level of sensitivity of Leishmania isolates circulating in French Guiana and to highlight potential in vitro pentamidine-resistant isolates. This sensitivity study was conducted on 36 patient-promastigote isolates for seven drugs (amphotericin B, azithromycin, fluconazole, meglumine antimoniate, miltefosine, paromomycin, and pentamidine) using the Cell Counting Kit-8 viability test. The IC₅₀ values obtained were heterogeneous. One isolate exhibited high IC₅₀ values for almost all drugs tested. Pentamidine, which is the first-line treatment in French Guiana, showed efficacy at very low doses (mean of 0.0038 μg/mL). The concordance of the in vitro pentamidine results with the patients' clinical outcomes was 94% (K = 0.82).

Intralesional Pentamidine: A Novel Therapy for Single Lesions of Bolivian Cutaneous Leishmaniasis

A novel therapy, intralesional (IL) pentamidine, was compared to intralesional therapy with antimony (ILSb), a World Health Organization-recommended therapy, for single Bolivian Leishmania braziliensis lesions. In Study 1, 90 patients were randomized equally between three injections of ILSb over 5 days, five injections of ILSb over 11 days, and three injections of IL pentamidine (120 μg/mm(2)lesion area [ILPenta-120-3]) over 5 days. Cure rates at 6 months were 57% for ILSb-3 injections, 73% for ILSb-5 injections, and 72% for ILPenta-120-3 injections. Adverse effects were local irritation and injection-site pain-ILSb (60 patients): mild (25), moderate (4); IL pentamidine (30 patients): mild (4), moderate (3). In Study 2, 60 patients were randomized equally between five injections of ILSb and three injections of a double dose of IL pentamidine (240 μg/mm(2)[ILPenta-240-3]). In Study 2, cure rates were 67% for ILSb-5 injections and 73% for ILPenta-240-3. For three IL injections of pentamidine, efficacy was optimized at a dose of 120 μg/mm(2)lesion area. The cure rate of that regimen was similar to that for ILSb-5 injections and nonstatistically larger than that of ILSb-3 injections. IL pentamidine is an attractive alternative to ILSb on the basis of efficacy for Bolivian L. braziliensis, the threat of Sb-resistant parasites, tolerance, and patient convenience of three visits over 5 days.

In vitro sensitivity of paired Leishmania (Viannia) braziliensis samples isolated before meglumine antimoniate treatment and after treatment failure or reactivation of cutaneous leishmaniasis

This study evaluated the in vitro sensitivity of paired Leishmania braziliensis samples isolated from the same patient before pentavalent antimonial treatment (Sample A) and after treatment failure or cutaneous leishmaniasis reactivation (Sample B) in patients undergoing intralesional administration or injections (5 mgSb(V)/kg/d) of meglumine antimoniate. Fourteen samples from 7 patients were studied. After 24 h of drug exposure, 50% lethal dose (LD50) values for promastigotes ranged from 0.37 mg/mL to 5.86 mg/mL for samples obtained before treatment (A) and 0.89 mg/mL to 7.80 mg/mL for samples obtained after treatment (B). After 48 h, LD50 values ranged from 0.37 mg/mL to 5.75 mg/mL and 0.70 mg/mL to 7.68 mg/mL for A and B samples, respectively. After 48 h, LD50 values for amastigotes ranged from 11.7 to 44.3 μg/mL for A samples and 13.7 to 52.7 μg/mL for B samples. Of 7 patients, 1 discontinued treatment and 6 were cured after retreatment with amphotericin B (4 cases) or meglumine antimoniate (2 cases). Overall the B samples had higher LD50 values than A samples; however the difference was not significant. These results do not support the hypothesis that low-dose and intralesional treatments induce selection of resistant parasites in vitro and suggest that other factors may influence therapeutic outcome in patients with poor response to initial treatment.

A comparative evaluation of amphotericin B and sodium antimony gluconate, as first-line drugs in the treatment of Indian visceral leishmaniasis

In a study to evaluate the relative efficacies of sodium antimony gluconate (SAG) and amphotericin B (AMB), each drug was used to treat 60 Indian cases of visceral leishmaniasis (VL). At the time of treatment, each case had recently been parasitologically confirmed. The patients received either 20 mg SAG/kg daily, by intramuscular injection, for 4 weeks, or 1 mg AMB/kg daily, infused slowly over 2 h, with no incremental dosage, for 20 days. The response of the patients was followed clinically and by the microscopical examination of bone-marrow aspirates (BMA). The infected macrophages in subsamples of the BMA collected pre-treatment were cultured so that the drug sensitivities of the parasites, to 20 microg SAG or 1 microg AMB/ml medium, could be determined in vitro. Other subsamples of the BMA were used to set up promastigote cultures that were then used to infect BALB/c mice. The responses of the mice to 5 days of treatment with SAG or AMB (at the same daily dosages as used in the clinical trials) were subsequently explored. SAG only cured 46.6% of the patients given the drug, only cleared amastigotes from 38.3% of the macrophage cultures, and only cured 53.3% of the infected mice. The corresponding values for AMB - 100%, 100% and 100% - were markedly higher (P <0.001 for each comparison). Although nine patients had to be withdrawn from the SAG group (all because of cardiac toxicity), all of the patients given AMB completed their treatment without any serious adverse effects (P <0.01). Two of the patients withdrawn from the SAG arm died shortly after their withdrawal; earlier withdrawal may have saved them. At least in the setting of the present study, AMB appears far superior to SAG as a first-line drug against VL and should replace it.

