Leishmania major: activity of tamoxifen against experimental cutaneous leishmaniasis

Leishmaniasis is a family of diseases caused by protozoan parasites of the genus Leishmania. Various Leishmania species can cause human infection, producing a spectrum of clinical manifestations. The current treatments are unsatisfactory, and in absence of a vaccine, there is an urgent need for effective drugs to replace/supplement those currently in use. Recent studies have shown that the antineoplastic drug, tamoxifen, had direct leishmanicidal effect on several Leishmania species in vitro. Moreover, in vivo testing was carried out on some of the species and showed promising results. The authors have carried out the present work to complement previous published studies by investigating in vivo activity of tamoxifen in an experimental model of cutaneous leishmaniasis (CL) caused by Leishmania major. Groups of infected mice were given tamoxifen, orally, at a dose of 20 mg/kg/day for 15 days. Efficacy was assessed clinically, parasitologically, histopathologically by light and transmission electron microscope (TEM). Results showed that untreated infected mice suffered from autoamputation of the inoculated foot pad. However, those which received tamoxifen showed marked improvement of the cutaneous lesions and reduction of parasite burden. TEM of the cutaneous lesions from infected mice revealed the fine structure of normal Leishmania amastigotes, whereas those from infected mice treated with tamoxifen showed considerable changes. All male mice that received tamoxifen showed scrotal swelling with evident histopathological changes in the testes that could seriously compromise fertility of male mice. In conclusion, although tamoxifen causes significant side effects to the male reproductive system in the mouse model, it could provide an alternative to current agents. Results of this study demonstrated in vivo activity of tamoxifen against Leishmania major, thus, suggesting that tamoxifen is a suitable lead for the synthesis of more effective and less toxic antileishmanial derivatives.     

Regional genetic differentiation of Phlebotomus sergenti in three Moroccan foci of cutaneous leishmaniasis caused by Leishmania tropica

Phlebotomus sergenti was identified morphologically in samples from three Moroccan foci of leishmaniasis caused by Leishmania tropica in the provinces of Azilal, Essaouira and Taza. Three primary mitochondrial DNA lineages were identified, and they could be markers for regionally distributed cryptic species. Greater mitochondrial diversity in Azilal indicated that this central province could have been the origin of dispersal of P. sergenti or the zone of secondary contact. All except one of the 21 mitochondrial haplotypes showed a marked regional distribution, and this indicates that vector control would not always be followed by rapid, long-distance reinvasion. Only mitochondrial haplotype SER18 was a putative marker for long-distance dispersal, for which there is no evidence of human assistance.     

Leishmania major and Leishmania tropica: I the in vitro effects of an immunomodulator, S2-Complex

This study was undertaken to try to determine the possible anti-leishmanial activity of S2-Complex, an organic complex of copper chloride, ascorbic acid, and nicotinamide. The promastigotes, axenic amastigotes, and intracellular amastigotes of both Leishmania major and Leishmania tropica were incubated with different concentrations of S2-Complex. The EC50 for each form was calculated. Results show that all forms of the parasites were dose dependently inhibited by S2-Complex. The promastigotes of both parasites were the most resistant with highest EC50 followed by axenic amastigotes. While intracellular amastigotes were the most sensitive with the lowest EC50.These results indicate that S2-Complex has a direct anti-leishmanial effect. When mice were treated with S2-Complex or BCG for four days before harvesting the macrophages, and the macrophages infected with both L. major and L. tropica, they showed increased phagocytosis and increased parasite killing. The results of S2-Complex were not statistically different from the immunomodulating agent BCG. These results indicate that S2-Complex has an immunomodulating effect in addition to the direct anti-leishmanial effect.     

Leishmania major: solid phase radioimmunoassay for antibody detection in human cutaneous leishmaniasis

A radioimmunoassay for the quantitative determination of antileishmanial antibody in sera from patients suffering from cutaneous leishmaniasis was developed. The assay, using as antigen either the soluble fraction from freeze-thawed sonicated Leishmania major (LRC-L137) promastigotes or a carbohydrate-lipid containing fraction obtained by extraction with hexane-isopropanol, was shown to be sensitive and reproducible. The sera of 95 patients were examined. These were from patients with cutaneous leishmaniasis (26 from the Jordan Valley and 13 from Sinai), kala-azar (9), malaria (24), schistosomiasis (10), toxoplasmosis (5), and leprosy (8); controls were 37 normal human sera. No significant antigen dependent differences were observed using sera from cutaneous leishmaniasis patients, although differences in the immunological response were observed between the two populations of these patients. Antileishmanial activity was not detected in sera from patients with malaria, schistosomiasis, or toxoplasmosis. Although sera from leprosy patients crossreacted with the carbohydrate-lipid containing fraction, it was nevertheless more strain specific than freeze thawed sonicated L. major.     

