Activity of oral drugs against Leishmania tropica in human macrophages in vitro

Because of the need for orally active antileishmanial agents, orally administrable drugs have sometimes been used to treat human leishmaniases without prior demonstration of efficacy in experimental models. The antileishmanial activity of such agents was tested against Leishmania tropica (a cause of cutaneous leishmaniasis) within human macrophages in vitro. Although trimethoprim + sulfamethoxazole and isoniazid + rifampin have been reported as efficacious orally in certain human studies of cutaneous disease, these drugs were ineffective in vitro (less than or equal to 40% parasite elimination) at peak achievable serum levels. The combination of allopurinol and Pentostam is being tested in humans. In vitro, allopurinol (5 micrograms/ml) augmented the antileishmanial effect of a low concentration of Pentostam (5 micrograms/ml) but not of a higher concentration of Pentostam (20 micrograms/ml). Nifurtimox is a nitrofuran which has questionable activity against human cutaneous disease. Nifurtimox was similarly only 50% effective in vitro at peak achievable serum levels (1.0-3.0 micrograms/ml). However, furazolidone, another orally administered nitrofuran, eliminated 92% of parasites at 1.0 micrograms/ml. Chlorpromazine and quinacrine are concentrated in tissues that are susceptible to infection by Leishmania. Chlorpromazine and quinacrine eliminated only 15% and 35% of organisms in vitro at achievable serum levels (less than or equal to 0.3 microgram/ml), but eliminated virtually all organisms in vitro at possible achievable tissue levels. Both the negative and the positive data of this report may aid in selection of effective orally active agents for in vivo trials.     

Activity of 8-aminoquinolines against Leishmania tropica within human macrophages in vitro

Antileishmanial activity of 8-aminoquinolines with substitutions on the quinoline ring or on the 8-amino side-chain was assessed in the Leishmania tropica-infected human macrophage in vitro model of leishmaniasis. The 4-methyl-5,6-dimethoxy compounds were more active than 6-methoxy compounds, which were approximately as active as 4-methyl-6-methoxy compounds. Certain 6-hydroxy compounds were the most active drugs tested. The precise composition of substituents on the 8-amino side-chain had little effect on activity. These investigations identify WR 226292 (a 4-methyl-5,6-dimethoxy compound) and WR 6881 and WR 49577 (6-hydroxy compounds) as the most active 8-aminoquinolines in this in vitro model. The 6-hydroxy compounds also can be considered to be the 6-demethyl derivatives of 6-methoxy-8-aminoquinolines. This study therefore indicates that 6-demethyl-8-aminoquinolines may be generally more active in vitro than the parent 6-methoxy structures against macrophage-contained Leishmania.     

The activity of nitrofurazone and furazolidone against Leishmania donovani, L. major and L. enriettii in vitro and in vivo

Furazolidone and nitrofurazone showed in vitro activity against amastigotes of Leishmania donovani, L. enriettii and L. major in macrophages, at concentrations which were also toxic to the macrophages. A low grade of activity was observed against L. donovani infections in BALB/c mice by furazolidone but not with nitrofurazone. Nitrofurazone, in two concentrations, was not active when applied to the lesions of cutaneous leishmaniasis due to L. enriettii (guinea-pig infection) or L. major strain P (BALB/c mouse infection). After systemic administration to BALB/c mice infected with L. major strain JISH 252 clone 1, low-grade activity was observed at the highest level tested.     

The parasiticidal effect of electricity on Leishmania major, both in vitro and in vivo

The effects of low electrical potentials on Leishmania major (MRHO/IR/75/ER) were investigated both in culture (in terms of promastigote viability) and in experimentally infected BALB/c and NMRI mice (in terms of the cure of pre-existing skin lesions). Exposure to direct-current potentials of 3, 6, 9 and 12 V (at 0.2-10.7 mA) killed all promastigotes in <15, <10, <10 and <10 min, respectively. When electrodes were used to pass similar direct currents across skin lesions on the tails of infected mice, all but the lowest voltage (3 V) caused unwanted ulceration. At 3 V, however, 3 weeks of electrotherapy, for 10 min twice weekly, initially appeared to cure all the lesions and the therapy was then halted. If given no electrotherapy, the BALB/c mice showed much greater Leishmania-attributable morbidity and mortality than the NMRI mice, and it was only in the treated BALB/c mice that relapses were observed, about 3 weeks after electrotherapy had ceased. The possible clinical use of electrotherapy in the treatment of human cutaneous leishmaniasis is discussed.     

