Intracellular parasitic protozoans of the genus Leishmania depend for their survival on the elaboration of enzymic and other mechanisms for evading toxic free-radical damage inflicted by their phagocytic macrophage host. One such mechanism may involve superoxide dismutase (SOD), which detoxifies reactive superoxide radicals produced by activated macrophages, but the role of this enzyme in parasite survival has not yet been demonstrated. We have cloned a SOD gene from L. tropica and generated SOD-deficient parasites by expressing the corresponding antisense RNA from an episomal vector. Such parasites have enhanced sensitivity to menadione and hydrogen peroxide in axenic culture, and a markedly reduced survival in mouse macrophages. These results indicate that SOD is a major determinant of intracellular survival of Leishmania .
Antisense oligonucleotides have been considered as inhibitors of growth of intracellular parasites such as Leishmania , but only limited inhibition has been observed in vitro . We have encapsulated an antisense oligonucleotide, complementary to the Leishmania universal miniexon sequence, in cationic liposomes. Low concentrations (4 μ M) of encapsulated oligonucleotides specifically reduced the amastigote burden within cultured macrophages by 80%. This result illustrates the importance of effective delivery for efficient antiparasitic activity of antisense oligonucleotides.