The natural absence of RPA1N domain did not impair Leishmania amazonensis RPA-1 participation in DNA damage response and telomere protection

We have previously shown that the subunit 1 of Leishmania amazonensis RPA (LaRPA-1) alone binds the G-rich telomeric strand and is structurally different from other RPA-1. It is analogous to telomere end-binding proteins described in model eukaryotes whose homologues were not identified in the protozoan´s genome. Here we show that LaRPA-1 is involved with damage response and telomere protection although it lacks the RPA1N domain involved with the binding with multiple checkpoint proteins. We induced DNA double-strand breaks (DSBs) in Leishmania using phleomycin. Damage was confirmed by TUNEL-positive nuclei and triggered a G1/S cell cycle arrest that was accompanied by nuclear accumulation of LaRPA-1 and RAD51 in the S phase of hydroxyurea-synchronized parasites. DSBs also increased the levels of RAD51 in non-synchronized parasites and of LaRPA-1 and RAD51 in the S phase of synchronized cells. More LaRPA-1 appeared immunoprecipitating telomeres in vivo and associated in a complex containing RAD51, although this interaction needs more investigation. RAD51 apparently co-localized with few telomeric clusters but it did not immunoprecipitate telomeric DNA. These findings suggest that LaRPA-1 and RAD51 work together in response to DNA DSBs and at telomeres, upon damage, LaRPA-1 works probably to prevent loss of single-stranded DNA and to assume a capping function.

Antimony resistance in leishmania, focusing on experimental research

Leishmaniases are parasitic diseases that spread in many countries with a prevalence of 12 million cases. There are few available treatments and antimonials are still of major importance in the therapeutic strategies used in most endemic regions. However, resistance toward these compounds has recently emerged in areas where the replacement of these drugs is mainly limited by the cost of alternative molecules. In this paper, we reviewed the studies carried out on antimonial resistance in Leishmania. Several common limitations of these works are presented before prevalent approaches to evidence antimonial resistance are related. Afterwards, phenotypic determination of resistance is described, then confronted to clinical outcome. Finally, we detail molecular mechanisms and targets involved in resistance and already identified in vitro within selected mutant strains or in clinical isolates.

Comparative efficacies of two antimony regimens to treat Leishmania braziliensis-induced cutaneous Leishmaniasis in rhesus macaques (Macaca mulatta)

This study compared the efficacies of two N-methylglucomine antimoniate (MA) dose regimens for treating macaques with Leishmania braziliensis-induced chronic skin disease. Whereas all animals treated with the full dose (20 mg MA/kg/day) were cured, 50% of the monkeys receiving a low-dose regimen (5 mg MA/kg/day) relapsed. The antimony concentrations in macaque plasma and tissue samples were greater in the full-dose group than in that receiving a subtherapeutic MA regimen. Our data also suggest the presence of drug-induced hepatic pathology.

Mucosal leishmaniasis . Current scenario and prospects for treatment

Leishmaniasis causes significant morbidity and mortality and thus constitutes a serious public health problem. Even though it has long been endemic in developing countries, in recent years the economic globalization and the increased volume of international travel have extended its prevalence in developed countries. In addition, native populations may be exposed to the infection through blood transfusion and the use of blood products produced from infected asymptomatic individuals. Mucosal leishmaniasis (ML) is a chronic form of this infection, which attacks the mucosa. In most cases this form of leishmaniasis results from the metastatic spread of Leishmania (Viannia) braziliensis from cutaneous lesions. It is a healthcare issue because of its wide demographic distribution, its association with significant morbidity levels, and because of the pressing concern that tourists who travel to endemic areas might present the disease even years later. The treatment currently available for ML is based on drugs such as pentavalent antimony-containing compounds, amphotericin B deoxycholate and pentamidine and often guarantees a satisfactory clinical response. Nevertheless, it also frequently provokes serious side effects. This review offers a critical analysis of the drugs now available for the treatment of ML as also of the future prospects for the treatment of the disease.

SENSITIVITY OF LEISHMANIA BRAZILIENSIS PROMASTIGOTES TO MEGLUMINE ANTIMONIATE (GLUCANTIME) IS HIGHER THAN THAT OF OTHER LEISHMANIA SPECIES AND CORRELATES WITH RESPONSE TO THERAPY IN AMERICAN TEGUMENTARY LEISHMANIASIS

The first line drugs for the treatment of leishmaniasis are antimonial derivatives. Poor clinical response may be credited to factors linked to the host, the drug, or the parasite. We determined the sensitivity of Leishmania sp. promastigotes and amastigotes by counting parasites exposed to increasing concentrations of meglumine antimoniate (Glucantime). Leishmania braziliensis promastigotes were significantly more sensitive than those belonging to other species. The sensitivity of L. braziliensis isolates from patients with unfavorable clinical outcome, such as therapeutic failure or relapse, was significantly lower than those from patients who had clinical cure. Poor clinical response to therapy (therapeutic failure or relapse) was also associated with inadequate antimonial therapy. We also found a significant and positive correlation between promastigotes and intracellular amastigotes with regard to their in vitro susceptibilities to meglumine antimoniate. Our data provide evidence for an association between the sensitivity of promastigotes to antimonials in vitro and clinical response to therapy in American tegumentary leishmaniasis. The high sensitivity of the local L. braziliensis to meglumine antimoniate in vitro provides an explanation for the good clinical response of cutaneous leishmaniasis in the municipality of Rio de Janeiro, Brazil, even when low-dose regimens are employed.