Efficacy of voriconazole on leishmaniasis by Leishmania major: An in vitro and in vivo study

Objective: To appraise the activity of voriconazole against Leishmania major(L. major) in vitro and its effectiveness on wound regeneration in cutaneous leishmaniasis in BALB/c mice Methods: The IC_(50) of voriconazole against promastigotes and intra-macrophage amastigotes of L. major was investigated in vitro. The in vivo study was performed by treating the L. major infected BALB/c mice. When the wounds appeared in the base of tail, treatment was started by administration of 30 mg/kg voriconazole for 28 consecutive days orally. Results: The IC_(50) of voriconazole against promastigotes and intra-macrophage amastigotes were 0.74 and 0.89μM, respectively. Voriconazole decreased lipid peroxidation and IL-6 level. Histopathologica findings indicated accelerated healing in the voriconazole treated group compared to other groups. Conclusions: Our results demonstrate that voriconazole can be an option in treating the cutaneous leishmaniasis by L. major.     

Promising antileishmanial effectiveness of doxorubicin and Doxil against Leishmania major: An in vitro assay

Objective: To evaluate the effect of doxorubicin and its pegylated liposomal formulation(Doxil, Caelyx) on in vitro susceptibility of promastigote and amastigote stages of Leishmania major. Methods: Throughout in vitro assays the IC50 was calculated in the promastigotes and amastigotes forms in J774 macrophage cell line. Also as cytotoxicity in J774 cell line macrophages. Results: Doxorubicin and Doxil showed the same activity against promastigote form with IC50 values of 10.49 μg/m L and 9.63 μg/m L, respectively. Similarly, the amastigote stage was susceptible at concentration of at least 1 μg/m L when compared to positive control(P0.000 1). Also, cytotoxicity assay against macrophage revealed no toxicity on the host cells at IC50 concentrations. Conclusions: Our findings demonstrated the efficacy of both doxorubicin and its pegylated liposomal formulation on Leishmania major at low concentrations. Further researches are needed for evaluating the safety of drugs in animal model particularly as topical formulation.     

Antileishmanial activity of azithromycin against Leishmania (Leishmania) amazonensis, Leishmania (Viannia) braziliensis, and Leishmania (Leishmania) chagasi

Azithromycin, an azalide antibiotic, is highly concentrated within different phagocytic cells, especially macrophages. The potential antileishmanial activity of azithromycin against three species of Leishmania from the New World was assessed using in vitro models. Azithromycin decreased viability of promastigote cultures of Leishmania (Leishmania) amazonensis, Leishmania (Viannia) braziliensis, and Leishmania (Leishmania) chagasi as determined by the colorimetric Alamar blue assay. In amastigote intracellular cultures, a significant decrease in infected macrophages counts was observed for all three species with IC(50) of 20.83 (27 micromol/L), 2.18 (2.7 micromol/L), and 6.12 (7.8 micromol/L) microg/mL, respectively. Azithromycin showed in vitro activity against L. (L.) amazonensis, L. (V.) braziliensis, and L. (L.) chagasi and may offer an alternative to current leishmaniasis treatment.     

Activity of azithromycin against cryptosporidia in immunosuppressed rats.

Dexamethasone-immunosuppressed rats infected with Cryptosporidium parvum were used to assess the macrolides azithromycin and spiramycin for anticryptosporidial activity. Azithromycin consistently prevented ileal infection, while spiramycin was ineffective. The anticryptosporidial activity of azithromycin was dose-related, 200 mg/kg/day being the minimum dose that prevented infection. Therapeutically, azithromycin eliminated an established overt infection of the small intestine in immunosuppressed rats, but the infection recurred after azithromycin treatment was stopped. These findings suggest that azithromycin is a potentially useful anticryptosporidial agent and that long-term continuous administration may be necessary to treat cryptosporidiosis in the immunocompromised host.     

Activity of azithromycin or erythromycin in combination with antimalarial drugs against multidrug-resistant Plasmodium falciparum in vitro

Azithromycin, an azalide analog of erythromycin was assayed for its in vitro activity against multidrug-resistant Plasmodium falciparum K1 strain by measuring the ³H-hypoxanthine incorporation. Azithromycin caused inhibitory effects on the parasite growth with IC₅₀ and IC₉₀ values of 8.4 ± 1.2 μM and 26.0 ± 0.9 μM, respectively. Erythromycin inhibited growth of P. falciparum with IC₅₀ and IC₉₀ values of 58.2 ± 7.7 μM and 104.0 ± 10.8 μM, respectively. The activity of antimalarial drugs in combination with azithromycin or erythromycin against P. falciparum K1 were compared. Combinations of chloroquine with azithromycin or erythromycin showed synergistic effects against parasite growth in vitro. Combinations of quinine–azithromycin and quinine–erythromycin showed potentiation. Additive effects were observed in mefloquine–azithromycin and mefloquine–erythromycin combinations. Similar results were also produced by pyronaridine in combination with azithromycin or erythromycin. However, artesunate–azithromycin and artesunate–erythromycin combinations had antagonistic effects. The in vitro data suggest that azithromycin and erythromycin will have clinical utility in combination with chloroquine and quinine. The worldwide spread of chloroquine-resistant P. falciparum might inhibit the ability to treat malaria patients with chloroquine–azithromycin and chloroquine–erythromycin in areas of drug-resistant. The best drug combinations against multidrug-resistant P. falciparum are quinine–azithromycin and quinine–erythromycin.     

