Importance of sterols in the mitochondrial function of Leishmania tarentolae promastigotes

Leishmania are protozoa that cause visceral and (muco)cutaneous leishmaniasis in humans and animals. They contain a single mitochondrion, which is crucial for ATP generation. Essential constituents of cellular membranes, including outer mitochondrial membranes, are sterols. The predominant sterols in Leishmania are ergosterol-like triene sterols, making sterol biosynthesis pathway an ideal drug target. Therefore, the following sterol-targeting substances were investigated to determine, whether modifying sterol composition and permeability of leishmanial membranes is associated with impairment of their mitochondrial function. Amphotericin B, an antifungal and antileishmanial drug, binds to ergosterol, thereby increasing permeability of leishmanial membranes. The antifungal drug miconazole inhibits ergosterol biosynthesis by inhibiting sterol 14-demethylase and possesses antileishmanial activity. Synthetic endoperoxides from ergosterol and dehydrocholesterol were recently shown to inhibit leishmanial viability. The mitochondrial function of Leishmania tarentolae promastigotes (LtP), the flagellated form of this protozoan species, was assessed from their oxygen consumption rates after batch incubations for 0–48 hours with sterol-targeting substances. The coupling efficiency of intact LtP was studied artificially using the ATP synthase inhibitor oligomycin and the uncoupler CCCP. The physiological capacity of oxidative phosphorylation was measured in digitonin-permeabilised LtP consuming succinate as respiratory substrate and converting ADP into ATP. Significant inhibition of LtP growth, oxygen consumption rates and respiratory control values was observed with 8 μM ergosterol endoperoxide, 20 nM amphotericin B, and 650 nM miconazole, while 2 μM dehydrocholesterol endoperoxide showed marginal effects. In summary, targeting sterol biosynthesis pathway and/or altering sterol composition of LtP can affect their cell growth and mitochondrial bioenergetic function.