Drug resistance in leishmaniasis

Leishmaniasis is a complex disease, with visceral and cutaneous manifestations, and is caused by over 15 different species of the protozoan parasite genus Leishmania. There are significant differences in the sensitivity of these species both to the standard drugs, for example, pentavalent antimonials and miltefosine, and those on clinical trial, for example, paromomycin. Over 60% of patients with visceral leishmaniasis in Bihar State, India, do not respond to treatment with pentavalent antimonials. This is now considered to be due to acquired resistance. Although this class of drugs has been used for over 60 years for leishmaniasis treatment, it is only in the past 2 years that the mechanisms of action and resistance have been identified, related to drug metabolism, thiol metabolism, and drug efflux. With the introduction of new therapies, including miltefosine in 2002 and paromomycin in 2005-2006, it is essential that there be a strategy to prevent the emergence of resistance to new drugs; combination therapy, monitoring of therapy, and improved diagnostics could play an essential role in this strategy.

Responses of Leishmania (Viannia) braziliensis Cutaneous Infection toN-Methylglucamine Antimoniate in the Rhesus Monkey (Macaca mulatta) Model

The antileishmanial efficacy of the reference drug N-methylglucamine antimoniate (Glucantime) was evaluated in groups of rhesus monkeys with acute and chronic Leishmania (Viannia) braziliensis cutaneous infection. The therapeutic responses in experimental animals to either a low dose (5 mg/kg body wt/day for 28 days) or a routine dose (20 mg/kg/day for 28 days) of pentavalent antimony were similar to those reported in the human disease. Primates were cured of their lesions after treatment, but with cryptic parasitism and/or relapse. The rhesus model of L. (V.) braziliensis cutaneous leishmaniasis therefore provides an additional resource for preclinical trials with newer drugs.

Practical progress and new drugs for changing patterns of leishmaniasis

The problems surrounding leishmaniasis are changing. An increase in travel, the Indian and Sudanese epidemics of visceral leishmaniasis, parasite resistance to antimony and the emergence of AIDS-related leishmaniasis have all increased the urgency for new drugs, and led to reappraisals of the old ones, as discussed here by Piero Olliaro and Anthony Bryceson.

Mechanisms of drug resistance in Leishmania

The emergence of drug resistance in protozoan parasites is a major obstacle to their control. Since vaccines are not yet in sight for several of these parasites, there is on urgent need to develop new and better drugs. These antimicrobial agents will possibly be more expensive, and will therefore impose on additional burden in health-care costs and in the planning of public health policies of the developing countries. A better understanding of drug resistance, to try to circumvent or overcome it, and the search for new specific cellular targets of parasites are warranted. The development, in vitro, of drug-resistant parasite cell lines has been instrumental in our understanding of the mechanisms of drug resistance in parasitic protozoans. Marc Ouellette and Barbara Popodopoulou here present on overview of the recent progress on the elucidation of mechanisms of drug resistance in the protozoan parasite Leishmania, selected under laboratory conditions.

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.

New world cutaneous leishmaniasis in returned travellers: treatment failures using intravenous sodium stibogluconate

Treatment outcome was determined among a cohort of travellers who returned to the UK between February 2000 and February 2001 with New World cutaneous leishmaniasis caused by species of the Leishmania (Viannia) subgenus. Among 18 patients who completed treatment with 20 mg/kg/d of i.v. sodium stibogluconate (NaSb) for 20 d, early relapse of disease occurred in 2 patients with regional dissemination in 1 and mucocutaneous involvement in the other. Drug susceptibility testing in vitro of the clinical isolate from 1 of these patients confirmed tolerance to high concentrations of NaSb.

An intermittent schedule is better than continuous regimen of antimonial therapy for cutaneous leishmaniasis in the municipality of Rio de Janeiro, Brazil

This study reviews a series of cutaneous leishmaniasis cases diagnosed and treated in outpatient units in the municipality of Rio de Janeiro, where the intermittent schedule of antimonial therapy was replaced by the continuous regimen. Both schedules were based on daily intramuscular injections of pentavalent antimonial. Forty-nine subjects received the intermittent regimen, consisting of three ten-day series alternated with ten-day rest intervals whereas seventy-one patients received the continuous regimen during 20 consecutive days. The study groups had similar composition regarding age, sex and clinical condition. The cure rate was significantly higher in the group receiving the intermittent schedule than in the group receiving continuous therapy (89.8% vs 63.3%). Moreover, loss to follow-up was significantly more frequent in the group receiving continuous therapy (19.7% vs 4.1% in the intermittent therapy). Under field conditions, the intermittent regimen provided higher effectiveness and adherence than the continuous schedule.