Activity of immunoglobulin G-coated red cell ghosts containing pentamidine against macrophage-contained Leishmania in vitro

Pentamidine is an antileishmanial agent that is often toxic at therapeutic dosages. The obligate intramacrophage localization of Leishmania indicates that encapsulation of pentamidine within a carrier phagocytized by macrophages (IgG-coated sheep red cell ghosts) might improve activity. In in vitro experiments, treatment of infected mouse macrophages for 1 hour with a mean of 1.4 micrograms of encapsulated drug resulted in a calculated drug concentration of 180 micrograms/ml macrophage, and in 73% suppression of organism multiplication within the macrophages after 4-5 days of further cultivation. In comparison, 27 micrograms unencapsulated drug/ml was needed for similar suppression. Electron microscopic examination 5 hours after phagocytosis of IgG-ghosts revealed that 95% of organisms were adjacent to ghosts in phagolysosomes. Fusion of drug carrier with phagolysosome containing drug target is therefore an important step in carrier-mediated parasite suppression in this model. These results suggest that IgG-coated erythrocyte ghosts containing pentamidine have potential as an antileishmanial formation.     

In vivo activity of perifosine against Leishmania amazonensis

Miltefosine has been established as the first oral administration drug against cutaneous and visceral leishmaniasis. Other alkyl-phospholipids such as edelfosine have been tested against Leishmania showing an in vitro antiparasitic activity. Perifosine in vitro activity has been previously demonstrated against different Leishmania species including Leishmania amazonensis. In this study edelfosine and perifosine were orally administered to BALB/c mice at doses of 1 and 2.5 mg/kg/day during 28 days and 5 mg/kg/day during 14 days, starting the treatment 2 weeks after the first treatment scheme. Lesion sizes and parasitic burden as well as viability were determined in order to establish the treatment effectiveness. An assay to compare miltefosine at standard dose of 2.5 mg/kg/day during 28 days to an in vivo treatment with perifosine at the most effective treatment scheme observed in this study 5 mg/kg/day during 14 days, was also developed. Perifosine showed the higher activity in the in vivo assay and is showing as a new possibility within the alkyl-phospholipids group for the treatment against cutaneous leishmaniasis caused by L. amazonensis.     

Activity of azithromycin (CP-62,993) and erythromycin against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum in vitro.

Several antibiotics, including the macrolide erythromycin and the azalides azithromycin (CP-62,993) and CP-63,956, that inhibit protein synthesis on 70S ribosomes demonstrated antimalarial effects in vitro against two strains of Plasmodium falciparum, one sensitive to chloroquine and the other resistant. In 48-hr incubations, erythromycin was 10-fold less potent than the azalides against the chloroquine-resistant strain. Erythromycin and the azalides were essentially equipotent against the chloroquine-sensitive strain. An additive effect occurred with the azalides in combination with chloroquine against both strains, but this was not seen with erythromycin.     

Activity of imidazoles against Leishmania tropica in human macrophage cultures

The anti-leishmanial activity of four imidazoles has been determined in Leishmania tropica-infected human monocyte-derived macrophage cultures. One of the imidazoles, hydrolyzed ketoconazole [cis-1-[4-[2-(2,4-dichlorophenyl)-2-(1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl] methoxyphenyl]piperazine], eliminated 80 and 95% of the parasites at drug concentrations (2.0 and 2.5 microgram/ml) that are achievable in vivo by a structurally similar compound, ketoconazole. These results demonstrate that an imidazole has anti-leishmanial activity in a model system, and suggests that hydrolyzed ketoconazole should be considered for in vivo trials in animal models of the disease.     

Antileishmanial Activity of Compounds Derived from the Medicines for Malaria Venture Open Access Box against Intracellular Leishmania major Amastigotes

Leishmaniasis is a complex tropical disease caused by kinetoplastid parasitic protozoa of the genus Leishmania and is transmitted by the sand fly insect vector. Cutaneous leishmaniasis (CL) is the most common form of this disease, and CL infections often result in serious skin lesions and scars. CL remains a public health problem in many endemic countries worldwide because of the absence of effective, safe, and cost-effective drugs for treatment. One of the strategies we chose to use to find novel chemical entities worthy of further development as antileishmanials involved screening synthetic and natural products libraries. In our study, we developed a Leishmania major intracellular amastigote assay that uses the activity of luciferase as a measure of parasite proliferation and used this assay to screen a collection of 400 compounds obtained from Medicines for Malaria Venture (MMV) for their antileishmanial activity. Our results showed that 14 compounds identified by MMV as antimalarial drugs have antileishmanial activity and can potentially be optimized for CL drug development.     