Experimental cutaneous leishmaniasis. I. Nonspecific immunodepression in BALB/c mice infected with Leishmania tropica

Leishmania tropica in BALB/c mice causes a fatal infection accompanied by the development of multiple metastatic lesions. Spleen cells from these mice were shown to have depressed proliferative responses to concanavalin A (Con A), phytohemagglutinin (PHA), and lipopolysaccharide (LPS). Coinciding with this immunodepression was the development of a cell population capable of suppressing normal spleen cell responses to Con A. This suppressor cell activity was first observed at 6 wk and was present throughout the remainder of the infection. At 12 wk the suppressor cells could be removed by Sephadex G-10 passage or carbonyl iron treatment; however, Sephadex G-10 passage could not reverse the suppression at 18 wk. Indomethacin, a prostaglandin synthetase inhibitor, was found to abrogate the activity of the adherent suppressor cell, suggesting that prostaglandin production may be involved in the immunosuppression seen in these mice. In addition, Sephadex G-10 passage and indomethacin were found to markedly augment spleen cell responses to leishmanial antigen, indicating that the adherent suppressor cell is capable of regulating specific immunologic responses.     

Leishmanicidal activity of primary S-nitrosothiols against Leishmania major and Leishmania amazonensis: implications for the treatment of cutaneous leishmaniasis.

Nitric oxide (NO) is considered a key molecule in the defense against intracellular pathogens, particularly Leishmania. The expression of inducible nitric oxide synthase and consequent production of NO by infected macrophages has been shown to correlate with leishmaniasis resistance in the murine model as well as in human patients. Nitric oxide donors have been used successfully in the treatment of cutaneous leishmaniasis in humans, although their mechanisms of action are not fully understood. In the present work, the dose-dependent cytotoxic effects of the NO-donors S-nitroso-N-acetyl-l-cysteine (SNAC) and S-nitrosoglutathione (GSNO) against Leishmania were evaluated. GSNO inhibited the growth of Leishmania major and Leishmania amazonensis with in vitro 50% inhibitory concentrations (IC(50)) of 68.8+/-22.86 and 68.9+/-7.9 micromol L(-1), respectively. The IC(50) for SNAC against L. major and L. amazonensis were, respectively, 54.6+/-8.3 and 181.6+/-12.5 micromol L(-1). The leishmanicidal activity of GSNO, but not of SNAC, was reversed by ascorbic acid (AA) and dithiothreitol (DTT), suggesting that the mechanism of action of GSNO is related to the transnitrosation of parasite proteins. These results demonstrate that SNAC and GSNO have leishmanicidal activity, and are thus potential therapeutic agents against cutaneous leishmaniasis.     

Delayed in vitro Utilization of Glucose by Leishmania tropica Promastigotes*

Leishmania tropica promastigotes do not utilize glucose provided in the medium until late log phase. Rapid depletion of glucose from the medium, however, occurs during late log and stationary phases. At about the same time, the cells show maximal rates of glucose uptake as well as peak levels of phosphofructokinase and pyruvate kinase activities. The glucose analog, 2-deoxy-D-glucose inhibits glucose transport. Incorporation of this analog in the growth medium results in inhibition of growth. The hexokinase of L. tropica phosphorylates 2-deoxy-D-glucose. Pyruvate kinase is activated by fructose-1, 6-diphosphate and adenosine monophosphate.     

Protective immunity against Leishmania major induced by Leishmania tropica infection of BALB/c mice

Leishmania (L.) tropica is a causative agent of human cutaneous and viscerotropic leishmaniasis. Immune response to L. tropica in humans and experimental animals are not well understood. We previously established that L. tropica infection induces partial protective immunity against subsequent challenge infection with Leishmania major in BALB/c mice. Aim of the present study was to study immunologic mechanisms of protective immunity induced by L. tropica infection, as a live parasite vaccine, in BALB/c mouse model. Mice were infected by L. tropica, and after establishment of the infection, they were challenged by L. major. Our findings shows that L. tropica infection resulted in protection against L. major challenge in BALB/c mice and this protective immunity is associated with: (1) a DTH response, (2) higher IFN-γ and lower IL-10 response at one week post-challenge, (3) lower percentage of CD4⁺ lymphocyte at one month post-challenge, and (4) the source of IFN-γ and IL-10 were mainly CD4⁻ lymphocyte up to one month post-challenge suggesting that CD4⁻ lymphocytes may be responsible for protection induced by L. tropica infection in the studied intervals.     