Characterisation of atovaquone resistance in Leishmania infantum promastigotes

Atovaquone, an antiparasitic agent, could possibly represent an alternative therapy after relapse following classical treatment for visceral leishmaniasis. Atovaquone-resistant strains were selected in vitro by stepwise drug pressure to study the mechanism of resistance in Leishmania. Characteristics of a promastigote strain resistant to 250 microg/ml of atovaquone were compared with those of the wild type (WT) strain. Resistant strains were shown to have a high level of resistance (45 times). They were stable in drug-free medium for 6 months, and showed no cross-resistance with other antileishmanial drugs. Rhodamine uptake and efflux were studied. They were not modified in the resistant strain, indicating the absence of P-glycoprotein overexpession. The effect of atovaquone on membrane lipidic composition was determined in both WT and atovaquone-resistant promastigotes. Analysis of lipid composition of the atovaquone-resistant strain showed that sterol biosynthesis was decreased in atovaquone-resistant parasites. Cholesterol was found to be the major membrane sterol as opposed to the WT strain. Cholesterol, due to its ordering effect, could decrease membrane fluidity and subsequently block the passage of atovaquone through the membrane. Increased membrane cholesterol content and altered drug membrane fluidity resulted from possible decrease of ergosterol biosynthesis by atovaquone, incorporation of cholesterol by promastigotes in the culture medium, solubilisation of atovaquone by cholesterol and co-passage of the two compounds or influence of dimethylsulfoxide. These results indicate that different cellular alterations may participate in the resistant phenotype, by altering drug membrane permeability.

In vitro susceptibility to pentavalent antimony in Leishmania infantum strains is not modified during in vitro or in vivo passages but is modified after host treatment with meglumine antimoniate

BACKGROUND

Leishmaniasis is a common parasitic disease in Southern Europe, caused by Leishmania infantum. The failures of current treatment with pentavalent antimonials are partially attributable to the emergence of antimony-resistant Leishmania strains. This study analyses the in vitro susceptibility to pentavalent antimony of intracellular amastigotes from a range of L. infantum strains, derived from the same infected animal, during in vitro and in vivo passages and after host treatment with meglumine antimoniate.

RESULTS

SbV-IC50 values for strains from two distinct isolates from the same host and one stock after two years of culture in NNN medium and posterior passage to hamster were similar (5.0 +/- 0.2; 4.9 +/- 0.2 and 4.4 +/- 0.1 mgSbV/L, respectively). In contrast, a significant difference (P < 0.01, t test) was observed between the mean SbV-IC50 values in the stocks obtained before and after treatment of hosts with meglumine antimoniate (4.7 +/- 0.4 mgSbV/L vs. 7.7 +/- 1.5 mgSbV/L). Drug-resistance after drug pressure in experimentally infected dogs increased over repeated drug administration (6.4 +/- 0.5 mgSbV/L after first treatment vs. 8.6 +/- 1.4 mgSbV/L after the second) (P < 0.01, t test).

CONCLUSIONS

These results confirm previous observations on strains from Leishmania/HIV co-infected patients and indicate the effect of the increasing use of antimony derivatives for treatment of canine leishmaniasis in endemic areas on the emergence of Leishmania antimony-resistant strains.

Monitoring drug resistance in leishmaniasis

There are many factors that can influence the efficacy of drugs in the treatment of leishmaniasis. These include both an intrinsic variation in the sensitivity of Leishmania species, described for pentavalent antimonials, paromomycin, azoles and other drugs that have reached clinical trials, as well as acquired drug resistance to antimonials. Acquired resistance has been studied in the laboratory for several decades but it is only recently that clinical resistance in L. donovani field isolates has been demonstrated. The monitoring of resistance is problematic due to a reliance on the amastigote-macrophage culture assay to adequately correlate clinical and in vitro resistance and a lack of knowledge about the molecular and biochemical mechanisms of resistance to antileishmanial drugs.

Leishmania species, drug unresponsiveness and visceral leishmaniasis in Bihar, India

Sixteen isolates obtained, in January 1998-December 1999, from splenic aspirates from sodium stibogluconate-resistant cases of visceral leishmaniasis (VL; Indian kala-azar) and drawn from different districts of Bihar (India) were identified as Leishmania donovani. By isoenzyme analysis, all the strains were found identical to the WHO reference strain L. donovani MON-2 and differed from L. tropica MON-5. This study suggested that resistant cases of VL in Bihar were caused by L. donovani and not by L. tropica. No new strain responsible for drug unresponsiveness emerged during this period and other cause or causes of emergence of drug resistance should be sought. All the patients were cured with amphotericin B.

Mucosal leishmaniasis ("espundia") responsive to low dose of N-methyl glucamine (Glucantime) in Rio de Janeiro, Brazil

Response to treatment with antimonial drugs varies considerably depending on the parasite strain involved, immune status of the patient and clinical form of the disease. Therapeutic regimens with this first line drug have been frequently modified both, in dose and duration of therapy. A regimen of 20 mg/kg/day of pentavalent antimony (Sb5+) during four weeks without an upper limit on the daily dose is currently recommended for mucosal disease ("espundia"). Side-effects with this dose are more marked in elderly patients, more commonly affected by this form of leishmaniasis. According to our experience, leishmaniasis in Rio de Janeiro responds well to antimony and, in cutaneous disease, high cure rates are obtained with 5 mg/kg/day of Sb5+ during 30 to 45-days. In this study a high rate of cure (91.4%) employing this dose was achieved in 36 patients with mild disease in this same geographic region. Side-effects were reduced and no antimony refractoriness was noted with subsequent use of larger dose in patients that failed to respond to initial schedule.