Infectivity of the subspecies of the Leishmania braziliensis complex in vivo and in vitro

The infectivity of Leishmania braziliensis ssp. in relation to their growth kinetics in Senekjie's medium was determined using the human macrophage cell line U937 and inbred hamsters. In both systems, infectivity was shown to be distinctive for each subspecies. While L. b. panamensis promastigotes from 6-day-old cultures (early stationary phase) were more infective than parasites from any other culture day, L. b. guyanensis and L. b. braziliensis reached maximum infectivity on days 8-10 and day 10 (late stationary phase of growth), respectively. Although maximum infectivity occurred during stationary growth, strict growth phase dependency was not observed. The populations of parasites on these culture days were composed mostly of small, highly motile promastigotes with flagella 2-3 times the length of their cell bodies. These promastigotes resembled the infective forms transmitted by the sand fly vector. A distinct pathological picture characterized the disease caused by the different WHO reference strains for these subspecies in hamsters: L. b. guyanensis developed the most severe lesions, while moderate and inconspicuous lesions were observed when L. b. panamensis and L. b. braziliensis, respectively, constituted the inocula.     

CCL2-independent role of CCR2 in immune responses against Leishmania major

The chemokine CCL2 (MCP-1) and its receptor CCR2 modulate leucocyte migration and T helper differentiation. CCL2 or CCR2 knockout (KO) mice have divergent phenotypes following infection with the intracellular parasite Leishmania major (L. major). Compared to wild-type (WT) mice, intradermally infected CCR2 KO mice in the L. major-resistant C57BL/6j background become susceptible and fail to generate protective Th1 responses. In contrast, subcutaneously infected CCL2 KO mice in the L. major-susceptible BALB/c background are resistant and exhibit reduced pathogenic Th2 responses. Here we explore two variables that may account for this contrasting outcome, namely background strain and route of infection. We found that the CCR2-null state, both in the BALB/c and the C57BL/6j background, was associated with increased susceptibility to intradermal or subcutaneous L. major infection. Notably, the CCL2-null state did not change the ability of C57BL/6j mice to mount protective responses following intradermal infection. Dual genetic inactivation of CCR2 and CCL2 in the L. major-resistant C57BL/6j background resulted in a shift to a susceptible phenotype analogous to that of CCR2 KO in the C57BL/6j background. We concluded that CCL2-independent effects of CCR2 are indispensable for the control of L. major infection and the generation of protective immune responses.     

In vitro and in vivo antileishmanial efficacy of a combination therapy of diminazene and artesunate against Leishmania donovani in BALB/c mice

The in vitro and in vivo activity of diminazene (Dim), artesunate (Art) and combination of Dim and Art (Dim-Art) against Leishmania donovani was compared to reference drug; amphotericin B. IC50 of Dim-Art was found to be 2.28 ± 0.24 μg/mL while those of Dim and Art were 9.16 ± 0.3 μg/mL and 4.64 ± 0.48 μg/mL respectively. The IC50 for Amphot B was 0.16 ± 0.32 μg/mL against stationary-phase promastigotes. In vivo evaluation in the L. donovani BALB/c mice model indicated that treatments with the combined drug therapy at doses of 12.5 mg/kg for 28 consecutive days significantly (p < 0.001) reduced parasite burden in the spleen as compared to the single drug treatments given at the same dosages. Although parasite burden was slightly lower (p < 0.05) in the Amphot B group than in the Dim-Art treatment group, the present study demonstrates the positive advantage and the potential use of the combined therapy of Dim-Art over the constituent drugs, Dim or Art when used alone. Further evaluation is recommended to determine the most efficacious combination ratio of the two compounds.     

Protection of C3HeB/FeJ mice against Leishmania amazonensis challenge after previous Leishmania major infection

The Th1 response elicited in mice infected with Leishmania major has been used as a model to characterize cellular immune defects associated with L. amazonensis infection. However, it is not known if the immune response associated with the infection by virulent L. major parasites can promote resistance to a subsequent L. amazonensis infection. Our data demonstrate that C3HeB/FeJ mice infected subcutaneously with virulent L. major are resistant to an L. amazonensis challenge. The healing phenotype is characterized by a Th1 response as measured by increased production of interferon-gamma and low levels of interleukin-4 in the draining lymph node. Together, this indicates that the Th1 response associated with L. major infection can promote resistance to L. amazonensis infection and that it can be used as a tool to study the immune defects associated with L. amazonensis infection.