Leishmania tropica and Leishmania mexicana: cross-immunity in mice

The effect of a previous or concurrent Leishmania tropica major infection on a L. mexicana infection was studied. Mice which were recovering from or had recovered from a L. tropica infection were found to be totally resistant to L. mexicana. Infection of mice already carrying a L. mexicana infection with L. tropica resulted in subsequent ulceration and eventual healing of the lesions caused by both Leishmania species. Mice infected with L. mexicana were found normally to be no more susceptible to L. tropica than untreated mice: Only when L. tropica infections were located in the region of a draining lymph node already serving a L. mexicana infection did lesions of the former parasite persist.     

Leishmania major: the suitability of East African nonhuman primates as animal models for cutaneous leishmaniasis

The susceptibility of four species of East African nonhuman primates to experimental infection with Leishmania major was investigated. Four Syke's monkeys (Cercopithecus mitis), two vervet monkeys (Cercopithecus aethiops), two baboons (Papio cynocephalus), and two brown bushbabies (Galago garnettii) were each inoculated intradermally on the left eyelid, left ear, and nose with 0.1 ml of medium containing 1 x 10(7) promastigotes of a characterized L. major strain. All the nonhuman primates except the bushbabies developed erythema and conspicuous nodules on the eyelids and ears by 3 weeks PI. The nodules increased rapidly in size and ulceration was evident on the eyelids and ears by 49 days PI in the vervets, Syke's, and baboons. The aspirates were positive in culture or smears at 35, 49, 63, and 77 days PI. No parasites were observed in cultures or smears at 92, 105, 128, 147, and 161 days PI. The lesions in these animals began resolving by 84 days PI and were completely healed by 112 days PI. The exception was one baboon in which lesion healing did not start until around 147 days and was completely healed by 182 days PI. Cultures from the liver failed to demonstrate visceralization of the parasite in any of the animals throughout the 68 weeks of the experiment. Challenge with the same strain of L. major 6 months PI, corresponding to about 3 months after self cure, failed to produce infection in any of these experimental hosts. All the nonhuman primates except the bushbaby when challenged with the same strain of L. major at 12 months PI developed lesions and were positive for parasites at 14 and 28 days PI. Positive cultures were obtained from the eyelid and ear of one vervet up to 42 days PI. However, the lesion sizes in all these animals were smaller than in the initial infection and did not ulcerate. The nodules disappeared within 6 to 8 weeks as compared to 16 weeks in the initial infection. The histopathological appearance of the lesions varied from diffuse infiltration of plasma cells and lymphocytes which increased progressively to granulomata with epitheloid cells. This study shows that the vervets, Syke's, and the baboons are equally susceptible to L. major infection, while bushbabies are refractory. The vervets, Syke's, and baboons demonstrate a self-healing phenomenon within about 3 months which is comparable to that observed in humans infected with L. major. These three species of nonhuman primates are therefore considered as suitable models for drug or vaccine trials against human zoonotic cutaneous leishmaniasis.     

Active cutaneous leishmaniasis in Brazil, induced by Leishmania donovani chagasi

L.d. chagasi was isolated from active cutaneous leishmaniasis in both human and canine infections in an endemic area in Rio de Janeiro, Brazil. Both isolates were identified by molecular and immunological characterization of the parasite using three different methods: electrophoretic mobility of isoenzymes; restriction endonuclease fragment analysis of kDNA and serodeme analysis using monoclonal antibodies. This seems to be the first well documented case in the New World of a "viscerotropic" Leishmania inducing a case of cutaneous leishmaniasis. This observation emphasizes that the diagnosis of the etiologic agent of human or canine visceral leishmaniasis based solely upon clinical and epidemiological criteria may lead to erroneous conclusions.     