Amphotericin B deoxycholate treatment of visceral leishmaniasis with newer modes of administration and precautions: a study of 938 cases

Out of 938 parasitologically confirmed patients with visceral leishmaniasis treated with amphotericin B (1 mg/kg bodyweight daily infused in 2 h for 20 days), 935 were cured clinically, 933 parasitologically and 931 ultimately (no relapse within 6 months). Two parasitologically 'not cured' and 4 relapsed patients were cured with 25 infusions, and 1 with double relapse with 30 infusions. The treatment was started only when serum haemoglobin reached 5 g/dL, serum electrolyte imbalance was corrected and sodium stibogluconate-induced myocardial damage stabilized after 10 days' rest. Bronchopneumonia, cardiac failure and acute renal failure caused the death of 1 patient each. Nightblindness, angular stomatitis, neuritis, and petechial haemorrhages improved with appropriate treatment; 2 patients were given blood transfusion for post-treatment anaemia. Nausea and anorexia, and changes in serum creatinine and potassium, became normal in 2 weeks. Immediate withdrawal of the drug and restart after 10 days cured 2 patients who developed acute renal failure. Infusion-related toxicities--shivering, rigor and fever--were minimized but not eliminated by prior administration of hydrocortisone. Tuberculosis and visceral leishmaniasis were treated concurrently. Four pregnant patients were successfully treated without harmful effects on mother and child. It was concluded that the dosage of amphotericin B used was an effective and well-tolerated regimen and achieved 99% cure. Toxicity could be minimized with some precautions. All unresponsive and relapsed patients responded to more amphotericin and no resistance to the drug was seen.

The United States military and leishmaniasis

Leishmaniasis occurs not only in American travelers and military personnel alike but infects a significant portion of the world's population. The US military has made major contributions to the understanding of the complicated epidemiology of this parasite, the development of rapid reliable diagnostic tests, and to the development of safe, more efficient, and more effective treatment of leishmaniasis.

Involvement of thiol metabolism in resistance to glucantime in Leishmania tropica

Clinical resistance to pentavalent antimonials, in the form of pentostam (sodium stibogluconate) or glucantime (N-methylglucamine antimoniate), has long been recognized as a problem in Leishmaniasis. However, the mechanisms of resistance are unclear. We selected in vitro a Leishmania tropica line resistant to 1.2 mg/mL of Sb(V) of glucantime (GLU-R10). The cell line has a stable phenotype for at least 6 months and a resistance index of 1400-fold. The resistant line has no cross-resistance to pentostam or to SbCl3 and SbCl5. The resistance to glucantime was reverted by buthionine sulfoximine (BSO) and chlorambucil (CLB); however, thiol analyses by HPLC of wild-type and GLU-R10 cell lines, in the presence or absence of the drug, showed no differences between these two cell lines. The resistant line had a DNA amplification shown as a circular extrachromosomal element (G-circle) of approximately 22 kb. However, the specific probes for gamma-glutamyl cysteine synthetase, ornithine decarboxylase and trypanothione reductase did not recognize the G-circle amplified in the GLU-R10. The G-circle did not arise from the H region and was not related with P-glycoprotein Pgp-MDR- or Pgp-MRP-like genes. Northern blot analysis of the G-circle showed that a single transcript of approximately 6 kb was overexpressed in the resistant line. Molecular characterization of the G-circle would lead to the determination of the gene(s) involved in resistance to glucantime in Leishmania.

Gene amplification in Leishmania tarentolae selected for resistance to sodium stibogluconate

Leishmania tarentolae promastigotes were selected step by step for resistance to sodium stibogluconate (Pentostam). Mutants resistant to antimony-containing drugs and cross-resistant to arsenite were therefore obtained. Amplification of one common locus was observed in several independent sodium stibogluconate-resistant mutants, and the locus amplified was novel. The copy number of the amplified locus was related to the level of resistance to pentavalent antimony. The gene responsible for antimony resistance was isolated by transfection and was shown to correspond to an open reading frame coding for 770 amino acids. The putative gene product did not exhibit significant homology with sequences present in data banks, and the putative role of this protein in antimony resistance is discussed.

Pharmacokinetics of meglumine antimoniate after administration of a multiple dose in dogs experimentally infected with Leishmania infantum

Pharmacokinetics of meglumine antimoniate in dogs with experimentally induced leishmaniosis has been investigated. After infection, dogs received a dose of 75 mg kg-1 of meglumine antimoniate twice daily by subcutaneous injection for 10 days. Blood samples were collected throughout the treatment. No statistical differences were found in the kinetic behaviour of the drug administered as a single dose to healthy dogs and that administered as a multiple dose to infected animals. However, peak plasma concentrations (Cmax) of 30.8 +/- 12.8 micrograms ml-1 found after this dosage regimen were higher than those observed after the single dose administration of 100 mg kg-1 24 h-1. Furthermore, sustained antimony concentrations of 1.14 +/- 0.52 micrograms Sb ml-1 were detected throughout the treatment. No signs of toxicity were found in the animals treated indicating that this regimen would be very appropriate to treat canine leishmaniosis.

Leishmania braziliensis presenting as a granulomatous lesion of the nasal septum mucosa

Differential diagnosis of granulomatous lesions of the nasal mucosa is difficult. One of the possible causes is an infection with Leishmania braziliensis as reported in this case. Therefore leishmaniasis should be included in the differential diagnosis of granulomatous lesions of the nasal mucosa in patients who have travelled to endemic areas.

