Leishmaniasis

Canine visceral leishmaniasis: successful chemotherapy induces macrophage antileishmanial activity via the L-arginine nitric oxide pathway

Following successful chemotherapy in canine visceral leishmaniasis, monocyte-derived macrophages can induce antileishmanial activity via a gamma interferon-dependent mechanism in the presence of autologous lymphocytes. The killing of leishmania correlated with the induction of the NO synthase pathway, because it correlated with the generation of nitrogen derivative production and was abrogated in the presence of NG-monomethyl-L-arginine, a competitive inhibitor of the NO synthase pathway. The level of L-citrulline in serum, which was produced after activation of the NO synthase pathway, was markedly enhanced in dogs receiving successful chemotherapy. Taken together, these data indicate that following successful chemotherapy of visceral leishmaniasis, leishmania parasites are killed by macrophages activated by gamma interferon-producing lymphocytes via an NO-dependent mechanism.

In vitro study of the anti-leishmanial activity of biodegradable nanoparticles

Leishmania are obligate intracellular parasites, responsible for leishmaniasis. Leishmaniasis are transmitted via insect vector to vertebrate hosts including humans. The infection was reproduced in vitro with promastigotes which can infect murine resident peritoneal cells. Amphotericin B was incorporated into poly(D, L-lactide-co-glycolide) nanoparticles, biodegradable drug carriers, to allow specific targeting inside the cell. The interaction of the drug with infected cells was determined by exposing macrophage cultures to drug carriers. The toxic effects of polymeric drug carriers were defined prior to exposing cells to drug-loaded nanoparticles. For contact times up to 4h, cells tolerated polymer concentrations of 0.01%. The viability of parasites after treatment was determined. Infected macrophages were incubated at 26 degrees C (which allows the transformation of amastigote to promastigote) along with loaded and unloaded nanoparticles, as well as the free drug alone, and a count of the parasites in the medium was recorded. Anti-leishmanial activity was observed with drug-free nanoparticles. This activity may arise through the release of hydrogen peroxide following the activation of macrophages. The incorporation of amphotericin B did not enhance this effect. Interestingly, trehalose, a cryoprotector of the freeze-dried nanoparticles, altered parasite growth and activated macrophages.

Topical treatment of New and Old World cutaneous leishmaniasis in experimental animals

The effect of topical treatment with 15% paromomycin sulphate and 12% methylbenzethonium chloride in white soft paraffin on cutaneous leishmaniasis in Balb/c mice was studied. The Saudi Arabian strain of Leishmania major, although being the most virulent to the mice, showed the highest susceptibility to this treatment. After 10 days treatment, parasites were totally eliminated from the treated lesion and healing was complete. 3 American strains were also tested: L. mexicana amazonensis; L. braziliensis panamensis and L. mexicana mexicana. The first was the most virulent and the most resistant to local treatment, L. b. panamensis displayed an intermediate response, and L. m. mexicana was highly susceptible. The disease relapsed in 50% of the infected treated mice within 135 days (L. major), 120 (L. m. mexicana), 25 (L. b. panamensis), and 14 days (L. m. amazonensis) after the end of the treatment.

In vitro and in vivo anti-leishmanial activity of chlorpromazine alone and combined with N-meglumine antimonate

Chlorpromazine (CPZ) was effective in vitro against leishmanial promastigotes and amastigotes. CPZ at 7.5 micrograms ml-1 killed the promastigotes of Leishmania mexicana, L. aethiopica and L. major within 24 hours of exposure. A higher concentration was required to achieve the same effect against L. donovani. N-meglumine antimonate (MGA) was only partially effective against the promastigotes of the four strains studied. Even at 1000 micrograms ml-1 total destruction of the parasites did not occur within four days of treatment. Combination chemotherapy of CPZ and MGA generally showed an additive effect against promastigotes. However, a synergistic effect was observed in the case of L. donovani promastigotes and L. major amastigotes in vitro. No significant effect was obtained against the amastigotes of L. major and L. mexicana in vivo, in cutaneous lesions of BALB/c mice.

Topical treatment of cutaneous leishmaniasis

Sixty-seven patients, 19 females and 48 males, 4-66 years old, suffering from lesions of cutaneous leishmaniasis were treated topically with an ointment comprising 15% paromomycin sulfate and 12% methylbenzethonium chloride in white soft paraffin (P-ointment, U.K. patent GB117237A). After 10 days of treatment, twice daily, the lesions in 72% of the treated patients were free of parasites, 15% became free within an additional 20 days, without further treatment, and 13% failed to respond. Pigmentation developed in 18% of the treated lesions and inflammation of varying degree was associated with the treatment. These developments did not affect the clinical healing process which was generally completed in a period of 10-30 days after termination of treatment. In addition, 94% of the treated lesions healed with little or no scarring. No adverse clinical or laboratory side effects were observed except for a burning sensation at the site of treatment. Parasites isolated from patients who failed to respond to topical treatment were found to be susceptible to PR-MBCl in both in vitro infected macrophages and in vivo in experimentally infected BALB/c mice.

The surface membrane of Leishmania mexicana mexicana: comparison of amastigote and promastigote using freeze-fracture cytochemistry

The freeze fracture replica technique has been used to compare the plasma membranes of amastigote and promastigote stages of Leishmania mexicana mexicana with respect to intramembranous particle (integral protein) distribution and to beta-hydroxysterols content as revealed by the distribution of lesions induced by the polyene antibiotic filipin. Intramembranous particle (IMP) density was greater in promastigote than in amastigote plasma membranes. Intramembranous particles were more abundant in the protoplasmic face (PF) than in the exoplasmic face (EF) of promastigotes, but this situation was found to be reversed in amastigotes. Filipin-induced lesions in glutaraldehyde-fixed parasites indicated higher levels of beta-hydroxysterols in the amastigote than in the promastigote plasma membrane, and in the promastigote flagellar membrane than in the body membrane. Amphotericin B (a related polyene antibiotic used in chemotherapy of leishmaniasis) induced IMP aggregation in the PF of unfixed amastigotes but did not appear to influence sterol distribution as demonstrated by freeze-fracture of subsequently-fixed and filipin-treated organisms.

Development of topical treatment for cutaneous leishmaniasis caused by Leishmania major in experimental animals

Topical treatment, with drug-containing ointments, of cutaneous leishmaniasis caused by Leishmania major in BALB/c mice was studied. Twenty chemotherapeutic agents having potential or established antileishmanial activity were formulated in different ointment and cream bases. Only 15% paromomycin sulfate with 12% methylbenzethonium chloride, 12% benzethonium chloride, 12% cetalkonium chloride, or 12% dimethyl sulfoxide, all incorporated in white soft paraffin (United Kingdom patent application no. 2117237A), were completely effective. Topical treatment twice daily for 6 or more days caused total elimination of the parasites and healing of the lesion in all treated mice. All the other antileishmanial compounds, including sodium stibogluconate, pentamidine, amphotericin B, emetine hydrochloride, metronidazole, co-trimoxazole, allopurinol, and rifampin, either showed a slight effect on the parasites or were highly toxic to the animal host at the concentrations tested.