Molecular detection of Leishmania tropica in field caught Phlebotomus sand flies (Diptera: Psychodidae) from cutaneous leishmaniasis endemic focus of Pakistan

Cutaneous Leishmaniasis is endemic in tribal district Khyber for last more than one decade. The causative agent Leishmania tropica is known but sand fly species responsible for the transmission of disease still needs to be investigated. A total of 2647 Phlebotomus females belonging to 11 species were divided into 435 batches and subjected to PCR for detection of Leishmania in sand flies. A total of 50 batches belonging to three species i.e. Phlebotomus sergenti, Phlebotomus papatasi and Phlebotomus alexandri were detected positive for Leishmania tropica. Overall minimum infection rate was 1.89% (50/2647). Highest minimum infection rate of 2.11% (39/1710) was observed for Phlebotomus sergenti followed by 1.21% (8/661) for Phlebotomus paptasi and 1.82% (3/165) for Phlebotomus alexandri. Both blood fed (38%) and unfed (62%) sand flies were detected positive for the parasite DNA. Positive specimens were collected throughout the active season, from all collection sites of the study area. Detection of Leishmania parasite in multiple species of Phlebotomus indicates the possible role of these species as vector of disease in the tribal district Khyber of Pakistan. It also indicates the probable complex transmission cycle of the disease involving multiple vector species in the study area. Devising a control strategy by focusing on these vector species, may reduce the disease burden in the cutaneous leishmaniasis endemic tribal district Khyber.     

Leishmania tropica: cysteine proteases are essential for growth and pathogenicity

Leishmania parasites are responsible for a diverse collection of diseases of humans and other animals. Cysteine proteases are putative virulence factors of leishmania parasites. There are differences in the susceptibility of specific stages in different Leishmania species to cysteine protease inhibitors. Here, we establish a key role of cysteine proteases in growth, viability, and pathogenicity of Leishmania tropica by using a specific cysteine protease inhibitor (N-Pip-F-hF-VS Phenyl). Reduction or arrest of promastigote growth occurred at inhibitor concentration of 5 and 100 microM, respectively. This shows an essential role for cysteine proteases in viability and growth of L. tropica promastigotes. It confirms that the promastigote stage of L. tropica more closely resembles that of Leishmania major than that of Leishmania mexicana, which is refractory to this inhibitor. Pathogenicity of L. tropica amastigotes in mice, as assessed by footpad swelling, was also reduced by treatment with the cysteine protease inhibitor. This suggests that cysteine proteases are essential for pathogenicity of L. tropica amastigote in mammalian host, similar to both L. major and L. mexicana.     

Antigen-stimulated lymphokines from patients with cutaneous leishmaniasis induce monocyte killing of Leishmania major intracellular amastigotes

The specific immune response of patients with cutaneous leishmaniasis including the ability of their lymphokines to enhance the monocytes' leishmaniacidal activity was studied. In 16 patients with cutaneous leishmaniasis, their concanavalin A-induced lymphocyte proliferative responses, interferon-gamma and interleukin 2 activities and the ability of their concanavalin A-induced lymphokines to kill monocyte intracellular amastigotes were not different from normal controls. Antigen-stimulated lymphocyte cultures showed that 13 of 13 patients had an increased lymphocyte proliferative response; 11 of 16 produced interleukin 2 and 12 of 13 produced interferon-gamma; in addition, 10 of 11 of these antigen-induced supernatants increased the monocytes' killing of Leishmania major amastigotes. Antibody levels to parasite membrane antigens determined by radioimmunoassay showed that 8 of 13 titers were greater than 10 and 4 of 13 titers were 2 to 10 times higher than control. Our findings demonstrate that patients with cutaneous leishmaniasis elicit a specific immune response to L. major antigens and part of this response is the production of lymphokine capable of promoting monocyte killing of intracellular amastigotes.     

Leishmania (Leishmania) amazonensis: experimental cutaneous leishmaniasis associated with systemic amyloidosis in mice

We infected Swiss and C57BL/6 female mice in the left hind footpad with 10⁴Leishmania (L.) amazonensis promastigotes in stationary phase. The macroscopic examination showed a nodular non-ulcerated lesion at the site of inoculation and hepatic and spleenic enlargement. Histopathologically, the primary lesion showed an extensive liquefactive necrosis and inflammatory infiltrate, mainly consisting of macrophages filled with amastigotes, and rare lymphocytes. The inflammatory reaction in liver, spleen and kidney showed amyloid deposits. Additionally, C57BL/6 had accentuated amyloidosis in both ovarian cortical and medullar region and inflammatory infiltrates in the pancreas and adrenal gland.     

Inhibition of growth of Leishmania mexicana mexicana by Leishmania mexicana amazonensis during "in vitro" co-cultivation

Inhibition of one Leishmania subspecies by exometabolites of another subspecies, a phenomenon not previously reported, is suggested by our recent observations in cell cloning experiments with Leishmania mexicana mexicana and Leishmania mexicana amazonensis. Clones were identified using the technique of schizodeme analysis. The phenomenon observed is clearly relevant to studies of parasite isolation, leishmanial metabolism, cross-immunity and chemotherapy.