In vitro and in vivo resistance of Leishmania infantum to meglumine antimoniate: a study of 37 strains collected from patients with visceral leishmaniasis

Primary and secondary unresponsiveness to meglumine has long been described in human visceral leishmaniasis. However, no studies have been performed to elucidate if these therapeutic failures were due to strain variability in meglumine sensitivity or were related to host factors. We have studied the in vitro sensitivity of 37 strains of Leishmania infantum isolated from 23 patients (11 human immunodeficiency virus-infected and 12 immunocompetent patients) with visceral leishmaniasis. Sensitivity tests were performed by infecting murine macrophages with Leishmania parasites and culturing them in medium containing different concentrations of meglumine. For each test we calculated a 50% effective dose (ED50) corresponding to the meglumine concentration at which 50% of the Leishmania parasites survived. In vitro results were strongly correlated to immediate clinical outcome. All strains requiring an ED50 of >70 microg/ml were related to therapeutic failures, whereas all strains requiring an ED50 of <40 microg/ml corresponded to an initial efficiency of meglumine. Among those patients who were initially improved, relapses occurred in all immunocompromised patients and in most immunocompetent patients who had a short duration of treatment (15 days). Finally, we found that in vitro sensitivity of strains decreased progressively in relapsing patients treated with meglumine. Consequently, the physician may be encouraged to alternate meglumine with other treatments such as amphotericin B or pentamidine, especially in the case of relapsing patients.

An axenic amastigote system for drug screening

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

In vivo efficacy of oral and intralesional administration of 2-substituted quinolines in experimental treatment of new world cutaneous leishmaniasis caused by Leishmania amazonensis

The antileishmanial efficacies of 2-n-propylquinoline, chimanines B and D, 2-n-pentylquinoline, 2-phenylquinoline, 2-(3,4-methylenedioxyphenylethyl) quinoline, and two total alkaloidal extracts of Galipea longiflora were evaluated in BALB/c mice infected with Leishmania amazonensis or Leishmania venezuelensis. Animals were treated for 4 to 6 weeks postinfection with a quinoline by the oral route at 50 mg/kg of body weight twice daily for 15 days or by five intralesional injections at intervals of 4 days with a quinoline at 50 mg/kg of body weight. The reference drug, N-methylglucamine antimonate (Glucantime), was administered by subcutaneous or intralesional injection (regimens of 14, 28, or 56 mg of pentavalent antimony [Sbv] per kg of body weight daily). Twice-daily oral treatment with chimanine B at 50 mg/kg resulted in a decrease in lesion weight by 70% (P < 0.001) and a decrease in the parasite loads by 95% (P < 0.001). Five injections of chimanine B at intervals of 4 days reduced the lesion weight by 74% and the parasite loads in the lesion by 90% compared with the values for the group of untreated mice. Subcutaneous administration of N-methylglucamine antimonate at 28 mg of Sbv kg per day for 15 days reduced the parasite burden by 95% (P < 0.001), and five intralesional injections at the same concentration reduced the parasite burden by 96% (P < 0.001). Other 2-substituted quinolines, 2-n-propylquinoline administered by the oral and intralesional routes, 2-phenylquinoline administered by the oral route, 2-n-pentylquinoline administered by intralesional injection, and two total alkaloidal extracts of G. longiflora administered by the oral route, had intermediate effects. These findings suggest that chimanine B may be chosen as a lead molecule in the development of oral therapy against leishmaniasis.

Cutaneous leishmaniasis: schedules for intralesional treatment with sodium stibogluconate

BACKGROUND

Various therapeutic modalities have been used for treating cutaneous leishmaniasis. Intralesional pentavalent antimonial injection is one of the effective therapeutic modalities. In this study, the efficacy of three different intralesional schedules with sodium stibogluconate have been investigated.

METHODS

Ninety-six patients with 129 lesions were entered into the study, all with confirmed diagnosis of cutaneous leishmaniasis. The lesions were treated with three different schedules, including daily, alternate day, and weekly interlesional injections of sodium stibogluconate. The clinical response was then compared to arrive at the most effective schedule.

RESULTS

The clinical responses (complete and partial cure) were 67%, 97%, and 91% for the daily, alternate-day, and weekly schedules, respectively. Lesions with either partial cure or failure of treatment were injected weekly with the same medication until complete cure had been achieved. The final overall success rate of complete cure was 99.2%.

CONCLUSIONS

Alternate day or weekly intralesional treatment of cutaneous leishmaniasis with sodium stibogluconate are more effective than daily treatments.

Correlation between inhibition of growth and arginine transport of Leishmania donovani promastigotes in vitro by diamidines

Diamidines are known to possess potent antiprotozoal activity due to their property of binding with DNA minor groove. Pentamidine or 1,5-bis-(4'-amidinophenoxy)pentane, is the most known aromatic diamidine and is used to treat cases of antimony resistant leishmaniasis. Yet, it suffers from limited clinical application due to its adverse and toxic side effects. A set of four structural analogs of pentamidine along with the known antileishmanial diamidines viz., pentamidine, berenil and dibromopropamidine, were tested for their effect on growth of Leishmania donovani promastigotes in vitro using 3H-thymidine incorporation as the growth parameter. In view of structural similarity between amidino moiety of diamidines and guanidino group of L-arginine and also the previous report from this laboratory regarding presence of a novel arginine transporter in Leishmania donovani promastigotes, a parallel study was also conducted with the analogs and standard diamidines for their inhibitory effect on leishmanial arginine transport function. Bisbenzyl pentamidine and biscyclopropyl pentamidine were identified as considerably more potent inhibitors of growth and arginine transport function of leishmania promastigotes in vitro than the parent drug, pentamidine. A linear correlation was established between inhibition of parasite growth and arginine transport with regard to standard diamidines as well as novel analogs. Inhibition of arginine transport by dibromopropamidine and Pentamidine was competitive. The diamidines possibly gain entry into leishmania cells through arginine transporter.

