Antileishmanial activity of chlorpromazine.

The antiprotozoal activity of chlorpromazine against the pathogenic protozoan Leishmania donovani, in both its amastigote and promastigote stages, was characterized. Chlorpromazine at concentrations greater than or equal to 3.12 micrograms/ml (9.8 X 10(-6) M) produced a significant reduction in viable promastigotes. The minimal protozoacidal concentration for promastigotes, defined as that concentration which produced greater than or equal to 90% reduction in viable parasites after 18 h, was 13.8 micrograms/ml. The results were similar when promastigote viability was assessed by flagellar motility or by the ability of drug-exposed or control promastigotes to incorporate [3H]uridine and [3H]leucine. Exposure of promastigotes to 50 micrograms of chlorpromazine per ml reduced O2 consumption by 87% within 30 min and immobilized 97% of parasites. Morphological disruption of promastigotes was observed by electron microscopy. The mean minimal protozoacidal concentration of chlorpromazine for amastigotes was 13.2 micrograms/ml. Chlorpromazine given orally (20 mg/kg per day for 14 days) reduced the parasite burden in L. donovani-infected hamsters by 64.2% (P less than 0.01) as measured by the number of amastigotes in touch preparations of livers and by 67.9% (P = 0.03) as measured by the number of promastigotes derived from homogenates of spleens. This dose is ca. 10-fold greater than that tolerated by patients being treated for psychiatric illness. Although chlorpromazine will probably not be useful in the treatment of human visceral leishmaniasis, the data suggest that less-toxic phenothiazines might prove to be effective.

Differential survival of Leishmania donovani amastigotes in human monocytes.

Leishmania donovani is an important intracellular protozoal pathogen of man; it is found solely within macrophages in its amastigote stage in humans, and exists in its extracellular, flagellated promastigote stage in the sandfly, its arthropod vector. To determine if either stage of L. donovani was capable of surviving within monocytes--the oxidatively active precursors of tissue macrophages--interactions of the parasite with human monocytes were studied in vitro. Amastigotes and promastigotes were ingested to a comparable degree by monocytes; whereas 79% of promastigotes were killed within 48 hr, however, amastigotes survived and multiplied threefold over 5 days. Promastigotes, which have been shown to be sensitive to hydrogen peroxide-peroxidase-halide microbicidal mechanisms, elicited a phagocytic oxidative burst that was 49% of the response to serum-opsonized zymosan, as assessed by luminol-enhanced chemiluminescence. NBT was reduced to formazan in 71% of monocytes exposed to promastigotes. The death of promastigotes within monocytes could be attributed at least in part to oxidative microbicidal mechanisms because there was no significant decrease in the number of cell-associated parasites in monocytes from donors with chronic granulomatous disease of childhood. In contrast to promastigotes, amastigotes survived within monocytes, despite eliciting an oxidative response that was 27% of the response produced by serum-opsonized zymosan; this response was not significantly different from that produced by promastigotes. In a phagocyte-free system, amastigotes were found to be sevenfold more resistant than were promastigotes to the lethal effects of hydrogen peroxide. The survival of L. donovani in human monocytes is thus dependent on the parasite stage; promastigotes are ingested, they elicit an oxidative burst, and the majority are killed by oxidative microbicidal mechanisms, whereas amastigotes are ingested and survive to parasitize human monocytes successfully, despite eliciting a phagocytic oxidative burst.

Lethal effect of phenothiazine neuroleptics on the pathogenic protozoan Leishmania donovani.

Phenothiazine drugs, which are widely used for their antipsychotic, antianxiety, and antiemetic effects, have been found to have protozoacidal effects on the human pathogen Leishmania donovani. These compounds are lethal to both the extracellular stage of the organism, which is inoculated into humans by the sand fly, and the intracellular stage, which is found solely in human macrophages during established infection.

Interaction of Leishmania donovani promastigotes with human monocyte-derived macrophages: parasite entry, intracellular survival, and multiplication.

Leishmania donovani promastigotes were incubated with human monocyte-derived macrophages in vitro to assess the role of macrophages in the early stage of visceral leishmaniasis. Adherent mononuclear cells, obtained from nonimmune human donors, were cultivated on glass cover slips for 5 days and then incubated with axenically grown promastigotes in the presence of heat-inactivated autologous serum. Promastigotes attached to macrophages with either their flagellar or aflagellar ends, and macrophage pseudopodia formed around them. Intracellular parasites were identified within phagocytic vacuoles by electron microscopy, and the parasites assumed a form similar to that of amastigotes obtained from infected hamster spleens. Initially, 67 +/- 5% of the macrophages were infected with a mean of 4.2 +/- 0.7 parasites per infected cell. After 6 days of incubation, 79 +/- 7% of the macrophages were infected with 15.9 +/- 3.2 parasites per infected cell. The total number of parasites per monolayer increased from 4.8 +/- 0.8 x 10(5) to 1.8 +/- 0.4 x 10(6) (P less than 0.05). Dividing parasites were identified in macrophage vacuoles by electron microscopy. Human monocyte-derived macrophage vacuoles by electron microscopy. Human monocyte-derived macrophages can phagocytize promastigotes, allow the conversion of promastigotes to an amastigote-like state, and support intracellular multiplication.