Glucantime susceptibility of Leishmania promastigotes under variable growth conditions

Growth inhibition of Leishmania promastigotes by glucantime was compared in three different media. Glucantime inhibited the growth of Leishmania cultured in complex medium but did not affect parasite growth when added to cells cultured in defined or semi-defined media. Supplementation of the complex medium with biopterin partially reversed the glucantime effect in sensitive strains, although the addition of folic acid or oleic acid did not alter the activity of glucantime. Differences in fatty acid composition were observed between strains showing different degrees of glucantime susceptibility.

High level arsenite resistance in Leishmania tarentolae is mediated by an active extrusion system

Leishmania tarentolae cells selected for resistance to the oxyanions pentavalent or trivalent antimonials or to trivalent arsenicals exhibited cross-resistance to the other oxyanions. The basis for resistance in these mutants was studied by transport experiments using radioactive arsenite. All mutants exhibiting high level resistance to arsenite showed a marked decrease in the steady-state accumulation of arsenite. Decreased accumulation was also observed in antimonials-resistant mutants cross-resistant to various concentrations of arsenite. Cells depleted of endogenous energy reserves with metabolic inhibitors were loaded with radioactive arsenite; following addition of glucose, rapid efflux of arsenite was observed from arsenite mutant cells. Mutants resistant to high levels of arsenicals exhibited amplification of the P-glycoprotein related gene ltpgpA or of a linear amplicon of unknown function. However, the efflux-mediated arsenite resistance did not correlate with the amplification of the ltpgpA gene or with the presence of the linear amplicon. The calcium channel blocker verapamil and arsenite act in synergy in cells exhibiting the efflux system. Overall the oxyanion efflux system in Leishmania shares several properties with other resistance efflux systems mediated by transporters.

Cytokines in the treatment of leishmaniasis: from studies of immunopathology to patient therapy

The genus Leishmania, an obligate intramacrophage parasite, causes a wide spectrum of clinical diseases. It is worldwide in distribution and causes 20 million new cases annually with an at risk population of approximately 1.5 billion persons. The most severe forms are associated with high morbidity, mortality and relapses with conventional therapy. The therapeutic issues and responses to standard and alternative therapies are reviewed. Recent developments in molecular biology and immunology methods employed in the study of leishmaniasis have defined an intricate interaction of the parasite with host immune system. Perturbation of the host immune responses may be part of the survival mechanisms of Leishmania. In murine model, the finding of T helper cells that differ by their panel of cytokines has allowed a more precise definition of immunopathogenesis of leishmaniasis. Preliminary data from leishmaniasis patients lend support to this concept of altered immunomodulation. Furthermore, the data from leishmaniasis patients lend support to this concept of altered enhancement of therapeutic response by interferon-gamma has provided a new approach for treatment of patients using recombinant cytokines and for the study of the disease. Current research for early diagnosis, alternative therapies and need for vaccines are reviewed in the context of the immunopathology of leishmaniasis.

Canine leishmaniasis: clinical, parasitological and entomological follow-up after chemotherapy

Six naturally infected dogs [two with no signs of leishmaniasis ('asymptomatic'), two with a few signs ('oligosymptomatic') and two with many signs ('polysymptomatic')] were studied before and after chemotherapy. Another two, non-infected dogs were kept as controls. The dogs were studied clinically, haematologically and parasitologically five times over 11 months and their infectivity to sandflies was evaluated before and after the treatment. The 'asymptomatic' dogs were as infective to sandflies as the 'symptomatic' before treatment but all dogs were un-infective for at least a few months following chemotherapy. Treatment led to a temporary improvement in the clinical and biochemical condition of most of the dogs, the symptomatic dogs becoming asymptomatic, but parasitological cure was uncommon after 10 months' follow-up. There was often no correlation between clinical condition, parasitological condition and infectivity to sandflies. Some dogs from both the 'asymptomatic' and 'symptomatic' groups became infective to sandflies several months post-treatment.

Relapse in Ethiopian visceral leishmaniasis (VL) patients after therapy with pentavalent antimonials: a ten year observation

Relapse after chemotherapy using the pentavalent antimonials, sodium stibogluconate and meglumine antimoniate, was assessed in 135 patients diagnosed in the Aba Roba focus of south western Ethiopia during the period 1982-1991. Ten cases relapsed with a mean of 15.6 +/- 16.3 months following treatment. A 15-day course of 10 mg Sbv/kg b.wt. sodium stibogluconate used in 1982/1983 had a better outcome than a 15-day course of 17 mg Sbv/kg b.wt. of meglumine antimoniate used in 1990/1991. The relapse rate among patients treated with sodium stibogluconate 16-20 mg Sbv/kg b.wt. for 20 days in 1985-1990 was comparable to the relapse rate in patients treated with meglumine antimoniate 16-20 mg Sbv/kg b.wt. for 20 days in 1990/1991. Findings are discussed.

Leishmaniases of the New World: current concepts and implications for future research

Recent epidemiologic studies indicate that leishmaniasis in the Americas is far more abundant and of greater public health importance than was previously recognized. The disease in the New World is caused by a number of different parasite species that are capable of producing a wide variety of clinical manifestations. The outcome of leishmanial infection in humans is largely dependent on the immune responsiveness of the host and the virulence of the infecting parasite strain. This article reviews current concepts of the clinical forms, immunology, pathology, laboratory diagnosis, and treatment of the disease as well as aspects of its epidemiology and control. Recommendations for future research on the disease and its control are made.

Visceral infection caused by Leishmania tropica in veterans of Operation Desert Storm

BACKGROUND

Visceral leishmaniasis, usually caused by Leishmania donovani, has rarely been reported from eastern Saudi Arabia, so it was not expected to affect the soldiers of Operation Desert Storm.

METHODS

We evaluated eight soldiers with visceral leishmanial infection, examining their serum with an immunofluorescent-antibody assay, examining their marrow or biopsy tissue for amastigotes with an indirect immunofluorescent-monoclonal-antibody assay, and culturing the parasites. Cultured promastigotes were isolated and characterized by isoenzyme analysis.

RESULTS

None of the eight soldiers had classic signs or symptoms of visceral leishmaniasis (kala-azar). Seven soldiers had unexplained fever, chronic fatigue, malaise, cough, intermittent diarrhea, or abdominal pain that began up to seven months after they returned to the United States; one had no symptoms. Five had adenopathy or mild, transient hepatosplenomegaly. None had cutaneous manifestations. Diagnoses were made by bone marrow aspiration (seven patients) or lymph-node biopsy (one patient). Six isolates have been identified as L. tropica, which usually causes only cutaneous disease. Of the six patients treated with sodium stibogluconate, five improved and one remained symptomatic.

CONCLUSIONS

L. tropica can produce visceral infection that can cause unexplained systemic illness in persons returning from areas where this organism is endemic.

Plasticity in chromosome number and testing of essential genes in Leishmania by targeting

We attempted to generate homozygous dhfr-ts (dihydrofolate reductase-thymidylate synthase) knockouts in virulent Leishmania major, an asexual diploid protozoan parasite. Transfection of a neo (neomycin phosphotransferase) targeting fragment yielded heterozygous replacement lines with high efficiency. However, second transfections with a hyg (hygromycin B phosphotransferase) targeting fragment in the presence of metabolites shown to rescue homozygous knockouts in attenuated Leishmania did not yield the expected dhfr-ts- thymidine auxotrophs obtained previously with attenuated lines. Molecular karyotype, Southern blot, and flow cytometric DNA content analysis of clonal transfectants revealed three classes: (i) genomic tetraploids, containing two wild-type dhfr-ts chromosomes and one neo and one hyg replacement chromosome; (ii) aneuploid trisomic lines with one wild-type dhfr-ts and one neo and one hyg replacement chromosome; (iii) diploids bearing homologous integration of the targeting fragment without replacement. Aneuploid and tetraploid lines predominated. This confirms the common impression that natural populations of Leishmania are often aneuploid. The remarkable ability of these parasites to undergo and tolerate changes in chromosome number suggests a general method for testing whether genes are essential for growth in vitro, as the ability of Leishmania to simultaneously undergo homologous gene replacement while retaining wild-type genes by increasing chromosome number provides a diagnostic and positive experimental result. Our results show that virulent Leishmania require at least one copy of dhfr-ts and argue that DHFR-TS plays an unanticipated role in addition to its role in the de novo synthesis of thymidine. These results also have implications for genetic tests of the organization of Leishmania populations.

Decreased sensitivity to meglumine antimoniate (Glucantime) of Leishmania infantum isolated from dogs after several courses of drug treatment

Although unresponsiveness to antimonial drugs in human leishmaniasis appears to be increasing, resistance to antimony in Leishmania is not well documented. Treatment of leishmaniasis in dogs, the domestic reservoir of L. infantum, with meglumine antimoniate (Glucantime) is a common practice in many Mediterranean countries. The dogs, however, remain highly infective to the phlebotomine vectors, even after several courses of treatment. A study was therefore carried out to test the comparative susceptibility to meglumine antimoniate of L. infantum stocks isolated from four naturally-infected dogs, before (BT) and after treatment (AT) with three to six courses of the drug, and used to infect Balb/c mice. Significant differences in suppression between the BT and AT stocks were observed in the infected mice when they were given the drug at a rate of 0.01-10 mg kg-1 day-1 for five days. Each AT stock was between eight and 41 times more resistant to meglumine antimoniate than the BT stock from the same dog, in terms of the ratios of the AT ED50 values to the corresponding BT values, which were calculated as indices of resistance. This result underlines the futility and danger of repeated antimonial treatments of dogs with signs of leishmaniasis, as these may produce a permanent reservoir of parasites unsusceptible to the drugs in human clinical use.

Glucantime resistant Leishmania promastigotes are sensitive to pentostam

Growth inhibition in vitro tests were used to study the susceptibility to pentostam of different Leishmania strains involved in cutaneous and mucocutaneous leishmaniasis--one glucantime sensitive strain, three naturally glucantime resistant strains and one glucantime resistant line developed by in vitro drug exposure. Contrasting with the high degree of glucantime resistance, all strains were sensitive to pentostam. These differences suggest that there is some relationship between chemical structure and in vitro activity for these antimonial compounds. These data justify a clinical re-evaluation to compare therapeutic efficacy of glucantime and pentostam in the treatment of leishmaniasis.